During deployment to a war zone, military personnel are exposed to a variety of environmental hazards, such as dust, intense heat and sunlight, emissions from kerosene heaters, pesticides, and depleted uranium. Exposure to many such hazards has been associated with long-term adverse health outcomes. Many military personnel returning from the current conflicts in Iraq and Afghanistan are reporting health problems that they attribute to their exposure to emissions from the burning of waste in open-air “burn pits” on military bases. Throughout the current operations in Iraq and Afghanistan, the military has routinely used burn pits to dispose of waste.
Special controversy surrounds the burn pit used to dispose of solid waste at Joint Base Balad (JBB), near Baghdad, one of the largest military bases in Iraq and a central logistics hub for U.S. forces there. The Department of Defense (DoD) has been conducting environmental monitoring and health studies at JBB since 2004 and has previously asked the National Research Council (NRC) to review its Enhanced Particulate Matter Surveillance Program. Risk assessment studies released in May 2008 and June 2009 stated that burn pits posed an “acceptable” or “safe” health risk to personnel stationed at JBB. Nevertheless, articles in the popular press have generated widespread public concern about the pits by claiming that the JBB burn pit “may have exposed tens of thousands of troops, contractors, and Iraqis to cancer-causing dioxins, poisons such as arsenic and carbon monoxide, and hazardous medical waste.” The articles helped to trigger congressional hearings and proposed legislation requiring further study of the potential health effects of exposure to burn-pit emissions on bases in Iraq and Afghanistan.
COMMITTEE’S STATEMENT OF TASK
In response to the concerns expressed by military personnel and veterans, their families, and Congress, the Department of Veterans Affairs (VA) asked the Institute of Medicine (IOM) to establish a committee to address the following statement of task:
Determine the long-term health effects from exposure to burn pits in Iraq and Afghanistan. Specifically, the committee will use the Balad Burn Pit in Iraq as an example and examine existing literature that has detailed the types of substances burned in the pits and their by-products. The committee will also examine the feasibility and design issues for an epidemiologic study of veterans exposed to the Balad burn pit.
The committee will explore the background on the use of burn pits in the military. Areas of interest to the committee might include but are not limited to investigating:
- Where are burn pits located, what is typically burned, and what are the by-products of burning;
- The frequency of use of burn pits and average burn times; and
- Whether the materials being burned at Balad are unique or similar to burn pits located elsewhere in Iraq and Afghanistan.
COMMITTEE’S APPROACH TO ITS CHARGE
IOM appointed a committee of 14 experts to carry out the study. At its first meeting, the committee decided that its approach to its task would include gathering data from the peer-reviewed literature; requesting data directly from the DoD, the VA, and other experts in the field; reviewing government documents, reports, and testimony presented to Congress; and reviewing relevant NRC and IOM reports and other literature on veterans’ health issues, specific chemicals of concern, waste incineration and combustion processes, and approaches to cumulative risk assessment. The committee also held two public sessions to hear from veterans, representatives of the DoD and the VA, and other interested parties.
The committee decided that the best approach for determining the long-term health consequences of exposure to burn pit emissions was to follow the risk assessment process originally developed by the NRC in 1983, updated in 2009, and used by many federal and private organizations for protecting human and environmental health. The committee modified it to address specific issues necessitated by the statement of task. The process begins with field or laboratory measurements to characterize the nature and extent of environmental contamination. That is followed by an assessment of the magnitude of a person’s or population’s exposure to the contaminated environmental medium (primarily air in the case of JBB) and by a determination of the inherent toxicity of the chemical. All the information is then combined to predict the probability, nature, and magnitude of the adverse health effects that may occur from exposure.
Therefore, the committee focused first on research and data collection related to exposures and health effects reported for the populations at JBB. The committee then assessed health outcomes in other human populations potentially exposed to some of the contaminants found in burn pit emissions. On the basis of the latter information, potential exposures and health effects that might occur in the populations at JBB and other burn pit locations were assessed. Finally, the committee synthesized and summarized key findings and identified data gaps. Using the synthesis, it proposed design elements for a future epidemiologic study.
