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

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


Chemistry and Behavior

Elemental Mercury

Elemental mercury is a silver-white metal that is a heavy liquid at ambient temperatures. Due to its high surface tension, it forms small, compact spherical droplets when released. While the droplets themselves are stable, the high vapor pressure of mercury encourages its evaporation. Hence released or uncovered mercury can rapidly become an air hazard. The physical properties of elemental mercury are: molecular mass of 200.6, boiling point of 356.7° C, melting point of -38.87° C, vapor pressure of 0.3 Pa at 25° C, and solubility of 56 µg/L at 25° C.

Inorganic Mercury

The most prevalent valence states for mercury are Hg+1 and Hg+2. In these states it can form a variety of inorganic salts. Some of the more common mercury salts are mercuric chloride (HgCl2), mercurous chloride (Hg2Cl2), mercuric nitrate (Hg(NO3)2), mercuric sulfide (HgS), and mercuric sulfate (HgSO4). The solubilities of these chemical compounds varies greatly ranging from negligible (Hg2Cl2, HgS) to very soluble ( HgCl2, Hg(NO3)2). Mercuric sulfate decomposes when placed in water. In 2007, mercury tetrafluoride (HgF4) was synthesized under cryogenic conditions, confirming that mercury can also exist in the Hg+4 state.

Ionized forms of mercury are strongly adsorbed by soils and sediments and are desorbed slowly. Clay minerals adsorb mercury maximally at pH 6. Iron oxides also adsorb mercury in neutral soils. In acid soils, most mercury is adsorbed by organic matter. When organic matter is not present, mercury becomes relatively more mobile in acid soils, and evaporation to the atmosphere or leaching of mercury to groundwater occurs.

Organic Mercury

Mercury also can exist in organic forms with the most frequently encountered in nature being methylmercury ((CH3)2Hg). Mercury methylation is primarily a result of anaerobic microbial activity in sediments, which is typically enhanced in environments with high concentrations of organic matter.

While it is recognized that elemental mercury volatilizes easily and stays in the atmosphere for a long time, that ionic mercury deposits from the atmosphere readily and is very water soluble, and that fish and mammals easily absorb methylmercury when they ingest it via the food chain, there are significant behavioral differences among elemental mercury, ionic mercury, and organic and inorganic mercury compounds, in terms of accumulation in the aquatic food chain, atmospheric and oceanic residence times (the former greatly influencing long-range transport), and rates and forms of deposition. These differences are by no means fully understood.

Adapted from:

Leaching, Transport, and Methylation of Mercury in and around Abandoned Mercury Mines in the Humboldt River Basin and Surrounding Areas, Nevada
USGS Bulletin 2210-C, 2003.

Chapter 2 - Mercury: Forms, Fate & Effects.
Mercury in Massachusetts: an Evaluation of Sources, Emissions, Impacts and Controls, 1996.

Adobe PDF LogoBehavior of Metals in Soils
McLean, J.E. and B.E. Bledsoe.
EPA 540-S-92-018, 25 pp, 1992

This paper covers the fundamental processes that control the mobility of metals (lead, chromium, arsenic, cadmium, nickel, zinc, copper, mercury, silver, and selenium) in soil and describes laboratory methods used to evaluate the behavior of metals in soil.

Chapter 2 - Mercury: Forms, Fate & Effects
Mercury in Massachusetts: an Evaluation of Sources, Emissions, Impacts and Controls.
Massachusetts Department of Environmental Protection, 1996.
Contact: Mark Smith,

Adobe PDF LogoDevelopment and Example Application of a Pilot Model for the Biogeochemical Cycling of Mercury in Watersheds: SERAFM-NPS
C.D. Knightes.
EPA 600-R-09-114, 22 pp, 2009

This report presents a spreadsheet-based pilot model to simulate the biogeochemical cycling of mercury in watersheds. The watershed is divided into different land-use types (currently impervious, forest, grassland, agriculture/pasture, agriculture/row crops, and wetlands). The simple box-model approach uses mechanistic differential mass balance equations to describe the transformation and transport of speciated mercury (Hg(0), Hg(II), and MeHg) within each land use type, predicting soil mercury concentrations and transport processes (volatilization, erosion, leaching, runoff, and total flux to receiving water bodies). The model is dynamic, running on time steps of years, allowing for development of mercury concentrations over long time periods. The output of this model is designed to provide loading information to water body models, such as SERAFM and WASP.

