Meteorological and hydrogeochemical control on the co-occurrence of geogenic contaminants in the alluvial aquifers of northwest India

Innumerable studies have emphasized elevated fluoride (Fˉ) and uranium (U) levels in shallow aquifers in the semi-arid region of Punjab, India, endangering the groundwater-dependent population's health. This study examines the factors and mechanisms contributing to Fˉ and U co-occurrence in the region's aquifers to enhance the understanding of the contaminants' behaviour. Fˉ and U concentrations were higher in shallow aquifers (<60 m) compared to deeper (>60 m), and both the contaminants surpassed their respective permissible limits under excess EC, TDS, Clˉ, NO₃ˉ, SO₄²ˉ, Na⁺, and K⁺ levels. Elevated EC and TDS and their strong correlation with U and Fˉ suggest high salinity facilitated mobilization and co-contamination by increasing ionic strength and competitive behaviour through ion exchange mechanisms. Additionally, scanty precipitation, enhanced evapotranspiration, and aridity were significantly correlated to Fˉ and U, highlighting that these meteorological variables positively influence this co-contamination, particularly in the Malwa region. The mixed chemical composition of the groundwater emanated from rock-water interaction and evaporation, which further increased Fˉ and U and facilitated their co-occurrence. U existed predominantly as UO₂(CO₃)₂²ˉ and UO₂(CO₃)₃⁴ˉ (95%), which corroborated with a strong positive correlation with HCO₃ˉ, whereas fluoride existed mainly as free Fˉ (90%). The findings of this work will help the scientific community to address similar issues in other arid and semi-arid regions globally and investigate the potential synergistic effect and health risks associated with the co-occurrence of Fˉ and U in the groundwater.