The Regional Lung Deposition of Thoron Progeny Attached to the Particulate Phase of Environmental Tobacco Smoke

Abstract

A gamma emitting isotope of lead (212Pb), a decay product of thoron (220Rn), has been used to radiolabel the particulate phase of aged and diluted sidestream tobacco smoke in situ. The radiolabelled aerosol is suitable for studies with human volunteers and as a marker for lung deposition and clearance of the attached fraction of thoron progeny, as well as environmental tobacco smoke (ETS) in a variety of environmental situations. Total mean deposition values for nine male volunteers varied from 22% to 59% under different breathing conditions, including nasal as against mouth breathing. These data are higher than previously reported values for environmental tobacco smoke but are consistent with models of particle deposition in the lung. Data for regional deposition and clearance show deposition principally in the pulmonary region of the lung. Preliminary studies using radon (222Rn) to determine the degree of association of progeny in the presence of ambient particulate or environmental tobacco smoke confirm that the degree of attachment rises with increasing particle concentration, and is therefore likely to influence both the magnitude and site of deposition in the lung. 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 radon and thoron and their progeny in real-life situations.