Editing Methylmercury

{{short description|Toxic chemical compound}}
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| OtherCompounds = [[Ethylmercury]]<br/>[[Dimethylmercury]]
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[[File:MethylmercuryPrototypes.svg|thumb|Structures of two main types of complexes formed by methylmercury. X<sup>−</sup> = anion, L = neutral [[Lewis base]].]]

'''Methylmercury''' is an [[organometallic]] [[cation]] with the formula {{nowrap|[CH<sub>3</sub>Hg]<sup>+</sup>}}. It is the simplest [[organomercury]] compound. Methylmercury is extremely toxic, and its derivatives are the major source of organic mercury for humans. It is a [[bioaccumulative]] environmental [[toxicant]] with a 50-day [[half-life]].<ref>{{cite book |last1=Halliday |first1=Tim |last2=Davey |first2=Basiro |title=Water and health in an overcrowded world |publisher=[[Oxford University Press]] |location=Oxford |date=2007 |pages=79, 80, 95 |isbn=9780199237302}}</ref>{{clarify|Half life in the environment or the human body? If the former, what does it become?|date=February 2024}}
Methylmercury (derived biologically from [[dimethylmercury]]) is the causative agent of the infamous [[Minamata disease]].

==Structure and chemistry==
"Methylmercury" is a shorthand for the hypothetical "methylmercury cation", sometimes written ''methylmercury(1+) cation'' or ''methylmercury(II) cation''. This [[functional group]] is composed of a [[methyl group]] [[Chemical bond|bonded]] to an atom of [[Mercury (element)|mercury]]. Its [[chemical formula]] is {{chem2|CH3Hg+}} (sometimes written as {{chem2|MeHg+}}). The Methylmercury compound has an overall charge of +1, with Hg in the +2 [[oxidation state]]. Methylmercury exists as a substituent in many complexes of the type {{chem2|[MeHgL]+}} (L = Lewis base) and MeHgX (X = anion).<ref>{{cite journal |last1=Canty |first1=Allan J. |last2=Chaichit |first2=Narongsak |last3=Gatehouse |first3=Bryan M. |last4=George |first4=Edwin E. |last5=Hayhurst |first5=Glen |title=Coordination chemistry of methylmercury(II). Synthesis, hydrogen-1 NMR, and crystallographic studies of cationic complexes of Me ''Hg''(II) with ambidentate and polydentate ligands containing pyridyl and N-substituted imidazolyl donors and involving unusual coordination geometries |journal=[[Inorganic Chemistry (journal)|Inorganic Chemistry]] |volume=20 |issue=8 |pages=2414–2422 |year=1981 |doi=10.1021/ic50222a011}}</ref>

As a positively charged ion, it readily combines with [[anion]]s such as [[chloride]] ({{chem2|Cl-}}), [[hydroxide]] ({{chem2|OH-}}) and [[nitrate]] ({{chem2|NO3-}}). It has particular affinity for [[sulfur]]-containing anions, particularly [[thiol]]s ({{chem2|RS−}}). Thiols are generated when the [[amino acid]] [[cysteine]] and the [[peptide]] [[glutathione]] form strong complexes with methylmercury:<ref>{{cite journal |last1=Nolan |first1=Elizabeth M. |last2=Lippard |first2=Stephen J. |title=Tools and Tactics for the Optical Detection of Mercuric Ion |journal=Chemical Reviews |volume=108 |issue=9 |pages=3443–3480 |year=2008 |pmid=18652512 |doi=10.1021/cr068000q}}</ref>
:{{chem2|[MeHg]+ + RSH -> MeHg\sSR + H+}}

