Organohalogen concentrations and a gross and histologic ...

Discussion
Geographical Variation in OC Concentrations
Norstrom et al. (1998) conducted a study of geographical trends in OC concentrations
(ΣCBs (16 congeners), p,p’-DDE, ΣCHL (11 compounds) and dieldrin)
in polar bears around 1990 (samples taken during the period 1989-1993),
in which 320 adult bears (5 years of age and older) were sampled from 16
different Arctic locations and analysed within a single laboratory. The highest
concentrations were found in bears from Eastern Greenland and in the European
Arctic. Concentrations in samples from Canadian locations were intermediate
and those in Alaskan polar bears were the lowest observed. Later
studies by Andersen et al. (2001) and Lie et al. (2002) have shown that polar
bears from Franz Josef Land and the Kara Sea areas of the western Russian
Arctic had even higher concentrations of ΣCBs and organochlorine pesticides
than those in the Norstrom study. These later studies included data for bears
from Svalbard, the Siberian and the Chukchi seas that decreased in the order
mentioned. Recent data for CBs (29 congeners), HCHs, CHLs and CHL metabolites,
HCB and DDT and metabolites in polar bears from Barrow, Alaska
have confirmed that OC concentrations in polar bears from this area are
among the lowest in the Arctic (Kucklick et al., 2002).
The geographical trend described earlier has been confirmed by the more
recent data. The ΣCB concentrations in adult female polar bears within the
present study (mean of 8238 ng/g lw) were considerably higher than the
recent 1997-1999 data from Hudson Bay, varying between 2000-3000 ng/g
lw (Norstrom 2001; Fisk et al., 2003), even though a clear decrease had taken
place during the last ten years. The ΣDDT concentrations in adult female
polar bears from East Greenland (EG) (mean of 462 ng/g lw) are also higher
than those in animals from Hudson Bay (HB) where average concentrations
of 200 ng/g lw in adipose tissue were reported for 1997-1999, and in 2002
(Letcher et al. unpublished data). There were smaller differences between
East Greenland and Hudson Bay for ΣCHLs (mean concentrations EG: 2220
ng/g lw; HB: 1700-1800 ng/g lw) and ΣCBzs (mean concentrations EG: 100
ng/g lw; HCB: 60-70 ng/g lw).
OC Concentrations in Relation to Sex, Age and Season
Adult males were highest in ΣPCBs, ΣCBzs, ΣDDTs, mirex and dieldrin and
lowest in ΣCHLs. However, only S-CBzs were found to be significantly different.
Similar patterns have been found by e.g. Norstrom (1998), who also
found that concentrations of ΣCBs were significantly higher, but those of
ΣCHLs lower, in adult males than in adult females. The most probable explanation
for the lower concentrations in females are the transference of
many OC compounds both transplacentally to the foetus and to the cubs
during suckling (e.g. Polischuk et al., 1995, 2002; Bernhoft et al., 1997; Norstrom
et al., 1998). The lower concentrations of e.g. ΣCHLs in males are
harder to explain, but Polischuk et al. (2002) and Derocher et al. (2003) suggested
that sex-specific CHL metabolism was a possible factor in malefemale
differences. Norstrom et al. (1998) mentioned sex specific dietary
differences, the presence of a male specific CYP-enzyme, or the induction of
hepatic CYP2B enzyme protein concentrations in liver increasing the degradation
rate and so resulting in faster ΣCHLs clearance metabolism in males
as possible explanations. Letcher et al. (1996) showed that ΣCHL concentrations
in the liver of polar bear from Resolute Bay were strongly correlated
with immunologically quantified levels of CYP2B enzyme protein. In other
83