Genotoxicity of two pharmaceuticals in zebra mussels hemocytes and sperm cells, after ex vivo and in vivo exposure
Résumé
The growing global consumption of drugs by humans in association with a deficiency of water treatment plants to totally eliminate them resulted in the contamination of aquatic environment by pharmaceutical residues. Today, our knowledge on ecotoxicity and biological effects of these organic pollutants on aquatic biota is still scarce. Our survey focused on the evaluation of the genotoxicity of two pharmaceutical compounds: diclofenac and carbamazepine, a non-steroidal anti-inflammatory and an anti-epileptic agent respectively, which are frequently measured in surface and ground-waters at concentrations below 10 µg/L. The measure of the DNA damage by the comet assay (or SCGE assay) was studied in the zebra mussel (Dreissena polymorpha) as biomarker of genotoxicity. This assay was applied on two cell types: hemocytes and sperm cells after short term ex vivo exposures (1-6h) in laboratory experiments to the two tested contaminants and after a long-term in situ exposure (2 and 5 months) of mussels in mesocosms contaminated with diclofenac. Concentrations tested for both experiments (laboratory/mesocosms) were environmentally relevant (from 0.1 to 10 µg/L). Results showed a significant increase of DNA damage in hemocytes (after 6h) and sperm cells (from 1h to 6h) at all concentrations tested after ex vivo exposure to carbamazepine. No genotoxic effect of diclofenac was observed on hemocytes but a low genotoxicity in sperm cells after 1h and 3h exposure, with a return to a baseline level of DNA damage after 6h (no cytotoxic effect was observed in parallel). However, long-term exposure of mussels in mesocosms revealed the genotoxicity of diclofenac for both hemocytes and sperm cells, with a positive relationship in the degree of DNA damage for the two cell types. Our study is the first to reveal in the zebra mussel the interest to evaluate DNA integrity in sperm cells. Sperm cells appeared as a sensitive cell type with a faster response to a genotoxic stress than hemocytes. A possible repair of DNA damage by sperm cells was observed, but seems rapidly limited with the intensity of the genotoxic stress. Our results will be discussed according to the litterature data as well as mechanisms underlying genotoxicity of these pharmaceuticals, which still need to be elucidated.