Gray, ed.—Geologic Studies of Mercury by the U.S. Geologic

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Geologic Studies of Mercury by the

U.S. Geological Survey

Edited by John E. Gray

U.S. Geological Survey Circular 1248

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

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U.S. Geological Survey, Reston Virginia 2003

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Foreword

It is the goal of the U. S. Geological Survey (USGS) to enhance and protect the quality of 

life by describing and understanding the Earth around us. This volume summaries selected 

geologic studies of mercury in the United States by the USGS. The six geologic studies report 

concentrations of mercury in coal, sediment, soil, water, air, and fish; and discuss how the 

USGS is evaluating some of these areas of potential environmental mercury contamination. 

This collection of studies represents only a small portion of the ongoing worldwide research 

on mercury, and is not intended to be a comprehensive reference on the geochemistry of 

mercury. Numerous other mercury studies are in progress in the USGS, in other governmental agencies, in industry, and at universities throughout the world. These studies address the 

USGS Mineral Resources Program goal, which is to gain an understanding of the influence of 

mineral deposits, mineralizing processes, and mineral-resource development on environmental integrity, ecosystems, public health, and geologic hazards. 

 Kathleen M. Johnson

Mineral Resources Program Coordinator
Contents

Introduction, by John E. Gray .......................................................................................................... 1

Mercury in Coal and Mercury Emissions from Coal Combustion, by Robert B. Finkelman... 9

Mercury Mine Studies

 Environmental Impact of Mercury Mines in the Coast Ranges, California, 

 by James J. Rytuba .................................................................................................................. 13

 The Southwestern Alaska Mercury Belt, by John E. Gray and Elizabeth A. Bailey ...... 19

Studies of Mercury Contamination from Gold Mining

 Mercury Contamination from Hydraulic Gold Mining in the Sierra Nevada, 

 California, by Michael P. Hunerlach and Charles N. Alpers............................................. 23

 Mercury in the Carson River Basin, Nevada, by Stephen J. Lawrence .......................... 29

Volcanic Emissions of Mercury, by Todd K. Hinkley.................................................................. 35

Summary, by John E. Gray.............................................................................................................. 39

Figures

 1. Schematic diagram of mercury ........................................................................................... 2

 2–4. Photographs showing:

 2. Gold pan containing elemental mercury.................................................................... 3

 3. Cinnabar sample............................................................................................................. 3

 4. Inactive mercury mine in Nevada ............................................................................... 4

 5–7. Diagrams showing:

 5. Production of some mercury mines of the world ..................................................... 5

 6. Major species and transformations of mercury in the environment .................... 5

 7. Aquatic mercury cycle showing important mercury species ................................ 6

 8. Photograph of coal-fired electrification power plant near Farmington, 

 New Mexico............................................................................................................................ 9

 9. Map showing distribution of mercury in coal fields in the United States ................. 10

 10. Scanning electron micrograph of mercury selenide (HgSe) crystals in

 lignite coal from California ................................................................................................. 11

 11. Map showing mercury mineral belts in North America ................................................ 14

 12. Map showing mercury deposits in California mercury mineral belt ........................... 15

 13. Photograph showing typical mercury mine-waste calcines ........................................ 16

 14. Diagram showing total mercury concentration in acid-rock drainage 

 as a function of chloride concentration in the California mercury 

 mineral belt ........................................................................................................................... 16

 15. Map showing location of mercury mines in southwestern Alaska ............................. 20

 16. Photograph of elemental mercury spilled at Red Devil mine retort, 

 Alaska ................................................................................................................................. 20

 17. Diagram showing concentration of mercury versus methylmercury in 

 unfiltered water samples collected from near mercury mines and 

 uncontaminated baselines in southwestern Alaska...................................................... 21

 18. Diagram showing mercury concentration in muscle for fish collected 

 in southwestern Alaska ...................................................................................................... 22

V
 19. Map showing location of gold and mercury mines in California................................ 24

 20. Photograph showing water cannons used to break down gold-bearing 

 gravel deposits in the Sierra Nevada ............................................................................. 25

 21. Photograph showing gravel deposits being washed into sluices.............................. 25

 22. Diagram showing transport of mercury from a hydraulic mine pit 

 through a drainage tunnel and discharge into creeks and rivers ............................. 26

23. Photograph of sluice system, Siskiyou County, California........................................... 26

 24. Map showing location of sample sites in the Carson River basin, 

 Nevada ................................................................................................................................. 30

25–29. Photographs showing:

 25. View of Carson River in Dayton Valley ................................................................... 31

 26. Vivian quartz mill on Carson River........................................................................... 32

 27. Vapor and steam emanating from the Volcano Farallon de Pajaros, 

 Mariana Islands ......................................................................................................... 35

 28. Volcanic emissions from White Island, New Zealand ......................................... 36

 29. USGS scientists collecting volcanic gas samples ............................................... 37

Tables

1. Contributions of mercury to the atmosphere from natural and anthropogenic 

 sources ........................................................................................................................................ 2

2. Geologic and geochemical factors that control the composition of mine

 drainage from mercury deposits and mines in the California Coast Ranges ................ 15

3. Mercury and methylmercury concentrations ..................................................................... 40

VI
1

Introduction

By John E. Gray

Mercury in the Products We Use

A liquid at room temperature, mercury is a unique metal 

with unusual properties. Elemental mercury has long been used 

in thermometers because it responds to changes in temperature. 

In fact, mercury’s many diverse properties have made it useful 

for many products. Mercury is a good metallic conductor with a 

low electrical resistivity; it has been used in electrical products 

including electrical wiring and switches, fluorescent lamps, mercury batteries, and thermostats (Eisler, 1987). Mercury also is 

used in navigational instruments to measure changes in temperature and pressure. In the medical field, mercury is used as a 

component in dental fillings and as a preservative in many pharmaceutical products. Mercury has been used in industrial and 

agricultural applications such as in the production of chlorine 

and caustic soda, in nuclear reactors, in plastic production, for 

the extraction of gold (amalgamation) during mining, as a fungicide in seeds and bulbs, and as an antifouling agent in paper, 

paper pulp, and paint (Sznopek and Goonan, 2000). 

The Cycle of Mercury in the Environment

In addition to being contained in many products that people 

make and use, mercury is also present in a variety of forms in 

rocks, soil, water, coal, petroleum, and even air. Although the 

amount of mercury present in rocks and soils is generally minor, 

this mercury can make its way into air and water by evaporation 

and through natural weathering and erosion. Mercury is also 

added to the air in the form of gas and small particles that are naturally erupted from volcanoes throughout the world. (See Hinkley, this volume.) However, a significant amount of the mercury 

present in the Earth’s atmosphere is from burning fossil fuels, 

mostly coal, but also petroleum products. Coal is a common fuel 

used in many power plants to generate electricity throughout the 

world. Although the amount of mercury in coal is minor, large 

amounts of coal are typically used in coal electrification plants. 

Thus, burning coal is the largest human-caused contributor of 

mercury to the atmosphere. (See Finkelman, this volume.) Some 

mercury is also emitted to the atmosphere by the combustion of 

petroleum products such as gasoline in automobile and airplane 

engines. Other sources of mercury to the land, water, and atmosphere include the mining of mercury and gold, forest fires, incineration of waste from treatment plants, emissions from landfills, 

evaporation from oceans, and industrial runoff, seepage, and discharges (fig. 1). No matter where on Earth it originates, airborne 

mercury gas mixes in the atmosphere, can travel many thousands 

of miles, and is eventually redistributed around the world. Estimates suggest that the total contribution of mercury to the atmosphere from all sources worldwide is as much as 6,000 t (metric 

tons)/year (table 1). Some of the mercury in the atmosphere eventually deposits (most commonly in rain) on the Earth’s surface in 

soils, sediments, oceans, rivers, and lakes (Mason and others, 

1994). Although the concentration of mercury in lake and ocean 

water is low, these water bodies are large reservoirs of mercury 

because they have such a large volume of water. Mercury also 

evaporates from lakes and oceans, again contributing mercury to 

the atmosphere, completing the cycle.

Where Mercury Comes From

Mercury has been mined for more than 2,000 years and 

most of the mercury used historically by man has been produced through the mining of ore. Although mercury constitutes 

less than 1/100,000,000 of one percent of the Earth, and like 

many minerals and elements found in nature, mercury can be 

highly enriched in certain rocks called ore deposits. The most 

common mineral containing mercury in ore deposits is cinnabar, or mercury sulfide (HgS), but naturally occurring elemental 

mercury, or quicksilver (Hg°), is also found in some mercury 

deposits. Both cinnabar and elemental mercury are distinctive, 

making their identification relatively easy. Elemental mercury 

is a silver-colored liquid at room temperature (fig. 2); cinnabar 

is a distinctive red mineral (fig. 3). Roasting the ore in a furnace 

(fig. 4) easily converts cinnabar to elemental mercury; this ease 

of conversion is another reason why mercury has been mined 

for such a long time. Elemental mercury is the final product 

obtained through mining of cinnabar. The international unit of 

measurement of elemental mercury is a flask, which weighs 

about 34.5 kg or 76 pounds.

Historically, the largest mercury mines have been those in 

Spain, Italy, Slovenia, Peru, China, the former U.S.S.R., Algeria, Mexico, Turkey, and the State of California (fig. 5), but 

many other mercury mines are scattered throughout the world. 

Most mercury mines are presently closed owing to low demand 

and low prices for mercury worldwide, primarily as a result of 

environmental and health concerns surrounding mercury. Furthermore, considerable amounts of mercury-containing products are being recycled, especially in the United States, which 

also reduces the demand for mercury mining (Sznopek and 

Goonan, 2000). Although few mercury mines in the world are 

presently operating, closed and inactive mercury mines are sites 

of some of the highest mercury concentrations on Earth. At 

these mercury mines, mine wastes contain considerable cinnabar, elemental mercury, and other mercury compounds that are 

continually lost to surrounding environments through erosion, 

leaching, and evaporation.

Another significant mining use of mercury worldwide is the 

amalgamation of gold by mercury, a technique used for the 

extraction of precious metals in many mines. Although this 

practice is not generally used in the United States, it is still used 

in many developing countries. As a result of amalgamation 

practices, significant liquid mercury is lost to streams and rivers 

surrounding many gold mining areas throughout the world. In 

some of these areas, liquid mercury that was used decades ago 

remains in these rivers as a potential environmental problem. 

(See example of the Carson River, Nevada; Lawrence, this 

volume.)

1
2 Geologic Studies of Mercury by the U.S. Geological Survey

Table 1. Concentrations of mercury in the atmosphere and contributions of mercury to the atmosphere from natural and 

anthropogenic sources. 

[Mercury concentrations given (ng/m3

) are those in air above the sources listed, which are provided to give a relative comparison of various sources 

contributing mercury to the atmosphere. Estimated mercury contributed to the atmosphere represents that from all like sources combined throughout the 

world, for example, all oceans worldwide are estimated to contribute as much as 2,000 t of mercury per year to the atmosphere. ≈, approximated; ng/ m3, 

nanograms/cubic meter; kg/yr, kilograms/year; t/yr, metric tons/year]

Source References

 

Atmosphere 1 – 2 ng/m3 4,400 – 6,000 t/yr Fitzgerald (1986); Porcella (1994);

Lamborg and others (2002).

Volcanoes 28 – 1,400 ng/m3 60 t/yr # Fitzgerald (1986); Varekamp and Buseck

(1986); Ferrara and others (1994).

Land 1 – 6 ng/m3 ≈ 1,000 t/yr Varekamp and Buseck (1986); Gustin and 

 others (1994); Mason and others (1994).

Mines 2 – 5,000 ng/m3 ≈10 – 100 t/yr Ferrara and others (1991; 1998)

Gustin and others (1994; 1996; 2000).

Oceans 1 – 3 ng/m3 800 – 2,000 t/yr Mason and others (1994);

Lamborg and others (2002).

Anthropogenic ~10->900 kg/yr * 2,000 – 2,600 t/yr Mason and others (1994); Environmental Protection 

 Agency (2000); Lamborg and others (2002).

# Mercury emissions from some explosively erupting volcanoes indicate that this source of mercury to the atmosphere could be several times higher than 

shown here (Varekamp and Buseck, 1986).

*

Range of mercury emissions in 1999 from numerous power plants in the U.S.A. as reported to the EPA (Environmental Protection Agency, 2000).

