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 degrees 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 degrees 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 degrees C than at 21 degrees C. Our data support the usefulness of determining ChE activity in adductor muscle to identify the exposure of freshwater mussels to ChE-inhibiting pesticides.