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Selenium Hazards to Fish, Wildlife, and Invertebrates: A Synoptic Review

SUMMARY Ecological and toxicological aspects of selenium (Se) in the environment are reviewed, including its chemistry, background residues in biological and other materials, and toxic, sublethal, and latent effects (including the effects of Se deficiency). Recommendations are presented, including proposed Se criteria for protection of sensitive species of fish and wildlife. Most authorities agree on five points. First, Se deficiency is not as well documented as Se poisoning, but may be equally significant. Second, Se released as a result of anthropogenic activities (including fossil fuel combustion and metal smelting), as well as that in naturally seleniferous areas, poses the greatest threat of poisoning to fish and wildlife. Third, additional research is required on chemical and biological transformations among valence states, allotropic forms, and isomers of Se. Fourth, Se metabolism and degradation are both significantly modified by interaction with various heavy metals, agricultural chemicals, microorganisms, and numerous physicochemical factors, and until these interactions are resolved it will be difficult to meaningfully interpret Se residues in various tissues. And fifth, documented biological responses to Se deficiency or to selenosis vary widely, even among closely related taxonomic groups. It is generally agreed that Se deficiency may be prevented in fish, small laboratory mammals, and livestock by feeding diets containing 50 to 100 ppb of Se. The concentration range of total inorganic selenite currently recommended for aquatic life protection-35 ppb in freshwater to 54 ppb in marine waters-is below the range of 60 to 600 ppb that is fatal to sensitive aquatic species. In freshwater, it is also below the range of 47 to 53 ppb associated with growth inhibition of freshwater algae, anemia and reduced hatching in trout, and shifts in species composition of freshwater algae communities. Accordingly, current recommendations for Se with respect to aquatic life appear to afford an adequate measure of protection. However, some studies have shown that Se water concentrations of 9 to 12 ppb are associated with inhibited reproduction of certain freshwater teleosts, suggesting that the current Se criterion for protection of freshwater life should be revised downward. Also, high bioconcentration and accumulation of Se from water by numerous species of algae, fish, and invertebrates is well documented at levels of 0.015 to 3.3 ppb, which are substantially below the recommended range of 35 to 54 ppb. The significance of Se residues in aquatic biota is still unclear, and more research appears to be needed on Se pharmacokinetics …