Mechanism of arsenic release to groundwater, Bangladesh and West Bengal

• Published in: Applied geochemistry Vol. 15; no. 4; pp. 403 - 413
• Main Authors: Nickson, R.T., McArthur, J.M., Ravenscroft, P., Burgess, W.G., Ahmed, K.M.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.05.2000; Elsevier
• Subjects: Bangladesh; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Freshwater; Hydrology. Hydrogeology; India; India, West Bengal; Pollution, environment geology; Water resources; Bangladesh; West Bengal India; India; oxides; bacteria; water wells; ground water; biodegradation; SEM data; pollution; pyrite; water treatment; aquifers; hydrochemistry; alluvium; sulfides; scanning electron microscopy; iron sulfides; iron oxihydroxides; dissolution; water supply; arsenic; contamination; framboidal texture; prokaryotes; Asia; microorganisms; organic materials; reducing environment; sediments
• ISSN: 0883-2927; 1872-9134
• DOI: 10.1016/S0883-2927(99)00086-4

In some areas of Bangladesh and West Bengal, concentrations of As in groundwater exceed guide concentrations, set internationally and nationally at 10 to 50 μg l −1 and may reach levels in the mg l −1 range. The As derives from reductive dissolution of Fe oxyhydroxide and release of its sorbed As. The Fe oxyhydroxide exists in the aquifer as dispersed phases, such as coatings on sedimentary grains. Recalculated to pure FeOOH, As concentrations in this phase reach 517 ppm. Reduction of the Fe is driven by microbial metabolism of sedimentary organic matter, which is present in concentrations as high as 6% C. Arsenic released by oxidation of pyrite, as water levels are drawn down and air enters the aquifer, contributes negligibly to the problem of As pollution. Identification of the mechanism of As release to groundwater helps to provide a framework to guide the placement of new water wells so that they will have acceptable concentrations of As.