Lung Toxicity Testing of Simulated Military Waste Smoke from Smoldering and Flaming Combustions
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There is substantial evidence that military and civilian personnel returning from war zones (e.g., the Iraq and Afghanistan wars) have a high prevalence of adverse health outcomes associated with exposures to smoke emitted by burning waste (i.e., burn pits) in military bases but 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 simulated military burn pit combustion. 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 a mixture of plywood, cardboard and plastic under flaming and smoldering combustion phases. PM in the smoke was chemically analyzed and assessed for lung toxicity in CD-1 mice via oropharyngeal aspiration. Combustion efficiencies were 74% during smoldering and 96% during flaming phases. The combustion system sustained each phase for up to 60 min. The chemical analysis showed that plastic flaming or smoldering combustion emitted larger amounts of PM and polycyclic aromatic hydrocarbons than other burn pit materials on an equal fuel mass basis. The toxicity tests showed that smoldering plywood PM slightly induced lung toxicity (neutrophil influx) at 4 h post-exposure, but the most significant increase in neutrophil influx was observed in mice exposed to flaming plastic and mixture PM at 4 and 24 h post-exposure (on an equal PM mass basis). A significant but small alteration in lung ventilatory parameters was also observed in mice exposed to smoldering and flaming plywood and cardboard PM, and flaming mixture PM at 4 h post-exposure. PM samples did not produce any significant cellular damage in the lungs at any time point post-exposure. We demonstrate that on an equal mass basis, smoldering waste material PM caused minimal or no lung toxicity, whereas flaming PM caused significant effects following acute exposures. These findings suggest that different waste types and burning conditions can alter adverse health effects of burn pit smoke. Further research is needed to better understand lung toxicity caused by repeated, long-term exposures. [This abstract does not represent EPA policy; DoD Award # W81XWH-18-1-0731 to I.J.]