COHERE - strengthening cooperation within the Canadian government on radiation research

PURPOSE

Canadian Organization on Health Effects from Radiation Exposure (COHERE) is a government initiative to better understand biological and human health risks from ionizing radiation exposures relevant to occupational and environmental settings (<100 mGy, <6 mGy/h). It is currently a partnership between two federal agencies, Health Canada (HC) and the Canadian Nuclear Safety Commission (CNSC). COHERE's vision is to contribute knowledge to reduce scientific uncertainties from low dose and dose-rate exposures. COHERE will advance our understanding by bridging the knowledge gap between human health risks and linkages to molecular- and cellular-level responses to radiation. Research focuses on identifying sensitive, early, and key molecular events of relevance to risk assessment.

CONCLUSIONS

The initiative will address questions of relevance to better apprize Canadians, including radiation workers and members of the public and Indigenous peoples, on health risks from low dose radiation exposure and inform radiation protection frameworks at a national and international level. Furthermore, it will support global efforts to conduct collaborative undertakings and better coordinate research. Here, we describe a historical overview of the research conducted, the strategic research agenda that outlines the scientific framework, stakeholders, opportunities to harmonize internationally, and how research outcomes will better inform communication of risk to Canadians.

Is there a role for the adverse outcome pathway framework to support radiation protection?

PURPOSE

In 2012, the Organization for Economic Cooperation and Development (OECD) formally launched the Adverse Outcome Pathway (AOP) Programme. The AOP framework has the potential for predictive utility in identifying early biological endpoints linked to adverse effects. It uses the weight of correlative evidence to identify a minimal set of measurable key events that link molecular initiating events to an adverse outcome. AOPs have the capability to identify knowledge gaps and priority areas for future research based on relevance to an adverse outcome. In addition, AOPs can identify pathways that are common among multiple stressors, thereby allowing for the possibility of refined risk assessments based on co-exposure considerations. The AOP framework is increasingly being used in chemical and ecological risk assessment; however, its use in the development of radiation-specific pathways has yet to be fully explored. To bring awareness of the AOP framework to the Canadian radiation community, a workshop was held in Canada in June 2018 that brought together radiation experts from Health Canada, the Canadian Nuclear Laboratories, and the Canadian Nuclear Safety Commission.

METHODS

The purpose of the workshop was to share knowledge on the AOP framework, specifically (1) to introduce the concept of the AOP framework and its possible utility to Canadian radiation experts; (2) to provide examples on how it has advanced risk assessment; (3) to discuss an illustrative example specific to ionizing radiation; and lastly (4) to identify the broad benefits and challenges of the AOP framework to the radiation community.

RESULTS

The participants showed interest in the framework, case examples were described and areas of challenge were identified. Herein, we summarize the outcomes of the workshop.

CONCLUSIONS

Overall, participants agreed that by building AOPs in the radiation field, a network of data-sharing initiatives will enhance our interpretation of existing knowledge where current scientific evidence is minimal. They would provide new avenues to understand effects at low-dose and dose-rates and help to quantify the combined effect of multiple stressors on shared mechanistic pathways.

Evaluation of mean transit time of aerosols from the area of origin to the Arctic with 210Pb/210Po daily monitoring data

