Spatial and Temporal Variations of Groundwater Arsenic in South and Southeast Asia

Arsenic in Asia Millions of humans in South and Southeast Asia are exposed to potentially dangerous levels of the carcinogen arsenic via their drinking water every day. Although high arsenic levels are a known problem, a growing demand for drinking water drives the continued construction of new groundwater wells in these regions. Fendorf et al. (p. 1123) review chemical and hydrological factors controlling the release of arsenic in groundwater in South and Southeast Asia, which include the distribution of arsenic in groundwater aquifers used for drinking water and irrigation. Despite incomplete sampling and characterization of these factors across these regions, several key directions for improvements to water quality are presented. Over the past few decades, groundwater wells installed in rural areas throughout the major river basins draining the Himalayas have become the main source of drinking water for tens of millions of people. Groundwater in this region is much less likely to contain microbial pathogens than surface water but often contains hazardous amounts of arsenic—a known carcinogen. Arsenic enters groundwater naturally from rocks and sediment by coupled biogeochemical and hydrologic processes, some of which are presently affected by human activity. Mitigation of the resulting health crisis in South and Southeast Asia requires an understanding of the transport of arsenic and key reactants such as organic carbon that could trigger release in zones with presently low groundwater arsenic levels.