A position paper on selenium in ecotoxicology: a procedure for deriving site-specific water quality criteria

This paper describes a method for deriving site-specific water quality criteria for selenium using a two-step process: (1) gather information on selenium residues and biological effects at the site and in down-gradient systems and (2) examine criteria based on the degree of bioaccumulation, the relationship between measured residues and threshold concentrations for reproductive effects in fish and wildlife, and any observed reproductive impacts. Several outcomes are possible--criteria can be left unmodified, adjusted upward by a fixed amount (50%), or adjusted downward by one of three amounts (25, 50, or 75%). A criterion (existing or proposed) is lowered or raised by an amount that is proportional to the magnitude of bioaccumulation and toxic effects present--i.e., the degree of biological hazard. Criteria can be modified under two circumstances: (1) diagnostic residues and toxic effects must be coupled (present) in order to lower a criterion or (2) diagnostic residues and toxic effects must be coupled (absent) in order to raise a criterion. Coupling residues and effects makes the procedure sensitive to the natural inter- and intraspecific variation in bioaccumulation and toxic responses exhibited by fish and wildlife in aquatic ecosystems. The goal is to establish criteria that keep food-chain bioaccumulation below levels that result in toxicity to fish and wildlife. Precautions are given for those attempting to apply the generic EPA model for implementing national water quality criteria to a site-specific selenium criterion.