Correlations Between Daphnia magna and Fathead Minnow (Pimephales promelas) Chronic Toxicity Values for Several Classes of Test Substances

Chronic toxicity values were developed for Daphnia magna with six surfactants and a detergent builder, each selected on the basis of previously existing chronic fish test data. Predictive correlations were examined for testing end points between 21-d Daphnia chronics and 1-yr fish chronics to provide a short-term alternative chronic test species while developing toxicity data for an intermediate trophic level species. For the detergent materials tested, a strong correlation (r = 0.98) exists between Daphnia and fish no-effect concentrations. A replacement term, NOEC (no observed effect concentration), is suggested to clarify interpretive ambiguities associated with the definition of the MATC (maximum acceptable toxicant concentration) value. Additional chronic toxicity data from the current literature for these two test species and several test substances representing metals, polychlorinated biphenyl isomers, and pesticide formulations were similarly compared. A correlation analysis demonstrated an overall Pearson correlation coefficient of 0.79 for these data. Although significant outliers were evident from this correlation, these differences may be due primarily to differences in modes of toxic action of these test substances. The relatively short life cycle and 21-d duration of the test, small water volumes, ease in handling, high fecundity, and good correlation of 21-d chronic data with chronic fish toxicity data make Daphnia chronic tests an attractive alternative to the conduct of longer term fish tests. Key words: Daphnia, Pimephales promelas, toxicity tests, chronic, mortality, surfactants, metals, pesticides