As discussed in Section V, the critical dose (i.e., the amount of a contaminant actually taken in by the body necessary to cause some adverse health effect) is a combination of both the length of time an individual was exposed and the actual concentration to which the person was exposed.

Therefore, an exposure to a high concentration of a contaminant may become problematic only when the duration of the exposure results in the individual receiving a dose that exceeds the NOAEL standard for that particular contaminant. This fact has significant implications in assessing exposures received by Gulf War veterans. For example, while US personnel were exposed to high levels of PM10 during the Gulf War, the duration of these exposures averaged 153 days compared to occupational exposures, which can occur over a working lifetime. Therefore, the doses received by US personnel were not likely to have exceeded levels established to protect human health.

In general, PM may irritate healthy individuals’ eyes, nose, throat, and lungs, or cause more serious problems in sensitive populations. However, because PM consists of mixtures of different chemicals with different aerodynamic equivalent sizes, not everyone will experience the same effects. Most healthy adults will recover from short-term exposures without consequence. In general, the long-term risk from short-term exposures to PM is low.

Total dosages to silica and soot contained in PM were estimated to be below human health protection standards, and therefore, chronic health effects from these compounds are not expected. The HRA indicates that it is unlikely that a link exists between the exposures to silica and soot received in the KTO and the unexplained illnesses reported by some Gulf War veterans.

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