title: Numerical Modeling of Arsenic Mobility during Reductive Iron-Mineral Transformations.
abstract: Millions of individuals worldwide are chronically exposed to hazardous concentrations of arsenic from contaminated drinking water. Despite massive efforts toward understanding the extent and underlying geochemical processes of the problem, numerical modeling and reliable predictions of future arsenic behavior remain a significant challenge. One of the key knowledge gaps concerns a refined understanding of the mechanisms that underlie arsenic mobilization, particularly under the onset of anaerobic conditions, and the quantification of the factors that affect this process. In this study, we focus on the development and testing of appropriate conceptual and numerical model approaches to represent and quantify the reductive dissolution of iron oxides, the concomitant release of sorbed arsenic, and the role of iron-mineral transformations. The initial model development in this study was guided by data and hypothesized processes from a previously reported,1 well-controlled column experiment in which arsenic desorption from ferrihydrite coated sands by variable loads of organic carbon was investigated. Using the measured data as constraints, we provide a quantitative interpretation of the processes controlling arsenic mobility during the microbial reductive transformation of iron oxides. Our analysis suggests that the observed arsenic behavior is primarily controlled by a combination of reductive dissolution of ferrihydrite, arsenic incorporation into or co-precipitation with freshly transformed iron minerals, and partial arsenic redox transformations.
authors.affiliation: University of Western Australia , School of Earth and Environment, Perth, Western Australia 6009, Australia.|National Centre for Groundwater Research and Training , Adelaide, South Australia 5001, Australia.
authors.forename: Joey
authors.initials: J
authors.lastname: Rawson
authors.affiliation: University of Western Australia , School of Earth and Environment, Perth, Western Australia 6009, Australia.|National Centre for Groundwater Research and Training , Adelaide, South Australia 5001, Australia.|CSIRO Land and Water , Private Bag No. 5, Wembley, Western Australia 6913, Australia.
authors.forename: Henning
authors.initials: H
authors.lastname: Prommer
authors.affiliation: University of Western Australia , School of Earth and Environment, Perth, Western Australia 6009, Australia.|National Centre for Groundwater Research and Training , Adelaide, South Australia 5001, Australia.
authors.forename: Adam
authors.initials: A
authors.lastname: Siade
authors.affiliation: University of Western Australia , School of Earth and Environment, Perth, Western Australia 6009, Australia.|National Centre for Groundwater Research and Training , Adelaide, South Australia 5001, Australia.
authors.forename: Jackson
authors.initials: J
authors.lastname: Carr
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology , Ueberlandstrasse 133, 8600 Dübendorf, Switzerland.
authors.forename: Michael
authors.initials: M
authors.lastname: Berg
authors.affiliation: Earth Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: James A
authors.initials: JA
authors.lastname: Davis
authors.affiliation: Earth System Science Department, Stanford University , Stanford, California 94305, United States.
authors.forename: Scott
authors.initials: S
authors.lastname: Fendorf
mesh_terms: D001151:Arsenic / Q000032:analysis*; D018053:Arsenites / Q000737:chemistry; D003198:Computer Simulation; D005290:Ferric Compounds / Q000737:chemistry; D052203:Ferrosoferric Oxide / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry; D008903:Minerals / Q000737:chemistry*; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D012995:Solubility
chemical_list: D018053:Arsenites; D005290:Ferric Compounds; D008903:Minerals; C000499:ferric oxide; D019344:Lactic Acid; C092844:ferric oxyhydroxide; D007501:Iron; C015001:arsenite; D001151:Arsenic; D052203:Ferrosoferric Oxide