From 1962 to 1971, the US military sprayed herbicides over Vietnam to strip the thick jungle canopy that could conceal opposition forces, to destroy crops that those forces might depend on, and to clear tall grasses and bushes from the perimeters of US base camps and outlying firesupport bases.
Mixtures of 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), picloram, and cacodylic acid made up the bulk of the herbicides sprayed.
The herbicide mixtures used were named according to the colors of identification bands painted on the storage drums; the main chemical mixture sprayed was Agent Orange (a 50:50 mixture of 2,4-D and 2,4,5-T). At the time of the spraying, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic form of dioxin, was an unintended contaminant generated during the production of 2,4,5-T and so was present in Agent Orange and some other formulations sprayed in Vietnam; it is important to remember that Agent Orange is not synonymous with TCDD or dioxin.
In 1991, because of continuing uncertainty about long-term health effects of the sprayed herbicides in Vietnam veterans, Congress passed Public Law (PL) 102-4, the Agent Orange Act of 1991. That legislation directed the Secretary of Veterans Affairs to ask the National Academy of Sciences (NAS) to perform a comprehensive evaluation of scientific and medical information regarding the health effects of exposure to Agent Orange, other herbicides used in Vietnam, and the various components of those herbicides, including TCDD. The legislation also instructed the
Secretary to ask NAS to conduct updates every 2 years for 10 years from the date of the first report to review newly available literature and draw conclusions from the overall evidence.
In response to the first request, the Institute of Medicine (IOM) convened a committee, whose conclusions IOM published in 1994 in Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam (VAO). The work of later committees resulted in the publication of biennial updates (Update 1996, Update 1998, Update 2000, Update 2002, and Update 2004) and of focused reports on the scientific evidence regarding type 2 diabetes, acute myelogenous leukemia in children, and the latent period for respiratory cancer.
Enacted in 2002, PL 107-103, the Veterans Education and Benefits Expansion Act of 2001, mandated that the VAO biennial updates continue through 2014. Update 2006 was the first report published under that legislation. The current update presents this committee’s review of peer-reviewed scientific reports concerning associations between health outcomes and exposure to TCDD and other chemicals in the herbicides used in Vietnam that were published in October 2006– September 2008 and the committee’s integration of this information with the previously established evidence database.