Mercury contamination poses a significant environmental and health challenge, particularly for Inuit communities residing in the Arctic. This issue arises from the unique pathways mercury takes to reach northern latitudes and its subsequent accumulation within Arctic ecosystems, impacting human populations who rely on traditional food sources.
Mercury’s Global Journey to the Arctic
Mercury is released into the atmosphere from both natural and human-caused sources, subsequently traveling globally. Natural emissions stem from volcanic eruptions and the weathering of rocks, while human activities, such as coal combustion, mining, and industrial processes, significantly increase its presence in the environment. For instance, the burning of fossil fuels, particularly coal, is a major contributor. Estimated global anthropogenic mercury emissions to the atmosphere were approximately 2220 metric tons per year in 2015, marking a 20% increase from 2010 levels.
Once emitted, elemental gaseous mercury can remain in the atmosphere for about one year, allowing for long-range transport across continents. Atmospheric and oceanic currents facilitate its movement from industrialized regions, such as East Asia, Europe, and North America, towards the poles. The Arctic acts as a sink for these pollutants due to atmospheric deposition, where mercury eventually settles from the air onto land and water surfaces, including snow and ice.
Bioaccumulation and Biomagnification in Arctic Food Webs
Upon reaching aquatic environments in the Arctic, inorganic mercury undergoes a transformation into methylmercury. This process is primarily carried out by microorganisms in sediments of lakes, oceans, and wetlands. Methylmercury is a neurotoxin and is the most bioavailable and harmful form of mercury, readily entering the food web.
The entry of methylmercury into the food web involves two distinct processes: bioaccumulation and biomagnification. Bioaccumulation describes the build-up of a substance, such as methylmercury, within an individual organism over its lifetime as it takes in more than it excretes. Biomagnification, in contrast, refers to the increasing concentration of a substance at successive trophic levels in a food chain. As larger organisms consume many smaller organisms, the methylmercury becomes more concentrated in their tissues.
Arctic food webs demonstrate this biomagnification clearly. Small fish and invertebrates at lower trophic levels accumulate methylmercury from their environment. When these are consumed by larger predators, such as ringed seals or Arctic char, the mercury concentration in the predator’s tissues increases. Top predators, including polar bears and toothed whales like belugas, can exhibit some of the highest concentrations of methylmercury due to their position at the apex of the food chain.
Dietary Exposure and Inuit Vulnerability
The elevated levels of methylmercury in Arctic wildlife directly impact human communities, particularly the Inuit, whose traditional diet relies heavily on marine mammals and fish. This diet, often referred to as “country food,” provides essential nutrients and is central to Inuit culture and subsistence. However, many of these traditional food sources, being high on the Arctic food chain, contain elevated levels of methylmercury due to the process of biomagnification.
Species such as beluga whales, seals (including ringed seals), and certain fish accumulate significant amounts of methylmercury in their tissues. For instance, beluga muktuk and ringed seal liver have been identified as major dietary sources of mercury for Inuit children in Nunavut. Inuit communities can have some of the highest dietary mercury intakes globally. In some cases, mean estimated mercury intake has exceeded recommended guidelines, with a notable percentage of the population above the safety threshold.
This reliance on traditional foods, while culturally and nutritionally beneficial, inadvertently places Inuit communities at a higher risk of mercury exposure. The unique dietary patterns mean that mercury exposure levels in Inuit populations are often higher compared to those in southern regions. Studies have indicated that mercury levels in some Inuit populations are among the highest worldwide, with concentrations in blood samples often exceeding international health guidelines.
Climate Change’s Role in Mercury Dynamics
Climate change is increasingly influencing the dynamics of mercury in the Arctic, potentially exacerbating the existing contamination problem. One significant mechanism is the thawing of permafrost, which stores substantial amounts of mercury accumulated over thousands of years. As permafrost melts, this previously frozen mercury can be released into rivers, lakes, and coastal waters. This release increases the amount of mercury available for methylation, enhancing its entry into the food web.
Changes in ocean currents, driven by a warming climate, can also affect mercury transport and distribution within the Arctic marine environment. Altered currents may redistribute mercury-laden waters or influence the upwelling of mercury from deeper ocean layers. Reductions in Arctic sea ice cover also play a role in mercury cycling. Less ice allows for greater exposure of surface waters to sunlight and the atmosphere, which can influence both the deposition of atmospheric mercury and the processes of methylation and demethylation.
Warmer temperatures associated with climate change may also enhance methylmercury production in ocean and lake sediments, as well as in tundra soils. The increased bioavailability of mercury due to these climate-driven changes can intensify the mercury problem for Arctic ecosystems and the Inuit population.