AN EXPERIMENTAL APPROACH TO THE EVALUATION OF THE BIOPERSISTENCE OF RESPIRABLE SYNTHETIC-FIBERS AND MINERALS

The biopersistence of fibers and minerals in the respiratory tract is an important parameter in the toxicity of those materials. The biopers istence of respirable synthetic fibers and minerals in man can be most closely evaluated in an animal model. While acellular and in vitro sy stems are important for initial evaluation of solubility and durabilit y, they cannot simulate the dynamics of inhalation deposition and clea rance and the subsequent systemic temic reaction to fibers and mineral s that occurs in the animal. To evaluate the biopersistence of synthet ic fibers. male rats were exposed to a well defined rat respirable aer osol of man-made vitreous fibers (MMVF), 6 hr/day for 5 days. Followin g exposure, subgroups were sacrificed at intervals ranging from 1 hr t o 52 weeks. Following sacrifice, the lungs were removed, weighed, and immediately frozen at 20 degrees C for subsequent digestion by low tem perature plasma ashing. The number, size distribution, and chemical co mposition of the fibers in the aerosol and lung were determined. With this animal model the role of biopersistence in altering the geometry and clearance of fibers can be systematically evaluated. The model als o can be applied for the evaluation of the biopersistence of nonfibrou s minerals.