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Results of simultaneous radon and thoron measurements in 33 metropolitan areas of Canada

Results of simultaneous radon and thoron measurements in 33 metropolitan areas of Canada Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 Radiation Protection Dosimetry (2015), Vol. 163, No. 2, pp. 210–216 doi:10.1093/rpd/ncu141 Advance Access publication 19 April 2014 RESULTS OF SIMULTANEOUS RADON AND THORON MEASUREMENTS IN 33 METROPOLITAN AREAS OF CANADA Jing Chen*, Lauren Bergman, Renato Falcomer and Jeff Whyte Health Canada, Radiation Protection Bureau, 775 Brookfield Road, Ottawa, Canada, K1A 1C1 *Corresponding author: [email protected] Received 3 February 2014; revised 21 March 2014; accepted 22 March 2014 222 220 Radon has been identified as the second leading cause of lung cancer after tobacco smoking. Rn (radon gas) and Rn (thoron gas) are the most common isotopes of radon. In order to assess thoron contribution to indoor radon and thoron exposure, a survey of residential radon and thoron concentrations was initiated in 2012 with ∼4000 homes in the 33 census metropolitan areas of Canada. The survey confirmed that indoor radon and thoron concentrations are not correlated and that thoron concen- trations cannot be predicted from widely available radon information. The results showed that thoron contribution to the radi- ation dose varied from 0.5 to 6 % geographically. The study indicated that, on average, thoron contributes ∼3 % of the radiation dose due to indoor radon and thoron exposure in Canada. Even though the estimated average thoron concentration of 9 Bq m (population weighted) in Canada is low, the average radon concentration of 96 Bq m (population weighted) is more than double the worldwide average indoor radon concentration. It is clear that continued efforts are needed to further reduce the exposure and effectively reduce the number of lung cancers caused by radon. (4–10) INTRODUCTION from widely available radon information .In 2008 and 2011, simultaneous radon and thoron mea- Radon is a naturally occurring radioactive gas gener- surements were performed in a total of 370 Canadian ated by the decay of uranium- and thorium-bearing (5–7) homes in five communities . Based on those minerals in rocks and soils. Radon and its decay pro- results, it was estimated that thoron contributes 8% ducts are the major contributors to human exposure of the radiation dose due to indoor radon and thoron (1) from natural radiation sources . Radon has been (3) exposure . To confirm this estimate, a larger cross- identified as the second leading cause of lung cancer Canada survey was needed. (2) 222 after tobacco smoking . Rn (radon gas) and The Cross-Canada Survey of Radon Concentrations Rn (thoron gas) are the most common isotopes of (11) in Homes study was completed recently .However, radon. detectors used in that study were not sensitive to Radon is a member of the U decay chain thoron, and thoron information was not included as whereas thoron is a member of the Th decay chain. (12) part of the radon survey . Because radon and thoron are members of different In 2012, another survey was initiated in Canadian decay chains, their concentrations depend in part on metropolitan areas to estimate thoron contribution to the uranium and thorium levels in local soils and (13) indoor radon and thoron exposure . Results of this building materials. Because wood-frame construction 2012/2013 radon–thoron survey are reported here. is very popular for family houses, building materials contribute very little to indoor radon and thoron in Canada. Information on geographical distributions METHODS of uranium and thorium in the ground is limited or not available for many metropolitan areas of Canada, In order to assess thoron contribution to indoor radon as shown in Figures 1 and 2 of a previous publica- and thoron exposure combined, a survey of residential (3) tion . Nevertheless, the previous study was able to radon and thoron concentrations was designed for demonstrate that average indoor radon and thoron 4000 homes in all 33 census metropolitan areas (14) concentrations in an area correlate well with the (CMAs) specified by Statistics Canada , which cover average uranium and thorium concentrations in the 70 % of the Canadian population. The CMAs, from ground, even though the ratio of uranium and east to west, are St. John’s, Halifax, Moncton, Saint thorium concentrations could vary significantly from John, Saguenay, Que´bec, Sherbrooke, Trois-Rivie`res, one area to another. Montre´al, Ottawa-Gatineau, Kingston, Peterborough, Many studies have confirmed that there is no clear Oshawa, Toronto, Hamilton, St. Catharines—Niagara, correlation between radon and thoron concentrations Kitchener–Cambridge–Waterloo, Brantford, Guelph, and that thoron concentrations could not be predicted London, Windsor, Barrie, Greater Sudbury, Thunder # The Author 2014. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 RADON – THORON SURVEY IN CANADA Bay, Winnipeg, Regina, Saskatoon, Calgary, Edmonton, were conducted for a period of at least 3 months. Kelowna, Abbotsford-Mission, Vancouver and Victoria. Essential information (the start and stop time of the As the Cross-Canada Survey of Radon Concentrations test) had to be included with the returned detector. in Homes, there were several qualifying criteria that To determine the concentrations of radon and had to be satisfied for a participant to be eligible to thoron, a passive integrated radon–thoron discrim- take part in the study. First, participants had to be inative detector developed at the National Institute of the head of the household and 18 y of age or older. Radiological Sciences in Japan (commercially known Participants also had to be homeowners and be living as RADUET) was used in this survey. The principle in their primary residence. People who rented a home and technical descriptions of RADUET detectors (5, 16) were not included in the study because there is no re- have been given in previous publications .A quirement on the part of landlords to remediate high RADUET contains paired detection chambers, a radon–thoron levels if they are found in a home. In low-diffusion chamber and a high-diffusion chamber. addition, participants could not live on military bases In principle, the track densities in the low-diffusion or on-reserve, since these homes were, or were expected chamber (TD ) and high-diffusion chamber (TD ) L H to be, covered in other surveys. Homes that were built depend on both radon and thoron concentrations in on stilts or high-rise condo units that were above the the air: second floor did not qualify. Finally, homeowners could not have planned to move or be away during TD ¼ c ðRn  b Þþ c ðTn  bÞð1Þ L 11 1 12 2 the proposed timeline of the study. TD ¼ c ðRn  b Þþ c ðTn  bÞð2Þ The survey followed the procedure outlined in Health H 21 1 22 2 Canada’s guide for radon measurements in residential (15) dwellings . Radon levels in a home can vary signifi- where b and b are the background noise levels for 1 2 cantly over time. In fact, it is not uncommon to see radon and thoron concentration, respectively, i.e. they radon levels in a home change by a factor of 2 to 3 appear as radon or thoron concentration readings for over a 1-day period, and variations from season to blank control detectors. The values c , c , c and 11 12 21 season can be even larger. The highest radon levels c are the calibration coefficients. The low-diffusion are usually observed during winter months. As a chamber limits diffusion of thoron into the chamber, result, a long-term measurement period will give a therefore, c .. c . The high-diffusion chamber is 11 12 much better indication of the annual average indoor designed such that both radon and thoron can diffuse radon concentration. During a long-term measure- into the chamber easily, and c  c . 