Magnetic lung measurements of relation to occupational exposure in asbestos miners and millers of Quebec

Our plain-English summary of Magnetic lung measurements of relation to occupational exposure in asbestos miners and millers of Quebec, by D. Cohen, T.S. Crowther, G.W. Gibbs, et al (Environmental Research, 1981).

The study

• Authors: D. Cohen, T.S. Crowther, G.W. Gibbs, M.R. Becklake
• Journal: Environmental Research
• Published: 1981;26(2):535-50
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fe,O, particles (ferrimagnetic) are usually attached to asbestos fibers (nonferrimagnetic) in the chrysotile asbestos mining and milling industries; therefore, a magnetic measurement of Fe,O, in the lungs of workers in these industries could help determine the amount of asbestos which has been inhaled and retained in their lungs. As a first assessment of this method, magnetic measurements were made of Fe,O, in the lungs of 115 miners and millers in Quebec. These measurements at an industrial site were found to be feasible and practical; however, the amount of Fe,O, seen in the lungs of those with welding exposure was large enough to mask the Fe3O4 contributed by asbestos, and this subgroup was considered separately. For the remainder (nonwelders), the amount of Fe,O, was plotted against a total dust exposure index (asbestos and other dust) estimated for each worker. Although the correlation between these quantities was not high, it was statistically significant at the 1% level. Because retained asbestos is likely to increase with increasing exposure to total dust, this correlation suggests that a magnetic lung measurement of a chrysotile miner or a miller does reflect, to some extent, the amount of asbestos in his lung. There was considerable scatter in the data, partly due to individual variations in deposition and clearance, to which this method is sensitive. When the data of only the nonsmokers were plotted, the amount of Fe,O, was greater than for the total group of nonwelders. This is consistent with previous findings that less dust is deeply deposited in the lungs of smokers, due to constriction of small airways.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This study tested whether measuring magnetic iron oxide dust (Fe3O4, magnetite) in the lungs could indicate how much asbestos chrysotile miners and millers in Quebec had retained. The dust is usually attached to chrysotile fibers in mining and milling. The authors measured 115 men whose latest chest films showed no radiologic abnormality. On-site measurement proved feasible. Because men with large welding exposure had enough magnetite to mask the asbestos-related amount, all 62 men with any welding-fume exposure were analyzed separately. Average lung magnetite was 7.8 mg for welders and 1.3 mg for nonwelders. Among 51 nonwelders, lung magnetite correlated with each man's estimated total dust exposure index, which covered asbestos and other dust (rank correlation 0.50, significant at the 1% level), though with considerable scatter. Among 18 nonwelders who did not smoke, the rank correlation was 0.62. The authors concluded that the measurement reflects, to some extent, the amount of asbestos in the lung. They noted that the dust index covered exposure only up to 1967, and that magnetite may separate from fibers in the lung and be cleared differently.

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 measurement study: a first assessment of a magnetic lung measurement method, compared against estimated dust exposure indices
• Who was studied: 115 men working as chrysotile asbestos miners and millers in Quebec, aged 26 to 50, smokers and nonsmokers. All had been selected for a lung function study and had a most recent chest film read as 0/0 (ILO/UC). They were measured in 1974 at a clinic in Thetford Mines. The 62 men with any welding-fume exposure were analyzed separately from 53 nonwelders, of whom 51 had dust indices available. Five men were excluded because of magnetic contamination that could not be removed.
• Exposure: Dust in chrysotile mines and mills, which carries attached magnetite. Exposure was estimated as a total dust exposure index: airborne particle concentration (fibers and other particles, measured with the midget impinger) multiplied by years worked, summed over each job up to 1967, in millions of particles per cubic foot times years. Welding fume (including torch cutting) was measured in years of exposure.
• Main results:
  • Magnetic lung measurements at the industrial site were feasible and practical.
  • Workers with large welding exposure had enough lung magnetite to mask the magnetite from asbestos. For this reason, all 62 men with any welding-fume exposure were considered separately.
  • Average lung magnetite was 1.3 mg in nonwelders and 7.8 mg in welders.
  • Among 51 nonwelders, lung magnetite correlated with the total dust exposure index: Spearman rank correlation 0.50 and least-squares correlation 0.45, both significant at the 1% level.
  • Among the 18 nonwelders who were nonsmokers, the Spearman rank correlation was 0.62 and the least-squares correlation was 0.80, both significant at the 1% level. The authors took the steeper slopes as suggesting nonsmokers have more dust in their lungs than smokers.
  • The data showed considerable scatter, which the authors attributed partly to individual differences in dust deposition and clearance.
  • Lung magnetite correlated with welding exposure: rank correlation 0.37 for the 45 men with more than 0.1 year of welding, and 0.55 for the entire group of 115 men.
  • Neither auxiliary magnetic quantity (apparent viscosity, relaxation rate) showed a statistically significant correlation with the total dust exposure index.
• The authors' conclusion: The authors concluded that the correlation suggests a magnetic lung measurement of a chrysotile miner or miller reflects, to some extent, the amount of asbestos in his lung.
• Limitations the authors state:
  • The dust index covered exposure only up to 1967, while the magnetic measurement also reflects more recently acquired dust. This may have weakened the correlation.
  • Magnetite probably detaches from fibers in the lung and may be cleared differently, so the magnetite-to-asbestos ratio may change over time. This adds uncertainty to the method.
  • Comparing magnetic readings with asbestos recovered from autopsied lungs, or directly with lung abnormality, was not available, so only an indirect comparison with the dust index was made.
  • Measurements of field distribution were crude, and subject positioning needs improvement.
  • Some welder subgroups were too small for useful correlations.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Chrysotile, Deposition.

Related studies

• Ferromagnetic contamination in the lungs and other organs of the human body — D. Cohen (1973)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)
• Clinical measurement in Quebec chrysotile miners: use for future protection of workers — M.R. Becklake (1979)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)
• Mortality in the chrysotile asbestos mines and mills of Quebec — J.C. McDonald, A.D. McDonald, et al. (1971)

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