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Atmospheric and Surface Science Research Laboratory Mercury in the Environment

Idaho National Laboratory (INL) researchers are contributing to the scientific understanding of mercury (Hg) fate and transport in a local, regional, and global context.

Mercury, a toxic air pollutant, is a high-priority concern for the U.S. Environmental Protection Agency (EPA). In December 2000, EPA announced that for the first time it would require coal-fired power plants, considered to be the largest source of such emissions in the United States, to reduce their emissions of mercury. INL and other research laboratories across the nation are conducting fundamental research to better understand how mercury cycles in the environment. This information forms the science basis for EPA’s regulatory decisions.

EPA has outlined the key scientific questions regarding mercury: (1) transport, transformation, and fate; (2) risk management for combustion sources; (3) risk management for non-combustion sources; (4) ecological effects and exposure; (5) human health effects and exposure; and (6) risk communication.

Mercury in the Environment

Thanks to the Industrial Age, mercury is a common worldwide pollutant. Concentrations of the toxic metal are rising, both in the atmosphere and on land. The United States alone emits about 158 tons of mercury into the atmosphere every year.

Mercury is the only metal that is liquid at room temperature (see picture on left).

A variety of industrial and agricultural activities put mercury into the environment. Coal-fired power plants, bleaching, mining, and the incineration of medical waste are examples of industrial sources, and pesticides also contain mercury. INL’s primary source of mercury for many years was the New Waste Calcining Facility located at the Idaho Nuclear Engineering and Technology Center (INTEC). Mercury also gets into the environment through natural processes such as volcanic and geothermal activity and from natural mercury deposits. The U.S. Geological Survey (USGS) has prepared an informative fact sheet about mercury in the environment that is available on their website.

High levels of mercury in the environment are a hazard because, if consumed, mercury accumulates over time in the tissues of living organisms and can reach toxic levels. This process, called bioaccumulation, can threaten an entire food chain. Additionally, mercury is known to concentrate in the muscle tissue of fish and cannot be removed. As many as 31 states currently have warnings in effect advising people not to eat fish from specific locations. See the USGS Mercury Contamination of Aquatic Ecosystems website for more information.

Studying mercury in the environment

The INL (Abbott) participated in a USGS-led snow survey in the Wind River Range, Wyoming, collecting snow samples at 13,000 ft to assess regional background fallout of mercury (see picture on the right).

Research into the direction and rates of mercury exchange are important in understanding the overall dynamics of mercury and cycling in the environment. Mercury is a challenge to study because it is present in the environment in such low quantities and in different physical states. Once in the atmosphere, mercury is widely disseminated and can circulate for years, accounting for its widespread distribution.

Mercury is found in the atmosphere as a gas that consists primarily of elemental mercury but also other small amounts of other mercury containing compounds (e.g., mercuric chloride). Mercury also exists in the atmosphere in the liquid phase as water droplets (e.g., cloud water) and in precipitation (rain and snow). In addition to these forms of mercury in the atmosphere, mercury also is exchanged between the atmosphere and the earth's surface.

Snow is a primary sampling medium because it is a very efficient scavenger of atmospheric mercury and because it usually remains on the ground, allowing sampling after the precipitation event. INL sampling activities include sampling to measure mercury deposition in snow, concentrations in air, re-emission flux rates from soil, and to estimate the historical fallout load in lake sediment downwind from INL.

Flux measurements are made to investigate the potential for re-emission losses of historical calciner-deposited mercury in soils. Soil re-emission losses result from soil reduction of deposited divalent mercury (II) to non-reactive elemental mercury (0), which volatilizes to the atmosphere and does not locally deposit, thereby reducing the potential risks to human health and the environment. Flux measurements at INL are made using a custom-designed dynamic flux chamber and gold traps at three locations--a high fallout location northeast of INTEC, a low fallout location, and near a known mercury surface source.

The 13,745-ft high Fremont Peak stands as a backdrop over the Upper Fremont Glacier, Wind River Range, Wyoming, where INL and USGS researchers have measured regional background fallout rates of mercury (see picture on the right). A portable meteorological station provides data to help the researchers understand factors controlling mercury buildup in the snowpack.

Lake sediment core layers are sampled to determine if measureable mercury fallout occurred off INL throughout the history of INL calciner operations (1963 to 2000) and to assess the potential for bioaccumulation in the food-chain. Cores are taken at two important wildlife areas immediately downwind from the INL—Sandhole Lake at Camas National Wildlife Refuge and Mud Lake. Sediment layers (1-cm intervals) were dated using a Cs-137 radiodating technique, which will allow estimation of annual mercury fallout rates since pre-INL times.

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