Operation Ranch Hand

Pirkle J et al Estimates of the half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin in Vietnam veterans of Operation Ranch Hand. 7 Toxicol Environ Health 27 165, 1989... 

Michalck JE et al Pharmacokinetics of TCDD in veterans of Operation Ranch Hand 10 year follow-up. J Toxicol Environ Health 47 209, 1996... 

In its Agent Orange exposure study, the CDC identified 600 Vietnam veterans who had been present at times and in areas near where the Air Force s Operation Ranch Hand had sprayed Agent Orange and compared the concentrations of dioxin in the blood lipids (these concentrations are called body burdens ) of those veterans with the concentrations in some 100 other veterans who had never served in Vietnam. The dioxin concentrations in the exposed and nonexposed veterans were the same, and the concentrations in both groups fell within the concentrations measured in the general population.10... 

G. L. Henrikson et al., Serum Dioxin and Diabetes Mellitus in Veterans of Operation Ranch Hand, Epidemiology8 (1997) 252-58. 

W. H. Wolfe et al., Paternal Serum Dioxin and Reproductive Outcomes Among Veterans of Operation Ranch Hand, Epidemiology 6 (1995) 17-22. 

Michalek, J.E., J.L. Pirkle, S.P. Caudill, R.C. Tripathi, D.G. Patterson Jr., and L.L. Needham. 1996. Pharmacokinetics of TCDD in veterans of Operation Ranch Hand 10-year followup. J. Toxicol. Environ. Health 47(3) 209-220. 

Pirkle, J., Wolfe, W., Patterson, D., Needham, L., Michalek, J., Miner, J., Peterson, M., Phillips, D. (1989) Estimates of the half-life of 2,3,7,8-tetrachlorodibenzodioxin in Vietnam veterans of operation ranch hand. J. Toxicol. Environ. Health 27, 165-171. 

In general, workers involved in the manufacture of 2,4,5-TCP and subsequent products were exposed to far greater levels of 2,3,7,8-TCDD than those involved in the handling and application of chlorinated pesticides containing CDDs. Current serum lipid levels of 2,3,7,8-TCDD in a small number of U.S. Air Force veterans who were directly involved in the aerial spraying of herbicides (Agent Orange contaminated with 2,3,7,8-TCDD) in Vietnam as part of Operation Ranch Hand,... 

TCDD levels using a half-life of approximately 7 years. The 7.1-year half-life was derived from a study of 36 veterans involved in Operation Ranch Hand (Pirkle... 

No respiratory effects were associated with exposure to 2,3,7,8-TCDD-contaminated herbicides in a group of Vietnam Air Force veterans involved in Operation Ranch Hand examined more than 10 years after the war (Wolfe et al. 1985). In the 1987 follow-up (USAF 1991), no association was found between the initial or current serum level of 2,3,7,8-TCDD and incidences of asthma, bronchitis, pleurisy, pneumonia, or tuberculosis abnormal spirometric measurements were often associated with CDD blood levels, but according to the authors (USAF 1991), the differences in the mean level between high- and low-exposure subjects were not clinically important. The authors suggested that these findings may have been related to the association between 2,3,7,8-TCDD and body fat because obesity is known to cause a reduction in vital capacity. 

A health study of Vietnam veterans involved in Operation Ranch Hand indicated an association between high initial and current serum 2,3,7,8-TCDD levels and increased erythrocyte sedimentation (Wolfe et al. 1995), and an earlier study by Wolfe et al. (1985) indicated an increase in mean corpuscular volume however, these changes were minor and were not observed in the 1991 follow-up (USAF 1991). Higher serum 2,3,7,8-TCDD levels were also associated with positive dose-response trends for increases in white blood cell and platelet levels. 

In a follow-up study, Calvert et al. (1996) examined the association between exposure to 2,3,7,8-TCDD and serum lipids. In the follow-up the authors chose not to adjust the 2,3,7,8-TCDD serum concentrations for total lipids to avoid the problems of interpretation that would arise when adjusting a covariate by the dependent variable. Consequently, the results obtained in this study cannot be compared directly with those from the Operation Ranch Hand study (see below). The median serum 2,3,7,8-TCDD concentration among the workers was 406.6 femtograms/g serum (fg/g) compared with 36.9 fg/g among the referents. 

