Developing Site-Specific Water Quality Criteria

Abstract

The United States Environmental Protection Agency (USEPA) conducted a comprehensive review of information on selenium ecotoxicology and issued revised national freshwater criteria for selenium in 1987 (EPA 1987). Since that time, two divergent lines of evidence and thought have emerged regarding whether the criterion for chronic exposure (5 µg Se/L) is adequate to protect aquatic life. One line Supports the Position that the criterion is too high and should be lowered. For example, Winter Stress Syndrome in fish-a disruption of the normal annual cycle of metabolic and physiological changes in cold weather-can substantially increase fish sensitivity to selenium and cause concentrations approaching the criterion value to become toxic (Lemly 1993a, 1996). Moreover, in the western United States, agricultural irrigation has caused selenium to bioaccumulate to toxic levels in food chains and to poison fish and aquatic birds when waterborne concentrations were wellbelow 5 µg Se/L (eg, Skorupa and Ohlendorf 1991 Stephens et al. 1992 Hallock and Hallock 1993 Lemly 1995 Hamilton et al. 1996). The other line of evidence Supports the position that the criterion is too low and should be raised. For example, faunal surveys in Colorado streams showed abundant fish populations where waterborne selenium consistently exceeded the criterion. These observations have led some to conclude that the national criterion is overly conservative, and that the tolerated level should be raised to as much as 31 µg Se/L in some locations (eg, Guglielmone 1995 Canton and Van Derveer 1997 Van Derveer and Canton 1997).