analysis, a UHPLC separation was combined with a combined ion-trap-QqQ detector. In this investigation, 135 commercially available products (fruit, vegetables)
from the local markets in the Guizhou province (PRC) were examined for the
enantiomeric profile for the selected chiral pesticides. For most of the target substances, enantiomeric preferences were determined in the product samples. Thus, the
method was found to be interesting for source elucidation and consumer safety
evaluations (He et al. 2015).
The desorption and adsorption profile on soils is a crucial process for the
elucidation of environmental fate. Therefore, a currently published combined field
and laboratory study investigated the specific behaviour of metalaxyl in soil (Sukul
et al. 2013). Metalaxyl is an acylalanine fungicide (methyl N-(methoxyacetyl)-N(2,6-xylyl)-DL-alaninate). This study was conducted on natural and artificial soils
focusing on the impact of important soil components (e.g. montmorillonite and
ferrihydrite) on the sorption behaviour and if sorption–desorption may affect the
enantiomeric profile. The sorption–desorption characteristics of metalaxyl were
investigated by batch equilibration technique in a natural soil, two artificial soils
and in pure montmorillonite and ferrihydrite. After extraction, pesticide residues
were analysed by conventional and enantiomer-selective liquid chromatography
using tandem mass spectrometry. For the enantiomer-selective analysis, cellulosebased Lux 5 column (5 μm, Phenomenex, Torrance, Ca) was applied. The herecalculated Kd Sorp (2.3–6.5) suggests low level sorption of metalaxyl with an appreciable risk of run-off and leaching into the aquifer. Thus, metalaxyl poses a threat to
surface and groundwater contamination. Furthermore, desorption tests revealed a
hysteretic effect (H metalaxyl was found tightly bound to the adsorbents without desorbing readily
after the desorption cycle. Desorption of 22–56% of the total amount of the retained
metalaxyl was determined. Results confirm that an artificial soil derived from
different soil constituents can be used to assess their influence on sorption/desorption
processes. Furthermore, they showed that both montmorillonite and ferrihydrite play
a significant role in the sorption of metalaxyl. The sorption does not influence the
enantiomeric ratio of racemic metalaxyl. Thus, minor influence of metalaxyl loss in
soil may be expected caused by microbial transformation.
A Swiss research group focused as well on the enantiomer-selective transformation of metalaxyl in agricultural soils. In this earlier study, the scientists found,
however, microbial transformation in soil under certain conditions (Buerge et al.
2003). They investigated the enantiomer-selective degradation properties for
metalaxyl, and the transformation capacity in 20 different soils. The soil types
were primarily selected for covering a large range of soil properties (e.g. acidic/
alkaline, aerobic/anaerobic). Racemic metalaxyl was incubated in these soils, and the
degradation of the enantiomers, as well as the enantioselective formation/degradation of the primary major metabolite, metalaxyl acid, was followed over time under
laboratory-controlled conditions. Enantiomer-selective GC-MS methods were
applied after ethylation with diazoethane. In aerobic soils with pH>5, the fungicidally active R-enantiomer was degraded faster than the S-enantiomer (k(R)>k(S)),
leading to residues with a composition [S]>[R]. However, in aerobic soils with pH
208
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants
from the local markets in the Guizhou province (PRC) were examined for the
enantiomeric profile for the selected chiral pesticides. For most of the target substances, enantiomeric preferences were determined in the product samples. Thus, the
method was found to be interesting for source elucidation and consumer safety
evaluations (He et al. 2015).
The desorption and adsorption profile on soils is a crucial process for the
elucidation of environmental fate. Therefore, a currently published combined field
and laboratory study investigated the specific behaviour of metalaxyl in soil (Sukul
et al. 2013). Metalaxyl is an acylalanine fungicide (methyl N-(methoxyacetyl)-N(2,6-xylyl)-DL-alaninate). This study was conducted on natural and artificial soils
focusing on the impact of important soil components (e.g. montmorillonite and
ferrihydrite) on the sorption behaviour and if sorption–desorption may affect the
enantiomeric profile. The sorption–desorption characteristics of metalaxyl were
investigated by batch equilibration technique in a natural soil, two artificial soils
and in pure montmorillonite and ferrihydrite. After extraction, pesticide residues
were analysed by conventional and enantiomer-selective liquid chromatography
using tandem mass spectrometry. For the enantiomer-selective analysis, cellulosebased Lux 5 column (5 μm, Phenomenex, Torrance, Ca) was applied. The herecalculated Kd Sorp (2.3–6.5) suggests low level sorption of metalaxyl with an appreciable risk of run-off and leaching into the aquifer. Thus, metalaxyl poses a threat to
surface and groundwater contamination. Furthermore, desorption tests revealed a
hysteretic effect (H metalaxyl was found tightly bound to the adsorbents without desorbing readily
after the desorption cycle. Desorption of 22–56% of the total amount of the retained
metalaxyl was determined. Results confirm that an artificial soil derived from
different soil constituents can be used to assess their influence on sorption/desorption
processes. Furthermore, they showed that both montmorillonite and ferrihydrite play
a significant role in the sorption of metalaxyl. The sorption does not influence the
enantiomeric ratio of racemic metalaxyl. Thus, minor influence of metalaxyl loss in
soil may be expected caused by microbial transformation.
A Swiss research group focused as well on the enantiomer-selective transformation of metalaxyl in agricultural soils. In this earlier study, the scientists found,
however, microbial transformation in soil under certain conditions (Buerge et al.
2003). They investigated the enantiomer-selective degradation properties for
metalaxyl, and the transformation capacity in 20 different soils. The soil types
were primarily selected for covering a large range of soil properties (e.g. acidic/
alkaline, aerobic/anaerobic). Racemic metalaxyl was incubated in these soils, and the
degradation of the enantiomers, as well as the enantioselective formation/degradation of the primary major metabolite, metalaxyl acid, was followed over time under
laboratory-controlled conditions. Enantiomer-selective GC-MS methods were
applied after ethylation with diazoethane. In aerobic soils with pH>5, the fungicidally active R-enantiomer was degraded faster than the S-enantiomer (k(R)>k(S)),
leading to residues with a composition [S]>[R]. However, in aerobic soils with pH
208
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants