SUMMARY

Since the end of the Vietnam War, veterans have reported numerous health effects. Herbicides used in Vietnam, in particular Agent Orange, that contained the highly toxic chemical 2,3,7,8-tetrachloro-dibenzo-p-dioxin (also referred to as TCDD), have been associated with a variety of cancers and other long-term health effects. The Agent Orange Act of 1991 established a presumption of herbicide exposure for veterans who served in Vietnam and who developed one or more of the diseases associated with Agent Orange exposure. Such a presumption is necessary for a Vietnam veteran to receive disability compensation if he or she has an Agent Orange-associated disease. On the basis of the Institute of Medicine’s (IOM’s) Veterans and Agent Orange (VAO) reports and other information, the Department of Veterans Affairs (VA) has recognized the following 14 health effects as being associated with Agent Orange and other herbicide exposure: acute and subacute peripheral neuropathy, multiple myeloma, AL amyloidosis, non-Hodgkin’s lymphoma (NHL), chloracne, Parkinson’s disease, chronic B-cell leukemias, porphyria cutanea tarda, diabetes mellitus (type 2), prostate cancer, Hodgkin’s disease, respiratory cancers, ischemic heart disease, and soft-tissue sarcoma.

Before 1997, Vietnam veterans were eligible for a presumption of exposure if “during active military, naval, or air service, they had served in the Republic of Vietnam” unless there was evidence that they had not been exposed to Agent Orange. That broad policy was later narrowed so that service on the ground in Vietnam (ground troops) or on its inland waterways (Brown Water Navy) was required to receive a presumption of exposure. The VA further stipulated that “mere service on a deepwater naval vessel in waters off shore of the Republic of Vietnam is not qualifying service in Vietnam.” Those who served aboard deep-water naval vessels are the Blue Water Navy. Although that interpretation was



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 1
SUMMARY Since the end of the Vietnam War, veterans have reported numerous health effects. Herbicides used in Vietnam, in particular Agent Orange, that contained the highly toxic chemical 2,3,7,8-tetrachloro-dibenzo-p- dioxin (also referred to as TCDD), have been associated with a variety of cancers and other long-term health effects. The Agent Orange Act of 1991 established a presumption of herbicide exposure for veterans who served in Vietnam and who developed one or more of the diseases associated with Agent Orange exposure. Such a presumption is necessary for a Vietnam veteran to receive disability compensation if he or she has an Agent Orange-associated disease. On the basis of the Institute of Medicine’s (IOM’s) Veterans and Agent Orange (VAO) reports and other information, the Department of Veterans Affairs (VA) has recognized the following 14 health effects as being associated with Agent Orange and other herbicide exposure: acute and subacute peripheral neuropathy, multiple myeloma, AL amyloidosis, non-Hodgkin’s lymphoma (NHL), chloracne, Parkinson’s disease, chronic B-cell leukemias, porphyria cutanea tarda, diabetes mellitus (type 2), prostate cancer, Hodgkin’s disease, respiratory cancers, ischemic heart disease, and soft-tissue sarcoma. Before 1997, Vietnam veterans were eligible for a presumption of exposure if “during active military, naval, or air service, they had served in the Republic of Vietnam” unless there was evidence that they had not been exposed to Agent Orange. That broad policy was later narrowed so that service on the ground in Vietnam (ground troops) or on its inland waterways (Brown Water Navy) was required to receive a presumption of exposure. The VA further stipulated that “mere service on a deep- water naval vessel in waters off shore of the Republic of Vietnam is not qualifying service in Vietnam.” Those who served aboard deep-water naval vessels are the Blue Water Navy. Although that interpretation was 1

