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Characterizing Exposure ... Final Report
As it became apparent that some tasks were larger and more time-consuming than originally
thought or it became obvious that some records or databases could not be used for the intended
purposes of the research, the proposed projects were modified, augmented, or partly abandoned.
This report chronicles some of the activities undertaken by the Columbia University
researchers as they met the various challenges posed by the study and in response to continuing
communication with the TOM committee.
PROJECT 1:
MILITARY UNIT AND HERBICIDE SPRAYING DATABASES,
AND EXPOSURE ASSESSMENT MODEL DEVELOPMENT
The goal of Project ~ the primary task in the research effort was to construct a
transportable system for evaluating herbicide exposure of veterans who served in Vietnam. The
purpose of the system was to provide data for use in epidemiologic studies. The Columbia
University researchers outlined the following specific aims in their proposal:
T. Iclentify and fill in remaining gaps in the Military Unit Database-Vietnam (MUD-V) by
retrieving, evaluating, and abstracting primary source materials.
2. Develop additional mathematical models for use as exposure opportunity indices (EOls).
3. Carry out sensitivity analyses of models to characterize the robustness of exposure indices to
inaccuracies in the locations of the troops.
4. Where inaccuracies or inconsistencies are found, attempt to obtain and incorporate additional
or alternative troop-location data from primary sources.
5. Create a final database of troop locations that contains alternative exposure estimates from a
variety of models and their reliabilities.
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6. Incorporate the final database into user-friendly software that will permit future investigators
to use the models to assign exposures or to propose their own models.
Interview Division Chemical Officers who served in Vietnam and served as principal
advisers to division commanders on the use of all chemicals to complete to the extent
possible the record! of known spraying missions.
Thus, the central goal of the project was to develop a comprehensive database that contained
all known information on the military herbicide spraying that had been carried out under Air
Force Operation Ranch Hand; by the US Army for perimeter defense and other smaller localized
purposes; and in other, unintentional releases. An additional database was planned to contain
locations and dates of "residence" of US military units stationed in Vietnam.
Consolidation, Quality Control, and Standarcl~zation of Databases
Before the initiation of the contract, a set of individual geographic locations of military units
assigned to Vietnam were collected by Columbia University investigators Jeanne Mager
Stellman and Steven D. Stellman for use in the Agent Orange Veterans Payment Program
(AOVPP), in collaboration with Lt. Col. Richarc! Christian (ret.~. The Drs. Stellman were
consultants to the special master presiding over this program, which resulted Dom the Agent
Orange Product Liability Litigation a class-action lawsuit brought by Vietnam veterans and
their families regarding injuries allegedly incurred as a result of the veterans' exposure to
chemical herbicides cluring the Vietnam war. In that effort, the Columbia University researchers
created a military-unit database for claim evaluation. The database contained about 500,000
records, each of which provided an exposure opportunity indexi° for one military unit during a
discrete period. The exposure of any individual claimant was calculated by summing the tabled
exposures for his or her unit(s) during service in Vietnam. The database, the ``Military Unit
'I This exposure opportunity index (EOI) is an earlier formulation of the E4 EOI that was developed under the
contract. In general, an EOI may be defined as an estimate of the possibility that a person will come into contact
with a toxic chemical without regard to route of entry or later metabolism.
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Database-Vietnam (MUD-V)," although not intended for epidemiologic purposes, was viewed as
a prototype for the present study.
The Columbia University researchers undertook to examine the extent of coverage of the
MUD-V database, evaluate gaps in the data, assess the implications of misclassification of
exposure, and—given all these considerations—ascertain how much usable information
remained for epidemiologic investigations. One aim of Project 1 was to carry out a sensitivity
analysis of the data in MUD-V to determine the extent to which it could satisfactorily produce a
rank-ordered exposure rating for the military units.
On the basis of their previous experiences, the Columbia University researchers concluded
that many so-called gaps or inconsistencies in the secondary data sources were minor and would
not seriously affect the accuracy of epidemiologic studies. Indeed, they had developed methods
in the AOVPP for imputing reasonable locations and exposure scores where data were missing,
such as substituting average battalion locations for companies or using the highest computed
exposure among companies with known locations for a company whose location during a
particular period was not known. Nonetheless, one of the immediate tasks undertaken in this
contract was to re-examine the database and remove all imputed data. To accomplish that, the
researchers returned to the original troop-movement data that had been collected by the US
Army and Joint Services Environmental Services Group (ESG), now known as the US Joint
Services Center for Research of Unit Records.
