Framework for the Application of the Toxicity Equivalence Methodology for Polychlorinated Dioxins, Furans, and PCBs in Ecological Risk Assessment.

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) are persistent contaminants found widely in the environment. Several of these compounds bioaccumulate in the tissues of fish, birds, and mammals, and have been demonstrated to cause mortality and adverse effects on reproduction, development, and the immune system. This Framework is intended to assist EPA scientists in using a method known as the "toxicity equivalence methodology" to assess ecological risks from mixtures of these compounds. It relies on the fact that these compounds share a common mechanism of action for their health effects. Though the Agency has applied the methodology to human health risk assessment for many, application of this methodology in ecological risk assessments has proceeded more slowly, in part because of the variety of species from different taxonomic classes (e.g., fish, birds, and mammals) that need to be considered. As both data and experience with the methodology have accumulated, consensus continues to grow that the toxicity equivalence methodology can strengthen assessments of ecological risks. An external review draft is available electronically at The draft reflects recommendations from consultations and workshops with stakeholders and other federal partners, and is organized in accordance with EPA’s Guidelines for Ecological Risk Assessment (U.S. EPA, 1998). It is intended to assist EPA scientists in using the methodology in ecological risk assessments that involve dioxins and related compounds, as well as to inform EPA decision makers, other agencies, and the public about this methodology. The framework is scheduled from completion in 2006.