In this study, the activity concentrations of ²¹⁰Pb and ²¹⁰Po on the 22 daily air filter samples, collected at CTBT Yellowknife station from September 2015 to April 2016, were analysed. To estimate the time scale of atmospheric long-range transport aerosol bearing ²¹⁰Pb in the Arctic during winter, the mean transit time of aerosol bearing ²¹⁰Pb from its origin was determined based on the activity ratios of ²¹⁰Po/²¹⁰Pb and the parent-progeny decay/ingrowth equation. The activity ratios of ²¹⁰Po/²¹⁰Pb varied between 0.06 and 0.21 with a median value of 0.11. The aerosol mean transit time based the activity ratio of ²¹⁰Po/²¹⁰Pb suggests longer mean transit time of ²¹⁰Pb aerosols in winter (12 d) than in autumn (3.7 d) and spring (2.9 d). Four years ²¹⁰Pb and ²¹²Pb monitoring results and meteorological conditions at the Yellowknife station indicate that the ²¹²Pb activity is mostly of local origin, and that ²¹⁰Pb aerosol in wintertime are mainly from outside of the Arctic regions in common with other pollutants and sources contributing to the Arctic. The activity concentration ratios of ²¹⁰Pb and ²¹²Pb have a relatively constant value in summer with a significant peak observed in winter, centered in the month of February. Comparison of the ²¹⁰Pb/²¹²Pb activity ratios and the estimated mean ²¹⁰Pb transit time, the mean aerosol transit times were real reflection of the atmosphere transport characteristics, which can be used as a radio-chronometer for the transport of air masses to the Arctic region.

GHSI EMERGENCY RADIONUCLIDE BIOASSAY LABORATORY NETWORK - SUMMARY OF THE SECOND EXERCISE

The Global Health Security Initiative (GHSI) established a laboratory network within the GHSI community to develop collective surge capacity for radionuclide bioassay in response to a radiological or nuclear emergency as a means of enhancing response capability, health outcomes and community resilience. GHSI partners conducted an exercise in collaboration with the WHO Radiation Emergency Medical Preparedness and Assistance Network and the IAEA Response and Assistance Network, to test the participating laboratories (18) for their capabilities in in vitro assay of biological samples, using a urine sample spiked with multiple high-risk radionuclides (90Sr, 106Ru, 137Cs, and 239Pu). Laboratories were required to submit their reports within 72 h following receipt of the sample, using a pre-formatted template, on the procedures, methods and techniques used to identify and quantify the radionuclides in the sample, as well as the bioassay results with a 95% confidence interval. All of the participating laboratories identified and measured all or some of the radionuclides in the sample. However, gaps were identified in both the procedures used to assay multiple radionuclides in one sample, as well as in the methods or techniques used to assay specific radionuclides in urine. Two-third of the participating laboratories had difficulties in determining all the radionuclides in the sample. Results from this exercise indicate that challenges remain with respect to ensuring that results are delivered in a timely, consistent and reliable manner to support medical interventions. Laboratories within the networks are encouraged to work together to develop and maintain collective capabilities and capacity for emergency bioassay, which is an important component of radiation emergency response.

Activity concentration measurements of selected radionuclides in seals from Canadian Arctic

The activity concentrations of naturally occurring radionuclides (such as ²²⁶Ra, ²¹⁰Pb and ²¹⁰Po) and long lived ¹³⁷Cs were measured in a total of 119 tissue samples (43 blubber, 43 liver, and 33 muscle samples) from 40 ringed seals and 4 bearded seals collected in the Arviat area of Canada during the fall of 2014. Activity concentration of ²¹⁰Po was measured in all seal liver and muscle samples individually. The average ²¹⁰Po activity concentrations were 25 ± 7.6 Bq/kg fresh weight (fw) in muscle and 211 ± 58 Bq/kg fw in liver for ringed seals, and 20 ± 6.1 Bq/kg fw in muscle and 231 ± 150 Bq/kg fw in liver for bearded seals. Due to insufficient sample material for most samples collected, gamma counting for radioactive caesium and radiochemical analysis for ²²⁶Ra and ²¹⁰Pb were performed for pooled samples. Activity concentrations of ²¹⁰Pb and ²²⁶Ra were generally below detection limits. While ¹³⁴Cs activity concentration was not detectable, ¹³⁷Cs activity concentration was detected in muscle and liver samples. On average, the ¹³⁷Cs activity concentrations were 0.25 ± 0.05 and 0.12 ± 0.04 Bq/kg fw in muscle and liver samples of ringed seals, and 0.11 ± 0.02 and 0.10 ± 0.03 Bq/kg fw in muscle and liver samples of bearded seals, respectively. Neither ²¹⁰Po nor ¹³⁷Cs were detected in the blubber samples. This study confirmed that ²¹⁰Po is the dominant contributor to radiation doses resulting from seal consumption. Man-made contaminant ¹³⁷Cs only contributes less than 0.01% of the total ingestion dose obtained from Arviat seals.

