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2 Selenium in seleniferous <br />Environments <br />H. F. Mayland <br />USDA-Agricultural Research Service <br />Kimberly, Idaho <br />L. F. James and K. E. Panter <br />USDA-Agricultural Research Service <br />Logan, Utah <br />J. L. Sonderegger <br />Montana Bureau of Mines and Geology <br />Butte, Montana <br />ABSTRACT <br />Selenium is biologically important because (i) it is essential in animal and possi- <br />bly plant metabolism, (ii) in many areas diets do not contain sufficient Se to meet <br />animals' needs, and (iii) in other areas it is toxic to animals when it occurrs in high <br />concentrations in soil, water, plants, fly ash, or in aerosols. Animals require 0.05 <br />to 0.1 mg Se/kg in their diets to prevent Se deficiency but suffer Se toxicosis when <br />dietary levels exceed 5 to 15 mg Se/kg. The earth's crustal materials generally con- <br />tain <0.1 mg Se/kg. Higher concentrations are found in Cretaceous shales. The Se- <br />accumulator plants growing on the seleniferous soils may contain hundreds or even <br />thousands of mg Se/kg. However, the nonaccumulator grasses and fortis seldom ac- <br />cumulate > 50 mg Se/kg and more often contain < 5 mg Se/kg. Soils and plants may <br />discharge volatile forms of Se into the atmosphere. However, plants may also ab- <br />sorbmeasurable amounts of gaseous Se from the atmosphere. Anthropogenic activi- <br />tiesimpact the amount of Se entering our nation's lakes, rivers, and the atmosphere. <br />Combustion of coal and incineration of municipal waste exhaust Se into the environ- <br />ment. In addition, crop-fallow and irrigation practices that allow leaching waters to <br />pass through seleniferous strata prior to intersecting with surface flow, augment the <br />Se levels encountered by plant and animal life. <br />In 1857, U.S. Army Surgeon T.W. Madison described toxicity symptoms <br />in horses (Equus caballus) grazing near Fort Randall, SD (Rosenfeld & Beath, <br />1964). Since then, ranchers in that area have continued to experience livestock <br />losses. They associated the toxicosis with the saline seeps and outcrops, com- <br />Copyright ©1989 Soil Science Society of America and American Society of Agronomy, 677 <br />S. Segoe Rd., Madison, WI 53711, USA. Selenium in Agriculture and the Environment, SSSA <br />Special Publication no. 23. <br />15 <br />