Limitations of Exposure Information

Determining whether or not Gulf War veterans face an increased risk of illness because of their exposures during the Gulf War requires extensive information about each exposure (e.g., the actual agent(s), duration of exposure, route of entry, internal dose) and documentation of adverse reactions. Unfortunately, very little is known about most Gulf War exposures. After the ground war, an environmental monitoring effort was initiated primarily because of concerns related to smoke from oil-well fires rather than for the other agents to which the troops may have been exposed. Consequently, exposure data for other agents are lacking or are limited.

While a variety of exposure assessment tools are being used in ongoing research to fill gaps in exposure information there are limitations to accurate reconstruction of past exposure events. For example, surveys of veterans are used to obtain recollections about agents to which they may have been exposed, although survey results may be limited by recall bias (see Chapter 3). Models are being refined to estimate exposures to sarin and cyclosarin, however, it is difficult to accurately incorporate intelligence information, meteorological data, transport and dispersion data and troop unit location information. Extensive efforts are under way to model and obtain information on potential exposures to depleted uranium, smoke from oil-well fires, and other agents. Although modeling efforts are important for discerning the details of the exposures of Gulf War veterans, these efforts are not yet complete and will require external review and validation. Further, even if there were accurate troop locations, the location of individual soldiers would be very uncertain. Because of the limitations in the exposure data, it is difficult to determine the likelihood of increased risk for disease or other adverse health effects in Gulf War veterans.

Individual Variability

Differences among individuals in their genetic, biological, psychological, and social vulnerabilities add to the complexities in determining health outcomes related to specific agents. Sensitive individuals will exhibit different responses to the same agents than members of the population without the susceptibility. For example, an individual may be a poor metabolizer of a particular substance, depending on his or her genetic makeup. Such an individual may be at higher or lower risk for specific health effects due to exposure to certain agents. Researchers are investigating the genotypes coding for two forms of an enzyme that differ in the rate at which they hydrolyze certain organophosphates (including sarin). Lower hydrolyzing activity would mean that despite identical exposure to sarin, more sarin would be bioavailable in those individuals resulting in increased anticholinesterase effects (see Chapter 5).

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