MC7, the chromatograms indicated a small preference for the later eluting enantiomer in herring, salmon and seal, whereas in the penguin a small prevalence of the
earlier eluting enantiomer can be recognised.
Some of the separation problems encountered by Buser et al. with regard to
components of the technical chlordane mixture were overcome by Karlsson and
co-workers who used heptakis(2,3,6-O-tertbutyl-dimethylsilyl)-β-cyclodextrin as
chiral selector. The latter authors analysed Atlantic cod (Gadus morhua L.) samples
carrying out a very comprehensive study. Atlantic cod, on the winter migration from
the Barents Sea to the Lofoten Islands for spawning, was caught outside Kvaløya,
Tromsø (70
N, 17
E). Age, sex, size, as well as the maturation stage of the gonads,
were determined. Liver and gonads were weighted, and samples were taken including a portion of the filet. The extraction and clean-up procedure can be found in a
corresponding publication (Karlsson et al. 1997a, b).
As can be inferred from Tables 8.11 and 8.12, the enantiomeric ratios (ER; area of
(+)-/(À)-enantiomer or first eluting enantiomer divided by the second one] in
Atlantic cod deviate substantially from the racemic ratio. With a few exceptions,
the ER found in all three cod tissues are similar within the uncertainty of the method
(3–5%). This means that any tissue can be used for an ER determination. It is worth
noting that ER of the octa-chloro congener U82 was below one in cod and above one
in herring. No differences in the ERs between male and female herring were
observed. However, in all cod samples analysed by Karlsson et al., the ERs for
trans-chlordane and MC6 were very different between males and females. Enantiomer transformation was opposite in male and female cod leading to changes of the
ERs by a factor of 3–5. A similar but not so unequivocal trend was also obtained for
cis-chlordane. No gender difference was observed for U81 and U82. The differences
in the influence of sex on the ERs of the congeners cannot be explained yet. Karlsson
et al. (1997a, b) concluded that U81 and U82 have a 5+3 chlorine distribution
between ring 2 and 1, while all other congeners are of the 6+2 (octa-chloro
congeners) or 6+3 type (nona-chloro congeners). The technical pesticide chlordane
has shown a significant synergism concerning artificial estrogenic effects together
with other pesticides such as dieldrin (Arnold et al. 1996; Arnold and McLachlan
1996; Ribeiro et al. 2009; Chighizola and Meroni 2012). This might be an explanation for the different ERs in male and female cod. However, this does not explain the
missing gender influence at herring. Other factors such as position in the food chain
and unlike enzyme systems can also be of importance.
The enantioselective analysis of organochlorines in the Arctic food chain “cod/
seal/polar bear” carried out by Wiberg et al. (1998a, b, c) also included the chlordane
congeners MC4, MC5 and MC6. The results are summarised in Fig. 8.15.
Similar to the situation encountered in the case of α-HCH, near-racemic ERs were
found in the cod tissue extracts. With regard to the octachlordane MC5, the second
eluting enantiomer became more abundant up the food chain. Different enantiomeric
prevalence was observed for MC4: while the first eluting enantiomer dominated in
blubber and liver of the ringed seal, the second eluting enantiomer was preferentially
found in the liver tissue extract of the polar bear. In the case of MC6, both in the
ringed seal and polar bear tissues the second eluting enantiomer was dominating. A
152
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants
earlier eluting enantiomer can be recognised.
Some of the separation problems encountered by Buser et al. with regard to
components of the technical chlordane mixture were overcome by Karlsson and
co-workers who used heptakis(2,3,6-O-tertbutyl-dimethylsilyl)-β-cyclodextrin as
chiral selector. The latter authors analysed Atlantic cod (Gadus morhua L.) samples
carrying out a very comprehensive study. Atlantic cod, on the winter migration from
the Barents Sea to the Lofoten Islands for spawning, was caught outside Kvaløya,
Tromsø (70
N, 17
E). Age, sex, size, as well as the maturation stage of the gonads,
were determined. Liver and gonads were weighted, and samples were taken including a portion of the filet. The extraction and clean-up procedure can be found in a
corresponding publication (Karlsson et al. 1997a, b).
As can be inferred from Tables 8.11 and 8.12, the enantiomeric ratios (ER; area of
(+)-/(À)-enantiomer or first eluting enantiomer divided by the second one] in
Atlantic cod deviate substantially from the racemic ratio. With a few exceptions,
the ER found in all three cod tissues are similar within the uncertainty of the method
(3–5%). This means that any tissue can be used for an ER determination. It is worth
noting that ER of the octa-chloro congener U82 was below one in cod and above one
in herring. No differences in the ERs between male and female herring were
observed. However, in all cod samples analysed by Karlsson et al., the ERs for
trans-chlordane and MC6 were very different between males and females. Enantiomer transformation was opposite in male and female cod leading to changes of the
ERs by a factor of 3–5. A similar but not so unequivocal trend was also obtained for
cis-chlordane. No gender difference was observed for U81 and U82. The differences
in the influence of sex on the ERs of the congeners cannot be explained yet. Karlsson
et al. (1997a, b) concluded that U81 and U82 have a 5+3 chlorine distribution
between ring 2 and 1, while all other congeners are of the 6+2 (octa-chloro
congeners) or 6+3 type (nona-chloro congeners). The technical pesticide chlordane
has shown a significant synergism concerning artificial estrogenic effects together
with other pesticides such as dieldrin (Arnold et al. 1996; Arnold and McLachlan
1996; Ribeiro et al. 2009; Chighizola and Meroni 2012). This might be an explanation for the different ERs in male and female cod. However, this does not explain the
missing gender influence at herring. Other factors such as position in the food chain
and unlike enzyme systems can also be of importance.
The enantioselective analysis of organochlorines in the Arctic food chain “cod/
seal/polar bear” carried out by Wiberg et al. (1998a, b, c) also included the chlordane
congeners MC4, MC5 and MC6. The results are summarised in Fig. 8.15.
Similar to the situation encountered in the case of α-HCH, near-racemic ERs were
found in the cod tissue extracts. With regard to the octachlordane MC5, the second
eluting enantiomer became more abundant up the food chain. Different enantiomeric
prevalence was observed for MC4: while the first eluting enantiomer dominated in
blubber and liver of the ringed seal, the second eluting enantiomer was preferentially
found in the liver tissue extract of the polar bear. In the case of MC6, both in the
ringed seal and polar bear tissues the second eluting enantiomer was dominating. A
152
8 Enantiomer-Specific Fate and Behaviour of Chiral Contaminants