Estimated Hg contributed

to atmosphere worldwide

Hg concentration

or emission*

bioaccumulation

of Hg in fish

ocean

lakes

factory runoff

 crop burning

and forest fires

 release Hg 

natural volatilization

and runoff from land

coal electric plant

burning of fossil

fuels releases Hg

Hg vapor and runoff

from mines

sediments

industrial discharge

into aquatic systems

dry deposition of

particulate Hg

waste incineration

landfill

fish consumption 

is Hg pathway

to humans

wet deposition of Hg

from precipitation

Hg evaporation from

oceans and lakes

agriculture

volcanic eruptions

release Hg

sewage and seepage

into groundwater

Figure 1. Schematic diagram of mercury cycle showing important contributions of mercury to the environment from land, water, air, and 

anthropogenic sources.
Where Mercury Comes From 3

Figure 2. Gold pan with elemental mercury obtained from mercury-contaminated sediments. Such 

elemental mercury presently remains in sediments and abandoned sluice boxes at sites of historic 

gold mining in the California Sierra Nevada.

Figure 3. A sample of cinnabar (red mineral), the most common mercury ore in mercury mines worldwide.
4 Geologic Studies of Mercury by the U.S. Geological Survey

Mine-waste calcines

Condenser

Rotary furnace

Figure 4. Inactive mercury mine in Nevada. In the rotary furnace, mercury ore was burned producing mercury gas 

that was cooled, condensed as elemental mercury, and collected.

The Chemistry of Mercury

The properties and behavior of mercury depend on its oxidation state. Mercury in nature is found in three oxidation 

states: metallic or elemental mercury (Hg°), mercurous ion 

(Hg2

2+), and mercuric ion (Hg2+). All three forms of mercury 

present some degree of hazard to life forms—including 

humans—but mercury compounds containing the mercuric ion 

are the most toxic, especially organic-mercury compounds 

(World Health Organization, 1976). All forms of mercury can 

be converted to these toxic organic compounds, and thus, all 

mercury compounds are considered potentially dangerous. 

Mercury in water, soil, sediments, biota, and rocks and minerals 

is mostly in the form of inorganic ionic compounds and organic 

compounds (fig. 6). Most of the mercury in air is Hg°, and oxidized forms (for example, Hg2+) generally constitute less than 2 

percent of the mercury in air (Fitzgerald, 1989).

Any form of mercury that makes its way into an aquatic 

system has the potential to be converted into organic mercury, 

of which methylmercury (CH3Hg+) is generally the most toxic. 

The process of methylmercury formation (mercury methylation) is complex and results from chemical and biological activity; mercury methylation is dependent on pH, temperature, 

oxidation-reduction potential, the amount of organic matter, and 

other chemical factors (Ullrich and others, 2001). Bacterial 

conversion of inorganic mercury to methylmercury is the dominant methylation process typically in the sediment column in 

aquatic environments (Compeau and Bartha, 1985). An 

important mechanism of methylmercury formation around 

mines is the oxidation of Hgo

 to Hg2+, and the subsequent 

microbial formation of methylmercury. Methylmercury compounds are highly stable, are soluble in water and in the fats of 

organisms, and have the ability to penetrate membranes of living organisms. Once mercury is converted to methylmercury, 

biota in aquatic ecosystems rapidly absorb the mercury, and as a 

result, mercury tends to concentrate in tissues of fish and other 

aquatic organisms (bioaccumulation). Mercury also biomagnifies in the food chain, and it generally increases with increasing 

position in the food chain when environments are exposed to 

mercury (fig. 7). The most common pathway of mercury to 

humans and other higher order wildlife is through diet, primarily through consumption of fish and seafood products (Ullrich 

and others, 2001). Animals and humans that consume large 

quantities of fish are at the highest risk of mercury contamination because the form of mercury in fish is mostly (generally > 

90 percent) highly toxic methylmercury (National Academy of 

Sciences, 1978; Clarkson, 1990; U.S. Environmental Protection 

Agency, 1997). Methylmercury is more thoroughly absorbed in 

the human gastrointestinal system (about 95 percent absorption) 

compared to other forms of mercury such as elemental mercury 

(less than 10 percent absorption) (U.S. Environmental Protection Agency, 1997). Although humans take in most mercury 

through food sources, exposure breathing elemental mercury 

vapor is also possible, but more rare. For these reasons, scientists often measure the concentration of mercury and methylmercury to evaluate mercury contamination in specific areas.

4 Geologic Studies of Mercury by the U.S. Geological Survey
The Chemistry of Mercury 5

Alaska, USA (1,400 t)

Nevada, USA (12,000 t)

Huancavelica, Peru (52,000 t)

Monte Amiata, Italy (69,000 t)

Idrija, Slovenia (107,000 t) California, USA (98,000 t)

Almaden, Spain (260,000 t)

Others (120,000 t)

natural emission of Hg

Hg2+

Hgo

Hg(p)

deposition to

land and water

CH3Hg+

air

water

sediment

bacteria CH3Hg+

(methyl mercury) bacteria

bacteria

Hg2+

(mercuric)

Hg2

2+

(mercurous)

HgS

(mercury sulfide)

anthropogenic Hg

Hgo

 Hgo

(elemental mercury)

 Hg(p)

(particulate Hg)

deposition

Figure 5. Production of mercury (metric tons) from some mercury mines found throughout the world. Production from mines in 

China, the former U.S.S.R., Algeria, Mexico, and Turkey are grouped as “others.”

Figure 6. Major species and transformations of mercury in the environment (modified from Wood, 1974; Mason and others, 1994). Conversion

to methylmercury is most important because it is bioavailable and is transferred to water and biota.
6 Geologic Studies of Mercury by the U.S. Geological Survey

OUTFLOW

SEDIMENTATION

OUTFLOW

SEDIMENTATION

Hg DEPOSITION

AND RUNOFF

OUTFLOW

VOLATILIZATION

AND DEPOSITION

VOLATILIZATION

AND DEPOSITION

METHYLATION

REDUCTION

DEPOSITION

DIFFUSION & SEDIMENT

RESUSPENSION

BIOMAGNIFICATION

Hgo

Hg2+

Hg2+

CH3Hg+

CH3Hg+

DEMETHYLATION

OXIDATION

Figure 7. The aquatic mercury cycle showing important mercury species, mercury methylation and demethylation, and biomagnification 

of mercury in biota (modified from Hudson and others, 1994).

the Amazon River region of South America (Eisler, 1987; U.S. 

Environmental Protection Agency, 1997). These cases resulted 

from high concentrations of mercury in aquatic systems contaminated by industrial discharges, in agricultural products, by 

atmospheric deposition, by exposure to elemental mercury, and 

through mining activities. In North America, numerous lakes 

and reservoirs are known to contain fish that have mercury concentrations above the level considered safe for human consumption (Krabbenhoft and Rickert, 1995). As of December 2000, 

more than 2,200 water bodies in 41 States in the United States 

have advisories for high concentrations of mercury in fish, and 

State and Tribal governments have advised citizens against eating these fish (U.S. Environmental Protection Agency, 2001). In 

some of these instances, such as in California, mercury contamination is clearly related to past mining activities. (See Hunerlach 

and Alpers, this volume.) However, for most of these aquatic 

advisories, the source of the mercury is not related to any obvious mining or industrial discharges. In these cases, atmospheric 

mercury deposition is more probable (Fitzgerald and others, 

1998; Krabbenhoft and Wiener, 1999), but these aquatic systems 

need additional study.

Why the Public and Scientists Are Concerned 

About Mercury

Mercury is a heavy metal of environmental concern because 

elevated concentrations can be toxic to all living organisms. Mercury has no known metabolic function in animals and is not easily 

eliminated by organisms, including humans. High concentrations 

of mercury in humans adversely affect the central nervous system, especially the sensory, visual, and auditory parts that effect 

coordination (Fitzgerald and Clarkson, 1991). In extreme cases, 

mercury poisoning can lead to death (National Academy of Sciences; 1978; Eisler, 1987; U.S. Environmental Protection 

Agency, 1997). For all organisms, the early stages of development (especially embryos) are the most sensitive to mercury 

(Clarkson 1990; U.S. Environmental Protection Agency, 1997).

For several decades, scientists and governments have been 

aware of the toxic effects of mercury on humans and other 

organisms. Since the 1950s, numerous cases of mercury poisoning to humans and wildlife have occurred in Japan, Iraq, Scandinavia, Europe, the United States, Canada, the Philippines, and in 

6 Geologic Studies of Mercury by the U.S. Geological Survey
Why the USGS Is Studying Mercury 7

Why the USGS is Studying Mercury

As a result of its wide use, mercury is common in the environment in which we live. Because of its toxic nature, numerous 

studies of environmental mercury contamination are ongoing in 

the United States and throughout the world. In 1997, the U.S. 

Environmental Protection Agency (EPA) completed a report that 

was submitted to the U.S. Congress as required under the 1990 

Clean Air Act (U.S. Environmental Protection Agency, 1997). In 

this study, the EPA evaluated many aspects of mercury emissions 

in the U.S., the health and environmental implications of those 

emissions, and the availability and cost of emission control technologies. The EPA report also recommended areas for future 

research to aid in the understanding of sources, transport, and 

health effects related to mercury in the air, water, and through 

fish consumption. In addition, the EPA report contained recommendations concerning possible monitoring, control, remediation, and regulation of environmental mercury problems in the 

United States. Although the USGS is generally not involved in 

remediation or regulatory practices, the USGS contributes, 

through various monitoring and research studies, to the overall 

understanding of the geochemistry of mercury and how it enters 

and affects the environment.

References Cited

Clarkson, T.W., 1990, Human health risks from methylmercury in fish: 

Environmental Toxicology and Chemistry, v. 9, p. 957–961.

Compeau, C.C., and Bartha, R.A., 1985, Sulfate reducing bacteria—Principal methylators of mercury in anoxic estuarine sediment: Applied 

Environmental Microbiology, v. 50, p. 498–502.

Eisler, R., 1987, Mercury hazards to fish, wildlife, and invertebrates—A 

synoptic review: U.S. Fish and Wildlife Service Biological Report 85 

(1.10), 90 p.

Ferrara, R., Maserti, B.E., Andersson, M., Edner, H., Ragnarson, P., Svanberg, S., and Hernandez, A., 1998, Atmospheric mercury concentrations and fluxes in the Almaden District (Spain): Atmospheric 

Environment, v. 32, p. 3897–3904.

Ferrara, R., Maserti, B.E., Breder, R., 1991, Mercury in abiotic and biotic 

compartments of an area affected by a geochemical anomaly (Mt. 

Amiata, Italy): Water, Air, and Soil Pollution, v. 56, p. 219–233.

Ferrara, R., Maserti, B.E., De Liso, A., Cioni, R., Raco, B., Taddeucci, G., 

Edner, H., Ragnarson, P., Svanberg, S., and Wallinder, E., 1994, 

Atmospheric mercury emission at Solfatara Volcano (Pozzuoli, 

Phlegraean fields, Italy): Chemosphere, v. 29, no. 7, p. 1421–1428.

Fitzgerald, W.F., 1986, Cycling of mercury between the atmosphere and 

oceans, in Buat-Menard, P., ed., The role of air-sea exchange in 

geochemical cycling: NATO, Advanced Science Institutes Series, 

Dordrecht, Reidel Publishing Co., p. 363–408.

Fitzgerald, W.F., 1989, Atmospheric and oceanic cycling of mercury, in

Ripley, J.P., and Chester, R., eds., Chemical oceanography: New 

York, Academic Press, p. 151–186.

Fitzgerald, W.F., and Clarkson, T.W., 1991, Mercury and monomethylmercury—Present and future concerns: Environmental Health Perspectives, v. 96, p. 159–166.

Fitzgerald, W.F., Engstrom, D.R., Mason, R.P., and Nater, E.A., 1998, The 

case for atmospheric mercury contamination in remote areas: Environmental Science and Technology, v. 32, no. 1, p. 1–7.

Gustin, M.S., Lindberg, S.E., Austin, K., Coolbaugh, M., Vette, A., and 

Zhang, H., 2000, Assessing the contribution of natural sources to 

regional atmospheric mercury budgets: Science of the Total Environment, v. 259, p. 61–71.

Gustin, M.S., Taylor, G.E., Jr., and Leonard, T.L., 1994, High levels of mercury contamination in multiple media of the Carson River drainage 

basin of Nevada—Implications for risk assessment: Environmental 

Health Perspectives, v. 102, no. 9, p. 772–778.

Gustin, M.S., Taylor, G.E., Jr., Leonard, T.L., and Keislar, R.E., 1996, Atmospheric mercury concentrations associated with geologically and 

anthropogenically enriched sites in central western Nevada: Environmental Science and Technology, v. 30, no. 8, p. 2572–2579.

