Soldiers deployed during the 1991 Persian Gulf War were exposed to high concentrations of particulate matter (PM) and other airborne pollutants. Their exposures were largely the result of daily windblown dust, dust storms, and smoke from oil fires. On returning from deployment, many veterans complained of persistent respiratory symptoms. Studies of other populations have suggested that the increase in reported respiratory effects might be attributable, in part, to PM, among other exposures. With the renewed activity in the Middle East over the last few years, deployed military personnel are again exposed to dust storms and daily windblown dust in addition to other types of PM, such as diesel exhaust and particles from open-pit burning. At the beginning of military operations in Afghanistan in 2001 and in Iraq in 2003, the Department of Defense (DOD) initiated sampling of air, water, and soil to characterize the deployment environment where military personnel were stationed in the Middle East, including Egypt and central Asia. The most common airborne-pollutant measured was ambient PM. On the basis of the high concentrations observed and concerns about the potential health effects, DOD designed and implemented a study to characterize and quantify the PM in the ambient environment at 15 sites in the Middle East. The endeavor is known as the DOD Enhanced Particulate Matter Surveillance Program (EPMSP).
PARTICULATE-MATTER EXPOSURES IN THE MIDDLE EAST
Airborne PM concentrations are commonly measured as PM10 (particles less than 10 μm in diameter) and PM2.5 (fine particles, less than 2.5 μm in diameter) and less frequently as total suspended particulates (TSP). In the United States, sources of coarse particles (2.5-10 μm in diameter) include resuspension of soil from roads and streets; disturbance of soil and dust by agricultural, mining, and construction operations; and ocean spray. Sources of fine particles include emissions generated by motor-vehicle combustion, smelters, and steel mills. In the Middle East, major sources of particles may differ from those in the United States and other industrialized regions, where fossil-fuel combustion and vehicle emissions are the primary sources of PM. Some studies conducted in the
Middle East indicate higher concentrations of both PM10 and PM2.5 than in the United States and Europe. That may be partially explained by the resuspension of dust and soil from the desert floor, but there also may be substantial pollutant contributions from such combustion sources as traffic (for example, diesel emissions) and industry.
In humans, airborne PM in the ambient environment is deposited in the airways; PM10 reaches the upper airway and lung, and PM2.5 penetrates deeper and reaches the alveolar region of the lung. A large body of epidemiologic research has shown associations between short-term and long-term exposures to PM and a broad array of respiratory and cardiovascular effects in the general population and in susceptible people. The risk of various adverse health outcomes increases with exposure concentration, and there is little evidence of a concentration below which no adverse health effects are observed. However, despite the quantity of evidence, the health effects of PM in the relatively healthy, active military personnel deployed in the Middle East have not been well characterized. That may be due in part to the difficulty of conducting an exposure-assessment and health-surveillance study in a military zone, where such efforts are not essential to the military mission; there are a limited number of personnel and resources available to conduct the studies, and extreme and variable temperatures and lack of electricity create challenges in collecting ambient samples. In addition, difficulties in characterizing the multiple sources (dust storms, vehicle emissions, and emissions from burn pits) to which troops are exposed and the frequent movement of troops create challenges for health surveillance. Finally, because of differences in the concentrations and composition of PM and differences in the population of deployed military personnel, extrapolating from population-based epidemiologic studies in the United States and Europe to military populations deployed to the Middle East may not be valid.
THE DEPARTMENT OF DEFENSE ENHANCED PARTICULATE MATTER SURVEILLANCE PROGRAM
In 2005, the assistant secretary of defense for health affairs chartered the Joint Particulate Matter Working Group to identify the potential health risks associated with exposure to PM. In September of that year, a symposium was held at the National Institute for Occupational Safety and Health to review sampling results, potential health effects, and knowledge gaps pertaining to PM exposures of military personnel in the Middle East. It was concluded that there was a dearth of data to answer fundamental questions, so several suggestions were made, including the conduct of enhanced particulate-matter surveillance, performance of routine predeployment and postdeployment health evaluations, improvement in the collection of disease and non-battle-injury data, conduct of an epidemiologic study of potential adverse health effects of exposures to PM in
Middle East areas of operation, and assessment of the effects of particulate matter to which deployed personnel are exposed.
