An old[12]pound coin (density ~7.6 g/cm3) floats on mercury due to thebuoyancy force upon it and appears to float higher because of the strongsurface tension of the mercury.
Mercury is a heavy, silvery-white metal that is liquid at room temperature. Compared to other metals, it is a poor conductor of heat, but a fair conductor of electricity.[13]
It has amelting point of −38.83 °C[c] and aboiling point of 356.73 °C,[d][14][15][16] both the lowest of any stable metal, although preliminary experiments oncopernicium andflerovium have indicated that they have even lower boiling points.[17] This effect is due tolanthanide contraction andrelativistic contraction reducing the orbit radius of the outermost electrons, and thus weakening the metallic bonding in mercury.[14] Upon freezing, the volume of mercury decreases by 3.59% and its density changes from 13.69 g/cm3 when liquid to 14.184 g/cm3 when solid. The coefficient of volume expansion is 181.59 × 10−6 at 0 °C, 181.71 × 10−6 at 20 °C and 182.50 × 10−6 at 100 °C (per °C). Solid mercury is malleable and ductile, and can be cut with a knife.[18]
Table of thermal and physical properties of liquid mercury:[19][20]
Mercury dissolves many metals such asgold andsilver to formamalgams.Iron is an exception, and iron flasks have traditionally been used to transport the material.[22] Several other first row transition metals with the exception ofmanganese,copper andzinc are also resistant in forming amalgams. Other elements that do not readily form amalgams with mercury includeplatinum.[23][24]Sodium amalgam is a common reducing agent inorganic synthesis, and is also used inhigh-pressure sodium lamps.
Mercury readily combines withaluminium to form amercury-aluminium amalgam when the two pure metals come into contact.[citation needed] Since the amalgam destroys thealuminium oxide layer which protects metallic aluminium from oxidizing in-depth (as in ironrusting), even small amounts of mercury can seriously corrode aluminium. For this reason, 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.[25]
Mercury embrittlement is the most common type of liquid metal embrittlement, as mercury is a natural component of somehydrocarbon reservoirs and will come into contact with petroleum processing equipment under normal conditions.[26]
There are seven stableisotopes of mercury, with202 Hg being the most abundant (29.86%). The longest-livedradioisotopes are194 Hg with ahalf-life of 444 years, and203 Hg with a half-life of 46.612 days. Most of the remaining radioisotopes have half-lives that are less than a day.206 Hg occurs naturally in tiny traces as an intermediate decay product of238 U.199 Hg and201 Hg are the most often studiedNMR-active nuclei, having spins of1⁄2 and3⁄2 respectively.[13]
Etymology
The symbol forthe planet Mercury (☿) has been used since ancient times to represent the element
Hg is the modernchemical symbol for mercury.[27] It is an abbreviation ofhydrargyrum, aromanized form of theancient Greek name for mercury,ὑδράργυρος (hydrargyros).Hydrargyros is a Greek compound word meaning'water-silver', fromὑδρ- (hydr-), the root ofὕδωρ (hydor)'water', andἄργυρος (argyros)'silver'.[9] Like the English namequicksilver ('living-silver'), this name was due to mercury's liquid and shiny properties.[28]
The modern English namemercury comes from the planetMercury. In medievalalchemy, the seven known metals—quicksilver,gold,silver,copper,iron,lead, andtin—were associated with the seven planets. Quicksilver was associated with the fastest planet, which had been named after the Roman godMercury, who was associated with speed and mobility. The astrological symbol for the planet became one of thealchemical symbols for the metal, andMercury became an alternative name for the metal. Mercury is the only metal for which the alchemical planetary name survives, as it was decided it was preferable toquicksilver as a chemical name.[29][30]
History
Mercury was found inEgyptian tombs that date from 1500 BC;[31]cinnabar, the most common natural source of mercury, has been in use since theNeolithic Age.[32]
