# Long-Term Dynamics of Persistent Organic Pollutants in Water Bodies of the Aral Sea-Syrdarya Basin
## 4 Conclusions  
The Aral Sea disaster, also known as Aral Sea syndrome and ecological crisis has a special place among the global catastrophes of the world. It is one of the largest anthropogenic interferences with and destruction of the natural environment. There is no analog in the world where these profound processes and changes took place in the aquatic ecosystem of such large inland lakes. The catastrophic drop in the Aral Sea level and the intensive pollution of the entire Aral Sea region caused deep degradation of the natural environment and created environmental, social, and economic problems unprecedented in their acuteness and urgency. The widespread expansion of irrigated areas in Central Asia, including Kazakhstan, was accompanied by an increase in the use of water resources. Since 1961, when the runoff of the Amudarya and Syrdarya rivers, the two only tributaries into the Aral Sea lake, was dramatically reduced, the water level of the Aral Sea dropped down, and the lake was divided into two water basins: the Large Aral Sea and the Small Aral Sea. Intensive salinization continued, its salinity exceeded 100% by 2004, and it lost its fishery value. One of the most negative consequences of the Aral Sea desiccation is the wind-driven removal of salt and dust aerosols to the atmosphere from the dried lakebed [66]. One of the main causes of the deep degradation of the natural environment of the Aral Sea basin was the excessive use of pesticides in irrigated lands, i.e., their contamination of soils, drainage waters from irrigated areas, and all surface water resources in this basin. In 1991 and 1992, HCCH and DDT were detected in the water of the entire water area of the Large Aral Sea, while PCBs and low concentrations of POPs were also registered. The highest level of contamination of the Syrdarya River with OCPs and PCBs was registered in 1979-1988. At the same time, a significant increase in the content of toxicants was registered downstream of the river to the estuary zone due to increased pollution by such toxicants in the territory of Kazakhstan. Two peaks in the intra-annual regime of pesticides in river water were identified in the territory of Kazakhstan: the first one in September-November was caused by an intensive inflow of toxicants into the river system as part of CDW from irrigated areas, and the second one in early spring (March-May) was a result of pesticide washout from the surfaces of the catchment area and irrigated lands during winter thaws and spring snowmelt. The studies in the present period (in 2021 and 2022) showed the presence of pesticides, such as HCCH, DDT, heptachlor, aldrin, and PCBs, in the Syrdarya River water, the Small Aral Sea, and the reservoirs. The content of the PCBs in the river water in 2021 varied from 0.130 to 0.479 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L and in 2022 from 0.355 to 1.080 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L of the Syrdarya River. The average concentrations of HCCH and DDT were 0.022 and 0.130 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L, respectively, and the sum of all pesticides reached 1.58 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L, with 0.460 \(\mathrm{\SIUnitSymbolMicro\text{g}}\)/L on average for the Small Aral Sea and the reservoirs. The comparison of these data with the given multi-year material clearly shows a decrease in pesticide concentrations in the water of all water bodies of the Aral Sea basin by tens and hundreds of times. This was, first of all, the result of the reduction in the volume of pesticide applications used in the river basin by the Central Asian countries, including Kazakhstan. However, pesticides such as DDT and HCCH, the use of which has been prohibited in the world for a long time, are still used in the agricultural fields of the basin. Maximum concentrations of PCBs were registered in the transboundary flow, the Shardara Reservoir, and near the cities of Kyzylorda and Kazaly, indicating the presence of sources of pollution near them in the territory of Kazakhstan as well.