More than 200 million people are at risk of exposure to dangerous levels of geogenic arsenic in drinking water across Asia. Arsenic within rocks of the Himalayas is liberated to the sediment load of the major river systems and ultimately deposited within the massive deltas of Asia, particuarly the South and Southeast regions. Upon burial, arsenic is released to the aqueous phase through a complex web of microbially driven geochemical prococess, and its distribution determined by a coupling of biogeochemical reactions and groundwater hydrology. Generally, arsenic binds strongly to soil/sediment solids under aerated conditions; under anaerobic condition, aqueous concentrations increase, a phenomenon attributed to reduction of iron or arsenic—with arsenate reduction to arsenite being of greatest importance. Further challenging human health is arsenic entry into the major crop of the region, rice. Historic arsenic from sediment deposition coupled with irrigation of arsenic contaminated groundwater has resulted in danagerous levels of arsenic within rice, and in some cases declining yields. Here the fate controlling processes of arsenic and its entry into the food and water systems will be described.
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