View source for Mercury (element)

{{infobox mercury}}
'''Mercury''', also known as '''quicksilver'''<!--ref>{{cite web|url=http://dictionary.reference.com/browse/quicksilver|title=quicksilver definition|dateformat=mdy|accessdate=October 13 2008|publisher=Dictionary.com Unabridged (v 1.1)}}</ref---> or '''hydrargyrum''', is a [[chemical element]] with the symbol '''Hg''' ([[Romanization|Latinized]] {{lang-el|''hydrargyrum''}}, from "[[Wiktionary:en:hydr-|hydr-]]" meaning ''watery'' or ''runny'' and "[[Wiktionary:en:argentum|argyros]]" meaning ''silver'') and [[atomic number]] 80. Mercury is the only metal that is liquid at [[standard conditions for temperature and pressure]]; the only other element that is liquid under these conditions is [[bromine]].<ref>Green, J. and Damji, S. ''Chemistry'', Melton: IBID Press, 3rd ed. 2007</ref> With a [[melting point]] of −38.83 °C and [[boiling point]] of 356.73 °C, mercury has one of the broadest ranges of its liquid state of any metal. A heavy, silvery [[d-block]] [[metal]], mercury is also one of the five [[liquid metal|metallic]] chemical elements that are [[liquid]] at or near [[room temperature]] and pressure,<ref>{{cite web|url=http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/why-is-mercury-liquid.shtml| title=Why is mercury a liquid at STP?| accessdate=May 1, 2007| publisher=General Chemistry Online at Frostburg State University| author=Senese, F}}</ref><ref name="Norrby" /> the others being [[caesium]], [[francium]], [[gallium]], and [[rubidium]].

Mercury occurs in deposits throughout the world mostly as [[cinnabar]] ([[mercuric sulfide]]), which is the source of the red pigment [[vermilion]], and is mostly obtained by reduction from cinnabar. Cinnabar is highly toxic by ingestion or inhalation of the dust. [[Mercury poisoning]] can also result from exposure to soluble forms of mercury (such as [[mercuric chloride]] or [[methylmercury]]), inhalation of mercury vapor, or eating seafood contaminated with mercury.

Mercury is used in [[thermometer]]s, [[barometer]]s, [[manometer]]s, [[sphygmomanometer]]s, [[float valve]]s, some electrical switches, 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 favor 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 [[amalgam (dentistry)|amalgam]] material for [[dental restoration]]. It is used in lighting: electricity passed through mercury vapor in a phosphor tube produces short-wave [[ultraviolet light]] which then causes the phosphor to [[fluoresce]], making visible light.

==Properties==
===Physical properties===
[[Image:Pound-coin-floating-in-mercury.jpg|thumb|left|A [[One pound (British decimal coin)|pound coin]] (density ~7.6 g/cm<sup>3</sup>) floats in mercury due to the combination of the buoyant force and surface tension.]]
Mercury is a heavy, silvery-white metal. As compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity.<ref name=CRC/>

===Chemical properties===
Mercury has an exceptionally low melting temperature for a d-block metal. A complete explanation of this fact requires a deep excursion into [[quantum physics]], but it can be summarized as follows: mercury has a unique electronic configuration where electrons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, 5s, 5p, 5d and 6s subshells. As such configuration strongly resists removal of an electron, mercury behaves similarly to [[noble gas]] elements, which form weak bonds and thus easily melting solids. The stability of the 6s shell is due to the presence of a filled 4f shell. An f shell poorly screens the nuclear charge that increases the attractive [[Coulomb's law|Coulomb interaction]] of the 6s shell and the nucleus (see [[lanthanide contraction]]). The absence of a filled inner ''f'' shell is the reason for the much higher melting temperature of [[cadmium]]. Metals such as [[gold]] have atoms with one less 6s electron than mercury. Those electrons are more easily removed and are shared between the gold atoms forming relatively strong [[metallic bonds]].<ref name="Norrby">{{cite journal|author=Norrby, L.J.|title=Why is mercury liquid? Or, why do relativistic effects not get into chemistry textbooks?| journal= Journal of Chemical Education|volume=68|page=110 |year=1991}}</ref><ref>{{cite web|url=http://antoine.frostburg.edu/chem/senese/101/periodic/faq/why-is-mercury-liquid.shtml|accessdate=2009-07-07|title=Why is mercury a liquid at STP?}}</ref> At the melting point (−38.86 °C) its density is<ref name="GenChem Textbook">{{cite journal|title=Macroscopic Properties and Microscopic Models|url=http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Macroscopic-Properties-and-Microscopic-Models.html}}</ref> 13.534 g/cm<sup>3</sup>.

===Reactivity and compounds===
{{See also|Category:Mercury compounds}}
Mercury dissolves to form [[amalgam (chemistry)|amalgams]] with gold, zinc and many other metals. Because iron is an exception, iron flasks have been traditionally used to trade mercury. Other metals that do not form amalgams with mercury include tantalum, tungsten and platinum. When heated, mercury also reacts with oxygen in air to form [[mercury oxide]], which then can be decomposed by further heating to higher temperatures.<ref name=patnaik>{{cite book|last =Patnaik|first=Pradyot|year=2003|title=Handbook of Inorganic Chemical Compounds |publisher=McGraw-Hill|pages=560–576|isbn =0070494398|url=http://books.google.com/?id=Xqj-TTzkvTEC&pg=PA576|accessdate=2009-06-06}}
</ref>

Since it is below hydrogen in the [[reactivity series]] of metals, mercury does not react with most acids, such as dilute [[sulfuric acid]], though [[oxidizing acid]]s such as concentrated [[sulfuric acid]] and [[nitric acid]] or [[aqua regia]] dissolve it to give [[sulfate]], [[nitrate]], and [[chloride]] salts. Like silver, mercury reacts with atmospheric [[hydrogen sulfide]]. Mercury even reacts with solid sulfur flakes, which are used in mercury spill kits to absorb mercury vapors (spill kits also use [[activated carbon]] and powdered zinc).<ref name=patnaik/>

Some important mercury salts include:
*[[Mercury(I) chloride]] ([[calomel]]) is sometimes still used in [[medicine]], acousto-optical filters and as a standard in electrochemistry;<ref name=electrode>{{cite journal|doi=10.1126/science.93.2425.601-a|year=1941|author=Banus, Mg|title=A design for a saturated calomel electrode|volume=93|issue=2425|pages=601–602|pmid=17795970|journal=Science (New York, N.Y.)}}</ref>
*[[Mercury(II) chloride]] is a very [[corrosion|corrosive]], easily [[sublimation (chemistry)|sublimating]] and poisonous substance;<ref name=CRC>{{cite book|author=Hammond, C. R|title=The Elements, in Handbook of Chemistry and Physics 81st edition|publisher=CRC press|year=2000|isbn = 0849304814|url=http://www-d0.fnal.gov/hardware/cal/lvps_info/engineering/elements.pdf}}</ref>
*[[Mercury(II) fulminate|Mercury fulminate]], (a [[detonator]] widely used in [[explosive]]s);<ref name=CRC/>
*[[Mercury(II) oxide]], the main [[oxide]] of mercury;
*[[Mercury(II) sulfide]] (found naturally as the ore cinnabar, or [[vermilion]] which is a high-grade [[paint pigment]]);<ref name=CRC/>
*[[Mercury(II) selenide]], [[Mercury(II) telluride]], [[Mercury cadmium telluride]] and [[mercury zinc telluride]] are [[semiconductors]] and [[infrared detector]] materials.<ref>{{cite book|url=http://books.google.com/?id=4b3WLgomvd0C&pg=PA507|page=507|title=Infrared detectors|author=Rogalski, A|publisher=CRC Press|year=2000|isbn=9056992031}}</ref>

