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Characterizing Exposure ... Final Report
INTRODUCTION AND BACKGROUND
Origin of the Study
From 1962 to 1971, US military forces sprayed over 19 million gallons of herbicides over
Vietnam to strip the thick jungle canopy that helped conceal opposition forces, to destroy crops
that enemy forces might depend on, and to clear tall grass and bushes from around the perimeters
of US base camps and outlying fire-support bases. Most large-scale spraying operations were
conducted from airplanes and helicopters, but herbicides were also sprayed from boats and
ground vehicles and by soldiers wearing back-mounted equipment. After a National Institutes of
Health report concluded that a contaminant in 2,4,5-tr~chlorophenoxyacetic acid (2,4,5-T)~ne
of the primary herbicides used~ould cause malformations and stillbirths in mice, US forces
suspended its use. All herbicide spraying in Vietnam was halted in 1971.
In response to concerns about the possible health consequences of exposure to the spraying,
Congress passed Public Law 102-4, the Agent Orange Act of 1991.~ The legislation directed the
Secretary of Veterans Affairs to ask the National Academy of Sciences (NAS) to conduct a
comprehensive review and evaluation of available scientific and medical information regarding
the health effects of exposure to Agent Orange2, other herbicides used in Vietnam, and their
components, including the contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin, informally known
as TCDD or dioxin. A committee convened by the Institute of Medicine (IOM) of the National
Academies conducted the review and in 1994 published a comprehensive report, Veterans and
Agent Orange. Health Effects of Herbicides Used in Vietnam (IOM, 1994).
The committee responsible for the 1994 report encountered a severe lack of information
about the exposures of individual Vietnam veterans to herbicides. Most studies of veterans had
relied on rudimentary measures—self-reports of exposure, service in Vietnam, military
occupation, or service in combat zones or in branches of the military responsible for combat
' Codified as 38 USC§ 1 1 16.
~ Agent Orange, the most commonly used herbicide in Vietnam, was a 1:1 mixture of 2,4 dichlorophenoxyacetic
acid (2,4-D) and the n-butyl ester of 2,4,5-T.
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Characterizing Exposure . . . Final Report
operations that had limited power to differentiate the intensity and duration of exposure (IOM,
1 997). This lack of information had hampered previous attempts to study the effects of herbicide
exposure on the health of Vietnam veterans.
That committee felt, however, that it might be possible to develop better methods of
determining exposures of individual veterans by drawing on historical reconstructions. The
methods might take into account such factors as troop movements, ground and perimeter
spraying, herbicide shipments to various military bases, the terrain and foliage typical of the
locations sprayed, the military missions of the troops there, and biochemical techniques for
detecting low concentrations of dioxin in the blood. If better models of exposure could be
developed and validated, a number of important epidemiologic studies of exposure to herbicides
and health outcomes might become possible.
The 1994 report offered recommendations concerning additional scientific studies to resolve
continuing scientific uncertainty. Three of the recommendations addressed exposure-assessment
studies of Vietnam veterans (IOM, 19944:
.
A nongovernmental organization with appropriate experience in historical exposure
reconstruction should be commissioned to develop and test models of herbicide exposure
for use in studies of Vietnam veterans.
· The exposure reconstruction models developed...should be evaluated by an independent,
nongovernmental scientific pane] established for this purpose.
.
If the scientific panel proposed. . Determines that a valid exposure reconstruction model is
feasible, the Department of Veterans Affairs and other government agencies should
facilitate additional epidemiologic studies of veterans.
The Department of Veterans Affairs (VA), in response to that report, asked {OM to establish
a committee to oversee the development and evaluation of models of herbicide exposure for use
in studies of Vietnam veterans. The committee would develop and disseminate a request for
2
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Characterizing Exposure ... Final Report
proposals (RFP) consistent with the recommendations, evaluate the proposals received in
response to the REP and select one or more academic or other nongovernment research groups to
develop the exposure-reconstruction model, provide scientific and administrative oversight of the
work of the researchers, and evaluate the models developed by the researchers in a report to VA,
which would be published for a broader audience.
Conduct of the Study
The Committee on the Assessment of Wartime Exposure to Herbicides in Vietnam was
formed in ~ 996 to accomplish the model-development tasks. Its initial work resulted in the report
Scientific Considerations Regarding a Request for Proposals for Research Characterizing
Exposure of Veterans to Agent Orange and Other Herbicides Used in Vietnam (IOM, 1997).
The report—which comprised a statement of work, criteria for selecting researchers, and an
appendix providing background information for potential respondents—was released to the
public on March IS, 1997. It summarized the intent ofthe research as follows (IOM, 1997, p. 3~:
T. Develop and document a detailed methodology for retrospectively characterizing the
exposure of Vietnam veterans to the major herbicides used by the military in Vietnam-
2,4-D; 2,4,5-T; cacodylic acid; and picloram3—and the trace contaminants TCDD and its
congeners. The proposal should address how exposure to this array of chemicals will be
evaluated. However, the ability to separately identify or quantify exposures to each of
these substances is not necessarily a requirement for a successful proposal. The exposure
methodology proposed must be applicable to specific types of epidemiologic
investigations that could be conducted at a future date under a separate contract or
subcontract.
