Heavy Metal Contamination and Human Health Risks in the Nilüfer Stream (Bursa, Türkiye): An Integrated Surface Water Assessment

Heavy metal contamination of surface waters poses serious environmental and public health concerns, particularly in industrialized river basins. This study presents an integrated assessment of heavy metal pollution and associated human health risks in the Nilüfer Stream (Bursa, Türkiye) based on a five-year monitoring dataset (2020–2024). Seasonal water samples collected from 15 stations along the main stream and its tributaries were analyzed for total concentrations of As, Al, B, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. Pollution levels were evaluated using the Heavy Metal Pollution Index (HPI), Heavy Metal Evaluation Index (HEI), and Degree of Contamination (Cd), while non-carcinogenic and carcinogenic health risks for adults and children were assessed via ingestion exposure following USEPA guidelines. Mean concentrations of Al, Fe, Mn, As, and Ni exceeded international drinking water guideline values, indicating significant contamination within the basin. All indices classified the Nilüfer Stream as severely polluted (HPI = 274.32; HEI = 49.59; Cd = 49.59), with higher values during summer and autumn due to reduced dilution. Principal component analysis revealed strong associations among Al, Fe, Mn, Ni, Cr, and Cu, suggesting a common origin likely related to cumulative anthropogenic inputs, while arsenic exhibited a distinct pattern linked to toxicological risk. Health risk assessment showed that the hazard index exceeded safe thresholds for both age groups, with children being more vulnerable. Arsenic and nickel were the main contributors to both non-carcinogenic and carcinogenic risks, with arsenic posing an unacceptable lifetime cancer risk. Overall, the results indicate severe cumulative heavy metal pollution and associated health risks, highlighting the need for continuous monitoring, effective pollution control, and integrated river basin management.