Ecological risk assessment and source apportionment of potentially toxic elements in the Yongding river within the Beijing-Tianjin-Hebei urban agglomeration

Understanding the distribution, sources, and ecological risks of potentially toxic elements (PTEs) within urban agglomerations is critical for protecting water quality and promoting sustainable river management. In this study, the contamination levels and potential risks of 12 PTEs (Al, Ti, Mn, Co, Sn, Cu, Zn, As, Sb, Ba, Pb, and Sr) in Yongding River were evaluated by a method combining pollution indices and ecological risk indices. The elevated concentrations of Cu in surface water, which exceeded the Chinese limit of 90 % and the WHO recommendation of 82.61 % of sites, do not directly pose human health risk. At midstream sites, Co exhibited an extremely high enrichment factor (EF) (EF > 300). However, neither the pollution index (PI) nor the geoaccumulation index (I geo ) indicated pollution. Similarly, Ti and Sr showed moderate enrichment and widespread distribution. Positive matrix factorization (PMF) and principal components analysis (PCA) analysis identified four main sources: mining activity (30.06 %), industry-agriculture (29.60 %), natural-human (11.71 %), and traffic-industry (28.63 %). Although there were isolated hotspots for contamination, the overall ecological risk was low. The co-occurrence of metal enrichment in water and sediments highlighted the potential of remobilization under fluctuating pH, nutrient loading, and redox conditions. These findings emphasize the importance of targeted monitoring of Cu, Co, Ti, and Sr as well as support integrated sediment-water pollution management strategies in urbanized watersheds. • Cu, Co, Ti, and Sr were identified as priority potentially toxic elements in the Yongding River. • PMF and PCA analysis revealed four main sources: mining activity (30.06 %), industrial-agriculture (29.60 %), natural-human (11.71 %), and traffic-industrial (28.63 %). • The co-occurrence of metal enrichment in water and sediments highlighted the potential of remobilization under fluctuating pH, nutrient loading, and redox conditions.