# Antibiotics in Groundwater and River Water of Bialka--A Pristine Mountain River
## 4 Discussion
Among the reasons for such a situation may be their very long half-life values, of 20.3 days for sulfamethoxazole and <11.8 days for trimethoprim. The concentrations and percentage share of antimicrobial agents varied significantly between the examined water samples. Out of the seven sites, only one was not contaminated with antimicrobial agents, and it was groundwater collected high in the Tatra Mountains (c.a. at 1600 m a.s.l.). However, in groundwater collected at the border of the Tatra National Park (at c.a. 1000 m a.s.l. ), there were six antimicrobial agents detected with the total concentration of 27.29 ng/L. The three antibiotics with the highest concentrations in this GW sample comprised vancomycin, erythromycin and clindamycin. The high share of vancomycin was also observed in two other sites, considered as pristine (RW1) and low impact (RW2), where the total concentration of antimicrobial agents was 40.95 ng/L and 17.94 ng/L, respectively. Detection of this antibiotic both in surface water and in groundwater samples is not unprecedented. The authors in [20] reported the presence of this glycoptide antibiotic in both influents and effluents of STPs as well as in the receiving river waters (both downstream and upstream of the examined STPs, suggesting that the STP effluents are not the only sources of this antibiotic in the aquatic environment). One of the possible reasons for the detection of this antimicrobial agent in six out of the examined seven sampling sites, in relatively high share, is its relative resistance to degradation in conventional STPs (removal rate between 5 and 52%) [18]. The experiments carried out by [PERSON] et al. [25] on the metabolism and degradation of vancomycin demonstrated that this antibiotic is not metabolized in the liver and as such it is entirely excreted in the urine in an unchanged form. Moreover, the half-life of vancomycin in water is approx. 9-10 days, which allows this antibiotic to persist and be transferred in the aquatic environment. The mean and total concentrations of antibiotics increased dramatically by the discharge site from the STP (i.e., 9601.41 ng/L of all antimicrobials, the highest mean and maximum concentrations of most of the detected antibiotics and the highest number of antimicrobials detected). This observation is in line with the reports by other authors that the STP effluents play a major role in antimicrobials' input into the aquatic environment [4; 18; 20]. Moreover, while comparing the concentrations of antimicrobial agents in the sites upstream and downstream of the STP, it is also clear that apart from the STP, there might be other important sources of antibiotics in the aquatic environment. The total concentration of antibiotics in RW4 (c.a. 3 km downstream of the STP) is 1012.90 ng/L, while the total concentration in the RW5 site (c.a. 7 km downstream of the STP) is 2306.59 ng/L. Importantly, this site is characterized by the predominance of oxytetracycline, which is an important antimicrobial agent used not only in human but also in veterinary medicine. Its environmental input relies on, among others, surface runoff from fields fertilized with animal manure contaminated with this antimicrobial agent [21]. Generally, the evident differences in the concentrations of the examined antibiotics between the study sites affected their position in the cluster analysis shown in Figure 4. Pristine samples (GW1, GW2 and RW1) and one low impact sample (RW2) clearly stand out from the remaining sites, located downstream of the STP. A case study by [PERSON] et al. [10] was a preliminary investigation pointing to the examined STP as the major contributor not only to the antibiotic contamination of the aquatic environment in the Bialka river valley but also to the spread and dissemination of antibiotic-resistant bacteria and genetic determinants of some important resistance traits, such as extended-spectrum beta lactamase type of resistance among _E. coli_. However, this is not only the case of the Bialka river valley.