Research and Development

Health Canada's mandate is to maintain and improve the health of Canadians. In (National Calibration Reference Centre for Bioassay and In Vivo Monitoring (NCRC)'s area of responsibility, this mandate translates to:

1. being able to calculate as accurately as possible the doses resulting from radionuclide intakes and,
2. assessing the health effects of these intakes, so that intake levels can be lowered to appropriate levels and adverse health effects, minimized.

The factors that contribute most to the agreement of a dose estimate with the actual insult resulting from a radionuclide intake are two-fold:

1. Measurement results that are as accurate as state-of-the-art techniques and instrumentation will allow, and
2. Biokinetic models that mimic as closely as possible what actually happens to radionuclides in humans following intake and absorption.

Thus, our research and development activities include:

• projects for improving techniques for conducting measurements on which the dose calculations are based,
• studies on radionuclide metabolism and biokinetics,
• studies on the bioeffects of radionuclide ingestion (e.g., kidney bioeffects of long-term ingestion by humans of elevated levels of natural uranium in drinking water).

Methods Development:

The NCRC for Bioassay has an ongoing program for the improvement of techniques for the measurement of various radionuclides. Although the analysis of uranium in faecal samples has been developed by the NCRC, most of the techniques have been developed in urine samples, the matrix most commonly used for personnel monitoring in Canada. The thrust of this program is to improve both accuracy and precision of measurements at levels of internal contamination and resulting urine concentrations that are commonly encountered in routine monitoring as well as at regulatory trigger levels. Radionuclides studied include:

• Uranium
• Plutonium-239/240
• Americium-241
• Tritium
• Carbon-14
• Strontium-90
• Other Fission/Activation Products (Cs-137, Co-60, I-131, Mn-54)

These procedures have been documented and are available from the NCRC for Bioassay upon written request.

Representative Research Projects:

An in vitro study was conducted of the solubility of uranium dusts collected from Canadian mines and mills in simulated lung fluid. In addition to establishing the solubility of uranium compounds isolated at various stages of the uranium production process in a medium formulated to mimic the composition of lung fluid, this project also developed a technique useable in a small laboratory using a very simple set-up. Results obtained were in agreement with previous studies of the compounds, except perhaps for UO₃ which in our system behaved more like a Class D (or Type F) compound. This behaviour was found to be in agreement with results obtained by Stradling et al. in a subsequent rat study.

M. Limson Zamora, R. Falcomer and W. Hunt. (1988). In vitro dissolution characteristics of aerosols from uranium mills. Biological Assessment of Occupational Exposure to Actinides Workshop, Book of Abstracts, p.108, Versailles, France.

Quite often, principles applied in internal dosimetry are obtained from studies performed - for practical reasons - with laboratory animals. Knowledge thus obtained is then extrapolated to humans which may in certain circumstances, involve a leap of faith. Human studies, therefore, conducted when the opportunity presents itself can be very important in verifying the validity of extending the results of animal studies to the protection of human health. The human in vivo study of the effects on the kidney of long-term natural uranium ingestion in drinking water was undertaken by the NCRC for Bioassay for this very reason. The results of our study indicated that the kidney site most sensitive to uranium insult is the proximal tubule, the site where "optional reabsorption" of water and other small molecules such as electrolytes takes place, and which therefore plays a major regulatory role in the maintenance of water, acid-base and electrolyte balance, all of which are very essential to human health.

M. Limson Zamora, B.L. Tracy, J. M. Zielinski, D.P. Meyerhof and M.A. Moss. (1998). Chronic ingestion of uranium in drinking water: A study of kidney bioeffects in humans. Toxicological sciences, 43, 68-77.

 

 

 

 

 

 

 

 

 

A second human survey conducted with an aboriginal population was in agreement with the first study, and both support the results of animal studies. A report on the second study has been distributed among community members.

M. Limson Zamora, B.L. Tracy, J. M. Zielinski, R. Falcomer, K. Capello, G. Moodie, D.P. Meyerhof. (1998). Assessment of the effect on kidney function of long-term ingestion of uranium in drinking water by the Kitigan Zibi community: A report to the Medical Services Branch, Health Canada, on a study conducted by the Radiation Protection Bureau, Health Protection Branch.

An in vivo study was conducted of the gastrointestinal absorption rate, the f₁ factor for ingested uranium. Two groups were studied: a Canadian town where drinking water was obtained from deep wells and contained elevated levels of uranium, and an urban centre where the municipal system delivered water with uranium concentrations at background levels. The median value for the f₁ factor was found to be 0.009 while the 78 percentile value was 0.02. These data support the value for the uranium Gastrointestinal (GI) absorption rate (f₁ factor) recommended by International Commission for Radiological Protection (ICRP) 69 for adults and children 1 year old and older.

M. Limson Zamora, J. M.. Zielinski, D.P. Meyerhof , and B.L. Tracy (2002).
Gastrointestinal absorption of uranium in humans. Health Physics, 83(1): 35-45.