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International Agency for Research on Cancer (IARC) - Summaries & Evaluations

ASBESTOS

VOL.: 2 (1973) (p. 17)

5. Summary of Data Reported and Evaluation

5.1 Animal carcinogenicity data

Injection of asbestos into the pleural cavity has demonstrated that all major commercial forms can produce mesotheliomas. Experiments suggest that this is probably not due to contaminants such as oils and waxes or heavy metals. It is more likely that the size and shape of the particles are the main factors. Thin, long fibres (less than 0.5 mm diameter and more than 10 mm in length) seem to be most active in producing tumours. Fine glass fibres of similar diameter can also produce mesotheliomas. The carcinogenicity decreases as the materials are pulverised. Inhalation experiments in rats, guinea-pigs and monkeys can produce fibrotic lesions in the lung and pleura similar to those found in man. By inhalation, mesotheliomas and lung carcinomas have been produced in a small proportion of rats exposed to the four commercial types of asbestos.

5.2 Human carcinogenicity data

There is substantial evidence that the risk of lung carcinoma and mesothelioma is small in workers in chrysotile mines and mills, and the same is possibly true for amosite. Some crocidolite mining areas and mills have been associated with a higher risk of mesothelioma. Communities in the neighbourhood of these mines have had, in some instances, an appreciable exposure to asbestos dust. Mesotheliomas have been observed in these populations.

Industrial exposures to asbestos have usually been to mixed types of fibre, especially where manufacturing and application are undertaken, for example, textiles, insulation and asbestos cement, and have also occurred in the immediate vicinity. Mesotheliomas have occasionally been diagnosed among families of asbestos workers.

An important excess risk of lung cancer has usually resulted from past heavy exposures. The differences in risk between the several parts of the industry cannot be ascribed to one factor. The type of fibre, past dust levels, the form of dust produced by the process and the length of exposure are all relevant. The risk of lung carcinomas seems to be related to asbestosis.

In manufacturing and application industries mesotheliomas have been caused by exposure to crocidolite, and less frequently to amosite and chrysotile. The period between first exposure and development of tumours is long, usually more than 30 years. The tumours can occur in the absence of other asbestos-related disease.

At the present time, there is no evidence that exposure of the general population to past levels of asbestos dust in the ambient air or in beverages, drinking-water, food or pharmaceutical preparations increased the risk of cancer.

Cigarette smoking enhances the risk of lung carcinoma in asbestos workers to a much greater degree than in the rest of the population.

Subsequent evaluations: Vol. 14 (1977); Suppl. 7 (1987)


Last updated: 16 March 1998





















    See Also:
       Toxicological Abbreviations
       Asbestos (WHO Food Additives Series 13)
       ASBESTOS (JECFA Evaluation)