Six important studies of the effects of methyl mercury on human health 

1.    Minamata

This is probably the most famous incident of environmental poisoning since it was also one of the first. Minamata Bay, Japan, 1957 study of poisoning by methylmercury that was directly discharged into Minamata Bay by Chisso Company, Ltd. "Strange phenomena" were observed as cats, fish, and birds developed unusual symptoms and died. Fifty-four people died from methylmercury poisoning in this incident. Minamata Bay brought the dangers of methylmercury poisoning into international focus. The health effects of high levels of methylmercury consumption have been studied in great detail but the lack of scientifically rigorous information from the early stages limits what can be learned.

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2.    Iraq

Study of 1972 incident when seed grain treated with methylmercury was used to bake bread. Over 6,000 people were admitted to hospitals and over 400 people died in this unfortunate incident. Health effects were studied in detail; until recently, our current reference concentration for determining risk was based on studies at this incident.

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3.    Seychelles Islands

Principal Investigator: T. Clarkson

This was a longitudinal study of children evaluated at 6, 19, and 29 months of age who retested at about age 5.5 years. Physical, neurological, and psychological examinations were completed at each evaluation. The results did not show significant impacts of methyl mercury. This is contra to the Faroe Island study. This discrepancy was central to the major re-assessment of the impact of methyl mercury (Toxicological Effects of Mercury)

(An Overview of Human Studies on CNS Effects of Methylmercury, Roberta White, Philippe Grandjean, and Pal Weihe, as published in National Forum on Mercury in Fish: Proceedings, USEPA Office of Water, June 1995. EPA 823-R-95-002)

4.    Faroe Islands

Principal Investigator: P. Weihe

This investigation examines the relationship between prenatal exposure to methylmercury and measures of central nervous system function 7 years later. The results confirmed that some neurobehavioral dysfunction is related to maternal seafood intake during pregnancy. This study is now essentially complete and now forms a fundamental basis for the re-assessment of the risks from methyl  mercury. (see Toxicological Effects of Mercury)

(An Overview of Human Studies on CNS Effects of Methylmercury, Roberta White, Philippe Grandjean, and Pal Weihe, as published in National Forum on Mercury in Fish: Proceedings, USEPA Office of Water, June 1995. EPA 823-R-95-002)

5.    Canadian Study of 40,000

Principal Investigators: Brian Wheatley and Sylvain Paradis

This investigation studies 38,571 indigenous people in 514 native communities across Canada. Methylmercury levels were tested during a twenty-year time period, 1970 to 1992. No definite diagnosis of methylmercury poisoning was made for individuals with greater than 100 ppb in blood. Over the twenty-year time period, there was a general downward trend of methylmercury concentration in individuals with over 20 ppb in their blood or hair equivalent. Further analysis will be done to assess temporal trends by community and individuals, relationships between maternal and fetal levels of methylmercury, and, if possible, a re-assessment of potential risk.

(Exposure of Canadian Aboriginal Peoples to Methylmercury, Brian Wheatley and Sylvain Paradis, Water Air and Soil Pollution 80: 3-11, 1995. )