Browsing by Autor "Emmanuel Tessier"

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Accumulation of Methylmercury in the High-Altitude Lake Uru Uru (3686 m a.s.l, Bolivia) Controlled by Sediment Efflux and Photodegradation
(Multidisciplinary Digital Publishing Institute, 2020) Stéphane Guédron; Darío Achá; Sylvain Bouchet; David Point; Emmanuel Tessier; Carlos Heredia; Stéfany Rocha-Lupa; Pablo Fernandez-Saavedra; Marizol Giovana Flores; Sarah Bureau
In shallow aquatic environments, sediment is a significant source of monomethylmercury (MMHg) for surface water (SW). High-altitude aquatic ecosystems are characterized by extreme hydro-climatic constraints (e.g., low oxygen and high UV radiation). We studied, during two seasons, the diel cycles of MMHg in SW and sediment porewaters (PW) of Lake Uru Uru (3686 m a.s.l, Bolivia) contaminated by urban and mining activities. Our results show that diel changes in SW MMHg concentrations (up to 1.8 ng L−1) overwhelm seasonal ones, with higher MMHg accumulation during the night-time and the dry season. The calculation of MMHg diffusive fluxes demonstrates that the sediment compartment was the primary source of MMHg to the SW. Most MMHg efflux occurred during the dry season (35.7 ± 17.4 ng m−2 day−1), when the lake was relatively shallow, more eutrophicated, and with the redoxcline located above the sediment–water interface (SWI). Changes in MMHg accumulation in the PWs were attributed to diel redox oscillations around the SWI driving both the bacterial sulfate reduction and bio-methylation. Finally, we highlight that although MMHg loading from the PW to the SW is large, MMHg photodegradation and demethylation by microorganisms control the net MMHg accumulation in the water column.
Arsenic, selenium, and mercury speciation in hypersaline lakes of the Andean Altiplano: Link between extreme levels and biodiversity repartition
(Elsevier BV, 2024) Stéphane Guédron; Julie Tolu; David Amouroux; Emmanuel Tessier; Carlos A. Molina; Maı̈té Bueno; Adrien Mestrot; Delphine Tisserand; Darío Achá
Arsenic (As) and mercury (Hg) are highly toxic contaminants whereas selenium (Se) is both an essential trace element and potentially harmful at higher concentrations. The hyper-saline lakes of southern Bolivian Altiplano, which are ecological niches for endemic species, are also expected to be enriched in these toxic trace elements. The biogeochemistry of As, Hg, and Se in such high-altitude extreme environments (e.g., high UV radiation and salt content) remains poorly understood. In this study, we investigated the concentrations and chemical forms (speciation) of As, Hg, and Se in sediment, water, and air samples of Lagunas Colorada (LC), Verde (LV), and Blanca (LB) in the South Lipez region (>4200 m a.s.l.). We compared them with the repartition of biodiversity (invertebrates, algae, and bacteria). Extreme As concentrations were found in water (up to 82 mg L−1), and the main As species was inorganic As(V), with neither biogenic methylated As nor volatile As forms being detected in water and air, respectively. Se concentrations in water were of 0.1 to 1.4 μg L−1, and Se existed under different redox states, i.e., Se(IV), Se(VI), and reduced Se (0, -II), including biogenic methylated Se(-II) (trimethyl selenonium). Volatile Se compounds (e.g., dimethyl selenide) were detected in water and air samples. Hg was enriched in the surface water (6 to 30 ng L−1) compared to other regional water bodies, and a significant amount of methyl-Hg and gaseous Hg(0) was detected. The drastic disparity between As, Se and Hg concentrations and speciation between lakes has important implications for their cycling in these extreme aquatic systems. While As mostly accumulated in its oxidized and non-volatile form, Hg and Se concentrations can be controlled by significant conversion to reduced and methylated forms, allowing efficient evasion to the atmosphere. Finally, the salinity, including major ions, and high levels of As were among the main drivers of biodiversity repartition between lakes.
