Enantioselective Fate and Risk Assessment of Chiral Fungicide Metalaxyl in the Water-Sediment-Grass Carp ( <i>Ctenopharyngodon idella</i> ) System

Metalaxyl (MX) is a chiral fungicide widely used in aquaculture. Research indicates that there are significant differences in pharmacological activity and toxicity among the enantiomers of metalaxyl, but data on their enantioselective fate in aquaculture systems are limited. This study investigated the enantioselective behavior of metalaxyl in the water-sediment-grass carp ( Ctenopharyngodon idella ) system through spray administration. Results showed that S -metalaxyl is eliminated more rapidly in the kidney, liver, gills, and muscle of the grass carp, while R -metalaxyl degraded faster in sediment. No interconversion was observed between the enantiomers of metalaxyl in the aquaculture system, and five metabolites were identified, including hydroxylation, demethylation, and didemethylation products. Toxicity predictions suggest that metabolites may be more developmentally toxic and mutagenic than the parent compound, but that the ecological and dietary safety risks of MX are controllable.