Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
Table 5. Original HRTM default absorption parameter values for Type F, M, and S
materials (based on Publication 66, ICRP 1994a, Table 18) a
Type
Model parameters:
F(fast) M (moderate) S (slow)
Initial dissolution rate (d -1 ) sp 100 10 0.1
Transformation rate (d -1 ) spt 0 90 100
Final dissolution rate (d -1 ) st - 0.005 0.0001
Fraction dissolved rapidly
Approximate dissolution rates:
fr 1 0.1 0.001
Rapid (d -1 )
Slow (d
sr 100 100 100
-1 ) ss - 0.005 0.0001
Fraction to bound state fb
Uptake rate from bound state (d
0 0 0
-1 ) sb - - -
a
The model values sp, spt and st in this table are the original HRTM reference values i.e., the
recommended default values for use in the model. No ‘bound’ state was assumed for default
Types.
(137) The original default values for Types F, M and S (ICRP, 1994a,b, Table 5)
were not based on reviews of experimental data but on comparison with particle
transport rates. The value of 100 d –1 for the rapid dissolution rate, sr, was chosen to
equal the particle clearance rate from the nose (ET2) to the throat. Hence for Type F
about half the material deposited in ET2 is absorbed into blood and the rest
swallowed. The slow dissolution rate for Type S of 10 –4 d –1 was chosen to equal the
slowest particle transport rate from the AI region to the GI tract, to ensure that there
was some long term lung retention. Type M values were chosen to be intermediate
between the two. It has, however, been recognised that the parameter values for
default Type F and Type S represent extremes of 'fast' and 'slow' dissolution rather
than being representative of these classes of materials.
Review of absorption characteristics of inhaled materials
(138) In developing the subsequent parts of this document, detailed reviews were
conducted of the absorption characteristics of inhaled materials relevant to
radiological protection. They are summarised in the inhalation sections of each
element.
(139) Where information was available, specific parameter values were derived
from experimental data from both in vivo and in vitro studies. As described below,
these provided a database to give guidance on selecting values that are representative
of materials that are generally considered to clear at 'fast', 'moderate' or 'slow' rates.
Values selected on that basis for default Type F, M and S have been adopted in the
revised HRTM used in this series of documents.
(140) Material-specific rates of absorption have been adopted in the element
sections (and dose coefficients and bioassay functions provided for them on the
accompanying CD-ROM) for a limited number of selected materials, i.e., those for
which:
There are in vivo data from which specific parameter values can be derived;
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