EXAMPLES OF MAK VALUES AND CARCINOGENICITY CLASSIFICATION FOR MIXTURES

The German Commission for the Investigation of Health Hazards of Chemi cal Compounds in the Work Area (MAK Commission) generally sets MAK val ues for single pure substances. MAK values for mixtures are only estab lished after specific toxicological evaluation of the particular mixtu re. 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(R)), in whi ch the components of the mixture show comparable toxicological effects . For mixtures of isomers with different toxicological potentials, dif ferent MAK values for the single isomers are usually established. The only exception is for the isomer mixture of alpha- and beta-hexachloro cyclohexane, for which a mathematically calculated MAK value was propo sed. A safe threshold cannot be established for mixtures containing su bstances with a genotoxic and carcinogenic potential. These mixtures a re categorized either according to the proven carcinogenic of the mixt ure, such as alpha-chlorinated toluenes, or according to the carcinoge nic substances included, as for pyrolysis products such as coal tars. Copyright (C) 1997 Elsevier Science Ltd.