Establishment Of Rapid Detection Methods And Degradation Models Of Pesticide Residues In Typical Soils In China

Soil is the basis of agricultural production.The large-scale use of pesticides inevitably results in the residues of pesticides in soil,which enter the food chain through bioconcentration and endanger human health.Pesticide residues in soil and their degradation have received more and more attention year by year.In the present study,therefore,14 pesticides widely used in China are chosen to study establishment of rapid detection methods and degradation models of pesticide residues in typical soils in China using classic experiment techniques of pesticide environmental chemistry science.The objectives of this study are to provide reference for monitoring pesticide residues and risk assessment of pesticide contamination in soil.The main results are as follows:1.A rapid detection and analysis method for 14 pesticide residues in soil were studied and established.Based on the classical Qu ECh ERS extraction technique,different extractants and different purification agents were used to extract and purify the samples,and the pretreatment method[1.0%formic acid-acetonitrile（v/v）extraction,150 mg anhydrous magnesium sulfate+50mg C₁₈ purification]was optimized.UPLC-MS/MS was used to detect residues of 13 pesticides including pyraclostrobin,thifensulfuron-methyl,nicosulfuron-methyl,prochlorazuron,atrazine,isoprofen,diuron,rifauron,imazethapyr and imidazoquinoline in ypical soils.For pythromycin,its residues in soils was extracted by ethyl acetate and purified by 150 mg anhydrous magnesium sulfate+50 mg C₁₈ and detected by GC-ECD,respectively.2.The dynamic characteristics and laws of the degradation of 14 pesticides in 6 typical soils in China were studied and clarified.The results of indoor simulated degradation show that the degradation of 14 pesticides in the aerobic and anaerobic soil conditions followed the first-order kinetics.The degradation half-lives are as follows:chlorpyrifos 22.28～85.46 d,phoxim6.97～26.48 d,azoxystrobin 31.76～154.37 d,pyraclostrobin 12.50～76.33 d,isoxanil 16.93～73.66 d,procymidone 16.98～86.10 d,thifensulfuron-methyl 5.36～26.77 d,nicosulfuron 4.28～80.50 d,prochlorazuron 43.78～240.66 d,atrazine 43.78～240.66 d,diuron 108.81～301.35 d,elongation28.74～114.37 d,imidazonicotinic acid 25.66～133.29 d,and imidazoquinoline 43.81～224.30 d.The correlation analyses show that the degradation half-lives of pesticides in six typical soils in China were related to the nature of pesticides,soil characteristics and environmental factors.3.The degradation dynamics of 4 pesticides with the longer half-lives,such as azoxystrobin,isomuron,dimetron and imazethapyr,in different areas were studied and clarified.The degradation of pesticides in the cultivated and non-cultivated soils of Guizhou,Hebei and Liaoning provinces were followed the first-order kinetics,and there were obvious differences in the degradation rates of these 4 pesticides in different regions or under different cultivation environments,which were rapider than that in indoor soils.the half-lives of azoxystrobin,isomuron,dimetron and imazethapyr in the cultivated and non-cultivated soils were 7.86～11.35 d and 5.90～35.31、5.33～19.95 and 3.07～19.55 d、8.60～10.97 and 6.50～20.49 d、2.25～14.22 and0.67～5.32 d,respectively.4.The optimal mathematical models for simulating the degradation of different pesticides in different soil conditions were fitted and established.The 8 mathematical models suitable for simulating the degradation of 14 pesticide residues in soils were used to simulate the dynamics of pesticide residues in indoor and field soils,and a total of 1968 degradation models were fitted,in this shtudy,and 246 mathematical models of pesticide degradation under different soil conditions were selected.The corresponding prediction models of the pesticide degradation were established by Python.There was a high agreement between the prediction model and the experimental degradation dynamics of pesticides.