GHSI EMERGENCY RADIONUCLIDE BIOASSAY LABORATORY NETWORK: SUMMARY OF A RECENT EXERCISE

The Global Health Security Initiative (GHSI) established a laboratory network within the GHSI community to develop their collective surge capacity for radionuclide bioassay in response to a radiological or nuclear emergency. A recent exercise was conducted to test the participating laboratories for their capabilities in screening and in vitro assay of biological samples, performing internal dose assessment and providing advice on medical intervention, if necessary, using a urine sample spiked with a single radionuclide, 241Am. The laboratories were required to submit their reports according to the exercise schedule and using pre-formatted templates. Generally, the participating laboratories were found to be capable with respect to rapidly screening samples for radionuclide contamination, measuring the radionuclide in the samples, assessing the intake and radiation dose, and providing advice on medical intervention. However, gaps in bioassay measurement and dose assessment have been identified. The network may take steps to ensure that procedures and practices within this network be harmonised and a follow-up exercise be organised on a larger scale, with potential participation of laboratories from the networks coordinated by the International Atomic Energy Agency and the World Health Organization.

A study on the effect of the internal exposure to (210)Po on the excretion of urinary proteins in rats

This study was designed to assess the feasibility of a noninvasive urine specimen for the detection of proteins as indicators of internal exposure to ionizing radiation. Three groups of rats (five in each group) were intravenously injected with 1601 ± 376, 10,846 ± 591 and 48,467 ± 2812 Bq of (210)Po in citrate form. A sham-exposed control group of five rats was intravenously injected with sterile physiological saline. Daily urine samples were collected over 4 days following injection. Purification and pre-concentration of urinary proteins were carried out by ultrafiltration using a 3000 Da molecular weight cutoff membrane filter. The concentration of common urinary proteins, namely albumin, alpha-1-acid glycoprotein, immunoglobulins IgA and IgG, was measured by an enzyme-linked immunosorbent assay. Urinary excretion of albumin decreased dose-dependently (p < 0.05) 96 h post-injection relative to the control group. In contrast, no statistically significant effects were observed for other proteins tested. The dose-dependent decrease in urinary excretion of albumin observed in this study underscores the need for further research, which may lead to the discovery of new biomarkers that would reflect the changes in the primary target organs for deposition of (210)Po.

A study on the levels of radioactivity in fish samples from the experimental lakes area in Ontario, Canada

To better understand background radiation levels in country foods, a total of 125 fish samples were collected from three lakes (Lake 226, Lake 302 and Lake 305) in the Experimental Lakes Area (ELA) in Ontario of Canada during the summer of 2014. Concentrations of naturally occurring radionuclides ((226)Ra, (210)Pb and (210)Po) as well as anthropogenic radionuclides ((134)Cs and (137)Cs) were measured. This study confirmed that (210)Po is the dominant contributor to radiation doses resulting from fish consumption. While concentrations of (210)Pb and (226)Ra were below conventional detection limits, (210)Po was measured in almost all fish samples collected from the ELA. The average concentration was about 1.5 Bq/kg fresh weight (fw). None of the fish samples analysed in this study contained any detectable levels of (134)Cs. An average (137)Cs level of 6.1 Bq/kg fw was observed in freshwater fishes harvested in the ELA, almost twice that of samples measured in the National Capital Region of Canada in 2014 and more than 20 times higher than the levels observed in marine fish harvested from the Canadian west coast in 2013 and 2014. However, it is important to note that the concentrations of (137)Cs in fish samples from these inland lakes are considered very low from a radiological protection perspective. The resulting radiation dose for people from fish consumption would be a very small fraction of the annual dose from exposure to natural background radiation in Canada. The results indicate that fishes from inland lakes do not pose a radiological health concern.