Hudson, R.J.M., Gherini, S.A., Watras, C.J., and Porcella, D.B., 1994, Modeling the biogeochemical cycle of mercury in lakes—The mercury 

cycling model (MCM) and its application to the MTL study in lakes, in

Watras, C.J., and Huckabee, J.W., eds., Mercury pollution, integration and synthesis: Boca Raton, Fla., CRC Press, p. 473–523.

Krabbenhoft, D.P., and Rickert, D.A., 1995, Mercury contamination of 

aquatic ecosystems: U.S. Geological Survey Fact Sheet FS-216-95.

Krabbenhoft, D.P., and Wiener, J.G., 1999, Mercury contamination—A 

nationwide threat to our aquatic resources, and a proposed 

research agenda for the U.S. Geological Survey, in Morganwalp, 

D.W., and Buxton, H.T., eds., U.S. Geological Survey, Toxic Substances Hydrology Program, Water-Resources Investigations 

Report 99-4018B, p. 171–178.

Lamborg, C.H., Fitzgerald, W.F., O’Donnell, J., and Torgersen, T., 2002, A 

non-steady-state compartmental model of global-scale mercury biogeochemistry with interhemispheric atmospheric gradients: 

Geochimica et Cosmochimica Acta, v. 66, p. 1105–1118.

Mason, R.P., Fitzgerald, W.F., and Morel, F.M.M., 1994, The biogeochemistry of elemental mercury—Anthropogenic influences: Geochimica 

et Cosmochimica Acta, v. 58, p. 3191–3198.

National Academy of Sciences, 1978, An assessment of mercury in the 

environment: Washington, D.C., National Academy of Sciences, 

National Research Council, 185 p.

Porcella, D.B., 1994, Mercury in the environment—Biochemistry, in

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Sznopek, J.L., and Goonan, T.G., 2000, The materials flow of mercury in 

the economies of the United States and the world: U.S. Geological 

Survey Circular 1197, 28 p.

Ullrich, S.M., Tanton, T.W., and Abdrashitova, S.A., 2001, Mercury in the 

aquatic environment—A review of factors affecting methylation: 

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Why the USGS is Studying Mercury 7
BLANK PAGE 8
9

Mercury in Coal and Mercury Emissions from 

Coal Combustion

By Robert B. Finkelman

Abstract

Mercury emissions from coal-fired electric generating utilities are a major uncontrolled source of mercury in the environment. This mercury may be contributing to serious health 

problems in segments of our society. The USGS is compiling 

information on mercury in coal that may be useful in developing 

strategies for reducing mercury emissions from coal use. The 

USGS coal-quality database contains information on mercury 

concentrations in more than 7,000 coal samples. Detailed 

geochemical analysis has helped to determine that mercury in 

coal is commonly associated with pyrite, but other modes of 

occurrence may be locally important. Physical coal cleaning 

removes, on average, 37 percent of the mercury. Characterization of feed coal and its combustion byproducts is helping to further understand the behavior of mercury in utility boilers.

Introduction

The concentration of mercury in coal has been of concern 

since the passage of the 1990 Clean Air Act Amendment (TooleO’Neil and others, 1999). In 1994, the U.S. Environmental Protection Agency (EPA) estimated that about 50 t of mercury is 

emitted each year from coal-burning power plants in the United 

States, with lesser amounts coming from oil- and gas-burning 

units. In February 1998, the EPA issued a report citing mercury 

emissions from electric utilities as the largest uncontrolled 

source of mercury to the atmosphere (U.S. Environmental Protection Agency, 1997). The EPA estimates emissions from coalfired utilities (fig. 8) may exceed 25 percent of the total airborne 

emissions of mercury (natural plus anthropogenic) in the United 

States (table 1). The EPA suggested that utility mercury emissions are of sufficient potential concern for public health to merit 

further research and monitoring (U.S. Environmental Protection 

Agency, 1997). For the past 20 years, the USGS has been conducting research on the distribution and concentration of mercury in coal in the United States. More recently, the USGS has 

undertaken research to understand the forms of mercury in coal 

and its behavior during coal cleaning and combustion (TooleO’Neil and others, 1999).

Coal-Quality Database on Mercury

The USGS has compiled a coal-quality database containing 

information on the concentration of mercury in more than 7,000 

in-ground coal samples. The average concentration of total 

mercury in coal is about 0.2 μg/g (micrograms/gram); values 

exceeding 1 μg/g are rare. On an equal energy basis, the highest 

mercury concentrations are found in the Gulf Coast lignites (36 

lb of Hg/1012 Btu), and the Hams Fork region coal (Wyoming) 

has the lowest value (4.8 lb of Hg/1012Btu). Mean concentrations for total mercury in coal for the major coal basins in the 

United States are shown in figure 9. The data for individual samples can be found at: http://energy.er.usgs.gov/products/databases/coalqual/intro.htm.

The USGS is also developing a database that will contain 

information on the mercury content of coals being mined and 

burned in other major coal-producing countries. The data 

should help to establish worldwide contributions of mercury as a 

result of emissions from coal combustion—information that is 

presently not well known.

Forms of Mercury in Coal

As a result of the generally low concentration of total mercury in coal, and the high volatility of mercury, it is particularly 

difficult to determine the form(s) of mercury in coal. Recent 

research indicates that most of the mercury in coal is associated 

generally with secondary, arsenic-bearing pyrite (Finkelman, 

1981; Toole-O’Neil and others, 1999). The mercury was deposited with the pyrite in cleats and fractures when hydrothermal 

solutions percolated through coal (Toole-O’Neil and others, 

1999). Other forms of mercury that have been reported are 

organically bound mercury, elemental mercury, and mercury 

sulfides and selenides (fig. 10); (Finkelman, 1981). Mercury 

selenides may be the primary form of mercury in coal samples 

with little pyrite.

Figure 8. Four Corners coal-fired electrification power plant near 

Farmington, N. Mex. Emissions from such power plants that use coal 

for fuel are under study as sites of potential mercury contamination to 

local and regional environments.
10 Mercury in Coal and Mercury Emission from Coal Combustion

Reducing Mercury Emissions from Power Plants

Because mercury is often found in fracture-filling pyrite, 

conventional coal cleaning procedures are generally effective in 

reducing mercury levels in the coals being burned. Conventional 

coal cleaning typically uses physical methods based on density 

differences to separate coal and minerals such as pyrite. The 

USGS is researching ways to assess the ability to remove mercury from coal by conventional physical coal cleaning techniques. The results of these studies indicate that an average of 

37 percent of the mercury is removed by commercial coal cleaning procedures (Toole-O’Neil and others, 1999).

In addition to coal cleaning, several other methods exist for 

reducing mercury emissions. These include fuel switching—

switching to oil or gas or using coal having lower mercury contents; selective mining—disposing of or simply not mining parts 

of the coal bed or deposit that have high mercury contents; modifying combustion conditions—such as using fluidized-bed 

combustion1

; post-combustion pollution control—use of 

electrostatic precipitators or baghouses (fabric filter traps) to capture particulates, or flue-gas desulfurization systems to remove 

pollutants from the gaseous effluents. New pollution control systems, such as activated carbon injection specifically designed for 

mercury capture, are presently being developed and tested. 

Research scientists at the USGS are studying the distribution of 

mercury and the forms of mercury in coal that will be helpful for 

evaluating mercury pollution from coal and assessing ways to 

reduce such pollution through fuel switching, selective mining, 

and physical coal cleaning.

Continuing USGS Research on Coal Combustion

As discussed above, postcombustion pollution-control systems can remove some of the mercury volatilized by coal combustion. Chu and Porcella (1995) indicated that electrostatic 

precipitators and fabric filters that trap fly ash remove about 30 

percent of the mercury. The effectiveness of mercury removal 

by wet flue-gas-desulfurization systems varies widely, but on 

average about 45 percent, and as much as 90 percent, of the 

total mercury can be eliminated. The USGS had a project to 

determine the mercury content (as well as the concentrations of 

about 45 other elements) in feed coal, fly ash, bottom ash, and 

1

 This technique uses pulverized coal that is suspended by upward-flowing 

air in a “bed” of particles, commonly limestone. This process operates at 

lower temperatures than conventional power generators, and the limestone 

captures pollutants such as mercury.

50°

40°

30°

20°

140° 130° 120° 110° 100° 90° 80° 70° 60°

EXPLANATION

Coal areas with less than 30 samples

> 5 and ≤ 10 lb Hg/10 Btu 12

> 10 and ≤ 15 lb Hg/10 Btu

> 15 and ≤ 20 lb Hg/10 Btu

> 20 lb Hg/10 Btu

12

12

12

x = Mean

n = Number of samples

Pennsylvania

Anthracite

x=15.7

n=39

Northern Appalachian x=18.8

n=1506

Central Appalachian x=11.3

n=1648

Southern Appalachian

x=17.0

n=969

Gulf Coast

x=27.0

n=110

Raton Mesa

x=6.9

n=34

San Juan

x=7.4

n=173

Uinta

x=6.6

n=226

Green River

x=6.5

n=277

Wind River

x=15.9

n=42

Powder River

x=10.1

n=489

Fort Union

x=15.9

n=261 Western Interior

x=16.4

n=261

Eastern Interior

x=7.8

n=255

0 400 kilometers

200

200

0 miles

Figure 9. Distribution of mercury in coal fields in the United States. Data are given on an equal energy basis, in which mercury 

concentration is converted to weight percent and divided by Btu.
References Cited 11

Figure 10. Scanning electron micrograph of mercury selenide 

(HgSe) crystals (white spots) in lignite coal from California. Mercury 

selenide is a highly toxic mercury compound and is a rare example 

of a mercury mineral in coal. Scale bar is 10 micrometers.

flue-gas- desulfurization products (Breit and others, 1996). In 

this study, long-term (monthly sampling for 2 years) monitoring 

of coal samples from a power plant with units burning high- and 

low-sulfur coal indicated little variation in mercury content in 

either the feed coal or the coal-combustion products during the 

monitoring period. Therefore, few high-quality analyses of 

representative samples may adequately describe the Hg content 

of some feed coals.

References Cited

Breit, G., Eble, C., Finkelman, R., Affolter, R., Belkin, H., Brownfield, M., 

Cathcart, J., Hower, J., Leventhal, J., McGee, J. Palmer, C., Reynolds, R., Rice, C., and Zielinski, R., 1996, Systematic investigation of 

the compositional variations in solid waste products of coal combustion: 13th Annual International Pittsburgh Coal Conference, p. 

1356–1361.

Chu, P., and Porcella, D.B., 1995, Mercury stack emissions from U.S. 

electric utility power plants, in Porcella, D.B., Huckabee, J.W., and 

Wheatley, B., eds., Mercury as a global pollutant: Water, Air, and 

Soil Pollution, v. 80, p. 135–144.

Finkelman, R.B., 1981, Modes of occurrence of trace elements in coal: 

U.S. Geological Survey Open-File Report 81-99, 314 p.

Toole-O’Neil, B., Tewalt, S.J., Finkelman, R.B., and Akers, D.J., 1999, 

Mercury concentration in coal—Unraveling the puzzle: Fuel, v. 78, 

p. 47–54.

U.S. Environmental Protection Agency, 1997, Mercury study report to 

Congress, Volume I, Executive summary: U.S. Environmental Protection Agency Report EPA-452/R-97-003.

References Cited 11
BLANK PAGE 12
13

Mercury Mine Studies

Environmental Impact of Mercury Mines in the 

Coast Ranges, California

By James J. Rytuba

Abstract

The California Coast Ranges mercury mineral belt has been 

the largest producer of mercury in North America. Two types of 

mercury deposits are found in the mineral belt: hot spring and 

silica-carbonate. The primary ore mineral in both mercury 

deposit types is cinnabar, but small amounts of elemental mercury are present. Mercury mines recovered mercury by heating 

ores in a furnace or retort to a temperature above the stability of 

cinnabar in order to release mercury vapor. During roasting of 

mercury ores, new mercury compounds formed. The speciation 

of mercury in mine tailings indicates that metacinnabar, corderoite, schuetteite, and mercury chlorides formed during the processing of ores.

Mine drainage is associated with many of the mercury 

deposits, and the geology and geochemistry of the deposit is 

important in determining the pH and composition of mine drainage from the two types of mercury deposits. The presence of 

carbonate minerals and serpentinite associated with silica-carbonate deposits serve to mitigate the acidity of mine drainage 

except where high iron-sulfide content occurs and resultant acidity is as low as pH 2. High concentrations of total mercury (up 

to 450,000 ng/L) and methylmercury (up to 70 ng/L) were found 

in mine-drainage waters from both deposit types. Mercury and 

methylmercury from mine drainage is adsorbed onto iron-rich 

precipitates and is seasonally flushed in streams during periods 

of high water flow.

