Simultaneous measurements of indoor radon and thoron and inhalation dose assessment in Douala City, Cameroon

Mapping in a radon-prone area in Adamawa region, Cameroon, by measurement of radon activity concentration in soil

The radon-prone area of the Adamawa region in Cameroon is characterized by high natural radiation background resulting from the high concentrations of radium-226, thorium-232, and indoor radon. To produce a radon-risk map, radon measurements in soil were carried out in the city of Ngaoundere. The radon activity concentration in soil gas ranged from 256 to 166 kBq m-3 with a mean of 80 kBq m-3 and a standard deviation of 38 kBq m-3. The area is mostly classified as high risk (80%) according to the Swedish classification, and 20% as medium risk. A low-risk area was not observed. Granite-like geology sites were characterized by higher radon concentration. A ratio of about 295:1 was obtained for soil radon gas to indoor radon concentrations, with a positive correlation (R = 0.40), and a transfer factor of 3 per mil. These results demonstrate that in situ measurements of radon concentration in soil can provide accurate information on the level of indoor radon concentrations. Geostatistical and deterministic interpolation techniques have been used to obtain a radon map by comparing the suitability of ordinary kriging and inverse-distance-weighted (IDW) interpolation methods. It turned out that there is not much difference in the prediction errors of the two techniques (Root Mean Square Error = 34.4 for ordinary kriging and 34.3 for IDW). It is concluded that both methods give acceptable results. In situ measurements and geostatistical analysis allow assessment of expected indoor radon exposure in a given area at reduced costs and time required. However, for the investigated area, more research is needed to produce reliable radon-risk maps.

Estimating atmospheric radon deviation using statistical coefficients: Sulaymaniyah city, Iraq, as a case of study

The authors studied the atmospheric radon concentration with associated meteorological parameters variation during the dust events from July to November 2017. We obtained the meteorological parameters data in weather station of Sulaymaniyah city, Iraq. In the environmental monitoring plan, the atmospheric radon fluctuated from 15 to 48 Bq m^-3 around the mean value of 31.5 ± 7 Bq m^-3 within the summer. In autumn, varied from 22 to 46 Bq m^-3 with a mean value of 34 ± 12 Bq m^-3. We employed this to determine the radon level anomalously. Using the modified statistical coefficients, such as the residual deviation (RD), residual fluctuation ratio (RFR), F-test, and p-value coefficients. Among the atmospheric radon fluctuation values, particularly one anomalous (42 Bq m^-3) on 25 July was determined because the excessive value of the RD was 1.9 σ, and the RFR value was 66 %. Corresponding to our coefficients criteria, the minimum level of atmospheric radon (22 Bq m^-3) does not consider anomalous because of increasing wind speed. Based on this, our method for determining the atmospheric radon anomalies that are influenced by the missed factors beyond the mentioned meteorological parameters is accurate.

INDOOR RADON (222RN) MEASUREMENTS AND ESTIMATION OF ANNUAL EFFECTIVE DOSE IN MVANGAN LOCALITY, SOUTH CAMEROON

The present work was aimed at measuring indoor radon activity concentrations in dwellings in Mvangan locality, South Cameroon, in order to assess the extent of measures that may be necessary for controlling public indoor radon exposure in this area. Measurements were carried out using passive solid-state nuclear track detectors (RADONAVA Inc., RadTrak2, Sweden) following ISO 11665-4 standard. Radon concentration ranged between 36 ± 20 and 150 ± 30 Bq m-3 with arithmetic and geometric means values of 64 ± 25 and 60 ± 1 Bq m-3, respectively. These mean values were greater than worldwide values presented by United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which are, respectively, 40 and 30 Bq m-3. 96% of dwellings that have radon concentrations below the World Health Organization (WHO) reference level of 100 Bq m-3, whereas 4% of dwellings have radon concentrations higher than this level but lower than 300 Bq m-3, the International Commission on Radiological Protection (ICRP) reference level. Annual effective doses due to indoor radon ranged between 0.7 and 2.8 mSv y-1 with an arithmetic mean value of 1.2 ± 0.5 mSv y-1. These values were below the lower limit of the ICRP-recommended action level interval 3-10 mSv y-1. It has been observed that annual effective dose received by residents in cement bricks dwellings were not significantly different (P-value = 0.565) than those received by residents in mud dwellings in Mvangan locality. The mean number of persons expected to be diagnosed with or die from cancer (solid cancers and leukemia) were 162 ± 48 (61 ± 25 for males and 101 ± 41 for females) and 82 ± 24 (33 ± 13 for males and 49 ± 20 for females), respectively. The results obtained in this study prove that the populations of Mvangan locality are exposed to a relatively low potential risk of cancer incidence and mortality.

