Veterans and Agent Orange Update 2006 (2007) / Chapter Skim
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5 Exposure Assessment
5 Exposure Assessment
Pages 214-260
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From page 214... ...
We discuss exposure assessments from selected epidemiologic studies introduced in Chapter 4 and provide background information for the healthoutcome chapters that follow; health outcomes are not discussed here. Further discussion of exposure assessment and a detailed review of the US military's wartime use of herbicides in Vietnam can be found in Chapters 3 and 6 of Veterans and Agent Orange (VAO; IOM, 1994)
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From page 215... ...
Exposure assessments based on measurements of an environmental contaminant provide estimates of the amount of the contaminant that contacts a body barrier over a defined period. Exposure can occur through inhalation, skin contact, and ingestion.
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From page 216... ...
216 TABLE 5-1 Exposure Monitoring and Assessment Methods Used in Selected Epidemiologic Studies of the Health Effects of Herbicides Applied in Vietnam by US Military Forces and 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Ontario US Agri- New Seveso Army NIOSH Dow Farm cultural Zealand Seveso Women's Air Force Chemical Australian Cohort Cohort Health Health Herbicide Area Health Health Corps Veteran Exposure Method Study Study Study Study Sprayers Study Study Study Study Study Job title x x x x x x x x Self-reported chemical use x x x x Exposure duration x x x x x x x Exposure categories x x x x x x Review of records x x x Job–exposure matrix x x Proximity to source x x x Soil sampling x Air sampling x 2,4-D concentration in urine x TCDD concentration in serum x x x x x
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From page 217... ...
The most important marker in the context of Vietnam veterans' exposure to Agent Orange is the measurement of TCDD in serum, although it should be noted that TCDD and Agent Orange are not synonymous. The absorption, distribution, and metabolism of TCDD have been studied over the last 20 years.
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From page 218... ...
Exposure to Dioxin-like Compounds A major focus of the work of the current VAO update has been the analysis of studies concerning exposure to a single compound: TCDD, which is one of several of tetrachlorodibenzo dioxins. The committee recognizes that under real-world conditions exposure to TCDD virtually never occurs in isolation and that there are hundreds of similar compounds to which humans might be exposed, among them other polychlorinated dibenzodioxins (PCDDs)
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From page 219... ...
Finally, extrapolation of TEF values derived from blood or adipose tissue samples to a meaningful target dose can carry considerable uncertainty. Considering the many difficulties of interpreting exposures to chemical mixtures relative to the exposure of veterans to Agent Orange and other herbicides in Vietnam, the committee's analyses have focused primarily on TCDD exposures.
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From page 220... ...
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 Relevant 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 * None of the epidemiologic studies reviewed by the committee to date have specified exposure to cacodylic acid or picloram.
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From page 221... ...
The many studies that provide chemical-specific exposure information are far more informative for the committee's purposes. OCCUPATIONAL EXPOSURE TO HERBICIDES AND TCDD The committee reviewed many epidemiologic studies of occupationally exposed groups for evidence of an association between health risks and exposure to TCDD or to the herbicides used in Vietnam, primarily the phenoxy herbicides 2,4-D and 2,4,5-T.
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From page 222... ...
Other occupationally exposed groups include pulp-and-paper workers exposed to dioxins through bleaching processes that use chlorinated compounds, and sawmill workers exposed to chlorinated dioxins that can be contaminants of chlorophenates used as wood preservatives. Production Work US National Institute for Occupational Safety and Health Cohort Study One extensive set of data on chemical production workers potentially contaminated with TCDD has been compiled by NIOSH.
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From page 223... ...
(2005a) applied a concentration- and age-dependent elimination model to the NIOSH cohort data to determine the impact of these factors on estimates of serum TCDD concentrations.
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From page 224... ...
(1995) updated the cohort and added a quantitative exposure assessment based on blood or adipose measurements of polychlorinated dibenzo-p-dioxins
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From page 225... ...
Exposure assessment involved estimates of duration of employment from the start of work in a department where exposure was possible until the end of employment at the plant. Analysis was based on time since first exposure.
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From page 226... ...
Cumulative PCP and TCDD exposure indices were calculated for each subject by multiplying the duration of each exposed job by its estimated exposure intensity and then summing across all exposed jobs. Since Update 2004, Dow researchers have published a study of serum dioxin levels measured in 2002 in former chlorophenol workers (Collins et al., 2006)
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From page 227... ...
. Rather than measuring serum dioxin levels, both studies inferred dioxin exposure levels for individual workers on the basis of dioxin concentrations in air and also estimated exposures to PAHs by analyzing two urinary metabolites: 1-hydroxypyrene and 2-napthol.
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From page 228... ...
Ontario Farm Family Health Study The Ontario Farm Family Health Study has produced several reports on exposure to phenoxyacetic acid herbicides, including 2,4-D. A study of male pesticide exposure and pregnancy outcome (Savitz et al., 1997)
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From page 229... ...
Since Update 2004, eight epidemiologic studies have been published on the AHS cohort. All have developed pesticide exposure estimates or exposure categories from self-administered questionnaires (Alavanja et al., 2004, 2005; Blair et al., 2005; De Roos et al., 2005; Engel et al., 2005; Farr et al., 2004, 2006; Kirrane et al., 2005)
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From page 230... ...
(2005) evaluated farm pesticide exposure in men and women, respectively, in relation to the incidence of gilomas as part of the Upper Midwest Health Study.
