approach was reasonable, that the model for all its approximations held promise for developing exposure information suitable for epidemiologic studies of Agent Orange health effects, and that the model should be implemented by the Department of Veterans Affairs (VA). The application of the model for units or groups, even with very large-scale distinctions in time or location, has not been attempted. Other investigators have identified diferences in predicted ground-level spray deposition in the Stellman model compared with established pesticide-spray drift models, such as AgDRIFT. The lack of accuracy, precision, and completeness in troop-location data has also been identified as a limitation that would prevent the Stellman approach from being applied reliably to epidemiologic studies (Ginevan et al., 2009a,b). However, alternatives to the Stellman exposure-opportunity model have not been proposed. Concentrations of Agent Orange–associated TCDD in the Vietnamese environment during or shortly after the war or the number of military troops that might have been exposed to Agent Orange–associated TCDD have not been determined.

LIMITATIONS OF AND UNCERTAINTIES IN THE AVAILABLE INFORMATION

Numerous limitations and uncertainties are associated with the information that the committee used to come to its conclusions. Chief among them is the lack of environmental monitoring data on TCDD in Vietnam during the war. The committee relied on previous IOM reports (IOM, 1994, 2003, 2008, 2009) for an assessment of potential exposure of ground troops to TCDD, but those reports did not include exposure assessments for Brown Water Navy or Blue Water Navy personnel. Lack of information on the Brown Water Navy or Blue Water Navy activities, on the use of Agent Orange, and on environmental monitoring contributed to the uncertainties surrounding their potential exposure to TCDD. The committee accepted the conclusions of previous IOM committees that evaluated the utility of the Stellman exposure-opportunity model; however, the value of that model to the present committee’s charge was minimal in that no exposure values had been generated.

The committee did not believe that its charge included a review of the VA’s current approach to determining whether a Blue Water Navy veteran had been exposed to Agent Orange as that is a policy decision by



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