The roots of the arsenic crisis in the Ganges delta go back a generation to when most Bangladeshis drank water from rivers and ponds that were often contaminated by sewage. Thousands died each year from gastrointestinal diseases. International agencies such as UNICEF devised a plan to sink boreholes into the sands of the delta that covers much of Bangladesh and the neighbouring Indian state of West Bengal. Unfortunately, nobody thought to check the underground water for natural poisons until symptoms of arsenic poisoning began to emerge, first in West Bengal and later in Bangladesh. In 2000, there were more than 4 million such boreholes supplying water to 95 percent of Bangladesh's villagers.
Whole villages in Bangladesh now show symptoms of arsenic poisoning ranging from skin blemishes to lung diseases, skin cancers and liver failure. Doctors predict that unless urgent action is taken, there will be an epidemic of arsenic-related deaths across southern Bangladesh.
Detection of the estimated 2 million arsenic-polluted wells in Bangladesh is a major task because contamination vary drastically – even between neighbouring boreholes and cheap and easy-to-use testing kits are not available.
In Bangladesh, the village pumps lowered water levels and allowed oxygen to attack the arsenic-bearing iron pyrite deposits in the sediment. The resulting oxidation – and perhaps other mechanisms – released the arsenic into the water.
Another potential culprit in Bangladesh might be agricultural fertilisers. Screenings show unusually high phosphate concentration in the region's water, but it is not sure whether fertiliser is to blame.
The essential process in the release of arsenic into underground water in Bangladesh is not oxidation but reduction. Much of the arsenic is bound to iron oxyhydroxide compounds in the top 40 metres of the delta sediments. Away from the surface, rotting vegetation has consumed all the oxygen dissolved in water, creating an environment in which these compounds release iron and arsenic.
Pyrite oxidation would happen mainly in shallow wells (less than 10 metres deep) and the answer will be to dig deeper wells. But iron reduction would happen at deeper levels and the answer will be shallow wells. We can not decide what is the solution until there is more complete scientific data.