Half-life estimates of three polychlorodibenzofurans (PCDFs) were calculated using serial blood samples collected over a 15 to 19-year period. Blood fat PCDFs were modeled in eight individuals who were exposed to contaminated rice oil in Japan (Yusho, n = 5) and in Taiwan (Yucheng, n = 3). The elimination kinetics of PCDFs were concentration-dependent, with faster rates observed at higher concentrations and the apparent transition to slower rates occurring at about 1-3 ppb. Average half-lives of 1.1, 2.3, and 1.5 years above the transition concentration and 7.2, 5.7, and 3.5 years below it were estimated for 2,3,4,7,8-pentaCDF, 1,2,3,4,7,8-hexaCDF, and 1,2,3,4,6,7,8-heptaCDF, respectively. A positive linear correlation of half-life with age was observed for the combined group, with a rate of increase of 0.19, 0.12, and 0.05-year half-life per year of increase in age for penta-, hexa-, and hepta-CDF, respectively. The distinctly younger Yucheng patients exhibited far lower variability in half-lives and age-related trends that were quite consistent with the corresponding data on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for younger persons exposed in the Seveso incident. These age- and concentration-dependent half-lives for PCDFs may have important risk assessment implications for estimating body burdens. The current study provides limited additional evidence that PCDFs, like TCDD, are more rapidly eliminated in younger individuals.
