Laboratoire d’écophysiologie et écotoxicologie des systèmes aquatiques (Leesa), UMR CNRS 5805, Université Bordeaux 1, Place Dr Peyneau, 33120 Arcachon France, Institut national de la santé et de la recherche médicale (Inserm) U 625, Campus de Beaulieu, Université de Rennes 1, 35042 Rennes cedex France, Institut de veille sanitaire (InVS), Département Santé environnement, 12, rue du Val d’Osne, 94415 Saint Maurice cedex
- Key words: ecosystem, mercury, fishes, food chain, French Guiana, mercury poisoning, mercury, nervous system, mining, occupational exposure
- Page(s) : 167-79
- Published in: 2006
Gold mining in French Guiana causes mercury pollution through two pathways: discharge of the elemental form of the metal (Hg°), used as an amalgamation agent, and erosion of primeval soils from the Amazon basin, naturally rich in inorganic mercury (HgII). Besides occupational exposure via inhalation of gaseous Hg° (burning amalgams, gold refining), human populations are contaminated by eating fish, in particular, carnivorous or piscivorous species. These species accumulate high mercury concentrations, exceeding the safety level of 0.5 µgHg/g (fresh wt) because of the biomagnification along the food chain of mercury’s organic form, monomethylmercury (MMHg). MMHg is the product of the methylation of HgII by bacteria in anoxic aquatic environments (sediments, natural or artificial reservoirs, flood zones, etc.). Cumulative trophic transfers between prey and predators can create MMHg concentrations in the muscle tissue of carnivorous fish that are several tens of millions of times greater than those measured in the dissolved fraction of the water column. Thus, human populations that consume these fish on a daily basis and in large quantities have high mercury burdens, as confirmed by mercury levels in hair samples, which exceed the level recommended by WHO, currently 10 µgHg/g. These populations include Amerindian communities in the upper Maroni region in French Guiana. Epidemiological studies of psychomotor development carried out among their children show a slight deterioration in performance in motor coordination and visuospatial organisation. These results are consistent with data from several other countries for similar levels of exposure. Health authorities are currently working to reduce further contamination and to provide information for the Amerindian communities, especially for pregnant and nursing mothers and young children, to modify their eating habits and persuade them to eat the least contaminated fish species.