Arctic and Subarctic Bears' Exposure to Toxins

Mercury levels in brown bears was highest in those that relied on marine foods--such as salmon. Mercury levels decreased in older bears, likely due to their inability to compete with younger bears for prime fishing locations.

New research, conducted by Scandinavian and National Park Service scientists, reveals that levels of contaminants, such as arsenic, cadmium, mercury, and lead, in brown bears are related to what they eat and how old they are. Mercury was highest in populations and individuals that rely upon marine (ocean) resources like salmon.

The researchers thought that lead levels might be highest in Scandinavian bears, where bears feed on moose carcasses left behind by hunters who use lead ammunition. While Scandinavian bears did have the highest levels, bears in Gates of the Arctic National Park and Preserve--far from heavy moose-hunting pressure, also had high levels of lead in their blood.

Further investigation showed that bears that rely more upon terrestrial food sources, like vegetation and moose, had greater levels of lead and cadmium. Lead, cadmium, and arsenic all increased in older female bears, suggesting (bio) accumulation of these contaminants. In both male and female bears, mercury levels decreased in old bears. The researchers suspect that this is due to older bears not being able to compete with prime-age bears for key salmon fishing locations. The article concludes that anthropogenic emissions are a likely source of contaminants and that baseline knowledge concerning heavy metal concentrations is important in the face of increasing tourism, mining, and climate change.

Highlights from this article: (1) heavy metal emissions are distributed globally; (2) brown bears feeding on berries and insects are exposed to lead and cadmium; (3) bears that feed on salmon are exposed to mercury; (4) nature preserves do not protect bears from heavy metal contaminant exposure.

Environmental Research

Toxic elements in arctic and sub-arctic brown bears: Blood concentrations of As, Cd, Hg and Pb in relation to diet, age, and human footprint

Abstract

Contamination with arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) is a global concern impairing resilience of organisms and ecosystems. Proximity to emission sources increases exposure risk but remoteness does not alleviate it. These toxic elements are transported in atmospheric and oceanic pathways and accumulate in organisms. Mercury accumulates in higher trophic levels. Brown bears (Ursus arctos), which often live in remote areas, are long-lived omnivores, feeding on salmon (Oncorhynchus spp.) and berries (Vaccinium spp.), resources also consumed by humans.

We measured blood concentrations of As, Cd, Hg and Pb in bears (n = 72) four years and older in Scandinavia and three national parks in Alaska, USA (Lake Clark, Katmai and Gates of the Arctic) using high-resolution, inductively-coupled plasma sector field mass spectrometry. Age and sex of the bears, as well as the typical population level diet was associated with blood element concentrations using generalized linear regression models.

Alaskan bears consuming salmon had higher Hg blood concentrations compared to Scandinavian bears feeding on berries, ants (Formica spp.) and moose (Alces). Cadmium and Pb blood concentrations were higher in Scandinavian bears than in Alaskan bears. Bears using marine food sources, in addition to salmon in Katmai, had higher As blood concentrations than bears in Scandinavia. Blood concentrations of Cd and Pb, as well as for As in female bears increased with age. Arsenic in males and Hg concentrations decreased with age.

We detected elevated levels of toxic elements in bears from landscapes that are among the most pristine on the planet. Sources are unknown but anthropogenic emissions are most likely involved. All study areas face upcoming change: Increasing tourism and mining in Alaska and more intensive forestry in Scandinavia, combined with global climate change in both regions. Baseline contaminant concentrations as presented here are important knowledge in our changing world.

Fuchs, B., K. Joly, G. V. Hilderbrand, A. L. Evans, I. Rodushkin, L. S. Mangipane, B. A. Mangipane, D. D. Gustine, A. Zedrosser, L. Brown, and J. M. Arnemo. 2023. Toxic elements in arctic and sub-arctic brown bears: Blood concentrations of As, Cd, Hg and Pb in relation to diet, age, and human footprint. Environmental Research 229: 115952.