title: Synergistic effects of mining and urban effluents on the level and distribution of methylmercury in a shallow aquatic ecosystem of the Bolivian Altiplano.
abstract: Lake Uru Uru (3686 m a.s.l.) located in the Bolivian Altiplano region receives both mining effluents and urban wastewater discharges originating from the surrounding local cities which are under rapid development. We followed the spatiotemporal distribution of different mercury (Hg) compounds and other metal(oid)s (e.g., Fe, Mn, Sb, Ti and W) in both water and sediments during the wet and dry seasons along a north-south transect of this shallow lake system. Along the transect, the highest Hg and metal(oid) concentrations in both water and sediments were found downstream of the confluences with mining effluents. Although a dilution effect was found for major elements during the wet season, mean Hg and metal(oid) concentrations did not significantly differ from the dry season due to the increase in acid mine drainage (AMD) inputs into the lake from upstream mining areas. In particular, high filtered (<0.45 μm) mono-methylmercury (MMHg) concentrations (0.69 ± 0.47 ng L-1) were measured in surface water representing 49 ± 11% of the total filtered Hg concentrations (THgF) for both seasons. Enhanced MMHg lability in relation with the water alkalinity, coupled with abundant organic ligands and colloids (especially for downstream mining effluents), are likely factors favoring Hg methylation and MMHg preservation while inhibiting MMHg photodegradation. Lake sediments were identified as the major source of MMHg for the shallow water column. During the dry season, diffusive fluxes were estimated to be 227 ng m-2d-1for MMHg. This contribution was found to be negligible during the wet season due to a probable shift of the redox front downwards in the sediments. During the wet season, the results obtained suggest that various sources such as mining effluents and benthic or macrophytic biofilms significantly contribute to MMHg inputs in the water column. This work demonstrates the seasonally dependent synergistic effect of AMD and urban effluents on the shallow, productive and evaporative high altitude lake ecosystems which promotes the formation of natural organometallic toxins such as MMHg in the water column.
authors.affiliation: Géosciences Environnement Toulouse, UMR5563, IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France and Laboratorio de Hidroquímica, Instituto de Investigaciones Químicas, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, Casilla 3161, La Paz, Bolivia. stephane.guedron@ird.fr.
authors.forename: L
authors.initials: L
authors.lastname: Alanoca
authors.affiliation: Laboratorio de Hidroquímica, Instituto de Investigaciones Químicas, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, Casilla 3161, La Paz, Bolivia. stephane.guedron@ird.fr and Institut de Recherche pour le Développement, ISTerre, UMR 5275, F-38041 Grenoble, France and Université Grenoble Alpes, Institut des Sciences de la Terre (ISTerre), F-38041 Grenoble, France.
authors.forename: S
authors.initials: S
authors.lastname: Guédron
authors.affiliation: Laboratoire de Chimie Analytique Bio-inorganique et Environnement (LCABIE), Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc Pau Pyrénées, 2, av. P. Angot, 64053 Pau Cedex 9, France and Laboratorio de Calidad Ambiental (LCA), Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, Casilla 3161, La Paz, Bolivia.
authors.forename: D
authors.initials: D
authors.lastname: Amouroux
authors.affiliation: Géosciences Environnement Toulouse, UMR5563, IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France.
authors.forename: S
authors.initials: S
authors.lastname: Audry
authors.affiliation: Laboratoire de Chimie Analytique Bio-inorganique et Environnement (LCABIE), Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc Pau Pyrénées, 2, av. P. Angot, 64053 Pau Cedex 9, France.
authors.forename: M
authors.initials: M
authors.lastname: Monperrus
authors.affiliation: Laboratoire de Chimie Analytique Bio-inorganique et Environnement (LCABIE), Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux, IPREM UMR 5254 CNRS, Université de Pau et des Pays de l'Adour, Hélioparc Pau Pyrénées, 2, av. P. Angot, 64053 Pau Cedex 9, France.
authors.forename: E
authors.initials: E
authors.lastname: Tessier
authors.affiliation: Géosciences Environnement Toulouse, UMR5563, IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France.
authors.forename: S
authors.initials: S
authors.lastname: Goix
authors.affiliation: Laboratorio de Calidad Ambiental (LCA), Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, Casilla 3161, La Paz, Bolivia.
authors.forename: D
authors.initials: D
authors.lastname: Acha
authors.affiliation: Géosciences Environnement Toulouse, UMR5563, IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France.
authors.forename: P
authors.initials: P
authors.lastname: Seyler
authors.affiliation: Géosciences Environnement Toulouse, UMR5563, IRD UR 234, Université Paul Sabatier, 14 Avenue Edouard Belin, 31400 Toulouse, France and Laboratorio de Calidad Ambiental (LCA), Instituto de Ecologia, Universidad Mayor de San Andres, Campus Universitario de Cota Cota, Casilla 3161, La Paz, Bolivia.
authors.forename: D
authors.initials: D
authors.lastname: Point
mesh_terms: D001838:Bolivia; D002947:Cities; D017753:Ecosystem; D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry; D060106:Lakes / Q000737:chemistry*; D008628:Mercury / Q000032:analysis*; D019216:Metals, Heavy / Q000032:analysis*; D008767:Methylmercury Compounds / Q000032:analysis*; D008906:Mining; D012621:Seasons; D062065:Wastewater / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008628:Mercury; D019216:Metals, Heavy; D008767:Methylmercury Compounds; D062065:Wastewater; D014874:Water Pollutants, Chemical