Environmentally persistent free radicals (EPFRs) are formed on surfaces of transition metal oxides when molecules chemisorb on them. Electron transfer from the molecule to the metal results in reduction of the metal and the creation of spin density on the organic molecular adsorbate, i.e., formation of the EPFR. These "interfacial pollutants" are relatively stable (i.e., persisting for hours or days), so they can enter the environment and have deleterious health effects. Moreover, these systems are particularly prevalent at Superfund sites, so it is essential that they be studied and characterized in order to understand their roles in human health impacts in the vicinity of Superfund sites. However, these systems are complex and difficult to characterize, so we have designed this project to understand the detailed structural and chemical transformations that are responsible for their creation. Specifically, this project explores the physical and chemical characteristics of these particle-bound pollutants primarily using x-ray spectroscopy and TEM analysis. There are three Specific Aims: (1) Develop methods for controlled, reproducible generation of metal oxide-containing nanoparticles as surrogates of nanoclusters found in real-world environments, (2) Characterize the metal nanoparticles, structurally and electronically, and (3) Determine the surface processes and interactions of CHCs that lead to the formation of persistent free radicals and other toxic pollutants. This project characterizes the electron properties of the particle surface, which is indispensable for the other projects. Collaboration with Project 1 will lead to understanding of the structure and electronic properties of the EPFRs, which will allow those researchers to understand the factors affecting EPFR formation and reactivity. It generates background for studies of EPFRs in Superfund soils in Project 3. It similarly provides the chemistry necessary to understand the health effects induced by inhalation of EPFRs demonstrated in biomedical projects 2, 4, and 5. Finally, the structural characterization of the metal oxide particles and the surface-bound molecules will be indispensable for both the Computational Core, as well as the Materials Core.
Environmentally persistent free radicals associated with Superfund particulate matter may be a major source of the toxicity of the particles. Because these interfacial pollutants are composed of two components that are relatively benign individually, they are currently neither adequately recognized, nor characterized.
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