Organohalogen concentrations and a gross and histologic ...

Conclusions and final assessments
Our results suggested a decrease in adipose tissue concentrations of organohalogens
in East Greenland polar bears from 1990 to 1999-2001. Two of the
biological effect parameters (FA and enlarged clitoris) did not indicate a link
to the relatively high levels of organohalogens. But there were indications of
a strong relationship between various organochlorines and skull mineral
composition which could reflect endocrine disruption. In liver- and renal
tissue, the histopathological changes were ascribed to age and infectious agents.
However, based on knowledge from wild marine mammals, humans
and controlled laboratory experiments, long-term exposure to organohalogen
compounds and mercury cannot be ruled out as co-factors.
The organohalogen levels measured in the subcutaneous adipose tissue from
the East Greenland polar bears colleced 1999-2001 did not tell us anything
about the exposure in different life stages (foetus, cub, adult and old) by
each individual but gave us a level at time of sampling. Furthermore, we do
not know the quantity of absorption, metabolism, mobilisation and excretion
which, subsequently, makes the evaluation of potential relations between
individual levels of contaminants and our potential effects in biological parameters
(FA, BMD and histopathology) difficult. In addition, the large variability
in the OC concentrations of adult females showed that OC lipid mobilization
from peripheral tissue (primary fat) during reproductive cycles
and associated conditions occurs and thereby impact on the results (e.g. Polischuk
et al. 1995, 2002).
Beside the uncertainty of the organohalogen concentrations to reflect the
exposure during critical stages of life the relation between organohalogen
concentrations and our biological effect parameters studied (FA, BMD and
histology) is influenced by many factors which we cannot control or correct
for. To get an overview, a theoretical model describing the events of interactions
between the parameters studied and extrinsic factors affecting the intrinsic
feedback-loops is shown in Fig. 10.
As viewed in Fig. 10, many uncontrolled factors influenced the study of
fluctuating asymmetry. Therefore we could not track the individual history
of the bears nor the decadal lag from critical exposure phase (in utero) to the
point of subadult or adult expression which we measured. Regarding the
relation between individual organohalogen concentrations in subcutaneous
adipose tissue and fluctuating asymmetry we did not have a OHC gradient
(dose-response-curve) to examine the changes in FA in e.g. non, low and
high exposed groups. The concurrent OC concentrations available from
1999-2001 do not reflect in utero (transgenerational) or neonatal exposure
which probably are the most important life stages in the development of
organohalogen induced FA (e.g. Siegel and Doyle 1975a-c, Doyle et al. 1977,
Siegel et al. 1977a-b, Beckmen et al. 1999, Ylitalo et al. 2001). It is not possible
to say whether the levels found in the present East Greenland polar bears
are high enouth to increase skull fluctuating asymmetry in the bears (a doseresponse,
case-control study is needed for such an investigation). It is not
possible to say whether there could be a potential association between FA
and the other effect parameters (BMD and histopathology) investigated.
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