HR: 0830h
AN: B21B-0703    [PDF]
TI: Arsenic Cycling Within Bangladesh Sediments: Evidence for an Oxidative Front Causing Solid Phase Repartitioning
AU: * Polizzotto, M L
EM: mattyp@stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences, Building 320, Room 118, Stanford, CA 94305 United States
AU: Fendorf, S E
EM: fendorf@stanford.edu
AF: Stanford University, Department of Geological and Environmental Sciences, Building 320, Room 118, Stanford, CA 94305 United States
AU: Harvey, C F
EM: charvey@mit.edu
AF: MIT, Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 01239 United States
AU: Ali, M A
EM: ashraf@bdcom.com
AF: Bangladesh University of Engineering and Technology, Bangladesh University of Engineering and Technology, Dhaka, 1000 Bangladesh
AU: Ashfaque, K N
EM: ashfaq@mit.edu
AF: MIT, Ralph M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 01239 United States
AB: Arsenic is a contaminant in the groundwater of Bangladesh and has resulted in the exposure of millions of people to drinking water above the World Health Organization standard. Solid concentrations of arsenic within the aquifer sediments typically do not exceed world averages, and, therefore, the question arises as to why arsenic is partitioned in the solution rather than the solid phase. To address this question we have obtained well-preserved deep-sediment cores from the Munshiganj District of Bangladesh. Spectroscopic analyses have been conducted to determine the speciation of arsenic, iron, and sulfur within the sediments. Additionally, laboratory studies of the sediments, in conjunction with those on model compounds, have been performed to isolate plausible desorption mechanisms of arsenic and to define the underlying chemical processes controlling arsenic cycling. Our work points to a complex cycling of arsenic in which an oxidative front has caused destruction of arsenic-bearing sulfides (which appear preserved during transport and sediment deposition!) and the concomitant repartitioning of arsenic onto oxidized solids, primarily those of Fe. Subsequent to repartitioning on ferric (hydr)oxide mineral surfaces, microbial reductive dissolution of such phases, stimulated by injection of labile carbon, has led to the concomitant release of arsenic into solution. The entire cycle implies an additional (and previously dismissed) step in the release of arsenic into Bangladesh groundwater. As a consequence, minimizing the drawdown (and thus the oxidative front) or utilizing deeper wells may provide water that is less contaminated with arsenic.
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2003 Fall Meeting