Water-sediment controversy in setting environmental standards for selenium

A substantial amount of laboratory and field research on selenium effects t o biota has been accomplished since the national water quality criterion wa s published for selenium in 1987. Many articles have documented adverse eff ects on biota at concentrations below the current chronic criterion of 5 mu g/L. This commentary will present information to support a national water quality criterion for selenium of 2 mu g/L, based on a wide array of suppor t from federal, state, university, and international sources. Recently, two articles have argued for a sediment-based criterion and presented a model for deriving site-specific criteria. In one example, they calculate a crite rion of 31 mu g/L for a stream with a low sediment selenium toxicity thresh old and low site-specific sediment total organic carbon content, which is s ubstantially higher than the national criterion of 5 mu g/L. Their basic pr emise for proposing a sediment-based method has been critically reviewed an d problems in their approach are discussed.