OCR for page 1
2 BLUE WATER NAVY VIETNAM VETERANS AND AGENT ORANGE EXPOSURE challenged by Blue Water Navy veterans, the VA position was upheld in the 2008 case of Haas v. Peake and stands today. Since 2008, the VA has, case by case, recognized numerous Blue Water Navy ships as having entered the inland waterways of Vietnam or having docked in Vietnam at specific times and locations. Navy personnel who served aboard those blue-water ships during the specific times when their ships were in inland waters or docked are now eligible for the presumption of service connection for Agent Orange–associated diseases. Blue Water Navy Vietnam veterans along with other Vietnam veterans have become concerned about their potential exposure to the TCDD contaminant present in Agent Orange. Recent publications, such as that of an Australian study of potential TCDD enrichment of potable water aboard Royal Australian Navy ships as a result of the water- distillation process, have prompted additional concerns regarding exposure of Blue Water Navy veterans to TCDD. CHARGE TO THE COMMITTEE The growing concern of Blue Water Navy veterans that they were exposed to Agent Orange during their service in the Vietnam War prompted the VA to task the IOM with establishing a committee to study whether the Vietnam veterans in the Blue Water Navy experienced exposures to herbicides and their contaminants comparable with those of the Brown Water Navy Vietnam veterans and those on the ground in Vietnam. The focus was to be on Agent Orange and TCDD exposures. The VA asked that the report include historical background on the Vietnam War, Agent Orange legislation, and the three veteran categories (ground troops, Brown Water Navy personnel, and Blue Water Navy personnel); a comparison of possible routes of exposure of Blue Water Navy veterans on ships and of ground troops in Vietnam, and the potential mechanisms of herbicide exposures (such as water exposure from contamination of potable water, air exposure from spray drift, and food and soil contamination); a comparison of the risks of long-term adverse health effects in ground troop veterans, Blue Water Navy veterans, and other "era" veterans who served during the Vietnam War at other locations in light of possible TCDD exposure; and a review of studies of Blue Water Navy veterans for adverse health effects (if there have been studies of that specific cohort of veterans).

OCR for page 1
SUMMARY 3 COMMITTEE’S APPROACH At the heart of this report is the question of whether Blue Water Navy veterans had the potential for exposure to the tactical herbicides used in Vietnam, specifically Agent Orange, and particularly the TCDD contaminant of that herbicide, and whether that exposure, if any, could lead to an increased risk of long-term adverse health effects. The committee’s approach was to ask Whether it is possible to demonstrate that Blue Water Navy personnel were or were not exposed to Agent Orange–associated TCDD, and Whether it is possible to state with certainty that exposure of Blue Water Navy personnel, taken as a group, was qualitatively different from that of their Brown Water Navy and ground troop counterparts. Conceptual Approach The committee considered that the most appropriate approach for assessing the risks of long-term adverse health effects would be a risk- assessment framework. The framework begins with identifying the sources of Agent Orange and its TCDD contaminant and potential receptors (in this case, ground troops and Brown Water Navy and Blue Water Navy populations). The next step is to evaluate how Agent Orange could reach the receptors (for example, transport by soil, water, and air) and plausible routes of exposure (inhalation, dermal contact, and ingestion). The information on routes of exposure can be used in conjunction with toxicologic information to assess the health effects that TCDD may have on the receptors. The committee began by gathering information on how Agent Orange had been used in Vietnam and the quantity and geographic range of its application. The committee also considered data on the magnitude of TCDD contamination of Agent Orange. After reviewing information on releases of Agent Orange to the environment, the committee explored the fate and transport of Agent Orange and TCDD in air, fresh and marine water, sediment, soil, and food to assess the plausibility of Agent Orange and TCDD exposure of those military personnel that did not actually handle the herbicide themselves. The committee attempted to identify any monitoring data on TCDD that had been gathered during or shortly after the Vietnam War. The committee also considered fate and

