Exposure to Man-Made Mineral Fibers: A Summary of Current Animal Data

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Abstract
The inhalation of asbestos fibers (crocidolite, chrysotile and amosite) has been implicated in the development of a number of lung disorders including lung cancer, asbestosis, and mesothelioma. The mechanism responsible for these effects is not well characterized but is generally thought to be related to the fibrous nature of these materials. Therefore, concerns have also been raised as to the potential health impact of other fibrous materials including man-made mineral fibers. Man-made mineral fibers are being used as substitutes for asbestos in a wide range of products. However, relatively little data are available on the potential health impact of these fibrous materials. Epidemiology and clinical studies have served as an important source of information on the effect of various environmental pollutants, but have not been sufficient to date to fully address the potential health impact of man-made mineral fibers. This is due in part to the relatively recent introduction of a number of these materials, the long latency period before the onset of clinical symptoms, and in general, the lower exposure levels associated with these materials. Therefore, a number of animal studies have been performed to predict or confirm the toxicity of various man-made mineral fibers in humans. Both fibrosis and mesothelioma have been induced in experimental animals exposed to man-made mineral fibers although no disease has been consistently observed in occupationally exposed workers. While little is known about the mechanism of this response, information from animal and cell culture experiments indicate that dose, fiber dimension, and fiber durability are the most important factors in determining the biological activity of these materials. The purpose of this summary will be to review these and other properties of man-made mineral fibers from animal and in vitro cellular experimentation in an attempt to address the potential health impact of these materials. Particular attention will be placed on the route of exposure, fiber type and morphology, and species tested. Recommendations will be made as to future research needs.