' These four herbicides were used individually and in combination as the active ingredients of the "Agent"
formulations employed during the war: Agents Orange, Orange II, White, Blue, Pink, Purple, and Green.
3
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Characterizing Exposure ... Fina11t Report
2. Demonstrate the feasibility and appropriateness of the proposed methodology in
sufficient detail to permit the assessment of its potential for use in the conduct of
epidemiologic studies.
A formal, complete RFP, including the scientific input and contractual requirements, was
developed and was issued on June 30, 1997. It was initially sent to persons and organizations that
had requested it or were thought to have an interest in exposure-characterization research.
Availability of the RFP was publicized on the Web sites of IOM's Board on Health Promotion
and Disease Prevention and the Society for Risk Analysis and was posted to relevant e-mail lists.
Members of the veteran community and other interested persons were also informed of the RFP
through public events held by IOM committees involved in Vietnam-veteran health research and
through contacts made at meetings and conferences attended by committee members and staff.
Three proposals were submitted by the due date of September 4, 1997. Committee members
evaluated their technical and scientific merit on the basis of the criteria set forth in the RFP.
They concluded unanimously that a proposal submitted by researchers at Columbia University's
Mailman School of Public Health (Jeanne Mager Stellman, PhD, principal investigator) merited
funding.
The terms of the contract specified that the researchers were to submit scientific progress
reports every 6 months over the length of the contract. The progress reports were to include "a
description of the overall progress; descriptions of the specific work accomplished, including
problems encountered and corrective actions; pertinent data or other information in sufficient
detail to explain significant results achieved and any preliminary conclusions resulting from
analysis and scientific evaluation of data accumulated to date; and a description of the work to be
accomplished over the following six months." Progress reports were presented in public
meetings of the committee to disseminate the information to a larger audience and facilitate
interaction between the committee and the researchers. The first took place in a November 6,
1998, meeting of the committee, and the last occurred on January 13, 2003. Communication
between the Columbia University researchers and the committee was maintained between
meetings on a less formal basis.
4
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Characterizing Exposure ... Final Report
In April 2003, the committee issued an interim report based on the work that had been
completed (IOM, 2003). On the basis of a review of the contractor's 6-month update reports and
presentations and its published and draft papers, the committee reached the following findings:
The contractor has developed databases of wartime spraying and accidental dispersion of
herbicides, of troop locations and movements, and of land features and soil typology.
The contractor has developed an effective exposure assessment too! to assign a metric-
the E4 Exposure Opportunity Index (EOI)4—for herbicide exposure that is based on
proximity to spraying in space and time and on the amount and agent sprayed.
The range of calculated EOIs and information gathered to date on troop locations is
sufficient to demonstrate the feasibility of future epidemiologic studies. Additional
location data for troops not currently included in present databases appear to be available
at the National Archives5 for abstraction and use by researchers and other interested
parties in future studies.
Given current knowledge and available data, the contractor has adequately demonstrated
that the draft mode} is a valid means of assessing wartime herbicide exposure of Vietnam
veterans.
Given those findings, the committee concluded that a valid exposure-reconstruction mode}
for wartime herbicide exposures of US veterans of Vietnam was feasible. It therefore
recommended that the VA and other government agencies facilitate additional epidemiologic
studies of veterans by nongovernment organizations and independent researchers.
The intent of the present report is to summarize briefly the work done by the contractor over
the life of the study and to serve as a vehicle for cataloging and transmitting that work to VA.
The sections below delineate the work of the Columbia University researchers as it evolved from
proposal through delivery. It is based on the material provided by the Columbia University
4 The EOI is not intended for use in evaluating the exposure of groups who were responsible for applying herbicides,
although some of the information collected in the research effort may be useful in studies of these groups.
Formally, the US National Archives and Records Administration (CARAT
5
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Characterizing Exposure ... Final Report
researchers in their 6-month progress reports, presentations, draft materials, and final report; and
it quotes freely and extensively from these materials. A complete list of the materials produced
by the contractor in the course of its work is given in Appendix A; these materials are the
definitive references for the research summarized here.
The committee concludes here, on the basis of its review of the contractor's final report and
all previous work, that the Columbia University researchers have satisfactorily completed the
research project as defined in their proposal and modified in consultation with the committee. It
also affirms all the findings and conclusions reached in its own Interim Report (IOM, 2003).
The Interim Report details the reasoning that underlies the committee's conclusions
regarding the scientific quality of the contractor's work. As detailed in that earlier report, a
central issue was the demonstration that the draft model was a valid means of assessing the
wartime herbicide exposure of Vietnam veterans. The Columbia University researchers
implemented extensive quality control measures to assure the precision and completeness of their
data, and offered both qualitative and quantitative validation information for their model.
Considered together, this material led the committee to conclude that the exposure assessment
model was feasible.
The committee also notes that the Columbia University researchers' work has been subjected
to additional peer review as part of the processes that lead to the papers they have published in
Environmental Health Perspectives (Steliman IM et al., 2003) and Nature (StelIman SD et al.,
2003) and that they will soon publish in Journal of Clinical and Consulting Psychology and
Journal of Exposure Analysis and Environmental Epidemiology. Appendix A of this report notes
other papers that are presently under preparation and submission.
6
Representative terms from entire chapter:
herbicide exposure
