Occupational Intakes of Radionuclides Part 1 - ICRP

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DRAFT REPORT FOR CONSULTATION
measurements. The in vivo detection capability and minimum detection levels of in
vivo counting are strongly influenced by the presence of 40 K in the body.
(329) Excretion data from uranium and thorium series radionuclides may need
correction for dietary intakes. A ‘blank’ bioassay sample should be obtained from the
workers, prior to the commencement of work. When not possible, bioassay samples
from family members or from the population living in the same area should be taken
and analyzed, to allow natural or non-occupational intakes and occupational intakes to
be distinguished (Lipsztein et al, 2003; Lipsztein et al, 2001; Eckerman and Kerr,
1999). In cases of positive excreta results resulting from occupational exposures, the
background values should be subtracted from the monitoring results, before dose
calculations. This might not be simple, especially when dealing with faeces
monitoring results. Little et al (2007) describe a Bayesian method to identify a typical
excretion rate of uranium for each individual in the absence of occupational intakes.
(330) In addition it is important to evaluate the influence of radiopharmaceuticals
that may have been administered for diagnostic or therapeutic purposes.
(331) For long lived radionuclides, bioassay monitoring results might carry the
influence of intakes identified in preceding monitoring intervals. The retained activity
in the body from previous intakes should be taken into account.
6.3.6 Special monitoring situations
(332) In many situations exposure will be to a single radionuclide or a limited
number of radionuclides. For some elements, however, exposures may involve a
number of isotopes with different decay properties. Uranium and plutonium illustrate
the potential for exposure to complex mixtures. Various plutonium isotopes are
present in the nuclear industry. Studies have shown a significant difference in isotopic
behaviour of plutonium, due to differences in specific activity (Guilmette et al, 1992).
Workers exposed to uranium are always exposed to a mix of isotopes, in different
proportions depending on the enrichment level. Knowledge of the enrichment is
essential for the correct interpretation of bioassay monitoring results.
(333) Special considerations apply when direct bioassay measurements of
radioactive progeny are used to determine the body content of the parent radionuclide
(Section 3.2.3). Significant errors can arise if it is assumed that the progeny are
always in secular equilibrium. For example, the activity of 232 Th in the lungs can be
underestimated when determined from direct measurements of its 228 Ac, 212 Pb, 212 Bi
and 208 Tl progeny. Differences in lung retention among the measured element and the
radionuclide of concern contribute to the uncertainty of results. For the same reasons,
activity of 232 Th in the lungs can be underestimated when determined from
measurements of 220 Rn in breath.
(334) There are also situations when one radionuclide is used as a surrogate for
another, for example for in vivo bioassay monitoring. One example is the
determination of the level of internally deposited Pu in the lung which is often
estimated on the basis of 241 Am external monitoring of the chest. 241 Am generally
accompanies Pu in the work place or is produced in the body by decay of 241 Pu. This
procedure is often appropriate but depending on the solubility characteristics and
isotopic composition of the aerosols, the relative clearance rates from the lung might
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