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There are two forms of mercury: inorganic mercury and organic methylmercury (MeHg). When inorganic mercury evaporates, it is biotransformed into methylmercury through microbial methylation in saltwater and freshwater sediments. Methylmercury is a persistent environmental contaminant and it bioaccumulates once it enters the food chain, building up in larger organisms that eat smaller, contaminated organisms. This is why large predatory fish such as tuna and shark have notoriously high mercury levels. The process, known as biomagnification, occurs with many hydrophobic toxins.

Mercury causes nervous system defects in children and impedes fetal development. Numerous poisonings have highlighted the harmful effects of mercury use and mercury pollution.

The neuropsychiatric effects of mercury (and lead) exposure are discussed by Mark Filidei, of the San Francisco Preventive Medical Group, in an article, Toxic Metals and Mental Health.

Chemical Description

Inorganic mercury, also known as quicksilver or metallic mercury, is a silvery liquid at room temperature. It is the only metal that is liquid at room temperature, and it has a low boiling point, a high vapor pressure (it evaporates at room temperature), and a high density. It weighs 13.6 times as much as water, and stone and iron can float on its surface.

While all rocks contain some mercury, cinnabar (mercuric sulfide) contains the greatest amount of inorganic mercury (>80%). Elemental mercury is produced from cinnabar by condensing the vapor of heated ores. In the United States elemental mercury is produced primarily as a byproduct of mining.

Inorganic mercury can also combine with elements like chlorine, sulfur, or oxygen to form mercury salts. Mercury ions in the salts are either monovalent (Hg+, mercuric) or divalent (Hg2+, mercurous).

Mercury Cycle

Main Article: Mercury Cycle
The mercury cycle begins with the evaporation of mercury from land and sea sources. Volcanoes and the burning of fossil fuels, especially coal and wastes, account for a large proportion of mercury released. The vapor is absorbed and distributed evenly throughout the higher levels of the atmosphere, where it is oxidized to water-soluble ionic mercury and returned to the earth's surface in rain (#Clarkson, 2002). Because of this cycle, mercury is a worldwide pollutant and its levels do not vary from unpopulated regions to populated ones.

History of Use

Mercury's useful yet potentially harmful qualities were recognized thousands of years ago by the Ancient Romans, who made the winged messenger Mercury the god of merchants and commerce, as well as of thieves and vagabonds (#Gilbert, 2004). Its toxicity was recognized when Roman slaves mined it in Almaden, Spain; this mine remains a major mercury source to this day.

Mercury use is ubiquitous. The Chinese used cinnabar before 1000 BCE to make products as diverse as red ink, cosmetics, soaps, and laxatives before. The Peruvian Incas first used elemental mercury in gold mines in the 16th century. The mercury was used to bind to gold during sifting and over a period of days, the mercury would evaporate, leaving only the gold behind. This practice still occurs today in Central and South America, Africa, and the Philippines. It is estimated that it takes 3-5 kg of mercury to extract 1 kg of gold (#Gilbert, 2004). A large portion of the mercury contaminates the local area, but much of it evaporates, only to be rained down many miles or countries away.

Organic mercury has antifungal properties that make it beneficial when applied to grain seed, but people become very ill if they consume treated seeds. Throughout much of the twentieth century, seeds were coated with organomercury compounds to reduce destruction by certain fungi (#Gilbert, 2004). During the 1970s, a severe drought rocked Iraq, and a large amount of mercury-treated grain seed was donated as aid. These seeds were often colored pink to warn that they were for planting use only and should not be ground into flour for direct human consumption. However, the Iraqis did not know this, nor could they read the warnings written in English, and many Iraqis made flour and bread out of the seeds. Many people died and many more were disabled for life because of the mercury.

As recently as 1990, mercury compounds were added to interior and exterior paints to prevent bacterial and fungal growth. This practice was halted after adverse effects were seen in a four-year old boy whose unventilated bedroom had been painted with mercury-laden latex paint. The boy contracted acrodynia, a rare disease caused by mercury exposure and characterized by flushed cheeks, pink, scaling palms and toes, profuse sweating, insomnia, and irritability (#Gilbert, 2004).

In the 1800s, mercury was used in the development of photographs called dageurrotypes. Unfortunately, some people experienced mercury poisoning from using this process (Roberts, 1989).

Health Effects

Inorganic mercury causes the most harmful effects when its vapor is inhaled (#Gilbert, 2004). When elemental mercury vapor enters the body, it is readily absorbed into the bloodstream and easily crosses the blood-brain barrier and the placenta. After entering the brain, mercury is oxidized and will not transfer back across the blood-brain barrier. When continuous exposure occurs, mercury accumulates in the nervous system, leading to potentially debilitating nervous system afflictions. Health effects include tremors, drowsiness, depression, and decreased performance on memory and verbal tests.

