ABSTRACT
This chapter describes the ecological aspects of excess selenium (Se) on rangelands. The chemical forms of Se present in soils and sediments are closely related to the oxidation-reduction potential and pH of the soil. Inorganic Se exists in the selenate or selenite form in aerated, alkaline soils that predominate on western rangelands. J. W. Hamilton and O. A. Beath measured Se uptake by rangeland forbs and grasses from selenite, selenate, and organic Se sources. Generalizations concerning the acute toxicity of Se to animals are exceedingly difficult to make because of the large array of chemical compounds, aqueous solubility, methods of administration, animal species, and variability within species. Urine is the primary route of Se excretion by monogastric animals, regardless of whether the Se is given orally or injected. Volatile Se compounds are naturally released into the atmosphere as a result of biological activity in aquatic and terrestrial ecosystems.
