We are continuously exposed to respirable mineral particles. They are common constituents of soils and aeolian dusts, and they are often components of consumer and industrial products. Many mineral dusts are known to induce adverse biological responses under some conditions following inhalation (e.g., asbestos, quartz, some zeolites), so processes that increase our exposures to these minerals may also increase our risk of disease. Anthropogenic processes that increase our risk can often be altered to mitigate the potential hazard (e.g., the stabilization of friable, asbestos-containing material). However, these alterations can be costly or inconvenient, and often exposure to mineral dusts is unavoidable. Furthermore, non-anthropogenic processes can be significant sources of dusts (e.g., weathering of rock and volcanic emissions), and these are usually difficult to mitigate. Atmospheric processes can transport any of these dusts long distances [ Klein, 1993], causing widespread exposures and making any major dust source a global environmental problem. In other words, respirable mineral dusts are everywhere.
Risk assessment of inhaled-mineral hazards has been a major national concern. Although most of the focus has been on the asbestos minerals, crystalline silica has begun to elicit concern (e.g., two international conferences on the subject during 1993-1994), and zeolites may be next in line. Several geoscientific issues are integral to the risk assessment of inhaled minerals, including the evaluation of natural dust production, understanding the mechanisms of dust redistribution and transport, and the determination of the mineralogical mechanisms that stimulate pathogenesis. The latter aspect will be the focus of this section.