In-vivo measurement of deposition and absorption of unattached radon progeny

Twenty-one volunteers were exposed in a radon chamber during well-controlled aerosol and radon progeny conditions, with predominantly unattached radon daughters (Po-218, Pb-214 and Bi-214). The activity of these radionuclides deposited in the respiratory tract was measured in-vivo after the exposures. The results of these measurements are in agreement with predictions calculated with the ICRP Publication 66 Human Respiratory Tract Model (HRTM). Temporal analysis of the activity deposited in the head of the volunteers leads to the conclusion that a significant amount of the deposited activity associated with particle diameters of about 1 nm is not subject to fast particle transport to the gastrointestinal tract as generally reported for larger aerosol particles. Measurements of radon progeny in blood samples of these volunteers yielded absorption half-times of 20 to 60 min. Former determinations, mainly performed with much larger aerosol particles of diameters between 100 and 1000 nm, derived absorption half-times around 10 h. This indicates that the absorption from ciliated airways into blood is dependent upon particle size and particle composition.