Asbestos fibre burden in the lungs of patients with mesothelioma who lived near asbestos-cement factories

Our plain-English summary of Asbestos fibre burden in the lungs of patients with mesothelioma who lived near asbestos-cement factories, by P.G. Barbieri, D. Mirabelli, A. Somigliana, et al (The Annals of Occupational Hygiene, 2012).

The study

• Authors: P.G. Barbieri, D. Mirabelli, A. Somigliana, D. Cavone, E. Merler
• Journal: The Annals of Occupational Hygiene
• Published: 2012;56(6):660-70
• Cited by: 35 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Epidemics of malignant mesothelioma are occurring among inhabitants of Casale Monferrato and Bari never employed in the local asbestos-cement (AC) factories. The mesothelioma risk increased with proximity of residence to both plants.

Objectives: To provide information on the intensity of environmental asbestos exposure, in the general population living around these factories, through the evaluation of the lung fibre burden in mesothelioma patients.

Methods: We analysed by a scanning electron microscope equipped with X-ray microanalysis wet (formalin-fixed) lung tissue samples from eight mesothelioma patients who lived in Casale Monferrato or Bari and underwent surgery. Their occupational and residential history was obtained during face-to-face interviews. Semi-quantitative and quantitative indices of cumulative environmental exposure to asbestos were computed, based on residential distance from the AC plants and duration of stay.

Results: The lung fibre burden ranged from 110 000 to 4 300 000 fibres per gram of dry lung (f/g) and was >1 000 000 f/g in three subjects. In four cases, only amphibole fibres were detected. Environmental exposures had ceased at least 10 years before samples were taken. No patient had other definite or probable asbestos exposures. A linear relationship was observed between the lung fibre burden and all three indices of environmental cumulative exposure to asbestos.

Conclusions: Environmental exposure to a mixture of asbestos fibres may lead to a high lung fibre burden of amphiboles years after exposure cessation. The epidemiological evidence of an increased mesothelioma risk for the general population of Casale Monferrato and Bari, associated with asbestos contamination of the living environment, is corroborated.

In plain English

The authors measured asbestos fibres in lung tissue from eight people with pleural mesothelioma who lived near asbestos-cement factories in Casale Monferrato or Bari, Italy, which used chrysotile, crocidolite and amosite. None had definite or probable occupational exposure. Surgical tissue was examined by scanning electron microscope. Exposure indices combined home-to-plant distance with years of residence. Samples were taken 10 to 46 years after the last residential exposure. Counts ranged from 110 000 to 4 300 000 fibres per gram of dry lung. They exceeded 1 000 000, a suggested cut-off for occupational exposure, in three cases. Amphiboles were the only fibres found in four cases and predominant in three. Fibre burden showed a linear relationship with all three indices. The quantitative index was built on assumed past air levels. Using it, the regression estimated a rise of 26 700 fibres per gram (95% CI 17 200 to 36 100) per fibre-per-litre-year. The average (1 300 000) was significantly higher than in 13 people who died suddenly of heart disease (166 000). It partially overlapped values in occupationally exposed patients. The authors concluded this suggests environmental exposures had been substantial in the populations around the two plants.

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 series with lung fibre burden analysis by scanning electron microscopy with X-ray microanalysis, linear regression against ad hoc residential exposure indices, and comparison with previously studied occupationally exposed mesothelioma cases and an internal reference group
• Who was studied: Eight pleural mesothelioma patients (five men, three women; seven epithelial, one biphasic; mean age at diagnosis 54.0 years). Five had lived in Bari and three in Casale Monferrato, Italy. All were treated and registered by the Brescia and Veneto mesothelioma registries and had no definite or probable occupational asbestos exposure. Possible other exposures were recorded for some (for example, a household member's job or an ironing-table blanket). The reference group was 13 people with heart disease who died suddenly as inpatients in Brescia.
• Exposure: Residence near asbestos-cement plants. The Eternit plant in Casale Monferrato (1907 to 1986) used chrysotile, crocidolite (10% of all asbestos) and small amounts of amosite. The Fibronit plant in Bari (1934 to 1989) used chrysotile 80%, crocidolite 15% and amosite 5%. Exposure was estimated from residential distance bands and years of residence, using two semi-quantitative indices and one quantitative index in fibres per litre times years. The quantitative index was based on assumed ambient air concentrations by distance band.
• Main results:
  • Lung asbestos fibre concentration in the eight cases ranged from 110 000 to 4 300 000 fibres per gram of dry lung.
  • Concentration was above 1 000 000 fibres per gram, the cut-off suggested to distinguish occupational exposure, in three cases. In three further cases the 95% confidence interval included 1 000 000.
  • Amphibole fibres were predominant in three cases and the only fibres found in four cases. Chrysotile was present in only two cases and was not the predominant type in either.
  • Lung samples were taken 10 to 46 years (mean 22.2) after the last residential exposure.
  • Fibre burden showed a linear relationship with all three cumulative exposure indices. The best fit was with the quantitative index (Index 3), which relied on assumed past air concentrations. The regression coefficient was 26 700 fibres per gram (95% CI 17 200 to 36 100) per unit of cumulative exposure (fibres per litre times years).
  • Mean fibre burden was 1 300 000 (SD 1 400 000) fibres per gram in the eight environmental cases and 166 000 (SD 72 000) in the 13-person reference group. The difference was statistically significant.
  • The environmental cases' average was 50% of the mean for 24 mesothelioma cases exposed at work in non-asbestos industries (mean 2 800 000), and that difference was not statistically significant. The range overlapped that of 9 cases from asbestos industries (mean 136 400 000), whose mean was significantly higher.
• The authors' conclusion: The authors concluded that lung fibre burden was strictly related to indices of cumulative environmental exposure. In their view, this finding suggests environmental exposures had been substantial in the populations living around the two plants, in agreement with epidemiological evidence of increased mesothelioma risk. They presumed the predominance of amphiboles was due to slower lung clearance of amphiboles.
• Limitations the authors state:
  • Exposure in the reference group could be assessed less satisfactorily because only proxy interviews with next of kin were possible.
  • The semi-quantitative exposure indices are relatively crude, taking into account only residential distance from the sources.
  • For thin fibres, crocidolite and amosite could not be told apart, so they were grouped together as commercial amphiboles.

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-Cement, Casale Monferrato, Asbestos Exposure, Environmental Exposure, Amphibole Group, Cumulative Exposure.

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