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Answer to Question #644 Submitted to "Ask the Experts"Category: Instrumentation and Measurements — Personnel Monitoring (PM) The following question was answered by an expert in the appropriate field: Q
We have a research division where personnel use up to 5 mCi (mostly 1 mCi) of 32P, 33P, and 35S. The personnel monitoring with TLD badges records mostly less than 200 µSv per year. They also use infrequently smaller quantities of 3H and 14C. We would like to discontinue the TLD service as the doses are less than 1mSv. However the staff feels that some sort of monitoring is required for internal doses. Since the quantities that are handled are so small, will any form of bioassay be meaningful? Are there any accepted methods of bioassay in this scenario? What will be the economic burden against any benefits? We spend about $7,000 for TLD monitoring of the research staff—an expenditure we would like to avoid. Has the Nuclear Regulatory Commission got any guidelines on these? Any help will be greatly appreciated.
A
Working with the radionuclides that you mentioned (3H, 14C, 35S, 32P, and 33P) and the quantities that are involved, there is no question that monitoring for "whole body" exposure is unnecessary. While I realize you are in Australia, the U.S. Nuclear Regulatory Commission (NRC) sets a requirement for monitoring for those individuals who are likely to exceed 10 percent of the annual limit for both external and internal exposure (10 CFR 20.1502 "Conditions Requiring Individual Monitoring of External and Internal Occupational Dose"). You should, however, consider the frequency of use and the actual "hands on" handling time for the 32P used by each researcher, as well as any shielding that is used (such as plexiglass or perspex vial shields) to reduce exposure to extremities. The requirement for extremity monitoring can be determined by evaluating the "typical" handling times and placing ring TLD dosimeters in the geometry that the vials/materials are held and determining a µSv-s (or mrem/mCi-min) dose delivered. You should also be aware that 32P directly on the skin can deliver a dose that can quickly exceed the NRC limits if not promptly removed from the skin. Dose due to 32P contamination of the skin cannot reliably be measured using extremity monitors and must be evaluated by direct monitoring with portable survey instruments and a program like VARSKIN. As far as internal/bioassay monitoring requirements are concerned, look at two regulatory guidance documents (8.9, 8.20, and 8.32) as well as determining whether it is likely that greater than 10 percent of an ALI (annual limit of intake) will be intaken in a given year for routine use. For the quantities involved that you describe, this magnitude of intake is highly unlikely for any of the radionuclides mentioned. So I would say that no bioassay is really necessary. Most labeled compounds are highly stable and nonvolatile, as is the case with 3H, 14C, 32P, and 33P labeled compounds used in biomedical research. Unless you are using very volatile compounds and hundreds of mCi on the open benchtop, bioassay will not be required. It is suggested that potentially volatile materials be used, or initially open the source vials, in a properly functioning chemical fume hood. Although you did not mention it, watch the use of 125I and 131I labelings and make sure that monitoring is done via thyroid count or air sampling and the labelling is conducted inside a chemical fume hood (I have referenced an NRC Regulatory Guide below). Some 35S labeled compounds and incubations of cell cultures with 35S produce some 35S volatile products like H2S and CH3SH. 35S has occasionally been detected in a urine bioassay taken in the first day post use for individuals opening stock vials, but the clearance is very rapid and intakes of significance are rare (the ALI for 35S vapor is 104 µCi). For accident situations or spills involving personnel contamination, a urine bioassay analyzed via liquid scintillation counting will be more than adequate. If you have an existing liquid scintillation counter (LSC) and some standard solutions, the economic impact upon your program will be minimal. The cost of a new LSC might be in the $30,000 to $40,000 range in the United States. Traceable standard solutions are available at approximately (U.S. dollars) $300 to $500 per radionuclide. Other recommended references that might be useful to you are: ICRP Publications
Information about obtaining these publications can be found at the International Commission on Radiological Protection website. NCRP Publications
Information to obtain these reports can be found at the National Council on Radiation Protection & Measurements Reports Web page. NRC Publications
NRC Regulatory Guides can be found online at the NRC's Division 8 - Occupational Health Web page. Radionuclide sources can be purchased from the following sources (I do not know what shipping overseas might be, if it is possible):
Shawn W. Googins, MS, CHP
Answer posted on 29 January 2001. The information and material posted on this website is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Website. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.
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