Correlation between Ground 222Rn and 226Ra and Long-Term Risk Assessment at the at the Bauxite Bearing Area of Fongo-Tongo, Western Cameroon

The aim of the current work was to study natural radioactivity in soil and the correlation between 222Rn and 226Ra in the ground and to assess the onsite and indoor long-term excess cancer risk at the bauxite bearing area of Fongo-Tongo in Western Cameroon. 222Rn was measured in the ground at a depth of one meter, using Markus 10 detector. 226Ra, 232Th, and 40K activity concentrations were measured in soil by two techniques, in situ and laboratory gamma spectrometry. The mean values of 222Rn concentrations in the ground were 69 ± 18 kBqm−3 for Fongo-Tongo and 82 ± 34 kBq m−3 for the locality of Dschang, respectively. The mean values of 226Ra, 232Th, and 40K activity concentrations obtained with in situ gamma spectrometry were 129 ± 22, 205 ± 61, and 224 ± 39 Bq kg−1 for 226Ra, 232Th, and 40K, respectively, and those obtained by laboratory gamma spectrometry were 129 ± 23, 184 ± 54, and 237 ± 44 Bq kg−1, respectively. A strong correlation between 222Rn and 226Ra activity concentrations determined by in situ and laboratory measurements (R2 = 0.86 and 0.88, respectively) was found. In addition, it is shown that the total excess cancer risk has a maximum value of 8.6 × 10−3 at T = 0 year and decreases progressively in the long term. It is also shown that 226Ra makes a major contribution, i.e., above 70%, to the total excess cancer risk.

Assessment of Natural Radiation Exposure Due to 222Rn and External Radiation Sources: Case of the Far North, Cameroon

ABSTRACT

This paper assesses public exposure to natural radioactivity from radon and external radiation sources in the Far North region, Cameroon, and studies the correlation between radon data obtained using several techniques. The RADTRAK, RadonEye, and Markus 10 detectors were used to measure radon concentrations in dwellings and soil, respectively. To understand radon variations in the study area, a correlation coefficient between radon in soil and in dwellings was determined. The ambient equivalent dose rate was measured using a RadEye PRD-ER, and the effective doses from internal and external radiation were determined. In soil, 20% of the measuring points had a concentration above 50 kBq m-3, the action value for radon exposure from soil according to Swedish Radiation Protection Institute regulations. After 90 d of measurement using RADTRAK, half of the concentrations in the dwellings were greater than or equal to 160 Bq m-3, which is above the WHO reference level of 100 Bq m-3. The ambient equivalent dose rate and the external and internal radiation effective dose were 0.08 μSv h-1, 0.6 mSv y-1, and 2.86 mSv y-1, respectively. These results reveal a strong correlation between the radioactivity level of a locality and its geological and mineralogical structure. Although these different results in general do not present a very high risk of radiological exposure for the public, it is nevertheless necessary that the rules of radiation protection are respected in order to reduce it.

Soil gas radon, indoor radon and its diurnal variation in the northern region of Cameroon

Soil gas radon and indoor radon measurements have been carried out in Mayo-Louti and Benoué Divisions in northern Cameroon. Concentrations of radon in soil have been measured using Markus 10 at the depth of about 1 m. Radon concentration in soil varies from 0.9 to 13.8 kBq m^-3 with a mean value of 4.6 kBq m^-3. Average daily indoor radon concentrations measured with RadonEye+² detectors vary from 7 to 60 Bq m^-3 with an average of 17 Bq m^-3. Indoor radon concentrations measured with passive RADTRAK detectors range between 15 and 104 Bq m^-3 with a geometric value of 38 Bq m^-3 and a geometric standard deviation of 1.5. This geometric value is lower than the value of 30 Bq m^-3 given by UNSCEAR. Indoor radon inhalation dose ranges between 0.28 and 1.97 mSv a^-1 with geometric value of 0.72 mSv a^-1 (at 0.03 standard deviation). Outdoor radon inhalation ranges between 0.02 and 0.26 mSv a^-1 with a mean value of 0.09 mSv a^-1. The total annual effective dose due to indoor and outdoor radon exposure for this study area is 0.81 mSv a^-1, less than 1.15 mSv a^-1 the world average value given by UNSCEAR. There is no significant radiological risk for the inhabitants.

