Monitoring
for Intakes
Monitoring
for Intakes
How does radioactivity get into the body?
Since radioactivity is part of the world around us, we take it into our bodies
all of the time. One way is by inhalation, where radioactive material that
is suspended in the air is breathed into the lungs. Radioactive materials
become airborne just like dust and dirt. Heating, ventilation, and physical
movement serve to increase airborne concentrations in contaminated areas.
Another way is by ingestion, which is when radioactive materials are taken into the mouth and subsequently enter the digestive tract. Ingestion occurs when people eat, smoke, or drink in contaminated areas or with contaminated hands.
Other ways are through wounds and by direct absorption through the skin. However, absorption is only possible for a very few elements.
Are there limits on the amount of radioactivity that can be taken into
the body?
Just as there are regulatory limits on external radiation exposure, there
are also limits on the amount of radioactive materials you may take into
your body as a result of your work at a site that is licensed by the U. S.
Nuclear Regulatory Commission. These limits, which are above the radioactivity
we taken in on a daily basis by virtue of being alive, are typically known
as "Annual Limits on Intake".
How do I know if I have exceeded an Annual Limit on Intake?
There are basically two industry-standard methods for monitoring intakes
of radioactivity. These are direct bioassay (whole body counting), and indirect
bioassay (excretion analyses).
What is whole body counting?
Whole body counting is a colloquial term for the measurement of the penetrating
radiations emitted from radioactive materials that are contained in the human
body. This bioassay method can be used to determine the amount of radioactivity
present in the body at the time of measurement, but cannot directly determine
the amount that was present at some previous time. That quantity must be
inferred from the measured body content of the specific radioactive material,
followed by application of mathematical models which describe the behavior
of that material in the body.
What is indirect bioassay?
Indirect bioassay, or excretion analyses, refers to identifying and quantifying
radioactive materials that are excreted or removed from the body. Indirect
bioassay procedures are used routinely in radiation protection work to monitor
personnel for possible accidental intakes of radioactive materials.
After an intake has occurred by inhalation or ingestion, a portion of the radioactive material will be absorbed into the bloodstream and deposited in various body organs or tissues or excreted from the body. Therefore, by analyzing an individual's excreta, an indication of whether an intake has occurred can be obtained.
Examples of excreta that can be used for indirect bioassay include urine, feces, tissue, blood, fingernails, hair, teeth, saliva, sweat, and breath. However, for most routine internal radiation monitoring programs, urine bioassay, or urinalysis, is the methodology of choice.
Is urinalysis a sensitive monitoring method?
Yes, as time passes and the body begins to excrete radioactive materials
retained by various organs, standard indirect bioassay procedures can detect
the presence of smaller amounts of radionuclides than is possible by standard
whole body counting techniques. This difference in detection capability becomes
even greater when insoluble radioactive materials are involved.
How is urinalysis performed?
The actual procedures are specific for the type and form of radioactivity
being used in the work place. In general, however, one or more samples of
your urine are collected into a bottle, the bottle is sealed, and the sample
is shipped to a laboratory that performs radionuclide analysis.
Is the laboratory the same type as a medical laboratory?
No. A radioanalytical laboratory has no capability for performing the types
of procedures doctors or hospitals might order. Their equipment is only capable
of isolating and detecting radioactive atoms.
How will my sample be analyzed?
Again, the actual procedure is specific for the radioactivity in question.
One common method is to place the sample directly over a radiation detector
that is connected to a computer-based analyzer. This simple method is actually
quite sensitive and requires no sample preparation other than to measure
the total volume of the sample. Other methods generally require the sample
to be digested, mixed with certain chemicals, then poured through a device
that is designed to extract the radioactive element in question.
Where can I obtain technical information about urine bioassay?
The following articles and papers contain additional information on direct
and indirect bioassay:
Copyright © Integrated Environmental Management, Inc., 1997