Biological indicators of chrysotile exposure

Our plain-English summary of Biological indicators of chrysotile exposure, by B.W. Case (The Annals of Occupational Hygiene, 1994).

The study

• Author: B.W. Case
• Journal: The Annals of Occupational Hygiene
• Published: 1994;38(4):503-18, 410-1
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Chrysotile asbestos is retained in lung tissue, where it may be used as a marker of exposure. Studies include analysis of sputum and bronchoalveolar lavage fluid, but principally lung parenchyma from autopsy or surgically resected specimens. Asbestos bodies form on chrysotile fibres but are generally not a good indicator of human exposure to chrysotile because of their greater probability of formation on amphiboles. Chrysotile fibre analyses in lung have advantages and limitations. Chrysotile concentration is related to the level of environmental and occupational exposure, but in the latter situation owing to deposition, fibre alteration and clearance cumulative exposure and interval between end-exposure and death clearly affect results. Autopsy case series are biased toward increased proportions of asbestos-related diseases as compared to epidemiological cohort data. Analytical problems include potential contamination by chrysotile at autopsy, from fixatives, from post-fixative processing and in the analytical laboratory itself. These may have greatest effect in studies of individuals with low exposure, for tissue other than lung, and for short chrysotile fibres. Selection of control subjects should be contemporaneous with that of cases, and control subjects should fully reflect the hospital population at the time of case death. Limited data are available on fibre analysis in pleural tissue. More are needed. Issues requiring attention include avoidance of contamination, selection of controls, and sample site selection (parietal pleura, or tumour or plaque). For mesothelioma, two case-control studies of lung fibre burden show the principal relationship to be with long amphiboles, but some methodological problems exist. Lung cancer shows no such fibre-type differences. Asbestosis seems to be associated with long-fibre chrysotile and tremolite in one study and short fibres in others. Overall, lung retained dose is a useful indicator of chrysotile exposure if used cautiously in inference, and is very useful in the evaluation of historical exposures and industrial hygiene data in epidemiological studies.

In plain English

This paper, presented at a 1993 workshop, reviewed how well chrysotile retained in human tissue, mainly lung, serves as an exposure marker. The author reported that asbestos bodies generally did not reflect chrysotile fibre content. Reviewed studies showed lung chrysotile rising from background referents through environmental and household exposure to Quebec chrysotile miners and millers. The author warned that differences between laboratories make single cut-off values dangerous, and that cumulative exposure and time since last exposure affect results. The paper also discussed contamination at autopsy, in fixatives and in the laboratory, and autopsy series' bias toward severe disease. Two case-control studies of mesothelioma, from Canada and Australia, found the principal relationship with long amphibole fibres, though the Australian study also noted a significant relationship with chrysotile fibres 2 to 10 micrometres long. In the author's analysis of miners and millers, fibre type differences in lung cancer were not evident once smoking was accounted for. The author concluded that, with inferential limits in mind and enough exposure history, lung chrysotile and tremolite concentrations can be used to validate exposure assessments.

