Mercury is a naturally occurring element found in rocks, soil, water, and air. However, air currents transport mercury from human-caused sources such as burning coal, mining, and the burning of waste. These sources have greatly increased the amount of mercury cycling in the environment. In contrast to other pollutants such as ozone and particulate matter, mercury is usually not present in high enough concentrations in the air to present health risks associated with breathing. Rather, the risks to humans and wildlife come from the cumulative effects of eating large amounts of fish or other animals which have accumulated high levels of toxic mercury over time.
Research has found mercury in fish, vegetation, snow, and lake sediments in Glacier National Park. Once mercury is deposited in water, bacteria convert inorganic mercury into toxic methylmercury which then accumulates in fish and other aquatic organisms. Mercury in fish is the primary route of exposure for people and fish-eating wildlife. Accumulation of methylmercury can lead to reduced reproductive success, impaired growth and development, and decreased survival.
Mercury deposition monitoring has been ongoing in Glacier since 2003. Although health risks from eating fish are relatively low, consumption guidelines recommend eating smaller, younger fish which have had less time to accumulate contaminants.