Distribution and Transport of Total Mercury and Methylmercury in Mercury-Contaminated Sediments in Reservoirs and Wetlands of the Sudbury River, East-Central Massachusetts
J.A. Colman, M.C. Waldron, R.F. Breault, and R.M. Lent.
U.S. Geological Survey Water-Resources Investigations Report 99-4060, 21 pp., 1999.
Contact: John Colman,

The Effects of Sediment and Mercury Mobilization in the South Yuba River and Humbug Creek Confluence Area, Nevada County, California: Concentrations, Speciation, and Environmental Fate
U.S. Geological Survey Open-File Reports 2010-1325A and 2010-1325B, 2011

These reports comprehensively characterize Hg contamination at this particular site and the potential effects on downstream environments of sediment disturbance at locations with historical hydraulic mining debris. The field component assessed the potential effects of recreational suction dredging in terms of 1) its viability as an approach to clean up riverbed sediment contaminated with legacy Hg from historical gold-mining activity and 2) its effects (compared that caused by natural storm disturbances) on Hg remobilization, speciation, and the potential for the stimulation of toxic methylmercury production and bioaccumulation in downstream sediments. Hg bioaccumulation in the local invertebrate population was also evaluated. Results of the field studies indicate that the fine-grained fraction (silt-clay, less than 0.063 mm) contains the greatest concentration of Hg in contaminated sediment. Because the fine-grained fraction is the most susceptible to long-range fluvial transport, disturbance of Hg-contaminated sediment is likely to increase the concentration and load of Hg in downstream waters. As part of this larger study, lab experiments were conducted with various types of sediment collected in and around the confluence area to simulate in-stream transport, deposition, and potential methylation of Hg.

Enhanced Knowledge in Mercury Fate and Transport for Improved Management of Hg Soil Contamination
SNOWMAN Network, Project No. SN-03/08, 2014

The IMaHg project provides recommendations and highlights needs areas for improving the management of mercury-contaminated sites. The following reports are posted as part of the project output:

Handbook of Elemental Speciation, II: Species in the Environment, Food, Medicine and Occupational Health
R. Cornelis, J. Caruso, H. Crews, and K. Heumann, eds.
John Wiley & Sons, New York. ISBN 0-470-85598-3, 768 pp, 2005.

Covers the speciation of elements from aluminum to zinc, including arsenic, chromium, and mercury.

Adobe PDF LogoLeaching, Transport, and Methylation of Mercury in and around Abandoned Mercury Mines in the Humboldt River Basin and Surrounding Areas, Nevada
John E. Gray.
U.S. Geological Survey Bulletin 2210-C, 2003.
Contact: John Gray,

Adobe PDF LogoMercury Study Report to Congress Volume III: Fate and Transport of Mercury in the Environment
U.S. EPA, Office of Air Quality Planning & Standards and Office of Research and Development.
EPA 452-R-97-005, 376 pp., 1997.
Contact: Kathryn R. Mahaffey,

Adobe PDF LogoMercury Concentrations in Air During the Phase I Remediation of Lower East Fork Poplar Creek Floodplain at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee
M.O. Barnett, J.G. Owens, S.E. Lindberg, R.R. Turner.
Y/ER-281, 20 pp., 1997.

During excavation activities at a contaminated site, the mercury concentration in air was monitored continuously at a nearby off-site location to note the effects of soil disturbance and to ensure that the remediation did not adversely affect the off-site concentration of mercury in air.

Mercury Sources, Distribution, and Bioavailability in the North Pacific Ocean: Insights from Data and Models
E. M. Sunderland, D.P. Krabbenhoft, J.W. Moreau, S.A. Strode, W.M. Landing.
Global Biogeochemical Cycles, 23, GB2010, 2009.

Adobe PDF LogoOccurrence and Mobility of Mercury in Groundwater
Current Perspectives in Contaminant Hydrology and Water Resources Sustainability; P.M. Bradley (ed). InTech, Rijeka, Croatia. ISBN: 978-953-51-1046-0, Chapter 5: 117-149, 2013

Although a large reservoir of inorganic Hg exists in the environment, relatively less Hg is mobilized to groundwater than to surface water, in part because Hg can be attenuated by sorption to clays, iron oxides, and residual soil organic matter. Studies of the fate and transport of Hg in the subsurface reveal how transport from land surface to groundwater can occur and how Hg remains mobile within aquifers. Recent discoveries of Hg and MeHg inputs from submarine groundwater discharge indicate avenues for further investigations.

