Antioxidant biomarkers in freshwater bivalves, Unio tumidus, in response to different contamination profiles of aquatic sediments

Antioxidant systems were studied in the freshwater bivalve Unio tumidus transplanted from a control site to four different contaminated areas, in order to study the biological response according to the contamination characteristics. Reduced and oxidized glutathione (GSH, GSSG), the activities of antioxidant enzymes such as selenium-dependent and non-selenium-dependent glutathione peroxidases (SeGPx and non-SeGPx), and glutathione reductase (GRd) were measured in the gills and the digestive gland of the mussels after 15 days of exposure at different sites. Lipid peroxidation (LPO) was evaluated by means of malondialdehyde measurements (MDA). The four sites investigated were located in the valleys of Fensch (F), Moselle (M), Lot et Garonne (LG), and Sarthe (S). At each site, the bivalves were placed upstream (Up) from an identified pollution source (a cokery, a laundry, or a foundry) and downstream (Do), close to the effluent outfall (Do(1)) or farther (Do(2)). The goal was to study the antioxidant response in relation to the pollution gradient. Metals and congeners of PAHs, PCBs, and organochlorinated pesticides were analyzed in the river sediments of each station. The exposure of the bivalves at the most highly polluted sites or close to the pollution source led to a sharp depletion in some antioxidant parameters, namely GRd, SeGPx, and GSH. The decrease in enzyme activities could reach 80% for GRd and 70% for SeGPx, while GSH depletion could yield 70%, leading then in an induction of lipid peroxidation, either in the digestive gland or in the gills. The higher the MDA concentrations, the lower the activity of these three antioxidant parameters, suggesting that they could be biomarkers for toxicity. Yet, a depletion in these parameters was sometimes insufficient for cytotoxicity to be induced, since lipid peroxidation failed to appear in some cases where antioxidant depletion was clear, although not so severe. The response of the gills and the digestive gland was not always paralleled, which can be explained by differences in the bioavailability of pollutants. In some cases, a relationship was not found between the antioxidant response and the degree and the type of contamination in sediments, suggesting that the effects could result from nonidentified pollutants or/and be indicators of bioavailability. (C) 2000 Academic Press.