Abstract
A mobile whole-body exposure system was developed for exposing mice to concentrated ambient particulate matter smaller than 2.5 μm in mass median aerodynamic diameter (MMAD). Each 20-L exposure cage was designed to hold 9 mice within individual compartments. This allowed for transport and subsequent exposure. Airflow mixing and the potential for stagnant areas within the compartments were modeled using computational fluid dynamic modeling (CFD). CFD analysis showed no stagnant areas and good mixing throughout the exposure cage. The actual performance of the exposure system was determined for 0.5 to 2.0 μm diameter aerosols by measuring (1) uniformity of aerosol distribution and (2) particle deposition in the tracheobronchial and pulmonary regions of mice exposed in the system. A 0.6-μm MMAD (GSD = 2.0) cigarette smoke aerosol was used to experimentally measure the uniformity of aerosol distribution to the nine individual compartments. The average data from three runs showed no statistically significant difference among individual compartments. Particle deposition efficiency in adult male BALB/c mice was measured after exposure (30 min) in the system using monodisperse fluorescent polystyrene latex particles (0.5, 1, and 2 μm aerodynamic diameter). The measured deposition efficiency in this mobile exposure system for the combined tracheobronchial and pulmonary regions of the adult male BALBc mice was 21% for 0.5 μm, 11% for 1.0 μm, and 6.5% for 2.0 μm particles. These deposition efficiencies are similar to those reported for mice exposed in a nose-only exposure system, which indicates that particle losses to animal fur and exposure system surfaces were acceptable.
Highlights
The aerosol uniformity obtained in our study was not as good as that reported for nose-only exposure systems (Yeh et al, 1990; Cheng & Moss, 1995) or some large stationary wholebody exposure chambers (Moss et al, 1982; MacFarland, 1983; Cheng et al, 1989; Yeh et al, 1990); it is consistent with the values that have been reported for other large stationary whole-body exposure chambers (Schreck et al, 1981; MacFarland, 1983; Yeh et al, 1986; Cheng & Moss, 1995; O’Shaughnessy et al, 2003)
The aerosol uniformity of the mobile exposure system mean ±15% was judged acceptable since exposures occur 5 days/wk for 2 wk with mice randomly placed in individual compartments
The aerosol deposition efficiencies in BALB/c mice observed in our compact portable whole-body exposure system are similar to deposition efficiencies published by Raabe et al (1988) for a nose-only exposure system using a different strain of mice (CF1) (Figure 5)
Summary
The actual performance of the exposure system was determined for 0.5 to 2.0 μm diameter aerosols by measuring (1) uniformity of aerosol distribution and (2) particle deposition in the tracheobronchial and pulmonary regions of mice exposed in the system. The measured deposition efficiency in this mobile exposure system for the combined tracheobronchial and pulmonary regions of the adult male BALB/c mice was 21% for 0.5 μm, 11% for 1.0 μm, and 6.5% for 2.0 μm particles. These deposition efficiencies are similar to those reported for mice exposed in a nose-only exposure system, which indicates that particle losses to animal fur and exposure system surfaces were acceptable.
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