Trends in asbestos and non-asbestos fibre concentrations in the lung tissues of Japanese patients with mesothelioma

Our plain-English summary of Trends in asbestos and non-asbestos fibre concentrations in the lung tissues of Japanese patients with mesothelioma, by K. Sakai, N. Hisanaga, E. Shibata, et al (The Annals of Occupational Hygiene, 2014).

The study

• Authors: K. Sakai, N. Hisanaga, E. Shibata, M. Kamijima, G. Ichihara, Y. Takeuchi, T. Nakajima
• Journal: The Annals of Occupational Hygiene
• Published: 2014;58(1):103-20
• Read it: PubMed · Publisher

Abstract

Objectives: We aimed to elucidate changes in asbestos and non-asbestos fibre concentrations in the lung tissues of Japanese patients with mesothelioma over time.

Methods: Lung tissues were obtained from 46 patients with mesothelioma who died or underwent surgery between 1971 and 2005. All of the patients had a history of occupational asbestos exposure. We classified patients into four groups according to the period during which their lung tissue was obtained. Asbestos and non-asbestos fibre concentrations were determined by transmission electron microscopy with energy-dispersive X-ray analysis using a low-temperature ashing procedure.

Results: From the 1970s to the 2000s, we observed a decrease in the geometric mean of total asbestos concentration (67.4-1.05 million fibres per gram dry lung), chrysotile concentration (25.0-0.66 million fibres per gram dry lung), amphibole asbestos concentration (21.3-0.76 million fibres per gram dry lung), and non-asbestos fibre concentration (326-19.3 million fibres per gram dry lung). The mean duration of asbestos exposure decreased from 33.7 to 17.6 years, and the mean duration since the last exposure increased from 0.3 to 21.5 years. The percentage of longer fibres to total fibres tended to increase over time, whereas the mean fibre length did not differ significantly.

Conclusions: The present study suggested that asbestos and non-asbestos fibre concentrations in the lung tissues of Japanese patients with mesothelioma who have occupational histories of asbestos exposure may have decreased from the 1970s to the 2000s.

In plain English

This study measured asbestos and other mineral fibres in lung tissue from 46 Japanese patients with malignant mesothelioma (41 pleural, 5 peritoneal). All had work histories involving asbestos, and their tissue was obtained between 1971 and 2005. The authors grouped patients into four periods by when the tissue was obtained and counted fibres with transmission electron microscopy. The geometric mean concentration of total asbestos fell from 67.4 million fibres per gram of dry lung in the 1970s group (3 patients) to 1.05 million in the 2000 to 2005 group (13 patients). Over the same span, chrysotile fell from 25.0 to 0.66 million, amphibole asbestos from 21.3 to 0.76 million, and non-asbestos fibres from 326 to 19.3 million. No asbestos was detectable in four patients from the 2000s. Average years of exposure fell (33.7 to 17.6) and years since last exposure rose (0.3 to 21.5), but these did not differ significantly among periods. The authors concluded that concentrations decreased, possibly reflecting exposure duration and intensity and fibre clearance. They noted that patients were not randomly selected, numbers were small, there was no control group, and workplace exposure levels were unknown.

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: Lung-tissue fibre analysis of a case series of mesothelioma patients, compared across four sampling periods (1971–1979, 1980–1989, 1990–1999, 2000–2005) using transmission electron microscopy with energy-dispersive X-ray analysis after low-temperature ashing
• Who was studied: 46 Japanese patients with pathologically confirmed malignant mesothelioma (41 pleural, 5 peritoneal) who had occupational histories of asbestos exposure; lung tissue obtained 1971–2005 from deaths or surgery (3 patients in 1971–1979, 21 in 1980–1989, 9 in 1990–1999, 13 in 2000–2005)
• Exposure: Occupational asbestos exposure in varied jobs (e.g. electricians, plasterers, spinners, insulators, iron foundry workers, shipyard workers, steamfitters). The types of asbestos and the airborne concentrations each patient was exposed to were not known. Fibres measured in lung included chrysotile, amosite, crocidolite, actinolite, tremolite, and non-asbestos fibres (mainly aluminium silicate).
• Main results:
  • Geometric mean total asbestos concentration (million fibres per gram dry lung) was 67.4 in 1971–1979, 16.5 in 1980–1989, 3.22 in 1990–1999 and 1.05 in 2000–2005. The difference among periods was significant (P less than 0.01).
  • Geometric mean chrysotile fell from 25.0 (1970s) to 0.66 (2000s), and amphibole asbestos from 21.3 to 0.76 million fibres per gram dry lung. Total asbestos, chrysotile and amphibole concentrations were significantly lower in the 2000s than in the 1980s.
  • Chrysotile was detected in 3 of 3 patients in the 1970s, 20 of 21 (95%) in the 1980s, 7 of 9 (78%) in the 1990s and 3 of 13 (23%) in the 2000s. No asbestos was detectable in four patients sampled in the 2000s.
  • Geometric mean non-asbestos fibre concentration was 326 (1970s), 61.4 (1980s), 18.7 (1990s) and 19.3 (2000s) million fibres per gram dry lung. Asbestos and non-asbestos concentrations were correlated (r = 0.66).
  • Mean total duration of asbestos exposure fell from 33.7 years (1970s group) to 17.6 years (2000s group). Mean time since last exposure rose from 0.3 to 21.5 years. These differences among periods were not statistically significant.
  • Mean fibre lengths of chrysotile and amphibole did not differ significantly among periods. Mean fibre diameters were thickest in the 2000s.
  • In the 5 patients with peritoneal mesothelioma, geometric mean chrysotile and amphibole concentrations were 5.01 and 8.69 million fibres per gram dry lung. In patients with pleural mesothelioma, they were 1.74 and 2.98.
• The authors' conclusion: The authors concluded that asbestos and non-asbestos fibre concentrations in these patients' lungs decreased from the 1970s to the 2000s (the abstract says they 'may have decreased'). They suggested this may reflect the duration and intensity of exposure and the clearance of fibres from the lungs, and said the relative contribution of these factors remains unclear.
• Limitations the authors state:
  • Patients were not randomly selected, numbers were small (especially for the 1970s), and there was no control population. Results cannot be directly generalized to national trends in Japan.
  • Workplace exposure levels by asbestos type were not available for each patient.
  • The interval between exposure and receipt of the sample varied widely.

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, Asbestos Exposure, Transmission Electron Microscopy (TEM), Low-Temperature Ashing, Chrysotile, Amphibole Asbestos.

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