Stereoselective Bioaccumulation And Toxic Effects Of Neonicotinoid Chiral Pesticide Sulfenalazine In Zebrafish

Sulfoxaflor,a chiral pesticide,is the first fourth generation neonicotinoids insecticide,which is widely used to control rice planthopper.At present,there are few reports on the stereoselective environmental behavior of sulfoxaflor in aquatic ecological environment.In this paper,zebrafish was used as the model organism,and the chiral pesticide sulfoxaflor was used as the research object.The stereoselective bioaccumulation and elimination of sulfoxaflor in zebrafish and its toxicity to zebrafish were studied under semi-static water.The main research contents and conclusions are as follows:1.Four stereoisomers of sulfoxaflor were prepared by chiral separation of rac-sulfoxaflor using Chiralpak IG chiral column combined with high performance liquid chromatography(HPLC),and its absolute configuration were determined.A liquid chromatography-tandem mass spectrometry(LC-MS/MS)method was developed for the determination of four stereoisomers of sulfoxaflor in zebrafish and water.The results showed that the linear relationship was good in the range of 0.003-6 mg/L.The recoveries of sulfoxaflor stereoisomers in zebrafish were 76.86-90.19% with RSDs of 2.53-12.09%.The LOD and LOQ were 0.005-0.008 mg/kg and 0.016-0.024 mg/kg,respectively.The sensitivity,accuracy and precision of the developed method are in line with the experimental requirements.2.96 h acute toxicity test and 15 d exposure bioaccumulation experiment(1,10 mg/L)were carried out to study the stereoselective bioaccumulation and elimination of sulfoxaflor stereoisomers in zebrafish.The results showed that sulfoxaflor posed low acute toxicity to zebrafish(LC50 > 100 mg/L),and had stereoselectivity in the bioaccumulation in zebrafish,with priority accumulation of(+)-2S,3S-sulfoxaflor and(+)-2R,3S-sulfoxaflor.The EFA and EFB values of sulfoxaflor in water were maintained at about 0.5,indicating that sulfoxaflor has no stereoselectivity in water environment.The BCF value for each stereoisomer of sulfoxaflor was less than 10,indicating which is low-enriched in zebrafish.In the elimination phase,the degradation of four sulfoxaflor stereoisomers conformed to first order kinetics with half-lives of 0.94-2.47 d,indicating that the scavenging process of the sulfoxaflor stereoisomers was faster in zebrafish.The order of degradation rate of stereoisomers were(+)-2S,3S-sulfoxaflor >(-)-2R,3R-sulfoxaflor ≈(-)-2S,3R-sulfoxaflor >(+)-2R,3S-sulfoxaflor.The degradation of sulfoxaflor was stereoselective.The degradation rate of(+)-2S,3S-sulfoxaflor and(-)-2S,3R-sulfoxaflor were faster than its antipode.In addition,there were configuration transformations among the stereoisomers of sulfoxaflor in zebrafish.3.By studying the changes of antioxidant enzyme activity and oxidative stress biomarker content in zebrafish,the oxidative stress toxicity of rac-sulfoxaflor and enantiomers to zebrafish were evaluated.Compared with the control group,MDA content in all treatment groups changed significantly,indicating that rac-sulfoxaflor and stereoisomers caused oxidative stress effect in zebrafish.Compared with the control group,the content of MDA in the exposure groups of rac-sulfoxaflor,(-)-2R,3R-sulfoxaflor,(+)-2S,3S-sulfoxaflor and(+)-2R,3S-sulfoxaflor decreased during the whole exposure period.The content of MDA in(-)-2S,3R-sulfoxaflor exposed group was lower than that in the control group on 1 d,but it began to increase on 7 d and was higher than that in the control group.After 15 days of treatment,the MDA content in(-)-2S,3R-sulfoxaflor exposure group was the highest,while the MDA content in other exposure groups was lower than that in the control group,indicating that the oxidative stress injury caused by(-)-2S,3R-sulfoxaflor exposure group was the strongest.SOD activity in zebrafish for all treatment groups was higher than that in control group,and SOD activity was induced and activated.The SOD activity of(-)-2R,3R-sulfoxaflor exposure group was the lowest,and that of(+)-2S,3S-sulfoxaflor treatment group was the highest,indicating that(-)-2R,3R-sulfoxaflor exposure group had the least influence on the SOD activity of zebrafish,and(+)-2S,3S-sulfoxaflor exposure group had the greatest influence on the SOD activity of zebrafish.The activity of GST increased with time.The effects of stereoisomers and rac-sulfoxaflor on the GST activity of zebrafish were significantly different.The GST activity in the rac-sulfoxaflor exposure group was significantly lower than that in the control group and other exposure groups,indicating that the effect of rac-sulfoxaflor exposure group on the GST activity was greater than that in the other exposure groups.In this study,the stereoselective bioaccumulation-clearance and toxicity of sulfoxaflor in zebrafish were studied to provide a theoretical basis for evaluating the potential risks of chiral pesticide sulfoxaflor to aquatic organisms and ecological environment.