Given in Loving Memory of Raymond BraisUn Montgomery Scientist, R/V Atiantis maiden voyage 2 July - 26 August, 1931 Woods Hole Oceanographic Institution- Physical Oceanographer 1940-1949 Non-Resident Staff 1950-1960 Visiting Committee 1962-1963 Corporation Member 1970-1980 Faculty, New York University 1940-1944 Faculty, Brown University 1949-1954 Faculty, Johns Hopkins University 1954-1961 Professor of Oceanography, Johns Hopkins University 1961-1975 i □ : D D m a THE BIOLOGICAL EFFECTS OF ATOMIC RADIATION THE EFFECTS OF ATOMIC RADIATION ON OCEANOGRAPHY AND FISHERIES C.3 Report of the Committee on Effects of Atomic Radiation on Oceanography and Fisheries of the National Academy of Sciences Study of the Biological Effects of Atomic Radiation MAHiNE BIOLOGICAL L'^BORATORY LIBRARY WOODS HOLE, MASS. W. H. 0. I. Publication No. 551 National Academy of Sciences — National Research Council Washington, D. C. 4i. /IJ\ "(^ )9M Library of Congress Catalog Card No.: 57-60049 COMMITTEE ON THE EFFECTS OF ATOMIC RADIATION ON OCEANOGRAPHY AND FISHERIES Roger Revelle, Chairtnan, Scripps Institution of Oceanography. Howard Boroughs, Hawaii Marine Laboratory. Dayton E. Carritt, The Johns Hopkins University. Walter A. Chipman, U. S. Fish and Wildhfe Service. Harmon Craig, Scripps Institution of Oceanography. Lauren R. Donaldson, University of Washington. Richard H. Fleming, University of Washington. Richard F. Foster, General Electric Company. Edward D. Goldberg, Scripps Institution of Oceanography. John H. Harley, U. S. Atomic Energy Commission. BosTwiCK Ketchum, Woods Hole Oceanographic Institution. Louis A. Krumholz, University of Louisville. Charles E. Renn, The Johns Hopkins University. MiLNER B. ScHAEFER, Inter-American Tropical Tuna Commission. Allyn C. Vine, Woods Hole Oceanographic Institution. Lionel A. Walford, U. S. Fish and Wildlife Service. Warren S. Wooster, Scripps Institution of Oceanography. Consultants: Theodore R. Folsom, Scripps Institution of Oceanography. Theodore R. Rice, U. S. Fish and Wildlife Service. George A. Rounsefell, U. S. Fish and Wildlife Service. FOREWORD The studies of the biological effects of atomic radiation, of which the report published in this volume is a part, were undertaken by the National Academy of Sciences in 1955. The first formal reports issuing from the study were published by the National Academy of Sciences — National Research Council in June 1956 as "The Biological Effects of Atomic Radiation — Summary Reports." These noted briefly the findings of six com- mittees established to review broadly the status of knowledge in this field of vital im- portance to the welfare of man at the threshold of the atomic age. They considered the problem from the points of view of genetics, pathology, agriculture and food supplies, oceanography and fisheries, meteorology, and the disposal and dispersal of radioactive wastes. The Academy study is a continuing one. Each of the Committees in a manner appro- priate to its area of concern is pursuing its work. The Committee on the Effects of Atomic Radiation on Oceanography and Fisheries held two meetings prior to the publication of its "Summary Report": the first on March 3-5, 1956 and the second on April 13-16, 1956. Rough drafts of most of the materials published in this volume were prepared at the second meeting. These reports, which give the detailed technical background of the committee's findings and recommendations, have been completed during the past year. Although the different chapters are signed by individual authors, all members of the committee participated in planning and out- lining the materials covered. Valuable editorial assistance was given by Dr. George A. Rounsefell and Mr. Charles I. Campbell. A similar report was prepared by the Committee on Pathologic Effects of Atomic Radiation and published in the Fall of 1956 by the NAS-NRC as Publication Number 452. The Committee on the Disposal and Dispersal of Radioactive Wastes has nearly completed a similar detailed report of its considerations. After the publication of its Summary Report in June 1956, the Committee on the Effects of Atomic Radiation on Oceanography and Fisheries met informally with scien- tists from the United Kingdom on September 27 and 28, 1956. The discussions centered around the recommendations that could be made on the basis of existing knowledge and the nature of the research needed in planning disposal of radioactive waste at sea. Members of this Committee have also participated in the preparation of a report by Unesco to the UN Scientific Committee on the Effects of Atomic Radiation, concerning the oceanic disposal of radioactive wastes. As the use of atomic energy becomes more and more a part of our daily life it is essential that thoughtful attention in broad perspective be paid to the often subtle and perhaps profound effects of this new technology on man and his environment. The Academy study will continue to provide this review and to report its findings to the public when appropriate. The facts upon which the study's conclusions are based result from more than two decades of research which has been sponsored by the Academy and other private or- ganizations as well as by various government agencies. The current study has been financed by a grant from the Rockefeller Foundation. It has been greatly assisted by the generous and whole-hearted co-operation of the U. S. Atomic Energy Commission and other government agencies. Detlev W. Bronk, President, National Academy of Sciences. TABLE OF CONTENTS PAGE Foreword vii Contents ix General Considerations Concerning the Ocean as a Receptacle for Arti- ficially Radioactive Materials, Roger Revelle and Milner B. Schaejer 1 Chapter 1. Physical and Chemical Properties of Wastes Produced by Atomic Power Industry. Charles E. Remi 26 Chapter 2. Comparison of Some Natural Radiations Received by Selected Organisms. Theodore R. Folsom and John H. Harley 28 Chapter 3. Disposal of Radioactive Wastes in the Ocean: The Fission Product Spectrum in the Sea as a Function of Time and Mixing Char- acteristics. Harmon Craig 34 Chapter 4. Transport and Dispersal of Radioactive Elements in the Sea. Warren S. Wooster and Bosttvick Ketchum 43 Chapter 5. The Effects of the Ecological System on the Transport of Ele- ments IN the Sea. Bostwick H. Ketchum 52 Chapter 6. Precipitation of Fission Product Elements on the Ocean Bottom BY Physical, Chemical, and Biological Processes. Dayton E. Carritt and John H. Harley 60 Chapter 7. Ecological Factors Involved in the Uptake, Accumulation, and Loss of Radionuclides by Aquatic Organisms. Louis A. Krnmholz, Edward D. Goldberg and Howard A. Boroughs . . 69 Chapter 8. Laboratory Experiments on the Uptake, Accumulation, and Loss OF Radionuclides by Marine Organisms. Howard Boroughs, Walter A. Chipman and Theodore R. Rice .... 80 Chapter 9. Accumulation and Retention of Radioactivity from Fission Prod- ucts AND Other Radiomaterials by Fresh-Water Organisms. Louis A. Krumholz and Richard F. Foster 88 Chapter 10. Effects of Radiation on Aquatic Organisms. Lauren R. Donaldson and Richard F. Foster 96 Chapter 11. Isotopic Tracer Techniques for Measurement of Physical and Chemical Processes in the Sea and the Atmosphere. Harmon Craig 103 Chapter 12. On the Tagging of Water Masses for the Study of Physical Proc- esses in the Oceans. Theodore R. Folsom and Allyn C. Vine 121 Chapter 13. Large-Scale Biological Experiments Using Radioactive Tracers. Milner B. Schaejer 133 ix GENERAL CONSIDERATIONS CONCERNING THE OCEAN AS A RECEPTACLE FOR ARTIFICIALLY RADIOACTIVE MATERIALS^ Roger Revelle and Milner B. Schaefer, Scripps Institution of Oceanography and Inter-American Tropical Tuna Commission, La Jolla, California L Introduction In this report, we have attempted to sum- marize both the present knowledge and the areas of ignorance concerning the oceans that must be taken into account in considering the biological effects of radiation. [The oceans of the world furnish essential sources of food and other raw materials, vital routes of transportation, recreation, and a con- venient place in which to dispose of waste ma- terials from our industrial civilization. These different ways in which men use the sea, how- ever, are not always compatible. (The use of the sea for waste disposal, in particular, can jeopardize the other resources, and hence should be done cautiously, with due regard to the pos- sible effects. jWaste products from nuclear re- actions require special care: they constitute hazards in extremely low concentrations and their deleterious properties cannot be eliminated by any chemical transformations; they can be dispersed or isolated, but they cannot be de- stroyed. Once they are created, we must live with them until they become inactive by natural decay, which for some isotopes requires a very long time. Waste products from nuclear reactions arise in two ways: (1) from the slow controlled re- actions involved in laboratory experimentation, in the production of materials for nuclear weapons, the production of reactor fuels, and the "burning" of fuels in power reactors; (2) from the rapid, uncontrolled reactions involved in testing of weapons or in warfare. Up to the present time, the largest quantities of fission products introduced into the aquatic environ- ment have been from weapons tests; most of the products from controlled reactions have been isolated on the land, and only relatively small quantities have been introduced into the 1 Contribution from the Scripps Institution of Oceanography, New Series, No. 901. sea or fresh water. In the future, however, in dustrial nuclear wastes will present difficult dis- posal problems and the sea is a possible dis- posal site, particularly for small, densely popu- lated nations with long sea coasts. We have, therefore, given particular attention to the long- range problems that may arise from the large- scale disposal of both high-level and low-level industrial wastes, as well as to the effects of weapons tests. Among the variety of questions generated by the introduction of radioactive materials into the sea, there are few to which we can give precise answers. We can, however, provide con- servative answers to many of them, which can serve as a basis of action pending the results of detailed experimental studies. The large areas of uncertainty respecting the physical, chemical, and biological processes in the sea lead to re- strictions on what can now be regarded as safe practices. These will probably prove too severe when we have obtained greater knowledge. It is urgent that the research required to formulate more precise answers should be vigorously pur- sued. Fortunately, the use of radioactive iso- topes is one excellent means of acquiring the needed information, and the quantities of these isotopes required for pertinent experiments are well within limits of safety. Moderate quanti- ties of the very waste products we are concerned with can, therefore, provide one means of at- tacking the unsolved scientific problems. II. The Nature of the Ocean and Its Contained Organisms The ocean basins cover 361 x 10'^ square kilometers and have an average depth of 3,800 meters, giving a total volume of 1.37x10^ cubic kilometers. They are characteristically bordered by a continental shelf, which slopes gently out to a depth of about 200 meters. In- side it is a steeper slope extending down to the Atomic Radiatioti and Oceanography and Fisheries deep sea floor with depths of 4,000 meters or more. The average width of the continental shelf is about 30 miles, varying from almost nothing off mountainous coasts, such as the West Coast of South America, to several hun- dred miles in the China Sea. The shelf is not everywhere smooth, but is often intersected by submarine valleys and canyons. In the deep ocean basins there are high mountains and long, deep trenches, features larger than any on land. Some of the deeper parts are isolated by sub- marine ridges which restrict the exchange of water between adjacent areas. The waters of the oceans are stratified. Within a relatively thin layer at the surface, varying in thickness in different places but averaging about 75 meters, vertical mixing caused by winds is fairly rapid and complete. In conse- quence, the temperature, salinity and density are nearly uniform from top to bottom. Relatively fast wind-driven currents exist in this upper mixed layer; these are the "surface" currents of the oceans depicted on many charts. Here also the horizontal mixing is relatively rapid. The mixed layer is the region of the sea in which most of man's activity takes place. Below the mixed layer is a 2one within which the temperature decreases and the density in- creases rapidly with depth. This thermocline, or pycnocline, separates the surface mixed layer from the layers of intermediate and deep water, the latter extending to the bottom, within which there are gentle gradients of decreasing tem- perature and increasing salinity and density with depth. Vertical movement in the intermediate and deep layers is much slower than in the mixed layer, and horizontal currents are more sluggish. The strong density gradient across the pycnocline tends to inhibit physical transport across it, because work is required to move wa- ter vertically in either direction, and thus the pycnocline acts as a partial barrier between the mixed layer and the lower layers. There is, however, some interchange of both living and non-living elements; indeed the continued ex- istence of some marine resources depends on such interchange. MARINE RESOURCES Living resources I The most important extractive industry based on the resources of the sea is the harvesting of jits living resources. On land the cycle of life is relatively simple; we may describe it in four figurative stages. First is the grass, which by a subtle and complex chemistry captures the energy of sunlight and builds organic matter. Sheep and cows live on the grass; tigers and men eat them. The cycle is closed by bacteria, which decompose the dead bodies and the excreta of all living creatures, making their constituent substances again avail- able as building materials for the plants. In the sea, the cycle is longer. Instead of grass there are the tiny floating plants called phytoplank- ton; in place of cows, the zooplankton animals that eat the plants are small crustaceans, no bigger than the head of a pin. Many kinds of tigers eat the cows, but they are mostly also zooplankton, only a fraction of an inch in length. Other intermediate flesh-eaters exist between them and the fishes of our ocean har- vest. Because every link in this long food chain is inefficient, we reap from the sea only a small fraction of its organic production. Other characteristics of the ocean also tend to limit the harvest as compared to that from the land. One is its giant size; more than 70 per cent of all the sunlight that penetrates the atmosphere falls on the sea; moreover, this sunlight can act throughout the top 20 to 100 meters, thus the living space for plants and animals is far greater than on land. This great areal extent and volume, combined with the fluidity of the oceans, results in a low concentra- tion oif organisms per unit volume and therefore inefficiency in harvesting. On land, the standing crop of plants and animals is of the same order of magnitude as the amount of organic production per year, while in the ocean the crop is very small, com- pared to the production, because of rapid turn- over. The average rate of organic production per unit area is probably about the same on land and in the sea, but the efficiency of harvesting depends more on the size of the crop than on the total amount of organic matter produced. The plants of the sea, on which all other liv- ing things depend, grow only in the waters near the surface where bright sunlight pene- trates. These waters diflfer widely in fertility. Like the land, the ocean has its green pastures where life flourishes in abundance, and its deserts where a few poor plants and animals barely survive. The fertility of the land depends on four things: water, temperature, intensity of sun- light, and available plant nutrients — substances General Considerations that usually occur in very small amounts but are essential for plant growth. In the sea, water is, of course, always abundant; the plants are well adapted to the narrow range of temperature; the intensity of sunlight determines the length of the growing season and the depth of growth, but usually not the differences in fertility. These depend only on the plant nutrients in the wa- ters near the surface. As in any well-worked soil on land, the nutrients in the waters must be replenished each year. They are continually de- pleted by the slow sinking of plant and animal remains from the brightly lighted near-surface layers into the dark waters of the depths. Men plow the soil to restore its fertility; the fertility of the sea is restored when nutrient-rich deeper waters are brought up near the surface. The "plowing" of the sea is accomplished in three ways. In some regions winds drive the surface waters away from the coast or away from an internal boundary, and nutrient-rich waters well up from mid-depths. In other areas, the surface waters are cooled near to freezing in the winter, become heavy and sink, and mix with the deep waters. Elsewhere, violent mixing occurs along the boundaries between ocean cur- rents, and deeper waters are thereby brought into the brightly lighted zone. The influx of nutrients to the upper layer, and the corresponding loss from this layer by sinking of plant and animal remains, do not directly involve the deep waters. Upwelling and vertical mixing take place only in the upper few hundred meters. The exchange between these mid-depths and the abyssal deep is a very much slower process, of the scale of hundreds of years. Most of the commercially important marine organisms are harvested in coastal waters or in offshore waters not very far from land. Several factors are involved: (1) Profitable fisheries can be conducted more easily near ports and harbors; (2) the coastal waters are of high fer- tility, because of greater upwelling and turbu- lent mixing and the ease of replenishment of plant nutrients from the shallow sea floor, and perhaps also because of the supply of nutrients and organic detritus from land; (3) the stand- ing crop of plants and animals attached to or living on the bottom in coastal areas is large, relative to the total organic production. None of the animals of the great depths are the objects of a commercial fishery. Even the truly pelagic, high seas fisheries, such as the great offshore fisheries for tuna, herring, red- fish and whales, harvest animals that live pri- marily in the surface layer. Some of these ani- mals, however, do much of their feeding in the deeper layers. The sperm whales, for ex- ample, feed on deep-sea cephalopods at great depths. Moreover, much of the food for com- mercially harvested organisms consists of small animals, including crustaceans, squids, and fishes, that perform vertical diurnal migrations from several hundred meters depth to the sur- face. The sea fisheries produce about 25 million metric tons per year of fishes and marine in- vertebrates, in addition to about 4 million tons of whales. The great bulk of the harvest is taken, at present, ifrom the waters of the north- ern hemisphere, despite the fact that the south- ern oceans constitute 57 per cent of the world's sea area. The following table indicates the pro- duction in 1954 by latitude zones: TABLE 1 Harvest of Fishes and Marine Invertebrates in 1954, by Latitude Zones (From FAO, 1957) Millions of Zone metric tons % Arctic region 1.2 5 Northern hemisphere-temperate zone 17.5 72 Tropical zone 4.1 17 Southern hemisphere-temperate zone 1.4 6 Antarctic regions 0* 0* * About 4 million tons of whales were taken in the Antarctic, but few fish or marine invertebrates. The disproportionately large yield in the northern hemisphere is related to three factors: (1) Human populations are heavily concen- trated there; (2) the major fishing nations are the industrialized maritime nations, which are mostly located in the north; (3) except for some of the fisheries for tuna, salmon, her- ring, and whales, the important fisheries are located in the relatively shallow areas along the continents, and the extent of these areas is much greater in the northern than in the southern hemisphere. The sessile algae of shallow coasts are also the object of important industries in Japan, the United States, the United Kingdom, Norway, and some other countries. Some of these plants are used directly for human consumption, while Atomic Radiation and Oceanography and Fisheries others are employed indirectly in pharmaceutical and food products. Petroleum and natural gas It is estimated that about 30 million cubic meters of possible oil-bearing sediments underlie the 11.8 million square miles of the submerged continental shelves. These sediments contain some 400 billion barrels of recoverable crude oil. Exploitation of these deposits of petroleum and the associated natural gas has commenced in the waters of the Gulf of Mexico; intensive geophysical prospecting has been conducted off- shore from California and in the Persian Gulf. It may be expected that this source of fossil fuels will be extensively utilized in the near future. The resource is confined to the subsoil of the marginal seas, since only there do we find oil- bearing sediments. Minerals Extraction of sea salt for sodium chloride is an ancient industry, and is now highly developed also for production of sodium sulfate, potas- sium chloride, and magnesium chloride. Bro- mine is extracted directly from sea water for the manufacture of ethylene dibromide. Magnesium metal has been produced commercially from sea- water by chemical and electrolytical procedures for nearly two decades. All of these industries use sea water taken from near the surface at the shore but the quantity of water utilized is insignificant. For example, a single cubic kilometer of sea water contains over a million tons of magnesium, about five times the peak world annual produc- tion of this metal. The floor of the deep sea is known to contain low-grade deposits of cobalt, nickel and copper (0.1 to 0.7 per cent by weight of the metals) associated with deposits of iron and manganese. The problems of mining these materials, in the face of the great depths and pressure, have not been solved, and they certainly will not soon be economically useable. \ Ocean transportation Long-distance transportation of large cargos by sea is the indispensable basis of international commerce. The economy of the United States and of other industrial nations is in large part dependent on the sea-borne commerce that flows through the seaports. Contamination of the sea by nuclear wastes will certainly not present a hazard to shipping, since acceptable levels of such materials in the surface layer of the sea will be limited by other considerations (such as the effects on the fish- eries) to much lower levels than would consti- tute a hazard to ships' personnel. On the other hand, it is almost certain that nuclear power plants will be extensively used in merchant ves- sels; they are already in use in naval craft. Serious hazards may arise in confined waters from collisions in which the reactor is damaged and the fuel elements with their contained fis- sion products are lost in the water. Suppose for example that a 50,000 kilowatt reactor (prob- ably fairly typical for a large fast freighter) has been in service without refueling for one year on a ship that has spent half its time under way. Approximately 10 kilograms of fission- able material will have been used up and the total amount of fission products will be ap- proximately 10^ curies. If, owing to a collision, the reactor is lost in a harbor, say 8 miles long by 3 miles wide by 50 feet deep, and the fis- sion products become uniformly distributed, the water in the harbor would contain 10'^ curies per cubic meter giving an almost constant radia- tion dose of about 0.5 r per day on the surface. Dock pilings, ship bottoms and other structures covered with fouling organisms would accumu- late a much higher level of radioactivity, and local concentration in the water might be ex- tremely high. Recreation For coastal populations in the temperate, sub- tropical, and tropical regions, the sea and its contents provide healthful sports and satisfac- tion of men's curiosity and their desire for beauty. Boating, swimming, sport fishing, and other recreations are engaged in by millions of people, and are the basis of tourist and service industries of very considerable monetary value. JV^aste disposal), Disposal of domestic sewage and industrial wastes is often conveniently accomplished near coastal population centers by running them into the sea. The large volume and rapid mixing of the ocean waters dilute the wastes, and the bac- General Cojisideratiojis teria in the sea break down the organic con- stituents. Unless care is exercised, however, this discharge into inshore sea areas may be dele- terious to other resources. Dumping of excess volumes of sewage and industrial wastes, with- out proper regard to the local characteristics of the sea bottom, currents, and other factors, has already resulted in ruining some harbors and beaches for recreation, damage to the living resources of adjacent areas, and even serious problems of corrosion to ships. The use of the sea for the disposal of atomic wastes has, fortunately, been so far approached with great caution and with due regard to the possible hazards. The problems, because of the dangerous character of small amounts of atomic wastes, are of a different order of magnitude than those of the disposal of other kinds of wastes. III. Potential Hazards From Radioactive Materials Direct hazards A direct hazard to human beings from radia- tion may exist if the levels of radiation in the environment are sufficiently high. The natural radioactivity of the sea is very much lower than that of the land. According to Folsom and Harley (Chapter 2 of this report) , a man in a boat or ship receives only about half a millirad per year from the radio isotopes in the sea, compared with about 23 millirads per year from sedimentary rock or 90 millirads per year from granite. Thus, it would be necessary to increase the radioactivity of the sea many fold to equal the radiation that man normally receives from the land on which he lives. Due to the rather rapid mixing in the upper layers of the sea, and to its very large volume, even large quantities of activity introduced at the sur- face in the open sea become sufficiently dis- persed to constitute no direct hazard after a relatively short time, as has been shown by the dispersion of the activity resulting from weap- ons tests in the Pacific. If the direct hazard were the only consideration, sea disposal of radioac- tive wastes would give rise to difficulties only in small areas near the disposal sites. Some radioactive wastes have been disposed of in the sea by placing them in containers de- signed to sink to the sea bottom. In this way, the wastes are isolated and not dispersed by the ocean currents. Direct hazards could arise if the containers in some manner were to come into contact with humans, such as through ac- cidental recovery during fishing or salvage op- erations or if, through improper design, the containers were to float to the surface and come ashore. Indirect hazards The most serious potential hazards to human beings from the introduction of radioactive products into the marine environment are those that may arise through the uptake of radio iso- topes by organisms used for human food. There are several reasons why these indirect hazards are more critical than the direct hazards: (1) The radiation received from a given quantity of an isotope ingested as food is much greater than the dose from the same quantity in the external environment; (2) many elements, in- cluding some of those having radioactive iso- topes resulting from nuclear reactions, are con- centrated by factors up to several thousand by the organisms in the sea; (3) the vertical and horizontal migrations of organisms can result in transport of radioactive elements and thereby cause distributions diflferent from those that would exist under the influence of physical fac- tors alone ; for example, certain elements may be carried from the depths of the sea into the upper mixed layer in greater amounts than could be transported by the physical circulation. It is quite certain that the indirect hazard to man through danger of contamination of food from the sea will require limiting the permis- sible concentration of radioactive elements in the oceans to levels below those at which there is any direct hazard. Any part of the sea in which the contamination does not cause danger- ous concentrations of radioactive elements in man's food organisms will be safe for man to live over or in. A reduction of the harvestable living re- sources of the sea could conceivably occur through the eff^ects of atomic radiations on the organisms that are the objects of fisheries, or on their food. This might result from mortality in- duced by somatic eflfects, or from genetic changes. There is no conclusive evidence that any of the living marine resources have yet suf- fered from either of these, and they are not likely to be undesirably influenced at radiation levels safe from other standpoints. The knowl- Atomic Radiation and Oceanography and Fisheries edge of radiation effects on marine organisms is, however, inadequate for firm conclusions. Pollution in general The introduction of atomic wastes into the aquatic environment is but one aspect of the general problem of pollution. Man's record with respect to pollution of lakes, streams, and parts of the sea by sewage and industrial wastes has not been good. In many places, the waters have been ruined for recreation and useful living resources have been destroyed or made unfit for human consumption. This unhappy record results from two factors: (1) the insidious nature of pollution of the aquatic environment, and (2) the fact that the waters and most of their resources are not pri- vate property, but are the common property of a large community (in the case of the high seas, the whole world) ; what is everyone's business often becomes no one's business. The ruin of an aquatic resource by pollution seldom has been rapid. Quantities of waste products, at first very small, increase year by year until finally the concentrations become so large as to have obvious deleterious eflfects. For example, in the depletion of oxygen by organic wastes, sharp critical levels of tolerance of low oxygen content exist for some of the living re- sources, so that there is little adverse effect until a critical concentration of pollutant is reached, whereupon catastrophic mortality occurs. In other cases, the effects are more or less propor- tional to the concentrations. The destruction of a resource may then proceed gradually and it may not even be clear whether the pollutant has, indeed, been the cause rather than some other environmental change. For these reasons, it is necessary that the introduction of waste materials of any kind into the aquatic environ- ment be carefully monitored, so that the effects may be detected before they become serious. Unfortunately, such monitoring is seldom the concern of those who produce the pollutants. The record of the control and monitoring of the disposal of atomic pollutants has, so far, been excellent. We are, however, at the thresh- old of a tremendous growth of the atomic energy industry, and it behooves mankind to make sure that as much caution is exercised in the future as in the past. Ordinary pollutants in sewage and industrial wastes are rapidly neutralized by the chemical and biological processes in the sea, and when effects of pollution are detected they can be rather quickly reversed by the cessation of intro- duction of the waste. A number of the radio isotopes, on the other hand, are very long-lived. Having reached harmful concentrations in the sea, they will diminish only by very slow decay, so that the effect of any serious pollution is not reversible. For this reason, the prevention of atomic pollution is of paramount importance. URGENCY OF THE PROBLEM Estimates of the rate of economic develop- ment of nuclear power vary widely. This source of power is already competitive with conventional sources in some places, and re- search on reactor development with consequent reductions in cost is proceeding rapidly. Thus, we can expect that very large quantities of nu- clear power will be generated in the quite near future, even though the relative urgency of nuclear power requirements differs greatly in different countries. In countries with high costs from conventional (fossil) fuels there is en- couragement to proceed immediately with the commercial construction of reactors of proved design. In such countries as the United States, where conventional power costs are low, major efforts are being devoted to experimental con- struction of new types of reactors that hold promise of economical operation in the future. One megawatt-year of heat produced by a nuclear reactor results in 365 grams of fission products. The Committee on Disposal and Dis- persal of Radioactive Wastes, also a part of the National Academy of Sciences' study of the bio- logical effects of atomic radiation (1956), es- timates that by 1965 the United States will be generating about 11,000 megawatts of reactor heat, some 20 per cent of which will be for naval vessels. This will result in the produc- tion of about 4 tons per year of fission products. According to recent statements of government officials, reported in Nucleonics (1957), the United Kingdom has a 1965 target of 6,000 megawatts of electricity from Calder Hall-type reactors; "Euratom" has a goal of 15,000 mega- watts by 1967, and Japan will produce 1,000 megawatts by 1965 and 10,000 megawatts by 1975. If the reactors are of 25 per cent ef- ficiency in conversion of heat to electricity (the Calder Hall reactor has a net thermal efficiency of 21.5 per cent. Nucleonics 1956), for each General Considerations 1,000 megawatts of electrical power there will be produced 1.46 tons per year of fission prod- ucts. Thus, the fission products from the fore- going programs will amount to: United King- dom 8.8 tons, "Euratom" 21.9 tons, Japan 1.5 to 14.6 tons. If we further assume that all other areas of the world will in the next ten years develop nuclear power equal' to the sum of that gen- erated in the United States, Japan, the United Kingdom, and "Euratom," there will be a total of some 80 tons per year of fission products. This represents, after 100 days' cooling, accord- ing to the values given by Renn (see Chapter 1, Tables 2 and 3), 3.9 x 10* megacuries of beta radiation and 2.5 x 10* megacuries of gamma radiation, or over Via of the total natural radio- activity of all the oceans (Revelle, Folsom, Goldberg and Isaacs 1955). The annual pro- duction of the isotope of greatest long-range hazard, strontium 90, will be 200 megacuries. Craig (Chapter 3) has shown that a thousand tons of fission products per year would result from a 2.7-fold increase in the present world energy consumption of about five million mega- watts, if 10 per cent of this energy were derived from the heat of nuclear fission at 50 per cent efficiency. World energy consumption is now doubling once every thirty years and a 2.7-fold increase would be expected by about the year 2000. An annual production of a thousand tons of fission products corresponds to an equilibrium quantity of 7.7 x 10^ megacuries of radiation or about 1.6 times the total natural radioactivity of the oceans. The equilibrium amount of strontium 90, plus its daughter yttrium 90, would be 2.2 x 10^ megacuries. Carritt and Harley (Chapter 6) have made calculations based on an annual production of 4,000 tons of fission products, corresponding to two million megawatts per year of nuclear heat production from fission. If no new sources of power, such as thermonuclear reactions, become available, this production would be expected in the very early part of the twenty-first century because of the limited world fossil fuel reserves. Our knowledge of just what share of these fission products can be safely introduced into the oceans is woefully incomplete because we simply do not know enough about the physical, chemi- cal, and biological processes. If the sea is to be seriously considered as a dumping ground for any large fraction of the fission products that will be produced even within the next ten years, it is urgently necessary to learn enough about these processes to provide a basis for engineer- ing estimates. As shown in the several chapters of this re- port, the necessary information can be obtained only by extensive fundamental research. In the next decade we should attempt to learn far more about the ocean and its contents than has been learned since modern oceanography began 80 years ago. Some of the required investigations of physi- cal, chemical, and biological processes involve the employment of naturally occurring or ex- perimentally introduced radioactive tracers. Pol- lution of the seas by the dumping of atomic wastes, even at levels that are "safe" from the standpoint of human health hazards, will make such experiments progressively more difficult because the presence of introduced pollutants will add an unknown background variability. The sooner the work can be commenced and the cleaner our oceanic laboratory, the more precise will be the experimental results. At the very least, it is urgent that the details of any interim introductions of radio isotopes be carefully doc- umented, so that researchers can take account of them in their investigations. INTERNATIONAL IMPLICATIONS The oceans and their resources cannot be separated into isolated compartments ; what hap- pens in one area of the sea ultimately affects all of it. Moreover, the greater part of the oceans and their contained resources are the common property of all nations. Even the rela- tively narrow territorial seas are amenable only to juridical and not physical control; no nation can effectively modify the natural interchange of the biological and physical contents of its terri- torial sea with those of the high seas or of the territorial seas of other nations. The continuity of the oceans, and their status as international common property require that the oceanic dis- posal of radioactive wastes be treated as a world problem. It is, first of all, urgent that the nations of the earth formulate agreements for the safe oceanic disposal of atomic wastes, based on ex- isting scientific knowledge. Second, because of the vastness, complexity, and immediacy of the underlying scientific problems, it is important that pertinent oceanographic research be intensi- fied on a world-wide basis. Third, from the Atomic Radiation and Oceanography and Fisheries standpoint both of research and of proper con- trol of this new kind of pollution, careful rec- ords should be maintained of the kinds, quanti- ties, and physical and chemical states of all radio isotopes introduced into the seas, together with detailed data on locations, depths and modes of introduction. This can probably best be done by national agencies reporting to an international records center. Although we are urgently concerned with preventing possible deleterious effects of atomic wastes, atomic radiations can also be of benefit. Large-scale experiments employing radioactive isotopes might contribute importantly to our knowledge of the flux of materials through the food chains from the phytoplankton to the harvestable fishes, invertebrates, and whales (Schaefer, Chapter 13 of this report). Such knowledge will not only make possible assess- ment of the ocean's potential for providing food to mankind, but is a basic prerequisite for the effective conservation of marine populations, to permit maximum harvests to be taken year after year. Other experiments using radioactive trac- ers could lead to improved knowledge of the processes of circulation and mixing in the sea (Folsom and Vine, Chapter 12; Craig, Chap- ter 1 1 ) . In both types of experiments, inter- TABLE 2 Elements in Solution in Sea Water (Except Dissolved Gases) ^' 2 mg/kg Element CI = \9.QQ%o Chlorine 18,980 Sodium 10,561 Magnesium 1,272 Sulfur 884 Calcium 400 Potassium 380 Bromine 65 Carbon 28 Strontium 13 Boron 4.6 Silicon 0.02 -4.0 Fluorine 1.4 Nitrogen (comp.). 0.01 -0.7 Aluminum 0.5 Rubidium 0.2 Lithium 0.1 Phosphorus 0.001-0.1 Barium 0.05 Iodine 0.05 Arsenic 0.01 -0.02 Iron 0.002-0.02 Manganese 0.001-0.01 Copper 0.001-0.01 Zinc 0.005 Lead 0.004 Selenium 0.004 Cesium 0.002 Uranium 0.0015 Molybdenum 0.0005 Thorium < 0.0005 Cerium 0.0004 Silver 0.0003 Vanadium 0.0003 Lanthanum 0.0003 Yttrium 0.0003 Nickel 0.0001 Scandium 0.00004 Mercury 0.00003 Gold 0.000006 Radium 0.2-3 X 10 1 Sverdrup, H. U., M. W. Johnson 2 Revelle, R., T. R. Folsom, E. D Total in oceans (tons) 2.66 X 10" 1.48 X 10" 1.78 X 10^ 1.23 X 10^^ 5.6 Xio" 5.3 Xio" 9.1 X 10'" 3.9 X 10" 1.8 X 10" 6.4 XIO" 0.028-5.6 Xio^ 2 Xio'^" 0.14 -9.8 X 10" 7 Xio" 2.8 Xio" 1.4 Xio" 0.014-1.4 Xio" 7 X 10" 7 X 10" 1.4 -2.8 X 10" 0.28 -2.8 Xio" 0.14 -1.4 X 10" 0.14 -1.4 X 10" 7 Xio" 5.6 Xio" 5.6 Xio' 2.8 X 10" 2.1 XIO" 7 Xio« <7 Xio« 5.6 XIO' 4.2 XIO' 4.2 XIO' 4.2 XIO' 4.2 X 10' 1.4 XIO' 5.6 Xio^ 4.2 XIO' 8.4 XIO" 28 -420 Nuclide K* Rb^' T J238 U235 Th=== Natural activities Total (tons) 6.3 X 10' 56 Curies 4.6 X 10" 2.7 X 10' 1.18 X 10"^ 8.4 X 10' 2.8 XIO" 3.8 X 10' 2.1 X 10' 1.1 X 10 1.4 XIO' 8 X 10' Ra"" and R. H. Fleming, OCEANS (1942). Goldberg, and J. D. Isaacs (1955). 4.2 X 10^ 1.1 X 10" General Considerations national scientific cooperation will often be essential for optimum results. IV. Chemical Processes and Radioactive Materials Elements in sea water Sea water is a solution of a large number of dissolved chemicals containing small amounts of suspended matter of organic and inorganic ori- gin. The ratios of the more abundant elements are very nearly constant, despite variations in absolute concentrations in different parts of the sea. Lower than average absolute amounts are encountered in coastal areas and near river mouths, while higher amounts are encountered in areas of high evaporation, such as the Red Sea. Vertical variations are usually small; in general, in the open ocean in mid-latitudes, the quantity of dissolved materials, measured by the salinity, first decreases slightly with depth, then increases slowly in the deep water. Table 2 (from Carritt and Harley, Chapter 6) shows the concentrations of some of the ele- ments in solution in sea water at a chlorinity of 19.00^0, which is near average for the sea, and the total amounts in the ocean as a whole. Also shown are the total amounts and total radioactivity of the principal naturally occur- ring radio isotopes. In addition to the listed elements, there are variable amounts of dis- solved gases, including nitrogen, oxygen, and the noble gases. A range of values is given for some elements present in small quantities, such as nitrogen, phosphorus, silicon, iron, and cop- per. These are substances necessary for living organisms, and the inorganic phases may be re- duced to nearly zero in surface waters where they have been almost completely removed by organic uptake. Behavior of introduced materials A number of things can happen to materials introduced into the sea either in solution or as particles. The particles may go into solution. The dissolved substances may be precipitated as particles of colloidal or larger size either by co- precipitation with other elements, by sorption on organic or inorganic particles already present in the sea, or by interaction with other sea water constituents. Both dissolved materials and par- ticles may be ingested by organisms and enter into the biochemical cycles. Particles in the sea are continually removed by settling out on the bottom. The rates of settling depend on the size and density of the particles, as modified by various physical and biological factors. Normal removal of elements from sea ivater The results of geochemical studies provide very approximate estimates of the fractions of some elements supplied to the ocean that are eventually removed from solution. In Table 3 TABLE 3 Geochemical Balance of Some Ele- ments IN Sea Water (From Goldschmidt, Quoted in Rankama and Sahama, 1950, Table 16.19) Amount Total present supplied in ocean Transfer ement (ppm) (ppm) percentage Na ... 16,980 10,560 62 K .... 15,540 380 2.4 Rb ... 186 0.2 0.1 Ca ... 21,780 400 1.8 Sr .... 180 13 7.2 Ba ... 150 0.05 0.03 Fe ... 30,000 0.02 0.00007 Y 16.9 0.0003 0.002 La ... 11 0.0003 0.003 Ce ... 27.7 0.0004 0.001 are listed a number of elements, including some of the elements having long-lived fission-product isotopes, with their concentrations in the supply to the ocean and in the ocean itself. Assuming steady-state equilibrium, the ratio of the con- centration in the ocean to the concentration in the supply, the transfer percentage, indicates what share of the supply stays in solution. Large values of the transfer percentage indicate that a relatively large fraction remains dissolved; small values indicate that relatively much is removed. These data give no information on the re- moval processes or on the time rate of removal. The latter can be obtained from estimates of rates of natural sedimentation together with chemical analysis of sediments or from study of rates of sedimentation of radio isotopes follow- ing weapons tests or waste disposal operations (Carritt and Harley, Chapter 6) . Goldberg and Arrhenius (in press), from a study of natural sediments, have estimated resi- dence times in the ocean for several elements. They conclude that one half the amount of 10 Atomic Radiation and Oceanography and Fisheries strontium present at a given time is deposited in the sediments in about ten million years. For other elements the residence times relative to strontium are roughly proportional to the trans- fer percentages. Thus they estimate that the residence time for iron is of the order of a hun- dred years. Introduction of radioactive materials Radioactive materials in large quantities can be introduced into the sea from reactor wastes, from weapons tests, or in warfare. gradients of specific activity decreasing from the sites of introduction, and depending on the mixing characteristics of the ocean. Nuclear explosions have been the principal source of fission products introduced into the sea to date. The total quantity of fission power from such explosions so far may be estimated at 40 to 60 megatons of TNT equivalent, from the data summarized by Lapp (1956). This corresponds, with 20 kilotons equal to 1 kilo- gram of fission products (Libby, 1956a), to two to three metric tons of fission products. TABLE 4 Fission Product Activity After 100 Days Cooling From 10" Megawatt Hours of Nuclear Power Production i Curies at Specific activity Isotope Half-life Tons (metric) 100 days curies per ton 2 Kr^ 94 y 7.3 3.3 X 10' — Sr"* 55 d 86 2.3 X 10'' 0.128 Sr^ 25 y 463 7.5 X 10'" 0.0042 Y*° 62 h — 7.48 X 10'" 178 Y"' 57 d 111 2.8 X lO'' 6,660 Zr'' 65 d 152 3.2 X 10" — Nb"^ 35 d 161 6.3 X lO'" — Ru'"^ 45 d 46 1.3 X lO'" — Rh"^ 57 m — 1.3 X 10'° — Ru'"" 290 d 35 1.5 X 10" — Rh'"« 30 sec — 5.15X10'° — I'" 8.0 d — 5.2 X 10' 0.0743 Cs"*' 33 y 705 5.63 X 10'° 20.1 Ba"' 2.6 m — 5.1 X 10'° 0.728 Ba"° 12.5 d 2 1.5 X 10" 2.14 La"° 1.7 d — 2.5 X 10" 595 Ce"' 28 d 45 1.5 X 10" 268 Pr'" 13.8 d 2 1.4 X 10" — Ce'" 275 d 490 1.6 X 10'° 386 Pr'" 17 m — 2.4 X 10'° — Pm'" 94 y 7.3 3-3 X 10' — Sm'" 73 y 0.7 2.0 X 10^ — 1 Adapted from data of Culler (1954) and Revelle et al. (1955). 