==Sources==

===Environmental sources===
{{See also|Mercury cycle}}
[[File:MCYSHG10sm.svg|thumb|Structure of the complex of methylmercury and cysteine.<ref>{{cite journal |last1=Taylor |first1=Nicholas J. |last2=Wong |first2=Yau S. |last3=Chieh |first3=Peter C. |last4=Carty |first4=Arthur J. |title=Syntheses, X-ray crystal structure, and vibrational spectra of L-cysteinato(methyl)mercury(II) monohydrate |journal=Journal of the Chemical Society, Dalton Transactions |issue=5 |pages=438 |year=1975 |doi=10.1039/DT9750000438}}</ref> Color code: dark blue = Hg, yellow = S.]]
Methylmercury is formed from inorganic mercury by the action of microbes that live in aquatic systems including [[lake]]s, [[river]]s, [[wetland]]s, [[sediment]]s, [[soil]]s and the open [[ocean]].<ref>{{cite journal |last1=Ullrich |first1=Susanne |last2=Tanton |first2=Trevor |last3=Abdrashitova |first3=Svetlana |title=Mercury in the Aquatic Environment: A Review of Factors Affecting Methylation |journal=Critical Reviews in Environmental Science and Technology |volume=31 |issue=3 |pages=241–293 |year=2001 |s2cid=96462553 |doi=10.1080/20016491089226|bibcode=2001CREST..31..241U }}</ref> This methylmercury production has been primarily attributed to [[anaerobic bacteria]] in the sediment.<ref>{{cite journal |last1=Compeau |first1=G.C. |last2=Bartha |first2=R. |title=Sulfate-Reducing Bacteria: Principal Methylators of Mercury in Anoxic Estuarine Sediment |journal=Applied and Environmental Microbiology |volume=50 |issue=2 |pages=498–502 |date=1985-08-01 |issn=0099-2240 |pmc=238649 |pmid=16346866 |bibcode=1985ApEnM..50..498C |doi=10.1128/AEM.50.2.498-502.1985}}</ref> Capable bacteria that can methylate mercury are mostly the [[sulfate-reducing bacteria]] (SRB),<ref>{{Cite journal |last1=Compeau |first1=G. C. |last2=Bartha |first2=R. |date=August 1985 |title=Sulfate-Reducing Bacteria: Principal Methylators of Mercury in Anoxic Estuarine Sediment |journal=Applied and Environmental Microbiology |language=en |volume=50 |issue=2 |pages=498–502 |doi=10.1128/aem.50.2.498-502.1985 |pmid=16346866 |pmc=238649 |bibcode=1985ApEnM..50..498C |issn=0099-2240}}</ref><ref>{{Cite journal |last1=Gilmour |first1=Cynthia C. |last2=Henry |first2=Elizabeth A. |last3=Mitchell |first3=Ralph |date=November 1992 |title=Sulfate stimulation of mercury methylation in freshwater sediments |url=https://pubs.acs.org/doi/abs/10.1021/es00035a029 |journal=Environmental Science & Technology |language=en |volume=26 |issue=11 |pages=2281–2287 |doi=10.1021/es00035a029 |bibcode=1992EnST...26.2281G |issn=0013-936X}}</ref> iron-reducing bacteria (FeRB) <ref>{{Cite journal |last1=Wang |first1=Yuwei |last2=Roth |first2=Spencer |last3=Schaefer |first3=Jeffra K |last4=Reinfelder |first4=John R |last5=Yee |first5=Nathan |date=2020-12-22 |title=Production of methylmercury by methanogens in mercury contaminated estuarine sediments |url=https://academic.oup.com/femsle/article/doi/10.1093/femsle/fnaa196/6006876 |journal=FEMS Microbiology Letters |language=en |volume=367 |issue=23 |doi=10.1093/femsle/fnaa196 |pmid=33242089 |issn=1574-6968}}</ref> and [[methanogen]]s.<ref>{{Cite journal |last1=Wang |first1=Yuwei |last2=Roth |first2=Spencer |last3=Schaefer |first3=Jeffra K |last4=Reinfelder |first4=John R |last5=Yee |first5=Nathan |date=2020-12-22 |title=Production of methylmercury by methanogens in mercury contaminated estuarine sediments |url=https://academic.oup.com/femsle/article/doi/10.1093/femsle/fnaa196/6006876 |journal=FEMS Microbiology Letters |language=en |volume=367 |issue=23 |doi=10.1093/femsle/fnaa196 |pmid=33242089 |issn=1574-6968}}</ref><ref>{{Cite journal |last1=Hamelin |first1=Stéphanie |last2=Amyot |first2=Marc |last3=Barkay |first3=Tamar |last4=Wang |first4=Yanping |last5=Planas |first5=Dolors |date=2011-09-15 |title=Methanogens: Principal Methylators of Mercury in Lake Periphyton |url=https://pubs.acs.org/doi/10.1021/es2010072 |journal=Environmental Science & Technology |language=en |volume=45 |issue=18 |pages=7693–7700 |doi=10.1021/es2010072 |pmid=21875053 |bibcode=2011EnST...45.7693H |issn=0013-936X}}</ref> Significant concentrations of methylmercury in ocean water columns<ref>{{cite journal |last1=Mason |first1=R.P. |last2=Fitzgerald |first2=W.F. |title=Alkylmercury species in the equatorial Pacific |journal=Nature |volume=347 |issue=6292 |pages=457–459 |date=1990-10-04 |bibcode=1990Natur.347..457M |s2cid=4272755 |doi=10.1038/347457a0}}</ref> are strongly associated with nutrients and organic matter [[remineralization]], which indicate that remineralization may contribute to methylmercury production.<ref>{{cite journal |last1=Sunderland |first1=Elsie M. |last2=Krabbenhoft |first2=David P. |last3=Moreau |first3=John W. |last4=Strode |first4=Sarah A. |last5=Landing |first5=William M. |title=Mercury sources, distribution, and bioavailability in the North Pacific Ocean: Insights from data and models |journal=Global Biogeochemical Cycles |volume=23 |issue=2 |pages=GB2010 |date=2009-06-01 |issn=1944-9224 |citeseerx=10.1.1.144.2350 |bibcode=2009GBioC..23.2010S |s2cid=17376038 |doi=10.1029/2008GB003425}}</ref> Direct measurements of methylmercury production using stable [[mercury isotopes]] have also been observed in marine waters,<ref name=":0">{{cite journal |last1=Schartup |first1=Amina T. |last2=Balcom |first2=Prentiss H. |last3=Soerensen |first3=Anne L. |last4=Gosnell |first4=Kathleen J. |last5=Calder |first5=Ryan S.D. |last6=Mason |first6=Robert P. |last7=Sunderland |first7=Elsie M. |title=Freshwater discharges drive high levels of methylmercury in Arctic marine biota |journal=Proceedings of the National Academy of Sciences |volume=112 |issue=38 |pages=11789–11794 |date=2015-09-22 |issn=0027-8424 |pmc=4586882 |pmid=26351688 |bibcode=2015PNAS..11211789S |doi=10.1073/pnas.1505541112 |doi-access=free}}</ref><ref>{{cite journal |last1=Lehnherr |first1=Igor |last2=St.Louis |first2=Vincent L. |last3=Hintelmann |first3=Holger |last4=Kirk |first4=Jane L. |title=Methylation of inorganic mercury in polar marine waters |journal=Nature Geoscience |volume=4 |issue=5 |pages=298–302 |year=2011 |bibcode=2011NatGe...4..298L |doi=10.1038/ngeo1134}}</ref> but the microbes involved are still unknown. Increased methylmercury concentrations in water and fish have been detected after flooding of soils associated with [[reservoir]] creation (e.g. for [[hydroelectric power generation]]) and in [[thermokarst]] wetlands that form after [[permafrost]] thaw.<ref name=":0" /><ref>{{cite journal |last1=St.Louis |first1=Vincent L. |last2=Rudd |first2=John W.M. |last3=Kelly |first3=Carol A. |last4=Bodaly |first4=R.A. (Drew) |last5=Paterson |first5=Michael J. |last6=Beaty |first6=Kenneth G. |last7=Hesslein |first7=Raymond H. |last8=Heyes |first8=Andrew |last9=Majewski |first9=Andrew R. |title=The Rise and Fall of Mercury Methylation in an Experimental Reservoir |journal=Environmental Science & Technology |volume=38 |issue=5 |pages=1348–1358 |date=2004-03-01 |issn=0013-936X |pmid=15046335 |doi=10.1021/es034424f}}</ref><ref>{{cite journal |last1=Tarbier |first1=Brittany |last2=Hugelius |first2=Gustaf |last3=Kristina Sannel |first3=Anna Britta |last4=Baptista-Salazar |first4=Carluvy |last5=Jonsson |first5=Sofi |title=Permafrost Thaw Increases Methylmercury Formation in Subarctic Fennoscandia |journal=Environmental Science & Technology |volume=55 |issue=10 |pages=6710–6717 |date=2021-04-26 |issn=0013-936X |pmid=33902281 |pmc=8277125 |bibcode=2021EnST...55.6710T |doi=10.1021/acs.est.0c04108 |doi-access=free}}</ref> The increased methylmercury concentration is due to its ability to bio-accumulate and biο-magnify in aquatic food webs. <ref>{{Cite journal |last1=Chen |first1=Xiaojia |last2=Balasubramanian |first2=Rajasekhar |last3=Zhu |first3=Qiongyu |last4=Behera |first4=Sailesh N. |last5=Bo |first5=Dandan |last6=Huang |first6=Xian |last7=Xie |first7=Haiyun |last8=Cheng |first8=Jinping |date=2016-04-01 |title=Characteristics of atmospheric particulate mercury in size-fractionated particles during haze days in Shanghai |url=https://www.sciencedirect.com/science/article/pii/S1352231016301303 |journal=Atmospheric Environment |volume=131 |pages=400–408 |doi=10.1016/j.atmosenv.2016.02.019 |bibcode=2016AtmEn.131..400C |issn=1352-2310}}</ref>

