Groundwater residence time in alluvial aquifer using emanation from Rn-222(222Rn) and its health impact in different aquifers.

This study evaluates the spatial and temporal variation of radon-222 (²²²Rn) in groundwater and assesses the associated health risks across the alluvial and lateritic zones of Kasaragod district, Kerala, India. ²²²Rn, a naturally occurring radioactive gas, can dissolve in groundwater and may pose health hazards to humans. Groundwater samples (n = 70) were collected during pre- and post-monsoon seasons, and ²²²Rn concentrations were analyzed in relation to local lithology and associated physical parameters. The study observed significant seasonal variability, with higher ²²²Rn concentrations recorded during the pre-monsoon, reflecting the influence of recharge processes and reduced dilution. Spatial variability was more pronounced in isolated pockets and was closely linked to geological formations rich in uranium and radium bearing minerals. The study employed ²²²Rn as a natural tracer to estimate groundwater residence time in the alluvial aquifer, providing values ranging from 0.2 to 13.1 days. The results enhance understanding of surface water-groundwater interactions and the processes governing aquifer recharge in the area. Health risk assessments were carried out using age-specific dose conversion factors for both ingestion and inhalation pathways. The results indicated that infants receive the highest annual effective dose, followed by children and adults. Despite a few locations with elevated doses during the pre-monsoon season, the majority of the study area remains within WHO's safety guidelines. This research contributes to the understanding of ²²²Rn behavior in groundwater systems and highlights the need for ongoing monitoring to support safe drinking water management and protect public health.