EPA has published a framework designed to assist EPA scientists,policymakers and others in using the "toxicity equivalence methodology" to assess ecological risks from mixtures of dioxin-like chemicals,an important development in the agency's long-running efforts to assess and manage dioxin in air,water,and waste. A notice published in the Federal Register June 16 announces the availability of EPA's "Framework for Application of the Toxicity Equivalence Methodology for Polychlorinated Dioxins,Furans,and Biphenyls in Ecological Risk Assessment." The methodology relies on toxic equivalency factors (TEFs),which measure the toxicity of dioxin compounds relative to the most toxic form of the compound,known as 2,3,7,8 TCDD.Regulators then calculate the cumulative risks of dioxin mixtures based on the TEFs.This approach generally results in calculations of greater toxicity than if regulators were to calculate toxicity based on the risks posed by individual chemicals,an approach industry favors.
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