Journal of Environmental Radioactivity 243 (2022) 106811 Available online 8 January 2022 0265-931X/Crown Copyright © 2022 Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Environmental monitoring and external exposure to natural radiation in Canada Chuanlei Liu, Mike Benotto, Kurt Ungar, Jing Chen * Radiation Protection Bureau, Health Canada, 775 Brookfield Road, Ottawa, K1A1C1, Ontario, Canada A R T I C L E I N F O Keywords: Natural radionuclides Cosmic rays External exposure Environmental monitoring A B S T R A C T External sources of radiation originate from cosmic rays and natural radioactive elements, principally 40K and decay products in the uranium and thorium decay series occurring in the ground. People are exposed to terrestrial radiation and cosmic rays everywhere and at all times. To assess Canadians’ external exposure to natural radiation, five years (2016–2020) of real-time environment monitoring data recorded by Health Canada’s Fixed Point Surveillance (FPS) network were analysed for 36 monitoring stations across Canada. Absorbed dose rates in air from terrestrial radiation vary geographically and seasonally. Absorbed dose rates due to cosmic rays depend strongly on the elevation and vary with solar activities. The population-weighted annual outdoor ambient dose equivalent rates are 20 nSv/h for terrestrial radiation and 52 nSv/h for cosmic rays. Considering that, on average, Canadians spend 89% of their time indoors and 11% of the time outdoors, the population- weighted annual effective doses were calculated as 443 μSv (54 μSv outdoors and 389 μSv indoors), with 20.6% (91 μSv) from terrestrial radiation and 79.4% (352 μSv) from cosmic rays. 1. Introduction All living organisms are continually exposed to ionizing radiation, which has always existed naturally. For external exposure to natural radiation, the main sources are of terrestrial and cosmic ray origin (UNSCEAR, 2000). Naturally occurring terrestrial radionuclides (also called primordial radionuclides) are present in various degrees in all media in the environment. The main contribution to external terrestrial exposure comes from gamma-emitting radionuclides present in trace amounts in the soil, mainly 40K and the 238U and 232Th families. Most of this gamma radiation comes from the top 30 cm of soil (IAEA, 2003). Cosmic rays originate in outer space: they consist primarily of protons and alpha particles. Interactions in the upper layers of the earth’s at- mosphere create secondary components: the more important secondary particles from a dose-assessment view are muons, neutrons, electrons, positrons, and photons. Exposure to cosmic rays is strongly dependent on altitude and latitude (UNSCEAR, 2000). Health Canada operates the Fixed Point Surveillance (FPS) network, which consists of approximately 80 sodium iodide (NaI) detectors positioned across Canada, covering areas near nuclear facilities, port where nuclear-powered vessels berth and major Canadian population centres (http://www.hc-sc.gc.ca/ewh-semt/contaminants/radiation/s urveill/index-eng.php). The FPS network monitors radiation dose to the public in real-time due to radioactive materials in the terrestrial environment, whether they are airborne or on the ground. It includes contributions from both natural and man-made sources. Since 2016, the FPS network has added the capability to monitoring cosmic rays (Liu et al., 2018). In this paper, terrestrial and cosmic monitoring results from a subset of these stations are reported for 2016–2020 and the five-year average external exposure to natural radiation is assessed for the Canadian population. 