enthalpy ΔH degrees, the apparent change in entropy ΔS and the apparent change in
ΔΔH degrees and ΔΔS degrees. The thermodynamic parameters were calculated in
order to provide an understanding of the thermodynamic driving forces for enantiomer separation.
The enantiomer separation and uptake of soil-associated fipronil into the sludge
worm (Tubifex tubifex) is discussed in a recent paper (Liu et al. 2012). Fibronil was
spiked into fresh water for a 9-day exposure experiment. The enantiomer fraction in
tubifex tissue was approximately maintained at 0.58. In addition, a 14-day
bioaccumulation period was chosen for the spike-soil treatment and a more significant deviation of enantiomer fraction from 0.5 in tubifex tissue was detected, with
concentrations of the R-form higher than that of the S-form. Therefore, the
bioaccumulation of fipronil was enantiomer-selective in tubifex tissue for the two
treatments. For the spike-soil treatment, the concentrations of fipronil in overlying
water and soil were also measured. With the presence of tubifex worms, higher
concentrations of fipronil in the water phase compared to soil were detected. The
authors concluded that tubifex has a positive influence on the fipronil diffusion from
soil to overlying water and on the transformation of the soil-associated fipronil.
Enantiomer-selective transformation of the pesticide malathion (MA) was investigated in soil and water (Sun et al. 2012a, b). A HPLC-based method with CSP:
cellulose-tris(3,5-dimethylphenylcarbamate ¼ CDMPC) was used for the
enantiomer-selective analysis. The average recoveries for the here-applied method
for the two enantiomers were 88–102% in soil and 81–99% in water. Racemic and
enantiopure R-(+)- and S-(À)-MA were incubated in five soil and water systems. The
results of the degradation of racemate in all of the environment samples showed the
inactive S-(À)-enantiomer degraded more rapidly than the insecticide active R-(+)enantiomer, resulting in a relative enrichment of the R-enantiomer. In addition, after
the enantiopure S-(À)- and R-(+)-MA were incubated in three soil and water
samples, an unexpected inversion of the enantiomers was found. This indicates
that applying the optically pure enantiomer will not help to increase the bioactivity
and reduce environmental pollution.
For the examination of the transformation in soil, a new enantiomer-selective
HPLC-QqQ method for the separation of pyraclofos was developed on cellulose
tri-(4-chloro-3-methylphenylcarbamate) (Lux Cellulose-4) as CSP. Pyraclofos enantiomers were found to be stable in soils (no interconversion was observed during the
incubation of enantiopure S-(+)- or R-(À)-pyraclofos under native conditions). The
enantioselective transformation behaviour of chiral pyraclofos was dramatically
different in three soils under native conditions varying half-lives (t 1/2 ) of pyraclofos
in Nanchang in Jiangxi, Hangzhou in Zhejiang and Zhengzhou in Henan (NC, HZ
and ZZ) soils of 2.6, 13.4 and 7.8 days for S-(+)-pyraclofos and 9.2, 9.3 and 8.2 days
for R-(À)-pyraclofos (Xu et al. 2012). Compared to the half-lives (t 1/2 ) of
rac-pyraclofos of 21.5, 55.9 and 14.4 days in sterilised soils, the transformation
velocity was greatly improved in native soils, indicating that transformation was
mainly due to microbially mediated processes in agricultural cultivating soils. A
successful enantiomer-selective separation of pyraclofos was also achieved on
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8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants
ΔΔH degrees and ΔΔS degrees. The thermodynamic parameters were calculated in
order to provide an understanding of the thermodynamic driving forces for enantiomer separation.
The enantiomer separation and uptake of soil-associated fipronil into the sludge
worm (Tubifex tubifex) is discussed in a recent paper (Liu et al. 2012). Fibronil was
spiked into fresh water for a 9-day exposure experiment. The enantiomer fraction in
tubifex tissue was approximately maintained at 0.58. In addition, a 14-day
bioaccumulation period was chosen for the spike-soil treatment and a more significant deviation of enantiomer fraction from 0.5 in tubifex tissue was detected, with
concentrations of the R-form higher than that of the S-form. Therefore, the
bioaccumulation of fipronil was enantiomer-selective in tubifex tissue for the two
treatments. For the spike-soil treatment, the concentrations of fipronil in overlying
water and soil were also measured. With the presence of tubifex worms, higher
concentrations of fipronil in the water phase compared to soil were detected. The
authors concluded that tubifex has a positive influence on the fipronil diffusion from
soil to overlying water and on the transformation of the soil-associated fipronil.
Enantiomer-selective transformation of the pesticide malathion (MA) was investigated in soil and water (Sun et al. 2012a, b). A HPLC-based method with CSP:
cellulose-tris(3,5-dimethylphenylcarbamate ¼ CDMPC) was used for the
enantiomer-selective analysis. The average recoveries for the here-applied method
for the two enantiomers were 88–102% in soil and 81–99% in water. Racemic and
enantiopure R-(+)- and S-(À)-MA were incubated in five soil and water systems. The
results of the degradation of racemate in all of the environment samples showed the
inactive S-(À)-enantiomer degraded more rapidly than the insecticide active R-(+)enantiomer, resulting in a relative enrichment of the R-enantiomer. In addition, after
the enantiopure S-(À)- and R-(+)-MA were incubated in three soil and water
samples, an unexpected inversion of the enantiomers was found. This indicates
that applying the optically pure enantiomer will not help to increase the bioactivity
and reduce environmental pollution.
For the examination of the transformation in soil, a new enantiomer-selective
HPLC-QqQ method for the separation of pyraclofos was developed on cellulose
tri-(4-chloro-3-methylphenylcarbamate) (Lux Cellulose-4) as CSP. Pyraclofos enantiomers were found to be stable in soils (no interconversion was observed during the
incubation of enantiopure S-(+)- or R-(À)-pyraclofos under native conditions). The
enantioselective transformation behaviour of chiral pyraclofos was dramatically
different in three soils under native conditions varying half-lives (t 1/2 ) of pyraclofos
in Nanchang in Jiangxi, Hangzhou in Zhejiang and Zhengzhou in Henan (NC, HZ
and ZZ) soils of 2.6, 13.4 and 7.8 days for S-(+)-pyraclofos and 9.2, 9.3 and 8.2 days
for R-(À)-pyraclofos (Xu et al. 2012). Compared to the half-lives (t 1/2 ) of
rac-pyraclofos of 21.5, 55.9 and 14.4 days in sterilised soils, the transformation
velocity was greatly improved in native soils, indicating that transformation was
mainly due to microbially mediated processes in agricultural cultivating soils. A
successful enantiomer-selective separation of pyraclofos was also achieved on
212
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants