AEC aes Series 24 - Survival “of Food ¢ Tops — — - and Livestock in the Event — Nuclear War — U.S. ATOMIC ENEKGCY COMMISSION Office of Information Services Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices United States Department of Agriculture BEAR National Agricultural Library Survival of Food Crops and Livestock in the Event of Nuclear War Proceedings of a symposium held at Brookhaven National Laboratory Upton, Long Island, New York September 15—18, 1970 Sponsored by Office of Civil Defense U.S. Atomic Energy Commission U.S. Department of Agriculture .S. DEPARTMENT : Geena NATIONAL AGRICUL URAL LIdnat Editors David W. Bensen OCT 28 1996 Office of Civil Defense Arnold H. Sparrow ; Z Brookhaven National Laboratory g, CATALOGING PREP.* aX December 1971 U.S. ATOMIC ENERGY COMMISSION Office of Information Services ba December 1971 st ™ 92) © ™ — i ™ PS {ab} © (= =) za xe) pe © O oO ie) © Ww tae} O i?e) ep) feb) hes ie) S (e) O v— e) > 3 iae) = 2 =] USAEC Technical Information Center, Oak Ridge, Tennessee Printed in the United States of America FOREWORD Since its inception, the Brookhaven National Laboratory has had a deep and active interest in the effects of radiation, including radiation from fallout. As examples of this interest, we can list the East River Project, carried out in large part by the laboratory many years ago; the initial and continuing care of the Marshallese who were accidentally exposed to large doses of fallout radiation in 1954; and the extensive studies at Brookhaven on the effects of radiation on animals and plants. The particular interest at this symposium is radiation effects resulting from high-dose exposure, rather than the effects of low-level exposure (i.e., doses and dose rates commensurate with the radiation-exposure guides for radiation workers and for the public). These studies, of course, have a strong pragmatic component, in that the objective is to develop the ability to predict the potential effects of large doses of radiation on man directly and indirectly via possible detrimental effects on animals and food crops and via isotopes in the food chain. We must be able to evaluate the relative importance of these and other factors in the overall damage situation following nuclear warfare. However, I do not need to remind ycu that studies on the effects of radiation have led and will continue to lead to very basic findings, the importance of which transcends pragmatic considerations. For instance, Arnold Sparrow’s excellent work on the relation of the chromosome volume to radiation sensitivity has told us a great deal about the sensitive unit within the cell. The entire concept of repair at a molecular or biochemical level grew out of radiation studies. Whole new areas of scientific endeavor owe their effective origin to radiation studies. Cell and tissue kinetics, now a very large field involving many hundreds of investigators, grew from the need to understand these processes both in the context of the effects of radiation of the entire animal and plant and of radiotherapy. The FOREWORD field of tissue transplant, now progressing at an accelerated pace, owes its origin to early attempts to modify radiation injury in the mammal by means of bone-marrow transplants. Immunology also received enormous impetus from findings derived from studies of impaired immunological response following large doses of radiation. These examples remind us that, while many of the goals of this symposium are pragmatic, these investigators are indeed dealing with very basic problems in sciences. V. P. Bond Associate Director Brookhaven National Laboratory PREFACE Results of ongoing research and study reported in these symposium proceedings should significantly improve the ability to forecast and assess the postattack availability and safety of food should a nuclear attack on this country occur. This improvement could not have occurred, of course, without an accompanying expansion in knowl- edge of the basic scientific phenomena involved. A number of the problems that would confront the nation following nuclear attack were identified and discussed in the proceedings of a symposium on Postattack Recovery from Nuclear War held at Fort Monroe, Virginia, in November 1967. The consensus of the symposium was that, after such an attack, crippling problems of food, health, ecology, and long-term effects on man were unlikely. Major areas of greatest doubt and less optimism were those of postattack management (including both government and private sectors of the economy) and of motivations, incentives, and behavior of the population at all levels. Since the Fort Monroe meeting, significant new information on the food problem has been developed. In particular, sufficient new research data on the effects of fallout radiation—both beta and gamma—on food crops and livestock have accumulated to warrant a symposium to review and consolidate these data and to make them available for planning purposes. The conclusion of the earlier symposium that crippling problems of food appear unlikely remains valid when applied to the total resources that should be available to the nation. However, it is certain that there would be serious local shortages and that damage to individual crops and herds would be extensive. This symposium serves two other important purposes: (1) It provides an improved communication link between the users of research information and the scientists who produce it. (2) Perhaps of equal significance, it demonstrates a mutuality of interests among PREFACE the three sponsoring federal agencies, the Office of Civil Defense, the Atomic Energy Commission, and the Department of Agriculture. Although this symposium indicates that the broad dimensions of the postattack food-supply problems are generally understood, some uncertainties still exist. Through discussions and working group sessions, the types of additiona! research and study needed to clarify this important aspect of national survival were identified. To this end an Interagency Technical Steering Committee represented by the Office of Civil Defense, the Atomic Energy Commission, and the Department of Agriculture has been created for the purpose of coordinating and guiding research in which a mutuality of interest exists. Jobn E. Davis Director of Civil Defense Vi CONTENTS Session 1: The Hazard —Properties of Fallout Inchodulctotyvnematks, A. 2 . es 2 2 ae Soe & oS 1 Jack C. Greene Physical, Chemical, and Radiological Properties of Fallout CE or eM, AP ta cary ea a a eet eo J. H. Norman and P. Winchell Beta-Radiation Doses from Fallout Particles Depositedonthe; skin Mame 2 Pa sce oe Se Se ee A a ee od S. Z. Mikhail Measurement and Computational Techniques in Beta Dosimetry Pid Shey SAVE as ope Geese Be co8 oul James Mackin, Stephen Brown, and William Lane Measurement of Beta Dose to Vegetation PROM ClOscIMenallOuty sn, eras Boe ues =. ae eo nee OO Ainl:, ISQUREZ The Importance of Tritium in the GivileDetense:Gontext* 8.5)... 2° 2 2 20s se mw «se ow 7A J. R. Martin and J. J. Koranda Properties of Fallout Important to Agriculture ...... 81 Carl F, Miller Preparation and Use of Fallout Simulants in Biological Experiments a a er ae tT OF William B. Lane Vil CONTENTS Session II: Fallout-Radiation Effects on Livestock Fate of Fallout Ingested’by Dainy,C@ows: et eee eer To G. D. Petter, G. M. Vattuone, and D. R. McIntyre Fate of Fallout Ingested by SwinevandeBeaclesogt 4 12, a eee: fe eee ee ee Robert J. Chertok and Suzanne Lake Radionuclide Body Burdens and Hazards from Ingestion of Foodstuffs Contaminated by Hallout:— m0; soeinn ithe tie athe (Peden at ae IES Yook C. Ng and Howard A. Tewes Retention of Simulated Fallout by Sheep. and: Gattles ic 2° cc) ies Saks et a ee James E, Johnson and Arvin I. Lovaas Simulated-Fallout-Radiation Effects ON-SHEED Ac. AG oe ig ye eh cak Ma ee ene L. B. Sasser, M. C. Bell, and J. L. West Simulated-Fallout-Radiation Effects on Livestock Bh es A ge Se ee Re ie LC M. C. Bell, L. B. Sasser, and J. L. West Pathology of Gastrointestinal-Tract Beta-Radiation Injury .. . ee Poems. aes 5 /40he J. L.2West, M, C. Bell, and’L: B: Sasser, Responses of Large Animals to Radiation Injury, :.. . . . 224 David C. L. Jones Griteria-tor Radiationalnjury 2 |e" Sow eee ees John S. Krebs Species Recovery from RadiationtInjuny 3 ee eet) J. F. Spalding and L. M. Holland Radioiodine Air Uptake in Dairy Cows After a, Nuclear-Cratering Experiment © = 9a (een e een eh, Ronald E. Engel, Stuart C. Black, Victor W. Randecker, and Delbert S. Barth Problems in Postattack Livestock Salvage Uae coh oon paper S. A. Griffin and G. R. Eisele vill CONTENTS Session II]: Fallout-Radiation Effects on Plants Exposure-Rate Effects on Soybean Plant Responses to;Gamina InradiatliOnt = os aah 4 2 Ala so 4 «277 M. J. Constantin, D, D. Killion, and E. G. Siemer Effects of Acute Gamma Irradiation on Development and Yield of Parent Plants and Pestormanceior their O1isprme’ 67 Oe oP oe, bode 2ST E. G. Siemer, M. J. Constantin, and D. D, Killion Effects of Exposure Time and Rate on the Survival and Yield of Lettuce, Bareye cine WEA Ula Way wist ies ree MN Gs Fas Oe ata See oe, de =a. Ae, hace B00 P. J. Bottino and A, H. Sparrow Dose-Fractionation Studies and Radiation-Induced Protection Phenomena in African Violet ........ . 325 (Oe Broertjes Summary of Research on Fallout Effects on Crop. Plants in the Mederal Republicof Germany. >.) 2. +5 343 Hellmut Glubrecht Radiation Doses to Vegetation from Close-In EFalloueat Project; schOOnery 5. a. ac. 2. 2 4 a ie hs Gea OI2 W. A. Rhoads, H. L. Ragsdale, R. B. Platt, and E. M. Romney Survival and Yield of Crop Plants Pollowing beta, IeraGiatiOn | 2) Ga 3 Swi wu Seder He ves oO Robert K. Schulz Field Studies of Fallout Retention by Plants ..... . . 396 Jobn P. Witherspoon Retention of Near-In Fallout by Crops pe Se ah ee ee rec A. I. Lovaas and J. E. Johnson Session IV: Effects of Fallout Radiation on Agricultural and Natural Communities Predictiontolispecies, Radiosensitivity =>) 2 i. a a 4D Harvey L. Cromroy, Richard Levy, Alberto B. Broce, and Leonard J. Goldman ix CONTENTS Insect-Induced Agroecological Imbalances as an Analog to Fallout Effects ee ee ere oe ee ee Ryley Vernon M. Stern Ecological Effects of Acute Beta Irradiation from Simulated-Fallout Particles on a Natural:Plant:Community;, . e° f° ge h 1 Clearly the objective of a civil-defense system (or any other military offense or defense system) is to make this product as large as possible. It is equally clear that if any single transfer coefficient is critically small, there is no point in attempting to raise the others until the critical one is also raised. Each of these transfer coefficients will now be discussed in turn, both in terms of probable range of values and in terms of action needed either to lessen the uncertainties about the coefficients or to increase their values. Direct Weapons Effects. The transfer coefficient for direct weapon effects, a, represents the fraction of the preattack U. S. population surviving the blast and initial thermal and nuclear radiation. For today’s civil defense, a probably would be in the range of 0.5 to 0.8, depending on the type and weight of attack. Employment of antiballistic missiles, blast shelters, or preattack evacuation increases a. Fallout. The transfer coefficient for lethal fallout effects, b, represents the fraction of the population surviving the direct effects (a) and also surviving the *Those wishing to pursue a particular point or to obtain specific references may do so by communicating with me at the following address: Postattack Research Division, Office of Civil Defense, The Pentagon, 1E542, Washington, D. C. 20310; Phone: Area 202, 695-9613. INTRODUCTORY REMARKS S hazard of lethal fallout-radiation doses. Typical results of hypothetical attacks indicate that b would be in the range of 0.4 to 0.8. The value of b can be increased cheaply, at least on the margin; i.e., expenditures to save lives with a fallout shelter program are highly cost effective, as are expenditures to educate the public on the nature of the fallout threat and means of protecting against it. AWIL FLOW INPUT AAAAAABAAL Direct blast and thermal effects 1 to 2 days AAAAAA o | Lethal fallout-radiation effects 3 to 4 days ee Wty {5 ae) Trapped or not medically treated 2 to 7 days o tHtY [5 Inadequate life support 5 to 50 days AAA Epidemics and diseases Peis Economic chaos 1 to 2 years AAAL Late radiation effects 5 to 20 years Ht tle ‘Ecological catastrophe 10 to 50 years Wy Genetic damage aa OUTPUT Fig. 1 Flow-diagram model of U.S. society during and after nuclear attack, YAASNVYL (d) NOILV1NdOd MOVLLVLSOd e SINSIDIS33509 e) | p | 2 weeks to 1 year } 3 y 0) : : d(4""e) d(}"®) 2 to several generations d(!""e) 4 GREENE For just these reasons the emphasis of the current civil-defense program is on fallout protection, At this point the flow diagram may be used to illustrate the importance of viewing civil defense as a system. A certain tactic intended to raise b may appear highly attractive if a narrow perspective is applied (suboptimization). But if this tactic at the same time reduces some other transfer coefficient, say a, so that the product ab becomes less than it was before, the tactic obviously is not desirable. For example, a policy of sending people to the upper stories of high-rise buildings to increase fallout protection in target areas may decrease b, but the accompanying increase in a (deaths due to initial weapons effects) may result in a net decrease in the number of people surviving both effects. Table 1 indicates how a and b might vary as a function of the weight of attack. Table 1 TRANSFER COEFFICIENTS a AND b AND THEIR PRODUCT FOR VARIOUS WEIGHTS OF ATTACK* Transfer 1000 3000 5000 7000 9000 coefficient Mtt Mt Mt Mt Mt a 0.78 0.64 0.57 0.54 0.49 b 0.81 0.70 0.58 0.48 0.39 aah 0.63 0.45 0.33 0.26 0.19 *Data are based on a composite of damage-assessment studies by the Department of Defense. The attacks were assumed to be _ against military—urban—industrial targets, and people were assumed to use the best protection available in the normal place of residence. tUnits of attack weight are in megatons equivalent of TNT. Rescue and Medical Care, The transfer coefficient c is attributable to the effectiveness of emergency operations services, such as rescue and medical teams and represents the fraction of the population surviving blast, thermal, and fallout effects, not already foredoomed to die, which could and would be saved by rescue and emergency medical care. Contrary to much prevalent intuition, c probably is a fraction near 1. The reason for this is not that rescue and medical care are expected to be highly effective, but that the percentage of people that could be rescued in time or could be saved by medical care is very small. Therefore expenditures to increase c do not appear to very cost effective. (The value for c is probably greater than 0.95.) Life-Support Requirements, The transfer coefficient d represents survival during the very early postattack period when people in shelters or other isolated locations could be running out of food or water or the shelters (because of inadequate ventilation) might become intolerable. The value of d depends on INTRODUCTORY REMARKS 6) how rapidly food-, water-, and power-distribution systems can be reestablished and how rapidly an effective emergency management system evolves. In some localities and under some conditions, the problems could be severe. Very hot or very cold weather, radiological constraints, and disrupted transportation and communications systems could have a serious impact. This area requires more study and the development of individual plans tailored to the needs of individual localities and situations, On a national average, however, d is not likely to fall much below 1.0. Epidemics and Diseases, The transfer coefficient for epidemics and diseases is e. Postattack health problems could be exacerbated because of disrupted water and sewerage systems, malnutrition, and radiation exposures, The range of e might be wide, but, with reasonable precautions and attention, it probably could be kept high. The national average value for e should be above 0,95, Additional study and development of contingency plans for specific health problems that might occur are needed and are being undertaken. The Economy, The transfer coefficient accounting for the requirement that the economy become functional and produce the commodities essential to sustain the attack survivors before surviving inventories are used up is f, In this respect it is particularly fortuitous that the U.S. agricultural industry is highly efficient. About 6% of the U.S. population produces not only enough food to feed America but also vast quantities for export. Numerous studies show that the physical wherewithal (transportation, fertilizer and petroleum products, essential industry, etc.) to continue to provide food to sustain the survivors of a nuclear attack would also survive. This damaged economy could provide for an adequate diet and for the other items essential to survival without undue strain, and a surplus of labor, capital, and raw materials would be left with which to rebuild the economy, It is not enough, however, to say that the physical capacity to sustain survivors would exist. One has only to recall that there was no physical incapacity of the nation’s ability to produce in the late 1920’s and early 1930’s during the worst depression of U. S. history. The machine was in good shape; the problem was that management did not know how to operate it. To expect efficient or even adequate operation of an economy damaged by a massive nuclear attack, with the attendant social and psychological trauma, may be highly optimistic. If there is an Achilles’ heel in the postattack recovery system, it probably hes in f, the transfer coefficient relating to economic chaos, But this Achilles’ heel, if it exists, is not inherent; it would result from inadequate planning and preparations for management rather than from limitations of the physical capacity to produce. Late Radiation Effects, The transfer coefficient g accounts for the people who would die from bone cancer, leukemia, thyroid damage, and other radiation- induced effects. Although the impact on the survivors might well be detectable 6 GREENE (and might have a more important psychological than physiological impact), these late radiation effects pose little threat to the society’s survival. The value of g probably is a number greater than 0.99. The research in this area is done largely under AEC and U.S. Public Health Service sponsorship. Charles L. Dunham (former Director of the AEC Division of Biology and Medicine and currently the Chairman of the Division of Medical Sciences, Academy of Sciences) recently summarized the long-term effects with the following statement: ‘20,000 additional cases per year of leukemia during the first 15 to 20 years postattack followed by an equal number of cases of miscellaneous cancers, added to the normal incidence in the next 30 to 50 years, would constitute the upper limiting case. They would be an unimportant social, economic, and psychological burden on the surviving population.”’ (The Dunham statement was in reference to specific hypothetical attacks—one, CIVLOG, was a 455-weapon 2000-Mt attack; the other, UNCLEX, was an 800-weapon 3500-Mt attack. Current status of civil defense was assumed.) The yearly rate appearing today for the 200-million U.S. population is about 20,000 new cases of leukemia. There are about 15,000 deaths per year due to this cause. The Ecology, The transfer coefficient h accounts for the damage to the ecology which could occur from the nuclear attack. Probable ecological consequences of nuclear war are still uncertain, Extensive research programs are underway, and progress is being made, The most comprehensive program, at least in the Western World, is that of the Radioecology Section of the Oak Ridge National Laboratory —research partially supported by OCD over the last several years. The ‘“‘doom and gloom”’ predictions prevalent in the late 1950’s and early 1960’s are not supported by this research. The summary report of Project Harbor, a 1963 study of civil defense by a committee of the National Academy of Sciences under the leadership of Eugene Wigner, contains this statement: “Large-scale primary fires, totally destructive insect plagues, and ecological imbalances that would make normal life impossible are not to be expected.” In the 1969 study (again under the leadership of Dr. Wigner) intended to update the Project Harbor work, is the following statement: ‘‘A reasonable conclusion, therefore, is that the long-term ecological effects would not be severe enough to prohibit or seriously delay recovery.” Some perspective as to the possible ecological effects of a nuclear attack can be gained by considering that man is now, in peacetime, doing just about everything he can do to upset the ecological balances. The ultimate results on the ecology of water and air pollution and of widespread application of herbicides and insecticides are beyond our knowledge to predict; but, whether or not there is a nuclear war, these problems have to be faced and solved, At this point in the flow diagram, it is no longer feasible to ascribe a numerical value to the transfer coefficient. By the time these ecological consequences would manifest themselves, limiting the growth of population might have again become INTRODUCTORY REMARKS i a socially desirable goal. But to think that the ecological damage of nuclear war would be so severe as to limit flow in the concept of the diagram is just not justified. (Though verging on the macabre, it should be pointed out that a nuclear war could alleviate some of the factors leading to today’s ecological disturbances that are due to current high-population concentrations and heavy industrial production.) Genetic Effects, The transfer coefficient for genetic damage, 1, is included primarily for completeness. Genetic effects, like late radiation and ecological effects, are widely misunderstood, and consequently feared, and probably have aroused more emotional heat then the others. Although g, h, and i could be important, there is little question that they represent minor consequences compared with others, The genetic effects of radiation exposure have received a great deal of study—with animals in the laboratory and with humans in follow-up studies of people given radiation for therapeutic and diagnostic purposes, people involved in accidents, and the survivors of Hiroshima and Nagasaki. The Atomic Bomb Casualty Commission, a joint U.S.—Japanese study, has had an extensive program underway in Japan since the early days following World War II. Dr. Dunham, in the same summary referred to previously, said, ““The genetic effects would be lost, as at Hiroshima and Nagasaki, in all the other ‘background plane Se) noise’, The concepts that people harbor about late radiation, ecological, and genetic effects probably are far more severely distorted than those concepts about any of the other potential attack effects. To illustrate, in May 1970, The New Yorker magazine’s lead article contained the following statement: ‘Since the development of nuclear weapons, everyone has known. that an international crisis could lead to the extinction of the human species,’’ Other examples just as dramatic can be found in Robert Kennedy’s book on the Cuban crisis. The following quote is typical: ‘“‘Each one of us was being asked to make a recommendation which would affect the future of all mankind, a recommenda- tion which, if wrong and if accepted, could mean the destruction of the human race,’ (Italics in both references are used for emphasis.) I cannot prove by this flow-diagram model or by any other analytical device or line of reasoning that this country could survive and recover from a nuclear attack, any more than I can prove that we will satisfactorily solve our pollution or population-growth problems or work out a more acceptable rapprochement with our young. On the other hand, when people make dogmatic statements to me claiming that we could not survive and recover from a nuclear attack, I defy them to identify in accordance with this or with any other model the barrier or barriers that would be insuperable. In any case, I am firmly convinced that our chances of survival and recovery from a nuclear catastrophe, should it occur, will be much higher, the progress 8 GREENE much faster, and the trauma less severe if we have studied and understand the potential problems and have figured out the best ways of handling them, An absolute requisite at any stage of the recovery process is an adequate supply of food that is nutritionally sufficient and radiologically acceptable. The work that is being reported here constitutes, I believe, a giant step toward understanding the physical and physiological components of this food problem. More work is needed, especially work to improve the plans and procedures for allocation and distribution of food. If civil defense, like the army, “‘must travel on its stomach,” the work you are doing will help assure that the wherewithal to travel is in plentiful supply. PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES OF FALLOUT J. H. NORMAN and P. WINCHELL Gulf General Atomic Company, San Diego, California ABSTRACT The importance to a biological-damage model of physical chemistry associated with the sorption of fission products by fallout is suggested. Calculated sorption behavior for Small Boy fallout of several nuclide chains is demonstrated according to a condensed-state diffusion-limited sorption model. An experiment on glassy Johnie Boy fallout revealed a 3 diffusion-controlled profile of NPAC Sain partial support of the calculated model. To describe the biological activity of the various fission-product nuclides, we must understand the leaching properties of radionuclides in the fallout particles. As an initial report on our work in this field, we considered sorbed iodine transport in contact with (1) moist air and (2) solutions. Sodium and iodine leaching from several glasses was also studied. Leaching of fission products from a CaO—Al,03~—Si0 > glass a few days after recoil loading was studied. In these leaching studies the data were fitted to several models: surface-reaction-rate-limited, diffusion-limited, and desorption-limited processes. The ob- servation of the pertinence of several models suggests considerable complexity in a leaching model for fallout. The most important questions in characterizing fallout with respect to a biological-damage model are: 1. How much fallout has been deposited in the region of concern? 2. How much radioactivity as a function of time is associated with the fallout? 3. What is the distribution of the radioactivity with respect to the fallout particles? 4. What is the physical, chemical, and radiological behavior of the particles with respect to the environment? Tolerance levels for various radionuclide exposures must be established, of course. Nevertheless, the essential doses and dose rates resulting from an 9 10 NORMAN AND WINCHELL exposure to fallout are intimately connected with the description of the fallout. Therefore our premise is that knowledge of fallout properties is necessary for radiological-damage estimates, and thus a damage model must incorporate a fallout model as a base. During the last two decades, there has been a considerable effort to formulate a physical—chemical fallout-formation model. Fractionation of volatile fission products was noted early by Freiling.' Models have been constructed, for instance, by Freiling,’ Miller,? and Korts and Norman‘ to simulate fractionation. Considerable effort has been made to define the phenomena involved in fallout formation. Recently Freiling’ presented a good description of nonturbulent, nonagglomerating fallout formation in which fission-product sorption is described as controlled by one or more of three processes: gas-phase diffusion, condensed-phase diffusion, and surface condensa- tion. He presented a basic method for determining the importance of each of these processes to fallout formation. This method involves evaluating the basic chemical and physical parameters associated with each of these phenomena. Freiling lists these parameters as follows: . Particle radii and distributions thereof. . Vapor-phase diffusivities. . Condensed-phase diffusivities. . Henry’s law constants (distribution coefficients). . Condensation coefficients. . Mean molecular speed of the gas-phase species. Nm BW NY PR Information is available for most of these quantities for evaluating fallout formation. Particle-size distributions have been discussed many times.°’” Heft’s® bimodal particles certainly should be considered. Vapor-phase diffusivities and mean molecular speeds can be readily derived from knowledge of the gaseous species and the pressures and temperatures encountered during fallout forma- tion. Norman” presented an estimate of Henry’s law constants for silicates, and information on silicate diffusivities was presented by Winchell and Norman.'° Condensation-coefficient studies were performed by Adams, Quan, and Balk- well'’ and by Bloore et al.'* Russell’* also contributed to an understanding of several of these phenomena. Although the phenomenological studies have shown considerable promise, much less has been accomplished in terms of establishing a model incorporating the six parameters. Miller? provided the first physical—chemical model, which employed a step response in condensed-state diffusivity at a soil melting temperature, surface equilibrium, and Raoult’s law constants (1.e., fission products were assumed to condense in silicates according to ideal-solution law until particles froze, and thereafter they were assumed to surface deposit). Korts and Norman* constructed a more general model in which a set of Henry’s law constants’ was employed along with silicate-diffusion constants to make PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES fal approximate dynamic calculations of condensed-state profiles assuming that the gas phase was in equilibrium with the surfaces of the fallout particles. These models are very complex. An interdecaying population of fission products must be imposed on the kinetics of sorption. The set of differential equations to describe fully the decaying population and sorption by the three listed processes is extensive, and good, approximate solutions are difficult to achieve. The problem of obtaining a complete physical—chemical model, then, is discouraging to those looking for a quick answer. Some empirical models have been developed [e.g., the -U.S. Naval Radiological Defense Laboratory (USNRDL) RAD model*] which have proved quite useful, but they do not describe well some properties important to biological activity. At this point we will consider further the Korts—Norman model as a possible limiting physical—chemical description of fallout. Model features that should be important in fallout are the predicted fractionation, the nature of fission- product-penetration profiles, and the activity division according to particle size. These features can be calculated for a field of altered and unaltered fallout according to Heft’s suggestions.” Fractionation affects the quantity and type of fission products encountered in a given region of a fallout pattern since sedimentation rates are particle-size dependent. Profiles affect the beta-dose rates from particles, as discussed by Mikhail,’* and also the biological availability. The model output, together with a leaching description of the matrix, determines the mobility of fission products. The character of the fallout itself establishes the sorptive and leaching properties. Altered (from molten droplets to glassy spheres) and unaltered debris exhibit considerably different fission-product profiles. Late or peripheral entry of debris into the cloud is important, as are sorptive properties and leaching properties of the debris. The basic question is: What is necessary to provide a better physical— chemical description of fallout for use in a biological model? Our answer is twofold: (1) Establish fission-product profiles in fallout particles, and (2) estab- lish the degree of corrosion of and migration in fallout particles under appropriate conditions. The remainder of this paper bears on these two points. DESCRIPTION OF FALLOUT ACCORDING TO THE CONDENSED-STATE DIFFUSION-CONTROLLED FISSION-PRODUCT SORPTION MODEL The condensed-state diffusion model for fission-product absorption assumes (1) that the rate of fission-product sorption during the critical time—temperature regime is controlled by diffusion of surface-absorbed fission products into the bulk of fallout particles, (2) that the surface of a particle is in equilibrium with the neighboring gas, and (3) that the pressures of the gaseous fission products are locally constant (i.e., that gas-phase diffusion is fast enough that local fission-product pressure gradients are negligible). Descriptions of the calcula- 12 NORMAN AND WINCHELL TIME, sec 102! OR 190'9 1018 GAS-PHASE CONTENT, atoms 10'7E 1016 H 10'5 ooo (=) [o) (oie (>) © jo) jo) (jo) (o) SiS SS Sp oss oe Ses = TOON N N NN - — - - - TEMPERATURE, °K Fig. 1 Calculated gas-phase concentrations in 106 chain for Small Boy (ruthenium precursors and half-lives in seconds listed). tional methods and some parameter scaling for this model were presented by Korts and Norman.” A short description of the model was given by Norman et al.,'° and a parametric study including some simulated Small Boy calculations was presented by Norman et al.'° In this report, some additional data from our Small Boy calculations are presented to demonstrate the properties of the model which are important to a biological-activity model. The Small Boy time— temperature history is approximated on the abscissas of Figs. 1 and 2, and the PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 13 TIME, sec 10222 2 4 6 8 10 Xe(16) 102! 11072 Ba E c se] Re Cs(66) ke 2 10 = 1(1.5) Zz O oO LU a ints ae 10 o La ap) xt (e) few: Zo 24s O Eesccomr as oe d0uhy aoe a We nae 2 O ao O i gee © i, 102 Io waza co a O LW 2 =| : 10s Pe O GASEOUS FRACTION AT 800° K 90 95 103) “106; 250 Sle SZ OV ae Sr ZN Ru Rh Sb | | Cs Ba Fig. 4 Physical—chemical calculations for Small Boy. FALLOUT-PARTICLE GRADIENT STUDIES The condensed-state diffusion-limited model of fission-product absorption during fallout formation suggests that the concentration gradients of some radionuclides are very sharp. This is the result expected for radiocesium, for example. The importance of diffusion seems to be confirmed by the cursory experiment described in the following paragraph. PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES Ve Some large silicate fallout particles from shot Johnie Boy (supplied by USNRDL) were microscopically examined and divided into two sets, uncoated particles and iron- and lead-coated particles. Three particles were selected from the uncoated set for an experiment. Their gross appearance was that of a somewhat inhomogeneous, dark glass with obvious nodules of white material on the surface. Radii, rg, were about 0.05 cm. The presence of radiocesium in the particles was established by gamma analysis using a multichannel analyzer and a '37Cs standard for reference. After the particles were leached for 1 hr with 19% HCl, no significant loss of cesium was observed. Leaching studies were then made using 5% HF with subsequent washing, drying at 110°C for 1 hr, gamma analysis, and weighing on a microbalance. Microscopic examination of the particles throughout this process showed a continuous, but not uniform, radial attack. The experiment was concluded when the specimens lost their integrity. Results obtained in this experiment are shown in Table 1. The relative average Table 1 COMPOSITE !27Cs PROFILES IN THREE JOHNIE BOY PARTICLES r/To KC 0.973 3.4 0.921 1.8 0.880 1.6 concentration, C, of cesium in the leached section is presented according to a calculated average radius, r, given by the weight loss. A concentration gradient is apparent in this table. Although this gradient, if we assume a uniform attack, seems small compared with the model calculations, it appears to support diffusion phenomenology. INTERACTIONS OF FALLOUT PARTICLES WITH THE ENVIRONMENT One of the most important properties of fallout is leachability. The chemical availability of fission-product nuclides to the biosphere is largely determined by this step. In general, the important variables in leaching are time, temperature, particle size, particle composition, the chemical nature of the leachant, degree of agitation, nature of the nuclide, and the leaching mechanism. The concentration gradient of fission products within the particle and the surface concentration of fission products are, of course, very important in establishing the leaching rate. Since this subject cannot be treated fully in this paper, treatment has been necessarily restricted to a few examples. However, it is emphasized that reliable prediction of the biological availability of fission products depends on an understanding of the diverse variables involved in leaching. The experiments 18 NORMAN AND WINCHELL described here were performed in our laboratory. However, a large amount of pertinent information is reported in the literature, particularly in the glass and ceramics publications. For example, the studies of Douglas and El-Shamy’ ’ indicate that leaching may occur by diffusion of the leachant through a silica-rich layer with protons or alkali ions occupying surface sites. Elliot and Auty,'° investigating the leaching of borosilicate glasses containing fission products, proposed that a layer rich in silica and fission-product oxides was formed at the glass surface. They noted that the glass durability depended on cooling rate and reported the temperature dependencies of leaching. In several examples leaching of silicates appears to follow a desorption mechanism.'? 7! Locsei** described the importance of the degree of crystallinity in leaching of silicates. The removal of surface-adsorbed radionuclides may be considered the simplest step in leaching of fallout. In an experiment performed to study the loss of 131] from standard glass beads (National Bureau of Standards), tellurium dioxide was neutron irradiated in a Gulf General Atomic TRIGA reactor for 250 kw-hr and then allowed to decay for approximately 50 '*! Te half-lives. 'S'T transpired by humidified oxygen, The sample was then heated, and the was absorbed on the 1.17- to 1.65-mm beads at near room temperature. The beads were transferred to a flask equipped with a charcoal trap, and the fractional loss of '**1 from the beads in the laboratory atmosphere at room temperature was monitored by gamma analysis of the trap. The fractional release of '°'T as a function of time is shown in Fig. 5. Except for small, initial rapid release, the time dependence is linear with a loss of approximately 1% in about one week. The data are described well by EX 10> = 0.945 5:58 10 (1) where t is time (hours). The linearity of the data in Fig. 5 is consistent with several possible release mechanisms, for instance, vaporization, vapor-phase transport, or reaction-rate control. It is concluded that appreciable amounts of adsorbed radioiodine may be lost to the atmosphere from fallout particles at room temperature during the half-life of *°*1. After the air-release experiment, the beads were leached with distilled water to simulate rain. At intervals a small aliquot was removed, gamma analyzed, and replaced in the container. A small volume of saturated KI was then introduced, and the leaching was again monitored at various periods. The data are shown in Fig. 6. A solution of KI is apparently a better leaching agent than H)O since it provides a direct exchange for I or a solubilizing agent for I,. Most of the sorbed iodine could be removed with a KI solution. Another study involved the leaching of radioiodine-doped glass with a composition of the 1450 K eutectic from the CaO—Al, 03 —SiO, system. These data thus pertain to the special case of a refractory matrix containing PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 19 FRACTIONAL RELEASE (F X 103) O 0 20 40 60 80 100 120 140 160 180 TIME, hr Fig. 5 Fractional release of surface adsorbed i by glass spheres at 298K in laboratory air as a function of time. homogeneously distributed radioiodine. A portion of the glass was powdered, passed through a 100-mesh screen, and dried at approximately 100°C. Weighed samples were placed in double-thickness, No. 42 Whatman filter papers, which were supported in funnels equipped for aliquoting from the tip. Periodically 5 ml of leachant were added after the previous leachant was drained, and the aliquot was made up to 50 ml and gamma analyzed with the use of reproducible geometry. Leaching was carried out at room temperature without agitation. Because of the low leaching rates, initial leaching times were about 20 min; the longest experiment lasted 2 days. The following four leachants were used: Leachant pH Remarks HCl Z To represent the human stomach Tap water 8.3 Colorado River water Deionized water a To represent rain water NaOH 10 For comparison Although the adsorption characteristics of the paper may have been important, particularly in the deionized-water experiments, the effect was assumed to be negligible. Since a surface-area measurement has not been obtained for the 20 NORMAN AND WINCHELL (F) FRACTIONAL RELEASE e) 40 80 120 160 200 240 TIME, min Fig. 6 Leaching of adsorbed 'S1T from glass spheres with distilled water and Oo potassium iodide at 298 K as a function of time. prepared sample, the results can only be placed on a reciprocal weight basis at this time. By photomicrography the particles were found to be roughly 100 wu in “diameter.” The leaching data are shown in Fig. 7. At first it was felt that the mechanism of leaching might be diffusion-limited transport of the leachant into the matrix or of radioiodine out through the matrix. If this were the case, since only about 1% of the activity was removed, leaching should be proportional to t2 (Fick’s law). This dependence was not observed. However, the data can be described by the Elovich equation, which has found wide application in chemisorption: dO ee qe TaN | aQ) (2) PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 21 Tap water AMOUNT LEACHED (Q X 1073), cpm/g 6) 1 2 3 4 5 t X 10°*, min Fig. 7 Leaching of radioiodine from powdered 1450 K eutectic CaO— Al,03—SiOy doped with '?'1, where Q is the amount of material desorbed (sorbed), t is time, and a and q@ are constants at fixed temperature. By assuming that Q = 0 when t = 0, we can write the integrated form: aQ = In (1 + aat) (3) The data can be fitted to Eq. 3 by using the values of a and @ given in Table 2. The data fitted in this manner are shown in Fig. 8, where it is seen that their agreement with the Elovich equation is good. Leaching data reported by other 1921 Can also be fitted to this equation. The fact that leaching data can be fitted to the Elovich equation, at least for short times, should be regarded as an empirical fact. laboratories 22 NORMAN AND WINCHELL 7 Tap water 6 pH = 2 @ 2 days E f\ © ZN a #85 o) An x< S) L\ ae’ 4 pH = 10 LW = (fe 0 20 min B a ty 5 3 é =) = 5 a pH = 7 = y, A / e \/ i \/ 1 1 2 $} 4 LN (1 + aat), t in min Fig. 8 Leaching of radioiodine from powdered 1450 K eutectic CaO— Al, 03—SiO). The data have been fitted to the Elovich equation (see text). Table 2 COEFFICIENTS FOR THE ELOVICH EQUATION AT 300K a x One a x 10°, Leachant cpm/g/min (cpm/g) ! Distilled water 3235 2.33 NaOH Dae 1.25 HCl S377, 1.08 Tap water 6.62 JLB IES) To demonstrate further how a change in conditions can affect a change in mechanism, we performed a study of the leaching of sodium from a medium refractory glass. The matrix used for this study was purchased from the National Bureau of Standards in the form of glass spheres (Standard Reference Material PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 23 1019). The composition of this glass is similar to that of window glass. A set of standard sieves was used to screen the sample, and four subsamples were chosen. These samples are described in Table 3. Table 3 GLASS SAMPLES USED FOR LEACHING STUDIES Diameter, Number of Sample cm particles A 0259 to0:236 32 B 0.236 to 0.165 39 Cc O:265;t0 0.117 261 D 0.117 to 0.089 530 Before they were weighed, the samples were inspected for foreign material and were briefly washed with distilled water and dried. Irregular-shaped or inhomogeneous particles were discarded. After weighing, the samples were irradiated with neutrons in a Gulf General Atomic TRIGA reactor for 250 kw-hr. A multichannel gamma analysis to 2 MeV showed peaks at 0.51, 1.37, and 1.73 MeV which can be attributed to activated sodium (pair production, primary gamma, double escape from 2.75-MeV gamma) in the glass. The samples were placed in double-thickness, No. 44 Whatman filter papers, which were held in funnels equipped for aliquoting from the tip. Colorado River tap water with a pH of approximately 8.2 was used as the leachant. Periodically 10 ml of leachant was added to the glass samples after draining of the previous aliquot, which was integrally gamma counted above 0.4 MeV. Leaching was done at room temperature without agitation. The pH of the leachant remained constant throughout the leaching periods. The overall leaching period was approximately 30 hr. The results are shown in Fig. 9, where the total amount of activity leached per particle is plotted as a function of the square root of the time. Referring to this figure, we see that samples B, C, and D exhibited a short lag period but that the early loss by sample A was rapid. After this lag period, the losses are all linear functions of the square root of the time. The results of a least-squares fit of the data to the equation Q=a+bvt (4) where Q is the amount of leached radioactivity per particle (counts per minute) and t is the time (minutes), are given in Table 4. From Table 4 and Fig. 9, the leaching mechanism for sample A appears to differ from that of the other three 24 NORMAN AND WINCHELL AMOUNT LEACHED PER PARTICLE (Q), cpm 1/2) mint/2 Fig. 9 Leaching of radioactivity from glass spheres by tap water as a function of the square root of the time. samples. This result is not understood. For samples B, C, and D, the square-root time dependence indicates a diffusion mechanism. As expected, the parameter b (cpm/min® in Table 4) increases with the particle, surfaces area. hesemthree samples also showed evidence of etching. The lag period may be attributed to an initially slow attack of the glass surface with respect to the interior, as was observed by Elliot and Auty.'® The fractional release of the radioactivity by samples B, C, and D may be considered on the basis of diffusion from a sphere with zero surface PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 25 Table 4 COEFFICIENTS IN EQ. 4 a, b, ey an particle r cpm cpm/min? radius, cm b/R P18 0.0644 0.124 1269 1.64 0.100 164 Laos 133 0.071 26.4 Saal spa 0.689 0.052 2a) concentration. Since less than 1% of the activity was lost, this process is described by? ® \y Dry = (5) T where f = fractional release Re= raGius D = diffusion coefficient t = time Radius-corrected leaching “‘rates’’ are presented in the last column of Table 4 as b/R*. Although it is not certain that sodium-ion migration is the rate-controlling process, these data suggest this to be the case. From these data and from initial specifications, the average value of D associated with a sodium-ion-migration mechanism was calculated to be 2.2 X 10 '! cm?*/sec. A different matrix would probably yield different results. As an example, Locsei*? studied the leachability of a Nag O—CaO—MgO—AI, 03 —S10, system using 10% HCl. The character of the matrices ranged from 100% vitreous to 100% crystalline. His data are described well by an equation of the form ae >* (6) Nn \| where S is the solubility (grams per square meter per day), x 1s the percentage of crystallinity, and a and b are constants. The effect of crystallinity was pronounced, being roughly two orders of magnitude in S. Another of our studies involved the leaching of recoil-loaded glasses. The recoil loading was done to simulate fallout containing high radionuclide concentrations near the particle surface as described by the Korts—Norman fallout model." 26 NORMAN AND WINCHELL FRACTIONAL RELEASE (F X 103) tile. Fig. 10 Fractional release of fission products from eutectic glass during leaching; the average uncertainty is 15%. Two silicate matrices were used, vitreous Nevada soil and the glass of 1450 K eutectic composition from the CaO—Al,03—Si0O, system. The glasses were treated by heating them on flat platinum surfaces for several hours at 1400°C in air. A small piece of fully-enriched uranium foil was placed between the two flat glass surfaces when they had cooled, and the sample was irradiated with neutrons in a Gulf General Atomic, Inc., TRIGA reactor for 125 kw-hr. The radioactivity was allowed to decay for approximately 5 days. Then the glasses were separated from the foil and were lightly cleaned with fine carborundum paper to eliminate spalled uranium and fission products from the surfaces. After being cleaned and dried, the samples were subjected to leaching at room temperature in plastic beakers containing 5 ml of a slurry of 11.5 g of PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 27 FRACTIONAL RELEASE (F X 103) tiie. min!/2 Fig. 11 Fractional release of fission products from Nevada glass during leaching; the average uncertainty is 25%. montmorillonite in 750 ml of distilled water. The clay was used to provide an efficient sink for leached fission products. During leaching both the glasses and the leaching slurries were separately analyzed with a 4096-channel gamma analyzer equipped with a lithium-drifted germanium detector. The gamma spectra were then corrected by referring them to the irradiation time using the pertinent half-lives. Several nuclides were found in all spectra for the leaching slurries and for both glasses. The data are shown in Figs. 10 and 11, where the fractional releases of the glasses are plotted as functions of the square root of the time. From these figures the leaching process appears to be one of diffusion during the leaching period of 132 min. Several qualitative conclusions may be made concerning these data. 28 NORMAN AND WINCHELL Since the fractional releases are not highly correlated with mass number (recoil ranges are highly correlated with mass), the leaching process is not totally dependent on the recoil distribution of fission products. The approximate leaching penetration during the experiment can also be calculated. Assuming a recoil range of 10m for a nuclide in the eutectic glass and using a fractional release value of 5 X 10° for this nuclide, we calculate a penetration distance of approximately 200 A. Thus for volatile chains the degree of surface loading can play a dominant role in subsequent leaching. In the present study leaching rates differ by up to a factor of about 4 for all the nuclides studied in the two glasses. The reason for differences between nuclides is not known, but, if diffusion is rate controlling, such differences are expected. It is also observed that the order of leaching rates of different nuclides from the eutectic glass differs from that of the Nevada glass, and, surprisingly, the leaching rates are only slightly different for the two glasses. This is consistent with the similarity of these two glasses in high-temperature diffusion studies. Considering the studies reported in this section, it appears unlikely that any a priori unified scheme of transfer of radionuclides from fallout particles to the biosphere can be established now. Such a scheme would require the output of a model such as Korts and Norman have described. It would also require a good physical—chemical model involving chemical attack on fallout particles and migration of radionuclides in many environments. This latter task is formidable. It is not true that simple models to describe leaching of fallout should not be devised. This is exactly what should be done. However, these simple models should strive for as much realism as possible, and, in view of our present knowledge, we are quite limited, particularly in the leaching model. ACKNOWLEDGMENT This work was supported by the Department of the Army, Office of Civil Defense, under Contract DAHC20-70-C-0388. REFERENCES 1. E. C. Freiling, Fractionation. I. High-Yield Surface Burst Correlation, Report USNRDL- TR-385, U. S. Naval Radiological Defense Laboratory, Oct. 29, 1959. DIE eaC > Freilings * | GaekCrockera.and a C-aak. Adams, Nuclear-Debris Formation, in Radioactive Fallout From Nuclear Weapons Tests, Proceedings of the Second Confer- ence, Germantown, Md., Nov. 3—6, 1964, A. W. Klement (Ed.), AEC Symposium Series, Noy 3+(CONF-765) pp. l= 4351965: 3. C. F. Miller, Fallout and Radiological Countermeasures. Volume I., Report AD-410522, p. 26, Stanford Research Institute (Project No. IM-4021), 1963. 4.R. F. Korts and J. H. Norman, A Calculational Model for Condensed State Diffusion Controlled Fission Product Absorption During Fallout Formation, Report GA-7598, General Dynamics Corp., General Atomic Div., Jan. 10, 1967. 10. As: 12. 3. 14. iS: 16. fe U8: Lo: 20. PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES Zo _E. C. Freiling, Mass-Transfer Mechanisms in Source-Term Definition, in Radionuclides in the Environment, Advances in Chemistry Series, No. 93, pp. 1-12, American Chemical Society, Washington, D. C., 1970. . M. W. Nathans, R. Thews, and I. J. Russell, The Particle Size Distribution of Nuclear Cloud Samples, in Radionuclides in the Environment, Advances in Chemistry Series, No. 93, pp. 360—380, American Chemical Society, Washington, D. C., 1970. .R. C. Tompkins, I. J. Russell, and W. N. Nathans, A Comparison Between Cloud Samples and Close-In Ground Fallout Samples from Nuclear Ground Bursts, in Radionuclides in the Environment, Advances in Chemistry Series, No. 93, pp. 381—400, American Chemical Society, Washington, D. C., 1970. .R. E. Heft, The Characterization of Radioactive Particles from Nuclear Weapons Tests, in Radionuclides in the Environment, Advances in Chemistry Series, No. 93, pp. 254—281, American Chemical Society, Washington, D. C., 1970. . J. H. Norman, Henry’s Law Constants for Dissolution of Fission Products in a Silicate Fallout Particle Matrix, Report GA-7058, General Dynamics Corp., General Atomic Div., Dec. 29, 1966. P. Winchell and J. H. Norman, A Study of the Diffusion of Radioactive Nuclides in Molten Silicates at High Temperatures, in High Temperature Technology, Proceedings of the Third International Symposium, Asilomar, Calif., Sept. 17, 1967, p. 479, Butter- worth & Co. (Publishers) Ltd., London, 1969. C. E. Adams, J. T. Quan, and W. R. Balkwell, High Temperature Measurements of the Rates of Uptake of Molybdenum Oxide, Tellurium Oxide, and Rubidium Oxide Vapors by Selected Oxide Substrates, in Radionuclides in the Environment, Advances in Chemistry Series, No. 93, pp. 35—62, American Chemical Society, Washington, D. C., 1970. E. W: Bloore; R. F. Benck;, D..A. Furey, P: CG. Harris, B. L: Houseman; and L. A: Walker, The Mechanisms of Fallout Particle Formation, Annual Progress Report for Period Ending April 1969, Report NDL-SP-36, U. S. Army Nuclear Defense Laboratory, 1969. I. J. Russell, Fundamental Studies in Fallout Formation Processes, Progress Report, June 1, 1967, to: May 31,1968; USAEC Report NYO-3756-2, Boston College, June 1; 1968. S. Z. Mikhail, Beta-Radiation Doses from Fallout Particles Deposited on the Skin, this volume. J. H. Norman, P. Winchell, H. G. Staley, M. Tagami, and M. Hiatt, Henry’s Law Constant Measurements for Fission Products Absorbed in Silicates, in Thermodynamics of Nuclear Materials, 1967, Symposium Proceedings, Vienna, 1967, p. 209, International Atomic Energy Agency, Vienna, 1968 (STI/PUB/162). J-iGhs Normman,.“P.” Winchell, “Jo M: (Dixon, B:: W. Roos; and RK. F. Korts, Spheres: Diffusion-Controlled Fission Product Release and Absorption, in Radionuclides in the Environment, Advances in Chemistry Series, No. 93, pp. 13—35, American Chemical Society, Washington, D. C., 1970. R. W. Douglas and T. M. M. El-Shamy, Reactions of Glass with Aqueous Solutions, J. Amer. Ceram, Soc., 50: 1—8 (1967). M. N. Elliot and D. B. Auty, The Durability of Glass for the Disposal of Highly Radioactive Wastes: Discussion of Methods and Effect of Leaching Conditions, Glass Technol., 9: 5—13 (1968). J. Ralkova and J. Saidl, in Treatment and Storage of High-Level Radioactive Wastes, Symposium Series, Vienna, 1962, p. 347, International Atomic Energy Agency, Vienna, 1963 (STI/PUB/63). R. Bonniaud, C. Sombret, and F. Laude, in Treatment and Storage of High-Level Radioactive Wastes, Symposium Series, Vienna, 1962, pp. 366—368, 372—373, Inter- national Atomic Energy Agency, Vienna, 1963 (STI/PUB/63). 30 NORMAN AND WINCHELL 21. W. E. Clark and H. W. Godbee, in Treatment and Storage of High-Level Radioactwe Wastes, Symposium Series, Vienna, 1962, p. 430, International Atomic Energy Agency, Vienna, 1963 (STI/PUB/63). 22. B. P. Locsei, Acid Resistance of Vitroceramic Materials on a Feldspar-Diopside Base, in Symposium on Nucleation and Crystallization in Glasses and Melts, p. 71, American Ceramic Society, Columbus, Ohio, 1962. 23. j. Crank, The Mathematics of Diffusion, p. 87, Oxford University Press, London, 1956. BETA-RADIATION DOSES FROM FALLOUT PARTICLES DEPOSITED ON THE SKIN S. Z. MIKHAIL Environmental Science Associates, Burlingame, California ABSTRACT Absorbed beta-radiation dose expected from fallout particles deposited on the skin was estimated by use of the Beta Transmission, Degradation, and Dissipation (TDD) model. Comparison of computed doses with the most recent experimental data relative to skin response to beta-energy deposition leads to the conclusion that, even for fallout arrival times as early as 10° sec (16.7 min postdetonation), no skin ulceration is expected from single particles 500 uw or less in diameter. Doses from arrays of fallout particles of different size distributions were computed also for several fallout-mass deposition densities; time intervals required to accumulate doses sufficient to initiate skin lesions were calculated. In 1954 residents of Rongelap Atoll in the Marshall Islands were exposed to fallout arriving within hours after detonation of the Castle Bravo nuclear device. Several of the atoll’s inhabitants suffered severe skin burns. Primarily as a result of this experience, the possibility of “beta burn” from nuclear fallout has been recognized. However, to date, attempts to predict the acute or chronic skin effects that might be expected following exposure to fallout have been limited. This limitation results mainly from the lack of experimental data on the biologic response of the skin to particulate-source exposures, from incomplete under- standing of the relation of such response to that encountered in other localized exposures (e.g., collimated X-ray beams) for which data are available, and from the absence of reliable beta-dose calculational models. All these are required to relate dose to observed effect in a manner allowing prediction of the biological effects from knowledge of the expected fallout interaction. The literature indicates that work on the theoretical aspects of the beta-dose problem has progressed faster than have experimental efforts. As early as 1956 Loevinger, Japha, and Brownell devised an analytical representation (model) to calculate beta doses from “discrete radioisotope sources.”' By 1966 four models 31 29 MIKHAIL were available.” The most precise, though complex, of these models is the Transmission, Degradation, and Dissipation (TDD) model.” This paper is based on the TDD model and presents predicted beta doses that would result from skin deposition of nuclear-weapon fallout particles. A nuclear attack on the United States would be expected to result in low-intensity gamma-radiation fields over much of the fallout area that would develop. Exposure to the low-intensity field would pose little or no immediate or long-term whole-body gamma-radiation hazard. However, it has been suggested that in such situations contact of individual fallout particles with exposed skin could constitute a potential hazard. Individual particles can deposit on the skin via direct deposition during passage of the fallout cloud or following resuspension of particles at a later time. Each particle, if radioactive enough, is capable of producing a lesion. If several particles reside close enough in the same general skin area, their effects could be additive, in the sense of causing one lesion. However, at larger particle-separation distances, beta-radiation dose deliveries would not interact. That is, the dose contribution from one particle to the tissue in the vicinity of another particle would be negligible. This situation is treated separately in the next three sections. At small particle-separation distances, estimation of the dose delivered at any point in tissue would require summation of the dose contributions from all particles in the immediate vicinity. This latter situation is treated separately also. THE SINGLE-PARTICLE BETA-DOSE MODEL The TDD model for single particles 1s composed of six separate semr independent computer codes. The first (Code 1) is a nuclide-abundance code that calculates the activity of each radionuclide generated in the detonation of a nuclear device or weapon. This code also considers radioactive decay and calculates fission-nuclide activity at any postdetonation time. Code 2 computes the beta spectrum for each beta-emitting nuclide, given the end-point energies, beta branching fractions, and degree of forbiddenness of the beta transitions.* Output from this code is a sequence of values representing the probability that a beta particle will be emitted with an energy between E and E + AE, where AE = 0.04 MeV and values for E range from 0 to the maximum 6 energy, Emax. Individual fission-product beta spectra have been generated and are stored on tape for use with the composite-spectrum code (Code 3). Code 3 is a composite-spectrum routine that sums the individual beta spectra of the fission-product nuclides with appropriate weighting for the activity of each contributing nuclide, as determined by Code 1. Code 3 produces a point-source beta spectrum at a given time for the specific weapon under consideration. Output from this code is a sequence of values representing the number of betas per energy interval emitted by the source. BETA-RADIATION DOSES FROM FALLOUT PARTICLES 33 The electron spectrum from a fallout particle (assumed to be spherical in shape) differs from that produced by a point source because scattering and absorption processes within the particle degrade the spectrum. Calculation of the extent of degradation is complicated by the fact that in fallout particles some fission products are uniformly distributed within the particle material, others have condensed on the particle surface, and the rest behave in an intermediate fashion.” Korts and Norman developed a model,” termed the Condensed State Diffusion Controlled Model, which describes the mechanism of fission-product absorption in fallout material distributed in a radioactive cloud following a nuclear detonation. In this model they assumed that (1) the fallout material is glassy silicate; (2) the surface of a fallout particle is in equilibrium with the gas phase; and (3) the rate of transfer of fission products into the interior of the fallout particle is diffusion controlled. One output of this Condensed State Diffusion Controlled Model consists of a set of radial fission-product-concentra- tion profiles in fallout particles of different sizes. Using such concentration profiles, Korts and Norman calculated for each fission product the percentage of total nuclide present which would diffuse into the particle. In almost all cases examined, they found that “loadings” of 0, 25, 50, 62.5, 75, 82.5, and 100% (by weight) could be used to describe the portion of fission product present diffusing into the particle. (The complementary percentage in each of the seven classes represents the portion of the fission product present that remains at the particle surface.) Zero percent diffusion takes place when the fission product condenses on the particle surface, essentially without any diffusion during particle cooling; whereas. 100% diffusion represents complete diffusion leading to homogeneous distribution of the fission product in the silicate matrix. This Condensed State Diffusion Controlled Model was used in the manner described in the following paragraph to provide the geometric basis for the electron degradation within fallout particles. Degradation suffered by the emanating electron spectrum is handled by Code 4, a Monte Carlo program that starts with a given number of emitted betas in a specified energy interval and then computes the loss in electron energy and number due to scattering and absorption processes within the particle. The code outputs two sets of Monte Carlo determined energy-dependent loss coefficients, set A for homogeneously distributed fission products and set B for surface- condensed fission products. These coefficients are then applied to the composite beta spectrum from the point source of fission products (Code 3) by Code 5. Application of these loss factors is straightforward for the 0 and 100% diffusion cases (in which set B and set A, respectively, are utilized). For five intermediate diffusion cases, set A was applied to the percentage diffusing into the particle, and set B was applied to the percentage remaining at the surface. Output of Code 5 thus consists of a degraded beta spectrum emerging from a fallout particle of a specified size. 34 MIKHAIL Code 6 operates on the resulting composite degraded spectrum to com- pute the depth-dose rate in tissue. This is based on energy-dissipation factors for fast electrons as calculated by Spencer.°® The dose rate, D; (in rads per hour), at a tissue depth Z centimeters from a particle of volume V (in cubic centimeters) emitting N.(E,) beta particles per second per cubic centimeter in the energy interval AE with mean energy Eg (in million electron volts) (this is the emerging degraded spectrum in the present work) is given by: kfgV prot bmax ARM De=qay? Meg-ab/2 J) (dE/dr)g 4 Ne(Eo) oe where k=a constant, 5.76X 10° (rad-g-sec)/(MeV-hr), relating energy- transport rate to dose rate f = dimensionless correction factor for a semtrinfinite absorber, deter- mined from an auxiliary Monte Carlo program g = ratio of dose rate at a distance Y (in centimeters) from the center of a spherical source (radius R in centimeters) to the dose rate from a point source at .ther sametdistances (GYR); athe ratio assed dimensionless quantity given by SY Ro ve a) 22251 05a 02 in 2 BR? = ) in (X48 C2, J(x) = Spencer’s energy-dissipation-distribution function evaluated at tis- wn sue depth Z measured in units of the normalizing residual range, ro; x = z0/t9, p being the density of the absorbing medium® (dE/dr)g ) = stopping power of the absorber for electrons emitted from the particle with energy Eo The resulting dose rates, summed over the composite degraded spectrum, form the output of this part of the model. The final operation of the composite TDD model integrates the various dose rates (from each energy interval) computed via Eq. 1 over time to get the total absorbed dose. In practice, to reduce computation time, we carry out the integration by the use of time-integrated beta activities derived from the inventory code (Code 1) to make up a time-integrated composite beta spectrum. This spectrum is then degraded and deposited in tissue as explained previously; i.e., the time integration is done from the start rather than as the last step. Recently the six codes have been unified into a single modified composite program to reduce computer run time.’ Also, several new features have been introduced into the composite program to increase its ability to cope with a variety of beta-dose problems.* BETA-RADIATION DOSES FROM FALLOUT PARTICLES 39 EVALUATION OF THE SINGLE-PARTICLE MODEL Validity of the TDD-model dose predictions has been examined® by comparing the model-computed doses delivered by reactor-irradiated UC, particles with (1) doses from the UC, particles measured with a B-extrapolation chamber;’ (2) values for UC, particle dose obtained by a photographic-film dosimetry technique; and (3) dose values computed by applying a completely independent Monte Carlo calculational technique. Tests included doses at shallow as well as at relatively large depths (7500 p) in tissue and at points directly underneath the particle and points radially displaced to distances as far as 5000 uw. Particles of variable sizes and reactor irradiation times of different duration were also included in the comparisons. 2.4 ~ =) —_ [@>) DOSE RATIO (MODEL TO oS 00 EXTRAPOLATION CHAMBER READING) N =) b 0 85 105 125 230 250 270 290 PARTICLE CORE DIAMETER, yu Fig. 1 Ratio of calculated (TDD model) dose to dose measured with a B-extrapolation chamber (tissue depth, 30 y). Typical results obtained in the comparisons with data from the extrapolation chamber, the Monte Carlo program, and the photographic-film exposure technique are presented in Figs. 1, 2, and 3, respectively. The primary conclusions drawn from the comparisons were:® 1. On the whole, agreement between values obtained by use of the composite program and those obtained by experimentation and exercise of the cited Monte Carlo program was satisfactory. 36 MIKHAIL O, Extrapolation chamber fissions/ce. assumed in the particulate approach (Fig. 6). For a fixed maximum size, the difference decreases as the mean particle size decreases, but a factor of 5 was the smallest encountered for the cases considered. DOSE CRITERIA FOR MULTIPLE-PARTICLE DEPOSITION To date no criterion has been explicitly proposed for skin damage from multiple particles. However, the following points serve as guidelines for establishing such a criterion: 1. As in the case of single-particle sources, damage to the skin will occur when the survival level of the germinative cells is reduced to less than 0.001 over an area sufficiently large to preclude replacement of dead cells via prolifera- tron. + 2- Such?" areduction\/in ‘survival’ occurs, at a lower dose level’ from. a multiparticle source than from a single-particle source. Krebs estimates that a uniform 1300-rad dose from a multiparticle source would cause the same reduction in survival level brought about by a 1500-rad dose from a single-particle source.'* 42 MIKHAIL 3. In view of the difference between the predicted single-particle critical dose (1500 rads) and the corresponding experimentally determined value of 660 rads, an adjustment has to be made to the suggested multiple-particle value to bring it into line with experiment. 4. It seems reasonable to accept a proportional dose for the multiparticle situation; 1.e., (1300/1500) X 660 ~ 570 rads. That is, exposure of the skin (100-u depth) to a uniform deposited dose of 570 rads from a multiple source will be assumed sufficient to damage the skin in the manner described for the single-particle exposure. RESULTS AND DISCUSSION Doses from Single Particles Point depth doses (estimated at 100-u tissue depth directly below the fallout particle) and Krebs doses (estimated at a point radially displaced 4000 wu in a plane 100 yu below the skin surface) were computed for particles 50, 100, 200, 500, 750, and 1000 wu in diameter; for each particle size, doses were computed for Os” OE” 10°. and 10° sec of delay time (time between weapon detonation and deposition of the particle on the skin). The fallout particles were assumed to contain 10!° fissions per cubic centimeter. For all but exceptional situations, 10'° fissions/ce is considered the maximum expected fallout activity. Beta doses from fallout of higher fission density can be obtained from the values reported here by linear extrapolation. Figures 7 to 10 present samples of the computer-plotted doses as functions of particle retention time on the skin. It can be seen from Fig. 7, which presents Krebs doses for the earliest particle arrival time considered, that single fallout particles smaller than 500 wu in diameter, landing on the skin as early as 10° sec (16.7 min) after detonation, will not cause any skin burns. A single 500-u particle arriving even this early has to be retained about 10 hr before it delivers the 660 rads required for damage. Table 1 shows experimental data obtained at Oak Ridge National Laboratory (ORNL) for expected retention times of particles on human skin under normal conditions of temperature and humid- ity.'* Considering the values in Table 1, even a 500-y particle would obviously be incapable of producing a 1-mm lesion. Figure 8 presents the point depth doses delivered by the same particles under the same (early arrival) conditions. Comparison of Figs. 7 and 8 shows that point depth doses are higher than the corresponding Krebs doses by a factor of 107 to 10° depending on the particle size. Lower ratios correspond to larger particle SIZES. From Figs. 9 and 10, it can be seen that, after a delay of a little over 10° sec (about 2.8 hr), even a 1000-y particle can be tolerated, provided its retention time does not exceed its expected value in Table 1. BETA-RADIATION DOSES FROM FALLOUT PARTICLES 43 10° Particle diameter, 1000 750 500 10° 10! 10° 10° RETENTION TIME, hr Fig. 7 Krebs dose delivered to the skin by single fallout particles at an exposure starting time of 10° sec after detonation. Tissue depth, 100 yu. 10° : Particle diameter, 1000 750 500 10° s © T107 LW icp) O QO 10° 4anZ 10 10° 10! 10? 10° RETENTION TIME, hr Fig. 8 Point depth dose delivered to the skin by single fallout particles at an exposure starting time of 10° sec after detonation, Tissue depth, 100 x. 44 MIKHAIL Particle diameter, wu! rads DOSE, 10° 10! 10° 10° RETENTION TIME, hr Fig. 9 Krebs dose delivered to the skin by single fallout particles at an exposure starting time of 10 sec after detonation. Tissue depth, 100 yu. 104 Fin Pat ak _suiret. Fat Fen Papaetas, ? F Particle diameter, q 7 1000 4 | fea = 750 660 zara = 500 = 200 100 50 RETENTION TIME, hr Fig. 10 Krebs dose delivered to the skin by single fallout particles at an exposure starting time of 10° sec after detonation. Tissue depth, 100 yu. BETA-RADIATION DOSES FROM FALLOUT PARTICLES 45 Table 1 EXPECTED RETENTION TIMES-OF PARTICLES ON HUMAN SKIN* Particle diameter, u Time, hr 50 6.8 100 345 200 Doi) 500 Dae, 750 2.1 25 _~ — 1000 *From Ref. 14. Figure 10 shows further that, after a delay of 10° sec (about 28 hr), no single particle of any size can possibly cause a beta burn (except for the 1000-u particle retained for an inordinately long time). Doses from Multiparticle Fallout Samples of the data computed with the Multiparticle Model are shown in Figs. 11 to 15. In these figures time-integrated doses from fallout deposition densities of 100, 200, 500, 1000, 2000, and 5000 mg/sq ft for different particle-size distributions have been plotted as functions of fallout retention time. All computations are based on 10!° fissions/cc. Delay times of 10>. 10" 10°, and 10° sec are covered. Figure 11 shows that for a delay time of 10° sec even the lowest deposition density (100 mg/sq ft) of particles of 100-u mean diameter and 1000-u maximum diameter (size distribution A) can deliver to the skin in less than 1 hr more than the 570 rads required for damage in the multiparticle situation. However, as seen in Fig. 12, the same mass of fallout of 1000-u mean diameter and 2000-4 maximum diameter (size distribution B) delivers a maximum of only 300 rads, even if retained over 100 hr. Other size distributions give intermediate doses. The situation changes somewhat at the next higher fallout-arrival (delay) time, 10* sec. A 200 mg/sq ft deposit of size distribution A can be tolerated in this case for about 1.5 hr (Fig. 13). After a delay of 10° sec, a 2000 mg/sq ft deposit of size distribution A gives the critical 570 rads in about 1.5 hr (Fig. 14); after a delay of 10° sec (11.5 days), it takes 5000 mg/sq ft of the same size distribution about 10 hr to cause skin burns (Fig. 15). Other formulations of output data can be derived from the multiparticle dose computations. A few examples follow. 46 MIKHAIL 10° Deposition density, mg/sq ft 5000 e102 2000 me} ® ui 1000 icp) fo) (ce) ay 500 When young bean plants were exposed to ?°Y radiation,” both contact- source and beta-bath geometries produced plant sterility at estimated doses of 100,000 rads to leaves and 2000 rads to meristems. Although these few results only indicated a range of expected results, they verified the need for additional studies of beta-dose computation and measurement. The theoretical basis for the interpretation of beta dose was investigated by comparing the results of computational models*’* with experimental measure- ments made with lithium fluoride powder exposed to a variety of ?°Y sources.” In the simplest geometries the comparison was quite good, but the computa- tional procedures were not sufficiently developed to deal accurately with some 51 52 MACKIN, BROWN, AND LANE of the more complicated cases. In a damage-assessment context, however, the discrepancies were not large enough to make damage estimates grossly uncertain. In such a context, then, the agreement for the relatively simple geometries was adequate. Real fallout exposures are not even relatively simple, however; they deal with very complex geometries that would require an inordinate effort to model mathematically. Methods must be sought that can estimate beta damage with much less effort. APPROACH The specific objective of our investigation® was to develop better dosimetric methods for use in biological-effects experiments and thus to provide a means for relating observed effects to existing and revised computational methods. To this end, a small beta dosimeter was developed and tested in the laboratory and then was used to measure beta doses in field experiments conducted by cooperating investigators. Preparation of Sources In all cases the basic starting material for the preparation of each radiation source was an essentially carrier-free solution of ?°Y activity. Aliquots were taken from each solution to prepare sources in the form of (1) activity uniformly dispersed in gelatin, (2) evaporated aliquots of solution, and (3) synthetic fallout. The gelatin sources were prepared simply by adding measured amounts of active solution to stirred suspensions of gelatin in distilled water and pouring the gelatin into suitable molds for hardening. Sources prepared from liquid aliquots were made by stretching Mylar film over a given substrate, usually a clear plastic. A small aliquot was handpipetted onto the film and then air dried. The sources were stripped from the substrate after exposures were completed and were measured directly in the ionization chamber. The basic material employed for the preparation of solid sources was synthetic fallout of particles in the sieve size range of 88 to 177 u. The fallout simulant was prepared by spraving an aliquot of radionuclide solution on a sized portion of warm sand, heating it slowly to dryness, and then thermally treating it at high temperature so that the activity is fixed on the particle surfaces. Solid sources for surface-roughness experiments were prepared by dispersing the simulant in air and permitting the particles to fall under gravity. A cylindrical pipe 3 ft long and 6 in. in diameter, positioned over the substrate, was used to direct the particles uniformly over a circular area. In the field experiments the method of fallout-simulant dispersal was determined by the cooperating investigator. The University of North Carolina experiments used a shielded container from which the simulant was dispersed through a slit. The container was moved over the plots by hand. In the MEASUREMENT AND COMPUTATIONAL TECHNIQUES ye) University of California experiments, the method of dispersal utilized a motorized hopper that reciprocated across the plot while being moved down the plot on railings. Dispersal was accomplished by a rotary rod that fed simulant into a long slot as in a lawn seeder. Radiation Dosimetry A principal objective of the research was to develop a dosimetric method that was more convenient than the loose-powder method used in the previous work. The loose-powder method used thermoluminescent lithium fluoride (LiF) powder, which has a wide range of dose sensitivities (from a few millirads to kilorads), low energy dependence, reproducibility, and stability. A disadvantage of the loose-powder method is that much care must be exercised both in emplacement and in subsequent recovery of the material. To surmount this difficulty, we mounted a joint effort with Radiation Detection Co. to design a convenient dosimeter with the features mentioned previously. The dosimetric material was again LiF powder,* in the size range 80 to 200 mesh, which was obtained in quantity and standardized with °°Co. Calibration of each dosimeter independently was unnecessary. This simplified the experimental procedures since the dosimeters were completely inter- changeable. Calibration was based on exposure of aliquots of powder to °°Co and on the factor 0.807 rad/R. The factor was based on 0.869 rad deposited in air per roentgen and 0.929 for the ratio of stopping powers for °°Co gammas for LiF and air. The LiF powder was encapsulated in glass capillary tubing approximately 2mm in outside diameter and about 0.1 mm (31.8 mg/cm? ) thick and was sealed by flaming. The dosimeters, which averaged about 5 mm long and contained either 6 or 12 mg of LiF powder each, were individually tested for environmental closure by being allowed to stand under 30cm of water for 15 min or longer. When returned to Radiation Detection Co. for readout, they were placed in a special planchet, and the luminescence was measured directly through the glass in a Mark IV model 1100 TLD Reader. Method of Comparison Theory and experiment were compared in terms of the disintegration-rate multiplier (DRM). The DRM for experimental results is obtained by dividing the observed dose by the total number of disintegrations during the period of exposure: at Dai perm = 2 (1-2) (1) *The powder used was Radiation Detection Co. ‘‘Throwaway” Powder, Batch 8/69, having linear response to gamma radiation through 10,000 rads. 54 MACKIN, BROWN, AND LANE where D = dose, rads Bo = initial source strength, dis/sec/unit area, volume, or mass, as ap- propriate \ = decay constant for ?°Y (3.0 X 10 ©/sec) t = exposure time, sec : Infinite-medium methods, line-of-flight perturbation methods, or pseudo- source methods were used in the computation of beta dose. These models are described in another report® and will not be discussed here. In judging the adequacy of the comparisons, we developed the rule of thumb that agreement with a factor of 2, on the average, was acceptable. This degree of uncertainty has been shown to result in less than 10% uncertainty in damage-assessment results. Results of Experiments Several laboratory experiments were conducted to test the dosimeter. First, dosimeters were calibrated by exposure to an effectively infinite uniform-volume source. Next, verification of their performance was obtained with exposures at various distances from a point source. The geometrical backscattering effect previously reported was again observed. A series of exposures using a fallout-simulant source distributed on sized pebble substrates was then per- formed. The general features of the measured surface-roughness attenuation factor were similar to those found before, but the variation in the factor with substrate particle size was less pronounced than previously, probably because of differences in handling between dispersal and exposure. Several sets of field-exposure measurements were also conducted. Two plant communities were contaminated with fallout simulant by investigators from the University of North Carolina, and dose measurements were made with SRI dosimeters. The comparison of measured and calculated doses was satisfactory within the uncertainties of the exposure geometry. Next, a plot of corn plants was contaminated with fallout simulant by investigators from the University of California, Berkeley, and again dosimeters were distributed on and near the plants. Agreement was not so good as previously, because of difficulties in dispersing the simulant and recovering the dosimeters, but order-of-magnitude agreement was obtained. In a second University of California series plots containing wheat and potato plants were contaminated. Agreement between measured and calculated values was again found to be good, except where the computational model was clearly inappropriate. The final set of dose measure- ments, taken over a smooth plot of contaminated loam, yielded a surface- roughness factor of about 0.75. Reasonable agreement between edlcdlared and observed beta doses can therefore be obtained when sufficiently good input information can be provided for the computations. More effort is indicated to obtain better input values for such parameters as plant density and fraction of fallout retained on foliage. MEASUREMENT AND COMPUTATIONAL TECHNIQUES 55 Attention should also be given to empirical dose-prediction methods that do not depend so heavily on precise input information. REFERENCES 1.S. L. Brown, Disintegration Rate Multipliers in Beta-Emitter Dose Calculations, USAEC file No. NP-15714, Stanford Research Institute (SRI Project No. MU-5116), August 1965. 2.W. B. Lane and J. L. Mackin, Response of Bean Plants to Beta Dose Problems, Report TRC-68-16, Stanford Research Institute, November 1967. 3.S. L. Brown and O. S. Yu, Computational Techniques in Beta Dose Problems, Report TRC-68-13, Stanford Research Institute, January 1968. 4.S. L. Brown, Beta Radiation Effects on Agriculture, Report TN-RMR-34, Stanford Research Institute, June 1968. 5. J. L. Mackin, S. L. Brown, and W. B. Lane, Beta Radiation Dosimetry for Fallout Exposure Estimates: Comparison of Theory and Experiment, Report TRC-69-26, Stanford Research Institute, June 1969. 6.S. L. Brown, W. B. Lane, and J. L. Mackin, Beta Radiation Hazard Evaluation, Stanford Research Institute, (in press). MEASUREMENT OF BETA DOSE TO VEGETATION FROM CLOSE-IN FALLOUT A. D. KANTZ EG&G, Inc., Santa Barbara Division, Goleta, California ABSTRACT Dosimetry experiments are described in which both beta and gamma-ray doses to the environment and to vegetation were measured with thermoluminescent dosimetric tech- niques in the close-in fallout fields from the Plowshare cratering events Cabriolet and Schooner. The beta doses measured were found to be an order of magnitude greater than the gamma-ray doses at the same locations. This work was performed in support of ecological- and environmental-effects studies sponsored by the Environmental Sciences Branch of the Atomic Energy Commission’s Division of Biology and Medicine. Before the Plowshare Palanquin event in April 1965, radiation damage to vegetation from nuclear detonations, whether aboveground or belowground, was attributed largely to heat, blast, and thermal shock.'” After the Palanquin detonation, however, extensive damage to vegetation was observed over an area of about 4km?* in which there was no evidence of blast, shock, or thermal damage except in the immediate vicinity of the crater.'° Since an experimental study of the gamma-ray doses required to kill the various types of vegetation prevalent at the Palanquin site revealed that the amount of radiation encountered on the peripheries of the damage patterns was insufficient to account for the observed damage, it was hypothesized that beta radiation was a contributing factor. To validate this view, we developed special dosimetry techniques for measuring the gamma-ray and beta dose in the fallout fields of subsequent Plowshare cratering events. The objectives were to: 1. Determine the total dose to plants and distinguish clearly between gamma-ray and electron contributions. in) . Evaluate any low-energy photon contribution. 3. Specify as much information as possible regarding the energy and distribution of the beta sources. 56 MEASUREMENT OF BETA DOSE TO VEGETATION 57 This paper describes the dosimetry techniques and their application to radiation-dose measurements in support of ecological- and environmental-effects studies sponsored by the Environmental Sciences Branch of the Atomic Energy Commission’s Division of Biology and Medicine during the Cabriolet and Schooner cratering events at the Nevada Test Site in 1968. The assessment of vegetation damage is described in studies by Rhoads et al.'!"!? DOSIMETRY TECHNIQUES The general characteristics of fallout radiation expected from a cratering event include a 1-MeV gamma-ray component, an associated beta component with energies in the 1-MeV region, and a possible low-energy-photon character- istic. Two approaches for measuring this mixed field are equally valid: (1) measurement of fluence and interpretation of dose deposition or (2) direct measurement of absorbed dose in some material and correlation with another material through known absorption coefficients. Because of time constraints and the need for obtaining the best information possible on the beta source, we chose the more straightforward of the two methods, that of measuring fluence by determination of depth-dose profiles, for the Cabriolet and Schooner events. Dosimeter Design The dosimeters for these experiments had to be designed to accommodate very wide dose ranges and to be capable of withstanding weathering under severe winter conditions at an elevation of 6000 ft for a period of several weeks. Also, because of the large number of dosimeters required, logistical considerations made it desirable for the dosimeters to be easy to fabricate, field, and analyze. Calcium fluoride (CaF 2) appeared to fulfill these requirements, and_ther- moluminescent dosimeters (TLD’s) made up of hot-pressed chips of CaF,—Mn measuring 3 by 3 by 1.5 mm were constructed. The dosimeters, which were designed to simulate energy deposition from ionizing radiation in plant tissue, consisted of a 32-mm-square piece of 3-mm-thick plastic polycarbonate containing eight holes, each 7 mm in diameter (see Fig. 1). The CaF,—Mn chips, with individual shields, were placed in the holes, and the entire dosimeter was covered by a thin, light-tight film. The shielding for the chips during the Cabriolet event was as follows: (1) none except the thin, light-tight covering, (2) 0.17-mm Mylar, (3) 0.55-mm polycarbonate, (4) 1.55-mm polycarbonate, (5) 0.85-mm aluminum, and (6) 0.5-mm lead. Since the thickness of the TLD chips was sufficient to completely stop electrons with energies up to 1.0 MeV, readings on individual chips were proportional to energy fluence incident on the chip. The change in fluence (ergs per square centimeter) as mass was added in front of the TLD was used to infer the dose (ergs per gram). 58 KANTZ Fig. 1 Thermoluminescent dosimeters (TLD’s) constructed for the Cabriolet event. Shown from left to right are the open TLD holders, the holders with chips in place, and the dosimeters ready for use in the field. Shielding was selected to produce a gradual decrease in beta contribution, the thickest shield being capable of stopping the most energetic beta particles. This thickness, however, did not require significant correction for the absorption of 1-MeV gamma rays. The presence of a low-energy-photon component could be inferred by differences in the stopping power of polycarbonate and aluminum. These materials present equal absorption of electrons but have a Z dependence for absorption of low-energy photons. Thus a high reading for the polycarbonate-shielded chips signified a low-energy-photon component whose magnitude could be estimated. Field Arrangement For the Cabriolet event the dosimetry stations were positioned along two arcs (Fig. 2). This arrangement was based on records of the early dose rates for the preceding Palanquin event and on the availability of materials and personnel. The first arc was along a radius 610m (2000 ft) from ground zero (GZ), extending from 330° on the west to 90° on the east. The second arc, which was along a radius 915 m (3000 ft) from GZ, was much shorter than the first and covered the direction from GZ considered most likely to be contaminated on the basis of weather conditions anticipated at the time of the event. MEASUREMENT OF BETA DOSE TO VEGETATION 59 915 METERS (3000 FEET ) ) iS STATIONS |- 45 65° 610 METERS (2000 FEET ) SCALE IN FEET SCALE IN METERS ee ee Se | 0 500 1000 10) 100 200 300 Fig. 2 Map of the Cabriolet area, showing locations of arcs along which dosimetry stations were positioned. At each station along the arcs, the dosimeters were suspended from a vertical wire and were arranged in an array so that each dosimeter lay in a horizontal plane. The dosimeters were spaced above the soil surface at various distances to take advantage of the beta shielding represented by the air path from the ground to the dosimeter. The highest dosimeter was 150 cm above the soil surface; this was expected to be sufficient to raise it out of the beta bath. 60 KANTZ Plant Correlation Additional smaller dosimeters with only three chips were prepared and placed directly on shrubs in the vicinity of the vertical arrays. It was expected that the readings from the dosimeter 25 cm above the soil surface in the vertical array would closely resemble the average absorbed dose in the surrounding shrubs. The smaller dosimeters were fabricated with the following shielding: (1) minimum shielding, afforded by the thin cover, (2) a thick cover of lead capable of completely stopping the electrons so that no beta dose could be received, and (3) an intermediate shielding representing the gamma-ray background and a fraction of the beta contribution. The dosimeters were arranged carefully’-on the exterior of shrubs in the immediate vicinity of the vertical stations and were oriented so that one dosimeter was on the front of the shrub (toward GZ), one on the back, one on the top, and one at a third side. To further delineate the radiation levels, we fabricated a plant phantom for use as a fallout collector for each vertical array. The phantom consisted of two wire-mesh cylinders, one placed inside the other, with opposite ends closed. The cylinders were covered with cheesecloth, which had previously proved to be an efficient collector of radioactive debris. The retentive capacity of the phantoms for fallout was expected to be similar to that of actual shrubs. Dosimeters were placed on the shrub phantoms to correlate with the vertical arrays. These dosimeters successfully measured the small differences in both gamma-ray background and beta dose in the various geometries described. Dosimeter Readout and Analysis The dosimeter packages from the field were individually read out in a standard EG&G model TL-3 reader. Since the chips were calibrated against a standard °°Co source, the scale readings were a direct measure of the exposure in roentgens. The energy deposited in a CaF, —Mn chip when it is exposed to a calibrating °°Co source is E, = 86R(pAt) ergs (as) where R = exposure in roentgens p = density of the dosimeter A = area of the dosimeter t = thickness of the dosimeter The light emitted when the dosimeter is read is proportional to the energy (E, ): EA = cE, (2) MEASUREMENT OF BETA DOSE TO VEGETATION 61 When the dosimeter is exposed to low-energy beta radiation and subsequently read out, the energy deposited per unit area is Bat ps lea SORPAt 3 ? A cA px Ly roe (3) If the readout instrument is adjusted to read in roentgens (R — L, ), the final calibrating formula is od = 86pt X L, ergs/cm* (4) For a typical chip pt is 0.550 g/cm’. The calibrating relation is then @ = 47.3L, ergs/em? (5) where L2 1s the scale reading on the dosimeter. Dose may be inferred from the readings @,; and $2 on two dosimeters covered by absorbers having masses m, and m2: DME 1 — $2 (6) 19 OV pit) 09%) In this case dose is determined for the absorbing material. Data taken with the use of Mylar may be used to infer dose in water by multiplying by the stopping power for water and dividing by the stopping power for Mylar: (dE/dx) 1,0 i aaa (7) (dE/dx) Mylar DH,0 = DMylar RESULTS AND DISCUSSION Project Cabriolet Dosimetry The data from each array were plotted as a function of shield thickness. Station 7, near the center of the fallout pattern, shows the typical decrease in scale readings with increasing shield thickness (Fig. 3). The residual reading (from the lead-covered chip) was due to gamma-ray radiation. For every station the gamma-ray contribution was found to be the same for each vertical position, within a probable error of +3%. The contribution of the gamma-ray dose was subtracted and the beta contribution evaluated from plots for each of the stations recovered. The penetration by the beta source through the shielding indicated an average range 62 KANTZ of about 325 mg/cm* of Mylar. This corresponds to a beta source having a maximum energy of approximately 850 keV. The maximum gamma-ray dose encountered on the Cabriolet event in the center of the fallout pattern was approximately 700 rads (absorbed dose in water). Figure 4 shows the variation seen in the gamma-ray dose from the vertical array, from shrubs in the immediate vicinity of the stations, and on simulation shrub phantoms. 300 —O——0-,, 25 cm off ground -O-—-0-, 150 cm off ground —+—2-, Ground level 200 100 TLD READER RESPONSE 0 100 200 300 400 500 DEPTH, mg/cm? OF MYLAR Fig. 3 Depth dose at Station 7 (Cabriolet). Figure 5 illustrates the gamma-ray radiation doses experienced by Artemisia shrubs in the vicinity of the stations and the variations in the doses received by the fronts, tops, and backs of the shrubs. It is evident from the illustrated data that the fronts received the greatest gamma-ray dose; the backs were protected to some extent. As anticipated, the variations in the doses were greatest in the center of the fallout pattern where erratic distribution could be expected. The beta doses shown in Fig. 6 are derived for the dose that would be absorbed on the surface of vegetation located at that point. The pattern of the variations seen is somewhat different from the gamma-ray distribution. The beta doses tend to increase in the lower topographical regions where the gamma-ray contributions decreased. The protection of the backs of the shrubs is very marked in the center of the fallout pattern. The dependence is shown in Fig. 7. In regions outside the central pattern, the differences between front and back are negligible. 63 ‘QQajolaqe)) swoqueyd pur ‘sqnays ‘ssuts [291919 UO Sdd}aWTISOp Aq painsvou sv ‘QE 02 [ SUOTIIS Iv SasOp AvI-eWWS paseiaAy > ‘BIYq W ‘JONVLSIG IWLNOZIHOH 009 00S O0t OOE 002 OOL 0 5 a ee eee eee y eye eae ales ‘ON NOILWLS O€ 82 OG. 06 2G. 0G Ble Ol Vl CL ol 8 9 v Z UT | | 00d OO€ 00v (4NO} JO UBBW) SWO}UeU, ' i (9944) JO UB|W) Sqn4yUs ‘ | 00S (QAly JO UBAW) Sua}aWUISOP jedIA/ ‘ | 009 MEASUREMENT OF BETA DOSE TO VEGETATION (Y31VM NI 3SOG G3agYHOsEy) spe4 ‘43SOd 002 KANTZ 64 "Qopoliqey) sqnays visiiia74y UO suONtsOd d91U) 1” painsvau sv sasop Avs-euWIeD ¢ “BIT W “FJONVLSIG 1VWLNOZIYOH 009 00S OOP OO 002 00L 0 | | ie | T | al ON NOILVLS O€ 8z OC SUC = Cc, 0G 1 Ol Olu aratl ZL Ol 8 9 p Z 0 LN ee a) ge tae Ngee cS a Oe a ae Ga el | oe S =) EUCCCENTTEE 00c OO0€ OO0v eg’ | go A So \o) Ye) (YH3LVM NI 3SO0 G3gyOSsyv) spes ‘3S0G = aware enon quos+ ' | =) © ico) 002 65 MEASUREMENT OF BETA DOSE TO VEGETATION *(JajOLIqeD) SdXN] ¥I9q JUAPIIUI WIOI SAISOP UONLIPeLrRaIgG 9 ‘BI W ‘JONVLSIG 1VWLNOZIYOH 009 00S 00v OO€ 002d OOL 0 ‘ON NOILVLS 03 8C 9¢ vc cc OC Sl SL vi cl OL 8 9 v c 0 ) | Uy | | | | | J9AQa} PUNO * | punoib jyo wo GZ‘ fl punosb 440 Wo gg ’ | PasaA0991 LOK‘ [| int U 0002 000 000r 000S 0009 0002 (YALVM NI 3SOG G3agsyOSav) spe4 ‘3SO00 KANTZ 66 *Qa]O1IqeD) UOTIRIS YOR Iv SqnaYs vISIUUAaI4Y 991yI JO SyDeq pur ‘sdo} ‘s}UOJZ UO S1d}9UNISOp Aq PdANsRdUI Sv S9sOp kIDq JO ULI|F ZL ‘BI W “FJONVLSIG IWLNOZIYOH 009 00S 00r OO€ 00¢ OOL 0 [Sa ae a pene gee amen cap hy Preeti ana rae | ees eRe aoa ee) ‘ON NOILVLS O€ 8C 92 ve CC 0c .8l. 91 vi cl OL 8 9 v c 0 (US o> ed ene a a aes a a eae ele area i Ne eh ee | | | 0 0001 000¢ OO0€E Soear 000 cole 000S yuod4 * | 0009 (YH3LVM NI 3SO0 G3gHOSsv) spe ‘3SO0 0002 MEASUREMENT OF BETA DOSE TO VEGETATION 67 Project Schooner The area of ecological interest in the Schooner cratering event was a valley protected from the direct line of sight from GZ by canyon walls. The dosimetry instrumentation and techniques used to measure doses to the environment and vegetation were patterned closely after those used in the Cabriolet event. However, certain modifications and additions were incorporated based on the Cabriolet results. The beta penetration to 325 mg/cm? of tissue during Cabriolet indicated that dosimeters should be placed 3 to 4 m aboveground to escape the beta bath. Therefore during the Schooner event dosimeters were positioned at distances of 25, 100, and 300 cm above the soil surface in vertical arrays. Figure 8 shows the results of measurements at Station O near the edge of the central fallout pattern. The depth-dose profile obtained was very similar to that measured at Cabriolet, and the beta penetration was identical. 3000 —O— »- 25 cm — 1 —_-s- 100 cm 2---0---=-- , 300 cm TLD READER RESPONSE 0 100 200 300 400 500 DEPTH, mg/cm? Fig. 8 Depth dose at Station 0 (Schooner). For the Schooner event two of the eight CaF,—Mn chips in the dosimeters were provided with shielding only on the upper side or only on the lower side. Thus a beta source exclusively limited to the ground could be expected to contribute to the dose measured on one of the chips and a source from the sky to contribute exclusively to the other. The results of this directional lead 68 KANTZ Beta—dose source Lead—-covered chips 25 cm === Total beta dose cocccse(neooreee | ead covers Open up woe —-, Lead covers open down BETA DOSE (X 103) 20N 10N 0 10 20 30 40 STATION NO. Fig. 9 Distribution of beta source in the Schooner event. shielding presented interesting information for the interpretation of the beta source. The beta distribution data in Fig. 9 show that in the major fallout pattern (centered at Station 7N) the TLD chips with lead covers open toward the ground experienced three times the beta dose of those open toward the sky. In a secondary peak near Station 33, the contributions are essentially equal; the chips exposed to the sky show a slight additional beta dose compared to those open toward the ground. MEASUREMENT OF BETA DOSE TO VEGETATION 69 The marked differences in the absorbed dose observed at Cabriolet in the fronts, tops, and backs of shrubs were not detected. Instead, dosimeters placed at sthese positions smeceived,, the “Same, dose) within, (the statistics..of the measurements. Also, the type of vegetation damage observed after this event contrasted sharply with that observed at Cabriolet. the. eftects of close-in «fallout on, vegetation at the Schooner site are described in detail by Rhoads et al.'7 in this volume. Direct Dose Measurements for Future Events To supplement the method of determining the energy fluence and the interpretation in terms of absorbed dose, we can use a dosimeter material directly to measure absorbed dose if it absorbs only a negligible portion of the incident radiation (i.e., if, considering an absorption of the form Ege‘, the material is “thin” under the condition that pt © 0). From the experience gained in measuring depth dose in cratering fallout fields, we determined that a direct-reading dosimeter having a small thickness compared with the beta range of 325 mg/cm? could be made. This dosimeter, which consists of a 0.012-in. cube of hot-pressed CaF,—Mn, was found to have a stable geometry, and measurements made with it in radiation fields were consistent within a probable error of +3 R. This small cube can be placed directly alongside a stem, leaf, or branch or at a meristem; thus dosimetric measurements can be made at the vital points of interest to ecological studies. The gamma-ray contributions can be evaluated in a manner similar to that of the fluence measurements by shielding with sufficient material to absorb electrons entirely while producing a negligible effect on the gamma-ray component. In summary, the direct measurement of absorbed dose by the small, 12-mil cubes of CaF,—Mn_ greatly simplifies the logistics of making dosimetry measurements on cratering events. Such dosimeters have been fabricated for use in ecological and environmental studies of fallout effects during any future events. ACKNOWLEDGMENT This work was done under Contract No. AT(29-1)-1183 between Environ- mental Sciences Branch, Division of Biology and Medicine, U. S. Atomic Energy Commission, and EG&G, Inc., Santa Barbara Division. REFERENCES 1. Roy Overstreet et al., Preliminary Report, Trinity Survey Program, August 1947, USAEC Report, University of California, Los Angeles, 1947. 70 De 10. i I 12: KANTZ S. L. Warren and A. W. Bellamay (Comps.), The 1948 Radiological and Biological Survey of Areas in New Mexico Affected by the First Atomic Bomb Detonation, USAEC Report UCLA-32, University of California, Los Angeles, Oct. 12, 1949. .K. H. Larson etal., Alpha Activity Due to the 1945 Atomic Bomb Detonation at Trinity, Alamogordo, New Mexico, USAEC Report UCLA-108, University of California, Los Angeles, Jan. 5, 1951. . J. L. Leitch, Summary of the Radiological Finding in Animals from the Biological Surveys 1947, 1948, 1949, and 1950, USAEC Report UCLA-111, University of California, Los Angeles, Feb. 7, 1951. . K. H. Larson, J. H. Olafson, J. W. Neel, W. F. Dunn, S. H. Gordon, and B. Gillooly, The 1949 and 1950 Radiological Soil Survey of Fission Product Contamination and Some Soil-Plant Interrelationships of Areas in New Mexico Affected by the First Atomic Bomb Detonation, USAEC Report UCLA-140, University of California, Los Angeles, May, 3119545 . Lora M. Shields and P. V. Wells, Effects of Nuclear Testing on Desert Vegetation, Science, 22: 38—40 (1962). .W. H. Rickard and L. M. Shields, An Early Stage in the Plant Recolonization of a Nuclear Target Area, Radiat. Bot., 3: 41—44 (1963). .W. E. Martin, Close-in Effects of Nuclear Excavation and Radiation on Desert Vegetation, abstract in Radiation Effects on Natural Populations, a Colloquium Held in Philadelphia, May 23, 1965, George A. Sacher (Ed.), USAEC file No. NP-16374, pp. 7—9, Argonne National Laboratory, January 1966. . Janice C. Beatley, Effects of Radioactive and Non-Radioactive Dust upon Larrea divaricata Cav., Nevada Test Site, Health Phys., 11: 1621—1625 (1965). W. A. Rhoads, Robert B. Platt, and Robert A. Harvey, Radiosensitivity of Certain Perennial Shrub Species Based on a Study of the Nuclear Excavation Experiment, Palanquin, with Other Observations of Effects on the Vegetation, USAEC Report CEX-68.4, EG&G, Inc., May 1969. W. A. Rhoads, R. B. Platt, R. A. Harvey, and E. M. Romney, Ecological and Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and Short-Term Effects on the Vegetation from Close-in Fallout, USAEC Report PNE-956, EG&G, Inc., June 25, 1969. W. A. Rhoads, H. L. Ragsdale, and R. B. Platt, Radiation Doses to Vegetation from Close-in Fallout at Project Schooner, this volume. SE THE IMPORTANCE OF TRITIUM IN THE CIVIL-DEFENSE CONTEXT J. R. MARTIN and J. J. KORANDA Lawrence Radiation Laboratory, Bio-Medical Division, University of California, Livermore, California ABSTRACT The importance of tritium in the civil-defense context is assessed by comparing the dose rate and the 30-year dose integral for tritium from fusion with the external dose of gamma-emitting fission products. The tritium dose is computed by assuming equilibration of fallout tritium with water in the biosphere and with the body water of man. The fission-product gamma dose for late-time dose-significant nuclides is tabulated in roentgens per hour per kiloton per square mile as a function of time. Tritium is shown to be relatively unimportant in the civil-defense context when compared with the external gamma dose from an equal yield of fission products. The survival of man in an environment contaminated with radioactive fallout after a nuclear attack is the basis on which the importance of tritium in the civil-defense context can be assessed. Although tritium is a weak beta emitter, the radiation hazard to man can be significant because of the high yield of residual tritium from fusion devices. Also, tritium is relatively mobile and, as tritiated water, becomes rapidly dispersed in the environment where it is available for ingestion by man. On the other hand, the hazard is reduced somewhat by the dilution of tritium with the large amount of water in the environment. The importance of any single isotope can only be compared with respect to other radioisotopes produced in a nuclear explosion. As a first estimate, therefore, the radiation hazard to man from residual tritium is compared with that from fission-product radioactivity. When certain reasonable assumptions are made, the dose rate as a function of time and the 30-year dose integral can be determined per unit area and unit 71 72 MARTIN AND KORANDA explosive yield for residual tritium from fusion and for fission-product radioisotopes. For example, in the civil-defense context we assume a 2-week shelter period following the detonation of nuclear weapons with equal parts of fission and fusion. The 2-week shelter period eliminates blast, heat, shock-wave, and prompt-radiation effects from consideration. The assumption of equal parts of fission and fusion is necessary to normalize the explosive yield. The results obtained in this study can be scaled directly for any other ratio of fission to fusion. Finally, we assume that fallout is uniformly deposited over an area of 1 sq mile per kiloton of yield. The essential consideration of this assumption is that tritium is distributed in the same manner as the fission products are. Any deviation from uniform distribution will not affect the results of this study as long as the distribution of tritium and of fission-product fallout changes in the same way. The results can also be scaled directly for any area of deposition per unit explosive yield. Fleming’ provides a convenient summary of external gamma dose as a function of time for uniformly deposited, unfractionated plutonium fission products in roentgens per hour per kiloton per square mile. To simplify, we will consider in comparison with the tritium dose only the nuclides that contribute significantly to the external gamma dose at late mes. Many short-lived fission products are, of course, eliminated from consideration by the 2-week shelter period. The tritium dose rate can be expressed in the same terms as the gamma dose rate 1f we assume that the uniformly distributed residual tritium yield 1s thoroughly mixed and in equilibrium with water in the fallout environment by the end of the 2-week shelter period. The specific-activity approach then permits dose calculations based on equilibration of tritiated water with vegetation, livestock, and man. TRITIUM DOSIMETRY To use the specific-activity approach, we must determine the water compartment of the biosphere in which tritium fallout will be mixed. The water compartment can be estimated from studies of the behavior of tritium in a desert ecosystem by Koranda and Martin? and in the tropical rain-forest ecosystem by Martin et al.? and Jordan etal.* These studies show that tritium behavior in the environment is influenced largely by rainfall. These diverse ecosystems probably represent the extremes of the range of rainfall, from the low of 5 in./year in the desert to the high of 100 in./year in the rain forest. Tritium behavior can be considered in terms of a simple mixed-tank model. A single deposition of tritium is assumed to mix completely with a finite soil—water volume defined as the water-compartment capacity, C. The incoming flux of rainwater, F, which represents the flow through the compartment, Is IMPORTANCE OF TRITIUM 13 assumed to be immediately and completely mixed with the water compartment. The outgoing flux of water from the compartment, which must be equal to the incoming flux, contains the instantaneously diluted concentration of tritium. Thus the physical removal of tritium is exponential with time. The mean residence time for tritium, T, defined as the average time a tritium atom remains in the compartment, is given by the ratio of the capacity, C, to the flux, F: C = ab) F The exponential physical removal of tritium was demonstrated in the desert and rain-forest ecosystem studies. The capacity of the water compartment, C, can be determined from a measurement of the flux of rainwater, F, and the observed mean residence time, T: GFT (2) In the rain-forest experiment described by Jordan et al.,* the surface deposit of tritium moved down into the soil profile, giving a peaked distribution with depth. The peak tritium concentration moved deeper into the soil profile and became more diffuse with time. Martin et al.* described how the residence time was determined by plotting the integrals of the tritium depth-distribution curves with time. The mean residence time for tritium in the rain-forest ecosystem following a surface application was 42 days. The incoming flux of rain was 100 in./year, or 6.66 kg/m? /day; thus, from Eq. 2, the capacity of the water compartment is G= ET = 6.66% 42 — 280 ke/m- (2a) A similar pattern of tritium behavior with time was observed in the soil of the desert ecosystem at the Sedan crater. The mean residence time for tritium determined by Martin and Koranda® was 18.8 months, or 570 days. The incoming flux of rain was only 5 in./year, or 0.35 kg/m*/day; thus the water-compartment capacity 1s CF — 05355 70'=200ske/m- (2b) The agreement in the calculated values for the water-compartment capacity of these diverse ecosystems can be explained by the difference in the depth of the zone of interaction of their respective soils. Although the rain-forest soil had a relatively high average water content, only a shallow layer of soil water mixed with incoming rain. The water compartment of the wet tropical rain-forest soil corresponded to a depth zone of less than 2 ft. In the dry desert soils, significant interaction of tritium was observed at depths of 6 ft. The estimated water- 74 MARTIN AND KORANDA compartment capacity for the biosphere was therefore taken to be the average value, 240 kg/m?. This estimate is conservatively low with respect to dose calculations because desert plants growing at the Sedan crater typically had tritium concentrations in their water; this indicated a water compartment of three to nine times that of the measured value. There appeared to be greater dilution of the tritium than could be accounted for by the water compartment. This is apparently due to the fact that the tritium is not uniformly distributed in the soil. The plants draw water from selected depths in the soil, whereas the water compartment is determined from the integrated depth profile. The tritium concentration in the biosphere can be caiculated from a tritium yield of 2 g/kt dispersed over a 1sqmiule area and diluted by the water compartment of 240 kg/m’. The resulting specific activity of tritium, A, is a - 2 g/kt)(9800 Ci/g) (3.86 x 107 sq mile/m? ) . 240 kg/m? (3) = 3.15 X 10° Ci/kg/kt/sq mile If a man is equilibrated with this specific activity, the resulting dose rate, Do, Do = (3.15 X 10° Ci/kg/kt/sq mile) (7.44 R/hr/Ci/kg) = (4) = 2.34 X 10° R/hr/kt/sq mile The dose rate, D,, at any time, t, Is pee Doe (Apt art (5) where X, is the radiological decay constant for tritium (0.0565 year |) and Ap Is the physical-removal decay constant. The integrated dose, I, from t = 0 to t =t, 1s given by Do lee ial y Pa ee aie Ap + Ay The 30-year dose integral for no physical removal (A, = 0) is “4 ae a (8760 hr/year) (1 —e° °° °°") R/kt/sq mile (7) I30 == 5() R/kt/sq mile (9/4) If allowance 1s made for the physical residence time of tritium, the 30-year dose integral is much lower. Even when the most conservative observed value, IMPORTANCE OF TRITIUM 75 18.8 months (A, = 0.639 year '), in the desert ecosystem is used for the physical residence time, the dose integral becomes 130’ = 3 R/kt/sq mile G7D} FISSION-PRODUCT DOSIMETRY The dose rate at various times and the 2-week to 30-year dose integral for the late-time dose-significant gamma-emitting fission products are given in Table 1. The dose rates were taken directly from Fleming’s data,' in which the point of exposure is 3 ft above a smooth infinite plane uniformly contaminated with the nuclide in question. The late-time dose-significant nuclides are those which contribute 1% or more of the total external gamma dose integral from 2 weeks to 30 years. The nuclides listed account for more than 95% of the dose rate at any time after 2 weeks postdetonation. At early times after the 2-week shelter period, the dose rate is due mainly to fission products with half-lives in the range of several days to several weeks. The contribution of '*°Ba—!'*°La, for example, is half the total dose rate at t= 2 weeks. The contribution of these nuclides falls off rapidly with time because of their relatively short half-lives. The long-lived nuclides, such as ‘°° Ru—!°Rh and '?7Cs, contribute only a small fraction of the dose rate at t = 2 weeks but become increasingly significant at later times. At t = 2 years, for example, these nuclides account for 85% of the total external gamma dose rate of the uniformly deposited fission products. In the period from 2 weeks to 2 years, the major fraction of the dose rate is from nuclides with half-lives of the order of months which have relatively high yields, such as ?° Zr—?° Nb and '°*Ru. These nuclides account for more than 85% of the dose rate at t= 20 weeks and more than 60% of the dose rate at t = 50 weeks. These nuclides also account for more than 50% of the total 2-week to 30-year dose integral. Except for ?°Nb, the 2-week to 30-year dose integrals are computed for each significant nuclide by means of Eq. 6 with the physical decay constant Xp = 0. In computing the °>Nb dose integral, we must consider its growth from the decay of °° Zr. Since all other nuclides are produced at early times or have short-lived precursors, the change in dose rate with time is due only to radiological decay. The sum of all individual contributors gives a total 2-week to 30-year dose integral of 1124 R/kt/sq mile. Since the dose rate decreases rapidly with time, most of the integrated dose is delivered at early times postdetonation. For example, during the period from 2 to 20 weeks, 680 R/kt/sq mile, or more than 60% of the total 2-week to 30-year dose integral, is delivered. An additional 200 R/kt/sq mile is delivered in the period from 20 to 50 weeks. Thus nearly 80% of the 30-year total integrated gamma dose is delivered during the first year postdetonation. MARTIN AND KORANDA ayrur bs /a4/y ‘(savak QE 02 SYIIM 7) jeasajur as0q 76 ¢ OLX 871 PLOll=xX G3 pOrX eZ SHIIM OOZ OER ES OTR OT XCEZ pO! CC euOi iG, OL XSxz b OLX pak S OT xX OZ SYIIM OOT zOL X LPT ne PLO x0 p01 x 0's OM Cay, OT xX C8 OLX OF OT xX O'9 € O1Lx 97 ~ Ome Stan St, ~a SYIIM CG ayia bs /ay/ay/y ‘avi asoq OT X $76 OLX SL OT x OT OT xX S’°8 OL x ST OWE saa OT xX OT OT xX €°9 OLX C8 OR Salk OLX OF OL x97 SYIIM (YZ N ¢ > c 7 (e OT 0 Ol Ol OT Ol iu Ol Ol OT OT OT OT OT OT G= SHIIM Z SLONGOUd NOISSIA ONILLIWSA-VWWV9D LNVOISINDIS-ASOd AWLL-ALVT T 9G? [BIOL sI9yIO PNi ot l = ru 901 901 C Ss’ fuer Let opHPonN IMPORTANCE OF TRITIUM 77 COMPARISON OF TRITIUM DOSE WITH EXTERNAL GAMMA DOSE The dose rate and the 2-week to 30-year dose integrals for tritium and for the gamma-emitting fission products are listed in Table 2 in roentgens per hour per kiloton per square mile and roentgens per kiloton per square: mile, respectively. Table 3 lists the same data, except that here the tritium is assumed to have an 18.8-month xresidence time in the biosphere. It can be seen that in both cases the gamma dose rate is very much greater than the tritium dose rate, particularly at early times. The dose ratio is the ratio of the fission-product gamma to tritium dose rate. At early times the dose ratio 1s about Ore but it decreases rapidly to a ratio of about 70 at t=50 weeks. The decline with time then becomes more gradual until a minimum ratio of 7 is reached at about t=4 years. The ratio then increases slowly to a value of about 10 at t = 30 years. When the tritium residence time in the biosphere is assumed to be 18.8 months, the dose ratio has a minimum value of 50 at t = 2 years. In either case, the fission-product external gamma dose rate is always at least 7 times the tritium dose rate. When the physical residence time of tritium is considered, the tritium dose rate is never more than 2% of the external gamma dose from fission products. The comparison of tritium with the external gamma dose from fission products can also be made on the basis of the 2-week to 30-year dose integral. The dose integral for the fission products is 1124 R/kt/sq mile; the value for tritium is 30 R/kt/sq mile, or 3 R/kt/sq mile when the residence time is considered. The fission-product dose integral is thus at least 37 trmes the tritium dose integral and is more likely to be 370 times as much. CONCLUSIONS This analysis was done on a relative scale. The importance of other internal beta emitters and of activation products can be assessed in a similar manner, relative to the fission-product external gamma scale. The full significance of the fallout-radiation hazard to the survival of man in the event of nuclear attack will depend on assessment of the absolute values of dose rate and dose integrals. The extent of preventive or corrective measures to be taken against the fallout radiation hazard can then be determined. Many hypothetical attack situations that go beyond the scope of this paper will have to be considered in making the assessment of the absolute hazard. The task can be simplified somewhat by the approach presented here, which shows that tritium is relatively unimportant in the civil-defense context when compared with the external gamma dose from fission products. ACKNOWLEDGMENT This work was performed under the auspices of the U.S. Atomic Energy Commission. 78 MRE ee re ae un Le Ol L LI OL 00% Ole sjonpoid uolsst oni 9s0q O€ 5 Ol X60 b OLX 88 I b OL xX OTC OLX CCC peOt X6CC ,Ol xX €EC uOIsSn} JO UOJO[D] aod WIN rae OT. rie eOcke 1 eOlex US OLX LY , OL X $26 pO X 9ZZ —-BOISSIJ Jo UOIOTIy{ 19d j syonpoid uolssty [2101 Ses RP Tl gp dN 1 DRM een Se nda eee en ce eS Oe a a aqiur bs /34/41 savak O¢ SYIIM (OZ SyIoM OOT SYIIM OS SYIIM YZ SYIIM Z a ‘(savah (¢ 02 SYIIM Z) ayrur bs /3y4/a4/y ‘97e1 as0q jeasaqur asoq Sas Gr ce a OR rer ea ASOd LONGOUd-NOISSIA HLIM GAUYVdWOD ASOG NOLLVIGVY TVNYALNI WOALLPAL GHLVWILSH Z ANGEL . 79 eee UNA, OLE gO x ¢ OL OS OcT OOS relO) eas : syonpoid uolssty onei a9s0q € OF X08 < OLX $611 ¢_01 X bL'9 » OLX 9 » OLX 7st ,OLX 82% — woIsny Jo uoIOTI4 39d UNIT r71I ,OXTy , 01X82 - OLX 1S OILY I OL X +76 pOLX 977 —dUOISSIZ JO VOI] Ty Jad sionpoid uolssi4 [RIO L Dee ak ee 8 ae aqiu bs/34/4 savak OF SYIIM 0OZ S4IaM OOT SHIIM OS SHIIM OZ SHIIM Z ‘(srvaA Q¢ 02 SYI9M Z) 7 bs ‘9781 Os ‘qea8aqut asoq apiu bs/3y/1IY/Y 93e1 VSO] Te a a rn ee eee eT Ee WOAILIDL YOU AWLL ADNAGISAY HLNOW-8'8T NV SO dSN AHL HLIM ASOG LONGOUd-NOISSIA HLIM GAUVdWOD ASOG NOILVIGVY TVNUYALNIWOLLIYL GaALVWILSd CLAD 80 MARTIN AND KORANDA REFERENCES 1.E. H. Fleming, Jr., The Fission Product Decay Chains *3°Pu with Fission Spectrum Neutrons. Vol. II]. Roentgens per Hour per Kiloton per Square Mile vs. Time, USAEC Report UCRL-50243, Lawrence Radiation Laboratory, University of California, Mar. 31, 1967. 2.J. J. Koranda and J.R. Martin, Persistence of Radionuclides at Sites of Nuclear Detonations, in Biological Implications of the Nuclear Age, Livermore, Calif., Mar. 5—7, 1969, B. Shore and F. Hatch (Coordinators), AEC Symposium Series, No. 16 (CONF- 690303), pp: 159-187, 1969: 3. J. R. Martin, C. F. Jordan, J. J. Koranda, and J. R. Kline, Radioecological Studies of Tritium Movement in a Tropical Rain Forest, in Symposium on Engineering with Nuclear Explosives, Las Vegas, Nev., Jan. 14-16, 1970, USAEC Report CONF-700101 (Vol. 1), pp. 422—438, American Nuclear Society, May 1970. 4.C. F. Jordan, J. J. Koranda, J. R. Kline, and J. R. Martin, Tritium Movement in a Tropical Ecosystem, Bioscience, 20(14): 807 (1970). 5. J. R. Martin and J. J. Koranda, Distribution, Residence Time and Inventory of Tritium in Sedan Crater Ejecta, USAEC Report UCRL-72572, Lawrence Radiation Laboratory, University of California, Nov. 10, 1970; also Nucl. Technol., in preparation. PROPERTIES OF FALLOUT IMPORTANT TO AGRICULTURE CARE’ F. MILLER The Systems Operations Corporation, Hallock, Minnesota ABSTRACT The intrinsic properties of fallout associated with radiological hazards which could affect agricultural operations in the postattack period of a nuclear war include: (1) the radionuclide composition of the fallout material, which determines the energy composition of the gamma and beta radiation emitted, (2) the physical and chemical properties of the fallout particles (such as size, shape, composition, structure, and solubility) which influence their retention by surfaces, and (3) the solubility and biological availability of specific radionuclides. In terms of crop or agricultural-product output, both operational factors (effects on man and his social system) and biological factors (response of plants and animals) would be important. Since the degree of the hazard to the food-producing agricultural systems would generally depend more on external parameters (such as the available weapon system, form or mode of attack, level of attack, explosive yield of weapons, relative heights of burst, and local and regional weather patterns) than on the properties of the fallout, these parameters are discussed in detail. A major recent development in weapon systems which could have a significant impact on the type and extent of hazard to agriculture in a nuclear war is the Multiple Independent Targeted Reentry Vehicle (MIRV). Estimates of MIRV system capabilities, especially in terms of using many smaller-yield warheads on many smaller targets, are used to identify several important implications for future civil-defense planning and the role of civil-defense capabilities in the relative deterrence posture. If sufficient fallout shelters with protection factors of 130 or more were available for the U.S. population, it appears that the U.S.S.R. could not deploy sufficient SS-9 missiles to assure the destruction of the U.S. population within the next 800 years (even with MIRV) using currently available technology. Also, the effect of MIRV and the associated lower-yield warheads would be to almost eliminate the widespread fallout effects previously estimated for attacks in which land-surface detonations of weapons in the megaton-yield range have been postulated; a comparable degree of effect on agriculture might be achieved from attacks that are designed to kill more than 65% of the U.S. population if all detonations in rural areas were surface bursts. 81 82 MILLER The more important properties of fallout which could significantly affect agricultural operations after a nuclear war are those related to the total gamma- and beta-radiation emissions from the particles and the physical and chemical properties of the particles which influence their retention by plant and animal surfaces. In addition, physiochemical properties of the fallout, such as the solubility of individual radionuclides, can become important radiological-hazard problems in the production and consumption of specific agricultural products. A well-publicized example of this is the relative solubility of '*'I and _ its accumulation in milk produced by cows that have ingested fallout-contaminated food and water. In terms of radiobiological effects to agriculturally important plants and ani- mals, previous analyses have shown that the major cause of radiation damage would be the exposure of temporal units of the biota of rural farmland ecosystems to ionizing radiation.’ Under the subject of longer-term ecological effects, the major concern would be with the secondary effects to functional units of the biosphere including biological populations, communities, and ecosystems.” Secondary effects, in contrast to direct effects, are disturbances and injury or damage, usually caused by the direct effects, which do not become important or do not develop until some time later. One property of fallout that could affect the relative severity of short-term and long-term effects on agricultural plants and animals is the combined decay rate of the radionuclides in the fallout; another property is the energy spectrum of the absorbed radiation. SOURCE OF RADIOLOGICAL INJURY OR DAMAGE In a nuclear explosion more than a hundred radioactive fission-product nuclides and many additional neutron-induced radionuclides are produced. This radioactive mixture initially consists of radionuclides with radioactivity-decay half-life values that vary from a fraction of a second to many years. Since most of the radionuclides emit both beta particles and gamma rays when they disintegrate, these two types of ionizing radiation are present in a fallout environment as potential causes of biological damage to living tissue. The presence of all these radionuclides in an ecosystem thus constitutes a source of radiological hazard from fallout. The major radiological hazard to man is external gamma radiation from deposited fallout; this fact requires special recognition both in damage-assessment studies and in civil-defense planning. Fallout particles from land-surface detonations as nuclear-radiation sources consist of fused, sintered, and unchanged grains of soil minerals or other materials present at the point of detonation.* Also present to a minor extent in fallout particles are inert materials from the weapon or warhead, as well as the radioactive elements produced in the fission and neutron-capture processes occurring at detonation. Roughly, the relative amounts of soil minerals, bomb-construction materials, and radioactive elements in fallout particles are FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 83 (1) up to 1 Mt of soil per megaton of total weapon yield, (2) of the order of 1 ton of warhead materials per megaton of total weapon yield, (3) about 120 lb of fission products per megaton of fission yield, and (4) about 100 to 200 lb of induced radioactive atoms per megaton of total yield. Analyses of fallout particles from surface and near-surface detonations collected at weapons tests at both the Eniwetok Proving Ground and the Nevada Test Site show that the radioactive elements are either within the interior of fused and sintered particles or are attached to the exterior layers of all three types of particles.? Larger fallout particles are formed, not by the condensation of vaporized soil, but from individual or agglomerated soil particles that originally either existed as single soil grains or were produced through the breakup of a fused mass of liquid soil or rock. All three types of particles are drawn into the rising fireball and apparently serve as collectors for small vapor-condensed particles and as condensation centers for vaporized fission- product and radioactive neutron-induced atoms. On the basis of physiochemical properties of common metallic oxides of the chemical elements in soil and coral, it can be concluded that the fallout-forma- tion process does not begin until the fireball temperature (or the temperature of the gaseous material in the fireball) has decreased to about 3000°K, because at higher temperatures all materials tend to dissociate rather than to condense. As the fireball temperature decreases below about 3000°K, vapor-condensation processes should take place to produce very small liquid particles. Such small particles have been observed in worldwide fallout collections and as attached particles on unchanged coral grains in the fallout materials collected from weapons tests at the Eniwetok Proving Ground. As the fireball rises and coals and the crater materials are drawn up into its volume, the thermal action at the surfaces of entering molten particles should gradually change from a vaporization process to a condensation process in which the less volatile fission products condense onto and diffuse into the liquid phase of the particles. In addition, the larger molten soil particles, as they circulate through the fireball volume, would rapidly form agglomerates with a large fraction of the smaller, previously formed, vapor-condensed particles. Particles entering the fireball volume at later times may be heated to sintering temperature or may never be thermally altered. As the surface temperature of the particles decreases, the rate of diffusion of the condensed radioactive atoms into the interiors of the particles should also decrease so that the more volatile of the radioactive elements, which can condense only at lower temperatures, collect and concentrate on the exterior surface of the particles. Also, radioactive daughter atoms (even if not volatile) formed at later times from volatile parent nuclides, such as those from rare-gas elements, would be concentrated on the exteriors of the smaller particles. Because of the differences in volatility as a function of temperature among the various fission-product elements, fractional condensation would be expected to 84 MILLER occur throughout the whole fallout-formation process. The observed degree of solubility and biological availability of such radionuclides as °?Sr, °°Sr, and '37Cs from the fallout of nuclear-weapons tests strongly supports these views regarding the condensation process.” In general, two rather distinct periods of fallout formation by condensation processes have been postulated.* In the first period the condensation of volatile radioelements is considered to occur by deposition onto and diffusion into large molten soil particles and by agglomeration with smaller particles. The radioele- ments thus condensed would become fused within the volumes of the molten particles when they cooled and solidified. In the second period the remaining volatile gaseous radioelements condense onto the surfaces of relatively cold solid particles (most of which consist of late-entering, thermally unaltered grains of soil). The significant chemical property associated with the amount of a radioelement that condenses during the second period of formation is its potential solubility, whereby it can become biologically available for later assimilation by plants and animals. The more volatile radioelements in fallout are more soluble and more biologically available than the refractory elements. However, the fractional degree to which each element condenses in either period of condensation is expected to depend very much on both the temperature and the rate of temperature decrease, which determine the conditions and times at which diffusion into the particle effectively ceases and at which the condensing radioelement begins to concentrate on the surface of the particles. If all the materials produced in a land-surface nuclear detonation and all entering the fireball volume remained together for the first 5 or 10 min after detonation, the radioactive composition and the subsequent radioactive decay (and nuclide solubility) would be about the same for all fallout particles. However, it is known that all the entering particles do not remain together in the fireball and cloud for such periods of time. Immediately after the fireball expands to maximum size it begins to rise in the air. The upward movement of the hot gases sets in motion a large-scale toroidal circulation because of the drag forces of the surrounding air. This toroidal motion, with circulation velocities in excess of 100 mph, is probably responsible for setting up air motions whose forces are sufficiently strong to pull the blast-loosened soil from the crater and crater lip into the rising fireball. The circulation of the particles in the toroid should result in rapid separation of the larger particles from the circulating mass of condensing gases and should, by centrifugal force, move them to the periphery of the toroid. When the circulating particles reach the periphery or the bottom of the cloud and the pull of gravity begins to exceed the upward drag forces of the air near the base of the rising cloud, the particles should begin falling toward the earth. Other particles of the same size that are not yet near the periphery of the toroid may continue to circulate for a much longer time before they leave the base of the cloud. FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 85 These views of particle circulation and formation are suggested by (1) the relatively long period over which particles of a given size arrive on the ground, (2) the relatively early initial arrival times for close-in fallout, (3) the variation in composition of the radioelements carried by particles of different sizes, and (4) the variation in specific activity and radioelement composition among particles of a given size. The concentration of the volatile radioelements in the radioactive composti- tions carried by the larger particles is generally low. This relatively low concentration could occur only through the earlier ejection of the large particles from the volume of the fireball containing the radioelements (vapors plus small vapor-condensed particles). In addition, the large fallout particles from many low tower detonations do not contain or carry any soluble radioelements; therefore these particles must have been ejected from the rising fireball or cloud when the particle surfaces were still at a very high temperature. Thus the toroidal motion is considered to be partially responsible for the observed differences in gross radioactive decay and biological availability of different radioelements carried by fallout particles of different diameters. The toroidal motion, which apparently causes early ejection of the larger particles (1.e., early with respect to time-of-fall from the height of the stabilized cloud), can also cause prolonged apparent buoyancy of the smaller particles. The smaller particles should circulate for longer times and should remain in the toroid where they could adsorb the more volatile radioactive elements on their surfaces. Essentially all fallout particles, except those with diameters less than about 50 to 80 u, apparently leave the cloud volume under influences of toroidal circulation. No observed data exist on the properties of fallout from detonations on soils similar to those of likely targets in a nuclear war. In fact, only a few detonations at the Eniwetok Proving Ground and the Nevada Test Site have provided data useful for the development of fallout models for land-surface detonations. All the large-yield test devices were detonated over water, on coral atolls, or in the air. Most test detonations in the yield range of 1 kt to 1 Mt were mounted on towers. Consequently there is no evidence proving that all types of fallout information obtained from the weapons tests (even under suitable detonation conditions) are satisfactory for evaluating computational procedures developed to give quantitative estimates of properties of the fallout particles, as well as of their distribution over the country as a consequence of an assumed set of nuclear detonations on specified targets in the continential United States. Further theoretical developments and supporting experimental work are needed to evaluate and improve the validity of some available input data used in the formulation of many fallout models. The radionuclides in worldwide fallout from high airbursts, in contrast to those described for the close-in local fallout from near-surface detonations, are generally quite soluble. Therefore essentially all the radionuclides in long-range worldwide fallout are biologically available. Fused-type particles formed from 86 MILLER the warhead or bomb materials have been identified and found in fairly large numbers in stratospheric collections of bomb debris.° But a large fraction of the worldwide fallout from a large-yield nuclear airburst is apparently formed in the stratosphere at some time after detonation through processes of coagulation and coprecipitation of the radioactive atoms with the natural stratospheric aerosol particles. These particles, composed mainly of water-soluble ammonium sulfate compounds, apparently serve as carriers for eventually returning the longer-lived radioactive elements to earth. Under all conditions of detonation that lead to the production of fallout, the form and properties of the fallout particles are determined during the cooling period of the fireball and cloud; for the decay products of gaseous and several other radioelements, the attachment to particles occurs at later times. The materials in or entering the fireball at these times are particularly important factors in determining the properties of the fallout particles. These formation processes set the stage for all subsequent radiological interactions between the fallout materials and the biological and ecological environments in which they deposit. One of the chief difficulties in predicting fallout levels at a given location, in addition to the problem of defining the fallout-particle-cloud source, lies in the problems associated with analyzing and predicting the wind fields. The winds at all altitudes through which the particles fall, of course, determine how the fallout particles are distributed over the earth’s surface. Other major factors for which very little accurate data exist, especially for fallout from detonations over silicate soils, include (1) variation of the specific activity of fallout with particle size and (2) influence of weapon yield, burst height, and environmental material (soils and other likely target materials) on the gross particle-size distribution of the fallout (1.e., by particle number, mass, or radioactivity content). The radiation, chemical, and physical properties resulting from the fallout- formation processes and conditions may give rise to one or more of five major types of radiological hazard to biological species. These are (1) external gamma hazard, as mentioned for humans, (2) contact beta hazard, (3) beta-field hazard, (4) internal hazard from ingested radionuclides, and (5) inhalation hazard. The nature of the hazard and the response of biological species to it are perhaps better known and understood for external gamma radiation than for the other four hazards. Under most exposure situations occurring under nuclear war conditions, the external gamma hazard would be the major cause of serious direct radiation injury to large biological species. The contact beta hazard could arise when fresh fallout particles remained in contact with biological tissue for some period of time. Humans could easily avoid this type of exposure by wiping or brushing fallout particles from exposed skin. This hazard would develop only during and shortly after fallout deposition. After several days the fallout particles would no longer have the radioactive content necessary to cause serious damage to skin tissues. Some data on the retention of particles by humans® and on skin doses to animals’ have been FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 8/ reported. No reliable correlations of such data with fallout-deposition levels have yet been made, but unverified relations between the two have been proposed.® A few sets of computations and experimental measurements have been made of the contact beta dose to plants;’ data on the retention of fallout particles by the foliage of many different types of plants have been reported.° The beta-field hazard (sometimes called the ‘“‘beta-bath” hazard) could occur in certain confined radiation source geometries for humans. It would be expected to be severe for small plants, small animals, and insects whose habitats become covered with the deposited fallout particles. In such geometries the beta-to-gamma ratio (1.e., the rad-to-roentgen ratio) would generally be between 30 to 100 for fallout-radiation compositions similar to those of past weapons tests. No mathematical models on the beta-field hazard to small plants and animals or insects are known to exist; however, some related work on this hazard d.1°:!! The combined radiological hazards (external gamma, contact was reporte beta, and beta-field) for plants, animals, and insects should be considered in future research investigations. The internal hazard from ingested radionuclides and the consequent pattern of exposure of humans, animals, plants, and insects to this hazard after a nuclear war would depend mainly on their uptake and assimilation of biologically available (soluble) radionuclides. Several major processes are involved in the entry of the radionuclides into food chains (or webs). The internal hazard from fallout is characterized mainly by the fact that, at least in humans and other large vertebrate animals, most of the radiation sources (e.g., radioactive atoms) tend to concentrate in specific body organs and that assimilation occurs according to the biochemical properties of specific radionuclides. Thus evalua- tions of the internal hazard must consider the behavior patterns of each radioelement in the fallout. Data on absorbed doses from ingestion of radionuclides by adult humans have been developed in a significant research 5 re effort conducted by Morgan and co-workers'* over the past 15 years. Similar sets of data for the absorbed doses for young people during their growing years have yet to be developed. Kulp et al.'