## 1 Introduction  
The problem of water availability and quality is a fundamental issue of the 21 st century. Over the past two decades, there has been increasing concern regarding several biologically active environmental contaminants in the aquatic environment. Many of these compounds belong to the group of so-called contaminants of emerging concern (CECs). The CECs are naturally occurring, manufactured or human-made chemicals, or materials that have now been discovered or suspected in various environmental compartments and whose toxicity or persistence are likely to significantly alter a living being's metabolism. Such potential CECs should remain \"emerging\" if the information is scarce in the scientific literature or poorly documented issues regarding the associated potential problems that they could cause [1]. The contamination of environmental compartments, such as surface water, groundwater, and soil with these chemicals shows some potential to pose risks to the environment or human health. Still, they are not yet subjected to regulatory criteria or norms for protecting human health or the environment [1, 2]. The CECs include many micropollutants, among them certain pesticides and their degradation/transformation products, industrial chemicals (surfactants and surfactant residues, gasoline additives, brominated flame retardants, plasticizers, and perfluorinated compounds), disinfection by-products, personal care products (PCP), human and veterinary medicines and their metabolites, and nanomaterials, and so on. Some of these compounds also belong to the group of persistent organic pollutants (POPs) and endocrine-disrupting chemicals (EDCs) [3, 4]. The impact of chronic exposure to these or other contaminants on humans, animals, vegetation, and aquatic species is a matter of concern for the scientific community and regulatory and supervisory entities, since they may not only compromise the functioning and maintenance of ecosystems, which is crucial in promoting the ecosystem services on which humanity depends, but also causing various public health problems [5; 6]. Regarding human's health, special attention has been given to drinking water and the quality and contamination of raw water (surface and groundwater) used for its production. Therefore, the presence of these contaminants is an environmental issue. It has been the backbone for the development of EU's policy regarding the protection of water resources through the Water Framework Directives, which emphasize the need for well-developed monitoring programs as mechanisms for understanding the occurrence and fate of environmental contaminants, as well as assessing the risks that are associated with long-term exposure to low concentrations of these compounds or combined effects of mixtures. The guidelines will be proposed after the evaluation of these results, if necessary. Because of the diversity of structures, physico-chemicals and biological properties, special attention has been given to pharmaceutical active compounds (PhACs), because, in contrast to conventional pollutants, they are deliberately designed to have a biological impact, even at low concentrations [7; 8; 9]. The sources of PhACs, their metabolites, and degradation products include: (i) effluents of pharmaceutical plants; (ii) runoff from agriculture, livestock and aquaculture; (iii) domestic and hospital effluents; and, (iv) municipal wastewater treatment plants (WWTPs). The presence of these target compounds in the environment can have adverse effects on aquatic and terrestrial organisms, and they can occur at any biological hierarchy level, such as cell, organ, organism, population, and ecosystem. These effects can be observed in concentrations in the order of ng/L for certain compounds [10; 11]. It is difficult to predict which environmental and public health implications may arise from PhACs in freshwater ecosystems, since the individual concentrations that are usually found in the environment are lower than those that are able to cause direct adverse effects (acute toxicity).