Factors Affecting the DIL for Bioassay

DOE-STD-1121-98

workplace exposures, in stochastic DAC-h modified by a safety factor, that could lead to an HE,50 greater

than an IL. Internal dosimetry programs should establish DILs for each individual monitoring method

applied for the analysis of all radionuclides to which workers are likely to be exposed and document the

derivation of such DILs in the internal dosimetry technical basis documentation. The physical and

chemical characteristics of the radioactive material which may be taken into the body should be taken into

account in establishing DILs. If an internal dosimetry program chooses to use Reference Man (ICRP

Publications 23 and 30) default parameters in conjunction with modeling and assumptions recommended

in ICRP Publications 30 and 54 in deriving a DIL, these choices should be identified in the internal

dosimetry technical basis documentation. If one radionuclide is used as a tracer for a mixture of

radionuclides, the DIL should be based on the dose from the entire mixture, not just the tracer

radionuclide.

4.4.1 Factors Affecting the DIL for Bioassay

Factors such as significant clearance of a radionuclide in less than a year (e.g., tritium), the

frequency of bioassay monitoring, and the likelihood of multiple exposures during a year (or under

chronic intake conditions) should be considered in establishing a DIL. The DIL should be established so

that a committed effective dose equivalent of one IL from all intakes in a year is likely to be detected by

the monitoring program, i.e., the minimum detectable dose should be less than one IL. If a nonroutine or

an unexpected intake of a radionuclide or group of radionuclides occurs, the minimum detectable dose

may be calculated assuming a single intake that occurred on the date of the intake, if known, or the date

that would result in the largest committed effective dose equivalent. If intermittent or chronic intakes are

expected, the minimum detectable dose should be calculated assuming a chronic intake during the sample

period.

For nonroutine or unexpected intakes, the DIL for each independent radionuclide or group of

radionuclides ensures that a committed effective dose equivalent of not more than one IL would be missed

in the year from intakes of that radionuclide or group.

If it is known or is likely that an individual has or could have intakes during the year from different

sources that could result in doses above the IL, appropriately smaller DILs should be determined and the

basis for those DILs included in the internal dosimetry technical basis documentation.

4.4.2 Calculating the Derived Investigation Level for a Given Sample Frequency

The IDG states that an IL of 100 mrem (0.001 Sv) of committed effective dose equivalent from all

intakes occurring within a dosimetric calendar year should be used to establish DILs, and thus put an

upper limit on the MDA for measurements. The desired value of the MDA may be further reduced by the

need to confirm intakes by special follow-up bioassay: for rapidly clearing nuclides, a follow-up urine

sample will generally contain a lower concentration of analyte than the initial unexpectedly high sample,

but this lower concentration must still be detectable.

There are at least two approaches to calculating DILs as a function of sampling frequency. One

acceptable alternative is to set a derived screening level based on an intake corresponding to some

fraction of the IL (e.g., HE,50 = 1/10 IL or 10 mrem for workers). The intent is to ensure that the reason

and conditions of the intake are understood and that multiple intakes whose total would lead to an HE,50

approaching the IL could not be missed. This derived screening level is for each intake, while the IL is

for all intakes in a year. This simple approach is acceptable for exposures to multiple independent

sources and is adequate for use by DOE sites.