Increased cytotoxic and genotoxic tolerance of Eisenia fetida (Oligochaeta) to cadmium after long-term exposure.

Since life-cycle studies showed that the earthworm species Eisenia fetida can develop increased tolerance after long-term exposure to a sub-lethal concentration of Cd in the laboratory, we assessed both the cytotoxicity and genotoxicity of Cd in a long-term Cd-exposed population. We exposed E. fetida specimens from this population, from a laboratory control population and from a field population to various concentrations of CdSO(4) in artificial soil water. Toxic effects were measured using the MTT test and the comet assay. The group that had been exposed to Cd for more than a decade was found to be more tolerant to the deleterious effects of Cd at both cellular and molecular levels than the laboratory control population. The field population, which came from a severely metal polluted environment, displayed high tolerance at molecular level as well. The results provide novel biomarker evidence of increased Cd tolerance in E. fetida, but the mechanisms supporting the apparent tolerance, still need to be clarified.