Assessment of radionuclide distribution and associated radiological hazards for soils and beach sediments of Akwa Ibom Coastline, southern Nigeria

Abstract

In this study, the activity concentrations of natural radionuclides in soil and beach sediment samples collected from 15 randomly but uniformly distributed locations in the coastal area of Akwa Ibom (southern Nigeria) were measured using hyper pure germanium (HPGe) detector. The activity concentrations of 238U, 232Th and 40K varied from 9 to 44 Bq/kg, 3 to 72 Bq/kg and 35 to 250 Bq/kg respectively. These results are below the 1000, 1000 and 4000 Bq/kg upper limits of safety for 238U, 232Th and 40K respectively. Except 238U, 232Th and 40K show lower standard deviations than their mean values, which indicate that soils and sediments have high degree of uniformity. The spatial distribution of radionuclide concentrations is nearly uniform except at locations where carbonaceous materials and clay soils exist. Mean value of Th/U ratio across the area was ≤ 7, typical of reducing condition in the depositional environment, thus suggesting enrichment of carbonaceous materials and clays. Additionally, the concentration of 40K was observed to be slightly higher in locations where anthropic activities are prevalent. Apart from excess lifetime cancer risk (average concentration of 0.80 × 10−3), the average concentrations of other radiological parameters: radium equivalent (83 Bq/kg), absorbed dose rate (39 nGy/h), indoor annual effective dose equivalent (0.18 mSv/year), outdoor annual effective dose equivalent (0.05 mSv/y) and annual gonadal dose equivalent (259 μSv/y), are below permissible limits. Hence, the soils and sediments are safe and suitable for all purposes.