Study On The Residue Degradation Regularity Of Neonicotinoids And Its Residue Transfer In Processing Of Apple

Apple trees（Malus pumila Mill.）are often attacked by sap-sucking insect:such as aphids,planthoppers.Organicphosphorus and pyrethroids are usually used for control the pests.With the prohibition of chlorpyrifos and other highly toxic organophosphorus pesticides on fruit trees and the increasingly serious resistance of pyrethroids,neonicotinoids,such as imidacloprid,thiamethoxam and nitenpyram,have become the main insecticides for the control of sap-sucking insect.The extensive use of this kind of pesticides has brought some risk to the quality and safety of apple.The effective evaluation and prevention of the residues of neonicotinoids have become the focus of public concern.A two-year field experiment was conducted to study the degradation dynamics and final residues of 6 kind of neonicotinoids in apples and soils in Hebei,Beijing and Shanxi locations respectively,to determine the degradation half-life.The dietary risks of 6 kind of neonicotinoids in apples were evaluated according to the final residual values in each experimental site,which provided the basis for the rational use in fruit trees and the formulation of the maximum residual limits on apples.During laboratory simulated experiments,the residues change of 6 kind of neonicotinoids were studied in the processing of apple can,apple jam,apple wine and apple vinegar and according to the processing factors,the food safety of the processed products was evaluated.The results provide a reference for the healthy and safe apple products.The main results were as follows:（1）The HPLC method for the simultaneous determination of 6 kind of neonicotinoids in soils and apples was established.Take acetonitrile and 0.3%formic acid as mobile phase,gradient elution was used to obtain better separation effect and repeatability.In the process of sample extraction,vortex method is used instead of ultrasonic extraction.Solid purification materials（PSA,GCB,C-18,MgSO₄）are used to purify the sample without solid column.The experiments of recoveries indicated that the recovery rate,LOD and LOQ can meet the requirements of pesticide residue analysis.This method can provide the basis for the rapid detection of soil,apple,dried apple,apple can,apple jam,apple wine and apple vinegar.（2）The dissipation dynamics of 6 kind of neonicotinoids in apples and soils indicated that the average recoveries at spiked level of 0.05,0.1 and 1mg/kg in apples were in the range of 78.9¹09.8%,with relative standard deviation of 3.2⁸.7%（n=5）;and the average recoveries in soils were in the range of 80.8¹02.2%,with relative standard deviation of3.3⁶.8%（n=5）.The dissipation dynamics of 6 kind of neonicotinoids in apples and soils fitted the first-order kinetic equation,and the half-life of 6 kind of neonicotinoids in apples were 5.10¹2.84d,in soils were 4.25¹7.77d.It was easy to dissipate.According to the maximum residues of 6 kind of neonicotinoids in apples,the RQ of nitenpyram,thiamethoxam,imidacloprid,clothianidin,dinotefuran and acetamiprid were 0.0026,0.05,0.02,0.05,0.003 and 0.01 respectively.The RQ were all less than 1.It indicated that there was no dietary risks.（3）The effects of different drying methods（sun-drying,oven-drying,microwave drying and freeze-drying）on 6 kind of neonicotinoids in apples were studied.The results indicated that the processing factor of acetamiprid,nitenpyram and thiamethoxam were 0.9,0.8,0.8,respectively in sun-drying;the processing factor of imidacloprid,dinotefuran and clothianidin were 0.3,0.1,0.5,respectively.In oven-drying process,the processing factor of imidacloprid,clothianidin,nitenpyram were 1.6,1.4,1.3,respectively,which indicated that the residues were increased;the processing factor of dinotefuran was 0.3,which indicated that the residue was decreased;the processing factor of acetamiprid and thiamethoxam were 0.8 and 1.2,which indicated that the residue has no change.In microwave-drying,the processing factor were all lower than 0.8 except for acetamiprid,which indicated that the residue were reduced in the microwave-drying.In freeze-drying,the residue levels were all increased due to the decrease of water content,the processing factor of 6 kind of neonicotinoids were all higher than 1.3,which indicated that there was no process risk.（4）The transfer regularity of 6 kind of neonicotinoids in apple can and apple jam laboratory simulated procession were studied.The results indicated that the processing factor of 6 kind of neonicotinoids in apple can juice were all less than 0.8.The processing factor were all less than 0.8 in apple can except for the imidacloprid and clothianidin.Which indicated that the pesticide residues were reduced in apple can process and the pesticide residue in fresh fruit can be used to evaluate the safety of apple can.The processing factor in apple jam were 0.8¹.2,which indicated that there were no effect on pesticide residues in apple jam process.（5）The transfer regularity of 6 kind of neonicotinoids in apple wine and apple vinegar laboratory simulated procession were studied.The results indicated that the processing factor of 6 kind of neonicotinoids in apple wine and apple vinegar were all less than 0.8,which indicated that the pesticide residues were reduced in apple wine and apple vinegar process and the pesticide residue in fresh fruit can be used to evaluate the safety of apple wine and apple vinegar.Take acetonitrile as extraction solvent,acetonitrile and 0.3%formic acid as mobile phase,the high performance liquid phase detection method was established to detect 6 kind of neonicotinoids at the same time.The type and dosage of purification materials were optimized.The method was suitable for the detection of neonicotinoids in soil,apple,dried apple,apple jam,apple wine and apple vinegar.The results showed that 6 kind of neonicotinoids in apples and soils were all in accordance with the first-order kinetic equation.The half-life in apples was 5.10¹2.84d,the half-life in soils was 4.25¹7.77d,which indicated that 6 kind of neonicotinoids were all easy to degrade.The results of dietary rsik essessment showed that the RQ were all less than 1,there was no dietary risk.In different drying process,sun-drying,oven-drying and microwave-drying can reduce some residue,while freezing drying can increase all the residue of 6 kind of neonicotinoids.Microwave-drying or sun-drying were suggested for apple drying.In the apple jam procession,the processing factor was 0.8¹.2,it indicated that there was no effect on the residues of 6 kind of neonicotinoids.In the apple can,apple wine and apple vinegar,the processing factor were all less than 1,there was no residual risk.