Veterans and Agent Orange Update 1998 (1999) / Chapter Skim
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5 Exposure Assessment
5 Exposure Assessment
Pages 135-168
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From page 135... ...
Air Force's Operation Ranch Hand to defoliate inland hardwood forests, coastal mangrove forests, and to a lesser extent, cultivated land, by aerial spraying from C-123 aircraft and helicopters. 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~.
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From page 136... ...
The term Blue was first applied to cacodylic acid in a powder form that was mixed in the field with water. It was later replaced by the liquid formulation TABLE 5-1 Major Herbicides Used in Operation Ranch Hand: 1962-1971 No.
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From page 137... ...
According to military estimates of herbicide use, 90 percent of Agent Orange was used in Ranch Hand forest defoliation missions; 8 percent was used in Ranch Hand crop destruction missions; and 2 percent was sprayed from the ground around base perimeters and cache sites, waterways, and communication lines (NAS, 1974~. Orange II was introduced later in the program.
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From page 138... ...
military personnel exposed to herbicides is impossible to determine precisely, the majority of those assigned to Operation Ranch Hand can be presumed to have been exposed to Agent Orange and other herbicides. During the entire operation, approximately 1,250 military personnel served in Ranch Hand units.
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From page 139... ...
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 four to six weeks after the mission, when defoliation was complete and the herbicide had been biodegraded or photo degraded (U.S.
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From page 140... ...
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 141... ...
In investigating the possible health effects of exposure to herbicides in Vietnam, the committee also looked at available information on occupational and environmental exposures to dioxin, the contaminant found in 2,4,5-T. These studies included residents living in and around Seveso, Italy, who were exposed during industrial accidents; chemical plant workers who were occupationally 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 that contaminated wood preservatives; pulp and paper workers exposed to dioxin through the pulp bleaching process; and residents of China exposed to dioxin as a contaminant in a pesticide used to prevent schistosomiasis.
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From page 142... ...
EXPOSURE ASSESSMENT FOR EPIDEMIOLOGY The committee was asked to evaluate the scientific literature to determine, if possible, whether there is a statistical association between various health effects and herbicide use, taking into consideration the strength of the scientific evidence and the appropriateness of the methods used to detect the association. Estimation of health risks associated with herbicide exposure consists of two primary activities: (1)
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From page 143... ...
An analogous approach for Vietnam veterans might, for example, distinguish individuals by dates of service, proximity to herbicide spraying, and job responsibilities relative to herbicides.
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From page 144... ...
and estimated TCDD level at the end of exposure (r = .801. Group differences in serum TCDD levels can be useful in confirming that occupational exposure measures reflect true differences in exposure; this has been done in studies by the National Institute for Occupational Safety and Health (NIOSH)
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From page 145... ...
In August of 1997, the committee hosted a workshop for many of the researchers involved in studies of Vietnam veterans and individuals exposed to herbicides or dioxin. The goal of the workshop was to discuss the feasibility of using current data combination techniques (such as meta-analysis and data pooling)
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From page 146... ...
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 147... ...
When the questionnaire-derived indices were applied within each oh classification, days of skin exposure added significantly, but not substantially, to the variability explained by job alone. it 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., 1984 a,b; Stellman and Stellman, 1986; CDC, 1989~.
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From page 148... ...
Approximately 25 percent of interviewed Vietnam veterans reported that they had been exposed to Agent Orange. Fifty-two percent received the same score in both the index score and the self-reported Agent Orange exposure.
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From page 149... ...
In addition, none of the records-derived estimates of exposure and neither type of self-reported exposure to herbicides identified Vietnam veterans who were likely to have currently elevated serum TCDD levels (CDC, 1988~. The study concluded it is unlikely that military records can be used to identify a large number of U.S.
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From page 150... ...
(IOM, 19961. Production Workers The Netherlands Two plants in the Netherlands that manufactured phenoxy herbicides and chlorophenols between 1955 and 1986 were studied by Bueno de Mesquita et al.
