The History, Science and Risks of Defoliants Used in the Vietnam War

Information from historical records has been integrated with environmental fate data to provide the foundation for a joint United States-Vietnam study investigating potential residual risks in present-day Vietnam from wartime herbicide use. As a framing step, the historical use of defoliants (tactical herbicides) was summarized based on records recently made available by the United States Department of Defense and various chemical companies that produced the herbicides, and from interviews with Vietnam veterans involved in the herbicide deployment. Key information regarding the source term included the amount of dioxin contamination contained in the tactical herbicides (Orange, Purple and Pink), and specific locations where these herbicides were handled and stored in Vietnam. New data on the source term were combined with established scientific information on dioxin degradation and environmental fate to support the risk evaluations. Results indicated residual risks were unlikely except at a limited number of sites where large amounts of material were handled and residuals from unintentional releases may have persisted. Recent investigations (April 2007) confirmed that Da Nang and Bien Hoa Air Fields in Southern Vietnam have been designated as “hot spots” where spills occurred and dioxin residues have been detected. Additional site investigations and spatial analysis approaches may be warranted as a precautionary measure. The information and approaches developed under this project are relevant to ongoing research and remediation activities in Vietnam and other countries not only related to past herbicide use but to the management of environmental dioxin from other sources and other persistent organic contaminants.