2 Based on tonnage shown in Table 2. In Table 4 is a listing of the important fis- The amount of fission products reaching the sion products, their half-lives, and the quantities sea from nuclear explosions depends on a num- resulting from 10^^ megawatt hours of nuclear ber of factors such as the location of the burst, power production (Carritt and Harley, Chapter the distance above (or below) the surface, and 6). The column "specific activity" shows the the size of the weapon or device. For the ratio of the quantity of radioactivity of a par- smaller devices with a TNT equivalent of ticular isotope to the total amount of isotopes several kilotons, most of the fallout is immedi- of that element in the sea for this amount of ate and local, although an appreciable fraction energy. The specific activity will, of course, remains in the troposphere for a few weeks be lower for smaller amounts of fission. It is (Libby, 1956a, b). Subsurface explosions will also obvious that a uniform specific activity in result in local deposition of a larger fraction of all parts of the sea would be obtained only if the fission products; a deep underwater burst the fission products were evenly distributed, will deposit practically all of the activity locally, Since, under any practical method of introduc- with nearly /, being in the surface layer and tion, this will not occur, there are bound to be about § below (Revelle, 1957). In the case of General Considerations 11 large, megaton devices, half or more of the total fission products are injected into the strato- sphere from which there is a slow leakage into the troposphere (of the order of 10 per cent per year) and subsequent fallout fairly evenly over the entire northern hemisphere, with lesser amounts in the southern hemisphere (Libby, 1956a, b). Of this long-term fallout, up to 71 per cent falls on the oceans, since this is the proportion of the earth's surface covered by them. (The proportion of land to sea is higher in the northern hemisphere than in the south- ern, and since most of the long-term fallout occurs in the northern hemisphere, the amount entering the ocean will be less than 71 per cent.) On the other hand, some of the fallout on the land will eventually reach the sea through land drainage or river runoff. Except in the case of deep underwater bursts, all of the fission products reaching the sea from weapons tests are deposited in the upper layer of the ocean. Removal into the deeper water is relatively slow. Despite the rapid mix- ing within the upper layer by vertical and hori- zontal wind stirring, the products from a large weapon remain in measurable concentrations over many months. A survey made 13 months after the 1954 weapons tests in the Pacific showed low-level activity over a vast area (Har- ley, 1956). Radio isotopes in fallout on the land remain largely in the upper few inches of the soil. Fall- out on the sea, on the contrary, is rapidly dif- fused through the upper mixed layer, some 75 meters deep on the average. Consequently, for conditions of equal fallout, the concentrations of radio isotopes in the part of the sea from which they are taken up by man's food organ- isms are less than in the soil. Thus, even though the calcium concentration of sea water is lower than in most soils, the ratio of stron- tium 90 to calcium in the marine environment is now much less than in agricultural lands of the mid-western United States. In 1955 (Libby 1956b) these soils contained about .025 micro- curies of strontium 90 per kilogram of calcium available to growing plants. Revelle (1957) has calculated that for an equal amount of widely distributed fallout (from approximately 25 megatons TNT equivalent of fission) about .00015 microcuries of strontium per kilogram of calcium would be present in the upper mixed layer of the sea, half of one percent of the amount in soils. In addition to fission products, neutron ir- radiation of elements in the environment im- mediately after the detonation produces other radioactive isotopes. With ordinary land or marine materials, the amounts of this neutron- induced radioactivity are small (Libby, 1956a). However, soon after the 1954 tests in the Pacific, quantities of zinc 65 were discovered in marine fishes, and subsequently cobalt 60 was recovered from clams in the Marshall Islands. These isotopes probably originated from neu- tron irradiation of metals, other than the fis- sionable materials, in the test device. Comparison of table 2 and table 4 demon- strates that the mass of radioactive isotopes in- troduced into the sea from weapons tests, or which might be introduced from disposal of waste products, will be very small compared with the amounts of their normal isotopes al- ready present. The introduction of the radioac- tive material does not, therefore, appreciably modify the chemical and physical properties of normal seawater, so that the chemistry of the introduced radioactive substances is the same as for the corresponding non-radioactive isotopes in the sea. Introduced radioactive isotopes will partition into a soluble and an insoluble fraction. The physical states of a given element under equi- librium conditions depend upon whether or not the solubility product of the least soluble com- pound has been exceeded. Since the ionic ac- tivities of the elements in the complex chemical mixture that is sea water are not accurately known, it is difficult to attack this problem from theory. Greendale and Ballou (1954) have de- termined the distribution among soluble, col- loidal, and particulate states of important fission product elements by simulating the conditions of an underwater detonation; their results are given in Table 5. Elements of Groups I, II, V, VI and VII usually occur as ionic forms, while other elements, including the rare earths, occur as solid phases. Some of these results have been confirmed by field observations following weap- ons tests (see Chapter 6 of this report by Carritt and Harley, and Chapter 7 by Krumholz, Gold- berg and Boroughs). Those elements in Table 5 that have sufficiently long half-lives to con- tribute a significant share of the total activity after one year of decay are marked with an asterisk. Cesium 137 and strontium 89 and 90 12 Atomic Radiation and Oceanography and Fisheries remain in solution, while ruthenium 106, cerium 144, zirconium 95, yttrium 90 and 91, and niobium 95 are largely in the solid phase. The solid fractions, whether they be chemi- cal precipitates or solids produced by accumula- tion in the bodies of organisms, will tend to settle out. As they settle, they may encounter environmental conditions which will prevent or hinder deposition. There will be, however, some net transport toward the deeper water and the bottom from the settling process. Because of biological uptake, the removal of the par- TABLE 5 Physical States of Elements in Sea Water 1 (From Greendale and Ballou, 1954) Percentage in given physical state Element Ionic Colloidal Particulate Cesium * 70 7 23 Iodine 90 8 2 Strontium * 87 3 10 Antimony 73 15 12 Tellurium 45 43 12 Molybdenum 30 10 60 Ruthenium * 0 5 95 Cerium * 2 4 94 Zirconium * 1 3 96 Yttrium * 0 4 96 Niobium * 0 0 100 1 Elements introduced by simulated underwater detonation of atomic bomb, Greendale and Ballou, 1954. * Indicates element has important fission product isotope. tides from the upper layers of the sea may be quite slow. For example, cerium 144, a rare earth which has a half-life of 275 days, and which is present in the sea primarily in particu- late form, and its daughter Pr 144 were found to account for 80 to 90 per cent of the activity in plankton samples from the upper layer taken in the Pacific by the TROLL survey 1 3 months after weapons tests (Harley, 1956). A very rough idea of the reduction in ac- tivity that would eventually be obtained by removal from the ocean can be gained from the transfer percentages of Table 3. The fraction of an introduced fission product remaining in the sea will, at equilibrium, be equal to or greater than the transfer percentages for the correspond- ing element. (The transfer percentage reflects, in part, retention on land as well as sedimenta- tion from the sea.) An important factor is the time required for equilibrium to be reached ; if it is very long in relation to the half-life of the element in question, reduction of activity may be negligible. The long-lived and danger- ous isotope, strontium 90, has a relatively high transfer percentage and a long equilibrium or "residence" time; the same would be expected for cesium 137, which is an alkali and should behave somewhat like potassium or rubidium. Disposal of atomic wastes by deep sea burial in various sorts of packages has been proposed. Dispersion of the activity would then be by slow diffusion from concreted wastes, or would be delayed until rupture of an impermeable container occurred. Because the deep ocean sediments have appreciable exchange capacities, much of the wastes would be retained in this highly absorptive environment. The upper lay- ers of the sediments would, presumably, tend to become saturated, and the further removal of radioactive elements by exchange or absorption would be controlled by the rate of diffusion into the deeper sediments. There are wide gaps in our knowledge of many of the processes mentioned above. These, and suggestions for research needed to fill them, are discussed by Carritt and Harley (Chapter 6) . Much of the required information can be ob- tained by the use of radioactive tracers, intro- duced in weapons tests and experimental waste disposal operations, as well as in purposive experiments. V. Physical Processes and Radioactive Materials Physical structure of the sea The physical properties of sea water of im- portance to the present study are functions of temperature, salinity, and pressure. The tem- perature ranges from about 30° C to about — 2 ° C, which is the initial freezing point. The highest temperatures occur at the surface or in the mixed near-surface layer; below this the temperature decreases to about 5° C at 1,000 meters and to 1° to 2° at greater depths. In the deepest parts of the ocean there is a slight increase of temperature due to adiabatic heat- ing. Hydrostatic pressure increases about one atmosphere for each 10 meters of depth. In the open ocean in mid-latitudes the salinity gen- erally decreases slightly with depth in the upper few hundred meters, then increases slowly. In high latitudes the salinity normally increases with depth throughout the water column. General Considerations 13 The density of sea water increases with de- creasing temperature and with increasing sahnity and pressure. Except in quite dilute sea water, the temperature of maximum density is lower than the freezing point. The range of density in the open sea is between about 1.02 and 1.06. It may, of course, be lower in inshore waters in the vicinity of river mouths. At constant pressure the major changes in density in the sea are associated with temperature, so that to a first approximation the change of density (com- puted for constant pressure) with depth is in- versely proportional to the change of tempera- ture. Many processes in the sea depend on the density distribution. The ocean basins are largely filled with water of relatively high density formed in high latitudes ; overlying this dense water in middle and low latitudes, and separated from it by the pycnocline, is the sub- surface mixed layer, varying from a few meters to several hundred meters in thickness but averaging about 75 meters, of water of high temperature and low density. The relative rate of change of density with depth may be taken as a measurement of the vertical stability of the water (Sverdrup, Johnson and Fleming, 1942, p. 417). Stability in the region of the pycnocline is much higher than above or below it, so that exchange of water across it tends to be small. All parts of the ocean and its bordering seas are in communication with each other, and are in continuous motion. The rates of movement, however, differ greatly in different areas. Thus, although there is eventual complete interchange of water between all oceans and seas, some parts are partially isolated from others, the exchange between these parts being much slower than within them. Near-surface currents and mixing within the upper layer Currents in the upper, mixed layer of the sea are primarily generated by winds, and, con- sequently, the major horizontal surface currents of the ocean correspond to the field of wind stress (Munk, 1950). The average locations and velocities of the important surface currents are well known from numerous observations of merchant ships and research vessels, and appear on many charts. The velocities and volume transports of the major near-surface currents are large. For ex- ample, the mean speed of the Florida Current is about 193 cm/sec. and of the Kuroshio about 89 cm/sec. The volume of water flowing through the Florida Straits in 15 years is equal to the volume of the upper 500 meters of the whole North Atlantic, and the transport of wa- ter by the Kuroshio between the Northern Ryukus and Kyushu in 50 years is equal to the upper 500 meters of the whole North Pacific. Because of the large surface currents, intro- duced materials tend to be carried away from the sites of introduction to other parts of the upper mixed layer of the sea. Thus, no area of surface water in the ocean is isolated for long periods from the remaining areas. The currents are not steady streams, but have a complicated fine structure, with many eddies, jets, and filaments. In consequence of this turbulence, on both large and small scales, dis- solved materials in seawater are rapidly dis- persed horizontally. The rate of dispersion is about a million times the rate of molecular dif- fusion, and depends on wind speed, current shear, vertical and horizontal density gradients, direction of dispersion, and the dimensions of the area considered. Because of this large num- ber of variables and the lack of knowledge of turbulent processes, it is not possible to predict accurately the horizontal dispersion in particular areas. If even moderately precise values are re- quired, experiments must be conducted in the area of interest. Some of the results of such studies are reported by Wooster and Ketchum (Chapter 4) . The rate of vertical diffusion in the upper, mixed layer, although much less than that for horizontal dispersion, is nevertheless about a thousand times greater than molecular diffusion. The extent of vertical stirring in the upper layer depends on the magnitude and uniformity of the wind stress and on the vertical density gra- dient. Convective processes, and, in coastal areas, strong tidal currents, also contribute to vertical mixing. The mixing rate in the upper layer has been measured by changes in the ver- tical distribution of radio isotopes following weapons tests. Revelle, Folsom, Goldberg, and Isaacs (1955) report that in one such test the lower boundary of the radioactive water moved downward at about 10"^ cm/sec. until it reached the thermocline, where it abruptly stopped. 14 Atojjik Radiation and Oceanography and Fisheries Circulation and mixing within the intermediate and deep layer Within the pycnodine and for some distance below it, it is believed that most of the motion takes place along surfaces of constant potential density, so that transport and diffusion in the lateral direction are very much greater than in the vertical. This belief has been confirmed by experiments with radioactive tracers, reported by Revelle, Folsom, Goldberg, and Isaacs (1955), in which it was shown that the radioactive wa- ter spread out over an area of about 100 square kilometers while maintaining a thickness of the order of a few meters. Much of our knowledge of deep and inter- mediate currents has been inferred from the distributions of properties. These indicate that the average velocities of the deep currents are only a few cm/sec. or less. However, Wiist (1957) has recently made calculations on data from the Atlantic which indicate velocities of meridional currents of 3 to 17 cm/sec. in the deep sea, along the western margin of the west- ern trough, in depths between 3,000 and 5,000 meters. The calculated currents on the eastern side of the deep South Atlantic, especially in the region of the Angola Basin were, on the contrary, very weak. Dietrich (1957) has like- wise computed mean current velocities of about 10 cm/sec. for the deep Antarctic Circumpolar Current, and for the Subarctic Bottom Current in the northern North Atlantic, the latter in- creasing to as much as 40 cm/sec. when flow- ing across the Greenland-Scotland ridge. He states, however, that in the largest part of the ocean the bottom currents are below 2 cm/sec. Direct measurements of deep currents are technically difficult. The few successful meas- urements summarized by Bowden (1954) show mean velocities from less than a cm/sec. to 13 cm/sec. Recently Swallow (1955 and unpub- lished data) has measured subsurface currents by tracking a neutrally buoyant float at a fixed depth. His measurements in the North At- lantic give mean resultant velocities of 1.7 to 9.1 cm/sec. Tidal currents of about 10 cm/sec. have been obtained by Swallow and others in deep water. It appears that the mean current in many parts of the deep sea may be less than the periodic variable currents. The turbulence of these variable tidal cur- rents, especially near the bottom, contributes to vertical and horizontal mixing in deep water. Mixing should also occur along the boundaries of the rapid deep resultant currents indicated by Wiist and Dietrich, where there must be con- siderable shear. Dietrich (1957) also suggests that horizontal spreading of near-bottom water may occur in regions of turbidity currents, which occur es- pecially on the continental slopes. Exchange between the open sea and coastal areas In coastal areas and estuaries where precipita- tion and land runoff exceed evaporation, there is a net seaward drift of dilute surface water and an inshore drift of sub-surface water from the open sea. This is superimposed on the flow of wind-driven currents through the coastal areas. Some idea of the average time involved in interchange of coastal waters can be obtained from the volume in and transport through vari- ous areas along the American Atlantic seacoast. Calculations give a mean age of 2^ years for the waters over the Continental Shelf from Cape Hatteras to Cape Cod, about 3 months for the Bay of Fundy, and 3 to 4 months for Delaware Bay (Wooster and Ketchum, Chapter 4) . Exchange between the deep and intermediate layers and the mixed subsurface layer Evidence of local cross pycnocline interchange was obtained from measurements of the vertical distribution of radioactivity following the 1954 Pacific weapons tests (Japanese Fishery Agency, 1955 and Harley, 1956) ; it is not, however, clear whether the observed phenomena were en- tirely the result of physical exchange of the wa- ter and its contents or were in part due to settling of particles and to biological transport. The major exchange between the near-surface and deeper waters takes place in the following regions : In areas where the pycnocline is maintained, by the distribution of mass related to the gen- eral circulation, at a sufficiently shallow depth to be eroded away by wind stirring. Such areas exist near the equator, along the north edge of the Equatorial Counter Current, and at the centers of strong cyclonic eddies. In regions of upwelling, where vertical cur- rents carry water toward the surface and stir the surface and intermediate layers. Water from as deep as about 500 meters may be General Considerations 15 brought to the surface by this process. Upwell- ing occurs along the western coasts of continents in intermediate and low latitudes, wherever the wind-driven circulation removes surface water from the coast. This water is replaced by deeper water moving upward. Such coastal upwelling has been found to be of the order of 1 to 3 meters per day. Upwelling also occurs in mid- ocean where there are surface current diver- gences, most notably along the equator in the eastern and central Pacific. In regions of surface convergence, where sinking waters may extend to the oceanic depths, or may spread out at intermediate levels, ac- cording to their density. In tropical and tem- perate latitudes such sinking is confined to the upper few hundred meters, but at high latitudes the waters may reach great depths. Indeed, it is in the convergence regions of high latitudes that much of the intermediate and deep water of the oceans are formed. In regions where increase of surface density by evaporation, freezing out of ice, or cooling, causes the surface waters to sink and be replaced by the formerly deeper water. Deep thermal convection occurs in high latitudes and extends in some areas to the bottom ; for example, Ant- arctic bottom water is formed in the Weddell Sea by the cooling and sinking of the surface waters, and the Atlantic deep water is formed in a similar manner east of Greenland. Haline convection takes place in regions where evapora- tion exceeds precipitation or where freezing prevails over melting. The latter in high lati- tudes increases the intensity of the thermal convection. Haline convection in winter is re- sponsible for the characteristics of the deep water of the Mediterranean Sea. This water flows out into the North Atlantic at depths of 1,000 to 1,500 meters, and can easily be identi- fied even on the western side of the ocean. The exchange between the surface layer of the ocean and the deeper layers may be either continuous or discontinuous. Some idea of the rate of exchange can be obtained from various estimates of the "age" or average residence time of the water in the deeper layers. These es- timates, which differ widely depending on the data and assumptions used, have been sum- marized by Wooster and Ketchum (Chapter 4 of this report) and by Craig (Chapter 3) . Three estimates for the water in the inter- mediate layer of the Atlantic Ocean give resi- dence times between 7 and 140 years. Estimates for the water below 2,000 meters vary from 50 to 1,000 years. An estimated upper limit based on the measured heat flow through the sea floor under the Pacific Ocean indicates that the Pacific deep water is replenished in less than 1,000 years. The deep water in the Pacific may be older than in the Atlantic because of the larger volume of the Pacific. EXCHANGE FROM CONFINED BASINS The few data available for estimating the age of water in confined basins have been considered by Wooster and Ketchum (Chapter 4). These indicate that the mean residence time of water in the Mediterranean Sea is about 75 years. In the Caribbean Sea the mean age cannot be less than 6 years and, in the deeper part, may be as much as 140 years. The deep waters of the Black Sea apparently remain isolated for very long periods. Transport considerations lead to an estimated age of at least 2,500 years, while, from consideration of phosphorus accumulation, the age has been estimated at 5,600 years. VI. Biological Processes and Radioactive Materials Uptake and accumulation of elements in organ- isms Organisms take up from their environment and their food and incorporate into their bodies those elements required for their maintenance, growth, and reproduction. The proportion of various elements required by the organisms are different than the proportions in the environ- ment, and this results in concentrations of some elements in the biosphere. The energy that drives the whole life cycle is the energy of sunlight. This energy is bound chemically in organic compounds by the photo- synthesis of plants, and is passed along, through the food chain, in the food of all the organisms beyond the plants. The flux of energy, and hence the flux of carbon, through the various trophic levels measures the productivity of the organisms at each level. Since the efficiency at each stage of the chain is low (of the order of 10 per cent to 30 per cent) the flux decreases at each step. The standing crop, or biomass, of organisms at the different levels, or, in other words, the amount of carbon present in the or- ganisms at each level, may be greater or less 16 Atomic Radiation and Oceanography and Fisheries than the amount at the next lower level, de- pending on the rates of turnover of the popula- tions involved. In addition to the abundant elements carbon, oxygen and hydrogen, the bodies of organisms contain a number of elements in smaller amounts, such as nitrogen, phosphorus, calcium, strontium, copper, zinc, and iron, which are essential to the life processes. These may be ob- tained by organisms above the plants in the food chain either from their ingested food, or by direct uptake from the sea water. Since the requirements for different elements are different in different kinds of organisms, the fluxes of the of the populations of a particular part of the sea, and any quantities added will be soaked up by the biosphere very rapidly. Both dissolved and particulate materials can be taken up from the environment. Iron, for example, occurs in the sea almost entirely in particulate form and is used in that form by diatoms. Fishes can take up ionic calcium and strontium directly from the sea water. Observa- tions in conjunction with weapons tests, re- ported in Chapter 7 of this report, have shown that particulate feeders among the zooplankton ingest particles of inorganic compounds and retain them. TABLE 6 Approximate Concentration Factors of Different Elements in Members of the Marine Biosphere. The Concentration Factors Are Based on a Lfve Weight Basis (From Krumholz, Goldberg and Boroughs, Ch. 7 of This Report) Concentration factors Concentration Form in in sea water Element sea water (micrograms/1) Na Ionic 10' K Ionic 380,000 Cs Ionic 0.5 Ca Ionic 400,000 Sr Ionic 7,000 Zn Ionic 10 Cu Ionic 3 Fe Particulate 10 Ni * Ionic 2 Mo lonic-Particulate 10 V ? 2 Ti ? 1 Cr ? 0.05 P Ionic 70 S Ionic 900,000 I 50 * Values from Laevastu and Thompson (1956). various elements are variable from one to an- other, and at different trophic levels. The concentration factors of some of the im- portant elements in different kinds of organ- isms are tabulated in Table 6, taken from Krum- holz, Goldberg and Boroughs (Chapter 7 of this report). Certain elements, for example, sodium, occur in some organisms at lower con- centrations than in the water; they are selected against. On the contrary, those elements, such as phosphorus, that are essential to the organ- isms but occur in low concentration in the sea water, are concentrated by several orders of magnitude. In some parts of the sea, the phos- phorus may be nearly completely removed from the water by the organisms. Such elements are often limiting constituents for further increase Algae Invertebrates Vertebrates (non-cal- careous) Soft Skeletal Soft Skeletal 1 0.5 0 0.07 1 25 10 0 5 20 1 10 10 10 10 1,000 1 200 20 10 1,000 1 50 100 5,000 1,000 1,000 30,000 100 5,000 5,000 1,000 1,000 20,000 10,000 100,000 1,000 5,000 500 200 200 100 0 10 100 20 1,000 100 20 1,000 1,000 40 300 10,000 10,000 10,000 40,000 2,000,000 10 5 1 2 10,000 100 50 10 The uptakes of various elements by organ- isms are not entirely independent of one an- other. Elements of similar chemical properties tend to be taken up together very roughly in the same proportions as they exist in the environ- ment. This is true, for example, of calcium and strontium. Sometimes one element has an in- hibiting effect on another. There can also be synergistic effects, such as the enhancement of phosphorus uptake of diatoms by increased concentration of nitrogen. Certain elements are deposited, in large part, in particular organs. Perhaps the best known examples are the deposition of iodine in the thyroid glands of vertebrates, or the deposition of calcium and strontium in the bones of verte- General Considerations 17 brates and in the shells and other hard parts of invertebrates. The length of time an organism retains the average atom of a given element varies greatly from one element to another. This is some- times measured as the biological half-life, al- though the relative rate of loss is not a simple linear function of time as is the case with radio- active decay. Much is known about the reten- tion times of different elements in man (see, for example. Handbook 52 of the National Bureau of Standards, 1953), but there are few data for most marine organisms. The rate of excretion of an element and the amount ulti- mately retained, will be quite different if the element is taken up quickly from a single dose or is taken up slowly over a long time. The processes of uptake, accumulation, and loss of elements by marine and other aquatic organisms, are discussed in more detail by Boroughs, Chipman and Rice (Chapter 8 of this report), Krumholz, Goldberg, and Boroughs (Chapter 7), and by Krumholz and Foster (Chapter 9). Effects of organisms on spatial distributions of elements in the sea Those elements of which a large proportion is cycled through organisms are modified pro- foundly in their spatial distributions by the ef- fects of the biosphere, so that they are quite differently distributed in the sea than elements in which the distribution is determined only by physical and inorganic chemical processes. We have already mentioned phosphorus as a notable example. Ketchum (Chapter 5 of this report) has written a detailed discussion of the general effects of the ecological system on the distribu- ticfti of elements in the sea. The marine biosphere acts as a reservoir for those elements that are removed selectively from sea water by organisms. This reservoir is not stationary in space, however, because many of the living organisms make both vertical and horizontal migrations of large extent, while their dead bodies and fecal materials continu- ally fall toward the bottom under the influence of gravitation. The effects of the living reser- voir in the distribution of elements vary not only from one part of the sea to another, but also seasonally in the same area. Because organisms in the sea are more abun- dant in the upper layers than deeper down, those elements in scarce supply that are essen- tial to life tend to be retained by the biosphere in the upper layers and to be returned to solu- tion in the deeper layers. Stationary popula- tions, such as attached benthic organisms, act as a fixed reservoir. Where there are currents at different levels in opposite directions, the accumulation of ele- ments by pelagic organisms, together with grav- ity effects on their dead bodies and fecal ma- terials, can result in local concentrations of ele- ments at intermediate depths greater than the concentrations in either the overlying or the deeper waters. This pattern, as noted by Ketchum, is common in estuaries, continental shelves, and in the vicinity of coastal upwelling. Migration of organisms may result in a net transport of elements from areas of high con- centration to areas of lower concentration. Thus, for example, the vertical migrations of the or- ganisms of the deep scattering layer can result in a transport from the deeper layers into the upper mixed layer. Salmon which spawn and die in fresh waters after accumulating elements in the sea can transport significant quantities of some elements from the sea to fresh waters. Finally, the remains of organisms, falling out as particulate matter, are an important com- ponent of the sedimentation process in the deep sea, and are thus important in the geochemical cycle, as noted by Carritt and Harley (Chapter 6) and others. Although we have some understanding of the various processes involved, data for making useful quantitative assessments are almost en- tirely lacking. Effects of introduction of radioactive elements Since the isotopes of most chemical elements are similar in chemical behavior, it can be as- sumed that organisms do not appreciably dis- tinguish between the radioactive and non-radio- active isotopes, and that, to a good degree of approximation, the path of a radioactive element through the biological system is the same as that of its non-radioactive isotopes. The accumulation of radio isotopes in organ- isms will, therefore, depend on the same factors as the accumulation of normal isotopes (their concentration in the water where the organisms are located, the concentrations of other elements by which uptake is influenced, the size of the population of organisms concerned, the concen- 18 At0777'ic Radiation a?7d Oceanography and Fisheries tration factors of the organisms for each ele- ment, and the rates of excretion, and in addition will depend on the decay rates of the radioactive isotopes) . The most important radio isotopes from the standpoint of accumulation in organisms are, therefore, those which are concentrated in large degree by organisms, are retained by them for relatively long periods of time, and have slow decay rates. An additional consideration from the standpoint of human hazards is the uptake and biological half-life of the elements in hu- mans who may consume the marine organisms as food. The most important fission product from all these considerations is strontium 90 and its daughter yttrium 90. This isotope has a large fission yield and a long physical half-life, is concentrated by organisms, and can be tolerated in human food only in very low amounts. Ce 144 is another isotope with a large fission yield, which is concentrated by organisms (Har- ley, 1956), and has a moderately slow decay rate. Due to its small uptake and low retention by humans, it can, however, be tolerated in human food in much greater concentrations than Sr90. Zn 65 and Co 60, although not fission prod- ucts, are sometimes produced in relatively large quantities in weapons tests. They are concen- trated by very large factors in fish and mollusks used for human food, but fortunately they possess a relatively high tolerance level in humans. Because of its biological role both in marine organisms and in humans, strontium 90 dom- inates consideration of depositing mixed fission products in the sea. For other radioactive wastes, and for mixed fission products from which Sr 90 has been removed, other elements will be the critical determinants, but in most cases, prior removal of Sr 90 will permit the safe disposal in the sea of larger quantities than would otherwise be possible. The safe quantity of fission products depends on the concentrations that reach man's food or- ganisms. The quantity will be greater if sites of introduction are chosen to give either long periods of isolation of the wastes or high dis- persion (and thus low concentration) of the fractions that come into the environment (both physical and biological) of human food organ- isms. Somatic and genetic effects on marine organisms It is sometimes suggested that sufficient quan- tities of radioactive elements may be accumu- lated by marine organisms to endanger their populations, either by direct somatic effects or through genetic changes. Some aspects of this problem are discussed by Donaldson and Foster in Chapter 10 of this report. So far as somatic eflFects are concerned, ex- perimental data indicate that primitive forms are more resistant to ionizing radiation than the more complex vertebrates. It has not been possi- ble to demonstrate any large-scale radiation damage to marine populations in the vicinity of large weapons tests. Levels of radiation safe from the standpoint of human hazards are also probably safe for the populations of marine organisms that are used as human food. By analogy with results from genetic studies on laboratory animals, it may be inferred that significant genetic population effects will occur in marine organisms at much lower levels of radiation than will produce somatic effects. These genetic effects might be related to the in- crease in amount of total body radiation above the natural background. As shown by Folsom and Harley (Chapter 2), the normal radiation background of organisms in the deep sea is very low, so that appreciable quantities of radioactive wastes would significantly increase the radiation received by them. Craig (Chapter 3) has shown that the deposition of 1,000 tons per year of fission products in the deep sea would, at secular equilibrium, almost triple the average radiation level in the deep water. This could, conceivably, result in genetic effects in the marine popula- tions in these waters, which might seriously up- set the ecological system of the oceans. At the present state of knowledge, however, this is pure speculation. The matter does require, nevertheless, serious investigation. VII. Predicted Effects of Introduced Radioactive Materials Prediction of the effects of the introduction of radioactive materials into the different do- mains of the oceans must take into account the various physical, chemical, and biological proc- esses discussed above. While our knowledge of these processes is very imperfect, we can make rough evaluations of the effects of disposal of fission products in different parts of the sea. Because of the limitation of knowledge, these General Considerations 19 evaluations must, of necessity, be conservative. Under some circumstances this necessity could involve considerable cost to society. Those sites and methods of disposal, both on the land and in the sea, that provide the least hazard may also involve the greatest disposal costs, so that, to the extent we must include a safety factor be- cause of ignorance, there can be economic loss. In disposing of radioactive materials in the sea, we aim at two things: (1) isolation of the materials, so that their entry into the part of the sea and its contents used by man is limited, (2) dispersal of the materials that do enter the domain important to man, to keep the concen- trations of radioactive elements at tolerable levels. Depending on the quantity of materials to be dealt with, we may need to consider either or both of these possibilities. Introduction in the upper mixed layer Radioactive materials introduced into the up- per mixed layer will, because of the rapid transport and large horizontal and vertical mix- ing within this layer, be carried away from the site of introduction and rapidly dispersed. Dis- persion may be more rapid in coastal areas than in the open sea, but in some situations there may be a net transport inshore, particularly in or near estuaries, if the materials are introduced below the surface. Direct evidence of near-surface transport and dispersion of fission products in the open sea has been obtained by the surveys of the "Shunkotsu Maru" (Miyake, Sugiura and Kameda, 1955) and the "Taney" (Harley, 1956), respectively four and thirteen months after the Pacific weap- ons tests of March 1954. The indicated trans- port of these products was in good agreement with current velocities measured by conven- tional means. These data from the open sea and earlier measurements on the partially confined waters of Bikini Lagoon (Munk, Ewing and Revelle, 1949) demonstrate the rapid dispersal of fission products in the surface layer. Dispersion in an inshore situation (the Irish Sea) was measured with fluorescein by Selig- man (1955) as a preparatory study for the dis- charge of low-level wastes from a power reactor installation. Subsequent experience with libera- tion of the radioactive wastes (Anon., 1956) confirmed that they were rapidly dispersed. Radioactive materials introduced into coastal waters enter directly into that part of the ocean most utilized by man, from which he removes the greater share of his harvest of marine food organisms. The sessile algae, bottom living in- vertebrates, and fishes of these waters heavily concentrate certain of the elements, such as strontium, cesium, zinc, and cobalt that has radioactive isotopes most hazardous to man. While dispersion due to physical transport and dispersion in these waters is high, they are usually shallow, so that the volume is limited and there can also be considerable accumula- tion in shallow bottom sediments from which the isotopes can be again taken up by man's food organisms. In some coastal areas the combination of physical and biological processes can result in local concentrations of radioactivity in the wa- ters themselves (Ketchum, Chapter 5 ) . Because of the above considerations, the quantity of radioactive materials that can be in- troduced safely into coastal waters near shore is very limited, of the order of a few hundred curies per day. The particular physical, chemi- cal, and biological factors vary so widely from one coastal area to another, that careful study is required to determine the safe amount in any particular locality, and continuous monitoring should be conducted to guard against efi^ects of unforeseen variability in environmental factors. The rather low level of discharge of radioac- tive products that can be tolerated in coastal waters imposes the necessity of providing ade- quate safeguards against discharge of high-level atomic wastes from accidents to power reactors, either at locations on the shore or shipborne reactors. The quantity of radioactive material that can be safely deposited in the mixed layer in the open sea depends on such local characteristics as the direction and rate of transport, the rate of horizontal dispersion, the rate of uptake by organisms, and the contiguity of fishing areas. However, in general, the quantities will be much greater than those permissible for coastal waters. An idea of the order of magnitude of mixed fission products that can be safely intro- duced in a fairly typical situation is given by the results of weapons tests in the Pacific where a quantity of mixed fission products of the order of half a ton was introduced into the mixed layer in a short time period. That this was near the limit of safety is evidenced by the capture in adjacent areas of specimens of tunas and other fishes with sufficient radioactivity to be doubt- 20 Atomic Radiation and Oceanography and Fisheries ful for human consumption (Kawabata, 1956, and Hiyama and Ichikawa, 1956). Deep water introduction The only place in the ocean in which we can be confident at this time that radioactive wastes of the order of some tons a year can be safely deposited is in the depths of the sea. Knowl- edge is, however, insufficient to determine whether radioactive materials of the order of the expected production from power reactors in the next few decades could be disposed of in this way. Radioactive materials introduced into the deeper layers will be partially isolated from the upper layer for time periods related to the resi- dence time of the water in the deeper layer. During this time there will be a decrease of radioactivity due to decay, and dilution due to dispersion. Since, as we have noted above, the residence times are variable in different depths and different locations, a much greater time of isolation will be obtained in some places than others. The longest average time of isolation will be obtained in deep nearly enclosed basins such as the Black Sea. It has been suggested by Wiist (1957) that there may also be a long isolation period in the abyssal trenches of the central equatorial regions, such as the Romansch Deep or the Tonga Trench, but no data on currents in these deeps are now available. Craig (Chapter 3 of this report), assuming an estimated average residence time in the deep sea of 300 years, the introduction into the deep sea of 1,000 tons per year of fission products after 100 days cooling, and complete uniform mixing within the deep water, has calculated the activity in the deep and surface layers at secular equilibrium. This calculation indicates that the total fission product activity in the mxed layer would be about equal to that at present from natural sources (primarily K*°) . The concentra- tion of Sr 90 would, however, be about 6.5 x 10"^ microcuries per liter, or 0.16 microcuries per kilogram of calcium in solution in sea water. Studies of the uptake of strontium by marine fishes indicate a discrimination against strontium with respect to calcium approximately by a fac- tor between 3 and 10. Thus for human popula- tions such as the Japanese (Hiyama, 1956), in which much of the dietary calcium is obtained from marine fishes (including the bones and skin of some species), the amount of strontium 90 ingested per unit weight of calcium would be of the order of .04 microcuries per kilogram of calcium. A human population that obtained all its calcium from marine fishes after equilib- rium was established with about 1,000 tons of fission products per year (1.1 x 10^ megacuries of strontium 90) in the deep sea would have a burden, primarily in the bones, of approxi- mately .005 microcuries of strontium 90 per kilogram of calcium. This is 5 per cent of the maximum permissible concentration for the population at large, estimated by the National Bureau of Standards (1955). Weapons tests resulted in an average amount of .025 microcuries of strontium 90 per kilo- gram of calcium available to growing plants in the United States in 1955. By 1970, the amount will be .08 microcuries per kilogram of calcium even in the absence of further weapons tests (Kulp, Eckelmann, and Schulert, 1957). Be- cause of discrimination against strontium with respect to calcium in food grains and grasses, and the additional discrimination in cows' milk and in human beings, it is expected that by 1970 an average of about .002 microcuries of strontium 90 per kilogram of calcium will exist in the United States population, 2 per cent of the maximum permissible concentration. From the above considerations it is uncertain whether reactor-fuel wastes of the order of 1,000 tons a year could be deposited safely in the deep sea. Craig's calculation is most useful in orienting our thinking, but is, of course, very much oversimplified. No account is taken of the removal of activity from the sea by sedi- mentation. On the other hand, it does not take into account any biological transfer of material across the pycnocline, nor can we assume that effective concentration of Sr 90 per unit weight of calcium for some commercially important or- ganisms will not be greater than the values we have taken. Moreover, such a calculation assumes even distribution of the radioactive materials through- out the deep layer. This could only occur if they were evenly distributed when introduced, or if there were uniform and complete mixing in all parts of the deep layer. A priori we should expect that neither the physical circulation and mixing in the deep sea nor the transfer between the deep layer and the mixed layer would be uniform. There is General Considerations 21 some evidence, however, from carbon 14 meas- urements made by the Lamont Geological Ob- servatory that in fact fairly complete mixing occurs within the deep sea during the average residence time of a water particle. Another calculation, based on very conserva- tive assumptions concerning the mixing proc- esses, was made in the report of a meeting of scientists from the U.S. and U.K. (Anon., 1956). It was assumed that fission products deposited on the ocean floor in mid-latitudes would drift and disperse for at least 10 years before surfacing, at which time the contami- nated area would be a disc about 2 km. thick and 70 km. in diameter, which would be sub- sequently dispersed throughout the surface layer. Repeated deposits of 1 megacurie of Sr 90 (0.4 tons of mixed fission products) made at the rate of ten per year would result in an average con- centration of Sr 90 of not over 10'^ microcuries per liter in the mixed layer, or .025 microcuries per kilogram of calcium. Although we cannot say at this time with any precision what quantities of reactor-waste prod- ucts can be safely deposited in the deep sea, it appears certainly safe to employ quantities up to a few tons a year in careful experimental studies. It is not impossible that 1,000 tons a year can be safely disposed of in deep, isolated basins where the residence time is much greater than the 300-year average estimated for the deep sea generally. For quantities of the order of 100 tons a year or more, effects on the animal popu- lations of the deep sea, and resulting effects on the whole ecology of the sea could become im- portant; as to this no information is at present available. VIII. What We Need to Know Our knowledge of most of the processes in the oceans is altogether too fragmentary to per- mit precise predictions of the results of the in- troduction of a given quantity of radioactive materials at any particular place. In order to obtain the necessary knowledge, an adequate, long-range program of research on the physics, chemistry, and geology of the sea, and on the biology and ecology of its contained organisms is required. Such research must be directed toward the understanding of general principles, not simply to the ad hoc solution of a particu- lar local problem for immediate application. The latter sort of study is, of course, desirable in order to provide engineering solutions to par- ticular waste-disposal problems as they arise. Such engineering solutions must necessarily be of limited application and, moreover, they must always be conservative, at least until sufficient broad understanding is obtained. MAJOR UNSOLVED PROBLEMS Some of the major basic problems that should be included in the research program can be briefly outlined: 1 . Dispersion in the upper mixed layer Fairly extensive information is available on the mean velocities and transport of the major surface currents. The transient currents and eddies that result in dispersion in both the hori- zontal and vertical directions are, on the con- trary, not understood. Some empirical param- eters approximately describing the relationships of diffusivity to time and to size of area have been developed, but understanding of the de- tailed physical principles is lacking. In con- sequence, it is not possible to predict on the basis of more elementary properties the disper- sion of materials introduced into the upper layer at a given point. Direct measurements must be made, and these are costly and not necessarily reliable. Basic research on the turbulent motion of water in the upper layer is needed. 2. Circulation in the intermediate and deep layers For the region of the sea below the surface layer, we not only do not understand the nature of the turbulent motion, we do not even have a description of the mean currents. The chart- ing of the deep currents, and investigations toward elucidating the physical principles in- volved should be vigorously pursued. 3. Exchange between the surface layer and deeper layers It is important to determine the average rate of exchange of water between the surface and the deep layers, as a basis of estimating average "hold up" times of dissolved materials deposited in the deep layer. It is probably even more im- portant to measure the heterogeneity in the ex- change system, that is to measure the rates of exchange in different areas and depths. We 22 Atomic Radiation and Oceanography and Fisheries know that vertical exchange is much more rapid in some parts of the oceans than others, but de- scribing it in quantitative terms can be done only in a very sketchy manner. Quantitative data on this subject are required as one basis of arriving at estimates of the amount of atomic wastes that can be deposited safely in specified parts of the deep sea. 4. Sedimentation processes Sedimentation processes constitute an im- portant mechanism for removing atomic wastes from the waters of the oceans. In order to evalu- ate their role, however, we need to measure the average times that different elements remain in the sea before being deposited in the sediments, the rates of sedimentation in different parts of the deep sea, and the ability of the sediments to capture and retain various fission products. 