Adverse health effects from overexposure to methylmercury are much more common and have been observed through several tragic case studies (highlighted below in the #History of Use section). The first case of widespread methylmercury poisoning was in Minamata, Japan, where an abnormally high number of children experienced symptoms similar to cerebral palsy.

Mercury is a known human developmental toxicant. The U.S. National Research Council states, "60,000 newborns annually may be at risk for adverse neurodevelopmental effects from in utero exposure to methylmercury (MeHg)" (#Gilbert, 2004). Autopsies of the developing brains of those affected in the Minamata, Japan mercury tragedy show widespread damage to all areas of the brain. Tissues from fetuses killed in the Iraq Mercury Poisoning episode showed disrupted cellular patterns and underdeveloped tissues (#Clarkson, 2002).

Symptoms of exposure arise only after a latency period during which no effects are observed. The length of the latency is indirectly proportional to the level of exposure: the higher the exposure, the less time it takes for the symptoms to be observed.

Mercury Tragedies

Common Sources and Precautions

Common Sources:

  • Switches in gas furnaces, heaters, etc.
  • Major household appliances (tilt switches in freezers, dryers, etc.)
  • Irons (tilt switches)
  • Automobile switches
  • Bilge pumps, sump pumps, etc. (float switches)
  • Dental amalgam
  • Measuring devices and laboratory equipment, such as barometers, manometers, etc.
  • Medical equipment and supplies
  • Batteries
  • Computers
  • Novelty items
  • Film pack batteries

    Fish and Shellfish
    Fish and shellfish have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury. Species of fish that are high on the food chain, such as shark, swordfish, king mackerel, albacore tuna, and tilefish contain higher concentrations of mercury than other species.

One should eat the above fish in moderation. Women of childbearing age should limit the amount of canned tuna they eat to about one can (six ounces) per week. A woman who weighs less than 135 pounds should eat less than one can of tuna per week. Children under six should eat less than one half a can of tuna (three ounces) per week. Specific weekly limits for children under six range from one ounce for a twenty pound child, to three ounces for a child weighing about sixty pounds. Follow the guidelines in the Physicians for Social Responsibility's fish consumption guide.

Household Devices
Compact fluorescent lights (CFLs) do contain a very small amount of mercury, but it is fully contained as long as the bulb is not broken. Fossil fuels release mercury into the environment when burned to produce energy, so CFLs help to reduce overall mercury emissions. (In 2004, 67 percent of CFL lamps sold contained 5 mg Hg or less per bulb, while 96 percent contained 10 mg or less. A voluntary commitment in 2007 by bulb manufacturers belonging to NEMA, the National Electrical Manufacturers Association, has capped mercury content to even lower levels).

If a CFL breaks in your home, close the doors leading to other areas of the house if you can, then immediately get out of the house for an hour or more to allow the mercury to dissipate. For guidelines on cleaning up spilled mercury, see this EPA website. Call the Poison Control Center for additional advice. Do not throw spent CFLs in the garbage: take them to a local household hazardous waste (HHW) drop-off site.

Old thermometers contain mercury and are prone to breakage. Switch to digital thermometers, and take mercury thermometers to the HHW site.

Flu Vaccine
Thimerosal is a mercury-containing preservative used in vaccines, especially in the flu vaccine. It has purportedly been removed from all child vaccines other than the flu vaccine. If you get the flu shot annually, request a mercury-free mist or a preservative-free flu vaccine (if available). From a mercury exposure standpoint, this is especially important for babies, children, and pregnant or nursing women. The mist vaccine is not approved by the Food and Drug Administration (FDA) for pregnant women, so if pregnant or nursing, check with your doctor for the preservative-free vaccine.

Paula Dorf Cake Mascara (raven) contains thimerosal (the mercury-containing preservative) (#CosmeticsDatabase). Avoid mascara, skin lightening creams, or any cosmetic product that lists mercury or thimerosal in the ingredients. To find specific products to avoid, search the Environmental Working Group's Cosmetics Database.

Hopefully these products are on the wane, but beware of cheap or imported silver jewelry, or cheap jewelry bought on a vacation. These may contain mercury or lead.

Amalgam is about 50% mercury and the mercury is slowly released, causing health problems for some people. Go to a mercury-free dentist, or do not have any new mercury fillings put in.

Button Batteries
Keep toys with these batteries out of young children's reach. Dispose of spent batteries at a household hazardous waste site. Consider avoiding any trinkets and gadgets with button batteries.

Arts and Crafts
Gilding may use a mercury-bearing alloy. Artist paints and papermaking intensifiers may contain mercury. Ask the manufacturer if necessary to find out if their materials are mercury-free.

For more recommendations see here

Current Events

For the latest news articles on mercury, visit Environmental Health News and do a search for "mercury."

February 5, 2010

Fish for Thought from Sightline Institute's The Daily Score.

March 7, 2008
Concern rising over lack of monitoring of Columbia River. See full Oregonian article.

March 7, 2008
Schenectady, New York citizens pressure state to more tightly limit emissions of mercury. See full Daily Gazette article.

