Mercury (element)

This article is about the element. For other uses, seeMercury (disambiguation).

Mercury is a chemical element with symbol Hgand atomic number 80. It is commonly known asquicksilver and was formerly named hydrargyrum(/haɪˈdrɑrdʒərəm/).[3] A heavy, silvery d-block element,mercury is the only metallic element that is liquid atstandard conditions for temperature and pressure; theonly other element that is liquid under these conditionsis bromine, though metals such as caesium, gallium, andrubidium melt just above room temperature.Mercury occurs in deposits throughout the world mostlyas cinnabar (mercuric sulfide). The red pigmentvermilion, a pure form of mercuric sulfide, is mostly ob-tained by reaction of mercury (produced by reductionfrom cinnabar) with sulfur. Mercury poisoning can re-sult from exposure to water-soluble forms of mercury(such as mercuric chloride or methylmercury), inhalationof mercury vapor, or eating seafood contaminated withmercury.Mercury is used in thermometers, barometers,manometers, sphygmomanometers, float valves, mercuryswitches, mercury relays, fluorescent lamps and other de-vices, though concerns about the element’s toxicity haveled to mercury thermometers and sphygmomanometersbeing largely phased out in clinical environments infavour of alternatives such as alcohol- or galinstan-filledglass thermometers and thermistor- or infrared-basedelectronic instruments. Likewise, mechanical pressuregauges and electronic strain gauge sensors have replacedmercury sphygmomanometers. Mercury remains inuse in scientific research applications and in amalgammaterial for dental restoration in some locales. It is usedin lighting: electricity passed through mercury vapor ina fluorescent lamp produces short-wave ultraviolet lightwhich then causes the phosphor in the tube to fluoresce,making visible light.

1 Properties

1.1 Physical properties

Mercury is a heavy, silvery-white metal. As compared toother metals, it is a poor conductor of heat, but a fair con-ductor of electricity.[4] Mercury has a freezing point of−38.83 °C and a boiling point of 356.73 °C,[5][6][7] both

A pound coin (density ~7.6 g/cm3) floats in mercury due to thecombination of the buoyant force and surface tension.

exceptionally low for a metal, and it is the only elementalmetal known to melt at a generally cold temperature. Acomplete explanation of this delves deep into the realmof quantum physics, but it can be summarized as follows:mercury has a unique electron configuration where elec-trons fill up all the available 1s, 2s, 2p, 3s, 3p, 3d, 4s,4p, 4d, 4f, 5s, 5p, 5d, and 6s subshells. Because this con-figuration strongly resists removal of an electron, mercurybehaves similarly to noble gas elements, which formweakbonds and hence melt at relatively low temperatures.The stability of the 6s shell is due to the presence of afilled 4f shell. An f shell poorly screens the nuclear chargethat increases the attractive Coulomb interaction of the6s shell and the nucleus (see lanthanide contraction). Theabsence of a filled inner f shell is the reason for the some-what higher melting temperature of cadmium and zinc,although both these metals still melt easily and, in addi-tion, have unusually low boiling points.On the other hand, gold, which is one space to the left ofmercury on the periodic table, has atoms with one fewer6s electron thanmercury. Those electrons are more easilyremoved and are shared between the gold atoms formingrelatively strong metallic bonds.[6][5]

1.2 Chemical properties

Mercury does not react with most acids, such as dilutesulfuric acid, although oxidizing acids such as concen-trated sulfuric acid and nitric acid or aqua regia dissolveit to give sulfate, nitrate, and chloride salts. Like silver,mercury reacts with atmospheric hydrogen sulfide. Mer-

1

2 2 ETYMOLOGY AND HISTORY

cury even reacts with solid sulfur flakes, which are usedin mercury spill kits to absorb mercury vapors (spill kitsalso use activated carbon and powdered zinc).[8]

1.2.1 Amalgams

Mercury-discharge spectral calibration lamp

Mercury dissolves many other metals such as gold andsilver to form amalgams. Iron is an exception, andiron flasks have been traditionally used to trade mer-cury. Several other first row transition metals with theexception of manganese, copper and zinc are reluctantto form amalgams. Other elements that do not readilyform amalgams with mercury include platinum and a fewother metals.[9][10] Sodium amalgam is a common reduc-ing agent in organic synthesis, and is also used in high-pressure sodium lamps.Mercury readily combines with aluminium to form amercury-aluminium amalgam when the two pure met-als come into contact. Since the amalgam destroys thealuminium oxide layer which protects metallic aluminiumfrom oxidizing in-depth (as in iron rusting), even smallamounts of mercury can seriously corrode aluminium.For this reason, mercury is not allowed aboard an air-craft under most circumstances because of the risk of itforming an amalgamwith exposed aluminium parts in theaircraft.[11]

Mercury embrittlement is the most common type of liq-uid metal embrittlement.

1.3 Isotopes

Main article: Isotopes of mercury

There are seven stable isotopes of mercury with 202Hg being the most abundant (29.86%). The longest-livedradioisotopes are 194Hg with a half-life of 444 years, and 203Hg with a half-life of 46.612 days. Most of the remainingradioisotopes have half-lives that are less than a day. 199Hg and 201Hg are the most often studied NMR-active nuclei, havingspins of 1⁄2 and 3⁄2 respectively.[4]

The symbol for the planet Mercury ( ) has been used since an-cient times to represent the element

2 Etymology and history

Mercury was found in Egyptian tombs that date from1500 BC.[12]

In China and Tibet, mercury use was thought to prolonglife, heal fractures, and maintain generally good health,although it is now known that exposure to mercury va-por leads to serious adverse health effects.[13] The firstemperor of China, Qín Shǐ Huáng Dì—allegedly buriedin a tomb that contained rivers of flowing mercury on amodel of the land he ruled, representative of the riversof China—was killed by drinking a mercury and pow-dered jade mixture formulated by Qin alchemists (caus-ing liver failure, mercury poisoning, and brain death) whointended to give him eternal life.[14][15]