* developed a bone model for the uptake of °°Sr in worldwide fallout. Models for estimating the absorbed dose from assimilation of radionuclides in organs of humans have been developed. !* The inhalation hazard would be associated with the inhalation and deposition in the respiratory system of small fallout particles of a narrow size range. All the available data on exposure of animals in fallout areas at weapons tests and in laboratories, on air-filter samples in various fallout environments, and on fallout-particle resuspension in air give negligible results for the inhalation hazard. Therefore this hazard is considered to be minor relative to other possible radiological hazards. The major primary radiological hazards that apparently would cause most damage to farmland (and wild land) ecosystems are external gamma and beta radiation and internal beta radiation from assimilation of radionuclides. It is significant for biological repair and recovery processes that injury sustained from 88 MILLER external radiological hazards under nuclear war conditions would generally be more comparable to an acute assault than to a chronic assault, whereas the assimilation of radionuclides would be mainly a chronic exposure to low levels of nuclear radiation. The general effect of radionuclide cycling in species of ecosystems appears from all available data to be mainly a long-term public-health problem rather than a cause of injury leading to the death of biological species. Because of the large variability in the radiosensitivity of plants according to species, age, and period between growth and reproduction cycles, the gross effects in plant population from exposure to gamma radiation would depend a great deal on the time of year, perhaps of month, when an attack occurred. Thus the total consequence would depend on the targeting pattern for many agricultural areas; the Midwestern states, for example, could receive high levels of fallout from high-yield surface detonations on missile sites in neighboring states and in the Rocky Mountain area. RADIOLOGICAL DAMAGE ASSESSMENTS Current Weapons Systems In most damage-assessement analyses, military targets normally play an important role in establishing the pattern of weapon delivery for any hypothetical attack. For many military targets it is appropriate to assume ground-surface detonations to assure destruction of the target components. Therefore in such attack patterns, called counterforce attacks, a large amount of local fallout 1s produced. Furthermore, in such studies rather large weapon yields are customarily assigned to military targets, perhaps for consistency with the assured destruction concept.* The relative area of the continental United States within a given standard (H+ 1) exposure-rate contour (using an open-field radiation source as the reference condition) asa function of attack level in total megatons detonated is shown in Fig.1 (Ref. 15). The relative area of the continental United States at a given attack level is shown in Fig. 2 as a function of the standard exposure-rate-contour level. For hypothetical nuclear attacks on the United States in which most individual weapon yields are assumed (or assigned) to be in the range of 1 to 10 Mt, pure: counterforces attacks at-atrack. levels. very, much jlarcer juhan 10,000 Mt would not be realistic, at least on a first-strike basis, because of the limit in number of military targets. Thus the extrapolation of the solid lines in Fig. 1 to the higher attack levels probably does not represent any real situation. *The assured destruction concept is an extension of the notion that a weapon system or attack pattern can be designed or deduced to perform as envisioned by calculation, within a specified degree of assurance or a stated degree of reliability, ipso facto. The concept is to some degree a technical embellishment evolved by military technicians and analysts to provide a logical basis for deterrence policies. NN ————————E *(suodvam 89 uOISSIJ %0S) 2YBIOM YORE JO UOTIOUNF B SB SANOIUODS S] PI9II9IJ9S UIYIIM PIsSO]IUD $9IFIS Pswuyy, [PJUIUTIUOD 9} jO Pore JO JUDIIIG YT “B1y GQ4LVNOLIAG SNOLVOAW IVWLOL gOl pol e0l z0L OL Ol AE FESR ai ey ea el re |e Eo / We / VA, / IS WSs We Ve /) 7, lo Ol SHiNOD SOWA Vad vy tOL sO zENaOuad (sising punoisb %O/ 01 QG) sy9e11e paxil) ‘—_—_—_ — — (sising punosb %QG 01 QZ) syoe}}e adsOJ4a}UNOY ' FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE susa}yed ynojjey YA-|1 Buiddejsaaouou Aq paiaAo0d eal ‘—-———-- OOL MILLER 90 ‘(suodvam UOISSIZ %OG) SIYBIIM YORIIE P9IDI]IS 1OJ S1N0QUOD S] UTYITM pasopud sa7z¥Ig paiUA [eyUIUTQUOD ay) JO Bale JO WUDIIIg «7 “BIY dy | ye 4u/y “| Ol ,Ol 501 201 Ol 01 ie) . 0 S m . D ~ Se (sising punosb %QG) O NS \ syoeye paxil, ‘-—-———- Ors .S DN (sising punos6 %06 01 OZ) = SS as Syoe}e adsOJIa}UNOD ' = Ne 4 . S Se = SN a Ne > Be) Ne 2 ~ > NG = ~ nN “~~ Ole S O COoNs 2 O/ E D Wy 007, = O 00; ~ ee a _— ee iy — -_— FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE ol As a general guide, I, values up to 10 R/hr at 1 hr for fallout from fission S weapons do not represent a serious direct radiological hazard to humans or to most other biological species. At I, values greater than 100 R/hr at 1 hr, extended (but variable) stay times in shelter generally would be required to avoid possible effects of radiation sickness to humans. The |, values of about 1000 R/hr at 1 hr and greater represent a serious radiological hazard for a fairly long time after attack; sickness and possible fatalities among poorly sheltered or unsheltered people could result. For I, values of 10,000 R/hr at 1 hr and greater (radiation levels that generally would occur only as a result of overlapping fallout patterns), survival would be possible only in the best available fallout shelters with facilities for an extended stay time plus decontamination requirements for a reasonably short reoccupation time after attack. For the weather conditions usually assumed for the hypothetical counter- force and mixed attacks (the latter may include some ground bursts on urban targets) with a total delivered explosive yield of less than about 10,000 Mt, the areas within extremely high I, contours would enclose less than 10% of the land area of the United States, and essentially all such areas would be rural forested or agricultural areas. Since the current Soviet nuclear force capability is estimated to be more than 10,000 Mt.?° the delivery of such a force in a counterforce or mixed attack such as those represented in Figs. 1 and 2 would likely involve the coverage of more than 40% of the continental United States by I, values of 100 R/hr at 1 hr and more than 25% of the area by I, values of 1000 R/hr at 1 hr. Although these relative coverages of the land area are rather large, the associated degree of damage to or decrease in the yield of specific agricultural products by the respective exposures cannot be deduced from the curves of Figs. 1 and 2. To deduce damage, the relative geographic locations of the crops, targets, and assumed points of detonation, along with the meteorological inputs for each hypothetical attack must be considered; this procedure has been used in recent analyses. !° Future Weapon Systems Over the past several years, one of the major developments in weapon systems has been the Multiple Independent Targeted Reentry Vehicle (MIRV). Certain information and estimates of apparent U.S.S.R. and U.S. progress and capabilities in the development of MIRV systems, especially with respect to their missile-carrying capacities, have been released to the press by various Department of Defense officials, including Secretary Laird. The following statements on Soviet nuclear force capabilities and MIRV system characteristics were provided by William Beecher’ ’ ina special article in the New York Times, Oct. 28, 1969: * As recently as last November, for example, the intelligence community predicted that the Soviet Union would stop deploying more interconti- nental missiles when they had roughly equaled the 1054 in the American arsenal. 92 MILLER ®The Soviet Union has in place or going into place about 1350 inter- continental ballistic missiles, roughly 300 more land-based units than the United States and 150 more than reported by American officials last spring. ® The Soviet Union has been testing a new swing-wing medium-range bomber, presumably for use against targets in Western Europe and Asia, even though it already has a fleet of 750 medium bombers. With aerial refueling, the new bomber could be used on round-trip strikes against the United States. *The Russians are testing a new medium-range ballistic missile, though they already have more than 700 such missiles aimed at targets in Western Europe and Asia. ® The SS-9 can carry a single warhead of from 9 to 25 Mt (9 to 25 million tons of TNT) or three warheads of 4 to 5 Mt each. The SS-11 carries a warhead of 1 Mt, similar to the payload of the Minuteman missile. ® john S. Foster, Jr., the Pentagon’s research and development chief, said that 420 SS-9’s carrying three separately targetable warheads with one-quarter- mile accuracy could destroy about 95% of the 1000 Minutemen in their underground silos. ® The Soviet Union is now believed to have about 280 such giant missiles in various stages of construction. At the present rate of deployment, they could have the Minuteman killer force in three more years. ® The Minuteman-3 is designed to carry three warheads of about 100 kt, and the Poseidon submarine-based missiles, 10 warheads of 30 to 40 kt each. By comparison, the Soviet SS-9 is being tested with three warheads of about 5 Mt each, 50 times more powerful than each Minuteman-3 warhead. On Jan. 6, 1970, the Washington Daily News, under a dateline from London, quoted the following statements: ® The Institute of Strategic Studies said the Soviet Union should have the capability to fit multiple nuclear warheads to its most powerful rockets by LOTS: ®The influential study group, specializing in international defense devel- opments, said the Soviets could have 500 of the multiple-warhead missiles ready for use by 1975. ® The multiple warheads are to be fitted to SS-9 Scarp rockets, “extremely powerful” three-stage missiles with a maximum range of 9800 miles, the report said. It estimated that each launcher cost between $25 and $30 million. ® About 250 of the SS-9’s are believed to have been installed already in the Soviet Union, but these are not armed with the multiple warheads, the institute said. ® The Soviet SS-9 rocket originally was designed to carry a single warhead of between 10 and 25 Mt. On January 7, 1970, Secretary of Defense Melvin Laird provided the following information to newsmen: FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE gs @ The Russians could have a knockout missile force in place earlier than the 1974 period forecast to Congress last year. ® The discussion centered around Laird’s estimate last summer that the Soviets could have about 420 of the huge SS-9 missiles in readiness by 1974. Such a force, Laird said then, could destroy 95% of this country’s Minuteman missiles in a surprise first attack. ® He declined to say how many of the SS-9’s, capable of hurling a single 25-Mt warhead or three warheads of 5 Mt each, are now in place or under construction. There have been unofficial estimates running up to about 279. Defense officials, the news media, prominent scientists, and politicians have repeated similar information to the public over the past 10 months or more. The statements indicate that for the SS-9 missile the number of warheads apparently depends on the explosive yield of each warhead according to the relation nn» = 866W * (1) where n,, is the maximum number of warheads carried by the missile and W is 5 the explosive yield of each warhead. Similarly, for the Minuteman-3 missile 7% 9, Nm = 09 W (2) and for the Poseidon and SS-11 missiles = 477 34 Nyy = LOOW (3) Values of ne for the SS-9 missile, the maximum explosive load, and the total target area enclosed by the 35-psi overpressure contour for selected warhead yields are given in Table 1 (for the case where all weapons are airburst at the height for which the area enclosed by the selected overpressure contour 1s Table 1 CALCULATED VALUES FOR SS-9 MISSILE* WwW Nm Ny,W Am (35 psi) megatons (samheads megatons sq miles warhead missile missile missile O.1 40 4.0 1-8 0.3 19 Si, 31.4 1.0 8 8.0 295 3.0 4 12.0 307, 10.0 1 10.0 AS AY) 1 2220 BE) 94 MILLER maximized and at ground zero locations that are arranged in a hexagonal pattern in which the overpressure contours overlap in such a way that no point within the target receives less than 35 psi). Table 1 shows that A,, (35 psi) is maximum at values of W which yield integer values of n,, in Eq. 1. For n,, equal to 2.0 warheads per missile, for example, W is 9.0 Mt. For this yield A (5 psi) “is (3 1.9% squimilles/missile; although for the single 10-Mt warhead selected, A, (35 psi) is only 17.1 sq miles/missile. In this case additional smaller warheads could be added to the capacity of the missile as appropriate to increase the value of A,, over that given. If the target area is less than 30 to 32 sq miles and n,, is more than 2, decoys could be used to replace some of the warheads. Neglecting anv possible effect of decoys and of active defense capabilities, the MIRV system using a maximum number of warheads, in contrast to a single warhead of maximum yield, apparently would provide no advantage in decreasing the number of missiles for imposing a selected minimum overpressure on a single target on an area basis. However, if the shape of the target area 1s considered, MIRV system weapons could achieve_area enclosure within. a selected overpressure contour with a smaller number of missiles and a smaller total explosive yield than could a single-warhead missile system. For example, a single SS-9 missile loaded with 40 100-kt warheads (4.0-Mt total yield) could, according to Table 1, enclose an area about 32 miles long and 1 mile wide within the 35-psi contour. Lengthwise coverage by the same overpressure contour would require five SS-9 missiles if each carried a single 25-Mt warhead (125-Mt total yield). If the MIRV system could be employed with essentially no constraint on warhead dispersion among neighboring targets and if full use could be made of such capabilities to deliver warheads to targets, then any set of estimates of single-weapon missile force requirements may be directly converted to missile requirements for a system with MIRV. Under such conditions estimates of the number of SS-9 missiles required to cause specified levels of fatalities among the 1970 U.S. population sheltered in wood-frame structures exposed to selected minimum overpressures are given in Table 2 for weapon yields of 0.1, 1.0, and 10 Mt.* The lowest number of missiles for a given percentage of fatalities always occurs for a weapon yield of about 100 kt or less for the urban-center target areas.7° Thus the general dependence of missile requirements on fatalities or area by a given overpressure contour relative to target size apparently ceases to be important for weapon yields less than about 100 kt. This independence 1s shown especially for the smaller high-density urban areas that would comprise the first set of targets for an antipopulation attack; a similar situation pertains for the smaller urban target areas listed in Table 2 in the range of 55 to 65% of the total population. *These estimates are based on information from the Japanese experience at Hiroshima and Nagasaki in World War II as discussed in Refs. 15, 18, and 19. Table 2 FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 05 ESTIMATED MINIMUM NUMBER OF SS-9 MISSILES WITH MIRV REQUIRED FOR SPECIFIED LEVELS OF FATALITIES AMONG THE 1970 U. S. POPULATION SHELTERED IN WOOD-FRAME STRUCTURES Minimum overpressure Fatalities, % 10 psi 15 psi 20 psi 35 psi W = 0.1 Mt 20 28 87 82 a, 30 28 220 184 250 40 70 470 348 473 50 20* 4,698 aye fe) 770 60 16,850 4,450 1,063 70 32550" PAO) Do 0 80 126307 15,590 100 15,5007 W = 1.0 Mt 20 PAE IGA 187 114 100 lees 30 10,950* 1,094 27.0 pap ap) 292 40 6,615 903 420 542 50 24,020* 5,454 833 870 60 18,530 5,063 a 7?) 70 35,430* 139,20 5,832 80 3103930" £6;920 100 124,500* W=10Mt 20 6,848 924 nag 340 324 30 2310" 1,541 1,408 707 669 40 16,260 6,178 07 L7 50 46,000* 14,010 5,008 2,208 60 36,520 135290 4,319 70 65,610* 26,910 14,270 80 100,900* 3:5,900 100 218,800* *F¢(max) is 0.28 at 5 psi, 0.45 at 10 psi, 0.62 at 15 psi, 0.80 at 20 psi, and 1.00 at 35 psi. In other words, a further significant reduction in overkill and wastage of explosive energy associated with the detonation of large-yield weapons on small- size targets would not be achieved by the use of weapons with yields less than 100 kt on U.S. urban centers as a target system. However, for attacks designed to cause more than about 65% fatalities under the conditions assumed in Table 2, the various states or the country as a whole would become a single 96 MILLER target, and on an area basis the number of missiles required would be essentially independent of weapon yield for missiles carrying maximum payload. The. Sovietis ‘estimated: 1970 simetercontinental™ nuclears force; irom, the previously quoted statements, is approximately 11,000 Mt, assuming a one-way mission or refueling of 750 bombers carrying a payload of 5 Mt each, 1100 SS-11’s carrying 1 Mt each, and 250 SS-9’s carrying 25 Mt each. These estimates do not include the submarine force of perhaps 200 vessels, because it is assumed that its mission would be that of a reserve or second-strike force. Such a ready force, if delivered in an antipopulation attack with 100% reliability and accuracy in the most efficient manner (1.e., by allocating the 1-Mt weapons to densely populated cities with smal] areas and the 25-Mt weapons to less densely populated urban centers covering larger areas) utilizing full-target coverage by 20- or 35-psi overpressure contours, could result in fatalities amounting to about 42% of the population if all were sheltered in wood-frame structures. This percentage of fatalities 1s equivalent to the entire 1970 population of the 680 largestsWe S_.Cities: If this same nuclear striking force were converted to efficient and maneuverable MIRV systems with 100-kt warheads, the single 5-Mt warhead assumed for the bombers would convert to thirteen 100-kt warheads; the single 1-Mt warhead taken for the SS-11 would convert to four 100-kt warheads; and the single 25-Mt warhead for the SS-9 would convert to about forty 100-kt warheads. The combined striking power for these warheads is then 2375 Mt, which, if delivered according to the assumptions in Table 2, could produce about 52% fatalities among the 1970 U.S. population. This combined nuclear striking force would be equivalent to a total of 593 deployed SS-9 missiles with the MIRV system, all armed with 100-kt warheads. Assuming such an SS-9 MIRV force to be in existence, estimated minimum deployment times. and costs in 1970 U.S: dollars: tor both==the cotalyand additional SS-9 missiles (each fitted with 40 100-kt warheads) required to cause stated relative fatality levels among the 1970 U. S. population for the conditions of Table.2 are givenun Table.3.| Whe year of tnalideployment 1s based onthe assumption of both a constant rate of production and one that increases linearly from 50 to 100 missiles per vear from 1970 to 1980. Note: that the calculations “are™ based =oni-the 1970 *U2S. population distribution; thus, for the fatality percentage having Y,; and Y. values significantly larger than 1970, the number of required missiles, the values of Y, and Y,, and the added cost are all underestimates (except for the 100% level of fatalities). Since the estimated number of missiles refers to weapons delivered on target, these figures are, by definition, underestimates of force requirements for the stated fatality levels. These estimates suggest that at the current rate of production the most economical and effective SS-9 MIRV system could not impose, through air-blast weapons effects, the current popular view of assured and complete destruction of the 1970 U.S. population in a nuclear attack until sometime after the year FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE Oy, Table 3 ESTIMATED NUMBER OF SS-9 MISSILES WITH MIRV, YEAR OF FINAL DEPLOYMENT, AND COSTS FOR CAUSING A STATED PERCENTAGE OF FATALITIES AMONG THE 1970 U.S. POPULATION BY BLAST EFFECTS ON PEOPLE IN WOOD-FRAME STRUCTURES Total required Additional required Fatalities, | number of SS-9 number of SS-9 Nar va Added cost, % missiles missiles (year) (year) 10’ $(U.S., 1970) 20 80 30 180 40 340 50 530 60 1,060 467 1979. Lo77 13 70 5,310 4,717 2064 2005 130 80 15,600 15,010 L270 20377 413 90 38,700 38,110 LT 32 2084 1050 100 L500 114,900 4268 2175 3200 *Y, = 0.02N,,, + 1958, at a constant rate of 50 SS-9 missiles per year. ape COFEN 137)2+ 1960, at a rate of 50 (1 + 0.1t) SS-9 missiles per year, where toa, — 1:9 7.0; 3000. With a constantly increasing rate of production of the missile system, however, the force required for such a level of fatalities might be assembled and deployed in 100 to 200 years. The cost of such a system could be two times the estimated $3 trillion (1970 dollars); this is about 1000 times the current yearly Gross National Product of the U.S.S.R. Methods for estimating the intermediate-range fallout from 100-kt-yield weapons detonated as airbursts to give maximum area coverage of a given overpressure contour are not immediately available. Thus the general extent or degree of the radiological hazard to agricultural areas downwind from any of the larger urban centers hit in such an attack cannot be given. The effects of detonating the 100-kt weapons at ground level were investigated in an alternate assumed attack mode. This alternative is suggested since the fallout levels in the vicinity of ground zero appear to be maximized at a yield of around 100 kt. The areas enclosed by exposure-dose contours of 400 and 1200 R over a period of 100 hr after fallout arrival for 100-kt-yield (100% fission) and 1-Mt-yield (50% fission) surface detonations are shown in Fig. 3. The 400-R contour indicates generally the limiting extent (outer boundary) at which a significant number of persons sheltered in wood-frame houses would experience radiation sickness. The 1200-R contour indicates generally the limiting boundary at which essentially all persons sheltered in wood-frame houses over the specified 100-hr period would eventually die. In other words, all 98 MILLER see Potential exposure dose greater than 1200 R in 100 hr after fallout arrival 5 (tes Potential exposure dose greater than 400 R in 100 hr after fallout arrival Se W = 100 kt % 5 B = 100% fission Oo -5 0 5 10 15 20 5 30 35 40 45 za x ke n = 40 W 1 Mt i B = 50% fission Vw = 29 mph -10 ) 10 20 30 40 50 60 70 80 90 DISTANCE, miles Fig. 3. Area enclosed by exposure-dose contours of 400 and 1200 R for fallout from 100-kt- and 1-Mt-yield surface detonations. persons in the shaded area of Fig. 3 who were in shelters with a protection factor of 2 (or more at central locations) would become fatalities. The full significance of the total fallout-radiation hazard within the two elliptically shaped areas, in terms of number of fatalities, cannot be readily incorporated into the described antipopulation attack patterns (in which the only hazard considered was blast overpressure from air detonations) without using a large-scale computer program. However, a conceptional view of the relative hazard to people in small wood-frame structures can be obtained from simple arithmetic estimates if only the circular portion of the potentially lethal area around ground zero is considered. The radius of this area is 1.9 miles for the 100-kt detonation and 2.5 miles for the 1-Mt detonation. Thus the potential lethal radius for the fallout hazard from the 100-kt surface detonation under the assumed exposure conditions is 3.4 times the lethal radius for the overpressure hazard. from the 100:kt. ar burst. (thevarea sratiogisealmost 2.0 o1)in comparison, these radius and area ratios for the 1-Mt detonation are only 2.1 and 4.4, respectively. Another way of stating the relative extent of these two hazards for the specified exposure conditions is that the area coverage of the 100% lethal fallout level from a 100-kt surface burst is equal to that of the overpressure effects from a 4-Mt air detonation. FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE Be For people inside concrete buildings with a protection factor of 100, the radius of the 600-R lethal-exposure dose from ground-zero-region fallout from the 100-kt surface detonation is almost 0.5 mile, only slightly larger than the radius of the 48-psi contour (100% lethal for occupants of concrete structures) for the 100-kt air burst. The same relative potential hazard from fallout does not occur for the 1-Mt surface detonation since the absolute magnitudes of the fallout levels near ground zero are smaller in this case; also, the time of fallout arrival is shorter for the smaller-yield detonation. The general dispersion of ground-zero- and downwind-fallout patterns, as represented by the 1200-R potential-exposure-dose contour, for closepacking of the ground-zero patterns to cover circular-shaped urban areas is illustrated in Figs. 4 and 5. In these figures Ay is the largest inscribed circular area enclosing an urban target area, and Ap is the area within the downwind 1200-R exposure-dose perimeter for fallout from cloud altitudes. Figure 5 shows that Ay, for 16 and 28 detonations includes a portion of several cloud-fallout patterns; in addition, the maximum downwind extent of the perimeter of the = 100% FISSION We = 100eKT B Via) = 25 MPH WwW Ag(7) = 179 SQ MILES Ay(7) = 72.2 SQ MILES Fig. 4 Geometric configuration of Aj and AR for the 1200-R exposure-dose perimeter when Ar is equal to the maximum circular area covered by seven overlapping ground-zero fallout patterns. 100 MILLER Ag(7) = 184 SQ MILES ArR(16) = 304 SQ MILES Ar(28) = 439 SQ MILES A+(7) = 66.5 SQ MILES A+(16) = 200 SQ MILES A-+(28) = 400 SQ MILES Fig. 5 Geometric configuration of Ay and AR for the 1200-R exposure-dose perimeter when Af is equal to the maximum circular area covered by 7, 16 and 28 overlapping ground-zero fallout patterns. 9) 1200-R exposure-dose contours is essentially constant and independent of the size of the circular target. The average, or midrange, values of Ay and Ap are plotted as a function of the number of weapons detonated (or the number of ground-zero patterns) giving full circular coverage of the target area. No real, single, smooth curve of Ay and/or Ap as a function of the number of detonations or weapons exists for target-area coverage requiring one to seven weapons per target. The curves in Fig. 6 tend to follow midrange values of Ay and Ap; as the number of weapons per target increases, the percentage spread in possible values of these two parameters decreases. The curves in Fig. 6 were used to estimate the number of weapons per target required to enclose each of the 500 largest U.S. cities or urban places within the 1200-R contour and the relative amount of land area outside the urban areas that would also be enclosed (assuming no overlapping of the fallout patterns from these targets and no loss of fallout to areas outside the country). The calculated cumulative explosive yield of the 100-kt weapons, the total rural land area enclosed, and the number of people involved (i.e., those FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 101 1000 8 € a AR t WwW oc a 100 (an Ww n) oO sa) oO za vy, LW 10 1.0 10 100 NUMBER OF WEAPONS PER TARGET Fig.6 Variation of Ay and AR with number of weapons detonated or number of ground-zero fallout patterns. residing in the area given by A, who would be fatally involved if sheltered in wood-frame houses) are given in Table 4. ihe Fealculations, in, Table 4) indicate. that, for the «500 most densely populated cities or urban places, coverage of the respective Ay with at least the 1200-R exposure-dose contour could be accomplished with a total explosive yield of about 103 Mt (1.e., 1030 delivered weapons yielding 100 kt each) and that almost 1.0% of the land area of the United States outside the cities would be enclosed within the specified 1200-R exposure-dose contour. As shown, the 500 most densely populated cities or urban places contain about 35% of the 1970 U.S. population; the estimated number of 100-kt airbursts required to cause 35% fatalities by air-blast effects among the population sheltered in wood-frame structures would be about 14,000. Thus, if the major portion of the U.S. population were in shelters with a protection factor of 2 at the time of attack, the number of SS-9 missiles with an 102 MILLER Table 4 CUMULATED TOTAL YIELD OF 100-KT SURFACE BURSTS TO ENCLOSE THE 50 TO 500 MOST DENSELY POPULATED CITIES AND NEARBY RURAL AREAS WITHIN THE 1200-R EXPOS URE-DOSE CONTOUR Target AR; AR/3.6 x 10; , Cumulated percent number M, Mt sq miles % of total population 50 il S52 4,470 0.12 12.8 100 23:3 7,920 0.21 L5E9 200 41.5 14,190 O39 21.4 300 62.3 21,240 0.59 Ziel 400 LILO 27,690 0.76 30.4 500 103.4 355700 0.99 35.0 idealized MIRV system and 100-kt weapons required to cause a given level of fatalities would be about a factor of 13.5 less for an attack in which all explosions are ground bursts instead of airbursts (1.e., 1f the fallout effect instead of the air-blast effect were used against the population). This result suggests that, without reasonably good fallout protection in the cities, the planned use of surface-detonated 100-kt weapons could reduce the time scale required to construct a force that could assuredly destroy the 1970 U.S. population from about a century or two to about a decade or two (especially if all technical problems of production of such a force would be solved without causing extended delays in deployment). This rather high relative degree of potential effectiveness of the fallout hazard from the 100-kt surface detonation could, of course, be countered by the provision and use of shelters with protection factors higher than 2. Increasing the protection against the fallout radiation would decrease the lethal radius from fallout radiation. In turn, a larger number of warheads and missiles would be required to accomplish the same level of population destruction by either fallout radiation or air blast. The times for producing the needed force would then be increased beyond the minimum of the decade or two indicated previously. For a shelter protection factor of 130, the 100% lethal radius for the very close-in fallout from a 100-kt true surface burst would be equal to the 100% lethal radius for the population sheltered in concrete buildings subjected to the air-blast overpressure from a 100-kt airburst. In such a protective posture, the limiting force requirements for assured destruction of the 1970 population would be 160,000 SS-9 missiles carrying 100-kt warheads with MIRV’s for the smaller targets. Such a force, built at the previously assumed rates which increase continuously with time, could be deployed approximately by the year 2760 at a cost of about $4.5 trillion (1970 U. S. dollars). FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 103 The apparent advantage of the reduction in force requirements gained when lower-yield warheads with MIRV are allocated to small urban places, missile sites, and other military targets, together with the fact that area coverage for the circular prompt weapons-effect contours is independent of weapon yield, could suggest a gradual conversion of existing stockpiled weapons to lower-yield warheads in all nuclear arsenals soon after MIRV capabilities become opera- tional. If this is the case, some major changes in civil-defense policies, programs, and operational plans could be considered to provide an appropriate response to salient features of the revised-force capabilities. Two major options are: (1) the provision of increased protection to the population and to other resources in urban areas against the prompt weapons effects (1.e., blast, thermal, shock, and initial nuclear radiation) and (2) the evacuation of cities when there is sufficient warning time. The first option would include the provision of shelters with a minimum protection factor of 130 to negate the advantage of the 100-kt surface burst. For the second option, some difficulties could occur if ground bursts were used; however, the downwind extent and width of the fallout pattern from the 100-kt surface detonation is much less than that from detonations in the megaton-yield range, as shown in Fig. 3. This associated reduction in fallout areas for attack patterns including only urban-area targets (65% or less of the 1970 population) would leave essentially all the rural areas and the agricultural sector free of direct exposure to any weapons effects. If shelters were available in urban areas, postattack evacuation to rural areas free of fallout would be a feasible operational alternative. As previously mentioned, exposure doses from fallout radiation near ground zero are greater for detonations with yields close to 100 kt because of the early fallout arrival times and the rather heavy local deposits surrounding the point of detonation. Further insight into these ramifications of the fallout hazard would require a more detailed analysis than that given here; such an analysis could be readily accomplished with the aid of computers. Specific consideration of the people, animals, and plants that could be exposed to radiological hazards from the downwind fallout has been neglected here. However, practically no human fatalities would occur from fallout in the downwind area from the 100-kt surface burst if shelters with a protection factor of 130 were available and were used. In the described antipopulation attacks (similar results would apply to a pure counterforce attack), the downwind boundary of the 1200-R exposure- dose contour extends a distance of 20 to 30 miles from the downwind edge of the urban areas. Thus the size of the rural farm areas receiving moderately heavy fallout levels from the 100-kt surface bursts would be approximately equal to the size of the urban areas subjected to direct attacks. Consequently agricultural problems caused by fallout would be limited to regions near target cities or target military installations. This pattern would persist until more than about 65% of the population (all urban places) was involved. For much heavier attacks, with 100-kt-yield ground-burst weapons, however, the radiological effects on 104 MILLER agriculture could approach those predicted for the counterforce and mixed attacks using larger-yield weapons. SUMMARY AND CONCLUSIONS The intrinsic properties of fallout associated with radiological hazards which could affect agricultural operations in the postattack period of a nuclear war include: (1) the radionuclide composition of the fallout material, which determines the energy composition of the gamma and beta radiation emitted, (2) the physical and chemical properties of the fallout particles (such as size, shape, composition, structure, and solubility) which influence their retention by surfaces, and (3) the solubility and biological availability of specific radio- nuclides. In terms of crop or agricultural-product output, both operational factors (effects on man and his social system) and biological factors (response of plants, animals, birds, and insects) would be important. The degree of the hazard to the food-producing agricultural systems would generally depend more on external parameters, such as the available weapon system, form or mode of attack, level of attack, explosive yield of weapons, relative heights of burst, and local and regional weather patterns, than on the properties of the fallout. The latter would tend to influence the form rather than the degree of the hazard. A major recent development in weapon systems that could have a significant impact on the type and extent of hazard to agriculture in a nuclear war is the Multiple Independent Targeted Reentry Vehicle. Indeed, estimates of MIRV system capabilities, especially in terms of using many smaller-yield warheads on many smaller targets, may be used to identify several important implications for future civil-defense planning. One estimate involves the relatively high levels of the fallout hazard near ground zero, which apparently has a maximum for a surface detonation at a yield of about 100 kt. The implication of this effect on weapon-system cost and times of deployment for the Soviet Union and its SS-9 missile system is that, if the U.S. fallout-shelter system were poor and a majority of people had to remain in their houses during an attack, the Soviets could build and deploy at a cost of about $30 billion within the next 10 to 20 years a nuclear force of sufficient capability to essentially assure the destruction refers to the ’ of the entire U.S. population. In this case “sufficient capability’ use of the force in an antipopulation attack in which local fallout would be the main cause of fatalities. On the other hand, if fallout shelters with protection factors of 130 or more were available and were used, no advantage in force requirements would accrue by the use of surface bursts. Instead, the more reliable overpressure effects would be used. In the limit, the assured destruction of the U.S. population by blast effects would require at least 160,000 SS-9 missiles. Even at reasonable increases in production rates, the Soviets would have difficulty in deploying such a force within the next 800 years (using currently FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 105 available technologies); the cost of such a force would be prohibitive at more than $4.5 trillion (1970 U. S. dollars). The major implication for agricultural systems of the possible use of MIRV and the associated lower-yield warheads in a nuclear war is that the fallout would be of the intermediate or worldwide type for attacks in which air-blast effects are emphasized and that, where the fallout effects are emphasized by use of ground bursts, the heavy downwind deposits of local fallout would be limited to a distance of about 30 miles from the downwind edge of any target independent of the size of the target. In other words, the effect of MIRV and the associated lower-yield warheads would be to almost eliminate the widespread fallout effects previously estimated for attacks in which land-surface detonations of weapons in the megaton-yield range have been postulated. With the described Soviet SS-9 missile system with MIRV capabilities, a comparable degree of effect on agriculture might be achieved from attacks designed to kill more people than the entire U.S. urban population (1.e., more than 65% of the 1970 U.S. population) in which all detonations programmed for the rural areas would be surface bursts. Further detailed calculations are required before the potential of such an attack to cause significant adverse effects on agriculture can be evaluated, given the current public fallout-shelter system as a basis for estimating population survival. REFERENCES fC. -Millervand PB: D:. LaRiviere, Introduction to Longer-lerm Biological Effects of Nuclear War, SRI Project IMU-5779, Stanford Research Institute, 1966. 2. R. B. Platt, Ecological Effects of Ionizing Radiation on Organisms, Communities, and Ecosystems, in Radioecology, Reinhold Publishing Corporation, New York, 1963. .C. F. Miller, Fallout and Radiological Countermeasures, Vols. 1 and II, SRI Project IMU-4021, Stanford Research Institute, 1963. 4.K. H. Larson and J. W. Neel, Summary Statement of Findings Related to the Distribution, Characteristics, and Biological Availability of Fallout Debris Originating from Testing Programs at the Nevada Test Site, USAEC Report UCLA-438, University of California, Los Angeles, Sept. 14, 1960. 52) seb aenicnd,. Ho WwW. «beely; P. W. Krey.. Jo-Spar,. and “A. Walton, The High Altitude Sampling Program, Report DASA-1300 (Vols. 1, 2A, 2B, 3, 4, and 5), Defense Atomic Support Agency, Aug. 31, 1961. 6. C. F. Miller, Operation Ceniza-Arena: The Retention of Fallout Particles from Volcan Irazu (Costa Rica) by Plants and People, Parts Two and Three, SRI Project IMU-4890, Stanford Research Institute, 1967. 7. National Academy of Sciences—National Research Council, Damage to Livestock from Radioactive Fallout in Event of Nuclear War, Publication No. 1078, Washington, D. C., 1 96)3;. 8. National Committee on Radiation Protection and Measurements, Exposure to Radiation in an Emergency, Report No. 29, 1962. 9. J. L. Mackin, S. L. Brown, and W. B. Lane, Beta Radiation Dosimetry for Fallout Exposure Estimates: Comparison of Theory and Experiment, SRI Project 7402, Stanford Research Institute, 1969. w 106 MILLER 10. ts: 132 14. 19° ZO: S. L. Brown, Disintegration Rate Multipliers in Beta-Emitter Dose Calculations, SRI Project IMU-5116, Stanford Research Institute, 1965. J. D. Teresi and C. L. Newcombe, An Estimate of the Effects of Fallout Beta Radiation on Insects and Associated Invertebrates, Report AD-633024, Naval Radiological Defense Laboratory, Feb. 28, 1966. . Report of ICRP Committee on Permissible Dose for Internal Radiation (1959), J. Health Phys:, 31960). J. L. Kulp and A. R. Schulert, Strontium-90 in Man and His Environment, USAEC Report NYO-9934 (Vols. I, II, and III), Columbia University, 1961 and 1962; also R. S. Hirshman and A. R. Schulert, Strontium-90 Assay of Various Environmental Materials, USAEC Report NYO-9934(Vol. III) Ext., Columbia University, 1961. C. F. Miller and S. L. Brown, Models for Estimating the Absorbed Dose from Assimilation of Radionuclides in Body Organs of Humans, SRI Project IMU-4021, Stanford Research Institute, 1963. .C. F. Miller, Assessment of Nuclear Weapon Requirements for Assured Destruction, URSRC Report 757-6, URS Research Company, 1970. .R. K. Laurino, National Entity Survival Following Nuclear Attack, SRI Project IN-OAP-28, Stanford Research Institute, 1967. . William Beecher, Soviet Arms Gain Detected by U.S., New York Times, 1969. . Ashley W. Oughterson and Shields Warren, Medical Effects of the Atomic Bomb in Japan, Division VIII, Vol. 8, National Nuclear Energy Series, McGraw-Hill Book Company, Inc., New York, 1956. Raisuke Sirake, Medical Survey of Atomic Bomb Casualties, Research on the Effects and Influences of the Nuclear Bomb Test Explosives, Volume II, Japan Society for the Promotion of Science, Tokyo, 1956. C. F. Miller, Protection of People by Structures from the Initial Radiation, Blast, and Thermal Phenomena of Nuclear Explosives, Research Report No. 7, Office of Civil Defense, Department of Defense, 1962. PREPARATION AND USE OF FALLOUT SIMULANTS IN BIOLOGICAL EXPERIMENTS WILLIAM B. LANE Stanford Research Institute, Menlo Park, California ABSTRACT Facilities developed by the Office of Civil Defense for the production of synthetic fallout are described. The capability for simulating nuclear fallout is reported and is exemplified by a description of the production (1) of a 300-lb batch of synthetic fallout tagged with 15 Ci Aleve : : , x : Ore ; : of Cs and (2) a small routine batch of synthetic fallout tagged with Y, which is produced once or twice a month. The nuclear weapons test-ban treaty, which effectively prohibits the detonation of nuclear weapons in the atmosphere, has made necessary the development of alternative experimental techniques for obtaining data on the interaction of radioactive fallout with the environment. Procedures for preparing synthetic fallout that simulates some of the important properties of fallout generated by nuclear weapons have been developed over the past few years. Synthetic radioactive fallout can be employed in many experimental programs directed toward obtaining operational and technical data used to develop plans for survival and recovery measures during and after a nuclear war. Procedures developed to simulate many properties of real fallout’ * have been used in the hot-cell facility at Camp Parks to prepare batches of synthetic fallout for studies sponsored by the Office of Civil Defense. Investigators at the U.S. Naval Radiological Defense Laboratory (USNRDL), Cornell University, Oak Ridge National Laboratory (ORNL), University of Tennessee, University of California, Lawrence Radiation Laboratory, Colorado State University, Uni- versity of North Carolina, and Stanford Research Institute all have used synthetic fallout prepared to their specifications. Stanford Research Institute now operates the Camp Parks hot cell for the Office of Civil Defense. 107 108 LANE SYNTHETIC-FALLOUT PRODUCTION PROCESS The steps in producing synthetic fallout include: (1) mineral processing to produce sized particles in ton quantities, (2) radioisotope processing in the hot cells, (3) radiotagging the mineral particles in concrete mixers and high- temperature furnaces, and (4) testing and control to ensure the radiochemical, chemical, and physical properties of the synthetic fallout. Mineral Processing Radioactive particles from 44 to 700 yu in diameter comprise a very large fraction of local fallout from a land-surface nuclear detonation. Four particle- size groups——44 to 88, 88 to.175, 175 to 350; and 350 to: 700 1——are- produced to cover the range. Carload lots of feldspar, quartz, and clay, the principal minerals in the earth’s crust, were purchased. Some required crushing and pulverizing, but most were in the form of sand and required only sieving. to produce the full range of particle sizes. The particles were separated into sized groups on a commercial sieving machine manufactured by Novo Corp. A wet centrifugal method was used to remove fine particles from the 44- to 88-u material. Sieving efficiency was measured and controlled by frequent determinations of particle size made with Tyler sieves and a Ro-Tap machine. Each of the size groups was produced in ton quantities and stored in color-coded bags and barrels. If extremely clean cuts were required, pound lots of these stored particles were further processed on the Ro-Tap by wet sieving. Some important physical properties of the four particle-size groups of Wedron sand were measured by careful sieving into a large number of intermediate sizes. The data permitted calculations of the properties as shown in Tables: Table 1 PHYSICAL PROPERTIES OF WEDRON SAND Number of Average surface Average particle Group, particles area per particle, diameter, LU per gram cm Ll 44 to 88 6.98 x 10° 6.69 x 10° 47 88 to 175 6.20 x 10° 3.21 x 10" 101 175 to 350 7.54 x 10" 1.39x 10° 210 350 to 750 7.09 x 10° 7.85x10°> 500 FALLOUT SIMULANTS IN BIOLOGICAL EXPERIMENTS 109 Radioisotope Processing Two hot cells are provided for radioisotope handling. Each cell has an inside floor area 8 by 8 ft. Shielding is provided by 2-ft-thick concrete walls, and there is a 2-ft-thick zinc bromide-filled viewing window.” One cell is fitted with a pair of model 8 Hevi-Duty Master-Slave manipulators and the other cell with a pair of model 4 manipulators. Ventilation 1s provided by blowers that maintain a slight negative pressure inside the cells. Leakage air, amounting to about 500 cfm, is exhausted through absolute filter banks. A '5-ton monorail hoist provides access to the cells and to a shielded alleyway. One cell is equipped with a ‘4-ton jib crane that remains inside the enclosure. Each cell has through-wall holes for sample removal and for pressure, vacuum, and water lines. Each cell is supphed with a 100-amp three-phase four-wire electrical service. Work tables consist of stainless-steel trays atop cubic-yard concrete blocks that are carried on warehouse dollies. A 15-gal drum is cast into the center of the concrete block to serve as a receptacle for waste disposal. Separate work tables set up for specific operations are wheeled into the hot cell as needed. Solid waste is collected in polyethylene-lined drums and then transferred to approved shipping boxes. Liquid waste is poured into 5-gal polyethylene carboys and then solidified with Micro-Cell E(a Johns-Manville product). Ultimate disposal is contracted to a licensed company such as Nuclear Engineering of Walnut Creek, Calif. Radioisotopes that have been processed include kilocuries of eboreand Pl. muUleicuries.;of Sr, St. Zr. “Nb; Ru, |’ RU, Dlg aCs Ce." a. sand ~ Au. imillicuries of "Rb and * Cs: and gross fission product. 140 Ba, 140 [ea ) Many of these radioisotopes have been produced by neutron irradiation in the nearby General Electric Company test reactor at Vallecitos. Tools and equipment for encapsulating, testing, and opening the irradiated capsules are available in the hot cells. Radiotagging Mineral Particles Radiotagging consists in spraying a weak acid solution of a selected radioisotope on a charge of mineral particles as they are tumbling in a rotating mixer. The particles are then dried by the direct application of heat or by introduction of heated air to the mixer. Subsequent treatment determines the solubility or availability of the radioisotope. A nonleaching synthetic fallout is produced by “fixing” the radioisotope with an overcoat of sodium silicate. This 1s accomplished by spraying a solution of sodium silicate on the dry radiotagged particles while they are still in the mixer; after this spraying they are again dried. The amount of sodium silicate 1s adjusted to produce a layer less than 1 yu thick. Tagged particles are then removed from the mixer and placed in a furnace at 2000°F to fuse the sodium 110 LANE silicate layer and seal in the radionuclide. The physical properties of the mineral particles are not appreciably altered by this treatment. However, in many cases a realistic and specified solubility of the radionuclide is desired. This 1s accomplished by heating the radiotagged mineral particles (without sodium silicate) to previously determined temperatures that alter the particle surface and control the combined chemisorption and diffusion of the radionuclide in the particle matrix. The batch size of mineral particles dictates which of the available rotating mixers is selected for a particular operation. Ball mills and twin-shell blenders are used for gram and pound lots. Portable 1-cu-ft concrete mixers are used for lots of up to 100 1b. Specially modified 2-yd concrete mixers are used for 500-lb batches. The latter are charged with mineral particles by lift truck and hoppers. The radioisotope is sprayed on, the particles are dried, the sodium silicate is sprayed on, and the particles are dried again; the synthetic fallout is then discharged on an endless belt that conveys it to a bucket elevator and a metering hopper where it is placed in stainless-steel pans. The pans are pushed by hydraulic ram along skid rails into a gas-fired furnace. After spending an hour in the furnace at 2000°F, the pans are pushed out the other end of the furnace where the synthetic fallout cools. Further pushing automatically dumps the pans and discharges the cooled synthetic fallout on to another endless belt for transfer to shielded hoppers. All these operations are performed from a remote and shielded location to minimize the radiation dose to personnel. Several electric furnaces are available for heating gram and pound lots of synthetic fallout. A large number of lead and concrete containers are available to meet a wide range of volume and shielding requirements. Testing and Control of Synthetic Fallout Radiation-measuring equipment for analytical purposes consists of a 4-p1 ionization chamber, a gamma spectrometer, a scintillation crystal counter, and a Geiger counter. 1. The 4-pi ionization chamber is used to assay all incoming shipments of radioisotopes and all outgoing batches of synthetic fallout. Over the years it has proved to be a reliable instrument, and the results obtained with it are considered very accurate. The 4-pi ionization chamber is filled with argon to 600 psig at 70 F. The cylindrical steel chamber is 11 in. in diameter and 14 in. high and has a reentrant sample thimble 1% in. in internal diameter by 12 in. deep. The entire chamber is shielded by 3 in. of lead. Current produced in the chamber by ionizing radiation is applied to suitable load resistors; the resulting voltage drop drives a plate-difference amplifier and is read out on a microammeter. The useful ionization current ranges between 4 X 10 '° and 3 X 10° ma. All readings are normalized to a standard response of 5.60 X 10 ’ ma for 100 ug of radium. The FALLOUT SIMULANTS IN BIOLOGICAL EXPERIMENTS ia response (milliamperes per disintegration per second) of many radioisotopes has been accurately determined.” 2. The gamma spectrometer is used to verify the radiochemical purity of all incoming radioisotopes and all outgoing batches of synthetic fallout. It is composed of a pulse-height analyzer, a paper-tape printer, and an X—Y plotter. The Technical Measurement Corp. (TMC) Gammascope analyzes signals whose pulse height is proportional to photon energy and sorts the signals into one of 100 channels, depending on their peak amplitude. The accumulated data are presented on a display oscilloscope and then read out on a TMC paper-tape printer or a Moseley X—Y plotter. 3. The scintillation counter consists of a 3- by 3-in. sodium iodide crystal with a 14- by 2-in. deep well mounted on an E&M Instruments Co., Inc., 3-in. photomultiplier tube whose output is fed directly into a Systron model 1091-3 scaler. The scaler is controlled by a Nuclear Dual Timer. A John Fluke Manufacturing Company, Inc., model 412A high-voltage power supply provides dynode string voltage for the photomultiplier tube. Shielding consists of a lead cylinder 3 in. thick, 9 in. in internal diameter, and 22 in. high. A 2-in.-thick lead cover moves in and out to permit sample access to the well crystal. 4.A Geiger counter consisting of a thin-walled Geiger tube and a Berkeley scaler measures activity on filter papers that are used to collect air samples or to swipe floors or bench tops. Instruments for radiation safety and contamination control consist of 1-cfm constant-flow air samplers, El-Tronics, Inc., CP30 meters (Cutie Pie), and Nuclear Electronics XX2 survey instruments. SYNTHETIC-FALLOUT PRODUCTION Synthetic-fallout production can be illustrated and the capability exem- plified by reporting on two production batches. Cesium-137 Tagged Synthetic Fallout Investigators at ORNL requested a synthetic fallout for an ecological study they were conducting for the Office of Civil Defense. The study measured effects of '*’Cs ona controlled ecological system over a period of years. Three hundred pounds of 88-to 175-u sand was tagged with '*’Cs in a 1-cu-ft mixer in two batches. The first batch of 140 lb had a specific activity of 36.6 mCi/Ib, and the other batch of 160lb had a specific activity of 46.7 mCi/Ib. All the tagged sand was heated to 900°C and held at that temperature for 2 hr. The resulting synthetic fallout was leached overnight by 0.1N HCl. Overnight leaching of 2-g samples of the resulting synthetic fallout by 20 ml of 0.1N HCl removed 21% of the '*7Cs activity. 112 LANE Since the ORNL study was designed to continue for several years, leaching data covering a few hours seemed inadequate to predict the availability of cesium. Accordingly, long-term tests were initiated to measure the leaching of cesium at extreme dilutions. This was accomplished by setting aside the 20-ml aliquot of 0.1N HCl that resulted from, overnight leaching and adding a second, similar aliquot to the once-leached synthetic fallout. This process of leaching the same mineral fraction for random time intervals with fresh aliquots was continued for 1250 days and resulted in the accumulation of 28 successive leaching aliquots. The mechanism for the first 10 days of leaching appeared to be a chemisorption process that was well described by a Freundlich adsorption equation of the form C= ke? (1) where C,, is the average cesium concentration in the mineral particles and C 1s the concentration in the leaching solution. 3 It appeared that the longer-term leaching behavior (from 10 days to more than 3 years) was described by a diffusion-limiting mechanism corresponding to the solution of Frick’s law for diffusion from a sphere: exp (— pv? 7? Dt/r2) (2) ore Jo rz Dw 1R When t is sufficiently large, the first term of the series is a good approximation, so that CG 6 O it WN where Co = initial average cesium concentration in the mineral C,, = concentration after various leaching times t = time of leaching = radius of the fallout particle ro} | diffusion coefficient = I In this approach the leaching of radionuclides from fallout particles for long periods of time can be predicted if the numerical values of k, n, and D in Eqs. 1 and 2 are Known. FALLOUT SIMULANTS IN BIOLOGICAL EXPERIMENTS tS Monthly Batch of Multicurie °° Y Tagged Synthetic Fallout A 250-mCi °° Sr “cow” was started in a lead-shielded Berkeley glove box about 3 years ago to supply °° Y for a study of beta effects on beans. To satisfy requirements for several OCD studies, the activity level was soon raised to 30 Ci. This was accomplished by wheeling the shielded box inside one of the two hot cells to ensure double containment and simply adding 30 Ci of carrier-free ?° Sr to the 400-ml beaker that already contained 250 mCi and 2g of inactive strontium nitrate. Yttrium-90 is “milked”? from the equilibrium mixture by taking the dry strontium nitrate up in 25 ml of distilled water. Strontium nitrate is then precipitated by adding 125 ml of 90% nitric acid. The acid solution containing the ?°Y is removed through a filter frit by suction and transferred to the second hot cell where it is evaporated to dryness. The carrier-free ?° Y is taken up in 25 ml of water, and 2 g of inactive strontium nitrate is added and precipitated with 125 ml of 90% nitric acid. The acid solution of ?°Y is again filtered off, evaporated to dryness, and taken up in 100 ml of 0.1N HNO3. About 20 Ci of °°v are usually available at this point. A 100-ul aliquot of this solution is assayed in the 4-pi ionization chamber to determine the volume required for tagging the particular batch of sand. In the meantime, the °° Sr cow in the Berkeley box is slowly evaporated to dryness and taken up in 25 ml of water to make ready for the next milking. Sufficient Wedron sand to meet the batch requirements is prepared by wet sieving and Ro-tapping to’ensure that all particles are within the specified size range. The sand (up to 600 g) is added to the rotating drum of a ball mill that is operating inside the second hot cell, and the calculated volume of carrier-free ?°¥V solution is sprayed on the tumbling particles. The radiotagged sand is dried by the heat from a hot plate placed directly under the metal drum, after which 10 ml of sodium silicate is sprayed into the rotating drum to overcoat the particles. After the particles are again dried, the synthetic fallout is transferred to a crucible and placed in a muffle furnace at 1950°F for 1 hr. The synthetic fallout is removed from the furnace, cooled, and returned to the hot cell for assay. When it is determined that the specific activity is within acceptable limits, the synthetic fallout is packaged and shipped. The ?°Sr cow has been milked 25 times for the University of California, 22 times ‘for “the University of Tennessee,.and\13 ‘times for studies at Stanford Research Institute. ACKNOWLEDGMENT This work was done by Stanford Research Institute under Office of Civil Defense Work Unit 3211C. 114 LANE REFERENCES 1. William B. Lane, Fallout Simulant Development: The Sorption Reactions of Cerium, Cesium, Ruthenium, Strontium, and Zirconium—Niobium, Project No. MU-5068. Stan- ford Research Institute, November 1965. 2. William B. Lane, Fallout Simulant Development: Temperature Effects on the Sorption Reactions of Cesium on Feldspar, Clay, and Quartz, Project No. MU-6014, Stanford Research Institute, March 1967. 3. William B. Lane, Fallout Simulant Development: Temperature Effects on the Sorption Reactions of Strontium on Feldspar, Clay, and Quartz, Project No. MU-6503, Stanford Research Institute, March 1968. 4. William B. Lane, Argon Improves ZnBrz Shielding Windows, Nucleonics, 22: 88-89 (February 1964). 5. Carl F. Miller, Response Curves for USNRDL 4-pi Ionization Chamber, Report USNRDL-TR-155, Naval Radiological Defense Laboratory, May 1957. FATE OF FALLOUT INGESTED BY DAIRY COWS G. D. POTTER, G. M. VATTUONE, and D. R. McINTYRE Lawrence Radiation Laboratory, Bio-Medical Division, University of California, Livermore, California ABSTRACT The fate of fallout ingested by dairy cows—its retention, absorption from the gut, deposition in tissues, and transport to man——is of direct concern when we consider survival of livestock and ingestion of their by-products by man in the event of a nuclear war. The data presented here are from two cows fed debris from a nuclear cratering event. The first of these was given a single dose of debris, and the second received a daily administration of debris. The gamma-emitting radionuclides observed in milk were Poel 13276 140R,. bet Ww. 187we and 188yw_188R, and in urine, aN 103Ru 1317. 1327. 18lw 187 We and 188w_ 1188p. Maternal and fetal tissues in the second cow were analyzed for gamma-emitting radionuclides and compared with the maternal plasma levels of these nuclides. Maternal kidney, liver, and spleen concentrated TA Ag but fetal tissues had none. Both maternal and fetal thyroids concentrated ST by 10° over maternal plasma. Fetal bone was the primary target organ for EoO'Ba: The radiotungstens were concentrated by fetal bone and by maternal kidney, liver, spleen, and bone. Elimination patterns of the nonabsorbed radionuclides from debris are also presented. The fate of fallout ingested by livestock——its retention, absorption from the gut, deposition in tissues, elimination in urine or feces, and transport to man via meat and milk——is of direct concern when we consider the survival of livestock in the event of a nuclear war or the hazard related to ingestion of food products derived from contaminated livestock. Probably the most damaging effects from the ingestion of large amounts of fallout by animals are the early effects of radiation damage and their sequelae leading to radiation sickness and subsequent death. If livestock survive these initial insults, then their suitability as sources of food for man becomes important in long-range considerations. In recent years the only debris from actual nuclear tests which has been available for study has come from the Plowshare nuclear cratering program. Our LS 116 POTTER, VATTUONE, AND McINTYRE studies are concerned primarily with the biological availability of debris radionuclides from a specific Plowshare nuclear cratering experiment, the Schooner event. This most recent Plowshare nuclear cratering experiment consisted of a 31-kt nuclear detonation executed on Dec. 8, 1968, at the Nevada Test Site. Debris from this event was administered orally to a lactating cow and to a near-term pregnant cow for maternal—fetal transfer studies. These experiments deal primarily with the distribution of gamma-emitting radio- nuclides in the dairy cow fed debris from this event. METHODS Debris from the base-surge area of the Schooner event was collected in fallout trays or in a cyclone-type separator. In both cases the debris consisted of fine dust particles that passed through an 88-u sieve. One hundred ninety-two grams of the debris from the tray were fed to a lactating cow in 1% -0z gelatin veterinary capsules administered with a balling gun. The animals were catheterized and maintained in metabolic stalls to facilitate collection of urine and feces. Samples of feces, urine, and milk for each 24-hr collection period were pooled and mixed in order to obtain homogeneous samples for counting. Heparinized blood samples were taken following each morning’s milking. Samples consisting of 200 g of each of the metabolic products were placed in aluminum tuna cans with formalin added as a preservative and were sealed for counting. In the second experiment, the maternal—fetal transfer study, 895 g of debris from the cyclone collector was divided into four equal daily doses and administered to a near-term pregnant cow in the same manner. Smaller tissues were minced and suspended in a 2% agar solution in order to ensure constant counting geometry. All samples were counted on a solid-state germanium—lthium [Ge(L1)] drifted detector using a 2048-channel analyzer (gain = 1.0 keV/channel). The high resolution of these Ge(Li) systems has made them extremely useful for the analysis of complex mixtures of gamma-emitting radionuclides. The resulting gamma-ray spectra were recorded on magnetic tape and analyzed by using a computer code to quantitate the area under each of the gamma peaks, which were then listed in order by energies. The peaks of interest for specific radioisotopes were then selected and processed with a second code, which corrected for physical decay and subsequently calculated the activity per unit weight, the recovery as a fraction of the administered dose for each collection, and the fraction of the administered dose per unit weight of each sample. In addition, this code also plotted the recovery of milk, urine, feces, and plasma as a percent of the administered dose per kilogram vs. time after administration. FATE OF FALLOUT INGESTED BY DAIRY COWS 7. RESULTS AND DISCUSSION Experiment |: Single Administration of Debris Table 1 shows the nuclides recovered in milk, urine, and feces of the cow following a single oral administration of 92g of early (5 days postshot) Schooner, idebris from, fallout trays. Arsenic, ruthenium, iodine, tellurium, barium, tungsten, and rhenium were recovered in milk and/or urine. Manganese, cobalt, yttrium, zirconium, gold, and lead were observed only in feces or were in Table 1 RADIONUCLIDES IN FECES, URINE, AND MILK FOLLOWING ORAL ADMINISTRATION OF SCHOONER DEBRIS TO A LACTATING COW Administered dose, % Nuclide Feces Urine Milk 54 Min 98.99 ND* ND 58Co 109.9 ND ND 74 As 50.8 29.9 ND Soy 78.9 ND ND 897 71.0 ND ND POOR 91.4 7.06 ND 131] 46.4 35.9 2.23 132 Te 87.4 1.28 0.07 PO BRa= ica 93.4 ND 0.05 18lw 60.1 9.6 0.31 187 w 82.4 8.8 0.18 188w_188 Re 80.4 34.8 0.43 196 Ay 97.6 ND ND 203 pH 96.4 ND ND *The abbreviation ND, no data, indicates amounts too low for quantitation. levels too low to quantitate in milk or urine. The total amounts of individual radionuclides in the debris were relatively low compared with those of the radiotungstens, which were at least two to three orders of magnitude greater than any of the other radionuclides present. Although !?° Au was not observed in milk or urine, it was observed in plasma. The recovery of '®*°W was greater than 100%. This anomaly is due to the fact that the 155-keV peak of '®* Re was used to measure the '88w. The '88Re (Ty, = 16.8 hr), the daughter of BSW (Ty, = 69 days), was in equilibrium in the debris at the tme of administration, and, since the samples were counted shortly after collection, both the ER nin the debris and the '®®Re derived from '®*W are present in them. Rhenium is 118 POTTER, VATTUONE, AND McINTYRE very rapidly absorbed from the gut, probably directly in the rumen, and is very rapidly excreted, especially in urine and milk, as observed in single isotope experiments. Therefore, since the first two collections of urine and milk reflect rhenium absorption and excretion in addition to the '®*W absorption and excretion, a high recovery results. Figure 1 shows a typical fecal excretion curve for a nonabsorbed nuclide, 3 5 7 ; AG in feces, 88y_ Figure 2 shows the curves for a readily absorbed nuclide, urine, milk, and plasma. The curves for urinary and fecal excretion of '*'I are quite similar. The leveis in milk initially exceed those in plasma but fall more 10! —D ~~ ose se es n oO @) Q w 10° oc lw bh n” < = QO <6 10%! 0 20 40 60 80 100 120 140 HOURS POSTADMINISTRATION Fig. 1 Typical fecal excretion curve for a nonabsorbed radionuclide (ENG) following a single oral administration of Schooner debris. Concentrations in milk, urine, and plasma are too low for quantitation or are not detected. Fecal curves tor> "6. 8 oV. 2 7) NBR eRe 110M, 4 140p, 14074 141¢¢, 18274, 19° Au, and 793 Pb were almost identical. FATE OF FALLOUT INGESTED BY DAIRY COWS LVS) 10! 10° %/kg 1105 | ADMINISTERED DOSE, 1072 10-3 0 20 40 60 80 100 120 140 HOURS POSTADMINISTRATION Fig. 2. Uptake and disappearance curves for 1317 in feces (F), urine (U), milk (M), and plasma (P) following a single oral administration of Schooner debris. rapidly since inorganic iodine is secreted in milk, whereas the plasma level reflects, in addition, the presence of organic or protein-bound iodine as well as recycled iodine. Experiment Il: Repeated Administration of Debris and Maternal—Fetal Transfer A near-term pregnant cow was fed 895 g of Schooner debris from the cyclone collector. This debris, recovered 6 weeks after the detonation, consisted of particles less than 88 u, the bulk of which were between 20 and 50 yu. The debris was administered in four equal daily doses. The procedure was the same as 120 POTTER, VATTUONE, AND McINTYRE in the previous experiment except that at 144 hr the cow was anesthetized and exsanguinated and maternal and fetal tissues were removed for counting. Figure 3 shows the fecal excretion curve for °* Y, which is typical of nuclides that were not appreciably absorbed from the gut. These included °*Mn, >7Co, S87 897, Oty, Omi Op tA Meee Teme nn 10! — x xe r ep) je) ra la wm 10° om LW = ” a = O W and 188w were almost identical with the exception of 188wW mentioned in the text. f 7* As was present in milk solutions, except that 0.1% of the administered dose o and 1.1% of the '®°Re was found in feces. Since the levels of radioactivity of the various isotopes in the debris were at least two to three orders of magnitude lower than those of the tungstens, some radionuclides would be expected to be present at or below the limits of detection. Table 2 shows the tissue-to-maternal-plasma (T/P) ratios, in which fetal tissues are considered to be organs of the maternal organism. At the time the debris was fed, most of the shorter-lived nuclides had decayed. Those observed in tissue were DOAN let i Ba | ba wcandathe tungstens. Debris radio- ’ nuclides not observed in tissues were omitted from the table. In maternal tissues 122 POTTER, VATTUONE, AND McINTYRE Table 2 TISSUE-TO-MATERNAL-PLASMA RATIOS* OF MATERNAL AND FETAL TISSUES FROM A PREGNANT COW FED DEBRIS FROM PLOWSHARE NUCLEAR TEST Tissue 74 Ng 131] 140p, 18lw 185 w 188w_188pe Maternal spleen 98 NDt ZZ 3.4 3.0 353 Fetal spleen ND ND 45) 0.18 ND 0.23 Maternal kidney 45.7 145) 1EZ5 oA O29 OES, Fetal kidney ND 1.85 ND 0.38 ND O27 Maternal plasma 1.0 1.0 120 1.0 1.0 1.0 Fetal plasma ND 5.04 3:25 0.24 ND 0.20 Maternal muscle 6.5 ND Pyphe) 0.16 ND 0.13 Fetal muscle ND 0.14 0.62 0.09 ND 0.09 Maternal heart sell 4.56 ND 0.36 0.35 0.38 Fetal heart ND 132 ND 0.18 ND O.11 Maternal thyroid ND (186% 1102 ND 1.90 ND 1.30 Fetal thyroid ND 1.8x 10° ND 1.60 ND 1.20 Maternal liver 11.8 O93 ND 4.54 4.16 4.36 Fetal liver ND 1273 ND 129 1.58 0.43 Maternal RBC 3.0 O83 ND 0.47 0.41 0.43 Fetal RBC ND 0.81 ND 0.11 ND ND Maternal bone ND ND ND 2.80 3.00 3.00 Fetal bone ND 0.80 CU 5.00 5.90 5.60 Maternal cerebellum ND ND ND OPI ND 0.11 Fetal brain ND ND ND 0.60 ND ORI, Maternal cerebrum 3.0 ND ND 0.09 ND 0.09 Maternal bone marrow ND ND ND 0.36 ND 0.20 Maternal salivary gland ep ND ND 0.63 ND 0.56 Maternal omental fat ND ND ND 0.12 ND On2 Maternal mammary gland 2.8 2.30 ND 133 E32 29 Maternal placenta 5.4 2.10 ND 5 1.46 1:33 Fetal amniotic fluid Bae! 0.49 0.75 1.01 0.96 1.04 Fetal thymus ND ND 3.90 0.10 ND ND Fetal lung ND ND 3.90 OZ ND 0.10 Fetal skin ND 1.78 0.92 0.20 ND 0.20 *The tissue-to-maternal-plasma ratio = (cpm/100 g tissue)/(cpm/100 g maternal plasma). tThe abbreviation ND, no data, indicates amounts too low for quantitation. FATE OF FALLOUT INGESTED BY DAIRY COWS 123 f '"As were generally greater than unity in kidney, liver, spleen, the ratios o salivary gland, and muscle (listed in decreasing order of concentration); ’* As was not observed in fetal tissues. It is also of interest that, although relatively large amounts of 74 As were observed in the maternal urine, it was not observed in milk. The '7!1 was low at this time (7 weeks postshot), but large amounts were concentrated both in’ the maternal “and the fetal thyroids. Fhe T/P ratios for 140B, were greater than unity in fetal plasma, spleen, thymus, and lung as well as in maternal spleen, kidney, and muscle. The T/P ratios for radiotungsten (Bet W, Pee W rand Wa °° Re) were essentially the same for each tissue; this 181 SlW was indicates that all the tungsten isotopes behaved similarly. The determined by counting its X rays with an Nal counter at a later time, the '°*> W by measuring its 125-keV peak from the Ge(Li) spectrum, and the '®°W by measuring the 155-keV peak of the newly formed '**Re after that originally present had decayed. Maternal kidney, liver, thyroid, and bone had T/P ratios greater than 1. Fetal bone had a T/P ratio almost twice that of maternal bone; this indicates that bone 1s a principal target organ for radiotungsten in the fetus. A comparison of tungsten levels in fetal tissues generally shows that the placenta acts as a partial barrier to tungsten. However, tungsten that does cross the placenta is concentrated primarily in the developing bone. Despite such obvious sources of variation as differences in physical and chemical form in which radionuclides might exist in debris, inherent errors in counting statistics, and disparity of radionuclide concentrations in debris, a comparison of data from cows fed debris from different Plowshare experiments as well as carrier-free radionuclides shows excellent correlation. Transport of ions across the gut depends on many predictable factors; these include surface or mass distribution of radionuclides within fallout particles, their solubility product in the gut contents at different hydrogen ion concentrations (e.g., the formation of insoluble precipitates), and the binding of specific ion species to insoluble gut contents such as lignins or cellulose residues. Within single-debris experiments fecal elimination curves expressed as percentages of the administered dose per unit weight are essentially identical for the nonabsorbed radionuclides. This appears to demonstrate that the fecal elimination of debris radionuclides associated with particles less than 88 yu depends primarily on the rate of passage of digesta through the gut. Many of the nuclides in debris fall in this category (erga, =*Mn, °®Co, °° Co, 2? Zr, '*1Ce, etc.). On the other hand, a number of radionuclides are absorbed to varying degrees, and each of these have unique transfer coefficients to specific organs as metabolic pools. Examples of these include the iodines, arsenic, the tungstens, molybdenum, rhenium, sodium, and tritium. This group requires more-detailed studies. The data from such studies are necessary as input for the construction of predictive models such as those presented by Ng (this volume). 124 POTTER, VATTUONE, AND McINTYRE SUMMARY We have presented data on the fate of gamma-emitting radionuclides in debris from the Schooner event administered orally to lactating cows. Nuclides appearing in milk were '°"1, '°*Te, 17°Ba, *®*W, °7W, and 1®®w—'®®Re, and those appearing in urine were ’* As, '°?Ru, '7'1,'??Te, 18! w, '87w, and '88w_!®5Re Levels of the other nuclides were too low for quantitation in biological products. At the time the maternal—fetal transport experiment was 1317 1405, Vel 18s and es we) See were present in adequate amounts for quantitation. The 7* As did not appear to cross 4 carried out, only ‘As, the placenta. The concentration of '*'T was similar in both the maternal and fetal thyroid glands. Fetal bone and spleen concentrated '*° Ba. Bone appeared to be the primary target organ for tungstens in the fetus. Transfer coefficients derived from such experimental data can be used for predicting milk and meat contamination and internal organ burdens. ACKNOWLEDGMENT This work was performed under the auspices of the U.S. Atomic Energy Commission. FATE OF FALLOUT INGESTED BY SWINE AND BEAGLES ROBERT J. CHERTOK and SUZANNE LAKE Lawrence Radiation Laboratory, Bio-Medical Division, University of California, Livermore, California ABSTRACT The increased use of nuclear energy necessitates thorough investigation of the biological availability of radionuclides released to the biosphere. The radionuclides produced by a nuclear event occur in a variety of chemical and physical forms and are associated with particles of various sizes. Therefore distribution or retention data from laboratory experiments with a single, pure radionuclide cannot reasonably be extrapolated to a radionuclide in a complex mixture, as in debris. The Plowshare nuclear cratering experiments offer a unique opportunity to study the biological availability of radionuclides associated with debris from nuclear detonations. We have taken advantage of these events to determine the retention and excretion of the gamma-emitting radionuclides produced by three Plowshare detonations and one other event. Near-surface atmospheric debris was administered orally to the experimental animals (two for each study), which were then confined to metabolic cages for the duration of the experiment (5 to 9 days). For two events the experimental animals were beagles, and for two others they were peccaries (7ayassu tajacu). Daily whole-body analyses were performed with a lithium-drifted germanium [Ge(Li)] detector. Daily collections of urine and feces were analyzed similarly on the same detector. In these studies the percentage of dose absorbed is the sum of the percentage excreted in the urine and the percentage remaining in the whole body at the conclusion of the experiment. Our results indicate that for some radionuclides the percentage absorbed varies not only from literature values but also from event to event. Admittedly these variations may be due to species differences, but they are more likely due to variations in the chemical and/or physical form of the radionuclide in the debris of different events. For the radionuclides analyzed so far, ranges of absorption for the four events are >4Min, 1.0%; 8 Co, 4.3%; /* As, 45.4%; PF y, 1.1%; 7? Mo, 11.5 to 31.0%; }9° Ru, not detectable (ND) to Bose) a SN AtONtG 4.2%. 4 132 7sto 78.5% hes0.9.t0. 24.5%. | -Ba— La, 0.5 to RICE Ae weGeM NID AONOE5 9,1 We 7 Otora A%. OW Re, 182%, and > “Au, 4.1 to 7.7% (the radionuclides for which only one value is given were measured in only one event). The increased use of nuclear energy necessitates investigation of the fate of radionuclides released to the biosphere. The radionuclides produced by atomic 125 126 CHERTOK AND LAKE explosions occur in a variety of chemical and physical forms and are associated with particles of various sizes. Thus the radionuclides in debris usually differ in biological activity from the simple forms encountered in laboratory experiments. In the nuclear cratering excavations carried out as part of the Plowshare Program for the study of peaceful uses of atomic energy, we have a unique Opportunity to study the biological availability of the radionuclides in the atmospheric debris produced by an atomic detonation. We are therefore conducting as many experiments as possible in conjunction with these events to accumulate enough information to develop predictive capability in terms of the absorption and excretion rates of radionuclides produced by different kinds of nuclear events and to furnish input for models that predict the biological impact of radioactive fallout. To date we have studied four events, of which all but the first were Plowshare tests. In these experiments atmospheric debris was collected at 1000 to 4000 ft from the sites of detonation, weighed, and placed in gelatin capsules. These were then orally administered to the experimental animals (two animals per experiment). The animals used in Events! and II were beagles; those in Events III and IV were peccaries (Tayassu tajacu). The peccary, a wild pig native to the southwestern United States, was chosen as an experimental animal because its small size is an advantage in whole-body counting and because its physiology closely resembles that of man. The animals were confined in metabolic cages for the duration of the experiment and were analyzed daily for the gamma-emitting radionuclides by whole-body counting with a solid-state germanium (lithitum-drifted) detector and a 2048-channel pulse-height analyzer. Daily urine and feces samples were collected, preserved with formaldehyde, sealed in tuna cans of approximately 200 cc capacity, and analyzed for the gamma-emitting radionuclides on the same detector. This procedure was followed until the excreta and whole-body activities reached very low levels, between 5 and 9 days. All the radionuclides discussed in this report are listed in Table 1 under each event, along with the percentages retained in the whole body and recovered in the urine and feces. The table also includes the values listed by the International Commission on Radiological Protection (ICRP)’ for the fraction transferred from the gastrointestinal tract to blood. All values are corrected for physical decay. The values for radionuclide absorption used in this presentation represent the sum of the radionuclides excreted in the urine and those remaining in the whole body at the termination of the experiment. Of course, this restricted definition omits consideration of any portions absorbed and excreted by other routes (e.g., excreted in bile) or portions completely unabsorbed and still remaining in the lumen of the gastrointestinal tract. For the first radionuclide listed, °*Mn, the absorption (whole- body + urinary excretion) was 1.0% of the dose. The ICRP value is listed as 10.0%. However, Furchner et al.* demonstrated that >*Mn was poorly absorbed ™ N — FALLOUT INGESTED BY SWINE AND BEAGLES OL'O O88 L?¢ OC 5°96 Ol OO S°S6 eL dN 2: Be 1) OS 'O (Moo 7) OO L1S eed! 61 OT'O GL9 OL GN Ee 8'OF por 0-001 CIN 50 OTT CIN Cet) ele ee) COO O'+6 CN SO bL6 pa | Sc O c'69 OFEE Gr 8°S8 O'€ OO'T €°8S b'6E Vit OSC SCL O'9 VLC 8 OF €0'0 GOL OV CN O OCT GE £0'O b'L8 cic O'€ S68 LO) CO SCE Pe O8'O as C6 OC 109 8 IT pOb 6°78 CN Ey £0'O C 6F VoeV OT OO O'L8 CN cP OO C16 CN O'l (dao) poojq saxaq foulaqy. = fApoq”s sada foutQ, = FApoq:— sada fA 0229" “TD JJOUM JTOUM UlOI} UOIIVIA > 3 : eee: A] 1U9Ag 1] }U9AY [[ }U9AY ‘pod 019p JOU SUPIOL CIN UONPIAIIQGE OU Lt “JUDAD DIBPYUSMO]d BP YOU SPM JT USA, L9 NV 961 OY O61 Year Meet 90 Mig | GN oT sc a OE dott b'$ 8 66 £°O 90 Ley GGl 6 69 6 6C 8°C Tiey OT W774 dN L°66 GN dN ny col CL VEL O'LC OY CIN: 6 Age oven OI 9 UW Ys JApoq = sa904 foulig fApog apryppnu 9TOUM 9TOUM -OIpey «| 1UaAg ASOG IVLOL AO SADVLNADUAd SV GASSHUdXA SAGITIDANOIGVYA SRIAAG AO NOILAYOXA GNV NOILNA LAY AGO A TOHM PoIgey 128 CHERTOK AND LAKE from the gut of mice, rats, monkeys, and dogs and that after oral administration rapid fecal excretion resulted in a whole-body retention of less than 1%. Heinrich and Gabbe® reported that inorganic °°Co administered orally to rats was excreted in 2 days, 90% in the feces and 15% in the urine; that remaining in the body (0.9%) had a biological half-life of 18 days. Our experiment indicates that 4.3% of the dose of °>8Co was absorbed; the ICRP value is 30%. According to Schroeder and Balassa,* pentavalent and trivalent arsenic differ markedly in their metabolism. Pentavalent arsenate, normally nontoxic, is rapidly excreted by the kidneys, whereas toxic trivalent arsenic is excreted mainly by the intestines. It seems possible that the debris of Event [V contained both forms since we found 45.4% of the administered dose to be absorbed; the ICRP value is 3%. For ®®Y, 1.1% of the administered dose was absorbed. The ICRP value is less than 0.01%. These two values are probably statistically the same. Chemically yttrium is closely related to the lanthanides, and, on the basis of its chemical properties and metabolic behavior, °*Y can be grouped with the heavy lanthanides.” According to the results of Durbin et al.,° other heavy lanthanides are poorly absorbed. The absorption of 2? Mo ranged from 11.5 to 31.0%, compared with an ICRP value of 80%. Bell et al.’ reported that in swine 79% of the orally administered dose was excreted in the urine and about 12% in the feces in the first 5 days; the rate of urinary excretion was increased when the °° Mo was diluted with carrier molybdenum. Admittedly species differences may be involved, but it is probable that the chemical and/or physical state of the 2? Mo in the debris is a major factor. The radionuclides in debris are associated with particles of various sizes and may be either surface distributed or volume distributed; both particle size and mode of distribution affect the availability of the nuclide for absorption from the gut. Van Dilla® found '°*Ru to be poorly absorbed by the gut in the rat. Our values ranged from nondetectable levels to 5.5%; the ICRP value is 3%. Moskalev” showed that about 3% of orally administered 12°Sb is absorbed 122 Sb are in agreement; our from the gastrointestinal tract of rats. Our data for range 1s from 4.0 to 4.2%. The ICRP value is 3%. ites. ak absorption in our experiments ranged from 32.7 to 78.5% of the administered dose; the ICRP value is 100%. According to the results of Busnardo and Cassan,'? however, iodine from the body pool is excreted in part in the feces. This may account somewhat for our lower absorption values, but it is '31T was a major factor. probable that the chemical—physical state of the Wright and Bell' ' found that, in swine given a single oral dose of 1? 7Te, over 70% was excreted in the feces and approximately 20% in the urine within 120 hr. Moskalev? reported similar values in rats; 10 to 25% of orally administered '*’Te was absorbed. Our range of absorption for "3? Te was from 0.9 to 24.5% of the dose; the ICRP value is 25%. FALLOUT INGESTED BY SWINE AND BEAGLES 129 The isotopes of lanthanum are not absorbed through the intestinal wall to a : Ayan 4 ; : i ae : significant degree,° but '*° Ba is absorbed.'* The major part of an equilibrium mixture of '*°Ba—'*°La injected intraperitoneally in rats was eliminated in the Ler) 140 d 140 feces; “ the kidney appeared to differentiate between Ba an La and to retain )*°La. In our experiments the animals were fed an equilibrium mixture of 140 et La. Our results indicate the two radionuclides, and the nuclide measured was an absorption range from 0.5 to 4.1% of the dose. The ICRP values are 5% for barium and less than 0.01% for lanthanum. I Gee too..4S poorly absorbed by the gut in It has also been shown that rats.° Our values for '*'Ce indicate a range from nondetectable amounts to 0.5% of the dose. The ICRP value is less than 0.01%. Considering the difficulties in measuring such small quantities of '*'Ce and the counting statistics, the values are probably statistically the same. Kaye!” has reported that a total of approximately 44% of the orally administered dose of '®° Wand !®7W was excreted in the urine of rats. Our data foresee Woand +o ow? eRe range from 7 to 40.8%. The ICRP value is 10%. Other data from this laboratory indicate that 71% of the orally administered dose of '®! W (as K, WOgq) is absorbed by beagles. About 15% of '?®Au administered by mouth or rectum to humans in the form of colloidal or salt solutions was absorbed and excreted rather rapidly.’ % For a Au and. 7 “Au our range of absorption is from 4.1 to 7.7% of the dose. Phe iGRe value is !O%. In summary, the differences between our data obtained with debris and the ICRP values can be attributed to species differences and/or the chemical— physical form of the radionuclides in debris. The importance of the latter consideration 1s demonstrated by our finding that absorption for the same radionuclides sometimes varies from event to event. ACKNOWLEDGMENT This work was performed under the auspices of the U.S. Atomic Energy Commission. REFERENCES 1. International Commission on Radiological Protection, Report of Committee II on Permissible Dose for Internal Radiation (1959), pp. 154—230, Pergamon Press, Inc., New York, 1960. 2). E Eurchner, C: RK. Richmond, and G: A. Drake, Comparative Metabolism of Radionuclides in Mammals. III, Health Phys., 12: 1415—1423 (1966). 3. H. C. Heinrich and E. E. Gabbe, Stoffwechselverhalten des anorganischen Kobalts und des in der vitamin B;2-bzw. Vitamin B; 2 coenzyme-struktur organisch gebundenen Kobalts in saugetier-organismus, 7. Naturforsch., B, 19: 1032—1042 (1964). 4. H. A. Schroeder and J. J. Balassa, Abnormal Trace Metals in Man: Arsenic, J. Chron. Dis., 19: 85—106 (1966). 130 CHERTOK AND LAKE De 10. is Bs 3): 14. DH, Copp; J G. Hamilton, De Ca Jones DEM. Dhomsonand ©. Cramer dhe bitech or Age and Low-Phosphorus Rickets on Calcification and the Deposition of Certain Radioactive Metals in Bone, Transactions of the Conference on Metabolic Interrelations, VOl=3:ppa22O=2 23 lobe .P. W. Durbin, M. H. Williams, M. Gee, R. N. Newman, and J. G. Hamilton, Metabolism of the Lanthanons in the Rat, Proc. Soc. Exp. Biol. Med., 91: 78—85 (1956). .M. C. Bell, B. H. Diggs, R. S. Lowry, and P. L. Wright, Comparison of °° Mo Metabolism in Swine and Cattle as Affected by Stable Molybdenum, J. Nutr., 84: 367—372 (1964). .M.A. Van Dilla, Zinc-65 and Zirconium-95 in Food, Science, 131: 659—660 (1960). .Y. I. Moskalev, Distribution of Antimony-124 and Tellurium-127, in Raspredelenie, Biologicheskoe Deistvie, Uskorenie Vyvedeniya Radioaktivnykh Izotopov, pp. 62—70, Meditsina, Moscow, 1964. (In Russian) B. Busnardo and F. Casson, Aspects of Fecal Iodine Excretion in Man, Acta Isotop., 5: ase (L 965). P. L. Wright and M. C. Bell, Comparative Metabolism of Selenium and Tellurium in Sheep and Swine, Amer. J. Physiol., 211: 6—10 (1966). .V. R. Sastry and L. K. Owens, Fission Products: Retention and Elimination of the Parent—Daughter Radionuclide Pair Barium-140—Lanthanum-140 by Rats, Toxicol. Appl. Pharmacol., 9: 431—444 (1966). S. V. Kaye, Distribution and Retention of Orally Administered Radiotungsten in the Rat, Health Phys., 15: 399—417 (1968). H. Kleinsorge, Absorption of Therapeutic Gold Salts and Gold Sols, Arzneim.-Forsch., 17: 100—102 (1967). RADIONUCLIDE BODY BURDENS AND HAZARDS FROM INGESTION OF FOODSTUFFS CONTAMINATED BY FALLOUT YOOK C. NG* and HOWARD A. TEWESt *Bio-Medical Division and tK Division, Lawrence Radiation Laboratory, University of California, Livermore, California ABSTRACT A method developed for predicting the internal dose that could result when radionuclides are released to the atmosphere and deposited on agricultural land has been used to extend earlier studies of the problems associated with food contamination following a nuclear attack. The study considers activation products as well as fission products and attempts to take into account recent data on retention and rate of loss by weathering of both small and large particles on plants, on uptake of nuclides into dietary constituents, and on biological availability of nuclides in nuclear debris. In this study potential levels of food contamination and internal dose commitment are estimated both for the immediate postattack period and for the year closely following the attack when the initial deposition rates of stratospheric debris would be highest. The results are discussed in the light of the modifying factors that would influence them. A method for predicting the internal dose that could result when radionuclides are released to the atmosphere and deposited on agricultural land’ was developed to assess the potential burden and dosage to man which could result from the release of nuclides to the biosphere from any source. By means of this analysis, we can identify the nuclides that could contribute most to the internal dose and determine the contribution of each nuclide to the total dose. This paper considers the application of this method to examine possible postattack levels of contamination of terrestrial foods and the dosages that could result from their consumption and extends earlier studies of the problems associated with food contamination immediately following a nuclear attack.” * The work considers activation products as well as fission products and takes into account more-recent data on retention of small and large particles on plants and their subsequent rate of loss by weathering, on uptake of nuclides into dietary 131 {32 NG AND TEWES constituents, and on biological availability of nuclides in nuclear debris. It also attempts to assess the levels of food contamination that could result from the initial deposition rates of the nuclear debris injected into the stratosphere. We make certain simplifying assumptions in order to apply our models to estimate the potential levels of contamination of foods and the internal dose commitment to man. We then examine the results and note how various modifying factors would influence them. METHOD FOR ESTIMATION OF DOSAGE Our predictive model combines source, transport, and interaction terms to estimate possible levels of contamination of foodstuffs and possible internal dosages that could result from their consumption. ‘‘Source’”’ refers to the radionuclides produced and their quantities. The source term consists of the activity of each radionuclide produced in the detonation. “‘Transport”’ refers to the transport of nuclides from the site of detonation and their subsequent distribution to the biosphere. The combination of transport and source terms vields either the deposition or the rate of deposition from the atmosphere. “Interaction” refers to the interaction of the nuclides with the biosphere, 1.e., their entry into food chains and subsequently into the tissues of man. The interaction terms directly relate deposition or deposition rates and air concentrations to levels of contamination in foods and to internal dosages. The general approach is described in detail elsewhere,’’> and the input parameters required for the analysis are available in a continuously updated handbook.*® The present analysis is confined to contamination of terrestrial foods as a result of foliar contamination by fallout. Early deposition of local and tropospheric fallout would usually result in a far greater level of contamination of vegetation than that from subsequent root uptake of the fallout deposited on soil. Similarly, the early rates of deposition of stratospheric debris can be expected to cause higher levels of plant contamination than would subsequent root uptake from the cumulative deposition in soil. This analysis focuses on the forage—cow—milk and plant—herbivore—meat pathways. Both milk and meat are important constituents of the human diet, and much is known regarding their input parameters. Since relatively large contaminated areas can be grazed daily by cows and other herbivores, the milk and meat pathways are important for many nuclides. For milk the period between the deposition of fallout and the ingestion of the contaminated food can be especially short. *No attempt is made in this paper to list the input parameters used in the calculations. Input parameters and a comprehensive bibliography of the sources from which they were obtained appear in a continuously updated handbook.°® Many of the parameters used are updated values that will appear in the forthcoming revision of the handbook. This issue will be available on request. RADIONUCLIDE BODY BURDENS 133 This analysis considers both the immediate postattack impact on food contamination, which is attributable to local and tropospheric fallout, and the longer-term impact, which is attributable to the continuous deposition of nuclides from the stratosphere. Case studies of hypothetical nuclear attacks on the United States provide a useful frame of reference for the analysis of problems relating to civil defense. For example, two cases of hypothetical attacks, the CIVLOG and the UNCLEX, were used as starting points in planning for postattack recovery.’ Other cases of hypothetical attacks were used by Brown and his associates at the Stanford 3 The general magnitude and structure of these attacks in large measure compare with those of CIVLOG and UNCLEX. For the immediate purpose of predicting the dosage that could result from Research Institute in the assessment of “‘national entity vulnerability. the ingestion of contaminated foods, we do not need to make fine distinctions. Thus we have simply adopted some of the features of these case studies. We arbitrarily assumed an attack of about 1000 surface-detonated weapons with a total yield of 4000 Mt. These weapons are assumed to be half-fission half-fusion devices with individual yields between 1 and 10 Mt. It will be readily apparent how the results would scale with other combinations of total and individual yields. RADIONUCLIDE SOURCE TERMS The radionuclides produced by the detonation of thermonuclear weapons include fission products, activities induced in device and environmental materials, and tritium. In this section source terms are derived for the 1-Mt-vyield explosive, which is taken as the unit to be scaled linearly to higher vields. Fission Products Fission products derived from weapons test have been studied extensively i “tae : 5 8 over the past 20 years. We used the fission yields listed by Weaver et al. Neutron-Activation Products of Device and Environmental Materials From the standpoint of potential external dose from the fallout gamma field, the fission products resulting from the hypothetical half-fission half-fusion 1-Mt explosive represent the most important contribution, although nuclides resulting from neutron interactions with unburned fissionable material can represent up to 40% of the total activity of the weapon debris.” However, because of special concentrating mechanisms, “‘minor’’ neutron-activation products could still contribute appreciably to the internal dose following their entry into certain food chains. Therefore the total production is estimated for a number of these activation products that were not considered heretofore in the estimation of fallout fields from weapon detonations. 134 NG AND TEWES Activation of Unreacted Fissionable Materials Predominant isotopes in the category of unreacted fissionable materials are (Uren Urea aNpwand Np (Ref. 9). However, neither the 7°" U nor the *4°Np source terms are estimated since their relatively short half-lives (23.5 min and 60 min, respectively) preclude their contributing to internal doses delivered via food chains. Kimura,!° as quoted by Miller,!! indicates that for the Bravo detonation, there were 0.3 neutron captures per fission in 7*°U; thus for 500 kt of fission a total of 2.2 X 10° atoms of the mass-239 chain (77? U> ???Np> 7??Pu) would be produced. This estimate can be compared with that of Langham and Anderson’? that 3600 Ci of ?7°?Pu are produced per megaton of fission (the equivalent of about one neutron capture per fission in 7°*%U). This more conservative estimate is used in the present assessment. Kimura!” determined that approximately 0.15 atom of **7U per fission was produced by the Bravo event of 1952. Using this source term, we find that 500 kt of fission results in the formation of about 1.1 X 10*° atoms of 7°7U. Activation of Device Materials (Including Canister) A considerable body of work has been reported on atmospheric concentra- tions and burdens of radioactive species produced during the nuclear tests of 1961 and 1962. Summaries by Feely et al.'* and by Thomas et al.'* indicate that the stratospheric residence half-time of all weapon-produced radionuclides is approximately 10 months; hence total atmospheric burdens of the predomi- nant radioactive species measured in 1963 or later must characterize uniquely the 1961-41962) injections: As confirmation of this hypothesis, Feely et al.'* determined that the total atmospheric burden of ?°Sr (corrected to July 1, 1962) was 10 MCi; since the total fission yield of the 1961—1962 atmospheric detonations has been estimated as 101 Mt'* and the ?°Sr production from a “‘typical’’ device has #12 Je can see that the been reported as 0.1 MCi per megaton of fission, measured burden represents essentially the total calculated inventory of ?°Sr. At the same time, Feely et al.'* found the total atmospheric burden of >* Mn to be about 57 MCi (corrected to July 1, 1962); this represents a production source term of about 0.0056 atom per fission. In an independent study, Thomas et al.'* determined that the activity ratio of °*Mn to '*7Cs, as measured on filters mounted on high-volume near-surface air samplers, was about 3.9. If we assume that 0.14 MCi of '37Cs is produced per megaton of fission, we find that the production source term for >* Mn is 0.0036 atom per fission. When the two determinations are averaged, the production of **Mn appears to be of the order of 0.0046 atom per fission. Since *As quoted by Eisenbud.' © RADIONUCLIDE BODY BURDENS 135 the total vield of the 1961—1962 detonations'*> was 337 Mt, an average source term of 1.4 X 10° Ci of >*Mn per megaton of total vield can be inferred. Table 1 summarizes activity ratios for a number of radionuclides measured in air and gives the references from which the ratios were abstracted. This table also includes some heretofore unpublished isotope ratios measured in debris from the 17 Schooner event. Table 1 AGCMIVITY RATIOS (RELATIVE TO >4 Min) FOR A NUMBER OF NEUTRON ACTIVATION PRODUCTS Activity ratio * Nuclide (Relative to >4 Min) Source Ref. 22Na tax 10) 1961-1962 test series 14 °° Mn 6700 Schooner 63 >> Re 2.0 1961—1962 test series 64 a Fe 0.091 Schooner 63 . "Co 0.65 Schooner 63 0G 321 Schooner 63 eneo DIO 1961—1962 test series 14 oan 2 4x10 1961-1962 test series 14 lOmag DO AO; 1961-1962 test series 14 Eo Gs Ox 10). 1961-1962 test series 14 * Activity ratios obtained from debris resulting from the 1961—1962 test series were calculated for July 1, 1962; activity ratios from the Schooner experiment were corrected to the time of detonation. Activation of Environmental Materials One of the potentially significant radionuclides created by nuclear detona- tions conducted in the atmosphere is '*C. Machta'® estimates that the total production over all atmospheric tests to date is 9.17 X 10°° atoms; since the cumulative yield of such tests’*® is about 511 Mt, the average production is about 20,000 Ci/Mt. Since most of the «nuclear tests of the 1961—1962 -series were airbursts, smaller quantities of soil activation products were produced and injected into the atmosphere than would be expected from surface bursts of the same total megatonnage. Certain radionuclides of environmental origin can be expected to be potentially important contributors to the internal radiation dose following entry into food chains and consumption by man. For example, **P, **Na, =°Rb, ~°Ca, °*Rb, *?*Cs, *7Ca, and **Na are neutron-activation products of soil and rock that are potentially important via milk.' Except for **Na and '54Cs, measurements of neutron-activation products of soil and rock produced by nuclear device testing have not been reported in the open literature. The 136 NG AND TEWES production of these nuclides was therefore estimated using a calculational approach previously reported in the literature.’ ?**° The neutron-activation calculations assume that 14-MeV neutrons are incident on granite. By assuming 14-MeV neutrons, we maximize the production of **Rb, *’Ca, and *?.Na. The neutron yield per megaton of fusion is assumed 2 lt we to be 1.45 X 1077 neutrons, the oft-cited figure assumed by Leipunsky. accept the estimate of '*C production reported in this section and assume that essentially all the neutrons released to the environment are captured by atmospheric nitrogen with the resultant formation of @ some 2 Xa l0e- neutrons are released to the environment per megaton of fusion. This assumption is not unreasonable since most of the nuclear tests of the 1961—1962 series were airbursts and since the bulk of the neutron-absorption cross section of the atmosphere 1s attributable to nitrogen. Furthermore, the calculations of Lessler and Guy?” indicate that for airbursts at a height of 1000 m only about 1% of the neutrons released to the environment are captured by soil at ground level. The release of 2 X 10°° neutrons per megaton combined with the total production of 1.45 X 10°” neutrons per megaton of fusion suggests that some 13 to 14% of the neutrons produced are released to the environment. This compares with the 20% escape fraction previously assumed by Libby.*? Our estimates therefore assume that 400 moles of neutrons per megaton of fusion are released to the environment; this is equivalent to an escape fraction of about one-sixth. One-half of the neutrons escaping the device (i.e., 200 moles per megaton of fusion) are assumed to be captured in rock or soil following a surface detonation. Estimates of the production of 7*Na and '°*Cs based on the activity ratios of Table 1 suggest that, in the 1961—1962 test series, 3 to 4 moles of neutrons were released to soil per megaton. This observation is not inconsistent with our assumption if we remember that the 1961—1962 detonations were largely airbursts. Furthermore, special neutron-shielding materials would have to be employed to reduce the neutrons released to the environment to levels as low as 3 or 4 moles per megaton of fusion. Tritium Dose estimates from tritium are considered elsewhere in this volume,”* but its source term is included here for the sake of completeness. Leipunsky*! indicated that the amount of residual tritium per megaton of thermonuclear vield was about 0.7 kg. Miskel*> gave a range of from 0.7 to 5 kg/Mt, and, more recently, Tewes*° reported that the residual tritium was on the order of 2 kg per megaton of thermonuclear yield. We will use the Tewes estimate. Summary of Radionuclide Source Terms The data in the preceding section are summarized in Tables 2 and 3. Table 2 lists the source terms for fission products, and Table 3 lists the source terms for RADIONUCLIDE BODY BURDENS 137 Table 2 FISSION-PRODUCT SOURCE TERMS FOR IM FISSION EXPLOSIVE Nuclide Curies produced * Nuclide Curies produced* 8° Sr sc tOe pon Te 20x10" OSE 8.8 x 107 ta 4.4 x 10° 99 Mo 62 x 10° ae 1.55610" tO Ru 325 x 10" nee PALO? Me Ri DA 10° Dak es 20x10" = Sn Door Ue TGs 1.5 x 10° 42 Sh 32x 10" Pes 115010" here Me 6.0 x 10° Lt Ge 2.6 %10° *Values are corrected to detonation time. tritium and activation products. Included in Table 3 are not only the specific production terms in atoms and curies per megaton but also the “equivalent fission yields” of the various species. From the standpoint of contribution to the gamma fallout field, neutron-activation products represent a relatively small fraction when compared with fission products. Figure 1 shows the number of curies of radioactivity resulting from the detonation of the hypothetical 1-Mt explosive and the decay of this radioactivity with time. The radionuclides produced by neutron activation of the unfissioned uranium represent a significant fraction of the total radioactivity during the first few weeks after detonation. We should emphasize at this point that the radioactivity source term developed here does not necessarily represent that which would be produced by any existing nuclear weapon; however, the various radionuclides considered here would certainly be produced in some quantity by the surface detonation of any weapon. Details of device construction and variations in soil composition obviously could drastically affect the amounts that would be formed of almost every species. This work, however, is expected to give at least some guidance in the estimation of possible internal radiation exposures from nuclides other than fission products and possibly to serve to identify isotopes that could be especially troublesome. PREDICTION OF THE INTERNAL DOSAGE FROM EARLY DEPOSITION We define a standard fallout field as one that would deliver an exposure rate of 100 R/hr at 1 hr postdetonation. The total dose resulting from exposure to such a field starting at H + 8 hr would be about 250R. (For a more detailed discussion of this subject, see Ref. 9, Chap. IX.) The total dose resulting from exposure beginning at H+4hr would be about 300 R. The dosages would 138 NG AND TEWES Table 3 TRITIUM AND ACTIVATION-PRODUCT SOURCE TERM FORA-Mi_NUGLEARSEXPLOSIVIES Equivalent fission yield,t kt Total produced Dose rate Dose (H + 1 Nuclide Source = Atoms Curies (H + 1 hr) hr to a5 1 Xx TOs” 1hODeO” LG 2 16S xclOns Dix or 9 9) - AN 2 21007 ANS 10> 2 Oe 0.25 eA Na 2 3 cOne exelOr 9 60 32 22 5 ea) 2 2 ail Oa 4x 10° Ook 2 3° 102° 1 20° 8x10" 0.4 Se DD. 4 Ca 2 3 x 10 4x10 54 23 5 4 Mn 3 2x10 1.4.x 10 3x10 1.0 56Mn 3 ACOs 9 x 108 4 Sine 3 Teodee aR Oy 3x10> RE 3 2 alOre 1.3 x 107 5x10" Deore hers 3 fete tOse 9x 10+ 2 lOn 8x102 : : : ere 3 Mactan 4x 10° elector 0.7 or 3 Bc 10c4 3x 105 RSA 4x102 OT 3 Zeal Se Oe 4x10° ODCLO C2 RE 2 7 xeTOre 1.1 x 10° 7x10. fete TOK ee Rb 2 7 XAMOCE 425 108 fil x10" AX MOIS OR 2 2 Ors x10" 6x10" eeeoe PNG 3 Scie 3x 107 2a 5x 10° 134... x9) x RB} =) Cs 2 1.8 x 10 5x10 2x10 0.16 237 25 eh 4 else eate 4 x 10° 0.14 9 >) ?3°Np 4 7 AOE. 6 x 10° 3 70 *Values are calculated exclusive of fission products and assuming 500 kt of fission and 500 kt of fusion yield. tThe equivalent fission yield®> of a radionuclide, expressed as a dose rate at H + 1 hr, is defined as “that amount of fission required to produce fission products which, at H+ 1hour, will emit gamma-ray energy at the same rate as does the amount of the particular radionuclide under consideration.’ Similarly, the equivalent fission yield of a radionuclide, expressed as total dose delivered after H +1 hr, is defined as “that amount of fission required to produce fission products which will emit (after H + 1 hour) the same total amount of gamma-ray energy as will the amount of the particular radionuclide under consideration.” +The numbers indicate the following sources: 1, residue from thermonuclear reactions; 2, from neutron activation of environmental material; 3, from neutron activation of explosive components; and, 4, from neutron activation of unfissioned uranium. RADIONUCLIDE BODY BURDENS 139 101! a Fission products 19'9 10° RADIOACTIVITY, Ci 108 10’ 1 10 100 1000 POSTDETONATION TIME, hr Fig. 1 Radioactivity from 1-Mt explosive with a fission-to-fusion ratio of 1.0. The activity values are derived from Table 3. actually be about 0.7 as great, because of terrain shielding, and would be further reduced if protection were available and were utilized. Thus a unit-time dose rate not exceeding 100 R/hr would be compatible with effective survival of a substantial segment of the population.2’ Roughly 50% or more of the land area of the nation would be outside the 100 R/hr contour from the hypothetical attack."” Fractional Deposition of Early Fallout If we accept a theoretical unit-time dose rate of 3700 R/hr in association with the uniform deposition of 1 kt of fission products per square mile of surface, a unit-time dose rate of 100 R/hr from unfractionated fission products is equivalent to a deposition of 1.05 X 10° kt of fission products per square meter of surface. (See Ref. 9, Sec. 9.183—9.184.) We have assumed that the 140 NG AND TEWES contributions of neutron-activation products to the gamma field are small and, conservatively, that a unit-time dose rate of 100 R/hr is equivalent to a deposition of fission products totaling 10° kt/m*. By these assumptions, an equivalent yield of neutron-activation products would be produced by the 10° kt of fusion and would also be deposited per square meter. For a single 1-Mt detonation, a deposition of 10° kt/m? corresponds to a fractional deposition of Ore per square meter and, for a 10-Mt detonation, to a fractional deposition of 10'* per square meter. Fallout levels observed subsequent to nuclear-device testing at the Nevada Test Site indicate that fractional depositions in the range from 10'' to 10‘? per square meter could be expected within 20 hr after detonation.’ ® Both neutron-activation products and fission products are assumed to be deposited as unfractionated activities. The implications of assuming unfractioned deposition are considered later. Initial Retention on Vegetation and Rate of Loss by Weathering Physical Character of Deposition The cloud from a single 1-Mt surface burst in the latitude band 30 to 90° N can be expected to stabilize between altitudes of 26,000 and 53,000 ft; the cloud from a single 10-Mt burst can be expected to stabilize*” between 50,000 and 100,000 ft. Calculations based on Stoke’s law can be made to estimate the minimum size of particles that can be deposited from these elevations under the influence of @ravity alone: (See Ref. 9,)Sec59: 1186-92187 9) These* estimates suggest that, if the 100 R/hr contour represented fallout deposited 4 to 12 hr after detonation, particles of diameter >200 ut would deposit inside the contour and particles of diameter <50 u would deposit outside. A dominant particle- diameter range of 50 to 200 uw could be expected in the fallout deposited along the 100 R/hr contour from a single surface burst. Dry deposition of nonfalling particles would not be significant at these early times.°° Taking into account the total of all surface bursts contributing to the 100 R/hr fallout field, we anticipate (1) earlier times of arrival than previously assumed, which means deposition of particles larger than 200yu, and (2) deposition of particles less than 50, originating from the more distant detonations. Small particles could also be deposited by rain. Predictions for the concentrations of nuclides in foods subsequent to the deposition of fallout should take into account the particle-size distribution that would be encoun- tered. Accordingly two sets of predictions have been made. One set is based on data obtained from large particles, 1.e., particles 50 to 200 mu and greater in diameter; the other is based on data obtained from small particles (<30 uw) and worldwide fallout. We anticipate that, in general, the estimates of higher dose rates would more properly be based on the estimates of food contamination from large particles, whereas the estimates of lower dose rates would be based on those from small particles. RADIONUCLIDE BODY BURDENS 141 Bebavior of Small Particles The initial retention of small particles on vegetation 1s based on Chamber- lain’s analysis?! of data from short-term experimental releases of vapors and aerosols. The fraction of the deposited activity initially retained on vegetation, p, is approximated by the relation [2p s="exip "LW (i) where pu is the absorption coefficient in square meters per kilogram and w_ is the herbage density in kilograms per square meter of dry matter. The initial retention of small particles (< 30 uw in diameter) on grass was characterized by u values of 2.3 to 3.3 m*/kg. On the basis of Chamberlain’s analysis, the initial retention factor for herbage densities between 0.2 and 0.4 kg/m? would vary between 30 and 70%. In our treatment the initial retention factor for small particles on forage is assumed to be two-thirds (67%). In Thompson’s review of the half-residence time and effective half-life of fallout on pasture plants, the half-residence time was noted to be independent of isotope and to vary in most cases between 9 and 14 days.°? Recently Chamberlain?! examined the data obtained from field experiments on the loss of small-particle activity from foliage. The field-loss coefficient was found to be of the order of 0.05 per day during the growing season, but lower values were observed in winter. Our estimates assume that the half-residence time of small particles on forage is 14 days; this is equivalent to a rate of loss by weathering of 0.05 per day. Bebavior of Large Particles Table 4 is a summary of data obtained from field experiments. by 4.35 3 Witherspoon and Taylor®* and Johnson and Lovaas® on the initial retention of large-particle fallout simulant on forage plants. The table also includes retention data of volcanic particles as reported by Miller.°° The initial retention is expressed where possible both as the percentage of fallout initially intercepted and retained by foliage and as the plant contamination factor, a. The plant contamination factor was defined by Miller as _ activity per unit mass dry matter on foliage activity per unit area of ground A main feature of the design of the experiments of Table 4 is the early sampling, which permitted the measurement of plant retention before significant field losses could occur. We excluded from Table 4 the initial retentions obtained under ‘“‘damp”’ conditions (relative humidity >90%). Plant contamination factors of volcanic particles as reported by Miller were enhanced by about a factor of 2 under damp 142 NG AND TEWES Table 4 INITIAL RETENTION OF LARGE PARTICLES ON FORAGE PLANTS Initial retention Average Particle Average i or range, Wind, Rain, Species diameter, u (range), % m* /kg mph in. Ref. Lespedeza 44 to 88 Td Seal OREOR/.) e2258t0.3 35 88 to 175 19 0.93 OnLOM/ eZ ston 35 Alfalfa 88 to 175 6.5 0.45 6 35 17 0.8 Oto 10 35 23) (4O.t0;3'5) ibs None Trace 34, 35 Tea WDeto 12 2) 0.28 0 to 20 34, 35 TAS CONS o.OR sl5 0.65 4 Dew 3 0.17 6 6 OF25 2 to 10 3 d4(2 Latoul3=1;) 0.24 None 34439 Bromegrass 88:to- 175 4.5 0.3 6 aj) LA (Bale tor lol) .OF74 None Lightrain 34, 35 L7.575t0.3, 50) 30:4 0.04 7 35 5.5 (4.6 to 6.3) OFS race 34 3D Sundan grass 88to175 8:5 0.4 2to4 5 17 tO BONS a /eD O:25 2to4 “Grass” is 6.7 0 to 2 36 Barley grasst = 2A COZ Om pal tO.S 36 Oat grasst zi 2.4 to 7.3 1 to 8 36 Rye grasst i 22 tO. LOVEs Aton? 36 Wheat grasst 5 2:1 to 10.4 - 1:to 9 36 *Estimated range of particle size is 10 to 250 uw, and mass median diameter is ~50 to 80 x. +With reference to cereal grains, ‘‘grass’’ means the aerial parts prior to the development of grain heads. conditions of exposure. In this connection Johnson and Lovaas noted that the retention on bromegrass of particles 88 to 350 in diameter approached or reached 100% in the presence of heavy dew. We also excluded measurements obtained when exposure was accompanied by strong winds (>20 mph). Typical amounts of rain were encountered during some of the experiments represented in Table 4. The data of Witherspoon and Taylor®?* and Johnson and Lovaas suggest that 0.5 to 0,6 m? /kg might be a typical value for the plant contamination factor for 88- to 350-u particles on forage plants. Under these 34,35 RADIONUCLIDE BODY BURDENS 143 conditions a cow consuming 10 to 12 kg of dry matter per day would effectively graze about 5 to 7 m* of contaminated land per day. This is about one-fifth of the 30 m?/day assumed to be utilized by the cow when small particles are deposited [‘‘utilized area factor’? (UAF), 45 m? /day; plant retention factor, 0.67]. Miller’s data®® suggest that the plant contamination factor for local fallout on forage plants would be an order of magnitude greater, 1.e., about 5 to 6m*/kg. The land area effectively utilized daily by a cow consuming 10 to 12 kg/day of dry matter would then be about 60 m?/day, which is comparable within a factor of 2 to the area assumed to be utilized by the cow when small particles are deposited. The volcanic ash studied by Miller apparently was of a somewhat smaller range of particle sizes, having a maximum diameter of about 240 uw and a mass median diameter we estimate to be about 50 to 80 y, as far as can be determined. Interestingly, a plant contamination factor of 3.7 m? /kg was obtained by Witherspoon and Taylor for 44- to 88-u particles on lespedeza. The half-residence time of large particles on forage plants was also studied in these experiments. In the experiments of Witherspoon and Taylor,?? the retention curve of simulated fallout particles on crop plants was characterized by a number of weathering half-lives. We estimated the integrated retention on lespedeza from these data and found it to be about 5.4 days for 44- to 88-u particles and 6.7 days for 88- to 175-u particles. If we assume a simple exponential retention function, these integrated retentions correspond to a half-residence time of 3.7 to 4.7 days. In the experiments of Johnson and °° Jess rainfall occurred and somewhat longer half-times were noted. Lovaas, Half-times on alfalfa, bromegrass, and sudan grass were about a week or longer. Miller’s data®® on volcanic particles suggest a much more rapid rate of loss by weathering, with half-times being measured in hours. For example, on the basis of the median wind-weathering factor obtained for broadleaf grasses, the field-loss coefficient would be 0.2 per hour when the average wind speed is 2 mph; this is equivalent to a half-residence time of 3.5 hr (about 0.15 day), which represents about a hundredfold reduction of the 14-day half-residence time assumed for small particles on forage. On the other hand, a small fraction of the particles deposited on vegetation, of the order of 2 to 10%, was found to be “‘nonremovable”’ and was quantitatively retained. The effect of large-particle deposition on the estimates of food contamina- tion and dosage is evaluated later by assuming a plant contamination factor of 33 0.5 m*/kg, in accord with the observations of Witherspoon and Taylor~~ and See IN plant contamination factor of this magnitude is Johnson and Lovaas. equivalent to a retention of 12 to 13%, which is about one-fifth that assumed for small-particle deposition. The estimates for large-particle deposition will be made assuming a half-residence time on forage of 4 days. This is consistent with our integrated retention calculated from the observations of Witherspoon and Taylor and does not depart significantly from the somewhat longer half-times observed by Johnson and Lovaas. 144 NG AND TEWES Forage—Cow—Milk Pathway (Small Particles) In the forage-cow—milk model,’ the fallout deposited on pasture is continuously ingested by the grazing cow. The UAF is assumed to be 45 m*/day; i.e., the cow is assumed to utilize 45 m* of pasture daily. This value is based on Koranda’s review of agricultural factors affecting the intake of dairy cows, in which a median UAF value of 45 m*/day was found for dairy cows in the United States.*’ nuclide (Ig) in microcuries per day is then given by The initial daily rate of ingestion by the cow of a given In =R X UAF X Fo (2) where R is the initial retention factor and Fo is the initial deposition in microcuries per square meter. In presenting the estimates of food contamination and dosage, we report the results for small particles first since they are higher. Please recall that R 1s assumed to be 0.67 for small particles. Concentration of Nuclides in Milk Tables 5 and 6 list the estimated peak concentrations in milk from the deposition of small particles; Table 5 shows the results for fission products and Table 6 the results for activation products. In these tables fyq is the transfer coefficient to milk, the fraction of the element ingested daily by the cow which is secreted per liter of milk. These transfer coefficients include corrections for the observed biological availability, where it is known, of the nuclide in fallout.® Some of the correction factors were obtained by Potter ©. in experiments of the kind reported in this volume. The peak concentrations in milk, Cyy, are given both as the fraction of the initial daily intake, Ig, per liter and in microcuries per liter. The concentrations were calculated on the basis of the rate of disappearance of nuclides in milk following a single administration to the lactating cow. If the turnover rate of a nuclide in milk was not available from the literature, an instantaneous steady state was assumed with respect to the secretion of activity in milk following deposition on forage. In these cases, Cyy expressed as a fraction of Io is numerically the same as fyy. Note that input parameters are well known for the nuclides that contribute most to the dosage. Estimated Dosage via Milk Tables 7 and 8 present the dosage estimates via milk from the deposition of small particles. Table 7 presents the estimates for fission products and Table 8 those for activation products. The first column of each table lists the total activity ingested assuming milk consumption at the rate of 1 liter/day. The second and third columns of each table list the dose commitment to the whole body and bone of an adult. As previously recognized, the nuclides that Table 5 RADIONUCLIDE BODY BURDENS ESTIMATED PEAK CONCENTRATION IN MILK FROM DEPOSITION OF SMALL PARTICLES (FISSION PRODUCTS ONLY)* Cyt Fraction of Radionuclide fy /liter/dayt I, per liter uCi/liter 8 Sr 9.0 (—4) 674) 3.1500) Cost 9.0 (—4) 7244} 19:2) 2? Mo 75 (=A) 35: (=4) 6.5 (1) De 1.0 (—6) 1.0 (—6) (O12) ee Ru 1.0 (—6) 1.0 (—6) 6.3 (—4) FS 10:3) [-0\(=3) 8.0 (0) re Sb 5.0 (—6) 5.0 (—6) 4.9 (—4) oa Une 1.25 (—4) Ss 5) 1.5 (2) Pee Te 125-4) D5) 1.4 (0) UP ae 1.25 (—4) A. 3 (25) 5.6 (0) ey 5.0 (—3) 25(—3) 1.46, (2) ae 5.0 (—3) 1.0:(=3) 4.6 (2) PSs AS (3) 3k2 3) 1.9 (1) Pes 753) 4.8 (—3) 21a) De Ba 15 (4) WBN =5) 5.1 (0) ae or 220 (5) DO —5) DAD) 145 *Deposition is assumed to be 10° kt of fission products per square meter. tThe numerical value in parentheses signifies the exponential power of 10; thus 9.0 (—4) signifies 9.0 x 10%. contribute most to the dose commitment via milk are the fission products eds 7.0 Gre 2? Mo. be Tee eh ee PSO Ce ATs. atid 1405 and the activation products of soil and rock, tA Nate ANA Ca. Cay UR, -oRib.amd 'S4Cs. All the parameters required for the forage—cow—milk model are adequately known for all these nuclides. Activation products of device materials do not contribute appreciably to the total dose commitments. The isotopes whose input parameters via milk are not well known include '**Sn (Table 7) and pee iAon 2H and 2 Nip (Table 8). Since conservative estimates were assumed, the dosages may be overconservative. These isotopes, however, do not make substantial contributions to the total dosage. The estimates of dosage to the whole body and bone via milk (Tables 7 and 8) should be compared with the corresponding estimates for the thyroid. For the adult thyroid the dosage estimate corresponding to the 4.6-rad whole-body dosage from '*'1 is 2500 rads; the corresponding estimate from NST is: 5 00"rads (assuming deposition occurs at 8 hr postdetonation). 146 NG AND TEWES Table 6 ESTIMATED PEAK CONCENTRATION IN MILK FROM DEPOSITION OF SMALL PARTICLES (ACTIVATION PRODUCTS ONLY)* Cyt Fraction of Radionuclide fyq/liter/day t I, per liter uCi/liter 22Na eS —=2) 4.5 (—3) 142) 2Na 52D) 1.9 (—4) 11) 22p 202) 3 (2) 3.3 (0) i BO) 28(—4) 2.0 (1) Ca ib An(=2) ikcte(=2) DGC Tea (AND) TCD) 16344) >4 Min 1.0 (5) 1kO=5) Ae (= A) 2 Fe 4.0 (—5) 4.0 (—5) 3.6 (3) >? Fe 4.0 (—5) 4.0 (—5) 1.6 (—4) 276 4.0 (—4) 4.0 (—4) et (2) 2 Go 4.0 (—4) 4.0 (—4) 49) 2) ro 4.0 (—4) 4.0 (—4) 3.6 (—5) OSTA 10x 2) 102) 9.0 (—3) 82 Br (>) (ee?) Tea) Rb 152) 8.4 (—3) 3 (a0) S°Rb 1.5 (—2) 53) 1.0 (0) ORNs 5:08) 5.0 (—3) 4.5 (4) PSeGs 75123) a7, (E23) 1.4 (—2) eo 7 1.5 (—4) 1e5n(a) 1.8 (1) 22° Np 5.0 (—5) 5.0 (—5) 9.0 (1) *Deposition is assumed to be 10° kt of neutron-activation products from fusion per square meter. tThe numerical value in parentheses signifies the exponential power of 10; thus 1.5 (—2) signifies 1.5 x Ol Plant—Herbivore—Meat Pathway Since most of our cattle and sheep remain on pasture throughout the year, meat potentially could contribute relatively large quantities of nuclides to the diet following their deposition on vegetation. The plant—herbivore—meat model represents a preliminary attempt to evaluate the importance of meat contamina- tion following the release of nuclides to the biosphere. In the model the fallout deposited on pasture is continuously ingested by grazing livestock and deposits in their muscle. The concentration of nuclides in the muscle of the 500-kg standard herbivore having a muscle mass of 200 kg was estimated from the daily rate of ingestion of contaminated vegetation and the turnover rate in muscle. RADIONUCLIDE BODY BURDENS 147 Table 7 ESTIMATED DOSAGE VIA MILK TO WHOLE BODY AND BONE FROM FISSION PRODUCTS DEPOSITED AS SMALL PARTICLES ett’ Dose commitment, * = rads Total activity ingested,*t Ske Radionuclide Ci Whole body Bone 89 Cy 6isscl) 0.56 4.4 Bust Aoi) 0.70 5.7 °°? Mo 3.5 (2) 0.45 0.63 PRY Baan) 7 (4) 1 (-3) HO Rt 12 25 (4) 3) aS 4.8 (1) 0.028 0.13 Cy 9:73) 4 (6) 1 (5) a es 3.0(=1) 9 (—4) (t= 3) Ire 4.8 (0) 2 (3) Da (2) US 2 atv At CA) 0.054 0.06 oe 1343) 4.6 2.4 iad 1253) 0.93 0.68 Lec es 3512) 5.9 5.9 Me Les 6.7 (0) 0.45 0.45 SNS 8.1 (1) 0.13 0.95 Pt Ce Aa (1) 1i(=5) Ai(==5) Total dose commitment 14 21 *The numerical value in parentheses signifies the exponential power of 10; thus 6.5 (1) signifies 6.5 x 10°. tValues are based on a daily intake of 1 liter of milk having radionuclide concentrations as listed in Table 5. +Dose commitment is calculated as the 30-year dose to an adult (standard man). For these estimates conservative but reasonable values were assumed for the fractional uptake to muscle by ingestion; these uptake values were estimated on the basis of experimental data from animals. The studies of Potter?” and Chertok,*! as reported in this volume, were useful for this purpose. The biological half-life in muscle was then estimated from these fractional uptakes and from the stable-element concentrations in meat and forage plants as reported in the literature.° Minor corrections were applied to the fractional uptakes and turnover rates on the basis of radionuclide burdens reported for pull sai, animal muscle and vegetation.*?°** Details of this procedure will be reported = cy 3 x subsequently. The fractional uptake and turnover rates of ?°Sr, '*!1, and '*7Cs are comparable with previously assumed values.” * 148 NG AND TEWES Table 8 ESTIMATED DOSAGE VIA MILK TO WHOLE BODY AND BONE FROM ACTIVATION PRODUCTS DEPOSITED AS SMALL PARTICLES parents Dose commitment,* = rads Total activity ingested,*t Radionuclide uCi Whole body Bone 2?2Na 8.1 (—1) 0.015 0.015 2 Na 132) 0.22 0.022 Sop 4.6 (1) 0.34 1.95 Hak 03°04) 0.011 0.011 SGA 5.9 (0) 0.053 0.52 Buren 1.3 (0) 0.0042 0.041 >4Min 8A (=3) 15) i) >>'Fe TeieG2) Die=5) 355) ae DeA3) 9 (-6) i= 5) *T@o Dat (=a) 1 (—4) 9 (—5) NICO aed) 0.003 0.002 oC Go TDA) 8 (—6) 6 (—6) 6S 7 17a) 0.001 0.002 82 Br 1.4 (0) 0.003 0.003 So Rb 5.2 (0) 0.18 0.18 SOR 2 Gi) 0.24 0.24 see S63) Tea) 0.001 Hi NGs 4.5 (-1) 0.050 0.050 rapes 1622) 0.002 0.003 ?3°Np 2.6 (2) DES) 1 (—4) Total dose commitment ibe 3.0 *The numerical value in parentheses signifies the exponential power of 10; thus 8.1 (—1) signifies 8.1 x 1Oie tValues are based on a daily intake of 1 liter of milk having radionuclide concentrations as listed in Table 6. *Dose commitment is calculated as the 30-year dose to an adult (standard man). Concentrations of Nuclides in Meat Peak concentrations of nuclides in herbivore muscle were estimated assuming small-particle deposition. The standard herbivore, such as the cow, is assumed to utilize 45 m? of pasture daily and actually to consume daily the small particles deposited on 30 m? (initial retention factor, two-thirds). The half-residence time on forage is assumed to be 14 days. Table 9 lists the estimated peak concentrations for fission products in herbivore muscle from the deposition of small particles, and Table 10 lists concentrations for activation products. The estimates are presented for nuclides RADIONUCLIDE BODY BURDENS 149 Table 9 ESTIMATED PEAK CONCENTRATION IN HERBIVORE MUSCLE FROM DEPOSITION OF SMALL PARTICLES (FISSION PRODUCTS ONLY)* Ratio of CmeatT Cmeat to CM, = Radionuclide (uCi/kg)/(uCi/m) uCi/kg (uCi/kg)/(uCi/liter) 22 Sr 4952 3)) 4.9 (-1) 0.2 PSP 53) Bt) 0.2 Ru 142) 322) 300 aOR DOK =D) 201) 400 ek 2.52) 4.4 (0) 0.9 ee Sb 6.8 (—3) 52) 30 fei DA (=D) Biss) 6 ean BD) af (1) 0.3 Poe. a5 (1) 6.0 (1) 3 BOTs 1.1 (0) 1.0 (0) 5 Te Ba 5.3.(—4) 301) 0.08 tr Ge Du(e=3) SD) 2 *Deposition is assumed to be 10 ® kt of fission per square meter. tThe numerical value in parentheses signifies the exponential power of 10; thus 4.9 (—3) signifies 4.9 x Or +The peak concentrations in milk, Cy, are given in Table 5. having half-lives greater than 7 days. The concentrations in muscle (Cmeat) in microcuries per kilogram are presented both for unit deposition and for the 10° kt/m* hypothetical deposition. The last column of each table lists for each nuclide the ratio of peak concentration in meat to that in milk. Meat-to-milk ratios greater than 10 are noted for Oe Ru a Ride aniduss Sb (Table 9) and for °*Mn, °*Fe, and °° Fe (Table 10). These nuclides were found earlier to be relatively unimportant via milk, but they could potentially represent a greater hazard via meat. Estimated Dosage via Meat Table 11 presents the dosage estimates for fission products via meat from the deposition of small particles and Table 12 the dosage estimates for activation products. We assumed for the estimates that the animal is slaughtered when the concentration in muscle is maximal and that meat consumption begins immediately and proceeds for a 6-month period at the rate of 300 g/day. Although these assumptions appear to be both overconservative and unrealistic, they serve to emphasize the relative unimportance of the meat pathway in comparison with the milk pathway. 150 Table 10 ESTIMATED PEAK CONCENTRATION IN HERBIVORE MUSCLE FROM DEPOSITION OF SMALL PARTICLES (ACTIVATION PRODUCTS ONLY)* Ratio of omens Cmeat to CM,t Radionuclide (uCi/kg)/(uCi/m~ ) uCi/kg (uCi/kg)/(uCi/liter) 22 NG 1.0 (0) eceorle (2) 4 220 23 (=1) 1.3 (0) 0.4 LCA 5°7(=2) 320K(=2) 0.1 >4Min 1kG\(—=2) 15552) 40 2 ire 37.51( 2) 72) 20 2 2iRe Dila(—2) 1.8 (—3) 10 166 Dt ( 2) 1032) 1 >2Co 17 (2) 4.6 (—2) 1 o0Co 253 (=?) 4.6 (—S) 1 Oo 7h DAN 1) 473) 0.5 84Rb 5.0 (—1) 31011) 1 8 Rb 4rte(=1) 1.2 (0) 1 LOMAS PED) 1eSu(=4) 0.03 12s 1.0 (0) TRON =2) 5 *Deposition is assumed to be 10° kt of neutron-activation products from fusion per square meter. tThe numerical value in parentheses signifies the exponential power of 10; thus 1.0 (0) signifies 1.0 x 10°. tThe peak concentrations in milk Cy are given in Table 6. Table 11 ESTIMATED DOSAGE VIA MEAT TO WHOLE BODY AND BONE FROM FISSION PRODUCTS DEPOSITED AS SMALL PARTICLES Dose commitment,*z rads Total activity ingested,*t Radionuclide uCi Whole body Bone St 2.4 (1) 0.087 0.67 POST 4.5 (-1) 0.24 2.0 aa 5.3 (1) 0.22 0.32 OCR 1.4 (1) 0.59 1.5 ean 1.8 (1) 8 (—3) 0.036 b23.Sb 7.6(=1) 3°(=4) 9 (—4) De Te 1.2 (0) 3:6 (3) 5.5 (—3) eee hak (D) 0.38 0.20 PEs 3.4 (2) 5.7 5.7 LLG: 5.7 i) 3.9 3.9 TBA 2.2 (0) 2.8) (= 3) 0.021 ire 6 (—5) 2 (—4) Total dose commitment 11 14 *The numerical value in parentheses signifies the exponential power of 10; thus 2.4 (1) signifies 2.4 x 10'. t Values are based on a daily intake of 300 g for a 6-month period of meat having radionuclide concentrations as listed in Table 9. tDose commitment is calculated as the 30-year dose to an adult (standard man). RADIONUCLIDE BODY BURDENS 151 Table 12 ESTIMATED DOSAGE VIA MEAT TO WHOLE BODY AND BONE FROM ACTIVATION PRODUCTS DEPOSITED AS SMALL PARTICLES eal Dose commitment,* + rads Total activity ingested ,*t i Radionuclide uCi Whole body Bone 75:9) Na 3.1 (0) 0.057 0.057 2p 7.8 (0) 0.058 0.33 Bee 1.2 (0) 0.010 0.10 54 Min 671) iepne3) 5553) oie 3.6 (0) 3) ie Fe =e) > Fe B32) 1 (—4) 1.4) CO 551) 3(=4) 34) SoCo 1.2 (0) A =3)) a3) oC Go DAN =3) 31(—5) 25) OIG 2.0) less) ee a Se Rb 4.2 (0) 0.14 0.14 BeRb 1.0 (1) 0.11 0.11 LOR 6.3 (3) 5 (4) 8 (—4) bets 3.5 (0) 0.40 0.40 Total dose commitment 0.78 12 *The numerical value in parentheses signifies the exponential power of 10; thus 3.1 (O) signifies 3.1 x 110°, tValues are based on a daily intake of 300 g for a 6-month period of meat having radionuclide concentrations as listed in Table 10. ¢Dose commitment is calculated as the 30-year dose to an adult (standard man). The nuclides that could contribute most to the dose commitments via meat include some of those previously singled out in the discussion of the milk pathway: Sete a Sree tile 2° Cs. and |°'’ Cs (Table 11) and 22 Na. 22\p. Ga Rb oo Rpt and 2 wes (Table 12). Of the nuclides having meat-to-milk concentration ratios greater than 10, only '°*Ru and '°°Ru could contribute substantially to the dose commitment. The input parameters required in the plant—herbivore—meat model for isotopes of ruthenium cannot be regarded as being firmly established. Activation products of device origin do not contribute appreciably to the dose commitments via meat. The estimates of dosage to the whole body and bone should be compared with the corresponding estimate for the thyroid from '?"1, a dosage of 200 rads. Estimated Dosage from Deposition of Large Particles Tables 13 and 14 present the dosage estimates for fission products and for activation products, respectively, via milk and meat from the deposition of large 152 NG AND TEWES Table 13 ESTIMATED DOSAGE TO WHOLE BODY AND BONE FROM FISSION PRODUCTS DEPOSITED AS LARGE PARTICLES Dose commitment, rads*t Via milk= Via meat § Radionuclide Whole body Bone Whole body Bone east 0.038 0.29 0.013 0.10 oo Sr 0.040 0.33 0.036 0.29 2? Mo 0.064 0.089 Oo Ra 5 (—5) 7 (5) 0.021 0.030 100 Rai 3.(=5) 8 (—5) 0.044 0.11 Leen 0.007 0.032 0.001 0.005 22S D7) 6(=7) 25) 6 (—5) eee 6 (—6) 1 (—4) 4 (—4) 64) Lee te es) 4 (—4) Pe Te 0.007 0.008 ie 0.48 0.25 0.053 0.028 1337 0.16 0.12 138 Ce 0.54 0.54 0.71 0.71 ace 0.026 0.026 0.32 0.32 DOR a 0.010 0.074 524) 0.003 Hee 6(=7) (6) A= 6) (ES) Total dose 1.4 1.8 1, 1.6 commitment *The numerical value in parentheses signifies the exponential power of 10; thus 5 (—5) signifies 5 x 10m tDose commitment is calculated as the 30-year dose to an adult (standard man). = Values are based on a daily milk intake of 1 liter. § Values are based on a daily meat intake of 300 g for a 6-month period. particles. Please recall that these estimates were made by assuming an initial retention of 13% and a half-residence time on forage of 4 days. In other respects the dosage estimates were made in the same manner as those from deposition of small particles. Summary of Dosage Estimates Table 15 summarizes the dosage estimates from deposition of small and large particles via milk, and Table 16 summarizes those via meat. For both routes and both kinds of deposition, the dose to the thyroid from iodine isotopes is the highest of all doses listed. The thyroid doses via milk exceed the total doses to whole body and bone by two orders of magnitude and via meat by one order of magnitude. The dosages from fission products exceed the dosages from RADIONUCLIDE BODY BURDENS 153 Table 14 ESTIMATED DOSAGE TO WHOLE BODY AND BONE FROM ACTIVATION PRODUCTS DEPOSITED AS LARGE PARTICLES Dose commitment, mrad*t Via milk= Via meat§ Radionuclide Whole body Bone Whole body Bone 9) Na 0.86 0 86 4.5 4.5 ZONA 41 41 22p 30 170 69 39 OK Daa 24 Gs 29. 32 0.93 94 BGA 0.52 Si ann 8 (—4) A 3) Ord 0.53 Re 13) (3) 0.074 Ord SRE 6i(=4) TAD 0.011 0.012 Go srs) 613) 0.027 0.020 C6 0.19 0.14 0.35 0.26 Me (4) 4 (—4) 0.002 0.001 Oo 7 0.07 Oe 0.10 0.18 82 br 0.55 0.55 ORD 12 12 16 16 BC Rs 20 20 14 14 110m Ag 0.04 0.06 0.04 0.06 ree 3.0 3.0 34 34 oe 0.27 O83 222 Nip a3) Di(=-3) Total dose 110 290 ohh 120 commitment *The numerical value in parentheses signifies the exponential power of 10; thus 8 (—4) signifies 8 x iiOuwe tDose commitment is calculated as the 30-year dose to an adult (standard man). + Values are based on a daily milk intake of 1 liter. § Values are based on a daily meat intake of 300 g for a 6-month period. 154 NG AND TEWES Table 15 SUMMARY OF SOURCE CONTRIBUTIONS TO THE ESTIMATED DOSAGE VIA MILK FROM DEPOSITION OF SMALL AND LARGE PARTICLES* Small particles, rads. Large particles, rads Source Whole body Bone Thyroid Whole body Bone Thyroid Fission 14 DA 3000T 1.4 1.8 340T Neutron ical 3 O.11 0.29 activation Total iS) 24 135 Deal *This table summarizes the dosage estimates of Tables 7, 8, 13, and 14. +The thyroid dosage is attributed to De iandie vel Table 16 SUMMARY OF SOURCE CONTRIBUTIONS TO THE ESTIMATED DOSAGE VIA MEAT FROM DEPOSITION OF SMALL AND LARGE PARTICLES* Small particles, rads Large particles, rads Source Whole body Bone Thyroid Whole body Bone Thyroid Fission 11 14 200+ 12 1.6 28t Neutron 0.78 LEZ 0.077 Ost activation Total 12 15 153 U7) *This table summarizes the dosage estimates of Tables 11, 12, 13, and 14. +The thyroid dosage is attributed to ae activation products by about an order of magnitude. Most of the dose commitment from activation products ts attributable to nuclides derived from rock and soil. The total doses to the whole body and bone are about the same via milk and via meat. In view of the overconservative and unrealistic assumptions involved in making the dosage estimates via meat, this similarity serves to emphasize the much greater importance of the milk pathway following single depositions on vegetation. The thyroid dose from iodine isotopes via milk exceeds that via meat by an order of magnitude; this further emphasizes the importance of the milk pathway. When we consider the dose commitment to a child, the importance of the milk pathway 1s magnified still further. For both pathways the dosage estimate for a child’s thyroid would be higher by about a factor of 10 than that shown in Tables 15 and 16 for an adult. However, a child RADIONUCLIDE BODY BURDENS 155 is likely to consume a liter of milk daily but would be likely to consume meat at a much lower rate than 300 g/day. The estimates of dosage from large-particle deposition are almost uniformly one-tenth those from small-particle deposition. The differences would be greater if we assumed a retention factor less than 13% and/or a half-residence time on forage less than 4 days. Uncertainties in the Estimates Some of the uncertainties in predicting food contamination and dosage relate to the assumptions adopted. In the estimates of milk contamination, we assumed that cows are continuously grazing on pasture. If cows were feeding on stored feed collected before the deposition of fallout, milk contamination could be expected to be lower by one to two orders of magnitude. Similarly, our assumption that milk consumption begins immediately with no delay for processing and handling leads to estimates that are overconservative for the particularly short-lived nuclides such as ??Mo, '?'™Te, '?71, **Na, “7K, and ®2 Br. The dosages would also be lower if milk consumption were delayed. The same considerations apply to the estimates via the meat pathway, where delays associated with processing and handling would be greater. As we have pointed out, the conservative, unrealistic assumptions adopted for the meat pathway serve to emphasize the much greater importance of the milk pathway following single depositions of radionuclides on vegetation. Additional uncertainties in the predictions are attributable to uncertainties in the transport and interaction terms. We have assumed unfractionated deposition of nuclides. Among the nuclides that were shown to make important peB at which have rare-gas precursors. We can reasonably expect that nuclides with rare-gas z : 3 x contributions to the dosage are °?Sr, ?°Sr, '?7Cs, and precursors would be distributed to a greater extent on the smaller particles. Consequently food contamination and dosage from large particles may be overestimated, whereas those from small particles may be underestimated. The actual differences between the dosage estimates from small and large particles would then be greater than those shown in Tables 15 and 16. The actual extent of food contamination by the other important nuclides sinpled woutsc. Mow 4) ule 4. (Gs Na, *-Na,. >> Pe’ Ga, *" Rb, °° Rb, and '34Cs) depends similarly on their partitioning between small- and large-particle fractions. Most of these nuclides would be expected to exhibit intermediate behavior with respect to fractionation. The refractory nuclide ??Mo, which would contribute to the dosage via milk at early times, could be expected to be distributed to a greater extent in the larger particles. The major uncertainty in the interaction term ts the biological availability of the nuclide in fallout, which depends in turn on the partitioning of the nuclide between small- and large-particle fractions. The biological availabilities of 77 Na, 89 90 99 131 : , Sie Si Mo, 3 Ip aa et OS ; OC and !