Toxicological and epidemiological studies on effects of airborne fibers: coherence and public [corrected] health implications.

Airborne fi bers, when suffi ciently biopersistent, can cause chronic pleural diseases, as well as excess pulmonary fi brosis and lung cancers. Mesothelioma and pleural plaques are caused by biopersistent fi bers thinner than ∼ 0.1 μ m and longer than ∼ 5 μ m. Excess lung cancer and pulmonary fi brosis are caused by biopersistent fi bers that are longer than ∼ 20 μ m. While biopersistence varies with fi ber type, all amphibole and erionite fi bers are suffi ciently biopersistent to cause pathogenic eff ects, while the greater in vivo solubility of chrysotile fi bers makes them somewhat less causal for the lung diseases, and much less causal for the pleural diseases. Most synthetic vitreous fi bers are more soluble in vivo than chrysotile, and pose little, if any, health pulmonary or pleural health risk, but some specialty SVFs were suffi ciently biopersistent to cause pathogenic eff ects in animal studies. My conclusions are based on the following: 1) epidemiologic studies that specifi ed the origin of the fi bers by type, and especially those that identifi ed their fi ber length and diameter distributions; 2) laboratory-based toxicologic studies involving fi ber size characterization and/or dissolution rates and long-term observation of biological responses; and 3) the largely coherent fi ndings of the epidemiology and the toxicology. The strong dependence of eff ects on fi ber diameter, length, and biopersistence makes reliable routine quantitative exposure and risk assessment impractical in some cases, since it would require transmission electronic microscopic examination, of representative membrane fi lter samples, for determining statistically suffi cient numbers of fi bers longer than 5 and 20 μ m, and those thinner than 0.1 μ m, based on the fi ber types. Abbreviations: ACGIH American Conference of Governmental Industrial Hygienists, AM Alveolar macrophage, BAL bronchoalveolar lavage, BMRC British Medical Research Council, CNT carbon nanotube, FEV 1 forced expiratory volume in 1 s, FVC forced vital capacity, HEI-AR Health Eff ects Institute-Asbestos Research, IARC International Agency for Cancer Research, IL-1 β Interleukin 1 β IL-6 Interleukin 6, IL-8 Interleukin 8, IP intraperitoneal, an in vivo dose delivery technique for fi bers, IRIS EPA ’ s Integrated Risk Information System IRIS, ISO International Standards Organization, IT intra-tracheal, an in vivo dose delivery technique for fi bers, LA , Libby (MT) amphibole fi ber, MMMF Man-made mineral fi ber, an alternate name for SVF, MMVF Man-made vitreous fi ber, an alternate name for SVF, MPPCF Millions of particles per cubic foot, MTD Maximum tolerated dose, NRC National Research Council, NIOSH National Institute for Occupational Safety and Health, OSHA Occupational Safety and Health Administration, PAH polynuclear aromatic hydrocarbon, PCOM Phase-contrast optical method (determining fi ber count concentration), PEL Permissible exposure limit, PMN Polymorphonuclear leukocytes, RCF Refractory ceramic fi ber, RNS Reactive nitrogen species, ROS Reactive oxygen species, SEM Scanning Electron Microscopy, SH Spontaneously hypertensive rat, SHHF Spontaneously hypertensive heart failure rat, SIC silicon carbide, SIR Standardized incidence ratio, SMR Standardized mortality ratio, SVF Synthetic vitreous fi ber, TEM Transmission electron microscopy, TLV Threshold limit value, UICC International Union Against Cancer (English translation of name of organization in French), UK United Kingdom, US United States, WHO World Health Organization, WKY Wistar Kyoto rat.