Stereoselective transformation of triadimefon to metabolite triadimenol in wheat and soil under field conditions.

Racemic triadimefon (TF) was applied to wheat and soil at three sites (Beijing, Huaibei, and Zhengzhou in China) under open field conditions. Its enantioselective degradation and stereoselective transformation to the major metabolite, triadimenol (TN), in wheat straw, grain and soil were investigated. At all sites, the degradation of TF enantiomers in straw and soil followed first-order kinetics. In soil from Beijing and Zhengzhou R-(-)-TF was preferentially degraded; however, preferential enantioselective degradations were not recorded in soil from Huaibei or in the straw from all sites. There were noticeable differences in the stereoselective formation of TN stereoisomers in all straw and soil samples. TN diastereomer A with high animal toxicity was preferentially produced via a reductive reaction in straw. In contrast, diastereomer B, was preferential in soil across the experimental period. Different TN concentrations were found in the order of SR-(-)-TN>RR-(+)-TN>RS-(+)-TN>SS-(-)-TN in straw, and RR-(+)-TN>SS-(-)-TN>SR-(-)-TN>RS-(+)-TN in soil. Neither TF nor TN was found in wheat grain at harvest. Because of differences in degradation, formation, and toxicity, the characterization of enantiomers and stereoisomers in this study contributes toward comprehensively assessing the fate and risk of chiral agrochemicals in the environment and food.