Environmental Health Perspectives 105, Supplement 5, September 1997

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Approaches to Characterizing Human Health Risks of Exposure to Fibers

Vanessa T. Vu and David Y. Lai

Office of Pollution Prevention and Toxics, U.S. Environmental Protection Agency, Washington, D.C.

Abstract
Naturally occurring and man-made (synthetic) fibers of respirable sizes are substances that have been identified by the U.S. Environmental Protection Agency (U.S. EPA) as priority substances for risk reduction and pollution prevention under the Toxic Substances Control Act (TSCA). The health concern for respirable fibers is based on the link of occupational asbestos exposure and environmental erionite fiber exposure to the development of chronic respiratory diseases, including interstitial lung fibrosis, lung cancer, and mesothelioma in humans. There is also considerable laboratory evidence indicating that a variety of fibers of varying physical and chemical characteristics can elicit fibrogenic and carcinogenic effects in animals under certain exposure conditions. This paper discusses key scientific issues and major default assumptions and uncertainties pertaining to the risk assessment of inhaled fibers. This is followed by a description of the types of assessment performed by the U.S. EPA to support risk management actions of new fibers and existing fibers under TSCA. The scope and depth of these risk assessments, however, vary greatly depending on whether the substance under review is an existing or a new fiber, the purpose of the assessment, the availability of data, time, and resources, and the intended nature of regulatory action. In general, these risk assessments are of considerable uncertainty because health hazard and human exposure information is often incomplete for most fibers. Furthermore, how fibers cause diseases and what specific determinants are critical to fiber-induced toxicity and carcinogenicity are still not completely understood. Further research to improve our knowledge base in fiber toxicology and additional toxicity and exposure data gathering are needed to more accurately characterize the health risks of inhaled fibers. -- Environ Health Perspect 105(Suppl 5):1329-1336 (1997)

Key words : respirable fibers, mineral fibers, man-made vitreous fibers, synthetic fibers, asbestos, risk assessment

This paper is based on a presentation at The Sixth International Meeting on the Toxicology of Natural and Man-Made Fibrous and Non-Fibrous Particles held 15-18 September 1996 in Lake Placid, New York. Manuscript received at EHP 26 March 1997; accepted 15 April 1997.

The views and opinions expressed by the authors do not necessarily reflect the official position or policies of the U.S. Environmental Protection Agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.

Address correspondence to Dr. V.T. Vu, U.S. Environmental Protection Agency (7403), 401 M Street, SW, Washington D.C. 20460. Telephone: (202) 260-1243. Fax: (202) 260-1283. E-mail: vu.vanessa@epamail.epa.gov

Abbreviations used: IT, intratracheal instillation; MF, modifying factor; MOE, margin of exposure; NOAEL, no observed adverse effect level; OPPT, Office of Pollution Prevention and Toxics; PMN, premanufactured notice; RCF, refractory ceramic fiber; ROS, reactive oxygen species; SNUR, significant new use rule; TSCA, Toxic Substances Control Act; UFs, uncertainty factors; U.S. EPA, U.S. Environmental Protection Agency; WOE, weight of evidence.

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Last Update: December 1, 1997