Natural radioactivity in building materials, indoor radon measurements, and assessment of the associated risk indicators in some localities of the Centre Region, Cameroon

The objective of the current study is to investigate the natural radioactivity of some building materials, the resulting long-term external and internal effective dose equivalents (EEDE and IEDE) analysis followed by indoor radon measurements, and the assessment of some radiological risk indicators associated with radon exposure. A total of 37 samples of building materials were analyzed with a sodium iodide detector (NaI (Tl)), and the computer code RESRAD-BUILD was used for the analysis of the EEDE and IEDE of the structural elements of the houses (walls and floor). For indoor radon measurements, 140 houses were selected, and in each of them was placed 01 RADTRAK dosimeter. Inhalation dose, total dose, and some radiological risk indicators were calculated. The specific activities of ²²⁶Ra, ²³²Th, and ⁴⁰K for the overall sampled building materials were found to vary between 10 ± 2-52 ± 7, 10 ± 1-95 ± 10, and 31 ± 1-673 ± 20 Bq kg^-1, respectively. The dwelling types with bare brick walls, cement mortar plastered walls, and concrete floors show EEDE and IEDE values well below the recommended limits. The corresponding dwelling type contributions to the measured average indoor radon concentration (42 ± 12 Bq m^-3) are 22%, 13%, and 16%, respectively. Inhalation dose resulting from the measured indoor radon concentrations varies from 0.35 to 3.24 mSv y^-1 with a mean value of 0.96 ± 0.55 mSv y^-1, which represents about 65% of the total dose simulated (1.49 ± 0.88 mSv y^-1) by the RESRAD-BUILD code. The overall analysis of indoor radon-related radiological risk indicators shows low levels of risk relative to permissible limits.

STUDIES OF RADON LEVELS, RADIUM CONCENTRATION, AND ESTIMATED EFFECTIVE DOSE IN DWELLINGS AND SOILS IN GOLD MINING TOWNS IN ABIREM OF EASTERN REGION OF GHANA

Studies have been carried in 126 dwellings for indoor radon levels and 43 soil samples for radium and radon exhalation rate of Abirem communities in Eastern region of Ghana. The measurements were done using CR-39 and HPGe techniques. Indoor radon and mean concentration ranged from 23.8 to 125.7 Bq/m3, 54.7 ± 23.7 Bq/m3. Bedroom, kitchen, and sitting varied from 30.8 to 125.7 Bq/m3, 23.8-63.9 Bq/m3 and 23.8 to 58.4 Bq/m3. Strong and weak Pearson correlation were found between radium and radon in soil, radium and indoor radon concentration. Radium concentration and mean were found to be varied from 19.5 to 38.9 Bq/kg, 29.0 ± 16.0 Bq/kg. The radon exhalation rate and mean in soil were also found to be varied from 21.3 to 112.1 μBq/m2h, 65.1 ± 27.6 μBq/m2h. Indoor radon values and radium concentration in dwellings and soil recorded 8% and 38%, respectively, more than action proposed by WHO and UNSCEAR 2000. The estimated annual effective doses and cancer risk were less than the average values recommended by UNSCEAR and ICRP.

Identifying indoor radon sources in Pa Miang, Chiang Mai, Thailand

Radon is the leading source of lung cancer mortality after smoking in Chiang Mai, Thailand. Finding a source of carcinogens is one of the important measures for preventing the cancer risk for this region. Specific sites at Pa Miang, Doi Saket have the highest incidences of lung cancer and have a combination of factors that influence indoor radon concentration. Our study identified the sources of indoor radon within several houses. The results indicate that geological and topographic characteristics, including active faults and mountain terraces, are the main sources of indoor radon, especially for wooden houses. Besides building materials, the design of the houses, ventilation conditions, and lifestyle choices are all factors influencing indoor radon concentrations and its associated risk. Although radon levels (29–101 Bq m⁻³) and total indoor annual effective doses (0.9–3.8 mSv year⁻¹) received from all sources at these sites have shown no significant health risk due to radon exposure , this investigation will be useful as a starting point to guide strategies to respond and prevent the risk of lung cancer, especially in Chiang Mai.

