GAMMA RADIOACTIVITY LEVELS AND THEIR RADIOLOGICAL HAZARD INDICES IN SUSPENDED PATICULATE MATTER (SPM) IN UYO, AKWA IBOM STATE, NIGERIA

Aims: This study was aimed to measure the concentrations of primordial radionuclides in particulate matter and evaluate the potential radiological health risk to the inhabitants of Uyo, Nigeria.
Study Design: This study involved sampling of dust particulate matter by gravity deposition and analysing by radiochemical technique.
Place and Duration of Study: The study was conducted at the Uyo metropolis between October, 2012 and May, 2013.
Methodology: NaI (Tl) gamma ray spectrometer was used to determine the activity concentration of naturally occurring radionuclides (232Th, 238U, and 40K) in dust particulate samples in some selected locations of Uyo Metropolis. Enrichment factor of radionuclides were calculated to determine their origin. The radiological indices were estimated using mathematical models for Absorbed Dose Rate (ADR), Annual Effective Dose (AED), Radium Equivalent Dose Rate (Raeq), External Hazard Index (Hex) and Internal Hazard Index (Hin).
Results: The activity concentrations of the radionuclides from the selected samples were in the ranges of 27.3±9.71 – 49.9±16.01 Bqkg-1, 19.3±9.74 – 35.9±10.23 Bqkg-1, and 283.8±54.26 – 834.2±128.96 Bqkg-1 for 238U, 232Th and 40K respectively. EF values show 238 K as the major anthropogenic contributor to ambient air radiations with moderate enrichment, while 232Th and 40K are of crustal origin. The calculated ranges for the indices were 54.11 – 82.42µGyh-1, 44.12 – 69.20µSvy-1, 93.28 – 141.64Bqkg-1, 0.25 – 0.38Bqkg-1, and 0.33 – 0.52Bqkg-1 respectively for ADR, AED, Raeq, Hex, and Hin. The results obtained were examined on the basis of existing International recommended limits by the Organization for Economic Cooperation and Development. The results showed that activity concentration of the radionuclides were within recommended values except activity of 40K in Uniuyo, Itu road and Uruan Street which slightly exceeded world recommended values of 500Bqkg-1. Raeq, AED, Hex and Hin were within recommended limits of 370Bqkg-1, 70µSvy-1, 1 and 1 respectively.
Conclusion: Findings indicate no radioactivity threat associated with dust particulate in Uyo metropolis presently. However, continuous monitoring of radionuclide contents of dust particulates in the area is advocated.