3. Effects of the biosphere on the distribution and circulation of elements As we have noted, marine organisms have profound effects in modifying the distribution and circulation of elements in the sea. It is vitally necessary that the biological processes be studied in sufficient detail to enable their effects to be quantitatively evaluated. Such investiga- tions need to include: The flux of various ele- ments through the different trophic levels, and the variations in different ecological realms such as inshore coastal waters, offshore surface waters and the deep sea; the effects of vertical and horizontal migrations of organisms on redis- tribution of elements ; the effects of the uptake, modification of the physical state, and elimina- tion of elements by members of the marine biosphere on their subsequent distribution in the sea. 6. Uptake and retention of elements by organ- isms used as food for man Related to the foregoing, but of separate im- portance, is the study of the quantities of radio- active elements deposited in different situations in the sea that can be expected to be taken up by organisms harvested for food, the length of time such elements are retained in the food or- ganisms, and, consequently, the levels of con- centration. Some parts of some organisms are not eaten by man, but are discarded or used for other purposes. The sites of accumulation of different radioactive elements in the organisms must therefore be determined. 7, Ejects of atomic radiation on populations of marine organisms In order to determine what quantities of atomic wastes can be safely deposited in the sea without upsetting the ecology of the sea through destruction of important populations of organ- isms, research is needed on the somatic and ge- netic effects of atomic radiation on marine popu- lations. This is especially important for organ- isms of the deep sea which may come in contact with very high concentrations of radioactive elements, if deep sea disposal of large quantities proves feasible in other respects. RESEARCH METHODS Much of this required research can be ac- complished by the intensive application of classical techniques of physics, chemistry, ge- ology, and biology. In addition, however, the availability of radioactive isotopes provides us with a powerful new tool, which is especially valuable for studying processes. The use of radioactive elements as tracers permits the paths of various elements, both in the physical en- vironment and within the biosphere, to be de- termined, and the fluxes of the elements through various parts of the system to be measured. Radioactive tracers are useful both in labo- ratory experiments and in field studies of vari- ous kinds. The use of tracers in the laboratory and in small scale field experiments is already familiar. Information from the tracers intro- duced into the sea by weapons tests has provided valuable information. What has not yet been done, and what we believe will be a fruitful approach, is the employment of fairly large quantities of radio isotopes to study the various processes in the open ocean in a planned fash- ion. In Chapters of this report by Folsom and Vine and by Schaefer, suggestions are made for some experiments that should be useful and are currently feasible. Naturally occurring radioactive isotopes can also provide a fruitful means of attack. Craig, in Chapter 11, discusses some of these avenues of research in detail. FACILITIES REQUIRED The Committee has not attempted to draw up detailed estimates of men, ships, and facili- General Considerations 23 ties which will be required for an adequate attack on this problem. These requirements will, however, be large. The problems outlined above are among the most difficult in the marine sciences. Adequate solutions will demand the collection of much more knowledge about the sea and its contents than the total obtained in the past hundred years. Because of the urgency of these problems, and because of the large costs involved, it is essential that research be coordinated on both the national and international levels. Coordina- tion among scientists engaged in these studies should be easier in the future than it has been in the past. OTHER BENEFITS OF THE RESEARCH TO MANKIND The potential requirement for disposal of atomic wastes in the sea is sufficient reason for pursuit of these investigations. However, man- kind will derive additional, and perhaps even greater, benefits in other ways. For example, the flux of materials through the various trophic levels of the biosphere is the fundamental proc- ess underlying the harvest of the sea fisheries. This process must be studied to provide part of the basis for atomic waste disposal, but its elucidation will also provide much of the scien- tific base for the optimum exploitation and con- servation of the seas* living resources by man. IX. Conclusions and Recommendations We repeat here the conclusions and recom- mendations that were agreed upon by the mem- bers of the Committee at the time they prepared the Summary Report published by the Academy in 1956: 1. Tests of atomic weapons can be carried out over or in the sea in selected localities with- out serious loss to fisheries if the planning and execution of the tests are based on adequate knowledge of the biological regime. The same thing is true of experimental introduction of fission products into the sea for scientific and engineering purposes. 2. Within the foreseeable future the prob- lem of disposal of atomic wastes from nuclear fission power plants will greatly overshadow the present problems posed by the dispersal of ra- dioactive materials from weapons tests. It may be convenient and perhaps necessary to dispose of some of these industrial wastes in the oceans. Sufficient knowledge is not now available to predict the effects of such disposal on man's use of other resources of the sea. 3. We are confident that the necessary knowl- edge can be obtained through an adequate and long-range program of research on the physics, chemistry, and geology of the sea and on the biology of marine organisms. Such a program would involve both field and laboratory experi- ments with radioactive material as well as the use of other techniques for oceanographic re- search. Although some research is already un- der way, the level of effort is too low. Far more important, much of the present research is too short-range in character, directed towards ad hoc solutions of immediate engineering problems, and as a result produces limited knowledge rather than the broad understanding upon which lasting solutions can be based. 4. We recommend that in future weapons tests there should be a serious effort to obtain the maximum of purely scientific information about the ocean, the atmosphere, and marine organisms. This requires, in our opinion, the following steps: (1) In the planning stage com- mittees of disinterested scientists should be consulted and their recommendations followed; (2) funds should be made available for scien- tific studies unrelated to the character of the weapons themselves; (3) the recommended scientific program should be supported and car- ried out independently of the military program rather than on a "not to interfere" basis. 5. Ignorance and emotionalism characterize much of the discussion of the effects of large amounts of radioactivity on the oceans and the fisheries. Our present knowledge should be suf- ficient to dispel much of the overconfidence on the one hand and the fear on the other that have characterized discussion both within the Government and among the general public. In our opinion, benefits would result from a con- siderable relaxation of secrecy in a serious attempt to spread knowledge and understanding throughout the population. 6. Sea disposal of radioactive waste materials, if carried out in a limited, experimental, con- trolled fashion, can provide some of the in- formation required to evaluate the possibilities of, and limitations on, this method of disposal. Very careful regulation and evaluation of such operations will, however, be required. We, therefore, recommend that a national agency, 24 Atomic Radiation and Oceanography and Fisheries with adequate authority, financial support, and technical staff, regulate and maintain records of such disposal, and that continuing scientific and engineering studies be made of the resulting effects in the sea. 7. We recommend that a National Academy of Sciences — National Research Council com- mittee on atomic radiation in relation to ocean- ography and fisheries be established on a con- tinuing basis to collect and evaluate informa- tion and to plan and coordinate scientific re- search.* 8. Studies of the ocean and the atmosphere are more costly in time than in money, and time is already late to begin certain important studies. The problems involved cannot be attacked quickly or even, in many cases, directly. The pollution problems of the past and present, though serious, are not irremediable. The atomic waste problem, if allowed to get out of hand, might result in a profound, irrecoverable loss. We, therefore, plead with all urgency for im- mediate intensification and redirection of scien- tific effort on a world-wide basis towards build- ing the structure of understanding that will be necessary in the future. This structure cannot be completed in a few years; decades of effort will be necessary and mankind will be fortunate if the required knowledge is available at the time when the practical engineering problems have to be faced. 9. The world-girdling oceans cannot be sepa- rated into isolated parts. What happens at any one point in the sea ultimately affects the waters everywhere. Moreover, the oceans are interna- tional. No man and no nation can claim the exclusive ownership of the resources of the sea. The problem of the disposal of radioactive wastes, with its potential ha2ard to human use of marine resources, is thus an international one. In certain countries with small land areas and large populations, marine disposal of fission products may be essential to the economic de- velopment of atomic energy. We, therefore, recommend: (1) that cognizant international agencies formulate as soon as possible conven- tions for the safe disposal of atomic wastes at sea, based on existing scientific knowledge; (2) that the nations be urged to collaborate in studies of the oceans and their contained organ- * The President of the Academy, Dr. Detlev W. Bronk, has requested that the present committee undertake to develop and carry forward this con- tinuing program. isms, with the objective of developing compara- tively safe means of oceanic disposal of the very large quantities of radioactive wastes that may be expected in the future.** 10. Because of the increasing radioactive con- tamination of the sea and the atmosphere, many of the necessary experiments will not be possi- ble after another ten or twenty years. The recom- mended international scientific effort should be developed on an urgent basis. 11. The broader problems concerned with full utilization of the food and other resources of the sea for the benefit of mankind also re- quire intensive international collaboration in the scientific use of radioactive material. REFERENCES Anon. 1956. Report of a meeting of United Kingdom and United States scientists on biological effects of radiation in oceanog- raphy and fisheries. Nat. Acad. Sci. — Nat. Research Council, Oct. 31, 1956, 8 pp. (mimeographed) . BowDEN, K. F. 1954. The direct measurement of subsurface currents in the oceans. Deep Sea Research, Vol. 2, pp. 33-47. Culler, F. L. 1954. Notes on fission product wastes from proposed power reactors. ORNL Central File No. 55-4-25. Dietrich, G. 1957. Selection of suitable ocean disposal areas for radioactive waste. (A preliminary report with 6 charts.) M.S., 10 pp. Food and Agriculture Organization of UNESCO. 1957. Yearbook of fishery statistics. FAO, Rome, Vol. 5 (1954-55). Goldberg, E. and Arrhenius, G. O. S. 1957. Chemistry of Pacific pelagic sediments. In press. Greendale, a. E., and N. E. Ballou. 1954. Physical state of fission product elements following their vaporization in distilled water and sea water. USNRDL Document 436, pp. 1-28. Harley, John E. (Editor). 1956. Operation Troll. U.S., A.E.C., N.Y. Operations office 1956. 37 pp. ** As a first step in this direction an informal dis- cussion was held by members of this committee with scientists from the United Kingdom at North Fal- mouth, Massachusetts, on September 27 and 28, 1956. A brief summary of the meeting was published by the National Academy of Sciences (Anon., 1956). General Considerations 25 HiYAMA, Y. 1956. Maximum permissible con- centration of Sr 90 in food and its environ- ment. Records of Oceanographic Work in Japan, Vol. 3, No. 1, March 1957, pp. 70-77. HiYAMA, Y., and R. Ichikawa. 1956. Move- ment of fishing grounds where contami- nated tuna were caught. Japan Society for the Promotion of Science; Research in the Effects and Influences of the Nuclear Bomb Test Explosions, pp. 1079. Japanese Fishery Agency. 1955. Report on the investigations of the effects of radiation in the Bikini region. Res. Dept., Jap. Fish. Agency, Tokyo, 191 pp. Kawabata, T. 1956. Movement of fishing grounds where contaminated tuna were caught. Japan Society for the Promotion of Science; Research in the Effects and In- fluences of the Nuclear Bomb Test Explo- sions, pp. 1085. Krauskopf, K. B. 1956. Factors controlling the concentration of thirteen rare metals in sea water. Geochim. et Cosmochim. Acta 9, pp. 1-32. KuLP, J. L., Eckelmann, W. R., and A. R. SCHULERT. 1957. Strontium 90 in man. Science, Vol. 125, No. 3241, pp. 219-225. Laevastu, T., and T. G. Thompson. 1956. The determination and occurrence of nickel in sea water, marine organisms, and sedi- ments. ]our. dti Cons., Vol. 21, pp. 125- 143. Lapp, Ralph E. 1956. Strontium limits in peace and war. Bidl. Atomic Scientists, Vol. 12, No. 8, pp. 287-289, 320. LiBBY, W. F. 1956a. Radioactive fallout and radioactive strontium. Science, Vol. 123, pp. 657-660. 1956b. Radioactive strontium fallout. Proc. Nat. Acad. Sci., Vol. 42, No. 6, pp. 365- 390. MiYAKE, J., SuGiURA, Y., and K. Kameda. 1955. On the distribution of radioactivity in the sea around Bikini Atoll in June 1954. Pap. Meteorol. Geophys., Tokyo, Vol. 5, No. 3-4, pp. 253-262. MuNK, W. H. 1950. On the wind-driven ocean circulation. Jour. Meteorol., Vol. 7, No. 2, pp. 79-93. MuNK, W. H., EwiNG, G. C, and R. R. Re- velle. 1949. Diffusion in Bikini lagoon. Trans. Am. Geophys. Union, Vol. 30, No. 1, pp. 59-66. National Bureau of Standards, 1953. Maximum permissible amounts of radio isotopes in the human body and maximum permissible concentrations in air and water. U.S. Dept. of Commerce, Nat. Bureau Standards. Handbook 52, 45 pp. 1954. Radioactive waste disposal in the ocean. Nat. Bureau of Standards. Hand- book 58, 31 pp. Nucleonics. 1956. Calder Hall, over-all de- scription. Nucleonics, Vol. 14, No. 12, pp. SlO-Sll. 1957. Roundup of key developments in atomic energy. Nucleonics, Vol. 15, No. 6, pp. 17-28. Rankama, K., and T. C. Sahama. 1950. Geo- chemistry. Univ. of Chicago Press, 1950. Revelle, R. R. 1957. Statement by Professor Roger Revelle before the joint Committee on atomic energy, 28 May 1957. The Na- ture of Radioactive Fallout and its Effects on Man ; Hearings before the Special Sub- committee on Radiation of the Joint Com- mittee on Atomic Energy. Congress of the United States, 1957. Revelle, R. R., Folsom, T. R., Goldberg, E. D., and J. D. Isaacs. 1955. Nuclear Science and Oceanography. Int. Conf. on the Peaceful Uses of Atomic Energy. A/Conf. 8/P/277, 22 pp. (mimeo- graphed ) . Seligman, N. 1955. The discharge of radio- active waste products into the Irish Sea. Part I: First experiment for the study of movement and dilution of released dye in the sea. Proc. Int. Conf. on Peaceful Uses of Atomic Energy, United Kingdom paper number 418, 25 pp. Sverdrup, H. U., Johnson, M. W., and R. H. Fleming. 1942. The Oceans. Prentice Hall, New York, 1942, 1060 pp. Swallow, J. C. 1955. A neutral -buoyancy float for measuring deep currents. Deep Sea Research, Vol. 3, pp. 74-81. Vinogradov, A. P. 1953. The elementary composition of marine organisms. Sears Foundation for Marine Research, Memoir No. 2, 647 pp. WiJST, G. 1957. Report on the current veloci- ties, volume transports and mixing effects in the Atlantic deep sea as physical proc- esses important to the transport and dis- persal of radioactive wastes. M. S. (mime- ographed), 19 pp. Chapter 1 PHYSICAL AND CHEMICAL PROPERTIES OF WASTES PRODUCED BY ATOMIC POWER INDUSTRY Charles E. Renn, The Johns Hopkins University Department of Sanitary Engineering and Water Resources The ultimate forms and radioactivities of wastes delivered for sea disposal will be deter- mined by conditions that have not yet been fully evaluated. Present and projected wastes will undoubtedly be modified by requirements for storage, transport, and economical handling, and the ultimate form of wastes with which we may be concerned will be further conditioned by what we learn in early disposal practice. The following represents the characteristics of high- level reactor wastes that now exist, and which are likely to appear soon. The primary radioactive wastes result from the chemical extraction of inhibitory fission products from metallic reactor elements. A strong nitric acid solution of aluminum heavily contaminated with a variety of fission products is obtained after the useful reactor fuel is re- covered. To conserve tank space and shielding, the solutions are concentrated by evaporation. Where storage is to be made in steel containers, the solution may be neutralized and made slightly alkaline with commercial caustic. A neutral or alkaline salt solution or slurry is developed — the concentration of salts may ap- proach or exceed saturation values at storage temperature. The neutral salt concentration of the waste determines its density. Some types of reactor elements are not directly soluble in nitric acid and require solution in combinations of other mineral acids and catalysts; most ulti- mately require conversion to nitrates before complete extraction, however. The cladding and alloying metals of the reac- tor elements are also discarded in the wastes. Aluminum is the most common and abundant of the metals used ; it appears in concentrations as high as 80,000 ppm. in final wastes. Zir- conium will also be present. Of the various non-radioactive components in the wastes, the properties of the high-density- producing salts, of the high nitrate concentra- tions, and of aluminum are of greatest interest. The presence of these at present limit the prac- tical production of selectively adsorbed fission waste products. If the wastes are concentrated for economical storage and transportation and neutralized to limit corrosion, the densities of the waste liquids will exceed that of sea water. The temperatures for precipitation of super- saturated salts in the various wastes are not known, but it may be assumed that further sludges will be formed on cooling to deep sea temperatures — some corrosion-product sludges already exist. The solubilities of both normal and radio- active components of the waste will be condi- tioned by the presence of nitrates in concentra- tions exceeding equivalence. Aluminum nitrate precipitates as a light floe in sea water at con- centrations as low as 1 ppm. Al. At present there are no data on its solubility in a sea water waste mixture. Neither do we know what the adsorption characteristics of the aluminum floe in sea water may be. The range of physical and radiochemical characteristics that may be anticipated in con- centrated fuel re-processing wastes and approx- imate quantities of wastes produced are indi- cated in the three tables following. 26 Chapter Properties of Atomic W^astes 27 TABLE 1 Gross Physical and Chemical Char- acteristics OF Strong Aqueous Wastes From Reactor Fuel Recovery Processes ^ (Concentrations of non-radioactive components before evaporation, neutralization, and treatment for fission removal.) Range of Molar Component Concentrations H 0.07 - 7.0 Al 0.04 - 1.6 Fe 0.05 Zr 0.03 - 0.5 NH4* 0.05 - 2.0 Cr 0.01 - 1.0 Ni 0.03 Sn 0.02 Mn 0.001 Hg 0.001- 0.01 F 0.05 - 3.0 NO3- 0.14 - 7.0 SOr 0.2 - 0.5 Specific Gravity (unconcentrated) . 1.07 - 1.25 Curies/gal. (100 days cooling).. 80 -5200 BTU/hr./gal. (10 days cooling— 50% gamma, 50% beta) 1.37 - 29.4 1 From Tables 4 and 5, Status Report on the Dis- posal of Radioactive Wastes, ORNL-CF-57-3-114, F. L. Culler. TABLE 2 Short-lived Fission Products per 1000 Gm U""^ Reactor Charge At 100 Days Cooling with 30 Per Cent Burnup ^ Fission Half Beta Gamma products life 2 Grams curies curies Y-90 62 h 4.63 748 — Rh-106 30 s 0 1,514 515 Ce-144 275 d 4.90 16,332 4,900 Zr-95 65 d 1.52 32,647 62,356 Nb-95 35 d 1.61 63,657 65,657 Y-91 57 d 1.11 28,239 — Sr-89 55 d 0.86 23,253 — Ru-103 45 d 0.46 13,236 6,618 Ce-l4l 28 d 0.45 10,004 20,008 Ba-137 2.6 m — — 508 Ru-106 290.0 d 0.35 1,514 — Pr-143 13.8 d 0.02 1,465 — Ba-140 12.5 d 0.02 1,222 305 La-140 1.7 d — 1,222 1,331 1-131 8.0 d — 23 29 Total 15.93 195,076 162,227 1 From presentation by F. L. Culler, Oak Ridge Na- tional Laboratory, before Meeting on Ocean Disposal of Reactor Wastes, Woods Hole Oceanographic In- stitution, August 5-6, 1954. - Abbreviations are s for seconds, m for minutes, h for hours, and d for days. TABLE 3 Long-lived Fission Products per 1000 Gm U'^ Reactor Charge At 100 Days Cooling with 30 Per Cent Burnup 1 Half Beta Gamma Fission products life Grams curies curies Cs-137 33 y 7.05 563 — Sr-90 25 y 4.63 748 — Pr-144 17 m 4.90 16,333 17,966 Te-129 72 m 0.03 1,217 2,435 Total long-lived 16.61 18,861 20,401 Inactive fission products . . 230.00 2 Short T i 15.93 198,564 152,325 Grand total 262.54 217,425 172,726 1 From presentation by F. L. Culler, Oak Ridge Na- tional Laboratory, before Meeting on Ocean Disposal of Reactor Wastes, Woods Hole Oceanographic In- stitution, August 5-6, 1954. - Short-term fission products from table 2. Chapter 2 COMPARISON OF SOME NATURAL RADIATIONS RECEIVED BY SELECTED ORGANISMS^ Theodore R. Folsom, Scripps Institution of Oceanography, La Jolla, California and John H. Harley, Health and Safety Laboratory, U. S. Atomic Energy Co?nmission In attempting to consider in numerical terms possible consequences to populations from mu- tations caused by very low levels of artificial radioactivity, it is instructive to collect for quick comparison some estimates of the natural doses to which certain organisms have been exposed for geological periods. These data emphasize that doses from natural sources vary widely and depend not only upon the habitat but also upon the physical size of the organism; this natural radiation background varies particularly widely amongst aquatic organisms. A very useful summary of natural and arti- ficial radiation to which human beings are now exposed has been published by Libby (1955) ; it has already been quoted and some of his com- parisons will be repeated here. Nevertheless, additional radiological factors must be included whenever the natural exposures of marine or- ganisms are to be evaluated. Only sources contributing substantially to the average dose to the organisms as a whole will be listed here. The major contributors are (a) cosmic rays, (b) radioactivity in local sur- roundings, and (c) radioactivity spread through the tissue inside the organism itself. Cosmic rays Cosmic ray intensity decreases far more rap- idly from sea level downward than it increases with increasing elevation above the earth. Fig- ure 1 and Table 1 show the trend of the ioniz- ing component of these rays with elevation above sea level, and with depth in water. The absolute dose which is used in Table 3 and Figure 2 is the average of the two values Libby 1 Contribution from the Scripps Oceanography, New Series, No. 904. Institution of (1955) uses for the geomagnetic equator and for 55° geomagnetic north latitude. (See Fig- ure 1 and Table 1.) External activity Most organisms live close to either (a) igne- ous or metamorphic rock, (b) sedimentary rock, or (c) water. Sea water has a characteristic natural radioactivity — much lower than that of terrestrial rocks but quite appreciable when ELEVATION (FEET) 20,000 r- 10.000 - 400 MRAD/YR 40 MRAC YR 200 1- OEPTH IN SEA (METERS) Figure 1 28 Chapter 2 Natural Radiation of Selected Organisms 29 TABLE 1 Trend of Cosmic Rays with Distance our comparisons the same average radioactivities Above and Below Sea Level used by Libby (1955) are used here for granite Variation with elevation above sea level, values of ^nd sedimentary rocks, intensity of ionizing component (in mrads/year) taken from Libby (1955). , , , f ,• •, Internal sources of activity Mrad/year ' --^. — — ' The bodies of large animals contain a much Elevation in feet Equator ^'' (mag) higher concentration of potassium than is found 0 33 37 in sea water. A value of 0.2 per cent is used 5,000 40 60 herein for human tissue (Burch and Spiers, lO'OOO 80 120 1954) and 0.3 per cent is used for the potas- 15,000 160 240 • . F ^ ^ ^ J 2^000 300 450 ^^""^ concentration ot large nsh (Vinogradov, 1953). Since radio-potassium contributes the Variation with depth in water values computed ^^- portion, aside from cosmic rays, of the from average attenuation compiled by George (1952) ,. . ,. -u .• . .i j i.^ Tuu • u 1 * • * •* c ^\r. o^l radiation contributing to the average dose to using Libby s average absolute intensity tor mean sea o o level. the total body of any marine organisms, the Percent of surface character and distribution of this important Depth in meters Mrad/year value natural activity has been compiled in Table 2. 0 35 100 10 10.1 28.8 20 4.86 13.9 Geometrical factors influencing dose 50 1.40 4.0 100 0.47 1.35 A man standing above a granite plane surface 200 0.15 0.42 receives from the granite roughly one half the 300 0.074 0.21 radiation which might strike him if he were 1,000 '.'.'.'.'.'.'.'.'.'. 0^009 ao25 completely surrounded by granite; likewise a 4*000 .......... 0.007 0.002 man in a row boat receives from the sea only one half the dose which the sea gives to any compared to that of most natural fresh waters. submerged organism. The major activity in sea water comes from Potassium yields both beta and gamma ac- radiopotassium (Revelle, Folsom, Goldberg and tivity; roughly three fourths of the total energy Isaacs 1955), and only this constituent will be comes from the beta rays. Nevertheless, because considered here. Of the metamorphic and igne- of its short range, the beta particle from the ous rocks, granite has the highest activity; for potassium in the surrounding sea contributes TABLE 2 Potassium Radiation Data Distribution and Intensities Material Potassium content Beta rays Gamma rays d/m/g mrad/yr d/m/g mrad/yr Sea water 0.038% (1) 0.66 2.7 0.068 0.9 (35%o salinity) Man 0.2% (2) 3.5 15 0.36 2.3 (4) Fish (large) 0.3% (3) 5.8 24 0.3 3.7 (4) Physical Nature of Potassum Activity Beta activity = 29 d/s/gram of total potassium Beta ray energy (average) = 0.5 mev Gamma activity = 3 d/s/gram of total potassium Gamma ray energy ^1.5 mev Sample Calculations for Potassium Activity Beta d/m/g X 1440 X 365 m/yr X 0-5 mev/d X 1-6 X 10^ erg/mev 1000 ^ ^^^^^^^ ^^^^^ ^j^j^j^ ^^^^^^^ 100 erg/rad to. Beta d/m/g X 4.2 = mrad/yr beta; and correspondingly, Gamma d/m/g/ X 12.6 = mrad/yr gamma. (1) Sverdrup, Johnson and Fleming (1942). (2) Sherman (1941). (3) Vinogradov (1953). (4) Assume half of the gamma rays from internal activity are absorbed inside the body. 30 Atomic Radiation and Oceanography and Fisheries very little to the total dose of a large animal. On the other hand the beta rays from the sur- roundings can appreciably affect very small or- ganisms and can in fact become the predom- inant contributor to dose whenever the organ- ism has dimensions much smaller than the range of the beta particles in water and tissue. The effect of beta rays starting from internal sources also depends upon the size of the organ- ism. If the organism is very small the beta bombardment from the outside sources may con- tribute much more than does internal activity even though the source of activity is more con- centrated in the tissue than it is in the surround- ing water. It would appear from the character of beta penetration (Friedlander and Kennedy, ■10,000 feet / COSMIC RAYS RAYS FROM INTERNAL POTASSIUM RAYS FROM LOCAL EXTERNAL SOURCES \ ^\ \ -' '/ 1 \\A\\r ' \ 90 \ \ \ \GRANITE. \ SEDIMENTARY ROCK TOTAL NATURAL DOSES (mrad/year) Man over granite Man over sedinnentary rock Man over sea Large fish in sea Micro-organism in sea 10.000 m.sJ. 75 52 at surf. lOOm. at surf. lOOm. 207 142 64 30 39 5 Figure 2 Chapter 2 Natural Radiation of Selected Organisms 31 1949) that any potassium beta particle which originates inside a small organism will deposit most of its energy outside the organism; appar- ently less than 10 per cent of the total ioniza- tion can take place inside a sphere having a mean radius of 0.1 mm, and perhaps from the activity concentrated inside a phytoplankter hav- ing a mean radius of 0.01 mm only 1 per cent of the energy would be felt by the organism itself. Thus we see that the constitution of the surrounding medium dominates the life of the marine microorganism in a radiological sense as well as in those other manners more familiar to biologists. Units used For quantitative statements concerning such feeble radiations as these it is logical to use a very small unit and preferably one which is defined in terms of energy absorbed; the milli- rad per year (mrad/yr) is such a unit and is used here. The rad unit is only slightly larger than the more familiar roentgen unit, since 1.0 rad by definition causes 100 ergs to be absorbed per gram of matter, and this is approximately the energy deposited by 1.1 roentgen of gamma rays. For converting beta activity to equivalent rad dosage the average beta energy of potassium has been taken as being 0.5 mev. Comparison of natural doses in several dojnains Figure 2 attempts to bring into a single pic- ture the magnitudes of the main components making up the radiation in each of several do- mains of interest. The approximate total dose to the organism is listed below the figure so that numerical comparisons can be made. In the sea and in deep lakes the dose to small or- ganisms must be evaluated separately from that experienced by large organisms. Circumstances in each domain are given in more detail in Table 3. (See Figure 2 and Table 3.) Discussio7t Small organisms must be considered sep- arately from large ones. Only a small fraction of the energy coming from activity inside a very small organism can be absorbed by the organ- ism, whereas a large organism cannot escape so well from its own radioactivity. Near the sea surface a large fish receives about half its total natural exposure from the rays originating in the radio-potassium in its own tissues. On the other hand near the sea surface cosmic rays appear to outweigh all other radiations received by a microorganism. At depths of the order of 100 meters the attenuated cosmic rays no longer contribute sig- nificantly to marine organisms either large or small. However, the beta and gamma rays from potassium in sea water can give small organisms doses amounting to about ten per cent of the total dose they receive at the sea surface; the small marine organism cannot escape this expos- ure to radioactivity in the surrounding water. It is the deep fresh water which makes pos- sible the most extreme variation in natural ex- posure. In the deeper waters living things can hide from external bombardment; fresh water generally contains such small amounts of radio- activity that this source can be neglected even in comparison with the feeble effect of cosmic rays remaining at depths of several hundred meters or more. In pure fresh water the total dose from strongly ionizing rays depends largely upon the size of the organism and upon its living habits. If the organism is small in the sense already discussed, if it lives in deeper waters, if it stays away from the bottom sediments, if it avoids the neighborhood of large masses of living tis- sue or of detritus, and if it avoids as far as pos- sible accumulating excessive amounts of those elements which can be radio-active — then it can remain remarkably free from the ionizing bombardment received by all other living things. It would be interesting to find out how the phytoplankton that seek the deeper portion of the euphotic zone of clear lakes respond to their extremely low external dose. If morphological or other differences are discovered between sur- face specimens and deep-water specimens, then one of the origins of these differences might possibly be the extremely different amounts of strongly ionizing rays in the two biospheres. Geneticists should not overlook another as- pect of the minute cell in feeble radiation; an individual cell has an extremely small proba- bility of being struck at all during one genera- tion. In a deep lake the radiation intensity can be so low that only one phytoplankter in about five hundred would experience an ionizing ray before it divided ; at least this is the probability of a cosmic ray hitting an area 0.1 mm square 32 Atomic Radiation and Oceanography and Fisheries at 100 meters depth. Furthermore, should an individual plankter accidentally concentrate an excessive amount of radioactive material in its tissue there is little probability that this indi- vidual would ever pass along any effect of it; there would be very little chance of a disinte- gration occuring before division. Purely physi- cal reasoning therefore indicates that mutations leading to a capability for accumulating rela- tively large amounts of activity might be car- ried to offspring for ten or more generations before any nuclear energy would be released in any cell whatever. Because of the "patchiness" of the radiation, the use of a unit like the millirad per year for feeble doses of strongly ionizing radiation un- fortunately cannot convey the complete picture of the interesting bombardments which must be experienced by the very small organism. TABLE 3 Radiations in Eleven Radiological Domains Man over granite 1. At 10,000' elevation Cosmic rays 100 -f granite 90 + internal 17 2. At sea surface Cosmic rays 35 + granite 90 + internal 17 Man over sedimentary rock 3. At sea level Cosmic rays 35 + rock 23 + internal 17 Man over sea 4. Cosmic rays 35 -\- sea 0.5 ^ + internal 17 Large fish in sea 5. Near surface Cosmic rays 35 + sea 0.9 ^ -finternal 28 6. 100 meters deep Cosmic rays ^ -f- sea 0.9 ^ + internal 28 Total mrads/year = 207 = 142 = 75 = 52 = 64 = 30 Micro-organism (mean radius 0.01 mm or less) in water 7. Near sea surface Cosmic rays 35 + sea 3.6 ^ -j- internal ^ =39 8. 100 meters deep in sea or more Cosmic rays 0.5 -f sea 3.6 ^ -|- internal 3 =: < 5 9. Buried in deep sea sediments Cosmic rays 0.000 -f clay 40-620 + internal * = 40-620 10. Near fresh water surface Cosmic rays 35 + water activity - -|- internal - ^35 11. 100 meters deep in a fresh lake Cosmic rays < 0.5 -|- water activity - + internal - = < 0.5 1 For every radiopotassium disintegration there are 10 betas having average energy 0.5 mev and also one gamma ray having 1.5 mev. The man receives half the gammas from activity in the sea; the large fish, substantially all the gammas; while the micro-organism receives gammas and betas together. 2 In fresh water natural activity is extremely low and little of this energy stays in the cell. For example (Robeck et al., 1954) in the Columbia River the beta background of the water is at or below 1 X 10"* micro- curie per ml (2 X 10"* d/m/g) while the activity of aquatic organisms is at or below 1 X 10"* microcuries per gram (2 X 10"^ d/m/g). For comparison, the beta activity in normal sea water is 0.66 d/m/g. 3 The marine microplankton probably carries more internal activity than does the lake plankton, never- theless effect can be neglected unless activity is concentrated more than 100 fold. * All deep-water organisms have not escaped radiations. Micro-organisms buried in true deep-sea sedi- ments have exceptionally high exposure to radium (Love, 1951); they receive 40-620 mrads/year de- pending upon the type of sediment. CONCLUSIONS 1. Some humans actually live under exposure levels surprisingly near the magnitude, 10 roent- gen during 40 years, which has been suggested as a genetic tolerance level, i.e., see Figure 2 and Table 2 (domain 1, high elevation over granite) . 2. A man may experience 207 mrad/year on high mountains, or 142 on a sandy shore; he may reduce this further by half, say, by staying aboard a ship. 3. A large fish experiences a 50 per cent reduc- tion in dose when going to a depth of 100 Chapter 2 Natural Radiation of Selected Organisms 33 meters; it carries along its own source of in- ternal radiation, however. 4. A marine microorganism, having a mean radius of 0.01 mm, receives only about 10 per cent of the surface dose at a depth of 100 meters in the sea; most of the dose comes from sea water activity unless exceptionally high in- ternal activities are accumulated. 5. In a deep fresh water lake those microor- ganisms living in deep water (but not right at the bottom) receive from their surroundings what is probably the lowest natural ionizing dose within the biospheres of the earth. It would ap- pear that geneticists should consider seeking evidence of abnormal mutation rates amongst microorganisms which live in deep waters of clear lakes, particularly amongst those which have low affinity for radioactive elements. REFERENCES BuRCH, P. R. J., and F. W. Spiers. 1954. Ra- dioactivity of the human being. Science 120:719-720. Friedlander, G., and J. W. Kennedy. 1949. Introduction to radiochemistry. J. Wiley and Sons, New York: xiii-f4l2. George, E. P. 1952. Progress in cosmic rays. J. C Wilson, ed. '52 Interscience, North- Holland Publ. Co.: xviii + 557. LiBBY, W. F. 1955. Dosages from natural ra- dioactivity and cosmic rays. Science 112 (3158): 57-58. Love, S. K. 1951. Natural radioactivity of water. Ind. Eng. Chem. 43:1541. Revelle, R. R., T. R. Folsom, E. D. Gold- berg, and J. D. Isaacs. 1955. Nuclear science and oceanography. International conference on the peaceful uses of atomic energy, Geneva. Paper no. 277:22. Robeck, G. G., C. Henderson, and R. C. Palange. 1954. Water quality studies on the Columbia River. U. S. Dept. of Health, Education, and Welfare. Robert A. Taft Sanitary Engineering Center; Cin- cinnati, Ohio: viii + 294. Sherman, H. C. 1941. Chemistry of food and nutrition. 6th Ed., McMillan, New York: x-f6ll. Sverdrup, H. U., M. W. Johnson, and R. H. Fleming. 1942. The oceans, their physics, chemistry and general biology. Prentice- Hall, Inc.: x + 1087. Vinogradov, A. P. 1953. The elementary chemical composition of marine organisms. Trans. Julia Efron and Jane K. Setlow, Sears Foundation for marine research, Yale Univ., New Haven: xiv-f 647. Chapter 3 DISPOSAL OF RADIOACTIVE WASTES IN THE OCEAN: THE FISSION PRODUCT SPECTRUM IN THE SEA AS A FUNCTION OF TIME AND MIXING CHARACTERISTICS ^ Harmon Craig, Scripps Institution of Oceanography, University of California, La Jolla, California I. Introduction: Estimated output of nuclear heat and fission products at "steady state" nuclear power production In two other papers in this report, Wooster and Ketchum discuss mixing rates in the oceans on the basis of oceanographic data, and the present writer reviews the natural isotopic stud- ies which bear on the problem. In this paper we attempt to construct a detailed quantitative picture of the fission product spectrum in the ocean, in steady state with a given fission rate. Such an attempt may well be termed premature, in view of our sketchy knowledge of the in- ternal mixing rate in the sea. Nevertheless, we know a good deal more today than was known five years ago, enough at least to make some simple model calculations which may well yield correct results to an order of magnitude. More- over, the construction of a model and the cal- culation of its characteristics are often highly informative, and, at the very least, provide a basis for the orientation of future studies. The following figures, available in various sources, are pertinent to the estimation of fu- ture consumption rates of nuclear power. Present U. S. electrical energy: 6x 10^ mwh/yr. Present world electrical energy: 10^ mwh/yr. Present world energy consumption (all sources) is about 4.5 X lO^" mwh/yr, doubling every 30 years. For the present calculations, we shall assume a stationary world fission rate of U--^ equal to 1000 metric tons/yr, supplying all the fission products to be disposed of in the sea. We shall then attempt to construct as reasonable a ^ Contribution from the Scripps Institution of Oceanography, New Series, No. 902a. picture as possible of the fission product ac- tivity in the sea, when this activity reaches steady state with the rate of fission, i.e., when the decay rate of each fission product in the sea is equal to the rate at which it is being dumped into the sea, so that its concentration remains constant. We shall also make some calculations for a linear build up to such a fission rate in 50 years. Since 1 gram of U^^^ is equivalent to 24 mwh, our assumed fission rate of 1000 tons of U235 pej. ygar is equivalent to 2.4 x 10^° mwh/ yr of nuclear heat. At 50 per cent efficiency, this is equivalent to a world nuclear power consumption of 1.2 xlO^** mwh/yr. If this latter figure represents 10 per cent of the total world energy utilization, we are then assuming a world consumption of 1.2x10^^ mwh/yr, which seems not unreasonable as an estimate for the year 2000 A. D. Thus a fission rate of 1000 tons of U-^^/yr represents a 2.7 fold increase in the present world energy consumption, 10 per cent being derived from nuclear heat with 50 per cent efficiency, which should be reached in about the year 2000 based on the present trend in energy consumption (see above) . Our calcu- lations will all be linear with the fission rate, so that data for other fission rates are easily derived from the present calculations. The build up of fission products in a reaactor is given by: where / = fission yield (per cent of fissions yielding an individual fission product, the sum equalling 200 per cent) , R is the rate of fission (atoms U^^Yyr) here assumed constant and equivalent to 1000 tons of U^^^/yr, and N = the 31 Chapter 3 Effects of Time and Mixing Characteristics 35 number of atoms of an individual fission prod- uct present in the reactor at any time.- Integration v/ith appropriate hmits gives the number of atoms of a given fission product in the reactor as a function of time: N = ^(1 ') (1) where the build up factor (1— e"^^) varies from 0 to 1 as / varies from 0 to infinity, and gives the fraction of the equihbrium amount attained at any time. At secular equilibrium in the reactor, dN/dt=.0, and xN = fR; we then have: N -B. ^^eqlb — ^ (2) from which one sees that at any time in the reactor, N = N,g,s (1-^-^0 • The assumed fission rate of 1000 tons U-^^/yr is equivalent to 2.2 x lO*' megacuries of fission (1 curie=3.7x 10^" disintegrations/sec), and since the sum of the fission yields is 200 per cent, at equilibrium the total activity of all fission products present in the world, in mega- curies, could be roughly estimated by multi- plying 4.4x10^ by the average number of radioactive members per fission chain. The amount of an individual fission product would be fR/k, using the appropriate decay constant, and its activity would simply be fR, using the appropriate fission yield. The lengths of the fission chains are diffi- cult to estimate because of the extremely short half-lives of the first members. However, Dr. E. C. Anderson (personal communication) has 2 The above equation actually applies only to the first member of a fission chain; for the build up of the second member (y) of a chain with initial mem- ber (x), the correct expression is: dt = [/,(! _^-V )+/,,] R_X,N, where fx and fy are the individual direct fission yields, and so forth for the succeeding members of each mass number chain. However the decay constants are very large for the first members of a chain, and thus one can neglect the exponential terms and assume a fission yield which is the total yield of the isotope under consideration plus all preceding members of the chain, for all irradiation times with which we shall be concerned. The experimental fission yield figures gen- erally refer to the total chain yield, but because of the very low production of the later members of a chain by direct fission, there is no error involved in apply- ing them to the first significantly long-lived chain member. Studied the experimental data on the activity of fission product mixtures directly after fission, and concludes that for times beyond one day after cessation of fission, on the average only ^ of the chains are still active (i.e. from this time on there are left only about 0.3 radioactive members per pair of fission chains initiated). Thus he points out that assuming a fission rate of 1000 tons U^^^/yr as used above, and taking one day as an assumed minimum delay between accumulation and disposal, the steady activity in the sea for continuous stripping and disposal after one day would be roughly 7 x 10^ mega- curies. This is about the same total activity as that found below for an average irradiation time of one year with a 100-day cooling period before disposal, namely 7.7 xlO^ megacuries (see calculations in Section IV and Table 1). The rough agreement of these numbers merely emphasizes the great predominance of the few long-lived isotopes of high fission yield in the fission product activity after very short times. II. Rate of introduction of fission products into the sea A more realistic picture is obtained by con- sidering the irradiation time, or reactor holding time for uranium slugs, which is limited by structural weakening from irradiation, poison- ing by fission products, etc., and the cooling period necessary for safe handling and for the growing in of plutonium in breeder piles. We assume the fission products of the world are distributed between (1) reactors, (2) cooling pits, and (3) the oceans (or any gross disposal site for that matter). The distribution among these reservoirs and the fission product spec- trum in each depends on the irradiation and cooling times. We shall assume an irradiation time of t^ years, equivalent to any of the following physi- cal interpretations: 1. The reactors of the world are operated, on the average, t^ years, then stripped down and rebuilt. 2. The reactor slugs are continuously pushed through the reactors, each spending, on the average, tj. years in the reactor. 3. Continuous stripping into a holding tank which is opened every t^. years for removal of fission products. 36 Atomic Radiation and Oceanography and Fisheries From these sources, the fission products are assumed to enter the coohng pits, from which they are dumped into the sea. At the end of the irradiation time /,., the amount of a fission product is given by (1) as: A ^ -X?,- (3) Assuming for the moment no coohng time, the fission products are stripped out every t^ years and dumped into the sea. Thus the introduc- tion rate into the sea of a given fission product is equal to its activity Ag in the sea at steady state, and is given by Nt,./tr or: .=£(.-. ) (4) where /^ denotes the coohng time, here assumed to be 0. The activity of the fission products in the world reactors at any time, A,., may be evaluated in the following way. The fission products are stripped out every /,. years, and N,., the amount in the reactors, varies from 0 to N(,. in cycles, as / varies from 0 to t^. For many reactors operating independently (the sum of the fission rates being R) with random distribution on the /,. cycle, we take the average of N^ consistent with R by integrating equation (1) from 0 to /,. and dividing by /,.; i.e., the steady state value of N,. is: N.= fR (l-e-^*)dt Performing the integration, and setting A,.z= \Nr, we have for the steady state activity of a fission product in the reactors of the world: AJ~lXt,-(l-e^^'r>^-] A',- (5) and from equations (4) and (5) we see that Ng + N^ = fR/X = N,,j,f„ the total amount of the fission product in the world, as of course it must. Still neglecting cooling time, the fraction of the world total of a fission product which is in the sea is given by N,/Np^,5 = /l.,/^c,^;b =Fg, and: Fmif-o)-. (1 -xf, Xtr (6) Neglecting cooling time, the effect of irradia- tion time may be demonstrated by considering the long and short-lived radioisotopes of stron- tium, calculating the fraction of the world totals, for the assumed fission rate, which is in the sea, as a function of t^, as given below. tr (years) 5;-9o (28^) Sr^^ {5 Ad) 0.1 99.9 79.8 0.5 99.4 38.6 1 98.8 21.2 2 97.5 10.7 10 88.5 2.1 Equation (6) shows the following character- istics: For long half-lives (A/r small): Fg = \ — -^ . . .(approaching 1). For short half-lives (A/;.>5): Fg = Xtr For /,. = 1 year, and for any isotope with a half- life of less than 60 days: Fg = 0.4/^/0 (where /i/., is here in days, /<,= 0). Thus, as shown above, increasing the irradia- tion time from 0.1 to 1 year cuts the fraction in the sea of a 60 day isotope by ^-, neglecting cooling time effects, but does not affect the long-lived isotopes. We next interpose the cooling time between the reactor stripping and the disposal in the sea. The amount of an isotope left after the cooling period is: N, = Ntre~^'<' and from (4), the steady state activity of a given fission product in the sea, equal to its introduction rate, now becomes: ■ A/, ^ and F, is reduced to A. = l^ {I -e-''r>^{e -'''=) (7) >-t r\ /^->''( F,= Xfr (8) III. Fission product concentration in the sea as a junction of linearly increasing fission rate We can get some idea of the transient char- acteristics of the fission product spectrum in the sea by examining the build-up of fission products with an increasing rate of fission. We Chapter 3 Effects of Time and Mixing Characteristics 37 \t-XN shall take R, the world rate of fission, as 0 at the present time (^ = 0) and increasing linearly from the present time until it reaches the 1000 ton rate in 50 years. We shall further assume continuous stripping of fission products into the sea, and examine the transient character- istics of long-lived and a short-lived fission product. The rate of increase of a fission product in the sea is given by: dN ,{R\ where {R/t) is a constant by virtue of the assumed linear increase from R = 0. N is now the amount of a fission product in the sea at any time t. We thus have: dN+{xN-{jR/t)tyt = 0 Multiplication by e'^^ makes the equation exact, and the solution is: Evaluating the constant from N = 0 at / = 0, we have the general solution: N, = i|[A/- (1-^-0} (9) where N^ is the amount in the sea at the time /, Multiplication by A. to give the activity is seen to give an equation of the same form as (5) for the steady state amount in reactors, except that in (9) both R and / are variables, with R/t being constant. We take i?