Increased lung cancer mortality among chrysotile asbestos textile workers is more strongly associated with exposure to long thin fibres

Our plain-English summary of Increased lung cancer mortality among chrysotile asbestos textile workers is more strongly associated with exposure to long thin fibres, by D. Loomis, J.M. Dement, L. Elliott, et al (Occupational and Environmental Medicine, 2012).

The study

• Authors: D. Loomis, J.M. Dement, L. Elliott, D. Richardson, E.D. Kuempel, L. Stayner
• Journal: Occupational and Environmental Medicine
• Published: 2012;69(8):564-8
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Animal data and physical models suggest that the carcinogenicity of asbestos fibres is related to their size and shape.

Objectives: To investigate the influence of fibre length and diameter on lung cancer risk in workers at asbestos textile mills in North Carolina and South Carolina, USA.

Methods: Men and women (n=6136) who worked ≥30 days in production and were employed between 1940 and 1973 were enumerated and followed for vital status through 2003. A matrix of fibre size-specific exposure estimates was constructed using determinations of fibre numbers and dimensions through analysis of 160 historical dust samples by transmission electron microscopy. Associations of lung cancer mortality with metrics of fibre exposure were estimated by Poisson regression with adjustment for age, sex, race and calendar year.

Results: Exposure to fibres throughout the range of length and diameter was significantly associated with increased risk of lung cancer. Models for fibres >5 μm long and <0.25 μm in diameter provided the best fit to the data, while fibres 5-10 μm long and <0.25 μm in diameter were associated most strongly with lung cancer mortality (log rate about 4% per IQR, p<0.001). When indicators of mean fibre length and diameter were modelled simultaneously, lung cancer risk increased as fibre length increased and diameter decreased.

Conclusions: The findings support the hypothesis that the occurrence of lung cancer is associated most strongly with exposure to long thin asbestos fibres. The relationship of cancer risk and fibre dimensions should be examined in cohorts exposed to other types of fibres.

In plain English

This study pooled data on 3717 men and 2419 women who worked at least 30 days in production at four asbestos textile mills in North Carolina and South Carolina, USA. The mills used chrysotile asbestos, apart from limited amosite and crocidolite in specific operations. Workers were followed until 2001 or 2003. Fibre lengths and diameters were estimated from 160 historical dust samples examined by electron microscope. There were 361 deaths with any mention of lung cancer. Cumulative exposure to fibres of every size category was significantly associated with lung cancer death. The strongest association was for fibres under 0.25 micrometres wide and 5 to 10 micrometres long: the log death rate rose by 0.041 per interquartile range (IQR) of exposure. When average fibre length and diameter were analysed together, longer and thinner fibres went with higher risk. The authors noted that the dust samples were few and all came from 1964 to 1971, and that exposures to different sizes were highly correlated. They concluded that lung cancer was associated with fibres of all sizes but most strongly with long thin fibres.

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: Retrospective cohort study: a pooled analysis of two existing asbestos textile worker cohorts, using Poisson regression of lung cancer mortality on exposure estimates specific to fibre size
• Who was studied: 3717 men and 2419 women who worked at least 30 days in textile production departments at four asbestos textile mills in North Carolina and South Carolina, USA. They were employed 1950 to 1973 in North Carolina or 1940 to 1965 in South Carolina. Vital status was followed through 31 December 2001 (South Carolina) and 31 December 2003 (North Carolina).
• Exposure: Chrysotile asbestos in textile production. There was limited amosite in a small insulation operation at one North Carolina plant (1963 to 1976) and limited crocidolite yarn at the South Carolina plant (1950s to 1975). Fibre size-specific cumulative exposure (fibre-years per millilitre) was estimated by transmission electron microscopy of 160 historical dust samples collected 1964 to 1971, in categories of length and diameter.
• Main results:
  • Follow-up covered 218 631 person-years at risk, with 3356 deaths from all causes and 361 deaths with a mention of lung cancer.
  • Cumulative exposure to total fibres counted by electron microscopy, and to fibres in every length and diameter category, was significantly associated with lung cancer mortality.
  • For total fibres counted by electron microscopy, the log lung cancer rate rose by 0.039 per IQR (95% CI 0.020 to 0.057). For fibres counted by the standard phase contrast microscopy method, it rose by 0.032 per IQR (95% CI 0.014 to 0.049).
  • The largest associations were for fibres less than 0.25 micrometres in diameter. Fibres 5 to 10 micrometres long in this group had a coefficient of 0.041 per IQR (p less than 0.001). Other lengths in that diameter range had coefficients between 0.03 and 0.04 per IQR, including very short fibres 1.5 micrometres long or less.
  • Exposures in all size categories were strongly intercorrelated (Pearson correlation coefficients 0.75 to 0.98). A model with all 21 size categories at once fitted better, but its individual estimates were unstable.
  • When indicators of mean fibre length and mean fibre diameter were modelled together, lung cancer mortality rose as mean fibre length increased and mean diameter decreased. The diameter coefficient became negative in the joint model.
• The authors' conclusion: The authors concluded that lung cancer mortality was associated with exposure to fibres of all sizes but most strongly with long thin fibres. They suggested this tendency may extend to other fibre types, including amosite, crocidolite and engineered nanofibres, which should be examined in other cohorts. They also concluded that the association with fibres under 0.25 micrometres in diameter supports using electron microscopy and other improved methods to assess exposure.
• Limitations the authors state:
  • Far fewer samples could be analysed by electron microscopy than the over 9000 standard air measurements available. The authors expected the resulting statistical noise to dampen rather than enhance associations by fibre size.
  • The electron microscopy samples came only from 1964 to 1971, a small part of the exposure period.
  • Workers were exposed to fibres across the whole range of sizes, and the resulting correlations made it hard to identify size ranges independently associated with lung cancer.
  • The authors could not determine whether the apparent association for thick fibres (over 3 micrometres in diameter) was an artifact of their correlation with other long fibres.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Chrysotile, Transmission Electron Microscopy (TEM).

Related studies

• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)
• Lung cancer mortality among asbestos textile workers: a review and update — J.M. Dement, D.P. Brown (1994)
• Long fibre asbestos in a chrysotile textile worker — A. Churg, R.A. Harley (1984)
• Lung cancer mortality and fibre exposures among North Carolina asbestos textile workers — D. Loomis, J.M. Dement, et al. (2009)
• Asbestos fibre dimensions and lung cancer mortality among workers exposed to chrysotile — D. Loomis, J. Dement, et al. (2010)

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