Uptake of radioactive lead following inhalation and injection

Experiments have been made with human volunteers to determine the fate of 212Pb (ThB) after inhalation. Two subjects inhaled the activity as a submicron aerosol and one also inhaled it as a vapour. The two subjects also received injections of 212Pb in saline solution, so that the levels in blood following the two routes of entry could be compared. Measurements of the activity in excreta were also made. The activity was removed from the lung with a biological half-life of about ten hours. At 24 hours after inhalation about three-quarters of the particulate activity initially retained in the lung was found in the blood. The removal from blood to permanent sites of deposition and by excretion was comparatively slow. When a vapour of 212Pb was inhaled, however, there was substantial faecal excretion (37 per cent of the retained dose in 72 hours). This is attributed to activity deposited on the ciliated epithelium of the upper respiratory tract and subsequently brought up and swallowed.