Journal of Radiation Protection and Research

The Korean Association for Radiation Protection (대한방사선방어학회)
권호 표지
DOI QR코드

DOI QR Code

From Radon and Thoron Measurements, Inhalation Dose Assessment to National Regulation and Radon Action Plan in Cameroon

  • Saidou (Research Centre for Nuclear Sciences and Technology, Institute of Geological and Mining Research) ;
  • Shinji Tokonami (Institute of Radiation Emergency Medicine, Hirosaki University) ;
  • Masahiro Hosoda (Institute of Radiation Emergency Medicine, Hirosaki University) ;
  • Augustin Simo (National Radiation Protection Agency) ;
  • Joseph Victor Hell (Research Centre for Nuclear Sciences and Technology, Institute of Geological and Mining Research) ;
  • Olga German (Department of Nuclear Safety and Security, International Atomic Energy Agency) ;
  • Esmel Gislere Oscar Meless (Department of Technical Cooperation, International Atomic Energy Agency)
  • Received : 2021.05.26
  • Accepted : 2022.02.21
  • Published : 2022.12.31
Download PDF
⟨ Previous Next ⟩

Abstract

Background: The current study reports measurements of activity concentrations of radon (220Rn) and thoron (220Rn) in dwellings, followed by inhalation dose assessment of the public, and then by the development of regulation and the national radon action plan (NRAP) in Cameroon. Materials and Methods: Radon, thoron, and thoron progeny measurements were carried out from 2014 to 2017 using radon-thoron discriminative detectors (commercially RADUET) in 450 dwellings and thoron progeny monitors in 350 dwellings. From 2019 to 2020, radon track detectors (commercially RADTRAK) were deployed in 1,400 dwellings. It was found that activity concentrations of radon range in 1,850 houses from 10 to 2,620 Bq/㎥ with a geometric mean of 76 Bq/㎥. Results and Discussion: Activity concentrations of thoron range from 20 to 700 Bq/㎥ with a geometric mean of 107 Bq/㎥. Thoron equilibrium factor ranges from 0.01 to 0.6, with an arithmetic mean of 0.09 that is higher than the default value of 0.02 given by UNSCEAR. On average, 49%, 9%, and 2% of all surveyed houses have radon concentrations above 100, 200, and 300 Bq/㎥, respectively. The average contribution of thoron to the inhalation dose due to radon and thoron exposure is about 40%. Thus, thoron cannot be neglected in dose assessment to avoid biased results in radio-epidemiological studies. Only radon was considered in the drafted regulation and in the NRAP adopted in October 2020. Reference levels of 300 Bq/㎥ and 1,000 Bq/㎥ were recommended for dwellings and workplaces. Conclusion: Priority actions for the coming years include the following: radon risk mapping, promotion of a protection policy against radon in buildings, integration of the radon prevention and mitigation into the training of construction specialists, mitigation of dwellings and workplaces with high radon levels, increased public awareness of the health risks associated with radon, and development of programs on the scientific and technical aspects.

Keywords

Acknowledgement

The International Atomic Energy Agency (IAEA) is thanked for its support within the framework of the CMR9009 TC Project on "Establishing a National Radon Plan for Controlling Public Exposure due to Radon Indoors." Japanese Society for the Promotion of Science (JSPS) is acknowledged for funding through JSPS KAKENHI Grant Number 26305021. The Ministry of Scientific Research and Innovation, Cameroon is thanked for permanent support through Public Investment Budget 2015-2020.