21 22 ment, there are no requirements for the occupants to To determine the above-mentioned coefficients, change their life-style once the measurement devices several groups of RADUETs were randomly taken have been put in place. Therefore, Health Canada from 5000 detectors (purchased at different times) recommends the placement of at least one long-term and exposed to three different known radon and detector in a home for a minimum of 3 to 12 months thoron concentrations at the National Institute of (12 months is optimal). For periods ,12 months, the Radiological Sciences and Hirosaki University in testing period should include a mix of seasons or be Japan. The coefficients in Equations 1 and 2 were in a mid-season to best provide a measurement that then determined to be c ¼ 0.029, c ¼ 0.001, c ¼ 11 12 21 reflects the annual average level. The ideal 3-month 0.028, c ¼ 0.022, b ¼ 0.8 and b ¼ 0.7. This cali- 22 1 2 testing period would be in the typical heating season bration is necessary to account for possible changes that runs from October through to April. The least in the detectors after the storage period and variations ideal period is during the summer since open window in the reader system and/or etching process. conditions often prevail. RADUET detectors returned for analysis were The study was designed to recruit during the sum- etched according to manufacturer’s instructions. A mer of 2012 with the testing to occur in the 2012– commercial alpha-track reader (RadoSys) was used 2013 fall/winter (October to March) periods. Each to obtain total track densities in paired low- and high- CMA was targeted to recruit 122 participants. diffusion chambers (TD and TD ). With these raw L H Participants were recruited over the telephone by a data, TD and TD , and the calibration coefficients L H contracted market research firm, Prairie Research determined earlier, radon and thoron concentrations Associates (PRA), which employed random digit are calculated as the solution of Equations 1 and 2. dialing with a sampling product of ASDE Survey Based on the fact that concentration in one Sampler. Test kits were then mailed out in October chamber depends on the other and the calculation (17) 2012 to those who agreed to participate. procedure given by Currie , the detection limits Instruction was given to all participants that the were estimated to be 3 Bq m for radon and 4 Bq 23 (18) detector should be deployed in the lowest lived-in m for thoron . Even though the theoretically esti- level of the home where someone spends at least 4 h a mated detection limits are low, it was decided to only day. In order for the result to be indicative of the report radon and thoron concentrations of .15 Bq average annual radon and thoron exposure, all tests m to the survey participants due to uncertainties of 211 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 J. CHEN ET AL. many environmental factors and variations in the radon–thoron detectors in their homes for 3 months, field deployment. All results below 15 Bq m were after which they were reminded to mail the detectors reported as ,15 Bq m . back to the Health Canada for analysis. The survey (3) As assessed in the previous publication , the had a return rate of 79 %. Five participants decided annual effective dose due to indoor radon exposure to withdraw from the survey. A total of 3215 test for a population in a given area, E (nSv), was results were reported directly to the survey partici- Rn assessed based on the formula given by the pants. Due to mechanical damage or other technical (1) UNSCEAR report : reasons, test results could not be generated for 11 par- ticipants. Among them, nine participants agreed to E ¼ C  0:4  7000  9 ð3Þ Rn Rn conduct a re-test during the 2013/2014 test season. For those detectors returned without start and end where C is the arithmetic mean (AM) radon con- dates recorded, a test duration of 91 d is assumed. Rn centration (in Bq m ), the typical value of 0.4 was This assumed exposure period was included and used as the equilibrium factor for radon indoors, a explained in the results letter sent to the participants. 23 21 recommended value of 9 nSv (Bq m h) was used Duplicate detectors were placed side-by-side in to convert radon equilibrium-equivalent concentra- every ten homes for quality control purposes. A total tion (EEC) to population effective dose and an 80 % of 319 duplicates were returned. Twelve duplicates home occupancy time, i.e. 7000 h, was assumed. The had one of the two RADUETs damaged. Radon con- population dose due to indoor radon exposure is pro- centrations measured with those randomly distributed portional to the AM radon concentration in an area. duplicates ranged from 7 to 1175 Bq m with an The population effective dose due to indoor thoron average of 104 Bq m whereas thoron concentrations exposure, E (nSv), was assessed based on the were much lower and ranged from non-detectable to Tn (1) 23 23 formula given in the UNSCEAR report : 164 Bq m with an average of only 8 Bq m . Good agreement in radon results was obtained from the E ¼ C  0:02  7000  40 ð4Þ Tn Tn duplicates placed side-by-side. The average relative deviation of radon concentrations was 8 %. However, where C is the AM thoron concentration (in Bq Tn a rather large deviation of 78 % in thoron concen- m ), the typical value of 0.02 was used as the equi- trations was observed among the same duplicates. This librium factor for thoron indoors and a recommended is mainly due to thoron concentrations that were below 23 21 value of 40 nSv (Bq m h) was used to convert the detection limit in about half of homes surveyed. thoron EEC to the effective dose. As in the case of In those cases, one detector showed non-detectable radon, the population dose due to indoor thoron whereas the duplicate recorded a value slightly above exposure is proportional to the AM thoron concen- the detection limit. It should also be mentioned that tration in an area. detectors have finite dimensions and can be .10 cm The total effective dose is the sum of the effective apart even when placed side-by-side and bound toge- doses due to exposures to indoor radon and thoron. ther. Because of its short half-life, the thoron measure- Thoron contribution to the radiation dose due to ment is more sensitive to variations in air flow around indoor radon and thoron exposure can then be deter- detectors, and more dependent on distances from mined as follows: thoron sources. This can explain the relatively large de- viation in readings from detectors for thoron concen- Tn trations in comparison with radon measurements. For ð5Þ homes with control detectors, average radon and E þ E Rn Tn thoron concentrations from those duplicate detectors were reported. Among the 3215 test-kits returned, both