Mineral fibre analysis and routes of exposure to asbestos in the development of mesothelioma in an English region

Our plain-English summary of Mineral fibre analysis and routes of exposure to asbestos in the development of mesothelioma in an English region, by D. Howel, A. Gibbs, L. Arblaster, et al (Occupational and Environmental Medicine, 1999).

The study

• Authors: D. Howel, A. Gibbs, L. Arblaster, L. Swinburne, M. Schweiger, E. Renvoize, P. Hatton, F. Pooley
• Journal: Occupational and Environmental Medicine
• Published: 1999;56(1):51-8
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To compare the concentrations of inorganic fibres in the lungs in cases of mesothelioma and controls: to determine whether concentrations of retained asbestos fibres differ with the different exposures identified from interview; and to investigate the existence of a cut off point in concentrations of asbestos fibres that indicates occupational exposure.

Methods: Case-control study; 147 confirmed cases of mesothelioma and 122 controls identified from deaths occurring in four districts of Yorkshire between 1979 and 1991. Surviving relatives were interviewed to determine lifetime exposure history to asbestos. Mineral fibre analysis was carried out on lung tissue from postmortem examinations.

Results: Odds on high concentrations of retained asbestos fibres were greater in cases than controls. After excluding subjects with occupational and paraoccupational exposure, the odds on high concentrations were still greater in cases than controls, but only significantly so for amphiboles. There was only a weak relation between probability of occupational exposure to asbestos and concentrations of retained asbestos fibres, and no significant difference in fibre concentrations was found between subjects who had been exposed to asbestos through different routes: these comparisons were only based on small groups. There was considerable overlap in concentrations of retained asbestos fibres between cases and controls with and without histories of occupational exposure.

Conclusions: The study has confirmed previous results of higher concentrations of asbestos fibres in cases than controls, and has shown that this is still found in subjects with little evidence of occupational and para-occupational exposure. The overlap in concentrations of retained asbestos for different groups of subjects did not suggest a clear cut of value.

In plain English

This case-control study compared lung mineral fibres in 147 people who died of confirmed malignant mesothelioma and 122 who died of other diseases. All died in four Yorkshire districts, 1979 to 1991. Relatives were interviewed about each person's lifetime asbestos exposure. Postmortem lung tissue was analysed by electron microscopy without knowing which samples came from cases. 'High' meant the top third of values for each fibre type. After adjusting for age, year of death, district and other fibres, high crocidolite (odds ratio 13.9, 95% confidence interval 5.6 to 34), high total amphiboles (12.4, 5.2 to 29) and high amosite (3.0, 1.4 to 6.5) were linked with mesothelioma. Chrysotile and non-asbestos links were no longer statistically significant. Excluding people with likely or possible work exposure (26 cases, 48 controls), crocidolite and amphibole odds ratios stayed high, with very wide confidence intervals. Fibre levels were only weakly related to the likelihood of work exposure. No significant difference was found between exposure routes, but those groups were small. Levels overlapped widely, and the authors found no clear cut-off indicating occupational exposure.