Introduction

Mercury has been mined in North America since the early 

1800s with over 3,800,000 flasks (about 130,000 t) of mercury 

being produced from several mercury mineral belts (fig. 11). 

The California Coast Ranges mineral belt has been the largest 

producer of mercury. It contains more than 50 mines that have 

produced more than 1,000 flasks each—including New Almaden 

(fig. 12), the largest mercury mine in North America, which produced about 2,800,000 flasks. Much of the elemental mercury 

produced in North America was used in the recovery of gold 

from placer and hard-rock mines, using the mercury amalgamation process. Because of environmental concerns and the consequent low price of mercury, large-scale mercury mining 

ceased by about 1990 in North America. In the United States, 

mercury is now produced only as a byproduct from presently 

operating gold mines where environmental regulations require 

its recovery and from the reprocessing of precious-metal-mine 

tailings and gold-placer sediments.

Many of the mercury mines in the California Coast Ranges 

pose an environmental concern because of the presence of mine 

waste rock that contributes mercury-rich sediment to nearby 

watersheds. At some of the mines, acidic drainage adversely 

affects the water quality of surrounding streams. The release of 

mercury in mine drainage is a significant source of mercury to 

watersheds, where it may bioaccumulate in biota, including fish.

Mineralogy of the Coast Ranges Mercury 

Deposits

The California mercury mineral belt extends for 400 km in 

the southern and central Coast Ranges and contains two distinct 

types of mercury deposits—silica-carbonate and hot-spring 

deposits (fig. 12); (Rytuba, 1996). The primary ore mineral in 

both these deposits is cinnabar, but elemental mercury is also 

found in small amounts (table 2). In some of the silica-carbonate deposits, metacinnabar, the high temperature polymorph of 

cinnabar, is an important ore mineral. Mercury chloride and 

mercury sulfate minerals are rare, but in a few deposits they constitute the primary ore minerals. In hot-spring deposits, pyrite 

and native sulfur are found in only small amounts. In silica-carbonate deposits, iron-sulfide minerals such as pyrite and marcasite are common. In some silica-carbonate deposits, iron 

sulfides constitute as much as 50 percent of the ore minerals, but 

iron sulfides are generally minor in hot-spring deposits. Iron 

sulfides tend to be environmentally adverse because they generate acidic water upon weathering.

Mercury Compounds in Mine Wastes

Mercury mines in the Coast Ranges were typically small, 

affecting areas of a square kilometer or less. The mercury ores 

were mined and processed at the same site, and only rarely were 

ores transported to a central processing facility. The primary 

recovery method consisted of roasting mercury ore in a furnace 

or retort to a temperature above that for the stability of cinnabar 

in order to release mercury vapor and sulfur. The mercury vapor 

was then cooled in a condenser system, and elemental mercury 

was recovered in a water-cooled trough at the base of the condensing columns. Inefficiencies in the roasting process produced mercury vapor and mercury-rich particulates that were 

released to the atmosphere and deposited downwind from the 

furnace site. Soot that accumulated in the condensing columns 

was periodically removed and reprocessed in a retort to recover 

any remaining mercury. Condenser soot has the consistency of 
14 Environmental Impact of Mercury Mines in the Coast Ranges, California

Arkansas

California

Coast

Ranges

Great

Basin

Pacific

Northwest

Southwest

Alaska

Pinchi

Lake

Mexico

West

Texas

Hot-spring type

Silica-carbonate type

Mercury mineral belt

Mercury occurrence

EXPLANATION

ash and can be readily redistributed by wind. Discarded soot is 

an environmental concern because it may contain as much as 

several weight percent mercury, primarily as elemental mercury 

and soluble mercury sulfates and chlorides.

The process of heating ore to vaporize mercury from ore is 

a type of calcination process, and the resultant mercury mine 

wastes are termed calcines. These calcines have a characteristic 

red color that results from the oxidation of iron sulfides during 

ore roasting and the presence of fine-grained cinnabar (fig. 13). 

Lime (CaO) was also added to the mercury ore to remove sulfur. 

Mercury mine-waste calcines were typically discarded adjacent 

to the furnace site or into nearby stream channels. Flood events 

periodically transported the calcines downstream, thus continually providing space for disposal of additional mine wastes. As a 

result, calcines are typically found in stream channels and overbank material for several kilometers downstream from mines. 

Mine wastes were also used for road construction adjacent to 

mines as another method of discarding the wastes.

In California, the concentration of total mercury in calcines 

typically ranges from 10 to 1,500 μg/g depending on the efficiency of the roasting process. In addition to the concentration 

of total mercury in calcines, determination of the specific mercury compounds present in the wastes is important for the 

understanding of mercury bioavailability in surrounding ecosystems. For example, the amount of various mercury compounds 

has an effect on mercury methylation and subsequent uptake by 

biota. Several mercury compounds are commonly formed during roasting of mercury ore including metacinnabar, corderoite 

(Hg3

S2Cl2), schuetteite (Hg(SO4 )

2

H2O), and mercury chlorides 

and oxides (Kim and others, 2000). All these compounds are 

more soluble than cinnabar, and as a result, they are more reactive and release Hg2+, with the potential to form bioavailable 

methylmercury (Rytuba, 2000). 

Mercury in acid-mine drainage and sediment

The mineralogy and geochemistry of the mercury deposits 

(table 2) are important factors in determining the pH and the 

composition of drainage downstream from the mines. For 

example, mine drainage from some silica-carbonate deposits is 

extremely acidic, as low as pH 2.2, owing to the presence of 

Figure 11. Mercury mineral belts in North America. Mercury mines shown have significant mercury production (> 1,000 flasks or 34 t), 

and mercury occurrences have little or no production. Modified from Rytuba (2003).
13

Hot-spring Hg deposit

Clear Lake 0.01-2.1

Hg-Au (0.0-0.8 Ma)

Au-Ag-Hg (1.4-2.1 Ma)

Sb-Hg-Au (9.2 Ma)

Sutter Buttes

0.6 Ma

Sonoma-Tolay 2.7-13 Ma

Berkeley Hills

 7.5-11.5 Ma

Quien Sabe 7.0-14.5 Ma

Eagle Crags

15.2-18.7 Ma

Soledad 17-21.5 Ma

Au-Hg (18.6 Ma)

Neenach

San Emigdio

 21 Ma

Pinnacles 22 to 24 Ma

23.0 Ma

7.5 Ma

14.5 Ma

3.0 Ma

2.0 Ma

Conejo

(12-16 Ma)

Santa Cruz

San Clemente

POINT OF FIRST COLLISION

WITH EAST PACIFIC RISE

29 Ma

Glendora

El Modeno

San Joaquin

Neogene volcanic field

Great Valley forearc

sediments

Franciscan Complex

Mendocino triple

 Volcanic field and ore

 deposit type

Hg-Au (9.2)

 junction location

Silica-carbonate Hg 

22-24 Ma

EXPLANATION

New Almaden Hg mine Fault 

0 100 KILOMETERS

Figure 12. Mercury deposits in California mercury mineral belt. Age in Ma (million years).

Table 2. Geologic and geochemical factors that control the composition of mine drainage from mercury 

deposits and mines in the California Coast Ranges.

 Silica-carbonate deposits Hot-spring deposits

Trace metals Ni-Co-Cr-Sb-Zn-Cu Au-As-Sb-Li-W.

Alteration Carbonates-quartz Adularia-quartz-clays.

Sulfides Pyrite and marcasite (5–50%) Pyrite (2–5%).

Host rocks Serpentinite, minor shale Clastic rocks, lesser volcanic rocks.

Structural control Serpentinite contacts Faults and volcanic vents.

Ore minerals Cinnabar, minor elemental Hg Cinnabar.

Secondary minerals Mercury sulfates and chlorides Mercury sulfates and chlorides.
16 Environmental Impact of Mercury Mines in the Coast Ranges, California

large amounts of acid-water-generating iron-sulfide minerals. 

Acidic drainage from such mines is environmentally adverse 

because mercury and other metals are more mobile in low-pH 

conditions. Where acid-mine drainage flows through and reacts 

with mine wastes, soluble mercury compounds are leached, 

resulting in higher total mercury concentrations in water 

(fig. 14). High concentrations of total mercury (as much as 

450,000 ng/L (nanograms/liter)) and methylmercury (as much 

as 70 ng/L) are found in such mine drainage (see table 3, p. 34). 

The mercury and methylmercury concentrations in these mine 

waters are several orders of magnitude higher than uncontaminated baseline sites (table 3) and indicate that mercury mines 

in the California Coast Ranges are sites of significant mercury 

contamination.

In addition to acid-mine drainage, mercury mines with 

abundant iron sulfides also produce high concentrations of dissolved iron (> 8,000 mg/L (milligrams/liter)), which leads to 

precipitation of iron oxyhydroxides (Rytuba, 2000). Iron precipitates, as well as clay minerals, have a high capacity to sorb mercury; and as a result, they are an important source of mercury 

released from mercury-mine drainage. Such iron- and clay-rich 

sediment derived from mine wastes is the main source of mercury, where mercury contents are as high as 220 μg/g and methylmercury is as high as 110 ng/g. Particulate mercury is released 

from these sediments into streams during periods of high precipitation and resultant high runoff, which is common in the California winter climate. Particulate mercury released during highflow becomes available to bacteria that methylate mercury later 

in the season, especially under the oxygen-depleted aquatic conditions typical in late summer. Methylmercury generated around 

these mine sites becomes bioavailable to organisms in the 

aquatic food web, especially fish. In some instances, mercury 

contents in fish collected downstream from some mercury mines 

exceed the 0.5 μg/g safe level for edible portions of fish established by the State of California (table 3). Mercury mines typically generate the highest concentrations of mercury-rich 

sediment and runoff with elevated mercury (some of which is 

acidic), and these sites are the primary sources of mercury that 

enters surrounding ecosystems in the California Coast Ranges.

Figure 13. Typical mercury mine-waste calcines. Red-brown 

character of these mine wastes is a result of presence of iron oxide 

and fine-grained cinnabar.

Figure 14. Total mercury concentration in acid-rock drainage from silica-carbonate and hot-spring-type mercury deposits in the 

California mercury mineral belt as a function of chloride concentration.

Silicacarbonate

type Hg

deposit

Hot-spring

type Hg

deposit

EXPLANATION

CHLORIDE IN MILLIGRAMS PER LITER

TOTAL MERCURY IN MICROGRAMS PER LITER

1,000

100

10

1

0.1

0.01

0.001

1 10 100 1,000 10,000
References Cited 17

References Cited

Kim, C.S., Brown, G.E. Jr., and Rytuba, J.J., 2000, Characterization and 

speciation of mercury-bearing mine wastes using X-ray absorption 

spectroscopy (XAS): Science of the Total Environment, v. 261,

 p. 157–168.

Rytuba, J.J., 1996, Cenozoic metallogeny of California, in Coyner, A.R., 

and Fahey, P.L., eds., Geology and ore deposits of the American 

Cordillera: Geological Society of Nevada Symposium Proceedings, 

Reno/Sparks, Nev., April 1995, p. 803–822.

Rytuba, J.J., 2000, Mercury mine drainage and processes that control its 

environmental impact: Science of the Total Environment, v. 260, p. 

57–71.

Rytuba, J.J., 2003, Mercury from mineral deposits and potential environmental impact: Environmental Geology, v. 43, p. 326–338.

References Cited 17
BLANK PAGE 18
19

The Southwestern Alaska Mercury Belt

By John E. Gray and Elizabeth A. Bailey

Abstract

Abandoned mercury mines are scattered over several thousand square kilometers in southwestern Alaska, primarily in the 

Kuskokwim River basin. Mercury ore is dominantly cinnabar, 

but elemental mercury is present at some mines. About 1,400 t 

of mercury have been produced from the region, but mines in the 

area have been closed since the 1970s. Stream-sediment samples collected downstream from the mines can contain total mercury concentrations as high as 5,500 μg/g. Such high mercury 

concentrations are related to the abundance of cinnabar, and in 

some instances minor elemental mercury, which are visible in 

streams below mine sites. Unfiltered mine-water samples contain total mercury as high as 2,500 ng/L; whereas, corresponding 

water samples filtered at 0.45 μm contain total mercury contents 

of less than 50 ng/L. These water data indicate that most of the 

mercury transported downstream from the mines is as finely suspended material rather than dissolved mercury. Although methylmercury contents (as much as 31 ng/g in sediments and 1.2 ng/

L in stream water) represent only a small portion of the total 

mercury, these results indicate that part of the mercury is converted to bioavailable methylmercury. Muscle samples of fish 

collected downstream from mines contain total mercury concentrations as high as 0.62 μg/g (wet weight), of which 90 – 100 

percent is methylmercury. However, the concentration of mercury in these fish is below the 1.0 μg/g action level for mercury 

in edible fish established by the U.S. Food and Drug Administration (FDA). Salmon contain total mercury contents of less than 

0.1 μg/g and were the lowest mercury contents found for fish in 

the study, and well below the FDA action level.