The ancient Greeks used mercury in ointments; theancient Egyptians and the Romans used it in cosmeticswhich sometimes deformed the face. In Lamanai, once amajor city of theMaya civilization, a pool of mercury wasfound under a marker in aMesoamerican ballcourt.[16][17]By 500 BC mercury was used to make amalgams (Me-dieval Latin amalgama, “alloy of mercury”) with othermetals.[18]

Alchemists thought of mercury as the First Matter fromwhich all metals were formed. They believed that dif-ferent metals could be produced by varying the qualityand quantity of sulfur contained within the mercury. Thepurest of these was gold, and mercury was called for inattempts at the transmutation of base (or impure) metalsinto gold, which was the goal of many alchemists.[19]

Hg is the modern chemical symbol for mercury. It comesfrom hydrargyrum, a Latinized form of the Greek wordὑδράργυρος (hydrargyros), which is a compound wordmeaning “water-silver” (from ὑδρ- hydr-, the root of

3

ὕδωρ, “water,” and ἄργυρος argyros “silver”) – since itis liquid like water and shiny like silver. The elementwas named after the Roman god Mercury, known forhis speed and mobility. It is associated with the planetMercury; the astrological symbol for the planet is alsoone of the alchemical symbols for the metal; the Sanskritword for alchemy is Rasavātam which means “the way ofmercury”.[20] Mercury is the only metal for which the al-chemical planetary name became the common name.[19]

The mines in Almadén (Spain), Monte Amiata (Italy),and Idrija (now Slovenia) dominated mercury productionfrom the opening of the mine in Almadén 2500 yearsago, until new deposits were found at the end of the 19thcentury.[21]

3 Occurrence

See also: Category:Mercury minerals and Category:Mercury minesMercury is an extremely rare element in Earth’s crust,

Mercury output in 2005

having an average crustal abundance by mass of only 0.08parts per million (ppm).[22] However, because it doesnot blend geochemically with those elements that con-stitute the majority of the crustal mass, mercury orescan be extraordinarily concentrated considering the ele-ment’s abundance in ordinary rock. The richest mercuryores contain up to 2.5% mercury by mass, and even theleanest concentrated deposits are at least 0.1% mercury(12,000 times average crustal abundance). It is found ei-ther as a native metal (rare) or in cinnabar, corderoite,livingstonite and other minerals, with cinnabar (HgS) be-ing the most common ore.[23] Mercury ores usually occurin very young orogenic belts where rocks of high densityare forced to the crust of Earth, often in hot springs orother volcanic regions.[24]

Beginning in 1558, with the invention of the patio pro-cess to extract silver from ore using mercury, mercury be-came an essential resource in the economy of Spain andits American colonies. Mercury was used to extract silverfrom the lucrative mines in New Spain and Peru. Initially,the Spanish Crown’s mines in Almadén in Southern Spainsupplied all the mercury for the colonies.[25] Mercury de-posits were discovered in the New World, and more than100,000 tons of mercury were mined from the region of

Huancavelica, Peru, over the course of three centuries fol-lowing the discovery of deposits there in 1563. The patioprocess and later pan amalgamation process continued tocreate great demand for mercury to treat silver ores untilthe late 19th century.[26]

Native mercury with cinnabar, Socrates mine, Sonoma County,California. Cinnabar sometimes alters to native mercury in theoxidized zone of mercury deposits.

Former mines in Italy, the United States and Mexico,which once produced a large proportion of the world sup-ply, have now been completely mined out or, in the caseof Slovenia (Idrija) and Spain (Almadén), shut down dueto the fall of the price of mercury. Nevada's McDermittMine, the last mercury mine in the United States, closedin 1992. The price of mercury has been highly volatileover the years and in 2006 was $650 per 76-pound (34.46kg) flask.[27]

Mercury is extracted by heating cinnabar in a current ofair and condensing the vapor. The equation for this ex-traction is

HgS + O2 → Hg + SO2

In 2005, China was the top producer of mercury with al-most two-thirds global share followed by Kyrgyzstan.[28]Several other countries are believed to have unrecordedproduction of mercury from copper electrowinning pro-cesses and by recovery from effluents.Because of the high toxicity of mercury, both the miningof cinnabar and refining for mercury are hazardous andhistoric causes of mercury poisoning.[29] In China, prisonlabor was used by a privatemining company as recently asthe 1950s to create new cinnabar mercury mines. Thou-sands of prisoners were used by the Luo Xi mining com-pany to establish new tunnels.[30] Worker health in func-tioning mines is at high risk.The European Union directive calling for compactfluorescent bulbs to be made mandatory by 2012 has en-couraged China to re-open deadly cinnabar mines to ob-tain the mercury required for CFL bulb manufacture. As

4 4 CHEMISTRY

a result, environmental dangers have been a concern, par-ticularly in the southern cities of Foshan and Guangzhou,and in Guizhou province in the southwest.[30]

Abandoned mercury mine processing sites often containvery hazardous waste piles of roasted cinnabar calcines.Water run-off from such sites is a recognized source ofecological damage. Former mercury mines may be suitedfor constructive re-use. For example, in 1976 SantaClara County, California purchased the historic AlmadenQuicksilver Mine and created a county park on the site,after conducting extensive safety and environmental anal-ysis of the property.[31]

4 Chemistry

See also: Category:Mercury compounds

Mercury exists in two main oxidation states, I and II.Higher oxidation states are rare (e.g., mercury(IV)fluoride, HgF4), but have been detected under extraordinaryconditions.[32]

