Significant shortcomings of the US Environmental Protection Agency's latest draft risk characterization for dioxin-like compounds

The United States Environmental Protection Agency (U.S. EPA) has concluded that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is a human carcinogen, and it has stated that the lifetime all-cancer mortality risk attributable solely to the current background body burden of dioxin-like compounds could be as high as 1.3 per 100. U.S. EPA's most current human cancer risk estimate was obtained from a linear dose-response model fit to the data from three epidemiology studies of TCDD-exposed chemical workers. Herein it is shown that the U.S. EPA model fails to provide an adequate fit to that data, whereas an intercept-only model, having no slope whatsoever, is entirely adequate. Although the epidemiology data used by U.S. EPA are consistent with a significant elevation in all-cancer mortality, by about 32%, among TCDD-exposed workers, this elevation should not be attributed to the workers' TCDD exposure.