2. Monitoring system and data sources For this work, a total of 36 monitoring stations were selected to es- timate local and national exposure levels to both terrestrial and cosmic ray radiation. These stations collectively represent the diverse and densely-populated areas in 13 geographical regions in Canada. A map of these selected stations is given in Fig. 1. In the FPS network each monitoring station contains a RS250 type 3′′x3′′ NaI(Tl) spectrometer detector that provides 15-min duration spectral measurements in nearly real-time to a data centre in Ottawa. The terrestrial radiation dominates the region from 0 to 3 MeV of ac- quired spectra whereas the cosmic ray radiation registers as a single * Corresponding author. E-mail address: jing.chen@hc-sc.gc.ca (J. Chen). Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad https://doi.org/10.1016/j.jenvrad.2022.106811 Received 6 October 2021; Received in revised form 20 December 2021; Accepted 3 January 2022 http://www.hc-sc.gc.ca/ewh-semt/contaminants/radiation/surveill/index-eng.php http://www.hc-sc.gc.ca/ewh-semt/contaminants/radiation/surveill/index-eng.php mailto:jing.chen@hc-sc.gc.ca www.sciencedirect.com/science/journal/0265931X https://www.elsevier.com/locate/jenvrad https://doi.org/10.1016/j.jenvrad.2022.106811 https://doi.org/10.1016/j.jenvrad.2022.106811 https://doi.org/10.1016/j.jenvrad.2022.106811 http://crossmark.crossref.org/dialog/?doi=10.1016/j.jenvrad.2022.106811&domain=pdf http://creativecommons.org/licenses/by/4.0/ Journal of Environmental Radioactivity 243 (2022) 106811 2 count rate channel for energies 3 MeV and above. All data are routinely quality checked, bad data due to gain shift and noise are removed, and dead-time effect corrected. In 0–3 MeV energy range, the measured energy spectrum was con- verted to air Kerma, K, and ambient dose equivalent, H*(10), by using two pre-determined dose conversion curves. These curves were obtained from a series of calibration measurements at the Ionizing Radiation Standards group at the Canadian National Research Council with several gamma emitting radionuclides at various exposure angles. The cosmic ray contribution in this energy range has also been estimated from field measurements over a large body of water (Grasty et al., 2001) and subtracted. It was found that cosmic rays could amount to about 2.6–3.0 nGy/h in this energy range, depending on the actual geographical location and altitude of the monitoring station. After subtracting this cosmic ray component, the dose rate reported from the monitoring system is resulting from terrestrial radiation (Some stations have a Thorium rod mounted on them for gain stabilization purposes; for these, the dose contribution from the rod has been subtracted). The cosmic ray doses in this work were estimated from the spectral data (i.e., the instrument count rate at energy above 3 MeV) and a linear function that converts the cosmic count rate to dose rate. As shown in Liu et al. (2018), this function was obtained by parameterizing the relationship between the high-energy channel measurements and the analytical dose rates from EXPACS (Sato, 2015) at about thirty FPS sites. These sites were selected to represent the geographic variations in Canada in terms of latitude, longitude and elevation. The cosmic dose results in this work contain contributions from all cosmic ray compo- nents, and are reported in H*(10) and effective dose rate, E. The air kerma dose rate is not applicable in this case because of the charged cosmic ray component. 