ASSESSING THE TOXIC THREAT OF SELENIUM TO FISH AND AQUATIC BIRDS

A procedure is given for evaluating the toxic threat of selenium to fi sh and wildlife. Toxic threat is expressed as hazard, and is based on the potential for food-chain bioaccumulation and reproductive impairme nt in fish and aquatic birds, which are the most sensitive biological responses for estimating ecosystem-level impacts of selenium contamina tion. Five degrees of hazard are possible depending on the expected en vironmental concentrations of selenium, exposure of fish and aquatic b irds to toxic concentrations, and resultant potential for reproductive impairment. The degree of hazard is given a numerical score: 5 = high hazard, 4 = moderate hazard, 3 = low hazard, 2 = minimal hazard, and 1 = no identifiable hazard. A separate hazard score is given to each o f five ecosystem components; water, sediments, benthic macroinvertebra tes, fish eggs, and aquatic bird eggs. A final hazard characterization is determined by adding individual scores and comparing the total to the following evaluation criteria: 5 = no hazard, 6-8 = minimal hazard , 9-11 = low hazard, 12-15 = moderate hazard, 16-25 = high hazard. An example is given to illustrate how the procedure is applied to seleniu m data from a typical contaminant monitoring program.