Deposition and clearance of 212Pb in humans

Radiation exposure due to the inhalation of 212Pb has been identified as one of the major hazards encountered in the chemical processing of monazite. Volunteers were exposed to 212Pb in the thorium hydroxide storage facility. Personal air samplers were used to determine the concentration of 212Pb in air. The 212Pb in the chest was measured using a whole body counter and the decay in the chest was followed up for 24 h. From the decay, mean effective half-life for the inhaled 212Pb was estimated as 6.63 +/- 0.23 h. A comparison of the chest burden with the assumed intake indicates that 55-76% of the inhaled 212Pb is deposited in the respiratory system. From the chest monitoring data, it is possible to estimate the working level exposure due to thoron progeny.