ESTIMATION OF NATURAL RADIOACTIVITY AND HEAVY METAL CONCENTRATION IN SOIL SAMPLES FROM RAYFIELD - DU MINING SITE JOS, NIGERIA

ABSTRACT

Mining of tin and other related activities have been active and thus leading to economic growth in the Jos area of Nigeria for more than a century. However, mining of minerals has been confirmed to enhance the concentrations of heavy metals and natural radioisotopes in the soil, air and water bodies in the environment. In an attempt to evaluate the radiological impact of NORM and heavy metals (HM) burdens resulting from tin mining activities at Rayfield-Du area of Jos. Specific activities of natural occurring radioactive nuclei (238U, 232Th and 40K) and HM concentrations were evaluated in soil samples collected from the mining site. The soil samples were classified as normal soil (S), tailings (T) and mineral soils (M) and their corresponding mean activities for 238U, 232Th and 40K were analysed using a well calibrated HPGe detector based gamma spectrometric system. While the HM concentrations in the soils were evaluated using Energy Dispersed X-ray Fluorescence spectrometric system. The mean activity concentration for 238U, 232Th and 40K were 323.44, 877.63 and 864.99 Bqkg-1; 138.84,

469.31 and 578.65 Bqkg-1; and 168.83, 436.08 and 346.1 Bqkg-1 respectively for M, T and S samples. The calculated radiation dose parameters for the soil samples were all higher than the recommended safety limit. For all the collected soil sample, the external hazard risk Hext were 2.21, 2.81 and 4.44 for S, T and M respectively while the mean calculated radium equivalent was 819, 1057 and 1645 Bqkg-1 for S, T, and M respectively. The excess life cancer risk (ELCR) estimated for the mine was more than the world average value. The radio ecological dose rate estimate for non-human biota in the mine revealed that all non-human species except lichen and bryophyte had absorbed dose rate less than the 10 µGyh-1 screening dose. Generally, the potential of developing radiation induced health defects as a result of high radiation absorbed dose rate by the miners and dwellers around the mine is very high. The analysis of eight HM (Cr, Cu, Zn, Pb, Co, As, Cd, and Ni) concentrations showed that they were above the Nigerian reference level except for Co and Ni. For S, T, and M soil classification, the pollution index of the considered HM concentration was 0.67, 1.49, and 0.71 respectively. The corresponding ecological risk indices was 102,172, and 56 for S, T, and M. These can be classified as low pollution except T soil with moderate potential ecological risk index.