TOXICITY OF ORGANOPHOSPHORUS INSECTICIDES IN THE ZEBRA MUSSEL, DREISSENA-POLYMORPHA P

The 96-h toxicity of four organophosphates (thiometon, disulfoton, mal athion, and demeton-S-methyl, the oxygen analogue of thiometon) in the freshwater bivalve mollusc Dreissena polymorpha was tested using diff erent nominal concentrations ranging between 6 and 50 mg/L. No mortali ties were observed in mussels exposed to malathion and demeton-S-methy l (26 mg/L and 6 mg/L, respectively), and at the lowest concentrations of thiometon and disulfoton (6 and 10 mg/L, respectively). At higher thiometon and disulfoton concentrations, mortalities occurred. At the highest concentrations of 50 mg thiometon/L and 30 mg disulfoton/L, mu ssel mortalities of 88 and 93%, respectively, were determined. Organop hosphate concentrations of up to a factor 10 times higher than in the ambient water were found in exposed mussels, irrespective of whether t hey were alive or dead. The search for organophosphate metabolites via GC/MS analysis of mussel tissue extracts was negative, suggesting lac king or low oxidative activation of the insecticides used. The mollusc is highly resistant to toxic effects of organophosphate insecticides and their biological active oxygen analogues.