TEQ / TEF (Toxic Equivalency)
A weighting system used for dioxin and dioxin-like compounds — each congener's toxicity is expressed relative to the most toxic form (TCDD = 1) and summed to give a single WHO-TEQ value for compliance.
Toxic Equivalency Factor (TEF) and Toxic Equivalent Quantity (TEQ) are used for dioxins and dioxin-like compounds (No.37 in Directive (EU) 2026/805), analogous to the RPF system used for PFAS. Each individual congener (PCDD, PCDF, and dioxin-like PCB) is multiplied by its WHO-assigned TEF relative to 2,3,7,8-TCDD (TEF = 1) to give TCDD-equivalents. The sum of all congener TEQs is the total WHO-TEQ. Compliance is assessed against the EQS expressed in WHO-TEQ units. The EQS for dioxins is 3.5×10⁻⁵ μg/kg ww in biota (sediment EQS not established separately). TEF values were last revised by WHO in 2005.
Legal reference
Directive (EU) 2026/805 Annex VI (No.37); WHO 2005 re-evaluation of TEFs