Enantioselective degradation of fipronil in Chinese cabbage (Brassica pekinensis)

Chiral pesticide enantiomers often show different bioactivity and residual toxicity, but this property is usually ignored when evaluating the environmental risk and public safety. In this study, a convenient and precise chiral method was developed and validated for measuring fipronil enantiomers in Chinese cabbage (Brassica pekinensis) based on a high-performance liquid chromatography (HPLC) using (R,R) Whelk-O 1 column. Then the proposed method was successfully applied to the study of enantioselective degradation of fipronil in Chinese cabbage under field conditions. The results showed that the degradation of the two enantiomers in Chinese cabbage was proved to be enantioselective and followed pseudo first-order kinetics (R2 ⩾ 0.98). The (R)-enantiomer degraded faster than the (S)-enantiomer, resulting in the relative enrichment of (S)-enantiomer in residue. The detected metabolites MB46513 (desthio), MB45950 (sulfide) and MB46136 (sulfone) by GC–MS suggested that degradation was mainly contributed by oxidization, reduction and photodegradation. Due to the more insecticide activity and lower mammalian toxicity of S-form, the higher concentration of S-fipronil may result in higher activity in crop protection and lower risk to environment and human beings compared to the recemate. This result should be considered in future environmental risk and food safety evaluation.