4.1 Compounds of mercury(I)

Different from its lighter neighbors, cadmium and zinc,mercury usually forms simple stable compounds withmetal-metal bonds. Most mercury(I) compounds arediamagnetic and feature the dimeric cation, Hg2+2. Stable derivatives include the chloride and nitrate.Treatment of Hg(I) compounds complexation with strongligands such as sulfide, cyanide, etc. induces dispropor-tionation to Hg2+and elemental mercury.[33] Mercury(I) chloride, a color-less solid also known as calomel, is really the compoundwith the formula Hg2Cl2, with the connectivity Cl-Hg-Hg-Cl. It is a standard in electrochemistry. It reactswith chlorine to give mercuric chloride, which resists fur-ther oxidation. Mercury(I) hydride, a colorless gas, is thecompound with the formula HgH, containing no Hg-Hgbond.Indicative of its tendency to bond to itself, mercury formsmercury polycations, which consist of linear chains ofmercury centers, capped with a positive charge. One ex-ample is Hg2+3(AsF−6)2.[34]

4.2 Compounds of mercury(II)

Mercury(II) is the most common oxidation state and isthe main one in nature as well. All four mercuric halidesare known. They form tetrahedral complexes with other

ligands but the halides adopt linear coordination geome-try, somewhat like Ag+ does. Best known is mercury(II)chloride, an easily sublimating white solid. HgCl2 formscoordination complexes that are typically tetrahedral, e.g.HgCl2−4.Mercury(II) oxide, the main oxide of mercury, ariseswhen the metal is exposed to air for long periods at ele-vated temperatures. It reverts to the elements upon heat-ing near 400 °C, as was demonstrated by Joseph Priest-ley in an early synthesis of pure oxygen.[8] Hydroxidesof mercury are poorly characterized, as they are for itsneighbors gold and silver.Being a soft metal, mercury forms very stable derivativeswith the heavier chalcogens. Preeminent is mercury(II)sulfide, HgS, which occurs in nature as the ore cinnabarand is the brilliant pigment vermillion. Like ZnS, HgScrystallizes in two forms, the reddish cubic form and theblack zinc blende form.[4] Mercury(II) selenide (HgSe)and mercury(II) telluride (HgTe) are also known, theseas well as various derivatives, e.g. mercury cadmium tel-luride and mercury zinc telluride being semiconductorsuseful as infrared detector materials.[35]

Mercury(II) salts form a variety of complex derivativeswith ammonia. These includeMillon’s base (Hg2N+), theone-dimensional polymer (salts of HgNH+2)n), and “fusible white precipitate” or [Hg(NH3)2]Cl2.Known as Nessler’s reagent, potassium tetraiodomercu-rate(II) (HgI2−4) is still occasionally used to test for ammonia owing toits tendency to form the deeply colored iodide salt of Mil-lon’s base.Mercury fulminate is a detonator widely used inexplosives.[4]

4.3 Higher oxidation states

Oxidation states above +2 in a non-charged speciesare extremely rare, although a cyclic mercurinium(IV)cation, with three substituents, may be an intermediatein oxymercuration reactions.[36][37] In 2007, a report ofsynthesis of a mercury(IV) compound, mercury(IV) flu-oride, was published.[38] In the 1970s, there was a claimon synthesis of a mercury(III) compound, but it is nowthought to be false.[39]

4.4 Organomercury compounds

Main article: Organomercury compound

Organic mercury compounds are historically impor-tant but are of little industrial value in the westernworld. Mercury(II) salts are a rare example of sim-ple metal complexes that react directly with aromatic

5.1 Medicine 5

rings. Organomercury compounds are always divalentand usually two-coordinate and linear geometry. Unlikeorganocadmium and organozinc compounds, organomer-cury compounds do not react with water. They usu-ally have the formula HgR2, which are often volatile, orHgRX, which are often solids, where R is aryl or alkyland X is usually halide or acetate. Methylmercury, ageneric term for compounds with the formula CH3HgX,is a dangerous family of compounds that are often foundin polluted water.[40] They arise by a process known asbiomethylation.

5 Applications

The bulb of a mercury-in-glass thermometer

Mercury is used primarily for the manufacture of indus-trial chemicals or for electrical and electronic applica-tions. It is used in some thermometers, especially oneswhich are used to measure high temperatures. A still in-creasing amount is used as gaseous mercury in fluorescentlamps, while most of the other applications are slowlyphased out due to health and safety regulations and is insome applications replaced with less toxic but consider-ably more expensive Galinstan alloy.[41]

5.1 Medicine

Amalgam filling

See also: Amalgam (dentistry)

Mercury and its compounds have been used in medicine,although they are much less common today than theyonce were, now that the toxic effects of mercury andits compounds are more widely understood. The firstedition of the Merck’s Manual featured many mercuriccompounds[42] such as:

• Mercauro

• Mercuro-iodo-hemol.

• Mercury-ammonium chloride

• Mercury Benzoate

• Mercuric

• Mercury Bichloride (Corrosive Mercuric Chloride,U.S.P.)

• Mercury Chloride

• Mild Mercury Cyanide

• Mercury Succinimide

• Mercury Iodide

• Red Mercury Biniodide

• Mercury Iodide

• Yellow Mercury Proto-iodide

• Black (Hahnemann), Soluble Mercury Oxide

• Red Mercury Oxide

• Yellow Mercury Oxide

• Mercury Salicylate

• Mercury Succinimide

• Mercury Imido-succinate

• Mercury Sulphate

• Basic Mercury Subsulphate; Turpeth Mineral

• Mercury Tannate

• Mercury-Ammonium Chloride

The element mercury is an ingredient in dental amalgams.Thiomersal (called Thimerosal in the United States) isan organic compound used as a preservative in vaccines,though this use is in decline.[43] Thiomersal is metabo-lized to ethyl mercury. Although it was widely speculatedthat this mercury-based preservative could cause or trig-ger autism in children, scientific studies showed no evi-dence supporting any such link.[44] Nevertheless, thiom-ersal has been removed from, or reduced to trace amounts

