Technical Bulletin No. 0567: Biological Risk Assessment for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin

An assessment was conducted of the biological relevance of estimating human exposure limits for 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-T4CDD) by extrapolating toxicity data observed at exposure levels that produced measurable affects in laboratory animals and other test systems. While adequate data were available demonstrating the tumorigenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin in rats, there was substantial evidence that the occurrence of liver tumors was associated with concurrent liver toxicity and unique morphological characteristics of livers of aging rats. In addition, the dose-response relationship for liver tumor development was highly nonlinear.