# Long-Term Dynamics of Persistent Organic Pollutants in Water Bodies of the Aral Sea-Syrdarya Basin
## 3 Results and Discussion
### Sydarya River Basin
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Sampling Site** & **DDT (Metabolites)** & **Hetpachlor** & **Aldrine** & **HCCH (\(\upalpha\), \(\upbeta\), \(\upgamma\)–Isomers)** \\ \hline Kokbulak HP & 0.007 & n/d & 0.001 & 0.003 \\ \hline Tributary of the Keles River & 0.006 & 0.001 & 0.002 & 0.002 \\ \hline Shardara Reservoir—dam & 0.006 & n/d & 0.002 & 0.001 \\ \hline Before Koksarai Reservoir & 0.003 & 0.001 & 0.001 & 0.001 \\ \hline Koksarai Reservoir—dam & 0.003 & n/d & n/d & 0.001 \\ \hline Tributary of the Arys River & 0.011 & 0.001 & n/d & n/d \\ \hline Tomenaryk HP & 0.002 & n/d & 0.002 & 0.001 \\ \hline Before Kyzylorda city & 0.007 & n/d & 0.001 & 0.001 \\ \hline After Kyzylorda city & 0.004 & n/d & 0.001 & 0.002 \\ \hline Zhosaly HP & 0.005 & 0.001 & 0.001 & 0.003 \\ \hline Kazaly HP & 0.005 & n/d & 0.001 & 0.001 \\ \hline River mouth & 0.015 & n/d & 0.001 & 0.001 \\ \hline \multicolumn{5}{c}{Lakes in the Syrdarya delta} \\ \hline Kamystybas—eastern part & 0.001 & n/d & n/d & 0.002 \\ \hline Kamystybas—western part & 0.006 & n/d & 0.001 & 0.002 \\ \hline Tuschy & 0.007 & n/d & 0.001 & 0.001 \\ \hline \end{tabular} Note: HP—hydrological post, n/d—no data (no toxicant).  
\end{table} 
Table 1: Concentrations of organochlorine pesticides (\(\upmu\)g/L) in the Syrdarya River water and its tributaries in 2022. We have not found such a large number of PCB congeners, 33 in the waters of the Syrdarya River (Figure 7), in other water bodies of Kazakhstan. According to [PERSON] and [PERSON]. [64; 65], a wider structural diversity of PCB congeners is a sign that sources of different origins are involved in the pollution of the water body and the watercourse with these toxic compounds. These may include contamination by industrial PCB mixtures, atmospheric transport, and pyrogenic origin, for instance, as a consequence of reed burning, due to industrial and domestic waste incineration processes. The toxicity of natural waters in relation to PCBs is obviously determined not only by the total concentration of a toxicant but also by the content in them with more toxic \"marker\" congeners, especially dioxin-like ones. The content of the \"marker\" congeners in 2021 varied in the river water samples from 0.032 to 0.053 \(\upmu\)g/L, and their relative contents in some samples ranged from 15 to 35%. The highest relative proportion of the PCB 153 congener was found in the water of the Syrdarya River mouth. Similar data were obtained in May 2022, where the concentrations of the \"marker\" congeners in the river and reservoir waters were found to range from 0.030 to 0.059 \(\upmu\)g/L, and their relative contents in some samples ranged from 9 to 17%. The concentration of highly toxic dioxin-like congeners in 2021 ranged from 0.038 to 0.056 \(\upmu\)g/L. Their relative concentrations varied in separate samples ranging from 8% in the water of Shardara Reservoir to 41% and in the water samples taken in the river delta near the Karateren hydrological post. It should be also noted that increased concentrations of PCBs (0.370 \(\upmu\)g/L) were detected in the water samples taken from the Syrdarya River downstream of Kyzylorda. Dioxin-like congeners PCB 114 and the \"marker\" PCB 138 were registered in this sample, representing 37% of the total PCB amount. The analysis of water samples collected in 2022 showed that the contents of dioxin-like isomers ranged from 0.031 to 0.052 \(\upmu\)g/L, and their relative contents were in a range from 8 to 11%. Thus, the absolute and relative contents of the \"marker\" and dioxin-like congeners in the Syrdarya River water and reservoirs in 2021 and 2022 were characterized by close values, which allowed for general assumptions about the close levels of river water toxicity in these years with respect to PCBs. In 2022, two main tributaries of the Syrdarya River, namely, Keles and Arys, were studied.