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From page 231... ...
Only one study has provided information on serum TCDD concentrations in herbicide applicators. Smith et al.
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From page 232... ...
Data on serum TCDD concentrations in Zone A residents have been presented by Mocarelli et al.
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From page 233... ...
Those findings demonstrate a significant association between zone of residence and serum TCDD, but much of the variability in TCDD concentrations is still unexplained by the models. A number of studies of the Seveso population have used lipid-adjusted serum TCDD concentrations as the primary exposure metric (Baccarelli et al., 2002; Eskenazi et al., 2002a,b, 2003, 2004; Landi et al., 2003)
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From page 234... ...
(2002) sampled 24 volunteers from this same population for lipid-adjusted serum dioxin concentrations.
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From page 235... ...
. Residents near a rural incinerator had significantly higher serum dioxin concentrations than did a control group (38 vs 24 pg TEQ/g of fat)
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From page 236... ...
(2006) measured serum dioxin levels in New York sports fishermen as part of a study of thyroid function.
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From page 237... ...
. Bien Hoa City is in the southern part of South Vietnam, and the surrounding area was treated heavily with Agent Orange.
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From page 238... ...
. The RFP resulted in the project, Characterizing Exposure of Veterans to Agent Orange and Other Herbicides in Vietnam, which was carried out under contract by a team of researchers from Columbia University's Mailman School of Public Health.
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From page 239... ...
20% isobutyl ester 2,4,5-T Orange 50% n-butyl ester 2,4-D, 1,033 g/L acid equivalent 1965–1970 42,629,013 L 45,677,937 L (could 50% n-butyl ester 2,4,5-T (11,261,429 gal) include Agent Orange II)
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From page 240... ...
Analysis of the TCDD concentration in stocks of Agent Orange remaining after the conflict, which either had been returned from South Vietnam or had been procured but not shipped, ranged from less than 0.05 ppm to almost 50 ppm and averaged 1.98 and 2.99 ppm in two sets of samples (NAS, 1974; Young et al., 1978)
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From page 241... ...
Air Force Health Study Major defoliation activities in Vietnam were conducted by Air Force personnel as part of Operation Ranch Hand. These veterans became the first subpopulation among Vietnam veterans to receive special attention in regard to Agent Orange, and have become known as the Ranch Hand cohort within the Air Force Health Study (AFHS)
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From page 242... ...
Each of these four models tested was significantly related to serum TCDD, although the models explained only 19–27 percent of the variability in serum TCDD concentrations. Days of skin exposure had the highest correlation.
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From page 243... ...
The study involved 720 veterans who served in Vietnam, and 25 veterans who did not serve in Vietnam. The exposure index was based on Agent Orange spray patterns across military regions in which Korean personnel served, time-location data on the military units stationed in Vietnam, and an exposure score derived from self-reported activities during service.
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From page 244... ...
However, the concentrations reported in the Korean veterans' study are significantly lower than those reported for American Vietnam veterans in the 1988 CDC Agent Orange Validation Study, which was nonetheless unable to distinguish Vietnam veterans from non-Vietnam veterans on the basis of serum dioxin assay (CDC, 1988b)
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From page 245... ...
. In 1987, CDC conducted the Agent Orange Validation Study to test the validity of the various indirect methods used to estimate exposure of ground troops to Agent Orange in Vietnam.
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From page 246... ...
, a description of the GIS for characterizing exposure to Agent Orange and other herbicides in Vietnam (Stellman et al., 2003b) , and an explanation of the exposure opportunity models based on that work (Stellman and Stellman, 2004)
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From page 247... ...
Finally, they note that the GIS-based exposure opportunity model has not yet been validated through measurement of serum dioxin levels in veterans (Young, 2004)
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From page 248... ...
1994. Principles of Exposure Assessment in Epidemiology.
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From page 249... ...
2001. Serum dioxin and cognitive functioning among veterans of Operation Ranch Hand.
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From page 250... ...
1985. Agent Orange Projects Interim Report Number 2: Exposure Assessment for the Agent Orange Study.
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From page 251... ...
2002. Dioxin reservoirs in southern Viet Nam -- a legacy of Agent Orange.
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From page 252... ...
2002b. Serum dioxin concentrations and endometriosis: A cohort study.
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From page 253... ...
Presented to the Institute of Medicine Commit tee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides. Illinois Agent Orange Committee, Vietnam Veterans of America.
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From page 254... ...
2003b. Characterizing Exposure of Veterans to Agent Orange and Other Herbicides Used in Vietnam: Interim Findings and Recommendations.
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From page 255... ...
2001. A study on the correlation between catego rizations of the individual exposure levels to Agent Orange and serum dioxin levels among the Korean Vietnam veterans.
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From page 256... ...
2001a. Serum dioxin and hepatic abnormalities in veterans of Operation Ranch Hand.
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From page 257... ...
2005. Did TCDD exposure or service in Southeast Asia increase the risk of cancer in Air Force Vietnam veterans who did not spray Agent Orange?
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From page 258... ...
2004. Exposure opportunity models for Agent Orange, dioxin, and other military herbicides used in Vietnam, 1961–1971.
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From page 259... ...
2004. Serum dioxin concentrations and age at menarche.
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From page 260... ...
2004a. Assessing possible exposures of ground troops to Agent Orange during the Vietnam War: The use of contemporary military records.
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