Several types of data were useful to the committee: information on environmental releases and concentrations of combustion products at JBB, information on possible human exposure at JBB and elsewhere, and the potential for long-term health effects of that exposure. Characterizing environmental releases and concentrations depends mainly on information on pollutant sources, qualitative and quantitative information on the pollutants present in emissions from those sources, and pollutant fate and transport in the environment. It is also necessary to identify exposed human populations and their routes of exposure.
DoD provided raw air-sampling data collected in 2007 and 2009. The raw data were useful for determining which chemicals had been analyzed for at JBB and which ones were detectable in the ambient air. All those detected were considered worth evaluating. The committee asked the DoD for information on the types and volumes of waste burned at JBB and elsewhere in Iraq and Afghanistan, but the DoD was unable to provide the committee with any information specific to the waste stream at JBB; it did, however, provide generic information on waste streams for burn pits at U.S. bases in Kosovo, Bosnia, and Bulgaria.
The committee assumed that deployed personnel were exposed to burn pit emissions mainly by inhalation, although it recognized that some ingestion and dermal exposures were possible. On the basis of the air monitoring data received from the DoD, the committee determined the adverse health effects that might be associated with the individual chemicals that were detected or that otherwise were expected to pose the greatest risk to personnel stationed at JBB. The committee relied on published summaries from diverse sources for health effects information, including IOM and NRC reports; government reports, such as those from the U.S. Environmental Protection
Agency (EPA) and the Agency for Toxic Substances and Disease Registry (ATSDR); and established databases. The committee did not re-examine the underlying data or methods for those sources but relied on them as established sources of health-effects information.
For such chemical mixtures as burn pit emissions, toxicity and other health-effects data on mixtures themselves are generally scarce or nonexistent. Therefore, the committee sought information on health effects in other populations that were exposed to chemical mixtures that might include at least some of the constituents of burn pit emissions. The committee gave special attention to studies of other military populations, wildland and urban firefighters, municipal incinerator workers, and residents who lived near municipal waste incinerators. Some of those studies provide data on populations that had characteristics that were similar to those of the people at JBB—for example, they were young (in 2008, 62% of active-duty personnel were 18–30 years old), healthy (deployed personnel must meet health standards), predominantly male (only 14–15% of active-duty personnel are women), and exposed to similar pollutants (chemical mixtures produced by burning).
On the basis of its data collection and literature review, the committee summarized key findings on materials burned at JBB and other military burn pit locations, health-effects data on the combustion products detected at JBB, and studies of health effects in non-Balad populations potentially exposed to similar chemicals. The committee commented on its confidence in those findings and on their utility in providing the VA with information for medical followup and future studies. The committee also considered the possible effects of coexposure to local and regional air pollution from sources other than the JBB burn pit.
The committee identified gaps in the information available on possible health effects of exposure to burn pits and discussed design and feasibility issues related to an epidemiologic study of health effects to address the gaps.
USE OF MILITARY BURN PITS
Open-air waste burning has long been used by the military when other waste-disposal options have not been available. Technologic advances in recent military conflicts mean that new items are being burned—plastic bottles and electronics, for example—and the burning of such items presents new health risks.
The uncontrolled burning of waste in pits has been the primary solid-waste management solution in Afghanistan and Iraq from the beginning of the conflicts in 2001 and 2003, respectively. The use of burn pits by the U.S. military in those countries was restricted in 2009. By December 31, 2010, their use in Iraq had gradually been phased out, but it continues in Afghanistan, where 197 burn pits were operating as of January 2011.