OCR for page 1
4 BLUE WATER NAVY VIETNAM VETERANS AND AGENT ORANGE EXPOSURE transport models that could be used in conjunction with the limited available data to examine the plausibility of exposure of ground troops and Blue Water Navy veterans to the chemicals. The committee attempted to determine where Blue Water Navy ships were during the war, their missions, how close they came to the Vietnamese coast, and the activities conducted aboard the ships by the sailors in performance of their duties and during their leisure time. To determine whether Blue Water Navy personnel had exposures to TCDD comparable with those of ground troops and Brown Water Navy personnel, the committee sought to determine whether there were plausible exposure pathways between releases of Agent Orange and TCDD (specifically, the spraying of Agent Orange during the Operation Ranch Hand missions) and the three populations. The long-term adverse health effects of Agent Orange and TCDD have been examined by other IOM committees, particularly the VAO committees, and by other organizations, such as the International Agency for Research on Cancer. For this reason, the present committee did not review all the primary literature related to TCDD exposure and health effects, such as studies of occupational cohorts and toxicological studies with laboratory animals. Rather, it focused its literature searches and other efforts on identifying epidemiologic studies of health effects seen in Vietnam veterans that included Navy personnel as a specific population and studies that divided Navy personnel into those who may have served in the Blue Water Navy, in the Brown Water Navy, or onshore. Information Sources Many data sources and methods were identified and pursued by the committee, including published peer-reviewed literature, models for assessing the environmental concentrations of Agent Orange and TCDD, anecdotal information from veterans and other interested parties on veteran experiences during the war and afterwards, and such other information sources as written and published accounts of the war (including memoirs), government documents, and ships’ deck logs. Although much of the information reviewed by the committee was not new, some fresh sources and documents were identified, including new VA policies, Blue Water Navy veterans’ reports, materials specific to the operations of the Blue Water Navy, and further documentation of the use of Agent Orange in Vietnam.

OCR for page 1
SUMMARY 5 The committee recognized the need to hold open sessions to hear directly from veterans about their experiences with Agent Orange while they served in the Vietnam War. In addition, it was agreed that much of the information that the committee would need to complete its task was not available in the published literature and that veterans would be able to provide critical information. The committee held three open sessions to collect veterans’ input. At the first two sessions, held in Washington, DC, the committee heard from the VA, several veterans service organizations (for example, the Blue Water Navy Vietnam Veterans Association), numerous individual veterans, and other interested parties. The third open session was held aboard the USS Midway, an aircraft carrier that is now a museum, so the committee could view firsthand the distillation plants used aboard a Vietnam-era ship. Committee members found all that information to be useful in framing their approach to the committee’s task and appreciating life aboard Blue Water Navy ships during the war. The committee talked with veterans of all ranks and experiences, from vice admirals to enlisted men. Numerous other information sources also proved useful to the committee. Many of them were government documents from the VA and the Navy; other Navy documents, such as deck logs and maps; and reports from the Australian government about Australian Vietnam veterans. Several Web sites also provided useful compendiums of information, such as the site maintained by the Blue Water Navy Vietnam Veterans Association (http://www.bluewaternavy.org/) and the Virtual Vietnam Archive at Texas Tech University. Other sources of information included peer-reviewed literature and interviews with retired Navy personnel. HISTORICAL BACKGROUND The US government commissioned a series of studies in the middle to late 1960s evaluating possible health risks for American troops and the Vietnamese population exposed to Agent Orange. On the basis of those studies, in October 1969 the United States began limiting its use of herbicides in Vietnam; spraying ceased entirely in 1971. Additional concerns about the health dangers posed to Vietnam veterans arose after the war. Beginning in 1979, Congress enacted several laws to determine whether exposures to herbicides in Vietnam were associated with

