error of rejecting the null hypothesis when it is true) and type II error (the error of failing to reject the null hypothesis when the alternative hypothesis is true)” (IOM 2000a). Several of the health outcomes potentially related to exposure to burn pit emissions identified in Chapter 6 (asthma, chronic obstructive pulmonary disease [COPD], and cardiovascular disease) are sufficiently common that if large numbers of military personnel or veterans deployed to JBB can be recruited, there should be sufficient power to study the effect of such exposure. Other outcomes of interest, such as various cancers or neurological diseases, may be too uncommon for there to be adequate power to assess whether they are associated with burn pit exposures.
The committee recommends that a pilot feasibility study be conducted to assess whether there will be sufficient power to study specific health outcomes given the currently unknown number of military personnel who might have been exposed to burn pit emissions.
Exposure assessment characterizes the frequency, magnitude, and duration of exposure to an agent of concern in a population. Accurately characterizing exposure is an essential step in conducting a well-designed environmental epidemiologic study. There are a variety of methods for collecting exposure information, but the most desirable is to measure exposures quantitatively at the individual level. Individual exposure measurements can be obtained through personal monitoring data or biomonitoring. However, if individual monitoring data are not available, and they rarely are, individual exposure data may also be estimated from modeling of exposures, self-reported surveys, interviews, job exposure matrices, and environmental monitoring. At JBB, the only environmental monitoring data currently available for the period when the burn pit operated are limited numbers of measured 24-hour average air concentrations (see discussion of environmental monitoring data for JBB in Chapter 4).
Long-term average concentrations are likely to be predicted by dispersion modeling, so that such modeling might be useful in estimating gradients across JBB in long-term average exposures. If further information on the time course of quantities of material burned becomes available (that is, if records are available, or if it can be confirmed that the total amount burned was approximately proportional to the numbers of persons on the base), such information could be incorporated in the dispersion modeling, although there is no guarantee of a linear relationship between emissions and quantities burned. Such estimates of a concentration gradient might be combined with location information for persons on the base (either self-reported or based on job and housing location) to estimate differential exposures to individuals.
Biomonitoring assesses an individual’s exposure to environmental agents by measuring the concentrations of the agents in biological samples, usually blood or urine but possibly adipose tissue, hair, or nails. The biomarker can be the external substance itself (for example, lead), or a metabolite of the external substance processed by the body (for example, cotinine, a metabolite of nicotine) and it indicates the absorbed dose or allows an estimate of target-tissue dose for the time of exposure. A chemical with a short half-life in the body might be detected for only a short time after exposure and be indicative of only recent exposure; whereas, chemicals with a long half-life that are not readily metabolized or excreted tend to stay in the body and may be indicative of past and cumulative exposure. For example, serum level of dioxin, which has a long half-life in the body, has been used as a biomarker of exposure to Agent Orange for some Vietnam War veterans (Henriksen et al. 1997). As described in Chapter 4, dioxins have been measured in the air at sampling sites near the JBB burn pit; these environmental measurements might be used as a marker of exposure to burn pit emissions because there is a concentration gradient with distance from the burn pit, taking wind direction into account.
Biomonitoring may be conducted using blood specimens that are available for military personnel through the DoD Serum Repository (see below). More research is needed to identify useful, meaningful, reliable, and implementable biomarkers and methods to measure exposure to dioxins and other chemicals in burn pit emissions. The value of serum dioxin as a biomarker of exposure for residents living near municipal incinerators has been studied in Spain and Taiwan, but serum levels were not well correlated with either measured atmospheric concentrations of dioxins or distance from the incinerators (Gonzalez et al. 2000; Huang et al. 2007). An initial attempt to use serum dioxin measurements in JBB personnel did not provide useful information (Taylor et al. 2008), and the predicted increments in serum concentrations based on an estimate of air exposures are low compared with background