The International Toxicity Equivalency Factor (I-Tef) Method for Estimating Risks Associated with Exposures to Complex Mixtures of Dioxins and Related Compounds

The International Toxicity Equivalency Factor (I-TEF) method of risk assessment is a revised interim procedure for assessing the risks associated with exposures to complex mixtures of chlorinated dibenzo-p-dioxins and dibenzofurans (CDDs and CDFs). This updated scheme was developed by a working group of the North Atlantic Treaty Organization’s Committee on the Challenges of Modern Society and has been officially adopted by the U.S. Environmental Protection Agency (EPA), Canada, Ontario Ministry of the Environment, the Nordic countries, the Netherlands, and the United Kingdom. Prior to the development of the I-TEF method, at least ten slightly different schemes had been used throughout the world which complicated communication among scientists and regulatory agencies concerning the toxicological significance of complex mixtures of CDDs and CDFs. The I-TEF approach facilitates risk communication internationally by reducing large volumes of analytical data into a single number-international Toxicity Equivalents (I-TEQ). As a result, the I-TEF method represents an improvement in an already useful risk assessment/regulatory tool.