Veterans and Agent Orange Update 11 (2018) (2018) / Chapter Skim
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2 Background
2 Background
Pages 25-44
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From page 25... ...
, which contain more detailed descriptions of the topics under discussion. THE CURRENT POPULATION OF VIETNAM VETERANS Although the conflict ended more than 40 years ago, there are a substantial number of Vietnam veterans who are still living and who, because of herbicide exposure in Vietnam, may have a higher risk than the general public for various negative health effects.
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Vietnam era 8/4/64 – 1/27/73 8.7 NOTE: BLS, Bureau of Labor Statistics; DoD, Department of Defense; VA, Department of Veterans Affairs. military personnel or to track their survival.
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identified above are shown in Figure 2-1. Herbicides were identified by the color of a band on 55-gallon shipping containers and were called Agent Pink, Agent Green, Agent Purple, Agent Orange, Agent White, and Agent Blue.
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Cacodylic Acid [75-60-5] CI NH2 O HO CI As O N OH CI FIGURE 2-1 Chemical structures and Chemical Abstracts Service (CAS)
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20% isobutyl ester of 2,4,5-T 50% n-butyl ester of 2,4-D, 1,033 g/L acid 1965– 42,629,013 L 45,677,937 Orange 50% n-butyl ester of 2,4,5-T equivalent 1970 (11,261,429 L (could gal) include Agent Orange II)
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. Tests of TCDD concentrations were conducted in stocks of Agent Orange that remained after the conflict that had been returned from South Vietnam or had been procured but not shipped.
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However, two groups have been identified as high-risk subpopulations among veterans: Air Force personnel involved in Operation Ranch Hand and members of the Army Chemical Corps. Additional units and individuals handled or sprayed herbicides around bases or communication lines.
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. Exposure among Ranch Hands and the comparison group was evaluated by objective measurements of TCDD in serum samples drawn in 1987 or later, and serum TCDD concentrations were often used as the primary exposure metric for epidemiologic classification in the AFHS (AFHS, 1991a; Kern et al., 2004; Michalek et al., 2001a, 2003; Pavuk et al., 2003)
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FIGURE 2-2 Median serum TCDD levels in various study populations. NOTE: AOVS = Centers for Disease Control and Prevention's Agent Orange Validation Study (CDC, 1989a)
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For example, as part of Operation PACER IVY, Air Force personnel who were separate from, but who were also assisted by, the Ranch Hands and Army Chemical Corps were responsible for removing stocks of Agent Orange from Vietnam to Johnston Island in the central Pacific Ocean (Young, 2009)
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Agent Orange Validation Study measured TCDD concentrations in blood serum from a relatively large sample of Vietnam veterans and other Vietnam-era veterans (CDC, 1989a) but did not find a statistically significant difference in mean serum TCDD concentrations between the groups.
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. The National Academies convened the Blue Water Navy Vietnam Veterans and Agent Orange Exposure Committee to address that specific issue; its report found that there was inadequate information to determine the extent of exposure experienced by Blue Water Navy personnel, but that there were possible routes of exposure (IOM, 2011b)
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From page 37... ...
and have found pervasive exposure to dioxins more than 50 years after the Vietnam War. Dioxin concentrations in breast milk reflect the residence location of the mothers, with levels and TEQs being elevated in areas where herbicides were sprayed or stored during the war.2 Another study compared men who had lived in and around the Phu Cat airbase for 50 years or more with men who lived in the unsprayed Kim Bang district of Ha Nam Province in North Vietnam (Manh et al., 2014)
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Since over time metabolic processes would have reduced the initial chemical concentrations by many half-lives, collecting new samples would not provide valuable information about exposures that occurred during the Vietnam War even among individuals who were likely highly exposed, such as some of the Ranch Hands. For example, serum TCDD measurements taken in 2002 from the Ranch Hands were still sufficiently elevated to distinguish exposed and unexposed
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With the passage of several decades, serum concentrations decrease exponentially, and newly drawn serum samples are thus unlikely to be useful metrics for assessing health outcomes in surviving Vietnam veterans, occupational cohorts, or Seveso residents. The factors influencing TCDD's half-life are discussed in Chapter 4.
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That variable conveys a degree of authenticity that this and the prior committee strongly suspected is unmerited because there is little documentation about the source of information used to make this classification -- deployment status, entry on the Agent Orange Registry, the veteran's self-report, a physician's observation that the patient has a condition presumed to be service-related, results of serum TCDD measurements performed on some patients, or perhaps some other criterion. Regardless, none of these approaches offers a reliable method of determining whether an individual was truly exposed to herbicides (above some unspecified level)
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Studies that analyzed for dioxin-like PCDF and PCB congeners and expressed the results in terms of TEQs have also been considered since Update 1998. 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 U.S.
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Exposure Opportunity Index Model Following from recommendations contained in the first VAO report (IOM, 1994) , VA asked the National Academies to issue a request for proposals seeking individuals and organizations to develop historical exposure-reconstruction approaches suitable for epidemiologic studies of the herbicide exposure of U.S.
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DETERMINING INCREASED RISK IN VIETNAM VETERANS Part of the committee's charge -- derived from the text of Public Law 102-4 -- was to determine, to the extent permitted by the available scientific data, the increased risk of disease among veterans exposed to herbicides or the contaminant TCDD during service in Vietnam. Estimating the magnitude of risk of each particular health outcome among herbicide-exposed Vietnam veterans requires quantitative information about the dose–time response relationship for the health outcome in humans, information on the extent of herbicide exposure among Vietnam veterans, and estimates of individual exposure.
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Prior committees have thought it unlikely that additional information or more sophisticated methods would permit any sort of quantitative assessment of Vietnam veterans' increased risks of particular adverse health outcomes that are attributable to exposure to the chemicals associated with herbicide spraying in Vietnam. Even if one accepts an individual veteran's serum TCDD concentration as the best available surrogate for overall exposure to Agent Orange and the other herbicide mixtures sprayed in Vietnam, not only is it nontrivial to make this measurement, but the hurdle of accounting for biologic clearance and extrapolating to the proper timeframe remains.
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