In response to an identified data need, the EPMSP was designed and implemented by the U.S. Army Center for Health Promotion and Preventive Medicine (USACHPPM)1. Fifteen sites in the Middle East were selected for sampling because of potential exposures of military personnel. At each location, military preventive-medicine or public-health personnel stationed at the sites followed sampling protocols and collected PM (TSP, PM10, and PM2.5) and bulk soil samples. Data were collected for 12 months in 2006-2007.
The U.S. Army asked the National Research Council to review the EPMSP report (Appendix D is a copy of the EPMSP report). In its evaluation, the National Research Council was asked to consider the potential acute and chronic health implications on the basis of information presented in the report. It was also asked to consider epidemiologic and health-surveillance data collected by the USACHPPM, to assess potential health implications for deployed personnel, and to make recommendations for reducing or characterizing health risks. In response, the National Research Council convened the Committee for Review of the DOD’s Enhanced Particulate Matter Surveillance Program Report, which prepared the present report.
SAMPLING DESIGN AND ANALYTIC METHODS
At each of the 15 sites2 studied by the EPMSP, TSP, PM10, and PM2.5 samples were collected with MiniVol particle samplers. Three types of particle filters were used at each site (Teflon, quartz fiber, and Nuclepore3), and the three types were analyzed with different methods. Samples were collected on a 1-day-in-6 sampling schedule in which one sample set4 was collected on a given sampling day. During a period of 1 month, there were two sampling days each for Teflon and quartz-fiber filters and one sampling day for Nuclepore filters.
Teflon and quartz-fiber filters were analyzed for mass concentration. Chemical analyses conducted on the filters included analyses for elements, soluble anions and cations, and carbon and carbonate. Individual particles were also characterized. At each of the 15 sites, one bulk sample was collected from the top layer of soil. Those samples were air-dried, and a subsample was taken for
soil chemistry, elemental composition, and mineral content. The analytic approaches used in the study were appropriate, standard methods that have been extensively used for analysis of ambient-aerosol samples.
The DOD EPMSP report presents the mass and chemical analytic data collected. The program found that PM concentrations exceeded the USACHPPM 1-year Military Exposure Guideline concentration of 15 μg/m3 for PM2.5. The chemical composition of the particles was related to the area’s geology and generally showed high concentrations of crustal materials, such as calcium and silicon. Metals, such as lead and zinc, were also identified. The EPMSP report concluded that PM “dusts” were similar in composition to those from regions in the United States that are substantially impacted by geologic material and that the three likely primary sources of air pollution were geologic dust, burn pits, and sources of metals, such as lead-smelting and manufacturing sites, although the actual sources of air pollution and their relative contributions were not confirmed. Few specifics on the quality-control and quality-assurance procedures used in collecting and analyzing the data are presented in the EPMSP report.
DEPARTMENT OF DEFENSE HEALTH-EFFECTS STUDIES
In addition to the data collected in the EPMSP, the USACHPPM conducted two epidemiologic studies that examined acute and chronic outcomes and a medical-surveillance project to investigate the potential for adverse health effects of exposure to PM during military deployment in the Middle East. Toxicologic studies were conducted by the Navy to test specific hypotheses related to the exposures that may be encountered in the field.5
One of the epidemiologic studies described by USACHPPM used a case-crossover design to evaluate the association between daily average PM2.5, PM10, and TSP concentrations collected at the 15 sites in the EPMSP and cardiovascular and respiratory health outcomes on the basis of data collected from various military medical-record databases. No statistically significant associations were found between any of the PM metrics and the health outcomes. The study authors concluded that the results were difficult to interpret because the study suffered from a lack of statistical power owing to a paucity of health-outcome events and exposure data. The second epidemiologic study used a retrospective cohort design to examine the association between time-weighted average PM2.5 and PM10 collected in the EPMSP and postdeployment cardiovascular or respiratory disease diagnoses in a cohort defined by deployment and location data. No
statistically significant increases in diagnosis rates were found after adjustment for many confounding factors. The data were limited by potential exposure and outcome misclassification and by a relatively short followup period after deployment.
The USACHPPM’s pilot medical-surveillance project was conducted at one military site and used spirometry to assess potential respiratory effects after exposures to PM. Mean postdeployment forced vital capacity and forced expiratory volume in 1 second were not significantly different from predeployment values. However, this study also suffered from inadequate statistical power and a lack of specific exposure data.
