Many parameters that influence aerosol deposition have been studied. To acknowledge the possibility of particle redistribution during a measured exposure period, the term retention is used to refer to the amount and distribution of particles in lungs at any time after an exposure to an aerosol. Even during a brief exposure to radon progeny (30 to 60 min), there may be loss and redistribution of deposited particles, especially in the large ciliated airways. Retention, but not deposition, is influenced by clearance and translocation. The distinction between retention (the amount of an aerosol present in the lungs at any time) and deposition (the initial attachment of suspended particles to a surface) should be kept in mind. In addition, many papers and books reviewing deposition and clearance processes are available (Altshuler et al., 1957 Hatch and Gross, 1964 Aharonson et al., 1976 Brain et al., 1977 Lippmann, 1977 Raabe et al., 1977 Brain and Valberg, 1979, 1985 Heyder et al., 1980 Lippmann et al., 1980 Clarke and Pavia, 1984 Stuart, 1984 Morén et al., 1985). Published symposia serve as excellent sources of information in this area, for example, the First (Oxford), Second (Cambridge), Third (London), Fourth (Edinburgh), Fifth (Cardiff), and Sixth (Cambridge) International Symposia on Inhaled Particles (Davies, 1961, 1964 Walton, 1971, 1977, 1982 Dodgson and McCallum, 1988). Many aspects of the deposition of aerosols in mammalian lungs have captured the energy and imagination of many investigators, and only a brief summary is provided here. The impact of changes in breathing pattern and the effects of chronic lung disease on particle retention are also discussed in this chapter. Such factors as metabolic rate, breathing pattern, and lung structure determine the deposition of radon progeny and may differ among individuals. Thus, even if the inspired concentration of radon progeny were similar, the dose deposited in the lungs may vary. However, exposure-dose relationships can vary in different individuals (e.g., children versus adults). The chapter also discusses approaches that can be used to describe the amount and distribution of doses and, finally, some factors that are known to influence the amount and distribution of retained aerosols.Ī major goal of this chapter is to understand and predict differences in response to similar concentrations of inhaled radon progeny among different groups. This chapter summarizes aerosol deposition and clearance mechanisms and discusses how both of these influence the amount of alpha energy from radon progeny delivered to target sites. Since exposure does not equal absorbed dose, it is important to describe adequately the variables that determine exposure-dose relationships. Although epidemiological and animal studies provide information on the risks of lung cancer in relation to exposure, linkage of exposure to dose is essential for extrapolating the risk from the mining to the indoor environment.
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