Organohalogen concentrations and a gross and histologic ...

Individual levels and biological effect parameters
In conclusion, the large individual variability due to sex, age and season
makes group comparisons of individual organohalogen levels between degrees
of pathological changes within groups of bio-logical effect parameters,
difficult (FA, BMD and histology). The levels more or less reflect a “random”
subcutaneous adipose concentration due to unknown individual sex
(reproductive), age and season history. It would statistically and biologically
be easier to compare groups if the body burden levels simply accumulated
by age – as e.g. mercury in liver and kidney – which then could reflect the
total body burden without influence from age, sex and season. Another
complexity of the subcutaneous adipose tissue organohalogen content is the
unknown biological activity (toxicity) of the levels (more or less inactive
when deposited in the adipose but active when relased to the blood stream).
The levels of organohalogens and their metabolites in the liver and kidney
would perhaps be more useful in the present study. As discussed in the
introduction the activity of the metabolites in the bears is unknown although
these are known to covariate with the original compound (e.g. Sandala et al.
2004) and in addition to this is the unknown effect from synergism and antagonism
of the compounds.
In the Introduction Chapter we showed that the assumption for calculating a
rough estimate of the organohalogen exposure to East Greenland polar
bears, is based on the daily intake of known contaminated East Greenland
ringed seal blubber. During the period from 1999 to 2002, where the ringed
seal data are from, the bears must have been more or less equally exposed
per kg body weight (no 10- or 100-fold differences as in rat experiment
studies). But of course this calculation does not take into account that the
exposure prior to 1999 was significantly higher (which make the old bears
relatively more exposed compared to the subadults in our sample) and it
does not take into account the mobilisation during gestation and lactation –
which probably make adult females more susceptible to organohalogens as
discussed earlier. In addition we do not know the in utero exposure which
may be the most important in studies of organohalogen toxicity. Therefore,
when we investigate our effect parameters (FA, BMD and histology) in relation
to individual levels of organohalogens in adipose tissue, we compare
more or less random levels reflecting age, sex, season, metabolic capacity
and individual sensibility to organohalogens at sampling time. This has been
pointed out earlier by e.g. Pertoldi et al. (1997). The optimal way to find
cause and effect relation would be the use of a non exposed polar bear subpopulation
(or relevant top predator) to compare effect parameters between
groups instead of comparing individual East Greenland polar bears more or
less equally exposed. This difficulty will be discussed later in relation to FA,
BMD and histology.
In the present thesis, the individual levels of organohalogens from the present
Paper (∑-PCBs, ∑-DDTs, dieldrin, ∑-HCHs, ∑-CHLs and HCB) as well
as ∑-PBDEs, will be evaluated in relation to biological effect parameters (FA,
BMD and histopathology) of the individual bears. To our knowledge, this
has not previously been conducted on other Arctic mammals.
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