The present report is the third comprehensive review and evaluation of the newly published scientific evidence regarding associations between health outcomes and exposure to dioxin and other chemical compounds in herbicides used in Vietnam. In accordance with P.L. 102–4, the committee was asked to determine, to the extent that available data permitted meaningful determinations, (1) whether a statistical association with herbicide exposure exists, taking into account the strength of the scientific evidence and the appropriateness of the statistical and epidemiologic methods used to detect the association; (2) the increased risk of the disease among those exposed to herbicides during Vietnam service; and (3) whether there is a plausible biologic mechanism or other evidence of a causal relationship between herbicide exposure and the disease.
DVA also asked the committee to examine the possible association between the herbicides of concern in this report and AL-type primary amyloidosis, a condition not examined in previous Veterans and Agent Orange reports.
In conducting its study, the IOM committee operated independently of the DVA and other government agencies. The committee was not asked to and did not make judgments regarding specific cases in which individual Vietnam veterans have claimed injury from herbicide exposure. Rather, the study provides scientific information for the Secretary of Veterans Affairs to consider as the DVA exercises its responsibilities to Vietnam veterans.
Chapter 2 provides an overview of the methods and conclusions of the previous Veterans and Agent Orange series reports. Chapter 3 updates the experimental toxicology data on the effects of the herbicides and 2, 3, 7, 8-TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin, commonly referred to as TCDD, or “dioxin”), a compound found as a contaminant in the herbicide 2,4,5-trichloro-phenoxyacetic acid (2,4,5-T). These data contribute to the biologic plausibility of potential health effects in human populations. Chapter 4 briefly describes the methodological considerations that guided the committee’s review and its evaluation. Chapter 5 addresses exposure assessment issues. Chapter 6 provides a general review of the epidemiologic studies used to assess the potential association between herbicides and specific health outcomes. The chapter is organized to reflect similarities and differences in the nature of exposure among three types of study populations: occupationally exposed, environmentally exposed, and Vietnam veterans. Health outcomes are addressed in the remaining chapters: Chapter 7 focuses on cancer outcomes; Chapter 8, on reproductive effects; Chapter 9, on neurobehavioral disorders; and Chapter 10, on other (noncancer) health effects including respiratory, immune system, metabolic, digestive, and circulatory disorders. Many epidemiologic studies assess multiple health outcomes. These chapters provide detailed information on and citations for the research discussed below.