Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
other material deposited in BB and ET2 is cleared to the alimentary
tract by particle transport.
Type M: 20% absorbed with a half-time of ~6 hours and 80% with a half-time
of ~140 d. There is rapid absorption of ~20%, 5% and 0.5% of material
deposited in bb, BB and ET2, respectively. About 80% of the deposit in
AI eventually reaches body fluids.
Type S: 1% absorbed with a half-time of ~6 hours and 99% with a half-time of
~7000 d. There is rapid absorption of ~1%, 0.25% and 0.03% of
material deposited in bb, BB and ET2, respectively. About 30% of the
deposit in AI eventually reaches body fluids.
(156) For absorption Types F, M, and S, some the material deposited in ET1 is
removed by extrinsic means. Most of the material deposited in the respiratory tract
that is not absorbed is cleared to the alimentary tract by particle transport. The small
amounts transferred to lymph nodes continue to be absorbed into body fluids at the
same rate as in the respiratory tract.
Decay products formed in the respiratory tract
(157) Note that the following applies specifically to decay products formed in the
respiratory tract after inhalation of the parent radionuclide. Decay products formed
before inhalation and inhaled with the parent are generally treated as separate intakes,
and so each decay product is assumed to adopt the biokinetics appropriate to the
element of which it is an isotope. Many issues relating to the behaviour of decay
products in the respiratory tract arise in connection with the natural decay series,
which are therefore shown in Figures 10 (uranium-238 series), 11 (uranium-235
series) and 12 (thorium-232 series).
(158) Publication 66 (ICRP, 1994a, Paragraph 272) noted that it would be expected
that:
the rate at which a particle dissociates is determined by the particle matrix and
therefore the dissolution parameter values of the inhaled material would be
applied to decay products formed within particles in the respiratory tract
('shared kinetics');
decay products formed as noble gases, including radon, would be exceptions
because they would diffuse from the particles;
the behaviour of dissociated material would depend on its elemental form, and
so, for example, bound fraction parameter values for a decay product would
not be those of the parent ('independent kinetics').
(159) These points are considered in turn below. However, it should be noted that in
previous applications of the HRTM (e.g. Publications 68, 71, 72 and 78), with the
exception of noble gases, the absorption parameters of the parent were applied to all
members of the decay chain formed in the respiratory tract (shared kinetics). After
consideration (see below) the same approach is taken in this series of documents.
Retention in the particle matrix
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