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(48-05) A systemic approach to mercury biomagnification in rivers affected by goldmining activities (French Guiana). BOUDOU, Alain*,1, MAURY-BRACHET, Régine1, COQUERY, Marina2, DAUTA, Catherine3, DURRIEU, Gilles1, 1 LEESA, University Bordeaux 1/CNRS, Arcachon, France2 INERIS,Analytical Dept, Verneuil-en-Halatte, France3 CESAC, University Toulouse III, Toulouse, France ABSTRACT- Since the late eighties, high mercury levels were reported in carnivorous fish species from rivers and lakes in the Amazon basin, with excessive exposure of human populations and significant alterations in nervous system functions. It is commonly accepted that the main source of contamination is the release of elemental mercury by gold mining activities, but erosion of soils naturally rich in Hg may constitutes an anthropogenic process increasing the loading of Hg to adjacent river systems. Here we present a systemic study of Hg distribution within the main abiotic and biotic compartments of a small river in French Guiana with gold mining activities on its watershed. Total Hg and methylmercury (MeHg) were analyzed in the water column (dissolved and particulate phases) and sediments, jointly with classical physico-chemical parameters. Bioaccumulation levels were determined on a large number of aquatic species - rooted macrophytes, periphyton, plant supplies from the river banks, pelagic and benthic invertebrates, fish - according to their position within the trophic networks (herbivorous, detritivorous, omnivorous, benthivorous, carnivorous, piscivorous). Four major results emerge from this systemic approach: (i) 80 % of Hg was associated to the particulate fraction in the water column, with very low concentrations in the dissolved phase (3-8 ng/L for total Hg, with around 1 % of MeHg); (ii) extremely marked differences were observed between fish contamination levels according to their food regime, the average ratio between [Hg]piscivorous/[Hg]herbivorous being close to 500; (iii) very low Hg concentrations were measured at the basis of the food webs, except in periphyton samples which represent a important site for HgII methylation; (iv) all the top predator species were over the WHO safety limit of 0.5 mg/kg (fresh weight), with estimated BAF ([Hg]muscle/[Hg]water) higher than 60 millions in piscivorous fish, on the MeHg basis. Key words: mercury, goldmining, biomagnification, freshwater systems |