The Navy’s toxicologic studies included an evaluation of the potential for desert sand to induce pulmonary and systemic injury after exposure; exposures were benchmarked against silica as a positive control and titanium dioxide as a negative control. The Navy also evaluated the potential for cigarette smoke to potentiate injury caused by desert sand. The data showed that high-dose exposures to desert sand caused modest injury that appeared transient, as much of the short-term injury resolved following long-term monitoring. The injury and inflammation from cigarette smoke were substantially greater than injury following exposure to desert sand.
CONCLUSIONS AND RECOMMENDATIONS
The DOD EPMSP was an ambitious effort, as it was one of the first studies to measure and characterize exposures to PM in an effort to assess the health effects on military personnel in the Middle East. The committee applauds the DOD’s ability to carry out such a large-scale exposure-monitoring study in the midst of a military operation, despite the inherent challenges that result from a harsh climate and a lack of personnel and resources. The results of the EPMSP provide the basis for planning future exposure monitoring efforts that can be tied to health-effects studies, and it can and should serve as a precedent for future research and surveillance.
Although the ability to conduct such a study is a critical milestone, the design and conduct of the EPMSP and health-effects studies limit their usefulness.6 The EPMSP achieved data recovery of 88%, which is impressive in light of the challenges of implementing protocols and operating samplers in a Middle East war zone. In addition, the sampling design and analysis captured many of the important physical and chemical properties of PM that have been shown in previous studies to affect health outcomes. The EPMSP, however, did not clearly articulate its objectives a priori, nor did it demonstrate how the sampling design and analyses would address these objectives. The MiniVol sampler, although
evaluated in the United States, has not been validated at the high PM concentrations observed in this study, for example, through collection of replicate samples. The sampling strategy, which was designed to collect only one set of filters at a time, collected insufficient particle mass and species data on a consistent basis to be useful for quality assurance (QA) and for health-effects studies. Finally, the use of different filter media, which were analyzed with different techniques, introduces artifacts that make it difficult to compare results, so source-apportionment and mass-balance assessments are infeasible.
Although interpretation of the epidemiologic and health-surveillance studies was encumbered by uncertainties regarding the actual exposures, the small number of study subjects, and the limited amount of exposure data, the EPMSP results clearly document that military personnel deployed in the Middle East during the current Afghanistan and Iraq conflicts are exposed to high concentrations of PM and that the particle composition varies considerably over time and space.
The committee concludes that it is indeed plausible that exposure to ambient pollution in the Middle East theater is associated with adverse health outcomes. Some of the outcomes may present themselves as acute, affecting troop readiness during service, and some as chronic, occurring years after exposure. Therefore, to investigate further the health effects of exposure to a complex mixture of pollutants, the monitoring strategy needs to be tailored to the specific goals and hypotheses that future health-surveillance and research studies are designed to address. That includes matching the monitoring period with the deployment period of the military personnel being studied. In particular, different types of exposure monitoring may be required for the study of potential persistent effects, such as asthma and chronic obstructive pulmonary disease, compared to the study of acute effects, such as day-to-day variability in respiratory or cardiac responses.
Future monitoring studies need to include other ambient pollutants that military personnel may be exposed to in the field and that may be relevant to human health, such as ozone, air toxics, and other gaseous materials. In addition, more repeated sampling with the same filter type (for example, Teflon) would provide a greater library of gravimetric and chemical-specific data and thus increase statistical power. Finally, increasing the sampling frequency will make it possible to estimate more accurate annual-average concentrations of particle mass and chemical components.
The committee developed several overarching recommendations that cut across the entire EPMSP, including sampling, analytic approaches, and health effects. The incorporation of these recommendations would strengthen the exposure-surveillance study design and the robustness of the health-outcome analyses.
In the development of future studies by the DOD, it is important that study objectives be clearly defined to ensure that the environmental-sampling strategy meets the desired study objectives. That is, the questions that are being asked should be clearly specified a priori. Therefore, it is critical that future epidemiologic studies be undertaken in conjunction with appropriate monitoring studies so that exposure and health outcomes can be examined simultaneously.
