Understanding the Causes of and the Permanent Solutions for Groundwater Arsenic Poisoning in Bangladesh

Abstract

The groundwater arsenic poisoning in Bangladesh is the largest disasterin the history of human civilization: more than 100 million people havebeen drinking arsenic-poisoned water on a daily basis. A large number ofscientists believe that the groundwater arsenic poisoning in Bangladeshis a natural disaster, that the poisoning has been present for thousandsof years, and that reduction of ancient soil with ferrichydroxide-bearing arsenic is the main mechanism for the mobilization ofarsenic into groundwater. However, historical groundwater use data fromthe dug wells and the tube wells, historical medical data, arsenictoxicological data, hydrological, bydro geological and geochemicalparameters reject the reduction hypothesis an d suggest that thegroundwater arsenic poisoning in Bangladesh is a recent, man madedisaster and that exposure and oxidation of arsenic minerals previouslybelow the water table is probably the principal mechanism for releasingarsenic into groundwater.The oxidation of arsenic-bearing minerals present in the Bengal deltasediments is responsible for the release of arsenic oxides in solutionto the groundwater. The subsequent migration of thisarsenic-contaminated groundwater through the upper layers of deltaicsediments is the principal cause of arsenic poisoning in Bangladesh.Arsenic-bearing minerals of several kinds are associated with theorganic-rich sediments present in deltaic environments. Availablesources for arsenic are the ocean, coal beds in India, and mountains tothe north. Minerals formed in these reducing environments below thegroundwater table would be stable unless they were exposed tooxidizing-environments. The groundwater table is lowered by increasedirrigation during the dry season and in the cone of depression formed bypumping-tube wells and irrigation wells drilled below the zone offluctuation. The arsenic minerals in the newly exposed sediments oxidizeand release the arsenic when the water table recovers and exposes theoxidized minerals to a reducing-environment.Increased irrigation did become necessary during India's 30 years ofunilateral diversion of river water from the Ganges, Tista and 28+common rivers of Bangladesh and India which cut the normal flow of the30+ rivers during the dry season. The solution to the arsenic problem isto restore the natural river flow of the Ganges, Tista and other commonrivers of Bangladesh and India. This would restore the groundwater levelto a level that existed in Bangladesh prior to the construction andcommission of Farakka Barrage in 1975.Other man-made environmental disasters created by the Farakka, Tista andother barrages/dams constructed in the common rivers of Bangladesh andIndia would also be solved if these barrages were removed and a normalflow restored. The riverbeds could then be dredged and groundwaterproduced at a safe yield rate. A comprehensive plan not only for watersupplies but associated waste disposal should be worked out for all ofBangladesh. Individual units within the plan could then be developed onthe bases of need and tied into the overall plan as it develops.