0.22 demonstrating also here that the (À)-trans-chlordane was the most abundant
enantiomer. For the distribution of oxy-chlordane and B9-1679 enantiomers, no
species-dependent differences were found. For all species, ER values between 0.3
and 0.8 were determined. Thus, also for oxychlordane and B9-1679, the (À)enantiomers are the most dominating stereoisomers in the birds of prey eggs
analysed.
The transformation pathways of Toxaphene
®
-related compounds are still under
investigation. Vetter et al. performed a series of experiments on the elimination
profile and transformation pathways of selected chlorobornanes (Vetter et al.
2001a, b). The authors followed the enantiomeric change for 2-exo,3-endo,6exo,8,9,10-hexachlorobornane (B6-923) in naturally contaminated fish maintained
under toxaphene-free conditions. A GC/MS method with a CSP consisting of 25%
tert-butyldimethylsilylated β-cyclodextrin in PS086 (β-BSCD) was applied.
Whereas the enantiomeric ratio (ER) of B6-923 was near racemic at the start of
the elimination experiment, it had increased several fold by the end of 60 days.
Estimated as first-order kinetics reaction, (+)-B6-923 was eliminated twice as fast as
its mirror image, resulting in half-lives of 7 and 13 days, respectively. These results
suggest that the more or less stable ERs observed for many chiral organochlorines in
higher organisms are the result of competing processes as illustrated here for
uptake vs. elimination of chlorobornanes (steady state). As a follow-up study on
the elimination and transformation pathways, Maruya and co-workers studied the
temperature dependence of Toxaphene
® elimination in caged and exposed fish
(Maruya et al. 2005). Congener- and enantiomer-specific toxaphene residues were
monitored in Fundulus heteroclitus. A previous study performed under warm water
conditions (T mean ¼ 25
C) demonstrated relatively rapid (t (1/2) of ca. 7–14 days) and
enantioselective elimination of the reductive dechlorination metabolites 2-exo,3endo,6-exo,8,9,-10-hexachlorobornane (B6-923 or Hx-Sed) and 2-endo,3-exo,5endo,6-exo,8,9,10-heptachlorobornane (B7-1001 or Hp-Sed). As expected, repetition of this experiment at cooler water temperatures (Tmean ¼ 15
C) resulted in a
decrease in overall (i.e. both enantiomers) first-order elimination rate constants.
Enantiomer fractions or ratios (EFs/ERs) during elimination, however, varied by
congener, ranging from racemic for very rapidly eliminated C l5 homologues to
increasingly non-racemic for selected Cl 6 –Cl 8 homologues (including 86-923, several unknown Cl 7 compounds, B8-1414 and B8-1945). As a result, we propose a
classification to describe the environmental persistence of chiral Toxaphene
® pollutants based on congener-specific elimination kinetics and susceptibility to biotransformation as measured by EFs/ERs.
8.2.3 Chiral Organochlorines in Soils and Ambient Air
In this section, the focus will be directed to investigations aiming at transformation
and accumulation of chiral pollutants in soils. Furthermore, the aspect of transport
processes between soil and air will be discussed. With regard to the problem related
to “chirality and crop protection”, the reader should refer to the comprehensive
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
187
enantiomer. For the distribution of oxy-chlordane and B9-1679 enantiomers, no
species-dependent differences were found. For all species, ER values between 0.3
and 0.8 were determined. Thus, also for oxychlordane and B9-1679, the (À)enantiomers are the most dominating stereoisomers in the birds of prey eggs
analysed.
The transformation pathways of Toxaphene
®
-related compounds are still under
investigation. Vetter et al. performed a series of experiments on the elimination
profile and transformation pathways of selected chlorobornanes (Vetter et al.
2001a, b). The authors followed the enantiomeric change for 2-exo,3-endo,6exo,8,9,10-hexachlorobornane (B6-923) in naturally contaminated fish maintained
under toxaphene-free conditions. A GC/MS method with a CSP consisting of 25%
tert-butyldimethylsilylated β-cyclodextrin in PS086 (β-BSCD) was applied.
Whereas the enantiomeric ratio (ER) of B6-923 was near racemic at the start of
the elimination experiment, it had increased several fold by the end of 60 days.
Estimated as first-order kinetics reaction, (+)-B6-923 was eliminated twice as fast as
its mirror image, resulting in half-lives of 7 and 13 days, respectively. These results
suggest that the more or less stable ERs observed for many chiral organochlorines in
higher organisms are the result of competing processes as illustrated here for
uptake vs. elimination of chlorobornanes (steady state). As a follow-up study on
the elimination and transformation pathways, Maruya and co-workers studied the
temperature dependence of Toxaphene
® elimination in caged and exposed fish
(Maruya et al. 2005). Congener- and enantiomer-specific toxaphene residues were
monitored in Fundulus heteroclitus. A previous study performed under warm water
conditions (T mean ¼ 25
C) demonstrated relatively rapid (t (1/2) of ca. 7–14 days) and
enantioselective elimination of the reductive dechlorination metabolites 2-exo,3endo,6-exo,8,9,-10-hexachlorobornane (B6-923 or Hx-Sed) and 2-endo,3-exo,5endo,6-exo,8,9,10-heptachlorobornane (B7-1001 or Hp-Sed). As expected, repetition of this experiment at cooler water temperatures (Tmean ¼ 15
C) resulted in a
decrease in overall (i.e. both enantiomers) first-order elimination rate constants.
Enantiomer fractions or ratios (EFs/ERs) during elimination, however, varied by
congener, ranging from racemic for very rapidly eliminated C l5 homologues to
increasingly non-racemic for selected Cl 6 –Cl 8 homologues (including 86-923, several unknown Cl 7 compounds, B8-1414 and B8-1945). As a result, we propose a
classification to describe the environmental persistence of chiral Toxaphene
® pollutants based on congener-specific elimination kinetics and susceptibility to biotransformation as measured by EFs/ERs.
8.2.3 Chiral Organochlorines in Soils and Ambient Air
In this section, the focus will be directed to investigations aiming at transformation
and accumulation of chiral pollutants in soils. Furthermore, the aspect of transport
processes between soil and air will be discussed. With regard to the problem related
to “chirality and crop protection”, the reader should refer to the comprehensive
8.2 Transformation/Accumulation of Chiral Xenobiotics in Higher Organisms
187