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About 107 000 people die every year from mesothelioma and other asbestos-related diseases.1 Although all asbestos fibres have been declared carcinogenic, ambiguity exists regarding the definition of asbestos and about which fibres should be regulated.2 Roughly 400 minerals arise naturally in a fibrous form (table ).3 Of these, only six (actinolite, amosite, anthophyllite, chrysotile, crocidolite, and tremolite) are regulated because, at the time when regulations were introduced, these were the only mineral fibres used commercially, based on the assumption that only commercial use could lead to widespread substantial human exposure.
Asbestos has many definitions depending on context. The commercial definition is based on its industrial properties; mineralogical and geological definitions describe asbestos according to its shape, chemical composition, and physical properties; regulatory definitions identify minerals to be regulated; and analytical definitions give rules according to fibre count. From a public health and media perception, the generic term asbestos evokes the notion of fibrous minerals causing disease.
Several groups of silicate minerals have a fibrous form, including serpentine, amphibole, zeolite, or palygorskite.3 Colloquially, the term asbestos is used to qualify fibres that possess physical properties similar to commercial asbestos. Similarly, the WHO definition of asbestos included all fibres with the physical and chemical properties of commercial asbestos. Nevertheless, regulatory health agencies regulate only the six commercial varieties of asbestos. This restricted regulation leads the population at large to believe that these six mineral fibres are the only dangerous forms of asbestos.
The main factors in the toxic effects of asbestos are fibre dimension and biopersistence.4...