Enantioselective degradation, abiotic racemization, and chiral transformation of triadimefon in soils

Triadimefon is a widely used triazole fungicide with one chiral carbon center. In soils, plants, and animals, triadimefon could be metabolized to triadimenol by reduction of the carbonyl group to an alcohol, resulting in the occurrence of a second chiral carbon in triadimenol. The enantioselective degradation of triadimefon and its chiral transformation to triadimenol in two soils, a Baoding alkaline yellow soil and a Wuhan acidic red soil, were investigated. The results showed the occurrence of enantioselectivity with R-(-)-triadimefon preferentially degraded in both soils. Abiotic racemization was observed by incubation of enantiopure triadimefon enantiomers. The racemization was clearly pH dependent and took place much more rapidly in Baoding alkaline soil than in Wuhan acidic soil. Further enantioselective analysis of converted triadimenol showed that triadimenol stereoisomer concentration invariably followed the order 1R,2R>1S,2S>1S,2R>1R,2S in Baoding soil, regardless of racemic triadimefon or single enantiomers initially treated. However, in the case of Wuhan soil, different triadimenol stereoisomer patterns could be produced depending on initial triadimefon composition at the time of application. The abiotic racemization was documented to have a great influence on the chiral profiles of triadimefon and its metabolite triadimenol. The mechanism and structural consideration of the racemization were further discussed, underscoring the importance of considering configurational stability in proper evaluation of environmental fate and risk of chiral pesticides.