3. Results and discussion Using daily records from each of the 36 monitoring stations selected for this study, measured quantities were averaged monthly for each station from January 2016 to December 2020. Results of five-year av- erages of measured quantities and derived quantities are summarized in Table 1, sorted by station longitude from east to west. Air kerma, ambient dose equivalent rates H*(10) for terrestrial radiation were taken from direct real-time readings from the FPS netwrok. Likewise, ambient dose equivalent rates H*(10) for cosmic radiation were calcu- lated directly from real-time readings from the FPS network which also allowed estimates of the effective dose for cosmic rays. When necessary, the terrestrial air kerma and ambient dose equivalent rates H*(10) were corrected for contributions from instrument internal standards of Th- 232 or Th-232 and K-40. Effective dose rates from terrestrial radia- tion, Ėterr in nSv/h, were derived from the measured quantity, air Kerma in nGy/h, using the conversion coefficient of 0.7 Sv/Gy (UNSCEAR, 2000). Ambient dose equivalent rates (H*(10)) are reported here for the purpose of data submission to UNSCEAR Global Survey (https://www. unscear.org/unscear/en/about_us/surveys.html). Effective dose rates are used in the subsequent external exposure assessment. Soil concentrations of 40K and the uranium and thorium series vary over a factor of 20 from place-to-place in the United States and Canada (Grasty and LaMarre, 2004). Therefore, absorbed dose rates in air have shown significant geographic variation. In Table 1, the Ėterr varied widely from 3.63 nSv/h in Resolute to 31.85 nSv/h in Fredericton. The population-weighted average Ėterr is 11 nSv/h from 2016 to 2020. In addition to geographic variation, gamma dose rate in air varies also with moisture content in the ground, rain and overburden of snow. Considering variation in rainfall and the fact that much of the country is covered by snow several months each year, significant changes in attenuation by precipitation of radiation emitted by the soil occur throughout the year, affecting the absorbed dose rate in air. These sea- sonal variations can be clearly observed from real-time recorded data in the FPS network. A few examples of monthly averaged air Kerma are shown in Fig. 2. In the upper panel of Fig. 2, monthly averaged data are shown for three stations. They are Dartmouth on the east coast, Winnipeg in centre of Canada, and Victoria on the west coast. The average annual snowfall Fig. 1. A map of the selected FPS stations used in this study. These stations are 1. Dartmouth, 2. Trois Riv- ieres, 3. Quebec City, Port Elgin, 5. Kingston, 6. St. Catharines, 7. Scarborough, 8. Pickering, 9. Oshawa, 10. Markham, 11. Ajax, 12. Ottawa, 13. Petawawa, 14. Chalk River, 15. St. Johns, 16. Whitehorse, 17. Iqaluit, 18. Resolute, 19. Haida Gwaii, 20. Saskatoon, 21. Kelowna, 22. Fredericton, 23. Edmonton, 24. Amherstburg, 25. Vancouver, 26. Yellowknife, 27. Regina, 28. Calgary, 29. Winnipeg, 30. Thunderbay, 31. Montreal, 32. Charlottetown, 33. Saint John, 34. Saanich, 35. Victoria and 36. Nanaimo. Markers 7, 8, 9 and 10 are hidden behind marker 11; maker 13 is behind marker 14; marker 25 is behind marker 36; maker 34 is behind maker 35. C. Liu et al. https://www.unscear.org/unscear/en/about_us/surveys.html https://www.unscear.org/unscear/en/about_us/surveys.html JournalofEnvironmentalRadioactivity243(2022)106811 3 Table 1 Air kerma, ambient dose equivalent rates, H*(10), and effective dose rates, Ė, from terrestrial radiation and cosmic rays in 36 monitoring stations across Canada. Station ID City/county/town Population Kerma Ėterr Ėcosm Ėtotal H*(10) terrestrial H*(10) cosmic H*(10) total nGy/h nSv/h nSv/h nSv/h nSv/h nSv/h nSv/h 7000_10 St. John’s 178427 24.39 17.08 37.60 54.67 30.63 46.27 76.90 7000_9 Charlottetown 44739 21.26 14.88 36.04 50.93 26.87 44.49 71.37 10000_2 Dartmouth 92301 26.50 18.55 37.90 56.44 33.28 46.61 79.89 8000_5 Saint John 58341 29.57 20.70 38.72 59.42 37.62 47.55 85.18 7000_17 Fredericton 59405 45.50 31.85 35.86 67.71 56.29 44.29 100.57 7000_12 Iqaluit 7082 27.86 19.50 38.22 57.72 35.39 46.98 82.37 2000_6 Quebec City 800296 6.61 4.63 38.44 43.07 8.78 47.23 56.01 2000_5 Trois