Exposure to carbon black: a cancer risk?

Lung cancer is one of the most serious health problems in the industrial nations and is therefore of great public and scientific interest. Although inhalative cigarette smoking is without doubt the main cause for the increasing frequency of lung cancer, during recent years there has been more and more public interest in other substances in the environment or at the work place that are assumed to be potentially carcinogenic especially due to experiences with fibrous particles such as asbestos and their effects. Enhanced attention is also directed to inert or nuisance dusts such as carbon black. Evaluation of the possibly increased risk for humans should first be based on exact epidemiology data. In the absence of those data--as in the case of carbon black--experimental data in animals serve as the point of orientation, especially results gained in rats in long-term inhalation studies. Pathologic anatomy investigations of human lungs under similar exposure conditions, however, render results quite different from those obtained in rats and, thus, preclude ready interpretation of animal results to human risk assessment. This is particularly true for the development of lung tumors in rats under overload conditions as well as for certain tumor types not observed in human lung tissues. It is therefore quite understandable that many researchers propose to interpret the changes observed in rat lung tissues after inhalation of carbon black as rat-specific reaction mechanisms that cannot be applied to human tissues, which in the past have led to the wrong conclusions regarding human risk assessment due, among other factors, to incorrect experimental design and inaccurate nomenclature of tumorous lesions in rats.