THE REGIONAL LUNG DEPOSITION OF THORON PROGENY ATTACHED TO THE PARTICULAR PHASE OF ENVIRONMENTAL TOBACCO-SMOKE

A gamma emitting isotope of lead ((Pb-212), a decay product of thoron (Rn-220)), has been used to radiolabel the particulate phase of aged a nd diluted sidestream tobacco smoke in situ. The radiolabelled aerosol is suitable for studies with human volunteers and as a marker for lun g deposition and clearance of the attached fraction of thoron progeny, as well as environmental tobacco smoke (ETS) in a variety of environm ental situations. Total mean deposition values for nine male volunteer s varied from 22% to 59% under different breathing conditions, includi ng nasal as against mouth breathing. These data are higher than previo usly reported values for environmental tobacco smoke but are consisten t with models of particle deposition in the lung. Data for regional de position and clearance show deposition principally in the pulmonary re gion of the lung. Preliminary studies using radon (Rn-222) to determin e the degree of association of progeny in the presence of ambient part iculate or environmental tobacco smoke confirm that the degree of atta chment rises with increasing particle concentration, and is therefore likely to influence both the magnitude and site of deposition in the l ung. Assuming that the physical behaviour of radon and thoron progeny are the same with respect to attachment to particulate, the resulting data will allow better quantification of risk in existing models for r adon and thoron and their progeny in real-life situations.