References

  1. United Nations Scientific Committee on the Effects of Atomic Radiation. Effects of ionizing radiation (Volume 1: UNSCEAR 2006 report to the General Assembly with Scientific Annexes). New York: United Nations Scientific Committee on the Effects of Atomic Radiation; 2008.
  2. International Atomic Energy Agency. Radiation protection and safety of radiation sources: international basic safety standards. Vienna: International Atomic Energy Agency; 2014.
  3. Salupeto-Dembo J, Szabo-Krausz Z, Volgyesi P, Szabo C. Radon and thoron radiation exposure of the Angolan population living in adobe houses. J Radioanal Nucl Chem. 2022;325:271-282.
  4. Chege M, Hashim N, Nyambura C, Mustapha A, Hosada M, Tokonami S. Radon and thoron; radioactive gases lurking in earthen houses in rural Kenya. Front Public Health. 2019;7:113. https://doi.org/10.3389/fpubh.2019.00113
  5. Saidou, Abdourahimi, Tchuente Siaka YF, Bouba O. Indoor radon measurements in the uranium regions of Poli and Lolodorf, Cameroon. J Environ Radioact. 2014;136:36-40. https://doi.org/10.1016/j.jenvrad.2014.05.001
  6. Saidou, Abdourahimi, Tchuente Siaka YF, Kwato Njock MG. Natural radiation exposure of the public in the oil-bearing Bakassi Peninsula, Cameroon. Radioprotection. 2015;50(1):35-41. https://doi.org/10.1051/radiopro/2014025
  7. Saidou, Modibo OB, Joseph Emmanuel NN, German O, Michaux KN, Abba HY. Indoor radon measurements using radon track detectors and electret ionization chambers in the bauxite-bearing areas of Southern Adamawa, Cameroon. Int J Environ Res Public Health. 2020;17(18):6776. https://doi.org/10.3390/ijerph17186776
  8. Saidou, Tokonami S, Janik M, Samuel BG, Abdourahimi, Joseph Emmanuel NN. Radon-thoron discriminative measurements in the high natural radiation areas of southwestern Cameroon. J Environ Radioact. 2015;150:242-246. https://doi.org/10.1016/j.jenvrad.2015.09.006
  9. Ndjana Nkoulou Ii JE, Ngoa Engola L, Hosoda M, Bongue D, Suzuki T, Kudo H, et al. Simultaneous indoor radon, thoron and thoron progeny measurements in betare-oya gold mining areas, Eastern Cameroon. Radiat Prot Dosimetry. 2019;185(3):391-401.
  10. Tokonami S, Hosoda M, Joseph Emmanuel NN, Akata N, Flore TS, Modibo OB, et al. Natural radiation exposure to the public in mining and ore-bearing regions of Cameroon. Radiat Prot Dosimetry. 2019;184(3-4):391-396. https://doi.org/10.1093/rpd/ncz176
  11. Serge Didier TS, Saidou, Tokonami S, Hosoda M, Suzuki T, Kudo H, et al. Simultaneous measurements of indoor radon and thoron and inhalation dose assessment in Douala City, Cameroon. Isotopes Environ Health Stud. 2019;55(5):499-510. https://doi.org/10.1080/10256016.2019.1649258
  12. Saidou, Tokonami S, Hosoda M, Flore TS, Ndjana Nkoulou Ii JE, Akata N, et al. Natural radiation exposure to the public in the uranium-bearing region of Poli, Cameroon: from radioactivity measurements to external and inhalation dose assessment. J Geochem Explor. 2019;205:106350. https://doi.org/10.1016/j.gexplo.2019.106350
  13. Modibo OB, Saidou, Ndjana Nkoulou Ii JE, Suzuki T, Kudo H, Hosoda M, et al. Occupational natural radiation exposure at the uranium deposit of Kitongo, Cameroon. Radioisotopes. 2019; 68(9):621-630. https://doi.org/10.3769/radioisotopes.68.621
  14. Bineng GS, Saidou, Tokonami S, Hosoda M, Tchuente Siaka YF, Issa H, et al. The importance of direct progeny measurements for correct estimation of effective dose due to radon and thoron. Front Public Health. 2020;8:17. https://doi.org/10.3389/fpubh.2020.00017
  15. Tokonami S, Takahashi H, Kobayashi Y, Zhuo W. Up-to-date radon-thoron discriminative detector for a large-scale survey. Rev Sci Instrum. 2005;76(11):113505. https://doi.org/10.1063/1.2132270
