Retention patterns of asbestos fibres in lung tissue among asbestos cement workers

Our plain-English summary of Retention patterns of asbestos fibres in lung tissue among asbestos cement workers, by M. Albin, F.D. Pooley, U. Strömberg, et al (Occupational and Environmental Medicine, 1994).

The study

• Authors: M. Albin, F.D. Pooley, U. Strömberg, R. Attewell, R. Mitha, L. Johansson, H. Welinder
• Journal: Occupational and Environmental Medicine
• Published: 1994;51(3):205-11
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Retention patterns in lung tissue (determined by transmission electron microscopy and energy dispersive spectrometry) of chrysotile, tremolite, and crocidolite fibres were analysed in 69 dead asbestos cement workers and 96 referents. There was an accumulation of tremolite with time of employment. Among workers who died within three years of the end of exposure, the 13 with high tremolite concentrations had a significantly longer duration of exposure than seven in a low to intermediate category (medians 32 v 20 years; p = 0.018, one sided). Crocidolite showed similar patterns of accumulation. In workers who died more than three years after the end of exposure, there were no correlations between concentrations of amphibole fibres and time between the end of exposure and death. Chrysotile concentrations among workers who died shortly after the end of exposure were higher than among the referents (median difference in concentrations 13 million fibres (f)/g dry weight; p = 0.033, one sided). No quantitative differences in exposure (duration or intensity) could be shown between workers with high and low to intermediate concentrations. Interestingly, all seven workers who had had a high intensity at the end of exposure (> 2.5 f/ml), had low to intermediate chrysotile concentrations at death, whereas those with low exposure were evenly distributed (31 subjects in both concentration categories); hence, there was a dependence between last intensity of exposure and chrysotile concentration (p = 0.014). Among 14 workers with a high average intensity of exposure, both those (n = 5) with high tissue concentrations of chrysotile and those (n = 10) with high tissue concentrations of tremolite fibres had more pronounced fibrosis than those with low to intermediate concentrations (median fibrosis grades for chrysotile: 2 v 1, p = 0.021; for tremolite: 2 v 0.5, p = 0.012). Additionally, workers who died shortly after the end of exposure with high concentrations of chrysotile and crocidolite had smoked more than those with low intermediate concentrations (medians for chrysotile 35 v 15 pack-years, p = 0.030; for crocidolite 37 v 15 pack-years, p = 0.012). The present data indicate that chrysotile has a relatively rapid turnover in human lungs, whereas the amphiboles, tremolite and crocidolite, have a slower turnover. Further, chrysotile retention may be dependent on dose rate. Chrysotile and crocidolite deposition and retention may be increased by tobacco smoking; chrysotile and tremolite by fibrosis.

In plain English

This Swedish study used lung tissue kept from necropsies at Lund University Hospital. Using electron microscopy, the authors measured chrysotile, tremolite and crocidolite fibres in 69 dead asbestos cement workers and 96 matched referents. The 20 workers who died within three years of the end of exposure had higher chrysotile concentrations than the referents, with a median difference of 13 million fibres per gram of dry tissue. Among these 20, those exposed for longer had higher tremolite concentrations. A separate crocidolite analysis took 1966, when crocidolite use ended, as the end of exposure and showed the same pattern in 17 workers. All seven workers with a high final exposure intensity had low to intermediate chrysotile levels. Among workers with high average exposure, those with high chrysotile or high tremolite levels had more fibrosis. Among workers who died within three years of the end of exposure, high chrysotile and high crocidolite levels went with heavier smoking, though the chrysotile link might have been confounded by duration and year of employment. The authors concluded that amphibole concentrations rise with exposure duration while chrysotile concentrations do not. They cautioned that their methods were crude.

