Hydrogeochemical assessment of radon exposure with associated ingestion doses and risks in groundwater of Lesser Kumaon Himalayan region, India.

Access to clean water is essential for human survival and well-being to sustain life. The present study investigates the radon levels in potable groundwater sources across various locations of the Champawat district of the Lesser Kumaon Himalaya, India, using a scintillation-type Smart RnDuo Monitor coupled with a water bubbler. Alongside radon measurements, key physicochemical parameters were also recorded. Radon concentrations in water samples ranged from 0.5 ± 0.1 to 177.4 ± 4.6 Bq/L by showing a wide variation, with a mean (± SD) of 23.8 (± 39.7) Bq/L. The mean exceeds the USEPA guideline of 11.1 Bq/L but is below the WHO limit of 100 Bq/L. Notably, groundwater shows higher values of radon compared to spring and tap water sources. Spatial distribution mapping of radon and TDS was carried out for visualization purposes. A notable positive correlation, indicated by a Pearson r value of 0.62, was found between radon concentration and total dissolved solids. Radiological dose assessment displayed that the adults received a higher age-dependent annual effective ingestion dose (322.14 µSv/y) than infants and children, with groundwater posing a greater exposure risk than other sources. Comparatively, the organ-specific effective dose analysis indicated that the stomach and lungs received a higher dose of 38.66 µSv/y for adult males, with a corresponding elevated excess lifetime cancer risk. Overall, geological heterogeneity and thrust zones suggest spatial variation in radon levels by highlighting the role of geology and geomorphology in radon mobilization. The current findings will significantly improve water quality and provide valuable insights for epidemiological studies in the future.