Rivieres 156042 13.96 9.77 36.76 46.53 17.40 45.32 62.71 7000_8 Montreal 1,704,690 15.25 10.68 37.92 48.59 19.10 46.63 65.73 6000_1 Ottawa 934243 14.89 10.42 37.08 47.50 19.22 45.67 64.89 5000_11 Kingston 117660 15.05 10.53 37.75 48.29 18.73 46.45 65.17 6000_2 Petawawa 13,701 28.71 20.10 39.58 59.67 36.31 48.53 84.83 6000_4 Chalk River 1029 38.18 26.73 38.42 65.15 47.78 47.21 94.99 5000_6 Oshawa 379848 16.17 11.32 38.31 49.63 20.50 47.09 67.58 5000_8 Ajax 119677 24.69 17.28 36.92 54.20 30.82 45.50 76.32 5000_5 Pickering 91771 19.55 13.68 37.03 50.71 24.47 45.62 70.08 5000_7 Markham 328966 22.11 15.48 37.86 53.34 27.63 46.57 74.20 5000_1 Scarborough 112603 13.84 9.68 41.04 50.73 17.21 50.21 67.41 5000_12 St. Catharines 406,074 9.68 6.77 42.14 48.91 12.26 51.46 63.71 3000_5 Bruce county 68147 14.56 10.19 41.96 52.15 18.59 51.25 69.84 7000_1 Amherstburg 13910 20.50 14.35 38.31 52.66 26.47 47.09 73.56 7000_7 Thunderbay 93952 18.65 13.06 39.16 52.22 23.39 48.06 71.45 7000_13 Resolute 198 5.18 3.63 41.44 45.07 6.60 50.66 57.26 7000_6 Winnipeg 705244 13.81 9.67 39.40 49.07 17.33 48.33 65.66 7000_4 Regina 214631 24.84 17.39 47.22 64.61 31.82 57.27 89.09 7000_15 Saskatoon 246376 25.93 18.15 45.61 63.76 32.45 55.42 87.87 7000_18 Edmonton 932546 19.42 13.60 54.58 68.18 24.52 65.67 90.19 7000_5 Calgary 1392609 15.50 10.85 66.81 77.66 19.54 79.64 99.2 7000_3 Yellowknife 18884 30.82 21.57 41.17 62.74 39.22 50.35 89.57 7000_16 Kelowna 151,957 38.96 27.27 46.32 73.60 48.68 56.24 104.92 7000_2 Vancouver 631,486 16.22 11.36 37.18 48.54 20.85 45.80 66.65 9000_3 Victoria 85792 5.39 3.77 37.38 41.15 7.07 46.02 53.08 9000_1 Saanich 114148 7.64 5.34 36.71 42.06 9.82 45.26 55.08 9000_4 Nanaimo 104936 12.93 9.05 41.75 50.80 16.21 51.01 67.23 7000_14 Queen Charlotte 852 19.22 13.45 36.70 50.15 24.02 45.25 69.27 7000_11 Whitehorse 25085 35.05 24.54 54.96 79.50 43.79 66.11 109.9 Averagea 16.14 11.30 42.91 54.21 20.37 52.33 72.71 a Population-weighted averages using Census 2016 population (Statistics Canada, 2020). C. Liu et al. Journal of Environmental Radioactivity 243 (2022) 106811 4 is 230 cm in Dartmouth, 111 cm in Winnipeg and 44 cm in Victoria (htt ps://www.statista.com/statistics/553393/average-annual-snowfa ll-canada-by-city/). The effect of winter snow is clearly seen for the data collected in Dartmouth and Winnipeg while little variation is observed in Victoria owing to its mild climate in the coast area of marine environment. Snowfall accumulation and presence over a number of months also affect gamma dose rate significantly, as shown in the lower panel of Fig. 2. Resolute and Yellowknife are in the arctic region of Canada with average annual temperature below freezing point albeit with moder- ately low to moderate annual snowfalls of 111 cm and 158 cm, respectively. In contrast to significant geographic and seasonal variations in absorbed dose rate in air from terrestrial radiation, fluctuations in dose rate from cosmic rays are relatively small, as shown in Fig. 3. Here ex- amples of monthly averaged cosmic-ray effective dose rates at the sta- tions in Dartmouth, Winnipeg, Victoria, Resolute and Yellowknife are provided. Since the atmosphere attenuates the cosmic ray flux experi- enced on the earth’s surface, the cosmic ray intensity increases with altitude, doubling approximately every 2000 m. For this reason, the five- year averaged cosmic-ray effective dose rates relate very well with the elevation, as demonstrated in Fig. 4. The R2 value of the linear fit in- dicates that ~91% of the variance of cosmic-ray dose rate are related to the elevation effect. The unaccounted 9% variance can be explained by other influence factors such as latitude (at a level of 7% from 30◦ N to 70◦ N) as well as instrumental differences, which is a few percent in magnitude (Liu et al., 