Oxidative stress responses of two different ecophysiological species of earthworms (Eutyphoeus waltoni and Eisenia fetida) exposed to Cd-contaminated soil.

The aim of this study was to assess the biomarkers of oxidative stress [reduced glutathione (GSH), glutathione-S-transferase (GST), superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), glutathione reductase (GR), aldehyde dehydrogenase (ALDH) and lipid peroxidation (LPO)] in earthworms of different ecological categories [epigeic Eisenia fetida (E. fetida) and anecic Eutyphoeus waltoni (E. waltoni)] exposed to cadmium (Cd)-polluted soil (30, 60 and 120 mg kg) for 28 days. Cd accumulation in earthworms increased significantly with increasing exposure dose and duration. However, E. fetida showed a relatively higher level of Cd accumulation until day 21; thereafter, depletion in the Cd level was recorded for the highest exposure dose. In E. waltoni, the detoxification enzymes and GSH level increased significantly with increasing exposure dose and Cd accumulation for 14 days (acute phase). In contrast, in E. fetida, acute exposure to Cd increased detoxification enzymes with decrease in GSH levels. For both species, sub-chronic exposures (28 days) increased lipid peroxidation with decrease in detoxification enzymes. GPx and ALDH responses of Cd-exposed earthworms showed a similar trend. Thus, these enzymes can be used as general biomarkers in these two species. The consistent variations in GST, GPx and ALDH activities suggest that E. waltoni may be used as a bioindicator species; this further signifies the use of endemic earthworms as a bioindicator to assess the risk of soil contamination. The present investigation indicates that Cd accumulation and biomarker responses in earthworms depend on dose and duration of exposure and on the concerned species.