There are various sources of inorganic mercury that may indirectly contribute to the production of methylmercury from microbes in the environment. Natural sources of mercury released to the atmosphere include [[volcano]]es, [[wildfire|forest fires]], volatilization from the ocean<ref>{{cite web|url=http://www.usgs.gov/themes/factsheet/146-00/|title=Mercury in the Environment|publisher=U.S. Geological Survey|access-date=2013-09-20|archive-date=2015-07-18|archive-url=https://web.archive.org/web/20150718192245/http://www.usgs.gov/themes/factsheet/146-00/|url-status=dead}}</ref> and [[weathering]] of [[Cinnabar|mercury-bearing]] [[Rock (geology)|rocks]].<ref>Tewalt, S. J.; Bragg, L. J.; Finkelman, R. B., 2005, [http://pubs.usgs.gov/fs/fs095-01/ Mercury in U.S. coal -- Abundance, distribution, and modes of occurrence], U.S. Geological Survey Fact Sheet 095-01. Access-date=January 12, 2006.</ref> [[Human impact on the environment|Anthropogenic]] sources of mercury include the burning of wastes containing inorganic mercury and from the burning of [[fossil fuel]]s, particularly [[coal]]. Although [[Inorganic compounds|inorganic]] mercury is only a trace constituent of such fuels, their large scale combustion in utility and commercial/industrial boilers in the [[United States]] alone results in release of some 80.2 [[Ton#Units of mass|ton]]s (73 [[Tonne|metric ton]]s) of elemental mercury to the [[Earth's atmosphere|atmosphere]] each year, out of total anthropogenic mercury emissions in the United States of 158 tons (144 metric tons)/year.<ref name=":2">U. S. Environmental Protection Agency, 1997, [http://www.epa.gov/ttn/oarpg/t3/reports/volume2.pdf "Mercury study report to congress, Volume II: An inventory of anthropogenic mercury emissions in the United States"] {{webarchive |url=https://web.archive.org/web/20080911071400/http://www.epa.gov/ttn/oarpg/t3/reports/volume2.pdf |date=2008-09-11}}, table ES-3, sum of Utility boilers and Commercial/industrial boilers. Report: EPA-452/R-97-004.</ref>

In the past, methylmercury was produced directly and indirectly as part of several industrial processes such as the manufacture of [[acetaldehyde]]. However, currently there are few direct [[Human impact on the environment|anthropogenic]] sources of methylmercury [[pollution]] in the United States.<ref name=":2" />

Whole-lake ecosystem experiments at [[Experimental Lakes Area|IISD-ELA]] in [[Ontario]], Canada, showed that mercury falling directly on a lake had the fastest impacts on aquatic ecosystems as opposed to mercury falling on the surrounding land.<ref name=":3">{{cite web|date=2017-09-23|title=Mercury: What it does to humans and what humans need to do about it|url=https://www.iisd.org/ela/blog/commentary/mercury-humans-humans-need/|access-date=2020-07-03|website=IISD Experimental Lakes Area}}</ref> This inorganic mercury is converted to methylmercury by bacteria. Different [[Isotope analysis|stable isotopes]] of mercury were added to lakes, [[wetland]]s, and [[Upland and lowland|uplands]], simulating rain, and then mercury concentrations in fish were analyzed to find their source.<ref name=":4">{{cite journal |last1=Grieb |first1=Thomas M. |last2=Fisher |first2=Nicholas S. |last3=Karimi |first3=Roxanne |last4=Levin |first4=Leonard |title=An assessment of temporal trends in mercury concentrations in fish |journal=Ecotoxicology |volume=29 |issue=10 |pages=1739–1749 |date=2019-10-03 |issn=1573-3017 |pmid=31583510 |s2cid=203654223 |doi=10.1007/s10646-019-02112-3}}</ref> The mercury applied to lakes was found in young-of-the-year [[yellow perch]] within two months, whereas the mercury applied to wetlands and uplands had a slower but longer influx.<ref name=":3" /><ref name=":4" />