In these compounds, mercury displays two oxidation states: +1 and +2. The +1 state oxidation involves the dimeric cation, Hg{{su|b=2|p=2+}}. Solutions of {{chem|Hg|2|2+}} are in equilibrium with {{chem|Hg|2+}} and metallic mercury:

: {{chem|Hg|2+}} + Hg {{eqm}} {{chem|Hg|2|2+}}

This equilibrium causes solutions of {{chem|Hg|2|2+}} to have a small amount of {{chem|Hg|2+}} present. Consuming the {{chem|Hg|2+}} by another reaction, such as complexation with strong ligands or precipitation of an insoluble salt, will cause all the {{chem|Hg|2|2+}} to fully disproportionate to {{chem|Hg|2+}} and elemental mercury.<ref name="henderson">{{cite book| title = Main group chemistry| author = Henderson, W.|location=Great Britain| publisher = Royal Society of Chemistry|year = 2000| isbn = 0854046178|page=162}}</ref>

Besides {{chem|Hg|2|2+}}, mercury also forms other [[mercury polycations]] such as {{chem|Hg|3|2+}}.<ref>{{cite doi|10.1021/ic00194a020}}</ref>

Higher oxidation states of mercury were confirmed in September 2007, with the synthesis of [[mercury(IV) fluoride]] ({{chem|HgF|4}}) using matrix isolation techniques.<ref name="WangX">{{cite journal|title=Mercury Is a Transition Metal: The First Experimental Evidence for HgF4|journal=Angewandte Chemie International Edition|publisher=Wiley|location=Weinheim|volume=46|issue=44|page=8371|doi=10.1002/anie.200703710|year=2007|pmid=17899620|last1=Wang|first1=X|last2=Andrews|first2=L|last3=Riedel|first3=S|last4=Kaupp|first4=M|pages=8371–5|author1=Wang, X|author2=Andrews, L|author3=Riedel, S|author4=Kaupp, M}}</ref>

Laboratory tests have found that an electrical discharge causes the [[noble gases]] to combine with mercury vapor. These compounds are held together with [[van der Waals force]]s and result in Hg·Ne, Hg·Ar, Hg·Kr, and Hg·Xe (see [[exciplex]]). Organic mercury [[chemical compound|compounds]] are also important. [[Methylmercury]] is a dangerous compound that is widely found as a [[pollution|pollutant]] in water bodies and streams.<ref name="methylHg">{{cite book| url = http://books.google.com/?id=BPvWJbBMd7wC|title = Toxicological effects of methylmercury|author = National Research Council (U.S.) - Board on Environmental Studies and Toxicology| publisher = National Academies Press|year = 2000|isbn = 9780309071406}}</ref>

===Mercury and aluminium===
[[File:Mercury discharge tube.jpg|thumb|left|Mercury discharge (spectrum) tube]]
Mercury readily combines with [[aluminium]] to form a [[aluminium amalgam|mercury-aluminium amalgam]] when the two pure metals come into contact. However, when the amalgam is exposed to air, the aluminium oxidizes, leaving mercury behind. The oxide flakes away, exposing more mercury amalgam, which repeats the process. This process continues until the supply of amalgam is exhausted. Because this process releases mercury, a small amount of mercury can "eat through" a large amount of aluminium over time, by progressively forming amalgam and relinquishing the aluminium as oxide.<ref name="CorrAl">{{cite book |author =Vargel, C.; Jacques, M.; Schmidt, M. P.| title = Corrosion of Aluminium|year =2004| isbn = 20049780080444956|publisher = Elsevier |url=http://books.google.com/?id=NAABS5KrVDYC&pg=PA158|page=158}}</ref>

Aluminium in air is ordinarily protected by a molecule-thin layer of its own oxide, which is not porous to oxygen. Mercury coming into contact with this oxide does no harm. However, if any elemental aluminium is exposed (even by a recent scratch), the mercury may combine with it, starting the process described above, and potentially damaging a large part of the aluminium before it finally ends.<ref name="CorrAl"/><ref name="Gray">{{cite web| author=Gray, T.| title=The Amazing Rusting Aluminum|publisher =[[Popular Science]]| date =2004-09-22|url=http://www.popsci.com/scitech/article/2004-09/amazing-rusting-aluminum|accessdate=2009-07-07}}</ref> For this reason, restrictions are placed on the use and handling of mercury in proximity with aluminium. In particular, mercury is not allowed aboard an aircraft under most circumstances because of the risk of it forming an amalgam with exposed aluminium parts in the aircraft.<ref name="CorrAl"/>

===Isotopes===
{{Main|Isotopes of mercury}}
There are seven stable [[isotope]]s of mercury with {{chem|202|Hg}} being the most abundant (29.86%). The longest-lived [[radioisotope]]s are {{chem|194|Hg}} with a [[half-life]] of 444 years, and {{chem|203|Hg}} with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day. {{chem|199|Hg}} and {{chem|201|Hg}} are the most often studied [[Nuclear magnetic resonance|NMR]]-active nuclei, having spins of {{frac|2}} and {{frac|3|2}} respectively.<ref name=CRC/>

==History==
[[Image:Mercury symbol.svg|thumb|left|The symbol for [[Mercury (planet)|the planet Mercury]] (☿) has been used since ancient times to represent the element]]
Mercury was found in [[Ancient Egypt|Egyptian]] tombs that date from 1500 BC.<ref>{{cite web|title=Mercury and the environment — Basic facts|publisher=[[Environment Canada]], Federal Government of Canada| year=2004|url=http://www.ec.gc.ca/MERCURY/EN/bf.cfm|accessdate=2008-03-27}}</ref> It was also known to the ancient Chinese.<ref>{{cite web|title=Mercury — Element of the ancients|publisher=Center for Environmental Health Sciences, [[Dartmouth College]]| url=http://www.dartmouth.edu/~toxmetal/metals/stories/mercury.html|accessdate=2008-03-27}}</ref> In [[China]] and [[Tibet]], mercury use was thought to prolong life, heal fractures, and maintain generally good health. One of China's emperors, [[Qin Shi Huang|Qín Shǐ Huáng Dì]] — allegedly buried in a tomb that contained rivers of flowing mercury on a model of the land he ruled, representative of the rivers of China — was killed by drinking a mercury and powdered [[jade]] mixture (causing [[liver failure]], [[poison]]ing, and [[brain death]]) intended to give him eternal life.<ref>{{cite web|title=Qin Shihuang|publisher=Ministry of Culture, [[People's Republic of China]]| year=2003|url=http://www.chinaculture.org/gb/en_aboutchina/2003-09/24/content_22854.htm|accessdate=2008-03-27}}</ref><ref name="wright">{{cite book|title=The History of China|year=2001|author=Wright, David Curtis|publisher= Greenwood Publishing Group|isbn=031330940X|page=49}}</ref> The [[ancient Greece|ancient Greeks]] used mercury in ointments; the [[ancient Egyptians]] and the [[Roman Empire|Romans]] used it in [[cosmetics]] which sometimes deformed the face. By 500 BC mercury was used to make [[amalgam (chemistry)|amalgams]] with other metals.<ref>{{cite book|url=http://books.google.com/?id=DIWEi5Hg93gC&pg=PA120|page=120|title=Jewelrymaking through history|author=Hesse R W|publisher=Greenwood Publishing Group|year= 2007|isbn=0313335079}}</ref> The Indian word for [[alchemy]] is ''[[Rasavātam]]'' which means "the way of mercury".<ref>{{cite book|url=http://books.google.com/?id=ykEN2zHvCpQC&pg=PA260|page=260|title=The Pillar of Celestial Fire|author=Cox R|publisher=1st World Publishing|year= 1997|isbn=1887472304}}</ref>

