Géochimie du mercure dans le continuum de la retenue de Petit-Saut et de l'estuaire du Sinnamary, Guyane française Auteur(s) : Muresan Paslaru, Bogdan Éditeur(s) : Université Bordeaux 1 Résumé : The mercury cycle was explored in the Petit-Saut reservoir / Sinnamary Estuary continuum in French Guiana. Main processes involve (i) photo-induced reduction, (ii) adsorption and desorption at the particle surfaces, (iii) methylating bacterial activity, (iv) precipitation and dissolution of iron oxyhydroxides and sulfides. Sources of mercury to the Petit-Saut reservoir consist of the partly impacted river-tributaries, the atmospheric deposition and the flooded soils or vegetation. Once into the reservoir, divalent mercury undergoes a large spectrum of transformations including speciation and phase changes. We, here, probe these processes and demonstrate that the Petit-Saut reservoir behaves as a privileged site for atmospheric recycling and in situ methylation. At the air / water interface, the mercury evasion exceeds by 50 % the direct atmospheric deposition. The in situ monomethylmercury (MMHg) production mostly occurs at the water-column chemocline and near the benthic interface. It reaches, for the whole reservoir, 8.1 moles yr-1 which corresponds to a 0.06 % d-1 methylation rate. We calculated that the 2003/04 period MMHg outputs from the reservoir to the Sinnamary Estuary averaged 13.5 moles yr-1 while the inputs were 5.4 moles yr-1. The dynamic Sinnamary Estuary is the genuine geochemical reactor of the continuum. There, the divalent mercury undergoes rapid yet profound partitioning among phases, recycling to the atmosphere and methylation processes. Those mostly originate from the long-scale oxygen paucity of the dam discharged waters. The expression of marked redox gradients and the intense organic matter turnover enhance the production of methylable inorganic mercurial species and tend to favor the sulfate reducing bacteria (methylating agents) activity. As a result, the dynamic Sinnamary Estuary exports 60 % more MMHg than it does import: 27 versus 17 moles yr-1. Further at large, in the saline estuary, we determined: (i) a non conservative behavior of dissolved (< 0.2 µm) mercury, (ii) a lowering of the mercury level of particles during mixing with the Amazon plume and (iii) a gradual dilution of the estuarine mercury concentrations by oceanic waters. La retenue de Petit-Saut et, à l'aval, l'estuaire du Sinnamary sont deux centres d'altération du cycle naturel du mercure. Les processus sont, entre autres, (i) la photoréduction, (ii) la sorption / désorption en surface des particules, (iii) l'activité méthylante des bactéries, (iv) la dissolution / précipitation des oxyhydroxydes et des sulfures de fer. Les sources de mercure vers la retenue sont variées. Elles regroupent, en premier lieu, les affluents (partiellement orpaillés), l'atmosphère, les sols et la végétation ennoyés. Dans la colonne d'eau, les formes divalentes du mercure subissent un train complet de transformations couplant changements de phase et de spéciation. Nos résultats illustrent ces processus et démontrent que la retenue constitue un site privilégié de recyclage vers l'atmosphère et de méthylation. A l'interface air / eau, les exports en mercure de la retenue excèdent de 50 % le dépôt atmosphérique. La production endogène de monométhylmercure (MMHg) a lieu dans des sites particuliers : la chemocline et l'interface benthique. Elle atteint pour l'ensemble de la retenue 8,1 moles a-1 soit un taux de méthylation de 0,06 % j-1. On estime que la retenue exporte vers l'estuaire du Sinnamary 13,5 moles a-1 de MMHg alors qu'elle n'importe que 5,4 moles a-1. L'estuaire dynamique du Sinnamary constitue le véritable réacteur chimique du système fonctionnant en liaison avec celui de la retenue. Le mercure y décrit un cycle rapide aux processus de partition, de recyclage et de méthylation marqués. Ces processus résultent de l'oxygénation incomplète et durable des masses d'eau anoxiques exportées par la retenue de Petit-Saut. L'expression de gradients rédox prononcés conjuguée à un intense recyclage de la matière organique y favorise la production de formes méthylables de mercure ainsi que l'activité des bactéries sulfatoréductrices (agents de la méthylation). C'est pourquoi, l'estuaire dynamique du Sinnamary exporte 60 % plus de MMHg qu'il n'importe : 27 contre 17 moles a-1. Plus en aval, dans l'estuaire salin, nous avons mis en évidence : (i) un comportement non conservatif du mercure dissous, (ii) un appauvrissement du mercure des particules suite au mélange avec le panache de l'Amazone et (iii) une dilution des concentrations par les masses d'eau océaniques. Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/2006/these-1508.pdf http://archimer.ifremer.fr/doc/00000/1508/ | Partager Voir aussi Atmosphere Estuary Reservoir French Guiana Methylmercury Mercury Atmosphère Estuaire Retenue Guyane française Télécharger |