*°Ba in small-particle debris 156 NG AND TEWES (<50 wu) with respect to milk secretion have been found to be comparable to those of tracers used in experiments within a factor of 2 or 3. The biological Peete eles AAR AS 47 84 8 6 136 availabilities of Na, iP (Cae Case bs Rb, and Cs have not been determined. The biological availabilities of some nuclides in large particles may be less than in small particles by virtue of differences in physical state, which would lead to lower estimates from large-particle deposition. PREDICTION OF THE INTERNAL DOSAGE FROM LONG-TERM DEPOSITION BASED ON CHRONIC-CONTAMINATION MODEL It is estimated that a land-surface burst in the 1-Mt range would inject about 50% of its radioactivity into the stratosphere.” Therefore we shall assume that 50% of the nuclides produced would enter the stratosphere and be deposited as long-term fallout. At the same time we can reasonably assume an equivalent injection into the stratosphere originating from retaliatory detonations initiated by friendly forces. On this basis we have simply assumed that all the activity produced would be injected into the stratosphere, as would be the case for airbursts involving weapons of the size assumed. Air Concentrations and Rate of Deposition of Nuclides The estimated rate of deposition of nuclides from the stratosphere is based on Peterson’s empirical model for estimating worldwide deposition from nuclear debris injected into the stratosphere.*? According to this model the maximum annual surface deposition of ?°Sr in the 30 to 50° N latitude band for a 1-MCi injection into the lower polar stratosphere (9 to 17 km altitude) would be expected to vary between 250 and 400 kCi. For a 1-MCi injection into the upper polar stratosphere (17 to 50 km altitude), the maximum annual deposition could be expected to vary between 50 and 170 kCi. The cloud from a 1-Mt burst in the latitude band 30 to 90° N can be expected to stabilize in the lower polar stratosphere, whereas a 10-Mt burst in this region can be expected to stabilize in the upper polar stratosphere. Accordingly we have based our estimates on an intermediate value of 200 kCi of °° Sr deposited in one year in the 30 to 50° N latitude band per megacurie injected into the stratosphere. It can be readily shown that an annual deposition of 1 kCi in the 30 to 50° N latitude band is equivalent to a deposition rate of 1.7 X 10° uCi/m? /hr. An apparent deposition velocity of 40 m/hr has been determined empirically from the observed monthly deposition rates and average surface-air concentra- tions of ?°Sr in the Northern Hemisphere.** An apparent deposition velocity of 40 m/hr has also been determined on the basis of quarterly deposition rates and average surface-air concentrations from U.S. stations alone.*° A deposition velocity of 40 m/hr, together with these assumptions regarding the deposition rate of stratospheric debris, leads to an estimate of 8.5 X 10” uCi/m® for the average concentration of ?°Sr in surface air during any 12-month period closely RADIONUCLIDE BODY BURDENS 157 following the injection of 1 MCi into the stratosphere. For present purposes we can simply round this off to 1 x 10° uCi/m*, which is the value we have assumed for all the nuclides of interest. The assumption that 10° uCi/m® is the average surface-air concentration in the 30 to 50°N latitude band following the injection of 1MCi into the stratosphere is consistent with measurements reported by Thomas et al.'* Table 17 shows ground-level air concentrations measured at Richland, Wash. (46° N). The table compares the spring concentration maxima measured in 1963 Table 17 RELATION BETWEEN GROUND-LEVEL AIR CONCENTRATION ey oO STRATOSPHERIC BURDEN AT RICHLAND, WASH. (46 N), IN 1963! Spring concentration maxima Saneosnnent burden ee Nuclide dis/min/10° ft” uCi/m> MCi MCi 4 NAn i Apeor 22x10! 5.7x 10! 3 Oslo OCR 7.0 x 10° et On DectOs 5 xekOr: Fe iSb 9.0 x 10° 1.4x107 313 «10: 4.4x10° Eos 75x AOe axon 1510" 82x10” bate 1.0 x 10° oreOe 3.6 x 107 A510!” with the megacuries injected into the stratosphere in the 1961—1962 series. As mentioned previously, the total fission yield of the 1961—1962 atmospheric detonations was about 100 Mt. The ratio between the air concentration in microcuries per cubic meter and the stratospheric burden in megacuries varied between 4X 10” and 8 X 10°; if the ratio were calculated with the average concentration for the year, it would of course be smaller. A large fraction of the stratospheric burden from the 1961—1962 test series was injected into the upper stratospheric compartment. By assuming a higher value of 10° for the ratio of alr concentration to stratospheric burden, we allow for injections into the lower stratospheric compartment, from which initial deposition rates will be greater. Deposition of Nuclides on Vegetation To estimate the dosage that could result from the continuous deposition of radionuclides on vegetation, we estimated the steady-state deposition of particles on forage, Feg, as the quotient of the deposition rate, R, and the rate of loss by weathering, Ay: 158 NG AND TEWES Since the deposition rate, R, is related to the air concentration, L, by the deposition velocity, Vg, ‘oh (4) the equilibrium deposition on forage can be expressed in terms of the air concentration: Vie = wel) The food contamination and dosage from the continuous deposition of nuclides from the stratosphere were estimated from equilibrium depositions, Feg, determined as outlined previously. The deposition velocity, Vg, was assumed to be 40 m/hr, and the rate of loss by weathering, Ay, was assumed to be 0.05 per day, which is equivalent to a half-residence time on forage of 14 days. Forage—Cow—Milk Pathway The forage—cow—milk model, as previously described for small particles, assumes a UAF of 45 m*/day and an initial retention factor of two-thirds. Concentrations of Nuclides in Milk Table 18 lists the estimated average concentrations for fission products in milk from stratospheric deposition during a year closely following the Table 18 ESTIMATED AVERAGE CONCENTRATIONS IN MILK AND MEAT FROM THE STRATOSPHERIC DEPOSITION DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK (FISSION PRODUCTS ONLY) Cu* Cmeat* uCi/liter uCi/kg Ratio of Radionuclide uGi/im:= uCi/liter uCi/m> uCi/kg Creat toLeM 2S: 3.9 (2) 13) 6.4 (1) 1.9 (—4) 0.2 Be 4.9 (2) 8.6 (—4) SG) 5 (4) 0.2 OR Sse (an) 115) 1.8 (3) 358, (2) 3000 255 2.7 (0) 1745) 3.5 (3) ED) 1000 Ee Gs 4.1 (3) 12) 4.7 (4) 1eaeat) 10 Mae Ce 1.0 (1) 3.0 (—4) BO hak (=p) 30 *The numerical value in parentheses signifies the exponential power of 10; thus 3.9 (2) signifies 3.9 x One RADIONUCLIDE BODY BURDENS 1:59 hypothetical attack. Table 19 gives the estimates for activation products. The nuclides listed are those having half-lives greater than 45 days. The concentra- tions are both for unit air concentration and for the estimated average concentration for the year. Table 19 ESTIMATED AVERAGE CONCENTRATIONS IN MILK AND MEAT FROM THE STRATOSPHERIC DEPOSITION DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK (ACTIVATION PRODUCTS ONLY) CoM * Cmeat* uCi/liter uCi/kg Ratio of Radionuclide uCi/m> uCi/liter uCi/m> uCi/kg Cmeat to-CmM NA 8.1 (3) isos) 6.2 (4) Gige(=3) 7 2 2'Ca TAG) 23 (3) 723) Pols) 0.3 54 Min 5.3 (0) 63-6) 5.0 (2) 6.0 (—4) 100 hers DOs) 9.9 (—5) Gaines) 2 -3i(=2) 300 Mireles Deen) 57-4) 143) 12Ou(=3) 7 >°Go 1.8 (2) AAs) 8.4 (2) OA) 4 oe CO DDD) 125) 1.8 (3) 9.6 (—6) 0.8 OO a 5.2 (3) et(=4) 1.6 (4) 3.5 (—4) 3 aed D6) STC 6) 6.4 (3) 1.4.5) 2 Te Gs 4.0 (3) 5.6 (—4) 4.5 (4) 6238) 10 *The numerical value in parentheses signifies the exponential power of 10; thus 8.1 (3) signifies 8.1 x Oe. Estimated Dosage via Milk Tables 20 and 21 present estimates of the average dose rate via milk to adult whole body and bone from the nuclides depositing from the stratosphere during a year closely following the hypothetical attack. Fission products are considered in Table 20 and activation products in Table 21. The rates of ingestion were calculated assuming milk consumption of 1 liter/day. The dose rates to whole body and bone assume that the concentration of the nuclide in tissue has reached a steady state with respect to the constant rate of ingestion.* The total dose rate from fission products (Table 20) is about 1 rad/year in the whole body = MC seandito 9 : Nese a lesser extent, ° Sr, contribute most to the dose rate from fission products. and about 6 rads/year in bone. It comes as no surprise that 2 OC re *The dose commitment (rads) from a given nuclide would be estimated as the product of the dose rate (rads/year) and the mean residence time of the nuclide in the stratosphere (year). 160 NG AND TEWES Table 20 ESTIMATED AVERAGE DOSE RATE VIA MILK TO WHOLE BODY AND BONE FROM FISSION PRODUCTS DEPOSITING FROM THE STRATOSPHERE DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK Dose rate,* rads/year Rate of ingestion, * Radionuclide uCi/year Whole body Bone oo Sr Ant) 3263) 0.028 oss OED 0.62 5.4 eR Ate (3) 1 (—4) 4 (—4) aS 4.9 (—3) Bi) 5 (—6) ues 4.4 (0) 0.29 0.29 144, i: iS Ce ieigeet) 3 (—6) ES) Total dose rate 0.91 es *The numerical value in parentheses signifies the exponential power of 10; thus 4.2 (—1) fee =f signifies 4.2 x 10. Table 21 ESTIMATED AVERAGE DOSE RATE VIA MILK TO WHOLE BODY AND BONE FROM ACTIVATION PRODUCTS DEPOSITING FROM THE STRATOSPHERE DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK ai ena Dose rate,* mrads/year Rate of ingestion,” Radionuclide uCi/year Whole body Bone DD Na A my EG 76 Boren 8D (21) 7.2 72 Seta Dist (=3) An(=3) (=D) ire 3.6 (—2) 1 (2) Die2) Sees 503 C=2) 312) (CD 866 1622) 62) (=D) eGo 4.2 (—4) 5 (—3) 353) OO 7 GD) 0.3 0.47 Pe Aes BAM (Ep 0.16 0.26 TGs Dili 23 23 Total dose rate 38 100 *The numerical value in parentheses signifies the exponential power of 10; thus 4.1 (—1) signifies 4.1 x 10 . RADIONUCLIDE BODY BURDENS 161 A comparison of Tables 20 and 21 reveals that the dose rate to the whole body from fission products would exceed that from activation products by about a factor of 20; the dose rate to bone from fission products would exceed that from activation products by about a factor of 50. The activation products of Table 21 which would contribute most to the dosage via milk are the neutron-activation products of soil and rock, 22Na, Ga and '34Cs. The dose rates listed in Table 21 are expressed in millirad units. Activation products of device origin would contribute relatively little to the total dose rate. Plant—Herbivore—Meat Pathway The estimates via meat, like those via milk, were made as previously described for small particles, assuming a UAF of 45 m*/day and an initial retention factor of two-thirds. Concentration of Nuclides in Meat Tables 18 (for fission products) and 19 (for activation products) list the estimated average concentrations in meat from stratospheric deposition during a year closely following the hypothetical attack. The nuclides listed have half-lives greater than 45 days. The concentrations are both for unit air concentration and for the estimated average concentration for the year. The meat-to-milk ratios of average concentrations, given in the last column of these tables, suggest that, except for isotopes of calcium and strontium, the nuclide concentrations in meat would be about the same as, or greater than, those in milk. According to these 25 ; ; - 106 tiie calculations, the average concentration of >Ru and Sb in meat would exceed their average concentration in milk by three orders of magnitude. The : 5 5s . 3 a E average concentration of >” Fe in meat would exceed its average concentration in milk by more than a factor of 100. Estimated Dosage via Meat Tables 22 and 23 present the estimates of the average dose rate via meat to the adult whole body and bone from the nuclides depositing from the stratosphere during a year closely following the hypothetical attack. Fission products are considered in Table 22 and activation products in Table 23. The rate of ingestion was calculated assuming meat consumption at the rate of 300 g/day. Again ?°Sr and '*’Cs make major contributions to the total dose rate via meat; in addition, '°®Ru makes a substantial contribution. As mentioned earlier, the input parameters required for ruthenium isotopes via this pathway are open to question. The dose rate to the whole body from fission products via meat totals 1.2 rads/year, whereas that to bone totals 1.8 rads/year. The dose estimates from activation products are again less by about an order of magnitude. The neutron-activation products singled out in Table 23 include 22 4 sa nae ees Nav Ga, and Cs, the same nuclides of environmental origin previously 162 NG AND TEWES Table 22 ESTIMATED AVERAGE DOSE RATE VIA MEAT TO WHOLE BODY AND BONE FROM FISSION PRODUCTS DEPOSITING FROM THE STRATOSPHERE DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK Rate of ingestion,* Dose rate,* rads/year Whole body 0.03 OZ S\(—4) 1.0 Bone 145 (=3) 0.27 0.45 23) 1.0 Radionuclide uCi/year ce Si DE) 1.8 (—4) 90 Sr 1.6 (—2) Oe 4.2 (0) 152'5 : Sb 2-O(O) LST es 1.5 (1) Lae 1.2 (0) Total dose rate 35D) (4) 1.8 *The numerical value in parentheses signifies the exponential power of 10; thus 2.1 (—2) signities 2-0 x 10 < Table 23 ESTIMATED AVERAGE DOSE RATE VIA MEAT TO WHOLE BODY AND BONE FROM ACTIVATION PRODUCTS DEPOSITING FROM THE STRATOSPHERE DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK Rate of ingestion,* Radionuclide uCi/year Died Na 9.6 (—1) Ca 7822) 4 Mn 6.6 (—2) ae 3.1 (0) Divers ieee) PEG 2.2 (—2) es Theil (8) Oi 3) A 186123) od 69} Total dose rate Dose rate,* mrads/year Whole body ILL 0.68 O.11 0.93 0.07 0.08 0.01 0.25 O.1 Td) 96 Bone 17 6.8 O25 1.4 0.05 0.06 0.01 0.43 0.2 77 | 100 | *The numerical value in parentheses signifies the exponential power of 10; thus 9.6 (—1) signifies 9.6 x LOE é RADIONUCLIDE BODY BURDENS 163 singled out via milk. In addition, °° Fe, of device origin, would make a small contribution. Summary of Dosage Estimates Table 24 summarizes the dosage estimates from stratospheric deposition. The table shows the dominant role of fission products, whose contributions to the dosage exceed those of activation products by more than a factor of 10. The Table 24 SUMMARY OF SOURCE CONTRIBUTIONS TO THE ESTIMATED AVERAGE DOSE RATES VIA MILK AND MEAT FROM STRATOSPHERIC DEPOSITION DURING AV YEAR-GLOSELY FOLLOWING THE HYPOTHETICAL ATTACK Milk pathway, rads/year Meat pathway, rads/year Source Whole body Bone Whole body Bone Fission 0.9] ae%, 1.2 1.8 Neutron activation 0.038 0.10 0.096 0.10 Total 0.95 5.8 1s £29 table also shows that the dose rates via the two routes (via milk and via meat) would not differ greatly. Thus, for continuous deposition extending in time, the meat and milk pathways would be more comparable in importance. For the single discrete depositions previously considered, the milk pathway assumes a far greater importance. Interpretations of the Estimates Before discussing the dosage estimates from nuclides initially depositing from the stratosphere, let us consider briefly the validity of the model for chronic contamination. This model involves the derivation of a proportionality factor between the average nuclide concentration in milk or meat and the average nuclide concentration in surface air. The relation of air concentration of a nuclide to food contamination obviously involves factors relating to plant-retention characteristics, the local environment, and agricultural feeding practices. Wilson* 7 developed an ecologically based quantitative model of the transport of ! 37Cs from fallout to milk. This model can predict to a high degree of precision the mean quarterly levels of '37Cs in milk from the mean surface concentrations in air. The linear correlation between mean quarterly OES levels in milk and mean surface-air concentrations during the growing season for 164 NG AND TEWES various milksheds across the nation was characterized by a value of 710 pCi/liter in milk per picocurie per cubic meter in surface air. This particular correlation was associated with dry-lot feeding. The Seattle milkshed exhibited a different correlation, which by our calculations is characterized by a value of 4100 pCi/liter in milk per picocurie per cubic meter in surface air. The response of the Seattle milkshed was thought to be characteristic of pasture feeding. Our model assumes that the animals providing the milk and the meat are '37Cs concentration in milk listed in Table 18 is continuously on pasture. The equivalent to 4100 pCi/liter per picocurie per cubic meter in surface air. This close correspondence to the Seattle value obtained by Wilson is, of course, fortuitous. An inspection of milk concentrations and surface-air concentrations of neues and ?°Sr measured from the middle of 1963 at Ispra, Italy (as reported in the HASL series of reports from the Health and Safety Laboratory, U.S. Atomic Energy Commission*®), indicates that the correlation between | * 7 Cs concentra- tions in milk and air would be about 5200 (pCi/liter)/(pCi/m® ). For ?° Sr the correlation at Ispra would be about 960 (pCi/liter)/(pCi/m*). When the concentrations of ?°Sr in milk from the Seattle milkshed*? were compared with the surface-air levels over Seattle,** the correlation was estimated to be 620 (uCi/liter)/(uCi/m? ). The concentration of °°Sr listed in Table 18 is 490 (uCi/liter)/(uCi/m*> ). If we assume that pasture feeding was the dominant practice at Ispra and Seattle, the values listed in Table 18 for the concentrations of. Csand -~Srintmailk appear to be reasonable. Since field data on concentrations of nuclides in meat are far less abundant than those in milk, particularly for °° Sr, we simply compared the predicted and observed ratios of the concentration in meat to that in milk. The concentration of stable strontium per gram of calcium in meat is about twice that in milk: The concentration of ?°Sr per gram of calcium in meat also was found to be twice that in milk in the United Kingdom diet of 1963 and 1964 (Refs. 51 and 52). On the basis of the stable calctum content of milk and meat (1.3 g Ca/liter and 0.1 g Ca/kg, respectively® ), the ratio of the average concentration of Sion meat to that in milk could be expected to be 0.15. (We assumed that the St burdens of 1963 and 1964 are largely attributed to direct contamination.) The ratio can be expected to vary with geographical location. Thus the ratio of the average yearly concentration of ?°Sr in meat to that in milk in the Danish diet from 1962 to 1964 varied from 0.20 to 0.26 (Refs. 53—55). After examining the tri-city data on ?°Sr concentration in foods from 1962 to 1964 (from the HASL reports’ *°), we estimated the increments of the burdens that were associated with recent deposition. The estimated ratio of the average concentration of Sr attributable to direct contamination in meat to that in milk was about 0.11 to 0.14 in the San Francisco and Chicago diets. The concentration of °° Sr reported for meat in the New York diet was relatively insensitive to fresh contamination, and the meat-to-milk ratio was less than 0.05. The ratio listed in Table 18, 0.2, is within the range reported. RADIONUCLIDE BODY BURDENS 165 Meat and milk together have been the main dietary sources of '*’Cs. The f 137 concentration o Cs in meat could be expected to exceed that in milk; e.g., 7Cs contents in beef and milk in Sweden from the correlation between the 1962 to 1966 is characterized by a concentration ratio (picocurie per kilogram of meat to picocurie per liter of milk) averaging 4.3 (Ref. 56). The ratio of the average yearly concentration of '*’Cs in meat to that in milk in the United Kingdom from 1961 to 1964 varied from 3.2 to 5.3 (Ref. 52). The ratio in Denmark was 5.8 in 1963 (Ref. 54) and 5.3 in 1964 (Ref. 55). The meat-to-milk ratio of '*7Cs listed in Table 18 is 10. The predicted concentration of ?°Sr and '37Cs in meat appears to be acceptable in view of the wide variation that could be expected. Thus the average concentration of '*7Cs in beef sampled at various slaughterhouses in Norway from 1965 to 1967, ranged from 120 to 1700 pCi/kg (Rieti 7). “The: “average “concentration in. mutton .ranged from 520 to 4800 pCi/kg. This variation points out the important role of differences in local environmental factors and feeding practices. Let us now consider the dosage estimates presented in Tables 20 and 23 for the nuclides depositing from the stratosphere. If both the concentrations of the nuclides in milk and meat and the ingestion rates were as we have supposed, we could accept these estimates at face value. The dose rates shown in these tables for the year closely following the initial injection of the nuclides into the stratosphere, combined with the decreasing dose rates that would be associated with nuclide deposition in succeeding years, would constitute a long-term internal dose commitment. This dose commitment would make a substantial contribution to the dose commitment for the individual who was adequately protected from the gamma field in the few weeks immediately following an attack and who also avoided contaminated foods during this period. It is interesting to compare the estimated yearly dose rates from fission products via milk (Table 20) with the corresponding estimated doses from local and tropospheric deposition at early times (Table 7). The total yearly dose rate to the whole body and bone from stratospheric deposition is somewhat less than the total dose commitment to these organs from the 10° kt/m? deposition at early times. However, the yearly dose rate from stratospheric deposition, which is attributable to ?°Sr and '*7Cs, is comparable to the dose from the early deposition of these nuclides. This simple comparison points out the significance of the stratospheric compartments for these long-lived nuclides. The initial deposition rate from the stratosphere, and hence the initial average dose rate, may be either greater or less than our estimate. But, since the residence time of stratospheric debris 1s measured in months or years rather than in decades, essentially all the stratospheric burden of ?°Sr and '27Cs would reach ground level where it could then contribute to the internal dose commitment before radioactive decay. It is also interesting to compare the external and internal dosages that would be associated with long-term deposition. The internal and external dosages 166 NG AND TEWES IWS} 7 1.°8°5 resulting from Cs deposition are estimated to be equa ” Since over 80% of the activity injected into the lower and upper polar stratospheric compart- ments can be expected to deposit in the hemisphere of injection,”” the average 'S7Cs in the Northern Hemisphere following the cumulative deposition of hypothetical injection of 2000 Mt of fission products into this region of the stratosphere would be about 1.2 uCi/m*. The average deposition in the 30 to 50° N latitude band would be about twice as great,*? or 2.4 uCi/m?. A dose-conversion factor of 0.04 (rad/year)/(uCi/m” ) coupled with a mean life of 44 years leads to an external dose commitment of 4.2 rads from '?7Cs (Ref. 59). The actual dose to the gonads and bone marrow would be about one-fifth as great, or about 0.85 rad, because of shielding by building structures and screening by the human body.°” The internal dose commitment to these tissues from stratospheric '*7 Cs, assuming milk consumption at the rate of 1 liter/day, is estimated according to our present scheme as the product of the dose rate, 0.29 rad/year (Table 20), f '°7Cs in the stratosphere. The half-residence time of debris and the mean life o is estimated to be 5 months in the lower polar stratosphere and about 2 years in 9 3 . the upper polar stratosphere.” ’ If we assume a half-residence time of 1 year, the = on 3 = . 5 dose commitment from !°7Cs via milk would be 0.42 rad. This seems to be a reasonable value in relation to the total estimated external or internal dose commitment of 0.84 rad since milk is known to contribute a substantial fraction Peart si7, of the dietary c n 3 . n ° - predominant pathway for the entry of '*7Cs into foods.°° Bear in mind that Cs and since direct contamination is regarded as the this analysis 1s confined to the contamination of food as a result of direct contamination of vegetation. For ?°Sr, uptake from soil over the long term can be expected to make a major contribution to the contamination of terrestrial foods.°° Although the external and internal dosages from '*7 Cs deposition would be comparable, it is important to note that initially the internal dose rate will exceed the external dose rate. The cumulative ground deposition of '*7Cs from stratospheric deposition would be about 1.0 uCi/m* at the end of the year following the hypothetical attack. The gamma field associated with such a deposition of '*’Cs is 0.04rad/year, which is considerably less than the estimated initial average dose rate via milk (0.29 rad/year) shown in Table 20. If we consider the other dietary sources of '*7Cs and at the same time make more reasonable assumptions regarding average rates of ingestion, the internal dose rate would still initially exceed the external dose rate to the degree shown above or to an even greater degree. Evaluation of Risk This analysis was undertaken to estimate potential levels of food contamina- tion and dosage to individuals and 1s not intended to evaluate risk from radiation exposure either to individuals or to populations. If the dosage estimates are to be RADIONUCLIDE BODY BURDENS 167 used for risk evaluation, we must take into account two factors: how the dose from a given nuclide is spatially distributed among tissues and the relative susceptibility of the cell types involved.°’ The °° Sr, for example, concentrates in bone. The risk of developing malignant diseases, which is associated with ?° Sr deposition, is a consequence of the dosages delivered to the cells that line bone surfaces and to bone marrow. The dose delivered to the cells that line bone surfaces has been estimated to be about one-half and that to bone marrow about 7) RELATIVE RETENTION, % o 6) 2 4 6 8 10 12 14 DAY OF EXPERIMENT Fig. 1 Typical retention of 88- to 175-y sand at four locations on the back of cow 712: curve 2, between tuber coxa; curve 4, between shoulders; curve 6, paralumbar fossa; and curve 8, over shoulder joint. RETENTION OF SIMULATED FALLOUT WAS) 100 Feedlot % 10 INITIAL RETENTION, Pasture ) 2 4 6 8 10 12 14 DAYS POSTE XPOSURE Fig. 2 Composite normalized retention on the backs of cows, comparing particle size and cattle kept under pasture conditions and under feedlot conditions. Curves 1 and 3 are for 88- to 175-u sand; curves 2 and 4, for 175- to 350-u sand. RATE OF PASSAGE OF NEAR-IN FALLOUT IN THE GUT The radiation dose to segments of the gut would be from unabsorbed near-in fallout reaching the gut by either ingestion or inhalation. The radiation dose to the whole gut or to any segment is proportional to the average time that 176 JOHNSON AND LOVAAS particles spend in any location. The definition of the mean retention time or mean transit time is the summation of times that individual particles spend in the gastrointestinal tract divided by the total number of particles. By this definition, however, mean retention time is very difficult to determine. If the ruminant gut is considered in a one-compartment model where mixing of digesta is very rapid and emptying is by first-order kinetics, the mean retention time can be calculated very simply. It is the reciprocal of the first-order rate constant, or 1.44 times the biological half-time. A typical excretion curve of 88- to 175-u sand particles in sheep is given in Fig. 3. The true estimate of the mean retention time (7) from such data is the weighted average abscissal value (.e., the centroid of the curve), and, if the function of the curve is not known, mean retention time must be determined by approximation methods. From our data, however, the area under the buildup portion of the curve is small compared with the total area, and there is little error in calculating 7 from the measured half-life. RELATIVE CONCENTRATION IN FECES 0 40 | 80 120 160 200 TINIES ir Fig. 3. Typical excretion function of a single dose of 88- to 175-u ‘7’ Lu- labeled sand in sheep. RETENTION OF SIMULATED FALLOUT 177 There is actually a great amount of data in the animal-science literature on the rate of passage of digesta in ruminants since this is an important factor in determining nutritional efficiency of feedstuffs.’ Rate of passage as calculated from our model is simply the average mass of rumen digesta at any time divided NA. The values observed from our study are shown in Table 1. They are, in general, greater than those reported in the literature for feedstuffs of the same particle size. The data in Table 1 show little difference caused by sand particle size but an appreciable difference between sheep and cattle. Table 1 MEAN LIFETIMES OF SIMULATED NEAR-IN FALLOUT IN THE GUT OF SHEEP AND CATTLE Lifetime in Lifetime in Sand size, u sheep, days cattle, days 88 to 175 2 4.8 i703 0 15 A very important finding was that for both sizes of sand and with both sheep and cattle there was 98 to 100% recovery. This implies that very little, if any, of the sand particles are trapped in fine structures of the GI tract. Again we must stress that our data correspond to normal intake conditions. If dose to the GI tract is sufficient to cause appreciable damage, then decreases in motility are to be expected; this would increase retention times and further increase the dose. REFERENCE 1.C. C. Balch and R. C. Campling, Rate of Passage of Digesta Through the Ruminant Digestive Tract, in Physiology of Digestion in the Ruminant, pp. 108-123, Second International Symposium, Ames, Iowa, 1964, R. W. Dougherty et al. (Eds.), Butter- worth & Co. (Publishers) Ltd., London, 1965. SIMULATED-FALLOUT -RADIATION EFFECTS ON SHEEP L. BSSASSER, MU GC] BELL andy. ib. WESt UT—AEC Agricultural Research Laboratory, Oak Ridge, Tenn. ABSTRACT Sixty-four yearling lambs were exposed to the following radiation treatments: (1) °°F¥ beta irradiation of the gastrointestinal tract (2.4 mCi/kg of body weight for 3 consecutive days, (2) 90V beta irradiation of the skin (57,000 rads), (3) 69Co irradiation of the total body (240 R), or (4) all possible combinations of these treatments. Irradiation of the gastrointestinal tract produced severe injury to the rumen and abomasum and resulted in severe anorexia and diarrhea and a significant loss (> 20%) of body weight. Nearly 50% of the lambs subjected to combined gastrointestinal and whole-body irradiation died within 60 days, but lambs in other treatment groups were able to recover from the initial irradiation insult. Skin irradiation caused no immediate threat to life but affected survival several months postirradiation. Implications of multiple irradiation trauma on animal survival are discussed from a postattack recovery viewpoint. In the event of a surface thermonuclear detonation, farm livestock located downwind from the site of attack would be vulnerable to fallout radiation. The response of grazing livestock to fallout radiation would result from the combined insults of external whole-body gamma irradiation, irradiation from contaminated feed, and beta irradiation to animals’ skin. Considerable informa- tion is available on the effects of whole-body gamma radiation on large animals,'’? and incidences of skin irradiation from radioactive fallout have been reported in livestock*’* as well as in man.° Less is known about the response of the gastrointestinal tract of large animals to ingested radioactive materials. Nold, Hayes, and Comar,°® measuring internal radiation doses in dogs and goats using implanted glass-rod dosimeters, reported that, when a soluble °°V solution was given, the greatest doses were measured in the lower large intestine. Lethal levels of ingested soluble '**Ce—'**Pr severely damaged the rumen and omasum of sheep.’ More recently it has been shown that ingestion by sheep of insoluble °°y-labeled fallout simulant at levels to be expected in fallout contamination 178 SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP VAS) severely affected animal health and productivity but was seldom lethal.® Furthermore, the sites of major damage were confined to the rumen and abomasum. Even though previous studies demonstrate the effects of radiation on livestock, few studies have been conducted to determine the interaction of simultaneous administration of multiple modes of irradiation. Baxter et al.” reported that the additional trauma of thermal burns increased mortality in whole-body X-irradiated (400 R) swine. George, Hackett, and Bustad!° irra- diated lambs by three different methods (whole-body X-ray, oral '*"1, and beta irradiation of the skin) to study the additive effects at two planes of nutrition. None of the single or combined treatments were lethal, and weight gain appeared to have been influenced mainly by the nutritional treatments. The need for information on the survival of large animals in a postattack fallout situation was recently emphasized,’' and this study was initiated to investigate these interactions. EXPERIMENTAL PROCEDURES Yearling wether lambs of mixed breeding were treated for parasites, shorn, and gradually adjusted to a 680-g ration of pelleted alfalfa preconditioned with 140 g of water. The ration, which was supplemented with trace-mineralized salt, represented about 80% of ad libitum consumption. The sheep, averaging 31.1 + 0.6 kg in weight, were placed in collection stalls approximately 7 days before irradiation. One wether was randomly assigned to each of eight treatment groups: (1) control, (2) gastrointestinal irradiation (GI), (3) whole-body gamma irradiation (WB), (4) skin irradiation (Skin), (5) WB + Skin, (6) GI + Skin, (7) GI + WB, and (8) GI + WB + Skin. Eight replicates of each treatment were made over a period of 9 months. A sublethal bilateral exposure of 240 R (midline dose of 145 rads) at 1 R/min from °°Co sources'* was used for whole-body gamma irradiation. Sheep assigned to the four treatments requiring gamma irradiation were simultaneously irradiated 12 to 16 hr before gastrointestinal and skin irradiation began. Four 43-by-28-cm, flexible, sealed ?°Sr—?°Y plaques'* with surface dose rates ranging from 913 to 1570 rads/hr were used to irradiate about 12% of the body area. A plaque was affixed to the thoracolumbar region of the back of each sheep and left until a total beta dose of 57,000 rads had been delivered. The ratio of skin beta dose to whole-body gamma dose in the combined treatments was 240 to 1—the ratio estimated for the cattle exposed during the Trinity shot® in 1945. The insoluble labeled fallout simulant (°° Y-labeled silica sand 88 to 175 Min size) was mixed with the daily ration and fed for 3 consecutive days, as previously described.® An initial activity of 2.4 mCi/kg of body weight was fed on day 1, but, because of ?°Y decay, only 1.8 and 1.4 mCi/kg remained when 180 SASSER, BELL, AND WEST the ration was fed on days 2 and 3, respectively. The specific activity of the various batches of sand ranged from about 5 to 10 mCi/g; thus 6 to 17 g of sand were fed daily. The half-life, energy, and particle size of the synthetic fallout were selected to simulate fallout from a 1-Mt or greater surface nuclear burst at a distance sufficient for most livestock to survive the gamma dose. The gastrointestinal dosimetry procedure and results are described in detail by Wade et al.!* Consumption of feed and water and excretion of feces and urine were recorded daily. Six to seven weeks after treatment, the animals were removed from the collection stalls and fed an alfalfa—grass hay and grain ration ad libitum. Body weights were recorded periodically throughout the study. Fecal samples were oven dried at 60°C, and bremsstrahlung was counted with a well-type gamma scintillation counter set to exclude all pulses less than 2 MeV. This technique required a shorter decay period before counting than did beta counting and eliminated the detection of any ?°Sr contaminate. Standards were prepared by adding known quantities of °° Y-labeled sand to non- radioactive fecal material. Necropsies were performed on all sheep at death and on surviving sheep slaughtered 40 to 64 weeks postirradiation. Selected tissues were preserved in 10% buffered formalin for microscopic examination (detailed histopathology is reported elsewhere’ > ). RESULTS Clinical Observations Clinical signs of digestive disturbances were manifest in all sheep ingesting the synthetic fallout. Anorexia appeared between the fourth and tenth day after irradiation and continued in many of the sheep for several weeks (Fig. 1). There were no significant differences in severity of anorexia among the various Gl-treatment groups; however, the duration of anorexia was less in sheep subjected to both GI and Skin irradiation. A significant interaction (P < 0.05) was observed among trials for feed intake, but this difference could not be correlated with the specific activity or the amount of sand fed. Feed intakes of all non-GI treatments did not differ from those of the control animals. From minor to severe diarrhea was observed in the sheep after ingestion of °°y-contaminated feed. Fecal water began to increase 3 to 4 days after initiation of ?°Y feeding, reached a maximum at the fifth or sixth day, and then declined, probably as a result of the anorexia (Fig. 2). Another increase in fecal water, occurring between days 11 and 17, was not synchronous among all Gl-treatment groups. The severe diarrhea was frequently accompanied by a slight mucous discharge and occasionally by a discharge of bright red blood, but hemorrhagic diarrhea was not evident. Marked changes in fecal water were not SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 181 CONTROL 100 80 60 pal , GI + Skin , GI + WB , GI + WB + Skin 40] % OF CONTROL 20 0 10 20 30 40 50 60 DAYS AFTER IRRADIATION Fig. 1 Effect of gastrointestinal irradiation on feed consumption by sheep as a percent of feed consumption by control sheep. Feed intake of sheep receiving whole-body (WB) gamma and skin irradiation did not differ from that of control sheep. observed in sheep of the non-Gl-treatment groups during the 3-week period, nor was diarrhea a frequent occurrence among the surviving sheep after 3 to 4 weeks. A marked increase in both water consumption and urine excretion (P < 0.05) was also associated with the severe illness of the Gl-treatment groups (Table 1). The WB-treatment group also showed a less pronounced drop in water intake and urine excreta. However, no significant change in percentage of body water per kilogram of body weight as measured by tritium dilution was observed in a study using many of these animals (unpublished data). An increase in body temperature was frequently observed in sheep of the Gl-treatment groups, but this condition was neither continuous nor consistent. Pyrexia, however, usually was observed prior to death. The changes in body weight during the 10-week period after irradiation are shown in Fig. 3. By the second week all the Gl-treatment groups had lost approximately 20% of their initial body weight; this was probably a reflection of the severe anorexia and diarrhea. The animals receiving the triple insult continued losing weight; in this they differed significantly (P< 0.05) from the 182 SASSER, BELL, AND WEST y_Gl + WB + Skin fa PT hache TP hd = WB + Skin ~ a GI + Skin 10) Yo MOISTURE, Sere Sie elena ee Sea eas) Control 0 5 10 15 20 25 DAYS AFTER IRRADIATION Fig. 2. Effect of irradiation on the moisture content of fecal excreta. Diarrhea occurred only in Gl-irradiated sheep. other Gl-treatment groups by the fifth week. A sharp increase in body weight of the GI, Gl +Skin, and GI + WB groups occurring between days 24 and 35, synchronous with the partial recovery in appetite, was probably a reflection of rumen fill. Skin and Skin + WB irradiated sheep were unable to maintain their body weight on the restricted ration and lost over 10% of their weight by the seventh week. The WB-irradiated and control animals nearly maintained initial weight during this period of feed restriction. During the recovery period of ad libitum 183 SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP LO + CCP 8C + BIV 61+ Te cS + 96h 89 + 9L8 IS ILL v9 + £98 6S + 9L9 6C + LIP ICE VEE EC + OLE Of + 809 1? + 9€9 Oc + L99 LI + Ib9 bce 9s LV EAE EC+ OVE VE + ILE Ob+ STS 8E + $69 Ver SCO OV +995 Le + C6S CVE S8E GE LVe BEF TbY 09+ 219 vS + v08 by + 9LL BE + ECL 8L + 689 , ABp/pur ‘aul p79 OL 81% ¢eT TT OVL 901T qusunean 19jye skeq +8 ¥ 07S LO = VIC SOT # 0SS 99 F 998 98 F 80E +6 + O£6 6£1 F 698 O81 F619 CLE TEL Pel F O8ZI LITE L66 6E1 = Get 801 F 96S CZO FCS? 78 F £87 ZS = ACOA Lel $ 7£6 9ST + £00I LELE OLS COT poy LOI ¥F £46 Cp a7 CZT ELT FOSIT 6£1 F 90TI , A@p/pur $1978 MA tZ 01 61 81 01 ¢T ZI OL ‘10119 PAPpUvIS F Sanjea urop, 8c + CL9 Srl + S88 PST + 8E8 ScI+ £28 6b + TL8 Tet + 089 CVT + CSL £91 + 676 9 01T qudUeIQ Ide SAV UMS + AM + ID aM + ID Uns + 1D uUInS + AM ID urs aM jomu0y QUdUIVIIT, dHHHS AY NOILYYOXA ANTIUN AGNV NOILUWOSNOD YUALVM ATIVG NO SLNAWLVAUL NOILVIGVA SNOTYVA AO SLOFDdAa CLAD 184 SASSER, BELL, AND WEST , Skin + WB , GI + WB , GI + Skin , GI + Skin + WB , Control , WB , Skin % OF INITIAL WEIGHT 0 2 = 6 8 10320 (2 4 6 8 10 WEEKS AFTER IRRADIATION Fig. 3. Effects of irradiation on body weight (expressed as a percentage of the initial weight) of sheep fed a restricted diet for 7 weeks and then fed ad libitum. feeding, all surviving animals gained weight. Survival weight at 40 weeks (Table 2) was significantly (P< 0.05) lower than that of control sheep for all treatments except WB, and the weight gain of GI + Skin and GI + Skin + WB groups was significantly less (P< 0.05) than that of all other treatment groups. Table 2 EFFECT OF GI, WB, AND SKIN IRRADIATION ON SURVIVAL OF SHEEP Initial Survival* ets ce READS meas Treatment weight, kg weight, kg No. Days postirradiation Control 31.3 55.6°t WB (240 R gamma) 31.1 56.5° 1 614 Skin (57,000 rads beta) 31.1 47.5 3 55,4 114, 120 GI (2.4 mCi 9° Y/kg) 32.6 50.5> 3 25, 102.8 1336 WB + Skin 33.1 48.8 2 156, 239 GI + Skin 31.4 36.3° 2 134,§ 1728 GI + WB 30.2 52 7P 4 5,17, 19, 68§ GI + WB + Skin 30.5 37:85 4 20, 30, 47, 61 *Forty weeks postirradiation. tThe values followed by the same letter (a, b, or c) are not different at the 5% level of significance. + Accidental death not attributable to radiation. § Killed following the development of ruminal and/or abomasal fistulae. SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 185 ?°Y Excretion and Dosimetry Fecal ?°Y excretion levels (as a percentage of the total dose) increased rapidly and reached a peak by the third or fourth day (Fig. 4). After feeding of the fallout simulant was discontinued, fecal radioactivity declined with an effective half-time of less than 1 day. Ninety-nine percent of the ?°Y had decayed or had been excreted by 8 to 10 days after feeding. There were no significant differences in excretion among the various Gl-treatment groups. 30 20 e. Gl QO ,GIl+ WB @; Gl + Skin , Gl + WB + Skin 90v IN FECES, % (o>) —_»— 6) 5 10 15 DAYS AFTER IRRADIATION Fig. 4 Fecal excretion of 90V-Jabeled sand (percentage of total dose) fed for three consecutive days. Radiophotoluminescent glass-rod dosimeters were used to estimate the absorbed dose from the ingested fallout simulant in 13 wethers of a similar weight and age.'* The total dose, measured 7 to 10 days after initiation of feeding, was greatest in the fundic region of the abomasum (4.8 to 35 krads), a site of severe radiation damage. However, the doses measured in the affected 186 SASSER, BELL, AND WEST areas of the rumen were only 0.5 to 5.3 krads and were not different from doses measured in the undamaged pyloric region of the abomasum (1.0 to 10.2 krads). This was probably due to the inability of the relatively large dosimeters to measure the dose delivered by the sand particles lodged among the papillae, rather than to a tissue-sensitivity effect. Lethality and Gross Pathology The number of deaths occurring in each treatment group and the number of days between irradiation and death are presented in Table 2. Early deaths occurred only in the Gl-treatment groups, except for an accidental death of a Skin-irradiated sheep. Nearly 50% of the sheep receiving the two treatments involving a combination of GI and WB irradiation died within 60 days, a death rate significantly greater (P< 0.01) than the mortality from any of the other treatments. Of the 24 sheep receiving Skin irradiation either as the only insult or in combination with GI or WB irradiation, six died between weeks 16 and 39. Four additional sheep were in poor condition at 40 weeks, but the remainder of the surviving Skin-irradiated sheep appeared to be healthy. Abomasal prolapse through a hernial ring occurred in five sheep of the Gl-treatment groups 68 to 172 days after treatment (Fig. 5a). In one sheep a small rumen fistula developed about 1 cm cranial to the prepuce 134 days after treatment, and a fistuous tract was seen in a sheep that died 60 days after irradiation. All these sheep were euthanatized due to their terminal condition. The radiation damage to the gastrointestinal tract of the Gl-treatment groups was similar to damage previously reported from ?°Y irradiation alone.® Major gastrointestinal lesions of sheep dying during the early period were usually confined to the ventral and lateral regions of the rumen and to the fundic—pyloric junction and associated laminae of the abomasum. The ventral and lateral regions of the rumen usually contained three to four areas of yellow polyplike fibrino-necrosis, which became friable and detached with time, leaving a smooth, pale, underlying base. By 40 to 60 days, tan or dark-colored scar tissue with a central erosion or necrosis was usually present. The abomasum was characteristically inflamed and edematous, with a large area of hemorrhagic necrosis at the caudal fundus and cephalic pylorus. The laminae were generally inflamed and edematous, and the pylorus was occasionally hyperemic and edematous. Only a slight increase in hemorrhage could be attributed to the added insult of WB irradiation. In several cases there were fibrino-hemorrhagic serosal adhesions of the abomasum and rumen to each other and/or to the abdominal wall. A purulent exudate was usually associated with the adhesions. Damage to the intestines was limited to mild hyperemia and edema of the duodenal mucosa. Although the laminae of the omasum was congested in several sheep, necrosis of this organ was seen in only one sheep. Hydropericardium, dilatated cardiac ventricles, and heavy and edematous lungs were observed in SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 187 these sheep at necropsy. Sheep of the Gl-treatment groups surviving 40 to 52 weeks had residual ruminal and/or abomasal scars when slaughtered, and in many cases the scars contained eroded or necrotic centers as shown in Fig. 5b. The locations of major damage in the gastrointestinal tract in these sheep differ from results predicted from dosimetric studies® in dogs and goats following an ingested dose of soluble ?°v and studies’ in sheep receiving lethal levels of soluble 1**CGe—!*4 € Pr. The passage of sand particles through the rumen and abomasum appears to be independent of that of feed or fluids; thus sedimentation and concentration of these particles in the ventral portion of these organs resulted in significantly greater doses than expected from soluble material. In the intestinal tract the passage of sand in a homogeneous mixture with the less-fluid ingesta prevented settling of the particles and thus reduced the dose to the mucosa of the intestine. Beta irradiaton of the skin produced erythema, cessation of wool growth, moist reaction of plasma exudate, and a gradual formation of a firm crusted mat of the wool during the first 4 to 6 weeks. The wool was easily removed if mechanically disturbed, but in most cases epilation was not complete until 10 to 16 weeks after irradiation (Fig. 6a). Along with epilation was sloughing of the epidermal layer leaving exposed a hemorrhagic necrotic dermal tissue. The healing and repair process was characterized by epithelialization of the periphery (2 to 4cm) of the wound with the sequential development of an ivory horny or leaflike material. The central area of the injury of most sheep was still covered with necrotic tissue or a granulating surface when the sheep were slaughtered (Fig. 6b). The size of the irradiated area had decreased from 43 by 28 cm to approximately 25 by 16 cm. On one sheep retained for extended observation, 6- by 3-cm horny keratinizations about 3 cm thick developed by 62 weeks. Hydropericardium, dilatated cardiac ventricles, and heavy edematous lungs were observed in Skin-irradiated sheep at death. However, milder manifestations of these abnormalities were common among Skin-irradiated sheep killed 40 to 64 weeks after irradiation. The exact mode of death and the relation between the respiratory and cardiac involvement and the irradiation treatment of these sheep are not clear. DISCUSSION These results demonstrate that the additional stress of gastrointestinal irradiation injury from contaminated feed may cause not only a great loss of animal production but also a greater death rate than anticipated from WB irradiation alone. The early deaths were practically all due to WB and GI insults. The whole-body, gamma LDs5o of sheep at the dose rate used in the present study was approximately 200 rads (midline tissue dose).' However, when GI irradiation damage was imposed, the LDso was reduced to 145 rads. With due regard for the limited sample size of this study, this is approximately a 25 to 188 SASSER, BELL, AND WEST te Fig. 5a Mucosal surface of the abomasum of a sheep showing the fistula through which the lamina of the abomasum had prolapsed 14 weeks after the animal received °°Y-labeled sand. Note the congested and hemorrhagic condition of the prolapsed tissue. : P< : ppc ee 2%, : : cae : oe Pes is rs a = : Be eee” a Fig. 5b Residual scar tissue in the rumen of a sheep 14 weeks after it received °°Y-labeled sand. Similar scar tissue existed in all these animals slaughtered at 40 to 64 weeks. Note the necrotic center of the scar tissue. SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 189 “e a8 Fig. 6a The irradiated area (43 by 28 cm) of a sheep’s back 12 weeks after irradiation. Note the area of necrosis and the firm mat of undisturbed wool. Fig. 6b The irradiated area (28 by 17 cm) of a sheep’s back 40 weeks after irradiation. Note the ivory horny or leaflike material at the periphery, the nodular necrotic center, and the marked decrease in size of the irradiated area. 190 SASSER, BELL, AND WEST 30% reduction in the LDs9 from the whole-body gamma-ray dose. The mortality and secondary effects, such as loss of body weight, would certainly be critical to the livestock industry and would be of national importance as far as the food reserve is concerned in an emergency situation. A substantial radiation dose to the gastrointestinal tracts of livestock could result in reduction of meat production and reduced or lost milk production without causing death to the animal. The additional stress of beta irradiation of the skin did not affect survival to a great extent for several months postirradiation. The loss in body weight was statistically significant (P < 0.05), but this might not have occurred if the ration had not been restricted. The large contiguous area of irradiated skin is probably an extreme situation, complete healing being virtually impossible. The fallout injury to the backs of the Alamogordo cattle was not uniform, and areas with minor or no injury probably influenced the healing of more severely affected areas.’ The fact that major injury from skin irradiation was delayed may have allowed partial recovery from WB and GI trauma before the additional stress of skin irradiation was manifest. Thus skin injury from beta burns probably would not contribute significantly to sheep mortaility during the period immediately following a nuclear attack. However, this does not preclude possible effects of skin irradiation on longevity or other physiological mechanisms which can lead eventually to abnormal conditions. Several deaths resulting from secondary effects occurred several months after irradiation. The development of hernias and fistulae would affect the sheep’s longevity but not its value for food. However, accumulation in the meat of soluble fallout material such as }°7 Cs and ?°Sr would be of concern. Most sheep with severely damaged skin could be used for food; few cases of liver abscesses or internal infection were apparent in these animals at death. During summer months vigilance was required in treating the injured skin to prevent severe damage from fly larvae. In winter the loss of heat from the damaged skin would be a problem and could affect the ability of these animals to grow or even to survive. The type of care necessary to prevent animal losses would be practically impossible to provide under range conditions. Nevertheless, in cases of food shortages, these survivors could still be sources of food if slaughtered prior to the ; : 1 onset of serious illness,! ° even though the meat quality and production per animal would probably be reduced. Consideration must be given to the probability of animal exposure at the levels used in the present study. We can assume that a sheep must graze a pasture area of 6.8 m* to equal the daily feed intake of the sheep in this study and that 160 mCi/m? of gross fission products would be present at time H + 24 hr in any area having had an exposure rate of 100 R/hr atH + 1 hr.’ Thus approximately 1100 mCi of fission products could be produced by time H + 24 hr on the area grazed by one sheep during a 24-hr period. The forage would have to retain only 7% of the fallout to produce the activity fed in the present study on day 1. Recent studies of retention of fallout sand indicate values at this level, but SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 191 varying to some degree depending on the particle size, wind conditions, and pasture type and density.'® Because of decay, the fallout arrival time would influence the amount of contamination at a given area, but, with due concern for all the variables involved, the activity fed in this study is considered to be a realistic level. From the estimated exposures of the Alamogordo cattle,° a ratio of skin beta dose to whole-body gamma dose of 240 to 1 was used to determine the skin dose, but recent data indicate a beta-to-gamma ratio on plants of 12 to 1 from venting of underground nuclear devices.’ ? A beta-to-gamma ratio of 10 to 1 was not sufficient to produce the severe effects observed in cattle exposed to beta irradiation.’ This matter is probably not critical for postattack planning purposes, since even the high doses and the large areas of involvement in the present study did not affect animal survival for several months. When predicting the vulnerability of farm livestock to fallout radiation, we must consider the effect of multiple radiation assaults on the survival and productivity of livestock. Many of our underground missile defense systems are located in areas of grazing livestock, and the possibility of surface nuclear attacks raises the question of the vulnerability of the livestock to fallout radiation. ACKNOWLEDGMENTS The UT—AEC Agricultural Research Laboratory is operated by the Tennessee Agricultural Experiment Station for the U.S. Atomic Energy Commission under Contract AT-40-1-GEN-242. This work was supported by funds from the U.S. Office of Civil Defense and is published with the permission of the Dean of the University of Tennessee Agricultural Experiment Station, Knoxville. REFERENCES 1. D. G. Brown, R. G. Cragle, and T. R. Noonan (Eds.), Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, Apr. 29—May 1, 1968, Oak Ridge, Tenn., USAEC Report CONF-680410, UT—AEC Agricultural Research Laboratory, July 12, 1968. 2.D. G. Brown, Clinical Observations on Cattle Exposed to Lethal Doses of Ionizing Radiation, J. Amer, Vet. Med. Ass., 140: 1051—1055 (1962). 3. D. G. Brown, R. A. Reynolds, and D. F. Johnson, Late Effects in Cattle Exposed to Radioactive Fallout, Amer. J. Vet. Res., 27: 1509—1514 (1966). 4.C. F. Tessmer, Radioactive Fallout Effects on Skin. 1. Effects of Radioactive Fallout on Skin of Alamogordo Cattle, Arch, Pathol., 72: 175—190 (1961). 5. R. A. Conrad, The Effects of Fallout Radiation on the Skin, in The Shorter-Term Biological Hazards of a Fallout Field, Dec. 12—14, 1956, Washington, D.C., G. M. Dunning and J. A. Hilcken (Eds.), USAEC Report M-6637, pp. 135-141, U.S. Atomic Energy Commission and the Department of Defense, 1956. 192 SASSER, BELL, AND WEST [Oz 1 it 122 133 14. ibe 16. Wis 18. 19. .M. M. Nold, R. L. Hayes, and C. L. Comar, Internal Radiation Dose Measurements in Live Experimental Animals—II, Health Phys., 4: 86—100 (1960). .M. C. Bell, Airborne Radionuclides and Animals, in Agriculture and the Quality of Our Environment, N.C. Brady (Ed.), pp. 77-90, Symposium No. 85, American Association for the Advancement of Science, Washington, D. C., 1967. .M. C. Bell, L. B. Sasser, J. L. West, and L. Wade, Jr., Effects of Feeding 90V_-T abeled Fallout Simulant to Sheep, Radiat. Res., 43: 71—82 (1970). . H. Baxter, J. A. Drummond, L. G. Stephens-Newsham, and R. G. Randall, Reduction of Mortality in Swine from Combined Total-Body Radiation and Thermal Burns by Streptomycin, Ann. Surg., 137: 450—455 (1953). L. A. George, Jr., P. L. Hackett, and L. K. Bustad, Triple Radiation Assault on Debilitated Lambs, USAEC Report HW-42540, General Electric Company, April 1955. M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to Fallout Radiation. Final Report, USAEC Report TID-24459, UT—AEC Agricultural Research Laboratory, Sept. 7, 1967. J.S. Cheka, E. M. Robinson, L. Wade, Jr., and W. A. Gramly, The UT—AEC Agricultural Research Laboratory Variable Gamma Dose-Rate Facility, Health Phys,, 20: 337—340 CL9OZO): M. C. Bell, Flexible Sealed ?79Sr—?¥Y Sources for Large Area Skin Irradiation, Jnt. J. Appl. Radiat. Isotop., 21: 42—43 (1970). Lo Wade, Jr, «R- Es Hall: LBs Sasser, -andaiM~ C.4Bell-) Radiationm Dose stomthe Gastrointestinal Tract of Sheep Fed an Insoluble Beta-Emitter, Health Phys., 19: 57—59 (1970). Jo “Ls. West, °M. G: ‘Bell, sand’ > Bs Sasser) Pathology. of (Gastrointestinal Mract Beta-Radiation Injury, this volume. J. H. Rust, Report of the National Academy of Sciences Subcommittee for Assessment of Damage to Livestock from Radioactive Fallout, J. Amer. Vet. Med. Ass., 140: Z31—23 900962): National Academy of Sciences—National Research Council, Damage to Livestock from Radioactive Fallout in Event of Nuclear War, Publication 1078, Washington, D.C., Dec: 20-1963" J. E. Johnson and A. I. Lovaas, Deposition and Retention of Simulated Near-In Fallout by Food Crops and Livestock. Technical Progress Report No. 1, Report AD-695683, Colorado State University, May 1969. W. A. Rhoads, R. B. Platt, R. A. Harvey, and E. M. Romney, Ecological and Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and Short-Term Effects on the Vegetation from Close-In Fallout, UsAEC Report PNE-956, EG&G, Inc., Aug. 23, 1968. SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK M. C. BELL, L. B. SASSER, and J. L. WEST UT—AEC Agricultural Research Laboratory, Oak Ridge, Tennessee ABSTRACT Cattle ingesting 9°V Jabeled fallout simulant at the rate of 2 mCi/kg of body weight were more severely affected than those given 57,000 rads beta irradiation to 8% of the dorsal body surface. Whole-body irradiation of 240 R from ©°Co at 1 R/min affected only blood platelets and leukocytes. When these three treatments were combined on eight steers, all died within 54 days. Cattle were more sensitive to simulated-fallout radiation than sheep, but major damage from ingested radioactivity was in the rumen and abomasum of both species. No data were found on combined fallout-simulant effects on simple-stomach animals, but effects are predicted to be less than in ruminants. Sheltering cattle in barns would be the most effective practical measure to increase animal survival and reduce productivity losses in the survivors. Corralling animals to prevent their grazing heavily contaminated pastures would be an alternative where barns are not available. About 80% of the 112 million U.S. cattle are on pasture. In a 4hr roundup time, it is estimated that this percentage could be reduced to 34% by corralling about 43 million cattle and by placing about 31 million in barns. In the event of nuclear war, major farm livestock losses from airbursts would be caused principally by blast and thermal injury, whereas losses from surface bursts would be caused by fallout-radiation injury. Airbursts would be expected to be concentrated on urban areas and would not involve a large number of livestock, but fallout from surface bursts would probably include areas with heavy livestock populations. Grazing livestock would be exposed to gamma radiation to the entire animal, beta radiation to the skin, and beta radiation to the gastrointestinal tract. Most of the gamma exposure would come from ground fallout, but the total exposure would include the gamma component of fallout ingested and also from particles retained on the skin. Early reports’ indicated that beta irradiation was of little consequence in affecting livestock survival and production, but more-recent data show that, 193 194 BELL, SASSER, AND WEST owing to stratification of simulated fallout particles in the gastrointestinal tract, beta irradiation can severely affect survival and productivity of sheep.’** The early reports, based on dosimeter readings in dogs and goats fed soluble TN have recently been reconfirmed by Ekman, Funkgqvist, and Greitz,? who fed goats soluble '>*Sm and '*°La. The purpose of this paper is to ‘report the effects of simulated-fallout radiation on yearling beef calves and to predict the impact of fallout radiation on the livestock industry. EXPERIMENTAL PROCEDURE Sixty-four vearling Hereford steers averaging 184 kg were divided into eight groups and randomly assigned to the treatments listed in Table 1. Bilateral Table 1 RADIATION-TREATMENT EFFECTS ON WEIGHTS AND SURVIVAL OF YEARTING CAGTEE Weights, kg eae poet Sd i alg re de Days after Treatment Initial After 5 weeks No. treatment Control 183.4* £6.9 198.9 + 6.6 0 WB 133 25e= 59 193.5 +6.1 O Skin 186.4 £6.5 193.9+6.2 0 Ei 184.3 4.9 149.4 46.5 3 14, 44, 61 WB + Skin LESSiO ee Oe 7, 189.1£4.2 1 168 GI + Skin 140g = eo 145.144.4 4 25 5367.83 GI + WB 135.54 429 1415p e5 5 LAO RAO: 54 GI + WB + Skin LS325)22°583 13535)=.955 8 Le hOR LON 25) INS, AT) e BreXe Sy! Starved control ly Aly fas ype! SSS <7 asiS 233 O *Mean values + standard error. exposure to whole-body gamma (WB) irradiation of an air dose of 240 R was made at a dose rate of 1 R/min with a °°Co facility.> Whole-body exposure was made 12 to 20hr before the initiation of the other treatments. Exposure of about 8% of the body surface® (Skin) to beta irradiation was accomplished by placing two flexible sealed °° Sr—?° Y sources’ over the thoracolumbar region to sive 57,000 rads_at the surfaceyok the hain ache rmatenon li, stoe2 > mads/mine Gastrointestinal (GI) irradiation was accomplished by feeding 2 mCi of °°v-labeled sand per kilogram of body weight using the previously described procedure.” In addition to these three treatments and all possible combinations SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 195 of treatments, there was a control group and a group whose feed was restricted to that consumed by the GI group. One animal was exposed to each of the treatments at a time with eight replications over a period of 11 months. During a period of adjustment before treatment and for 5 weeks thereafter, the cattle were kept in individual stalls” for separation and collection of urine and feces. During this time they were daily fed 2.7 kg of alfalfa pellets moistened with 0.8 kg of water. The ?° Y-labeled sand was mixed with the moistened alfalfa for each animal for three consecutive days. The ’°Y averaged 9.4 mCi/g of sand (88 to 175 wu) at the time of feeding. Steers weighing 184 kg were fed 368 mCi of °°v in 39g of sand on day 1; this quantity had decayed to 284 mCi by day 2 and to 219 mCi by day 3. Control animals were fed the same quantity of nonradioactive sand for each of the 3 days. Feed intake, body temperature, and signs of radiation injury were recorded daily. After 5 weeks of close observation in the collection stalls, the steers were grouped together by trial in large pens with shelter, access to limited pasture, and free access to grass hay, water, and trace-mineralized salt. In addition, they were fed enough 15%-protein grain mixture to provide a growth rate of about 0.4 kg daily for the control animals. Body weights and general recovery were observed periodically for 40 weeks after treatment. In addition to these treatment groups, four yearling Hereford steers of comparable size and origin were implanted with glass-rod dosimeters into several segments of the gastrointestinal tract by a previously described procedure.’ After 3 weeks they were fed 2 mCi’ °Y sand for 3 days. They were subjected to necropsy 13 days later, and the recovered dosimeters were read. Necropsy examinations were performed on all dead animals, and specimens of selected tissues were photographed and then preserved in 10% formalin for histological examination. RESULTS Table 1 shows that deaths occurred only in treatment groups including GI irradiation, with the exception of one steer that died 168 days after WB and Skin irradiation. Of the 20 deaths, 17 occurred within 60 days after treatment, and only 7 of the 17 occurred within 30 days. From these data it appears more reasonable to use LDso/69 than LDso/39 for grazing cattle exposed to combina- tions of fallout exposures. Most of the early deaths were associated with combinations of GI and WB exposures with the resulting hemorrhagic necrotic involvement. Damage in the four major ‘‘pockets” of the rumen was more extensive than was observed in sheep. The rumen floor contained large fibrinous masses. In addition, sections of the ventral reticular honeycombs of most of the cattle were filled with a rubbery, yellow, glandular-appearing material. Minor fibrinous necrotic areas were seen in the omasum of most of the steers. Major areas of hemorrhagic necrosis were surrounded by edematous hyperemic laminae in the abomasum of 196 BELL, SASSER, AND WEST all cattle fed 7° Y. Adhesions among the rumen, abomasum, and reticulum were frequent, and some involved a mass of gelatinous serosal exudate. Gross lesions in the large intestine were restricted to minor areas in the cecum and colon of a few steers fed ?°Y sand. Several animals showed degenerative changes in the heart. Necropsy results are given in more detail in an accompanying paper. ° Data summarized in Table 1 also show that the combinations of radiation sources were more detrimental than single exposures not only to survival but also to body weight of the animals at 5 weeks after exposure. No animals given the combined GI + Skin + WB irradiation treatments survived longer than 54 days. At 35 days the three surviving steers had lost an average of 48 kg, which was the greatest loss by any treatment group. Only the “starved” control steers and the steers fed ?°Y sand lost weight. Although feed intake by the starved controls was restricted to that of the Gl-treated steers, the Gl-treated steers lost 25% of body weight, while the starved controls lost 9% and the normal controls gained 8%. The excess weight loss by the Gl-treated steers was probably due to pyrexia and mild-to-severe diarrhea. The depression in feed intake by the Gl-treated steers was dramatic, but only minor differences were noted among the four groups fed °° Y sand (these data are pooled in Fig. 1). After 9 days, feed intake averaged less than 5% of the controls for the remainder of the 28-day period of observation. Comparable data on sheep, also shown in Fig. 1, indicate that depression of feed intake occurred later and that appreciable recovery was evident by day 28. Feed consumption by cattle and sheep receiving WB, Skin, and WB + Skin treatments was not different from the untreated control animals for each respective species. Since all cattle were group fed after 28 days of individual feeding, no feed data are available on the treatment groups after that time. Observations on the surviving cattle are incomplete at this writing, but the 40 weeks of observations O—O , Sheep e—e, Cattle % OF CONTROL DAYS AFTER IRRADIATION Fig. 1 Feed consumption by sheep and cattle fed 2°V-labeled fallout simulant. Feed consumed by WB- and Skin-irradiated animals was the same as that consumed by controls. SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 197 are complete on four of the eight replications. During this period the average kilograms of weight gained per surviving animal for each treatment group were: control, 118; WB, 131; Skin, 66; GI, 48; Skin + WB, 58; GI + WB, 36; and GI + Skin, 22. None of the animals receiving GI + WB + Skin treatment survived beyond 54days (Table 1). These data show that Gl-treated survivors had regained much of the weight lost in the first 28 days (Table 1). Body temperature was not significantly different among the controls, WB, Skin, and WB + Skin treatment groups for the 25-day postexposure period. All cattle fed ?°Y-labeled sand showed elevated body temperature, which persisted longer in those with combined GI and WB irradiation. The starved control group showed a drop in body temperature, indicating a lowered metabolic rate (Hable 25). Except for the larger exposure area, the skin irradiation changes developed similarly to those described by George and Bustad.'' A moist reaction developed during the first 3 weeks, with crusted plasma and epilation in 8 to 12 weeks, followed by a hemorrhagic necrosis. Whole-body gamma irradiation of 240 R at 1 R/min alone did not give the characteristic visible signs of radiation sickness. These animals did show the depression of white blood cells and platelets. All steers fed ?° Y-labeled sand had mild-to-severe watery diarrhea. The onset of diarrhea varied from 6 to 15 days after initiation of the °° Y feeding. In about half of the animals, this was followed by regurgitation of feed and water. Also about half of the animals were audibly grinding their teeth constantly. The loss of body fluids from diarrhea and vomiting probably contributed to the death of many of these animals. DISCUSSION General The results of these investigations on simulated-fallout-radiation effects on beef cattle are similar to the data obtained on sheep.” Nevertheless, there were differences in response between the two species which would prevent the exclusive use of sheep as models for beef cattle. Both species are grazing ruminants with many similar physiological functions, but they differ in size and grazing habits. These data clearly demonstrate that cattle exposed to simulated-fallout grazing conditions were so severely affected by the combination of treatments that there were no survivors at nonlethal levels of WB exposure where no physical signs of radiation sickness were seen from WB exposure alone. Skin Exposures No deaths occurred from Skin exposure alone, but, in combination with other treatments, Skin exposure apparently contributed to increased mortality BELL, SASSER, AND WEST 198 C10 318-001 C036" EOT COR C-SOT ZOO TOl Ox 9 101 JO Fi COl C2029 TOT CO SapeOT C0326 TOT St 91 TZ rit Overy (5) KO) 70 F O'+OT 7.0 3b vOr C20 avCOl C0 cos GOs COL COT OLCOT G20 CON TOF OTOT O07 91 OT Z'0 F 6'00T £0 =F O'FOI EOF b'bOl iO ce SOL CO IGICOl LO 0°20! O22, LOT CO 101 TeOl-ce AeOT ST OV TE “IOIII PIBPUPIS a dinqyeisdurdy MIYUSIYR YY UBIO y Os. LOT 7OFOTOT (6(6) S aalctiy GOT Cop GOEL CO C0: VO TOF TC EOL C0 0120" EOE OF EO) EO 6sl ON Ore Ol GOzS TOL eO=eLe Lor C027 TOL C0 =.0' COT (Gy LcOv TOFS IOI «6 TOI OT aa ¢ OT uoHeipea ase sAvq SLNAWLVAUL NOILVIGVY OL GASOdxXH JOAIUOD PIYATBIS US + aM + ID aM + TD ulys + ID UINS + €M Uly}S aM joauO’ JUIUNPII YT, HILLVO dO aaNLVUadWAL AGO” ¢ AGF L SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 199 rates» Although the flexible; «sealed “sources exposed rectangular areas of 28 by 43 cm fairly uniformly, these areas resembled the beta-damaged areas on the Alamogordo cows.'* damaged area by the end of 40 weeks of observation. No data are available on Healing around the edges reduced the severely the dimensions of the original damaged areas of the cattle exposed in 1945, but in 1950 hyperkeratosis was evident from the anterior withers to the tail head and extended up to about 23 cm laterally from the midline of one of these cattle. Some areas of extensive hyperkeratotic plaques and horns measured on the preserved hide taken from the same cow in 1960 were 13 by 10 cm with an elevation of about 2 cm over most of this surface. The skin exposure of the Alamogordo cattle was not uniform, but apparently some of these areas could have originally been as large and the damage as extensive as those seen on our cattle from the exposed rectangular areas of 28 by 43 cm. Some healing and tissue repair is already evident in the Skin-irradiated areas on the cattle, but the extensive hyperkeratosis has not developed in those exposed in July 1969. A few areas of moderate hyperkeratosis and scaling have developed. Frequent insecticide spraying was required to reduce the fly problem on the skin-damaged areas during warm weather. Since these cattle had free access to shelter and shade, exposure to weather extremes was considerably reduced. Animals in other areas of the United States could be exposed to greater climatic extremes, and many would have much less protection. The loss of the dorsal hair coat covering 8% of the body surface would be expected not only to increase thermal losses but also to increase nutrient requirements for tissue repair. This is evident by the limited data showing that the Control steers gained 52 kg more than the Skin-irradiated steers during the 40 weeks of observation. GI Exposure Feeding steers 2 mCi of ?°Y sand per kilogram of body weight was more detrimental than feeding 2.4 mCi/kg to sheep. This was reflected in greater reduction of feed consumption, increased mortality, and increased organ damage. The reduction in feed intake was accompanied by a more severe diarrhea, vomiting, and grinding of teeth. Fallout-simulant feeding was calcu- lated to represent a 9% forage retention with the calculation procedure described previously.’ Since this corresponds closely to the level of 7% calculated for sheep,” the results were expected to be quite similar. Possibly cattle are more sensitive to GI beta irradiation, or perhaps the larger accumulation of ?°v-Jabeled sand in the damaged areas produced a greater exposure. Dosimetry data are incomplete, but preliminary data indicate that the rumen exposure was greater than that observed in sheep.’ The long-term effects of GI exposure in cattle survivors appear to be less than in sheep. None of the surviving cattle developed rumen fistulae or abomasal hernia and prolapse, but six sheep fed ?°Y sand developed these sequelae. The greater thickness of cattle tissue probably reduced the eventual extent of 200 BELL, SASSER, AND WEST injurious effects on tissues adjacent to the primary site of injury, and no adhesions were found between affected organs and the abdominal wall. These data show that feeding a particulate fallout simulant of size and density similar to early fallout produces results quite different from using ; 4, soluble fallout simulants.*’!°? Early fallout particles would be expected to collect in pockets in the gastrointestinal tract of ruminants as shown in this and ee aon similar studies. WB Exposure No cattle died from exposure to 240 R at 1 R/min unless this treatment was used in combination with other radiation exposures. Except for depressed white blood cells and blood platelets, none of these steers showed the depressed appetite and other symptoms of radiation sickness described by Brown.’ 4 Brown established an Ldso/39 of 543 R in a study of 70 adult female Hereford cattle exposed to 450 to 700 R at 0.9 R/min; about 10% of the cattle exposed to 450 R were lost. More-recent unpublished data-from the same laboratory show a loss of five of 120 Hereford heifers exposed to 300 R at 0.7 R/min and no losses from 200 R exposure. None of these deaths occurred during the second 30 days after exposure, but four of the eight deaths from a combination of WB + GI + Skin exposures were observed in the first 30 days and the other four during the second 30-day period. Animals surviving the WB component of fallout exposure of 240 R alone would be expected to produce almost as well as nonirradiated animals. During the 40 weeks of observation, the weight gain of the four WB-irradiated cattle averaged 131kg, while the controls gained 118 kg. Data on other animals indicate life-shortening WB-irradiation effects, but, when aged cattle cease producing or production becomes uneconomical, they are normally culled and replaced by young breeding stock. Combined Effects Although no cattle died at a WB exposure of 240 R and all died from a combination of WB + GI + Skin, there are no data available for cattle on what might be expected from a different forage-retention level or from other combinations of exposures. It would be prohibitively expensive to obtain data on all possible combinations, but the need for more data is clearly indicated, and threshold lethality levels should be determined. These data show that combina- tions of two or more radiation injuries are lethal to a greater percentage of animals and severely affect productivity of survivors. Whole-body exposures affect the bone marrow as the most sensitive target system, and beta exposure to the skin and gastrointestinal tract affects the local tissue primarily, but abscopal effects are also observed on mineral metabolism.” Whole-body gamma radiation from °°Co is reduced by 50% in about 18 cm of unit-density tissue, whereas SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 201 beta penetration from °° Y is reduced by 50% by a thickness of only 1 mm of unit-density tissue. IMPLICATIONS Livestock Inventories Since the 1967 report on livestock and postattack recovery,’ * the inventory and productivity of the major classes of livestock have increased. Cattle number above 112 million and supply over 50 kg of meat and over 150 kg of dairy products per person in the United States annually. Production and consumption of pork and poultry products have also increased, With the increase in the livestock inventories, the estimated market value for cattle alone has now increased to over $20 billion. This is indeed a food reserve worth evaluating in terms of reliable vulnerability estimates for fallout effects on survival and production of these animals. Cattle can produce highly nutritious food when fed products not usable for human consumption. However, if 90% of the breeding cattle were lost, about 11 years would be required to replenish the inventory of breeding animals;'” this further emphasizes the need to consider vulnerability and protective measures. In contrast, the inventory of poultry and swine is small; about 1 year is required to replenish a 90% loss of breeding stock.'° In even greater contrast is the radiation resistance and small inventory of seed grains required to resume normal production of food crops. These food crops are sensitive to fallout radiation only during the growing season, but livestock are sensitive at all seasons of the year. The importance of livestock production in helping to improve world protein supplies has been reemphasized by Director General Boerma of the Food and Agriculture Organization of the United Nations in a new “Indicative World Plan.”’ In the short run, he recommended that swine and poultry production be increased and that in the more distant future ruminant livestock inventories be built up to provide more meat and milk. Recommendations were made also to simultaneously increase production of cereals and crop products in the developing nations.’ ® Loss Predictions In estimating survival of livestock populations in a nuclear war, most builders of damage-assessment models have used gamma radiation as the only criterion. Some estimate that, under the same conditions, half the human deaths will result from causes other than gamma irradiation. Soft targets, such as major cities, would probably get mostly airbursts, which would cause many thermal and blast fatalities among the population. Hard targets would be expected to be hit by surface bursts, which increase the fallout fatalities. Livestock are widely dispersed and would be affected mostly by fallout from surface bursts. Nevertheless, some losses would occur around population centers. In 1969 the 202 BELL, SASSER, AND WEST livestock yards in Chicago, IIl., handled 1.1 million cattle and 1 million hogs; those in Omaha, Nebr., handled 1.5 million cattle and 1.8 million hogs.’ 7 Although marketing is being decentralized, many livestock are in transit through large population centers in addition to those destined for slaughter. The limited data available in this and the preceding paper® show definitely that, regardless of the conclusions based on dosimeter readings in animals fed soluble radioisotopes, grazing livestock losses from fallout radiation would not be limited to gamma irradiation alone. The 1970 Swedish paper* based on dosimeter readings in goats given a solution of '>*Sm and '*°La neglects the physical characteristic of fallout particles in combination with the physiological functions of the ruminant gastrointestinal tract. Fallout particles from a surface nuclear burst deposited downwind on forage in an area where the gamma exposure would be above 200 R would be expected to collect in “pockets” in the rumen and abomasum owing to the strong muscular movements of the different compartments of these organs. This has been demonstrated not only by recovery of sand particles but also by observation of damaged areas and by dosimetry measurements. Radiation irritation to the colon would be expected to reduce the further beta exposure by increasing the rate of passage and by reducing water reabsorption in the lower large intestine. The reports from dosimeter readings in dogs and goats*’'? are from levels of soluble isotopes which showed minor to no physiological responses. Soluble isotopes would be expected to adsorb to feed particles and move in a homogeneous mixture with the ingesta. Early fallout levels apt to affect livestock survival would not be expected to have a solubility above 10%, but radiations from '*?Sm and '*°La appear to be characteristic of beta and gamma-ray emissions of mixed fission products. For animal research the gamma radiation from '°*Sm and miaalea would increase the hazard to personnel using these isotopes to label fallout- simulant sand particles, but the beta energy would be more characteristic of early fallout than that from °° Y used in most other studies. Data available on grazing livestock indicate that cattle are the most sensitive species to combinations of fallout exposures. Therefore damage-assessment estimates should concentrate on cattle since they supply more food products and require more time to replenish breeding stock than any other U. S. food source. Since there were no losses of cattle exposed to 240 R of gamma radiation but there was 100% loss of those exposed to 240 R of WB + GI + Skin irradiation, it is difficult to estimate the LDso9 gamma exposure when combined with the beta exposure. Based on the limited data available, very rough estimates of LDs50/69 exposures for livestock in barns and corrals or pens and for those grazing heavily contaminated pastures are presented in Table 3. Data on sheep represent a 7% forage retention of fallout with the combined effects being lethal to four of eight animals;° data on cattle are for 9% forage retention with a loss of eight out of eight exposed animals. Apparently differences between these species are greater than can be accounted for by forage-retention differences. No data are available on cattle consuming forage at SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 203 Table 3 ESTIMATED LIVESTOCK LETHALIT Y (LDs0/60) FROM FALLOUT-GAMMA-RADIATION EXPOSURE ALONE AND IN COMBINATION WITH BETA RADIATION LDs0/60, total gamma exposure, R Barn Pen or corral Pasture * (WB) (WB + Skin) (WB + Skin + GI) Cattle 500 450 180 Sheep 400 350 240 Swine 640 600t 550t Equine 670 600T 350tT Poultry 900 850T 800T *Assumed forage retention of 7 to 9%, tNo data available. the extremes of 5 to 25% forage retention reported by the Colorado workers’ ® using 88- to 175-u sand. Also, no data are available on the effects of smaller radioactive fallout-simulant particles on the gastrointestinal tract of sheep or cattle. Estimates in Table 3 on combined effects on swine, equine, and poultry were obtained, not from research results, but from estimates based on grazing habits and on gastrointestinal anatomical and physiological functions of these species. To determine the number of animals which might be exposed, we can make assumptions on the different management practices for the classes of livestock within each species. A very rough estimate has been made of the normal numbers of the 112 million cattle expected to be on pasture, in penned or corralled areas, and in shelters (Table 4). The 4-hr roundup time does not imply that livestock producers would neglect other emergency procedures to protect livestock, but only what might be done in 4 hr to help protect cattle. Removal from pasture offers the greatest protection to grazing livestock, as shown in Table 3. Pastured dairy cows are normally near the milking parlors and would be much easier to confine than other cattle. Milk cows and some calves creep-fed on pasture would get supplemental grain, and thus their intake of radioactive fallout would be diluted, but almost all other grazing cattle would depend entirely on pasture forages and mineral supplements. It would be futile to attempt to corral animals in the large range cattle operations in a short time, and 4 hr is insufficient time for many range operations. The operators of small family farms, which are typical of most of Tennessee farms, would be able to confine cattle in a short time. For this reason the surveys by Griffin’? are more optimistic than the data presented in Table 4. His pilot survey covered 176 farms in Tennessee, but no data were found for the entire United States. Again it should be emphasized that the greatest reduction in the number of lethalities can 204 BELL, SASSER, AND WEST Table 4 ESTIMATED NUMBERS OF U.S. CATTLE SHELTERED OR CORRALLED INITIALLY AND AFTERA 4-HR ROUNDUP EFFORT Number in millions Milk Feedlot Other cows cattle cattle Total Shelter No warning 3 found the highest beta concentration in aah : z 5 140 the terminal colon of adult goats treated with a mixture of 3Sm and ae 208 PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 209 The omasum was the organ severely damaged in the majority of sheep orally treated with soluble '**Ce—'**Pr; injury to the rumen was found in only one animal. No changes were observed in the large intestines at levels that were lethal to about 25% of the sheep.® Plutonium microspheres in gelatin capsules administered to miniature swine by stomach tube produced macroscopic necrotic and inflammatory areas in the lymphoid tissue at the ileo—cecal junction. Focal microscopic changes were detected throughout the small intestine.’ Clark reported that insoluble °°Sr administered orally to pigs produced areas of damage in the ileum, cecum, and colon but that the principal lesions occurred in the stomach (see discussion of Ref. 7). The paucity of information regarding the effects in ruminants resulting from the ingestion of radioactive fallout products and the necessity of these data for arriving at a more realistic evaluation of the results of a nuclear detonation prompted this study. EXPERIMENTAL PROCEDURE The experimental design for these studies has been previously described.” 1! Of the experimental animals, 63 yearling wether lambs of mixed breeding, including 8 untreated controls, and 17 treated yearling Hereford steers were subjected to necropsy. Procedures involving the preparation and feeding of °° v-Jabeled sand were previously reported.’ Skin of the dorsal thoracolumbar region was beta irradiated by the method described by Bell’? to expose about 8 and 12% of the body surfaces of steers and sheep, respectively. An estimated 57,000 rads was delivered to the exposed skin area in a 3-day period. In animals subjected to bilateral whole-body irradiation, an exposure of 240 R from °° Co sources was delivered at 1 R/min. The number of sheep examined and the treatments were: 38 sheep fed 1.0 to 4.0 mCi of ?° Y-labeled sand per kilogram of body weight for 1 to 3 consecutive days; 7 sheep fed ?° Y-labeled sand and exposed to skin irradiation; 3 sheep fed ’° Y-labeled sand and exposed to whole-body irradiation; and 7 sheep subjected to a combination of the three treatments. Steers were similarly treated: 3 steers fed ’° Y-labeled sand at the rate of 2.0 mCi per kilogram of body weight for 3 consecutive days; 3 steers fed °° v-labeled sand and exposed to skin irradiation; 4 steers fed ’° Y-labeled sand and exposed to whole-body irradiation; and 7 steers subjected to the combined treatments. Most of the animals were examined in extremis or promptly after death. Some animals were destroyed and examined several months posttreatment (PT). The day of postmortem examination indicates the time period between final treatment and examination; e.g., day 2 indicates that the animal was examined 48 hr after the last dose of ?° Y. Representative blocks of tissues were fixed in 10% buffered formalin, dehydrated in alcohol, mounted in paraffin, sectioned at 6m, and routinely stained with hematoxylin and eosin or special staining procedures if conditions indicated. 210 WEST, BELL, AND SASSER RESULTS General In both ovine and bovine species, the most extensive pathologic changes occurred in the floor of the caudal half of the ventral ruminal sac (VRS). Frequently involvement of the VRS and posterior ventral blind sac (PVBS) was continuous. Changes in decreasing severity and extent were present in the anterior ventral blind sac (AVBS), the PVBS, and the posterior dorsal blind sac (PDBS) of the rumen. Frequently groups of papillae 2 to 5 cm in diameter in the vicinity of necrotic lesions were “‘matted”’ together or coalesced and were dull reddish gray and rather firm. Other individual papillae were enlarged and deep red, and the apexes were shrunken and hard. The posterior wall and/or the floor of the reticulum was principally affected in cattle but was seldom affected in sheep. Omasal alterations were minor and involved the ventral or free aspects of the major laminae, usually adjacent to the reticulo—omasal orifice. In the abomasum the greater curvature of the caudal fundus and adjacent pylorus were the predominant sites of injury. Frequently the involvement extended for variable distances anteriorly between two or more fundic spiral folds. The mucosa was edematous, hyperemic, and frequently studded with petechial and ecchymotic hemorrhages. Spiral folds surrounding ulcers often had sloughed. Subserous hemorrhages and gelatinous infiltration occurred frequently, espe- cially over mucosal lesions. Fibrinous and fibrous adhesions were commonly observed between organs and/or the abdominal floor. The entire thickness of the walls of the rumen, reticulum, and abomasum was affected in moderately severe and severe lesions. Sheep The severity of lesions was variable; usually lesions produced were proportional to the amount of radionuclide fed. The usual biologic variation, however, was observed.” >"! 3 Oral Treatment No lesions were detected in sheep examined at days 0, 1, and 2. An ovoid, tan, elevated, necrotic plaque (3 by 4cm) with several polypoidlike nodules around the periphery was observed in the VRS on day 3. Five smaller, soft, fluctuating, tan, polypoidlike nodules were in the floor of the PVBS. Similar ruminal changes were observed on day 5, and a few small hematomas involved two omasal laminae. Similar and somewhat more extensive changes were found in all ruminal compartments on day 6. A small tan nodule was observed in the reticulum. A few superficial erosions and ecchymotic hemorrhages were seen on a few omasal laminae. The abomasal mucosa was hyperemic, with a few lineal hemorrhages on the free borders of a few fundic spiral folds. An area of PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 211 hemorrhagic necrosis (3 by 4 cm) with a fibrinous exudate was observed in the caudal fundus. Ruminal changes were similar but more extensive by day 7, but the reticulum and omasum were unchanged. A large area of hemorrhagic necrosis involved the abomasum. On day 9 more extensive but similar ruminal involve- ment and a few yellowish nodules in the reticulum were observed. A few major omasal laminae had superficial linear erosions and a few adherent yellowish nodules. Abomasal changes were somewhat less severe than on day 7. Similar but less extensive ruminal changes were observed on days 10 and 11. The reticulum and omasum were not affected. The abomasal mucosa and submucosa were markedly edematous and hyperemic with a small area (1 by 1.5 cm) of hemorrhagic necrosis. Ruminal changes on day 13 were similar to those observed on day 9, and there were no alterations in the reticulum and omasum. The abomasal mucosa was slightly hyperemic and edematous. A Y-shaped, partially healed scar with scattered necrotic tags was observed in the AVBS on day 17. Fibrino-necrotic plaques in the other compartments were detaching at the edges or “rolling up”, exposing granular hemorrhagic bases. Similar changes were seen on day 18, but the surface exposed by the detaching, friable, necrotic plaques was pale and smooth. Similar ruminal changes were observed on day 21. An elliptical area of hemorrhagic necrosis in the abomasum was covered with a mottled, reddish-tan, fibrino-necrotic exudate. There was a moderate amount of sanguineous fluid and of clear, yellowish fluid in the abdominal and thoracic cavities, respectively. The lungs were expanded, heavy, reddish gray in color, and edematous. Stellate bluish scars with scattered necrotic tags were seen in ruminal compartments on day 57. The caudal fundus and cephalic pylorus of the abomasum over an area measuring 7 by 10cm were firmly adherent to the abdominal wall by dense fibrous tissue. An ulcer 4 cm in diameter extended almost to the skin. The skin overlying this area was cyanotic and rather firm. Sheeps examined, one days 72.5298) 7307, 344. 365, and, 372 had stellate, grayish-white, ruminal and abomasal scars. Several scars were studded with variable-sized superficial erosions. The mucosa of the proximal duodenum was frequently congested and edematous. Changes in other portions of the intestines were insignificant. Severe Complications One sheep developed a ruminal fistula on day 132. A thick-walled, fistulous tract 3.5 cm in length and 1.5 by 2.5 cm in diameter extended from the anterior aspect of the posterior pillar of the VRS to the exterior, emerging about 1.3 cm anterior to the prepuce. The pillar was eroded. A deep ulcer surrounded by dense fibrous tissue was found in the adjacent PVBS. The rumen in this area was firmly adherent to the abdominal wall by fibrous connective tissue. A soft, fluctuating, epilated, pendulous enlargement (4 by 6.5 cm) anterior and sagittal to the prepuce was observed in a sheep on day 66. The hernial sac 212 WEST, BELL, AND SASSER contained 5.5 by 6cm of the caudal abomasal fundus. The abomasum was firmly attached to the hernial ring and a dirty yellow necrotic exudate covered the mucosa of the herniated tissue. A scar (3 cm) extended into the pylorus from the diverticulum. Eversion-type abomasal prolapse developed in three sheep on days 81, 169, and 201. A similar lesion developed on day 171 ina sheep that received combined oral and skin-plaque treatment. Since the caudal fundus was firmly adherent to the hernial ring by dense fibrous tissue, the cephalic pylorus constituted the major part of the prolapsed tissue. The prolapsed tissue was hyperemic, markedly edematous, and studded with superficial necrotic focl. Oral and Skin-Plaque Treatment Combined oral and skin-plaque treatment did not appear to influence significantly the extent of stomach changes; however, these animals were examined 171,176; 315,350) 4393-and 447 days Pie -lerissob interest: to; nore that the pericardial fluid was increased in these animals. Myocardial atony and dilated, thin-walled ventricles were associated with this finding. Oral and Whole-Body Treatment Three sheep exposed to combined oral and whole-body irradiation were examined 2, 15, and 365 days PT. The exudate of the ruminal lesions of the animal examined on day 15 was blood stained. A large area of hemorraghic necrosis involved the abomasum (Fig. 1). Oral, Whole-Body, and Skin-Plaque Treatment Ruminal lesions of a sheep examined on day 19 following combined oral, whole-body, and skin-plaque irradiation were not increased in size, but the exudate contained a significant admixture of blood (Fig. 2). Three fistulous tracts originating from ruminal scars were found in a sheep examined on day 58. These tracts were surrounded by dense, reactive, fibrous tissue. Ruminal scars with superficial erosions were present in a sheep examined 419 days PT. Steers Oral Treatment Steers fed ?° Y-labeled sand were examined 13, 42, and 59 days PT. The pharyngeal mucosa of one steer was moderately congested and edematous (day 13). Ruminal changes were grossly similar to those in sheep. These changes consisted of elevated, yellowish to yellowish-green, necrotic plaques frequently accompanied by polypoidlike masses of similar composition. Detachment of the friable necrotic exudate at the borders exposed a roughened, hemorrhagic surface (day 42). The necrotic plaques measured up to 12 by 21 cm and involved aoe 4 & 6 7 6 510) 2 34 5S 6 or 8 2 2 sas ge 213 ES ERS SSS: Sa sae Cees S : & ; Fig. 1 Abomasum of sheep 41, 15 days after oral and whole-body irradiation. A 5.5- by 11-cm area of hemorrhagic necrosis involving the fundic—pyloric region. Spiral folds in the necrotic area have sloughed. The mucosa and submucosa of the entire organ is hyperemic, edematous, and _ focally hemorrhagic. Fig. 2. Rumen and reticulum of sheep 10, 19 days after oral, whole-body, and skin-plaque irradiation. Rumen PDBS (left) fibrino-necrotic plaque; PVBS (lower left) fibrino-hemorrhagic-necrotic plaque; VRS (below) large fibrino- hemorrhagic-necrotic plaque; and AVBS (right) large area of fibrino-necrosis with a large hemorrhagic ulcer in the center. Reticulum (right) is normal. 214 WEST, BELL, AND SASSER the entire thickness of the wall. Gelatinous exudation, hemorrhage, and fibrinous or fibrous adhesions to adjacent organs (or less frequently to the abdominal wall) were seen. A tortuous, thick-walled, fistulous tract extended from the postero-medial floor of the VRS to the medial wall of the abomasum (day 59). Variable-sized scars partially.covered with necrotic exudate were seen in the ruminal compartments. An area of necrosis (5 by 7 cm) was observed in the reticulum (day 13). A scar (1.5 by 17 cm) studded with small superficial erosions was observed on day 42. Omasal changes were limited to focal congestion of a few major laminae. An area of hemorrhagic necrosis (5 by 8 cm) involved the cephalic pylorus of the abomasum of one steer. The necrotic process had extended into the submucosa of the contiguous fundus (day 13). A tear-shaped scar (5 by 21cm) with scattered necrotic tags was observed (day 42). The communicating fistulous tract (day 59) from the rumen entered the medial aspect of the terminal abomasal fundus. The spiral folds surrounding the tract had sloughed. A healed scar (3 by 7 cm) was seen in the caudal fundus. The surrounding mucosa was edematous and dirty brownish red in color. Scattered areas of congestion were observed. in the mucosa of the small intestine. A thickened area consisting of numerous nodules up to 1.5 cm in diameter was observed at the ceco—colic junction. The centers of some of the nodules contained yellow, necrotic plugs (day 42). The ileal and colic mucosae (and possibly the submucosa) of one steer were dull grayish red in color and appreciably thickened by transverse ridges (day 59). An estimated 16 liters of sanguineous ascitic fluid containing yellowish fibrinous aggregates was seen in the steer examined on day 13. Fibrinous tags were adherent to the parietal and visceral peritoneum. Three liters of clear ascitic fluid was present in the steer examined on day 42. Oral and Skin-Plaque Treatment Ruminal changes were comparable to those in the previous group (days 20 and 51). Superficial erosions studded the scars of the animal examined on day 300. Depressed stellate scars (2 by 8 cm and 1.5 by 16 cm) were observed in the reticulum (days 20, 51, and 300). Linear erosions and small yellowish nodules of necrotic exudate were observed on some major omasal laminae (day 20). Variable-sized scars (12 to 21 by 2 to 4cm) were observed in the wall of the greater curvature of the abomasum (days 20 and 51). The scars extended for several centimeters between five laminae (day 20). The surfaces of the scars were partially covered with yellowish-green necrotic exudate. There was a stellate scar (2 by 12 cm) in the caudal fundus and a second scar (1 by 11 cm) in the cephalic pylorus of the abomasum of the steer examined on day 300. Intestinal changes were comparable to those in the previous group. Oral and Whole-Body Treatment Elevated, linear and ovoid, dull gray, superficial erosions studded the mucosa of the thoracic portion of the esophagus of steers examined on days 17 and 37. PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY Z15 Ruminal involvement was of increased extent and severity, some plaques measuring’, 2-5) by (25 .7by 30:cm. In addition to: ‘the thick, yellowish or yellowish-green, friable plaques with polypoid masses (Fig. 3), there were elevated, yellowish areas covered with enlargea, sparse papillae. Some necrotic plaques (up to 5 by 12 by 14cm) had completely detached and exposed a hemorrhagic granular surface. Necrosis of the reticulum was increased in extent and severity and consisted of large yellow or yellowish-green plaques and areas of hemorrhagic necrosis with sparse necrotic exudate (Fig. 3). Small linear erosions and focal, yellowish, necrotic plaques were observed on a few major omasal laminae in three steers. Abomasal changes were comparable to those in the previous group, the alterations consisting of large areas of hemorrhagic necrosis (Fig. 4) partially covered with yellowish, necrotic exudate (days 12, 15, and 17). The fundic spiral folds were moderately to markedly edematous with scattered ecchymotic hemorrhages. Deep erosions or ulcers occurred between several spiral folds. A scar with a hemorrhagic base was partially covered with cream-colored, necrotic exudate (day 37). The overlying serosa was congested, roughened, and covered with fibrino-hemorrhagic tags. The duodenal mucosa was congested and edematous with small irregular and linear hemorrhages. Several gray and hemorrhagic nodules 4 to 5 mm in diameter had developed in the mucosae of the lower jejunum, ileum, and the midportion of the cecum (day 37). Oral, Whole-Body, and Skin-Plaque Treatment Superficial, grayish-red, linear streaks were observed in the esophageal mucosa (day 12). Changes in the rumen and reticulum were comparable to those in the preceding group. Omasal changes were similar but more extensive, consisting of linear erosions and hemorrhagic necrosis with necrotic exudate. The cavity of the omasum of one steer (day 17) was completely filled with a currant-jelly type of blood clot. There were areas of hemorrhagic necrosis (up to 8 by 28cm) in the abomasum. The fundic spiral folds were edematous and hyperemic with scattered petechial and ecchymotic hemorrhages. A bluish, depressed, stellate scar (3 by 13 cm) was present in the abomasum of the steer surviving for 52 days. The mucosa of the small intestine was congested, and in some there were ecchymotic hemorrhages in the wall (days 12, 16, 17, and 18). In one (day 17) several areas of hemorrhage (2 to 7 cm) in the wall with fibrino-hemorrhagic organizations attached to the mucosa were seen. There were fluid blood and blood clots in the lumina. In one steer an ulcer had developed in the mucosa over a large area of subserous hemorrhage (day 18). Cecal changes included scattered ecchymotic hemorrhages in the wall (day 17), solitary ulcers (days 18 and 31), a large ulcer over an area of submucosal hemorrhage (day 18), and an area (4 by 7cm) with several small ulcers (day 31). The lumina of both the cecum and colon contained fluid blood and blood clots or bloody ingesta. The 216 WEST, BELL, AND SASSER Fig. 3 Rumen and reticulum of steer 185, 17 days after oral and whole-body irradiation. Reticulum (left) with large area of hemorrhagic necrosis. Ruminal compartments (left to right), AVBS, VRS, PVBS, have necrotic plaques with variable-sized polypoidlike masses of exudate. Fig.4 Abomasum of steer 185, 17 days after oral and whole-body irradia- tion. A 7- by 19-cm area of hemorrhagic necrosis involving the fundic—pyloric region. Spiral folds in the area are necrotic and have sloughed. The mucosa and submucosa are hyperemic, edematous, and focally hemorrhagic. PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 217 mucosa was congested and studded with petechial and ecchymotic hemorrhages with similar hemorrhages being deeper in the wall. Microscopic Observations Preliminary microscopic observations are based on the examination of tissues from 12 sheep exposed to oral treatment only. Days 1 and 2 Foci of “ballooning” or enlarged, rounded, pale staining cells were observed in the mucosae of the rumen and omasal laminae. There were a few foci of superficial necrosis of the abomasal mucosa. Day 3 Small and larger microcysts formed by rupture of variable numbers of epithelial cells were seen in the ruminal mucosa. Although some cysts involved only the upper layers of cells, in larger cavities the entire epithelial thickness was affected. The cysts contained granular eosinophilic material and cellular debris. The eosinophilic material in many cysts was vacuolated. Larger cysts were covered by the parakeratotic layer only, but the upper border of some smaller cysts was composed of epithelial cells in addition to the parakeratotic layer. The cysts were primarily seen in the apical two-thirds of the affected papillae. The underlying propria was edematous and infiltrated with polymorphonuclear leucocytes (PMN cells). There were numerous areas consisting of groups of enlarged papillae. The lamina propria was edematous and contained strands of fibrin, and the submucosa was moderately edematous. Foci of necrosis, PMN-cell infiltration, and edema were seen in the abomasal mucosa. A slight fibrino- cellular exudate covered the necrotic surface. Day 5 Focal sloughing of groups of necrotic ruminal papillae exposed the submucosa in some areas. Groups of several papillae were distended with plasma and fibrin; this situation created a honeycomb effect within the propria. There were large areas of fibrino-necrosis of the mucosa (Fig. 5). Hemorrhage and large numbers of PMN cells, many degenerating, occurred in the necrotic mass. The upper submucosa was moderately edematous and extensively infiltrated with PMN cells. The blood vessels were dilated, and the walls of some vessels were necrotic. The vascular endothelium was swollen, vacuolated, or hyperchromatic. In some vessels the endothelial cells were not evident. The deeper submucosa and circular muscle layer were slightly to moderately edematous and infiltrated with inflammatory cells. There were foci of necrosis and sloughing of the omasal mucosa. The submucosa was moderately edematous and infiltrated with PMN cells. There were foci of hemorrhage. Large areas of hemorrhagic necrosis involved the abomasal mucosa. In some areas a thin layer of necrotic epithelium covered a thick layer of hemorrhage which appeared to rest on a thin rim of necrotic 218 WEST, BELL, AND SASSER Fig.5 Rumen of sheep 191, 5 days after oral treatment. Right to left, marked subserous edema. The mucosa is necrotic and covered with a thick fibrinous organization. Remnants of necrotic mucosa on the surface and two necrotic laminae propria (left lower center). mucosa and the muscularis mucosae. It appeared that rapid and forceful hemorrhage had “‘lifted’’ the necrotic mucosa into the lumen. Blood vessels at the base of the mucosa and adjacent glands were dilated. Some of the vessels were characterized by necrotic walls and some by thrombosis. The muscularis mucosae was focally interrupted. The submucosa was markedly thickened by edema and hemorrhage and was extensively infiltrated with PMN cells. Some blood vessels in the upper submucosa had necrotic walls, and some of these vessels contained thrombi. The inner muscle layer bundles were separated by edema. Day 9 There were large areas of fibrino-necrosis of the ruminal mucosa. Groups of papillae were distended with plasma containing fibrin. The submucosa beneath the large, necrotic, mucosal areas had necrosis and edema and only a few inflammatory cells. Numerous blood vessels in this area were necrotic and thrombotic. In other areas the submucosa was edematous, focally hemorrhagic, and extensively infiltrated with PMN cells. Focal necrosis of the inner muscle layer occurred beneath the more severely affected mucosa and submucosa. Foci of superficial necrosis and large areas of hemorrhagic necrosis involved the abomasal mucosa (Fig. 6). A large fibrino-hemorrhagic organization was ¢ Fig.6 Abomasum of sheep 175, 9 days after oral treatment. Right to left, extensive submucosal edema and focal hemorrhage. Necrosis and interruption of the muscularis mucosa. Hemorrhagic necrosis of the mucosa with dilated, necrotic, and thrombosed vessels at the base of the mucosa. The surface of the hemorrhagic-necrotic exudate is covered with a thin layer of necrotic mucosa. attached to the surface in one area. Other changes were similar to those found on day 5. Day 11 Large areas of fibrino-necrosis of the ruminal mucosa were covered at some sites by necrotic epithelium and the parakeratotic layer. The latter was quite well preserved. Epithelial cells bordering the necrotic areas were enlarged and rounded and the nuclei were pyknotic. Some rete pegs were irregular in shape and of increased length. The underlying propria was edematous and extensively infiltrated with PMN cells. The submucosa was moderately edematous and focally hemorrhagic. There was a moderate infiltration of PMN cells with fewer lymphocytes and mononuclear cells. Collagen fibers in the upper submucosa were anuclear, swollen, and dull red, and some fibers were ‘‘frayed.’’ The walls of some blood vessels were necrotic, and some vessels were thrombotic. The abomasal changes were comparable to those observed on day 9. Days 13 and 18 The changes were similar to those found on day 11. Day 59 The lining of large areas of the rumen consisted of a mixture of vascular granulation tissue and fibroblasts. The fibroblasts were oriented parallel to a 220 WEST, BELL, AND SASSER surface that was “‘ragged’’ and superficially necrotic. The underlying collagen fibers were swollen. In other areas a layer of dark epithelium with a thickness of two to three cells formed the inner lining. The undulant surface had no papillae. Rete pegs were absent, sparse and short, or sparse, long, and irregular. The edematous submucosa was extensively infiltrated with macrophages. Several blood vessel walls were eccentrically thickened. Changes in the abomasal mucosa included dilated glands, glandular atrophy, atrophy and glandular degeneration with moderate mononuclear infiltration and slight infiltration of lymphocytes and PMN cells, focal superficial necrosis, necrosis of the entire mucosa, and ulcer formation. A few colonies of large bacterial rods were seen beneath the necrotic mucosa. A large area of the submucosa forming the base of the ulcer was replaced by vascular granulation tissue and fibroblasts. This tissue was moderately infiltrated with macrophages and PMN cells. Coagulation necrosis involved another large area of the submucosa beneath the ulcer. Several dilated, necrotic, and thrombosed vessels were seen in this area. A band of caseous necrosis involved the lower submucosa and a portion of the thin muscle layer. The atrophic muscle layer rested on a thick layer of collagenous fibers and contained islands of granulation tissue and fat. Skin was not present on the sections. DISCUSSION Regressive cellular changes and cellular necrosis produced by irradiation are not pathognomonic.'* '* Similar changes have been produced by a variety of causes.'° The exact mechanism or mechanisms by which cellular changes are produced by irradiation are not known but are probably multiple.’ ere The pharyngeal mucosa and submucosa were congested and edematous, and the esophageal mucosa of a few steers had linear and ovoid erosions. It is probable that these changes occurred during regurgitation of ruminal fluids rather than as a consequence of ingestion of feed containing the radionuclide. Yttrium-90-labeled sand ingested by sheep and cattle collects in rather specific ruminal and abomasal sites and produces characteristic pathologic lesions. Sand particles lodge between ruminal papillae in these areas and appear to be indefinitely retained by the ensuing inflammatory and necrotic exudate. Ruminal contractions and compartmentalization by the pillars probably are important in determining the areas where radioactivity will be concentrated. Ina few early lesions, focal accumulation of plasma beneath and within the mucosa resulted in dome-shaped, yellowish elevations sparsely covered with enlarged papillae. Later, necrosis of the mucosa, increased vascular damage, extensive effusion of plasma, and extensive inflammatory cell infiltration produced the characteristic large fibrino-necrotic plaques or masses observed in sheep. Probably the grossly similar lesions seen in cattle would be comparable microscopically. Detachment of the necrotic masses at the borders exposed a PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 221 hemorrhagic, granular base or a smooth, pale surface, the appearance depending upon the age of the lesion. A pale, depressed, stellate scar was apparent on detachment of the exudate. Several months after treatment necrotic tags and superficial erosions were seen on the surfaces of numerous scars. The reticulum was mildly affected in a few sheep. In contrast, necrotic plaques or areas of hemorrhagic necrosis were seen in the reticulum of a significant number of steers. We have no explanation for this species difference. In general, minor lesions only were seen in the omasum of a few sheep. In steers the changes were of appreciably greater incidence and severity. The omasum of one steer was filled with a currant-jelly blood clot. An area of hemorrhagic necrosis between two laminae had apparently eroded into a large blood vessel. Characteristically injury occurred at the fundic—pyloric region on the greater curvature of the abomasum. This selective location is probably due to gravitational forces, the sand particles settling in the lowest area of the organ. Several variable-sized extensive areas of hemorrhagic necrosis developed in this area. Some lesions were covered in part with a thick fibrino-necrotic exudate. Anorexia (in the absence of more-severe complications) following treatment for variable periods resulted in appreciable weight loss. Ruminal fistula, abomasal hernia, and eversion-type abomasal prolapse occurred in six sheep. Another sheep probably would have developed an abomasal fistula if it had survived. Fibrinous and fibrous adhesions of organ to organ and/or to the abdominal floor occurred frequently in sheep. Similar adhesions between organs were frequently seen in steers. Only two steers developed ruminal adhesions to the abdominal floor. In one steer a long, tortuous, communicating fistulous tract extended from the rumen to the abomasum. The cause of this development is obscure. Fibrous adhesions of organ to organ or to the abdominal floor would interfere with normal function and conceivably could result in strangulation. Transportation and other stress-producing experiences may cause separation of adhesions and subsequent peritonitis.’ ° The absence of significant intestinal lesions in sheep was unexpected. Intestinal lesions found only in orally treated steers were not severe. The ileal, cecal, and colic mucosae (and possibly submucosae) of the intestine of one steer were appreciably thickened by transverse ridges. This change was not believed to be associated with irradiation, but microscopic examination has not been completed. Whole-body irradiation superimposed on oral treatment appeared to increase the extent and severity of gastrointestinal changes. Focal microcyst formation and foci of epithelial necrosis were early ruminal mucosal changes. Microcysts were probably the result of cellular imbibition of fluid and subsequent rupture of the cells. The cysts were frequently multiple on papillae and involved the apical portions of the affected papillae. The underlying lamina propria was edematous and infiltrated with numerous PMN cells. Microcysts, which are not an unusual ruminal mucosal change in sheep, 222 WEST, BELL, AND SASSER apparently occur as a result of altered physiology.” These cysts are not associated with inflammation of the lamina propria. Focal effusions of plasma into the mucosa caused marked swelling of groups of papillae. The epithelium of these papillae was degenerative or focally necrotic. The propria was distended with proteinaceous fluid and fibrin; this distention created a honeycomblike enrect. In more advanced lesions large areas of fibrino-necrosis involved the mucosa. This exudate consisted of necrotic mucosa, fibrin, and extensive PMN-cell infiltration. In some areas the exudate had sloughed and exposed a congested, ragged submucosa. The submucosa was edematous, focally hemorrhagic, and extensively infiltrated with PMN cells. The blood vessels were dilated. Many were necrotic and several thrombosed. The necrotizing reaction extended to the serosa in more severely affected areas. The inner surface of a ruminal scar was formed by granulation tissue and fibroblasts or a thin (2- to 3-cell thickness) layer of hyperchromatic epithelium with no or with scattered, short rete pegs. The submucosa was edematous and extensively infiltrated with macrophages. Minor changes of focal necrosis of the omasal mucosa with edema and cellular infiltration of the submucosa were seen. Hemorrhagic necrosis was the characteristic change seen in the abomasal mucosa. The submucosa was markedly edematous and focally hemorrhagic. Many blood vessels were necrotic and thrombosed. In one animal a chronic ulcer had developed. The underlying submucosa was replaced in one area by vascular granulation tissue and fibroblasts, which were infiltrated with PMN and mononuclear cells. A large area of coagulation necrosis involved an adjacent area of the submucosa beneath the ulcer, indicating concomitant repair and continuation of an acute reaction. Intestinal changes in sheep were minimal. Comparable treatment of cattle induced significant lesions. Bacterial invasion of tissue was observed in only a few animals. The conclusion that sheep are less sensitive to the radiation procedures employed than are cattle appears to be justified. ACKNOWLEDGMENTS The UT—AEC Agricultural Research Laboratory is operated by the Tennessee Agricultural Experiment Station for the U.S. Atomic Energy Commission under Contract AT-40-1-GEN-242. This work was supported by funds from the U. S. Office of Civil Defense and is published with the permission of the Dean of the University of Tennessee Agricultural Experiment Station, Knoxville. REFERENCES 1. National Academy of Sciences—National Research Council, Damage to Livestock from Radioactive Fallout in Event of Nuclear War, Publication 1078, Washington, D. C., Dec. 20, 1963. 2: 1D). To? PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 223 J. H. Rust, Report of the National Academy of Sciences Subcommittee for the Assessment of Damage to Livestock from Radioactive Fallout, J. Amer. Vet. Med. Ass., 140:.73:1— 235. (1962). -H. A. Smith and T. C. Jones, Veterinary Pathology, pp. 658-673, Lea & Febiger, Philadelphia, 1966. .M. M. Nold, R. L. Hayes, and C. L. Comar, Internal Radiation Dose Measurements in Live Animals, Health Phys., 4: 86-100 (1960). . L. Ekman, B. Funkqvist, and U. Greitz, Beta- and Gamma-Dose Measurements in the Gastrointestinal Tract of Goats with LiF Dosimeters After a Single Intake of Simulant Mixed Fission Products, Report FAO-4-4418, The Research Institute of National Defense, Stockholm, Sweden, March 1970. .M. C. Bell, Airborne Radionuclides and Animals, in Agriculture and the Quality of Our Environment, N.C. Brady (Ed.), pp. 77-90, Symposium No. 85, American Association for the Advancement of Science, Washington, D. C., 1967. a Verromith, F.cA: Ragan, B. J. “MeClanahan, J 'L.. Beamer; and J.°L. Palotay, The Passage Time of Plutonium Oxide in Pigs, in Gastrointestinal Radiation Injury, M. F. Sullivan (Ed.), Report of a Symposium held at Richland, Wash., Sept. 25—28, 1966, Report CONF-660917, pp. 518—523, Exerpta Medica Foundation, New York, 1968. . Alfred Trautmann and Josef Fiebiger, Fundamentals of the Histology of Domestic Animals, pp. 182—183, Translated and revised from the eighth and ninth German editions, 1949, by Robert E. Habel and Ernst Biberstein, Comstock Publishing Associates, Ithaca, N. Y., 1952. Ma eeBell,, ll. Bo Sasser, Jo lb. West, and, L., Wade, Jr..-Ettects of Feeding 90V Labeled Fallout Simulant to Sheep, Radiat. Res., 43: 71—82 (1970). 3. Bs sasser,.M..C, Bell, and J). L.. West, Simulated-Fallout-Radiation Effects on ‘Sheep; this volume. .M. C. Bell, L. B. Sasser, and J. L. West, Simulated-Fallout-Radiation Effects on Livestock, this volume. _M. C. Bell, Flexible Sealed ?°Sr—?°Y Sources for Large Area Skin Irradiation, Jnt. J. Appl. Radiat. Tsotop., 21: 42—43 (1970). .W. A. D. Anderson, Pathology, Vol.I., pp. 166—188, The C. V. Mosby Company, St. Louis, Mo., 1966. . A. R. Moritz and F. W. Henriques, Jr., Effects of Beta Rays on the Skin as a Function of the Energy, Intensity, and Duration of Radiation. II. Animal Experiments, Lab. Invest., tis, 1O7—LS 561952: Philip Rubin and G. W. Casarett, Clinical Radiation Pathology, Vol. 1, pp. 1-37, W. B. Saunders Company, Philadelphia, 1968. K. Nieberle and P. Cohrs, Textbook of the Special Pathological Anatomy of Domestic Animals, revised by Paul Cohrs, translated by R. Crawford, pp. 364—369, Pergamon Press, Inc. London, 19677. RESPONSES OF LARGE ANIMALS TO RADIATION INJURY DAVID C. L. JONES Stanford Research Institute, Menlo Park, California ABSTRACT Recent data pertaining to the relations between dose rate and lethality in sheep exposed to dose rates ranging from high (hundreds of roentgens per hour) to low (less than 1 R/hr) are incorporated in a review of the field. It is concluded that even within the high dose-rate range there is a significant inverse relation between LDs0/69 and dose rate and that discernible radiation injury does accrue even at dose rates less than 1 R/hr. The chronology of lethality and hematologic changes in sheep during continuous exposure to death at dose rates of 3.74 and 1.96 R/hr are compared with those observed during terminated exposure at 0.84 R/hr. At 1.96 R/hr there is no indication of reduction in survival time by overirradiation, whereas at 3.97 R/hr there is a marked compression in the range of survival times. Chronology and extent of changes in circulating leukocyte counts vary appreciably with dose rate during protracted exposure. In April 1968, at the symposium on dose rate in mammalian radiation biology,’ Dr. Norbert Page gave an overview of the effects of dose protraction on radiation lethality in large animals. His summary, together with some other papers presented at that symposium, furnished an excellent statement of the state of the art at that time. In his summary of the entire symposium, Edward Alpen pointed up the importance of describing the effects of variation in dose rate in considering recovery processes and the untenability of the view that a single ce unique recovery “‘constant”’ exists, even for a given species. My objective is to update the information presented at the 1968 symposium, with particular reference to the sheep. This species is of major interest to this present symposium because the sheep is an economically important domestic animal resource and because it is the large animal that has been most systematically studied with respect to the relations between dose rate and response to radiation. 224 RESPONSES OF LARGE ANIMALS TO RADIATION INJURY 225 The information presented comes principally from the most recent technical reports of the Naval Radiological Defense Laboratory (NRDL) program in large animal radiobiology, published during the last months of that laboratory’s existence, and from the initial studies under the Office of Civil Defense (OCD) program now located at the Stanford Research Institute (SRI). Two specific areas are considered: (1) the relation between dose rate and the LDso/60 aS measured in the terminated type of exposure to a predetermined dose and (2) the relation between dose rate and mortality and hematological responses during continuous exposure to death. LD5o/60 AS A FUNCTION OF DOSE RATE The LDso/69 for animals exposed to high dose rates is of interest from two standpoints: Lethality does appear to vary with dose rate even within the range of high dose rates usually described as ‘“‘acute,”’ and the response to high-dose-rate exposure is used as the standard against which responses to low-dose-rate exposure are compared. For example, one standard way of comparing recovery after, or even during, a low-dose-rate exposure 1s to compare the LDso/69 at a high dose rate in animals previously exposed at the low dose rate with that of previously unexposed, comparable animals. The difference between the two LDso/6o’s is considered to represent the residual injury remaining from the initial low-dose-rate exposure, and the difference subtracted from the dose given at the low dose rate represents the amount of recovery that has occurred. Figure 1 summarizes the available information on LDsq/g9 in sheep (California-bred wethers) exposed to dose rates ranging from 30 to 660 R/hr (midline air). All exposures were bilateral (1 MVp X ray) or quadrilateral (Ce): and the two types of radiation sources have been shown to have similar depth-dose characteristics.” The data from Refs. 2, 3, and 7 were included in Page’s 1969 presentation. Since that time there have been five more determina- tions of the LDsoj69 at dose rates in excess of 30 R/hr—two at SRI, two at NRDL,*’> and one at the Air Force Weapons Laboratory.° The composite of the data of Hanks et al. reported in 1966 and the data of some additional groups reported in 1969 by Taylor et al.* changed the original estimate of 252 R to 258 R. One can question whether the 30 R/hr value of Page et al. is a part of the high-dose-rate continuum. It is included here because the exposures took less than a day and because its fit with the protracted dose-rate LDso/69 data to be considered is even less apparent. When plotted on a graph, these nine data points appear to be adequately fitted by a linear regression (correlation coefficient, —0.82) expressed by a= 93) 0) 10s LOX (1) 226 JONES 400 350 250 0 100 200 300 400 500 600 700 DOSE RATE, R/hr Fig. 1 Relation between LDso/69 (midline air) and dose rate in sheep exposed at a high dose rate. where Y is the LDso/69 in roentgens and X is the dose rate in roentgens per hour. Since the 95% confidence interval of the slope (0.093) is less than the computed slope itself (0.156), there is a significant variation of LDso/69 With variation in dose rate. Thus, even at dose rates in the so-called acute range, it appears that we should specify the dose rate precisely when describing the LDso/60, and, in using acute dose-rate responses to evaluate injury accumulation and recovery at protracted dose rates, we should take into account this variation. Figure 2 summarizes the presently available LDso/69 information for pro- tracted dose rates where the exposure time is of the order of days or weeks. Results of the work by Jones and Krebs, which is currently in progress at SRI, are not sufficient to provide any reliable estimate of the confidence limits for the computed LDso/69 at 0.84 R/hr, since there were only three deaths among the five groups of 12 animals exposed. The computed LDso/69 of 1084 R is based on one death after exposure at 777 R, one at 837 R, and two at 897 R (the highest dose tested). Evaluation of the characteristics of the relation between dose rate and LDso/69 from about 4R/hr on down appears to be unwarranted until further information is acquired. That there is a tremendous RESPONSES OF LARGE ANIMALS TO RADIATION INJURY 227 1200 @ Jones and Krebs, 1000 1970 800 Page et al., B00 9 1968 LOS 60 A a: 0.5 1.0 15 2.0 2.5 3.0 3.5 4.0 400 DOSE RATE, R/hr Fig. 2. Relation between LDs50/69 (midline air) and dose rate in sheep exposed at a low dose rate to °"Co gamma radiation. change in LDso/690 aS compared with acute dose rates is, of course, quite apparent. It may even be that below some dose rates (presumably less than 1 R/hr) the conventional statistics relating exposure dose and mortality do not apply. CONTINUOUS EXPOSURE TO DEATH Figure 3 summarizes lethality and exposure data for the two relatively recent studies of lethality and hematologic changes during continuous (23 hr/day) protracted exposure to death. The first of these was done by Still et al.® at NRDL, and the second was done at SRI. At 1.96 R/hr the first death occurred on the 25th day of exposure, the median survival time was 42.5 days, and the last animal died on day 60. Deaths were spread out more or less uniformly throughout the period from days 25 to 60. At 3.79 R/hr, however, there was a marked difference in the lethality pattern. The first death occurred slightly earlier, on day 22, and all the remaining animals died within the next 6 days, the median survival time being 24.5 days. With continuous exposure to death, we are always faced with the concept of irradiation after accrual of a dose lethal to the individual animal. From Fig. 3 it appears that the effect of this so-called ‘‘wasted radiation” is a function of the dose rate. At 3.79 R/hr, further exposure after accrual of a potentially lethal dose results in a compression of survival time. It is as though at this dose rate there are no ‘“‘low-lethal” doses, and animals die with survival times similar to those observed after doses in the high-lethal range for acute exposure. For example, the work of Page et al.’ indicates that the LDso/60 for terminated exposure at 3.6 R/hr is 495 R. In continuous exposure at 3.79 R/hr, this dose was accrued in 5.7 days. Subtracting this from the mean survival time of 24.7 days gives a survival time after accrual of an LDso/6o of 228 JONES 3000 2500 24 cc uy 2000 20 oc 2 a) : < lu 16 a Q 1500 ” zr E < < 2 2 2 12 E =) LL © 1000 re) cc ) Gastrointestinal . . Se Se injury | Cerebral 2 injury SURVIVAL TIME, days (oe) | 12.5 25 50 100 200 400 800 1600 3200 6400 DOSE, rads Fig. 2 Generalized relation of cause and time of death, dose rate, and total-dose whole-body exposure. Perhaps the most significant factor involved in species recovery from exposure to 1onizing radiation is dose rate. The relation between dose rate and mean lethal dose or recovery capability as the dose rate progresses from protracted or chronic to acute for an animal with an LD5 9/39 of about 450 rads is shown in Fig. 3. Although the degree of this dose-rate effect varies from one 248 SPALDING AND HOLLAND 1000 F 800 F 600 MEAN LETHAL DOSE, rads 400 § 200 : + Ost 05>) 120 5 Om 0 50 100 500 1000 DOSE RATE, rads/hr Fig. 3. Graphic relation between dose rate and mean lethal dose for a mammal with an acute LDs59/39 of 450 rads. The acute lethal-dose LDs5 0/30 is shown on the right. As the dose rate changes from acute to chronic effects (right to left), the mean lethal dose can be expected to increase. species to another, the general dose-rate-effect relation should apply to all mammals. RATE OF REPAIR AND GENETIC INVOLVEMENT OF HEMATOPOIETIC RECOVERY Although experience suggests that no mammalian species has been denied the capability of repairing radiation injury, there is ample evidence that this capability varies widely among species. Variations of repair in mammals have been reviewed by Page,* who rated several species according to their response or recovery capability from protracted radiation exposures. Mice and swine are rated as having the most efficient recovery capability, and, as in the case of the LDs509/30, there appears to be no easily recognized correlation between repair efficiency and phenotypic or genotypic species characteristics. Recovery rate of hematopoietic tissue has been shown to be independent of size of acute conditioning dose in mice* and independent of total accumulated dose from continuous exposures.” Mice exposed to °° Co gamma rays at a dose rate of 4.5 rads/hr for 188 and 355 hr showed similar lag times (approximately 10 to 12 days) from termination of the gamma-ray stress to the maximum SPECIES RECOVERY FROM RADIATION INJURY 249 depression in red blood cell count (RBC). Recovery from the point of maximum depression to the 50% level was also similar (approximately 7 to 9 days) for the two groups in spite of a dose-difference factor of 1.89. These observations are shown graphically in Fig. 4. Independence of the repair rate of size of protracted gamma-ray dose has also been observed in monkeys. Peripheral blood characteristics of monkeys exposed to 500, 750, or 100 90 80 70 60 50 oa of exposure 40 RED CELL COUNT, % of control 30 20 TIME, days Fig. 4 Red blood cell (RBC) repopulation in peripheral blood following protracted gamma-ray exposure of the mouse. Exposure for all groups was started on day 1. The exposure was continued to death for group 1 and was terminated after 188 hr for group 2 and after 355 hr for group 3. Delayed response and recovery are shown for groups 2 and 3 following gamma-ray exposure. ©, group 1; @, group 2; 4, group 3. 1000 rads of gamma rays during a 10-day period are shown in Figs. 5 and 6. Animals receiving 500 rads showed only slightly depressed RBC characteristics; however, those exposed to 750 and 1000 rads showed dose-related injury but dose-independent recovery (Fig. 5). The lymphocyte response, plotted in Fig. 6, also shows dose-dependent response or injury and recovery rates independent of dose. Response to radiation injury from protraction of ionizing radiation dose varies widely among mammalian species. The degree to which a species responds to injury from ionizing radiation 1s, no doubt, genetically inherent to the given species. This genetic influence on radiation resistance may be expressed as resistance to or repair of radiation injury. Recent investigations with mice suggest that different responses to radiation injury within the same mouse strain 250 SPALDING AND HOLLAND oO ea Me IR SS al BS a as eS a rE E k——10-day exposure —++-———— 60-day _ rest phase —————*+}+*— 2nd 30-day —— se BEL performance phase 4 io) L J mn 7 Wen = =| wn Me + | 6 = > eal | So) Sie | = r 4 Sa a) oc Ww PACKED CELL VOLUME, % Jee arate 2 Je Boll t ad ] ae bine \\ ps O L NG Pes / | ro) ein 7 9 10 \ Mee i 1 uw 9 E \ i} = \ / 8 L ‘ we J jes 3 4 4 7) renee eee ee Slee ee es | [aie ale RO 0 4 #10 14 #20 24 30 36 43 50 57 63 71 78 85 95 101 105 116 120 126 TIME, days Fig. 5 Radiation-induced depression and recovery of hemoglobin, packed cell volume, and red-blood-cell count in the peripheral blood of monkeys following 0 (—c—), 500 (---e---), 750 (- -4- -), and 1000 (——0o—-) rads of gamma rays protracted over 10 days of exposure. may be due to a resistance factor rather than to inherent differences in the rate of repair from radiation-induced injury. In Fig. 7 the packed cell volume (PCV) from peripheral blood samples of two mouse substrains is plotted during and after 21 days of gamma-ray exposure at a dose rate of 4.1 rads/hr. The difference in radiation response between the two sublines, as shown in the figure, can be attributed to differences in resistance to radiation (either dose rate or total dose) rather than to hematopoietic recovery (repair-rate) differences between the two substrains. If the LDs9/39 method had been used on day 32 (11 days after exposure, Fig. 7) to determine the repair rate, one might have erroneously attributed the substrain difference in response to radiation to highly significant differences in repair rate of hematopoietic tissue. This problem may exist to some degree in recovery rates reported for different mammalian species where the degree of injury in the repair half-time test is assumed to be SPECIES RECOVERY FROM RADIATION INJURY 251 14,000 10-day exposure 12,000 10,000 8,000 6,000 4,000 2,000 LYMPHOCYTES, ABSOLUTE NUMBERS 0 TIME, days Fig. 6 Radiation-induced depression and recovery of lymphocytes in the peripheral blood of monkeys following 0 (9), 500 (@), 750 (4), and 1000 (0) rads of gamma rays protracted over 10 days of exposure. Values are the averages of surviving animals per group. 140 PCV, % of preexposure 20 Gamma-ray exposure at 4.1 rads/hr Recovery period 0 7 14 185) 321 25 (28 32,8239 39 42 49 BLEEDING SCHEDULE, days Fig. 7 Radiation-induced depression and recovery of packed cell volume in the peripheral blood, during and following gamma-ray bone-marrow block, of two substrains of mice with different radiation-resistance characteristics. ©, resistant strain; ©, nonresistant strain, 252 SPALDING AND HOLLAND completely dose dependent but is otherwise unknown. The radiation-resistance factor given in Fig. 7 has been shown to be genetic® and to be consistent with a single-gene-locus hypothesis. ’ BONE-MARROW RESILIENCE AND “IRREPARABLE INJURY” As stated earlier, in successful recovery from radiation injury, the bone marrow (hematopoietic tissue) is the organ of primary concern. Thus a knowledge of bone-marrow resilience from continuous or repeated radiation stress, or both, in the mammal is elementary to an understanding of the ‘irreparable’? component of radiation injury and repair kinetics. Protracted or fractionated exposures, or both, are required to produce this kind of information. Investigations using protracted and fractionated exposures showed mouse bone marrow to be extremely resilient to injury from ionizing % = O fas 30 les Acute dose in rads at 56-day intervals { { { { f { t { f t sa 100 100 100 100 100 100 100 100 100 100 140 == fre ola “ 12S E ies See 5 5 = liz 0 cs) Ol : U j HM a E sj Q o—O Ww O a U ro) @ @ Ori, OS o~ 6” Z| ON ‘a OW 0-9 e-e—e etal! poo NZ 2 O—O O z 5 | 0 80 160 240 320 400 480 560 TIME, days Fig. 8 Peripheral blood characteristics of monkeys 27 and 51 days after 10 100-rad gamma-ray exposures at 56-day intervals. Monkeys in this group were given no gamma-ray-insult exposure before the fractionated exposures. 4, packed cell volume; 0, white blood counts; ¢, lymphocytes; ©, neutrophils. SPECIES RECOVERY FROM RADIATION INJURY 255 radiation.*’? Irreparable injury was observed using the method of reduced LDs50/30 from radiation insult doses after allowing 90 days for repair.® The resilience of bone marrow and irreparable injury in the mouse have been well documented. Monkeys are being investigated to make similar determinations on larger mammals. Four groups of monkeys were given challenge or insult gamma-ray exposures of 0 (control), 500, 750, or 1000 rads protracted over 10 days. They were then allowed 14 months to recover from injury inflicted by the insult doses. After the recovery period all groups were placed on a gamma-ray-exposure regime that subjected them to a 100-rad exposure (at 35 rads/hr) every 56 days. Bone-marrow resilience and irreparable injury were examined periodically in terms of peripheral blood analysis. Figures 8 to 11 are graphs of packed cell volumes and white blood cell values at 27 and 51 days after each exposure during the first 560 days of this gamma-ray-exposure regime. These figures illustrate quite clearly the resilience, or recovery capability, of hematopoietic / teYA > O a Acute dose in rads at 56-day intervals S ‘ , § 4 3 h 4 3 § 100% 1007 100°, 100 100° -100* 100°: 100° 100° 100 ~ E £ (op) ro) Ww zy Ei] Ww O a) (e) O mm co 0 80 160 240 320 400 480 560 TIME, days Fig. 9 Peripheral blood characteristics of monkeys 27 and 51 days after 10 100-rad gamma-ray exposures at 56-day intervals. Monkeys in this group were given an initial 500-rad gamma-ray-insult exposure 14 months before the fractionated exposures. 4, packed cell volume; 5, white blood counts; e, lymphocytes; © neutrophils. 254 SPALDING AND HOLLAND Acute dose in rads at 56-day intervals t t t t t t t 100) Qe 1005 2.100% 3100); 9100),5, 100% e001 100 oe oe A BLOOD CELLS, 103/mm? 0 80 160 240 320 400 480 560 TIME, days Fig. 10 Peripheral blood characteristics of monkeys 27 and 51 days after 10 100-rad gamma-ray exposures at 56-day intervals. Monkeys in this group were given an initial 750-rad gamma-ray-insult exposure 14 months before the fractionated exposures. 4, packed cell volume; 2, white blood counts; e, lymphocytes; ©, neutrophils. tissue in the monkey. It can also be seen from Figs. 8 and 11 that, if an irreparable lesion was caused by the 1000-rad insult dose in the third group (Fig. 11) or in the other two groups subjected to insult doses (Figs. 9 and 10), it is not expressed as a decrement in hematopoietic repair observable in peripheral blood. The resilience of the Macaca mulatta bone marrow to this radiation regime is of particular interest because earlier investigations with Macaca arctoides,'° using the fractionation method of exposure but in a more stressful regime, showed the monkey to have poor recovery characteristics. Almost since the discovery of the injurious effects of ionizing radiation, attempts have been made to equate biological injury and recovery to mathematical models. Hollister, Vincent, and Cable’? pointed to some of the frustrations of predicting early radiation lethality over a wide range of exposure conditions; however, under a given set of exposure conditions, predictions of lethality and irreparable injury have been quite accurate.’~ Thus it seems SPECIES RECOVERY FROM RADIATION INJURY 255 PCV, % Acute dose in rads at 56-day intervals 4 ' 4 ¢ 4 ' t 100 100 100 100 100 100 = 100 BLOOD CELLS, 103/mm3 0 80 160 240 320 400 480 560 TIME, days Fig. 11 Peripheral blood characteristics of monkeys 27 and 51 days after 10 100-rad gamma-ray exposures at 56-day intervals. Monkeys in this group were given an initial 1000-rad -gamma-ray-insult exposure 14 months before the fractionated exposures. 