Potentially Toxic Elements in the River–Lake System of the Dongting Lake Basin, China: Spatial Distribution, Partitioning Behavior, and Ecological Risk

Abstract The river–lake systems regulate the transport, retention, and redistribution of potentially toxic elements (PTEs), but their water–sediment partitioning behavior and ecological implications remain insufficiently understood. We analyzed surface water and sediment samples from 31 sites in the Dongting Lake Basin to assess the spatial distribution, water–sediment partitioning behavior, ecological risks, and potential sources of Cu, Zn, Ni, Pb, Cr, Cd, and As. Surface water PTE concentrations were low, and all mean and maximum values met the Chinese national surface water quality standards. In contrast, sediments showed greater PTE accumulation, indicating mild to moderate contamination and low to moderate ecological risks, with substantial spatial heterogeneity. Cd was the principal contaminant and risk contributor, showing localized enrichment, particularly along inflow channels and nearshore zones. Partitioning analysis indicated strong particulate affinity for Cr and Pb, whereas Cu and Zn exhibited relatively higher mobility. Multivariate analysis suggested three main source groups: mixed transportation, industrial, and domestic inputs; natural geochemical sources; and agricultural runoff. These results indicate that sediment-bound Cd should be prioritized in monitoring at river–lake interfaces, hydrodynamic exchange zones, and nearshore areas. Multiseasonal sampling, metal speciation, and source-specific investigations are needed to validate these screening-level findings.