The DoD estimates that an average of 8–10 lb of waste is generated each day by each person in theater. On the basis of the average populations of large bases in Iraq and Afghanistan (those with more than 1,000 personnel), an average of about 30–42 tons of solid waste per day might be produced on a base. JBB, with a population that sometimes surpassed 25,000—including U.S. troops, host-nation soldiers, coalition troops, civilians, and contractors—burned perhaps 100–200 tons of waste a day in 2007. In 2009, when three incinerators were operational at JBB, about 10 tons of waste was burned daily in the pit; the burn pit ceased operation as of October 1, 2009. A 2010 Army Institute of Public Health study of burn pits in Iraq and Afghanistan reported that large bases burned waste that consisted generally of 5–6% plastics, 6–7% wood, 3–4% miscellaneous noncombustibles, 1–2% metals, and 81–84% combustible materials (further details on waste composition were not available).
In response to personnel complaints of odor, poor visibility, and health effects attributed to burn pit emissions, the U.S. Army Center for Health Promotion and Preventive Medicine (CHPPM, now the U.S. Army Public Health Command) and the Air Force Institute for Operational Health conducted ambient-air sampling and screening health-risk assessments of burn pit exposures at JBB in 2007 and again in 2009. The assessments were designed to detect potentially harmful inhalation exposures of personnel at JBB to chemicals expected to be released by the burn pit. The CHPPM reports indicated that the risk of acute health effects of all chemicals detected, except coarse particulate matter (PM), was low and that long-term health risks were “acceptable” (that is, for noncancer endpoints a hazard index of less than 1.0; for cancer endpoints a risk ranging from 1 in 10,000 to 1 in 1,000,000 or lower).
AIR-MONITORING DATA FOR JBB
The committee received raw air-monitoring data on JBB from CHPPM to use in its analysis of the expected sources and nature of air pollutants. The monitoring data were used to compare the average chemical composition of air pollution at different locations on the base and with pollution profiles for other locations around the world. Of the three monitoring locations at JBB, one was considered a background site (a mortar pit) that was usually upwind of the burn pit, and the other two locations (H-6 housing/CASF and a guard tower and transportation field) were considered to be downwind of the burn pit.
Sources of regionally and locally generated air pollutants at JBB include windblown dust, local combustion sources, and volatile evaporative emissions. The local combustion sources include the burn pit or incinerators for refuse, compression ignition vehicles, aircraft engines, diesel electric generators, and local industry and households. Volatile evaporative emissions come primarily from refueling and other fuel-management activities on the base. Each of those sources emits a complex mixture of particulate and gaseous pollutants that include volatile organic compounds (VOCs), particle-phase and vapor-phase semivolatile organic compounds, metals, and PM.
Ambient air concentrations of polychlorinated dibenzo-p-dioxins and dibenzo-p-furans (PCDDs/Fs), polyaromatic hydrocarbons (PAHs), and VOCs were measured at JBB, and the committee has used the values to estimate the effect of the burn pit on air pollution at JBB. Sampling data were evaluated for composition and concentration at each of the sites with a goal of determining differences that may be attributed to the burn pit and other known sources. The conclusions of the analyses are as follows:
- Background ambient-air concentrations of PM at JBB were high, on the average higher than U.S. air-pollution standards. The high background PM concentrations were most likely derived from local sources, such as traffic and jet emissions, and regional sources, including long-range anthropogenic emissions and dust storms, although emissions from the burn pits may have contributed a small amount of PM.
- PCDDs/Fs were detected at low concentrations in nearly all samples, and the burn pit was probably the major source of these chemicals. The toxic equivalents of the concentrations were higher than those in the United States and even in polluted urban environments worldwide, but they were below those associated locally with individual sources.
- Ambient VOC and PAH concentrations were similar to those reported for polluted urban environments outside the United States, and the major sources of those pollutants were regional background, ground transportation, stationary power generation, and the JBB airport.
Although many air pollutants were measured, some probably went unmeasured because they were not targeted. Notably, the CHPPM measurement campaigns did not include ozone, carbon monoxide, nitrogen dioxide, or sulfur dioxide—which are criteria pollutants in the United States—or other chemicals associated with combustion, such as hydrogen cyanide. The burn pit is likely to have been a source of such pollutants, so the evaluation of air-monitoring data alone cannot provide a complete picture of the potential effects of burn pit emissions. The committee appreciates the air-monitoring campaigns conducted at JBB and elsewhere in the Middle East, but flaws in the sampling design and protocols prevent a thorough understanding of the nature and sources of the air pollutants detected at JBB. The committee indicates where air-monitoring campaigns might be improved for future efforts.
