Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
Figure 16 137 Cs Wound, Particle Category; predicted values (Bq per Bq intake) following
acute intake.
(206) The presence of wounds, abrasions, burns or other pathological damage to the
skin may greatly increase the ability of radioactive materials to reach subcutaneous
tissues and thence the blood and systemic circulation. Although much of the material
deposited at a wound site may be retained at the site, and can be surgically excised,
soluble (transportable) material can be transferred to the blood and hence to other
parts of the body.
(207) As noted in Section 3.1, the assessment of internal contamination resulting
from wounds is in practice treated on a case-by-case basis using expert judgement. In
many cases, the amount of a radionuclide transferred from a wound site to blood may
be assessed directly from urine bioassay data. No dosimetric models are
recommended by ICRP for calculating doses from radionuclides transferred from
wound sites to blood and to other organs and tissues, and no dose coefficients are
given.
3.5 Biokinetic Models for Systemic Radionuclides
3.5.1 General patterns of behaviour of systemic radionuclides
(208) Radionuclides entering blood may distribute nearly uniformly throughout the
body (e.g., 3 H as tritiated water), they may selectively deposit in a particular organ
(e.g. 131 I in the thyroid), or they may show elevated uptake in a few different organs
(e.g., 239 Pu or 241 Am in liver and bone). If a radionuclide that enters blood is an
isotope of an essential element (e.g., 45 Ca or 55 Fe), it is expected to follow the normal
metabolic pathways for that element. If it is chemically similar to an essential element
(e.g., 137 Cs as a chemical analogue of potassium, and 90 Sr as a chemical analogue of
calcium), it may follow the movement of the essential element in a qualitative manner
but may show different rates of transfer across membranes. The behaviour of a
radioisotope of a non-essential element after its uptake to blood (e.g., 106 Ru, 125 Sb,
232 239 241
Th, Pu, or Am) depends on such factors as the extent to which it can be
sequestered by the reticuloendothelial (RE) system, its affinity for specific biological
ligands, its filterability by the kidneys, and the ability of the body to eliminate it in
liver bile or other secretions into the gastrointestinal tract. In some cases, the
biokinetics of an isotope of a non-essential element may resemble that of an essential
element to some extent due to common affinities for some but not all components of
tissues and fluids. For example, the behaviour of plutonium in blood and liver is
related to that of iron due to an affinity of plutonium for certain proteins that transport
or store iron (e.g. transferrin), but as a whole the biokinetic behaviour of plutonium in
the body differs greatly from that of iron. Also, the behaviours of lead and uranium in
the skeleton bear some resemblance to that of calcium because these elements can
replace calcium to some extent in bone crystal, although the biokinetic behaviours of
lead and uranium in other parts of the body show greater differences compared with
calcium. Nevertheless, it is important to emphasise that the use of chemical or
biological anologues has its limits (Ansoborlo et al, 2006).
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