Introduction

In addition to the large mercury mines in the California 

Coast Ranges, a much smaller belt of mercury mines and deposits is located in southwestern Alaska (fig. 15). Similar to some 

of the deposits in California, the mercury deposits in Alaska 

were formed near the Earth’s surface in hot-spring environments 

(Gray and others, 1997). The Alaska mercury belt consists of 

numerous deposits and abandoned mines covering a wide area, 

mostly along the Kuskokwim River basin (fig. 15). Like most 

mercury mines worldwide, cinnabar is the dominant ore mineral, 

but native mercury is also found in a few localities. These mines 

are presently closed, but they produced about 41,000 flasks of 

mercury (1,400 t) from mining in the early 1900s through the 

1970s. Although this mercury production is small compared 

with much larger mines throughout the world (fig. 5), the mines 

in southwestern Alaska produced more than 99 percent of all 

mercury mined in the State.

There are presently significant mine wastes containing cinnabar ore and minor amounts of elemental mercury near retorts 

(fig. 16). Mercury remaining at these sites poses potential environmental hazards to the population and wildlife because mine 

drainage enters streams and rivers that are part of local ecosystems. To evaluate environmental concerns, the USGS measured 

concentrations of total mercury and methylmercury in stream 

sediment, soil, stream water, vegetation, and fish collected near 

these mines (Gray and others, 1996; Bailey and Gray, 1997; 

Gray and others, 2000; Bailey and others, 2002). Similar samples were also collected distant from the mines to compare total 

mercury and methylmercury concentrations in samples unaffected by mercury mining (table 3).

Stream-Sediment, Soil, and Vegetation Samples

Stream-sediment and soil samples collected near the mines 

in southwestern Alaska can contain total mercury concentrations as high as 5,500 μg/g (Gray and others, 1996; Bailey and 

Gray, 1997). Such high mercury concentrations are due to the 

abundance of cinnabar and minor amounts of elemental mercury present in these samples. Cinnabar is resistant to surface 

weathering and thus is common around these sites and in 

streams draining the mines. Concentrations of highly toxic 

methylmercury (as much as 41 ng/g in the stream-sediment and 

soil samples; table 3) are low relative to the high concentrations of total mercury in the stream-sediment and soil samples. Vegetation collected near the mines studied were also 

highly elevated in total mercury (as much as 970 ng/g) and 

methylmercury (as much as 11 ng/g) (Bailey and others, 2002). 

On a percentage basis, methylmercury generally composes less 

than one percent of the total mercury in the sediment, soil, and 

vegetation samples.

Stream Water and Fish

Stream waters draining the mercury mines are neutral to 

slightly alkaline, ranging in pH from 7.0 to 8.5. Acid-water-generating iron-sulfide minerals are rare, and as a result, near-neutral water pH is common around these mines. In addition, 

cinnabar is generally insoluble in water and does not readily 

form acid water during weathering. Thus, acidic mine water in 

streams is generally insignificant. 

Unfiltered stream-water samples collected below the mines 

contained total mercury as high as 2,500 ng/L (fig. 17). Total 

mercury concentrations were several times higher in unfiltered 

stream water than in corresponding filtered-water samples, indicating that mercury transport is mostly as suspended particulates, probably particulate cinnabar. Most stream waters 

contained total mercury concentrations below the 2,000 ng/L 

drinking-water standard (fig. 17) recommended by the State of 

Alaska (Alaska Department of Environmental Conservation, 
20 The Southwestern Alaska Mercury Belt

0

0

50

50 MILES

100 KILOMETERS

Bristol

 Bay

Kuskokwim 

 Bay

Bethel

Aniak

62°

164° 160° 156°

60°

Dillingham

Hg prospect

 Hg mine

64°

Sleetmute

Yukon River

Iliamna

 Lake

KuskokwimRiver

ALASKA RANGE

Cinnabar Creek mine

 EXPLANATION

ALASKA

Study Area

Elemental mercury, retort at Red Devil, Alaska

1994), but exceed the 12 ng/L standard that the EPA has suggested may result in chronic effects to aquatic life (U.S. Environmental Protection Agency, 1992). As recommended by the EPA, 

when total mercury in stream water was found to exceed the 12 

ng/L EPA chronic aquatic life standard, edible portions of fish 

were analyzed to determine their mercury contents (discussed in 

the next paragraph). Methylmercury concentrations in the 

stream-water samples were as much as 1.2 ng/L (table 3). 

Figure 15. Location of mercury mines in southwestern Alaska.

Figure 16. Elemental mercury spilled at Red Devil mine retort, Alaska. Oxidation of elemental mercury to Hg2+ and subsequent 

methylmercury formation is a significant environmental concern around all mercury mines. The retort facility and nearby elemental mercury contamination have been removed from the Red Devil site and additional remediation efforts are ongoing.

20 The Southwestern Alaska Mercury Belt
Summary of the USGS Studies in Alaska 21

0

1

10

100

1,000

10,000

0.01 0.1 1 10

METHYLMERCURY, IN NANOGRAMS PER LITER

TOTAL MERCURY, IN NANOGRAMS PER LITER

Uncontaminated baselines

EPA-aquatic life standard

State drinking water standard

Similar to the results for the stream-sediment and soil samples, 

methylmercury concentrations in the stream-water samples constituted a small fraction, generally less than 3 percent of total 

mercury. However, methylmercury contents in unfiltered mine 

waters were generally higher than that found in unfiltered water 

from regional baseline sites uncontaminated by mercury mining 

(≤ 0.3 ng/L; table 3).

Samples of muscle from freshwater fish (fillets) collected 

near these mercury mines contained as much as 0.62 μg Hg/g 

(wet weight basis) (fig. 18). Of this, methylmercury makes up 

more than 90 percent of the total mercury (Gray and others, 

2000), which is typical for most fish (National Academy of Sciences, 1978; U.S. Environmental Protection Agency, 1997). The 

mercury results for these fish indicate that part of the mercury is 

biologically available to the fish, especially fish collected nearest 

the mines. For example, fish collected near the Cinnabar Creek 

mine contained total mercury concentrations several times 

greater than mercury in fish collected distant from the mines. 

The State of Alaska has not established a regulatory standard for 

mercury contents in fish, and thus Alaska uses the Federal 

“action level” for mercury of 1.0 μg/g in edible portions of fish 

(fish muscle) established by the U.S. Food and Drug Administration (FDA) (Federal Register, 1979). All of the mercury contents in the fish collected in southwestern Alaska were below the 

FDA action level; when this concentration is exceeded, advisories are posted and the sale of fish is restricted. However, methylmercury contents in some fish collected from Cinnabar Creek 

(Gray and others, 2000) exceed the newly established standard 

of 0.3 μg-methylmercury/g-fish (U.S. Environmental Protection 

Agency, 2001). Perhaps most importantly, all salmon collected 

by the USGS in this study contained total mercury concentrations less than 0.1 μg/g, the lowest mercury concentrations in 

this study, and below the recommended safe levels for mercury 

in fish (fig. 18). These results are significant because salmon are 

the most commonly consumed fish by residents and sport fishermen in the region.

Summary of the USGS Studies in Alaska

The concentration of total mercury is highly elevated especially in stream-sediment and soil samples collected from 

around the mercury mines in Alaska. These high mercury concentrations are related to the presence of cinnabar, which is a 

stable form of mercury with a low reactivity in water. Concentrations of methylmercury measured in the samples collected 

indicate that only minor conversion to this highly toxic form of 

organic mercury, but the elevated total mercury concentrations 

in fish collected near the mines indicate that some mercury is 

bioavailable to fish. Mercury concentrations in fish are useful 

for understanding the pathway of mercury in the food chain that 

can eventually affect humans. Although total mercury contents 

in sediment and water collected near the mines are elevated, all 

of the fish analyzed contained total mercury concentrations 

below the safe level for edible fish recommended by the FDA. 

Figure 17. Concentration of mercury versus methylmercury in unfiltered water samples (red diamonds) collected from near mercury mines and 

uncontaminated baselines in southwestern Alaska. State of Alaska drinking water standard for mercury (2,000 ng/L) and EPA aquatic life mercury standard for adverse chronic effects to biota (12 ng/L) also shown for reference.
22 The Southwestern Alaska Mercury Belt

0

0.2

0.4

0.6

0.8

1.0

1.2

1 2 3 4 5

MERCURY IN FISH MUSCLE, IN MICROGRAMS PER GRAM

Salmon

Arctic grayling

Northern pike

Dolly Varden

Cinnabar Creek

 data in red

FDA action level

Figure 18. Mercury concentration in muscle for fish collected in southwestern Alaska. Fish collected nearest Cinnabar Creek mercury 

mine contain highest mercury concentrations. FDA action level is shown for reference.

References Cited

Alaska Department of Environmental Conservation, 1994, Drinking water 

regulations: State of Alaska, Department of Environmental Conservation Report 18-ACC-80, 195 p.

Bailey, E.A., and Gray, J.E., 1997, Mercury in the terrestrial environment, 

Kuskokwim Mountains region, southwestern Alaska, in Dumoulin, 

J.A., and Gray, J.E., eds., Geologic studies in Alaska by the U.S. Geological Survey, 1995: U.S. Geological Survey Professional Paper 

1574, p. 41–56.

Bailey, E.A., Gray, J.E., and Theodorakos, P.M., 2002, Mercury in vegetation and soils at abandoned mercury mines in southwestern Alaska, 

USA: Geochemistry—Exploration, Environment, and Analysis, v. 2, p. 

275–286.

Federal Register, 1979, Action level for mercury in fish, shellfish, crustaceans, and other aquatic animals: Comment from the Department of 

Health, Education, and Welfare, Food and Drug Administration, v. 44, 

no. 14, p. 3990–3993.

Gray, J.E., Gent, C.A., Snee, L.W., and Wilson, F.H., 1997, Epithermal mercury-antimony and gold-bearing vein deposits of southwestern 

Alaska: Economic Geology Monograph 9, p. 287–305.

Gray, J.E., Meier, A.L., O'Leary, R.M., Outwater, C., and Theodorakos, 

P.M., 1996, Environmental geochemistry of mercury deposits in 

southwestern Alaska—Mercury contents in fish, stream-sediment, 

and stream-water samples, in Moore, T.E., and Dumoulin, J.A., eds., 

Geologic studies in Alaska by the U.S. Geological Survey, 1994: U.S. 

Geological Survey Bulletin 2152, p. 17–29.

Gray, J.E., Theodorakos, P.M., Bailey, E.A., and Turner, R.R., 2000, Distribution, speciation, and transport of mercury in stream sediment, 

stream water, and fish collected near abandoned mercury mines in 

southwestern Alaska, U.S.A.: Science of the Total Environment, v. 

260, p. 21–33.

National Academy of Sciences, 1978, An assessment of mercury in the 

environment: Washington, D.C., National Academy of Sciences, 

National Research Council, 185 p.

U.S. Environmental Protection Agency, 1992, Water quality standards; 

establishment of numeric criteria for priority toxic pollutants; states' 

compliance; final rule: Federal Register, 40 CFR Part 131, v. 57, no. 

246, p. 60847–60916.

U.S. Environmental Protection Agency, 1997, Mercury study report to 

Congress, Volumes I–VIII: U.S. Environmental Protection Agency 

Report EPA-452/R-97-003.

U.S. Environmental Protection Agency, 2001, Water quality criterion for 

the protection of human health—Methylmercury: U.S. Environmental Protection Agency Report EPA-823-R-01-001.
23

Studies of Mercury Contamination from Gold Mining

Mercury Contamination from Hydraulic 

Gold Mining in the Sierra Nevada, California

By Michael P. Hunerlach and Charles N. Alpers

Abstract

Mercury contamination from the mining and recovery of 

gold during the late 19th and early 20th centuries is widespread 

in watersheds where there are historic placer-gold mines in the 

Sierra Nevada, California. Hydraulic mining has severely modified the region’s geomorphology and hydrology, leading to 

increased turbidity of the natural waters, siltation of riverbeds, 

and contamination of the bottom sediments of reservoirs downstream of the mines. Both elemental mercury and methylmercury, which are potential risks to human health and to 

surrounding ecosystems, have been detected in the watersheds 

where hydraulic mining was widespread. Since 1998, the USGS 

has been characterizing specific “hot spots” in the Sierra Nevada 

to identify elevated concentrations of total mercury and methylmercury in water, soil, and biota. High levels of mercury bioaccumulation in various fauna, from mine sites and receiving 

waters, and visible elemental mercury in sediments and on bedrocks downstream of mines indicate a large part of the mercury 

used in gold ore processing was lost to the environment. The 

most elevated total mercury concentrations in the water and sediment were found in ground and tunnel sluices, the sites of historical gold recovery. Mercury bioaccumulation in fish in 

reservoirs and streams has prompted local officials to issue consumption advisories.

