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, meaning watery or liquid silver) and atomic number 80. A heavy, silvery d-block metal, mercury is one of six elements that are liquid at or near room temperature and pressure. The others are the metals caesium, francium, gallium, and rubidium, and the non-metal bromine. Of these, only mercury and bromine are liquids at standard conditions for temperature and pressure.
Mercury is used in thermometers, barometers, manometers, sphygmomanometers, float valves, and other scientific apparatus, though concerns about the element's toxicity have led to mercury thermometers and sphygmomanometers being largely phased out in clinical environments in favour of alcohol-filled, digital, or thermistor-based instruments. It remains in use in a number of other ways in scientific and scientific research applications, and in dental amalgam. Mercury is mostly obtained by reduction from the mineral cinnabar.
Mercury is an extremely rare element in the earth's crust, having an average crustal abundance by mass of only 0.08 parts per million. However, because it does not blend geochemically with those elements that constitute the majority of the crustal mass, mercury ores can be extraordinarily concentrated considering the element's abundance in ordinary rock. The richest mercury ores contain up to 2.5% mercury by mass, and even the leanest concentrated deposits are at least 0.1% mercury (12,000 times average crustal abundance).
It is found either as a native metal (rare) or in cinnabar, corderoite, livingstonite and other minerals, with cinnabar (HgS) being the most common ore. Mercury ores usually occur in very young orogenic belts where rock of high density are forced to the crust of the Earth, often in hot springs or other volcanic regions.
Over 100,000 tons of mercury were mined from the region of Huancavelica, Peru, over the course of three centuries following the discovery of deposits there in 1563; mercury from Huancavelica was crucial in the production of silver in colonial Spanish America. Many former ores in Italy, the United States and Mexico which once produced a large proportion of the world's supply have now been completely mined out or in the case of Slovenia and Spain shut down due to the fall of the price of mercury in the international markets. The metal is extracted by heating cinnabar in a current of air and condensing the vapor. The equation for this extraction is
- HgS + O2 → Hg + SO2
In 2005, China was the top producer of mercury with almost two-thirds global share followed by Kyrgyzstan, reports the British Geological Survey. Several other countries are believed to have unrecorded production of mercury from copper electrowinning processes and by recovery from effluents.
Due to minimal surface disruption, mercury mines lend themselves to constructive re-use. For example, in 1976 Santa Clara County, California purchased the historic Almaden Quicksilver Mine and proceeded to create a county park on the site, after conducting extensive safety and environmental analysis of the property.
Releases in the environment
Preindustrial deposition rates of mercury from the atmosphere may be in the range of 4 ng/L in the western USA. Although that can be considered a natural level of exposure, regional or global sources have significant effects. Volcanic eruptions can increase the atmospheric source by 4–6 times.
- 65% from stationary combustion, of which coal-fired power plants are the largest aggregate source (40% of U.S. mercury emissions in 1999). This includes power plants fueled with gas where the mercury has not been removed. Emissions from coal combustion are between one and two orders of magnitude higher than emissions from oil combustion, depending on the country.
- 11% from gold production. The three largest point sources for mercury emissions in the U.S. are the three largest gold mines.
- 6.8% from non-ferrous metal production, typically smelters.
- 6.4% from cement production.
- 3.0% from waste disposal, including municipal and hazardous waste, crematoria, and sewage sludge incineration. This is a significant underestimate due to limited information, and is likely to be off by a factor of two to five.
- 3.0% from caustic soda production.
- 1.4% from pig iron and steel production.
- 1.1% from mercury production, mainly for batteries.
- 2.0% from other sources.
The above percentages are estimates of the global human-caused mercury emissions in 2000, excluding biomass burning, an important source in some regions.
Mercury also enters into the environment through the disposal (e.g., landfilling, incineration) of certain products. Products containing mercury include: auto parts, batteries, fluorescent bulbs, medical products, thermometers, and thermostats. Due to health concerns (see below), toxics use reduction efforts are cutting back or eliminating mercury in such products. For example, most thermometers now use pigmented alcohol instead of mercury. Mercury thermometers are still occasionally used in the medical field because they are more accurate than alcohol thermometers, though both are being replaced by electronic thermometers. Mercury thermometers are still widely used for certain scientific applications because of their greater accuracy and working range.
The United States Clean Air Act, passed in 1990, put mercury on a list of toxic pollutants that need to be controlled to the greatest possible extent. Thus, industries that release high concentrations of mercury into the environment agreed to install maximum achievable control technologies (MACT). In March 2005 EPA rule added power plants to the list of sources that should be controlled and a national cap and trade rule was issued. States were given until November 2006 to impose stricter controls, and several States are doing so. The rule was being subjected to legal challenges from several States in 2005.
