Id ■ ^ %
U.S. DEPARTMENT OF THE INTERIOR - BUREAU OF LAND MANAGEMENT
Byron N. Van Zandt
SUft Library Q
p 0.^ xc ^;* 2 5_0047
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
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
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
(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
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
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.
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.
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