Indoor radon survey in a university campus of Nigeria

Simultaneous indoor radon/thoron and in situ outdoor gamma dose measurements and estimation of annual effective dose in a tin mining area of Jos Plateau, Nigeria

Radon, a radioactive gas can increase the risk of lung cancer when breathe in. Indoor Rn-222 and Rn-220 concentrations were determined using passive radon monitor in some dwellings in a Sn mining area of Jos Plateau. Outdoor gamma radiation was also measured with a hand-held survey meter. The range of Rn-222 and Rn-220 concentrations was from 7-53 Bq m-3 to 41-267 Bq m-3 with averages of 27 ± 17 and 92 ± 65 Bq m-3, respectively. The mean total effective dose due to Rn-222 + Rn-220 was estimated as 2.84 ± 1.57 mSv y-1. Rn-220 contributed between 50 and 95% to the total annual effective dose. There was no correlation between indoor Rn-220 and Rn-222 concentrations in the dwellings. Outdoor gamma radiation measured was between 0.31 ± 0.06 and 0.62 ± 0.08 μSv h-1, and mean annual effective dose calculated was 1.14 ± 0.21 mSv y-1. It is concluded from this study that thoron should not be neglected in dose assessment.

Radiometric evaluation of indoor radon levels with influence of building characteristics in residential homes from southwestern Nigeria

Indoor radon (²²²Rn) measurements were carried out using solid state nuclear track detectors (SSNTD) in some dwellings from southwestern Nigeria. This was aimed at statistically assessing influence of building characteristics on the measured radon and estimating excess lifetime cancer risks (ELCR). The measured radon concentrations followed lognormal distribution and were significantly influenced by some building properties. The arithmetic mean (1.60 mSv) of annual effective doses (AEDs) due to indoor radon was observed to be higher than the world average level (1.15 mSv) but less than lower limit (3 mSv) of International Commission on Radiological Protection (ICRP). The evaluated excess lifetime cancer risk ranged from 1.5 to 28.1 (MPy)^-1 with an average value of 6.3 (MPy)^-1, indicating that after exposure to indoor radon for 70 years, 6 people in every 1000 are likely to suffer the risk of developing lung cancer. Adequate ventilation systems were recommended for houses with high level of radon to avoid unnecessary exposure to radon. However, the investigated data would form important component of the database required to set up guidelines and policy of controlling radon at home.

SURVEY OF INDOOR RADON LEVELS IN SOME UNIVERSITIES IN SOUTH WESTERN NIGERIA

Indoor radon investigation was carried out in offices of three university campuses located in South-Western part of Nigeria; Federal University of Technology Akure (FUTA), Ekiti State University (EKSU) and Federal University Oye-Ekiti (FUOYE) using CR39 detectors. The mean activity concentration of indoor radon for the investigated offices of all three university campuses was estimated to be 222 ± 44 Bq m-3, which was below the reference level of 300 Bq m-3 recommended by the International Commission on Radiological Protection (ICRP 115). For the three institutions, the probability of lung cancer induction at age 70 years with respect to age of exposure (40, 50, and 60 years) ranged between 1.06 × 10-7 and 6.24 × 10-5. The expected mortality rate due to exposure to a radon activity concentration ranging from 7 to 1358 Bq m-3 was estimated to range from 0 to 44 deaths among a population of 10,000 persons.

Radon level in a Nigerian University Campus

Background

Globally, radon is a natural contaminant that affects indoor air quality. Several epidemiological studies have implicated high radon levels in the causality of lung cancer. The study therefore determined the environmental level of radon in selective offices in the Obafemi Awolowo University, Ile-Ife. The study employed a descriptive cross-sectional design. A Pro 3-series radon detector was used to determine the radon levels in randomly selected offices. The instrument was set-up in each office and after 48 h, reading was taken and recorded on a proforma data sheet. The structural characteristics of the offices were also assessed by observation.

Results

The result revealed that the radon level obtained in the sampled offices ranged from 0.0 to 5.3 pCi/L (196 Bq/m³). The median concentration of radon obtained from sampled offices was 0.9 pCi/L. Almost all (95 %) of the offices had radon levels within the ‘permissible’ reference level recommended by World Health Organization. Radon levels also showed a statistically significant decline with height of office building with the mean concentration of radon in offices located on the basement, ground floor and first floor being 1.54 ± 1.32, 0.99 ± 0.56, 0.63 ± 0.41 pCi/L respectively, (F statistic 5.8, p < 0.001).

Conclusion

The radon levels obtained in most assessed offices in Obafemi Awolowo University were found to be within the permissible reference levels. Mitigation measures should be put in place in the few offices above permissible levels.

Radon measurements by nuclear track detectors in dwellings in Oke-Ogun area, South-Western, Nigeria

An indoor radon survey of a total of 77 dwellings randomly selected in 10 districts in Oke-Ogun area of Oyo state, South-western Nigeria was carried out using CR-39 detectors. The CR-39 detectors were placed in the bedrooms and living rooms and exposed for 6 months and then etched in NaOH 6.25 N solution at 90 °C for 3 h. Mean concentrations amount to 255 ± 47 and 259 ± 67 Bq m(-3) in the living rooms and bedrooms, respectively. The lowest radon concentration (77 ± 29 Bq m(-3)) was found in Igbeti, whereas the highest was found in Okeho (627 ± 125 Bq m(-3)). The annual exposure of dwellers was estimated to fall <10 mSv (6.4 and 6.5 mSv y(-1) n living rooms and bedrooms, respectively), which is the upper range of action levels recommended by the International Commission on Radiological Protection. The average excess lung cancer risk was estimated 24.8 and 25.2 per million person-years in both living rooms and bedrooms. It is believed that the high radon level in this part of the country may be attributed to its geographic location. The data presented here will serve as a baseline survey for radon concentration in dwellings in the area.

Radon measurements by nuclear track detectors in secondary schools in Oke-Ogun region, Nigeria

Radon measurements were performed in secondary schools in the Oke-Ogun area, South-west, Nigeria, by solid state nuclear track detectors (SSNTDs). About seventy CR-39 detectors were distributed in 35 high schools of the Oke-Ogun area. The CR-39 detectors were exposed in the schools for 3 months and then etched in NaOH 6 N solution at 90 °C for 3 h. The tracks were counted manually at the microscope and the radon concentration was determined at the Radioactivity Laboratory, Department of Physics, University of Trieste, Trieste, Italy. The overall average radon concentration in the surveyed area was 45 ± 27 Bq m(-3). The results indicate no radiological health hazard. The research also focused on parameters affecting radon concentrations such as the age of the building in relation to building materials and floor number of the classrooms. The results show that radon concentrations in ground floors are higher than in upper floors.