Environmentally persistent free radicals (EPFRs) are formed on the surfaces of transition metal-containing particles by chemisorption of a molecular precursor and electron transfer from the organic to the metal, resulting in reduction of the metal and formation of the EPFR. Association of some radicals with the metal increases their stability and reduces their rate of reaction with oxygen such that they can persist for several days in the environment. EPFRs have been found associated with soot and fly-ash produced from the combustion of hazardous wastes and Superfund soils from a former wood-treatment facility contaminated with pentachlorophenol. EPFRs are formed in high concentrations in the thermal and cool-zones of incinerators and other thermal treatment devices for remediation of Superfund sites where they can also react, primarily by radical-radical recombination, to form polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). This project explores the origin and fate of EPFRs in thermal treatment devices through four Specific Aims: 1) Identify the mechanisms of EPFR formation and stabilization on transition metal surfaces;2) Determine the role of iron oxide-containing, combustion-generated particles in the formation of PCDD/F from chlorobenzenes and chlorophenols;3) Assess the effect of particle size on EPFR and PCDD/F formation for Fe2O3 - containing particles;and 4) Develop Reaction Kinetic Models of Surface-Mediated Formation of EPFRs and PCDD/Fs. This project provides the basic chemistry needed for the other projects in the Center. Collaboration with Project 6 will lead to understanding how the structure and chemical properties of particles affect EPFR formation and reactivity. It provides the background for study of formation and stabilization of EPFRs in contaminated Superfund soils in Project 3. It also provides the basic biological chemistry necessary to understand the cardiac and pulmonary dysfunction induced by inhalation of EPFRs demonstrated in Biomedical Projects 2, 4, and 5. Collaboration with the Oxidative Stress Core, Materials Core, and Computational Core has already shown EPFR-particle systems participate in long chain cycles in biological media producing hydroxyl radical that initiates oxidative stress in the exposed host.
Environmentally persistent free radicals associated with Superfund particulate matter may be key intermediates in the formation of new molecular pollutants, as well as a source of the toxicity of the particles. Because they are bound to the particles, they are difficult to detect and analyze, and, as such, represent a previously unidentified environmental threat.
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