Acute methylmercury poisoning can occur either directly from the release of methylmercury into the environment or indirectly from the release of inorganic mercury that is subsequently methylated in the environment. For example, methylmercury poisoning occurred at [[Asubpeeschoseewagong First Nation|Grassy Narrows in Ontario, Canada]] (see [[Ontario Minamata disease]]), as a result of mercury released from the mercury-cell [[Chloralkali process]], which uses liquid mercury as an electrode in a process that entails electrolytic decomposition of brine, followed by [[mercury methylation]] in the aquatic environment. An acute methylmercury poisoning tragedy occurred also in [[Minamata, Kumamoto|Minamata, Japan]], following release of methylmercury into [[Minamata Bay]] and its tributaries (see [[Minamata disease]]). In the Ontario case, inorganic mercury discharged into the environment was methylated in the environment; whereas, in Minamata, Japan, there was direct industrial discharge of methylmercury.

===Dietary sources===
Because methylmercury is formed in aquatic systems, and because it is not readily eliminated from organisms, it is [[biomagnification|biomagnified]] in aquatic [[food chain]]s from [[bacteria]], to [[plankton]], through [[macroinvertebrate]]s, to [[herbivorous]] [[fish]] and to [[piscivorous]] (fish-eating) fish.<ref name="wiener">reviewed in Wiener, J.G., Krabbenhoft, D.P., Heinz, G.H., and Scheuhammer, A.M., 2003, "Ecotoxicology of mercury", Chapter 16 ''in'' Hoffman, D.J., B.A. Rattner, G.A. Burton, Jr., and J. Cairns, Jr., eds., ''Handbook of Ecotoxicology'', 2nd edition.: Boca Raton, FL: CRC Press, p. 409–463.</ref><ref name=":1">{{cite journal |last1=Lavoie |first1=Raphael A. |last2=Jardine |first2=Timothy D. |last3=Chumchal |first3=Matthew M. |last4=Kidd |first4=Karen A. |last5=Campbell |first5=Linda M. |title=Biomagnification of Mercury in Aquatic Food Webs: A Worldwide Meta-Analysis |journal=Environmental Science & Technology |volume=47 |issue=23 |pages=13385–13394 |date=2013-11-13 |pmid=24151937 |issn=0013-936X |bibcode=2013EnST...4713385L |doi=10.1021/es403103t}}</ref> At each step in the food chain, the [[concentration]] of methylmercury in the organism increases. The concentration of methylmercury in the top-level aquatic [[predator]]s can reach a level a million times higher than the level in the water.<ref name="wiener" /><ref name=":1" /> This is because methylmercury has a half-life of about 72 days in aquatic organisms resulting in its [[bioaccumulation]] within these food chains. Organisms, including humans,<ref>{{cite news |last=Burros |first=Marian |title=High Mercury Levels Are Found in Tuna Sushi |url=https://www.nytimes.com/2008/01/23/dining/23sushi.html |newspaper=The New York Times |date=2008-01-23}}</ref> fish-eating birds, and fish-eating mammals such as [[otter]]s and [[cetacean]]s (i.e. [[whale]]s and [[dolphin]]s) that consume fish from the top of the aquatic food chain receive the methylmercury that has accumulated through this process, plus the toxins in their habitat.<ref name="wiener" /><ref name=":1" /> Fish and other aquatic [[species]] are the main source of human methylmercury exposure.<ref name="wiener" />

The concentration of mercury in any given fish depends on the species of fish, the age and size of the fish and the type of water body in which it is found.<ref name="wiener" /> In general, fish-eating fish such as [[shark]], [[swordfish]], [[marlin]], larger species of [[tuna]], [[walleye]], [[largemouth bass]], and [[northern pike]], have higher levels of methylmercury than herbivorous fish or smaller fish such as [[tilapia]] and [[herring]].<ref>[http://www.cfsan.fda.gov/~frf/sea-mehg.html Mercury Levels in Commercial Fish and Shellfish] {{webarchive |url=https://web.archive.org/web/20060110235714/http://www.cfsan.fda.gov/~frf/sea-mehg.html |date=2006-01-10}} Accessed March 25, 2009.</ref><ref>[http://www.epa.gov/waterscience/fish/advice/ What You Need to Know about Mercury in Fish and Shellfish] Accessed March 25, 2009.</ref> Within a given species of fish, older and larger fish have higher levels of methylmercury than smaller fish. Fish that develop in water bodies that are more [[acid]]ic also tend to have higher levels of methylmercury.<ref name="wiener" />

