Bliss L. Tracy

Increased environmental gamma-ray dose rate during precipitation: a strong correlation with contributing air mass

It has long been observed that the environmental gamma-ray dose rate increases noticeably during precipitation intervals. This increase, due to the presence of radon progeny in the rain droplets (or snow flakes), can affect the reliability of the monitoring of artificial radioactivity and long term estimates of exposure to ambient natural radionuclides in surveillance network. Predicting the amplitude of the dose increase has been shown to be surprisingly challenging. In this work, standard air mass back trajectory analysis is used to show that the amplitude of the increase can be quantitatively linked to the history of the air mass where the precipitation is occurring. Furthermore, we show how back trajectory analysis, environmental gamma and rain data can be used to obtain estimations of relative radon emanation rates for locations far from the actual point of detection.

Assessment and Management of Residential Radon Health Risks: A Report from the Health Canada Radon Workshop

Epidemiologic studies of uranium miners and other underground miners have consistently shown miners exposed to high levels of radon to be at increased risk of lung cancer. More recently, concern has arisen about lung cancer risks among people exposed to lower levels of radon in homes. The current Canadian guideline for residential radon exposure was set in 1988 at 800 Bq/m3. Because of the accumulation of a considerable body of new scientific evidence on radon lung cancer risks since that time, Health Canada sponsored a workshop to review the current state-of-the-science on radon health risks. The specific objectives of the workshop were (1) to collect and assess scientific information relevant to setting national radon policy in Canada, and (2) to gather information on social, political, and operational considerations in setting national policy. The workshop, held on 3–4 March 2004, was attended by 38 invited scientists, regulators, and other stakeholders from Canada and the United States. The presentations on the first day dealt primarily with scientific issues. The combined analysis of North American residential radon and lung cancer studies was reviewed. The analysis confirmed a small but detectable increase in lung cancer risk at residential exposure levels. Current estimates suggest that radon in homes is responsible for approximately 10% of all lung cancer deaths in Canada, making radon the second leading cause of lung cancer after tobacco smoking. This was followed by a perspective from an UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation) working group on radon. There were two presentations on occupational exposures to radon and two presentations considered the possibility of radon as a causative factor for cardiovascular disease and for cancer in other organs besides the lung. The possible contribution of environmental tobacco smoke to lung cancers in nonsmokers was also considered. Areas for future research were identified. The second day was devoted to policy and operational issues. The presentations began with a perspective from the U.S. Environmental Protection Agency, followed by a history of radon policy development in Canada. Subsequent presentations dealt with the cost-effectiveness of radon mitigation, Canadian building codes and radon, and a summary of radon standards from around the world. Provincial representatives and a private consultant were given opportunities to present their viewpoints. A number of strategies for reducing residential radon exposure in Canada were recognized, including testing and mitigation of existing homes (on either a widespread or targeted basis) and changing the building code to require that radon mitigation devices be installed at the time a new home is constructed. The various elements of a comprehensive national radon policy were set forth. This workshop was sponsored by the Radiation Protection Bureau of Health Canada, and was held in collaboration with the McLaughlin Centre for Population Health Risk Assessment at the University of Ottawa. We are grateful to Anar Baweja, Barry Hauck, Sonia Johnson, Ed Korpach, and Trevor Stocki for support in organizing and carrying out the workshop. Jack Cornett, Director of the Radiation Protection Bureau, is thanked for his support and encouragement to the workshop. Most of all, we thank all those who attended the workshop and shared their views.