[[Alchemy|Alchemists]] thought of mercury as the [[Prima materia|First Matter]] from which all metals were formed. They believed that different [[metals]] could be produced by varying the quality and quantity of [[sulfur]] contained within the mercury. The purest of these was gold, and mercury was called for in attempts at the [[wiktionary:Transmutation|transmutation]] of base (or impure) metals into gold, which was the goal of many alchemists.<ref name="Stillman">{{cite book |title = Story of Alchemy and Early Chemistry|author = Stillman, J. M.| publisher = Kessinger Publishing|year = 2003|isbn = 9780766132306|pages = 7–9|url = http://books.google.com/?id=hdaAGF5Y1N0C}}</ref>

Hg is the modern [[chemical symbol]] for mercury. It comes from ''hydrargyrum'', a [[Latin]]ized form of the [[Greek language|Greek]] word Ύδραργυρος (''hydrargyros''), which is a compound word meaning "water-silver" (hydr- = water, argyros = silver) — since it is liquid like water and shiny like silver. The element was named after the Roman god [[Mercury (mythology)|Mercury]], known for speed and mobility. It is associated with the planet [[Mercury (planet)|Mercury]]; the astrological symbol for the planet is also one of the [[alchemical symbol]]s for the metal. Mercury is the only metal for which the alchemical planetary name became the common name.<ref name="Stillman"/>

The mines in [[Almadén]] (Spain), [[Monte Amiata]] (Italy), and [[Idrija]] (now Slovenia) dominated the mercury production from the opening of the mine in Almadén 2500 years ago until new deposits were found at the end of the 19th century.<ref name="MercHz">{{cite book|title =Mercury hazards to living organisms|author= Eisler, R.| publisher = CRC Press|year = 2006|isbn = 9780849392122|url = http://books.google.com/?id=gqc8wUvsI8cC&pg}}</ref>

==Occurrence==
{{See also|:Category:Mercury minerals|:Category:Mercury mines}}
[[Image:Mercury output2.PNG|thumb|left|300px|Mercury output in 2005]]<!-- map shows the U.S. has non-zero output, but article says all U.S. mines are closed Two points: Mercury is sometimes a by-product in gold mines and therefore no mercury mine does not mean no mercury production. Second point there are two sources for those kinds of information the US geological survey and the British geological survey: the USGS Mercury production: NA; Hg mines : None. BGS: Mercury production 15t ; Hg mines : no info -->

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 (ppm).<ref>{{cite book|url=http://books.google.com/?id=GerdDmwMTLkC&pg=PA265|page=265|title=Geomicrobiology|author=Ehrlich H L, Newman D K|publisher=CRC Press| year=2008isbn=0849379067 | isbn=9780849379062}}</ref> However, because it does not blend [[geochemistry|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 [[mineral]]s, 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 [[volcano|volcanic]] regions.<ref>{{cite web|accessdate=2009-07-07|title=Mercury Recycling in the United States in 2000|publisher=USGS|url=http://pubs.usgs.gov/circ/c1196u/Circ_1196_U.pdf}}</ref>

Beginning in 1558, with the invention of the [[patio process]] to extract silver from ore using mercury, mercury became an essential resource in the economy of Spain and its American colonies. Mercury was used to extract silver from the lucrative mines in [[New Spain]] and [[Peru]]. Initially, the Spanish Crown's mines in Almaden in Southern Spain supplied all the mercury for the colonies.<ref>{{cite book|author=Burkholder, M. and Johnson, L.|title=Colonial Latin America|publisher=Oxford University Press|year= 2008|pages=157–159}}</ref> Mercury deposits were discovered in the New World, and more than 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. The patio process and later [[pan amalgamation]] process continued to create great demand for mercury to treat silver ores until the late 1800s.<ref>{{cite book|url=http://books.google.com/?id=a4hPCX2XWDIC&pg=PA33|page=33|title=Domestic Architecture and Power|author=Jamieson, R W|publisher=Springer|year=2000|isbn=0306461765}}</ref>

Former mines in [[Italy]], the [[United States]] and [[Mexico]] which once produced a large proportion of the world supply have now been completely mined out or, in the case of [[Slovenia]] ([[Idrija]]) and Spain ([[Almadén]]), shut down due to the fall of the price of mercury. [[Nevada]]'s [[McDermitt]] Mine, the last mercury mine in the United States, closed in 1992. The price of mercury has been highly volatile over the years and in 2006 was $650 per 76-pound (34.46&nbsp;kg) flask.<ref name="brooks_usgs">{{cite web|url=http://minerals.usgs.gov/minerals/pubs/commodity/mercury/mercumcs07.pdf|format=PDF|title=Mercury|author=Brooks, W. E.|year=2007|publisher=U.S. Geological Survey|accessdate=2008-05-30}}</ref>

Mercury is extracted by heating cinnabar in a current of air and condensing the vapor. The equation for this extraction is
:HgS + O<sub>2</sub> → Hg + SO<sub>2</sub>

In 2005, China was the top producer of mercury with almost two-thirds global share followed by [[Kyrgyzstan]].<ref>{{cite book|title=World Mineral Production|date= 2001-05|publisher= British Geological Survey, NERC|location= London|year= 2007}}</ref> Several other countries are believed to have unrecorded production of mercury from copper [[electrowinning]] processes and by recovery from effluents.

Because of the high toxicity of mercury, both the mining of cinnabar and refining for mercury are hazardous and historic causes of mercury poisoning. In China, prison labor was used by a private mining company as recently as the 1950s to create new cinnabar mercury mines. Thousands of prisoners were used by the Luo Xi mining company to establish new tunnels.<ref name="GREEN"/> In addition, worker health in functioning mines is at high risk.

The [[European Union]] directive calling for compact [[fluorescent bulbs]] to be made mandatory by 2012 has encouraged China to re-open deadly cinnabar mines to obtain the mercury required for CFL bulb manufacture. As a result, environmental dangers have been a concern, particularly in the southern cities of [[Foshan]] and [[Guangzhou]], and in the [[Guizhou]] province in the south west.<ref name="GREEN">{{cite news|author=Sheridan, M. |url=http://www.timesonline.co.uk/tol/news/world/asia/article6211261.ece |title='Green' Lightbulbs Poison Workers: hundreds of factory staff are being made ill by mercury used in bulbs destined for the West|date=May 3, 2009|publisher=The Sunday Times (of London, UK)}}</ref>

Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabar calcines. Water run-off from such sites is a recognized source of ecological damage. Former mercury mines may be suited for constructive re-use. For example, in 1976 [[Santa Clara County, California]] purchased the historic [[Almaden Quicksilver County Park|Almaden Quicksilver Mine]] and created a county park on the site, after conducting extensive safety and environmental analysis of the property.<ref>{{cite book|url=http://books.google.com/?id=C6N03Lww1YsC&pg=PA8|page=8|title=New Almaden|author=Boulland M|publisher=Arcadia Publishing|year= 2006|isbn=0738531316}}</ref>

==Releases in the environment==
[[Image:Mercury fremont ice core.png|thumb|right|Amount of atmospheric mercury deposited at Wyoming's Upper Fremont Glacier over the last 270 years]]

Preindustrial deposition rates of mercury from the atmosphere may be about 4&nbsp;ng /(1 L of ice deposit). 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.<ref>{{cite web|url=http://toxics.usgs.gov/pubs/FS-051-02/|title=Glacial Ice Cores Reveal A Record of Natural and Anthropogenic Atmospheric Mercury Deposition for the Last 270 Years|publisher=United States Geological Survey (USGS)|accessdate=May 1, 2007}}</ref>

