Toxicological and Epidemiological Studies of Effects of Airborne Fibers: Coherence and Public Health Implications

摘要

Airborne fibers, when sufficiently biopersistent, can cause chronic pleural diseases not caused by their chemical components, as well as excess lung cancers. Mesothelioma and pleural plaques are caused by biopersistent fibers thinner than ～0.1 μm and longer than ～5 μm. Excess lung cancer and pulmonary fibrosis are caused by biopersistent fibers that are longer than 15 μm. While biopersistence varies with fiber type, all amphibole and erionite fibers are sufficiently biopersistent to be highly toxic, while the greater in vivo solubility of chrysotile fibers makes them less toxic for lung diseases, and much less toxic for pleural diseases. Most synthetic vitreous fibers (SVFs) are more soluble in vivo than chrysotile, and pose little pulmonary or pleural health risk, but some specialty SVFs are sufficiently biopersistent to be toxic. These conclusions are based my literature review on: 1) epidemiologic studies that specified the origin of the fibers by type, and especially those that identified their fiber length and diameter distributions; 2) laboratory-based toxicologic studies involving fiber size characterization and/or dissolution rates, and long-term observation of biological responses; and 3) the largely coherent findings of the epidemiology and the toxicology. The strong dependence of effects on fiber diameter, length, and biopersistence makes reliable routine quantitative exposure and risk assessment impractical in some cases, since it requires TEM examination of representative membrane filter samples for statistically sufficient numbers of fibers longer than 5 and 15 μm, and thinner than 0.1 μm, by fiber types.