Editing Methylmercury (section)

===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.