PCB-related exposure and effects in ringed seals (Pusa hispida) frequenting a locally-contaminated marine environment in Labrador




Brown, Tanya

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The release of 260 kg of polychlorinated biphenyls (PCBs) by a military radar station into Saglek Bay (Labrador) in the eastern Canadian Arctic contaminated adjacent marine sediments, and some fish, seabirds, and ringed seals. However, attributing the PCBs found in high trophic level and highly mobile marine mammals to any point source is, in most cases, impossible. This thesis demonstrated the extent to which a local PCB source at Saglek Bay led to the contamination and health effects in ringed seals. The dominance of PCBs at this contaminated marine site afforded a unique opportunity to evaluate the effects of this single class of industrial chemical in a manner that has not been previously possible in marine mammals. We used a variety of tools to characterize the contribution of local PCB contamination in the Labrador ringed seal food web. These tools included: 1) univariate and multivariate statistical exploration of contaminant patterns; 2) stable isotope ratios and fatty acid signatures to describe feeding ecology; and 3) satellite telemetry to track the movements of seals on the coast. Divergent PCB congener profiles and contaminant ratios enabled an assignment of seals into either ‘local’ or ‘long-range’ categories, with up to 60% of ringed seals sampled exhibiting patterns consistent with the local source. PCB concentrations in locally-contaminated adult males were 2-fold higher than in those exposed only to long-range PCB sources. Seals with smaller home ranges had an increased likelihood of feeding on prey contaminated by the local PCB source. Similar fatty acid profiles between those seals with ‘local’ PCB profiles and those with ‘long-range’ or background profiles indicate little support for the possibility that differential feeding ecologies explained the divergent PCB profiles. Ringed seals fed predominantly on zooplankton (Mysis oculata and Themisto libellula), dusky snailfish (Liparis gibbus) and arctic cod (Boreogadus saida). Heavier PCB profiles in the Saglek food web, compared to the same species exposed to only background contaminants, provided additional insight into the mechanisms of localized PCB contamination of some Labrador ringed seals. In addition to ascertaining the importance of a point source to contamination in ringed seals, we assessed the effects of PCBs on their health through quantitative real-time polymerase chain reaction (qPCR) assay. Levels of mRNA transcripts for five gene targets, including aryl hydrocarbon receptor (Ahr), interleukin-1 beta (Il1b), estrogen receptor alpha (Esr1), insulin-like growth factor receptor 1 (Igf1) and glucocorticoid receptor alpha (Nr3c1), correlated with increasing levels of PCBs, indicating an effect of this persistent organic pollutant (POP) in these seals. Threshold values were calculated for these five genes, with the most conservative value being 1,380 ng/g lipid weight (lw). Approximately 14% of the seals sampled exceeded this threshold, suggesting a risk of adverse effects in a proportion of the local population attributed to PCBs. While the implications for these sublethal molecular changes at the individual or population level are unclear, contaminant-related changes in endocrine, immune, and molecular endpoints have been observed in ringed seals from the Baltic Sea exhibiting reproductive and developments abnormalities, and virus epizootics. Results of this study improve our understanding of the effects of PCBs in free-ranging marine mammals and provide new information needed to inform mitigation and monitoring efforts, both for ringed seals in the north and other seals around the world.



polychlorinated biphenyls, diet, ringed seal, Pusa hispida, fatty acids, Labrador, satellite telemetry, habitat use, marine mammals, gene expression