A ban on asbestos must be based on a comparative risk assessment

© 2001 Canadian Medical Association or its licensors In this issue (page 489), Joseph LaDou and colleagues on behalf of the Collegium Ramazzini call for an immediate and total ban on “asbestos” products because the current health risks associated with the use of “asbestos” are not acceptable, “controlled use” is not possible and “safer” substitutes are readily available. The logic is indisputable, but the premises are not. First, the risks associated with chrysotile, the type of asbestos used nowadays, are exaggerated by relying on a single and aberrant study. Second, the statements on controlled use and substitutes are supported neither by evidence nor by references. Finally, the Collegium fails to consider the technical efficiency of chrysotile and its substitutes when used in brakes and thermal insulation. A distortion of the evidence might result in a useless ban and possibly increased risk. This commentary presents critical evidence omitted by the Collegium and argues that any decision to ban “asbestos” should rely on a comparative risk assessment of chrysotile and its substitutes. Which asbestos products are at stake specifically? “Asbestos” is a group of heterogeneous mineral fibres that have some common physical characteristics and commercial uses. The risk of developing asbestos-related diseases depends on the dose, dimensions, durability (biopersistence) and surface reactivity of inhaled materials. The greatest differences in the physicochemical properties are between curly chrysotile and the more biopersistent needle-like amphiboles (tremolite, amosite and crocidolite). These differences entail different industrial applications and different toxicities. For instance, amphibole fibres were heavily used in buildings, blast furnaces and ships until 1980 in Europe because they resist high temperatures and chemically aggressive environments better than chrysotile. These uses and the 25–50-year latency of mesothelioma are responsible for mesothelioma clusters in ship-building areas around the world and for the predicted peak of the mesothelioma epidemic at around 2020 in Europe. The much lower incidence of mesothelioma in chrysotile industries (mining, cement, textiles and friction products) probably results from the much shorter biopersistence and lower iron content of chrysotile. Yet, an “asbestos” ban will only replace short, and thus less toxic, chrysotile fibres with certain substitute materials in new high-density cement and friction products, or it will replace fibre-containing products with other products altogether (e.g., steel, polyvinyl chloride [PVC]). It will not address the main cause of the mesothelioma epidemic: extant friable products in buildings that contain amphibole fibres. What risks are associated with chrysotile fibres? The Collegium claims that all asbestos fibres are associated with similar risks of lung cancer and asbestosis, and only marginally different risks of mesothelioma. Experienced scientists in the field strongly disagree with this view. Risk assessments and reviews generally attribute peritoneal mesotheliomas exclusively to amphibole fibres. The 47 cohorts of individuals working with asbestos reviewed in the most recent and comprehensive risk assessments show higher risks in those working with amphibole than in those working with chrysotile. Thus, excess lung cancers occur 3 times, pleural mesothelioma 12 times and peritoneal mesotheliomas 30 times more frequently in mainly amphibole than in chrysotile industries for an equal number of expected cases (see additional data in the Table on the CMAJ Web site at www.cma.ca/cmaj/vol-164/issue-4 .htm). Exposure–response comparisons of studies with meaningful exposure data suggest that chrysotile workers were 4–24 times less at risk of asbestos-induced lung cancer than amphibole workers at equal exposure. To put this in perspective, based on the exposure–response estimate of the US Environmental Protection Agency (EPA), the lifetime risk of an asbestos-induced lung cancer in smoking male workers exposed for 20 years to 20 fibres per millilitre of air in primarily chrysotile industries was about 2%–10%, compared with 40% in smoking male workers in industries using amphiboles. Risk in nonsmoking asbestos workers was about 15 times lower in both cases. The mining and milling industry is most informative because fibre types are not mixed, and because it produces fibres of different sizes for all the asbestos industries. Of all the pleural mesotheliomas reported among chrysotile workers, 70% occurred among Quebec miners and millers, and most were traced to coexposures to amphiboles. The dosespecific risks of asbestosis, lung cancer and mesothelioma are 15–50 times lower in chrysotile miners than in amphibole miners. This seems true also for nonoccupationally exposed populations. In contrast to the Collegium’s interpretation of our research, my colleagues and I found that the absence of excess lung cancers among residents of A ban on asbestos must be based on a comparative risk assessment