Arsenic and Phosphorus contamination in sediments along the urban river continuum in Yerevan (Armenia)

Urban rivers worldwide often contain contaminated sediments. This study investigates spatial (nine sites) and temporal (2019–2024) sediment contamination patterns along the Hrazdan River (Yerevan, Armenia), including first measurements of arsenic (As) and phosphorus (P). We assessed their clustering with other elements and water parameters (pH, conductivity, dissolved solids and oxygen) and evaluated As ecological risk. Mean sediment concentrations (mg/kg) of zinc (Zn: 161 ± 16), copper (Cu: 82 ± 14), and lead (Pb: 50 ± 18) exceeded threshold effect levels by 1.3–2.3×, with clear spatial differences. As (6.3 ± 0.5) remained near thresholds. Lake Yerevan had higher pH than upstream and downstream sites, upstream showed elevated P and solids, and downstream had higher Mn than both locations. Principal component analysis (64.4% variance) identified geological, water chemistry, and anthropogenic (inputs Zn, Cu, Pb and P) influences. Hierarchical clustering revealed shifting associations of As and P with other elements across river sections, with Lake Yerevan playing a key role, due to its lentic nature and high pH and Ca. Although sediment As poses low ecological risk, high pH of the overlying water may mobilize As into the water column, potentially increasing exposure in the ecosystem and irrigation waters. Future research should therefore assess ecosystem accumulation to clarify ecological and human health risks.