Introduction

Mercury contamination from historic placer-gold mines in 

the Sierra Nevada, California, represents a potential risk to 

human health and the environment (fig. 19). Elemental mercury 

that was used in the late 1800s and early 1900s for the recovery 

of gold at the mines and processing sites continues to enter local 

and downstream water bodies. Rivers, reservoirs, flood plains, 

and estuaries have been affected by the transport of mercury 

associated with contaminated sediments downstream from the 

mines. Since 1998, the USGS has been characterizing specific 

“hot spots” in the Sierra Nevada to identify elevated concentrations of total mercury and methylmercury in water, soil, and 

biota. Unfiltered mine waters sampled in 1998 contained total 

mercury concentrations ranging from 40 to 10,400 ng/L, and 

concentrations of methylmercury in corresponding unfiltered 

water samples ranged from 0.01 to 1.1 ng/L. In addition, samples of sluice-box sediments contained total mercury concentrations ranging from 600 to 26,000 μg/g. 

Although these sluice-box sediments are highly elevated in 

mercury, sediments collected from the Sacramento River farther downstream from the mines show significant dilution of 

mercury with concentrations similar to those found in sediments collected from uncontaminated baseline sites in North 

America (table 3). Based on these studies, the USGS estimates 

that hundreds to thousands of pounds of elemental mercury may 

remain at each of numerous sites affected by hydraulic placergold mining in the Sierra Nevada (Hunerlach and others, 1999). 

Total mercury concentrations in muscle samples of black bass 

(Micropterus spp.), including largemouth, smallmouth, and 

spotted bass collected from areas affected by historic gold mining in the Sierra Nevada, ranged from 0.20 to 1.5 μg/g (wet 

weight basis) in five Sierra Nevada reservoirs affected by historic hydraulic gold mining (table 3); (May and others, 2000). 

The mercury content in many of these fish exceeded the 

1.0 μg/g FDA action level and the 0.5 μg/g safe level used by 

the State of California (table 3). Based on USGS studies, a better understanding is emerging of mercury distribution, ongoing 

transport, transformation processes, and the extent of biological 

uptake in areas affected by gold mining in the Sierra Nevada 

(Hunerlach and others, 1999; May and others, 2000).

Origins of Hydraulic Mining in California

Hydraulic mining began in California between 1852 and 

1853, shortly after the discovery of gold. Vast gravel deposits 

in rivers within the Sierra Nevada gold belt contained large 

quantities of placer gold that provided the basis for the first 

large-scale mining in California. California had all the essential 

materials for the cheap and efficient method of hydraulic mining. Water was abundant, vast Tertiary-age gravels were rich 

with fine-grained gold, and elemental mercury (used for gold 

recovery) was being produced extensively in the Coast Ranges 

mercury mines (Alpers and Hunerlach, 2000; Rytuba, this volume). Hydraulic mining used high-pressure water spraying 

(fig. 20) to deliver large volumes of water that stripped the 

ground of soil, sand, and gravel above bedrock. The water and 

sediment formed slurries that were directed through large sluice 

boxes at sites near the discovery of gold (fig. 21), where the 

gold was recovered. An extensive water transfer system of 

ditches, canals, and vertical pipes was constructed to provide 

the sustained water pressure necessary for hydraulic mining. 

As mining progressed into deeper gravels, tunnels were constructed to facilitate drainage and to provide an exit route for 

mining debris from the bottom of hydraulic mine pits. The 
24 Mercury Contamination from Hydraulic Gold Mining in the Sierra Nevada, California

Los 

Angeles

San

Diego

San 

Francisco

Gold mines

Mercury mines

EXPLANATION

Klamath-Trinity Mountains

Sierra Nevada

N

Elemental Mercury Use in Hydraulic Mining

The capability of elemental mercury to alloy or amalgamate 

with gold has been well known for more than 2,000 years. Miners used elemental mercury to recover gold throughout the western United States at both placer (alluvial) and hardrock (lode) 

mines. The vast majority of elemental mercury lost to the environment in California was from placer-gold mines, which used 

hydraulic, drift, and dredging methods to process more than 5.5 

billion cubic yards of gold-bearing gravels. In placer mine operations, loss of elemental mercury during gold recovery was 

reported to be as much as 30 percent or higher, depending upon 

the efficiency of the gold recovery apparatus (Averill, 1946). 

More than 100,000 t of mercury was produced in California since 

1850, of which more than 10,000 t was used to extract gold by 

amalgamation from the gold-bearing gravels (Churchill, 1999). 

In a typical sluice system, hundreds of pounds of elemental 

mercury were added to riffles and troughs to enhance gold 

recovery. The density of elemental mercury is between that of 

gold and the gravel slurry, so gold and gold-quicksilver amalgam 

would sink, while the sand and gravel would pass over the elemental mercury and through the sluice. Gravel and cobbles that 

entered the sluices caused the elemental mercury to flour, or 

break into small particles. Flouring was aggravated by agitation, 

exposure of elemental mercury to air, and other chemical reactions. Eventually, the entire bottom of the sluice became coated 

with elemental mercury. Some mercury escaped from the sluice 

through leakage and was transported downstream with the placer 

tailings. Because such large volumes of turbulent water flowed 

through the sluice, many of the finer grained gold particles 

attached to elemental mercury particles were washed through 

and out of the sluice before they could settle in the riffles laden 

with elemental mercury. A modification of the sluicing technique known as an undercurrent (fig. 23) was developed to 

address this loss. Fine-grained sediment was allowed to drop 

onto the undercurrent, where gold and gold-mercury amalgam 

were caught.

As a result of the extensive use of mercury for amalgamation during gold recovery and its subsequent loss, elemental 

mercury is commonly present in riverbanks, soils, and drainages 

throughout the region of historic gold mining operations. Mercury concentrations in sediments are generally higher in areas of 

large-scale gold mining and processing activities. In sluice 

boxes, where gold was recovered, and in areas where mining 

debris is continually reworked by seasonal runoff, total mercury 

concentrations can be as much as 1,000 μg/g in tailings. Farther 

downstream, the San Francisco Bay is the recipient of more than 

150 years of contaminated sediment transport, where close correlation exists between total mercury concentrations and percentage of fine-grained sediments in the bay (Hornberger and 

others, 1999). In general, total mercury concentrations tend to 

increase with the amount of fine-grained material because the 

amount of surface area available for adsorption increases with an 

increase in the amount of fine-grained material. Throughout the 

Sierra Nevada millions of cubic yards of both coarse- and finegrained placer tailings are subject to continued mercury remobilization from either natural or anthropogenic effects.

tunnels provided a protected environment for sluices and a way 

to discharge processed sediments (placer tailings) to adjacent 

waterways (fig. 22).

Hydraulic mines operated on a large scale from the 1850s to 

the 1880s in California’s northern Sierra Nevada region displacing a total of more than 1.6 billion cubic yards of sediment. In 

1884, an important legal judgment (the Sawyer Decision) prohibited discharge of mining debris in the Sierra Nevada region (Gilbert, 1917), but not in the Klamath-Trinity Mountains (fig. 19), 

where hydraulic mining continued until the 1950s. Hydraulic 

mining spread quickly throughout the western United States gold 

mining districts and continues today on a limited permit basis 

n Alaska, although elemental mercury is rarely used for gold 

recovery in the United States.

Underground mining of placer deposits (drift mining) and of 

hardrock gold-quartz vein deposits produced most of California’s 

gold from the mid-1880s to the early 1900s. Dredging of goldbearing sediments in the Sierra Nevada foothills has been an 

important source of gold since the early 1900s. Elemental mercury was used extensively until the early 1960s in the dredging of 

large flood-plain deposits of gravel and topsoil (Alpers and 

Hunerlach, 2000). Elemental mercury lost during historic gold 

mining is recovered today as a byproduct from large- and smallscale dredging operations in many placer districts throughout the 

United States.

Figure 19. Location of gold and mercury mines in California.

24 Mercury Contamination from Hydraulic Gold Mining in the Sierra Nevada, California
Elemental Mercury Use in Hydraulic Mining 25

Figure 20. Water cannons used tremendous volumes of water under high pressure to 

break down the gold-bearing gravel deposits in the Sierra Nevada (Malakoff Diggings, 

about 1860). (Photograph courtesy of California Department of Parks and Recreation.)

Figure 21. Gravel deposits were washed into sluices where gold was recovered by gravity separation. Amalgamation with elemental mercury was then used to extract the gold (about 1850). 

(Photograph courtesy of Siskiyou County Historical Society.)

Elemental Mercury Use in Hydraulic Mining 25
26 Mercury Contamination from Hydraulic Gold Mining in the Sierra Nevada, California

undercurrent

sluice

creeks and rivers

 placer

 tailings

metamorphic bedrock

highwall gold-bearing

Tertiary gravels

drainage tunnel 

(sluice)

 drift

mine

ground

 sluice

 partially blocked

 mine workings

hydraulic 

mine pit

lake

Hydraulic

gold mines

Hg (0) Hg (II) 

Au

Au Hg

CH3Hg+ 

Figure 22. Schematic diagram showing transport of mercury and placer tailings from a hydraulic mine pit through a drainage tunnel and discharge into creeks and rivers.

Figure 23. View of sluice system, Siskiyou County, California (about 1860). (Photograph courtesy of Siskiyou County 

Historical Society.)
References Cited 27

References Cited

Alpers, C.N., and Hunerlach, M.P., 2000, Mercury contamination from historic gold mining in California: U.S. Geological Survey Fact Sheet 

FS-061-00, 6 p.

Averill, C.V., 1946, Placer mining for gold in California: California State 

Division of Mines and Geology Bulletin 135, 336 p.

Churchill, R., 1999, Insights into California mercury production and mercury availability for the gold mining industry for the historical record: 

Geological Society of America Abstracts with Programs, v. 31, no. 6, 

p. 45.

Gilbert, G.K., 1917, Hydraulic-mining debris in the Sierra Nevada: U.S. 

Geological Survey Professional Paper 105, 155 p.

Hornberger, M.I., Luoma, S.N., van Geen, A., Fuller, C., and Anima, R., 

1999, Historical trends of metals in the sediments of San Francisco 

Bay, California: Marine Chemistry, v. 64, p. 39–55.

Hunerlach, M.P., Rytuba, J.J., and Alpers, C.N., 1999, Mercury contamination from hydraulic placer-gold mining in the Dutch Flat mining 

district, California: U.S. Geological Survey Water-Resources Investigations Report 99-4018B, p. 179–189.

May, J.T., Hothem, R.L., Alpers, C.N., and Law, M.A., 2000, Mercury bioaccumulation in fish in a region affected by historic gold mining—

The South Yuba River, Deer Creek, and Bear River watersheds, 

California, 1999: U.S. Geological Survey Open-File Report 00-367, 

30 p.

References Cited 27
BLANK PAGE 28
29

Mercury in the Carson River Basin, Nevada

By Stephen J. Lawrence

Abstract

The Carson River from Carson City, Nevada, to the Carson Sink is one of the most severe cases of mining-related mercury contamination in the United States. Elemental mercury 

was used to extract gold and silver in ore mined between 1863 

and 1900 from the Comstock Lode near Virginia City, Nevada. 

During this time, about 7,000 t of elemental mercury was lost 

to the environment in spent mine tailings contaminated with 

mercury. These tailings and associated elemental mercury 

were eroded, transported, and dispersed throughout the lower 

Carson River, Lahontan Reservoir, and the Carson Sink by 

floods that occurred 19 times between 1861 and 1997. Total 

mercury concentrations in Lahontan Reservoir bottom sediments were as much as 80 μg/g and 100 μg/g in deep-water 

and deltaic sediments, respectively. Total mercury concentrations in unfiltered water samples from the Carson River were 

as much as 28 μg/L. Methylmercury concentrations in bottom 

sediments of the Carson River and Lahontan Reservoir were as 

much as 29 ng/g, whereas methylmercury contents in unfiltered water were as much as 21 ng/L. Fish collected from the 

lower Carson River and Lahontan Reservoir contained as much 

as 16 μg/g of total mercury in their tissues, and crayfish contained as much as 50 μg Hg/g.

