Particle analysis of surgical lung biopsies from deployed and non-deployed US service members during the Global War on Terrorism

Abstract

The role that inhaled particulate matter plays in the development of post-deployment lung disease among US service members deployed to Southwest Asia during the Global War on Terrorism has been difficult to define. There is a persistent gap in data addressing the relationship between relatively short-term (months to a few years) exposures to high levels of particulate matter during deployment and the subsequent development of adverse pulmonary outcomes. Surgical lung biopsies from deployed service members and veterans (DSMs) and non-deployed service members and veterans (NDSMs) who develop lung diseases can be analyzed to potentially identify residual deployment-specific particles and develop associations with pulmonary pathological diagnoses. We examined 52 surgical lung biopsies from 25 DSMs and 27 NDSMs using field emission scanning electron microscopy (FE-SEM) with energy dispersive x-ray spectroscopy (EDS) to identify any between-group differences in the number and composition of retained inorganic particles, then compared the particle analysis results with the original histopathologic diagnoses. We recorded a higher number of total particles in biopsies from DSMs than from NDSMs, and this difference was mainly accounted for by geologic clays (illite, kaolinite), feldspars, quartz/silica, and titanium-rich silicate mixtures. Biopsies from DSMs deployed to other Southwest Asia regions (SWA-Other) had higher particle counts than those from DSMs primarily deployed to Iraq or Afghanistan, due mainly to illite. Distinct deployment-specific particles were not identified. Particles did not qualitatively associate with country of deployment. The individual diagnoses of the DSMs and NDSMs were not associated with elevated levels of total particles, metals, cerium oxide, or titanium dioxide particles. These results support the examination of particle-related lung disease in DSMs in the context of comparison groups, such as NDSMs, to assist in determining the strength of associations between specific pulmonary pathology diagnoses and deployment-specific inorganic particulate matter exposure.

Fig 1. Overall particle group distribution: Particle counts.

Fractions of total particles (from all samples, n = 52) for each major particle group. About 95% of all documented particles came from six main particle groups: clays, feldspars, quartz/silica, titanium dioxide, and two mixture groups (both including aluminosilicates, most likely clays).

Fig 2. SEM images of examples of cluster types.

All images are at 2000x magnification. (a) Elliptical cluster; (b) blocky clusters; (c) smaller clusters distributed throughout lung tissue.

Fig 3. Relative abundance of particle groups in biopsies from DSMs and NDSMs.

(a) Shows the most frequently occurring particle groups; (b) shows the minor particle groups.

Fig 4. Relative frequency of particle group types across different branches of service.

The number of samples for each is shown as (n). Each color represents a branch of service, and the dark/light tone represents DSM/NDSM.

Fig 5. Relative particle abundance by region.

Relative particle abundance across deployment regions for DSMs and overall NDSMs.

Fig 6. Particle distribution by diagnosis.

Median particle count with median absolute deviation (MAD) error bars for the most frequently occurring diagnoses.

Fig 7. Average particle chemistry by diagnosis.

Average (adjusted for “n”) (a) major and (b) minor particle group chemistry by diagnosis.

Fig 8. Geologic ternary plots for DSMs.

(a) QtFL (quartz–feldspar–lithics) plot of DSM particles. With DSM particles dominated by clays (lithics), no distinctive grouping occurs. (b) QAP (quartz–alkali feldspar–plagioclase feldspar) plot of DSM particles. There is more variation and perhaps less inhalation or sampling bias using these particle groups.