The problem of environmental contamination with pharmaceutical chemicals has been widely recognised over the past 20 years. The current literature is strongly dominated by studies focused at assessing the exposure concentrations in abiotic matrices (e.g. water and sediments) while the reports on the pharmaceutical concentrations in aquatic organisms remain comparatively scarce. However, when considering the possible biological effects, the aqueous exposure concentrations are only an indirect measure of potential toxicity, while the key parameter which determines the substance's potential for adverse effects is its internal concentration in the organism. Consequently, this project aims to provide new insights into the bioaccumulation and metabolic behaviour of pharmaceuticals in freshwater organisms, which is essential for an improved risk assessment of these contaminants as well as for their scientifically-sound prioritization. The project plan includes several interconnected phases, from method development and laboratory-controlled exposure experiments to field studies. Highly specific analytical methods for quantitative multiresidue determination of trace levels of selected pharmaceutical compounds in different environmental matrices (biota, water, sediment) will be developed and validated. These methods will be applied in carefully planned model and field experiments focusing on the characterization of pharmaceutical exposome in freshwater fish. The model bioaccumulation experiments will be performed using zebrafish (Danio rerio) as target organism, while considering different exposure scenarios. The biochemical responses in fish will be followed by measuring induction of the major cytochrome P450 detoxification enzymes. As its final step, the project includes a ground-truthing study in the Sava River to assess the environmental relevance of the pharmaceutical exposome and to collect the critical data for prioritization of individual pharmaceutical contaminants.