LESSONS FROM ARSENIC RESEARCH IN BANGLADESH: ITS IMPLICATION FOR THE SUSTAINABILITY OF AQUIFERS AS LONG TERM SAFE WATER SOURCES

Arsenic is a highly toxic and ubiquitous metalloid found in the atmosphere, soils and rocks, natural water and organisms. It is mobilized in the environment through a combination of natural processes such as weathering reactions, biological activity and volcanic emissions as well as through a range of anthropogenic activities such as mining, pesticides usage. Most arsenic problems related to drinking water exposure, however, are the result of arsenic mobilization under natural conditions. A number of large aquifers throughout the world have been identified with arsenic contamination, made it as a crucial water quality problem in many parts of the world, particularly in Bangladesh where about 40,000 arsenicosis patients have been identified. Further, an alarming number of people are still exposed to arsenic poisoning due to lack of knowledge and experiences, improper information distribution, unplanned safe water device installation and finally lack of coordination among the implementation agencies.

The spatial extent of the problem and the fact that the most severely contaminated areas are in the geologically distinct low-lying flood plain, support the idea that the sediments themselves are the most likely arsenic source. However, the mobility of arsenic in the subsurface is influenced by a combination of the dissolved species present, minerals in aquifer solids, microbial activity, and by ambient geochemical parameters such as redox conditions. The results from a detailed biogeochemical investigation of As in lower Pleistocene aquifers provides a unique opportunity to better understand the hydrological, geochemical and microbial interactions. A series of laboratory anaerobic incubations were conducted in replicate over 90 days using preserved Pleistocene orange sands duly amended by organic substrates; lactate and inoculated with metal-reducing bacteria "Shewanella sp. ANA-3". The observations indicate that metal-reducers such as Shewanella can trigger As release to groundwater by converting sedimentary As to a more mobilizable form without the addition of high levels of labile carbon. Such interactions need to be better understood to determine the vulnerability of low-As aquifers from which drinking water is increasingly drawn in Bangladesh and/or in similar deltaic environments in the world.