Natural sources, such as [[volcano]]es, are responsible for approximately half of atmospheric mercury emissions. The human-generated half can be divided into the following estimated percentages:<ref name=Pacyna/><ref>{{cite web|url=http://www.epa.gov/mercury/|title=What is EPA doing about mercury air emissions?|publisher=United States Environmental Protection Agency (EPA)|accessdate=May 1, 2007}}</ref><ref>{{cite web|url=http://www.orionmagazine.org/index.php/articles/article/176/ |title=Winged Mercury and the Golden Calf|author=Solnit, R.|date=September/October 2006|publisher=Orion Magazine|accessdate=2007-12-03}}</ref>
*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.<ref name=Pacyna/>
*11% from gold production. The three largest point sources for mercury emissions in the U.S. are the three largest gold mines. Hydrogeochemical release of mercury from gold-mine tailings has been accounted as a significant source of atmospheric mercury in eastern Canada.<ref>{{cite journal|doi=10.1021/es048962j|title=Determination of Mercury Evasion in a Contaminated Headwater Stream|year=2005|last1=Maprani|first1=Antu C.|journal=Environmental Science & Technology|volume=39|page=1679|last2=Al|first2=Tom A.|last3=MacQuarrie|first3=Kerry T.|last4=Dalziel|first4=John A.|last5=Shaw|first5=Sean A.|last6=Yeats|first6=Phillip A.}}</ref>
*6.8% from [[non-ferrous metal]] production, typically [[smelter]]s.
*6.4% from [[cement]] production.
*3.0% from [[waste disposal]], including [[municipal waste|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.<ref name=Pacyna>{{cite journal |journal= Atmos Environ |year=2006 |volume=40 |issue=22 |page=4048|title= Global anthropogenic mercury emission inventory for 2000 |author= Pacyna E G, Pacyna J M, Steenhuisen F, Wilson S |doi=10.1016/j.atmosenv.2006.03.041}}</ref>

Current atmospheric mercury contamination in outdoor urban air is (0.01–0.02&nbsp;µg/m<sup>3</sup>) indoor concentrations are significantly elevated over outdoor concentrations, in the range 0.0065–0.523&nbsp;µg/m<sup>3</sup> (average 0.069&nbsp;µg/m<sup>3</sup>).<ref>{{cite web|url=http://www.newmoa.org/prevention/mercury/MercuryIndoor.pdf|accessdate=2009-07-07|title=Indoor Air Mercury|date=May 2003}}</ref>

Mercury also enters into the environment through the improper disposal (e.g., land filling, incineration) of certain products. Products containing mercury include: auto parts, [[battery (electricity)|batteries]], fluorescent bulbs, medical products, thermometers, and thermostats.<ref>{{cite web|url=http://www.epa.gov/epaoswer/non-hw/reduce/epr/products/mercury.htm|title=Mercury-containing Products|publisher=United States Environmental Protection Agency (EPA)|accessdate=May 1, 2007}}</ref> Due to health concerns (see below), [[waste management|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 (1990)|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<ref>{{cite web|url=http://www.epa.gov/air/mercuryrule/|title=Clean Air Mercury Rule|publisher=United States Environmental Protection Agency (EPA)|accessdate=May 1, 2007}}</ref> added power plants to the list of sources that should be controlled and a national [[emissions trading|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 and decision was made in 2008. The Clean Air Mercury Rule was struck down by a Federal Appeals Court on February 8, 2008. The rule was deemed not sufficient to protect the health of persons living near coal-fired power plants. The court opinion cited the negative impact on human health from coal fired power plants' mercury emissions documented in the EPA Study Report to Congress of 1998.<ref name="nj vs epa">{{cite news|url=http://pacer.cadc.uscourts.gov/docs/common/opinions/200802/05-1097a.pdf |title=State of New Jersey et al., Petitioners vs. Environmental Protection Agency (Case No. 05-1097)]|publisher=United States Court of Appeals for the District of Columbia Circuit. Argued December 6, 2007, Decided February 8, 2008|accessdate= May 30, 2008}}</ref>

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.<ref>{{cite web|publisher = [[United States Department of Energy]]|work = [http://www.hss.energy.gov/healthsafety/ohre/new/findingaids/epidemiologic/oakridge1/index.html Y-12 Mercury Task Force Files: A Guide to Record Series of the Department of Energy and its Contractors]|title = Introduction|url = http://www.hss.energy.gov/healthsafety/ohre/new/findingaids/epidemiologic/oakridge1/intro.html}}</ref>

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]].<ref>{{cite web|url=http://www.env.go.jp/en/chemi/hs/minamata2002/|title=Minamata Disease The History and Measures|publisher=Ministry of the Environment, Government of Japan|accessdate=2009-07-07}}</ref>

===Mapping of industrial releases in the United States===
One tool that maps releases of mercury<ref>[http://toxmap.nlm.nih.gov/toxmap/tri/mapIt.do?chemicalName=mercury]</ref> to particular locations in the United States<ref>{{cite web|url=http://toxmap.nlm.nih.gov/toxmap/tri/mapIt.do?chemicalName=mercury |title=TRI Releases Map |publisher=Toxmap.nlm.nih.gov |accessdate=2010-03-23}}</ref> and also provides additional information about such releases is [[TOXMAP]]. TOXMAP is a Geographic Information System (GIS) from the Division of Specialized Information Services of the [[United States National Library of Medicine]] (NLM) that uses maps of the United States to help users visually explore data from the [[United States Environmental Protection Agency]]'s (EPA) [[Toxics Release Inventory]] and [[Superfund Basic Research Program]]s. TOXMAP is a resource funded by the US Federal Government. TOXMAP's chemical and environmental health information is taken from NLM's Toxicology Data Network (TOXNET)<ref>[http://toxnet.nlm.nih.gov TOXNET - Databases on toxicology, hazardous chemicals, environmental health, and toxic releases]</ref> and [[PubMed]], and from other authoritative sources.

==Applications==
[[Image:Maximum thermometer close up 2.JPG|thumb|right|The bulb of a [[mercury-in-glass thermometer]]]]
Mercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic applications. It is used in some thermometers, especially ones which are used to measure high temperatures. A still increasing amount is used as gaseous mercury in [[fluorescent lamps]], while most of the other applications are slowly phased out due to health and safety regulations and is in some applications replaced with less toxic but considerably more expensive [[Galinstan]] [[alloy]].

===Present use===
====Medicine====
[[Image:Amalgam.jpg|thumb|right|Amalgam filling]]
[[Image:Germicidal UV discharge tube glow.jpg|thumb|The deep violet glow of a mercury vapor discharge in a [[germicidal lamp]], whose spectrum is rich in invisible ultraviolet radiation.]]
{{seealso|Amalgam (dentistry)}}
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. The element mercury is an ingredient in [[amalgam (dentistry)|dental amalgams]]. [[Thiomersal]] (called ''Thimerosal'' in the United States) is an [[organic compound]] used as a [[preservative]] in [[vaccine]]s, though this use is in decline.<ref>{{cite web|author = FDA|url = http://www.fda.gov/Cber/vaccine/thimerosal.htm|title = Thimerosal in Vaccines|accessdate=October 25, 2006}}</ref> Another mercury compound [[Merbromin]] (Mercurochrome) is a topical antiseptic used for minor cuts and scrapes is still in use in some countries.