2018). The total annual outdoor effective dose rate is the sum of outdoor Fig. 2. Monthly averaged air kerma in nGy/h from the stations in Dartmouth, Winnipeg and Victoria (upper panel), and from northern stations in Resolute and Yellowknife (lower panel). C. Liu et al. https://www.statista.com/statistics/553393/average-annual-snowfall-canada-by-city/ https://www.statista.com/statistics/553393/average-annual-snowfall-canada-by-city/ https://www.statista.com/statistics/553393/average-annual-snowfall-canada-by-city/ Journal of Environmental Radioactivity 243 (2022) 106811 5 effective dose rate from terrestrial radiation and cosmic rays. From Table 1, we can see that on average, cosmic-ray effective dose rate contributes about 75% of the total effective dose rate. This ratio varied from 53% in Fredericton to 92% in Resolute. People are exposed to terrestrial radiation and cosmic rays every- where and at all times. According to the General Social Survey - Cana- dians at work and home (Statistics Canada, 2017; Matz et al., 2014), the average daily time spent in major locations by age groups are as sum- marized in Table 2. The population-weighted average daily time spent in major locations for all Canadians are 70% indoors at home, 19% indoors other than homes, and about 11% for outdoor activities including time spent in vehicles. On average, Canadians spend 89% of their time in- doors and only 11% of the time outdoor, in other words, 7796.4 h in- doors and 963.6 h outdoor per year. For estimates of radiation dose received indoors, we have followed the procedure adopted by UNSCEAR (2000) which is to estimate the average indoor effective dose from the outdoor value using a conversion Fig. 3. Monthly averaged cosmic-ray effective dose rates measured at the stations in Dartmouth, Winnipeg, Victoria, Resolute and Yellowknife from 2016 to 2020. Fig. 4. Five-year averaged cosmic-ray effective dose rates as a function of elevation for the 36 monitoring stations selected in this study. Table 2 Daily time spent in major locations by age groups and population-weighted average daily time spent in major locations for all Canadians (daily percent- ages in bracket). Age group Population Location Mean time spent (hours) Infants (<1 year) 383216 Indoors at home 21.38 (89%) Indoors away from home 1.17 (5%) Outdoors 0.95 (4%) In vehicle 0.50 (2%) Young children (1–4 years) 1559575 Indoors at home 17.73 (74%) Indoors away from home 3.67 (15%) Outdoors 1.82 (8%) In vehicle 0.78 (3%) Children (5–11 years) 2771399 Indoors at home 17.12 (71%) Indoors away from home 4.27 (18%) Outdoors 1.80 (8%) In vehicle 0.81 (3%) Adolescents (12–19 years) 3235477 Indoors at home 16.67 (69%) Indoors away from home 4.98 (21%) Outdoors 1.48 (6%) In vehicle 0.87 (4%) Adults (20–59 years) 19925692 Indoors at home 16.03 (67%) Indoors away from home 5.13 (21%) Outdoors 1.32 (6%) In vehicle 1.52 (6%) Seniors (60+ years) 8234128 Indoors at home 18.63 (78%) Indoors away from home 2.98 (12%) Outdoors 1.32 (6%) In vehicle 1.07 (4%) Canadiansa 36109487 Indoors at home 16.89 (70%) Indoors away from home 4.46 (19%) Outdoors 1.39 (6%) In vehicle 1.26 (5%) a Population-weighted averages using Census 2016 population (Statistics Canada, 2020). C. Liu et al. Journal of Environmental Radioactivity 243 (2022) 106811 6 factor. The indoor-to-outdoor ratio of 0.90 as being typical for buildings of wood-frame construction (Grasty et al., 1984, NCRP, 2009) was used in this study. With outdoor effective dose rates given in Table 1, 89% of the time indoors and 11% of the time outdoor as well as indoor-to-outdoor con- version factor of 0.9, the annual external exposures to terrestrial radi- ation and cosmic rays are calculated and summarized in Table 3. The population-weighted annual effective doses are 54 μSv outdoors and 389 