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Technology - From Flood To Drought: Understanding The Water Dilemma And Arsenic Crisis In The Ganges Basin

Dr. Shafiqul Islam
10/16/2006

Overabundance and scarcity of water are real challenges for the prosperity and sustainability of the Ganges basin. Perhaps nowhere in the world is water so abundant and yet so scarce than in the Ganges basin. From food to fish to fiber, livelihood of rural population of this flood plain critically depends on water. In a typical year, over half of the basin is flooded during the Monsoon season; yet, during the dry season water is important not only for food production but also to maintain navigation in the interior rivers, minimize salinity intrusion in coastal areas, preserve wetlands from continued shrinkage due to extensive use of groundwater resources for irrigation, and sustain a complex matrix of terrestrial and aquatic production systems.

Even though surface water is abundant, it is usually polluted and not safe to drink. To reduce the health risks and infant mortality, Bangladesh and West Bengal have converted most of their drinking water supply from surface water supplies to groundwater wells beginning in the 1950s. Tragically, those wells may be responsible for the largest mass arsenic poisoning in history. UNICEF led the effort to switch from surface water to groundwater sources after the 1950s in response to epidemics of cholera, dysentery and a high infant mortality rate. Created with the best intentions, this initiative has led to one of the most severe environmental disasters of our time. Many of these wells now contain water with arsenic concentration of 500 to 1000 parts per billion (ppb) and some as high as 2,000 ppb of arsenic. The allowable standard in the United States is only 50 ppb. It has been estimated that over 75 million people are at risk of developing health problems associated with the ingestion of arsenic.

Arsenic as a public health problem was first identified in West Bengal, India, where the geological formations, economic conditions, food habits, and tube wells are similar to those in Bangladesh. In the early 1990s, people started to develop arsenicosis, a disease that begins with skin rashes but can lead to fatal problems with the lungs, kidneys, and bladder. Symptoms varied widely, depending on the arsenic level in the water, the victim’s nutritional condition, and individual reaction. Some people may show skin blisters in six months of drinking the water, while other people can go for years before symptoms appear. Facing a deluge of cases in West Bengal, health workers started looking for similar problems in Bangladesh. Currently, over one third of the tube wells in Bangladesh pump up water exceeding the arsenic standard of 50 ppb.

Working with collaborators at the Tufts University, Massachusetts Institute of Technology, University of British Columbia, University of Tokyo, ETH in Switzerland, and the Bangladesh University of Engineering and Technology, we are exploring two research questions: Our first research question is: Why are arsenic concentrations so high in the groundwater of the Ganges basin? Once we have developed an understanding of the cause of high arsenic concentrations we will consider a second question: How will arsenic concentrations change over time and space? This project is currently funded by a multi-year grant from the National Science Foundation of the United States.

Groundwater pumping for irrigation has grown very rapidly in the Ganges Delta since the 1970’s.  This groundwater extraction has enabled irrigated dry-season rice to greatly increase food production so that the region has remained food self sufficient even as the population has nearly tripled over the last five decades.  Our research suggests that these elevated arsenic levels appear to be linked to dry-season irrigation pumping, which carries water from below ground to where it is needed to grow rice. It appears that deep groundwater is being replaced by surface water that is rich in organic material, which then mobilizes previously insoluble arsenic. Monsoon season, which deluges the countryside from July to October, carries organic materials and rainwater down into the wells to replace what has been pumped out and creates favorable conditions for biogeochemical reactions that take the arsenic from a safe solid phase to an unsafe liquid state.

One possible remedy which has already begun to be used is to dig deeper wells. Unsafe levels of arsenic are associated with wells that are about 100 feet deep. Deeper wells have virtually no arsenic; a safer depth may be more than 400 feet. Use of deeper well water for drinking appears to be a good solution as long as one can establish that these deeper wells will not also become contaminated with time. A drawback to the deeper wells is their greater expense. It can be five to ten times more expensive to make these deeper wells.

Our research results are published in recent issues of Science, Nature and several other technical journals and news paper articles. This article is a summary of these published articles. For more information about this complex problem, please look at the following two sources: Bangladesh Arsenic Mitigation and Water Supply Program at http://www.bamwsp.org/ ; and West Bengal India and Bangladesh Arsenic Crisis Centre at http://bicn.com/acic/.

(Shafiqul Islam is the Associate Dean of Engineering for Research and the Bernard M. Gordon Senior Faculty Fellow in Engineering at Tufts University. For further information, visit http://ase.tufts.edu/cee/reason. )

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