Adsorption Of Thiamethoxam And Clothianidin In Farmland Soils And Clay Minerals

In order to acquaintance the degradation dynamics of thiamethoxam and clothianidin in soils after it was used.Detection methods of thiamethoxam and clothianidin in soil was established by adding recovery tests and its degradation dynamics were simulated in the indoor simulation.In addition,the adsorption behavior and its influencing factors of thiamethoxam and clothianidin in different soils and clay minerals were studied,which provided basic data and scientific basis for the evaluation of thiamethoxam and clothianidin in the ecological environment.The main conclusions of this paper are as follows:（1）A method of determining residual of Thiamethoxam and clothianidinin soil samples was established by high performance liquid chromatography with ultraviolet detector.The soil samples were extracted with acetonitrile and salted out.HPLC-UV detection conditions:the mobile phase is V（methanol）:V（water）=30:70,the flow rate is0.9ml/min and ultraviolet absorption wavelength is set at 260 nm.The results showed that:in the range of0.01⁵.00mg/L,thiamethoxam and clothianidin showed a good linear relationship between the peak area and mass concentration and its corresponding linear equations as follows:thiamethoxam:y=66.07x+0.222（R²=1）;clothianidin:y=84.7x-0.34（R²=1）.In 0.05¹.00mg/kg levels,the average recovery of thiamethoxam in the range of 76.7%⁸6.6%,the relative standard deviation（RSD,n=5）in 3.1%⁴.9%;the average recovery rate of clothianidin in 90.7%⁹2.9%,the relative standard deviation（RSD,n=5）in 2.5%⁷.8%.The pretreatment process of this method is simple which is consistent with the technical requirements of pesticide residue analysis.（2）The degradation dynamics of thiamethoxam and clothianidin in tide soil and red soil are studied through the laboratory tests,the results are as follows:the degradation of thiamethoxam and and clothianidin in soils accord with first-order kinetic equation:Ct=C₀e^-kt.The half-lives of Thiamethoxam in red soil and tide soil were 36.28d and 21.65d;the half-life of clothianidin in red soil and tide soil were 29.87d and 16.11d;thiamethoxam and clothianidin were more prone to degradation in red soil and tide soil and were belong to easily degradable pesticides.（3）This paper studies the adsorption behavior and effect factors of thiamethoxam and clothianidin in two kinds of soils by batch equilibrium techique;The results showed that the adsorption capacity of tide soil is stronger than red soil on two pesticides.The adsorption law of Thiamethoxam and clothianidin in two kinds of soil tested showed that clothianidin was easier to be adsorbed than Thiamethoxam.The adsorption of Thiamethoxam and clothianidin on tested soils could be well described by the Linear model,Freundlich model and Langumir model and the correlation coefficients are above 0.870 which reached significant level（P≤5%）.The adsorption isotherm of thiamethoxam and clothianidin is"L",which is nonlinear.With the increase of pH,the adsorption amount of thiamethoxam and clothianidin showed a decreasing trend in soils.The adsorption trends of thiamethoxam and clothianidin were approximately the same and reached the maximum at 25℃。（4）The paper systematically research the adsorption behavior and effect factors of thiamethoxam and clothianidin in six kinds of clay minerals by batch equilibrium techique;The results showed that the adsorption equilibrium time of Thiamethoxam and clothianidin in six kinds clay minerals were 16h-24h.The adsorption of Thiamethoxam and clothianidin on tested clay minerals could be well described by the pseudo-second-order model and fitted well with the Freundlich isotherm adsorption model.The correlation coefficient of Freundlich isotherm adsorption modelare above 0.937 which reached significant level（P≤1%）.The adsorption isotherm is"S".The amount of adsorption was positively correlated with the concentration of the solution,which the higher the concentration,the greater the amount of adsorption.With the increase of pH,the adsorption amount of thiamethoxam and clothianidin showed a decreasing trend in clay minerals.The adsorption trends of thiamethoxam and clothianidin were approximately the same and reached the maximum at 25℃。（5）when added different adsorbents,adsorption of thiamethoxam and clothianidin in soils showed such a regularit:Biochar>Straw charcoal>Charcoal>Rice husk charcoal>Chitosan>β-Cyclodextrin...