Comparative effects of Cd and Pb on biochemical response and DNA damage in the earthworm Eisenia fetida (Annelida, Oligochaeta).

There are rising concerns about the hazardous effects of cadmium (Cd) and lead (Pb) on the environment in China. Biochemical and comet assays were conducted on the earthworm Eisenia fetida, a suitable bio-indicator organism for evaluating soil pollution after exposure to two heavy metals, Cd and Pb. Protein content increased at low Cd concentrations (p<0.05) and decreased at the highest concentration of 10 mg kg(-1), compared to control (p<0.05). Pb showed an inhibitory effect on protein content at low concentrations but demonstrated no significant effect at higher concentrations. There were no significant differences between control and treated groups at the doses of 1 and 10 mg kg(-1) Cd while at a dose of 0.1 mg kg(-1) Cd the cellulase activity was significantly increased compared to control. Cellulase activities of Pb-treated E. fetida increased in a dose dependent fashion. Results of the comet assay indicated toxicant induced DNA damage. Cd exposure caused significant differences between control and treatment groups (ANOVA, p< 0.05, p< 0.01) and a positive dose-response profile. As for Pb treatment, there were no significant differences between the groups treated with 50 and 500 mg kg(-1) of Pb and the control. Results showed that DNA damage from Cd was more serious than that from Pb. And this indicated that the earthworm was more sensitive to the effects of Cd.