Carcinogenic Potential of Silica Compounds
Summary and Conclusions
Silicate fibers have been shown to produce cancer in man and animals. Cancer of the lung, pleura and peritoneum (mesothelioma), gastro-intestinal system and several other sites may frequently occur. This is now identified as an important pUblic health problem.
A variety of such fibers of different chemical and crystallographic structure are active: chrysotile, amosite, crocidolite, anthophyllite, tremolite. These have a number of trace element contaminants.
The mass of dust needed to produce disease is small (often less than 0.25–0.50 g in the lungs, in extensive asbestosis), although the number of particles and their surface area are very large. The amount of fibrous silicate dust exposure needed to produce cancer is as little as may occur in the households of asbestos workers or in neighborhoods about asbestos factories.
Not all tissues respond to the presence of these fibers with cancer; they may be found in some organs without increased cancer risk. At present the reasons for differences among tissues are not known.
Silica (quartz) does not reproduce these carcinogenic effects. Among silica exposed individuals, we have found no mesothelioma, nor increase in gastro-intestinal cancer.
While we have found, as expected, ample evidence of pulmonary fibrosis (silicosis), comparable with the extent of fibrosis with asbestos (asbestosis), there was a far smaller increase of lung cancer. There was thus a dissociation between fibrogenic and carcinogenic potentials of silica and asbestiform fibrous silicates. Further, silicotic fibrosis was associated with tendency to concomitant tuberculosis. This was not seen with asbestosis.
An influence of shape and size of the particles is currently being considered, on the basis of experimental studies. Appropriate human data are presently not available on this aspect of the problem.
KeywordsDust Lymphoma Influenza Tuberculosis Smoke
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