Water supplies worldwide are impacted by concentrations of dissolved arsenic above acceptable health levels. These health concerns have prompted a reduction in the U.S. drinking water standard for arsenic (from 50 to 10 □g l~(-1)) and focused attention on widespread areas of the Indian-subcontinent, central and southeast Asia, and South America with large populations at risk for adverse health impacts. Although estimates vary, elevated arsenic concentrations in groundwater have the potential to adversely impact on the order of 90 million people (1-3), including 13 million in the U.S. (4, 5). Arsenic in the environment is derived from both natural and anthropogenic sources, including occurrences in sediments, soils, coal, and ore deposits, and releases from mining, coal-burning, and industrial processes. Although arsenic toxicity is not as severe at low levels as that of metals such as lead, mercury, or cadmium, natural occurrences of arsenic above background concentrations are widespread and common. Thus, cumulative effects may impact large populations, particularly in countries where unmonitored groundwater is the primary source of drinking water.
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