Dietz, R. 2008: Contaminants in Marine Mammals in Greenland – with linkages to
trophic levels, effects, diseases and distribution. Doctor’s dissertation (DSc). National
Environmental Research Institute, University of Aarhus, Denmark. 120 pp + 30
articles.
Summary
The present dissertation provides a review of key determining parameters (age, sex, season, food and climate),
trends (geographic and temporal), bioaccumulation, human exposure and effects of contaminants in top predators
in the Greenland marine ecosystem. Furthermore, the dissertation links the contaminant issue to marine mammal
distribution and stock separations monitored mainly by satellite telemetry. The review and conclusions are based
on 30 key publications as well as selected supporting literature.
Setting the stage
The Arctic has previously been regarded a pristine environment. It is a region with limited industry, almost no
agriculture and only a few local areas where some organohalogenated compounds (OHCs) have been used for
pest control. However, during the 1970s and 80s it became evident that contaminants such as heavy metals and
OHCs were present in significant concentrations in the higher trop-hic levels of marine ecosystems and in Inuit
populations that use them for food. Since then, a substantial effort has been addressed to resolve the contaminant
questions relating to origins, transport, geographical and temporal trends as well as toxicity and biological effects.
The Arctic has become an important place to study contaminants, well suited for the study of chemical
persistence, bioaccumulating and biomagnificating properties, long-range transport and adverse effects that are
important criteria identified under international agreements and Conventions aimed at regulating OHCs or
persistent organic pollutants (POPs).
The focus area
Some of the highest human exposure levels to persistent toxic contaminants are found in the Arctic. This is due to
the long-range transport of contaminants to the region, long marine food chains that include slow-growing
species, and the fact that marine mammal predators at the top of these food-chains constitute an important part of
the Inuit consumer’s food intake. In addition, the focus on the Greenland ecosystem is of major importance as the
Greenland Inuit population were found to have the highest exposures of any people in the Arctic when it comes to
Hg, PCB, DDE, oxychlordane and toxaphene. Diets including marine mammals were identified as the major
source of the contaminant exposure to the Greenlanders and other Arctic populations. Therefore, the marine
environment, and in particular species at the higher trophic levels, such as certain marine mammals, including
polar bears, became a focus of my work over the past years, and therefore also the subject of this dissertation. Data
are also presented for lower trophic levels that were part of the screening of the entire eco-system and provide
information that explains where the exposures are the highest.
Structure of the dissertation
This dissertation addresses three main topics: 1) Marine contaminant loads, 2) Contaminants related pathological
effects and diseases, and 3) Marine mammal migration and stock separations.
Conclusions
The main conclusions are:
(i) Basic parameters such as age and sex of the animal, tissue type, season of collection, affect contaminant loads. It
was documented that older animals tend to have higher concentrations of Hg and Cd and for some OHC groups
adult males tend to have the higher concentrations in the Greenland marine ecosystem. Mercury concentrations
are highest in liver, Cd is highest in kidney and OHC are highest in adipose tissue or liver. Seasonal differences
may in some cases be substantial and should be taken into account in geographical and temporal trend
comparisons.
(ii) Ecosystems, differences in trophic le-vel, bioaccumulation and climatic differences will have an affect on
contaminant loads. Due to the longer food chains and hence higher trophic position of most marine top predators,
Hg, Cd and OHC loads are higher than those found in the terrestrial ecosystem. There is clear evidence of
bioaccumulation of Hg, OHCs, and to certain extent Cd throughout the Arctic marine food chain. Differences in
trophic level of food, which can also be associated with climatic change or variability, is important information
that needs to be taken into account in geographical and temporal trend comparisons, and predictions of future
trends.
(iii) Geographical patterns can be detected in contaminant loads within Greenland and other Arctic marine
mammal populations. Northwest Greenland and the central Canadian Arctic have the highest concentrations of
Hg; Central West Greenland and Northwest Greenland have the highest concentrations of Cd; while East
Greenland together with Svalbard and still further east the Kara Sea have the highest loads of most lipophilic
OHCs. This information provides an indication of where possible effects of contaminants due to high levels are
most likely to occur, and where the lowest exposed animals for use as reference groups may be found.
(iv) Temporal trends in contaminant loads are detectable in key species in the Greenland ecosystem. Long-term
studies in appropriate media reveal increases of Hg with a substantial anthropogenic contribution. These increases
appear to be continuing in Northwest Greenland and the Central Canadian Arctic. Mercury levels east of
Greenland and levels of “legacy OHCs”, such as PCBs, DDTs, HCHs, HCB, chlordanes, dieldrin, and coplanar
PCBs are showing declines. Time series on toxaphene, PCDDs and PCDFs are more uncertain, but may be
decreasing. Increases in concentrations of a number of “new” OHCs such as the PBDEs and the PFCs took place
prior to the turn of the millennium in the entire Arctic. PFCs continue to increase in Greenland, but there is some
evidence that in recent years, PFCs and PBDEs may have decreased again in some areas.
(v) The most highly exposed groups in the Arctic ecosystem, the top-level carnivores, are affected by
contaminants. Mercury levels are high enough to cause effects in some top predators. Neuropsychological
dysfunction in humans and the first histopathological and neuro-chemical receptor biomarker investigations
indicate effects of Hg, but these are subtle effects and more investigations are needed. Selenium, being present in
surplus in the Arctic marine ecosystem, is likely to reduce the effect of Hg. Although Cd concentration in several
marine species is above threshold levels for effects, Cd has not yet been shown to cause effects in Arctic wildlife.
Examples of effects from high exposure to OHC include reduced size of reproductive organs, tissue alterations
found in liver and kidney, reduction of bone mineral density, and impairment of the immune system. However,
no linkage could be documented between contaminant exposure and pseudohermaphroditism, immunological
response and skull pathology in East Greenland polar bears. Skull asymmetry showed linkages to contaminants in
only some of the investigations. In well defined mass mortality events, such as the two PDV outbreaks in recent
years, it has not been possible to make a clear linkage between contaminants, immune suppression and the
number of deaths caused by the disease. A large number of confounding factors can play a significant role for such
disease events.
(vi) The Inuit population can minimize their contaminant intake and risk of health problems by reducing their
intake of internal organs (Hg, Cd, PBDEs and PFCs), adipose tissue (OHCs), and preferential consumption of
lower trophic species. Intake of young animals will result in lower Cd and Hg and in some cases OHC exposure.
For OHCs adult females will be less polluted compared to adult males. At the same time, these foods are sources
of important nutrients and changes in diet can bring other health risks.
(vii) Marine mammal distribution is of major importance in planning contaminant studies and in interpreting
results of such studies. In some regions contaminant samp-les and samples for investigation of effect parameters
can only be obtained during tagging operations. Satellite tagging together with contaminant analysis in samples
from the same animals has the potential for linking contaminant levels with dispersal, behaviour and possible
effects on the tagged animals. In cases where tagging has proven difficult to conduct, genetics and contaminants
analyses can be used to elucidate population relationships.