Where does arsenic in West Bengal water come from?
Seema Singh -
Thursday, July 24, 2008 3:08 PM
Unsafe levels of arsenic in drinking water are common in several parts of West Bengal and other south-east Asian regions. The levels are so high that they are now impacting staple crops like rice.
Where does this arsenic come from? It is agreed that arsenic contamination in the ground water of south and south-east Asia is a consequence of arsenic dissolving from naturally deposited sediments (eroded Himalayan sediments). But the location within the sediment profile, the time period, and the effect of hydrology on arsenic release are not quite known, even though this information is crucial for planning remedial responses and for estimating future arsenic concentrations.
One of the puzzling issues for researchers has been the localization of arsenic within sedimentary aquifers. In other words, it's been difficult to explain how wells with severely contaminated water can have safe wells (with no arsenic contamination) just within 10 metres.
In a first ever study tracing the source of contamination, authors from Stanford and Boise State (Idaho) Universities and Resource Development International in Cambodia report in today's Nature that they studied the minimally disturbed Mekong delta in Cambodia ( in contrast, Ganges and other Asian river deltas have experienced intensive agricultural practices) and found that arsenic is released from near-surface, river-derived sediments and transported through the underlying aquifer back to the river.
Due to similarities in geologic deposition, aquifer source rock and hydrology, the authors claim their results provide a model for understanding pre-disturbance conditions of other deltas in Asia, including the Ganges.
That is, by using this model groundwater researchers and managers can discover where does arsenic in the Gangetic delta aquifer come from and how anthropogenic (or man-made) factors like groundwater pumping for irrigation, changes in agricultural practices, etc. will impact arsenic in the groundwater.
"Moreover, these results suggest a shift in the appropriate model from dominant geochemical control towards substantial hydrologic control of arsenic in southeast Asian ground water," they say. Clearly, this could also effect a shift in health management of tens of millions of people in the region.