AIRBORNE FIBER CONCENTRATIONS AND LUNG BURDEN COMPARED TO THE TUMOR RESPONSE IN RATS AND HUMANS EXPOSED TO ASBESTOS

The excess risk of tumours exposed to asbestos were previously compare d with the results of rat inhalation experiments. It could be demonstr ated that humans at the workplace suffer from a tumour risk at fibre c oncentrations which are 300 times lower than those needed in the rat i nhalation model to produce the same risk. However, the estimation of h uman risk was based on the study of workers at a chrysotile textile fa ctory, whereas animal experimental results were related to exposure to amphiboles. Since for this comparison the risk of cancer due to expos ure to amosite or crocidolite fibres at the workplace is of interest, quantitative exposure-response relationships for lung cancer and mesot helioma for the white workforce of South African amosite and crocidoli te mines were discussed. On comparing the risk of lung cancer in this study with the risk of lung cancer for chrysotile textile workers, it can be concluded, that the risk of lung cancer and mesothelioma from c rocidolite and amosite was higher than in the chrysotile textile facto ry. It could be also demonstrated, on the basis of a study of the lung burden of mesothelioma cases and of controls, that a significantly in creased odds ratio of about 5 was established at amphibole concentrati ons of between 0.1 and 0.2 f mu g(-1) dry lung (WHO fibres longer than 5 mu m from TEM analysis). On the other hand, carcinogenic response w as observed at a fibre concentration 6000 times higher in animal inhal ation experiments with crocidolite asbestos (SEM analysis of WHO fibre s). As a result of these findings, it has been concluded that inhalati on studies in rats are not sufficiently sensitive for the detection of hazards and risks to humans exposed to man-made fibres.