Sulfhydrylation of chlorothalonil in pak choi from cultivation to sample analysis and exposure risk assessment

The rapid sulfhydrylation of chlorothalonil (CHT) in sulfur-rich vegetable matrices was observed in our previous study. However, the formation pathway, residual behavior, and toxicity of sulfhydrylated CHT remain unclear. In this study, we reveal that 4-sulfhydryl chlorothalonil (4-SH-CHT) can be formed by the reaction of CHT with H₂S species. CHT sulfhydrylation mainly occurs in tissue-destroyed pak choi, as H₂S and various H₂S donors are released along with tissue destruction. Over 50 % of CHT was transformed during pak choi homogenization at room temperature (25 °C). Liquid nitrogen with solvent acidification has been proposed to inhibit rapid sulfhydrylation during the analysis of CHT and its degradation products. The analytical method developed to simultaneously detect CHT, 4-SH-CHT, and 4-hydroxy chlorothalonil demonstrated good accuracy, high sensitivity, and satisfactory repeatability. At the maximum recommended dose of CHT, the terminal concentration of CHT in pak choi was higher than the maximum residue level, suggesting a potential chronic risk. The acute toxicity of 4-SH-CHT was higher than that of CHT, and the main target organs were the liver and heart. The consumption of 4-SH-CHT in several tissue-destroyed pak choi samples was higher than the threshold level. This study provides valuable information for further comprehensive safety evaluations of CHT in sulfur-rich vegetables and related foods.