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Methylmercury is an organic form of the heavy metal mercury (follow the link to the main article in Wikipedia). This page is about environmental health issues of methylmercury.

Biological effects

Mercury is toxic in all of its forms[1], MeHg being the greatest concern to human health due to its high biomagnification potential. Humans are primarily exposed to MeHg through their diet. Moreover, in most foodstuffs mercury is dominantly in its inorganic form, leaving fish and fish products the dominant source of the toxic MeHg in the diet[2]. MeHg binds into proteins and is thus significantly distributed into edible parts (muscles and fillet) in fish. From fish MeHg is readily absorbed and distributed throughout the human body and it easily crosses the placenta and consequently accumulates in the foetus[3]. Following in utero exposure, nervous system and foetal brain are the principal target tissues for the health effects of MeHg, due to the MeHg’s high binding capacity to proteins and concomitant high requirement for protein synthesis in the foetal brain. It is suggested that methylmercury exposure affects the adult cardiovascular system. However, the data for these effects is insufficient for a quantitative analysis[4].

The effects of MeHg on adults differ both qualitatively and quantitatively from the effects seen after prenatal or early postnatal exposures. The general population does not face a significant health risk from a moderate MeHg exposure. However, clinical and epidemiological evidence indicate that prenatal life is much more sensitive to the toxic effects of MeHg than adult life. For instance, a report by [5] showed higher mercury concentrations in umbilical cord blood than the mercury concentration in the blood of the pregnant mother. This supports the idea that prenatal period is susceptible time for mercury poisoning.

Especially noteworthy from a risk management point of view is that MeHg -caused severe developmental and behavioral deficits on foetal and infant outcome can appear without any obvious symptoms of Hg poisoning in mothers during pregnancy. MeHg affects normal neuronal development and can lead to altered brain architectures (e.g. heterotopic cells, and decreased brain size) in children. Studies conducted after the mass outbreak of MeHg poisoning in Iraq, where people were exposed to MeHg through consumption of bread loaves prepared from wheat seed grain treated with an MeHg-containing fungicide, found that maternal hair mercury concentrations as low as 10-20 µg/g during pregnancy are associated with the lowest level (5%) risks of first MeHg-caused symptoms to the children. Consequently, it has been estimated that a hair mercury concentration 50 µg/g poses an equivalent risk for the adults. [6]

Consumption recommendations

In 1995 U.S. Environmental Pollution Agency (EPA) derived a reference dose (RfD) 1.0 x 10-4 mg per kilogram of bodyweight for MeHg, and total blood mercury concentration for women of childbearing age should remain lower than 5.8 µg/L[7]. Pregnant women are advised to avoid eating large predatory fish species such as pike.

  • The European Commission has recommended the following[8].

See also


  1. Gupta and Sastry 1999
  2. European Commission 2008
  3. Diéz et al 2008
  4. Poulin and Gibb 2008
  5. Vahter et al 2000
  6. McElhatton 2000, WHO 1990
  7. Schober et al 2003
  8. European Commission recommendation for methyl mercury. European Commission, Sanco, Directorate E - Safety of the Food chain. 21 April 2008 (D/530286)