# Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River
## 5 Conclusions  
The study of heavy metals in water along the Ile River within the territory of Kazakhstan revealed the presence of heavy metals at all sampling points. Among the measured metal concentrations, copper always, and nickel with one exception, and cadmium and zinc during summer 2024, exceeded the maximum permissible concentrations for fishery (MPC\({}_{t}\)). The self-purification capacity (SPC) was determined for cadmium to be 28-81%, copper 15-66%, zinc 22-37%, and cobalt 5-9%, while nickel self-purification of water did not occur. The SPC in the Ile River is strongly influenced, besides other factors, by sedimentation, sorption, and storage processes within the Kapshagai reservoir. The comparative analysis of the level of concentration of trace elements upward to the Kapshagai reservoir showed that a significant pollution of river water by heavy metals is caused mainly by the introduced toxicants with transboundary runoff and the inflow of metals from the Sharyn River to the reservoir. The heavy metal concentrations registered in the transboundary runoff at the border gauging station were significantly decreasing in the reservoir water, which can be explained by the constant deposition of toxicants with suspended solids in the humic and silt reach bottom layer of the reservoir. Due to this amount of pollution, the ecological self-regulation system of the Ile River cannot cope with this load. The river's ability for self-purification is very limited and, in some cases, is almost exhausted. Currently, the ability of the Ile River for self-purification is not stable, and first of all, it depends on the volume of pollutants introduced by tributaries along the river by surface runoff from settlements and from irrigated lands that have lost the self-purification ability. At least it depends on a sufficient runoff of the river, which is especially limited during the summer period. These results indicate that the water resources of the Ile River continue to experience anthropogenic load leading to significant heavy metal pollution. The main polluters are industrial and municipal facilities, cities, large settlements, and agriculture. Transboundary inflow from the territory of the People's Republic of China has an important place in the anthropogenic pollution of the Ile River. Therefore, the implementation of works in this direction is extremely important as these rivers provide water to the south-eastern part Kazakhstan, the most densely populated area of the country, and also fill Lake Balkash. The situation is more complicated by water intake and water use in the Xinjiang Uygur Autonomous Region (XUAR) of China, whose economic development has been rapid in recent decades. Under such conditions, it is critical to monitor both the quantity and quality of incoming water. Based on the obtained scientific results, in order to restore the natural state and preserve the normative water quality in the Ile River basin, it is recommended that the State Nature Protection Authorities take measures to reduce the volume of flow withdrawal from the river in the territory of the PRC and cease the inflow of toxic compounds along the river. It is also necessary to conduct the constant monitoring of the quality of transboundary flow on hydrochemical, toxicological, and biological indicators using automatic stations to control the quality of river water at the river's border section. It is required to take measures to exclude the polluting influence of the Sorbulak water storage facility on the river and continue research on water protection zones, as well as to continue research on water protection zones and the status of the implementation of water protection measures to assess the level of water pollution in the Ile River basin. The results obtained from this paper will be useful (1) for future research, (2) for monitoring by public authorities, (3) for policy makers, and (4) for land users (industry, agriculture, etc.). Conceptualization, N.A.