Application of capillary electrophoresis to study the enantioselective transformation of five chiral pesticides in aerobic soil slurries

The enantiomers of five chiral pesticides of environmental interest, metalaxyl, imazaquin, fonofos (dyfonate), ruelene (cruformate), and dichlorprop, were separated analytically using capillary electrophoresis (CE) with cyclodextrin chiral selectors. For metalaxyl, imazaquin, and fonofos, aqueous slurries of soil samples from two sites in Georgia and one in Ohio were spiked with the racemate of each pesticide at 50-60 mg/L of aqueous phase of the slurry, and CE analyses were performed at various time intervals to determine enantiomer fractions (EF). Metalaxyl underwent enantioselective transformation; in one soil, the half-life of the target active R-(+)-enantiomer was 17 days while that for the S-(-)-enantiomer was 69 days. Transformation occurred more slowly in the other two soils but was still selective for the R-(+)-enantiomer. Imazaquin and fonofos exhibited nonselective enantiomer loss over their 3 months of incubation time; this could have been due to abiotic or nonselective microbial reactions. Ruelene and dichlorprop were transformed selectively in a variety of soils in a previously reported study (7) that showed the influence of environmental changes on the transformation of chiral pollutants in soils; analytical methods used in that study are reported here to further illustrate the application of CE. CE is shown to be a simple, efficient, and inexpensive way to follow the transformation of chiral pesticides in laboratory microcosms where concentrations can be made high enough (25-50 mg/L initial racemate concentration) for detection of residual parent enantiomers during most of the process.