The committee’s conclusions suggest that the greatest pollution concern at JBB may be the mixture of regional background and local sources—other than the burn pit—that contribute to high PM. This PM, which was characterized in a different study and at different locations at JBB, consists of substantial amounts of windblown dust combined with elemental carbon and metals that arise from transportation and industrial activities. On the basis of the high concentrations in the previous studies of potentially toxic constituents of ambient PM, the air-pollution literature that focused on PM and gaseous pollutant coexposures was considered relevant to the potential morbidity of military personnel at JBB and at other sites in the Middle East.
HEALTH EFFECTS OF AIR POLLUTANTS DETECTED AT JBB
One step in the committee’s analysis of the air-monitoring data was to evaluate how often a particular pollutant was detected in the samples taken. The committee decided to focus in its assessment on the 47 pollutants that were detected in at least 5% of the air-monitoring samples collected at JBB in 2007 and 2009. The committee included an additional four pollutants (1,2,4-trichlorobenzene, 1,3-dichlorobenzene, 1,3-butadiene, and 1,2-dichlorobenzene) that were detected in fewer than 5% of samples because they are expected to be present in burn pit emissions on the basis of previous experiments on combustion products released from burning waste in barrels. The committee’s report summarizes the long-term health effects of 51 pollutants. Specific cancer and noncancer health-effects data on the 51 pollutants were obtained from EPA’s Integrated Risk Information System (IRIS), the ATSDR Toxicological Profiles, the National Institute for Occupational Safety and Health, and the National Library of Medicine’s Hazardous Substance Data Bank.
Chemicals in all three major classes of chemicals detected at JBB—PCDDs/Fs, VOCs and PAHs, and PM—have been associated with long-term health effects. A wide array of health effects has been observed in humans and animals after exposure to the specific air pollutants detected at JBB, including eye and throat irritation, organ-weight changes, histopathologic changes (for example, lesions and hyperplasia), inflammation, and reduced or impaired function. The effects have been found in many organs and systems, including adrenal glands, blood, lungs, liver, kidneys, stomach, spleen, and cardiovascular, respiratory, reproductive, and central nervous system.
The health effects of PCDDs/Fs and PM are well characterized on the basis of toxicologic, clinical, and observational epidemiologic studies. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), one PCDD congener, is classified as carcinogenic by the International Agency for Research on Cancer and as a likely carcinogen by EPA. TCDD-contaminated Agent Orange (a herbicide used in Vietnam during the war) has been associated with soft-tissue sarcoma, non-Hodgkin’s lymphoma, Hodgkin disease, and chronic lymphocytic leukemia. The health effects of exposure to dioxins and dioxin-like compounds include cancer, diabetes and other endocrine system effects, immunologic responses, neurologic effects, reproductive and developmental effects, birth defects, and wasting syndrome. Such health effects as cardiovascular and respiratory morbidity and mortality and lung cancer have been associated with exposure to PM.
The health-effects data on the other pollutants detected in more than 5% of the air samples were compiled from a variety of sources that reviewed animal studies and, less often, epidemiologic investigations. The exposure conditions in many of the studies bear little resemblance to those experienced by military personnel at JBB or other base locations; the animal studies were conducted in highly controlled environments, and many of the epidemiologic studies were conducted on general populations in rural or urban areas in relatively temperate climates. Health effects associated with five or more detected chemicals include:
- Neurologic effects and reduced CNS function.
- Liver toxicity and reduced liver function.
- Cancer (stomach, respiratory, and skin cancer; leukemia; and others).
- Respiratory toxicity and morbidity.
- Kidney toxicity and reduced kidney function.
- Blood effects (anemia and changes in various cell types).
- Cardiovascular toxicity and morbidity.
- Reproductive and developmental toxicity.
