Natural radiation and radioactivity in soil and groundwater of Jos Plateau, Nigeria

Abstract

This study aimed to establish baseline data on the natural environmental gamma radiation and radioactivity levels as well as to evaluate the corresponding radiological health impacts for Jos plateau, Nigeria. It employed the use of portable NaI(Tl) survey meter and hyper pure germanium spectrometer to measure external gamma dose rate and to determine the specific activity concentration of terrestrial radionuclides, 226Ra, 232Th and 40K in soil samples, respectively. External gamma dose rates were measured at 811 locations while activity concentration were determined for 102 soil samples. The mean value for the measured gamma dose rate was found to be approximately four times the world average value while the mean values for the activity concentration of 226Ra, 232Th and 40K were found to distinctly exceed their corresponding world reference values for continental soil. Gamma dose rate and activity concentration of the terrestrial radionuclides for each geological formation and soil type of the area are presented. Statistical relationships between gamma dose rate with the different geological formations and soil types of the area are established. Younger granites geological formation and Haplic acrisols soil type were found to contribute the highest to the natural background radioactivity and 232Th was found to be the highest contributor to the terrestrial gamma dose rate for the study area. Various groundwater samples were also measured for concentration of U and Th using inductive coupled plasma mass spectroscopy and the concentrations of U ranged from 1.4 to 35 ??g L-1 with a mean value of 13.15 ??g L-1 while for Th ranged from 0.10 to 11.1 ??g L-1 with a mean value of 1.85 ??g L-1. Few groundwater samples were found to have values exceeding the recommended limit of U provided by WHO and USEPA for drinking water. Radiological health impact parameters namely radium equivalent, external hazard index, annual effective dose, collective dose and excess lifetime cancer risk due to soil radioactivity and annual ingestion dose as well as radiotoxicity risks due to ingestion of groundwater were also evaluated. It is found that, an individual leaving in this area is most likely to incur a radiological health related risks due to natural radiation. Isodose maps for gamma rates and the spatial distribution pattern of activity concentration of 226Ra, 232Th and 40K for the study area were produced using ArcGIS mapping software. The results revealed that Jos Plateau has above normal levels of natural background radiation. The data here presented will be useful for radio–geochemical investigation and as a reference data to asses possible changes in the environmental background radiation levels due to local and transnational releases of radioactive materials from artificial sources and also useful for preparing radiological map for Nigeria.