# A Snapshot on the Occurrence and Risk Assessment of Organic Pollutants in an Urban River
## 3 Results and Discussion
### Comparative Analysis of CECs in Relation to Previously Available Data  
The literature published after 2008 in Portugal and Europe in freshwater ecosystems was searched considering the CECs included in the current approach. Extensive data were found for water in Europe and less for Portugal. For sediments, the existing research is much less abundant (Table S1). Due to the general data lack for sediments, this analysis is mainly centered on water. Contrarily to River Liz (Portugal) and other European rivers, the paracetamol concentrations were \(\leq\)0.05 ng\(\cdot\)L\({}^{-1}\) in the Fervenca river. In several surveyed European rivers, the concentrations of ibuprofen exceed 1 ug\(\cdot\)L\({}^{-1}\) in water. Even in the monitored Portuguese rivers, the observed concentrations exceeded those detected in the Fervenca waters, except the Douro tributaries Tinhela, Rabacal, and Cabrum, which flow throughout natural areas with almost no human occupation. Ibuprofen has a high ubiquity in surface water because it is one of the most prescribed drugs in Europe [95; 96] and Portugal [37], and together with diclofenac, it is considered to be 'pseudo-persistent', as their constant use results in their continuous replenishment within receiving environments [97]. Similarly, diclofenac seems to have a high ubiquity both in water and sediment in Fervenca. The same range concentrations to those found in F3 (398.35 ng\(\cdot\)L\({}^{-1}\)) were detectedin Kalamas river (Greece), Thames river, and several German streams (Table S1). Similar concentrations were found in the Ave river (Portugal) in autumn [98]. However, unlike the Ave and some other European rivers that flow through densely urbanized, industrialized areas and where very intensive agriculture is practiced, the Fervenca flows through areas with low population density, being non-industrialized and with more extensive agriculture. Thus, one would expect to always find lower concentrations in the Fervenca even in F3 (located downstream of the WWTP). Nevertheless, it should be noted that although our results were obtained in February, the river had flow values similar to those of late summer due to the lack of precipitation, which allows us to assume that the concentrations observed for diclofenac and the other contaminants are concentrations typically observed in late summer before the first rains. Concerning carbamazepine, the obtained concentrations (higher in F3: 52.10 ng\(\cdot\)L\({}^{-1}\)) are in line with those obtained in other rivers such as river. Ouse (UK). Ofloxacin, in F3, showed one of the highest concentrations when compared with other similar studies (Table S1). Caffeine concentrations ranged from 3.17 (F1) to 167.38 ng\(\cdot\)L\({}^{-1}\) in F3. Regarding the observed concentrations, it is verified that they are of an identical order of magnitude to those found in other Portuguese and European rivers located in more densely urbanized and industrialized areas (Table S1). For HHCB, the observed concentrations in F3 are in line with the highest concentrations reported for river Prut (Romania) and Leca River (Portugal). The observed concentrations for AHTN are of the same magnitude as those reported for river Molgora (Italy) (Table S1). However, contrarily to what we observe in the Fervenca, most authors (Table S1 and [99]) have found that the HHCB/AHTN ratio is always greater than one in the environment. According to [100], the larger concentrations of HHCB are explained by the higher photodegradation rates of AHTN in the natural environment. However, in Fervenca, this ratio is lower than one at the sampling period. AHTN concentrations in Fervenca are one of the highest found in literature. BPA also demonstrated relatively high concentrations when compared to other European rivers (Table S1).