L'episode d'intoxication grave a Minamata au Japon dans les annees 1950 a mis en evidence la neurotoxicite du methylmercure notamment pour le foetus. La contamination par le methylmercure est planetaire, rendant particulierement vulnerables les populations dont l'alimentation inclut une forte consommation de poisson. Des atteintes neurologiques plus moderees (retard a la marche entre autres) ont ete observees lors d'une exposition accidentelle en Irak a des concentrations de mercure total dans le cheveu maternel de l'ordre de 10 μg/g. Les etudes plus recentes dans des populations exposees de facon chronique en raison de leur consommation de poisson importante donnent des resultats assez coherents, a l'exception notable de l'etude des iles Seychelles. Les differents outils d'evaluation utilises montrent des deficits dans les scores sur differents tests de developpement neuropsychologique chez l'enfant a des niveaux aussi bas que 4 μg/g dans le cheveu maternel. La norme actuelle la plus restrictive de l'Environmental Protection Agency (EPA) aux Etats-Unis recommande de limiter l'apport hebdomadaire de methylmercure a 42 μg, en particulier chez les femmes enceintes. Cette norme est aisement respectee en France metropolitaine, mais probablement depassee dans certaines populations des territoires d'outremer.
The severe toxicity of methylmercury-contaminated fish which occurred in Minamata (Japan) in the 1950s has revealed the neurotoxic potential of methylmercury and the specific sensitivity of the foetus. Contamination by methylmercury is worldwide, thereby making fish-eating populations particularly vulnerable to its neurotoxic action.Milder neurologic consequences (retarded walking for instance) have been observed in a subsequent toxicity study in Iraq at levels above 10 μg/g in maternal hair. More recent studies in chronically exposed fish-eating populations show coherent results except for the study in the Seychelles Islands. Deficits in the scores on different neuropsychological tests have been observed at levels as low as 4 μg/g in maternal hair.The most conservative standard currently proposed by the US Environmental Protection Agency recommends that the weekly intake of methylmercury be limited to 42 μg, especially among pregnant women. This recommendation is easy to follow in metropolitan France, but very likely to be exceeded in some isolated populations in remote French territories.