The Residue Of Uniconazole In Citrus And Its Adsorption In Soil And Clay Minerals

In order to study the residual situation of uniconazole on citrus and its adsorption behavior in soil and clay minerals,a method for the analysis and determination of uniconazole residue in citrus samples was established by liquid chromatography mass spectrometry.The residual situation of uniconazole in citrus samples was studied,and the dietary risk of uniconazole was identified.The adsorption behavior of uniconazole on Soil and clay minerals was discussed The effects of environmental factors and six kinds of low molecular weight organic acids on the sorption behavior of uniconazole in soil and clay minerals were investigated.The main results of this study are as follows:（1）A method for the determination of uniconazole residues in citrus was established.The samples were extracted with acetonitrile,concentrated in water bath,and purified by PSA and neutral alumina.The linear relationship between uniconazole concentration and corresponding peak area was good in the concentration range of0.01-1 mg/L,and the correlation coefficient was greater than 0.999.The addition recovery rate of uniconazole in citrus pulp and whole fruit was 84-110%,RSD was1-6%,and the limit of quantification was 0.01 mg/kg.The method met the technical requirements of pesticide residue analysis and detection in China（2）The results of residue test in 12 sites from 2018 to 2019 showed that:After3%uniconazole·14 hydroxybrassinosterol was applied,the residual content of uniconazole in citrus pulp was<0.01～0.014 mg/kg,and that in Citrus whole fruit was<0.01～0.086 mg/kg;After the use of 3%uniconazole·14 hydroxybrassinosterol,in normal harvest period,uniconazole residue in citrus pulp was<0.01～0.014 mg/kg,and in Citrus whole fruit was<0.01～0.086 mg/kg;According to the dietary patterns of different registered crops and Chinese residents,the total dietary exposure risk of uniconazole was evaluated.The total NEDI value of uniconazole in different foods was 0.816μg/（kg bw·d）,and the RQ was 0.0408.The results showed that the reasonable use of uniconazole in Citrus had low dietary health risk to consumers and the risk to human body was acceptable.（3）The adsorption kinetics of uniconazole in the tested soils and minerals included fast adsorption stage and slow adsorption equilibrium stage,the adsorption kinetics curve of the adsorbent accords with the pseudo first order and quasi second order kinetic equations.The adsorption isotherms of uniconazole in the tested soils and minerals were in accordance with Freundlich and Langmuir equations.The order of sorption strength of uniconazole in soil and clay minerals was montmorillonite>kaolinite>alluvial soil>red soil（4）The effect of environmental factors on the adsorption of uniconazole by soil and clay minerals was studied.The results showed that the concentration of Ca Cl₂had little effect on the adsorption of uniconazole in soil,but the presence of Ca Cl₂inhibited the adsorption of uniconazole in clay minerals.With the increase of Ca Cl₂concentration,the adsorption capacity of uniconazole by clay minerals decreased;the p H value had a greater influence on the adsorption of uniconazole by soil and clay minerals The adsorption capacity of uniconazole in soil and clay minerals was larger under alkaline conditions than in neutral conditions;the adsorption capacity of uniconazole in soil and clay minerals decreased with the increase of temperature（5）FTIR analysis showed that uniconazole was bound to the clay mineral surface by hydrogen bond during the adsorption process,and the adsorption process was accompanied by charge transfer.XRD analysis showed that the chemical bond of kaolinite was occupied and the interlayer spacing was smaller after adsorption of uniconazole;the molecular spacing of montmorillonite increased after adsorption of uniconazole,indicating that uniconazole and montmorillonite not only produce surface adsorption,but also enter the inner layer of montmorillonite,and bond in the inner layer.（6）Under the condition of low molecular weight organic acids,the adsorption kinetics curves of uniconazole in soil and clay minerals conform to the quasi second order kinetic equation,and the adsorption isotherm conforms to Freundlich equation;The results showed that the presence of low molecular weight organic acids increased the adsorption capacity of uniconazole in soil and clay minerals;in the concentration range of low molecular organic acids,low concentration of lactic acid increased the adsorption capacity of uniconazole in soil and clay minerals,but high concentration of lactic acid reduced the adsorption capacity;other low molecular organic acids had no inhibitory effect on the adsorption of uniconazole by soil and clay minerals...