Veterans and Agent Orange Update 2012 (2014) / Chapter Skim
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3 Exposure to the Herbicides Used in Vietnam
3 Exposure to the Herbicides Used in Vietnam
Pages 54-79
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From page 54... ...
Further discussion is presented to underscore the difficulties of assessing exposure in the complex environment that characterized Vietnam during the period of interest and to describe two modeling approaches that address exposure of ground troops to Agent Orange and that lead to different conclusions. Exposure of human populations can be assessed in a number of ways, including use of historical information, questionnaires and interviews, measurements in environmental media, and measurements in biologic specimens.
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From page 55... ...
All those exposure-assessment approaches have been used in studies of Vietnam veterans. MILITARY USE OF HERBICIDES IN VIETNAM Military use of herbicides in Vietnam took place from 1962 through 1971.
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From page 56... ...
Orange II 50% n-butyl ester of 2,4- 910 g/L acid After -- Unknown; D, 50% isooctyl ester of equivalent 1968 at least 2,4,5-T 3,591,000 L shipped White Acid weight basis: 21.2% By acid 1966– 19,860,108 L 20,556,525 L triisopropanolamine salts weight, 240 1971 (5,246,502 of 2,4-D, 5.7% picloram g/L 2,4-D, 65 gal) g/L picloram Blue Cacodylic acid Acid, 65% 1962– -- 25,650 L powder (dimethylarsinic acid)
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From page 57... ...
Agent Pink, Agent Green, Agent Purple, Agent Orange, and Agent Orange II all contained 2,4,5-T and were contaminated to some extent with TCDD. Agent White contained 2,4-D and picloram.
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From page 58... ...
reacts with chloroacetic acid.
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From page 59... ...
EXPOSURE OF VIETNAM VETERANS Determination of exposures of US military personnel who served in Vietnam has been perhaps the greatest challenge in the study of health effects associated with herbicides and TCDD. Some military personnel stationed in cities or on large bases may have received little or no herbicide exposure, whereas troops who moved through defoliated areas soon after treatment may have been exposed through soil contact, drinking water, or bathing.
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From page 60... ...
As described below, exposures of ground troops are difficult to define, so this group has not been studied as intensively. In accord with Congress's mandated presumption of herbicide exposure of all Vietnam veterans, VAO committees have treated Vietnam-veteran status as a proxy for some herbicide exposure when more specific exposure information is not available.
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From page 61... ...
. Blood samples collected from 50 Vietnam veterans in 1996 showed an association between reporting of spraying herbicides and higher serum TCDD concentrations; this finding was confirmed in a followup study of a larger fraction of the cohort (Kang et al., 2006)
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From page 62... ...
was responsible for handling, transport, and storage of Agent Orange from the time it was delivered to Vietnam until loading onto Operation Ranch Hand aircraft, Agent Orange exposures of Allied troops during these procedures may have been negligible. Exposure of Ground Troops In light of the widespread use of herbicides in Vietnam for many years, it is reasonable to assume that many military personnel were inadvertently exposed to the chemicals of concern.
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From page 63... ...
Efforts to develop exposurereconstruction models for US Vietnam veterans are discussed later in this chapter. One other effort to reconstruct exposure has been reported by researchers in the Republic of Korea who developed an exposure index for Korean military personnel who served in Vietnam (Kim et al., 2001, 2003)
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From page 64... ...
The National Academies convened the Blue Water Navy Vietnam Veterans and Agent Orange Exposure Committee to address that specific issue; its report (IOM, 2011) found that information to determine the extent of exposure experienced by Blue Water Navy personnel was inadequate, but that there were possible routes of exposure.
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From page 65... ...
However, dioxin concentrations in breast milk, even in women who lived in sprayed areas or hot spots, were lower than those documented in previous publications. The differences were attributed to the fact that the study characterized dioxin in the general population compared with the highly exposed populations of previous studies.
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From page 66... ...
, are available in the Public Access File for this project. This ongoing dispute about modeling of Vietnam veterans' exposure to herbicides played no role in the conclusions reached by the committee for this update.
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From page 67... ...
The AgDRIFT model predicts a much smaller area under the spray path and Agent Orange concentrations lower by several orders of magnitude than the EOI estimates for the same set of sample flight paths. That effect is particularly pronounced at points distant from the spray path; the AgDRIFT model predicts Agent Orange exposures up to 20 orders of magnitude lower than the EOI model at a point 4 km away from the flight-path centerline.
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From page 68... ...
The Stellman and Stellman model, for example, predicts potential exposure to troops on the basis of military data on spray history and troop locations. The AgDRIFT Tier III model, in contrast, predicts ground concentrations and their spatial dispersion; by design, the AgDRIFT model does not consider troop-location data.
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From page 69... ...
If either model is used in epidemiologic studies to predict exposure, results should be interpreted in light of the model limitations noted. The controversy surrounding the use of the EOI and AgDRIFT models points to the difficulties inherent in assessing Agent Orange exposures of Vietnam veterans.
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From page 70... ...
Those populations are discussed in detail in Chapter 5. We focus here on several key methodologic issues that complicate development of accurate estimates of exposure of the Vietnam-veteran population and the other study populations discussed in this report: the latent period between exposure and disease, exposure misclassification, and exposure specificity.
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From page 71... ...
Only a few herbicidal chemicals were used as defoliants during the Vietnam conflict: esters and salts of 2,4-D and 2,4,5-T, cacodylic acid, and picloram in various formulations. Many scientific studies reviewed by the committee report exposures to broad categories of chemicals rather than to those specific chemicals.
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From page 72... ...
aNone of the epidemiologic studies reviewed by the committee to date has specified exposure to cacodylic acid. cides" and adverse health outcomes, and others have used the category of "herbicides" without identifying specific chemicals.
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From page 73... ...
Among the various chemical classes of herbicides that have been identified in published studies reviewed by the committee, phenoxy herbicides, particularly 2,4-D and 2,4,5-T, are directly relevant to the exposures experienced by US military forces in Vietnam. On the basis of the assumption that compounds with similar chemical structure may have analogous biologic activity, information on the effects of other chemicals in the phenoxy herbicide class -- such as Silvex, 2-methyl-4-chlorophenoxyacetic acid, 2-(2-methyl-4-chlorophenoxy)
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From page 74... ...
1989b. Comparison of Serum Levels of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin with Indirect Es timates of Agent Orange Exposure Among Vietnam Veterans: Final Report.
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From page 75... ...
2009a. Assessing exposure to allied ground troops in the Vietnam War: A comparison of AgDRIFT and exposure opportunity index models.
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From page 76... ...
2008. The Utility of Proximity-Based Herbicide Exposure Assessment in Epidemiologic Studies of Vietnam Veterans.
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From page 77... ...
2006. Health status of Army Chemical Corps Vietnam veterans who sprayed defoliant in Vietnam.
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From page 78... ...
In Public Access File for the Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides: Ninth Biennial Update (received January 7, 2013)
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From page 79... ...
2011. Agent Orange exposure and attributed health effects in Vietnam veterans.
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