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Full text of "Selenium poisoning"

Form 1220-5 
(July 1970) 



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TECHNICAL NOTE 



Technical 

Note 



Filing Code 
Date Issued 



151 
12-2-70 






U.S. DEPARTMENT OF THE INTERIOR - BUREAU OF LAND MANAGEMENT 



SELENIUM POISONING 

Byron N. Van Zandt 
Socorro District 



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Selenium in the Soil 




Seleniferous soils have been identified in many regions in the western part 
of the United States. 

Soils capable of supporting seleniferous vegetation have been found only in 
arid or semi-arid regions where the mean annual rainfall is less than 20 
inches, and so is insufficient to leach out water-soluble selenium compounds. 
High rainfall probably accounts for the fact that no seleniferous vegetation 
has been reported east of Kansas. 

The occurrence of selenium has been shown to be correlated with certain 
geological formations. The seleniferous formations studied have been found 
to range in age from Pennsylvanian to Recent (Beath, et v al. , 1953). These 
formations and accompanying seleniferous plants have been found throughout 
15 western states. 



During the Cretaceous period there was extensive volcanic activity that left 
volcanic sediments, which are now believed to have contained selenium in the 
molten rock stage. This would account for the presence of selenium in 
weathered Cretaceous soils. Some tertiary formations have selenium because 
they were originally Cretaceous soils. 

Other possibilities of selenium sources are the influences of land plants, 
marine organisms, and selenium- accumulating plants. 

The chemical forms of selenium are not definitely known due to the small 
amounts of selenium in the soil. About fifty percent of the soils tested 
have shown about two ppm. 

Selenium may be present, in part at least, as a primary constituent of the 
igneous rock from which the sediments were derived. In this case the 
selenium is likely to be present as a selenide. Selenium may otherwise 
be present as a selenide in association with iron sulfide. Elemental 




Additional copies of Technical Notes are available from Director, Portland Service Center, Box 3861, Portland Ore. 97208 



GPO 859 -436 




selenium may be present in small amounts since fungi, algae, and bacteria 
are capable of reducing selenites and selenates to the elemental forms. 
Some soils have selenium in the form of insoluble selenides associated 
with sulfides. 

Selenium is sometimes present in water soluble forms that are immediately 
available to the plants. Selenium may also be present in soils in three 
forms that become available to plants only by slow processes of hydrolytic 
action. These are free selenium, selenides, and basic ferric selenites. 

Selenium in the Plants 

The accumulation of selenium by a plant is dependent upon two groups of 
conditions: (1) the selenium-accumulating power of the plant and (2) the 
selenium- supplying power of the soil. Each of these, in turn, depends 
upon a number of other factors. 

I. Selenium-accumulating power of the plant, depending upon: 

A. Species of plant 

B. Phase of growth 

C. Physiological condition of the plant 

II. Selenium-supplying power of the soil, depending upon: 

A. Nature of selenium compounds dissolved in the soil solution. 

B. Concentration of the selenium compounds in the soil solution. 

C. Kinds and concentrations of other substances present in the 
soil solution. 

The ability of a plant to accumulate selenium may be expressed by the ratio 
of the selenium in the plant to the selenium in the soil solution. This 
accumulation ratio is determined chiefly by the physiological nature of 
the particular species of plant (Trelease and Beath, 1949) . 

Absorption by plants of large amounts of selenium brings about various 
symptoms of injury, including stunting of growth, changes in color of the 
foliage, withering and drying of leaves, and premature death of the plant. 

The various chemical forms of selenium supplied have different degrees of 
toxicity, and the toxic effects may be modified by the substances, partic- 
ularly sulfates, accompanying the selenium compound (Shrift, 1958). 

Selenium Indicator Plants 




It was early noted by Wyoming investigators that eight species of native 
plants always contained selenium when collected on soils derived from 
certain geological formations laid down in Cretaceous and Eocene periods 



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(Beath, et. al. , 1934). Field evidence from collections in fifteen of 
the Western States has shown a definite correlation between the occurrence 
of the selenium accumulators and the presence of selenium in the soil„ 

Native seleniferous plants may be conveniently placed in two broad groups, 
primary and secondary (Beath, et. al. , 1953). 

Primary absorbers . This group includes those native plants that are 
believed to require selenium for normal growth. Representative plants 
include all of the species in the genera Stanleya , Xylorrhiza , and Oonopsis. 
Also, certain species of Astragalus are placed in this group. 

Secondary absorbers . This group may be defined as those which are generally 
seleniferous if rooted in selenium-bearing soils, but which are not confined 
in their growth to such soils. Representative plants in this group include 
several Aster species, Machaeranthera ramosa , Sideranthus grindelioides , 
Castilleja sp„ , Gutierrezia sarothrae , Atriplex nuttallii, and A. canescens . 