Economic evaluation of health consequences of prenatal methylmercury exposure in France. Auteur(s) : Pichery, Céline Bellanger, Martine Zmirou-Navier, Denis Fréry, Nadine Cordier, Sylvaine Roue-LeGall, Anne Hartemann, Philippe Grandjean, Philippe Auteurs secondaires : École des Hautes Études en Santé Publique [EHESP] (EHESP) Institut de recherche, santé, environnement et travail [Rennes] (Irset) ; Université d'Angers (UA) - Université des Antilles et de la Guyane (UAG) - Université de Rennes 1 (UR1) - École des Hautes Études en Santé Publique [EHESP] (EHESP) - Institut National de la Santé et de la Recherche Médicale (INSERM) - Structure Fédérative de Recherche en Biologie et Santé de Rennes ( Biosit : Biologie - Santé - Innovation Technologique ) Département santé environnement ; Institut de Veille Sanitaire Service de Santé Publique ; Centre Hospitalier Régional Universitaire de Nancy (CHRU Nancy) Nutrition-Génétique et Exposition aux Risques Environnementaux (NGERE) ; Institut National de la Santé et de la Recherche Médicale (INSERM) - Université de Lorraine (UL) Institute of Public Health ; UNIVERSITY OF SOUTHERN DENMARK Department of Environmental Health ; Harvard School of Public Health Éditeur(s) : HAL CCSD BioMed Central Résumé : International audience UNLABELLED: ABSTRACT: BACKGROUND: Evidence of a dose-response relationship between prenatal exposure to methylmercury (MeHg) and neurodevelopmental consequences in terms of IQ reduction, makes it possible to evaluate the economic consequences of MeHg exposures. OBJECTIVE: To perform an economic evaluation of annual national benefits of reduction of the prenatal MeHg exposure in France. METHODS: We used data on hair-Hg concentrations in French women of childbearing age (18-45 years) from a national sample of 126 women and from two studies conducted in coastal regions (n = 161and n = 503). A linear dose response function with a slope of 0.465 IQ point reduction per μg/g increase in hair-Hg concentration was used, along with a log transformation of the exposure scale, where a doubling of exposure was associated with a loss of 1.5 IQ points. The costs calculations utilized an updated estimate of €2008 17,363 per IQ point decrement, with three hypothetical exposure cut-off points (hair-Hg of 0.58, 1.0, and 2.5 μg/g). RESULTS: Because of higher exposure levels of women in coastal communities, the annual economic impacts based on these data were greater than those using the national data, i.e. € 1.62 billion (national), and € 3.02 billion and € 2.51 billion (regional), respectively, with the linear model, and € 5.46 billion (national), and € 9.13 billion and € 8.17 billion (regional), with the log model, for exposures above 0.58 μg/g. CONCLUSIONS: These results emphasize that efforts to reduce MeHg exposures would have high social benefits by preventing the serious and lifelong consequences of neurodevelopmental deficits in children. ISSN: 1476-069X inserm-00769338 http://www.hal.inserm.fr/inserm-00769338 http://www.hal.inserm.fr/inserm-00769338/document http://www.hal.inserm.fr/inserm-00769338/file/1476-069X-11-53.pdf DOI : 10.1186/1476-069X-11-53 | Partager |
Monomethylmercury sources in a tropical artificial reservoir Auteur(s) : Muresan, B Cossa, Daniel Richard, Sophie Dominique, Y Éditeur(s) : Elsevier Résumé : The distribution and speciation of mercury (Hg) in the water column, the inputs (wet deposition and tributaries) and the outputs (atmospheric evasion and outlet) of an artificial partially anoxic tropical lake (Petit-Sa-Lit reservoir, French Guiana) were investigated oil a seasonal basis in order to appraise the cycling and transformations of this metal. The total mercury (HgT) concentrations in the oxygenated epilimnetic waters averaged 5 +/- 3 pmol L-1 in the unfiltered samples (HgTUNF) and 4 +/- 2 pmol L-1 in the dissolved (HgTD) phase (< 0.45 mu m). On average, the monomethylmercury (MMHg) constituted 8%, 40%, and 18% of the HgT in the dissolved phase, tile particulate suspended matter