From mine to lake: Source, fate and budget of mercury species in the high-altitude watershed of a fast-developing Andean city (El Alto, Bolivia)
(Elsevier BV, 2025) Stéphane Guédron; Djamilatou Dabré; Céline Duwig; David Amouroux; Jonathan Fin; Sylvain Campillo; Romain Biron; Hélène Guyard; Emmanuel Tessier; Isabel Moreno
In Situ Photochemical Transformation of Hg Species and Associated Isotopic Fractionation in the Water Column of High-Altitude Lakes from the Bolivian Altiplano
(American Chemical Society, 2022) Sylvain Bouchet; Emmanuel Tessier; Jérémy Masbou; David Point; Xavier Lazzaro; Mathilde Monperrus; Stéphane Guédron; Darío Achá; David Amouroux
Photochemical reactions are major pathways for the removal of Hg species from aquatic ecosystems, lowering the concentration of monomethylmercury (MMHg) and its bioaccumulation in foodwebs. Here, we investigated the rates and environmental drivers of MMHg photodegradation and inorganic Hg (IHg) photoreduction in waters of two high-altitude lakes from the Bolivian Altiplano representing meso- to eutrophic conditions. We incubated three contrasting waters in situ at two depths after adding Hg-enriched isotopic species to derive rate constants. We found that transformations mostly occurred in subsurface waters exposed to UV radiation and were mainly modulated by the dissolved organic matter (DOM) level. In parallel, we incubated the same waters after the addition of low concentrations of natural MMHg and followed the stable isotope composition of the remaining Hg species by compound-specific isotope analysis allowing the determination of enrichment factors and mass-independent fractionation (MIF) slopes (Δ199Hg/Δ201Hg) during in situ MMHg photodegradation in natural waters. We found that MIF enrichment factors potentially range from -11 to -19‰ and average -14.3 ± 0.6‰ (1 SE). The MIF slope diverged depending on the DOM level, ranging from 1.24 ± 0.03 to 1.34 ± 0.02 for the low and high DOM waters, respectively, and matched the MMHg MIF slope recorded in fish from the same lake. Our in situ results thus reveal (i) a relatively similar extent of Hg isotopic fractionation during MMHg photodegradation among contrasted natural waters and compared to previous laboratory experiments and (ii) that the MMHg MIF recorded in fish is characteristic for the MMHg bonding environment. They will enable a better assessment of the extent and conditions conducive to MMHg photodegradation in aquatic ecosystems.
Linking Microbial Activities and Low-Molecular-Weight Thiols to Hg Methylation in Biofilms and Periphyton from High-Altitude Tropical Lakes in the Bolivian Altiplano
(American Chemical Society, 2018) Sylvain Bouchet; Marisol Goñi‐Urriza; Mathilde Monperrus; Rémy Guyoneaud; Pablo Fernandez; Carlos Heredia; Emmanuel Tessier; Claire Gassie; David Point; Stéphane Guédron
The sources and factors controlling concentrations of monomethylmercury (MMHg) in aquatic ecosystems need to be better understood. Here, we investigated Hg transformations in sediments, periphyton associated with green algae's or aquatic plants, and benthic biofilms from the Lake Titicaca hydrosystem and compared them to the occurrence of active methylating microorganisms and extracellular Hg ligands. Intense Hg methylation was found in benthic biofilms and green algae's periphyton, while it remained low in sediments and aquatic plants' periphyton. Demethylation varied between compartments but remained overall in the same range. Hg methylation was mainly carried out by sulfate reducers, although methanogens also played a role. Its variability between compartments was first explained by the presence or absence of the hgcAB genes. Next, both benthic biofilm and green algae's periphyton exhibited a great diversity of extracellular low-molecular-weight (LMW) thiols (13 or 14 compounds) present at a range of a few nmol L-1 or μmol L-1 but clearly dominated by cysteine and 3-mercaptopropionic acid. Hg methylation was overall positively correlated to the total thiol concentrations, albeit to different extents according to the compartment and conditions. This work is the first examining the interplay between active methylating bacterial communities and extracellular ligands in heterotrophic biofilms and supports the involvement of LMW thiols in Hg methylation in real aquatic systems.
Mercury contamination level and speciation inventory in Lakes Titicaca & Uru-Uru (Bolivia): Current status and future trends
(Elsevier BV, 2017) Stéphane Guédron; David Point; Darío Achá; Sylvain Bouchet; Pascale A. Baya; Emmanuel Tessier; Mathilde Monperrus; Carlos I. Molina; Alexis Groleau; Laurent Chauvaud
Synergistic effects of mining and urban effluents on the level and distribution of methylmercury in a shallow aquatic ecosystem of the Bolivian Altiplano
(Royal Society of Chemistry, 2016) L. Alanoca; Stéphane Guédron; David Amouroux; Stéphane Audry; Mathilde Monperrus; Emmanuel Tessier; Sylvaine Goix; Darío Achá; Patrick Seyler; David Point
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-2 d-1 for 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.