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Kevin R. Smith,¹ Seongheon Kim,² Julian J. Recendez,¹ Stephen V. Teague,¹ Margaret G. Ménache,³ David E. Grubbs,⁴ Constantinos Sioutas,² and Kent E. Pinkerton¹

¹Center for Health and the Environment, University of California, Davis, California, USA; ²Civil and Environmental Engineering, University of Southern California, Los Angeles, California, USA; ³Department of Pediatrics, University of New Mexico, Albuquerque, New Mexico, USA; ⁴Department of Biology, College of Science and Mathematics, California State University, Fresno, California, USA

Abstract

Epidemiologic studies have shown that airborne particulate matter (PM) with a mass median aerodynamic diameter < 10 µm (PM₁₀) is associated with an increase in respiratory-related disease. However, there is a growing consensus that particles < 2.5 µm (PM_2.5) , including many in the ultrafine (< 0.1 µm) size range, may elicit greater adverse effects. PM is a complex mixture of organic and inorganic compounds ; however, those components or properties responsible for biologic effects on the respiratory system have yet to be determined. During the fall and winter of 2000-2001, healthy adult Sprague-Dawley rats were exposed in six separate experiments to filtered air or combined fine (PM_2.5) and ultrafine portions of ambient PM in Fresno, California, enhanced approximately 20-fold above outdoor levels. The intent of these studies was to determine if concentrated fine/ultrafine fractions of PM are cytotoxic and/or proinflammatory in the lungs of healthy adult rats. Exposures were for 4 hr/day for 3 consecutive days. The mean mass concentration of particles ranged from 190 to 847 µg/m³. PM was enriched primarily with ammonium nitrate, organic and elemental carbon, and metals. Viability of cells recovered by bronchoalveolar lavage (BAL) from rats exposed to concentrated PM was significantly decreased during 4 of 6 weeks, compared with rats exposed to filtered air (p < 0.05) . Total numbers of BAL cells were increased during 1 week, and neutrophil numbers were increased during 2 weeks. These observations strongly suggest exposure to enhanced concentrations of ambient fine/ultrafine particles in Fresno is associated with mild, but significant, cellular effects in the lungs of healthy adult rats. Key words: concentrated ambient particles, fine particles, particulate matter, pulmonary inflammation, ultrafine particles. Environ Health Perspect 111:902-908 (2003) .