Evaluation of natural radionuclides and associated radiation hazard indices in soil and water from selected vegetable farmlands in Lagos, Nigeria

Uptake of natural radionuclides by vegetables cultivated on contaminated soil may contribute significantly to the radiation exposure of a population. This study evaluated the activity concentrations of Ra-226, Th-232, and K-40 in 27 soil and 27 irrigation water samples from different farms in Lagos using Hyper Pure Germanium (HPGe) detector. Activity concentrations of Ra-226, Th-232, and K-40 from soil samples were used to estimate some radiological hazard indices. The mean values of the activity concentrations for Ra-226, Th-232, and K-40 in irrigation water were 2.29 +/- 0.28, 0.38 +/- 0.03, and 2.17 +/- 0.51 Bq/l, respectively. The values for Th-232 and Ra-226 were 62% lower and 129% higher than their respective reference values while the value for K-40 was within the values reported by similar studies. The mean specific activity for Ra-226, Th-232, and K-40 in soil samples were 10.99 +/- 3.75, 11.20 +/- 5.36, and 19.38 +/- 15.81 Bq/kg. These were 70, 75, and 81% lower than their respective world's average values. The values of the hazard indices, radium equivalent, representative level index (RLI), mean absorbed dose, outdoor annual effective dose, internal hazard index, external hazard index, and excess lifetime cancer risks (ELCRs) were 28.50 Bq/kg, 0.20, 12.50 nGy/h, 15.35 mu Sv/yr, 0.11, 0.08, and 0.05 x 10(-3), respectively. These values were 92, 80, 72.27, 78.07, 89, 92, and 82.76% below their respective world's average values and safe limits. The soils in the study area do not present any potential radiological effects. The use of surface water for irrigation, however, poses radiological risks to consumers of vegetables. Irrigation water is, therefore, a potential source of elevated concentrations of Ra-226 in vegetables cultivated in Lagos metropolis.