ABSTRACT

One of the major concerns in the San Joaquin Valley, California, is the hazardous levels of selenium (Se) in evaporation ponds comprised of agricultural drainage water. Seleniferous salts from drainage waters accumulate in the sediments of these evaporation ponds. Drainage water carries primarily selenate (Se042-) and selenite (S e032-) as oxidized species of Se. Their residence time varies in evapora­ tion ponds, but the fate is most likely controlled by various microbial transforma­ tions including reduction with subsequent precipitation of elemental selenium (Se°) in the sediment and methylation/volatilization resulting in a volatile gaseous Se2-species.