radon and RESULTS thoron measurements were available for 3184 homes. During the summer of 2012, the research firm PRA Thirty-one participants received only radon results due dialled over 100 000 telephone numbers in order to to damage to the high-diffusion chamber. The charac- recruit at least 4000 participants from 33 metropol- teristics of the radon and thoron concentrations in the itan areas. About 92.5 % of households phoned were 33 CMAs are summarised in Table 1. Radon and eligible to participate. Overall, the response rate was thoron concentrations in individual homes were not 13.5 % and the refusal rate was 30.9 %, which were correlated, as shown in Figure 1 for the entire data set. expected for a study of this nature. By the end of This is also true for individual CMAs. October 2012, detectors were mailed to a total of Radon was present in all homes in varying concen- 4064 participants. Detailed breakdown in the trations with the highest measured concentration of numbers of participants for each CMA is given in 2117 Bq m . The population-weighted AM concen- Table 1. According to the instruction included in the tration of radon and the standard deviation (SD) were mail-out, the participants deployed the alpha-track 96 and 87 Bq m , respectively. 212 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 RADON – THORON SURVEY IN CANADA Table 1. Sample distribution and test results in 33 CMAs. 23 23 CMA Population Number of Results Number of Rn, Bq m Tn, Bq m E / Tn (thousands) participants reported Tn , DL AM + SD AM + SD (E þ E ) (%) Rn Tn Abbotsford- 178.1 122 90 38 58 + 53 11 + 17 4.1 Mission Barrie 196.0 122 88 44 85 + 88 10 + 16 2.5 Brantford 140.5 122 89 43 108 + 96 12 + 19 2.5 Calgary 1309.2 123 99 64 135 + 106 6 + 6 0.9 Edmonton 1230.1 122 97 51 113 + 68 8 + 9 1.6 Greater Sudbury 164.0 122 96 56 131 + 113 8 + 13 1.4 Guelph 142.9 122 102 59 131 + 153 8 + 10 1.3 Halifax 413.7 125 102 48 185 + 269 12 + 17 1.4 Hamilton 756.6 122 87 42 85 + 67 10 + 20 2.5 Kelowna 184.7 122 108 63 134 + 135 8 + 11 1.4 Kingston 165.5 122 97 53 165 + 131 11 + 19 1.5 Kitchener– 505.1 122 102 55 66 + 37 9 + 18 2.8 Cambridge– Waterloo London 500.0 122 81 43 85 + 60 7 + 8 1.9 Moncton 143.0 122 95 47 77 + 77 8 + 11 2.3 Montreal 3957.7 122 99 48 120 + 143 9 + 9 1.6 Oshawa 375.6 122 96 42 61 + 48 12 + 16 4.0 Ottawa-Gatineau 1273.3 122 109 61 108 + 91 11 + 21 2.2 Peterborough 122.4 122 100 52 100 + 60 8 + 7 1.7 Quebec 769.6 122 99 58 115 + 152 9 + 22 1.7 Regina 226.3 121 96 69 302 + 254 7 + 12 0.5 Saguenay 152.6 124 100 44 89 + 104 11 + 21 2.6 Saint John 128.9 154 116 54 115 + 131 13 + 24 2.4 Saskatoon 284.0 122 104 65 152 + 78 9 + 13 1.3 Sherbrooke 203.5 122 104 60 238 + 344 8 + 9 0.8 St. Catharines— 405.8 122 87 32 56 + 36 11 + 12 4.3 Niagara St. John’s 200.6 123 97 52 88 + 63 7 + 7 1.7 Thunder Bay 127.1 122 94 53 156 + 133 10 + 16 1.4 Toronto 5941.5 123 91 33 57 + 37 9 + 8 3.3 Trois-Rivieres 148.3 122 95 30 43 + 22 11 + 12 5.4 Vancouver 2463.7 121 98 40 28 + 25 8 + 7 6.0 Victoria 363.1 122 102 46 37 + 26 8 + 8 4.5 Windsor 333.4 122 94 55 154 + 121 11 + 23 1.6 Winnipeg 778.4 122 101 50 257 + 210 8 + 9 0.7 Total or average 24 285 4064 3215 48 % 96 + 87 9 + 11 2.7 In two cases, only radon results were available. In one case, only radon result was available. In three cases, only radon results were available. On average (population weighted), 48 % of homes to Equation 5. Results are given in Table 1. Thoron surveyed had thoron concentration below detection contribution to the radiation dose varied widely, (5–7) limit. As done in previous thoron studies ,a ranging from 0.5 to 6.0 % geographically. On average thoron concentration at half of the detection limit, i.e. (population weighted), thoron contributes 2.7 % of 2Bqm , was assigned to those below the detection the radiation dose due to indoor radon and thoron ex- limit for the purpose of statistical analysis. Thoron posure in Canada. was present in about half of the homes surveyed in this study with the highest measured value being 210 DISCUSSION Bq m . The population-weighted AM concentration 23 (5–7) of thoron was 9 + 11 Bq m . Based on limited measurements in ,400 homes , For each CMA using the measured AM radon and it was estimated that thoron contributes 8 % of the thoron concentrations, thoron contribution to the radiation dose due to indoor radon and thoron expos- (3) total indoor radon exposure was determined according ure . The current study provided simultaneous 213 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 J. CHEN ET AL. radon and thoron measurements in .3000 homes in concentrations could be due to different measurement 33 CMAs across Canada. It is confirmed that thoron protocols being followed in previous and current (5–7) contributes a small fraction, 3 % of the dose from studies. In the previous thoron studies , instruc- exposure to indoor radon. Consistent with previous tions were given to participants to place RADUET thoron studies, thoron was not detectable in about detectors in the basement and within 50 cm of the ex- half of the homes surveyed. ternal foundation wall, in order to increase thoron de- Among the 33 metropolitan areas, thoron contri- tection capability. The average distance between butions were determined in three metropolitan areas detector and foundation wall was 7 cm with an SD of (5–7) in previous studies . They are Halifax, Ottawa- 10 cm, and the average distance between detector and Gatineau (the National Capital Region, NCR) and basement floor was 42 cm with an SD of 30 cm in the (6) Winnipeg. Table 2 provides the results of all available 2008 Winnipeg thoron study . radon or radon–thoron studies or surveys in those In the current study, participants were required to three areas. Thoron concentrations were significantly follow Health Canada’s guide for radon measurements (15) lower than the results previously observed in all three in residential dwellings . In addition to other envir- cities listed in Table 2. The consistently lower thoron onmental factors, the Guide specifies the preferred de- tector location being by an interior wall at a height of 0.8–2 m from the floor in the typical breathing zone, however, at least 50 cm from the ceiling and 20 cm from other objects so as to allow normal airflow around the detector. Potential measurement locations include family rooms, living rooms, dens, playrooms and bedrooms. A lower level bedroom is preferred because people generally spend more time in their bed- rooms than in any other room in the house. Similarly, if there are children in the home, the lowest level bed- rooms or other areas such as a playroom are preferred. Detectors should be placed 40 cm from an interior wall or 50 cm from an exterior wall. Among a total of 3215 measurements, 1775 tests were conducted in upper floors, 1294 in basements and 146 had no test lo- cation specified. While all tests were performed in base- ments in previous thoron studies, only 40 % of tests were located in basements in this study. However, by Figure 1. Result distribution of paired radon–thoron measurements in 3215 Canadian homes. following the radon measurement protocol, this study Table 2. Comparison of current results with results from previous studies in Halifax, Ottawa-Gatineau (NCR) and Winnipeg. Sample size Rn . 