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From page 151... ...
analysis (Saracci et al., l991~. A follow-up of the cohort included a more detailed exposure assessment using serum TCDD levels of a subset of workers to model historical exposure levels (Hooiveld et al., 1996~.
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From page 152... ...
A cumulative exposure score was calculated for each subject for each chemical, based on the individual's work history and knowledge of the determinants of exposure such as department or job, use of personal protective equipment, contact with chemicals and other factors (Kauppinen et al., 1994~. In the case-control analysis, the cumulative exposure scores for each chemical were divided into low-, medium-, and highexposure categories (Kogevinas et al., 1995~.
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From page 153... ...
Exposure was estimated from job records according to the length of time working in processes involving TCDD contamination and the total length of employment at the plant; serum TCDD levels were measured in a sample of 253 workers. Data on current TCDD levels demonstrated a good correlation with the duration of employment.
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From page 154... ...
All of the plants were involved in the production of phenoxy herbicides or chlorophenols. Exposure assessment involved the estimation of duration of employment from the start of work in a department with suspected exposure until the end of employment at the plant.
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From page 155... ...
Some studies attempted to validate self-reported information, based on verification using written records, signed statements, or telephone contacts with coworkers or former employers (Carmelli et al.,1981; Woods and Polissar,1989~. Herbicide and Pesticide Sprayers Studies of herbicide sprayers are relevant because it can be presumed that applicators had more sustained exposure to herbicides; however, applicators were also likely to be exposed to a multiplicity of chemicals, complicating the assessment of any individual or group exposure specifically to phenoxy herbicides or TCDD.
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From page 156... ...
The Seveso cohort continues to be monitored, including a 15-year follow-up of mortality (Bertazzi et al., 1997) and a continuing examination of serum TCDD levels (Pesatori, 1995; Needham et al., 1997~.
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From page 157... ...
TCDD Half-Life Investigations The pharmacokinetics of TCDD in humans its absorption, distribution, and passage through the body are not fully understood, which makes individual serum TCDD levels difficult to interpret and also complicates the interpretation of epidemiologic studies that rely on these measures of exposure. A complex, poorly understood process distributes dioxins among body tissues and slowly clears them from the body.
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From page 158... ...
Also during this review a study investigating the reliability of serum TCDD measurements using paired samples from 46 Ranch Hands veterans was reported. The coefficient of reliability for these repeated measurements was 0.87 when the measurement was made at 50 ppt dioxin or less.
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From page 159... ...
They measured the levels of dioxin and dibenzofuran congeners in blood samples. They found average 1,2,3,4,6,7,8HpCDD levels 13 times higher than the average TCDD levels and average 1,2,3,4,6,7,8,9-OCDD levels 88 times higher than average TCDD levels.
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From page 160... ...
They found TCDD levels greater than 5 ppt in 16 (32 percent) of these Vietnam veterans.
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From page 161... ...
at the time of last exposure by extrapolating back from more current serum TCDD measurements (Fingerhut et al., 1989; Ott et al., 1993; Flesch-Janys et al., 1995~. In each case the authors chose a half-life estimate for TCDD that applied to all members of the cohort and assumed a one-compartment first-order kinetics model of TCDD levels.
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From page 162... ...
, exposure duration was assumed to be a good surrogate for TCDD level. Aylward has estimated the peak, average, and AUC TCDD levels of the Ranch Hand (Aylward et al., 1997)
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From page 163... ...
1982. Operation Ranch Hand: The Air Force and Herbicides in Southeast Asia 1961-1971.
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From page 164... ...
1984b. Vietnam Veterans' Risks for Fathering Babies with Birth Defects.
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From page 165... ...
1995. Indices of TCDD exposure and TCDD body burden in veterans of Operation Ranch Hand.
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From page 166... ...
1989. Estimates of the half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin in Vietnam veterans of Operation Ranch Hand.
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1990. Mortality and morbidity among Army Chemical Corps Vietnam veterans: a preliminary report.
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From page 168... ...
Presentation to the Institute of Medicine Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides. December 8, 1992.
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