=:0 at the present time, increas- ing linearly to 1000 tons U-^Yyear in 50 years. As noted previously, this rate is equivalent to 2.2x10^ megacuries of fission, and thus R/t — 4.4 X 10* megacuries/year. Thus the activity of a fission product in the sea at any time / is given by: At^AAxlO'Uxt-il-e-^t)'] (10) A where A^ is in megacuries, A = yrs-^, / is in years, and / is the fission yield. We tabulate below the increasing activity in the sea for a long-lived and a short-lived isotope with con- tinuous stripping into the sea. Activity (megacuries) in the sea SfOO 1131 /i/2 = 28}/ t-,/^_ — Sd t (years) / = 0.05 / = 0.028 1 26.4 1200 10 2640 12,300 50 4.8x10* 6.2x10* 100 1.4x105 1.2x105 200 3.5x105 2.4x105 1000 2.1 xlO^ 1.2x10*5 At 50 years, when the fission rate of 1000 tons/year is reached, the Sr^o activity is half the amount which would be in steady state with this fission rate with an irradiation time of 1 year (see below and Table 1 ) . If R continues to increase at the same rate, the steady state Sr^** activity for constant R is reached in about 100 years, and thereafter the activity increases lin- early at a rate given by: At = 2200{t — A0), the mean life of Sr^o being 40 years. The factor (l_^-\f) grows in to 95 per cent at 3 mean lives or 4 half-lives. With a constant fission rate of 1000 tons U-^5y'year, irradiation time one year, and no cooling time, the I^^^ steady state activity in the sea would be 2000 megacuries (calculated as in Table 1, but with no cooling time) . With the linear increase of fission rate and continu- ous stripping as shown above, this level is sur- passed in two years. These data illustrate rather strikingly how rapidly the short half-life iso- topes build up to secular equilibrium with an increasing fission rate. Sr^** does not equal the P^^ activity until after 100 years of dumping into the sea, under the above conditions. For all species which have grown into secular equi- librium with the increasing fission rate, the ac- tivity ratios in the sea are simply given by the fission yield ratios. IV. Steady state fission product spectrum in a homogeneous, rapidly mixed sea The first three columns of Table 1 list all the fission products of any significance, together with their half-lives and fission yields. Col- umns 4 and 5 show the total amounts of each isotope in the sea, in metric tons and mega- curies of activity respectively, in secular equi- librium with a fission rate of 1000 tons U-^5 38 Atomic Radiation and Oceanography and Fisheries per year (2.2 xlO*' megacuries of fission), as- suming an irradiation time (Z^) of one year, and a cooling time (/g) of 100 days (0.274 years). With such conditions, the expression for the activity of each fission product in the sea, as given by equation (7), becomes: A,= ~{l-e-^){e'<^-^-''-^) X 2.2 X 10*^ megacuries (11) where A is in years- ^. For half-lives greater than 1 year there is essentially no reduction in the oceanic activity by the cooling time. For all isotopes with half- lives greater than 5 years, more than 90 per cent of the isotope will be in the sea at steady state. Of the 30 isotopes shown, 22 are independ- ent and 8 are short-lived daughters which come quickly into secular equilibrium with their par- ents, decaying thereafter with the activity of the parent. Cs^^^ has a branching decay with 8 per cent going directly to the ground state of Ba^^^; thus the secular activity of Ba^^"'" is only 92 per cent of the parent activity. The activities listed are beta activities only, for all isotopes except Bais'"^, Tei^sm, and Cd^^m^ which decay from their excited states by gamma emission. The Sm and Eu activities depend on the actual rate of burn-up in the reactors, and may vary considerably with different reactor conditions. In the calculations, the first long-lived mem- ber of each fission chain was taken, and the fission yield for the entire chain was used for this isotope. The direct fission yield for the 11 -day Nd which lies above the 2. 5 -year Pm in the 147 fission chain is not known, and thus this isotope has been neglected; the Nd comes quickly into secular equilibrium in the reactor, so that the total chain fission yield can be used for the Pm calculation. The fission products are listed in order of decreasing total activity in the sea, with radio- active daughters paired with their parents. The total amount of all fission products in the sea is found to be about 3200 metric tons, cor- responding to almost one million megacuries of activity. This represents almost twice the pres- ent activity in the sea, which is mainly due to the radioactivity of potassium 40. The figures for K*" and Rb^^ are shown for comparison, the activity of the other radioactive elements in the sea being negligible relative to these isotopes. We shall now discuss the effects of the mix- ing barrier at the thermocline in the sea on the distribution of the fission products between the deep sea and the upper mixed layer of the sea. V. Distribution of fission products between the deep sea and the mixed layer We shall assume a simple model, convenient for calculation, in which we divide the ocean into two geophysical reservoirs: a mixed layer above the thermocline, and the bulk of the ocean, termed the "deep sea," below the ther- mocline. The exchange of fission products be- tween these two reservoirs is assumed to be a first order process, the rate of removal of a fission product from a reservoir being simply proportional to the amount of the isotope in the reservoir. The thermocline is assumed to represent the boundary across which the hold-up in mixing takes place. Thus, for example, the rate of transfer of water from the mixed layer to the deep sea is assumed to be k^N^, where N,^ is the mass of water in the mixed layer and k^ is the exchange rate constant for transfer of material from the mixed layer to the deep sea. In general, we write ki as the fraction of material in reservoir / removed per year. The residence time of a molecule in a reser- voir, T, is defined as the average number of years a molecule spends in the reservoir before being removed by the physical mixing process. The meaning of t may be shown by the follow- ing derivation which gives a rigorous definition. Assume a reservoir with a steady-state fixed content of N molecules of a substance, and a continuous flux into and out of the reservoir of is thus in "mega- curies of flux," = atoms/sec divided by 3.7 X 10^°. We wish to ask what steady-state activity per unit volume of water will be in the mixed layer, as a function of the rate of cross-thermo- cline exchange of sea water and fission products. The water balance between the reservoirs is given by: k,,N„, = kaNa or, neglecting density differences which are not important for these calculations, ^ = — ^ (12) The fission products are introduced into the deep sea with a rate of introduction for any give isotope 0. The radioactive balance in the two reservoirs is then given by: Deep sea: 4> + K,Nn, = kJS!i+xN^ Mixed layer : k^N^ = k„,N* + AN,' Total : = A (N,; -}.N*a)=A, = A,^ -f- A, From (12) and (14) NJ (13) (14) (15) — "^"^ _L \ or: ^d _ D-m A, + \ra Thus for a stable element (A = 0) the partition- ing is simply statistical. From (15): -^m = D/m + \Ta (16) which gives the total activity of any fission product in the mixed layer as a function of decay constant, relative sizes of the mixed layer and deep sea, and exchange rate between the reservoirs as given by ra- Various estimates of the value to be assigned to Td may be obtained from the separate papers by Wooster and Ketchum, and by Craig, in this report, and are discussed in relation to this 40 Atomic Radiation and Oceanography and Fisheries particular model in the paper by Craig. From these discussions, we choose for the present calculations a value Td=300 years as perhaps the best guess. As discussed by the writer in a separate chapter of this report, radio carbon data indicate a residence time for water of about 1000 years, as a world-wide average. Mixing in the Atlantic is probably a good deal faster than in the Pacific, and 300 years is probably a safe lower limit estimate for the Atlantic, con- sidering the material to be deposited on the bottom. Thus the mixed-layer activities we cal- culate should be upper limits, which would be approached more closely in the Atlantic than in the Pacific. The average world-wide depth of the mixed layer, w, is taken as 100 meters, and the average depth of the sea is taken as 3800 meters. The volume of the sea is 1.4xl02i liters; thus the volume of the mixed layer is taken as 1/38 of this or 3.7x10" liters. Putting these nu- merical values into (16), and noting that ^ = Ag, we have for the activity of any fission prod- uct per unit volume of sea water in the mixed layer: 10-3 A a^= ^^ dps/liter (17) '" 300A+38 ^ ' ^ ' in disintegrations per second per liter, where Ag is in megacuries, as tabulated in column 5 of Table 1, and A is in years^^ From this equation the values tabulated in column 8 of Table 1 were calculated, and were converted to microcuries per liter for column 9. From the relation aa/a„^= {A^Vm/^mVd) = (Aa/A,„) (m/D-m) we obtain: — =At,h-1-1 where Tm> the residence time of a water mole- cule in the mixed layer, is given by (12) as 1/37 of Td = S.l years. We thus write: -^=8.1A+1: (18) from which, given the values of a^n computed above, the values of a^ tabulated in column 7 of Table 1 were computed. We call a the "oceanographic partition factor." It is a func- tion of the mixing rate of the sea and the decay constant of the individual isotope, and is a measure of the effectiveness of the cross-thermo- cline exchange rate in buffering the mixed layer from the fission products introduced into the deep sea. Values of a are tabulated in column 6 of the table, and range from about 1 for the longest lived isotopes to about 250 for an isotope with a half-life of 8 days. For stable isotopes A is 0, a is 1, and (18) reduces to simple statistical partitioning. From (17) we see that as A, the decay con- stant of an isotope, increases, the activity in the mixed layer decreases; i.e., if more of the isotope can be removed from the deep sea by decay, less needs to be transferred to the mixed layer to preserve the steady state. If the half- life were so long that the radioactivity did not affect the distribution between the mixed layer and the deep sea, we would have simply a sta- tistical partitioning of the isotope between these reservoirs, such that the activity per unit volume in each reservoir would be the same. From the above equations we can derive the ratio of the activity in the mixed layer for an isotope to the activity per unit volume which would be ob- served if the partitioning were statistical: / X -- (19) a^{stat) aTa+Tm a and we see that a~^ is approximately the frac- tion of the statistical activity per unit volume attained by a fission product in the mixed layer. Equation (19) can be written exactly as: _ ^1/ a^(stat) /1/2 + 5.5 (20) where /^/o is the half-life of the isotope in years. The ratio a„J a^-y^{stat) is plotted in Figure 1 as a function of the half -life, and one reads, for example, that an isotope with a 5 year half- life attains about 48 per cent of the activity per unit volume in the mixed layer which it would have if its half-life were so long, relative to the mixing rate in the sea, that its radio- activity had no effect on its distribution. The values of a^^, a^, and a are tabulated in Table 1, in which the isotopes are arranged in order of their activity in the deep sea. For comparison, the activities of potassium 40 and rubidium 87, which provide essentially all the radioactivity in the sea, are also listed. In the deep sea, the predicted fission product activity is 19.3 disintegrations per second per liter, as compared with the natural activity of 12.2 dps/ liter; thus the fission products in steady state with the 1000 ton fission rate would almost triple the deep-sea activity. Chapter 3 Ejfects of Time and Mixing Characteristics 41 TABLE 1 Fission Product Spectrum in the Ocean At Steady State Disposal into Deep Sea. Calcu- lated FOR Fission Rate of 1000 Tons U^Vyr (2.4 X lO"' mwh/yr of Nuclear Heat), Irradiation Time of 1 Yr and Cooling Time of 100 Days. Average Life of a Water Molecule in the Deep Sea Taken as 300 Years; Average Depth of the Mixed Layer Taken as 100 Meters. Total amount in ocean Activity (dps/liter) , A ^ ^ A ^ am Half- Fission Metric Activity a = aa am Microcuries Isotope life yield % tons megacuries ad/a™ Deep sea Mixed layer per liter 5oCs"' 33 y 6.3 1750 1.4X10' 1.17 3.64 3.12 8.4X10"' seBa^'"" 2.6 m — — 1.3X10' — 3.35 2.87 7.7X10"' ssSr"" 28 y 5.0 780 1.1 X lO' 1.20 2.90 2.42 6.5X10"' sflY"" 64 h — 0.20 1.1 X 10' — 2.90 2.42 6.5 X 10"' ssCe'" 280 d 5.3 19 6.0X10* 8.32 1.62 0.19 5.2X10"" BsPr"* 17.5 m — — 6.0X10* — 1.62 0.19 5.2X10"" eiPm"' 2.5 y 2.6 48 4.6X10* 3.24 1.23 0.38 1.0X10"' 62Sm''' 100 y 0.7 630 1.5X10* 1.06 0.40 0.38 1.0X10"' «,Zr" 65 d 6.4 0.58 1.2X10* 32.5 0.33 1.0X10"= 2.7X10"' uNb"' 36 d — 0.32 1.2X10* — 0.33 1.0 X 10"" 2.7X10"' 39Y" 60 d 5.9 0.39 9.4 X 10' 35.1 0.25 7.2 X 10"' 1.9 X 10"' 44Ru'°" 1 y 0.5 2.0 6.6 X 10' 6.6I 0.18 2.7 X 10"^ 7.2 X 10"' isRh^"" 35 s — — 6.6 X 10' — 0.18 2.7 X 10"' 7.2 X 10"' 38Sr"« 54 d 4.6 0.22 6.0 X 10' 38.9 O.I6 4.1 X 10"' 1.1 X 10"' u^xx^'^ 40 d 3.7 7.2 X 10"' 2.3 X 10' 52.0 6.1 X 10"' 1.2 X 10"' 3.2 X lO"* ioRh^"' 55 m — — 2.3X10' — 6.1X10"' 1.2X10"' 3.2X10"" ssCe'*^ 32 d 5.7 6.3X10"' 1.8 X 10' 65.0 4.9X10"' 7.6X10"* 2.0X10^ esEu^" 2y 0.03 0.44 5.1X10' 3.8 1.4X10"' 3.6X10"' 9.7X10^ ooTe^"'" 33 d 0.3 3.4X10"' 1.0 X 10' 63.4 2.8X10"' 4.4X10"' 1.2X10"" saTe^" 70 m — — 1.0 X 10' — 2.8X10"' 4.4X10"' 1.2X10"" 59Pr"' 13.7 d 5.4 — 40 151 1.1X10"' 7.2X10"" 2.0X10"" BeBa"" 12.8 d 6.1 — 30 161 8.0X10"* 5.0X10"" 1.3X10"" 57Lai*" 1.7 d — — 30 — 8.0 X 10"* 5.0 X 10"" 1.3 X 10"" 5oSn^ 130 d 1.2 X 10"' — 6.8 16.8 1.8 X 10"* 1.1 X 10"' 3.0 X 10"" Xd"'" 44 d 8 X 10"* — 0.64 47.4 1.7 X 10"' 3.6 X 10"' 9.8 X 10"" B3P' 8 d 2.8 — 0.35 256 9.5 X 10"" 3.7 X 10"^ 1.0 X 10"'' esEu^'" 15.4 d 0.01 — 0.15 134 4.0X10"" 3.0X10"' 8.0X10"" bbCs"" 13.7 d 0.01 — 7.5X10"' 151 2.0X10"" 1.3X10"' 3.6X10"" BoSn^' 10 d 0.02 — 1.7 X 10"' 206 4.7 X 10"' 2.3 X 10"" 6.2 X 10"** 47Ag*" 7.6 d 0.018 — 1.4X10"' 268 3.9X10"' 1.4X10"" 3.9X10"*' Totals: 3230 7.7 X 10' 19.3 12.1 3.2 X 10"* Natural potassium and rubidium in the sea: K*" 6.3 X 10" 4.6 X 10' 1 12 12 3.2 X 10"* Rb" 1.2 X 10** 8.4 X 10' 1 0.22 0.22 5.9 X 10"" All activity values are Beta activities only, except where isomeric transitions are indicated. Conversion: 1 disintegration per second ^ 2.7 X 10"' microcuries. 1 curies: 3.7 X 10*" disintegrations per second. 42 Atomic Radiation and Oceanography and Fisheries 0.1 .4 .5 2 3 4 5 iO HALF-LIFE (YEARS) Figure 1 30 40 50 100 However, the effect of the internal mixing rate of the sea in the model adopted, is to cut the activity in the mixed layer down to 12.1 dps/liter which is, by coincidence, just equal to the natural activity and which would thus just double the activity in the mixed layer. It should be noted that the figures given in the table for the predicted activities in the mixed layer refer only to cross-thermocline mix- ing by physical processes, exclusive of biological transfer through the thermocline. However, the figures listed provide a basis for speculation on the hazardous effects of the mixed layer activity, in that comparison may be made with biological concentration factors, discussed else- where in this report, to predict the activity levels in marine organisms. In this way, rough predictions may be made of the hazard to man, not only by direct exposure to the waters of the mixed layer of the sea, but by the activity con- centrated in marine organisms used for food. Chapter 4 TRANSPORT AND DISPERSAL OF RADIOACTIVE ELEMENTS IN THE SEA ' Warren S. Wooster, Scripps Institution of Oceanography, La Jolla, California and BosTWiCK H. Ketchum, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts The fate of radioactive elements in the sea differs from that of non-radioactive elements since they are subject to radioactive decay. Otherwise, concentrations of radioactive ele- ments are changed by the same physical and biological processes as are those of other iso- topes in the same physical state. Thus the fate of radioactive material introduced into the sea depends on: 1. What is introduced — the nuclide, its radio- active properties (half -life, nuclear reaction, kind and energy of radiation), its physical state in sea water (whether particulate, colloidal or ionic) and its chemical properties (including its role in biological processes). 2. Where it is introduced — position and depth with respect to the density and velocity struc- ture of the sea. This paper describes the physical processes whereby radioactive elements in true solution are diluted by mixing and are carried from one part of the ocean to another. Although all parts of the open ocean appear to be in continuous motion and in communication with each other, the rates of this motion and exchange cover such a wide range that it is convenient to con- sider separately the questions of near-surface vertical and horizontal exchange, intermediate and deep circulation, and the exchange between the deep sea, coastal areas and enclosed basins. Near-surface circulation In middle and low latitudes the surface layer of the ocean, from 10 to 200 meters thick, is '^ Contribution from the Scripps Institution of Oceanography, New Series, no. 903. Contribution no. 870 from the Woods Hole Oceanographic Institution. This paper, in part, represents results of research car- ried out by the University of California under con- tract with the Office of Naval Research. Reproduction in whole or in part is permitted for any purpose of the United States Government. separated from the colder deep waters by a layer of rapid density change and great sta- bility, the pycnocline or thermocline. This intermediate layer varies in depth and stability from time to time and from place to place. At times there are two such layers, the seasonal thermocline and a deeper main thermocline. The surface layer is often called the "stirred" or "mixed" layer ^ because of its relative uni- formity in temperature and in concentrations of dissolved substances. It is believed that radioactive material in- troduced into this surface layer will be rapidly distributed vertically throughout the layer. The general uniformity of concentrations within this layer suggests that forces are present which tend to bring it about. Because density increases only slightly with depth through the layer, little energy is required for vertical stirring. Some evidence of the rapidity of vertical mixing in the upper layer is given by Folsom (Revelle, Folsom, Goldberg and Isaacs, 1955), who observed that when fission products were introduced at the surface in an area where the surface layer was about 100 meters thick, the lower boundary of the radioactive water reached the bottom of this layer in about 28 hours. Within this period of time radioactivity had be- come uniformly distributed vertically through- out the layer. Rapid vertical mixing in the upper layer is brought about primarily by the following two processes: 1. Convection: When the density of surface water is sufficiently increased, owing to either 2 A distinction is made here between stirring and mixing. In stirring, one causes relative motion of different parts of the liquid, and the average value of the gradient is increased. Mixing then takes place, the gradients disappearing and the liquid becoming homogeneous (Eckart, 1948). 43 44 Atomic Radiation and Oceanography and Fisheries a decrease in temperature or an increase in salinity, the surface water sinks and mixes with deeper water. Convection is maintained by (a) surface coohng due to long wave radiation and heat conduction to the atmosphere, (b) the loss of latent heat and water vapor in evapora- tion, or (c) the increase of surface salinity from free2ing of surface water. 2. Wind stirring: Vertical turbulence in the upper layer results from wind action on the sea surface. The extent of wind stirring depends both on the magnitude and uniformity of wind stress and on the vertical density gradient. Stir- ring is effective only to a depth where there is sufficient energy to overcome the effect of sta- bility. Both the homogeneity and the depth of the upper layer are affected by wind. Single gales have been observed to deepen the surface layer on the average by about 20-30 feet, (Francis and Stommel, 1953). Rapid vertical mixing may be brought about by other processes. Thus in shallow coastal areas stirring by strong tidal currents is im- portant. Stirring may also be accomplished by the vertical component of currents, particularly in regions of upwelling and sinking. It should be noted that even above a well- developed pycnocline there is not complete ho- mogeneity within the so called "mixed" layer. Concentrations of those elements affected by biological activity (such as oxygen and phos- phorus) may show significant variation within the euphotic zone. Even so-called "conserva- tive" concentrations (temperature and salinity) may not be uniform within the surface layer. Such heterogeneity may be attributed to in- complete vertical mixing or to vertical shear in the surface layer. When radioactive materials are introduced into the near-surface layer, they are transported away from the area of introduction by surface currents. These currents extend, in general, through the entire depth of the upper layer and seem to be driven, directly or indirectly, by the wind. The average locations and velocities of the important surface currents of the world ocean have been studied for many years and are well known (see, for example, Deutsche Seewarte, 1942; U. S. Navy Hydrographic Office, 1947 a and b, 1950; Sverdrup, Johnson, and Flem- ing, 1942, ch. 15). This knowledge comes primarily from averages of countless ship-drift observations, and from computations based on the observed subsurface distribution of density. These calculations give mean speeds as high as 193 cm/sec (90 miles per day) in the Florida Current (Montgomery, 1938a) and 89 cm/sec (41 miles per day) in the Kuroshio (Koenuma, 1939). The volume of water flow- ing through the Florida Straits in 15 years is about equal to that of the upper 500 meters of the whole North Atlantic. Similarly, between the northern Ryukyus and Kyushu, the Kuro- shio transports a volume equivalent to that of the upper 500 meters of the North Pacific in about 50 years. It seems likely that there is no area of surface water in the ocean that can be considered as isolated from the remaining surface waters. Recent intensive studies of the Gulf Stream and other surface currents, using such modern instruments as the bathythermograph, electronic navigational aids, and geomagnetic electro-kine- tograph (GEK), have revealed complicated fine structures, with filamentous jets and counter- currents not apparent in the average picture (Fuglister, 1951). Characteristic maximum sur- face velocities measured by GEK and Loran dead reckoning in the Gulf Stream were found to fluctuate between 150 and 300 cm/sec or 70 to 140 miles per day (von Arx, Bumpus and Richardson, 1955). Thus, in estimating the time at which radioactive materials will be found at various distances from the area of introduction, one must be cautious in the use of average surface current speeds. Direct evidence of the transport of radio- active materials by surface currents in the western Pacific is given by "Shunkotsu-Maru" survey (Miyake, Sugiura and Kameda, 1955) and the "Taney" survey (U. S. Atomic Energy Commission, 1956) four months and thirteen months respectively after nuclear weapons tests in the Marshall Islands in March, 1954. The earlier survey found significant levels of radio- activity at a distance of 2000 kilometers from Bikini, suggesting a westward drift of more than 9 miles per day (about 20 cm/sec) . The later survey found significant levels of radio- activity at least 7000 kilometers downstream from Bikini ; this gives about the same minimum westward drift. In addition to being drifted away from the area of introduction, radio-active materials are Chapter 4 Transport and Dispersal 45 dispersed by diffusion. Diffusion in the ocean is caused by turbulence or eddies, and the coefficient of eddy diffusivity is usually more than a million times the corresponding molecu- lar coefficient. The rate of eddy diffusion de- pends on wind speed, current shear, density gradient, gradient of the diffusing concentra- tion, direction of diffusion, and the dimensions of the phenomenon. The calculated rates de- pend upon the magnitudes of eddy diffusivity coefficients used, and they have been estimated by a number of methods (Sverdrup et al., 1942, p. 484-485; Munk, Ewing and Revelle, 1949). Because of both the large number of variables concerned and the present unsatisfactory state of our quantitative knowledge of turbulence in the ocean, it is difficult to predict the diffusion of radioactive materials under any given cir- cumstances. The most satisfactory approach at present is to conduct diffusion studies and ex- periments at the place and under the conditions of contemplated release. The results are only applicable to the particular areas. During the 1946 preliminary survey in Bikini Lagoon, the state of turbulence was determined by a variety of measurements, and the subse- quent observed distribution of radioactivity was in close agreement with the predicted values (Munk, Ewing and Revelle, 1949) . A mean value for the radius of the contaminated area was 3 km., which approximately doubled be- tween the first and second days after the burst. The initial distribution of radioactivity as de- posited by the atomic bomb was patchy, and the turbulent eddies, which spread the con- tamination over a larger area, did not appreci- ably reduce this patchiness during the first three days. Another pertinent study was made by Ketchum and Ford (1952) who examined the rate of dispersion of acid-iron wastes in the wake of a barge at sea. Computed mixing coefficients showed a tendency to increase with increasing time, and thus with the dimensions of the mix- ing field, and the radius of the contaminated area was observed to double in time periods ranging from 0.5 minutes to 35 minutes. It should be noted that the scale of this phenom- enon was about 10-- that of Munk, Ewing and Revelle (1949) ; they show that the ratio of lateral eddy diffusivity coefficient to the radius of the area considered is relatively constant over a range of radius between 10^ and 10^ cm. A large scale tracer experiment was carried out in the Irish Sea prior to the discharge of radioactive effluent (Seligman, 1955). During each experiment, 10 tons of 6.7 percent fluores- cein solution were introduced near the surface during a 20-minute period, and the sensitivity of subsequent detection was believed to be of the order of 1 part in 10^. Maximum concen- trations detected directly after release were 10~* of the original concentration; 12 hours after release, they were down to 5 x 10"^ of the original concentration. The trial area was prob- ably part of an eddy and was subject to tidal mixing, so the results may not be generally applicable. Exchange hetiveen near-surface and intermediate xaaters Since the surface layer is separated from deeper waters by a layer of rapid density in- crease, and hence of great stability, vertical transfer of materials across this layer by eddy diffusion must be much less rapid than is ver- tical diffusion in the upper layer. Thus radio- activity introduced at the surface by fallout may remain in the upper layer for a long time and be diluted by only a small part of the total volume of the sea. Conversely, radioactive ma- terials introduced below the pycnocline should only slowly contaminate the upper layer where they are most likely to endanger human ac- tivities. However, organisms and particles of sufficient density may readily cross the pyc- nocline, due both to gravity and to vertical migrations. There are few observations which show di- rectly the existence of cross-pycnocline exchange on a local scale. In the western Pacific, both the "Shunkotsu-Maru" survey (Japanese Fishery Agency, 1955) and the "Taney" survey (U. S. Atomic Energy Commission, 1956) reported patches with significant concentrations of radio- activity below the thermocline four months and thirteen months, respectively, after mixed fis- sion products were introduced at the surface in the Marshall Island area. It is not known, how- ever, whether this exchange was effected by mixing processes, or by particulate or ecological processes. Exchange of properties between the near- 46 Atomic Radiation and Oceanography and Fisheries surface and deeper waters is most likely to take place under the following conditions: 1. In regions where the pycnocline is suffi- ciently shallow to be eroded at the top by wind stirring. In coastal waters the pycnocline is usually shoaler than in midocean, and shallow pycnoclines may also be found in high lati- tudes, at the equator, along the north edge of the Equatorial Countercurrent, and at the cen- ter of strong cyclonic eddies. This process is not effective to great depths, but could serve to bring radioactive materials into the surface wa- ters from the pycnocline layer. 2. In regions of up welling, where the pycno- cline is relatively weak and where vertical cur- rents not only carry water toward the surface but also stir surface and deeper waters. It is unlikely that water from depths of more than 500 meters is ever brought to the surface by this process. Upwelling is common along west- ern coasts of continents in the trade wind belt, such as the coasts of Peru and Northern Africa. In a simple sense, the persistent trade winds blowing parallel to or offshore develop an off- shore component of transport in the surface waters, and deeper waters upwell to maintain the volume continuity. Upwelling may also occur along other coasts when the winds are suitable. The process has been extensively stud- ied along the coast of California where it is not continuous because of the variability of the winds (Sverdrup et al., 1942, p. 725). The speed of coastal upwelling has been variously estimated as 0.6 m/day (McEwen, 1934), 2.25 m/day (Saito, 1951) and 2.7 m/day (Hidaka, 1954) . However, since these estimates are theo- retical mean values, they may differ significantly from actual instantaneous upwelling rates. Midocean upwelling, associated with diver- gence of the surface currents, occurs in a band along the equator in the eastern and central Pacific Ocean (Cromwell, 1953). Observations indicate that the effects of this upwelling ex- tend to 50 meters in the eastern Pacific and to 100-150 meters in the central Pacific (Wooster and Jennings, 1955). Similar but less pro- nounced upwelling has been observed in the equatorial Atlantic (Bohnecke, 1936) . 3. In regions of surface convergence, where sinking waters may fill the depths of the ocean, or may spread at intermediate depths according to their density. In tropical and temperate latitudes such sinking is confined to the surface layer. In such regions mixing in the upper layer may be facilitated but exchange across the pycnocline probably is not, since the sinking water tends to increase the density gradient in the pycnocline. In high latitudes, on the other hand, sinking waters may reach great depths, and it is in such regions that most of the intermediate and deeper water masses of the ocean are formed. The most extensive and pronounced of these convergences is the Antarctic Convergence which occurs at 50 to 60° S in a band around the entire Antarctic Continent. The cold, low-salinity water which sinks there forms an identifiable water mass, the Antarctic Intermediate Water, which spreads at depths between 800 and 1200 meters in all southern oceans. This water can be identified everywhere in the South Atlantic and extends across the equator as far as 22 °N in the North Atlantic (Deacon, 1933; Iselin, 1936). In the Irminger Sea, between Iceland and Greenland, and in the Labrador Sea, warm high salinity water of the Gulf Stream is partly mixed with cold low-salinity water flowing out of the Arctic Ocean. The resulting mixture may spread in small quantities as Arctic Intermediate Water, or when sufficiently dense may form the deep and bottom water of the North Atlantic (the possibility that the formation of this deep water is not a continuous process is discussed later) . Intermediate waters of the North Pacific are probably formed in winter at the convergence between the Kuroshio Extension and the Oya- shio (Sverdrup et al, ch. 15). There is ap- parently no deep or bottom water formed by this process in the Pacific. 4. In regions where the density of surface waters is so increased by evaporation, cooling or freezing, that they sink to intermediate or greater depths. Active formation of Antarctic Bottom Water takes place in the Weddell Sea due to the freezing of high salinity surface waters. In the Mediterranean and Red Seas, bottom water is formed by winter cooling of waters whose salinity has been greatly increased by evaporation. Mediterranean water flows out into the North Atlantic at depths of 1000 to 1500 meters and can readily be identified near Bermuda, 2500 miles from its source. In summary, exchange between near-surface and deeper waters takes place most commonly (1) in high latitudes, (2) along the equator. Chapter 4 Transport and Dispersal 47 and (3) in coastal regions, particularly along the western coasts of continents. Conversely, such exchange is least likely in temperate and tropical latitudes in the vast central regions of the northern and southern oceans. Exchange betiveen the open sea and coastal areas In coastal areas or enclosed basins where precipitation exceeds evaporation, there is a seaward surface drift of diluted water and a landward subsurface drift of water derived from the open sea. If radioactive materials were released in such a coastal area, the ma- terial which remained in the surface layer would be carried seaward, but the part of the material which mixed or settled to the deeper water would move toward shore and the estuaries of rivers. Conversely, if radioisotopes were lib- erated in the open sea, some would eventually be carried inshore as a result of the coastal and estuarine circulation. It is clear that the ultimate distribution in coastal areas of radioactive materials added to the sea would depend on the location of the release, the vertical distribution of radioactivity and density in the area of release, the length of time required for the transport to the coastal area or estuary, and the location of the source sea water which provides for the counter drift. The number of variables involved makes it difficult to discuss the effects in general terms, but it is worthwhile to note that the circulation in coastal areas is rapid, and water bathing the North Atlantic beaches is not uncommonly 90 per cent sea water even off large rivers such as the Hudson and Delaware. An idea of the lengths of time involved in the coastal circulation can be obtained from the mean age of waters in various parts of the At- lantic seacoast. Such mean ages are computed from the volume of water contained in the region and the estimated transport of water through the region. The waters of the con- tinental shelf from Cape Hatteras to Cape Cod have a mean age of about 2\ years, those of the Bay of Fundy about 3 months, and those of Delaware Bay from the ocean to the height of tide about 3-4 months (Ketchum and Keen, 1953, 1955). The source sea water for all of these circulations is the "slope water" which is formed between the Gulf Stream and the edge of the continental shelf. A few data are available for confined basins and seas from which estimates of the mean age of the water can be derived. In most cases, however, the sources of water entering into the circulation are uncertain, and it should be em- phasized that in all cases some of the waters within the basin will be older or younger than the mean age. The source waters of the Florida Current are funnelled through the Caribbean Sea. The mass transport is 26 million cubic meters a second (Sverdrup et al., 1942, p. 638), so that this current carries annually a volume of water equivalent to one-sixth of the total volume of the Caribbean. However, there is evidence that the renewal of the deep water of the Caribbean proceeds at a much slower rate than the six year mean age that this ratio implies. Wor- thington (1955) has calculated, on the basis of loss of oxygen from this deep water during the last 30 years, that the age of the deep water in the various parts of the Caribbean may range from 93-142 years. The mean age of the waters above 2000 meters would be reduced to about 5 years if the deepest \ of the volume of the basin is isolated from the present circulation. The same current passes through the Yucatan channel into the Gulf of Mexico, before emerg- ing as the Florida Current. No estimate of the mean age of the waters of the Gulf of Mexico is possible, however, since the current data in the Gulf indicate an anticyclonic eddy in the western portion, and suggest that the waters of the Gulf of Mexico are drawn into the Florida Current to only a slight extent (Die- trich, 1939, Sverdrup et al., 1942, p. 642). The Black Sea probably contains the most isolated and the oldest deep water to be found anywhere in the oceans. Precipitation and run- off exceed evaporation, and the surface waters are dilute (salinities less than 18 per cent) and isolated from the deep water by an intense density gradient. The deep waters are anaero- bic; hydrogen sulfide reaches large concentra- tions below about 200 meters. The sill at the Bosporus is only 90 meters below the surface so that this deeper water is isolated from the more rapid surface circulation. The inflow of sea water is so small that it would take about 2500 years to replace the deep water in the basin (Sverdrup et al., 1942, p. 651). The mean replacement time for the surface layers 48 Atomic Radiation and Oceanography and Fisheries to a depth of 200 meters is equivalent to about 200 years. Gololobov (1949) has computed the mean age of the deep water on the basis of the annual contribution of phosphorus in the river inflow and the quantity accumulated in the depths. This computation indicates an accumulation time of 5600 years. The Arctic Basin receives its major inflow north of Scotland and a much smaller inflow through the Bering Strait. Additional sources are from the river runoff and excess of precipi- tation over evaporation. The outflow is pri- marily through the Denmark Strait (Sverdrup et al., 1942, p. 655). These flows would pro- vide a volume equal to that of the Arctic Ocean in about 160 years. The Arctic is also stratified because of the addition of fresh water from rivers and melting ice, and it is not known how isolated some of the waters in the deeper basins may be. However, recent analyses have shown that the deeper water in the Arctic Ocean is far from anaerobic, so that it seems unlikely that this water can be considered as isolated from the circulation. The Mediterranean is a basin in which evaporation exceeds precipitation and runoff^. Through the Strait of Gibralter there is an inflow of oceanic surface water and a sub- surface outflow of high salinity Mediterranean water. The exchange is sufficiently rapid to replace the entire Mediterranean in about 75 years (Sverdrup et al., 1942, p. 647). The Mediterranean is divided into eastern and west- ern basins by a 500-meter sill between Sicily and Tunisia, and it is not know to what extent the deep waters of these basins are involved in the over-all exchange. Deep circulation Most of our present knowledge of the inter- mediate and deep circulation (see Sverdrup et al., 1942, ch. 15) has been obtained in- directly from the observed distribution of prop- erties. The general uniformity of temperature and dissolved substances in deep water suggests that deep currents are very slow, perhaps at most a few centimeters per second. But deep currents cannot be computed by the geostrophic method because only relative velocities can be thus obtained. Furthermore, small errors in the measurement of salinity or temperature produce uncertainties in velocity of the same magnitude as the currents being computed. The direction of movement in the deep and bottom water has been deduced from the observed distribution of properties such as salinity and potential temperature, but little can be learned about current speeds from such observations. Existing direct measurements of subsurface currents have been summarized by Bowden (1954). Such measurements have been made since the time of the CHALLENGER Expedi- tion (1873-76), but because of practical diffi- culties (such as the problem in the open sea of referring observations to a fixed frame of reference) they have taught us little about the deep oceanic circulation. The few successful measurements at depths greater than 1000 me- ters reported by Bowden showed mean speeds ranging from "negligible" to about 13 cm/sec. At nearly all stations and depths at which current measurements have been made, semi- diurnal tidal currents of the order of 10 cm/sec. have been recorded. Recently measurements of subsurface currents have been made in the North Atlantic by track- ing for three days a neutral-buoyant float sta- bilized at a given depth (Swallow, 1955 and unpublished). These measurements show small resultant speeds (1.7 to 9.1 cm/sec or 0.8 to 4.2 miles/day at depths from 600 to 1900 meters), tidal components of about 10 cm/sec, and in two successive three-day measurements at 1900 meters, a change in direction of 124°. Thus it seems likely that motion below the pycnocline is characterized by more variation, periodic or otherwise, than previously supposed and indeed that the mean drift may represent only a small part of the total motion. Little is known about the nature and extent of lateral and vertical mixing in the deep sea. It is generally believed, however, that flow and mixing take place along surfaces of constant potential density (isentropic surfaces) and that below the upper layer vertical mixing is very slow except near coastlines and areas where upwelling may occur (Montgomery, 1938). An observation supporting this belief was reported by Revelle, et al. (1955). Introduction of mixed fission products below the pycnocline led to the formation of a lamina of high radio- activity about one meter thick and 100 or more square kilometers in area. The radioactive water apparently spread out along an isentropic sur- face and resisted destruction by vertical mixing for at least three days. Chapter 4 Transport and Dispersal 49 Age of intermediate and deep waters It is generally accepted that intermediate and deep waters in most parts of the oceans acquired their characteristics while at or near the surface. Thus the low temperature and relatively high oxygen content of deep water can only be ex- plained by assuming an exchange between deep and surface waters. The problem of the dis- posal of radioactive wastes in the deep sea has stimulated the oceanographer's natural curiosity as to the rate of this exchange. The North Atlantic receives surface waters from the South Atlantic and loses deep water to the South Atlantic. Assuming a surface flow from the South to the North Atlantic of 6 million cubic meters per second (Sverdrup et al., 1942, p. 685), and considering only the upper kilometer of the North Atlantic to be affected, the mean replacement time is about 140 years. The gyral in the North Atlantic, which includes the Gulf Stream, carries about ten times the volume of water exchanged be- tween the South and North Atlantic, so that the mean circulation time is only about one- tenth the replacement time. This surface exchange between the North and South Atlantic is balanced by a deep current from North to South. The mean displacement time for the deep water of the North Atlantic (2000-4000 meters) is calculated as about 250 years. This time is in reasonable agreement with more recent estimates of the age of the deep water discussed below. Between these surface and deep layers are the intermediate waters which appear to circu- late even more rapidly. Deacon (1933) calcu- lated rapid rates of northward flow of the Antarctic intermediate water in the South At- lantic, based upon alternate maxima and minima in the concentrations of oxygen in the oxygen minimum layer. These were interpreted as rep- resenting annual cycles when the waters were formed at the surface. He estimated a transit time of about 4^ years between the Antarctic convergence and the equator. Seiwell (1934) has similarly computed rapid flows and a mean transport time of 7-8 years for the drift of the oxygen minimum layer of the North Atlantic Ocean. Deacon's and Seiwell's interpretations have been questioned (see Riley, 1951, p. 77) on various grounds. However, their rates of flow agree with direct current measurements at comparable depths (see earlier) which also indicate rapid rates of circulation. The deep outflow from the Mediterranean sinks from sill depth to 1000-1500 meters in the North Atlantic Ocean. This water, although much diluted by Atlantic water, is characterized by relatively high salinity and temperature, and spreads out in a sheet which may be identified in most of the temperate North Atlantic, and some spreads into the South Atlantic. It can be readily identified near Bermuda, 2500 miles from its source. Iselin (1936) computed that sufficient excess salt would be produced by the Mediterranean outflow to produce the observed anomaly in 12-15 years. He pointed out that the actual replacement would be more rapid because he neglected admixture of Atlantic water in the immediate vicinity of the Straits of Gibraltar. Defant (1955) has evaluated the mixing processes involved in dissipating the Mediterranean water within the Atlantic Ocean, and has concluded that the total accumulation in the Atlantic Ocean represents the contribu- tion resulting from six years of flow through the Straits of Gibraltar. The rapid dissipation of this large water mass at mid depths suggests a more rapid circulation than had been gen- erally accepted for intermediate waters. During recent years other lines of investiga- tion have led to the belief that the overturn of water in the ocean basin takes place in less than a thousand years and probably in 200 years or less. Evidence supporting this belief follows. (Carbon-l4 and carbon dioxide ex- change estimations are discussed in greater detail by Craig elsewhere in this report.) 1. Heat fiow measurements: Measurements re- ported by Revelle and Maxwell (1952) have shown a heat flow through the floor of the Pacific Ocean of 1.2x10"'' calories per square centimeter per second, or 38 calories per square centimeter per year. If not dissipated by circu- lation and mixing, this heat flow would lead to warming of the deep and bottom water during its passage from the Antarctic to the equator. From considerations of meridional circulation, observed temperature gradients and mixing in the deep sea, Revelle and Maxwell estimate that the deep water is replenished in less than 1000 years. 2. Secular change of oxygen: Worthington (1954) has shown that the North Atlantic Deep Water has suffered a loss of dissolved 50 Atomic Radiatio7j and Oceanography and Fisheries oxygen of about 0.3 ml/L over the last twenty years. Assuming a steady rate of attrition he computes that the date at which this water was saturated, presumably while at the surface, was about 1810. A further study (Worthington, 1955) suggests that the Caribbean Deep Water was formed at the same time. Thus it seems possible that formation of the North Atlantic Deep Water, which composes about half of the contents of the Atlantic, is not continuous but sporadic. 3. Carbon- 14 dating: In recent years the tech- niques of carbon-l4 age determination have been applied to deep sea water samples. The most reliable measurements (Rubin, unpub- lished), of samples from east of the Lesser Antilles, show the carbon at 1750 meters to be about 200 years older than the surface carbon. Present estimates of the age of deep waters are based primarily on measurements in the North Atlantic and on geochemical calculations for the entire world ocean. That the deep cir- culation of the Pacific is significantly slower than that of the Atlantic is suggested by the apparent absence of regions of deep and bottom water formation in the Pacific and the rela- tively high nutrient salt content and low dis- solved oxygen content of deep Pacific waters. In order to determine whether the deep waters of the Pacific would provide a longer period of isolation for radioactive wastes than elsewhere, deep Pacific oceanographic data must be care- fully scrutinized. REFERENCES BoHNECKE, G. 1936. Atlas: Temperatur, Salz- gehalt und Diclite an der Oberflache des Atlantischen Ozeans. Deutsche Atlantische Exped. Meteor, 1925-27, Wiss. Erg. 5: vii + 76 pp. BowDEN, K. F. 1954. The direct measurement of subsurface currents in the oceans. Deep- Sea Res. 2:33-47. Cromwell, T. 1953. Circulation in a meri- dional plane in the central equatorial Pa- cific. /. Marine Res. 12:196-213. Deacon, G. E. R. 1933. A general account of the hydrology of the South Atlantic Ocean. Discovery Rep. 7 :l71-2?>8. Defant, a. 1955. Die Ausbreitung des Mit- telmeerwassers im Nordatlantischen Ozean. Pap. Mar. Biol, and Oceanogr., Deep-Sea Res., suppl. to 3:465-470. Deutschen Seewarte. 1942. Weltkarte zur Ubersicht der Meeresstromungen. Deutschen Seewarte No. 2802. Dietrich, G. 1939. Das Amerikansiche Mit- telmeer. Gesellsch. Erdkunde zu Berlin, Zeitschr., 108-130. ECKART, C. 1948. An analysis of the stirring and mixing processes in incompressible fluids. /. Marine Res. 7:265-275. Francis, J. R. D., and H. Stommel. 