# Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River
## 4 Discussion
The processes of self-purification of flowing (and stored-in-reservoirs) river water from heavy metals depend on seasonal changes in the amount and temperature of runoff or discharges, which are important natural prerequisites for ACC, and, of course, they depend on the situation with the intake of heavy metals, both natural and anthropogenic, including man-made processes. Consequently, our study of the dynamics of these processes allowed a deeper understanding of the influence of certain lithological and anthropogenic factors in the basin on the formation of the chemical composition and the quality of river water. However, the research conducted under our grant funding is limited in the time aspect, so the results obtained on the basis of a short period (1 year) are not sufficient to build the dynamics of the analysis. The study of this issue is especially important to assess the level of pollution of transboundary waters from neighboring countries entering the territory of Kazakhstan, taking into account that Kazakhstan is located in the lower reaches of all major transboundary rivers entering Kazakhstan. Currently, the qualitative state of water and water bodies, according to the authors [26,36,38], is assessed using four categories: clean--rivers in the mountainous part of the basin, outside zones of anthropogenic pollution, with water quality that is close to natural; slightly polluted--rivers or their sections moderately affected by surface runoff from small settlements located at the mountain outlets; polluted--rivers or sections significantly affected by runoff from settlements and irrigated lands; and heavily polluted--rivers or sections that have lost their self-purification capacity and are unsuitable for all types of water use. Based on the results of self-purification capacity calculations, the lower reaches of the Ile River on the territory of Kazakhstan fall into the 'polluted' category, being significantly affected by runoff from settlements and irrigated areas. In this study, an attempt was made to identify the forms of heavy metals present in the aquatic environment of the Ile River, to assess the level of contamination at various sections of the river, and to analyze the river's capacity for natural self-purification. The data obtained confirm that the transformation and distribution of heavy metals in the water are influenced by both natural factors (such as the geochemical background and weathering processes) and anthropogenic activities, including wastewater discharge and intensive agricultural practices. The results demonstrate spatial variability in the level of contamination, which is particularly pronounced in the lower reaches of the river, where the accumulation of pollutants is more evident. This supports the assumption that local sources of pollution and the reduced dilution capacity in this part of the river play a significant role. Furthermore, the observed values of self-purification capacity suggest that the Ile River possesses a certain natural potential for recovery, which is likely influenced by a combination of factors, including hydrological conditions, the physicochemical properties of the water, and the intensity of biogeochemical processes within the ecosystem. The identified differences in self-purification efficiency for individual metals highlight the important role of their chemical nature and speciation in determining the effectiveness of natural removal mechanisms.