8153

• UCREFRP Catalog Number: 8153
• Author: Jacobs, e. L. W.
• Title: Editor
• USFW Year: Series
• USFW - Doc Type: 1989
• Copyright Material: YES

44 MAYLAND ET AL.
quirements in many areas, and (iii) its toxicity to animals and plants in other
areas where it occurs in high concentrations in soil, water, plants, or in
aerosols. Animals require 0.05 to 0.1 mg Se/kg in their diets to prevent Se
deficiency, but suffer Se toxicosis when dietary levels exceed 5 to 15 mg Se/kg.
If plants require Se, the critical level is <0.08 mg/kg.
Selenium occurs in several valency states controlled by the pH and Eh
of the soil. The Seb+, and to a lesser extent Se4+, salts are water soluble
and are the predominant forms absorbed by plants. Animals easily absorb
selenate and to a lesser extent selenite sources, but seem to best utilize the
amino and proteinaceous forms found in plants.
The earth's crustal materials generally contain <0.1 mg Se/kg. Higher
concentrations are found in Cretaceous shales. The Se-accumulator plants
growing on seleniferous soils may contain hundreds or even thousands of
mg Se/kg. However, the nonaccumulator grasses and fortis seldom accumu-
late >50 mg Se/kg and more often contain <5 mg Se/kg.
Anthropogenic activities impact the amount of Se entering our nation's
lakes, rivers, and the atmosphere. Combustion of coal and incineration of
municipal waste exhaust Se into the environment. In addition, crop-fallow
and irrigation practices that allow leaching waters to pass through selenifer-
ous strata, prior to intersecting with surface flow, augment the Se levels en-
countered by various segments of plant and animal life.
An improved understanding of Se in the agroecosystem will allow us
to constructively manage this element in areas where it is now deficient for
animal nutrition and other areas where it exists at levels leading to toxicosis
in animals and plants.
ACKNOWLEDGMENTS
The authors thank Drs. W.H. Allaway, E.E. Cary, A.C. Chang, O.E.
Olson, M. Coburn Williams, and the anonymous reviewers for their helpful
comments. The senior author especially thanks Dr. I.S. Palmer for allowing
access to his extensive file of Se literature.
REFERENCES
Abuereish, G.M., and J.N. Lahham. 1987. Selenium in soils and plants of the Jordan Valley.
J. Arid Environ, 12:1-7.
Abu-Erreish, G.M., E.I. Whitehead, and O.E. Olson. 1968. Evolution of volatile selenium from
soils. Soil Sci. 106:415-420.
Adriano, D.C. 1986. Trace elements in the terrestrial environment. Springer-Verlag, New York.
Allaway, W.H. 1968. Agronomic controls over the environmental cycling of trace elements.
Adv. Agron. 20:235-274.
Allaway, W.H., E.E. Cary, and C.F. Ehlig. 1967. The cycling of low levels of selenium in soils,
plants and animals. p. 273-296. In O.H. Muth (ed.) Symposium: Selenium in biomedi-
cine. AVI Publishing Co., Westport, CT.
Anderson, J.W., and A.R. Scarf. 1983. Selenium and plant metabolism. p. 241-275. In D.A.
Robb and W .S. Pierpoint (ed.) Metals and micronutrients: Uptake and utilization by plants.
Academic Press, New York.