200 Radon AM+ SD, Thoron AM+ SD, 23 23 23 Bq m (%) Bq m Bq m Halifax 2011 study 64 32 259+ 475 50+ 46 2012 survey 103 14 105+ 176 — This study 102 29 185+ 269 12+ 17 NCR 2008 study 95 12 110+ 168 56+ 123 2012 survey 126 9.5 88+ 134 — This study 109 10 108+ 91 11+ 21 Winnipeg 1990 study Basements 3669 31 197+ 194 — Bedrooms 4238 13 121+ 136 — 2009 study 116 20 143+ 101 34+ 45 2012 survey 66 12 113+ 80 — This study 101 49 257+ 210 8+ 9 214 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 RADON – THORON SURVEY IN CANADA provided a more realistic estimate of the radon and ACKNOWLEDGEMENTS thoron exposure of the occupants. Nevertheless, the The authors thank Dr Janik (National Institute of specified detector locations may be further away from Radiological Sciences, Japan) and Dr Tokonami potential thoron sources and resulted in relatively (Hirosaki University, Japan) for providing radon and lower thoron concentrations due to the very short half- thoron calibration services for the RadoSys Radon/ life of thoron gas. Thoron Detection System used in this survey. One can see from Table 2, except in the NCR where radon characteristics agreed reasonably well among REFERENCES three studies, that fluctuations in radon characteristics were clearly observed in Halifax and Winnipeg from 1. United Nations Scientific Committee on the Effects of different studies/surveys. Such large fluctuations are Atomic Radiation (UNSCEAR). Effects of ionizing not unusual for a sample size of 100 in a metropol- radiation. Volume I: Sources-to-effects assessment for itan area. Winnipeg is a city of 778 400. From 1983 to radon in homes and workplaces. ISBN 978-92-1- 142263-4. United Nations, (2006). 1990, Health Canada conducted a case–control study (19) 2. World Health Organization (WHO). WHO Handbook for radon and lung cancer in Winnipeg . There on Indoor Radon. ISBN 978-92-4-154767-3, 2009. were 3669 tests conducted in basements and 4238 in Available on http://whqlibdoc.who.int/publications/ bedrooms on upper floors. Averaged over 8000 mea- 2009/9789241547673_eng.pdf. surements in basements and bedrooms, the average 3. Chen, J., Dessau, J. C., Frenette, E., Moir, D. and radon concentration in Winnipeg homes was estimated Cornett, J. Preliminary assessment of thoron exposure in to be 159 + 165 Bq m . The three subsequent studies Canada. Radiat. Prot. Dosim. 141, 322–327 (2010). had a sample size of only 100. Even with such small 4. Shang, B., Chen, B., Gao, Y., Wang, Y., Cui, H. and Li, sample sizes, the estimated AM radon concentrations Z. Thoron levels in traditional Chinese residential dwell- ings. Radiat. Environ. Biophys. 44, 193–199 (2005). were well within the SD of the more accurate estimate 5. Chen,J., Tokonami,S., Sorimachi, A., Takahashi, H.and of AM ¼ 159 Bq m determined from several thou- Falcomer, R. Results of simultaneous radon and thoron sand measurements. Repeated studies have demon- tests in Ottawa.Radiat. Prot.Dosim. 130, 253–256 (2008). strated that radon concentrations in some Canadian 6. Chen, J., Schroth, E., Fife, I., MacKelay, E., Tokonami, S. homes are above the recommended action level of 200 222 220 and Sorimachi, A. Simultaneous Rn and Rn measure- Bq m . Taking the city of Winnipeg for example, ments in Winnipeg, Canada. Radiat. Prot. Dosim. 134, .20 % of Winnipeg homes were .200 Bq m 30 y 75–78 (2009). ago, and it still is the case now. 7. Chen, J., Moir, D., Pronk, T., Goodwin, T., Janik, M. and Tokonami, S. An update on thoron exposure in 222 220 Canada with simultaneous Rn and Rn measure- CONCLUSIONS ments in Fredericton and Halifax. Radiat. Prot. Dosim. 147, 541–547 (2011). Strong evidence has demonstrated that domestic 222 8. McLaughlin, J., Murray, M., Currivan, L., Pollard, D., radon exposure causes lung cancer. Rn (radon) Smith, V., Tokonami, S., Sorimachi, A. and Janik, M. and Rn (thoron) are the most common isotopes of Long-term measurements of thoron, its airborne progeny radon. In order to assess thoron contribution to and radon in 205 dwellings in Ireland. Radiat. Prot. indoor radon and thoron exposure, a survey of resi- Dosim. 145, 189–193 (2011). dential radon and thoron concentrations was initiated 9. Szeiler, G., Somlai, J., Ishikawa, T., Omori, Y., Mishra, in 2012 in 4000 homes in the 33 metropolitan areas R., Sapra, B. K., Mayya, Y. S., Tokonami, S., Csordas, A. and Kovacs, T. Preliminary results from an indoor of Canada. The survey had a return rate of 79 %. It radon thoron survey in Hungary. Radiat. Prot. Dosim. confirmed that indoor radon and thoron concentra- 152, 243–246 (2012). tions are not correlated and that thoron concentra- 10. Janik, M., Tokonami, S., Kranrod, C., Sorimachi, A., tions cannot be predicted from widely available radon Ishikawa, T., Hosoda, M., McLaughlin, J., Chang, B. U. information. The results showed that thoron contribu- and Kim, Y. J. Comparative analysis of radon, thoron and tion to the radiation dose varied geographically from thoron progeny concentration measurements. J. Radiat. 0.5 to 6.0 %. The study indicated that on average, Res. 54, 597–610 (2013). thoron contributes 3 % of the radiation dose due to 11. Health Canada. Cross-Canada survey of radon concentra- indoor radon and thoron exposure in Canada. tions in homes—final report (2012). Available on http:// www.hc-sc.gc.ca/ewh-semt/alt_formats/pdf/radiation/ Even though the estimated average thoron concen- radon/survey-sondage-eng.pdf. tration of 9 Bq m (population weighted) in Canada 12. Chen, J. and Moir, D. A study on the thoron sensitivity of is low, the estimated average radon concentration of 23 radon detectors available to Canadians. J. Radiol. Prot. 96 Bq m (population weighted) is more than 32, 419–425 (2012). double the worldwide average indoor radon concen- 13. Health Canada. Radon – thoron survey in Canadian 23 (1) tration (AM ¼ 39 Bq m , population weighted) . metropolitan areas (2012). Available on: http://www.hc- It is clear that continued efforts are needed to further sc.gc.ca/ewh-semt/radiation/radon/thoron-eng.php. reduce the exposure and effectively reduce the 14. Statistics Canada. Population of census metropolitan number of lung cancers caused by radon. areas. Population as of July 1st 2012. (2013). Available 215 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 J. CHEN ET AL. on: http://www.statcan.gc.ca/tables-tableaux/sum-som/ 17. Currie, L. A. Limits for qualitative detection and quanti- l01/cst01/demo05a-eng.htm. tative determination. Anal. Chem. 40, 586–593 (1968). 15. Health Canada. Guide for Radon Measurements in 18. Tokonami, S., Takahashi, H., Kobayashi, Y., Zhuo, W. Residential Dwellings (Homes) (2008). Available on: and Hulber, E. Up-to-date radon-thoron discriminative http://www.hc-sc.gc.ca/ewh-semt/alt_formats/hecs-sesc/ detector for a large scale survey. Rev. Sci. Instrum. 76, pdf/pubs/radiation/radon_homes-maisons/radon_ 113505–113509 (2005). homes-maisons-eng.pdf. 19. Letourneau, E. G., Krewski, D., Choi, N. W., Goddard, 16. Zhuo, W., Tokonami, S., Yonehara, H. and Yamada, Y. M. J., McGregor, R. G., Zielinski, J. M. and Du, J. A simple passive monitor for integrating measurements of Case-control study of residential radon and lung cancer in indoor thoron concentrations. Rev. Sci. Instrum. 73, Winnipeg, Manitoba, Canada. Am. J. Epidemiol. 140, 2877–2881 (2002). 310–322 (1994). http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Radiation Protection Dosimetry Oxford University Press

