Characterization of exposure and dose of man made vitreous fiber in experimental studies

The use of fibrous test materials in in vivo experiments introduces a number of significant problems not associated with nonfibrous particulates. The key to all aspects of the experiment is the accurate characterization of the test material in terms of fiber length, diameter, particulate content, and chemistry. All data related to fiber properties must be collected in a statistically sound manner to eliminate potential bias. Procedures similar to those outlined by the National Institute of Occupational Safety and Health (NIOSH) or the World Health Organization (WHO) must be the basis of any fiber characterization. The test material to which the animal is exposed must be processed to maximize the amount of respirable fiber and to minimize particulate content. The complex relationship among the characteristics of the test material, the properties of the delivery system, and the actual dose that reaches the target tissue in the lung makes verification of dose essential. In the case of man-made vitreous fibers (MMVF), dose verification through recovery of fiber from exposed animals is a complex task. The potential for high fiber solubility makes many of the conventional techniques for tissue preservation and digestion inappropriate. Processes based on the minimum use of aggressive chemicals, such as cold storage and low temperature ashing, are potentially useful for a wide range of inorganic fibers. Any processes used to assess fiber exposure and dose must be carefully validated to establish that the chemical and physical characteristics of the fibers have not been changed and that the dose to the target tissue is completely and accurately described.