RADIOLOGICAL RISK ASSESSMENT OF PHOSPHATE FERTILIZER ON FARMLAND IN ONDO STATE, SOUTHWESTERN NIGERIA

Abstract

The exposure of man to naturally occurring radionuclides through food and water intake gives rise to a dose which varies depending on the location, diet and habit of the individuals concerned. The activity concentrations of 40K, 232Th and 238U have been measured in soils, rice and maize samples collected from some cities in Ondo State. Activity concentration measurements were carried out using a co ̶axial type high purity germanium (HpGe) detector. Spectral analyses were performed using spectrometry Software (MAESTRO ̶32). Potassium ̶ 40 was found to have the highest activity concentration in all the foodstuffs (Rice and Maize). The activity concentration of 40K, 232Th and 238U in the soil has the highest value of 533.06 ± 79.96 Bq Kg ̶1 .While the activity concentration of 40K 232Th and 238U in the rice samples has the highest value of 46.47 ± 12.06 Bq Kg ̶1. The 40K 232Th and 238U activity concentration for Maize has the highest value of 18.91 ± 3.36 Bq Kg ̶1. The mean absorbed dose rates due to the presence of 40K, 232Th and 238U in the soil samples is 17.05 ± 2.65 nGy h-1. The mean annual effective doses equivalent to individuals from the consumption of rice and Maize from Ondo state ranged from 1.33 mSv y ̶1 to 1.45 mSv y ̶1 while the mean annual effective dose equivalent in the farms due to soil radioactivity in Ondo State is 26.08 mSv y ̶ 1. This implies that there is low exposure for either farmer or worker dealing with transportation of soil in which phosphate fertilizers have been used and that soil could pose a significant health hazards when used for building constructions and when it is being inhaled while that of rice and Maize are less than the Maximum permissible dose of 2.4 mSv y ̶1 world average recommended for the public by International Commission on Radiological Protection (ICRP 1991).