  16. Omori Y, Janik M, Sorimachi A, Ishikawa T, Tokonami S. Effects of air exchange property of passive-type radon-thoron discriminative detectors on the performance of radon and thoron measurements. Radiat Prot Dosimetry. 2012;152(1-3):140-145. https://doi.org/10.1093/rpd/ncs210
  17. Hosoda M, Tokonami S, Omori Y, Ishikawa T, Iwaoka K. A comparison of the dose from natural radionuclides and artificial radionuclides after the Fukushima nuclear accident. J Radiat Res. 2016;57(4):422-430. https://doi.org/10.1093/jrr/rrv102
  18. Pornnumpa C, Oyama Y, Iwaoka K, Hosoda M, Tokonami S. Development of radon and thoron exposure systems at Hirosaki University. Radiat Environ Med. 2018;7(1):13-20.
  19. Zhuo W, Iida T. Estimation of thoron progeny concentration in dwellings with their deposition rate measurements. Jpn J Health Phys. 2000;35(3):365-370. https://doi.org/10.5453/jhps.35.365
  20. Sorimachi A, Tokonami S, Kranrod C, Ishikawa T. Preliminary experiments using a passive detector for measuring indoor 220Rn progeny concentrations with an aerosol chamber. Health Phys. 2015;108(6):597-606. https://doi.org/10.1097/HP.0000000000000284
  21. Tamakuma Y, Nugraha ED, Suzuki T, Hosoda M, Tokonami S. Calibration chamber for radon, thoron and their progenies at Hirosaki University, Japan. Proceedings of the 15th International Congress of the International Radiation Protection Association; 2021 Jan 18-19; Seoul, Korea.
  22. International Standard Organization. Measurement of radioactivity in the environment - Air-radon 220: integrated measurement methods for the determination of the average activity concentration using passive solid-state nuclear track detectors. Geneva, Switzerland: International Standard Organization; 2014. ISO 16641:2014.
  23. International Standard Organization. Measurement of radioactivity in the environment-Air: radon-222. Part 4: integrated measurement method for determining average activity concentration using passive sampling and delayed analysis. Geneva, Switzerland: International Standard Organization; 2020. ISO 11665-4:2020.
  24. Hosoda M, Kudo H, Iwaoka K, Yamada R, Suzuki T, Tamakuma Y, et al. Characteristic of thoron (220Rn) in environment. Appl Radiat Isot. 2017;120:7-10. https://doi.org/10.1016/j.apradiso.2016.11.014
  25. United Nations Scientific Committee on the Effects of Atomic Radiation. Sources and effects of ionizing radiation (Volume 1). New York, NY: United Nations Scientific Committee on the Effects of Atomic Radiation; 2000.
  26. Tirmarche M, Harrison JD, Laurier D, Paquet F, Blanchardon E, Marsh JW, et al. ICRP Publication 115. Lung cancer risk from radon and progeny and statement on radon. Ann ICRP. 2010;40(1): 1-64. https://doi.org/10.1016/j.icrp.2011.08.011
  27. Paquet F, Bailey MR, Leggett RW, Lipsztein J, Marsh J, Fell TP, et al. ICRP Publication 137. Occupational intakes of radionuclides: part 3. Ann ICRP. 2017;46(3-4):1-486. https://doi.org/10.1177/0146645317734963
  28. United Nations. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation: sixty-sixth session (10-14 June 2019). New York, NY: United Nations; 2019.
  29. Soumayah B, Saidou, Ndjana Nkoulou Ii JE, Haman F, Kwato Njock MG. Natural radiation exposure and radiological hazard analysis in a radon-prone area of the Adamawa Region, Cameroon. Radiat Prot Dosimetry. 2022;198(1-2);74-85.
  30. Mbida Mbembe S, Akamba Mbembe B, Manga A, Ele Abiama P, Saidou, Ondo Meye P, et al. Indoor radon, external dose rate and assessment of lung cancer risk in dwellings: the case of Ebolowa town, Southern Cameroon. Int J Environ Anal Chem. 2021 Aug 27 [Epub]. https://doi.org/10.1080/03067319.2021.1946684.