OCR for page 1
6 BLUE WATER NAVY VIETNAM VETERANS AND AGENT ORANGE EXPOSURE possible long-term health effects. In 1991, Public Law (PL) 102-4, the Agent Orange Act, was passed. It required the VA to ask the IOM to conduct periodic reviews of the available scientific and medical evidence of health effects that followed exposure to herbicides used in Vietnam, including Agent Orange and its contaminant TCDD; there is currently evidence of an association between 14 health effects and exposure to Agent Orange. Two IOM committees assessed an exposure-opportunity model developed by Columbia University principal investigator Jeanne Stellman. The model assigned an exposure-opportunity index value to individuals or groups that had homogeneous exposure characteristics (location and time); the index value was based on proximity to flight paths of aerial herbicide spraying missions and time concordance between spraying and presence in the affected areas. Full application of the exposure-opportunity model to ground troops in Vietnam was never accomplished and has never been proposed for Brown Water Navy or Blue Water Navy personnel. Although other investigators have identified differences in predicted ground-level spray deposition in the Stellman model compared with established pesticide-spray drift models such as AgDRIFT, and noted the lack of certainty in troop-location data, no alternatives to the Stellman exposure-opportunity model have been proposed. Because of the impossibility that most Vietnam veterans could prove that they had been exposed to Agent Orange or other herbicides in Vietnam during the war, the 1991 Agent Orange Act created a presumption of service connection; that is, exposure to herbicides in Vietnam was presumed for any Vietnam veteran who became ill with a disease found to be associated with TCDD exposure. That presumption—a mechanism of disability compensation that the VA has used in other contexts—allows veterans to receive disability compensation and treatment for a medical condition without having to provide proof that the condition was “incurred in or aggravated by” their military service. The VA denies Blue Water Navy Vietnam veterans presumptions of service connections for herbicide-related conditions unless a veteran was aboard a ship at the time of docking in Vietnam or, if shore docking did not occur, the evidence shows that the ship operated in Vietnam’s close coastal waters for extended periods, members of the crew went ashore, or smaller vessels went ashore regularly from the ship with supplies or personnel. However, a ship that was in a deep-water harbor, for example,

OCR for page 1
SUMMARY 7 Da Nang, would not count as being in “brown water.” The VA continues to develop a list of blue-water ships documented to have entered inland waters and the dates on which they did so. Underlying the controversy of Blue Water Navy Vietnam veterans’ claims to a presumption of herbicide exposure are the legal mandates to compensate veterans for their current health problems. Vietnam veterans who served on the ground and on the inland waterways of Vietnam are eligible for compensation for their Agent Orange–associated medical problems regardless of the time they spent in Vietnam and the potential for their exposure to Agent Orange during the war. SELECTED CHEMICALS USED DURING THE VIETNAM WAR By far the most widely used herbicide in Vietnam was Agent Orange, followed by Agent White; other tactical herbicides that were used during the war include Agent Blue, Agent Purple, Agent Pink, and Agent Green. Of the herbicides used in Vietnam, only those containing 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) were contaminated with TCDD. Agent Orange was composed of equal parts 2,4,5-T and 2,4- dichlorophenoxyacetic acid as the active ingredients. TCDD occurred as a contaminant in 2,4,5-T and was present in Agent Orange at concentrations from 6.2 to 14.3 ppm (average, 13.25 ppm). It has been estimated that about 43 million liters of Agent Orange were used in Vietnam during 1965–1970. Agent Orange was applied to broad swaths of land in Vietnam, primarily via specially modified US Air Force C-123 fixed-wing aircraft during Operation Ranch Hand. A small proportion of the herbicide was also applied by other means, such as backpack sprayers, spray trucks, helicopters, and boats by the US Army Chemical Corps. An additional route of herbicide application was direct spraying of riverbanks by the Brown Water Navy. Vietnam veterans were also exposed to other chemicals during the war. For example, in an effort to control the incidence of malaria in US ground troops in Vietnam, in 1967, the military initiated Operation Flyswatter and used modified Ranch Hand C-123 aircraft, also known as Bug Birds, to spray malathion. Unlike the C-123s used for herbicide spraying, the Bug Birds flew alone without escort aircraft and were not camouflaged. Malathion was sprayed over nine major US bases and adjacent sites every 11–14 days. Environmental conditions were similar to those used for herbicide spraying—maximum winds of 10 knots,

