The Residual Degradation Of Clothianidin And Pymetrozine In Citrus And Its Adsorption In Clay Minerals

In order to fully and accurately understand the residue degradation behavior of clothianidin and pymetrozine in citrus orchards after 30% clothianidin and pymetrozine suspension was used in citrus orchards,to evaluate the dietary risk of clothianidin and pymetrozine residues.To provide scientific basis for guiding the rational use of related preparations containing clothianidin and pymetrozine in citrus.It also provides technical guidance for remediation of environmental pollution caused by clothianidin and pymetrozine.In this paper,the experimental method of adding and recovering is adopted.With the help of liquid chromatography tandem mass spectrometry(HPLC-MS/MS)detection technology,a method for the determination of clothianidin and pymetrozine residues in citrus and soil samples was established.The degradation of clothianidin and pymetrozine residues in citrus and soil was studied by field experiments.Then the batch balance method is adopted.Adsorption behavior of clothianidin and pymetrozine in seven clay minerals(Attapulgite,diatomite,illite,natural zeolite,sepiolite,kaolinite,montmorillonite)and their influencing factors were systematically studied.The main conclusions are as follows:1.The residual clothianidin and pymetrozine in citrus and soil samples were extracted by oscillating extraction with alkaline acetonitrile solution(pH=8.5).The extract was purified by solid phase extraction with neutral alumina dispersion.Then it was detected by HPLC-MS/MS.This method can be used for the determination of clothianidin and Pymetrozine residues in citrus and soil.2.The half-life of clothianidin in citrus was 5.13-19.80 days from Changsha in Hunan,Gaoan in Jiangxi,Nanning in Guangxi and Xiamen in Fujian.The half-life of Pymetrozine in citrus was 3.98-10.66 days.3.Soil Residual degradation dynamics of citrus orchards in Changsha,Zhangjiajie and Hangzhou,Hunan Province were tested: The half-life of clothianidin in soil was 5.54-8.88 days,and that of Pymetrozine in soil was 9.76-11.74 days.4.The final residue test of citrus was carried out in 12 representative areas in China.The results showed that: The supervised trials median residue(STMR)of clothianidin and Pymetrozine were less than 0.05 mg/kg(The quantitative limit).The median residual valueof clothianidin was 0.02 mg/kg,and the maximum residual value(HR)was 0.21 mg/kg.The supervised trials median residue of Pymetrozine residue test was 0.03 mg/kg,and the maximum value of Pymetrozine residue(HR)was 0.11 mg/kg.It is recommended that 21 d be the safe interval for the new mixtures of clothianidin and Pymetrozine suspensions.5.The daily intake of clothianidin(NEDI)was estimated to be 2.36 mg according to the pesticide registration and the per capita dietary structure of Chinese residents.37.5% of the daily allowable intake.The daily intake of Pymetrozine(NEDI)was 0.57 mg,accounting for 30.0% of the daily allowable intake.Therefore,it can be concluded that clothianidin and Pymetrozine do not pose unacceptable risks to the health of the general population.The recommended MRL of clothianidin in citrus was 0.5 mg/kg,and that of Pymetrozine in citrus was 0.2 mg/kg.6.Adsorption of clothianidin and Pymetrozine in seven clay minerals tested:(1)Adsorption kinetics process: The adsorption process of thiamethoxamide and Pymetrozine can be roughly divided into two stages: fast adsorption and slow adsorption.The results showed that illite had the best adsorption effect on clothianidin and natural zeolite had the best adsorption effect on pymetrozine.(2)Adsorption kinetics fitting: clothianidin and Pymetrozine had the best fitting degree in the adsorption kinetics experiment.The pseudo-second-order kinetics equation,Elovich equation and particle diffusion equation are suitable for describing the adsorption kinetics.The correlation is very significant.(3)Isothermal adsorption fitting: Linear model and Freundlich model can well fit the data of adsorption of clothianidin and Pymetrozine on seven clay minerals.Freundlich model has the highest fitting degree and Langmuir model has the lowest fitting degree.(4)Adsorption experiments of clothianidin and Pymetrozine in seven clay minerals by pH value: The adsorption of clothianidin was less affected by pH value than that of pymetrozine.In acidic condition,sepiolite is preferred to adsorb clothianidin,and its adsorption effect is the best.Under alkaline conditions,kaolinite has more advantages in adsorbing clothianidin.Under neutral conditions,the adsorption of clothianidin by seven clay minerals was not obvious.The adsorption of Pymetrozine in neutral environment was the same as that of clothianidin,but the adsorption was not obvious.Under acidic conditions,montmorillonite and natural zeolite were selected as the preferential adsorbents forpymetrozine.In alkaline condition,illite was used to adsorb pymetrozine,and the effect was the best.(5)Infrared spectra of clothianidin and pymetrozine in seven clay minerals tested showed that the adsorption mode of clothianidin and pymetrozine in seven clay minerals was mainly physical adsorption and charge transfer.Hydrogen bonding,strong electron-withdrawing effect of Cl atoms,coordination and coordination.