Background on Arsenic Contamination of Underground Water

Scientists agree that in Bangladesh the cause of the arsenic is natural (geological) and that it is not introduced by human activity such as mining. However, controversy persists over how the arsenic ends up dissolved in the water; there are three main theories:

1) Pyrite Oxidation Hypothesis: It poses that a lowering groundwater table draws in oxygen, which oxidizes sulphides and thus releases arsenic; this hypothesis implies that dams/barrages built across rivers upstream deplete Bangladesh of water, thus lowering the groundwater table, etc. 2) Agro-chemical Hypothesis:  It shifts the blame to the use of phosphate fertilizer by farmers in Bangladesh with the supposed effect of contaminating the soil with arsenic. Drawing water from a pond filter in Noakhali, Bangladesh (Photograph courtesy, UNICEF/ Shehzad Noorani)

3) Oxihydroxide Reduction Process:

It reportedly takes place in shallow (<150m) younger deltaic sediments with large organic components (high oxygen demand); this was concluded by the British Geological Survey (BGS) and their associates after an extensive survey of tubewells throughout Bangladesh, reported June 2000. According to this report, deeper (>150m), older, "flushed" aquifers are much less contaminated or not at all; this suggests a possible solution.

Principal Approaches to the Arsenic Problem

The Arsenic Problem in Bangladesh is currrently tackled from three angles:

Medical: treatment of patients already suffering. Though urgent and necessary, this does not remove the cause of the problem.

Engineering: removal of arsenic from the water. Many techniques are on offer, but it remains unclear which one merits large-scale introduction, and only those capable of purifying large volumes of water would offer a modicum of relief.

Geological: avoidance of contaminated sources, based on our current understanding of the mechanisms of deposition and remobilization of arsenic, and the identification of safe sources. 

• Arsenic poisoning through drinking water from groundwater sources

• Conference on Arsenic Crisis in Asia and the Pacific

Back to top