==Biological impact==

===Human health effects===
{{see also|Minamata disease}}
[[Ingested]] methylmercury is readily and completely absorbed by the [[gastrointestinal tract]]. It is mostly found complexed with free cysteine and with proteins and [[peptide]]s containing that amino acid. The methylmercuric-cysteinyl complex is recognized by amino acids transporting proteins in the body as [[methionine]], another [[essential amino acid]].<ref>{{cite journal |last1=Kerper |first1=L. |last2=Ballatori |first2=N. |last3=Clarkson |first3=T.W. |title=Methylmercury transport across the blood–brain barrier by an amino acid carrier |journal=American Journal of Physiology |volume=262 |issue=5 Pt 2 |pages=R761–765 |date=May 1992 |pmid=1590471 |doi=10.1152/ajpregu.1992.262.5.R761}}</ref> Because of this mimicry, it is transported freely throughout the body including across the [[blood–brain barrier]] and across the [[placenta]], where it is absorbed by the developing [[fetus]]. Also for this reason as well as its strong binding to proteins, methylmercury is not readily eliminated. Methylmercury has a [[half-life]] in human [[blood]] of about 50 days.<ref>{{cite journal |last1=Carrier |first1=G |last2=Bouchard |first2=M |last3=Brunet |first3=RC |last4=Caza |first4=M |title=A Toxicokinetic Model for Predicting the Tissue Distribution and Elimination of Organic and Inorganic Mercury Following Exposure to Methyl Mercury in Animals and Humans. II. Application and Validation of the Model in Humans |journal=[[Toxicology and Applied Pharmacology]] |volume=171 |issue=1 |pages=50–60 |year=2001 |pmid=11181111 |doi=10.1006/taap.2000.9113|bibcode=2001ToxAP.171...50C }}</ref>

