CAS: Oxidation from the Top Down and the Bottom Up by the OH Radical: Lifetimes and Fates of Important Ingredients of Pesticides, Pharmaceuticals, and Consumer Products

With support from the Environmental Chemical Sciences Program in the Division of Chemistry, Professor Barbara Finlayson-Pitts and her team at the University of California, Irvine will study the degradation of contaminants of emerging concern in the environment. These include a broad spectrum of human-made products, including pesticides, pharmaceuticals, and consumer products. Their deleterious impacts on humans and the environment often become apparent only after such compounds have become distributed widely in air, water, and soils. This is to a significant extent due to their degradation in the environment to form unanticipated products that are more toxic than the parent compound. The focus of this project is on compounds that contain nitrogen. The goals are to measure how fast selected members of this group, which includes pesticides and pharmaceuticals, degrade on contact with atmospheric constituents, and to identify the products that are formed. The data generated in this project will form the core needed to assess how these synthetic chemicals are degraded under atmospheric conditions. Through a partnership with a local environmental justice community group, high school students from historically disadvantaged communities will join the team to work in their labs during the summer. The proposed research will also provide training to undergraduates and postdoctoral fellows in the integration of experiment and theory to address current important environmental problems. Two different environmentally relevant oxidation systems will be explored: hydroxyl radical (OH) oxidation from the top down, representing gas phase OH impinging on a solid, and OH oxidation from the bottom up, representing oxidation of an adsorbed organic by OH generated from a nitrite ion or TiO2 substrate. Top-down studies will probe the oxidation of thin films of the organics using attenuated total reflectance-Fourier transform infrared (ATR)-FTIR spectroscopy or in situ oxidation of organic particles in a flow system. Bottom-up studies will use OH from photolysis of solid nitrite salts or TiO2 in the presence of water. Loss of the organics and formation of products will be monitored using IR, UV and a variety of mass spectrometric techniques. The structures of the strongest binding complexes between OH and the organics will be predicted using semi-empirical quantum chemical calculations, and molecular dynamics simulations will be applied to each of these complexes in order to provide insights into the molecular basis for the experimental results. This combination of experiment and theory will help elucidate the role of OH oxidation in the degradation and fates of these synthetic compounds by these two different oxidation systems. 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.