et al. 2015; Munier et al. 2016; Wang et al. 2017). It is found in the environment
wherever p,p
0 -DDT was applied or is being found due to atmospheric transport
processes (Shen et al. 2005; Li et al. 2011; Zhang et al. 2015). Both DDT isomers are
being microbially transformed by similar pathways, anaerobically to o,p
0 - and p,
p
0 -DDD and o,p
0 - and p,p
0 -DDE or aerobically to o,p
0 - and p,p
0 -DDA
(2-(2-chlorophenyl)-2-(4-chlorophenyl)ethanoic acid and 2,2-bis(4-chlorophenyl)
ethanoic acid, respectively). Microbial transformation of these compounds appears
to be very slow and is confirmed to be enantioselective (Niu et al. 2016; SanchezOsorio et al. 2017). Also today, due to the restricted usage of DDT as tool against
malaria prevention, an abundance of studies confirms the presence and distribution
of DDT in virtually all environmental media (Thomas et al. 2008; Zhang et al.
2012a, b, c; Man et al. 2014; Bosch et al. 2015; Lovecka et al. 2015; Grewal et al.
2016; Sanchez-Osorio et al. 2017). Recent observations on the occurrence of
unequal concentrations of the enantiomers of o,p
0 -DDT in soil (Wang et al. 2009;
Yuan et al. 2014; Bosch et al. 2015; Niu et al. 2016), in sediment (Yang et al.
2010a, b; Jin et al. 2017), in plants (Liu et al. 2009; Niu et al. 2017), in molluscs
(Zhou et al. 2014a, b), in Atlantic cod liver oil (Koske et al. 1999; Wong et al. 2002)
and humans (Xu et al. 2016) as a brief selection.
The early study by Garrison et al. focussed mainly on o,p- and p,p
0 -DDT
degradation by plant enzymes as a potential phytoremediation process. Their experimental approach is based on the observation that selective plant enzymes can
degrade organic pollutants (Garrison et al. 1997; Dhakal et al. 2018). These include,
for example, nitro-reductases that reduce nitro moieties to amines (Bommer et al.
2014; Misal et al. 2014; Zhang et al. 2017a, b; Qiu et al. 2018) and reductive
dehalogenases that replace halogen substituents with hydrogen (Marzorati et al.
2006; Mattes et al. 2018; Wang et al. 2018). For instance, aliphatic halocarbons
such as hexachloroethane and carbon tetrachloride are readily reduced to compounds
with a lower degree of halogenation by dehalogenase enzymes that occur in a variety
of plants. Some of these enzymes have been extracted and partially characterised.
However, the authors cannot fully exclude a priori that a concurrent microbial
enzymatic degradation may take place.
For the plant degradation experiments, 20 grams of Canadian waterweed Elodea
(Elodea canadensis L.) was collected from the surface water of a local lake. The
plant material was rinsed with distilled water and placed in each of a series of serum
bottles containing 100 mL of the boiled aqueous extracts of a sample of the lake
sediment. The water in the bottles was dosed with 1 μg/mL each of o,p
0 - and p,
p
0 -DDT, and the bottles were sealed. The combination of Elodea and water in the
sample was blended and extracted with a 1:1 mixture of n-hexane and acetonitrile,
evaporated to dryness, resolved in methanol, diluted with water and concentrated on
an unmodified C 18 solid-phase extraction (SPE) tube. The methanol eluate was
analysed for the DDT congeners by cGC using modified cyclodextrins as chiral
selector and for acidic degradation products, such as DDA, by enantioselective
capillary zone electrophoresis (CZE). Garrison et al. used a permethyltrifluoroacetoxypropyl-cyclodextrin phase which provided baseline separation of
the enantiomers of o,p
0 -DDT and, for the needs of their experiment, adequate
8.1 Microbial Transformation of Chiral Environmental Pollutants
117
wherever p,p
0 -DDT was applied or is being found due to atmospheric transport
processes (Shen et al. 2005; Li et al. 2011; Zhang et al. 2015). Both DDT isomers are
being microbially transformed by similar pathways, anaerobically to o,p
0 - and p,
p
0 -DDD and o,p
0 - and p,p
0 -DDE or aerobically to o,p
0 - and p,p
0 -DDA
(2-(2-chlorophenyl)-2-(4-chlorophenyl)ethanoic acid and 2,2-bis(4-chlorophenyl)
ethanoic acid, respectively). Microbial transformation of these compounds appears
to be very slow and is confirmed to be enantioselective (Niu et al. 2016; SanchezOsorio et al. 2017). Also today, due to the restricted usage of DDT as tool against
malaria prevention, an abundance of studies confirms the presence and distribution
of DDT in virtually all environmental media (Thomas et al. 2008; Zhang et al.
2012a, b, c; Man et al. 2014; Bosch et al. 2015; Lovecka et al. 2015; Grewal et al.
2016; Sanchez-Osorio et al. 2017). Recent observations on the occurrence of
unequal concentrations of the enantiomers of o,p
0 -DDT in soil (Wang et al. 2009;
Yuan et al. 2014; Bosch et al. 2015; Niu et al. 2016), in sediment (Yang et al.
2010a, b; Jin et al. 2017), in plants (Liu et al. 2009; Niu et al. 2017), in molluscs
(Zhou et al. 2014a, b), in Atlantic cod liver oil (Koske et al. 1999; Wong et al. 2002)
and humans (Xu et al. 2016) as a brief selection.
The early study by Garrison et al. focussed mainly on o,p- and p,p
0 -DDT
degradation by plant enzymes as a potential phytoremediation process. Their experimental approach is based on the observation that selective plant enzymes can
degrade organic pollutants (Garrison et al. 1997; Dhakal et al. 2018). These include,
for example, nitro-reductases that reduce nitro moieties to amines (Bommer et al.
2014; Misal et al. 2014; Zhang et al. 2017a, b; Qiu et al. 2018) and reductive
dehalogenases that replace halogen substituents with hydrogen (Marzorati et al.
2006; Mattes et al. 2018; Wang et al. 2018). For instance, aliphatic halocarbons
such as hexachloroethane and carbon tetrachloride are readily reduced to compounds
with a lower degree of halogenation by dehalogenase enzymes that occur in a variety
of plants. Some of these enzymes have been extracted and partially characterised.
However, the authors cannot fully exclude a priori that a concurrent microbial
enzymatic degradation may take place.
For the plant degradation experiments, 20 grams of Canadian waterweed Elodea
(Elodea canadensis L.) was collected from the surface water of a local lake. The
plant material was rinsed with distilled water and placed in each of a series of serum
bottles containing 100 mL of the boiled aqueous extracts of a sample of the lake
sediment. The water in the bottles was dosed with 1 μg/mL each of o,p
0 - and p,
p
0 -DDT, and the bottles were sealed. The combination of Elodea and water in the
sample was blended and extracted with a 1:1 mixture of n-hexane and acetonitrile,
evaporated to dryness, resolved in methanol, diluted with water and concentrated on
an unmodified C 18 solid-phase extraction (SPE) tube. The methanol eluate was
analysed for the DDT congeners by cGC using modified cyclodextrins as chiral
selector and for acidic degradation products, such as DDA, by enantioselective
capillary zone electrophoresis (CZE). Garrison et al. used a permethyltrifluoroacetoxypropyl-cyclodextrin phase which provided baseline separation of
the enantiomers of o,p
0 -DDT and, for the needs of their experiment, adequate
8.1 Microbial Transformation of Chiral Environmental Pollutants
117