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Sumas Mountain chrysotile induces greater lung fibrosis in Fischer 344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite
Citation:
Cyphert, J., A. Nyska, R. Mahoney, M. Schladweiler, U. Kodavanti, AND S. Gavett. Sumas Mountain chrysotile induces greater lung fibrosis in Fischer 344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite. TOXICOLOGICAL SCIENCES. Society of Toxicology, RESTON, VA, 130(2):405-15, (2012).
Impact/Purpose:
Comparison of pulmonary toxicity of 4 samples of naturally occurring asbestos (NOA) fibers showed that Sumas Mountain chrysotile (SM) was more fibrogenic than Libby amphibole (LA), El Dorado Hills tremolite (ED) and Ontario ferroactinolite cleavage fragments (ON) in rats 3 months after exposure. The results suggest that environmental exposure to NOA in the absence of mining has the potential for adverse health effects and highlights the need for further study of more sites within the United States.
Description:
The physical properties of different types of asbestos may strongly affect health outcomes in exposed individuals. This study was designed to provide understanding of the comparative toxicity of naturally occurring asbestos (NOA) fibers including Libby amphibole (LA), Sumas Mountain chrysotile (SM), El Dorado tremolite (ED) and Ontario ferroactinolite cleavage fragments (ON). Rat-respirable fractions (PM2.5) were prepared by water elutriation. Surface area was greater for SM (64.1 m2/g) than all other samples (range: 14.1-16.2 m2/g), while mean lengths and aspect ratios for LA and SM were comparable and greater than ED and ON. Samples were delivered via a single intratracheal (IT) instillation at doses of 0.5 and 1.5 mg/rat. One day post-IT, low-dose NOA exposure resulted in a 3-4 fold increase in bronchoalveolar lavage fluid (BALF) cellularity compared to dispersion media (DM) controls, whereas high-dose exposure had a more severe effect on lung inflammation which varied by source. Although inducing less neutrophilic inflammation than ON and ED, exposure to either LA or SM resulted in a greater degree of acute lung injury. Three month post-IT, most BALF parameters had returned to control levels, while the development of fibrosis persisted and was greatest in SM-exposed rats (SM>LA>ON>ED). These data demonstrate that fiber length and higher aspect ratio are directly correlated with the severity of fibrosis and that, in the rat, exposure to SM is more fibrogenic than LA which suggests that there may be cause for concern for people at risk of being exposed to NOA from the Sumas Mountain landslide.