The natural radioactivity concentrations in soil samples collected from 186 locations across 18 cities in the six geo-political zones of Nigeria have been determined using gamma-ray spectrometry. Results show that the concentrations of (40)K, (238)U and (232)Th in the soil samples varied from below detection limits (BDL) to 1459.4 Bq kg(-1) with a mean of 73.3 +/- 18.5 Bq kg(-1) for (40)K, whereas for (238)U and (232)Th values varied from 9.2 to 113.7 Bq kg(-1) with a mean of 33.9 +/- 7.4 Bq kg(-1) and from BDL to 175.7 Bq kg(-1) with a mean of 12.4 +/- 3.1 Bq kg(-1), respectively. The average gamma absorbed dose rate in air across the cities ranged between 19 +/- 5 and 88 +/- 44 nGy h(-1) and the gross mean was 42.0 +/- 21.0 nGy h(-1). Using available population data in the study areas, about 2.84% of the population is exposed to a radiation dose rate of less than 20 nGy h(-1), 52.40% to a radiation dose rate between 20 and 30 nGy h(-1), 31% to a radiation dose rate between 30 and 60 nGy h(-1) and about 13.76% to dose rates greater than 60 nGy h(-1).

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In the industrialized area of Lagos, vegetables are mostly cultivated through surface water irrigation. Untreated surface water has the potential of being contaminated with radionuclides from industrial effluents. This study evaluated the concentration of radionuclides in the leafy vegetables cultivated through surface water irrigation in Lagos metropolis and the potential health risks associated with their consumption. The specific activities of 226 Ra, 232 Th and 40 K in some commonly consumed leafy vegetables were determined using High Purity Germanium (HPGe) detector. To assess the radiation hazards associated with the consumption of these vegetables, annual effective dose (AED) and excess lifetime cancer risk (ELCR) were also determined. The specific activities of 226 Ra, 232 Th and 40 K in the investigated samples ranged from 0.49±044 to 6.00±1.19 Bq/kg, with an average value of 2.08±0.59 Bq/ for 226 Ra, from 0.10±0.07 to 0.61±0.12 Bq/kg with an average value of 0.85 ±0.08 Bq/kg for 232 Th and from 28.69±3.09 to 126.71±5.86 Bq/kg with an average value of 72.56±5.36 Bq/kg for 40 K. The mean activities of 226 Ra and 232 Th were 40 and 56 times higher than the World Health Organization (WHO) reference values for 226 Ra and 232 Th in leafy vegetables respectively. The AED estimated from the consumption of vegetables was 0.048 mSv/y, which is about 16 % of the reference AED value for radionuclides of natural origin in the total diet while leafy vegetable represents about 8 % of the total diet of an adult in Lagos. The ELCR obtained from this study was this is lower than the world's average value. This study has found elevated concentrations of 226 Ra and 232 Th in leafy vegetables, and noticeable increase in AED associated with 226 Ra exposure in the consumption of leafy vegetables cultivated in Lagos. There are therefore potential radiological health risks to the health of the public from long-term consumption of leafy vegetables cultivated through surface water irrigation in Lagos, Nigeria.

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