Hydrogeochemical evaluation and human health risk assessment of uranium and radon in the coastal aquifers of southern Tamil Nadu

Groundwater contamination by geogenic radionuclides, such as uranium and radon, poses significant public health risks, particularly in hard-rock and coastal aquifers of southern India, where lithological controls favour their mobilisation. This study assesses the spatial distribution and age-dependent radiological health risks of uranium and radon in groundwater from Kadaladi Taluk, Southern Tamil Nadu. Forty-four samples were analysed for uranium using an LED fluorimeter and radon using a RAD7 radon detector. Uranium concentrations ranged from 0.01 to 35.58 µg/L (mean 4.70 µg/L), with exceedances at selected locations and elevated hazard quotient (HQ) values in children, indicating potential non-carcinogenic risks. Lifetime Average Daily Dose (LADD) and excess cancer risk estimates for U-238 and U-234 revealed localised chronic exposure. Radon concentrations varied from 69 to 640 Bq/L (mean 246 Bq/L), with 29.55 % of samples yielding annual effective doses above three mSv y⁻¹ . Infants were the most exposed group due to higher water intake per unit body mass. Statistical residual analysis showed that uranium variability was site-specific, whereas radon exhibited broader regional geological control. The co-occurrence of uranium and radon hotspots highlights the need for integrated hydrogeochemical and radiological management. Mitigation strategies, such as point-of-use treatment, wellhead aeration, improved ventilation, and continuous monitoring, are recommended to reduce exposure risks in high-risk zones. • Uranium and radon levels assessed in groundwater as per WHO and BIS standards. • 22 uranium and 29.55 % radon samples exceeded safe drinking water limits. • Health risk analysis shows infants and children are more vulnerable to exposure. • Radon exposure mainly through inhalation due to poor ventilation and storage. • Uranium and radon hotspot overlap calls for integrated groundwater risk management.