Historically, one of the largest releases was from the Colex plant, a lithium-isotope separation plant at Oak Ridge. The plant operated in the 1950s and 1960s. Records are incomplete and unclear, but government commissions have estimated that some two million pounds of mercury are unaccounted for.
One of the worst industrial disasters in history was caused by the dumping of mercury compounds into Minamata Bay, Japan. The Chisso Corporation, a fertilizer and later petrochemical company, was found responsible for polluting the bay from 1932–1968. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known as Minamata disease.
The element mercury is the main ingredient in dental amalgams. Controversy over the health effects from the use of mercury amalgams began shortly after its introduction into the western world, nearly 200 years ago,[How to reference and link to summary or text]. In 1845, The American Society of Dental Surgeons, concerned about mercury poisoning, asked its members to sign a pledge that they would not use amalgam [How to reference and link to summary or text]. The ASDS disbanded in 1865 [How to reference and link to summary or text]. The American Dental Association formed three years after and currently takes the position that "amalgam is a valuable, viable and safe choice for dental patients," In 1993, the United States Public Health Service reported that "amalgam fillings release small amounts of mercury vapor," but in such a small amount that it "has not been shown to cause any … adverse health effects". This position is not shared by all governments [How to reference and link to summary or text] and there is an ongoing dental amalgam controversy. A recent review by an FDA-appointed advisory panel rejected, by a margin of 13-7, the current FDA report on amalgam safety,[How to reference and link to summary or text] stating the report's conclusions were unreasonable given the quantity and quality of information currently available. Panelists said remaining uncertainties about the risk of so-called silver fillings demanded further research; in particular, on the effects of mercury-laden fillings on children and the fetuses of pregnant women with fillings, and the release of mercury vapor on insertion and removal of mercury fillings.[How to reference and link to summary or text] In Norway new dental amalgam fillings are banned from 1 January 2008. The Minister of the Environment and International Development announced the ban in a press release 21 December 2007. The ban implies for mercury in nearly all products.. The ban is law regulated by changes in The Product Control Act. 
Mercury and its compounds have been used in medicine, although they are much less common today than they once were, now that the toxic effects of mercury and its compounds are more widely understood.
Mercury(I) chloride (also known as calomel or mercurous chloride) has traditionally been used as a diuretic, topical disinfectant, and laxative. Mercury(II) chloride (also known as mercuric chloride or corrosive sublimate) was once used to treat syphilis (along with other mercury compounds), although it is so toxic that sometimes the symptoms of its toxicity were confused with those of the syphilis it was believed to treat. It was also used as a disinfectant. Blue mass, a pill or syrup in which mercury is the main ingredient, was prescribed throughout the 1800s for numerous conditions including constipation, depression, child-bearing and toothaches. In the early 20th century, mercury was administered to children yearly as a laxative and dewormer, and it was used in teething powders for infants. The mercury containing organohalide Mercurochrome is still widely used but has been banned in some countries such as the U.S.
Since the 1930s some vaccines have contained the preservative thiomersal, which is metabolized or degraded to ethyl mercury. Although it was widely speculated that this mercury-based preservative can cause or trigger autism in children, scientific studies showed no evidence supporting any such link. Nevertheless thiomersal has been removed from or reduced to trace amounts in all U.S. vaccines recommended for children 6 years of age and under, with the exception of inactivated influenza vaccine.
Mercury in the form of one of its common ores, cinnabar, remains an important component of Chinese, Tibetan, and Ayurvedic medicine. As problems may arise when these medicines are exported to countries that prohibit the use of mercury in medicines, in recent times, less toxic substitutes have been devised.
Today, the use of mercury in medicine has greatly declined in all respects, especially in developed countries. Thermometers and sphygmomanometers containing mercury were invented in the early 18th and late 19th centuries, respectively. In the early 21st century, their use is declining and has been banned in some countries, states and medical institutions. In 2002, the U.S. Senate passed legislation to phase out the sale of non-prescription mercury thermometers. In 2003, Washington and Maine became the first states to ban mercury blood pressure devices. Mercury compounds are found in some over-the-counter drugs, including topical antiseptics, stimulant laxatives, diaper-rash ointment, eye drops, and nasal sprays. The FDA has “inadequate data to establish general recognition of the safety and effectiveness,” of the mercury ingredients in these products. Mercury is still used in some diuretics, although substitutes now exist for most therapeutic uses.
Mercury and most of its compounds are extremely toxic and are generally handled with care; in cases of spills involving mercury (such as from certain thermometers or fluorescent light bulbs) specific cleaning procedures are used to avoid toxic exposure.
