Temporal changes in TCDD levels in 1419 Air Force Vietnam-era veterans not occupationally exposed to herbicides.

We summarize temporal changes in the distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) measurements made in serum drawn in 1987, 1992, and 1997 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 TCDD contaminant in Air Force veterans of Operation Ranch Hand, the unit responsible 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 serum TCDD measurements in a subgroup of 33 veterans who had detectable levels in both 1987 and 1992. The paired measurements suggested that serum TCDD levels decreased with time, including those near the limit of detection.