2011 GSA Annual Meeting in Minneapolis (912 October 2011)
Paper No. 281-2
Presentation Time: 1:55 PM-2:15 PM

BIOGEOCHEMISTRY OF ARSENIC IN GROUNDWATER AND ITS IMPLICATION FOR EVALUATING THE SUSTAINABILITY OF AQUIFERS AS A LONG-TERM SAFE WATER SOURCES

DHAR, Ratan, Geology Discipline, Earth and Physical Sciences, York College of City University of New York, 94-20 Guy R. Brewer Blvd, Jamaica, NY 11451, rdhar@york.cuny.edu

Arsenic is a highly toxic and ubiquitous metalloid. 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, it has turned to be a serious life threatening issue. 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 arsenic in an area of Bangladesh provide a unique opportunity to better understand the hydrological, geochemical and microbial interactions. A series of anaerobic incubations were conducted in replicate over 90 days using natural orange sands from deeper orange-colored Pleistocene sands initially containing 0.14 mg kg-1 phosphate-extractable As, >99% as As(V), and 0.8 g kg-1 of 1 hr HCl-leachable Fe, mostly as Fe(III). The sediment was resuspended in artificial groundwater, with or without lactate as a labile carbon source, and inoculated with metal-reducing Shewanella sp. ANA-3. Within 23 days, dissolved As concentrations increased to 17 mg L-1 with lactate, mostly as As(III), and 2 mg L-1 without lactate. The controls showed < 1 mg L-1 solute As, even though significant Fe and Mn were released with lactate. Sedimentary phosphate-extractable As increased to 4-fold to ~ 0.6 mg kg-1 by Shewanella (with or without lactate) in 23 days, with significant proportion as As(III) by 92 days. These 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 these low-As containing sustainable aquifers from which drinking water is increasingly drawn in Bangladesh.

2011 GSA Annual Meeting in Minneapolis (912 October 2011)
General Information for this Meeting
Session No. 281
Monitoring and Understanding Our Landscape for the Long Term through Small Catchment Studies II: A Tribute to the Career of Owen P. Bricker
Minneapolis Convention Center: Room M100HI
1:30 PM-5:30 PM, Wednesday, 12 October 2011

Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 669

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