Restoring the Troop-Movement Database
The original troop-movement database was stored on 9-in. magnetic reels in virtual address
extension (VAX) backup format, which is no longer manufactured. Recovery entailed first
locating a working Digital Equipment Corporation VAX and obtaining licenses for appropriate
operating systems and other software. Eventually, the original data and directory structure were
restored, original research notebooks were located, and data were made compatible with current
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Characterizing Exposure ... Final Report
software systems. The data library was documented and written to CD-ROM. All programs and
databases are now VAX-independent.
The AOVPP database exposures were calculated by using {-month periods. However, the
original data sources contain considerably finer time detail for many military units; in many
instances, biweekly data exist; and in a few cases, daily coordinates were abstracted. The
researchers went back to the original tapes to make the more detailed data available. All data
were converted from the Universal Transverse Mercator (UTM) coordinate system used by the
US military to a Cartesian" system more amenable to the required modeling. The researchers
also appended the Department of Defenses (DOD) uniform unit-identification system
designation, the Unit Identification Code (UTC), to the information in the files.
Identifjir~g Units That Served in Vietnam
In addition to reconstructing the existing troop-movement databases and determining where
gaps or inconsistencies existed, the researchers updated the UIC LIST, a compilation of all the
unit-identification numbers developed by ESG for military units with service in Vietnam. The
UIC LIST had not been designed to be a comprehensive catalog of the units but rather was
developed by ESG for its work in support of VA and the Centers for Disease Controls (CDC), as
a recordkeeping system. It thus represented, to a large extent, units to which a VA or CDC study
subject may have been assigned and units that had been identified for other study-specific
purposes. The Columbia University researchers systematically examined the UIC LIST,
compared and combined it with other data sources on military units, and created a master list.
The master list is the first easily accessible and cross-referenced comprehensive list of all
Army units that were stationed in Vietnam and the numbers of troops assigned to them in
Vietnam. Where possible, the database also includes the identification of the next-higher
command to which a unit was assigned. The next-higher command provides important
" The Cartesian system expresses coordinates in terms of latitude and longitude.
|2 Now called the Centers for Disease Control and Prevention.
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information about unit location and enables researchers to locate military records more easily at
the National Archives and in other reference materials.
Classifying and Modeling the Mobility of Military Units
The Columbia University researchers developed a new concept for studying troop movement
for use in reconstructing herbicide-exposure histories based on a concept they called the mobility
factor. The mobility factor is a three-part classification system for characterizing the location and
movement of military units in Vietnam. It comprises a mobility designation (stable, S; mobile,
M; or elements mobile, E), a distance designation (usually in a range of kilometers) to indicate
how far the unit might travel in a clay, and a notation of the modes of travel available to the unit
(air; ground—truck, tank, or armored personnel carrier; or water). They then assigned a mobility
factor to every unit that served in Vietnam. The mobility-factor concept simplifies the task of
characterizing exposure of military personnel to hazardous substances and conditions during the
course of military conflict.
The mission of the organization had to be considered in conjunction with the organizational
structure when mobility factors were being assigned. For example, if the mission was
transportation, the mobility of the unit would vary with the command. In some cases, the
mobility factor was determined in whole or in part by the type of installation to which it was
assigned (for example, an airfield or a fire-support base).
Not all stable units remained in the same location throughout the war. The researchers wrote
a program that provides a list of all stable units that "moved", according to the database. In
assessing the data, they found that in most cases the "move" was real—a unit was reassigned to a
different location. In some cases, however, typographic errors were responsible for the ostensible
movement. In other cases, units were reclassified because some elements were, indeed, mobile.
Because the mobility factor was a new concept, the researchers assembled a panel of military
experts to review the concept itself and to examine the designations given to the military units
stationed in Vietnam. In general, the concept was strongly endorsed by the panel, and the
mobility assignments given to particular units were approved.
