mittee discusses the selection and characteristics of the surrogate populations, the methods used for the literature searches, the criteria to distinguish key and supporting studies, and the categories of association on which the committee’s conclusions were based.

Populations of Interest

The committee reviewed and evaluated the epidemiologic literature for studies on populations with inhalation exposure to chemical mixtures that were considered to be similar to burn pit emissions, that is, mixtures formed by combustion of a variety of materials and waste in occupational and environmental exposure settings. Two occupational groups were identified as most likely to have comparable exposures: firefighters, including those with exposures to wildland and chemical fires, and incinerator workers. Firefighters are exposed to highly complex chemical mixtures (McGregor 2005; IARC 2010). The short intermittent spikes in exposure for firefighters are likely to differ from the long-term, chronic exposures to burn pit emissions on military bases; nevertheless, studies on firefighters are useful as the best available representation of exposures to mixtures of combustion products.

The waste disposed in burn pits is described by the DoD as municipal waste (Taylor et al. 2008). Therefore, occupational exposures to emissions from municipal incinerators were considered to be another surrogate for exposure of military personnel to burn pit emissions. Furthermore, because military personnel at JBB and other burn pit locations not only work on the base but also live there, the committee considered the literature on the health effects seen in residents living near municipal incinerators to be of interest. The committee acknowledges that exposures to emissions from municipal waste incinerators likely differ from exposures to burn pit emissions, and the value of these studies in understanding the health effects of burn pit exposures is limited.

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 among Gulf War veterans are particularly useful because of the common background exposures (for example, dusty environment, vehicle exhaust, munitions) and personnel characteristics (for example, underlying health, exposure to stressors, general demographics) shared by those deployed to Operation Enduring Freedom (OEF) in Afghanistan and Operation Iraqi Freedom (OIF) in Iraq.

The committee acknowledges that its ability to compare exposures among the populations of interest is restricted by the unknown degree to which exposures of varying intensity, duration (short-term, intermittent exposure to combustion products for firefighters; chronic exposures for incinerator workers and those living near incinerators; short-term exposure to oil-well–fire smoke in Kuwait), and composition can be extrapolated to the burn pit exposure of military personnel at JBB and elsewhere. Military personnel at JBB might have been exposed for a few days or up to 12 months as they lived and worked on the base whereas firefighters and incinerator workers might experience occupational exposure for many years, and residents near incinerators might be subject to a lifetime of exposure to pollutants. The committee recognized that JBB personnel may have had days of high exposures when smoke and emissions from the burn pits spread across the camp, but on other days there may have been less smoke, and the overall level of emissions was unknown. Exposure to burn pit emissions via ingestion and dermal contact is an even greater unknown as no sampling of surfaces and soil was conducted. Exposure to combustion products among all groups is likely affected by time-dependent changes in engineering or other controls. For example, some firefighter studies cited in this chapter were conducted before the use of self-contained breathing apparatus and other protective gear was common, while other studies assessed firefighters using protective gear that minimized exposure. The same is true for occupational and environment exposure to incinerator emissions; engineering controls to minimize hazardous emissions have been implemented over time. At JBB, the composition and volume of the burn pit changed as practices to separate waste and the use of incinerators were implemented. Since the composition of combustion products varies greatly depending on burn characteristics and fuel, and little is known about specific exposures to the burn pits at JBB and elsewhere, the committee was unable to directly compare constituents and concentrations of the pollutants that military personnel at JBB and the surrogate populations were exposed to, nor was it able to compare the duration and frequency of these exposures.

Furthermore, all the groups considered in this chapter experience a variety of additional exposures independent of their exposure to combustion products from burn pits, fires, or municipal incinerator emissions. These additional exposures include emissions from diesel engines (aircraft, vehicular, and machinery), kerosene heaters, and other

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