Berg, Martin Van denBirnbaum, LindaBosveld, Albertus T.C.Brunstrom, BjörnCook, PhilipFeely, MarkGiesy, JohnHanberg, AnnikaHasegawa, RyuichiKennedy, Sean W.Kubiak, TimothyLarsen, John ChristianLeeuwen, F.X. Rolaf vanLiem, A.K. DjienNolt, CynthiaPeterson, Richard E.Poellinger, LorenzSafe, StephenSchrenk, DieterTillitt, DonaldTysklind, MatsYounes, MagedWaern, FredrikZacharewski, Tim2023-08-262023-08-261998M Van den Berg, L Birnbaum, A T Bosveld, B Brunström, P Cook, M Feeley, J P Giesy, A Hanberg, R Hasegawa, S W Kennedy, T Kubiak, J C Larsen, F X van Leeuwen, A K Liem, C Nolt, R E Peterson, L Poellinger, S Safe, D Schrenk, D Tillitt, M Tysklind, M Younes, F Waern, and T Zacharewski (1998). Environmental Health Perspectives. Vol. 106, No. 12. https://doi.org/10.1289/ehp.98106775https://hdl.handle.net/10388/14930Reproduced with permission from Environmental Health Perspectives EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted.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 dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinated biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Based on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were revised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachlorinated DF, and PCB 77. These mammalian TEFs are also considered applicable for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in vivo evidence to continue the use of TEFs for some di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:1049-1067 (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, as 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 mono-ortho PCBs is most noticeable compared to mammals and birds. Uncertainties that could compromise the TEF concept were also reviewed, including nonadditive interactions, differences in shape of the dose-response curve, and species responsiveness. In spite of these uncertainties, it was concluded that the TEF concept is still the most plausible and feasible approach for risk assessment of halogenated aromatic hydrocarbons with dioxinlike properties.enCC0 1.0 Universaltoxic equivalency factors (TEFs)risk assessmentmammalian TEFsWHO 1997Article10.1289/ehp.98106775