## 3 Results and Discussion
### Occurrence of PhACs in the Five WWTPs and Surface Waters
The most representative PhACs were the analgesic drug acetaminophen (APAP), the psychostimulant caffeine and three NSAIDs, ibuprofen, naproxen, and diclofenac, with median concentration values of 115.4 \(\mu\)g/L, 40.9 \(\mu\)g/L, 12.1 \(\mu\)g/L, 8.0 \(\mu\)g/L, and 1.7 \(\mu\)g/L, respectively (Table 3). The concentration of the two most representative NSAIDs, IBUP and NPX, was about one-tenth and one-fifth of the median concentration of acetaminophen and caffeine concentrations. Except for acetaminophen, the obtained concentrations of these five PhACs were similar to those found in recent studies in other two Portuguese WWTP, Beirolas WWTP and Faro WWTP [25]. The median concentrations of acetaminophen were much higher than those found in other WWTP influents in Portugal [23; 34; 35; 36] and in Europe [8]. The obtained values for this PhAC were double than the median concentration in influents of the two biggest WWTPs in Portugal, Beirolas WWTP and Faro WWTP [26]. In these reported studies, caffeine, acetaminophen, ibuprofen, naproxen, and diclofenac were consistently identified as the PhACs found in the highest concentrations in wastewater influents. For the remaining PhACs, the median concentration values ranged between 0.044 (sulfadiazine) and 0.92 \(\mu\)g/L (atenol). Except for sulfadiazine, the antibiotics' median concentration was higher than 0.1 \(\mu\)g/L, with values between 0.12 (erythromycin) and 0.31 \(\mu\)g/L (sulfamethoxazole). Eight of 18 PhACs found in WWTP influents showed a high frequency of detection with several positive samples higher than 95% (CAF, NPX, IBUP, DCF, ATN, CBZ, APAP, and SMX). For five of 18 PhACs, the frequency of detection ranged between 50% and 88% (SPD, PPNL, CTS, BZF, and TTE). The frequency of these PhACs was higher for ten compounds (ATN, CAF, CBZ, NPX, DCF, APAP, SMX, SPD, PPNL, and CTS) with frequency values higher than 2.5 (50% of target WWTP). The occurrence profile of PhACs in effluents was different from those obtained in the WWTP influents. The most representative PhACs in effluents were diclofenac, carbamazepine, and caffeine, with 100% of positive samples, a frequency of 4.8, and a median concentration of 1.6, 0.35, and 0.16 \(\mu\)g/L, respectively. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**PhACs**} & \multicolumn{8}{c}{**Acidic Method**} \\ \cline{2-11}  & \multicolumn{4}{c}{**Upstream (\(\mu\)g/L)**} & \multicolumn{4}{c}{**Downstream (\(\mu\)g/L)**} \\ \cline{2-11}  & **Min** & **Max** & **Med** & **Pos (\%)** & **Freq** & **Min** & **Max** & **Med** & **Pos (\%)** & **Freq** \\ \hline \multicolumn{11}{c}{**Basic method**} \\ \hline BZF & 0.046 & 0.11 & 0.078 & 18 & 0.5 & 0.039 & 0.12 & 0.077 & 24 & 0.8 \\ IBUP & 0.090 & 0.097 & 0.094 & 18 & 0.5 & 0.093 & 0.10 & 0.098 & 12 & 0.4 \\ DCF & 0.036 & 2.5 & 0.85 & 55 & 1.5 & 0.49 & 3.5 & 1.6 & 82 & 2.8 \\ E1 & — & — & — & 0 & 0 & — & — & — & 0 & 0 \\ E3 & — & — & — & 0 & 0 & — & — & — & 0 & 0 \\ E2 & — & — & — & 0 & 0 & — & — & — & 0 & 0 \\ EE2 & — & — & — & 0 & 0 & — & — & — & 0 & 0 \\ DES & — & — & — & 0 & 0 & — & — & — & 0 & 0 \\ ERT & 0.14 & 0.14 & 0.14 & 9 & 0.25 & — & — & — & 0 & 0 \\ FLX & — & — & — & 0 & 0 & — & — & — & 0 & 0 \\ CLR & — & — & — & 0 & 0 & — & — & — & 0 & 0 \\ AZM & 0.094 & 0.11 & 0.10 & 18 & 0.5 & 0.92 & 0.092 & 0.092 & 6 & 0.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: _Cont._The second group of target PhACs in effluents included naproxen, atenol, and sulfamethoxazole, with median concentration values of 0.25, 0.15, and 0.095 \(\upmu\)g/L, respectively. The frequency in target WWTPs varied between 4.2 and 4.4, and the positive samples between 88% and 92%. IBUP and APAP showed a significant decrease in median concentrations compared to influents, 0.32 and 0.18 \(\upmu\)g/L, respectively. However, the positive samples were equal to or lower than 50%, with a frequency of 2.4 and 2, respectively. The remaining positive samples showed median concentrations lower than 0.10 \(\upmu\)g/L or a frequency lower than 2.