title: Association of Arsenic and Phosphorus with Iron Nanoparticles between Streams and Aquifers: Implications for Arsenic Mobility.
abstract: The microbial oxidation of organic matter coupled to reductive iron oxide dissolution is widely recognized as the dominant mechanism driving elevated arsenic (As) concentrations in aquifers. This paper considers the potential of nanoparticles to increase the mobility of As in aquifers, thereby accounting for discrepancies between predicted and observed As transport reported elsewhere. Arsenic, phosphorus, and iron size distributions and natural organic matter association were examined along a flow path from surface water via the hyporheic zone to shallow groundwater. Our analysis demonstrates that the colloidal Fe concentration (>1 kDa) correlates with both colloidal P and colloidal As concentrations. Importantly, increases in the concentration of colloidal P (>1 kDa) were positively correlated with increases in the concentration of nominally dissolved As (<1 kDa), but no correlation was observed between colloidal As and nominally dissolved P. This suggests that P actively competes for adsorption sites on Fe nanoparticles, displacing adsorbed As, thus mirroring their interaction with Fe oxides in the aquifer matrix. Dynamic redox fronts at the interface between streams and aquifers may therefore provide globally widespread conditions for the generation of Fe nanoparticles, a mobile phase for As adsorption currently not a part of reactive transport models.
authors.affiliation: Environmental Research Institute, School of Science, Faculty of Science and Engineering, University of Waikato , Hamilton, New Zealand.
authors.forename: Adam
authors.initials: A
authors.lastname: Hartland
authors.affiliation: School of Geography, Planning and Environmental Management, The University of Queensland , Brisbane, Australia.
authors.forename: Joshua R
authors.initials: JR
authors.lastname: Larsen
authors.affiliation: Connected Waters Initiative Research Centre, UNSW Australia , 110 King Street, Manly Vale, NSW 2093, Australia.
authors.forename: Martin S
authors.initials: MS
authors.lastname: Andersen
authors.affiliation: Centre for Environmental NanoScience and Risk, Arnold School of Public Health, University of South Carolina , Columbia, South Carolina 29208, United States.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Baalousha
authors.affiliation: Connected Waters Initiative Research Centre, UNSW Australia , 110 King Street, Manly Vale, NSW 2093, Australia.
authors.forename: Denis
authors.initials: D
authors.lastname: O'Carroll
mesh_terms: D000327:Adsorption; D001151:Arsenic / Q000032:analysis*; D005591:Chemical Fractionation; D003102:Colloids; D019015:Geologic Sediments / Q000737:chemistry; D060587:Groundwater / Q000032:analysis / Q000737:chemistry*; D007501:Iron / Q000032:analysis*; D053768:Metal Nanoparticles / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D008962:Models, Theoretical; D053758:Nanoparticles; D009517:New South Wales; D010084:Oxidation-Reduction; D010316:Particle Size; D010758:Phosphorus / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis
chemical_list: D003102:Colloids; D014874:Water Pollutants, Chemical; D010758:Phosphorus; D007501:Iron; D001151:Arsenic