Variation in static acute toxicity test results with Daphnia magna exposed to refinery effluents and reference toxicants

Toxicity tests were conducted with Daphnia magna exposed to refinery effluents and reference toxicants in order to compare inter- and intralaboratory variation in acute toxicity test results, and to evaluate the utility of conducted 24 h screening tests on effluents. Significant differences in dose-response curves and EC50 for animals exposed to reference toxicants occurred within and among laboratories.

The 48-h EC50s and dose response slopes obtained within laboratories for any effluent sample were reproducible; however, variability among laboratories was considerable and dose-response slopes were not comparable. Analysis of screening test data using a fixed criterion, e.g., 80% survival after 24-h, indicated that survival proportions as low as 62.5% and as high as 92.5% were not significantly different from an 80% criterion.