Asbestos fibre dimensions and lung cancer mortality among workers exposed to chrysotile

Our plain-English summary of Asbestos fibre dimensions and lung cancer mortality among workers exposed to chrysotile, by D. Loomis, J. Dement, D. Richardson, et al (Occupational and Environmental Medicine, 2010).

The study

• Authors: D. Loomis, J. Dement, D. Richardson, S. Wolf
• Journal: Occupational and Environmental Medicine
• Published: 2010;67(9):580-4
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To estimate exposures to asbestos fibres of specific sizes among asbestos textile manufacturing workers exposed to chrysotile using data from transmission electron microscopy (TEM) and to evaluate the extent to which the risk of lung cancer varies with fibre length and diameter.

Methods: 3803 workers employed for at least 1 day between 1 January 1950 and 31 December 1973 in any of three plants in North Carolina, USA that produced asbestos textile products and followed for vital status through 31 December 2003 were included. Historical exposures to asbestos fibres were estimated from work histories and 3578 industrial hygiene measurements taken in 1935-1986. Exposure-response relationships for lung cancer were examined within the cohort using Poisson regression.

Results: Indicators of fibre length and diameter obtained by TEM were positively and significantly associated with increasing risk of lung cancer. Exposures to longer and thinner fibres tended to be most strongly associated with lung cancer, and models for these fibres fit the data best. Simultaneously modelling indicators of cumulative mean fibre length and diameter yielded a positive coefficient for fibre length and a negative coefficient for fibre diameter.

Conclusions: The results support the hypothesis that the risk of lung cancer among workers exposed to chrysotile asbestos increases with exposure to longer fibres. More research is needed to improve the characterisation of exposures by fibre size and number and to analyse the associated risks in a variety of industries and populations.

In plain English

This study looked at 3,803 workers employed for at least one day between 1950 and 1973 at three asbestos textile plants in North Carolina, USA. Records indicate that only chrysotile was used, except for limited amosite in a small insulation operation at one plant. There were 181 lung cancer deaths. The authors combined historical air measurements with electron microscope (TEM) analysis of archived dust samples from 1964 to 1971. From these they estimated each worker's cumulative exposure to fibres of different lengths and diameters, then related these estimates to lung cancer death rates. Models for longer fibres generally fit the data best and showed the strongest associations, with the best fit for fibres 20 to 40 micrometres long. When average fibre length and diameter were modelled together, length had a positive coefficient and diameter a negative one, consistent with higher risk from longer, thinner fibres. The authors concluded that the results support the hypothesis that lung cancer risk rises with exposure to longer fibres. They could not control for smoking, and the 8 mesothelioma deaths were too few to analyse.

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: Cohort mortality study with internal exposure-response analysis (Poisson regression)
• Who was studied: 3803 workers (2419 men, 1384 women) employed at least 1 day between 1 January 1950 and 31 December 1973 in any of three asbestos textile plants in North Carolina, USA; vital status followed through 31 December 2003
• Exposure: Chrysotile asbestos in textile manufacturing, except a small insulation operation in one plant where limited amounts of amosite were used between 1963 and 1976. Cumulative exposure was estimated in fibre-years/ml by fibre length and diameter categories using TEM analysis of archived dust samples combined with phase-contrast microscopy (PCM) estimates.
• Main results:
  • The analysis covered 124 029 person-years of follow-up, with 1681 total deaths and 181 deaths from lung cancer.
  • Among the 3803 workers, mean cumulative fibre exposure was 989.4 f-y/ml when estimated by TEM, compared with 59.2 f-y/ml by PCM (both lagged 10 years).
  • Cumulative exposure to all TEM fibres was significantly associated with lung cancer, but this model fit less well than the PCM-based model (LR 9.6, p 0.002 for PCM vs LR 7.6, p 0.006 for total TEM fibres).
  • For all TEM and PCM exposure indicators, lung cancer risk increased by about 3% for an increase in exposure equal to 1 interquartile range.
  • When length was considered alone, the best model fit and the strongest associations with lung cancer were for fibres 20 to 40 micrometres long.
  • With length and diameter combined, several categories of shorter, larger-diameter fibres were not significantly associated with lung cancer.
  • With length and diameter combined, stronger, statistically significant associations were seen for longer and thinner fibres, particularly those over 20 micrometres long and 0.25 to under 1.0 micrometres in diameter.
  • When mean fibre length and mean fibre diameter were modelled together, the length coefficient stayed positive and the diameter coefficient became negative.
  • Short, thin fibres were the majority counted by TEM and were also associated with lung cancer. The authors stated they could not yet tell whether this was spurious, due to correlations among size categories.
• The authors' conclusion: The authors concluded that the results support the hypothesis that lung cancer risk among workers exposed to chrysotile asbestos increases with exposure to longer fibres. They added that the results provide some evidence the effects are most pronounced for long fibres 0.25 to 1.0 micrometres in diameter, while uncertainty remains about the relative carcinogenicity of specific fibre sizes.
• Limitations the authors state:
  • There were insufficient data to control for smoking.
  • For about a quarter of the cohort, occupational histories gave only the plant and department, not the job title.
  • A medical surveillance program that ended exposures of at-risk workers may have weakened the observed association.
  • Dust samples for TEM were available only for 1964 to 1971. Fibre-size distributions were assumed stable over the whole period, with no data to test this.
  • Random measurement error from the small number of samples and the lack of fine detail in the exposure assessment may have reduced power and weakened associations.
  • Strong correlations among fibre-size measures prevented modelling several fibre-size indicators at once.
  • The 8 mesothelioma deaths were too few to analyse.

Topics

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

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

Related studies

• 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)
• An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers — L. Stayner, E. Kuempel, et al. (2008)
• Lung cancer mortality in North Carolina and South Carolina chrysotile asbestos textile workers — L. Elliott, D. Loomis, et al. (2012)
• Lung cancer mortality and fibre exposures among North Carolina asbestos textile workers — D. Loomis, J.M. Dement, et al. (2009)
• Quantitative relationships of exposure to chrysotile asbestos and mesothelioma mortality — D. Loomis, D.B. Richardson, et al. (2019)
• Follow-up study of chrysotile asbestos textile workers: cohort mortality and case-control analyses — J.M. Dement, D.P. Brown, et al. (1994)

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