Troubles de l’attention, hyperactivité : la piste du mercure et du plomb / Kids exposed to mercury or lead more likely to have ADHD symptoms, Canadian study finds

Grâce à des analyses du sang ombilical, les chercheurs du Centre de recherche du CHU de Québec et de l’Université Laval (Canada), ont mesuré l’exposition prénatale au mercure de la population inuit du Nunavik (photo George-Flammer), une région située dans le Nord du Québec et autrefois appelée le Nouveau Québec. Pourquoi ces populations précisément ? Parce qu’elles sont particulièrement exposées au mercure, du fait de leur forte consommation de chair provenant de mammifères marins. Résultat, les enfants dont le sang de cordon présentait les concentrations les plus élevées en mercure ont vu leur risque de TDAH multiplié par trois, en comparaison des autres. Selon l'Organisation mondiale de la Santé (OMS), «  l’exposition au méthyl-mercure in utero peut résulter de la consommation par la mère, de poissons ou de crustacés ». C’est pourquoi en France, l’Agence nationale de Sécurité sanitaire de l’Alimentation de l’Environnement et du Travail (ANSES) recommande aux femmes enceintes et aux enfants de moins de 30 mois « d’éviter de consommer les poissons les plus contaminés : requins, lamproies, espadons, marlins… »."

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In english (source Environmental Health News):

Children exposed to higher levels of mercury or lead are three to five times more likely to be identified by teachers as having problems associated with Attention Deficit Hyperactivity Disorder, according to a scientific study published today. The study, of Inuit children living in Arctic Canada, is the first to find a high rate of attention-deficit symptoms in children highly exposed to mercury in the womb. In addition, the Inuit children more often had hyperactivity symptoms if they were exposed to the same low levels of lead commonly found in young U.S. children. Laval University scientist Gina Muckle said the findings are important because they show for the first time that the effects of mercury in children are not just subtle, but are actually noticeable to teachers. They “may be clinically significant and may interfere with learning and performance in the classroom,” the study says. For lead, the school teachers reported much more frequent ADHD symptoms at levels far below the CDC's newly developed health guideline. Dr. Bruce Lanphear, of Simon Fraser University in Vancouver, said evidence is mounting that toxic compounds are “shifting children’s behavior...There seem to be a whole host of different toxicants that are associated with ADHD." One of the most intriguing findings was that mercury was linked to attention deficits while lead was associated with hyperactivity. The difference may be the timing of the exposures: in the womb for mercury and during childhood for lead. The findings "suggest the brain may be sensitive to different environmental chemicals at different times in development," said Harvard epidemiologist Joe Braun.

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