Natural radiation exposure due to radon

and thoron indoors in the mining and ore bearing regions of Cameroon: from

measurement, inhalation dose assessment to a national radon plan

SAÏDOU1, Shinji TOKONAMI2, Masahiro HOSODA2

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Nuclear Technology Section, Institute of Geological and Mining Research, Cameroon

Institute of Radiation Emergency Medicine, Hirosaki University, Japan

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The Ninth International Symposium on Naturally Occurring Radioactive Material

23-27 September 2019 - Denver, Colorado, USA

Outline

❖Introduction

❖Material and methods▪RADUET detectors (Rn and Tn)

▪Thoron progeny monitors (TnP)

❖Results▪ Indoor Rn, Tn, TnP and inhalation dose

▪Achievements of CMR9009

❖Conclusion and perspectives

Introduction• Since 2005 several research

studies of natural radiation exposure to the public wereperformed in the following areas:– Uranium bearing region of Poli

– Uranium and thorium bearingregion of Lolodorf

– Gold mining region of East Cameroon

– Bauxite bearing region of South Adamawa

– Oil bearing Bakassi Peninsula

– Yaounde and Douala cities

• Focus on radon indoors since 2012 using Electrets ionization chambers and Raduet detectors from 2014

• Most of the study areas are mining or ore bearing areas.

Material and methods

Metasomatite uranium deposit of Kitongo: 10 000- 25 000 tU

at a grade of 0.05-0.1%

Status: Exploration (UDEPO, 2016)

Material and methods

House built on a high naturalradiation area at Bikoue (Mvengue) Lolodorf (August 2016)

Intrusive uranium deposit of Lolodorf: 1 000-2 500 tU

at a grade of 0.05-0.1%

Status: Exploration (UDEPO, 2016)

Material and methodsStudy area Number of Raduet

detectors deployed

Number of TnP

monitors deployed

Uranium bearing

region of Poli

100 40

Thorium bearing

region of Lolodorf

220 170

Gold mining areas of

Betare Oya

50 50

Douala city 70 70

Total 450 330

Material and methods

Study areas Inhabited areas

Uranium bearing region of Poli Fignole, Gompou, Gode, Poli,

Kitongo

Thorium bearing region of Lolodorf Awanda, Akongo, Ngombas, Bikoue,

Lolodorf, Kribi, Logbatindi, Eseka

Gold mining areas of Betare Oya Betare Oya, Mali

Douala city Douala I, Douala II, Douala III

Detectors collected after 2-3 months and sent back to Hirosaki

University in Japan for analysis.

Material and methods

Radon, thoron and progeny indoors

Material and methods

Microscope method Image-J method

Results

Study area Radionuclide Mean concentration

(Bq.m-3)

Range (Bq.m-3)

Poli 222Rn 82 46-143

220Rn 94 18-238

Lolodorf 222Rn 97 27-937

220Rn 160 6-700

Betare Oya 222Rn 133 88-282

220Rn 92 4-383

Douala 222Rn 139 31-436

220Rn 80 4-246

Rn and Tn concentrations

Results

Study area Rn>100

Bq.m-3 (%)

Tn>100

Bq.m-3 (%)

Rn>300

Bq.m-3 (%)

Tn>300

Bq.m-3 (%)

Poli 20 42 0 0

Lolodorf 47 54 1 10

Betare-Oya 76 25 3 3

Douala city 27 27 0 0

Reference Levels : 100 and 300 Bq.m-3

Results

Reference Level (RL)=100 Bq.m-3

• 43% of houses have Rn > RL

• 37% of houses have Tn > RL

Reference Level (RL)=300 Bq.m-3

• 1% of houses have Rn > RL

• 3.3% of houses have Tn > RL

Results

• When setting a reference level, various national factors such as the distribution of radon, the number of existing homes with high radon concentrations, the arithmetic mean indoor radon level and the prevalence of smoking should be taken into consideration.

• The lower the national reference level, the more the overall population risk from radon exposure would be mitigated.

Results

Study area Mean EETC

(Bq.m-3)

Range

(Bq.m-3)

Mean Equilibrium

Factor

Range

Poli 6.4 4-9 0.08 0.01-0.3

Lolodorf 10.3 0.4-36 0.1 0.01-0.6

Betare Oya 6 0.6-19 0.1 0.01-0.5

Douala city 4.6 1.5-13 0.07 0.02-0.3

Equilibrium Equivalent Thoron Concentrations (EETC)

❑ The world mean value of the Equilibrium Factor for thoron (FTn=EETC/Tn)

given by UNSCEAR is 0.02.

❑ High Equilibrium Factor leads to high corresponding inhalation dose.

