Chemical Processes Governing The Equilibrium Between Organic and Inorganic Carbon: Probing The Mechanisms of Iron Catalyzed Reactive Oxygen Species Production

This study examines the oxidation of organic carbon that occurs concurrently with the autoxidation of Fe(II) to determine the role that geochemical constituents have on both the autoxidation of Fe(II) and subsequent ROS production. The reaction between reduced carbon and oxygen is thermodynamically favorable, but kinetically proceeds slowly. Fe(II) facilitates the equilibration of reduced carbon and oxygen. This equilibration occurs naturally in saline estuaries, where oxygen rich seawater mixes with anoxic groundwater. We characterized a saline estuary at the Baruch Institute and used those characterizations to recreate natural water conditions in the lab. Using simulated natural water we then examined the role geochemical constituents like NOM and bromide have in the formation of reactive oxygen species subsequent to autoxidation of Fe(II). Superoxide forms when Fe(II) is oxidized by oxygen. Hydrogen peroxide forms when superoxide reduced by Fe(II) and when superoxide dismutates. The yield of H2O2 and the rate in which it is formed are both affected by geochemical constituents like bromide and natural organic matter. H2O2 goes on to form an additional oxidant species whose identity is in dispute. Hydroxyl radical and the ferryl ion have been proposed as the species formed. Upon examination of the yield of oxidation products in differing ionic strength solutions we determined that the hydroxyl radical is likely responsible for the oxidation observed. Finally, we examined the role that Br- and NOM play in the formation of the hydroxyl radical. We found the highest concentrations of hydroxyl radical in acidic solutions when bromide is present. Though the environmental conditions examined cover a range of conditions on earth, that range is by no means exhaustive. Nonetheless, the experimental approach employed in this study offers essential insight into how the natural environment moderates the equilibration between oxygen and reduced carbon