Assessment of radiological risks in soils from different land use types within southwest Nigeria

Abstract

Land can be put into different uses with little consideration of attendant effects on human health and environment. This study aimed to assess the levels of natural radioactivity (40K, 226Ra and 232Th) and associated radiological hazards in soil samples from selected land use types in parts of Abeokuta metropolis, southwest Nigeria. A total of thirty (30) composite surface (0–30 cm) soil samples from six (6) different land uses—abattoir waste site (ABT), cement block making site (BMS), textile dye-contaminated site (DCS), automobile mechanic village site (MVS), welding & fabrication site (W&FS) and grassland (GLS) were collected and determined for activity concentration (AC) of natural radionuclides using NaI (Tl) scintillation detector. Radiological hazard indices (RHI) were later calculated using established UNSCEAR relations. The results of soil natural radioactivity levels revealed that the average ACs of 226Ra (57.66 ± 33.48–156.67 ± 48.78 Bq/kg) and 232Th (131.68 ± 41.10–213.96 ± 45.00 Bq/kg) in all investigated land uses were higher than their corresponding global mean values of 39 and 45 Bq/kg, correspondingly. The soils from all selected land uses had average AC of 40K (206.34 ± 69.98–316.68 ± 67.54 Bq/kg) below the weighted world average value of 420 Bq/kg. Average values of RHI such as annual dose rate (118.90–196.39 nGyhr−1), outdoor annual effective dose equivalent (145.82–240.86 μSv/yr), annual gonadal dose equivalent (821.28–1350.53 μSv/yr), gamma level index (1.89–3.09) and activity utilization index (2.21–3.69) of soils in all selected land uses were above the global average standards. Excess lifetime cancer risk values ranged from 0.51 to 0.84 × 10−3, exceeding the global average of 0.29 × 10−3. Multivariate statistics revealed that 232Th is the primary contributor to the radiological hazard. This study revealed considerable radiological risks from natural radionuclides in the topsoils of investigated land use types.