The enantioselective degradation of quizalofop-ethyl and its metabolite quizalofop-acid in two soils, a Wuhan acidic soil and a Baoding alkaline soil, was investigated. The dissipation of quizalofop-ethyl consisted of two phases, a rapidly deceasing first phase that lasted 1 day and a slowly decreasing second phase that extended till the end of the incubation. It is shown that S-quizalofop-ethyl degraded slightly faster than R-quizalofop-ethyl in the two soils. Further incubation of enantiopure enaniomers showed that quizalofop-ethyl was configurationally stable in soil. Quizalofop-acid was produced quickly, and its amount reached a maximum at 1-6 days time and then decreased slowly with half-lives ranging from 11 to 21 days. The results also showed that quizalofop-acid degraded faster in the acidic Wuhan soil than in the alkaline Baoding soil. At last, significant enantiomerization from S-quizalofop-acid to R-quizalofop-acid was observed, and the enantiomerization was fast, resulting in residues enriched with R-quizalofop-acid whatever racemic quizalofop-ethyl or pure enantiomers were initially applied in the soils.

Profenophos, which has one chiral center and exists as two enantiomers, is a widely used organophosphorus insecticide. In this paper, the degradation of (±)-profenophos and (+)-profenophos in five soils was investigated using enantioselective high-performance liquid chromatography (HPLC). Our results showed that profenophos was degraded fast in soils with halflives ranging from 4.2 h to 495.1 h. Further chiral analysis demonstrated the occurrence of enantioselectivity during the degradation of (±)-profenophos. Also, it was observed obviously that different enantioselectivities were showed in different soils. In Tianjin and Hubei alkaline soils, the (+)-enantiomer was degraded faster than the (-)-enantiomer. However, in Baoding alkaline soil both enantiomers were degraded at similar rates, and in Hubei and Guangdong acidic soils the enantioselectivity was reversed. In order to evaluate the effects of soil pH on the enantioselective degradation of profenophos, a Tianjin alkaline soil was acidified to pH 5.53 and the degradation of profenophos in this soil resulted in slower degradation rate and similar enantioselectivity. At last, during the degradation of enantiomer pure (+)-profenophos, no enantiomerization was observed in both nonsterilized and sterilized soils.