Influence of Soil Properties on the Enantioselective Dissipation of the Herbicide Lactofen in Soils

Abstract

A scheme was developed to elucidate the dissipation behaviors of the two enantiomers of the herbicide lactofen in soils using a normal-phase high-performance liquid chromatograph (HPLC) with UV detector and a column with a cellulose-tri-(3,5-dimethylphenylcarbamate)-based chiral stationary phase (CDMPC-CSP). Eight soils with a wide range of soil properties were studied. Racemic and the enantiopure (S)-(+)- and (R)-(-)-lactofen were incubated under aerobic and anaerobic conditions. The data from sterilized controls indicated that the dissipation of lactofen was biological. The dissipation was shown to be enantioselective with (S)-(+)-enantiomer being degraded faster than the (R)-(-)-enantiomer, resulting in residues enriched with (R)-(-)-lactofen when the racemic compound was incubated. Lactofen was configurationally stable in soil, showing no interconversion of (S)-(+)- to (R)-(-)- enantiomer and vice versa. Significant correlations of the enantioselectivity, expressed as ES = (k((S)) - k((R)))/(k((S)) + k((R))) of lactofen with soil pH were observed under aerobic and anaerobic conditions. In addition, we found that the enantioselectivity correlated with the soil texture rather than the organic carbon.

Enantioseparation and Enantioselective Analysis of Chiral Herbicides

“…The dissipation was shown to be enantioselective with S-(+)-enantiomer being degraded faster than the R-(-)-enantiomer, resulting in residues enriched with R-(-)-lactofen when the racemic compound was incubated. Lactofen was configurationally stable in soil, showing no interconversion of S-(+)-to R-(-)-enantiomer and vice versa (Diao et al, 2009). The enantioselective degradation of lactofen enantiomers was proved in a report by Zhou et al (Diao et al, 2010b).…”

“…Ethoxyfen-ethyl and lactofen were separated using HPLC on polysaccharide CSPs by Zhou et al (Wang et al, 2006, Tian et al, 2010, Hou et al, 2002, Diao et al, 2009). Enantioseparation of a novel herbicide ethoxyfen-ethyl was conducted on self-prepared CDMPC, and with the content of IPA in hexane in mobile phase decreased to 1%, the resolution factors increased to 3.95 (Hou et al, 2002).…”

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)].…”

Enantioselective Activity and Toxicity of Chiral Herbicides

“…This herbicide is applied as a foliar spray on target weeds and is used to control broadleaf weeds in soybeans, cereal crops, potatoes, and peanuts (Diao et al, 2009).…”

“…The dissipation and degradation of the herbicide lactofen are enantioselective processes: under laboratory conditions using enantioselective HPLC, the S-(+)-enantiomer is degraded faster than the R-(-)-enantiomer, producing residues enriched with R-(-)-lactofen when the racemic compound is incubated under aerobic and anaerobic conditions in sediments (Diao et al, 2009). The enantioselective acute toxicity of individual enantiomers of lactofen and its metabolite, desethyl lactofen, were studied in D. magna.…”