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Deciphering Processes Responsible for the Arsenic-Induced Largest Mass Poisoning in History



Arsenic is a widely distributed element in soils and sediments. Although mining and other industrial processes can often enrich soils and waters with arsenic, naturally occurring minerals can also provide ample levels of this toxic element. The main exposure path to arsenic is through drinking water; fortunately, its tendency to bind strongly to soil and sediment solids (minerals) usually limits the dissolved concentrations available for consumption. However, there are conditions where arsenic is destabilized and released from the solids into groundwater—potentially with devastating consequences as presently noted in Asia.

As many as one hundred million people living in the large river deltas of South and Southeast Asia (e.g., West Bengal – India, Bangladesh, Cambodia, Myanmar, and Vietnam) routinely consume well water with unsafe arsenic levels (often 20 to 50 times, and up to more than 100 times, the recommended limit set by the World Health Organization). While there is general agreement that arsenic is naturally derived, the processes governing aqueous concentrations in groundwater remain unresolved, limiting our ability to predict arsenic concentrations in space (between wells) and time (future concentrations) and to assess the impact of human activities on the arsenic problem. Long-term exposure to high levels of arsenic has resulted in arsenicosis and cancers. However, because most surface water sources are contaminated with pathogens, people continue to drink well water, forced to choose arsenic poisoning over surface water-borne (pathogen) diseases.

In order to define how arsenic transfers from the soils or sediment into groundwater, and to deduce the overall cycling of arsenic, we are conducting an extensive array of laboratory and field studies. Our laboratory studies seek to decipher biological and chemical reaction pathways controlling the dissolved concentrations of arsenic, and the rates at which these processes occur. Our field work, seeks to integrate our knowledge gained from laboratory studies with a determination of field (biogeochemical) conditions, placed within the physcial framework of the aquifer systems, in order to decipher the hydrologic and biogeochemical processes governing arsenic concentrations and mobility within the aquifers of Asia.