Quantitative Elucidation of the Role of Natural Organic Matter Fractions and Models on the Redox Reactivity of Iron Oxide Minerals

The Environmental Chemical Sciences Program in the Chemistry Division funds Professors Lee Penn and Bill Arnold of the University of Minnesota for this project. They study pollutant degradation reactions that occur on iron oxide mineral particles in the presence and absence of natural organic matter (NOM). NOM can be found in most natural waters. It is formed from the decomposition of plant material and produced by algae and other microorganisms. NOM is a complex mixture of molecules, with some inhibiting and others facilitating reactions that occur at the liquid-mineral interface. This means that NOM impacts the persistence of pollutant molecules in the environment. The types of NOM molecules in the environment change when exposed to mineral surfaces. The NOM remaining in the water will evolve with exposure to the minerals in environmental systems, a process called fractionation. Little is known about how different fractions of NOM impact the reactivity of iron oxide mineral surfaces. Answering this question will bridge major gaps between laboratory and field studies. Results from the collaboration between the investigators will deepen fundamental understanding of the nature and evolution of NOM in environmental systems and the impact of NOM on reactions involving common organic contaminants. The broader impacts of this work include potential societal benefits caused by improved understanding of the chemical behavior of mineral surfaces in environmental systems. The major educational component focuses on high school students through a collaboration with a science teacher from a Minnesota Public School. Students receive instruction and hands on experience in using quantitative camera phone colorimetry with simulated water treatment using straw columns filled with various materials, including mineral coated sands and carbon produced from biomass.<br/><br/>A major project focus is the progressive fractionation of NOM as a function of exposure to mineral surfaces. NOM fractionation is accomplished by a combination of chemical and physical methods. The amount of NOM used in a reactor is normalized to the total organic carbon. The rate of pollutant degradation is studied in the presence of minerals and different amounts and fractions of NOM. In addition, mineral particles are characterized using advanced materials characterization methods before, during, and after reactions to identify where on the particles the reaction occurs and how the NOM fractions affect the reaction location. Results enable elucidation of the nature of NOM fractions that most strongly (and weakly) impact reactivity and thus the persistence of pollutants. The team uses NOM standards obtained from the International Humic Substances Society (IHSS) and NOM samples collected from the environment.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.