Since 1850,French Guiana is subjected to intense gold-mining,which represents the second largest export activity.As a large part of these mining activities is illegal,amalgamation of gold with liquid Hg(0)is the main exploitation process contrarily to legal gold-mining.This study aims to participate to the Hg geochemical cycle comprehension in the Amazon region but also to estimate the anthropogenic part of Hg sources in the hydrosystem.Total mercury concentration,speciation and isotopic fractionations in hair,sediments,water and fish are analyzed along the Oyapock River,in both pristine and mining areas.In this region,we can distinguish three sources of Hg: i)natural rock weathering and soil erosion of the drainage basin,ii)direct liquid Hg(0)released by illegal amalgamation and iii)Hg-rich soils intensive erosion during mining activities.Hg0 can be oxidized in HgⅡ which can be methylated in water by bacterial activity and bioaccumulated in the aquatic food-chain.In terms of mass dependent fractionation(MDF)and mass independent fractionation(MIF),Hg isotopic signatures of natural Hg(uncontaminated sediments from pristine area)and anthropogenic liquid Hg0 are different and allow us to trace mercury sources in the different compartments.Hg isotopic signatures of sediments sampled in the mining area appear to be binary mixtures between two end-members: natural geochemical background and anthropogenic mercury measured from liquid mercury sampled in the area.In small catchments of the Camopi R.,we calculated that Hg released from gold mining activities reached almost 50%of the total Hg measured in surface sediments.Regarding the impact on human health of the high Hg impregnation of the environment,surprisingly,human hair from communities living in the pristine area upstream show higher Hg concentrations than the same Amerindian communities living in the mining area.Nutrition inquiries were conducted on native population of both pristine and contaminated areas to relate their Hg exposure with their food habits and the MMHg contents and isotopic fractionations of the fish species caught in the Oyapock River by the local population.For the first time,Hg speciation and stable isotopes fractionation study in French Guiana allows us to determine the real impact of gold mining on native population and their environment and resources.