Subtoxic cadmium-concentrations reduce copper-toxicity in the earthworm Enchytraeus buchholzi

The toxicity of copper (Cu) and cadmium (Cd) for the earthworm Enchytraeus buchholzi was investigated in an aquatic test system. Cu was much more toxic than Cd. The 2 day-LC50-values amounted to 0.43 mg Cu/l and 9.0 mg Cd/l, respectively. The Cu-toxicity was significantly reduced when the worms were pre-exposed to the subtoxic Cd-concentration of 0.1 mg/l for 2 days. Cd induces a gene encoding a cysteine-rich, non-metallothionein 25 kDa-protein, designated CRP. The CRP-gene is induced at only minimal levels by Cu. However, Cu enhances CRP-gene expression when CRP is once induced by pre-exposure of worms to Cd.