Medicines are administered to restore, improve or modify physiological functions, and to diagnose diseases. The number of medicines developed and prescribed is gradually increasing, which consequently increases the number and concentration of disposed medicines. The pharmacologically active components of medicines are so-called active substances, which enter the aquatic environment either directly as waste, or indirectly as a consequence of drug administration to the patient, and may pose a serious toxic risk to aquatic organisms. In this Master's thesis, in silico methods were used to develop an ecotoxicological profile of ten selected active substances that are commonly prescribed and detected at higher concentrations in aquatic systems: ciprofloxacin, diclofenac, carbamazepine, gabapentin, tramadol, paracetamol, caffeine, bisoprolol, valsartan and metformin. Using computer programmes and different models, we predicted their fate in the environment and toxicity to aquatic organisms. We determined their sediment retention, biodegradability and bioaccumulation capacity and predicted LC50 values for three aquatic organisms. The predicted data were compared with literature data from the ECOTOX database. The selected active substances are poorly biodegradable, however devoid of potential for bioaccumulation. The predictive strength of our programmes proved to be low. We found that active substances with higher logP values persist longer in the sediment and bioaccumulate better and more easily, while having lower LC50 values, and therefore generally pose a higher risk for causing toxic effects on the aquatic ecosystem. The literature describes the active substances as difficult to biodegrade, bioaccumulative substances that tend to persist in sediment rather than in water. Based on the actual concentrations measured in the Slovenian aquatic environment, the studied active substances are predicted not to pose a risk to the aquatic ecosystem; however, other properties such as different degradation pathways, accumulation, and the combination of different active substances in the same aquatic environment, may significantly increase their toxicity. Since the predictive strenght of our programmes proved to be low it would be reasonable to develop methods for efficient ecotoxicity testing. On the other hand, due to the pollution of the enovironment with active substances, it would be necessary develop methods for efficient drug substances removal from already contaminated environments.
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