Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife

An expert meeting was organized by the World Health Organization (WHO) and held in Stockholm on 15-18 June 1997. The objective of this meeting was to derive consensus toxic equivalency factors (TEFs) for polychlorinated diben zo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinat ed biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Bas ed on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were re vised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachl orinated DF, and PCB 77. These mammalian TEFs are also considered applicabl e for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in viva evidence to continue the use of TEFs for so me di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:10 49-1067 (1994)]. In addition, TEFs for fish and birds were determined. The WHO working group attempted to harmonize TEFs across different taxa to the extent possible. However, total synchronization of TEFs was not feasible, a s there were orders of a magnitude difference in TEFs between taxa for some compounds. In this respect, the absent or very low response of fish to mon o-ortho PCBs is most noticeable compared to mammals and birds. Uncertaintie s that could compromise the TEF concept were also reviewed, including nonad ditive interactions, differences in shape of the dose-response curve, and s pecies responsiveness. In spite of these uncertainties, it was concluded th at the TEF concept is still the most plausible and feasible approach for ri sk assessment of halogenated aromatic hydrocarbons with dioxinlike properti es.