Organohalogen concentrations and a gross and histologic ...

temperature extremes and/or food availability (e.g. Siegel and Doyle 1975ac,
Doyle et al. 1977, Siegel et al. 1977a-b, Nilsson 1994, Carrascal et al. 1998).
Higher climatic fluctuations (against higher temperature) in the first period
(ca. 1930 and ca. 1960) could explain lower food availability and thereby a
higher degree of developmental instability in the polar bears compared to
the second period (Førland 2002). However, a temperature effect is not
likely, as temperatures above normal have been experienced in East Greenland
during the last two decades which should limit the food resources
(ringed seals) for the bears and thereby increase the FA (Ibid.).
FA and organohalogen levels
No clear pattern in the relationship between FA and individual level of organohalogens
was found probably due to the large individual variability in
contaminant levels, and because FA likely resulted from prenatal in utero
disruptions and therefore rather related to contaminant exposure at the time
of development than at the time of sampling. Few previous studies of
mammals have linked FA to organohalogen contaminant concentrations on
an individual by individual basis. Pertoldi et al. (1997) examined such correlations
(DDTs and PCBs) in the Eurasian otter (Lutra lutra), but did not
find a relationship between FA and individual contaminant burdens. The
authors explained the lack of correlation by the high individual variability of
organohalogens including seasonal patterns and sex differences which
probably also is the case of the East Greenland polar bear as discussed in
Chapter 1. In addition, individual sensitivity may reduce such a pattern
especially if the exposure range and number of examined individuals are
low.
To give an impression of the levels of Σ-PCBs and Σ-DDTs in the present
bears compared to levels in populations of marine mammals where period
differences (non polluted and polluted respectively) were found in FA
(skulls) and linked to organohalogen exposure, these are compared in Table
3. For Σ-PCBs, the levels in the polar bears were comparable to the lower
levels of the Kattegat harbour seal before 1988, where effects on the FA was
documented, while for Σ-DDTs the level was 2-10 times lower and it could
therefore be suspected that the threshold of FA was not reached in the bears
(subeffect exposure) (Blomkvist et al. 1992; Schandorff 1997a,b; Zakharov
and Yablokov 1990). For the grey seals the differences were even larger.
Which compounds cause FA has not been documented to date.
Table 3
Range in levels of ∑-PCBs and ∑-DDTs in the blubber (µg/g l.w.) believed to cause FA in juvenile,
subadult and adult Kattegat harbour seals (Phoca vitulina) and Baltic grey seals (Halichoerus
grypus) populations from before and around 1988 compared to the East Greenland polar
bears in the present study. n: number of observations (data from: Blomkvist et al. 1992; Schandorff
1997a,b and Zakharov and Yablokov 1990).
Study Compound
n Concentration Range in East Greenland polar
bear adipose tissue (n)
Kattegat harbour seal ∑-PCBs 38 6-110 1-20 (77)
Kattegat harbour seal ∑-DDTs 38 2.0-13 0.1-1.1 (77)
Baltic grey seal ∑-PCBs 37 32-5300 1-20 (77)
Baltic grey seal ∑-DDTs 37 11.0-1600 0.1-1.1 (77)
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