Several studies indicate that methylmercury is linked to subtle developmental deficits in children exposed ''in utero'' such as loss of IQ points, and decreased performance in tests of language skills, memory function and attention deficits.<ref name="rice">{{cite journal |last1=Rice |first1=DC |last2=Schoeny |first2=R |last3=Mahaffey |first3=K |title=Methods and rationale for derivation of a reference dose for methylmercury by the U.S. EPA |url=https://zenodo.org/record/1230585 |journal=Risk Analysis |volume=23 |issue=1 |pages=107–115 |year=2003 |pmid=12635727 |s2cid=6735371 |doi=10.1111/1539-6924.00294|bibcode=2003RiskA..23..107R }}</ref> Methylmercury exposure in adults has also been linked to increased risk of [[cardiovascular disease]] including [[Myocardial infarction|heart attack]].<ref>{{cite journal |last1=Salonen |first1=J. T. |last2=Seppänen |first2=K. |last3=Nyyssönen |first3=K. |last4=Korpela |first4=H. |last5=Kauhanen |first5=J. |last6=Kantola |first6=M. |last7=Tuomilehto |first7=J. |last8=Esterbauer |first8=H. |last9=Tatzber |first9=F. |last10=Salonen |first10=R. |title=Intake of Mercury from Fish, Lipid Peroxidation, and the Risk of Myocardial Infarction and Coronary, Cardiovascular, and Any Death in Eastern Finnish Men |journal=Circulation |volume=91 |issue=3 |pages=645–655 |year=1995 |pmid=7828289 |doi=10.1161/01.CIR.91.3.645}}</ref><ref name=myocardialrisk>{{cite journal |last1=Guallar |first1=E |last2=Sanz-Gallardo |first2=MI |last3=Van't Veer |first3=P |last4=Bode |first4=P |last5=Aro |first5=A |last6=Gómez-Aracena |first6=J |last7=Kark |first7=JD |last8=Riemersma |first8=RA |last9=Martín-Moreno |first9=JM |last10=Kok |first10=FJ |author11=Heavy Metals Myocardial Infarction Study Group |title=Mercury, fish oils, and the risk of myocardial infarction |journal=The New England Journal of Medicine |volume=347 |issue=22 |pages=1747–1754 |year=2002 |pmid=12456850 |s2cid=23031417 |doi=10.1056/NEJMoa020157 |doi-access=free}}</ref><ref>Choi, A.L., Weihe, P., Budtz-Jørgensen, E., Jørgensen, P.J., Salonen, J.T., Tuomainen, T.-P., Murata, K., Nielsen, H.P., Petersen, M.S., Askham, J., and Grandjean, P., 2009, [https://archive.today/20120530200446/http://www.ehponline.org/docs/2008/11608/abstract.html Methylmercury Exposure and Adverse Cardiovascular Effects in Faroese Whaling Men:] ''Environmental Health Perspectives'', v. 117, no. 3, p. 367–372.</ref> Some evidence also suggests that methylmercury can cause [[Autoimmune diseases|autoimmune]] effects in sensitive individuals.<ref>{{cite journal |last1=Hultman |first1=P |last2=Hansson-Georgiadis |first2=H |title=Methyl mercury–induced autoimmunity in mice |journal=Toxicology and Applied Pharmacology |volume=154 |issue=3 |pages=203–211 |year=1999 |pmid=9931279 |doi=10.1006/taap.1998.8576|bibcode=1999ToxAP.154..203H }}</ref> There is some evidence suggesting a possible connection between post-natal mercury exposure and autism; however, it is not clear whether methylmercury intake in particular is linked in a similar way.<ref>{{Cite journal |last=Azevedo |first=Lara Ferreira |last2=Karpova |first2=Nina |last3=Rocha |first3=Bruno Alves |last4=Barbosa Junior |first4=Fernando |last5=Gobe |first5=Glenda Carolyn |last6=Hornos Carneiro |first6=Maria Fernanda |date=January 2023 |title=Evidence on Neurotoxicity after Intrauterine and Childhood Exposure to Organomercurials |url=https://www.mdpi.com/1660-4601/20/2/1070 |journal=International Journal of Environmental Research and Public Health |language=en |volume=20 |issue=2 |pages=1070 |doi=10.3390/ijerph20021070 |issn=1660-4601 |pmc=9858833 |pmid=36673825 |doi-access=free}}</ref><ref>{{Cite journal |last=Netto |first=Bruna Bittencourt |last2=da Silva |first2=Elica Pizzolo |last3=de Aguiar da Costa |first3=Maiara |last4=de Rezende |first4=Victória Linden |last5=Bolan |first5=Sofia Januário |last6=Ceretta |first6=Luciane Bisognin |last7=Aschner |first7=Michael |last8=Dominguini |first8=Diogo |last9=Gonçalves |first9=Cinara Ludvig |date=2024 |title=Critical period of exposure to mercury and the diagnostic of autism spectrum disorder: A systematic review |url=https://onlinelibrary.wiley.com/doi/10.1111/jnc.16076 |journal=Journal of Neurochemistry |language=en |volume=168 |issue=9 |pages=2092–2104 |doi=10.1111/jnc.16076 |issn=1471-4159}}</ref><ref>{{Cite journal |last=Stojsavljević |first=Aleksandar |last2=Lakićević |first2=Novak |last3=Pavlović |first3=Slađan |date=December 2023 |title=Mercury and Autism Spectrum Disorder: Exploring the Link through Comprehensive Review and Meta-Analysis |url=https://www.mdpi.com/2227-9059/11/12/3344 |journal=Biomedicines |language=en |volume=11 |issue=12 |pages=3344 |doi=10.3390/biomedicines11123344 |issn=2227-9059 |pmc=10741416 |pmid=38137565 |doi-access=free}}</ref> Although there is no doubt that methylmercury is toxic in several respects, including through exposure of the developing fetus, there is still some controversy as to the levels of methylmercury in the diet that can result in adverse effects. Recent evidence suggests that the developmental and [[cardiovascular toxicity]] of methylmercury may be mitigated by co-exposures to [[omega-3 fatty acid]]s and perhaps [[selenium]], both found in fish and elsewhere.<ref name=myocardialrisk /><ref>{{cite journal |last1=Choi |first1=AL |last2=Cordier |first2=S |last3=Weihe |first3=P |last4=Grandjean |first4=P |title=Negative confounding in the evaluation of toxicity: The case of methylmercury in fish and seafood |journal=Critical Reviews in Toxicology |volume=38 |issue=10 |pages=877–893 |year=2008 |pmc=2597522 |pmid=19012089 |doi=10.1080/10408440802273164}} Review. Erratum in: {{cite journal |title=Erratum |journal=Critical Reviews in Toxicology |volume=39 |page=95 |year=2009 |s2cid=218989377 |doi=10.1080/10408440802661707}}</ref><ref>{{cite journal|pmid=18590765|year=2008|last1=Strain|first1=JJ|last2=Davidson|first2=PW|last3=Bonham|first3=MP|last4=Duffy|first4=EM|last5=Stokes-Riner|first5=A|last6=Thurston|first6=SW|author6-link=Sally Thurston|last7=Wallace|first7=JM|last8=Robson|first8=PJ|last9=Shamlaye|first9=CF|last10=Georger|first10=LA|last11=Sloane-Reeves|first11=J|last12=Cernichiari|first12=E|last13=Canfield|first13=RL|last14=Cox|first14=C|last15=Huang|first15=LS|last16=Janciuras|first16=J|last17=Myers|first17=GJ|last18=Clarkson|first18=TW|title=Associations of maternal long-chain polyunsaturated fatty acids, methyl mercury, and infant development in the Seychelles Child Development Nutrition Study|volume=29|issue=5|pages=776–82|doi=10.1016/j.neuro.2008.06.002|pmc=2574624|journal=Neurotoxicology|bibcode=2008NeuTx..29..776S }}</ref><ref>{{cite journal|pmid=19374471|year=2009|last1=Khan|first1=MA|last2=Wang|first2=F|title=Mercury-selenium compounds and their toxicological significance: Toward a molecular understanding of the mercury-selenium antagonism|volume=28|issue=8|pages=1567–77|doi=10.1897/08-375.1|journal=Environmental Toxicology and Chemistry|s2cid=207267481}} Review.</ref><ref>{{cite journal|pmid=20079371|year=2010|last1=Heath|first1=JC|last2=Banna|first2=KM|last3=Reed|first3=MN|last4=Pesek|first4=EF|last5=Cole|first5=N|last6=Li|first6=J|last7=Newland|first7=MC|title=Dietary selenium protects against selected signs of aging and methylmercury exposure|volume=31|issue=2|pages=169–79|doi=10.1016/j.neuro.2010.01.003|pmc=2853007|journal=Neurotoxicology|bibcode=2010NeuTx..31..169H }}</ref>

There have been several episodes in which large numbers of people were severely poisoned by food contaminated with high levels of methylmercury, notably the dumping of [[industrial waste]] that resulted in the [[Minamata disease|pollution and subsequent mass poisoning]] in [[Minamata]] and [[Niigata, Niigata|Niigata]], [[Japan]]<ref>{{Cite journal
 | last1=Myers | first1=G.J. | last2=Davidson | first2=P.W.
 | last3=Weiss | first3=B.
 | title=Methyl mercury exposure and poisoning at Niigata, Japan
 | journal=SMDJ Seychelles Medical and Dental Journal
 | volume=7 | issue=Special Issue | year=2004 | pages=132&ndash;133
 | url=http://www.seychelles.net/smdj/SECVA.pdf
 | access-date=January 12, 2006
 | archive-url = https://web.archive.org/web/20060505115116/http://www.seychelles.net/smdj/SECVA.pdf
 | archive-date = May 5, 2006
}}</ref> and the situation in [[Iraq]] in the 1960s and 1970s in which wheat treated with methylmercury as a preservative and intended as seed grain was fed to animals and directly consumed by people (see [[Basra poison grain disaster]]). These episodes resulted in [[neurology|neurological]] [[symptom]]s including [[paresthesia]]s, loss of physical coordination, [[dysarthria|difficulty in speech]], [[Visual field loss|narrowing of the visual field]], [[hearing impairment]], [[blindness]], and death. Children who had been exposed in utero through their mothers' ingestion were also affected with a range of symptoms including motor difficulties, sensory problems and [[intellectual disability]].

