Classification of Bioassay Measurements

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

5.3.1 Classification of Bioassay Measurements

Bioassay measurements can be classified according to the primary reason for their performance.

This is a useful practice for historically documenting why a worker participated in a bioassay program.

Numerous reasons for bioassay measurements may be defined for specific facilities; some suggested

common classifications are as follows:

Baseline measurements are used to establish a pre-exposure condition, either for a new

employee or as a result of a new work assignment. The RCS recommends baseline measurements

if workers are considered likely to receive intakes resulting in greater than 100-mrem CEDE. It is

a good practice to perform such measurements for newly hired employees, intra-company

transferees, or workers transferred from facilities where bioassay measurements may not have

been required. In addition, baseline measurements can verify workers' status for special work

assignments. For uranium bioassay, baseline measurements made before any occupational

exposure can be expected to yield no detectable results using current technology.

A special consideration is the evaluation of intakes that include natural materials such as uranium.

The sensitivity of urine sampling as a uranium bioassay tool is limited by the presence of

environmental levels of uranium, which is subject to some uncertainty in interpretation. Knowledge

of background level of uranium excretion is an important factor in analysis and interpretation of

urine or feces for uranium bioassay purposes. In ICRP Publication 23, model values for excretion of

uranium by Reference Man are given as 0.05 to 0.5 g/day in urine and 1.4 to 1.8 g/day in feces.

There are two distinct decisions to be made: whether a result differs from an analytical blank, and if

so, whether the amount detected is greater than what would be expected in a population that is not

occupationally exposed (Long et al. 1994). For example, the internal dosimetry program at Hanford

distinguishes between the environmental decision level LC and the analytical decision level DL

(Carbaugh et al. 1995) using inductively coupled plasma mass spectrometry (ICP/MS) to look for

the presence of 236U. Since the 236U isotope does not occur in nature, it is used as a flag to indicate

occupational exposure.

Exempting workers from baseline bioassay implies accepting any detectable results as likely

attributable to current occupational exposure. However, requiring baseline measurements can

potentially impact the schedule of short-term jobs; the time required to obtain a chest count and a

large-volume urine sample may add a day or two delay to entry procedures. Moreover, missing a

baseline for a long-term employee who will be placed on a routine bioassay program is not likely to

be as troublesome as not obtaining a baseline for a short-term worker who provides a termination

sample that shows detection of uranium after the worker has left the site and is difficult to reach for

follow-up.

Routine, or periodic, measurements are performed on a predetermined schedule (e.g., an

annual or quarterly frequency).

Special bioassay measurements are performed as follow-up to unusual routine results or

suspected intakes.

End of assignment or termination measurements are performed following completion of

specific work or at the time of termination of employment. The RCS (DOE 1999) recommends

that workers who participate in bioassay programs have appropriate termination measurements.

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