AbstractThe biopersistence of nine fibers was evaluated using an inhalation model. The fibers studied were compositions with different in vitro acellular solubility. The commercial and new glass wool fibers were essentially sodium borosilicates and the commercial and new stone wools were essentially calcium modified silicates. Fischer 344 male rats were exposed to a well-defined rat respirable aerosol (mean diameter of ∼1 μm) at a concentration of 30 mg/m3, 6 h/day for 5 days with postexposure sacrifices at 1 h, 1 day, 5 days, 4 wk, 13 wk, and 26 wk. At sacrifice, the whole lung was removed, weighed, and frozen at -20°C for subsequent digestion by low-temperature plasma ashing. The number and bivariate size distribution of the fibers in the aerosol and lung were determined. At 1 h following the last exposure, the 9 fibers were found to have lung burdens ranging from 7.4 to 33 ° 106 fibers/lung with geometric mean diameters (CMD) of 0.40–0.54 μm. The range of initial lung burdens was found to reflect the d...