Plutonium Biokinetics in Human Body A. Luciani - Kit-Bibliothek - FZK

for three default classes, namely SR-0, SR-1 and SR-2, which characterize different solubility
and reactivity features of inhaled compounds.
The ICRP model describing the behaviour of ingested radionuclides is given in
Publication 30 [58]. It is composed of four compartments describing the kinetics in the
stomach, small intestine, upper large intestine and lower large intestine. The uptake into blood
takes place from the small intestine and is quantified by a transfer factor (even called gut
uptake factor), f 1, that specifies the fraction of activity in the small intestine transferred to
blood. Its value is related to the chemical properties of the ingested compounds.
For other routes of intake, such as absorption through the intact skin or wound, less
information is available. Thus no general model has been developed, although some attempts
for modelling a contamination via wound were made [59, 60].
Systemic models are also proposed by ICRP for modelling the metabolism of
radionuclides after the uptake into blood. These models are used in connection with the above
intake models in case of a contamination via inhalation or ingestion, but they are applied also
directly in case of a systemic contamination (e.g. by injection or skin contamination from
tritiated water). Specific models are given for each radionuclide or for groups of chemically
similar radionuclides. As the Plutonium kinetics is the main subject of this work, a detailed
description of the related ICRP systemic model is given in the last section of this first chapter.
1.3.3 MEASUREMENT TECHNIQUES
The individual monitoring for internal dosimetry purposes may be carried out by
means of body and organ activity measurements (named also in vivo or direct measurements),
bioassay measurements (named also in vitro or indirect measurements), environmental
sampling, or a combination of these techniques.
The choice of the suitable measurement technique depends on several factors such as
type and energy of emitted radiations, biokinetic behaviour of the contaminant taking into
account its retention/excretion and radioactive decay, sensitivity, availability and convenience
of the technique [55]. For some radionuclides, only one measurement technique may be
feasible, such as urine excreta analysis for a contamination with tritiated water, whereas for
other radionuclides a combination of techniques might be preferable if difficulties of
measurements and interpretation of data occur, as is the case with a Plutonium contamination.
When different methods of similar and adequate sensibility are available, the order of
preference with regard to the accuracy of dose assessment is: Direct measurements, indirect
measurements and environmental measurements [52]. The advantages of direct measurements
in comparison with indirect measurements are: More accurate determination of intake
activity; insoluble materials that are not excreted can be detected; fast execution; body or
organ activities can be determined without using metabolic models; the body contents of
multiple radionuclides can be determined simultaneously. On the other hand, the
disadvantages in comparison with indirect measurements are a higher detection limit, external
and not removable contamination cannot be discriminated by an internal contamination,
dedicated and often more expensive facilities are generally required [61]. Particular care
should be taken when environmental measurements, as air or surface contamination, are used
for a quantitative determination of intake. Air concentrations and above all surface
contamination measurements are often difficult to relate to intake; the former because the
suspended activity can significantly differ from the inhaled activity, particularly when it
results from the worker's own actions and movements; the latter because the resuspension
factors determining the fraction of activity released in air and then inhaled are hardly
determinable [62]. Thus, they should be used mainly to complement hard information about
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