Asbestos and its substitutes: International coordination and independent research needed

Asbestos-related risks have been estimated on the basis of extrapolations from the past, when high-dose occupational exposures were frequent. The linear no-threshold (LNT) dose-response pattern has generally been assumed for the low exposure levels. However, applicability of the LNT hypothesis to low asbestos exposures has never been proven. Asbestos fibers are present in the natural environment in some places due to erosion of surface deposits. Inhalation, degradation and discharge of the fibers occur normally [1,2], probably being in a dynamic equilibrium. Existence of a threshold “no-effect” level for the exposure to mineral fibers has not been demonstrated so far, but can be assumed by analogy with other environmental factors that have induced evolutionary adaptation [3,4]. Certainly, this supposition cannot be adopted as a working hypothesis without verification in large-scale bioassays. Research into nonlinear, threshold cancer risk models is warranted not only for chrysotile [5], but also for other forms of asbestos and its man-made substitutes.