# Change in Water Quality of the Vistula River During the Emergency Discharge of Untreated Wastewater
## 3 Results and Discussion
** & **S1** & **S2** & **S3** & **S4** & **S5** & **S6** & **S7** & **S8** \\ \hline COD & mg\(\cdot\)L\({}^  
greater problem is surface runoff from agricultural and urbanized areas and leaky septic tanks. Excess nitrogen in humans is associated with a decrease in the level of calcium in the body, a burden on the liver and kidneys, and an increased risk of kidney stone formation [47]. The greatest increase in pollution was observed in the case of N-NH4+ because, in the mixing zone, the concentrations were six times higher than in the urban area. The N-NH4+ concentration in the urban area is 3.1 mg\(\cdot\)L\({}^{-1}\), while in the mixing zone, it is 0.51 mg\(\cdot\)L\({}^{-1}\) (Figure 4). The situation was similar in the case of N-NO3\({}^{-}\) and N-NO2\({}^{-}\). For N-NO3\({}^{-}\), a fourfold increase in contamination was observed, and the concentrations were 2.66 and 0.70 mg\(\cdot\)L\({}^{-1}\), respectively. The situation was different in the case of N-NO2\({}^{-}\) because only a small increase in the contamination from 0.010 to 0.012 mg\(\cdot\)L\({}^{-1}\) was observed (Table 3, Figure 4). Concentrations showed differences resulting from different sampling depths and the location of municipal sewage outflows [48]. Researchers in China found that the main cause of ammonia pollution is the inflow of sewage from septic tanks [49]. In turn, excessive nitrate and nitrite pollution is mainly caused by surface runoff from agriculture. Research on agricultural areas in Poland indicates an average nitrate-nitrogen concentration in water of 5 mg\(\cdot\)L\({}^{-1}\)[50]. Due to the concentration of N-NO2\({}^{-}\), N-NO3\({}^{-}\), and N-NH4+, water samples in the mixing zone do not meet the standards of good ecological status corresponding to threshold value [37]. Due to the concentration of N-NH4+, N-NO3\({}^{-}\), and N-NO2\({}^{-}\), water samples from stations in the urban area meet the standards for drinking water. However, in the mixing zone, the threshold value for N-NH4+ of 1.5 mg\(\cdot\)L\({}^{-1}\) is significantly exceeded. Under the influence of factors such as temperature and pH, ammonium nitrogen turns into ammonia. Ammonia in high concentrations can penetrate the blood-brain barrier, leading to severe brain dysfunction. Exceeding the standard levels of ammonia in the blood three times may indicate a liver disease that is dangerous to human health, and exceeding the standard value fivefold may imply hepatic coma [51]. Some results highlight the beneficial effect of the consumption of plant-derived nitrates and nitrites on cardiovascular diseases [52]. There is also some evidence of the antioxidant properties of nitrates and their positive impact on physical performance [53]. However, high consumption of these compounds from processed foods of animal origin is associated with an increased risk of stomach and intestinal cancer due to the formation of nitrosamines. Nitrates consumed in high concentrations may irritate the mucosa of the small intestine and cause malabsorption syndrome. Drinking water with an N-NO3\({}^{-}\) concentration above 10 mg\(\cdot\)L\({}^{-1}\) is dangerous to human health [54; 55]. A threefold increase in water pollution of the Vistula was found in the case of total phosphorus (TP) and a fourfold increase in the case of P-PO4\({}^{3+}\). The TP concentration increased at 0.22 to 0.68 mg\(\cdot\)L\({}^{-1}\) for UA and MZ, respectively. The concentration of P-PO4\({}^{3+}\) increased at 0.08 to 0.29 mg\(\cdot\)L\({}^{-1}\) in UA and MZ, respectively (Table 3, Figure 4). The concentration of total phosphorus in urban sections of the Yangtze River was 0.16-0.26 mg\(\cdot\)L\({}^{-1}\)[48]. The increased phosphorus load is an important factor in the increase in primary production and an element controlling eutrophication processes. The concentration of phosphorus and orthophosphates in the mixing zone exceeded the threshold value of good ecological status (Tables 2 and 3). Total phosphorus content is used as one of the measures of reservoir eutrophication.