Burn Pit Smoke Respiratory Effects in Mice Differ by Burn Temperature, Material, and Particle Filtration
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Exposure to smoke from combustion of synthetic materials in municipal solid waste or military burn pits may be associated with reduced respiratory function or pulmonary inflammation, similar to effects observed after wildfire smoke exposures. We examined the comparative respiratory and inflammatory effects in mice of acute exposures to smoke generated by military burn pit-related materials, plywood (PW) and cardboard (CB), under smoldering (510 °C) and flaming (640 °C) conditions. We also assessed the role of the gas phase of combustion by removing PM with HEPA filtration for a subset of each exposed group. Female Balb/cJ mice were exposed 1 hour on each of 2 consecutive days to whole or filtered smoke or clean air in a nose-only exposure tower. Smoldering combustion emissions contained ~40 (whole) or ≤ 0.2 (filtered) mg/m3 PM. Flaming conditions emitted ~4 mg/ m3 of PM in unfiltered smoke with an increase in gas phase components relative to smoldering conditions. Respiratory function was assessed by head-out plethysmography 20 min before, during, and 10 min after exposure. Whole smoke reduced breathing frequency to similar degrees in smoldering PW (-151 breaths/min vs. clean air baseline) and CB (-126), but flaming conditions caused significantly less impairment (-66.5 for PW; -73 for CB). For smoldering conditions, HEPA filtration significantly improved breathing parameters during PW exposures. However, there were no significant differences between whole and filtered CB smoke exposures. The average increase in expiratory time (Te) on both days for whole PW relative to pre-exposure (199%) was reduced to 82% with filtration, while Te increased 168% with whole CB and 148% during filtered CB. The flaming exposures showed a similar trend; PW exposure alterations was ameliorated by filtration, with CB parameters being unaffected. Bronchial lavage fluid taken 4 hours post exposure and showed no significant changes in cell population for any groups. Our data suggest that material and combustion type influence respiratory responses to burn pit combustion emissions and that PM filtration provides significant protective effects only for certain material types. (This abstract does not represent U.S. EPA policy; DoD award #W811XWH-18-1-0731 to I.J.)