Unexpectedly long half-lives of blood 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) levels in Yusho patients

Background: Dioxins and dioxin-like compounds have half-lives typically between 7.2 years and 15 years. Our previous study of patients poisoned by extremely high concentrations of 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) in the 'Yusho incident' in 1968 found that in some the half-life of blood 2,3,4,7,8-PeCDF tended towards infinity. This suggests that there are two groups of Yusho patients, those with 2,3,4,7,8-PeCDF half-lives around 10 years, and those with half-lives near infinity. We sought to establish the proportions of each in a cohort of 395 Yusho patients, and whether the proportions were changing over time. Methods: We undertook longitudinal measurement of the blood concentration of 2,3,4,7,8-PeCDF in our cohort between 2002 and 2010. We estimated the change in concentration for each patient using linear regression for measured 2,3,4,7,8-PeCDF concentration, then compared the distribution of changes in concentrations with our previous study. Results: In patients in whom the blood concentration of 2,3,4,7,8-PeCDF exceeded 50 pg/g lipid, the proportion 8.0 % of patients exhibiting half-lives less than 13.3 years fell compared with our previous study (28.2 %), while the proportion with near infinity half-lives increased. Conclusion: The prolongation of the half-lives was likely a consequence of age-related factors.