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Comparative Toxicology of Libby Amphibole and Naturally Occurring Asbestos
Citation:
Gavett, S. Comparative Toxicology of Libby Amphibole and Naturally Occurring Asbestos. Asbestos-Like Mineral Fibers in the Upper Midwest: Implications for Mining and Health, Duluth, MN, October 06 - 07, 2015.
Impact/Purpose:
Summary of recent studies: Comparative toxicology of Libby amphibole (LA) and site-specific naturally occurring asbestos (NOA) provides new insights on physical properties influencing health effects and mechanisms of asbestos-induced inflammation, fibrosis, and tumorigenesis.
Description:
Summary sentence: Comparative toxicology of Libby amphibole (LA) and site-specific naturally occurring asbestos (NOA) provides new insights on physical properties influencing health effects and mechanisms of asbestos-induced inflammation, fibrosis, and tumorigenesis.Introduction/Background: Fiber chemistry, length, aspect ratio, surface area and dose are critical factors determining mineral fiber-associated health effects including cancer and asbestosis. Residents of communities impacted by NOA have expressed concerns about health effects of exposure. To support risk assessment in EPA Regions, comparative acute and long-term toxicological effects of LA, amosite, and site-specific NOA were investigated. Methods: Health effects of LA and amosite asbestos were evaluated using in vitro epithelial cell cultures and in vivo exposures of rats by intratracheal (IT) instillation and inhalation. Effects were also examined after IT exposure of rats to LA and NOA samples, including Sumas Mountain, WA chrysotile (SM), El Dorado Hills, CA tremolite (ED), and Ontario ferroactinolite cleavage fragments (ON).Results: In vitro studies showed that fiber surface area and length are better predictors of inflammatory response to fibers than fiber mass or number. Intratracheal (IT) exposure studies in rats showed that long-fiber RTI amosite caused greater fibrotic effects than LA. Short-term and subchronic inhalation exposures of rats to LA or UICC amosite (similar in fiber size distribution) showed correlations of fiber length with deposited dose, inflammation and tumor formation. Persistent production of pro-inflammatory cytokines may mediate tumorigenicity. Exposure of rats to NOA with high proportions of particles and shorter fibers (ED, ON) caused acute inflammation, but longer fiber LA and SM caused greater long-term fibrosis, while only SM induced persistent effects on lung function.Conclusions: This research points to the need for careful consideration of fiber characteristics and dose metrics which best describe health effects of environmental asbestos.(This abstract does not represent U.S. EPA policy.)