March 6, 2008
Bush administration reconsiders stance on mercury pollution limits following lawsuits by nine states. See full Mlive article.

March 5, 2008
Residual mercury left from Gold Rush era mines presents modern-day challenges in California. See full Recordnet article.

February 8, 2008
The U.S. Court of Appeals for the District of Columbia Circuit struck down the Bush administration approach to limiting mercury emissions from power plants. They threw out a rule known as cap-and-trade that would have allowed power plants that fail to meet emission targets to buy credits from plants that did, rather than having to install their own mercury emissions controls. See the Seattle Post Intelligencer Article.

March 21, 2007
Researchers Find Substantial Amount of Mercury Entering Ocean Through Groundwater. See the Woods Mass Article.

October 24, 2006
A recent consortium has found disturbing news concerning the plausibility of regulating mercury. Two thirds of all fish contamination cases worldwide are a result of mercury buildup. Scientists are investigating whether the pollution is from "old" mercury, which has been emitted in the past from any number of sources, and if regulating "new" mercury is cost-effective. See the report here at USGS.

September 13, 2006
The Environmental Protection Agency will likely not recommend a halt to surplus mercury sales, nor even take a strong stand condemning it. The mercury that is traded is excess mercury recovered from the manufacturing process. The Environmental Protection Agency mandates that this mercury must be recycled only because there is no viable method of disposal: in essence, there is nowhere to put the mercury that is derived from manufacturing. Sen. Barack Obama (D-ILL) has introduced S. 3627, The Mercury Minimization Act (introduced June 29, 2006), that would ban mercury exports starting in 2010. This approach is in line with that of the European Union. See full article from Environmental Policy Alert.
Please see Barbara Scott Murdoch of the University of Minnesota School of Public Health's letter to Science espousing the perils of mercury trading under the title of "Mercury Stockpile."


Inorganic Mercury- ATSDR - minimal risk level (MRL) - 0.2ug/m^3

  • OSHA - permissible exposure limits (PEL) - 0.05 mg/m^3
  • ACGIH - threshold limit value (TLV) - TWA - 0.05mg/m^3

Organic Mercury:

  • FDA - 1 ppm in commercially harvested fish (e.g. tuna)
  • FDA - action level - 0.47 ug/kg per day
  • ATSDR - minimal risk levels (MRL) - 0.30 ug/kg
  • Washington State - total daily intake - 0.035-0.08 ug/kg per day
  • EPA - Reference Dose (RfD) - 0.1 ug/kg per day (In 1997 the EPA estimated that 7% of women of childbearing age in the United States exceed the established RfD of 0.1 ug/kg per day.)
  • 41 states have issued over 2000 fish consumption advisories related to mercury

Teaching Resources

European, Asian, and International Agencies

  • World Health Organization - Mercury. UN Committee recommends new dietary intake limits for mercury. Online. (accessed: 7 June 2004). This program aims to develop a global assessment of mercury and its compounds, including an outline of options for addressing any significant global adverse impacts of mercury. Site has a global prospective on mercury health effects.

North American Agencies

  • Dartmouth Toxic Metals Research Project on Mercury
  • Maine Department of Environmental Protection, Augusta, Maine. Health Effects of Methylmercury with Particular Reference to the U.S. Population Statement of Deborah C. Rice, Ph.D. Hearing by the Senate Committee on Environment and Public Works, July 29, 2003. One of the best brief statements on the health effects of mercury. (accessed: 17 May 2004).
  • Health Canada - Mercury. Health Canada provides information on the health effects and environmental distribution of mercury. (accessed: 9 April 2003).
  • U.S. NAS-Mercury Study. By the Committee on the Toxicological Effects of Methylmercury, Board on Environmental Studies and Toxicology, National Research Council.
  • Mercury and PBTs - Water Resources Education Center in Vancouver, Washington (accessed June 2, 2004).

Non-Government Organizations

  • Mercury Consensus Statement. (pdf) - Documents concerns about the health effects of mercury and encourages U.S. EPA to take a more active role in reducing human and environmental exposure.
  • The Mercury Policy Project (MPP). "MPP works to raise awareness about the threat of mercury contamination and promote policies to eliminate mercury uses, reduce the export and trafficking of mercury, and significantly reduce mercury exposures at the local, national, and international levels."
  • The Learning Disabilities Association of America (LDA), the National Education Association (NEA), and the Arc of the United States released a brochure on March 14, 2005 that identifies mercury pollution as one of the greatest threats facing developing fetuses, infants, and young children.
  • The Madison Declaration on Mercury Pollution. Developed at the Eighth International Conference on Mercury as a Global Pollutant in August 2006 in Madison, Wisonsin, the declaration is a synopsis of the latest scientific knowledge about the danger posed by mercury pollution. It presents 33 principal findings from five synthesis papers prepared by the world's leading mercury scientists and published in the same issue of Ambio.


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