Environmental Engineering Reference
In-Depth Information
In current dosimetric models, the implicit assumption was made that epithelial cells on bronchial
airway surfaces will receive the same average dose. In contrast, Báláshazy and Hoffman (2000)
proposed that the target should be divided into two fractions:
1. The fraction of the surface without any particles being deposited there (i.e., the dose is
zero)
2. The remaining fraction, which may have many more particles deposited than indicated by
the average deposition density
Since it has been recently suggested that the number of multiple cellular hits may play a crucial
role in the extrapolation of lung cancer from occupational to domestic environments, maximum
enhancement factors may serve as a measure of the probability of multiple hits.
In spite of the fact that the nature of hits to lung cells from alpha particles and nanometer-sized
and ultraine particles is completely different, it is interesting to compare these numbers for a given
concentration (we can call “hits” for alpha particles and “touchdowns” for nanometer particles). The
number of hits from alpha particles of radon decay products is given in Tables 2-14 of BEIR VI 1999.
4.7 CONCLUSION
The main physical (dosimetric) characteristics related to the biological effect of aerosols are as
follows:
For radioactive aerosols (attached versus unattached),
1. Concentration (Bq/m
3
)
2. Exposure (Bq/m
3
) s
3. Dose (absorbed dose) (J/kg)
For nonradioactive aerosols,
1. Particle concentration (particle size distribution, PSD) (m
−3
)
2. Surface area concentration (m
−1
)
3. Mass concentration (g/m
3
)
4. Exposure (concentration multiplied by time)
5. Dose (number of particles, surface area, mass)
The concepts of dose for radioactive and nonradioactive aerosols are different. In the case of alpha,
beta, or gamma aerosols, we are talking about absorbed energy in the lung tissue at the target cells.
In the case of nonradioactive aerosols, dose represents the number of particles per mm
2
of the
lung surface, surface of the aerosol particle, or mass of the particles, depending on the range of
sizes. Special attention should be given to nanometer-sized particles and high deposition areas in
the lung. The main sources of uncertainty in the dose assessment are nonradioactive characteristics:
space and time distribution of aerosol concentration and PSD, especially differences in the breath-
ing and sampling site, changes in humidity and temperature inside the lungs, and unknown charac-
teristics of biokinetic processes.
REFERENCES
Báláshazy, I. and Hoffman, W., Quantiication of local deposition pattern of inhaled radon decay products in
human bronchial airway bifurcations,
Health Phys
., 78, 147-158, 2000.
Banse, D.F. et al., Particle counting eficiency of TSI CPC 3762,
J. Aerosol Sci
., 32, 157-161, 2001.
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