FILE - In this Aug. 9, 2012, file photo, a warning sign stands in a field contaminated with dioxin near Danang airport, during a ceremony marking the start of a project to clean up dioxin left over from the Vietnam War, at a former U.S. military base in Danang, Vietnam. The sign reads, "Dioxin contamination zone - livestock, poultry and fishery operations not permitted." (AP Photo/Maika Elan, File)