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Stable Units An important distinction made by the researchers was that the great majority of
military units assigned to Vietnam were "stable"; that is, their missions did not require routine
movement around Vietnam, and they were assigned to a specific base-camp location. Thus, the
military-occupancy probability assigned to these units would be 100% for the grids that they
occupied.
Initially, the Columbia University researchers made a rough working estimate of the
exposure-opportunity scores for the stable units. Most units were in the low-exposure category
for aerial applications because the strategy underlying the herbicide projects was to defoliate or
destroy crops in areas away from the main support-troop locations. However, some stable units
were in heavily sprayed areas, and the perimeters of the base camps were also subject to
backpack and other, more poorly documented spraying.
In investigating the issue further, the researchers identified a previously unrecognized source
of supplementary data in the National Archives. From those data, they decluced that each time an
installation or base camp was built or occupied by American forces, a formal land-transfer
agreement was executed between the governments of South Vietnam and the United States.
These agreements contained specific maps and descriptions of, for example, base camps and
power stations. The researchers reviewed those documents and extracted extensive quantitative
data, including complete dimensions of about 200 base camps, locations of airfields, water
supplies, and hospitals. In addition, they were able to identify the precise locations of 36
military units that were stationed in those installations. They also obtained coordinates for a large
number of perimeters of U.S. installations. The data were used for additional quality control of
the stable-units database.
The stable-units database of base-camp locations and dates of residence created by the
researchers covers about 80°/O of the troops stationed in Vietnam.
Mobile-Troop :Location Modeling The Columbia University researchers developed and tested
algorithms and programs for describing and analyzing the movement of mobile battalions and
their elements to further the goal of developing models of troop movement and unit dispersion.
The ultimate aim was to assign military-occupancy probabilities to specific grids in the map of
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Vietnam for every military unit, down to the company level, for the duration of its assignment in
South Vietnam.
The primary problem in characterizing mobile units' locations was incomplete data. A
critical issue was to determine whether data on a unit for particular dates were missing simply
because the unit did not move and therefore did not report its continued residence at one location
or whether the gaps are missing data. To develop statistical methods that could be used to
evaluate the data in the entire database, the researchers studied patterns of movement of units on
which substantial data already existed. That exercise yielded criteria for identifying data that
indicated "short-term location stability" (where there may not have been consistent recording of
location but there were not data gaps), which in turn helped to identify units for which "true"
gaps existed. The researchers could then more reliably impute missing locations for these units.
A preliminary cleaning and analysis of a large dataset of troop locations of Army combat
battalions assigned to Military Region III~3 suggested that data sources available in the National
Archives (including Daily Journals, After-Action Reports, and Operation Reports-Lessons
Learned) could be used to resolve most of the data problems encountered. That indicated to the
researchers that it should be possible to assemble location databases for other mobile units—an
important finding because such units are likely to have been among the most heavily exposed to
herbicides.
Herbicide Dispersion Data
The Columbia University researchers determined that a major aspect of linking a military
location with an exposure opportunity rests in the computerized records of herbicide application
commonly known as the HERBS files. Records indicate that 95% of all herbicide used during the
war were dispersed under Operation Ranch Hand, the US Air Force aerial spraying program
(Stellman IM et al., 2003). Those records, although incomplete, are by far the most important
i3 Military Region III, also known as the III Corps Tactical Zone (III CTZ), comprises a large area in the south of
Vietnam surrounding Ho Chi Minh City (formerly Saigon). It was an area of heavy combat and wartime spraying.
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records available for exposure-assessment purposes. In 1974, the National Research Council
organized data into a file, known as the HERBS tape, that contained coordinate points for more
than 6,200 missions flown by fixed-wing aircraft and included date, type of herbicide, gallons
applied (gallonage), and purpose of mission (NAS, 1974). The data in the HERBS file are given
in UTM coordinates; a mission is recorded as a series of turning points in the flight path.
Algorithms were written to translate from UTM to Cartesian coordinates so that spray-mission
data could be integrated with other geographic information. Other programs transformed the
discrete turning points into continuous flight paths so that exposure potential could be evaluated
over complete spray routes.
