Current understanding of the impact of United States military airborne hazards and burn pit exposures on respiratory health

Abstract

Millions of United States (U.S.) troops deployed to the Middle East and Southwest Asia were exposed to toxic airborne hazards and/or open-air burn pits. Burn pit emissions contain particulate matter combined with toxic gasses and heavy metals. Ongoing research has demonstrated that exposures to the airborne hazards from military burn pits have profound and lasting health and wellness consequences. Research on the long-term health consequences of exposure to open burn pits has been limited. Work continues to understand the scope of the health impacts and the underlying pathobiology following exposures and to establish care standards. The U.S. Sergeant First Class Heath Robinson Honoring our Promise to Address Comprehensive Toxics (PACT) Act was signed into law August 2022. This act expands the benefits and services to U.S. Veterans exposed to toxicants, requires the Veterans Health Administration to provide toxic exposure screening, and supports increased research, education, and treatment due to toxic occupational exposures. This review highlights the state of the science related to military burn pit exposures research with an emphasis on pulmonary health. Clinical data demonstrate areas of reduced or delayed pulmonary ventilation and lung pathologies such as small airways scarring, diffuse collagen deposition and focal areas of ossification. Identification and characterization of foreign matter deposition in lung tissues are reported, including particulate matter, silica, titanium oxides, and polycyclic aromatic hydrocarbons. These data are consistent with toxic exposures and with the symptoms reported by post-deployment Veterans despite near-normal non-invasive pulmonary evaluations. On-going work toward new methods for non-invasive pulmonary diagnoses and disease monitoring are described. We propose various studies and databases as resources for clinical and health outcomes research. Pre-clinical research using different burn pit modeling approaches are summarized, including oropharyngeal aspiration, intranasal inhalation, and whole-body exposure chamber inhalation. These studies focus on the impacts of specific toxic substances as well as the effects of short-term and sustained insults over time on the pulmonary systems.

Keywords: Airborne hazards; Burn Pits 360; Burn pit; Implementation; Inflammation; Inhalation; Military; PACT Act; Pulmonary; Veterans.

Fig. 1

U.S. Military Burn Pit Locations in the Middle East and Southwest Asia. The images illustrate the environmental and health hazards posed by burn pits, highlighting the scale of smoke and airborne toxicants released and providing context for discussions on toxic exposures and their potential health impacts on military personnel. A, Regions and countries where burn pits were located. The fire icons indicate the approximate locations of U.S. military sites with burn pits. B, Burn pit emissions at Balad Air Base, Iraq. Photos of the Balad Burn Pit by Dr. Julie Tomáška (Ret. Air National Guard) in 2005, with permission. C, The Balad Air Base burn pit was one of the largest documented and equivalent to 7.6 American football fields. For reference, one football field is 5352 m², and the burn pit size was approximately 40,466 m². Images adapted from Perveen et al. 2023 [5]

Fig. 2

Conceptual diagram of military burn pit exposure health effects. PM and toxins are generated by incomplete combustion in burn pits. A portion of PM becomes airborne and is inhaled by personnel in the area. Inhaled PM enters the lungs where accumulation occurs coincident with activation of systemic inflammatory response. Exposure to airborne toxicants from burn pits can lead to the bioaccumulation of PM and heavy metals in the body. These toxic substances accumulate over time in various organs and tissues, creating a reservoir of harmful compounds with prolonged adverse effects [15]. Bioaccumulation contributes to systemic inflammation, a chronic immune response marked by elevated inflammatory cytokines that can affect multiple organ systems. Systemic inflammation has been identified as a key factor in the development of DRRDs, such as bronchial asthma, constrictive bronchiolitis, and interstitial lung disease. Persistent inflammation can damage lung tissues, promote fibrosis, and impair respiratory function. Moreover, chronic systemic inflammation, combined with carcinogenic substances like PAHs, can increase the risk of lung cancer by causing genetic mutations, promoting cellular proliferation, and inhibiting apoptosis [25]

Fig. 3

Burn pit simulator and rodent whole body inhalation exposure chamber system. A, iTOX Burn Pit Surrogate Generator schematic. Custom mixed pellets are used to feed fuel material into burner. Because of the modular nature, and high air flow volume, high resolution control and air sampling are possible in the burn generator and exposure chamber. HEPA: high efficiency particulate air filer; MFC: mass flow controller; LPM: liters per minute; VOC: volatile organic compound; PAH: polyaromatic hydrocarbon, GC/MS: gas chromatography/mass spectrometry. Exhaust is filtered prior to release above the Health Sciences Center roof. The entire system is enclosed in a walk-in safety hood. B, Military burn pit surrogate generator (left) and aerosol exposure system which can house rodent cages (right) contained in the WVU iTOX Inhalation Facility

Fig. 4

Characterization of emissions from rodent exposure chambers generated in the WVU iTOX burn pit simulator. Representative aerosol profile made in real-time in the exposure chamber produced by combustion of mixed wood pellets, plexiglass and JAA in the combustion chamber. A, Particle concentration. B, Size distribution determined by scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS). C, Size distribution determined by high resolution electrical low-pressure impactor (ELPI +). D, Transmission electron microscopy image of representative PM in emissions. Lower left, size bar