- Main article: mercury poisoning
Due to the health effects of mercury exposure, industrial and commercial uses are regulated in many countries. The World Health Organization, OSHA, and NIOSH all treat mercury as an occupational hazard, and have established specific occupational exposure limits. Environmental releases and disposal of mercury are regulated in the U.S. primarily by the United States Environmental Protection Agency.
Case control studies have shown effects such as tremors, impaired cognitive skills, and sleep disturbance in workers with chronic exposure to mercury vapour even at low concentrations in the range 0.7–42 μg/m3.
A study has shown that acute exposure (4-8 hours) to calculated elemental mercury levels of 1.1 to 44 mg/m3 resulted in chest pain, dyspnea, cough, hemoptysis, impairment of pulmonary function, and evidence of interstitial pneumonitis.
Acute exposure to mercury vapor has been shown to result in profound central nervous system effects, including psychotic reactions characterized by delirium, hallucinations, and suicidal tendency. Occupational exposure has resulted in broad-ranging functional disturbance, including erethism, irritability, excitability, excessive shyness, and insomnia. With continuing exposure, a fine tremor develops and may escalate to violent muscular spasms. Tremor initially involves the hands and later spreads to the eyelids, lips, and tongue. Long-term, low-level exposure has been associated with more subtle symptoms of erethism, including fatigue, irritability, loss of memory, vivid dreams, and depression.
Research on the treatment of mercury poisoning is limited. Currently available drugs for acute mercurial poisoning include chelators N-acetyl-D,L-penicillamine (NAP), British Anti-Lewisite (BAL), 2,3-dimercapto-1-propanesulfonic acid (DMPS), and dimercaptosuccinic acid (DMSA). In one small study including 11 construction workers exposed to elemental mercury, patients were treated with DMSA and NAP. Chelation therapy with both drugs resulted in the mobilization of a small fraction of the total estimated body mercury. DMSA was able to increase the excretion of mercury to a greater extent than NAP.
Mercury in fish
Fish and shellfish have a natural tendency to concentrate mercury in their bodies, often in the form of methylmercury, a highly toxic organic compound of mercury. 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 others. This is because mercury is stored in the muscle tissues of fish, and when a predatory fish eats another fish, it assumes the entire body burden of mercury in the consumed fish. Since fish are less efficient at depurating than accumulating methylmercury, fish-tissue concentrations increase over time. Thus species that are high on the food chain amass body burdens of mercury that can be ten times higher, or more, than the species they consume. This process is called biomagnification. The first occurrence of widespread mercury poisoning in humans occurred this way in Minamata, Japan, now called Minamata disease.
The complexities associated with mercury transport and environmental fate are described by USEPA in their 1997 Mercury Study Report to Congress. Because methylmercury and high levels of elemental mercury can be particularly toxic to unborn or young children, organizations such as the U.S. EPA and FDA recommend that women who are pregnant or plan to become pregnant within the next one or two years, as well as young children avoid eating more than 6 ounces (one average meal) of fish per week. In the United States the FDA has an action level for methyl mercury in commercial marine and freshwater fish that is 1.0 parts per million (ppm), and in Canada the limit for the total of mercury content is 0.5 ppm.
Species with characteristically low levels of mercury include shrimp, tilapia, salmon, pollock, and catfish (FDA March 2004). The FDA characterizes shrimp, catfish, pollock, salmon, and canned light tuna as low-mercury seafood, although recent tests have indicated that up to 6 percent of canned light tuna may contain high levels.
In the European Union, Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (See RoHS) bans mercury from certain electrical and electronic products, and limits the amount of mercury in other products to less than 1000 ppm.
Besides, in the European Union there are restriction for mercury concentration in packaging (the limit is 100 ppm for sum of mercury, lead, hexavalent chromium and cadmium) and batteries (the limit is 5 ppm)..
In July 2007, European Union also banned mercury in non-electrical measuring devices, such as thermometers and barometers. The ban applies to new devices only, and contains exemptions for the healthcare sector and a two-year grace period for manufacturers of barometers. 
In Norway, there is a total ban on use of mercury in the manufacturing as well as import or export of mercury products. The ban is effective as of January 1, 2008. Lakes in Norway are already polluted by mercury.
- Kolev, S.T. Bates, N. Mercury (UK PID). National Poisons Information Service: Medical Toxicology Unit (London Centre).
- Jahn, Robert G. "Physics of Electric Propulsion" McGraw-Hill Series in Missile and Space Technology, McGraw-Hill, (1968)
- ↑ Fred Senese. Why is mercury a liquid at STP?. General Chemistry Online at Frostburg State University.
- ↑ World Mineral Production 2001-05, British Geological Survey, NERC, London, 2007
- ↑ Glacial Ice Cores Reveal A Record of Natural and Anthropogenic Atmospheric Mercury Deposition for the Last 270 Years. United States Geological Survey (USGS).
