ABSTRACT
Selenium (Se) is recognized as a micronutrient that is essential to mammals, birds, fish, algae, and many bacteria for growth and survival (Stadtman, 1979; Burau, 1985). In environmental and biological samples, Se can exist in inorganic forms as elemental Se (Se[O]), metal selenides, selenite (Se[IV]), and selenate (Se [VI]), and as volatile or nonvolatile organic species with direct Se-carbon bonds such as methylated compounds, selenoamino acids, and selenoproteins. The forms and concentrations of Se in soil solution are governed by various physical-chemical factors expressed in terms of pH, dissociation constants, solu bility products, and oxidation-reduction potentials (Geering et al., 1968). In addition, recent research has indicated that soil microbial populations can affect the concentration and forms of Se (Maiers et al., 1988; Frankenberger and Karlson, 1989). Because of its toxicological effects on waterfowl, Se has become one of the major contaminant problems in irrigation drainage waters in the western portion of the United States. An overview of the Se problem in California evapora tion ponds including the Kesterson Reservoir (evaporation ponds) has been pre sented by Ohlendorf and Santolo (1994).
