Dissipation of Fungicide Thiophanate-methyl Residue in Foxtail Millet during Cultivation and Profiling of the Endogenous Metabolites

Abstract

Foxtail millet is a staple food source in semiarid region of East Asia such as China, Japan, Russia, India and Korea. The dissipation characteristic of thiophanate-methyl including the behavior of its metabolite carbendazim was investigated in foxtail millet (grain and straw) after spraying thiophanate-methyl 40% suspension concentrate formulation. For the field experiment, the pesticide was treated on 4 plots and each plot was to set to be replicated three times. The residue of the thiophanate-methyl and carbendazim were analyzed using LC-MS/MS and the methodological limit of quantitation (MLOQ) were 0.02 mg/kg in both compounds. The coefficient of determination (r2) of calibration curve was higher than 0.998 on the range of 0.025-0.5 ng. In grain, the residual amount of plot 4(14,7 days before harvest) was 4.62 mg/kg, but in plot 1, it was lower than MLOQ, in straw, it decreased from 34.17 to 0.20 mg/kg. These results can be used to establish pre-harvest interval (PHI) of thiophanate-methyl for cultivation of foxtail millet. The endogenous metabolites were also analyzed not only for foxtail millet but also white rice, brown rice, rice bran, sorghum and millet in order to find out the properties of each grain using metabolomics method. Degree of milling for rice was also regarded in this study. For this study, LC-MS/MS and GC-MS/MS were used to profile their endogenous metabolites. Principal Component Analysis (PCA) and Partial least squares Discriminant Analysis (PLS-DA) score scatter plot and loading scatter plot were used as the statistical tool in order to characterize each sample.