Wildland-Urban Interface Fires: Toxic Physicochemical Properties of Emitted Particulate Matter and Impacts on Lung Macrophages

Due to the growth of urban areas in close proximity to wildlands, wildfires increasingly burn both biomass and man-made materials. The physicochemical properties of emitted particulate matter (PM) from such "wildland-urban interface (WUI)" fires may differ substantially from those of wildland fires and other ambient PM sources. However, the associations between properties and hazards of WUI fire PM have not been studied. Here, we employed a wildfire simulator (WiFS) to reproduce biomass and WUI fires by combusting pinewood and a simplistic WUI fire model (1:1 mixture of pinewood and polyethylene), respectively. WUI fire PM contained high concentrations of the highly toxic and carcinogenic PAH benzo[c]fluorene and significant amounts of highly bioactive alkyl and oxygenated PAHs, which were both absent in biomass fire PM, and had a carcinogenicity potential (benzo[a]pyrene equivalents, BaP_Eq) 20 times higher than biomass fire PM. Additionally, exposure of THP-1 macrophages to WUI fire PM, but not biomass fire PM, caused significant reductions in viability and mitochondrial potential, significantly decreased phagocytosis of 1 μm beads, and substantial dysregulation of gene expression. These findings suggest that WUI fire PM exposure may be more hazardous than wildland fire PM exposure, likely due to differences in their chemical profiles.