6 5 APPLICATIONS

in all U.S. vaccines recommended for children 6 years ofage and under, with the exception of inactivated influenzavaccine.[45]

Another mercury compound, merbromin (Mer-curochrome), is a topical antiseptic used for minor cutsand scrapes is still in use in some countries.Mercury in the form of one of its common ores, cinnabar,is used in various traditional medicines, especially intraditional Chinese medicine. Review of its safety hasfound that cinnabar can lead to significant mercury in-toxication when heated, consumed in overdose, or takenlong term, and can have adverse effects at therapeuticdoses, though effects from therapeutic doses are typicallyreversible. Although this form of mercury appears to beless toxic than other forms, its use in traditional Chinesemedicine has not yet been justified, as the therapeutic ba-sis for the use of cinnabar is not clear.[46]

Today, the use of mercury in medicine has greatly de-clined in all respects, especially in developed countries.Thermometers and sphygmomanometers containingmer-cury were invented in the early 18th and late 19th cen-turies, respectively. In the early 21st century, their use isdeclining and has been banned in some countries, statesand medical institutions. In 2002, the U.S. Senate passedlegislation to phase out the sale of non-prescription mer-cury thermometers. In 2003, Washington and Mainebecame the first states to ban mercury blood pressuredevices.[47] Mercury compounds are found in some over-the-counter drugs, including topical antiseptics, stimu-lant laxatives, diaper-rash ointment, eye drops, and nasalsprays. The FDA has “inadequate data to establish gen-eral recognition of the safety and effectiveness” of themercury ingredients in these products.[48] Mercury is stillused in some diuretics although substitutes now exist formost therapeutic uses.

5.2 Production of chlorine and causticsoda

Chlorine is produced from sodium chloride (commonsalt, NaCl) using electrolysis to separate the metallicsodium from the chlorine gas. Usually the salt is dissolvedin water to produce a brine. By-products of any suchchloralkali process are hydrogen (H2) and sodium hy-droxide (NaOH), which is commonly called caustic sodaor lye. By far the largest use of mercury[49][50] in the late20th century was in the mercury cell process (also calledthe Castner-Kellner process) where metallic sodium isformed as an amalgam at a cathode made from mercury;this sodium is then reacted with water to produce sodiumhydroxide.[51] Many of the industrial mercury releases ofthe 20th century came from this process, although mod-ern plants claimed to be safe in this regard.[50] After about1985, all new chloralkali production facilities that werebuilt in the United States used either membrane cell ordiaphragm cell technologies to produce chlorine.

5.3 Laboratory uses

Some medical thermometers, especially those for hightemperatures, are filled with mercury; however, theyare gradually disappearing. In the United States, non-prescription sale of mercury fever thermometers has beenbanned since 2003.[52]

Mercury is also found in liquid mirror telescopes.Some transit telescopes use a basin of mercury to form aflat and absolutely horizontal mirror, useful in determin-ing an absolute vertical or perpendicular reference. Con-cave horizontal parabolic mirrors may be formed by ro-tating liquid mercury on a disk, the parabolic form of theliquid thus formed reflecting and focusing incident light.Such telescopes are cheaper than conventional large mir-ror telescopes by up to a factor of 100, but the mirrorcannot be tilted and always points straight up.[53][54][55]

Liquid mercury is a part of popular secondary ref-erence electrode (called the calomel electrode) inelectrochemistry as an alternative to the standard hydro-gen electrode. The calomel electrode is used to work outthe electrode potential of half cells.[56] Last, but not least,the triple point of mercury, −38.8344 °C, is a fixed pointused as a temperature standard for the International Tem-perature Scale (ITS-90).[4]

In polarography both the dropping mercury electrode[57]and the hanging mercury drop electrode [58] use ele-mental mercury. This use allows a new uncontaminatedelectrode to be available for each measurement or eachnew experiment.

5.4 Niche uses

Gaseous mercury is used in mercury-vapor lamps andsome "neon sign" type advertising signs and fluorescentlamps. Those low-pressure lamps emit very spectrallynarrow lines, which are traditionally used in optical spec-troscopy for calibration of spectral position. Commercialcalibration lamps are sold for this purpose; however sim-ply reflecting some of the fluorescent-lamp ceiling lightinto a spectrometer is a common calibration practice.[59]Gaseous mercury is also found in some electron tubes,including ignitrons, thyratrons, and mercury arc recti-fiers.[60] It is also used in specialist medical care lamps forskin tanning and disinfection (see pictures).[61] Gaseousmercury is added to cold cathode argon-filled lamps toincrease the ionization and electrical conductivity. An ar-gon filled lamp without mercury will have dull spots andwill fail to light correctly. Lighting containing mercurycan be bombarded/oven pumped only once. When addedto neon filled tubes the light produced will be inconsistentred/blue spots until the initial burning-in process is com-pleted; eventually it will light a consistent dull off-bluecolor.[62]

• The deep violet glow of a mercury vapor discharge

5.5 Historic uses 7

in a germicidal lamp, whose spectrum is rich in in-visible ultraviolet radiation.

• Skin tanner containing a low-pressure mercury va-por lamp and two infrared lamps, which act both aslight source and electrical ballast

• Assorted types of fluorescent lamps.

5.4.1 Cosmetics

Mercury, as thiomersal, is widely used in the manufactureof mascara. In 2008, Minnesota became the first state inthe United States to ban intentionally added mercury incosmetics, giving it a tougher standard than the federalgovernment.[63]

A study in geometric mean urine mercury concentra-tion identified a previously unrecognized source of ex-posure (skin care products) to inorganic mercury amongNew York City residents. Population-based biomonitor-ing also showed that mercury concentration levels arehigher in consumers of seafood and fish meals.[64]

5.5 Historic uses

A Single-Pole, Single-Throw (SPST) mercury switch.

