(ER ¼ 0.55–0.92), PCB135 (ER ¼ 0.63–0.76) and PCB149 (ER ¼ 0.58–0.91)
revealed an ee of the second eluting enantiomer in almost all sample extracts. No ee
was found for PCB132 and PCB149 in one sample each. The differences observed in
the enantiomeric ratios of the atropisomeric PCBs could not be explained by the
relationship between structure and metabolism. PCB95, PCB132, PCB135,
PCB136, PCB149, PCB174 and PCB176 belong to the readily metabolised PCBs.
They possess vicinal hydrogen atoms in both ortho-/meta- and meta-/para-positions
(PCB132), in two meta-/para-positions (PCB95, PCB136) or in one meta-/paraposition (PCB135, PCB149, PCB174, PCB176). It is, therefore, not possible, on the
basis of its structure, to explain why PCB95 (with two vicinal H atoms in meta-/
para-positions) only shows slight enantiomeric enrichment, while PCB149 (with
only one free meta-/para-position) exhibited higher enantiomeric enrichment. Thus,
Reich et al. conclude that the differences found in the metabolic transformation
pathway between the two atropisomers of these PCBs could be better explained by
the enantioselective character of the enzymatic biotransformation process.
Wong et al. (2002) provided a first overview of enantiomer signatures of chiralchlorinated organic pollutants in certified reference materials. In their survey, they
covered the most important chiral organochlorine pesticides, as well as
atropisomeric polychlorinated biphenyls. In their study, the authors investigated
the enantiomeric profiles of cis- and trans-chlordane, heptachlor exo-epoxide,
oxychlordane, U82, MC5, MC6, MC7, o,p'-DDT, as well as the atropisomeric
PCB congeners 91, 95, 136, 149, 174, 176 and 183. The enantiomeric fractions
(EF) of the respective compounds were determined in SRM 1588a (organics in cod
liver oil), SRM 1945 (organics in whale blubber), Marine Mammal Quality Assurance Exercise Control Material IV (NIST IV, organics in whale blubber), CRM trout
and CRM EC-5 (sediment). For EC-5 (sediment), mainly racemic EFs for OCP and
atropisomeric PCBs were determined. In contrast, SRM1588 (cod liver oil) was
characterised by non-racemic EFs, especially for PCBs. “CRM trout” also showed
mainly non-racemic EFs. The enantiomer residues in the two pilot whale reference
materials (SRM 1945 and NIST IV) were racemic for many target analytes. This
feature is mainly explained by a combination of metabolisation and non-chiral
accumulation in cetaceans. This first comprehensive survey extended the value of
the here-investigated certified materials and should be followed up by a proper robin
round laboratory intercomparison.
The enantiomeric profile was determined in a study on 11 harbour porpoise livers
(Phocoena phocoena) found dead in the southern North Sea (Chu et al. 2003a, b).
The concentration levels and enantiomeric ratios (ER) for polychlorinated biphenyl
(PCB) atropisomers PCB 95, PCB 149 and PCB 132, were measured. Non-racemic
enantiomeric ratios (ERs) were found in several individuals. The value of ERs in
three of the four juvenile porpoises was close to racemic. However, the ERs in all
adults differed from racemic and ranged from 1.31 to 2.54 for PCB 95; from 1.19 to
1.81 for PCB 149 and from 0.45 to 0.94 for PCB 132. There were no relationships
between the total concentration of PCBs and ERs found in this investigation. A
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
169
revealed an ee of the second eluting enantiomer in almost all sample extracts. No ee
was found for PCB132 and PCB149 in one sample each. The differences observed in
the enantiomeric ratios of the atropisomeric PCBs could not be explained by the
relationship between structure and metabolism. PCB95, PCB132, PCB135,
PCB136, PCB149, PCB174 and PCB176 belong to the readily metabolised PCBs.
They possess vicinal hydrogen atoms in both ortho-/meta- and meta-/para-positions
(PCB132), in two meta-/para-positions (PCB95, PCB136) or in one meta-/paraposition (PCB135, PCB149, PCB174, PCB176). It is, therefore, not possible, on the
basis of its structure, to explain why PCB95 (with two vicinal H atoms in meta-/
para-positions) only shows slight enantiomeric enrichment, while PCB149 (with
only one free meta-/para-position) exhibited higher enantiomeric enrichment. Thus,
Reich et al. conclude that the differences found in the metabolic transformation
pathway between the two atropisomers of these PCBs could be better explained by
the enantioselective character of the enzymatic biotransformation process.
Wong et al. (2002) provided a first overview of enantiomer signatures of chiralchlorinated organic pollutants in certified reference materials. In their survey, they
covered the most important chiral organochlorine pesticides, as well as
atropisomeric polychlorinated biphenyls. In their study, the authors investigated
the enantiomeric profiles of cis- and trans-chlordane, heptachlor exo-epoxide,
oxychlordane, U82, MC5, MC6, MC7, o,p'-DDT, as well as the atropisomeric
PCB congeners 91, 95, 136, 149, 174, 176 and 183. The enantiomeric fractions
(EF) of the respective compounds were determined in SRM 1588a (organics in cod
liver oil), SRM 1945 (organics in whale blubber), Marine Mammal Quality Assurance Exercise Control Material IV (NIST IV, organics in whale blubber), CRM trout
and CRM EC-5 (sediment). For EC-5 (sediment), mainly racemic EFs for OCP and
atropisomeric PCBs were determined. In contrast, SRM1588 (cod liver oil) was
characterised by non-racemic EFs, especially for PCBs. “CRM trout” also showed
mainly non-racemic EFs. The enantiomer residues in the two pilot whale reference
materials (SRM 1945 and NIST IV) were racemic for many target analytes. This
feature is mainly explained by a combination of metabolisation and non-chiral
accumulation in cetaceans. This first comprehensive survey extended the value of
the here-investigated certified materials and should be followed up by a proper robin
round laboratory intercomparison.
The enantiomeric profile was determined in a study on 11 harbour porpoise livers
(Phocoena phocoena) found dead in the southern North Sea (Chu et al. 2003a, b).
The concentration levels and enantiomeric ratios (ER) for polychlorinated biphenyl
(PCB) atropisomers PCB 95, PCB 149 and PCB 132, were measured. Non-racemic
enantiomeric ratios (ERs) were found in several individuals. The value of ERs in
three of the four juvenile porpoises was close to racemic. However, the ERs in all
adults differed from racemic and ranged from 1.31 to 2.54 for PCB 95; from 1.19 to
1.81 for PCB 149 and from 0.45 to 0.94 for PCB 132. There were no relationships
between the total concentration of PCBs and ERs found in this investigation. A
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
169