Results of simultaneous radon and thoron measurements in 33 metropolitan areas of Canada

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Abstract

Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 Radiation Protection Dosimetry (2015), Vol. 163, No. 2, pp. 210–216 doi:10.1093/rpd/ncu141 Advance Access publication 19 April 2014 RESULTS OF SIMULTANEOUS RADON AND THORON MEASUREMENTS IN 33 METROPOLITAN AREAS OF CANADA Jing Chen*, Lauren Bergman, Renato Falcomer and Jeff Whyte Health Canada, Radiation Protection Bureau, 775 Brookfield Road, Ottawa, Canada, K1A 1C1 *Corresponding author: [email protected] Received 3 February 2014; revised 21 March 2014; accepted 22 March 2014 222 220 Radon has been identified as the second leading cause of lung cancer after tobacco smoking. Rn (radon gas) and Rn (thoron gas) are the most common isotopes of radon. In order to assess thoron contribution to indoor radon and thoron exposure, a survey of residential radon and thoron concentrations was initiated in 2012 with ∼4000 homes in the 33 census metropolitan areas of Canada. The survey confirmed that indoor radon and thoron concentrations are not correlated and that thoron concen- trations cannot be predicted from widely available radon information. The results showed that thoron contribution to the radi- ation dose varied from 0.5 to 6 % geographically. The study indicated that, on average, thoron contributes ∼3 % of the radiation dose due to indoor radon and thoron exposure in Canada. Even though the estimated average thoron concentration of 9 Bq m (population weighted) in Canada is low, the average radon concentration of 96 Bq m (population weighted) is more than double the worldwide average indoor radon concentration. It is clear that continued efforts are needed to further reduce the exposure and effectively reduce the number of lung cancers caused by radon. (4–10) INTRODUCTION from widely available radon information .In 2008 and 2011, simultaneous radon and thoron mea- Radon is a naturally occurring radioactive gas gener- surements were performed in a total of 370 Canadian ated by the decay of uranium- and thorium-bearing (5–7) homes in five communities . Based on those minerals in rocks and soils. Radon and its decay pro- results, it was estimated that thoron contributes 8% ducts are the major contributors to human exposure of the radiation dose due to indoor radon and thoron (1) from natural radiation sources . Radon has been (3) exposure . To confirm this estimate, a larger cross- identified as the second leading cause of lung cancer Canada survey was needed. (2) 222 after tobacco smoking . Rn (radon gas) and The Cross-Canada Survey of Radon Concentrations Rn (thoron gas) are the most common isotopes of (11) in Homes study was completed recently .However, radon. detectors used in that study were not sensitive to Radon is a member of the U decay chain thoron, and thoron information was not included as whereas thoron is a member of the Th decay chain. (12) part of the radon survey . Because radon and thoron are members of different In 2012, another survey was initiated in Canadian decay chains, their concentrations depend in part on metropolitan areas to estimate thoron contribution to the uranium and thorium levels in local soils and (13) indoor radon and thoron exposure . Results of this building materials. Because wood-frame construction 2012/2013 radon–thoron survey are reported here. is very popular for family houses, building materials contribute very little to indoor radon and thoron in Canada. Information on geographical distributions METHODS of uranium and thorium in the ground is limited or not available for many metropolitan areas of Canada, In order to assess thoron contribution to indoor radon as shown in Figures 1 and 2 of a previous publica- and thoron exposure combined, a survey of residential (3) tion . Nevertheless, the previous study was able to radon and thoron concentrations was designed for demonstrate that average indoor radon and thoron 4000 homes in all 33 census metropolitan areas (14) concentrations in an area correlate well with the (CMAs) specified by Statistics Canada , which cover average uranium and thorium concentrations in the 70 % of the Canadian population. The CMAs, from ground, even though the ratio of uranium and east to west, are St. John’s, Halifax, Moncton, Saint thorium concentrations could vary significantly from John, Saguenay, Que´bec, Sherbrooke, Trois-Rivie`res, one area to another. Montre´al, Ottawa-Gatineau, Kingston, Peterborough, Many studies have confirmed that there is no clear Oshawa, Toronto, Hamilton, St. Catharines—Niagara, correlation between radon and thoron concentrations Kitchener–Cambridge–Waterloo, Brantford, Guelph, and that thoron concentrations could not be predicted London, Windsor, Barrie, Greater Sudbury, Thunder # The Author 2014. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 RADON – THORON SURVEY IN CANADA Bay, Winnipeg, Regina, Saskatoon, Calgary, Edmonton, were conducted for a period of at least 3 months. Kelowna, Abbotsford-Mission, Vancouver and Victoria. Essential information (the start and stop time of the As the Cross-Canada Survey of Radon Concentrations test) had to be included with the returned detector. in Homes, there were several qualifying criteria that To determine the concentrations of radon and had to be satisfied for a participant to be eligible to thoron, a passive integrated radon–thoron discrim- take part in the study. First, participants had to be inative detector developed at the National Institute of the head of the household and 18 y of age or older. Radiological Sciences in Japan (commercially known Participants also had to be homeowners and be living as RADUET) was used in this survey. The principle in their primary residence. People who rented a home and technical descriptions of RADUET detectors (5, 16) were not included in the study because there is no re- have been given in previous publications .A quirement on the part of landlords to remediate high RADUET contains paired detection chambers, a radon–thoron levels if they are found in a home. In low-diffusion chamber and a high-diffusion chamber. addition, participants could not live on military bases In principle, the track densities in the low-diffusion or on-reserve, since these homes were, or were expected chamber (TD ) and high-diffusion chamber (TD ) L H to be, covered in other surveys. Homes that were built depend on both radon and thoron concentrations in on stilts or high-rise condo units that were above the the air: second floor did not qualify. Finally, homeowners could not have planned to move or be away during TD ¼ c ðRn  b Þþ c ðTn  bÞð1Þ L 11 1 12 2 the proposed timeline of the study. TD ¼ c ðRn  b Þþ c ðTn  bÞð2Þ The survey followed the procedure outlined in Health H 21 1 22 2 Canada’s guide for radon measurements in residential (15) dwellings . Radon levels in a home can vary signifi- where b and b are the background noise levels for 1 2 cantly over time. In fact, it is not uncommon to see radon and thoron concentration, respectively, i.e. they radon levels in a home change by a factor of 2 to 3 appear as radon or thoron concentration readings for over a 1-day period, and variations from season to blank control detectors. The values c , c , c and 11 12 21 season can be even larger. The highest radon levels c are the calibration coefficients. The low-diffusion are usually observed during winter months. As a chamber limits diffusion of thoron into the chamber, result, a long-term measurement period will give a therefore, c .. c . The high-diffusion chamber is 11 12 much better indication of the annual average indoor designed such that both radon and thoron can diffuse radon concentration. During a long-term measure- into the chamber easily, and c  c . 