Superfund Research Program
The Role of Iron in Formation of Dioxins and Persistent Free Radicals (ARRA Funded)
- Project Summary
Project Summary (2009-2011)
Although iron oxide can be present in 10x the concentration of copper oxide, its role in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) has not been researched. It is unclear why this is the case, especially since is now known, through the generation of preliminary data from Dr. Dellinger’s lab, that it also catalyzes the formation of PCDD/F from chlorinated benzenes (which are 10-100 times the concentration of chlorinated phenols in full-scale combustors) as well as chlorinated phenols. Based on previous studies, the yields of PCDD/F from these precursors for iron oxide is equal to or greater than that observed for copper oxide at identical concentrations and reaction conditions. This clearly indicates that iron can play a greater role in PCDD/F emissions than copper. In addition, new data indicates that the PCDD to PCDF ratio is lower over iron oxide than copper oxide. This may resolve a longstanding issue that laboratory studies of PCDD/F formation from chlorinated phenols over copper oxide give a PCDD to PCDF ratio of >1, while the PCDD to PCDF ratio from full-scale combustors is «1. This further supports the possibly dominant role of iron in PCDD/F formation.
Equally importantly, the researchers also suspect that it promotes the formation and stabilization of halogenated semiquinone- and phenoxyl-type PFRs that are key intermediates in formation of PCDD/F and have been shown to be highly toxic. Free radical damage induced by PFRs is the focus of the three biomedical projects. These projects are studying the effects of PFR-copper oxide particles because there is extensive chemical data on the nature of PFRs associated with copper oxide-containing ultrafine particles. Dr. Dellinger, along with Dr. Poliakoff, is focusing on iron. Thus, they are generating the chemical data necessary for the future study of the toxicology of PFR/iron-containing ultrafine particles.
In summary, this project focuses on significant new sources of PCDD/F and PFRs involving surface mediated reactions of iron. The researchers also incorporate newly developed techniques to characterize these PFRs and study the effect of particle size on their activity.