Storage Stability Of10Organophosphorus Insecticides And8Fungicides Residue In Representative Fruits And Vegetables

Normally, the pesticide residue samples need to storage for a period before the residue determination. But some reasearches reported the change of residue during the storage period, even though at freezing condition. This might influence the accuracy of the determination, and caused the improper assessment of the pesticide. Hence the research on storage stability of pesticide residues was very essential. In this paper, some representative fruits and vegetables were selected refer to the commodity categories and the principles of extrapolation of OECD (Organization for Economic Co-operation and Development). The storage stability of some commonly used organphosphours insecticide and fungicides under different conditions were researched.The result of the stability of10organphosphours insecticide (dichlorvos, phorate, diazinon, dimethoate, pirimifos-methyl, chlorpyrifos, malathion, fenthion, quinalphos and methidathion) in7representative fruits and vegetables (cabbage, tomato, lettuce, potato, carrot, grape and orange) at three storage temperatures (room temperature,4℃and-20℃) showed that temperature was an important factor for stability. Lower temperature could increase the stability of sample in storage period. The result showed that dimethoate, chlorpyrifos and quinalphos were stable; however phorate, malathion and fenthion were relatively unstable. At room temperature, the stable period of phorate was worst, less than1day in5matrices (except tomato and grape); at4℃condition, the storage of fenthion in cabbage, potato and carrot were worst, and less than3days; at-20℃, malathion showed worst stability, with the period of less than15days in potato, carrot and grape. Compared the stabilities abount different matrices, tomato and lettuce were more stable, and potato and grape were relatively unstable. It may have relationship with carbohydrate content and pH of the matrix. According to the principles of extrapolation by OECD, the stable period of10organphosphours insecticide were summarized in "high water content category","high starch content category" and "high acid content category" at three temperatures.The stabilities of8fungicides (pyrimethanil, fludioxonil, tebuconazole, iprodione, procymidone, cyprodinil, kresoxim-methyl and pyraclostrobin) in5representative fruits and vegetables (cabbage, tomato, potato, grape and orange) at two temperatures (room temperature and4℃) were studied. It was unstable of the residue of fludioxonil in tomato and kresoxim-methyl in potato at room temperature, and the residue of kresoxim-methyl in tomato and potato at4℃. For few numbers of unstable fungicides and matrices, it needed more reseaches to conlude the tendency. According to the principles of extrapolation of OECD, these8fungicides were stable in "high acid cintent category", they could be stable in7days at room temperature and in30days at4℃.Some methods were tried to improve the stability. By changing the status of samples, the storage stability could be affected. For grape and orange, the homogenizd status showed the tendency to stable, and for carrot, coarse chop showed the tendency to stable. For further research, some methods was adopted to improve the stability of organphosphours insecticide in cabbage and potato at room temperature:①By adjusting the pH of samples, the stability of diazinon, pirimifos-methyl, chlorpyrifos, malathion, quinalphos and methidathion in both cabbage and potato were improved.②By adding heavy metal ion Cu2+, the stability of diazinon, pirimifos-methyl, chlorpyrifos, fenthion, quinalphos and methidathion in cabbage and diazinon, pirimifos-methyl, chlorpyrifos in potato were improved, however, the stability of quinalphos in potato was decreased.③By adding sulfur powder, the stability of diazinon, pirimifos-methyl, chlorpyrifos, fenthion, quinalphos in cabbage and diazinon, pirimifos-methyl, chlorpyrifos and quinalphos in potato were improved.④The method of adding organic solvent (methanol or dichloromethane) was the most effective one. By adding dichloromethane, the stability of phorate, diazinon, pirimifos-methyl, chlorpyrifos, malathion, fenthion, quinalphos and methidathion in cabbage were improved to stable level after7days storage.⑤By treating the sapmles with microwave, the stability both of homogenate and coarse chop could be improved, however, the stability of phorate in carrot was decreased.