Browsing by Autor "David Amouroux"

Now showing 1 - 9 of 9

Algal Bloom Exacerbates Hydrogen Sulfide and Methylmercury Contamination in the Emblematic High-Altitude Lake Titicaca
(Multidisciplinary Digital Publishing Institute, 2018) Darío Achá; Stéphane Guédron; David Amouroux; David Point; Xavier Lazzaro; Pablo Fernandez; Géraldine Sarret
Algal blooms occurrence is increasing around the globe. However, algal blooms are uncommon in dominantly oligotrophic high-altitude lakes. Lake Titicaca, the largest freshwater lake in South America, located at 3809 m above the sea level, experienced its first recorded algal bloom covering a large fraction of its southern shallow basin in March–April 2015. The dominant algae involved in the bloom was Carteria sp. Water geochemistry changed during the bloom with a simultaneous alkalinization in heterotrophic parts of the lake and acidification in eutrophic shallow areas. A decrease in oxygen saturation (from 105 to 51%), and a dramatic increase in hydrogen sulfide (H2S) concentrations (from <0.02 to up to 155 µg∙L−1) resulted in the massive death of pelagic organisms. Such changes were brought by the exacerbated activity of sulfate-reducing bacteria (SRB) in this sulfate-rich lake. Although levels in total mercury remained stable during the event, MMHg % rose, highlighting higher conservation of produced MMHg in the water. Such an increase on MMHg % has the potential to produce exponential changes on MMHg concentrations at the end food web due to the biomagnification process. Our physicochemical and climatological data suggest that unusually intense rain events released large amounts of nutrients from the watershed and triggered the bloom. The observed bloom offers a hint for possible scenarios for the lake if pollution and climate change continue to follow the same trend. Such a scenario may have significant impacts on the most valuable fish source in the Andean region and the largest freshwater Lake in South America. Furthermore, the event illustrates a possible fate of high altitude environments subjected to eutrophication.
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.
Association of a Specific Algal Group with Methylmercury Accumulation in Periphyton of a Tropical High-Altitude Andean Lake
(Springer Science+Business Media, 2016) William G. Lanza; Darío Achá; David Point; Jérémy Masbou; L. Alanoca; David Amouroux; Xavier Lazzaro
Diurnal variability and biogeochemical reactivity of mercury species in an extreme high-altitude lake ecosystem of the Bolivian Altiplano
(Springer Science+Business Media, 2015) L. Alanoca; David Amouroux; Mathilde Monperrus; E. Tessier; Marisol Goñi‐Urriza; Rémy Guyoneaud; Darío Achá; Claire Gassie; Stéphane Audry; M.E. García
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
Hg Speciation and Stable Isotope Signatures in Human Hair As a Tracer for Dietary and Occupational Exposure to Mercury
(American Chemical Society, 2011) Laure Laffont; Jeroen E. Sonke; Laurence Maurice; Selma Luna-Monrroy; J. Chincheros; David Amouroux; Philippe Behra
Exposure of humans and wildlife to various inorganic and organometallic forms of mercury (Hg) may induce adverse health effects. While human populations in developed countries are mainly exposed to marine fish monomethylmercury (MMHg), this is not necessarily the case for developing countries and diverse indigenous people. Identification of Hg exposure sources from biomonitor media such as urine or hair would be useful in combating exposure. Here we report on the Hg stable isotope signatures and Hg speciation in human hair across different gold miner, indigenous and urban populations in Bolivia and France. We found evidence for both mass-dependent isotope fractionation (MDF) and mass-independent isotope fractionation (MIF) in all hair samples. Three limiting cases of dominant exposure to inorganic Hg (IHg), freshwater fish MMHg, and marine fish MMHg sources are used to define approximate Hg isotope source signatures. Knowing the source signatures, we then estimated Hg exposure sources for the Bolivian gold miner populations. Modeled IHg levels in hair correspond well to measured IHg concentrations (R = 0.9), demonstrating that IHg exposure sources to gold miners can be monitored in hair samples following either its chemical speciation or isotopic composition. Different MMHg and inorganic exposure levels among gold miners appear to correspond to living and working conditions, including proximity to small towns, and artisanal vs large scale mining activity.
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.
Mercury compound-specific stable isotope fractionation in high-altitude lake ecosystems of the Bolivian Altiplano
(Elsevier BV, 2025) Jérémy Masbou; David Point; Sylvain Bouchet; Jeroen E. Sonke; Carlos A. Molina; Carla Ibañez; Anne Lorrain; Julio Pinto; Darío Achá; David Amouroux
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.