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Is dietary mercury of neurotoxicological concern to wild polar bears (Ursus maritimus)?

Authors

  • Niladri Basu,

    Corresponding author
    1. Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, Michigan 48109, USA
    • Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, Michigan 48109, USA
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  • Anton M. Scheuhammer,

    1. Wildlife and Landscape Science Directorate, National Wildlife Research Centre, Environment Canada, Carleton University, Ottawa, Ontario K1A 0H3, Canada
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  • Christian Sonne,

    1. Section of Contaminants and Marine Mammals, Department of Arctic Environment, National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, PO Box 358, DK-4000 Roskilde, Denmark
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  • Robert J. Letcher,

    1. Wildlife and Landscape Science Directorate, National Wildlife Research Centre, Environment Canada, Carleton University, Ottawa, Ontario K1A 0H3, Canada
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  • Erik W. Born,

    1. Greenland Institute of Natural Resources, PO Box 570, DK-3900 Nuuk, Greenland, Denmark
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  • Rune Dietz

    1. Section of Contaminants and Marine Mammals, Department of Arctic Environment, National Environmental Research Institute, University of Aarhus, Frederiksborgvej 399, PO Box 358, DK-4000 Roskilde, Denmark
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  • Published on the Web 8/21/2008.

Abstract

Polar bears (Ursus maritimus) are exposed to high concentrations of mercury because they are apex predators in the Arctic ecosystem. Although mercury is a potent neurotoxic heavy metal, it is not known whether current exposures are of neurotoxicological concern to polar bears. We tested the hypotheses that polar bears accumulate levels of mercury in their brains that exceed the estimated lowest observable adverse effect level (20 μg/g dry wt) for mammalian wildlife and that such exposures are associated with subtle neurological damage, as determined by measuring neurochemical biomarkers previously shown to be disrupted by mercury in other high-trophic wildlife. Brain stem (medulla oblongata) tissues from 82 polar bears subsistence hunted in East Greenland were studied. Despite surprisingly low levels of mercury in the brain stem region (total mercury = 0.36 ±0.12 μg/g dry wt), a significant negative correlation was measured between N-methyl-D-aspartate (NMDA) receptor levels and both total mercury (r = —0.34, p < 0.01) and methylmercury (r = —0.89, p < 0.05). No relationships were observed among mercury, selenium, and several other neurochemical biomarkers (dopamine-2, gamma-aminobutyric acid type A, muscarinic cholinergic, and nicotinic cholinergic receptors; cholinesterase and monoamine oxidase enzymes). These data show that East Greenland polar bears do not accumulate high levels of mercury in their brain stems. However, decreased levels of NMDA receptors could be one of the most sensitive indicators of mercury's subclinical and early effects.

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