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INHALATION EXPOSURE OF RATS TO LIBBY AMPHIBOLE (LA) AND AMOSITE ASBESTOS
Citation:
GAVETT, S. H., A. M. JARABEK, E. W. Tewksberry, E. Bermudez, V. A. Wong, E. A. Gross, G. A. Wilson, H. G. Wall, AND D. E. Dodd. INHALATION EXPOSURE OF RATS TO LIBBY AMPHIBOLE (LA) AND AMOSITE ASBESTOS. Presented at ASTM Johnson Conference, Burlington, VT, July 25 - 29, 2011.
Impact/Purpose:
Two week inhalation exposure to Libby amphibole causes equivalent or greater lung injury than a comparable concentration of amosite asbestos, in contrast to prior intratracheal instillation studies.
Description:
Inhalation toxicology studies are being conducted to inform the risk assessment ofLibby amphibole. The overall purpose of these studies is to compare the toxicity of inhaled Libby amphibole fibers to a positive control fiber sample (UICC amosite). A 2-week study was conducted to set exposure levels for a subsequent subchronic study. F344 rats were exposed nose-only to air (control), 3 concentrations of LA, or 1 concentration of amosite 6 hr/d, 5 d/wk, for 2 wk. Target and actual mean mass (mg/rrr') concentrations were: air (0, 0.077); low (0.5, 0.56), medium (3.5, 3.52), and high (25, 28.23) LA; and amosite (3.5, 3.67). One day after exposure, indicators of acute inflammation correlated well with exposure levels (e.g. neutrophils in bronchiolar lavage fluid: control 0.8%; low LA 2.1%; medium LA 10.5%; high LA 47.2%; and amosite 7.4%). Other indices of acute inflammation were significantly increased in the high LA group compared to control or amosite, while a few indices in the medium LA group were higher than in the amosite group at the same mass concentration. Four days after exposure, separate groups of rats were evaluated for trachea and lung histopathology. The medium LA group had minimal to moderate alveolar inflammation which was slightly more severe than in the amosite group. Tissue samples are being analyzed to determine bivariate fiber size distribution. The subchronic exposure study, using 3 concentrations of LA2007 and 1 concentration of UICC amosite, will evaluate toxicity, pathology, fiber dose and fiber recovery after a 3-month exposure, with necropsies up to 2 years after exposure. These studies complement ongoing intratracheal instillation toxicology studies comparing the effects of LA with other site-specific fiber samples. (This abstract does not represent US EPA policy).