Dietz, R. 2008: Contaminants in Marine Mammals in <st1:place w:st="on">Greenland</st1:place> – with linkages to trophic levels, effects, diseases and distribution. Doctor’s dissertation (DSc). National Environmental Research Institute, <st1:place w:st="on"><st1:City w:st="on">University of Aarhus</st1:City> , <st1:country-region w:st="on">Denmark</st1:country-region></st1:place> . 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 <st1:place w:st="on">Greenland</st1:place> 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 <st1:place w:st="on">Greenland</st1:place> 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 <st1:place w:st="on">Greenland</st1:place> 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.
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