Assessment of radon levels and radiological risk in groundwater of Al-Ahsa Oasis, Eastern Saudi Arabia

This study evaluated the radon activity in groundwater from 35 wells across Al-Ahsa Oasis in Eastern Saudi Arabia, and calculated the associated radiological health risks, as sampled between October and December 2024. Radon activity concentrations in water were measured using a RAD7 detector coupled with RAD-H2O accessories. Annual effective doses were estimated using dose models recommended by UNSCEAR and the ICRP. Measured radon concentrations ranged from 0.19 to 14.44 Bq L −1 , with a mean of 2.10 Bq L −1 , which is well below the United States Environmental Protection Agency (USEPA) reference concentration level of radon of 11.1 for water. Mean annual ingestion doses of radon varied from 1.13 to 83.74 μSv.y −1 for infants and from 0.50 to 36.89 μSv.y −1 for adults, while the corresponding inhalation doses, as released indoors, were negligible (0.00005–0.036 μSv.y −1 ). Estimated lifetime cancer risks ranged from 1.91 × 10 −4 to 142.08 × 10 −4 , with a mean of 20.66 × 10 −4 . Statistical analysis showed marked spatial variability in groundwater radon (coefficient of variation, CV = 113%) and a depth dependence, with higher activities observed in deeper wells. Radon levels showed only weak correlations with pH, salinity, and total dissolved solids (TDS). Overall, the findings indicate that groundwater in Al-Ahsa Oasis is radiologically safe for domestic use with respect to radon; however, the levels observed in a few deep wells warrant continued monitoring.