Veterans and Agent Orange Update 2004 (2005) / Chapter Skim
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5 Exposure Assessment
5 Exposure Assessment
Pages 165-200
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From page 165... ...
This chapter reviews information on occupational and environmental exposures to herbicides and TCDD, including exposure of Vietnam veterans. It discusses exposure assessments from selected epidemiologic studies introduced in Chapter 4 and provides background information for the health-outcome chapters that follow; health outcomes are not discussed here.
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From page 166... ...
Similarly, the assessment of markers that could be markers of effect -- such as DNA adducts -- shows promise, but does not necessarily provide accurate measurements of past exposure; that is, there is little evidence that currently measured DNA adducts are related to occupational or environmental exposures experienced years before. Because quantitative assessments based on environmental or biologic samples are not always available for epidemiologic studies, investigators rely on a mixture of qualitative and quantitative information to derive estimates.
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From page 167... ...
The most important marker in the context of Vietnam veterans' exposure to Agent Orange is the measurement of TCDD in serum. Studies of the absorption, distribution, and metabolism of TCDD have been conducted over the past 20 years.
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From page 168... ...
Although it is considered among the best of the approaches for assessing the relative risk posed by exposure to complex mixtures of the contaminants, it presents several uncertainties. TEFs are determined through inspection of the available congener-specific biologic and biochemical data on a compound and then assignment of a relative toxicity for that compound in comparison with TCDD.
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From page 169... ...
Other occupationally exposed groups include workers in agriculture and forestry who spray herbicides, sawmill workers exposed to chlorinated dioxins from contaminated wood preservatives, and pulp-and-paper workers exposed to dioxins through the pulp-bleaching process. 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 170... ...
Results of the analysis were used to estimate serum TCDD over time that was attributable to occupational exposure for all 3,538 workers in the subcohort defined in 1999. Crump et al.
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From page 171... ...
International Agency for Research on Cancer Cohort Studies A multisite study by the International Agency for Research on Cancer (IARC) involved 18,390 production workers and herbicide sprayers in 10 countries (Saracci et al., 1991)
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From page 172... ...
(1998) reported on an update of a mortality study of workers (production workers who had known exposure to dioxins, workers in herbicide production, non-exposed production workers, and workers known to be exposed as a result of an accident that occurred in 1963)
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From page 173... ...
Cumulative PCP and TCDD exposure indexes were calculated for each subject by multiplying the duration of each exposed job by its estimated exposure intensity and then adding the products across all exposed jobs. Other Production Worker Studies Several other occupational studies for chemical production plants have relied on job titles as recorded on individual work histories and company personnel records to classify exposure (Coggon et al., 1986, 1991; Cook et al., 1986; Ott et al., 1980; Zack and Gaffey, 1983; Zober et al., 1990)
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From page 174... ...
. Agriculture, Forestry, and Other Outdoor Work Occupational studies for agricultural workers have had various methods to estimate exposure to herbicides or TCDD.
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From page 175... ...
Herbicide Spraying Studies of herbicide applicators are relevant because they can be presumed to have had more sustained exposure to herbicides. However, because they also are likely to be exposed to a variety of compounds, assessment of individual or group exposure to specific phenoxy herbicides or TCDD is complicated.
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From page 176... ...
Other studies of the agricultural use of pesticides published recently do not provide specific information on exposure to 2,4-D, TCDD, or other compounds relevant to Vietnam veterans' exposure (Bell et al., 2001a,b; Chiu et al., 2004;
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From page 177... ...
Pulp and paper production workers also are likely to be exposed to other compounds, depending on the type of paper mill or pulping operation and the product manufactured (Henneberger et al., 1989; Jappinen and Pukkala, 1991; Robinson et al., 1986; Solet et al., 1989)
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From page 178... ...
have not changed the exposure assessment approach. The validity of exposure classification by zone was tested recently as a part of the Seveso Women's Health Study (Eskenazi et al., 2001)
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From page 179... ...
(2000) reported on an investigation of apparent clusters of cases of soft-tissue sarcoma and non-Hodgkin's lymphoma in the vicinity of a municipal solid-waste incinerator in Doubs, France.
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From page 180... ...
It is not clear whether the analysis included adjustments for age, body mass index, or education, all of which are significant predictors of dioxin concentrations. Other Studies Several epidemiologic studies have been conducted in association with industrial-facility emissions, or in regions with documented differences in dioxin
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From page 181... ...
A study of soft-tissue sarcomas in the general population was conducted in northern Italy around the city of Mantua (Costani et al., 2000)
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From page 182... ...
The herbicides were primarily used by the US Air Force's Operation Ranch Hand to defoliate inland hardwood forests; coastal mangrove forests; and, to a lesser extent, cultivated land. In 1974, a National Academy of Sciences committee estimated the amount of herbicides sprayed from helicopters and other aircraft using Operation Ranch Hand records gathered from August 1965 to February 1971 (NAS, 1974)
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From page 183... ...
Agent Orange was used from 1965 through 1970, and a slightly different formulation (Agent Orange II) probably was used after 1968.
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From page 184... ...
184 II) on a on least records records (could Orange at shipped additional L L L sprayed; shown L but L L procured)
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From page 185... ...
Air and Ground Spraying of Herbicides The number of US military personnel who directly handled (mixed, loaded, or applied) herbicides is impossible to determine precisely, but most of those assigned to Operation Ranch Hand can be presumed to have been exposed to Agent Orange and other herbicides.
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From page 186... ...
EXPOSURE ASSESSMENT IN STUDIES OF VIETNAM VETERANS Different approaches have been used to estimate the exposure of Vietnam veterans, including self-reports, record-based exposure estimates, and assessments of biologic markers of TCDD exposure. Each approach has a limited ability to ascribe individual exposure.
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From page 187... ...
. The exposure index initially proposed in the Air Force Ranch Hand study relied on military records of TCDD-containing herbicides (Agents Orange, Purple, Pink, Green)
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From page 188... ...
The authors concluded that Agent Orange exposure was a likely contributor to TCDD concentrations in Vietnam veterans who had a history of spraying herbicides. The main study of 5,000 Vietnam veterans, including analysis of an additional 900 blood specimens, continues.
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From page 189... ...
. A few attempts have been made to estimate exposure of the Vietnam veterans who were not part of the Ranch Hand or Army Chemical Corps groups.
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From page 190... ...
. Vietnam veterans were selected for further study on the basis of the estimated number of Agent Orange hits, derived from the number of days on which at least one company location was within 2 km and 6 days of a recorded Agent Orange spray.
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From page 191... ...
, 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 192... ...
1983. Lung cancer and other causes of death among licensed pesticide applicators.
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From page 193... ...
1989. Health Status of Vietnam Veterans.
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From page 194... ...
1984b. Vietnam Veterans' Risks for Fathering Babies with Birth Defects.
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From page 195... ...
Presented to the Institute of Medicine Com mittee 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 196... ...
2001. US army chemical corps Vietnam veterans health study: preliminary results.
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From page 197... ...
1986. Mortality among production workers in pulp and paper mills.
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From page 198... ...
1991. Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols.
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From page 199... ...
1990. Mortality and morbidity among Army Chemical Corps Vietnam veterans: a preliminary report.
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From page 200... ...
1983. A mortality study of workers employed at the Monsanto company plant in Nitro, West Virginia.
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