Relative biological effectiveness (RBE) of 210 Po alpha-particles versus X-rays on lethality in bovine endothelial cells

Purpose : Alpha-radiation from polonium-210 (210 Po) can elevate background radiation dose by an order of magnitude in people consuming large quantities of meat and seafood, particularly caribou and reindeer. Because up to 50% of the ingested 210 Po body burden is initially found in the blood, a primary target for the short range alpha-particles is the endothelial cells lining the blood vessels. This study examined the relative biological effectiveness (RBE) of 210 Po alpha-particles versus 250 kVp X-rays in producing injury to cultured bovine aortic endothelial cells. Materials and methods : Radiation effects on cells were measured in four different ways: the percentage viable cells by trypan blue dye exclusion, the number of live cells, the lactate dehydrogenase (LDH) release to medium and the ability to form colonies (clonogenic survival). Results : Comparison of dose-response curves yielded RBE values of 13.1 ±2.5 (SEM) for cell viability, 10.3 ±1.0 for live cell number and 11.1 ±3.0 for LDH activity. The RBE values for clonogenic survival were 14.0 ±1.0 based on the ratio of the initial slopes of the dose-response curves and 13.1, 9.9 and 7.7 for 50, 10 and 1% survival rate, respectively. At X-ray doses <0.25 Gy, a pronounced stimulatory effect on proliferation was noted. Conclusions : Exposure to 210 Po alpha-particles was seven to 14 times more effective than X-ray exposure in causing endothelial cell damage.

Polonium-210: lessons learned from the contamination of individual Canadians

This paper describes the radioactive poisoning episode in London in 2006 and the Health Canada response to locate and test any Canadians who might have been contaminated by this event. The search strategies and testing methods are explained and the results given. The lessons learned are summarised and implications for vulnerable populations are discussed. The greatest public health impact was probably the generation of fear and concern, especially among those prone to health-related anxiety disorders. The groups of individuals at risk were effectively managed by a single point of contact system combined with rapid triage and counselling that was provided to everyone to address their individual concerns.

Radon control systems in existing and new construction: a review.

In support of the implementation of the new Canadian radon guideline, a comprehensive review of radon mitigation techniques used in countries around the world was undertaken, with particular emphasis on North America and Europe that have climates and construction techniques similar to Canada. The results of this review are presented here as an aid to administrators of radon control programmes, companies offering radon testing and mitigation services and other concerned parties, both in Canada and elsewhere, who are facing issues of implementing a radon control strategy. A wide variety of radon mitigation strategies have been employed worldwide and all have achieved some success in reducing radon concentrations. Generally, active mitigation techniques involving physical alterations to a house (e.g. sub-slab depressurisation) are more effective in achieving a sustained and substantial radon reduction than passive techniques (e.g. improved ventilation or sealing of cracks). To a large extent, the choice of an optimal mitigation strategy will depend on the building type, soil conditions and climate. Radon levels should be measured at periodic intervals after remediation, perhaps once every 5 y, to ensure that concentrations continue to remain at acceptable levels.

Relative biological effectiveness (RBE) of alpha radiation in cultured porcine aortic endothelial cells.

Purpose: Northern peoples can receive elevated radiation doses (1 – 10 mSv/y) from transfer of polonium-210 (210Po) through the lichen-caribou-human food chain. Ingested 210Po is primarily blood-borne and thus many of its short range alpha particles irradiate the endothelial cells lining the blood vessels. The relative biological effectiveness (RBE) of alpha particles vs. x-rays was examined in porcine aortic endothelial cells as a surrogate for understanding what might happen to human endothelial cells in northern populations consuming traditional foods. Materials and methods: Cultured porcine aortic endothelial cells were exposed to x-ray and 210Po alpha particle radiation. Alpha irradiation was applied to the cell cultures internally via the culture medium and externally, using thin-bottomed culture dishes. The results given here are based on the external irradiation method, which was found to be more reliable. Dose-response curves were compared for four lethal endpoints (cell viability, live cell fraction, release of lactate dehydrogenase [LDH] and clonogenic survival) to determine the relative biological effectiveness (RBE) of alpha radiation. Results: The alpha RBE for porcine cells varied from 1.6 – 21, depending on the endpoint: 21.2 ± 4.5 for cell viability, 12.9 ± 2.7 for decrease in live cell number, 5.3 ± 0.4 for LDH release to the medium but only 1.6 ± 0.1 for clonogenic survival. The low RBE of 1.6 was due to x-ray hypersensitivity of endothelial cells at low doses.

