Deposition and Clearance of Glass Microballoons: Aerosols of Large Physical Size and Low Density

Abstract

spheres) so the bulk density is < 0.01 g ml 1 and a balloon of physical diameter 50 urn has an aerodynamic diameter of approximately 5 um. These considerations suggest that in the course of normal production and use there is a possibility that a proportion of the GMBs will be dispersed in air and their low aerodynamic diameter may result in penetration to the lower respiratory tract. The investigations reported here were primarily intended to determine whether any accumulation of such large particles could lead to the formation of agglomerates and consequent obstruction of the small airways. The investigations were conducted in rats because they are an accepted model for man and because the smaller size of the terminal airways in the rat would exacerbate any potential problem. Although the respirable limit for rats is a little below that for man (Snipes et al., 1989) the size range of the GMBs is such that a significant proportion is rat-respirable. MATERIALS AND METHODS GMBs were obtained from Nobel's Explosive Co. Ltd as a finely divided highly mobile powder. Male specific pathogen free Alpk:APfSD (Wistar derived) albino rats were obtained from the colony maintained by Zeneca Ltd at Alderley Park Cheshire U.K. Rats were maintained under standard laboratory conditions with food and water available ad libitum except during the exposures. Atmosphere generation was by a rotating table type of dust generator with air ejection. Powder is aspirated from a groove cut into a circular rotating table. The groove is replenished by a hopper and scraper system. Concentration is adjusted by changing the combination of size of groove, speed of rotation and air flow. Two experiments were performed. The first, of 4 h exposure duration, was designed to test the generation methods, to ensure that the integrity of the GMBs was retained and to determine whether the observed deposition pattern was as