The Arctic at Risk:
A Circumpolar Atlas of Environmental Concerns

by Stephanie Pfirman, Kathleen Crane, Kim Kane, and Tania Simoncelli

Review Draft: Not for Citation

Heavy Metals

Metals occur naturally in the earth's crust and are introduced into the environment by weathering and other natural processes. In addition, human activities have also resulted in increased emissions of metals. Heavy metals include those whose atomic weight is greater than approximately 50. The nonessential metals, which include mercury, cadmium, and lead (presented here), are toxic to most organisms even at relatively low concentrations (Lockhart et al., 1992). Some metals also bioaccumulate in organisms, which can adversely affect the organism as well as people who consume it.

In the Arctic, there are both local and long-range sources of natural and anthropogenic metal contamination. Mining activities and releases from the Distant Early Warning (DEW) military sites in North America contribute to local pollution. Deposition of Arctic haze from the atmosphere contributes pollutants from distant sources. Toxic metals, introduced to the atmosphere by industrial processes, deposit in approximately equal amounts as wet and dry deposition (Galloway et al., 1982). Small particles and gases can be transported high in the troposphere (lower atmosphere), become incorporated into raindrops, and deposit as wet deposition (Galloway et al., 1982). Larger particles tend to deposit mostly as dry deposition. In regions with acidified rainfall or ambient conditions, naturally occurring metals may be leached from the soil and enter the terrestrial and aquatic ecosystems. Rivers draining contaminated watersheds introduce metals to coastal environments; rivers are generally the main source of metals in seawater. In addition, deposition from atmospheric Arctic haze onto the surface of sea ice results in metal concentrations that are as high as are found in snow near industrialized regions (Melnikov, 1992).

Once particular metals are introduced to the environment, their fate depends largely on the physical and chemical environment (e.g. pH and salinity), which affect their solubility in water and adsorption onto particles. Particles that metals are mainly associated with are clay minerals, iron and manganese oxi-hydroxides, and organic matter (Laane, 1992). As a result, muddy sediments tend to have higher contaminant levels than sandy sediments.

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