Classification of carcinogenic chemicals in the work area by the German MAK Commission: Current examples for the new categories

The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area (MAK Commission) introduced an extended classification scheme in 1998. In addition to the traditional three categories still used to date, now called: Category 1 (human carcinogen); Category 2 (animal carcinogen); and Category 3 (suspected carcinogen), two new Categories (4 and 5) were added. Classification of substances into the new Categories 4 and 5 is based on the knowledge of mode of action and the potency of carcinogens. The essential feature of substances classified in the new Categories 4 and 5 is that exposure to these chemicals does not contribute significantly to the risk of cancer to man, provided that an appropriate exposure limit (MAK value) is observed. Chemicals known to act typically by non-genotoxic mechanisms are classified in Category 4. Genotoxic chemicals for which low carcinogenic potency can be assessed on the basis of dose-response relationships and toxicokinetics are classified in Category 5. Since the use of this scheme for 3 years, various chemicals have been classified in one of the new categories. However, in several cases data to sufficiently substantiate a MAK value are missing. Such substances are now classified in a subcategory of Category 3, called Category 3 A, which indicates that further data are required for final classification. Examples are given for classification of dichloromethane into Category 3 A, chloroform and sulfuric acid into Category 4 and ethanol into Category 5.