Distribution of radionuclides and heavy metals in the bituminous sand deposit in Ogun State, Nigeria - A multi-dimensional pollution, health and radiological risk assessment

Pollutants in soils and other environmental matrices can directly pose significant human health risks through various exposure pathways, especially for local population. The concentration and distribution of heavy metals (Pb, Ni, Cd, Cr, Fe and Zn) and the gamma ray emitting (238U, 232Th, and 40K) radionuclides in bituminous soils were analyzed using well calibrated atomic absorption spectrophotometer (AAS) and γ-ray spectrometry using NaI(TI) detector. The average concentration of Pb, Ni, Cd, Cr, Fe and Zn were 28.2, 24.1, 5.16, 42.5, 170 and 226 mg kg−1 respectively. The average activity concentration of 238U, 232Th, and 40K were 42.6 ± 6.50, 113 ± 10.5 and 461 ± 24.3 Bq kg−1 respectively. These values were above the world average value, although only six samples were higher than the world average value. The average activity concentrations, radium equivalent and dose rate of measured radionuclides were compared with other literature values and country's maximum allowable limit for heavy metals. The geo-accumulation index (Igeo), contamination factor, pollution loading index (PI), enrichment factor, and potential ecological risk index (PERI) were calculated to assess the heavy metals pollution level in soils. The total hazard index (THI) and carcinogenic risk (CR) were used to assess human health risk of heavy metals. The pollution level using the four pollution assessment model were in the order Pb > Cd > Ni > Cr > Fe > Zn. The estimated carcinogenic risk (CR) for children and adults obtained were all higher than the safe limit (1 × 10−6) while the non-carcinogenic risk (THI) was below the safe limit (THI ˂ 1). Pollution sources were identified using multivariate statistical analysis. It was found that Cr contributed >97% to the overall cancer risk (CR) for children and adults. The pollution sources were identified using multivariate statistical analysis. Therefore, the federal and state ministry of environment, health and solid minerals must rise to the urgent need of remediating the bituminous soil which may pose great health risk to human population in the study area.