Determination of lung-to-blood absorption rates for lead and bismuth which are appropriate for radon progeny

The ICRP Publication 66 Human Respiratory Tract Model (HRTM) treats clearance as a competitive process between absorption into blood and particle transport to the gastrointestinal tract and lymphatics. The ICRP recommends default absorption rates for lead and bismuth in ICRP Publication 71 but states that the values are not appropriate for short-lived radon progeny. This paper describes an evaluation of published data from volunteer experiments to estimate the absorption half-times of lead and bismuth that are appropriate for short-lived radon progeny. The absorption half-time for lead was determined to be 10 ± 2 h, based on ²¹²Pb lung and blood retention data from several studies. The absorption half-time for bismuth was estimated to be about 13 h, based on ²¹²Bi urinary excretion data from one experiment and the ICRP biokinetic model for bismuth as a decay product of lead.