# Antibiotics in Groundwater and River Water of Bialka--A Pristine Mountain River
## 4 Discussion
Similar or even higher concentrations of antimicrobial agents in STP effluents and surface waters were observed by other authors. The authors of [20] examined two Polish STPs and their receiving surface water bodies (one in southern Poland, one in northern Poland) in terms of detection and quantification of 26 antimicrobial agents. Similarly, as in our study, the concentrations of antimicrobials detected in the examined samples varied within wide ranges. For instance, mean concentration of clindamycin in STP effluents ranged from 166 to 290 ng/L in the receiving river water upstream of the STP from 2.3 to 78 ng/L and downstream from 25.4 to 134 ng/L. For ciprofloxacin, the values were as follows: effluents of STPs--from 184 to 312 ng/L, river water upstream of the STPs--from 12 to 108 ng/L, downstream--from 95 to 182 ng/L [26]. In another European study, [27] identified both STPs and farming areas as the main emission sources of antibiotics in the Ebro river basin in Spain. Enrolfloxacin and ciprofloxacin (fluoroquinolones) were the most frequently detected antibiotics, followed by sulfamethoxazole, sulfadazine (sulfonamides) and trimethoprim (around 60% of samples). In STP effluents, azithromycin (macrolide) was detected in the highest concentrations, exceeding 5000 ng/L. The second antimicrobial with this respect was enrolfloxacin (mean concentration of 1300 ng/L) and the third was sulfadiazine (300 ng/L). The effluents of slaughterhouses were characterized by high concentrations of azithromycin and trimethoprim. In a Portuguese case study, [4] observed ciprofloxacin to be most prevalent in groundwater (43% of samples), while clarithromycin, erythromycin and ciprofloxacin were the most prevalent in surface water samples (46 and 38% of samples). On the other hand, [PERSON] et al. [28] examined more than 200 aquatic samples in eastern China and found sulfapyridine, sulfamethoxazole, ciprofloxacin, levofloxacin, norfloxacin,chloramphenicol, florfenicol, doxycyclineline and metronidazoleazole at concentrations ranging from 0.3 to 3.9 ng/L in river water and from 1.3 to 12.5 ng/L in sewage. As stated by numerous authors, consumption of antibacterials, which is very country-specific, is one of a few important factors affecting their presence in the aquatic environment [18; 20; 23]. In the considered period, the highest consumption was recorded for penicillins (for both human and veterinary medicine). This was followed by glycoptide and MLS antibiotics in 2019 in human medicine and by other \(\beta\)-lactams and trimethoprim/sulfamethoxazole in 2020 [15]. In veterinary medicine, the second and third highest consumption were recorded for tetracyclines and the MLS group of antibiotics in both 2019 and 2020 [14]. This, however, is not reflected in the values of antibiotic detection in our study. Similarly, as in our study, [4] or [5] could not establish a clear link between the detection of antibiotics in STP effluents and their consumption. This was due to a number of reasons, including antibiotic metabolism in the human body, their chemical and biological stability, mobility in the environment and sewage treatment efficiency [4; 5; 29]. The authors in [18] explain rare detection of penicillins in the aquatic environment and in STP effluents by their chemical instability due to, e.g., physicochemical interactions (such as zinc and copper-mediated degradation), easy biodegradation (c.a. 90%) during STP treatment processes or widespread presence of \(\beta\)-lactamase producing bacteria in the environment. On the other hand, tetracyclines, which were detected in the highest concentrations in our study, are reported to be among the most persistent in the environment [7; 30]. However, regardless of the examined discrepancies between the consumption vs. detection of antimicrobials, what needs to be emphasized at this point is that the detected concentrations of antibiotics are in most cases sublethal, and it can be considered that they may select bacterial resistance [31].