Converter plants . These plants are seleniferous plants that convert the 
normally unavailable selenium into forms which can be taken up by other 
groups of plants. 

Selenium Poisoning in Animals 

Most of the highly seliniferous plants are rather unpalatable to livestock. 
Odors, tastes, and individual preferences are the main reasons highly toxic 
plants are not readily taken. Forage plants that are moderately toxic, and 
not having offensive odors, are the most dangerous. 

Pathology . In acute poisoning the outstanding pathologic changes were 
necrosis and hemorrhages due to capillary damage. In sub-acute poisoning 
various degrees of repair and early fibrosis were observed in all the organs. 
Chronic selenosis was subdivided into two groups: "blind staggers and 
alkali disease. In blind staggers on a low grade, chronic injury, an acute 
exacerbation was superimposed. The tissues showed chronic degenerative 
changes with acute toxic reaction. In alkali disease, chronic, toxic 
degenerative changes were observed in all organs, and acute irritation was 
absent. (Rosenfeld and Beath, 1946) . 

In all cases there is a sloughing of hoofs and horns. Also, a loss of hair 
is noted. 

Acute poisoning . At the onset, the movement and posture of the animal become 
abnormal. Dark, watery diarrhea usually develops. The temperature is ele- 
vated to 103° or 105° F. The pulse is rapid and weak. Respiration is labored, 
and there may be bloody froth from the air passages. Bloating is accompanied 
by abdominal pain. Urine excretion is greatly increased. 



The pupils are dilated. Before death there is complete prostration and 
apparent unconsciousness. Death is due to respiratory failure. The duration 
of the illness is from a few hours to several days (Trelease and Beath, 1949). 

Chronic poisoning . Blind staggers shows three stages. The first is a 
tendency to wander, frequently in circles. In this stage the body tempera- 
ture and respiration are normal. The animal shows little desire to eat or 
drink. Sometimes evidence of impairment of vision is noticed. 

The second stage is an increased desire to wander. The animal insists upon 
going forward and will not swerve to miss an object. The temperature and 
respiration are still normal. There is an increase in blindness. There is 
no desire to eat or drink. 

The third or last stage prior to death is a paralytic stage. The tongue and 
the mechanism of swallowing become partially or totally paralyzed. The 
animal is nearly blind. Respiration becomes labored and accelerated. There 
is great abdominal pain accompanied with grating of the teeth. The body 
temperature is subnormal. The cornea is distinctly cloudy. The immediate 
cause of death is respiratory failure (Trelease and Beath, 1949). 

Prevention and Control 




The effects of poisoning can be reduced by feeding the animals a ration 
high in protein and vitamin A. Recovery generally takes about 30 days. 
Caution should be taken to feed iodine-free salt in selenium areas. Iodine 
will increase the susceptibility of animals to selenium poisoning. 

The following control measures, if followed, will reduce livestock loss, 
toxicity of crops, and possible danger to public health. 

First, all seleniferous areas should be mapped with indications of degrees 
of toxicity on each area. Ranchers should be able to recognize poisonous 
range plants. Withdrawal of toxic areas to crops and grazing should be 
followed. The symptoms of selenosis should be known and treatments should 
be studied. 

LITERATURE CITED 

Beath, 0. A., J. H. Draize, H. F. Eppson, C. S. Gilbert, and 0. C. McCreary. 
1934. Certain poisonous plants of Wyoming activated by selenium and their 
association with respect to soil types. American Pharmaceutical Assoc. 
Jour. 23:94-97. 

Beath, 0. A. 1937. Seleniferous vegetation in Wyoming. Wyo. Agric. Exper. 
Sta. Bull. No. 221:29-61. 

Beath, 0. A., C. S. Gilbert, H. F. Eppson, and Irene Rosenfeld. 1953. 
Poisonous plants and livestock poisoning. Wyo. Agri. Exper. Sta. Bull. 
No. 324:48-50. 




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Rosenfeld, I., and 0. A. Beath. 1946. Pathology of selenium poisoning. 
Wyo. Agric. Exper. Sta. Bull. No. 275:1-27. 

Trelease, S. F. , and 0. A. Beath. 1949. Selenium. New York. 267 pgs. 

Schmutz, E. M. , B. N. Freeman, and R. E. Reed. 1968. Livestock-Poisoning 
plants of Arizona. The University of Arizona Press. Tucson. 176 pgs. 

Shrift, A. 1958. Biological activities of selenium compounds. Botanical 
Review. 24:550-584. 




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