Three Gorges Dam-driven redistribution, sediment-water partitioning, and health risks of heavy metals in the Yangtze River

Abstract

The Three Gorges Dam (TGD), the largest hydraulic project on the Yangtze River mainstream, has altered hydrodynamic regimes and sediment transport. However, how its interplay with basin-scale pollution control policies regulates heavy metal behavior remains poorly understood. The spatiotemporal dynamics of eight priority heavy metals (As, Cd, Cr, Cu, Ni, Pb, Zn, Mn) in surface water and sediments along the Yangtze mainstream from 2016 to 2022 were investigated, with the TGD employed as a critical hydrological boundary. Sediment–water partition coefficients were calculated, geo‑accumulation and health risk indices were applied, and source apportionment was performed using positive matrix factorization. The results showed that most metals peaked in 2018 and subsequently declined, a pattern that coincides with the phased implementation of the Yangtze River Protection Strategy and suggests a measurable response to strengthened pollution controls. Arsenic, however, exhibited increasing upstream and decreasing downstream, highlighting its redox sensitivity to dam-altered hydrodynamics. TGD operation created two distinct geochemical regimes: sedimentary sequestration upstream and enhanced aqueous mobilization downstream. Partition coefficients increased over time, with Cr showing an 80.41% rise upstream (2016 vs 2022), indicating strengthened sedimentary retention. Source apportionment revealed a transition from direct industrial inputs upstream to mixed sources dominated by legacy contamination resuspension downstream. Non‑carcinogenic health risk assessments identified Cr and As as key drivers, with children facing potential risks primarily through dermal contact. These findings establish a dual-control framework wherein policy interventions reduce overall metal loads while dam regulation redistributes metals and associated risks across sediment-water phases, necessitating spatially differentiated management strategies for large regulated rivers.