Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
had been assigned to Publication 30 inhalation Classes D, W, and Y were assigned to
HRTM absorption Types F, M, and S respectively. In the element sections of this
series of reports, information is reviewed on the lung clearance characteristics of
different chemical forms of each element, within the framework of the HRTM. The
opportunity has been taken to update some aspects of the HRTM in the light of
information that has become available since Publication 66 was issued, as
summarised in Section 1.5.2 above, and described in Section 3.2 below.
(86) For ingestion of radionuclides, the HATM (ICRP, 2006) is applied. The
model is also used for radionuclides in particles cleared to the throat from the
respiratory tract after inhalation. In the HATM, fractional absorption of radionuclides
is specified by the alimentary tract transfer factor, fA, instead of the f1 value as given
for the gastrointestinal tract (GIT) model described in Publication 30 (ICRP, 1979).
The fA value describes total absorption from all regions of the alimentary tract,
although the default assumption is that all absorption takes place in the small
intestine.
(87) ICRP has generally not given advice on assessing doses from intakes of
radionuclides transferred from wound sites to blood and other organs and tissues.
Internal exposure resulting from wounds almost always arises because of accidents in
the workplace, rather than as a result of routine operations that are subject to the
normal environmental controls. Uptake from wounds can vary greatly depending on
the circumstances of a particular incident and in practice the assessment of internal
contamination is treated on a case-by-case basis. As a result, provision of generic dose
coefficients or bioassay data would be of limited value. Information on the transfer of
radionuclides from wound sites has, however, been reviewed by a Scientific
Committee of NCRP and these data have been used to develop a model to describe
the transfer of material from wounds after intakes in different physico-chemical forms
(NCRP, 2007). Section 3.4 summarises the main features of the NCRP model, since
this information may be of use in the prospective assessment of doses and the
interpretation of bioassay data for individual cases of wound contamination.
(88) For each route of intake, a proportion of the radionuclide entering the body is
absorbed to blood and distributed systemically. The systemic distribution of
radionuclides in the body can be diffuse and relatively homogeneous, as for the
examples of tritiated water and radioisotopes of potassium and caesium, or may be
localised in certain organs or tissues, as for the examples of radioisotopes of iodine
(thyroid), alkaline earth elements (bone), and plutonium (bone and liver). Systemic
biokinetic models are used to describe the distribution and excretion of radionuclides
absorbed to blood. The systemic models for the elements have been reviewed and
revised as necessary to take account of more recent information and provide models
that are appropriate for both dosimetry and bioassay interpretation.
(89) Removal of deposited material from the body occurs principally by urinary
and faecal excretion although radionuclides may also be lost by exhalation or through
the skin (e.g. tritiated water (HTO)). Urinary excretion is the removal in urine of
radionuclides from blood following filtration by the kidneys. Faecal excretion has two
components: systemic (endogenous) faecal excretion which represents removal of
systemic material via the alimentary tract, due to biliary secretion from the liver and
secretions at other sites along the alimentary tract; and direct (exogenous) faecal
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