Natural Radionuclides 222Rn and 226Ra in Shallow Groundwater of Nysa County (SW Poland): Concentrations, Background, and Radiological Risk

Natural radionuclides may occur in groundwater and pose health risks when present in elevated concentrations. This study evaluates the quality of shallow groundwater in Nysa County (SW Poland) based on the activity concentrations of natural radionuclides radon (222Rn) and radium (226Ra) and estimates the associated radiological risk from water ingestion. Twenty-three groundwater samples were collected from private wells located within two distinct geological units: the Fore-Sudetic Block and the Opole Trough. Activity concentrations of 222Rn and 226Ra were measured using the liquid scintillation counting method. A spatial distribution model for 222Rn was developed using inverse distance weighting in QGIS. Local hydrogeochemical background levels were determined using the Q-Dixon test, interquartile range, and Shapiro–Wilk normality test. The background ranged from 2.6 to 3.9 Bq·L−1 in the Opole Trough and from 0 to 10.7 Bq·L−1 in the Fore-Sudetic Block. The lower detection limit (0.05 Bq·L−1) for 226Ra activity concentration measurements was not exceeded. Effective dose rates were calculated in accordance with the recommendations of the International Commission on Radiological Protection and United Nations Scientific Committee on the Effects of Atomic Radiation. Doses ranged from <1 µSv to over 120 µSv·y−1. Although all samples met national regulatory standards (≤1 mSv·y−1), the World Health Organization reference level (0.1 mSv·y−1) was exceeded in two cases. The results support the need for the radiological monitoring of unregulated private wells and provide a scientific basis for the refinement of legal frameworks and health protection strategies.