13 - Physical factors: fiber carcinogenesis (including crystalline silicates)

Summary

Asbestos

Although known in Roman times, it was not until the late nineteenth century that fibrous silicate minerals were found to be commercially useful and were employed widely in fire-proofing and in the reinforcement of cement in construction material. The modern asbestos industry dates from the discovery of large deposits of chrysotile in Canada and Russia (Bogovski et al., 1973). Asbestos fibers are now regarded as representing an important and possibly unique carcinogenic hazard in the ambient environment or work-place and are probably the most important occupational risk ever identified.

Nature of asbestos

Asbestos is the generic name used for a group of naturally occurring mineral silicate fibers of the serpentine and amphibole series with length/diameter ratios of over 3:1. Government agencies in various countries and industrial groups currently characterize six fibrous silicates as ‘asbestos’ (Speil & Leineweber, 1969; Mossman & Gee, 1989): the fibrous serpentine mineral chrysotile and the fibrous amphiboles actinolite, amosite, anthophyllite, crocidolite and tremolite. Current usage of the term asbestos is restricted to these specific silicates. Many other minerals with a fibrous crystalline structure occur naturally, but either do not possess the properties of asbestos, such as heat stability, thermal and electrical insulation, the ability to be woven, stability in acids/alkalis, or they do not occur in sufficient concentrations for commercial exploitation.