PW15 Environmental Toxicology, Environmental Assessment
Exhibit Hall
8:00 AM - Wednesday
(PW247) Aquatic hazard assessment for selenium: limitations of a simplified hazard assessment protocol.
Narloch, B, Stenhouse, P, Wright, W,
ABSTRACT- Selenium is an essential nutrient at low environmental concentrations but has been implicated in several toxic episodes including avian malformations and population declines in Kesterson Reservoir, California; and fish depletions in Belews Lake, North Carolina. A simplified hazard assessment protocol was recently proposed to evaluate hazards of selenium in fish and avians. Evaluation criteria used in this protocol include toxic effect thresholds and ranges of effects-based concentrations. Selenium, represented by the maximum concentration measured in each of five environmental compartments, is compared to these evaluation criteria, and a hazard score is calculated. As with any screening-level risk assessment methodology, this simplified protocol has several limitations including (1) use of maximum concentrations to represent environmental exposures, (2) failure to consider the selenium form, and (3) effect thresholds that may be inappropriate for species inhabiting a watershed. For example, the surface water toxicity threshold for fish and avians is given as 2 ug/L in the simplified protocol; 5 ug/L is assigned a hazard score of high. The reproductive threshold for selenium in dietary items of fish is given as 3 ug/g (dry wt), and 4 ug/g (dry wt) in whole body tissues. Investigations conducted on the Blackfoot River watershed in Southeastern Idaho identified a maximum selenium concentration of 6.8 ug/L in background surface water samples and up to 400 ug/L immediately downstream of seeps from phosphate mining overburden shales. Laboratory investigations on indigenous cutthroat trout failed to identify adverse effects on mortality or reproduction at up to 15 ug/g (dry wt) selenium in the diet and up to 11 ug/g (dry wt) selenium in whole body samples. These observations indicate that the proposed hazard assessment protocol for selenium may be applicable as a screening tool, but should not be used for the determination of safe watershed concentrations of selenium.
Key words: aquatic toxicity, Selenium, hazard assessment