Li Zhaoyany, Zhang Zhichao, Zhang Ling, Leng Lian
College of Science, Hebei University of Science and Technology, Shijiazhuang, Hebei Province 050018, China.
Chemosphere. 2009 Jul;76(4):509-16. doi: 10.1016/j.chemosphere.2009.03.015. Epub 2009 Apr 7.
Fenpropathrin and fenvalerate are two widely used pyrethroid insecticides. Due to one and two asymmetrical centers, fenpropathrin and fenvalerate consist of two and four stereoisomers, respectively. In the present study, the degradation of fenpropathrin and fenvalerate in two soils, an alkaline soil and an acidic soil, was investigated using enantioselective high-performance liquid chromatography (HPLC) and the following results were obtained. (i) Degradation of fenpropathrin and fenvalerate in alkaline soil was slightly enantioselective with S-fenpropathrin and alphaS,2R-fenvalerate being faster degraded, respectively. (ii) Fenpropathrin and fenvalerate were found configurationally unstable in alkaline soil and significant racemization at the chiral alpha-C position took place along with the degradation process. The racemization is chemically induced since it occurred under both nonsterilized and sterilized conditions. (iii) No racemization was observed in acidic soil. The soil pH dependent effect of the racemization was further validated by incubating S-fenpropathrin and alphaS,2R-fenvalerate in methanol-buffer solutions with different pH values. (iv) Fenvaleric acid was identified as the main metabolite of fenvalerate, formed by cleavage of the ester bond, during fenvalerate degradation in alkaline soil. Formation of fenvaleric acid in alkaline soil was slightly enantioselective, resulting in an enrichment of S-fenvaleric acid in the soil.
甲氰菊酯和氰戊菊酯是两种广泛使用的拟除虫菊酯类杀虫剂。由于甲氰菊酯和氰戊菊酯分别具有一个和两个不对称中心，它们分别由两个和四个立体异构体组成。在本研究中，使用对映体选择性高效液相色谱法（HPLC）研究了甲氰菊酯和氰戊菊酯在两种土壤（一种碱性土壤和一种酸性土壤）中的降解情况，并获得了以下结果。（i）甲氰菊酯和氰戊菊酯在碱性土壤中的降解具有轻微的对映体选择性，S-甲氰菊酯和αS,2R-氰戊菊酯分别降解得更快。（ii）发现甲氰菊酯和氰戊菊酯在碱性土壤中构型不稳定，在手性α-C位置发生了显著的外消旋化，且外消旋化与降解过程同时发生。由于外消旋化在未灭菌和灭菌条件下均会发生，因此它是由化学诱导的。（iii）在酸性土壤中未观察到外消旋化。通过在不同pH值的甲醇-缓冲溶液中孵育S-甲氰菊酯和αS,2R-氰戊菊酯，进一步验证了外消旋化对土壤pH的依赖性影响。（iv）氰戊菊酸被确定为氰戊菊酯在碱性土壤中降解时通过酯键断裂形成的主要代谢产物。氰戊菊酸在碱性土壤中的形成具有轻微的对映体选择性，导致土壤中S-氰戊菊酸富集。
