## 3 Results and Discussion
### Environmental Risks of Target PhACs  
As shown in Figure 5a and Table S1, in the effluents, the RQs for SMX and DCF were higher than 1.0 in all WWTPs, indicating they probably pose high risks to aquatic organisms. The RQs for SMX ranged between 3.12 (effluent of RM WWTP) and 11.4 (effluent of Borba WWTP). Due to the recalcitrant properties of DCF, it was present in effluents and the downstream environment in high concentrations. Thus, the RQs ranged between 6.76 (effluent of Portel WWTP) and 84.7 (effluent of Borba WWTP). The obtained values for these two PhACs were higher than those reported by other authors [30; 37], but the concentrations and frequency of detection of both compounds in effluents and the downstream environment were higher too.  
Other WWTP's effluents showed RQ values higher than 1.0 for certain PhACs: namely, APAP and NPX in Borba WWTP; NPX, IBUP, and AZM in Portel WWTP; and APAP in Redondo WWTP.  
All WWTPs showed RQs between 1.0 and 0.1 for SPD, PPNL, and ERT, indicating medium risks. These values of RQs were also observed for APAP (Borba and Portel WWSTPs), CAF (Borba WWTP), and NPX (Evora, RM, and Redondo WWTPs).  
Only ATN showed RQs lower than 0.1 in target WWTPs. CAF and CBZ also showed RQs lower than 0.1 for most WWTPs, indicating they may pose low risks to aquatic organisms.  
It is difficult to compare the obtained results because the number of studies is scarce and the target PhACs are different. [PERSON] et al. [30] reported RQs higher than 1 for certain PhACs, namely, sulfamethoxazole, sulfradiazine, erythromycincin, carbamazepine, and ofloxacin in the WWTP effluents in China. Although the dilution by receiving water and the adsorption to sediments will lower the PhACs concentrations when the WWTP effluent is discharged, the continuous input of PhACs also requires a risk assessment evaluation considering long-term exposure scenarios [30,37]. Therefore, the downstream environments were also evaluated.  
With respect to receiving waters (downstream environments), the profile of environmental risk assessment (RQs) is similar. Except for SMX and DCF, the values of RQs were lower because of the dilution of target PhACs and the potential sorption to the sediments. In receiving waters, SMX and DCF showed high values of RQ. These values may be underestimated due not only to the limited number of sampling points but also because the samples were examined in periods with a good flow of surface water. Additionally, in receiving waters, due to climate-driven variability, significant variations in water flowrates can occur due to water scarcity, which is typical of this region mainly in summer periods. In certain downstream environments, higher percentages of effluents in the surface water were observed, with the river flow composed almost exclusively by the WWTP effluent of this region.  
The simultaneous presence of different xenobiotics can result in toxic effects at concentrations lower than the PNEC for each contaminant [47]. Regarding PhACs, due to their similar pharmacological mechanisms, mainly in PhACs of the same therapeutical class, additive or synergetic effects may occur. As a result, the risks associated with residual PhACs in the downstream environments are probably higher than the calculated values [37,48].  
In addition, the transformation by-products of PhACs in WWTPs or the environment (biodegradation, photolysis, and oxidation, among others) may pose additional risks.