DIFFERENCES IN ACUTE TOXICITY TEST-RESULTS OF 3 REFERENCE TOXICANTS ON DAPHNIA AT 2 TEMPERATURES

Ten 48-h static acute toxicity tests were conducted with Daphnia magna Straus and Daphnia pulex Leydig with each of the three reference toxicants - sodium dodecyl sulfate (SDS), sodium pentachlorophenate (NaPCP), and cadmium (Cd) (as CdCl2)-at 20 and 26-degrees-C to investigate the effect of temperature on test results at the temperature extremes usually encountered during field studies. The mean 48-h LC50 value for SDS with Daphnia pulex at 26-degrees-C was lower (10.2 mg/L) than at 20-degrees-C (12.6 mg/L), but the difference was not significant (alpha = 0.05). For Daphnia magna the mean LC50 was significantly (alpha = 0.05) lower at 26-degrees-C (10.8 mg/L) than at 20-degrees-C (13.5 mg/L). Sensitivity of either species to NaPCP was not significantly different (alpha = 0.05) at the two temperatures. The data show a fourfold increase in sensitivity to Cd at the higher temperature with Daphnia magna (mean LC50 = 0.038 mg/L at 20-degrees-C and 0.009 mg/L at 26-degrees-C) and a sevenfold increase with Daphnia pulex (mean LC50 = 0.042 mg/L at 20-degrees-C and 0.006 mg/L at 26-degrees-C). These data indicate that toxicity tests conducted at 20 and 26-degrees-C may give significantly different results with Daphnia. Because test precision, control survival, and the likelihood of obtaining valid tests are better at 20-degrees-C, that temperature is recommended for acute toxicity tests with Daphnia.