Environmental and occupational medicine, 4th edition. Rom WN, Markowitz SB, eds. Philadelphia, PA: Lippincott Williams & Wilkins, 2006 Dec; :525-542
In addition to asbestos, coal, and silica, a wide variety of other mineral species may give rise to pneumoconiosis, industrial bronchitis, interstitial lung injury, or obstructive airway disease. Virtually any inorganic dust may elicit some pulmonary reaction; even so-called nuisance dusts may cause bronchitis or respiratory symptoms in some workers. The dusts discussed in this chapter may produce radiographic changes and pulmonary reactions; less commonly, the injury progresses to impairment and respiratory disability. Workers employed in mining, milling, ore processing, tunneling, quarrying, or other occupations that expose them to minerals, clays, or rocks may be at risk. The form of the mineral (habit) is important for predicting its biologic effect (e.g., if the habit is fibrous, the mineral may be more biologically active). There are three broad categories of rocks: igneous (90% of the upper 10 miles of the earth's crust), sedimentary (5%), and metamorphic (5%). Igneous rocks are formed by the cooling and subsequent solidification of fluid rock mass called magma. The common minerals in igneous rocks are quartz, cristobalite, tridymite, fibrous mica, tuffs (including those containing zeolites), and olivine. There are two types of igneous rock, intrusive and extrusive; the former type cools beneath the earth's surface, and the latter cools at or near the surface. Intrusive rocks cool more slowly, and larger crystals are formed. Sedimentary rocks are formed from existing rock masses that are altered through weathering, for example by oxygen, water, and acids. Common minerals in sedimentary rock include quartz and other silica polymorphs, feldspars, micas, clays, carbonate minerals, limestone, shale, and sandstones. Metamorphic rocks form when existing rocks are altered by high pressures and temperatures and by chemical reactions. These rocks are frequently biologically active and include slate as well as minerals such as silicates, quartz, asbestiform amphiboles and serpentine, graphite, talc, and aluminum silicates. Mixed-dust pneumoconiosis results from exposure to multiple types of dusts, such that the pathologic and clinical features are atypical of classic pneumoconiosis such as silicosis, asbestosis, or coal workers' pneumoconiosis. Mixed-dust pneumoconiosis is typically seen in miners of ore-bearing bodies that contain free silica and are contaminated with a mineral that may have a fibrous habit. An example is "Labrador lung," which occurs in iron ore miners in Labrador who are exposed to silica and asbestos amphiboles in the gangue, or host rock. The best-known mixed pneumoconioses are anthracositicosis in coal miners who tunnel through siliceous rock and silicosiderosis in iron foundry workers. Other combinations are silicoaluminosis in alumina abrasive workers, argyriasiderosis in silver finishers, and various combinations of reactions to talc, silica, asbestos, and kaolin. Complex and multiple biopsy-confirmed lung injury patterns have been seen in workers with mixed exposures. For example, a worker who fashioned molds made up of asbestos and talc with a silicone coating and who filled them with beryllium-copper alloy developed silicosis, asbestosis, takosis, and berylliosis, all confirmed by biopsy. Mixed-dust and synthetic dust-induced lung injuries may become more common in the future as new natural and man-made mineral products are introduced as new products and substitutes for traditional more toxic varieties such as asbestos. An example of previously unrecognized workplace lung disease is the respiratory injury from nylon flock reported in North America and Europe. A number of specific silicates and other dusts reported to cause respiratory diseases are reviewed in this chapter.