A NORTH AMERICAN ANALOG FOR HIGH ARSENIC GROUNDWATER FROM BANGLADESH AND WEST BENGAL, INDIA: THE CASE OF THE MISSISSIPPI RIVER DELTA (Invited Presentation)

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. Studies in southern Louisiana (USA), and particularly, those within the lower Mississippi River delta, 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. 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.