Study On The Stereoselectivity Degradation,Bioactivity And Toxicology Of Chiral Herbicide Carfentrazone-ethyl

Enantiomers of chiral pesticides always exhibit significant stereoselective degradation,bioactivity and ecotoxicity in the chiral environment.Using traditional risk assessment method to evaluate the chiral compounds can hardly provide accurate and scietific guidence for the corresponding risk assessment which could result a series of potential safety hazard for human being and environment.So,it has becoming a imperative problem to investigating the enantioselective behavior of chiral compounds in organisms and environment.This article started from the enantioselective seperation and absolute configuration confirm of carfentrazone-ethyl and its metabolite carfentrazone by liquid chromatography-tandem mass spectrometry(LC-MS/MS).And then the simultaneous determination method for the enantiomers of carfentrazone-ethyl and its metabolite in eight matrices(rice plant,brown rice,rice husk,wheat plant,wheat,corn plant,corn,and soil)were established.On the basis of the determination method,the stereoselective behavior of carfentrazone-ethyl and its metabolite in rice,wheat,corn and soil were investigated for the first time.Besides,the enantioselective bioactivity and acute toxicity of carfentrazone-ethyl and its metabolite were studied systemicly and the mechanism of bioactivity for the target organism was explored.The results and conclusions were shown below:1.A method for separating carfentrazone-ethyl and its metabolite carfentrazone was established by LC-MS/MS with reverse phase chiral stationary phase.The conditions of separating and mass spectrometry were optimized and the optimized detection conditions was selected with Superchiral S-AD-RH chiral column,2mM ammonium formate,0.1%formic acid buffer and methanol acid as the mobile phase,the flow rate of 0.4 mL/min and gradient elution,the column temperature was kept at 35?.MS detection was performed by positive modes with ESI+and the parameters obtained by the pattern of MRM.After optimization,the quantitative ion m/z of carfentrazone-ethyl was 429.05>412.00,the qualitative ions m/z were 429.05>346 and 429.05>366;quantitative ion m/z of carfentrazone oxalic acid was 401.00>383.90,qualitative ions m/z were 401.00>365.90 and 401.00>345.85.2.The absolute configuration of carfentrazone-ethyl and its metabolite carfentrazone enantiomers was confirmed by comparing the experimental and predicted ECD spectra.3.A simple and reliable method for the simultaneous determination of carfentrazone-ethyl and its metabolite carfentrazone enantiomers in rice plants,wheat plants,corn plants,brown rice,rice husk,wheat grain,corn grain and soil were established by LC-MS/MS and all samples were purified by the QuEchERS method.Acetonitrile and water were used as the extraction solvent,PSA and GCB as the adsorbent matrix dispersed solid phase for purification.carfentrazone-ethyl and its metabolites carfentrazone put up excellent precision and accuracy in all matrices.The mean recoveries ranged from 77.5 to 102.8%,with 0.4-10.7%intra-day RSD.The LODs and LOQs for this method in eight matrices were calculated at 0.5-6.0 ?g kg-1 and 1.7-20 ?g kg-1.This study provided a method for simultaneous determination of carfentrazone-ethyl and its metabolites carfentrazone enantiomers in agricultural products and soil.4.The stereoselective environmental behavior of carfentrazone-ethyl and its metabolite stereoisomers was investigated in wheat plant,corn plants,rice plant,paddy soil and three kinds of soils under aerobic condition,respectively.The results showed that the concentration of carfentrazone-ethyl enantiomers decreased with time,and the metabolite firstly increased and then decreased;The carfentrazone-ethyl and its metabolite enantiomer were degraded very fast in plants and soils.The degradation rate in plant was faster than soil.There was no remarkably enantioselective degradation was observed with EF value from 0.5 to 0.571 for carfentrazone-ethyl enantiomers in wheat plant,corn plants and rice plant.Whereas remarkable enantioselective