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: Case-control study comparing lung mineral fibre analysis with interview-based exposure histories
• Who was studied: 147 confirmed malignant mesothelioma cases and 122 controls (necropsy cases who died of other diseases), from deaths in four Yorkshire districts, January 1979 to December 1991; both groups had interview exposure histories and lung mineral fibre analyses, split into 45 matched sets
• Exposure: Retained lung fibres measured by transmission electron microscopy (fibres longer than 0.5 µm), as millions of fibres per gram dry lung: amosite, crocidolite, chrysotile, total amphiboles and non-asbestos fibres. Exposure routes from interviews were occupational, paraoccupational (domestic handling of items brought home), incidental and residential (living within 0.5 km of one of 278 potential industrial sources). Exposure in the last 15 years of life was not counted.
• Main results:
  • All subjects (147 cases, 122 controls), odds ratios for high fibre levels adjusted for age, year of death, district and other fibres: crocidolite 13.9 (95% CI 5.6 to 34), total amphiboles 12.4 (5.2 to 29), amosite 3.0 (1.4 to 6.5), chrysotile 1.9 (0.96 to 3.8), non-asbestos 1.4 (0.7 to 2.8). Before adjustment for other fibres, all types were significantly higher in cases. After adjustment, the relation with non-asbestos and chrysotile fibres was no longer significant.
  • Excluding subjects with likely or possible occupational exposure (26 cases, 48 controls), adjusted odds ratios were: crocidolite 25.9 (1.9 to 352), total amphiboles 17.4 (1.6 to 193), chrysotile 2.4 (0.5 to 11.1), amosite 0.63 (0.05 to 7.4). Excluding likely occupational or likely paraoccupational exposure (47 cases, 83 controls), they were: crocidolite 16.4 (3.6 to 75), total amphiboles 6.8 (1.9 to 25). Confidence intervals widened as numbers fell.
  • Median lung concentrations (million fibres/g), cases compared with controls: chrysotile 2.4 vs 0.4; amosite 0.7 vs less than 0.1; crocidolite 2.6 vs less than 0.1; total amphiboles 5.7 vs less than 0.1.
  • The relation between the probability of occupational exposure and fibre concentration was weak. A significant trend was found only for amosite and total amphiboles among cases, and for amosite among controls. Some subjects with no identified occupational exposure had relatively high crocidolite and chrysotile levels.
  • No significant difference in typical fibre concentrations was found between subjects with different dominant exposure routes, within cases or within controls. Some high asbestos levels, particularly chrysotile, were seen in subjects apparently exposed only incidentally or by living near an industrial source.
  • Among the 80 cases with likely occupational exposure, 4% had no detectable total amphibole fibres, compared with 60% of the 61 controls with no known exposure. For chrysotile, 22% of these cases and 34% of these controls had none detectable.
  • Fibre concentrations overlapped between occupationally exposed cases and unexposed controls, and some unexposed controls had amphibole levels up to 30 million f/g. The authors found no obvious threshold indicating occupational exposure.
• The authors' conclusion: The authors concluded that the study confirmed earlier findings of higher asbestos fibre concentrations in cases than controls. They concluded that this was still seen in subjects with little evidence of occupational or paraoccupational exposure, and that the overlap between groups did not suggest a clear cut-off value.
• Limitations the authors state:
  • Very small numbers in some exposure-route groups meant low power to detect anything but large differences.
  • Too few subjects had only incidental or residential exposure to say much about those routes; a larger study is needed.
  • Exposure histories came from relatives' recollections, which can be incomplete or unreliable.
  • Not all subjects had lung tissue blocks available.
  • Chrysotile is generally not retained in the lungs, so fibre analysis does not adequately reflect lifetime chrysotile exposure.
  • Analyses used whatever single lung tissue samples were available, not the recommended pooled samples.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Occupational Exposure, Case-Control Study, Exposure History, Amphibole Group, Take-home Exposure.

Related studies

• Routes of asbestos exposure and the development of mesothelioma in an English region — D. Howel, L. Arblaster, et al. (1997)
• The development of glass-fibre bodies in the lungs of guinea-pigs — S.K. Botham, P.F. Holt (1971)
• Guidelines for mineral fibre analyses in biological samples: report of the ERS Working Group. European Respiratory Society — P. De Vuyst, A. Karjalainen, et al. (1998)
• Development of asbestos bodies on amosite, chrysotile and crocidolite fibres in guinea-pig lungs — S.K. Botham, P.F. Holt (1971)
• Persistence of man-made mineral fibres (MMMF) and asbestos in rat lungs — B. Bellmann, H. Muhle, et al. (1987)
• Mineral fibres, fibrosis, and asbestos bodies in lung tissue from deceased asbestos cement workers — M. Albin, L. Johansson, et al. (1990)

Browse more research in Occupational and Environmental Medicine, or return to medical research.