Louisiana State University (Dellinger)

Summary

Project investigators are developing demonstrable and practical models for the formation of polychlorinated dibenzo-pdioxins and dibenzofurans (PCDD/F), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/F), and mixed bromo and chloro congeners (PCBDD/F) in combustion and thermal processes (cumulatively referred to as PXDD/F). It is well documented that PCDD/F will be formed in virtually any combustion/thermal process that contains a source of chlorine and carbon as well as a catalytically active transition metal such as copper, there is emerging data that PBDD/F and PCBDD/F will also form if there is a source of bromine. Since Superfund Sites contain a high concentration of both chlorinated and brominated hydrocarbons, PXDD/F represent a significant health hazard from thermal treatment or accidental fires of hazardous wastes. PCDD/F and PBDD/F may be formed by gas-phase or surface mediated pathways. Dr. Dellinger's team is characterizing the nature of combustion-generated nanoparticles and synthesizing nearly monodisperse and chemically characterized nanoparticles for further study of their catalytic properties. The investigators are also synthesizing standards for study of thermal reactions of brominated hydrocarbons and providing basic mechanistic information on their formation. These results will be used to generate data on surface mediated reactions that form PXDD/F, and perform selected studies of key elementary reactions involved in PXDD/F formation. Specifically, the researchers are:

• Determining the role of combustion-generated nanoparticles in the formation of PXDD/F and other bromo/chlorohydrocarbons.
• Formulating a mechanism of PXDD/F formation.
• Measuring and calculating the rates of key elementary reactions.
• Consolidating this information into detailed elementary reaction kinetic models.
• Identifying particles, pollutant mixtures, and combustion conditions that are most likely to have human health impacts.