Introduction

The Carson River in Nevada presents one of the most 

severe cases of mining-related mercury contamination in the 

United States. As much as 7,000 t of elemental mercury, which 

was used to extract gold and silver ores, is estimated to have 

been lost to the Carson River basin during the Comstock Lode 

mining period beginning in the 1850s (Smith, 1943). Elemental 

mercury lost or discarded during mining of the Comstock Lode 

has contaminated sediments of the Carson River (figs. 24 and 

25). 

Little thought was given to the potential environmental 

effects of mercury in the Carson River until the 1970s. In 1973, 

the USGS completed the first assessment of mercury in the Carson River (Van Denburgh, 1973). Since Van Denburgh (1973), 

additional studies have evaluated the association of mercury 

with sediment and organic material, its movement within the 

river, mercury methylation, and mercury accumulation in 

aquatic organisms in this ecosystem (for example, Gustin and 

others, 1994; Miller and others, 1995; Bonzongo and others, 

1996; Wayne and others, 1996; Lechler and others, 1997; Hoffman and Taylor, 1998; Marvin-DiPasquale and Oremland, 

1999). As a result of these studies, the Carson River, including 

the Stillwater Wildlife Refuge, Stillwater Wildlife Management 

Area, and Fallon Wildlife Refuge, was listed on the EPA 

National Priorities List in 1990 as the Carson River Mercury 

Superfund site (fig. 24).

History of the Comstock Lode Mining Period

The Comstock Lode was discovered in the spring of 1859 

(Smith, 1943). Two groups of prospectors, working within a 

mile of each other, found gold-bearing rock near the areas that 

eventually became the towns of Virginia City and Gold Hill. 

These discoveries became the richest silver lode in the United 

States. The lode took its name from Henry Comstock, who 

gained a share of the most famous discovery, called the Ophir 

mine. Initially, placer mining was used to extract gold from 

gravel deposits despite a troublesome blue mud that was later 

identified as silver. Eventually, placer deposits played out and 

miners began using hardrock methods such as underground tunneling in order to follow rich gold ore. By 1863, the discoveries 

by individual prospectors had become the property of shrewd 

businessmen, such as James Fair and John Mackay, who had 

business, political, and mining knowledge. Mining companies 

and corporations were formed and generated operating capital 

by selling mining stocks to investors as far away as San Francisco and New York.

Soon after hardrock mining began, stamp mills were rapidly constructed to process the ore; and by 1863, 66 stamp mills 

were operating in the Carson River basin (fig. 26), primarily 

from Carson City to about 6 km downstream from Dayton (fig. 

24). These mills used a mechanized amalgamation system, 

called the Washoe process, to rapidly extract gold and silver 

from the ores. In this process, rock is finely ground, then mixed 

with elemental mercury, and steam heated in pans to eliminate 

the sulfides in the ore that inhibit the recovery of gold and silver. 

The heat also vaporized mercury from the gold and silver amalgam, leaving gold and silver concentrates behind. The vaporized 

mercury was collected, cooled and condensed back to the liquid 

form, and collected for reuse. The remaining rock slurry, which 

contained small amounts of elemental mercury, was discarded 

either to the river or to tailings ponds near the mills. For every 

ton of ore processed using the Washoe method, as much as 1.5 

pounds of elemental mercury was lost in the tailings (Smith, 

1943). In the late 1800s, cyanide leaching began to replace mercury amalgamation as the preferred extraction method because 

of the higher rate of success of gold and silver recovery. Beginning about 1901, cyanide leaching became widely used in the 

basin.

More than 16,000,000 t of ore were estimated to have been 

removed from mines of the Comstock Lode, and about 

70,000,000 oz of silver (2,500 kg) and 5,000,000 oz of gold (180 

kg) were produced (Smith, 1943). The monetary value of gold 
30 Mercury in the Carson River Basin, Nevada

1

2 3

4

5

6

7

8

9

10

Reno

Sparks

Virginia

City

Fort

Churchill

Dayton

Carson

City

Quartz

Stamp

Mills

Fallon

Carson Sink

Fallon National

Wildlife Refuge

Stillwater

National

Wildlife

Refuge

Stillwater

Wildlife

Mgmt

Area

Lahontan

Reservoir

Washoe

Lake

Truckee

River

Carson River

Lake

Tahoe

Pyramid

Lake

CALIFORNIA

NEVADA

Carson River

basin

0

0 20 30 KILOMETERS

10 20 MILES

10

100

10

1

0.1

0.01

100

10

1

0.1

0.01

100

10

1

0.1

1 2 3 4 5 678 9 10

SAMPLE SITES

Unfiltered water Maximum

Minimum

Bottom sediment

Biological tissue Crayfish

Fish

TOTAL MERCURY, 

IN MICROGRAMS PER GRAM

TOTAL MERCURY,

IN MICROGRAMS PER LITER

Figure 24. Location of sample sites in the Carson River basin, Nevada, and total mercury concentrations in unfiltered water, bottom sediment, and biological tissues collected from the Carson River.
Mercury in Soils, Bottom Sediment, Water, and Fish 31

and silver recovered (1859–1920) was about $350,000,000 

(1920 dollars)(Smith, 1943).

Mercury in Soils, Bottom Sediment, Water, 

and Fish

The Carson River flooded 19 times between 1861 and 

1997. These floods eroded, transported, and dispersed mercurybearing mine tailings throughout the Carson River basin. Mine 

tailings and mercury-bearing stream-bottom sediments present 

throughout the basin contain total mercury concentrations as 

high as 1,610 μg/g (table 3). Total mercury concentrations 

exceeding 25 μg/g are common in flood-plain soils near Dayton, 

Fort Churchill, and the Carson Sink, and greater than 500 μg/g 

on the alluvial fans where Gold and Six Mile Creeks meet the 

Carson River (Hoffman and others, 1989).

Because of alluvial dispersion and dilution, the concentration of total mercury in sediment and soil becomes progressively 

lower farther downstream from contaminated tailings. Where 

soil washes into the river and mixes with bottom sediment, the 

total mercury concentrations measured in these sediments 

decline by nearly an order of magnitude. In 1998, total mercury 

concentrations in river-bottom sediments were significantly 

higher at sites near Fort Churchill (60 μg/g, site 5; fig. 24) compared with sites upstream from Carson City (0.01 μg/g, site 1; 

fig. 24), where the farthest upstream stamp mills were located. 

At Fort Churchill, the river is actively eroding sediments that 

were deposited on flood plains in the last century. Before 1915, 

mercury-contaminated sediments were deposited in the Carson 

Sink, a large, natural evaporation basin for Carson River water. 

After 1915, when the Lahontan Dam was completed, all mercury-contaminated sediment collected in the Lahontan Reservoir. Deep-water-bottom and deltaic-bottom sediments contain 

most of the mercury in the reservoir. The concentration of total 

mercury is as much as 80 μg/g in deep-water-bottom sediments 

and as much as 100 μg/g in deltaic-bottom sediments in Lahontan Reservoir. USGS research suggests that Lahontan Reservoir 

acts as an imperfect sediment trap. Mercury-laden sediment 

escapes the reservoir, especially during large episodic floods 

such as the flood of January 1997 (fig. 25); (Hoffman and Taylor, 

1998).

Figure 25. View of Carson River in Dayton Valley following flooding in January 1997. (Photograph by Pat Glancy, U.S. Geological Survey.)
32 Mercury in the Carson River Basin, Nevada

Figure 26. Vivian quartz mill on Carson River (about 1870). (Photograph courtesy of Nevada Historical Society.)

Mercury is present primarily in its elemental form in tailings and bottom sediments between Carson City and Dayton 

(Lechler and others, 1997). USGS research suggests that as 

these tailings and sediment move downstream toward Lahontan 

Reservoir, the elemental mercury is absorbed onto clays, organic 

matter, and iron and manganese coatings. In the lower Carson 

River and in Lahontan Reservoir, methylmercury concentrations 

in sediments are as much as 29 ng/g, significantly higher than 

that in uncontaminated baseline sediments (table 3). These high 

methylmercury concentrations are probably related to the oxidation of elemental mercury and high organic-carbon contents, 

which are favorable for mercury methylation (Hoffman and others, 1989). Unfiltered water samples generally contain total 

mercury at concentrations similar to those in bottom sediments, 

particularly when flow in the Carson River exceeds 1,000 cubic 

feet per second (cfs). At this and higher stream flows, the river 

transports sediment particles (often mercury-laden) both from 

the stream bottom and from eroding banks (Hoffman and Taylor, 

1998). Total mercury concentrations in unfiltered water samples 

collected from sites near Carson City are similar to those in samples from near Dayton (fig. 24). However, unfiltered water samples collected from Fort Churchill contain total mercury 

concentrations as high as 28 μg/L (table 3). Methylmercury 

contents in unfiltered water collected from Lahontan Reservoir 

were as much as 7.8 ng/L (Hoffman and Thomas, 2000) and as 

much as 21 ng/L (Gustin and others, 1994). Similar to the 

results for bottom sediments, mercury and methylmercury contents in unfiltered water samples collected from the Carson 

River system were significantly higher than that from uncontaminated baseline sites throughout the United States (table 3).

Total mercury concentrations in the tissues of crayfish and 

various fish species show downstream increases that parallel 

those in water and bottom-sediment mercury concentrations (fig. 

24). Total mercury concentrations in fish tissue (walleye) in 

Lahontan Reservoir were found to be as high as 16 μg/g (U.S. 

Environmental Protection Agency, 2002; Wayne Praskins, U.S. 

Environmental Protection Agency, Region 9, oral commun., 

December 2002), which greatly exceeds the FDA action level 

for Hg (1.0 μg/g) for human consumption of fish (table 3). A 

total mercury concentration of about 50 μg/g was measured in 

whole crayfish during a severe drought in 1992 at Fort Churchill 

(fig. 24). The Nevada Division of Wildlife has issued an advisory against consumption of fish from the lower Carson River 

and Lahontan Reservoir. Due to the severity of mercury contamination, the USGS continues to monitor and study the Carson River.

32 Mercury in the Carson River Basin, Nevada
References Cited 33

References Cited

Bonzongo, J.C., Heim, K.J., Warwick, J.J., and Lyons, W.B., 1996, Mercury levels in surface waters of the Carson River-Lahontan Reservoir 

system, Nevada—Influence of historic mining activities: Environmental Pollution, v. 92, p. 193–201.

Gustin, M.S., Taylor, G.E., Jr., and Leonard, T.L., 1994, High levels of mercury contamination in multiple media of the Carson River drainage 

basin of Nevada—Implications for risk assessment: Environmental 

Health Perspectives, v. 102, no. 9, p. 772–778.

Hoffman, R.J., Hallock, R.J., Rowe, T.G., Lico, M.S., Burge, H.L., and 

Thompson, S.P., 1989, Reconnaissance investigation of water quality, bottom sediment, and biota associated with irrigation drainage in 

and near Stillwater Wildlife Management area, Churchill County, 

Nevada, 1986 – 87: U.S. Geological Survey Water Resources Investigations Report 89-4105, 150 p.

Hoffman, R.J., and Taylor, R.L., 1998, Mercury and suspended sediment, 

Carson River basin, Nevada—Loads to and from Lahontan Reservoir 

in flood year 1997 and deposition in reservoir prior to 1983: U.S. Geological Survey Fact Sheet FS-001-98, 6 p.

Hoffman, R.J., and Thomas, K.A., 2000, Methylmercury in water and bottom sediment along the Carson River system, Nevada and California, 

September 1998: U.S. Geological Survey Water Resources Investigations Report 00-4013, 17 p.

Lechler, P.J., Miller, J.R., Hsu, L.C., and Desilets, M.O., 1997, Mercury 

mobility at the Carson River Superfund Site, west-central Nevada, 

USA—Interpretation of mercury speciation data in mill tailings, 

soils, and sediments: Journal of Geochemical Exploration, v. 58, p. 

259–267.

Marvin-DiPasquale, M., and Oremland, R.S., 1999, Microbial mercury 

cycling in sediments of the Carson River system, in Sakrison, R., and 

Sturtevant, S., eds., Watershed management to protect declining 

species: Proceedings of the Water Resources Conference, Seattle, 

Wash., Dec. 5–9, 1999, p. 517–520.

Miller, J.R., Lechler, P.J., Rowland, J., Desilets, M., and Hsu, L.C., 

1995, An integrated approach to the determination of the quantity, distribution, and dispersal of mercury in Lahontan Reservoir, 

Nevada, U.S.A.: Journal of Geochemical Exploration, v. 52, 

p. 45–55.

