Residual Distribution And Elimination Of Two Pesticides And Metabolites In Rice Grain

In recent years,the high frequency of rice pests has increased the use of pesticides in irrigated rice.Chlorpyrifos and carbosulfan,which are commonly used in rice production by permeating or inner attracts,bring about more toxic metabolites by hydrolysis reaction.Therefore,not only the residual behavior of pesticide active ingredients but also the residual law of toxic metabolites in grain should be explored.At present,many assays concerning the residual behavior of the two pesticides and their metabolites in rice plants and environment have been reported.、Owing to the pesticide residues can be continued to the rice harvest stage,leading to the contamination of rice grains,researches on pesticides and metabolites distribution characteristics in grain and removal of pesticide residues in rice processing are necessary to be carried out.In this paper,in order to provide experimental basis and theoretical support for a deeper understanding of the transportation,accumulation and other metabolic processes,field experiment on distribution characteristics and accumulation regularity of the two pesticides and metabolites in rice plants has been conducted.Furthermore,laboratory simulation system for removal of pesticides and metabolites effected by rice processing and edible processing has been studied,which is significant for the risk assessment of pesticide and metabolite dietary exposure.1.The parameters such as spray voltage and collision energy were manually selected,and the effects of different mobile phase composition and elution gradient on the resolution and sensitivity were compared.Finally the analytes were separated by Eclipse XDB-C18 column and eluted by a mobile phase gradient consists of methanol-5mmol/L ammonium formate aqueous solution containing 0.1%formic.The compounds were analyzed by modified QuECh ERS pretreatment technology with extracted by 0.1%（v/v）formic acid acetonitrile and purified by two solid phase extraction agents of C₁₈ and PSA.A stable and sensitive method of LC-MS/MS coupled with modified QuECh ERS was developed for the simultaneous determination of five compounds in rice.The experiment provides scientific methods and technical support for the further study of the distribution and residual behavior of pesticides and metabolites in grains.2.The digestion dynamics of pesticides in rice leaves and grains were opposite,the half-lives of chlorpyrifos and carbosulfan in leaves and grains were 2.7d,1.4d and 1.1d,2.1d respectively.However,the degradation rate of the two pesticides in the leaves and grains was more than 90%at the 14th day after the application.The final residues of the two pesticides in the grains were higher than those in the leaves,and the three toxic metabolites were accumulated and digested in the grains with the degradation process of the parent compound.In addition,the distribution of pesticides and metabolites in different tissues of grains showed that pesticides and metabolites were concentrated almost entirely in rice hull and bran,with the distribution ratio over 90%.During the application to the harvest period,chlorpyrifos and carbofuran were gradually transfered from the rice hull to the bran,while carbosulfan was transported from bran to rice hull.3,5,6-TCP was mainly distributed in bran,with the distribution ratio from 76%to 85%,while the distribution ratio of the rice hull and polished rice only between 15%and24%.At the same time,study on the effects of different doses of pesticides showed that the application dose could not significantly affect its distribution trend in the grain.3.The results of laboratory simulation showed that the pesticide residue in rice could be significantly removed by multi-processing procedures,such as drying,hulling and polishing.The individual processing factors were in the range from 0.140 to 0.918,and composite processing factor was in 0.058-0.580.The residual levels of carbosulfan and 3-hydroxycarbofuran in processed rice were lower than the limit,whereas the residue of chlorpyrifos and carbofuran exceeded the ACA and EU residue limits standard.The washing processing of rice can substantially remove the residues of carbosulfan and metabolite carbofuran and 3-hydroxycarbofuran,but has no significant effect on the residual level of chlorpyrifos.Although the residual concentration of 3,5,6-TCP was significantly decreased,the final concentration（0.217±0.004 mg/kg）is still high.The results of this study showed that atmospheric pressure cooking can remove 80%of chlorpyrifos,carbosulfan,carbofuran and3-hydroxycarbofuran in rice,but only about 26%of 3,5,6-TCP,which can be removed by 87%with high pressure cooking.