Hydrology Driven Redistribution and Integrated Risk Assessment of Heavy Metals in the Flood Prone Agricultural Wetland: Kuttanad, South India

Heavy metal contamination of floodplain agricultural wetlands is an increasing environmental and public-health concern driven by intensive agrochemical use, wastewater inputs, and hydrological extremes. This study evaluated the concentrations, spatial distribution, ecological risks, human health implications, and soil–water partitioning behavior of Pb, Cd, Co, Ni, Cu, Zn, and Fe in the seasonally flooded Kuttanad Wetland System, South India. Surface water and agricultural soil samples were collected from 30 monitoring stations during the dry and wet seasons of 2023–2024. An integrated framework combining Water Quality Index (WQI), Heavy Metal Pollution Index (HPI), Principal Component Analysis coupled with Absolute Principal Component Score–Multiple Linear Regression (PCA–APCS–MLR), geo-accumulation index (Igeo), potential ecological risk index (RI), human health risk assessment, and soil–water partitioning analysis was employed. Surface-water quality deteriorated, with marginal exceedances of Pb, Ni, and Fe, indicating persistent anthropogenic pressures. Agricultural soils acted as major sinks for metal accumulation, with Cd enrichment contributing the highest ecological risk, particularly during the dry season. Soil–water partitioning revealed strong retention of Cd, Co, Ni, Cu, and Zn, whereas Pb and Fe exhibited comparatively greater mobility. Agricultural inputs, sewage discharge, and runoff were identified as the dominant contamination sources, highlighting the need for integrated management of vulnerable floodplain wetlands.