21 22 ment, there are no requirements for the occupants to To determine the above-mentioned coefficients, change their life-style once the measurement devices several groups of RADUETs were randomly taken have been put in place. Therefore, Health Canada from 5000 detectors (purchased at different times) recommends the placement of at least one long-term and exposed to three different known radon and detector in a home for a minimum of 3 to 12 months thoron concentrations at the National Institute of (12 months is optimal). For periods ,12 months, the Radiological Sciences and Hirosaki University in testing period should include a mix of seasons or be Japan. The coefficients in Equations 1 and 2 were in a mid-season to best provide a measurement that then determined to be c ¼ 0.029, c ¼ 0.001, c ¼ 11 12 21 reflects the annual average level. The ideal 3-month 0.028, c ¼ 0.022, b ¼ 0.8 and b ¼ 0.7. This cali- 22 1 2 testing period would be in the typical heating season bration is necessary to account for possible changes that runs from October through to April. The least in the detectors after the storage period and variations ideal period is during the summer since open window in the reader system and/or etching process. conditions often prevail. RADUET detectors returned for analysis were The study was designed to recruit during the sum- etched according to manufacturer’s instructions. A mer of 2012 with the testing to occur in the 2012– commercial alpha-track reader (RadoSys) was used 2013 fall/winter (October to March) periods. Each to obtain total track densities in paired low- and high- CMA was targeted to recruit 122 participants. diffusion chambers (TD and TD ). With these raw L H Participants were recruited over the telephone by a data, TD and TD , and the calibration coefficients L H contracted market research firm, Prairie Research determined earlier, radon and thoron concentrations Associates (PRA), which employed random digit are calculated as the solution of Equations 1 and 2. dialing with a sampling product of ASDE Survey Based on the fact that concentration in one Sampler. Test kits were then mailed out in October chamber depends on the other and the calculation (17) 2012 to those who agreed to participate. procedure given by Currie , the detection limits Instruction was given to all participants that the were estimated to be 3 Bq m for radon and 4 Bq 23 (18) detector should be deployed in the lowest lived-in m for thoron . Even though the theoretically esti- level of the home where someone spends at least 4 h a mated detection limits are low, it was decided to only day. In order for the result to be indicative of the report radon and thoron concentrations of .15 Bq average annual radon and thoron exposure, all tests m to the survey participants due to uncertainties of 211 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 J. CHEN ET AL. many environmental factors and variations in the radon–thoron detectors in their homes for 3 months, field deployment. All results below 15 Bq m were after which they were reminded to mail the detectors reported as ,15 Bq m . back to the Health Canada for analysis. The survey (3) As assessed in the previous publication , the had a return rate of 79 %. Five participants decided annual effective dose due to indoor radon exposure to withdraw from the survey. A total of 3215 test for a population in a given area, E (nSv), was results were reported directly to the survey partici- Rn assessed based on the formula given by the pants. Due to mechanical damage or other technical (1) UNSCEAR report : reasons, test results could not be generated for 11 par- ticipants. Among them, nine participants agreed to E ¼ C  0:4  7000  9 ð3Þ Rn Rn conduct a re-test during the 2013/2014 test season. For those detectors returned without start and end where C is the arithmetic mean (AM) radon con- dates recorded, a test duration of 91 d is assumed. Rn centration (in Bq m ), the typical value of 0.4 was This assumed exposure period was included and used as the equilibrium factor for radon indoors, a explained in the results letter sent to the participants. 23 21 recommended value of 9 nSv (Bq m h) was used Duplicate detectors were placed side-by-side in to convert radon equilibrium-equivalent concentra- every ten homes for quality control purposes. A total tion (EEC) to population effective dose and an 80 % of 319 duplicates were returned. Twelve duplicates home occupancy time, i.e. 7000 h, was assumed. The had one of the two RADUETs damaged. Radon con- population dose due to indoor radon exposure is pro- centrations measured with those randomly distributed portional to the AM radon concentration in an area. duplicates ranged from 7 to 1175 Bq m with an The population effective dose due to indoor thoron average of 104 Bq m whereas thoron concentrations exposure, E (nSv), was assessed based on the were much lower and ranged from non-detectable to Tn (1) 23 23 formula given in the UNSCEAR report : 164 Bq m with an average of only 8 Bq m . Good agreement in radon results was obtained from the E ¼ C  0:02  7000  40 ð4Þ Tn Tn duplicates placed side-by-side. The average relative deviation of radon concentrations was 8 %. However, where C is the AM thoron concentration (in Bq Tn a rather large deviation of 78 % in thoron concen- m ), the typical value of 0.02 was used as the equi- trations was observed among the same duplicates. This librium factor for thoron indoors and a recommended is mainly due to thoron concentrations that were below 23 21 value of 40 nSv (Bq m h) was used to convert the detection limit in about half of homes surveyed. thoron EEC to the effective dose. As in the case of In those cases, one detector showed non-detectable radon, the population dose due to indoor thoron whereas the duplicate recorded a value slightly above exposure is proportional to the AM thoron concen- the detection limit. It should also be mentioned that tration in an area. detectors have finite dimensions and can be .10 cm The total effective dose is the sum of the effective apart even when placed side-by-side and bound toge- doses due to exposures to indoor radon and thoron. ther. Because of its short half-life, the thoron measure- Thoron contribution to the radiation dose due to ment is more sensitive to variations in air flow around indoor radon and thoron exposure can then be deter- detectors, and more dependent on distances from mined as follows: thoron sources. This can explain the relatively large de- viation in readings from detectors for thoron concen- Tn trations in comparison with radon measurements. For ð5Þ homes with control detectors, average radon and E þ E Rn Tn thoron concentrations from those duplicate detectors were reported. Among the 3215 test-kits returned, both radon and RESULTS thoron measurements