Russel Rolphe Caroll Moubakou Diahou

This study aimed to measure radon concentration in Djiri River water and to evaluate the associated equivalent doses, effective doses, and lifetime cancer mortality risks for the population of Brazzaville, Republic of Congo. Radon concentration was measured in 29 water samples collected from the Djiri River using an AlphaGUARD PQ2000 PRO radon detector. Polyethylene terephthalate (PET) bottles were evaluated for sample storage in order to estimate radon losses during storage. To enable a direct comparison with the National Research Council (1999) reference values, the estimated cancer mortality risks were normalized to the same reference radon concentration. Measured radon concentrations ranged from 0.23 to 0.73 Bq/L, with a mean value of 0.425±0.12 Bq/L (equivalent to 425±120 Bq/m³). These concentrations are low and indicate that radiation exposure through drinking water ingestion is minimal under the investigated conditions. The estimated annual effective doses from water ingestion were 5.37×10⁻6 mSv/year for infants, 4.45×10⁻3 mSv/year for 1-year-old children, 2.03×10⁻3 mSv/year for 5-year-old children, 1.18×10⁻3 mSv/year for 10-year-old children, 4.38×10⁻6 mSv/year for 15-year-old children, and 4.02×10⁻3 mSv/year for adults. All estimated doses remained well below the World Health Organization guideline value of 0.1 mSv/year for drinking water. The estimated lifetime cancer mortality risks for males, females, and the total population were 6.35×10⁻7, 9.45×10⁻7, and 7.68×10⁻7, respectively. After normalization to the same radon concentration, these estimates were consistent with the projections reported by the National Research Council (1999). Although the estimated doses and risks are very low and do not indicate a significant radiological health concern, the results support periodic monitoring of radon in the Djiri River as part of routine environmental and public health surveillance.

In this study, the activity concentrations of radon (²²²Rn), thoron (²²⁰Rn) and thoron progeny were measured simultaneously in Djeno (Pointe-Noire, Republic of Congo) using RADUET detectors to evaluate the air quality and the radiological risks due to the inhalation of these radionuclides. Activity concentrations of radon progeny were calculated from those of radon. Indoor radon, thoron and progenies followed a lognormal distribution ranging between 20 and 40, 6 and 62, 8 and 17.6 and 0.4 and 19.6 Bq m⁻³ for radon, thoron, radon progeny and thoron progeny, respectively. Mean values for radon were lower than the worldwide values estimated by the United Nation Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), which are 40 Bq m⁻³ (arithmetic mean) and 45 Bq m⁻³ (geometric mean). Radon concentrations in the dwellings under study were below the World Health Organization and the International Commission on Radiological Protection recommended reference levels, which are, respectively, 100 and 300 Bq m⁻³. The mean concentration of thoron was twice the world average value of 10 Bq m⁻³ estimated by UNSCEAR. Thoron progeny mean concentration was sharply greater than the typical value (0.3 Bq m⁻³) for indoor atmosphere provided by UNSCEAR. Annual effective dose ranges were 0.40–0.87 mSv (arithmetic mean, 0.57 ± 0.11 mSv) for radon and 0.10–4.14 mSv (arithmetic mean, 0.55 ± 0.77 mSv) for thoron. The mean value for radon was lower than the value (1.15 mSv) estimated by UNSCEAR, while the mean value for thoron was five times higher than the UNSCEAR value (0.10 mSv). The study showed that the use of the typical equilibrium factor value given by UNSCEAR to compute effective dose led to an error above 80%. Finally, the results of this study showed that the excess relative risk of radon-induced cancer was low, below 2% for the population under 55 y. The results presented in the present study prove that the population of Djeno is exposed to a relatively low potential risk of radon- and thoron-induced cancer.

The main objective of the present study was to assess natural radioactivity level from soils of an abandoned potash mine and its surroundings at Holle locality in Hinda district, the Republic of Congo. Samples were analyzed using an HPGe gamma spectrometer. Activity concentration values obtained varied from 21.01 ± 6.47 to 117.3 ± 2.69 Bq/kg with a mean value of 46.15 ± 4.69 Bq/kg of 40K; that of 238U varied from 17.36 ± 10.74 to 40.04 ± 8.58 Bq/kg with a mean value of 25.14 ± 10.06 Bq/k, while that of 232Th varied from 8.68 ± 3.7 to 27.33 ± 2.69 Bq/kg with a mean value of 18.16 ± 2.94 Bq/kg. Mean activity concentration values obtained for 238U, 232Th and 40K were relatively low compared to the world average values. Radiological hazard indices associated were also calculated and found to be under recommended limits. Results pointed out that radioactivity level in the region was relatively low. Consequently, soils of the surrounding abandoned potash mine can be used for buildings construction.