PULMONARY DEPOSITION AND CLEARANCE OF GLASS-FIBER IN RAT LUNGS AFTER LONG-TERM INHALATION

In this study Wistar male rats were exposed to glass fiber obtained by the disintegration of a binderless glass fiber filter, for 6 hr/day, 5 days/week for 12 months. The mass median aerodynamic diameter (MMAD) of the fiber, determined with an Andersen sampler, was 2.6 mu m. The count median diameter and length of the fibers measured by scanning electron microscopy (SEM) were 0.51 and 5.5 mu m, respectively. The daily average exposure fiber concentration was 2.2 +/- 0.6 mg/m(3). Some rats were sacrificed 24 hr after removal from the exposure chamber following the 12 months' exposure. Others were sacrificed 12 months after the end of exposure. The wet organ weights were recorded at the time of death and the silicon content of the lungs was determined by absorption spectrophotometry. After 12 months' exposure. the amount of glass fiber retained in the rat lungs was 1.49 mg, and after 12 months' clearance it was 0.61 mg. The biological half-life in a single exponential model was to be 8.7 months, much longer than the predicted Value of 1.5 months obtained in a previous experiment in which rats were exposed for 4 weeks to the same glass fiber.