Stereoselective Degradation Of Chiral Fungicide Penthiopyrad On Cucumber And Tomat

Penthiopyrad is a new type of amide chiral fungicide,also known as succinate dehydrogenase inhibitor.Due to its broad bactericidal spectrum,low toxicity,good penetration and excellent systemic properties,penthiopyrad is usually used to control the diseases in vegetables and crops.This paper aimed to establish a chiral analytical method to determine the concentrations of penthiopyrad and its metabolite PAM in cucumber and tomato.The developed method was successfully used to investigate the dissipation dynamics and final residue of racemic penthiopyrad in cucumber and tomato under open field and greenhouse conditions.Based on the field trial data and dietary risk assessment models,the dietary intake risk and safety of penthiopyrad on cucumber and tomato were evaluated at the enantiomer level.Penthiopyrad stereoisomers and PAM were separated on a Superchiral S-OD（4.6×150 mm,5μm）column.Cucumber and tomato samples were extracted with acetonitrile.After vortex and centrifugation,the residues were purified by 50 mg of PSA.Finally,the concentrations of analytes were detected by liquid chromatography with tandem mass spectrometry.The developed approach showed good linearity（determination coefficients≥0.992）.The limits of detection and quantitation in two matrices were 3.3μg/kg and 10μg/kg,respectively.The average recoveries of penthiopyrad stereoisomers and PAM in cucumber and tomato were 74.6%-110%and91.0%-102%,respectively,with relative standard deviations<13%.Through field experiments,the dissipation,residual tendency and enantiomer selectivity of penthiopyrad in cucumber and tomato were studied.The results show that the degradation of penthiopyrad in cucumber and tomato conforms to the first-order kinetic model,wit correlation coefficients>0.90.Penthiopyrad stereoisomers dissipated faster in cucumber and tomato samples with half-life<8 d,compared with open-ground tests in greenhouses(t_1/2<3.90 d)than greenhouses(t_1/2<7.85 d).The dissipation of racemic penthiopyrad in cucumber and tomato was stereoselective that the S-（+）-stereoisomers was preferentially dissipated.PAM was found during the dissipation process of penthiopyrad in cucumber and tomato samples under open field and greenhouse conditions,and the concentrations of PAM decreased after increased as the sampling interval increased and were less than 10μg/kg.In the final residue trials,the concentrations of penthiopyrad decreased with the extension of the sampling interval.The final residues of penthiopyrad in cucumber and tomato samples were<10-271μg/kg and<10-130μg/kg,respectively.The dietary intake risk assessment results indicated that about 80%of the acute dietary intake risk quotients（RQ_as）and about 50%of the chronic dietary intake quotients（RQ_cs）were less than 0.1%in cucumber samples.And more than 90%of RQ_as were<0.1%and more than 50%of RQ_cs were<0.2%in tomato samples.All the RQ values were greatly less than 100%,which demonstrated that according to the recommended dosage and spraying method,the acute and chronic dietary intake risk of penthiopyrad in cucumber and tomato samples under open field and greenhouse conditions could be negligible for different groups of Chinese consumers.