Stereoselective Impacts of Flusulfinam on Daphnia magna: Stability, Behavior, Oxidative Stress, and Metabolomics Insights

Flusulfinam, a novel chiral herbicide, has attracted considerable attention because of its high efficacy against common paddy weeds and its favorable crop safety profile. However, information regarding its enantioselective toxicity toward aquatic organisms remains scarce. In this study, single-crystal X-ray diffraction was employed to determine the absolute configurations of flusulfinam enantiomers. The results indicated that the enantiomers can stably persist in the aquatic environment of Daphnia magna , with no detectable configurational transformation or degradation. Both racemic flusulfinam and its individual enantiomers exhibited low toxicity to D. magna . At sublethal concentrations (0.95 and 9.5 mg/L), R-flusulfinam and S-flusulfinam induced short-term inhibition (24 h) followed by long-term stimulation (48–72 h) of swimming distance and speed in D. magna . Oxidative stress assessments showed increased activities of superoxide dismutase (SOD) and catalase (CAT), with R-flusulfinam producing more pronounced effects than S-flusulfinam. Metabolomic analyzes further revealed that both enantiomers interfered with nucleotide and purine metabolism in D. magna , while R-flusulfinam caused more severe metabolic disturbances. Overall, these findings demonstrate that R-flusulfinam exhibits greater toxicity to D. magna than S-flusulfinam, providing important insights for the environmental risk assessment of flusulfinam.