Age-Specific Radiological Risk of 222Rn in Drinking Water Wells Along the Sultandağı Fault Zone (Türkiye): A One-Year Monitoring Study

Background: Radon in drinking water is a potential source of ionizing radiation exposure, yet long-term monitoring data from active tectonic regions remain limited. This study investigated 222Rn activity concentrations in drinking-water wells along the Sultandağı Fault (Afyonkarahisar, Türkiye) and assessed age-dependent radiological risks. Methods: 222Rn concentrations were measured at two-week intervals in 15 drinking-water wells between June 2021 and June 2022 using a WG-1001 water–gas separation system and an AB-5R radiation monitor. Annual effective dose (AED) and excess lifetime cancer risk (ELCR) were calculated for infants, children, and adults. Results: 222Rn concentrations ranged from 0.05 to 26.64 Bq L−1, with a mean of 6.12 ± 2.79 Bq L−1. Only one well exceeded the USEPA guideline level (11.1 Bq L−1), whereas all measurements remained below the WHO reference level (100 Bq L−1). Seasonal mean concentrations varied between 5.48 ± 2.53 and 7.08 ± 3.32 Bq L−1. Mean AED values were 35.94, 13.17, and 15.63 μSv y−1 for infants, children, and adults, respectively. Corresponding ELCR values were 1.26 × 10−4, 0.46 × 10−4, and 0.55 × 10−4. Conclusions: The results indicate generally low radiological risk from radon in drinking water within the study area, although elevated values were observed in some wells. Higher age-specific dose and risk estimates were obtained for infants. These findings provide long-term data on groundwater 222Rn variability in an active fault zone and support regional radiological risk assessment.