1953. How much does a gale mix the surface layers of the ocean. Quart, f. Roy. Me- teorol. Soc. 79:534-536. Fuglister, F. C. 1951. Multiple currents in the Gulf Stream System. Tellus 3(4): 230-233. Gololobov, Y. K. 1949. Contribution to the problem of determining the age of the present stage of the Black Sea (in Rus- sian). Dokl. Akad. Nauk SSSR 66:451- 454. HiDAKA, K. 1954. A contribution to the theory of upwelling and coastal currents. Trans. Am. Geophys. Union 35(3) :431-444. IsELiN, C. O'D. 1936. A study of the circula- tion of the western North Atlantic. Pap. Rhys. Oceanogr. Meteorol. 4(4): 1-101. Japanese Fishery Agency. 1955. Report on the investigations of the effects of radia- tion in the Bikini region. Res. Dept., Japanese Fishery Agency, Tokyo, 191 p. Ketchum, B. H., and W. L. Ford. 1952. Rate of dispersion in the wake of a barge at sea. Trans. Am. Geophys. Union 33 (5) : 680-684. Ketchum, B. H., and D. J. Keen. 1953. The exchanges of fresh and salt waters in the Bay of Fundy and in Passamaquoddy Bay. /. ¥ish. Res. Bd. Can. 10:97-124. 1955. The accumulation of river water over the continental shelf between Cape Cod and Chesapeake Bay. Pap. Mar. Biol, and Oceanogr., Deep-Sea Res., suppl. to vol. 3: 346-357. KoENUMA, K. 1939. On the hydrography of south-western part of the North Pacific and the Kuroshio. Kobe Imper. Marine Observ., Memoirs 7:41-114. McEwEN, G. F. 1934. Rate of upwelling in the region of San Diego computed from Chapter 4 Transport and Dispersal 51 serial temperatures. Fifth Pac. Set. Congr., Toronto 3:1763. MiYAKE, Y., Y. SuGiURA, and K. Kameda, 1955. On the distribution of radioactivity in the sea around Bikini Atoll in June, 1954. Pap. Meteorol. Geopbys., Tokyo 5(3, 4):253-362. Montgomery, R. B. 1938a. Fluctuations in monthly sea level on eastern U. S. coast as related to dynamics of western North Atlantic Ocean. /. Marine Res. 1:165- 185. 1938b. Circulation in upper layers of south- ern North Atlantic deduced with use of isentropic analysis. Pap. Phys. Oceanogr. Meteorol. 6(2): 1-5 5. MuNK, W. H., G. C. EwiNG, and R. R. Re- velle. 1949. Diffusion in Bikini Laqoon. Trans. Am. Geophys. Union 30(1) :59- 66. Revelle, R., and A. E. Maxwell. 1952. Heat flow through the floor on the eastern North Pacific Ocean. Nati/re 170:199. Revelle, R., T. R. Folsom, E. D. Goldberg, and J. D. Isaacs. 1955. Nuclear science and oceanography. United Nations Inter- national Conference on the Peaceful Uses of Atomic Energy, Geneva, Paper no. 277: 22 pp. Riley, G. A. 1951. Oxygen, phosphate and nitrate in the Atlantic Ocean. Bull. Bing- ham Oceanogr. Coll. 13, Art. 1:1-126. Saito, Y. 1951. On the velocity of the vertical flow in the ocean. /. Inst. Polytech., Osaka City Univ. 2(1) Ser. B.:l-4. Seiwell, H. R. 1934. The distribution of oxygen in the western basin of the North Atlantic. Pap. Phys. Oceanogr. Meteorol. 3(l):l-86. Seligman, H. 1955. The discharge of radio- active waste products into the Irish Sea. Part 1. First experiments for the study of movement and dilution of released dye in the sea. Proceedings of the International Conference on the Peaceful Uses of Atomic Energy, Geneva. Paper 9:701-711. SvERDRUP, H. U., M. W. Johnson, and R. H. Fleming. 1942. The oceans, their physics, chemistry and general biology. Prentice- Hall, N. Y., x+1087 pp. Swallow, J. C. 1955. A neutral-buoyancy float for measuring deep currents. Deep- Sea Res. 3:74-81. U. S. Atomic Energy Commission. 1956. Operation Troll. U. S. Atomic Energy Commission, New York Operations Office, NYO 4656, Ed. by J. H. Harley, 37 pp. U. S. Navy H\T)ROGraphic Office. 1947a. Atlas of surface currents, north Atlantic Ocean. H. O. Pub. 571, First Ed., re- printed 1947. 1947b. Atlas of surface currents, northeast- ern Pacific Ocean. H. O. Pub. 570, First Ed. 1950. Atlas of surface currents, northwestern Pacific Ocean. H. O. Pub. 569, First Ed., reprinted 1950. Von Arx, W. S., D. F. Bumpus, and W. S. Richardson, 1955. On the fine structure of the Gulf Stream front. Deep-Sea Res. 3:46-65. WoosTER, W. S., and F. Jennings. 1955. Exploratory oceanographic observations in the eastern tropical Pacific, January to March, 1953. Calif. Fish and Game 41: 79-90. Worthington, L. V. 1954. A preliminary note on the time scale in North Atlantic circulation. Deep-Sea Res. V.lAA^l'bX. 1955. A new theory of Caribbean bottom- water formation. Deep-Sea Res. 3:82-87. Chapter 5 THE EFFECTS OF THE ECOLOGICAL SYSTEM ON THE TRANSPORT OF ELEMENTS IN THE SEA ' BOSTWICK H. Ketchum, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts Some elements may be profoundly influenced by the biological cycle and their resulting dis- tribution in the sea may be quite different from the distribution of elements that are affected only by the circulation of the water. Numer- ous examples of the modification of distribution by biological activities could be given but it may suffice to review briefly the vertical distri- bution of phosphorus in the ocean. The photosynthetic fixation of carbon is lim- ited to the surface hundred meters or less of the sea by the penetration of light, and the plant nutrients, including phosphorus, are as- similated there. The surface concentration of these elements may be reduced to virtually zero. Below the photosynthetic zone, the con- centrations of these nutrients increase, reaching maximum values at depths of 200 to 1000 meters, the actual depth depending upon loca- tion and the oceanic circulation. These maxi- mum concentrations are produced by two proc- esses. The water at intermediate depths is formed by cooling at high latitudes in the ocean, where it sinks and spreads out. At the time of sinking, it contains some inorganic phosphorus and organic matter which is de- composed, liberating the plant nutrients and decreasing the oxygen content. Additions to the organic matter from the surface waters occur everywhere, increasing the nutrient maxi- mum concentration and decreasing the oxygen minimum. Below the nutrient maximum-oxygen minimum layer the concentration of phosphorus decreases again reaching values which are gen- erally constant and uniform from a depth of about 1500 meters to the bottom (Redfield, 1942). The general patterns of distribution of the elements important in plankton growth on an ocean-wide scale are thus quite different from 1 Contribution No. 871 from the Woods Hole Oceanographic Institution. the pattern of distribution of the major ele- ments. The processes which must be considered in order to evaluate biological effects on the ultimate distribution of radioisotope wastes or contaminants in the sea include (1) the assimi- lation or adsorption of the elements by the bio- logical populations, (2) the effects of gravity, (3) vertical migrations, (4) horizontal migra- tions, and (5) the effects of stationary popula- tions in flowing systems. It has been shown in another section of this report that biological populations may concen- trate by several orders of magnitude various elements and their radioisotopes. To evaluate the possible significance of this in the oceans, it is necessary to determine the quantity of living material present (the biomass) and the rate of production of the populations of the ecological system. The biomass, when combined with the known concentration factor, will indicate how much of an element in the water may be com- bined in the living organisms. The most active concentration of elements may occur during the rapid growth of populations; consequently it is also essential to know the rate of production of the various populations involved. A few data on both the biomass and the rate of production of various populations in the sea are given in Tables 1 and 2. The biomass figures indicate that concentra- tion factors of 12,500 or more would be re- quired, under static conditions, to incorporate half of an element in a cubic meter of water within the ecological system even in the high concentrations of living material found in red- tide blooms. However, the biological popula- tions are not static; those movements which are independent of the motion of the water can, by repetition, transport larger proportions of elements than is indicated by static equilibrium conditions. The productivity values in Table 2 indicate that several times the standing crop of phytoplankton is produced annually. Both 52 Chapter 5 Ecological Systems and Transport 53 TABLE 1 Estimates of Biomass of Marine Populations. All Values Have Been Converted to Volume (Wet Weight) Per Cubic Meter (Parts Per Million) Population Phytoplankton . Zooplankton cc/m' 10 25 41 18.2 1.2 0.3 0.08 — 1.0 0.08 — 0.8 0.006 — 0.09 1.0 0.042 0.055 0.124 a. Complete utilization of maximum phosphorus concentrations; conversion P = 0.5 per cent of wet weight. b. Ketchum and Keen, 1948, 17-21, Table 1. Conversion as in a. c. Riley, Stommel and Bumpus, 1949, Table VI; conversion C^IO per cent wet weight. d. Redfield, 1941, drained volumes, vertical tows, assumed mean depth 100 meters. e. Riley, et al., 1949, Table V, displacement weight. f. Unpublished data, W. H. O. I., surface tows at night, drained volumes. g. Unpublished data, S. I. O., oblique tows 200-300 meters to surface, wet plankton volumes. Location and character .Maximum Atlantic Maximum Pacific Red Tide Blooms Long Island Sound Coastal Water Sargasso Sea . Gulf of Maine Coastal Water Sargasso Sea N. African Upwelling Eastern North Pacific Eastern Tropical Pacific Peru Current Source a a b c c c d e f,e f g g g the depth of the photosysthetic zone and the production rate at various depths, are variable, thus the values for production cannot be re- duced without excess over-simphfication to a volume basis which would permit direct com- parison with Table 1. However, Riley's (1941) maximum value for the standing crop of phyto- TABLE 2 Estimates of the Productivity of Marine Phytoplankton Populations Location and gC/m"/ cc/m"/ character Source year year i Sargasso Sea (Atlan- tic) a 18 180 Coastal Areas (Atlan- tic) a 1100 11000 Open Ocean (Pacific) . . a 50 500 Equatorial Divergence (Pacific) a 140 l400 Coastal Areas (Pacific) . a 200 2000 Oceanic Mean a 55 550 Long Island Sound min b 95 950 max 1000 10000 N. Atlantic 3°-13°N. . b 278 2780 Oceanic Mean c 340 ± 220 1200-5600 a. Steemann Nielsen (1954). Carbon-l4 method. This is given as gross production, but Ryther (1954) suggests that it may be net (gross minus respiration) production in nutrient poor areas. b. Riley (194l). Gross production, oxygen method. c. Riley (1944). 1 Conversion assuming one gram of carbon = 10 cc of wet plankton. plankton in Long Island Sound, 1.82 gC/m^, showed a production of 0.187 gC/myday and the annual production was twenty times as great as the maximum standing crop observed at any one time. Estimates of the growth of zooplank- ton populations have given values ranging up to 5 per cent of the standing crop per day. It is a truism in ecology that the total quan- tity of living material which can be produced decreases as the trophic level of the organisms considered increases. In some ecological sys- tems the biomass reflects this progression, i.e., at any one time there will be a larger standing crop of plants than of herbivores and the stand- ing crop becomes progressively smaller as one goes through the various higher steps of the food web. In the oceans, however, this is not necessarily true. It is common to find rather high concentrations of the herbivorous zoo- plankton when phytoplankton are scarce. Large populations of herbivores will quickly decimate the plants on which they feed. A balance may be maintained as a result of the different lengths of the life cycle of the various parts of the food web. A population of phytoplankton can double in a period of time ranging from hours to days, whereas the life cycles of zooplankton are more commonly measured in terms of weeks or months and the life cycles of the higher elements of the food web, such as fish, are 54 Atomic Radiation and Oceanography and Fisheries measured in terms of seasons or years. A com- paratively small population of phytoplankton doubling rapidly can provide the energy and nutrients of an equivalent or even larger animal population which is increasing more slowly. The size of various populations and their rate of production in the English Channel has been evaluated by Harvey (1950) and his re- sults are given in Table 3. These illustrate the above conclusions, since the average biomass of animals exceed that of the plants, but the rate TABLE 3 Average Quantity, Throughout the Year, of Plants and Animals Below Unit Area of Sea Surface in the English Channel i Dry wt of organic matter Standing crop Production Organism g-/m^ g./mVday Phytoplankton 4.00 0.4-0.5 Zooplankton 1.50 0.1500 Pelagic Fish 1.80 0.0016 2 Bacteria 0.04 — Demersal Fish 1.25 0.0010 Bottom Fauna 17.00 0.0300 ^ Bottom Bacteria 0.10 — 1 From Harvey (1950), depth equals 70 meters. 2 Based on estimated mortality of 30 per cent per annum. 3 Based on estimated mortality of 60 per cent per annum. of production of the plants exceeds that of the animal populations. The plankton organisms in the open sea pro- vide by far the largest quantity of living ma- terial and by even more the largest organic absorptive surface. Those radioisotopes which are adsorbed will become bound to the organ- isms, and they are as subject to the effects of gravitation and migration as if they had been assimilated and utilized. Gravity affects the organisms in a population and can thus modify the distribution of ele- ments which become incorporated in the bio- logical cycle. Ultimately only two fates await most of the plankton which grows in the sur- face layers. It may be eaten by the herbivores or it may sink out of the illuminated zone and decompose at greater depths. If the plankton is eaten by a herbivore, a proportion of the organic matter is incorporated into the herbivore body but an even larger proportion is returned to the water as excretion or faecal pellets. The excretions may be present in the water inhabited by the plankton and reused in situ. The faecal pellets settle into the deeper water where they decompose. Gravity thus imposes on elements which become incorporated in the biological system a modification of the distribution which would be produced by movements of the water alone, since they tend to accumulate at some intermediate depth in the water column, or on the bottom. One of the unsolved problems of marine biology is the definition of the proportion of organic matter which is decomposed by the time the particulate material sinks to various depths. This problem must be solved before an evalua- tion of the biological effects on the distribution of radioisotope contamination of the seas can be made. It may be worthwhile to summarize some of the present thinking on this problem. In the first place, everywhere that samples have been taken in the deep sea, living organ- isms have been found. Since we know of no mechanism other than photosynthesis at the sur- face which can provide the organic material necessary to support these populations, it is clear that some of the surface produced material must reach all depths of the ocean. It may be argued by some that the bacterial chemosyn- thetic processes are a source of fixed carbon which has not been considered, but the condi- tions in the deep sea are not suitable for the formation of organic matter by any of these processes. The presence of the nutrient maximum-oxy- gen minimum layer at intermediate depths in the sea has led to the conclusion that most of the organic matter formed at the surface must be oxidized by the time it has sunk to a depth of 1000 meters (Redfield, 1942). Analyses of organic phosphorus in the equatorial Atlantic Ocean showed considerable amounts in the waters above 1000 meters, but none at greater depths (Ketchum, Corwin, and Keen, 1955). There is no present evaluation of the quantity of organic carbon which can sink to greater depths, nor is it possible to evaluate whether this quantity would be sufficient to support the known populations of archibenthic organisms. These two extremes thus define the dilemma. Namely that some organic matter must reach the great depths, but, at the same time, most of the decomposition appears to occur above a depth of 1000 meters. The secular change of oxygen in the deep Chapter 5 Ecological Systems and Transport 55 sea which has been found by Worthington (1954) in the North Atlantic, provides one means of computing the total quantity of or- ganic matter required. Worthington observed a decrease of 0.3 milliliters of oxygen per liter in thirty years at depths between 2500 meters and the bottom. In the Atlantic Ocean this corresponds to an average thickness of 1500 meters and the total quantity of organic matter required to produce this change in oxygen is equivalent to the decomposition of 8 grams of organic carbon per square meter per year in this layer. This quantity of organic matter is nearly 15 per cent of the annual mean produc- tion according to Steemann Nielsen (1954) and from 1.4 to 7 per cent of the mean sug- gested by Riley (1944). Part of the secular change in oxygen may have been produced by eddy diffusion into the oxygen minimum layer, which would reduce the quantity of organic carbon reaching greater depths. The effects of gravity may be accentuated when the surface currents are opposed to the currents in the deeper layers. This type of circulation pattern is very common in estuaries, on continental shelves, and in those areas where offshore winds produce upwelling of the deeper waters. In all of these cases the nutrient rich deep water is carried inshore in a sub-surface drift, and brought to the surface by upwelling or vertical mixing. The nutrients are assimilated by the plankton in the surface layers and are carried offshore in the surface current. "When the organisms sink, they again reach the on- shore sub-surface current where they decompose liberating more nutrients into water which is already relatively rich. Thus the elements in- volved in biological processes follow a different cycle from the circulation of the water and this cycle leads to an accumulation of elements greater than can be found in either of the source waters (Strom, 1936; Hulburt, In press). Nutrient elements are commonly concentrated by this type of mechanism in fjords. Where the deepest water is relatively stagnant and isolated from the intermediate and surface layers, con- siderable concentrations of organic derivatives can be developed. In the Norwegian fjords with a relatively shallow sill, for example, anaerobic conditions may be produced in the bottom water and the nutrients are five to ten times as concentrated as in either of the source waters (Strom, 1936). In the Black Sea the deep water is isolated from the surface by a strong density gradient and its average age has been estimated at 2500-5000 years (Sverdrup, Johnson and Fleming, 1942, p. 651). Very large accumulations of organic derivatives are found in this deep water. (Gololobov, 1949.) Opposed currents can, however, work in the opposite way and lead to a decrease in the concentration of elements involved in the bio- logical cycle. The classic example of this type of circulation is the Mediterranean, where the nutrients available for plant growth are less than half of the concentration available in the adjacent parts of the Atlantic. In the Mediter- ranean the supply comes from the surface wa- ters of the North Atlantic which are already impoverished by plant growth. Since evapora- tion exceeds precipitation in the Mediterranean the water becomes more saline, sinks and is lost as a deep outflow over the sill at Gibraltar (Thomsen, 1931). The accumulation of ele- ments in sinking organisms transfers these ele- ments from the inflowing surface water to the outflowing deep water. They are eventually lost from the Mediterranean. A similar process apparently applies to the entire North Atlantic. There is a large inflow of South Atlantic sur- face water which contains low concentrations of elements involved in the ecological cycle. The outflow from the North Atlantic required to balance the water budget occurs at depths and this water contains considerable quantities of the elements which had been returned to the water (Sverdrup et al., 1942). In summary the various peculiarities of dis- tribution which can be attributed to gravitational effects on the ecological cycle are therefore (1) the accumulation of elements at inter- mediate depths as a result of sinking and de- composition, (2) the concentration of elements in areas of opposed flow where the deep water is brought to the surface by upwelling or ver- tical mixing and (3) the impoverishment of areas where the supply of water is from the surface and the loss from greater depths. In addition to the passive gravitational effects on organisms, animal plankton forms exhibit vertical migrations. A considerable literature has developed in this field over the last ten years, but the effects of these vertical migrations on the distribution of elements has not been studied directly and must be inferred from our knowledge of the ecological system. 56 Atomic Radiation and Oceanography and Fisheries Historically, a few studies of the vertical migration of zooplankton had been made prior to the war. Great impetus was given these studies when a false bottom was repeatedly observed on echo sounding recorders (Dietz, 1948; Hersey and Moore, 1948). This has been called the scattering layer. Although there is still controversy as to which organisms are the principal scatterers in the sea, it has been established that one or more layers are com- monly found which migrate vertically over a depth of as much as 800 meters, being at or near the surface at night and at great depths at mid-day. No observations of the changes of elements involved in the biological cycle which may be associated with vertical migrations have been made. Most of our analytical techniques are too insensitive to detect the day to day changes which might be expected in biologically active elements if our present evaluation of the density of the populations and their respiration and excretion rates is correct. It is known, however, that direct assimilation of some elements is possible by invertebrate forms and vertical trans- port of radioisotopes might be expected to re- sult. Indeed, the transport of radioisotopes might prove an excellent tool for the study of vertical migrations if a source were provided at one depth within the range of the migration. Ecologically the following effects might be expected as a result of vertical migration. The zooplankton are certainly in the area of the most dense concentration of their food, the phytoplankton, when they are at the surface at night. During the hours of darkness they may therefore be expected to consume the living material in the water, and some of this, at least, would be excreted or passed as faecal pellets at depth in the day time. This process would thus augment the effects of gravity on those elements incorporated in the biological system. There is also evidence that the zooplankton can as- similate dissolved elements from sea water. If elements were assimilated at depth they might be excreted or exchanged near the surface and thus directly modify the vertical distribution in the sea. It should not be neglected that larger or- ganisms can certainly migrate vertically over greater distances than we have discussed above. Certainly whales, tuna and sharks, and pre- sumably the smaller forms upon which they feed are known to go to considerable depths in the ocean. Quantitatively, of course, these members high on the food chain are propor- tionally small compared to the plankton or- ganisms. However, their effects on vertical dis- tribution of materials may not be negligible over periods of several decades. Horizontal migrations of organisms may also result in the transport of material involved in the biological cycle and are also independent of the currents of the ocean. Here again man does not know enough to assess these quantita- tively, but their possible effects should not be ignored. The migrations of pelagic fishes may be of considerable interest in this regard. The salmon for example reach maturity in the open sea, then migrate in enormous numbers to coastal areas to breed. Such a horizontal migration could transport radioisotopes, since the salmon could accumulate materials from large volumes of the sea and, by their migration, concentrate them many thousand-fold in the rivers and estuaries. Many other fish also exhibit extensive migra- tions. Even though some of these do not enter the rivers to breed, they may enter the areas where they are available for commercial cap- ture, thus becoming some of the food supply of the nation. Unfortunately, in many of these species we do not know the complete life his- tory and most of our information concerning their occurrences and migrations is obtained only during the period of year when they are caught. The Atlantic tuna, for example, are caught in the early spring in the Caribbean and off the Bahama Banks. As spring and summer progresses they migrate northward along the coast, and maximum catches occur in New England in late summer and early fall. The winter habitat and breeding area of these large and important food fish is largely unknown, though preliminary data suggest that they prac- tically circumnavigate the North Atlantic Ocean (Mather and Day, 1954). Similarly the mack- erel catches are first concentrated in the south- ern part of the Atlantic coastline in the late spring and early summer. The large catches off New England occur in August and Septem- ber. This species breeds on the Atlantic con- tinental shelf during its summer northward migration (Sette, 1943, 1950). Additional examples of mass migrations into Chapter 5 Ecological Systems and Transport 57 the coastal regions are found in the Pacific sardine and the North Atlantic herring. In all of these cases materials assimilated at sea may be concentrated in inshore waters as a result of these migrations, which may cover thousands of miles. Such migrations certainly make it difficult to select any area in the oceans as being sufficiently remote and isolated from human interest to insure that the discharge of radio- isotope wastes might not be transported into those areas man is most interested in protecting. It should, however, be pointed out that this is a quantitative problem, and our knowledge is not sufficiently detailed to permit evaluating the quantity of radioisotopes which could be transported in mass migrations of fish. In addition to the movements of organisms which are independent of the circulation of the water resulting from gravity and vertical and horizontal migrations, many populations remain stationary in a flowing stream of water. The organism is thus able to concentrate remarkably the constituents of the water masses which pass by. Harvey (1950) estimated, for example, that the bottom population was nearly 70 per cent of the total population at a station in the English Channel (see Table 3) . The most apparent of these stationary popu- lations are those which live on or in the bottom. Much of our knowledge concerning such popu- lations is confined to those which occupy shal- low waters such as the clams, the oysters, and other economically important species. Stationary populations may be exposed to and feed on populations in many cubic miles of sea water during the course of an active growing season. Although most of our knowledge is confined to shallow water forms, it is known that such stationary populations are a main source of food for many bottom-feeding commercial fishes. The haddock and cod fisheries of New England and the halibut fishery of the Pacific Coast, for example, are ground fisheries. These impor- tant species of fish feed on sedentary or sta- tionary populations. Even in the great depths of the ocean such sedentary populations have been found wherever man has had the oppor- tunity to search for them. Although little is known of their location in the food web and dynamics of the ocean, it seems certain that they play a part. The importance of such stationary popula- tions is that they can concentrate enormously the density of organic matter in those locations suitable for their survival. In unique situations they may concentrate by several orders of mag- nitude the available organic matter in the ocean. Less obvious stationary populations are plank- tonic and unattached, and one would expect them to be transported away from a given area by the currents. It has been found in some cases, however, that in spite of horizontal cur- rents of considerable velocity, the centers of some planktonic populations can remain rela- tively stationary. Presumably there is a con- stant drain from these populations as a result of the currents which carry away some of the organisms, but the rate of production of the population is sufficient to maintain the popula- tion in spite of this drain. Examples of such populations are to be found in almost all estu- aries which tend to maintain endemic species different from those commonly found in the adjacent sea (Ketchum, 1954; Bousfield, 1955). Even in the open ocean similar stationary popu- lations have been found (Redfield, 1939, 1940, 1941 ; Johnson and co-workers, unpublished observations) . It is necessary to have a rate of reproduction of the population as a whole suffi- cient to balance the circulatory drain. This rapid rate of reproduction will, of course, lead to the concentration of materials from the v»'ater mass moving past. A special case of biological concentration of materials which probably involves several of the above phenomena is found in the "red tide." It has been shown that the concentration of total phosphorus in the colored water of these dinoflagellate blooms is commonly ten to twenty times as great as the concentration which can be found in any of the adjacent waters (Ketchum and Keen, 1948). Most of this phosphorus is combined in the living cells, and very little is present in the inorganic form. One of the explanations for these high concen- trations involves the accumulation of the organ- isms at the surface because of their buoyancy, and the subsequent further concentration of the surface film by convergence of water masses (Ryther, 1955). In the red tides which have occurred in recent years off the west coast of Florida, the organism involved, Gymnodinium brev}s, produces a toxin which is lethal to the fish and other organisms in the water, and vast numbers of fish have been killed as a result of these dinoflagellate blooms (Gunter, et al.. 58 Atomic Radiation and Oceanography and Fisheries 1948). Recent evidence indicates that the or- ganisms are almost always present in the water (Collier, A., unpublished), but in such low concentrations that there is no marked fish mortality. It is only after the concentration produced by the biological and hydrographic system that mortalities result. In evaluating the discharge of radioisotope wastes at sea, the factor of safety must be sufficient so that safe levels of radioactivity can be maintained, even after the various mecha- nisms of biological accumulation. REFERENCES BousFiELD, E. L. 1955. Ecological control of the occurrence of barnacles in the Mira- michi Estuary. Nat. Mus. Canada Bull. No. 137, Biol. Ser. No. 46, pp. 1-69. DiETZ, R. S. 1948. Deep scattering layer in the Pacific and Antarctic oceans. /. Mar. Res. 7:430-442. GOLOLOBOV, Y. K. 1949. (Contribution to the problem of determining the age of the present stage of the Black Sea) in Russian. Dokl. Akad. Nauk SSSR. 66:451-454. GuNTER, G., R. H. Williams, C. C. Davis, and F. G. Walton Smith. 1948. Cata- strophic mass mortality of marine animals and coincident phytoplankton bloom on the west coast of Florida, November, 1946 to August, 1947. Ecol. Monogr. 18:309- 324. Harvey, H. W. 1950. On the production of living organic matter in the sea oflF Ply- mouth. /. Mar. Biol. Assoc. U. K. 29: 97-137. Hersey, J. B., and H. B. Moore. 1948. Prog- ress report on scattering layer observations in the Atlantic Ocean. Trans. Amer. Geophys. Union. 29:341-354. HuLBURT, E. M. In press. The distribution of phosphorus in Great Pond, Massachu- setts. (Submitted to /. Mar. Res.) Ketchum, B. H. 1954. Relation between cir- culation and planktonic populations in estuaries. Ecol. 35:191-200. Ketchum, B. H., N. Corwin, and D. J. Keen. 1955. The significance of organic phos- phorus determinations in ocean waters, Deep-Sea Res. 2:172-181. Ketchum, B. H., and D. J. Keen. 1948. Unusual phosphorus concentrations in the Florida "red tide" sea water. /. Mar. Res. 7:17-21. Mather, F. J., Ill, and C. G. Day. 1954. Observations of pelagic fishes of the tropi- cal Atlantic. Copeia, 1954, no. 3:179-188. Redfield, a. C. 1939. The history of a popu- lation of Limacina retroversa during its drift across the Gulf of Maine. Biol. Bull. 76:26-47. 1941. The effect of the circulation of water on the distribution of the calanoid com- munity in the Gulf of Maine. Biol. Bull. 80:86-110. 1942. The processes determining the con- centration of oxygen, phosphate and other organic derivatives within the depths of the Atlantic Ocean. Pap. Phy. Oceanog. Meteorol. 9:1-22. Redfield, A. C, and A. Beale. 1940. Fac- tors determining the populations of chae- tognaths in the Gulf of Maine. Biol. Bull. 79:459-487. Riley, G. A. 1941. Plankton studies. III. Long Island Sound. Bingham Oceanog. Coll. Bull. 7(3): 1-93. 1941a. Plankton studies. V. Regional sum- mary. /, Mar. Res. 4:162-171. 1944. The carbon metabolism and photo- synthetic efficiency of the earth as a whole. Amer. Sci. 32:129-134. Riley, G. A., H. Stommel, and D. F. Bumpus. 1949. Quantitative ecology of the plank- ton of the western North Atlantic. Bing- ham Oceanog. Coll. Bull. 12:1-169. Ryther, J. H. 1954. The ratio of photosyn- thesis to respiration in marine plankton algae. Deep-Sea Res. 2:134-139. 1955. Ecology of autotrophic marine dino- flagellates with reference to red water con- ditions. Luminescence of Biological Sys tems: 387-414. Sette, O. E. 1943. Biology of the Atlantic mackerel {Scomber scombrus) of North America. Part I: Early life history. Fish. Bull. 38:149-237. Sette, O. E. 1950. Biology of the Atlantic mackerel (Scomber scombrus) of North America. Part II. Migrations and habits. Fish. Bull. 51:251-358. Chapter 5 Ecological Systems and Transport 59 Steemann Nielsen, E. 1954. On organic production in the oceans. /. Con. Internal. Explor. Mer. 19:309-328. Strom, K. M. 1936. Land-locked waters. Hy- drography and bottom deposits in badly ventilated Norwegian Fjords with remarks upon sedimentation under anaerobic condi- tions. Norske Vidensk. Akad. 1. Mat. Naturv. Klasse No. 7, 85 pp., Oslo. SvERDRUP, H. U., M. W. Johnson, and R. H. Fleming. 1942. The Oceans, their physics, chemistry and general biology, x+1087 pp., Prentice-Hall, Inc., New York. Thomsen,' H. 1931. Nitrate and phosphate contents of Mediterranean water. Danish Oceanog. Exped. 1908-1910. 3:14 pp. WORTHINGTON, L. V. 1954. A preliminary note on the time scales in North Atlantic circulation. Deep-Sea Res. 1:244-251. Chapter 6 PRECIPITATION OF FISSION PRODUCT ELEMENTS ON THE OCEAN BOTTOM BY PHYSICAL, CHEMICAL, AND BIOLOGICAL PROCESSES Dayton E. Carritt, The Johns Hopkins University and John H. Harley, Health and Safety Laboratory, U. S. Atomic Energy Commission Introduction It has been suggested that naturally occurring processes will remove radioactive waste mate- rials from solution or suspension in the oceans, carrying them to the ocean floor where they will be kept out of the human environment until natural radioactive decay destroys them. In this section we will attempt to define the processes by which materials may be carried to the bottom, to note the conditions under which these several processes can be expected to op- erate, and to assess the extent to which these processes have been responsible for the removal of activity to the bottom in cases where bottom accumulation has been measured. It should be noted that the deposition of fis- sion products on the bottom has not been stud- ied in such a way as to permit an evaluation of the mechanisms responsible for the deposition and retention of the activities. Measurements of bottom-held activities have been made pri- marily to estimate the total activity. We will discuss later the kind of information that might be obtained in connection with weapons tests and large-scale tracer experiments, and which is needed for a better evaluation of the extent to which deposition processes remove fission product elements from the ocean. Sources of Fission Products The oceans may receive fission products from two sources, materials from each of which have unique properties important to deposition. The two sources are: (1) Radioactivities resulting from bomb bursts, either in weapons testing or military use of bombs in war time. Partial controls can be put on the location and time of weapons tests to take advantage of desirable dispersal or con- centrating properties of the oceans. (2) Radioactivity obtained from nuclear power production plants and released to the oceans for containment or dispersal. The time and location of introduction of wastes of this type can be controlled to obtain optimum oceanic charac- teristics, and the character of the wastes might be altered by the removal of one or more un- desirable active or inactive constituents. In both cases it can be expected that the fission products will partition into a soluble and an insouble fraction. An estimate of the ele- ments that will appear in each fraction is given in another part of this report. This division into soluble and insoluble frac- tions presents essentially two different systems so far as deposition or dispersal processes are concerned. Deposition and Retention Processes Deposition and retention of fission product waste on the ocean floor will occur when the waste is sufficiently denser than sea water to permit it to settle to the bottom, and when the stability of a waste-bottom component complex is sufficiently greater than the stability of soluble complexes that might form to prevent its re- dissolving. Solid formation The "denser-than-sea-water" requirement can be met when one of two processes occur: (1) the formation of insoluble substances by inter- action of the radioactive components of the wastes with a sea water component, and (2) sorption of the radioactive components of the 60 Chapter 6 Precipitation on the Ocean Bottotn 61 wastes by solids naturally occurring in sea water or by solids formed by interaction of non-radio- active components of the wastes with sea water constituents. Certain generalizations can be made with re- gard to the formation of a solid phase — a precipitate, by the interaction of radioactive constituents with sea water components. Pre- cipitation may occur when the solubility product of a substance has been exceeded. Funda- mentally, in order to be able to predict when this condition has been met, knowledge of the ionic activities of the species involved must be known. Ionic activity is used here in the thermo- dynamic sense, and is not related to activity in the radioactive sense. Unfortunately practically nothing is known about ionic activities of fission product elements in sea water. The theoretical approach through this route appears, therefore, to be impractical. The mass of radioactive elements that might be introduced into the ocean from any expected level of power production or foreseeable use of bombs, will be small when compared to the quantities of similar elements already in the ocean. Thus, it is to be expected that chemical precipitation of radioisotopes will occur only in ocean regions where precipitation occurs nor- mally. This process includes precipitation in the usual sense and co-precipitation — the proc- ess in which similar elements are simultaneously removed from solution. For example, during the precipitation of calcium carbonate, stron- tium, a minor element, usually is co-precipitated and carried along with the calcium carbonate. Sorption processes involving inactive solids provide another set of mechanisms that may pro- duce radioactive solids. The solids that are present in sea water or might be produced from inactive waste components are generally finely divided, have large area to volume ratio, and are charged. The sorption of radioactive and in- active dissolved constituents onto the solids, in the ratio of their relative concentration, is fa- vored by these characteristics. Thus, in cases where an element normally present in sea water is known to be taken up by suspended solids it can be expected that radioisotopes of the same or chemically similar elements will also be taken up. The oceans contain inorganic and organic, living and dead suspended solids — all have sorption properties and may remove active and/ or inactive constituents from solution. Settling characteristics The sinking of particles in the sea is usually described in terms of Stokes' Law which as- sumes, in its simplest form, smooth, rigid, spherical particles of a stated diameter and den- sity, sufficiently widely spaced so as not to im- pede one another. It provided an adequate de- scription of the behavior of these solids with a restricted particle size range. For particles larger than about 100 microns (0.1 mm) the law must be modified to take into account turbulence around the particle that has a net effect of re- ducing the settling rate. Also, particles of col- loidal and near-colloidal dimensions, less than TABLE 1 Settling Velocity of Quartz Spheres (In Distilled Water) Settling Diameter velocity , '- V Time to settle (mm) (microns) (m/day) 1000 m 1.0 1000 14,000 0.07 days 0.1 100 800 1.25 " 0.01 10 8 125 0.001 1 0.08 34 years 1/1024 0.98 0.07 39 1/2048 0.49 0.02 137 1/4096 0.25 0.004 685 1/8192 0.12 0.001 2,740 about a half micron, settle at a rate less than predicted by Stokes' Law, presumably because of charge interaction between particles and dis- solved components. Table 1 gives the settling velocities for par- ticles of a stated size in distilled water, has been calculated from Stokes' Law and is subject to the criticisms noted above. This table is a highly simplified and idealized picture of the actual settling properties of solids that normally occur in the oceans, and especially of particles in the small size range. Particles in this range probably will be the main concern when considering the deposition of fission prod- ucts. They are also in the size range that will permit ocean circulation to alter markedly any predicted location of deposition or of time to reach the bottom. The density and shape factors that effect settling characteristics are important when con- sidering organic solids or living organisms. The density approaches that of sea water which 62 Atomic Radiation and Oceanography and Fisheries reduces the settling rate, and the shape may vary considerably from the smooth sphere as- sumed for Stokes' Law. The particle-size distribution of solids sus- pended in the ocean as shown by sediments is broad, varying from over a millimeter in di- ameter for sands found near shore, to 0.1 micron or less for sediments taken from the open ocean. The median diameter of open-ocean particles is in the range 1 to 8 microns. The accumulation of solids on the ocean floor is a relatively slow process. Table 2 (Holland and Kulp, 1952) indicates the rate of sedimen- tation on the several parts of the ocean floor. TABLE 2 Sedimentation Rates Fraction of sea Sedimentation Type of sediment water rate x 10'* gm/cm^ per year Shelf 0.08 40 Hemipelagic 0.18 1.3 Pelagic 0.74 globigerina\ pteropod I ^-^^ 0-5 red clay 0.28 0.2 diatom "I ^ , ^ „ , , J. , . \ 0.10 0.15 radiolarian J A weighted average gives approximately 0.75 mg/cm2 per year for the oceans. If the area of the ocean floor is 3.6 x 10^^ cm^, the total depo- sition will be 2.7 x 10^^ grams or 2.7 x 10^ tons per year. Retention Prior to actual deposition on the bottom, radioactive solids that have been formed above the bottom may encounter changes in environ- ment that will tend to return them to solution and prevent or hinder deposition. For example, resolution of precipitates with increasing pres- sure (calcium carbonate), releases of radioac- tivity from solids as they fall through uncon- taminated water, vertical migration of organ- isms, and vertical components of circulation are all possible mechanisms that will tend to pre- vent the deposition of radioactive material on the bottom and, when coupled with horizontal circulation features, will tend to disperse the radioactivity over large areas. The retention of radioactive material on the ocean floor once it has been deposited there will depend upon the stability of the floor relative to erosion, to further deposition, and to tur- bidity currents, and upon the chemical features of the bottom relative to those through which the solids have settled. The deep ocean basins are the regions of greatest stability in all respects. Regions near shores and shelves are subject to the greatest variations in deposition and erosion; in regions where rivers enter the seas, relatively wide changes in chemical properties take place. Discussion of existing data Three sources of information give some insight into the probable behavior of fission product elements in sea water. They are: (1) existing information concerning the solution chemistry of the elements in question, (2) the behavior of radioactive debris observed in con- nection with bomb tests in the Pacific, and (3) information concerning the geochemistry of the elements in question. In utilizing information from these sources to assess the probable fate of fission product ele- ments in the oceans the chemical properties of the oceans are of major importance. Table 3 lists the elementary composition of sea water together with an estimate of the amounts of natural activities present. In Table 4 are listed fission product elements, together with their half lives and the equilib- rium quantities that would be in existence after 100 days cooling when formed in connection with 10^^ megawatt hours per year of nuclear power production. Also listed are the specific activities that would result were these activities to be mixed throughout the oceans. It will be obvious from a consideration of oceanic prop- erties, presented in other sections of this re- port, that under any practical method of intro- duction of wastes, attainment of uniform specific activity of any given element throughout the oceans will not occur. There will be gradients of radioactivity, decreasing from the region of introduction. The figures for specific activities are, therefore, unrealistic and are included only as a basis for making a better estimate when the effects of circulation and fractionation can be provided. In a few cases, knowledge of the fraction of an element, that would be normally removed by geochemical processes will permit an estimate to be made of the fraction of a radioisotope that will be removed for a given loading. Con- Chapter 6 Precipitation on the Ocean Bottom 63 TABLE 3 Elements in Solution in Sea Water (Except Dissolved Gases)1'2 mg/kg , Element CI = 19.00% Total in oceans (tons) Nuclide Chlorine 18,980 2.66 X 10'" Sodium 10,561 1.48 X 10'" Magnesium 1,272 1.78 X 10'' Sulfur 884 1.23 X 10'' Calcium 400 5.6 X 10" Potassium 380 5.3 X 10" K" Bromine 65 9.1 X 10" Carbon 28 3.9 X lO'^ C" Strontium 13 1.8 X 10" Boron A.6 6.4 X lO'^ Silicon 0.02 -4.0 0.028-5.6 X lO'^ Fluorine 1.4 2 X lO'^ Nitrogen (comp) . 0.01 -0.7 0.l4 -9.8 X 10" Aluminum 0.5 7 X 10" Rubidium 0.2 2.8 X 10" Rb*' Lithium 0.1 1.4 X 10" Phosphorus 0.001-0.1 0.014-1.4 X 10" Barium 0.05 7 X 10" Iodine 0.05 7 X 10'" Arsenic 0.01 -0.02 1.4 -2.8 X 10'° Iron 0.002-0.02 0.28 -2.8 X 10'° Manganese 0.001-0.01 0.14-1.4 X 10'° Copper 0.001-0.01 0.14 -1.4 X 10'° Zinc 0.005 7 X 10' Lead 0.004 5.6 X 10* Selenium 0.004 5.6 X 10' Cesium 0.002 2.8 X 10° Uranium 0.0015 2.1 X 10° U^' Molybdenum 0.0005 7 X 10' LP' Thorium < 0.0005 <7 X 10' Th^^' Cerium 0.0004 5.6 X 10' Silver 0.0003 4.2 X 10' Vanadium 0.0003 4.2 X 10' Lanthanum 0.0003 4.2 X 10' Yttrium 0.0003 4.2 X 10' Nickel 0.0001 1.4 X 10^ Scandium 0.00004 5.6 X 10^ Mercury 0.00003 4.2 X 10^ Gold 0.000006 8.4 X 10° Radium 0.2-3 X 10"'° 28 -420 Ra==' iSverdrup, H. U., M. W. Johnson, and R. H. Fleming, OCEANS (1942) 2Revelle, R., T. R. Folsom, E. D. Goldberg, and J. D. Isaacs (1955). Natural activities Total (tons) 6.3 X 10' 56 Curies 4.6 X 10'^ 2.7 X 10' 1.18 X 10" 8.4 X 10° 2.8 X10° 3.8 X 10' 2.1 Xio^ 1.1 X 10' 1.4 Xio' 8 X 10 4.2 X 10- 1.1 xio° versely, observations of the behavior of radio- active isotopes would lead to a better under- standing of the geochemistry of a given element. Operational data Of the fission products listed several are either rare earths or rare-earth-like — such prod- ucts all have very similar chemical properties. All form relatively insoluble hydroxides of the type R(OH)3. The solubility products of the rare earth elements listed by Latimer (1952) all fall in the range 10"-° to lO'So. Although a quantitative comparison of the conditions that actually exist in the sea cannot be made with these constants, it would appear from the scant information available concerning the quantities of rare earth elements in the sea that marine waters are saturated with respect to these ele- ments and that a major portion of the rare earth elements are dispersed in the sea as solids. This is generally confirmed by American and Japa- nese observations of the distribution of fission product activities in the Pacific following bomb tests. In most cases, however, it is difficult to differentiate between "solid fractions" that have been precipitated as solids by chemical processes, and radioactive solids that have been accumu- 64 Atomic Radiation and Oceanography and Fisheries lated by microscopic plankton organisms. Both will be collected by filtration or centrifugation. Goldberg (1956), however, noted that informa- tion obtained during Operation WIGWAM suggests a fractionation of a portion of the fission product activities into solids that are col- lected and concentrated by filter feeding or- ganisms. The activity within the filter feeding TABLE 4 Fission Product Activity After 100 Days Cooling from 10^^ Megawatt Hours of Nuclear Power Production i Specific activity Half- Tons Curies at curies per Isotope life (metric^ 100 days ton 2 Kr^^ . . . 