Comparison of forest soil microcosm and acute toxicity studies for determining effects of fenitrothion on earthworms

The effects of the organophosphate pesticide fenitrothion on Eisenia fetida Savigny and Dendrobaena octaedra Savigny were studied using the OECD acute toxicity test and microcosms containing forest organic matter. In the acute toxicity study, both species were relatively susceptible to fenitrothion, although D. octaedra (LC50 = 393.9 ml/cm2) was approximately eight times more sensitive than E. fetida (LC50 = 54.1 ml/cm2). E. fetida was unable to utilize oak/maple litter for growth, and attempts to use this species in microcosms were abandoned. In microcosm studies, reproduction of D. octaedra was affected at the expected environmental concentration (EEC), whereas growth and maturation rates did not decrease until 100x the EEC was used. Even at 100x EEC, a significant effect on survival of D. octaedra in microcosms was not demonstrated. The use of microcosm studies to provide insight into possible ecological effects of pesticides is discussed.