Indoor radon (Rn), thoron (Tn) and thoron progeny (TnP) were simultaneously measured in the gold mining areas of Betare-Oya using RADUET detectors and TnP monitors. Rn and Tn concentrations range between 88-282 and 4-383 Bq m-3, respectively, with the arithmetic means of 133 ± 39 and 93 ± 76 Bq m-3. The 76% of houses for Rn and 25% for Tn exceed the WHO reference level of 100 Bq m-3 and 3% of the houses exceed the ICRP threshold of 300 Bq m-3. The equilibrium equivalent thoron concentration ranges between 1 and 19 Bq m-3 with a mean value of 6 ± 4 Bq m-3. The thoron equilibrium factor ranges between 0.01 and 0.55 with arithmetic mean of 0.11, higher than the world average value of 0.02 given by UNSCEAR. The total inhalation dose due to Rn, Tn and their progeny ranges between 1.8 and 6.2 mSv y-1 with the arithmetic mean of 3.8 ± 1.1 mSv y-1.

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.

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.

This paper reports the levels of radon (Rn), thoron (Tn), and their progeny (TnP) concentrations in dwellings; studies factors influencing these concentrations; and assesses the associated lung cancer risk in Akonolinga’s area in Cameroon, where rutile deposits have been identified but are not yet industrially exploited. Indoor Rn and Tn were determined using CR39-based detectors. Additionally, Rn in soil gas, ²²⁶Ra, and ²³²Th concentrations in soil were measured using Markus 10, high purity germanium detector (HPGe), respectively. On average, indoor Rn, Tn concentration, and the equilibrium equivalent Thoron concentration (EETC) or TnP were 39.5, 68.1, and 5.0 Bq m⁻³, respectively. Average concentrations of Rn in soil gas, ²²⁶Ra, and ²³²Th in soil were 24.3 kBq m⁻³, 17 Bq kg⁻¹, and 27 Bq kg⁻¹, respectively. Correlation analysis indicates that indoor radon and thoron levels were tightly linked with factors such as their precursor concentrations in soil, the building materials, dwelling architecture, and inhabitant living habits. Furthermore, it was observed that Rn and TnP were the major contributors to the inhalation effective dose, accounting for 39.6% and 56.7% of the total, respectively. The estimated excess lifetime cancer risk (ELCR) from the exposition to Rn and TnP was found to be 2.93 × 10⁻³ and 4.36 × 10⁻³, respectively, exceeding the global average, raising health concerns.

Background: This study aims to reevaluate natural radiation exposure, following up on our previous study conducted in 2019, and to assess the associated risk of lung cancer to the public residing in the gold mining areas of Betare-Oya, east Cameroon, and its vicinity.Materials and Methods: Gamma-ray spectra collected using a 7.62 cm×7.62 cm in NaI(Tl) scintillation spectrometer during a car-borne survey, in situ measurements and laboratory measurements performed in previous studies were used to determine the outdoor absorbed dose rate in air to evaluate the annual external dose inhaled by the public. For determining internal exposure, radon gas concentrations were measured and used to estimate the inhalation dose while considering the inhalation of radon and its decay products.Results and Discussion: The mean value of the laboratory-measured outdoor gamma dose rate was 47 nGy/hr, which agrees with our previous results (44 nGy/hr) recorded through direct measurements (in situ and car-borne survey). The resulting annual external dose (0.29±0.09 mSv/yr) obtained is similar to that of the previous study (0.33±0.03 mSv/yr). The total inhalation dose resulting from radon isotopes and their decay products ranged between 1.96 and 9.63 mSv/yr with an arithmetic mean of 3.95±1.65 mSv/yr. The resulting excess lung cancer risk was estimated; it ranged from 62 to 216 excess deaths per million persons per year (MPY), 81 to 243 excess deaths per MPY, or 135 excess deaths per MPY, based on whether risk factors reported by the U.S. Environmental Protection Agency, United Nations Scientific Committee on the effects of Atomic Radiation, or International Commission on Radiological Protection were used, respectively. These values are more than double the world average values reported by the same agencies.Conclusion: There is an elevated level of risk of lung cancer from indoor radon in locations close to the Betare-Oya gold mining region in east Cameroon. Therefore, educating the public on the harmful effects of radon exposure and considering some remedial actions for protection against radon and its progenies is necessary.