Enantiomeric Selectivity in the Environmental Degradation of Dichlorprop As Determined by High-Performance Capillary Electrophoresis

Abstract

The chiral herbicide dichlorprop (2,4-dichlorophenoxy-2-propionic acid), which is sold and applied as the racemic mixture, was observed to degrade completely in soil within 31 days, with a half-life of 6.6 d. Degradation occurred with enantiomeric selectivity, indicating biologically mediated reactivity as opposed to strictly abiotic degradation. The S-(−)-isomer degraded significantly faster (t 1/2 = 4.4 d) than the R-(+)-isomer (t 1/2 = 8.7 d); this is contrary to other published results that show selective degradation of the R-(+)-enantiomer, although in other media. Soil samples taken from a field plot at increasing time intervals after application of Foxtril, a commercial herbicide formulation, were solvent-extracted and analyzed for total dichlorprop by capillary zone electrophoresis (CZE), using an acetate buffer at pH 4.7. Heptakis (2,3,6-tri-O-methyl)-β-cyclodextrin, a chiral reagent, was then added to the buffer to effect separation of the (+)- and (−)-isomers of dichlorprop. Baseline resolution allowed calculation of relative concentrations (enantiomer ratios) of the two isomers. CZE is a fast and efficient technique for the analysis of ionic organic species (such as the anion of dichlorprop), including their enantiomers, in pesticide formulations as well as in environmental samples. It thus was possible to analyze Foxtril directly after dilution with water for ioxynil (2,6-diiodo-4-cyanophenol) as well as for dichlorprop. Ioxynil also was detected in the soil extract on the day of application. The hydrolysis product [methyl 2-nitro-5-(2,4-dichlorophenoxy) benzoic acid] of bifenox methyl ester, another herbicide component of Foxtril, was detected in the soil samples taken at 17 and 31 d.

Environmental behavior of the enantiomers of the chiral fungicide metalaxyl in Mediterranean agricultural soils

“…It is well known that the degradation of chiral pesticides in soil is usually enantioselective, primarily due to the enantioselectivity of soil biological degradation processes (Buerge et al, 2006;Garrison et al, 1996;Kurt-Karakus et al, 2005;Li et al, 2006;Ramezani et al, 2010); however, information on factors influencing such enantioselective degradation is still scarce (Buerge et al, 2003;Garrison, 2006;Lewis et al, 1999;Romero et al, 2001;Tan et al, 2008).…”

Enantioseparation and Enantioselective Analysis of Chiral Herbicides

“…The S-enantiomers of MCPP, DCPP and 2,4-D were preferentially degraded under aerobic conditions (Zipper et al, 1999). The S-(-)-DCPP degraded significantly faster (t 1/2 ) = 4.4 d) than the R-(+)-isomer (t 1/2 = 8.7 d) in soil (Garrison et al, 1996). No preferential degradation of the R-and S-enantiomers of MCPP and of DCPP took place in an aerobic field-injection experiment (Rugge et al, 2002, Jarman et al, 2005.…”

“…The hydrolysis product [methyl 2-nitro-5-(2,4-dichlorophenoxy) benzoic acid] of bifenox methyl ester, another herbicide component of Foxtril, was detected in the soil samples taken at 17 and 31 d. The acetate separation buffer was 50 mM at pH 4.65 and was composed as follows: 0.05 M glacial acetic acid: 0.05 M sodium acetate, 1:1, v:v. The cyclodextrincontaining buffer for enantiomeric separation was prepared by dissolving TM--CD in the acetate separation buffer to a final concentration of 25 mM cyclodextrin. (Garrison et al, 1996) Fig. 3-3.…”

“…A large number of papers have discussed the enantioselectivity of DCPP and MCPP (Zipper et al, 1999, Rugge et al, 2002, Schneiderheinze et al, 1999, Zipper et al, 1998, Jarman et al, 2005, Garrison et al, 1996, Messina et al, 2007, Kurt-Karakus et al, 2010, Buser et al, 1997b, Muller et al, 1997, Wen et al, 2010), thereinto Bidleman et al (Kurt-Karakus et al, 2010 reviewed the concentrations and stereoisomer ratios of DCPP, MCPP and metolachlor. Mostly, the S-enantiomer of these herbicides degraded faster than the R-enantiomer (Zipper et al, 1999, Zipper et al, 1998, Garrison et al, 1996, Messina et al, 2007, Buser et al, 1997b, Muller et al, 1997. Enantioselective microbial degradation increased the enantiomeric ratio of R-to S-MCPP during groundwater passage of the landfill leachate (Zipper et al, 1998).…”

Toxicity and bioaccumulation of ethofumesate enantiomers in earthworm Eisenia fetida

“…In theory, enantiomers have identical physical and chemical properties and abiotic degradation rates (Garrison et al, 1996), whereas their individual toxicity, biological activity, and microbial degradation rates have been shown to differ (Overmyer et al, 2007;Diao et al, 2010;Liu et al, 2012;Sun et al, 2012). Several studies have reported that ethofumesate enantiomers showed an enantioselectivity in biochemical processes.…”