Many historic applications made use of the peculiar phys-ical properties of mercury, especially as a dense liquidand a liquid metal:

• Quantities of liquid mercury ranging from 90 to 600grams (3.2 to 21.2 oz) have been recovered fromelite Maya tombs or ritual caches at six sites. Thismercury may have been used in bowls as mirrors fordivinatory purposes. Five of these date to the Clas-sic Period ofMaya civilization (c. 250–900) but oneexample predated this.[65]

• In Islamic Spain, it was used for filling decorativepools. Later, the American artist Alexander Calderbuilt a mercury fountain for the Spanish Pavilionat the 1937 World Exhibition in Paris. The foun-tain is now on display at the Fundació Joan Miró inBarcelona.[66]

Mercury manometer to measure pressure

• Mercury was used inside wobbler lures. Its heavy,liquid form made it useful since the lures madean attractive irregular movement when the mercurymoved inside the plug. Such use was stopped due toenvironmental concerns, but illegal preparation ofmodern fishing plugs has occurred.

• The Fresnel lenses of old lighthouses used to floatand rotate in a bath of mercury which acted like abearing.[67]

• Mercury sphygmomanometers (blood pressure me-ter), barometers, diffusion pumps, coulometers, andmany other laboratory instruments. As an opaqueliquid with a high density and a nearly linear ther-mal expansion, it is ideal for this role.[68]

• As an electrically conductive liquid, it was usedin mercury switches (including home mercury lightswitches installed prior to 1970), tilt switches usedin old fire detectors, and tilt switches in some homethermostats.[69]

• Owing to its acoustic properties, mercury was usedas the propagationmedium in delay line memory de-vices used in early digital computers of themid-20thcentury.

• Experimental mercury vapor turbines were installedto increase the efficiency of fossil-fuel electricalpower plants.[70] The South Meadow power plantin Hartford, CT employed mercury as its working

8 5 APPLICATIONS

fluid, in a binary configuration with a secondary wa-ter circuit, for a number of years starting in the late1920s in a drive to improve plant efficiency. Severalother plants were built, including the Schiller Sta-tion in Portsmouth, NH, which went online in 1950.The idea did not catch on industry-wide due to theweight and toxicity of mercury, as well as the adventof supercritical steam plants in later years.[71][72]

• Similarly, liquid mercury was used as a coolant forsome nuclear reactors; however, sodium is proposedfor reactors cooled with liquid metal, because thehigh density of mercury requires much more energyto circulate as coolant.[73]

• Mercury was a propellant for early ion engines inelectric space propulsion systems. Advantages weremercury’s high molecular weight, low ionization en-ergy, low dual-ionization energy, high liquid den-sity and liquid storability at room temperature. Dis-advantages were concerns regarding environmen-tal impact associated with ground testing and con-cerns about eventual cooling and condensation ofsome of the propellant on the spacecraft in long-duration operations. The first spaceflight to use elec-tric propulsion was amercury-fueled ion thruster de-veloped by NASA Lewis and flown on the SpaceElectric Rocket Test "SERT-1" spacecraft launchedby NASA at its Wallops Flight Facility in 1964. TheSERT-1 flight was followed up by the SERT-2 flightin 1970. Mercury and caesium were preferred pro-pellants for ion engines until Hughes Research Lab-oratory performed studies finding xenon gas to bea suitable replacement. Xenon is now the preferredpropellant for ion engines as it has a high molecularweight, little or no reactivity due to its noble gas na-ture, and has a high liquid density under mild cryo-genic storage.[74][75]

Others applications made use of the chemical propertiesof mercury:

• The mercury battery is a non-rechargeableelectrochemical battery, a primary cell, that wascommon throughout the middle of the 20th century.It was used in a wide variety of applications and wasavailable in various sizes, particularly button sizes.Its constant voltage output and long shelf life gaveit a niche use for camera light meters and hearingaids. The mercury cell was effectively banned inmost countries in the 1990s due to concerns aboutthe mercury contaminating landfills.[76]

• Mercury was used for preserving wood, develop-ing daguerreotypes, silvering mirrors, anti-foulingpaints (discontinued in 1990), herbicides (discon-tinued in 1995), handheld maze games, cleaning,and road leveling devices in cars. Mercury com-pounds have been used in antiseptics, laxatives,antidepressants, and in antisyphilitics.

• It was allegedly used by allied spies to sabotage Luft-waffe planes: a mercury paste was applied to barealuminium, causing the metal to rapidly corrode;this would cause structural failures.[77]

• Chloralkali process: The largest industrial use ofmercury during the 20th century was in electroly-sis for separating chlorine and sodium from brine;mercury being the anode of the Castner-Kellner pro-cess. The chlorine was used for bleaching paper(hence the location of many of these plants nearpaper mills) while the sodium was used to makesodium hydroxide for soaps and other cleaning prod-ucts. This usage has largely been discontinued, re-placed with other technologies that utilize mem-brane cells.[78]

• As electrodes in some types of electrolysis, batteries(mercury cells), sodium hydroxide and chlorine pro-duction, handheld games, catalysts, insecticides.

