# Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River
## 4 Discussion
On the territory of Kazakhstan, the main pollutants of the Ile River are public utilities of settlements (mostly cities: Almaty city and the small towns Esik, Talgar, and Kaskelen); agriculture, in particular drainage water from irrigated fields; and the specific impact of various industrial enterprises. The studied region's industry is one of the dynamically developing sectors of the regional economy, with a total share in industrial production of more than 60%, and occupies leading positions in the domestic commodity markets of grape wines, tobacco products, sugar, malt, and electric batteries. There are 1928 industrial enterprises in the region, of which 175 are large- and medium-sized, 93.5% are in the manufacturing industry, 0.5% are in the mining industry, and 6% are in the production and distribution of electricity, gas, and water. The leading place in industrial production is occupied by the production of food products (35%), pulp and paper industry and publishing (9.4%), production of non-metallic mineral products (10.6%), and metallurgical industry and production of fabricated metal products (14.3%) [44; 45; 46; 47]. Due to limited water management, and sewage treatment capacity, all these land users and producers can be sources of heavy metal inputs into river water. A number of publications [28; 29; 48; 49] have been devoted to the study of hydrochemical, and some toxic, indicators in the water of the Kapshagai reservoir and the Ile River. However, they do not contain enough information for the detailed consideration of the main regularities of the anthropogenic transformation of water quality on the scale of the whole basin. There is a reason to state the insufficiency of actual data on the content of toxic compounds entering the river and Kapshagai reservoir, runoff from Shengeldinsky, Akdala irrigation massiffs, and Sorbulak wastewater accumulator, as well as on the self-purifying capacity (SPC) of the river. An important factor of the increasing pollution level by metal concentrations within the Kapshagai reservoir (Figures 4-6) is the polluted runoff from a number of tributaries on the south side and on the north side from the Shengeldy irrigation massif. The tributaries in the upper part of the Ile River delta are exposed to pollution by sewage effluents of cities coming from the Sorbulak technical reservoir and Akdala irrigation massif, which are characterized by increased contents of salts and heavy metals. Calculations have revealed that in the section from the border station to 37 km downstream of the HPP, the self-purification process is better than in other sections due to the significant contribution of the Kapshagai reservoir. The water entering the reservoir is influenced by natural factors and gradually cleansed of the contaminants that have entered the reservoir. There is a sorting process of solid particles by their specific weights (settling them to the bottom). As a consequence of the pollution in the water mass of the reservoir, a closer contact of pollutants with dissolved oxygen in water takes place. This is one of the essential drivers in the mineralization of organic matter, in the oxidation of decomposition products, and in the sedimentation of these resulting products by the settling of suspended-in-water particles to the bottom [50]. Thus, there are cases when the concentration of heavy metals in the river water in the lower reach exceeds the initial concentration and, accordingly, the self-purification capacity at these sites is with the \"negative\" sign while the positive value of the SPC indicator is less than 100%, i.e., there is a process of self-purification, but it is weaker than the process of pollution. The calculation of the SPC of the river for heavy metals is very important, not only for the assessment of a number of components of chemical balance and biological productivity but also for knowing the intensity of erosion-accumulative processes occurring in the river basin.