Washington State University

Revised 3-02
Radiation Safety Office


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In order to ensure the health and safety of individuals working with certain radionuclides which may be taken into the body, the Radiation Safety Office (RSO) operates a bioassay program.

Bioassays permit the estimation of the radiation dose to the body from the concentration of internally-deposited radionuclides.

State regulations require all persons identified as participants in the bioassay program to receive baseline, routine, and termination bioassays. (WAC 246-221-100 and 246-221-015)

NOTE: Routine and termination bioassays must be conducted within the time intervals specified by the RSO in order to guarantee effectiveness. See below.


Persons working with specified quantities of radioisotopes 3H, 125I, and 131I must receive routine bioassays.

Any individual involved in an uptake of radiation regardless of isotope must receive a special (ingestion/inhalation) bioassay.


The RSO provides equipment, supplies, and trained personnel to conduct all required bioassays. The RSO arranges for any contracted bioassay service necessary to confirm analytical results or perform bioassays beyond the RSO's capabilities.

Each authorized user must ensure that required bioassays are both scheduled with the RSO and subsequently completed.


Radioiodine Bioassays

Each person handling more than 0.1 mCi (37 MBq) of radioiodine (125I or 131I) in volatile form in a calendar quarter must be included in an in vivo thyroid bioassay program conducted by the Radiation Safety Office.

Detailed requirements based on the form of radioiodine utilized are included in the table below.

(DoH Regulatory Guide 8.20-6 [Table 1])


Activity Handled in
Unsealed Form
Making Bioassay Necessary

Types of Operation


Bound to Nonvolatile Agent*

Processes in open room or bench, with possible escape of iodine from process vessels.

1 mCi

10 mCi

Processes with possible escape of iodine carried out within a fume hood of adequate design, face velocity, and performance reliability.

10 mCi

100 mCi

Processes carried out within gloveboxes, ordinarily closed, but with possible release of iodine from process and occasional exposure to contaminated box and box leakage.

100 mCi

1000 mCi

*Quantities may be considered the cumulative amount in process handled by a worker during a 3-month period; e.g., the total quantity introduced into a chemical or physical process over a 3-month period, or on one or more occasions in that period, by opening stock reagent containers from which radioactive iodine may escape. Quantities in the right-hand column may be used when it can be shown that activity in process is always chemically bound and processed in such a manner that 125I or 131I will remain in nonvolatile form and diluted to concentrations less than 0.1 mCi/mg of nonvolatile agent. Capsules (such as gelatin capsules given to patients for diagnostic tests) may be considered to contain the radioiodine in nonfree form, and bioassay would not be necessary unless a capsule were inadvertently opened (e.g., dropped and crushed). However, certain compounds where radioiodine is normally bound are known to release radioiodine when the material is in process, and the left-hand column may then be applicable. In those laboratories working only with 125I in radioimmunassay (RIA) kits, the quantities of 125I are very small and in less volatile forms; thus bioassay requirements may be judged from the right-hand column. In field operations, where reagent containers are opened outdoors for simple operations such as pouring liquid solutions, the above table does not apply; bioassay should be performed whenever an individual employee handles in open form (e.g., an open bottle or container) more than 50 mCi at any one time.
Operations involving the routine use of 125I or 131I in an open room or bench should be discouraged. Whenever practicable, sealed bottles or containers holding more than 0.1 mCi of 125I or 131I should be opened at least initially within hoods having adequate face velocities of 0.5 m/sec or more.

Each program participant must receive the following:

Conditions Under Which Bioassay is Necessary

Routine bioassay is necessary when an individual handles unsealed quantities of radioactive iodine that exceed 10 percent of those shown in the table above. The quantities shown in the table apply to both the quantity handled at any one time and to the cumulative amount handled over any 3-month period. (Based on DoH Regulatory Guide 8.20 (C) criteria.)

Except as stated above, bioassay is not required when process quantities handled by a worker are less than 10 percent of those in the table above. (DoH Regulatory Guide 8.20 (C))


Each person who has received a baseline bioassay must receive at least one measurement each calendar quarter. The measurement should be made several days after the radioiodine work but no later than the end of the calendar quarter.

Each person who directly handles more than 1 mCi (37 MBq) of radioiodine on any single occasion must have a thyroid bioassay measurement taken by the Radiation Safety Office within 6 to 72 hours of completion of the work.

Control Bioassays

Each laboratory having at least one person participating in the thyroid bioassay program must designate a control person. The control person is to work in the laboratory but not handle or use radioiodine.

The control person is required to have a thyroid bioassay during the 20-day window period between calendar quarters, i.e., December 21 through January 10, March 21 through April 10, June 20 through July 10, September 20 through October 10.


A bioassay is required for an individual involved in a radiation incident in which radioactive iodine may have entered the body or been internally deposited.

Tritium (3H) Bioassay

Detailed requirements for a tritium (3H) bioassay are set forth in the DoH Regulatory Guide 8.99. See the reprint of Regulatory Guide 8.99 below. The requirements described below were derived from that document.