94 y 7.3 3.3 Xio" — Sr* ... 55 d 86 2.3 Xio'^ 0.128 Sr** ... 25 y 463 7.5 Xio" 0.0042 Y^o 62 h — 7.48 X 10" 178 Y*! 57 d Ill 2.8 Xio'^ 6,660 Zr^ '.'.'.' 65 d 152 3.2 Xio'^ — Nb"^ . . . 35 d 161 6.3 Xio'" — Ru^-^ .. 45 d 46 1.3 XIO'^ — Rh^*^ .. 57 m — 1.3 XIO'" — Ru^'^ .. 290 d 35 1.5 XlO'^ — Rh^°« .. 30 sec. — 5.15 X 10'" — T13X 8.0 d — 5.2 X 10" 0.0743 Cs"'' '. ". '. 33 y 705 5.63 X 10'" 20.1 Ba'^^ .. 2.6 m — 5.1 X 10'" 0.728 Ba^*° .. 12.5 d 2 1.5 Xio'' 2.14 La»° .. 1.7 d — 2.5 Xio" 595 Ce^*^ .. 28 d 45 1.5 Xio'^ 268 Pr^« .. 13.8 d 2 1.4 Xio'^ — Ce^" .. 275 d 490 1.6 Xio'^ 386 Pr^" .. 17 m — 2.4 Xio"' — Pm^^^ . . . 94 y 7.3 3.3 Xio" — Sm^^^ .. • 73 y 0.7 2.0 Xio^ — lAdap ted from data 3f Culler (1954b) and Revelle, et al. (1955). 2 Based on tonnage shown in Table 3. organisms — ones adapted to the removal of particulate material from suspension — showed a high percentage of rare earth elements that previously were noted as probably being pre- dominantly dispersed as solids in the oceans. These organisms were collected in the mixed layer of the sea. About a year after the 1954 nuclear tests were completed. Operation TROLL undertook a survey of the region west from the test site, including the region just off the Phillipines and northward off the coast of Japan (U. S. Atomic Energy Commission, 1956). Seventy water and plankton samples taken during this cruise were analyzed radiochemically. When compared on an equal weight basis (1000 gms wet plankton vs. 1 liter of water) the plankton contained on the average 470 times the activity of the water. Significantly, 80 to 90 per cent of the activity of the plankton was due to Ce^** (and its Pr^** daughter) . Cerium is a rare earth. No informa- tion is yet available concerning the species and the relative quantities of organisms responsible for the concentration of activity. A comparison of the total activity per unit weight of macro- and micro-plankton indicated approximately a one and one half times greater concentration by the micro-plankton. It is noteworthy that the observations made on Operations TROLL and WIGWAM revealed a system in which the properties, with the ex- ception of radioactive element content, were es- sentially those of normal sea water. The sys- tem can be imagined as being essentially sea water to which had been added the radioactive material — a procedure which because of the extreme dilution of the contaminant, in a chemical sense, would not affect the sea water properties. Furthermore, these observations were made on samples taken in the mixed layer (the upper 100 to 300 m) . These results, though largely qualitative in na- ture, suggest the following conclusions regard- ing the behavior of fission product elements in the mixed layer of the open oceans: 1. Radioactive material will be retained in the mixed layer for periods of at least a year during which time horizontal motion may carry them a few thousand miles. (Operation TROLL and SHUNKOTSU-MARU data.) 2. Rare earth elements appear to be dispersed primarily as solids and accumulated by the plankton. (Operations TROLL and WIG- WAM.) 3. The initial accumulation of rare earth ac- tivities is predominantly by filter feeding or- ganisms, presumably by retention of finely di- vided solids in their feeding apparatus. 4. The cycle of rare earth activities through the biota is unknown. Nevertheless, biological agencies undoubtedly have an important influ- ence in the deposition mechanisms. The physical state of fission product elements in sea water is important in all of the processes that have been previously mentioned. Table 5 sets forth several fission product elements, the percent of total activity present one year after removal from a reactor and an estimate of the Chapter 6 Precipitation on the Ocean Bottom 65 physical state of each if dispersed in sea water. The estimates of physical states have been ob- tained from oceanographic studies following bomb tests and from considerations of the "solution chemistry" of the elements. It should be emphasized that the terms "solid" and "solu- tion" are relative terms. Measurements made during oceanographic studies invariably base the division upon filterability. Such a division TABLE 5 An Estimate of Solid and Soluble Fractions for Fission Products in Sea Water TABLE 6 Geochemical Balance of Some Elements in Sea Water (from Gold- SCHMIDT, Quoted in Rankama and Sahama, 1950, Table 16.19) Element Sr^« Sr^o +Y°° Zr"" Cs^' -f Ba^ Pm"^ Per cent of total activity at end of Physical state in one year sea water 3.8 Solution 1.7-1- 1.7 Solution -f solid 7.2 Solid 15 Solid 2.5 -j- 2.5 Mostly in solution 1.5 -f- 1.5 26 -f26 5.6 Solution Solid Solid obviously will place soluble elements that are utlized by organisms in the solid or solution -{- solid category. The settling characteristics of elements so combined will depend upon prop- erties of the organisms. To what extent anoma- lies of this kind are in the estimate above can- not be stated. However, the estimates agree qualitatively with those made from knowledge of the behavior of elements in systems where biological activity is not a major variable. Culler (1954a), has noted that low level ac- tivities discharged to White Oak Creek end up primarily with the clay in a retention basin. The character of the waste was not noted. Krumholz (1954), however, found considera- ble uptake of radioactivity in the biota with subsequent relocation and dispersion in the same region. Geochemical data An estimate of the behavior of several sea water constituents can be obtained from the re- sults of geochemical studies. These studies per- mit an evaluation of the fraction of an element supplied to the oceans that is removed from so- lution. The removal processes may include one or more of those previously mentioned. The results permit no choice of mechanisms. Table 6 lists several elements found in sea water, the Total supplied Element (ppm) Na 16,980 K 15,540 Kb 186 Ca 21,780 Sr 180 Ba 150 Fe 30,000 Y 16.9 La 11 Ce 27.7 Amount present in ocean Transfer (ppm) percentage 10,560 62 380 2.4 0.2 0.1 400 1.8 13 7.2 0.05 0.03 0.02 0.00007 0.0003 0.002 0.0003 0.003 0.0004 0.001 quantities supplied to and present in the oceans and a quantity, the transfer percentage, which is the percentage of "present" to "supplied." Large values of transfer percentage indicate that relatively large fractions of the elements supplied to the oceans stay in solution — small values of transfer percentage that relatively much is removed. Using the transfer percentages listed for cesium, strontium, and cerium, and estimates of the specific activities that would occur in the oceans as a result of 10^^ megawatt hours nu- clear power production, the reduction through geochemical processes has been calculated. The figures are given in Table 7. TABLE 7 Activity Reduction By Geochemical Processes Specific Specific Transfer activity activity percent- after (c/gm) age removal Element (no removal) (c/gm) Cesium 8.6 X 10"^ 0.005 4.3 X 10"^ Strontium 6.8 X 10"' 7.2 4.9 X IQ-'" Cerium 1.8 X 10"^ 0.001 1.8 X lO"'" Laboratory data Floccing, possible in the disposal of wastes rich in iron or aluminum, may assist in removal of fission products. Unless settling times of nat- ural or artificial floes are short, resolution and biological uptake may reduce the settling factor markedly. Goldberg (1954) has described the copre- cipitation processes with iron and manganese. While none of the fission product elements are treated, analyses show that the amounts of trace (>e Atomic Radiation and Oceanography and Fisheries elements in the sediments are proportional to the iron or manganese content. In addition, fil- ter feeders show concentrations indicating up- take of undifferentiated particulates. Several experiments have been reported in which the reactions between fission product ac- tivities (mixed and individual isotopes) and suspended solids have been studied. In the fol- lowing examples both marine and fresh water experiments are noted. Gloyna in Goodgal, Gloyna, and Carritt (1954) noted that 58 per cent of mixed fission product activity (initially less than 1000 cpm) could be removed from solution during cen- trifugation of untreated Clinch River water, 70 ppra solids, pH 8.4 and alkalinity 92 ppm (Ca- CO3). No attempt was made to determine which elements were removed. Carritt and Goodgal (1954) studied the up- take of phosphate, iodide, iron III, strontium sulphate and copper II on samples of Chesa- peake Bay sediments. Measurements were made under controlled but varied pH, temperature, salinity, concentration of solids, and specific ac- tivities. Of the elements studied strontium, io- dide and sulphate are of interest here — sul- phate because of the similar chemical behavior of tellurium. Iodide showed no uptake at con- centrations applicable to the present discussion. Under conditions where strontium carbonate did not precipitate, strontium was absorbed ac- cording to the following isotherm: x/m= 0.0032 C"-** x/m=jug atoms Sr per milligram of solids C= equilibrium concentration of strontium in jLtg atoms Sr per liter. This isotherm was valid over the range 52 to 5200 ^g atoms Sr per liter. The uptake of sulphate showed strong pH dependence. At pH above 4.5 very little uptake was noted. With decreasing pH, uptake in- creased, suggesting that the bisulphate is more active than sulphate. At pH 3.3 (an unlikely marine condition) the uptake followed the isotherm: x/m = 0.0013 C0-S2 over an initial sulphate concentration range of 10». Several proposals on ocean waste disposal would allow introduction of packaged waste into the bottom by sea burial. Dispersion of ac- tivity would be a slow diffusion process as from concreted wastes or would be delayed until rup- ture of an impermeable container. In either case, the activity released would go into the highly absorptive environment of the sediments. One form of packaging for the disposal of active waste has been proposed by Hatch (1954). He has described the problems en- countered with the absorption of fission prod- ucts onto montmoriilonite clays, followed by fir- ing to 800° C, to produce a high density, high specific activity, insoluble waste. When given appropriate pretreatment, it was estimated that fission products could be removed from reactor wastes to yield clays with an activity of about 10 curies per gram. The practicability of utili2- ing solids of this kind apparently depends upon the demonstration of long term stability under deep ocean conditions and upon the economics of production and transportation. It should be noted that short term stability tests suggest that the fired montmoriilonite clays would be ex- tremely stable. Deep ocean deposits have appreciable base exchange capacities. Revelle measured this to be in the range 30-60 millequivalents per 100 gram of solids. Soluble waste components can be expected to react with solids on the bottom surface and to be removed from solution by base exchange reactions, and isotopic exchanges. No estimate seems possible of the depth into the sediments that this kind of reaction would take place. Certainly the surface layer of sediments would become saturated and reaction with deep sediments would be controlled by diffusion into the sediments. Further data required A survey of available literature reveals many gaps in our knowledge in this field. Basic data on the settling processes of natural sedimenta- tion are few, and the carrying processes by which tracer concentrations of isotopes would be removed from the oceans have been almost entirely neglected. From a practical point of view, the data most needed are measures of the gross sedimentation rate of radioactivity. This would be an integral of the effects of many processes — empirical information that would permit a statement concerning the sedimentation rate of activity without reference to the many mechanisms involved. Chapter 6 Precipitation on the Ocean Bottom 61 Nevertheless, for an understanding of the overall process — so that predictions for condi- tions other than those existing at the time of observations can be made, and to provide infor- mation useful to other studies, many individual processes should be studied. The following studies, grouped according to the primary source of information, and thought to be pertinent to the sedimentation and retention problem, would provide some insight into these processes. Ob- viously, information obtained from one group of studies may be of value in the solution of problems in others. Data from weapons tests 1. Measurement of the immediate partition of weapons test debris among large-sized immedi- ate fallout, water-borne activity and the air- borne material which may be quite uniformly distributed over the world. 2. Measurement of partition of individual iso- topes in sea water between particulate material and solution. (Dynamic and equilibrium con- ditions). 3. Mechanism of sorption of radioisotopes on natural suspended solids under the conditions existing in ocean water. 4. Measurement of settling rates of natural in- organic particulates, probably by tracer tech- niques. 5. Measurement of detrital settling rates, in- cluding plankton average life. 6. Measurement of uptake and element differ- entiation in organisms which may become de- trital material. Data from waste disposal experiments Certain studies here can be combined with tracer studies, designed primarily to give infor- mation on basic oceanographic problems: 1. Life expectancy of burial containers. 2. Diffusion rate from concreted or sintered blocks as a function of size, and the concentra- tion and istopic composition of wastes. 3. Regardless of what disposal system is adopted, there will be liquid wastes produced, and studies must be made of liquid waste dis- persal. The pertinent effects will be more re- lated to the weapons test data requirements since this is a surface to bottom transfer. Tracer experiment data 1 . Coprecipitation of individual fission products with their stable isotopes normally occurring in sea water, and the particle size distribution of the solids formed, and their sedimentation rate. 2. Similar data on coprecipitation by isomor- phous replacement, for example the carrying of radiostrontium with inactive calcium. 3. Rate of entry of diffused material into the basic biological systems. This includes the bot- tom to surface movement as modified by sedi- mentation. 4. Exchange capacities of sediments for the ra- dioisotope ions in sea water medium, and rate of diffusion of these isotopes into the undis- turbed bottoms. In all studies in which dispersion, partition, concentration and localization occur, measure- ments that would permit a balance sheet to be made (all the activity should be accountable) seem desirable and necessary. SUMMARY The only semi-quantitative data relevant to the problem of activity removal from the ocean surface are the geochemical data. These indicate a reduction factor of 14 for strontium, 2,000 for cesium, and 100,000 for cerium (and proba- bly all rare-earth-type elements). No informa- tion is available on such elements as ruthenium, rubidium, and iodine. Other mechanisms de- scribed may contribute to activity removal, but their effects cannot be evaluated with present knowledge. The reduction factors are for equilibrium con- ditions, and the high sea water activity found a year after the Castle tests (Operation TROLL) indicate that equilibrium is reached slowly. Activity introduced on the bottom through sea burial will be subject to entirely different removal processes. No estimate can be made of their effectiveness. Carritt, D. E., and S. Goodgal. 1954. Sorp- tion reactions and some ecological impli- cations. Deep-Sea Research 1:224-243. Culler, F. L. 1954a. Unpublished results. Culler, F. L. 1954b. Notes on Fission Prod- uct Wastes from Proposed Power Reac- tions. ORNL Central File No. 55-4-25. 68 Atomic Radiation and Oceanography and Fisheries Goldberg, E. D. 1954. Marine Geochemis- try 1. Chemical Scavengers of the Sea. /, Geol. 62:249. Goldberg, E. D. 1956. Unpublished results. Presented at Princeton, N. J., March 3, 4, 5, 1956 meeting of NAS Study Group on Oceanography and Fisheries. GooDGAL, S., E. Gloyna, and D. E. Carritt. 1954. Reduction of radioactivity in water. ]our. Amer. Water Works Assoc. 46, No. 1:66-78. Hatch, L. P. 1954. Clay adsorption of high level wastes. Ocean dispersal of reactor wastes, meeting at Woods Hole Oceano- graphic Institution, Woods Hole, Mass., August 5-6. Holland, H. D., and J. L. Kulp. 1952. The distribution of uranium, ionium and ra- dium in the oceans and in ocean bottom sediments. Lamont Geological Observatory Technical Report No. 6. Rankama, K., and T. G. Sahama. 1950. Geo- chemistry. University of Chicago Press. Krumholz, L. a. 1954. A summary of find- ings of the ecological survey of White Oak Creek, Roane County, Tenn., 1950-1953. USAEC-ORO 132. Latimer, W. M. 1952. Oxidation Potentials. Prentice Hall, New York. Revelle, R., T. R. Folsom, E. D. Goldberg, and J. D. Isaacs. 1955. Nuclear Science in Oceanography. International Conference on the peaceful uses of atomic energy. A/ conference 8/P/277. Scripps Institution of Oceanography contribution No. 794. Sverdrup, H. U., M. W. Johnson, and R. H. Fleming. 1942. The Oceans. Prentice Hall, New York. U. S. Atomic Energy Commission. 1956. Operation TROLL. U. S. Atomic Energy Commission, New York Operations Office, NYO 4656, ed. by J. H. Harley, 37 pp. Chapter 7 ECOLOGICAL FACTORS INVOLVED IN THE UPTAKE, ACCUMULATION, AND LOSS OF RADIONUCLIDES BY AQUATIC ORGANISMS ' Louis A. Krumholz, Department of Biology, University of Louisville, Louisville, Kentucky Edward D. Goldberg, Scripps Institution of Oceanography, University of California, La Jolla, California Howard Boroughs, Hawaii Marine Laboratory, University of Hawaii, Honolulu, T. H. Introduction This paper is concerned with the uptake, ac- cumulation, and loss by living organisms, of radioactive materials that may be added to or induced in an aquatic environment. These aquatic organisms may live in either fresh, salt, or brackish water and include vascular plants, algae, protozoans, plankton, all the other in- vertebrate forms such as aquatic insects, bottom- living crustaceans and molluscs, and representa- tives of each of the five classes of vertebrate animals. The accumulation and loss of any radioiso- tope will depend not only upon its own physical half-life but also upon the biological factors that contribute to its incorporation in, reten- tion by, and disappearance from the organism involved. In general, all isotopes of any one chemical element are similar in chemical behav- ior, and thus it can be assumed, when tracing the paths of most chemical elements through biological systems, that a radioactive atom will behave in the same way as a non-radioactive atom of the same species. However, relatively little is known about the actual mechanisms of uptake, accumulation, and loss by marine and fresh-water organisms of the elements whose isotopes constitute fission products and other radiomaterials. For the purposes of this discussion, the fol- lowing terms will be defined: Uptake is the amount of material that enters the organism in question and the speed at which the material enters is the rate of uptake. 1 Contribution No. 9 (New Series) from the De- partment of Biology, University of Louisville. Con- tribution from the Scripps Institution of Oceanography, New Series, No. 901a. Contribution from the Hawaii Marine Laboratory, No. 94. Loss is the amount of material that leaves the organism, and the speed at which it leaves is the rate of loss. Accumulation is the amount of material that is present in the organism at a given time, and the rate of accumulation is the amount accumulated per unit time. In practice, the accumulation is the difference between the uptake and the loss. Metabolic processes include all the chemical changes concerned in the building up and de- struction of living protoplasm. During these changes, energy is provided for the vital proc- esses and for the assimilation of new materials. Specific activity is the ratio between the amount of radioactive isotope present and the total amount of all other isotopes of that same ele- ment, both radioactive and stable. Most com- monly, it is given as the microcuries of radio- isotope per gram of total element. Although the higher animal forms are de- pendent upon the primary concentrators, the plants, for their source of energy, these animals may or may not be dependent upon the lower forms for many elements. Some elements may enter the bodies of the higher forms directly from the water, while others must be supplied from the lower trophic levels through the food web. These food webs are not the same for all organisms and may even be different for the same organism at various seasons of the year. In some instances certain elements, although present in the environment, are not in the proper physical and/or chemical state to be util- ized by the organisms and thus are not available for metabolism. Radionuclides may become associated with an organism either through adsorption to surface areas, through engulfment, or through metabolic 69 70 Atomic Radiation and Oceanography and Fisheries processes; in some instances assimilation may take place following the engulfment of living or inert particulate matter. A radionuclide may also be incorporated into an organism by simple exchange of the radioactive isotope for the sta- ble isotope of the same species. It is therefore important to know the physical and chemical state necessary for metabolism, the mode of entry, and the ability of all organisms at each of the different trophic levels to concentrate the various radionuclides. Physical and Chemical Factors Concerned with the Uptake of Radionuclides by Living Organisms a. Acute versus chronic exposure Chronic exposure of an aquatic organism, even to low concentrations of radiomaterials, usually has a markedly different effect on the organism than an acute exposure; the principal difference lies in the amount of radiomaterial accumulated in the tissues. Because many aquatic organisms have the ability to concentrate radiomaterials from their environments by fac- tors up to several hundred thousand, much ra- diomaterial may be accumulated during a chronic exposure for a relatively long period of time. A state of equilibrium is ultimately reached at which there is a constant uptake and a constant loss with a resultant constant maxi- mum level of accumulation. Conversely, in an acute exposure, such as a single feeding or a single injection of radiomaterials, only a certain relatively small fraction of the radiomaterial is accumulated in the body and the remainder is lost. In such an instance, the maximum level to which an organism is capable of accumulating the radiomaterial in question is seldom reached and certainly not maintained. Krumholz and Rust (1954) reported an ac- cumulation of one microcurie of strontium 90 per gram of bone in the entire skeleton of a muskrat {Ondatra zibethica) which had been utilizing foods of its own choice in the area contiguous to the Oak Ridge National Labora- tory. Certainly this instance can be presumed to represent a chronic exposure inasmuch as the animal was at least two years old and had probably lived in the area during her entire life- time. Aquatic organisms in the Columbia River below the Hanford Works and those in White Oak Creek, Tennessee, below the Oak Ridge National Laboratory, have all suffered chronic exposures to radiomaterials and have accumu- lated considerable amounts of those materials in their tissues. Hiatt, Boroughs, Townsley, and Kau (1955) found that the daily feeding of strontium 89 to the fish Tilapia for short pe- riods of time (four days) did not increase the level of strontium retention after an apparent steady-state condition had been reached. How- ever, there are no published reports of the re- sults of long-term, controlled experiments of chronic exposures of aquatic organisms to radio- materials. The literature contains many reports con- cerned with acute exposures of aquatic organ- isms to radiomaterials. Martin and Goldberg (unpublished data), who gave single feedings of strontium 90 to Pacific mackerel (Pneumato- phorus japonic us die go), found that less than five per cent of the amount fed was retained in the body after 48 hours. Much of the five per cent that was incorporated in the skeleton re- mained there for the duration of the experiment (235 days). Boroughs et al. (1956) reported that between only one and two per cent of the strontium 89 fed to ten yellowfin tuna {Neo- thunnus macropterus) remained in the body after 24 hours. The small amount retained in the body was largely incorporated into the skele- tal structures. However, other fish {Tilapia) which had been fed similarly prepared stron- tium 89 capsules retained about 20 per cent of the ingested material after 24 hours. After four days, the amount retained finally levelled off at values that ranged from 1.5 to 19.5 per cent of the amount ingested; the average amount re- tained was about 7.5 per cent. Here, again, the retained materials were incorporated mainly in the skeletal structures and integument. b. Chemical and physical states of the ele- ments in the environment. The chemical composition of the marine en- vironment cannot be rigorously defined. The concentrations of elements depend upon the type and location of the water mass. Although more than 90 per cent of marine waters occur at depths greater than 1000 meters, the majority of chemical analyses have been made for shal- lower waters. Because of the biological ac- tivity of the oceans and the movements and origins of water masses, the abundance of cer- tain elements appears to vary by factors greater than two orders of magnitude. However, as a Chapter 7 Ecology of Uptake by Aquatic Organisms 71 first approximation, the chemical constituents may be considered to be much the same in all places. Fairly good approximations of the con- centrations of elements in sea water are listed in Table 1 as the numbers of atoms per million atoms of chlorine. The reported values of con- centrations of elements on which Table 1 is based frequently fail to distinguish between the solid and dissolved phases. Whereas the oceans may be considered very roughly as a homogeneous mass, most bodies of fresh water must be examined on an individual basis because of the tremendous range in their physical and chemical characteristics. Many of the elements that occur normally in the oceans are in concentrations too small to be detected by present methods or are present in only trace amounts in fresh water. The pH of fresh waters ranges from perhaps as low as 2.2 to a high of about 10.5 although the pH of most lakes and streams falls somewhere between 6.5 and 8.5. The total dissolved solids in fresh waters ranges TABLE 1 Chemical Abundances in the Marine H\'drosphere mg/1 H 108,000 He 0.000005 Li 0.2 Be B 4.8 C 28 N 0.5 O 857,000 F 1.3 Ne 0.0003 Na 10,500 Mg 1,300 Al 0.01 Si 3 P 0.07 S 900 CI 19,000 A 0.6 K 380 Ca 400 Sc 0.00004 Ti 0.001 V 0.002 Cr 0.00005 Mn 0.002 Fe 0.01 Co 0.0005 Ni 0.0005 Cu 0.003 Zn 0.01 Ga 0.0005 Ge < 0.0001 As 0.003 Se 0.004 Br 65 Kr 0.0003 Rb 0.12 Sr 8 Y 0.0003 Zr Nb Mo 0.01 Tc Ru Rh Pd atoms/ 10^ atoms CI 202,000,000 50 .002 830 4,300 70 100,000,000 130 0.03 850,000 100,000 0.7 200 4 52,000 1,000,000 28.5 18,000 19,000 0.002 0.04 0.08 0.002 0.07 0.3 0.02 0.02 0.09 0.3 0.01 < 0.003 0.07 0.1 1,500 0.007 2.2 160 0.006 0.2 atoms/ 10' mg/1 atoms CI Ag 0.0003 0.005 Cd 0.000055 0.0009 In < 0.02 < 0.3 Sn 0.003 0.05 Sb < 0.0005 < 0.008 Te I 0.05 0.7 Xe 0.0001 0.001 Q 0.0005 0.005 Ba 0.0062 0.008 La 0.0003 0.004 Ce 0.0004 0.005 Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hg Ta W 0.0001 0.001 Re Os Ir Pt Au 0.000004 0.00004 Hg 0.00003 0.0003 Tl < 0.00001 < 0.00009 Pb 0.003 0.03 Bi 0.0002 0.002 Po At Rn 9.0 X 10"'^ 8.0 X 10" Fr Ra 3.0 X 10"" 2.0 X 10" Ac Th 0.0007 0.006 Pa 0.003 0.03 U 72 Atomic Radiation and Oceanography and Fisheries from very low concentration (less than 5 ppm) in the "battery-water" lakes to very high concen- trations (more than 400 ppm) in the "alkali" lakes. The fertility of fresh waters ranges from the almost sterile bog lakes to the highly pro- ductive lakes in the midwestern prairies. The physical states and ionic speciation of elements in sea water cannot be as well defined as their absolute concentrations. However, us- ing the known physicochemical constants, and assuming a pH of 8 and a salinity of 35 parts per thousand for sea water, Krauskopf (1956) postulated that the principal valence states of the ions of a number of metals in sea water are as listed in Table 2. From these data it may TABLE 2 Calculated Valence States for Metallic Ions in Sea Water (From Krauskopf, 1956) Element Ion Zinc Zn-f +, ZnCl+ Copper Cu++, CuCI-f Bismuth BiO-f Cadmium CdCl-f, CdCU Nickel Ni+-f , NiCl+ Cobalt Co-f + Mercury HgClr Silver AgCIa" Gold AuCIr (Calculated by Goldberg) Chromium CrOr Vanadium HsVOr, HaVoOr" Magnesium Mg-| — \- Calcium Ca+-f- Strontium Sr-\ — \- Barium Ba+-|- be concluded that most monovalent or divalent ions, except the noble metals, will occur as ca- tions whereas most metals with valences higher than two, and the noble metals, will occur as anions. The physical states of a given element under equilibrium conditions depend upon whether or not the solubility product of the least soluble species has been exceeded. Greendale and Bal- lou (1954) have determined the distribution of elements among the soluble, colloidal, and par- ticulate states by simulating the conditions of an underwater detonation of an atomic bomb. Their data are presented in Table 3. It is not known whether the elements that occur in colloidal or particulate phases are homogeneous entities or are sorbed in other solid phases. Nevertheless, it appears that ele- ments of Groups, I, II, V, VI, and VII usually occur as ionic forms in sea water, whereas other elements, excluding the rare gases, occur pre- dominantly as solid phases. These generaliza- tions have been confirmed in field tests after underwater detonations where more than 50 per cent of the resultant radioactivity was associated with solid phases retained by a molecular filter of pore size 0.5 micron (Goldberg, unpublished data) . Although the data supplied by Greendale and Ballou (1954) are of value for the physical states of elements following the detonation of an atomic bomb, they are at best only suggestive of the steady-state conditions which might re- sult from the continuous spilling of fission product wastes into the sea on a long-term basis. TABLE 3 Physical States of Elements in Sea Water (From Greendale and Ballou, 1954) Percentage in given physical state Element Ionic Colliodal Particulate Cesium 70 7 23 Iodine 90 8 2 Strontium 87 3 10 Antimony 73 15 12 Tellurium 45 43 12 Molybdenum 30 10 60 Ruthenium 0 5 95 Cerium 2 4 94 Zirconium 1 3 96 Yttrium 0 4 96 Niobium 0 0 100 Metabolic processes concerned with the uptake, accumulation, and loss of radionuclides There are many factors concerned with met- abolic processes which are to be considered among the biological aspects of the accumula- tion of radiomaterials. It has been demonstrated that the metabolism of all form.s of life is re- markably similar at the cellular level even though the morphological differences among aquatic organisms range from the bacteria through the vertebrate forms, and from the algae through the vascular plants. Nevertheless, differences do exist. These differences are gov- erned by the complex anatomies, life histories, and physiological processes, and the relation- ships of the organisms with each other and with their environment. All of these differences must be considered in the light of the physical and chemical states of the elements involved. Chapter 7 Ecology of Uptake by Aquatic Organisms 73 In different organisms, ionized or particulate fission-product wastes and other radiomaterials may be either adsorbed, engulfed, or accumu- lated by metabolic processes. For example, Rothstein and his associates (1951) demon- strated that uranium as the uranyl ion was ad- sorbed by yeast cells. Hamilton and co-workers (see Hevesy, G., 1948, p. 441) showed that particulate radiomaterials such as various un- complexed rare earths at physiological pH's were adsorbed by the gut lining of rats. In these experiments practically no accumulation of these particular radiomaterials by the animal was observed. On the other hand, Goldberg (1952) demonstrated with radioactive iron that a marine diatom assimilated particles of hy- drated iron oxide, but that these organisms were unable to take up ionic iron in a complexed form. The first biological experiments in which ra- dioactive atoms were used were performed by Hevesy in 1923. In those classical experiments it was demonstrated that plants could take up lead from solution and translocate it throughout the vascular system. The accumulation of radioelements is also de- pendent upon many chemical characteristics of the water in question. Among the parameters affecting accumulation are the salinity, percent- age composition of the dissolved solids, pH, the oxygen-carbon dioxide ratio, and the presence of complexing agents. a. Chemical composition of marine organisms A modern systematic study of the inorganic constituents of marine organisms is yet to be made. The best summary of existing knowledge may be found in Vinogradov (1953). However, certain generalizations can be drawn from the recent literature on the concen- tration of metals by marine organisms. Gold- berg (in Treatise of Marine Ecology, volume II, edited by J. Hedgpeth, in press) has pointed out that the marine biosphere tends to concen- trate such heavy metals as copper, nickel, zinc, etc., over the marine hydrosphere by factors of 100 to 100,000 on a weight-f or- weight basis (Table 4) . These metals are strongly bound in the organisms and cannot be easily removed by elution. Further, the elements most strongly concentrated in the biosphere are those that form the most stable complexes with organic chelating agents. As an example, copper is con- centrated over sea water in the soft parts of most marine organisms by factors of 10^ to 10* whereas calcium shows concentration factors of less than 1 to 50. Copper forms very strong complexes with many organic compounds whereas calcium does not. Although the exact role of most metals in the physiology of organ- isms is not known, nevertheless, one might a priori expect that some heavy metals introduced into the ocean from nuclear reactions would concentrate in the biosphere. b. Concentration in the etivironment The concentration of a given radiomaterial by an organism is sometimes proportional to the concentration of that material in the en- vironment. This generalization applies both to aquatic and to terrestrial organisms. The uptake of cesium 137 by the oyster (Crassostrea vir- ginica) has been shown to be dependent upon the external concentration of cesium in the sea water (Chipman, et al., 1954). Prosser, et al. (1945), noted that with the addition of stron- tium to the environment there was an increase in the uptake of that element by goldfish {Car as • sitis auratus). Also, it has been demonstrated that as the carrier concentration in the nutrient environment is increased, the concentration fac- tor for a particular fission product in terrestrial plants tends to increase (Rediske, et al., 1955). c. Effect of the presence of one element on the uptake of another element The uptake of one radioelement by an organ- ism may be altered by the relative abundance of another element in the environment. In instances in which more than one element is involved, one of three phenomena may be observed : First, elements of similar chemical properties may substitute for one another. For example, it has been shown by Prosser, et al. (1945), that when the amount of calcium in the water was low, there was an increase in the uptake of strontium 89 by goldfish. Conversely, as the amount of calcium was increased, the uptake of strontium decreased. Rice (1956) observed that cells of Carteria grown in artificial sea water took up strontium in proportion to the stron- tium/calcium ratio in the medium. Bevelander and Benzer (1948) have shown that a modifica- tion of the constituents of sea water resulted in a change in the constituents of the shells de- posited by mollusks. Second, some elements may have an inhibi- tory effect on others. A classical example of this 74 Atomic Radiation and Oceanography and Fisheries phenomenon is that in which calcium inhibits the stimulatory action of potassium on heart muscle. Third, there may be a synergistic effect of one element on another. Ketchum (1939) has shown that the uptake of phosphorus by marine diatoms was enhanced with increased concen- trations of nitrogen. d. Specificity of organisms and tissues for given elements The specific activity of a radionuclide in any present in the flight muscles of some birds and it has been shown that radiophosphorus is in- corporated into the flight muscles of migratory waterfowl (Krumholz, 1954). Although many different kinds of aquatic or- ganisms have the ability to concentrate phos- phorus in their tissues, there are few that show such a specificity for that element as the various plankters. The uptake of phosphorus 32 by plankton algae in a lake has been demonstrated by Coffin and his associates (1949) and others, TABLE 4 Approximate Concentration Factors of Different Elements in Members of the Marine Biosphere. The Concentration Factors are Based on a Live Weight Basis. Concentration Factors Concentration Algae Form in in seawater (Non-cal- Element Seawater ( micrograms/ 1.) careous) Na Ionic 10' 1 K Ionic 380,000 25 Cs Ionic 0.5 1 Ca Ionic 400,000 10 Sr Ionic 7,000 20 Zn Ionic 10 100 Cu Ionic 3 100 Fe Particulate 10 20,000 Nil Ionic 2 500 Mo lonic-Particulate 10 10 V ? 1 1,000 Ti ? 1 1,000 Cr ? 0.05 300 P Ionic 70 10,000 S Ionic 900,000 10 I Ionic 50 10,000 1 Values from Laevastu and Thompson (1956). Invertebrates Vertebrates Soft Skeletal Soft Skeletal 0.5 0 0.07 1 10 0 5 20 10 — 10 — 10 1,000 1 200 10 1,000 1 200 5,000 1,000 1,000 30,000 5,000 5,000 1,000 1,000 10,000 100,000 1,000 5,000 200 200 100 — 100 — 20 — 100 — 20 — 1,000 — 40 — 10,000 10,000 40,000 2,000,000 5 1 2 — 100 50 10 — organism is dependent upon the ability of the organism or any of its parts to concentrate that nuclide. If the stable counterpart of the radio- nuclide does not normally enter into the physio- logical processes of an organism, neither will the radioactive material. It is well known that certain tissues have a predilection for concentrating specific elements. For instance, iodine is concentrated in the thy- roid tissue of animals and hence radio-iodine will also be concentrated there. Strontium, like calcium, is a bone seeker and the radioisotopes of both of those elements will be concentrated in the bony skeletons of animals. Similarly, both strontium and calcium are concentrated in certain parts of vascular plants and so are the radioisotopes. Phosphorus is one of the princi- pal constituents of bone and radiophosphorus is also concentrated in that tissue. The com- pound adenosine triphosphate is commonly and Whittaker (1953) showed that phyto- plankters from the Columbia River concentrated radiophosphorus by factors as great as 300,000. Krumholz (1954, 1956) found that attached fresh-water algae (Spirogyra) concentrated ra- diophosphorus by a factor of 850,000, and that many fresh-water zooplankters concentrated that radionuclide by factors of more than 100,000. Approximate concentration factors for marine organisms are given in Table 4. e. Osmotic and ionic regulation Osmotic and ionic regulation are known to occur in a variety of ways. The usual pathways of excretion are through the urine, feces, skin, respiration, and particle ejection, and the method of excretion depends upon the particu- lar organism and element involved. Ionic regu- lation may also occur by way of the chloride secreting cells in the gills of those fishes that migrate from salt to brackish water (Keys, Chapter 7 Ecology of Uptake by Aquatic Organisms 75 1931). Unfortunately, no experiments on such ionic regulation have been performed with ra- dionuchdes. f. Reproductive processes The reproductive processes of plants and ani- mals range from simple fission among the unicellular organisms to the very complex rela- tionships among the gametogenic forms. Dur- ing reproduction there is a transfer of materials from the parent to the offspring. In simple fission, the parent cell splits in two and each offspring receives approximately half of the parent material and thus only half of any radiomaterial that may have been pres- ent. Under conditions of chronic exposure, the offspring of organisms that reproduce by fission will incorporate usable radiomaterials into their bodies and a state of equilibrium eventually will be reached. Among the egg-laying forms, most of the material received by the offspring is derived from the contents of the egg. In this form of reproduction, once the egg is laid there will be no further loss of radiomaterials from the mother or gain to the offspring. This applies even when the environment is contaminated and there is chronic exposure of the parents, because the protective coverings of the egg pre- vent the entrance of radiomaterials. Among the forms that bear their young alive, however, there is usually some continuous trans- port of materials between the mother and the embryo. In such an instance it is probable that the embryo will accumulate radiomaterials with a resultant loss to the mother. If chronic ex- posure of a mother carrying an embryo con- tinues during pregnancy, a state of equilibrium may eventually be reached between the mother and the environment and between the mother and the embryo. During embryological development of all kinds there is a "biological dilution" of radio- materials through cell division and growth. This statement applies primarily if there has been an acute exposure to radiomaterials or if the ex- posure has stopped with the commencement of the embryological development. g. Molting In instances where the embryos pass through a series of metamorphic stages, there is a loss of radiomaterials from stage to stage as, for ex- ample, the loss from instar to instar in insects through molting. Furthermore, it has been demonstrated by Chipman and coworkers (per- sonal communication) that there is an increased accumulation of elemental constituents in crus- taceans prior to molting, and a loss of such ma- terials when the carapace is lost. h. Age and groivth It has been established (Olson and Foster, 1952) that younger, more rapidly growing fishes accumulate relatively greater amounts of radiomaterials than do older, more slowly grow- ing individuals. This phenomenon is probably a reflection of the more rapid metabolism that accompanies the growth of the younger fishes. It is not known whether the accumulation of radiomaterials by other aquatic vertebrates and invertebrates is a function of age and growth. i. Effect of temperature on cold-blooded and luarm-blooded animals In general, the body temperatures of warm- blooded animals are more or less constant whereas the body temperatures of cold-blooded animals largely depend upon the temperature of the environment. Similarly, the rate of metab- olism in warm-blooded animals is generally in- dependent of temperature changes in the en- vironment while that in the cold-blooded animals is largely dependent upon external temperatures. Changes in temperature affect the rates of chemical reactions and hence chemi- cal processes that involve the accumulation of elements in the body tissues are temperature dependent. Generally speaking, all cold-blooded aquatic organisms exhibit seasonal changes in the up- take and accumulation of radiomaterials from the environment. Davis, et al. (1953), and Krumholz (1954, 1956) have shown that there is a direct correlation between an increase in temperature and an increase in the accumulation of radiomaterials in fishes of the Columbia River, Washington, and of White Oak Lake, Tennessee, respectively. This increase in accumu- lation is apparently a reflection of the increase in the speed of the metabolic processes with rising water temperatures. However, Krumholz (1956) suggested that the fishes in White Oak Lake entered a period of dormancy following August 1 and lost about two-thirds of their ac- cumulated radioactivity during the subsequent two months even though the water tempera- tures were much the same as they were during the earlier part of the summer. In studies of the uptake of strontium 89 by 76 Atomic Radiation and Oceanography and Fisheries oysters and other shellfish at the Radiation Laboratory of the Fish and Wildhfe Service (Chipman, unpublished data) it was found that the rate of uptake was slowed down and the re- tention time was extended when the animals were kept in sea water at low winter tempera- tures. Conversely, the rate of uptake was speeded up and the retention time was short- ened when the animals were kept at summer temperatures. In other experiments at the same laboratory, it was found that larvae of the win- ter flounder {Pseudopleuronectes americanus) took up strontium 89 much more rapidly at higher water temperatures than at lower. So far as is known, there is no demonstrable seasonal pattern of accumulation of radioma- terials among the warm-blooded aquatic verte- brates. It is generally believed that inasmuch as the body temperatures of those animals remain more or less constant throughout the year there will be no marked seasonal changes in the up- take of radiomaterials based on changes in rates of metabolism. j . Effect of light Light affects the uptake and accumulation of radioelements by plants. For example, it has been clearly shown by Scott (1954) that the up- take of radiocesium by the algae Fucus and Rhodymenia was greatly enhanced in the pres- ence of light. k. Radiation effects Many aquatic organisms have the ability to concentrate radiomaterials in amounts deleteri- ous to their well-being. These deleterious effects range from those in which only the individual is concerned to those in which the population as a whole may be affected. Elsewhere in this series of reports there is a paper on the effects of radiation on aquatic organisms. Aspects of the accumtdation of radionuclides through, the ecosystem For purposes of this paper, the aquatic bio- sphere can be divided into three trophic levels based on energy sources : 1. Primary producers, such as the photosyn- thetic plants. 2. Primary consumers, the herbivores, such as water fleas (cladocerans) . 