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.<ref>{{cite news|author=Pimple, K.D. Pedroni, J.A. Berdon, V.|date=July 9, 2002|url=http://www.indiana.edu/~poynter/sas/lb/syphilis.html|title=Syphilis in history|publisher=Poynter Center for the Study of Ethics and American Institutions at Indiana University-Bloomington|accessdate= April 17, 2005}}</ref> It is 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.<ref>{{cite news|title = Did Mercury in "Little Blue Pills" Make Abraham Lincoln Erratic?|author=Mayell, H.|url= http://news.nationalgeographic.com/news/2001/07/0717_lincoln.html|work= [[National Geographic Society|National Geographic News]] |date= 2007-07-17|accessdate = 2008-06-15
}}</ref> 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 [[merbromin]] (sometimes sold as Mercurochrome) is still widely used but has been banned in some countries such as the U.S.<ref>{{cite web|url=http://www.straightdope.com/columns/read/2518/what-happened-to-mercurochrome|accessdate=2009-07-07|title=What happened to Mercurochrome?|date=July 23, 2004}}</ref>

Since the 1930s some [[vaccine]]s have contained the preservative [[thiomersal]], which is metabolized or degraded to [[ethyl mercury]]. Although it was [[Thiomersal controversy|widely speculated]] that this mercury-based preservative can cause or trigger [[autism]] in children, scientific studies showed no evidence supporting any such link.<ref>{{cite journal |journal=Pediatrics |year=2004 |volume=114 |page=793|title= Thimerosal-containing vaccines and autistic spectrum disorder: a critical review of published original data |author= Parker SK, Schwartz B, Todd J, Pickering LK |doi=10.1542/peds.2004-0434 |pmid=15342856|issue=3 |pages=793–804}} [http://pediatrics.aappublications.org/cgi/content/full/115/1/200 Erratum] (2005). ''Pediatrics'' 115 (1): 200. {{DOI|10.1542/peds.2004-2402}} PMID 15630018.</ref> 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.<ref>{{cite web |date=2007-09-06 |url=http://www.fda.gov/cber/vaccine/thimerosal.htm |accessdate=2007-10-01 |title= Thimerosal in vaccines |publisher= Center for Biologics Evaluation and Research, U.S. Food and Drug Administration}}</ref>

Mercury in the form of one of its common ores, cinnabar, remains an important component of [[traditional Chinese medicine|Chinese]], [[Tibetan medicine|Tibetan]], and [[Ayurveda|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. [[Mercury-in-glass thermometer|Thermometers]] and [[sphygmomanometer]]s 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 [[Medical prescription|non-prescription]] mercury thermometers. In 2003, [[Washington (U.S. state)|Washington]] and [[Maine]] became the first states to ban mercury blood pressure devices.<ref>{{cite web|url=http://www.noharm.org/details.cfm?ID=782|title=Two States Pass First-time Bans on Mercury Blood Pressure Devices|date=June 2, 2003|publisher=Health Care Without Harm|accessdate=May 1, 2007}} {{Dead link|date=September 2010|bot=H3llBot}}</ref> Mercury compounds are found in some [[over-the-counter drug]]s, including topical [[antiseptics]], stimulant laxatives, [[diaper rash|diaper-rash]] [[ointment]], [[eye drops]], and [[nasal spray]]s. The [[Food and Drug Administration|FDA]] has “inadequate data to establish general recognition of the safety and effectiveness,” of the mercury ingredients in these products.<ref>{{cite web|url=http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=310.545&SearchTerm=mercury| title=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|publisher=United States Food and Drug Administration|accessdate=May 1, 2007}}</ref> Mercury is still used in some diuretics, although substitutes now exist for most therapeutic uses.

====Cosmetics====
Mercury, as [[thiomersal]], is widely used in the manufacture of [[mascara]]. In 2008, Minnesota became the first state in the US to ban intentionally added mercury in cosmetics, giving it a tougher standard than the federal government.<ref>{{cite news|url=http://www.cidpusa.org/mercury.htm|publisher=CIDPUSA|title=Mercury in your eye?|date=2008-02-16|accessdate=2009-12-20}}</ref><!--10.1111/j.1600-0536.1996.tb02225.x-->

====Production of chlorine and caustic soda====
[[Chlorine]] is produced from [[sodium chloride]] (common salt, NaCl) using [[electrolysis]] to separate the metallic [[sodium]] from the chlorine gas. Usually the salt is dissolved in water to produce a brine. By-products of any such [[chloralkali process]] are hydrogen (H<sub>2</sub>) and [[sodium hydroxide]] (NaOH), which is commonly called caustic soda or [[lye]]. By far the largest use of mercury<ref>{{cite book|title=The CRB Commodity Yearbook (annual)|year= 2000|page=173|issn=1076-2906}}</ref><ref name="USEPA">{{cite web|url=http://www.epa.gov/nrmrl/pubs/600r02104/600r02104chap3.pdf|format=PDF|author=Leopold, B. R.|year=2002|title=Chapter 3: Manufacturing Processes Involving Mercury. ''Use and Release of Mercury in the United States''|publisher=National Risk Management Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, Ohio|accessdate=May 1, 2007 |archiveurl = http://web.archive.org/web/20070621093346/http://www.epa.gov/nrmrl/pubs/600r02104/600r02104chap3.pdf |archivedate = June 21, 2007}}</ref> in the late 1900s was in the mercury cell process (also called the [[Castner-Kellner process]]) where metallic sodium is formed as an [[amalgam (chemistry)|amalgam]] at a [[cathode]] made from mercury; this sodium is then reacted with water to produce sodium hydroxide.<ref>{{cite web|url=http://www.eurochlor.org/animations/mercury-cell.asp| title=Chlorine Online Diagram of mercury cell process| publisher=Euro Chlor| accessdate=2006-09-15}}</ref> Many of the industrial mercury releases of the 1900s came from this process, although modern plants claimed to be safe in this regard.<ref name="USEPA"/> After about 1985, all new chloralkali production facilities that were built in the United States used either [[Sodium hydroxide#Methods of production|membrane cell or diaphragm cell technologies]] to produce chlorine.

====Gold and silver mining====
Historically, mercury was used extensively in hydraulic gold mining in order to help the gold to sink through the flowing water-gravel mixture. Thin mercury particles may form mercury-gold amalgam and therefore increase the gold recovery rates.<ref name=CRC/> Large scale use of mercury stopped in the 1960s. However, mercury is still used in small scale, often clandestine, gold prospecting. It is estimated that 45,000 metric tons of mercury used in California for [[placer mining]] have not been recovered.<ref>{{cite web |url=http://pubs.usgs.gov/fs/2005/3014/ |title=Mercury Contamination from Historical Gold Mining in California |accessdate=2008-02-26 |author=Alpers, C. N.; Hunerlach, M. P.; May, J. Y.; Hothem, R. L. |publisher=U.S. Geological Survey}}</ref> Mercury was also used in silver mining.<ref>{{cite web |url=http://corrosion-doctors.org/Elements-Toxic/Mercury-amalgamation.htm |title=Mercury amalgamation|accessdate=2009-07-07}}</ref>

====Other present uses====
[[Image:Mercuryvaporlamp.jpg|thumb|Skin tanner containing a low-pressure mercury vapor lamp and two infrared lamps, which act both as light source and [[electrical ballast]]]]
[[Image:Leuchtstofflampen-chtaube050409.jpg|thumb|Assorted types of fluorescent lamps.]]
Gaseous mercury is used in [[mercury-vapor lamp]]s and some "[[neon sign]]" type advertising signs and [[fluorescent lamps]]. Those low-pressure lamps emit very spectrally narrow lines, which are traditionally used in [[optical spectroscopy]] for calibration of spectral position. Commercial calibration lamps are sold for this purpose; however simply reflecting some of the fluorescent-lamp ceiling light into a spectrometer is a common calibration practice.<ref>{{cite book|title = A guide to the use and calibration of detector array equipment| author = Hopkinson, G. R.; Goodman, T. M.; Prince, S. R.| publisher = SPIE Press| year = 2004| page = 125| isbn = 0819455326}}</ref> Gaseous mercury is also found in some [[Gas filled tube|electron tubes]], including [[ignitron]]s, [[thyratron]]s, and [[mercury arc rectifier]]s.<ref>{{cite book|author=Howatson A H|title=An Introduction to Gas Discharges|isbn=0080205755|publisher=Pergamon Press|location= Oxford|year= 1965|chapter=8}}</ref> It is also used in specialist medical care lamps for skin tanning and disinfection (see pictures).<ref>{{cite book|url=http://books.google.com/?id=-_9lhR_z6j8C&pg=PA104|page=104|title=Transformation of human diploid fibroblasts|author=Milo G E, Casto B C|publisher=CRC Press|year=1990|isbn=0849349567}}</ref> Gaseous mercury is added to [[cold cathode]] [[argon]]-filled lamps to increase the [[ionization]] and [[electrical conductivity]]. An argon filled lamp without mercury will have dull spots and will fail to light correctly. Lighting containing mercury can be [[bombarding|bombarded]]/oven pumped only once. When added to [[neon]] filled tubes the light produced will be inconsistent red/blue spots until the initial burning-in process is completed; eventually it will light a consistent dull off-blue color.<ref>{{cite book| page = 363| title= Phosphor handbook| author = Shionoya, S.| publisher = CRC Press| year = 1999| isbn = 0849375606}}</ref>

