# Change in Water Quality of the Vistula River During the Emergency Discharge of Untreated Wastewater
## 3 Results and Discussion
Orthophosphates are considered the most available form of nutrients and can be used by cyanobacteria [23; 56]. Due to the elevated concentration of P-PO4\({}^{3+}\), water samples from all stations meet the standards for drinking water. Excessive phosphorus intake in the daily diet may lead to high phosphorus levels in the body. Daily phosphate intake exceeding 4.0 g\(\cdot\)day\({}^{-1}\) causes only a marginal increase in blood phosphate levels if distributed adequately throughout the day. However, delivering large amounts of phosphates over several hours may result in transient hyperphosphatemia [57]. Research indicates that hyperphosphatemia is a direct stimulus for the development of atherosclerosis, particularly in chronic kidney disease [58]. In cases of chronic hyperphosphatemia, calcium salts may form deposits, contributing to bone diseases, vascular calcification, and cardiovascular diseases [59]. Drinking water with a P-PO4\({}^{3+}\) concentration above 0.5 mg\(\cdot\)L\({}^{-1}\) is dangerous to human health [38]. The electrical conductivity (EC) of water serves as an indicator of water purity in various industries. In the case of EC, a statistical increase in concentration was observed for MZ compared with UA. The EC level increased from 776 to 981 \(\mu\)S/cm before and after the  
Figure 4: Distribution of analyzed parameters within stations classified as mixed zone (MZ, marked green) and urban area (UA, marked violet). place of failure, respectively. Notably, high EC values ranging from 540 to 1130 \(\upmu\)S/cm were recorded in Saint Petersburg, with sewage outlets reaching up to 1970 \(\upmu\)S/cm [60]. Research conducted in Bialystok on the Biala River shows an average EC of 459-838 \(\upmu\)S/cm [61]. Conversely, in agricultural areas in the Ciemiega Valley, the average EC concentration was 708-763 \(\upmu\)S/cm [62]. These studies indicate that EC levels depend on the season and the amount of surface runoff. Electrical conductivity (EC) is an indirect indicator of pollution, closely associated with the level of salt dissolved in water. Due to high EC values exceeding the threshold value, the water in the mixing zone did not meet the standards of good ecological status [37]. The presence of dissolved salts is a key factor limiting the biodiversity of aquatic life [63]. Our analyses revealed that the average Cl\({}^{-}\) concentration was 150 mg\(\cdot\)L\({}^{-1}\) in MZ and 140 mg\(\cdot\)L\({}^{-1}\) in UA (Table 3, Figure 4). The chloride concentration in the Ganges River during the pre-monsoon season ranges from 43 to 120 mg\(\cdot\)L\({}^{-1}\)[64]. In the Bystrzyca and Biala Rivers, the concentrations of Cl\({}^{-}\) were 47-78 mg\(\cdot\)L\({}^{-1}\)[61; 65]. Due to high chloride concentrations twice exceeding the threshold value, the water did not meet the standards of good ecological status [37]. Chloride levels exceeding 100 mg\(\cdot\)L\({}^{-1}\) are common in surface waters loaded with intense surface runoff [66]. The concentration of suspended solids (SS) in the Vistula River was 67 and 60 mg\(\cdot\)L\({}^{-1}\) in MZ and UA, respectively. The total dissolved solids (TDS) concentration was 630 and 580 mg\(\cdot\)L\({}^{-1}\) in MZ and UA, respectively. Given the TDS value, the Vistula was classified as a freshwater body with TDS < 1000 mg\(\cdot\)L\({}^{-1}\). However, the concentration of TDS and SS water samples in the mixing zone does not meet the standards of good ecological status corresponding to the threshold value [37]. In terms of TDS, pH, SO\({}_{4}\)\({}^{2-}\), and Cl\({}^{-}\) concentrations, water contaminants did not exceed the limits for drinking water. However, concerning EC and SS, applicable standards were exceeded [37]. Elevated concentrations of SS can adversely impact fish stocks and escalate water treatment costs [67]. Additionally, chlorine concentrations reached alarmingly high values. Excessive chloride levels may be associated with conditions such as Cushing's syndrome and kidney disease.