Termination and Ending - Task Bioassay Participation

DOE-STD-1121-98

Some criteria for initiating special bioassay can be found in the RadCon Standard (DOE 1999e).

Typically, site technical basis documents or programmatic manuals provide additional guidance. The

criteria of Example 5.4 should be considered more as qualitative guidelines than quantitative

requirements. The decision to select any particular contamination level as a criterion for initiating special

bioassay is highly subjective. For example, a hot particle on a shoe cover would not necessarily warrant

special bioassay, even though the contamination level may exceed the alpha or beta/gamma

contamination level shown above. Likewise, a single spot of contamination on the side of the face would

be less likely to warrant special bioassay than substantially lower levels of contamination covering the

mouth and nose area. While it is certainly conservative to perform bioassay when any of the listed

criteria are exceeded, an excellent internal dosimetry program will factor in the unique aspects of each

occurrence and exercise good professional judgment in prescribing special bioassay.

There are potential pitfalls in relying on some indicators as a basis for not performing special

bioassay. For example, no detectable activity on nasal smears following a suspected inhalation does not

necessarily mean that no intake occurred - a worker who has nasal congestion or is a mouth breather

would not necessarily show activity detectable by nasal smears following an inhalation intake. Wounds

involving alpha-emitting nuclides need special attention because the contamination could be completely

shielded by overlying skin, tissue, blood, or serum moisture. Blood smears should be dried before

counting with an alpha detector.

In some cases, workplace detection methods can be adequate to moderate the need for immediate

bioassay measurements. For example, high-energy beta or photon emitters such as 90Sr, 137Cs, and 60Co

can be readily detected using portable Geiger-Mller (GM) survey meters. The typical sensitivity of such

instruments is sufficient to determine the relative severity of a potential intake by a wound. If

contamination is not detectable by these instruments at the time of the injury, then it is highly unlikely

that there is any significant wound intake. This knowledge can permit a more relaxed approach to special

bioassay, rather than precipitate a crisis response. Deciding the duration and extent of a special bioassay

program also calls for professional judgement. It should be recognized that early excreta bioassay

(collected earlier than 1 to 2 hours following the intake) will not necessarily reflect sufficient equilibrium

to allow an accurate assessment of intake. Urine collected earlier than 1 hour after intake is likely to

reflect the pre-intake condition. Likewise, feces voided within a few hours of an inhalation intake may be

too early to have permitted passage of radioactivity through the gastrointestinal (GI) tract. In vivo

measurements made shortly after intake may also reflect rapidly changing clearance. Residual external

contamination on an in vivo bioassay subject is sometimes a problem near the time of intake. Thus,

multiple bioassay measurements over several days following an intake provide a better tool for

quantifying the magnitude than a single sample. These may include longer term measurements at weeks,

months, and even years after an intake to accurately characterize the biokinetics and provide accurate

intake and dose assessments.

5.5 TERMINATION AND ENDING-TASK BIOASSAY PARTICIPATION

When a worker completes an assignment requiring routine bioassay, an ending-task bioassay

measurement is used to indicate the worker's status when the potential for further exposure has ended.

Ideally, this measurement should be made as soon as the work assignment is completed. If the

measurement is not made until employment is ended, then the measurement is actually an employment

termination measurement and documents the status of the worker when no further occupational exposure

under that employer will occur. Ideally, the termination measurement would be performed on the last day

of employment. The need for both ending-task and termination samples is a matter of company policy. If

ending-task measurements are performed and the cognizant radiation protection organization is confident