A health study in Vietnam veterans involved in Operation Ranch Hand found no liver diseases linked to... 

TCDD serum levels (USAF 1991). The diabetes finding remained significant even after adjusting for body fat. Furthermore, subclinical effects in thyroid function (significant decrease in mean T3 uptake and increases in mean TSH) were reported for Operation Ranch Hand veterans with high current... 

The results of a further examination of Operation Ranch Hand veterans was recently published (Burton et al. 1998). The cohort consisted of 930 exposed subjects and 1,200 comparison individuals who served in SEA during the same period but who were not involved with spraying herbicides. The authors examined the associations between serum dioxin levels and a) chloracne, b) occurrence of acne relative to the tour of duty in SEA, and c) anatomical location of acne after service in SEA. Initial dioxin levels were computed using a first-order pharmacokinetic model with a constant half-life of 8.7 years. Four exposure categories were defined 1) comparisons, with current dioxin levels of 10 ppt 2) background Operation Ranch Hand veterans, with current dioxin levels of 10 ppt 3) low category, with current dioxin levels exceeding 10... 

A health study of Vietnam veterans involved in operation Ranch Hand did not find any correlations between clinically significant immunological alterations and serum 2,3,7,8-TCDD levels (USAF 1991). 

The effects of 2,3,7,8-TCDD exposure on gonadal function (production of germ cells and secretion of sex hormones) has not been extensively investigated. A health study in Vietnam veterans involved in Operation Ranch Hand found a significant association between decreased testicular size and serum... 

In a study of Vietnam veterans participating in Operation Ranch Hand (Wolfe et al. 1995), an increase in nervous system defects with increasing paternal serum lipid 2,3,7,8-TCDD levels was observed (statistical analysis was not performed due to the small number of defects 3/981 in comparison group, 0/283 in Ranch Hand veterans with current 2,3,7,8-TCDD levels of 10 ppt, 2/241 in veterans with current... 

In an earlier study by Wolfe et al. (1985) of Air Force personnel involved in Operation Ranch Hand, a significant increase in the number of reported neonatal deaths (no additional details provided), as compared to a comparison group of Air Force military employees not stationed in Vietnam, was observed. The incidence of major defects, prematurity, learning disabilities, or infant deaths was not increased in the Ranch Hand personnel. A significant increase in the incidence of minor health effects such as birth marks, rashes, and neonatal jaundice was reported by the Ranch Hand veterans. It should be noted that the pregnancy outcomes were self-reported, and this finding was not corroborated by the follow-up study (Wolfe et al. 1995) which used birth certificates, medical records, and death certificates to assess possible relationships between paternal exposure to 2,3,7,8-TCDD and developmental effects in offspring. 

Endocrine Effects. No biochemical evidence of thyroid dysfunction, as evaluated by serum levels of T4, triiodothyronine, and TSH, were reported in a group of 18 workers examined 17 years after an industrial accident during the manufacture of 2,4,5-T (Jennings et al. 1988). The small sample size, the fact that no measure of exposure was provided, and the long period of time between exposure and examination preclude any conclusion regarding possible effects of 2,3,7,8-TCDD. Zober et al. (1994) found a significant increase in the incidence of thyroid disease (no further details provided) 35 years after the BASF accident. An increased incidence of diabetes and subclinical decreases in thyroid function were found in Vietnam veterans who participated in operation Ranch Hand (USAF 1991). 

Most recently, Michalek et al. (1998) measured levels of 2,3,7,8-TCDD in 1,302 unexposed Air Force Vietnam-era veterans. These veterans served as controls in the 20-year epidemiologic study of Air Force veterans of Operation Ranch Hand, the unit responsible for aerial spraying of Agent Orange in Vietnam. These authors reported mean 2,3,7,8-TCDD concentrations in blood of 4.32 2.53 ppt for the control group. The 99th percentile of the distribution was less than or equal to 10.4 ppt. 

Burton JE, Michalek JE, Rahe AJ. 1998. Serum dioxin, chloracne, and acne in veterans of Operation Ranch Hand. Arch Environ Health 53 199-204. 

Henriksen GL, Ketchum NS, Michalek JE, et al. 1997. Serum dioxin and diabetes mellitus in veterans of operation ranch hand. Epidemiology 8 252-258. 

---