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Rick A. Rogers,¹ James M. Antonini,¹ Hjalmar Brismar,¹ Jean Lai,¹ Thomas W. Hesterberg,² Eben H. Oldmixon,¹ Philippe Thevenaz,³ and Joseph D. Brain¹

¹Department of Environmental Health, Harvard School of Public Health, Boston, MA 02115 USA
²Johns Manville International, Denver, CO 80162 USA
³Research Consulting Company Ltd., Füllinsdorf, Switzerland

Abstract

Hamsters breathed, nose-only, for 13 weeks, 5 days/week, 6 hr/day, either man-made vitreous fiber (MMVF) 10a, MMVF33, or long amosite asbestos at approximately 300 World Health Organization (WHO) fibers/cc or long amosite at 25 WHO fibers/cc. [World Health Organization fibers are longer than 5 µm and thicker than 3 µm, with aspect ratio >3.] After sacrifice, fiber burden was estimated (left lungs) by ashing and scanning electron microscopy (ashing/SEM) or (right middle lobes) by confocal laser scanning microscopy (CLSM) in situ. In situ CLSM also provided three-dimensional views of fibers retained, undisturbed, in lung tissue. Fibers of each type were lodged in alveoli and small airways, especially at airway bifurcations, and were seen fully or partly engulfed by alveolar macrophages. Amosite fibers penetrated into and through alveolar septa. Length densities of fibers in parenchyma (total length of fiber per unit volume of lung) were estimated stereologically from fiber transsections counted on two-dimensional optical sections and were 30.5, 25.3, 20.0, and 81.6 mm/mm³ for MMVF10a, MMVF33, and low- and high-dose amosite, respectively. Lengths of individual fibers were measured in three dimensions by tracking individual fibers through series of optical sections. Length distributions of amosite fibers aerosolized, but before inhalation versus after retention in the lung were similar, whether determined by ashing/SEM or in situ CLSM. In contrast, the fraction of short MMVF10a and MMVF33 fibers increased and the geometric mean fiber lengths of both MMVFs decreased by approximately 60% during retention. Most likely due to fiber deposition pattern and differences in sampling, fiber burdens [MMVF10a, MMVF33, and amosite (high dose ; 269 WHO fibers/cc) ] determined by ashing/SEM were 1.4, 1.5, and 3.5 times greater, respectively, than those calculated from in situ CLSM data. In situ CLSM is able to provide detailed information about the anatomic sites of fiber retention and also fiber lengths and burdens in good agreement with ashing/SEM results. Key words: aerosol, amosite asbestos, ashing, confocal microscopy, fiber burden, man-made fibers, MMVF, respirable, three-dimensional. Environ Health Perspect 107:367-375 (1999) . [Online 26 March 1999]

http://ehpnet1.niehs.nih.gov/docs/1999/107p367-375rogers/ abstract.html

Address correspondence to R.A. Rogers, Department of Environmental Health, Building I, Room 1315, Harvard School of Public Health, 665 Huntington Avenue, Boston, MA 02115 USA.

We express our thanks for the expert technical support of Bruce A. Ekstein, Emily Sullivan, Kafi Meadows, Jenny Roberts, Michael Roberts, and Karl Mink for assistance in quantitative confocal microscopic analysis. We also wish to thank William C. Miiller of Johns Manville Technical Center for providing ashing/SEM data. This work was supported by HL453510, HL33009, the North American Insulation Manufacturers Association, NIEHS-ES00002, and NIOSH-109979.

Received 13 October 1998 ; accepted 14 January 1999.