Stereoselective Degradation Behavior Of Chiral Fungicide Penthiopyrad In Soil

Pesticides play an important role in agricultural production,more than 28%of pesticides are chiral at present.The enantiomers of chiral pesticides have different biological activities and environmental degradation behaviors,therefore the stereoselective environmental behavior of chiral pesticides has become an important research direction for environmental chemistry,which has important theoretical and practical value for the rational use of chiral pesticides and environmental safety assessment of chiral pesticides.In this paper,the chiral separation of penthiopyrad enantiomers was separated by high performance liquid chromatography(HPLC);and the detection method was established in soils;finally the selective degradation behavior of penthiopyrad enantiomers in soil was studied.The main results are as follows:Firstly,the penthiopyrad enantiomers were separated in the OD-H chiral column by HPLC.The chromatographic conditions of chiral separation were as follows:the mobile phase was V(hexane):V(isopropyl alcohol)=90:10;the column temperature was room temperature;the flow rate was 0.8 mL/min;the detection wavelength was 228nm.Secondly,the detection method of penthiopyrad enantiomers was established in soil.The soil samples were extracted using acetonitrile,cleaned up by SPE(Florisil column)and determined by HPLC.The results showed that in soils with different pH and organic matter contents,this method has good linearity and the correlation coefficients R2 were greater than 0.9940.Within the range of 0.2 to 10mg/kg,the recovery rate of penthiopyrad enantiomers in soil was between 76%and 106%,the relative standard deviation(RSD)was 1.45%?9.31%,the limit of detection(LOD)was 0.05 mg/kg and the limit of quantitation(LOQ)concentration was 0.2 mg/kg.The accuracy and precision of the method are consistent with the requirements of residue detection.Finally,in order to study its degradation dynamics and stereoselective degradation behavior in soil,the quantitative penthiopyrad was added to soil in room cultivation;the main factors causing degradation of penthiopyrad enantiomers were analyzed by soil sterilization;cultivation test of penthiopyrad purity enantiomer,clear transformation behavior in different pH value soil.Results show:(1)Under the condition of non-sterilization,the trend of penthiopyrad enantiomers degradation was in accordance with the first-order kinetics in the six soil.The half-life of degradation was 36.7?58.7 d in acid soil,the half-life of was 42.1?59.8 d in near-neutral soil and the half-life of degradation was f 48.3?59.6 d in alkaline soil.The pH value was similar,but half-life was different which is related to the content of organic matter.According to the EF value of six kinds soil,the priority degradation of Peakl-penthiopyrad was in acid,neutral and alkaline soils.(2)Under the sterilization condition,degradation rate was less than 15%in soil with three different pH value,which indicated that the main reason for the degradation of penthiopyrad was the participation of microorganisms.Microbial degradation is much larger than non-biodegradation in the the same experimental conditions.In different pH values of soil degradation speed of penthiopyrad is acidic soil>near-neutral>alkaline soil,and there was a significant difference(P<0.05)which indicating that pH value had an effect on degradation of penthiopyrad.While under alkaline conditions penthiopyrad is not easy to degrade,which of reason may be that it is stable in the alkaline condition,and there is no selective degradation under the conditions of sterilization.(3)Under the condition of non-sterilization soil culture,the mutual conversion was not found between Peak1-penthiopyrad and Peak2-penthiopyrad.The results showed that the penthiopyrad enantiomers was stable and not easy to occur conversion in the soil environment.