OCR for page 1
8 BLUE WATER NAVY VIETNAM VETERANS AND AGENT ORANGE EXPOSURE maximum temperature of 30°C, and no rainfall during or for 1 hour after spraying. Blue Water Navy and Brown Water Navy personnel were also exposed during the Vietnam War to many chemicals needed to operate and maintain their ships. Exposure may have occurred by ingestion, inhalation, dermal contact, or a combination of these routes. Exposure opportunity varied greatly with a sailor’s occupation, the class of ship, and the nature of the activity that required the chemical (for example, painting a ship). Many of the chemicals used aboard are known to be toxic and have been demonstrated to elicit both short-term and long-term adverse health effects. The committee found it important to identify and describe some of the chemicals, their uses, and their health effects. Chemicals used aboard naval ships included solvents, jet fuel, polychlorinated biphenyls, asbestos, trichloroethylene, lead, and mercury. The committee also notes that many naval personnel smoked aboard ships with the potential for exposure to numerous toxic chemicals in cigarette smoke and exposure to secondhand smoke for nonsmokers. Shipboard environments are influenced by ventilation systems that run throughout the entire ship. The systems have the potential to spread airborne materials collected at one site to other sites if not properly designed and maintained. The potential spread of occupationally produced airborne materials could have a serious influence on the health of shipboard personnel. FATE AND TRANSPORT OF AGENT ORANGE AND TCDD IN THE VIETNAMESE ENVIRONMENT Potential exposure of Blue Water Navy personnel to Agent Orange and its contaminant TCDD is related to the fate of these chemicals in the Vietnamese environment. The committee considered using a mathematical model to estimate likely TCDD concentrations based on Agent Orange inputs to the environment. All models require a host of input parameter values such as standard physical-chemical properties of TCDD, characteristics of the Vietnamese environment, and chemical- and environment-specific parameter values such as rates of TCDD degradation in the Vietnamese environment and seasonally and spatially specific knowledge of air and water movement. The committee found that input data and, importantly, data with which to evaluate model performance, were not available. Furthermore, tremendous uncertainty

OCR for page 1
SUMMARY 9 would accompany any attempt to model overall TCDD fate by scaling up from modeling emissions from individual spray paths for which data are available, to estimate TCDD concentrations along hundreds of miles of coastline and in coastal waters. Thus, the committee concluded that using models to estimate likely concentrations of TCDD in the Vietnamese environment to which Blue Water Navy personnel might be exposed would not be possible because of the lack of data with which to parameterize the model. Even if a model could be parameterized, data are not available to evaluate model performance. Without evaluating the model, the uncertainty of model results would be far too great and thus, the committee could not be confident that such results were reasonable. The committee explored the variability and uncertainty of many of the input parameters that would be needed for assessing the fate and transport of TCDD in the Vietnamese environment. The goal of this exercise was to assess qualitatively the fate of TCDD released during the Vietnam War. The discussion acknowledges the importance of location- specific factors that mediate the chemical fate and transport, notably the tropical climate and geography of Vietnam. Since most of the literature on chemical fate of dioxins originates from temperate areas such as Europe and North America that differ significantly from the Vietnamese environment, the committee was mindful of these differences as its understanding of the fate TCDD in Vietnam was developed. It has been estimated that 87% of the Agent Orange sprayed in Vietnam reached the forest canopy, while the remaining 13% drifted and was subject to atmospheric transport or degradation processes. The committee assumed that Agent Orange that did not reach the forest canopy or soils could enter the water either by direct spraying over waterways or deposition of spray drift or indirectly via land runoff. The committee concluded that Agent Orange and TCDD would have entered waterways from riverbank spraying (although this was a small fraction of the total Agent Orange applied in Vietnam) or as runoff from soil, particularly in the Mekong delta area that was heavily sprayed and that experienced frequent flooding. This river loading would be highly diluted by river flows. A considerable fraction of particles and humic material to which TCDD would absorb, would be expected to have settled in the delta region or estuaries. TCDD would enter the coastal marine water from river discharge and spray drift. The contribution of TCDD to marine waters from these transport routes would be reduced to a great extent by two main processes: dilution in river water and dispersion in air, as well as by

