FRESH-WATER MUSSEL DIE-OFF ATTRIBUTED TO ANTICHOLINESTERASE POISONING

In 1990, we investigated a die-off of freshwater mussels in north-cent ral North Carolina. An estimated 1,000 mussels of several species were found dead or moribund, including about 111 Tar spinymussels (Ellipti o steinstansana), a federally listed endangered species, The die-off o ccurred during a period of low flow and high water temperature in a st ream reach dominated by forestry and agriculture. Pathological examina tions did not show any abnormalities and indicated that the die-off wa s an acute event. Chemical analyses of mussels, sediments, and water r evealed no organophosphorus or carbamate pesticides. Cholinesterase ac tivity in adductor muscle from Eastern elliptios (Elliptio complanata) collected at the kill site and downstream was depressed 73 and 65%, r espectively, compared with upstream reference samples. The depression is consistent with a diagnosis of anticholinesterase poisoning. This i s the first documented case in which cholinesterase-inhibiting compoun ds have been implicated in a die-off of freshwater mussels.