Cross-media partitioning, ecological-health risks, and source apportionment of heavy metals in a river-sediment...

As the primary water source for the Middle Route of the South-to-North Water Diversion Project, water security in the Danjiang River Basin is critical. This study systematically investigated the concentrations, solid-liquid distribution characteristics, and ecological risks of Cd, Cr, Zn, Cu, Pb, Ni, As, and Hg in surface water across the Henan section of the Danjiang River Basin and in sediments from typical river reaches. Source apportionment was conducted using Positive Matrix Factorization (PMF) and Self-Organizing Maps (SOM). Most HMs were enriched in sediments, with Cd and Hg contributing most to pollution levels and ecological risks. Distribution coefficients (K_d) showed pronounced elemental differences and solid-phase heterogeneity. Cu, Zn, and Pb displayed strong particle affinity, whereas Cd and Hg showed higher cross-media migration potential, increasing downstream water quality risks. Redundancy and correlation analyses indicated that sediment organic matter and iron-manganese oxides were the dominant factors controlling HM distribution. For the investigated sediment samples, PMF analysis suggested that sediment HMs were mainly associated with agricultural runoff (18.59%), industrial and atmospheric deposition (27.09%), natural sources related to soil parent material (25.46%), and transportation and industrial activities (28.86%). SOM clustering further classified sediment samples into groups with different contamination levels and source characteristics, indicating a transition from relatively low contamination to anthropogenic disturbance and localized point source influence. This study clarifies HM behavior in surface water and typical sedimentary reaches of a key water source basin, providing scientific support for targeted pollution control.