## 1 Introduction  
Anthropogenic pressures and climate change are currently responsible for extreme changes in raw water availability and quality as well as the degradation of water sources. Regarding anthropogenic pressures, there has been growing concern about several biologically active environmental contaminants in the aquatic environment, mainly regarding the group of so-called contaminants of emerging concern (CECs). The CECs include many contaminants, such as pesticides, industrial chemicals (surfactants, gasoline additives, brominated flame retardants, plasticizers, and perfluorinated compounds), personal care products, pharmaceutical active compounds (PhACs), nanomaterials, etc. Although their occurrence is usually in a low concentration range (from ng/L to ug/L) they are of environmental and health concern due to their potential toxic behavior, such as endocrine-disrupting and mutagenicity, among others [1]. Furthermore, CECs are a growing source of concern due to their presence in the environment as a result of inadequate treatment of wastewaters, which can lead to the pollution of water sources that are destined for human consumption [2]. In this group of contaminants, special attention has been given to PhACs. They are introduced to the aquatic environment via several routes, including direct discharge of raw or treated wastewater from municipal wastewater treatment plants [3; 4], hospital effluents [5], landfill leachate [6], and surface runoff from agricultural areas where treated wastewater, sludge, or manure waste was used [4; 7]. Among the aforementioned sources, WWTPs are of particular interest since they continuously discharge these target compounds into the environment [8]. Regarding antibiotics, they may also accelerate the development of antibiotic resistance genes and bacteria, which shade health risks to humans and animals [9; 10]. The presence of PhACs indicates a gap in the removal of these compounds in current conventional wastewater treatment plants (WWTPs) [11], and efforts have been made to improve the knowledge and data available on sources of PhACs, namely in wastewaters (influents and effluents) and in potential receiving waters. The impact on the environment will depend on the quality of the treated effluents. If the WWTP is not efficient in the treatment of the influents, the receiving water bodies will be negatively impacted due to the insufficient dilution effect of the treated effluents. Conversely, if the treatment is efficient, the effluents may be used as a way of replenishing streams that would otherwise be dry [12]. Aguas de Portugal (AdP) is a group of several Portuguese companies responsible for the collection, treatment, quality control, and distribution of drinking water, which includes the management of WWTPs. As of 2015, AdP is responsible for the management of over 900 WWTPs of varying treatment capacities [13]. Many of these WWTPs are in rural regions that are significantly affected by drought, and often, the discharge areas of these facilities can be heavily impacted. In the Alentejo region, it is common to experience drought and restrictions to water use along with high temperatures during the summer period. This combination of factors can lead to a reduction in the influent flows that reach WWTPs, which can result in higher concentrations of contaminants due to a lack of dilution effect. This phenomenon will most likely propagate throughout the WWTP facility, causing whatever contaminants that were not removed during the treatment process to be present in the effluents in higher concentrations [14]. As such, any receiving surface water or stream that is mainly composed of insufficiently treated wastewater effluents can have high concentrations of contaminants such as hydrocarbons, metalloids, pesticides, pharmaceutical active compounds (PhACs), and pathogenic microorganisms, among others [15; 16].