CLEARANCE OF REFRACTORY CERAMIC FIBERS (RCF) FROM THE RAT LUNG - DEVELOPMENT OF A MODEL

Chronic exposure and postexposure experiments have been recently perfo rmed in rats to evaluate the biological responses of inhaled refractor y ceramic fibers (RCF) at different concentration levels. The lung bur den data in the accessory lobe of the rat lung were collected during a nd after different exposure and postexposure periods. The size distrib ution of retained fibers in the lung at different time points was also measured. We used these data to develop a mathematical model of fiber clearance from the rat lung. It was found that the clearance rate did not depend significantly upon fiber size but there was a clear depend ence on lung burden. As lung burden increased, the clearance rate was found to decrease. An empirical equation was derived for the clearance rate as a function of lung burden. At low burdens, rats had a retenti on half-time of about 126 days for RCF compared to a typical half-time of about 60 days for insoluble nonfibrous particles. (C) 1994 Academi c Press, Inc.