Biochemical biomarkers are widely used for the monitoring environmental quality since they can act as early warning signals, for potential ecosystem degradation caused by contaminants. In order to investigate the acute and chronic effects of a commercial formulation of glyphosate on antioxidant defenses (glutathione peroxidase, GPx; glutathione-S-transferase, GST; and reduced glutathione, GSH) and oxidative damage (malondialdehyde levels, MDA), Eisenia sp was exposed in plastic containers to natural soils contaminated with Glyphosan SL (100 g kg-1 of soil) during 7 and 21 days. Following exposure for 21 days, another group of worms were placed on herbicide-free soils to recovery for 30 days. Treatment with the herbicide significantly affected to all the biochemical markers evaluated. Antioxidant defenses (GSH, GPx and GST) and MDA, in general, increased at both exposure periods. These results showed that Glyphosan SL; the active ingredient (glyphosate) and/or its chemical additives exerts its toxic effects in Eisenia sp by altering cellular antioxidant defenses, inducing a condition of oxidative stress. During the recuperation phase of the earthworms previously exposed for 21 days to the herbicide, GPx decreased to values similar to those of the control group and MDA although decreased, control values were not reached. These results indicate that in 30 days Eisenia sp exhibits a partial recovery of the oxidative stress induced by the herbicide exposure, probably the activation of mechanisms clearance of the Glyphosan SL metabolites justify the high levels of GSH and GST at this stage. In conclusion, herbicide exposure induced changes in the biochemical responses of Eisenia sp highlight the importance of these responses as useful tools in the evaluation of impacts by pesticides in terrestrial organisms.
Key words: Biomarker, Eisenia, glyphosate, antioxidant enzymes, glutathione, lipid peroxidation.