Selected other effects and TEFs.

The half-lives and tissue distribution of chlorinated dibenzodioxins and dibenzofurans in humans are reviewed. An attempt is made to correlate adverse effects observed in humans such as chloracne, Yusho, Yucheng, and Seveso with tissue levels. No causal inferences should be made in the Ranch Hand studies because TCDD serum levels are slightly higher in older persons and in persons who have diseases related to their lipid metabolism and their age. These differences cannot be used in the context of a dose-response relationship but should be used in the context of variations in the distribution of PCDD and PCDF levels within different subpopulations. Based on these observations in humans, TEF values for mixtures of PCDD and PCDF are poor predictors of human risk.