Acute aquatic toxicity of metofluthrin metabolites in the environment

Acute aquatic toxicity of eight major metabolites of the pyrethroid insecticide metofluthrin, potentially formed via oxidation and ester cleavage in the environment, was examined using three representative species, fathead minnow (Pimephales promelas), Daphnia magna and green alga (Pseudokirchneriella subcapitata). All metabolites showed a wide range of toxicity but were more than a hundredfold and tenfold less toxic than metofluthrin to pyrethroid-sensitive (fish and daphnid) and -insensitive (algal) taxa, respectively; 0.44 to >120 mg/L (fish 96-hr LC50), 6.3 to >120 mg/L(daphnid 48-hr EC50), and 2.6 to >110 mg/L (algal 96-hr E gamma C50). The structural modification via ester cleavage and/or oxidation was found to significantly control the acute aquatic toxicity of the metabolites. The decreased lipophilicity in the metabolites generally resulted in much less acute toxicity, the extent of which was dependent on an introduced functional group such as formyl as a toxicophore and carboxyl causing a higher acidity. Pesticide Science Society of Japan