At present, exposures of this magnitude are rarely seen and are confined to isolated incidents. Accordingly, concern over methylmercury pollution is currently focused on more subtle effects that may be linked to levels of exposure presently seen in populations with high to moderate levels of dietary fish consumption. These effects are not necessarily identifiable on an individual level or may not be uniquely recognizable as due to methylmercury. However, such effects may be detected by comparing populations with different levels of exposure. There are isolated reports of various clinical health effects in individuals who consume large amounts of fish;<ref>For example: {{cite journal
 | doi = 10.1289/ehp.5837
 | last1=Hightower | first1=JM | last2 = Moore | first2=D
 | title = Mercury levels in high-end consumers of fish
 | journal = Environmental Health Perspectives
 | volume = 111 | issue = 4 | pages = 604–8 | year=2003
 | pmid = 12676623 | pmc = 1241452}}</ref> however, the specific health effects and exposure patterns have not been verified with larger, controlled studies.

Many governmental agencies, the most notable ones being the [[United States Environmental Protection Agency]] (EPA), the United States [[Food and Drug Administration]] (FDA), [[Health Canada]], and the [[Directorate-General for Health and Food Safety|European Union Health and Consumer Protection Directorate-General]], as well as the [[World Health Organization]] (WHO) and the United Nations [[Food and Agriculture Organization]] (FAO), have issued guidance for fish consumers that is designed to limit methylmercury exposure from fish consumption. At present, most of this guidance is based on protection of the developing fetus; future guidance, however, may also address cardiovascular risk. In general, fish consumption advice attempts to convey the message that fish is a good source of nutrition and has significant health benefits, but that consumers, in particular pregnant women, women of child-bearing age, nursing mothers, and young children, should avoid fish with high levels of methylmercury, limit their intake of fish with moderate levels of methylmercury, and consume fish with low levels of methylmercury no more than twice a week.<ref>Information on characteristic levels of methylmercury by species can be found at {{cite web |url=http://www.cfsan.fda.gov/~frf/sea-mehg.html |title=FDA - Mercury Levels in Commercial Fish and Shellfish |access-date=2006-01-03 |url-status=dead |archive-url=https://web.archive.org/web/20060110235714/http://www.cfsan.fda.gov/~frf/sea-mehg.html |archive-date=2006-01-10}}</ref><ref>A wallet-card guide for consumers can be found at http://www.nrdc.org/health/effects/mercury/protect.asp</ref>

===Effects on fish and wildlife===
[[File:NATIONAL WATER QUALITY LABORATORY, 30 DAY GROWTH OF JORDANELLA. THE BOTTLES, LEFT TO RIGHT, CONTAIN, 1-THE CONTROL... - NARA - 551591.tif|thumb|Four vials of larvae of ''[[Jordanella floridae|Jordanella]]'' after one month in normal water for the first batch, and in water containing 0.6PPB and 1.26PPB and 2.5PPB (parts per billion) of methylmercury for the three bottles at right.]]
In recent years, there has been increasing recognition that methylmercury affects fish and wildlife health, both in acutely polluted ecosystems and ecosystems with modest methylmercury levels. Two reviews<ref name="wiener"/><ref>{{cite journal |last1=Scheuhammer |first1=Anton M. |last2=Meyer |first2=Michael W. |last3=Sandheinrich |first3=Mark B. |last4=Murray |first4=Michael W. |title=Effects of Environmental Methylmercury on the Health of Wild Birds, Mammals, and Fish |journal=Ambio: A Journal of the Human Environment |volume=36 |pages=12–19 |issue=1 |year=2007 |issn=0044-7447 |pmid=17408187 |s2cid=13126984 |doi=10.1579/0044-7447(2007)36[12:EOEMOT]2.0.CO;2}}</ref> document numerous studies of diminished reproductive success of fish, fish-eating birds, and mammals due to methylmercury contamination in aquatic ecosystems.

===In public policy===
Reported methylmercury levels in fish, along with fish consumption advisories, have the potential to disrupt people's eating habits, fishing traditions, and the livelihoods of the people involved in the capture, distribution, and preparation of fish as a foodstuff for humans.<ref>{{cite journal |last1=Wheatley |first1=B |last2=Wheatley |first2=M |title=Methylmercury and the health of indigenous peoples: a risk management challenge for physical and social sciences and for public health policy |journal=The Science of the Total Environment |volume=259 |issue=1–3 |pages=23–29 |year=2000 |pmid=11032132 |bibcode=2000ScTEn.259...23W |doi=10.1016/S0048-9697(00)00546-5}}</ref> Furthermore, proposed limits on mercury emissions have the potential to add costly pollution controls on coal-fired utility boilers. Nevertheless, substantial benefits can be achieved globally by introducing mercury emission reduction measures because they reduce human and wildlife exposure to methylmercury.<ref>Jozef M. Pacyna, Kyrre Sundseth, Elisabeth G. Pacyna, Wojciech Jozewicz, John Munthe, Mohammed Belhaj & Stefan Aström (2010), "An Assessment of Costs and Benefits Associated with Mercury Emission Reductions from Major Anthropogenic Sources", ''Journal of the Air & Waste Management Association'', 60:3, 302–315, DOI: 10.3155/1047-3289.60.3.302</ref>