μSv indoors, for a total of 443 μSv. Terrestrial radiation accounts for 20.6% (91 μSv) and 79.4% (352 μSv) is from cosmic rays. 4. Conclusions Real-time environmental monitoring data collected over a period of five years (2016–2020) from 36 monitoring stations across Canada indicate that the Canadian population-weighted annual outdoor ambient dose equivalent rates are 20 nSv/h for terrestrial radiation and 52 nSv/h for cosmic rays. Considering that, on average, Canadians spend 89% of their time indoors and 11% of the time outdoors, the population- weighted annual effective doses were calculated as 54 μSv outdoors and 389 μSv indoors, for a total of 443 μSv, Approximately a fifth of this (91 μSv) is due to terrestrial radiation and the remaining major part (352 μSv) is from cosmic rays. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References Grasty, R.L., Carson, J.M., Charbonneau, B.W., Holman, P.B., 1984. Natural background radiation in Canada. Geological Survey of Canada 360. Bulletin, Ottawa. Grasty, R.L., et al., 2001. Calibration of a 7.6 cm x 7.6 cm sodium iodine gamma ray spectrometer for air kerma rate. Radiat. Protect. Dosim. 94, 309–316. Grasty, R.L., LaMarre, J.R., 2004. The annual effective dose from natural sources of ionizing radiation in Canada. Radiat. Protect. Dosim. 108, 215–226. International Atomic Energy Agency (IAEA), 2003. Guidelines for Radioelement Mapping Using Gamma Ray Spectrometry Data. IAEA-TECDOC-1363. Liu, C., Zhang, W., Ungar, K., Korpach, E., White, B., Benotto, M., Pellerin, E., 2018. Development of a national cosmic-ray dose monitoring system with Health Canada’s Fixed Point Surveillance network. J. Environ. Radioact. 190–191, 31–38. Matz, C.J., Stieb, D.M., Davis, K., Egyed, M., Rose, A., Chou, B., Brion, O., 2014. Effects of age, season, gender and urban-rural status on time-activity: Canadian Human Activity Pattern Survey. Int. J. Environ. Res. Publ. Health 11, 2108–2124. National Council on Radiation Protection and Measurements (NCRP),, 2009. Ionizing Radiation Exposure of the Population of the United States. NCRP Report No.160. Bethesda. Sato, T., 2015. Analytical model for estimating terrestrial cosmic ray fluxes nearly anytime and anywhere in the world: extension of PARMA/EXPACS. PLoS One 10 (12), e014467. Statistics Canada, 2017. General Social Survey: Canadians at work and home. Detailed information for 2016 (cycle 30). Available at: http://www23.statcan.gc.ca/imdb/ p2SV.pl?Function=getSurvey&SDDS=5221. (Accessed 21 August 2021). Statistics Canada, 2020. Estimates of Population (2016 Census and Administrative Data), by Age Group and Sex. Table: 17-10-0134-01. Available at: https://www150.statcan. gc.ca/t1/tbl1/en/tv.action?pid=1710013401. (Accessed 15 August 2021). United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), 2000. Sources and Effects of Ionizing Radiation (2000 Report to the General Assembly) (New York). Table 3 Annual effective doses in μSv for outdoor, indoors and from terrestrial radiation and cosmic rays in 36 monitoring stations across Canada. outdoor indoor Terrestrial Cosmic City/county/town Population terrestrial cosmic total terrestrial cosmic total total total St. John’s 178427 16.45 36.23 52.68 119.82 263.82 383.64 136.28 300.05 Charlottetown 44739 14.34 34.73 49.07 104.43 252.91 357.34 118.77 287.64 Dartmouth 92301 17.87 36.52 54.39 130.14 265.91 396.06 148.02 302.43 Saint John 58341 19.94 37.31 57.25 145.22 271.69 416.91 165.16 309.00 Fredericton 59405 30.69 34.56 65.24 223.46 251.64 475.10 254.15 286.19 Iqaluit 7082 18.79 36.83 55.62 136.85 268.18 405.03 155.64 305.01 Quebec City 800296 4.46 37.04 41.50 32.48 269.73 302.21 36.94 306.77 Trois Rivieres 156042 9.41 35.42 44.84 68.55 257.95 326.50 77.96 293.38 Montreal 1,704,690 10.29 36.54 46.82 74.92 266.05 340.96 85.20 