Occupational Intakes of Radionuclides Part 1 - ICRP

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5.3.1 Routine Monitoring
DRAFT REPORT FOR CONSULTATION
(278) Routine monitoring programmes may involve only one type of measurement
or a combination of techniques, depending on the sensitivity that can be achieved. For
some radionuclides, only one measurement technique is practical, e.g. urine
monitoring for assessment of intakes of tritium. For radionuclides such as plutonium
isotopes that present difficulties for both measurement and interpretation, various
techniques may have to be employed. If different methods of adequate sensitivity are
available, the general order of preference (highest first) in terms of accuracy of
interpretation is:
body activity measurements;
excreta analysis;
exposure monitoring in the workplace.
(279) These techniques are, in general, complementary and not mutually exclusive.
For example, results of monitoring of the working environment (area monitoring) can
provide early indication of worker exposure, and can therefore be used to trigger
special bioassay monitoring, or they may provide information that assists in
interpreting the results of individual monitoring, e.g. information on airborne activity,
particle size, chemical form and solubility, and time of intake.
(280) Urine monitoring provides a measure of systemic uptake to organs and tissues
after inhalation and ingestion for those elements for which urine excretion rates are
sufficiently high. It can also be used to determine the fraction of activity deposited in
a wound site that transfers to the systemic circulation.
(281) Caution should be exercised in using urine monitoring for materials that are
absorbed relatively slowly from the respiratory tract (i.e. 'insoluble' materials). In
these circumstances, it is usually the lung dose that makes the greatest contribution to
effective dose, and uncertainties on the knowledge of the absorption characteristics of
the material can result in significant errors in assessed dose. For insoluble materials,
significant improvements in sensitivity can be achieved by using faecal monitoring in
addition to urine monitoring. This is because significant fractions of insoluble
material deposited in both the extrathoracic airways and the lungs are cleared via the
gastro-intestinal tract to faeces.
(282) Interpretation of faecal monitoring data needs to take account of a number of
factors that are specific to the faecal excretion pathway. Excretion of faeces is a
discrete process (even though it is usually modelled using first-order kinetics), and so
it is advisable to sum the amounts excreted over a 3-day period to obtain a daily
excretion rate.
(283) In the workplace, individuals may be exposed to a variety of radionuclides,
such as those that occur in fuel reprocessing or manufacturing plants. In such
circumstances it may be feasible to use a radionuclide that is readily detectable to
assess the potential for exposure to other radionuclides in the plant. For example
screening for 144 Ce could be used to assess the potential for exposure to actinides
(Doerfel et al, 2008).
(284) The results of workplace monitoring for air contamination may sometimes be
used to estimate individual intakes if individual monitoring is not feasible. However
the interpretation of the results of air sampling measurements in terms of intake is
subject to much greater uncertainty and bias.
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