Assessment of Natural Radioactivity, Radon Distribution, and Radiological Hazards in Soil and Groundwater of Al-Ahsa region, Eastern Saudi Arabia

Naturally occurring radioactive materials (NORMs) in soil and groundwater are important indicators of environmental quality and potential radiological health risks. However, integrated assessments of radionuclide distribution and radon occurrence in the Al-Ahsa region of eastern Saudi Arabia remain limited. This study evaluated the activity concentrations of 238 U, 226 Ra, 232 Th, and 40 K, in soil and the concentration of 222 Rn in groundwater samples that had been collected from different agricultural areas of Al-Ahsa. Radiological hazard parameters, including radium equivalent activity (Ra eq ), absorbed dose rate, annual effective dose equivalent (AEDE), excess lifetime cancer risk (ELCR), external hazard index (H ex ), internal hazard index (H in ), and gamma activity index (I γ ), were calculated and compared with international reference values. The results showed that the average activity concentrations of 238 U, 226 Ra, 232 Th, and 40 K, were significantly lower than the corresponding global averages reported by UNSCEAR. In addition, radon concentrations in groundwater from same locations of soil samples showed a level that ranged from 0.19 to 14.44 Bq L -1 , with a mean value of 2.77 Bq L -1 . These values are remaining below the permissible levels recommended by the World Health Organization (WHO) and the United States Environmental Protection Agency (USEPA). The highest radon concentration was observed in a deep groundwater well (S8,with depth 350 M). Also the soil sample (S8) showed highest 238 U(4.63±0.35), 226 Ra (5.62±0.44) activity concentration this explain the influence of hydrogeological conditions, groundwater residence time, and radionuclide rich geological formations in studied sample. Spatial distribution analysis revealed relatively uniform radionuclide concentrations across the study area, with localized enrichment at selected sampling locations. All calculated radiological hazard indices (Ra eq D, ELCR, AEDE H ex, H in and I γ ) were below their recommended permissible limits, indicating minimal radiological risk to the local population. The findings establish a baseline database for environmental radioactivity in Al-Ahsa eastern region of Saudi Arabia and provide valuable information for future environmental monitoring, groundwater management, and public health protection programs.