3. Secondary consumers, the carnivores, such as the largemouth bass or the tunas. The community biomass (the total weight of all organisms in the community) is unequally divided between the three trophic levels. Usu- ally there is a progressive decrease in both the biomass and the number of organisms from the first trophic level through the third, and a pro- gressive increase in the size of the organisms. However, most community populations are con- stantly changing and are affected by seasonal, diurnal, and other cycles of abundance. These changes frequently have a profound effect on the environment and any changes in the en- vironment in turn affect the stability of the community. Generally speaking, the smaller organisms have a higher reproductive potential, a shorter life span, and a shorter time between genera- tions ; the length of the life span and the time between generations usually give a fair indica- tion of the length of the embryological period. Furthermore, the smaller animals usually serve as food for the larger ones. The discussion will consider the following aspects of the accumulation of radiomaterials in the three trophic levels: (1) the distribution of elements among the three levels, (2) the concentration factors in different organisms within the same level, and (3) the transport of radiomaterials from one trophic level to another. Problems of the distribution of radionuclides among the trophic levels and the degree of con- centration of radionuclides by different organ- isms can be approached most readily through separate consideration of the effects from an acute exposure and those from a chronic ex- posure. A steady-state condition will be approximated when the amounts of radiomaterials introduced into the environment is equal to the amount that disappears through physical decay. Any organisms living in such an environment will suffer chronic exposure to the radioactivity, the level depending, of course, on their ability to concentrate the radiomaterials introduced and on the steady-state concentration of these ma- terials in the surrounding medium. An approxi- mation of the concentration factors for some organisms is given in Table 4. Davis and co-workers (1952) showed that there was a progressive decrease in the amount of radioactivity found in the aquatic organisms of the Columbia River downstream from the Hanford Works. There, the principal radionu- Chapter 7 Ecology of Uptake by Aquatic Organisms 77 elide was phosphorus 32, which has a physical half -life of about 14 days. It is apparent that when following the steady-state transport of radiomaterials through the ecosystem the follow- ing parameters must be considered: (1) the physical half-life of the radionuclide, (2) the distance of the organism from the source of radioactive contamination, and (3) the dilution of the radiomaterials between the point of in- troduction and the area in which the organism lives. The results from acute exposure cannot be as definitely approximated as for chronic exposure. In such instances, the time element is very im- portant, and the following must be known: (1) the rate of dilution of the radioactive water mass with non-radioactive water; (2) the rate of transfer of radiomaterials from one trophic level to another with the concurrent dilutions and losses or gains in concentration by the or- ganisms; and (3) the life span of the organ- isms involved. In general, the radiomaterials taken up by organisms of the first trophic level will be pri- marily in the ionized state although a certain amount of particulate radiomaterials will be ad- sorbed to the body surfaces. When uptake oc- curs, the rate of uptake will probably be more rapid than the rate of uptake in the other trophic levels. Particulate radiomaterials tend to be concen- trated in the second trophic level. Findings from the Wigwam and Castle tests (Goldberg, unpublished data) showed that the principal or- ganisms which concentrated particulate radio- materials were the mucous, ciliary, and pseudo- podial feeders among the zooplankters. These organisms contained much more radioactivity per unit weight than either the algae or the setal or rapacious feeders. In addition to the differences in concentration of radiomaterials from one trophic level to an- other, there are marked differences among spe- cies in the same level. For instance, it has been shown by Chipman, et al. (1953), that some phytoplankters will concentrate radiostrontium by a factor of about 20 times whereas others will concentrate the radioelement by factors as much as 1500 times. Comparable data have been recorded by Krumholz (1954) for the accumu- lation of radiophosphorus by the phytoplankters of White Oak Lake. Differences also exist between individuals of the same species. Very large differences in the amounts of radiomaterials accumulated by indi- vidual fishes in White Oak Lake were described by Krumholz (1956) . For instance, he reported that the amounts of radiostrontium in the bones of three bluegills {Lepomis macrochirus') dif- fered by more than five-fold. These three fish were taken from the same place in the lake on the same day, August 27, 1952. Comparable differences were found in the amounts of ac- cumulated radiomaterials in most other tissues. The transfer of radiomaterials from one trophic level to another is not only dependent upon the concentration of the radiomaterial in the organism but also is governed by the rate of growth of the organism and the rate of in- crease in the size of the population. These fac- tors of transfer are of particular importance in the event of an acute exposure because the dilu- tion brought about through cell division and growth may well minimize any radiation effect. In any event, there is always a loss in the total amount of radiomaterials in the transfer from one trophic level to another (though not nec- essarily a decrease in the concentration in indi- vidual organisms). Such a loss may be rela- tively small or it may be very great depending upon the organism and the particular food web involved. Not all radiomaterials that enter the first trophic level are passed on to higher levels. At each trophic level there are certain species that, for one reason or another, are not widely used as food by the organisms of higher levels. Also, some of the plants of the first trophic level may die before they are eaten and thus will be re- turned to the environment as organic matter. In this case the primary producers may be of little or no importance as a source of radioma- terials to the organisms of the second and third trophic levels. If relatively large quantities of radiomaterials are accumulated in certain hard parts of an or- ganism, such as the shell of an oyster or the bones of a fish, they will, in all probability, re- main in those parts during the greater part of the life of the animal concerned, and will not be available to other animals in the biosphere until the animal dies. Chipman and co-workers (1953) showed that oysters fed on Cblorella assimilated only very little of the radiophosphorus from these 78 Afom/c Radiation and Oceanography and Fisheries algae. On the other hand, oysters fed upon other phytoplankters that contained no more ra- diophosphorus than the Chlorella accumulated relatively large amounts of radiophosphorus and incorporated that element into their tissues as organic phosphorus compounds. It appears that the particular food web used by any organism is of primary importance in the transfer of ra- diomaterials from one trophic level to another. Problems for further research One of the fundamental questions to be an- swered concerns the mechanism of incorpora- tion of the heavier elements, such as the fission products, in aquatic organisms. To date, no metal heavier than molybdenum has been shown to be necessary for metabolic processes. Spe- cifically, we need to know: 1. How are the radioactive elements passed through membranes and where and why do they concentrate in the organisms ? 2. What are their biological half-lives of the different radioactive elements in different or- ganisms ? 3. What are the average and extreme concen- tration levels of these elements in various or- ganisms and in the biosphere ? The revolution in biological thought brought about by the use of labelled atoms is manifest in all branches of biological research today. Radioisotopes have permitted the study of rate processes that could not have been investigated in any other way. Such processes include the pumping rates of water and other biological fluids, and the transfer of molecules or portions of molecules from tissue to tissue, or, on the ecological level, from organism to organism. REFERENCES Bevelander, G., and P. Benzer. 1948. Cal- cification in marine molluscs. Biol. Bull. 94:176-83. Boroughs, H., S. J. Townsley and R. W. HiATT. 1956. The metabolism of radio- nuclides by marine organisms. I. The uptake, accumulation and loss of strontium 89 by fishes. Biol. Bull. 111:336-351. Chipman, W. a., T. R. Rice, and T. J. Price. 1953. Accumulation of radioactivity by marine invertebrate animals. U. S. Fish and Wildlife Service Radioisotope Labora- tory, Progress Report, April 1953, (Type- written). 1954. Accumulation of fission products by marine plankton, fish, and shellfish. U. S. Fish and Wildlife Radioisotope Labora- tory, Progress Report, July-December 1954, (Typewritten). Coffin, C. C, F. R. Hayes, L. H. Jodrey, and S. G. Whiteway. 1949. Exchange of ma- terials in a lake as studied by the addition of radioactive phosphorus. Canad. Jour. Research 27:207-222. Davis, J. J., R. W. Coopey, D. G. Watson, C. C. Palmiter, and C. L. Cooper, 1952. The radioactivity and ecology of aquatic organisms of the Columbia River. In Bi- ology Research — Annual Report, 1951, USAEC Document HW-25021, pp. 19-29. Goldberg, E. D. 1952. Iron assimilation by marine diatoms. Biol. Bull. 102, lA'h-S. Greendale, a. E., and N. E. Ballou. 1954. Physical state of fission product elements following their vaporization in distilled water and seawater. USNRDL Document 436, pp. 1-28. Hevesy, G. 1923. Absorption and translocation of lead by plants. Biochem. Jour. 17:439- 45. 1948. Radioactive indicators. Interscience Publishers, New York, xvi + 555 pages. HiATT, R. W., H. Boroughs, S. J. Townsley, and Geraldine Kau. 1955. Radioisotope uptake in marine organisms with special reference to the passage of such isotopes as are liberated from atomic weapons through food chains leading to organisms utilized as food by man. Hawaii Marine Laboratory, Annual Report, AEC project number AT (04-3) 56, pp. 1-29, (Mimeo- graphed). Ketchum, B. H. 1939. The adsorption of phosphate and nitrate by illuminated cul- tures of Nitzchia closterium, Am. J. Botany 26:399-402. Keys, A. B. 1931. Chloride and water secre- tion and absorption by gills of the eel. Zeitsch. Vergl. Physiol. 15:364. Chapter 7 Ecology of Uptake by Aquatic Organisms 79 Krauskopf, K. B. 1956. Factors controlling the concentrations of thirteen rare metals in sea water. Geochim. et Cosmochim. Acta 9:1-32. Krumholz, L. a. 1954. A summary of find- ings of the ecological survey of White Oak Creek, Roane County, Tennessee, 1950- 1953. USAEC Document ORO-1 32, pp. 1- 54, (Mimeographed) . 1956. Observations on the fish population of a lake contaminated by radioactive wastes. Bull. Amer. Mus. Nat. Hist. 110(4) :277- 368. Krumholz, L. A., and J. H. Rust. 1954. Osteogenic sarcoma in a muskrat from an area of high environmental radiostrontium. A.M.A. Arch. Path. 57:270-278. Laevastu, T., and T. G. Thompson. 1956. The determination and occurrence of nickel in sea water, marine organisms and sedi- ments. ]. duCons.2l:l25-\A^. Olson, P. A., Jr., and R. F. Foster. 1952. Effect of pile effluent water on fish. In Biology Research — Annual Report, 1951. USAEC Document HW-25021, p. 41. Prosser, C. L., W. Pervinsek, Jane Arnold, G. SviHLA, and P. C. Tompkins. 1945. Accumulation and distribution of radio- active strontium, barium-lanthanum, fission mixture and sodium in goldfish. USAEC Document MDDC-496, October 13, 1954. Rediske, J. H., J. F. Cline, and A. A. Selders. 1955. The absorption of fission products by plants. In Biology Research — Annual Report, 1954. USAEC Document HW- 35917, pp. 40-46. Rice, T. R. 1956. The accumulation and ex- change of strontium by marine and plank- tonic algae. Limnology and Oceanography 1(2):123-138. RoTHSTEiN, A., and R. Meier. 1951. The re- lationship of cell surface to metabolism VI, the chemical nature of the uranium com- plexing groups of the cell surface. /. Cell. Comp. Physiol. 38:245-70. Scott, R. 1954. A study of cesium accumula- tion by marine algae. Proc. Second Radio- isotope Conference, pp. 373. Vinogradov, A. P. 1953. The elementary composition of marine organisms. Sears Foundation for Marine Research, Memoir No. 2. Whittaker, R. H. 1953. Removal of radio- phosphorus contaminant from the water in an aquarium community. In Biology Research- Annual Report, 1952. USAEC Document HW-28636, pp. 14-19. Chapter 8 LABORATORY EXPERIMENTS ON THE UPTAKE, ACCUMULATION, AND LOSS OF RADIONUCLIDES BY MARINE ORGANISMS ^ Howard Boroughs, Hawaii Marine Laboratory, University of Hawaii, Honolulu, Hawaii Walter A. Chipman, Fishery Radiobiological Laboratory, U. S. Fish and Wildlife Service, Beaufort, North Carolina Theodore R. Rice, Fishery Radiobiological Laboratory, U. S. Fish and Wildlife Service, Beaufort, North Carolina What happens to radioactive materials that are introduced into the oceans may be studied by a marine biologist from at least two points of view. As a physiologist, he will be interested in the uptake, accumulation, and loss of radioele- ments as a function of the element, and its con- centration; in the physical factors of tempera- ture, light, and salinity; and in differences between species of organisms, as well as their age and sex, to mention some of the most im- portant parameters. As an ecologist, he will be interested in these same parameters under a steady-state condition. The physiologist would profit most by exposure of the organism to a single dose of radioactive material, while the ecologist must concern himself with the results of chronic exposure. Both types of biologists may be interested in tracing the history of an element through the food webs of the various trophic levels. Un- fortunately, the experimental data involving the metabolism of radionuclides by marine organ- isms is extremely meager. In this section some experiments will be described on the uptake, accumulation, and loss of radionuclides by vari- ous marine organisms in the three trophic levels. It must be emphasized that the results of these few experiments must be extrapolated with ex- treme caution in predicting what may happen to radioactive materials introduced into the oceans from nuclear reactor plants, bomb deto- nations, or from any other sources. ^ Work performed at the Fishery Radiobiological Laboratory of the U. S. Fish and Wildlife Service and the Hawaii Marine Laboratory (Drs. H. Boroughs, S. J. Townsley, and R. W. Hiatt). Contribution No. 95, Hawaii Marine Laboratory. In discussing the uptake of radionuclides by marine organisms, it is sometimes difficult to state exactly what constitutes a single or a chronic exposure. For a unicellular alga, a few hours may represent chronic exposure, while a few weeks may be insufficient for a fish to reach a steady-state condition. No long-term repeti- tive feeding experiments have been done, so for the purpose of this report, we will discuss the metabolism of the various radionuclides solely on the basis of the trophic level concerned. The term uptake implies passage through a membrane. Radioactive material may be pres- ent in the gut of an organism, but until it enters the organism through a membrane, it can play no role in the metabolism of that organism ex- cept by producing radiation effects or by inter- fering with a chemical reaction occurring within the gut. In some of the experiments to be de- scribed, particularly those involving phytoplank- ton, it was not established whether or not the radioisotope was actually incorporated into the organism, or merely adsorbed to the surface. For simplicity, we will therefore discuss uptake in the sense that the radioisotope is associated with the organ or organism in question. Isotopes of a given element usually have similar chemical behavior, so that in tracing the path of most elements in biological systems, it can be assumed that a radioactive atom will be- have in the same way as a non-radioactive atom of the same species. The only parameters to be considered in the discussion to follow will be the species and age of the organism, the ele- ment, the concentration of the element, the tem- perature, and the duration of exposure or treat- ment. No work using radioisotopes has been 80 Chapter 8 Laboratory Experhnents on Uptake 81 done on the mineral metabohsm of marine or- ganisms relative to sex. The data that will be presented were collected either at the Fishery Radiobiological Laboratory of the United States Fish and Wildlife Service (R.L.F.W.S.) or the Hawaii Marine Laboratory, University of Hawaii (HML). First trophic level Experiments performed at the R.L.F.W.S. very clearly show that different species of planktonic algae have remarkably different abili- ties to concentrate a particular element from the sea water medium. Algae were grown in the presence of radiostrontium obtained from Oak TABLE 1 The Differential Uptake of Radio- active Strontium and Yttrium By Algae Percentage Percentage activity activity from from Species strontium yttrium Carteria sp 100.0 0.0 Thoracomonas sp 50.4 49.6 Amphora sp 10.0 90.0 Navicula sp 8.5 91.5 Chromolina sp 8.2 91.8 Chlamydomonas sp 6.5 93.5 Nitzschia dosterium 6.0 94.0 Nannochloris atomus 5.7 94.3 Chlorella sp 5.3 94.7 Porphyridium curentum . . . 4.4 95.6 Gymnodinium splendins . . . 4.1 95.9 Gyrodinium sp 2.3 97.7 Ridge. The material used contained both Sr^^ and Sr«»; the latter decays to form Y^^. By counting the algal samples immediately after they were removed from the culture medium, and again after several weeks, in order to allow the secular equilibrium of the Sr^^-Y^" pair to be reached, it was possible to determine what percentage of the original radioactivity was due to strontium. Table 1 shows that Carteria sp. accumulated strontium 89 and 90 from the iso- topic mixture, and that Gyrodinium sp. removed almost no strontium 89 or 90, but instead ac- cumulated yttrium 90. It was found that Nitz- schia closteriujn under an apparent steady state condition concentrated strontium 17 times over its concentration in sea water (weight of algae/ weight of water) . The concentration factor for strontium Carteria sp. was found to vary with condition of culture but was much greater than for Nitzschia dosterium. Experiments using cesium^^^ show that while different species concentrate cesium to different degrees (Table 2) none of the nine species TABLE 2 Concentration of Cesium By Marine Algae Concentration Algae factor ^ Bacillariaceae Nitzschia dosterium 1.2 Amphora sp 1,5 Nitzschia sp 1.7 Chlorophyceae Chlamydomonas sp 1.3 Carteria sp 1.3 Chlorella sp 2.4 Pyramimonas sp 2.6 Nannochloris atomus 3.1 Rhodophyceae Porphyridium curentum 1.3 1 The concentration factor is reported as the ratio of Cs"^ in the algae (wet weight) to that in an equivalent weight of sea water at an apparent steady- state condition. tested from three families showed any marked concentration of this element from sea water. The effect of the concentration of an element on its uptake by Nitzschia cells is shown in Figure 1. Nitzschia cells were grown in sea water to which had been added labelled zinc at three different concentrations. From the graph 0. 1 mg./^ • 5 irig./i. m 80- 40 60 HOURS Figure 1. Uptake of Zinc®^ by Nitzschia Cells from Culture Medium Containing Different Concen- trations of Zinc. O 0.1 mg./l O 1 mg./l • '5 mg./l 82 Atomic Radiation and Oceanography and Fisheries it is evident that at low concentrations all the zinc was removed after about four days. The lowest concentration used was still ten times higher than the average zinc concentration of sea water. The rate of uptake of zinc"^ by Nitzschia cells is shown in Figure 2. At the normal con- FiGURE 2. Uptake of Zinc^^ by Nitzschia Cells from Culture Medium Containing 10 Micrograms of Zinc/Liter. centration of zinc in sea water, a dividing cul- ture of Nitzschia depleted the zinc'^'' in a closed system in less than one day. Apparently phyto- plankton cells concentrate zinc relative to sea water and any radioactive zinc present in the water will be quickly taken up in large amounts. The radioisotopes so far discussed are very likely always ionic in sea water. Ruthenium solution, however, forms colloids and particles when put into sea water. Ruthenium^o*^ ob- tained as an acid solution from Oak Ridge was added to a sea water culture of Nitzschia cells. Figure 3 shows that the cells continued to take up the ruthenium for the 12 days of the experi- ment. Tlie amount of ruthenium per cell de- creased, however, since the cells of the culture were dividing continually. One may conclude from this experiment, that since the ruthenium concentration in sea water is low, dividing planktonic algae would take up large amounts of any radioactive ruthenium present. Second trophic level The work reported in this section was also done at the R.L.F.W.S. Larvae of the brine shrimp Artemia were put into filtered sea water containing radiostrontium and the daughter 16 / the sea, while about 0.9 megacunes have fallen for this isotope, it appears that some 23,500 , , , r t^ r , • -, ~ 1 ^(j-m = 0-l4, where k is the fraction of the carbon in the atmosphere transferred to the mixed layer per year (Craig, 1957 (a)). The average annual exchange flux of carbon dioxide, into and out of the sea each year, is thus found to be about 2x10'^ mioles per square centimeter of sea surface. This rate is lower by a factor of 10,000 than the rate re- cently obtained by Dingle (1954) from consid- eration of the various rate constants involved, and the discrepancy thus serves to emphasize the power of natural isotopic studies to yield quantitative data, as compared with more tra- ditional methods. An entirely independent calculation of the atmospheric residence time, not based on steady- state considerations, may be made from the magnitude of the so-called Suess effect described previously. It is known that since the begin- ning of the industrial revolution, man has added an amount of carbon dioxide to the atmosphere by fuel combustion equivalent to about 12 per cent of the amount originally present. The degree of dilution of radiocarbon activity in contemporaneous wood by incorporation of C^*- free COo, measured relative to the activity of 19th century wood, is then a measure of the rate at which the dead CO2 has been removed from the atmosphere into the sea. The first measurements of this effect, made by Suess (1953), indicated a dilution of about 3 per cent, and from these data Suess deduced an atmospheric CO^ residence time of 20-50 years. More recent and extensive measurements by Suess (1955) have shown that the figure of Chapter 11 Tracer Studies of the Sea and Atmosphere 117 3 per cent is higher than the average world- wide figure, and represents an increased local contamination in trees growing near sites of industrial activity. The latest measurements in- dicate a world-wide effect of about 1 .7 per cent. Revelle and Suess (1957) have discussed the relationships between the exchange rate, the Suess effect, the effect of an increase in the atmospheric CO, content on the atmospheric and oceanic reservoirs, and the buffering effect of the sea water alkalinity on carbon transients. They conclude that, all things considered, the residence time of COg in the atmosphere, rela- tive to exchange with the sea, is of the order of 10 years. Though the uncertainty in their esti- mate is a good deal larger than in the case of the steady-state considerations discussed above, the close agreement of the figures obtained by these different considerations is gratifying, and indicates that the factors governing the natural distribution of radiocarbon are now fairly well understood. The size of the terrestrial biosphere and the annual rate of photosynthesis on land have been estimated by Schroeder and Noddack, and from their figures it appears that the terrestrial plants consume about 3 per cent of the atmospheric CO2 per year, corresponding to an atmospheric residence time before entrance into the bio- sphere of 33 years. With a residence time of 7 years, prior to exchange into the sea, the total residence time of a CO2 molecule in the atmos- phere is 6 years, after which it goes either into the sea (9 chances out of 11) or into the ter- restrial biosphere (2 chances out of 11). Thus the carbon dioxide flux into the sea is about 4.5 times larger than the flux into the biosphere, and about 82 per cent of the COo leaving the atmosphere goes into the sea, while only about 18 per cent goes into the terrestrial plants. This ratio represents a considerable departure from previous estimates, and indicates that the spatial distribution of plants and soils is probably not the dominant factor in determining the steady- state CO, concentration in the atmosphere. In fact it appears more likely that the spatial pat- tern of absorption and release of CO„ by the sea, and the seasonal variations in this pattern, are the dominant factors. The various considerations outlined above are all consistent with any deep-sea residence time of carbon up to a few thousand years, and do not yield any closer estimate for this figure. Recent unpublished data by Broecker and co- workers at the Lamont Geological Observatory indicate that the bicarbonate of deep ocean waters probably averages about 8 per cent lower in C^* content than the surface mixed layer, corresponding to a radiocarbon "age" of the order of 670 years. However, considerations by Craig (in press), based on a second order oceanic model in which the deep sea reservoir is exposed to the atmosphere in high latitudes, show that about half of the radiocarbon in the deep sea is derived directly from the atmosphere. The other half enters the deep sea from the surface mixed layer of the ocean by the mixing and interchange of water. Because of this dual source of radiocarbon, the residence time calculated for carbon in the deep sea is only about half of the actual resi- dence time of a water molecule in the deep sea relative to the mixed layer; thus the deep-sea residence time of water relative to the mixed layer is probably of the order of 1000 years as a world-wide average. However the actual inter- pretation of such residence times in the sea is quite complicated, and reference is made to the paper cited above for a detailed discussion of carbon and water residence times. Deuterium and Oxygen 18 As discussed previously, the stable isotopes are of great value in the study of ocean water mixing as additional parameters related to salin- ity. One particular case in which information can be gained from such studies is the problem of meltwater dilution of the oceans in the polar regions. A salinity decrease can be caused by addition of fresh water from river runoff, or from the melting of sea ice, and from salinity data alone these sources cannot be differentiated. However, the isotopic composition of the two sources is quite different; the sea ice should have a composition quite similar to that of the ocean water, while, as shown above, the runoff of rivers in polar areas is greatly depleted in deuterium and oxygen 18 relative to ocean water. Thus from consideration of salinity and isotopic data taken together, a quantitative eval- uation of the mixing conditions can be made. Friedman of the U. S. Geological Survey is currently studying such problems with deute- rium analyses of Atlantic waters. The isotopic data should also be useful in material balance 118 Atomic Radiation and Oceanography and Fisheries studies over various sections of the oceans, because of the latitudinal decrease in deuterium and oxygen 18 concentration of oceanic water vapor, and the known temperature dependence of the isotopic selection in evaporation. Craig, Boato, and White (1956) have shown how deuterium and oxygen 18 measurements can be usesd to determine the proportions of juvenile or magnetic water to reheated ground water in thermal springs, and volcanic steam. These isotopes, together with tritium, have im- portant applications to practically all hydrologic problems, and the exploitation of such tech- niques has barely begun. Tritium and Strontium 90 As described in Part II, the tritium measure- ments made by Libby and his co-workers fur- nish an independent value for the mixing rate in the sea; more detailed studies will surely provide important information on the oceanic mixing phenomena. The production of tritium in thermonuclear explosions provides an iso- topic tracer for determination of atmospheric mixing times across the face of the earth and storage times in the atmosphere. The measurement of the world-wide distribu- tion of strontium 90 produced by nuclear deto- nations has been done by W. F. Libby and E. A. Martell at the University of Chicago. The results of their work have recently been described by Libby (1956 a, b). The radio- nuclides produced by low-yield kiloton weapons, and part of the activity produced by the higher- yield megaton weapons, are distributed within the troposphere in a belt corresponding to the latitude of the test site. This material has a tropospheric life which is a function of particle size; some of the activity may circle the earth two or three times within the hemisphere in which it was produced before being washed out of the atmosphere. However, the mean life of this tropospheric material is only a few weeks. More interesting is the fact that Libby and Martell find that half or more of the radio- strontium produced by the megaton weapons is distributed over both hemispheres and falls out much more slowly, the mean storage time in the atmosphere being of the order of ten years. They conclude that this material is car- ried up into the stratosphere, above the tropo- pause, where it is mixed horizontally in a time comparable to the storage time at this level. The contrast between the distribution of megaton weapon produced radiostrontium and tritium is extremely significant. As noted in Part III, Begemann and Libby find that the artificially produced tritium is confined to a single hemisphere and is rapidly washed out of the atmosphere; this material thus follows the pattern of the activities which remain in the troposphere. The tritium and fission prod- uct data thus show that over a period of months there is virtually no cross-hemispheric mixing in the troposphere, but that over a period of years the stratosphere is well-mixed horizontally. The failure to detect tritium carried up into the stratosphere with the megaton weapon produced radiostrontium may be due to the instantaneous combustion of tritium to HTO by the catalytic action of the oxides of nitrogen produced in the blast (Harteck, personal communication). As water, the tritium may be frozen out at the lower cold trap, in the tropopause, where the temperature is about — 70°C, and thus pre- vented from entering the stratosphere. On the other hand, Martell points out (per- sonal communication), that the thermal energy of the fireball is still quite large by the time a fireball produced by a megaton weapon has risen to the height of the tropopause. In order for HTO to condense and thus be trapped be- low the tropopause, it is necessary to assume that the lighter constituents of the fireball have diffused into the cooler outer layers. Martell suggests that if such is the case, then the actual explanation may be that the portion of the cloud containing the HTO may not have sufficient thermal energy to penetrate the tropopause, and as a result, this portion of the cloud merely expands horizontally below the tropopause. V. Conclusions From the discussion in the preceding parts of this report, it is apparent that the advent of manmade nuclear reactions introduced a series of geophysical and geochemical experiments on a vast scale. It is fortunate that the introduction of such experiments came at a time when geo- chemists were well underway towards the under- standing of natural transfer phenomena by means of studies based on naturally CKCurring isotopes in their steady state biogeochemical cycles. It should be clear that the need for this knowledge is such that every effort should be Chapter 11 Tracer Studies of the Sea and Atmosphere 119 made to prevent irreversible procedures which might ehminate the opportunity to study such mixing at the natural level where evaluation of the long term variables is possible. On the other hand, it is also evident that the introduction of artificially produced radioisotopes into the geo- sphere has been productive of a great deal of new knowledge that might otherwise not have been obtained. The importance of continuous monitoring of the levels of such substances as tritium cannot be overemphasized. As an example of this, it may be pointed out that one reason that carbon 14 is such a powerful tool for the evaluation of ocean-atmosphere interaction that we have relatively precise records on just how much dead carbon has been produced by the combustion of fossil fuels ; were this information not available the use of radiocarbon in such studies would be exceedingly difficult, if not impossible. From the carbon 14 inventory discussed in Part II, and assuming an average depth of about 150 meters for the oceanic thermocline, it appears that about 4 per cent of the carbon 14 in the sea lies above the thermocline; this corresponds to an activity of about 10 mega- curies. It is thus evident that introduction of artificially produced radiocarbon in 10,000 curie amounts above the thermocline would begin to produce a critical level which would interfere with the natural radiocarbon studies of such fundamental importance. Introduction of 100- 1000 curie amounts above the thermocline would produce activity sites which could be traced for years, but such experiments could not be done more than once every decade or so if the natural level is to be preserved. It would thus seem highly desirable that some international body be constituted to record and monitor the material put into the sea and the atmosphere as wastes and for tracer experi- ments. It is a truism to point out that a con- taminated laboratory is rather easily replaced, but that the laboratory of the earth scientists is not easily renovated. -CONCLUSIONS Anderson, E. C. 1953. The production and distribution of natural radiocarbon. Ann. Rev. Nuclear Science 2:63-78. Arnold, J. R., and H. A. Al-Salih. 1955. Beryllium-7 produced by cosmic rays. Science 121:451-453. Arnold, J. R., and E. C. Anderson. 1957. The distribution of carbon- 14 in nature. Tellus 9:28-32. Begemann, F. 1956. Distribution of artifi- cially produced tritium in nature. Nuclear Processes in Geologic Settings: Proceed- ings of the Second Conference. National Academy of Sciences — National Research Council Publication 400:pp. 166-171. Benioff, p. a. 1956. Cosmic-ray production rate and mean removal time of Beryllium-7 from the atmosphere. Phys. Rev. 104: 1122-1130. Craig, H. 1953. The geochemistry of the stable carbon isotopes. Geochim. et Cosmochim. Acta 3:53-92. 1954. Carbon 13 in plants and the relation- ships between carbon 13 and carbon 14 variations in nature. /. of Geology 62: 115-149. 1957 (a). The natural distribution of radio- carbon and the exchange time of carbon dioxide between atmosphere and sea. Tel- lus 9:1-11. 1957 (b). Distribution, production rate, and possible solar origin of natural tritium. Phys. Rev. 105:1125-1127. In press. The natural distribution of radio- carbon: II. Mixing rates in the sea and residence times of carbon and water. Tellus. Craig, H., and G. Boato. 1955. Isotopes. At7n. Rev. Phys. Chem. 6:403-432. Craig, H., G. Boato, and D. E. White. 1956. The isotopic geochemistry of thermal wa- ters. Nuclear Processes in Geologic Set- tings: Proceedings of the Second Confer- ence. National Academy of Sciences — National Research Council Publication 400 :pp. 29-38. Currie, L. a., \V. F. Libby, and R. L. Wolf- gang, 1956. Tritium production by high- energy protons. Phys. Rev. 101:1557- 1563. De Vries, H. 1956. Purification of CO, for use in a proportional counter for i*C age measurements. Appl. Sci. Res. (B) 5: 387-400. Dingle, A. N. 1954. The carbon dioxide exchange between the North Atlantic ocean and the atmosphere. Tellus 6:342-350. Dole, M., G. A. Lane, D. P. Rudd, and D. A. Zaukelies, 1954. Isotopic composition 120 Atomic Radiation and Oceanography and Fisheries of atmospheric oxygen and nitrogen. Geo- chim. et Cosmochim. Acta 6:65-78. Epstein, S., and T, K. Mayeda. 1953. Varia- tion of O^^ content of waters from natural sources. Geochim. et Cosmochim. Acta 4:213-224. Fireman, E. L., and F. S. Rowland. 1955. Tritium and neutron production by 2.2- Bev protons on nitrogen and oxygen. Phys. Rev. 97:780-782. Friedman, I. 1953. Deuterium content of natural water and other substances. Geo- chim. et Cosmochim. Acta 4:89-103. Harteck, p. 1954. The relative abundance of HT and HTO in the atmosphere. /, Chem. Rhys. 22:1746-1751. Kaufman, S., and W. F. Libby. 1954. The natural distribution of tritium. Rhys. Rev. 93:1337-1344. Lane, G. A., and M. Dole. 1956. Fractiona- tion of oxygen isotopes during respiration. Science 123:574-576. Libby, W. F. 1955. Radiocarbon dating. Univ. of Chicago Press, Chicago: 2nd edition, 175 pp. 1956(a) Radioactive fallout and radioactive strontium. Science 123:656-660. 1956(b) Radioactive strontium fallout. Rroc. Nat. Acad. Sci. 42 :?> 65-590. Morrison, P., and J. Pine. 1955. Radiogenic origin of the helium isotopes in rock. Ann. New York Acad. Science 62:69-92. Rafter, T. A. 1955. ^*C variations in nature and the effect on radiocarbon dating. New Zealand J. Sci. Tech. (B) 37:20-38. Rakestraw, N., D. Rudd and M. Dole. 1951. Isotopic composition of oxygen in air dissolved in Pacific ocean water as a func- tion of depth. /. Amer. Chem. Soc. 73: 2976. Revelle, R., T. R. Folsom, E. D. Goldberg, and J. D. Isaacs. 1955. Nuclear science and oceanography. Intern. Conf. on Peace- ful Uses of Atomic Energy, Geneva, also Contr. Scripps Inst. Ocean. N. S. 794: 22 pp. Revelle, R., and H. E. Suess. 1957. Car- bon dioxide exchange between atmosphere and ocean and the question of an increase in atmospheric COg during the past dec- ades. Tellus 9:18-27. Suess, H. E. 1953. Natural radiocarbon and the rate of exchange of carbon dioxide between the atmosphere and the sea. Nu- clear Processes in Geologic Settings. Na- tional Academy of Sciences — National Research Council Publication, pp. 52-56. Suess, H. E. 1954. Natural radiocarbon meas- urements by acetylene counting. Science 120:5-7. 1955. Radiocarbon concentration in modern wood. Science 122:415-417. Von Buttlar, H., and W. F. Libby. 1955. Natural distribution of cosmic-ray pro- duced tritium. 2. /, Inorganic and Nuclear Chem. 1:75-91. Chapter 12 ON THE TAGGING OF WATER MASSES FOR THE STUDY OF PHYSICAL PROCESSES IN THE OCEANS^ Theodore R. Folsom, Scripps Institution of Oceanography, La Jolla, California and Allyn C. Vine, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts Finding, identifying, and plotting the courses of characteristic masses of water in the oceans are major activities of the physical ocea- nographer. Assistance from the new techniques that have come with the use of radioactive materials has been welcomed by him; some of these techniques have already been put into service for tracing the water. It is not gen- erally realized how much experience has been gained, beginning with the 1946 tests in Bi- kini Lagoon, in tracing water masses contam- inated with radioactive materials from weapons' tests. And many thoughts are now turning toward the radioactive tagging of ocean water by other means in regions where knowledge of underlying physical processes are meager, espe- cially in the very deep waters. Proposals for the disposal in the sea of atomic energy wastes cannot be properly evaluated until estimates can be improved concerning the motion of this deep water. Many of the advantages (familiar in the laboratory) of using radioactive identifying tags can be realized at sea, even though rendered difficult by the very large physical dimensions of the oceans. What appeals most to the ocea- nographer is his new ability, under certain cir- cumstances, to make very rapid identifications of water lying on the surface or deep below his ship; thus allowing large volumes to be sur- veyed in three dimensions and in more detail than ever before possible. Three layers in the ocean are distinguished 1 Contribution from the Scripps Institution of Oceanography, New Series, No. 905. Contribution No. 929 from Woods Hole Oceano- graphic Institution. Part of Table 2 was computed with the collaboration of John Harley of AEC, New York City Operations Office, who gave much other counsel for which the authors are grateful. clearly by structure and behavior: the mixed layer near the surface; the intermediate layer lying just below wherein the temperature changes rapidly with depth (this thermal stratification bringing about great stability) ; and finally, the large, nearly uniform bottom water mass ex- tending to the sea floor with so little variation in density that very stable stratification is not possible. Each water mass reacts differently when disturbed, and therefore, mixing occurs differently in response to currents and mass intrusions. Experiments conducted in any one of these domains must take into consideration the special features that exist, and must call upon equipment most suited to these sections. Equipment specialized for radiological survey work in any of these oceanographic domains is still primitive. However, it can be said that equipment for detecting and measuring radia- tion is not a bit less highly developed than are the equipment and techniques needed for navi- gating a ship, and for maneuvering detectors at sea, especially at great depth. So much in- formation now can be reported by radiological means in a short time that a ship now has more reason than heretofore for precise navigation. In some cases, the depth and position of the detector relative to the ship must be known instantly, and almost always must be controlled far better than has been accepted by traditional hydrography. It is difficult to record data in full detail in many cases, and in others it is difficult to evaluate features rapidly enough to alter maneuvers to best advantage; an ocea- nographer can now expect to be aware of a strongly active layer in less than one second after his electronic probe makes contact, and he even may make use of a fast moving airplane to outline radioactive areas on the surface. 121 122 Atomic Radiation and Oceanography and Fisheries Instrument Sensitivity and Natural Backgrounds Many promising measuring schemes have been proposed. However, it is profitable to com- pare the equipment and techniques which have been used already at sea. At the top of Table 2 is presented the background radiations coming from cosmic rays and from the natural potas- sium in the sea, and the activity level now believed tolerable for drinking water also is given for comparison. At the bottom of Table 2 are listed, in the brief numerical form in which they are com- monly stated, the sensitivities of three measur- ing techniques which actually have been used for radiological exploration at sea. Many as- pects of the measurement problem are over- simplified by a comparison of this sort, but the table does indicate that present shipboard beta analysis is capable of measuring beta tracer ac- tivity below the background beta activity due to the potassium in the sea water, whereas gamma detectors so far have been limited at levels above the gamma backgrounds of the sea. On surveys covering large distances, such as on Operation TROLL (U. S. Atomic Energy Commission 1956), and on the SHUNKOTU MARU Expedition (Mujoke, Sugiura, and Ka- meda 1954), there is ample time for water analyses, and advantage can be made of beta techniques. Nevertheless, there are many circum- stances where direct measurements by gamma devices are necessary for rapidly locating small contaminated water masses, and it is likely that gamma techniques will be perfected so as to allow use at levels far below their present capability. There are occasions at sea in which a gamma detector must indicate the presence of tracer activity within a few seconds after making con- tact. The limitations imposed by this sort of time restriction in the presence of statistical fluctuations in the signals are discussed in Ap- pendix A, and are summarized in Table 3. Other important details concerning the radio- active background in the sea have not been thoroughly explored. It may be too late to estimate the background level that existed a decade ago for some isotopes, and this should not be forgotten in planning future surveys. Of particular interest are background condi- tions near the sea floor where radium and thorium activity are known to accumulate in sediments; but little is known in detail about the lateral distribution of bottom activity. More complete utilization of iveapons' tests for the marine sciences It appears likely that large weapons will continue to be tested in oceanic areas and that radioactive materials will be strewn from time to time over the surface of the sea. Valuable oceanographic data already has come from such sources ; for example, direct measurements have been made of the rate of mixing downward from the surface to the thermocline, and also, direct information has been obtained regarding mass motion and lateral mixing. One special feature of benefit in studying weapons tests is the unique initial boundary condition provided by the arrival of fallout activity almost simul- taneously over an area having dimensions very large compared with the depth of water in- volved; downward mixing appears as a rela- tively simple phenomena following this initial condition, and can be studied under almost ideal circumstances. Two expeditions mentioned above have proven that further information concerning lateral mixing and flow can be gained for many months after a weapons' test, and obviously this fact should be exploited fully by marine scientists of all nations. Ancillary benefits might come from more or less fixed monitoring stations; if, for example, following the 1954 test, repeated sampling had been done off Guam it would have furnished data of value for in- terpolating observations made in the two fol- low-up cruises mentioned. Bottom exploration following weapons' tests has not been given deserved attention, and in- sufficient attention has been paid to getting even purely oceanographic information from these sources into the form needed by those people who are charged with making decisions regarding the ominous waste disposal problem. Hazards involved in the deliberate tagging of ocean waters Safety of the research staff is always a con- sideration; at sea because of special circum- stances the handling of extremely large amounts of activity is not too difficult or hazardous. Pro- tection can be secured very cheaply by towing the larger sources of radioactivity aft of the Chapter 12 Tagged Water Masses for Studying the Oceans 123 ship, preferably slightly submerged on a suit- able barge or special vessel. Bringing large quantities of activity to the waterfront prom- ises to be more expensive, but practical experi- ence in this should be valuable for later plan- ning of large-scale disposals. The more controversial question of how much radioactivity can safely be introduced into the sea is not without reasonable solutions; but the recommendations depend upon the cir- cumstances, especially, upon the particular part of the oceans to be studied. At the outset, barren areas of ocean rather than those produc- tive of things leading to human food must be selected since the former can yield equally good information regarding purely physical phenomena. Deliberate tagging of surface waters (^Opera- tion PORK CHOP) Surface waters mix in a turbulent manner due to forces not yet fully understood. Better knowledge of this layer is badly needed justi- fying the consideration of water tracing experi- ments involving introduction of fairly large amounts of activity. Greatest care must be exercised here because these waters are those most close to humans, in several senses. Rate of mixing to the bottom of the mixed layer, and rate and character of lateral motion as functions of the usual parameters of the sea are of most immediate interest, and observa- tions lasting even a few days or few weeks would be of great value at the outset, especially if repeated frequently. A simple surface water experiment now will be proposed in briefest possible outline. Figure 1 presents schematically some of the procedure which might be used and some of the phenomena to be expected. Guided by suitable navigational aids, here represented by deep-anchored buoys No. 1 and No. 2, the ship A proceeds on a straight course while dropping two quantities of radioactive materials (a and a') mixed with enough surface water to leave near the surface a small contaminated patch having nearly neutral buoyance. These are essentially point-source initial conditions in this scale of dimensions; although, they are not as convenient as the plane-source initial conditions BUOY » 2 OPERATION "PORK CHOPS' Figure 1 124 Atomic Radiation and Oceanography and Fisheries provided by fallout, they have some mathemati- cal simplicity. It would appear economical and informative to drop two sources almost simul- taneously, some distance apart — say one to ten kilometers; this would permit large-scale ad- vection also to be studied at little extra ship cost. From the sources s and s' will grow a larger more dilute patch of water finally ceasing to penetrate rapidly downward at depth d. The rate and lateral spread prior to this time as functions of wind velocity are of special in- terest. After further downward penetration is retarded, the areas a and a' move and expand to the larger areas A and A' conserving most of the original radioactive material, and the product of activity and area should be almost constant after correction is made for the known rates of decay of radioactive constituents. Dual ship operations Experience has shown that operations on the scale of this sort can scarcely hope to be suc- cessful unless more than one ship is used ; even with the best facilities one ship may lose con- tact with the invisible patch and waste valuable time locating it. One ship, X, must stay in or near the tagged mass while the other one, Y, may survey the area in detail, inspecting sections across the mass, studying the bottom for ref- erence features, and chasing missing buoys if necessary. Ultimate disposal of hazard in surface waters Reduction of activity to a level below that of the natural activity of sea water is one cri- terion which has been used for planning dis- posals (Glueckoff 1955), and this is fairly reassuring provided the specifically dangerous and the long-lived activities are eliminated, for example, after radiostrontium and radiocesium are removed from raw fission wastes. Present evidence permits the conclusion that in the open ocean, when winds are above the critical white-cap level and under circumstances where mixing ceases at a depth of about 30 to 50 meters, as much as 1,000 curies would mix to a safe dilution in less than 40 days. An ex- ample of the dispersal rate in the open sea will now be given. Brief outcome of an experimental tagging of surface waters in the open sea Surface water made active by introducing fis- sion products concentrated within a few square kilometers was intercepted by a ship 36 days after inoculation and traversed for 10 days. After corrections were made for the drift of the water during the survey, and for radioactive decay, a synoptic picture could be drawn roughly locating the contours of activity. This estimate of radioactive distribution was referred to the time of 40 days after the start of dispersal. The contamination had mixed significantly only to about 30 to 60 meters, although the thermocline lay nearer to 100 meters depth. The following tabular description of this synop- tic sketch can be made. TABLE 1 Approximate Distribution of Radio- activity Found in the Surface Waters of the Open Seas 40 Days After Being Introduced Sud- denly AS A ""Point Source." (A Synoptic Picture Computed from Measurements Made on Several Different Days.) Concentration Areas inside of radio- Areas inside con- the contours activity (as tours of equal as percentages per cent of concentration of the area of the maximum in square the maximum concentration kilometers. contour. measured). 