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3 Exposure to the Herbicides Used in Vietnam
Pages 46-64

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From page 46...
... In some cases, more detailed information is available for quantitative exposure estimates, and these can be used to construct what are sometimes called exposure metrics. The metrics integrate quantitative estimates of exposure intensity (such as chemical concentration in air or extent of skin contact)
From page 47...
... Such biologic markers of exposure integrate absorption from all routes, and their interpretation requires knowledge of pharmacokinetic processes. All those approaches have been used in studies of Vietnam veterans.
From page 48...
... Orange II 50% n-butyl ester of 2,4-D, 50% isooctyl ester 910 g/L acid equivalent After 1968 -- Unknown; at least of 2,4,5-T 3,591,000 L shipped White Acid weight basis: 21.2% triisopropanolamine By acid weight, 240 g/L 1966–1971 19,860,108 L 20,556,525 L salts of 2,4-D, 5.7% picloram 2,4-D, 65 g/L picloram (5,246,502 gal) Blue powder Cacodylic acid (dimethylarsinic acid)
From page 49...
... Agent Blue (powder and liquid) contained cacodylic acid.
From page 50...
... reacts with chloroacetic acid.
From page 51...
... EXPOSURE OF VIETNAM VETERANS Determination of exposure among US military personnel who served in Vietnam has been a great 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 exposures, whereas troops who moved through defoliated areas soon after treatment may have been exposed through soil contact, drinking water, or bathing.
From page 52...
... In the Air Force Health Study (AFHS) , the members of this Ranch Hand cohort were contrasted with Air Force personnel who had served elsewhere in Southeast Asia during the Vietnam era.
From page 53...
... . At the same time, the Center for Disease Control undertook what came to be called the Agent Orange Validation Study, measuring TCDD in the serum portion of blood from a relatively large sample of Vietnam veterans and veterans who served elsewhere during the Vietnam era (CDC, 1989b)
From page 54...
... Most vessels serving offshore but within the territorial limits of the Republic of Vietnam converted seawater to drinking water through distillation. Higher than expected mortality among Royal Australian Navy Vietnam veterans prompted a study of potable-water contamination on ships offshore during the Vietnam conflict (Mueller et al., 2001, 2002)
From page 55...
... In its charge to the original VAO committee, the Department of Veterans Affairs asked the committee to include military personnel who served in inland waterways, offshore of the Republic of Vietnam, and in the airspace above the Republic of Vietnam. A presumption of exposure to Agent Orange and other herbicides used as defoliants applied to each of those groups as well as to those who served on land.
From page 56...
... , issued a request for proposals seeking individuals and organizations to develop historical exposure-reconstruction approaches suitable for epidemiologic studies of herbicide exposure among US veterans during the Vietnam War (IOM, 1997)
From page 57...
... . The report concluded that "despite the shortcomings of the exposure assessment model in its current form and the inherent limitations in the approach, the committee agreed that the model holds promise for supporting informative epidemiologic studies of herbicides and health among Vietnam veterans and that it should be used to conduct studies." METHODOLOGIC ISSUES IN EXPOSURE ASSESSMENT Analyses of Vietnam-veteran studies have been an important source of information for understanding associations between the herbicides used in Vietnam and specific health outcomes, but, as discussed in Chapter 2, the committee has extended its review of the scientific literature to other populations in which exposure could be estimated with greater accuracy.
From page 58...
... Misclassification Exposure misclassification in epidemiologic studies can affect estimates of risk. A typical situation is in a case–control study in which the reported measurement of exposure of either group or both groups can be misclassified.
From page 59...
... Reports that define exposure in the more restricted category of "herbicides" are of greater relevance but are of little value unless it is clear from additional information that exposure to one or more of the herbicides used in Vietnam occurred in the study population, for example, TABLE 3-2  Current Committee Guidance for the Classification of Exposure Information in Epidemiologic Studies That Focus on the Use of Pesticides or Herbicides, and Relevance of the Information to the Committee's Charge to Evaluate Exposures to 2,4-D and 2,4,5-T (phenoxy herbicides) , Cacodylic Acid, and Picloram Relevance to Specificity of Exposure Committee's Reported in Study Additional Information Charge Pesticides Chemicals of interest were not used or no Not relevant additional information Chemicals of interest were used Limited relevance Herbicides Chemicals of interest were not used Not relevant No additional information Limited relevance Chemicals of interest were used Relevant Phenoxy herbicides Highly relevant 2,4-D or 2,4,5-T Highly relevant Cacodylic acida Highly relevant Picloram Highly relevant aNone of the epidemiologic studies reviewed by the committee to date have specified exposure to cacodylic acid.
From page 60...
... First, exposure of Vietnam veterans to substantial amounts of the other compounds, relative to exposure to TCDD, has not been documented. Second, the most important mechanism for TCDD toxicity involves its ability to bind to and activate the AHR.
From page 61...
... 2005. The Third Australian Vietnam Veterans Mortality Study 2005.
From page 62...
... 2001. US Army Chemical Corps Vietnam Veterans Health Study: Preliminary results.
From page 63...
... 1995. Indices of TCDD exposure and TCDD body burden in veterans of Operation Ranch Hand.
From page 64...
... 1993. Letter to the Institute of Medicine Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides regarding draft version of the IOM chapter on the US military and the herbicide program in Vietnam, May 20.


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