Effects of two cholinesterase-inhibiting pesticides on freshwater mussels

The freshwater mussel Elliptio complanata and the Asiatic clam Corbicula fluminea were exposed for 96 h at 21°C to aldicarb, a carbamate pesticide, and acephate, an organophosphate pesticide. Test pesticide concentrations ranged from 0 to 320 mg/L. We found no mortality under these conditions. Relative to controls, cholinesterase (ChE) activity in adductor muscle from E. complanata was significantly depressed at concentrations as low as 0.1 mg aldicarb/L and 1.3 mg acephate/L. Higher pesticide concentrations were required to inhibit ChE activity in whole bodies of C. fluminea than in adductor muscle of E. complanata. Raising the experimental temperatures from 21 to 30°C increased pesticide-induced mortality, with mussels dying at aldicarb or acephate concentrations of only 5 mg/L. Cholinesterase activities of adductor muscle depressed 94 to 96% relative to controls began to recover within 2 and 12 d, but they were not fully recovered for 12+ and 24+ d following aldicarb and acephate exposures. Both aldicarb and acephate at 5 mg/L reduced shell closure responsiveness of mussels, with more pronounced effects observed at 27°C than at 21°C. Our data support the usefulness of determining ChE activity in adductor muscle to identify the exposure of freshwater mussels to ChE-inhibiting pesticides.