Study On Residue And Metabolism Of Carbosulfan In Cucumber And Chinese Cabbage

Pesticide residues is a big problem existing in food safety in China. Carbosulfan is a broad-spectrumcarbamate insecticide and have been widely used in China. In the food and environment, thecarbosulfan could metabolize first to carbofuran, and then to3-hydroxycarbofuran and3-ketocarbofuranwhich were more toxic. Therefore, in the study of carbosulfan residue in the agricultural products, it isnecessary to study the main metabolites of carbosulfan at the same time. Pesticides may degrade ormetabolize in the sample storage and reducing the credibility of residue analysis data. The study ofpesticide stability in storage has not received enough attention and become the weak work for safetyevaluation of pesticide residues in China. Cucumber and Chinese cabbage has been extensivelycultivated in China, carbosulfan was often used on these two vegetables to control pests. However, thereare few reports focused on analytical methods, stability in sample storage and environmental behaviorof carbosulfan and its metabolite in them. Therefore, it is very important for the study of multi-residueanalytical method and dissipation dynamics of carbosulfan in cucumber and Chinese cabbage.This paper focus on the simultaneous analysis of carbosulfan and its three metabolites, study stabilityof carbosulfan during samples storage, the metabolism and terminal residues of carbosulfan incucumber and Chinese cabbage from field trial, the main contents and results are as follows:(1) An analytical method was developed for simultaneous determination of carbosulfan and othermetabolites in Chinese cabbage. The analytes were extracted from the dispersed samples with diatomiteby accelerated solvent extraction (ASE) using methylene chloride as solvent, purified with solid phaseextraction column (SPE), analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS)in positive electro-spray interface (ESI+) with multi-reaction monitoring (MRM) mode, and quantifiedby matrix internal standard method. The limits of detection (LOD) and quantification (LOQ) were0.002-0.010mg/kg and0.005-0.020mg/kg, respectively.The recoveries ranged from85%to122%withrelative standard deviations (RSD) varying between2.3%and12.5%. Then the developed method wassuccessfully applied to cucumber, the limits of detection (LOD) and quantification (LOQ) were0.001-0.005mg/kg and0.002-0.010mg/kg, respectively.The recoveries ranged from74%to115%withrelative standard deviations (RSD) varying between2.9%~9.1%.(2) The influences of stograge time and sample shapes on the stability of carbosulfan residue duringsample storage were investigated. The results showed that carbosulfan in cucumber and Chinese cabbagwould degrade tp carbofuran soon. Different sample shapes would affect the degradation of carbosulfan,compared to pieces, cucumber and Chinese cabbage were suitable for storage homogenized samples.Additionaly, in order to ensure the accuracy of the analytical results, the homogenized sample should beanalyzed in30days as soon as possible.(3) The fild trials of carbosulfan in cucumber and Chinese cabbage were achieved in Beijing, Hunanand Zhejiang in2010and2011. The results demonstrated that the dissipation and metabolism ofcarbosulfan were fast after it was sprayed on vegetables. The main metabolites were carbofuran and 3-hydroxy-carbofuran in cucumber, and carbofuran,3-hydro-carbofuran and carbofuran-3-keto inChinese cabbage. The metabolism of carbosulfan in two plants had some differences. The half-lives ofcarbosulfan were0.8-2.5d and those containing all metabolites that were inverted into carbosulfan were1.5-3.3d in cucumber, while those in Chinese cabbage were0.7-2.3d and0.7-2.8d, respectively.According to results from terminal residue trial, the following method can be recommended: theapplication method of carbosulfan was spray twice with dose of120g a.i./ha, and the preharvestinterval (PHI) should be7days in cucumber and14days in Chinese cabbage. However, these PHIs arenot consistent with the practial production of these two vegetables. Thus, we suggest that the maximumresidue limits (MRLs) of carbosulfan and carbofuran should be evaluated again, or the efficient and safeapplication technologies of carbosulfan on cucumber and Chinese cabbage should be optimized.