Environmental Behavior of the Chiral Aryloxyphenoxypropionate Herbicide Diclofop-Methyl and Diclofop: Enantiomerization and Enantioselective Degradation in Soil

In this study, the degradation of diclofop-methyl (DM) and its main metabolite, diclofop (DC), in two soils under aerobic and anaerobic conditions were investigated using enantioselective HPLC. Under aerobic or anaerobic conditions, rapid hydrolysis to the corresponding acid diclofop (DC) was observed. The results from this study revealed that the degradation of DM in the two soils is not enantioselective, and the calculated half-lives (612) for the two soils were both less than 1 day. However, the degradation of DC in the two soils is enantioselective both under aerobic and anaerobic conditions, and the S-(-)-DC was preferentially degraded, resulting in relative enrichment of the R-(+)-form. The calculated t(1/2) values of the enantiomers of DC ranged between 8.7 and 43.3 days for aerobic incubation experiments and between 14.7 and 77.0 days for anaerobic incubation experiments, respectively. The enantiopure S-(-)- and R-(+)-DC were incubated under aerobic conditions, and it revealed significant enantiomerization with inversion of the S-(-)-enanfiomer into R-(+)-enantiomer, and vice versa, and the S-(-)-DC showed a significantly higher inversion tendency than the R-(+)-DC.