# A Snapshot on the Occurrence and Risk Assessment of Organic Pollutants in an Urban River
## 2 Materials and Methods
### Water and Sediment Samples and Contaminant Determination  
The concentrations of pollutants tend to increase during dry periods. The occurrence of such periods has become more frequent due to the climate change situation in which we are living, and this was the case with the sampling campaign for this piece of research that took place by the end of the mentioned dry period, on 12 February 2018. The most representative sampling site was selected at each riverine section: F1, F2, and F3. The selection of the pollutants to be assessed was based on the following criteria: (i) they are present in the EU's watch list for emerging water pollutants, or (ii) they are candidates to follow-up EU's watch lists, or (iii) they may have a relevant potential impact on human and environmental health. To characterize each sample site, several environmental parameters--temperature, pH, dissolved oxygen (DO), conductivity, and total dissolved solids (TDS)--were measured at each point. In addition, total phosphorus (TP) and phosphate (SRP) were determined in the lab according to [53]. In addition, the degree of fine interstitial sediments' deposition and the disturbance of riparian wood was visually evaluated in each sampling site (Figure 1). Concerning the analysis of contaminants, three replicated 150 mL of water were sampled at 0.2 m depth, in the middle of the river, onto glass bottles previously rinsed with 10% nitric acid and acetone. Bottle caps were Teflon-laminated on the inner part that might be in contact with the sample. Surface sediments were randomly sampled in triplicate, from the top 5 to 10 cm depth, using a core sampler, and pooled and mixed together. Immediately after collection, the sediment samples were stored in acid-rinsed sterilized polyethylene bags. Sediments lixiviates were prepared [54] by stirring 4 parts of milli-Q water and 1 part of sediment during 24 h. The resulting fluid was allowed to decant for ca. 1 h. The supernatant fluid was filtered through paper with a pore size ca. Figure 1: (**A**): Location of Fervenca River, Braganca city, sampling sites and WWTP and (**B**): Riverbed conditions F1, F2, and F3. 20-25 \(\upmu\)m that had been previously washed with distilled water and then dried. The first 10 mL of supernatant liquid were rejected to reduce the amount of impurities. Both water and sediment samples were stored in the dark in a refrigerated container and then frozen at \(-\)20 \({}^{\circ}\)C until analysis. Extraction of CECs was carried out by SPE with polymeric cartridges of Waters Oasis HLB and elution with methanol. Samples were concentrated on a rotary evaporator under N2 and the obtained concentrate was redissolved in methanol or in the mobile phase according to the analytical technique. CECs analysis was carried out by HPLC/MS for all compounds except galaxolide and tonalide, using a Thermo Aquusil 3 mm, 150 mm \(\times\) 4.6 mm column. Elution was performed in gradient, as follows: A = water + 5 mM ammonium acetate, B = methanol + 5 mM ammonium acetate, T = 50 \({}^{\circ}\)C, injection volume 20 \(\upmu\)L, and 1 mL-min\({}^{-1}\). Detection was carried out in ESI+ and ESI\(-\) modes by HRMS. Galaxolide and tonalide were analysed by GC/MS using a J&W, DB-XLB 60 m \(\times\) 0.25 mm \(\times\) 0.25 mm column. Injection was performed on PTV mode; vol. of injection 9 \(\upmu\)L, T = 50 \({}^{\circ}\)C, splitless time 0.20 min, splitless flux 20 mL-min\({}^{-1}\), transfer velocity 3 \({}^{\circ}\)C-s\({}^{-1}\), and final temperature 300 \({}^{\circ}\)C (15 min). Elution was carried out as follows: 40 \({}^{\circ}\)C (5 min) to 200 \({}^{\circ}\)C at 10 \({}^{\circ}\)C-min\({}^{-1}\), to 300 \({}^{\circ}\)C at 30 \({}^{\circ}\)C-min\({}^{-1}\), to 300 \({}^{\circ}\)C (10 min). Constant flux at 1 mL-min\({}^{-1}\), transfer line 290 \({}^{\circ}\)C. Detection was performed by EI+ in tandem MS-MS.  
PAHs and PCBs were extracted by SPE with C18 J disks. Elution was carried out with ethyl acetate.