Enantioselective bioaccumulation and toxicity of rac-sulfoxaflor in zebrafish (Danio rerio)

Sulfoxaflor isa fourth-generation neonicotinoid insecticide mainly used to control sap-feeding pests. In this study, four stereoisomers of sulfoxaflor were separated using HPLC, and the absolute configurations of three stereoisomers were identified via single-crystal X-ray diffraction. First, the stability and isomerization of the four enantiomers and rac- sulfoxaflor in water and seven organic solvents were investigated. All enantiomers were extremely unstable in water with isomerization rates above 20%. The racemate did not isomerize in any of the solutions and was stable in water (degradation rate less than 7%). Therefore, we studied the acute toxicity, enantioselective behavior, and enzymatic activities of rac-sulfoxaflor in zebrafish. The bioaccumulation experiment demonstrated that the bioconcentration of sulfoxaflor in zebrafish was enantioselective, and the four enantiomers accumulated in zebrafish in the order (+)-2S,3S-sulfoxaflor (-)-2R,3R-sulfoxaflor > (+)-2R,3S-sulfoxaflor > (-)-2S,3R-sulfoxaflor. The effect of rac- sulfoxaflor on the enzymatic activities of zebrafish showed that superoxide dismutase and glutathione-S-transferase activities and malondialdehyde content were significantly enhanced as compared to those in control, whereas acetylcholinesterase was significantly reduced in the sulfoxaflor exposure treatment (p < 0.05), indicating that sulfoxaflor caused oxidative lesions and induced enzymatic activity in zebrafish. This study provides important information on the enantioselective behavior and toxic effects of sulfoxaflor, which can help assess the potential ecological risk of chiral pesticides to aquatic organisms.

Automated summary

This study investigated the stability and isomerization of sulfoxaflor stereoisomers and its racemate, as well as their toxic effects on zebrafish. The results showed that all enantiomers were extremely unstable in water, while the racemate was stable. Zebrafish exhibited enantioselective bioaccumulation of sulfoxaflor, and the presence of sulfoxaflor caused oxidative lesions and altered enzymatic activities in the fish. These findings provide important information for assessing the ecological risk of chiral pesticides to aquatic organisms.