## 3 Results and Discussion
### CECs  
Nineteen out of the thirty selected analytes were identified in the surface water samples: sulfamethoxazole (SMX), trimethoprim (TMP), ciprofloxacin (CIP), flumequine (FLU), amoxicillin (AMX), cefuroxime (CFX), dicloxacillin (DCX), carbamazepine (CBZ), pravastatin (PRV), erythromycinycin (ERY), piroxicam (PIR), ketoprofen (KET), diclofenac (DCF), naproxen (NAP), enilconazole (imazalil) (IMZ), clotrimazole (CLO), drospirenone (DRO), 17\(\alpha\)-Ethinylestradiol (EE2), and bisphenol A (BPA). The quantitative analysis results (in ng/L) are presented in Table 4.  
Table 5 shows the minimum (Min. ), maximum (Max. ), and average values of the CECs measured concentrations, the Predicted no-effect concentration (PNEC) and the detection frequency of the identified substances. The concentrations of pharmaceuticals in the analyzed surface waters varied between 1.04 ng/L (drospirenone) to 132 ng/L (diclofenac). Triazine pesticide enilconazole(imazalil) concentrations ranged from 4.8 to 31.4, while bisphenol concentrations ranged from 34.5 ng/L to 342 ng/L. Pharmaceuticals detected in almost all samples--sulfamethoxazole, trimethoprim, carbamazepine, and diclofenac--can be considered as river basin specific CECs. The widely used pharmaceutical diclofenac was detectable at 28 sampling sites, but the PNEC was exceeded only in 8 sampling points corresponding to Siret and Prut tributaries and Danube River in the points corresponding downstream Siret and Prut rivers, Galati town, and Prut-Girugiulesti. The measured concentration of \(\beta\)-lactam antibiotic dicloxacillin exceeded PNEC in two points: downstream Galati town and in the Prut River. For the remaining pharmaceuticals, the level does not exceed PNEC. Bisphenol A was detected in all the samples, the measured concentration exceeding PNEC in 4 sampling points in the tributary Siret and Prut rivers, indicating a risk to the aquatic environment. The agricultural impact on the ecosystem of the Danube River was shown by measured imazalil concentrations, with a peak of 31.4 ng/L in the Prut River confluence site. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c} \hline
**Site No. ** & **SMX** & **TMP** & **CIP** & **FLU** & **AMX** & **CFX** & **DCK** & **CBZ** & **PRV** & **ERY** & **FIR** & **KET** & **DCF** & **NAP** & **IMZ** & **CLO** & **DRO** & **EE2** & **BPA** \\ \hline
1 & 28.9 & 6.4 & ND & ND & 3.8 & 1  
To enable comparisons between variables with different orders of magnitude, the data were standardized. The univariate analysis resulted in a box plot that highlights the variation and presence of extreme values for each substance (Figure 2). Several substances, such as ethinylestradiol and bisphenol A, exhibit numerous extreme values, indicating possible sporadic pollution events or high variability in their concentrations. Compounds such as carbamazepine and diclofenac show higher variability compared to others, which may be attributed to diverse pollution sources or varying environmental factors. Regarding the spatial distribution, the highest number of pollutants was identified in the tributary rivers Siret and Prut, along with the sampling points corresponding to Ostrov village and the towns of Galati, Giurgiulesti, and Reni. In marine water, a significantly lower number of contaminants were found, including sulfamethoxazole, carbamazepine, diclofenac, and bisphenol A. Furthermore, the measured concentrations were lower than those in freshwater samples. The hierarchical clustering analysis (HCA) dendrogram