Variation in RBE for Survival of V79-4 Cells as a Function of Alpha-Particle (Helium Ion) Energy.

High linear energy transfer (LET) α particles are important with respect to the carcinogenic risk associated with human exposure to ionizing radiation, most notably to radon and its progeny. Additionally, the potential use of alpha-particle-emitting radionuclides in radiotherapy is increasingly being explored. Within the body the emitted alpha particles slow down, traversing a number of cells with a range of energies and therefore with varying efficiencies at inducing biological response. The LET of the particle typically rises from between ~70-90 keV µm(-1) at the start of the track (depending on initial energy) to a peak of ~237 keV µm(-1) towards the end of the track, before falling again at the very end of its range. To investigate the variation in biological response with incident energy, a plutonium-238 alpha-particle irradiator was calibrated to enable studies with incident energies ranging from 4.0 MeV down to 1.1 MeV. The variation in clonogenic survival of V79-4 cells was determined as a function of incident energy, along with the relative variation in the initial yields of DNA double-strand breaks (DSB) measured using the FAR assay. The clonogenic survival data also extends previously published data obtained at the Medical Research Council (MRC), Harwell using the same cells irradiated with helium ions, with energies ranging from 34.9 MeV to 5.85 MeV. These studies were performed in conjunction with cell morphology measurements on live cells enabling the determination of absorbed dose and calculation of the average LET in the cell. The results show an increase in relative biological effectiveness (RBE) for cell inactivation with decreasing helium ion energy (increasing LET), reaching a maximum for incident energies of ~3.2 MeV and corresponding average LET of 131 keV µm(-1), above which the RBE is observed to fall at lower energies (higher LETs). The effectiveness of single alpha-particle traversals (relevant to low-dose exposure) at inducing cell inactivation was observed to increase with decreasing energy to a peak of ~68% survival probability for incident energies of ~1.8 MeV (average LET of 190 keV µm(-1)) producing ~0.39 lethal lesions per track. However, the efficiency of a single traversal will also vary significantly with cell morphology and angle of incidence, as well as cell type.

Managing children during a radiological or nuclear emergency--Canadian perspectives.

Children have a higher chance of being contaminated by radioactive materials during a radiological or nuclear (RN) emergency. They are more sensitive to radiation health effects and suffer more significant psychosocial impacts than adults during emergency response. This paper presents a summary of recommendations on effective management of children during an RN emergency. These recommendations intend to be additional considerations for existing RN response protocols and procedures implemented at local, state/provincial, or national level.

Radon emanation in Saskatchewan soils.

Saskatchewan prairie soils in central Canada were studied from areas where many homes are known to exceed the Health Canada indoor radon guideline of 200 Bq m. This study sampled 32 soils from 11 sites, which varied in clay content and presence of bedrock materials. Soils were analyzed for (238)U, (226)Ra, (222)Rn in soil gas, bulk density, moisture, and particle size. Radon emanation from the soil samples varied from 10% to 43% and increased significantly with clay content with radon concentrations in soil gas of 18-38 kBq m(-3). Total uranium in soils was 2.1-4 ppm and 26-51 Bq kg(-1) dry weight for (238)U, (234)Th, and (226)Ra. Homes built on soils with high clay content may be at greater risk of high radon levels, particularly when the soils are dry and cracked, enhancing their permeability to gases such as radon. One sample of coal bedrock, originating from Tertiary marine shales, was particularly high for total uranium (53 ppm), (238)U, (234)Th, and (226)Ra activities (68-1,303 Bq kg(-1)) with radon emanation up to 1,363 kBq m(-3).

Would children be adequately protected by existing intervention levels during a radionuclear emergency?

The question arises as to whether radiation standards and guidelines set for adults are sufficiently protective of children. To answer this question, published literature values have been used to calculate radiation doses to children and adults from external and internal exposure to a suite of 30 radionuclides commonly found in the environment. It was found that older children and adults face about the same degree of risk from external radiation exposures, although doses may be ∼30 % elevated for infants due to their smaller body size. Inhalation risks in children are to a large degree offset by lower breathing rates and it is only in the case of iodine isotopes that children are more at risk. Ingestion of contaminated food products is more complex. Isotopes of iodine and the bone-seeking elements strontium and radium can give radiation doses up to an order of magnitude higher than for adults.

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.

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.

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.

Determining the sample size required for a community radon survey.

Radon measurements in homes and other buildings have been included in various community health surveys often dealing with only a few hundred randomly sampled households. It would be interesting to know whether such a small sample size can adequately represent the radon distribution in a large community. An analysis of radon measurement data obtained from the Winnipeg case-control study with randomly sampled subsets of different sizes has showed that a sample size of one to several hundred can serve the survey purpose well.

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.

Radiocesium in caribou and reindeer in northern Canada, Alaska and Greenland from 1958 to 2000.

This study summarizes the spatial and temporal trends of fallout (137)Cs concentrations in caribou and reindeer (Rangifer tarandus ssp.), reported in various programs in Canada, Alaska and Greenland, over a 40-y period. During the 1960s, the highest (137)Cs concentrations (2000-3000Bqkg(-1) wet weight in muscle) were found in the large caribou herds of central northern Canada, with levels about 50% lower in Alaska and Greenland. Concentrations varied by up to a factor of 6 between spring and fall. Concentrations in reindeer were comparable to those in caribou from the same regions. The highest (137)Cs concentrations (750Bqkg(-1)) in the late 1980s were found in the Caniapiscau herd of central Québec. The contribution from the Chernobyl accident in 1986 was estimated from (134)Cs measurements to be 10-40% of the total (137)Cs. Present concentrations have declined to 200-300Bqkg(-1). The effective half-life (T(eff)) of (137)Cs in Canadian caribou herds was estimated to be about 6 y. The potential impact on the health of northern residents is discussed.

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/m(3). 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.

Model results of kidney burdens from uranium intakes.

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.