*3.3. Spatial Distribution of PhACs and Antibiotics in ZR*

At Sukhna station, on a tributary not impacted by Assamra WWTP effluent, ∑PhACs were 8141–8178 ng L−<sup>1</sup> (Figure 2, Table S4). The high concentration of PhACs at this site was attributed to wastewater contamination and possible leakages of untreated wastewater from a pumping station upstream of Sukhna station. In addition, a small peri-urban community discharges its wastewater to the river, and sewage tankers illegally dump sewage close to the river. These are potential reasons for the high ∑PhACs in river water at Sukhna station.

The Twahin Eledwan station sampling site downstream of Assamra WWTP showed lower levels of ∑PhACs (970–1033 ng L<sup>−</sup>1) than in WWTP effluent (4032–4394 ng L−1). The dilution of PhACs can explain this, with surface runoff in the river channel. Thereafter, the concentration of ∑PhACs increased along the flow path in ZR and reached its highest level at Military station (1657–3154 ng L−1) (Figure 1). Thus, there are evidently notable side-inputs of PhACs from areas surrounding the river. In particular, a military facility located downstream seems to be a point source of PhACs to ZR (Figures 3 and 4). In Jerash stream, a small downstream tributary of ZR, surface water samples showed low detectable deficient levels of ∑PhACs (<3 ng L−1). The source of this tributary is spring water, and our sampling site was located just before the spring water flow mixed with other water from ZR.

It should be mentioned that the concentrations of individual PhACs differed significantly between all sampling sites. Paracetamol was detected at all sites but occurred in the highest concentrations at Sukhna station (4870–5900 ng L−1). Paracetamol concentration then decreased to reach 40–70 ng L−<sup>1</sup> as the water flowed downstream in ZR due to dilution and probable degradation. Carbamazepine was the dominant PhAC at all sites upstream and along ZR (800–2700 ng L<sup>−</sup>1). Interestingly, we found a negative correlation between the concentration of carbamazepine and TSS content in water samples, i.e., the concentration of carbamazepine in water decreased as the TSS content in the water increased. Adsorption of carbamazepine to river sediment has been reported elsewhere [48,49]. Metoprolol and bisoprolol were among the dominant PhACs detected in ZR water.

The six antibiotic substances detected in Assamra WWTP effluent (clarithromycin, erythromycin, ofloxacin, metronidazole, sulfamethoxazole, and ciprofloxacin) were also detected in water at the different sampling sites along with ZR (Figure 4). Ofloxacin showed the highest concentrations in all sites along with ZR, and its concentration increased downstream in the river to reach the highest level at Military station (334–595 ng L−1). It is not clear why this was the case. Still, we cannot exclude desorption of previously sorbed antibiotics from river sediment to water and illegal dumping of sewage sludge as contributing causes. Other studies have found that antibiotics (specifically sulfamethoxazole) decompose during transport within water systems [50]. In addition, the present study has shown the results of one-time sampling, but the river flow rate is subjected to seasonal change that would affect the concentration and retention time of the PhACs [51]. Therefore, more monitoring campaigns are recommended for future work.

The estimated mass flow of target substances in ZR water at Military station was 39–71 kg year−<sup>1</sup> for antibiotics and 60–110 kg year−<sup>1</sup> for other PhACs, based on water flow of 86×106 m<sup>3</sup> year<sup>−</sup>1. It should be pointed out that most of the water in ZR is used for the irrigation of vegetables and fodder crops [35]. The fate of antibiotics and other PhACs in irrigated soils in the study area was not analysed in this study. However, the transport of antibiotics within the ZR water system is alarming and there is likelihood that it poses a risk of developing and spreading antimicrobial resistance within the area. Upstream measures might be needed to reduce antibiotics in wastewater and limit the loads entering the water system and the environment. Such measures could include limiting the prescription and sale of antibiotics and increasing awareness among the public and pharmacists of the consequences of antimicrobial resistance.
