Bioassay/Internal Dose Assessment for Suspected Radionuclide Intakes

The extent of our involvement in this service varies. Often, we are the lead agency for both the bioassay measurements and when analytical results warrant it, the internal dose assessment as well. This has been the case with incidents involving workers who clean and repair intruments and gunsights containing tritium and laboratory technicians(15 males and 16 women) involved in handling P-32 labelled cytidine phosphate in a forensic DNA laboratory. Or, we may do the bioassay measurements for a suspected intake and collaborate with another agency in the dose assessment phase. This was the case in the internal contamination of a group of children who played with broken tritium lights that they found in a heliport in a northern Canadian town. And in still other cases, we may be asked to measure subsamples of urine specimens collected from contaminated individuals, as an audit of the bioassay results obtained by an in-house laboratory. This was our role in the well-publicized incident where a worker spiked the cooler water in a nuclear facility cafeteria with tritiated water, and in another incident where a service technician was exposed to organically bound tritium during maintainance work. Data from this incident is shown below.

Quality Audit of Tritium Bioassay Results

Sample	CNSC Bq/L	Bioassay Bq/L	Relative Bias (%) Based on NCRC/Bioassay
A	1.38E+09	1.428E+09	-3.4
B	9.40E+07	9.566E+07	-1.7
C	2.10E+07	2.283E+07	-8.0
D	3.30E+06	3.394E+06	-2.8
E	5.30E+06	5.533E+06	-4.2
F	1.00E+06	1.081E+06	-7.5

This table lists tritium results obtained by the CNSC on urine samples collected on six different days subsequent to tritium intake by a maintenance worker at a nuclear facility. Splits of the samples were sent to the NCRC's Bioassay Laboratories for QA purposes. Calculations, based on results obtained by the NCRC as the Reference Laboratory, gave the relative biases shown in the last column.

We may be requested for this service directly by the exposed individuals or the agencies they work for. We may also be approached to do this by the Canadian Nuclear Safety Commission (CNSC) when the bioassay measurements cannot be done by any other agency, on the strength of the Memorandum of Understanding (MOU) signed between the CNSC and Health Canada in 1995.

Our clients for this service may include nuclear energy workers (NEWs), workers who handle radioactive materials but are not technically classifed as NEWs, and members of the Canadian public such as the children mentioned above. Radionuclides measured have included:

• Tritium
• Carbon-14
• Phosphorus-32
• Cobalt-60
• Iodine-131
• Uranium