RETENTION AND CLEARANCE OF INHALED CERAMIC FIBERS IN RAT LUNGS AND DEVELOPMENT OF A DISSOLUTION MODEL

Male Wistar rats were exposed to aluminium silicate ceramic fibres by inhalation to study pulmonary deposition, clearance, and dissolution o f the fibres. Rats were killed at one day, one month, three months, an d six months after the termination of exposure, After exposure, fibres greater than 50 mu m in length were seen with a scanning electron mic roscope in the alveolar region of the lung. Fibres were recovered from the lungs with a low temperature ashing technique and their number, d iameter, and length were measured by scanning electron microscopy. The number of fibres remaining in the lungs declined exponentially with t ime after exposure and their silicon content also fell. The geometric median diameter of fibres decreased linearly with time. By six months after exposure, the surface of fibres recovered from the lungs had an eroded appearance. The results suggest that ceramic fibres are physica lly cleared from the lung and that they show signs of dissolution. Fin ally, the results were used to develop a theoretical model of fibre di ssolution that gives a satisfactory fit to the experimental data.