HR: 14:10h
AN: H13L-03 INVITED    [Abstracts]
TI: Mechanisms of Arsenic Mobilization and Attenuation in Subsurface Sediments
AU: * O'Day, P A
EM: poday@ucmerced.edu
AF: University of California Merced, School of Natural Sciences, PO Box 2039, Merced, CA 95340, United States
AU: Illera, V
EM: vramon@ucmerced.edu
AF: University of California Merced, School of Natural Sciences, PO Box 2039, Merced, CA 95340, United States
AU: Root, R
EM: rroot@ucmerced.edu
AF: University of California Merced, School of Natural Sciences, PO Box 2039, Merced, CA 95340, United States
AU: Choi, S
EM: schoi@ucmerced.edu
AF: University of California Merced, School of Natural Sciences, PO Box 2039, Merced, CA 95340, United States
AU: Vlassopoulos, D
EM: dimitri@sspa.com
AF: S.S. Papadopulos and Associates, Inc., 510 SW Third Ave., Suite 201, Portland, OR 97204, United States
AB: This talk will review molecular mechanisms of As mobilization and attenuation in subsurface sediments using examples from recent field studies that represent a range in oxidation-redox (redox) potential. As a ubiquitous trace element in sediments, As speciation and fate is linked to the abundance and biogeochemical behavior of the generally more abundant redox-active elements Fe, S, and Mn. All four elements are subject to oxidation, reduction, and pH-dependent processes such as sorption, desorption, precipitation, and dissolution, and which may include both biotic and abiotic reaction steps. We have used spectroscopic interrogation and geochemical modeling to characterize As speciation in subsurface sediments in several contrasting environments, including high and low S and Fe settings. Aquifers most at risk for contamination by As include those that are rich in organic matter and nutrients, stimulating high rates of microbial reduction and creating anoxic conditions, but limited in labile or available S and/or Fe that remove As by precipitation or adsorption. In subsurface sediments with low labile S and Fe, laboratory experiments and spectroscopic studies suggest that sediment Mn minerals are important in the oxidation of sorbed As(III) to As(V), but that they have a limited oxidation capacity. Arsenic attenuation and mobilization in the subsurface are affected by seasonal variations when hydraulic conditions are influenced by surface infiltration, which may induce transitions from oxidized to reduced conditions (or vice versa) in porewater.
DE: 0409 Bioavailability: chemical speciation and complexation
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0461 Metals
DE: 0466 Modeling
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2007 Fall Meeting