About 30% of the distributed mercury depositional input is from current anthropogenic sources, and 70% is from natural sources. The natural sources category includes re-emission of mercury previously deposited from anthropogenic sources.<ref>{{cite journal |last1=Pirrone |first1=N. |last2=Cinnirella |first2=S. |last3=Feng |first3=X. |last4=Finkelman |first4=R.B. |last5=Friedli |first5=H.R. |last6=Leaner |first6=J. |last7=Mason |first7=R. |last8=Mukherjee |first8=A.B. |last9=Stracher |first9=G.B. |last10=Streets |first10=D.G. |last11=Telmer |first11=K. |title=Global Mercury Emissions to the Atmosphere from Anthropogenic and Natural Sources |journal=Atmospheric Chemistry and Physics |volume=10 |issue=13 |pages=5951–5964 |year=2010 |bibcode=2010ACP....10.5951P |doi=10.5194/acp-10-5951-2010 |doi-access=free}}</ref> According to one study, based on modeled concentrations, pre-[[Anthropocene]] tissue-bound levels in freshwater fish may not have differed markedly from current levels.<ref>{{cite journal |last1=Hope |first1=Bruce K. |last2=Louch |first2=Jeff |title=Pre-Anthropocene Mercury Residues in North American Freshwater Fish |journal=Integrated Environmental Assessment and Management |volume=10 |issue=2 |pages=299–308 |year=2013 |pmid=24458807 |s2cid=205932358 |doi=10.1002/ieam.1500}}</ref> However, based on a comprehensive set of global measurements, the ocean contains about 60,000 to 80,000 tons of mercury from pollution, and mercury levels in the upper ocean have tripled since the beginning of the industrial revolution. Higher mercury levels in shallower ocean waters could increase the amount of the toxicant accumulating in food fish, exposing people to a greater risk of mercury poisoning.<ref>Carl H. Lamborg, Chad R. Hammerschmidt, Katlin L. Bowman, Gretchen J. Swarr, Kathleen M. Munson, Daniel C. Ohnemus, Phoebe J. Lam, Lars-Eric Heimbürger, Micha J. A. Rijkenberg & Mak A. Saito (2014) A global ocean inventory of anthropogenic mercury based on water column measurements, ''Nature'', 512, 65–68, doi:10.1038/nature13563</ref>

==See also==
* [[Canadian Reference Materials]] include some with methylmercury, e.g. DORM
* [[Dimethylmercury]], mercury with a second [[methyl group]]
* [[Ethylmercury]], a related cation
* [[Mercury poisoning]]
* [[Mercury regulation in the United States]]

==References==
{{Reflist|2}}

==External links==
* [https://www.atsdr.cdc.gov/toxfaqs/tfacts46.pdf ATSDR - ToxFAQs: Mercury]
* [https://web.archive.org/web/20020802220747/http://www.atsdr.cdc.gov/toxprofiles/phs46.html ATSDR - Public Health Statement: Mercury]
* [https://web.archive.org/web/20000115113813/http://www.atsdr.cdc.gov/alerts/970626.html ATSDR - ALERT! Patterns of Metallic Mercury Exposure, 6/26/97]
* [https://web.archive.org/web/20030802024248/http://www.atsdr.cdc.gov/MHMI/mmg46.html ATSDR - MMG: Mercury]
* [https://web.archive.org/web/20010718214647/http://www.atsdr.cdc.gov/toxprofiles/tp46.html ATSDR - Toxicological Profile: Mercury]
* [https://web.archive.org/web/20060425193836/http://www.npi.gov.au/database/substance-info/profiles/53.html National Pollutant Inventory - Mercury and compounds Fact Sheet]
* [http://GotMercury.Org Methylmercury-in-fish exposure calculator provided by GotMercury.Org, which uses FDA mercury data with the EPA's calculated safe exposure levels.]
* [http://www.csa.com/discoveryguides/mercury/review.php Methylmercury Contamination in Fish and Shellfish] {{Webarchive|url=https://web.archive.org/web/20131102155148/http://www.csa.com/discoveryguides/mercury/review.php |date=2013-11-02 }}
*[https://www.nytimes.com/2008/01/25/nyregion/25nyc.html?ref=nyregion nytimes.com, Tuna Fish Stories: The Candidates Spin the Sushi]
* [http://www.epa.gov/mercury/ U.S. Environmental Protection Agency's mercury site]
* [http://www.usgs.gov/mercury/ U.S. Geological Survey's mercury site] {{Webarchive|url=https://web.archive.org/web/20131102110310/http://www.usgs.gov/mercury/ |date=2013-11-02 }}
* [https://web.archive.org/web/20090305064902/http://www.ec.gc.ca/mercury/en/index.cfm Environment Canada's mercury site]
* [http://www.hc-sc.gc.ca/hl-vs/iyh-vsv/environ/merc-eng.php Health Canada's mercury site]
* International Conference on Mercury as a Global Pollutant [http://www.mercury2006.org/ 2006-Madison, WI USA] {{Webarchive|url=https://web.archive.org/web/20131104114027/http://www.mercury2006.org/ |date=2013-11-04 }}  [http://www.mercury2009.org/ 2009-Guizhou, China]  [https://web.archive.org/web/20090501161233/http://mercury2011.org/mercury2011/Home.html 2011-Halifax, NS Canada]

{{Mercury compounds}}
{{Monoamine neurotoxins}}

[[Category:Organomercury compounds]]
[[Category:Toxins]]
[[Category:Functional groups]]
[[Category:Methyl complexes]]
[[Category:Mercury(II) compounds]]
[[Category:Monoaminergic neurotoxins]]
[[Category:Aldehyde dehydrogenase inhibitors]]