Life Table Evaluation of Chronic Exposure to a Pesticide

Abstract

The copepod Eurytemora affinis and the cladoceran Daphnia pulex were cultured at sublethal concentrations of dieldrin to test the usefulness of the intrinsic rate of population increase, r, as a bioassay statistic. The 48-h LC50 for E. affinis was 23 μg/L, but population growth rate measured by the life table method was only 12% of its control value at 5 μg/L and was zero at 10 μg/L, indicating a substantial sublethal effect. In contrast, D. pulex had a higher EC50 (251 μg/L) and showed little impairment of population growth potential below 220 μg/L. We suggest that the cladoceran was less sensitive than the copepod in both short- and long-term tests because of its simpler life cycle and larger size at hatching. The life table estimate of r appears to be an ecologically realistic measure of sublethal stress and requires an equivalent or shorter time to conduct than conventional long-term tests.Key words: acute toxicity, chronic toxicity, life table, r, toxic substances, Daphnia pulex, Eurytemora affinis, pesticide, dieldrin