Migration and Transformation of Antimony at the Sediment–Water Interface: Insights from DGT Technique and Laboratory Simulation

Antimony (Sb) is a priority pollutant due to its toxicity and carcinogenicity, yet its speciation and transportation at the sediment–water interface (SWI) remain poorly understood. Here, we combine field investigations in the Taipu River with laboratory experiments to elucidate the distribution and biogeochemical transformation of Sb at the SWI. Pore waters exhibit Sb concentrations substantially higher than those in overlying waters, while sediment cores show maximum Sb accumulation at depths of 5–10 cm and lower concentrations in surface sediments. Diffusive gradients in thin films (DGTs) reveal decreasing labile Sb with depth, indicating upward diffusion of reduced Sb from anoxic zones; however, flux calculations demonstrate a dominant net downward transport driven by oxidative scavenging in oxic sediments. Laboratory simulations show complete oxidation of dissolved Sb(III) to Sb(V) within 42 days. X-ray photoelectron spectroscopy confirms that Fe/Mn (oxyhydr)oxides mediate this oxidation and immobilize Sb(V) through strong surface binding. Sediment incubations further reveal a transient increase in Sb bioavailability during Fe/Mn oxide dissolution, followed by long-term stabilization in residual phases. These results highlight the dual role of Fe/Mn minerals in regulating Sb redox cycling and sequestration, providing mechanistic insights into Sb mobility, ecological risk, and remediation strategies in riverine environments.