Routine bioassays are conducted on a scheduled and repeatable basis. An individual submits urine specimens to the RSO for bioassay or reports to the RSO for in vivo measurements. Either radiochemical bioassay of urine or in vivo counting is acceptable for estimating internal radioactivity burdens or intakes.

The RSO may wish to corroborate estimates from urinalysis data with in vivo determinations. (DoH Regulatory Guide 8.20 (C))

Each person who works directly with more than 100 mCi (3.7 GBq) of 3H in a month must be included in a 3H bioassay program. (Users of tritium absorbed on metal foils must obtain a bioassay in any instances of overheating the metal foil.)

Users who are required to submit a urine sample for a tritium bioassay are to:

Baseline Bioassay

When 3H work is with a single large quantity (greater than 100 mCi (3.7 GBq)), a preuse baseline measurement is required.

When it appears that smaller uses of tritium will total more than 100 mCi (3.7 GBq) in a month, establish a preuse baseline and make a monthly measurement.

Routine Bioassay

Make the after-use measurement within two days after each use where more than 100 mCi (3.7 GBq) is handled.

Post-Operational Bioassay

Take a termination (post-operational) bioassay within one month of the last possible exposure to tritium.

Incident of Ingestion/Inhalation

An individual involved in a radiation incident in which tritium may have entered the body must receive a bioassay.


The Radiation Safety Office (RSO) reviews all authorizations for use of 125I, 131I, and 3H to determine which authorized users might possess these radioisotopes in quantities that could require bioassays. The RSO checks radioisotope possession limits to determine which authorized users hold activity levels suggesting a need for bioassays.

Whenever an incoming shipment of radioactive materials includes 125I, 131I, or 3H above a specified threshold activity level, the RSO issues a Bioassay Verification Report.

Receiving laboratory personnel are to list the actual prospective users of the materials on the form. The Radiation Safety Office uses the verification form information to ensure that the individuals received proper bioassays.

The Radiation Safety Office contacts applicable authorized users by both memorandum and followup telephone call to remind them of their responsibility to ensure appropriate bioassay measurement.


The Radiation Safety Office withholds delivery of radioactive material to a noncomplying authorized user until he or she meets the requirements in this section.

The Director of the Radiation Safety Office reports instances of noncompliance to the Chair of the Radiation Safety Committee.

The Chair refers the case to the committee for action. The committee may take the following actions:



"Orders requiring furnishing bioassay services" (WAC 402-24-080) (1) indicates that the department may incorporate into a license provision requiring a specific program of bioassay measurements as necessary or desirable to aid in determining the extent of an individual's exposure to concentrations of radioactive material.

This guide provides criteria acceptable to the department for the development and implementation of a bioassay program for any licensee handling or the selection of workers who should participate in a program to detect and measure possible internal radiation exposure. THE GUIDE IS PROGRAMMATIC IN NATURE AND DOES NOT DEAL WITH MEASUREMENT TECHNIQUES AND PROCEDURES.


The topics treated in this guide include determination of (1) whether bioassay should be performed, (2) frequencies of bioassay, (3) who should participate, (4) the actions to take based on bioassay results, and (5) the particular results that should initiate such actions.

For the user's convenience, the following terms are presented with their definitions as used in this guide:

Bioassay-The determination of the kind, quantity, or concentration of radioactive material in the human body by urinalysis.

Intake-The total quantity of radioactive material entering the body.


1. Conditions Requiring Bioassay

A. Routine Bioassay is required when quantities processed by an individual at any one time, or total amount processed per month, exceed those for the respective forms of tritium as shown in the attached Table I.

B. Above 0.1 of, but less than, the levels in Table I, routine bioassay is required unless a written justification is submitted for not performing bioassays.

C. Except as stated in 1.D below, bioassay is not required for process quantities less than 0.1 of those in Table I.

D. Special bioassay measurements should be performed to verify the effectiveness of respiratory protection devices and other protective clothing. If an individual wearing a respiratory protective device or protective clothing is subjected to a concentration of tritium in air (in any form) such that his or her intake with no protection would have exceeded that which would result from exposure for 0 hours per week for 13 weeks at uniform concentrations of tritium in air as specified in WAC 402-24-220(2), Appendix A, Table I,* Column 1, bioassays should be performed to determine the resulting actual tritium intake. These special bioassay procedures should also be conducted, for personnel wearing respirators, if for any reason the average tritium concentration in air and the duration of exposure are unknown.

2. Who Should Participate

All workers involved in the processing of tritium, under conditions specified in Section 1 above, or sufficiently close that intake is possible, should participate.

3. What Types of Bioassays Should Be Performed

A. Baseline. (Including pre-employment, or pre-operational urinalysis, not more than one month prior to beginning work with tritium requiring bioassay under 1 above.)

