# A Snapshot on the Occurrence and Risk Assessment of Organic Pollutants in an Urban River
## 3 Results and Discussion
### PAHs and PCBs Presence in Surface Sediments
Both in F1 and F2, PCB 101 congen  
Figure 3: **(A)**: PAHs’ relative abundances in sediments in F1, F2, and F3; **(B)**: PAHs’ emissions from RWC (T y\({}^{-1}\)) in Braganca district (source: [101]). The name of the compounds and respective abbreviations are presented in Table 3.  
(1.32 and 1.56 ng\(\cdot\)g\({}^{-1}\) dw, respectively). Conversely, in F3, PCB 138 showed the highest concentration (1.63 ng\(\cdot\)g\({}^{-1}\) dw). The \(\Sigma\)(IPCBs) was higher in F3 (4.22 ng\(\cdot\)g\({}^{-1}\) dw) and lower in F2 (2.65 ng\(\cdot\)g\({}^{-1}\) dw). Concerning \(\Sigma\)(DLPCBs), the highest values were found both in F1 and F2 (4.11 and 3.42 ng\(\cdot\)g\({}^{-1}\) dw, respectively). The DLPCBs that contributed more for these observed values were PCB 105 and PCB 118 in both F1 (0.99 and 0.97 ng\(\cdot\)g\({}^{-1}\), respectively) and F2 (2.16 and 1.45 ng\(\cdot\)g\({}^{-1}\) dw, respectively). Similarly to PAHs, PCBs have a high bioaccumulation potential (Kow in Table S8). The flow regime, the sediment characteristics and the number of Cl atoms are crucial factors to explain the distribution and mobility of PCBs in sediments and from the sediments into the water and particulate organic matter [26,26,27,29,29,31]. The lack of heavy industry in the region where the Fervenca River is located, suggests the concentrations found in the present study might have resulted from atmospheric inputs and from deposition through rain wash [105]. According to [106,107], about 20 to 30% of the total amounts of PCBs discharged into municipal WWTPs originated from the surface runoff. This assumption could help explain the higher concentrations of IPCBs observed in F3. Besides, past dumping in domestic sewage or directly in the river of dyes, inks and other substances containing PCBs might be another explanation for the observed concentrations. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline  & \multicolumn{2}{c}{**F1**} & \multicolumn{2}{c}{**F2**} & \multicolumn{2}{c}{**F3**} & \multicolumn{2}{c}{**Hg g\({}^{-1}\)**} & \multicolumn{2}{c}{**Hg g\({}^{-1}\)**} & \multicolumn{2}{c}{**Hg g\({}^{-1}\)**} & \multicolumn{2}{c}{**Hg g\({}^{-1}\)**} \\  & \multicolumn{2}{c}{**Hg g\({}^{-1}\) dw**} & & & \multicolumn{2}{c}{**dw**} & & & **dw** & \\ \hline PCBs indicators & & & & & & & & \\ PCB28 & 0.05 & 0.581 & & 0.05 & 0.581 & & 1.16 & 1.88 & \\ PCB52 & 1.19 & 74.89 & & 0.05 & 3.125 & & 1.28 & 8.00 & \\ PCB101 & 1.32 & 6.471 & & 1.56 & 7.649 & & 0.05 & 0.245 & \\ PCB138 & 0.05 & 1.612 & & 0.05 & 1.613 & & 1.63 & 1.63 & 1.61 \\ PCB153 & 0.05 & 1.852 & & 0.05 & 1.852 & & 0.05 & 1.852 & \\ PCB180 & 0.05 & 1.471 & & 0.89 & 2.174 & & 0.05 & 1.174 & \\ Total & 2.71 & & 2.65 & & 4.22 & & & \\ \hline PCBs & & & & & & & & \\ “dioxin-like” & & & & & & & & \\ PCB81 & 0.05 & & 1.50 \(\times\) 10\({}^{-5}\) & 0.05 & & 1.50 \(\times\) 10\({}^{-5}\) & 0.05 & 1.50 \(\times\) 10\({}^{-5}\) \\ PCB77 & 0.05 & 6.250 & 5.00 \(\times\) 10\({}^{-6}\) & 0.05 & 6.250 & 5.00 \(\times\)  
Most studies (Table S2) only evaluate the presence of IPCBs (the most common PCBs across the compositional range of the most common technical mixtures), whereas the DLPCB used to assess human health risks are scarcely approached [107]. Therefore, in the present study, only IPCBs concentrations were compared with other European studies. Fervenca showed one of the lowest concentrations (Table S2).