# Long-Term Dynamics of Persistent Organic Pollutants in Water Bodies of the Aral Sea-Syrdarya Basin
## 3 Results and Discussion
### Sydarya River Basin
The chromatographic analysis of the collected water samples showed PCB con  
Figure 7: Total PCBs concentration changes along the Syrdarya River in September 2021.  
tamination of these rivers as well (Figure 7). The total concentration of toxicants in the Keles River water was 0.600 \(\upmu\)g/L, and 0.420 \(\upmu\)g/L in the Arys River water, i.e., within the maximum values registered in the water of the Syrdarya River. The Syrdarya River and other water bodies of the basin were exposed to pollution by the effluents of their tributaries within the territory of Kazakhstan. Ten congeners, including the \"marker\" congener PCBs 138 and 153 with concentrations of 0.048-0.055 \(\upmu\)g/L and the dioxin-like PCBs (PCBs 105, 114, and 118) with concentrations from 0.031 to 0.046 \(\upmu\)g/L were registered in the water of the tributaries. Among the lakes located in the delta zone of the Syrdarya River, water samples were taken from the largest lake Kamystbas and the periodically through-flowing lake Tushchy. PCBs were present in all water samples taken from these water bodies, despite the fact that Kamystbas Lake is a non-flowing water body. The total PCB content in the water of these lakes was found in 2021 within 0.093-0.220 \(\upmu\)g/L, and in 2022 within 0.324-0.648 \(\upmu\)g/L (Figure 8). Fifteen individual congeners were found, including the dioxin-like congeners PCBs 118, 105, and 114 and the \"marker\" PCBs 101, 138, and 153. In lake waters, the total content of toxicants in 2022 was almost twice as much as in 2021. The maximum content of PCBs was found in the water of the flowing lake Tushchy. The results of the 2013 winter campaign in the lower reaches of the Syrdarya River show the presence of PCBs in the water of the Syrdarya River in the amount of 0.083 \(\upmu\)g/L. In the Tushchy and Laikol lakes, the levels of accumulation of pollutants were significantly higher (2.18 and 4.70 \(\upmu\)g/L, respectively) than in the river water. PCBs were not detected in the water of Kamystbas Lake. After the Kokaral dam of the Small Aral Sea was built, a water body formed, which has a non-permanent connection with the northern end of the Large Aral Sea. This water body has no connection with the Syrdarya River. At the same time, a quite high accumulation of PCBs up to 23.12 \(\upmu\)g/L was registered in this water body during winter time. It is difficult to name direct sources of PCB pollution in this water body. However, one can only assume the influence of the so-called \"historical\" sources, such as military facilities that functioned for many years during the Soviet Union period on \"Vozrozhdenie\" Island (Renaissance Island) and other parts of this region and the atmospheric removal of pollutants from the surface of the dried lakebed. All the abovementioned data is an indicator of significant variability in the level of pollution of the deltaic lakes of the Syrdarya River by PCBs over time. This variability depends on the nature of their connection with the river, as well as the influence of  
Figure 8: PCB contents and their congeners in the water of the Syrdarya River delta lakes. atmospheric transfer of the toxicant from the surface of the dried bottom of the Large Aral Sea.