InChina andTibet, mercury use was thought to prolong life, heal fractures, and maintain generally good health, although it is now known that exposure to mercury vapor leads to serious adverse health effects.[33] The first emperor of a unified China,Qín Shǐ Huáng Dì—allegedly buried in atomb that contained rivers of flowing mercury on a model of the land he ruled, representative of the rivers of China—was reportedly killed by drinking a mercury and powderedjade mixture formulated byQin alchemists intended as an elixir of immortality.[34][35]Khumarawayh ibn Ahmad ibn Tulun, the secondTulunid ruler of Egypt (r. 884–896), known for his extravagance andprofligacy, reportedly built a basin filled with mercury, on which he would lie on top of air-filled cushions and be rocked to sleep.[36]
In November 2014 "large quantities" of mercury were discovered in a chamber 60 feet below the 1800-year-old pyramid known as theTemple of the Feathered Serpent, the third-largest pyramid ofTeotihuacan, Mexico, along with "jade statues, jaguar remains, a box filled with carved shells and rubber balls".[37] InLamanai, once a major city of theMaya civilization, a pool of mercury was found under a marker in aMesoamerican ballcourt.[38][39]
Alchemists thought of mercury as theFirst Matter from which all metals were formed. They believed that differentmetals could be produced by varying the quality and quantity ofsulfur contained within the mercury. The purest of these was gold, and mercury was called for in attempts at thetransmutation of base (or impure) metals into gold, which was the goal of many alchemists.[29]
The mines inAlmadén (Spain),Monte Amiata (Italy), andIdrija (now Slovenia) dominated 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.[42]
The location of major 18th century Spanish silver mine districs (crossedpickaxes) and the mines involved in mercury supply needed for silver mining (purple dots).
Beginning in 1558, with the invention of thepatio process to extractsilver fromore 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 inNew Spain andPeru. Initially, the Spanish Crown's mines in Almadén in Southern Spain supplied all the mercury for the colonies.[43] Mercury deposits were discovered in the New World, and more than 100,000 tons of mercury were mined from the region ofHuancavelica, Peru, over the course of three centuries following the discovery of deposits there in 1563.[44] In 1786 the main mine at Huancavelica suffered a sudden collapse that killed over 100 persons and greatly reduced the mine's output.[45] Through the legalization of scavanging known aspallaqueo mercury production rose again peaking in 1794–1796.[46] TheFrench Revolutionary Wars disrupted European mercury supply toSpanish America leading to an increasing reliance for the mines in present-day Peru and Bolivia on mercury from Huancavelica but this mines production was clearly by 1799 not enough to supply the demand in the Andean mines.[46] Spain abolished the royal mercury monopoly in 1813.[46]
Mercury is an extremely rare element in Earth'scrust; it has an average crustal abundance by mass of only 0.08 parts per million (ppm)[48] and is the 66th most abundant element in the Earth's crust.[49] Because it does not blendgeochemically 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 anative metal (rare) or incinnabar,metacinnabar,sphalerite,corderoite,livingstonite and otherminerals, with cinnabar (HgS) being the most common ore.[50][51] Mercury ores often occur inhot springs or othervolcanic regions.[52]
Native mercury withcinnabar, Socrates mine,Sonoma County, California. Cinnabar sometimes alters to native mercury in the oxidized zone of mercury deposits.
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'sMcDermitt 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 kg)flask.[53]
Mercury is extracted by heating cinnabar in a current of air and condensing the vapor. The equation for this extraction is:
Evolution of mercury price (U.S.) and production (worldwide)
In 2020, China was the top producer of mercury, providing 88% of the world output (2200 out of 2500 tonnes), followed byTajikistan (178 t), Russia (50 t) and Mexico (32 t).[54]
Because of the high toxicity of mercury, both the mining of cinnabar and refining for mercury are hazardous and historic causes of mercury poisoning.[55] In China, prison labor was used by a private mining company as recently as the 1950s to develop new cinnabar mines. Thousands of prisoners were used by the Luo Xi mining company to establish new tunnels.[56] Worker health in functioning mines is at high risk.
