TEQ

TEQ stands for Toxic Equivalency Quotient (also called toxic equivalent quantity). It is a metric used to express the overall toxicity of a mixture of dioxin-like compounds by relating the potency of each constituent to that of TCDD, the reference compound with the highest dioxin-like toxicity. Toxic equivalency factors, or TEFs, assign a relative potency to each congener within groups such as polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and certain coplanar polychlorinated biphenyls (PCBs). The TEQ of a sample is calculated as the sum over all congeners of TEF_i × C_i, where C_i is the concentration of congener i. This single value enables comparison of mixtures and informs risk assessment.

TEQ is widely used in environmental monitoring, food safety, and regulatory decision-making. International guidance from the World Health Organization provides standardized TEFs (WHO-TEFs) for PCDD/PCDF and certain PCB congeners, helping harmonize assessments across countries. TEQ values support derivation of reference doses, permissible levels, and emission limits.

Limitations include the assumption of dose additivity among congeners, potential variability in TEF values, and incomplete knowledge about certain interactions or non-dioxin-like effects. TEQ does not capture all toxic mechanisms, and results depend on the selected TEF set and exposure route.

In summary, TEQ provides a concise, standardized approach to assessing the toxic potential of complex mixtures of dioxin-like compounds, facilitating risk assessment and regulatory oversight.