Chronic Inhalation Toxicity of Fibrous Glass in Rats

Abstract

Inhalation studies were conducted to determine the chronic biological effects in rodents of respirable fractions of fibrous glasses having compositions representative of commercial insulation products. Rats were exposed nose-only, 6 hrs/day, 5 days/week, for 24 months to several concentrations (3, 16 and 30 mg/m3) of fibrous glass (FG). Positive control rats were exposed to chrysotile asbestos (10 mg/m3) and negative controls to filtered air. At 3 to 6 month intervals, interim sacrifices took place to monitor progression of pulmonary changes and to analyze lung fiber burden. Lung fibrosis was evident within 3 months of initial exposure to chrysotile asbestos. Asbestos also induced an elevation in lung tumors and pleural mesotheliomas by the end of the study. Lung burdens of FG increased dramatically after 78 weeks of exposure in the 16 and 30 mg/m3 exposure groups. Further, FG exposure resulted in a dose-related increase in inflammation and an increase in lung weights at the highest concentration (30 mg/m3). These effects indicate that the lung clearance mechanisms were being impaired at the highest doses of FG and provide evidence that the maximum aerosol concentration (MAC) had been reached or exceeded at the highest dose. No lung fibrosis or mesotheliomas were observed in the FG exposed animals. When FG exposed groups were compared to negative controls, there was also no statistically significant increase in lung tumor incidence.