Superfund Research Program
Remediation and Health Effects
Project Leader: Ian M. Kennedy
Grant Number: P42ES004699
Funding Period: 1995-2010
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Final Progress Reports
Past work that Dr. Kennedy’s team performed on this project has shown that simulated atmospheric aging of laboratory-generated Cr-containing particles can transform hexavalent chromium to the less toxic trivalent form. The researchers also found that feeding iron (Fe) along with chromium into the burner fuel lead to the formation of ultrafine particles composed of a mixed chromium-iron solid phase. In the past year the researchers have moved from the laboratory into the ambient environment in order to investigate the forms of chromium that are present in atmospheric fine particles. Micro-focused XANES analysis of particles collected in three different locations in Northern California has revealed that the mixed Cr-Fe phase is by far the dominant form of chromium, representing 60 - 80% of all of the Cr-containing particles. The only particles that contained hexavalent chromium were those from an urban site that is also downwind of a chromium-plating facility; approximately 20% of the Cr-containing particles at this site contained hexavalent chromium.
A laboratory study of iron oxide aerosol formation in diffusion flames was carried out. Bi-modal size distributions were observed with particles in a secondary size mode that were smaller than 10 nm; these very small particles were found along with larger (50-150nm) γ-Fe2O3 particles in the post flame aerosol. The sub-10 nm iron oxide particles were scavenged by soot particles when the iron oxide aerosol is generated in sooting hydrocarbon flames. The speciation of the sub-10 nm iron oxide particles is underway to evaluate the health effect of the iron oxide, as well as the combined iron/soot particles. Preliminary EELS measurements indicate that the smallest particles are FeO, a form of iron that generates •OH in cells.
The investigators have studied the toxicity of various metal oxide aerosols, including Fe2O3, with human aortic endothelial cell cultures. Preliminary results of this study have shown dose-dependent inflammatory responses, with concurrent changes in cell integrity observed by electron microscopy. Although hydroxyl radical (•OH) is one of the most strongly oxidizing biological radicals, few studies have examined whether particles generate (•OH) in biological fluids. To examine this issue the researchers have quantitatively measured the formation of •OH produced by mixing flame soot (ethylene as fuel) with simulated lung fluid (SLF) containing hydrogen peroxide (HOOH). The team has shown that •OH is indeed generated by soot particles in simulated lung fluid. However, carbon black does not generate •OH, showing that composition of ultrafine particles is important in determining toxicity.