B. Routine Urinalysis

C. Post-operational. Within one month of last possible exposure to tritium.

D. Diagnostic. Within one week of any sample exceeding levels given as action points in Section 5 below. See 5.A.(2)(d).

4. How Often

A. Initial Routine Samples

Within 48 hours following entry of an individual into an area where operations require bioassay according to Section 1.A and B above, and then every two weeks or more frequently thereafter as long as the individual is working with tritium.

B. After 3 Months

The sampling frequency selected in accordance with Section 4.A above may be changed to quarterly if, after 3 months, the following three conditions are met:

(1) The average urinary tritium concentration from specimens obtained during the 3-month period does not exceed 3uCi/liter,

(2) Where measurements of the concentration of tritium in air are required as a condition of the license, the quarterly average concentration (uCi/ml) to which workers are exposed, multiplied by the factor 6.3 x 108 ml, does not exceed 0.8 mCi, and

(3) The working conditions during the 3-month period, with respect to the potential for tritium exposure, are representative of working conditions during the period in which a quarterly urinalysis frequency is employed, and there is no reasonable expectation that the criteria given in (1) and (2) above will be exceeded.

5. Action Points and Corresponding Actions

A. Bi-Weekly or More Frequent Sampling

(1) If urinary excretion rates exceed 5 uCi/liter, but are less than 50 uCi/liter, the following course of action should be taken:

(a) A survey of the operations involved, including air and area monitoring, should be carried out to determine the cause(s) of exposure and evaluate potential for further large exposures.

(b) Implement any reasonable corrective actions indicated in the survey that may lower the potential for further exposures.

(c) A repeat urine sample should be taken within one week of the previous sample and should be evaluated within a week after collection.

(d) Any evidence from (a) and (b) indicating that further work in the area might result in an employee receiving a dose commitment in excess of the limits established in 402-24-220(2) should serve as cause to remove the employee from work in this operation until the source of exposure is discovered and corrected.

(2) If urinary excretion rates exceed 50 uCi/liter, the following course of action should be taken:

(a) Carry out all steps in (1)(a) to (d) above.

(b) If the projected dose commitment exceeds 5 rems, report the incident to the department in accordance with WAC 402-24-190(3).

(c) Refer the case to appropriate medical/health physics consultation for recommendations regarding therapeutic procedures that may be carried out to accelerate removal of tritium from the body and reduce the dose as low as reasonably achievable.

(d) Carry out repeated sampling (urine collections of at least 100 ml each) at approximately one-week intervals, at least until samples show an excretion rate less than 5 uCi/liter. If the tritium is in a form that there is a possibility of longer-term tritium exposure to certain body organs, continue sampling as long as necessary to ensure that appreciable exposures to these organs do not go undetected.

B. Quarterly Sampling

Carry out actions at levels as indicated under 5.A above, and if the excretion rate continues to exceed 5 uCi/liter, also reinstitute bi-weekly (or more frequent) sampling for at least the next 6-month period, even when urinary excretion falls below 5 uCi/liter.

(1) WAC 402-24-080 was recodified as WAC 246-221-100, effective 1/31/91.

(2) WAC 402-24-220 was recodified as WAC 246-221-290, effective 1/31/91.

(3) WAC 402-24-190 was recodified as WAC 246-221-250, effective 1/31/91.

* Multiplying the concentration given in WAC 402-24-220 (2), Appendix A, 5 x 10-6 uCi/ml, by 6.3 x 108 ml gives the corresponding quarterly intake of tritium by inhalation. This is assumed equal to the uptake of tritium (as HTO) by absorption through the skin unless the form of tritium in the air can be demonstrated to have lower uptakes. The total uptake, including skin absorption, would be assumed to be about 6.3 mCi, which delivers a dose commitment of about 1.25 rems to standard man.


Table I.



HTO Form
(& forms other than those on right-hand cols)

HT or T2 Gas
in Sealed Process Vessels

Nucleotide Precursors

HTO Mixed with More Than 10 Kg of Inert H2O or Other Substances

Processes in Open Room or Bench, with Possible Escape of Tritium from Process Vessels

0.1 Ci

100 Ci

0.01 Ci

0.01 Ci/Kg

Processes with Possible Escape of Tritium, Carried Out Within a Fume Hood of Adequate Design, Face Velocity, and Performance Reliability

1 Ci

1000 Ci

0.1 Ci

0.1 Ci/Kg

Processes Carried Out with Gloveboxes, Ordinarily Closed, but with Possible Release of Tritium from Process and Occasional Exposure to Contaminated Box Leakage

10 Ci

10,000 Ci

1 Ci

1 Ci/Kg

Quantities present (<10 Kg) may be considered either the amount processed by an individual at any one time (when accidental intake is more likely), or the amount of activity entered into process (throughout) during any one month (when routine handling of repeated batches is the more likely source of exposure).
Concentrations in the right-hand column may be used when activity in process is always diluted in more than 10 Kg of other reagents, as in nuclear reactor coolant systems.