Effect of Grain Size on Radionuclide Content in Sediment Samples from Kolo Creek, Bayelsa State, Nigeria

Abstract

The effect of grain sizes on radionuclide concentration in soil and sediment samples from Kolo creek, Bayelsa State was investigated using gamma spectroscopy. Eight (8) samples of sediment were collected around the oil spill site of the creek. All the samples were separated into four different grain sizes, A (0.5mm), B (1mm), C (1.5mm) and D (2mm), making a total of 32 sediment. The activity concentration in sediment samples of grain sizes 0.5 mm, 1.0mm, 1.5mm and 2mm were determined. In sediment samples of grain sizes 0.5mm(A), the activity concentration of 226Ra , 232Th and 40K ranges from 2.24  to 20.032.43Bq/kg, 3.21 to 5.591.32 Bq/kg  and 24.46  4.06  to 795.99  6.20 Bq/kg respectively. For grain size of 1.0mm (B) the activity concentration of 226Ra, 232Th and 40K varies from 2.661.30 to 26.64Bq/kg, 2.19 0.95 to 33.47 Bq/kg and 43.38  to 739.21Bq/kg respectively. For grain size of 1.5mm (C) the activity concentration of 226Ra, 232Th and 40K varies from 4.401.09 to 33.93± 3.65 Bq/kg, 2.14±1.72 to 26.15±5.3 Bq/kg and 39.90±3.54 to 471.36±6.12 Bq/kg respectively.   For grain size of 2.0 mm (D) the activity concentration of 226Ra, 232Th and 40K varies from 4.81±1.84 to 40.29±2.50 Bq/kg, 2.19±1.40  to 83.20±3.90 Bq/kg and 39.01 ±4.00 to 497.56±5.87Bq/kg  respectively.  The result obtained shows there was no clear trend in variation of activity concentration with grain sizes. The mean values obtained are below the world average of 35, 30 and 400 Bq/kg for 226 Ra, 232Th and 40K for grain sizes of 0.5, 1.0, 1.5 and 2.0 mm respectively in all the communities except samples from Kolo that recorded 471.36±6.12 to 795.99±6.44 Bq/kg in all the grain sizes. Radiological risk parameters such as Absorbed Dose Rate, Annual Effective Dose Equivalent, Annual Gonadal Dose Equivalent, Annual Utility Index, Radioactivity Level Index, Hazard Indices and Excess Life Cancer Risk were estimated and values were found to be within the word average. From this study, the sediment of the given grain sizes will pose no radiological health risk if used in farming and in building construction.