separation of the enantiomers of o,p
0 -DDD. The reductive dehalogenation products,
o,p- and p,p
0 -DDD, began to appear as soon as the levels of the parent compounds
started to decrease. p,p
0 -DDT degraded slightly faster than the o,p
0 -isomer. Both
DDD products slowly decayed from the reaction solution over several weeks. Plots
of the loss of o,p
0 -DDT and p,p
0 -DDT matched that for first-order kinetics; both
compounds were completely lost from the Elodea-water reaction medium is from
5 to 24 days, depending apparently upon the growth conditions of the plants when
harvested for use in the six kinetic runs. It turned out that the transformation of o,pDDT and formation of o,p
0 -DDD were not enantioselective. For both compounds,
each of the two enantiomers was always of the same concentration, at least within the
experimental error, throughout the course of the reduction reaction. Garrison et al.
speculated that the distance of the reactive centre from the chiral centre might
preclude enantioselectivity, but the authors of the present monograph are not in
favour of this explanation, because the chiral centre is assumed to be sufficiently
close to induce an enantioselective preference. Thus, further investigations are
needed to elucidate the enantioselective enzymatic degradation of o,p
0 -DDT and
its metabolites.
A partial microbial reduction cannot be ruled out a priori, although it would
presumably lead to an enantiomeric excess. In order to clarify this point, the authors
carried out a cobalt-60 (
60 Co-) gamma irradiation test in parallel experiments. The
irradiated samples were reduced faster than the non-irradiated controls, whereas they
should have reacted much slower if microbial degradation were occurring in the
non-irradiated samples. Therefore, Garrison et al. conclude that microbial degradation in this particular case plays no role in the DDT transformation.
Enzymatic microbial and enzymatic transformation is today considered the major
transformation route for most of the chiral pollutants in soil and aquatic systems.
Many recent examples illustrate the abundance of research conducted in this field
(Monkiedje et al. 2003; Pakdeesusuk et al. 2003; Monkiedje and Spiteller 2005;
Lehmler et al. 2010; Paulin et al. 2010; Cai et al. 2016). For the interested reader, we
recommend consulting the following reviews on this matter (Hühnerfuss and Shah
2009; Lehmler et al. 2010; Petrie et al. 2015; Sanganyado et al. 2017; Zhang et al.
2017a, b).
8.1.2 In Situ Investigations in Marine and Limnic Waters
Today, an abundance of scientific results is reported on the occurrence and distribution of chiral pollutants in marine and freshwater environments. The direct
quantitative determination of enantiomer distribution, however, requires
enantiomer-selective and highly sensitive analytical methods, which was a challenge
for the laboratories in the early beginning of chiral environmental pollution research.
As one of the early investigations in marine waters, Faller et al. [8] raised the
question “Do marine bacteria degrade α-HCH stereoselectively?” (Faller et al.
1991a, b). In this study, cGC with heptakis(3-O-butyryl-2,6-di-O-n-pentyl)-β118
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants
0 -DDD. The reductive dehalogenation products,
o,p- and p,p
0 -DDD, began to appear as soon as the levels of the parent compounds
started to decrease. p,p
0 -DDT degraded slightly faster than the o,p
0 -isomer. Both
DDD products slowly decayed from the reaction solution over several weeks. Plots
of the loss of o,p
0 -DDT and p,p
0 -DDT matched that for first-order kinetics; both
compounds were completely lost from the Elodea-water reaction medium is from
5 to 24 days, depending apparently upon the growth conditions of the plants when
harvested for use in the six kinetic runs. It turned out that the transformation of o,pDDT and formation of o,p
0 -DDD were not enantioselective. For both compounds,
each of the two enantiomers was always of the same concentration, at least within the
experimental error, throughout the course of the reduction reaction. Garrison et al.
speculated that the distance of the reactive centre from the chiral centre might
preclude enantioselectivity, but the authors of the present monograph are not in
favour of this explanation, because the chiral centre is assumed to be sufficiently
close to induce an enantioselective preference. Thus, further investigations are
needed to elucidate the enantioselective enzymatic degradation of o,p
0 -DDT and
its metabolites.
A partial microbial reduction cannot be ruled out a priori, although it would
presumably lead to an enantiomeric excess. In order to clarify this point, the authors
carried out a cobalt-60 (
60 Co-) gamma irradiation test in parallel experiments. The
irradiated samples were reduced faster than the non-irradiated controls, whereas they
should have reacted much slower if microbial degradation were occurring in the
non-irradiated samples. Therefore, Garrison et al. conclude that microbial degradation in this particular case plays no role in the DDT transformation.
Enzymatic microbial and enzymatic transformation is today considered the major
transformation route for most of the chiral pollutants in soil and aquatic systems.
Many recent examples illustrate the abundance of research conducted in this field
(Monkiedje et al. 2003; Pakdeesusuk et al. 2003; Monkiedje and Spiteller 2005;
Lehmler et al. 2010; Paulin et al. 2010; Cai et al. 2016). For the interested reader, we
recommend consulting the following reviews on this matter (Hühnerfuss and Shah
2009; Lehmler et al. 2010; Petrie et al. 2015; Sanganyado et al. 2017; Zhang et al.
2017a, b).
8.1.2 In Situ Investigations in Marine and Limnic Waters
Today, an abundance of scientific results is reported on the occurrence and distribution of chiral pollutants in marine and freshwater environments. The direct
quantitative determination of enantiomer distribution, however, requires
enantiomer-selective and highly sensitive analytical methods, which was a challenge
for the laboratories in the early beginning of chiral environmental pollution research.
As one of the early investigations in marine waters, Faller et al. [8] raised the
question “Do marine bacteria degrade α-HCH stereoselectively?” (Faller et al.
1991a, b). In this study, cGC with heptakis(3-O-butyryl-2,6-di-O-n-pentyl)-β118
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants