Metal contamination in Euphrates headwater sediments: Integrated risk assessment and PMF-based source apportionment...

Rivers are among the ecosystems most vulnerable to human activities, and mining is a major global source of metal pollution. This study assessed the concentrations of 14 metals in surface sediments of the Karasu River Basin, an important headwater of the Euphrates River in eastern Türkiye, following a recent gold mine failure. This research represents the first comprehensive post-failure assessment of sediment metal contamination in the Karasu River Basin, integrating sediment quality guidelines (TEC/PEC), multiple pollution and ecological risk indices, and Positive Matrix Factorization (PMF) source apportionment. Nickel and Cr emerged as the most critical contaminants, with Ni concentrations reaching up to 917 mg/kg and Cr up to 336 mg/kg. All Ni concentrations and 85% of Cr concentrations exceeded PEC thresholds (48.6 mg/kg for Ni and 111 mg/kg for Cr), indicating considerable ecological risk. In contrast, 30% of As and 35% of Cu concentrations fell within the TEC-PEC range. Spatial and cluster analyses identified sites K1 (near Erzincan province) and K9 (Çaltı Stream) as the most contaminated, primarily influenced by mining and wastewater inputs. The PMF model identified four principal metal sources, with mining activities suggested as a major contributor to Ni, Cr, and Co pollution, while natural geological contributions cannot be entirely excluded. Overall, the findings highlight the significant influence of mining on sediment quality and emphasize the need for continuous monitoring, stricter regulation, and targeted remediation to protect aquatic ecosystems and downstream communities.