Occurrence and risk assessment of contaminants of emerging concern in water from the Danube River and its tributaries in Serbia

Abstract Background This study investigated the occurrence of 116 contaminants of emerging concern (CECs) in surface waters of the Danube River section within Serbia, along with its major tributaries (the Tisa, Sava, and Tamiš rivers) and the Great Bačka Canal. Analysis was performed using liquid chromatography coupled with high-resolution mass spectrometry (LC-HRMS) system Q-Exactive Orbitrap. Surface grab water samples were collected at 24 locations during multiple sampling campaigns (November 2022, April 2023, and November 2023) to assess the prevalence, frequency, and spatial–temporal distribution of target CECs. The studied compounds, some of their metabolites and/or transformation products encompassed five classes: pharmaceuticals (100 analytes), sweeteners (6), pesticides (4), personal care products (3), and industrial chemicals (3). Results Of the 116 targeted CECs, 44 were detected, including 37 pharmaceuticals, 4 sweeteners, 2 industrial chemicals, and 1 UV filter. Caffeine, sulfamethoxazole, tramadol, and climbazole were found in 100% of samples. The frequent detection of caffeine, selected pharmaceuticals, and sweeteners (acesulfame, sucralose, and cyclamate, present in >90% of samples) indicated their widespread presence in the studied watercourses. Campaign-to-campaign variability was evident for certain anti-inflammatory compounds (salicylic acid, diclofenac, ketoprofen), antidepressants (venlafaxine, citalopram), and the UV filter sulisobenzone (BP4), which appeared in both November campaigns (November 2022 and November 2023) but was not detected in April 2023. The environmental risk assessment, expressed as risk quotients (RQs), suggested that most detected compounds posed negligible ecological risks (< 0.01). Conclusions This study provides a harmonized, network-scale overview of the occurrence of CECs across the investigated Serbian Danube River network, thereby complementing and expanding the existing data for Serbian surface waters and contributing to the broader evidence base on CECs in Western Balkan watercourses. While most individual risk quotient values indicated negligible screening-level ecological risk, the frequent detection of selected pharmaceuticals and artificial sweeteners points to continuous wastewater-related inputs and/or persistence in the studied watercourses. These findings may support the prioritization of selected CECs in future national and regional monitoring programmes and provide a useful evidence base for water-quality management and policy-oriented discussions.