Resistance of Eisenia fetida (Oligochaeta) to cadmium after long-term exposure

The reliance on earthworms as test organisms in risk assessment studies of polluted environments raises the question whether they can evolve resistanc e, e.g., by adaptation to specific toxicants, Protection criteria may be bi ased if sensitivity data from adapted populations are used. Increased resis tance to the heavy metal cadmium has not yet been determined for terrestria l Oligochaeta. Eisenia fetida was exposed to a sublethal concentration of c admium sulfate for more than 10 generations. Clitellate worms from this cul ture were used in experiments to determine the extent of possible tolerance for the heavy metal. Preexposed animals as well as worms with no previous history of exposure to cadmium were exposed to a control substrate without cadmium and also to two substrates with 600 and 1200 mu g g(-1) cadmium. Ch anges in biomass, cocoon production, and hatching success were monitored. T he results obtained indicated that in both substrates in which cadmium was present the preexposed worms performed better than the unexposed worms with respect to growth rate but not reproductively. In the substrate without ca dmium the preexposed worms exhibited signs of poisoning after a few weeks. Preexposed and unexposed worms were also exposed to concentrations of 1500 to 4000 mu g g(-1) cadmium sulfate in an artisol medium for a period of 2 w eeks. The preexposed worms survived higher concentrations of cadmium than t he unexposed group and some specimens from the unexposed group had a gross increase in body fluids. It is concluded that worms with a long-term histor y of exposure to the metal developed resistance to cadmium. (C) 1999 Academ ic Press.