4, packed cell volume; 5, white blood counts; e, lymphocytes; ©, neutrophils. inappropriate not to try to predict by use of a simple mathematical model the demise of the monkeys involved in this investigation. If we assume that the mean repair half-time (RT5 9) for all body organs, tissues, and related physiological functions essential to the sustenance of life is 28 days, that 10% of the exposure-dose-related injury is irreversible, and that, when the dose-equivalent injury to the whole body reaches 450 rads, 50% lethality can be expected, we can make the survival-prediction graph shown in Fig. 12. As shown in the figure, the four groups of monkeys in this investigation would theoretically have irreparable radiation lesions, which would be expected from acute gamma-ray exposures of 0, 50, 75, or 100 rads, or 10% of the insult doses they received 14 months before the fractionated-gamma-ray-exposure regime. Thus the four groups would have effective acute body burdens of 100, 150, 175, or 200 rads (Fig. 12) immediately following the first 100-rad gamma-ray fraction. Additional 100-rad gamma-ray fractions at 56-day intervals would add reparable and 256 SPALDING AND HOLLAND a a eee ee Ae : SND MISA PS Mss < ’ 2 Lethality probable 2s: wre 400 “Lethal-risk dose 2 t= Gamma-ray dose 100 2000 EPFECTIVE ACUTE DOSE, rads [Ea] [se] | (eth) | hi es ean Sh figel 56 168 280 392 504 616 728 840 952 1064 1176 1288 1400 1512 1624 1736 TIME, days Fig. 12 Graph of an effective-acute-dose (EAD) model to predict the accumulation of lethal-dose levels of fractionated gamma rays in monkeys with 0-, 500-, 750-, and 1000-rad insult doses 14 months before receiving 10 100-rad gamma-ray exposures at 56-day intervals. RT50 is assumed to be 28 days, and the irreparable component is assumed to be 10%. irreparable injury as shown by the line plots for each group, and a lethal body burden could be expected following 14 100-rad fractions for the group with a 1000-rad insult dose and following 22 100-rad exposures in the control group. Figures 8 to 11 show that, after 10 100-rad gamma-ray fractions, peripheral blood elements in all groups are at physiologically safe levels and hematopoietic tissue does not appear degenerate. Whether or not animals on this radiation-exposure regime will obligingly adjust their physiological state to conform with this model (Fig. 12) cannot now be said. One thing is evident, however: Even the monkey, previously rated low in terms of recovery capability, has a remarkable tolerance to radiation injury when exposure and repair conditions are optimum. INJURY, RESILIENCE, AND CONTINUITY OF GENETIC MATERIAL A discussion of species recovery from radiation injury would be wanting without a few words on the possible genetic effects of exposure to 1onizing radiations. It is commonly known that developing mammalian germ cells are among the most radiosensitive cells. Popular genetic theory also propounds that the sensitivity of germ cells to the lethal effects of ionizing radiation extends to a mutagenic sensitivity that can accumulate significantly and can result in severe genetic decrements to future generations. The statement that there is increasing evidence of biological effects of small exposures, particularly from a genetic standpoint is frequently heard or read. This theory has been perpetuated by notable scientific media and by such popular journals as Esquire. SPECIES RECOVERY FROM RADIATION INJURY 25, Several long-term investigations have been carried out in this and other countries to determine the possible genetic hazards of ionizing radiation. In one investigation each of 55 generations of male mouse progenitors received acute whole-body gamma-ray exposures of 200 rads. A similar experiment in man, with a generation time of 30 years, would require 1650 years; thus, for reliable data on man, it would have been necessary to start at about the time of the Roman Empire. A few comparative characteristics of control and irradiated lines of mice which are of possible interest to livestock breeders are shown in Fig. 13. LJ Control Experimental Sterility 0 6) Sex ratio, (males/total), % Birth 52.0 52.5 Weaning 51.5 53.5 Visible mutations (aes gtr) 1 @) | | 0 20 40 60 80 100 % OF CONTROL VALUE Fig. 13 Comparative breeding and litter characteristics in control mice and mice with up to 55 generations of X-irradiated male progenitors (100 breeding pairs per group). Experimental animals from 45 generations of irradiated male progenitors had a shorter fertile life but weaned larger litters (with slightly smaller weaning weights) and produced more total offspring (with longer life spans) than did control mice. However, none of these characteristics was significantly different from control values. After 55 generations, no sterility was observed in either line. Sex ratio at birth and weaning did not differ greatly. Only one viable mutation was observed—a spontaneous mutation for hairlessness in the control line. Although this investigation was carried out with intensive inbreeding (which in theory is an undesirable scheme to accumulate genetic injury), other investigations using different breeding methods have produced similar negative findings. Experimental evidence is contrary to the popular theory of radiation- induced genetic decrement mentioned previously. Not only is there ”o increased experimental scientific evidence of genetic effects from small exposures but also 258 SPALDING AND HOLLAND experimental results of long-term radiation genetics programs are so disgustingly negative that little or no interest can be generated to support such programs. ACKNOWLEDGMENT This work was performed under the auspices of the U.S. Atomic Energy Commission. REFERENCES 10. le . V. P. Bond, T. M. Fliedner, and J. O. Archambeau, Mammalian Radiation Lethality, A Disturbance in Cellular Kinetics, Academic Press, Inc., New York, 1965. .G. W. Casarett, Patterns of Recovery from Large Single-Dose Exposure to Radiation, in Comparative Cellular and Species Radiosensitivity, pp.42—52, Igaku Shoin, Ltd., Tokyo, 1969. .N. P. Page, The Effect of Dose-Protraction on Radiation Lethality of Large Animals, in The Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, D. G. Brown, R.G. Cragle, and T. R. Noonan (Eds.), Apr. 29—May 1, 1968, Oak Ridge, Tenn., USAEC Report CONF-680410, p.12.1—23, UT—AEC Agricultural Research Laboratory, July 12, 1968. . J. F. Spalding, T. T. Trujillo, and W. L. LeStourgeon, Dependence of Rate of Recovery from Acute Gamma-Ray Exposure on Size of the Conditioning Dose, Radiat. Res., 15: 378389 (1961): . J. F. Spalding and M. A. Van Dilla, Effect of Size of Dose from Protracted Gamma-Ray Exposure on Repair Rate of Hematopoietic Tissue, unpublished. . J. F. Spalding, D. M. Popp, and R.A. Popp, A Within-Strain Difference in Radiation Sensitivity in the RFM Mouse, Radiat, Res., 40: 37—45 (1969). . J. F. Spalding, D. M. Popp, and R. A. Popp, A Genetic Effect on Radiation Sensitivity Consistent with a Single Gene Locus Hypothesis, Radiat. Res., 44: 670—673 (1970). . J. F. Spalding, V. G. Strang, and F. C. V. Worman, Effect of Graded Acute Exposures of Gamma Rays or Fission Neutrons on Survival in Subsequent Protracted Gamma-Ray Exposures, Radiat. Res., 13: 415—423 (1960). . J. F. Spalding, Comparative Repopulation Recovery of Circulating Erythrocytes Following Graded Second Gamma-Ray Exposures in Mice, Radiat. Res., 29: 114-120 (1966). J. F. Spalding, L. M. Holland, and O.S. Johnson, Kinetics of Injury and Repair in Monkeys and Dogs Exposed to y-Ray Fractionation, Health Phys., 17: 11-17 (1969). H. Hollister, A. R. Vincent, and J. W. Cable, A Prediction of Early Radiation Lethality Using an Effective Dose, USAEC Report CONF-813-1, from the 10th Annual and First International Meeting of the Western Section of the Operations Research Society of America, September 1964, Honolulu, Hawaii (TAB-R-4). . J. F. Spalding, T. T. Trujillo, and W. L. LeStourgeon, The Predictability of Irreparable Biological Damage from Exposure to Ionizing Radiation, Radiat. Res., 15: 754-760 CL961));. RADIOIODINE AIR UPTAKE IN DAIRY COWS AFTER A NUCLEAR-CRATERING EXPERIMENT RONALD E. ENGEL,* STUART C, BLACK,+t VICTOR W. RANDECKER,”* and DELBERT S. BARTH* *Bureau of Air Pollution Sciences, Environmental Protection Agency, Research Triangle Park, North Carolina, and t Western Environmental Research Laboratory, Environmental Protection Agency, Las Vegas, Nevada ABSTRACT During a nuclear-cratering experiment, four lactating and three dry, pregnant dairy cows were exposed to the effluent cloud in an experiment designed to measure the transfer of radioiodine to milk, tissues, and excreta of the dairy cow when exposure was due primarily to inhalation during cloud passage. The lactating cows were milked twice daily. The dry cows were sacrificed at three different times after the event. Radioiodine was measured in all milk samples and in 50 different biological samples from each of the sacrificed animals. The “inhalation” exposure as calculated from air-sampler data was not sufficient to account for the observed milk levels; this indicated that the majority of the exposure occurred by inadvertent ingestion. The term ‘‘air uptake”’ was used to take into consideration all routes of entry. At 56 hr postevent the '?'I concentration was higher in the abomasal tissue than any other tissue except the thyroid and higher in abomasal contents than in the contents of the remainder of the gastrointestinal tract. The effective time in abomasal tissue and contents was also longer than in other samples, except in the thyroid. In maternal and fetal thyroids, the peak concentration occurred at 72 hr postexposure, when the thyroids contained 5.3 and 4.5%, respectively, of the estimated intake. However, the concentration in fetal thyroid was 2.4 times that of the maternal thyroid. Nuclear devices detonated in the atmosphere or in cratering experiments produce calculable quantities of radioiodines. However, the concentrations of radioiodine observed in the biosphere under different conditions are extremely variable. The chemical and physical forms of radioiodines following nuclear fission reactions are of major importance. Less is known, quantitatively, about 259 260 ENGEL, BLACK, RANDECKER, AND BARTH inhalation of radioiodine from field sources than about any other aspect of radioactivity resulting from these reactions.’ Radioiodines released into the atmosphere and available to the pulmonary system may be hazardous only under specific, pertinent conditions existing at the time of the release. Biological availability depends on such physical factors as the source of the radioiodines, the proximity of the source to the study, and meteorological conditions existing before and after release. It is difficult to investigate every facet of radioiodine fallout in detail. However, adequate exposure and dosage determinations are required for establishment of accurate radiation-protection guides. To make these determina- tions with regard to inhalation of radioiodines, we must answer the following questions:* 1. What are the potential sources of atmospheric radioiodine contamination? 2. What are the chemical and physical properties of both gaseous and particulate forms of radioiodines, and what is the degree of fractionation? 3. What is the particle size distribution inhaled by the animal and the biological availability of each size? 4. What fraction of the intake of radioiodines is retained in the body following inhalation? 5. What are the lung deposition, retention, translocation, and elimination factors of inhaled radioiodines in normal physiological states? 6. What is the distribution of radioiodines in specific tissues and organs of various species of animals? Nuclear-cratering experiments offer an excellent opportunity to study the distribution, deposition, and uptake of radioiodines in dairy cows following exposure to the radioactive cloud. This report, the scope of which is limited to question 6, deals with the concentrations of fan tissues, milk, and excreta of dairy cows following exposure to a radioactive cloud produced by the 4.3 + 0.4-kt Project Palanquin nuclear-excavation experiment. PROCEDURES Experimental Design Nineteen lactating and three nonlactating, pregnant Holstein cows were grouped for this experiment as shown in Table 1. Each animal used was free of obvious signs and symptoms of any infectious disease and had no physical defects. Assignments to the first four groups were based on a stratified random allocation. Lactating cows were first grouped by milk production, butterfat production, and days in production and were then randomly assigned to the experimental groups. The selection of Group V was based on milk production prior to the dry period. Groups I, II, and III remained at the dairy barn throughout the entire study period. These three groups, which were fed contaminated forage from the three RADIOIODINE AIR UPTAKE IN DAIRY COWS 261 Table 1 GROUPING OF DAIRY COWS Number of Group cows Location Type and duration of exposure* I 6 Dairy barn Average intake of 8.9 kg/day of contaminated green chop from Station 3 for 4 days II 6 Dairy barn Average intake of 7.1 kg/day of contaminated hay from Sta- tion 3 for 8 days II] 3 Dairy barn Average intake of 7.1 kg/day of contaminated hay from Station 2 for 9 days and 9.4 kg/day from Station 1 for 12 days IV 4 Station 3 Air uptake, exposed during and after cloud passage at Station 3 for 56 hr V 3 Station 3 Air uptake, exposed during and after cloud passage at Station 3 for 56 hr *The dairy barn was located approximately 70 km from ground zero. Station 1 was 4.7 km from ground zero at an azimuth of 350°; Station 2, 5.5 km from ground zero at an azimuth of 026°; and Station 3, 4.6 km from ground zero at an azimuth of fe) 004 . experimental stations, will not be discussed in this report. Groups IV and V, the subjects of this report, were maintained at Station 3 from April 6 to 16 and at the dairy barn thereafter. Station 3 was located 4.60 km from the detonation point at an azimuth of 4°. The station was located on a terrain that had a slight slope and a moderate cover of natural vegetation. Facilities for Station 3 consisted of seven portable milking stanchions designed to hold dairy cows comfortably while facing the ground zero.> Each cow was fitted with a blanket to reduce the exposure to cold, wind, and moisture. The stanchions were 0.6 meter apart to allow room for the milkers and also to reduce the physical contact between cows. Each stanchion had an automatic waterer and removable feed box. Time of milking was as close to the regular schedule as possible. Each cow in Group IV was milked with the same Surge milking bucket throughout the experiment and with the same equipment as normally used at the dairy barn.* Milking techniques were identical to those used during normal routine milking. Samples of milk, grain, water, and hay were taken daily for background determination prior to the event. Temperature and respiratory rates were taken for all seven cows in the morning and evening. Blood samples for hematology and blood chemistry were taken before and after the exposure. Just before the event the feed boxes were 262 ENGEL, BLACK, RANDECKER, AND BARTH removed and the waterers turned off and covered to prevent any further ingestion. Because of radiological health procedures, Group IV cows were not milked until 31 hr after cloud passage. They were subsequently milked at 40 and 54 hr postevent. Uncontaminated hay and grain were carried in by the milking team. Water was provided only during the milking period. Samples of hay, milk, grain, and water were taken at the trme of milking. Approximately 56 hr postevent all seven animals were returned to the dairy barn, were separated from Groups I, II, and III, and were maintained on uncontaminated hay, grain, and water. Tissue Sampling The Group V cows were sacrificed at intervals of 62, 76, and 125 hr after the detonation, and a complete and detailed necropsy was done on each animal. Milk samples were taken in cubitainers and counted by standard procedures.” Various types of biological samples were taken for gamma-spectrum analysis. Samples were put in 400-ml cottage-cheese containers and counted by placing the container directly on top of a 10- by 10-cm Nal(TI) crystal coupled to a Technical Measurement Corp. multichannel analyzer. The 200 channels used were calibrated at 10 keV per channel (0 to 2 MeV). The spectra were resolved by use of the matrix method. Whenever possible, repeat counts were done on all available tissues and contents. The minimum detectable activity was approxi- mately 100 pCi in the sample for a 20-min counting time. RESULTS AND DISCUSSION Cow Group Comparisons Groups of cows were compared for total serum protein (TP), thyroid binding index (TBI), and protein-bound iodine (PBI). The values were not significantly different among the groups except for a significantly higher PBI in Group V. The hematological values for the cows in the field (GroupsIV and V) were not essentially different from those for cows in the dairy barn (Groups I, II, and III). The variation in milk production of Group IV during the experimental period did not differ from that of Groups I, II, and III. Temperature and respiratory rates of animals in Groups IV and V did not differ significantly while they were at the field station. To develop the estimated intake of radioiodines for Groups IV and V, we must first assume that there was no physiological difference in any of the animals which would affect the metabolism of radioiodine. This assumption is justifiable for the following reasons: 1. On the basis of previous herd history, all groups of cows had equal stable iodine intakes throughout the study. RADIOIODINE AIR UPTAKE IN DAIRY COWS 263 2. On the basis of TBI, TP, and milk and butterfat production in the prior lactation, Group V cows were not significantly different from the rest of the herd. 3.On the basis of TBI, TP, and temperature and respiratory rates taken during the experiment, Group V cows were not essentially different from those in other groups except in stage of lactation. 4.On the basis of the necropsy findings of Group V cows, all cows were assumed to be normal and were in good physical condition during the study period. Air Concentration Since instrumentation located at Station 3 indicated that the leading edge of the base surge reached the station approximately 12 min after detonation, this is the reference time for our calculations. The end time for the calculations is set at H + 56 hr, at which time the cows were removed from Station 3. Data from a Gelman Instrument Company Tempest air sampler located 30 meters in front of the cows were used to determine the integrated air dose for the 56-hr period. After the sampler had operated for 30 hr postdetonation, the prefilter and charcoal cartridge were changed, and it ran for an additional 24 hr before sampling was discontinued. It is reasonable to assume that an insignificant exposure occurred during the final 2 hr. The integrated air concentration of '? "1 for the first 30 hr of exposure was 246 uCi-sec/m® (the prefilter was 190 uCi-sec/m? and charcoal cartridge was 56 uCi-sec/m?), and for the next 24 hr it was 18 uCi-sec/m*. The latter figure indicates that resuspension occurred, because the prefilter contained 99.7% of the total activity. Exposure Determinations The results for the cows exposed by “‘inhalation”’ are somewhat different from those expected for this type of exposure. The increased concentration in the second milking after exposure suggests a delayed absorption of radioiodine which is more characteristic of ingestion.® This is complicated by the reduced milk production of these cows caused by the 31-hr delay between exposure and first milking. Cows could have ingested radioiodines by licking the stanchion parts or the ground, or the clean feed and water brought to them during the reentry period could have been inadvertently contaminated by resuspended material. Another indication that inhalation was not the sole source of exposure for these cows is the incongruous result obtained by assuming the maximum possible inhalation [assuming that (1) the cow breathes at the rate of 100 liters/min (1.7 X 10° m?/sec) (Ref. 7), (2) deposition in the respiratory tract was 100%, and (3) the air sampler was 100% efficient] . The cows were exposed for 56 hr to integrated air concentrations of 246 uCi-sec/m* during the first 30 hr and 18 wCi-sec/m? for the next 24 hr. The deposition in the cow, with these assumptions, would have been: 264 ENGEL, BLACK, RANDECKER, AND BARTH (1.7 X 10° m?/sec) (246 UCi-sec/m? + 18 UCi-sec/m? ) = 0.45 uC (1) The average secretion in milk was 25.9 uCi, or about 57 times this calculated intake. Since the actual inhalation intake of the seven cows exposed at Station 3 is unknown, and since exposure—dose relations are required for the tissue- and content-distribution study in the three sacrificed cows, the milk-secretion data were used to estimate intake. Because we know that the average secretion of Groups II and III (also fed hay and grain) was 10.6%, it is reasonable to estimate the total '?'I exposure by assuming that cows in Group IV also secreted 10.6% of their total radioiodine intake.® Therefore the average milk secretion of the Group IV cows, 25.9 uCi, represents 10.6% of their estimated intake of 244 uCi of '*'TI. This is reasonable since subsequent field experiments have shown that the dairy herd averaged 10.7% '°'I secretion in milk under similar feeding regimens using different contaminants.°’? '* This average is similar to that found by most other investigators.*’'*7!? Thus, if our assumptions are correct, it is readily apparent that uptake of 1317 from inhalation contributed very little [(0.45 xX 100)/(244 — 0.45) = 0.18%] to the total dose. Therefore we use the term “‘air uptake,” which takes into consideration inhalation as well as other routes of entry; e.g., skin absorption, licking of surroundings, licking of nasal secretions. Milk Concentrations A peak milk concentration of 1.6 wCi/liter for Group IV occurred at the second milking. The time of peak was similar to that in controlled studies using diatomaceous earth aerosols’’?’'°’'* and in other studies using oral or intravenous doses of '7!] (Refs. 15, 16, and 20). The milk data indicate that some activity was taken in after the initial exposure. From 40 to 73 hr, the effective time (Tere) was 33.1 + 1.36 hr, and, from 73 to 154 hr, the Te¢¢ was 16.3 0.9 hr. For both time periods the Tegg was 18.1 +0.9 hr. For single- exposure studies the milk activity peaks at the first milking and then decreases, with a Te¢¢ of less than 24 hr. The foregoing results indicate that the Group V cows were consistent with those in other studies and that the exposure was due to an initial dose followed by continued intake while the cows were at ‘3! T-concentrating mechanisms of the field station. Tissue Concentrations from Air Uptake An average of 50 biological samples was removed from each of the Group V cows and analyzed specifically for '*'I. The rates of uptake, retention, and deposition derived from these data may be useful in developing mathematical prediction models and in analog computer simulation. RADIOIODINE AIR UPTAKE IN DAIRY COWS 265 The data from a different cow at each point in time was used to determine the transfer rates between the various body compartments. Effective half-life values were determined by assuming that the cows’ physiological states were equivalent for each point because no lesions of any significance were noted during postmortem examination. The half-life (T,,) was then determined by use of the linear-regression line drawn through the three points representing the f 131 three times of sacrifice. The concentration o I in the biological samples at 56 hr postevent, the time the animals were removed from further exposure, are listed in Table 2. These were calculated by using the Ty to correct for decay between removal from Station 3 and sacrifice. Table 2 CONCENTRATION OF !3! 1 IN BIOLOGICAL SAMPLES '31T sample Biological Total concentration, * Retention,t ¢ sample weight, g Half-life, hr uCi/g % Foregut tissue 14,600 34 205 {22 Foregut contents 41,350 34 760 12:9 Abomasum tissue 2,700 44 662 0.74 Abomasum contents 900 49 680 0.63 Hindgut tissue 7,120 3A 195 0.63 Hindgut contents 14,000 ep 680 Pere) Maternal thyroid 37 230 345,000 20 Fetal thyroid 13 833,000 4.46 Liver 10,000 29 a1 0.38 Respiratory tract 3,380 32 78 0.11 Kidney 1,605 44 115 0.07 Urine 309 20 880 0.11 All others: Blood, spleen, bone, muscle, skin 473,330 34 16 3.08 Total 570,000 313.0 * Activity was corrected to 56 hr postevent. t Retention is based on an estimated 244-wCi exposure. sample concentration x total weight Percenta eC = * 100. t g 244 uCi Certain conclusions are evident based on the Ty in the contents or tissues. There were no significant differences for Ty in foregut (rumen, reticulum, and omasum), hindgut (duodenum, jejunum, ileum, and colon), respiratory tract, and other tissues (blood, spleen, bone, muscle, and skin). The average Ty fOr these compartments, 31.5 + 2.4 hr, is considered the same as the transport time 21 of '°'I for nonthyroidal tissues. Lengemann’! observed two half-times for various compartments in the dairy cow, a short-lived portion of 17 and 22 hr for 266 ENGEL, BLACK, RANDECKER, AND BARTH blood and feces, respectively, and, later, 58 and 46 hr, respectively, over a 7-day period. When rats that had inhaled Ag'?'I were sacrificed near the time of thyroid peak, the gastrointestinal tract, liver, lung, kidney, and spleen were found to contain measurable amounts of radioactivity.2*’** This was considered a reflection of the iodine equilibrium beginning to establish itself in the plasma. By 50 hr the thyroid contained 60% of the body burden. Bustad?* listed the tissues containing '?'1 following establishment of }?1I equilibrium in the blood of sheep. The thyroid, feces, mandibular salivary gland, f '>'T higher than those found in the blood. Other tissues (listed in descending order) containing milk, abomasal wall, and urine contained concentrations o concentrations of '°'I lower than those in the blood were the parotid gland, liver, ovary, kidney, adrenal gland, pituitary gland, lungs, lacrimal gland, heart, pancreas, spleen, thymus, brain, and lens. Our data clearly show that the Ty of the abomasal tissue (44 hr) is longer than that of the other nonthyroidal tissues (32 hr) and shorter than that of the thyroid (9.6 days); the thyroid value has been reported to vary between 4.5 days for a single oral dose and 16 days for a single contaminating event.° Assuming an uptake of 244 uCi of '?'I, 33.6% of the total estimated exposure was found in 131 the tissues by the methods used in this study. The remainder of the I is assumed to have been eliminated via feces and urine; this assumption is 15.17.21 3nd tends to confirm the consistent with data reported by others calculated uptake. The high percentage of iodine recovered from the intestinal contents indicates uptake by ingestion, but it may have been due partly to elimination of a large percentage of the deposited particulate matter from the lung via the ‘“‘mucous—cilia escalator”; i.e., the material was coughed up, swallowed, and absorbed via the gastroenteric route. It has been suggested that the gastro- intestinal tract can be an important route of entry of inhaled material into the systemic circulation.2> The Ty of 9.6 days for the thyroid also indicates a continued uptake rather than a single-dose type of exposure. Barua, Cragle, and Miller*® reported that, by using a nonabsorbed marker-technique ('**Ce), they were able to determine the net absorption of orally administered radioiodine in young animals. The rumen appeared to be a major site of absorption, and the abomasum a major site of endogenous secretion. Net absorption occurred from the second section of the small intestine throughout the remainder of the tract. When sodium iodide was administered intravenously ‘4 hour before slaughter, a significantly greater concentration of radioactivity was found in the abomasum than in the first part of the small intestine. Our data tend to substantiate these findings. Our data indicate that, on an activity per weight basis, at 56 hr the foregut and hindgut tissue were approximately equal, each having about one-third the concentration of the abomasum. The concentration of '*'I in the contents of each was also similar, RADIOIODINE AIR UPTAKE IN DAIRY COWS 267 about one-half that of the abomasum contents. It appeared that net absorption of iodine was taking place throughout the tract at the same rate as was the net loss, 1.e., that secretion was equal to absorption. This suggests that, as shown by others,’ a constant physical relation, or equilibrium, exists in the lower tract for iodine. The percent of calculated intake in the thyroid of the adult and the fetus was in close agreement with that found in the literature.” °’*? Concentrations of 'S'T in the fetal thyroid during advanced gestation may be one to two times that in the adult thyroid of sows, two to three times that in the thyroid of ewes, and up to six times that in the thyroid of cows.?? In this experiment the fetal thyroid concentration was 2.4 times that of the maternal cow. Swanson, Lengemann, and Monroe®® found a rapid concentration of '?'J in the thyroid in the first two days with a slower increase to the peak uptake on the third day. The winter peak of 18.4% uptake was reached on the third day, but the summer peak of 18.0% was not reached until the fifth day. The estimated peak for our studies is at 72 hr, which is similar to the winter peak and at a concentration of 5.2% of the estimated dose. Garner et al.’* reported a peak uptake of 5% at 48 hr and an effective half-life of 4.5 days in dairy cows. REFERENCES 1. H. D. Bruner, Symposium on the Biology of Radioiodine: Statement of the Problem, Health Phys., 9: 1083 (1963). 2. R. E. Engel, Potential Hazards as a Result of Inhalation of Radioiodines: A Literature Survey, USAEC Report TID-22693, Southwestern Radiological Health Laboratory, Jan: 5,°1966. 3. Southwestern Radiological Health Laboratory, Radioiodine Study in Conjunction with Project Sulky, USAEC Report SWRHL-29-r, May 27, 1966. 4. Southwestern Radiological Health Laboratory, '*'I Dairy Cow Uptake Studies Using a Gaseous Aerosol, SWRHL, preliminary data, 1968. 5. D. S. Barth and M. S. Seal, Radioiodine Transport for a Synthetic Dry Aerosol Through the Ecosystem Air—Forage—Cow—Milk Using a Synthetic Dry Aerosol, in Radto- ecological Concentration Processes: Proceedings of the International Symposium, B. Aberg and F. P. Hungate (Eds.), Pergamon Press, Inc., New York, 1966. 6. L. K. Bustad, D:.H. Wood, E. E. Elefson, H..A. Ragan, and R. O. McClellan, 1-131.in Milk and Thyroid of Dairy Cattle Following a Single Contamination Event and Prolonged Daily Administration, Health Phys., 9: 1231 (1963). 7. National Academy of Sciences, Handbook of Respiration, W. B. Saunders Company, Philadelphia, 1958. 8. S.C. Black, R. E. Engel, V. W. Randecker, and D. S. Barth, Radioiodine Studies in Dairy Cows Following the Palanquin Event, USAEC Report PNE-914F, Southwestern Radiological Health Laboratory, 1971. 9.R. E. Stanley, S. C. Black, and D.S. Barth, '*'I Dairy Cow Studies Using a Dry Aerosol, USAEC Report SWRHL-42-r, Southwestern Radiological Health Laboratory, August 1969. 10. Southwestern Radiological Health Laboratory, '?'I Dairy Cow Uptake Studies Using a Submicron Synthetic Dry Aerosol (Project SIP), USAEC Report SWRHL-39-r, April nO 7Ale 268 ENGEL, BLACK, RANDECKER, AND BARTH tite 2: ili3% 14. iLaye 16. 17: 18. 19. 20. 7a be ah 23: 24. 29: 26. Dike 28. 29: 30. Southwestern Radiological Health Laboratory, '*'I Transport Through the Air— Forage—Cow—Milk System Using an Aerosol Mist (Project Rainout), Report SWRHL-43-r, 1967. S. C. Black, D. S. Barth, R. E. Engel, and K. H. Falter, Radioiodine Studies Following the Transient Nuclear Test (TNT) of a KIWI Reactor, USAEC Report SWRHL-26-r, Southwestern Radiological Health Laboratory, May 1969. W-. Shimoda, S.C: Black) K.JHs Falter, R20 >-Engels and = D=9S~ Barth,! ° The extensive research data of Sparrow et al.'° demonstrate the extent of differential response to ionizing radiation among species of plants and among developmental stages of the life cycle within species as influenced by exposure procedures and environmental conditions. Our research with plants of major food crops, which 1s of a civil-defense nature, has provided results that concur with this statement. Most of the work, however, was done at an exposure rate of 50 R/min, which is considerably higher than that expected in areas of radioactive fallout. Currently emphasis is being placed on studies involving exposure and exposure rates at different plant developmental stages in a number of species. In this report of progress, we present data on the response of soybean plants [Glycine max (L.) Merrill] to varying gamma-ray exposures as influenced by exposure rate. Results of split-exposure experiments are presented as evidence of repair processes that occur in the soybean plant and as one explanation for the exposure-rate effect observed. MATERIALS AND METHODS The experiments were conducted in two phases, one involving seedling growth of the variety Hill under environment-controlled conditions and the other involving plant growth and yield of the variety Kent under outdoor conditions. Plants in both cases were grown in a Perlite : soil : peat : sand me- dium (3: 2:1:1 by volume) with the pH adjusted to approximately 6.5 and with nutrients added. The °° Co variable-dose-rate facility of the UT—AEC Agri- cultural Research Laboratory was used for all experiments. In the seedling experiments four seeds were planted in each 6-in. pot, and the plants were thinned to two per pot at the time of irradiation. Plants were irradiated on day 2 or 3 postemergence, at which time the primary (unifoliolate) leaves were unfolding. Plants were removed from the environment-controlled room, taken to the °°Co source, irradiated, and then returned to the environment-controlled room (83 + 2°F, 16 hr of light daily, and 50 + 10% relative humidity). The different exposures and exposure rates caused the duration of irradiation to vary; therefore plants of all treatments were subjected to equal periods of time in the source building at a light intensity and temperature regime les. than that in the environment-controlled room. Sham controls were grown for each experiment. In the split-exposure experiment, light intensity and temperature in the source building were equal to those in the EXPOSURE-RATE EFFECTS 279 environment-controlled room. Plants were harvested at 25 to 30 days postirra- diation, and data presented are oven-dried weights of the shoot above the unifoliolate leaves. Axillary shoot growth is not included. In the outdoor experiments four plants were grown per 55-gal drum, which was cut in half crosswise. The plants were irradiated at 12 days after emergence; exposures (were \2'5 andi5.0 KR vat either 70.25;) 12:5, 25,:;or 50.R/min. The criteria of evaluation for plant response to gamma rays were stem length at varying times postirradiation and yield. Late planting caused the plants to be subjected to a killing frost prior to complete maturity; therefore, “‘yield”’ refers to the oven-dried weight of pods and immature beans. “Stem length” refers to the distance between the tip of the shoot apex and “‘ground”’ level. RESULTS A preliminary experiment (data not shown) with seedlings of Hill soybeans exposed to gamma rays at 5, 50, and 500 R/min indicated little or no exposure-rate effect at 2 kR, and at 4kR the response became independent of rate (the point at which response becomes independent of rate is hereafter referred to as exposure-rate saturation) at 50 R/min. A number of experiments have been conducted since then with exposure rate being one of the variables. Results in Fig. 1 show that shoot weight of soybean seedlings exposed to 4 kR at rates of from 3.125 to 400 R/min reached a rate saturation at approximately 50 R/min. 100 80 H C) ae oO « 60 5 5 4 kR O u_ O 40 3e \ 20 0 FEESO 100 200 400 Te EXPOSURE RATE, R/min 26. Fig. 1 Shoot dry weight of Hill soybean seedlings as influenced by 4 kR of oGe gamma radiation administered at exposure rates of 3.125 to 400 R/min. 280 CONSTANTIN, KILLION, AND SIEMER The results of another experiment (Fig. 2) show the relation that exists between exposure and exposure rate for soybean seedling response to gamma rays. Shoot dry weight was reduced to 50% of control (unirradiated) by either 3 or 5 kR, depending on whether the rate was 50 or 10 R/min, respectively. The magnitude of the interaction of exposure and exposure rate can be demonstrated by the ratio of shoot dry weight expressed as percent of control for the 10 R/min vs. the 50 R/min population. The ratios were 1.1, 6.8, 7.0, and 3.6 at 2, 4, 6, and 8 KR, respectively. 100 QO 80 Q S 60 oc 10 R/min Ee Zz S u 50 R/min O 40 se 20 ‘i 0 2 4 6 8 EXPOSURE, kR Fig. 2 Influence of exposure on the magnitude of exposure-rate effect demonstrated by shoot dry weight of Hill soybean seedlings following 6° Co gamma irradiation. An outdoor experiment with Kent soybeans was scored for (1) increase in stem length vs. time after irradiation, (2) stem length at maturity, and (3) yield. Results for indexes 1 and 2 are shown in Fig. 3. The seedlings were irradiated at O on the abscissa, which was 12 days postemergence (early log phase of growth). The plants ceased to increase in stem length at various times after irradiation; this response was dependent on exposure and exposure rate. At 2.5 kR stem length ceased to increase after 20 to 25 days postirradiation regardless of the exposure rate used. At 5 kR stem length ceased to increase after either 20 to 25 days postirradiation at 6.25 and 12.5 R/min or 5 to 7 days at 25 and 50 R/min. Stem length at maturity (54 days postirradiation) at 2.5 kR was approximately 50% of the controls and was unaffected by the various rates used. Stem length at maturity at 5 kR was 45 and 38% of control at 6.25 and 12.5 R/min and 19 and EXPOSURE-RATE EFFECTS 281 60 50 40 = [S) = (ao 2 30 e 9 + ~ yy pi L = LU k- (ep) 20 {) i=) C) C) ) 10 : O ,——&4 i——4 A 0 0) 10 20 30 40 50 60 TIME AFTER IRRADIATION, days Fig. 3 The effects of 2.5 and 5.0 kR of el Go gamma radiation, as influenced by exposure rate, on (1) the increase in stem length vs. time after irradiation and (2) stem length at maturity (54 days postirradiation) in Kent soybean plants irradiated at 12 days postemergence. Exposure, Exposure rate, Symbol kR R/min e O 0) O Dd 625" a 5 6.25 5 12:5 A 5) 25 & 5 50 *There was no difference among exposure rates at 2.5 kR; theretore a single curve is shown. 14% of control at 25 and 50 R/min, respectively. Thus it appears that for indexes 1 and 2 an exposure-rate saturation had been attained by 25 R/min. The third index of radiation response of these plants, yield, is shown in Fig. 4. Results of an analysis of variance indicate that at 2.5 kR yield was greater 282 CONSTANTIN, KILLION, AND SIEMER 100 80 =J eo) c 60 oe S ro) 2.5 kR Li Oo 40 se 20 5.0 kR 0) 6.25 12.5 25 50 EXPOSURE RATE, R/min Fig. 4 The effects of 2.5 and 5.0 kR of ©°Co gamma radiation, as influenced by exposure rate, on the yield of Kent soybean plants irradiated at 12 days postemergence. at.6:25 R/min-(P’< 0.05) than aw either 12.52 25.’or-50 R/min® Phis indicates that yield at this exposure showed a rate saturation at 12.5 R/min. However, at 5.0 kR there was no difference in yield at P< 0.05 between plants exposed at 6.25 and 12.5 R/min, and at 25 and 50 R/min there was essentially no yield. Results of experiments with split vs. continuous irradiation are shown in Table 1. The split exposures were done at a rate of 50 R/min, and the radiation-free periods were 30, 60, and 120 min. Rates for continuous exposures varied in accordance with total time of the different split-exposure treatments. Neither the duration of the radiation-free period in split exposures nor the exposure rate in continuous exposures caused any differences in the shoot dry weight of seedlings exposed to 2 kR (Table 1). In contrast to the results observed following 2-kR exposures, an increase in shoot dry weight was observed as the radiation-free period was extended from 30 to 60 min at 4kR (Table 1). An increase in radiation-free time to 120 min caused only a slight further increase in performance. A comparison of split vs. continuous exposures shows that a decrease in exposure rate (continuous expo- sures) from 36.4 to 20 R/min had a greater influence on seedling performance than did the increase in radiation-free period (split exposures at 50 R/min) from 30:to- 120) min: DISCUSSION 10 Sparrow etal. ~ emphasized that a large biological effect can be produced in one species by the same dose or dose rate that produces a negligible effect in EXPOSURE-RATE EFFECTS 283 Table 1 SHOOT DRY WEIGHT OF HILL SOYBEAN SEEDLINGS AS INFLUENCED BY 2 AND 4kR OF °°Co GAMMA RAYS ADMINISTERED EITHER AS A SPLIT OR A CONTINUOUS EXPOSURE * Exposure Radiation-free Exposure Shoot Type of rate, period, period, dry weight,t exposure R/min min min % of control 25kR Split 50 30 70 88.1+2.8 Continuous 28.6 O 70 84.3 +6.2 Split 50 60 100 81.2 241 Continuous 20 O 100 88.3 + 3.4 Split 50 120 160 $6:7-25::8 Continuous 1524 O 160 868.22 525 4 kR Split 50 30 110 5 Ote4 Continuous 36.4 O 110 5. Syste Split 50 60 140 3A A 13D Continuous 28.6 O 140 42.6+ 4.3 Split 50 120 200 3925532 Continuous 20.0 @) 200 6033°= 3:3 *Exposure rates were adjusted to provide the same total duration of irradiation. tValues are the mean per treatment + standard error. 1.1? demonstrated the range another species. In a later publication Sparrow eta in exposures (acute) and in exposure rate (roentgens per day for chronic exposure) which induces lethality and/or varying degrees of growth suppression in a large number of species. The species response was correlated to average interphase chromosome volume, and it was shown that on the basis of absorbed energy (electron volts) per interphase chromosome the species do not vary for comparable levels of damage.'' By extrapolation one could infer that this relation would hold true for exposure-rate effects observed during acute irradiations on the basis of energy absorbed per interphase chromosome per minute instead of per day. Thus sensitive species would undergo a saturation at lower exposure rates than tolerant species when considered in terms of roentgens rather than electron volts absorbed. Recently Bottino and Sparrow” have reported a constant ratio of 1.4 between simulated-fallout-decay rate over a 36-hr period and 16-hr constant-rate exposures for lethality and yield reduction in plants of eight species. Furthermore, they reported that 8-hr constant-rate exposures were equal to the simulated-fallout-decay rate for the eight species. 284 CONSTANTIN, KILLION, AND SIEMER The results presented here for soybean seedlings indicate a rate saturation at approximately 50 R/min for seedling studies (Fig. 1) and 25 R/min for stem length at maturity and for yield (Figs. 3 and 4)—-two different types of end points. It should be noted, however, that these data were obtained from experiments with different varieties of plants at slightly different stages of development. If we can assume that varietal differences will be minimal, then we can infer an effect of stage of development and/or end point on the rate-saturation phenomenon. Our results concur with those of McCrory and Grun,” who have reported a relation between dose and dose rate in diploid, hybrid clones of Solanum. A similar relation between dose and dose rate and end point and dose rate has been reported in experiments with mice.” Cromroy'” alluded to the problems created by dose-rate effects when cross comparisons are made either within or among species. Krebs and Leong'” concluded from recent experiments with mice that (1) there was no change in LDs9/4 when exposure rate was 3500 R/hr or higher, (2) LDs9 /q practically doubled with a decrease from 3500 to 400 R/hr, and (3) there was little or no change in LD; 9/4 when exposure rate was below 400 R/hr. The limited data we have on Dso at different rates (results in this report and unpublished data) indicate a trend similar to conclusions 1 and 2 above. We have too few Dsg9 values for rates below 10 R/min to determine whether our results will also show a plateau response at low rates. Results in Fig. 1 indicate that a plateau may be reached; however, Fig. 1 shows the response instead of the exposure required to induce a particular level of response. A rate-saturation constant for species of organisms based on their interphase chromosome volume would be valuable to explain certain radiobiological phenomena. Cromroy'? reports the interphase chromosome volume of labora- tory white mice as approximately 2.25 u°, and the results of Krebs and Leong! ® indicate for the mouse a rate saturation at 3500 R/hr for LDs509 /q caused by gastrointestinal damage. Hill soybean seedlings at 2 days postemergence have an interphase chromosome volume of 2.95 u° and show a rate saturation at approximately 50 R/min for exposure required to reduce shoot dry weight to 50% of control. For end points scored later in the life cycle of the plant, however, a rate saturation was reached at 25 R/min. Also, the Solanum hybrids used by McCrory and Grun? have an interphase chromosome volume of 6.48 1? and show a rate saturation at 70 R/min for lethality at an exposure of 9 kR. Further research may be justified because it is known that some interspecific hybrids deviate from expected radiosensitivity based on their interphase mi Sparrow et al.1° have shown that the required energy chromosome volume. absorbed per interphase chromosome varies within a species in accordance with the end point and level of response. It is known also that changes in nuclear and interphase chromosome volumes occur during the mitotic cycle of cells'* and with seasonal changes in forest trees.’ ° The data in Table 1 for split vs. continuous exposures for the same length of time indicate that repair takes place in the soybean seedling. This does not EXPOSURE-RATE EFFECTS 285 preclude the occurrence of recovery in the plant after irradiation. Table 1 data show a lack of a detectable repair at 2 kR with either split exposures or lowering the rate from 28.6 to 15.4 R/min. Also, there was no difference in shoot dry weight between split and continuous exposures delivered during the same time period. This agrees with the results in Fig. 2, which indicate the lack of an exposure-rate effect at 2 kR and also with results in the literature.” ’” At 4 kR an increase in shoot dry weight was observed with an increase in radiation-free time from 30 to 60 min, and an extension to 120 min caused only a slight further increase. It is inferred that repair processes reached a maximum expression within approximately 60 min for the conditions of exposure and exposure rate used. Apparently changes in exposure and exposure rate in split-exposure experiments would alter the extent of repair and the time during which it occurs (refer to Krebs and Leong'® for data on mice). Results with exposures of 4kR at 50 R/min (Figs. 1 and 2) and at 50 R/min split exposure with 30 min of radiation-free time are approximately equal; this indicates that little repair occurred during a 30-min period. Contrary to most results in the literature, we observed a greater increase in shoot dry weight (from 15.5 to 60.3% of control) by decreasing exposure rate from 36.4 to 20 R/min than that for split exposures with a radiation-free period of 60 and 120 min (Table 1). Since we have only the results of this experiment without any knowledge of the repair mechanism, it appears that further discussion of the phenomenon in the soybean seedling is unwarranted at this time. One last comment is warranted concerning a problem pertinent to research involving growth of seedlings (fresh and dry weight or stem length) following irradiation. Results shown in Fig. 3 demonstrate the fallacy inherent to a comparison of the data from experiments scored at different arbitrary times after treatment. To illustrate the point, consider the differences in stem length among plants of the various treatments when it was measured at intervals from 5 to approximately 25 days after irradiation. The response shows minimal effects of exposure and rates at 5 days and maximal effects from 25 days on. The time course of events would probably vary according to when the organism was irradiated, the species, and the environmental conditions. ACKNOWLEDGMENTS The UT—AEC Agricultural Research Laboratory is operated by the Tennessee Agricultural Experiment Station for the U.S. Atomic Energy Commission under Contract AT-40-1-GEN-242. This work was supported by funds from the U. S. Office of Civil Defense and is published with the permission of the Dean of the University of Tennessee Agricultural Experiment Station, Knoxville. 286 CONSTANTIN, KILLION, AND SIEMER REFERENCES le 10; it. 12s ES. 14. S. Hornsey and T. Alper, Unexpected Dose-Rate Effect in the Killing of Mice by Radiation, Nature, 210: 212—213 (1966). .G. J. McCrory and P. Grun, Relationship Between Radiation Dose Rate and Lethality of Diploid Clones of Solanum, Radiat. Bot., 9(1): 27—32 (1969). .A. P. Casarett, Radiation Biology, pp. 244—247, Prentice-Hall, Inc., Englewood Cliffs, Ne J; 1968. .G. A. Sacher, Reparable and Irreparable Injury: A Survey of the Position in Experiment and Theory, in Radiation Biology and Medicine, Walter C. Claus (Ed.), pp. 283—313, Addison-Wesley Publishing Company, Inc., Reading, Mass., 1958. .P. J. Bottino and A. H. Sparrow, Comparison of the Effects of Simulated Fallout Decay and Constant Exposure Rate Treatments on the Survival and Yield of Agricultural Crops, in Proceedings of the 4th International Congress of Radiation Research, Evian, France, p. 30 (Abstract), 1970. .M. J. Constantin, The Relative Advantages of Fast Neutron Irradiation to Induce Bud Sprouts in Ornamental Plants, in Proceedings of the 4th International Congress of Radiation Research, Evian, France, in preparation, 1970. .P. Pereau-Leroy, Facteurs affectant la déchimerisation par irradiation gamma chez Poeillet, Bulletin de la société botanique de France, Colloque de morphologie experimentale, pp. 55—60 (1967). . A. H. Sparrow, Comparisons of the Tolerances of Higher Plant Species to Acute and Chronic Exposures of Ionizing Radiation, Jap. J. Genet., 40(Supplement): 12—37 (1965): . A. H. Sparrow and L. Puglielli, Effects of Simulated Radioactive Fallout Decay on Growth and Yield of Cabbage, Maize, Peas, and Radish, Radiat. Bot., 9(2): 77—92 (19.69). A. H. Sparrow, R. L. Cuany, J. P. Miksche, and L. A. Schairer, Some Factors Affecting the Responses of Plants to Acute and Chronic Radiation Exposures, Radiat. Bot., 1(1): 10—34:41961). A. H. Sparrow, R. C. Sparrow, K. H. Thompson, and L. A. Schairer, The Use of Nuclear and Chromosomal Variables in Determining and Predicting Radiosensitivities, from Technical Meeting on the Use of Induced Mutations in Plant Breeding, Rome, 1964. [Radiat. Bot., 5 (Supplement): 101-132 (1965)]. H. L. Cromroy, Mammalian Radiosensitivity. Final Report for the Office of Civil Defense, Contract Number N00228-68-C-2658, p. 22, 1969. J. S. Krebs and G. F. Leong, Effect of Exposure Rate on the Gastrointestinal LDs59 of Mice Exposed to ©°Co Gamma Rays or 250 kVp X-Rays, Radiat. Res., 42: 601—613 (1970). H. Swift, Quantitative Aspects of Nuclear Nucleoproteins, Int. Rev. Cytol; 22 1-76 (1953). . F. G. Taylor, Jr., Nuclear Volume Changes in Southeastern Tree Species Before Spring Growth, Radiat. Bot., 5(1): 61—64 (1965). EFFECTS OF ACUTE GAMMA IRRADIATION ON DEVELOPMENT AND YIELD OF PARENT PLANTS AND PERFORMANCE OF THEIR OFFSPRING E, G. SIEMER,* M. J. CONSTANTIN, and D, D. KILLION UT—AEC Agricultural Research Laboratory, Oak Ridge, Tennessee ABSTRACT The effects of acute gamma irradiation on the development and yield of soybean, rice, and corn plants were determined. Plants were grown in containers outdoors and exposed once during their life cycle to es gamma radiation at 50 R/min. Performance of their offspring was determined under greenhouse conditions. Yield of soybean plants receiving 2.5kR was either unaffected or reduced to approximately 50% of control depending on their stage of development when irradiated. At early bloom 1kR reduced yield significantly and 3 kR eliminated it. Two weeks later, during late bloom, 2 kR reduced yield significantly and 6kR eliminated it. Branch abscission was a factor in the reduction of seed yield in soybeans. Yield of rice plants exposed to 25 kR was either reduced or eliminated depending on the stage of development when the plants were irradiated, The plants were most sensitive to radiation during the time from panicle initiation to anthesis. When plants were irradiated in small peat pots 2 days after emergence (DAE) with minimal radiation attenuation to the shoot meristem, 5 kR reduced yield significantly and 15 kR eliminated it. An exposure of 2.5 kR essentially eliminated yield of a corn plant irradiated during the period from tassel initiation through silking. An exposure of 500 R reduced yield significantly when 1-DAE plants were irradiated in small peat pots. Periods of relative tolerance to gamma irradiation were observed during early vegetative phase when sucker proliferation occurred and just prior to pollination and fertilization. It appears that, if the parent plant produces seed when it is irradiated prior to fertilization and embryogenesis, emergence and seedling growth of the offspring will be normal. If the parent plant produces seed when it is irradiated after fertilization, however, emergence and seedling growth of the offspring will reflect the decrease in sensitivity of the developing embryo, *Present address: Mountain Meadow Research Center, Colorado State University, Gunnison, Colo. 287 288 SIEMER, CONSTANTIN, AND KILLION The degree of damage suffered by food-crop plants subjected to radioactive fallout from nuclear war would depend on many factors, including kinds of radiation, exposure, exposure rate, stage of plant development, and environ- mental conditions.’’* Irradiation may either inhibit or alter development of the vegetative and reproductive structure of the parent plant and development of the embryo and food-storage tissues in the seed. These factors contribute to making seed yield, the primary end product of agronomic food crops, relatively sensitive to ionizing radiation. Bell and Cole® referred to the lack of information pertinent to the prediction of the magnitude of yield reduction to be expected if crop plants were subjected to radioactive fallout.:In this report we present data to show the effects of exposure and stage of development on the yield of corn, rice, and soybean plants exposed once during their life cycle to °°Co gamma radiation. Morphogenetic data for nonirradiated (control) and irradiated populations of plants are presented to help explain the degree of yield reduction observed. Data on emergence and growth of offspring are presented also to assess the effects of irradiation on the establishment of a crop the following year. MATERIALS AND METHODS Plants of corn (Zea mays L.‘WF-9 X 38-11’), rice (Oryza sativa L.‘CI- 8970-S’), and soybean [Glycine max (L.) Merrill ‘Hill’ and ‘Kent’] were grown to maturity under outdoor conditions in containers (55-gal drums cut in half crosswise). The growth medium was a soil: Perlite : peat mixture (2: 2: 1 by volume) for the 1968 studies, and a soil: Perlite: peat: sand mixture (2:3:1:1 by volume) for the 1969 studies. Nitrogen, phosphorus, and potassium were added to maintain vigorous plant growth, and the plants were irrigated as needed. All irradiations were done at the °°Co variable-dose-rate irradiation facility of the UT—AEC Agricultural Research Laboratory. Since young seedlings of corn and rice have their shoot meristem below ground level, when they were irradiated, the metal container, growth medium, and water attenuated the gamma radiation that reached the shoot meristem. Dosimetry indicated that the extent of radiation attenuation was approximately 65% at a vertical depth of 2.5 cm and that the attenuation increased sharply within the first centimeter below the surface. (The attenuation was caused by the horizontal rather than the vertical distance through the medium traversed by the radiation.) The shoot meristem of corn and rice reached the surface approximately 3 weeks after emergence, and thereafter there was no problem of radiation attenuation by the medium. To study the response of young seedlings of corn and rice without the problem of attenuation, we grew and irradiated seedlings in small peat pots and then transplanted them into the containers. Attenuation was less than 10% for plants in these experiments. The root system of all plants received less radiation than did the aboveground parts. EFFECTS OF ACUTE GAMMA IRRADIATION 289 Emergence and growth of the offspring from seeds harvested from parent plants subjected to different radiation treatments were determined in greenhouse benches using the same growth medium as in the containers. The development of control plants was studied in detail by dissection of three or more plants at each time of irradiation. Data were collected on the growth of the vegetative and reproductive structures of the plant, and the time of occurrence of such events as flower-bud initiation, anthesis, fertilization, etc., was noted. More-specific details concerning methodology are included in the presenta- tion of results for each crop. RESULTS Soybeans Results of the 1968 studies with Hill soybean plants are shown in Table 1. The length of the primary stem was affected most severely during the period from 3 to 24 days after emergence (DAE); the extent of damage decreased with time from 24 to 41 DAE, and, from 45 to 62 DAE, stem length of the irradiated plants was greater than that of the control plants. Bean yield was affected most severely when the plants were irradiated at their earliest seedling stages and at the time of early blooming. As the plant developed its vegetative structures during the period from 3 to 17 DAE, it became more resistant to gamma irradiation, The plant became increasingly sensitive to gamma radiation from the time of flower-bud initiation to the tme of early bloom (45 DAE), Thereafter resistance to gamma radiation increased; this reflects the increasing tolerance of the developing embryo and the increase in development of the food-storage tissues in the seed. Studies of the offspring indicate that percent of emergence and growth were affected only slightly when the parent plants were exposed to 2.5kR at 50R/min prior to the tme of fertilization, the period from 3 to approximately 38 DAE. In general, percent of emergence decreased by approxi- mately 40% when the parent plants were irradiated during the period from 41 to 62 DAE. A similar trend was observed for seedling growth as measured by dry weight of the seedling at 18 DAE. Data from exposure-response studies of Hill soybean plants at 46 DAE (early-blooming stage) and at 60 DAE (late-blooming stage) are listed in Tables 2 and 3. Stem length showed a maximum reduction of approximately 30% at 46 DAE even at an exposure of 10 kR; however, at 60 DAE stem length was increased up to 22% above the controls, and none of the exposures used caused a reduction. Plants exposed to 3 kR or more did not undergo senescence (i.e., they did not shed their leaves) at the same time as the control plants. This response was probably associated with the decrease and elimination of bean development. The number of pods per plant was reduced by 50% at approximately 5.5 kR at 290 SIEMER, CONSTANTIN, AND KILLION Table 1 EFFECTS OF EXPOSURE OF HILL SOYBEAN PLANTS TO °°Co GAMMA RADIATION (2.5 kR AT 50 R/MIN) ON STEM LENGTH AND BEAN YIELD OF PARENT PLANTS AND ON EMERGENCE AND OVEN-DRIED WEIGHT OF OFFSPRING* Parents Length of Yield of Time of SPE OSIYAS EE ee Olspring irradiation, % of Weight, t % of Emergence, + Weight, § DAE cmt control g control % g 3 23 40 4.6 11 92 0.091 4 28 49 5.0 2 96 0.068 6 24 42 11.6 29 96 0.066 7 26 46 11.4 28 84 0.064 10 25 44 7.0 17, 72 0.058 Act 7933 40 24.0 59 84 0.090 12 DS 44 10.0 DD 88 0.073 3 24 42 19.0 47 88 0.076 14 26 46 2I20 a2 88 0.084 17 Zi 47 30.0 74 96 0.082 20 29 yl 22.0 54 84 0.070 24 17 30 18.1 45 88 0.072 A2G | 33 58 22.4 55 64 0.084 31 29 51 11.0 Diy, 92 0.090 34 37 65 16.0 40 72 0.078 38 44 Ta. 10.3 26 96 0.077 41 57 100 9.0 yD, 64 0.049 45 53 93 7h} 18 64 0.052 48 67 118 8.3 21 84 0.059 aD 68 119 22D DD) 60 0.030 62 65 114 2525 63 68 0.033 Control 57 100 40.4 100 92 0.072 *Three plants per container and one container per treatment. tMean per plant. + Number of seedlings emerged divided by number of seeds planted times 100. § Mean oven-dried weight per seedling at 18 DAE. 46 DAE, but at 60 DAE there was no reduction for the exposures used. The yield of beans at 46 DAE was negligible at 3 kR and above, whereas at 60 DAE yield became negligible at 6kR and above. No beans were harvested from 46 DAE plants, and few beans were harvested from 60 DAE plants exposed to 6kR or more. Because the soybean experiment had to be replanted two times in 1969 the lateness of the last planting necessitated a switch to Kent, which is a short-season EFFECTS OF ACUTE GAMMA IRRADIATION 291 Table 2 EFFECTS OF EXPOSURE OF HILL SOYBEAN PLANTS TO ONGS GAMMA RADIATION (1 TO 10 kR AT 50 R/MIN) AT 46 DAE, i.e., EARLY-BLOOMING STAGE, ON STEM LENGTH, NUMBER OF PODS, AND BEAN YIELD OF PARENT PLANTS AND ON EMERGENCE AND OVEN-DRIED WEIGHT OF OFFSPRING* Parents Length of Yield of primary stem beans Offspring Exposure, % of Number We‘ght,t % of Emergence, Weight, § kR cmt control of podst control % g 1 66 105 89 15.0 a2 92 0.068 2 67 106 139 10.2 35 68 0.057 3 61 97 109 0.9 } 72 0,033 Ag 62 98 5 ro) 20 0 0.5 10 125 2.0 2:5 EXPOSURE, kR Fig. 6 WF-9 x 38-11 corn plants exposed to veo gamma radiation at 1 DAE in small peat pots; radiation attenuation at the shoot meristem was minimal. The response curves show the effect of 0.5 to 2.5 kR at 50 R/min on grain yield of the parent plants and emergence and weight of their offspring. Data are from the 1969 studies. @, yield; O, fresh weight of offspring at 13 DAE; 4, emergence; | , standard error. indicates that the decrease in tolerance in plants irradiated during their early seedling stage (Fig. 5) was probably caused by radiation attenuation by the medium, Emergence and fresh weight of the offspring of parent plants irradiated at 1 DAE showed little or no difference as exposure was increased to 2 kR. An exposure response study was conducted with WF-9 X 38-11 corn plants at 10 selected times after emergence. Response data are listed in Table 9; the pattern of response for stage of development was similar to that shown in Fig. 5. Plants irradiated at 22 and 36 DAE showed the highest degree of sensitivity; zero yield of grain was observed following exposures of 1.5 and 2 kR, respectively. Yield of grain showed an increased tolerance to gamma radiation when plants were exposed to 1.5 kR or more at 44 and 50 DAE. Plants exposed at 54 DAE, the zygotic and early embryonic stages, showed a relatively high sensitivity, which decreased with each later successive time of irradiation. The performance of offspring from grain harvested from irradiated parent plants was studied under greenhouse conditions. Response curves in Fig. 7 show the effects of stage of development at irradiation on the emergence and fresh weight of offspring from parent plants receiving 2.5kR at 50 R/min. The response for both of these end points was similar to that for yield of grain for the irradiated parent plants. The increase in tolerance of the developing embryo is evident from 60 to 95 DAE. Data on the emergence and fresh weight of offspring from the exposure-response study are shown in Tables 10 and 11, EFFECTS OF ACUTE GAMMA IRRADIATION 301 Table 9 EFFECTS OF EXPOSURE* OF WE-9 x 38-11 CORN PLANTS TO °°Co GAMMA RADIATION (1 TO 2.5 kR AT 50 R/MIN) ON GRAIN YIELDt Time of i igh f ita: Yield weightt at four exposures, g DAE 1.0kR 1.5kR 2.0kR 2.5kR 8 P28 83 +2 68 = 17 51+21 22 (on beara [| O O O 36 57 a7 14-29 0 0 44 57425 rl Se | 18s+8 Va? 50 81 = 4 87 +14 63 +2 40 +9 54 s9 +11 44 +9 2649 177 60 50 +49 106 +5 68 +2 83 +12 65 84+16 103 +11 88 +4 106 +3 ip. 100 +24 115 24 107+8 {21-3 81 115+4 110 +20 11314 95 +7 Control 95 +19 *Data from the 1969 studies. tThree plants per container and three containers at 2.5 kR and two containers for other exposures. + Mean per plant + standard error. respectively. Generally, emergence showed a relatively high tolerance to gamma radiation, and fresh weight showed a pattern of response similar to the yield of grain. The increase in fresh weight of the offspring from parent plants irradiated at 60 to 81 DAE shows the decrease in sensitivity of the developing embryo. DISCUSSION Irradiation can reduce the vegetative mass of the plant, the photosynthetic factory, and in so doing can reduce the carbohydrate supply available for storage in seeds. Soybean plants exposed to 2.5 kR produced fewer primary stem internodes and leaves and fewer and shorter branches. Some leaflets were reduced in size. Branches abscised before and after flowering and fruiting, and either seed potential or seed was lost. Rice plants irradiated at 2 DAE in small peat pots at 5 kR showed significantly less height and tillering than control plants 4 weeks later. Corn plants irradiated at 1 DAE in small peat pots showed a reduction in size following exposure to 500 R or more gamma radiation after 15 days. Specific irradiation effects observed in experiments included shortened internodes, shortened and decreased width of leaf blades, and shortened leaf sheaths. Others have shown that irradiation can reduce vegetative mass; e.g., the rice studies of Kawai and Inoshita* and the barley studies of Hermelin.° 302 SIEMER, CONSTANTIN, AND KILLION 140 120 100 ©O oO % OF CONTROL 2) o) 40 0 10 20 30 40 50 60 70 80 90 100 DAYS AFTER EMERGENCE Fig. 7 Response curves for WEF-9 x 38-11 corn plants exposed to ©°Co gamma radiation at different days after emergence, showing the effects of 2.5kR at 50 R/min to the parent plants on emergence and fresh weight of their offspring. Data are from the 1969 studies. © , emergence; @, fresh weight of offspring at 13 DAE. Irradiation can alter the normal developmental pattern of a plant or the timing of developmental events and thus can reduce grain yield. Corn has been bred and selected for maximum yield obtained from one or at most two ears on a single-stemmed plant. The 2.5-kR exposures increasingly inhibited parental shoot development in corn as irradiation took place later after shoot emergence. This inhibition pattern was attributed to increased irradiation of the apical meristem of the parental shoot as the underground stem elongated. Increasing inhibition of the parental shoot permitted development of axillary shoots until as many as three suckers developed. However, all this vegetative proliferation cost time and available carbohydrates, and grain yield declined sharply with sucker proliferation. When parental shoots were irradiated later, the sucker buds did not develop, and the plant died. Sucker proliferation has been reported by others, including Sparrow and Puglielli’ for corn and Davies” for wheat. Although the early developmental period of corn, rice, and possibly of any grass plant, is characterized by a decline in yield as irradiation is delayed, there is a period of relative tolerance to gamma irradiation. This is caused probably by the arrest of the primary shoot meristem which permits the development of one or more axillary buds that are more tolerant to gamma irradiation because of their developmental stage. EFFECTS OF ACUTE GAMMA IRRADIATION 303 Table 10 EFFECTS OF EXPOSURE OF PARENT WE-9 x 38-11 CORN PLANTS TO °°Co GAMMA RADIATION (1 TO 2.5 kR AT 50 R/MIN) ON THE EMERGENCE OF OFFSPRING* Time of ; ee Emergencet at four exposures, % of control irradiation, FE ie Seo me rg Oe DAE 1.0kR 1.5kR 2.0kR 2.5kR 8 OF 94 98 94 22 96 + £ < 36 | 61 i a3 44 94 86 86 55 50 79 84 82 ZS 54 78 55 62 63 60 78 89 69 36 65 97 98 85 77 Ie 98 ae oF 92 81 94 98 oF 84 Control, 100% *Sixty seeds planted for each of three replications. tMean of three replications. tNo seed produced by parent plants. Table 11 EFFECTS OF EXPOSURE* OF PARENT WE-9 x 38-11 CORN PLANTS TO °°Co GAMMA RADIATION (1 TO 2.5 kR AT 50 R/MIN) ON FRESH WEIGHT OF OFFSPRING HARVESTED AT 13 DAE ‘ oe ot Fresh weightt at four exposures, % of control irradiation, DAE 1.0kR 1.5kR 2.0kR 2.5kR 8 108 108 100 100 22 130 + + t 36 Te 38 + t 44 85 69 69 15 50 54 69 46 30 54 54 31 32 31 60 62 46 23 8 65 85 ae 3° i5 72 77. 69 54 39 81 85 Ti 62 54 Control, 1.3 g = 100% *Data from the 1969 studies. tMean of three replications. +No seed produced by parent plants. 304 SIEMER, CONSTANTIN, AND KILLION Irradiation can affect gametogenesis, the production of a functional egg and pollen. Hermelin® found that barley is sensitive to irradiation at meiosis, and Kawai and Inoshita* found the same for rice. The exposure of soybeans to 2.5kR at early bloom caused severe yield reduction. The exposures of rice plants to 25kR between 34 and 55 DAE (roughly from panicle initiation to anthesis) eliminated all grain yield. One-tenth this exposure (2.5 KR) apphed to corn between tassel initiation and a week before silking also eliminated grain yield. Corn plants exposed at about the time of ear initiation (32 DAE) died. The adaptive nature of the corn plant when irradiated at this time became apparent in that tiller buds among brace roots became floral and a small amount of grain was produced before complete plant death. This grain would not be harvestable, however. Corn has the capacity to form ears from the top ear downward. Since each lower ear is initiated slightly after the one above it, one might expect that the second or third ear would take over development when the top ear is damaged. This sometimes happens when top ears are bagged to prevent premature fertilization in a breeding program but was not observed in our experiments. Either all axillary buds were damaged similarly or the effects of death in the top ear unfavorably permeated to lower ones. Plants killed by irradiation died from the top downward, and death was preceded by an accumulation of anthocyanin in the leaf tissue. Also, the normal corn ear is terminal; 1.e., it arises on the end of the shank and is enclosed by husk leaves. Axillary ear buds frequently are initiated late in development above husk leaves, and, when the terminal ear is irradiated before silking, an axillary ear may eventually produce grain. A radioresistant stage for corn apparently exists just before silking. Plants irradiated at 2.5 kR within a week before the first emergence of silks produced relatively high grain yields; the grain had relatively high germination and produced relatively vigorous seedlings. This phenomenon is believed to be caused by the egg’s having achieved full development in preparation for silk elongation, pollination, and fertilization. This potential to form grain might not be achieved in a uniform corn field where most top ears would be in a comparable developmental state and where irradiation eliminated viable pollen. Our material had viable pollen available for fertilization. Donini and Hussain® found that irradiation was more detrimental to pollen formation than to egg formation in wheat. This needs to be investigated in corn. Gametogenesis and the flowering date of a plant can be advanced by irradiation.’ We observed this when 1-DAE corn plants were exposed to 4.5kR (data not presented). In our material, however, this occurred at the expense of building vegetative structure, and grain yield was reduced. When tiller prolifera- tion was encouraged by an irradiation insult to the parent shoot, the end result was late and incomplete ear formation. Upsetting the normal plant anthesis and silking pattern can reduce yields since pollen is not available when silks are receptive. EFFECTS OF ACUTE GAMMA IRRADIATION 305 Irradiation can reduce grain yield by direct effects on the zygote, later embryonic plant development, and endosperm development. Mericle and Mericle® found the zygote stage in barley to be especially sensitive. The sharp reduction in our corn yields immediately after first silking supports this conclusion, ACKNOWLEDGMENTS The UT—AEC Agricultural Research Laboratory is operated by the Tennessee Agricultural Experiment Station for the U.S. Atomic Energy Commission under Contract AT-40-1-GEN-242. This work was funded by the Office of Civil Defense, Work Order No. DAHC 20-69-C-0109 and is published with the permission of the Dean of the University of Tennessee Agricultural Experiment Station, Knoxville. REFERENCES 1. A. H. Sparrow and Leanne Puglielli, Effects of Simulated Radioactive Fallout Decay on Growth and Yield of Cabbage, Maize, Peas, and Radish, Radiat, Bot., 9: 77—92 (1969). 2. C. R. Davies, Effects of Gamma Irradiation on Growth and Yield of Agricultural Crops. I. Spring Sown Wheat, Radiat. Bot., 8: 17—30 (1968). 3.M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to Fallout Radiation. Final Report, USAEC Report TID-24459, UT—AEC Agricultural Research Laboratory, Sept. 7, 1967. 4.T. Kawai and T. Inoshita, Effects of Gamma Irradiation on Growing Rice Plants. I. Irradiation at Four Main Developmental Stages, Radiat, Bot., 5: 233-255 (1965). 5. T. Hermelin, Effects of Acute Gamma Irradiation in Barley at Different Ontogenetic Stages, Hereditas, 57: 297—302 (1967). 6.B. Donini and S. Hussain, Development of Embryo of Triticum durum Following Irradiation of Male or Female Gamete, Radiat. Bot., 8: 289—295 (1968). 7.K. Sax, The Stimulation of Plant Growth by Ionizing Radiation, Radiat. Bot., 3: 17 9-186-(1:963). 8. L. W. Mericle and R. P. Mericle, Radiosensitivity of the Developing Plant Embryo, in Fundamental Aspects of Radiosensitivity. Report of a Symposium Held June 5—7, 196, Upton, N. Y., USAEC Report BNL-675, pp. 262—286, Brookhaven National Laboratory. (Brookhaven Symposia in Biology Number 14.) EFFECTS OF EXPOSURE TIME AND RATE ON THE SURVIVAL AND YIELD OF LETTUCE, BARLEY, AND WHEAT P. J. BOTTINO and A. H. SPARROW Brookhaven National Laboratory, Upton, New York ABSTRACT Experiments were conducted to compare the effects of 177Cs gamma radiation given as either 1-, 4-, 8-, or 16-hr treatments at constant rates (CR) with 36-hr fallout-decay- simulation (FDS) or with buildup (Bu) and fallout-decay-simulation (Bu + FDS) treatments with variable exposure rates. Seedlings of lettuce were given Bu + FDS, FDS, and 1-, 4-, 8-, and 16-hr CR treatments. Barley and wheat seedlings were given FDS and 8- and 16-hr CR treatments. Following irradiation the lettuce plants were transplanted to the field, barley to the greenhouse, and wheat to a growth chamber. The criteria of effect used were survival and yield. Young barley seedlings were given a total exposure of 1600 R at 32 different rates ranging from 60 to 4800 R/hr. The first leaf of each seedling was measured after 8 days of growth. For equal total exposures, FDS treatments were more effective than 16-hr CR treatments in reducing survival and yield of all three crops. The ratio of 16-hr CR to FDS at LDs50 was 1.43 for lettuce, 1.23 for barley, and 1.37 for wheat. For yield the FDS was more effective only at exposures above the LDs5o. Lettuce survival increased with exposure time between 1 and 16 hr, but this was a linear increase only after 4 hr. Barley seedling height decreased as the exposure rate increased from 60 to about 1000 R/hr. Further increases in exposure rate above 1000 R/hr had no further effect on seedling height. The greater effectiveness of the high exposure rates observed in these experiments substantiates our conclusion that the increased effect of an FDS treatment compared with a 16-hr CR treatment is attributable to the high initial exposure rates of FDS. Similar results for survival and yield reduction for the 8-hr CR and the FDS treatments were observed. Hence investigators lacking the facilities to simulate fallout decay could use an 8-hr CR treatment to approximate the effects of simulated-fallout-decay treatments. For equal total exposures of gamma radiation, a treatment simulating fallout decay has been reported’ ° to be more effective in reducing survival and yield of crop plants than are prolonged constant-exposure-rate treatments. The greater effectiveness of the fallout-decay-simulation (FDS) treatment is thought to be due to the very high exposure rates encountered initially.'-° Thus study of the 306 | EFFECTS OF EXPOSURE TIME AND RATE 307 effects of a given amount of fallout or simulated fallout radiation seems to become basically a problem of the effect of variations in exposure rate. This paper presents some of our most recent data on the effects of the gamma component of simulated fallout on crop plants and additional data showing how variations in exposure rate can affect a plant’s response to radiation. These data give support to the conclusion that high exposure rates are the basis for the greater effectiveness of the fallout-decay treatments. The plants used in this study were lettuce, barley, and wheat. MATERIALS AND METHODS Facilities and Treatment Procedure The theory and facilities used to simulate fallout decay have been previously described in detail.’ Basically, a series of stainless-steel shields are lowered over a : 3 . . . a 12,000-Ci '’ ’Cs source at predetermined times to simulate exposure to fallout 2] . . 7 1-2 Jaw. Each shield is machined to radiation that decays according to the t reduce the intensity by one-half. The plants are placed in concentric arcs around the source, and an entire series of exposures is given at one time for either FDS or constant-rate (CR) exposures. Figure 1 shows the exposure-rate patterns for a total exposure of 5000 R for the treatments used in this study. The CR treatments simply extend for a specific time—in the present study this was for 1, 4, 8, or 16 hr. In the buildup and fallout-decay-simulation treatment (Bu + FDS), which 1s a close approxima- tion to a true fallout situation, the exposure rate starts out at a low level, builds up in 51 min to a peak, and then decreases in a stepwise pattern over the exposure period. In the FDS treatment the exposure rate starts out very high and decreases in a similar stepwise fashion. The steps on the buildup and decay curves represent shields being raised or lowered, and, although this is a stepwise relation, the curve for accumulating exposure is fairly smooth, as shown in Big. 2: Experimental Procedure In the first experiment seedlings of lettuce, Lactuca sativa ‘Summer Bibb,’ were exposed 26 days after sowing in 2-in. peat pots to the following treatments: (1) CR treatments for 1, 4, 8, or 16 hr or (2) changing-exposure-rate treatments given as either FDS or Bu+FDS for 36 hr. Fifteen exposures of 30 plants each, plus a nonirradiated control, were used for the 16-hr CR, FDS, and? *Buessr DS” treatments’ “and” seven “exposures’*ot TO*plants"each plus a nonirradiated control, were used for the 1-,.4-, and 8-hr CR treatments. The experiment was carried out in early June 1969. The exposure rates for a total exposure or sS0OO08Rswere 5000, 19250)'625. and 31275 R/hr tor the l-, 4-;8-, and 16-hr treatments, respectively. The exposure rates for other total exposures 308 EXPOSURE RATE, R/hr BOTTINO AND SPARROW 1300 1200 1100 = VSO=NhiRDS 1000) 4a eee , 36-hr Bu + FDS aI See rey OAR Tits oe lob GR 900 800 700 600 500 400 300 200 0 4 8 12 16 20 24 28 32 36 TIME, hr Fig. 1 Exposure-rate patterns for a total exposure of 5000R for the treatments used. EFFECTS OF EXPOSURE TIME AND RATE 309 16 14 = NO oO ee) , Theoretical fallout accumulation , FDS accumulation —————_—»«;Bu + “FDS. accumulation ACCUMULATED EXPOSURE, kR 0 4 8 U2 16 20 24 28 32 36 40 HOURS AFTER DETONATION Fig. 2) Accumulated exposures for the 36-hr FDS and 36-hr Bu + FDS at 1 m from the source compared with the theoretical accumulated exposures expected during the same period from decay according to the t!*? law. varied in proportion to the exposure time. After irradiation the plants were transplanted to the field. Survival data were collected every other day until no more deaths attributable to the radiation occurred. Yield data measured as fresh weight of the aboveground portion of each plant were collected at the conclusion of the experiment. In December 1969 seedlings of barley, Hordeum vulgare ‘Mari,’ 8 days after sowing in 2-1In. peat pots, were irradiated with the following treatments: (1) CR treatments for either 8 or 16 hr or (2) a changing-exposure-rate treatment given as a 36-hr FDS. For each treatment there were 14 exposures of 10 plants each, plus a nonirradiated control. After irradiation the plants were transplanted into 6-in. clay pots and moved to a heated greenhouse. Survival data were collected three times a week until no more deaths attributable to the radiation occurred. At the conclusion of the experiment, the seed was harvested and weighed. In February 1970 a similar experiment using the same treatments as used for barley was carried out with hard red spring wheat, Triticum aestivum ‘Indus.’ There were nine exposures of 10 plants each, plus a nonirradiated control for each treatment. The plants were transplanted into 4-in. clay pots and placed ina light- and temperature-controlled growth room. The light was cool white 310 BOTTINO AND SPARROW fluorescent and supplemental incandescent (approximately 1600 ft-c) on an 18-hr day, and the temperature was 68 + 2°F at night and 72 + 2°F during the day. Again survival data were collected three times a week, and the seed was collected and weighed at the end of the experiment. An experiment to study the effect of exposure rate was conducted with germinating seeds of barley, Hordeum vulgare ‘Himalaya.’ Dry seeds (approxi- mately 12% water content) were planted on blotters according to the method of Myhill and Konzak.* Irradiation began 24 hr after planting and the seeds were given an exposure of 1600 R delivered at 32 exposure rates ranging from 60 to 4800 R/hr for periods ranging from 26.6 hr to 19.8 min. Forty seedlings per exposure-rate treatment were used. After irradiation the seedlings were returned to a growth chamber and grown at 80°F under continuous fluorescent light. A constant high humidity was maintained in the chamber by bubbling air through a water reservoir. The height of the first leaf was measured 8 days after Irradiation. RESULTS The results of the lettuce experiment are given in Fig. 3. The survival data (Fig. 3a) are shown on a probit plot of survival as percent of control against exposure for the three treatments. The graph shows the computer-fitted lines and actual data points. No difference was found between the Bu + FDS and the FDS treatments. Both treatments were more effective in reducing survival than the 16-hr CR treatment. The LDs9 values for the three treatments were 4.79 + 0.10 kR for FDS, 4.97 + 0.12 kR for Bu + FDS, and 7.01 + 0.12 kR for the Lo-hr CR: The yield data (Fig. 3b) show very little difference between the three treatments at the low exposures. At the higher exposures there was no difference between the results of the Bu + FDS and FDS treatments, but both were clearly more effective in reducing yield than the 16-hr CR treatment. A considerable amount of growth stimulation was evident at the lower exposures for all three treatments. This was found to be caused by the increased production of axillary growth, which contributed to the augmented fresh weight of the plant. The survival results for the lettuce CR treatments are compared in Table 1. As the exposure time increased, the exposure required to produce the three given end points also increased. The nature of this relation is shown for the LDso values in Fig. 4, where LDso 1s plotted against the log of exposure time. There is little change in LDs9 for the 1- and 2-hr treatments. As the exposure time is increased, however, LDso9 increases almost with the square of the exposure time. The results from the barley experiment are shown in Figs. 5 and 6. Figure 5 shows the probit plot of survival against exposure for the FDS and 16-hr CR treatments. The data are somewhat variable because only 10 plants per exposure 99.9 99 98 95 £ 90 Cc 8 ee 80 je) se i S 50 > ao = cp) 20 10 5 2 1 0 2 4 6 8 EXPOSURE, kR (a) 220 200 180 5 = 160 = fe) oO Salad 3c = i 120 > 100 EXPOSURE, kR (b) Fig. 3 (a) Probit plot of survival as percent of control vs. exposure for lettuce given 16-hr CR (@) and 36-hr FDS (@) and Bu + FDS (0) treatments. (b) Mean weight per treated plant as percent of control vs. exposure for lettuce for the same three treatments. | indicates + standard deviation (Ref. 2). St 312 BOTTINO AND SPARROW Table 1 COMPARISON OF THE SURVIVAL END POINTS FOR 1-, 4-, 8-, AND 16-HR CR TREATMENTS FOR LETTUCE 1l-hr CR, KR +S.D.* 4-hrCR,kR+S.D. 8-hrCR,kR+S.D. 16-hrCR,kR+S.D. LD 0 23:92 10.06 3.03 70:15 Aste Oe lel Ons 2a Oni LDso 2.5 1:30.06 3.47 £0.10 5203) cs O107. He OMe Os07, LDog9 2.78 0.08 3290. OFZ 5:46) 102153 7.64 + 0.10 *The abbreviation S.D. is standard deviation. 1 Z 5 S¥el0 20 EXPOSURE TIME, hr Fig. 4 LDs5o9 vs. log of exposure time for lettuce irradiated for 1, 4, 8, and ~ 16 hr az constant rates. i indicates + standard deviation. were used, but the results are consistent with those for the other species in showing the FDS treatment to be more effective in reducing survival than the 16-hr CR treatment. The yield data (Fig. 6) resemble the lettuce data (Fig. 3b) in that there 1s little difference between the FDS and 16-hr CR treatments at the lower exposures, but at exposures of 4 KR or more the CR treatment is clearly less effective in reducing yield. The 16-hr CR values are consistently above the FDS values although they are not always significantly different from them. Representative plants from the surviving exposures of the three treatments are shown in Fig. 7. The probit plot of survival for wheat against exposure is given in Fig. 8, and again the FDS treatment was more effective in reducing survival than the 16-hr CR treatment. The yield data (Fig. 9) are similar to those for lettuce and barley EFFECTS OF EXPOSURE TIME AND RATE 313 @, FDS @, 16-hr CR SURVIVAL, % of control EXPOSURE, kR Fig. 5 Probit plot of survival as percent of control vs. exposure for barley given 36-hr FDS and 16-hr CR treatments. in that the FDS treatment is more effective in reducing yield than the 16-hr CR treatment at the high exposures only. Representative plants of the surviving exposures from all treatments are shown in Fig. 10. It wbecamemclear that saciclose jrelation. ‘might exist.between ‘the. effects produced) by “8-hr’ CR: itreatments and -36-hr FDS treatments... Therefore -a comparison between these two treatments for both survival and yield was made for all three crops. This comparison is given for survival in Table 2 and Fig. 11 and tonmvicidiain: Kissel 2 to. 14 .ihe effects of these, two, treatments are essentially the same, especially at the LD5,. Table 2 shows that the LDs 9 values for each crop were not significantly different at the 5% level. The situation 1s comparable when yield is the criterion of effect studied (Figs. 12 to 14). The results of the barley exposure-rate experiment are given in Fig. 15. The injury increased in proportion to the log of exposure rate between 60 and 314 BOTTINO AND SPARROW 50 — oO @ Fos @ 16-hrcR MEAN WEIGHT OF SEEDS PER PLANT, g oO 0 1 2 25 EXPOSURE, kR Fig. 6 Log mean weight of seeds per treated plant (in grams) vs. exposure for barley given 36-hr FDS and 16-hr CR treatments. | indicates 99% confidence interval. 1000 R/hr. However, very little change in the level of injury was found between 1000 and 4800 R/hr. DISCUSSION Most of the results given here may be explained on the basis of exposure rate; 1.e., for the same total exposure, more damage occurs with high exposure rates than with low exposure rates. This, of course, is not a new concept in radiobiology, and the literature on the subject is too extensive to be reviewed in EFFECTS OF EXPOSURE TIME AND RATE 3:15 EDS Fig. 7 Representative barley plants from the surviving exposures for 36-hr FDS, 8-hr CR, and 16-hr CR treatments. Exposures are given in kiloroentgens. BOTTINO AND SPARROW 316 *yeAsiaqut + PUIPIJUOD % GG SAIWSIPUL | “SIUIWIIIN YD IYy-9T pue SGy IYy-OE UDAIT yeaYyM 1oJ aansodxa ‘sa (surea3 ul) jueyd para sad spaas yo 1431aM uvau BOT 6 ‘314 Y> “JYNSOdxX3 v € c L 0 HO 44-91 '@ SGi ‘Bp - “Je A ed eg fg 6 ‘INV1d Y¥3d SG33S 4O LHOISM NVAW *SJUIWAVIN YD 1Y-9T pur SGA 1Y-9¢ UdAIs YeIYM OJ DINSOdX=d *sA [ON -u0d JO UadJad sv yeATAINS Jo O]d AIqGoIg g “31 Y> “JYNSOdx4I s) G v € c L OS HO 44-9l '@ Sci ‘a 86 66 “TVAIAYNS |O1]UOD JO % EFFECTS OF EXPOSURE TIME AND RATE 317 CONTROL —1.00/ ad Ane / 2.00. Cs . CONTROL 1.60) 2.00 women meme Naren! Fig. 10 Representative wheat plants from the surviving exposures of 36-hr FDS, 8-hr CR, and 16-hr CR treatments. Exposures are given in kiloroentgens. depth here. In the majority of the published work, the effect measured increases with increasing exposure rate. This has been found for survival in Solanum,” barley,° Neurospora,’ and aerobic HeLa cells;? for growth inhibition in 7-1 and barley roots; ' for chromosome aberrations in pea'* and barley seeds;'? and for mutations in barley® and Neurospora.’ An oxygen requirement has been shown for the expression of this exposure-rate effect.*'!* This need is Vicia presumably due to the presence of repair mechanisms that require oxygen and 318 BOTTINO AND SPARROW Table 2 COMPARISON OF LDsg VALUES FOR THE 8-HR CR AND FDS TREATMENTS FOR LETTUCE, BARLEY, AND WHEAT Crop Treatment ' LD59,kR+S.D.* Lettuce FDS 4.79 +0.05 NS¢ 8-hr CR 5.03 +0.07 Be Barley EDS 1.99 +0.08 ce 8-hr CR 1.91 +0.04 mi Wheat FDS 3.09 0.71 Re 8-hr CR 3:45 11-12 ser *The abbreviation §.D. is standard deviation. tThe abbreviation N.S. means not significant at the 5% level. 99.9 99 Lettuce Barley Wheat 98 95 O ate 5 90 oI = Je Ecol a) == 750 — 4 a | ire z 8 2 > 220 at = B 10 + E 4 5 a ats oO ail @ 2 | + al 1 ale sl 0.1 3 4 5 6 7 1 2 3 4 2 3 4 5 6 EXPOSURE, kR Fig. 11 Comparison of probit plots of survival as percent of control vs. exposure for lettuce, barley, and wheat given 8-hr CR (0) and 36-hr FDS treatments (M). EFFECTS'OF EXPOSURE TIME AND RATE SiS 100 \ le?) A ‘i za za < @® FDS LW 2 O, 8-hr CR 20 10 ) 1 2 3 4 5 EXPOSURE, kR Fig. 12 Log mean weight per treated plant (in grams) vs. exposure for lettuce given 8-hr CR and 36-hr FDS treatments. | indicates 99% confidence interval. function most efficiently at low exposure rates. There are some limits to the exposure-rate effect, however. At very high exposure rates, further increases in rate do not bring about further increases in effect. This is in part a limitation of the system, as shown in the work of McCrory and Grun? where the 100% lethality level imposes an upper limit to the rate effect. This is not to say that an additional exposure-rate effect could not be shown, however; if the total exposure was decreased, there probably would be an additional exposure-rate 320 BOTTINO AND SPARROW 20 — oO MEAN WEIGHT OF SEEDS PER PLANT, g oO 0 1 2 EXPOSURE, kR Fig. 13 Log mean weight of seeds per treated plant (in grams) vs. exposure for barley given 8-hr CR and 36-hr FDS treatments. | indicates 99% confidence interval. = EFFECTS OF EXPOSURE TIME AND RATE 321 10 MEAN WEIGHT OF SEEDS PER PLANT, g oO N 6) 1 2 3 EXPOSURE, kR Fig. 14 Log mean weight of seeds per treated plant (in grams) vs. exposure for wheat given 8-hr CR and 36-hr FDS treatments. | indicates 99% confidence interval. effect. At the other end of the response curve, where the exposure rate is very low, a point is reached where no difference between irradiated and nonirradiated plants can be detected. This was observed by Hall and Bedford'® for growth inhibition in Vicia roots and in some studies with chronic irradiation using many “17 This has led to the conclusion that, although the cumulative species. | exposure is important, the rate at which that exposure is delivered is a more important factor.' ’ Thus there is substantial evidence in the literature for the exposure-rate effect reported here. We have observed an increasing effect with increasing exposure rate and have also reached the point in rate where no additional changes in effect occur with increasing rate. Experiments examining the response to lower exposure rates are under way. The most important factors controlling the specific exposure-rate effect are the species and criterion of effect used, the total exposure, and the environmental conditions during and after irradiation. Manipulation of these factors, e.g., lowering the total exposure, may allow one 322 BOTTINO AND SPARROW Y = 233.0 — 126.2 log X + 18.1 (log X)? SEEDLING HEIGHT, % 50 100 200 500 1000 2000 5000 EXPOSURE RATE, R/hr Fig. 15 Seedling height as percent of control vs. log of exposure rate for barley seedlings given a total exposure of 1600 R. to demonstrate an effect at higher exposure rates since the capacity of the system to respond would be greater under conditions more conducive to expression of the effect. We have reported both here and previously’’* that the FDS treatment is more effective in reducing survival and yield than the 16-hr CR treatment. The ratios of exposures at the LDs9 for 16-hr CR to FDS are 1.43 for lettuce, 1.23 for barley, and 1.37 for wheat; these ratios agree well with the average of 1.4 for seven other species previously reported. The constant difference between the two treatments which was observed for survival was not observed for yield. At exposures up to the region of the FDS LDs 9, little difference between the two treatments was observed. Above this exposure the yield for the FDS treatment falls off much more rapidly than the yield for the 16-hr CR treatment, and there is clearly a difference between the two. This difference in effectiveness is due to the very high exposure rates encountered in the early part of the FDS treatment. The average exposure rate in roentgens per hour (weighted for the shield EFFECTS OF EXPOSURE TIME AND RATE 320 timings) for a 5000-R exposure was calculated to be 791 R/hr for an FDS treatment as compared with 312.5 R/hr for the same total exposure from a 16-hr CR treatment. Thus the greater effectiveness of the FDS treatment can be explained by this difference of about 2.5 times in exposure rate. The fact that the survival and yield criteria for the FDS and Bu + FDS treatments are not greatly different is due to the use of essentially the same exposure-rate patterns for the two types of treatments (see Fig. 1). The barley-seedling-height experiment shows that radiation damage increases with increasing exposure rate at rates below 1000 R/hr and provides additional support for our conclusion that the greater effectiveness of the FDS treatment is due to the initial high exposure rates. About 40% of the total exposure of 5000 R, which was lethal for lettuce, wheat, and barley, was given at 1300 R/hr. Although the criterion of effect studied was seedling-height reduction, it can be assumed that the survival and grain yield would also respond in a similar manner to variations in exposure rate. Thus the high overall exposure rate would be more than adequate to explain the increased effectiveness of the FDS treatment. The similarity in effect between the 8-hr CR treatment and the FDS treatment is interesting from a practical standpoint. The exposure rates for the two treatments, compared for a 5000-R exposure, were found to be 625 R/hr for the 8-hr CR exposure and 791 R/hr for the FDS exposure. On this basis we would predict a similar level of effect for the two treatments if exposure rate played an important role in determining the level of damage. This finding 1s important since it implies that laboratories lacking the facilities to simulate fallout decay may obtain similar results by using 8-hr CR treatments. Although the 8-hr CR wheat data deviate somewhat from the FDS data for survival, the similarity between the FDS and the 8-hr CR data for all crops is very good, and relevant data on survival and yield for other crops can be made by using 8-hr CR treatments. ACKNOWLEDGMENTS We wish to thank Brenda Floyd, Susan S. Schwemmer, E. E. Klug, Leanne Puglielli, J. Newby, R. Sautkulis, Pamela Silimperi, and J. Bryant for assistance with the irradiations and data collection; R. A. Nilan for supplying the barley seed; and C. F. Konzak for supplying the wheat seed. The assistance of K. H. Thompson with statistics and Virginia Pond and Susan S$. Schwemmer with critical comments on the manuscript is also acknowledged. This research was carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission and the Office of Civil Defense, Department of the Army, Washington, D. C., under Project Order No. DAHC20-69-C 0167, Work Unit 3133E. Contracting office technical representa- tive was D.W. Bensen. This report has been reviewed and approved for publication by the Office of Civil Defense. Approval does not signify that the contents necessarily reflect the views and policies of the Office of Civil Defense. 324 BOTTINO AND SPARROW REFERENCES ik2 10. te be 12. LES): 14. tS: 16. 7 A. H. Sparrow and Leanne Puglielli, Effects of Simulated Radioactive Fallout Decay on Growth and Yield of Cabbage, Maize, Peas and Radish, Radiat. Bot., 9: 77—92 (1969). . A. H. Sparrow, Brenda Floyd, and P. J. Bottino, Effects of Simulated Radioactive Fallout Buildup and Decay on Survival and Yield of Lettuce, Maize, Radish, Squash, and Tomato, Radiat. Bot., 10: 445—455 (1970). .G. M. Clark, F. Cheng, R. M. Roy, W. P. Sweaney, W. R. Bunting, and D. G. Baker, Effects of Thermal Stress and Simulated Fallout on Conifer Seeds, Radiat. Bot., 7: 167—175 (1967). .R. R. Myhill and C. F. Konzak, A New Technique for Culturing and Measuring Barley Seeds Crop Sct 272127 9-2/0 (1.967):. . J. McCrory and P. Grun, Relationship Between Radiation Dose Rate and Lethality of Diploid Clones of Solanum, Radiat. Bot., 9: 27—32 (1969). . A. Silvy and P. Pereau-Leroy, Effets genetiques d’irradiations gamma de courte duree et a differents debits de dose sur des plants d’orge (var. Piroline) en cours de developpement, in Induced Mutations in Plants, Symposium Proceedings, Pullman, Wash., 1969, pp. 181—193, International Atomic Energy Agency, Vienna, 1969 (STI/PUB/231). . F. J. de Serres, H. V. Malling, and B. B. Webber, Dose-Rate Effects on Inactivation and Mutation Induction in Neurospora crassa, in Recovery and Repair Mechanisms in Radiobiology, Brookhaven Symposia in Biology Number 20, June 5—7, 1967, Upton, N. Y., USAEC Report BNL-50058, pp. 56—76, Brookhaven National Laboratory. .E. J. Hall, J. S. Bedford, and R. Oliver, Extreme Hypoxia; Its Effect on the Survival of Mammalian Cells Irradiated at High and Low Dose Rates, Brit. J. Radtiol., 39: 302—307 (1966). .E. J. Hall and J. Cavanagh, The Oxygen Effect for Acute and Protracted Radiation Exposures Measured with Seedlings of Vicia faba, Brit. J. Radiol., 40: 128—133 (1967). E. J. Hall and J. S. Bedford, A Comparison of the Effect of Acute and Protracted Gamma Radiation on the Growth of Seedlings of Vicia faba, Part 1. Experimental Observations, /nt. J. Radiat. Biol., 8: 467—474 (1964). L. Cercek, M. Ebert, and D. Greene, RBE, OER, and Dose-Rate Effects with 14 MeV Neutrons Relative to 300 kVp X-Rays in Barley Roots, Int. J. Radiat. Biol., 14: 453—462 (1969). A. M. Akopyan, Effect of Different Types of Ionizing Radiations in Peas. I]. Dose and Dose Rate Effects on the Frequency of Chromosomal Aberrations of Pea Seeds After Gamma Irradiation, Genetika, 7: 34—38 (1967). K. A. Filev, Postirradiation Seed-Storage Effect as Related to Irradiation Dose and Rate, Dokl. Akad, Nauk SSSR, 169: 680—682 (1966). D. L. Dewey, An Oxygen Dependent X-Ray Dose-Rate Effect in Serratia marcescens, Radiat. Res., 38: 467—474 (1969). J. M. Bostrack and A. H. Sparrow, The Radiosensitivity of Gymnosperms. II. On the Nature of Radiation Injury and Cause of Death of Pinus rigida and P. strobus After Chrenic Gamma Irradiation, Radiat. Bot., 10: 131—143 (1970). G. M. Woodwell and A. H. Sparrow, Predicted and Observed Effects of Chronic Gamma Radiation on a Near-Climax Forest Ecosystem, Radiat. Bot., 3: 231—237 (1963). J. E. Gunckel, A. H. Sparrow, Ilene B. Morrow, and Eric Christensen, Vegetative and Floral Morphology of Irradiated and Non-Irradiated Plants of Tradescantia paludosa, Amer. J. Bot., 40: 317-332 (1953). DOSE-FRACTIONATION STUDIES AND RADIATION-INDUCED PROTECTION PHENOMENA IN AFRICAN VIOLET C. BROERTJES Institute for Atomic Sciences in Agriculture, Wageningen, The Netherlands ABSTRACT Leaves of African violet, which develop adventitious buds on petioles after rooting, have been used as test material for dose-fractionation studies with X rays and fast neutrons. The parameters used were survival of the leaves, production of adventitious plantlets per leaf, and mutation frequency. The aim of the experiments was to determine the relation between initial dose, time interval, and the extent of the radioinduced protection. The “optimal” initial dose inducing maximal protection (equivalent to approximately 3 krads) proved to be 500 rads of X rays and fast neutrons at an “‘optimal”’ time interval of 8 to 12 hr. Repeated irradiations with the optimal initial dose at 8-hr time intervals induce a protection much higher than that of a single pretreatment, reaching a maximum after approximately 10 irradiations. No qualitative differences were found between X rays and fast neutrons. The relative biological effectiveness (RBE) for protection is found to be 1, whereas the RBE for acute irradiations is 2. The results presented are discussed and compared with literature data dealing mainly with mammals. A few questions arise about the significance of the phenomena described in relation to radiotherapeutic procedures. African violet, Saintpaulia ionantha ‘Utrecht’, was used to study the effects of acute and chronic irradiation with Xrays and fast neutrons. During these experiments a very pronounced dose-rate effect was observed.’ Dose- fractionation experiments were carried out in an attempt to analyze the mechanisms involved; again both X rays and fast neutrons were used. The experiments described here were carried out to determine the interaction between various initial doses, time intervals, and repeated irradiations and the radiosensitivity of the material. The results are discussed in terms of radioinduced protection or improved radioinduced repair mechanism. It is impossible to decide which term should be 325 326 BROERTJES used without knowing exactly the mechanisms involved; protection implies prevention of part of the damage by the radiation, whereas improved repair speaks for itself. The word “protection” was chosen mainly to emphasize the difference between the normal repair that takes place after acute irradiation and the phenomena described, which occur after fractionated treatments. The explanation of these phenomena is not a simple one. Many authors have presented possible explanations, but so far none is completely satisfactory. These investigations do not include a study of the mechanisms involved but are concerned with more-practical mutation breeding and consequently do not contribute to an explanation of the protection phenomena observed. MATERIAL, PARAMETERS, AND IRRADIATION FACILITIES Material African violet, which belongs to the Gesneriaceae, was selected as an experimental plant for various reasons. It forms medium-size plants that can be grown without difficulties under proper greenhouse conditions throughout the year. The species reproduces easily from leaf cuttings, which, after rooting, produce 10 to 20 plantlets per leaf from adventitious buds formed at the base of the petiole. These adventitious plantlets can be separated from the mother leaf, transplanted in boxes or pots, and grown to maturity. This reproduction system, the so-called adventitious bud technique, was chosen for one important reason: Every adventitious plantlet ultimately originates from only one epidermal cell; this results in solid, nonchimeral mutants if this cell carries a mutation. After any mutagenic treatment, whether short (minutes) or very long (up to 4 weeks), the lower 5 mm of the petiole, the region where the adventitious buds are formed, was cut off. In this way it was ascertained that the epidermal cells situated higher up the petiole, which had undergone the whole treatment as nondividing, resting cells, were stimulated to develop the adventitious buds. This procedure avoided the consequences arising from differences in radiosensitivity caused by different cell-division stages as well as the chimera formation resulting from mutation induction in the developing multicellular meristems during a prolonged treatment (longer than 3 to 5 days). In general, 20 leaves per treatment were used. Parameters Three parameters were used to measure the effect of the irradiation: 1. Survival of the irradiated leaves (in percent of the control). Only leaves that produced at least one plantlet were considered to be alive. 2. Production of plantlets (average number per leaf in percent of the control). This is the most reliable parameter and generally reacts very sharply DOSE-FRACTIONATION STUDIES S27 depending on the intensity of the treatment. Untreated leaves produce approximately 15 plantlets per leaf. Survival and production were determined 4 to 5 months after planting during separation of the plantlets from the mother leaf. 3. Mutation frequency. This was determined approximately 3 months after the separation when the plants were large enough for variations in size, form, habit, and color of leaf and plant to be distinguished. This is the least reliable parameter since habit, size, and other visible characteristics vary with differences in climatic and other conditions and, in addition, are influenced by the previous treatments. The decision to consider a plant a mutant was often an arbitrary one. Irradiation Facilities X rays were applied with a Philips 250/25 deep-therapy apparatus, usually operating at 250 kV and 15 mA without an additional filter. The dose rate apphed was always 200 rads/min. Temperature was the only climatic condition controlled during irradiation. Fast-neutron irradiations were carried out in the sub-core irradiation room of the Biological Agricultural Reactor Netherlands (BARN). When the facility was operating at full power, a dose rate of 1000 rads/hr in H,O was obtained in the irradiation position. Since Saintpaulia leaves contain 97 to 98% H,0O, this may be considered as the dose rate in the material. The fast-neutron spectrum is similar to a fission spectrum and has an average energy of approximately 2 MeV. The gamma contamination amounts to 80 rads/hr (Ref. 2). RESULTS In this discussion of the results of the dose-fractionation experiments, I will refer often to the acute-dose-effect curves. As can be seen in Figs. 1 and 2, the form of the curves is almost identical for X rays and fast neutrons. The only difference is that on a rad basis fast neutrons from the BARN reactor have a relative biological effectiveness (RBE) for the three parameters used of approximately 2 compared with the X rays. The results presented here indicate that both radiations are qualitatively alike. The first experiment, in which two equal semilethal doses (50% of the sublethal X ray dose of 6 krads) were applied at various time intervals, clearly showed that after an interval of more than 8 to 12 hr the effect of the two fractions was identical with the effect of only one fraction for both survival (Fig. 3) and production (Fig. 4). It can be seen, especially from Fig. 4, that the first dose must have induced some kind of change resulting in a mechanism that develops in time, reaches a maximum after approximately 12 hr, and gradually breaks down in the following days; it was still noticeable, however, after 120 hr. 328 BROERTJES 100 80 Oo) (=) % OF CONTROL BSS ro) 20 ae 4.-°® Mutation DOSE, krads Fig. 1 Dose-effect curves after acute X-ray treatments (200 rads/min) of African violet leaves. 100 ——— or tae ' N 80 \ Production ‘e 60 % OF CONTROL 40 20 a Mutation @) 1 2 3 4 DOSE, krads Fig. 2 Dose-effect curves after acute fast-neutron treatments (1000 rads/hr) of African violet leaves. DOSE-FRACTIONATION STUDIES 329 100 80 60 secvecee, & Krads acute 40 _______, 6 krads acute SURVIVAL, % of control 20 0 48 96 144 TIME INTERVAL, hr Fig. 3. Effect on survival of two semilethal X-ray doses (3 krads) given at various time intervals. 100 eeoeeeveeoeoeoeoeoeeeeeoeeeeeeeeeeeeee8@ Ye) 5 80 Cc 9 oO — ) 3s 60 ae Oo rk S40 ra) srsieceee > OS Krads acute 2 ________, 6 krads acute ra 20 48 96 144 TIME INTERVAL, hr Fig. 4 Effect on production of two semilethal X-ray doses (3 krads) given at various time intervals. 330 BROERTJES As mentioned previously, it was decided to use the word “‘protection”’ for this mechanism. Various questions arise: (1) Can an optimal initial dose be determined which induces a maximal protective effect in the leaves? (2) What is the relation between protection and the time interval separating the initial dose and the second dose? (3) What is the extent of the protection? And (4) What is the effect of repeated irradiation with the optimal initial dose at the optimal time interval. Initial Dose Various initial doses have been applied, ranging from very small ones (1-, 10-, 30-, T5=, and 150-rad X-ray doses and comparable doses of fast neutrons) up to the semilethal X-ray dose of 3 krads. These were followed, after the optimal time interval (8 hr, see the following section), by a series of second doses, L.e., the semilethal X-ray dose of 3 krads, the sublethal dose of 6 krads and a number of lethal doses (7, 8, 9, and 10 krads) and comparable fast-neutron doses. The high second doses were given to test the extent of the protection. As can be seen in Figs. 5 and 6 (survival and production, respectively, after various initial doses of X rays or fast neutrons), a very pronounced protective effect is initiated by a first dose of 500 to 1000 rads of X rays or fast neutrons. The exact optimum is hard to define since a fairly large dose range, covering a few hundred rads, induces almost maximal protection. Moreover the optimum depends on the extent of the second dose. A larger second dose requires a larger initial dose for maximal protection; this indicates a small increase in protection with increasing initial dose in the dose range mentioned. To define the optimal initial dose, we must take into account the nonrepaired effects of the initial dose. They mask the effect of the protection, especially when higher initial doses are applied, because their contribution to the total effect increases with dose. The choice of the optimal initial dose has therefore fallen on an initial dose in the lower region of the dose range inducing nearly maximal protection, i.e., 500 rads of X rays or fast neutrons. Unfortunately some preliminary experimental results suggested that 170 rads of fast neutrons was the optimal initial dose in African violet. This means that a few experiments were carried out with repeated irradiations with fast neutrons at a suboptimal initial dose; these cannot be directly compared with the repeated X-ray irradiation using the optimal initial dose (see the section on repeated irradiation). Time Interval The initial dose, selected to study the effect of time interval (500 rads of X rays or 170rads of fast neutrons), was separated from the second dose (generally 3 krads of X rays or 1700 rads of fast neutrons and 6 krads of X rays DOSE-FRACTIONATION STUDIES 331 100 80 3 5 Cc 8 ems ={0) e) 32 zi = e > a =) (ep) 20 0 1 2 3 INITIAL DOSE, krads Fig. 5 Effect of various initial doses on survival. Second doses were 6-krad X rays (—) and 3.3-krad fast neutrons (- - - -); there was an 8-hr time interval between first and second doses. 100 80 60 % of control PRODUCTION, 0 1 2 3 INITIAL DOSE, krads Fig. 6 Effect of various initial doses on production. Second doses were 5-krad X rays (—-) and 2.5-krad fast neutrons (- - - -); there was an 8-hr time interval between first and second doses. 332 BROERTJES or 3400 rads of fast neutrons) by time intervals ranging from 1 to 12 hr and from 24 to 240 hr. As is shown in Figs. 7 and 8, a protective mechanism builds up very rapidly, reaching its maximum after 8 to 12 hours and gradually decreasing with increasing time interval. After approximately 120 hr the protective effect has disappeared almost completely regardless of the type of radiation used. 100 80 Survival % OF CONTROL 0 24 72 120 168 TIME INTERVAL, hr Fig. 7 Effect of various time intervals on survival and production at an initial X-ray dose of 500 rads and a second X-ray dose of 6 krads. At 6 krads there is approximately 10% survival and approximately 20% production; an X-ray dose of 6.5 krads is lethal. In relation to the repeated irradiations planned, the optimal time interval was defined as the shortest time needed for maximal protection. The selected time interval of 8 hr permitted 60 repeated irradiations of the material with the optimal initial dose within 20 days. A time interval of 12 hr would have extended the experiment to 30 days, which is too long for the separated leaves to remain in sealed plastic bags. Extent of Protection A series of high second doses, most of which are lethal when given as an acute single dose, were applied to test the extent of the radioinduced protection. As.-can, be seen in’ Fig.) 9) "even vatters an xGray, dose of 97 or 10 krads,.01 comparable fast neutron doses, on the basis of an RBE of 2.0, there is a surviving fraction corresponding to an acute single dose approximately 3 krads lower. In other words, a low initial dose of 500 rads induces a protective mechanism with an extent of approximately 3 krads. DOSE-FRACTIONATION STUDIES 333 100 80 60 40 % OF CONTROL 0 48 96 144 192 TIME INTERVAL, hr Fig. 8 Effect of various time intervals on survival and production at an initial fast-neutron dose of 170 rads and a second fast-neutron dose of 3.4 krads; fast-neutron doses of 3.3 and 3.5 krads are lethal. Acute \ fast ‘ neutrons SURVIVAL, % of control FAST NEUTRONS SECOND DOSE, krads Fig.9 Extent of protection induced by an initial X-ray dose of 600 rads (—@-—) or an initial fast-neutron dose of 500 rads (--4A--), tested by applying various second doses of X rays or fast neutrons after an 8-hr interval. 334 BROERTJES This is also very clearly demonstrated by an experiment in which an optimal initial X-ray dose (500 rads) or the suboptimal fast-neutron dose of 170 rads preceded a series of second doses of either fast neutrons or X rays by an 8-hr time interval. The distance between the acute lines and the other, parallel, lines is approximately 3 krads, as is shown in Figs. 10 and 11, again on the basis of an RBE of 2.0. 100 80 fast 60 neutrons \ 40 SURVIVAL, % of control 20 0 ~ 2 4 6 8 10 12 14 X RAYS 0 1 2 3 4 5 6 7, FAST NEUTRONS SECOND DOSE, krads Fig. 10 Effect on survival of the optimal initial dose (500 rads of X rays or 170 rads of fast neutrons) after various second doses of Xrays or fast neutrons. — A-—, both initial and second doses of X rays; — 4 -—, initial dose of X rays, second dose of fast neutrons; - - ™- -, both initial and second doses of fast neutrons; and - - 0--, initial dose of fast neutrons, second dose of X rays. Repeated Irradiation To investigate whether repeated irradiation with the optimal initial dose at optimal time intervals would result in increased, decreased, or equal protection, we applied 500-rad X-ray or 170-rad fast-neutron doses repeatedly at 8-hr intervals. During the treatment the leaves were sealed in plastic bags and kept in the dark except during handling and irradiation. The temperature was kept at approximately 20" Gs After 14.5) 105) ete too 0 repetitions, a series of higher doses was applied to test the protection, i.e., X-ray doses of 1.5, 3, 4.5, 6, 8, and 10 krads or fast-neutron doses of 0.8, 1.7, 2.5, 3.4, 5, and 6.8 krads. DOSE-FRACTIONATION STUDIES 335 PRODUCTION, % of control FAST NEUTRONS SECOND DOSE, krads Fig. 11 Effect on production of the optimal initial dose (500 rads of X rays or 170 rads of fast neutrons) after various second doses of X rays or fast neutrons. — 4—, both initial and second doses of X rays; — A —, initial dose of X rays, second dose of fast neutrons; - - @--, both initial and second doses of fast neutrons; - - 0 - -, initial dose of fast neutrons, second dose of X rays. As can be seen in Figs. 12 and 13, which are based on the same data but are presented differently (i.e., survival at an initial X-ray dose of 500 rads), the protection increases drastically with the number of repetitions. After from 5 to 60 repetitions, all high doses applied (including 10-krad X-ray doses) result in 100% survival. Similar results are obtained with fast neutrons (Figs. 14 and 15); these data also show clearly that the protection reaches a maximum after 5 to 15 repetitions and then decreases fairly rapidly. This can also be seen in Fig. 16, in which the values of Fig. 15 are corrected for accumulated unrepaired damage of the repeated irradiations as well as for storage. (Storage for 3 weeks causes a decrease in survival and production.) When the results obtained after repeated exposures are compared with those after a single pretreatment, it is obvious that the extent of the protection increases considerably after a few irradiations at the optimal initial dose and reaches a value that is much higher than the best single pretreatment. For 336 BROERTJES (Che ae ee ee —— SS Q | 80 co 3 r e : (o) e [S) e ae. 60 fs fe) 5 se *. : : S 40 . > :: ae 3 = Acute @ 20 ‘. 0 e 0) 2 4 6 8 10 LAST DOSE (X RAYS), krads Fig. 12 Effect on survival of repeated X irradiations of 500 rads at 8-hr intervals; various last doses of X rays were applied. - - -@.-- +, one pretreatment with 500 rads; - - - -, 5 to 60 repetitions. 6 krads SURVIVAL, % of control 1 10 20 30 40 50 60 NUMBER OF REPETITIONS Fig. 13 Effect on survival of repeated X irradiations of 500 rads at 8-hr intervals; various last doses of X rays were applied. SURVIVAL, % of control DOSE-FRACTIONATION STUDIES Seg ee 1 10 20 30 40 50 60 NUMBER OF REPETITIONS Fig. 14 Effect on survival of repeated fast-neutron irradiations of 170 rads at 8-hr intervals. Last doses of fast neutrons were 6.7 krads (--©- -), 5 krads (— @-—), 3.4 krads (- - A- -), 1.7 krads (— &—), and 170 rads (- - O- -). 125 oO __ ee Tere es 2 100 = 70 oO A sae = rah a Sa a Cc Se 8 EOe paca a 75 7 ~a ‘ aa xe v7 ~ 4 ry A / ar A A : S i H Be eae ke — A S / ae A Q ii Tea oe) / e@ A ~ jag 25 @ @ e Paes a i ) in ie e r) ~“~ A ee 0 Lo —_o=—1—___ 0 1 10 20 30 40 50 60 NUMBER OF REPETITIONS Fig. 15 Effect on production of repeated fast-neutron irradiations of 170 rads at 8-hr intervals. Last doses of fast neutrons were 6.7 krads (- - O--), 5 krads (— @—), 3.4 krads (-- A- -), 1.7 krads (— &—), and 170 rads (- - O- -). S37 338 BROERTJES @ 100 ® e ¢ 80 ° < ane ee ® : a se : ° o / No se 60 | ~~ e e i No fo) Z / Oo | > ° 5 A N 2 4ol_/ ~ O / Zoe Pd = Rs Pree Oo Age SS ® o LiF es GS A ~ oO | ii << au A 4 20 Py cele Ano A Cr. (ae es =. N. ERS a SS ' : Nn ft CREEPS ; 1 10 20 30 40 50 60 NUMBER OF REPETITIONS Fig. 16 Effect on production of repeated fast-neutron irradiations of 170 rads at 8-hr intervals; various last doses of fast neutrons were applied; and krads; — - —, 5*krads;and --:: +, 6.7 krads. example, a fast-neutron dose of 5 krads applied after 15 repetitions of 170 rads of fast neutrons gives a survival rate of approximately 90% (Fig. 14), whereas 5 krads after the optimal initial fast-neutron dose of 500 rads is just about lethal (Fig. 9). For an initial X-ray dose of 10 krads, these figures are 100 and 0%, respectively (Figs. 13 and 9). From these figures it would appear that fast neutrons are less effective in the induction of protection than are X rays. But it should be borne in mind that the repeated fast-neutron irradiations were carried out at the suboptimal initial dose of 170 rads. Moreover, the results presented in Figs. 10 and 11 counteract this impression, especially when the suboptimal 170-rad fast-neutron line is replaced by the optimal 500-rad fast-neutron line of Fig. 9. DISCUSSION Comparison of X Rays and Fast Neutrons As mentioned previously, no fundamental difference in action of X rays and fast neutrons from the BARN reactor is evident. It is known that 14-MeV neutrons have a much more pronounced direct effect and consequently do not show much dose-rate effect when compared with neutrons having an average energy of 2 MeV. This is demonstrated very clearly in Figs. 10 and 11, which DOSE-FRACTIONATION STUDIES 339 present the results of an experiment in which a pretreatment of X rays or fast neutrons was followed by second doses of X rays or fast neutrons after an 8-hr time interval. From the experimental results it appears that the optimal initial dose for protection is 500 rads of X rays or fast neutrons. Thus the RBE for protection is1, but, for survival and production [after both acute and fractionated exposures (Figs. 1 and 2 and 10 and 11, respectively)], the RBE has been found to be 2. No explanation of this interesting result can be given at the moment. Radiation-Induced Protection Most literature on this subject deals with microorganisms (Saccharomyces), with mammalian cells in vitro, or with animals (chickens, dogs, goats, mice, monkeys, pigs, rabbits, rats, and sheep). Generally, whole animals are used to study the effect of one or more pretreatments (initial dose, primary dose, conditioning dose) prior to a second total-body (mass) irradiation after various time intervals. Survival or mortality is generally the parameter used, as for example, by Christian et al.° for the chicken. Some experimenters irradiated only part of an animal; e.g., Bewley et al.* irradiated the skin of pigs and used skin reactions as a parameter. Others used repopulation as the parameter, as, for example, in the mice studies of Denekamp et al.” A number of authors have tried to review all the data on radioinduced protection and to classify the many different and often confusing observations obtained by various scientists.°? Krokowski’°® standardized the results, compared the LDs9’s of the radiation effects with and without preirradiation, and put them in a three-dimensional coordinate system. We can draw a number of general conclusions from all these data: 1. Preirradiation induces a protective mechanism. 2. This protection depends on the intensity of the initial dose, the optimal being approximately 10 to 20% of the LDs 9. 3. The protection also depends on the time interval between first and second doses. Generally, an interval of 10 to 14 days is required for optimal protection. The protection can last several weeks or even months. 4. A repeated preirradiation is less effective than a single initial irradiation. Krokowski'° reported the peculiar and interesting fact that radioinduced protection can be transmitted by injecting the serum from preirradiated animals into nonirradiated animals. The injected animals showed a striking increase in radioresistance. In plants most dose-fractionation investigations have dealt with the phenomenon of chromosome aberrations. Davies,'’ working with white clover, found that, depending on the temperature, protection could be induced by a low initial dose built up rapidly at 25°C and reaching a maximum after approxi- mately 8 hr. At a lower temperature the protection did not decrease even after 340 BROERTJES 4 days. Furthermore, the protection was also dependent on the presence of oxygen; in nitrogen no protection was obtained. The data presented here agree in part with those in the literature. The optimal initial dose mentioned in the literature is approximately 15% of the LDso9, and the extent of the protection induced (increase in tolerance with about 1.7) seems to fit fairly well with the data presented here. In contradiction, however, is the fact that the protection is reported to stay active in animals over an extremely long period whereas in the African violet most of the protective effect has disappeared after 5 days. Also in contradiction is the fact that in animals a single preirradiation induces a better protection than repeated preirradiations. The data presented here clearly demonstrate an optimal protection after a 10- to 20-fold repetition of the preirradiation dose. A last point to consider is the fact that a 25-fold irradiation with 200-rad X rays is often used in radiotherapy; 200 rads is approximately 5 to 7% of the lethal dose for mammalian cells and is comparable to the optimal initial dose for African violet (500 rads of X rays), which is also approximately 5 to 7% of the lethal dose. A 10- to 25-fold irradiation at this dose induces in African violet a maximal protective effect. This raises the question of whether a similar reaction can be demonstrated in animal tissue. If so, the next question is whether the reaction of normal cells is different from, for instance, that of tumor cells. If, again, this is the case, one wonders whether this could be of importance for radiotherapy in man, realizing, of course, that it is unrealistic to compare African violet with man in view of the differences in tissue, cell type, chemical composition, chromosome size, and oxygenation, to mention but a few. Mutation Frequency The original aim of the experiments on the effect of acute, chronic, and fractionation experiments in Saimtpaulia was to investigate whether a more efficient mutagenic treatment could be developed. Radiation has a very complex effect on living matter. The energy dissipated in the cells through ionizations is the starting point of a number of chain reactions that interfere with all kinds of metabolic and other processes and ultimately result in permanent physiological and genetic effects, in spite of the generally large repair capacity of the cells of the organism involved. The physiological effect, for instance, expressed in survival percentage of the irradiated plant parts, obviously depends on a great number of factors, e.g., the radiosensitivity of the plant species, the total dose, the dose rate, the type of radiation, and climatic and other environmental conditions before, during, and after the treatment. This is also the case with the genetic effect, expressed in mutation frequency, for instance, although the role of environmental conditions is much less obvious and for the greater part unknown. It would be of great importance for the practical plant breeder to have available clear-cut data on the optimal DOSE-FRACTIONATION STUDIES 341 method of irradiation which induces the highest possible frequency of useful mutants. Since repair of physiological and genetic effects a priori may be the result of partly different processes, it must be possible to separate the two by a proper treatment in such a way that the physiological damage to survival, growth, and fertility as well as the undesirable part of the genetic effect (chromosome aberrations) is minimal, whereas the desired genetic effect (gene mutations, favorable chromosome rearrangements, etc.) is maximal. The effect of various factors on mutation frequency is mentioned here only very incidentally for various reasons. First, the parameter itself is not so reliable as the two physiological parameters of survival and production. Second, the calculations are not advanced enough at the present time to give a clear-cut picture. Third, such a discussion actually belongs in an article dealing with mutation breeding. At the moment we can only say that an initial dose also protects against the genetic effect of a second irradiation or series of irradiations, but the protection is not so pronounced as in survival and production. By using these facts, we could obtain a greater number of mutants from a given number of irradiated leaves. This idea will be worked out in greater detail as soon as all data are available. ACKNOWLEDGMENTS I wish to thank my colleagues for their contributions in the form of positive discussions. Miss E. van Balen deserves special thanks for her efforts in the mathematical treatment of 10 years’ accumulation of data as well as for the large number of figures that had to be made. REFERENCES 1.C. Broertjes, Dose-Rate Effects in Samtpaulia, in Mutations in Plant Breeding II, Panel Proceedings, Vienna, 1967, pp. 63—71, International Atomic Energy Agency, Vienna, 1968 (STI/PUB/182). 2.K. H. Chadwick and W. F. Oosterheert, Neutron Spectrometry and Dosimetry in the Subcore Facility of a Swimming Pool Reactor, Atompraxis, 15: 178-180 (1969). 3.E. J. B. Christian et al., Mechanisms of y-Ray Induced Radioresistance to Early Mortality in the 3-Day Chick, Radiat. Res., 25: 179 (1965). 4.D. K. Bewley, S. B. Field, R. L. Morgan, B. C. Page, and C. J. Parnell, The Response of Pig Skin to Fractionated Treatments with Fast Neutrons and X Rays, Brit. J. Radiol., 40(478): 765—770 (1967). 5. J Denekamp,.J., F; Fowler, K. Kragt, C. J. Parnell, and $.B. Field, Recovery and Repopulation in Mouse Skin After Irradiation with Cyclotron Neutrons as Compared with 250-kV X rays or 15-MeV Electrons, Radiat. Res., 29: 71—84 (1966). 6. M. P. Dacquisto, Acquired Radioresistance. A Review of the Literature and Report of a Confirmatory Experiment, Radiat. Res., 10: 118—129 (1959). 342 BROERTJES 7. J. Maisin, E. van Duyse, A Dunjic, J. van der Merckt, A. Wambersie, and D. Werbrouck, 10. ia be Acquired Radioresistance, Radioselection, and Radioadaptation, Int. J. Rad. Biol., Suppl., Immediate Low Level Effects of Ionizing Radiations, Symposium Proceedings, Venice, June 22—26, 1959, pp. 183—194, Taylor & Francis Ltd., London, 1960. . E. Krokowski and V. Taenzer, Der Radiogene Strahlenschutz Effekt, Strablentherapie, 130: 139-145 (1966). .V. Taenzer and E. Krokowski, Acquired Radioresistance Following Whole Body Irradiation, Acta Radiol., Ther., Phys., Biol., 7(2): 88—96 (1968). E. Krokowski, Extraregionale Strahlenwirkungen, Strablentherapie, 135: 193-201 (1968). R. Roy Davies, The Effect of Dose Fractionation on Mutation Induction, Strahlenwirkung und Milieu, 160—170, 1962. SUMMARY OF RESEARCH ON FALLOUT EFFECTS ON CROP PLANTS IN THE FEDERAL REPUBLIC OF GERMANY HELLMUT GLUBRECHT Institut fur Biophysik der Technischen Universitat Hannover and Institut fur Strahlen- botanik der Gesellschaft fur Strahlen- und Umweltforschung mbH, Munchen, Germany ABSTRACT Two groups of experiments are discussed. The first was concerned with effects of stratospheric fallout with relatively low activities (10? to 10 * Ci/m?/day). Various species of plants were exposed to continuing artificial °?Sr, °° Sr, or '*7 Y fallout in special growth chambers. Uptake of the radionuclides by aboveground parts of the plants and by roots could be controlled, and the distribution in various plant organs was checked. Damaging effects could be observed only at activities of at least 10° Ci/m?/day. At lower fallout activities, however, some parameters (dry mass, plant height, etc.) were significantly increased as compared with the control. In the second group of experiments, the effects of external gamma irradiation were investigated in field experiments with barley, wheat, rye, and potatoes. Irradiation was performed at various stages of development and, on some cereals, also during hibernation. Parallel experiments on chronic exposure of the same crop species were carried out in a small gamma field. The results were in good agreement with data obtained by investigators in other countries. The radiation sensitivities of about 20 of the most common varieties of barley and wheat grown in West Germany were compared. Maximal differences of dose values resulting in the same degree of damage were + 30%. The effects of radioactive fallout on crop plants can be considered under two different points of view: 1. Radioactive contamination of the crop and transfer of radioactivity to man by the food chain. 2. Damaging effects on crop yield by external gamma and beta radiation as well as by radionuclides incorporated into the plants. It is now well known that, in the event of a nuclear war, the first group of effects would not play an important role as compared with the second group, at least as an acute hazard. The situation was different in the test explosions; cultivated land was reached only by tropospheric and stratospheric fallout, 343 344 GLUBRECHT and long time intervals had to be considered. In this case the fission products were soluble in water to a considerable degree, and long-lived radionuclides like ?°Sr and 1*7Cs played a role. In the acute situation after detonation of an atomic bomb, the fallout components would be insoluble, and incorporation into plants would be negligible. However, stratospheric fallout would occur after some time, and then the hazards for areas far from the place of detonation of the nuclear explosions would have to be considered. In this paper two sets of experiments concerned with these two different situations are described. Nearly all the data given here are from our laboratory. EFFECTS OF SIMULATED STRATOSPHERIC FALLOUT ON PLANTS Experiments of this type were performed in our laboratory first by Niemann,’ later by Naghedi-Ahmadi,* and most recently by Elmdust and Nassery.* Basic data were derived from the maximal beta activity of fallout measured in West Germany, Ag, which was 3.7 nCi/m*/day. The activity of fallout solutions was given in multiples of Ag. The plants were grown under controlled conditions in glass boxes, and the fallout solution was sprayed on them daily by an automatic device (Fig. 1). The plants investigated in these experiments were: 1. Lolium multiflorum Lam., as model of a pasture grass. 2. Arabidopsis’ thaliana’ -(.) “Heynh:, for research’ on: more than one generation. 3. Kalanchoe blosfeldiana, for long-time studies on vegetatively propagated plants. The ?°Sr, °°Sr, and 1?1I were applied as SrCl, and Nal in carrier-free solutions. Controls were treated with stable strontium and iodine. In Germany in 1963 the maximal concentration values of ?°Sr which had been observed were within 13% of the recommendations of the International Commission on Radiological Protection. The first question to be answered by our experiments was: Will the activity in the plants be increased proportionally at fallout activities of 10 to 10° Ag? The answer is clearly “‘no” because: 1. The radionuclides are taken up mainly by aboveground parts of the plants. This leads to saturation after a rather short time (Figs. 2 and 3). For ee) the saturation values are less than proportional to the fallout activity (Fig. 4). 2. Only 10 to 20% of the activity will be incorporated by the plants. If 20% of the soil surface is covered by plants, the total uptake is of the order of 2 to 4%. This percentage becomes lower for fallout activities greater than 10° Ao. SUMMARY OF RESEARCH ON FALLOUT EFFECTS 345 10 UCi/liter 1 Ci/liter COUNTS/MIN/4-cm2 LEAF SURFACE ¢) 2 4 6 8 10 eZ 14 DAYS UNDER FALLOUT CONDITIONS Fig.2 °°Sr content of growing leaves of Lolium multiflorum Lam. at daily °° Sr fallout. 346 eos nCi/g dry weight GLUB RECHT Ag = 37 nCi/m2/day 0 5 10 DAYS UNDER 15 20 FALLOUT CONDITIONS Fig. 3 8°Sr contamination in rosette leaves of Arabidopsis thaliana (L.) Heynh. at various fallout concentrations. ©, 5 x 10* A,;°5,5 x10? A,. I, pCi/g fresh weight 131 10 1:5 20 DAYS UNDER FALLOUT CONDITIONS Fig. 4 '°'I contamination in leaves fallout concentrations. --0--, 107 A,;— of Kalanchoe blosfeldiana at various o—, 10? Aji *tAer, Ao- 25 SUMMARY OF RESEARCH ON FALLOUT EFFECTS 347 Therefore the main hazard of stratospheric fallout would be the continuous contamination of the soil. But uptake of long-lived radionuclides like ?°Sr and '37Cs would be limited by the reduced availability of these ions after they are absorbed in the soil.” The next question concerned damaging actions of the radioactivity incorpo- rated in the plants. Radiation effects were observed at very low activities, as shown in Fig. 5, with the example of the flowering date of Arabidopsis. But these effects had: the~ character of “stimulation.” Other end points were influenced in a similar way; e.g., dry weight was 135% of control values at 50 Ag of ?°Sr. A good example of stimulation effects can be seen in Fig. 6, which shows control and treated Kalanchoe. 100 © se 80 care) =e oO Ww OL 60 ae E* 40 Ze —=|Koe erie OO 1415 16 17 18 19 20 21 22 23 24 25 26 JANUARY 1967 Fig. 5 Effect of ?° Sr fallout on first flower formation of Arabidopsis thaliana (L.) Heynh. --@-*, control; **—x—--, 5 A, °°Sr; —-A-—-, 50 A, °°Sr; ——o-——,5x 10? A, °°Sr;-—0o-,5 x 10° A, ?°Sr. Damaging effects were never observed at fallout activities lower than LO? Ag, which corresponds to 370 uCi/m*/day. After 1 year 135 mCi/m? would be accumulated in the upper layers of the soil. Since in actuality '>7Cs would be a component of stratospheric fallout in roughly the same concentration as Sus the annual dose at 1 m above the soil surface may amount to about 10 krads. Therefore, as far as damaging effects on crop plants are concerned, the external radiation cannot be neglected even in the case of stratospheric fallout. EFFECTS OF EXTERNAL GAMMA IRRADIATION ON CROP PLANTS In the situation discussed in the foregoing paragraph, external irradiation by fallout residues would be of the character of chronic irradiation. After a nuclear explosion the local fallout would act more like acute irradiation. The simulation 348 GLUBRECHT Fig. 6 Kalanchoe blosfeldiana exposed to °° Sr fallout. Right, control treated with inactive strontium (5 x10” g Sr/liter); left, fallout activity 5 A, = 1.85 x 10° Ci? ° Sr/m? /day. of the t':? decay of early fission products has been achieved by Sparrow and co-workers.” According to their results reasonable data can also be obtained by constant-rate irradiation for 16 hr. We started experiments with chronic and acute irradiation of cereals— to obtain data on crops cultivated under natural conditions wheat, barley, rye in our climate and to investigate the influence of various stages of development on radiation sensitivity. The acute irradiation time was 8 hr for all doses. The chronic irradiation was performed in a small gamma field with a 10-Ci}?7Cssource. For acute irradiation a portable 300-kV X-ray machine was used. Dose variation was achieved in both cases by varying the distances between radiation source and plants. The stages of irradiation were: 1. Two-leaf stage. 2. Four-leaf stage. 3. Posttillering. 4. Ear emergence. 5. Anthesis. Three repetitions were provided for each experiment, and the same experi- ment was repeated the following year. The varying climatic conditions in dif- ferent years had surprisingly little influence. The variation of radiation sensitivity at different stages was as striking as that observed by other investigators in pot experiments. One example of dose-effect curves is given in Fig. 7. Maximal sensitivity was always reached in either stage 3 or 4. SUMMARY OF RESEARCH ON FALLOUT EFFECTS 349 120 YIELD, % of control & 8 8 8 N [o) 2 4 10° 10 1 10 DOSE, R Fig. 7 Effect of acute X irradiation at various stages of growth on the seed yield of winter wheat....., four-leaf stage; ----, posttillering; car emergence; -—-—, anthesis. Yield of controls is 100%. Average exposures reducing grain yield to 50% of control are shown in Table 1 for chronic and acute irradiation of three species of cereals. Grain yield is related to unit area, i.e., to a constant number of seeds. The difference between summer and winter varieties was very surprising. Winter wheat and winter rye have extremely high sensitivity at ear emergence. The summer crops, however, are more sensitive at the posttillering stage, the total dose applied during chronic irradiation being at least three times higher than the acute dose. The winter varieties were exposed to chronic irradiation throughout the whole time from sowing to harvest. Therefore the factor of difference here is considerably higher. During the winter the cereals are apparently rather resistant to irradiation, but temperature seems to play a small role compared with the stage of development. In one experiment irradiation of winter wheat during the two-leaf stage had to be performed at —3°C in late February; in the other year it was in early April at 15°C. The dose values for equal effects were only 10% lower in the latter case. Different varieties of one species may vary in radiation sensitivity. It would be valuable to have especially resistant varieties. Greenhouse experiments have been made with 16 varieties of summer wheat grown in Germany. Irradiation was performed in the one-leaf stage (8 cm) with four dose values. After 8 weeks, plant height, dry mass, and number of tillers were checked. There was no deviation of more than 30% from the average values of all 16 varieties. The best way to avoid losses in crop yields in the case of a nuclear war seems to be to grow less-sensitive species. 350 GLUBRECHT Table 1 AVERAGE EXPOSURE VALUES FOR 50% REDUCTION OF GRAIN YIELD OF VARIOUS CEREALS RECEIVING ACUTE IRRADIATION AT DIFFERENT STAGES OF DEVELOPMENT OR CHRONIC IRRADIATION Acute irradiation, R Chronic Two-leaf Four-leaf Ear irradiation Crop species stage stage Posttillering emergence Anthesis (total dose), R Summer barley Breuns wisa 5000 3000 1000 1500 3000 3000 Summer wheat Opal 5000 4500 1300 1600 3000 3500 Winter wheat Jubilar 5000 5000 1200 400 5000 3500 Winter rye Petkuser 4000 3500 400 300 1500 2400 140 120 re 100 ie 9 O80 © as 0 60 =! a 7 AO 20 0 4 1 10° 10 DOSE, R Fig. 8 Effect of chronic gamma irradiation at various stages of growth on the yield of potatoes. ...., germination (May 22—June 12); ---, start of anthesis (June 12—July 1); —-—-, end of anthesis (July 1—20); —--—, yellow stage (July 20—Aug. 9); , ripening (Aug. 9—29). SUMMARY OF RESEARCH ON FALLOUT EFFECTS 15) In this regard some results of Keppel® with potatoes should be mentioned. He simulated fallout radiation by spreading °° Co beads on the soil between the plants. The vegetative period was divided into five periods of about 3 weeks each, during which chronic irradiation was applied. Only the germination stage seemed to be sensitive in the dose range below 10,000 rads (Fig. 8). Much more data are needed for a complete evaluation of the problems of damage in crop plants in the case of a nuclear war, but basic research on the mechanisms of different radiosensitivities should not be neglected. REFERENCES 1 pW E. -G. Niemann, Wirkung eines ktnstlichen ?°Sr-Fallout auf Pflanzen, Atompraxis, 7: 370— 375 (1961); also 8: 51—60 (1962). _J. Naghedi-Ahmadi, Uber die Wirkung aus dem Fallout inkorporierter Radionuklide in Pflanzen, Thesis, Technischen Universitat Hannover, Germany, 1967. .M. Elmdust and T. Nassery, Technischen Universitat Hannover, unpublished data. WR, ocote, Russell, Dietary. Contamination, Its Significance in “an “Emergency; “in Radiological Protection of the Public in a Nuclear Mass Disaster, H. Brunner and S. Pretre (Eds.), Proceedings of a Symposium, Interlaken, Switzerland, May 26—June 1, 1968, Report CONF-680507, pp. 279—306, Fachverband fuer Strahlenschutze e.V., 1968. . A. H. Sparrow, Brenda Floyd, and P. J. Bottino, Effects of Simulated Radioactive Fallout Buildup and Decay on Survival and Yield of Lettuce, Maize, Radish, Squash, and Tomato, Radiat. Bot., 10: 445—455 (1970). .H. Keppel, in Forschung im Geschaftsbereich des BML, Annual Report, Part Q, pp. 125—126, Bonn, 1969. RADIATION DOSES TO VEGETATION FROM CLOSE-IN FALLOUT AT PROJECT SCHOONER WAS RHOADS,* HL eRAGSDALE. Re BaPLATI ij andie. Ma ROMNEY = *EG&G, Inc., Santa Barbara Division, Goleta, California; tEmory University, Atlanta, Georgia; and = University of California, Laboratory of Nuclear Medicine and Radiation Biology, Los Angeles, California ABSTRACT Project Schooner was a nuclear cratering experiment in the Plowshare Program for peaceful application of nuclear explosives. On the basis of information from two earlier experiments, Palanquin and Cabriolet, special dosimeters for measuring both beta and gamma radiation were placed in the open environment and on shrubs in the downwind area where fallout was anticipated. In addition, polyethylene sheets were placed over some shrubs to determine whether the shrubs could thus be protected against radiation damage. The gamma radiation doses for shrubs not covered were found to be essentially the same as the doses measured in the open and away from shrubs, but there was a 15% reduction in dose under the sheets. The beta doses to unsheltered vegetation were, however, reduced by almost 50% compared with doses at 25 cm in the open. This reduction was attributed to self-shielding. Beta doses to the shrubs were reduced still further, to 31% of the 25-cm beta dose in the open, by shielding the shrubs from direct fallout contamination. The estimated LDs59 for Artemisia was 4449 rads, but the reduction in dose by the shelters was nearly sufficient to prevent damage to the shrubs, even though all other Artemisia shrubs in the center of the fallout pattern were killed. It was concluded that beta doses must be considered in protecting growing food crops and livestock and that even minimal shelter to prevent direct surface contamination would be of great importance. Project Schooner was a nuclear experiment in a layered tuffaceous medium, executed as a part of the Plowshare program for development of nuclear excavation. Detonation occurred Dec. 8, 1968, at 0800 (PST) in Area 20 of the Nevada Test Site (NTS). The resultant yield was 31 + 4 kt (Ref. 1). Other details are published elsewhere. This paper is concerned only with radiation doses and their effects on vegetation along an arc of dosimetry stations approximately 1800 m from ground zero (GZ). S52 RADIATION DOSES TO VEGETATION S03 The vegetation in the area is dominated by Artemisia arbuscula and Artemisia tridentata, two species of the sagebrush which hybridize. A. tridentata was of primary interest at Schooner. Unfortunately, the junipers, which were of interest in the earlier studies at Palanquin and Cabriolet,” 3 did not occur in the immediate downwind region of Schooner. Several other shrubs did occur, but only sporadically, and therefore were of little importance to this study. Artemisia has been previously shown to be a relatively sensitive shrub having an LD, 90 around 5500 rads (Ref. 3). Its occurrence in widespread and relatively pure stands makes it a good plant for use in the investigation of radiation effects. As background we will mention some results of two earlier experiments, * the first of these experiments, it was concluded that the vegetation damage was Palanquin and Cabriolet, in the same geographical area. From Palanquin, caused by radiation, probably mostly beta since the gamma-ray doses in much of the area, insofar as they could be derived, were too low to account for the extent of the damage. Another important result observed at Palanquin was the asymmetrical distribution of shrub damage, a damage pattern noted earlier in the Yucca Flat area of NTS by Shields and Wells.