Temporal dynamics of groundwater quality and associated health risks in a semi arid region of South India

This study investigates the seasonal variability of groundwater quality and the associated non-carcinogenic health risks from NO$$_{3}^{ - }$$and F$$^{ - }$$ in a semi-arid region of South India. A total of 61 groundwater samples collected during the pre- and post-monsoon seasons of 2020 were analyzed for major physicochemical parameters. Hydrogeochemical ratios, correlation analysis, principal component analysis (PCA), non-carcinogenic risk assessment for different age groups, and GIS-based spatial techniques were employed to identify the controlling processes and assess exposure risks. The results revealed a distinct seasonal shift in dominant cations from Na⁺ during the pre-monsoon to Ca²⁺ during the post-monsoon indicating the influence of silicate weathering, carbonate dissolution, and ion-exchange reactions. Bicarbonate HCO$$_{3}^{ - }$$and Cl$$^{ - }$$remained the dominant anions in both seasons. Temporal variations in Mg²⁺, Na⁺, Cl$$^{ - }$$, SO$$_{4}^{{2 - }}$$and NO$$_{3}^{ - }$$along groundwater flow paths and across land-use gradients reflected combined geogenic and anthropogenic contributions, with more pronounced impacts during the pre-monsoon period. These interpretations were further supported by geochemical ratios and multivariate statistical results. The Overall Water Quality Index (OWQI) indicated a 36.23% improvement in groundwater quality during the post-monsoon season, attributed to dilution from monsoonal recharge. Health-risk assessment showed that infants and children were the most vulnerable to ingestion-based exposure to NO$$_{3}^{ - }$$and F$$^{ - }$$, with the highest pre-monsoon hazard quotients observed for infants (mean = 4.51) and children (mean = 2.94), compared with adults (mean = 1.40). Dermal exposure posed a negligible risk for infants (mean = 0.01) and children (mean = 0.14), but contributed a moderate risk for adults (mean = 0.95), particularly in the pre-monsoon season. The study highlights the need for season-specific groundwater management and protection strategies in semi-arid regions. The findings provide critical insights into groundwater quality dynamics and health risks, contributing to the achievement of United Nations Sustainable Development Goal 6 (Clean Water and Sanitation).