Indoor Radon Measurements Using Radon Track Detectors and Electret Ionization Chambers in the Bauxite-Bearing Areas of Southern Adamawa, Cameroon

The current work deals with indoor radon (222Rn) concentrations and ambient dose-equivalent rate measurements in the bauxite-bearing areas of the Adamawa region in Cameroon before mining from 2022. In total, 90 Electret Ionization Chambers (EIC) (commercially, EPERM) and 175 Radon Track Detectors (commercially, RADTRAK2) were used to measure 222Rn concentrations in dwellings of four localities of the above region. A pocket survey meter (RadEye PRD-ER, Thermo Scientific, Waltham, MA, USA) was used for the ambient dose-equivalent rate measurements. These measurements were followed by calculations of annual doses from inhalation and external exposure. 222Rn concentrations were found to vary between 36 ± 8-687 ± 35 Bq m-3 with a geometric mean (GM) of 175 ± 16 Bq m-3 and 43 ± 12-270 ± 40 Bq m-3 with a geometric mean of 101 ± 21 Bq m-3 by using EPERM and RADTRAK, respectively. According to RADTRAK data, 51% of dwellings have radon concentrations above the reference level of 100 Bq m-3 recommended by the World Health Organization (WHO). The ambient dose equivalent rate ranged between 0.04-0.17 µSv h-1 with the average value of 0.08 µSv h-1. The inhalation dose and annual external effective dose to the public were assessed and found to vary between 0.8-5 mSv with an average value of 2 mSv and 0.3-1.8 mSv with an average value of 0.7 mSv, respectively. Most of the average values in terms of concentration and radiation dose were found to be above the corresponding world averages given by the United Nations Scientific Commission on the Effects of Atomic Radiation (UNSCEAR). Even though the current exposure of members of the public to natural radiation is not critical, the situation could change abruptly when mining starts.

Radon and thoron radiation exposure of the Angolan population living in adobe houses

This study investigates radon and thoron activity concentrations in adobe houses of Angola. Activity concentrations were recorded by passive detectors in rainy and dry seasons in 40 dwellings located at three areas with different climatic and geological backgrounds (Cabinda, Huambo, Menongue). Regarding seasonal and spatial variations, radon activity concentrations are higher in the rainy than in the dry season and both radon and thoron levels are the highest in Huambo, the central part of the country. The number of adobe houses above certain radon and thoron levels were estimated and the contribution of thoron to the inhalation dose was significant.

Importance of Discriminative Measurement for Radon Isotopes and Its Utilization in the Environment and Lessons Learned from Using the RADUET Monitor

Radon (222Rn) and thoron (220Rn), sources of natural background radiation, have been the subjects of long-standing studies, including research into radon and thoron as major causes of lung cancer at domestic and international levels. In this regard, radon and thoron measurement studies have been widely conducted all over the world. Generally, the techniques used relate to passive nuclear track detectors. Some surveys have shown that passive monitors for radon are sensitive to thoron, and hence some measured results have probably overestimated radon concentrations. This study investigated radon and thoron measurements in domestic and international surveys using the passive radon-thoron discriminative monitor, commercially named RADUET. This paper attempts to provide an understanding of discriminative measurements of radon isotopes and to present an evidence-based roadmap.

The Importance of Direct Progeny Measurements for Correct Estimation of Effective Dose Due to Radon and Thoron

Radon (Rn), thoron (Tn), and thoron progeny (TnP) were measured in seven inhabited areas of the uranium and thorium bearing region of Lolodorf, located in southwestern Cameroon. Then the equilibrium factor (F_Tn) between thoron and its progeny was determined in order to show the importance of direct progeny measurements for correct estimation of effective dose due to radon, thoron and their progenies. A total of 220 RADUET detectors were used to measure indoor radon and thoron and 130 TnP monitors for thoron progeny indoors. The arithmetic and geometric mean concentrations of Rn, Tn, and TnP were 103 and 89 Bq m⁻³, 173, and 118 Bq m⁻³, 10.7, and 7.4 Bq m⁻³, respectively. Total effective dose determined from radon, thoron, and their progenies was estimated at 4.2 ± 0.5 mSv y⁻¹. Thoron equilibrium factor varied according to seasons, the type of dwelling, building materials and localities. Thoron (Tn and TnP) contribution to effective dose ranged between 3 and 80% with the average value of 53%. Total effective dose estimated from the world average equilibrium factor of 0.02 given by UNSCEAR was 2.7 ± 0.2 mSv y⁻¹. The effective dose due to thoron varied greatly according to the different values taken by F_Tn and was different from that determined directly using TnP concentrations. Thus, effective dose due to thoron determined from the equilibrium factor is unreliable. Therefore, the risk of public exposure due to thoron (Tn and TnP) may therefore be higher than that of radon (Rn and RnP) in many parts of the world if F_Tn is no longer used in estimating total effective dose. This is not in contradiction with the UNSCEAR conclusions. It is therefore important to directly measure the radon and thoron progeny for a correct estimate of effective dose.