Biochemical responses of the earthworm Eisenia fetida andrei exposed to contaminated artificial soil: effects of lead acetate

Our aim was to investigate the effects of lead at different concentrations and exposure times, on the biochemical responses of the earthworm Eisenia fetida andrei (E. fetida andrei) to: (1) elucidate the effect of the exposure method on the mechanism of action of Pb; (2) explore the potential for using these responses as biomarkers for monitoring soils contaminated by metals or for use in sublethal assays to test chemicals in the laboratory. Thus, worms were exposed to increasing concentrations of lead acetate (AcPb) and for different periods of time using the standard soil test method. The following biochemical values were measured: methoxyresorufin-O-deethylase (MROD), NADH (NADH Red) and NADPH (NADPH Red) cytochrome reductases, glutathione-S-transferase (GST), catalase (CAT), glutathione reductase (GR) and acetylcholinesterase (AChE) activities, lipid peroxides (LP) and peroxidizable lipids (LPI), total glutathione (total GSH) concentration and percentage of oxidized glutathione (%GSSG). The results showed that Pb exerts its toxic effects in E. fetida andrei by inducing the formation of reactive oxygen species (ROS) and inhibiting specific enzymes. The bioavailability of Pb to the earthworm is dependent upon the method of exposure used. Nearly all the biochemical responses were dependent on the dose of metal or the duration of exposure. Significant changes were detected upon exposure to only 30 mg Pb kg−1 artificial soil. This demonstrated the sensitivity of these responses in E. fetida andrei. The effect of the different doses of Pb was most apparent when all the responses were analysed together. This suggests that the suite of biochemical responses of E. fetida andrei could be used as sublethal assay for chemical testing in the laboratory or for soil contamination surveys.