• Mercury was once used as a gun barrel borecleaner.[79][80]

• From the mid-18th to the mid-19th centuries, aprocess called "carroting" was used in the makingof felt hats. Animal skins were rinsed in an or-ange solution (the term “carroting” arose from thiscolor) of the mercury compound mercuric nitrate,Hg(NO3)2·2H2O.[81] This process separated the furfrom the pelt and matted it together. This solutionand the vapors it produced were highly toxic. TheUnited States Public Health Service banned the useof mercury in the felt industry in December 1941.The psychological symptoms associated with mer-cury poisoning inspired the phrase "mad as a hatter".Lewis Carroll's "Mad Hatter" in his bookAlice’s Ad-ventures in Wonderland was a play on words basedon the older phrase, but the character himself doesnot exhibit symptoms of mercury poisoning.[82]

• Gold and silver mining. Historically, mercury wasused extensively in hydraulic gold mining in or-der to help the gold to sink through the flowingwater-gravel mixture. Thin gold particles may formmercury-gold amalgam and therefore increase thegold recovery rates.[4] Large-scale use of mercurystopped in the 1960s. However, mercury is stillused in small scale, often clandestine, gold prospect-ing. It is estimated that 45,000 metric tons of mer-cury used in California for placer mining have notbeen recovered.[83] Mercury was also used in silvermining.[84]

5.5.1 Historic medicinal uses

Mercury(I) chloride (also known as calomel or mer-curous chloride) has been used in traditional medicine asa diuretic, topical disinfectant, and laxative. Mercury(II)

6.1 Releases in the environment 9

chloride (also known as mercuric chloride or corrosivesublimate) was once used to treat syphilis (along withother mercury compounds), although it is so toxic thatsometimes the symptoms of its toxicity were confusedwith those of the syphilis it was believed to treat.[85]It is also used as a disinfectant. Blue mass, a pill orsyrup in which mercury is the main ingredient, was pre-scribed throughout the 19th century for numerous con-ditions including constipation, depression, child-bearingand toothaches.[86] In the early 20th century, mercurywas administered to children yearly as a laxative and de-wormer, and it was used in teething powders for infants.The mercury-containing organohalide merbromin (some-times sold as Mercurochrome) is still widely used but hasbeen banned in some countries such as the U.S.[87]

6 Toxicity and safety

See also: Mercury poisoning and Mercury cycle

Mercury and most of its compounds are extremely toxicand must be handled with care; in cases of spills in-volving mercury (such as from certain thermometers orfluorescent light bulbs), specific cleaning procedures areused to avoid exposure and contain the spill.[88] Proto-cols call for physically merging smaller droplets on hardsurfaces, combining them into a single larger pool for eas-ier removal with an eyedropper, or for gently pushing thespill into a disposable container. Vacuum cleaners andbrooms cause greater dispersal of the mercury and shouldnot be used. Afterwards, fine sulfur, zinc, or some otherpowder that readily forms an amalgam (alloy) with mer-cury at ordinary temperatures is sprinkled over the areabefore itself being collected and properly disposed of.Cleaning porous surfaces and clothing is not effective atremoving all traces of mercury and it is therefore advisedto discard these kinds of items should they be exposed toa mercury spill.Mercury can be absorbed through the skin and mucousmembranes and mercury vapors can be inhaled, so con-tainers of mercury are securely sealed to avoid spills andevaporation. Heating of mercury, or of compounds ofmercury that may decompose when heated, is always car-ried out with adequate ventilation in order to avoid ex-posure to mercury vapor. The most toxic forms of mer-cury are its organic compounds, such as dimethylmercuryand methylmercury. Mercury can cause both chronic andacute poisoning.

6.1 Releases in the environment

Preindustrial deposition rates of mercury from the atmo-sphere may be about 4 ng /(1 L of ice deposit). Althoughthat can be considered a natural level of exposure, re-gional or global sources have significant effects. Vol-

1998 core 1991 core

Amount of atmospheric mercury deposited at Wyoming’s UpperFremont Glacier over the last 270 years

canic eruptions can increase the atmospheric source by4–6 times.[89]

Natural sources, such as volcanoes, are responsible for ap-proximately half of atmospheric mercury emissions. Thehuman-generated half can be divided into the followingestimated percentages:[90][91][92]

• 65% from stationary combustion, of which coal-fired power plants are the largest aggregate source(40% of U.S. mercury emissions in 1999). This in-cludes power plants fueled with gas where the mer-cury has not been removed. Emissions from coalcombustion are between one and two orders of mag-nitude higher than emissions from oil combustion,depending on the country.[90]

• 11% from gold production. The three largest pointsources for mercury emissions in the U.S. are thethree largest gold mines. Hydrogeochemical releaseof mercury from gold-mine tailings has been ac-counted as a significant source of atmospheric mer-cury in eastern Canada.[93]

• 6.8% from non-ferrous metal production, typicallysmelters.

• 6.4% from cement production.• 3.0% from waste disposal, including municipal andhazardous waste, crematoria, and sewage sludge in-cineration.

10 6 TOXICITY AND SAFETY

• 3.0% from caustic soda production.

• 1.4% from pig iron and steel production.

• 1.1% frommercury production, mainly for batteries.

• 2.0% from other sources.

The above percentages are estimates of the global human-caused mercury emissions in 2000, excluding biomassburning, an important source in some regions.[90]

Recent atmospheric mercury contamination in outdoorurban air was measured at 0.01–0.02 µg/m3. A 2001study measured mercury levels in 12 indoor sites chosento represent a cross-section of building types, locationsand ages in the New York area. This study found mer-cury concentrations significantly elevated over outdoorconcentrations, at a range of 0.0065 – 0.523 μg/m3. Theaverage was 0.069 μg/m3.[94]

Mercury also enters into the environment through the im-proper disposal (e.g., land filling, incineration) of cer-tain products. Products containing mercury include: autoparts, batteries, fluorescent bulbs, medical products, ther-mometers, and thermostats.[95] Due to health concerns(see below), toxics use reduction efforts are cutting backor eliminating mercury in such products. For example,the amount of mercury sold in thermostats in the UnitedStates decreased from 14.5 tons in 2004 to 3.9 tons in2007.[96]

