Establishment And Validation Of Safety Application Threshold Model For Thiamethoxam And Dimethomorph On Tomato,Cucumber And Spinach

Unreasonable use of pesticides will lead to excessive pesticide residues in agricultural products,which will give rise to food safety problems.Controlling pesticide dosage is an effective measure to prevent pesticides residue exceeding standard.On the premise of food safety,the safety threshold model is used to calculate the maximum permissible application dosage of pesticide on crops in different scenarios,so that pesticide residues in agricultural products will not exceed the standard at the application dose.So it can solve the problem of excessive pesticide residue in the application stage.In this paper,the parameter determination method and model validation method of the safety application threshold model was established.The rationality of the safety threshold model was verified by the field measurement of thiamethoxam and dimethomorph in tomatoes,cucumbers and spinach.The degradation characteristics of the edible pesticide residues in the process of multiple application of thiamethoxam and dimethomorph were also studied.This study could provide theoretical basis for safety application of pesticides in practical production.The results were as follows:An effective and sensitive analytical method was developed for determination of thiamethoxam and dimethomorph residues in tomato(fruit,stem,leaf),cucumber(fruit,stem,leaf)and spinach by ultra-performance liquid chromatography coupled with tandem mass spectrometry(UPLC–MS/MS).The samples were pretreated using a modified QuEChERS method.The homogenized samples were extracted with acetonitrile,and PSA,GCB were used as sorbents in the purification process.The recoveries of thiamethoxam and dimethomorph from both matrices were in the range of 83.2-99.8% and 83.1-103.2%,with relative standard deviations was ranged from 1.8% to 9.0% and 2.4% to 8.7%.The results meet the requirements of residue analysis method.The safety application threshold model was firstly constructed.Based on the first-order kinetics equation of pesticide residue digestion,the relationship between AER,WER,Interception,Drift,Biomass and the half-lives of pesticides was defined,and the determination methods of model parameters were established.The safety application threshold model was verified by field test.The results of the model validation experiment under the greenhouse conditions show that,the concentrations of thiamethoxam in tomato,cucumber and spinach were 0.95 mg/kg,0.5 mg/kg and 4.51 mg/kg respectively;the concentrations of dimethomorph in tomato,cucumber and spinach were 0.99 mg/kg,3.18 mg/kg and 7.69 mg/kg.In the model validation experiment under the open air condition,the measured concentrations of thiamethoxam in tomato,cucumber and spinach were 0.54 mg/kg,0.41 mg/kg and 3.44 mg/kg;the concentrations of dimethomorph in tomato,cucumber and spinach were 0.88 mg/kg,4.42 mg/kg and 24.81 mg/kg.The results showed that the deviation between Ct and MRL of thiamethoxam and dimethomorph in tomato,cucumber and spinach were generally lower than 1.0 logarithmic unites,which met the standard requirements of the model parameters.It is confirmed that the parameters of the model were suitable and the predicted application dose were safe,which can provide guidance for the safety application of pesticides on vegetables under the conditions of greenhouse and open air.