EURADOS intercomparison on emergency radiobioassay

Nine laboratories participated in an intercomparison exercise organised by the European Radiation Dosimetry Group (EURADOS) for emergency radiobioassay involving four high-risk radionuclides ((239)Pu, (241)Am, (90)Sr and (226)Ra). Diverse methods of analysis were used by the participating laboratories for the in vitro determination of each of the four radionuclides in urine samples. Almost all the methods used are sensitive enough to meet the requirements for emergency radiobioassay derived for this project in reference to the Clinical Decision Guide introduced by the NCRP. Results from most of the methods meet the requirements of ISO 28218 on accuracy in terms of relative bias and relative precision. However, some technical gaps have been identified. For example, some laboratories do not have the ability to assay samples containing (226)Ra, and sample turnaround time would be expected to be much shorter than that reported by many laboratories, as timely results for internal contamination and early decisions on medical intervention are highly desired. Participating laboratories are expected to learn from each other on the methods used to improve the interoperability among these laboratories.

Radon exhalation from sub-slab aggregate used in home construction in Canada

Exposure to elevated levels of radon in homes has been shown to result in an increased risk of developing lung cancer. The two largest contributors to indoor radon are radon in soil gas, formed from the rocks and soil surrounding the home, and building materials such as aggregate. This study measured the surface radon exhalation rates for 35 aggregate samples collected from producers across Canada. The radon exhalation rates ranged from 2.3 to 479.9 Bq m(-2) d(-1), with a mean of 80.7±112 Bq m(-2) d(-1). Using a simple, conservative analysis, the aggregate contribution to radon concentrations in an unfinished basement was determined. The maximum estimated radon concentration was 32.5±2.7 Bq m(-3), or ~16 % of the Canadian Radon Guideline. It can be concluded that under normal conditions radon exhalation from aggregate contributes very little to the total radon concentration in indoor air.

Excretion of volatile ¹³¹I from rats following administration of Na¹³¹I or MIBG-¹³¹I

Current practice for radiation protection associated with (131)I therapy mainly focuses on external and internal exposure caused by physical contamination of the hospital staff, other patients and family members. However, if volatile (131)I is excreted by the treated patients, these individuals could also be exposed through inhalation of (131)I. This study quantifies the amount of volatile (131)I excreted by rats after intravenous administration of metaiodobenzylguanidine (MIBG)-(131)I or Na(131)I, the two most common forms of (131)I therapy. The results indicate that in 4 d following administration, the total excretion of volatile (131)I was 0.036 and 0.17 % of the administered activities of MIBG-(131)I and Na(131)I, respectively. As administered activities for (131)I therapy are typically of the order of 1-10 GBq, the overall excretion of volatile (131)I from a patient can be as high as 20 MBq. As a result, a family member can receive up to 0.07 mSv committed effective dose from inhaling the volatile (131)I excreted by the patient.

Preliminary studies of an 18-crown-6 ether modified magnetic cation exchange polymer in rapid (90)Sr bioassay

A cation exchange polymer resin embedded with magnetic nanoparticles and modified with crown ether was developed for urinalysis to rapidly monitor levels of (90)Sr exposure in humans who have been involved in a nuclear event. Invention of the resin matrix of 2-acrylamido-2-methyl-1-propanesulfonic acid cross-linked with divinylbenzene incorporated a Sr(2+) chelating agent, di-tert-butyl-cyclohexano-18-crown-6 through surface immobilization using a molecular modifier 1-octanol. The performance of these magnetic cation exchange resin particles was investigated by separating (90)Sr in the presence of (90)Y progeny. Masking agents and precipitants were examined to ascertain that sodium hydroxide at pH 7.5 was capable of selectively removing 89 ± 2% (90)Y before subsequent (90)Sr uptake. Preliminary investigations in rapid urinalysis were successful in isolating 83 ± 2% (90)Sr when pH was optimized to 9, with a sample turnover time <2 h, which is promising for radiological emergencies.