Some medical thermometers, especially those for high temperatures, are filled with mercury, however, they are gradually disappearing. In the United States, non-prescription sale of mercury fever thermometers has been banned in 2003.<ref>{{cite news| title = Mercury Reduction Act of 2003|url = http://openlibrary.org/b/OL17617678M|accessdate = 2009-06-06| publisher = United States. Congress. Senate. Committee on Environment and Public Works}}</ref> Mercury is also found in [[liquid mirror|liquid-mirror telescopes]]. The mirror is formed by rotating liquid mercury on a disk, the parabolic form of the liquid thus formed reflecting and focusing incident light. Such telescopes are cheaper than conventional large mirror telescopes by up to a factor of 100, but the mirror cannot be tilted and always points straight up.<ref>{{cite web|archiveurl=http://web.archive.org/web/20030818233315/http://www.govertschilling.nl/artikelen/science/030314_sc.htm|url=http://www.govertschilling.nl/artikelen/science/030314_sc.htm|title=Liquid-mirror telescope set to give stargazing a new spin|date=2003-03-14|archivedate=2003-08-18|publisher=Govert Schilling|accessdate=2008-10-11}}</ref><ref>{{ cite journal|author = Gibson, B. K.|year=1991|title= Liquid mirror telescopes: history|format = PDF| url = http://citeseer.ist.psu.edu/cache/papers/cs/2683/http:zSzzSzwww-astro.physics.ox.ac.ukzSz~bkgzSzLMT_history.pdf/liquid-mirror-telescopes-history.pdf|journal=Journal of the Royal Astronomical Society of Canada|volume = 85|page = 158}}</ref>

Liquid mercury is a part of popular secondary reference [[electrode]] (called the [[Mercury(I) chloride|calomel electrode]]) in [[electrochemistry]] as an alternative to the [[standard hydrogen electrode]]. The calomel electrode is used to work out the [[electrode potential]] of [[half cell]]s.<ref>{{cite book|url=http://books.google.com/?id=M5pOAAAAIAAJ&pg=PA175|page=175|title=Physiological monitoring and instrument diagnosis in perinatal and neonatal medicine|author=Brans, Y W, Hay W W|publisher=CUP Archive|year= 1995|isbn=0521419514}}</ref> Last, but not least, the [[triple point]] of mercury, -38.8344 °C, is a fixed point used as a temperature standard for the International Temperature Scale ([[ITS-90]]).<ref name=CRC/>

===Proposed uses===
Liquid mercury has been proposed as a working fluid for a [[heat pipe]] type of cooling device for spacecraft heat rejection systems or radiation panels.<ref>{{cite web|accessdate=2009-07-07|url=http://www.aqpl43.dsl.pipex.com/MUSEUM/POWER/mercury/mercury.htm|title=Mercury as a Working Fluid}}</ref>

===Historic uses===
[[Image:Old mercury switches bionerd.jpg|thumb|Old mercury switches]]
[[Image:Barometer mercury column hg.jpg|thumb|Mercury [[manometer]] to measure pressure]]
Mercury was used for preserving wood, developing [[daguerreotype]]s, [[silvering]] [[mirror]]s, anti-fouling paints (discontinued in 1990), [[herbicide]]s (discontinued in 1995), handheld maze games, cleaning, and road leveling devices in cars. Mercury compounds have been used in [[antiseptic]]s, laxatives, [[antidepressant]]s, and in [[syphilis|antisyphilitics]]. It was also allegedly used by [[Western Allies|allied spies]] to sabotage [[Nazi Germany|German]] planes. A mercury paste was applied to bare [[aluminium]], causing the metal to rapidly [[Corrosion|corrode]]. This would cause structural failures.<ref name="Gray"/>
*[[Chlor-alkali plants]]: The largest industrial use of mercury during the twentieth century was in large electrolysis batteries for separating chlorine and sodium from brine. The chlorine was used for bleaching paper (hence the location of many of these plants near paper mills) while the sodium was used to make sodium hydroxide for soaps and other cleaning products. This usage has largely been discontinued with the replacement of other technologies using membrane cells.<ref>{{cite web|accessdate=2010-09-06|url=http://www.ehjournal.net/content/8/1/2|title=Default et al. Mercury from Chlor-alkali plants, Environmental Health 2009, 8:2}}</ref>
*[[Mercury switch]]es (including [[Light switch#Mercury switches|home mercury light switches]] installed prior to 1970), tilt switches used in old fire detectors, tilt switches in many modern home thermostats,<ref>{{cite book|url=http://books.google.com/?id=cxPEiSXh44cC&pg=PA260|page=260|title=Electrical Installations|author=Shelton, C|publisher=Nelson Thornes|year= 2004|isbn=0748779795}}</ref> [[electrode]]s in some types of [[electrolysis]], [[battery (electricity)|batteries]] ([[mercury battery|mercury cells]]), [[sodium hydroxide]] and [[chlorine]] production, handheld games, [[catalyst]]s, [[insecticide]]s and [[liquid mirror]] telescopes.<ref>{{cite web|accessdate=2009-07-07|url=http://www.astro.ubc.ca/LMT/lzt/index.html|title=The Large Zenith Telescope}}</ref>
*In [[Islamic Spain]] it was used for filling decorative pools. Later the American artist [[Alexander Calder]] built a [[mercury fountain]] for the Spanish Pavilion at the [[Exposition Internationale des Arts et Techniques dans la Vie Moderne (1937)|1937 World Exhibition in Paris]]. The fountain is now on display at the [[Fundació Joan Miró]] in [[Barcelona]].<ref>{{cite book|url=http://books.google.com/?id=pgUfSrD4gzQC&pg=PA10|page=10|title=Mercury|author=Lew K|publisher=The Rosen Publishing Group|year= 2008|isbn=1404217800}}</ref>
*Mercury was used inside [[wobbler (fishing)|wobbler]] lures. Its heavy, liquid form made it useful since the lures made an attractive irregular movement when the mercury moved inside the plug. Such use was stopped due to environmental concerns, but illegal preparation of modern fishing plugs has occurred.
*The [[Fresnel lens]]es of old [[lighthouses]] used to float and rotate in a bath of mercury which acted like a bearing.<ref>{{cite book|url=http://books.google.com/?id=oY8nG-6B6v0C&pg=PA29|page=29|title=Lighthouses|publisher=Osprey Publishing|year= 2003|isbn=0747805563|author=Pearson L F}}</ref>
*Mercury [[sphygmomanometer]]s (blood pressure meter), [[barometer]]s, [[diffusion pump]]s, [[Mercury coulometer|coulometers]], and many other laboratory instruments. As an opaque liquid with a high density and a nearly linear thermal expansion, it is ideal for this role.<ref>{{cite book|url=http://books.google.com/?id=G8QyI1Nf0VQC&pg=PA251|page=251|title=AIEEE Chemistry|author=Ramanathan E|publisher=Sura Books|isbn=8172542933}}</ref>
*Liquid mercury was used as a [[coolant]] for some [[nuclear reactor]]s; however, [[sodium]] is proposed for reactors cooled with liquid metal, because the high density of mercury requires much more energy to circulate as coolant.<ref>{{cite book|url=http://books.google.com/?id=2KYVftKE9NUC&pg=PA64|page=64|title=Introduction to Nuclear Power|author=Collier|publisher=Taylor & Francis|year=1987|isbn=1560326824}}</ref>
*Mercury was a propellant for early [[ion engines]] in [[electric propulsion|electric space propulsion]] systems. Advantages were mercury's high molecular weight, low ionization energy, low dual-ionization energy, high liquid density and liquid storability at [[room temperature]]. Disadvantages were concerns regarding environmental impact associated with ground testing and concerns about eventual cooling and condensation of some of the propellant on the spacecraft in long-duration operations. The first spaceflight to use electric propulsion was a mercury-fueled ion thruster developed by [[NASA Glenn Research Center|NASA Lewis]] and flown on the Space Electric Rocket Test "[[SERT-1]]" spacecraft launched by [[NASA]] at its [[Wallops Flight Facility]] in 1964. The SERT-1 flight was followed up by the SERT-2 flight in 1970. Mercury and [[caesium]] were preferred propellants for ion engines until [[Hughes Research Laboratory]] performed studies finding [[xenon]] gas to be a suitable replacement. Xenon is now the preferred propellant for ion engines as it has a high molecular weight, little or no reactivity due its [[noble gas]] nature, and has a high liquid density under mild cryogenic storage.<ref>{{cite web|publisher=NASA|accessdate=2009-07-07|url=http://www.nasa.gov/centers/glenn/about/history/ds1.html|title=Glenn Contributions to Deep Space 1}}</ref><ref>{{cite web|accessdate=2009-07-07|url=http://www.daviddarling.info/encyclopedia/E/electricprop.html|title=Electric space propulsion}}</ref>
*Experimental [[mercury vapor turbine]]s were installed to increase the efficiency of fossil-fuel electrical power plants.<ref>{{cite book|url=http://books.google.com/?id=9ycDAAAAMBAJ&pg=PA40|page=40|title=Popular Science|year=1931|volume= 118, No. 3|issn=01617370|publisher= Bonnier Corporation}}</ref>
*Mercury was once used as a gun barrel bore cleaner.<ref name='Francis1849'>{{cite book|author = Francis, G. W.| title = Chemical Experiments|publisher = D. Francis|year = 1849|page= 62}}</ref><ref name='Castles2005'>{{cite book|author = Castles, WT; Kimball, VF| title = Firearms and Their Use|publisher = Kessinger Publishing|year = 2005 |page= 104|isbn = 9781417989577}}</ref>

