US EPA

3101162 

Technical Report 

Current Concepts In Asbestos Fiber Pathogenicity 

Davis, JMG 

1979 

NIOSH/00129971 

Lemen 

45-49 

Current concepts in asbestos (1332214) fiber pathogenicity are discussed. Recent studies have indicated that asbestos shows a dose/response effect for both fibrosis and tumor induction. There is still no definite information, however, on the minimum dose of asbestos required to produce mesotheliomas once the dust has reached the pleural cavity. The question of the effect of total dose and fiber length on induction of fibrosis and cancer is discussed. In a long term study in which rats were exposed to 2 to 10 milligrams per kilogram (mg/kg) chrysotile (12001295), 10mg/kg amosite (12172735), or 5 or 10mg/kg crocidolite (12001284), dusts that did not contain fibers over 20 microns in length produced no bronchial carcinoma and very little lung fibrosis. The author concludes that the long fiber theory of asbestos pathogenesis and carcinogenicity appears to be correct. The biochemical reasons why only long fibers should be dangerous are still obscure. It is suggested that short fibers can be completely enclosed by a single phagocyte and are effectively encapsulated. Asbestos fibers that are so long that they can be only partially enclosed remain dangerous.