Risk Of Asbestosis In Crocidolite And Amosite Mines In South Africa

Our plain-English summary of Risk Of Asbestosis In Crocidolite And Amosite Mines In South Africa, by L.M. Irwig, R.S.J. Du Toit, G.K. Sluis-Cremer, et al (1979).

The study

• Authors: L.M. Irwig, R.S.J. Du Toit, G.K. Sluis-Cremer, A. Solomon, R. Glyn Thomas, P.P.H. Hamel, I. Webster, T. Hastie
• Published: Annals Of The New York Academy Of Sciences 330:34-52, December 14 (1979)
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library, J-M no. 001032. The article is still under copyright, so we describe it here rather than post it.

In plain English

The authors studied chest x-rays of white and mixed-race men working in crocidolite and amosite mines and mills in South Africa. Three experienced readers read each x-ray, and an abnormality counted only if at least two reported it. Of 1801 eligible men, 1692 were analyzed. Pleural abnormality (thickening, costophrenic angle obliteration or calcification) was found in 129 men (7.6%). Small irregular opacities graded at profusion 1/0 or greater on the x-ray scale, which the authors called parenchymal abnormality, were found in 123 men (7.3%). Any abnormality rose from 4.0% in men exposed for 1 year or less to 47.9% in men exposed for more than 15 years. Abnormality was also associated with age. Average fiber concentration did not predict pleural abnormality, but short-fiber concentration did predict parenchymal abnormality. Among crocidolite workers, mixed-race men had more pleural abnormality than white men. The authors concluded that parenchymal abnormality could be largely prevented by reducing exposure to fibers visible under the light microscope, but that this may not hold for pleural abnormality. They had no unexposed comparison group.

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: Cross-sectional chest x-ray survey of current mine and mill workers. Each x-ray was read independently by three readers using the ILO U/C classification, and an abnormality was counted if at least two readers reported it.
• Who was studied: Men employed in crocidolite and amosite mines and mills in South Africa. Of 1801 men who met the study criteria, 1692 (94%) were analyzed: 882 white and 262 mixed-race men who worked with crocidolite, and 548 white men who worked with amosite. Many had also worked in other mines, particularly gold mines. The years of the study are not given in the available text.
• Exposure: Work in crocidolite and amosite mines and mills. Exposure was measured as years of asbestos exposure (grouped from 1 year or less to more than 15 years) and as average short-fiber and long-fiber concentrations in fibers per milliliter.
• Main results:
  • Among all 1692 workers, pleural thickening was found in 76 men (4.5%), costophrenic angle obliteration in 54 (3.2%) and pleural calcification in 29 (1.7%).
  • Pleural abnormality (at least one of the three pleural findings) was found in 129 workers (7.6%). It rose from 2.5% in men with 1 year or less of exposure to 33.6% in men with more than 15 years.
  • Small irregular opacities of profusion 1/0 or greater (parenchymal abnormality) occurred in 123 men (7.3%). The prevalence rose from 2.3% in men with 1 year or less of exposure to 26.7% in men with more than 15 years. Small rounded opacities were found in only 12 men, and large opacities in only two.
  • Any abnormality, pleural or parenchymal, rose from 4.0% in men exposed for 1 year or less to 47.9% in men exposed for more than 15 years.
  • Abnormality was generally also significantly associated with age within each exposure-duration group. Adjusting for age only slightly reduced the slope of the exposure-response relationship.
  • Average short-fiber concentration did not predict pleural abnormality, and average long-fiber concentration gave a similar result. In the fiber-concentration analyses, 229 men with unknown fiber concentrations were left out.
  • In crocidolite mines and mills, mixed-race workers had a higher prevalence of pleural abnormality than white workers in each exposure-duration group.
  • Among white men exposed for more than 7 years, amosite workers had a higher prevalence of pleural abnormality than crocidolite workers. This difference was significant only at the 10% level.
  • Average short-fiber concentration did predict parenchymal abnormality, and long-fiber concentration had a similar but less significant effect. Race and asbestos type did not predict parenchymal abnormality.
• The authors' conclusion: The authors concluded that parenchymal abnormality in South African asbestos mine workers could be largely prevented by reducing exposure to fibers visible under the light microscope, but that this may not be the case for pleural abnormality.
• Limitations the authors state:
  • The study had no comparison group of people not exposed to asbestos. Workers with 1 year or less of exposure were used as the baseline for age adjustment.
  • Submicroscopic fibers, which the authors suggested might explain pleural abnormality, were not measured.

Topics

Medical terms in this study, explained in our Lexicon: Crocidolite, Amosite, Chest X-Ray, Costophrenic angle.

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