Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
Table 3 Regional deposition of inhaled 5 μm AMAD aerosols in Reference Workers engaged
in light work (% of inhaled activity)
Region Deposition (%) a,b,c
Male
ET1 47.94
ET2 25.82
BB 1.78
bb 1.10
AI 5.32
Total 81.96
a
Reference values are given to a greater degree of precision than would be chosen to reflect
the certainty with which the average value of each parameter is known.
b The particles are assumed to have density 3.00 g cm –3 , and shape factor 1.5. The particle
aerodynamic diameters are assumed to be log-normally distributed with geometric standard
deviation, σg of approximately 2.50. (The value of σg is not a reference value, but is derived
from the corresponding Activity Median Thermodynamic Diameter, AMTD (ICRP, 1994a)).
c Light work is defined on the following basis: 2.5 h sitting, at which the amount inhaled is
0.54 m 3 h –1 ; and 5.5 h light exercise, at which the amount inhaled is 1.5 m 3 h –1 . For both
levels of activity all the inhaled air enters through the nose. The deposition fractions are
therefore volume-weighted average values for the two levels of activity given for normal
nose-breathing adult males sitting and at light exercise in Publication 66, Annex F (ICRP,
1994a). However, as described in the text, the fractions deposited in ET1 and ET2 from
Publication 66 were summed to give the total deposit in the ET airways, and partitioned 65%
to ET1 and 35% to ET2.
Gases and Vapours
(96) For radionuclides inhaled as aerosols, the HRTM assumes that total and
regional deposits in the respiratory tract are determined only by the size distribution of
the inhaled particles. The situation is different for gases and vapours, for which
deposition in the respiratory tract depends entirely on the chemical form. In this
context, deposition refers to how much of the material in the inhaled air remains in
the body after exhalation. Almost all inhaled gas molecules contact airway surfaces,
but usually return to the air unless they dissolve in, or react with, the surface lining.
The fraction of an inhaled gas or vapour that is deposited in each region thus depends
on its solubility and reactivity.
(97) As for particulate forms of radionuclides, default parameter values are
provided for use in the absence of more specific information. The general defaults for
gases and vapours are 100% total deposition in the respiratory tract (regional
deposition: 20% ET2, 10% BB, 20% bb and 50% AI) with Type F absorption (Section
3.2.3). This classification is somewhat different from that recommended in
Publication 66, but simpler to apply. In particular, it is assumed by default that there
is no deposition in ET1. The SR-0, -1, -2, classification described in Publication 66
was not found to be helpful and is not used here.
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