====Hat making====
From the mid-18th to the mid-19th centuries, a process called "[[carroting]]" was used in the making of [[felt]] hats. Animal skins were rinsed in an orange solution (the term "carroting" arose from this color) of the mercury compound [[mercuric nitrate]], Hg(NO<sub>3</sub>)<sub>2</sub>·2H<sub>2</sub>O.<ref>{{cite book|title=Concise Inorganic Chemistry|author=Lee, J.D.|publisher=Wiley-Blackwell|year=1999|isbn=9780632052936}}</ref> This process separated the fur from the pelt and matted it together. This solution and the vapors it produced were highly toxic. The [[United States Public Health Service]] banned the use of mercury in the felt industry in December 1941. The psychological symptoms associated with mercury poisoning are said by some to have inspired the phrase "mad as a hatter".  [[Lewis Carroll]]'s "[[Mad Hatter]]" in his book ''[[Alice's Adventures in Wonderland]]'' was a play on words based on the older phrase, but the character himself does not exhibit symptoms of mercury poisoning.<ref>{{cite journal |journal= Br Med J (Clin Res Ed) |year=1983 |volume=287 |page=1961 |title= Did the Mad Hatter have mercury poisoning? |author= Waldron, HA |pmid=6418283 |doi= 10.1136/bmj.287.6409.1961 |issue= 6409 |pmc= 1550196}}</ref><!--http://www.jstor.org/pss/139669-->

==Safety==
{{See also|Mercury poisoning}}
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 [[mercury-in-glass thermometer|thermometers]] or [[fluorescent light bulb]]s) specific cleaning procedures are used to avoid toxic exposure.<ref>{{cite web|url=http://www.epa.gov/mercury/spills/index.htm|title=Mercury: Spills, Disposal and Site Cleanup|publisher=Environmental Protection Agency|accessdate=2007-08-11}}</ref> Essentially, it is recommended to physically merge smaller droplets on hard surfaces, combining them into a single larger pool for easier removal by using an [[eyedropper]], or by pushing it into a disposable container. Vacuum cleaners and brooms should not be used because they cause greater dispersal of the mercury. Afterwards, [[sulfur]] powder, [[zinc]] powder, or some other element that readily forms an amalgam (alloy) with mercury (e.g. finely-divided [[Copper|Cu]] or [[Bismuth|Bi]]) at ordinary temperatures is sprinkled over the area and subsequently collected and properly disposed of.  Cleaning porous surfaces and clothing is not effective at removing all traces of mercury and it is therefore advised to discard these kinds of items should they be exposed to a mercury spill.

Mercury can be inhaled and absorbed through the skin and mucous membranes, so containers of mercury are securely sealed to avoid spills and evaporation. Heating of mercury, or compounds of mercury that may decompose when heated, is always carried out with adequate ventilation in order to avoid exposure to mercury vapor. The most toxic forms of mercury are its [[organic compounds]], such as [[dimethylmercury]] and [[methylmercury]]. However, inorganic compounds, such as cinnabar are also highly toxic by ingestion or inhalation of the dust.<ref name=msds>{{cite web|url= http://msds.chem.ox.ac.uk/ME/mercuric_sulphide.html|title=Safety data for mercuric sulphide|accessdate=2009-07-07|publisher=Oxford University}}</ref> Mercury can cause both chronic and acute poisoning.

===Occupational exposure===
Due to the health effects of mercury exposure, industrial and commercial uses are regulated in many countries. The [[World Health Organization]], [[Occupational Safety and Health Administration|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 vapor even at low concentrations in the range 0.7–42 μg/m<sup>3</sup>.<ref name="ngim">{{cite journal|title=Chronic neurobehavioral effects of elemental mercury in dentists|journal=British Journal of Industrial Medicine|volume=49|page=782| year=1992|author1=Ngim, CH|author2=Foo, SC|author3=Boey, K.W.|author4=Keyaratnam, J}}</ref><ref name="liang">{{cite journal|author=Liang YX, Sun RK, Chen ZQ, and Li LH|title=Psychological effects of low exposure to mercury vapor: Application of computer-administered neurobehavioral evaluation system|journal=Environmental Research|volume=60|page=320| doi=10.1006/enrs.1993.1040|year=1993|pmid=8472661|last1=Liang|first1=YX|last2=Sun|first2=RK|last3=Sun|first3=Y|last4=Chen|first4=ZQ|last5=Li|first5=LH|issue=2}}</ref> A study has shown that acute exposure (4 – 8 hours) to calculated elemental mercury levels of 1.1 to 44&nbsp;mg/m<sup>3</sup> resulted in chest pain, [[dyspnea]], cough, [[hemoptysis]], impairment of pulmonary function, and evidence of interstitial [[pneumonitis]].<ref>{{cite journal|author=McFarland, RB and Reigel, H|journal=J. Occup. Med. |year=1978 |volume=20|page=532|doi=10.1097/00043764-197808000-00003|title=Chronic Mercury Poisoning from a Single Brief Exposure}}</ref> 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.<ref>{{cite book|publisher=World Health Organization|year=1976|title= Environmental Health Criteria 1: Mercury|location= Geneva|url=http://www.inchem.org/documents/ehc/ehc/ehc001.htm|isbn=9241540613
}}</ref><ref>{{cite book|publisher=World Health Organization|year=1991|title= Inorganic mercury. Environmental Health Criteria 118|location= Geneva|isbn=9241571187|url=http://www.inchem.org/documents/ehc/ehc/ehc118.htm|author=published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organisation, and the World Health Organization ; first draft prep. by L. Friberg}}</ref>