OCR for page 1
10 BLUE WATER NAVY VIETNAM VETERANS AND AGENT ORANGE EXPOSURE further dilution in the coastal waters. Given the paucity of monitoring information and the variability and uncertainty in the fate and transport information on TCDD as it pertains to Vietnam, the committee concluded that it is not possible to estimate the likely concentrations of TCDD in marine waters and air at the time of Blue Water Navy deployment. EXPOSURE ROUTES AND MECHANISMS The committee was tasked with comparing exposure among three military populations that served in Vietnam: troops on the ground, Brown Water Navy personnel, and Blue Water Navy personnel. The approach used by the committee to address the task of comparing exposure among the three populations was to evaluate possible pathways of exposure of each of the three populations (termed exposure opportunities) and to consider whether it is plausible that people in these groups could have been exposed, via these pathways, to Agent Orange– associated TCDD. The committee determined that any assessment of exposure must be qualitative rather than quantitative. Qualitative estimates should be informed by knowledge of the fate and transport of the chemicals of interest and by documented or anecdotal information on potential pathways of exposure. The committee recognized that in addition to possible differences in exposure potential among populations, there are differences among individuals. Even ground troops or Navy personnel with similar job descriptions would be expected to have experienced varied exposure because of differences in environmental concentrations, personal activities, and associated intake characteristics (such as exposure duration, food and water ingestion rates, inhalation rate, and body weight). The committee recognizes that there may be individuals in a given group whose experiences do not accord with the descriptions given in this report. It should be noted that ground troops and Brown and Blue Water Navy personnel also included an unknown fraction of personnel who were remote from spraying operations and possibly had no opportunity for exposure. The committee identified several plausible exposure pathways and routes of exposure to Agent Orange–associated TCDD in the three populations. Plausible pathways and routes of exposure of Blue Water

OCR for page 1
SUMMARY 11 Navy personnel to Agent Orange–associated TCDD include inhalation and dermal contact with aerosols from spraying operations that occurred at or near the coast when Blue Water Navy ships were nearby, contact with marine water, and uses of potable water prepared from distilled marine water. Large US Navy ships—such as aircraft carriers, cruisers, and destroyers—had their own potable-water supply and distribution systems that included water-treatment processes. Potable water is produced by distillation of marine water. Although the committee was told that Blue Water Navy ships did not typically make potable water within 12 miles of shore, the committee was also told that in exceptional circumstances a ship might take up water for distillation while relatively close to the coastline. The issue of distillation of marine water is important because of the finding by the committee that prepared the 2008 VAO update that Blue Water Navy veterans could have been exposed to TCDD via contaminated potable water. The Australian Department of Veterans Affairs determined that Royal Australian Navy personnel who served offshore were exposed to Agent Orange–associated TCDD in Vietnam because the distillation systems aboard the ships were thought to be able to concentrate TCDD in source water into the potable water during the evaporative process. This committee used a theoretical model to corroborate the findings of the experimental Australian study that found substantial codistillation of TCDD during production of potable water with a batch distillation unit that was commonly used in Blue Water Navy vessels. If Agent Orange–associated TCDD was present in the marine water, distilled potable water would be a plausible pathway of exposure. LONG-TERM ADVERSE HEALTH EFFECTS The long-term adverse health effects associated with exposure to dioxins have been studied in a variety of populations, including Vietnam veterans. The biennial IOM VAO reports have reviewed epidemiologic studies of Vietnam veterans, occupational studies, and population studies in an effort to determine whether Vietnam veterans are at increased risk for adverse health effects from exposure to Agent Orange during the Vietnam War. A few of the studies include veterans who served in the Blue Water Navy in Vietnam, but most of the studies do not distinguish

