Editing Methylmercury (section)

==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>