Objectives To evaluate the lungs asbestos fibres concentration in participants with malignant pleural mesothelioma (MPM) who have been occupationally exposed.
Methods The lung samples were obtained from pleuropneumonectomies or autopsies of 271 male MPMs. The lung samples were examined through scanning electron microscopy. Retrospective assessment was used to assess for asbestos exposure. This study includes 248 MPMs with an occupational exposure defined as either ‘definite’ or ‘probable’ or ‘possible’.
Results The participants had finished working in asbestos exposure conditions more than 20 years ago (on average 26.1±11.0 years). The fibre burden resulted with a geometric mean equal to 2.0 (95% CI 1.6 to 2.4) million fibres per gram of dry lung tissue. The burden was higher among participants employed in asbestos textiles industry and in shipyards with insulation material, if compared with construction workers or non-asbestos textile workers or participants working in chemicals or as auto mechanics. 91.3% of MPMs had a detectable amount of amphibole fibres. A strong lung clearance capability was evident among workers exposed to chrysotile fibres. Owing to that, the 1997 Helsinki Criteria for occupational exposure were reached in <35% of cases among participant working in construction, in metallurgical industry, in chemical or textile industry and among those performing brake repair activities.
Conclusions The MPM cases are now occurring in Italy in participants who ceased occupational asbestos exposure decades before the analysis. A large majority still shows a residual content of amphibole fibres, but given the lung clearance capability, attribution to occupational exposure cannot rely only on fibres detection.
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Contributors EM and PG contributed to all aspects of conception, study design, data collection and analysis, data interpretation, manuscript preparation and critical revision. AS perfomed fibre analyses and contributed to data interpretation, manuscript preparation and critical revision. PGB contributed to data collection, data interpretation and a critical revision of the manuscript.
Competing interests EM and PGB have been requested as expert witnesses for the office of public persecutor or for the office of the judge in criminal trials on asbestos diseased workers.
Ethics approval The study was approved by the Ethical Committee of the Local Authority Health of Brescia (n. 0162572, 1 December 2010, Brescia).
Provenance and peer review Not commissioned; externally peer reviewed.