# Long-Term Dynamics of Persistent Organic Pollutants in Water Bodies of the Aral Sea-Syrdarya Basin
## 3 Results and Discussion
### Small Aral Sea  
POPs in the waters of the Small Aral Sea were studied from 1991 to 2006, as well as in 2021 and 2022. The sum of pesticides in the Small Aral Sea water was 0.22-1.58 \(\upmu\)g/L in 1991 (HCCH, DDT, and some organophosphorus compounds were present). In 1992, only HCCH isomers in concentrations up to 0.09 \(\upmu\)g/L were detected here. In 1993, the species diversity of pesticides in water was significantly higher than in previous years. This was mainly due to the inflow of a significant volume of the Syrdarya runoff. Ten species were detected: HCCH, DDT, metaphos, TCM, and others. The average concentrations of HCCH and DDT were 0.022 and 0.130 \(\upmu\)g/L, respectively, and the sum of all pesticides reached 1.58 \(\upmu\)g/L, with 0.460 \(\upmu\)g/L on average. In June 1994, 12 pesticide species were detected in the water of the Small Aral Sea and 7 were recorded in autumn, and in 1996 and 1997, 6 species were detected. HCCH (68%) and DDT (52%) were usually the most common pesticides. Their concentrations in the water of the river flow distribution zone were one and two orders of magnitude higher than in its central and western parts. During 1996-2006, there was a clear trend of decrease in the level of pesticide pollution in the lakewater, primarily due to the decrease in number of recorded species (Table 2). In 1992-1997, the concentrations of PCBs in the water of the Small Aral Sea were extremely unstable. In 1992, they were registered in the amount of 7-9 \(\upmu\)g/L. In 1993, the PCBs concentration was 0.04 \(\upmu\)g/L at only one station. In 1996, 1997, and 2000, these toxicant concentrations were 0.04-0.4, 0.1-1.0, and 2.0 \(\upmu\)g/L, respectively [66]. Thus, the level of the Small Aral Sea pollution by toxic chemicals was characterized by significant fluctuations due to the volume of incoming and accumulated river flow, the amount of toxic substances used in the basin, the rate of their destruction in the aquatic environment, and their biogenic migration. The results of the study of OSPs in the water of the Small Aral Sea in 2022 are presented in Table 3. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Year, Month**} & \multirow{2}{*}{
\begin{tabular}{c} **Number of** \\ **Pesticides Found** \\ \end{tabular} } & \multicolumn{2}{c}{**HCCH (Isomers)**} & \multicolumn{2}{c}{**DDT (Metabolites)**} & \multicolumn{2}{c}{**Sum of Organochlorine and**} \\ \cline{3-6}  & & \(\upmu\)g/L & \% Occur.** & \(\upmu\)g/L & \% Occur.** & **Organophosphorus Pesticides, \(\upmu\)g/L** \\ \hline
1993, June & 10 & 0.022 & 82 & 0.130 & 91 & 0.506 \\
1994, June & 12 & 0.100 & 81 & 0.270 & 75 & 0.800 \\
1994, & 7 & 0.020 & 75 & 0.174 & 33 & 0.799 \\
1996, July & 6 & 0.050 & 58 & 0.052 & 37 & 0.128 \\
1997, June & 6 & 0.080 & 68 & 0.279 & 52 & 0.421 \\
1998, June & 3 & 0.015 & 83 & 0.138 & 93 & 0.163 \\
2000, August & 3 & 0.020 & 71 & 0.030 & 12 & 0.032 \\
2001, June & 3 & 0.015 & 60 & 0.480 & 40 & 0.495 \\
2002, July & 3 & 0.017 & 67 & 0.120 & 8 & 0.137 \\
2003, July & 1 & 0.019 & 92 & Absent & - & 0.019 \\
2004, August & 1 & 0.006 & 73 & Absent & - & 0.006 \\
2005, April & 1 & 0.010 & 50 & Absent & - & 0010 \\
2005, May–June & 2 & 0.011 & 24 & 0.0–0.0870 & 14 & 0.058 \\
2006, June & 1 & 0.046 & 73 & Absent & - & 0.046 \\
2006, August & 1 & 0.028 & 100 & Absent & - & 0.028 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Concentrations of pesticides in the water of the Small Aral Sea (average values). The data in Table 3 show the presence of DDT and HCCCH in all lakewater samples. Hexachlorobenzene, heptachlor, and allorin were detected in the waters of some parts of the Small Aral Sea. A comparison with the results in Tables 2 and 3 shows a significant decrease in HCCH and DDT concentrations in 2022 compared with data from 1993-2006. Surveys in 2021 and 2022 have detected PCB pollution in the whole water area. Their concentrations in 2021 ranged from 0.108 to 0.310 \(\mathrm{\SIUnitSymbolMicro g}\)/L and in 2022 from 0.321 to 0.362 \(\mathrm{\SIUnitSymbolMicro g}\)/L.