by Robin de la Motte
It has been known for some years that in South Asia, particularly in Bangladesh, large numbers of people are exposed to unsafe levels of naturally-occurring arsenic in water supplies drawn from groundwater. A recent study in the British medical journal The Lancet linked a fifth of all deaths in Bangladesh to arsenic contamination, and estimated that up to half the population (77 million people) had been chronically exposed. The problem affects substantial parts of South Asia, and arises due to the region’s increased use of groundwater in recent decades in order to avoid water-borne diseases found in surface water. The arsenic issue is just one aspect of Bangladesh’s water problems, which are likely to worsen in future. Climate change and population growth make it likely China and India will build new dams, reducing the volume of surface water Bangladesh receives downstream. Previous dams have already led to reduced water flows, causing problems of rivers silting up and increased salinity from seawater intruding in coastal areas.
A recent Geography Compass article (Benner and Fendorf 2010) examines the arsenic issue, which has been called the “largest mass poisoning in history”. Over 60 million people in the region are affected by arsenic contamination, with concentrations in drinking water sometimes over 100 times World Health Organization safety standards. Drinking water is the primary concern, but in addition contaminated water used for irrigation may – depending on local conditions – accumulate in soils and affect crops, particularly rice, although the health impacts of this are not well understood. Benner and Fendorf describe how the problems are caused by a combination of environmental conditions specific to the Asian deltas. The arsenic originates in Himalayan rocks, from where it is eroded and carried in river sediment to the delta floodplains, and then enters local aquifers. Benner and Fendorf note that the large increase in groundwater extraction (with nearly a million wells in Bangladesh by 2003) has unpredictable effects on arsenic concentrations, with both positive and negative effects possible; so far there is insufficient evidence of any effect. They note the potential of tapping deeper aquifers, which are largely uncontaminated, but also the risk of thereby drawing in contaminated water from shallower aquifers.
IRIN, 25 June 2010, “In brief: Millions of Bangladeshis poisoned by arsenic-laced water”
The Citizen (Tanzania), 24 September 2010, “Decades-old water dispute could destroy nation’s agriculture”
Benner, Shawn G., and Fendorf, Scott (2010), “Arsenic in South Asia Groundwater“, Geography Compass, Volume 4, Issue 10, pages 1532-1552