Genotoxicity assessment in Eisenia andrei coelomocytes: A study of the induction of DNA damage and micronuclei in earthworms exposed to B[a]P- and TCDD-spiked soils

Earthworms are useful indicators of soil quality and are widely used as model organisms in terrestrial ecotoxicology. The assessment of genotoxic effects caused by environmental pollutants is of great concern because of their relevance in carcinogenesis. In this work, the earthworm Eisenia andrei was exposed for 10 and 28 days to artificial standard soil contaminated with environmentally relevant concentrations of benzo[a]pyrene (B[a]P) (0.1, 10, 50ppm) and 2,3,7,8-tetrachloro-dibenzo-para-dioxin (TCDD) (1×10 ^-5, 1×10 ^-4, 2×10 ^-3ppm). Micronucleus (MNi) induction was evaluated in earthworm coelomocytes after DNA staining with the fluorescent dye DAPI. In the same cells, the DNA damage was assessed by means of the alkaline comet assay. Induction of MNi in coelomocytes, identified according to standard criteria, was demonstrated. B[a]P exposure for 10 and 28 days induced a significant increase in MNi frequency. In TCDD-treated earthworms, a significant effect on chromosomal damage was observed at all the concentrations used; surprisingly, greater effects were induced in animals exposed to the lowest concentration (1×10 ^-5ppm). The data of the comet assay revealed a significant increase in the level of DNA damage in coelomocytes of earthworms exposed for 10 and 28 days to the different concentrations of B[a]P and TCDD. The results show that the comet and MN assays were able to reveal genotoxic effects in earthworms exposed even to the lowest concentrations of both chemicals tested here. The combined application in E. andrei of the comet assay and the micronucleus test, which reflect different biological mechanisms, may be suggested to identify genotoxic effects induced in these invertebrates by environmental contaminants in terrestrial ecosystems.