Response of the bivalve Unio tumidus and freshwater communities in artificial streams for hazard assessment of methyl methacrylate

In artificial streams (pilot rivers) supplied with the river water of Gave de Pau (France), we studied the effects of methyl methacrylate (MMA) on the autochthonous bivalve Unio tumidus transferred into the streams and on natural freshwater communities colonizing the channels. Unio tumidus and freshwater communities were exposed to MMA for 15 and 30 d, respectively, at measured concentrations ranging from 0.6 to 122 mg/L. Biomarkers studied in the digestive gland and gills of U. tumidus comprised detoxication systems (namely, antioxidant enzyme activities and glutathione status) and lipid peroxidation as a marker of cytotoxicity. Biocoenotic indicators were used to evaluate effects on benthic invertebrates and diatoms. In bivalves, a decrease in antioxidant levels was found at the lowest concentrations tested (0.6 and 6 mg/L), whereas an increase in lipid peroxidation and mortality was registered at 30 mg/L after 15 d of exposure. Disturbances in freshwater communities occurred after 30 d at MMA concentrations of greater than 30 mg/L. Antioxidant responses in bivalves were recorded at the lowest MMA concentration tested, which was close to the predicted no-effect concentration (0.74 mg/L), and cytotoxicity was registered at a concentration corresponding to the 21-d no-observed-effect concentration for Daphnia magna. On the basis of the criteria studied, antioxidant biomarkers of bivalves appeared to be more sensitive than biocoenotic indicators to MMA.