Performance of a Portable Whole-Body Mouse Exposure System

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.

The authors thank Ali Hamade for technical assistance with the experimental studies and Susan Akhavan for administrative and editorial support. Research supported by U.S. EPA grant R827352 (to John Froines of the University of California Los Angeles), but not subjected to the agency's peer and policy review. Therefore, this report does not necessarily reflect the views of the agency, and no official endorsement should be inferred.