Enchytraeus bigeminus (Enchytraeidae, Oligochaeta) as a new candidate for ecotoxicological laboratory tests

Abstract

In enchytraeid reproduction tests lambda-cyhalothrin and pyrimethanil were examined under three different soil moisture levels (30, 50 and 70 % of the soil water holding capacity). The tests were performed with Enchytraeus bigeminus Nielsen & Christensen, 1963, a species that differs from other enchytraeid test species by its asexual mode of reproduction (fragmentation). The effect of chemical stressors depended on the soil moisture content. A higher toxicity was observed in soil with lower moisture levels. For lambda-cyhalothrin, the 21-day EC₅₀ values for reproduction at the three levels of soil moisture were calculated to be 1.33, 3.79 and 4.75 mg active substance/kg dry weight soil, respectively. For pyrimethanil the values were 435, 499 and 829 mg active substance/kg dry weight soil. Apart from the evaluation of the combined effects of chemical stress and soil moisture, the appropriateness of the fragmenting test species Enchytraeus bigeminus was assessed. E. bigeminus tolerated temperature and pH variations, allowed obtaining reliable concentration-response relationships and was easy to handle and to culture in the laboratory. Hence this fragmenting species is considered to be suitable as an additional test species in ecotoxicological standard tests.