- ↑ 4.0 4.1 4.2 4.3 Pacyna EG, Pacyna JM, Steenhuisen F, Wilson S (2006). Global anthropogenic mercury emission inventory for 2000. Atmos Environ 40 (22): 4048–63.
- ↑ What is EPA doing about mercury air emissions?. United States Environmental Protection Agency (EPA).
- ↑ Rebecca Solnit. Winged Mercury and the Golden Calf. Orion Magazine. URL accessed on 2007-12-03.
- ↑ Mercury-containing Products. United States Environmental Protection Agency (EPA).
- ↑ Clean Air Mercury Rule. United States Environmental Protection Agency (EPA).
- ↑ Introduction. Y-12 Mercury Task Force Files: A Guide to Record Series of the Department of Energy and its Contractors. Department of Energy.
- ↑ Statement on Dental Amalgam. American Dental Association.
- ↑ Bans mercury in products, Press release, 21.12.2007, Minister of the Environment and International Development Erik Solheim
- ↑ Amendments in Product regulations in Norway from 1 January 2008
- ↑ Pimple, K.D. Pedroni, J.A. Berdon, V. (2002, July 09). Syphilis in history. Poynter Center for the Study of Ethics and American Institutions at Indiana University-Bloomington. Retrieved on April 17, 2005.
- ↑ Hillary Mayell (July 17, 2001). Did Mercury in "Little Blue Pills" Make Abraham Lincoln Erratic?. National Geographic.
- ↑ Parker SK, Schwartz B, Todd J, Pickering LK (2004). Thimerosal-containing vaccines and autistic spectrum disorder: a critical review of published original data. Pediatrics 114 (3): 793–804. Erratum (2005). Pediatrics 115 (1): 200.
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- ↑ Thimerosal in vaccines. Center for Biologics Evaluation and Research, U.S. Food and Drug Administration. URL accessed on 2007-10-01.
- ↑ Two States Pass First-time Bans on Mercury Blood Pressure Devices. Health Care Without Harm.
- ↑ Title 21—Food and Drugs Chapter I—Food and Drug Administration Department of Health and Human Services Subchapter D—Drugs for Human Use Code of federal regulations. United States Food and Drug Administration.
- ↑ Mercury: Spills, Disposal and Site Cleanup. Environmental Protection Agency. URL accessed on 2007-08-11.
- ↑ Ngim CH, Foo SC, Boey KW, and Keyaratnam J (1992). Chronic neurobehavioral effects of elemental mercury in dentists. British Journal of Industrial Medicine 49: 782-790.
- ↑ Liang YX, Sun RK, Chen ZQ, and Li LH. Psychological effects of low exposure to mercury vapor: Application of computer-administered neurobehavioral evaluation system. Environmental Research 60: 320-327.
- ↑ McFarland, RB and H. Reigel. J Occup Med. 1978 Aug;20(8):532-4.
- ↑ WHO (1976) Environmental Health Criteria 1: Mercury, Geneva, World Health Organization, 131 pp.
- ↑ WHO. Inorganic mercury. Environmental Health Criteria 118. World Health Organization, Geneva, 1991.
- ↑ Bluhm, RE, et. Al. Hum Exp Toxicol 1992 May;11(3):201-10.
- ↑ EPA (1997). Mercury Study Report to Congress.
- ↑ FDA/EPA (2004). What You Need to Know About Mercury in Fish and Shellfish.
- ↑ includeonly>"FDA tests show risk in tuna", Chicago Tribune, January 27, 2006. Retrieved on 2007-05-01.
- ↑ Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment 2002/95/EC, Article 4 Paragraph 1. "Member States shall ensure that, from 1 July 2006, new electrical and electronic equipment put on the market does not contain lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE)." http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2003:037:0019:0023:EN:PDF
- ↑ Mercury compounds in European Union
- ↑ EU bans mercury in barometers, thermometers
- ↑ Norway to ban mercury
- ↑ Mercury in lake sediments, map
- NLM Hazardous Substances Databank – Mercury
- UNIDO/UNDP/GEM Global Mercury Project
- EPA fish consumption guidelines
- ATSDR — ToxFAQs™: Mercury
- WebElements.com – Mercury
- Material Safety Data Sheet – Mercury
- Hg 80 Mercury
- Global Mercury Assessment report 2002 by the UNEP.
- Natural Resources Defense Council (NRDC): Mercury Contamination in Fish guide — NRDC
- nytimes.com, Tuna Fish Stories: The Candidates Spin the Sushi
- ap.google.com, Japanese Sushi Lovers Shrug at Mercury
- NIOSH Mercury Topic Page
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