Monomethylmercury(MMHg)is the most common form of Hg known for its toxicity throughout the world: people are submitted to this toxic exposure through diet and mainly through fish consumption.Hair has been recognized as a good biomarker to evaluate human MMHg contamination.In French Guiana,several studies showed that Amerindian populations present high concentrations of Hg in hair,exceeding several times the WHO safety limit(10 ?g g-1).The use of Hg isotopes to trace processes and sources of Hg in the environment has emerged over the last decade as an interesting alternative method but is still little used in human samples.Our recent studies have demonstrated that Hg isotope signatures in human hair provide qualitative and quantitative information on MMHg sources related to human exposure via diet.The aim of our study(RIMNES Program)is to use the Hg isotope fractionations to trace and quantify the natural and anthropogenic sources in environmental compartments,from the aquatic food chain to human hair of exposed Amerindian communities.One first important result is that Hg concentrations in human hair of communities living along the Oyapock R.,are not in accordance with the Hg contents in sediment and fish of the same areas.Upstream,around Trois Sauts,Hg concentrations in sediment and fishes are lower compared to the Camopi area downstream,while human hair of Wayampis communities are more enriched upstream than in the gold mining area.We observed that 29%of the population living in Camopi(N=60)exceeds the next WHO limit(5 ?g g-1)against 65%in Trois Sauts(N=51),the pristine area.This variation can be attributed to differences in their dietary habits,upstream communities eating more local freshwater fish.These differences are confirmed with the anomaly variations of Hg stable isotopes: D201Hg in hair of women living upstream is significantly different from D201Hg of women living downstream in Camopi.An enrichment of~+2‰ for d202Hg without D201Hg change between local fish species and Camopi womens hair confirms this hypothesis.On the contrary,men living in Trois Sauts and in Camopi show an isotopic signature nearest from marine fish,suggesting the consumption of supplementary Hg food sources such as tuna fish in can for example.