ResultsInhalation dose due to radon and thoron

Study area Mean Rn

inhal. dose

(mSv.yr-1)

Range

(mSv.y-1)

Mean Tn

inhal. dose

(mSv.y-1)

Range

(mSv.y-1)

Mean

contribution

of Tn (%)

Range

(%)

Poli 1.5 0.9-2.6 1.8 0.34-6.2 49 12-67

Lolodorf 2 0.53-18.5 2.2 0.08-7.9 53 3-80

Betare Oya 2.5 1.7-5.3 2 0.13-4 31 7-70

Douala city 2.6 0.6-9 1 0.3-2.9 26 7-60

❑ World average value for radon+thoron (UNSCEAR): 1.26 mSv.y-1 (0.2-10)

❑ Uranium bearing region of Poli: 3.3 mSv.y-1 (1.3-8.8)

❑ Uranium and thorium bearing region of Lolodorf: 4.4 mSv.y-1 (0.7-26.5)

❑ RL=300 Bq.m-3 corresponds to, in terms of effective dose, approximately 10

mSv year for radon.

Results

❖The average contribution of thoron to the total

inhalation dose is 40% in the studied areas of

Cameroon.

❖Thus thoron can not be neglected in dose assessment

to avoid biased results in radio-epidemiological

studies.

❖Thus it would be advisable to define reference level

for Tn at the international scale or combine reference

level for radon and thoron

Results1. Saïdou et al. (2014). Indoor radon measurements in the uranium regions of Poli and Lolodorf, Cameroon.

Journal of Environmental Radioactivity 136, 36-40.

2. Saïdou et al. (2015). Natural Radiation Exposure of the Public in the oil-bearing Bakassi Peninsula,

Cameroon. Radioprotection, Vol 50, 35-41.

3. Saïdou et al. (2015). Radon-Thoron discriminative measurements in the high natural radiation areas of

Southwestern Cameroon. Journal of Environmental Radioactivity 150, 242-246.

4. Saïdou et al. Comparative study of natural radiation exposure in three uranium and oil regions of

Cameroon. Radioprotection, DOI: 10.1051/radiopro/2015017

5. Saïdou et al. (2016) Natural Radiation Survey in the uranium and thorium bearing regions of Cameroon.

Radiation Environment and Medicine.

6. Ndjana Nkoulou II et al. (2019). Simultaneous indoor radon, thoron and thoron progeny measurements in

Bétaré-Oya gold mining areas, Eastern Cameroon. Radiation Protection Dosimetry, 1-11.

7. Saïdouet al. (2019). Natural radiation exposure to the public in mining and ore bearing regions of

Cameroon. Radiation Protection Dosimetry.

8. Takoukam et al. (2019). Simultaneous measurements of indoor radon and thoron and inhalation dose

assessment in Douala City, Cameroon. Isotopes in Environmental and Health Studies.

9. Saïdou et al. (2019). Natural radiation exposure to the public in the uranium bearing region of Poli,

Cameroon: from radioactivity measurements to external and inhalation dose assessment. Journal of

Geochemical Exploration.

10. Oumar Bobbo et al. (2019). Occupational natural radiation exposure at the uranium deposit of Kitongo,

Cameroon. Radioisotopes.

11. Bineng et al. Equilibrium factor influence on internal dose estimation due to indoor radon, thoron and

progeny: case of the uranium and thorium bearing region of Lolodorf, Cameroon. Under review. Journal of

Environmental Radioactivity.

Results

❑A project (CMR9009) dealing with

Establishing a national radon plan for

controlling public exposure due to radon

indoors was elaborated and submitted to IAEA

in 2016.

❑Accepted for funding within the frame of TC

between Cameroon and IAEA, the project will

run from 2018 to 2019.

❑The project effectively started in March 2018.

CMR9009 kick-off meeting

in Yaounde, 20-22 March, 2018

Achievements of CMR9009

Inputs Achievements

Training of personnel on radon 3 staff (01 SV+02 FE) trained in Spain and

Hungary

Procurement of 2000 Radtrack detectors 1500 detectors delivered

Procurement of Radon Calibration System

- ATMOS12 and Alphaguard radon

monitors with the necessary

accessories

- Radon source

- Chamber + pre-chamber with

accessories

To be delivered shortly

Procurement of an in-situ gamma spectrometer

and radon-risk equipment

Ongoing

Organization of a National Training Course on

Regulatory control of public exposure to radon

in dwelling and in workplaces

Effective

• Drafting Regulation on radon

• Definition of Reference Levels

• Drafting National Radon Action Plan

Ongoing

Radon measurements campaign Ongoing (440 Radtrak deployed)

Radon deployment plan

Conclusion and perspectives

❑Radon and Thoron exposure occurs in Cameroon

❑Reference levels should be defined for radon.Thoron should not be disregarded.

❑Extensive radon indoors and geogenic radonmeasurements should be effective to establishradon-risk mapping of Cameroon

❑Regulation on radon and the National RadonAction Plan should be effective in Cameroon

❑Government should fund the implementation ofthe National Radon Action Plan

Acknowledgments

❑Hirosaki University, Japan

❑International Atomic Energy Agency (IAEA)

❑Ministry of Scientific Research and Innovation, Cameroon

❑UNESCO-SIDA

❑University of Lausanne, Switzerland

❑University of Douala, Cameroon

❑University of Yaounde I, Cameroon

Thank you for your kind

attention