Contribution of a specified component (or components) to the toxicity of a mixture of related substances.

Note 1: The amount-of-substance (or substance) concentration of total toxicity equivalent is the sum of that for the components B, C … N.

Note 2: Toxicity equivalent is most commonly used in relation to the reference toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-tetrachlorooxanthrene) by means of the toxicity equivalency factor (TEF, f) which is 1 for the reference substance. Hence, where c is the amount-of-substance concentration.