These properties, which differ among different mineralogic types of asbestos, strongly affect its in vivo persistence and toxicity. Chrysotile asbestos constitutes approximately 99 percent of airborne asbestos fibers in the general environment. Various regulatory agencies have estimated the risk of cancer from low asbestos exposure by extrapolating from the data for high asbestos exposure. The EPA model, applied to the measured asbestos concentrations in the local air, predicts approximately 75 excess deaths from lung cancer in the mining-area population. All have been shown in clinical, epidemiologic, and laboratory studies to be fully capable of causing lung cancer, mesothelioma, and the full range of asbestos-related diseases.
All forms appear to be equipotent in the capacity to cause cancer of the lung.
The most plausible explanation of the low mortality from lung cancer observed in the Camus et al study is that the women in the mining areas were exposed to an asbestos aerosol in which many particles were too large to reach their lungs. Previous studies have indeed established that the risk of cancer in the mining and milling industry is much lower than that in the industries that process and use asbestos, such as textile manufacture and insulation. In mining and milling, many large asbestos particles are suspended in the air, and they tend not to reach the pulmonary alveoli as efficiently as small particles. Thus, air sampling based on light microscopy in the mining environment produces a spuriously high estimate of true alveolar exposure. The EPA's current regulatory controls embody a level of caution commensurate with the hazard.