The data on single-pollutant exposures have little predictive value in connection with deployed personnel at JBB or other burn pit locations where exposures are to combinations of many pollutants from both burn pits and other local and regional sources. In addition, the exact combinations of pollutants, their magnitude, and the duration of exposure of JBB personnel are unknown. There was a general lack of data on which to base an exposure assessment. Although the committee assumed that some personnel stationed at JBB worked at or very near the burn pit, there was no indication of the number of people in the vicinity of the pit, their use of personal protective equipment, how often they were in the pit, whether there was housing downwind of the pit (other than the H-6
housing) and how many people lived there and for how long, the frequency of smoke events from the pit and what was being burned that resulted in the smoke, or how long most people were stationed at JBB and their activities. In addition, it would have been helpful to have a list of other air-pollution sources, both on base and off.
Evaluating the health effects associated with a particular pollutant yields hypotheses about potential health effects of pollutant mixtures. Such hypotheses can be investigated in two ways:
- Reviewing the epidemiologic literature on health outcomes associated with exposures to burn pit emissions (recent studies on military populations) or with exposure to emissions from combustion sources similar to burn pits (firefighters and others).
- Conducting new epidemiologic investigations.
HEALTH EFFECTS ASSOCIATED WITH COMBUSTION PRODUCTS
To determine the long-term health consequences of exposure to emissions from burn pits, the committee began by reviewing health studies of military personnel exposed to the pits in Iraq and Afghanistan. However, few such studies were available, so the committee decided to approach its review of the health effects by identifying populations that were considered to be the most similar to military personnel with regard to exposures to combustion products. Two occupational groups were identified as most likely to have comparable exposures: firefighters, including those with exposure to wildland and chemical fires, and incinerator workers. Firefighters are exposed to highly complex and variable chemical mixtures. The short intermittent spikes in firefighters’ exposures are likely to differ from the chronic exposures to burn-pit emissions that military personnel experience, but studies of firefighters are the best available representation of exposures to mixtures of combustion products. Household and industrial waste burned in municipal incinerators is similar to the waste reportedly burned in the pits on military bases in Iraq and Afghanistan, occupational exposures to emissions from municipal incinerators were considered to be another surrogate of exposure to burn pit emissions, although scrubbers and cleaning devices retain much of the emissions. Furthermore, because military personnel at JBB and other burn pit locations not only work on the base but live there, the committee considered the literature on people who lived near municipal incinerators to be of interest as well. Finally, studies of military personnel exposed to smoke from oil-well fires in Kuwait during the 1990–1991 Gulf War were also considered. Assessments of health effects in Gulf War veterans are particularly useful because the personnel exposed to burn pit emissions share background exposures (for example, dusty environment, vehicle exhaust, and munitions) and personnel characteristics (for example, underlying health, exposure to stressors, and general demographics) with those deployed to Operation Enduring Freedom (OEF) and Operation Iraqi Freedom (OIF).
Following the methods and criteria used by other IOM committees that have prepared reports for the Gulf War and Health series and the Veterans and Agent Orange series, the committee evaluated each epidemiologic study and designated it as a key or supporting study. The committee then discussed the weight of evidence and reached a consensus on the categories to which to assign the health outcomes considered in its report. The following categories of association were used:
- Sufficient evidence of a causal relationship: Evidence is sufficient to conclude that a causal relationship exists between exposure to combustion products and a health outcome in humans. The evidence fulfills the criteria for sufficient evidence of a causal association and satisfies several of the criteria used to assess causality: strength of association, dose–response relationship, consistency of association, temporal relationship, specificity of association, and biologic plausibility.
- Sufficient evidence of an association: Evidence is sufficient to conclude that there is a positive association. That is, a positive association has been observed between exposure to combustion products and a health outcome in human studies in which bias and confounding could be ruled out with reasonable confidence.
- Limited/suggestive evidence of an association: Evidence is suggestive of an association between exposure to combustion products and a health outcome in humans, but it is limited because chance, bias, and confounding could not be ruled out with reasonable confidence.