Uranium concentrations in air near a canadian uranium refinery

During 1981 and 1982 a project was undertaken to determine the possible health impact of airborne emissions from a Canadian uranium (U) refinery. High volume air samplers and dustfall collectors were located within 2 km of the refinery to obtain samples of U dust. Concentrations of U in air varied from 2 to 200 ng m−3 with a geometric mean of 20 ng m−3. Reasonable agreement was obtained between the measured concentrations and the predictions of a long-term atmospheric dispersion model. Measurements of particle sizes and deposition velocities of U-bearing dust indicated that its behaviour was typical of general urban dust. Thus standard dosimetric models could be used to estimate radiation doses. The dose to the nearest receptor from 1 year of refinery operation was estimated to be 0.16 millisieverts, and the collective dose to area residents was 0.14 person-sieverts. No observable health effects would be expected at these levels.

Model results of kidney burdens from uranium intakes.

Abstract— Uranium is a naturally occurring element, which is both radiologically and chemically toxic. When dealing with intakes of uranium, whether natural or depleted, chemical toxicity to the kidney usually predominates over radiological toxicity. This is especially true for uranium compounds in soluble (inhalation Type F) and moderately soluble (inhalation Type M) forms. To assess chemical toxicity, information on kidney burden per unit intake is required. This study summarizes the kidney burdens per unit intake for common exposures from uranium ingestion and inhalation. ICRP models developed for radiation dosimetry purposes can equally well be used to estimate kidney burdens from uranium intakes. While dosimetric quantities and data are tabulated in ICRP publications, data on uranium burdens in kidney are not explicitly given in these tabulations. In this work, the most recent ICRP models were utilized to generate a compilation of kidney burdens from common intakes. Calculations were made for four age groups from infant to adult. For all age groups, long-term chronic uranium ingestion will result in a kidney burden of 6.6% of daily uranium intake. Comparisons of kidney burdens due to acute ingestion and acute inhalation show that inhaled uranium compounds of Type F and Type M will generally result in higher burdens to kidney compared to the same amount of uranium compounds ingested.

Evaluating the radiological impact of uranium emissions in Port Hope, Ontario—A comparison of monitoring and modelling results

During 1988 and 1989, an environmental monitoring study was conducted to assess the possible health impact of airborne emissions from a Canadian uranium processing facility. Airborne U dust was collected using high-volume air samplers located within 2km of the facility. Weekly concentrations of U in air varied from the detection limit of 0.06 ng m−3 to 75.7ng m−3, with a geometric mean of 1.05ng m−3. Decreases in concentration during the summer facility slowdown period indicated that the observed levels of airborne U resulted primarily from processing operations, and not from the resuspension of previously emitted material. The committed inhalation dose to the nearest receptor from 1 year of facility operation was estimated to be 0.014 mSv. This was well below ICRP guidelines, and represented a small fraction of normal background radiation. No health effects would be expected at these levels. Results of the study were compared with the predictions of a longterm Gaussian dispersion model based on a hindcast approach to derive the best-fit emission rates. Predicted concentrations were generally within a factor of 2–3 of field observations. Discrepancies were due to inherent limitations of the model, uncertainties in the source emission characteristics, and variations between the long-term meteorological frequency distributions based on remote and local data.

A preliminary radon map for Canada according to health region

The recent publications of the combined analyses of residential radon studies in Europe and North America have shown that there is a significant risk of lung cancer at residential radon levels. In order to assess the population risk due to radon, the knowledge of the spatial distribution of indoor radon levels is essential. Here a preliminary radon map for Canada is presented, based on historical radon measurements collected in 6016 locations across Canada with the health region as the basic geographic units.