A newspaper claimed that an unidentifiedEuropean Union directive calling for energy-efficient lightbulbs to be made mandatory by 2012 encouraged China to re-open cinnabar mines to obtain the mercury required forCFL bulb manufacture. Environmental dangers have been a concern, particularly in the southern cities ofFoshan andGuangzhou, and inGuizhou province in the southwest.[56]
Abandoned mercury mine processing sites often contain very hazardous waste piles of roasted cinnabarcalcines. 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 1976Santa Clara County, California purchased the historicAlmaden Quicksilver Mine and created a county park on the site, after conducting extensive safety and environmental analysis of the property.[57][58]
All known mercury compounds exhibit one of two positive oxidation states: I and II. Experiments have failed to unequivocally demonstrate any higher oxidation states: both the claimed 1976 electrosynthesis of an unstable Hg(III) species and 2007 cryogenic isolation ofHgF4 have disputed interpretations and remain difficult (if not impossible) to reproduce.[59]
Compounds of mercury(I)
Unlike its lighter neighbors, cadmium and zinc, mercury usually forms simple stable compounds with metal-metal bonds. Most mercury(I) compounds arediamagnetic and feature the dimeric cation, Hg2+ 2. Stable derivatives include the chloride andnitrate. In aqueous solution of a mercury(I) salt, slight disproportion of Hg2+ 2 into Hg andHg2+ results in >0.5% of dissolved mercury existing asHg2+ . In these solutions, complexation of theHg2+ with addition of ligands such ascyanide causes disproportionation to go to completion, with all Hg2+ 2 precipitating as elemental mercury and insoluble mercury(II) compounds (e.g.mercury(II) cyanide if cyanide is used as the ligand).[60]Mercury(I) chloride, a colorless solid also known ascalomel, is really the compound with the formula Hg2Cl2, with the connectivity Cl-Hg-Hg-Cl. It reacts with chlorine to givemercury(II) chloride, which resists further oxidation.Mercury(I) hydride, a colorless gas, has the formula HgH, containing no Hg-Hg bond; however, the gas has only ever been observed as isolated molecules.[61]
Indicative of its tendency to bond to itself, mercury formsmercury polycations, which consist of linear chains of mercury centers, capped with a positive charge. One example isHg 3(AsF 6) 2 containing theHg2+ 3 cation.[62]
Compounds of mercury(II)
Mercury(II) is the most common oxidation state and is the main one in nature as well. All four mercuric halides are known and have been demonstrated to form linearcoordination geometry, despite mercury's tendency to formtetrahedral molecular geometry with other ligands. This behavior is similar to theAg+ ion. The best known mercury halide ismercury(II) chloride, an easilysublimating white solid.[63]
Mercury(II) oxide, the mainoxide of mercury, arises when the metal is exposed to air for long periods at elevated temperatures. It reverts to the elements upon heating near 400 °C, as was demonstrated byJoseph Priestley in an early synthesis of pureoxygen.[21] Hydroxides of mercury are poorly characterized, as attempted isolation studies ofmercury(II) hydroxide have yielded mercury oxide instead.[64]
Mercury(II) salts form a variety of complex derivatives withammonia. These includeMillon's base (Hg2N+), the one-dimensional polymer (salts ofHgNH+ 2) n), and "fusible white precipitate" or [Hg(NH3)2]Cl2. Known asNessler's reagent,potassium tetraiodomercurate(II) (K 2HgI 4) is still occasionally used to test for ammonia owing to its tendency to form the deeply colored iodide salt of Millon's base.[66]
Organic mercurycompounds are historically important but are of little industrial value in the western world. Mercury(II) salts are a rare example of simple metal complexes that react directly with aromatic rings. Organomercury compounds are always divalent and usually two-coordinate and linear geometry. Unlikeorganocadmium andorganozinc compounds, organomercury compounds do not react with water. They usually have the formula HgR2, which are often volatile, or HgRX, which are often solids, where R isaryl oralkyl and X is usually halide or acetate.Methylmercury, a generic term for compounds with the formula CH3HgX, is a dangerous family of compounds that are often found inpolluted water.[67] They arise by a process known asbiomethylation.
Mercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic applications. It is used in someliquid-in-glass thermometers, especially those used to measure high temperatures. A still increasing amount is used as gaseous mercury influorescent lamps, while most of the other applications are slowly being phased out due to health and safety regulations. In some applications, mercury is replaced with less toxic but considerably more expensiveGalinstanalloy.[68]
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. An example of the early therapeutic application of mercury was published in 1787 byJames Lind.[69]
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 has found that cinnabar can lead to significant mercury intoxication when heated, consumed inoverdose, or taken long term, and can have adverse effects at therapeutic doses, though effects from therapeutic doses are typically reversible. Although this form of mercury appears to be less toxic than other forms, its use in traditional Chinese medicine has not yet been justified, as the therapeutic basis for the use of cinnabar is not clear.[71]
Mercury(I) chloride (also known as calomel or mercurous chloride) has been used intraditional medicine as adiuretic, topicaldisinfectant, andlaxative.Mercury(II) chloride (also known as mercuric chloride or corrosive sublimate) was once used to treatsyphilis (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.[72] It is also used as a disinfectant.Blue mass, a pill or syrup in which mercury is the main ingredient, was prescribed throughout the 19th century for numerous conditions including constipation, depression, child-bearing and toothaches.[73] 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 organohalidemerbromin (sometimes sold as Mercurochrome) is still widely used but has been banned in some countries, such as the U.S.[74]
Thiomersal (calledThimerosal in the United States) is anorganic compound used as apreservative invaccines, although this use is in decline.[76] Although it waswidely speculated that this mercury-based preservative could cause or triggerautism in children, no evidence supports any such link.[77] 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 the inactivated influenza vaccine.[76]Merbromin (Mercurochrome), another mercury compound, is a topical antiseptic used for minor cuts and scrapes in some countries. Today, the use of mercury in medicine has greatly declined in all respects, especially in developed countries.[78]
Mercury is still used in somediuretics, although substitutes such asthiazides now exist for most therapeutic uses.[79] In 2003, mercury compounds were found in someover-the-counter drugs, including topicalantiseptics, stimulant laxatives,diaper-rashointment,eye drops, andnasal sprays. TheFDA has "inadequate data to establish general recognition of the safety and effectiveness" of the mercury ingredients in these products.[80]
Production of chlorine and caustic soda
Chlorine is produced fromsodium chloride (common salt, NaCl) usingelectrolysis to separate metallicsodium from chlorine gas. Usually salt is dissolved in water to produce a brine. By-products of any suchchloralkali process are hydrogen (H2) andsodium hydroxide (NaOH), which is commonly called caustic soda orlye. By far the largest use of mercury[81][82] in the late 20th century was in the mercury cell process (also called theCastner-Kellner process) where metallic sodium is formed as anamalgam at acathode made from mercury; this sodium is then reacted with water to produce sodium hydroxide.[83] Many of the industrial mercury releases of the 20th century came from this process, although modern plants claim to be safe in this regard.[82] From the 1960s onward, the majority of industrial plants moved away from mercury cell processes towardsdiaphragm cell technologies to produce chlorine, though 11% of the chlorine made in the United States was still produced with the mercury cell method as of 2005.[84]
Laboratory uses
Thermometers
Thermometers containing mercury were invented in the early 18th century byDaniel Gabriel Fahrenheit, though earlier attempts at making temperature-measuring instruments filled with quicksilver had been described in the 1650s.[85]: 23 Fahrenheit's mercury thermometer was based on an earlier design that used alcohol rather than mercury; the mercury thermometer was significantly more accurate than those using alcohol.[86] From the early 21st century onwards, the use of mercury thermometers has been declining, and mercury-containing instruments have been banned in many jurisdictions following the 1998Protocol on Heavy Metals.[87][88] Modern alternatives to mercury thermometers includeresistance thermometers,thermocouples, andthermistor sensors that output to a digital display.[89]
