Human evidence: lung cancer mortality risk from chrysotile exposure

Our plain-English summary of Human evidence: lung cancer mortality risk from chrysotile exposure, by J.M. Hughes (The Annals of Occupational Hygiene, 1994).

The study

• Author: J.M. Hughes
• Journal: The Annals of Occupational Hygiene
• Published: 1994;38(4):555-60, 415-6
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The linear, no-threshold model is commonly used for estimating lifetime lung cancer risk from asbestos exposures. Studies of chrysotile workers have observed shallow slopes for the exposure-response relationship for miners/millers, friction products manufacturing workers and asbestos-cement (primarily chrysotile) workers but a steeper slope (approximately 16 times higher) for textile workers. For chrysotile exposures in buildings, where short fibres constitute the great majority of the fibres, the shallow slope is judged more appropriate. Using this slope the data regarding exposure levels to building occupants and maintenance workers, the annualized risks of lung cancer would be approximately 0.01 and 0.6 per million for these groups, respectively. Using the higher slope would result in risks 16 times higher, still considerably lower than those commonly accepted. Contrary to the model's assumption of increased risk for any amount of exposure, a number of studies have demonstrated evidence that lung cancer risk is not associated with years exposed to low exposure levels. Moreover, the accumulating evidence that asbestos-induced lung cancer may require lung fibrosis suggests a practical threshold since detectable lung fibrosis will not result from environmental exposure levels. Evidence suggests that the relative risk to non-smokers bay be slightly higher than to smokers (by a factor of 1.8). However, if this is true, this has little effect on risk assessment due to the low absolute risk in non-smokers. Tremolite has been associated with an increased risk of lung cancer in a study of vermiculite miners; the slope of the exposure-response relationship was similar to that for crocidolite miners and much higher than that of chrysotile miners. In spite of a recent report indicating that asbestos-associated lung cancer risk may be limited only to adenocarcinomas, the bulk of the evidence fails to confirm this.

In plain English

This paper was read at a 1993 workshop on chrysotile asbestos. It was a review by the author of published evidence on lung cancer risk from chrysotile, not a new study. The author noted that four studies of workers exposed almost exclusively to chrysotile, in mining, friction product manufacturing and asbestos-cement manufacturing, reported exposure-response slopes of 0.0006 or less. Chrysotile textile manufacturing showed a steeper slope of approximately 0.01. The author judged 0.0006 more appropriate for chrysotile in buildings. With that slope, the author estimated lung cancer risks for production workers at assumed levels of 0.10 and 0.20 fibres per ml, and for maintenance workers, office workers and schoolchildren using published building air measurements. In one worked example, 0.2 fibres per ml for 20 years gave a relative risk of approximately 1.0024. The author also reviewed evidence on smoking, low exposure levels, tremolite in vermiculite miners and lung cancer cell type. The author argued that if lung fibrosis is a necessary precursor, a practical threshold is likely. The author stated that the questions about smoking and about low exposure levels remained unresolved.

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: Review (paper presented at a workshop) of published studies on lung cancer risk from chrysotile, with the author's own risk calculations based on those studies
• Who was studied: No new population was studied. The author reviewed published cohorts of asbestos workers (chrysotile miners, friction product, asbestos-cement and textile workers, crocidolite miners, and vermiculite miners exposed to tremolite) and published reviews of air measurements in buildings with asbestos-containing materials
• Exposure: Mainly chrysotile, in mining, friction product manufacturing, asbestos-cement manufacturing, textile manufacturing and buildings. Comparisons were made with crocidolite, mixed fibre exposures and tremolite associated with vermiculite
• Main results:
  • Four studies of primarily chrysotile-exposed workers in mining, friction product manufacturing and asbestos-cement manufacturing reported slopes of 0.0006 or less (cumulative exposure in fibres per ml-years)
  • The only steep slope for chrysotile workers, approximately 0.01, was in chrysotile textile manufacturing
  • The author judged a slope of 0.0006 more appropriate for a population exposed to non-textile chrysotile, such as in buildings
  • Worked example: a worker exposed to 0.2 fibres per ml of chrysotile for 20 years (cumulative exposure 4.0 fibre per ml-years) would have a relative risk of approximately 1.0024
  • In Table 1, production workers (men) were assigned assumed average concentrations of 0.10 and 0.20 fibres per ml for 30 years, giving estimated lifetime lung cancer risks of 12.6 and 25.2 per 100,000 (the row matching is reconstructed from the OCR-scrambled table and agrees with the stated slope and 7% background risk)
  • For building settings, a published review found that maintenance and repair workers in buildings with asbestos-containing materials had average annual exposure levels from a median of 0.002 to 0.02 fibres per ml at the 90th percentile, and building occupants from 0.00003 to 0.0005 fibres per ml
  • In a review of 198 buildings with asbestos-containing materials not involved in litigation, the overall mean airborne concentration was 0.00027 fibres per ml
  • A review by Berry and co-workers of six studies estimated that the relative risk due to asbestos was 1.8 times greater in non-smokers than in smokers. The author considered this not critical for projecting risk
  • Two analyses covering five cohorts indicated that years employed at the lowest intensity levels showed no effect on lung cancer risk
  • In the Libby, Montana vermiculite miners exposed to tremolite, the slope of approximately 0.013 was similar to that for crocidolite mining and much higher than that for chrysotile miners
  • In a case-control study of 29 lung cancer cases among asbestos-cement workers, adenocarcinomas made up 31% of cancers among exposed subjects and 15% among non-exposed subjects
• The authors' conclusion: The author concluded that the shallow chrysotile slope is more appropriate for building exposures. The author also argued that if lung fibrosis is a necessary precursor of asbestos-induced lung cancer, a practical threshold is likely, because detectable fibrosis is not expected from environmental exposure levels. On cell type, the author stated that further confirmatory findings are needed
• Limitations the authors state:
  • The finding of no effect at the lowest exposure intensities is also consistent with risks that went undetected because of small numbers and insufficient power. The author said the issue is not resolved
  • Whether the relative risk from asbestos differs between smokers and non-smokers has yet to be resolved
  • The assumed background lung cancer risks are likely too high, which would overestimate the asbestos-related risk estimates
  • Conclusions about lung cancer cell type require further confirmatory findings

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Chrysotile, Asbestos Exposure, Friction Products, Asbestos-Cement, Fibrosis, Environmental Exposure, Relative Risk.

Related studies

• Mesotheliomas and chrysotile — P. Elmes (1994)
• Malignant peritoneal mesothelioma in a 17-year-old boy with evidence of previous exposure to chrysotile and tremolite asbestos — A. Andrion, S. Bosia, et al. (1994)
• Deposition and clearance of chrysotile asbestos — A. Churg (1994)
• Increased lung cancer mortality among chrysotile asbestos textile workers is more strongly associated with exposure to long thin fibres — D. Loomis, J.M. Dement, et al. (2012)
• The human evidence: parenchymal and pleural changes — G. Hillerdal (1994)
• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.