302.58 Ottawa 934243 10.04 35.73 45.77 73.14 260.15 333.29 83.19 295.87 Kingston 117660 10.15 36.38 46.53 73.91 264.90 338.81 84.06 301.28 Petawawa 13,701 19.37 38.14 57.50 141.03 277.70 418.72 160.39 315.83 Chalkriver 1029 25.76 37.02 62.78 187.55 269.61 457.15 213.30 306.63 Oshawa 379848 10.91 36.92 47.82 79.42 268.83 348.25 90.33 305.75 Ajax 119677 16.65 35.58 52.23 121.25 259.07 380.32 137.90 294.64 Pickering 91771 13.19 35.68 48.86 96.01 259.81 355.83 109.20 295.49 Markham 328966 14.92 36.48 51.40 108.61 265.65 374.27 123.53 302.14 Scarborough 112603 9.33 39.55 48.88 67.96 287.99 355.95 77.29 327.54 St. Catharines 406,074 6.53 40.60 47.13 47.52 295.68 343.20 54.05 336.28 Bruce county 68147 9.82 40.43 50.25 71.50 294.41 365.91 81.32 334.84 Amherstburg 13910 13.83 36.92 50.75 100.69 268.84 369.52 114.52 305.75 Thunderbay 93952 12.58 37.74 50.32 91.61 274.79 366.40 104.20 312.53 Resolute 198 3.50 39.93 43.43 25.46 290.79 316.24 28.95 330.72 Winnipeg 705244 9.32 37.97 47.28 67.83 276.47 344.30 77.15 314.44 Regina 214631 16.76 45.50 62.26 122.02 331.36 453.38 138.78 376.86 Saskatoon 246376 17.49 43.95 61.44 127.35 320.01 447.36 144.84 363.95 Edmonton 932546 13.10 52.60 65.70 95.41 383.00 478.41 108.51 435.60 Calgary 1392609 10.45 64.38 74.83 76.12 468.79 544.91 86.57 533.17 Yellowknife 18884 20.79 39.67 60.46 151.38 288.87 440.25 172.17 328.54 Kelowna 151,957 26.28 44.64 70.92 191.36 325.04 516.40 217.63 369.68 Vancouver 631,486 10.94 35.83 46.77 79.68 260.90 340.58 90.62 296.73 Victoria 85792 3.64 36.02 39.65 26.48 262.26 288.74 30.11 298.28 Saanich 114148 5.15 35.38 40.53 37.50 257.60 295.11 42.65 292.98 Nanaimo 104936 8.72 40.23 48.95 63.52 292.94 356.47 72.25 333.17 Queen Charlotte 852 12.96 35.37 48.33 94.39 257.53 351.92 107.35 292.90 Whitehorse 25085 23.64 52.96 76.61 172.17 385.66 557.84 195.82 438.63 Averagea 11.03 42.45 53.48 80.29 309.12 389.41 91.32 351.57 a Population-weighted averages using Census 2016 population (Statistics Canada, 2020). C. Liu et al. http://refhub.elsevier.com/S0265-931X(22)00001-7/sref1 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref1 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref2 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref2 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref3 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref3 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref4 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref4 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref5 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref5 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref5 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref6 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref6 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref6 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref7 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref7 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref7 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref8 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref8 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref8 http://www23.statcan.gc.ca/imdb/p2SV.pl?Function=getSurvey&SDDS=5221 http://www23.statcan.gc.ca/imdb/p2SV.pl?Function=getSurvey&SDDS=5221 https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=1710013401 https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=1710013401 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref11 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref11 http://refhub.elsevier.com/S0265-931X(22)00001-7/sref11 Environmental monitoring and external exposure to natural radiation in Canada 1 Introduction 2 Monitoring system and data sources 3 Results and discussion 4 Conclusions Declaration of competing interest References