Natural Radioactivity Assessment and Radiological Health Risk Evaluation of Thermal and Mineral Springs in a Volcanic–Geothermal System of Northwest Iran

Natural radioactivity in spring waters is a key indicator of environmental radiation exposure, particularly in geothermal regions. In this study, gross alpha and gross beta activities were measured in 26 spring water samples from Ardabil Province, northwestern Iran, using liquid scintillation counting (Quantulus 1220) in accordance with ISO 11704:2018. The measured gross alpha activity concentrations ranged from below minimum detectable activity (MDA) to 3.05 Bq/l, with a mean value of 0.50 Bq/l, while gross beta activities varied from MDA to 6.52 Bq/l, with an average of 0.90 Bq/l.Spatial analysis revealed pronounced heterogeneity among sampling sites, with several springs exceeding the World Health Organization (WHO) screening levels of 0.5 Bq/l for gross alpha and 1.0 Bq/l for gross beta activity. The highest activity concentrations were observed in Saqzchi Nir Asli spring (3.05 Bq/l for alpha and 6.52 Bq/l for beta), followed by Berjolu, Qinarjeh, and Ilanjiq-2 springs. A strong positive correlation was found between gross alpha and gross beta activities (r = 0.984), indicating a common geogenic origin and similar hydrogeochemical controls. The annual effective dose (AED) due to ingestion of spring water ranged from <0.01 to 3.91 mSv/y, with several springs exceeding the WHO reference level of 0.1 mSv/y. Correspondingly, the excess lifetime cancer risk (ELCR) varied between approximately 5.4 × 10⁻³ and 2.17 × 10⁻¹.