Temporal changes in TCDD levels in 1419 Air Force Vietnam-era veterans notoccupationally exposed to herbicides

We summarize temporal changes in the distribution of 2,3,7,8-tetrachlorodib enzo-p-dioxin (TCDD) measurements made in serum drawn in 1987, 1992, and 19 97 from 1419 Air Force Vietnam-era veterans who served as comparisons in a 20-year prospective study of health and exposure to herbicides and their TC DD contaminant in Air Force veterans of Operation Ranch Hand, the unit resp onsible for aerial spraying of Agent Orange and other herbicides in Vietnam . Among comparison veterans, TCDD levels decreased significantly with time at a rate of -0.25 parts per trillion per year. We also describe paired ser um TCDD measurements in a subgroup of 33 veterans who had detectable levels in both 1987 and 1992. The paired measurements suggested that serum TCDD l evels decreased with time, including those near the limit of detection.