Mirrors
Sometransit telescopes use a basin of mercury to form a flat and absolutely horizontal mirror, useful in determining an absolute vertical or perpendicular reference. Concave horizontal parabolic mirrors may be formed by rotating liquid mercury on a disk, the parabolic form of the liquid thus formed reflecting and focusing incident light. Suchliquid-mirror 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.[90][91][92]
Gaseous mercury is used inmercury-vapor lamps and some "neon sign" type advertising signs andfluorescent lamps. Those low-pressure lamps emit very spectrally narrow lines, which are traditionally used inoptical spectroscopy for calibration of spectral position. Commercial calibration lamps are sold for this purpose; reflecting a fluorescent ceiling light into a spectrometer is a common calibration practice.[97] Gaseous mercury is also found in someelectron tubes, includingignitrons,thyratrons, andmercury arc rectifiers.[98] It is also used in specialist medical care lamps for skin tanning and disinfection.[99] Gaseous mercury is added tocold cathodeargon-filled lamps to increase theionization andelectrical conductivity. An argon-filled lamp without mercury will have dull spots and will fail to light correctly. Lighting containing mercury can bebombarded/oven pumped only once. When added toneon filled tubes, inconsistent red and blue spots are produced in the light emissions until the initial burning-in process is completed; eventually it will light a consistent dull off-blue color.[100]
The deep violet glow of a mercury vapor discharge in agermicidal lamp, whose spectrum is rich in invisible ultraviolet radiation.
Skin tanner containing a low-pressure mercury vapor lamp and two infrared lamps, which act both as light source andelectrical ballast
Assorted types of fluorescent lamps.
The miniaturizedDeep Space Atomic Clock is a linear ion-trap-based mercury ion clock, designed for precise and real-time radio navigation in deep space.
TheDeep Space Atomic Clock (DSAC) under development by theJet Propulsion Laboratory utilises mercury in a linear ion-trap-based clock. The novel use of mercury permits the creation of compact atomic clocks with low energy requirements ideal for space probes and Mars missions.[101]
Skin whitening
Mercury is effective as an active ingredient inskin whitening compounds used to depigment skin.[102] TheMinamata Convention on Mercury limits the concentration of mercury in such whiteners to 1 part per million. However, as of 2022, many commercially sold whitener products continue to exceed that limit, and are considered toxic.[103]
Mercury is used in illegal gold mining to help separate gold particles from a mixture of sand or gravel and water.[105] Small gold particles may form mercury-gold amalgam and therefore increase the gold recovery rates.[13] The use of mercury causes a severe pollution problem in places such asGhana.[105]
Historic uses
A single-pole, single-throw (SPST) mercury switchMercurymanometer to measure pressure
Many historic applications made use of the peculiar physical properties of mercury, especially as a dense liquid and a liquid metal:
Quantities of liquid mercury ranging from 90 to 600 grams (3.2 to 21.2 oz) have been recovered from eliteMaya tombs (100–700 AD)[37] or ritual caches at six sites. This mercury may have been used in bowls asmirrors fordivinatory purposes. Five of these date to the Classic Period of Maya civilization (c. 250–900) but one example predated this.[106]
As an electrically conductive liquid, it was used inmercury switches (includinghome mercury light switches installed prior to 1970), tilt switches used in old fire detectors and in some home thermostats.[110]
Owing to its acoustic properties, mercury was used as the propagation medium indelay-line memory devices used in early digital computers of the mid-20th century, such as theSEAC computer.[111]
In 1911,Heike Kamerlingh Onnes discoveredsuperconductivity through the cooling of mercury below 4 kelvin shortly after the discovery and production ofliquid helium.[112] Its superconductive properties were later determined to be unusual compared to other later-discovered superconductors, such as the more popularniobium alloys.[113][114]