Most thermometers now use pigmented alcohol insteadof mercury, and galinstan alloy thermometers are also anoption. Mercury thermometers are still occasionally usedin the medical field because they are more accurate thanalcohol thermometers, though both are commonly beingreplaced by electronic thermometers and less commonlyby galinstan thermometers. Mercury thermometers arestill widely used for certain scientific applications becauseof their greater accuracy and working range.Historically, one of the largest releases was from theColex plant, a lithium-isotope separation plant at OakRidge, Tennessee. The plant operated in the 1950s and1960s. Records are incomplete and unclear, but govern-ment commissions have estimated that some two millionpounds of mercury are unaccounted for.[97]

A serious industrial disaster was the dumping of mercurycompounds into Minamata Bay, Japan. It is estimatedthat over 3,000 people suffered various deformities, se-veremercury poisoning symptoms or death fromwhat be-came known as Minamata disease.[98][99]

6.2 Occupational exposure

Due to the health effects of mercury exposure, industrialand commercial uses are regulated in many countries.The World Health Organization, OSHA, and NIOSH all

treat mercury as an occupational hazard, and have es-tablished specific occupational exposure limits. Environ-mental releases and disposal of mercury are regulated inthe U.S. primarily by the United States EnvironmentalProtection Agency.Case control studies have shown effects such as tremors,impaired cognitive skills, and sleep disturbance in work-ers with chronic exposure to mercury vapor even at lowconcentrations in the range 0.7–42 μg/m3.[100][101] Astudy has shown that acute exposure (4 – 8 hours) to cal-culated elemental mercury levels of 1.1 to 44 mg/m3 re-sulted in chest pain, dyspnea, cough, hemoptysis, impair-ment of pulmonary function, and evidence of interstitialpneumonitis.[102] Acute exposure to mercury vapor hasbeen shown to result in profound central nervous systemeffects, including psychotic reactions characterized bydelirium, hallucinations, and suicidal tendency. Occupa-tional exposure has resulted in broad-ranging functionaldisturbance, including erethism, irritability, excitability,excessive shyness, and insomnia. With continuing expo-sure, a fine tremor develops and may escalate to violentmuscular spasms. Tremor initially involves the hands andlater spreads to the eyelids, lips, and tongue. Long-term,low-level exposure has been associated with more subtlesymptoms of erethism, including fatigue, irritability, lossof memory, vivid dreams and depression.[103][104]

6.3 Treatment

Research on the treatment of mercury poisoning is lim-ited. Currently available drugs for acute mercurialpoisoning include chelators N-acetyl-D, L-penicillamine(NAP), British Anti-Lewisite (BAL), 2,3-dimercapto-1-propanesulfonic acid (DMPS), and dimercaptosuccinicacid (DMSA). In one small study including 11 construc-tion workers exposed to elemental mercury, patients weretreated withDMSA andNAP.[105] Chelation therapy withboth drugs resulted in the mobilization of a small fractionof the total estimated body mercury. DMSA was able toincrease the excretion of mercury to a greater extent thanNAP.[106]

6.4 Fish

Main article: Mercury in fish

Fish and shellfish have a natural tendency to concen-trate mercury in their bodies, often in the form ofmethylmercury, a highly toxic organic compound ofmercury. Species of fish that are high on the foodchain, such as shark, swordfish, king mackerel, bluefintuna, albacore tuna, and tilefish contain higher con-centrations of mercury than others. As mercury andmethylmercury are fat soluble, they primarily accumu-late in the viscera, although they are also found through-out the muscle tissue.[107] When this fish is consumed

7.3 European Union 11

by a predator, the mercury level is accumulated. Sincefish are less efficient at depurating than accumulatingmethylmercury, fish-tissue concentrations increase overtime. Thus species that are high on the food chain amassbody burdens of mercury that can be ten times higherthan the species they consume. This process is calledbiomagnification. Mercury poisoning happened this wayin Minamata, Japan, now called Minamata disease.

7 Regulations

7.1 International

140 countries agreed in the Minamata Convention onMercury by the United Nations Environment Program(UNEP) to prevent emissions. [108] Convention is ex-pected to be open for signature in October 2013.[109]

7.2 United States

In the United States, the Environmental ProtectionAgency is charged with regulating and managing mercurycontamination. Several laws give the EPA this author-ity, including the Clean Air Act, the Clean Water Act,the Resource Conservation and Recovery Act, and theSafe Drinking Water Act. Additionally, the Mercury-Containing and Rechargeable Battery Management Act,passed in 1996, phases out the use ofmercury in batteries,and provides for the efficient and cost-effective disposalof many types of used batteries.[110] North America con-tributed approximately 11% of the total global anthro-pogenic mercury emissions in 1995.[111]

The United States Clean Air Act, passed in 1990, putmercury on a list of toxic pollutants that need to be con-trolled to the greatest possible extent. Thus, industriesthat release high concentrations of mercury into the en-vironment agreed to install maximum achievable con-trol technologies (MACT). In March 2005, the EPA pro-mulgated a regulation[112] that added power plants to thelist of sources that should be controlled and instituteda national cap and trade system. States were given un-til November 2006 to impose stricter controls, but af-ter a legal challenge from several states, the regulationswere struck down by a federal appeals court on 8 Febru-ary 2008. The rule was deemed not sufficient to protectthe health of persons living near coal-fired power plants,given the negative effects documented in the EPA StudyReport to Congress of 1998.[113]

The EPA announced new rules for coal-fired power plantson 22 December 2011.[114] Cement kilns that burn haz-ardous waste are held to a looser standard than are stan-dard hazardous waste incinerators in the United States,and as a result are a disproportionate source of mercurypollution.[115]

