Assessing the Use and Misuse of Toxicity Equivalency Factors (TEFs) When Evaluating Dioxin Data for Ecological Risk Assessments. J. H. Samuelian and W. R. Alsop, AMEC Earth & Environmental
Toxicity Equivalency Factors (TEFs) have been applied to dioxin/furan congener data to facilitate the assessment of the potential toxicity of the congener mixtures of these chemicals in environmental media. However, as with many muliti-component mixtures, the derivation of the exposure point concentrations (EPCs) must reflect both the intra-sample distribution of the congeners as well as the inter-sample variability of the congener mixtures. Using an artificial dataset, we will demonstrate how not properly accounting for these two components can result in generating inappropriate estimates of potential risks to ecological receptors. Furthermore, when fate and transport processes come into play, such as estimating media-specific congener concentrations across a receptor grid using the USEPA Region 6 Combustion Protocol, properly accounting for the intra-sample distribution and inter-sample variability becomes even more important. In 1995, EPA developed the Bioaccumulation Equivalency Factors (BEFs) for the dioxin and furan congeners in support of the Great Lakes Water Quality Initiative to assess congener concentrations in effluents in this system. We will examine whether this method (based on sediment-biota partitioning) could be used to account for intra- or inter-sample variability for other aquatic systems, and whether a similar approach based on terrestrial systems could also be derived.
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