# A Snapshot on the Occurrence and Risk Assessment of Organic Pollutants in an Urban River
## 3 Results and Discussion
### Environmental Risk Assessment  
Table 2 shows the HQs' values, determined for each evaluated compound from the selected PNEC values presented on Table S1. In water, the main concerns for aquatic organisms were: BPA (in F1 and F3 HQ > 10) and ofloxacin in F3 (HQ > 10). Moreover, in F3, the obtained HQs for ibuprofen and diclofenac were between 1 and 10, indicating a moderate risk. Despite the very high contribution of BPA for overall environmental risk as shown by TU, the remaining compounds together were not negligible: even without considering BPA in TU, the environmental risk lay between low and high, both in water and in lixiviates. PAHs' HQs are presented in Table 3. The HQs were compatible with the assumption that in all sampling sites, the sediment contamination by PAHs is low. Indeed, considering each compound, the environmental risk varied between negligible and low.  
Figure 4: Relative abundances of IPCBs (**A**) and DLPCBs (**B**).  
When considering TU values, the risk rose to moderate (F1 and F2) and was still considered low in F3.  
The results of risk assessment for PCBs are presented in Table 5 (derived from the PNEC and TFEs-Table S5). HQs values were compatible with the assumption that the environmental risk caused by the presence of PCBs was very high. Nine of the analyzed PCBs exceeded PNEC values and their global risk were high in all sampling sites. Nevertheless, in the case of some DLPCBs, when there were simultaneously available HQs and TEQ, they demonstrated important discrepancies (Table 4).  
Despite the limitations of the environmental risk assessment methodology, such as (1) PNEC values based on toxicity tests using model organisms or systems not taking into account the high complexity of ecosystems and species interactions [4; 83; 93; 108]; (2) the neglection of the behavior of compounds and their mixtures in the environment [2; 11; 75; 109]; and (3) the absence of ecotoxicological data for some compounds, this study has provided the very first perspective of the contamination scenario for the Fervenca river and the Portuguese part of river Douro Basin, indicating the potential exposures, which might result in adverse effects for environmental health. This river is contaminated with a mixture of substances: (1) pharmaceuticals and probably their metabolites [110; 111; 112; 113], and some, such as ofloxacin, with bactericidal activity even after being excreted [114]; (2) HHCB and AHTN and probably with their transformation products [12; 115]; (3) caffeine, that perhaps might need more attention, when associated with other contaminants such as paracetamol [15], which is present herein; (4) endocrine disruptors (BPA and some PCBs) and (5) those with toxic, mutagenic, carcinogenic, and teratogenic potential (PAHs and PCBs).  
It is expected that the measured concentrations and HQ values have been influenced by the extended dry period. It is general knowledge that the contaminants' concentrations can increase several times more than the average mean values during the low flow periods. Nevertheless, considering the climate change scenario, low flow periods are expected to be more frequent [116]. Therefore, the concentrations and HQ obtained during these low flow periods can be more relevant for implementing decision-maker tools for promoting preventive river management measures, such as habitat restoration and the improvement of WWTP efficiency.