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Technical Report 
EPA Report 
Recommended toxicity equivalence factors (TEFs) for human health risk assessments of 2,3,7,8-tetrachlorodibenzo-p-dioxin and dioxin-like compounds 
U.S. Environmental Protection Agency :: U.S. EPA 
U.S. Environmental Protection Agency, Risk Assessment Forum 
Washington, DC 
This document describes the U.S. Environmental Protection Agency's (EPA's) updated approach for evaluating the human health risks from exposures to environmental media containing dioxin-like compounds (DLCs). 2,3,7,8-tetrachlor odibenzo-p-dioxin (TCDD) and DLCs are structurally and toxicologically related halogenated aromatic hydrocarbons. The EPA recommends that the toxicity equivalence factor (TEF) methodology, a component mixture method, be used to evaluate humanhealth risks posed by these mixtures, using TCDD as the index chemical. The EPA recommends the use of the consensus TEF values for TCDD and the DLCs published in 2005 by the World Health Organization. EPA Program Offices and Regions have historically used TEF values in their risk assessments; this document recommends the 2005 WHO consensus TEFs, but does not address specific risk assessment applications of TEFs. The EPA recommends these TEFs be used for all effects mediated through aryl hydrocarbon receptor binding by the DLCs including cancer and noncancer effects. Using information that summarizes the range of relative toxicities of the DLCs, the EPA recommends that, for major risk assessments as determined by U.S. EPA Program Offices or Regions, the conduct of a sensitivity analysis be considered to illustrate the impactthe TEFs have on the toxicity equivalence (TEQ) value. The EPA will update all of these recommendations in the future based on the evaluation of new toxicity data for the DLCs, updates to available relative potency (ReP) data, including statistical summaries of RePs forindividual DLCs, and the results of new consensus processes undertaken to update the TEF approach. 
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