While some mercury occurs naturally in the environment for example from volcanic eruptions or forest fires, most is generated by burning fossil fuels. Marine and fresh water species bioconcentrate MeHg; consequently the main source of exposure for humans is from eating fish.

A team of researchers from across Europe used the DEMOCOPHES study of exposure to environmental chemicals to assess the impact of MeHg on humans. Hair samples of child-mother pairs, collected from 17 European countries, demonstrated that, as a lower estimate, 1,866,000 children are born in Europe exposed to toxic levels of MeHg. 232,000 of these are exposed to hazardous levels, five times higher. But not every child in Europe is equally at risk. When analysed per country, children born in Portugal and Spain were the most exposed to MeHg, and Hungary the least.

Exposure to MeHg in humans affects brain development, resulting in a lower IQ, and consequently a lower earning potential. The long term cost to society can be calculated as lifetime earning loss per person, although this estimate does not take into account other aspects of brain toxicity or risks of cardiovascular disease in adults.

Prof Philippe Grandjean explained, "If we convert the effects of MeHg on developing brains into IQ points then the benefits of controlling MeHg pollution equates to 700,000 IQ points per year and monetary benefits of €8,000 to €9,000 million per year for the whole of the EU. Exposure abatement would mainly benefit southern Europe ."

Once MeHg is formed, it cycles though the environment for thousands of years, exposing humans and other species to potentially toxic levels for generations. Commenting on the research Dr Elsie Sunderland said, "Mitigating the harm caused by methylmercury requires global-scale cooperation on policies and source reductions. Negotiations by the United Nations Environment Program are currently underway to address mercury emission levels."