died from motor vehicle accidents. Veterans combat exposure was assessed using information from military personnel records on military occupational specialty code (MOSC) and from psychological autopsy. Suicide was not associated with specific combat experiences or military occupation, however symptoms related to PTSD were observed more frequently among suicide cases than accident cases.

Several other studies of Vietnam veterans have evaluated suicide as an outcome (Lawrence et al., 1985; CDC, 1987; Fett et al., 1987). However, because of methodologic problems with these studies, including variability and lack of information on herbicide exposure, and inadequate consideration of potential confounding variables in the veterans' studies, such as combat experience, it was not possible to determine whether there is an increased suicide risk associated with herbicide or TCDD exposure.

There are few studies that directly assess the cognitive effects of herbicide exposure by using standardized neuropsychological tests. In two studies that have been completed—the Vietnam Experience Study conducted by the CDC (1988) and the New Jersey Pointman study (Fiedler and Gochfeld, 1992)—neither found consistent associations between exposure and decrements in performance. One explanation for this could be the length of time that elapsed between exposure and evaluation. If herbicide exposure was associated with cognitive effects at the time of exposure, it is likely that these effects would have disappeared or been compensated for in the time since exposure ceased. A poor measure of herbicide exposure could also lead to a lack of apparent differences; problems with self-reported exposures and the use of current serum TCDD levels to estimate prior dioxin exposure are discussed in Chapter 6.

Serum TCDD concentrations from 888 participants in Operation Ranch Hand were compared to those of 856 Air Force veterans who did not participate in Ranch Hand (AFHS, 1991). The highest levels were found among the ground crew, but the variation in individual TCDD scores was considerable. In the Ranch Hands, no associations were found between body burden of TCDD (current serum levels) and reports of sleep disturbances or SCL-90 variables (e.g., anxiety, depression, somatization). Although significant results were found between serum TCDD and certain elements of the self-administered Millon Chemical Multiaxial Inventory test, which assesses basic personality patterns, pathological personality disorders, and clinical symptom syndromes, these findings were not consistent with similar variables on the SCL-90-R and other reported information.

Summary of Cognitive and Neuropsychiatric Effects

The existing literature on neurobehavioral effects of occupational, environmental, and Vietnam veterans' exposure to herbicides and related compounds

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