Examples of MAK values and carcinogenicity classification for mixtures.

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) generally sets MAK values for single pure substances. MAK values for mixtures are only established after specific toxicological evaluation of the particular mixture. In practice, there are a few cases in which a common MAK value for the sum of all components was set, such as for mixtures of isomers (e.g. xylenes) or mixtures of related compounds (e.g. Kathon), in which the components of the mixture show comparable toxicological effects. For mixtures of isomers with different toxicological potentials, different MAK values for the single isomers are usually established. The only exception is for the isomer mixture of alpha- and beta-hexachlorocyclohexane, for which a mathematically calculated MAK value was proposed. A safe threshold cannot be established for mixtures containing substances with a genotoxic and carcinogenic potential. These mixtures are categorized either according to the proven carcinogenicity of the mixture, such as alpha-chlorinated toluenes, or according to the carcinogenic substances included, as for pyrolysis products such as coal tars.