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Effects of Air Toxics/Mercury on Ecosystems

Mercury, pesticides, and other air toxics threaten the natural resources the National Park Service is specifically charged with protecting. The major sources of air toxics in many national park ecosystems are emissions from coal-burning power plants, industrial facilities, and agriculture, which can be transported in the atmosphere for hundreds of miles and deposited in park ecosystems. Research and monitoring efforts across the 84 million acres represented by national parks include assessments of mercury, pesticides and other toxic compounds in insects, amphibians, fish, birds, water, sediment, snow, air, vegetation, and wildlife.

  • Basics
  • Processes
  • Toxic Impacts
  • Monitoring Air Toxics/Mercury
  • Resources

Why is NPS concerned about mercury & toxics?

Photo of a Florida panther at Everglades NP, Florida.
High mercury levels have been found in endangered Florida panthers (Puma concolor coryi) in Everglades NP, Florida.

The National Park Service is concerned about toxic air contaminants including pesticides and mercury due to their harmful effects on wildlife and human health. Such contaminants are transported to national parks by air currents from sources as far away as Europe and Asia, and as near as the local county. These contaminants have the potential to cause ecosystem impairment in national parks because the compounds are long-lasting, can accumulate in biological tissue of organisms, and may alter key ecosystem processes.

Anthropogenic sources of mercury in the atmosphere include the burning of coal in coal-fired power plants, hazardous waste incinerators, utility and industrial boilers, smelting, chlor-alkali plants, and gold extraction, as well as from uses of fungicides containing mercury in latex paints and the paper and pulp industry.

In contrast to other pollutants such as ozone and particulate matter, mercury and toxics are not usually present in high enough concentrations in the air to present health risks by breathing in these compounds. Rather, the risks to humans and wildlife come from the cumulative effects of eating large amounts of fish or other biota which has accumulated high levels of toxics over time. Toxic compounds that have been documented in national parks at concentrations above “concern thresholds” for fish, birds, or humans include industrial by-products such as PCBs; agricultural herbicides and insecticides such as DDT, dieldrin, endosulfans; and mercury.

What does mercury accumulate in organisms?

Photo of a Florida panther at Everglades NP, Florida.
Mercury has been detected in food webs from remote places such as Noatak National Preserve in Alaska.

Toxic air contaminants such as pesticides, PCBs, flame retardants (PBDEs), and other industrial or combustion by-products are generally manmade compounds that are emitted to the atmosphere through application methods, volatilization from or disturbance of contaminated soils, and manufacturing or combustion processes. Once airborne, these toxic contaminants are often carried towards polar or high elevation environments where, in cold conditions, they condense and are deposited. This is believed to account for the surprisingly high concentrations present in arctic environments, and in the indigenous peoples who live there.

While there are natural sources of mercury such as volcanoes, human activities have greatly increased the amount of mercury in the environment through processes such as burning coal for electricity, burning mercury-contaminated waste, and the production of chlorine. Once emitted to the air as an elemental or inorganic chemical, mercury can travel great distances before it is eventually returned to the earth by wet (rain, snow), dry (dust, other airborne particles), or occult (cloud, fog) deposition. In the environment, particularly in certain types of wetlands, natural biological processes convert these forms of mercury into a toxic, bio-available form called methylmercury. Methylmercury builds up in organisms and increases in concentration with each level of the food chain through a process called biomagnification.

What are the impacts of mercury and toxics?

Photo of a Florida panther at Everglades NP, Florida.
Mercury increases in concentration as it moves up the food chain, placing animals at higher trophic levels at greater risk.

Elevated concentrations of airborne contaminants in national park ecosystems pose health threats to wildlife and humans, as some of these compounds tend to biomagnify in the food chain. Effects of toxic airborne contaminants such as methylmercury (the toxic form of mercury) can include reduced reproductive success, impaired growth and development, behavioral abnormalities, reduced immune response, disease, and decreased survival of fish, birds, and wildlife.

Fish consumption is the most important pathway for human and wildlife exposure to methylmercury and other airborne toxics. States currently monitor mercury and other toxic contaminants in fish tissue from certain surface waters in order to develop public fish consumption advisories and warn the public regarding unsafe levels of contaminants in fish from specific waters. In the 2008 national listing of fish advisories, 43% of lake acres (excepting the Great Lakes) and 39% of river miles in the U.S. were under a fish advisory. While mercury is the leading cause of fish advisories, other contaminants such as pesticides may also invoke additional restrictions. more »

Additionally, “intersex”—the presence of both male and female reproductive structures in the same organism—is an abnormal condition which can be associated with exposure to certain contaminants (e.g., dieldrin, DDT). Intersex fish have been found in some remote national park lakes, but the degree to which this condition is influenced by exposure to airborne toxics is not fully understood.

How are mercury and toxics monitored?

Photo of a Florida panther at Everglades NP, Florida.
Measuring mercury levels in the snowpack sheds light on atmospheric inputs of the pollutant.

Mercury deposition and effects are being monitored in many national parks. Mercury in aquatic systems is of particular concern because mercury can be readily transformed into methylmercury, which biomagnifies in the food chain, potentially reaching toxic levels in important species such as fish, fish-eating birds (eagles, osprey), and alligators. Recent research indicates that terrestrial ecosystems can also be at risk when spiders and other insects that are part of the aquatic food web are ingested by terrestrial species such as songbirds. Research and monitoring projects are currently underway assessing mercury and other air toxics in national park ecosystems. States monitor mercury and other toxic contaminants in fish tissue to advise fish consumption guidelines, however few of these efforts take place in national parks.

The NPS monitors mercury in wet deposition at several parks across the country through the National Atmospheric Deposition Program (NADP)/Mercury Deposition Network (MDN). While these networks are valuable in measuring mercury deposition over time and space, the atmospheric deposition of mercury is not directly related to methylmercury in ecosystems. This is because conversion of mercury to methylmercury is controlled by microorganisms that are more active depending on environmental conditions such as the presence of wetlands, dissolved organic matter, and sulfur.

The Western Airborne Contaminants Assessment Project (WACAP) determined the risk to ecosystems and food webs in western and Alaskan national parks from long-range transport of such toxics as pesticides and mercury, analyzing the concentration and biological effects in air, snow, water, sediment, lichen, conifer needles, and fish from 2002 through 2007. The WACAP database contains all the physical, chemical, and biological data collected as part of the study and includes information for approximately 100 variables for over 2,000 samples. more »

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Last Updated: July 15, 2015