Enantioselective Environmental Behavior of the Chiral Herbicide Fenoxaprop-ethyl and Its Chiral Metabolite Fenoxaprop in Soil

Abstract

The enantioselective degradation behavior of fenoxaprop-ethyl (FE) and its chiral metabolite fenoxaprop (FA) in three soils under native conditions was investigated. Two pairs of enantiomers were analyzed by high-performance liquid chromatography (HPLC) with an amylose tri-(3,5-dimethylphenylcarbamate) (ADMPC) chiral column. The degradation of racemic FE in three soils showed the herbicidally inactive S-(-)-enantiomer degraded faster than the active R-(+)-enantiomer. FE was configurationally stable in soils because no interconversion to the respective antipodes was observed during incubation of the enantiopure S-(-)- or R-(+)-FE. The main metabolites of FE were confirmed as FA and 6-chloro-2,3-dihydrobenzoxazol-2-one (CDHB), and the formation of the chiral metabolite FA showed enantioselectivity in soils. The degradation of rac-FA was also enantioselective with the S-(-)-FA preferentially degraded: the half-life (t(1/2)) of the S-form in the three soils ranged from 2.03 to 5.17 days, and that of R-form ranged from 2.42 to 20.39 days. The inversion of the S-(-)-enantiomer into the R-(+)-enantiomer occurred in two of the three soils when the enantiopure S-(-)- and R-(+)-FA were incubated. The data from sterilized control experiments indicated that the enantioselectivity of FE and FA was attributed to microbially mediated processes.

Characterization of Diastereo‐ and Enantioselectivity in Degradation of Synthetic Pyrethroids in Soils

“…Many studies have shown that the enantioselectivity of chiral pesticides was significantly compound‐ and environment‐specific . Buerge et al found that the soil pH and redox conditions had great effects on the enantioselectivity of metalaxy, and alkalinization and acidification of a “nonenantioselective” soil prior to incubation resulted in enantioselective degradation, with the R ‐enantiomer and S ‐enantiomer preferentially degraded .…”

Isomerization of chiral pesticides in the environment

“…The (S)-enantiomers of aryloxyalkanoic acid herbicides and their esters are favorably degraded in aerobic soils, [78][79][80][81][82][83][84][85][86][87] but with no enantiomerization reported for the esters. 79,81,[85][86][87] In most cases, the degradation of each enantiomer is faster than the chiral conversion in either direction, and the (S) (R) conversion rate (k SR ) is larger than the opposite one (k RS ); such as k SR /k RS =1. 3 (4)].…”

Stereoselective Determination of a Novel Chiral Insecticide, Sulfoxaflor, in Brown Rice, Cucumber and Apple by Normal‐Phase High‐Performance Liquid Chromatography

“…It has been estimated that chiral pesticides account for over 40% of the total pesticides used in China, and that the proportion is expected to increase as compounds with more complex structures are registered for use. Enantiomers of chiral compounds, in spite of their very similar structure and appearance as a single compound in conventional analyses, can show very different toxicity, excretion, metabolism, and biological activities when exposed to asymmetric chemical or biological systems . In some cases, only one of the isomers of the pesticide is active, while the other may have less activity or even toxic effects against nontarget organisms .…”