Veterans and Agent Orange Update 2000 (2001) / Chapter Skim
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5 Exposure Assessment
5 Exposure Assessment
Pages 110-131
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From page 110... ...
Reviews of the most recent studies of the absorption, distribution, and passage of herbicides and dioxin through the body may be found under the discussions of toxicokinetics in Chapter 3 of this report. OCCUPATIONAL AND ENVIRONMENTAL EXPOSURES TO HERBICIDES AND DIOXIN The committee reviewed a large number of epidemiologic studies of occupationally or environmentally exposed groups for evidence of an association between health risks and exposure to TCDD and herbicides used in Vietnam, especially the phenoxy herbicides 2,4-D and 2,4,5-T, chlorophenols, and other compounds.
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From page 111... ...
The available information on occupational and environmental exposures to dioxin, the contaminant found in 2,4,5-T includes studies of residents living in and around Seveso, Italy, who were exposed during industrial accidents; chemical plant workers who were occupationally or accidentally exposed to TCDD during the production of 2,4,5-T or other phenoxy herbicides or chlorophenols such as hexachlorophene or trichlorophenol; sawmill workers exposed to higher chlorinated dioxins from contaminated wood preservatives; and pulp and paper workers exposed to dioxin through the pulp bleaching process. Occupational Studies Production Workers One of the most extensive sets of data on workers engaged in the production of chemicals potentially contaminated with TCDD has been compiled by NIOSH.
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From page 112... ...
This study included analysis by estimated maximum TCDD serum level. This was estimated for each member of the cohort by measuring serum TCDD levels for 144 subjects, including production workers known to be exposed to dioxins, workers in herbicide production, nonexposed production workers, and workers known to be exposed as a result of an accident that occurred in 1963.
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From page 113... ...
In addition, herbicide spraying is generally a seasonal occupation, and information may not be available on possible exposure-related activities during the rest of the year. One study provided information on serum TCDD concentrations in herbicide sprayers, that of Smith et al.
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From page 114... ...
The corresponding values for age-matched controls ranged from 2 to 11 ppt; the mean was 6 ppt. Serum TCDD levels were positively correlated with the number of months of professional spray application.
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From page 115... ...
None of these data correlated with serum TCDD levels, strongly suggesting that the exposure of importance was fallout on the day of the accident. The presence and degree of chloracne did correlate with TCDD levels; however, it appears that adults are much less likely to develop chloracne than children following an acute exposure, but surveillance bias may have played some role in this finding.
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From page 116... ...
Persons were considered exposed if they lived, worked, or had other contact for two years or more with TCDD-contaminated soil at levels of 20-100 ppb or for six months or more with soil contaminated with TCDD at levels greater than 100 ppb. Of the exposed population samples, 87 percent of adipose tissue TCDD levels were less than 200 ppt; however TCDD concentrations in 7 of the 51 exposed ranged from 250 to 750 ppt.
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From page 117... ...
According to military records of Operation Ranch Hand, from August 1965 to February 1971 a total of 17.6 million gallons of herbicide was sprayed over approximately 3.6 million acres in Vietnam (NAS, 1974~. Soldiers also sprayed herbicides on the ground to defoliate the perimeters of base camps and fire bases; this spraying was executed from the rear of trucks and from spray units mounted on the backs of soldiers on foot.
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From page 118... ...
Agent Green was a singlecomponent formulation of the n-butyl ester of 2,4,5-T, used primarily in defoliation missions (Young et al., 1978~. In January 1965, two additional herbicides, code named Orange and White, TABLE 5-1 Major Herbicides Used in Operation Ranch Hand: 1962-1971 No.
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From page 119... ...
On February 12,1971, U.S. Military Assistance Command, Vietnam, announced that herbicides would no longer be used for crop destruction in Vietnam, and the last Ranch Hand fixed-wing aircraft (C-123)
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From page 120... ...
During the entire operation, approximately 1,250 military personnel served in Ranch Hand units. Although the Air Force maintained complete records of its Operation Ranch Hand fixed-wing herbicide missions, documentation of spraying conducted on the ground by boat, truck, or backpack and authorized at the unit level was less systematic.
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From page 121... ...
GAO, 1979~. The Army added that exposure of ground troops was very unlikely since DoD personnel did not enter a Ranch Hand-sprayed area until approximately 4 to 6 weeks after the mission, when defoliation was complete and the herbicide had been biodegraded or photodegraded (U.S.
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From page 122... ...
Comparable manufacturing standards for the domestic use of 2,4,5-T in 1974 required that TCDD levels be less than 0.05 ppm (NAS, 1974~. Therefore, depending on which stocks were sampled, the level of dioxin contamination in Agent Orange could have been up to 1,000 times higher than the level of dioxin found in phenoxy herbicides domestically available at the time.
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From page 123... ...
Biomarker studies of the Ranch Hands are consistent with their exposure to TCDD as a group. When the Ranch Hand cohort was further classified by military occupation, a general increase in serum TCDD levels was detected for jobs that involved more frequent handling of herbicides.
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From page 124... ...
When the questionnaire-derived indices were applied within each job classification, days of skin exposure added significantly, but not substantially, to the variability explained by job alone. Other Vietnam Veterans Surveys of Vietnam veterans who were not part of the Ranch Hands or Chemical Corps groups indicate that 25 to 55 percent believe they were exposed to herbicides (Erickson et al., 1984a,b; Stellman and Stellman, 1986; CDC,1989~.
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From page 125... ...
The CDC initially concluded that "many veterans were in close enough proximity to applications of Agent Orange to be classified as highly likely to have been exposed to the herbicide" and that there was substantial variability in exposure scores among units and among individual veterans (CDC, 1985~. To test the validity of several indirect methods for estimating exposure of ground troops to Agent Orange in Vietnam, in 1987 the CDC Agent Orange Validation Study measured serum TCDD levels in a nonrandom sample of Vietnam veterans and Vietnam era veterans who did not serve in Vietnam (CDC,
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From page 126... ...
Army veterans who might have been heavily exposed to TCDD in Vietnam. In addition, these serum TCDD levels in Vietnam veterans suggest that the exposure to TCDD in Vietnam was substantially less, on average, than that of occupationally exposed workers; of persons exposed as a result of the industrial explosion in Seveso, Italy; or of the heavily exposed occupational workers that are the focus of many of the studies evaluated by the committee.
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From page 127... ...
1982. Operation Ranch Hand: The Air Force and Herbicides in Southeast Asia 1961-1971.
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From page 128... ...
1984a. Vietnam veterans' risks for fathering babies with birth defects.
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From page 129... ...
1995. Indices of TCDD exposure and TCDD body burden in veterans of Operation Ranch Hand.
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From page 130... ...
1991. Cancer mortality in workers exposed to chlorophenoxy herbicides and chlorophenols.
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From page 131... ...
1990. Mortality and morbidity among Army Chemical Corps Vietnam veterans: a preliminary report.
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