- Inadequate/insufficient evidence to determine whether an association exists: The available studies are of insufficient quality, consistency, or statistical power to permit a conclusion regarding the presence or absence of an association between exposure to combustion products and a health outcome in humans.
- Limited/suggestive evidence of no association: Several adequate studies, covering the full range of levels of exposure that humans are known to encounter, are mutually consistent in not showing a positive association between exposure to combustion products and a health outcome. A conclusion of no association is inevitably limited to the conditions, levels of exposure, and length of observation covered by the available studies. In addition, the possibility of a small increase in risk at the levels of exposure studied can never be excluded.
The studies discussed by the committee have limitations and uncertainties—some common to epidemiologic studies in general, and some specific to studies of working populations. The limitations and uncertainties include the healthy worker effect, exposure misclassification, lack of information on confounders, inadequate statistical power, disease misclassification, and publication bias.
On the basis of a review of the epidemiologic literature, the committee concluded that there is inadequate/insufficient evidence of an association between exposure to combustion products and cancer, respiratory disease, circulatory disease, neurologic disease, and adverse reproductive and developmental outcomes in the populations studied. However, there is limited/suggestive evidence of an association between exposure to combustion products and reduced pulmonary function in the populations studied. The committee further concluded that additional study of health effects specifically in OEF and OIF veterans is necessary. The research considered by the committee is a best attempt to use currently available information on combustion products to extrapolate to exposures of military personnel stationed at JBB; however, because of differences in exposure, stress, population characteristics, access to medical care, and monitoring of health, the results in firefighters, incineration workers, and people living near incinerators may not be generalizable to military personnel exposed to emissions from burn pits.
The committee based its conclusions regarding the long-term health consequences of exposure to emissions from burn pits in Iraq and Afghanistan on three sources of information: data on air monitoring at JBB, health-effects information on chemicals detected in more than 5% of the air-monitoring samples at JBB, and health-effects information on populations considered to be surrogates of military personnel exposed to combustion products from burn pits: firefighters, municipal incinerator workers, residents who live near incinerators, and veterans of the 1990–1991 Persian Gulf War who were exposed to smoke from oil-well fires.
The air-monitoring data suggest that the pollutants of greatest concern at JBB may be the mixture of chemicals from regional background and local sources—other than the burn pit—that contribute to high PM. The PM consists of substantial amounts of windblown dust combined with elemental carbon and metals that arise from transportation and industrial activities. On the basis of the high concentrations and the observation of potentially toxic constituents in ambient PM in previous studies, the air-pollution literature on PM and gaseous-copollutant exposures is considered relevant to the potential morbidity of military personnel at JBB and at other sites in the Middle East.
In light of its assessment of health effects that may result from exposure to air pollutants detected at JBB and its review of the literature on long-term health effects in surrogate populations, the committee is unable to say whether long-term health effects are likely to result from exposure to emissions from the burn pit at JBB. However, the committee’s review of the literature and the data from JBB suggests that service in Iraq or Afghanistan—that is, a broader consideration of air pollution than exposure only to burn pit emissions—might be associated with long-term health effects, particularly in highly exposed populations (such as those who worked at the burn pit) or susceptible populations (for example, those who have asthma), mainly because of the high ambient concentrations of PM from both natural and anthropogenic, including military, sources. If that broader exposure to air pollution turns out to be sufficiently high, potentially related health effects of concern are respiratory and cardiovascular effects and cancer. Susceptibility to the PM health effects could be exacerbated by other exposures, such as stress,
smoking, local climatic conditions, and coexposures to other chemicals that affect the same biologic or chemical processes. Again, further information on which to base an exposure assessment would have been helpful.
