New evaluation of toxicity equivalents for dioxins and dioxin-like compounds

The system of toxic equivalents (TEQ) was introduced to improve the assessment of the toxicity of dioxins and dioxin-like polychlorinated biphenyls (PCBs).  For substances with the same toxicological active profile but different potencies, the TEQ expresses the combined toxicity of the various substances in that mixture. Toxic equivalent factors (TEF) play a key role in calculating TEQs.

Under the system, the toxicity of individual substances is measured relative to 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD), which is considered the most toxic compound in the substance group and is also referred to as the Seveso dioxin.  As the reference substance, 2,3,7,8-TCDD is assigned a factor of one. Other compounds in the dioxin / dioxin-like PCB substance group are assigned lower values in line with their lower toxicity.  The various compounds account for different shares of the TEQ due their TEFs and the respective quantities in which they are present.  TEFs are determined in the course of scientific studies on the toxic risk of the various compounds. 

Consequently, the TEFs have to be updated at regular intervals, taking account of new findings.  In 1998, the World Health Organization (WHO) compiled a list of TEFs. This list used to be the basis for defining the EU's maximum permitted levels for dioxins and dioxin- like PCBs in foods. In 2005, the TEFs were reviewed. An evaluation of the studies resulted in new TEFs being proposed, based on mathematical and statistical considerations. These new TEFs led to dioxins and dioxin-like PCBs being rated as 10 to 20 percent less toxic than the 1998 TEFs, depending on the type of food. After reviewing the TEFs of 2005, the WHO again published new TEFs in November 2023 (2022 WHO TEF). These are based on a scientifically recognised approach to evaluation that had been successfully applied to a comprehensive dataset and to persuasive toxicological studies of individual compounds. In June 2026, the European Food Safety Authority (EFSA) published a risk assessment for human health based on the new TEFs. 

The maximum levels and action levels for dioxins and dioxin-like PCBs in food laid down in Regulation (EC) No 2023/915 are still based on the 2005 TEFs.