Accumulation of selenium in benthic bivalves and fine-grained sediments of San Francisco Bay, the Sacramento-San Joaquin Delta, and selected tributaries, 1984-1986

Fine-grained, oxidized, surface sediments and two benthic bivalves (Corbicula sp., a suspension-feeding freshwater clam, and Macoma balthica, a deposit-feeding brackish water clam) were used to examine spatial distributions of selenium within San Francisco Bay and the Sacramento/San Joaquin River Delta and to compare riverine with local inputs of biologically available selenium to this large, complex, urbanized estuary. Selenium concentrations in Corbicula were elevated in the western Delta and northern reach of San Francisco Bay compared to concentrations in Corbicula from river systems not enriched in selenium. Biologically available selenium did not appear to enter the southern Delta or northern reach of the Bay from the San Joaquin River, a possible source, in levels that could measurably influence bioaccumulation by Corbicula. Selenium concentrations in Macoma balthica also were elevated in southern South San Francisco Bay and near the western edge of Suisun Bay.