DNA damage (comet assay) and 8-oxodGuo (HPLC-EC) in relation to oxidative stress in the freshwater bivalve Unio tumidus.

The relationships between DNA damage and oxidative stress in the digestive gland, gills and haemocytes of the freshwater bivalve Unio tumidus were investigated. Two markers of genotoxicity were measured: DNA breaks by means of the comet assay, and oxidative DNA lesions by means of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) measured using high-performance liquid chromatography (HPLC) coupled to electrochemical detection. Lipid peroxidation was evaluated by measuring malondialdehyde (MDA) tissue levels. Effects were studied after exposure of bivalves for 6 days to benzo[a]pyrene (B[a]P) (50 and 100 microg l(-1)) and ferric iron (20 and 40 mg l(-1)), applied alone or in combination. Lipid peroxidation in the digestive gland and gills resulted from exposure to Fe3+ or B[a]P whatever the concentrations tested. DNA oxidatively formed lesions were induced in the two tissues at a higher level after B[a]P exposure than after Fe3+ treatment. No significant dose-response relationship was found with the two compounds and no synergistic effect was observed between Fe3+ and B[a]P. The gills appeared less sensitive than the digestive gland to DNA lesions expressed as 8-oxodGuo and comet results. Good correlations were noted between 8-oxodGuo and comet. MDA and DNA damage did not correlate as well, although it was stronger in the digestive gland than in the gills. Production of mucus by the gills likely served to prevent lesions by reducing the bioavailability of the chemicals tested, which could explain that dose-effect relationships and synergistic effects were not observed.

Relationship between two oxidative stress biomarkers, malondialdehyde and 8-oxo-7,8-dihydro-2'-deoxyguanosine, in the freshwater bivalve Unio tumidus.

This study addresses the question of the relation between cellular and genomic oxidative damages in freshwater bivalves in realistic conditions of exposure in the field. Membrane and genomic oxidative damages were studied by means of lipid peroxidation and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo), respectively. Malondialdehyde (MDA) was used as an indicator of lipid peroxidation. The biomarkers were measured in the digestive gland and the gills of mussels (Unio tumidus) after 7 and 21 days of exposure in four ponds of the Moselle Basin, during three field studies conducted in 1999 and 2000. Effects measured at three sites (1R, 3C and 4M) were moderate and lipid peroxidation was slightly enhanced in mussels transferred in these ponds. In contrast, an important degradation was observed at site 2V reflected by a sharp increase in MDA and 8-oxodGuo concentrations in 2000. The biomarker responses agreed with the results of physicochemical analyses that indicated a worsening of water quality at the same site. Globally, a relationship was found between MDA increase and 8-oxodGuo formation, in the digestive gland after 7 days of exposure, and later in the gills (21 days). Responses of the digestive glands and gills to the oxidative parameters appeared correlated only after 21 days of exposure. The biomarkers selected confirmed their sensitivity for appraising the water quality of hydrosystems.