Arsenic in Annex C, Land & Water Resources

Section 6 - Water Quality

6.3. Arsenic in Groundwater

Arsenic in groundwater was identified in Bangladesh in 1993, and a summary of its occurrence and the background issues are set out in Annex C Appendix 8. Previously there had been no policy to test for arsenic, as no problem was suspected. The full extent has yet to be identified but the problem is most strongly concentrated in the South West, South East and North East regions as shown on Figure 6.1, which shows the proportion of tube wells affected in each Thana. Some 20M people are now considered at risk from arsenic in their drinking water.

6.3.1 Preliminary Findings

• The distribution is far from uniform. In some hot spots all tube wells are contaminated while in other places both positive and negative results are obtained for different tube wells in close proximity.
• Some tube wells, which were not contaminated, are now affected.
• The problem mainly affects shallow tube wells and although some deep tube wells ate reported as contaminated, many reports ate based on erroneous data (feet instead of meters, the use of term “deep”). Wells over 250m deep are rarely contaminated.

• Is the problem becoming worse and if so, will it continue to worsen, or is it that more consistent and more accurate testing continues to record an increased incidence of arsenic?
• Has the increased development of groundwater for irrigation purposes caused arsenic to be mobilized and enter the groundwater?
• How acute is the risk that arsenic in irrigation water will enter the food chain?

• Further testing increases the known number of arsenic-infected wells, particularly since a new low cost field test kit has been developed in Bangladesh. Few kits can detect concentrations below 20ppb.
• Opinion was divided as to whether increased abstraction of water for irrigation has caused an increase in the concentration of arsenic in groundwater. There is no evidence to prove any linkage apart from the fact that the recorded increase in the incidence in arsenic in groundwater has coincided with the general increase in the use of groundwater for irrigation. At the same time, the number of tube wells for domestic water, and the number of people using this source of water, has substantially increased over the same period. The weight of opinion at present is that there is no connection.
• Recent research indicates that arsenic does not accumulate in the rice grains, but is concentrated in the roots. It has been shown in studies that some green leafy vegetables accumulate arsenic.

The issue of arsenic and the potable water supply is discussed further in Annex L. However, research is urgently needed to improve understanding of the mechanisms involved and the risks, particularly in the context of irrigated agriculture.

Farmers are likely to continue to use groundwater in irrigation unless an equally reliable and cheaper alternative becomes available. Should some crops be found to accumulate arsenic then controls on their production will have to be considered. However, this may be difficult to implement in a situation where the arsenic contamination of the water is unevenly distributed.

Solutions for the arsenic problem are essential, and options are discussed in Chapters 7 and 8 of the Main Report.

6.3.2.Variation of Quality with Depth