Chlorinated Biphenyls (PCB)
The German Commission for the Investigation of Health Hazards of Chemical Compounds in the Work Area has re‐evaluated the maximum concentration at the workplace (MAK value) of chlorinated biphenyls (PCB), considering all toxicity endpoints. Available publications are described in detail.
The Commission re‐evaluated the previous distinction of PCB in two groups: congeners with up to 3 and 4 or more chlorine atoms. Recent inhalation studies show that the lung is not expected to be the primary target organ of PCB 3 and PCB 11 but the liver. In feeding studies, Aroclor mixtures containing congeners with up to 3 chlorine atoms yield only liver adenomas but no carcinomas in rats, although some of these congeners are genotoxic. On the other hand, Aroclor mixtures with high amounts of congeners with 4 and more chlorine atoms lead to a high incidence of liver carcinomas in rats. Therefore, for congeners with up to 3 chlorine atoms, the genotoxicity is not decisive for the development of liver tumours but mainly the tumour promotion, which has also been shown for congeners with 4 and more chlorine atoms. The distinction between these two groups is therefore no longer retained and all PCBs are classified in Carcinogen Category 4. As a 4‐week inhalation study in rats with a PCB containing mainly congeners with up to 3 chlorine atoms does not give rise to toxicity at a concentration which is 35 times higher than the previous MAK value for congeners with 4 and more chlorine atoms, this MAK value of 0.003 mg/m3 is now set for all PCB. The assignment to Peak Limitation Category II with an excursion factor of 8 is retained due to the critical systemic effects and to the long half‐life of PCB. The assignment to Pregnancy Risk Group B is retained, as damage to the embryo or foetus cannot be ruled out even when the MAK value is observed. The genotoxic potency in vivo is regarded as very low if the MAK value is observed, and all PCB are grouped into Germ Cell Mutagen Category 5.