HR: 10:50h
AN: H32C-03    [Abstracts]
TI: Arsenic Mobilization Through Microbial Bioreduction of Ferrihydrite Nanoparticles
AU: * Tadanier, C J
EM: ctadanie@vt.edu
AF: Dept Geosciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061 United States
AU: Roller, J
EM: jorolle1@vt.edu
AF: Dept Geosciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061 United States
AU: Schreiber, M E
EM: mschreib@vt.edu
AF: Dept Geosciences, Virginia Tech, 4044 Derring Hall, Blacksburg, VA 24061 United States
AB: Under anaerobic conditions Fe(III)-reducing microorganisms can couple the reduction of solid phase Fe(III) (hydr)oxides with the oxidation of organic carbon. Nutrients and trace metals, such as arsenic, associated with Fe(III) hydroxides may be mobilized through microbially-mediated surface reduction. Although arsenic mobilization has been attributed to mineral surface reduction in a variety of pristine and contaminated environments, minimal information exists on the mechanisms causing this arsenic mobilization. Understanding of the fundamental biochemical and physicochemical processes involved in these mobilization mechanisms is still limited, and has been complicated by the often contradictory and interchangeable terminology used in the literature to describe them. We studied arsenic mobilization mechanisms using a series of controlled microcosm experiments containing aggregated arsenic-bearing ferrihydrite nanoparticles and an Fe(III)-reducing microorganism, Geobacter metallireducens. The phase distribution of iron and arsenic was determined through filtration and ultracentrifugation techniques. Experimental results showed that in the biotic trials, approximately 10 percent of the Fe(III) was reduced to Fe(II) by microbial activity, which remained associated with ferrihydrite surfaces. Biotic activity resulted in changes in nanoparticle surface potential and caused deflocculation of nanoparticle aggregates. Deflocculated nanoparticles were able to pass through a 0.2 micron filter and could only be removed from solution by ultracentrifugation. Arsenic mobilized over time in the biotic trials was found to be exclusively associated with the nanoparticles; 98 percent of arsenic that passed through a 0.2 micron filter was removed from solution by ultracentrifugation. None of these changes were observed in abiotic controls. Because arsenic contamination of natural waters due to mobilization from mineral surfaces is a significant route of human arsenic exposure worldwide, improved understanding of the biologically-mediated mechanisms that partition arsenic between solid and solution phases is required for development of effective treatment and remediation strategies.
DE: 1806 Chemistry of fresh water
DE: 1832 Groundwater transport
DE: 1065 Trace elements (3670)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting