# Long-Term Dynamics of Persistent Organic Pollutants in Water Bodies of the Aral Sea-Syrdarya Basin
## 3 Results and Discussion
### Sydarya River Basin  
The qualitative composition of water resources of the Syrdarya River depends on the flow formation zone and also on anthropogenic impacts. In the upper flow formation zone, within the territories of Tajikistan and Kyrgyzstan, the composition is predominately influenced by natural factors. In the lower flow zone of transition and dispersion, within Uzbekistan and Kazakhstan, it is mainly influenced by anthropogenic factors, such as river pollution by CDW and industrial effluents that contain various pesticides, metals, fertilizers, and mineral salts. Excessive deterioration of the natural water quality was one of the significant factors of the ecological crisis in the region. The highest level of pesticide pollution in the Syrdarya River was observed in 1979-1988. The maximum contents of toxicants in ug/L were as follows: the sum of HCCH isomers 3.575, DDT 13.386, DDE 1.096, and DDD 4.153. Among the organophosphorus pesticides (OPPs), the contents of metaphos and Rogor reached 3.579 and 176.25 ug/L, respectively [57]. According to annual surface water quality data from Kazhydrotomet [58], the contents of hexachlorocyclohexane (HCCH) and DDT were 0.376 ug/L for 1986 and 0.397 ug/L for 1987 in the Syrdarya River at the transboundary site of Kokbulak. This content was up to 0.860 ug/L in the Shardara Reservoir, and downstream of his reservoir, it was 0.544-0.633 ug/L. DDT was registered in concentrations up to 0.546-1.225 ug/L. Maximum concentrations of DDT up to 1.939-4.906 ug/L were recorded in the summer of 1985 near Szymlodata, and the HCCH content was 0.824 ug/L. Downstream, near Kazaly, HCCH and DDT were detected in amounts up to 1.022 and 0.892 ug/L, respectively, i.e., a substantial increase in the content of organochlorine toxicants from the downstream river to its estuary zone occurred, which was the result of considerable pollution of the river within the Kazakhstan territory. Therefore, the reviewed information of the Background State of the Environment [59] shows that the content of organochlorine pesticides in the water in 1980-1989 exceeded the background concentration for the Central Asian region by 1-2 orders of magnitude (DDT 1.6-48 ug/L, HCCH 0.5-84 ug/L) in the lower reaches of the Syrdarya and Amudarya. HCCH and DDT are the main substances of pesticide pollution in the Shardara Reservoir Water. The sums of the discovered pesticides of different classes were 0.007-10.2 ug/L in 1992 and 0.28-3.94 ug/L in 1993, with an average of 0.92 ug/L, i.e., in 1993, trends of  
Figure 5: Average pesticide contents in parts of and the whole Large Aral Sea water in 1991 and 1992.  
their concentration reduction were observed [60]. In the Syrdarya River water and the Shardara Reservoir, the PCBs were recorded in concentrations up to 2.0 \(\upmu\)g/L and 8.0 \(\upmu\)g/L in the spring and autumn of 1992, respectively, but in 1993, they were recorded only in a single sample with a concentration of 0.006 \(\upmu\)g/L. The analysis of intra-annual dynamics of organochlorine pesticides in river water near the Kokbulak boundary section revealed the dependence of these toxicants' concentrations on water discharge [61]. The pesticides inflow into the river network and their transformation within the water basin obviously depended not only on the water volume or discharge in a particular river basin. The dynamics of toxicant removal from irrigated massifs are caused by several factors, including the amounts of pesticides used in the basin; soils; orographic, hydrogeological, and drainage conditions of irrigated massifs and river valley sections, including the hydomorphological features; temperature regime; and precipitation in some seasons. Our analysis of Kazhydromet data for several years on four river sections located in Kazakhstan, namely, Kokbulak, Shardara, Kyzylorda, and Amanotkel, established two peaks in the intra-annual regime of pesticide concentrations in the river water.