Tuesday, November 6, 2007
186-7
Alterations in Arsenic Retention Upon Reductive Transformation of Alumino-Ferrihydrite.
Yoko Masue-Slowey1, Katharine Tufano1, Richard Loeppert2, and Scott Fendorf1. (1) Geological and Environmental Sciences, Stanford University, Bldg. 320, Rm. 118, Stanford, CA 94305, (2) Soil & Crop Sciences, Texas A&M University, 2474 TAMU, College Station, TX 77843
Iron (hydr)oxides such as ferrihydrite are ubiquitous in natural environments and often exert a dominant influence on arsenic retention within soils and sediments. Reductive transformation of ferrihydrite and its impact on arsenic retention have been studied extensively; however, little is known about how structural Al within ferrihydrite, a common substitution in natural system, alters biotransformation and arsenic retention. Here we examine the extent to which structural Al influences reductive transformations of ferrihydrite and resulting impacts on arsenic retention by characterizing reaction products. Specifically, reductive transformation of Al-substituted ferrihydrite by the dissimilatory iron reducing bacterium Shewanella sp. ARM-1 was studied in the presence and absence of adsorbed arsenate. Aluminum impedes reductive transformation of ferrihydrite due to the increased stability and resulting redox insensitivity of aluminized ferrihydrite. In the absence of arsenate, the presence of Al limited transformation of ferrihyrite to 20 mole-percent Fe (13% magnetite plus 7% goethite produced), compared to 80 mole-percent Fe transformed in its absence (48% magnetite plus 32% goethite produced). Furthermore, increased arsenate loading diminished solid-phase transformation of ferrihydrite more than that of Al-substituted ferrihydrite. The presence of aluminum will alter transformation pathways and may impact arsenic (and potentially other ion) retention relative to pure Fe (hydr)oxides.