HP3 Metals in the Environment: Regulatory and Risk Concerns
254 Portland Ballroom
1:20 PM - 5:20 PM, Thursday
() Reevaluation Of Effects Thresholds For Selenium.
Adams, William1, Brix, Kevin2, DeForest, David3, 1 Rio Tinto, Murray, Utah, USA2 EcoTox, Key Biscayne, Florida, UsA3 Parametrix, Inc., Kirkland, Washington, USA
ABSTRACT- Proposed toxicity thresholds for interpreting the biological significance of selenium concentrations measured in environmental media include 2 to 5 ug/L in water, 4 mg/kg dw in fish whole body tissue, 10 mg/kg dw in fish ovaries, 3 mg/kg dw in fish diets and 4 mg/kg dw in sediments. 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 do not appear to be consistently supported by the scientific literature. Considering the above, we re-examined the existing data and established alternative thresholds that we believe are supported by scientific evidence and are environmentally relevant. In summary, the scientific literature is not supportive of a nation-wide single water threshold, but is supportive of a tissue residue approach using whole body thresholds of 7.9 mg/kg dw for warmwater fish, ovary threshold of 17 mg/kg dw for warmwater fish, or fish dietary thresholds of 10-11 mg/kg dw for warmwater and coldwater fish. Some studies indicate larval coldwater anadromous fish may be more sensitive to selenium and may require a lower whole body threshold for protection. Additionally, we have developed a method for determining site-specific water quality standards for substances regulated based on tissue residues and have applied this to selenium. The method is fully reproducible, statistically rigorous and easily implemented.
Key words: water quality criteria, selenium, tissue residue threshold