Critical Review of Proposed Residue-Based Selenium Toxicity Thresholds for Freshwater Fish

Proposed fish toxicity thresholds for interpreting the biological significance of selenium concentrations measured in environmental media include 2 to 5 µg/L in water, 4 mg/kg dw in fish whole body tissue, 10 mg/kg dw in fish ovaries, and 3 mg/kg dw in fish diets. Use of these thresholds would likely identify fish populations as being at risk at numerous sites across the U.S. However, selenium effects on fish populations in the field have only been conclusively demonstrated at a few locations. Based on our critical review, these threshold values are not consistent with USEPA methodology for deriving criteria, in many cases are not supported by the scientific literature, and, as a result, are generally overly conservative. Based on currently available information, we believe the scientific literature is not supportive of generic sediment or water thresholds, but is supportive of alternative separate whole body thresholds of 9 mg/kg dw for warmwater fish and 6 mg/kg dw for larval coldwater anadromous fish, an ovary threshold of 17 mg/kg dw for warmwater fish, and fish dietary thresholds of 10 and 11 mg/kg dw for warmwater fish and larval coldwater anadromous fish, respectively.