were available for 3184 homes. During the summer of 2012, the research firm PRA Thirty-one participants received only radon results due dialled over 100 000 telephone numbers in order to to damage to the high-diffusion chamber. The charac- recruit at least 4000 participants from 33 metropol- teristics of the radon and thoron concentrations in the itan areas. About 92.5 % of households phoned were 33 CMAs are summarised in Table 1. Radon and eligible to participate. Overall, the response rate was thoron concentrations in individual homes were not 13.5 % and the refusal rate was 30.9 %, which were correlated, as shown in Figure 1 for the entire data set. expected for a study of this nature. By the end of This is also true for individual CMAs. October 2012, detectors were mailed to a total of Radon was present in all homes in varying concen- 4064 participants. Detailed breakdown in the trations with the highest measured concentration of numbers of participants for each CMA is given in 2117 Bq m . The population-weighted AM concen- Table 1. According to the instruction included in the tration of radon and the standard deviation (SD) were mail-out, the participants deployed the alpha-track 96 and 87 Bq m , respectively. 212 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 RADON – THORON SURVEY IN CANADA Table 1. Sample distribution and test results in 33 CMAs. 23 23 CMA Population Number of Results Number of Rn, Bq m Tn, Bq m E / Tn (thousands) participants reported Tn , DL AM + SD AM + SD (E þ E ) (%) Rn Tn Abbotsford- 178.1 122 90 38 58 + 53 11 + 17 4.1 Mission Barrie 196.0 122 88 44 85 + 88 10 + 16 2.5 Brantford 140.5 122 89 43 108 + 96 12 + 19 2.5 Calgary 1309.2 123 99 64 135 + 106 6 + 6 0.9 Edmonton 1230.1 122 97 51 113 + 68 8 + 9 1.6 Greater Sudbury 164.0 122 96 56 131 + 113 8 + 13 1.4 Guelph 142.9 122 102 59 131 + 153 8 + 10 1.3 Halifax 413.7 125 102 48 185 + 269 12 + 17 1.4 Hamilton 756.6 122 87 42 85 + 67 10 + 20 2.5 Kelowna 184.7 122 108 63 134 + 135 8 + 11 1.4 Kingston 165.5 122 97 53 165 + 131 11 + 19 1.5 Kitchener– 505.1 122 102 55 66 + 37 9 + 18 2.8 Cambridge– Waterloo London 500.0 122 81 43 85 + 60 7 + 8 1.9 Moncton 143.0 122 95 47 77 + 77 8 + 11 2.3 Montreal 3957.7 122 99 48 120 + 143 9 + 9 1.6 Oshawa 375.6 122 96 42 61 + 48 12 + 16 4.0 Ottawa-Gatineau 1273.3 122 109 61 108 + 91 11 + 21 2.2 Peterborough 122.4 122 100 52 100 + 60 8 + 7 1.7 Quebec 769.6 122 99 58 115 + 152 9 + 22 1.7 Regina 226.3 121 96 69 302 + 254 7 + 12 0.5 Saguenay 152.6 124 100 44 89 + 104 11 + 21 2.6 Saint John 128.9 154 116 54 115 + 131 13 + 24 2.4 Saskatoon 284.0 122 104 65 152 + 78 9 + 13 1.3 Sherbrooke 203.5 122 104 60 238 + 344 8 + 9 0.8 St. Catharines— 405.8 122 87 32 56 + 36 11 + 12 4.3 Niagara St. John’s 200.6 123 97 52 88 + 63 7 + 7 1.7 Thunder Bay 127.1 122 94 53 156 + 133 10 + 16 1.4 Toronto 5941.5 123 91 33 57 + 37 9 + 8 3.3 Trois-Rivieres 148.3 122 95 30 43 + 22 11 + 12 5.4 Vancouver 2463.7 121 98 40 28 + 25 8 + 7 6.0 Victoria 363.1 122 102 46 37 + 26 8 + 8 4.5 Windsor 333.4 122 94 55 154 + 121 11 + 23 1.6 Winnipeg 778.4 122 101 50 257 + 210 8 + 9 0.7 Total or average 24 285 4064 3215 48 % 96 + 87 9 + 11 2.7 In two cases, only radon results were available. In one case, only radon result was available. In three cases, only radon results were available. On average (population weighted), 48 % of homes to Equation 5. Results are given in Table 1. Thoron surveyed had thoron concentration below detection contribution to the radiation dose varied widely, (5–7) limit. As done in previous thoron studies ,a ranging from 0.5 to 6.0 % geographically. On average thoron concentration at half of the detection limit, i.e. (population weighted), thoron contributes 2.7 % of 2Bqm , was assigned to those below the detection the radiation dose due to indoor radon and thoron ex- limit for the purpose of statistical analysis. Thoron posure in Canada. was present in about half of the homes surveyed in this study with the highest measured value being 210 DISCUSSION Bq m . The population-weighted AM concentration 23 (5–7) of thoron was 9 + 11 Bq m . Based on limited measurements in ,400 homes , For each CMA using the measured AM radon and it was estimated that thoron contributes 8 % of the thoron concentrations, thoron contribution to the radiation dose due to indoor radon and thoron expos- (3) total indoor radon exposure was determined according ure . The current study provided simultaneous 213 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 J. CHEN ET AL. radon and thoron measurements in .3000 homes in concentrations could be due to different measurement 33 CMAs across Canada. It is confirmed that thoron protocols being followed in previous and current (5–7) contributes a small fraction, 3 % of the dose from studies. In the previous thoron studies , instruc- exposure to indoor radon. Consistent with previous tions were given to participants to place RADUET thoron studies, thoron was not detectable in about detectors in the basement and within 50 cm of the ex- half of the homes surveyed. ternal foundation wall, in order to increase thoron de- Among the 33 metropolitan areas, thoron contri- tection capability. The average distance between butions were determined in three metropolitan areas detector and foundation wall was 7 cm with an SD of (5–7) in previous studies . They are Halifax, Ottawa- 10 cm, and the average distance between detector and Gatineau (the National Capital Region, NCR) and basement floor was 42 cm with an SD of 30 cm in the (6) Winnipeg. Table 2 provides the results of all available 2008 Winnipeg thoron study . radon or radon–thoron studies or surveys in those In the current study, participants were required to three areas. Thoron concentrations were significantly follow Health Canada’s guide for radon measurements (15) lower than the results previously observed in all three in residential dwellings . In addition to other envir- cities listed in Table 2. The consistently lower thoron onmental factors, the Guide specifies the preferred de- tector location being by an interior wall at a height of 0.8–2 m from the floor in the typical breathing zone, however, at least 50 cm from the ceiling and 20 cm from other objects so as to allow normal airflow around the detector. Potential measurement locations include family rooms, living rooms, dens, playrooms and bedrooms. A lower level bedroom is preferred because people generally spend more time in their bed- rooms than in any other room in the house. Similarly, if there are children in the home, the lowest level bed- rooms or other areas such as a playroom are preferred. Detectors should be placed 40 cm from an interior wall or 50 cm from an exterior wall. Among a total of 3215 measurements, 1775 tests were conducted in upper floors, 1294 in basements and 146 had no test lo- cation specified. While all tests were performed in base- ments in previous thoron studies, only 40 % of tests were located in basements in this study. However, by Figure 1. Result distribution of paired radon–thoron measurements in 3215 Canadian homes. following the radon measurement protocol, this study Table 2. Comparison of current results with results from previous studies in Halifax, Ottawa-Gatineau (NCR) and Winnipeg. Sample size Rn . 