TCDD. Given the lack of exposure data on ground troops and the limited knowledge about exposure among Blue Water Navy veterans, the committee concluded that it was not possible to make quantitative exposure comparisons among the three military populations of interest to the VA. Therefore, the committee evaluated the plausibility of exposure of the three populations to Agent Orange and TCDD via various mechanisms and routes.

The committee recognized that considerable variability exists in the potential for TCDD exposure by Blue Water Navy personnel, ground troops, and Brown Water Navy personnel. Focusing on the Blue Water Navy, some personnel may have spent their entire tour of duty on aircraft carriers that never came close to the Vietnamese coast, whereas others served on ships that may have spent many days as close as 1 mile offshore. In addition to the variability in the location of Blue Water Navy personnel, there is extensive uncertainty regarding the experiences of individual sailors on those ships (for example, whether they were on a ship when it was near the Vietnamese coast, whether they went swimming, and whether they ate local food from Vietnam or Vietnamese waters).

The committee concluded that, qualitatively, ground troops and Brown Water Navy veterans had more plausible pathways of exposure (that is, there was a greater number of plausible exposure mechanisms) to Agent Orange–associated TCDD than did Blue Water Navy veterans. One exposure mechanism is specific to Blue Water Navy ships: possible TCDD contamination of potable water from onboard distillation plants. The committee’s assessment corroborates the Australian finding that in experiments simulating the water-distillation system used on Navy ships the system had the potential to enrich TCDD concentrations from the feed water to the distilled potable water. However, without information on the TCDD concentrations in the marine feed water, it is impossible to determine whether Blue Water Navy personnel were exposed to Agent Orange–associated TCDD via ingestion, dermal contact, or inhalation of potable water.

The committee was unable to state with certainty that Blue Water Navy personnel were or were not exposed to Agent Orange and its associated TCDD. Owing to a lack of data on environmental concentrations of Agent Orange and Agent Orange–associated TCDD and an inability to reconstruct likely concentrations, as well as the dearth of information about relative exposures among the ground troops and Brown Water Navy personnel and Blue Water Navy personnel, it is

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