===Treatment===
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.<ref>{{cite journal|author=Bluhm, RE, ''et al.'' |journal=Hum Exp Toxicol |year=1992 |volume=11|page=201|title=Elemental Mercury Vapour Toxicity, Treatment, and Prognosis After Acute, Intensive Exposure in Chloralkali Plant Workers. Part I: History, Neuropsychological Findings and Chelator effects|doi=10.1177/096032719201100308}}</ref> [[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.<ref>{{cite journal|pmid=1352115|year=1992|title=Elemental mercury vapour toxicity, treatment, and prognosis after acute, intensive exposure in chloralkali plant workers. Part I: History, neuropsychological findings and chelator effects.|volume=11|issue=3|pages=201–10|journal=Human & experimental toxicology|doi=10.1177/096032719201100308|author1=Bluhm, Re|author2=Bobbitt, Rg|author3=Welch, Lw|author4=Wood, Aj|author5=Bonfiglio, Jf|author6=Sarzen, C|author7=Heath, Aj|author8=Branch, Ra}}</ref>

===Fish===
{{Main|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. As mercury and methylmercury are fat soluble, they primarily accumulate in the viscera, although they are also found throughout the muscle tissue. When this fish is consumed by a predator, the mercury level is accumulated. 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 than the species they consume. This process is called [[biomagnification]]. [[Mercury poisoning]] happened this way in [[Minamata, Kumamoto|Minamata]], [[Japan]], now called [[Minamata disease]].

==Regulations==
In the United States, the [[United States Environmental Protection Agency|Environmental Protection Agency]] is charged with regulating and managing mercury contamination. Several laws give the EPA this authority, including the [[Clean Air Act#United States|Clean Air Act]], the [[Clean Water Act]], the [[Resource Conservation and Recovery Act]], and the [[Safe Drinking Water Act]]. Additionally, the [[Mercury-Containing and Rechargeable Battery Management Act]], passed in 1996, phases out the use of mercury in batteries, and provides for the efficient and cost-effective disposal of many types of used batteries.<ref name="epa regs">{{cite web|url=http://www.epa.gov/mercury/regs.htm|title=Mercury: Laws and regulations|date=April 16, 2008|publisher=[[United States Environmental Protection Agency]]|accessdate=2008-05-30}}</ref> North America contributed approximately 11% of the total global anthropogenic mercury emissions in 1995.<ref>{{cite web|url=http://www.ijc.org/php/publications/html/12br/english/report/chemical/rme.html |title=Reductions in Mercury Emissons|publisher=[[International Joint Commission]] on the [[Great Lakes]]}}</ref>

In the [[European Union]], the directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (see [[Restriction of Hazardous Substances Directive|RoHS]]) bans mercury from certain electrical and electronic products, and limits the amount of mercury in other products to less than 1000 [[Parts per million|ppm]].<ref name="eu regs">{{cite web|url=http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2003:037:0019:0023:EN:PDF |title=Directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment|date=2002/95/EC}} Article 4 Paragraph 1. e.g. "Member States shall ensure that, from July 1, 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)."</ref> There are restrictions 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).<ref>{{cite web|url=http://www.eiatrack.org/s/1785|title=Mercury compounds in European Union: |year=2007|publisher=[http://www.eiatrack.org/ EIA Track]|accessdate=2008-05-30}}</ref> In July 2007, the 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 health care sector and a two year grace period for manufacturers of barometers.
<ref name="eu reuters">{{cite news|url=http://www.reuters.com/article/environmentNews/idUSL0988544920070710|title=EU bans mercury in barometers, thermometers|author=Jones H.|date=July 10, 2007|publisher=Reuters|accessdate=2008-05-30}}</ref>

[[Norway]] enacted a total ban on the use of mercury in the manufacturing and import/export of mercury products, effective January 1, 2008.<ref name="norway">{{cite news|url=http://www.eubusiness.com/news-eu/1198237627.85|title=Norway to ban mercury|date=December 21, 2007|publisher=[http://www.eubusiness.com/ EU Business]|accessdate=2008-05-30}} {{Dead link|date=September 2010|bot=H3llBot}}</ref> In 2002, several lakes in Norway were found to have a poor state of mercury pollution, with an excess of 1&nbsp;mg/g of mercury in their sediment.<ref name="environment norway">{{cite journal|doi=10.1016/j.scitotenv.2005.09.059|year=2006|title=Atmospheric mercury in Norway: contributions from different sources.|volume=368|issue=1|pages=3–9|pmid=16310836|journal=The Science of the total environment|author1=Berg, T|author2=Fjeld, E|author3=Steinnes, E}}</ref>

==References==
{{Reflist|colwidth=30em}}

==Further reading==
*Jane M. Hightower ''Diagnosis: Mercury: Money, Politics, and Poison'' Island Press (October 1, 2008) ISBN 1597263958 ISBN 978-1597263955

== External links ==
{{commons}}
{{Wiktionary|mercury}}
*[http://www.atsdr.cdc.gov/tfacts46.html ATSDR — ToxFAQs: Mercury]
*[http://www.cdc.gov/niosh/topics/mercury/ Centers for Disease Control and Prevention - Mercury Topic]
*[http://www.epa.gov/ostwater/fishadvice/advice.html EPA fish consumption guidelines]
*[http://www.chem.unep.ch/mercury/Report/Final%20Assessment%20report.htm Global Mercury Assessment report 2002] by the [[United Nations Environment Programme|UNEP]].
*[http://www.globalmercuryproject.org/ Global Mercury Project]
*[http://www.theodoregray.com/PeriodicTable/Elements/080/index.s7.html Hg 80 Mercury]
*[http://www.foxnews.com/wires/2008Jan25/0,4670,JapanTaintedTuna,00.html Japanese Sushi Lovers Shrug at Mercury]
*[http://www.jtbaker.com/msds/englishhtml/m1599.htm Material Safety Data Sheet — Mercury]
*[http://www.oceana.org/mercury Mercury Contamination in fish and Source Control, Oceana]
*[http://www.intox.org/databank/documents/chemical/mercury/ukpid27.htm Mercury (UK PID)]. National Poisons Information Service: Medical Toxicology Unit (London Centre) - Kolev, S.T. Bates, N.
*[http://www.nrdc.org/health/effects/mercury/index.asp Natural Resources Defense Council (NRDC): Mercury Contamination in Fish guide] — [[NRDC]]
*[http://toxnet.nlm.nih.gov/cgi-bin/sis/search/r?dbs+hsdb:@term+@rn+@rel+7439-97-6 NLM Hazardous Substances Databank — Mercury]
*[http://commons.ucalgary.ca/mercury/ University of Calgary: How Mercury Causes Brain Neuron Degeneration]
*[http://www.webelements.com/webelements/elements/text/Hg/index.html WebElements.com — Mercury]
*[http://www.rsc.org/chemistryworld/podcast/element.asp Chemistry in its element podcast] (MP3) from the [[Royal Society of Chemistry]]'s [[Chemistry World]]: [http://www.rsc.org/images/CIIE_Mercury_48kbps_tcm18-133983.mp3 Mercury]
{{Compact periodic table}}

{{Good article}}

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[[Category:Chemical elements]]
[[Category:Mercury (element)]]
[[Category:Occupational safety and health]]

[[Category:Endocrine disruptors]]
[[Category:Transition metals]]
[[Category:Coolants]]
[[Category:Nuclear reactor coolants]]
[[Category:Neurotoxins]]
[[Category:Native element minerals]]

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