* In the areas peripheral to those where all or most plants were killed, this pattern of damage was a common characteristic; 1.e., the plants were extensively damaged across the sides of the shrub toward GZ in the direction from which the fallout material was carried by the wind. In extreme cases only small branches or twigs remained alive; in other cases protection from rocks or larger shrubs and small trees sheltered whole plants from damage. At Cabriolet,* the second experiment of interest preceding Schooner, an extensive dosimetry program was undertaken to measure both beta and gamma-ray doses to the environment and to the vegetation. The special dosimetry designed by Kantz and Humpherys® for this program provided what appears to be the first opportunity to make comprehensive measurements in a field environment. Dose measurements were made by placing dosimeters in the open away from vegetation, on the fronts, tops, sides, and backs of shrubs and phantom plants. Some of the dose data from this experiment were presented by Kantz° earlier in this symposium. The vegetation at Cabriolet showed a pattern of damage like that observed at Palanquin—the fronts of the shrubs were often damaged seriously, and, near the middle of the pattern, the Artemisia were entirely killed. This coincided with the pattern of doses, more particularly beta doses, observed there. It was concluded from this experiment that there was sufficient support for the hypothesis that beta radiation was primarily the cause of damage to the vegetation. This does not mean that gamma-ray doses were not important, however, since the two doses are additive. Both the Palanquin and Cabriolet devices were very small, less than 5 kt. The dosimetry stations were placed relatively close to GZ (at Cabriolet, about 610 m away) to ensure that the doses would be sufficiently great to be of interest. At 354 RHOADS, RAGSDALE, PLATT, AND ROMNEY that distance the killed Artemisia covered a segment of the arc less than 150 m long. At Schooner, where the yield was relatively much greater, there was an opportunity to look at a larger irradiated area located in different terrain. The vegetation was also different although Artemisia remained the dominant species. In addition, Schooner presented an opportunity to test the hypothesis that, if beta radiation were a primary cause of damage to vegetation, then sheltering the vegetation from fallout should provide important protection. METHODS Fallout Dosimetry Stations Dosimeters were located at 97 stations along an arc north and east of the proposed GZ at distances from 1700 to more than 2000 m. Figure 1 shows the locations of the stations with respect to GZ and the terrain features important to this study. Referring to the aerial photograph of the area shown in Fig. 2, we can relate the size of the crater to the doses to the environment and to the effects of those doses. The solid lines in Fig. 1 indicate the boundaries of the canyon in which the dosimetry stations were located. The bottom of the canyon was 30 to 100 m below the level of the land toward GZ and somewhat lower still than part of the area beyond the canyon. A combination of geography and the anticipated distances to which the base surge from the detonation was expected to reach determined the location of the stations. Although at the beginning of this experiment this very remote area of NTS was virtually without roads, trails, or other conventional landmarks, it was possible to enter the area with four-wheel- drive vehicles. The distance covered by the arc of stations shown in Fig. 1 was about 2.8 km, and the distance between stations was approximately 35 m. These stations were placed in position 3 weeks before Schooner. At the same time, dosimeters that had been given measured doses were placed in the field as a check on dosimeter fading. One set of these dosimeters was removed from the field on D day, and another was removed when the dosimeters were collected from the fallout pattern. These provided tests both for accumulation of doses attributable to possible radiation from unknown sources and for dose fading due to sunlight and temperatures in the desert environment. No loss or increase in doses was observed from these dosimeter checks. Vegetation Shelters and Dosimetry In addition to the dosimeters placed in vertical arrays, four dosimeters were placed on sheltered shrubs and four on shrubs in the open. In each case one dosimeter was placed on the front (toward GZ) and one on the back of the shrub. Attempts were made to place the dosimeters on symmetrical shrubs that RADIATION DOSES TO VEGETATION 355 ' NEVADA | | | AREA | NG OF TESTS | TESTN. a SITE oe | LAS VAGAS No oS \] —t~, APPROXIMATE \ / \ LIP , -APPROXIMATE EJECTA ieee if BOUNDARY \ \c / | APPROX. SCALE, SS Ee / Beco — m/ft \ / wee 0 610m \ ea ans 0 1000 2000ft TEL af nas ee Whe \ WZ Fig. 1 Schooner crater and the location of the dosimetry stations to the north and east of it. were not close to other shrubs. Generally, this was not possible among the sheltered shrubs, because of the limited numbers available. Polyethylene sheets 6 m square and 6 mils thick were spread over as many Artemisia shrubs as could be covered conveniently at alternate stations along the arc. Figure 3 shows a protective sheet in place and also provides a general view of the terrain and vegetation. Fallout from Schooner occurred to the north and northeast of GZ. The dosimeter stations were within the edge of the base surge at the north but were RHOADS, RAGSDALE, PLATT, AND ROMNEY 356 in il imate The point at which the tra 1 photograph of the Schooner area. the upper part of the photograph dead-ends at the cliff 1a 2 Aeri ig. F the approxi 1S P) cfs - Set iS) = iS) bar} } a) VY is ~ & 2 Zz Ce) S ©) 3 Nn | . =) (cP) ca) ww « a, . =) 3 iS) = ise] Set — 3 Ons Se >'S 4a ES c= vo 3 8 chin. ips = 0 e BO YP ene o 8 9 9 ‘DIDJUApla] VISIMAIAY [edIdAQ SI UOIILIIZIA JY “Spud-peap Ie 07 ay?) a19yM Z “3I,Y UL UMOYsS IVY? SI Ja3Uad Jaddn ur ZZ] ay Jo JUTOd dY YT ‘saaIM [RINIDA UO Pay ZUIAq SIDIDUNISOP IY? ‘SUOIIEIS JIIIUISOP JO SUOTIBIO] IYI YIVUT SQnaYs PIsaAOD ay2 JO IYSII dU IB SayeIS JY] "Sqnays vISiUaj4p J3AO ade]d ut Jaays aua;AYIaAjod asenbs-w-g ev Jo aed & SUIMOYS ‘NZT UOTHRIS ¢ “BIA RADIATION DOSES TO VEGETATION 358 RHOADS, RAGSDALE, PLATT, AND ROMNEY less so to the east. Some areas received an estimated fallout of up to 300 g/m’. Others received relatively little. On Dec. 20, 1968, at D+12 days, all dosimeters were removed from the field and the shrubs were uncovered. At this time no differences were observed between the shrubs that were covered and those left exposed, except that those exposed were very dusty. © Some of the polyethylene sheets were torn by heavy winds, but this damage was not severe except directly east of Schooner GZ at the mouth of the canyon, where, fortunately, the doses were too low to be of interest. At this time patches of snow, which had fallen about D +7 days, still remained, and sometimes ice and snow mixed with fallout had to be removed along with the polyethylene sheets. All dosimeters were returned to the laboratory for readout on D + 23 days. Reading of the dosimeters began on D + 29 days. RESULTS Gamma-Ray Doses and Data on Radiological Safety Monitoring Figure 4 shows the dose rates at each dosimeter station as read from conventional instruments for radiological safety monitoring as the dosimeters were removed from the field. Also shown for comparison are the gamma-ray doses measured by the dosimeters at 1 m. The purpose of the comparison is to illustrate that postevent safety monitoring may not provide an adequate basis for dose estimates. If field doses were calculated from the safety monitoring dose-rate data by multiplying by some systematic factor, there would be a considerable discrepancy between the estimated and the measured doses. That the curves are not parallel is probably attributable to continued deposition and redistribution after the initial deposit of early postdetonation material with its resultant high infinite dose. Radiation Doses 25 Cm Above the Soil Surface Radiation doses were measured 25 cm above the soil surface since this was judged to be a height at which doses appeared to have the greatest effect on the local vegetation. Dose measurements were also made at the soil surface, but these varied widely because surface irregularities caused the fallout material to accumulate nonuniformly. This was particularly apparent in the reading of the beta doses since they were derived much more from sources near the irradiated object than were gamma-ray doses. This is because gamma-ray doses accrue from relatively large areas, whereas beta doses are affected primarily by particles on and nearby the surface of the irradiated objects. 900 700 500 GAMMA-RADIATION DOSE, rads 300 100 RADIATION DOSES TO VEGETATION 359 DOSE RATE-RATE Af (Di+ 12 DAYS, AT 1M, mR/hr ZOeN 152 N SEN Os 5 I'S 25 35 45 W=——STATION:No;—*E Fig. 4 A comparison of the gamma-ray doses from dosimeters at 1 m and the dose rates taken by conventional radiological safety monitoring on D+ 12 days. The gamma-ray doses at 25 cm were essentially the same as those for 1 m (Fig. 4). The beta doses measured 25 cm aboveground by dosimeters placed on vertical wires away from vegetation are shown in Fig. 5. Figure 6 shows the ratios of the beta to gamma-ray doses obtained from these measurements. Two characteristics of these data are of interest. First, there appears to have been a systematic fluctuation in the dose ratio. Such a fluctuation was also observed at Cabriolet. The recurrence of this fluctuation is 360 RHOADS, RAGSDALE, PLATT, AND ROMNEY 9x 103 6a, 10° . icp) o) Qa 3 x 103 30 N 20 N 10 N 0 10 20 30 40 50 STATION No. Fig. 5 The beta radiation doses (in rads) measured at 25 cm above the soil surface in the fallout pattern of Schooner. probably more than chance; but, to be more than speculation, its explanation must come from those who design and execute the experiments. Second, the dose ratios are large, ranging from 5 to more than 14. Moreover, these ratios are slightly larger than those noted at Cabriolet, which ranged from 4 to 12.5. This difference may be due to an overestimate of gamma-ray doses at Cabriolet, or it may be due to differences in the source of the radioactive debris, i.e., in the device itself; discussion of the device is, of course, beyond the scope of this work. Doses to the Vegetation Gamma-Ray Doses Table 1 shows the doses for the main part of the central peak of radiation across the fallout pattern. Although there are differences at some stations between the gamma-ray doses at 25 cm and those measured on the shrubs, the RADIATION DOSES TO VEGETATION 361 = oO RATIO OF BETA TO GAMMA DOSES oO 30 N 20 N 10 N 0 10 20 30 40 50 STATION No. Fig.6 The ratios of beta- to gamma-radiation doses (both in rads) in the Schooner fallout pattern. mean difference is essentially zero. The difference between the gamma doses at 25 cm and those measured on the shrubs protected by the plastic sheets 1s 15%, however. This reduction might be anticipated considering the possibility of a low-energy gamma-ray component of the early postdetonation radioactive debris. Beta Doses The beta-dose data shown in Table 1, unlike the gamma-ray-dose data, indicate a reduction in the beta doses to the vegetation compared with the doses measured at 25 cm and away from the vegetation. In addition, the protection of the plastic sheets reduced the beta doses to the shrubs still further. Both reductions were large compared with the gamma-ray-dose reduction and were of important biological significance, as is shown subsequently. RHOADS, RAGSDALE, PLATT, AND ROMNEY 362 ‘paI9AOII OU Ja OUNISOC| t 6 OF 6 OF CTE 9'TS 6€ OL OLS 066 97 TZ OS OOS I OLS Oso 97 LY 006 Oc9OT OC 6 O06 O6IT7 67 L9 O9CT OO9E Ov v9 OrOT OVE OF 1S OSoT OVET O¢ Iv OS9Ol OST7 tC 6£ OLLI OT67 €€ Eb OE? OOOE 9T SL OOTTC OO6E SE 8 OLTE OF + RC 6 OOOE OSCS RC 6£ O6T7 OOOE Or €9 O6ST O9TT O¢ cS O¢9 OTTT PII9AOD uadg Pa1gaory) usdg asop qnays Wd-¢Z JO IUIDd.19d spel ‘asop AeLeiog OIrl OOTZC O8rE OStb OOS OrOS OS OP OSSss OOSL OSOZL OOTS O98 OS90T OO8ZL OCHE OOTZC Wd GZ 1v as0q 8 96 C6 16 P2IdA0'y fuadg pa19da0y WId-¢Z ‘SOSOP WID-¢Z 9YI WOIJ SOIUIIIFJJTIP JUDIII dg + "UMOYS JIB SOSOP UWID-¢Z ay WO BuLIdJJIp sasop AjUO, pn a7 Gre S'O+ urow g- 08 C+ 007 t 097 OLE o— OSS os OES aire 009 (Om 009 Ct O8h 9 099 c+ OLY 6 O19 OTL TT+ 008 cr OLL | Bing OSE SSc asop JO 1Udd.19d spea ‘asop Aei-eururery UOTIBIAIP paepurvys O8S OS8 OOL 06S 099 OSL O89 Or9 O090T O18 Oct quays ,uadg O¢cT OO OOE Ob Oc9 008 OCL 009 OS9 008 OS9 OOZL OCS OS6 OO8 O8E O87 WId $7 3v aSOq oT Nél “ON UO1INeIS SHNUHS OL GNV FAOVANNS TOS AHL AAOUV WO SZ LV NYALLVd LAOTIVA NIVW AHL SSOUODV ASOG T 919e 1 RADIATION DOSES TO VEGETATION 363 The decrease to 52.6% in shrub doses is attributed to “‘self-shielding,”’ which can be envisioned in terms of the masses of vegetation shadowing themselves. Shrubs that were protected from the direct fallout contamination showed even larger reductions in beta doses, however. For the stations shown in Table 1, the covered shrubs received only 31.2% of the beta dose at 25 cm in the open and away from shrubs. Effects on the Vegetation The vegetation along the arc of dosimetry stations was examined at biweekly intervals for a period of 6 weeks after the dosimeters were taken from the field; thereafter it was examined at less frequent intervals. No differences between irradiated and nonirradiated vegetation were detectable until late April when an absence of inflorescence development was first noted. As was previously observed at Cabriolet, the first evidence that Artemisia had been affected could be seen only by a careful comparison of the nonirradiated with the irradiated shrubs. Experience has shown that a conspicuous characteristic of Artemisia is the occurrence of primordial inflorescences at the beginning of the active growing season, even though Artemisia does not come to anthesis until September in the test area. The leaf-color changes that appeared in mid-May and other phenotypic characteristics that, foretold complete defoliation and apparent death by September were not evident beforehand. By the end of June (D + 7 months), all the damage characteristics previously noted at Cabriolet were also apparent at Schooner in the most heavily irradiated parts of the fallout pattern. There were also notable differences, which will be discussed later. Protected and Unprotected Shrubs During the months of July and August, two surveys were made of the vegetation along the arc of the dosimeter stations. These surveys revealed that all Artemisia shrubs at Stations 4N, 6N, and 7N were killed, with the exception of those shrubs which had been covered with the plastic sheets. There was no damage to covered shrubs except at Station ON, where four of the six shrubs covered had no damage and two had a small amount of defoliation. At all stations, 8N to 4 inclusively, around the arc, half or more of the uncovered Artemisia shrubs were 50 to 100% defoliated. Lesser damage was observed over many other stations. A 9-month LDs5 9 was derived from the August survey. The survey included all Artemisia shrubs within a 5-m radius of each dosimeter-support post. Eleven stations from 12N eastward to Station 13 were surveyed; only those stations at which either all or none of the Artemisia had been killed were excluded. The shrubs were grouped into two categories: (1) yellow brown to dark gray and 364 RHOADS, RAGSDALE, PLATT, AND ROMNEY dead or (2) gray green and living. Plants on the end of the radii with more than half their diameter beyond the 5-m limit were omitted. Those with more than half their diameter within the radii were counted. These counts were then used to determine the LDs9 by probit analysis. Data were determined from all stations even though half the stations did not have shrub doses determined by dosimeters on the shrubs. As shown in Fig. 7, the LD59 was 7760 rads. When Lethality 1.908 + 0.000398 (x) 1O:649514 dst 0.7 = 7760 rads % ARTEMISIA POPULATION, 4 6 8 10 DOSE, 10° rads Fig. 7 The LDs59 for Artemisia as of August 1969, 8 to 9 months postevent. The dose, reduced for the self-shielding factor, is 4449 rads. the beta dose is corrected by the factor 0.526 from Table 1, the dose becomes 4449 rads if, from Fig. 6, the beta-to-gamma ratio is assumed to be 10. It was not possible to derive an LDs5 9 with equal precision at Cabriolet, but an LD; 99 for Cabriolet is nearly identical to the LD;99 for Schooner when the value for Schooner from the 25-cm dose is reduced by the self-shielding factor. Both values are 5500 rads. RADIATION DOSES TO VEGETATION 365 Comparison of Sublethal Damage with That at Cabriolet In the peripheral parts of the fallout patterns of both Palanquin and Cabriolet, defoliation occurred in a characteristic pattern,” 2 1.e., the sides of the shrubs toward GZ and the tops of the shrubs were injured, but the backs remained relatively undamaged. At Schooner, however, along the arc of dosimeter stations, this pattern occurred infrequently, and another kind of damage pattern was observed. The lower twigs and branches all the way around the shrub were likely to be defoliated. An example of this is shown in Fig. 8, a photograph taken at D+ 9 months. The extent of the damage appeared to be correlated with the dose, and, in extreme cases at higher doses, only a few branches or even a single branch remained alive. There were other patterns of damage also, but this was the most frequently encountered. The developing inflorescences that are approaching flowering can be seen at the top of the shrub. Yet the entire bottom half of the shrub is without leaves. The photograph was made at Station 32, where the shrubs recorded a dose of 3150 rads of beta and 700 rads of gamma radiation. CONCLUSIONS AND DISCUSSION Dose Reduction by Self-Shielding and Terrain At Schooner no consistent differences were detectable between the gamma-ray doses received by the shrubs and those measured on the vertical-array dosimeters away from the shrubs. This was also the case at Cabriolet. The relatively large reduction in beta-radiation dose to the vegetation compared with the 25-cm dose appears, however, to be higher than that observed at Cabriolet. Although doses were measured on both fronts and backs of the shrubs at Schooner also, it was not possible to distinguish a difference between these doses. This was quite unlike the circumstances at Cabriolet, where the fronts of the shrubs received larger doses than the backs. These dose differences are summarized in Table 2. There are several speculative explanations for these differences which may contribute to the better understanding of damage from fallout. Cabriolet fallout occurred across the front and sides of a low hill without a significant increase in elevation between the crater and the hottest part of the fallout pattern. At Schooner the vegetation was in the bottom of a canyon where the Artemisia shrubs were generally larger than those at Cabriolet. They also appeared to occur in relatively larger clumps with possibly more open space between them. These characteristics are attributable to the differences in the phenology and pedology encountered on the shallow soils of the exposed hillside compared with conditions on the alluvial bottoms of the canyons. It seems evident that fallout deposition varied as a result of terrain differences. On the exposed hillsides, where there were moderate winds, RHOADS, RAGSDALE, PLATT, AND ROMNEY 366 "SIDUIISIIO]JUL JO JaqUINU ay? UT UO INpad ev aq Avur azayd ysnoyrye ‘yewsou Ajaaneyjas st dod ay] “paryeyojap uaaq sey YIYM JO J[VY-dU0 JaMO]T JUD ‘YSIY WET INOGe qnays wIsIMAaT4yY UW B ‘BIA Patsee ah J RADIATION DOSES TO VEGETATION 367 Table 2 PERCENT BETA-DOSE REDUCTION FROM THE 25-cm DOSE Means of fronts, tops,* and backs Backs only Schoonert —47.4 —47.4 Cabriolet t —18.4+11.3 —32.7413.1 *Doses were not measured in the tops of shrubs at Schooner. t+From the values in Table 1. tMeans and _— standard deviation’ for Stations 1 to 7. differences in front to back were expected and were measured. (Differential deposition of airborne volcanic dust was noted by Miller.°) At Schooner, where the wind direction was essentially at a right angle to the canyon, the wind-borne fallout apparently was not deposited differentially from front to back of shrubs, and, as a result, no dose differences were distinguishable. The Cabriolet shrubs, which were subjected to winds in an open, exposed location, appear to have stopped more fallout than was deposited nearby, when compared with the shrubs at Schooner, which were protected from winds by the canyon, and the amounts of fallout deposited around them in the bottom of the canyon. The increased reduction in the dose to the back of Cabriolet shrubs may thus be both a measure of self-shielding in the conventional sense and a sheltering effect from wind patterns about the shrubs analogous on a microscale to conditions in the canyon at Schooner. Another possibility, for which we do not have data, 1s that under some conditions windswept surfaces may intercept less fallout; this is probably a function of surface roughness. Dose Reduction by Polyethylene Cover Sheets The relatively large reduction in dose resulting from use of 6-mil poly- ethylene sheets was not entirely anticipated. The gamma-ray-dose reduction of 15.5% and the reduction of nearly 70% in beta dose must certainly be significant in terms of the subject of this symposium. Beta burns have been noted as an outstanding characteristic of fallout-radiation effects for both domestic ani- ae mals’’® and men.” Survival of Food Crops and Livestock The conditions resulting from close-in fallout under which this study was made, like those for Cabriolet and Palanquin, appear to be as nearly like conditions of nuclear warfare as can be simulated. In these experiments there 368 RHOADS, RAGSDALE, PLATT, AND ROMNEY were depositions of large amounts of particulate materials containing nuclear debris which arrived near time zero. In the last few years, fallout-decay dose rates have only been simulated in the laboratory, and it has been shown that certain crop plants are more sensitive than was previously predicted under these conditions.'° Since these experiments utilized only gamma radiation, there may be other effects associated with beta radiation and the higher beta energies of radioactive debris from near time zero not yet simulated in the laboratory. A few simple conclusions can be drawn. First, the relatively large doses to crops in the field, or to exposed seeds, from beta radiation must be considered. Perhaps some practical, simple dosimetry for beta radiation is needed. The large variations in the ratios of beta- to gamma-radiation doses and the possible errors in calculating doses from late postevent dose rates make beta-dose estimates difficult. These difficulties may decrease with increasing distances from GZ, but this is a problem for meteorologists, and for the present whether or not this occurs appears to be unknown. From the importance of beta radiation as an agent of damage, it follows that prevention of direct contamination by fallout particles is vital. Even a shield with as little mass as that afforded by 6 mils of polyethylene sheeting may be of critical importance. For livestock or crops that cannot be sheltered against direct contamination, the lee sides of any large object may provide some protection. It has frequently been observed that the presence of large shrubs and small trees decreased the airborne fallout damage to smaller shrubs downwind. In this matter geographical features themselves also appear to provide limited protection. Finally, it is obvious that more information from direct fallout effects will be very useful. ACKNOWLEDGMENTS This work was done under Contract No. AT(29-1)-1183 between Environ- mental Sciences Branch, Division of Biology and Medicine, U. S. Atomic Energy Commission, and EG&G, Inc., Santa Barbara Division. Part of the work was also done under Contract No. AT(40-1)-2412 between the USAEC and Emory University. REFERENCES 1. L. R. Anspaugh et al., Bio-Medical Division Preliminary Report for Project Schooner, USAEC Report UCRL-50718, University of California, Livermore, July 22, 1969. 2. W. A. Rhoads, R. B. Platt, and R. A. Harvey, Radiosensitivity of Certain Perennial Shrub Species Based on a Study of the Nuclear Excavation Experiment Palanquin, with Other Observations of Effects on the Vegetation, USAEC Report CEX-68.4, EG&G, Inc., May L969: LO} RADIATION DOSES TO VEGETATION 369 W. A. Rhoads, R. B. Platt, R. A. Harvey, and E.M. Romney, Ecological and Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and Short-Term Effects on the Vegetation from Close-In Fallout, USAEC Report PNE-956, EG&G, Inc., June 25, 1969. (Beta dosimetry methods are provided by A. D. Kantz and K. C. Humpherys in an appendix.) . Lora M. Shields and Philip V. Wells, Effects of Nuclear Testing on Desert Vegetation, Science, 135: 38—40 (1962). . A. D. Kantz, Measurement of Beta Dose to Vegetation from Close-In Fallout, this volume. . Carl F. Miller, The Contamination Behavior of Fallout-Like Particles Ejected by Volcano Irazu, Report AD-634901, Stanford Research Institute, April 1966. D. G. Brown and others, Late Effects in Cattle Exposed to Radioactive Fallout, Amer, J. Vet. Res., 27: 1509—1514 (1966). .M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to Fallout Radiation, USAEC Report TID-24459, UT—AEC Agricultural Research Labora- tory, Sept: 7, L967. . Samuel Glasstone (Ed.), The Effects of Nuclear Weapons, rev. ed., USAEC Report ACCESS-127, p. 601, Defense Atomic Support Agency, 1962. A. H. Sparrow and Leanne Puglielli, Effects of Simulated Radioactive Fallout Decay on Growth and Yield of Cabbage, Maize, Peas, and Radish, Radiat, Bot., 9: 77—92 (1969). SURVIVAL AND YIELD OF CROP PLANTS FOLLOWING BETA IRRADIATION ROBERT K. SCHUEZ Department of Soils and Plant Nutrition, University of California, Berkeley, California ABSTRACT Field experiments were carried out to investigate the effect of beta radiation on the growth of wheat, lettuce, and corn. The beta-radiation exposure was accomplished by fusing ?° Y onto 88- to 175-y silica sand, and applying the sand to the crops with a remote-control applicator. Treatment levels on the wheat and lettuce crops ranged up to 59.4 mCiof ?°Y per square foot. In the corn experiment the highest level was 71.3 mCi of ?°Y per square foot. Wheat grain production was severely reduced when 6.6 mCi/sq ft of ?° Y was applied. This corresponds to approximately 2700 rads at the surface of the plant near the apical merfstem. Lettuce yields were reduced significantly only at the highest treatment level, 59.4 mCi/sq ft, whitch corresponds to 9300 rads at the plant surface near the apical meristem. Some abnormalities could be seen on the lettuce at the 6.6 mCi/sq ft treatment level. Corn yield was not reduced and plant appearance was not changed in any of the treatments. The apical meristem of the corn plant was protected by about 1 cm of tissue, and it hence received very little ionizing radiation. In the event of nuclear war, standing crops would be exposed to ionizing radiation from fallout containing both beta and gamma radiation in generally similar amounts. The study reported here is an investigation of the possible effects from the beta component. Extensive literature exists on the effects of gamma radiation on plants in contrast to the very limited information available concerning the effects of beta exposure to plants. It is widely accepted that the relative biological effectiveness (RBE) of beta to gamma doses is essentially unity' in the moderate and high beta energies found in fallout resulting from a nuclear detonation. This means that, when given ergs of energy are transferred to a fixed amount of tissue, deleterious effects will be the same whether the ionizing radiation is beta or gamma. In spite of this consideration, few predictions can be made of beta damage from gamma data, because of geometrical effects. The gamma exposure tends to be uniform 370 SURVIVAL AND YIELD OF CROP PLANTS 7A throughout all the smaller plants, whereas beta exposure varies enormously because of absorption by plant tissue. Since the maximum range of the most energetic beta particles found in fallout is only a few millimeters in tissue, the more sensitive areas of the plant may receive little exposure to beta radiation. On the other hand, because of the fact that the beta energy is transferred to the tissue over a short path, the beta component could be very important where the sensitive plant parts are not protected. Rhoads et al.* have shown that the beta component in fallout at the Nevada Test Site has been primarily responsible for the death of some desert vegetation. Based on these considerations, it was felt that the beta investigation should be carried out under field conditions with normal plant densities and as normal an agricultural management as possible. In this work the effects of beta radiation on wheat, lettuce, and corn were investigated. MATERIALS AND METHODS The Kearney Horticultural Field Station of the University of California was used for carrying out the field research. Yttrium-90 was selected as the beta-emitting isotope because of its availability, its suitable half-life of 64.2 hr, and its average energy of 0.92 MeV. Although the half-life of 64.2 hr is somewhat longer than that of early fallout, ?° Y was felt to be the best choice among available single isotopes to represent a fallout situation. It was decided to apply °° Y to the crops as simulated fallout, aes,)tixed ‘on *88- to 175- silica sand. Before the field experimentation could be initiated, three problems had to be solved. (1) Extreme radiochemical purity of the °° Y fallout simulant had to be assured. The ?°Y was to be chemically separated from a 99S+—?° VY mixture, and, owing to radiation-safety requirements, the residual ?°Sr radioactivity could not exceed 10° of the ?°Y activity. (2) A method of applying the fallout simulant evenly had to be developed. Since a number of curies would be involved in each experiment, radiation-safety considerations again were important. (3) A beta- radiation-dosimetry system had to be developed for measuring the beta doses delivered to the plants. Radiochemical Purity of the °° Y Fallout Simulant The 88- to 175-u sand contaminated with various levels of °° Y was prepared by W. B. Lane of the Stanford Research Institute (SRI) at the Camp Parks Hot Cell facility. Basically Lane’s method? consists of separation of °° Y from a 99S? ° VY mixture by precipitation of Sr(NO3)2 in concentrated nitric acid. Carrier-free °° Y remaining in solution is then fused on the silica sand at 925°C. For radiation-safety considerations two modifications were made in this procedure. (1) The sand was eluted in water to remove all fine particles less than 88 wand returned to SRI for use in simulant preparation. (2) After the ?° Y was S72 SECHWEZ separated from the ?°Sr—?°Y mixture by SRI, it was purified in our laboratory to remove remaining traces of °°Sr contamination. The method used was a modification of the Brookhaven ?°Y generator.* Essentially this purification depended on complexing the cation yttrium to an anion, yttrium citrate. Strontium carrier was added to the solution, and the solution was then passed over an ammonium-saturated cation-exchange column. This method results in an overall radiochemical separation of ?°Sr from ?°Y of greater than 10’. The purified ?° Y was then returned to SRI for fixing on the sand. Fallout-Simulant Applicator An apparatus that would apply the fine, highly radioactive sand evenly to the crops with safety to the operator had to be constructed. This required glove-box loading of the machine and remote operation of the applicator. The sand was to be applied at the rate of 10 g/sq ft on 4- by 4-ft plots. The essential part of the applicator consists of a 6-in.-wide hopper of triangular cross section. A four-vaned, notched stirrer was mounted at the bottom, and the sand was discharged through No. 60 drill holes (Fig. 1). Sand delivery was started and stopped by a hopper valve operated by a rotary thts, Fig. 1 Sand hopper. Sand is agitated by notched stirrer and falls through No. 60 drill holes at bottom of hopper. Delivery of sand is started and stopped by solenoid-operated valve on bottom of hopper. SURVIVAL AND YIELD OF CROP PLANTS 373 solenoid. The rate of sand dispensing as a function of time is given in Fig. 2. It was found that, when 500 g of sand was placed in the hopper, the first 340 g was delivered at a uniform rate; then delivery became nonuniform. The delivery rate decreased, then increased briefly, and finally decreased again; this was not an experimental anomaly but a real, duplicable result. 340 g @-0-0-0-0-0 0-0-0, . 9-0-6 RATE OF SAND DISPENSING, g/30 sec CUMULATIVE TIME, min Fig. 2 Sand delivery from hopper as a function of time. Hopper contained 500 g 88- to 175-y silica sand at start of run. The hopper or dispersing head is mounted on an apparatus that moves the head across the plot while laying down a 6-in. swath of sand (Fig. 3). Before each end of the pass, the hopper valve closes while the head is reversing direction. The whole apparatus moves perpendicular to the line of head travel so that, when the head has completed one cycle (1.e., across the plot and back), it has moved perpendicularly 61in. This results in the uniform sand pattern depicted in Fig. 4. At the start and finish, there is a 6-in. by 4-ft isosceles triangle of single sand coverage. The rest of the area receives double coverage by the dispensing head. Speeds were calculated to give 10 g/sq ft. Actual rate of sand dispensing was checked by placing 30 1-qt ice-cream cartons within the 4- by 4-ft area. The amount of sand collected in each carton is given in Table 1. Standard deviation of a single value of 30 measurements was 0.09 g with a mean 374 SCHULZ Fig. 3 Complete sand applicator. Hopper moves back and forth across the plot laying down a 6-in. swath of sand while the whole apparatus moves perpendicular to the line of head travel. of 0.99 g per carton. This gives a calculated deposition of 10.3 g of sand per square foot. Beta-Radiation Dosimetry Development of a beta-radiation dosimetry system designed for use in the field was carried out with the cooperation of EG&G, Inc., Goleta, Calif. Micro-beta-radiation thermoluminescent dosimeters (TLD) consisting of CaF,—Mn chips sealed in thin, black polyethylene film were de- veloped. The dosimeters consist of approximately 0.25-mm cubes weighing approximately 40 yu. Initially the procedure consisted in reading the exposed dosimeters with an EG&G reader; each dosimeter was standardized after each reading by exposure to a standard cobalt source and again read out. This procedure was standardized against a primary standard electron source. This was done in two ways at the EG&G laboratory. Dosimeters were exposed to an electron beam from a Febetron, and the dose was calculated from the known energy and distance from the source. The dose was also determined by calorimetry. Finally, the dose was determined by the EG&G cobalt standardiza- tion readout procedure and compared with other results. The experiments were designed by Asher Kantz of EG&G. 375 SURVIVAL AND YIELD OF CROP PLANTS mi Fig. 4 Diagram of sand coverage. Sand is applied to plot with 6-in.-wide traveling head so that at the start and finish there is a 6-in. by 4-ft isosceles triangle of single sand coverage. The rest of the area receives double coverage. Table 1 SAND COLLECTED BY 1-qt ICE-CREAM CARTONS Carton Weight of Carton Weight of No. sand, g Carton Weight of No. sand, g sand, g Average weight per carton = 0.9933 +0.0911 SS ee 376 SCHULZ Table 2 COMPARISON OF ABSORBED DOSE IN MICRO TLD CHIPS Distance from Febetron Predicted Thermocouple TLD exit window to target, cm dose, krads dose, krads dose, krads 8.0 36.8 35.0 36.0 3.0 313 270 306 The electron source used was a Febetron 706, which 1s a field-emission diode device. The electrodes are charged to 600 keV, and the electrons are delivered in a 5-nsec pulse. The penetration of the electron beam has been measured and has the same characteristics as a 550-keV monoenergetic electron beam. The ratio of the dose to energy fluence from the beam was also measured, and again it was found that the energy was slightly above 500 keV. For satisfactory absorption characteristics, we found it necessary to maintain the target in a vacuum. At a given separation of the face of the electron tube and the target, the reproducibility of the absorbed dose from shot to shot was +12%. For a series of experiments, a CaF,—Mn chip was placed in a known position in the electron beam. A chromel—constantan thermocouple (0.002-in. wire) was attached to the chip with a minimum of pliabond cement. The temperature rise experienced by the CaF, was recorded and the absorbed energy calculated. The thermocouple was then detached, and the amount of thermoluminescence in the chip was measured in a standard EG&G TLD reader. The energy absorption by the TLD measurement was calibrated against the response in a °° Co-source range. Agreement of the electron energy absorption with the °°Co energy deposition verifies that the energy absorption from the two sources is equal. To compare these measurements against the energy absorption predicted by the placement at a given position, we took a series of 3 to 5 shots for each measurement. The summary of the results of two such measurements is given invlables2, The conditions of the electron source used for this experiment make it mandatory to have a CaF, chip that is thin compared with 500-keV electrons. The range of such electrons in CaF, is approximately 0.22 g/cm? or 0.028 in. Chips with a thickness from 0.007 to 0.015 in. were used for the thermocouple measurements. When the chips were broken into small volumes, the reproducibility was poor. Sawing the chips into 0.25-mm cubes gave a reproducibility within +3% for a given chip. To save on expense and time, we developed our own standardization and readout procedure. For this purpose we purchased an EG&G model TL-003A TLD reader and outfitted it for reading the micro dosimeter chips. A 47 exposure chamber constructed for standardization of each dosimeter using ?° Y SURVIVAL AND YIELD OF CROP PLANTS HATE of known concentration is illustrated in Fig. 5. Basically, it consists of two lucite cylinders, each having a 1-in. wall thickness and a 1-in. lucite bottom. The top of each cylinder is covered with a 0.00025-in.-thick (approximately 0.64 mg/cm” ) Mylar membrane. The dosimeters are placed on the membrane so that the distance to any wall exceeds the maximum range of the 7° Y radiation in water. The other cylinder is then inverted and secured to form a 47-geometry exposure chamber. Standardized ?° Y is then carefully introduced into both halves of the DOSIMETERS EXPOSED BETWEEN TWO MYLAR MEMBRANES 0.00025 IN. THICK FILLING AND REMOVAL BORES PLEXIGLAS hr - . BODY ALLL vag - -_ — a | O-RING A, 80Y SOLUTION) - -— —— rape SEALS ~ muspa SOLUTION: 5 8 Stay if pies iia 2a Exes : | FILLING AND Rempcaere area | REMOVAL BORES 13 5° Fig. 5 The 47 chamber for exposing TLD dosimeters to a known amount of beta radiation. ?° Y solution concentrations ranged from 0.5 to 500 uCi/ml. chamber to completely fill the apparatus; there must be no entrapped air. After the dosimeters have been exposed for a given time, the ?°Y solution is transferred back into the ?°Y storage bottle. Both halves of the chamber are rinsed with dilute HCl and water and then dried by flowing warm, dry air through the system. This is done to prevent dilution of the ?° Y solution as it is successively used in repeated filling of the chamber for various exposures of the dosimeters. The apparatus 1s illustrated in Fig. 6. Appropriate traps, air dryers, and filters prevent contamination of the atmosphere by the vacuum and air lines used in filling and drying the apparatus. The ?°Y solutions were supplied by the SRI Camp Parks Hot Cell facility. The concentrations were determined in our laboratory both by comparison with a?°Sr—?° Y standard source from which the ?° Sr radiation was absorbed out and by comparison with a standard *?P source. The agreement was to within 5%. A 1-ml sample of °° Y was taken from the storage bottle before and after each use of the ?°Y in the 47 chamber to monitor for any losses of ?°Y from the solution by deposition on surfaces. In the first experiment with the apparatus, dosimeters were exposed for various times and at various °°Y solution concentrations. The dose was computed with the aid of the equation given in Quimby and Feitelberg,° 378 SCHULZ 1-ML AUTOMATIC PIPETTE 3— IN. LEAD SHIELD 1-IN. LUCITE FRONT Fig. 6 Apparatus for filling, rinsing, and drying 47 exposure chamber. A Line to lower three-way K Line to atmosphere stopcock L Line to atmosphere B ?°¥Y introduction lines M Line to manometer C Line to sampling pipette N Line for removal of en- D Vacuum line for filling trapped air (bottom Ory, supply bottle chamber E Line to acid-wash bottle O Large line for drying air F Funnel for introduction of (bottom chamber) acid and water 2 Large line for drying air G Drain line (top chamber) H Vacuum line Q Drying-air exhaust line I 47 chamber vacuum line leading to filters J Samples vacuum where D = 73.8 cEgT (c is the concentration, Ez is the average beta energy, and Misisethe time): The results of this experiment are plotted in Fig. 7; the calculated dose is plotted against the dose reported by EG&G. The points shown are averages of data from 10 to 15 different dosimeters. The 45° line is shown for comparison. These results are somewhat erratic, but the agreement was generally encouraging. In the next experiment a large number of dosimeters were again dosed at varying rates in the 47 chamber and subsequently read out on the TLD reader. The results are shown in Fig. 8, in which the calculated dose is plotted against SURVIVAL AND YIELD OF CROP PLANTS 379 = (S) Ww CALCULATED DOSE, rads EG&G READING, rads Fig. 7 Calculated dose in the 47 exposure chamber plotted against dose reported by EG&G. the instrument reading. Again, each point is the average of a number of dosimeters receiving the same dose. The results again are somewhat erratic, but the relation appears to be linear. In future work we plan to calibrate each dosimeter individually to eliminate the variability caused by dosimeter size. To, test, -the* effectiveness: of the polyethylene packaging, we :dosed approximately 50 dosimeters equally in the 47 chamber and divided them into two lots. One lot was then exposed to the weather for a period of about 2 months, and the other lot was kept as a control. Both lots were then read in the EG&G reader. If we use Fig. 8 as a calibration curve, the control chips read at 4730 rads and the exposed chips read at 4480 rads. For the purposes of our subsequent field experiments, in which the chips are exposed to weather, this difference is not important. Absorption of ?°Y radiation by polyethylene was studied by placing polyethylene sheets of varying thickness between the chips and the Mylar 380 SCHPIEZ j=) s CALCULATED DOSE, rads — oO [es] 102 107! 1 10 102 102 EG&G METER READING, rads Fig. 8 Calculated dose in the 47 exposure chamber plotted against the reading of the EG&G instrument. membranes. Again using Fig. 8 as a calibration curve, we found the dose in rads. In these experiments the chips were packaged in 1.5-mil, black polyethylene, except for one case in which bare chips were exposed. The thickest polyethylene absorber was 0.5 in. The observed dose divided by the calculated dose from the 4m exposure chamber was then plotted against the absorber thickness, as shown in Fig. 9. Note that evidently there is a maximum in the curve. The point plotted on the ordinate is for bare chips, however, and it is not known whether the lower value is due to exposure to light or to a dose-depth effect. The value on the ordinate is, of course, 100% at 1.5 mils since this was also the packaging used in establishing the calibration curve. EXPERIMENTAL DATA Preliminary Experiment Before designing the field experiments, we carried out a preliminary experiment in a controlled-environment chamber. This experiment utilized a wide range of ?°Y concentrations to determine the general levels at which beta-radiation damage to wheat and lettuce plants occurs. The radioactive sand was applied to foliage of 6-week-old plants growing in pots by entraining the SURVIVAL AND YIELD OF CROP PLANTS 381 x 100, rads OBSERVED DOSE CALCULATED DOSE 0 40 80 120 160 200 ABSORBER THICKNESS, mils 0 25 50 100 250 480 APPROXIMATE RANGE, mg/cm? Fig.9 Absorption of °°¥Y beta radiation by polyethylene sheets of varying thickness. sand in an air stream, employing a modification of Shelby’s device,° and then dropping the sand down a tube onto the plant foliage and soil surface. The treatment levels were such that ?° Y was added to the pots at the rate of 125, 230 17-5. O72. and, 205. mCi/sq” ft... The. wheat was quite sensitive; grain production had ceased at the 17.5 mCi/sq ft level. Variability was rather large in this preliminary experiment, but the results were felt to be adequate to serve as a guide for planning the field experiments. The lettuce was somewhat more tolerant to °° Y exposure; the yield began to decrease at the 17.5 mCi/sq ft level. From this level to the highest level used, 205 mCi/sq ft, there was a gradual decrease in yield. Visual aberrations to plant growth occurred at a much lower level of beta exposure, At the lowest level of treatment, 1.5 mCi/sq.{t; some visual changes were noted, and at 5.3 mCi/sq ft obvious anatomical aberrations were present. Since visual changes in growth of the lettuce occurred at much lower levels than yield reduction, it was felt that microscopic examination of the apical meristems and other plant parts might prove interesting. Figure 10 is a photomicrograph of a normal apical meristem at the apex of the fleshy crown stem. Figure 11 gives detail of this meristem. Note that a single layer of cells forms the tunica, which overlies a corpus several cells thick. In normal tissues such as this, these cells are not vacuolated. Figure 12 shows a shoot meristem of a plant treated with ?°Y sand at 17.5 mCi/sq ft. Here there is no visible effect, SCHULZ 382 09 (X 09 ‘pasewep Aqyensia st queyd oe) ‘uonvolpiuseyp) 33 bs/iIgu 7g 1e paivan jueyd yo saavay Bunod ysnoyye jeursou sreadde waiswaw (KX 6IT ‘uoNeorsUsey) jo sjeixe ul pawoy saxade yooys jeusouqe OM] ¢T ‘814 ay bsigw co zt yw paiean juejd jo woaistiayw ZI ‘3Iy Seg tie > et AACE POR Pa 2 ee, br ee ei |e i ’ <7, LA ee tre: Gut P 5 ee ee 2 te 44 wut ps ae 4 3 asges ae Ge 6 A! bre. \ is ay < xi et % ‘ g 4A a, he “. 5. & i re ¥ 4 ‘ - * te ae ae We Se ee Te ae these ng Si rs eS Sc aan ES Ngee woke 7 gute SURVIVAL AND YIELD OF CROP PLANTS 384 SCHUIEZ even though the whole plant evidenced marked gross anatomical aberrations and yield reductions were becoming evident. Figure 13 shows one of a set of twin apexes found on a plant treated with ?°Y sand at 87 mCi/sq ft. This photomicrograph shows two abnormal shoot apexes formed in the axials of young leaves. The terminal meristem is at the upper left-hand corner. Figure 14 is a detail of Fig. 13 which shows the upper of the two shoot apexes formed in the leaf axials. Note that this secondary meristem is itself damaged by radiation. The cells of the tunica and corpus are vacuolated. Figure 15 shows the shoot apex of a plant treated with ?°Y sand at 205 mCi/sq ft. Here all cells are vacuolated and no cell division is occurring. Figure 16 shows cross section of young normal leaf near midrib. Note the prevalence of nonvacuolated cells in the epidermis and mesophyll. The bundle sheath surrounding the vascular bundle extends to form the rib of the leaf. The vascular bundle consists of, from top to bottom, xylem, phloem, and lactiferous ducts and fibers. Figure 17 shows a young leaf treated with °° Y sand at 205 mCi/sq ft. Here the midrib is swollen because of vacuolation and swelling of mesophyll. Distinction between the bundle sheath and mesophyll ts lost. Field Experiments The results of the preliminary experiment were used in the design of the field experiments carried out at the University of California Kearney Horticultural Field Station located near Fresno. The soil at the Kearney Station is a Hanford sandy loam formed on recent alluvium. The exchange capacity 1s about 5 milliequivalents per 100g and is Ca*” dominated. The salt content is very low, and the area is generally one of high agricultural productivity. The field plots are described in Fig. 18. Each plot is 8 by 20 ft. The entire area is surrounded by a radiation-safe wire fence with a 6-ft reed fence attached to the wire for wind control. In the first experiment lettuce (Cos) or wheat (Pitic 62) was planted in each 8-ft by 20-ft plot, but only a 4- by 4-ft area in the center of each plot was contaminated. The beta exposure was by means of °°v fused on 88- to 175-u quartz sand at 925°C. This material was prepared by W. B.Lane at SRI: The wheat and lettuce were planted on Mar. 27, 1969, and the 9°-V sand was applied on May 16, 1969. The lettuce was harvested on June 10, 1969, 75 days after planting. The wheat was harvested on July 10, 1969, giving a growing period of 105 days. On the day of ?°Y application, the lettuce had an average width of 18.7 cm, an average height of 14.5 cm, and an average weight of 56.3 g. At this time the wheat had an average height of 33 cm, and the apical meristems were approximately 1 cm above ground level. The sand was applied at rates of 0.26, 0.78, 2.25, 6.64, 19.8, and 59.4 mCi of ?°Y per square foot by remote control with the applicator previously described. Before the sand was applied, 212 micro dosimeters were placed at various locations in the plots, and their positions were recorded. The plots are shown at time of treatment in Fig. 19. 385 SURVIVAL AND YIELD OF CROP PLANTS (X 6LT ‘uoneoIzusey) ‘SuIIINIIO «SI UOISIAIP ]]99 OU pUe ‘pazejONdvA are s]]29 Ww (33 bssigui ¢gz Jo [aaa] JuauNvan ev xade yooys CT ‘814 ‘uoneipes Aq pasewep st ulaqsiiaur Arepuodas 3eY3 310N *X 6IT JO uonvoipiuseu ae ¢T ‘BI Jo peeq PT ‘314 386 SCHULZ Fig. 16 Cross section of normal young leaf. Note non- vacuolated cells in epidermis and mesophyll. (Magnification, 150 X.) Fig.17 Young leaf treated with °° Y at 205 mCi/sq ft. Midrib is swollen, and distinction between bundle sheath and mesophyll is lost. (Magnification, 150 X.) SURVIVAL AND YIELD OF CROP PLANTS 387 RADIATION-SAFE EENCE. A THREE STRANDS BARBED WIRE ABOVE 6-FT WELDED-WIRE x x x | MESH 6=Fil.. REED, FENCE < ATTACHED TO WIRE MESH FOR WIND CONTROL x 24' - 6" ——+ uv PLOT 90y EACH TREAT- ED 4- BY 4-FT WHEAT PLOT WAS x LETTUCE SURROUNDED WHEAT BY IDENTICAL LETTUCE PLANTING WHEAT LETTUCE WHEAT LETTUCE © fo) OnNOn FWNH— WHEAT LETTUCE WHEAT LETTUCE WHEAT LETTUCE WHEAT EETMUCE 6 6 9 9 5 5 4 4 0.0 0.0 0.0 0.2 0.2 0.7 0.7 2:2 22 6.6 6.6 9.8 9.8 9.4 9.4 an — Fig. 18 Arrangement of field plots for ?°Y beta-radiation experiment at Kearney Horticultural Field Station near Fresno, California. The ?°Y was fused on 88- to 175-~ quartz sand at 925°C. ERS Fig. 20 Accumulation of radioactive sand on corn leaves. Sensitive parts of corn plants are well protected from beta radiation, and no damage occurred at the highest level of treatment (71.3 mCi/sq ft). 389 ee i = a a Sa a a ee SURVIVAL AND YIELD OF CROP PLANTS Ly'O OF CIE GL Ly OOT oT Lb cI b6S Iv'l 19 6 60 6r ST 6r OC 6L 1) 861 O8'€ cel COV Or iL O€ Li cs Il Oro eeet adh vcr EVES eo Lt cv 9 68 6 SENG 97 Bl O8Y Cvs OS onl 15) 61 SL L 8L0 br vl CED OcS $9 61 (5 OC L6 S 97 0 v6 98C €°OS Iv cI 7 OV OC 9 € JONUOD 3 ‘IYSIOM Jaquinn uID i bs wD 14 bs iy bs sad iy bs/3 ‘squejd "ON yy bsyjigw “WYysI9H Jod ‘WYys19H jad sjuryd jo palip-1e 10|d ‘quoul ea es) JaquinN Jaquinn Jaquinn JO 1Y3I9M e390 ; . te. . Ao6 spray YIM SJdq]LL spray INOYIAM SIITILL YIMols [ey VLVG GTHIA LVAHM b GPL 9TOS og | 986 9LS6 C96 8b S6 bv 6S 9T ST CSOC cb97C T881 O66€ ICCE O9b9 8°61 zo fS | tvs 6711 Sf6 (Sse! 9COT LCLC OY) Glare 6€C SSE LEE LOY LSE 856 SOM OT 6 OTT SOC It OLT r9T ESE 8Z'0 Sez EL tL 6b bel cuss Sor 970 9°S ‘Ul TT IV (UL O3V “Ul 7T3V Ur 3V SpEA sped ay bsrgw "ON eoer Gold reece UI9}SII9UI UId3SII9UI pardde 10]d 3913] yeayM A 30n}197] eoUM 06 02 9s0q 02 as0q SLOTd AHL NI SNOILVOOT SNOIUVA LV SYALAWISOG OUOIW Ad GACUOOAA ASOG € A192 L 390 SCHUiRZ Table 5 LETTUCE YIELD DATA 90 Y treatment, ie mCi/sq ft Plot No. ‘Fresh weight, g Dry weight, % Control 4 305.3 7 .O 0.26 6 296.3 6.5 0.78 8 301.7 6.4 Vio) 10 250.0 fo 6.64 12 ZILA 6.4 19.8 14 258.1 8.2 59.4 16 148.6 aU Ar Dosimeters were placed on the plants as close as possible to the apical meristems and at 6 and 12 in. above the soil surface. The doses accrued during the experiment are given in Table 3. The yield data are given in Tables 4 and 5. After the wheat and lettuce were harvested, a corn experiment was carried out in the same area. The corn crop was contaminated with the radioactive sand 34 days after planting. At this time the apical meristem was about 23 cm above ground, and the plants were about 61 cm high and had a stem-base diameter of 2 cm. The rate of sand application was 10 g/sq ft, as in the previous experiment, and the specific activity was varied to give 6.74, 12.9, 34.6, and 71.3 mCi/sq ft. Although the sand is spread evenly on the area, it accumulates on the plants unevenly as shown in Fig. 20. No yield reduction (5% level) was observed even in the highest level of treatment. DISCUSSION It is seen from the wheat data that at 6.64 mCi/sq ft (corresponding to 2700 rads at the surface of the plant near the shoot meristem) grain production is severely reduced. Reduction in aerial growth, however, occurred only at the highest treatment level. In plot 13, there was no obvious damage to the plants other than the reduction in the grain. At the highest level, in plot 15, chlorotic leaves and stem shortening were observed. Photographs of tillers and grain from plot 13 are shown in Figs. 21 to 24. The lettuce plants are much less sensitive to the °° Y treatment. Yield was reduced significantly only at the highest level of treatment. In this case the plants were stunted in appearance, and brown necrotic areas developed on the leaf edges. The center of many of the plants had no new growth; where bolting occurred, the leaves were distorted. Figure 25 shows a damaged lettuce plant from the highest contamination level. In Fig. 26 a plant from the same plot has resumed growth and shows multiple growing points. SURVIVAL AND YIELD OF CROP PLANTS 3911 Fig. 21 Wheat head from control plot. Fig. 22 Wheat head from plant exposed to °°Y at 19.8 mCi/sq ft. Color is much darker brown than control. SY SCHULZ SELTELapbbet ee i2 3 Lt ae METRIC 14, 45 * ee 7-7 Fig. 24 Wheat grain from plot treated with 90¥ at 19.8 mCi/sq ft. The relation between the amount of radioactivity applied (in microcuries per square foot) and the dose (in rads) to the meristem for each crop is interesting (Fig. 27). In each case there is a linear relation between the applied radioactivity and the dose. Dosimeters tied near the apical meristem of the corn plants recorded a surface dose of about 5000 rads at the highest level of treatment, but the apical meristem was obviously well shielded by the large sheath protecting it. The protection afforded the shoot meristem can readily be seen by examination of the data presented in Fig. 9. This result suggests that consideration of the stage of development of the corn plant may be particularly important in assessing beta-radiation effects. In addition, the leaves exposed to the beta radiation were SURVIVAL AND YIELD OF CROP PLANTS 393 Fig. 25 Lettuce plant from plot treated with °° Y at 59.4 mCi/sq ft. Damage was generalized with no apparent recovery, no new growth in center of plant. Fig. 26 Lettuce plant from same plot as that in Fig. 25. Note that in this plant some recovery has taken place in the center of the plant. The new growth consists of multiple growing points as contrasted to the single growing point normally found in lettuce plants. 394 SCEiW EZ Lettuce 10 107! 1 10 102 102 290 APPLIED, mCi/sq ft Fig. 27 Relation between ?°Y applied to plots and dose measured at apical meristem of plants. Data for both wheat and lettuce are for an average of four plants each. quite resistant to damage; no visual aberrations were discernible. During the period when cell division is taking place to produce the leaf, the meristematic tissue is well protected by the older, nonsensitive leaves. No plants were killed in any of these experiments, even at the highest levels of treatments. This is in agreement swath jthe datay of mochulz and Baldar’ on wheat and lettuce exposed to beta radiation by immersion in °° Y solutions. The apparent resistance of the plants to death by beta-radiation exposure is probably due to the uneven plant exposure. Some plant parts are relatively protected, and the plant does not receive a whole-plant exposure such as it would with gamma radiation. From the data accumulated so far, the beta-exposure survival level for agricultural crops appears to be far above the level necessary to cause severe yield reduction; therefore yield rather than survival is the important criterion in assessing beta damage to food crops. SURVIVAL AND YIELD OF CROP PLANTS 395 ACKNOWLEDGMENTS This study was supported by the U. S. Atomic Energy Commission and the Office of Civil Defense, Department of the Army. REFERENCES il, Pay E. H. Quimby and S. Feitelberg, Radioactive Isotopes in Medicine and Biology, Vol. 1. Basic Physics and Instrumentation, p. 142, Lea & Febiger, Philadelphia, 1963. W. A. Rhoads, R. B. Platt, R. A. Harvey, and E. M. Romney, Ecological and Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and Short-Term Effects on the Vegetation from Close-In Fallout, USAEC Report PNE-956, EG&G, Inc., June 25, 1969. . W. B. Lane, Fallout Simulant Development, SRI Project No. MU-7236, Stanford Research Institute, 1969. (OCD Work Unit 3211C.) R. F. Doering, W. D. Tucker, and L. G. Stang, Jr., A Simple Device for Milking High Parity Yttrium-90 from Strontium-90, J. Nucl. Med., 4: 54-59 (1963). .E. H. Quimby and S. Feitelberg, Radioactive Isotopes in Medicine and Biology, Vol. 1, Basic Physics and Instrumentation, pp. 112-113, Lea and Febiger, Philadelphia, 1963. _W. E. Shelby, J. L. Mackin, and R. K. Fuller, Artificial Surface Dirts for Detergency Studies with Painted Surfaces, Ind. Eng. Chem., 46: 2572 (1954). .R. K. Schulz and N. Baldar, Beta Radiation Effects on Plants, paper presented at the Symposium on Vulnerability of Food Crops and Livestock Production to Fallout Radiation, Colorado State University, Fort Collins, Colo., June 1969. FIELD STUDIES OF FALLOUT RETENTION BY PLANTS JOHN P. WITHERSPOON Ecological Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee ABSTRACT Several field studies on the retention by plants of local fallout particles (particles exceeding 44 uw in diameter) are summarized. Although initial fractions of fallout intercepted varied as a function of plant-foliage characteristics and particle size, average initial retention values are similar for studies done with a wide variety of plants in different geographical regions. Rapid losses of particles from foliage and other plant parts due to weathering occurred generally during the first week following initial particle deposition. Losses from tree species during this period were several times greater than losses from crop plants. In a period of 1 to 2 weeks following deposition all plants lost 90% or more of the fallout particles initially intercepted. After about 3 weeks the loss of particles was relatively constant and proceeded at a slow rate (average weathering half-life of 21.3 + 3.9 days) regardless of subsequent rain and wind conditions. The formulation of realistic predictions of the biological effects of fallout on vegetation requires information on both the radiosensitivity of plants exposed to radiation in fallout geometries and the capacity of vegetation to intercept and retain fallout particles. Since about 64% of the total radiation dose from fallout is delivered during the first week after detonation of a nuclear device, initial interception, sites of deposition, and early losses of particles are critical events in estimating dose to contaminated plants. This paper reviews some field studies on contamination of plants by local fallout and discusses the significance of these studies in the evaluation of short-term biological hazards involved in using nuclear devices for peaceful or military purposes. Studies on retention of local fallout particles by plants have been made under both varying geographic and varying particle-source conditions. However, 396 : FIELD STUDIES OF FALLOUT RETENTION 397 in many of these studies, the early losses of fallout from plants due to weathering have not been determined. This is particularly true of local fallout particles exceeding 44 u in diameter. Deposits of particles exceeding 44 yw usually contain an appreciable fraction of fallout radioactivity, and they can represent a major source of radiation dose to plant tissues, although they may be briefly retained. Small particles constitute the bulk of radioactive debris deposited as worldwide fallout, but they lose much of their radioactivity via physical decay before deposition and are of greater biological significance as a major source of entry of radioactivity into food chains. INITIAL RETENTION OF FALLOUT BY PLANTS The initial retention of fallout by a given plant species depends on a number of factors. Such plant characteristics as surface area (mainly foliage), density, and surface characteristics of leaves are important variables. Meteorological conditions during deposition, particularly wind velocity and relative humidity, also influence initial retention. Finally, the size and amount of falling particles influence the degree to which plants are contaminated. Several field studies have been conducted in which the initial contamination of plants has been determined and related to one or more of these factors. The initial retention of fallout by plants can be expressed in two ways. One is the foliage contamination factor (a7) used by Miller: ! ay = Ci? /m; sq ft/g (1) where Ci® is the quantity in microcuries of radionuclide initially intercepted per gram of dry weight of foliage and mj; is the quantity in microcuries of radionuclide deposited per square foot of soil surface area. Another expression of initial retention is the fraction (F) of fallout which is intercepted by plants or foliage: F = ajw) (2) where w; is the biomass of foliage, or of the plant, in grams per square foot of soil surface area. Values of a; for plants sampled after nuclear tests have been smaller than values reported in other field tests where nonnuclear sources of fallout were applied. Miller,’ reviewing a; values for plants sampled following weapons tests, reported a range of 2 X 10° to 0.013 sq ft/g. Other estimates have been made by Martin.* Values from three weapons tests (Priscilla, Buffalo Round 2, and Sedan) ranged from 0.002 to 0.012, with an average of 0.004 sq ft/g. Most of the plant samples taken after nuclear detonations were collected several days after initial deposition of fallout or after some losses due to weathering had 398 WITHERSPOON occurred. Also, results from test-site fallout fields were usually obtained in areas of light to moderate fallout. Plant contamination values derived from several field studies with local fallout and, where samples were taken before appreciable weathering, are fairly consistent. The a; values for a variety of different plant species were taken by Miller’ in Costa Rica following deposition of fallout from the Irazu volcano. A median value of 0.05 sq ft/g was reported for dry exposure conditions and particles having a median diameter between 50 and 100u. In studies at Oak Ridge National Laboratory, Witherspoon and Taylor® reported an average a; value of 0.057 + 0.024 sq ft/g for five species of crop plants treated with 88- to 175-u diameter particles. In similar studies* values of 0.035 and 0.005 sq ft/g were reported for oak and pine tree foliage, respectively. Values for relatively small-leaved plants such as pine” COLOO5S))? lespedeza* (0.010), and fescue grass (0.011) tend to be smaller than those for large-leaved plants. Therefore an a; value of 0.05 sq ft/g seems reasonable for calculating initial beta-exposure doses to plants in areas of local, dry fallout deposition (or where particles exceed 50 uw in diameter). A value of about 0.01 may represent a good estimate for most narrow-leaved plants. Under damp conditions (relative humidity greater than 90%), or where foliage surfaces are wet, a; values have been reported to increase by an average of two to four times those obtained under dry conditions.’ °° Reported values of F, initial fraction of fallout intercepted by plants relative to amount deposited per open soil surface area, are summarized in Table 1. Table 1 INITIAL RETENTION OF SIMULATED FALLOUT DEPOSITED IN AN ACUTE MODE UNDER DRY CONDITIONS Retention, % : Foliage area 44-to 88-u 88-to175-u 175-to 350-u Soil surface area Plant density, Plant particles particles particles sq ft/sq ft g/sq ft of soil White pine** 24.2 446 Red oak* 34.9 9.9 Squash” 100.0 88.5 172 6.4 Soybean™ 100.0 100.0 3.11 11.4 Lespedeza® sD 1:9 0.51 159 Peanut™ 9.8 5.8 0.91 4.4 Sorghum 48.9 10.8 1.25 5.4 Fescue” 45.4 19.6 17.4 Pasture grass° Ue 525 OZ Alfalfa® 23.0 5.0 19.5 Corn® 44.0 *Reference number. FIELD STUDIES OF FALLOUT RETENTION Sk Initial retention can be seen to vary both with plant-foliage types and with particle size. Where retention values for different particle sizes can be compared, there is an average of two to three times less initial retention when particle size range is increased by a factor of 2. This is particularly evident in plants having small leaves and small foliage surface area relative to soil surface area. Mass loading of particles used in the studies summarized in Table 1 varied from about 0.5 to 13.6 g of particles per square foot of open soil surface. In one series of studies® where mass loading was varied, initial retention was found to be independent of mass loading over this range. Sites of retention other than foliage can be important in determining biological effects of fallout radiation on plant species. Table 2 gives the average Table 2 FRACTION OF TOTAL INITIAL RETENTION IN PLANT PARTS* Fraction of Fraction of Plant Plant part 44-to 88-u particles 88-to 175-u particles Squash Stem 0.051 0.037 Flowers 0.007 0.032 Foliage 0.942 O93 Sorghum Stalk OF259 0.086 Foliage 0.741 0.914 White pine —_ Bud clusters 0.160 Foliage 0.840 *Fallout applied under dry conditions at a mass loading of from 4.5 to 6.6 g per square foot of open soil surface. fraction of total initial retention associated with various plant parts. For these particular species the foliage intercepted most of the fallout, but small fractions were intercepted by radiosensitive structures such as flowers and buds. In the white pine, a relatively radiosensitive plant species, a large fraction of fallout is trapped in clusters of buds on the ends of branches. Since these buds contain meristematic tissues, which are the most radiosensitive parts of the vegetating plant, these trapping sites represent critical regions. Particles trapped in these structures also are retained longer than particles intercepted by pine foliage.* Flowers also may intercept small fractions of fallout. In squash plants, Table 2, initial interception by flowers of particles 44 to 88 u in diameter was less than that of 88- to 175-u particles applied at the same mass loading. The larger particles may have had a tendency to bounce or roll off foliage into open flowers, whereas smaller particles were more efficiently intercepted by foliage and stem surfaces. Smaller particles, in the 44- to 88-u range, were intercepted by vertical structures, such as sorghum stalks, with much greater efficiency than 400 WITHERSPOON larger particles. Grasslike plants such as sorghum, corn, and fescue have effective particle-trapping sites in the leaf axils, angles between the leaves and stems.*’?® Unless particles contain enough radioactivity to produce damage to tissue from contact doses, however, these trapping sites may not be biologically important since they are somewhat removed from more radiosensitive meristematic regions. LOSS OF FALLOUT FROM PLANTS DUE TO WEATHERING The major meteorological factors that influence retention of fallout by plants are wind speed and rainfall. Estimation of early losses of fallout particles from plants, particularly for the first week following initial deposition, is critical in determining dose to contaminated plants. Results from studies on retention indicate that concentrations of radionuclides on fallout-contaminated plants can be expected.to decrease at rates significantly higher than would be predicted on the basis of physical, radioactive decay. Beta-radiation-exposure geometries may be expected to change rapidly from a contact to a bath mode of exposure. Loss of fallout from foliage during the first day following deposition is rapid under dry conditions with relatively gentle wind speeds. Table 3 illustrates Table 3 PROMPT LOSSES OF 88- TO 175-u PARTICLES FROM FOLIAGE Time after Initial interception Wind, Rain, Plant deposition, hr remaining, % mph in. Corn®* 24 94 0 to 20 Alfalfa® 24 82 0 to 20 Squash” 36 52 OFtO%5 Soybean” 36 49 0 to 5 Sorghum> 36 90 Oto 5 Peanut? 36 44 Oto 5 Lespedeza” 36 74 OstOrd _ Fescue> 18 34 0 to 1.5 White pine” 1 90 0 to 12 White pine” 24 6.3 0 to 15 0.9 Red oak* 1 9.5 0 to 12 Red oak* 24 0.4 0 to 15 0.9 *Reference number. prompt losses for 10 plant species studied under similar conditions of deposition mode and weather. In most cases these losses amount to 50% or more of the amounts initially intercepted. Studies with smaller particles (44 to 88 wu) have indicated that first-day losses are as great as with 88- to 175-u particles.» Rapid particle loss from other plant structures also may be expected. Table 4 gives FIELD STUDIES OF FALLOUT RETENTION 401 Table 4 LOSSES OF 88- TO 175-u PARTICLES FROM SQUASH AND SORGHUM DUE TO WIND ACTION Retention, %* Squash Sorghum Time, Wind, days mph Foliage Flowers Stem Foliage Stalk 0.5 Oltoyd 86.2 37:5 93:0 96.8 5324 Ld O to 5 52.4 14.8 90:0 90.0 33.8 7 Oto 7 36.0 10.0 44.1 47.0 220 *Percent of initial interception value. retention values for stem and flowers of squash and for sorghum stalks. Rate of loss of particles from squash foliage was greater than that from the stem over a period of 1 week after initial deposition. It is probable that stems, which are prostrate and under the large leaves, intercepted some of the particles dislodged from foliage by gentle winds during this period. The more rapid loss rate from flowers was due, in this case, to wilting and loss of petals during this period—a phenological event. Rapid losses from structures such as the vertical stalks of sorghum were expected. Some generalizations concerning the probable retention of fallout by trees vs. agricultural plants may be made. Table 5 gives average foliage-retention values for five crop species® that vary in growth habit and leaf-surface characteristics and for two tree species that represent very common tree-foliage types. Initial Table 5 AVERAGE RETENTION* OF 88- TO 175-4 PARTICLES BY PLANTS UP TO 5 WEEKS AFTER DEPOSITION Average Time after retention of | Accumulated : Accumulated eke : ; Average retention, % i application, five crop rainfall, rainfall, days species,» % in. White pine* Red oak* in. 0.04 @) 91-O;E1.010 9.50+0.81 0 1 74.0 £ 8.3 0 6.3+0.8 0.39 + 0.06 0.90 15 61.8 + 8.7 0 4.5+£0.4 0.25 + 0.04 0.90 7. 33.0+ 4.6 0.25 2.5.2 0.2 0.02 + 0.003 1.30 14 9.444.7 1.28 Dal OD 0.015 0.001 1.43 Dil Df ile?) DOW 19: = O03 0.012 0.001 1.47 28 Dy S2= AS) 2567, 16722 O82 0.010 + 0.002 2.88 35 26E=N6 2.67 2 Onl 0.010 £ 0.002 3.46 * Average percent of initial interception + 1 standard error. P p 402 WITHERSPOON particle losses, up to 1 week, were much greater for the trees. The data for trees reflect, however, the effects of one rain which fell 12 hr after initial deposition. The losses from crop plants for the first 6 days were due to wind action only. Nevertheless, with comparable rainfall for the duration of these studies, up to 5 weeks after deposition, losses from trees were greater. Smooth-leaved trees, such as the red oak, retained only a small fraction of the initial deposition after 1 week. All these plants lost the major portion (90%) of the fallout in 1 to 2 weeks, a period in which the major portion of fallout-radiation dose is delivered. Not only did the trees lose particles faster than the crop species tested but also, from the standpoint of dose, this loss is more important for trees. Particle loss can also be interpreted as a change in beta-exposure geometry from a contact to a bath mode, and the most radiosensitive structures (meristems and flowers) are located at greater distances from the ground in trees than in crop plants. Therefore bath doses from fallout on the ground would be less serious, impart less dose, to trees than to crop plants because of their relatively greater height. Retention of particles beyond 2 weeks was relatively stable for trees and crop plants regardless of amount of wind and rainfall. By this time most of the fallout has probably become trapped in sites upon which subsequent weathering has little effect. Retention characteristics after this tme may be important from the standpoint of chronic low-level dose or transfer into food chains. Data on fallout retention of plants or plant parts plotted vs. time typically take the form of an exponential curve. In the calculation of half-lives, however, it is difficult to express these data in terms of a singie weathering or effective half-life.* Rapid particle losses during the first day or week and subsequent loss-rate changes after early weathering imply that retention data should be compartmentalized into appropriate time components for half-life analyses. Table 6 gives weathering half-lives for 88- to 175-u particles on seven species of plants. These half-lives are given for three time components: initial deposition to 1.5 days, when very rapid loss rates occur; 1.5 to 14 days; and 14 to 33 days, when loss rates tend to stabilize at a very slow rate. Averaging these weathering half-lives gives some indication of general particle retention for a wide variety of plants. Such averages may be useful in dose calculations for periods up to several weeks following deposition. Environmental half-lives (e.g., half-life rates of loss due to causes other than radioactive decay) of radionuclides on fallout-contaminated plants were reported by Martin’ for plants in the Sedan fallout field. Bartlett et al.* reported these values for plants sprayed with fission-product solutions. In the Sedan fallout field from 5 to 30 days after detonation, the environmental half-lives for fallout 8°Sr and '*'I were 28 and 13 to 17 days, respectively.’ Fission products sprayed on grass exposed to wind and rain up to 60 days had an average environmental half-life of about 14 days.® The average weathering half-life for the 14- to 33-day time component in Table 6 is 21.3 + 3.9 days. Thus it appears that weathering or environmental half-life values for different kinds of vegetation growing in different geographical FIEED STUDIES-OF “FALLOUT RETENTION 403 Table 6 WEATHERING HALF-LIVES OF 88- TO 175-U PARTICLES ON FOLIAGE FOR THREE TIME COMPONENTS Half-life Half-life Half-life for 0 to for 1.5 to for 14 to 1.5 days, Rain, 14 days, Rain, 33 days, Rain, Plant days, in. days, in. days, in. White pine4* 0.69 0.9 13.09 1.43 26.14 1.97 Red oak* 0.64 0.9 6.11 1.43 42.58 1.97 Squash® 1.62 0 7.36 1.28 15.06 1.39 Soybean® 1.47 0 7.19 1.28 15.97 1.39 Sorghum® 4.10 0 7.43 1.28 19.43 1.39 Peanut” 1.33 0 15:71 1.28 16.07 1.39 Lespedeza> 2.88 0 7.55 1.28 14.07 1.39 Average +1 standard error 1.82 + 0.48 9,20 + 1.33 21.33 + 3.96 *Reference number. regions may be similar after the rapid initial losses during the first week or so have occurred. The average values for different species (1.82 + 0.48 days for the Or comeo.day ucomponent, and; 9.20 £1.33. “days dor, \the.1.5-.to 14-day component) and the ranges given in Table 6 suggest that weathering half-lives may differ only by a factor of slightly over 1 to about 6.5 between species during the periods of rapid initial particle loss. The similarities in results from field studies in which particle size approximates that of local fallout are striking. Both initial contamination factors, such as the a; value, and weathering half-lives for time components may be in close enough agreement so that the use of averages, such as those presented here, would give reasonable estimates of dose from fallout when used in appropriate models. ACKNOWLEDGMENT This research was sponsored by the U.S. Atomic Energy Commission under contract with Union Carbide Corporation and the Office of Civil Defense, Department of Defense. REFERENCES 1.C. F. Miller and H. Lee, Operation Ceniza-Arena. Part One, SRI Project MU-4890, Stanford Research Institute, 1966. 404 WITHERSPOON 2. W. E. Martin, Early Food-Chain Kinetics of Radionuclides Following Close-In Fallout WwW from a Single Nuclear Detonation, in Radioactiwe Fallout from Nuclear Weapons Tests, Germantown, Md., Nov. 3—6, 1964, A. W. Klement (Editor), AEC Symposium Series, No: 3D: (CONE-765), 1965: . J. P. Witherspoon and F. G. Taylor, Interception and Retention of a Simulated Fallout by Agricultural Plants, Health Phys., 19: 493-499 (1970). . J. P. Witherspoon and F. G. Taylor, Retention of a Fallout Simulant Containing eS by Pine and Oak Trees, Health Phys., 17: 825-829 (1969). .R. C. Dahlman, in Progress Report in Postattack Ecology. Interim Report, USAEC Report ORNL-TM-2983, Oak Ridge National Laboratory, December 1970. . J. E. Johnson and A. I. Lovaas, Deposition and Retention of Simulated Near-In Fallout by Food Crops and Livestock, Technical Progress Report 3223C, Colorado State University, 1969. . W. E. Martin, Losses of OSE BST and Sy from Fallout-Contaminated Plants, Health Phys., 4: 275-284 (1964). .B. O. Bartlett, L. F. Middleton, G. M. Milbourn, and H. M. Squire, The Removal of Fission Products from Grass by Rain, in Surveys of Radioactivity in Human Diet and Experimental Studies, British Report ARCRL-5, pp. 52—54, 1961. RETENTION OF NEAR-IN FALLOUT BY CROPS A. 1. LOVAAS and J. E. JOHNSON Colorado State University, Fort Collins, Colorado ABSTRACT Near-in fallout simulant, 88- to 175- and 175- to 350 sand labeled with '77Lu, was dispersed over field crops. Initial retention and weathering half-time were measured for alfalfa, corn, barley, bromegrass, sudan grass, and sugar-beet tops. Papers in this session have considered the biological effects of gamma and beta radiation on plants, especially crop plants, with the intent of evaluating parameters for models that postulate biological consequences of fallout radiation.’ Constantin, Siemer, and Killion* showed the stage specific effects on uniformly administered gamma radiation. Bottino and Sparrow* extended the study of biological effects to a gamma field decreasing in intensity over time. Rhoads et al.* described combined gamma and beta effects of actual test-site fallout. Both Shulz* and Witherspoon* dealt with the biological effects of applied deposits of beta-emitting fallout simulant. This report is on retention experiments employing a material similar to that used by Witherspoon. Our interest is in bulk contamination of potential animal feed as well as in the finer features of particle retention on plants.” A body of related data on volcano dust has been detailed by Miller’s group® at Sanford Research Institute (SRI). BACKGROUND We have studied the capacity of plant canopies to retain sand-size falloutlike particles. A simulant was chosen to be similar to material swept into the air by a nuclear blast over a silicate-soil region. Of all the particles produced by or swept *This volume. 406 LOVAAS AND JOHNSON into a nuclear cloud, we are concerned with those in the size range of 100 y, i.e., near-in or local fallout as distinguished from the worldwide variety.” Particles much smaller than 20 to 40 yu are preferentially carried beyond near-in deposits, whereas particles of several hundred microns, 1.e., approaching 1 mm, are rapidly depleted.* We used batches of sand of 88 to 175 and 175 to 350 wu for these exposures. The sand is from the reserve of fallout-simulant materials maintained and supplied by SRI. Two processes may be considered to constitute the mechanism of external retention of particles by plants. Small particles adhere to rough or sticky surfaces, and cupping structures are effective means of holding the larger particles that would otherwise bounce or roll off. Both the initial retention governed by these two processes and the lasting retentive properties of plant surfaces and structures are modified by weathering, observably by the wetting of rain, buffeting by wind, and tearing by hail. OBJECTIVES AND EXPERIMENTS At Colorado State University our field experiments seek to show initial and persistent retention characteristics of species, some weather effects on initial retention, and the step changes they cause in retention functions. We exposed standing field crops to the simulant of near-in fallout. Radioactivity was used only as a particle tracer and not to produce biological effect. The study attempted to simulate portions of near-in fallout derived from silicate soil in respect to particulate material, particle size, particle fall conditions, and amount of deposited material (mass load). Since we wished to follow foliar deposits of particles and not foliar absorption of radionuclides, an essentially insoluble form of radiotracer was used. The nuclide employed was '771 u. This labeled material was prepared by W. B. Lane of SRI.° In the winter of the first crop year of our study, some nonradioactive releases were carried out in an enclosed chamber (Fig. 1). This permitted the determination of retention under conditions of still air and controlled surface moisture (Fig. 2). Plants for the chamber releases were from greenhouse stock. Chamber results showed that overall retention was commonly doubled by maximum spray wetting. Readily wetted and fairly flat bean-leaf surfaces that accumulate droplets retained up to 15 times as much sand when spray wetted as before treatment. Since, when leaves dry, much of the sand pattern approxi- mates that of the evaporated droplets, it is clear that the excess retention by wet surfaces depends largely on the area and depth of surface moisture that a leaf can retain and support. Under the stable conditions of the enclosed chamber, it was also possible to use a grain crop at several growth stages to observe retention efficiency of the developing stand. The increasing stem-to-leaf ratio with growth was manifested as lowered specific retention for barley. 407 RETENTION OF NEAR-IN FALLOUT BY CROPS Fig. 1 Simulated-fallout exposure chamber. 408 LOVAAS AND JOHNSON Fig. 2 Microplot of grass in exposure chamber. For the field studies circular plots 20 ft or more in diameter were fitted with greased disk impactors to monitor deposition (Fig. 3). The simulant was dispersed over a field plot from an elevated platform by means of a blower (Fig. 4). The actual release took place over a period of from 5 to 50 min depending on the stability of wind direction. Crop clippings taken at intervals over a 2-week period after contamination were counted by gamma spectrometry to reveal the retention functions (Fig. 5). Crops of eastern Colorado that were tested are alfalfa, corn, irrigated pasture bromegrass, sudan grass, sugar beets, and barley. Table 1 gives the conditions for the experiments of the 1969 crop year. Experimental results for two crop years are shown in Tables 2 to 6 and Figs. 6 and 7. RESULTS AND DISCUSSION Table 2a gives measured initial retention of near-in simulant on field crops. In most cases neither particle size nor loading in the ranges tested was important compared with the retention differences characterisuc of the target species. Bulk contamination of alfalfa is typically 5 to 10%. Contamination of pasture grass under dry, windy exposure conditions is contrasted with much higher initial ‘s1oz1uOW UODIsOdap YIM JoO]d pjaly ¢ “BI “”) a: O oc O > aa k- =) O a 2 0:25 239 9 2 L 35 0.1 0.65 we iL 32 Barley 6 Otol S 5.8 0.04 0.1 5 1 to 2 IE 5.8 0.04 0.1 Sugar Beets 7 4 Drizzle S 40 0.25 3 8 7 H,O drops L 4 0.015 0.2 * Abbreviations are S, small (88 to 175 uw); and L, large (175 to 350 yw). Table 3 WEATHERING TIME OF EXTERNAL CONTAMINATION Retainer Alfalfa Bromegrass Sudan grass Corn Barley Sugar beets Experiment De ee 15, 16 1 2relel 17,18 1920 4,3 1On9 65 7,8 Half-time, days 88- to 175-u sand 175- to 350-u sand 10 Experiment cut short 7 6 6 1 day for 3 days, 14 then 19 days 1 day for 3 days, then flat* for both sand sizes se) Flat* 6.5 6.5 12 12 ah 11 3, before rain Flat* 5, after rain *Curve is relatively flat; half-time appears to be infinite. RETENTION OF NEAR-IN FALLOUT BY CROPS 415 100 10 Zz o ‘oe Fd LW be Ww or 1 Rain, 0.55 in. Rain, 0.17 in. Rain, 0.61 in. 0.1 : 6) 2 4 6 8 10 12 14 16 DAY OF EXPERIMENT Fig.6 Retention of 88- to 175-u sand by a plot of alfalfa. X, percent retention; D, m’/kg, dried, x100; W, m’ /kg, wet, x100. 100 D x x D 10 W x x x a fo) D D D D 5 W WwW od WW oc W y W W i 1 D W Rain, 0.47 in. 0.1 0 2, 4 6 8 10 12. 14 DAY OF EXPERIMENT Fig. 7 Retention of 88- to 175-u sand by a plot of irrigated pasture bromegrass. X, percent retention; D, m’ /kg, dried, x10; W, m? /kg, wet, x10. 416 LOVAAS AND JOHNSON Table 4 RAIN WEATHERING OF SAND FROM CROPS Median retention, % 88- to 175-u sand 175- to 350-y sand Length of Before After Before After Crop experiment, days Rain,in. weathering weathering weathering weathering Alfalfa 3 G27 7. :: 3 sd ‘ 10 12 0.6 2, es Bromegrass 10 0.47 8 3 =i = Sudan grass 5 0.47 6 4 6 4 Corn 6 0.25 and 8.5 3 8.5 3 hail Barley 4 0.25 and = “ +d x hailt Sugar beets 5 0.38 20 10 e : *Little effect: tPart of fields. Table 5 WIND WEATHERING OF SAND FROM CROPS Number of Half-time monitored (T/2), Crop releases Sand size* days MPH* T/2 x MPHt Alfalfa 2 S 2 iG, 6.5 Z2 14.3 Bromegrass 2p S 1,19 DD 2.2, 41.8 2 i ietlats 2.2, large Sudan grass 1 S os5 1.8 AeA 1 L Flatt Large Corn 2 Seale 6.5 i 7.8 2 S3b > 12 359 >46.8 Barley 1 S 1 i 11 1.8 19.8 Sugar beets 1 S 4 352 12.8 1 L Flatt Boe Large ie ee eee ee, ee Se ee ee Se ee eS ee ae SS SS * Abbreviations are S, small (88 to 175 uw); and L, large (175 to 350 uy). +MPH is average wind speed. £Curve is relatively flat; half-time appears to be infinite. Table 6a mith SAMPLING OF DISTRIBUTION OF SAND ON PLANT PARTS Crop Localization distribution Corn Two-segment lengths, stem and leaf Stems with leaf angles vs. bodies of leaves Barley Heads vs. stems Beet Tops vs. bases Alfalfa Not fractionated Bromegrass Not fractionated Table 6b REDISTRIBUTION OF SAND ON CORN BY WEATHERING Sand size, yu Experiment Retention Segmental Distribution on 14-Segment Stalks 88 to 175 10 Broad maximum (2 x top segments), maximum 3 to 6 segments from top 175 to 350 ©) Broad maximum (3 x top segments), maximum 7 to 10 segments from top Leaf Vs. Leaf + Stem with Leaf Angle Start 9 days 88 to 175 10 0.2 0.03 4 0.1 0.02 1751t0<3: 50 9 0.5 0.05 3 0.5 0.1 Table 6c REDISTRIBUTION OF SAND BY WEATHERING Retention, fraction Sand size, yu Experiment Initial 17 days 19 days Barley, Heads Vs. Heads + Stems 88 to 175 6 0.8 0.7 175 to 350 5) 0.9 0.3 Sugar Beets, Tops Vs. Tops + Base 88 to 175 7 0.9 0.1 175 to 350 8 0.2 0.03 418 LOVAAS AND JOHNSON SUMMARY We have presented data on initial retention and weathering of simulated near-in fallout particles from alfalfa, corn, barley, irrigated pasture bromegrass, sudan grass, and sugar-beet tops. Initial retention of the particles ranged from complete to practically no retention, depending on weather conditions at the time of exposure and on the plant structure. Observed weathering half-times were from 1 day or less to more than 2 weeks. The data may be applied to calculate bulk contamination of forage and radiation dose to growing plants. ACKNOWLEDGMENTS This study is supported by the Office of Civil Defense under contract DAH20-68-C-0120. D. W. Wilson was the original principal investigator of the project. REFERENCES 1.S. L. Brown and V. F. Pilz, U. S. Agriculture: Potential Vulnerabilities, SRI Project No. MU-6250-052, Stanford Research Institute, January 1969. 2.M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to Fallout Radiation, USAEC Report TID-24459, UT—AEC Agricultural Research Labora- tory, Sept. 7, 1967. .C. F. Miller, Operation Ceniza-Arena: The Retention of Fallout Particles from Volcan Irazu (Costa Rica) by Plants and People. Part III, Report AD-673202, Stanford Research Institute, December 1967. 4.G. M. Dunning, Health Aspects of Nuclear Weapons Testing, USAEC Report TID-20723, U.S. Atomic Energy Commission. 5. D. E. Clark and W. C. Cobbin, Some Relationships Among Particle Size, Mass Level, and Radiation Intensity of Fallout from a Land Surface Nuclear Detonation, Report USNRDL-TR-639, Naval Radiological Defense Laboratory, Mar. 21, 1963. 6. W. B. Lane, Fallout Simulant Development, Final Report to OCD, Stanford Research Institute, September 1969. Ww PREDICTION OF SPECIES RADIOSENSITIVITY HARVEY L. CROMROY, RICHARD: LEVY, ALBERTO B. BROCE, and LEONARD J. GOLDMAN Departments of Entomology and Radiology, Division of Nuclear Sciences, University of Florida, Gainesville, Florida ABSTRACT A study was made on the feasibility of using the mammalian columnar epithelial cell of the duodenum and the insect endothelial cell of the midgut as biological indicators of radiation sensitivity. Thirty species of mammals and twenty species of insects were used. Data demonstrating situations where the respective cells would be most useful as parameters for radiosensitivity are presented. The major aim of our research was to determine biological indicators that could serve as predictors of radiation sensitivity. Previous research by Sparrow and co-workers! * established that the radiosensitivities of plants to ionizing radiation could be predicted on the basis of a regression line measured by the interphase chromosome volume (ICV) against the lethal dose required to kill 50% of a given population (LDs 9) for established irradiated species. The ICV was defined as the nuclear volume of a cell divided by the diploid chromosome number of the species. Conger,* who initiated this research project, further substantiated this hypothesis with his work on Florida gymnosperms. We began our research to determine whether this type of correlation also exists in insects and mammals. The biological- indicator cells, selected because of their established sensitivity to ionizing radiation, were the endothelial cells lining the midgut of insects and the columnar epithelial cells of the duodenal intestinal mucosa of mammals. The initial publication was on seven species of mammals and eight species of insects.> At that time it was reported that the mammalian species studied had a slope with a positive declination, whereas the insects had a negative declination to the slope conforming with Sparrow’s previous work.° Simply, the mammalian 419 420 CROMROY, LEVY, BROCE, AND GOLDMAN slope indicated that the larger the ICV, the less sensitive the animal was to ionizing radiation; the inverse relation holds true for insects and plants. Later research amplified the data to include 22 species of mammals and 11 species of insects. We found contradictions within the mammals, in the rodent species in particular, which presented a number of problems. Our current data on 20 species of insects and 30 species of mammals are presented here. For purposes of clarity this paper is subdivided into two sections; the first deals with mammals and the second with insects. MAMMALS The order Rodentia presented so much scatter when included with the other orders of mammals that we arbitrarily lumped all rodent data together. Mammals Other Than Rodents The data in Fig. 1 are for the midline air dose in roentgens with a 1-MVp X-ray unit. The LDs59’s, except the one for sheep, were done at the Naval Radiological Defense Laboratory, San Francisco, Calif., by Ainsworth et alee The data on sheep were obtained through the cooperation of the Radiobiology Laboratory, Biophysics Branch, Air Force Weapons Laboratory, Kirtland Air 900 Rabbit Y = 73.8X + 203 r=+0.93 700 Monkey @ fae S 500 2 jo) ite) ‘a = 300 100 0 2.0 4.0 6.0 8.0 ICV, us Fig. 1 Relation of interphase chromosome volume to LD5 9/30 exposure dose (midline air dose with 1-MVp X ray) in mammals other than rodents. PREDICTION OF SPECIES RADIOSENSITIVITY 421 Force Base, N. Mex. The regression equation, or predictor formula, is Y = 74X + 203, where Y is LDs50/30 days 1n roentgens, midline air dose, and X is ICV. The coefficient of correlation, r, is +0.93, where r indicates a linear relation between points. If r equals +1, a perfect correlation exists. A high value for r indicates that this is an excellent predictor for X radiation and exposure considerations only. Rodents Figure 2 presents an analysis of 11 species of rodents. The ICV’s presented are the average of the male and female of the species, and the LDs 9/3 9’s were taken from the literature.’'* The three families of rodents represented are Muridae, Cricetidae, and Heteromyidae. The analysis of points by least squares has a slope equation of Y = 122X + 688, where Y is the LDs 9/39 absorbed dose Y = 122X + 688 1200 r= 0.40 1000 iz) T 2 fo) 2 rs 0 800 =) 600 400 0.5 1 1:5 2 25 3 3:5 4 ICV, us Fig. 2 Relation of interphase chromosome volume to LDs5 09/309 absorbed dose for rodent species. ©, average ICV for male and female of species. MM, Mus musculus PM, Peromyscus maniculatus MP, Microtus pinetorum PPA, Perognathus parvus MU, Meriones unguiculatus PPO, Peromyscus polionotus OP, Oryzomys palustris RF, Mus musculus, RF strain PFO, Perognathus formosus RNO, Rattus norvegicus PLE, Peromyscus leucopus 422 CROMROY, LEVY, BROCE, AND GOLDMAN in rads from °°Co and X is the ICV. The coefficient r is +0.40. This figure is strongly influenced by points OP and PFO. Removal of these two points would change the analysis considerably. Figure 3 is a graphical representation of the analysis of 13 different species of male rodents. The ICV’s plotted are for males only. Again there is a positive declination to the slope and a high degree of scatter. The predictor equation is Y = 152X + 544, andr equals +0.46. Y = 152X + 544 1200 r= 0.46 1000 800 LD50/30, rads 600 400 0.5 1 125 2 2.5 3 3:5 4 ICV, us Fig. 3. Relation of interphase chromosome volume of male rodent species to LD5 0/30 absorbed dose. CG, Cricetulus LrISeUs PPA, Perognathus parvus MM, Mus musculus RF, Mus musculus, RF strain MP, Microtus pinetorum RH, Reithrodontomys humilis ON, Ochrotomys nuttalli RNO, Rattus norvegicus OP, Oryzomys palustris SH, Sigmodon hispidus PLE, Peromyscus leucopus WA, Rattus rattus, Wistar PM, Peromyscus maniculatus Albino strain Figure 4 pictures the analysis of 12 different female rodent species. There is a negative declination to the slope, indicating an inverse relation to the slope obtained with male rodents. In this case the predictor equation is Y = —137X +1102, and r is —0.46. Therefore the contribution from the male species is the factor that accounts for the positive slope obtained in Fig. 2. PREDICTION OF SPECIES RADIOSENSITIVITY 423 Y = 2137X 4.1102 1200 r=-0.46 1000 72) T g Oo 2 (o} He 800 4 600 400 0.5 1 125 2 2.5 3 3.5 4 ICV, ys Fig. 4 Relation of interphase chromosome volume of female rodent species to LDs5 0/30 absorbed dose. MA, Mesocricetus auratus RNO, Rattus norvegicus MM, Mus musculus SD, Rattus rattus, Sprague MP, Microtus pinetorum Dawley strain OP, Oryzomys palustris SW, Mus musculus, Swiss PLE, Peromyscus leucopus Webster strain PM, Peromyscus maniculatus WA, Rattus rattus, Wistar PPA, Perognathus parvus Albino strain RF, Mus musculus, RF strain Table 1 presents a comparison of male and female ICV’s. The male almost always has a larger ICV than the female, but the LDs9/39 of the male may be larger or smaller than that of the female. This causes the poor predictive values for the species. Figure 5 compares Fry’s data'* on mean survival times for massive doses of whole-body irradiation with our ICV data. A negative slope is obtained, with Y = —61X + 264 and r = —0.65; this indicates a much better correlation between points. If we combine Fry’s data and those of Dunaway et al.,’ we obtain the slope shown in Fig. 6. In this case, Y = 0.40X + 215, and r equals —0.68. Table 2 compares the observed and the predicted mean survival times (MST). This relation appears to be much more valid for predictive purposes. 424 TABLE 1 COMPARISON OF MALE AND FEMALE RODENT ICV AND LDs50/30 Observed Predicted Species Sex ICV LD>5 0/30, rads* LD5 0/30, radst Rattus norvegicus f 2.88 949 707 m 3.07 US 1011 Mus musculus f 1.62 802 880 m 1.81 851 818 Peromyscus leucopus f 1.07 1043 25,5 m 2.50 1091 924 Microtus pinetorum f 1.30 1004 Q24 mS 883 775 q Oryzomys palustris f 2.04 484 823 { m 2202 584 848 *Data are taken from Dunaway et al.® tPredicted value is taken from either Fig. 3 or Fig. 4, depending on sex. 250 Y = -60.8X + 264 r = -0.65 c< 200 if 2 _ | < = 150 > iam = Y z x LW = 100 50 -— , ~ 0.5 1 1.5 2 2.5 3 3.5 4 ICV, us Fig. 5 Relation of interphase chromosome volume to mean survival time of mammals exposed to large doses of whole-body irradiation. CG, Cricetulus griseus PLE, Peromyscus leucopus CL, Chinchilla laniger PLO, Perognathus longimembris MM, Mus musculus RNO, Rattus norvegicus PREDICTION OF SPECIES RADIOSENSITIVITY 425 220 Y = -0.40X + 215 r = -0.68 @ PLO 180 ra 7 2 = ef a 140 2 > cc =) ”n 100 60 0.5 1 1.5 2 25 3 3.5 4 ICV, u3 Fig. 6 Relation of interphase chromosome volume to mean survival time of mammals exposed to large doses of whole-body irradiation. CG, Cricetulus griseus PLE, Peromyscus leucopus CL, Chinchilla laniger PLO, Perognathus longimembris MM, Mus musculus RF, Mus musculus, RE strain MP, Microtus pinetorum RNO, Rattus norvegicus OP, Oryzomys palustris Discussion of Results Table 3 summarizes the predictor equations and coefficients for Figs. 1 to 6. As can be seen, the slope for data from mammals other than rodents is the best predictor; its very high coefficient indicates a good degree of reliability. The work with LDs59/39 and ICV in rodent species is still unsatisfactory. The scatter plus the positive slope for the males vs. the negative slope for the females makes predictability inaccurate. Part of the problem is undoubtedly the fact that the LDs50/309 data were taken from the literature, and consequently different dose rates were used to obtain the respective LDs 9/39’s. It may well be that the new formula suggested by Dunaway et al.” [Y = 20.75.X — 2.77, where Y is rads per gram and X is red blood cell count/(27r) intestine] may be one of the better rough predictors of LDs 9/30. Before the rodent data can have any validity as a predictor for LDs9/30, much more study must be done on the parameters affecting the radiation sensitivity of the species. It appears that the use of the ICV for mean-survival- time predictions is good since this provides good estimates. 426 CROMROY, LEVY, BROCE, AND GOLDMAN TABLE 2 COMPARISON OF MEAN SURVIVAL TIMES (MST) FOR LARGE DOSES OF WHOLE-BODY RADIATION WITH ICV IN RODENTS Observed Predicted Species* ICV MST, hr MST, hr Perognathus longimembris, average 1295 192 136 Peromyscus leucopus, male 2.50 1 13 Peromyscus leucopus, average 1.80 132 142 Cricetulus griseus, male 2.28 118 122 Rattus norvegicus, male 2.88 82 98 Mus musculus, male 1.80 5 142 Chinchilla laniger, male 22315 128 19 Microtus pinetorum, average 1.41 154 IS 7 Oryzomys palustris, average 2.03 144 132 Mus musculus, RF strain, average ED'S 122 136 Rattus norvegicus, average 2.98 98 94 Mus musculus, average Ibs 7/al 139 145 *The term “‘average’’ after species indicates that the ICV given is the average of the values for the male and female of the species. TABLE 3 SUMMARY OF THE PREDICTOR EQUATIONS AND THEIR COEFFICIENTS FOR FIGS. 1 TO 6 Figure Predictor Coefficient Fig. 1, Mammals other than rodents Y'=/73).8.20 + 203 r= +0.93 Fig. 2, ICV with LDs 9 in rodents Y = 122X + 688 r= +0.40 Fig. 3, ICV with LDsog in male rodents Y =152X + 544 r= +0.46 Fig. 4, ICV with LDsq in female rodents WV = 13 7x 1102 r= —0.46 Fig. 5, MST with ICV Y = —61X + 264 r= ~0,65 Fig. 6, MST with ICV Y = —40X + 215 r= —0.68 INSECTS Our initial studies on insects were done with 11 species. The LDso9 was taken for 24 hr and the biological indicator cell was the endothelial cell lining the midgut. A 24-hr period was selected on the basis of the large variation in life-spans of insects and the requirements of culture rooms for sustained life-history studies. The 11 species studied gave a predictor formula of Y = 2.67X + 163.42, where Y is LDs5 9/24 py 1n roentgens and X is the ICV. PREDICTION OF SPECIES RADIOSENSITIVITY 427 Figure 7 presents a graphical analysis of 17 species of insects, the majority of which were irradiated with °° Co at identical dose rates with three replications per point for verification of LDs5o. All insects were in the adult stage and were of the orders Coleoptera, Diptera, Orthoptera, Hemiptera, Homoptera, and Anoplura. There is a negative declination to the slope; Y equals —4.06X + 184, and r equals —0.46. This agrees with Sparrow’s data® indicating that the larger = -4,06X + 184 = -0.46 320 260 200 LDs50/24 nr KR 140 80 1 5 9 113 We PA 25 ICV, us Fig. 7 Relation of interphase chromosome volume of 17 species of insects to 60 : ayes LDs0/24 hr exposure dose (Co irradiation). AD, Acheta domestica PE, Prodenia eridenia BB, Brevicoryne brassicae PF, Periplaneta fuliginosa BG, Blatella germanica PH, Pediculus humanus bumanus CL, Cimex lectularts SC, Stomoxys calcitrans LM, Leucophaea maderae SO, Sitophilus oryzae MD, Musca domestica TCA, Tribolium castaneum NC, Nauphoeta cinerea TCO, Tribolium confusum OS, Oryzaephilus surinamensis T™, Tenebrio molitor PA, Periplaneta americana the ICV, the more sensitive the insect species is to ionizing radiation. In Fig. 8 the Orthopteran species are analyzed separately. Note that a positive slope 1s obtained; however, r is +0.12, indicating a very poor linear relation between points. For the Coleopteran species, Fig. 9, nuclear volume is plotted against LDs50/24 hr because so few chromosome numbers are available for many of the beetles. A negative, declining slope is obtained, and r equals —0.27. This is also a 428 CROMROY, LEVY, BROCE, AND GOLDMAN Y = 6.4X + 1.3 w= OZ 150 oc x fe tO zt NY jo) ite) ‘a 70 30 : 0 5 10 15 20 25 ICV, us Fig. 8 Relation of interphase chromosome volume of Orthopteran species to LD50/24 hr exposure dose. AD, Acheta domestica NC, Nauphoeta cinerea BG, Blatella germanica PA, Periplaneta americana LM, Leucophaea maderae PF, Periplaneta fuliginosa poor indication of linear relation between points. Plotting the dose required to reduce the life-span of the insect species by one-half under laboratory conditions against the ICV gives the curve shown in Fig. 10. The predictor equation is Y = —0.73X + 11.04, where Y is dose in kiloroentgens required to reduce life-span 50%. In this case r is —O.72; this indicates a high linear relation between points, and good predictive values are obtained. The dose data used in Figs. 10 and 11 1521 pig. ure 11 compares LDs 0/28 days in kilorads and ICV. The predictor equation is Y = —0.89X% + 12, where Y is LDs 0/28 day dose in kilorads and r is —0.82. are extrapolated from a series of research reports by other workers. Discussion of Results The data on insects appear to be best when either life-span shortening or LDs0/28 days 1S considered. In all probability the life-span shortening parameter will turn out to be best since there is such considerable variation in insect life-spans; for example, the American cockroach’ > has a life-span of approxi- mately 400 days under laboratory conditions, whereas the house fly’® has a life-span of only 25 days. The overall graph of 17 species is not so good a PREDICTION OF SPECIES RADIOSENSITIVITY 429 = -0.33X + 217 300 = -0.27 N fo) io) LDs50/24 hr, KR 100 0 40 80 120 160 200 NUCLEAR VOLUME, y3 Fig.9 Relation of nuclear volume of Coleopteran species to LDs509/24 hr exposure dose. GP, Gibbium psylloides SO, Sitophilus oryzae LS, Lasioderme serricorne TCA, Tribolitum castaneum MA, Mezium americanum TCO, Tribolium confusum OS, Oryzaephilus surinamensis TM, Tenebrio molitor predictor as was expected; there are several explanations for this, however. Preliminary cytogenetic investigations by several authors'?’?° showed the existence of unique chromosome structures in different orders of insects, such as chromosomes with diffuse centromeres or polycentric chromosomes (1.e., each chromosome has more than one region for spindle fiber attachment). If polycentric chromosomes are subjected to ionizing radiation, the chromosome fragments produced will very likely possess at least one centromere and thus could function as independent chromosomes; this would reduce the probability of lethal mutations. The rate of deoxyribonucleic acid turnover in the midgut is another factor since the true plant feeders may differ considerably from the seed and grain feeders as well as from the blood feeders. Since the mechanisms by which radiation produces mortality in insects are still largely undetermined, selection of the proper parameter as an end-point measurement of radiation sensitivity presents many problems. A number of other parameters that have been used in estimating radiosensitivity of insects include: 1. Body weight. The larger the insect, the lower the dose required to kill. 430 CROMROY, LEVY, BROCE, AND GOLDMAN Y =-0.73X + 11. = -0.72 MEAN MORTALITY DOSE, kr 8) XS 5:0 75 10 1225 ICV, us Fig. 10 Relation of insect interphase chromosome volume to LDs9/28 day dose. AD, Acheta domestica TCA, Tribolium castaneum BG, Blatella germanica TCO, Tribolium confusum OS, Oryzaephilus surinamensis TM, Tenebrio molitor PA, Periplaneta americana 2. Phylogenetic relations. 3. Physical activity. This is a difficult parameter to quantify. 4. Life-span. Longer-living insects are supposed to be more sensitive to 1onizing radiation. We believe that the best predictor formula will probably be a combination of several of these parameters combined with interphase nuclear volume. SUMMARY Mammalian species other than rodents provide the best predictor slope for LDs50/30 exposure doses. The interphase chromosome volume for rodents is useful as a predictor only when we are dealing with the gastrointestinal form of death measured in mean survival time. The amount of scatter in rodent species obtained with the ICV’s makes them questionable as the sole predictor sources for LD; 0/30: PREDICTION OF SPECIES RADIOSENSITIVITY 431 14 Y = -0.89X + 11.82 M2 r= 0.82 10 fee) LDs50/28 days, krads 0 2.5 5 75 10 12.5 ICV, us Fig. 11 Relation ot interphase chromosome volume of insects to mean mortality expressed as kilorad dose required to reduce life-span by one-half. AD, Acheta domestica SO, Sitophilus oryzae BG, Blatella germanica TCA, Tribolium castaneum OS, Oryzaephilus surinamensis TCO, Tribolium confusum PA, Periplaneta americana The interphase chromosome volume serves as a good predictor when we are considering LDs0/28 days Or mean mortality in insects. It is not so good when we are dealing with LDs 9/24 hr. ACKNOWLEDGMENTS This research was supported by the Office of Civil Defense. Many of the specimens used were obtained through the cooperation of Paul Dunaway, Ecological Sciences Division, Oak Ridge National Laboratory; T. J. O’Farrell, Battelle—Northwest; R.J.M. Fry, Argonne National Laboratory; Norman French, Laboratory of Nuclear Medicine and Radiation Biology, University of California; and M. Kinsella, Veterinary Sciences Division, Univer- sity of Florida. REFERENCES 1. A. H. Sparrow and H. T. Evans, Nuclear Factors Affecting Radiosensitivity. I, The Influence of Nuclear Size and Structure, Chromosome Complement, and DNA Content, 432 CROMROY, LEVY, BROCE, AND GOLDMAN i) 10. 14. 2? 13: 14. 15: in Fundamental Aspects of Radiosensitivity, Report of a Symposium, June 5—7, 1961, Upton, N. Y., USAEC Report BNL-675, pp. 76—100, Brookhaven National Laboratory, 1961. . A. H. Sparrow, L. A. Schairer, and R.C. Sparrow, Relationship Between Nuclear Volume, Chromosome Numbers, and Relative Radiosensitivities, Science, 141: 163—166 (1963). . A. H. Sparrow, A. G. Underbrink, and R.C. Sparrow, Chromosomes and Cellular Radiosensitivity. 1. The Relationship of Dg to Chromosome Volume and Complexity in Seventy-Nine Different Organisms, Radiat. Res., 32: 915—945 (1967). . A. D. Conger and H. L. Cromroy, Radiosensitivity and Nuclear Volume in the Gymnosperms, Report OCD-PS-64-69, Office of Civil Defense, University of Florida, 1966. .H. L. Cromroy, Cellular Response to Radiation, Report TRC-67-40, Office of Civil Defense, University of Florida, 1967. . E. J. Ainsworth, N. P. Page, J. F. Taylor, G. F. Leong, and E. T. Still, Dose-Rate Studies with Sheep and Swine, in The Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, Apr. 29—May 1 1968, Oak Ridge, Tenn., D. G. Brown, R. G. Cragle, and T.R. Noonan (Eds.), USAEC Report CONF-680410, pp. 4.1—4.21, UT—AEC Agricultural Research Laboratory, July 12, 1968. .W. F. Belk and A. E. Gass, Jr., Relative Resistance of Gerbils and Rats to Acute Cobalt-60 Irradiation, Report SAM-TR-69-16, School of Aerospace Medicine, Brooks AFB, Texas, 1969. . P. B. Dunaway, L. L. Lewis, L. D. Story, J. A. Payne, and J. M. Inglis, Radiation Effects in the Soricidae, Cricetidae, and Muridae, in Symposium on Radioecology, Proceedings of the 2nd National Symposium May 15—17, 1967, Ann Arbor, Mich., D. J. Nelson and F.C. Evans, (Eds.), USAEC Report CONF-670503, pp. 173—184, AEC Division of Biology and Medicine and Ecological Society of America, March 1969. .P. B. Dunaway, J. T. Kitchings III, J. D. Story, L. E. Tucker, and H. F. Landreth, in Health Physics Division Annual Progress Report for Period Ending July 31, 1969, USAEC Report ORNL-4446, pp. 63—65, Oak Ridge National Laboratory, October 1969. F. B. Golley and J. B. Gentry, Response of Rodents to Acute Gamma Radiation Under Field Conditions, in Symposium on Radioecology, Proceedings of the 2nd National Symposium May 15—17, 1967, Ann Arbor, Mich., D. J. Nelson and F. C. Evans, (Eds.), USAEC Report CONF-670503, pp. 166—172, AEC Division of Biology and Medicine and Ecological Society of America, March 1969. Thomas P. O'Farrell, Effects of Acute Ionizing Radiation in Selected Pacific Northwest Rodents, in Symposium on Radioecology, Proceedings of the 2nd National Symposium, May 15-17, 1967, Ann Arbor, Mich., D. J. Nelson and F.C. Evans, (Eds.), USAEC Report CONF-670503, pp. 157-165, AEC Division of Biology and Medicine and Ecological Society of America, March 1969. W. H. Pryor, Jr., W. G. Glenn, and K. A. Hardy, The Gamma Radiation LDs0(30) for the Rabbit, Radiat. Res., 30: 483—487 (1967). J. E. Traynor and E. I. Still, Dose Rate Effect on LDs59/39 in Mice Exposed to Cobalt-60 Gamma Irradiation, Report SAM-TR-68-97, School of Aerospace Medicine, Brooks AFB, Texas, 1968. R. J. Michael Fry, A. B. Rieskin, W. Kisieleski, A. Sallese, and E. Staffeldt, in Comparative Cellular and Species Radiosensitivity, V. P. Bond and T. Sugahara (Eds.), pp. 255—268, Igaku Shoin Ltd., Tokyo, 1969. M. M. Cole, G. C. La Breque, and G. S. Burden, Effect of Gamma Radiation on Some Insects Affecting Man, J. Econ. Entomol., 52: 448-450 (1959). 16. AT: 18. Lo: 20. 20 PREDICTION OF SPECIES RADIOSENSITIVITY 433 J. M. Cork, Gamma-Radiation and Longevity of the Flour Beetle, Radiat. Res., 7: So1-5:97 (L957): P. B. Cornwell (Ed.), The Entomology of Radiation Disinfestation of Grain, pp. 1—17, 119—141, Pergamon Press, Inc., New York, 1966. E. F. Menhinick and D. A. Crossley, Jr., A Comparison of Radiation Profiles of Acheta domestica and Tenebrio molitor, Ann, Entomol. Soc. Amer., 61: 1359-1365 (1968). E. F. Menhinick and D. A. Crossley, Jr., Radiation Sensitivity of Twelve Species of Arthropods, Ann. Entomol. Soc. Amer., 62: 711—717 (1969). D. T. North and G. G. Holt, in Isotopes and Radiation in Entomology, Symposium Proceedings, Vienna, 1967, pp. 391—403, International Atomic Energy Agency, Vienna, 1968 (STI/PUB/166). E. W. Tilton, W. E. Burkholder, and R. R. Cogburn, Effects of Gamma Radiation on Rhyzopertha dominica, Sitophilus oryzae, Tribolium confusum, and Lasioderma serricorne, J, Econ, Entomol., 59: 1363—1368 (1966). ADDITIONAL READING LIST Cromroy, H. L., Cellular Indicators of Radiosensitivity, OCD Report TRC-68-49, University of Florida, 1969. Cromroy, H. L., Mammalian Radiosensitivity, OCD Report TO-3140-(68), University of Florida, 1969. INSECT-INDUCED AGROECOLOGICAL IMBALANCES AS AN ANALOG TO FALLOUT EFFECTS — VERNON M. STERN Department of Entomology, University of California, Riverside, California ABSTRACT Many species in the classes Insecta and Arachnida are phytophagous and compete with man and his domestic animals for food, and others attack man and animals directly or transmit plant and animal diseases. On the other hand, there are tremendous numbers of beneficial species; among them are plant pollinators, insects that aid in the decomposition and recycling of plant and animal debris, and thousands of other beneficial insects and mites that attack and kill the destructive species. Crop losses from insects amount to nearly $4 billion annually. Control measures (mainly chemicals) for crop protection in the field and for stored crop products cost nearly $750 million annually. Many insect-pest populations rise to damaging levels year after year in agroecosystems although this is rather uncommon in natural communities. The monoculture is a special type of agroecosystem resulting from man’s technical efforts to control nature to meet his need for food and other products. It is somewhat doubtful whether we can change the monoculture into a more diversified agroecosystem despite the annual plagues of insect pests. Fallout radiation is somewhat similar to the pesticides that often cause ecological disruptions. Even though pest insects may be eliminated from certain areas by fallout radiation, they can be expected to become reestablished in these areas soon and again to compete with man for his food. For these and other reasons discussed, both beneficial and pest species will be important factors in food production in the event of nuclear war. During biological history four groups of organisms, reptiles, birds, mammals, and insects, have at some time during their evolution developed the power of true flight. Wings evolved but once and early in the evolutionary history of insects, and this ancestral pattern gave rise to the vast majority of present-day forms. Their ability to move rapidly from one area to another gives them a great flexibility and advantage in selecting suitable environments for survival, growth, and reproduction.’ They also possess a great genetic variability that has permitted them to adapt to almost every conceivable habitat. Most species have 434 INSECT-INDUCED AGROECOLOGICAL IMBALANCES 435 a high reproductive potential and produce several generations per year; this permits them to increase rapidly in numbers during the favorable season. Eighty-five percent of all insect species have complete metamorphosis, which permits specialization in different phases of their life history. Thus feeding and growth occur during the larval period; differentiation occurs in the pupal period; and mating, migration, and reproduction occur during the adult stage. Mobility, genetic variability, high reproductive potential, and complete metamorphosis have contributed greatly to the biological success of this diverse group of organisms. As a group insects are highly resistant to radiation, and many species have additional survival potential from fallout radiation because they spend a part of their life cycle protected in the soil, within plant tissue, within the plant debris near the soil surface, etc. There are about 2 million arthropod species. Many of those in the classes Insecta and Arachnida are phytophagous and compete with man and his domestic animals for food, and others attack man and animals directly or transmit plant and animal diseases. On the other hand, there are tremendous numbers of beneficial species. Some insects are plant pollinators; others aid in the decomposition and recycling of plant and animal debris; and, finally, there are thousands of predators and parasites that attack and destroy the destructive species.” For these and other reasons, both the destructive and the beneficial forms can certainly be considered important factors in the production of food in the event of nuclear disaster. This does not mean that insects are more important than fungi, bacteria, or viruses attacking plants and animals or that insects are more important than the hundreds of weed species competing with our commercial crops. The successful manipulation and control of all these organisms play important roles in high-quality and -quantity food production. Crop losses from pests amount to billions of dollars each year, and costs of pest control add an additional burden (Table 1). (The data in the table, which were accumulated from the U.S. Department of Agriculture,’ do not include losses to livestock.) The data in Table 1 show that during the period from 1951 to 1960 the average cost of pesticides and application for insect control amounted to nearly $750 million per year. Because of resistance problems and an increasing number of pests, there is every reason to believe that this figure has increased markedly since 1960. Likewise, many herbicides were still in the development stage during 1951 to 1960, and therefore at present herbicides make up much more than 8% of the total of the controls. With the exception of weed control (cultivation, disking, and plowing are still the major means of combatting weeds), agricultural chemicals carry the main burden of crop protection against potentially devastating losses. I calculated agrochemicals to be about 34% of the annual control costs during the period from 1951 to 1960. At the same time, the use of these chemicals adds greatly to disruptions in the agroecosystem. 436 STERN Table 1 SUMMARY OF ESTIMATED AVERAGE ANNUAL LOSSES TO AGRICULTURAL | COMMODITIES FROM VARIOUS HAZARDS AND COST OF CONTROLLING THESE LOSSES AND OF INSPECTION AND QUARANTINE PROGRAMS CLO Sie IG) = Thousands of dollars Loss in Cost of Type of Kind of loss and control program value control control, % Loss of Crops, Pasture, and Range Plants During production Diseases of crops and 3,251,114 115,800 Chemicals, 94 pasture and range plants Disease-free plants, 6 Nematode damage 372,335 16,000 Nematocides, 100 Injurious insects 3,812,406 425 OOOt Insecticides, 99 Cultural and biological, 1 Weeds in crops, pasture, 2,459 630 2,551,050 Cultural, 92 and range land Herbicides, 8 After production During storage (due to insect 1,042,063 279,302 Primarily insecticides and other losses) Control Programs Cooperative plant-pest 24,521 Chemicals and other control programs contro! measures Plant quarantine and 4,162 Chemicals and other regulatory programs control measures Total 10,937,548 3,415,835 Chemicals, 34 *The estimates indicate not only preventable reductions in production but also, in some cases, losses not avoidable with present technical knowledge. For various reasons these must be interpreted as losses to the public rather than to farmers. (See USDA Agricultural Handbook No:291- Ret. 3.) + Figures include cost of controlling insects affecting crops, man, animals, and households. AGROECOSYSTEMS AND NATURAL COMMUNITIES Agroecosystems as well as natural communities are usually considered to be self-sufficient habitats where the living organisms and the nonliving environment interact in the exchange of matter and energy in a continuing cycle.*’"* The natural community can exist without man, but the agroecosystem is manipu- lated by him and represents his efforts to control nature and to meet his need for food and other products. The degree of man’s dominance in agroecosystems varies considerably from one area to another. Moreover, the causes of agroecological-induced arthropod disturbances are multitudinal and can often be correlated with the degree of man’s activity in the systems. INSECT-INDUCED AGROECOLOGICAL IMBALANCES 437 An example of a simple agroecosystem with very little manipulation by man can be found on the rocky slopes and along the stream beds on the southwest coast of Turkey. This simple system extends from Izmir 200 to 300 miles south toward Antalya. For centuries a small number of people have lived in this area, surviving along the stream beds on small patches of grain and some vegetables, a few fish from the Aegean Sea, and some sheep and goat products. Recently the Food and Agriculture Organization of the United Nations supported the planting of thousands of olive trees on the nonproductive brush-covered slopes in 40-to-50-ft spaced natural contours to avoid erosion. In addition to his previous meager food sources, the Turkish peasant now has an olive crop, of sorts, but he does little more to the environment than keep the brush from closing in on the contoured olive-tree plantings. The original arthropod fauna in this area has changed slightly in response to the increased olive crop. There is now a higher number of olive fruit flies, Dacus oleae (Gmelin); olive moths, Prays oleae; oleander scales, Aspidiotus hederae (Vallot); and black scales, Saissetia oleae (Bernard). But these changes have been minor. At tne other extreme is the once barren Imperial Valley in soutnern California, carved out of an ancient seabed and made into one of the most highly productive agroecosystems on earth. This valley receives about 1 to 3 in. of rainfall per year and is entirely dependent on irrigation water from the Colorado River 50 to 60 miles away. Agricultural production consists of a wide variety of fall, winter, and spring vegetables, citrus fruits, forage crops, vegetable seed crops, sugar beets, cotton, small grains, melons, beef cattle, etc. Only a minute fraction of the raw or processed products is consumed or used by the small number of inhabitants of the valley. Throughout the year irrigation water, fertilizers, insecticides, herbicides, fungicides, and nematocides are added to the environment as various fields are plowed, special crops are planted and harvested, and the plant debris is plowed under in preparation for the next crop. With the exception of high solar energy input nearly 365 days per year and the parent soil, this agroecosystem is entirely artificial and totally dependent on manipulation by man for its existence. Sixty years ago this valley was essentially uninhabited by man. There were a few insects present which were pests elsewhere, but they were of no concern in this valley since they did not compete with man for existence. Because of the present abundance of food and the very high temperatures in summer and moderate temperatures in winter, this valley is a perfect insectary. It now supports a large number of insect- and mite-pest species; in addition to the original potential pests, a large number of others have come from outside sources. Owing to a high input of pesticides with wide toxicity spectrum and to the continuous planting and plowing of short-lived annual crops, pest popula- tions are often present in damaging or potentially damaging abundance throughout the year in contrast to arthropods in natural communities. 438 STERN Although the Imperial Valley is superficially different from agroecosystems in the midwestern, southern, and eastern United States, the causes of imbalance and eruption of pest species are similar in all agroecosystems. From one extreme to the other, the different types and structures of agroecosystems represent a type of stability because of the general continuity of man’s special food plants grown under the prevailing climate as well as varying degrees of disturbance. By contrast, in natural communities where a wide variety of plant and animal species are meshed in complex food chains, it is uncommon that plants are massively destroyed by phytophagous insects. There are of course special cases where destruction occurs periodically, for example, the attacks on balsam fir in eastern Canada® by the spruce budworm, Choristoneura fumiferana (Clemens); the attacks on lodgepole pine in California and elsewhere’ by the lodgepole needle miner, Coleotechnites milleri (Busck); and the historical cases of plagues of grasshoppers and locusts in parts of Africa and Asia.® The reasons for more-balanced population regulation in natural communities are generally believed to be the high degree of diversity, continuity, and stability in natural plant—animal communities as compared with simplified agroeco- systems.’’!° However, it is still debatable how these three factors interact to hold populations in check so that a single or a few species rarely cause disruption in these evolutionary-oriented ecological systems. In other words, in natural communities a very strict police state exists and appears to be regulated by the organisms themselves to preserve an orderly population abundance system. In the evolution of all species at various trophic levels and in the complex interrelations of eating and being eaten, varying degrees of governing mecha- nisms have evolved to hold species populations in check.* Governing mecha- nisms that help to determine population levels within the framework or the potential set by other environmental elements include not only immediate or direct factors producing premature mortality, retarded development, or reduced fecundity'* but also all aspects of the environment. In contrast to this orderly system, in the agroecosystem man operates and controls the plant life and 1s often the main disrupting force. MAN AND HIS ARTHROPOD COMPETITORS In the past several centuries, man has developed a technology that permits him to greatly modify environments to meet his need for food and space. Modifying the environment for the competition between man and other Organisms would appear to favor man, as is attested by the decimation of vast vertebrate populations, as well as populations of other forms of life.'* But when man eliminated many species as he changed the natural communities into *Some definitions and explanations of terms are given in the appendix (pages 451—452) to clarify certain parts of this paper. INSECT-INDUCED AGROECOLOGICAL IMBALANCES 439 agroecosystems, a number of other species, particularly the arthropods, became his direct competitors.’ ; Thus, when early man subsisted in undisturbed natural communities as a huntsman or foraged for food from uncultivated sources, he was rarely confronted with exploding insect populations, except for sporadic eruptions of plagues of grasshoppers and locusts. Today, by contrast, as man’s population continues to increase and his food-production activities are intensified, he is now in direct competition with thousands of phytophagous arthropod species.'* The increase in population numbers of a particular species to pest status may be the result of a single factor or a combination of factors. First, by changing or manipulating the environment, we can create conditions that permit certain species to increase their population density.'° The rise of the Colorado potato beetle, Leptinotarsa decemlineata (Say), from an unimportant species to one of major importance occurred in this manner (Fig. 1). Before 1850 this beetle existed in very low numbers feeding on sand burr, Solanum rostratum Dunal, and other plants along the eastern slopes of the Rocky Mountains. When the American pioneers moved westward, they planted Economic\ threshold General equilibrium position > after widespread potato culture ——» ke ” a Ww (a) Zz Oo k- < 2) ee Gk O at <+— General equilibrium position prior a re! to widespread potato culture 0 TIME——~> 1850 1860 1870 Fig. 1 Change in general equilibrium position of the Colorado potato beetle, Leptinotarsa decemlineata, after development of widespread potato culture in the United States. (For a discussion of the significance of economic-injury levels and economic thresholds in relation to the general equilibrium position, see section on the severity of pests and the definitions in the appendix.) 440 STERN the potato widely as one of their main food sources. Widespread cultivation of the potato was a change in the environment which was favorable to the beetle, and this enabled it to quickly become an important pest. Not only the increase of a new food source but also the plowing of the prairie and the destruction of forested regions aided in the expansion of its range of distribution. In a few years it was a pest in all of eastern North America. This beetle was unknowingly transported to Europe after World War I and is now a major pest in that region also. Similarly, when alfalfa, Medicago sativa L., was introduced into California about 1850, the alfalfa butterfly, Colias eurytheme Boisduval, which had previously occurred in low numbers on native legumes, found a widespread and favorable new host plant in its environment and subsequently became an economic pest.' © A second way in which arthropods have risen to pest status is by being transported across geographical barriers and leaving behind their specific predators, parasites, and diseases.'’ For example, the cottony-cushion scale, Icerya purchasi Maskell (Fig. 2), was introduced into California from Australia on ornamental acacia plants in 1868. Within two decades it increased in abundance to the point where it threatened economic disaster to the entire wz |ntroduction of Cryptochaetum iceryae and Rodolia cardinalis Resurgence produced by DDT in San Joaquin Valley Economic-injury level General equilibrium position ——> POPULATION DENSITY ——~> 0 ; 1868 1888-1889 1892 1947 MWe ———— Fig. 2. Fluctuations in population density of the cottony-cushion scale, Icerya purchasi, on citrus from the time of its introduction into California in 1868. After the successful introduction of two of its natural enemies in 1888, this scale was reduced to noneconomic status except for a local resurgence produced by DDT treatments about 1947. INSECT-INDUCED AGROECOLOGICAL IMBALANCES 441 citrus industry in California. Fortunately the timely importation and establish- ment of two of its natural enemies [the vedalia, Rodolia cardinalis (Mulsant) and Cryptochaetum iceryae (Williston)] from Australia resulted in the complete suppression of I. purchasi as a citrus pest.'® The cottony-cushion scale again rose to major pest status in 1947 when the widespread use of DDT eliminated the vedalia on citrus in the San Joaquin Valley.’ ” A third cause for the increasing number of pest arthropods has been the establishment of progressively lower economic thresholds. This can be illustrated by lygus bugs, Lygus species, on lima beans. Not many years ago the blotches caused by lygus bugs feeding on an occasional lima bean were of little concern, and the bugs were considered a minor pest on this crop. With the emphasis on product appearance in the frozen-food industry, however, a demand was created for a near-perfect bean. For this reason very low economic-injury thresholds were established, and lygus bugs are now considered serious pests on lima beans. In addition to food-product appearance, which is often related to competi- tive marketing, certain marketing standards dictate a minimum degree of damage or insect parts permissible in or on raw or processed products.*° At present these standards often impose severe requirements for chemical pest control. In a situation of critical food shortage following nuclear disaster, insects that affect commodity appearance or the presence of a few insect parts in or on food would undoubtedly be ignored. This in turn would help to alleviate any shortage of insecticides, and the chemicals available could be used in situations where entire crops are threatened. A fourth way by which insects can rise to pest status is by the elimination of biological control agents that hold a potential pest in check.”’ Recent examples include the outbreak of the beet armyworm, Spodoptera exigua (Hubner); the cabbage looper, Trichoplusia ni (Hubner); and bollworm, Heliothis zea (Boddie), following treatments with Azodrin, Bidrin, and other chemicals to control lygus bugs in cotton fields in the San Joaquin Valley.* The outbreak of the cotton leaf perforator, Bucculatrix thurberiella Busck, the beet armyworm, and the cabbage looper following widespread chemical treatments for control of the pink bollworm, Pectinophora gossypiella (Saunders), in the Imperial Valley are others among many examples. The increased pest severity due to elimination of beneficial species by pesticides is of special interest in relation to radioactive fallout. At present, other than studies of radiation effects on honeybees and a few insect predators and parasites, there are few or no data to indicate whether radiation might act differentially on the entomophagous species (1.e., those feeding on other arthropods) in comparison with the phytophagous species. More research 1s needed in this area, particularly in the insect orders Hemiptera (sucking bugs), Coleoptera (beetles), Hymenoptera (bees, ants, and wasps), and Diptera (flies *R. van den Bosch, University of California, unpublished data. 442 STERN and mosquitoes), which contain large numbers of beneficial species in addition to pest species. As matters now stand, nearly all the research on effects of radiation on arthropods has been conducted on pest species in relation to the male-sterilization technique for pest control.” 7'7° SEVERITY OF VARIOUS PEST SPECIES To determine the relative economic importance of pest species, we must consider both the economic threshold and the general equilibrium position of the pest. The general equilibrium position and its relation to the economic threshold, in conjunction with the frequency and amplitude of fluctuations about the general equilibrium position, determine the severity of a particular pest problem. In the absence of permanent modification in the environment, the density of a species tends to fluctuate about the general equilibrium position as changes occur in the biotic and physical components of the environment. As the population density increases, the density-governing factors respond with greater and greater intensity to check the increase; as the population density decreases, these factors relax in their effects. The general equilibrium position is thus determined by the interaction of the species population, the density-governing factors, and the other natural factors of the environment. A permanent alteration of any factor of the environment, either physical or biotic, or the introduction of new factors may alter the general equilibrium position. ° The economic threshold of a pest species can be at the level of or at any level above or below the general equilibrium position. Some phytophagous species utilize our crops as a food source but even at their highest attainable density are of little or no significance to man (Fig. 3). Such species can be found associated with nearly every crop of commercial concern. Another group of arthropods rarely exceeds the economic threshold and consequently are occasional pests. Only at their highest population density will chemical control be necessary (Fig. 4). When the general equilibrium position is close to the economic threshold, the population density will frequently reach this threshold (Fig. 5). In some cases the general equilibrium position and the economic threshold are at essentially the same level. Thus insecticidal treatment is necessary each time the population fluctuates up to the level of the general equilibrium position. In such species the frequency of chemical treatments is determined by the fluctuation rate about the general equilibrium position, which in some cases necessitates almost continuous treatment.’ * Finally, for some pest species the economic threshold lies below the general equilibrium position. These constitute the most severe pest problems in entomology (Fig. 6). The economic threshold may be lower than the level of the lowest population depression caused by the physical and biotic factors of the INSECT-INDUCED AGROECOLOGICAL IMBALANCES 443 Economic-injury level General] equilibrium | position POPULATION DENSITY ———> ive —— Fig. 3 Noneconomic population whose general equilibrium position and highest fluctuations are below the economic threshold, e.g., Aphis medicaginis Koch on alfalfa in California. Required treatments Economic-injury level POPULATION DENSITY ———> Fig. 4 Occasional pest whose general equilibrium position is below the economic threshold but whose highest population fluctuations exceed the economic threshold, e.g., Grapholitha molesta Busck on peaches in California. 444 POPULATION DENSITY ————> STERN Required treatments Economic) threshold | | General equilibrium position POPULATION DENSITY ——» ve ——— Fig. 5 Perennial pest whose general equilibrium position is below the economic threshold but whose population fluctuations frequently exceed the economic threshold, e.g., Lygus species on alfalfa seed in the western United States. General equilibrium position Required treatments Economic-injury level | — EU Sea Fig. 6 Severe pest whose general equilibrium position is above the economic threshold and for which frequent and often widespread use of insecticides is required to prevent economic damage, e.g., Musca domestica in Grade A milking sheds. INSECT-INDUCED AGROECOLOGICAL IMBALANCES 445 environment, e.g., many insect vectors of viruses. In such cases, particularly where human health is concerned, there is a widespread and almost constant need for chemical control. This produces conditions favorable for development of insecticide resistance and other problems associated with heavy treatments. DISPERSION OF PEST SPECIES A species population is flexible and undergoes constant change within the limits imposed upon it by its genetic constitution and the characteristics of its environment. Typical fluctuations in population density and dispersion are shown in Fig. 7. The population dispersions shown at the three points in time, B OO General equilibrium position INSECT DENSITY ie Fig. 7 Population trend and population dispersion of a pest species over a long period of time. —, fluctuations in the population density with time; ---, general equilibrium position. A, B, and C, population dispersion at specific times. The basal area of models A, B, and C reflects the distributional range, and the height indicates population density. Population densities above the economic threshold are black. A, B, and C, are not static but rather are instantaneous phases of a continuously changing dispersion.’ ° Thus at point A, when the population is of greatest numerical abundance, it also has its widest distributional range (as depicted by the maximum diameter of the base of the model) and is of maximum economic status (as depicted by the number and magnitude of the blackened pinnacles representing penetrations of 446 STERN the economic threshold). At point B, on the other hand, when the species population is at its lowest numerical abundance, it is generally most restricted in geographical range and is of only minor economic status. Point C represents an intermediate condition between points A and B. Figure 8, which is related to Fig. 7, illustrates the relation between the geographic distribution of a species and the interrelatedness of physical and ABSOLUTE LIMIT \ Zone 1 Stable zone of permanent occupancy; most nearly optimal physical conditions. Zone 2 Intermediate zone of permanent occupancy; physical conditions intermediate. Zone 3 Marginal zone of permanent occupancy; physical conditions rigorous, mostly unfavorable; at very limited places permanently permissive. Zone 4 Zone of only temporary occupancy; physical conditions only temporarily permissive anywhere; dependent on immigration. Fig. 8 Geographic distribution of a species population and the interrelation of conditioning and regulating forces. Physical factors are never permissive for occupancy beyond zone 4. (Data from C. B. Huffaker and P. Messenger, The Concept and Significance of Natural Control, in Biological Control of Insect Pests and Weeds, P. DeBach (Ed.), Chap. 4, Reinhold Publishing Company, New York, 1964.) biotic factors in the environment. Each circle (zone) of the concentric series represents a type of environment. The irregular patches in each zone represent localized areas of relative permanent favorability in regard to physical conditions, and the interspaces represent the degree of waxing and waning of such areas in time. The relative sizes of these zones as shown here have no significance. One species, such as the corn earworm, H. zea, may range over thousands of square miles; another species may be restricted to one or two states or even less. INSECT-INDUCED AGROECOLOGICAL IMBALANCES 447 The environment of zone 1 has nearly optimal climatic conditions, at least during a certain part of the year, and permits an increase in numbers generation after generation. In the environment of zone 4, at the other extreme, only temporary existence is possible. If any part of the species population is eliminated in part of its range by pesticides, radioactive fallout, use of sterile males, unfavorable heat or cold, elimination of food, etc., the survivors in the adjoining areas will repopulate the disturbed area once the unfavorable factor has disappeared. The rate of reinvasion will depend on prevailing physical factors and on the flight habits, behavior, and ecology of the species involved. In the environment of zone 1, essentially the total area is represented by maximum favorability in the physical framework of the environment; hence there is little room for changing physical conditions to alter population potential. In the environment of zone 3, on the other hand, permanently favorable localized habitats are greatly reduced. Thus the waxing and waning of population potentials is a dominant feature relative to climatic factors causing population change. However, the role of physical forces and natural enemies 1s still the same as in the environments of zones 1 and 2. In the environment of zone 4, migrants from the more favorable areas are necessary to populate the area when favorability 1s temporarily permitted. THE MONOCULTURE AND ITS INHERENT ARTHROPOD PROBLEMS Earlier in this discussion arthropod populations in a very simple agroeco- system with little interference from man (the southwest coast of Turkey) and in a highly intensified system with great interference from man (the Imperial Valley) were contrasted to arthropod populations in natural communities. Another type of agroecosystem that is quite similar to the Imperial Valley but differs in plant and animal composition is the monoculture developed in parts of the Midwest and in sections of the western United States. In these systems the tendency of pest populations to appear in damaging numbers year after year is almost an accepted fact. A good example of a monoculture occurs on the west side of the San Joaquin Valley. This particular portion of the valley is 30 to 40 miles wide and about 150 miles long. Farming operations are very large in comparison with other parts of the United States. The individually owned and corporate farms range from very small operations of 3 to 4 square miles of irrigated farm land upward to nearly 175 square miles of highly intensified irrigated agriculture. The only trees and shrubs in this area are those planted around a few widely scattered ranch headquarters. The commercial plants, literally the only plants permitted to grow in this area, are pure stands of cotton, safflower, cantalopes, alfalfa as a seed crop, barley, tomatoes, and sugar beets. Rarely is a crop planted in a field smaller than 160 acres. All other plants are destroyed by a preplant 448 STERN herbicide or by cultivation. Weeds germinating along the edges of fields and roads after the winter rains are disked under in early spring after the rains cease, or they are destroyed by desiccating oils. Increasing to damaging numbers each year are tremendous populations of lygus bugs, Lygus besperus Knight and L. elisus Van Duzee; cabbage loopers, T. ni; beet armyworms, S. exigua; bollworms, H. zea; spider mites, Tetranychus species; spotted alfalfa aphid, Therioaphis trifolii (Monell); and other insects. Lygus bugs increase to high numbers in the winter safflower crop and in the * When the safflower begins to dry in late spring, the lygus alfalfa seed crop.” bugs fly to cotton, and chemical treatments begin. Nearly all the lepidopterous pests increase to high numbers following the early chemical treatments for lygus bugs, which destroy the predators and parasites of these pests.