International workshop on emergency radiobioassay: considerations, gaps and recommendations

An international workshop on emergency radiobioassay was held in Ottawa, Canada, 1-3 September 2010. Sixty-five scientists and public health officials from five countries attended the workshop and gave 36 presentations. During the workshop, many considerations were raised, gaps identified, and recommendations given for emergency radiobioassay for both preparedness and response in case of a radiological or nuclear incident. In short, some bioassay methods and protocols need to be developed, validated, and exercised; national and international radiobioassay laboratory networks should be established; and communications and collaborations among public health officials, monitoring experts, and medical staff are encouraged. All these activities are required to make us better prepared for an RN emergency.

Canada's efforts in developing capabilities in radiological population monitoring

Population monitoring is an important component of radiological and nuclear emergency preparedness and response. Since 2002, Canada has been investing in developing national capabilities in radiological population monitoring. This paper summarizes Canada's efforts in developing methods and techniques in biological dosimetry and in vivo and in vitro bioassay techniques. There are still many gaps to fill that require further efforts. Integration of different monitoring methods and techniques in order to have the best assessment of radiation dose to support medical management and integration of Canada's efforts with international efforts are recommended.

Biokinetics of ²¹⁰Po in rats: excretion via urine and faeces and retention in tissues and organs

Daily excretions of ²¹⁰Po from rats via urine and faeces following i.v. administration of polonium citrate, from Day 2 to Day 5, were reported, together with retentions in tissues and organs on Day 5. Emphasis is given to the methods of measurement and data quality rather than to the discussion of the observations. The authors aim to contribute data for developing or refining the biokinetic model for ²¹⁰Po metabolism.

Is alpha spectrometry reliable for ²¹⁰Po urine bioassay?

Typically the bioassay method for (210)Po in urine by alpha spectrometry (AS) involves wet decomposition of the sample, which may cause a loss of (210)Po if volatile species are present. To test this hypothesis, urine samples collected from two rats that were i.v. administered with polonium citrate were measured by both AS and liquid scintillation counting, where urine samples were mixed with a scintillation cocktail without any treatment. A split-plot design method was used to compare results from the two measurement methods, showing no evidence of a difference between the two methods. This suggests that the AS method is reliable for (210)Po urine bioassay.

Method comparison for 241Am emergency urine bioassay

241Am is one of the high-risk radionuclides that might be used in a terrorist attack. 241Am in urine bioassay can identify the contaminated individuals who need immediate medical intervention and decontamination. This paper compares three methods for the measurement of 241Am in urine, namely liquid scintillation counting (LSC), inductively coupled plasma mass spectrometry (ICP-MS) and gamma spectrometry (GS), at two levels, 20 and 2 Bq l(-1). All three methods satisfied the ANSI N13.30 radio-bioassay criteria for accuracy and repeatability. ICP-MS offered the best sensitivity and fastest sample turnaround; however, the ICP-MS system used in this work may not be available in many bioassay laboratories. LSC and GS are more commonly available instruments. GS requires minimal or no sample preparation, which makes it a good candidate method. Moreover, the sample throughput can be significantly improved if the GS and LSC methods are automated.

Metabolism of 210Po in rats: volatile 210Po in excreta

Polonium-210 ((210)Po) is one of the most toxic radionuclides and was used as a poison in the Alexander Litvinenko case. In this study of the metabolism of (210)Po in rats, volatile (210)Po in excreta was measured, filling a knowledge gap of the previous studies. Five rats were intravenously administrated with 2 kBq and another five with 10 kBq of (210)Po (citrate form). They were housed in a glass Metabowl system for 4 d following the administration. Volatile (210)Po from the excreta was collected in a trapping system filled with liquid scintillation cocktail and was measured by liquid scintillation counting. Results showed that the daily excretion of volatile (210)Po by the rats is in a very small percentage (0.002-0.009 %) of the administered amounts. However, if the administered amount is large, the excretion of volatile (210)Po can be significant.