Spinach or amaranth may represent highest residue of thiophanate-methyl with open field application on six leaf vegetables.

Abstract

To select representative crop among leaf vegetables which may contain the highest residue after fungicide uses, open field applications with thiophanate-methyl on six crops including pakchoi, rape, crown daisy, amaranth, spinach and lettuce were designed and conducted. In this study, a high-performance liquid chromatography and electrospray ionization-tandem mass spectrometry with selected reaction monitoring was used to simultaneously determine thiophanate methyl and its metabolite carbendazim residue in various samples. The limit of quantification for thiophanate methyl and carbendazim were established in the range of 0.005-0.01 mg kg(-1) for all samples. It was shown that recoveries ranged from 67.8 % to 102.3 % for thiophanate methyl, and 72.0 %-112.6 % for carbendazim at spiked levels of 0.01-0.1 mg kg(-1). It's found that thiophanate methyl converts to carbendazim very quickly. In supervised field trials, the half-lives of thiophanate methyl in six leaf vegetables were in the range of 1.26-2.65 days, and the half-lives of carbendazim were in the range of 2.53-4.28 days. It was also found that thiophanate methyl residue in spinach and amaranth was higher than others after application. It's recommended that spinach or amaranth can be selected as representative crop in leaf vegetables in study of systemic fungicides with similarity as thiophanate methyl.