and in tile unfiltered samples, respectively. Covariant elevated concentrations of particulate MMHg and chlorophyll a in the epilimnion suggest that phytoplankton is ail active component for the MMHg transfer in tile lake. In the anoxic hypolimnion the HgTUNF averages 13 +/- 6 pmol L-1 and tile HgTD 8 +/- 4 pmol L-1. The averages of MMHgP and MMHgD in hypolimnetic waters were two and three times the corresponding values of the epilimnion, 170 +/- 90 pmol g(-1) and 0.9 +/- 0.5 pmol L-1, respectively. In the long dry and wet seasons, at the flooded forest and upstream dam sampling stations, the vertical profiles of MMHgD concentrations accounted for two distinct maxima: one just below the oxycline and the other near the benthic interface. Direct wet atmospheric deposition accounted for 14 moles yr(-1) HgTUNF, with 0.7 moles yr(-1) as MMHgUNF, while circa 76 moles yr(-1) of HgTUNF, with 4.7 moles yr(-1) as MMHgUNF, coming from tributaries. Circa 78 moles (similar to 17% as MMHg) are annually exported through tile dam, while 23 moles yr(-1) of Hg-0 evolve in the atmosphere. A mass balance calculation suggests that the endogenic production of MMHgUNF attained 8.1 moles yr(-1), corresponding to a methylation rate of 0.06% d(-1). As a result, tile Petit-Saut reservoir is a large man-made reactor that has extensively altered mercury speciation in favor of methylated species. Applied Geochemistry (0883-2927) (Elsevier), 2008-05 , Vol. 23 , N. 5 , P. 1101-1126 Droits : 2008 Elsevier Ltd All rights reserved. http://archimer.ifremer.fr/doc/2008/publication-4198.pdf DOI:10.1016/j.apgeochem.2007.11.006 http://archimer.ifremer.fr/doc/00000/4198/ | Partager |
Amazonian former gold mined soils as a source of methylmercury: Evidence from a small scale watershed in French Guiana Auteur(s) : Guedron, Stephane Grimaldi, Michel Grimaldi, Catherine Cossa, Daniel Tisserand, Delphine Charlet, Laurent Éditeur(s) : Pergamon-elsevier Science Ltd Résumé : Total mercury (HgT) and monomethylmercury (MMHg) were investigated in a tropical head watershed (1 km(2)) of French Guiana. The watershed includes a pristine area on the hill slopes and a former gold mined flat in the bottomland. Concentrations of dissolved and particulate HgT and MMHg were measured in rain, throughfall, soil water and at three points along the stream. Samples were taken in-between and during 14 storm events at the beginning and middle of the 2005 and 2006 rainy seasons. Dissolved and particulate HgT concentrations in the stream slightly increased downstream, while dissolved and particulate MMHg concentrations were low at the pristine sub-watershed outlet (median = 0.006 ng L-1 and 1.84 ng g(-1), respectively) and sharply increased at the gold mined flat outlet (median = 0.056 ng L-1 and 6.80 ng g(-1), respectively). Oxisols, which are dominant in the pristine area act as a sink of HgT and MMHg from rain and throughfall inputs. Hydromorphic soils in the flat are strongly contaminated with Hg (including Hg droplets) and their structure has been disturbed by former gold-mining processes, leading to multiple stagnant water areas where biogeochemical conditions are favorable for methylation. In the former gold mined flat high dissolved MMHg concentrations (up to 0.8 ng L-1) were measured in puddles or suboxic soil pore waters, whereas high dissolved HgT concentrations were found in lower Eh conditions. Iron-reducing bacteria were suggested as the main methylators since highest concentrations for dissolved MMHg were associated with high dissolved ferrous iron concentrations. The connection between saturated areas and stagnant waters with the hydrographic network during rain events leads to the export of dissolved MMHg and HgT in stream waters, especially at the beginning of the rainy season. As both legal and illegal gold-mining continues to expand in French Guiana, an increase in dissolved and particulate MMHg emissions in the hydrographic network is expected. This will enhance MMHg bio-amplification and present a threat to local populations, whose diet relies mainly on fish. Water Research (0043-1354) (Pergamon-elsevier Science Ltd), 2011-04 , Vol. 45 , N. 8 , P. 2659-2669 Droits : 2011 Elsevier Ltd All rights reserved. http://archimer.ifremer.fr/doc/00035/14628/12134.pdf DOI:10.1016/j.watres.2011.02.022 http://archimer.ifremer.fr/doc/00035/14628/ | Partager Voir aussi Mercury Methylmercury Tropical watershed Gold placers Stream water Oxisols Hydromorphic soils Télécharger |