Adobe PDF LogoThe Origin and Fate of Mercury Species in the Environment
Munthe, J., Ingvar Wängberg, and L. Shang.
Euro Chlor Science Dossier 14, 42 pp, 2009

Speciation influences the mobility of mercury in air, water, soil, and also (especially the methylmercury fraction) determines to a large extent the uptake and negative health effects of mercury in humans and wildlife. This paper examines mercury in the atmosphere, mercury species in terrestrial and aquatic ecosystems, and the role of mercury species in the environmental cycling of mercury.

Adobe PDF LogoPartition Coefficients for Metals in Surface Water, Soil, and Waste
Allison, Jerry D. (HydroGeoLogic, Inc., Herndon, VA); Terry L. Allison (Allison Geoscience Consultants, Inc., Flowery Branch, GA).
Report No: EPA 600-R-05-074, p , July 2005

This report presents metal partition coefficients for the surface water pathway and for the source model used in the multimedia, multi-pathway, multi-receptor exposure and risk assessment (3MRA) technology under development by U.S. EPA. Literature searches, statistical methods, geochemical speciation modeling, and expert judgment were used to provide reasonable estimates of partition coefficients for antimony, arsenic, barium, beryllium, cadmium, chromium, cobalt, copper, lead, molybdenum, mercury, methylated mercury, nickel, selenium, silver, thallium, tin, vanadium, and zinc.

Adobe PDF LogoPre-Construction Biogeochemical Analysis of Mercury in Wetlands Bordering the Hamilton Army Airfield Wetlands Restoration Site
E.P.H. Best, H.L. Fredrickson, V.A. McFarland, et al.
ERDC/EL-TR-05-15, ADA439941, 155 pp, Sep 2005

This interim report describes site-specific information on the microbial, geochemical/geophysical, and predominant plant- and animal-related interactions that affect stabilization and mobilization of Hg and MeHg in the sediments/soils of a coastal wetlands area.

Adobe PDF LogoPre-Construction Biogeochemical Analysis of Mercury in Wetlands Bordering the Hamilton Army Airfield (HAAF) Wetlands Restoration Site. Part 2
E.P.H. Best, H.L. Fredrickson, H. Hintelmann, O. Clarisse, B. Dimock, C.H. Lutz, G.R. Lotufo, R.N. Millward, A.J. Bednar, and J.S. Furey.
ERDC/EL TR-07-21, 222 pp, 2007

This interim technical report describes studies focused on (1) site-specific rates of methylation and demethylation, as well as characterizations of sedimentary microbial communities; (2) mercury dynamics in decomposing plant litter; (3) mercury dynamics in food webs; and (4) bioavailability of sediment-associated mercury of existing marsh sediments to macrobenthos. In addition, a new time-integrative method for measuring and monitoring mercury cycle-related biogeochemical parameters in marshes was developed, and the role of marsh vegetation as a vector in mercury species transport was quantified.

Sediment-Water Interactions Affecting Dissolved-Mercury Distributions in Camp Far West Reservoir, California
James S. Kuwabara, et al.
U.S. Geological Survey Water Resources Investigations Report 03-4140, 2003.
Contact: James S. Kuwabara,

Subtask 1.8 — Mercury Release from Disturbed Anoxic Soils
Jaroslav Solc and Bethany A. Bolles, Energy & Environmental Research Center, Univ. of North Dakota.
2001-EERC-07-05, 123 pp., 2001. (abstract)
Contact: Richard Read, 412-892-5721

This report was prepared to provide information on the secondary release of mercury from contaminated anoxic sediments to an aqueous environment after disturbance/change of in situ physical conditions. The report also evaluates mercury migration and partitioning under controlled conditions, with the implications of these processes for treatment of contaminated soils. The stability observed for mercury in undisturbed anoxic sediments might represent an opportunity for treating wastewater highly contaminated with mercury and other toxic metals in natural or engineered anoxic ponds (reactors).