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Epidemiologic Notes and Reports Serum 2,3,7,8-Tetrachlorodibenzo-p-dioxin Levels in Air Force Health Study Participants -- Preliminary Report

In 1978, the United States Air Force responded to a congressional mandate to initiate an epidemiologic study of the possible health effects of exposure to herbicides and their 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) contaminants in Air Force veterans who served in the Ranch Hand defoliation operation during the Vietnam conflict. Accordingly, the Air Force conducted a nonconcurrent prospective study, the Air Force Health Study, of all 1,267 members of the Ranch Hand unit and a series of matched controls (1).

The controls were selected from the Air Force veterans who served in air cargo units stationed in Southeast Asia (but not in Vietnam) during the same period as the Ranch Hand unit and were individually matched to the Ranch Hand personnel by date of birth, rank (officer, enlisted), and occupation. Investigators assumed that the controls had not been exposed to herbicides or TCDD during the war. Both groups were given physical examinations in 1982 (2), 1985 (3), and 1987-1988. They will be examined again in 1992, 1997, and, finally, during the concluding year, 2002.

Recently, CDC scientists developed a method for measuring TCDD in human serum (4). This lipid-based measurement, which is highly correlated with paired measurements of TCDD in adipose tissue (r= 0.98) (5), has been applied to U.S. Army veterans (6) as well as to participants in the phase of the Air Force Health Study reported here.

This phase of the Air Force study focused on measuring serum TCDD levels in 150 Ranch Hand veterans and 50 controls. All participants were enlisted men; the Ranch Hand veterans had been either herbicide loaders or herbicide specialists in Vietnam. Serum samples from all 200 participants were collected at four Red Cross Centers (Atlanta, Cleveland, Los Angeles, and Tulsa) according to a standardized protocol. One hundred forty-seven of the specimens obtained from Ranch Hand personnel and 49 of those from controls yielded serum TCDD levels that met the quality control criteria (4).

The demographic and health characteristics of Ranch Hand personnel and controls were similar (Table 1); however, their serum TCDD levels differed markedly (Figure 1). The mean serum level of the 147 Ranch Hand personnel was 49 parts per trillion (ppt) (median, 26 ppt); 62% had TCDD levels above 20 ppt, which is considered the upper limit for U.S. residents without known TCDD exposure (7). The mean serum level of the 49 controls was 5 ppt (median, 5 ppt); 2% (1 person) had a level above 20 ppt. Additionally, 79% of the Ranch Hand personnel and 2% of the controls had TCDD levels at or above 10 ppt (chi-square test, pless than 0.0001).

The five highest TCDD levels in the Ranch Hand group were 201, 210, 211, 303, and 313 ppt. The one control who had a level greater than 20 ppt (21.3 ppt) reported exposure to industrial chemicals since 1980 in a steel foundry in Indiana. Reported by: COL WH Wolfe, MD, MPH, JE Michalek, PhD, LTC JC Miner, DVM, MPH, LTC MR Petersen, DVM, MPH, DrPH, US Air Force, Brooks Air Force Base, Texas. Toxicology Br, Div of Environmental Health Laboratory Sciences, Center for Environmental Health and Injury Control, CDC. Editorial Note: The serum TCDD measurement provides a direct assessment of exposure. The distribution of TCDD levels in this phase of the Air Force Health Study indicates that some Ranch Hand personnel had unusually heavy TCDD exposure. The one control who had a TCDD level above background level had been exposed to industrial chemicals in the recent past. No threshold level has been determined as yet for the health effects of TCDD in humans.

The half-life of TCDD in humans has been calculated as approximately 7 years (8) on the basis of TCDD levels in serum samples taken in 1982 and 1987 from 36 of the Ranch Hand personnel who had TCDD levels above 10 ppt in 1987. A half-life of 7 years suggests that only about two to four TCDD half-lives have elapsed since potential exposure of Ranch Hand personnel in Vietnam and that serum TCDD can serve as a biological marker for previous TCDD exposure of Air Force Health Study participants.

A report on the entire 1987-1988 Air Force Health Study will be published after TCDD measurements have been completed for all participants and after the report has been reviewed by the Agent Orange Working Group of the Domestic Policy Council (Executive Branch). The result of the half-life study will be reported in a separate publication. References

  1. Lathrop GD, Wolfe WH, Albanese RA, Moynahan PM. Epidemiologic investigation of health effects in Air Force personnel following exposure to herbicides: study protocol. Brooks Air Force Base, Texas: USAF School of Aerospace Medicine, 1982; National Technical Information Service document no. AD A 122 250.

  2. Lathrop GD, Wolfe WH, Albanese RA, Moynahan PM. An epidemiologic investigation of health effects in Air Force personnel following exposure to herbicides: baseline morbidity study results. Brooks Air Force Base, Texas: USAF School of Aerospace Medicine, 1984; National Technical Information Service document no. AD A 138 340.

  3. Lathrop GD, Machado SG, Karrison TG, et al. Air Force Health Study: an epidemiologic investigation of health effects in Air Force personnel following exposure to herbicides: final report. Brooks Air Force Base, Texas: USAF School of Aerospace Medicine, 1987; National Technical Information Services document no. AD A 188 262.

  4. Patterson DG Jr, Hampton L, Lapeza CR Jr, et al. High-resolution gas chromatographic/high- resolution mass spectrometric analysis of human serum on a whole-weight and lipid basis for 2,3,7,8-tetrachlorodibenzo-p-dioxin. Anal Chem 1987;59:2000-5.

  5. Patterson DG Jr, Needham LL, Pirkle JL, et al. Correlation between serum and adipose tissue levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin in 50 persons from Missouri. Arch Environ Contam Toxicol 1988;17:139-43.

  6. Centers for Disease Control. Serum dioxin in Vietnam-era veterans--preliminary report. MMWR 1987;36:470-5.

  7. Byard JL. The toxicological significance of 2,3,7,8-tetrachlorodibenzo-p-dioxin and related compounds in human adipose tissue. J Toxicol Environ Health 1987;22:381-403.

  8. Pirkle JL, Wolfe WH, Patterson DG Jr, et al. Estimates of the half-life of 2,3,7,8- tetrachlorodibenzo-p-dioxin in Ranch Hand veterans. Presented at Dioxin '87, Las Vegas, Nevada, October 4-9, 1987.

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