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 the 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 U.S. to reduce their emissions of mercury. The INL and other research laboratories across the nation are conducting fundamental research to better understand how mercury cycles in the environment. Such 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 U.S. alone emits about 158 tons of mercury into the atmosphere every year. This graph shows the worldwide mercury levels in the environment since the 1700s.
Mercury is the only metal that is liquid at room temperature.
A variety of industrial and agricultural activities put mercury into the environment. Coal-fired power plants, bleaching, mining, and the incineration of medical wastes are examples of industrial sources, and pesticides also contain mercury. The 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 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 U.S.G.S Mercury Contamination of Aquatic Ecosystems web site 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.
Research into the direction and rates of mercury exchange are important in understanding the overall dynamics of mercury as well as 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 wide-spread distribution.
Mercury is found in the atmosphere as a gas which 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 is also exchanged between the atmosphere and the earth surface.
Snow is a primary sampling medium because it is a very efficient scavenger of atmospheric Hg and because it usually remains on the ground, allowing sampling after the precipitation event. INL sampling activities include sampling to measure Hg deposition in snow, concentrations in air, re-emission flux rates from soil, and to estimate the historical fallout load in lake sediment downwind from the INL.
Flux measurements are made to investigate the potential for re-emission losses of historical calciner-deposited Hg in soils. Soil re-emission losses result from soil reduction of deposited divalent Hg(II) to non-reactive elemental Hg(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 that 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 Hg surface source.
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. 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 Hg fallout occurred off the 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 (NWR) and Mud Lake. Sediment layers (1-cm intervals) were dated using a Cs-137 radiodating technique which will allow estimation of annual Hg fallout rates since pre-INL times.
- Contacts:
- Michael L. Abbott, (208) 526-8596, Send E-mail