* These worm species come from outside sources, survive because of resistance to the chemical, or are protected in the soil and elsewhere at the time of treatment. With the elimination of their predators and parasites, these pests are free to increase unhindered. Treatments with some chemicals, such as Azodrin or Bidrin, are more drastic in their ecological effects than treatments with Dylox. In fact, the disruptive effects of Azodrin on birdlife and the resurgence of secondary insect-pest species following treatment are very noticeable; thus this chemical cannot be used in California after July 15 each year. Theoretically this should permit a time interval for the predators and parasites to reenter the treated fields and become reestablished. However, our preliminary data indicate that, once the arthropod food chain is destroyed, the insect usually does not become reestablished for the remainder of the season. If pest control could be considered as a single factor, work toward the development of complex polycultures as opposed to the monoculture type of agriculture would be highly desirable. The interplanting of various species and varieties of crops in complex polycultures may result in yields of total biomass equal to or greater than those produced in monocultures. However, pest control is only one aspect of food production. It remains to be seen whether American farming systems can be devised which are of satisfactory efficiency in carrying out all the agronomic practices in such a complex mixture of crops. Converting monocultural systems back to mixed agriculture demands further economic study since much of the success of the American farmer stems from research and development leading to simplifying the agroecosystem. Likewise, the physical factors of soil and climate often predetermine special types of crops most economically productive for a given area. Furthermore, the era of the family-type diversified farm is past, and farmers on a regional basis find it most profitable to concentrate on a few specialized crops best suited for that area. *V.M. Stern and R. van den Bosch, University of California, Riverside, unpublished data. INSECT-INDUCED AGROECOLOGICAL IMBALANCES 449 This is quite noticeable when we survey the acreages of rice, corn, potatoes, vegetables, peas, beans, sugar beets, sugarcane, soybeans, vineyards, and ° ° . i. 5 orchards as they are distributed in the United States.’ SIMILARITY OF PESTICIDES AND FALLOUT RADIATION With the exception of field tests of relatively small size and laboratory radiation studies on 100 to 200 insect and mite species selected from the 2 million arthropod species, there is little information concerning the effects that fallout may have on arthropod populations over wide areas.2” However, some comparisons might be made between the ecologically disruptive effects of the use of widely toxic pesticides and radioactive fallout. This comparison requires some information concerning the development and nature of commercial pesticides. One reason for ecological disruption arising from modern pesticides stems from the manner in which these compounds are developed commercially. During development and in registering, essentially no ecological considerations enter into the search for new compounds. The candidate materials are screened on the basis of maximum kill on 8 to 12 laboratory cultures of pest species and for phytotoxicity. The basic considerations as to whether a particular compound will be developed are: (1) the size of the potential market for the compound, (2) competing products in that market and the company’s patent control over the new product and its competitors, (3) the possibilities of recouping development costs and returning a profit, and (4) certain safety factors with respect to residues, application, and human health. Under this system the ideal material from the commercial viewpoint is one that can be registered and labeled for use against a very broad spectrum of pests on a wide variety of crops. It is precisely this type of compound with a broad toxicity spectrum which kills not only pest species but also beneficial insects (plant pollinators, predators, and parasites). As a result, a large proportion of these compounds are ecologically disruptive.* °°"! ? When pesticides are used for control, they involve only immediate and temporary reduction of populations and do not contribute to permanent pest-density regulation. Theoretically they are employed to reduce pest species that rise to dangerous levels when natural enemies of the pest and other environmental pressures are inadequate. On some occasions the pest outbreak and the application of a pesticide for its control may cover a wide area, e.g., the outbreak of the spruce budworm, C. fumiferana, in northeastern Canada® or of lygus bugs, L. besperus and L. elisus, in the San Joaquin Valley.** In other instances damaging numbers of pests may occur in restricted locations. In either case these outbreaks occur during the season favorable to the pest, with the relaxed environmental pressures occurring 450 STERN sometime before the outbreak. As mentioned previously, in our agroecosystems we often simplify and change the environment to such a degree that the environmental pressures holding pests in check are totally inadequate. Since most pest species have wide ranges of distribution (often hundreds of miles and from one state to another), the treated area is always subjected to reinvasion from individuals outside the area or by rapid resurgence from those not destroyed within the treated area.” ? In some ways, other than genetic changes induced by radiation and phytotoxicity, radioactive fallout can be similar to insecticides. It is well known that some insecticides do exhibit differential killing effects on various species when applied at commercial dosages. Of course, 20 lb of actual Azodrin per acre will probably eliminate all the exposed arthropods, and probably the plants as well; so will radiation doses of 100 kR. However, LaChance?® in discussing insect sterility data, points out that radiation also has differential effects on arthropods. Most Dipteran species can be sterilized with doses under 10 kR, but within this order a threefold difference was noted. The Hymenoptera require about 6 to 10 kR, and most Coleoptera seem to sterilize at 4 to 10 kR. On the other hand, the Lepidoptera, essentially all species of which are phytophagous and which includes some of the most ravaging species on earth, requires very large doses to produce sterility. Thus radiation can be similar to insecticides as far as its differential effects on insects are concerned. In both cases the reasons for these differential effects is not entirely clear. In regard to radiation, more research on interphase nuclear volumes or nuclear DNA content may be required before comparisons are meaningful.” * The data of Miller?® and Callahan etal.*’ indicate that after a nuclear disaster there will be areas with sufficiently low radiation fields to permit survival of many pest arthropods because as a group these insects are quite tolerant to radiation and most pest species have wide ranges of distribution. The pest species can be expected to reinvade the disturbed area as soon as the effects of radiation are low enough for plants to become established. The mobility of insect-pest species attacking our major food crops and their reinvasion time after elimination from wide areas were reported previously.” ” For the reasons mentioned, radioactive fallout would appear to act similarly to an insecticide in its disruptive effects on arthropods. Pesticides are usually added to a restricted segment of the environment to eliminate a localized population. Because insecticides and radioactive fallout are nonreproductive, have no searching capacity, and are more or less nonpersistent (as far as continuous killing effects are concerned), they constitute short-term, restricted pressures. These types of materials cannot permanently change the general equilibrium position of the pest population, nor can they restrain an increase in abundance of the pest without repeated applications. Therefore to destroy pests they must be added to the environment at varying intervals of time. After a chemical application the pest population density may be far below the economic threshold and below its general equilibrium position, but, since the INSECT-INDUCED AGROECOLOGICAL IMBALANCES 451 insecticide is not a permanent part of the environment, the pest usually returns to a high level when the effects of the insecticide are gone. These killing measures have little influence on the pest in adjoining areas except as localized population depressants. In the highest-radiation field, certain insect species would undoubtedly be nearly completely eliminated. Away from the high-radiation field, there would be less mortality and various types of genetic change. Whether the offspring of these individuals could survive and compete in nature 1s unknown. However, individuals from low-radiation areas would be invading the disturbed area even before the radiation had disappeared. By continuous reinvasion individuals would eventually become established as soon as plant species were available for food. For these and the reasons mentioned earlier, pest insects and their control can be expected to be important considerations in food production in the event of nuclear disaster. APPENDIX: DEFINITION OF TERMS Biological control. The action of parasites, predators, or pathogens on a host or prey population which produces a lower general equilibrium position than would prevail in the absence of these agents. Biological control is a part of natural control, and in many cases it may be the key mechanism governing the population levels within the framework set by the environment. If the host or prey population is a pest species, biological control may or may not result in economic control. Economic control. The reduction or maintenance of a pest density below the economic-injury level. Economic-injury level. The lowest population density that will cause economic damage. Economic damage is the amount of injury which will justify the cost of artificial control measures; consequently the economic-injury level may vary from area to area, from season to season, or with man’s changing scale of economic values. Economic threshold. The density at which control measures should be determined to prevent an increasing pest population from reaching the economic-injury level. The economic threshold is lower than the economic- injury level to permit sufficient time for initiation of control measures and for these measures to take effect before the economic-injury level is reached. General equilibrium position. The average density of a population over a period of time (usually lengthy) in the absence of permanent environmental change. The size of the area involved and the length of the period of time will vary with the species under consideration. Temporary artificial modifications of the environment may produce a temporary alteration of the general equilibrium position (1.e., a temporary equilibrium). 452 STERN Governing mechanism. The actions of environmental factors, collectively or singly, which intensify as the population density increases and relax as this density falls so that population increase beyond a characteristic high level is prevented and decrease to extinction is made unlikely. The governing mecha- nisms operate within the framework or potential set by the other environmental elements. Natural control. The maintenance of a more or less fluctuating population density within certain definable upper and lower limits over a period of time by the combined actions of abiotic and biotic elements of the environment. Natural control involves all aspects of the environment, not just those immediate or direct factors producing premature mortality, retarded development, or reduced fecundity but remote or indirect factors as well. For most situations, governing mechanisms are present and determine the population levels within the framework or potential set by the other environmental elements. Natural control of a pest population may or may not be sufficient to provide economic control. Population. A group of individuals of the same species that occupies a given area. A population must have at least a minimum size and occupy an area containing all its ecological requisites to display fully such characteristics as growth, dispersion, fluctuation, turnover, dispersal, genetic variability, and continuity in time. The minimum population and the requisites in an occupied area will vary from species to species. Population dispersion. The pattern of spacing shown by members of a population within an occupied habitat and the total area over which the given population may be spread. Temporary equilibrium position. The average density of a population over a large area temporarily modified by a procedure such as continued use of insecticides. The modified average density of the population will revert to the previous or normal density level when the modifying agent is removed or expended. (Cf. General equilibrium position.) REFERENCES 1.R. D. O’Brien and L. S. Wolfe, Radiation, Radioactivity, and Insects, Academic Press, Inc., New York, 1964. 2.P. DeBach (Ed.), Biological Control of Insect Pests and Weeds, Reinhold Publishing Corporation, New York, 1964. 3. U. S. Department of Agriculture, Losses in Agriculture, Agriculture Handbook No. 291, Superintendent of Documents, U. S. Government Printing Office, Washington, D. C., August 1965. 4.R. F. Smith and R. van den Bosch, Integrated Control, in Pest Control, W. W. Kilgore and R. L. Doutt (Eds.), Chap. 9, Academic Press, Inc., New York, 1967. 5. R. van den Bosch and V. M. Stern, The Integration of Chemical and Biological Control of Arthropod Pests, Ann. Rev. Entomol., 7: 367—386 (1962). 6. 10. it: 2 13% te IES) 16. es 18. 19. 20. Zl 22: 23% 24. 28 26. P71 fe INSECT-INDUCED AGROECOLOGICAL IMBALANCES 453 R. F. Morris (Ed.), The Dynamics of Epidemic Spruce Budworm Populations, Mem. Entomol. Soc. Can., No. 31, 1963. . A. D. Telford, Features of the Lodgepole Needle Miner Parasite Complex in California, Can. Entomol., 93(5): 394—402 (1961). .O. B. Lean, FAO’s Contribution to the Evaluation of International Control of the Desert Locust, 1951—1963, Food and Agriculture Organization of the United Nations, Rome, 1965. .C. B. Huffaker, Summary of a Pest Management Conference—a Critique, in Concepts of Pest Management, R.L. Rabb and F.E. Guthrie (Eds.), pp. 227—242, University of North Carolina Press, Chapel Hill, 1970. R. L. Doutt, Biological Control, in Pest Control, W. W. Kilgore and R. L. Doutt (Eds.), Chap. 1, Academic Press, Inc., New York, 1967. C. B. Huffaker and P. Messenger, The Concept and Significance of Natural Control, in Biological Control of Insect Pests and Weeds, P.DeBach (Ed.), Chap. 4, Reinhold Publishing Company, New York, 1964. W. L. Thomas, Jr. (Ed.), Man’s Role in Changing the Face of the Earth, The University of Chicago Press, Chicago, 1956. V. M. Stern, R. F. Smith, R. van den Bosch, and K.S. Hagen, The Integration of Chemical and Biological Control of the Spotted Alfalfa Aphid. The Integrated Control Concept, Hilgardia, 29(2): 81—101 (1959). C. W. Sabrasky, How Many Insects Are There? Insects, Yearbook of Agriculture, pp. 1—7, U.S. Department of Agriculture, Washington, D. C., 1952. G. C. Ullyett, Mortality Factors in Populations of Plutella maculipennis (Tineidae: Lep.) and Their Relation to the Problem of Control, South African Dept. Agr. and Forestry Ent. Mem., 2(6): 77—202 (1947). R. F. Smith and W. W. Allen, Insect Control and the Balance of Nature, Sci. Amer., 190(6): 38—42 (1954). R. F. Smith, The Spread of the Spotted Alfalfa Aphid, Therioaphis maculata (Buchton), in California, Hilgardia, 28(21): 647—691 (1959). R. L. Doutt, Vice, Virtue and the Vedalia, Ent. Soc. Amer., Bull., 4(4): 119-123 (1958). W. H. Ewart and P. DeBach, DDT for Control of Citrus Thrips and Citricola Scale, Calif. Citrograph, 32: 242—245 (1947). California State Department of Agriculture, Agriculture Code, Standardization Pro- visions of Administrative Code and Standardization Procedures, Sacramento, 1964. R. van den Bosch and V. M. Stern, The Integration of Chemical and Biological Control of Arthropod Pests, Ann. Rev. Entomol., 7: 367—386 (1962). V. M. Stern, Insect Pests of Major Food Crops, Their Reinvasion Potential and the Effects of Radiation on Arthropods, OCD Work Unit No. 3145B, University of California, 1969. L. E. LaChance, C. H. Schmidt, and R. C. Bushland, Radiation-Induced Sterilization, in Pest Control, W. W. Kilgore and R. L. Doutt (Eds.), Chap. 4, Academic Press, Inc., New York, 1967. V.M. Stern et al., Lygus Control by Strip Cutting Alfalfa, Report AXT-241, University of California, Agricultural Extension Service, 1967. U. S. Department of Commerce, Bureau of the Census for the 1959 Census of Agriculture, Superintendent of Documents, U.S. Government Printing Office, Washing- ton, DiC.) 1965: C. F. Miller, Fallout and Radiological Countermeasures. Vols. 1 and 2, SRI Project No. 1M-4021, Stanford Research Institute, 1963. E. D. Callahan et al., The Probable Fallout Threat Over the Continental United States, Report No. TO-B60-13, Technical Operations Inc., 1960. ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION FROM SIMULATED- FALLOUT PARTICLES > ON A NATURAL PLANT COMMUNITY PETER G. MURPHY* and J. FRANK McCORMICK Department of Botany, University of North Carolina, Chapel Hill, North Carolina ABSTRACT 7 : pe SK) Simulated-fallout particles overcoated with ~~ Y granite-outcrop plant communities. The experiment resembled conditions expected at a site were applied at two levels of activity to 170 miles downwind of a 2.5-Mt detonation with a wind velocity of 15 mph. Mean community dose levels were 7000 and 4000 rads. In the 7000-rad communities, the ratio of mean ground-surface dose (8770 rads) to mean canopy dose (5092 rads) was 1.7. In the 4000-rad communities, the mean ground-surface dose (4824 rads) was 1.6 times higher than the mean canopy dose (2996 rads). In the 7000-rad communities, the death of 46% of all terminal buds in the dominant Viguiera portert resulted in a 37% height-growth reduction, a compensatory lateral branch development, a 16% reduction in community biomass, and a lower, more clumped, vertical distribution of leaves in the canopy. Comparison with earlier studies indicated that acute beta irradiation may be twice as effective as chronic gamma irradiation at equivalent total doses in causing height-growth reduction in V. porter. No radiation-induced change in the metabolism of the outcrop ecosystem was detected through measurements of CO, exchange 43 days after fallout dispersal. The mean rate of net production on clear days in both July and September (9:30 a.m. to 4:40 p.m.) was 12g C/m?/hr. Early nighttime rates of respiration (9:30 to 10:10 p.m.) averaged 2.9 ¢g C/m?/hr in July and2.2g C/m? /hr in September. Only since 1959 have the effects of ionizing radiation on entire plant communities and ecosystems been experimentally investigated. McCormick’s study of a granite-outcrop plant community’ and Woodwell’s study of a Long Island forest” were among the first investigations of radiation effects in natural plant communities. A common finding of these and subsequent studies has been that ecosystems respond to radiation stress much as they do to other *Present address: Department of Botany and Plant Pathology, Michigan State University, East Lansing, Mich. 454 ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 455 environmental stresses. An overall setback in successional status is a basic pattern observed. Ionizing radiation therefore becomes of interest as a tool for studying mechanisms of adjustment, or homeostasis, in ecosystems. Platt? pointed out that ionizing radiation is an environmental stress on organisms and ecosystems and as such must be considered as another environmental factor. In an interesting discussion Odum* explained that many of the consequences of ionizing radiation in ecosystems are not unique and can result from a variety of nonnuclear forces in the biosphere. Woodwell? discussed ionizing radiation and fallout as model pollutants and in a subsequent article® pointed out similarities between radiation effects and the effects of fire, oxides of sulfur, and herbicides. It is apparent that studies of the interaction of ionizing radiation with biological systems are of ecological interest not only for the information they supply on specific radiation effects but also for their contribution toward an understanding of the relation between structure and function in ecosystems. In studies of the effects of radiation on vegetation, the tendency has been to consider only gamma radiation of importance if the dose is from sources external to the vegetation and beta radiation of significance only as an internal factor. Until recently it was generally assumed that the limited penetrating ability of external beta radiation would prevent its causing serious damage to vegetation. Rhoads, Platt, and Harvey,’ however, reported that, in the Palanquin nuclear excavation experiment, sagebrush appeared much more sensitive to fallout than predictions based on experiments with gamma radiation from a °° Co source indicated that it should be. This finding led to the proposal that the sagebrush retained fallout particles relatively efficiently and that the beta component of the fallout radiation was important in producing the observed effects. It is now generally recognized that plant tissues near exposed plant surfaces are vulnerable to external beta radiation.® The dose received by such tissues as meristems may be large because of the high linear-energy-transfer coefficient of beta radiation. Within the last several years, a number of studies have been initiated using laboratory-produced radioactive particles as a fallout simulant; beta and gamma radiations were considered independently. Witherspoon and Taylor’ '' studied the effects of external beta radiation, including the effect from simulated fallout particles, on higher plants and determined the doses necessary to produce various degrees of response. Apical meristems were killed by beta-bath doses of 925 rads in white pine, 2315 rads in red oak, and 5400 rads in cocklebur when the doses were administered over a 1- to 3-day period. Other studies employed beta-emitting gauze strips applied to leaves'* and cylinders placed over buds” to study external beta effects. kane and Mackin,'* who studied bean plants, were among the first to approach the issue of external beta radiation, and their data indicated that beta doses of 100,000 rads to leaves and 2000 rads to whole plants produced sterility. None of the relatively few reports concerning the gross 456 MURPHY AND McCORMICK effects of external beta radiation on plants have dealt with entire plant communities. The primary objective of this study is to determine, qualitatively and quantitatively, the changes that occur in a natural plant community due to an acute exposure to external beta radiation from particles of a size range found in close-in fallout: Related = objectives are. (1) to describe the patter: or the radiation field produced by simulated fallout; (2) to obtain an index of the severity of beta effects relative to gamma effects observed in other studies, i.e., an ecological relative biological effectiveness factor (RBE); and (3) to describe some of the relations of structure and function in an ecosystem exposed to environmental stress. THE GRANITE-OUTCROP ECOSYSTEM Plants occur in small communities wherever soil accumulates in depressions on granite outcrops in the southeastern United States. The communities are found in small, often circular, depressions as well as in strips along the edges of forests adjacent to the rock. There are approximately 40 plant species that are considered characteristic of these communities although more than twice that many may occur in a community.'*® The species are zoned within the communities in response to intensity gradients of biotic and abiotic factors, soil depth and soil moisture being most important. The larger, deeper-rooted plants occur in the deeper soil, and in circular communities the zones are represented by concentric bands of the various species. The same attributes that favored the use of outcrop communities in the early work with gamma radiation’ are also favorable attributes for analysis of beta-radiation effects. Their relatively simple composition and well-defined boundaries make them especially attractive for experimentation. An entire community can be studied as a microcosm, or small segments can be isolated and studied independently. Simulated rock outcrops can be constructed of concrete, as they have been at Emory University and the University of North Carolina, and the small ecosystems transplanted for more closely controlled investigation.’ * There is an extensive literature dealing with various aspects of granite- outcrop ecosystems. Lugo'* presented a survey of this literature along with energy, water, and carbon budgets for the system. The first published reports of an ecosystem experimentally irradiated in nature dealt with a granite-outcrop ‘TeTS and data from these early studies showed that gamma ecosystem,’ radiation from °°Co had both stimulatory and inhibitory effects on plant growth. Species interactions at the community level reflected radiation effects on individual plants. The small size, relative simplicity, and adaptability for transplantation make these systems ideal experimental units. The considerable history of ecological research further enhances their suitability. For these several reasons the ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 457 granite-outcrop ecosystem was selected for initial studies of the ecological effects of beta radiation from simulated fallout particles. METHODS Simulated Outcrops Five experimental communities were transplanted from Mt. Arabia, Ga., to two large concrete pads in the North Carolina Botanical Garden. Each pad had four circular depressions 2 m in diameter and 20 cm deep which had previously been coated with a thin layer of tar and covered with powdered granite as described by Cumming'” to simulate the natural granite substrate. A sampling grid of 20- by 40-cm quadrats was established in each community. Four of the communities, in the process of being treated with fallout simulant, are shown in Figs i: bess ~ x Ms . a < Sia Ss Fig. 1 Simulated granite-outcrop communities in the process of being treated with fallout simulant. 458 MURPHY AND McCORMICK Each circular community was divided through the center by a plexiglass sheet 1 cm thick and 1.2 m high. One-half of each of four communities was treated with radioactive fallout simulant, and the other half served as a control. (Each semicircle is referred to as a community.) A “low” dose of beta radiation was administered to two of the communities and a “high” dose to the other two. One-half of the fifth divided circular community was treated with nonradio- active fallout simulant as a control on physical particle effects. In studying radiation effects, we compared each irradiated community (semicircle) with the immediately adjacent control community on the opposite side of the plexiglass partition. The summer flora was selected for irradiation. Between June and October the annual herb Viguiera porteri (A. Gray) Blake, a member of the Asteraceae, dominates the outcrop community. Since the structure of the summer community is most dependent on this species, Viguiera was studied more intensively than the other species were. Irradiation and Dosimetry The fallout simulant, supplied by Stanford Research Institute (SRI), consisted of albite (sodium feldspar) particles 44 to 88 uw in diameter with the beta-emitting isotope °° Y overcoated on the particles with sodium silicate. Yttrium-90 has a 64.2-hr half-life and a beta energy of 2.26 MeV. The isotope solubility was 0.1 to 0.01%. These properties provided for an acute exposure to beta radiation from particles of a size range found in close-in fallout. The simulant was dispersed on July 31, 1969. Two communities were treated with simulant of 1.85 mCi/g activity, and the other two received simulant of 4.74 mCi/g. The density dispersed was the same in all applications, 111g per square meter of plant community (each community was 1.9 m? in area). The doses obtained from these applications were intended to be within a range capable of causing biological effects in outcrop plants, as previously shown in gamma-field studies.'® Nonradioactive fallout simulant was applied to one-half of the fifth divided community (111 g/m’). The experiment most closely resembled conditions expected at a site 170 miles downwind of a 2.5-Mt detonation with a wind velocity of 15 mph according to calculations by Lane (personal communication) based on the procedures of Clark and Cobbin.”° A hand-held applicator consisting of two concentric plastic cylinders, the central cylinder containing the fallout simulant and the space between the two cylinders containing water for shielding, was used to disperse the simulant over the communities (Fig. 1). A sampling grid was used to help keep the distribution of particles uniform. After fallout dispersal the communities were covered with a light cheesecloth tent for 1 week to reduce wind velocity and fallout redistribution from the concrete pad to the surrounding area. A 1.5-cm rainfall 24 hr after fallout dispersal washed all visible particles off exposed surfaces of ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 459 the vegetation onto the soil surface. No radioactive particles were detected with a portable G—M counter off the concrete pad containing the experimental communities. Lithium fluoride thermoluminescent dosimeters (3 mm square and 1 mm thick), wrapped in light-shielding material and sealed in polyethylene packages, were placed in all treatment and control communities at two vertical levels (ground surface and 40 cm above the ground) on thin wooden rods. Forty-five dosimeters were placed in each treatment community and 12 1n each control community. The 40-cm height represented the average height of terminal buds in the summer-dominant Viguiera porteri. When Landauer & Co. read the dosime- ters after a 33-day exposure, less than 0.1% of the initial radioactivity remained. Ibandauers values were then. -multiplied by a correction factor ‘of 1.18 determined from exposure of six dosimeters to known dose levels of beta radiation from a calibrated ?° Y source”! by J. Mackin at SRI. Ten glass-vial dosimeters containing lithium fluoride were arranged vertically on a String, five in each of the high-dose communities. These dosimeters, which were collected after the first 27 hr of exposure by W. Lane of SRI, provided an estimate of initial dose rates and vertical stratification of doses before the fallout simulant was washed from the vegetation by rain. The percentage of retention of the fallout simulant was estimated by using nonradioactive simulant. Twenty planchets (total area, 151 cm”) were placed on the soil surface, and the percentage of dispersed particles falling through the vegetation canopy into the planchets was determined on a weight per unit area basis. This experiment was repeated three times, and the results were averaged. Twenty days after fallout dispersal, samples of terminal buds, leaf axils, leaf blades, and stems were collected from V. porter: plants in each irradiated community. Three surface and three subsurface (0.5-cm) soil samples were also collected from each community. To determine the relative radioactivity per unit area of plant parts and soil, we pressed all samples flat in planchets for counting. Stems and buds were sectioned longitudinally and oriented so that their external surfaces faced the detector. Community Analysis Ecosystem Metabolism A Beckman Instruments, Inc., model 215 infrared gas analyzer was used to measure rates of net production and respiration, based on the difference between concentrations of carbon dioxide (CO,) in ambient air and in air sampled from the experimental communities. Bourdeau and Woodwell?? reviewed infrared absorption techniques for measuring rates of CO, exchange. Lugo'” measured rates of CO, exchange in granite-outcrop communities using techniques similar to those presented here. 460 MURPHY AND McCORMICK The gas-analysis system is shown in Fig. 2. The transparent metabolism chamber (Fig. 3) was partitioned through the center so that air could be sampled alternately from control and treatment communities. Two fans approximately 50cm in diameter, one in each half of the chamber, supplied an airflow averaging 34cm/sec across each community and maintained the internal TELETHERMOMETER | METABOLISM aarti hve gy UESEETS DEES | es CAM TIMER = pum] FLOWMETER | pee ——_qo@Or“™ [EEC er] DESICCATOR DUST INFRARED FILTER GAS ANALYZER _ Fig. 2. Diagram of the system used to measure rates of CO exchange in the experimental outcrop communities. Arrows indicate direction of airflow. chamber temperature within +3°C of outside ambient air. Airflow was measured at nine points over the cross section of each half of the chamber with a hot-wire anemometer. On the average, the volume of air in each half of the chamber was replaced 13 times per minute. Known concentrations of CO, in nitrogen were used to calibrate the gas analyzer. The following relation was used to convert differences between CQO, concentrations in ambient air and those in chamber air to rates of ecosystem net production or nighttime respiration in grams of carbon per square meter of ecosystem per hour (g C/m? /hr): ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 461 Fig. 3 Transparent chamber used for measuring rates of ecosystem CO exchange. The chamber is shown in position over one of the experimental outcrop communities. exG/m- jit — flow rate difference 243 12 g C/mole et ao X 60 min/h (liters/min) inCO, (ppm) temp.in K_ 22.4 liters/mole pees ecosystem area (ne )oxCn0° ul/liter Measurements of CO, exchange rates were taken over a 4-day period 12 days before fallout dispersal and over a 4-day period 43 days after fallout dispersal. Each of the four irradiation and control communities was measured for one clear, sunny day before and after the irradiation period. Ambient-air and chamber-air samples were analyzed at the following times during the day for calculation of rates of net production: 9:30 to 10:10a.m., 12 noon to 1:10 p.m., and 4:00 to 4:40 p.m. To calculate a reference rate of nighttime respiration, we analyzed ambient-air and chamber-air samples between 9:30 and 10:10 p.m. These rates were considered representative of early nighttime only (Lugo'*® found rates of nighttime respiration in outcrop communities to be maximum between 9:30 and 10:10 p.m. in June 1968). Each half of the divided chamber and the ambient air were sampled for 10 min in a 30-min cycle during each of the sampling periods. Ten readings were taken during each 10-min period. 462 MURPHY AND McCORMICK Species Composition All plants were identified and counted in each of the communities 20 days before and 56 days after fallout dispersal. For lichens, mosses, and sedges, percent cover rather than numbers of individuals was estimated by using a 20-cm? wire frame as a gauge. Biomass One 20- by 40-cm quadrat was harvested from the center of each community 69 days after fallout dispersal. Fhe plants in each sample (almost exclusively V. porteri) were divided into stem (with roots), leaf, and flower-head portions, oven dried for 24 hr at 105°C, and weighed. Leaf-Area Index The ratio of leaf area to ground area was estimated in all communities by suspending a weighted string over each intersection of grid lines (15 measure- ments per community). The number of leaves (of any plants) touching the vertical string was taken as an estimate of leaf-area index, and an average value was calculated for each community. This method was developed by Odum.?? The estimation was made 4 days before and 49 days after fallout dispersal. Canopy Stratification To determine the magnitude of the shift in canopy height with plant growth, we positioned a graduated aluminum rod perpendicular to the ground at each intersection of grid lines (15 per community) and recorded the height of all leaves touching the rod. The number of leaves in each increment of height above the ground for the 15 positions was calculated. This measurement was taken 4 days before and 49 days after fallout dispersal in all communities. Litter Accumulation Four aluminum pans with a total area of 380 cm? were placed in each experimental community to catch fallen plant debris. The oven-dry (24 hr at 105°C) weight of accumulated matter was determined 54 and 82 days after fallout dispersal. The mean weight per community was converted to a square meter basis. Analysis of the Summer-Dominant V/gu/era porteri Height Growth The distance from ground level to terminal buds was measured 20 days before and 56 days after fallout dispersal in 60% or more of all Viguiera plants in ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 463 all communities. The measured individuals were selected at random. Growth was expressed as percent increase in height during the period between fallout dispersal and the measurement 56 days later. Terminal Bud Mortality The terminal buds of 50 randomly selected Viguiera plants in each community were classified 70 days after fallout dispersal as either normal or dead, based on whether they showed signs of growth. The number of dead buds was expressed as a percentage of the 50 buds observed in each community. Pigment Diversity To document a possible change in coloration, we determined the yellow-to- green-pigment ratio** (Margalef ratio) 21 days before and 65 days after fallout dispersal. Pigments were extracted from three samples of three leaves each from each community. Leaves were ground in 90% acetone to extract pigments.’* Optical densities of the samples were measured with a spectrophotometer at two wavelengths, 430 and 665 mu. The ratio of the optical density at 430 my to that at 665 mp was taken as the pigment-diversity ratio. RESULTS Dosimetry Dose levels obtained on the ground and in the vegetation canopy are given in Table 1. In the low-dose communities, the mean ground-surface dose (4824 rads) was 1.6 times higher than the mean canopy dose (2996 rads). In the high-dose communities, the ratio of mean ground-surface dose (8770 rads) to mean canopy Table 1 MEAN COMMUNITY DOSE LEVELS AFTER 33 DAYS OF EXPOSURE TO FALLOUT SIMULANT* Dose, rads Mean Treatment Soil surface Canopy (canopy and surface) Low dose 4824 + 882 2996 + 326 4037 +768 Control 1.5 O13 2.00+0.2 18 aOe2 High dose 8770 £676 5092 £743 7082 + 38 Control 3.0 210; AN Sete 107 3.8+1.8 *Each value (+ 1 standard error) represents the mean of two replicate communities. 464 MURPHY AND McCORMICK dose (5092 rads) was 1.7. The mean integrated high dose (mean of ground and canopy) was 7082 rads, 1.8 times higher than the mean integrated low dose (4037 rads). The doses recorded by the glass-vial lithium fluoride dosimeters after their 27-hr exposure in the high-dose communities are shown in Fig. 4. About a third (2000 rads) of the mean integrated dose (7082 rads) was received during the initial 27-hr period in the high-dose communities. Ground-surface doses were 1.8 times higher than canopy doses during the early period. DISTANCE ABOVE GROUND, cm 1000 : | 2000 3000 DOSE, rads Fig. 4 Initial 27-hr doses recorded by the 10 lithium fluoride dosimeters in the high-dose communities. Experiments with nonradioactive fallout simulant showed that 40% by weight of all particles dispersed over the communities was initially retained on vegetation. The radioactivity per unit area of plant surfaces relative to that of the soil surface 20 days after fallout dispersal is shown in Fig. 5. The surfaces of leaf axils and terminal buds apparently collected more radioactive particles than did other plant parts, but even these surfaces were only 23 and 14%, respectively, as radioactive as the soil surface. The surfaces of leaf blades and stems were less than 5% as radioactive as the soil surface. At a depth of 0.5 cm, there was no radioactivity above background in the soil. ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 465 { for successive intervals after contamination. Particle mass load (m) and foliar retention (C,) from Table 3 were determined experimentally, and contamination factors (a; ) were calculated according to the relation This expression allows an estimation of time-dependent vegetation contamina- tion in future situations based on knowledge of plant density and soil-surface fallout deposits and assuming that the affected plant communities exhibit similar retenticn characteristics. For a single fallout deposit, then, maximum retention and contamination factors are observed at tg and decrease thereafter (Table 3). Retention at t+ 1 hris taken as ty, and the az, factors for fescue were 0.009 and 0.004 for fine and coarse materials, respectively. Within 2 days the values had decreased by a factor of 2 and att + 1 week by a factor of 4, but they changed very little during the second week of the field observation. Effective weathering had occurred within 1 week; thereafter the slower particle loss rate predomi- nated. The contamination-factor expression originally was derived in connection with project Sedan and later was applied to volcanic fallout deposits around volcano Irazu in Costa Rica. Miller and Lee® reported retention values and determined a, factors (Table 3) for Costa Rican grasses which compare favorably with those reported here. The ay factors herein derived for tall fescue 503 PREDICTION OF RADIONUCLIDE CONTAMINATION ‘Bleep ajqeieduios ON § ‘usodap paisyieam ‘poriad-3uoy ‘aydijnwi ‘s pur ‘usodap pasayieamun poriad-1ioys ‘gq se paieudisap st uontsodap inoyyey aque, t ‘Ayaaradadsaa ‘susodap asivod pur duty 105 15 bs/3 OT F 7'6 PUR SOF OTT St Ww asaym ‘w/45 st Tey ‘ase1jo} JO uleld jad sayoiyied jo surei3 st dy. uontsodap Bsutindal YUM ulel “Ul-¢°€ ¢00°0 92 €00°0 OTOO'0 600°0 610 OTO0'O TTO'O tC O OLT L100°0 9T0'0 670 TTOO'O clO 0 ECO 88°9 § 07000 8100 €£°0 F100 0 c¢10'0 L7O c3s uomtsodap surinsa1 YUM UleI “Ul-€ cto 0 cc00'0 0c0'0 9¢°0 L+00'0 cSO'0 +60 88°C d ‘dureq S00 S ‘Aid c00'0 92 LOO ¢£00°0 cEO'O 9¢°°0 8£00'0 c+O'0 cZ0 EST S ‘29M TO 02 ¢0'0 d ‘Aiq 100°0 8£00°0 ce00 19°O OZ00°0 LLO Sigel ¢L0 (44 T) § L€00'O reo 0 09°0 6800 0 860'0 at cr0 0 {suonipuos 8/13 bs 8/13 bs 3/3 yz bs/3 3/13 bs 3/3 ay bs/3 sAep uontsodag “Te 4‘Te rs ‘dy ‘u0onuaja1 ale ady ‘u01U9}941 ‘SUIT ] 9A19995Fq JAIIIIIFA gSUOINIpUOD ainsodxa pue $1019¥J UOTIVUIUIEIUOD Yse-eUdIY-ezIUaD sapoiased asiv0D sapoised suty $10}9¥J UONVUIWPIU0D pure U0IU9}91 JNISI 4 NOSTYVdWOD YOU SYOLOVA NOILVNIWV INOS HSV-VNAYV-VZINAO HLIM DNOTV SUALAWVUVd (Te) YOLOVA-NOILVWNIWV.LNOO GNV (45) NOILNYLAY-YVITON ANOSAA € 1921 504 DAHLMAN ranged from 0.004 to 0.007 at days 1 and 2 under dry conditions (80% relative humidity and no wind). The Ceniza-Arena a, factors derived by Miller and Lee for an equivalent period ranged from 0.001 to 0.07 for dry conditions and from 0.05 to 0.1 for wet conditions. Good agreement obviously exists among the results from the two different assessments of foliar retention and for the calculated contamination factors irrespective of initial mode of fallout deposi- tion. It seems that dense vegetation in subhumid or humid climates demonstrates similar patterns of early retention. It is likely that total radionuclide transfer to plant parts would be greatly influenced by fallout-particle distribution in the canopy. In a subhumid environment, however, plant structures can assimilate much of the nuclide that is leached from fallout materials and transferred to plant surfaces. This argument is verified by using the derived a, for coarse particles (0.0039) to predict eG contamination of fescue for the 10- by 10-m plots tagged in August 1967, in which a prediction of grass contamination is compared with an independent observation of radiocesium assimilation by the fescue community.’° The fraction retained by the vegetation canopy is estimated from Miller’s plant- retention relation: EE = a, Wy (4) when a, is 0.004 and wy, is 65 g/sq ft, the plant density at the time of contamination. F; is 0.254, which, when multiplied by the activity-application rate: (2.06rumCi/sq: ft). «is thes total F, = 2.06 X 0.254 = 0.523 mCi/sq ft (expressed in terms of activity content of Cs contamination of foliage [1.e., vegetation)]. It was observed from laboratory tests that 15% of the radiocesium will leach from the particle in an aqueous system. If the leachate is assimilated directly by vegetation, then, 0.523 mCi/sq ft X 0.15 = 78 uCi/sq ft is the activity of vegetation shortly after contamination. The observed radiocesium content of vegetation’ ° at t+8 days was 78uCi/sqft, showing a remarkably good agreement between that predicted from contamination-factor parameters and that measured after the contamination event. It can therefore be concluded from this analysis of a field test that foliar contamination-factor expression coupled with fallout leachability provides a good estimation of vegetation contamination in a grass community. Source-Term Evaluation Model Estimation of radiological hazards, from either direct particle deposit or nuclide assimilation, depends on identification of a source term or entry of the contaminant into the food chain. At least four different source terms (Fig. 3; compartments =P, El, and F)r can serve sas. the, initial imple. tommche grass—cow—man food chain. Dissimilar contamination phenomena and contam1- nant behavior patterns are manifest for each source term. Short-term hazards 505 PREDICTION OF RADIONUCLIDE CONTAMINATION ‘p Jqe] Ul pazenyead ase $]UdID1JJIOD JaJsuLI] ‘sapoiazed juepnurs-ynoyeJ YIM UONeUTUTEIUOD Jaze ssvIS ands} JO suOIIe]IaI WI9}-29IN0S ¢ ‘BI NOILVNINWWLNOS WOS 5 NOILN3LSY AIDILYWd WY3L-DONOT NOILVNINVLNOO 49VINO4 WH 3L-ONO1 NOILVNINVLNOOS Y5L111 NOILVNINVLNOO LOOU Y +3 td 1 NOILVNIWVLNOO 49VI104 TWNYALXS NOILISOd30 AVOILYVd SENOMsI VS NOILVNINVLNOO Q34S YO ‘LINGUS ‘YSMO14S NOILVNINVLNOOS dvi TWNYSLNI NOILN3L34Y AIDILYVd TVILINI ‘@ a 506 DAHLMAN Table 4 TRANSFER FUNCTIONS FOR SOURCE-TERM EVALUATION MODEL Transfer functions Cj W Definitions f(m), initial fraction of fallout mass load Ld i f(L), fraction moving from litter to soil = Particle weathering function = 1—P where P = @ + Ge=ayen* =if(P) sfraction OF nuclide movement from particle to foliage Nuclide weathering function = 1—E where E =a + Ber: =.fCE)) fraction ot nuclide movement from external to internal plant parts = f(I), fraction of internally assimilated nuclide movement to roots = f(R), fraction of root contaminant moving to current season’s growth = f(1), fraction of leaf nuclide moving to seed = f(R), fraction of root nuclide moving to seed = f(S), fraction of soil nuclide taken up by plant Values for fescue grass a=0.2 A= 0.26 O74 Onl 0.1 0.001 Source Experimental Calculated Inferred from litter de- composition rate (Koelling and Kucera? ® ) Regression of particle reten- tion on time Measured aqueous leachability Regression of nuclide reten- tion on time Inferred from Levi?! (bean plants) Experimental Assumption Inferred from Levi?! (bean plants) Assumption Inferred from Nishita et a 1.22 PREDICTION OF RADIONUCLIDE CONTAMINATION 507 would be related to particle deposition and retention on foliage, whereas long-term problems could derive from assimilation and equilibration of the nuclide in the plant community. The model couples interrelations among principal source terms in order to estimate contamination potentials as a function of time, particle behavior, and intraplant nuclide movements. Transfer and weathering functions (Table 4) are used to predict the fate of radiocesium applied in the form of fallout-simulant particles to a fescue meadow. For subhumid environments, importance of the source term proceeds in Fig. 3 from left to right (compartments P to I) according to the approximate time sequence: P, 1 to 10 days; E, 7 to 100 days; I, 3 months to several years; F, any time interval prior to seed production. In practice, the model will predict the character and extent of contamination at successive intervals after fallout deposition. Knowledge of deposition forms, fallout behavior, and source-term magnitudes will foster more-intelligent decisions concerning grazing of pastures in the event of widespread contamination from nuclear explosions. ACKNOWLEDGMENTS This research was sponsored by the U. S. Atomic Energy Commission and the Office of Civil Defense under contract with the Union Carbide Corporation. The assistance of John Beauchamp of the ORNL Mathematics Division in derivating the negative exponential regression equations is_ gratefully acknowledged. REFERENCES 1. L. Baurmash, J. W. Neel, W. K. Vance III, H. K. Mork, and K. H. Larson, Distribution and Characterization of Fallout and Airborne Activity from 10 to 160 Miles from Ground Zero, Spring, 1955, USAEC Report WT-1178, University of California, Los Angeles, September 1958. 2. D. E. Clark, Jr., and W. C. Cobbin, Some Relationships Among Particle Size, Mass Level, and Radiation Intensity of Fallout from a Land Surface Nuclear Detonation, Report USNRDL-TR-639, Naval Radiological Defense Laboratory, Mar. 21, 1963. 3. C. F. Miller and Oliver S. Yu, The Mass Contour Ratio for Fallout and Fallout Specific Activity for Shot Small Boy. Final Report, SRI Project MU-6358, Stanford Research Institute, 1967. 4. C. F. Miller, Operation Ceniza-Arena: The Retention of Fallout Particles from Volcano Irazu (Costa Rica) by Plants and People. Part II, Appendices, SRI Project MU-4890, Stanford Research Institute, 1966. 5.C. F. Miller, The Retention by Foliage of Silicate Particles Ejected from the Volcano Irazu in Costa Rica, Radioecological Concentration Processes, B. Aberg and F. P, Hungate (Eds.), Proceedings of an International Symposium, Stockholm, Apr. 25—29, 1966, pp. 501—526, Pergamon Press, Inc., New York, 1967. 508 DAHLMAN 6. 10. if RY 2 13% 14. ily 16. 17; 18. 19: 20. PAE 22. Zz: C. F. Miller and H. Lee, Operation Ceniza-Arena: The Retention of Fallout Particles from Volcano Irazu (Costa Rica) by Plants and People. Part I, Report AD-637313 (SRI Report No. MU-4890), Stanford Research Institute, January 1966. . Janice C. Beatley, Effects of Radioactive and Nonradioactive Dust upon Larrea divaricata Cav., Nevada Test Site, Health Phys., 11: 1621—1624 (1965). .W. A. Rhoads, R. B. Platt, R.A: Harvey, and E- M. Romney, Ecological and Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and Short-Term Effects on the Vegetation from Close-In Fallout, USAEC Report PNE-956, University of California, Los Angeles, Aug. 23, 1968. .S. L. Brown and U. F. Pilz, U. S. Agriculture: Potential Vulnerabilities. Final Report, SRI Project MU-6250-052, Stanford Research Institute, 1969. R. C. Dahlman, S. I. Auerbach, and P. B. Dunaway, Behavior of '* 7 Cs Tagged Particles in a Fescue Meadow, Environmental Contamination by Radioactive Materials, Seminar Proceedings, Vienna, Mar. 24—28, 1969, pp. 153-165, International Atomic Energy Agency, Vienna, 1969 (STI/PUB/226). J. E. Johnson and A. I. Lovaas, Deposition and Retention of Simulated Near-In Fallout by Food Crops and Livestock, Progress Report No. DAHC 20-68-C-0120, Colorado State University, 1969. J. P. Witherspoon and F. G. Taylor, Jr., Interception and Retention of a Simulated Fallout by Agricultural Plants, Health Phys., 19: 493—499 (1970). E. M. Romney, R. G. Lindberg, H. A. Hawthorne, B. G. Bystrom, and K. H. Larson, Contamination of Plant Foliage with Radioactive Fallout, Ecology, 44: 343 (1963). W. E. Martin, Early Food-Chain Kinetics of Radionuclides Following Close-In Fallout from a Single Nuclear Detonation, in Radioactive Fallout from Nuclear Weapons Tests, Germantown; “Md... Nov. 3—6; 1964,. A:W.. Klement, (Ed) pp: 758 782— sAEG Symposium Series, No. 5 (CONF-765), 1965. W. B. Lane, Fallout Simulant Development: The Sorption Reactions of Cerium, Cesium, Ruthenium, Strontium, and ‘Zirconium—Niobium, Report AD-635547 (SRI-MU-5068), Stanford Research Institute, November 1965. W. B. Lane, Fallout Simulant Development: Temperature Effects on the Sorption Reactions of Strontium on Feldspar, Clay, and Quartz, Report SRI-MU-6503, Stanford Research Institute, 1968. W. B. Lane, Fallout Simulant Development: (1) Synthetic Fallout Facilities at Camp Parks, and (2) Two-year Leaching of Cesium from Synthetic Fallout and Fission Products from Shasta Fallout, Report SRI-MU-7236, Stanford Research Institute, 1969. C. F. Miller and P. D. LaRiviere, Introduction to Long-Term Biological Effects of Nuclear War, USAEC file No. NP-16462 (SRI-MI-5779), Stanford Research Institute, April 1966. W. E. Martin and F. B. Turner, Transfer of 8° Sr from Plants to Rabbits in a Fallout Field, Health Phys., 12: 621—631 (1966). J. P. Witherspoon, Particle Retention by Sorghum, Oak Ridge National Laboratory, personal communication, 1970. E. Levi, Uptake and Distribution of USTs Applied to Leaves of Bean Plants, Radiat. Bot., 6: 567—574 (1966). H. Nishita, E. M. Romney, and K. H. Larson, Uptake of Radioactive Fission Products by Plants, Radioactive Fallout, Soils, Plants, Foods, Man, E. B. Fowler (Ed.), American Elsevier Publishing Company, Inc., New York, 1965. M. R. Koelling and C. L. Kucera, Dry Matter Losses and Mineral Leaching in Bluestem Standing Crop and Litter, Ecology, 46: 529—532 (1965). RESPONSES OF SOME GRASSLAND ARTHROPODS TO IONIZING RADIATION CLARENCE E. STYRON* and GLADYS J. DODSON Ecological Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee ABSTRACT Responses of arthropod communities to ionizing radiation and the interactions of radiation with other environmental parameters are being investigated in (1) studies of biological and physical dosimetry of beta and gamma radiation from simulated fallout in a grassland area, (2) long-term field observations on interactions of the fallout radiation with seasonal changes in composition and structure of the arthropod community, and (3) short-term laboratory studies on interactions of fallout radiation with population dynamics of selected insect species. Beta- and gamma-radiation levels in the simulated fallout area were determined by thetmoluminescent dosimetry. Lithium fluoride microdosimeters attached to grasshoppers and crickets in the fallout field indicated that these closely related organisms received significantly different radiation doses owing to differences in habitat. Numbers of soil-, litter-, and grass-inhabiting arthropods collected in the simulated-radioactive-fallout field varied significantly among months and taxa. There was no significant difference in variation between arthropod communities of field enclosures before application of the simulant. The only significant differences among numbers of individuals in taxa comprising the arthropod communities of control and contaminated areas occurred 4 months after contamination. No significant increase in species composition dissimilarity between the contaminated and control areas appeared during the second year following application of the fallout. Consequently the threshold for effects of fallout radiation on_ species composition of the arthropod community must be above the ~13 rads/day delivered over this time. Data on exposure of laboratory populations of Folsomia (Collembola) to beta radiation from ?°Sr—9°Y fallout indicate that population dynamics were affected primarily by sensitivity of fertility rates rather than by sensitivity of adults. Dose rates estimated to give an LDs509/30 Or LDs0/69 for adults were more than twice as high as dose rates required to reduce fertility rates to zero. *Present address: Division of Mathematics and Natural Science, St. Andrews Presby- terian College, Laurinburg, North Carolina. 509 510 STYRON AND DODSON Many ecological situations may be upset by effects of radioactive fallout on insect populations.’ In particular, beta radiation from fallout may be hazardous to small insects and to insects that pass developmental stages in the soil and litter. Although some information is available on arthropod responses to beta and gamma radiation, it is meager and must be augmented to predict patterns of ecological responses to a nuclear attack and to plan postattack agricultural procedures. The objective of this study is to assess effects of ionizing radiation from fallout on insects. Collembola were chosen for the laboratory experiments because they are among the most numerous microarthropods in the soil fauna and are important in soil formation. The study, a correlation of field and laboratory data, deals with succeeding levels of ecological complexity: (1) effects of chronic beta radiation on population mortality and fertility and (2) responses of the structure of an arthropod community in a managed grassland ecosystem to beta and gamma radiation. This paper covers the first 2 years of observations on the arthropod community. Antecedent to any evaluation of radiation effects is the necessity of selecting an accurate, dependable, and practical method of determining radiation levels. Standard means of measuring radiation levels in contaminated areas (ionization chambers, scintillation counters, G—M counters, or silver-activated metaphos- phate glass dosimeters) were not feasible in this study, in some instances owing to expense and/or component materials. Furthermore, these devices are not well suited for measurements of dose rates in microhabitats where radiation levels may be low, and most do not measure beta radiation. Existing mathematical models’ * for predicting beta- and gamma-radiation dose rates from fallout were inadequate for this study because models are limited in ecological situations by restrictions in geometry, such as surface conditions, presence of grass, and movement of fallout.” Thermoluminescent dosimeters were selected for use since they are mechanically rugged, are available in several geometries and sizes, and measure doses as low as 5 mrads. METHODS The study of the effects of simulated radioactive fallout on an in situ arthropod community was conducted at the 0800 Ecology Research Area at the Oak Ridge National Laboratory (ORNL). A quantity of simulated fallout® ® (2.44 Ci of '*7Cs on silica sand grains) estimated to give a dose rate of 100 mR/hr at 1 m above ground was applied” in July and August 1968 to a 100-m? field enclosure of the managed grassland ecosystem dominated by Festuca arundinacea Schreb. Three sites in the field, one fenced with sheet metal, one fenced and contaminated with fallout, and one roped off, were sampled bimonthly during the first year and monthly thereafter. The roped area was established for comparison with the uncontaminated pen to detect possible ‘ RESPONSES OF SOME GRASSLAND ARTHROPODS 511 effects of the fencing, which was utilized to rodent-proof the pens and to minimize dispersal of the fallout simulant. Sampling was begun 4 months before application of the fallout simulant. Seventy-eight arthropod taxa were sorted from samples collected with pitfall traps (12.2 cm deep by 6.7 cm in diameter), soil cores (5.0 cm long by 4.4 cm in diameter), ! ° and biocoenometers (cylindri- cal cages 0.25 m? by 1 m in height).’ : Beta- and gamma-radiation dose rates in the contaminated enclosures were determined by using cleaved (1 mm*) and extruded 0.5- by 6.0-mm crystals of LiF (Harshaw Chemical Co. TLD-100). This material was used because it 1s essentially energy independent for beta and gamma radiation. Beta and gamma point dosimetry was begun with the first application of fallout simulant. Extruded crystals of LiF were suspended at several heights above the ground. Some dosimeters were unshielded, and others were enclosed in 2-mm-thick nylon capsules, which were sufficient to shield out the beta radiation but not the gamma radiation. Extruded crystals were placed in and on grass stems and leaves; cleaved crystals were attached to insects during the eighth week after application of fallout simulant. For the Collembola population study, albite sand grains (44 to 88 wu in diameter) coated with 2 OG pe? Day (Ref. 12) were suspended in glycerol and painted onto charcoal—calcium sulfate substrates in culture jars 4 cm in diameter. Nonradioactive sand grains in glycerol were similarly applied to charcoal—calcium sulfate substrates to prepare control culture jars. Surface dose RALCSHOlN Suomen LOLs) alae Lo.) On uk 4. 22.9290, 29.5, 35.4, 45.9, 66.0, 71.8, 89.1, and 341.7 rads/hr were determined for these plane sources using 0.5- by 6.0-mm extruded LiF crystals. Groups of 8 to 12 adult Folsomia species were placed in 10 control and in 19 experimental culture jars. The culture jars were maintained at 20°C, and the substrates were kept saturated with water. The Collembola were fed brewer’s yeast, and numbers of adults, juveniles, and eggs were scored biweekly for a period of 98 days. RESULTS AND DISCUSSION Soil, litter, and grass components of the grassland arthropod community received significantly different beta- and gamma-radiation exposures owing to changes in distribution of the fallout simulant and to the short range of '*7Cs beta particles. Gamma and gamma + beta dose rates integrated over the first week in the middle of the contaminated field enclosure (Fig. 1) can be used to estimate the beta-radiation dose rates. Beta particles in air and vegetation have limited ranges, of course, and beta dose rates were used to estimate the vertical distribution of fallout for the point at which the series of dosimeters was suspended. Beta-radiation dose rates during the first week following application indicated that 25 to 30% of the simulant was present on the ground surface, 45 to 50% in the litter layer, and 20 to 30% on leaf surfaces. Eleven weeks after the 2) STYRON AND DODSON Ww oO @ Beta + gamma 20 DISTANCE ABOVE GROUND, cm RADIATION DOSE RATE, rads/hr Fig. 1 Distance above ground plotted against gamma and beta + gamma dose rates in the middle of the contaminated enclosure at the 0800 Ecology Research Area during the first week after application of simulated radioactive fallout. The distance between the two dose-rate lines represents the beta- radiation dose rate. N for each point is 2. first application and eight weeks after the second dosing of simulant (Fig. 2), 50 to 55% of the beta dose appeared on the ground surface, 25 to 30% was delivered in the litter layer, and less than 10% was present at the height of leaf surfaces. Microdosimeters placed on and in grass stems and leaves (Fig. 2) showed that most of the intercepted simulant had been removed from leaf surfaces but some remained trapped in leaf axils. Beta + gamma dose rates in axils ranged from 931 to 1145 mrads/hr, as compared with air dose rates at the same height above ground of 200 to 250 mrads/hr. Grasshoppers (Melanoplus species) and crickets (Acheta domesticus) with cleaved crystals of LiF attached to their thorax and abdomen were released in the contaminated enclosure the eighth week after the second application of fallout simulant (Table 1). The dosimeters integrated the dose received by the insects as they moved through various dose-rate levels and thereby provided realistic estimates of “ecological dosimetry.”!* Differences between dose rates to thorax and abdomen of the same insects were not significant, but there was a significant difference (P< 0.01) between total exposures of the living grass- hoppers and crickets. These two insects are closely related taxonomically, but they occupy different habitats. Crickets dwell primarily on and in litter, where, RESPONSES OF SOME GRASSLAND ARTHROPODS 51S ©, Beta + gamma @® Gamma 30 20 == 0:931) IN-AXIL 1.145 IN AXIL = 0:200: AT- STEM +— 0.203: IN: STEM DISTANCE ABOVE GROUND, cm 0 0.2 0.4 0.6 RADIATION DOSE RATE, rads/hr Fig. 2. Distance above ground plotted against gamma and beta + gamma dose rates in the middle of the contaminated enclosure at the 0800 Ecology Research Area during the eleventh week after the first application and the eighth week after the second application of simulated radioactive fallout. The distance between the two dose-rate lines represents the beta-radiation dose rate. Beta, gamma, and the combined dose rates observed for a fescue plant also are presented. N for each point on the dose-rate lines, as well as for the fescue plant, is 2. Table 1 DOSE RATE TO CRICKETS (Acheta domesticus) AND GRASSHOPPERS (Melanoplus SPECIES) FROM SIMULATED RADIOACTIVE FALLOUT EIGHT WEEKS AFTER APPLICATION OF 2.44 CI/100 M2 OF !37¢s Dose rate, rads/hr* Organism Thorax Abdomen Acheta domesticus, living 022" 0,003 O31 = 02010 Melanoplus species, living 0:09°+ 0.011 0.10 + 0.007 Melanoplus species, phantom 0.11 £0.005 0.20 + 0.006 *Plus or minus standard error; N = 10. 514 STYRON AND DODSON in this instance, they were exposed to more beta radiation; grasshoppers dwell higher, on blades of grass. Thus any attempt to predict ecosystem responses to radioactive fallout based on different radiation sensitivities must also deal with the problem of differential radiation exposure. Biological data in the form of numbers of individuals of each arthropod taxon collected from the managed grassland arthropod community by each pitfall trap, soil core, or biocoenometer are too extensive for presentation here and will be included in a later report. A sequential three-way analysis of variance was applied to data from 26 sampling dates (Apr. 1, 1968, to Mar. 18, 1970) to detect significant changes in structure of the community. Variation among sites, taxa, and sampling dates was first calculated by using the seven sampling dates (Apr. 1 to June 25, 1968) before application of the fallout simulant. An F test indicated significant differences among dates (P < 0.01) and taxa (P< 0.01) but not between the control and the contaminated pens nor between either pen and the roped area. Differences among sampling dates would be expected because of seasonal responses of the arthropod community, and differences among taxa would be expected because the taxa normally occur at different population densities. Since original areas possessed comparable arthropod species composi- tions, subsequent differences in community structure cannot be attributed to any pretreatment variabilities. An analysis of all 26 sampling dates confirmed the difference among dates (P < 0.01) and among taxa (P S 0.01) as well as the lack of a significant difference among sites. When initial sampling dates were sequentially deleted and the analysis of variance repeated after each deletion, the only significant difference appearing between the control and the contaminated communities occurred 18 weeks after application of the fallout simulant (P< 0.05). At this time the soil component of the arthropod community had received 1789 rads of beta+ gamma dose (Table 2), the litter component 1724 rads, and the grass component 373 to 1295 rads (variable as a function of height). Continuation of this analysis indicated no other significant differences between the arthropod communities. At the time of the 26th sampling date (Mar. 18, 1970), the soil component of the arthropod community had received 7786 rads of beta + gamma dose, the litter component 7165 rads, and the grass component between 1594 and 5404 rads. For interpreting changes in arthropod community structure through time, an 4-17 was calculated for each sampling index of species composition dissimilarity date and site pair combination: control enclosure vs. roped area, control enclosure vs. contaminated enclosure, and roped area vs. contaminated enclo- sure. The number of individuals of each arthropod taxon collected from a site on d!>:!® and used to calculate in Euclidean each sampling period was transforme hyperspace the species composition distance, d, between each pair of sites by the following equations: X = log (y + 1) (1) dj; = (OnGis =a Ge + UGE F = 295) a yest (X78; — X78,j)° RESPONSES OF SOME GRASSLAND ARTHROPODS 515 Table 2 TOTAL DOSE FROM SIMULATED RADIOACTIVE FALLOUT TO THREE COMPONENTS OF THE MANAGED GRASSLAND ARTHROPOD COMMUNITY * ums BEtCL Total doses to simulant ; AP arthropod compartments, ¢ rads Sampling application, Year date weekst Soil surface Litter Grass 1968 Aug. 20 2.0 338 407 77 to 300 Sept. 10 4.9 601 645 131 to 481 Sept. 24 6.9 Tay 810 168 to 605 Oct. 30 12.0 1245 1230 262 to 922 Dec. 10 18.0 1789 1724 37 3 tOTI 295 1969 Feb. 12 27 A 2459 2232 501 to 1685 Mar. 6 30.4 2914 2744 602 to 2066 Mar22,7 33.4 3186 2991 658 to 2253 Apr. 30 38.1 3613 3378 744 to 2545 May 6 39.0 3694 3452 761 to 2601 July 1 46.9 4411 4103 907 to 3092 July 15 48.9 4592 4267 944 to 3216 Aug. 8 52.4 4910 4555 1009 to 3434 Oct. 9 61.3 5717 5288 1173 to 3987 Oct. 24 63.4 5908 5461 1212 to 4117 Nov. 26 68.1 6334 5848 1299 to 4409 Dec. 17 71.1 6606 6095 1354 to 4596 1970 Feb dt 79.1 7332 6753 1502 to 5093 Mar. 18 84.1 7786 7165 1594 to 5404 *No radiation dose was detected during seven sampling periods from Apr. 1 to June 25, 1968, prior to fallout-simulant application. tDate of final application of fallout simulant was Aug. 5, 1968. Soil component is at 0.0 cm above ground, litter component at 0.1 to 2.5 cm, and grass component at 2.6 to 32.5 cm. dij = (di;)? (3) where y = number of each taxon collected from each site dj; = species composition distance between sites 1 and | X,,; = value of taxon 1 for site 1 X1,; = value of taxon 1 for site ] The lower the value of d, the greater is the similarity between sites, and vice versa. Results of this analysis (Fig. 3) indicate a seasonal cycle in species composition. Minimums were reached during the winter months, and maximums 516 STYRON AND DODSON 5.0 r) > oc ° xt — 4.0 A = ®@ 3 n 2) ray A \ Oo ro) Zz © 3.0 os ere A wD @ . re) e ray 2 as Ne (e) 4 ie g A O \ 8° @— e@ CS rQhoe e@ ray A A e ray ie) a fo) — | Roe S ; rate 67 rN 7p) el OF 0 fife) Q = ; [eee al ae See(eeles eal | pg Be Pe ANE peta a7)o Edy et oe ut lO) [vec Uolnue tts seats ee I fon eo ee a (el fey | oS On fos (2) CP eS q 2.5 3 2-040 Ss OSes « = 05 ao 200 > ola = 1968 1969 1970 MONTH AND YEAR Fig. 3. Index of species composition dissimilarity for the control enclosure vs. the roped area (©), for the control enclosure vs. the contaminated enclosure (@), and for the roped area vs. the contaminated enclosure (4) plotted against each sampling date. The effects of changes in species composition in the enclosures is superimposed on a seasonal cycle with minimums of species composition in winter and maximums in summer. occurred during the summer months. During the winter fewer taxa are active, and the inactive taxa would not contribute to a higher index of dissimilarity. A larger number of active taxa during the summer leads to a greater possible dissimilarity between sites. This sensitive technique’® for comparison of data shows no significant or consistent change in the dissimilarity between the contaminated pen and either the control pen or the roped area. This analysis indicates that effects of fallout radiation on arthropod species composition of the grassland would not be expected below 13 rads/day delivered over a period of 19 months, a fact also demonstrated in the less rigorous analysis of variance. A likely explanation for this lack of radiation effect lies in the homeostatic mechanisms that enable the community to react to radiation stress in the same manner as to other environmental stresses.” The possibility also exists that, in the context of an entire ecosystem, populations exhibit threshold responses to ionizing radiation. Future analyses, to determine whether either of these suggestions is correct, will be directed toward describing responses of popula- tions and of the soil—litter—grass compartments of the arthropod community. RESPONSES OF SOME GRASSLAND ARTHROPODS 517 Additional insights into population responses in fallout areas have been provided by a correlative laboratory study on Folsomia species. Survival and reproductive ability of these Collembola were reduced at all 19 beta dose rates tested. The LDRs5 0/30 (dose rate estimated to kill 50% of the population in 30 days) for chronically irradiated adults was estimated by least-squares regression analysis to be 174.5 rads/hr (total dose in 30 days of 125.6 krads) and the LDR50/60 to be 38.1 rads/hr (total dose in 60 days of 54.9 krads). The effects of chronic beta radiation on fecundity rates (Fig. 4) could not have been 19,20 Of the effects of acute irradiation alone. After an anticipated from studies acute dose of ionizing radiation, fecundity rate of each population was reduced. Under chronic irradiation conditions, however, all fecundity rates were initially at control levels; but.jrates . were reduced. through time .as. doses were accumulated. Change in fecundity rates under chronic irradiation conditions must therefore be represented as the slope of a regression line rather than as a FECUNDITY, eggs/adult/day 0 20 40 60 80 100 TIME, days Fig. 4 Isometric projection of fecundity in eggs per adult per day on time in days and ?°Sr—?°Y beta—radiation dose rate for Folsomia species for continuous exposure at the indicated dose rates. The fecundity rates for each dose rate are presented as a regression on time since the fecundity of each population changed as the total doses of radiation were accumulated. 518 STYRON AND DODSON point. At dose rates greater than 5 rads/hr, fecundity rates rapidly approached zero. Egg mortality (Fig. 5) was increased by chronic dose rates above 13.5 rads/hr, and no eggs hatched at dose rates above 17.4 rads/hr. At 14.5 rads/hr, 38% of the eggs matured into adults, but all were sterile. These data demonstrate that radiosensitivity of a population of Folsomia to beta radiation is manifest primarily in the effect on fertility rates (number of 100 -@>) ——_ o2 —_ eo —__ © 80 % @ : sy 60 70 rads/hr). At the 80 60 40 20 MEAN NET % MORTALITY 2 Sune 0 ee She OS ie 5 10n 22 5 DOSE RATE, rads/hr Fig. 2 Net percent mortality after 20 days expressed as a function of dose rate for young adult crickets (Acheta domesticus) after they received about 5000 rads of gamma radiation. SURVIVAL OF CRICKETS 525 lower dose rate, mortality was significantly less (P<0.05) than that at the > for higher rates. Similar results were reported by Sievert and Forssberg*’ X irradiation of Drosophila eggs. They found that dose rates of less than 300 rads/hr were only slightly injurious to developing eggs and that doses delivered at very high intensities (>280,000 rads/hr) killed a larger proportion of eggs than did similar doses at moderate intensities. Banham® demonstrated that survival of adult flour beetles, Tribolium confusum, at 4000 rads/hr was much reduced compared with that at 2000 rads/hr for a given total gamma dose. For dose rates ranging from 1500 to 4700 rads/hr, Jefferies and Banham' reported an increase in mortality to a given total gamma dose for the grain pests Tribolium, Oryzaephilus, and Sitophilus. Fertility 1s also reduced by increasing dose rate for a given dose in Tribolium.’ McMahan® reported that both 2520 and 36,900 rads/hr resulted in increased mortality of three termite species, but the dose rate had to be high before the total dose received could produce significant differential mortality. A leveling oft wot the dose-rate-effect, curve (Fig. 2) began at’ about 200) rads/ hrs mo significant jditterences- occurred at. -the higher .dose rates (P< 0.05). This leveling off of the dose-rate-effect curve has been reported for '+6>7-9 and has led several investigators to conclude that other insect species commonly used laboratory irradiation dose rates do not vary enough to produce a significantly different radiosensitivity end point.'°°!' On the basis of the ISGL7 8 this results of the present study and on those of several earlier works, conclusion should be modified to apply only to the plateau region of the dose-rate-effect curve since significant differential radiosensitivity does occur in the lower regions of the curve. CONCLUSIONS This study indicates that, when mortality is used as a biological end point, Orthoptera may be irradiated at relatively high dose rates to achieve an effect similar to that expected from exposure to chronic fallout radiation. This is particularly true when the results of a laboratory study are applied to conditions that would exist during the first few weeks immediately following fallout deposition when the majority of the biological damage from fallout radiation would occur.'* During this time the dose rate is undergoing a rapid exponential reduction, and the range of dose rates would fall within those found not producing significantly different biological effects in laboratory studies. The primary advantage of using high dose rates in irradiation studies is that lethal exposures may be attained in short periods of time. This is an important consideration since the life-span of most arthropod species is such that accumulation of a lethal dose from fallout radiation would require several generations. The immediate effects of fallout radiation on survival of the population would not be discernible. Any effects on survival would probably show up in the F; or F2 generation. 526 VAN HOOK ACKNOWLEDGMENTS This research was sponsored by the U.S. Atomic Energy Commission and the Office of Civil Defense, Department of Defense, under contract with Union Carbide Corporation. I wish to thank Gladys J. Dodson for technical assistance during the course of this investigation. J.J. Beauchamp, Statistics Department, Mathematics Division, ORNL, assisted with the statistical analyses of the data. Portions of this study were conducted in the °° Co whole-body irradiator at the UT—AEC Agricultural Research Laboratory, Oak Ridge, Tenn. REFERENCES ike kale We D. J. Jefferies and E. J. Banham, The Effect of Dose Rate on the Response of Tribolium confusum Duv., Oryzaephilus surinamensis (L.) and Sitophilus granarius (L.) to ONCE Gamma Radiation, in The Entomology of Radiation Disinfestation of Grain, P.B. Cornwell (Ed.), pp. 177-85, Pergamon Press, Inc., New York, 1966. .E. F. Menhinick and D. A. Crossley, Jr., A Comparison of Radiation Profiles of Acheta domesticus and Tenebrio molitor, Ann. Entomol. Soc. Amer., 61(6): 1359—1365 (1968). .E. S. Deevey, Jr., Life Tables for Natural Populations of Animals, Quart. Rev. Biol., 22: ZOOS oO AT). .R. Sievert and A. Forssberg, The Time Factor in the Biological Action of X Rays, Acta Radiol ped 75 3))—5) leo): .R. Sievert and A. Forssberg, The Time Factor in Rontgen Radiations of Extremely Short Duration, Investigations on Drosophila Eggs, in Third International Congress of Radiology, Resumes des Communications, p. 263, Paris, 1931. .E. J. Banham, The Susceptibility of the Confused Flour Beetle (Tribolium confusum Duv.) to Gamma Radiation, British Report AERE-R-3888, March 1962. .K. K. Nair and G. Subramanyam, Effects of Variable Dose Rates on Radiation Damage in the Rust-Red Flour Beetle, Tribolium castaneum Herbst, in Radiation and Radioisotopes Applied to Insects of Agricultural Importance, Symposium Proceedings, Athens, Apr. 22—26, 1963, pp. 425—429, International Atomic Energy Agency, Vienna, 1963 (STI/PUB/74). . E. A. McMahan, Effects of Ionizing Radiation on Three Neotropical Termite Species, Ann. Entomol. Soc. Amer., 62(1): 120—125 (1969). .G. A. Zakladnoi, Influence of the Gamma Irradiation Dose Rate on the Lifetime of Granary Weevils, Radiobiologiya, 6(3): 199—201 (1966). .C. Packard, The Relationship Between Age and Radiosensitivity of Drosophila Eggs, Radiology, 25: 223—230 (1936). R. D. O’Brien and L. S. Wolfe, Radiation, Radioactivity, and Insects, Academic Press, Inc., New York, 1964. C. F. Miller and P. D. LaRiviere, Introduction to Long-Term Biological Effects of Nuclear War, USAEC file No. NP-16462 (SRI Report MU-5779), Stanford Research Institute, April 1966. EFFECTS OF BETA-GAMMA RADIATION OF EARTHWORMS UNDER SIMULATED-FALLOUT CONDITIONS DAVID E. REICHLE, JOHN P. WITHERSPOON, MYRON J. MITCHELL,* and CLARENCE E. STYRONT Ecological Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee ABSTRACT Experiments on Oo gamma and 70S? °F” beta radiosensitivity of Lumbricus terrestris and dosimetry models of soil systems were designed to study the effects of fallout radiation on natural earthworm populations. Epithelial tissues (skin and/or intestinal) were the primary sites for radiation damage. The LDs9/30 days for gamma was 67.8 krads; no significant increase in mortality occurred for beta irradiations up to 102.4 krads. In situ dosimetry models with 137 gs show that beta radiation is important only for direct contact (because of soil shielding) and that gamma radiation typically would contribute from 68 to 100% of the external body dose of natural populations. Habitat shielding, high radioresistance of earthworms, and radioactive decay preceding particle incorporation into soil suggest minimal population mortality due to radiation from anticipated weapon yields. The delivery of external radiation exposure dose to biological systems at specific locations in a fallout field is generally in the form of an acute or short-term dam- ' Because of the paucity of data on effects of beta dose on age phenomenon. invertebrates,” the effects of beta and gamma radiation from nuclear fallout generally had been assumed to be comparable. Recent information on contaminated-particle retention by vegetation® and contact doses from beta radiation” suggests that areas of serious damage to organisms from fallout will be larger than previously estimated from gamma radiation alone. Since fallout deposition initially tends to move toward and concentrate at the soil surface *Present address: Environmental Sciences Center, The University of Calgary, Alberta, Canada. tPresent address: Division of Mathematics and Natural Science, St. Andrews Pres- byterian College, Laurinburg, North Carolina. 527 528 REICHEER EivA through the action of meteorological factors, estimates of a total effective fallout dose® 40 times that previously considered have raised concern about the response of litter- and soil-dwelling invertebrate populations to nuclear fallout. Earthworms, a major element of the soil fauna, are important in maintaining many natural soil characteristics, e.g., aeration, water permeability, and nutrient turnover. The space occupied by earthworm burrows may account for as much as two-thirds of the air capacity of some soils, whereas a moderate-density field population (25/m*) may consume and turn over from 25 to 30 metric tons per hectare of aboveground organic-matter products.° Therefore not only could the effects of radiation on this fauna have far-reaching implications in the ecosystem but their ecology could also play a major role in the redistribution of fallout particles within the soil. The experiments described in this paper on adult Lumbricus tervestris estimated their °°Co gamma and ?°Sr—?°Y beta radio- sensitivity and the incorporation of '*”’Cs-tagged surface litter into soil profiles The effects of external fallout radiation in the natural environment were estimated from dosimetry models based on anticipated weapon yields. METHODS Adult Lumbricus terrestris with mean live weight of 3.8 g, obtained from a commercial supplier (Sterchi Bait & Tackle Co., Knoxville, Tenn.), were main- tained in damp peat moss at 5 C. Earthworms were irradiated at 5 C in groups of 10- with: three=replications ‘at each dose level: 0925265 5278, 76.8.9 and 102.4 krads for both beta and gamma irradiations. Irradiated groups of 10 animals were maintained at 5-C in 1 liter of old, damp peat moss under constant darkness. Cultures were examined thrice weekly and scored for mortality and obvious histological damage. Gamma irradiations were performed with a Gammacell 200 °° Co irradiator (Atomic Energy of Canada Ltd.) with an exposure dose rate between 8.16 and 8.11 rads/sec during the course of the experiments. Beta irradiations were administered from a ?°Sr—?°Y plaque source’ with a surface dose rate of 1.38 rads/sec (Ref. 8). Mean beta-particle energy from the source was 0.9 MeV. RESULTS AND DISCUSSION Mortality scores for irradiated animals were converted to normits’ for linear regressions. To estimate longevity of irradiated animals, we regressed the normit of percent mortality on time for each dose level. Resulting values of LTs59 (time for 50% lethality in the population) are presented in Table 1. Mean life-span for controls under culture conditions was 66 days, although no mortality occurred until day 24 of the experiments. The LT59 dropped precipitously with increasing gamma dose, the mean life-span of earthworms irradiated at 102.4 krads being only 16 days with 97.5% population mortality after 30 days. EFFECTS OF B—y RADIATION OF EARTHWORMS 529 Table 1 NORMIT ANALYSIS FOR LTs59 OF Lumbricus terrestris TO GAMMA RADIATION* Gamma Dose, rads LT>9, days Syxt r? 0 66 0.2906 0.6765 25,600 D3 0.08 37 0.9104 51,200 42 0.09 34 0.9509 76,800 38 0.1301 0.9349 102,400 16 0.2907 0.8988 *Values are based on eight 5-day sequential mortality estimates on groups of 10 earthworms replicated three times for each dose. tSy is the standard error of the estimate (Y). ns is the coefficient of determination. Table 2 NORMIT ANALYSIS FOR LDs59 OF Lumbricus terrestris TO GAMMA RADIATION* Time, days LDs 0, krads Syxt r¢ 10 147.9 0.2388 0.8000 15 124128 0.3316 0.7372 20 94.1 0.4140 0.7561 25, 83.2 0.4011 0.8191 30 67.8 0.3267 0.8278 34 61.5 0.2832 0.8191 *Values are based on five dose levels using groups of 10 earthworms replicated three times for each dose. i is the standard error of the estimate (Y). tr is the coefficient of determination. Mean lethal doses were similarly calculated by regressing the normit of percent mortality on dose for varying time end points (Table 2). The well-known time-dependent dose phenomenon was apparent; increasingly lower doses were required to effect 50% mortality (LDs 9) as the time over which the effect could be expressed increased. The LDs0/30 days was calculated to be 67.8 krads. These data suggest that Lumbricus are more radioresistant than previously reported by Hancock.’° Although Hancock’s dose rate was higher (16.7 rads/sec of X rays), his estimate of 100 krads for an LD509/35 1s higher than that found in the present study. He also found no lethal effect at 45 krads after 67 days. The radiation sensitivity of other invertebrate species comprising the soil 11-14 fauna is greater than that reported here for earthworms. 530 REICHLE ET AL. Although identical surface-air doses were administered for both beta and gamma radiation, no significant mortality was observed for beta irradiations up to 102.4 krads during the 30-day experimental period. Unlike the gamma source, the beta plaque delivered, not a “‘bath” dose, but rather a contact dose with a plane source. The mean beta-particle ranges in soft tissue would be 2.1 mm for °°v and 0.33 mm for ?°Sr. In an adult Lumbricus of approximately 5 mm diameter, over 60% of the worm and its vital internal organs would be shielded. Therefore these data are not valid for comparisons of relative biological effectiveness. When Lumbricus began to die after exposure to radiation, there was a general loss of pigment—probably protoporphyrin and protoporphyrin methyl ester’ >and an associated loss of motor response in the posterior region. Sites of radiation damage for both beta and gamma radiation were the skin epithelium (blistering) and the intestinal epithelium (necrosis). Since beta irradiations were administered from the ventral surface with a plaque source, many earthworms showed a gradation in histological damage along the dorsoventral axis (Fig. 1). Note the necrotic condition of the ventral gut epithelium (0.5 to 0.7 mm); dorsal epithelium (1.5 to 1.8 mm) does not exhibit necrosis. Similar damage to epithelial tissue was noted throughout the intestinal tract and also for the epidermis (not shown in Fig. 1). Soil and muscle shielding would reduce the effect of most low-energy beta radiations from external sources (beta bath); however, the volume of soil consumed in the digestive process and the direct contact of soil particles with the radiosensitive intestinal epithelium could be important factors in highly contaminated soil. It would take internal contamina- tion of the order of several microcuries per square centimeter to deliver acute tissue doses of the order of LDs 9 values. Dose from fallout radiation to soil dwellers such as earthworms would be much reduced by the shielding properties of soil. For example, Table 3 gives 137¢Cs5 in four beta and gamma exposure rates at various soil depths from different geometries. It was assumed that the activity was evenly dispersed in a 100-m? surface area of 0, 5, 10, and 20cm tthickness. A soil density of 1.46 g/em* was used to calculate dose rate. In a true fallout situation, initial activity would be on the soil surface. This would be followed by an exponential decrease in dose rate with depth as soluble radionuclides and particles became redistributed in the mineral soil. Thus soil-dwelling organisms below 5 to 10 cm would be exposed to less radiation than if the activity were evenly distributed through a given soil thickness with the organisms in the middle of this “‘slab source.” On the basis of calculations for PK Gt about 743 Ci/m* would have to be deposited on the soil surface to deliver 67.8 krads (the LDs59/30) in 24 hr to earthworms located 1 cm below the surface. Every additional 5.5 to 8.5 cm of depth (depending on soil moisture) would represent a tenth value layer and thus would afford more shielding for worms below the 1-cm depth. EFFECTS OF B—y RADIATION OF EARTHWORMS 531 Fig. 1 Tissue necrosis 11 days postirradiation in the earthworm Lumbricus terrestris resulting from beta irradiation (51.2 krads ventral surface dose). vc, ventral nerve cord; vge, ventral gut epithelium; gl, gut lumen; dge, dorsal gut epithelium. Photograph is a transverse section in the region of the posterior pharynx. (Magnification, 82 x) Table 4, calculated from data reported by Wong,” gives estimated infinity doses of gamma and beta radiation from fallout on the soil surface following a 10-Mt weapon burst. Gamma doses between the 1000- and 2000-rad exposure- rate contours (rads/hr at 1 hr) are well below LDs5 9 values for earthworms. Although the contact beta doses for these areas are above LDs5o values, shielding by 1 cm of soil should essentially reduce the beta dose to zero. 532 REICHLE Et AL. Table 3 EXPOSURE DOSE RATES IN SOIL FROM LCs IN DIFFERENT GEOMETRIES Distribution of activity Depth % of d Surface area, Depth, Source for exposure, Dose rate, ores m? cm geometry cm mrad/hr/Ci Gamma Beta 100 O Plane 1.0 38 100.0 O 100 Oto 5 Slab DS 84 68.7 SilieS 100 Oto 10 Slab 520 61 78.4 2.6 100 Oto 20 Slab 10.0 33 80.3 ORT. Table 4 APPROXIMATE INFINITY BETA AND GAMMA DOSES AT GROUND-SURFACE CONTACT RESULTING FROM A 10-MT WEAPON BURST WITH 50% FISSION YIELD* Exposure-rate Infinity contour, Area within Infinity beta dose rads/hr contour, gamma dose,t at contact, at 1 hr sq miles rads rads 1 46x10" 4.6 1.4 x 10? 10 D5 x 110" 4.6 x10! GI 10> 50 1.4x 10° Dex 105 8.9 x 10° 100 01x 10" 4.6 x 107 1.9 x 107 200 6.7 x 10° 9.3.x 10° All x AOn 500 3.8x 10° 23x 10> lstexato™ 1000 20x 105 4.6 x 10° D6 x 108 2000 TB AOn 9.3x 10° 6.0 x 10° : sc 4 *Data are recalculated from the original source. t+Tissue dose. Thus it seems reasonable that large-scale lethal effects on adult earthworms would not be expected as a consequence of detonations of nuclear devices. Other stages of the earthworm’s life history may, however, be more radio- sensitive. If we assume that 10% of the LDs9 dose may affect reproductive stages of a population, then fallout radiation doses and radioactivity values discussed here could be ecologically significant. The degree of significance would depend on the proportion of the total population represented by more radiosensitive stages and the soil depth in which they characteristically reside. Egg stages, for example, are immobile and tend to reside at a fixed soil depth. After fallout radiation levels have decayed to a small fraction of the initial dose rates, earthworms may be important in distributing activity through soil. They would come into intimate contact with particles at this time, but dose to EFFECTS OF B—y RADIATION OF EARTHWORMS 533 organisms from external and internal sources would be small due to time and decay factors. Time required for turnover of topsoil in the 0 to 10 cm horizon due to the activity of earthworms has been estimated to range from 20 to 60 years, depending on habitat type.° Thus the role of earthworms in the incorporation of a surface deposition of fallout would not appear to exceed other biotic and physical mechanisms. However, if the radioactive material should become associated with organic debris, earthworm activity could be significant. The quantity of organic material eaten or buried by earthworms is often limited solely by availability, rather than their ability to ingest it.° In laboratory experiments Lumbricus terrestris rapidly consumed forest leaf litter. At a density of 120g live weight/dm’, worms completely removed 40 g of litter tagged with '?’Cs from the surface within 1 month. The associated }*7Cs was detectable to depths of 45 cm, highest concentrations occurring in the 15- to 30-cm zone. Since the various earthworm genera may be active to considerable depths in soil (0 to 25 cm for Allobophora, 0 to 50 cm for Octolasium, and up to 100 cm for Lumbricus), these animals could be important in the rapid mixing of fallout particles within soil horizons. CONCLUSIONS Earthworms appear to be among the least radiosensitive of the invertebrate organisms comprising the soil fauna. The LDs5o/39 for gamma radiation was 67.8 krads. No significant increases in mortality occurred at beta doses below 102.4 krads, probably because of muscle shielding from the external radiation field. In a natural situation with nuclear fallout deposition on the soil surface, earthworms would be substantially shielded from beta radiation and from a large portion of the gamma radiation. Even with subsequent mixing of fallout particles with soil, beta radiation would be significant only for direct contact and internal dose from absorbed radionuclides. Both intestinal and skin epithelia would receive gamma radiation and would be in physical contact with low-energy beta radiations and the abrasive action of soil particles. The time required for such mixing is long, even if earthworms are involved. Decay of fission products over this time would greatly reduce the quantities of radioactivity available for external or internal irradiation of the organisms. The high radioresistance of earthworms to both gamma and beta radiation indicates that there would be minimal population mortality due to radiation from anticipated weapons yields. Although immediate mortality would not be expected for adult earthworms at these fallout doses, this does not preclude the possibility of effects on juveniles or other population parameters such as fecundity, fertility, or other genetic responses. Generally, however, the soil fauna seem to be well shielded from the short-lived components of nuclear fallout radiation. 534 REICHEE ERA ACKNOWLEDGMENTS This research was sponsored by the Office of Civil Defense, Department of Defense, and the U.S. Atomic Energy Commission under contract with the Union Carbide Corporation. We are indebted to our colleagues F. G. Taylor and M. H. Shanks for assistance during the course of these experiments. RE iit iw) 14. 152 FERENCES C. F. Miller and P. D. LaRiviere, Introduction to Long-Term Biological Effects of Nuclear War, USAEC file No. NP-16462 (SRI Report MU-5779), Stanford Research Institute, April 1966. .J. D. Teresi and C. L. Newcombe, An Estimate of the Effects of Fallout Beta Radiation on Insects and Associated Invertebrates, Report AD-633024 (USNRDL-TR-982), Naval Radiological DefensesaLaboratory, Feb. 28, 1966. . J. P. Witherspoon and F. G. Taylor, Jr., Interception and Retention of a Simulated Fallout by Agricultural Plants, Health Phys., 19: 493—499 (1970). .P. W. Wong, Initial Study of the Effects of Fallout Radiation on Simple Selected Ecosystems, Report USNRDL-TR-68-11, Naval Radiological Defense Laboratory, 1967. . A. Broido and J. D. Teresi, Analysis of the Hazards Associated with Radioactive Fallout Material. I. Estimation of y and 6 Doses, Health Phys., 5: 63—69 (1961). . J. E. Satchell, Lumbricidae, in Soil Biology, A. Burges and F. Raw (Eds.), pp. 259—322, Academic Press, Inc., New York, 1967. _E. F. Menhinick, ?°Sr Plaques for Beta Radiation Studies, Health Phys., 12: 973—979 (1966). o Jp dé. Roti, Roticand SV. Kaye. Galibration: of race 20M, Plaques for Irradiating Insects, USAEC Report ORNL-TM-1921, Oak Ridge National Laboratory, July 18, 1967. . J. Berkson, Estimate of the Integrated Normal Curve by Minimum Normit Chi-Square with Particle Reference to Bio-Assay, J. Amer. Statist. Ass., 50: 529—549 (1950). +R} Lb. ‘Hancock, Lethal Doses of Irradiation for Lumbricus Life, Sci. Vi 625-628 (1962). .S. 1. Auerbach, D. A. Crossley, Jr., and M. D. Engelman, Effects of Gamma Radiation on Collembola Population Growth, Science, 126: 614 (1957). .R. V. O'Neill and C. E. Styron, Applications of Compartment Modeling Techniques to Collembola Population Studies, Amer. Midland Natur., 83: 489—495 (1970). .D. E. Reichle and R. I. Van Hook, Jr., Effect of Temperature and Radiation Stresses on the Survivorship of Isopods: Armadillidium vulgare and Cylisticus convexus, Radiat. Res., 1n preparation. C. A. Edwards, Effects of Gamma Irradiation on Populations of Soil Invertebrates, in Symposium on Radioecology, May 15—17, 1967, Ann Arbor, Mich., D. J. Nelson and F.C. Evans (Eds.), USAEC Report CONF-670503, pp. 68—77, AEC Division of Biology and Medicine and Ecological Society of America, March 1969. M. S. Laverack, The Physiology of Earthworms, pp. 10—11, Pergamon Press, Inc., New York, 1963. CESIUM-137 ACCUMULATION, DOSIMETRY, AND RADIATION EFFECTS IN COTTON RATS D. DIGREGORIO, P. B. DUNAWAY, J. D. STORY, and J. T. KITCHINGS III* Ecological Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee ABSTRACT Cesium-137 accumulation, dosimetry, and radiation effects were determined in cotton rats 3 Cs-labeled sand. Cesium-137 levels were relatively high 6 months after application of the fallout simulant but living in their natural environment, which was contaminated with decreased as the simulant descended from the vegetation toward the ground. Radioactivity levels in organs and tissues, in general, paralleled those of the whole body. Dose rate to cotton rats paralleled radioactivity levels in the whole body. No effects on peripheral blood or body weight due to irradiation were observed in this study. In natural environments contaminated by nuclear fallout debris, mammals receive both external and internal radiation, the latter resulting primarily from ingestion of contaminated food and fallout particles. Both internal and external radiation must be considered in determining the total dose the animal will receive. Radionuclide accumulation is important because it causes tissue irradiation in the individual animal and because each animal occupies a role in the food chain and 1s eventually a contaminated food source. One of the major radionuclides in fallout is '*7’Cs. Many studies of radionuclide cycling have demonstrated that wild mammals readily accumulate radiocesium.' > Movement of radiocesium in the food chain was demonstrated by Hanson, Palmer, and Griffin; Pendelton et al.;> and Jenkins, Monroe, and Golley,! who showed that predators accumulated more '* Cs than did their po- tential prey in the same geographical area, thus showing increasing '* 7 Cs con- centration at the secondary consumer levels of the food chain. Therefore, in ad- dition to evaluating internal dose, we must determine total radionuclide *Present address: Quality Control Department, Hardee Food Products, Cedartown, Georgia. 535 536 DIGREGORIO ET AL. accumulation to predict both transfer in food chains and concentration at higher trophic levels. Information concerning effects of acute and chronic irradiation on caged animals is abundant.° > Accumulation and excretion of radiocesium have also - . . - . — 2) been studied in great detail in caged animals and human volunteers.’ }? 1637 : ae : eee Cs accumulation and effects of chronic internal and external However, irradiation in mammals living in natural environments have seldom been investigated under replicated conditions. This paper presents results of a study to determine effects and degree of 137s accumulation in cotton rats (Sigmodon hispidus) living in outside enclosures contaminated with '*7Cs-labeled sand. Of primary concern were measurements of in vivo dosimetry, whole-body radio- activity, radioactivity of internal organs and tissues, radioactivity of gastro- intestinal contents, and effects on the hemopoietic system. MATERIALS AND METHODS Study Area In 1968 eight 100-m* enclosures were constructed in an existing fescue (Festuca arundinacea) community on the U.S. Atomic Energy Commission reservation, Oak Ridge, Roane County, Tenn. Each enclosure was constructed with steel sheeting buried 18 in. and standing 24 in. above ground. Geological, soil, floral, and climatological data of the area have been summarized ; 13 previously. In August 1968 four of the eight enclosures were contaminated with '*’Cs-labeled silica sand particles (particle diameter, 88 to 177 Ml) at a mass load of 72 g/m’; this gave a radioactivity level of 2.2 Ci per enclosure. Details of the fallout-simulant characteristics and application have been described earlier.’* Our study was conducted in four enclosures (two contaminated and two control) during the period from December 1968 to April 1970. The sides of each enclosure were topped with an electrically charged wire to contain rodents and repel nonavian predators, and each enclosure was covered with a nylon net to preclude avian predation. Experimental Procedure Adult, laboratory-born cotton rats were used in this study. Two weeks before being placed in the enclosures, each rat was weighed and bled to determine preexperimental values. Our hematological methods are described in detail elsewhere.’° Three to four days before rats were placed in the enclosures, two glass-rod dosimeters encased in nylon capsules were injected subcutaneously (one dorsally and one ventrally) in each rat according to the method of Kaye.’ ° Four animals were released into each enclosure at various times during the year and were trapped 30 days later. Sexes were kept in separate contaminated and control enclosures. In the spring and fall of 1969, half the animals trapped CESIUM-137 IN COTTON RATS bo/ at the 30-day sample were re-released into the enclosures to be recaptured for a 60-day sample. At time of capture all animals were weighed and then assayed for whole-body radioactivity in a Packard Instrument Co. Armac liquid scintillation detector, and the dosimeters were removed. Internal organs (heart, liver, spleen, and kidneys) of the radioactive rats were weighed and counted for radioactivity in the whole-body counter. The gastrointestinal (GI) tract was excised from the terminal end of the esophagus to the anus and separated into its four components: stomach, small intestine, cecum, and large intestine. These components were cleared of contents with 1N sodium acetate buffer solution, weighed, and counted for radioactivity. Gastrointestinal contents were assumed to be comprised of two components, fallout simulant and organic matter, and separation of contents was based on this assumption. Contents of each GI component were triturated and washed with 30% hydrogen peroxide. Organic matter rose to the top of the hydrogen peroxide, and fallout simulant settled to the bottom. Both fallout simulant anc organic matter were then counted as described. Total in vivo gamma dosimetry from both internal and external sources was determined with Toshiba low-Z glass rods (1 by 6 mm) read on a Toshiba fluoro glass dosimeter, type FGD-38, using National Bureau of Standards standards. Internal beta dose rate (rads/day) was determined from our data by the method of Hine and Brownell,’ ” by using the beta and electron mean energies and mean number per disintegration from Dillman.'® It was assumed that the range of beta particles was small relative to dimensions of the cotton rat; therefore beta energy was assumed to be completely absorbed.'? Gamma-ray dose rate (rads/day) was calculated from the equation Da, > 21 2CR, (1) where D. = gamma-ray dose rate 51.2 = dis/day X g-rad/MeV C = isotope concentration (UCi/g) E, = total gamma + X-ray energies 8 and absorbed fractions for Photon energies were determined from Dillman,’ photon sources were determined for a mass of about 118 g by using the data of Snyder. ect al.27° For both internal beta- and gamma-dose-rate calculations, uniformly distributed isotope was assumed. RESULTS AND DISCUSSION Dosimetry The major contribution to whole-body total dose rate was from external gamma irradiation. Amounts of external and internal irradiation contributing to DIGREGORIO ET AL. 538 91 b0'0 c'O ¢00'O 186 LESEC COT 9 OL6T [udy oT +00 (anv) S000 0'86 6£ °C thc € OL6t Asenur f BE 60°O SO 7100 S°S6 PE? St’? b 696T J9QUIDAON bc 90°0 £°O 800°0 Cc L6 Ipc 8b? v 696T 4990190 6'S 910 8°0 1z0°0 b'£6 bS°7 CLG 9 6961 Ainf L's 81° 80 $Z0'0 L°€6 S67 Sie b 6961 APW VUr 8£°O Sail TSo'O 688 bO'E Cre c 6961 [adv LaCN 9¢°0 LN ¢Z0°0 S°S8 LEE Itt c 6961 Asensqay} [#102 Jo % Aep/spei [2302 Jo % Aep/spei [#102 Jo % Aep/spei Aep/spei po, dues poiiod ajdwues ‘97¥1 aSOp ‘9181 ISOp ‘9281 aSOp ‘(vI9q + PWS) syeuiue B19q [eUujDIU] NOILVIGVUAT VLA TVNYALNI GNV VWWV)D JIVNYALXYH GNV TVNYALNI FO NOLLAETYLNOO eulues ;eusIaU] BWUWIeS [VUIDIX |] 3181 SSOP [VI0 |, ALVad ASOd AGOP-HIOHM IVLOL HHL OL T 919®L jo Jaquinyy CESIUM-137 IN COTTON RATS 059 whole-body total dose rate and to Gl-tract total dose rate are shown in Tables 1 and 2. Internal beta irradiation contributed more to both the whole-body and the Gl-tract total dose rates than did internal gamma irradiation because the size of the cotton rat permitted complete absorption of the beta energy but considerably less of the gamma. During the early months of the investigation, Table 2 CONTRIBUTION OF GI-CONTENTS GAMMA AND BETA IRRADIATION TO TOTAL GI-TRACT DOSE RATE* Number of Total dose rate Internal beta Internal gamma animals (gamma + beta), dose rate, dose rate, Sample period sampled rads/day rads/day rads/day February 1969 2 0.805 0.71 0.095 April 1969 2 O.555 0.49 0.065 May 1969 4 0.249 O22 0.029 July 1969 6 0.103 0.09 0.013 October 1969 4 O;245 0.19 0.025 November 1969 4 O81 0.16 0.0241 January 1970 3 0.068 0.06 0.008 April 1970 6 O13 0.10 0.013 *Beta contribution was 88.3% of the total and gamma contribution 11.7%. internal beta- and gamma-irradiation contribution to the total whole-body dose rate was 12.7 and 1.7%, respectively, whereas the external gamma contribution “| was 85.5%. Later, however, when KS Cs intake by the animals was reduced (see discussion in the following paragraphs), internal beta and gamma irradiation contributed only 1.6 and 0.2%, respectively, to the total whole-body dose rate, whereas the external gamma contribution was 98.1%. It appears that internal beta irradiation 1s of more consequence early after fallout arrival than it is later. Average gamma dose rates from both external and internal sources in cotton rats ranged from 3.84 rads/day in February 1969 to 2.35 rads/day in November 1969 (Fig. 1). Regression analysis showed that from February to July the dose rates decreased 0.008 rad/day per day but from July to April 1970 there was no significant change. The initial decrease in dose rate probably was caused by changing geometry of the radiation fields in pens as the fallout simulant descended through the vegetation to the ground. Most of the fallout simulant 1s now on the ground, forming an irregular plane source and resulting in a relatively stable dose rate of approximately 2.46 rads/day. Radioactivity Radioactivity in cotton rats is shown in Fig. 2. The four measurements (whole body, total tissue, organic matter, and fallout simulant), in general, 540 DIGREGORIO ET AL. 4.5 a fe) is?) D m7 ze C5325 in < re 3:0 LW Y O O 2.5 2.0 : ® id ~ . o . Go 8 bec @e JS vSis Ss ov eerie, es aa Sy Bl et eS SS a One eee Olli foe cei 1968 1969 1970 Fig. 1 Gamma dose rate to cotton rats living in ‘37 Cs-contaminated enclosures from February 1969 to April 1970. e, means of dorsal and ventral dosimeters. Vertical lines represent standard error of the mean, and absence of vertical lines denotes standard error too small to plot. oO, Whole body = 4, Whole body without gastrointestinal contents Ss A e, Organic matter in gastrointestinal tract Sa 4, Fallout simulant in gastrointestinal tract E 2 fe Q k- O < r 2 n Q ~ 7 Cs equilibrium by 30 days and that gain or loss would be negligible for an additional 30 days. Radioactivity in the rats was contained mostly in the residual carcass (Fig. 3). The two major compartments of residual carcass are muscles and skeleton, which comprised about 49 and 7%, respectively, of total body wet weight.” 7 It is well established that '°7 larger amounts than in any other mammalian tissue.”’??"?* The data in Table 3 support these findings. Pelt, which includes skin and hair, accounted for 8.9% of Cs is accumulated in muscle in much the whole-body radioactivity. In terms of weight most of the pelt is muscle. Because of both tissue specificity for '?7Cs and amount of muscle in the mammalian body, it is apparent that most of the body burden was contained in muscle. Average radioactivity in cotton-rat Gl-tract contents was 27% of the whole-body radioactivity. Of the total amount of radioactivity in the GI contents, 79% was in organic matter and 20.9% was in fallout simulant. The radioactivity contribution of fallout simulant in the early part of the experiment was approximately 10 times that in April 1970, our last sample period. Weathering caused leaching of }*7Cs from the fallout simulant into the native soil and onto the plants. Also, the simulant is becoming mixed with the soil. Consequently '*7Cs is still present, but it is not so readily ingestible in the form of fallout simulant. With increasing time vegetation radioactivity will reflect radioactivity levels in the soil; therefore future body burdens of herbivores and saprovores living in the contaminated areas will reflect '*’Cs levels in living and dead vegetation. Radiation Effects We saw no effects of the }*’Cs radiation on either body weight or peripheral blood of cotton rats. Any slight changes in body weight or general blood measurements probably were results of seasonal variations in the general environment since similar measurements were obtained for both control and experimental animals. For cotton rats general environmental fluctuations may be of more immediate consequence than low-level irradiation. Previous studies with cotton rats showed that relatively high acute doses of radiation were required to affect body weight® and blood.** In January 1970 our animals were exposed to 90) Tt Ke) "S}RUIIUR TE JO IYSIOM URdUI IIe saNn[eA , I8'rs 7E00'0 0900°0 €0TO'O ¢S00'0 cECO O LOEO'O 89L0°0 FSOTO aposnyw LST6LI 8100°0 LT00'0 O£00°0 €€00°0 T800°0 0800'0 ¢¢$c0'0 L0cO'0 42d 661€ T +4000°0 6c00 0 6c00 0 6Z00'°0 OcIO 0 €€TOO Ort0'0 bEbO'O 3UTIS92UI ase] NOILVLH9O4A ANV INV TOWIS LNOTITVA GALVNINVINOD-SD FETI'T €000°0 9700°0 T£00'0 ¢£00'0 OcTO'O 9¢T0'O 8ITE00 O1TSO'O uinday O89t'C 9000'0 T€00°0 8£00°0 L€00°0 S900 ra ROO) T9E€0'0 +6S0°0 3UI}S92UI TTeurs 686c I +000°0 €€00°0 8€00°0 9€00°0 CLIO 0 007¢0°0 00S0°0 S£90°0 yoeulors cIvO T bLLO'0 43 ‘2YSI9 M4 19M 0c00'0 6£00°0 £900°0 £900°0 6€TO'O L9T0°0 6L+0'0 £8+0°0 +000'0 TcO00'O TOTO'O TZ00°0 F9TO'O CeST0 L8ST 0 C840 0 R/T ‘AWADIVOIpEY Aouply uaajds € 1921 ErPS6 TT00'O cc00'0 9€00°0 9€00'°0 £900°0 6800°0 cOcO'0 6¢70 0 JOAVT Let sets'o Z000'0 6c00°0 $+00°0 £900'0 cTtoo cr to 0 L9S0°0 1I9E00 ed P20 TE00°O 0£00°0 8900°0 9+00'0 bc710'0 E¢>1O'O 86c0 0 T¢+0'0 Apoq s}OUM T€ CN Si NO SE Se: NO pa|dures sjeuiue jo Joquiny HO NOILSHONI OINOYHO HAO SAV 09 OL OF MALAV SANSSIL GNV SNVOYO LVY-NOLLOO AO LHDIHM GNV ALIAILOVOICVY OL6I [Udy OL6I Asenuel 6961 J9QUISAON 696T 41990190 6961 A[nf 6961 ABW 6961 Judy 6961 Aieniqa4 potiad ajdures 544 DIGREGORIO ET AL. several days of 0 F temperatures and precipitation. After 30 days, only three of eight experimental animals and two of eight control animals were recovered alive. Dunaway and Kaye’® reported similar mortality in free-ranging cotton rats during cold weather. Percent recovery during the present study was considerably higher in favorable weather. Ecological Significance The degree of internal exposure from '*7 Cs is determined ultimately by the quantity of isotope in the diet,”’ its absorption, and its turnover rate. If '*7Cs enters the diet primarilv through material deposited on vegetation, internal dose will be proportional to retention of the fallout. If, however, the isotope 1s incorporated predominantly through the root systems of plants, the dose will be proportional to the total amount of isotope in the soil. Our results support these contentions in part. Tables 1 and 2 and Fig. 2 show the decreasing dose rate with decreasing internal radioactivity as the fallout simulant descends to the ground Regardless of the mechanism of incorporation of radioisotope, one of the major consequences of fallout is the creation of a contaminated food source in the food chain. Results of a study with one herbivore, the cotten rat, are presented in this paper, but contamination transfer in the ecosystem will not cease at the vegetation—cotton rat link in the food chain. Jenkins, Monroe, and Golley’ determined trophic-level-increase ratios for the predator—prey relation involving the gray fox and the cotton rat to be 2.0 and 5.6, the latter determined from an area with “a general lack of potassium.” Similarly, from their data, increase ratios for the bobcat—cotton rat relation can be determined as 6.9 and 18.7, the latter again being from the area low in potassium. Analysis of soil in our area indicated no lack of potassium.**® Since the same predator—prey relations of gray fox—cotton rat and bobcat—cotton rat presumably exist in and around Oak Ridge, contamination levels can be predicted for the gray fox and the bobcat by using the increase ratio of 2.0 and 6.9, respectively. In February 1969, when radioactivity in cotton rats was highest (0.04 uCi/g), radioactivity in gray foxes and bobcats would have been about 0.08 and 0.28 uCi/g, respectively. In November 1969, when cotton-rat radioactivity was lowest (0.007 uCi/g), radioactivity in gray foxes and bobcats would have been about 0.014 and 0.048 uCi/g, respectively. During November 1969 a 7000-g gray fox could accumulate 98 wCi, and a 7000-g bobcat could accumulate 336 MCi (0.336 mC1) The body burden for the bobcat would therefore be approximately 112 times greater than the maximum permissible body burden allowed for man under 29 occupational conditions and even greater than that for man in the nonoccupational category. CONCLUSIONS Our results indicate that, for cotton rats in situations similar to ours, we could expect the following: CESIUM-137 IN COTTON RATS 545 1. Within a 30- or 60-day time period, neither weight nor blood will be appreciably affected by chronic low-level radiation (2.44 to 4.41 rads/day) from '37Cs. Changes in these measurements will be caused by changes in environmental factors, such as temperature. 2. Radioactivity levels for whole body, tissues, and GI contents will, in general, parallel each other. Approximately 1 year after fallout arrives, whole- body radioactivity will be only about one-tenth that of early levels but will remain at this lower level for a long period, perhaps years. 3. Such internal organs as heart, liver, spleen, and kidneys will accumulate a relatively small amount of '*7Cs. 4. Most of the accumulated '*7Cs in tissue will be in muscle because of the relatively high affinity of '*7Cs for muscle and the large proportion of muscle in the body. 5. For the first 6 to 12 months after arrival of fallout, dose rate will decrease rather sharply. After this initial decrease equilibrium will be reached and dose rate decrease will be negligible. 6. Although there may be seasonal fluctuations in dosimetry and whole-body radioactivity levels, they will probably be slight. ACKNOWLEDGMENTS mhiseresearch was sponsored by the Office of Civil Defense and the U.S: Atomic Energy Commission under contract with the Union Carbide Corpora- tion. We gratefully acknowledge the competent assistance of our colleague L. E. Tucker, without whose help this investigation would have been very laborious. Special gratitude is expressed to W.S. Snyder and Mary R. Ford of the Health Physics Division, Oak Ridge National Laboratory, for their help with internal- dose calculations. REFERENCES Poche wyenkins. J Ro Monroe, sand F." B. ‘Golley, Comparison. of— Fallout Pes Accumulation and Excretion in Certain Southeastern Mammals, in Symposium on Radioecology, May 15—17, 1967, Ann Arbor, Mich., D.J. Nelson and F.C. Evans (Eds?) "USAE@) Report (CONF -670503, ‘pp. 623-626, AEC’ Division of Biology and Medicine and Ecological Society of America, March 1969. ZG or UimmMer dl). Me Pullen, |r, and bE Provost, Cesium-137 ‘andva Population of Georgia White-Tailed Deer, in Symposium on Radioecology, May 15—17, 1967, Ann Arbor, Mich. D. J. (Nelson and F.C. Evans (Eds.), USAEC Report CONF-670503, pp. 609-615, AEC Division of Biology and Medicine and Ecological Society of America, March 1969. 3.S. V. Kaye and P. B. Dunaway, Estimation of Dose Rate and Equilibrium State from Bioaccumulation of Radionuclides by Mammals, in Radioecology, Proceedings of the First National Symposium, Sept. 10—15, 1961, Fort Collins, Colo., V. Schultz and 546 DIGREGORIO ET AL. 10. i 122 13% 14. PS: 20. Zale A.W. Klement, Jr. (Eds.), pp. 77—111, Reinhold Publishing Corporation, New York, 1963. .W. C. Hanson, H. E. Palmer, and B. I. Griffin, Radioactivity in Northern Alaskan Eskimos and Their Foods, Summer 1962, Health Phys., 10: 421—429 (1964). .R. C. Pendelton, C. W. Mays, R. D. Lloyd, and B. W. Church, A Trophic Level Effect on 137s Concentration, Health Phys., 11: 1503—1510 (1965). .V. P. Bond et al., Mammalian Radiation Lethality: A Disturbance in Cellular Kinetics, pp. 106—110, Academic Press, Inc., New York, 1965. .E. H. Betz, Chronic Radiation Effects: Damage of Hematopoiesis, in Nuclear Hematology, E. Szirmai (Ed.), pp. 357—377, Academic Press, Inc., New York, 1965. .P. B. Dunaway, L. L. Lewis, J. D. Story, J. A. Payne, and J. M. Inglis, Radiation Effects in the Soricidae, Cricetidae, and Muridae, in Symposium on Radioecology, May 15—17, 1967, Ann Arbor, Mich., D.J. Nelson and F.C. Evans (Eds.), USAEC Report CONF-670503, pp. 173-184, AEC Division of Biology and Medicine and Ecological Society of America, March 1969. .S. L. Hood and C. L. Comar, Metabolism of Cesium-137 in Rats and Farm Animals, Arch. Biochem. Biopbys., 45(2): 423—433 (1953). G. V. LeRoy, J. H. Rust, and R. J. Hasterlik, The Consequences of Ingestion by Man of Real and Simulated Fallout, USAEC Report ACRH-102, Argonne Cancer Research Hospital. T. E. Hakonson and F. W. Whicker, Uptake and Elimination of nee by Mule Deer, in Symposium on Radioecology, May 15—17, 1967, Ann Arbor, Mich., D. J. Nelson and F.C. Evans (Eds.), USAEC Report CONF-670503, pp. 616—622, AEC Division of Biology and Medicine and Ecological Society of America, March 1969. J. T. Kitchings III, P. B. Dunaway, and J. D. Story, Uptake and Excretion of ieGs from Fallout Simulant and Vegetation by Cotton Rats, Health Phys., 17: 265—277 GEOG). J. M. Kelly, P. A. Opstrup, J. S. Olson, S. I. Auerbach, and G. M. Van Dyne, Models of Seasonal Primary Productivity in Eastern Tennessee Festuca and Andropogon eco- systems, USAEC Report ORNL-4310, Oak Ridge National Laboratory, June 1969. R. C. DahIman, S. I. Auerbach, and P. B. Dunaway, Behavior of 137 Cs-Tagged Particles in a Fescue Meadow, in Environmental Contamination by Radioactive Materials, Seminar Proceedings, Vienna, 1969, pp.153—165, International Atomic Energy Agency, Vienna, 1969 (STI/PUB/226). L. L. Lewis and P. B. Dunaway, Techniques for Hematological Studies of Wild Mammals, USAEC Report ORNL-3806, Oak Ridge National Laboratory, June 1965. .S. V. Kaye, Use of Miniature Glass Rod Dosimeters in Radiation Ecology, Ecology, 46(1 and 2): 201—206 (1965). .G. J. Hine and G. L. Brownell (Eds.), Radiation Dosimetry, p. 824, Academic Press, Inc., New York, 1956. .L. T. Dillman, Radionuclide Decay Schemes and Nuclear Parameters for Use in Radiation-Dose Estimates, J. Nucl. Med., 10(Suppl. No. 2): 7—32 (1969). .H. L. Fisher, Jr., and W. S. Snyder, Variation of Dose Delivered by 137Cs5 as a Function of Body Size from Infancy to Adulthood, in Health Physics Division Annual Progress Report for Period Ending July 31, 1966, USAEC Report ORNL-4007, pp. 221—228, Oak Ridge National Laboratory, October 1966. W. S. Snyder, M. R. Ford, G. G. Warner, and H. L. Fisher, Jr., Estimates of Absorbed Fractions for Monoenergetic Photon Sources Uniformly Distributed in Various Organs of a Heterogeneous Phantom, J. Nucl. Med., 10(Suppl. No. 3): 7-52 (1969). P. B. Dunaway, J. T. Kitchings III, J. D. Story, and L. E. Tucker, Mammal Studies in Field Enclosures, in Health Physics Division Annual Progress Report for Period Ending 22% 72 2) 24. 2s 26. Di 28. paoks CESIUM-137 IN COTTON RATS 547 July 31, 1969, USAEC Report ORNL-4446, pp. 48—50, Oak Ridge National Labora- tory, October 1969. T. P. O’Farrell, S. I. Auerbach, and P. B. Dunaway, Incorporation of a Thymidine Analog by Indigenous Rodents, USAEC Report ORNL-3907, Oak Ridge National Laboratory, March 1966. J. G. Hamilton, The Metabolism of Fission Products and the Heaviest Elements, Radiology, 49: 325—343 (1947). J. G. Kereiakes, D. D. Ulmer, A. T. Krebs, and T. D. Sterling, Cesium-137 Retention and Distribution in X-Irradiated Rats, Report AMRL-504, U.S. Army Medical Research Laboratory, Sept. 4, 1961. J. T. Kitchings HI, P. B. Dunaway, and J. D. Story, Blood Changes in Irradiated Cotton Rats and Rice Rats, Radiat. Res., 42(2): 331—352 (1970). P. B. Dunaway and S. V. Kaye, Cotton Rat Mortality During Severe Winter, J. Mamm., 42(2): 265-268 (1961). Samuel Glasstone (Ed.), The Effects of Nuclear Weapons, USAEC Report ACCESS-127, pp. 611—612, Defense Atomic Support Agency, 1962. R. C. DahIman, Ecological Sciences Division, Oak Ridge National Laboratory, personal communication, 1970. Recommendations of International Commission on Radiological Protection, Report of Committee II on Permissible Dose for Internal Radiation, ICRP Publication 2, 1959. THE SIGNIFICANCE OF LONG-LIVED NUCLIDES AFTER A NUCLEAR WAR R. SCOTT RUSSELL, B. O. BARTLETT, and R. S. BRUCE Agricultural Research Council, Letcombe Laboratory, Wantage, Berkshire, England ABSTRACT The radiation doses from the long-lived nuclides ?°Sr and '*7Cs, to which the surviving population might be exposed after a nuclear war, are considered using a new evaluation of the transfer of ?° Sr into food chains. As an example, it is estimated that, in an area where the initial deposit of near-in fallout delivered 100 R/hr at 1 hr and there was subsequent worldwide fallout from 5000 Mt of fission, the dose commitment would be about 2 rads to the bone marrow of the population and 1 rad to the whole body. Worldwide fallout would be responsible for the major part of these doses. In view of the possible magnitude of the doses from long-lived nuclides, the small degree of protection that could be provided against them, and the considerable strain any such attempt would impose on the resources of the community, it seems unrealistic to consider remedial measures against doses of this magnitude. Civil-defense measures should be directed at mitigating the considerably higher doses that short-lived nuclides would cause in the early period. It is now widely recognized that long-lived fission products would make a negligible contribution to the radiation exposure of the population in heavily contaminated areas shortly after a nuclear attack. The external radiation dose would usually be dominant, and, if simple precautions were taken to avoid the superficial contamination of foodstuffs, the entry of '*"I into milk would cause the only important problem of dietary contamination. Thus, for example, infants probably would not receive doses of more than 0.1 rad to bone marrow from ?°Sr nor more than 0.01 rad from '*7Cs in the weeks after a nuclear attack if they were fed continuously with milk produced in an area where the external dose rate at 1 hr after detonation had been 100 R/hr. Doses to the '>"T might, however, exceed 200 rads.' Considerably higher doses from dietary contamination were expected until it became evident that the thyroid from 548 SIGNIFICANCE OF LONG-LIVED NUCLIDES 549 physical properties of near-in fallout much reduce the entry of radioactivity into food chains. In more lightly contaminated areas, especially where deposition does not occur for many hours or days, internal radiation would give rise to a larger fraction of the total radiation dose, partly because short-lived nuclides would have decayed before fallout descended and partly because fission products contained in the more finely divided and soluble distant fallout enter food chains more readily. The relative contributions of '*"1, ?°Sr, and + ?7Cs to the internal radiation dose would, however, be comparable to those in near-in localities. Civil defense planning is naturally concerned primarily with this early period when external radiation is dominant, but this is not the whole story. Years after a nuclear war, long-lived nuclides will remain in the soil and will continue to descend in worldwide fallout. Therefore two questions are relevant: (1) What radiation doses will be received from these sources by the survivors of a nuclear war? (2) Is it prudent and realistic to prepare plans for long-term remedial action against the contamination of agricultural produce? This paper discusses these questions in relation to dietary contamination. For obvious reasons the long-term problems will be caused largely by ?°Sr, the extent to which it will enter food chains from the soil many years after deposition being a question of major relevance. It is therefore appropriate to review information on this question in some detail. ENTRY OF °°Sr INTO FOOD CHAINS FROM THE SOIL Our understanding of the behavior of 9%Sr in the soil has been much aided by experiments in which weapon debris or measured quantities of °° Sr, °° Sr, or °° Sr have been incorporated into the soil, but quantitative relations that can be confidently applied to wide areas cannot be obtained from these small-scale studies. The best approach is to analyze the results of surveys of deposition of worldwide fallout and contamination of foodstuffs, thus partitioning the contamination of food between direct contamination (i.e., the retention of the recent deposits on vegetation) and that resulting from uptake from the soil. Many of the uncertainties that arise in extrapolating from limited data are thus avoided, The first analysis of this type was made at the initiative of Tajima by the United Nations Scientific Committee on the Effects of Atomic Radiation? (UNSCEAR) in 1958. Like most subsequent studies, his work was concerned with the contamination of milk, because of its importance in the transfer of °°Sr to human diet. Using the available survey data on the contamination of milk and the deposition of fallout, he attempted to solve simple empirical equations of the following type: C=p,F, + paFa (1) 950 RUSSELL, BARTLETT, AND BRUCE where C = annual mean ratio of ?°Sr to calcium in milk (pCi : °Sr/g Ea) F, = deposit of ?°Sr in the year in question (mCi/km? ) Fq cumulative total deposit after allowance for radioactive decay (mCi/km* ) Pr, Pd = proportionality factors Our discussion of the use of this and other procedures is concerned mainly with relations in the United Kingdom, but, as will be shown later, the situation there seems relatively typical of temperate regions. From survey data up to 1961, p, and pq were estimated to be 0.76 and 0.19 (Ref. 3). Annual milk levels calculated on this basis for past years agreed reasonably with those observed (Fig. 1b), but the defects of Eq. 1 were nonetheless obvious. First, the equation assumed that all °?°Sr entering milk which was not attributable to the entrapment of the current deposit on vegetation came from the cumulative total in the soil, whereas it was evident from agricultural considerations that the direct entrapment of ?°Sr on vegetation in the previous year must make an appreciable contribution (the “‘lag-rate” effect). Second, the assumption that a constant fraction of the cumulative deposit in the soil enters plants each year was clearly incorrect because of the mechanisms (to which further reference is made later) which either remove it from the rooting zone or otherwise reduce its accessibility to plants. Refinement to take account of these two defects was, however, impossible until more-extensive survey data were assembled. This was particularly true with respect to the second defect, since a reliable estimate of the manner in which pg decreased with time could be expected only when ?°Sr that had been deposited in soil for many years contributed a major fraction of the contamination in milk. In the early years the direct contamination of vegetation was the dominant source of ?°Sr in diet. Accordingly, in long-term assessments it was at first necessary to assume a factor by which uptake from the soil decreased annually. The value of 2%, chosen by UNSCEAR in its first assessment of dose commitments from worldwide fallout,* was retained in the most recent assessment. No factual justification for the use of this value has been advanced, however. By the end of 1964, sufficient survey data existed to make possible some revision of Eq. 1. A marked lag effect of fallout in the previous year was implied by the fact that Eq. 1 led to an overestimate of the contamination of milk when the fallout at that time was low; the reverse was true when fallout was high (Fig. 1b). An improved but still empirical equation gave a significantly better fit to the data:° C= prF, + piFi + paFa (2) The symbols are the same as those in Eq. 1, except that F; represents the deposit in the last half of the previous year and p, the lag-rate proportionality factor. CONCENTRATION IN MILK, pCi sr/g Ca CALCULATED OBSERVED RATIO: SIGNIFICANCE OF LONG-LIVED NUCLIDES Cumulative deposit ANNUAL DEPOSIT, mCi 99Sr/km2 \N \. Annual ‘deposit nN 1958 1960 1962 1964 1966 1968 (a) ibe Ast Eq. 1 (1961) --O--, Eq. 2 (1964) 1958 1960 1962 1964 1966 1968 (b) Fig. 1 Strontium-90 in fallout and milk in the United Kingdom, 1958 to 1969. (a) Mean results of surveys of deposition and contamination in milk conducted by the Atomic Energy Research Establishment, Harwell,*>’ and Letcombe Laboratory,’’ respectively. (b) Annual average ratios of °° Sr to calcium in milk calculated by alternative equations and expressed relative to observed values. Dates in parentheses indicate the most recent information available when the proportionality factors for the equation were derived. 551 80 60 40 20 CUMULATIVE DEPOSIT, mCi 99Sr/km2 552 RUSSELL, BARTLETT, AND BRUCE This lag effect was found to be more closely related to the deposit in the last half of the previous year than to that in the whole year or in the summer months only. The following values for the proportionality factors were derived from survey data up to 1964: p, = 0.70, pj = 1.13, and pg = 0.11. The annual average milk levels calculated in this manner not only agreed with those observed within 8% but also remained in equally good agreement in the two subsequent years (Fig. 1b), 1.e., until 1966. Thereafter, however, when the rate of fallout was low and the cumulative deposit became the dominant source of contamination, the concentration in milk was consistently and increasingly overestimated. This defect was still more obvious with Eq. 1. Therefore, as anticipated, pg was apparently decreasing with time after the entry of °°Sr into the soil. Revised calculations by both equations with the use of survey data up to 1969 gave lower values for pg than had been derived when results for the earlier years only were available. However, the appropriate procedure was clearly to expand the third term of Eq. 2 to take account of the progressive reduction of pg with time after deposition. The data being insufficient to permit the estimation of independent values for each preceding year, an exponential decrease in uptake from the soil was assumed:° G=p, hy pprop pac. Poe aoe ks Li eines 54) (3) where C = annual ratio of ?°Sr to calcium in milk (pCi ’°Sr/g Ca) in the current year (here designated year 1) F,, Fy, F3,...= deposits of ~°Sr am year 1 and each- previous, year atten correction for decay to midpoint of year (mCi/km’ ) a, b = first and second halves of year 2, respectively 90 if s=reduction factor by which the uptake o Sr from soil decreases annually through processes other than the decay of radioactivity Pi, P2, P3 = proportionality factors The first two terms on the right-hand side of the equation are similar to those in Eq. 2 but are not identical since they reflect the total effect of fallout, including the small contribution of uptake from the soil at the times in question, whereas in Eq. 2 uptake from the soil throughout the entire period is included in the third term. Simplifying Eq. 3 by considering F, as a whole was attempted, but a poorer fit to the data was obtained. This is in accord with the observation in the derivation of Eq. 2 that the lag-rate factor operated predominantly in the second half of the previous year. The values of the coefficients in Eq. 3 derived from survey data up to 1969 are p, = 0.70, pp = 1.41, p3 = 0.20, and s = 0.86. As shown in Fig. 1b, the content of ?°Sr in milk calculated on this basis agreed reasonably with that observed for each year between 1958 and 1969. Though still empirical, Eq. 3 SIGNIFICANCE OF LONG-LIVED NUCLIDES 553 describes the relation between the deposition of fallout and the contamination of milk considerably better than Eqs. 1 and 2; further improvement must await the availability of survey data for a longer period. From the viewpoint of predicting dietary contamination over long periods, the particular advantage of Eq. 3 is that it provides an objective basis for estimating the extent to which the uptake of ?°Sr from the soil changes with time and thus dispenses with the need to make arbitrary assumptions. The value of 0.86 for s indicates a decrease by some 14% annually after allowance has been made for the decay of radioactivity. This value is in surprising agreement with the findings of Van der Stricht et al.,’ who, applying a different type of analysis to survey results from Ispra in nothern Italy, deduced an annual reduction in uptake from the soil by about 13%. These values are considerably higher than 2%, the value assumed by UNSCEAR,” but it had long been evident that in some circumstances 2% was a gross underestimate. United Kingdom experiments showed that pasture grasses can remove 2 to 5% of recently introduced ?°Sr from soil in a single summer.® Beyond this the downward movement of ?° Sr in the soil by only a few centimeters will frequently cause an appreciable reduction in absorption since the roots of pasture plants draw nutrients largely from the upper soil layers.” Strontium-90, like calcium, can be leached to greater depths in the soil, and in some soils physicochemical changes may bring about a small reduction in uptake by plants.'° All these processes operate conjointly, and the value of s now derived does not appear to conflict with any known facts. Note that, in addition to demonstrating a more rapid decrease in uptake of °° Sr from the soil, Eq. 3 also indicates that absorption from this source is initially appreciably higher than was previously inferred. The value for p3 is 0.20, whereas according to Eq. 2 pg was estimated to be 0.11. The limitations of the present analysis should be recognized, however. The time of year when fallout descends is likely to have an appreciable effect, especially, in the first. year, and. no account can yet be,.taken. of. this. fact. Furthermore, although exponential decrease in uptake from the soil has been assumed, there may be appreciable and as yet undetected changes in s with time; in particular, it is possible that this rate of change in the uptake of °° Sr will slow down when ?°Sr has been present in soil for a longer period. Nonetheless, since Eq. 3 describes closely the situations in 1968 and 1969 (see Fig. 1), when the mean interval since the deposition of ’°Sr was 6 to 7 years, any eventual change in s should not have a large effect on the calculation of integrated doses. Table 1 shows how improved calculations have modified estimates of the integrated total of ?°Sr that would enter milk in the United Kingdom from a given deposit. In the calculations using Eqs. 1 and 2 the UNSCEAR? value of 2% per annum decrease in uptake from the soil was assumed; no such assumption 1s required with Eq. 3. The earliest calculation (Eq. 1) appears to overestimate the integrated contamination of milk by a factor of about 2. This undoubtedly results largely from the assumption of only 2% annual reduction in uptake from 554 RUSSELL, BARTLETT, AND BRUCE Table 1 ESTIMATES OF THE INTEGRATED TOTAL OF °° Sr ENTERING MILK IN THE UNITED KINGDOM AFTER DEPOSITION OF 1 mCi ? ° Sr/km? Integrated Fraction contamination attributable of milk, to uptake Method* pCi °° Sr year/g Ca from soil Equation 1 (1961) 4.9 0.84 Equation 2 (1964) 3.6 0.65 Equation 3 (1969) 233 0.47 *The dates in parentheses indicate the most recent data available when the calculation was made. With Eqs. 1 and 2,a 2% annual reduction in uptake from the soil is assumed following UNSCEAR;° no such assumption is needed with Eq. 3. the soil; if a 5% reduction had been assumed, the integrated total derived by Eq. 1 would have been reduced by more than 30%. Therefore estimates of dose commitments from ?°Sr could have little quantitative validity until an objective basis was available for estimating the manner in which absorption from the soil would decrease with time. This comment implies no criticism of UNSCEAR for having assumed a considerably slower reduction in the uptake of °° Sr from the soil than is now suggested. When information is lacking, the only safeguard against underestimating risk is to adopt cautious postulates, but the uncertainty they introduce must be remembered. Unfortunately information on the transfer of ?°Sr to food chains, of the type provided by Eq. 3 for the United Kingdom, 1s not available for the majority of countries. Thus we must consider whether the relations derived for the United Kingdom by Eq. 3 are a reasonable guide to the general situation in other temperate regions. Here UNSCEAR? helps. Its tabulation of milk levels from 14 localities in the North Temperate Zone between 1955 and 1967 shows that the year-to-year trends in the United Kingdom were very close to the average (Fig. 2), the correlation coefficient being 0.99. The integrated total for the United Kingdom was about 10% higher (United Kingdom, 151 pCi year/g Ca; average, 137 pCi year/g Ca). Accordingly, for lack of better data, the United Kingdom relations for milk (derived by Eq. 3) will be assumed to be approximately representative of the average situation in other temperate countries until a more nearly complete assessment becomes available. SIGNIFICANCE OF LONG-LIVED NUCLIDES 555 $ —o— , United Kingdom -@- North Temperate Zone (mean from UNSCEAR, 1969) 90s; IN MILK, pCi 2Sr/g Ca 1955 1957 1959 1961 1963 1965 1967 Fig. 2 Comparison of the annual average ratios of °° Sr to calcium in milk in the United Kingdom with the mean values derived by UNSCEAR? for the North Temperate Zone. RADIATION DOSES FROM LONG-LIVED FISSION PRODUCTS IN DIET AFTER A NUCLEAR WAR Long-lived fission products from both the initial near-in deposit and the subsequent worldwide fallout will expose the survivors of a nuclear war to radiation. To illustrate problems that might arise, we will consider the situation in an area receiving an external radiation dose of 100 R/hr from early fallout 1 hr after the detonation of a weapon (the total amount of fission occurring in the entire war being 5000 Mt). From this model it is easy to scale upward or downward to any preferred case. Attention is confined to doses received after sufficient time has elapsed for the contribution from short-lived fission products to be insignificant, for agricultural production to be resumed, and for dietary contamination from worldwide fallout to have reached its peak. For convenience, the 12-month period when this situation is attained is described as “postwar year 1,”’ but we must realize that the length of time before this occurs could vary appreciably depending on many factors; it would not be likely to exceed 2 years, however. Since doses from long-lived fission products received before postwar year 1 would be small relative to the integrated total dose thereafter, little error 1s introduced by ignoring the earlier period. 556 RUSSELL, BARTLETT, AND BRUCE Dose from ’° Sr Assumptions on the composition of fission products, on the relation between deposition and external gamma radiation dose, and on fractionation, summarized in Appendix A, indicate that near-in fallout would deposit approximately 1000 mCi of ?°Sr per square kilometer in a fallout field of 100 R/hr at 1 hr. The large particle size of the debris will undoubtedly lower its solubility by a considerable factor, but, pessimistically, 500 mCi of °°Sr per square kilometer is assumed to be present in forms accessible to plant roots in postwar year 1. The results of surveys of worldwide fallout combined with estimates of the quantity of nuclear fission released by nuclear tests, which are reviewed in Appendix B, suggest that 5000 Mt of fission would give rise to a deposit of about 1100 mCi of ?° Sr per square kilometer in the first year, with a half-residence time in the atmosphere of about 12 months; these estimates refer to temperate latitudes in the hemisphere where detonation occurred. Applying the coefficients derived earlier for Eq. 3, we can derive the levels of °°Sr in milk caused by the initial deposit and by worldwide fallout. These values, along with the fraction of the total contamination attributable to absorption from the soil in each year, are shown in Table 2. Table 2 CONTAMINATION OF MILK WITH ?°Sr AFTER A NUCLEAR WAR* Contamination of milk, pCi ?° Sr/g Ca Uptake from soil Direct contamination Fraction Years of plants with Worldwide Near-in attributable postwar worldwide fallout fallout deposit Total to soil 1 1150 85 100 1340 0.14 je 570 200 85 860 0.33 3 290 230 Te 590 0.52 + 140 230 60 430 0.67 5 Ti. 210 50 330 0.78 6 36 180 42 260 0.86 7 18 160 35 210 0.91 8 9 130 30 170 0.95 9 + 110 25 140 0.97 10 2 95 21 120 0.98 Total Years 1 to 10 2290 1630 520 4450 0.48 Years 1 to « 2290 2130 630 5060 0.55 Fa eee eR ep i Pe ee ec eee *For the calculations it is assumed that near-in fallout delivered 100 R/hr at 1 hr and that total fission in the hemisphere is 5000 Mt. SIGNIFICANCE OF LONG-LIVED NUCLIDES 557 It is now widely recognized that, because of the risk of leukemia, the radiation dose to bone marrow is the appropriate basis for assessing risks from °°Sr. To estimate the highest dose to this tissue which any individual could receive annually, we have assumed that the entire bone of infants in the first year of life is in equilibrium with diet each year, that the ratio of ?°Sr to calcium in their bone is 0.25 of that in the diet, and that 1 pCi ?°Sr/g Ca in 1l On this basis, infants in bone will deliver 0.82 mrad/year to bone marrow. their first year will receive the radiation doses shown in Fig. 3. In postwar year 1 the doses to bone marrow would be about 0.25 rad/year. Over the next few years the dose would decrease relatively rapidly to about 0.1 rad/year in the fourth year and about 0.03 rad/year after 10 years. ms : sssessy Soil: near-in fallout 0.25 |— i Soil: worldwide fallout Direct: worldwide fallout 0.20 0.10 DOSE TO BONE MARROW, rads/year j=) a 0.05 @) J Baaeeee Lo 1 2 3 5 9 — POSTWAR YEAR Fig. 3. Estimates of the radiation doses from ?°Sr to bone marrow which might be received in the first year of life by infants born during the decade after a nuclear war (for assumptions, see text). 558 RUSSELL, BARTLETT, AND BRUCE Alternatively, the dose commitment to the population can be estimated by using the procedure of UNSCEAR.® In this calculation it is necessary to assume the relation between the ratio of ?°Sr to calcium in the total diet and that in milk. In the majority of countries where these ratios have been examined, the ratio in the total diet is 1 to 1.5 times that in milk. In the present calculation the higher (pessimistic) value of 1.5 was used. On this basis, the dose commitment from ?°Sr is about 1 rad, nearly all of which is received in the first 10 years (Table 3). Table 3 DOSE COMMITMENT FROM ?