troops or troops that served in the military during the war but were not deployed to Vietnam (era veterans).

The committee began with the assumption that it would be possible to determine whether Blue Water Navy personnel were exposed to Agent Orange, how many might have been exposed, and the extent of their exposure. After a review of the available information, the committee decided that it would be necessary to approach its task by evaluating

  • Whether it is possible to demonstrate that Blue Water Navy personnel were or were not exposed to Agent Orange–associated TCDD, and

  • Whether it is possible to state with certainty that exposure of Blue Water Navy personnel to TCDD, taken as a group, was qualitatively different from that of their Brown Water Navy and ground troop counterparts.

PRIOR EXPOSURE ASSESSMENTS

Since the 1970s, IOM committees and other groups have attempted to determine or reconstruct Vietnam veterans’ potential exposure to Agent Orange and TCDD. In particular, two IOM committees assessed an exposure-opportunity model developed by Columbia University principal investigator Jeanne Stellman (IOM, 2003, 2008). The Stellman model is based on the Department of Defense Herbicide Reporting System files on Operation Ranch Hand spraying missions and military personnel records of veterans who served on the ground in Vietnam, including Army, Marine, Navy, and Air Force personnel. The model assigned an exposure-opportunity index value to individuals or groups that had homogeneous exposure characteristics (location and time) that were based on proximity to flight paths of aerial spraying missions and time concordance between spraying and presence in the affected areas. Full application of the exposure-opportunity model to ground troops in Vietnam was never accomplished and has never been proposed for Brown Water Navy or Blue Water Navy personnel.

The suitability of the model for classifying ground troops by degree of probable exposure for the purposes of epidemiologic study has been the subject of some discussion and analysis. The IOM report The Utility of Proximity-Based Herbicide Exposure Assessment in Epidemiologic Studies of Vietnam Veterans (IOM, 2008) concluded that the Stellman



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