Know the Risks: Wildland Fire Smoke Is Not Created Equally
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Wildland fires are increasing in size and incidence across the world. Moreover, structures and other man-made objects at or near the wildland urban interphase (WUI) are increasingly being involved in these fires raising the possibility for more toxic emissions from these combustion episodes but this is not well understood. In addition to wildland fires, prescribed burns may also impact human health although how smoke differs from wildfires in terms of chemistry and toxicity is not known. We developed an automated furnace system to generate various combustion smoke emissions from different fuels with reproducible complex physico-chemical characteristics. Smoke samples were analyzed for a complete spectrum of particle and gas-phase chemical constituents. We also used an oxidation flow reactor to simulate photochemical aging of wildland fire smoke emissions. Toxicity of the smoke samples was evaluated by lung toxicity in mice (after inhalation and oropharyngeal aspiration exposures) and mutagenicity in Salmonella to assess adverse health outcomes. For the inhalation studies in mice, the atmospheres were delivered as whole smoke or filtered smoke to determine the relative contribution of gas-phase components. We demonstrated (1) how smoke emissions varied between the different types of wildland fires (e.g., peat fires, forest fires, WUI fires, and prescribed fires) and the health consequences of exposure to the smoke emissions, (2) how atmospheric photochemical aging affected the chemistry and resulting toxicity of the wildfire smoke emissions, and (3) how exposure duration and particle filtration affected breathing patterns. Our findings will help to (1) determine whether wildfire smoke is more or less toxic than urban air pollutants, (2) better understand health effects of smoke exposures from burning homes, structures, and man-made materials in the WUI areas during wildfires and (3) link observed health effects to different types and classes of chemicals (including particle versus gas phase constituents) through non-targeted bioinformatics analysis. The results will also provide chemico-toxico explanations for contrasting particle effects seen across different regions in U.S. during fire events and provide guidance on key chemical tracers required for exposure studies.