Biochemical response of earthworm, Eisenia fetida to heavy metals toxicity.

Soil heavy metal pollution is widespread and has severe adverse effects on soil organisms. Earthworms are the major soil organisms which perform several beneficial ecological functions butare vulnerable to damage from heavy metal pollution of soil. The present study was conducted to evaluate the potential toxicity of arsenic (As) and chromium (Cr) on the biochemical response of the earthworm, Eisenia fetida. Following exposure to various sub-lethal concentrations ofAs (34, 68, 102 and 136 mg/kg) and Cr(26, 51, 77 and 102 mg/kg ) for 28 days, the levels of several biochemical markers, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), Glutathione-S-transferase (GST) and malondialdehyde (MDA) content were assessed. The results showed that both heavy metals significantly (p<0.05) impacted the antioxidant enzyme activities and MDA content during the entire exposure period. Compared with the control, SOD, CAT, POD and GST activities increased significantly (p<0.05) by (6.21-23.23, 6.32-18.6, 15.87-34.18 and 0.84-5.45% respectively) at 14th day, but after prolonged exposure, these activities were significantly (p<0.05) decreased (9.58-38.13, 10.09-30.03, 19.05-53.16 and 2.26-9.36% respectively) at 28th day. The contents of MDA showed significant (p<0.05) increase (17.84-45.59%) in all exposure groups for entire exposure period. Therefore, it can be concluded that antioxidants play a direct role in the adaptive response of E. fetida for survival in heavy metal contaminated soil. This adaptive antioxidant response can be used as an important biomarker to assess the toxicity of heavy metals in the soil ecosystems. [ABSTRACT FROM AUTHOR]