Effect of sulfate concentration on acute toxicity of selenite and selenate to invertebrates and fish. Final report

The effect of sulfate concentration on the acute toxicity of selenite (Se IV) and selenate (Se VI) to freshwater organisms was evaluated using toxicity test data generated from this study and toxicity data obtained from the open literature. The acute toxicity of Se IV and Se VI to fathead minnows and two amphipod species, Gammarus pseudolimnaeus and Hyalella azteca, were determined in four different sulfate concentrations. The newly generated toxicity data combined with the data obtained from the literature were evaluated using analysis of covariance to determine if there was a significant relationship between acute toxicity and sulfate concentration. The analysis of the Se IV data indicated that there was not a significant relationship between the acute toxicity of Se IV and sulfate concentration. A significant relationship was found between the acute toxicity of Se VI to freshwater organisms and sulfate concentration. Statistically significant slopes describing the relationship between Se VI toxicity and sulfate concentration were determined for individual species and for the combined data. A sulfate-based equation was constructed using the pooled slope to modify the criterion maximum concentration (CMC) for selenate: CMC = e{sup [0.4259(ln[sulfate]) + 4.6305]}.