Multicentric study on malignant pleural mesothelioma and non-occupational exposure to asbestos
C Magnani, A Agudo, CA González, A Andrion, A Calleja, E Chellini, P Dalmasso, A Escolar, S Hernandez, C Ivaldi, D Mirabelli, J Ramirez, D Turuguet, M Usel and B Terracini

Cancer Epidemiology Unit, S Giovanni B Hospital and Regional Centre for Cancer Epidemiology and Prevention, Torino, Italy; Department of Epidemiology and Cancer Registration, Catalan Institute of Oncology (ICO), Av. Gran Via s/n, Km 2.7, E-08907, L’Hospitalet de Llobregat, Spain; Department of Pathology, Ospedale Martini, Torino, Italy; entre de Seguretat i Condicions de Salut en el Treball (CSCST), Barcelona, Spain; Epidemiology Unit, Center for Study and Prevention of Cancer Firenze (CSPO), AO Careggi, Firenze, Italy; Department of Preventive Medicine and Public Health, Hospital Universitario Puerta del Mar, Cádiz, Spain; Agency for Environmental Protection (ARPA) Piemonte, Torino, Italy; Department of Pathology, Hospital Clinic, Barcelona, Spain; Former Documentation Services, Instituto Nacional de Seguridad e Higiene en el Trabajo, and Centro de Investigación y Desarrollo de Barcelona (CSIC), Barcelona, Spain; Geneva Medical Inspectorate of Factories (OCIRT) and Geneva Cancer Registry, Geneva, Switzerland

Summary Insufficient evidence exists on the risk of pleural mesothelioma from non-occupational exposure to asbestos. A population-based case–control study was carried out in six areas from Italy, Spain and Switzerland. Information was collected for 215 new histologically confirmed cases and 448 controls. A panel of industrial hygienists assessed asbestos exposure separately for occupational, domestic and environmental sources. Classification of domestic and environmental exposure was based on a complete residential history, presence and use of asbestos at home, asbestos industrial activities in the surrounding area, and their distance from the dwelling. In 53 cases and 232 controls without evidence of occupational exposure to asbestos, moderate or high probability of domestic exposure was associated with an increased risk adjusted by age and sex: odds ratio (OR) 4.81, 95% confidence interval (CI) 1.8–13.1. This corresponds to three situations:
cleaning asbestos-contaminated clothes, handling asbestos material and presence of asbestos material susceptible to damage. The estimated OR for high probability of environmental exposure (living within 2000 m of asbestos mines, asbestos cement plants, asbestos textiles, shipyards, or brakes factories) was 11.5 (95% CI 3.5–38.2). Living between 2000 and 5000 m from asbestos industries or within 500 m of industries using asbestos could also be associated with an increased risk. A dose–response pattern appeared with intensity of both sources of exposure. It is suggested that low-dose exposure to asbestos at home or in the general environment carries a measurable risk of malignant pleural mesothelioma. © 2000 Cancer Research Campaign

Keywords: asbestos; environmental exposure; mesothelioma; case–control studies

There is convincing evidence that pleural malignant mesothelioma is associated with occupational exposure to all commercial forms of asbestos (Landrigan, 1998; WHO, 1998). Although most cases of mesothelioma show a definite history of asbestos exposure at work, in population studies there is a proportion of cases that do not report any occupational exposure throughout their working life. Therefore, attention has turned to the potential risk associated with exposure at the lower doses in the general environment (Landrigan 1998).

Two circumstances for possible non-occupational exposure to asbestos have been investigated: domestic and environmental exposure. The former results from asbestos fibres brought home by workers exposed in the workplace (Gardner and Saracci, 1989). Environmental exposure may result from residence in the vicinity of asbestos mines, mills, or factories using asbestos. In many studies there is a single well-identified source of asbestos pollution termed a ‘neighbourhood exposure’. Another kind is due to residence in areas where the soil is naturally rich in asbestos or similar fibres. Both sets of circumstances have led to localized outbreaks of pleural mesotheliomas, large enough to be first recognized in the absence of formal epidemiological studies (Gardner and Saracci, 1989). The latter are needed, however, to investigate whether the industrial use of asbestos may produce sufficient environmental pollution to cause asbestos-related disease. Rarely, mesotheliomas may occur in recognizable geographical or temporal clusters when the exposure is relatively high, but they will go unnoticed when exposure is low. Although asbestos is widely found in the environment, insufficient evidence exists on the risk of mesothelioma as a consequence of general environmental exposure (Siemiatycki and Boffeta, 1998). The extent to which the general population is exposed and the potential effects of such low-dose exposure are a matter of controversy.

A multicentric population-based case–control study was therefore carried out with the main aim of measuring risk associated with low-intensity, non-occupational exposure to asbestos.