On 17 to 21 October 2022 the World Health Organization (WHO) held an ad-hoc expert consultation in Lisbon, Portugal during which the 2005 WHO toxic equivalency factors (TEFs) for dioxin-like compounds, including some polychlorinated biphenyls (PCBs), were re-evaluated.
Background
Since the early 1990's, WHO has organized expert consultations with the objective to harmonize the TEFs for dioxins and dioxin-like compounds on the international level, thereby giving recommendations to national regulatory authorities. TEF expresses the toxicity of dioxins, dibenzofurans and dioxin-like PCBs relative to the most toxic form of dioxin, 2,3,7,8-TCDD. The latest WHO TEFs for dioxin and dioxin-like compounds were established by WHO through a similar expert consultation in 2005.
Since the previous 2005 consultation, a large amount of congener-specific data has been published on estimates of relative potency (REPs) and potential TEF selections. These relative potency data from individual studies have been added to an updated REP database, and these data have been used in a Bayesian meta-regression approach to determine whether or not changes in TEFs would be warranted. The methods applied for this TEF re-evaluation directly follow recommendations made by the 2005 WHO expert consultation.
Preceding the 2022 expert consultation, WHO has worked for more than two years with a group of international recognized dioxin experts to prepare for this meeting. Based on the recommendations of this group, and with the support and collaboration of the European Food Safety Agency (EFSA) - two contractors, ToxStrategies and KeyToxicology, were engaged. These contractors prepared a refined database of relative potency estimates, to develop a consensus-based REP weighting and conducted a peer review of the new data added to the REP database. To further validate the data and models used to refine the TEF values, WHO engaged with experts from the U.S. National Institute of Environmental Health Sciences (NIEHS) to conduct a comprehensive assessment of the Bayesian methods and its application to the REP database. This methodology and level of peer review is unprecedented in the evolution of the REP database. It provides additional confidence in the data that 2022 WHO experts used upon making changes to any of the TEF values. The background data and models used to derive these updated 2022 TEF values will be published in the peer-reviewed literature after the WHO has published the 2022 updated WHO TEF values.