40,000 (km^) 100% 10% 24,000 65 20 14,000 38 30 8,000 22 40 800 2 60 490 1 80 35 0.1 100 At the end of 40 days, the center of gravity of this distribution was about 120 miles from the point of inoculation and the pattern was about four times longer than broad. The wind was 3 and 4 of Beaufort's scale for the first 20 days, but was much calmer for the last 20 days. If the average mixing depths are taken as 50 meters, then, 1,000 curies distributed over 40,000 square kilometers would result in an average concentration of 1.5 X 10-^°/yu,c/ml. This would certainly be safe sea water in most senses; and even in the smaller areas where much less than the average dispersal took place the water should also be safe. In fact, the experiment indicated that it is likely that after 40 days, following the introduction of 1,000 Chapter 12 Tagged Water Masses for Studying the Oceans 125 curies of activity into the surface waters of the by considerations of hazard to humans. Two open sea, only about 0.1 per cent of the total more difficult experiments will now be de- area should retain contamination above the scribed, tolerance concentration permitted for potable water, and even in this small region the residual investigations in the thermocline layer by use artificial activity would amount to less than the ^j radioactivity normal natural activity of sea water. It is evident from Table 2 and Table 3 that The thermocline lying between perhaps 100 shipboard beta measurements would suffice to meters depth on an average, and 800 meters detect the more radioactive spots if there were or more, can be thought of as being a lid which initially 1,000 curies of slowly decaying beta restrains deeper water from reaching the sur- activity; it is apparent, however, that direct face. Experiments in this stable region must measurements by gamma detectors might be take into consideration the fact that any liquid sufficient for several days or even weeks. Sur- introduced here will seek the level of its own face experiments are by far the easiest to con- density and will then spread out in a very thin duct and implement — they are limited largely layer. An experiment in this layer has been TABLE 2 Approximate Sensitivities of Three Detecting and Measuring Techniques Presently Available for Use At Sea Compared With the Activity of Sea Water and With That of Fresh Water. A Common background radiation levels: d/m/1 curies/1 microcuries/ml rad/hr 2 mrad/yr ^ Activity in normal sea water due to potassium: ^ Gamma rays 70 3 X 10"" 3 X 10"* 1 X 10"^ 0.9 Beta rays 660 3.0 X 10"'" 3.0 X 10"^ — — Maximum permissible * concentration of unknown mixed beta activities in drinking water: Beta rays 220 l\ X 10"'° 1 X 10"^ — — Cosmic ray background at sea surface: ^ At equator 61 — — — 33 At 55°N (mag) — — — 37 B Sea water activities at which present measurements are significant. Shipboard water analysis ^ for mixed beta emitters, 60 minutes count after removal of potassium: 50 ± 15 2 X 10"" 2 X 10"* — — Uuderwater gamma detector,'' 1956 scintillation rate-meter of AEC-NYOO: 220 (approx) — — 1.4 X 10"^ 1.2 (0.6 MEV gammas assumed) Underwater gamma detector,^ 1935 geiger instruments of SIO. {counting pulses): (See also table 3 for other cases) Case A: Used in deep water where net background is 15 CPM, assume photons of 0.6 Mev; assume short measurements required, t = 5 sec. 6600 3 X 10"' 3 X 10^ 3.8 X 10^ 30 Case B: Towed on surface, assume constant background 60 CPM, assume photons of 0.6 Mev; assume long measurements permitted, t ^ 5 min. 520 2 X 10"'° 2 X 10"' 0.3 X 10^ 3 1 Assuming normal sea water has 3.8 X 10"* gk/g sea water, that beta activity is 29 d/s/gk and that gamma activity is 3 d/s/gk. 'The rad unit is somewhat larger than the more familiar roentgen unit; 1 rad z= 1.1 roentgen approximately for gamma rays. Values in this column were computed upon the assumption that the activity was uniformly distributed in the water and that the detector was a meter or more from any boundary. 3 Referring to beta ray activity in rad units in roentgen units is a dangerous practice — much further spe- cification depending upon the individual experiment is required. * Handbook 52 of the National Bureau of Standards. The values given refer to the case where the nature of the activity is unknown; certain radioisotopes can be tolerated at much higher levels. 5 See Table 1 in the accompanying paper "Comparisons of Some Natural Radiations Received by Selected Organisms" by T R. Folsom, and John H. Harley for variation of cosmic rays with depth and altitude. s Cosmic rays are counted by most geiger counters at the average rate of approximately one count/min/sq cm of counter area. ^ This information was supplied by J. H. Harley from personal communication with H. D. LeVine of the New York City Operations Office of the Atomic Energy Commission who designed this equipment. s This detector was not intended previously for use at low intensities, but rather for measuring a wide range of intensities of gamma rays. Additional geiger tubes might easily be added to increase the sensitivity by at least five fold. Still more sensitive gamma devices are now used in oil well logging. 126 Atomic Radiation and Oceanography and Fisheries TABLE 3 Comparison of Minimum Detectable Concentrations Using Several Measuring Times AND Assuming Several Backgrounds (a) Minimum detectable anomolous activity if potassium of the sea produced the only background, i.e., B=: 1.2 X 10"^ gammas/sec/ml. Rads/hour Counting time Minimum detectable Net signal , ^ ^ in sees. concentration counts/min Total net Photons Photons t 7/sec/ml = 7/min/l CaVe=30Ca counts 30Cat .6 mev 1.5 mev Ca 3 19 11,000 5.7 17 6.5X10^ 16X10^ 5 11 6,600 3.3 17 3.8 9.5 60 010 600 0.3 18 .3 .8 180 0039 230 .12 22 .13 .33 300 0026 160 .078 23 .09 .22 600 0016 _ 99 .048 30 .06 .14 Very large 0.025/ Vt (b) Minimum concentration detectable if backround were 15 CPM, i.e., an actual background signal ex- perienced in deep water. Cb 3 19 11,000 5.7 17 6.5X10"^ 16X10-" 5 11 6,600 3.3 17 3.8 9.5 60 010 590 .29 17 .33 .84 180 0058 350 .17 32 .20 .50 300 0049 290 .15 45 .17 .42 600 0032 190 .096 58 .11 .28 Very large 0.067/ Vt~ (c) Minimum detectable concentration if total background were 60 CPM, i.e., an actual background signal experienced at the sea surface. Cc 3 205 12,000 6.1 18 7.1 X 10"^ 18 X 10"^ 5 133 8,000 4.0 20 4.6 12 60 0222 1,330 .67 40 1.9 7.5 180 0116 700 .35 63 .4 1.0 300 0087 520 .26 78 .3 .74 600 0059 354 .17 102 .2 .51 Very large 0.13/" Vt~ described in some detail by Revelle, Folsom, Goldberg, and Isaacs (1955), and discussed in several of the accompanying papers. It will be discussed here only in the matter of difficulty of survey. Although mixing is known to be very slow in the thermocline, it is not certain how direct is the path from this fringe biosphere to human food supply, so that the hazard of a long remaining concentration of activity is not easily evaluated. Revelle et al., prefer to sug- gest the experimental use of the conservative amounts of 10 to 100 curies, and they then show that such small sources of radioactivity might be practical none the less. Actual field experience has shown that layers as thin as one or two meters thick are extremely difficult to sample for water analyses even after being located by gamma ray detectors. Folsom (1956) has emphasized that future deep sur- veys with radioactive tags must rely heavily upon discovery of radioactive water by means of gamma detectors, and has urged that special- ized forms of these be brought to perfection. In this particular layer, geometric factors are not adverse for maneuvering a detector into the water mass to be studied ; a probe is dropped rapidly and more or less vertically so as to intersect and pierce a rather broad horizontal lamina, sharply confirming the activity. Some difficulty would be encountered in holding the probe in the thin layer long enough to permit accurate measurements after the activity falls to such a low level that statistical fluctuation becomes the predominant source of error; how- ever, the major difficulty even at these depths is holding the ship in the general area of active pools of small size. Any area of less than a square mile below the surface is a tiny detail in the open sea, and oceanographers never be- fore have realized how hard it is to navigate and maneuver to study areas so small. Multi- ship operation, the use of the best position- Chapter 12 Tagged Water Masses for Studying the Oceans 127 locating gear, and careful crew training and teamwork are necessary for subsurface radio- logical surveys even at these moderate depths. Outline of tagging experiment in the thernio- cline layer Figure 2 illustrates certain features which must be considered in this region. The ship, A, may lower a gamma sonde through an activated pool and detect its presence by the receiving of a signal like tliat shown on the right side of the figure; the hydrographer may obtain a water sample by triggering electrically a water sampler at the moment the detector indicates that the sampler is within the active layer. The data in Table 3 make it clear that rapid response is important during this sort of measurement; a statistically significant signal must be accumu- lated in the short period during which the probe is passing through the active layer. Attention is called to the need for naviga- tional and maneuvering aids here by including schematically the parachute-drogue C. It is difficult to maneuver a weighted detector hori- zontally in order to study the lateral distribution in detail. The use is suggested of towed gamma detectors depressed to the desired level by hydrofoils controllable from the surface, more or less as illustrated schematically at the left of Figure 2. By means of a swivel-clamp, SC, a pennant several meters long containing a row of Geiger tubes or other gamma detectors, might be suspended above the depressor so as to pre- sent a vertical, linear array, thus giving a high probability of intersecting wide lateral distri- butions of activity. This sort of gear should not be too awkward nor fragile for deck handling at sea. Signals might be recorded partially, or entirely inside the depressor, or reported to the ship electronically or sonically. Ship A or a sister ship with similar gear might stay in the pool during the whole experi- ment, however, if the pool were lost after its depth was established, then Ship B would likely be the first to find it again with its towed detector. Difficulties in sounding and exploring very deep ivaters Bottom exploration so far has been confined largely to sonic plotting and sounding by solid cable; very deep wire casts are very time con- suming and difficult; the ship generally is moved laterally by surface currents before the OPERATlOM "poker CHIP" Figure 2 128 Atomic Radiation and Oceanography and Fisheries wire touches bottom. Oceanographers seldom hope to place their sondes and coring tools upon any pre-selected topographic detail of small area. However, it is quite likely that a technique can be perfected for dragging a de- tecting instrument along the bottom in many areas of the oceans' floor, and with a dragged detector a large region might be traversed rap- idly, and tagged water masses near the sea floor might be located and surveyed. A proposal for tagging bottom waters now will be outlined. Difficulties in tagging bottom waters Fortunately, little hazard to human popula- tions would result from putting into the deep bottom waters in certain latitudes almost any amount of activity which might be readily available in the near future, or which would be easy to handle safely ashore and on ordinary surface vessels. After all, these amounts would be only the feeble forerunners of what may have to follow. The problem is that of displaying even a rela- tively large radioactive source economically in face of the immensity of the abyssal reaches. One can think of many things which must not be done; heavy, radioactive liquid cannot be merely poured overboard, for example. Match- ing density at intermediate layers or attempting to insert a strata at a selected depth also would appear experimentally difficult in view of the limited knowledge presently available; an un- equilibrated liquid mass might wander about like a sinking dinnerplate — and soon become lost. In the absence of the restraining forces found in more stable waters, the pouring of streams of dense solution downward from a height above the bottom, or alternately the re- leasing of lighter material upward from the bottom would surely cause mass motion which might not cease until the streams had moved long distances and perhaps had curled into con- figurations quite unsuited as initial boundary conditions for water tracing experiments. Fur- thermore, activity spread initially in more or less vertical lines would make very poor targets for detectors trailing on the end of wires three miles long, and would be wasteful in terms of radioactive material and of expedition time. One might, of course, carefully select a per- fect basin, and might gently introduce into it a dense radioactive solution. This certainly should be considered since only a small amount of activity might suffice for tagging the waters in a small basin and valuable information re- garding motion and dispersion in basins might result, but results would not lead to a realistic picture of the large scale flow over bottom which may have to disperse the wastes dumped in the future. The results of an experiment set up in this way would be inadequate, and, in fact, might be misleading in a dangerous direc- tion. Production and use of horizontal line-sources near the bottom "Operation HARE and HOUND" It is evident that distribution of activity in a horizontal line near the bottom would be most easy to intercept by a detector dragged along the bottom, and it appears also to be something which would be relatively easy to produce, and economical. It should be possible to hold tagged water near the bottom by mixing it with a very dense solution; and there are two ways im- mediately evident for effectively spreading streaks of dense solution for long distances over the bottom terrain. Figure 3 illustrates the two methods proposed for tagging bottom water, and the method pro- posed for locating the tagged masses later. The Ship B' is shown dragging a "Hare" D, across the bottom leaving behind a streak of contami- nated water. Alternately, Ship B is shown just after it has dropped to the sea floor a specialized water blending device which might well be called a "quern" ^, C, which generates for a few minutes or hours, a stream of dense, radio- active solution on the slope of a carefully se- lected large topographical ridge b — d ; this stream flows away very much like one of the submarine currents which are now called "tur- bidity currents" by geologists. Violence of this sort of free current might theoretically be con- trolled through wide limits by adjusting the densities of the solution. The essential features of a water-tagging quern are shown in the upper right of Figure 3. Radioactive material, AS, is combined in predetermined proportions with a heavy salt solution by metering pump, P, and the two are then fed to a fan-type mixer, and are there blended with a large volume of 1 Old English name for a mill for grinding all sorts of things. (RuggoflF, 1949.) Chapter 12 Tagged Water Masses for Studying the Oceans 129 OPERATION "hare AND HOUND" Figure 3 local water. There are several reasons for pre- ferring a design leading to inexpensive construc- tion and single use; the cost of decontamination of apparatus of this type would outweigh any benefit from repeated use. Suggestion is made of the use of a salt such as sodium nitrate which has both high solubility, and an endothermic heat of solution which would serve to overcome the adiabatic heat set free during lowering. It would appear that one or more tons of a nitrate salt, mixed into bottom water by use of a few kilowatt hours of energy, stored in oil-sealed accumulators, could produce a compact body of very heavy water which would rush like a freight train across the terrain dropping a streak of traceable radioactive eddies as it trav- eled. A fixed, water-mixing quern, of the sort described, might produce a tagged water mass behaving in a manner appearing realistic to both the disposal planner and the submarine geologist; however, its use is not likely to lead directly to the extremely simple results needed for the very first experiments. The employment of a dragged hare might be preferable at the outset — and its metering machinery might be somewhat less elaborate than that of the quern just described. One might contemplate using 1,000 or more curies for making streaks several kilometers long so that location would not be difficult with a simple gamma device dragged by a ship. In Figure 3, Ship A is shown dragging such a de- tector which might be called a "hound" for obvious reasons. For very great depths, no elec- trical wire is presently available with the dura- bility equal to that of an ordinary dredging cable. It would, therefore, be wise to first con- sider the use of a compact multichannel chart recorder inside the dragged pressure shell E so as to make permanent records of signals picked up by a set of gamma detectors suspended by an 130 Atomic Radiation and Oceanography and Fisheries oil-filled float F. Numerous accessories might profitably ornament this sort of gear, but the one which might prove most rewarding would be a sound producer capable of reporting the moment of contact with the tagged water mass ; even a crude sonic signal sent from a transducer on the float, F to the ship, A, via the towed hydrophone, H, would suffice. Details of the gamma signals need only be recorded so that they might be inspected later on the recorder chart, however, it would be important for the navigator to recognize instantly when contact was made so that he could maneuver the ship economically. The operations proposed above are not un- like those used successfully by cable ships when retrieving submarine wires. Careful preliminary surveys of the whole area, the selection of iden- tifying landmarks, and the laying of the mark- ing buoys also appear essential for success in work of this type. The final results might have the general char- acter of the hypothetical signals shown graphi- cally at lower right in Figure 3. Change in amplitude and displacement, and skewness of the signal records should lead to estimates of both velocity and rate of mixing. If each survey included ten or more intersectings, and if each contact brought separate gamma signals from several detectors distributed along the hound's vertical "tail," then the data of the sort needed would accumulate quickly. Rough estimate of effectiveness of 1,000 curies for tagging bottom waters It appears possible to distribute radioactivity uniformly along the course of a device dragged over the sea bottom, and it would appear pos- sible also to deposit the material so gently that it would come to rest within a few meters of the precise course. If, for a rough evaluation, we assume that local difl^usion sooner or later produced a uniform distribution within a radius of 10 meters, and that the total activity, M, was 1,000 curies, then the length of the water mass which might be tagged can be stated 0) /= C7rr2 where C is the average concentration of activity within the tagged mass. If now we assume that only 10 seconds can be allotted for traversing 20 meters (that is the ship's speed is about 4 knots), then the equa- tion (9) of Appendix A indicates that a single detector like the 1955 SIO Geiger instrument could detect, in the presence of a realistic deep- water background of 15 cps, a limiting gamma source concentration of 0.061 disintegrations/ sec/ml, or C = 0.06l/3.7 x lO'^o curies/ml, and the length of traverse which could be tagged with 1,000 curies would be, under these as- sumptions. /= 1000 1.65x10-12^(1000)2 - = 1900 Km (2) It would appear feasible to locate and allocate by ordinary navigational means a geographical line in the deep sea floor of less than two kil- ometer's length, so that the hypothetical ex- ample just given suggests that 1,000 curies could equally well be used to produce a very concentrated streak of activity having a length of two or three kilometers which might still be detected with ease after it had difl^used, mixed, or decayed to less than one percent of its initial concentration. Thus it can be concluded that 1,000 curies, or even less activity, put into bot- tom water would be quite adequate for tracing movements on a scale large enough to contrib- ute information useful in disposal planning. SUMMARY AND CONCLUSIONS 1. Consideration has been given some of the problems involved in tagging water masses in the open ocean. 2. The problems are different in the three major strata; the surface layers, the thermocline, and the deep water layer. 3. It appears that under certain circumstances water tagged with even moderate quantities of activity can be followed for at least several weeks; surface waters contaminated by large activities such as result from fallout can cer- tainly be followed for a year or more. 4. Much field experience in radiological ocea- nography has been gained already. A fairly clear direction for development of instruments has been indicated. 5. The need is seen for attention to the perfec- tion of navigational aids, for use of specialized vessels and gear, and for the use of several ves- sels simultaneously in oceanic surveys of this sort. Chapter 12 Tagged Water Masses for Studying the Oceans 131 APPENDIX A In practice, many factors tend to limit the effectiveness of an under sea gamma detector, but the random fluctuation of a feeble radiation may alone prevent its recognition in the pres- ence of a background of similar magnitude. The lowest detectable concentration, limited only by statistical considerations, may be expressed in terms of the strength of the background, the time permitted for measurement, and the meas- uring efficiency of the instrument. Let the sea water be contaminated with a con- centration of radioactivity N curies/ml, and let this activity cause m counts/sec to be indicated by the instrument, and let the average back- ground be b counts/sec. The relative accuracy, n, of a single measurement made during t sec- onds will depend upon signal strength and background strength; if the fluctuations are purely random, the error, 95 per cent of the time will be equal to, or less than. mt 2V O-jlf — (Tb 2yjmt-^ht mt mt and solving for the net signal gives, mt — 2-\-2^\-^nht A.l A.2 Now, the counting efficiency of the instru- ment logically should be derived from the ratio of counts recorded to the photons striking the instrument. This ratio would be impossible to evaluate, but it is approximated when the instru- ment is small, and easily penetrated by. ;;?/ 3.7xlO"Nz// A.3 that is by the ratio of the net counts recorded to the photons emitted in a volume of liquid, v, equal to that displaced by the detector. Solv- ing this equation for concentration, mt N= iJxlO^'^t^et A.4 curies/ml, and substituting here the value for net count, mt, obtained in equation (2) when the background rate is b, and accuracy is, n, the limiting concentration can be expressed, N = 2 + 2\/l + }i-bt b.lxlQ^^n-vet A.5 curies/ml, wherein b expresses the background rate actually indicated when the instrument is surrounded by clean sea water. If no other back- ground exists except that coming from a sur- rounding solution having specific activity B, and if the instrument counts this activity with the same efficiency, e, than the limiting detectable concentration becomes, in curies/ml, N= 2 + 2\/l+Bn-vet ^.1 XlO^'^n-vet A.6 Numerical examples applying to an actual un- dersea instrument The sensitive portion of the 1955 model of the Scripps Institution of Oceanography's Geiger instrument has a volume of about 1,000 ml. The ratio e, applying to hard gamma rays, was measured directly by submerging the in- strument in a tank containing potassium solu- tion of known concentration, and was found to be approximately 0.03. If by "detection" is meant the measurement of the concentration with an error of not more than 50 per cent, then, n=:0.5. Formulas (5) and (6) may now be applied to three characteristic background circum- stances: Case 1: Here no other background is evi- dent except that caused by a solution having specific activity 6=1.2x10'^ gammas/sec/ml such as comes from the natural potassium in normal sea water. From (6), the limiting de- tectable concentration, C,: 2 + 2V 1+0.009^ iJt A.7 gammas/sec/ml, and when t becomes very large this approaches, C^^—^ A.8 Case 2: In deep water cosmic rays may be neglected, and the S. I. O. probe is likely to indicate a total background of about 15 CPM, or b = 0.25 counts/sec, therefore, the concentra- tion just delectable is. 2 + 2Vl-f 0.063/ C2 — . — ■ A.9 gammas/sec/ml, which approaches as t in- creases to a large value, 0.067 Co= — = A.IO Case 3: In shallow water where cosmic rays are unattenuated, the background on the S. I. O. probe amounts to about 60 CPM, or b=1.0 132 Atomic Radiation and Oceanography and Fisheries counts/sec, therefore the minimum detectable concentration becomes. C,= 2 + 2V1 + O.25/ T^t A.U gammas/sec/ml which approaches for very large values of t, C = 0.13 A.12 Tabulations Table 3 compares the effect of increasing the period of measurement with the effect of di- minishing the background. It is evident that a substantial change in background has relatively small practical effect on any measurement made so rapidly that only a very poor sample is taken out of the fluctuating signal; however, when sufficient time can be alloted for good sampling, the background level becomes the limiting fac- tor. It should not be overlooked that in practi- cal field work, instrument imperfections may contribute to the overall error more or less pro- portionally with time of measurement, and that measurement time must be spent economically on almost all oceanographic expeditions. It is apparent therefore that efforts should be made towards increasing the counting rate, ve, while reducing the relative value of the background count by all possible means. Technique for cleanliness and for discrimination of back- ground by electronic means have not yet been fully developed for this purpose. REFERENCES FoLSOM, Theodore R. 1956. Problems pecul- iar to direct radiological measurements at sea. Paper presented at Nat. Acad, of Sci- ence Meeting, 29 Feb.-l Mar. 1956. Wash- ington, D. C. Proceedings (in press) . Glueckoff. 1955. Long term aspects of fis- sion product disposal. United Nations Con- ference on the Peaceful Uses of Atomic Energy, Geneva. Paper No. 398: 11 pp. Miyake, Y., Y. Sugiura, and K. Kameda, 1954. On the distribution of radioactivity in the sea around Bikini Atoll in June 1954. Paper in meteor and geophys., Me- teorol. Research Institute, Tokyo, 5:253- 262. Revelle, R. R., T. R. Folsom, E. D. Gold- berg, and J. D. Isaacs. 1955. Nuclear science and oceanography. United Nations International Conference on the Peaceful Uses of Atomic Energy, Geneva. Paper No. 277:22 pp. RuGGOFF, Milton D. (Editor) Why the sea is salt (an abstract from a translation from the Norse by Sir George Weble) pp 672- 676 in Harvest of World Folk Tales. XViii + 734 pages. Viking Press. U. S. Atomic Energy Commission and Of- fice OF Naval Research. 1956. Opera- tion TROLL. Health and Safety Labora- tory, U.S.A.E.C, New York Operations Office, NYO-4656, Ed. by J. H. Harley: 37 pp. U. S. Department of Commerce. 1953. Maximum permissible amounts of radio- isotopes in the human body, and maximum permissible concentrations in air and water. National Bureau of Standard Handbook 52:445 pp. Chapter 13 LARGE-SCALE BIOLOGICAL EXPERIMENTS USING RADIOACTIVE TRACERS^ MiLNER B. SCHAEFER, hiter-American Tropical Tuna Commhsion, Scripps Institution of Oceanography, La Jolla, California One of the major difficulties in evaluating the probable results of the introduction of radio- active materials into the sea is the lack of ade- quate knowledge respecting the effects of the organisms in the sea on the distribution and transport of such materials. Some information, which has been reviewed in earlier sections of this report, has been obtained on the uptake and excretion of elements by different kinds of marine organisms. This information is, however, not sufficiently extensive. The even more important problems of the quantitative interrelationships and movements of the popu- lations of organisms at the several trophic levels are among the least understood biological phe- nomena of the oceans. These, together with physical factors, will determine the fluxes of the radioactive materials. Measurements of the fluxes of materials through physical-biological systems, or ecosys- tems in the sea are of vast and fundamental importance not only for evaluating the probable distribution of radio-active products introduced into the sea, but also as a basis of evaluating the sea as a source of food and other biological products for the use of mankind. With the approaching full utilization of the land, in- creasing attention is being directed to the sea as a source of such products, but the basic bio- logical knowledge for realistic evaluation of the potential harvest of the sea is quite inadequate. The availability of rather large quantities of radioactive materials, as by-products of the de- velopment and utilization of nuclear energy, makes possible the study, in situ, of the biologi- cal and ecological processes in the sea by the use of tracer techniques. A start has been made, in connection with the introduction of radio- isotopes into the marine and fresh waters by 1 Contribution from the Scripps Institution of Oceanography, New Series, No. 903a. weapons tests and by the disposal of low-level wastes, but the opportunities for obtaining use- ful information by these means have not been fully exploited. Also it should be possible by introducing radioisotopes in a planned, con- trolled, and purposive fashion to obtain even better information than is possible through ob- servation of introductions ancillary to opera- tions having a different primary purpose. Observation in connection with weapons tests Observations in connection with weapons tests have the advantages that (1) very large quantities of radioisotopes are introduced into the sea, sometimes over a rather large area, so that radioactivity is sufficiently high to be de- tected in the sea waters and organisms over a considerable time after the event, and (2) the difficulty of being certain that the organisms have actually remained in the water containing the isotopes is minimized. On the other hand, the determination of exact amounts of isotopes introduced, of their spatial distribution, and of their physical state presents some difficulty. Biological studies, in connection with the various weapons tests in the Western Pacific ocean, have been primarily directed toward de- termining the concentration of gross activity in different organisms, the localization of such activity in different parts of the organism, and the rates of decline of activity with time. There has also been limited determination of the isotopes concerned. The most extensive data are from the lagoons of the atolls at and near the test sites. In the open sea, outside the lagoons, usually only limited collections of or- ganisms have been made, incidental to other operations. Following the test series of 1954, however, two rather extensive surveys were made of the distribution of activity in the sea, and in organ- 133 134 Atomic Radiation and Oceanography and Fisheries isms at different trophic levels, over a large sea area at intervals of approximately 4 months and 13 months after the test. These observations have been directed pri- marily to possible human hazards through con- tamination of edible marine products. Only minor attention has been given to ecological processes, probably because of lack of facilities for the extensive, systematic collecting required. Soon after the underwater test in the Eastern Pacific in the spring of 1955, some collections were made that indicate which organisms in the food chain are the primary concentrators of certain radioisotopes, and that give some indi- cation of the time scale in passage to the next step of the food chain. Unfortunately, it was not possible to follow the passage of isotopes farther through the system. Following a weapons test a series of obser- vations and collections taken in a carefully planned pattern in space and time could pro- vide information on the time scale involved in the passage of material through the system of prey and predators, and on the efficiency of this transfer from one stage to another, two of the little understood basic problems in marine ecol- ogy. Data from experiments with radioactive tracers, together with more limited field data, indicate that the transfer efficiencies are differ- ent for different elements. In those situations, following weapons tests, where there is a fairly extensive body of water containing radioisotopes at some particular level, say at the surface, it should be possible by means of collections at various depths over a period of time to obtain worthwhile information on the vertical migrations of organisms, and also to determine how the feeding and excretion patterns of such organisms transport radioiso- topes from one level to another. These and similar studies would require the assignment of a vessel, with necessary equip- ment and a team of scientists, to the exclusive pursuit of such studies. Since results will de- pend on systematic, serial observations, the ves- sel must be available to take them when and where required, which precludes the commit- ment of the vessel to other activities. Although a sizable cost is involved, it is believed that the results to be obtained are of sufficient value to more than justify it. It should also be pointed out that effective planning of such studies requires considerable knowledge of the types of organisms to be en- countered in the test area, the sizes of their populations, and some knowledge of their mi- gration patterns, as well as data on the currents and other physical parameters to be considered. A pre-survey of the test areas by standard methods of biological investigation is, therefore, an important element in the adequate planning and execution of post-test investigations by means of the radioisotopes produced by the test. Observations in connection ivith waste disposal The disposal of wastes from the fission in- dustry by introduction into the marine en- vironment offers another means of studying the uptake of elements by aquatic organisms, their fluxes in the ecosystem, and their effects on the organisms concerned. Advantages over weapons tests are: (1) the wastes are usually introduced in such a manner that their amount, distribution and physical state can be readily determined, (2) disposal is usually continuous, even though not of constant magnitude, thus permitting systematic study over considerable periods of time. Disposal in the United States has consisted of relatively low-level wastes introduced into fresh waters by the Hanford works on the Columbia River, the Oak Ridge National Lab- oratory, and the Plant on the Savannah River. At the first named locality, field observations, supplemented by laboratory experiments, are being made on the uptake of radioisotopes by organisms, their fluxes through the food chain, and their distribution in the river as the result of the combined effects of physical and bio- logical processes. The phosphorous cycle has been investigated in particular detail. At the Oak Ridge Laboratory, observations were made over a period of years on the uptake of fission products by various organisms, the sites of deposition of radioisotopes in the organisms and the effects on some of their populations. Continuous disposal into marine waters is not practiced at present in this country. Reports by H. Seligman, H. J. Dunster, D. R. R. Fair and A. J. McLean at the 1955 Geneva Con- ference on Peaceful Uses of Atomic Energy describe introduction of low-level wastes into the Irish Sea, and briefly review studies of the uptake of various isotopes by different kinds of organisms. Chapter 13 Large-Scale Biological Experiments with Tracers 135 With the exception of hmited work at Han- ford and Oak Ridge, it appears in all these cases that primary attention has been concentrated on monitoring aspects, that is measurement of the quantity and distribution of radioisotopes to insure against hazards to human or other animal populations. The work of Richard Foster and others on the radiophosphorus cycle in the Columbia River, and the work of Louis A. Krumholz on seasonal variations in quantities of fission products in different groups of organ- isms, indicate however, that locations where wastes are being continuously introduced into aquatic environments offer a good opportunity to study the ecological processes of the aquatic populations through the tracers provided by the introduced isotopes. It may be expected with the development of the fission industry in the next few years, that there will be disposal of some low-level wastes into marine waters, which will provide opportunities to investigate the ecology of estuaries and inshore ocean waters by these means. These introductions also constitute large-scale experiments on both the direct and genetic effects of long-term exposure of marine organ- isms to atomic radiations. It is important that these eflFects be carefully investigated, because it is possible that the larger organisms in the sea, which are subjected to much lower rates of natural radiation than terrestrial forms (due to the shielding effects of water on cosmic rays, as well as to the low gamma-ray activity per unit volume of sea water compared with the rock and soil of the land), may show propor- tionally a greater genetic effect from a given amount of radiation. Planned experiments Much useful information may be obtained by well conceived biological observations in con- nection with weapons tests and routine disposal of industrial atomic wastes. Much more pre- cise information could be obtained, however, by planned experiments introducing measured quantities of known isotopes into the marine environment in a controlled manner. Further- more, it is evident that the fluxes of different elements through the ecosystem vary according to their abundance in the sea and their physio- logical roles in the organisms. Some of the most important elements biologically are not fission products, nor are they present in wastes in appreciable quantity. The outstanding ex- ample is carbon. The energy which supports most of the life in the sea, as on the land, is fixed as chemical energy of complex carbon compounds synthesized by plants. To study the flux of energy through the different trophic levels of the ecosystem it is necessary, therefore, to measure directly or indirectly the flux of carbon. One of the most promising possibili- ties, discussed further below, is the use of radio- carbon in tracer experiments on a scale larger than the present laboratory-type experiments. The need for large scale experiments under natural conditions arises because we require knowledge concerning the quantitative interre- lationships of the various populations of or- ganisms, and it is not possible to reproduce natural marine communities, especially the pe- lagic elements, in the laboratory. It is probably not possible yet to study some aspects of open- sea communities by radioactive tracers, either, but it may be possible to improve on present techniques by larger scale in situ experiments than have been attempted. Large scale experiments, employing either mixed fission products or single isotopes iso- lated from mixed fission products, appear feasi- ble (at least in selected locations in the open sea) to determine what organisms take up which elements and the quantitative aspects of how these elements are passed through the food chain. It may also be feasible to introduce sufficient quantities of radioisotopes in particu- lar situations to make possible a study of the transport of such elements by migrations of organisms. In general, however, in the open sea, it will be necessary to confine attention to those elements which are naturally present in seawater in very small concentrations, so that the organisms may be expected to take up a relatively large fraction of the isotope in ques- tion. In the case of elements such as carbon, only a small fraction of which is taken up by the organisms, experiments in unconfined vol- umes of open sea would appear to require larger quantities of the radioisotope than are feasible on a cost basis, and experiments there- fore will have to be limited, in the near future at least, to small enclosed arms of the sea or artificially bounded volumes of water in the open sea. In order to conduct experiments in the open sea it is necessary to (1) introduce the radioiso- topes into an area sufiiciently large so that it can be located and followed, to insure the or- 136 Atomic Radiation and Oceanography and Fisheries ganisms under study being in it over a known period of time, and (2) have a sufficiently high radioactivity that it may be followed from ship- board. If we use only fission products which organisms concentrate; then, since longer count- ing periods are feasible for samples of the organisms than are feasible for the equipment used to locate and follow the water mass, the radioactivity required to determine the position of the contaminated water mass is expected to be the limiting factor in the experiment. Revelle, Folsom, Goldberg and Isaacs (1955) have indicated that, in the slow-mixing levels of the sea below the thermocline, vertical mix- ing is almost negligible, so it may be expected that while the area in which the isotopes can be detected spreads over a radius of 4.1 km., vertically it will be limited to about 1 meter. In these circumstances, it has been calculated that 10 curies of gamma emitter may be detected until it has spread laterally to a radius of 4 km., or a mean concentration of about 2x10"^ curies per cubic meter. They do not specify the time involved, but it may be presumed to be of the order of one week to one month. For biological experiments, it would be necessary to make observations over a longer period of time, also we cannot commence significant biological ob- servations until the contaminated area is suffi- ciently large to ensure knowledge of which animals are or have been in the active water. For these reasons the time involved should perhaps be increased by a factor of 10. If the diffusion of the contaminated water, both ver- tically and horizontally follows the "random walk" law, the volume containing the activity will increase linearly with time, and, in conse- quence, about 100 curies of gamma activity will be required. Experiments in the upper mixed layer will require much larger quantities of fission prod- ucts. Mixing to the top of the thermocline is very rapid; according to the authors above cited the lower boundary of radioactive water moves down at about 10'^ cm/second. If we select an area, such as that off Central America where there is a fairly shallow sharp thermo- cline at a mean depth of about 20 meters, mix- ing down to the top of the thermocline would be complete in less than ten hours. Thereafter downward mixing should be negligible. Recent experiments suggest that the radius over which the water spreads laterally is increased as about the 0.8 power of time. In Bikini lagoon it has been found that the radius of the radioactive area increased to 4 kilometers in 3 days. If we ran an experiment for 90 days, which is probably the time necessary to follow the flux of radioelements through two or more trophic levels, we would, then, expect the radius to approximate r= 4 (30) -8=: 60 kilometers. The volume would then be (with a 20 meter thermocline) 77X36x10^x20 cubic meters or about 225 X 10^ cubic meters To be still detectible at this dilution, using the above estimate of 2 x 10""^ curies/cubic meter, an initial quantity of some 4x10* curies would be required. The logistics of handling large quantities of fission products will be difficult, but not perhaps impossible. Because of the smaller volume of water to be dealt with, it may be most desirable, at least initially, to conduct such experiments in a small enclosed arm of the sea. Such an environment is diflferent in many respects from the open ocean, but much useful information about fluxes of radioelements through the several trophic levels could be obtained. It would not be diffi- cult to select a small bay, with a narrow, shal- low entrance, which could be cut off temporarily from the sea for this purpose. A body of, say, one square kilometer with an average depth of ten meters might be used, giving a volume of lO'' cubic meters. Since the problem of locating the water mass is eliminated, and fairly large volumes of water can be filtered for organisms, rather small quantities of fission products, which would not be hazardous, could be employed. One curie would be ample, and the contamina- tion of the water itself would be within safe levels for human hazards. It was noted earlier that one of the important fundamental ecological problems is to measure the flux of carbon through different trophic levels. Since the fraction of the carbon taken up by plants is a very small part of the total in the sea water, experiments with radio-carbon in the open sea are not feasible. Experiments using samples in bottles have been conducted in situ in recent years, but these have two de- ficiencies: (1) the surface and other effects of the container modify the environment so that the resulting computations for photosynthesis probably are not those that would have occurred Chapter 13 Large-Scale Biological Experiments with Tracers 137 naturally in the sea and (2) only the uptake of carbon at the phytoplankton level is meas- ured. It seems feasible to improve on the ex- periments in bottles by conducting experiments in small lagoons, or by employing larger partly- enclosed volumes in the open sea. From experience with such experiments in bottles, it can be shown that there is sufficient uptake of carbon by the phytoplankton, if grown in a concentration of 0.3 micro-curie per liter for one day, to measure it if a one liter sample is filtered and the radioactivity of the filtered plants determined in a counter of 20 per cent efficiency. By increasing either the counting time or the volume of water filtered, the initial concentration of C^* can be decreased correspondingly. For an experiment in a lagoon, we might use a body of water of, say, 500 meters long by 200 meters wide with an average depth of 10 meters, giving a volume of 1x10^ cubic meters or 1 x 10^ liters. By filtering 100 liters of water for phytoplankton, C^* at a concen- tration in the water of 3x10"^ curies per liter would suffice, or 3 curies for the experiment. Since there is probably between a 50 per cent and 90 per cent loss at each step up the food chain, correspondingly larger volumes would have to be strained for the higher forms, but this is a simple problem by the use of standard nets, etc. To get improved measurements of the uptake of carbon by phytoplankton in the open sea, and the passage of carbon to the smaller grazing organisms, it is suggested that a moderately large rubber tank open at the surface be em- ployed to isolate a piece of the top of the sea, yet have a sufficiently small surface-to-volume ratio that the processes will more nearly ap- proach normal conditions than is obtained in bottle experiments. We might employ such an apparatus of 20 meters diameter by 10 meters deep, having a volume of tt 10^ cubic meters, or ttXIO^ liters. By filtering 10 liter samples for phytoplankton, with 20 per cent efficient counting equipment, we would need to provide about 3x10"^ curies per liter, or a total of about 1/10 curie of O*. So?77e cost and logistic considerations For the two experiments with C^*, discussed immediately above, the problems of handling the amounts of activity involved present no particular difficulty. Since C^* is a pure beta emitter, the shielding problem for even the experiment requiring 3 curies is a simple matter. The cost of the isotope, however is fairly high; at present about $30,000 per curie. This might be reduced somewhat if the present demand were to increase. The cost, notwithstanding, however, the information to be gained is well worth the outlay. In the case of an experiment using gamma emitters in the slow-mixing layer below the thermocline, where about 100 curies would be required, it is suggested that mixed fission products from wastes from processing of reactor fuel elements be used. A large quantity of such wastes will be available, probably at no charge. If one used HNO3 salted waste product from a natural uranium-plutonium reactor, after 100 days "cooling," the reactor waste will contain about 200 curies/gallon. Approximately half a gallon will be needed, requiring about 10" of lead shielding for transportation and han- dling. A cubical container will require 10.05 cubic feet of lead, weighing 7,175 pounds. This is feasible to handle by freight and on shipboard. For the kilocurie quantities required for an experiment in the upper mixed layer of the sea, the handling problem reaches a different order of magnitude. It becomes quite infeasible to handle waste liquids in the volume required. It may be possible, because of the much higher activity per unit volume to employ slugs of U^^^ from a reactor, which, after 30 per cent burning and 100 days "cooling" have about 2x10^ curies per kilo of fairly long term gamma activity. Even then some 2/10 kilos of "used" U^^^ would be required. The prob- lems of transporting and handling this are somewhat difficult as are methods of dissolving and liberating the material at sea, but probably feasible. Further detailed consideration needs to be given to this problem. It may, of course, be that the use of an explosive reaction — a small nuclear detonation for oceanographic and biological experimental purposes — is the only logistically feasible method. REFERENCES Revelle, R., T. R. Folsom, E. D. Goldberg, and J. D. Isaacs. 1955. Nuclear Science and Oceanography. United Nations Inter- national Conf. on Peaceful Uses of Atomic Energy, Geneva, Paper no. 277:22 pp. iMplisSliiirlSffiiSliillifl^ i.i,jir immimiitaaaaatiiasssae^