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: Comparison of asbestos fibre concentrations in lung tissue taken at necropsy from dead asbestos cement workers and from matched referents (controls), with fibres analysed by transmission electron microscopy
• Who was studied: Lung tissue from asbestos cement factory workers whose specimens were preserved at Lund University Hospital, Sweden. Of 75 workers, the 69 with exposure information were analysed, along with 96 referents. Median age at death was 68 years for workers and 67 for referents. Each group included five women, and the median year of death was 1972 in both groups.
• Exposure: Chrysotile was the major exposure, with tremolite a known contaminant of commercial chrysotile. Some amosite was used up to 1956 and crocidolite until 1966, both intermittently. Among the 69 workers, mean duration of employment was 18 years (median 15), and the mean estimated average intensity of exposure was 1.7 fibres/ml (median 1.2).
• Main results:
  • The 20 workers who died within three years of the end of employment had higher chrysotile concentrations than the 96 referents. The median difference was 13 million fibres per gram, p = 0.033, one sided.
  • Among the 20 workers who died within three years of the end of exposure, the 13 with high tremolite concentrations had a median exposure duration of 32 years. The 7 in the low to intermediate category had a median of 20 years (p = 0.018, one sided).
  • Among workers who died more than three years after the end of exposure and who were postulated to have had high tremolite concentrations when exposure ended, time from end of exposure to death was not significantly associated with tremolite category at death. The high group (n = 8) had a median of 13 years and the low to intermediate group (n = 4) a median of 10 years, p = 0.67.
  • The crocidolite analysis took 1966, when crocidolite use ended, as the end of exposure. Among the 17 workers who died within three years of that date, those in the high concentration category (n = 9) had a median exposure duration of 32 years. Those in the low to intermediate category (n = 8) had a median of 25 years (p = 0.027).
  • All seven workers with a high exposure intensity at the end of exposure (above 2.5 fibres/ml) had low to intermediate chrysotile concentrations at death. The association between last intensity and chrysotile concentration category was significant (p = 0.014). No such relation was seen for average intensity.
  • Among 14 workers with a high average intensity of exposure, median fibrosis grades were as follows. For chrysotile, workers with high concentrations had a median grade of 2 and those with low to intermediate concentrations a median of 1 (p = 0.021). For tremolite, the medians were 2 and 0.5 (p = 0.012).
  • Among the 20 workers who died within three years of the end of exposure, those with high chrysotile concentrations had a median of 35 pack-years of smoking and those with low to intermediate concentrations a median of 15 (p = 0.030). Stratification suggested this relation might be confounded by duration (and year) of employment.
  • Among the 17 workers who died within three years of the 1966 end of crocidolite use, those in the high crocidolite category had a median of 37 pack-years and those in the low category a median of 15 (p = 0.013). Stratification did not indicate confounding by age or duration of employment.
  • Amphibole concentrations in workers who died of mesothelioma (pleural mesothelioma, 7 workers), lung cancer (2) or lung fibrosis (2) were generally higher than in workers who died from other causes. No such pattern was found for chrysotile.
• The authors' conclusion: The authors concluded that amphibole and chrysotile fibres show different kinetics in human lung tissue: amphibole concentrations increase with duration of exposure, whereas chrysotile concentrations do not. They also found indications of impaired clearance in workers with fibrosis and in heavy smokers. They stated that the findings support the hypothesis that adverse effects are associated with the fibres retained (amphiboles) rather than with those being cleared (largely chrysotile).
• Limitations the authors state:
  • Exposure may have been misclassified for the early period because no dust measurements were made before 1956.
  • Information on each worker's tasks and on respirator use was incomplete.
  • Fibre type was not identified in the sampled workplace dust, and each worker's crocidolite and amosite exposure was poorly defined.
  • Exposure intensity and duration were intercorrelated, which made it harder to evaluate them separately.
  • Only crude methods could be used, and no quantitative estimates of clearance rates were possible.
  • The sample site within the lung was usually unspecified, so it could not be accounted for.
  • The cause-of-death comparisons rested on small numbers in each asbestos-related diagnosis group.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Transmission Electron Microscopy (TEM), Chrysotile, Tremolite, Crocidolite, Amphibole Group, Fibrosis, Deposition.

Related studies

• Mineral fibres, fibrosis, and asbestos bodies in lung tissue from deceased asbestos cement workers — M. Albin, L. Johansson, et al. (1990)
• Fibre type and concentration in the lungs of workers in an asbestos cement factory — B. Gylseth, G. Mowé, et al. (1983)
• Radiological changes in asbestos cement workers — K. Jakobsson, U. Strömberg, et al. (1995)
• Genetic polymorphism for glutathione-S-transferase mu in asbestos cement workers — K. Jakobsson, A. Rannug, et al. (1994)
• Determination of mineral fibre in human lung tissue by light microscopy and transmission electron microscopy — A.J. Rogers (1984)
• Effects of cigarette smoke on tissue uptake and retention of iron oxide in the guinea pig — B. Gilks, J. Wright, et al. (1988)

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