# Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River
## 1 Introduction
Pollutants enter watercourses mainly with wastewater from industrial and agricultural production, as well as from municipal and public utilities. Rivers are not only natural drains for water runoff but also forced collectors of all wastewater in their watersheds. In the case of the absence or poor development of sewage systems, the most part of domestic wastewater was purified naturally, filtered through soil and rock passages. Nowadays, with the growth of cities and the development of industrial production, including medium and small businesses, wastewater has an unimpeded access to water reservoirs through sewerage systems and discharge channels of agricultural lands. Most of the relatively small- and medium-sized rivers located in industrial and densely populated areas are particularly polluted [25; 26]. Although the largest enterprises for the extraction and processing of mineral and organic substances have treatment facilities, unfortunately, the efficiency of treatment is still not high enough. A number of researchers [26; 27] have pointed out that, as a rule, industrial production using heavy metals increases the pollution of natural and artificial water bodies and watercourses. Therefore, questions about the ability of rivers and reservoirs to achieve self-purification and the permissible load of their wastewater are becoming increasingly important [26]. The self-purification potential of the natural environment of river basins can be considered as an integral ecological assessment of anthropogenic processes that occur under pollution in the conditions of anthropogenic activity. At the same time, through the determination of the self-purification potential of the aquatic ecological system, it is possible to determine the degree of influence of anthropogenic activities in the formation of the ecological and water management states of river catchments. The self-purification potential of the natural environment of river catchments determines a river's geo-ecological resistance to anthropogenic impacts. Any anthropogenic interference in the metal migration processes in river catchments leads to a direct or reverse chain reaction that causes ecological disturbances in the aquatic environment. This effect especially manifests itself in the rivers trans-accumulative zone, which requires the need for environmental and water management assessment, taking into account the level of change in external factors, under the conditions of anthropogenic activities [27]. In accordance with the abovementioned status quo, the aim of this paper is to identify the forms of heavy metal presence 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. It is assumed that the transformation of heavy metals in the water occurs under the influence of both natural factors (geochemical background, weathering processes) and anthropogenic pressures (wastewater discharge, agricultural activities). It is expected that the level of heavy metal pollution in the river varies depending on the degree of human impact, especially in the lower reaches, where the accumulation of pollutants is more pronounced. The hypothesis is also put forward that the Ile River possesses a certain potential for self-purification, which depends on hydrological conditions, the physicochemical properties of the water, and the intensity of biogeochemical processes within the ecosystem.