# Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River
## 2 Materials and Methods  
### Research Area  
The Ile River basin is a unique natural-technical complex river catchment. Five climatic zones (mountainous zone, foothill steppe, forest-steppe, steppe, semi-desert), starting from glaciers of Tanirtau and ending with hot deserts of Balkhash Lake area, are located here in a relatively small territory. The basin is one of the most densely populated areas of the Republic of Kazakhstan, where peculiar climatic conditions, fertile lands, provided by the flow of mountainous rivers, allowed the development of irrigated agriculture and animal husbandry and the development of industrial complexes. Intensive processes of substance circulation occur in the different sections of the Ile catchment--in the mountainous area of the basin: moisture condensation, its accumulation in glaciers and the formation of underground and surface runoff of numerous rivers; in the basin of Lake Balkhash: water evaporation, accumulation of pollutants, and salts and sediments washed away by water from the entire basin area [28]. The Ile River is the main waterway of the Balkash Lake basin. It originates on the Muzart glaciers in the Central Tanirtau (Kazakhstan) by the source of the Tekes River. Then, it flows through the territory of the People's Republic of China, where it merges with the Kunes and Kash rivers, and at 250 km from the merge, it enters the Republic of Kazakhstan again, where it flows into Lake Balkash. The total length of the Ile River is 1439 km. The average annual precipitation in summer is 150-250 cubic meters. The river occupies 815 km in its length in Kazakhstan. About 30% of the river's water resources are formed on the territory of Kazakhstan. The largest tributaries are the Turgen, Talgar, Charyn, Kaskelen, Kurty, Usek, and Shelek. The Ile River crosses several natural zones. In China, it flowsthrough mountainous terrain; in the middle part of the flow, it crosses plains; and in the lower part, the river passes through the Saryseik-Atyrau desert [28; 29]. The Ile River basin is the main source of water resources for the south-eastern part of Kazakhstan. Due to the transboundary origin of the Ile River, which drains intensively used agricultural, mining, industrial, and urban catchment areas both in Northwest China upstream and in Kazakhstan downstream, it is necessary to analyze not only the content of toxic compounds in the Ile River water but also the processes of their accumulation and migration. The present work utilizes original research data on heavy metal concentrations in the Ile River basin, collected between October 2023 and September 2024, as part of a systematic monitoring effort of water resources under anthropogenic pressure. This is part of and aimed at regular observation of the state of water resources under conditions of anthropogenic influences. It allows tracking the dynamics of pollution at key control sites. Key monitoring points in the Ile River basin are shown in Figure 1 and Table 1.  
For a comprehensive approach to water quality assessment, sampling was conducted at the Dobyn transboundary hydrological point, where water comes from China and enters Kazakhstan. Water samples were taken there and at other key points along the Ile River and analyzed on a monthly basis. The water sampling points included hydropost 164--after the transboundary section, hydropost 37 km lower Kapshagay HPP--to analyze the impact of hydraulic structures on water composition, and the Ushzharma hydropost and Kokzhide village area--to assess water quality before the Ile River flows into Lake Balkhash (Table 1). The studies also included water sampling across the entire water area of the Kapshagai reservoir and its main tributaries (Figure 1). This allowed a comprehensive assessment of the water conditions of the reservoir to identify the heavy metal concentrations and  
Figure 1: Scheme of key sampling points along the Ile River in Kazakhstan. their seasonal variability.