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Scientific Review of Agent Orange in C-123 Aircraft

VA's Office of Public Health has investigated the potential exposure to Agent Orange among crew members of C-123 aircraft used previously in spraying missions during the Vietnam War.

Although residual TCDD – the toxic substance in Agent Orange – may be detected in C-123 aircraft by sophisticated laboratory techniques many years after its use, the Office of Public Health concluded that the existing scientific studies and reports support a low probability that TCDD was biologically available in these aircraft. Therefore, the potential for exposure to TCDD from flying or working in contaminated C-123 aircraft years after the Vietnam War is unlikely to have occurred at levels that could affect health.

In 2011 and 2012, the Office of Public Health reviewed available scientific reports and peer-reviewed literature related to potential adverse health effects, such as:

  • Physical properties of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin)
  • Routes of exposure (inhalation, ingestion, dermal) and bioavailability (ability to enter the body) of TCDD over extended periods
  • Known levels of safe exposure and threshold levels of TCDD toxicity

We will continue to review new scientific information on this issue as it becomes available.

We've also asked the Institute of Medicine of the National Academy of Sciences, an independent non-governmental organization, to study possible health effects from Agent Orange in C-123 post-Vietnam crew members. Results are expected in late 2014.

Properties of TCDD

TCDD may be inhaled as an aerosol. The reports and literature demonstrated that in the vapor stage, TCDD has an atmospheric lifetime of only about three days. Dried TCDD on interior aircraft surfaces does not aerosolize when exposed to temperatures found inside aircraft during any conceivable use. There is a low probability that dried TCDD would aerosolize during routine crew use and present a risk to health by inhalation. Also, there are no data from the U.S. Air Force or other sources confirming dioxins in air samples taken from post-Vietnam C-123 aircraft.

Routes of exposure

Ingestion as a route of exposure on these aircraft would require that TCDD would need to have entered the mouth through contaminated food or water or by hands contaminated with TCDD. There is a low probability that transfer of TCDD in food or water or from hand-to-mouth could occur among these crew members, especially given that the sampling for TCDD on the aircraft surfaces required use of a solvent (hexane) to displace and dissolve any residue.

Solid TCDD can be extremely stable in the absence of direct sunlight. Once TCDD dries on hard surfaces, such as on an aircraft, it does not readily cross through human skin. Even if the dried material were to come into contact with perspiration or oils on skin, the skin would act as a barrier prohibiting further penetration of TCDD. There is a low probability that TCDD penetrated through the skin of these aircrews.

Scientific review and analysis

The Office of Public Health reviewed the following studies and reports, and will continue to review new findings relevant to this issue as they become available.

Air Force sampling reports

  • Aircraft Sampling: Westover AFB, MA. Prepared by W.W. Conway, USAF Occupational and Environmental Health Laboratory, Brooks AFB, TX; 1979.
  • Memorandum for 645 MedGrp/SGB: Consultative Letter AL/OE-CL-1994-0203, review of Dioxin Sampling results from C-123 Aircraft, Wright-Patterson AFB, OH and Recommendations for Protection of Aircraft restoration Personnel. Prepared by WH Weisman and RC Porter, Armstrong Laboratory, Brooks AFB, TX; 1994.
  • Memorandum for HQ AFMC/SGC: Consultative Letter, AL/OE-CL-1997-0053, Cleanup of Contaminated Aircraft, Aerospace Maintenance and Regeneration Center. Prepared by RC Porter, Armstrong Laboratory, Brooks AFB, TX; 1997.
  • Dioxin and Herbicide Characterization of UC-123K Aircraft – Phase I. Prepared for Director of Operations, 505 Aircraft Sustainment Squadron and Hazardous Waste Program Manager, 75CEG/CEVC, Hill AFB, UT (prepared by Select Engineering Services, Layton, UT); 2009.

Peer-reviewed literature

Risk assessment reports

Summaries of TCDD

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