Differential In Vitro Lung Cell Toxicity of Fresh and Photochemically Aged Smoke Aerosol Emissions from Simulated Wildland Fires of Duff and Surface Fuels.

We investigated the effects of the fuel moisture content and photochemical aging on the toxicity of smoke particulate matter (PM) emissions in simulated wildland fires. We burned fuel beds consisting of surface fuels and duff under moderate and low moisture contents, representative of prescribed fires (Rx) and drought-induced wildfires (Wild), respectively. The Wild emissions were photochemically aged in an oxidation flow reactor (Wild-Aged). We exposed human bronchial epithelial cells to PM extracts from each permutation. PM extracts from all experimental permutations (Rx, Wild, Wild-Aged) induced oxidative stress, evidenced by a significant increase in 8-isoprostane concentration in the cell media compared to control. However, the increase of 8-isoprostane was significantly less in Wild-Aged compared to that in Wild and Rx, indicating loss of oxidative potential due to photochemical aging. Based on the release of lactate dehydrogenase in the cell media, the level of lipid peroxidation, and the magnitude of gene fold-changes, Rx PM extracts were more toxic than Wild. Chemical composition analysis suggests that toxicity was driven by levels of aromatic species in the PM, which were highest in Rx, followed by Wild and Wild-Aged. Overall, these results highlight the complex dependence of the toxicity of wildland-fire smoke on combustion conditions and atmospheric processing.