Although herbicide operations in Vietnam began in August 196T, the HERBS file contains
data only from 1965 on. During the course of their work, the researchers found additional
information on pre-HERBS-file spraying in a variety of sources, including two early Air Force
documents (Buckingham, 1982; CHECO, 1967), the Air Force Herbicide Project folders housed
at the National Archives (which contain detailed information on the planning and execution of
most Air Force herbicide missions), publications produced by the US Military Assistance
Command, and information retrieved from the government of South Vietnam "202 Tasks
Realized" report.
In the early 1980s, ESG assembled a tape to supplement HERBS the Services-HERBS
tape consisting of helicopter, backpack, truck, and other smaller-scale spraying data. The
database also included some information on aborted spray missions, leaks, and other
unintentional releases. The combined data from those two sources comprised over 8,800
individual military spray missions. However, several discrepancies existed between the two files.
Many could be resolved by a careful comparison between consecutive legs with cross-
referencing to the map of Vietnam or by reference to the Daily Air Activity Reports (DAARS).
When discrepancies could not be resolved, a panel of military experts assembled by the
contractor reviewed the missions and determined whether it was clear that the error was
typographic and whether it was possible to resolve the differences. if it was impossible to resolve
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a difference, the mission was flagged as questionable in the database so that it could be included
or excluded at the discretion of the user.
As a result of that exercise, the researchers developed a composite HERBS file that contains
. .
the date of spraying, coordinates of the spray mission, type of herbicide, number of gallons,
mode of application, type of aircraft (if appropriate), and where available area sprayed. For
missions flown with aircraft, the file also contains connectivity indicators that enable one to trace
the path of spraying.
During the researchers' reinspection of the DAARS, it became clear that individual missions
were associated with particular targets and that identifying numbers (project numbers) were
assigned to the targets. An earlier NAS report (1974) described how herbicide operations were
organized into projects to be approved by various committees. In re-examining the original
HERBS file obtained from NARA and ESG, the researchers found a field that could be related to
the project numbers on the DAARS. When the HERBS file was grouped according to this field,
all the Ranch Hand missions fell into specific projects. That was a major breakthrough in
understanding the herbicide-spraying program because it allowed several thousand spray
missions to be rationalized into a few hundred projects for analysis purposes. It is described in
greater detail in a paper by the researchers that was featured on the cover of Nature on April 17,
2003 (StelIman IM et al., 20034.
Combining and validating data from all those sources produced a final composite spray-
mission database that comprised 9,141 missions (19,977 sorties~4) that dispersed 19,491,090 gal
of herbicide in ~ 961-1971 (Steliman and Stellman, 2003~. Depending on the assumptions used,
the researchers estimate that the herbicides contained 487-807 lb (221-336 kg) of TCDD
(Stellman IM et al., 2003~.
|4 A mission was executed by one to four aircraft. Each aircraft's flight was considered a sortie.
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Approach to Exposure Assessment
The Columbia University researchers proposed the EO] as a useful alternative to such
traditional toxicology-based measures as blood or adipose-tissue concentrations. It was not
meant to be a substitute; neither method is perfect, and both can yield valuable information about
potential exposure. The EOI method used in this project was originally developed and published
by the researchers during the 1980s (Stellman and Stellman, 1986). Its central feature is the
comparison of the geographic location of a potentially-exposed military unit with all known
locations of herbicide release. Total exposure opportunity for the unit is the sum of the EOI
estimates for all temporally-appropriate!: data in the database.
Four models to quantitatively assess exposure opportunity were developed by the Columbia
University researchers in the course of this and previous work. They incorporate increasingly
realistic (and more complex) exposure concepts of distance and time of potential exposure to
herbicide application. The simplest, E1 (the "hit" model), simply counts the instances in which a
person was within a specified distance of a known spray. The second, E2, also counts hits but
makes close hits count more by weighting each hit according to inverse distance from the spray.
The third model, E3, begins with distance-weighted hits and factors in the total time during
which the person is considered to have been exposed. E1 and E2 can be regarded as representing
acute or direct exposures, since no allowance is made for exposure engendered by entering a
sprayed area after the spraying has occulted or for the length of time spent in the sprayed area.
E3 is analogous to acute followed by chronic exposure.