The committee recognizes the difficulty of performing sampling and health studies in an active theater. However, it also recognizes that exposure sources in this environment are more complex and potentially more toxic than in the United States and Europe, where health studies are traditionally conducted. A more complete inventory of all major sources of ambient pollutants and potential emissions in the theater should be constructed before assessment of health effects to ensure that all relevant pollutants are monitored. Such an exercise could be based mainly on an inventory of processes, substances, and materials disposed of in burn pits. Pollutants may include the criteria pollutants (fine and coarse particle mass, carbon monoxide, lead, nitrogen dioxide, ozone, and sulfur dioxide) and other hazardous air pollutants (for example, metals, selected volatile organic compounds, and PM-associated organic compounds, such as polycyclic aromatic hydrocarbons).
After conducting an inventory of toxicants of concern and potential sources of those toxicants, health surveillance and epidemiologic studies that investigate the consequences of those exposures could benefit greatly from coordination with other large-scale efforts that are underway. An example is the Millennium Cohort Study, which has explored the impact of deployment on respiratory health.
Given the complexities of pollutant exposures and the potential acute and chronic health effects associated with these exposures, the military should consider establishing an independent multidisciplinary advisory group composed of internal and external members to provide guidance in the development and conduct of future exposure-assessment and epidemiologic studies of military personnel in combat. The advisory group—comprising experts in statistics, analytic chemistry, exposure assessment, epidemiology, toxicology, and occupational and environmental medicine—would provide guidance on and review of study objectives, study design, protocols, and results. For example, the Ranch Hand Advisory Committee was established in 1981 by the secretary of the Department of Health and Human Services to provide oversight of the Ranch Hand Study and the Vietnam Veterans Health Study.
To conduct a well-designed epidemiologic study of the potential adverse health effects of exposure to PM in deployed military personnel in the current Middle East conflict, a major effort of many units and possibly multiple military branches will be required. Such a study will be organizationally and logistically challenging, given the temporally and spatially comprehensive monitoring of PM and other pollutants and the large number of samples that would be needed.
In designing a comprehensive monitoring scheme, a set of study objectives should be developed that provides the rationale and selection of the samplers, filter media, sampling frequency, and data-quality standards to be used.
Future studies should use particle samplers that operate reliably on the basis of field testing in environmental conditions that are similar to the conditions in which they are likely to be used. For the EPMSP, such field testing was not conducted, and high PM concentrations may have led to overloading of the samplers, judging by prior results from Kuwait.
The frequency of sampling and the types of analyses applied to the samples should be tailored to the study objectives. Such an approach maximizes the benefits of the resources expended on the study.
In future monitoring studies, it is critical that QA and control procedures be implemented and specified in writing to ensure the integrity of the samples collected and analyzed.
Replicate samples should be collected at selected sites during future monitoring efforts, where feasible, to assess sampler performance.
Measurement uncertainties should be reported for all PM components. That will make it possible to interpret, with caution, the concentration data on PM components whose concentrations are mostly below the detection limit of the analytic method, as in the case of the x-ray fluorescence data.
Mass closure (that is, comparison of particle mass with the sum of the individual-particle components) should be performed as part of the overall QA process.
Because this is likely to be a continuing effort, the military might consider developing real-time continuous particulate-matter monitoring equipment whose use is recommended in the EPMSP report. Such equipment could be based on commercially available models but adapted to withstand the theater environment, including extreme temperatures, moisture, and particle concentrations; rough handling; and minimal maintenance. The monitors should be battery-powered and should report particle-size mass concentrations.
The committee recognizes the importance of this initial effort to characterize the composition of PM and to understand the potential for health effects of exposures in the active theater. The feasibility of conducting future exposure assessment and health surveillance has been demonstrated. The committee strongly endorses DOD’s effort and encourages it to continue and to expand its surveillance and research protocols to characterize health outcomes related to air-pollution exposures during military service. DOD should consider expanding
medical surveillance, especially for deployed personnel, to include additional data (for example, results of pulmonary-function tests) that could be used to assess health outcomes. The information currently collected by the military in medical databases is not designed for use in research studies to assess associations with air-pollution exposures. However, collection and use of that medical information, with an eye to developing a more robust surveillance system, could strengthen the ability to study environmental-health issues of concern.
The committee also considers that, whenever feasible, efforts should be made to minimize exposures of the troops. There are a number of ways to accomplish that; for example, if there is a prevailing wind direction, emission sources (such as burn pits and incinerators) could be located downwind of bases. For periodic emissions, such as from waste-burning, burns should take place when the prevailing meteorologic conditions favor dispersion of the emissions. That would be a general approach for reducing exposures and improving health.