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:

• Toohey, R. E., Palmer, H. E., Anderson, L., Berger, C. D., Cohen, N., Eisele, G., Wachholz, B., and Burr, W., “Current Status of Whole Body Counting as a Means to Detect and Quantify Previous Exposures to Radioactive Materials”, Health Physics, Vol. 60, Sup. 1, pp. 7-42, 1991.
• “Performance Criteria for Radiobioassay”, American National Standards Institute, Report No. ANSI N13.30, 1987.
• “American National Standard for Internal Dosimetry for Mixed Fission and Activation Products”, American National Standards Institute, Report No. ANSI N343, 1978.
• “Use of Bioassay Procedures for Assessment of Internal Radionuclide Deposition”, National Commission on Radiation Protection and Measurements, NCRP Report No. 87, 1987.