7.3 European Union

In the European Union, the directive on the Restrictionof the Use of Certain Hazardous Substances in Electri-cal and Electronic Equipment (see RoHS) bans mercuryfrom certain electrical and electronic products, and lim-its the amount of mercury in other products to less than1000 ppm.[116] There are restrictions for mercury con-centration in packaging (the limit is 100 ppm for sumof mercury, lead, hexavalent chromium and cadmium)and batteries (the limit is 5 ppm).[117] In July 2007, theEuropean Union also banned mercury in non-electricalmeasuring devices, such as thermometers and barome-ters. The ban applies to new devices only, and containsexemptions for the health care sector and a two-year graceperiod for manufacturers of barometers. [118]

7.4 Norway

Norway enacted a total ban on the use of mercury inthe manufacturing and import/export of mercury prod-ucts, effective 1 January 2008.[119] In 2002, several lakesin Norway were found to have a poor state of mer-cury pollution, with an excess of 1 µg/g of mercury intheir sediment.[120] In 2008, Norway’s Minister of En-vironment Development Erik Solheim said: “Mercury isamong the most dangerous environmental toxins. Satis-factory alternatives to Hg in products are available, and itis therefore fitting to induce a ban.” [121]

7.5 Sweden

Products containing mercury were banned in Sweden in2009.[122][123]

7.6 Denmark

In 2008, Denmark also banned dental mercuryamalgam,[121] except for molar masticating surfacefillings in permanent (adult) teeth.

8 See also

• Mercury poisoning

• Minamata disease

• Methylmercury

• Red mercury

• Amalgam (dentistry)

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[107] Cocoros, G.; Cahn, P. H.; Siler, W. (1973). “Mercuryconcentrations in fish, plankton and water from threeWestern Atlantic estuaries”. Journal of Fish Biology 5 (6):641–647. doi:10.1111/j.1095-8649.1973.tb04500.x.

[108] “Minamata Convention Agreed by Nations”. United Na-tions Environment Program. Retrieved 19 January 2013.

[109] http://www.un.org/apps/news/story.asp?NewsID=43963&Cr=mercury&Cr1=#.UPt4ikfdP5M

[110] “Mercury: Laws and regulations”. United States Environ-mental Protection Agency. 16 April 2008. Retrieved 30May 2008.

[111] “Reductions in Mercury Emissons”. International JointCommission on the Great Lakes.

[112] “Clean Air Mercury Rule”. United States EnvironmentalProtection Agency (EPA). Retrieved 1 May 2007.

[113] “State of New Jersey et al., Petitioners vs. EnvironmentalProtection Agency (Case No. 05-1097)". United StatesCourt of Appeals for the District of Columbia Circuit. Ar-gued 6 December 2007, Decided 8 February 2008. Re-trieved 30 May 2008.

[114] “Oldest, dirtiest power plants told to clean up”. BostonGlobe. 22 December 2011. Retrieved 2 January 2012.

[115] Howard Berkes (10 November 2011). “EPA RegulationsGiveKilns Permission To Pollute”. NPR. Retrieved 2 Jan-uary 2012.

[116] “Directive 2002/95/EC on the Restriction of the Use ofCertain Hazardous Substances in Electrical and ElectronicEquipment”. 27 January 2003. Article 4 Paragraph 1.e.g. “Member States shall ensure that, from July 1, 2006,new electrical and electronic equipment put on the mar-ket does not contain lead, mercury, cadmium, hexava-lent chromium, polybrominated biphenyls (PBB) or poly-brominated diphenyl ethers (PBDE).”

[117] “Mercury compounds in European Union:". EIA Track.2007. Retrieved 30 May 2008.

[118] Jones H. (10 July 2007). “EU bans mercury in barome-ters, thermometers”. Reuters. Retrieved 30 May 2008.

[119] “Norway to ban mercury”. EU Business. 21 December2007. Archived from the original on 21 January 2008.Retrieved 30 May 2008.

[120] Berg, T; Fjeld, E; Steinnes, E (2006). “Atmospheric mer-cury in Norway: contributions from different sources”.The Science of the total environment 368 (1): 3–9.doi:10.1016/j.scitotenv.2005.09.059. PMID 16310836.

[121] Edlich, Richard F.; Rhoads, Samantha K.; Cantrell,Holly S.; Azavedo, Sabrina M. and Newkirk, Anthony T.Banning Mercury Amalgam. US FDA

[122] Sweden to ban mercury – The Local. Thelocal.se (14 Jan-uary 2009). Retrieved on 30 December 2012.

[123] Sweden may be forced to lift ban on mercury – The Local.Thelocal.se (21 April 2012). Retrieved on 30 December2012.

10 Further reading• Andrew Scott Johnston, Mercury and the Makingof California: Mining, Landscape, and Race, 1840-1890. Boulder, CO: University Press of Colorado,2013.

11 External links• Chemistry in its element podcast (MP3) from theRoyal Society of Chemistry's Chemistry World:Mercury

• Mercury at The Periodic Table of Videos (Universityof Nottingham)

• ATSDR – ToxFAQs: Mercury

• Centers for Disease Control and Prevention – Mer-cury Topic

16 11 EXTERNAL LINKS

• EPA fish consumption guidelines

• Global Mercury Assessment report 2002 by theUNEP.

• Global Mercury Project

• Hg 80 Mercury

• Material Safety Data Sheet – Mercury

• Mercury Contamination in fish and Source Control,Oceana

• Natural Resources Defense Council (NRDC): Mer-cury Contamination in Fish guide – NRDC

• NLM Hazardous Substances Databank – Mercury

• BBC – Earth News – Mercury 'turns’ wetland birdssuch as ibises homosexual

• Changing Patterns in the Use, Recycling, and Ma-terial Substitution of Mercury in the United StatesUnited States Geological Survey

• Thermodynamical data on liquid mercury.

17

12 Text and image sources, contributors, and licenses

12.1 Text• Mercury (element) Source: http://en.wikipedia.org/wiki/Mercury%20(element)?oldid=649537145 Contributors: Lee Daniel Crocker,

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18 12 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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