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: Review (workshop paper) organized as questions and answers, drawing on published studies and on some unpublished analyses by the author
• Who was studied: Published and unpublished studies of retained fibres in human tissue, mainly lung from autopsy or surgery. Many concern Quebec chrysotile miners and millers and South Carolina chrysotile textile workers, plus environmentally exposed residents, referents and children.
• Exposure: Chrysotile asbestos, measured as retained dose (fibres and asbestos bodies in tissue), with tremolite discussed as a co-exposure and commercial amphiboles discussed for comparison
• Main results:
  • Across the exposed groups reviewed, asbestos body concentrations generally did not reflect chrysotile fibre content.
  • Within a single laboratory, the reviewed studies showed lung chrysotile rising from background referents, through environmental and household exposure, up to chrysotile miners and millers. Differences between laboratories made single cut-off values unreliable.
  • In the study by Sebastien et al. (1989), 93% of 89 Quebec chrysotile miners and millers and 79% of 72 South Carolina chrysotile textile workers had lung chrysotile above 1 fibre per microgram dry lung (fibres longer than 5 micrometres).
  • In the Sebastien et al. (1989) data, chrysotile concentration not corrected for time since last exposure correlated poorly with cumulative exposure in fibre-years (r = 0.038). Rank correlation was significant (R = 0.54), and for tremolite the rank correlation was R = 0.84.
  • In the author's group's study of the lungs of American children (Case et al., 1994), asbestos bodies were absent in 57 of 60 cases. Chrysotile levels tended to cluster by hospital, which the author read as highly suggestive of contamination during autopsy processing.
  • In an unpublished 16-year retrospective study by the author of over 400 consecutive autopsies of chrysotile miners and millers, one third of the men died of lung cancer and one in 20 of mesothelioma. Epidemiologically established death rates for the same period were 0.7% for mesothelioma and 11% for lung cancer. The author attributed the difference to selection bias.
  • In a Canadian case-control study by McDonald and colleagues (78 matched pairs), multivariate analysis showed long amphibole fibres responsible for approximately 65-70% of mesotheliomas and chrysotile essentially for none.
  • An Australian case-control study (Rogers et al., 1991) showed similar findings, but noted a significant relationship between mesothelioma status and concentrations of chrysotile fibres 2 to 10 micrometres long.
  • In the author's analysis of over 60 chrysotile miners and millers with smoking data, 18 of whom had lung cancer, the lung cancer cases had smoked longer. Fibre type differences were not evident once smoking was accounted for.
  • In the author's examination of the Sebastien et al. (1989) data, Quebec miners and millers with asbestosis on autopsy reports (55 of 89) had significantly greater concentrations of tremolite fibres longer than 8 micrometres than other workers: mean 0.96 versus 0.14 fibres per microgram dry lung.
  • In the Sebastien et al. (1989) comparison, chrysotile and tremolite levels were systematically higher in Quebec miners and millers than in South Carolina textile workers, although the miners and millers had less disease. The higher levels remained after matching for time since last exposure.
• The authors' conclusion: The author concluded that the lung is the ultimate personal dosimeter. If inferential limits are kept in mind and enough exposure history exists to correct for clearance and cumulative exposure, chrysotile and tremolite lung concentrations can be used to investigate and validate exposure assessments.
• Limitations the authors state:
  • Contamination of specimens by chrysotile cannot be avoided, only anticipated, identified, quantified and corrected for.
  • Differences in methods between laboratories make comparisons difficult or impossible, so single cut-off values are dangerous.
  • Autopsy series are biased toward the worst cases and do not fully represent the exposed population.
  • Lung analysis at one point in time cannot account for lifetime clearance or fibre dissolution.
  • Fibre concentrations vary from lobe to lobe and between adjacent samples, so analyses of a single individual may not be accurate.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Sputum, Bronchoalveolar Lavage (BAL), Parenchyma, Autopsy, Asbestos Bodies, Amphibole Group, Occupational Exposure.

Related studies

• Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry — A. Tossavainen, E. Kovalevsky, et al. (2000)
• Chrysotile biopersistence in the lungs of persons in the general population and exposed workers — A.M. Langer, R.P. Nolan (1994)
• Patterns of inflammation, cell proliferation, and related gene expression in lung after inhalation of chrysotile asbestos — T.R. Quinlan, K.A. BéruBé, et al. (1995)
• The toxicological response of Brazilian chrysotile asbestos: a multidose subchronic 90-day inhalation toxicology study with 92-day recovery to assess cellular and pathological response — D.M. Bernstein, R. Rogers, et al. (2006)
• Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite — J.M. Cyphert, A. Nyska, et al. (2012)
• Evaluation of the exposure, dose-response and fate in the lung and pleura of chrysotile-containing brake dust compared to TiO2, chrysotile, crocidolite or amosite asbestos in a 90-day quantitative inhalation toxicology study - Interim results Part 1: Experimental design, aerosol exposure, lung burdens and BAL — D.M. Bernstein, B. Toth, et al. (2020)

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