Characterizing Exposure of Veterans to Agent Orange and Other Herbicides Used in Vietnam: Final Report (2003)

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INTRODUCTION AND BACKGROUND 1 INTRODUCTION AND BACKGROUND ORIGIN OF THE STUDY From 1962 to 1971, US military forces sprayed over 19 million gallons of herbicides over Vietnam to strip the thick jungle canopy that helped conceal opposition forces, to destroy crops that enemy forces might depend on, and to clear tall grass and bushes from around the perimeters of US base camps and outlying fire-support bases. Most large-scale spraying operations were conducted from airplanes and helicopters, but herbicides were also sprayed from boats and ground vehicles and by soldiers wearing back-mounted equipment. After a National Institutes of Health report concluded that a contaminant in 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)—one of the primary herbicides used—could cause malformations and stillbirths in mice, US forces suspended its use. All herbicide spraying in Vietnam was halted in 1971. In response to concerns about the possible health consequences of exposure to the spraying, Congress passed Public Law 102–4, the Agent Orange Act of 1991.1 The legislation directed the Secretary of Veterans Affairs to ask the National Academy of Sciences (NAS) to conduct a comprehensive review and evaluation of available scientific and medical information regarding the health effects of exposure to Agent Orange2, other herbicides used in Vietnam, and their components, including the contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin, informally known as TCDD or dioxin. A committee convened by the Institute of Medicine (IOM) of the National Academies conducted the review and in 1994 published a comprehensive report, Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam (IOM, 1994). The committee responsible for the 1994 report encountered a severe lack of information about the exposures of individual Vietnam veterans to herbicides. Most studies of veterans had relied on rudimentary measures—self- reports of exposure, service in Vietnam, military occupation, or service in combat zones or in branches of the military responsible for combat 1 Codified as 38 USC§1116. 2 Agent Orange, the most commonly used herbicide in Vietnam, was a 1:1 mixture of 2,4 dichlorophenoxyacetic acid (2,4- D) and the n-butyl ester of 2,4,5-T. 

INTRODUCTION AND BACKGROUND 2 operations—that had limited power to differentiate the intensity and duration of exposure (IOM, 1997). This lack of information had hampered previous attempts to study the effects of herbicide exposure on the health of Vietnam veterans. That committee felt, however, that it might be possible to develop better methods of determining exposures of individual veterans by drawing on historical reconstructions. The methods might take into account such factors as troop movements, ground and perimeter spraying, herbicide shipments to various military bases, the terrain and foliage typical of the locations sprayed, the military missions of the troops there, and biochemical techniques for detecting low concentrations of dioxin in the blood. If better models of exposure could be developed and validated, a number of important epidemiologic studies of exposure to herbicides and health outcomes might become possible. The 1994 report offered recommendations concerning additional scientific studies to resolve continuing scientific uncertainty. Three of the recommendations addressed exposure-assessment studies of Vietnam veterans (IOM, 1994): • A nongovernmental organization with appropriate experience in historical exposure reconstruction should be commissioned to develop and test models of herbicide exposure for use in studies of Vietnam veterans. • The exposure reconstruction models developed…should be evaluated by an independent, nongovernmental scientific panel established for this purpose. • If the scientific panel proposed…determines that a valid exposure reconstruction model is feasible, the Department of Veterans Affairs and other government agencies should facilitate additional epidemiologic studies of veterans. The Department of Veterans Affairs (VA), in response to that report, asked IOM to establish a committee to oversee the development and evaluation of models of herbicide exposure for use in studies of Vietnam veterans. The committee would develop and disseminate a request for