Acute and chronic toxicity of sodium selenate toDaphnia magnastraus

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Abstract
The acute and chronic toxicity toDaphnia magnaStraus of selenium introduced as sodium selenate was examined, as was the acute toxicity of selenium introduced as sodium selenite. Acute toxicity was determined by standard, static 48‐h tests. Chronic toxicity was determined by a 32‐d static renewal test. Nominal, initially measured and finally measured total and dissolved selenium concentrations were determined during the chronic test. Analysis of the chronic toxicity data was based on days to first brood, number of young per brood and total number of young produced per adult. These analyses indicate that with one exception, no statistically significant effects (p ≤ 0.05) were observed at < 2.0 mg/L Se, giving rise to a maximum acceptable toxicant concentration (MATC) of 1.73 mg/L Se. Dry‐weight analyses of adults at the termination of the chronic test and for fifth‐brood young indicate an MATC of 1.2 mg/L Se. The 48‐h EC50 for selenate was 5.3 ± 0.6 mg/L Se. The 48‐h EC50 for selenite was 1.1 ± 0.2 mg/L Se. However, a 7‐d EC50 determined during chronic selenate exposure was 1.9 (1.78–2.01) mg/L Se. This lethal threshold concentration is not significantly different from the chronic MATC.

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