Success is the sum of small efforts, repeated day in and day out. Robert Collier, Author of The Secret of the Ages iv ACKNOWLEDGMENTS I would like to thank Jay Thompson and David Peate for their generosity with the ICP-MS. Jay played a crucial role in developing the arsenic analytical method, and always provided me with a tuned and sensitive instrument for sample analysis. I would also like to thank Ed O'Loughlin, Max Boyanov, and Argonne National Laboratory for their willingness to provide XAS

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... data for my project. My advisor, Michelle Scherer, has taught me a great deal about aquatic geochemistry and the scientific method through the opportunity she provided me to research in the laboratory. She has also provided invaluable guidance in solving problems, maintaining focus, and making sense of data. If anyone is capable of gleaning information out of this thesis, it is due to her ability to present information in an approachable manner. The research assistants in Michelle's group helped me through countless struggles. I doubt I would even know how to pipette correctly without their guidance. I would like to thank Rob Handler, especially, for providing me with the basic knowledge and tools to pursue scientific inquiries. He was always willing to help, even in the midst of writing his own dissertation. Lastly, I thank my friends and family for helping me keep things in perspective and providing love and support. The journey hasn't always been easy, but it has been very rewarding. This research was generously funded by CGRER at The University of Iowa. v ABSTRACT Iron is ubiquitous in the environment, ranking fourth in abundance in the earth's crust. Iron is responsible for many environmental mechanisms including the distribution of plant nutrients and pollutants. Iron can exist in several minerals, including iron oxides. Arsenic is a naturally occurring metalloid which has been confirmed by the EPA as a carcinogen. Recently, an arsenic epidemic has developed in Bangladesh, poisoning an estimated 70 million people. Arsenic contamination does not exist only in the third world, but also in the United States, including Iowa. Due to the widespread distribution of arsenic and the potential for it to be leached into groundwater supplies, there has been a growing interest in establishing removal mechanisms. Atomic absorption (AA) spectroscopy and inductively coupled plasma optical emission spectrometry (ICP-OES) have been the traditional methods to measure arsenic. There has been a shift in arsenic analysis methods with the advent of more sensitive methods such as the inductively coupled plasma mass spectrometer (ICP-MS). We recently acquired a Thermo Scientific XSERIES ICP-MS at The University of Iowa, which we used to develop an arsenic analysis method in preparation for the research conducted in this study. The ICP-MS, however, only measures total arsenic concentration. As this study focused on the redox chemistry of arsenic, an alternative means for determining oxidation state was developed. As(V)-selective cartridges were used to adsorb arsenate (AsO 4 3-), while letting arsenite (AsO 3 3-) run through. This method was checked for effectiveness and used to determine aqueous arsenic oxidation state. X-ray absorption spectroscopy (XAS) was used to determine the oxidation state of arsenic adsorbed onto the surface of the iron oxide. vi Goethite (α-FeOOH) and magnetite (Fe 3 O 4 ) are both known to strongly adsorb arsenic. In this work, the potential for As(III) oxidation and As(V) reduction by goethite was studied. As documented by Amstaetter et al. (2010) , there was some evidence for adsorbed As(III) oxidation by an Fe(II)/goethite system. This study, however, also showed some evidence for oxidation of adsorbed arsenite in the presence of goethite alone. As(V) reduction by magnetite was also studied. Magnetite is capable of having different stoichiometries, or ratios of Fe(II) to Fe(III). Both an oxidized, x = 0.27, and a near-stoichiometric, x = 0.49, magnetite were studied for their ability to reduce arsenate. There was no evidence for As(V) reduction in the aqueous or adsorbed phase for either system.