| Succinate dehydrogenase inhibitor（SDHI）fungicides have become the fastest growing fungicides in the market over the past decade due to their novel mechanism of action,strong efficacy and long-lasting effect.Previous studies have shown that SDHIs fungicides were not readily degradable in the environment and that were highly toxic to aquatic organisms.Previous studies by our group showed that there were significant enantioselectivity differences in the degradation of SDHI chiral pesticide penthiopyrad in soil and the toxicity to human Hep G2 cells.However,the information on the toxic effects of SDHIs chiral pesticides on non-target organisms was concentrated at the racemate level,and there are few systematic studies at the enantiomeric level.Therefore,as a widely used chiral pesticide in the SDHIs fungicide,penthiopyrad was selected for this study to prepare optically pure chiral pesticide monomers by chiral chromatographic separation and to conduct exposure tests on zebrafish at different life stages to clarify the enantioselective toxic effects of penthiopyrad on zebrafish and its mechanism of action.The implementation of this study is of great significance for a comprehensive evaluation of the environmental behavior of the SDHI chiral pesticide penthiopyrad and its ecotoxicological assessment.The main experimental contents and main research results obtained in this paper are as follows:（1）The half-lethal concentrations of penthiopyrad racemate and its enantiomer exposed to zebrafish embryos at 96 h were 2.784（Rac-penthiopyrad）,3.528（R-（-）-penthiopyrad）and 1.882 mg/L（S-（+）-penthiopyrad）,respectively.Penthiopyrad exposure induced abnormal voluntary movements,slowed heart rate and delayed hatching in zebrafish embryos,and caused developmental toxic effects such as pericardial edema and yolk sac edema in zebrafish embryos.In addition,penthiopyrad and its enantiomer exposure induced differential expression of mitochondrial respiratory chain complex II（succinate dehydrogenase）,cardiac development and lipid metabolism-related genes in the early life stages of zebrafish.S-（+）-penthiopyrad induced a higher embryotoxic effect in zebrafish.We infer that the mechanism of the toxic effect of penthiopyrad on zebrafish embryos was through the inhibition of succinate dehydrogenase in zebrafish embryos,which inhibits mitochondrial function and induces disruption of lipid metabolism leading to abnormal development.（2）Under two exposure concentrations（0.03 mg/L and 0.3 mg/L）,a 35-day exposure test（bioaccumulation: 21 days,elimination: 14 days）was carried out;based on ultra-high performance liquid chromatography-mass spectrometry,the enantioselective bioaccumulation and elimination of penthiopyrad in zebrafish were determined.The results showed that penthiopyrad had an enantioselective bioaccumulation in zebrafish with preferential accumulation of S-（+）-penthiopyrad.No enantiomeric conversion of penthiopyrad and production of major metabolites were observed throughout the exposure period.（3）The oxidative stress effect after exposure to penthiopyrad was assessed by measuring the activity and content of three biomarkers（SOD,CAT and MDA）in the liver of zebrafish.The results showed that S-（+）-penthiopyrad induced a higher oxidative stress effect than R-（-）-penthiopyrad.The relative expression of related genes based on real-time fluorescence quantitative analysis showed that exposure to penthiopyrad and its enantiomer induced differential expression of genes related to mitochondrial respiratory chain complex Ⅱ,mitochondrial DNA synthesis,lipid metabolism and apoptosis in the liver of adult zebrafish;S-（+）-penthiopyrad significantly reduced the relative expression of most of the above genes,showing higher toxicity;the difference in gene expression induced between different enantiomers was 1.14-160.5 times.In addition,sex-specific differences were found in the expression of the above-mentioned related genes.We infer that the underlying toxic mechanism of penthiopyrad might be that penthiopyrad exposure induces oxidative damage,mitochondrial dysfunction and lipid metabolism disorder in zebrafish,which in turn leads to apoptosis and even DNA damage.In conclusion,the test results provide ecological risk data of individual enantiomers for evaluating the ecotoxicological effects of penthiopyrad on non-target organisms,and provide scientific reference for the rational application and effective management of penthiopyrad. |
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