You are here:
Subchronic Inhalation Exposure of Rats to Libby Amphibole and Amosite Asbestos: Effects at 18 Months Post Exposure###
Citation:
Willson, G., D. Dodd, K. Roberts, H. Wall, AND S. Gavett. Subchronic Inhalation Exposure of Rats to Libby Amphibole and Amosite Asbestos: Effects at 18 Months Post Exposure###. Presented at Society of Toxicologic Pathology, Washington, DC, June 22 - 26, 2014.
Impact/Purpose:
The purpose of this study was to determine the pathologic effects of subchronic inhalation exposure to Libby amphibole exposure in rats, in order to assess the relative potency of this form of asbestos compared to other more common forms.
Description:
Increased asbestosis, lung cancer, and mesothelioma rates are evident after exposures to Libby amphibole (LA). To support dosimetry model development and compare potency, a subchronic nose-only inhalation study (6 hr/d, 5 d/wk, 13 wk) was conducted in male F344 rats. Rats were exposed to air (control), LA (LO, MED, HI; 1.01, 3.32, 10.06 mg/m3; 159, 693, 1522 fibers/cc), or amosite (AM; 3.34 mg/m3; 230 f/cc). Toxicity endpoints, pathology, and fiber burden evaluation were determined 18 mo post-exposure. Fiber exposure had no effect on survival. Mononuclear cell leukemia was the main cause of death prior to scheduled necropsy in all groups except the LA 3.3 group. BAL cell numbers, LDH, and protein in AM and LA groups were not statistically different from controls (n=8 rats/group), indicating resolution of earlier inflammation. Histopathology of the left lung, trachea, sternum, pleura, epididymis and testes, and gross tissue lesions was conducted on 50 rats/group. Alveolus inflammation, pleural fibrosis, lung interstitial fibrosis, and foreign bodies were noted in all fiber-exposed groups. A greater incidence of chronic tracheal inflammation was noted in the LA groups. Alveolar bronchiolar adenoma occurred in 2 rats in each of the AM, MED LA, and HI LA groups, and 1 alveolar bronchiolar carcinoma was observed in the HI LA group. No pleural mesotheliomas were observed in any group. In conclusion, both AM and LA induced dose-related lung fibrotic responses; tumor incidences were apparently increased but not beyond historical control ranges. (This abstract does not represent US EPA policy.)