Assessment of environmental risks, associated with increasingly complex assemblages of hazardous organic contaminants in the aquatic environment, requires a comprehensive approach, based on a simultaneous application of bioassays to assess possible biological effects and a thorough chemical characterisation of individual toxicants [1]. The application of effect-directed analyses (EDA) approach has been successfully demonstrated with various environmental matrices and represents currently the most promising tool for scientificallybased prioritization of organic contaminants [2]. This paper describes EDA approach, applied for the characterisation of hazardous chemical contamination in the Sava River basin, which included analyses of the municipal wastewater of the city of Zagreb as the predominant input into the Sava River as well as analyses of river water and sediments along the well-defined pollution gradients. Water and sediment samples were comprehensively characterised using tailored sample preparation protocols, a combination of chemical analytical methods and a battery of bioassays. Ecotoxicity profiling of the investigated samples, included cytotoxicity, chronic toxicity, EROD activity ; inhibition of the multixenobiotic resistance (MXR), genotoxicicity and estrogenic potential, while chemical characterization involved highresolution gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/quadrupole time-of-flight mass spectrometry (LC-QTOFMS). Regarding of dissolved contaminants, the results revealed the most significant contribution to be present in the polar fraction, while the contribution of classical contaminants such as PAH and PCBs was estimated to be very low. On the contrary, the highest toxic responses in the river sediment extracts were shown to be mainly associated with hydrophobic contaminants. The results obtained in this study confirmed the importance of investigative monitoring for resetting the priorities in the monitoring activities, applied in the Sava River basin. More generally, they indicated the need to re-design current pollutant monitoring strategies in aquatic systems by putting more emphasis on the polar contaminants.

Biology,Earth science