The estimation of elimination rates of persistent compounds: A re-analysis of 2,3,7,8-tetrachlorodibenzo-p-dioxin levels in Vietnam veterans

The elimination rate of TCDD was re-estimated from measurements of internal concentrations in Vietnam veterans with a model that can account for age dependent body composition, and both age and (calender) time dependent background intake. Estimates of the specific elimination rate, which is independent of body composition, did not differ much between fits with different simplifications of this model for this particular data set. However, the assumption that the associated half-life is constant over the human lifespan is improper. The overall elimination rate and half-life are only constant when background intake and body composition are approximately constant. For example, our model predicts that half-life ranges between 5.5 in young adults and 11 years in elderly men. The change of half-life with age should be accounted for in toxicokinetic calculations.