Aerosol Dose - Aerosols: Measurement, Dosimetry, and Health Effects - page 75

4 Aerosol Dose
Lev S. Ruzer, Michael G. Apte, and Richard G. Sextro
CONTENTS
4.1 Introduction ............................................................................................................................ 75
4.2 Environmental Dosimetry ...................................................................................................... 76
4.3 Exposure and Dose Deinition................................................................................................ 78
4.4 Uncertainty in the Dose Assessment ...................................................................................... 79
4.5 Aerosol Concentration Standards ........................................................................................... 79
4.6 Nonuniformity of Deposition and Ultraine/Nanometer-Sized Particles ............................... 80
4.7 Conclusion .............................................................................................................................. 81
References........................................................................................................................................ 81
All substances are poisons,
there is none that is not a poison.
The right dose differentiates
a poison and a remedy.
Paraselsus (1493-1541)
4.1 INTRODUCTION
A well-deined pharmacokinetic relationship exists between chemicals administered orally, der-
mally, or intravenously and the quantity of substance delivered to the speciic target site. Certainly,
some variability in dose exists due to interindividual differences in metabolism and transport kinet-
ics, but it is relatively easy to deine the inal delivery of an agent to the target site. In the case of
aerosols, the understanding of this relationship is complicated for several reasons:
1. Aerosols are a complex medium consisting of particles in a very wide size range, with
diameters ranging from nanometers to tens of micrometers (4-5 orders of magnitude).
2. Diversity in particle size results in different mechanisms of interaction inside the three
main branches of the lung: the extrathoracic, tracheobronchial, and alveolar regions.
3. The particle size distribution is altered inside the lung due to changes in humidity and
temperature.
4. In each branch of the lung, the particle size distribution differs due to selective iltration.
5. Individual breathing characteristics and lung morphology vary widely.
6. The variability in clearance, translocation, and other biokinetic processes taking place
after aerosol delivery to the site of the lung must be considered.
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