RELATIONSHIP BETWEEN LUNG BIOPERSISTENCE AND BIOLOGICAL EFFECTS OF MAN-MADE VITREOUS FIBERS AFTER CHRONIC INHALATION IN RATS

This article describes the relationship between fiber biopersistence a nd the chronic toxicity of different chemical compositions of man-made vitreous fibers (MMVF) in the lung. Rats were exposed in ''nose-only' ' inhalation chambers, 6 hr/day, 5 days/week, for 24 months to aerosol concentrations of 30 mg/m(3) containing comparable fiber numbers and similar dimensions of fibrous glass (FG) or refractory ceramic fiber ( RCF). Interim sacrifices were performed periodically to monitor fiber number and dimensions in the lung and the progression of pulmonary alt erations. At each interim sacrifice, three to six recovery animals wer e removed from each exposure group and held until two years to determi ne the biopersistence of fibers after different exposure times. Fibers were recovered from the ashed lungs, counted, and measured using opti cal and scanning electron microscopy (SEM). Fiber chemistry was assess ed in 91-week recovery lungs using energy dispersive spectroscopy (EDS ) analysis. RCF induced lung fibrosis and an elevation in lung tumors and pleural mesotheliomas. FG exposure resulted in no lung fibrosis, n o statistically significant increase in the lung tumor incidence, and no mesotheliomas. After two years of continuous exposure, the number o f World Wealth Organization fibers per milligram dry lung recovered fr om RCF and FG exposed lungs was comparable. EDS analysis of recovery l ungs showed that most of the alkalis and alkaline earths had leached f rom the FG fibers over time. A slight change in RCF chemistry was obse rved. These findings indicate that the change in the chemical composit ion of fibers may be an important determinant of the chronic toxicity of MMVFs.