In Vivo Monitoring cont'd

DOE-STD-1128-98

Large-volume urine samples are necessary for bioassay monitoring due to the very

small urinary excretion rates. Ideally, 24-hour total samples would be preferred;

however, such samples often impose substantial inconvenience on workers, resulting

in noncompliance with the instructions. As an alternative, total samples can be

simulated by either time-collection protocols or volume normalization techniques.

One method of time-collection simulation (NCRP, 1987b; Sula et al., 1991) is to

collect all urine voided from 1 hour before going to bed at night until 1 hour after

rising in the morning for two consecutive nights. This technique has been reviewed

with regard to uranium by Medley et al. (1994) and found to underestimate daily

urine excretion by about 14%. Such a finding is not unexpected, since the time span

defined by the protocol is likely to be about 18 to 22 hours for most people.

The volume normalization technique typically normalizes whatever volume is

collected to the ICRP Reference Man daily urine excretion volume of 1400 mL.

Reference Woman excretion (1000 mL/d) may be used for gender-specific programs.

As a matter of practicality, routine monitoring programs do not usually use gender as

a basis of routine data interpretation, particularly since results are anticipated to be

nondetectable under normal conditions.

A third method calls for collection of a standard volume (e.g., 1 liter) irrespective of

the time over which the sample is obtained. This method uses the standard volume as

a screening tool only for routine monitoring. It does not attempt to relate measured

routine excretion to intake, relying on well-defined and timely supplemental special

bioassay to give true or simulated daily excretion rates.

The most common sample collection containers are 1-liter polyethylene bottles.

Although glass bottles are also used, they pose additional risks of breakage. Wide-

mouthed bottles are preferred for convenience and sanitation. The number of bottles

included in the kit should be appropriate to the protocol; for a total 24-hour protocol

as much as 3 liters can be expected. Special provisions, such as a funnel or transfer

cup, may improve the esthetics of sample collection and provide for added worker

Some concerns can exist with length of sample storage before analysis. Storage may

come from delays before batching samples in-house or due to transportation times to

an offsite laboratory. The longer a sample stands, the more chemical and biological

change it can undergo, typically manifesting itself as sedimentation and plateout on

container walls. While samples can be preserved by acidification or freezing, good

radiochemistry techniques should assure essentially complete recovery of any

plateout or sediment. Samples sent offsite for analysis can be preserved with acid, but

this method imposes hazardous material shipping requirements. Freezing samples can

preserve them, but plateout and sedimentation upon thawing should still be expected.

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