Experimentalmercury vapor turbines were installed to increase the efficiency of fossil-fuel electrical power plants.[115] The South Meadow power plant in Hartford, CT employed mercury as itsworking fluid, in abinary configuration with a secondary water circuit, for a number of years starting in the late 1920s in a drive to improve plant efficiency. Several other plants were built, including the Schiller Station in Portsmouth, NH, which went online in 1950. The idea did not catch on industry-wide due to the weight and toxicity of mercury, as well as the advent ofsupercritical steam plants in later years.[116][117]
Similarly, liquid mercury was used as acoolant for somenuclear reactors; however,sodium is proposed for reactors cooled with liquid metal, because the high density of mercury requires much more energy to circulate as coolant.[118]
Mercury was a propellant for earlyion engines inelectric space propulsion systems. Advantages were mercury's high molecular weight, low ionization energy, low dual-ionization energy, high liquid density and liquid storability atroom 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 atNASA Glenn Research Center and flown on the Space Electric Rocket Test "SERT-1" spacecraft launched byNASA at itsWallops Flight Facility in 1964. The SERT-1 flight was followed up by the SERT-2 flight in 1970. Mercury andcaesium were preferred propellants for ion engines untilHughes Research Laboratory performed studies findingxenon 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 to itsnoble gas nature, and high liquid density under mild cryogenic storage.[119][120]
Other applications made use of the chemical properties of mercury:
Themercury battery is a non-rechargeableelectrochemical battery, aprimary cell, that was common in the middle of the 20th century. It was used in a wide variety of applications and was available in various sizes, particularly button sizes. Its constant voltage output and long shelf life gave it a niche use for camera light meters and hearing aids. The mercury cell was effectively banned in most countries in the 1990s due to concerns about the mercury contaminating landfills.[121]
It was allegedly used byallied spies to sabotage Luftwaffe planes: a mercury paste was applied to barealuminium, causing the metal to rapidlycorrode; this would cause structural failures.[125]
Mercury was once used as a gun barrel bore cleaner.[126][127]
From the mid-18th to the mid-19th centuries, a process called "carroting" was used in the making offelt hats. Animal skins were rinsed in an orange solution (the term "carroting" arose from this color) of the mercury compoundmercuric nitrate, Hg(NO3)2.[128] This process separated the fur from the pelt and matted it together. This solution and the vapors it produced were highly toxic. TheUnited States Public Health Service banned the use of mercury in the felt industry in December 1941. The psychological symptoms associated with mercury poisoning inspired the phrase "mad as a hatter".[129]Lewis Carroll's "Mad Hatter" in his bookAlice'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.[130]
Historically, mercury was used extensively inhydraulic gold mining (see#Mining. 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 forplacer mining have not been recovered.[131] Mercury was also used in silver mining to extract the metal from ore through thepatio process.[132]
Due to its physical properties and relative chemical inertness, liquid mercury is absorbed very poorly through intact skin and the gastrointestinal tract.[134] Mercury vapor is the primary hazard of elemental mercury. As a result, containers of mercury are securely sealed to avoid spills and evaporation. Heating of mercury, or of compounds of mercury that may decompose when heated, should be carried out with adequate ventilation in order to minimize exposure to mercury vapor. The most toxic forms of mercury are itsorganic compounds, such asdimethylmercury andmethylmercury. Mercury can cause both chronic and acute poisoning.[135][136]
Releases in the environment
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 ng per 1 L of ice deposited. Volcanic eruptions and related natural sources are responsible for approximately half of atmospheric mercury emissions.[137]
