Radiographic abnormalities and mortality in subjects with exposure to crocidolite

Our plain-English summary of Radiographic abnormalities and mortality in subjects with exposure to crocidolite, by N.H. de Klerk, A.W. Musk, W.O. Cookson, et al (British Journal of Industrial Medicine, 1993).

The study

• Authors: N.H. de Klerk, A.W. Musk, W.O. Cookson, J.J. Glancy, M.S. Hobbs
• Journal: British Journal of Industrial Medicine
• Published: 1993;50(10):902-6
• Cited by: 12 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Plain chest radiographs from a one in six random sample of the workforce of the asbestos industry at Wittenoom, Western Australia between 1943 and 1966 have been classified for degree of profusion and pleural thickening by two independent observers according to the 1980 UICC-ILO Classification of Radiographs for the pneumoconioses to clarify the effect of degree of radiological abnormality on survival. A total of 1106 subjects were selected. Each subject's age, cumulative exposure to crocidolite, and time since first exposure were determined from employment records, the results of a survey of airborne concentrations of fibres > 5 mu in length conducted in 1966, and an exposure rating by an industrial hygienist and an ex-manager of the mine and mill at Wittenoom. By the end of 1986 193 subjects had died. Conditional logistic regression was used to model the relative risk of death in five separate case-control analyses in which the outcomes were deaths from: (1) all causes, (2) malignant mesothelioma, (3) lung cancer, (4) asbestosis, and (5) other causes excluding cancer and asbestosis. Up to 20 controls per case were randomly chosen from all men of the same age who were not known to have died before the date of death of the index case. After adjustment for exposure and time since first exposure, there were significant and independent effects of radiographic profusion and pleural thickening on all cause mortality. The effect of profusion was largely a result of the effect on mortality from malignant mesothelioma and asbestosis but not lung cancer. The effect of pleural thickening was greatest on mortality from other causes, mainly ischaemic heart disease. This study has shown that degree of radiographic abnormality has an independent effect on mortality from malignant mesothelioma, asbestosis, and all causes even after allowing for the effects of age, degree of exposure, and time since first exposure.

In plain English

This study tested whether chest X-ray abnormalities predicted death among crocidolite workers at Wittenoom, Western Australia, in 1943-1966. Two observers graded, by the 1980 ILO classification, radiographs found for 921 of 1106 men, a random one in six sample of male workers. By the end of 1986, 193 had died, including 12 from mesothelioma, 19 from lung cancer and nine from asbestosis. Adjusted for cumulative exposure and time since first exposure, X-rays two to five years before death were linked to all-cause death: relative risk 1.3 (95% CI 1.1-1.5) per minor ILO category of profusion, and 1.3 (1.1-1.5) per 25% increase in pleural thickening. With X-rays from the same period, profusion per minor ILO category was linked to death from malignant mesothelioma (1.9, 1.3-2.9) and asbestosis (1.6, 1.1-2.3). Neither exposure nor X-ray findings significantly affected lung cancer deaths, which the authors said the study had little power to detect. Pleural thickening was linked to deaths from other causes, mainly ischaemic heart disease, possibly by chance, the authors suggested. The authors concluded that profusion had an independent effect on mortality from malignant mesothelioma and asbestosis.

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: Five case-control analyses (conditional logistic regression) nested within a random sample of a worker cohort, with up to 20 age-matched controls per death
• Who was studied: 1106 men, a one in six random sample of all male workers in the crocidolite industry at Wittenoom Gorge, Western Australia, employed 1943 to 1966, including men who had sought compensation. Radiographs were found for 921 men. Of these, 740 had films at or after starting work and 467 had films more than six months after starting. Deaths were followed to the end of 1986.
• Exposure: Cumulative exposure to crocidolite in fibres/ml-years. It was estimated from work histories and a 1966 survey of airborne fibres longer than 5 micrometres in various workplaces.
• Main results:
  • Of 193 deaths among the 1106 men, 12 were from mesothelioma, 19 from lung cancer, 24 from other cancers and nine from asbestosis
  • Death from all causes, X-rays two to five years earlier, in a model that also included log cumulative exposure and log time from first exposure: relative risk 1.3 (95% CI 1.1-1.5), p 0.006, per minor ILO category of profusion
  • Death from all causes: relative risk 1.3 (95% CI 1.1-1.5), p 0.002, per 25% increase in pleural thickening (as labelled in the table)
  • Death from malignant mesothelioma, X-rays two to five years earlier: relative risk 1.9 (95% CI 1.3-2.9), p 0.002, for profusion (per minor ILO category). For log cumulative exposure it was 2.5 (95% CI 1.6-4.0), p less than 0.001.
  • Death from asbestosis, X-rays two to five years earlier: relative risk 1.6 (95% CI 1.1-2.3), p 0.02, for profusion (per minor ILO category). For log cumulative exposure it was 4.0 (95% CI 1.8-8.8), p less than 0.001.
  • Lung cancer deaths: no significant effect of exposure or of X-ray abnormality. For log cumulative exposure the relative risk was 1.2 (95% CI 0.9-1.6), p 0.12.
  • Pleural thickening was associated with deaths from other causes (excluding cancer and asbestosis): relative risk 1.5 (95% CI 1.3-1.8), p less than 0.001. These deaths were mainly from ischaemic heart disease.
  • For all-cause deaths, the effect of profusion weakened the further back the X-ray was taken. It was not significant for films more than 20 years earlier. For pleural thickening, the effect was not significant for films more than 30 years earlier.
  • Among the 467 men with later films, age at first exposure, time since first exposure and log cumulative exposure each significantly predicted profusion and pleural thickening on the final X-ray
• The authors' conclusion: The authors concluded that the degree of profusion of small irregular opacities on chest X-ray has an independent effect on mortality from malignant mesothelioma and asbestosis, even after allowing for age, degree of exposure and time since exposure.
• Limitations the authors state:
  • There were few lung cancer deaths, so the study had little power to detect an effect of exposure or X-ray abnormality on lung cancer
  • The link between pleural thickening and deaths from other causes may be a chance association
  • Deaths that were not detected probably explain the falling mortality from other causes with time since first exposure

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, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Crocidolite, Chest X-Ray, Wittenoom, Pleural Thickening, UICC, ILO Classification, Cumulative Exposure, Relative Risk.

Related studies

• The radiographic pleural abnormalities in asbestos exposure: relationship to physiologic abnormalities — R.N. Jones, T. McLoud, et al. (1988)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)
• The mental health of asbestos-exposed subjects with pleural abnormalities — P. Franklin, M. Robinson, et al. (2015)
• Prevalence of radiographic asbestosis in crocidolite miners and millers at Wittenoom, Western Australia — W.O. Cookson, N.H. De Klerk, et al. (1986)
• Environmental exposure to crocidolite and mesothelioma: exposure-response relationships — J. Hansen, N.H. de Klerk, et al. (1998)
• Natural history of pleural thickening after exposure to crocidolite — N.H. de Klerk, W.O. Cookson, et al. (1989)

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