Natural radioactivity measurement of water and sediment from the historic Ikogosi warm and cold spring, Nigeria

Abstract

Natural radioactivity measurement and the resultant risk assessment in the water and sediments from the historic Ikogosi warm and cold spring were carried out. A total of 8 samples (4 water and 4 sediment samples) were collected from the Ikogosi spring resort. A sample each was collected from the warm spring, cold spring, meeting point and a sample outside the resort. The samples were thoroughly prepared following the IAEA recommended procedures and analyzed for ⁴⁰K, ²³⁸U, and ²³²Th using NaI(Tl) detector. The activity concentrations of ⁴⁰K, ²³⁸U and ²³²Th in water samples range from 40.14 ± 17.83 to 67.59 ± 19.87 Bq L^-1, 8.15 ± 2.84 to 11.14 ± 3.78 Bq L^-1 and 5.71 ± 1.32 to 8.24 ± 2.61 Bq L^-1 respectively. The activity concentration of sediment samples range from 136.31 ± 17.01 to 246.21 ± 34.93 Bq kg^-1, 17.98 ± 7.64 to 28.32 ± 5.98 Bq kg^-1 and 9.57 ± 3.15 to 16.12 ± 3.41 Bq kg^-1 respectively. These values compared reasonably well with the worldwide average concentrations of 400 Bq kg^–1, 40 Bq kg^–1, 40 Bq kg^–1 for ⁴⁰K, ²³⁸U, and ²³²Th respectively. The mean absorbed dose rate in air obtained for sediment was 40.33 nGy h^–1, while the annual outdoor effective dose equivalent was 49.46 μSv y^-1, which is lower than the world average of 70 μSv y^-1 specified by UNSCEAR for an outdoor effective dose. The total annual effective dose due to ingestion of radionuclides in the water for 3 age groups range from 13.414.87 to 18.856.43 mSv y^-1, 2.751.03 to 5.722.13 mSv y^-1 and 2.621.01 to 4.951.43 mSv y^-1 for infants (0 – 1 y), children (7 – 12 y) and adult (>17 y) respectively. These values were higher than 1 mSv y^-1 recommended by ICRP.

Keywords: Natural Radioactivity, Activity concentrations, Cold spring, Ikogosi, Nigeria