Specifically, none of the individual chemical constituents of the combustion products emitted at JBB appears to have been present at concentrations likely to be responsible for the adverse health outcomes studied in this report. However, the possibility of exposure to mixtures of those chemicals raises the potential for health outcomes associated with cumulative exposure to combinations of the constituents in burn pit emissions. As a preliminary step toward understanding possible long-term health effects of multiple contaminants or cumulative exposure, the committee looked at all the detected pollutants and the target organs or specific effects associated with them. Because a specific adverse health outcome may be influenced by several chemicals in a mixture, the overall effect of the mixture may be to increase the likelihood or severity of the outcome. Many of the chemicals detected at JBB are known to produce similar health effects—for example, anemia, reduced liver function, and birth defects—or to act on the same organs or organ systems, such as the liver, kidneys, central nervous system, and cardiovascular system.
NEW STUDY DESIGN AND FEASIBILITY
The available epidemiologic studies considered by the committee for this report are inconsistent in quality, were conducted with varied methodologic rigor, and had considerable variations in study design and sample size. The CHPPM report that described several health outcomes in personnel stationed at JBB is the first step in addressing some of those issues, but the period of followup was too short to detect long-term health effects. In addition, the difficulties in determining exposure are apparent, and better exposure assessment is critical if one is to attribute adverse health outcomes to burn pit exposures rather than to exposures common to war and desert environments.
Most critically, the database on the nature and extent of exposure to combustion products is incomplete. Given an awareness of the data gaps and analytic limitations in the studies reviewed for this report, the committee recommends a prospective study of the long-term health effects of exposure to burn-pit emissions in military personnel deployed at JBB. To determine the incidence of chronic diseases or cancers that have long latency, people must be followed for many years. Thus, it is critical that observation for health effects begin at first deployment to JBB and continue long enough after active duty is completed to detect latent health effects. The committee recommends that pilot studies be conducted to address issues of statistical power and to develop design features for specific health outcomes. It is important to note that once a prospective cohort infrastructure has been established, multiple health outcomes can be studied in the cohort over time. Intermediate outcomes on the pathway to the development of chronic diseases can also be studied in a serial manner.
To characterize exposures to the complex mixture of burn pit emissions in light of the presence of other sources of air pollutants in the ambient environment, the committee recommends a tiered approach. The three tiers of the recommended study are characterized by the decreasing specificity of exposure and would answer different research questions, as follows:
- Tier 1: Did proximity to burn pit operations at JBB increase the risk of adverse health outcomes?
Assess individual exposure to JBB burn pit emissions (for example, low, medium, and high) on the basis of dates of deployment, duties on base, and location of housing relative to the burn pit, taking account of wind-dispersion models. The exposure effect can be assessed by comparing subgroups with more and less exposure among all potentially exposed people, that is, those stationed at JBB during the period of full burn-pit operation (2003–2007). The use of soil dioxin concentrations at various locations at JBB should be considered as a potential marker of exposure to burn pit emissions.
- Tier 2: Did installation of incinerators at JBB reduce the incidence of disease or intermediate outcomes (for example, the rate of lung-function decline or the increase in intima–media thickness)?
Assess exposure (yes or no) to the JBB burn pit according to date of initial deployment. This approach considers the installation of incinerators during 2008–2010 to replace the burn pit as an intervention. Chronic health outcomes in those deployed before and those deployed after the burn pit was shut down can be compared, and the increased use of incinerators over 2 years can be factored in.
- Tier 3: Did deployment at JBB during full burn pit operation increase the risk of adverse health outcomes compared with deployment elsewhere in Iraq or Afghanistan or with no deployment?
Assess exposure (yes/no) to the total JBB environment, recognizing that the burn pit emissions occurred in the presence of PM and other air pollutants from other sources. This broad definition of exposure can be assessed by comparing the health experience of military personnel deployed at the JBB during the period of burn pit operation to that of military personnel deployed to Iraq and Afghanistan at locations without a burn pit or that of military personnel not deployed to the Middle Eastern theatre during the same time. This approach was used to conduct the short-term health studies described in Chapter 6. Although there are limitations to this approach, it may be possible to find an appropriate unexposed comparison group—preferably another deployed population unexposed to burn pits but exposed to PM and other chemicals identified at JBB from other sources. The recommendation for a nondeployed comparison group is based on the committee’s judgment that pollution in the region from sources other than burn pits may pose greater health risks than burn pit emissions.