Additivity of substances in a mixture with known toxicity and classified for the same endpoint is applied for certain endpoints in the classification criteria of the UN GHS and the EU CLP Regulation. This is applied in cases where data on the mixture itself is not available, and classification is based on the classification of substances. This approach has been explicitly described for acute toxicity, corrosion/irritation to skin, serious eye damage/eye irritation and, under certain conditions, for Specific Target Organ Toxicity (STOT). This is based on the assumption that all substances exerting this hazardous effect contribute to the overall hazard of the mixture in proportion to their concentration and potency. A mixture is classified as hazardous when the sum of the concentrations of such substances present in the mixture above the specified cut-off value (applying a weighting factor for potency where appropriate) exceeds the applicable concentration limit specified in the regulatory text. For these hazard classes, additivity applies irrespective of the mode of action of the various substances as long as the hazard endpoint is the same for the ingredient substances. Following Article 11(1) of CLP, such an approach is equally applicable for substances containing constituents displaying the above hazard property. It is currently being explored whether the principle of additivity is applicable in certain cases when classifying mixtures (or complex substances) for other hazard endpoints, especially for CMR endpoints where classification is to be based on available information for the substances rather than for the whole mixture. In this context, the objective of this project was to conduct a detailed scientific assessment to provide the information base for the assessment and selection of different options for how the principle of additivity Additivity of substances in a mixture with known toxicity and classified for the same endpoint is applied for certain endpoints in the classification criteria of the UN GHS2 and the EU CLP Regulation. This is applied in cases where data on the mixture itself is not available, and classification is based on the classification of substances. This approach has been explicitly described for acute toxicity, corrosion/irritation to skin, serious eye damage/eye irritation and, under certain conditions, for Specific Target Organ Toxicity (STOT). This is based on the assumption that all substances exerting this hazardous effect contribute to the overall hazard of the mixture in proportion to their concentration and potency. A mixture is classified as hazardous when the sum of the concentrations of such substances present in the mixture above the specified cut-off value (applying a weighting factor for potency where appropriate) exceeds the applicable concentration limit specified in the regulatory text. For these hazard classes, additivity applies irrespective of the mode of action of the various substances as long as the hazard endpoint is the same for the ingredient substances. Following Article 11(1) of CLP, such an approach is equally applicable for substances containing constituents displaying the above hazard property. It is currently being explored whether the principle of additivity is applicable in certain cases when classifying mixtures (or complex substances) for other hazard endpoints, especially for CMR endpoints where classification is to be based on available information for the substances rather than for the whole mixture. In this context, the objective of this project was to conduct a detailed scientific assessment to provide the information base for the assessment and selection of different options for how the principle of additivity could be applied to carcinogenic, mutagenic and reprotoxic (CMR) PAH constituents of petroleum and coal (PetCo) substances. In order to support the European Commission and the ECHA Risk Assessment Committee (RAC) in the preparation of options for potential PAH additivity, the current study focused on the following activities: - Task 1 - Compile available additional scientific information on the CMR toxicity of PAH constituents of petroleum and coal-derived UVCB (unknown or variable composition, complex reaction products or of biological materials) and multi-constituent substances registered under the Registration, Evaluation, Authorisation, and restriction of Chemicals (REACH) regulation and their modes of action (MoA). - Task 2 - Identify groups of PAHs for which additivity could potentially be applied. PAHs included in the scope of this project have the following characteristics: - PAHs which only contain carbon and hydrogen (homocyclic). Heterocyclic PAHs have not been included. - Unsubstituted and alkylated PAHs with 2-7 rings and, in the case of alkylated PAHs, a maximum chain length of 4 carbons. PAHs substituted with non-alkyl groups have not been included.
