Predictive modeling, environmental fate, and governance of per- and polyfluoroalkyl substances (PFAS) in India: integrating monitoring, remediation, and policy for sustainable risk management

Per- and polyfluoroalkyl substances (PFAS) are a class of persistent organic contaminants characterized by extreme chemical stability, environmental mobility, and resistance to conventional degradation processes, raising significant concerns regarding their long-term accumulation in aquatic systems. Despite growing global attention, quantitative understanding of PFAS fate and transport under diverse hydroclimatic and anthropogenic conditions remains limited, particularly in developing regions. In this study, a process-based conceptual and numerical framework to simulate long-term PFAS dynamics in surface water systems across seven representative Indian states (Andhra Pradesh, Gujarat, Maharashtra, Punjab, Rajasthan, Tamil Nadu, and West Bengal) over the period 2024–2074. The model integrates key physicochemical and hydrological processes, including advection, diffusion, sorption, and limited degradation, while explicitly incorporating seasonal hydrological variability, especially monsoon-driven discharge fluctuations, and parameter uncertainty. Model simulations reveal a consistent long-term increase in PFAS concentrations across all regions, driven not solely by intrinsic persistence but by the interaction of sustained anthropogenic inputs and hydrological controls. Industrialized states such as Gujarat and Maharashtra exhibit the highest projected accumulation, primarily due to continuous inputs from wastewater treatment plant effluents and industrial discharges, which are identified as dominant sources through sensitivity analysis. In contrast, semi-arid regions such as Rajasthan show gradual accumulation due to limited dilution capacity, while coastal and monsoon-influenced systems (Andhra Pradesh and Tamil Nadu) demonstrate enhanced PFAS mobility and redistribution linked to seasonal recharge and runoff dynamics. Regions with mixed land use, including Punjab and West Bengal, display moderate but persistent increases driven by diffuse sources such as agricultural return flows. Uncertainty analysis indicates that although absolute concentration ranges vary, the increasing trend remains robust, highlighting a persistent imbalance between continuous inputs and limited removal processes. The model further demonstrates that short-chain PFAS are more mobile and less bioaccumulative, whereas long-chain compounds contribute more significantly to retention in aquatic systems. These findings highlight the critical role of source strength and hydrological variability in regulating PFAS distribution and persistence, providing a process-based basis for interpreting long-term trends in surface water systems.