Smith, G.H., 1943, The history of the Comstock Lode, 1850–1920: Nevada 

University Bulletin, v. 37, no. 3, 305 p.

U.S. Environmental Protection Agency, 2002, National priorities list sites 

in Nevada, Carson River mercury site: U.S. Environmental Protection Agency, www.epa.gov/superfund/sites/npl/nv.htm, accessed 

12/17/02.

Van Denburgh, A.S., 1973, Mercury in the Carson and Truckee River 

basins of Nevada: U.S. Geological Survey Open-File Report 73-352, 

14 p.

Wayne, D.M., Warwick, J.J., Lechler, P.J., Gill, G.A., and Lyons, W.B., 

1996, Mercury contamination in the Carson River, Nevada—A preliminary study of the impact of mining wastes: Water, Air, and Soil 

Pollution, v. 92, p. 391–408.

References Cited 33
BLANK PAGE 34
35

Volcanic Emissions of Mercury

By Todd K. Hinkley

Abstract

Measurement of mercury emissions from some representative volcanoes has aided in understanding volcanic contributions 

to the overall atmospheric budget of mercury. Present estimates 

suggest that all volcanoes worldwide contribute about 60 t of 

mercury to the atmosphere each year. Volcanic sources of mercury to the atmosphere are small on a global scale.

Introduction

Emissions from volcanoes have been known for many years 

as a source of mercury to the atmosphere. Chemical constituents, including mercury, emanating from quiescently degassing 

(or non-explosive) volcanoes (fig. 27) have been measured by 

scientists in recent decades. The amount of mercury contributed 

to the atmosphere from this natural geological source may assist 

in understanding (1) the relative contributions and total amount 

of mercury in the atmosphere that comes from volcanoes and 

other natural sources; and (2) how much of the total mercury in 

the environment in pre-industrial times came from volcanoes, 

when the total amount of mercury in the air may have been 

lower.

Mercury, as well as many other trace elements and 

gases, is emitted and put into the air by volcanoes. In addition to mercury, surprisingly large amounts of several toxic 

elements, including lead, cadmium, and bismuth, are present 

in the plumes of volcanoes. The USGS has been involved in 

efforts to determine the amount of some of those metals 

emitted by volcanoes on a worldwide basis (Hinkley and others, 1999).

Measuring Mercury Emissions from Volcanoes

Efforts to measure the amount of mercury emitted from 

quiescently degassing volcanoes have centered on Mount St. 

Helens (Washington, U.S.A.), White Island (New Zealand; fig. 

28), and Kilauea (Hawaii, U.S.A.). The collection of mercury 

emitted from volcanoes requires specialized sampling apparatus 

(fig. 29). Methods for sample preparation and measurement 

have been recently refined for better quantitative measurement 

of total mercury (Vandal and others, 1993; Ferrara and others, 

Figure 27. Vapor and steam emanating from Volcano Farallon de Pajaros, Mariana Islands (plane wing in 

foreground). USGS scientists are currently measuring mercury emissions from several volcanoes worldwide.
36 Volcanic Emissions of Mercury

Figure 28. Volcanic emissions from White Island, New Zealand.

1994). Because of the complexity of sampling, costs, and safety 

issues, mercury emissions have been measured only during 

limited time intervals at a few quiescent volcanoes; continuous 

monitoring for mercury emissions at all volcanoes worldwide is 

not possible. However, the total output of sulfur from volcanoes 

worldwide has been reliably estimated. If both mercury and sulfur emissions are measured during sampling at several volcanoes 

(Ferrara and others, 1994), and these measurements are assumed 

to be representative of that from volcanoes throughout the world, 

it is possible to obtain a reliable estimate for worldwide volcanic 

emissions of mercury. Based on these measurements, mercury 

emissions from volcanoes are approximately 1/1,000,000 of the 

amount of sulfur emitted, although at a few volcanoes the fraction of mercury is larger, perhaps 1/10,000.

Explosive volcanic eruptions also inject mercury into the 

atmosphere, adding significantly to the total mass of mercury 

put into the air by volcanic sources. However, because of the 

difficulty of taking such measurements safely, the amount of 

mercury coming from explosive eruptions is more difficult to 

estimate accurately than that from quiescently degassing volcanoes. Explosive volcanoes may contribute as much mercury as 

is emitted by quiescent volcanoes (Varekamp and Buseck, 

1986).

Worldwide Contribution of Mercury 

from Volcanoes

The total contribution of mercury to the atmosphere from all 

sources worldwide is estimated to be about 6,000 t/year (Fitzgerald, 1986). Mercury emissions from quiescent volcanoes are 

estimated to be about 25–30 t/year worldwide (Varekamp and 

Buseck, 1986; Fitzgerald, 1986). Thus, mercury emissions from 

volcanoes probably account for less than one percent of the total 

global contribution of mercury to the atmosphere. If the amount 

of mercury emitted from explosive volcanic eruptions is also 

considered, the fraction is larger, but the total volcanic output of 

mercury is probably less than 60 t/year (table 1). In pre-industrial times, mercury emitted from volcanoes was probably similar to the amount today, but because the total amount of mercury 

contributed to the atmosphere was smaller in pre-industrial 

times, the volcanic contribution was a larger portion of the total. 

In fact, the amount of other trace metals emitted by volcanoes in 

pre-industrial times has been shown by the USGS to account for 

most of the total mass of a suite of volatile trace metals that were 

deposited in annual layers of ice preserved in the Antarctic ice 

sheet (Matsumoto and Hinkley, 2001).
References Cited 37

Figure 29. USGS and university scientists collecting volcanic gas samples for the measurement of mercury and other chemical 

constituents.

References Cited

Ferrara, R., Maserti, B.E., De Liso, A., Cioni, R., Raco, B., Taddeucci, G., 

Edner, H., Ragnarson, P., Svanberg, S., and Wallinder, E., 1994, Atmospheric mercury emission at Solfatara Volcano (Pozzuoli, Phlegraean fields, Italy): Chemosphere, v. 29, no. 7, p. 1421–1428.

Fitzgerald, W.F., 1986, Cycling of mercury between the atmosphere and 

oceans, in Buat-Menard, P., ed., The role of air-sea exchange in 

geochemical cycling: Dordrecht, Reidel Publishing Co., NATO, 

Advanced Science Institutes Series, p. 363–408.

Hinkley, T.K., Lamothe, P.J., Wilson, S.A., Finnegan, D.L., and Gerlach, 

T.M., 1999, Metal emissions from Kilauea, and a suggested revision 

of the estimated worldwide metal output by quiescent degassing 

of volcanoes: Earth and Planetary Science Letters, v. 170, no. 3, 

p. 315–325.

Matsumoto, A., and Hinkley, T.K., 2001, Trace metal suites in 75,000 years 

of Antarctic ice are consistent with emissions from quiescent 

degassing of volcanoes worldwide: Earth and Planetary Science 

Letters, v. 186, p. 33–43.

Vandal, G.M., Fitzgerald, W.F., Boutron, C.F., and Candelone, J.P., 1993, 

Variations in mercury deposition to the Antarctic over the past 

34,000 years: Nature, v. 362, p. 621–623.

Varekamp, J.C., and Buseck, P.R., 1986, Global mercury flux from volcanic and geothermal sources: Applied Geochemistry, v. 1, p. 

65–73. 

References Cited 37
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39

Summary

By John E. Gray

The studies presented in this volume outline a few sources 

of potential contamination of mercury to air, water, land, and 

biota. In the United States and throughout the world, emissions 

from coal-fired electrification power plants contribute a significant proportion of the mercury found in the atmosphere (table 

1). Numerous research studies are attempting to evaluate 

whether mercury in these power plant emissions contributes to 

environmental contamination of the air, water, and land (U.S. 

Environmental Protection Agency, 1997). The USGS is presently contributing to these studies by studying the geochemistry 

of mercury in coal (Finkelman, this volume). Some of the highest mercury contents on Earth are found around mercury and 

gold mines. Mine wastes and soil remaining at some of these 

sites contain percent-level concentrations of mercury and some 

highly soluble compounds of mercury. More important is mercury-laden mine runoff that affects downstream ecosystems, 

especially contamination of water and aquatic organisms. Studies of mercury mines in the California Coast Ranges (Rytuba, 

this volume) show that some of these mines produce acid-water 

runoff that carries considerable mercury, which exceeds regulatory standards for water. Water collected downstream from 

mercury mines in Alaska also exceeds regulatory standards in 

some cases (Gray and Bailey, this volume). Furthermore, formation of the highly toxic methylmercury compound has led to 

mercury bioavailability, uptake, and contamination of local fish 

near some mercury mines (table 3). In addition to mercury 

entering ecosystems as a result of mercury mining, significant 

amounts of elemental mercury were used to recover gold during 

periods of historic gold mining in the United States; much of this 

elemental mercury was lost or was discarded to streams and rivers around these mine sites. In two of these areas, the California 

Sierra Nevada (Hunerlach and Alpers, this volume) and the Carson River in Nevada (Lawrence, this volume), USGS studies 

have shown that mercury contents are highly elevated in riverbottom sediment, water, and fish proximal to these areas. In 

both of these areas, significant mercury methylation has led to 

high mercury concentrations in fish, at levels that commonly 

exceed regulatory standards (table 3). Finally, the USGS is 

actively involved in the study of mercury emissions from volcanoes (Hinkley, this volume). This ongoing research aids in the 

study of mercury emissions from volcanic sources and the overall understanding of atmospheric global mercury cycling.

39
40

Summary Location Unfiltered water Coal, sediments, calcine, or soil Fish Hg (ng/L) Methylmercury (ng/L) Hg (μg/g) Methylmercury (ng/g) (μg/g, wet weight)

Coal, USGS national database -- -- 0.003–2.9 -- --Mercury mines, Coast Ranges, Calif.

Below mines 1–450,000 0.01–70 0.4–220 1.1–150 0.1–1.71

Mine-waste calcines -- -- 10–1,500 -- --

Mercury mines, southwestern Alaska

Below mines 1.0–2,500 0.01–1.2 0.90–5,500 0.05–31 0.1–0.62Mine-waste calcine and soil -- -- 3.5–46,000 0.2–41 --

Hydraulic gold mines, Sierra Nevada

Streams below mines 40–10,400 0.01–1.1 600–26,000 0.1–0.3 0.20–1.5Sacramento River 2 0.03–105 0.02–1.2 0.02–0.35 0.27–2.8 --

Carson River, Nevada

Below mines 1–28,000 0.08–7.8 0.01–100 0.56–22 0.1–16 (crayfish up to 50 μg/g)

Other Carson River studies 3-10 3–35,400 0.4–21 0.02–1,610 0.55–29 0.1–1.4 (whole body)

Comparative baselines distal from mines

Lake San Antonio, Calif.4 0.6–1.8 -- -- -- 0.05–0.2

Truckee River, Nevada 3, 9 4.4 -- 0.02–0.28 -- --

Pyramid Lake, Nevada4 1.9 -- -- -- ≤ 0.2

Baselines streams, southwestern Alaska11 0.1–1.4 0.04–0.2 0.02–0.78 0.1– 0.3 0.01–0.2

Uncontaminated streams, Canada12 -- -- 0.01–0.7 -- --

Antarctica streams and lakes13 0.27–1.9 0.02–0.33 -- -- --

0.72–3.0 0.05–0.50 0.001–0.14 ≤ 0.01 --

Regulatory standards

Alaska/Nevada, State drinking water standard 2,000 -- -- -- --EPA, acute aquatic life water standard 2,400 -- -- -- --EPA, chronic aquatic life water standard 12 -- -- -- --FDA, action level for fish -- -- -- -- 1.0California, safe level for fish -- -- -- -- 0.5EPA, fish recommendation (methylmercury)16 -- -- -- -- 0.3

1Schwarzbach and others (2001). 2Domagalski (2001). 3Van Denburgh (1973). 4Gill and Bruland (1990). 5Hoffman and others (1989). 6Gustin and others (1994). 7Miller and others (1995). 8Bonzongo and

others (1996). 9Wayne and others (1996). 10Chen and others (1996). 11Gray and others (2000). 12Painter and others (1994). 13Lyons and others (1999). 14Watras and others (1994). 15Gilmore andReidel (1995). 16U.S. Environmental Protection Agency (2001).

Table 3. Mercury and methylmercury concentrations from samples discussed in this report, comparative baselines, and regulatory standards.[ng/L, nanograms/liter; μg/g, microrams/gram; ng/g, nanograms/gram; -- indicates no data or not applicable]

Wisconsin remote seepage lakes14, 15
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southwestern Alaska, U.S.A.: Science of the Total Environment, v. 

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