Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
intermediate phase were about 18% ILD after slow inhalation and 6% ILD after
normal inhalation. Deposition in the BB, bb and AI regions calculated using three
different models showed good agreement with, on average, 17%, 63% and 18% ILD,
respectively, after slow inhalation and 30%, 26% and 43% after normal inhalation.
Thus, there was a strong correlation between predicted bronchiolar deposition and the
amount cleared in the intermediate phase, suggesting that the intermediate phase was
associated with about 25% of particles deposited in the bronchioles.
(108) Svartengren et al (2001) found very similar retention in each subject when 6
µm dae particles were inhaled as a shallow bolus and by slow inhalation on separate
occasions. One interpretation was that slow clearance is a characteristic of the
bronchioles, and the pattern of deposition was very similar, even though the
techniques were so different, a view supported by complementary deposition
modelling. However, the possibility could not be excluded that the deposition patterns
were different, with more bronchial deposition following bolus inhalation than
following slow inhalation, and as assumed in the HRTM, slow clearance occurring to
a similar extent in both large and small airways.
(109) Philipson et al (2000) investigated the effect of dp directly by administering
particles with the same dae, and hence the same lung deposition pattern, but different
densities and so different values of dp (dae ≈ dp√ρ where ρ is the particle density).
Volunteers inhaled 6 µm dae particles of polystyrene (PSL, density 1.05 g cm –3 ) and
Teflon (density 2.13 g cm –3 ). The geometric diameter, dp, of the Teflon was smaller
(4.5 µm) than that of the PSL (6.1 µm), and the HRTM predicts fs to be greater (14%
versus 5%). However, retention of the two particles was similar in each subject.
(110) Smith et al (2007, 2008) tested these alternative hypotheses more critically,
also administering two particles of the same dae, but with a greater difference in
densities, and as shallow boluses to minimise alveolar deposition. In one study,
volunteers inhaled 5 µm dae PSL and gold (ρ = 19.3 g cm –3 ) particles; corresponding
dp values were 5 and 1.2 μm and values of fs were about 10% and 50%, respectively.
Hence, according to the HRTM, lung retention of the gold should have been much
greater than that of the PSL. However, no significant difference was observed
between them in any subject. In another study, 8 µm dae PSL and gold particles were
used and broadly similar results were obtained.
(111) These results are thus inconsistent with the dependence of fs on dp assumed in
the HRTM. However, the apparent discrepancy with the results of the bolus
experiments on which the Publication 66 assumptions were based has not been
resolved. A possible explanation may be that the inferred dependence on dp was
fortuitous. It was based mainly on measurements made with relatively large particles
(dp or dae > 4 µm), and there were relatively few such measurements available at the
time.
(112) Another recent study showed inconsistencies with the original HRTM's
assumptions on slow particle clearance from the bronchial tree. Gregoratto et al
(2010), in analysing alveolar retention in the study by Philipson et al (1996) (see
below), observed that there was far less lung clearance between 7 and 50 days after
inhalation than predicted by the HRTM as a result of slow clearance from the BB and
bb regions, even assuming no clearance from the AI region over that period.
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