200 Radon AM+ SD, Thoron AM+ SD, 23 23 23 Bq m (%) Bq m Bq m Halifax 2011 study 64 32 259+ 475 50+ 46 2012 survey 103 14 105+ 176 — This study 102 29 185+ 269 12+ 17 NCR 2008 study 95 12 110+ 168 56+ 123 2012 survey 126 9.5 88+ 134 — This study 109 10 108+ 91 11+ 21 Winnipeg 1990 study Basements 3669 31 197+ 194 — Bedrooms 4238 13 121+ 136 — 2009 study 116 20 143+ 101 34+ 45 2012 survey 66 12 113+ 80 — This study 101 49 257+ 210 8+ 9 214 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 RADON – THORON SURVEY IN CANADA provided a more realistic estimate of the radon and ACKNOWLEDGEMENTS thoron exposure of the occupants. Nevertheless, the The authors thank Dr Janik (National Institute of specified detector locations may be further away from Radiological Sciences, Japan) and Dr Tokonami potential thoron sources and resulted in relatively (Hirosaki University, Japan) for providing radon and lower thoron concentrations due to the very short half- thoron calibration services for the RadoSys Radon/ life of thoron gas. Thoron Detection System used in this survey. One can see from Table 2, except in the NCR where radon characteristics agreed reasonably well among REFERENCES three studies, that fluctuations in radon characteristics were clearly observed in Halifax and Winnipeg from 1. United Nations Scientific Committee on the Effects of different studies/surveys. Such large fluctuations are Atomic Radiation (UNSCEAR). Effects of ionizing not unusual for a sample size of 100 in a metropol- radiation. Volume I: Sources-to-effects assessment for itan area. Winnipeg is a city of 778 400. From 1983 to radon in homes and workplaces. ISBN 978-92-1- 142263-4. United Nations, (2006). 1990, Health Canada conducted a case–control study (19) 2. World Health Organization (WHO). WHO Handbook for radon and lung cancer in Winnipeg . There on Indoor Radon. ISBN 978-92-4-154767-3, 2009. were 3669 tests conducted in basements and 4238 in Available on http://whqlibdoc.who.int/publications/ bedrooms on upper floors. Averaged over 8000 mea- 2009/9789241547673_eng.pdf. surements in basements and bedrooms, the average 3. Chen, J., Dessau, J. C., Frenette, E., Moir, D. and radon concentration in Winnipeg homes was estimated Cornett, J. Preliminary assessment of thoron exposure in to be 159 + 165 Bq m . The three subsequent studies Canada. Radiat. Prot. Dosim. 141, 322–327 (2010). had a sample size of only 100. Even with such small 4. Shang, B., Chen, B., Gao, Y., Wang, Y., Cui, H. and Li, sample sizes, the estimated AM radon concentrations Z. Thoron levels in traditional Chinese residential dwell- ings. Radiat. Environ. Biophys. 44, 193–199 (2005). were well within the SD of the more accurate estimate 5. Chen,J., Tokonami,S., Sorimachi, A., Takahashi, H.and of AM ¼ 159 Bq m determined from several thou- Falcomer, R. Results of simultaneous radon and thoron sand measurements. Repeated studies have demon- tests in Ottawa.Radiat. Prot.Dosim. 130, 253–256 (2008). strated that radon concentrations in some Canadian 6. Chen, J., Schroth, E., Fife, I., MacKelay, E., Tokonami, S. homes are above the recommended action level of 200 222 220 and Sorimachi, A. Simultaneous Rn and Rn measure- Bq m . Taking the city of Winnipeg for example, ments in Winnipeg, Canada. Radiat. Prot. Dosim. 134, .20 % of Winnipeg homes were .200 Bq m 30 y 75–78 (2009). ago, and it still is the case now. 7. Chen, J., Moir, D., Pronk, T., Goodwin, T., Janik, M. and Tokonami, S. An update on thoron exposure in 222 220 Canada with simultaneous Rn and Rn measure- CONCLUSIONS ments in Fredericton and Halifax. Radiat. Prot. Dosim. 147, 541–547 (2011). Strong evidence has demonstrated that domestic 222 8. McLaughlin, J., Murray, M., Currivan, L., Pollard, D., radon exposure causes lung cancer. Rn (radon) Smith, V., Tokonami, S., Sorimachi, A. and Janik, M. and Rn (thoron) are the most common isotopes of Long-term measurements of thoron, its airborne progeny radon. In order to assess thoron contribution to and radon in 205 dwellings in Ireland. Radiat. Prot. indoor radon and thoron exposure, a survey of resi- Dosim. 145, 189–193 (2011). dential radon and thoron concentrations was initiated 9. Szeiler, G., Somlai, J., Ishikawa, T., Omori, Y., Mishra, in 2012 in 4000 homes in the 33 metropolitan areas R., Sapra, B. K., Mayya, Y. S., Tokonami, S., Csordas, A. and Kovacs, T. Preliminary results from an indoor of Canada. The survey had a return rate of 79 %. It radon thoron survey in Hungary. Radiat. Prot. Dosim. confirmed that indoor radon and thoron concentra- 152, 243–246 (2012). tions are not correlated and that thoron concentra- 10. Janik, M., Tokonami, S., Kranrod, C., Sorimachi, A., tions cannot be predicted from widely available radon Ishikawa, T., Hosoda, M., McLaughlin, J., Chang, B. U. information. The results showed that thoron contribu- and Kim, Y. J. Comparative analysis of radon, thoron and tion to the radiation dose varied geographically from thoron progeny concentration measurements. J. Radiat. 0.5 to 6.0 %. The study indicated that on average, Res. 54, 597–610 (2013). thoron contributes 3 % of the radiation dose due to 11. Health Canada. Cross-Canada survey of radon concentra- indoor radon and thoron exposure in Canada. tions in homes—final report (2012). Available on http:// www.hc-sc.gc.ca/ewh-semt/alt_formats/pdf/radiation/ Even though the estimated average thoron concen- radon/survey-sondage-eng.pdf. tration of 9 Bq m (population weighted) in Canada 12. Chen, J. and Moir, D. A study on the thoron sensitivity of is low, the estimated average radon concentration of 23 radon detectors available to Canadians. J. Radiol. Prot. 96 Bq m (population weighted) is more than 32, 419–425 (2012). double the worldwide average indoor radon concen- 13. Health Canada. Radon – thoron survey in Canadian 23 (1) tration (AM ¼ 39 Bq m , population weighted) . metropolitan areas (2012). Available on: http://www.hc- It is clear that continued efforts are needed to further sc.gc.ca/ewh-semt/radiation/radon/thoron-eng.php. reduce the exposure and effectively reduce the 14. Statistics Canada. Population of census metropolitan number of lung cancers caused by radon. areas. Population as of July 1st 2012. (2013). Available 215 Downloaded from https://academic.oup.com/rpd/article/163/2/210/1650066 by DeepDyve user on 13 July 2022 J. CHEN ET AL. on: http://www.statcan.gc.ca/tables-tableaux/sum-som/ 17. Currie, L. A. Limits for qualitative detection and quanti- l01/cst01/demo05a-eng.htm. tative determination. Anal. Chem. 40, 586–593 (1968). 15. Health Canada. Guide for Radon Measurements in 18. Tokonami, S., Takahashi, H., Kobayashi, Y., Zhuo, W. Residential Dwellings (Homes) (2008). Available on: and Hulber, E. Up-to-date radon-thoron discriminative http://www.hc-sc.gc.ca/ewh-semt/alt_formats/hecs-sesc/ detector for a large scale survey. Rev. Sci. Instrum. 76, pdf/pubs/radiation/radon_homes-maisons/radon_ 113505–113509 (2005). homes-maisons-eng.pdf. 19. Letourneau, E. G., Krewski, D., Choi, N. W., Goddard, 16. Zhuo, W., Tokonami, S., Yonehara, H. and Yamada, Y. M. J., McGregor, R. G., Zielinski, J. M. and Du, J. A simple passive monitor for integrating measurements of Case-control study of residential radon and lung cancer in indoor thoron concentrations. Rev. Sci. Instrum. 73, Winnipeg, Manitoba, Canada. Am. J. Epidemiol. 140, 2877–2881 (2002). 310–322 (1994).

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