Residue Analysis, Degradation, Adsorption-desorption And Leaching Characteristics Of Profenachlor In Soil

Flumioxazin,an N-benzimide herbicide developed by Japan's Sumitomo Corporation,was widely used to control annual broad-leaved and dicotyledonous weeds in soybean,cotton,and peanut fields.In this paper,a method for the residual analysis and detection of flumioxazin was established,and a systematic study on its degradation,adsorption-desorption and migration and leaching behavior in soil was conducted.In addition,in view of soil pollution and environmental risks caused by flumioxazin,three different biochars(corn stalks,rice husks,bamboo)were selected to investigate the effect of biochar on the degradation of flumioxazin in soil,and the results might provide a scientific reference for the prevention and treatment of soil contaminated by pesticides.The specific research results were listed as follows:(1)A liquid chromatography-tandem mass spectrometry(LC-MS/MS)method was developed to determine the residue of flumioxazin in soil.Soil sample was extracted by acetonitrile,purified with 50 mg C₁₈,and detected on an Agilent ZORBAX SB-C₁₈column(4.6×150 mm,5?m).Within the mass concentration range(0.05-10 mg/L),the standard curve of the solvent and matrix of flumipropin showed a good linear relationship,R²is 0.9954-0.9955.At the added concentration of0.01-1 mg/kg,the average daily recovery rate in four soils were 78.8-102.8%,and the relative standard deviations(RSD)were 0.2-3.2%;the average daily recovery rate were 82.0%-100.8%,and the RSD were 0.6%-3.2%;limit of detection(LOD)is 0.003mg/kg,and limit of quantification(LOQ)is 0.01 mg/kg.The method fit the detection requirements for pesticide residue.(2)The degradation behavior of flumioxazin under different conditions(soil type,temperature,moisture content,microorganisms and organic matter(OM))in soil was studied.The results indicated that the degradation rate of flumioxazin in the soil was related to the soil type.The degradation rate order was HLJ soil>AH soil>GZ soil>HN soil with the respective half-lives of 10.9,11.2,15.3,and 21.1 d.With the increase of moisture content,the degradation rate of flumioxazin was accelerated,and the half-lives were 15.3,13.5,11.6 and 9.9 d under moisture content of 24%,32%,40%and ponding,respectively.As the temperature increases,the degradation rate of flumioxazin became fast with the order of 15?<25?<35?.Under sterile condition,the half-lives of flumioxazin in HLJ soil,AH soil,GZ soil and HN soil were 18.1,21.0,36.9 and 50.6 d,respectively,which were much longer than those in the nonsterile soil samples,indicating that microorganism was the main factor affecting the degradation of flumioxazin in soil.Under OM-free condition,the half-lives of flumioxazin in HLJ soil,AH soil,GZ soil and HN soil were 12.7,13.2,17.4 and 24.8 d,respectively,which were longer than those in untreated soil samples,indicating that OM could improve the degradation of flumioxazin in soil.Three potential transformation products were identified by ultra-high performance liquid chromatography with high resolution mass spectrometry during the degradation process,and the possible pathways were cleavage of the imide linkage,cleavage of the amide linkage and opening of the cyclic imide.(3)The standard batch equilibrium method was used to study the adsorption kinetics,desorption kinetics,and isothermal adsorption-desorption behavior of flumioxazin in HLJ soil,AH soil,GZ soil and HN soil.The results demonstrated that the adsorption-desorption isotherms of flumioxazin in all soil samples fitted the Freundlich isotherm equation.The K_ads(F)values were 72.55,50.39,47.33 and 22.38 in HLJ soil,AH soil,GZ soil and HN soil,respectively.The adsorption capacity order was HLJ soil>AH soil>GZ soil>HN soil.The adsorption capacity of flumioxazin increased with the increase of OM in soil.The adsorption free energy was all negative which indicated that the adsorption of flumioxazin in soil was physical adsorption.The hysteresis coefficient values(H)were 0.53-2.09,which showed that a hysteresis occurred during the adsorption process.The difference in the adsorption capacity of flumioxazin in different soil samples might be attributed to the comprehensive effect of various physical and chemical properties of the tested soil.(4)The soil thin layer chromatography(TLC)was used to study the migration and leaching behavior of flumioxazin in soil.The results illustrated that the R_fvalues of flumioxazin were 0.31-0.56 in four types of soil,and flumioxazin had poor mobility in HLJ soil and AH soil,while it had better mobility in GZ soil and HN soil.The mobility was relatively weak in four types of soil and negatively related to cation exchange capacity(CEC)and OM content.Through the calculation of the groundwater ubiquity score(GUS)of flumioxazin,we found that the GUS valuesof fluoxazin were 0.69-1.12,indicating that under normal application condition the groundwater will be unlikely polluted by flumioxazin.(5)By adding three different types of biochar to soil,the effect of biochar on the degradation of flumioxazin in soil was evaluated.The results showed that the addition of biochar delayed the degradation rate of flumioxazin in four types of soil.The degradation of flumioxazin in biochar-amended soil varied with the change of biochar type,pyrolysis temperature,and soil type.The effect of biochar on flumioxazin degradation in soil was complicated,which might be influenced by the interaction between its specific surface area,p H,percentage of key chemical elements,moisture content,etc.,rather than any single property of biochar.