Rivers are subject to multiple pressures from chemical contaminants. In this study, we analysed seven potentially toxic elements (PTEs: Pb, Cd, As, Cr, Ni, Cu, Zn), phosphorus (P), and rare earth elements (REEs: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in soils, river sediments, suspended particulate matter (SPM), and river water under the varying hydrological conditions. The investigation was conducted in two lithologically distinct catchments: the carbonate-dominated Koppány catchment in Hungary and the siliciclastic Ledava catchment in Slovenia. Total concentrations of PTEs in river water increased substantially during high-flow events due to the mobilization of SPM, whereas dissolved concentrations remained largely below the environmental quality standards of the EU Water Framework Directive. Most PTEs, with low bioavailability (acetic acid-extractable fraction less than 10%), indicated limited environmental risk. Enrichment factors revealed anthropogenic enrichment for Cd, Pb, and P. Elevated P levels in Koppány sediments and SPM were primarily linked to diffuse agricultural sources and point-source wastewater discharges, while Cd enrichment was more associated with urban runoff. Multivariate statistical analysis combined with REE geochemistry shows that element distribution across the different matrices is controlled by two main processes. The first is hydrodynamic sorting during fluvial transport, which selectively enriches fine-grained phases from soils through sediments to SPM. The second is primary lithological provenance, which distinguishes the carbonate-dominated, recycled, loess-derived Koppány catchment from the siliciclastic Ledava catchment across all three solid matrices. REE patterns further supported these interpretations, showing associations with Fe–Mn oxyhydroxides, aluminosilicate clay minerals, and heavy minerals, along with progressive enrichment in the fine-grained suspended fraction via surface complexation during transport. These results highlight that an integrated approach, incorporating PTEs and P as contaminants and REEs as tracers, provides a robust framework for distinguishing lithogenic sources, hydrodynamic processes, and anthropogenic inputs in geochemically complex river systems.
Ščančar et al. (Sun,) studied this question.