Time is an essential characteristic of the current, E4 EOI model. Any person or entity that is
present on the day of spray would be considered to have "direct exposure". Those entering a
sprayed location after that time and those remaining in the location after having been directly
exposed would be considered to have "indirect exposure", that is, exposure to any residual
Is The exposure assessment software that implements the model allows the user to set the time period over which
potential exposure should be factored. This may be relatively short if the user is examining herbicide ingredients that
break down in sunlight or extremely long for a chemically-stable compound like dioxin.
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herbicide or dioxin that is present. The E4 EOI may be expressed mathematically as a product of
three factors:
· Concentration of the toxicologically active substance in the herbicide mixture.
· A person's distance from spray paths.
· Residence time at an exposed location.
Thus, E4 EOI = concentration factor x distance factor x time factor. The E4 EOI for a given
mission is calculated as the sum of the component E4 values for all its legs.
The researchers expanded the scope of assessment for the models in three important ways: by
giving greater consideration to the questions of dispersion of individual troops than to reported
locations of their units, using nonlinear error methods; by carrying out sensitivity analyses to
account for spray-coordinate errors introduced by deviation of aircraft from flight paths and wind
dispersion of herbicides; and by investigating other exposure models as extensions of or
alternatives to the above. Two elements needed improvement for exposure-opportunity models:
incorporation of gallonage of herbicide and consideration of connectivity of fixed-wing aircraft
flight paths.
The intent of this work was thus to attempt to improve the modeling of herbicide dispersal by
creating a mathematical means of estimating the herbicide release along the entirety of flight
paths rather than at points along flight paths.
Modeling Herbicide Exposure
As the project evolved, the Columbia University researchers refined their approach to
calculating the EOI. Rather than estimating it directly for a military unit on the basis of its
location, they chose to calculate an exposure score for a series of contiguous grids that cover
Vietnam and a military-unit occupancy probability, which represents the likelihood that an
individual military unit will occupy any specific grid. These grids are 0.01° x 0.01°, which is
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equal to ~1.2 km2 on average. The "ridding concept permits use of statistical methods to evaluate
exposure of units whose locations are known only probabilistically. It also makes it possible to
superimpose contours of exposure on maps of Vietnam to visualize regions of especially high
and low exposure. Finally, it permits more rigorous treatment of the various geophysical
characteristics that may affect exposure to and bioavailability of herbicides (soil type, presence
of water, and the like). The geographic information system (GIS) developed by the researchers
transforms exposure estimation into a more efficient process.
The researchers digitized an existing soil map of the former Republic of Vietnam that was
incorporated into the GIS to extend exposure modeling to account for differential environmental
decay of herbicides (or dioxin) that may depend on soil typology. The map was derived from a
1961 field survey that was carried out by the EN Food and Agricultural Organization (FAO) for
the Vietnam Ministry of Agriculture (Moormann, 19614. The original FAO map was scanned,
ant! each of the 925 contours was traced manually. A point-in-polygon algorithm was used to
assign to each of the GIS grids an integer corresponding to the soil contour in which it fell. This
allows the EOf for a grid to be computed by using a half-life appropriate to the soil type.
To make the GIS more easily accessible to researchers, the contractors developed a user-
friendly software interface called "Herbicide Exposure Assessment-Vietnam" (HEA-V). The
MEA-V employs information from various components of the database highs paths of aerial
spray missions, number of gallons sprayed (gallonage), and chemical agents; documented spray-
mission targets; herbicide storage, transport, and unplanned-dispersal information; military-unit
identification codes; locations of military units, bases, structures, air Relets, and lancling zones;
movements of combat troops; land features ~ 6; soil typology; and locations of civilian
populations to calculate exposure opportunity. A paper published in the March 2003 edition of
the journal Environmental Health Perspectives details the development and application of the
GTS ant! associated software system (Steliman SD et al., 20034.
i6 Including coordinates of a variety of: elevations and land contours, rivers and streams, mountains and highlands,
coastal areas and mangrove forests, bays and estuaries, and such structures as roadways and utilities.
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While the research effort was directed at characterizing the exposures of US veterans of
Vietnam, the databases and model created by the Columbia University researchers could be
adapted for use in studies of other countries' veterans and of Vietnam residents.
