The Deposition and Clearance of Radioactive Particles in the Human Lung

Volunteers inhaled monodisperse iron oxide particles tagged with /sup 198/Au or /sup 51/Cr. Clearance was determined by external monitoring. Rapid clearance in first day (50% of initial) was followed by an additional 10% lost the first week with slower rates after that. During the first day, there was rapid clearance in the first 2 to 4 hr followed by a second, slower phase lasting 10 to 18 hr. Larger particles (e.g., 5 ..mu..m) deposited higher in bronchial tree and were cleared more rapidly than smaller (e.g., 3 ..mu..m) particles. Total first day clearance is from bronchi, as increase in abdomen radioactivity indicates swallowing of cleared particles.