Radioactivity level and heavy metal speciation of oil impacted soils around mechanic workshop in Akure, Nigeria.
This study determined the elemental composition and heavy metal speciation of the soils around mechanic workshops in Akure, Nigeria, identified the naturally occurring radionuclides in the soils, evaluated the levels of radiological hazard indices from the radionuclide activity concentration and assessed the pollution status of the study area. These were with a view to evaluating the pollution status of the mechanic workshops with respect to heavy metals and radionuclide levels. A total of fifteen (15) soil samples comprising of ten (10) oil-impacted soil samples collected from the mechanic workshops and five (5) control soil samples collected from areas with little or no anthropogenic inputs within Akure, Ondo State, Nigeria. The concentrations of metals in the soil samples were determined using Atomic Absorption Spectrometry while the activity levels of the radionuclides were determined using Gamma ray spectrometry. The results showed that the total mean concentrations of Pb, Cu, Zn, Cd, Cr, Mn, As and Fe in the oil-impacted soils were 3.93 ± 0.09, 85.20 ± 0.95, 13.93 ± 0.09, 6.15 ± 0.07, 6.91 ± 0.08, 14.80 ± 0.10, 1.73 ± 0.03 and 162.90 ± 1.35 µg/g respectively. The heavy metals in the oil-impacted soils were considerably higher than those of the control soils. The data collected was subjected to descriptive statistical analysis to determine the geo-accumulation index (Igeo), pollution index (PI) and enrichment factor (EF) indicated that the mechanic workshops have uncontaminated to moderate contamination for Cu (0.51), Zn (0.49), Cd (0.86), Mn (0.67) and Fe (0.63), while there was moderate contamination for Pb (1.25), Cr (1.58) and As (1.45). The PI results suggested that the mechanic workshops are contaminated with all the heavy metals as the PIs are greater than 1. The EF results indicated minor enrichment for Pb (1.53), Cd (1.17), Cr (1.92), Mn (1.02) and As (1.76), while it indicated no enrichment for Cu (0.92) and Zn (0.90). The results of the extraction showed relatively low bioavailability and mobility potential with more proportion retained in the residual fraction for all the metals. The mean activity concentrations of the radionuclides 232Th, 238U and 40K in the oil-impacted soils were 0.89 ± 0.08, 132.13 ± 0.16 and 51.52 ± 0.06 Bq/Kg respectively. The radiological assessments in terms of the mean values of absorbed dose rate were (63.93 nGy/hr), annual equivalent dose rate (0.55 mSv/yr), internal hazard index (0.72 Bq/Kg), external hazard index (0.37 Bq/Kg), annual gonadal dose equivalent (428.22 µsvy-1), representative gamma index (0.92) and radium equivalent (137.38 Bq/Kg). The study concluded that the mechanic workshops studied were impacted with the analyzed heavy metals whose concentrations exceeded those of the control samples and standard permissible limits. The radiological assessment also indicated that long-term exposure of the radionuclides might pose intrinsic hazards to human health.