Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia

Our plain-English summary of Comparison of measures of exposure to asbestos in former crocidolite workers from Wittenoom Gorge, W. Australia, by N.H. de Klerk, A.W. Musk, V. Williams, et al (American Journal of Industrial Medicine, 1996).

The study

• Authors: N.H. de Klerk, A.W. Musk, V. Williams, P.R. Filion, D. Whitaker, K.B. Shilkin
• Journal: American Journal of Industrial Medicine
• Published: 1996;30(5):579-87
• Cited by: 48 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Determinations of exposure-response relationships between crocidolite and the major asbestos-related diseases in the Wittenoom cohort have previously depended on the validity of estimates of airborne exposure to asbestos. This work aims to validate the airborne exposure measurements by obtaining measurements of the concentrations of uncoated crocidolite fibers and asbestos bodies retained in the lungs of individual workers, and to estimate the half-life of crocidolite fibers in the lungs. Samples of lung tissue, excluding tumor, of all former Wittenoom workers known to have died in Western Australia (WA) were sought from teaching hospitals, pathology departments, and the Coroner's pathologist. The lung specimens were processed using Pooley's method with TEM for counts of fibers of all types and using Smith and Naylor's method with conventional light microscopy for asbestos bodies (AB). Multiple linear regression was utilized to examine the associations between crocidolite concentrations in the lung and duration of employment at Wittenoom, time since last employed at Wittenoom, nature of job, estimated average fiber concentration at the worksite, and estimated cumulative crocidolite exposure (CCE) in fiber-years/ml for each subject. Lung tissue from 90 cases was processed and there was good agreement between counts of crocidolite fibers, asbestos bodies, and CCE. Correlations were 0.77 for AB and fibers, 0.54 for AB and CCE, and 0.58 for CCE and fibers, after log transformation. The half-life of crocidolite fibers in the lung was estimated at 92 months (95% CI 55-277 months). Previous estimates of airborne exposure to Wittenoom crocidolite have been reasonably reliable. The relatively simple technique of light microscopy for counting ABs in lung tissue also provides a useful and reliable indication of the level of past occupational exposure to crocidolite in subjects whose exposure has been only to crocidolite. The half-life of crocidolite fibers in the lungs of former Wittenoom workers is about 7-8 years.

In plain English

This study examined lung tissue from 90 former miners and millers of crocidolite asbestos at Wittenoom Gorge, Western Australia, who had died. Of these, 27 had malignant mesothelioma and 20 had lung cancer. The authors wanted to check whether earlier estimates of how much airborne asbestos these workers had breathed were reliable. One scientist, without knowing the workers' exposure histories, counted uncoated crocidolite fibers with an electron microscope and asbestos bodies with a light microscope. On a logarithmic scale, asbestos body counts and fiber counts correlated at 0.77. Estimated cumulative airborne exposure correlated at 0.58 with fiber counts and at 0.54 with asbestos body counts. The authors compared workers with different lengths of time since their last exposure. From this they estimated a clearance rate of about 9% per year, which implied a half-life of crocidolite fibers in the lung of about 92 months (95% CI 55 to 277 months). Asbestos body counts had no significant association with time since last exposure. The authors concluded that earlier airborne exposure estimates were reasonably reliable. They noted that agreement between the measures was far from perfect.

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: Study of post-mortem lung tissue (lung fiber and asbestos body counts) from deceased members of a worker cohort, compared with estimated airborne exposure using multiple linear regression
• Who was studied: 90 former Wittenoom crocidolite miners and millers who had died in Western Australia, including 27 with malignant mesothelioma and 20 with lung cancer. Seventy (78%) had some known asbestos-related disease. Counts were done from 1993 to 1994.
• Exposure: Crocidolite at the Wittenoom mine and mill. Estimated cumulative airborne exposure ranged from 0.03 to 497.4 fibers/ml years.
• Main results:
  • Crocidolite fiber counts ranged from less than one to nearly 10,000 per microgram of dry lung tissue.
  • Asbestos body counts and crocidolite fiber counts in the lungs had a Pearson correlation of 0.77, with both on a logarithmic scale.
  • Estimated airborne exposure correlated at 0.54 with asbestos body counts and at 0.58 with uncoated fiber counts.
  • Time since last exposure had a significant effect on lung fiber levels across workers. From this the authors estimated a clearance rate of about 9% per year and a half-life of about 92 months (95% CI 55-277 months).
  • Asbestos body counts were related to intensity and duration of exposure. Their association with time since last exposure was small and not statistically significant (p greater than 0.20).
  • Counts of long fibers (over 4 microns) and short fibers (4 microns or less) were closely correlated (Pearson correlation 0.95).
  • Among the 60 subjects with smoking information, those who were current smokers in 1979 had proportionately fewer asbestos bodies than non- or ex-smokers (the article gives 16%, 95% CI 6%-47%).
• The authors' conclusion: The authors concluded that previous estimates of airborne exposure to Wittenoom crocidolite were reasonably reliable. They also concluded that light-microscope counting of asbestos bodies gives a useful indication of past exposure in people exposed only to crocidolite, and that the half-life of crocidolite fibers in these workers' lungs is about 7-8 years.
• Limitations the authors state:
  • The authors stated that agreement between the different exposure measures was far from perfect, and that this measurement error could bias estimates.
  • The authors stated that it is not known which measure, if any, best estimates actual dose.
  • The authors stated that the finding of fewer asbestos bodies in current smokers needs further investigation.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Wittenoom, Western Australia

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Crocidolite, Wittenoom, Asbestos Bodies, Pathology, Fiber Year, Occupational Exposure.

Related studies

• Malignant pleural and peritoneal mesotheliomas in former miners and millers of crocidolite at Wittenoom, Western Australia — G. Berry, N.H. de Klerk, et al. (2004)
• Malignant mesotheliomas in former miners and millers of crocidolite at Wittenoom (Western Australia) after more than 50 years follow-up — G. Berry, A. Reid, et al. (2012)
• The natural history of asbestosis in former crocidolite workers of Wittenoom Gorge — W. Cookson, N. De Klerk, et al. (1986)
• Morphology of bronchogenic carcinoma in workers formerly exposed to crocidolite at Wittenoom Gorge in Western Australia — J.E. Baker, D.C. Reutens, et al. (1986)
• Migration and work in postwar Australia: mortality profile comparisons between Australian and Italian workers exposed to blue asbestos at Wittenoom — A. Reid, E. Merler, et al. (2018)
• Retinol supplementation and mesothelioma incidence in workers earlier exposed to blue asbestos (Crocidolite) at Wittenoom, Western Australia — H.S. Alfonso, A. Reid, et al. (2010)

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