Natural radioactivity and metal concentration in the Thyspunt area, Eastern Cape Province, South Africa

Abstract

Naturally occurring radionuclides and metals have adverse human health impacts when they occur at higher activity and concentration above the threshold value, respectively, in the water supply system. This study aimed to establish the baseline radionuclide and metal content in rocks, soils, and water in the Thyspunt area of the Eastern Cape Province, South Africa, which is selected as a potential site for the development of a nuclear power plant. Extensive sampling of rocks, soils, groundwater, and surface water was conducted in the area. The employed methods of sample analyses include ICP-MS, gamma-ray spectrometery (RS 230), and accelerator mass spectrometry. The results indicate that the Ceres Subgroup shale and the Skurwerburg formation quartzite of the Table Mountain Group (TMG) contain the highest activity of most radionuclides, including 238U, 235U, 234U, 226Ra, 232Th, and 210Pb; these are linked to the natural geochemistry of the rocks that have been facilitated by the low-grade metamorphism to which the local geology was subjected. The metamorphism-related radionuclide enrichment is also apparent in the soils and groundwater associated with these rocks. The activity of the radiotoxic and carcinogenic uranium (238U and 235U) and radium (226Ra and 224Ra) isotopes in water was found to be well above the WHO guideline of 0.03 and 1Bq/L, respectively. The exposure dose rate was the highest in the Ceres Subgroup shales (185.7 nS/h), and this is linked to the elevated natural radioactivity in the rocks. The estimate of the ingestion-related effective dose indicates high doses associated with the uranium and radium isotopes, thus signifying the potential adverse impact on human health associated with the ingestion of the widely used groundwater in the area.