Low level exposure to asbestos: is there a cancer risk?

Our plain-English summary of Low level exposure to asbestos: is there a cancer risk?, by J.M. Davis, J.C. McDonald (British Journal of Industrial Medicine, 1988).

The study

• Authors: J.M. Davis, J.C. McDonald
• Journal: British Journal of Industrial Medicine
• Published: 1988;45(8):505-8
• Type of article: Review
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000898).

Summary of the article

This editorial asked whether low occupational and environmental exposures to asbestos carry a cancer risk, and whether there is a safe threshold below which asbestos does not cause tumours. The authors reviewed experimental and epidemiological evidence. In rats, exposure for one day gave results similar to those in unexposed controls. In injection studies with doses from 25 mg down to 0.01 mg, the time to tumour lengthened as dose fell. The most dangerous fibres were longer than 8 µm and thinner than 0.25 µm. A short-fibre amosite preparation produced neither fibrosis nor tumours, and chrysotile was cleared from lung tissue much faster than amosite. The authors stated that epidemiological studies become increasingly unreliable as exposure falls. For example, no significant rise in lung cancer would have been detected among nearly 2000 chrysotile mine and mill workers employed at least 20 years at about 20 fibres/cc. They suggested that mesothelioma in people reputedly exposed only to chrysotile may largely result from tremolite contamination. Female mesothelioma mortality showed no apparent increase in a combined population of some 300 million, from which they concluded that the risk from non-occupational exposure must be extremely small. They concluded that zero risk at very low exposure may be impossible to prove or disprove. Any lung cancer increase below current control limits would not be detected. Priorities for reducing such risks were for society, not science, to decide.

PubMed has no abstract for this study, and the article doesn't print one. We wrote this summary from the full article with the help of AI. It is not the authors' wording.

In plain English

This was an editorial in the British Journal of Industrial Medicine, not an original study. The authors reviewed animal experiments and studies of human populations to ask whether low level exposure to asbestos carries a cancer risk. They described rat studies in which chrysotile, amosite and crocidolite injected into the peritoneal cavity produced tumours in a dose-related way. In other rat studies, a short-fibre amosite preparation that was inhaled produced neither fibrosis nor tumours. They noted that among chrysotile mine and mill workers, no statistically significant increase in lung cancer deaths would have been detected in nearly 2000 men employed at least 20 years at about 20 fibres/cc. National data showed no significant increase in mesothelioma mortality among women, while men's rates rose steeply. They suggested that tremolite contamination probably explains much of the mesothelioma risk in people reputedly exposed only to chrysotile. The authors concluded that it may be impossible to prove or disprove a zero cancer risk at very low exposure. They also concluded that any increase in lung cancer risk below current control limits would not be detected. They noted limitations of both animal and human evidence.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Editorial (narrative review of experimental and epidemiological evidence); no new data collected
• Who was studied: No study population of its own; the authors reviewed experimental studies in laboratory animals (mainly rats) and epidemiological studies of exposed human populations
• Exposure: Low level occupational and environmental exposure to asbestos, discussed by fibre type (chrysotile, amosite, crocidolite, and tremolite as a contaminant) and fibre length
• Main results:
  • The authors described rat studies (Davis) in which crocidolite, amosite and chrysotile were injected into the peritoneal cavity at doses from 25 mg down to 0.01 mg. A clear dose response was found for all three. Crocidolite did not produce tumours at the lowest dose, but chrysotile and amosite did.
  • In long term rat inhalation studies the authors described, the short-fibre amosite preparation produced neither fibrosis nor tumours. The long-fibre dusts produced large amounts of fibrosis and many pulmonary tumours.
  • The authors stated that in chrysotile mine and mill workers, no statistically significant increase in lung cancer mortality would have been detected in nearly 2000 men with at least 20 years employment at an average of about 20 fibres/cc.
  • The authors described a cohort of vermiculite miners and millers exposed only to contaminating tremolite. Dose for dose, their lung cancer and mesothelioma experience was many times worse than that of Quebec chrysotile miners and millers.
  • The authors judged it probable that even the relatively low mesothelioma risk in people reputedly exposed only to chrysotile may largely result from tremolite contamination.
  • In national trends cited by the authors (United States, Canada, Britain, probably Scandinavia), annual mesothelioma mortality was about 1-2 per million in both men and women until the 1950s. Since then mortality in men rose steeply, while in women there was no significant increase.
  • The authors stated that any increase in lung cancer risk at exposure below today's control limits would not be detected.
• The authors' conclusion: The authors concluded that they cannot say, and it may be impossible to prove or disprove, that the cancer risk at very low asbestos exposure is zero. They added that any increased lung cancer risk below current control limits would not be detected, and that the same applies to mesothelioma for commercial chrysotile, with less confidence for crocidolite and amosite. They wrote that it is for society, not science, to decide what priority to give such risks.
• Limitations the authors state:
  • The authors noted that animals' short life span makes direct extrapolation of animal results to humans difficult.
  • The authors noted that epidemiological studies suffer from great uncertainty about the nature and intensity of past exposure.
  • The authors noted that animal studies of a range of doses given over a long period had not been undertaken.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Environmental Exposure, Amosite, Fibrosis, Chrysotile, Lung Cancer, Mesothelioma, Tremolite Contamination, Non-Occupational Exposure.

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