Post-Vietnam military herbicide exposures in UC-123 Agent Orange spray aircraft

During the Vietnam War, approximately 20 million gallons of herbicides, including ~10.5 million gallons of dioxin-contaminated Agent Orange, were sprayed by about 34 UC-123 aircraft subsequently used by the United States Air Force Reserves (~1971-1982) without decontamination. After many years without monitoring, tests revealed the presence of dioxin. All but three aircraft were smelted in 2009. Current Air Force and Department of Veterans Affairs policies stipulate that "dried residues" of chemical herbicides and dioxin in the post-Vietnam war use of the aircraft had not lead to meaningful exposures to flight crew and maintenance personnel, who are thus ineligible for Agent Orange-related benefits or medical examinations and treatment. We used three complementary approaches for modeling potential exposures to dioxin in these aircraft, based on the sparse monitoring data available, and found the body-burden for dermal-oral exposure for flight crew and maintainers exceeded existing guidelines. The surface wipe samples taken by the Air Force exceeded Army screening level guidelines. Two models show that the surface residues led to airborne contamination and dioxin dust adsorption. Thus inhalation, ingestion and skin absorption in aircrew and maintainers were likely to have occurred during post-Vietnam use of the aircraft. Current Air Force and Department of Veterans Affairs policies are not consistent with the available industrial hygiene measurements or with widely accepted models for semivolatile organic compounds like dioxin.