Occupational Intakes of Radionuclides Part 1 - ICRP

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included, and bronchial and bronchiolar retention is represented by the BB’ and bb’
compartments, respectively. The three AI compartments of the original HRTM have
been replaced by the ALV compartment, from which particles either clear to the
ciliated airways or penetrate to the interstitium (the INT compartment). Particles clear
very slowly from the INT compartment to the lymph nodes.
Anterior
nasal
Nasooropharynx/
larynx
Bronchi
Bronchioles
Alveolar
interstitial
Extrathoracic
LNET
LNTH
Thoracic
0.001
ETseq
53
ET2
ET1
0.03
10
0.01
BBseq BB2 BB1
0.01
bbseq
0.00002
0.03
bb2
bb1
2
0.0001 0.001 0.02
AI3 AI2 AI1
1
100
Environment
GI tract
Figure 5. Compartment model representing time-dependent particle transport from each
respiratory tract region in the original HRTM. Rates shown alongside arrows are reference
values in units of d –1 . It was assumed that: (i) the AI deposit is divided between AI1, AI2 and
AI3 in the ratio 0.3:0.6:0.1; (ii) the fraction of the deposit in BB and bb that is cleared slowly
(BB2 and bb2) is 50% for particles of physical size 2.5 μm, and the fraction retained in the airway wall (BBseq and bbseq) is 0.7% at all sizes;
(iii) 0.05% of material deposited in region ET2 is retained in its wall (ETseq) and the rest in
T E which clears rapidly to the GI tract.
compartment 2