°Sr TO BONE MARROW AFTER A NUCLEAR WAR* Dose to bone marrow, rads Years postwar Source 1to10 1to=x Worldwide fallout Direct contamination 0.38 0.38 Uptake from soil 0.27 0.35 Early fallout Uptake from soil 0.08 0.10 Total OF73 0.83 *For the calculations it is assumed that near-in fallout delivered 100 R/hr at 1 hr and that total fission in the hemisphere is 5000 Mt. Some 90% of the total dose commitment would come from worldwide fallout, the early fallout in an area where the external gamma dose was 100 R/hr at 1 hr contributing only a minor fraction of the total. This latter component could be scaled up to take account of situations in areas of much higher initial contamination. This would almost certainly be unrealistic, however, since the large particle size of the deposits in such areas would usually contain relatively insoluble fission products, whereas 50% solubility has been assumed in the present calculations. An appreciably larger contribution from this source might result, however, if the plumes from several weapons overlapped. Dose from '?’C€s So far we have considered doses from ?°Sr only. Cesium-137 must also be taken into account. Assessment of doses from this nuclide might be thought to be much simpler than that of doses from ?°Sr since, as is well known, the fixation of '*’Cs in clay minerals causes it to enter food chains to only a very small extent a year or two after deposition. Unfortunately, however, the basis SIGNIFICANCE OF LONG-LIVED NUCLIDES 559 for estimating doses from '*7Cs is less certain than that for ?°Sr, partly because, even though this discussion is concerned primarily with dietary contamination, it 1s logical to consider external as well as internal exposure from this nuclide and partly because its behavior cannot be related so precisely to that of a widely studied stable element as can that of strontium. However, the paucity of information regarding '*’Cs must be attributed largely to the fact that, when worldwide fallout first received notice, the isotopes of strontium were the dominant if not the sole preoccupation of many workers in this field. Such data as are available now have been reviewed by UNSCEAR.° The dose commitment to the bone marrow of the population from '*’Cs in worldwide fallout appears to be about 90% of that from ?°Sr, the same dose from '*7Cs being received by all tissues, of course. Within the limits of accuracy practicable in the present discussion, we may therefore assume that the dose commitment from '*7Cs to all tissues after the postulated war would be similar to that from ? Sr to the bone marrow, i.e., about 1 rad. The Total Dose For present purposes it is unnecessary to consider nuclides other than ?° Sr and '*’Cs. Other fission products will be trivial sources of dietary contamina- '*C can be ignored because it would deliver considerably smaller tion, and annual doses in the decades following the war and because there is no prospect of influencing its transfer from the atmosphere into food chains. Accordingly we may conclude that, after a nuclear war involving 5000 Mt of fission, the dose commitment from ?°Sr and !*7Cs to the inhabitants of the hemisphere in which the war took place would be approximately 2 rads to the bone marrow and 1 rad to the whole body from long-lived nuclides. For persons living near the target area, the doses would be only slightly higher than the average. DISCUSSION This assessment is, of course, approximate, but it may assist in a more realistic appraisal of the problems to which long-lived nuclides might give rise in the decades following a nuclear war. Even when the maximum allowance is made for uncertainties, the following facts are evident: 1. Doses from long-lived nuclides will be trivial relative to those received from short-lived activities in the earlier period in areas of appreciable near-in fallout. 2. Assuming that a nuclear war is of considerable magnitude (5000 Mt is in this category), worldwide fallout and not near-in debris would usually be the dominant source of dietary contamination with long-lived nuclides. 3. The direct contamination of growing crops is likely to be responsible for about half the dietary contamination with ? °Sr. 560 RUSSELL, BARTLETT, AND BRUCE This last conclusion should not cause surprise. It is now over a decade since unequivocal evidence became available’ * that in times of relatively high fallout the direct contamination of plants and not, as it was first suggested, absorption from the soil was the major route by which ?°Sr entered diet. Implicit also in the analyses that could be made at that time was the fact that the average extent to which ?°Sr would enter plants from the soil over a long period was likely to be overestimated, but by a factor that could not be suggested until investigations had continued for a much longer period. That stage has now been reached. If the soil were low in calcium, the °°Sy contribution could be greater than is suggested here. However, in a survival situation the need to achieve the maximum food production would probably be the most cogent reason to remedy such situations (If sufficient calcium is present in soil for good crop growth, uptake of ?"Sr from the soil should not be appreciably greater than the average.) So far this discussian has been concerned with the first question posed at the beginning of this paper, namely, “What radiation doses would long-lived nuclides portend after a nuclear war?’’ Now we will turn to the second question: “Is it prudent and realistic to prepare plans for long-term remedial action?’ The literature contains numerous suggestions for modifying the transfer of fission products through food chains, but unfortunately the majority of them do not relate to situations likely to arise in practice. A quarter or more of the casualties from long-lived nuclides after a nuclear war would apparently be due to external radiation from '*’Cs; this risk could not be mitigated over a wide area by any practicable method. Reduction of the average level of radioactivity in agricultural produce by a large factor also seems impossible. Figure 3 shows that, during the early years when doses would be highest, the major part of the internal dose from ’°Sr and, of course, almost the entire internal dose from '*’Cs comes from entrapment of the deposit on growing plants. Under normal agricultural conditions, reducing direct contamina- tion of crops without destroying them would be impossible. Since we are unable to prevent either nuclide from entering the food chain, can we do anything to reduce transfer to man? The decontamination of milk has been widely discussed. Since milk products in all forms make a large contribution to the total contamination of diet, in round terms about half the dose commitment from °°Sr and less than half the internal dose from ‘*’Cs could be spared by decontamination of the total milk supply. At one time it was imagined that this procedure would give greater protection to infants, especially from ?°Sr, than to adults, but, when it was recognized that ?°Sr is rapidly eliminated from the bones of the young,'®* it became evident that the benefit was much smaller. Some other possible remedial measures have been suggested. When diets are low in calcium, the addition of that element reduces the retention of °° Sr in the body, but increasing the calcium intake above that common in many western diets gives little benefit. Various therapeutic treatments have been discussed, SIGNIFICANCE OF LONG-LIVED NUCLIDES 561 but, since the risks from the therapy may be comparable to those from the anticipated radiation doses, the treatments cannot be considered seriously. Modification of the composition of diet, which has been suggested, would, in general, have no great effect 1f conventional methods of agricultural production were retained. Unfortunately the discrimination against strontium relative to calcium in passage from the diet of cattle to milk is offset by the greater direct contamination of the herbage cattle graze. Avoidance of foods that accumu- late’ * 7Cs would seem equally impracticable. Therefore it seems that the intake of radioactivity in diet could be reduced by a considerable factor only if stocks of stored foods were available for several years or if crops were grown in greenhouses to protect them from direct contamination by fallout. The following conclusions are inescapable: A large part of the dose from long-lived nuclides could not be avoided, and procedures available for mitigating some fraction of the dose would involve considerable effort and would possibly restrict food supphes. Would it be reasonable to place this burden on the surviving population? In other words, would it be likely that casualties from radiation could be reduced enough to make the expenditure of effort worthwhile? This final question can be considered in two ways; the expected dose from long-lived nuclides can be compared with that to which the community is inescapably committed from natural background, or casualties to which long-lived nuclides would give rise in the absence of remedial action can be estimated. Since the average natural background is about 0.1 rad/year, the dose commitment from long-lived fission products to the survivors of a war involving 5000 Mt of fission should be less than one-third of that received from background in the average life-span of man and considerably lower than that received in areas of high natural background. One could scarcely blame survivors of a nuclear holocaust if they felt that this risk was not worthy of consideration. However, to satisfy ourselves further, we will consider the number of casualties that might occur. An International Commission on Radiological Protection (ICRP) report'* suggested that 1 rad delivered to one million persons might cause about 20 cases of leukemia and about 20 cases of other fatal cancers, the majority of which would not be in bone. On this basis we could expect about 40 leukemias per million of the population from the estimated total of 2 rads to bone marrow and about 20 cancers in other tssues receiving about 1 rad from SGseonly. more recent assessment'° suggests that these figures may be underestimated a total of about 60 cases per million people. However, since a because of insufficient information on the length of the latent period, we will assume for prudence that up to 200 people per million might eventually die from cancer induced by the long-term components of fallout. The figure, of course, becomes more alarming when applied to a large population. Among 200 million persons, approximately the population of the United States, there might 562 RUSSELL, BARTLETT, AND BRUCE be 40,000 casualties during the recovery period. Although this is a large number, it is smaller than the number of annual fatalities on the roads of this country and of many other countries that are called advanced. In short, the total deaths caused by long-lived nuclides seem broadly comparable to the annual traffic death rate. Without expressing an opinion on the correctness of the community’s attitude toward road safety, we would point out that road casualties could be greatly restricted by action that would impose a vastly smaller load on the resources of the community than would any measures to reduce casualties from long-lived nuclides after a nuclear war. Thus, by the standards the community now accepts, remedial action against the risks from long-lived nuclides would not seem justified; the number of casualties would be so small relative to the total loss and the difficulty of avoiding them would be so great that remedial action could not reasonably be contemplated. We may conclude therefore that, in so far as our responsibilities lie in the field of civil defense, efforts to mitigate doses from radiation should be devoted solely to the early period when short-lived nuclides predominate. That is a sufficient problem. APPENDIX A: DEPOSITION OF ’°Sr IN NEAR-IN FALLOUT WHEN EXTERNAL GAMMA DOSE IS 100 R/HR AT 1 HR Dunning and Hilcken'® estimated that a deposition of 800 MCi of mixed fission products per square mile 1 hr after fission would give an external gamma dose rate of 4000 R/hr at 3 ft above a theoretically flat plane. Assuming that the roughness of the ground would attenuate the external radiation dose by a factor of 2, that ?°Sr contributes 0.0013% of the total fallout activity at 24 hr’’ (adjusted for a half-life of 28 years), that mixed fission products are deposited in fission yield, and that they decay by a factor of 36 in 24 hr, the expected deposit of ?°Sr would be 5000 mCi/km? when the external gamma dose rate is 100 R/hr at 1 hr. An alternative calculation based on Glasstone'® gives about one-third of this value, but we used the higher figure here, having in mind possible variability in different circumstances. We must, however, take account of the fractionation of fission products; the volatility of ?°Kr, the gaseous precursor of ?°Sr, is likely to deplete ?°Sr in the near-in deposit by a factor that may be conservatively estimated'® *? at 5. Thus a deposit of 1000 mCi of ?°Sr per square kilometer is expected when the external gamma dose rate is 100 R/hr at 1 hr. There is much evidence’? ** that the deposit in such areas will be of low solubility (probably not more than 10%), but, to avoid understatement of the quantities of °?°Sr which may enter food chains in subsequent years, we assumed 50% becomes soluble in the soil. SIGNIFICANCE OF LONG-LIVED NUCLIDES 563 APPENDIX B: RELATION BETWEEN THE EXTENT OF NUCLEAR FISSION AND WORLDWIDE FALLOUT IN THE SAME HEMISPHERE The pattern of fallout from the series of nuclear tests in 1962 provides a basis for estimating the deposition of ?°Sr in worldwide fallout after a nuclear war. Tests in the USSR are estimated to have yielded 60 Mt of fission** with a mean time of origin?® at mid-September 1962. The average deposition of ?°Sr in the United Kingdom in 1963 was 19 mCi/km*, and measurements of fission-product ratios’’ indicated that, in the spring and summer of that year, 70% of the ?°Sr was from tests held in 1962. This includes a small contribution from the United States 1962 equatorial tests. If we assume that 60 Mt of fission caused 0.7 X 19 = 13.3 mCi °°Sr/km? to be deposited in the year after the detonations occurred, then, assuming similar latitude and height of injection, 5000 Mt of fission would give rise to 1100 mCi of ?°Sr per square kilometer in the first year after detonation. The deposition in subsequent years would decrease at a rate depending on the residence time of the debris in the stratosphere and on interhemispheric transfer. From 1963 to 1966 the total content of the atmosphere decreased at a fairly steady rate, corresponding to a half-time for deposition estimated at 10 to 13 months; estimates of the longer half-time for interhemispheric transfer lie between 1.5 and 3.5 years.7® °° For present purposes a round figure of 1 year has been taken as the effective half-time for the transfer of ?°Sr from the stratosphere onto the earth’s surface. REFERENCES 1. R. S. Russell, Dietary Contamination—Its Significance in an Emergency, in Radiologi- cal Protection of the Public in a Nuclear Mass Disaster, pp. 279—306, Fachverband fiir Strahlenschutz, Interlaken, 1968. 2. United Nations, Report of the Scientific Committee on the Effects of Atomic Radiation, General Assembly Official Records, Thirteenth Session, Supplement No, 17 (A/3 838), New York, 1958. 3. B. O. Bartlett and R. S. Russell, Prediction of Future Levels of Long-Lived Fission Products in Milk, Nature, 209: 1062—1065 (1966). 4. United Nations, Report of the Scientific Committee on the Effects of Atomic Radiation, General Assembly Official Records, Seventeenth Session, Supplement No. 16 (A/5216), New York, 1962. 5. United Nations, Report of the Scientific Committee on the Effects of Atomic Radiation, General Assembly Official Records, Twenty-fourth Session, Supplement No. 13 (A/7613), New York, 1969. 6. B. O. Bartlett, An Improved Relationship Between the Deposition of Strontium-90 and the Contamination of Milk in the United Kingdom, in Agricultural Research Council, Letcombe Laboratory, Annual Report 1970, p. 27, 1971. 564 RUSSELL BARTLET AND BRUCE Ws 10. a Gis 28 13% 14. 15: 16. 17: 18. 19: 20. 2Ae Pep by Z3e 24. 2D): E. Van der Stricht, P. Gaglione, and M. de Bortoli, Predictions of Strontium-90 Levels in Milk on the Basis of Deposition Values, Abstract of paper given at 2nd International Congress of the International Radiation Protection Association, May 3—8, 1970, Brighton, England, Health Phys., 19: 119 (1970). See also C. Stievenart and E. Van der Stricht. L’Evolution de la radioactivité ambiante au cours des années 1962 a 1966 et ses consequences pour la contamination radioactive de la chaine alimentaire, Euratom Report EUR4212f, 1968. _G. M. Milbourn, The Uptake of Radioactive Strontium by Crops Under Field Conditions in the United Kingdom, J. Agr. Sci., 55: 273—282 (1960). . P. Newbould, The Absorption of Nutrients by Plants from Different Zones of the Soil, in Ecological Aspects of Mineral Nutntion of Plants, 1. H. Rorison (Ed.), pp. 177-190, Blackwell Scientific Publications Ltd., Oxford, 1969. H. M. Squire, Long-Term Studies of Strontium-90 in Soils and Pastures, Radiat. Bot., 6: 49—67 (1966). Medical Research Council, The Assessment of the Possible Radiation Risks to the Population from Environmental Contamination, Her Majesty’s Stationery Office, London, 1966. R.S. Russell, Radioisotopes and Environmental Circumstances: The Passage of Fission Products Through Food Chains, in Radioisotopes in the Biosphere, R. S. Caldecott and L. A. Snyder (Eds.), pp. 269—292, University of Minnesota Press, Minneapolis, 1960. W. Fletcher, J. F. Loutit and D. G. Papworth, Interpretation of Levels of Strontium-90 in Human Bone, Brit. Med. J., ii: 1225—1230 (1966). International Commission on Radiological Protection, The Evaluation of Risks from Radiation, ICRP Publication 8, Pergamon Press, Inc., Oxford, 1966. International Commission on Radiological Protection, Radiosensitivity and Spatial Distribution of Dose, ICRP Publication 14, Pergamon Press, Inc., Oxford, 1969. G. M. Dunning and J. A. Hilcken (Eds.), The Shorter-Term Biological Hazards of a Fallout Field, USAEC Report M-6637, Division of Biology and Medicine and Armed Forces Special Weapons Project, December 1956. R. C. Bolles and N. E. Ballou, Calculated Activities and Abundances of 7**U Fission Products, USAEC Report USNRDL-456, Naval Radiological Defense Laboratory, Aug. 30, 1956. S. Glasstone, The Effects of Nuclear Weapons, USAEC Report ACCESS-127, Defense Atomic Support Agency, 1962. G. M. Dunning, Biological Effects of a Nuclear Attack, USAEC Report TID-5563, Division of Biology and Medicine, September 1959. K. Edvarson, K. Low, and J. Sisefsky, Fractionation Phenomena in Nuclear Weapons Debris, Nature, 184: 1771—1774 (1959). E. C. Freiling, Radionuclide Fractionation in Bomb Debris, Science, 133: 1991—1998 (1961). J. F. Loutit and R. S. Russell, The Entry of Fission Products into Food Chains, Progress in Nuclear Energy, Series VI, Vol. 3, Pergamon Press Inc., New York, 1961. E. A. Schuert, A Fallout Forecasting Technique with Results Obtained at the Eniwetok Proving Ground, in The Nature of Radioactive Fallout and Its Effects on Man, pp. 280—321, U. S. Congress Hearings, 1957. T. Triffet, Basic Properties and Effects of Fallout, in Biological and Environmental Effects of Nuclear War, pp. 61—100, U. S. Congress Hearings, 1959. Federal Radiation Council, Estimates and Evaluation of Fallout in the United States from Nuclear Weapons Testing Conducted Through 1962, F.R.C. Report No. 4, Superintendent of Documents, U.S. Government Printing Office, Washington, D. C., May 1963. 26. 27. 28. 29: 30. a 3/2: SIGNIFICANCE OF LONG-LIVED NUCLIDES 565 R. S. Cambray, E. M. R. Fisher, G. S. Spicer, C. G. Wallace, and T. J. Webber, Radioactive Fallout in Air and Rain: Results to the Middle of 1963, British Report AERE-R-4392, Nov. 18, 1963. R. S. Cambray, E. M. R. Fisher, G. S. Spicer, C. G. Wallace, and T. J. Webber, Radioactive Fallout in Air and Rain: Results to the Middle of 1964, British Report AERE-R-4687, November 1964; and R. S. Cambray, personal communication. D. H. Peirson and R. S. Cambray, Interhemispheric Transfer of Debris from Nuclear Explosions Using a Simple Atmospheric Model, Nature, 216: 755—758 (1967). P. Fabian, W. F. Libby and C. E. Palmer, Stratospheric Residence Time and Interhemispheric Mixing of Strontium-90 from Fallout in Rain J, Geophys. Res., 73: 3611—3616 (1968). P. W. Krey and B. Krajewski, HASL Model of Atmospheric Transport, USAEC Report HASL-215, New York Operations Office (AEC), September 1969. R. S. Cambray, E. M. R. Fisher, W. L. Brooks, and D. H. Peirson, Radioactive Fallout in Air and Rain: Results to the Middle of 1969, British Report AERE-R-6212, November 1969; and R. S. Cambray, personal communication. Agricultural Research Council, Letcombe Laboratory, Annual Report 1969, Report ARCRL-20, 1970. CONTROL OF FALLOUT CONTAMINATION IN THE POSTATTACK DIET J. C. THOMPSON, JR., R. A. WENTWORTH, and C. L. COMAR Department of Physical Biology, New York State Veterinary College, Cornell University, Ithaca, New York ABSTRACT Radioactive fallout from nuclear weapons testing has resulted in widespread research efforts designed to define pathways, establish deposition and uptake models, and develop predictive capabilities for radionuclide levels and their associated hazards. Within this broad research effort are methods that offer promise for reducing dietary radionuclide intake levels. The various alternatives considered for the radionuclides of primary importance ('?71, ?°Sr, and ‘?7Cs) are discussed. Much of the actual direction and use of such procedures would depend on the severity of the nuclear attack since many other problems (health, nutrition, etc.) could easily require more-immediate control than those of radionuclide intake. Maximum use of available procedures might occur in releases from a single, isolated event where maximum recovery forces were operating. In contrast, mass nuclear attacks would reduce the immediate priority for controlling radionuclide intake levels, and only the most effective methods might be considered feasible. Under a widespread attack there would be a need for additional guidelines that respond to tolerance or survival levels of radioactivity rather than to the minimum-exposure concept, as all current guidelines do. Any consideration of the postattack dietary situation must be based on some estimate of the nature and scope of the attack. For example, if the attack were a full-scale strike (maximum effect) followed by extensive retaliatory response and similar secondary retaliations, conditions would be extremely critical throughout the country. If, however, the first strike were directed toward neutralizing the offensive and defensive capabilities to make retaliation null or minimal, the scale of catastrophe might be lessened for certain parts of the country. A strike mediated by antimissile defenses or by the limited offensive capabilities of an aggressor country would have even further reduced effects. Such a strike might be called a limited attack resulting in localized or regionalized disruptions and contamination. The next lower level of disruption would include individual or 566 CONTROL OF FALLOUT CONTAMINATION 567 isolated nuclear events arising from accidents, sabotage, or intentional large-scale releases in the single-event category. Reactions or recovery operations after any detonation can be classified as short-term and long-term activities. The most severe attacks would require maximum initial effort during the short-term period to reestablish some semblance of normal order, since most of the population would be in the same general state of disorder. Long-term considerations might not enter into planning until the recovery stage was well under way. In contrast, smaller scale disturbances might easily permit a maximum effort for both short- and long-term activities because of lesser disruption of productive facilities and greater recovery capabilities. The degree and capability of response to fallout in the diet quite clearly depend on the severity of the initial attack. In reality the response would probably be inversely related to the size of the strike. The larger the attack, the lower the priority of fallout considerations would be; simple human survival would be of greatest importance. Primary civilian emphasis would first center on the maintenance of health and nutrition for the surviving population rather than on concern for any carryover of deleterious effects to succeeding generations. External radiation levels would have to be considered in the context of other hazards at the time. However, radiation considerations should not receive a disproportionate part of the recovery effort at the expense of more critical needs. Radiation safeguards already incorporated into our planning are probably more comprehensive than are plans for many other types of environmental insult. It would be poor operational procedure to initiate efforts to reduce dietary contamination from 10 R to 1 R when general external radiation levels were = |OOUR “and: *alstate: (of pestilence threatened. Thus the impact of radioactivity in diet would receive a much lower rating when people were faced with the threat of pestilence, hunger, or starvation. Such factors as chemical and biological contamination might warrant much greater attention than radiological concerns during the initial recovery period. As the degree of destruction was reduced or as recovery got under way, more effort could be directed toward radiological considerations with programs designed to minimize the short- and long-term hazard. The greatest efforts in this area could be mobilized after a single nonoffensive type of detonation because of the almost complete availability of resources and facilities. The apparent conflict between the recovery capability and the total need as illustrated here may ultimately provide better guidelines for emergency conditions. Since the possibility of small disruptions appears greater than that of mass catastrophes, many of the extensive capabilities available during small events can be selectively sorted and programmed for use in larger emergencies. Thus the most effective and direct measures can be assigned use priorities and called upon in a logical order as the needs develop. 568 THOMPSON, WENTWORTH, AND COMAR GUIDELINES For the major radionuclides the Federal Radiation Council established graded scales of intake’’* based on Radiation Protection Guides developed in 1960. These scales were not designed for accidental releases or environmental releases not under the control of the government. Misunderstandings arose over the application of these guidelines in 1961 and 1962, however, and a general guidance concept was established in 1964 (Ref. 3) and 1965 (Ref. 4) using the Protective Action Guide (PAG). This represented the projected absorbed dose to individuals in the general population sufficient to warrant protective action following a contaminating event. Intake for the projection is that received by individuals from a contaminating event for which no protective action was taken. Operationally, protective action is needed if the average projected intake by a suitable sample of the exposed population equals one-third of the PAG. Protective actions encompass a variety of measures ranging from simple diet alterations to widespread changes in food production techniques and consump- tion patterns. Typical action measures have been outlined for the major SoS reat and !3’Cs) in Federal Radiation Council publications.°’* Special consideration is given to the transmission pathways of radionuclides (°° Sr, radioactive materials and the type of contaminating event. Protective-action guides were designed for use by the general population where a suitable sample of the exposed population is available. The concept is designed to minimize the risk associated with the use of nuclear energy. Situations expected under nuclear attack are not fully covered, because the basis for the guides is minimum exposure rather than tolerance to radiation levels. In a postattack environment there would be a real need for new guidelines or exposure indexes that specifically consider tolerance. These guidelines would be of an emergency nature, designed especially for certain segments of the population and specifying something between radiation death or incapacitation levels and protective-action guides. They might be called survival action guides. Such guides must take into account differences in age, sex, occupation, location, etc. Preparing guides for the postattack environment would require the establishment of such graded scales of action. In effect, a system of radiation-exposure priorities that became operational when an attack occurred would be necessary. The present practice of determining decontaminating or clean-up measures based on minimum-exposure levels has considerable merit in that a wide range of possibilities is explored. However, with increasing degrees of attack, the capability for action would be restricted, and only the most effective measures would be utilized. A selection process based on survival conditions under extreme stress is needed, rather than one based on concepts developed for peaceful uses of nuclear energy or for a world at peace. The development of such survival action guidelines would provide the proper basis for action measures CONTROL OF FALLOUT CONTAMINATION 569 after a nuclear attack. Predictive models and techniques now available for translating contamination levels to exposure commitments could be used to determine appropriate measures to stay within any newly developed guidelines for survival. CURRENT-ACTION STATUS OF DIETARY DECONTAMINATION Once priorities based on exposure guidelines for attack conditions are established, the most appropriate dietary control measures for each population group can be selected. Historical data from past fallout studies provide the basis for determining the most important radionuclides, pathways, and remedial measures. During the initial period after a contaminating event, dietary habits would be altered while external radiation dangers persisted. This would require the use of stored or uncontaminated foods until external levels were minimal. As the danger from external radiation subsided the major hazard would become internal in nature, and a time-related ranking of major radionuclides would evolve as follows: Initial concern: °? Sr and !3!1. 7 Intermediate concern: °?Sr, ?°Sr, '3!1, and 13’Gs. 7 Long-term concern: 7 OSeand’: 2. Es, Since data from fallout programs have established the validity of using milk as one of the most effective indicators of contamination, it is useful to direct most of our efforts to this product. The importance of milk in U.S. dietary habits is well recognized, as is the general pattern of milk production, distribution, and storage. Extensive facilities provide a unique capability for a partial or complete return to productivity soon after interruption. Milk therefore becomes the primary indicator and/or control product for general and specific radiocontamination levels. Milk The ability to predict the levels of radionuclide contamination expected in milk following an attack is important for assessing the danger to the population consuming this food, for judging the effect of countermeasures, and for making intrafood comparisons. Many methods have been developed for predicting milk contamination levels from fallout concentrations in the soil or on forage crops. However, with the use of such projections, the greater the distance between fallout deposition and milk secretion, the greater are the uncertainties and assumptions encountered. A prediction method that eliminates many of these uncertainties is an approach developed primarily by Lengemann and colleagues,’ '° which is based 570 THOMPSON, WENTWORTH, AND COMAR on modeling of experimental data from dairy cows. Using this method, we can estimate the total intake commitment of specific radionuclides from milk by measuring concentrations of these radionuclides in the milk on any given and known day after the start of consumption by cattle of contaminated pasture or forage. This approach gives us some valuable assistance in the matter of surveillance, determination of conditions under which action is to be initiated, and time relations. The technique has been developed for predicting the intake commitments for !3!], ®?Sr, Gis and !37Cs. We will explain the general 131 principles using I as an example. Figure 1 shows an experimentally derived curve and points representing actual field observations which indicate concentra- tionssof Lisl in milk as a function of time after contamination. Figure 2 illustrates the calculation of so-called F factors, which represent the ratio of the total area under the curve to the level on any given day. Thus, from a determination of the evel in milk in a particular sample and a table of F factors, we can calculate the total |?! I intake commitment of humans drinking the milk. The important factor that gives validity to this method 1s that the shapes of the curves are such that they give constant F values no matter how the absolute height of the secretion curves varies. Calculated relative standard errors of F factors based on F values calculated from secretion curves for individual cows range from a high of 7% for '* ’Cs and 3.3% for '*'I on the first day after pasture contamination to a low of 0.2% for both radionuclides a few days later. Such F factors have been calculated for radioisotopes of iodine, strontium, and cesium and have been refined to account for other variables, such as varying deposition rates of fallout on pasture, single or multiple depositions of fallout, pasture loss rates, and transit times of milk before it is consumed. In a postattack situation the milk radionuclide-secretion functions and accompanying F factors would be of value in (1) predicting the effect of time on concentrations of radionuclides in milk when cows are on pasture, (2) calculat- ing the intake commitment by humans drinking milk, (3) calculating the effectiveness of removing cows to clean feed or invoking other countermeasures, and (4) predicting the effect of returning cows to pasture feeding. The effectiveness of two obvious and important countermeasures to reduce radionuclide intake via milk, namely, to stop drinking contaminated milk and to move cattle from pasture to uncontaminated feed, can easily be judged from the secretion functions. As shown in Fig. 3, if a man stops consuming contaminated milk on a given day, the reduction of his intake commitment can be calculated by the ratio of the appropriate areas under the curve. The same procedure can be used if animals are removed from contaminated pasture, as shown in Fig. 4. The net results are presented in Fig. 5, which allows us to make some important generalizations about the one most important factor governing the extent of reduced intake which can be attained—time. Note that, at early times (2 days), 131 stopping milk consumption as a countermeasure against I is about twice as effective as shifting cows to uncontaminated food; thereafter the difference CONTROL OF FALLOUT CONTAMINATION 571 Equation 0.5 @ Colorado pasture Normalized «0, Colorado barn feeding * , Salt Lake City 0.1 se © 1 Ww = «0/05 | = oc WwW oa 5 4 0.02 = ie a 0.01 0.005 | 0.002 | 0.001 0 20 40 60 DAYS AFTER CONTAMINATION Fig. 1 Experimentally derived curve showing relation between '°'T levels in milk (%/liter) and time after contamination. becomes progressively smaller. Action must be taken within about 4 days if the effectiveness is to be of the order of 90% (Refs. 6, 10, and 11). These procedures will involve various logistic problems of replacement of fresh milk by stored or processed milk and replacement of cattle feed by stored rations. The same model can be used to predict the levels of radiocontamination ' when cows are returned to pasture or fed contaminated forage. As depicted in BZ THOMPSON, WENTWORTH, AND COMAR 0.5 For a given day: =e total area 0.2 US fen trail ; 131 | intake from milk 13st 3 lin milk _ total 0.1 =) fo) a 0.02 0.01 INITIAL 'S'| PER LITER, % 0.005 0.002 0 20 40 60 DAYS AFTER CONTAMINATION Fig. 2. Illustration of F value calculations used to determine '*'I intake commitments. Fig. 6, the milk-secretion curve is displaced to the right to the selected day when the cows are to be returned to grazing and is adjusted downward by the appropriate pasture loss and decay factors. The total intake commitment by persons drinking the milk after the cows are returned to pasture is thus the original precountermeasure commitment adjusted downward by the pasture loss and decay factors. In this example, removing cows from pasture on day 1 results in an 8% intake commitment, and returning the cows to pasture on day 21 produces an additional 6% intake commitment. CONTROL OF FALLOUT CONTAMINATION 573 0.5 If man stops consuming contaminated milk on day X: shaded area x 100 total area 0 Oo % dose commitment = 0.1 se ac 0.05 LW = _l ac LW a = 4 002 ai < KE 0.01 = 0.005 0.002 0 Xx 20 40 60 DAYS AFTER CONTAMINATION 1317 Fig. 3. Calculation of contaminated milk is stopped. intake commitment when consumption of The model is also applicable to nongrazing management practices and is directly applicable when freshly harvested forages are fed to cattle daily. When contaminated postattack forages are harvested, stored, and fed out during winter ee months, the same equations will apply, except that the “‘pasture-loss-rate”’ factor drops out and a “‘biological-availability” factor is introduced. Total Diet Although direct measurement of radionuclide intake through total dietary assessment provides better estimates than projections from individual food items, the time and effort necessary for collection, analysis, and representative sampling favor the monitoring of the more important individual food indicators. Relations can then be established between such products and total diet to give a 574 THOMPSON, WENTWORTH, AND COMAR 0.5 If cows are removed from | contaminated feed on day X: | : _ area | + area II total dose commitment = SOTalGreAr en 100 0.2 0.1 xe ~ 0.05 cc Ww ke = oc Ww a =e O102 o —| ESP Doe 23 San Francisco Dairy products 16° 42.0 IZ 3 1.6 13 1.8 2. Op ad 2 Dall Cereals 0.9 0.9 0.7 0.6 0.5 0.8 0.6 0.6 0.8 0.8 Fruits and vegetables 0.4 O.4 ~~ 0.7 107 (40:3 ~ O04 —O4- 033" O33" 10:3 Meat, fish, poultry, and eggs 1.1 0.5 0.7 0.8 1.8 1.8 1.8 1.8 1.4 0.9 *Ratios are calculated by dividing ®°Sr/g Ca of total diet by ?° Sr/g Ca of appropriate food group. tStudies were conducted by the Health and Safety Laboratory, U. S. Atomic Energy Commission. Additional work on the relation between levels of '*’Cs in blood and body f 137 burdens o Cs have also been reported.” 7 In general, the whole-body levels for male subjects (picocuries per gram of potassium) can be estimated by '37¢€s content of the blood (picocuries per kilogram) by a factor multiplying the of 3. This procedure seems appropriate for individuals in the North Temperate Zone. Since the primary dietary consideration may be the quantity and availability of food, we must know the general level and location of food supplies available for use in emergency conditions. Various surveys have been made?®°?? which show the normal amount of food supplies on hand by geographic areas in the United States. In Table 2 the normal food supplies in marketing channels are shown for typical conditions expected throughout the country. Although there are some regional variations, in most cases a 100-day food supply (based on a daily intake of 2000 cal per person) is normally available. The supply by area 578 THOMPSON, WENTWORTH, AND COMAR 99SR TOTAL DIET/MILK RATIO 1961 62 63 64 65 66 67 68 69 YEAR Fig. 7 Linear-regression and confidence-interval estimates for °° Sr diet-to- milk ratios, worldwide data, 1961—1968. ranges from 81 to 326 days, and some definite seasonal variations are indicated. A much larger supply would be available if all feeds and animals were converted into food equivalents, as shown in Table 3. In this case the range in supplies 1s extremely wide, extending from more than 9 years in the wheat belt to less than 90 days in the populous Northeast. It is unlikely that we would have the need or the capacity for such an extensive conversion, because it would destroy our animal productivity. An average supply level of about 90 days for most of the country should give us an opportunity to restore some of our agricultural productivity. Except during the winter season, this time period would be adequate to restore much of the productivity of edible plant crops. In the event of a fall or winter attack, much of the new productivity might have to be temporarily concentrated in the warmer areas of the country. However, the prospect of continuing food production seems to be good. Some special provisions might be necessary to initiate the return to productivity; for example, to make seeds available, a national seed stock or reserve would perhaps be warranted. Allocation of food stocks or rationing would also be a vital part of total-diet considerations to ensure adequate supplies and to maintain minimal nutritive CONTROL OF FALLOUT CONTAMINATION 579 '37CS TOTAL DIET/MILK RATIO 1961 62 63 64 65 66 67 68 69 YEAR Fig. 8 Linear-regression and confidence-interval estimates for '*’Cs diet-to- milk ratios, worldwide data, 1961—1968. balances. When external levels of radioactive contamination declined, there might be some need to modify diets to minimize radionuclide intake. Much of this effort must take into consideration nutritive needs, occupational status, age, etc. Programs have been described for most fruits and vegetables which take into account the nutritive vs. the radionuclide contributions to maintain nutritional balance, minimize radionuclide intake, and still retain some degree of individual preference or selection.°° Examples of this approach are shown in Tables 4 and 5. In Table 4 the results of such changes are shown for a diet for the New York City area. The major diet categories are indicated, together with their ?° Sr and calcium contributions. Fruits and vegetables are listed separately to show the differences in intake arising from processing and substitution practices. Total-diet summaries are presented under each of the conditions considered for the fruit-and-vegetable category (Substitution 1 considers taste and preference criteria, and Substitution 2 considers the maximal ?°Sr reduction). Processing fruits and vegetables can reduce total dietary ?°Sr intake by 13%, whereas 580 THOMPSON, WENTWORTH, AND COMAR 9°SR TOTAL DIET/VEGATABLE RATIO 1960 61 62 63 64 65 66 67 68 69 YEAR Fig. 9 Linear-regression and confidence-interval estimates for °° Sr diet-to- vegetable ratios, worldwide data, 1960—1968. processing, coupled with substitution alternatives, reduces the total intake by 21 and 26%. Similar reductions occur in the level of ?°Sr per gram of calcium. Calcium intake under all conditions has been maintained at 93 to 97% of initial levels. In addition, vitamin A, ascorbic acid, and iron intake levels were also maintained well above recommended standards. Substituting in a nondairy diet would produce some additional reductions in the ?°Sr intake. However, the deletion of dairy products would result in a major calcium loss, a loss that could not be recovered by increases in the consumption of other foods. An example of this approach is shown in Table 5, where dairy products have been deleted from the diet for the New York City area. Although the net ?°Sr intake has been reduced by 46 to 67%, the calcium intake has also been reduced by more than 60%. Such a diet would require considerable calcium supplementation to maintain adequate nutrition since it provides for an intake of only 138 to 156g of calcium, whereas recommended diet levels are 290 to 510 g, depending on the age of the subject. Supplemental additions of inorganic CONTROL OF FALLOUT CONTAMINATION 581 Y = 0.4148 — 0.0026x 90SR TOTAL DIET/FRUIT RATIO 1960 61 62 63 64 65 66 67 68 69 YEAR Fig. 10 Linear-regression and confidence-interval estimates for °° Sr diet-to- fruit ratios, worldwide data, 1960—1968. calcium could be used to further reduce the ?°Sr per gram of calcium, but proper medical investigations must be made before such practices become available for general use. Other dietary alterations, such as using various additives, stopping consump- tion of certain highly contaminated foods, and using supplementary products, are also effective under certain conditions. They are briefly discussed for the three major radionuclides. Dietary Alterations and '°'I Intake Previous discussions under the section on milk indicate the effects on total dose commitment of stopping milk consumption (Fig. 5). If consumption stops within the first few days, the dose commitment is less than 10% of the total possible dose. In any event, action must be taken within the first week if a 50% reduction in total dose commitment is to be obtained. Other methods of reducing '*'I effects on a large population, such as the administration of high levels of stable iodine or other chemicals to cattle or to man, either are not effective or would be difficult to apply on a large scale.’ However, the use of 582 THOMPSON, WENTWORTH, AND COMAR Table 2 NORMAL FOOD SUPPLIES IN THE UNITED STAGES TALI G3 a Normal supply, days Area January 1 July 1 Region 1, Northeast 94 81 Region 2, Mid-Atlantic 82 Ta Region 3, Southeast 122 101 Region 4, North Central 125 109 Region 5, South Central iLab7/ 106 Region 6, Great Plains 197, 142 Region 7, West 150 94 Region 8, Northwest 326 136 U. S. average 125 98 *Estimates are based on food considered ready for use (excluding unprocessed grains, live animals, etc.) and converted to caloric equivalents. Daily consumption level is taken to be 2000 calories per person. Table 3 TOTAL SUPPLIES OF ALL FOOD STOCKS IN THE UNITED STATES, JULY 1967* Supply, days Area 3000 cal 2000 cal Region 1, Northeast 84 HZ Region 2, Mid-Atlantic 197 262 Region 3, Southeast 223 297 Region 4, North Central 2029 2699 Region 5, South Central 474 630 Region 6, Great Plains 3402 4525 Region 7, West 210 220k) Region 8, Northwest 1022 1359 *Estimates assume conversion of all animals and grains into edible supplies. CONTROL OF FALLOUT CONTAMINATION Table 4 RELATION OF SUBSTITUTION PRACTICES AMONG FRUITS AND VEGETABLES TO TOTAL ANNUAL DIETARY °° Sr INTAKE FOR NEW YORK CITY AREA (3-YEAR AVERAGE, 1961—1963) Dairy products Grain products Meat, fish, and eggs Diet subtotal Fruits and vegetables Unprocessed Processed Substitution 1t Substitution 2+ Classification of fruits and vegetables in diet: Unprocessed Processed Substitution 1t Substitution 2+ *?° Sr determinations were obtained from Tri-City Diet Study, Health and Safety Laboratory Fallout Program Reports.’ ” tSubstitution 1 classifies fruits and vegetables into use, taste, and preference subcategories so that dietary changes are in accord with normal practices. Substitution 2 uses maximal possible reductions without concern for taste or preference criteria. stable iodine to block thyroid accumulation o 99S, intake, * pCi/year Food Groups 3762 1039 162 4963 2582 1583 989 636 Total Diet 7545 6546 5952 5999 f 131 Calcium intake, g/year 238.22 58.72 44.78 341.72 64.07 D318 38.82 34.63 405.79 394.90 380.54 376.35 90 Sr pCi/g Ca eae) 17.8 3.4 14.5 40.3 298 2335 18.4 19x) 16.6 £5. 14.2 583 I from inhalation could be very useful under certain conditions, particularly in the event of reactor accidents.°7’?? The blocking dose to man is about 30 mg, but the time for complete blocking is decreased to about ' hr if a 100-mg dose is used; after such a single dose, the uptake returns to normal in about 8 days. Repeated doses can be used to maintain blocking. Schedules of from 35 mg every 12 hr to 250 mg every 4 hr have been proposed. 584 THOMPSON, WENTWORTH, AND COMAR Table 5 EXAMPLE OF SUBSTITUTION PRACTICES AMONG FRUITS AND VEGETABLES FOR A NONDAIRY DIET FOR NEW YORK CITY AREA (3-YEAR AVERAGE, 1961-1963) PRS EE oy Calcium intake, * intake, USE: pCi/year g/year pCi/g Ca Food Groups Grain products 1039 58.72 17.8 Meat, fish, and eggs 162 44.78 3.4 Diet subtotal 1201 103.50 11.6 Fruits and vegetables Unprocessed 2582 64.07 40.3 Processed 1583 53.18 29.8 Substitution 1t 989 38.82 2 5e5 Substitution 2+ 636 34.63 18.4 Total Diet Classification of fruits and vegetables in diet: Unprocessed 3783 O75 7) 22.6 Processed 2784 156.68 17.8 Substitution 1t 2190 142.32 15.4 Substitution 2+ 1837 138.13 13.3 *? °Sr determinations were obtained from Tri-City Diet Study, Health and Safety Laboratory Fallout Program Reports.’ * tSubstitution 1 classifies fruits and vegetables into use, taste, and preference subcategories so that dietary changes are in accord with normal practices. Substitution 2 uses maximal possible reductions without concern for taste or preference criteria. Dietary Alterations and ?° Sr Intake In regard to ?°Sr, we are primarily interested in remedial measures of chronic nature since we assume that the input will remain contaminated over long periods of time. We have pointed out that, for manipulation of diet to produce a minimum body burden of radioactive strontium, we should aim for a minimum value of O.R.jbody/diet divided by the percent calcium in the diet? * where CONTROL OF FALLOUT CONTAMINATION 585 Sr/Ca of body O-Rbody/diet = Sr/Ca of diet 1) In experimental studies with rats, we have been able to reduce the strontium burden by a factor of almost 10 by adjustment of diets containing high levels of calcium, phosphorus, and magnesium.*° Similar results have not been tested rigorously with human beings. It is possible to reduce the strontium-to-calcium ratio of milk by a factor of 2 to 4 by increased calcium feeding of dairy cows.°°® Such dietary interventions are not feasible, however, for two main reasons: (1) unknown possible side effects over long times and (2) difficulty of implementation. (As a side note, we should emphasize that supplemental calcium should originate from an uncontaminated source, 1.e., inorganic as opposed to animal sources. A study of commercial calcium tablets showed that many of them were derived from bone meal carrying a higher 7° Sr-to-calcium ratio than the contemporary diet.° ’) The extent of reductions possible by modifications of dietary habits is of interest. Two time periods are compared: (1) early after the contamination event when surface deposition is prominent and (2) later when the soil—plant—animal- products pathway is more important. From our knowledge of discrimination processes, we have been able to predict the relative degrees of contamination among various types of foods. We now have some data to support these ideas, and the following discussion is based primarily on survey data, with calculated modifications based on experimentation. Table 6 shows a typical pattern of calcium and ?°Sr contribution to the diet during a period shortly after a contaminating event.°® Note that dairy products and fruits and vegetables are the major contributors in terms of absolute amounts. Table 7 shows the effect of removing 90% of the ?° Sr from milk; note that there is less than a 50% reduction in the ?°Sr-to-calcium ratio of the total diet. For infants or others on a normal diet consisting almost entirely of milk, however, the net effect would be greater. The same general effect could be Table 6 TYPICAL CALCIUM AND °° Sr CONTRIBUTION TO TOTAL DIET IN NEW YORK CITY, 1961—1963 Calcium, ZO Sr, Food group g/year pCi/year 2 Sr/Ca Dairy products 238 3784 Grain products a9 1050 Meat, fish, and eggs 45 153 Fruits and vegetables 64 2560 Total 406 7547 18.6 586 THOMPSON, WENTWORTH, AND COMAR Table 7 EFFECT OF MILK DECONTAMINATION ON CALCIUM AND °°Sr DIETARY INTAKE IN NEW YORK CITY, 1961—1963 Calcium, ao Sr: Food group g/year pCi/year °° Sr/Ca Dairy products 238 378 Grain products 59 1050 Meat, fish, and eggs 45 153 Fruits and vegetables 64 2560 Total 406 4141 102 Table 8 EFFECT OF ELIMINATING MILK FROM DIET IN NEW YORK CITY, 1961—1963 Calcium, 9° Sr, Food group g/year pCi/year °° Sr/Ca Grain products 59 1050 Meat, fish, and eggs 45 153 Fruits and vegetables 64 2560 Total 168 3763 22.4 produced by eliminating milk from the diet and substituting inorganic, uncontaminated calcium. Table 8 shows what happens if milk is eliminated from the diet; two detrimental effects occur—a lowered calcium intake and a high °°Sr-to-calcium ratio. If fruits and vegetables are rigorously processed and selected for a low ?° Sr-to-calcium ratio, only a small benefit (about 20%) can be attained (Table 9).°° Table 10 summarizes the possible effects of various treatments on the ?°Sr-to-calcium ratio of the total diet. Even with the most diligent efforts, only a factor of 3 appears to be attainable. The situation for 1967, representative of a low fallout rate, is also shown in terms of possible reductions.?” The main points are that milk decontamination and manipulation of fruits and vegetables would be comparatively less effective during low fallout than under conditions of high fallout rate. Within recent years two substances, aluminum phosphate gel and alginates, have been shown to reduce the absorption of strontium from the gut much more than that of calcium. The effect of phosphate gels was first noted by Spencer and colleagues.*° Using Phosphajel produced by Wyeth Laboratories, Spencer reported average reductions in strontium uptake in man of about 87% as compared to reductions in calcium uptake of about 37%. Studies with dairy CONTROL OF FALLOUT CONTAMINATION 587 Table 9 PROCESSING AND SELECTING VEGETABLES FOR LOW ?° Sr CONTENT— EFFECT OF DIETARY INTAKE IN NEW YORK CITY, 1961—1963 Calcium, 2OSps Food group g/year pCi/year °° Sr/Ca Dairy products 238 3784 Grain products 59 1050 Meat, fish, and eggs 45 153 Fruits and vegetables 39 966 Total 381 39535 15.6 Table 10 COMPARISON OF VARIOUS TECHNIQUES FOR REDUCING ?°Sr IN TOTAL DIET IN NEW YORK CITY, 1961—1963 AND 1967 Technique 1961-1963 1967 1. Normal 18.6 15.6 2. Milk 90% decontaminated 10:2 10.4 3. Milk eliminated 22.4 24.1 4. Fruits and vegetables selected 15.6 15.6 5. Combination of techniques 2 and 4 6.0 10.4 cows have shown little effectiveness in reduction in strontium levels in milk because the amounts of phosphate gel that must be fed are impractical."’ There has been considerable interest in the use of alginates. The selective inhibition of strontium absorption following the administration of sodium alginate to rats was first reported by Skoryna, Paul, and Waldron—Edward*! of Canada; they observed a 50 to 80% reduction of radiostrontium absorption with no significant reduction in calcium absorption. Similar inhibition of radio- strontium absorption by sodium alginate has since been observed in rats and humans by others.** *4 Commercially available alginates are salts of naturally occurring compound polymers of mannuronic and guluronic acids (alginic acid) which are extracted from brown seaweed (Phaeophyceae). Sodium alginate, which is water soluble, is already widely used in the food industries in such products as ice creams, Jellies, jams, puddings, etc., as an emulsifying and stabilizing agent. Alginates with a high guluronic acid content, such as those derived from certain Laminaria species, appear to be most effective. When such products are fed to rats at the rate of 10% of their diet, typical reductions in strontium 588 THOMPSON, WENTWORTH, AND COMAR absorption range from about 75 to 80%, whereas changes in radiocalcium absorption have varied between —29 and +33% (Refs. 42 to 44). Hesp and Ramsbottom in 1965 and Sutton in 1967 reported a reduction in radiostrontium uptake of 64 to 89% when 10g of sodium alginate derived from Laminaria species was fed to adult humans who had fasted overnight.*°’*® When sodium alginate derived from Macroystis pyrifera, which has a lower guluronic acid content, was administered as a jelly to human adults, strontium retention was reduced by about 56%, whereas radiocalcium retention was reduced by only 18% (Ref. 42). Humphreys*’ and Tanaka etal.*® described alginate derivatives, some of which appear to be more effective than sodium alginate. A derivative containing 95% L-guluronic acid fed to rats at a rate of 10% of their ration reduced radiostrontuum absorption by 84% with no inhibition of calcium absorption, and, when it was consumed by humans, a reduction in the absorption of 87m Sy by 83 to 85% was indicated.*?°*© Tanaka et al.*® after studying several degradation products of alginates, concluded that their strontium binding capacities in vivo are only partly dependent on the presence of a high guluronic acid content. In a very recent study*® of the absorption of *’Ca and °° Sr in four human volunteers with and without sodium alginate, the alginate decreased the retention of °° Sr by 70% and of Pea by 7%. The stable elements Na, K, Mg, and P were also studied, and no change was observed in their excretion pattern or plasma level. There has been some indication that alginate interferes with iron metabolism because of its strong binding potential for ferric ion, but this issue is still equivocal. Our own studies show that sodium alginates have a selective inhibition of 1l As in rats and humans, the source of the strontium absorption in the bovine. alginate is important in determining its effectiveness. Using sodium alginate derived from Laminaria species, we observed a reduction of about 70 to 80% in milk radiostrontium levels when 5 to 7% of the ration was sodium alginate. A serious problem of palatability of sodium alginate exists with cows. Most cows reject this material when it is included in their rations at levels above 5 to 7%, and some cows will not eat their feed when 1% sodium alginate 1s included. We are presently attempting to see what the maximum reduction might be by using a combination of various substances that have been effective individually (Ca, POg, Mg, Phosphajels, alginates). The possible effects on other essential trace minerals is a problem that would have to be explored before any long-term large-scale application could be implemented. Dietary Alterations and '*" Cs Intake The general methods that tend to reduce '?!1 and radiostrontium also tend to reduce '*’Cs exposures via milk. In contrast to the other radionuclides, however, at early times '*’Cs could be an appreciable contaminant of meat. CONTROL OF FALLOUT CONTAMINATION 589 The feeding of Prussian blue (ferric ferrocyanide) has been of recent interest . a) : -o F . . as a countermeasure against '* ’Cs. Nigrovic? °°?’ observed that oral administra- f '27Cs by as much as 99% in rats. In tion of Prussian blue reduced absorption o addition, excretion of parenterally administered '*7Cs was accelerated when Prussian blue was fed. Madshus et al.°”? reported that feeding young dogs 1.5 to 3 g of Prussian blue daily for 10 days and following by 11 days of whole-body counting reduced the '?’Cs biological half-time to 59% of that measured in control dogs. Two of these investigators then ingested 1 uCi of '?7Cs and 10 months later started to consume 3 g of Prussian blue per day.’* The biological half-time dropped from 110 to 115 days to about 40 days. Our own studies have confirmed Nigrovic’s observations in respect to the effects of Prussian blue fed to rats.1! Furthermore, this material was shown to be effective in the ruminant. Radiocesium levels in the milk of cows have been reduced to about 1% of control levels by feeding Prussian blue simultaneously with the radiocesium. When Prussian blue was administered some time after the ingestion of '°7Cs or '?*Cs, the decline in radiocesium levels in milk with time was accelerated by as much as a factor of about 5. This effect has been observed at times of even 100 days after the ingestion of cesium. Current studies at our laboratory indicate that Prussian blue is also effective against absorption of radiocesium in such other meat-producing animals as hogs and sheep. Slight constipation is the only side effect yet observed following ingestion by humans of Prussian blue. The binding mechanism of Prussian blue for cesium in the gastrointestinal tract appears to be so selective that potassium metabolism is not greatly affected.°* DECONTAMINATION Insofar as decontamination is concerned, most work has been done with milk through cooperative studies by the U.S. Department of Agriculture (USDA), U.S. Atomic Energy Commission (USAEC), and U.S. Public Health Service. Pilot and full-scale facilities that demonstrate the feasibility of removing more than 90% of the major radionuclides by various ion-exchange pro- cesses’ *"°® have been developed. Costs have been estimated in the range of 1 to 2¢ per quart, and there is little deterioration of quality. Although this procedure removes radionuclides in milk, the feasibility of employing such a system remains questionable. The advance preparation and planning, coupled with equipment and capital needs, make it an extremely costly procedure. Imple- mentation of widespread milk decontamination facilities would have to be balanced against many other needs during emergency conditions. Similar problems must be faced in removing contaminants from the land. Procedures have been developed®’'*® for removing the top layers of contami- 590 THOMPSON, WENTWORTH, AND COMAR nated soil which reduce contamination levels by more than 90%. However, the resultant disposal problem and the loss in soil productivity present strong physical and economic limitations. Other practices, such as deep plowing, leaching, addition of lime, etc., offer possibilities under certain conditions. Perhaps alterations in farming systems or changes in primary production centers could provide adequate reductions in plant radionuclide levels under most postattack conditions. Massive fallout contamination might require the implementation of these more drastic measures but only for restricted geographic areas. Their use on a nationwide basis seems hardly likely because, if conditions warrant such uses, the capabilities or capacities to initiate them will already have been lost. The simplest and most logical decontamination techniques are already available and are in use in the case of most plant foods. Normal food preparation and processing practices in the home and factory remove a significant fraction of the surface-deposited radionuclides. Table 11, which gives a general summary of the normal removal rates, shows that 30 to 60% removal is readily attainable for P3 ty e’sr and 4° ’Gs. Greater reductions, up to 80 and 90%, are also possible by using more-extensive preparation techniques (several washings, scraping, peeling, cooking, and discarding cooking water). Table 11 DECONTAMINATING FRUITS AND VEGETABLES* eB 20S r: SAGs: % reduction % reduction % reduction Fruits 25 to 50 20 to 50 20 to 60 Vegetables Leafy 30 to 50 25 to 50 30 to 60 Podded 30 to 80 40 to 80 25 to 50 Root 20 to 40 20 to 80 Other 25 to 60 25 to 75 10 to 50 *General ranges of values were obtained from controlled experiments and fram data reported in the literature. Existing treatment facilities for most of the operating water-treatment plants can also remove many of the radionuclides that would be deposited after an attack. Conventional processes such as coagulation and settling remove about 75% of the fallout debris.°°’®° Many of the slightly soluble fallout particles can be precipitated as metal hydroxides by adding coagulating chemicals. Removal of the soluble particles requires ion-exchange or distillation methods. Individual home water softeners also are very effective, removing more than 90% of the radioactive materials.°°°°° In shallow ponds or lakes, however, initial and CONTROL OF FALLOUT CONTAMINATION 591 continuing contamination might be a serious problem during the immediate postattack period. SUMMARY Postattack dietary measures would depend on the nature and scope of the initial nuclear attack. Changes in dietary makeup designed to reduce radio- nuclide intake might be of limited value if mass devastation occurred, because other more pressing needs (survival, health, nutrition) would have much higher priority for a considerable time during the recovery cycle. Once immediate needs were met and a fair degree of recovery were under way, there would be greater need and desire to initiate dietary radionuclide-reduction techniques, particu- larly for selected population groups important to succeeding generations. The lighter the degree of devastation, the earlier this phase would probably occur, being of primary importance in a single event or when the contamination was limited to a small area. Although a wide variety of techniques for reducing dietary radionuclide intake is available, there is no single procedure that fits all the requirements considered essential to public health (i.e., effective, safe, practical, and feasible for implementation). The broadest capability for action rests with procedures developed for fluid milk because of its importance in dietary structure and its use as an indicator product. However, despite the wide array of techniques, no single step or procedure solves the problem. Thus supplementary efforts in reducing soil, water, plant, and animal radionuclide contributions would continue to be necessary for maximum possible reductions. They should form an ordered listing of feasible actions available for use when recovery conditions permit. In line with the use of dietary remedial measures or countermeasures, the need for a survival action guideline becomes apparent. Current philosophy underlying the minimum-radiation-exposure concept does not meet the needs of an attack environment when exposure levels would be much higher for the survivors. Our present planning must be revised to include some concept of special exposure guidelines expected in a postattack environment. REFERENCES 1. Federal Radiation Council, Background Material for the Development of Radiation Protection Standards, Report No. 1, Superintendent of Documents, U.S. Government Printing Office, Washington, D. C., May 1960. 2. Federal Radiation Council, Background Material for the Development of Radiation Protection Standards, Report No. 2, Superintendent of Documents, U.S. Government Printing Office, Washington, D. C., September 1961. 3. 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Menzel, Reclamation of Agricultural Land Following Accidental Radioactive Contamination, in Protection of the Public in the Event of Radiation Accidents, Proceedings of WHO/FAO/IAEA Seminar, Nov. 18—22, 1963, Geneva, World Health Organization, Geneva, 1965. . Agricultural Research Service, Protection of Food and Agriculture Against Nuclear Attack, USDA Handbook No. 234, p. 10, 1962. W. J. Lacy, Civil Defense and Municipal Utilities, Municipal South, 9(3): 19-25 (March 1962). .C. P. Straub, Removal of Radioactivity by Water-Treatment Processes, in Low-Level Radioactive Wastes, pp. 155—202, Superintendent of Documents, U.S. Government Printing Office, Washington, D. C., 1964. SENSITIVITY ANALYSIS OF AGRICULTURAL DAMAGE ASSESSMENT STEPHEN L. BROWN Stanford Research Institute, Menlo Park, California ABSTRACT This paper discusses the sensitivity of conclusions drawn from damage-assessment studies of fallout effects on agriculture to variations in the assumptions, parameter values, and models used. Among the parameters analyzed for sensitivity were the assumed date of nuclear attack; the type, weight, and efficiency of the attack with respect to agriculture; the season over which feed and food crops were assumed to be vulnerable; the lethal and threshold dose criteria; the dose-rate multiplier; and the beta-to-gamma dose ratio (which is, in turn, influenced by foliar retention, time of arrival, and the soil-roughness attenuation factor). The sensitivities are compared both qualitatively and quantitatively. The Office of Civil Defense (OCD) is continually faced with decisions about how to allocate its scarce resources to best serve its mission, which, in highly simplified terms, is to make preparations that would lessen the impact of nuclear war on the nation if an attack should in fact occur. The allocations must be made in such a way that the net estimated improvement in the nationwide postattack situation is maximized, no matter what budget level OCD may designate. Allocations both for plans and operations and for research are affected by such considerations. A major purpose of the National Entity Survival (NES) studies is, therefore, to identify the elements of the national entity that are most vulnerable so that additional research or operational preparations in those areas will be of most benefit to the nation. The emphasis, as mentioned previously, is on the long-term national benefit, whether or not the short-term benefits would seem to accrue preferentially to some specific localities or some special-interest groups. In this context the NES approach is, in effect, a large-scale sensitivity analysis in which many smaller-scale analyses are em- bedded. The agriculture part of the NES is, therefore, undertaken to assess the vulnerability of agriculture relative to other elements of the national entity and, 595 596 BROWN within the sphere of agriculture, to identify the most vulnerable factors and the most sensitive uncertainties. A clearly identified vulnerability would be a subject for operational preparations, whereas a highly sensitive uncertainty would be a candidate for additional research funds. Agricultural damage assessment, which is concerned with estimating the magnitude of agricultural damage in comparison with damage to other segments of the national entity, is accomplished by operating on a set of basic agricultural data with a mathematical model of attack effects based on a hypothetical attack pattern. The agricultural data are usually reasonably accurate for the year in which they were acquired, but they become less representative as time goes on. The attack pattern can be considered a pure assumption, and the structure of the mathematical model is only a highly simplified representation of reality, having parameter values which are set by using the best empirical or theoretical knowledge available but which may be badly in error. Because so many possibilities exist for introducing errors into a damage- assessment calculation, the conclusions reached about the relative vulnerability of agriculture vis-a-vis other elements of the national entity are always uncertain. The degree of uncertainty in the conclusions is affected by the degrees of uncertainty in the input assumptions, and the quantification of these relations constitutes a sensitivity analysis. Sensitivity analyses can generally be carried out in either of two ways. The brute-force method repeats all the model computations for each of the permissible values of each parameter. This method is attractive because of its simplicity and unambiguity. When the computational scheme is complex and the number of parameters large, however, the brute-force method becomes rather unwieldy and expensive. A sophisticated method, on the other hand, operates on the partial derivatives of the computational output with respect to each input parameter, evaluated at the standard values of each parameter and at other selected parameter sets. This method has the virtues of elegance and of the ability to dispense with many computational details necessary in the brute-force method. This approach depends on expressing the input data and mathematical relations in reasonably analytic form, however, and becomes increasingly cumbersome as the number of discontinuities and ranges of validity* become large. The agricultural problem is characterized both by tabular data not analytically determined and by multiple ranges of validity. A compromise approach can be taken to meet the challenge of these difficulties. Basically the brute-force method can operate on a much simplified set of data and computational procedures. The parameters can be varied in only two or three steps, e.g., “‘standard’”’ and ‘“‘worst-case’”’ values. The standard values, at least at the time they are first set, should be the most probable values, perhaps with a somewhat conservative bias. The worst-case values are much more difficult to set, and undoubtedly an “‘even worse”’ value for some will eventually *These are branches in the computation. SENSITIVITY ANALYSIS 397 be found. However, an attempt should be made to choose values that would be the worst with, say, about 90% confidence, although such probability assignments are clearly no more than intuitive. AGRICULTURAL DAMAGE ASSESSMENT In this section agricultural-damage-assessment models and the data bases upon which they operate are reviewed. A detailed description of this damage-assessment system has been reported before,’ and only the most general features are described here. Basically the purpose of agricultural damage assessment is to predict the capability of the United States to produce food crops and livestock during the year following a hypothetical nuclear attack. The scope of the study 1s limited to the direct effects that fallout radiation has on this capability. Neither the farm losses due to lack of input resources, such as petroleum, agricultural chemicals, and seed, nor the more subtle effects of degraded management capabilities are considered in this discussion. Furthermore, nothing is implied about the state of the food-processing and distribution functions. Thus the data base consists of the amounts of food and feed crops and the livestock herds produced in one year. The base year for these studies is 1959; the Census of Agriculture for 1959 reports the number of harvested acres for food and feed crops and the number of animals on farms for every county in the United States.” Only the major crop and livestock categories were used in the studies reported here—the term “‘major” being defined principally in terms of caloric value. A summary of the data base as stored on magnetic tape 1s shown in Table 1. In the standard damage assessment, the data base is processed county by county, and the surviving quantities of resources are cumulated by state, region, and nation. As pointed out earlier, however, this procedure 1s virtually impossible for sensitivity analyses. To surmount this difficulty, we placed the data for each resource category in rank order according to the concentration of the resource (acres harvested per unit area of the county or number of head of livestock per unit area). We then totaled these to form a cumulative distribution function showing the percent of a year’s production grown as a function of the percent of the U.S. area represented by the producing counties. Figure 1 is an example of such a distribution function for soybeans. Functions were also established in the same manner for only those acres on which crops were growing and were vulnerable on the postulated date of attack (June 15). (See Ref. 3 for a more detailed discussion.) All the agricultural resources studied yielded cumulative distribution functions very similar to those in Fig. 1, and each could be reasonably well represented by the analytic function fy =a (1 —e Afa) (1) 598 BROWN Table 1 AGRICULTURAL DATA BASE Livestock* Cropst Chickens Shae Corn 724 Alfalfa 42 Hogs and pigs 72 Sorghum app Potatoes 50 Milk cows 3 Winter wheat 23 Green peas$ 51 Bulls, steers, and calves 14 Spring wheat 24 Sugar beets 56 Winter oats 25 Tomatoes § 57 Sheep and lambs 15 Spring oats 26 Sweetcorn 61 Winter barley 27 Snap beans$ 64 Spring barley 28 Cabbage § 68 Rice 29 Dry onions§ 72 Dry beans§ Sel Carrots§ 73 Soybeans 32 Lettuce § 76 *Each record contains a region—state—county code, the national location code, the latitude and longitude of the “‘center’’ of the county, the area of the county, and the numbers of animals. tEach record contains a region—state—county code, the national location code, the latitude and longitude of the ‘‘center’’ of the county, the crop number code, the number of acres harvested, the yield per acre in tons, the normal planting and harvest dates, and the area of the county. =Numerical code for resource is used for identification. $ These items were used in the sensitivity analysis but not in the basic damage assessment. 0.8 0.6 0.4 0.2 CUMULATIVE FRACTION VULNERABLE 0 0.05 0.10 0.15 CUMULATIVE FRACTION OF U.S. AREA Fig. 1 Cumulative vulnerability of soybeans. SENSITIVITY ANALYSIS 999 where fy, is the cumulative fraction of the resource vulnerable and f, 1s the associated cumulative fraction of the U.S. area. The parameters a@ and A vary with the resource; @ is unity if the entire crop 1s assumed vulnerable but is less if only the growing crop is vulnerable on the date of attack, and A is a measure of the concentration of the resource. In the standard damage assessment,’ the assumed attack pattern 1s processed by a fallout-prediction system to yield the standard intensities, accumulated doses, and times of arrival of the fallout at thousands of standard locations throughout the nation. These are related to the counties in which they appear, and the crop or livestock resource is then assumed to be exposed to a corresponding distribution of gamma doses. The dose and intensity distributions are further processed to determine a distribution of entry times at which farmers can resume tending their crops. If a planting or harvest date is missed, then the possible fraction harvestable is reduced accordingly. The gamma doses are also compared with the lethal doses (LD; 9) for the livestock herds; the entire herd is assumed to be lost if the dose exceeds the LDs 9 and to survive if it is lower. The total dose to crops is compared with a 100 50 YIELD, % LD/8 LD log DOSE Fig. 2. Reduced yield. survival curve (Fig. 2) determined by two parameters, lethal dose (LD; 00), above which no yield survives, and threshold dose (LD/8), below which 100% yield is obtained. Selected lethal doses used are shown in Table 2. The total dose to crops is obtained from the gamma dose by application of a total-to-gamma dose ratio that accounts for the contribution of beta radiation to the total dose. 600 BROWN The total-to-gamma dose ratio depends on the time of fallout arrival and on several parameters of the plant and source geometries, including the size of the Table 2 LETHAL DOSES Crop Rads Most grains 4,000 Rice 20,000 Soybeans 14,000 Potatoes 12,500 Sugar beets 13,500 plant, the fraction of fallout retained on plant foliage, and the surface-roughness attenuation factor for beta particles. The size of the plant is characterized by the height and radius of a vertical cylinder. The radiation-sensitive tissue is assumed to lie at the center of the upper end of this cylinder, and doses are calculated at that point. The fraction of fallout retained on foliage is assumed to be a function of the density of plant matter at the time of attack; both this parameter and the radius and height of the cylinder depend on the plant’s age at the time of attack. All the values for input parameters were selected on the best available data at the time, but many were no more than educated guesses. One observation that is not particularly dependent on the exact specification of all the input variables is that beta dose is quite important for most crop plants, leading to total-to-gamma dose ratios considerably larger than 1. The total-to-gamma dose ratio can be written as ; h where f) is the fraction retained on foliage, Qg, is the soil-roughness attenuation factor, and Rg, is the ratio of beta-to-gamma doses above a smooth plane source. Selected values for Rgy asa function of radius, height, and time of arrival are shown in Table 3. The beta contribution will be negligible only if both f) = 0 and Qg = 0. The surviving fractions of agricultural resources were adjusted by the possible fractions harvestable; these were cumulated and expressed as a fraction of the normal annual yields. Selected results for a medium-weight (1300-Mt) counterforce attack are shown in Fig. 3. The values shown include both beta- and gamma-dose damage as well as losses due to denial of entry to farmers. Individual figures are also available. In general, the surviving fractions indicate that agriculture is approximately as vulnerable as population (about 80% survived this attack). The balance in survival fractions is also relatively good, and the overall postattack agriculture picture appears better than for many other elements of the national entity. SENSITIVITY ANALYSIS 601 Table 3 BETA-TO-GAMMA DOSE RATIOS Radius, Height Height Height Arrival time cm of 0.3 cm of 10 cm of 300 cm 15 min O.1 33 18 2.6 0.3 14 7.8 1.5 1.0 12 0.8 0.2 16 hr O.1 22, 12 1.0 0.3 5.6 Bee, 0.5 1.0 0.4 0.3 O.1 100 ~N ol PERCENT OF PREATTACK HARVESTED ACRES OR LIVESTOCK HERDS N oO ol jo) 0 es es wn 2 tL WwW z uw 2 i, 5 So a co < te we vo n Set PWR ENS uniS, oy Sub eeks oe «og O = m7) o 0 moO =O ae Fig. 3. Survival of major crops and livestock (Attack SRI A). 602 BROWN These conclusions, however, are not necessarily any more certain than the input parameters and assumptions were. As was mentioned, the uncertainties in input parameters are often quite large, and it is not unreasonable to voice concern over the validity of the output results. The sensitivity analyses reported in the next section were performed to test the effects of uncertainties in inputs on uncertainties in outputs. SENSITIVITY ANALYSES Perhaps the most obvious uncertainty is when the attack should be assumed to occur. A conservative assumption is that the attack occurs at the time of maximum vulnerability for agricultural resources. This will surely be during the growing season, and perhaps rather early in the season because of the increased beta vulnerability of young plants. Therefore June 15 was chosen as the date of attack for the standard damage assessment. A_ brute-force analysis was undertaken, to test the validity of this assumption, and the entire assessment was run over again for a series of the attack dates. To reduce the effort to a manageable level, only the results for OCD Region 6 were obtained; these* are shown in aggregated fashion in Fig. 4. Survival is never 100%, because some g 90 (ee) oO PERCENT OF NORMAL CALORIES ~ ro) JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC. DATE OF ATTACK Fig. 4 Total food value, Region 6. -—, human calories; ----, animal calories; - - -, total calories. farmers are killed and never gain access to their crops. The variation in radiation sensitivity over the year, however, does lead to decreased survival during the period from May to September, and June 15 appears to be as conservative as any assumption, Because the total-to-gamma dose ratio (Mg,) is so important to the calculation and because many of the parameters determining it are not well known, an analysis of the variation of Mg, with the fraction of fallout retained on foliage and the soil-roughness attenuation factor was conducted. Equation 2 SENSITIVITY ANALYSIS 603 was computed for several reasonable values of the height and radius of the plant stem and for several times of arrival, assuming Qg = 0.5, 0.2, and 0.1 and f) = O01" 40,03, 01,703, and’ 1.0) Typical results are shown in Fig. 5, which indicates that misestimation of either Qg or f; over fairly wide ranges would lead to misestimates of Mg, by a factor of 2 or less. A concurrent investigation 100 TOTAL-TO-GAMMA DOSE RATIO S) h = 300 cm 0.01 0.1 1 FRACTION OF FALLOUT RETAINED ON FOLIAGE Fig. 5 Variation of the total-to-gamma dose ratio. assessing the effect of the assumed distribution of the fraction retained on foliage revealed that again the model currently in use (which assumes that the foliar fraction is all deposited on a plane at height h/2) reasonably represents Mg, for most combinations of the parameters. (See Ref. 4 for a more detailed discussion.) The principal sensitivity analysis summarized here tested the effect of the assumptions in Table 4 for standard and worst-case values.*> The damage- assessment model was highly simplified, and the agricultural resource distribu- tions represented by the functions of Eq. 1 were used. The f,(W,I), the fraction 604 BROWN Table 4 PARAMETERS OF THE SENSITIVITY ANALYSIS Parameter Type of attack Weight of attack Season of vulnerability Efficiency of attack Lethal dose Dose-rate multiplier Total-to-gamma dose ratio Lethal-to-threshold dose ratio Symbol IAT W ISV Mt Assumptions Counterforce Mixed 100, 200, 400, 700, 1000, 2000, 4000, 7000, 10,000, 20,000, 40,000, 70,000, and 100,000 Mt Vulnerable (standard) Growing Year (worst case) Random (standard) Maximum (worst case) D) rads (standard) D,/4 rads (worst case) 2.0 hr (standard) 3.33 hr (worst case) Mg (standard) 2 Mgy (worst case) Crops: 8 (standard) 16 (worst case) Livestock: 1 (standard) 2 (worst case) of the U.S. area covered by fallout of a given attack weight (W) and standard intensity (I), was as computed by Miller? for counterforce and mixed attacks. If an attack fallout pattern 1s random with respect to a given agricultural resource, the probability of damage, fy, at a given level, intensity, and yield is just equal to the total fraction of the resource vulnerable (@) times the fraction of the area covered (f,). However, if the attack pattern is of maximum efficiency against the resource, the area of growing crops or livestock can be covered with a much smaller W for a given I. In this case the fraction vulnerable to damage is given by ae ro, Se aD) (3) The dose delivered by standard intensity I is given by SENSITIVITY ANALYSIS 605 where Mg, is the total-to-gamma dose ratio and M; 1s the dose-rate multiplier that converts gamma dose rate to gamma dose on the basis of time of arrival and period of exposure. The total fraction damaged is then given by a I df. ip = i kin diy (5) 0 where k and |, (the threshold intensity) can be computed from Eq. 4 and the analytic expression for Fig. 2. This fraction was computed for each of the assumptions in Table 4, and typical results plotted as a function of weight of attack are shown in Fig. 6.* 0.25 Maximum 0.20 0.10 7se=- Standard AE wise One-step sensitivity 0.05 1000-kVp X ray dzD Bilateral 314 189 ity 250-kVp X ray Thee) Bilateral 389 245 6 ACO) 4.35 Bilateral 318 194 9 &° Co 0.5 Bilateral 338 206 9 &°'Co 0.3 Multisource 524 2058 19 SEXO 0.06 Free moving§ 495 302 9 GO 0.033 Free moving§ 637 389 9 Swine INGO 50.0 Bilateral 350 to 400 240 2 1000-kVp X ray 30.0 Bilateral 510 2508" 4 SK Go) 18 to 29 4 pi 393 228 20 eEO 18 to 29 4 pi 335 218 20 1000-kVp X ray 27.0 Bilateral 425 255 21 2000-kVp X ray 15.0 Bilateral 350 to 400 230m 4 PCO Lalie5 Bilateral 375 260 22. AK Gro) 10.0 Bilateral 400 to 450 270 2 1000-kVp X ray 9 to 10 Bilateral 399 270 3 22 CO 1.0 Bilateral 650 to 700 425 2 CO 0.85 Multisource 618 370** 13 CO 0.067 Free moving 2000 to 2500 1350 to 1700 10 *Only studies in which a relatively homogeneous depth-dose distributions were obtained are presented in this table. Those in which unilateral or dorsal—ventral exposures or low-energy radiations were utilized are not included. + Value is estimated by Trum.' * t Estimate is based on data presented in the reference cited. § Value is estimated by Bond.’ § Although they were exposed from one direction, the animals’ random-movement resulted in equal exposure to both sides, providing an effective bilateral exposure. **Value is estimated by D. Brown.’ VULNERABILITY OF LIVESTOCK 651 Table 2 SURVIVAL OF SHEEP AND GOATS EXPOSED CONTINUOUSLY TO °° Co RADIATION Dose per day Mean survival Mean cumulative Species and dose rate time, days lethal dose, R Sheep?? = 46 R at 0.033 R/min 43 (males) 1975 Goat?* = 40 R at 0.033 R/min 57 (males) 2280 50 (females) 2000 30 R at 0.025 R/min 85 (males) 2590 81 (females) 2430 15 Rat 0.013 R/min 240 (males) 3600 161 (females) 2415 7.2 Rat 0.007 R/min 1152 (males) 8330 384 (females) 2650 Table 3 SURVIVAL OF LARGE ANIMALS EXPOSED TO FRACTIONATED DAILY EXPOSURES OF °°Co RADIATION* Dose per day Mean survival Mean cumulative Species and dose ratet time, days lethal dose, R Burro Single dose 25 400 R at 0.28 R/min 8 3,320 200 R at 0.14 R/min 14 2,820 100 R at 0.07 R/min ZS, papejehe) 50 R at 0.035 R/min 30 1,510 25 Rat 0.017 R/min 63 125. Cattle Single dose 20 100 R at 0.07 R/min 52 3,200 50 R at 0.035 R/min 45 EPOX) Swine Single dose 15 100 R at 0.07 R/min 39 3,900 50 R at 0.035 R/min 205 10,250 *These studies were conducted at the UT—AEC Agricultural Research Laboratory; the multiple-source (°° Co) exposure at a dose rate of 0.5 to 0.85 R/min wasused (Brown’ ). tDose rate in roentgens per minute calculated as though the daily exposure was continuous for the entire 24 hr per day. 652 APPENDIX B The data in Table 2 for goats and sheep exposed continuously until death at rates of a few roentgens per hour dramatically show the relation of dose rate to lethality, as do the fractionated data of Table 3. The total data are consistent with the generally accepted conclusion that effectiveness of the dose is diminished as the dose rate is diminished or as the period of exposure is protracted. However, it is clear that the relation between dose rate and LDs 9 1s not linear, especially at the lower dose rates. This was discussed by Page” in another paper, from which most of the data for these tables were taken. There must be a mechanism to explain the loss of effectiveness with decreasing dose rate or protraction of radiation exposures. Recovery from part of the exposure during the continued exposure is probably the explanation. A number of recovery studies®’>’*!°°'* have been done with large domestic animals. The recovery rates of the various species can be estimated from these studies; the species, ranked in descending order of recovery, are swine (fastest), goats, sheep, and burros. These studies used the “‘split-dose”’ or “‘paired-dose”’ technique to determine the recovery; this technique consists essentially in determining the change in LDso9 with time after a sublethal conditioning radiation exposure. The data show that the recovery for large animals may vary from the very slow early recovery seen in sheep, goats, and burros to the rapid early recovery seen in swine. A resistance or overrecovery occurs in sheep and swine, with the resistance of swine appearing to be rather long lasting, at least to 100 days. Swine appear to be unique in this long-lasting resistance. Goats recover to a normal state but, unlike sheep, do not show a period of overresistance. For burros it appears that there is no overrecovery and that the recovery process 1s very slow indeed. If subjected to close analysis, the data show that recovery is somewhat dependent on the size of the initial conditioning exposure or initial injury. Although most recovery studies used two-thirds of the LDs5o as a conditioning dose, one study?* with sheep used a conditioning dose of one-third of the LDs9. This study indicated the strong influence of the size of the initial radiation injury on subsequent recovery: the pattern of the recovery curve was similar for sheep conditioned with either one-third or two-thirds of the LDso exposure, but, quantitatively, recovery occurred at a more rapid rate, and overrecovery was greater for animals conditioned with a smaller exposure. The cause of death for most of the animals exposed at rates that may reasonably be expected from fallout gamma radiation appeared to be hemato- poietic damage. Usually there was an early and a rapid drop in the mononuclear white cells followed by a severe drop in blood platelets. If the dose was less than lethal, the blood elements showed a return toward normal with time, Le., recovery. However, if the exposure continued or if the initial exposure was of sufficient magnitude, the blood elements continued to decrease and death occurred. An exception to this case is the burro. In burros a number of early deaths were noted; these were associated with a central nervous system (CNS) type of VULNERABILITY OF LIVESTOCK 653 syndrome. Apparently this CNS syndrome at relatively low total doses is unique to the burro, although we know of at least one adult cow that died within 2 hr after an exposure of less than 500 R of °°Co. This was a leukemic animal in poor condition initially, however, and, since she was not observed during the period, her movements were not recorded. In general, what is known regarding the vulnerability of livestock to gamma radiation can be summarized as follows: The midline-tissue doses would be of the order of one-half to two-thirds of the midline-air exposures and would probably be omnidirectional. Radiation doses causing lethality would be of the order of 125 to 300 rads, but the rate at which the exposure is received would have a great bearing on the effect. In general, the lower the rate of delivery, the greater is the lethal dose. However, the few studies in which animals have been continually exposed until death at low rates show that, at about 20 to 40 R/day, a steady state cannot be maintained. Median survival times are prolonged, up to 40 to 80 days, but death ensues. The goats exposed by Hupp?* to about 7 R/day had median survival times of 384 days for females and 1152 for males; this shows a great difference due to sex. All the studies indicate that recovery will occur when the initial exposure is less than lethal or when the dose rate is sufficiently low. Again, however, there is a great difference in the recovery times for the various species, as well as in the patterns of recovery. It is worthwhile to note that, in all the studies reported, the experimental subjects were usually young adult or mature animals. The response of younger animals to radiation would be of interest: Would it be about the same as for the adults? Would the recovery patterns be similar? Would the young have more or less tolerance? There are few studies involving cattle, especially regarding median lethal doses, and horses. Whether it is valid to extrapolate from sheep and goat or burro data should be resolved. A very important aspect for civil-defense consideration is the development of a simplified set of descriptive symptomatology that the lay person (1.e., the owner or herdsman) can use in the field. The response of livestock to gamma radiation is reasonably characterized under laboratory conditions, especially for exposures at the higher rates and, to some extent, for exposures at protracted rates. The experienced individual can easily detect small changes in the condition of an exposed animal when various laboratory and diagnostic procedures are available to him. But these procedures are not a “tool” in the average farmer’s inventory. What is needed is a straightforward guideline that will tell the farmer what procedures he should follow if he recognizes certain signs exhibited by exposed animals and what the likely outcome will be for the animals that show these changes. Such a guideline would be of considerable value in helping the farmer plan his future actions. 654 APPENDIX B REFERENCES al: ay 10% skate 25 lS): 14. [5 NO: WW) V.P. Bond and C. V. Robinson, A Mortality Determinant in Nonuniform Exposures of the Mammal, Radiat. Res., Suppl., 7: 265 (1967). .D. G. Brown and R. Cragle (Eds.), Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, Apr. 29—May 1, 1968, USAEC Report CONF-680410, UT—AEC Agricultural Research Laboratory, July 12, 1968. .D. S. Nachtwey, E. J. Ainsworth, and G. F. Leong, Recovery from Radiation Injury in Swine as Evaluated by the Split-Dose Technique, Radiat. Res., 31: 353—367 (1967). . J. L. Tullis, F. W. Chambers, J. E. Morgan, and J. H. Zeller, Mortality in Swine and Dose Distribution Studies in Phantoms Exposed to Supervoltage Roentgen Radiation, Amer. J. Roentgenol., Radium Ther., Nucl. Med., 67: 620 (1952). G. E. Hanks, N. P. Page, E. J. Ainsworth, G. F. Leong, C. K. Menkes, and E. L. Alpen, Acute Mortality and Recovery Studies in Sheep Irradiated with °° Co Gamma Rays or 1-Mvp X Rays, Radiat. Res , 27: 397—405 (1966). .T. S. Mobley, W. R. Godden, and J. deBoer, Median Lethal Dose (LD, ,/,,,) Studies in Sheep Following 250-kvp X Irradiation, Report AD-631189, Air Force Weapons Laboratory, Kirtland AFB, N. Mex., March 1966 (AFWL-TR-65-200). .D. G. Brown, R. E. Thomas, L. P. Jones, F. H. Cross, and D. P. Sasmore, Lethal Dose Studies with Cattle Exposed to Whole-Body Co®°® Gamma Radiation, Radiat. Res., 15: 675-683 (1961) _ E:T. Sull, NoP. Page, J. F. Taylor, W.GyY Wisecup, E.J.-Ainsworth, and Gy F.Weong, Acute Mortality and Recovery Studies in Burros Irradiated with 1-Mvp X Rays, Radzat. Res. 39 580—593-(1969): .N. P. Page, Effect of Dose Protraction on Radiation Lethality of Large Animals, in Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, Apr. 29—May 1, 1968, D.G. Brown and R. Cragle (Eds.), USAEC Report CONF- 680410, pp. 12.1—12.23, UT—AEC Agricultural Research Laboratory, July 12, 1968. J. E.. Taylor, N. Ps Page,-E. Tsull, Gor. Leong, and: E.-}, Ainsworth. the: Effector Exposure Rate on Radiation Lethality in Swine, Report USNRDL-TR-69-96, Naval Radiological Defense Laboratory, 1969. E. T. Still, J. F. Taylor, G. F. Leong, and E. J. Ainsworth, Mortality of Sheep Subjected to Acute and Subsequent Protracted Irradiation, Report USNRDL-TR-69-32, Naval Radiological Defense Laboratory, 1969. J. F. Taylor, E. T. Still, N. P. Page, G. F. Leong, and E. J. Ainsworth, Acute Lethality and Recovery of Goats After 1-Mvp X irradiation, Radiat. Res., 45: 110—126 (1971). J. H. Rust, B. F. Trum, J. L. Wilding, C. S. Simons, and C. L. Comar, Lethal Dose Studies with Burros and Swine Exposed to Whole-Body Cobalt-60 Irradiation, Radiology, 62: 569—574 (1954). J. H. Rust, J. L. Wilding, B. F. Trum, C. S. Simons, A. W. Kimball, Jr., and C. L. Comar, The Lethal Dose of Whole-Body Tantalum'** Gamma Irradiation for the Burro (Equus asinus), Radiology, 60: 579—582 (1953). B. F. Trum, J. J. Lane, U.S. G. Kuhn III, and J. H. Rust, The Mortality Response of the Burro (Equus asinus) to a Single Total-Body Exposure of Gamma Radiations from Zr°*° /Nb°*, Radiat. Res., 11: 314-325 (1959). M. O. Schultze, V. Perman, N. S. Mizuno, F. W. Bates, J. H. Sautter, H. S. Isbin, and M. K. Loken, Effects of Gamma Radiation on Calves, Radiat.Res., 11: 399—408 (1959). P. W. Edmondson and A. L. Batchelor, Clinical and Pathological Response of Goats to Whole-Body Irradiation by Gamma-Rays and Fission Neutrons, Int. J. Radiat. Biol., 10: 451—478 (1966); also Eye Findings in Goats During the 3 Years After Acute Whole-Body Neutron and Gamma Irradiation, Int. J. Radiat. Biol., 13: 147—153 (1967). 18. 19’. 20. 2h, 225 23% 24. VULNERABILITY OF LIVESTOCK 655 G. M. Krise, J. W. Austin, and E. W. Hupp, Lethal Effects of Acute and Continuous Radiation in Goats, Radiat. Res., 35: 532 (1968). B. F. Trum, in Agricultural Research Program. Semiannual Progress Report for Jan. 1, 1955, to June 30, 1955, USAEC Report ORO-145, University of Tennessee, November 1955. F. W. Chambers, Jr., C. R. Biles, L. J. Bodenlos, and J. H. Dowling, Mortality and Clinical Signs in Swine Exposed to Total-Body Cobalt-60 Gamma Irradiation, Radiat. Res., 22: 316—333 (1964). V. P. Bond, in Operation GREENHOUSE. Scientific Director’s Report, Annex 2.2. Control Studies Performed in the United States and at Eniwetok, Parts I, II, IV, and VI, USAEC Report WT-18, 1951. N. P. Page, D. S. Nachtwey, G. F. Leong, E. J. Ainsworth, and E. L. Alpen, Recovery from Radiation Injury in Sheep, Swine, and Dogs as Evaluated by the Split-Dose Technique, Radiat. Res., 25: 224 (1965). Br. ocill J Fs Payvlor,. Gy-F. eong, and, EB...) Ainsworth). Survival ‘Time: and Hematological Responses in Sheep Subjected to Continuous °° Cobalt Gamma Irradia- tion, Report NRDL-TR-69, 1969. E. W. Hupp, Texas Woman’s University, Denton, Tex., personal communication, 1970. RADIATION EFFECTS ON FARM ANIMALS: A REVIEW M. C. BELL UT—AEC Agricultural Research Laboratory, Oak Ridge, Tennessee ABSTRACT Hematopoietic death would predominate in food-producing animals exposed to gamma radiation under fallout conditions leaving animal survivors. Gamma-radiation doses of about 900 R would be lethal to 50% of poultry, and about half this level would be lethal for cattle, sheep, and swine. Grazing cattle and sheep would suffer most from combined radiation effects of skin-beta and ingested-beta radioactivity plus the whole-body gamma effects. The LD,,/,, for combined effects in ruminants is estimated to be at a gamma exposure of around 200 R in an area where the forage retention is 7 to 9%. Either external parasites or severe heat loss could be a problem in skin irradiated animals. Contrary to early reports, bacterial invasion of irradiated food-producing animals does not appear to be a major problem. Productivity of survivors of gamma radiation alone would not be affected, but, in an area of some lethality, the productivity of surviving grazing livestock would be severely reduced owing to anorexia and diarrhea. Sheltering animals and using stored feed as countermeasures during the first few days of livestock exposure provide much greater protection than shielding alone. The purpose of this review is to summarize the data available on the effects of ionizing radiation on food-producing animals which would be of value in predicting the effects that could be encountered from radioactive fallout in the event of nuclear war. Most of the data are limited to somatic effects of gamma and beta radiation on survival and productivity of cattle, swine, and sheep. Although much more information is available on radiation effects in small laboratory animals, it is difficult to extrapolate these data to large food-pro- ducing animals exposed to a combination of internally and externally applied radiation. Some attention is also given to measures that could be used to reduce radiation exposure of food-producing animals. Ionizing radiation from radioactive fallout occurs principally as beta particles and gamma rays. The median beta energies are between 0.3 and 0.4 MeV, but the maximum may be up to 5 MeV. Most of the data available on beta 656 RADIATION EFFECTS ON FARM ANIMALS 657 irradiation effects on food-producing animals were obtained by using either ?° Y or ?°Sr—?° Y, which have higher average energies than are characteristic of local fallout. Information on gamma irradiation was obtained principally by exposing large animals to °° Co or ' °7Cs, which have penetration characteristics similar to gamma fallout radiation. Limited information is given on neutron exposures, and none is given on alpha radiation since neither of these emissions is expected to be of any consequence in radioactive-fallout effects on food-producing animals. RADIATION LETHALITY General Exposures to gamma radiation at dose rates expected under fallout conditions causing early deaths in about half of the animals are expressed as a dose lethal to 50% in either 30 or 60 days (LDs50/39 or LDs5o/60). This mortality level varies with dose rate, quality and type of radiation, animal species, and a number of other variables. The upper and lower limits of the distribution of radiation deaths for adult cattle, swine, and burros are shown by the typical sigmoid curves in Fig. 1. The data obtained from °° Co exposure to 80 se as [fs —| x Fk og oO = 40 0) 400 600 800 1000 DOSE, R Fig. 1 Mortality of three species exposed to °° Co at a dose rate between 0.5 and 1 R/min. ©, cattle; +, swine; @, burros;+73, 95% confidence interval. (Data from D. G. Brown, UT—AEC Agricultural Research Laboratory.) 658 APPENDIX B dose rates of 0.5 to 1 R/min show the species variation among these large animals. This variation is much greater at the 99% mortality level than for 1% mortality. The gamma-radiation dose levels are usually expressed as either midline “air 9) dose” or midline absorbed dose as discussed by Page.’ Because of tissue mass, the gamma-radiation midline dose from fallout would be reduced by at least 50% in adult cattle, but for poultry the reduction would be inconsequential. In this review the gamma-radiation exposures are listed as the air dose to the animals, and the units are in roentgens. The data most applicable for gamma radiation from fallout in which there would be at least 20% survival of continuously exposed animals would be in fallout-deposition areas where the dose rate would not be expected to exceed 2 R/min for a period of over 1 hr. An exception to this rule would be animals that might be moved from a heavily contaminated field into a protective shelter until the early fallout had decayed to a nonlethal level. A review by Page’ showed that dose-rate effects are considerable in swine and very slight in sheep and burros. Sheep were more sensitive than swine at all dose rates reported. Reduction of the dose rate from 2 R/min to 0.1 R/min increased the estimated LDs9 dose to sheep by 20% and to swine by 340%. Swine also show 50% recovery in 3 days from acute gamma-radiation exposure, whereas sheep require about 13 days.” In a review article Brown and Cragle* reported that the swine LD59/309 at 0.85 R/min was 618 R but at 18 to 29 R/min only 310 R. They also reported that young cattle are more sensitive to gamma irradiation than adult cattle. In general, it is assumed that the young are more sensitive to radiation; however, Case and Simon* reported that at a dose rate of 4 R/min the LDs59/39 for newborn pigs was 375 R, which is near the estimated LDs5 9/39 for older swine. Data for predicting dose-rate effects in cattle are very limited, but, in general, the higher the dose rate, the lower the LDs50/30 1s in the species studied (Fig. 1). Fallout dose rate varies with weapon yield, type of burst, distance downwind, wind speed, and number and frequency of detonations. Considering both fallout and animal species variables, it appears that the most useful data would be those obtained on animals continuously exposed to early fallout, but no such data were found; therefore only information on animals exposed to a gamma dose rate of from 0.1 to 2 R/min is considered. Symptoms of Gamma-Fallout-Radiation Sickness The primary symptoms expected from gamma radiation alone at levels to produce some deaths in farm animals are those associated with damage to the hematopoietic system. These usually include a severe drop in blood platelets to the point that blood would be lost into intracellular spaces and from both the respiratory and gastrointestinal (GI) tracts owing to failure in blood clotting. Increased capillary permeability also contributes to loss of blood ceils, plasma, and electrolytes. Most of these losses occur between 14 and 30 days after RADIATION EFFECTS ON FARM ANIMALS 659 exposure when there are also low white-cell counts, sometimes accompanied by pyrexia and bacterial invasion.” Cattle exposed to 200 to 600 R at dose rates of 0.5 to 1 R/min usually show mild anorexia and slight pyrexia for about 24 hr; they then appear normal until about 14 days, when there is a marked pyrexia in those lethally irradiated; the survivors show a mild pyrexia. Anorexia and vomiting, which may be associated with the gastrointestinal death syndrome, would be expected in few if any of those surviving gamma irradiation. At the exposure and dose rate considered, the central nervous system (CNS) may be affected in some burros.* Data on burros are included since meat of equine origin is consumed at the annual rate of 2 to 3 kg per person in some European countries. The CNS and gastrointestinal death syndromes in gamma- irradiated animals would be expected only if the dose rate were higher than 2 R/min. Vomiting, anorexia, and weight loss were reported in swine exposed to 250 to 700 R of °°Co gamma radiation at 21 R/min giving an approximate ED29/ 30008 335 KR for 33-Ke swine.° None of these symptoms were seen in 30-kg growing swine surviving an exposure to 450R at 0.6 R/min from a multisource °° Co field.’ Pigs that died showed anorexia and blood loss for only 2 days prior to death, which occurred 16 to 20 days after exposure. Case and Simon* observed a mild transitory diarrhea in newborn pigs exposed to °°Co and found an LDs09/39 of 375 R at 4 R/min. These pigs had diarrhea at 2 to 5 days after irradiation and cutaneous hemorrhages at 9 to 14 days; all deaths occurred between 10 and 29 days postirradiation. Therefore it appears to be very important to consider the dose rate in determining the symptoms and LD>509/30 1M Swine exposed to gamma radiation. These data would probably also apply to other species of food-producing animals, but available data are insufficient for definite conclusions. Beta-Radiation Effects Predictions by the National Academy of Sciences—National Research Council (NAS-NRC) committee,® based primarily on data gained from dosimeter readings in dogs and goats fed sublethal levels of ?° YCI, solution,” were that the large intestine would be the critical organ and that fallout ingested by grazing livestock would be of little consequence compared with gamma- radiation effects. These conclusions were based on the assumption that fallout would be homogeneously mixed with the contents of the GI tract. Although no research data are cited, a 1965 USSR textbook! ® entitled Civil Defense in Rural Regions states that inflammation of the mucosa of lips, gums, and the deep part of the oral cavity occurs in livestock consuming contaminated feed and water. These symptoms appear after 7 to 11 days, when the animals become lethargic and refuse to eat. They also noted considerable hair loss, and the further course of radiation illness depended on the degree of injury to internal organs. In 1967 Bell'’ reported that the omasum and rumen were the organs most severely affected in sheep given 144 Ce—!4* Pr chloride solution in 660 APPENDIX B their feed. These data on sheep were obtained for levels at which 50% of the sheep developed diarrhea and half of those with diarrhea died. More recently Bell et al.'? showed that feeding an insoluble fallout simulant can be lethal to sheep and that it severely affects the productivity of survivors. The simulant consisted of 7° Y fused to 88- to 175-u sand to provide about 10 mCi/g of sand. The primary symptoms from feeding 0.8 to 3.2 mCi/kg of body weight were anorexia, diarrhea, weight loss, and pyrexia. Sufficient radioactive sand had “‘pocketed”’ in areas of the rumen and abomasum to cause ulceration and fibrin infiltration of the mucosa. Readings from microdosimeters implanted in the “pockets” of the abomasum averaged eight times as high as those in the small and large intestine. No gross lesions were found in the large intestine of the sheep. These data demonstrate the importance of using characteristic insoluble fallout simulants at levels to cause some deaths instead of depending on dosimeter measurements. An animal suffering from GI radiation injury will react quite differently physiologically from an animal under little or no radiation stress. Anorexia was accompanied by rumen stasis, which prevented the normal passage of ingesta. This was followed by severe diarrhea and weight loss. Fallout irradiation injury to skin was observed!’ in cattle exposed at Alamogordo in 1945 and in cattle at the Nevada Test Site (D. S. Barth, personal communication, 1970). Minor-to-severe beta-irradiation injuries occurred al- though no lethalities were observed within 150 days in any of these cattle. Skin-irradiation injury appears similar to thermal burns except that the visible effects of thermal burns are immediate and the obvious effects of beta skin irradiation may not be observed for 3 or 4 weeks. The skin-irradiation damage to the Alamogordo cattle was described by Brown, Reynolds, and Johnson'* as the development of areas or zones of hyperkeratosis which formed plaques and cutaneous horns on the skin of the dorsa of the cattle. After 15 years three of the exposed cows developed squamous cell carcinoma of the skin in irradiation-damaged areas. In areas less severely affected, there was some alopecia and graying of the red hair. The location of these cattle in relation to the bomb is not known, but it is estimated that the radiation dose was 150 R gamma and 37,000 rads beta to the dorsal skin. There was no evidence of radiation damage on the ventral surfaces as has been predicted to result from the beta-bath exposure from radioactive fallout on the ground. Combined Radiation Effects Research on the effects of combining beta with gamma irradiation has recently been initiated with sheep (31 kg) and cattle (184 kg) at the UT—AEC Agricultural Research Laboratory. Results summarized in Table 1 show that these animals were much more susceptible to the combined radiation sources than to any one alone. Radiation levels chosen were slightly less than those expected to cause death from the ingested fallout simulant or the whole-body RADIATION EFFECTS ON FARM ANIMALS 661 Table 1 SHEEP AND CATTLE 60-DAY MORTALITY AFTER EXPOSURE TO SIMULATED FALLOUT Number of deaths* Treatment Sheep Cattle Control O O Whole body (WB) 240 R ®°°Co gamma at 1 R/min 0 0 Skin 57,000 rads beta 1 O Gastrointestinal (GI) + 1 2 GI + Skin O 2. WB + Skin 0) O WB + GI 3 5 WB + GI + Skin + 8 *Eight animals were exposed to each treatment. tAccidental death. * +Sheep were fed 2.4 mCi of °° Y-labeled sand per kilogram of body weight, and cattle were fed 2.0 mCi of °° V-labeled sand pér kilogram of body weight. gamma radiation. Using the NAS—NRC procedure,* we calculated the ingested level of 2.4 mCi per kilogram of body weight to simulate a 7% forage retention for sheep and that of 2 mCi/kg to simulate 9% forage retention for cattle exposed to 240-R gamma radiation. Whole-body gamma from. six o?' CO sources'* was used to give a bilateral air dose of 240 R at 1 R/min. Skin irradiation of the dorsa of these animals from flexible, sealed, beta-irradiation sources’ gave a dose of approximately 57,000 rads to the surface of the hair or wool. The 7 to 9% forage retention levels are well within the range of 5 to 23% retention of 88- to 175-u particles on alfalfa and pasture grasses.’ ° Exposure of 12% of the body surface of sheep and 8% of the body surface of cattle provided a beta-to-gamma ratio comparable to the ratios estimated for the cattle exposed in 1945 at Alamogordo.'? Skin irradiation alone under these conditions did not affect feed intake, but after 60 days skin-irradiated sheep weighed only 80% as much as the controls and as those exposed only to whole-body gamma irradiation. Sheep surviving a combination of whole-body gamma and skin and GI beta weighed only 60% as much as the controls in 60 days. Whole-body gamma radiation of 240 R at 1 R/min affected neither body weight nor feed consumption of sheep and cattle when no other radiation was given. The importance of considering combined irradiation effects on survival of grazing livestock is convincing for the simulated-fallout conditions used to obtain the data summarized in Table 1. However, grazing livestock might be exposed to many different fallout conditions that would alter both mortality 662 APPENDIX B and productivity. For damage-assessment calculations, additional data are needed for alternative models, such as using different-size fallout-simulant particles, lower beta-energy exposures, different forage-retention levels, effects of absorbed isotopes (principally iodine), and different levels and rates of gamma exposures. No data were found on the combined effects of beta and gamma irradiation in horses, swine, or poultry. Grazing equine might be severely affected by ingested fallout, but the damage would probably be greatest in the stomach and cecum. Alexander!’ described the gastric and cecal contractions in horses which would probably cause some stratification of ingesta, with the heavier fallout particles collecting in pockets as observed in the rumen and abomasum of cattle and sheep. Swine are normally fed in drylot and probably would not ingest enough radioactivity to increase losses that would occur above those from gamma irradiation alone. Data are not available on pasture-fed swine, but the effect would probably be minor. Ingested fallout would not be expected to be a problem in poultry production. Data on lethality are meager for food-producing animals under simulated- fallout conditions. Estimates listed in Table 2 were obtained from published data Table 2 ESTIMATED LIVESTOCK CETHALITY (LD aie) HROM FALLOUT-GAMMA-RADIATION EXPOSURE ALONE AND IN COMBINATION WITH BETA RADIATION* Total gamma exposure, R Barn Pen or corral Pasturet Animal (WB) (WB + Skin) (WB + Skin + GI) Cattle 500 450 180 Sheep 400 350 240 Swine 640 600 SD On: Equine 670 6002 350% Poultry 900 8505 800 *Data from: M. Ge Bells= 13 B: Sassers anda iyell. West. Simulated-Fallout-Radiation Effects on Livestock, this volume. tAssumed forage retention of 7 to 9%. *No data available; estimates are based on grazing habits, anatomy, and physiology of species. on gamma lethality for the various species. Estimates for combined effects on cattle and sheep were made from research in progress at UT—AEC. Estimates for combined effects on swine, horses, and poultry were made by considering the grazing habits, anatomy, and physiology of these species since no data are available. RADIATION EFFECTS ON FARM ANIMALS 663 RADIATION EFFECTS ON LIVESTOCK PRODUCTIVITY Meat and Milk Production Gamma radiation at levels below the lethal dose and at rates expected from fallout radiation would have minor to no measurable effects on livestock productivity. Animals surviving gamma radiation at dose rates of 0.1 to 2 R/min '® and irradiated dairy cows produce almost as 131] gain just as well as the controls,” 120 Tactation can, however, be reduced by much milk as controls. destruction of thyroid tissue, as shown by Miller and Swanson,*’ who gave one of each pair of identical-twin dairy heifers doses of 99 to 180 wCi of '*'1 per kilogram of body weight. These heifers averaged 305 kg at the time of treatment, and in their first lactation they averaged 54% of the production of the untreated twins. Radioisotopes of iodine are the major absorbed fission products of concern in early fallout during the first few weeks after detonation. 1 . 'S TT over a period of However, grazing livestock are more likely to consume several weeks than in a single ingestion as described. Garner** estimated from data on sheep that cattle consuming 1500 wCi of '*'I daily would show a decline in milk yield and reduced viability of offspring. More-recent data indicate that cattle are less sensitive to '*! I injury than sheep. Radioisotopes of iodine represent 15% of the total radioactivity 24 hr after fission, but most of these are short-lived isotopes.2* Actual '*'I contributes only 0.8% at H + 24 hr and 3.5% at H + 4 days. Thyroid uptake by dairy cows at 24 hr reaches about 70% of the maximum uptake, which occurs at 72 hr.** Thus the decay factors and the rate of thyroid uptake would reduce the '?"1 equivalent effective values to about 4% for H + 24 hr. The effectiveness of the radioiodine would be further reduced by the low solubility of early fallout. Comar, Wentworth, and Lengemann,? ° using a double tracer technique in six cows, found only 20% as much radioiodine from a fallout simulant in milk as from a soluble radioiodine. Ekman, Funkgqvist, and Greitz?° report 10% solubility for early fallout. Neutron irradiation of 500 to 750 rads severely reduced feed intake, body weight, and milk production of dairy cows. Those exposed to the higher levels died within 40 days.'? Nonlethal neutron irradiation of 300 rads significantly 7 é However, neutron reduced growth of swine with no effect on feed intake. irradiation is not expected to be of significance compared with fallout radiation. Fallout-simulant beta irradiation of the GI tract of cattle and sheep severely reduces feed intake and weight. Animals surviving this type of radiation usually return to normal feed consumption within 60 days, but considerably more time is required to recover the weight loss. In a UT—AEC study involving 32 sheep (31.1 £ 0.6 kg) fed a fallout simulant, five of the survivors developed abomasal hernias, and one developed a rumen fistula in the areas most severely affected by the beta radiation. These lesions did not develop until 60 days after treatment when the animals had regained appetites. Some of the lesions ruptured to the 664 APPENDIX B outside as late as 300 days after treatment. Rumen and abomasal tissue around these openings was firmly attached to the body cavity with no evidence of peritonitis and/or bacterial invasion. There is no evidence that these animals could not be used for food, especially if food were scarce. Preliminary results from experiments with cattle indicate that hernias and fistulae would not be a problem, because of the greater thickness of the tissue involved. At present the research in progress with 184-kg beef calves indicates that feeding 2 mCi of 2° v-Jabeled sand per kilogram of body weight for 3 days severely affects feed intake and body weight, but no calves died from either 240-R gamma at 1 R/min or from beta irradiation of 8% of the body surface over the dorsum. When these three treatments were combined, however, all calves died within 60 days (Table 1). Neither beta irradiation to the skin nor whole-body gamma irradiation had an effect on feed intake, but weight gain was considerably reduced by skin irradiation of both sheep and cattle. During the winter months the loss of body heat would be expected to be much greater in a colder climate than in Tennessee, where the experimental animals had access to shelter. During the warm months the fly problem required frequent attention, starting about 30 days after skin irradiation. The fly-larvae damage could have caused increased animal losses if insecticides had not been used. It appears that most surviving sheep and cattle suffering from skin injury from fallout or from GI injury in combination with whole-body gamma irradiation could eventually be used for food under emergency conditions. Research in progress at UT—AEC (Griffin and Eisele, personal communication, 1970) indicates that bacterial invasion is not a problem in swine dying from gamma irradiation given at a dose rate of 1 R/min. Until more data are available, it is recommended that, for 15 to 60 days after exposure to levels to cause some mortality, only muscle meat from surviving animals be used for food. Poultry A review by Wetherbee?® showed that young irradiated chicks developed hypotension and that the survivors had a reduced rate of growth. Egg production was reduced only when layers were exposed to 600 R and above from SO Corat 0.9 R/min, and the survivors gradually regained their normal levels of egg production. Most of the reduction in egg production occurred between days 11 and 20. More recently Maloney and Mraz’? showed that survivors of a group of White Leghorn hens exposed to 400 to 800 R °°Co at 5 R/min had a 10-day temporary drop in egg production starting 10 days after exposure. This drop in egg production lasted 40 days when the total dose remained constant and the dose rate was increased to 45 R/min. Exposure of incubated, fertilized eggs to less than 80 R of X rays accelerated the development of the embryo, but higher doses retarded development. Hatchability increases of 10% over the controls have been claimed by using RADIATION EFFECTS ON FARM ANIMALS 665 exposures of up to 30 R of X rays.2® The unincubated, fertile egg is relatively resistant to gamma-radiation effects. Sensitivity increased the first 3 days of development then decreased through day 12, when it leveled off at an LD5 9/30 of about 750 R. A second period of radiation sensitivity was found at incubation day 18. Beta irradiation of the GI tract and skin of poultry would not be expected to be a problem in poultry production. Even the few turkeys on the range depend mostly on feed supplements and very little on range pasture. Reproduction Studies of radiation effects on reproduction in food-producing animals have rightly been concentrated on gamma radiation. Neither ingestion nor skin irradiation from beta particles would be expected to have a direct effect on reproduction, but there could be abscopal effects in addition to anorexia and weight loss. Whole-body °°Co gamma radiation of beef heifers has not affected the long-term reproductive performance of 179 survivors for 8 years postirradia- tion.’° Acute radiation sickness and mortality occurred in a large number of these cattle exposed to 200 to 400 R at 0.7 R/min from °° Co; however, there were no differences that could be attributed to radiation in the performance of offspring in comparison with offspring of the 40 controls. Neither did exposure of beef cows to the first atomic bomb at Alamogordo have a measurable effect on reproductive performance. The ovaries, which are well protected in adult cows, would receive about 40% of the air dose. In addition, it has been estimated that over twice the lethal level given directly to the ovaries would be required to sterilize females.°°°?! There is a high percentage of bone deformities in offspring of pregnant females gamma irradiated with 100 rads or more during a short period in their gestation: gestation days 32 to 34 in cattle and 22 to 24 in sheep. At this stage of development, the limb buds are just starting to form in the embryos, and they are very sensitive to gamma radiation.’ Siecle The developing fetus concentrates '*!1 much more than its dam,** and fetal thyroid takes up almost as much '?'I as the dam thyroid.*° However, thyroid insufficiency can be counteracted by using thyroxin or by feeding iodinated casein if the thyroid is damaged by '*' I irradiation. Males surviving fallout gamma radiation at levels of 200 R or more would be expected to be temporarily sterile starting about 6 weeks after exposure, but this would last for only a few weeks.°° Since a large number of females can be bred to one male either naturally or through artificial insemination, male sterility is not expected to be a problem in food-producing animals. Work Shetland ponies surviving gamma-radiation exposure of 50 R/week at 25 R/hr for a total of 650 R have been used in the study of radiation effects on 666 APPENDIX B work performance and several other physiological parameters. After recovery from the early radiation effects, the irradiated ponies performed as well as their 1 control teammates over a period of 2 years.'* Genetic and Life-Span Effects Although gamma-irradiated animals show an increase in chromosome aberrations,’ ’ the chance of observing genetic changes in offspring of large animals is rather small. Mullaney and Cox?® reported that pigs sired by boars after they had recovered from 300 R of X rays to the testes were not adversely affected. In these studies involving over 3000 litters of pigs, irradiation of the maternal grandsire decreased (P< 0.01) the number of stillborn pigs in one of the two breeds studied. Survivors of the lifetime Hereford cows at UT—AEC (discussed in the section on reproduction) show no indication of genetic effects on offspring over the past 8 years of observation.' ® Since unproductive food-producing—breeding animals are normally culled and used for food, there is little concern for life-span effects in large animals unless there is a shortage of breeding animals. From the limited data available,’ ® it appears that life-span and productive life-span of swine and cattle are slightly reduced in long-term survivors of whole-body radiation. Life-span lengthening of 37% in males and 16% in females has been reported in 10 generations of mice irradiated from drinking water containing 1 wCi of °° Sr and 4 uCi of '* "Cs per liter. These mice also showed improved reproductive efficiency in the study using 255 litters. Mice drinking water with 100 times these concentrations of °° Sr and '*’Cs showed adverse effects on both life-span and reproduction.®” No data were found on large animals subjected to these types of tests. COUNTERMEASURES The countermeasures that can be recommended to save the largest number of grazing food-producing animals in a heavy fallout field are sheltering and using stored feed. In an area where gamma irradiation alone would be lethal to a small percentage of grazing animals, any shelter that groups and restricts the animals provides mutual shielding,*° prevents them from grazing pastures contaminated with early fallout, and probably ensures that most cattle and sheep would survive instead of dying from exposure to a combination of whole-body gamma and beta irradiation to the skin and GI tract. Shelters providing large protection factors would be desirable but are not *? Buildings available for shelters on these farms gave an average protection factor of only available on most farms, as shown in a pilot survey in Tennessee. 1.8, but the real importance of these buildings would be to prevent fallout damage to the skin, to prevent ingestion of forage contaminated with high levels of fallout, and to provide mutual shielding. RADIATION EFFECTS ON FARM ANIMALS 667 The limited data available show that preventing livestock from eating contaminated feed during the first 72 hr after fallout arrival is one of the most important countermeasures available. Anorexia, diarrhea, and GI injury and perhaps thyroid injury could greatly increase the lethality percentage. Weight and productivity of the survivors of grazing livestock would be severely affected. If no shelter were available, confining animals in a fenced corral, ravine, or woods would be desirable to increase mutual shielding and prevent ingestion of forage contaminated with early fallout. Skin damage from fallout increases heat loss and parasitic problems but is probably of less consequence than beta ingestion and whole-body gamma damage. The USSR textbook'® recommends blankets and canvas as improvised means of protecting the skin of animals. It was also suggested that valuable breeding animals could get added protection from a chemically treated, protective muzzle bag that would prevent the animal from eating contaminated feed and reduce the radioactivity inhaled when animals are being taken out of a contaminated area. ACKNOWLEDGMENTS The UT—AEC Agricultural Research Laboratory is operated by the Tennessee Agricultural Experiment Station for the U.S, Atomic Energy Commission under Contract AT-40-GEN-242. This work was supported in part by the U.S. Office of Civil Defense and is published with the permission of the Dean of the University of Tennessee Agricultural Experiment Station, Knoxville. REFERENCES 1. N. P. Page, The Effect of Dose Protraction on Radiation Lethality of Large Animals, in Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, Apr. 29—May 1, 1968, Oak Ridge, Tenn., D. G. Brown, R. G. Cragle, and T. R. Noonan (Eds.), USAEC Report CONF-680410, pp. 12.1—12.23, UT—AEC Agricultural Research Laboratory, July 12, 1968. Z2E Je Ainsworth. "Nu PaPage +E: Daylor’G. F-veong, and E/T. Sull, Dose Kate-Studies with Sheep and Swine, in Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, Apr. 29—May 1, 1968, Oak Ridge, Tenn., D. G. Brown, R. G. Cragle, and T.R.. Noonan (Eds.), USAEC Report CONF-680410, pp. 4.1—4.21, UT—AEC Agricultural Research Laboratory, July 12, 1968. 3. D. G. Brown and R. G. Cragle, Some Observations of Dose-Rate Effect of Radiation on Burros, Swine, and Cattle, in Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, Apr. 29—May 1, 1968, Oak Ridge, Tenn., D. G. Brown, R. G. Cragle, and T.R. Noonan (Eds.), USAEC Report CONF-680410, pp. 5.1—-5.16, UT—AEC Agricultural Research Laboratory, July 12, 1968. 4.M. T. Case and J. Simon, Whole-Body Gamma Irradiation of New-Born Pigs: The LD. 9/39. Amer. J. Vet. Res., 31: 113-115 (1970). 5.D. G. Brown, Clinical Observations on Cattle Exposed to Lethal Doses of lonizing Radiation, J. Amer. Vet. Med. Ass., 140: 1051—1055 (1962). 668 6. LOE ie 1G: 256 26. APPENDIX B F. W. Chambers, C. R. Biles, L. J. Bodenlos, and J. H. Dowling, Mortality and Clinical Signs in Swine Exposed to Total-Body Cobalt-60 Gamma Irradiation, Radiat. Res., 22: 316=33)3' (1964): .R. S. Lowrey and M. C. Bell, Whole-Body Irradiation in the Young Pig: Growth, Hematology and Metabolism of ** Ca and °° Sr, Radiat. Res., 23: 580—593 (1964). . National Academy of Sciences—National Research Council, Damage to Livestock from Radioactive Fallout in Event of Nuclear War, Publication 1078, Washington, D. C., 1963. .M. M. Nold, R. L. Hayes, and C. L. Comar, Internal Radiation Dose Measurements in Live Experimental Animals, Health Phys., 4: 86—100 (1960). Civil Defense in Rural Regions, Military Publishing House of USSR Ministry of Defense, Moscow, 1965. .M. C. Bell, Airborne Radionuclides and Animals, in Agriculture and the Quality of Our Environment, N. C. Brady (Ed.), American Association for the Advancement of Science, Symposium No. 85, pp. 77—90, Washington, D. C., 1967. .M. C. Bell, L. B. Sasser, J. L. West, and L. Wade, Jr., Effects of Feeding °° Y-Labeled Fallout Simulant to Sheep, Radiat. Res., 43: 71-82 (1970). .D. G. Brown, R. A. Reynolds, and D. F. Johnson, Late Effects in Cattle Exposed to Radioactive Fallout, Amer. J. Vet. Res., 27: 1509—1514 (1966). . J. S. Cheka, E. M. Robinson, L. Wade, Jr., and W. A. Gramly, The UT—AEC Agricultural Research Laboratory Variable Gamma Dose-Rate Facility, Health Phys., 20: 337-340 (1971): M. C. Bell, Flexible Sealed ?° Sr—?° Y Sources for Large Area Skin Irradiation, Int. J. Appl. Radiat. Isotop., 21: 42—43 (1970). J. E. Johnson and A. I. Lovaas, Deposition and Retention of Simulated Near-In Fallout by Food Crops and Livestock, First Technical Progress Report, Colorado State University, Fort Collins, Colo., 1969. . F. Alexander, Digestion in the Horse, in Progress in Nutrition and Allied Sciences, D. P. Cuthbertson (Ed.), pp. 259—268, Oliver and Boyd, Ltd., Edinburgh, 1963. . UT—AEC Agricultural Research Laboratory, Annual Progress Report, Jan. 1—Dec. 31, 1968, USAEC Report ORO-672, October 1969. .R. G. Cragle, J. K. Miller, E. W. Swanson, and D. G. Brown, Lactation and Radionuclide Metabolism Responses of Dairy Cattle to Lethal Doses of Gamma and Neutron Radiation, J. Dairy Sci., 48: 942—946 (1965). . E. W. Swanson, R. G. Cragle, and J. K. Miller, Effects of Irradiation upon Lactation, J. Dairy Sci., 48: 563—568 (1965). . J. K. Miller and E. W. Swanson, Effects of lodine-131 Thyroid Damage on Lactation and Thyroid Function in the Bovine, J. Dairy Sci., 52: 95-100 (1969). .R. J. Garner, Environmental Contamination and Grazing Animals, Health Phys., 9: 597 =609 (1.963): .R. V. Petrov, V. N. Pravetskii, Yu. S. Stepanov, and M. I. Shal’nov, Radioactive Fallout. Physics, Biological Effects, and Protective Measures, USAEC Report AEC-tr-6634, translation of Zashchita ot Radioaktivnykh Osadkov, Gosudarstvennoe Izdatel stvo, Meditsinskoi Literatury, Moscow, 1963. . E. W. Swanson, F. W. Lengemann, and R.A. Monroe, Factors Affecting the Thyroid Uptake of '*’ Tin Dairy Cows, J. Anim. Sci., 16: 318—327 (1957). C. L. Comar. R. A. Wentworth, and F. W. Lengemann, A Study of Metabolism of Selected Radionuclides Fed in Various Physical Forms to Dairy Cows, Final Report, OCD Report TRC-67-33, Cornell University, Ithaca, N. Y., 1967. L. Ekman, B. Funkqvist, and U. Greitz, Beta- and Gamma-Dose Measurements in the Gastrointestinal Tract of Goats with LiF Dosimeters After a Single Intake of Simulant Mixed Fission Products, Swedish Report FOA-4-4418, March 1970. Dadi 28. 29% 30. 3k 32: SIE) 34. Ie 36; ade 38. 39). 40. 41. RADIATION EFFECTS ON FARM ANIMALS 669 H. Rosas and M. C. Bell, Effects on Swine of Unilateral Neutron Irradiation, Calcium and Zinc, Radiat. Res., 39: 164—176 (1969). D. K. Wetherbee, Gamma Irradiation of Birds’ Eggs and the Radiosensitivity of Birds, USAEC Report TID-24521, Massachusetts Agricultural Experiment Station, October 1966. M. A. Maloney and F. R. Mraz, The Effect of Whole-Body Gamma Irradiation on Survivors’ Egg Production in the White Leghorn and Bobwhite Quail, Poultry Sci., 48: 1939-1944 (1969): B. H. Erickson, Radioresponse of the Prepuberal Porcine Ovary, Int. J. Radiat. Biol., 13: 57-07 (1967): B. H. Erickson, Effect of Gamma Radiation on the Prepuberal Bovine Ovary, Radiat. Res., 31: 441—451 (1967). B. H. Erickson and R. L. Murphree, Limb Development in Prenatally Irradiated Cattle, Sheep, and Swine, J. Anim. Sci., 23: 1066—1071 (1964). A. F. McFee, R. L. Murphree, and R.L. Reynolds, Skeletal Defects in Prenatally Irradiated Sheep, ‘Cattle and Swine, J. Anim. Scz.,.24: 1131-1135 (1965). P. W. Aschbacher, R. G. Cragle, E. W. Swanson, and J. K. Miller, Metabolism of Oral Iodine and 3,5-diiodosalicylic Acid in the Pregnant Cow, J. Dairy Sc1., 49: 1042—1045 (1966). J. K. Miller, E. W. Swanson, P. W. Aschbacher, and R. G. Cragle, Iodine Transfer and Concentration in the Prepartum Cow, Fetus and Neonatal Calf, J. Dairy Sci., 50: 13 ON 1309) (1907): B. H. Erickson, Radiation Effects on Gonadal Development in Farm Animals, J. Anim. Sct., 24: 568-583 (1965). A. F. McFee, M. W. Banner, and Mary N. Sherrill, Influence of Animal Age on Radiation-Induced Chromosome Aberrations in Swine Leukocytes, Radiat. Res., 41: 425—435 (1970). P. D. Mullaney and D. F. Cox, Effects of Paternal X-Irradiation on Litter Size and Early Postnatal Mortality in Swine, Mutat. Res., 9: 337—340 (1970). K. Nishio, T. Megumi, and M. Yonezawa, Effects of '?’7Cs and °° Sr Administered Continuously and Through Generations upon Mice. VI. Ann. Rep. Radiat. Center Osaka Prefect., 9: 86—93 (1968). K. Mills and K. Evans, Protecting Livestock from Radioactive Fallout, University of Kentucky Extension Service Miscellaneous Publication 338, 1966. S. A. Griffin, in Civil Defense Research Project. Annual Progress Report March 1968—March 1969, USAEC Report ORNL-4413(Pt. 1), pp.94—96, Oak Ridge National Laboratory, October 1969. THE EFFECTS OF EXTERNAL GAMMA RADIATION FROM RADIOACTIVE FALLOUT ON PLANTS, WITH SPECIAL REFERENCE TO CROP PRODUCTION A. H. SPARROW, SUSAN S. SCHWEMMER, and P. J. BOTTINO Brookhaven National Laboratory, Upton, New York ABSTRACT This paper describes the major problems involved in attempting to predict for economically useful plants the degree of radiation damage that would arise from exposure to high-level radioactive fallout. Since almost no data exist on the deleterious effects inflicted on crops by actual fallout radiation, it is necessary to extrapolate from the existing radiobotanical data concerned with the effects of gamma radiation on survival and yield of plants. A number of factors can modify the effects of the radiation and hence influence the accuracy of predictions of postattack injury. The most important variables are (1) species differences in interphase chromosome volume (the larger this value, the more sensitive the plant), (2) exposure rate (high rates are more effective than lower rates), (3) stage of development of the plant (a complex and difficult variable to assess), (4) postirradiation time (generally the longer the time, the greater the degree of damage), and (5) numerous environmental factors such as moisture, temperature, light, competition, etc., which normally modify plant growth and yield. These factors, acting singly or in various combinations, can have a considerable effect on the radiation response and thereby make more difficult the prediction of postattack injury. Survival and yield data obtained from irradiation of growing plants are presented for many species. The most useful values in comparing sensitivities are LD,,, LD,,, and LD, , (exposures required to reduce survival by 10, 50, and 90%), and YD,,, YD,;,, and YD,, (exposures required to reduce yield by 10, 50, and 90%). A log-log regression of LD, 9 vs. YD,, for 36-hr fallout-decay-simulation (FDS) gamma exposures has a slope not significantly different from +1; this indicates that, in general, an exposure producing an LD,, will reduce yield by 50%. Other LD, , values may also be predicted from regressions of interphase chromosome volume on LD, ,. Predicted YD,, values following FDS exposures are given for 89 crop plants and for 82 woody plants for a 16-hr constant-rate exposure. Using these predictions and the available radiobiological data, we can draw some conclusions concerning the vulnerability of crop plants to fallout radiation. The cereals (wheat, barley, oats, and maize), which are probably our most important group of crop plants, would be the most sensitive, having YD, , values ranging from about 1 to 4 kR (rice is much more resistant). The legumes (peas and beans) include both sensitive and resistant species, having YD,, values ranging from less than 1 to 12 kR. Root crops (onions, garlic, beets, potatoes, and radishes) have a wider range in 670 EFFECTS OF EXTERNAL GAMMA RADIATION 671 sensitivity; YD,, values range from 1 to 16 kR. For pasture and forage crops, YD, , varies from 2 to 20 kR. Of the herbaceous crop species, 70% fall in the predicted sensitivity range between 4 and 16 kR. Woody species have a range of predicted LD, , values between about 0.4 and 8 kR, the gymnosperms predominating below 2 kR. These predictions are for average conditions only. We still lack a significant amount of radiobiological data required to make confident predictions of the expected response of many species to high-level fallout-gamma exposure. Also, inadequate information about beta-radiation injury and its possible interaction with gamma radiation makes extrapolation to actual fallout conditions even more difficult. Plants in areas receiving radioactive fallout will be exposed to two types of external radiation, gamma and beta; the relative biological effectiveness of these two types of radiation was recently shown’ to be approximately 1. In areas of heavy fallout, either type of radiation alone could seriously reduce the growth or yield of plants, at least at certain stages of plant development. Under conditions of lighter fallout, the combined exposures from both types of radiation could also produce very serious effects, up to complete destruction of some crops. However, this report reviews only known or expected effects of gamma radiation on various species of plants given a range of exposures at one or more stages in their life cycles. The hazards of direct contamination of foodstuffs by fallout radionuclides have been discussed elsewhere.” > The long-lived nuclides are not now considered as serious a hazard as was previously thought.° Although the dislocations in agricultural practices and food distribution associated with other disturbances and/or the reduced availability of manpower and horsepower which would result from a nuclear war are important in the overall context of postattack recovery, we shall not consider them here. Previous studies on the effects of gamma radiation on growing plants are many and varied.” '* Unfortunately, however, many different exposure rates have been given under differing conditions with various criteria of effect being used. No previous attempt has been made to assemble the majority of the pertinent data and devise a means of presenting them in a _ uniformly comprehensible manner. This paper reviews the major modifying factors, such as exposure rate and duration, stage at irradiation, environmental conditions, etc.; surveys the available pertinent data; indicates what currently appear to be the general trends of response to fallout or simulated-fallout gamma radiation; and predicts the probable responses for plant species for which no data are currently available. BACKGROUND INFORMATION The wide range of radiosensitivity among different plant species to external X or gamma radiation is well documented.'!’!*’'*"?° Radiosensitivity varies by at least 100-fold among species and by over 50-fold within a species irradiated at different stages. Certain stages of flower-bud development are known to be 672 SPARROW, SCHWEMMER, AND BOTTINO much more sensitive than others and also more sensitive than meristem cells in the vegetative stage.°° *? Radiation injury expresses itself after a few days, weeks, or, in some cases, years as abnormal shape or appearance, reduced growth or yield, loss of reproductive capacity, sometimes wilting, and, finally, at the higher exposures death. Although we recognize the importance of genetic effects, we shall not attempt here to survey the vast body of literature on this subject. It is now known that the wide range in sensitivity of plant species irradiated and grown under uniform experimental conditions can be attributed largely to variation in the size of the chromosomes of the plants.''°*!®*!?’?°"?? A direct relation between chromosome size (measured as the average volume of an interphase chromosome) and sensitivity to gamma radiation given under specified conditions has been established, showing that, as the size of the chromosomes increases from one species to another, the amount of radiation required to produce a specified effect decreases (Figs. 1 and 2). The consistency of this relation is the basic premise on which our predictions are based [see Radiosensitivity Predictions (Based on ICV Data)]. When plants are irradiated under uniform conditions with a range of exposures which, depending on their magnitude, will produce measurable decreases in yield and/or survival, response curves can be obtained. Values not actually observed to occur at any of the exposures given can be calculated from these data. Survival end points that have been found to be most useful in describing radiation effects on plants are LD;9, LDs9, LDoo, and LD; oq; the exposures required to reduce plant survival by 10, 50, 90, and 100%, respectively. Similarly, for yield reduction the particular end points of most use are YD,9, YDso0, and YDogo, the exposures required to reduce growth or yield by 10, 50, and 90%, respectively. There is extensive literature on growth stimulation in plants after exposure to ionizing radiation, and some investigators claim statistically significant increases in yield after exposures usually referred to as low doses, although a wide range of exposures is used. Surveys of the available data have been given in various publications.’ ’?° 33 In our opinion the probability of beneficial effects of fallout radiation on crop yield is so far outweighed by the probability of deleterious effects that no further consideration will be given here to possible enhanced growth or yield. A particularly useful relation between a survival end point and a yield end point is shown in Fig. 3. For all practical purposes, for the plant species studied, the exposure that produces an LDj9 also produces a YDso. Thus the determination of the LD; 9 for any species should provide a fair approximation of the YDs59. This is an advantage because determination of YDs5o generally requires experiments of greater magnitude, with better facilities and more manpower. Also, survival data for a crop for which no yield data exist can be converted to an estimated effect on yield. EFFECTS OF EXTERNAL GAMMA RADIATION 100 50 20 0.5 Ow Ow Oo On 36-hr FDS 0.2 -1 Slope 0.1 1 2 5 10 20 50 100 200 INTERPHASE CHROMOSOME VOLUME, yp? Fig. 1 Log-log regression of LD,, against ICV for 10 species of economic plants given a 36-hr FDS exposure as young seedlings. Allium cepa 5 Avena sativa 6 Brassica oleracea 7 8 hwnd = Hordeum vulgare Lactuca sativa 9 Triticum aestivum Phaseolus limensis 10 Zea mays Pisum sativum 11 Zea mays Raphanus satwus 673 674 SPARROW, SCHWEMMER, AND BOTTINO 100 50 20) == al Ow Oy on 0.5 -—- 36 -hr FDS O72 - 1 Slope | 1 2 5 10 20 50 100 200 INTERPHASE CHROMOSOME VOLUME, yp? Fig. 2 Log-log regression of LD, , against ICV for eight species of economic plants given a 36-hr FDS exposure as young seedlings. 1 Allium cepa 7 Pisum sativum 3 Brassica oleracea 8 Raphanus sativus 5 Lactuca sativa 9 Triticum aestivum 6 Phaseolus limensis 11 Zeamays EFFECTS OF EXTERNAL GAMMA RADIATION 675 36-hr FDS + 1 Slope 0.1 0.2 0.5 1 2 5 10 Fig. 3. Log-log regression of YD, against LD, , for six species of economic plants given a 36-hr FDS exposure as young seedlings. 1 Cucurbita pepo 5 Pisum sativum 2 Hordeum vulgare 6 Triticum aestivum 3 Phaseolus limensis 7 Zeamays 4 Pisum sativum Other effects of importance for consumable economic crops are changes in starch,?* sugar (personal communication from R. S. Russell and Ref. 35), and - 36 ; SiH ; 37-39 protein content and minor variations such as differences in taste, 0-4 2 44 4 4 shape, color,** and perhaps wholesomeness. MODIFYING FACTORS General Considerations Basic research in radiobiology has shown that there are many biological, radiological, and environmental factors that determine or modify radio- sensitivity. A partial list of these factors is given in Table 1; no indication of the extent or direction of the change in sensitivity is given, however. To emphasize the possible significance of such factors, we have made estimates of the degree of SPARROW, SCHWEMMER, AND BOTTINO BIOLOGICAL, RADIOLOGICAL, AND ENVIRONMENTAL FACTORS THAT CONTRIBUTE TO VARIATIONS IN RADIOBIOLOGICAL RESPONSES OF PLANTS* Biological factors Cytological and genetic Chromosome number Chromosome volume DNA content per chromosome Heterochromatin (amount of) Genotype or taxonomic group Length of mitotic cycle Percentage of cells dividing Stage of nuclear cycle (especially in meiosis) Morphological organization and development Type of cell or tissue Stage of differentiation (e.g., vegetative or floral) Portion(s) of plant irradiated Size of plant or depth of sensitive organs Physiological or biochemical Age of plant Metabolic rate Stage of growth cycle (active or dormant) pH of cells (and soil) Nutritional state Concentration of growth hormones Concentration of protective or sensitizing substances Radiological factors Kinds of radiation(s) Energy or LET of radiation Exposure fractionation and previous exposures Exposure rate Exposure duration Depth dose Location of radioisotope Shielding (various) Relative humidity Moisture content of soil and plants Density of soil Chemical composition of plants and soil (for neutrons) Distance from detonation Time after detonation Environmental factors Temperature Wind velocity Dust or fallout (amount and particle size) Moisture content of air, soil, and plants Insects or other pests Competition (other plants) Season (day length, etc.) Available sunlight Soil fertility *Modified from Gunckel and Sparrow. ® modifying effect of a few of the more important ones that might apply in an actual fallout situation. These, along with the accumulated effect of all the factors acting in the same direction, are given in Table 2. Of course, the probability that all these factors would simultaneously act in the same direction is remote. However, the exercise clearly emphasizes why we cannot assign an absolute sensitivity value to a given crop or species unless most of the radiological, biological, and environmental conditions are clearly stated. EFFECTS OF EXTERNAL GAMMA RADIATION 677 Table 2 MAJOR FACTORS THAT DETERMINE OR MODIFY RADIOSENSITIVITY OF PLANTS AND EXTENT OF EFFECT PRODUCED BY EACH FACTOR WHEN ALONE AND WHEN CUMULATED WITH ALL OTHER FACTORS (ASSUMING THEM TO BE CUMULATIVE) Maximum Maximum Change that (or estimated) cumulative Factor increases effect effect interaction Species (chromo- some size*)! © Larger ICV 100 100 Stage or aget Various 50 5,000 Environmental Various a 25,000 Exposure rate** Higher rates 4 100,000 6+ ¥ interaction Combination 2 200,000 RBE? ° More densely 20 4,000,000 ionizing radiation *ICV (interphase chromosome volume). tSee Table 4. {Estimates considered to be conservative. Table 3 RATIOS OF LD,, VALUES* FOR VARIOUS EXPOSURE TIMES WITH CONSTANT-RATE, FDS, AND BU + FDS EXPOSURES (THE 16-HR LD, , BEING GIVEN AN ARBITRARY VALUE OF 1.00) Treatment Exposure Fallout decay time, hr Constant rate simulation Buildup + FDS 36 0.76T 1.40 1.41 16 1.00 8 1.40 4 2.00 1 2.70 7 *Based on data from lettuce irradiations? 7 except where noted. tBased on data from squash, cabbage, pea, and maize irradia- tions.??»*! Influence of Exposure Rate and Duration Exposure rate and duration are major variables which, under many conditions, modify the extent of injury produced by a given amount of radiation. Though studies done on the same species with different rates of exposure are desirable, they are not often made. However, as shown in Table 3, a 678 SPARROW, SCHWEMMER, AND BOTTINO given exposure delivered at a higher rate (shorter exposure time) is more effective than the same exposure at a lower rate (longer exposure time). There are some limits to this effect, however. At very high exposure rates, further 4 — neal ene increases in rate may not bring about additional increases in effect, very low rates a point is reached where no external differences between irradiated and nonirradiated plants can be detected.'*°*®°*? This complete range in exposure-rate effects has recently been reported in one system.>° Unfortunately current knowledge of exposure-rate effects is generally too inadequate to allow the application of mathematical models that would permit the prediction of effects at several different exposure rates from the results obtained at one exposure rate since the critical exposure rate may vary from species to species. For these reasons, the actual conditions of exposure for each experiment reported have been given when available since they do differ considerably. Recent data show that for equal total exposures a 36-hr fallout-decay- simulation (FDS) treatment with decreasing exposure rates is more effective in reducing survival and yield than the previously used standard 16-hr constant-rate (CR) treatment.*?’*°*?! The average ratio of 16-hr CR to FDS treatment for several crop species at the LDs9 exposure is 1.4 (Table 3). The greater effectiveness of the FDS treatment is due to the very high initial exposure rates encountered with this type of exposure.*” For yield reduction the FDS is more effective only at the higher exposures. It has been shown also that there was no significant difference between equal total exposures of an FDS treatment and an 8-hr CR treatment.** This is attributable to the fact that there is very little difference between the average exposure rate for an FDS treatment and the exposure rate for an 8-hr CR treatment. With exposure times less than 8 hr, the effectiveness of a given exposure increases with decreasing time (Table 3; see also Tables:8, 9 and 2): Influence of Age and Stage Irradiated It is well known that the age of a plant or its stage of differentiation or development can have a major influence on the amount of radiation required to produce a common end point.°* °* The significance of stage of development at the time of irradiation is clearly indicated in Table 4, which gives data for sensitivity of various stages of development of the corn plant. The data presented indicate that the difference between the most sensitive stage (meiosis) and the most resistant stage (dry seed) exceeds 50-fold. Fortunately in most plant species the highly sensitive stage of meiosis is a fairly short one, lasting at most a few days. The high radiosensitivity of pollen may be important, especially since all of the most important cereal crops are wind pollinated. Because of their small size, most pollen grains would be vulnerable to injury from beta radiation both on the plant and in the air. Since the beta dose might exceed the gamma dose in most fallout situations, the total effect on pollen EFFECTS OF EXTERNAL GAMMA RADIATION 679 Table 4 RADIOSENSITIVITY OF VARIOUS DEVELOPMENTAL STAGES OF MAIZE (ZEA MAYS) Exposure, Duration and Stage End point kR type of exposure Dry seed”? 10.6% moisture LD, (survival at 20 days) 54 2.7 kR/min gamma 1.9% moisture 10 2.7 kR/min gamma Young plants 50% reduction in seed yieldt 1 50 R/min gamma LD,, (at maturity)*’ 5.1 16 hr acute gamma LD), > (atimaturity)?* 6.5 16 hr acute gamma 10% reduction in seed yield*? if 16 hr acute gamma 50% reduction in seed yield®’ 4.3 16 hr acute gamma 100% reduction in seed yield*' 6 16 hr acute gamma Meiosis 43% reduction in fresh weight of ale 50 R/min gamma offspringt Pollen (mature) LD, for flowers producing 12 1.2 kR/min gamma seed” ? *Varies with stage of meiosis. Meiotic prophase is very sensitive but is of short duration. +M. J. Constantin, UT—AEC Agricultural Research Laboratory, unpublished data, 1970. could have a significant effect on yield, at least for the more sensitive species. This would also be true for very small seedlings or plant parts small enough for penetration by beta radiation. The variation in sensitivity measured as reduced yield after irradiation at several stages during the growing period is given for five major crops in Fig. 4. The sensitivity for each crop can vary during the growing period from almost no effect to total loss of yield after identical exposures. Each crop has its own characteristic period of peak sensitivity, which varies from 6 days after emergence for soybeans to 195 days after emergence for winter barley. These data indicate not only the degree of variation in sensitivity with stage for a single species but also the variation among species. Not all these crops, however, would be expected to be at their stage of maximum sensitivity in a specific fallout situation. Differences in sensitivity with respect to yield of various economic plants irradiated at different stages of development are given in the section on deleterious effects on yield and survival of economic plants. Influence of Postirradiation Time Of considerable significance, particularly for economic plants, is the time after irradiation at which the radiation effects first become evident or first produce a serious effect. There are wide variations among species in the timing of specific responses to irradiation.°* Some plants show adverse effects or die 680 SPARROW, SCHWEMMER, AND BOTTINO 100 80 60 40 se Z 60 fe) - O 5 40 WwW oc = i 20'D= > 0 0 20 40 60 80 (c) (d) 100 80 60 Rice 40 20 | 0 0 20 40 60 80 (e) DAYS AFTER EMERGENCE Figure 4 EFFECTS OF EXTERNAL GAMMA RADIATION 681 within a few days or at most a few weeks after irradiation, whereas others do not manifest such effects for many months, or even years for woody plants. ' ' Results of experiments with tomato have shown that fruit production 1s considerably delayed by irradiation and the extent of delay increases with increasing exposure (Fig. 5). When the growing season is short, such a delay in production or ripening could essentially eliminate any useful harvest. Before the delayed effect becomes serious, however, some crop plants with a long latent period might be of value as forage crops. Adverse effects on progeny from irradiated plants or seed also must be considered. Experiments done with a few species have shown that, depending on the stage of development at which the parent plant was irradiated (see previous discussion), the resultant yield from plants grown from seed of the parent crop may be seriously or moderately affected or not affected at all (see Table 5). Experiments with perennial plants, including various species of trees used as sources of lumber or edible fruits and nuts, have shown that deleterious effects may continue to manifest themselves years after the radiation treatment, particularly in the reproductive system.°*’®® Influence of Environmental Variables The main environmental variables known to influence radiation-induced injury in plants are listed in Table 1. Except for dry-seed studies, very few experiments have been done testing the magnitude of effect produced by variation of one or more of these factors in concert with radiation treatment. However, some preliminary results are discussed here. Lettuce plants given low exposures of radiation show considerably more stimulation of yield early in the growing season under conditions of longer day length than later in the season when the day is shorter.?’ Also, the effects ultimately manifested by perennial plants irradiated during different seasons 12,66,67 (while the plants are active or dormant) or during different photo- periodic stages°*® may differ considerably. The effect of variations in light intensity and temperature on postirradiation survival of Arabidopsis, shown in Fig. 4 Seed yield reduction of five crops after exposure to °°Co gamma radiation at different days after seedling emergence. (a) ‘Dayton’ barley after exposure to 1 kR at 20 R/min. Maximum reduction was 95% at day 195. Plants irradiated before 130 days after emergence did not survive winter conditions. (b) ‘Seneca’ wheat after exposure to 1.6 kR at 20 R/min. Maximum reduction was 90% at day 175. Plants irradiated before 85 days after seedling emergence did not survive winter conditions. (c) Maize (WF-9X38-11) after exposure to 2.5 kR at 50 R/min. Maximum reduction was 100% at days 15 to 48. (d) ‘Hill’ soybeans’° after exposure to 2.5 kR at 50 R/min. Maximum reduction was 90% at days 6 and 45. (e) Rice (CI 8970-S) after exposure to 25 kR at 50 R/min (redrawn from Siemer et al.°'), Maximum reduction was 100% at days 37 to 57. 682 SPARROW, SCHWEMMER, AND BOTTINO 100 oO <7; z 5 oer | Le Seat x aos a coer Q Week 16 fe 50° )\— 0 is s O LU O CO) = 0 0 af Week 14 Q OQ Zz 20 5 ‘ Q n 10 Week 10 E ¥ Q =) names LL = Week 7 b O O be = sot 1 O 1 3 5 7 9 11 jer 1S EXPOSURE, kR (a) 15 — ow _ at) TIME POSTIRRADIATION FOR 50% FRUIT SET, weeks oO 1 2 5 10 15 20 EXPOSURE, kR (b) Fig. 5 Data from tomato plants given a 16-hr CR treatment. (a) Percent of plants with fruit vs. exposure at 7, 10, 14 and 16 weeks after irradiation. (b) Postirradiation time in weeks for 50% fruit set vs. exposure.>’ EFFECTS OF EXTERNAL GAMMA RADIATION 683 Table 5 EFFECTS ON YIELD OF THE SUBSEQUENT CROP OF ACUTE GAMMA IRRADIATION DELIVERED AT VARIOUS STAGES OF GROWTH TO SPRING WHEAT, SPRING BARLEY, AND POTATOES? ? Yield of crop, % of control Stace of mroarth Grain of spring wheat* Grain of spring barley * of parent crop Dose, Parent Subsequent Parent Subsequent when irradiated rads crop crop crop crop Two leaf 250 115 93 105 96 500 wath OF 61 103 1000 68 98 5 Four leaf 250 98 101 90 101 500 95 101 50 105 1000 62 102 t Ear emergence 250 86 82 87 96 500 83 89 59 89 1000 48 71 Anthesis 500 all 87 84 86 1000 i) 62 76 47 Postanthesis 500 114 92 85 88 2000 85 45 89 13 Potato tubers Parent crop Subsequent crop Shoot emergence 2000 51 98 4000 15 66 Stolon formation 2000 74 81 4000 33 77 Tuber initiation 2000 78 96 4000 TS) 54 8000 2D a5 *Yield of parent crop figured in grams per plant; yield of subsequent crop in grams per square meter. tPlants died before maturity. £Yield of both crops figured in grams per plant. Fig. 6, demonstrates that increased temperature is synergistic with radiation treatment in producing deleterious effects.°* Competition or stress among plants is also known to be a factor in the eventual total effect exhibited by irradiated plants,°? 73 as well as combined effects evident in ecosystem analysis. ' 8 The maximum difference in effect (a factor of 5) given in Table 2 is considered to be a conservative estimate and may be exceeded in some cases. 684 SPARROW, SCHWEMMER, AND BOTTINO 50 40 Ww oO ACCUMULATED % DEAD N fo) DAYS POSTIRRADIATION Fig.6 Relation between accumulated percent dead and number of days postirradiation for plants of Arabidopsis thaliana receiving a 16-hr acute gamma exposure to 25 kR and grown under three different sets of conditions of temperature and light: H, 83 to 87 F, full light; G, 68 to 73°F, natural + supplemental light; and M, 68 to 72° F, two-thirds light. Plants were irradiated 13 to 15 days after germination.°® * Maximum percent dead: H, 53%; G, 7%; M, 0%. DELETERIOUS EFFECTS ON YIELD AND SURVIVAL OF ECONOMIC PLANTS Although there is a large amount of general information concerning the radiobiological responses of higher plants, there are relatively few published data on deleterious effects on crop yield. The pertinent data available at present are summarized in this section. EFFECTS OF EXTERNAL GAMMA RADIATION 685 Irradiation of Seed Grain, Seed Potato Tubers, Onion Transplants, Bulbs, etc. The amount of data available for assessing second-generation effects on grain yield from irradiated grain is quite small, though much information exists for other criteria of effect. Radiosensitivities for dry seed of 30 plants of economic value are given in Table 6.’* However, certain crops not listed, such as peas, Table 6 LD,, (kR) VALUES FOR 30 PLANTS OF ECONOMIC VALUE AFTER © °Co GAMMA IRRADIATION OF DRY SEED* Dose rate, LD, ,, Common name Scientific name R/min kR Alfalfa Medicago sativa 844 38 to 62 Barley Hordeum vulgare 844 to 850 13 to 20 Clover, button Medicago orbiculatus 844 21 Clover, crimson Trifolium incarnatum 844 to 1240 25 to >64 Clover, red Trifolium pratense 795. CO1270 35 to >108 Clover, sweet Meliotus species 844 a9 Cowpea Vigna sinensis 1260 11 Dallis grass Paspalum dilatatum 710 32 Fescue Festuca elatior 844 19 Grape Vitis species 790 to 1240 <4 to <5 Guava Psidium guajava 1240 17 Lespedeza, Korean Lespedeza stipulacea G25 <40 Lupine, blue Lupinus angustifolius 750 > 40 Maize Zea mays 840 > 5 Millet, German Setaria ttalica 760 14 Oats Avena sativa 840 7-tO, 27 Orchard grass Dactylis glomerata 844 ir Papaya Carica papaya 650 12 Peanut Arachis hypogea 1260 10 Pepper Capsicum frutescens 1260 24 Pigeon pea Cajanus cajan 1260 1 Ui) Rice Oryza sativa 650 to 1260 <15 to 42 Rye Secale cereale 714 to 840 8 to 16 Sericea Lespedeza cuneata 795 to 840 37 to 46 Sorghum, grain Sorghum vulgare 1260 > 40 Soybean Glycine max 1260 11 Tomato Lycopersicon esculentum 609 to 1240 LSAtO.3i4, Vetch, hairy Vicia villosa 840 iby) Watermelon Citrullus vulgaris 1280 60 Wheat Triticum vulgare 670 to 840 14 to 25 *Modified from Osborne and Lunden. 7 * 686 SPARROW, SCHWEMMER, AND BOTTINO broad beans, and onions, are much more sensitive than those listed. In a very general way, seed radiosensitivity is related to plant radiosensitivity; 1e., rank order is similar, but actual exposures tolerated are quite different and are highly dependent on moisture content. The least effect on irradiated seeds of cereals is found at moisture contents of about 10 to 13%, and the seeds are more sensitive at moisture contents above or below this level.’° Depending on the seed moisture content, variations in exposure rate can be as significant for seed irradiation as for irradiation of growing plants but are generally less significant. 76-79 although this is an experimentally induced variable not generally applicable to seed under Seed radiosensitivity is also dependent on the oxygen effect, natural or agricultural conditions. Exposure of seed potato tubers to 300 R before planting had no effect on yield; 1.2kR brought about a moderate decrease, and 4.8 kR resulted in a negligible yield.°° In an experiment using X rays, survival was reduced to 63% by an exposure of 4.0kR.°! For small onion transplants an FDS exposure of 2.0 kR resulted in negligible bulb yield; 1.4 kR caused about a 50% reduction; and exposures of 1.1 kR or less produced very little effect on yield (see Table 10). In another study®* using higher exposure rates, 600 R reduced yield by 28% and 1.0kR by 78%. Several ornamental bulbs are known to be highly sensitive or are predicted to be from ICV data. Predicted LDs59 values for FDS exposures are given in Table 7 for a number of species of horticultural interest. Irradiation of Growing Plants Because of the significance of stage of development and exposure times or rates on degree of injury produced, it was deemed necessary to specify these details in the summary tables. In many cases only one experiment was performed for a given crop at a specific stage, and in some cases the dosages chosen did not cover the most appropriate range. Also, in most cases the plants were irradiated under laboratory conditions and grown in a greenhouse or growth chamber. Almost no field irradiations have been made. The data on yield and survival have been subjected to computer analysis, which provided estimates (with errors) of the exposures required to reduce yield or survival by about 10, 50, or 90% of unirradiated control. We have used the terms YD;9, YDso0, or YDoo as a shorthand method of specifying the exposure reducing the yield by 10, 50, or 90%, as is usually done for survival, 1.e., LD509, etc. It should be emphasized here that it is not only possible but even quite probable that gamma radiation exposures under actual fallout conditions might produce effects greater or less than those indicated in the summary tables (Tables 8 to 12). In other words, these tables can be used only as a general guide to anticipated effects. It is hoped that experiments planned or now under way will greatly improve the accuracy of these tables, at least for some crops. The effects of the beta component of fallout are considered elsewhere.**? However, if a plant or plant (Text continues on page 693.) EFFECTS OF EXTERNAL GAMMA RADIATION Table 7 PREDICTED RADIOSENSITIVITIES (36-HR FDS EXPOSURE) OF 25 SPECIES OF ECONOMICALLY IMPORTANT ORNAMENTAL Common name Anemone, flame Belladonna lily Bluebell, Spanish Crocus Daffodil Fritillary, checkered Gladiolus Glory-of-the-snow Grape hyacinth Hyacinth Lily, Easter Lily, Formosa Lily, regal Lily-of-the-valley Mariposa lily Narcissus Squill, Siberian Star-of-Bethlehem Tigerflower Torchlily Tritonia (montbretia) Tulip, Darwin Tulip, Foster (red emperor) Tulip, waterlily Zephyr lily Scientific name Anemone fulgens Amaryllis belladonna Scilla hispanica Crocus (average of 3 species) Narcissus pseudo-narcissus Fritillaria meleagris Gladiolus (average of 4 varieties) Chiondoxa luciliae Muscari (average of 2 species) Hyacinthus (average of 3 varieties) Lilium longiflorum Lilium formosanum Lilium regale Convallaria majalis Calochortus (average of 2 species) Narcissus (average of 3 species) Scilla sibtrica Ornithogalum virens Tigridia pavonia Kniphofia uvaria Tritonia crocata Tulipa species Tulipa fosteriana Tulipa kaufmanniana Zephyranthes species PLANTS GROWN FROM BULBS* 39.6 82:9 52.8 1729 GAZ 8.7 59.8 3535 32.6 Ta, Predicted LD,, + S.D.,kR 2.04 + 0.61 1.05 = 0:31 1.08 + 0.32 0.98 +:0,29 0.93 + 0.28 0.65 + 0.19 12.66 + 3.78 2.81 + 0.84 3.94+1.18 1.06 + 0.32 1.14 + 0.34 0.89 + 0.27 0.91 + 0.27 1.86 + 0.56 2.15 + 0.64 1.50 + 0.45 0.72 + 0.21 1.12 + 0.34 3.32 + 0.99 0.84 + 0.25 6.84 + 2.04 0.99 + 0.30 1.07 + 0.32 1.83 + 0.54 0.82 + 0.24 *Used in the general sense, to include bulbs, corms, tubers, and rhizomes. 687 099 + bO86‘b O9T + 09G'T OLI F tL F boos ‘Zz If ¥ 098 br + OIb + O€7'E OL7 ¥ 090'@ O€E F © OIZ ¥ 000'r OL + OSE OLT F = OIL #O8€‘€ ZL ¥ 060'€ OI F om 09S + boss's Orl = O8ZL'T OOL + 5 OLT + O€L‘Z 009 + 006 CL F a O8b + OO8'E O€l + bOTH'T Ob ¥ = 006'€T + OO7‘Lt 00S 9 + OOE ‘FI OOOT + SG OZ * O8E'Z O¢ + OS6'T Of + ar 067 * O87‘ OLI + O@H'E O9T * = OFS ¥060'L O£1 + OIZ'Z ee: = O£8 + bOz76'9 O17 + bOTZ'Z OIL + = OT? 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Herbaceous Species Cereals (Table 8). Five of the most important cereal crops, which vary appreciably in sensitivity, were studied. For FDS or 8-hr CR exposures to young seedlings, YDs59 values vary from about 1.4 kR for barley to 4.5 kR for maize, with intermediate values of about 2.0 kR for oats and about 2.1 kR for wheat. No FDS data are available for rice, but for several reasons, it can be expected to be appreciably more resistant than maize. As is generally true, the higher- exposure-rate (30 or 50 R/min) data mostly show greater damage for a given total exposure. For instance, YDso values vary from about 500 to 600 R for barley to 2.2 kR for oats; wheat and maize are intermediate, and rice, by far the most resistant, has a YDs5o9 of about 14 kR. At present no yield data exist for three other major cereal crops, namely, rye, sorghum, and pearl millet. It is known that stage of development at time of exposure influences yield (see previous discussion). Barley and wheat at young-seedling stages are more sensitive than at later stages.” ey However, data on lima beans,°* corn, and rice (Fig. 4) indicate that in these plants meiotic stages are considerably more sensitive than the seedling stage. We should keep in mind that varietal differences are known to exist for several cereals.2*-8° Differences are generally rather small, but in wheat varietal differences greater than fourfold have been demonstrated.* 4 Legumes (Table 9). So far four different edible legumes (peas, broad beans, lima beans, and soybeans) have been irradiated, and all are highly sensitive or have highly sensitive stages. The YDs5o for seed yield after FDS seedling irradiation varies from about 1.0 kR for peas to about 3.3 kR for lima beans and, after high-exposure-rate treatments, about 200 R for broad beans. Flower-bud stages are much more sensitive, as shown by both the pea and the lima-bean experiments in which YDsq values of approximately 250 and 110R, respec- tively, were found following high-dose-rate exposures. Root Crops (Table 10). The five root crops so far studied vary from an FDS YDs5o of about 1.4 kR for onions to 8.9 kR for radishes. However, poor texture and bad taste were noted in radishes grown from seedlings irradiated at the higher exposures. Potatoes and sugar beets irradiated at 80 R/min as young plants have YDso values of 1.66 kR and 1.85 kR, respectively. More data are needed for sugar beets since the standard error is large. We should note, however, that reduction in sugar content may be more susceptible to radiation than reduction in root weight, and, as shown in one study, sugar content decreases at a faster rate (R. S. Russell, personal communication), but the decrease does not occur under chronic irradiation.® ” Only survival data are available for garlic; however, the LDso9 of 1.12 kR indicates that this species is fairly sensitive with regard to yield reduction. 694 SPARROW, SCHWEMMER, AND BOTTINO Miscellaneous Fruit and Vegetable Crops (Table 11). Experiments have been conducted with cabbage, lettuce, pineapples, spinach, squash, and tomatoes, but only survival data are available for cabbage, pineapples, and spinach, which have LDs59 values of approximately 11.2 (FDS), 9.0, and 11.8 (FDS) kR, respec- tively. The tomato experiment is more difficult to summarize because the YDs5 9 was highly dependent on time after irradiation. However, at 10 weeks after exposure, the YDs9 was approximately 3 kR. Preliminary X-ray experiments with strawberries and raspberries irradiated in the dormant stage indicated only a mild effect on growth at a 16kR exposure. No yield data were obtained (Sparrow, unpublished). Irradiation of strawberry stolons at 17 R/min produced a YDso of about 6.5 KR. The survival data available for pineapple indicate that crown sections are rather resistant to irradiation, having an LDso9 of about 9 kR. Limited data for irradiated sugarcane cuttings indicate an LDso9 of approxi mately 3 kR.3® Pasture and Forage Crops (Table 12). Three grasses and two types of clover have been studied to date. Perennial rye has a YDsqo of about 1.6 kR and is about one-half as resistant as meadow fescue, which has a YDs9 of 3.7 KR. White clover, with a YD5o9 of 24 kR, is much more resistant than the grass species at any stage examined. For sweet clover, however, a severe effect (80% reduction) on growth was observed at 4.0kR after 16-hr acute exposures (Sparrow, unpublished). Only survival data are available for crested wheatgrass and this only at an exposure rate 10 times as high as for white clover and the two grasses. Woody Species (Fruit, Nut, and Forest Trees, etc.) Many of the more important forest trees, especially gymnosperms, are extremely sensitive to X or gamma radiation.’’''’!?’*® Recently reported Soviet work has confirmed this high sensitivity by exposing trees to beta irradiation from a number of radionuclides using exposures extending over several years.°” Brookhaven work showed LDs 0 values for a 16-hr exposure for Table 13 LD,, FOR FIVE SPECIES OF COMMON COMMERCIAL HARDWOODS''’ Common name Species LD GS DR: Eastern red oak Quercus borealis 3650 + 150 var. maxima Yellow birch Betula lutea 4280 + 520 Sugar maple Acer saccharum 4720+ 150 Red maple Acer rubrum 5110 + 230 White ash Fraxinus americana 7740 + 260 Average 5100 + 700 EFFECTS OF EXTERNAL GAMMA RADIATION 695 a number of species to be less than 1.0 kR. Experiments with angiosperms (deciduous trees, including the fruit- and nut-producing trees) have shown them to be more resistant, with LDs 9 values covering a much wider range. LDs 9 data from these experiments are given in Tables 13 and 14 (see also Table 11). Although all these values are based on actual experimental data, no absolute value of radiosensitivity can be given for any plant species growing under field conditions since a large number of variables influence the amount of injury finally produced by a given exposure. Of particular importance for these woody species is the changing radiosensitivity between the active and dormant stages, | | the latter being more resistant by a factor of approximately 1.65. Table 14 AVERAGE LD,, FOR EIGHT GENERA (15 SPECIES) OF GYMNOSPERMS'!'! Number Number of Average LD, , Genera of species experiments Range of LD,,,R + §.D.,R Pseudotsuga 1 1 461+ 71 Pinus 3 3 473 to 818 6922-110 Tsuga 1 2 690 to 701 696 + 6 Picea 4 6 626 to 1186 O17 = 94 Larix 2 2 705 to 834 770 + 65 Abies 1 1 93:9 226 Taxus 2 é) 475 to 1203 9524233 Thuja 1 it 970 2°63 All genera 15 19. 461 to 1203 826 + 54 RELATION BETWEEN RADIOSENSITIVITY AND INTERPHASE CHROMOSOME VOLUME As explained previously, the 36-hr FDS treatment appears to be a reasonable approximation of the exposure regime to which plants would be exposed during postattack fallout. The inverse relation between interphase chromosome volume (ICV) and radioresistance, also referred to previously, is applicable for a 36-hr FDS exposure as well as for shorter exposure times. The regression of ICV vs. LD;5 9 for young plants of species of economic value is given in Fig. 1. The regression slope is not significantly different from —1 at the 5% level of significance and is drawn as such. The regression of ICV vs. LD; 0 also has a slope not significantly different from —1 (Fig. 2). Postirradiation yield and survival data collected for many species of plants indicate a direct relation between LD;9 and YDso (see Fig. 7 and Table 15). When the data from economic crops only are plotted in this manner (Fig. 3), the 696 SPARROW, SCHWEMMER, AND BOTTINO 100 o, Crops 50 e@ , Other species 1 2 5 10 20 50 100 LD./kR Fig. 7 Log-log regression of YD,;, against LD, , for 25 species of plants given a 16-hr CR exposure as young plants. (See list of species names in Table 15.) structure is small enough to allow penetration by beta radiation, the amount of regression also fits a +1 slope passing approximately through the origin (0.1, 0.1). Thus the determination of an LD, 9 for any species should provide a fair approximation of the expected YDs 0. Survival data were collected after 16-hr acute gamma irradiation for 28 species of woody plants, and LDso values were determined. The regression for ICV vs. LDso for these species (both angiosperms and gymnosperms), which has been published,’' should be used for predictions for woody species since it is appreciably different from the regression for herbaceous plants. RADIOSENSITIVITY PREDICTIONS (BASED ON ICV DATA) The regressions described previously were used to predict from ICV measurements the probable sensitivities of many as yet unirradiated plant species. Predicted YDso values for FDS exposures are given for 89 species of economic crops (Tables 16 and 17). With the exception of rice (Group 7), the cereal crops are concentrated in the four most sensitive groups. Legumes are EFFECTS OF EXTERNAL GAMMA RADIATION 697 Table 15 LIST OF 25 SPECIES OF PLANTS WITH THEIR YD,, AND LD, , VALUES FOR 16-HR ACUTE GAMMA IRRADIATIONS (AS IN FIG. 7) No. Species YD,,,kR LD,,,kR 1 Haworthia fasciata 1.65 137 2 Pisum sativum 1.45 2.03 3 Hordeum vulgare 1.80 2.16 4 Aloe brevifolia 155 227 5 Nigella damascena 2.20 2.79 6 Triticum aestivum 3.11 3.70 7 Zea mays (hybrid) 4.20 4.19 8 Zea mays 4.00 4.66 9 Rumex orbiculatus 7.80 5.38 10 Cyanotis somaliensis 3.35 5.64 et Chrysanthemum lacustre 6.75 6.49 12 Rumex hydrolapathum 6.00 7.95 13 Rumex stenophyllus 24.10 8.32 14 Rumex aquaticus 12.80 10.32 i) Rumex sanguineus 2,40 10.46 16 Rumex pulcher 15.20 11.00 17 Rumex obtusifolius 15.30 11559 18 Rumex palustris 16.40 13.04 19 Rumex maritimus 12.00 us Fe Io 20 Rumex confertus 9.60 14:92 21 Sedum rupifragum 21.00 15.00 Ze Rumex conglomeratus 16.00 16.04 23 Rumex pseudonatronatus 17.80 16.54 24 Rumex crispus ZA LO 18.33 25 Trifolium repens 12325 20.32 distributed over Groups 3 to 6. Root crops are scattered from Groups 2 to 7. Pasture or forage crops are widely distributed from Groups 3 to 8. Numerically, the majority of crop plants have estimated YDs5 9 values between 4 and 16 kR. Only seven plants fall above 16 kR, and none of these is a major food crop. Also, the actual sensitivity of one of these (acorn squash) is considerably less than its predicted YDs ee Although few if any data are available on yield reduction for the fruit- and nut-producing trees, it would be expected, as found for herbaceous plants, that the YD59 would be appreciably less in each case than the LDs 9. Predicted LDs 9 values for 16-hr acute exposures for 82 woody plants of economic value (for wood products or for edible fruit and nuts) are given in Table 18. These predictions are based on ICV’s from actively growing trees. Trees irradiated while in the dormant stage are somewhat more resistant. However, FDS LDs5 0 exposures would be expected to be somewhat less. 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Little bluestem Dill Celery Asparagus Swiss chard Kale Cauliflower Bush red pepper (Bell) Watermelon Muskmelon Acorn squash Buckwheat Cotton Group 5 (6 to 8 kR) (continued) Nicotiana tabacum Pastinaca sativa Phleum pratense Saccharum officinarum Vigna sinensis Common tobacco Parsnip Timothy Sugarcane Cowpea Group 6 (8 to 12 kR) Agave rigida Beta vulgaris Brassica campestris Brassica birta Brassica napobrassica Brassica nigra Brassica oleracea var. italica Brassica pekinensis Cucumis melo var. cantalupensis Cynara scolymus Daucus carota var. sativa Glycine max Medicago sativa Petroselinum crispum Phaseolus aureus Raphanus sativus Ricinus communis Sesamum indicum Solanum melongena Trifolium pratense Sisal hemp Beet Bird rape White mustard Rutabaga Black mustard Broccoli Chinese cabbage Cantaloupe Globe artichoke Carrot Soybean Vernal alfalfa Parsley Mung bean Radish Castor bean Oriental sesame Eggplant Red clover Group 7 (12 to 16 kR) Bouteloua gracilis Brassica juncea Brassica oleracea var. gemmufera Brassica rapa Fragaria species Ipomoea batatas Linum usitatissimum Mentha spicata Oryza sativa Paspalum dilatatum Blue grama Indian mustard Brussels sprouts Turnip Strawberry Sweet potato Flax Spearmint Rice Dallis grass Group 8 (16 to 20 kR) Andropogon gerardi Cucurbita moschata ‘Butternut’ Mentha piperita Big bluestem Butternut squash Peppermint Group 9 (20 to 24 kR) Cucurbita maxima Cucurbita pepo var. medullosa Winter squash Zucchini squash Group 10 (>24 kR) Brassica napus Hibiscus esculentus Winter rape Okra +Boldface type indicates those species for which actual FDS data are available. These data have been used to place the species in their appropriate groups. 700 SPARROW, SCHWEMMER, AND BOTTINO Table 18 PREDICTED 16-HR (ACUTE) GAMMA LD, , EXPOSURES FOR 82 WOODY PLANTS OF ECONOMIC VALUE"? Common name Scientific name LD,, + S.D.,.kR Almond Prunus amygdalus Batsch See ANG ‘Nonpareil’ Apple, common Pyrus malus L. ‘Northern Spy’ 4.60 + 1.75 Apricot Prunus armeniaca L. ‘Blenheim’ 3.00 + 1.12 Arborvitae, eastern Thuja occidentalis L. 1.50+ 0.55 Arborvitae, giant Thuja plicata Donn 1.70 + 0.63 Ash, white Fraxinus americana L. Piss eer 77/7 Aspen, quaking Populus tremuloides Michx. 4.80 + 1.83 Avocado, American Persea americana Mill. 2.81 + 1.05 Beech, American Fagus grandifolia Ehrh, 6.41 + 2.48 Birch, yellow Betula lutea Michx. f. 6:63 22207 Blueberry, highbush Vaccinium corymbosum L., 5.54 + 2.13 Blueberry, lowbush Vaccintmm angustifolum Ait. 32S 9.22125 Buckeye, yellow Aesculus octandra Marsh. Zeala e 7259/7/ Cassava Manihot dulcis Pax ‘Valenca’ 3550.2 ese Cedar, eastern red Juniperus virginiana L. 1.35 + 0.50 Cedar-of-Lebanon Cedrus libani Loud, 0.84 + 0.31 Cherry, mazzard Prunus avium L. ‘Windsor’ 3.60 + 1.36 Cherry, sour Prunus X cerasus L, DSoat 2.2/9 Chestnut, American Castanea dentata (Marsh.) Borkh. 3577. We Ad Cranberry Vaccinium macrocarpon Ait. 6.41 + 2.48 Cryptomeria Cryptomeria japonica D. Don 1.22 + 0.45 ‘Araucarioides’ Cypress, bhutan Cupressus duclouxiana Hickel 1.58 + 0.58 Cypress, common bald Taxodium distichum (L.) Rich. 1.71 + 0.63 Eucalyptus, messmate Eucalyptus obliqua L' Her. 3:00 1712 stringy bark Fig, common Ficus carica L. ‘Celeste’ 6.21 + 2.40 Fir, alpine Abies lasiocarpa (Hook.) Nutt, O62" 0:23 Fir, balsam Abies balsamea (L.) Mill. OF7-5** 0:28 Fir, Douglas Pseudotsuga douglasi Carr. 0.99 + 0.37 Fir, grand Abies grandis Lindl. 0.62 + 0.23 Fir, white Abies concolor Hoopes 0.81 + 0.30 Grape Vitis species ‘Concord’ ODED 2 5 Grape Vitis species ‘Delaware’ D269 U2 9 Grapefruit Citrus paradisi Macf. S27 = leas Hemlock, Canada Tsuga canadensis (L.) Carr. O87 2. = O27, Hemlock, Pacific Tsuga heterophylla Sarg. 0.80 + 0.30 Hickory, bitternut Carya cordiformis (Wang.) K. Koch 7.69 + 3.01 Hickory, mockernut Carya tomentosa (Poir.) Nutt. 7.69 + 3.01 Hickory, shagbark Carya ovata (Mill.) K. Koch 6:0322 2232 Hickory, shellbark Carya laciniosa (Michx. f.) Loud. 4.10 + 1.55 Juniper, common Juniperus communis L. 1.49+0.55 Larch, eastern Lanx laricina (Duroi) K. Koch 0.69 + 0.26 Larch, European Larix decidua Mill. O27 7 2.0529 Larch, Japanese Lanx leptolepis Gord. 0.85 + 0.31 Larch, western Lanx occidentalis Nutt. 0.85 + 0.31 EFFECTS OF EXTERNAL GAMMA RADIATION Common name Table 18 (Continued) Scientific name Lemon Linden, American Locust, black Maple, sugar Oak, blackjack Oak, eastern red Oak, post Oak, swamp chestnut Oak, white Orange, mandarin Orange, sweet Peach Pecan Pine, Austrian Pine, eastern white Pine, Himalayan Pine, Japanese red Pine, loblolly Pine, ponderosa Pine, pitch Pine, red Pine, Scotch Pine, shore Pine, slash Pine, sugar Pine, Virginia Plum, garden Redwood Sequoia, giant Spruce, black Spruce, Colorado Spruce, engelmann Spruce, Norway Spruce, red Spruce, white Walnut, eastern black Walnut, Persian Yew, Canada Citrus limonia Burm, f. ‘Villa Franca’ Tilia americana L. Robinia pseudoacacia L. Acer saccharum Marsh. Quercus marilandica Muenchh. Quercus borealis Michx. f. var. maxima (Marsh.) Ashe Quercus stellata Wang. Quercus prinus L. Quercus alba L. Citrus reticulata Blanco ‘Cleopatra’ Citrus sinensis Osbeck ‘Parson Brown’ Prunus persica (L.) Patsh, Carya illinoensis (Wang.) K. Koch ‘Sioux’ Pinus nigra Arnold Pinus strobus L. ‘Pendula’ Pinus griffithu McClel. Pinus densiflora Sieg. et Zucc. ‘Umbraculifera’ Pinus taeda L. Pinus ponderosa Dougl. Pinus rigida Mill. Pinus resinosa Ait. Pinus sylvestris L. Pinus contorta Loud, Pinus caribaea Morelet Pinus lambertiana Dougl. Pinus virginiana Mill. Prunus domestica L. Sequoia sempervirens Endl. Sequotadendron giganteum Buchholz Picea mariana (Mill.) BSP. Picea pungens Engelm. Picea engelmanni Parry Picea abies (L.) Karst. Picea rubens Sarg. Picea glauca (Moench) Voss Juglans nigra L. Juglans regia L. Taxus canadensis Marsh. a oe Coen Swear ers =" oO [eS se) AE ale A _ ioe) I+ _ 58 4.60 + 1.75 2.90 + 1.08 0.61 + 0.23 0.52 + 0.20 0.50 + 0.19 0.60 + 0.22 0.63 + 0.23 0.58 + 0.22 0.67 + 0.25 0.70 + 0.26 0.62 + 0.23 0.70 + 0.26 0.77 + 0.29 0.41 + 0.16 0.69 + 0.26 4.60 + 1.75 1.46 + 0.54 1.72 + 0.64 0.84 + 0.31 0.76 + 0.28 0.73 + 0.27 0.73 + 0.27 0.57 + 0.21 0.77 + 0.29 3.83 + 1.45 4.80 + 1.83 0.99 + 0.36 701 702 SPARROW, SCHWEMMER, AND BOTTINO on the effective exposure dose actually received by the plants. Partial shielding by soil, water, or other plants, which has not been considered, could be important in certain instances. Predicted values of LDs59 (in kiloroentgens) for the dominant woody species in the major types of ecosystems are given in Table 19. A fallout gamma exposure of 1 to 2 kKR would be expected to virtually eliminate the productive capacity of coniferous forests during a season of active growth and might seriously affect the natural balance of species in other forests and thus increase the possibility of secondary damage from fire, flood, and loss of nutrients. It must be remembered that these predictions are made from regressions based on experiments handled under specific conditions. Any of a number of variables (see previous discussion of variables) can alter the predicted values in either direction and thus must be taken into account in planning experiments, evaluating radiobiological data, or assessing damage. SUMMARY AND CONCLUSIONS 1. Problems are encountered in trying to anticipate the degree of damage to native or cultivated plants which would be produced by the radiation released by high-level fallout from nuclear detonations. Since almost no pertinent data resulting from such a disaster exist, it is necessary to extrapolate from other radiobotanical data. For short-term consideration of postattack damage, the gross radiation effects of greatest economic importance are reduced vegetative growth, reduced yield, and plant deaths. Alterations in normal plant tolerance to environmental stress also may occur, as may secondary effects resulting from the death of plants, such as loss of nutrients and increased probability of flood or fire damage. Although plants receiving postattack fallout would be exposed to both beta and gamma radiation, this report discusses mainly the results expected from the latter. Present data indicate an RBE of about 1 for these two radiations, but distribution and depth dose is a problem with beta radiation. The possibility of an interaction between the two types of radiation injury is very real and must be considered. 2. There is a wide range in radiosensitivities of plants determined or influenced by many biological, radiological, and environmental factors. Varia- tion in exposure rate is an important factor, high rates being generally more effective (by a factor as great as 4) than low rates in reducing survival and yield. Variation in radiosensitivity among species exceeds a factor of 100. Within a species the stage of development of the plant may also affect its sensitivity by as much as a factor of 50; seeds are most resistant, and certain stages of meiosis are most sensitive (Table 4). Hence the seasonal timing of the exposure is an important variable. 3. Among the most important environmental conditions influencing the radiation response are temperature, light, and competition (Table 1). Experi- Table 19 703 PREDICTED SENSITIVITY TO GAMMA RADIATION OF MAJOR WOODY ECOSYSTEMS AND THEIR DOMINANT PLANT SPECIES Major ecosystem and vegetation type Dominant species Common name * Predictedt 16-hr acute gamma 50 — LD,, + $.D.,kR Coniferous Forests Boreal Abies balsamea Balsam fir 0.89 + 0.03+ Picea glauca White spruce 0.85 + 0.05¢ Subalpine Abies lasiocarpa Alpine fir 0.62 + 0.23 (Rocky Mts.) Picea engelmanni Engelmann spruce 0.7352 0:27 Montane Pinus ponderosa Ponderosa pine 0.58 + 0.22 (Rocky Mts.) Pseudotsuga douglas Douglas fir 0.99 + 0.37 Sierra Cascades Abies concolor White fir 0.81 + 0.36 Pinus jeffreyi Jeffrey pine 0.67 + 0.25 Pinus lambertiana Sugar pine 0.41 + 0.16 Pinus ponderosa Ponderosa pine 0.58 + 0.22 Pseudotsuga douglas Douglas fir 0.46 + 0.074 Pacific conifer Abies grandis Grand fir 0.62 + 0.23 Thuja plicata Giant arborvitae 1.70 + 0.63 Tsuga heterophylla Western hemlock 0.80 + 0.30 Deciduous Forests Mixed mesophytic Acer saccharum Sugar maple 4.80 + 1.79 Fagus grandifolia American beech 6.41 + 2.48 Linodendron tulipifera Yellow poplar 3.00 + 1.12 Magnolia acuminata Cucumbertree magnolia 3.71 + 140 Quercus alba White oak 2.93 + 1.10 Tilia americana American linden 6.03 + 2.32 Beech—maple Acer saccharum Sugar maple 4.80 + 1.79 Maple —basswood Fagus grandifolia American beech 6.41 + 2.48 Tilia americana American linden 6.03°£ 2:32 Tsuga canadensis Canada hemlock 0.72 + 0.27 Hemlock— Acer saccharum Sugar maple 4.724 0.15% hardwood Betula lutea Yellow birch 4.28 + 0.524 Pinus resinosa Red pine 0.78 + 0.034 Pinus strobus Eastern white pine 0.47 + 0.01} Tsuga canadensis Canada hemlock 0.70 + 0.05¢ Oak—chestnut Castanea dentata American chestnut = by ese bee 74 Pinus rigida Pitch pine 0.67 + 0.25 Quercus coccinea Scarlet oak 4.60 + 1.75 Quercus prinus Swamp oak 3.11 + 1.16 Oak—hickory Carya cordiformis Bitternut hickory 7.09 3.01 Carya laciniosa Shellbark hickory 4.10 + 1.55 Carya ovata Shagbark hickory 6.03 + 2.32 Carya tomentosa Mockernut hickory 7.69.4 3.01 Pinus taeda Loblolly pine 0.63 + 0.23 Quercus alba White oak 2°93 271. 10 Quercus borealis Eastern red oak 3.36 + 1.26 var. maxima Quercus marilandica Blackjack oak 3.45, 2 1.30 Quercus stellata Post oak 3.96 + 1.50 Quercus velutina Black oak 5.025271 92 *From Standardized Plant Names. ° *® tBased on calculations of ICV from active meristems. tObserved mortality in actual experiments.’ ' 704 SPARROW, SCHWEMMER, AND BOTTINO mental data suggest that these factors could cause the response to vary by as much as a factor of 10, excluding the effects of drought. Since significant exposures to radiation can be expected to delay flower initiation and ripening, plants with a growing season clearly limited by conditions of climate (e.g., tomato) might survive through the growing ‘season but would produce essentially no useful yield. Also, since different species die at different rates after lethal irradiation, plants that die very quickly would be virtually worthless under postattack conditions, but those dying more slowly might be of some limited value. 4. The viability and vigor of seed from irradiated plants must be considered. The seed is used to produce the next crop, and adverse effects are sometimes present even in seed that superficially looks perfectly normal. Also, deleterious effects on growth or yield may be manifested in the subsequent crop (for annuals), and in some cases these effects appear several years after exposure (for perennials), especially in the reproductive processes. 5. It is useful to have a yield end point that can be compared for all crops, e.g., the exposure required to reduce yield by 50% (YDs50). Because seeds are generally relatively resistant compared with growing plants of the same species, they probably would not present a problem while in storage. The seedling LDs 0 for irradiated dry seeds is above 10kR for most but not all crop plants (Table 6). Other propagules, such as seed potato tubers and small onion transplants, are more sensitive, having a YDs5 9 value of about 1.5 kR. 6. A brief summary of existing sensitivity data on crop and other cultivated plants follows. (Keep in mind that modifying factors can have a large effect on response and there is no such thing as an absolute value under field conditions.) Most of the small grain cereals are relatively sensitive, having YDs59 exposures that range from 0.5 to 5.0 kR (Table 8). Rice is an exception, having a YDso9 of about 14.0kR for young seedlings. Edible legumes vary more in sensitivity; exposures of 220R to about 6.0kR to vegetative stages produce a YDso (Table 9). For flowering stages YDso values range between about 100 and 400 R. The YDso values for root crops vary from 1.4 kR for onions to about 9.0kR for radishes; potatoes and sugar beets are intermediate in sensitivity (Table 10). The miscellaneous crops (in order of increasing resistance: lettuce, pineapple, strawberry, squash, spinach, cabbage, and tomato) have YDs5q or LD; values ranging from 4.5 to 12 kR (Table 11). The pasture and forage crop plants have a very wide range in sensitivity; YDs9 or LD; 9 values range from about 1.5 to 23kR (Table 12). Finally, some woody plants of economic importance are highly sensitive. The gymnosperms studied have an average LDs 9 value of 826 R (Table 14). The deciduous trees are somewhat more resistant, generally having LDso9 values ranging from 3.6 to 7.7kR (Table 13). The exposures seriously affecting their economic usefulness would be much lower. 7. The inverse relation between ICV and radioresistance holds for simulated- fallout-decay gamma exposures as reported previously for acute and chronic EFFECTS OF EXTERNAL GAMMA RADIATION 705 gamma exposures. A regression of YDs5o9 vs. LD; 9 has a slope not significantly different from +1 (Figs. 3 and 7). Thus an LD; 9 for any species can be used as a fair approximation of the YDs59. A table of YDs5o predictions based on ICV is given for 89 species of economic plants showing the distribution of various crop plants over the entire range of sensitivity from less than 1 to more than 24kR (Tables 16 and 17). Predictions of LDso9 are also given for 25 species of ornamental plants (Table 7) and 82 species of woody plants (Table 18). 8. These predictions of survival and yield, although based on a large amount of experimental data, are for stated experimental conditions and average environmental conditions. They can be expected to vary considerably under actual fallout conditions and should not be considered absolute for any species. However, they should be useful in damage-assessment work because they give some advance indication of which crops might survive at various radiation levels and be available for human and/or animal consumption. For example, most small grain cereals (not including maize and rice) would be virtually useless where fallout gamma exposures exceed about 2.0 kR. Therefore only fields in fringe areas or away from the main fallout patterns would produce normal yields. 9. Finally, we should point out that the amount of radiobiological data is still highly inadequate to permit confident predictions of expected responses of many important species from high-level fallout-gamma exposure. This is especially true for yield and is even more critical if exposure occurs during meiosis or development of reproductive structures. Inadequate information about beta-radiation injury and possible interaction or synergism between beta and gamma radiation further complicates the problem. Clearly a much greater research effort is needed to fill the gaps in our radiobiological knowledge of economically important plant species. (See also the recommendations of the various working groups of this symposium, especially those concerned with the vulnerability of crops to beta and gamma radiation.!°°°!9!) ACKNOWLEDGMENTS This research was carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commission. We wish to thank J. Bryant, Brenda Floyd, E. E. Klug, Anne F. Nauman, Virginia Pond, Leanne Puglielli, L.A. Schairer, and Pamela Silimperi for technical assistance and K. H. Thompson for statistical analyses. We gratefully acknowledge the use of unpublished data from several sources. These data are acknowledged in the appropriate tables. 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Scarascia Mugnozza, Effects of Gamma Radiation on the Gametes, Zygote and Proembryo in Nicotiana tabacum L., Radiat. Bot., 4: 373—386 (1964). T. Hermelin, Effects of Acute Gamma Irradiation in Barley at Different Ontogenetic Stages, Hereditas, 57: 297—302 (1967). T. Kawai and T. Inoshita, Effects of Gamma Ray Irradiation on Growing Rice Plants. I. Irradiations at Four Main Developmental Stages, Radiat. Bot., 5: 233-255 (1965). L. W. Mericle and R. P. Mericle, Radiosensitivity of the Developing Plant Embryo, in Fundamental Aspects of Radiosensitivity, Report of a Symposium, June 5—7, 1961, Upton, N. Y., USAEC Report BNL-675 (Brookhaven Symposia in Biology, Number 14), pp. 262—286, Brookhaven National Laboratory. L. M. Monti and M. Devreux, Action des rayons gamma sur les gamétes, le zygote et le proembryon d'un pois fourrager, Caryologia, 17: 433—441 (1964). 61. 62. 63. 64. 65: 66. 67. 68. 69. 70. TN WIE 13: 74. TD: 76. TH. 78. Pe EFFECTS OF EXTERNAL GAMMA RADIATION 709 E. G. Siemer, M. J. Constantin, and D. D. Killion, Effects of Acute Gamma Irradiation on Development and Yield of Parent Plants and Performance of Their Offspring, this volume. A. Yamashita, Effects of Acute and Chronic Gamma-Ray Irradiations on Growing Barley Plants, Gamma Field Symp., 6: 71—95 (1967). A. H. Sparrow and S. S. Schwemmer, The Effect of Postirradiation Temperature on Survival Times in Herbaceous Plants Exposed to Gamma Radiation, Radiat. Res., 43: 227:(1970). L. Decourtye, Stérilité, gamétique partielle provoquée par une irradiation gamma sur la variété de pommier Golden Delicious, Radiat. Bot., 10: 1—5 (1970). T. D. Rudolph, Effects of X-Irradiation of Seed on X, and X, Generations in Pinus banksiana Lambert, Radiat. Bot., 7: 303—312 (1967). A. H. Sparrow, L. A. Schairer, R. C. Sparrow, and W. F. Campbell, The Radiosensi- tivity of Gymnosperms. I. The Effect of Dormancy on the Response of Pinus strobus Seedlings to Acute Gamma Irradiation, Radiat. Bot., 3: 169—173 (1963). F. G. Taylor, Jr., Predicted Seasonal Radiosensitivity of Southeastern Tree Species, Radiat, Bot., 6: 307—311 (1966). G. N. Brown and F. G. Taylor, Interaction of Radiation and Photoperiodism in Xanthium pensylvanicum, Effects of Radiation During the Light and Dark Periods of Photoinduction, Radiat. Bot., 7: 67—72 (1967). G. M. Clark, F. Cheng, R. M. Roy, W. P. Sweaney, W. R. Bunting, and D. G. Baker, Effects of Thermal Stress and Simulated Fallout on Conifer Seeds, Radiat. Bot., 7: 167 —17.9' (1967): J. F. McCormick, Changes in a Herbaceous Plant Community During a Three-Year Period Following Exposure to lonizing Radiation Gradients, in Radioecology, Proceedings of the Symposium held Sept. 10—15, 1961, V.Schultz and A. W. Klement, Jr. (Eds.), pp. 271—276, Reinhold Publishing Corporation, New York, 1963. J. F. McCormick and R. E. McJunkin, Interactions of Gamma Radiation and Other Environmental Stresses upon Pine Seeds and Seedlings, Health Phys,, 11: 1643-1652 (1965): L. N. Miller, Changes in Radiosensitivity of Pine Seedlings Subjected to Water Stress During Chronic Gamma Irradiation, Health Phys., 11: 1653—1662 (1965). R. B. Platt, lonizing Radiation and Homeostasis of Ecosystems, in Ecological Effects of Nuclear War, G. M. Woodwell (Ed.), USAEC Report BNL-917, pp. 39—60, Brookhaven National Laboratory, August 1965. T. S. Osborne and A. O. Lunden, The Cooperative Plant and Seed Irradiation Program of the University of Tennessee, Int. J. Appl. Radiat. Isotop., 10: 198—209 (1961). R. A. Nilan, The Cytology and Genetics of Barley, 1951—1962, Washington State University Press, 1964. A. Ehrenberg, L. Ehrenberg, and G. Lofroth, Radiation-Induced Paramagnetic Centers in Plant Seeds at Different Oxygen Concentrations, Abb. Deut. Akad. Wiss. Berlin, Kl. Med., 1962(Nr.1): 229—231 (1962). R. L. Latterell and D. M. Steffensen, The Oxygen Effect and Its Relation to Changes in Radiosensitivity During Seed Germination, Mutat. Res., 4: 191—200 (1967). R. A. Nilan, C. F. Konzak, R. R. Legault and J. R. Harle, The Oxygen Effect in Barley Seeds, in Effects of lonizing Radiations on Seeds, Conference Proceedings, Karlsruhe, 1960;,-pp.- 139-154, ~ International Atomic. Energy .Agency, Vienna, 1961 (STI/PUB/1 3). | R. A. Nilan, C. F. Konzak, J. Wagner, and R. R. Legault, Effectiveness and Efficiency of Radiations for Inducing Genetic and Cytogenetic Changes, Radiat. Bot., Suppl., 5: T1895 GIG)? 710 80. 81. 82. 83. 84. 85. 86. 87. 88. 89. 90. ot 92: 93: 94: 95: 96. OTF SPARROW, SCHWEMMER, AND BOTTINO A. H. Sparrow and E. Christensen, The Effects of X-Ray, Neutron and Chronic Gamma Irradiation on Growth and Yield of Potatoes, Amer. J. Bot., 37: 667 (1950). A. Heiken, Spontaneous and X-Ray-Induced Somatic Aberrations in Solanum Tuberosum \.., Acta Acad. Reg. Sci. Upsaliensis, 7: 1-125 (1960). R. S. Kahan, Differential Effects of Small Doses of Ionizing Radiation on the Growth of Onion Seed and Bulblets and on Crop Yields, Radiat, Bot., 9: 175—178 (1969). R. K. Schulz, Survival and Yield of Crop Plants Following Beta Irradiation, this volume. B. Donini, G. T. Scarascia Mugnozza, and F. D’Amato, Effects of Chronic Gamma Irradiation in durum and Bread Wheats, Radiat. Bot., 4: 387—393 (1964). M. Stoilov, G. Jansson, G. Eriksson, and L. Ehrenberg, Genetical and Physiological Causes of the Variation of Radiosensitivity in Barley and Maize, Radiat. Bot., 6: 457—467 (1966). Y. Ukai, Studies on Varietal Differences in Radiosensitivity in Rice. III. Radio- sensitivities with Respect to the Reduction in the Number of Dividing Cells and the Occurrence of Chromosome Bridges, Jap. J. Breed., 18: 221—228 (1968). J. D. Spikes, Radiation Effects and Peaceful Uses of Atomic Energy in the Plant and Soil Sciences, in Radioecology, Proceedings of the Symposium held Sept. 10—15, 1961, V.Schultz and A.W. Klement, Jr. (Eds.), pp. 5—11, Reinhold Publishing Corporation, New York, 1963. D. I. T. Walker and N. S. Sisodia, Induction of a Nonflowering Mutant in Sugarcane (Saccharum*sp.), Crop Sci 9: 551-92 (1969): R. M. Alexakhin, R. T. Karaban, N. V. Kulikov, A. A. Molchanov, M. A. Naryschkin, S. V. Tarchevskaya, F. A. Tikhomirov, E. B. Tyuryukanova, and P. I. Yushkov, Some Aspects of Radioactive Fission Products Migration in the Forest Biogeocenoses and the Effects of Ionizing Radiations on the Woody Plants, in Symposium International de Radioecologie, Sept. 8-12, 1969, Cadarche, Report CONF-690918, Vol. 2, pp. 999—1023, Commissariat a |’Energie Atomique, 1970. H. H. Smith, D. C. Joshua, N. C. Combatti, and K. H. Thompson, Relative Effects of Fission Neutron vs. X Irradiation of Seeds over a Wide Range of Genotypes, Doses and Moisture Levels, in Symposium on Neutrons in Radiobiology, USAEC Report CONF-691106, pp. 173-191, UT—AEC Agricultural Research Laboratory. N. K. Notani and B. K. Gaur, Paradoxical Modifications in Radiosensitivity of Maize and Barley Seeds Stabilized for Different Moisture Contents, in Biological Effects of Ionizing Radiation at the Molecular Level, Symposium Proceedings, Brno, 1962, pp. 443—453, International Atomic Energy Agency, Vienna, 1962 (STI/PUB/60). L. M. Josephson, data cited by T.S. Osborne and A. O. Lunden, The Cooperative Plant and Seed Irradiation Program of the University of Tennessee, Int. J. Appl. Radiat, Isotop., 10: 198—209 (1961). C. R. Davies and S. F. Young, Effects of Irradiation of Parent Plants on Crop Yields, in Annual Report of Agricultural Research Council, Letcombe Laboratory, British Report ARCRE-20; pp, 12-—15,.1969: C. Y. Harn, J. K. Choi, and Y. S. Koh, Studies on Garlic Breeding Using Radiation. II. Morphological Effects on Gamma-Ray-Induced R, Generation in Garlic, Allium satwwum, J. Nucl. Sci. (Seoul), 8: 121—125 (1968). (In Korean) H, Irizarry and J. Vélez Fortufio, Effect of Gamma Radiation Dosages on Rooting of Pineapple Crown Sections, Shoot Emergence and Growth, J. Agr. Univ. Puerto Rico, D425 t—- 058.1 9:70);, S. Matsumura and T. Fujii, Radiosensitivity in Plants, II. Irradiation Experiments with Vegetatively Propagated Plants, Seiken Zib6d, 10: 22—32 (1959). W. S. Boyle, Radioresistance of F, Hybrids in the Triticeae, Radiat. Bot,, 8: 1—6 (1968). EFFECTS OF EXTERNAL GAMMA RADIATION 711 98. American Joint Committee on Horticultural Nomenclature, Standardized Plant Names, 2nd ed., J. Horace McFarland Co., Harrisburg, Penn., 1942. 99.D. D. Killion and M, J. Constantin, Fallout Radiation and Crop Productivity. Part B, UT—AEC Agricultural Research Laboratory Annual Report, OCD Work Unit 3223B, L969: 100, Report of Committee 2 on Vulnerability of Crops to Fallout Beta Irradiation, Appendix A, this volume. 101. Report of Committee 3 on Vulnerability of Crops to Fallout Gamma Irradiation, Appendix A, this volume. LIST OF ATTENDEES DONALD R. ADAMS Health Service Laboratory U. S. Atomic Energy Commission Idaho Falls, Idaho BAWE ALLEY OCD Region Six Federal Regional Center Denver, Colo. ARNA J. ANDERSON 105 Buck Jones Road Raleigh; Ne © CHARLES ANDERSON Systems Sciences, Inc. Bethesda, Md. JOHN J. B. ANDERSON College of Veterinary Medicine University of Illinois Urbana, III. STANLEY I. AUERBACH Ecological Sciences Division Oak Ridge National Laboratory Oak Ridge, Tenn. H. JAMES BARTH 6456 Woodridge Road Alexandria, Va. YNZ NED D] BAYLEY Director, Science and Education U. S. Department of Agriculture Office of the Secretary Washington, D. C. Ma.G] BE Ire UT—AEC Agricultural Research Laboratory Oak Ridge, Tenn. DAVID W. BENSEN Postattack Research Division Office of Civil Defense (OSA) Washington, D. C. VICTOR P. BOND Associate Director Brookhaven National Laboratory Upton, Long Island, N. Y. PAUL J. BOTTINO Biology Department Brookhaven National Laboratory Upton, Long Island, N. Y. CORNELIS BROERTJES Institute for Atomic Sciences in Agriculture Wageningen, The Netherlands ElIsSmiOR AltENDEES STEPHEN L. BROWN Stanford Research Institute Menlo Park, Calif. A] K. BURDITI. JR. Agricultural Research Service U. S. Department of Agriculture Beltsville, Md. J. A. J. CARRIERE Animal Disease Research Institute Canada Department of Agriculture Hull, Que., Canada ROBERT CHERTOK Bio-Medical Division Lawrence Radiation Laboratory Livermore, Calif. RICHARD COLE Environmental Science Associates Burlingame, Calif. MILTON J. CONSTANTIN UT—AEC Agricultural Research Laboratory Oak Ridge, Tenn. A. H. CORNER Head, Histopathology Section Animal Disease Research Institute Canada Department of Agriculture Hull, Que., Canada G. E. COSGROVE Biology Division Oak Ridge National Laboratory Oak Ridge, Tenn. WILLIAM T. COX Extension Service U.S. Department of Agriculture Washington, D. C. HARVEY L. CROMROY University of Florida Gainesville, Fla. 713 ROGER DAHLMAN Ecological Sciences Division Oak Ridge National Laboratory Oak Ridge, Tenn. JAMES A. DAVIS Agricultural Stabilization and Conservation Service U. S. Department of Agriculture Washington, D. C. KoE-DIBHE Animal Health Division U. S. Department of Agriculture Harrisburg, Pa. DONATO DIGREGORIO Ecological Sciences Division Oak Ridge National Laboratory Oak Ridge, Tenn. PAUL DUNAWAY Ecological Sciences Division Oak Ridge National Laboratory Oak Ridge, Tenn. BRUCE M. EASTON Agricultural Stabilization and Conservation Service U.S. Department of Agriculture Washington, D. C. RONALD E. ENGEL National Air Pollution Control Administration Bureau of Criteria and Standards Durham, N. C. H. E. ERDMAN Battelle—Northwest Richland, Wash. GEORGE F. FRIES Animal Sciences Research Division U. S. Department of Agriculture Beltsville, Md. 714 LIST OF ATTENDEES JOHN F. GAMBLE Environmental Engineering University of Florida Gainesville, Fla. HAL GAUT RADEF Officer OCD Region Two Olney, Md. HELLMUT GLUBRECHT Institut fur Strahlenbiologie Technische Universitat Hannover Hannover, West Germany JACK C. GREENE Postattack Research Division Office of Civil Defense (OSA) Washington, D. C. SUMNER A. GRIFFIN UT—AEC Agricultural Research Laboratory Oak Ridge, Tenn. NATHAN S. HALL T—AEC Agricultural Research Laboratory Oak Ridge, Tenn. R. L. HALSTEAD Soil Research Institute Canada Department of Agriculture Ottawa, Ont., Canada RICHARD I. C. HEDE OCD Region One Federal Regional Center Maynard, Mass. DAVID E. HEIMAN OCD Region Seven Santa Rosa, Calif. A. HEKKING 3 Burke Heights Drive Wallingford, Conn. F. P,. HUNGATE Biology Department Battelle—Northwest Richland, Wash. PAUL E. JAMES Agricultural Research Service U. S. Department of Agriculture Beltsville, Md. GORDON C. JANNEY Agricultural Research Service U. S. Department of Agriculture Madison, Wis. BILLY G. JOHNSON Agricultural Research Service U. S. Department of Agriculture Hyattsville, Md. JAMES E. JOHNSON Department of Animal Science Colorado State University Fort Collins, Colo. DAVID C. L. JONES Stanford Research Institute Menlo Park, Calif. ERIC W. JONES Box 22 Hazeldean, Ont., Canada ASHER D. KANTZ Santa Barbara Division EG&G, Inc. Goleta, Calif. CHARLES KETCHAM OCD Region Four Federal Center Battle Creek, Mich. DONALD D. KILLION UT—AEC Agricultural Research Laboratory Oak Ridge, Tenn. LIST OF ATTENDEES 715 WILLIAM KITTEL Food and Drug Emergency Preparedness U.S. Department of Health, Education, and Welfare Rockville, Md. JOHN S. KREBS Stanford Research Institute Menlo Park, Calif. C. Z. KWAST Agricultural Research Service U. S. Department of Agriculture Beltsville, Md. GEORGE B. LANDERKIN Food Research Institute Canada Department of Agriculture Ottawa, Ont., Canada WILLIAM B. LANE Stanford Research Institute Menlo Park, Calif. DARWIN LAPHAM OCD Staff College Federal Center Battle Creek, Mich. HOWARD F. LEHNERT, JR. Agricultural Research Service U. S. Department of Agriculture Beltsville, Md. EDWIN W. LINDQUIST, JR. USAMEDD Veterinary School Chicago, Ill. ARVIN I. LOVAAS Department of Animal Science Colorado State University Fort Collins, Colo. JOHN McAULAY 20 Windermere Road West Wickham Bromley, Kent, England W. D. McCLELLAN Agricultural Research Service U.S. Department of Agriculture Beltsville, Md. FRANK McCORMICK Department of Botany University of North Carolina Chapel Hill, N. C. J. MARTIN Lawrence Radiation Laboratory Livermore, Calif. SAAD Z. MIKHAIL Environmental Science Associates Burlingame, Calif. CARE. F. MILLER The Systems Operations Corporation Hallock, Minn. DONALD MILLER Agricultural Research Service U. S. Department of Agriculture Hyattsville, Md. K. B. MISTRY Biology Division Bhabha Atomic Research Centre Trombay, Bombay, India WILLIAM B. MORTON Division of Communications and Electronics U. S. Forest Service Washington, D. C. ROBERT MULLEN Santa Barbara Division EG&G, Inc. Goleta, Calif. PETER G. MURPHY Department of Botany University of North Carolina Chapel Hill, N. C. 716 EIST OF ATTENDEES WILLIAM F. NAPE Agricultural Research Service U. S. Department of Agriculture Springfield, Ill. Wet Lk. NEALE Ministry of Agriculture, Fisheries and Food London, England YOOK NG Bio-Medical Division Lawrence Radiation Laboratory Livermore, Calif. JOHN H. NORMAN Gulf General Atomic, Inc. San Diego, Calif. WILLIAM S. OSBURN, JR. Environmental Sciences Branch Division of Biology and Medicine U. S. Atomic Energy Commission Washington, D. C. EANSPETERS Oak Ridge National Laboratory Oak Ridge, Tenn. M. K. POMEROY Cell Biology Research Institute Canada Department of Agriculture Ottawa, Ont., Canada GILBERT POTTER Bio-Medical Division Lawrence Radiation Laboratory Livermore, Calif. H. L. RAGSDALE Emory University Atlanta, Ga. DAVID E. REICHLE Ecological Sciences Division Oak Ridge National Laboratory Oak Ridge, Tenn. WILLIAM A. RHOADS Santa Barbara Division EG&G, Inc. Goleta, Calif. _E. M. ROMNEY Laboratory of Nuclear Medicine and Radiation Biology University of California Los Angeles, Calif. fp RUDOLPH Institute of Forest Genetics U. S. Forest Service Rhinelander, Wis. RESCOTERUSSERE Agricultural Research Council Letcombe Laboratory Wantage, Berkshire, England PAUL SAND Agricultural Research Service U.S. Department of Agriculture Hyattsville, Md. LYLE B. SASSER UT—AEC Agricultural Research Laboratory Oak Ridge, Tenn. A. M.-SCHEIDY Consumer and Marketing Service U. S. Department of Agriculture Denton, Tex CLAUDE H. SCHMIDT Agricultural Research Service U. S. Department of Agriculture Beltsville, Md. ROBERT K. SCHULZ University of California Berkeley, Calif. E. C. SHARMAN Agricultural Research Service U. S. Department of Agriculture Washington, D. C. LIST OF ATTENDEES EUGENE G. SIEMER Colorado Department of Agriculture Fort Collins, Colo. ROBERT E. SIMPSON Bureau of Foods Food and Drug Administration Washington, D. C. J. F. SPALDING Los Alamos Scientific Laboratory University of California Los Alamos, N. Mex. ARNOLD H. SPARROW Biology Department Brookhaven National Laboratory Upton, Long Island, N. Y. MARLOW J. STANGLER Chief, RADEF Branch, PO(EO) Office of Civil Defense Washington, D. C. BURKE STANNARD Defense Research Board Defense Research Analysis Establishment National Defense Headquarters Ottawa, Ont., Canada VERNON M. STERN University of California Riverside, Calif. EY STEEL Division of Biology and Medicine U. S. Atomic Energy Commission Washington, D. C. WALMER E. STROPE Office of Civil Defense (OSA) Washington, D. C. CLARENCE E. STYRON Mathematics and Natural Science Division St. Andrews Presbyterian College Laurinburg, N. C. T. TANADA Agricultural Research Service U. S. Department of Agriculture Beltsville, Md. Fol. TAY LOR Oak Ridge National Laboratory Oak Ridge, Tenn. MICHAEL TERPILAK Division of Environmental Radiation U. S. Public Health Service Rockville, Md. J. C. THOMPSON Cornell University behacas. NY. KENNETH R. THOMPSON Agricultural Research Service U. S. Department of Agriculture Jacksonville, Fla. D. E. TORKELSON Agricultural Research Service U. S. Department of Agriculture Austin, Tex. JOSERIIW. TURELEE 275 Bryn Mawr Avenue Bryn Mawr, Pa. ROBERT VAN HOOK Ecological Sciences Division Oak Ridge National Laboratory Oak Ridge, Tenn. GEORGE H. WALTER U.S. Department of Agriculture Washington, D. C. EDMUND G. WARNER Agricultural Research Service U. S. Department of Agriculture Moorestown, N. J. 718 LIST OF ATTENDEES WILLIAM WEBSTER OCD Region Five Federal Regional Center Denton, Lex: L. C. WELDON Agricultural Research Service U. S. Department of Agriculture Oklahoma City, Okla. R. WENTWORTH Cornell University Ithaca Neve JcL WEST UT—AEC Agricultural Research Laboratory Oak Ridge, Tenn. EDWARD F. WILLIAMS, JR. USASTRATCOM-NCC(P) Springfield, Va. RICHARD WILLIAMS Health Physics Department Brookhaven National Laboratory Upton, Long Island, N. Y. A. A. WILSON School of Veterinary Medicine University of Cambridge Cambridge, England - EDWARD J. WILSON U. S. Department of Agriculture Hyattsville, Md. WILLIAM E. WISEMAN Agricultural Research Service U. S. Department of Agriculture Chillicothe, Ohio JOHN P. WITHERSPOON Ecological Sciences Division Oak Ridge National Laboratory Oak Ridge, Tenn. J. H. WOMMACK Agricultural Research Service U. S. Department of Agriculture Sacramento, Calif. PAUL E. ZIGMAN Environmental Science Associates Burlingame, Calif. BROOKHAVEN NATIONAL LABORATORY J-c-BATEMAN A. JAHN RC SAURKUETS L. COGGINS H. M. KALBACH LvA] Ss CHAIRER N. C. COMBATTI H. Z. KONDRATUK SUSAN S. SCHWEMMER R. A. CONARD C. B. MEINHOLD H. W. SIEGELMAN F. P. COWAN A. NAUMAN RUTH C. SPARROW BRENDA FLOYD LE FNIMS Gs SVANGBY. D. D. GREENBERG J. OCONNOR N. TEMPEL B. ReHOLT JS: ROBERTSON A. G. UNDERBRINK AUTHOR INDEX Adams, D. R., 633 Anderson, J. J. B., 627 Auerbach, S. I., 643 Barth, D. S., 259 Bartlett, B. O., 548 Bell, M. C., 178, 193, 208, 627, 656 Black, S..C.,°259 Bond, V. P., iii Bottino, P. J., 306, 633, 670 Broce, A. B., 419 Broertjes, C., 325, 633 Brown, S. L., 51, 595, 639 Bruce, R. S., 548 Burdett, A. K., Jr., 645 Chertok, R. J., 125, 627 Cole, R., 639 Comar, Cb 566 Constantin, J. J., 277, 287, 633 Cox Ws T3627 Cromroy, H. L., 419, 643 Dahlman, R. C., 492, 639 Davis, J. A., 627 Davis, J. E., v DiGregorio, D., 535, 643 Dodson, G. J., 509 Dunaway, P. B., 535, 643 Easton, B. M., 608, 645 Eisele, G. R., 269 Engel Ra Be (259.627, Gamble, J. F., 643 719 Gaut, H. A., 645 Glubrecht, H., 343, 633 Goldman, L. J., 419 Greene, J.-C., 1,°645 Griffin, S. A., 269, 645 Hall, N. S., 645 Hede, R., 639 Hekking, A. M., 639 Holland, L. M., 245 Holt, B. R., 482, 643 Hungate, Fo P.5°630 Johnson, J. E., 173, 405 Jones; (D.C, 224,627 Kantz, A. D., 56, 637 Killion;*Dz2"D:,.277..287, 633 Kicehings;. J. 1., 11-535 Kittel, W., 645 Koranda, jc Juie7 Krebs, J..S., 234 Lakes Ss 125 Lane, W. B., 51, 107, 637 Lapham, D.;639 Lehnert, H. F., 633 Levy, R., 419 Lindquist, E. W., Jr., 643 Lovaas, A. I., 173, 405, 630 McAulay, J., 630 McCormick, J. F., 454, 643 Meintyre, DR. 115 Mackin, J., 51 720 Martin, J. R., 71 Mikhail, S. Z., 31, 627 Miller, C. F., 81, 639 Mistry, U. B., 645 Mitchell, M. J., 527 Murphy, P. G., 454, 643 Nape, We. 627 Neal, W. T. L., 616, 645 INgwsYe Gs, 13152639 Norman, J. H., 9, 637 Pages Ni.P., 048 Peters, L. N., 630 Plate RB soe Potter, G. D., 115, 627 Ragsdale, H. L., 352 Randecker, V. W., 259 Reichle, D. E., 527, 643 Rhoads, W. A., 352, 630 Romney, E. M., 352, 630 Rudolph, T. D., 633 Russell, R. S., 548, 633 Sand, P. F., 645 Sasser, L. B., 178, 193, 208, 627 Schmidt, C. H., 643 Schulz._Rz K3.70;.630 Schwemmer, S., 670 Sharmon, E. C., 645 Siemer, E. G., 277, 287, 633 Simpson, R. E., 645 AUTHOR INDEX Spalding, J. F., 245 Sparrow, A. H., 306, 633, 670 Stangler, M. J., 645 Stannard, B., 643 ter Vi Mies Still, E. T., 627, 648 Story, Ds, 35 Strope, W. E., 645 Styron; Gy Es -509%527,.643 Tanada. i 2633 Taylor, F. G., 630 Tewes, H. A., 131 Thompson, J. C., Jr., 566 Thompson, K. R., 627 Torkelson, D. E., 627 Van Hook, Rk jr. 5214 643 Vattuone, G. M., 115 Walter, G. H., 645 Warner, E. G., 645 Weldon, L. C., 627 Wentworth, R. A., 566 West; Jis L178) 193% 208627 Wilson, A. A., 627 Winchell, P., 9 Witherspoon, J. P., 396, 527, 630 Wommach, J. H., 627 Woodwell, G. M., 482, 643 Zavitkovski, J., 633 Zigman, P., 637 SUBJECT INDEX" Abomasal tissue, concentration of air- borne radioiodine in, 259 Abomasum radiation-induced prolapse of, 186 radiation injury of, 178, 193, 210 Absorption of ingested °° Sr, 586 inhibition of, 586 Acheta domesticus (L.) (see Cricket) Action measures to control radionuclide ingestion, 568 Activation products in meat, 161 in milk, 144-145, 159-161 Acute gamma irradiation of plants, 287 Adventitious buds, radiation response of, 325 AET (2-aminoethylisothiouronium bro- mide hydrobromide), radioprotective effectiveness of, 239 Agricultural damage assessment, 596-597 data base, 597 of assessed resources, 598 radiological considerations, 597 sensitivity analysis of, 602 use of research data in, 611 Agricultural defense planning committee report on, 645 information needs for, 645 use of damage-assessment data in, 608 Agricultural resource distribution, sensi- tivity analyses of, 603 Agriculture damage assessment of, 596-597 data base of assessed resources of, 598 hazard of fallout on systems of, 496 of the Imperial Valley, 437, 447 postattack productivity of, 578 of the San Joaquin Valley, 447 vulnerability of, 595-596 sensitivity analysis of, 596 targeting pattern on, 88 Agroecosystems comparison with natural communities, 436-438 simple, 436 Air concentration of radionuclides in, 156 17 Cs in, 164 gas analysis of, in irradiated plant communities, 460 uptake of radioiodine through, 259 Air-sampler data, use in exposure calcula- tions, 259 Air uptake of radioiodine by dairy cows, 259-267 Airborne radioiodine uptake by dairy cows, 260 *For many subjects listed in this in- Algae, radiosensitivity of, 485 dex, only the initial page of the discussion Alginate feed supplements, 586 is given. reduction of ?°Sr absorption by, 586 v21 722 SUBJECT INDEX Allobophora, role of, in fallout redistribu- tion, 533 Allocation of postattack food supplies, 578-579 Aluminum phosphate gel feed supplement, 586 reduction of ?°Sr absorption by, 586 Animal feed, food equivalents of, 578 Animals See also Cattle; Farm animals; Livestock; Mammals; and specific animals feeding of synthetic fallout to, 178 fractionated exposure of large, 651 mean survival time of large, 651 meat yield of, 622 salvage of irradiated, 269 survival of enhancement of, 625 in fallout areas, 193 in relation to cell destruction, 238 Annual production loss of corn, 605 Anorexia, internal radiation-induced in sheep, 180 Anterior ventral blind sac, pathological changes in, in sheep, 210 Anthocyan accumulation in irradiated plants, 304 Arabidopsis thaliana, fallout exposure of, 344 Artemisia, radiosensitivity of, 353 Arthropod community chronic beta irradiation of, 510 threshold of radiation effects on, 509 Arthropods benefits of, 435 control of, 435 cost of, 435 immediate effects of radiation on popu- lations of, 525 life-span of, 521 long-term effects of radiation on, 509 radiosensitivity of, 521 Assessment of early crop damage, 634 of radionuclide contamination in diet, 573 Assimilation of fallout by plants, 504 of fallout radionuclides, 87 of ingested radionuclides, 125-129 Asteraceae beta irradiation of, 458 in outcrop plant communities, response to irradiation of, 468 Attack antipopulation, 94-104 casualties of, estimation, 561 - counterforce, 88 credibility of directed, 606 damage assessment of, 614 date of, sensitivity analysis of, 602 dietary situation after, 566 environment after, action guides for, 568 hypothetical nuclear, 88-104 loss of pasture in, 622 radiation exposure guidelines for en- vironment of, 591 specified levels of fatalities in, 94 survival of major crops and livestock in, 601 weight of, 605 sensitivity analysis of, 605 Auxin, destruction of, in irradiated plant, 478 Axillary crevices, weathering of fallout from, 500 Axillary growth of irradiated lettuce plants, 310 Axillary shoots of irradiated plants, 302 Barley attack loss of, 622 chronic radiation injury to, 348 constant-rate exposure of, 322 radiation injury to germinating seeds of, 310 response of irradiated seedlings of, 306, 30852313 height, 307, 323 lethality, 306, 318, 322 United Kingdom stocks of, 619 yield of irradiated plants, 683 Beagles, fate of fallout ingested by, 125 Beta burns, skin, 31 See also Radiation injury Beta dose computation of, 31, 51 contact, 351, 501, 530 internal measurement of, 185-186 measurement of, 51, 637 multiple-particle model of, 39 to papillae of abomasum, 185-186 SUBJECT INDEX 723 of rumen, 185-186 single-particle model of, 32 to skin from fallout particles, 31, 39 TDD model of, 31-37 Beta dosimetry, 51, 185-186, 374, 509 committee report on, 637 lithium fluoride, 51 Beta-field hazard of fallout, 86, 623 Beta-to-gamma ratio of fallout radiation, 190-191, 601 Beta irradiation, fallout of corn, 370 ecological effects of, 454, 458, 510 of gastrointestinal tract, 193 of lettuce, 370 of outcrop plant communities, 458 of skin, 31, 187, 193, 199 multiple-particle injury criteria, 41 single-particle injury criteria, 37 of vegetation, 353, 362-363, 455 of wheat, 370 Beta radiation See also Beta radiation, fallout; Fallout radiation contribution of, to fallout radiation dose, 623 dose (see Beta dose) dosimetry, 51, 185-186, 374, 509, 637 ecological effects of, 454, 458, 510 effects on farm animals, 565, 627, 662 effects on insects, 510 effects on plants, 51, 362-363, 370, 455 internal effects of, 185-186, 193, 659 lesions of the skin from, 37 measurement of, 51 Relative Biological Effectiveness of, 477 shielding of, by soil, 531 source, 528 sensitivity to of earthworms, 527 of plants, 631 Beta radiation, fallout, 31, 51, 56 contact dose of, 530 field, 476 hazard of, 86, 623 importance of, 623 livestock information needs, 628 radiobiological effects of, 634 skin lesions from, 37 summary of effects of, on livestock, 627 vulnerability of crops to, 630 Beta radiosensitivity of earthworms, 527 of plants, 631 Biological considerations availability of radionuclides, 125 contamination of postattack foods, 567 control of insects, 451 dosimetry, 509 end points of radiation injury, 234-235 fallout hazard, 492 half-life of '27Cs, 589 indicators of species radiosensitivity, 419 Biomass of irradiated plant communities, 468, 478 of irradiated Viguiera porteri, 477 yield of irradiated plant communities, 462 Biota, release of nutrients from, 487 Blood assay, determination of }?!Cs body burden by, 576 Body burden 137Cs determination of, 576 radionuclide, urinary assay of, 576 Body weight of internally irradiated sheep, 180 of irradiated cotton rats, 542 Bone dose to, 161 radionuclides in, 117-124 fetus, 117-123 tungsten, 122-124 Bone marrow biological indicator of radiation dose in, 235 DNA content of, 237 recovery from radiation injury, 252 °?%Sr dose to, 557 Buildup plus fallout-decay-simulated (Bu + FDS) radiation exposure of plants, 306-307, 310, 323 Bulbostylis capillaris, radiation response of , 476 Burro LD, of, 650 mean survival time of, 651 radiation lethality of, 657 Cabriolet, fallout radiation from, 353 724 SUBJECT INDEX Calcium deficiency in nondairy diet, 580 in feed, effect on strontium-to-calcium ratio in milk, 585 supplementation in nondairy diet, 580 Calculational techniques of beta dosime- try, 637 Canopy of irradiated plant communities, 462 retention of fallout by, 504 stratification in irradiated plant com- munities, 470 Carbon dioxide exchange rate of irradiated plant communities, 465, 474, 479 Casualties, estimates of attack, 561 Cattle See also Animals; Dairy cows, Farm animals; and Livestock diarrhea in irradiated, 197 effect of fallout on, 662 fallout retention by, 173 hyperkeratosis of skin irradiated, 199 internal radiation injury of, 210 pathology of, 210 LD,, of, 650 mean survival time of, 651 passage of ingested fallout by, 177 radiation injury of, 193 radiation lethality of, 657 simulated-fallout effects on mortality of, 661 Cell destruction as related to animal sur- vival, 238 Cells doubling time of, 242 radiosensitivity of, 237 Cereal-grain crops, retention of fallout by, 501 Cereals postattack requirement for, 624 postattack yield of, 624 radiosensitivity of, 688, 693 stocks of, in United Kingdom postattack availability of, 619-620 postattack requirements for, 619-620 Cerium-144, ingested, internal injury in sheep caused by, 178 Cesium-137 See also Radiocesium accumulation and retention by cotton rat of fallout, 536, 539-542 assay of body burden of, 576 biological half-time of, 589 control of secretion in milk by Prussian blue, 589 inhibition of absorption of, by Prussian blue, 589 intake commitment from milk, 570 internal dose contribution of whole- body, 549 irradiation by of barley, 306 of lettuce, 306 of wheat, 306 in milk, 163 as radiation source, 307, 483 in surface air, 164 Cesium-tagged synthetic fallout, accumu- lation by cotton rat, 536 Chemical contamination of postattack foods, 567 Chemical properties of fallout, 82-86 Chronic beta irradiation of an arthropod community, 510 Chronic contamination by worldwide fallout, 156 Chronic irradiation of barley, 348 of forest, 483 of a natural plant community, 483 of rye, 348 of trees, 483 of wheat, 348 Cities, evacuation of, 103 Climatic conditions, effect on radio- sensitivity of plants, 348 Close-in fallout, simulated exposure of plant communities to, 458 °°'Y tagged, 458 Cobalt-60 irradiation of sheep, 179 as source of gamma radiation, 455 stimulation of plant growth by irradia- tion with, 456 Collembola (Folsomia) population study of irradiated, 511 radiosensitivity of, 509-510, 517-518 Colony-forming unit (CFU), 235 Color of irradiated crops, 675 Combined radiation effects on livestock, 660 Communities, radiosensitivity of plant, 485 Condensation of fission products, 83 SUBJECT INDEX 725 Coniferous forest, radiosensitivity of, 489 Constant-rate exposure of barley, 322 of crop plants, 306-307, 310, 313, 322 comparison with FDS, 322-323 of lettuce, 310, 322 of wheat, 322 Contact beta dose, 351, 501, 530 Contact beta hazard, 86 Contamination (see Fallout, contamina- tion from) Contamination factor of fallout retention on crops, 494, 501 Control of insect pests, 439-442, 448, 451 Corn (Zea Mays) See also Maize annual production loss of fallout irradi- ated, 605 beta injury of fallout irradiated, 370 Cost of decontaminating milk, 589 Cotton rat (Sigmodon hispidus) accumulation of fallout cesium by, 536, 539-542 body weight of irradiated, 542 distribution of ingested cesium in, 541- 542 internal beta irradiation of, 539 internal gamma irradiation of, 539 in vivo dosimetry of, 536 retention of fallout cesium by, 536 Counterforce attack, 88 Countermeasures to '37Cs absorption, 589 to livestock exposure, 666 to radionuclide intake from milk, 570 to °° Sr absorption, 588 Cows, dairy (see Cattle; Dairy cows; and Livestock) Crabgrass (Digitaria species), radiosensi- tivity of, 486 Cricket [Acheta domesticus (L.)] dose-rate effect on, 524 dosimetry of, 512 irradiation of, 522 lethality of, 522 Crops See also Agriculture; Plants; and specific crops color of irradiated, 675 committee report on, 630, 633 beta radiation vulnerability of, 630 gamma radiation vulnerability of, 633 constant-rate exposure of, 306-307, 310, 313 322-325 contamination of, by fallout, 343 contamination factor of fallout retention on, 494, 501 damage assessment of, 597, 634 fallout effects on, 288, 632, 635, 702 fallout retention of, 401-402, 405 forage, 144, 158, 692, 694 ED, 5,0! 313 period of vulnerability of, 607 protein content of irradiated, 675 radiation exposure of, 288 radiation injury of, 634 radiation lethality of, 600 radiation reduction of yield of, 670 radiosensitivity of, 704 root, radiosensitivity of, 690, 693 starch content of irradiated, 675 sugar content of irradiated, 675 survival of irradiated, 313 taste of irradiated, 675 in United Kingdom attack losses of, 622-623 stocks of, 619 yield of irradiated, 313 Dairy cows See also Animals; Cattle; and Livestock control of }37Cs secretion in milk of, 589 fate of fallout ingested by, 115 ingestion of fallout by, 144 uptake of airborne radioiodine by, 239-207 Damage, radiation See also Radiation injury fallout, 82 to plants, 347 Damage-assessment analysis, 88 of agriculture, 596-597 of current weapons systems, 88-91 of food crops and livestock, 597 of future weapons systems, 91-104 of nuclear attack, 614 use of research data in, 611 Damage-assessment data application in agricultural defense planning, 608 source of, 610 Date of attack, sensitivity analysis of, 602 726 SUBJECT INDEX Debris, fallout See also Fallout ingestion by dairy cows, 115 from Plowshare, 115, 125 Deciduous forest, radiosensitivity of, 489 Decontamination effectiveness of, 590 of food, 590 of land, 589 of milk, 560, 589 of water, 590 Defense planning, agricultural (see Agri- cultural defense planning) Deposition of fallout radionuclides, 156- 157 Detector, radiation, lithium-drifted germanium, 125 Development of irradiated plants, 287, 301-302 Device materials, neutron activation of, 133-135 Diarrhea in irradiated sheep, 180 in irradiated steers, 197. Diet : See also Food; specific foods alginates in, to control SS absorption, 586 consequence of eliminating milk from, 580, 586 contamination of, food indicators of, 573 control by of 131] intake, 581 of populations, 569 of radionuclide ingestion, 579 importance of milk in, 586 on calcium intake, 586 on ?°Sr-to-calcium ratio, 586 postattack conditions relating to, 566 Prussian blue in, as countermeasure against '*7Cs, 589 radionuclide contamination of, 573 °° Sr level in, estimation of, 575 Diffusion of fallout radionuclides, 83 Direct fallout contamination of food, 549-554 Dispersal of food stocks, 618 Dispersion of insect pest species, 445-447 Dose See also Radiation dose from activation products in meat, 161-163 beta (see Beta dose) bone, 161 estimation of, 144 fallout commitment from °° Sr, 558 internal, 137 large particle, 161-163 reduction by polyethylene covers, 367 from fallout }77Cs, 558 from fallout-contaminated food, 131 from fission products in meat, 161-163 fractionated of fast neutrons, 325, 338-339 of X-rays; 325, 338-339 gamma-ray, estimation of, 358 from ingested ?°Sr, 556 internal, 156 See also Internal dose from ingested fission products, 555- 559 from large fallout particles, 161 measurement of, 353 direct, 69 from meat, 161-163 from milk, 144 model of, 156 from small fallout particles, 158-159, 163 thyroid, 161 total, from ingested fallout, 559 to vegetation from Schooner fallout, 360-361 whole body, 161, 539 Dose fractionation, protection induction Of; 32955332,1339 Dose-rate effect, 225 on cricket, 524 plateau region of curve for insects, 525 Dose-rate multiplier, sensitivity analysis of, 605 Dosimeter beta, 51 design, 57 glass-rod, 536 micro-, lithium fluoride, 509 for sheep, 185 thermoluminescent, lithium fluoride, 459, 464 Dosimetry, 463-464 of beta and gamma radiation, 509 of beta radiation, 51, 374, 637 SUBJECT INDEX 727 of cotton rats, 537-539 in vivo, 536 of crickets, 512 of fallout radiation, 354 of fission products, 75 of grasshoppers, 512 of grassland vegetation, 509 of insects, 509 of plant communities, 458 of shrubs, 354 of tritium, 72-75 Early fallout, internal dose from, 137 Earthworms (Lumbricus terrestres) beta irradiation of, 533 sensitivity to, 527 fallout effects on, 533 importance of, 528 irradiated fecundity of, 533 fertility of, 533 histological damage of, 530 injury of, 530 intestinal necrosis of, 530 lethality of, 529, 532 irradiation of, 533 lethal time (LT, , ) of, 528-529 radiosensitivity of, 527-528 redistribution of fallout by, 532-533 Ecological effects of beta radiation, 454, 458, 510 of fallout, 82 radio-, 643 of simulated fallout, 454, 458 Economic-injury level of insect pests, 451 Economic plants deleterious radiation effects on, 684 LD, , of 30 species of, 685 Economic threshold of insect pests, 451 of pest arthropods, 441 Ecosystems See also Agroecosystems fallout effects on, 82 granite outcrop, description, 456 irradiated carbon dioxide exchange of 459-461, 465, 474, 479 metabolism of, 449-461, 465, 474-476 net production of, 459-461, 465, 474 respiration of, 459-461, 465, 474 structure of, 483 radiation exposure of, 454 radiosensitivity of, 703 species diversity in, 475 species succession in, 475 stress of radiation on, 474 Emergence of seedlings of irradiated parent plants, 289 Energy, plant fixation of, 486 Energy flow in ecosystems, 475 in irradiated plant communities, 479 Environment, influence on plant radio- sensitivity, 670, 679-681, 702 Environmental materials, neutron activa- tion of, 133-136 | Equilibrium position of insect pests, 442 general, 451 temporary, 452 Equine, fallout radiosensitivity of, 662 Erythropoietin response, 235 Excretion of fallouty 115; 123; 173 of radionuclides, 125 Exposure calculations, use of air-sampler data in, 259 Exposure duration, response of lettuce to variations of, 310 Exposure index of radiation, 568 Exposure rate, radiation constant (see Constant-rate exposure) decay of, 307 response of barley to variations of, 313 response of plants to variations of, 306- 3077340; 3145)317-323 Exposure-rate contours of fallout, 531 Exposure-rate pattern of plant irradiation, 307, 323 Exposure time, response of plants to varia- tions of, 306, 308 External gamma hazard of fallout, 82, 86 External irradiation of earthworms, 533 Fallout See also Debris, fallout; and Fallout radiation assimilation by plants, 504 of radionuclides from, 87 beta (see Beta radiation, fallout) beta and gamma exposures, 353 beta and gamma radiation dose, 56 728 Fallout (continued) livestock vulnerability to, 627 beta exposure of vegetation, 353, 362- 363 beta-to-gamma ratio, 190-191, 601 beta-radiation field, 476 hazard of, 86, 623 biological availability of, 84, 125 biological hazard of, 492 chemical properties of, 82-86 close-in, 102 simulated, 458 contact beta dose from, 531 contamination from of crops, 343 of diet, indicator of, 569 of food, 496 direct, 549-554 of grass, 494 of meat, 161 of milk, 144, 549, 554, 569 comparison of U.K. and N. Temperate Zone levels, 554 lag effect of, 548-550, 554 rate of °°Sr uptake from soil, 553 of postattack diet, 567 of shrubs from Project Schooner, 352 surface, 352 damage to plant communities, 483 decay of radiation exposure rate, 307 deposition of, 156-157 diffusion of, 83 direct contamination of food by, 549 distribution of, 86, 639 dose (see Dose) ecological effects of, 82 effects on plants, 670 effects on vegetation, 363 excretion of, 115-123, 173 exposure of Arabidopsis thaliana to, 344 exposure of plant communities to, 455 exposure rate, contours of, 531 forage—cow—milk pathway, 144, 158 small particles. 144 formation of, 83-86 See also Fallout formation gamma and beta radiation dose, 56 gamma radiation, 56, 82, 86 See also Gamma radiation dose, 358 hazard, 86 SUBJECT INDEX gamma-ray exposure of vegetation, 360-361 hazard to agriculture, 496 hazard, 100% lethal radius, 102 ingestion of, 115, 125, 131, 178, 193 inhalation hazard of, 86 initial retention by plants, 397, 493 interception by plants, 501 intermediate range, 97 internal dose from, 137 large particles of, 161 dose from, 161-163 leaching of, 17-28 local, biological hazard of, 492 model, particle weathering function, 496 movement of, 533 particles of, 82 See also Fallout particles pattern, exposure-dose perimeter, 99 physical properties of, 82-86 Plowshare,t'5. 125 properties of, 82-86, 639 protection (see Fallout protection) radiation from (see Fallout radiation) radiation damage of, 82 radiation dose from, 161, 163, 623 See also Dose radiation field of, 639-640 radiation field of simulated, 472 radioactivity from (see Fallout radio- activity) radiobiological effects of, 82 radiological hazard of, 86-88 radionuclides from (see Fallout radio- nuclides and Radionuclides) rate of passage through gut, 175 redistribution of, by earthworms, 532- 533 retention of by agricultural plants, 401-402 by animals, 86 by2cattles173 by cereal and grains, 501 by crops, 396, 405 in fetal tissues, 115 by humans, 86 by maize, 501 in maternal tissues, 115 negative exponential model of, 496 by plant foliage, 87, 501 contamination factor of, 501 SUBJECT INDEX 7129 by plants, 396, 397, 401-402, 405, 493, 504 by sorghum, 499 by trees, 401-402 Schooner, 117-124 secretion in milk, 115-123 shelters, 97-98 simulant (see Fallout simulant) simulated (see Simulated fallout) specific activity of, 86 stratospheric, 85-86, 156-157, 163, 343 synthetic, 107-108 use of, 173, 178, 193 tritium, 74-75 tropospheric, 343 uptake of residual, by food crops, 549 weathering loss from plants, 400, 496, 500 worldwide deposition of, 85-86, 156- 157, 163 Fallout beta radiation (see Beta radiation, fallout) Fallout decay simulation (FDS), 306 comparison with uniform exposure, 322 of plant radiation exposure, 306, 313, 322 Fallout field, gamma and beta doses in, 56 Fallout formation agglomeration of particles, 84 condensation of fission products, 83 Condensed-State Model of, 11-17 diffusion of radionuclides, 83 fireball interactions, 83 fractional condensation of radionu- clides, 83 model of, 10 vaporization of radionuclides, 83 Fallout gamma-ray dose, estimation of, 358 radiological monitoring data for, 358 Fallout particles agglomeration of, 84 computation of beta doses from, 31-50 fission-product profile in, 11 radioelements in, 83 radiological dose from, 158-159, 163 retention by terminal buds, 473 Fallout protection (PF) of concrete buildings, 98 of wood-frame buildings, 97 Fallout radiation assessment of agricultural losses from, 597 beta-to-gamma ratio in, 87 from Cabriolet, 353 decay rate of, 82 direct dose measurement of, 69 dosimetry of, 354 effects on crops, 288, 632, 635 information needs, 632, 635 effects on farm animals, 656 effects on a grass community, 542 effects on hemopoietic system, 536 effects on livestock, 628-629, 662 information needs, 628-629 energy spectrum of, 82 gamma, exposure of vegetation to, 360- 361 gamma component of, 306 hazard of, 496 immediate effects on insects, 525 intensity of, 493 internal hazard of, 87 long-term effects on arthropods, 509 radioecological effects of, 643 standard intensity (I,) of, 91 total-to-gamma dose ratio, 600, 603 Fallout radiation dose, contribution of beta radiation, 623 Fallout radiation field committee report on, 639 prediction of, 639-640 Fallout radioactivity accumulation by cotton rat, 536 content of intestinal tract of cotton rat, 536 Fallout radionuclides See also Radionuclides; specific radio- nuclides assimilation by man and animals, 87 biological availability of, 84 in bone, 115 contamination of food chains by, 87 excretion of, in urine, 115-123 CMAs. Wl 517,120 Poe 5 7 et 20 Pos Rue 115,117,120 poe Ret dA Sle7, AO Tew 115) 117, 220 SW pS tt 7. 212.0 ee We Re 5, £17, 1220 ingestion of, 87, 131 maternal—fetal transport of, 117-124 730 SUBJECT INDEX Fallout radionuclides (continued) potential solubility of, 84 secretion in milk, 115 Fallout simulant, 107 See also Simulated fallout; Synthetic fallout application of, 372 fate of, 541 leachability of, 495 mass load of, 495 particle size of, 495 properties of, 494 86 Rb labeled, 494-495 °°V, radiochemical purity of, 371 Fallout weathering, semilogarithmic regression model of, 500-501 Farm animals See also Animals; Cattle: Livestock; and specific animals ecological effects of beta radiation on, 569;,627, 662 radiation effects on, 628-629, 656, 662 Feed aluminum phosphate gel supplement, 586 animal, food equivalents of, 578 intake of, by internally irradiated sheep, 180 Feeding of synthetic fallout to animals, 178 Festuca arundinacea Schreb, fallout contamination of, 510 Field studies of fallout retention by crops, 396 Fireball, nuclear, 83 toroidal motion in, 84 Fission products, 133-137 biological availability of, 11 condensation of, 83 dosimetry of, 75 fractionation of, 10 incorporation in meat, 161 ingested dose from, 555-559 ingestion of, 131 leaching of, 17-28 mobility of, 11 radionuclides in, 82 secretion in milk, 144-145, 158 transfer of, 560 Foliar retention of fallout, 87, 501 Folsomia (Collembola) [see Collembola (Folsomia)| Food See also Diet; Foodstuffs; and specific foods availability, survey of, 577 average U.S. supply of, 578 chemical contamination of postattack, 567 contamination model, source term, 504 decontamination effectiveness of processing, 590 emergency use of, 577 equivalents of animal feeds, 578 fallout contamination of, 496, 549 remedial action plans, 560 imports of United Kingdom in peace- time, 617 postattack allocation of, 578-579 postattack rationing of, 578-579 postattack resources in United Kingdom (see United Kingdom) °° Sr contamination of, 579 milk, 554 processing reduction of, 579 stocks dispersal of, 618 geographic distribution of, in United States, 577 normal quantities on hand in United Kingdom, 617 quantities in marketing channels, 577 Food chain, transfer of fission products in, 560: Food-crop plants (see Crops) Food indicators of dietary radionuclide contamination, 573 Food stocks (see Food) Foodstuffs See also Diet; Food; and specific foods fallout contamination of, 131 worldwide fallout contamination of, 549 Forage, fallout contamination of, 144 Forage—cow—milk pathway passage of small-particle activity, 144 transfer of large-particle activity, 158 Forage crops, radiosensitivity of, 692-694 Forest See also Plants; Trees; Vegetation; and specific plants coniferous, radiosensitivity of, 489 SUBJECT INDEX deciduous, radiosensitivity of, 489 radiation response of, 483-486 Fruit set, tomato, influence of postirradi- ation time on, 682 Fruit trees, radiosensitivity of, 691, 694 Fungi, radiosensitivity of, 485 Gametogenesis, radiation effects on, 304 Gamma component of fallout radiation, 306 Gamma exposure rate, response of soybean plants to variations of, 277 Gamma irradiation acute, of plants, 287 internal, of the cotton rat, 539 of livestock, 624 summary of information on, 628 of soybean plants Hill, 278-280 Kent, 278-280 tolerance of plants to, 302 Gamma radiation See also Fallout radiation acute exposure to, 245 beta-to-gamma ratio of fallout, 190-191 dose, 358 dosimetry of, 509 effects, livestock information needs, 629 effects on farm animals, 627, 656 fallout, 56, 82, 86, 306 external hazard of, 82, 86 whole-body dose of, 539 protracted exposure of, 245 source of, 455, 528 Gamma-ray dose, estimation of, 358 Gamma-ray exposure, 353 of soybean (Glycine max (L.) Merrill), PATA of vegetation, 360-361 Gas analysis of air, 460 of irradiated plant communities, 460 Gastrointestinal contents of cotton rat 137Cs concentration of, 541-542 fallout radioactivity of, 536 Gastrointestinal pathology of irradiated livestock, 208, 210, 212 Gastrointestinal radiation injury of live- stock, 208, 210, 212 microscopic observations of, 217 of sheep, 186 731 Gastrointestinal tract beta irradiation of, 193 beta radiation injury of, 659 137Cs content of, tissue of cotton rat, 536, 541-542 dose rate to cotton rat, for internal and external irradiation, 539 irradiation of, 178-179 measurement of beta dose in, 185-186 pathology of beta radiation injury of, 208, 210 rate of fallout passage through, 176 General equilibrium position of insects, 442,451 Genetic effects of radiation, 248, 666 Genetic injury of nonlethal exposures, 245 Genetic involvement of hematopoietic recovery, 248 Genetic response of irradiated earth- worms, 533 Germinal cells, skin, radiation response of, 236 GI tract (see Gastrointestinal tract) Glass-rod dosimeter, 536 Goat continuous irradiation of, 651 LD, of, 650 mean survival time of, 651 Governing mechanism of insect popula- tions, 452 Grain postattack yield of, in the United Kingdom, 624 seed, irradiation of, 685 stocks of, in the United Kingdom, 619-620 Granite-outcrop ecosystem, description of, 456 Granite-outcrop plant community plasticity of, 478 radiation exposure of, 454 Grass, fallout contamination of, 494 Grasshopper (Melanoplus species), dosimetry of, 512 Grassland, dosimetry of, 509 Grazing of contaminated pasture, 193 Growth of irradiated Viguiera porteri, 462, 471, 476-477 Growth stimulation of irradiated lettuce, 310 732 SUBJECT INDEX Guides, postattack action, 568 Gut (see Gastrointestinal tract) Hardwood trees, radiosensitivity of, 694 Hematologic changes in irradiated sheep, 227. Hematopoietic recovery, 248 Hemopoietic system, radiation response of, 536 Herbs, radiosensitivity of, 485 Hernial ring, radiation-induced prolapse of, 186 High shrubs, radiosensitivity of, 485 Higher plants, radiosensitivity of, 483 Histological damage of irradiated earthworms, 530 Home water softeners, decontamination effectiveness of, 590 Homeostasis of irradiated plant communi- ties, 478 Human cells, radiosensitivity of, 237 Hyperkeratosis of skin-irradiated cattle, 199 Hypothetical nuclear attack, 88-104 See also Attack ICV (see Interphase chromosome volume) Imperial Valley agriculture, 437, 447 Index of dissimilarity of species composition, 514 leaf area, for irradiated plant com- munities, 462, 469, 477-478 radiation exposure, 568 Ingested dose from fission products, 555-559 Ingested fallout, 115, 125, 131, 178, 193 elimination of, 115-123 fate of, 115-124 internal concentration of, 115-123 retention in fetal tissues, 115 retention in maternal tissues, 115 secretion in milk, 115 Ingested radionuclides, retention of, in internal organs bone, 115 kidney, 115 liver, 115 spleen, 115 Ingestion of fallout1155 125. 1313078. 193 of fission products, 87, 131 of radioactivity by livestock, 193 of radionuclides, 87, 131 of synthetic fallout, 193 Inhalation hazard of fallout, 86 Initial retention of fallout by plants, 397, 493 Injury (see Radiation injury) Insect pests control of, 439-442, 448, 451 destruction by of balsam fir by spruce budworm, 348 economic threshold of, 451 of lodgepole pine by needle miner, 348 dispersion of, 445-447 equilibrium position of, 442 origin of, 439-442 species of, 439-442 of the San Joaquin Valley, 448 Insects See also Insect pests; specific insects adaptability of, 434 beta-radiation effects on, 510 biological control of, 451 dose-rate effect curve, plateau region for, 525 dosimetry of, 509 economic control of, 451 economic-injury level of, 451 equilibrium position of, 442 general, 442, 451 temporary, 452 immediate effects of fallout radiation on, 525 irradiated, life-span shortening of, 428 mortality, 522 natural control of, 452 population dispersal of, 452 prediction of radiosensitivity of, 426-430 radiosensitivity of, 434 temporary equilibrium position of, 452 Interception of fallout by plants, 501 Intercontinental missiles, 91-92 Minuteman-3, 92 Poseidon, 92 SS-9 Scarp rocket, 92 SS-11, 92 Intermediate-range fallout, estimation of, 97 Internal dose, 156 See also Dose; Internal radiation dose from fallout, 137 SUBJECT INDEX 733 from fallout-contaminated food, 131 from ingested fission products, 555-559 from stratospheric fallout, 163 Internal hazard of fallout, 86 Internal irradiation of cotton rat, 539 of earthworms, 533 Internal organs of cotton rat 137Cs content of, 541-542 fallout radioactivity of, 536 Internal radiation dose, relative con- tribution to of 137Cs, 549 Of 21549 of °°Sr, 549 Interphase chromosome volume (ICV) indicator of species radiosensitivity, 673, 695-696, 419 prediction of LD,, for plants, 673 Intestinal epithelium, radiation response of, 235 Intestine necrosis of, in irradiated earthworms, 530 radiation injury of, 186 Iodine-131, 260 See also Radioiodine blocking of, in thyroid, 581 contribution to internal dose, 549 dietary control of intake of, 581 intake commitment of, from milk, 570 secretion in milk, 115, 118 thyroid irradiation, 548 Ion exchange, decontamination of milk, 589 Irradiated ecosystems (see Ecosystems, irradiated) Irradiated plant communities, 458 appearance of, 465 biomass of, 462, 468-478 canopy stratification of, 462, 470 carbon dioxide exchange in, 459-461, 465, 474, 479 energy flow in, 479 gas analysis of air in, 460 homeostasis of, 478 leaf-area index of, 462, 469, 477-478 litter accumulation of, 462, 471, 478 Margalef pigment-diversity ratio of, 474, 478 metabolism of, 465, 474-476 pigment diversity of, 463, 472, 478 species composition of, 462, 468 Irradiated sheep (see Sheep) Irradiation (see specific types of irradiation; specific classes of plants and animals; and specific plants and animals) Kalanchoe blosfeldiana, fallout exposure of, 344 Lactuca sativa (see Lettuce) Land decontamination, 589 Latent period of insect mortality, 522 LD, , (lethal dose) of plants, 674 correlation with ICV, 674 LD, , (lethal dose), 599 of barley, 306, 318, 322 of burro, 650 of cattle, 650 of cricket, 522 of crops, 313 of earthworm, 528-529 effect of dose rate on, 225 of 82 species of woody plants, 700-701 of fallout-exposed livestock, 648, 656 of goat, 650 of insects, 428 of large animals, 225 of lettuce, 306, 310, 318, 322 comparison of constant-rate and FDS exposure, 322 of livestock, 648, 656, 662 of offspring of irradiated seeds, 685 of plants, 322, 673 correlation with ICV, 673 in relation to ICV, for mammals, 420-425 of sheep, 187, 225, 650 of swine, 650 of 30 economic plants, 685 of wheat, 306, 318, 322 comparison of constant-rate and FDS exposure, 322 Leachability of fallout simulant, 495 Leaching of fallout particles, 17-28 mechanism of, 17-28 Leaf-area index of irradiated plant com- munities, 462, 469, 477-478 Leaf blades retention of fallout by, 501 weathering of fallout from, 500 734 SUBJECT INDEX Legumes, radiosensitivity of, 689, 693 Lethal dose (see LD,, and LD, ,) Lethal fallout area, radius of, 102 Lethal radiation exposure, 246 Lethal time (LT, , ) of earthworm, 528 Lethality See also LD, , and LD, , effect of postirradiation time on plant, 684 of irradiated earthworms, 529, 532 Lettuce (Lactuca sativa) beta irradiation of, 370 constant-rate (CR) exposure of, 310, 322 effect of dose rate on, 323 fallout-decay-simulation (FDS) exposure of, 322 growth stimulation of irradiated, 310 irradiation of, 306-307, 310 LDA. 0f 306, 3105 3187322 Lichens, radiosensitivity of, 485 Life-span radiation effects on, 666 shortening of, in irradiated insects, 428 LiF (see Lithium fluoride) Lithium detector, 125 Lithium fluoride microdosimeter, 509 Lithium fluoride thermoluminescent dosimeter, 459, 464 Litter accumulation in irradiated plant communities, 462, 471, 478 Liver abscesses in irradiated sheep, 190 Livestock See also Animals; Cattle; Dairy cows; and specific animals beta-radiation effects on, 627 beta-radiation injury to abomasum, 193, 210 internal, 659 Omasum, 210 pathology of, 210 combined radiation effects on, 660 committee report on vulnerability of 627 concentration of airborne radioiodine in, 259 damage assessment of, 597 fallout protection of, 666 fallout radiation effects on, 628-629, 662 gamma-radiation vulnerability of, 628 gastrointestinal tract ’ irradiation of, 193 radiation injury of, 208, 210, 212, 2A, ingestion of radioactivity by, 193 irradiated causes of death of, 648 recovery of, 648 reproduction of, 665 salvage of, 269 LD,, of, 648, 656, 662 pasture requirement of, 621 postattack survival of, United Kingdom estimates of, 621 productivity of effects of fallout on, 193 radiation effects on, 663 radiation effects on, 193, 656, 663 radiation-induced diarrhea in, 197 radiation-induced pyrexia in, 196 retention of airborne radioiodine by, 259 skin beta irradiation of, 193, 199 whole-body irradiation of, 193 Local fallout, biological hazard of, 492 Lodgepole needle miner[Coleotechnites millert (Busck)] , 348 Lolium multiflorum, fallout exposure of, 344 Low shrubs, radiosensitivity of, 485 Lumbricus terrestres (see Earthworms) Lungs, radiation injury of, 187 Maize (Zea Mays) See also Corn radiosensitivity of, 679 retention of fallout by, 501 Mammals See also specific categories of mammals irradiated, mean survival time of, 420 radiosensitivity of, 420 recovery from radiation injury of, 245 Margalef pigment-diversity ratio of irradiated plant communities, 474, 478 of irradiated Viguiera porteri, 463 Mass load of simulated fallout, 495 Mean expectation of future life (ey) of insects, 522 Mean survival time See also under specific plants and animals of irradiated mammals, 420 SUBJECT INDEX 135 Measurement See also Dosimetry of beta dose, 51, 637 of radiation dose, 353 of radiation injury, 235 Meat See also Food activation products in, 161 animal yield of, 622 fallout contamination of, 161 internal dose from, 161-163 postattack availability of, 622 radiation effects on production of, 663 Meristems, beta exposure of, 455 Metabolism of irradiated ecosystems, 459-461, 465, 474-476 Microarthropods, radiosensitivity of, 485 Military targets, nuclear attack on, 88 Milk See also Food activation products in, 144-145, 159-161 137Cs contamination of, 163 decontamination of, 560, 589 effect of elimination of, from diet, 580, 586 effect of feed calcium on strontium- to-calcium ratio of, 585 fallout contamination of, 144, 549, 554, 569 comparison of levels in U.K. and N. Temperate Zone, 554 indicator of diet contamination, 569 fission-product contamination of, 144-145 importance in diet, 586 internal dose from, 144 nuclide contamination of, 158 radiation effects on production of, 663 radionuclide intake from, 570 reduction of '37Cs secretion in, 589 reduction of radionuclide intake from, 570 secretion of radionuclides in, 115-123 yO Ba, 115118 USL 151108 me 2The 1152 118 POY W115, 118 VeW TTS 118 eee wart’ Re 11'52 418 °° Sr contamination of, 164, 553-554, 556 from initial fallout, 556 from soil, 553 from worldwide fallout, 556 ° °Sr secretion in, 164, 553-554, 556 Mineral nutrients loss from biota, 487 MIRV (see Multiple independently targetable reentry vehicle) Missiles (see Intercontinental missiles) Model of fallout retention by plants, 496 Mortality, equation of insect, 522 Mosses, radiosensitivity of, 485 Mouse See also Rodents radiation response of, 235 Multiple independently targetable reentry vehicle (MIRV) active defense against, 94 effectiveness of, 94-104 fatalities from, 94-104 use of decoys against, 94 vulnerability of cities to, 103 vulnerability of population to, 103 National entity survival, study of, 595 National survival, sensitivity analysis of, 595 Natural communities comparison with agroecosystems, 436- 438 response of, to radiation dose rates, 521 Natural control of insect populations, 452 Necrosis of irradiated earthworms, 530 Negative exponential model of fallout retention by plants, 496 Net production of irradiated ecosystems, 459-461, 465, 474 of plants, 486 Neutron activation of device materials, 133-135 of environmental materials, 133-136 Nevada Test Site (NTS), 352 Nondairy diet, calcium deficiency of, 580 Nuclear arsenal, 103 Nuclear attack (see Attack) Nuclear cratering experiment (Plowshare), eS 125 debris, 115, 125 distribution of fallout radioiodine, 260 inhalation of radioiodine by cows, 259 Palanquin, 260 program, 352 736 SUBJECT INDEX Nuclear cratering experiment (Plowshare) (continued) Schooner event, 117-124, 352 uptake of radioiodine by cows, 260 Nuclear force deployment of, 96 second strike, 96 Nuclear weapons active defense against, 94 decoys, 94 potential lethal radius of, 98 Nuclides (see Radionuclides) Nutrients availability of, 486 inventory of, in plant communities, 483 mineral, loss from biota, 487 Oats, United Kingdom stocks of, 619 Observed ratio (O.R.body/diet) of °° Sr, 584 Octolasium, fallout redistribution by, 533 Old-field vegetation, radiosensitivity of, 485 Omasum, sheep necroses of, 186 radiation damage of, 186, 210 Onion irradiation of bulbs, 685 irradiation of transplants, 685 Organic matter, radioactivity of, 541 Ornamental plants, radiosensitivity of, 687 Orthoptera, radiosensitivity of, 525 Outcrop plant communities homeostasis of irradiated, 478 response to simulated-fallout contami- nation of, 457 species response of irradiated, 468 Particle agglomeration, 84 Particle loss of fallout from vegetation, 496 Particle size of simulated fallout, 495 Pasture attack loss of, 622 grazing of contaminated, 193 postattack requirement for livestock, 621 radiocontamination of, 572 Pasture crops, radiosensitivity of, 692, 694 Pathology of abomasum, 210 of anterior ventral blind sac, 210 in extremis, 209 of gastrointestinal radiation injury, 208 of irradiated livestock, 208 of irradiated sheep oral irradiation, 210, 217 microscopic observations, 217 oral and skin irradiation, 212 oral and whole-body irradiation, 212 oral, whole-body, and skin irradia- tion, 212 of irradiated steers oral irradiation, 212 oral and skin irradiation, 214 oral and whole-body irradiation, 214 oral, whole-body, and skin irradiation, 215 of omasum, 210 of posterior dorsal blind sac, 210 of posterior ventral blind sac, 210 of reticulum, 210 of ventral ruminal sac, 210 Pelt of cotton rat, }?!Cs content of, 541-542 Performance of offspring of irradiated plants, 287 Peripheral blood of irradiated cotton rat, 542 Pesticides, similarity with radiation effects on insects, 449 Photosynthesis of irradiated ecosystems, 474 Physical dosimetry, 509 Physical properties of fallout, 82-86 Pigment-diversity ratio of irradiated Viguiera porteri, 463,472, 478 Placenta, radionuclide movement across, 122-124 Plant application of fallout simulant, 372 Plant communities beta irradiation of, 465-472 irradiated (see Irradiated plant com- munities) leaf-area index of, 462 litter accumulation of, 462 nutrient inventory in, 483 outcrop (see Outcrop plant communt- ties) productivity of, 486 SUBJECT INDEX 737 radiation effects on structure of, 483, 486 radiation exposure of, 454 radiosensitivity of, 485 respiration of, 483 retention of simulated fallout by, 459 succession of, 483 Plant—herbivore—meat pathway, 161 of large fallout particles, 161 Plant outcrop communities (see Outcrop plant communities) Plants See also Agriculture; Crops; Forest; Vegetables; Vegetation; and specific plants application of fallout simulant to, 372 economic, 684-685 energy fixation by, 486 fallout contamination of, 501 factor for, 501 fallout effects on, 363, 670 interception of fallout by, 501 irradiated climatic effects on response of, 348 development of axillary shoots on, 302 development and yield of, 287 developmental pattern of, 301 radioresistant stage of, 304 seed viability and vigor of, 704 survival of, 705 vegetative yield of, 301 yield reduction of, 698-699 prediction of, 705 irradiation of acute gamma, 287 exposure-rate pattern of, 307, 323 ED 22073 net production, 486 populations, stability of, 468 probit plot of survival of, 30 radiation effects on, 670 beta, 51, 362-363, 370, 455 radiation injury of, 672 See also Radiation injury, of plants radiocesium contamination of, 504 radiosensitivity of (see Radiosensitivity, of plants) respiration of, 486 response of to exposure rate, 306-307, 310, 314, 317-323 to exposure time, 306, 308 radiobiological, 676 stimulation of growth by radiation, 347, 456 cetention of fallout by, 396-397, 401- 402, 405, 493, 504 sensitivity of, to fallout beta radiation, 631 Plasticity of granite-outcrop plant com- munity, 478 Plowshare [see Nuclear cratering experi- ment (Plowshare) | Population of insects, 452 dispersion of, 452 protection of, 103 regulation in natural communities, 438 Populations, stability of plant, 468 Postattack dietary situation, 566 Postattack environment, establishment of action guides for, 568 Postattack radiation exposure, survival action guidelines for, 591 Posterior dorsal blind sac of sheep, pathological changes in, 210 Posterior ventral blind sac of sheep, pathological changes in, 210 Potatoes attack losses of, 622 irradiation of tubers, 685 simulated-fallout irradiation of plants, 351 United Kingdom stocks of, 619 yield of irradiated plants, 683 Poultry fallout exposure of, 662 radiation effects on, 664 Prediction of LD,, of woody plants, 700-701 of radionuclide contamination of milk, 71-572 of radionuclide intake from milk, 570 of radiosensitivity of arthropods, 521 of yield of irradiated plants, 698-699 Primary production of plants, 486 Probit plot of plant survival, 30 Processing, reduction of ?° Sr contamina- tion by, 579 Productivity of plants, 486 of plant communities, 486 Project Schooner, 352 738 SUBJECT INDEX Protection, radioinduced (see Radioin- duced protection) Protection factor, 97-98 Protective Action Guide (PAG), 568 of radionuclide intake, 568 Protective agent, radiation, 239 Protein content of irradiated crops, 675 Prussian blue (ferric ferrocyanide) cesium absorption by, 589 as control of cesium secretion in milk, 589 as dietary countermeasure, 589 Pyrexia of internally irradiated sheep, 181 of internally irradiated steers, 196 Radiation attenuation of plant containers, 288 beta (see Beta radiation; Beta radiation, fallout) damage, repair of, 522 effects See also Radiation injury; Radiation sickness combined, on livestock, 660 of fallout on a grass community, 542 on life-span, 666 on livestock, 193, 663 on livestock productivity, 663 on meat production, 663 on milk production, 663 on performance of work, 665-666 on plants, 670 on poultry, 664 on sheep, 178, 180 exposure to (see Radiation exposure) fallout (see Fallout radiation) from fallout particles, 31 gamma (see Gamma radiation) genetic effects of, 245, 248, 666 hazard of fallout, 496 inhalation exposure to, calculation from air-sampler data, 259 internal, hazard of postattack foods, 555-559 lethal exposure to, 246 lethality See also LD, , of crops, 600 of livestock, 657 long-term effects on arthropods, 509 recovery of bone marrow from, 252 reduction of seed yield by, 680 response of adventitious buds to, 325 safeguards of dietary fallout contamina- tion, 567 sensitivity to See also Radiosensitivity of plants, 349 of soil invertebrates, 529 shielding of vegetation from, 367 short-term effects on insects, 509 sickness, symptoms of, 658 source (137Cs), 483 stimulation of plant growth by, 347 Radiation dose See also Dose; Radiation exposure biological indicators of, 235-237 in bone marrow, 235 DNA content of bone marrow, 237 DNA content of spleen, 237 germinal cells of skin, 236 intestinal epithelium, 236 stem cells, 235 weight of spleen, 237 weight of testes of mice, 235, 237 weight of thymus, 237 estimation of, by radiological safety monitoring, 358 measurement of, 353 from ?°Sr in bone marrow, 557 threshold, 599 Radiation dose rate, response of natural populations to, 521 See also Dose-rate effect Radiation dosimeter, 57 See also Dosimeter Radiation effects (see Radiation) Radiation exposure of arthropods, 521 calculations of, use of air-sampler data in, 259 continuous to death, 227 duration of, response of plants to variations of, 306, 308, 310 fallout (see Fallout radiation) guidelines of, 568 hematologic changes following, 227 index of, 568 of insects, 509 of large animals, 224, 227 nonlethal, 246 rate of (see Exposure rate) recovery from, 245 SUBJECT INDEX 739 of shrubs, 353 of soybean plants, 282 Radiation field See also Fallout radiation field I, (standard intensity), 91, 597 simulated fallout, 472 Radiation injury of abomasum, 178, 193, 210 of barley, 348 germinating seeds, 310 beta induced, 31, 37, 199 biological end points of, 234-235 of Bulbostylis capillaris, 476 of cattle, 193, 210, 659 criteria of, 234 of earthworms, 530 gastrointestinal, 186, 208, 210, 212, 217 hematopoietic recovery from, 248 irreparable component of, 252 of large animals, 224 of liver, 190 of livestock, 193, 210, 659 of lung, 187 measurement of, 235 colony-forming unit (CFU), 235 erythropoietin response, 235 stem cells, 235 survival fraction (S/S, ), 235 of plants climatic effects on, 348 expression of, 672 influence of exposure duration on, 677 influence of postirradiation time on, 679 influence of stage of development on, 678 time of development of, 670 recovery from, 245 rate of, 248 repair of, 241, 285, 522 replacement of destroyed tissue from, 241 response curve of, 672 of rumen, 178, 193 of sheep, 178, 180, 186, 193 See also Sheep of vegetation, 363 of Viguiera porteri, 475 Radiation protective agent, 239 Radiation sickness, symptoms of, 658 Radiation source ®°Co, 455 *?7Cs, 307, 483 Radioactive contamination of crops by fallout, 343 Radioactive fallout, 107 See also Fallout; Fallout simulant; Simulated fallout; and Synthetic fallout contamination of crops by, 343 of stratospheric debris, 343 of tropospheric debris, 343 Radiobiological effects of fallout, 82 Radiobiological response of plants, 676 biological factors, 676 environmental factors, 676 radiological factors, 676 Radiobiological research requirements, 636 Radiocesium See also Cesium-137 content of vegetation, 504 Radiochemical purity of °° Y fallout simulant, 371 Radioecological effects of fallout, com- mittee report on, 643 Radioinduced protection of initial dose, 325, 330 of multiple irradiations, 325, 334 of time between irradiations, 325, 327, 330 Radioiodine, 259-260 See also lodine-131 in abomasal tissue of dairy cows, 259 airborne, inhalation by dairy cows, 259 distribution of fallout, 260 in thyroid of dairy cows, 259 Radiological hazard of external gamma radiation, 82, 86 of fallout, 86 I, (standard intensity) assessment of, 91 Radiological safety monitoring, estima- tion of radiation dose by, 358 Radionuclides See also Fallout radionuclides; specific radionuclides assimilation of ingested, 125-129 7 As, 125-129 178 Au, 125-129 sguBbaee far 25-129 Cel 2 5-129 5 Comdi25-129 31) 125-129 °*Mn, 125-129 740 SUBJECT INDEX Radionuclides (continued) °°Mo, 125-129 Po Ru, 125-129 12 7'Sb, 125-129 132Te 125-129 SIN ADS 29 188w—!88 Re, 125-129 biological availability of, 125 body burden of, urinary assay of, 576 diffusion in fallout particles, 83 excretion of, 125 See also Fallout radionuclides, excre- tion of fission product, 82 formation of by neutron capture, 82 by nuclear fission, 82 fractional condensation of, 83 ingestion of, 131 control of, 268 protective action measures against, 568 intake dietary control of, 579 indicators of, 574 intake commitment from milk, 570 in meat, 161 activation product, 161 concentration of, 161 fission product, 161 retention of ingested, 115, 125 secretion in milk, 144, 158 stratospheric fallout of, 156-157 time-related ranking of major, 569 vaporization of, 83 Radioprotective agent, AET, 239 Radioresistant stage of plant development, 304 Radiosensitivity of algae, 485 of arthropod populations, 521 of cereal crops, 688, 693 of coniferous forests, 489 correlation with ICV, 419 of crabgrass (Digitaria species), 486 of crop plants, 704 of deciduous forests, 489 of earthworms (Lumbricus terrestris), to beta radiation, 527-528 of edible legumes, 689, 693 of 82 species of woody plants, 700-701 of 89 species of economic plants, 698-699 of equine to fallout, 662 of Folsomia (Collembola), 509-510, 517- 518 of forage crops, 692-694 . of forest vegetation, 483-486 of fruits, 691, 694 of fungi, 485 of herbs, 485 of human cells, 237 of insects, 434 prediction of, 426-430 of lichens, 485 of maize (Zea Mays), 679 of mammals, prediction of, 420-425 of microfauna, 485 of mosses, 485 of old-field vegetation, 485 of Orthoptera, 525 of pasture crops, 692, 694 of plants, 88, 302, 349, 670, 704 to beta radiation, 631 effect of exposure rate on, 670 effect of stage of development on, 670 environmental influences on, 670, 679-681, 702 competition, 702 light, 702 temperature, 702 modifying factors influencing, 675-677 ornamental, 687 prediction of, 670, 685, 687-692, 694, 695, 697-701, 703 interphase chromosome volume (ICV), 670, 673-674, 695-696 range of, 702 of rodents, prediction, 421-426 of root crops, 690, 693 of sedge (Carex pensylvanica), 486 seed, correlation with plant radio- sensitivity, 686 of shrubs, 485 of Sinella curviseta, 518 of trees, 483, 485, 694 of 25 species of ornamental plants, 687 ot vegetable crops, 691, 694 of weeds, 485 of woody ecosystems, 703 of woody plants, 694 Radiotungsten in fetal bone, 115 in maternal organs, 115 SUBJECT INDEX 741 Rate of hematopoietic recovery, 248 Rationing of postattack food supplies, 518-579 RBE (see Relative Biological Effective- ness) Recovery of disturbed vegetation, 487 of radiation injury, 285 rate of hematopoietic, 248 Redistribution of fallout by earthworms, 532-533 Relative Biological Effectiveness (RBE) of beta radiation, 477 Remedial action plans for control of contaminated food, 560 for decontamination of milk, 560 Repair of radiation injury, 241, 245, 248, 285, 522 Reproduction of irradiated livestock, 665 of irradiated Viguiera porteri, 477 Research data, use in agricultural damage assessment, 611 Residual carcass, }?7Cs concentration in cotton rat, 541-542 Respiration of irradiated ecosystems, 459-461, 465, 474,479 of plant communities, 483 of plants, 486 Response curve of radiation injury, 672 Retention See also Fallout, retention of of ingested radionuclides, 125 of simulated fallout by plant com- munity, 459 Reticulum, pathological changes in sheep, 210 Rodents See also Mouse prediction of radiosensitivity of, 421- 426 Root crops, radiosensitivity of, 690, 693 Rubidium-86 fallout simulant, 494-495 Rumen, radiation injury to, 178, 193 Rye, chronic irradiation of, 348 Salvage of irradiated livestock, 269 San Joaquin Valley agriculture of, 447 important insect pests of, 448 Schooner fallout ingestion by cows, 117-124 secretion in milk, 117-124 Sedge (Carex pensylvanica), radiosensi- tivity of, 486 Seed grain, irradiation of, 685 Seed radiosensitivity correlation with plant radiosensitivity, 686 effect of moisture content on, 686 effect of oxygen on, 686 Seed yield, radiation reduction of, 680 Seedlings of irradiated parent plants, emergence of , 289 irradiation of, 307, 310 Semilogarithmic regression model of fall- out weathering, 500-501 Sensitivity analysis of agricultural assessment parameters, 602 of agricultural resource distribution, 603 of agricultural vulnerability, 596 of attack date, 602 of attack weight, 605 of crop vulnerability, 607 of dose-rate multiplier, 605 of national survival, 595 of total-to-gamma dose ratio, 602 Shape of irradiated crops, 675 Sheep beta irradiation of skin of, 187 impairment of wool growth due to, 187 beta irradiation of abomasum of, 185 body weight of internally irradiated, 180 6 °Co irradiation of, 179 continuous irradiation of, 651 excretion of fallout by, 173 fallout exposure of, 662 feed intake of irradiated, 180 gamma irradiation of, 178 gastrointestinal irradiation of, 178 hematologic changes in irradiated, 227 EDs 08, 187 1225,,690 lethality of continuously irradiated, 227 mean survival time of, 651 measurement of GlI-tract beta dose of, 185-186 pathology of internal radiation injury of, 210 742 SUBJECT INDEX Sheep (continued) radiation-induced injury of, 180, 186, 193 to abomasum, 178, 210 prolapse, 186 adhesions, 186 anorexia, 180 diarrhea, 180 edematous laminae, 186 gastrointestinal, 186 microscopic observations of, 217 hemorrhage, 186 hyperemic pylorus, 186 to intestine, 186 liver abscesses, 190 to lung, 187 necrosis of omasum, 186, 210 pyrexia, 181 to rumen, 178 simulated-fallout effects on mortality of, 661 skin irradiation of, 178 use of dosimeters in GlI-tract of, 185 weight loss of irradiated, 181 Shielding, soil, 530 of beta radiation, 531 of earthworms, 533 Shielding of soil-dwelling organisms, 530 Shoot dry weight of irradiated soybean plants, 280 Short-term radiation exposure of insects, 509 Shrubs fallout contamination of, 352 radiation exposure of, 353 Simulated fallout, 454, 458 See also Fallout simulant; Synthetic fallout contamination of outcrop plant com- munities by, 457 effects on cattle, 661 effects on sheep, 661 experimental use of, 510 exposure to of higher plants, 455 of potato plants, 351 rate of, 307 internal effects of ingested, 178 mass load of, 495 radiation effects on livestock, 193 radiation field of, 472 retention by plant communities, 459 °° 'V tagged, 458 Sinella curviseta, radiosensitivity of, 518 Skin beta burns of, 31 ’ beta irradiation of, 187, 193 beta lesions of, 37 beta radiation effects on, 199 erythema of irradiated, 187 germinal cells, 236 hyperkeratosis of irradiated, 199 irradiation of sheep, 178 Sodium alginates, inhibition of °° Sr ab- sorption by, 588 Soil beta exposure of surface, 476 ingress of simulated fallout, 472 radioactivity of, 464 shielding of beta radiation by, 531 shielding of earthworms by, 533 shielding properties of, 530 °°Sr in, food contamination by, 549 Soil invertebrates radiosensitivity of, 529 shielding of, 530 Soil-uptake contamination of food, analysis of, 549-554 Sorghum, fallout retention by, 499 Source term, fallout, of food contamina- tion, 504 Soybean (Glycine max (L.) Merrill), response to gamma-ray exposures, 277 Soybean plants irradiated, 277-280 recovery of, 285 repair of, 285 shoot dry weight of, 280 stem length of, 280 yield of, 281-282 split-exposure irradiation of, 278 Species composition dissimilarity, index of insect, 514 Species of ecosystem, diversity of, 475 Spleen DNA content of, 237 weight in mice, 237 Split-exposure irradiation of soybean plants, 278 Spring wheat (Triticum aestivam), irradia- tion of, 308 Spruce budworm [Chorestoneura fumif- erana (Clemens)] , 348 SUBJECT INDEX 743 Stage of plant development, effect on radiation response of, 288 Standard intensity (I<), 91 prediction of, 597 of residual fallout radiation, 91 Starch content of irradiated crops, 675 Stem cells, indicator of radiation injury, 239 Stem length of irradiated soybean plants, 280 Stimulation of plant growth by radiation, 347 Stockpiles, weapons, 103 Stratospheric fallout, contamination of crops by, 343 Stress of radiation on ecosystems, 474 Strontium-90 absorption of, from the gut, 586 body burden of reduction of, 584 urinary assay of, 576 bone-marrow dose from, 557-558 contamination of food processing reduction of, 579 from soil uptake of, 553 contamination of food chains, soil contribution to, 549 decontamination of milk, 585 estimation of dietary levels of, 575 fallout contamination of milk, 164, 553-554 comparison of U.K. and N. Temperate Zone, 554 initial, 556 worldwide, 556 feeding countermeasures to control ab- sorption of, 586 alginates, 586 aluminum phosphate gel, 586 intake commitment from milk, 570 dietary control of, 579, 585 effect of milk on, 586 reduction by supplemental calcium, 580 internal dose from, 549 secretion in milk, 164, 553-554, 556 reduction of, 584 selective inhibition of absorption of, 588 effect of alginates on, 588 in surface air, 164 Structure of plant communities, 483, 486 radiation effects on, 483, 486 Subhumid environment, assimilation of fallout by plants in, 504 Succession of natural ecosystems, 475 of plant communities, 483 Sugar content of irradiated crops, 675 Surface contamination, beta radiation hazard of fallout, 352 Survey of worldwide fallout contamination of food, 549 Survival of animals effect of fallout on, 193 enhancement of, 193, 625 in relation to cell destruction, 238 of irradiated crops, 313 of irradiated lettuce seedlings, 308, 310 of irradiated plant seedlings, 310 of irradiated plants, 306, 322, 688 national, sensitivity analysis of, 595 Survival action guidelines, development of, 568 Survival end points of radiation injury, 672 LD, ,, 672 LED O72 LD, ,, 672 EDi6o5 O72 VD, 672 Vir 672 Vis O02 Survival fraction (S/S, ), 235 Survival guidelines of postattack radiation exposure, 591 Survival time of continuously irradiated goats, 651 of continuously irradiated sheep, 651 Swine fallout exposure of, 662 fate of fallout ingested by, 125 LD, , of, 650 mean survival time of, 651 radiation lethality of, 657 Symptoms of radiation sickness, 658 Synthetic fallout, 107 See also Simulated fallout cesium tagged, accumulation by cotton rat, 536 ingestion by livestock, 178, 193 preparation of, 108 744 SUBJECT INDEX Tall fescue (Festuca arundinacea, Shreb), fallout retention by, 493 Targeting, pattern of, 88 effects on agricultural vulnerability, 88 Taste of irradiated crops, 675 Temporary equilibrium position of insect populations, 452 Terminal buds lethality of irradiated, 479 mortality of irradiated Viguiera portert, 463, 471 radiosensitivity of, 477 retention of fallout by, 464, 473 Testes, radiation effects on weight of mice, 236 Thermoluminescent dosimetry of beta and gamma radiation, 509 Threshold economic of insect pests, 451 of pest arthropods, 441 radiation, of effects on‘an arthropod community, 509 Threshold dose (LD/8) of radiation, 599 Thymus, radiation effects on weight of, PEST | Thyroid concentration of airborne radioiodine in, 259 1317 dose to, 548 ingested fallout dose to, 161 prevention of '??I accumulation by, 581 use of stable iodine in, 581 Tissue abomasal, concentration of airborne radioiodine in, 259 fallout **!Cs accumulation by cotton rat, 536. 541 Tomato plants, fruit set of irradiated, 682 Total-to-gamma dose ratio of fallout, 600, 603 sensitivity analysis of, 602 Total intake commitment of radionuclides from milk, 572 Transfer, of fission products in food chain, 560 Trees See also Forest chronic irradiation of, 483 fruit, radiosensitivity of, 691, 694 hardwood, radiosensitivity of, 694 radiosensitivity of, 483, 485 retention of fallout by, 401-402 Tritium, 136 dose from, 77 comparison with external gamma dose, tl dosimetry of, 72-75 fallout of, 74-75 importance of, 71-77 Tropospheric fallout, contamination of crops by, 343 United Kingdom grain stocks in, 619-620 barley, 619 oats, 619 wheat, 619 peacetime food imports of, 617 postattack availability of meat in, 622 postattack food resources of, 616 postattack requirement for grain in, 624 postattack survival of livestock in, 621 postattack yield of grains in, 624 potato stocks in, 619 °° Sr contamination of milk in, 554 total food stocks in, 617 United States, geographic distribution of food in, 577 Uptake of inhaled radioiodine, 259 Urinary assay of radionuclide body burden, 576 Vaporization of radioelements, 83 Vegetables, radiosensitivity of, 691, 694 Vegetation See also Forest; Plants; and specific types of vegetation dosimetry of, 354 fallout beta-radiation exposure of, 319:395-302-303,149 5 fallout contamination of, 501 factor for, 501 fallout gamma-ray exposure of, 360-361 fallout radiation injury of, 363 recovery of disturbed, 487 Vegetative yield of irradiated plants, 301 Ventral ruminal sac of sheep, 210 radiation-induced pathological changes in, 210 Viguiera porteri (A. Gray) beta irradiation of, 458 SUBJECT INDEX 745 growth in irradiated plant communities, 462, 468 irradiated biomass of, 477 growth of, 462, 471, 476-477 lateral branching of, 479 Margalef ratio of, 463 pigment changes of, 478 pigment-diversity ratio of, 463, 472 reproduction of, 477 response of, 475 stunting of, 478 terminal-bud mortality of, 463, 471 response of, to stress, 479 Vulnerability See also Radiosensitivity of agriculture to nuclear attack, 495-596 of crops to fallout beta radiation, 630 of livestock to fallout radiation, 627 Vulnerable period of crop growth, 607 Water decontamination, 590 effectiveness of home water softeners in, 590 effectiveness of water-treatment processes in, 590 Weapons system current, 88-91 future, 91-104 MIRV, 91-104 Weathering of fallout from plants, 400, 500 of fallout from vegetation, 496 Weathering function of fallout particles on plants, 496 Weeds net productivity of, 486 radiosensitivity of, 485 Wheat attack loss of, 622 beta irradiation of, 370 chronic irradiation of, 348 irradiated dose-rate effects on lethality of, 323 constant-rate exposure of, 322 fallout-simulated exposure of, 322 survival of, 310 yield of, 683 irradiation of, 306 ED, 4.08, 306,318, 322 United Kingdom stocks of, 619 Whole-body dose of fallout gamma radiation, 161, 539 Whole-body fallout radioactivity of cotton rat, 536, 541 Whole-body irradiation lethality of, 224 of livestock, 193 of sheep, 227 Wholesomeness of irradiated crops, 675 Woody plants LD, of, 700-701 radiosensitivity of, 694 Wool growth, radiation impairment of, 187 Work, radiation effects on performance of, 665-666 Worldwide fallout, contamination of food- stuff by, 549 YD,;,)/LD, , relation, 675, 696-697 YD,, (yield-reduction factor) of economic plants, 698-699 Yield of irradiated barley, 683 of irradiated crops, 313 of irradiated lettuce seedlings, 308, 310 of irradiated plants, 287, 306, 322, 684, 704 of irradiated potatoes, 683 of irradiated soybean plants, 281-282 of irradiated wheat, 683 Yield-reduction factor (see YD, , ) Yttrium-90 fallout simulant, radiochemical purity of, 371 ingestion of, 178, 193 by livestock, 193, 210, 627, 659-660 by sheep, 173, 178, 180, 186 irradiation of plant communities, 458 synthetic fallout label of, 178, 193 Yttrium-90 tagged sand beta dose from, 473 fallout simulant of, 178, 193, 371 NOTICE This book was prepared under the sponsorship of the United States Government. Neither the United States nor the United States Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights. AEC CRITICAL REVIEW SERIES As a continuing series of state-of-the-art studies published by the AEC Office of Information Services, the AEC Critical Reviews are designed to evaluate the existing state of knowledge in a specific and limited field of interest, to identify significant developments, both published and unpublished, and to synthesize new concepts out of the contributions of many. SOURCES OF TRITIUM AND ITS BEHAVIOR UPON RELEASE TO THE ENVIRONMENT December 1968 (TID-24635) $6.00 D. G. Jacobs Oak Ridge National Laboratory REACTOR-NOISE ANALYSIS IN THE TIME DOMAIN April 1969 (TID-24512) Nicola Pacilio Argonne National Laboratory and Comitato Nazionale per |’Energia Nucleare $6.00 PLUME RISE November 1969 (TID-25075) $6.00 G. A. Briggs Environmental Science Services Administration THE ANALYSIS OF ELEMENTAL BORON November 1970 (TID-25190) $3.00 Morris W. Lerner New Brunswick Laboratory ATMOSPHERIC TRANSPORT PROCESSES Part 1: Energy Transfers and Transformations December 1969 (TID-24868) $6.00 Part 2: Chemical Tracers January 1971 (TID-25314) $6.00 Elmar R. Reiter Colorado State University AERODYNAMIC CHARACTERISTICS OF ATMOSPHERIC BOUNDARY LAYERS May 1971 (TID-25465) $3.00 Erich J. Plate Argonne National Laboratory and Karlsruhe University NUCLEAR-EXPLOSION SEISMOLOGY September 1971 (TID-25572) Howard C. Rodean Lawrence Livermore Laboratory $3.00 Available from the National Technical Information Service, U. S. Department of Commerce, Springfield, Virginia 22157. A TROPICAL RAIN FOREST A Study of Irradiation and Ecology at El Verde, Puerto Rico HOWARD T. ODUM ROBERT F. PIGEON Editor and Project Director Associate Editor An intensive ecological study of several hectares of montane rain forest was made during the 1960s in the Luquillo National Forest in eastern Puerto Rico. The operation of the normal forest was studied and compared with a zone that for three months received gamma- radiation stress from a 10,000-curie cesium source that had been airlifted into the forest. The book reports the scientific results of the project, which used many techniques of systems ecology in the quest of understanding one of the most complex ecosystems on earth. Included in nine main divisions (111 chapters) are maps, tables of tree numbers, and taxonomic keys to facilitate new efforts at the El Verde site toward finding the best designs for man and nature in ‘ broad tropic lands. 1678 pp. 1170 illus., 8/, x 11. Published in 1970 by the Office of Information Services, U.S. Atomic Energy . Commission. Contents THE RAIN FOREST PROJECT THE RAIN FOREST AT EL VERDE THE RADIATION EXPERIMENT PLANTS AND THE EFFECTS OF RADIATION ANIMALS AND THE EFFECTS OF RADIATION MICROORGANISMS AND THE EFFECTS OF RADIATION CYTOLOGICAL STUDIES WITHIN THE IRRADIATED FOREST MINERAL CYCLING AND SOILS FOREST METABOLISM AND ENERGY FLOWS Available as TID-24270 for $10.00 from National Technical Information Service U.S. Department of Commerce Springfield, Virginia 22151 WNL 102 NUCLEAR SCIENCE ABSTRACTS Nuclear Science Abstracts, a semimonthly publication of the U.S. Atomic Energy Commission, provides comprehensive abstracting and indexing coverage of the international literature on nuclear science and technology. It covers (1) research reports of the U. S. Atomic Energy Commission and its contractors; (2) research reports of other govern- ment agencies, universities, and industrial research organizations on a worldwide basis; and (3) translations, patents, conference papers and proceedings, books, and articles appearing in technical and scientific journals. INDEXES Indexes covering subject, author, corpo- rate author, and report number are in- cluded in each issue. These indexes, which are cumulated and sold separately, provide a detailed and convenient key to the world’s nuclear literature. EXCHANGE Nuclear Science Abstracts is available on an exchange basis to universities, research institutions, industrial firms, and publishers of scientific information; in- quiries regarding the exchange provision should be directed to the USAEC Tech- nical Information Center, P.O. Box 62, Oak Ridge, Tennessee 37830. 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AEC SYMPOSIUM SERIES Progress in Viedical Radioisotope Scanning (TID-7673), 1963, $6.00 Reactor Kinetics and Control (TID-7662), 1964, $6.00 Dynamic Clinicai Studies with Radioisotopes (TID-7678), 1964, $6.00 Noise Analysis in Nuclear Systems (TID-7679), 1964, $6.00 Radioactive Fallout from Nuclear Weapons Tests (CONF-765), 1965, $6.00 Radioactive Pharmaceuticals (CONF-651111), 1966, $6.00 Neutron Dynamics and Control (CONF-650413), 1966, $6.00 Luminescence Dosimetry (CONF-650637), 1967, $6.00 Neutron Noise, Waves, and Pulse Propagation (CONF-660206), 1967, $6.00 Use of Computers in the Analysis of Experimental Data and the Control of Nuclear Facilities (CONF-660527), 1967, $6.00 Compartments, Pools, and Spaces in Medical Physiology (CONF-661010), 1967, $6.00 12 Thorium Fuel Cycle (CONF-660524), 1968, $6.00 13 Radioisotopes in Medicine: In Vitro Studies (CONF-671111), 1968, $6.00 14 Abundant Nuclear Energy (CONF-680810), 1969, $6.00 15 Fast Burst Reactors (CONF-690102), 1969, $6.00 16 Biological Implications of the Nuclear Age (CONF-690303), 1969, $6.00 17 Radiation Biology of the Fetal and Juvenile Mammal (CONF-690501), 1969, $6.00 18 Inhalation Carcinogenesis (CONF-691001), 1970, $6.00 19 Myeloproliferative Disorders of Animals and Man (CON F-680529), 1970 , $9.00 20 Medical Radionuclides: Radiation Dose and Effects (CON F-691212), 1970, $6.00 21 Morphology of Experimental Respiratory Carcinogenesis (CONF-700501), 1970, $6.00 22 Precipitation Scavenging (1970) (CONF-700601), 1970, $6.00 23 Neutron Standards and Flux Normalization (CON F-701002), 1971, $6.00 24 Survival of Food Crops and Livestock in the Event.of Nuclear War (CONF-700909), 1971, $9.00 _ 1022312223 OOON ODOR WDM —_" om = AVAILABLE FROM: National Technical Information Service U.S. Department of Commerce Springfield, Virginia 22151