The determination of earthworm species sensitivity differences to cadmium genotoxicity using the comet assay

The concept of species sensitivity differences is important in ecotoxicology and environmental risk assessment, but testing usually focuses on lethality of toxicants. The effects on the suborganismal level are mostly ignored; therefore, the present study assessed a biomarker of genotoxicity (the alkaline comet assay) to compare species sensitivities. Five earthworm species (Amynthas diffringens, Aporrectodea caliginosa, Dendrodrilus rubidus, Eisenia fetida and Microchaetus benhami) were exposed for 48 h to sublethal concentrations of cadmium sulphate in reconstituted soil water and DNA integrity was evaluated with the parameter Tail DNA %. Significant amounts of DNA damage were detected in three (A. caliginosa, D. rubidus and E. fetida) species. E. fetida exhibited the highest level of DNA damage, although D. rubidus showed the highest increase (3-fold) in DNA damage from the control. All exposed earthworms accumulated Cd, although body loads did not correspond with DNA damage levels; most of the Cd was probably sequestrated and rendered harmless.