ASSESSMENT OF ACTIVITY CONCENTRATIONS AND RADIOLOGICAL HAZARD OF NATURAL RADIONUCLIDES IN GRANITES FROM OSUN STATE, SOUTHWESTERN NIGERIA.

Abstract

In this work, activity concentrations of natural radionuclides in granites from eight major operational quarries in Osun State, Southwestern Nigeria were assessed. Eighty granite samples comprising 34 inch, 12 inch and stone-dust were collected from Wolid, Slava, Ayofe, Espro, Ife/Modakeke, Krystal Vountein, Clario and Omidiran quarries in the State. Measurement was done using high purity germanium (HPGe) detector. The statistical analysis was carried out using Statistical Package for Social Sciences (SPSS) software to determine if granite size has impact on the activity concentrations. The results revealed that the mean activity concentrations of 238U (12.64 ± 1.89 Bq Kg-1) and 232Th (16.93 ± 2.46 Bq Kg-1) were highest in 34 inch granite and lowest in stone-dust (5.01 ± 0.77 and 8.97 ± 1.37 Bq Kg-1 respectively), whereas 40K is highest in the 34 inch (266.19 ± 35.53 Bq Kg-1) and lowest in 12 inch (151.85 ± 25.09 Bq Kg-1) granite. Espro has the highest (23.75 ± 3.74 Bq Kg-1) while Wolid has the lowest (4.11 ± 0.73 Bq Kg-1) 238U activity concentration and Slava has lowest for 232Th (8.21 ± 1.12 Bq Kg-1) and 40K (109.54 ± 11.06 Bq Kg-1). Average values of the absorbed dose rate (D), annual effective dose equivalent (AEDE), radium equivalent activity (Raeq), annual gonadal dose equivalent (AGED), external hazard index (Hex), internal hazard index (Hin), representative gamma index (Iγ) and excess lifetime cancer risk (ELCR) for 34 inch, 12 inch granite and stone-dust respectively were 13.94 nGy h-1, 17.10 μSv y-1, 43.84 Bq kg-1, 150.98 mSv y-1, 0.12, 0.14, 0.33 and 0.06 respectively; 6.08 nGy h-1, 7.45 μSv y-1, 27.44 Bq kg-1, 88.85 mSv y-1, 0.07, 0.09, 0.20 and 0.03 respectively; and 6.16 nGy h-1, 7.55 μSv y-1, 22.76 Bq kg-1, 76.54 mSv y-1, 0.06, 0.07, 0.17 and 0.03 respectively. Based on quarry, the range of values of D, AEDE, Raeq, AGED, Hex, Hin, Iγ and ELCR were 7.41 – 21.02 nGy h-1, 9.09 – 25.78 μSv y-1, 22.54 – 81.56 Bq kg-1, 78.87 - 266.08 mSv y-1, 0.06 – 0.22, 0.07 – 0.28, 0.60 – 0.36 and 0.03 -0.09 respectively. Espro has the highest mean values of radiological hazard parameters except representative gamma index while Ayofe has the lowest, although, all the calculated radiation hazard indices were lower than the permissible limits. Therefore, people working in the quarries, granite end-users and the general public from the study area are safe from radiological health risks from the sites, since there is no significant health risk.