Atmospheric mercury contamination in outdoor urban air at the start of the 21st century was measured at 0.01–0.02 μg/m3. A 2001 study measured mercury levels in 12 indoor sites chosen to represent a cross-section of building types, locations and ages in the New York area. This study found mercury concentrations significantly elevated over outdoor concentrations, at a range of 0.0065 – 0.523 μg/m3. The average was 0.069 μg/m3.[138]
Half of mercury emissions are attributed to mankind. The sources can be divided into the following estimated percentages:[139]
65% from stationary combustion, of whichcoal-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.[139]
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.[140]
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.[139]
A seriousindustrial disaster was the dumping of waste mercury compounds intoMinamata Bay, Japan, between 1932 and 1968. It is estimated that over 3,000 people suffered various deformities, severe mercury poisoning symptoms or death from what became known asMinamata disease.[141][142]
China is estimated to produce 50% of mercury emissions, most of which result from production ofvinyl chloride.[143]
Joss paper burning on the street, a common tradition practiced in Asia, Hong Kong, 2023
Mercury also enters into the environment through the improper disposal of mercury-containing products.[144] Due to health concerns,toxics use reduction efforts are cutting back or eliminating mercury in such products. For example, the amount of mercury sold in thermostats in the United States decreased from 14.5 tons in 2004 to 3.9 tons in 2007.[145]
Thetobacco plant readily absorbs and accumulatesheavy metals such as mercury from the surrounding soil into its leaves. These are subsequently inhaled duringtobacco smoking.[146] While mercury is a constituent oftobacco smoke,[147] studies have largely failed to discover a significant correlation between smoking and mercury uptake by humans compared to sources such as occupational exposure, fish consumption, andamalgam tooth fillings.[148]
A less well-known source of mercury is the burning ofjoss paper,[149] which is a common tradition practiced in Asia, including China,[150] Vietnam, Hong Kong, Thailand, Taiwan and Malaysia.[151]
Spill cleanup
Mercury spills pose an immediate threat to people handling the material, in addition to being an environmental hazard if the material is not contained properly. This is of particular concern for visible mercury, or mercury in liquid state, as its unusual appearance and behavior for a metal makes it anattractive nuisance to the uninformed.[152] Procedures have been developed to contain mercury spills, as well as recommendations on appropriate responses based on the conditions of a spill.[153][154] Tracking liquid mercury away from the site of a spill is a major concern in liquid mercury spills; regulations emphasize containment of the visible mercury as the first course of action, followed by monitoring of mercury vapors and vapor cleanup. Several products are sold as mercury spilladsorbents, ranging from metal salts to polymers andzeolites.[155]
Sediment contamination
Sediments within large urban-industrialestuaries act as an important sink forpoint source and diffuse mercury pollution withincatchments.[156] A 2015 study of foreshore sediments from theThames estuary measured total mercury at 0.01 to 12.07 mg/kg with mean of 2.10 mg/kg and median of 0.85 mg/kg (n = 351).[156] The highest mercury concentrations were shown to occur in and around the city ofLondon in association with fine grain muds and high total organic carbon content.[156] The strong affinity of mercury for carbon rich sediments has also been observed in salt marsh sediments of theRiver Mersey, with a mean concentration of 2 mg/kg, up to 5 mg/kg.[157] These concentrations are far higher than those in the salt marsh river creek sediments of New Jersey andmangroves of Southern China, which exhibit low mercury concentrations of about 0.2 mg/kg.[158][159]
Occupational exposure
EPA workers clean up residential mercury spill in 2004
Due to the health effects of mercury exposure, industrial and commercial uses are regulated in many countries. TheWorld Health Organization,[160]OSHA, andNIOSH all treat mercury as an occupational hazard; both OSHA and NIOSH, among other regulatory agencies, have established specific occupational exposure limits on the element and its derivative compounds in liquid and vapor form.[161][162] Environmental releases and disposal of mercury are regulated in the U.S. primarily by theUnited States Environmental Protection Agency.
