Acute toxicity of sodium selenate to two daphnids and three amphipods

This study evaluated the acute toxicity of sodium selenate to two daphnid a nd three gammarid amphipod species. The daphnids, Ceriodaphnia dubia and Da phnia pulex, were evaluated in 48-hour static tests and the amphipods, Gamm arus pseudolimnaeus, Gammarus lacustris, and Hyalella azteca, were evaluate d in 96-hour static and flow-through tests. Tests resulted in mean LC50's o f 1.92, 9.12, 1.82, 3.05, and 1.95 mg/L selenium for C. dubia, D. pulex, G. pseudolimnaeus, G. lacustris, and H. azteca, respectively. The LC50's for the G. pseudolimnaeus tests are more than 30-fold higher than previously re ported LC50's for the same or similar species. The explanation for these di ffering results appears to be partially, but not entirely, explained by dif ferences in ambient pH between the new studies and previous ones. Depending on how the new data are included in U.S. EPA's selenium freshwater quality criterion data set, the selenate acute water quality criterion (i.e., Crit erion Maximum Concentration) increases from 12.8 to as high as 583 mug/L se lenium. (C) 2001 by John Wiley & Sons, Inc.