Superfund Research Program
The Role of Iron in Formation of Dioxins and Persistent Free Radicals (ARRA Funded)
- Project Summary
Final Progress Reports
Dr. Dellinger's research group is comparing the roles of iron oxide and copper oxide contained in fine and ultra-fine, combustion-generated particles in the surface-mediated formation of hazardous compounds. The role of iron-containing fine and ultra-fine particles on the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) from chlorinated benzenes under post-flame combustion conditions is being investigated using a high-temperature flow reactor equipped with in-line gas chromatography-mass spectroscopy. Detailed reaction kinetic models of the formation of PCDD/F from chlorinated benzenes are being developed in collaboration with the Computational Core.
During the ten months since the award of their ARRA-funded center, the researchers have focused their efforts on environmentally persistent free radical (EPFR) formation over Fe2O3-containing particles and the comparison of nanoparticles and fine particles on pollutant product distributions and yields. They have discovered substituted aromatic pollutants react with the surfaces of transition metal-containing particulate matter to form free radicals. The resulting particle-associated radicals are stabilized against decomposition and resistant to oxidation, which results in their environmental persistence with half-lives in ambient air of up to several days. These environmentally persistent free radicals have been found associated with PM emissions from thermal processing of hazardous materials and soils contaminated with hazardous wastes. When produced in extremely high concentrations in combustion and thermal processes, they can react with each other to form new pollutants, including polychlorinated dibenzo-p-dioxins and dibenzofurans. However, at somewhat lower concentrations, they persist on particulate matter and are biologically active in an exposed host.
This research identifies the mechanism by which polychlorinated dibenzo-p-dioxins and dibenzofurans and environmentally persistent free radicals are formed in thermal treatment of hazardous substances. This knowledge can be used to minimize their formation and emissions by combustion modification, including thermal quenching the cool-zone as well as avoidance of combinations of catalytic metals and potential precursors.