Changes in the classification of carcinogenic chemicals in the work area -(Section III of the German List of MAK and BAT values)

Carcinogenic chemicals in the work area were previously classified into thr ee categories in section III of the German List of MAK and BAT values (the list of values on maximum workplace concentrations and biological tolerance for occupational exposures). This classification was based on qualitative criteria and reflected essentially the weight of evidence available for jud ging the carcinogenic potential of the chemicals. In the new classification scheme the former sections IIIA1, IIIA2, and IIIB are retained as categori es 1, 2, and 3, to correspond with European Union regulations. On the basis of our advancing knowledge of reaction mechanisms and the potency of carci nogens, these three categories are supplemented with two additional categor ies. The essential feature of substances classified in the new categories i s that exposure to these chemicals does not contribute significantly to the risk of cancer to man, provided that an appropriate exposure limit (MAK va lue) is observed. Chemicals known to act typically by non-genotoxic mechani sms, and for which information is available that allows evaluation of the e ffects of low-dose exposures, are classified in category 4. Genotoxic chemi cals for which low carcinogenic potency can be expected on the basis of dos e/response relationships and toxicokinetics and for which risk at low doses can be assessed are classified in category 5. The basis for a better diffe rentiation of carcinogens is discussed, the new categories are defined, and possible criteria for classification are described. Examples for category 4 (1,4-dioxane) and category 5 (styrene) are presented.