Accueil > Actualités > Séminaires > Séminaire de Karen Johannesson


Titre : Biogeochemistry of arsenic in groundwater flow systems
Nom du conférencier : Karen Johannesson
Son affiliation : Department of Earth and Environmental Sciences, Tulane University, Louisiane
Laboratoire organisateur : METIS
Date et heure : 21-10-2016 14h00
Lieu : Lieu à définir
Résumé :

Arsenic (As) is a highly toxic and carcinogenic metalloid that can cause serious health effects, including increased risk of cancers (e.g., skin, lung, bladder, and kidney), infant mortality, and reduced intellectual and motor function in children to populations chronically exposed to As-contaminated drinking water.  Recent estimates suggest that in excess of 140 million people worldwide are drinking As-contaminated groundwater (i.e., As ≥ 10 µg kg-1), and the most severely affected region is the Ganges-Brahmaputra-Meghna (GBM) delta in Bangladesh and India (i.e., Bengal Basin). Investigations in the Murshidabad District of West Bengal, India, indicate As concentrations can exceed 4000 µg kg-1 in well waters, which is 400-fold higher than recommended by the WHO for drinking water consumption. Arsenic appears to be mobilized by reductive dissolution of Fe oxides in aquifer sediments with the source of the labile organic matter occurring in the aquifer sediments.
Studies in southern Louisiana (USA), and particularly, those within the lower Mississippi River delta, also reveal high As concentrations (up to ~640 µg kg-1) in shallow groundwaters. Although some rural populations rely on shallow groundwaters as drinking water, it is not known what affects, if any, the elevated groundwater As has had on these communities. The regional extent of high As shallow groundwaters is controlled, in part, by the distribution of Holocene sediments, deltaic deposits, and organic-rich sediments, which is similar to the Bengal Basin. Field and laboratory batch incubation studies suggest that the As is largely of geogenic origin, and further that microbial reduction of Fe(III)/Mn(IV) oxides/oxyhydroxides within the sediments likely contributes the bulk of the As to the shallow groundwaters. The incubation studies are supported by biogeochemical reactive transport modeling, which also indicates reductive dissolution of metal oxides/oxyhydroxides as the likely source of As to these shallow groundwaters. Finally, reactive transport modeling of As in shallow groundwaters suggests that sorption to aquifer mineral surfaces limits the transport of As after mobilization via reductive dissolution, which may explain, in part, the heterogeneous distribution of As in groundwaters of southern Louisiana and, perhaps, the Bengal Basin.

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