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Internal exposures - Bioassay
Bioassay measurements used for demonstrating the compliance
with the occupational dose limits should be conducted often enough to identify
any quantify potential exposure, during any year, are likely to
collectively exceed 0.1 times the ALI (Reg. Guide 8.9, 10CFR 20).
A bioassay is
required whenever personal contamination or injury caused by a contaminated
object occurs, or if airborne radioactivity may have been inhaled. Routine bioassays, at intervals determined by
the radionuclides used, are required from each user who handles more than certain threshold
quantities of dispersible radioactive materials.
A routine bioassay may be waived when appropriate surveys for
contamination, conducted during and after each use of radioactive material
according to recommended procedures, demonstrate that there was essentially no
exposure to unconfined, dispersible radioactive material and as authorized by the
A radiation user who
handles a cumulative quantity of radioactive materials in dispersible form of
less than 1 ALI per month, averaged over the bioassay interval, is unlikely to
experience an annual intake of 0.1 ALI and does not require routine
bioassays. If a worker is exposed to contamination exceeding the levels specified
under "Conditions Requiring Bioassays", however, a non-routine
bioassay will be required.
At ISU, a radiation user who handles a cumulative quantity of radioactive
materials in dispersible form of more than 1 ALI per month, averaged over the
bioassay interval, is considered to be potentially exposed to an annual intake
of more than 0.1 ALI. Such an individual must perform or obtain bioassays routinely unless the
records of contamination surveys of both the user and the RSO verify that there
was no exposure to unconfined radioactive materials exceeding the levels
who handle dispersible radioiodine compounds may be required to obtain in
vivo measurements of radioiodine in the thyroid, performed by the RSO, at
specified intervals. Individuals who
handle other radionuclides in dispersible forms may be required to perform
assays of radioactivity in urine on a routine basis to document the absence of
radioactivity in the body or to determine the magnitude of any exposure. Other types of assays may be utilized if, in
the judgment of the RSO, such assays
will meet the intent of this policy more effectively.
|Conditions requiring bioassay:
The optimum time for performing a
bioassay is within a few days after a potential exposure, and therefore each user will perform a screening
assay within a few days after handling any unusually large quantities, or after
performing any procedure involving a greater than usual opportunity for
exposure. Subsequent routine bioassays would not be required again until the
end of another full bioassay interval unless another unusual exposure situation
The Technical Safety Office will notify users when a bioassay is due
(upon delivery of the radioactive material), i.e. the expiration of the
bioassay interval, but it is the responsibility of the user to complete the
bioassay is required within 5 days for each individual having contamination of
the skin or hair exceeding 10 RCL.
bioassay is required within the normal bioassay interval for any individual
having skin or hair contamination exceeding 1 RCL.
bioassay is required within 5 days for each individual involved in a spill, or
other uncontrolled release, of >0.5 ALI of radioactive material outside of a
properly functioning fume hood or >5 ALI inside a hood.
bioassay is required within 5 days for each individual who was present in an
area during a time when removable contamination exceeding 100 RCL was present
on any readily accessible surface.
bioassay is required within the normal bioassay interval for each individual
who was present in an area during a time when removable contamination exceeding
10 RCL was present on any readily accessible surface.
bioassay is required within the normal bioassay interval for personnel who work
in laboratories that have >1 ALI of cumulative quantity handled, averaged
over the bioassay intervals. The determination of the cumulative quantity
handled will be based primarily on records of receipts and disposals of
radioactive materials, with adjustments for individual work assignments as
defined by the responsible user. Routine bioassays may be waived at the discretion of
the RSO if the records of contamination surveys of both the user and the
RSO verify that there was no exposure to unconfined radioactive materials
exceeding the levels specified above and no incidents of personal
contamination since the last bioassay. When mixtures of radionuclides are
present in the laboratory, the necessity of a bioassay will be based upon
a sum of the fractions evaluation.