Expan(ling Perimeter Spraying Database
Seven Army divisions served in Vietnam during the years in which herbicide spraying took
place (1965-1970~. A Division Chemical Officer, who generally held the rank of lieutenant
colonel or major, served in each division. Each officer served for a 1-year tour of duty, although
some may have served for shorter periods and some for more than one tour. An objective of this
Project 1 task was to attempt to learn how much perimeter spraying and local spraying took place
during the Vietnam War for which no records exist on the Services-HERBS tape.
The researchers intended to identify Division Chemical Officers from available military
records, such as the Daily Journals and the Morning Reports, and interview them. They also
anticipated retrieving further data on people in the Chemical Corps from the National Personnel
Records Center (NPRC) in St. Louis, which holds all military records for the armed services ant!
Coast Guard. An exchange of correspondence occurred among the investigators, NPRC,
representatives of the individual branches of the services, the DOD Privacy Board, the Secretary
of Defense, and the Defense Manpower Data Center (DMDC) (which maintains the Vietnam
file) to secure more information. The records requested—unit assignments, military occupational
specialties, and awards won are releasable public records, in contrast with medical records and
Social Security numbers, which are considered private records. The armed services have set up
"routine-use" mechanisms by which private records may be released to federal contractors but
have not established routine-use mechanisms for the release of releasable records. After
negotiations among VA, NPRC, and DOD, it was agreed that a contract would be drawn between
VA and NPRC for finding Social Security numbers of the chemical officers. The results of the
search would be given to NAS, the VA contractor, and then to Columbia University, the NAS
subcontractor.
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A text file containing 983 records of Chemical Corps officers and enlisted personnel was
given to NAS to transfer to VA for transfer to NPRC. Each record contained either Army serial
number or Social Security number. Of the 983 records, NPRC was able to match AS, 160 of
them officers. Social Security numbers—the most straightforward means of tracing the
veterans were available for just 29 of these officers. Given the additional challenges of locating
the surviving veterans in this truncated cohort and the fact that only some of them would have
been involved in herbicide spraying operations, the researchers concluded that this approach was
unlikely to yield enough data to warrant its pursuit. In consultation with the committee, the task
was abandoned.
Continuing Work
The researchers have indicated that they hope to pursue further information-gathering and
analysis of veterans' exposure to herbicides, using funding from other sources. Among the
materials submitted in fulfillment of the contract with NAS (listed in Appendix A) is a draft Web
site and its associated documentation. The intent of the Web site is to gather voluntarily
submitted information on the locations of military units that served in Vietnam directly from
individuals or organizations. That would be used to fill gaps in data on the highly mobile combat
units that server! in Vietnam.
Accomplishments
.
Expansion and cleaning of an archive of previously tracked locations of combat battalions.
Development of an approach to classifying military units so that they can be broken down by
the degree to which their mission required frequent changes in location. The approach has
permitted the development of a database of locations of about 80°/O of all Army troops, most
Air Force personnel, and Navy personnel assigned to construction battalions or permanent
installations and calculation of exposure opportunity and hit scores for them.
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.
.
.
Expansion and cleaning of herbicide-spray data (the HERBS and Service-HERBS files) that
had been used extensively by the researchers and others in the past. That work has led to a
substantially expanded inventory of spraying and to a higher estimate of the amount of
dioxin likely to have been deposited in the Republic of Vietnam during the war.
Refinement of the computational approach of a previously developed EO! and refinement of
the model itself to account for gallonage and direct-hit exposures better.
Development of a GIS for Vietnam into which were placed extensive databases, such as the
HERBS file of spraying missions, an exposure table of hits and exposure-opportunity scores,
military-unit identification codes, and military locations.
Design ant! development of a unique user-friendly software system—the Herbicide Exposure
Assessment-Vietnam that implements the GTS and may serve as an archetype for other
epidemiologic software for GIS-based analyses.
Exploiting the National Archives data resulted in a revision of both the tasks and the
timetable for the Columbia University researchers' work. The committee, who were consulted
on the changes, felt that they were appropriate and desirable. It should be noted that although
these data have substantially expanded knowledge about spray activities, they do not constitute a
complete accounting of all herbicide releases. Indeed, it is not possible to document the myriad
opportunities for in-country exposure. The best that any database of wartime herbicide exposures
can do is to provide a basis for better-informed epidemiologic studies of veterans.
25
Representative terms from entire chapter:
university researchers
