Experimental inhalation of metallic silver

Dogs were tracheally intubated and exposed to airborne particles produced by exploding radioactive silver wires. The particles were agglomerates of spherical primaries and had activity median aerodynamic diameters near 0.5 mi. The deposition fraction in the respiratory tract was 0.17 ± 0.05; absolute deposition averaged about 1 mg/kg of body weight. Translocation and clearance of the deposited material was followed by external gamma ray detectors collimated to measure activity at several sites in each animal. Clearance data were analyzed into exponential components. The lung had biological clearance half lives of 1.7, 8.4 and 40 days accounting respectively for about 59, 39 and 2 % of the total amount deposited. Corresponding values for the liver were 9 (97 %) and 40 days (3 %). Excretion was predominantly fecal, the major portion of which was believed to have been secreted into the bile. Sacrifice measurements showed that the liver was a major site for the deposition of silver. Lung, brain and muscle also contained relatively large accumulations. Results showed that existing ICRP biological values for evaluating the hazards from radioactive silver are unreliable for inhalation. For example, considerably more silver (perhaps 90 % of that initially deposited in the lungs) was absorbed into the body for general internal distribution, than would be calculated from the ICRP figures.