Proc. Natl Acad. Sci. USA doi: 10.1073/pnas.0710477105 (2008)

Credit: J. HOLMES/PANOS

Dissolved arsenic was discovered in the groundwater of the Bengal Basin of Bangladesh and India more than twenty years ago. With deeper wells, safe drinking water might be provided for more than 90% of this region, according to an analysis by Holly Michael and Clifford Voss of the US Geological Survey (USGS) in Reston, Virginia.

The release of arsenic into the basin's groundwater is mainly caused by reduction of iron oxyhydroxides, which tends to take place near the surface. Most wells in the area pump from the contaminated zone, even though the polluted groundwater rarely reaches deeper than 100 metres.

The USGS model of groundwater flows in the basin suggests that water taken from depths of 150 metres or more will not, in most areas, be tainted by arsenic for a millennium.