Lung Toxicity of Particulate Matter from Smoldering Combustion of Simulated Military Waste
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A burn pit was a common way to get rid of waste at the United States military bases in Iraq and Afghanistan between 2001 and 2011. Consequently, many deployed military and civilian personnel were exposed to burn pit smoke. While there is a higher prevalence of respiratory conditions in veterans returning from service in these locations, the relationship to burn pit smoke exposure is not well understood. We used a quartz-tube furnace coupled to a multistage cryotrap system to collect smoke particulate matter (PM) from a simulated smoldering military burn pit. We burned four materials common to burn pits: plywood (military spec wooden box), cardboard (military spec weather resistant box), plastic (a mixture of LDPE, HDPE, PET and PS), and mixture (a mixture of plywood, cardboard and plastic). PM in smoke was chemically analyzed and assessed for lung toxicity in mice via oropharyngeal aspiration and mutagenicity in Salmonella strain TA98 +/-S9. Combustion efficiency ranged from 68% to 78%. The plastic burn simulations emitted the highest PM mass, followed by the mixture, the plywood and the cardboard. PM was comprised of 42% to 64% total carbon and very low levels of polycyclic aromatic hydrocarbons (<0.1 wt%). On an equal mass basis (100 µg of PM condensate), PM from burning plywood induced small but significant lung toxicity (neutrophil influx) at 4-h post-exposure. A significant alteration in lung ventilatory parameters was also observed in mice exposed to the plywood and cardboard smoke PM at 4-h post-exposure. No effects on the lungs were observed with exposures to other smoke PM. None of the PM samples showed significant mutagenic responses. Previously we have reported that lung toxicity of biomass smoke PM is significantly greater for flaming than smoldering combustion, on an equal mass basis (Kim et al., EHP 126: 017011, 2018). Similarly, here we demonstrate that PM in smoke derived from smoldering combustion (low temperature and flameless) of different burn pit materials caused minimal or no lung toxicity and mutagenicity following acute exposures. Further studies are needed to evaluate lung toxicity of flaming combustions of these and other materials by both instillation and inhalation routes of exposures. [This abstract does not represent EPA policy; DoD Award # W81XWH-18-1-0731 to I.J.]