OCR for page 1
12 BLUE WATER NAVY VIETNAM VETERANS AND AGENT ORANGE EXPOSURE Navy veterans, let alone Blue Water Navy veterans, from other Vietnam- veteran populations. In addition to reviewing previous VAO reports, the committee heard from a number of veterans and is aware that many veterans attribute their current illnesses to exposure to Agent Orange in Vietnam. The committee valued these accounts for descriptive purposes but did not have a way to use that information in its study because without a relevant control population to demonstrate that the veterans’ diseases are attributable to Agent Orange–associated TCDD exposure and not other factors, the exact causes of their illnesses cannot be determined. For Navy veterans as a whole, the Australian cancer-incidence study indicated a significantly higher risk of lung cancer (although the study did not adjust for smoking) and prostatic cancer, both of which are currently recognized as TCDD-related malignancies. The Australian study also found significant associations with melanoma and colon cancer, neither of which has been categorized as TCDD-related by the IOM or the VA. The Australian mortality study corroborated the Australian cancer-incidence findings on lung cancer and melanoma. However, both Australian reports found significantly lower risk of NHL, one of the first cancers the IOM found to be associated with Agent Orange exposure. One study found neither higher nor lower risk of NHL in Vietnam-era Navy veterans. In contrast, the Centers for Disease Control and Prevention Selected Cancers Study found a significantly higher prevalence of NHL in US Blue Water Navy Vietnam veterans. Finally, in a small study, testicular cancer was associated with service in the Navy (although the Blue Water Navy was not specified) in Vietnam veterans, although testicular cancer has not been found by the IOM to be associated with Agent Orange exposure. Overall, the committee concludes that because of the small number of studies and their limitations, there is no consistent evidence to suggest that Blue Water Navy Vietnam veterans were at higher or lower risk for cancer or other long-term adverse health effects associated with Agent Orange exposure than shore-based veterans, Brown Water Navy veterans, or Vietnam veterans in other branches of service. CONCLUSIONS Since the 1970s, IOM committees and other groups have attempted to reconstruct Vietnam veterans’ potential exposure to Agent Orange and

OCR for page 1
SUMMARY 13 TCDD. Given the lack of exposure data on ground troops and the limited knowledge about exposure among Blue Water Navy veterans, the committee concluded that it was not possible to make quantitative exposure comparisons among the three military populations of interest to the VA. Therefore, the committee evaluated the plausibility of exposure of the three populations to Agent Orange and TCDD via various mechanisms and routes. The committee recognized that considerable variability exists in the potential for TCDD exposure by Blue Water Navy personnel, ground troops, and Brown Water Navy personnel. Focusing on the Blue Water Navy, some personnel may have spent their entire tour of duty on aircraft carriers that never came close to the Vietnamese coast, whereas others served on ships that may have spent many days as close as 1 mile offshore. In addition to the variability in the location of Blue Water Navy personnel, there is extensive uncertainty regarding the experiences of individual sailors on those ships (for example, whether they were on a ship when it was near the Vietnamese coast, whether they went swimming, and whether they ate local food from Vietnam or Vietnamese waters). The committee concluded that, qualitatively, ground troops and Brown Water Navy veterans had more plausible pathways of exposure (that is, there was a greater number of plausible exposure mechanisms) to Agent Orange–associated TCDD than did Blue Water Navy veterans. One exposure mechanism is specific to Blue Water Navy ships: possible TCDD contamination of potable water from onboard distillation plants. The committee’s assessment corroborates the Australian finding that in experiments simulating the water-distillation system used on Navy ships the system had the potential to enrich TCDD concentrations from the feed water to the distilled potable water. However, without information on the TCDD concentrations in the marine feed water, it is impossible to determine whether Blue Water Navy personnel were exposed to Agent Orange–associated TCDD via ingestion, dermal contact, or inhalation of potable water. The committee was unable to state with certainty that Blue Water Navy personnel were or were not exposed to Agent Orange and its associated TCDD. Owing to a lack of data on environmental concentrations of Agent Orange and Agent Orange–associated TCDD and an inability to reconstruct likely concentrations, as well as the dearth of information about relative exposures among the ground troops and Brown Water Navy personnel and Blue Water Navy personnel, it is

OCR for page 1
14 BLUE WATER NAVY VIETNAM VETERANS AND AGENT ORANGE EXPOSURE impossible to compare actual exposures across these three populations. Furthermore, the committee concludes that because of the small number of studies and their limitations, there is no consistent evidence to suggest that Blue Water Navy Vietnam veterans were at higher or lower risk for cancer or other long-term adverse health effects associated with Agent Orange exposure than shore-based veterans, Brown Water Navy veterans, or Vietnam veterans in other branches of service. The committee’s judgment is that exposure of Blue Water Navy Vietnam veterans to Agent Orange–associated TCDD cannot reasonably be determined.