U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division



Mercury (Hg) occurs naturally in the environment and can be found in metallic, inorganic, and organic forms. The most common natural forms of mercury found in the environment are metallic mercury, mercuric sulfide (cinnabar ore), mercuric chloride, and methylmercury. Mercury and its compounds have a long history of human use for industrial, medicinal, cosmetic, and spiritual purposes. Modern uses for mercury include electrical switches, thermometers, dental amalgams, lighting (mercury vapor and fluorescent lamps), flow meters, batteries, fungicides, electrochemistry, catalysis, explosives, gold recovery, and bactericides.

Mercury is the only metal that is liquid at room temperature (20° C). The element is easily separated from its parent minerals through the application of heat, which enhances its ability to be recovered in a pure state. Mercury has the highest solubility in water of any metal and easily vaporizes into the air; these two properties make it very mobile in the environment. Mercury vapor can be carried over great distances in the atmosphere and be deposited into lakes and streams. Some microorganisms (bacteria and fungi) and natural processes can change the mercury in the environment from one form to another, usually under anaerobic (oxygen-deficient) conditions. The most common organic mercury compound that these microorganisms and natural processes generate from other forms is methylmercury.

Over time, we have discovered that mercury, particularly in the organic methylmercury form, is a potent neurotoxin capable of impairing neurological development in fetuses and young children and damaging the central nervous system of adults. People are most likely to be exposed to harmful quantities of mercury through consumption of fish contaminated with methylmercury. Exposure to elemental mercury vapor in indoor air also can cause serious harm. Exposure to inorganic mercury also can occur from drinking contaminated water and touching contaminated water and soil, although harmful exposures are much less likely through these routes.

The understanding that bioaccumulation of mercury in the food chain can harm populations of animals and humans has been the main impetus for greater regulatory control of mercury. In the past, management and regulatory responses to the problem of bioaccumulation generally have been constrained by a lack of information on sources, methods of transport, chemical interaction, and biological significance of mercury in the environment. Significant research advances during the past decade have allowed scientists to identify, examine, and measure mercury in the environment, which has given regulators the information needed to develop more protective policy and guidelines for mercury management, disposal, and cleanup.

Though mercury contamination and health issues are still being extensively studied, tremendous volumes of information are available concerning industrial processes that cause mercury to enter environment, the prevention or mitigation of such entry, the behavior of mercury in different media, and its health effects on animals and people. This site will include relatively recent examples of general information on these topics; however, these pages will focus primarily on methods for the detection, characterization, and cleanup of mercury in the environment. The references usually are available online, though a few materials, such as commercially published books, have been listed because they are cited extensively in the literature.

Adobe PDF LogoGroundwater Information Sheet: Mercury
California State Water Resources Control Board, 8 pp, 2009.

This brief groundwater information sheet provides general information (fate and transport, health effects, testing and remediation methods) and identifies where high levels of the compound are found in California. The information is pulled from a variety of sources, and a bibliography is provided.

Groundwater Information Sheet: Mercury
Streets, D.G., Z. Lu, L. Levin, A.F.H. ter Schure, and E.M. Sunderland.
Science of the Total Environment 615:131-140(2018) [Abstract]

Coal combustion is one of the largest contemporary sources of anthropogenic Hg. Combustion releases geologically sequestered Hg to the atmosphere, and the Hg in the fly ash can contaminate terrestrial and aquatic systems. While Europe and North America were the major contributing regions until 1950, Asia was responsible for 69% of the total releases of Hg from coal combustion to the environment by 2010. Control technologies installed on major emitting sources capture mainly particulate and divalent Hg; hence, the fraction of elemental Hg in emissions from coal combustion has increased over time from 0.46 in 1850 to 0.61 in 2010. About 31% of the total has been transferred to land and water bodies through disposal or utilization of Hg-containing combustion waste and collected fly ash/flue-gas desulfurization sludge discarded to waste piles or ash ponds.