Geogenic Weathering, Spatial/Seasonal Variability, and Nonpoint Pollution Govern the Aquatic Ionic Probability Exceedance and Associated Health Risks in the Ganga and Yamuna Rivers

This study evaluated the seasonal hydrogeochemical characteristics and metal risks in water samples from the Ganga and Yamuna rivers. The research used hydrogeochemical analyses, statistics, and risk evaluations. Findings indicated that evaporation significantly impacted both rivers, particularly in the pre-monsoon season, increasing concentrations of major ions and metals. Notably, geogenic processes such as carbonate and silicate weathering displayed significant spatial and seasonal variability, with carbonate weathering more pronounced in the Yamuna river. Higher carbonate levels in the pre-monsoon suggested dilution by rainfall in the post-monsoon season. Probability exceedance analysis revealed greater spatial differences between the rivers, with the Ganga river showing pronounced reductions in ion concentrations, attributed to its larger flow rate and shorter residence time. Arsenic mobilization was linked to competitive desorption involving HCO3– and PO43–, particularly in the Ganga. Multivariate analyses showed that tanneries and industries interact with geogenic factors, leading to greater impacts in the Yamuna during the post-monsoon season. Infants were particularly at risk from both non-carcinogenic and carcinogenic exposures. The significance of the study lies in the fact that the Ganga–Yamuna river water is the major source of groundwater recharge used for irrigation that supports one-sixth of the human population.