## 3 Results and Discussion
### CECs
The widespread presence of carbamazepine, despite its relatively low usage compared to NSAIDs, suggests its high resistance to conventional wastewater treatment processes and its potential to serve as a tracer of anthropogenic pollution. Sulfamethoxazole and trimethoprim, commonly used antibiotics, were detected in 31 and 25 sites, respectively, with concentrations reaching 36 ng/L (SMX) and 12 ng/L (TMP) (Table 4). These findings are comparable to those reported in the Danube basin by [23], who identified sulfamethoxazole concentrations ranging from 10 to 50 ng/L in Romanian and Bulgarian sectors of the river. Additionally, a study on the Tiber River in Italy found sulfamethoxazole at similar concentrations (50-70 ng/L), suggesting that antibiotic contamination is a widespread issue in European riverine ecosystems [56]. Bisphenol A (BPA), a known endocrine disruptor, was found in all analyzed samples, with concentrations ranging from 34.5 to 342 ng/L (Table 4). These values are consistent with those reported in other studies, such as those from the Ebro River in Spain (50-450 ng/L) [57]. A comprehensive 19-year study analyzing 5057 samples from European and North American water bodies found that BPA was detected in 67% of the samples, indicating significant contamination. In European surface waters, reported concentrations varied between 7 ng/L and 300 ng/L, with a median of 29 ng/L in marine waters [58]. The synthetic estrogen 17\(\alpha\)-ethinylestradiol (EE2) was also detected in the present study, in low concentrations (1.15-3.05 ng/L) (Table 4), which are consistent with the values reported for surface waters in the UK (1.5-5 ng/L), France (1.0-2.9 ng/L), and Greece (3.0 ng/L) [59]. A review of monitoring studies reports higher EE2 concentrations ranging from 0.2 ng/L in Spain to 101.9 ng/L in Portugal, with median values of 5.6 ng/L in Poland, 2.0 ng/L to 34 ng/L in Italy, 1.5 ng/L to 5 ng/L in the UK, and 0.8 ng/L to 17.2 ng/L in Germany [59]. These values exceed the proposed European environmental quality standard (EQS) of 0.035 ng/L, highlighting the potential risks for aquatic life. The concentrations obtained in this work for sulfamethoxazole, ciprofloxacin, amoxicillin, and carbamazepine (Table 5) are lower than the values reported for JDS4 2019 survey of the entire river length (1.55-71.7 ng/L SMX; 8.53-24.87 ng/L CIP; 0.84-52.46 ng/L AMX; 0.13-57.6 ng/L CBZ) [33], while for trimethoprim and diclofenac, our values (Table 5) are higher than the JDS4 ones (<LOQ-1.78 ng/L TMP; 2.12-63.15 ng/L DCF) [33]. For dicloxacillin, the values are similar with the JDS4 findings (3.34-5.49 ng/L DCX) [33], with the average concentration presented in Table 5 (5.5 ng/L) being close to the maximum value of JDS. While for the cumulative CECs concentrations in Danube water, an increasing spatial profile was detected in the three sites comprised in the JDS4 monitored sector in the SE part of Romania (JDS4-48 (Chiciu-Silistra), JDS4-50 (Reni), and JDS4-51 (Vylkovo, Chilia branch)) [31] (Annex Figure A, page 329), our results drawn in Figure S3a (Supplementary Materials) reveal a different trend, with a strong influence of emission sources related to large cities and Siret and Prut tributaries in Braila-Reni sector. When BPA concentrations are taken into account at calculation of the cumulative CECs concentrations (Figure S3b, Supplementary Materials), these influences are more pronounced, even for the river mouth corresponding to the Chilia RO-UA transboundary artery (site 22--Musura bay). These findings may suggest the necessity of establishing much denser regional monitoring networks in order to assess the contribution of a larger number of localities to the contaminant emissions.