Enantioselective Degradation,Residue,and Risk Assessment Of Chiral Diniconazole In Four Kinds Of Fruits

Triazole fungicides are the most widely used fungicides in modern plant protection.More than 84%of triazole fungicides are chiral pesticides.Enantiomers often differ in their biological activity,toxicity,and environmental behavior due to stereoselective interactions between enantiomers and receptor molecules.Traditional pesticide analysis methods mainly focus on racemes and ignore the complex characteristics between enantiomers,which may affect the accuracy of risk assessment.Diniconazole is a widely used triazole fungicide with one chiral center and contains two enantiomers,but its enantioselective behavior in fruits has not been reported.In this study,the chiral triazole fungicide diniconazole was used as the research object,and the absolute configuration of the diniconazole enantiomer was determined by quantitative calculation and comparison of the experimental spectrum;Based on supercritical fluid chromatography-tandem mass spectrometry（SFC-MS/MS）,an efficient and environmentally friendly method for the separation and analysis of diniconazole enantiomers and residue detection methods in four kinds of fruits were established;The enantioselective degradation behavior of diniconazole enantiomers in pear,peach,jujube and apple was studied through field experiments,and dietary risk assessment was carried out.The results of the study will provide data support for the risk assessment of the enantiomer level of diniconazole and provide a theoretical basis for the rational use of diniconazole.The main results are as follows:（1）Using electron circular dichroism spectroscopy,the absolute configuration of the enantiomer of diniconazole was determined by comparing the variation trend of the difference of the absorption coefficient between the calculated ECD spectrum and the experimental CD spectrum with wavelength,that is,the diniconazole monomer 1 is S-diniconazole,the diniconazole monomer 2 is R-diniconazole.（2）A rapid method for the enantiomeric analysis of dinaconazole based on supercritical fluid chromatography-tandem mass spectrometry（SFC-MS/MS）was established for the determination of the enantiomeric content of diniconazole in four kinds of fruits.By comparing the effects of different chiral chromatographic columns,mobile phases,proportion of mobile phases,column temperature,BPR pressure and flow rate on the separation of enantiomers of diniconazole,the CHIRALPAK OZ-3 chromatographic column was determined to be used for the separation of enantiomers of diniconazole.The mobile phase was CO₂/methanol（90:10,v/v）.The column temperature,BPR pressure and flow rate were 35℃,10 MPa and 2.5 m L/min,respectively.The determination of the diniconazole enantiomer can be completed in 1.5 min.By detecting the enantiomeric monomer and racemic of diniconazole under the final optimized conditions,it was determined that S-diniconazole was eluted preferentially and R-diniconazole was eluted later.The average recoveries of enantiomers in the four fruits ranged from 80.2%to 119%,with intraday and interday RSD values of 0.3～15.5%and 2.3～11.6%,respectively.The limit of quantification of enantiomers in pear,peach,jujube and apple was 0.5μg/kg（minimum spiked concentration）.（3）The selective degradation behavior of chiral diniconazole in four kinds of fruits was studied by field experiments.The results showed that the degradation half-life of enantiomers in four kinds of fruits was 2.51～7.94 d.The degradation of enantiomers in pears was the fastest（2.51～5.25 d）,and that in jujube was the slowest（7.12～7.94 d）.The EFs of the enantiomers of diniconazole in the four kinds of fruits were all greater than 0.5,and the ES values were all less than 0.The results showed that selective enantiomer degradation of diniconazole in the four kind of fruits was obvious,and S-diniconazole was preferentially degraded in the four kinds of fruits.The residual concentrations of pear,jujube and apple were lower than the EU MRL（0.01 mg/kg）on the 40th（harvest time）,30th and 10th days after application,respectively.However,in peaches,the residual concentration of diniconazole was still higher than that of MRL after 60 days.（4）Assessing the chronic dietary risk of diniconazole using consumption data by age group and gender.The results showed that the dietary risk order of the two enantiomers and racemates of dinconazole was peach>pear>jujube>apple,all of which were lower than 1.57%,indicating that the chronic dietary risk of dinconazole was acceptable.Children will be at higher risk than adults,and R-diniconazole is more at risk than S-diniconazole.These results will contribute to the rational use and risk assessment of chiral diniconazole.