degradation was observed for carfentrazone enantiomers.The order was as follows:rice plant(EF=0.754-0.854)>corn plant(EF=0.520-0.684)>wheat plant(EF=0.333-0.379).The S-(+)-carfentrazone was preferentially degraded and the R-(-)-carfentrazone was accumulated in rice and maize.However,R-(-)-carfentrazone was preferentially degraded in wheat plant.In wheat soil,no obvious selective degradation of carfentrazone-ethyl enantiomers was observed with EF value from 0.503 to 0.553;There was remarkable enantioselective degradation was observed for metabolite enantiomer with EF value from 0.533 to 0.723.The S-(+)-carfentrazone was preferentially degraded,and the R-(-)-carfentrazone was accumulated in wheat soil.Enantioselective degradation was observed for carfentrazone and its metabolite in soils under indoor aerobic conditions.The order of enantioselectivity for carfentrazone-ethyl was Anhui(EF=0.513-0.667)>Jilin(EF=0.524-0.645)>Jiangxi(EF=0.514-0.567);The order of the metabolite of was Jilin(EF=0.675-0.881)>Jiangxi(EF=0.638-0.764)>Anhui(EF=0.642-0.748).Both the S-(+)-carfentrazone-ethyl and S-(+)-carfentrazone were preferentially degraded,and the R-(-)-carfentrazone-ethyl and R-(-)-carfentrazone was accumulated in the soil.5.The stereoselective biological activity of the carfentrazone-ethyl and its metabolite carfentrazone was investigated.Stereoselectivity difference was observed for both carfentrazone-ethyl and its metabolite on the growth inhibition of corn root.The relative toxicity of the metabolite to was greater than carfentrazone-ethyl.For carfentrazone-ethyl,the relative toxicity of S-(+)-carfentrazone-ethyl was about 2.04 and 1.1 times than R-(-)-carfentrazone-ethyl and Rac-carfentrazone-ethyl respectively.For its metabolite,the relative toxicity of S-(+)-carfentrazone was 1.9 times than R-(-)-carfentrazone;The relative toxicity of Rac-carfentrazone was 1.5 and 2.9 times than the S-(+)-carfentrazone and R-(-)-carfentrazone,respectively.There was synergism between the carfentrazone enantiomers.In addition,we investigated the different binding modes of carfentrazone-ethyl and its metabolite to target proteins through the homology modeling and molecular docking technology.The results showed that the activity of S-(+)-carfentrazone and S-(+)-carfentrazone-ethy were both higher than that of S-(-)-carfentrazone and S-(-)-carfentrazone-ethyl.The reason of biological activity differences for carfentrazone-ethyl and its metabolite was explained by the molecular simulation.6.The enantioselective acute toxicity of carfentrazone-ethyl and its metabolite carfentrazone in kinds of aquatic organism(Pseudokirchneriella subcapitata,Daphnia magna straus,Zebra fish)were researched for the first time.Resuts shown that different species of aquatic organisms are differently sensitive to carfentrazone-ethyl and its metabolite carfentrazone which following a order that Pseudokirchneriella subcapitata>Zebra fish>Daphnia magna straus.The acute toxicity of R-(-)-carfentrazone-ethyl and Rac-carfentrazone-ethyl was high for Pseudokirchneriella subcapitata.However,S-(+)-carfentrazone-ethyl showed moderate toxicity to Pseudokirchneriella subcapitata.The acute toxicity of S-(+)-,R-(-)-and Rac-carfentrazone-ethyl was low for Daphnia magna straus.As for Zebra fish,the acute toxicity of S-(+)-,R-(-)-and Rac-carfentrazone-ethyl was low.Significant enantioselective toxicity of the carfentrazone-ethyl and its metabolite enantiomers for Pseudokirchneriella subcapitata was observed which following a order that R>Rac>S,the toxicity of R-(-)-carfentrazone-ethyl was 5.0 folds and 2.8 folds higher the S-(+)-and Rac-carfentrazone-ethyl respectively.No stereoselective toxicity was observed of carfentrazone-ethyl enantiomers for the Daphnia magna straus and Zebra fish.Racemic carfentrazone-ethyl possess highest toxity to Daphnia magna straus and Zebra fish compared with its enantiomers which could decided by the cell structure of aquatic organism,protein inside,enzyme and corresponding difference of chiral envirenment.The mechanism for the enantioselective difference of toxicity should been explored in further study.