Fish andshellfish have a natural tendency to concentrate mercury in their bodies, often in the form ofmethylmercury, a highly toxic organic compound of mercury. Species of fish that are high on thefood chain, such asshark,swordfish,king mackerel,bluefin tuna,albacore tuna, andtilefish contain higher concentrations of mercury than others. Because mercury and methylmercury are fat soluble, they primarily accumulate in theviscera, although they are also found throughout the muscle tissue.[163] Mercury presence in fish muscles can be studied using non-lethal musclebiopsies.[164] Mercury present in prey fish accumulates in the predator that consumes them. Since fish are less efficient at depurating than accumulating methylmercury, methylmercury concentrations in the fish tissue increase over time. Thus species that are high on thefood chain amass body burdens of mercury that can be ten times higher than the species they consume. This process is calledbiomagnification.Mercury poisoning happened this way inMinamata, Japan, now calledMinamata disease.[141][142]
Cosmetics
Some facial creams contain dangerous levels of mercury. Most contain comparatively non-toxic inorganic mercury, but products containing highly toxic organic mercury have been encountered.[165][166]New York City residents have been found to be exposed to significant levels of inorganic mercury compounds through the use of skin care products.[167]
Toxic effects include damage to the brain, kidneys and lungs. Mercury poisoning can result in several diseases, includingacrodynia (pink disease), Hunter-Russell syndrome, andMinamata disease. Symptoms typically include sensory impairment (vision, hearing, speech), disturbed sensation and a lack of coordination. The type and degree of symptoms exhibited depend upon the individual toxin, the dose, and the method and duration of exposure.Case–control studies have shown effects such as tremors, impairedcognitive skills, and sleep disturbance in workers with chronic exposure to mercury vapor even at low concentrations in the range 0.7–42 μg/m3.[168][169]
A study has shown that acute exposure (4–8 hours) to calculated elemental mercury levels of 1.1 to 44 mg/m3 resulted in chest pain,dyspnea, cough,hemoptysis, impairment of pulmonary function, and evidence of interstitialpneumonitis.[135] 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, includingerethism, 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.[136][170]
Treatment
Research on the treatment of mercury poisoning is limited. Currently available drugs for acute mercurial poisoning includechelatorsN-acetyl-D,L-penicillamine (NAP),British Anti-Lewisite (BAL),2,3-dimercapto-1-propanesulfonic acid (DMPS), anddimercaptosuccinic acid (DMSA). In one small study including 11 construction workers exposed to elemental mercury, patients were treated with DMSA and NAP.[171]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.[171]
The United StatesClean 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, the EPA promulgated a regulation[176] that added power plants to the list of sources that should be controlled and instituted a nationalcap and trade system. States were given until November 2006 to impose stricter controls, but after a legal challenge from several states, the regulations were struck down by a federal appeals court on 8 February 2008. The rule was deemed not sufficient to protect the health of persons living near coal-fired power plants, given the negative effects documented in the EPA Study Report to Congress of 1998.[177] However newer data published in 2015 showed that after introduction of the stricter controls mercury declined sharply, indicating that the Clean Air Act had its intended impact.[178]
The EPA announced new rules forcoal-fired power plants on 22 December 2011.[179]Cement kilns that burn hazardous waste are held to a looser standard than are standardhazardous wasteincinerators in the United States, and as a result are a disproportionate source of mercury pollution.[180]
European Union
In theEuropean Union, the directive on the Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment (seeRoHS) bans mercury from certain electrical and electronic products, and limits the amount of mercury in other products to less than 1000ppm.[181] There are restrictions for mercury concentration in packaging (the limit is 100 ppm for sum of mercury,lead,hexavalent chromium andcadmium) and batteries (the limit is 5 ppm).[182] In July 2007, the European Union also banned mercury in non-electrical measuring devices, such asthermometers andbarometers. 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.[183]
Scandinavia
Norway enacted a total ban on the use of mercury in the manufacturing and import/export of mercury products, effective 1 January 2008.[184] In 2002, several lakes in Norway were found to have a poor state of mercury pollution, with an excess of 1 μg/g of mercury in their sediment.[185] In 2008, Norway's Minister of Environment DevelopmentErik Solheim said: "Mercury is among the most dangerous environmental toxins. Satisfactory alternatives to Hg in products are available, and it is therefore fitting to induce a ban."[186] Products containing mercury were banned in Sweden in 2009,[187][188] while elemental mercury has been banned from manufacture and use in all but a few applications (such as certain energy-saving light sources and amalgam dental fillings) in Denmark since 2008.[189]
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