Natural asbestiform minerals: The case for considering them “asbestos”

The hazards of asbestos, including chrysotile, are protean and well documented. The term “asbestos” is obsolete: it properly refers to a heterogeneous collection of fibrous silicates, defined by commercial use at the time they were so designated, many years ago. There are other fibrous silicates, besides the minerals currently arbitrarily designated as asbestos, that have similar effects and similar potency. However, regulation of exposure to these mineral dusts has been unnecessarily complicated because they are not identified as asbestos. For regulatory purposes, then, non-vitreous fibrous silicates could simply be deemed to be asbestos, expanding the definition of asbestos to natural fibrous silicates. They include talc (when contaminated with tremolite; talc is characterized by a small aspect ratio), Libby mineral (resembling and sometimes continuous with tremolite), zeolites (such as erionite), and fibrous mordenite, among natural minerals. This means that zeolites, which are very similar and appear to have the same toxic properties (and which are in fact in commercial use, although as catalytic agents) are not considered to be asbestos although they behave almost identically to conventional varieties of asbestos. Exposure to fibrous silicates is common in construction and earth-moving work in places where they naturally occur. Libby mineral has been well studied and clearly mimics the effects of tremolite with high potency. Revising the de jure definition of asbestos would bring these hazardous exposures under a common and effective regulatory regime without the need for time-consuming deliberation and classification. The US National Institute for Occupational Safety and Health released a “science blog” identifying erionite as an occupational hazard on 22 November 2011. This is a step forward toward recognition of the hazard of nonasbestos fibrous silicates.