These episodes resulted in neurological symptoms including paresthesias, loss of physical coordination, difficulty in speech, 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; 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 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.
According to one study, based on modeled concentrations, pre-Anthropocene tissue-bound levels in fish may not have differed markedly from current levels. 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. 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
External links
ATSDR - ToxFAQs: Mercury
ATSDR - Public Health Statement: Mercury
ATSDR - ALERT! Patterns of Metallic Mercury Exposure, 6/26/97
ATSDR - MMG: Mercury
ATSDR - Toxicological Profile: Mercury
National Pollutant Inventory - Mercury and compounds Fact Sheet
Methylmercury-in-fish exposure calculator provided by GotMercury.Org, which uses FDA mercury data with the EPAs calculated safe exposure levels. Methylmercury Contamination in Fish and Shellfish Archived 2013-11-02 at the Wayback Machine
nytimes.com, Tuna Fish Stories: The Candidates Spin the Sushi
U.S. Environmental Protection Agencys mercury site
U.S. Geological Surveys mercury site Archived 2013-11-02 at the Wayback Machine
Environment Canadas mercury site
Health Canadas mercury site
International Conference on Mercury as a Global Pollutant 2006-Madison, WI USA  2009-Guizhou, China  2011-Halifax, NS Canada