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Article

Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River

by
Ainur Mussakulkyzy
1,
Christian Opp
2,*,
Nariman Amirgaliev
1,
Azamat Madibekov
1,3,*,
Laura Ismukhanova
1,3 and
Askhat Zhadi
1,4
1
Laboratory of “Hydrochemistry and Environmental Toxicology”, JSC «Institute of Geography and Water Security», Almaty 050010, Kazakhstan
2
Faculty of Geography, Philipps-Universität Marburg, D-35032 Marburg, Germany
3
Department of Meteorology and Hydrology, Al-Farabi Kazakh National University, Almaty 050010, Kazakhstan
4
Water, Land and Forest Resources Faculty, Department Water Resources and Reclamation, Kazakh National Agrarian Research University, Almaty 050010, Kazakhstan
*
Authors to whom correspondence should be addressed.
Appl. Sci. 2025, 15(12), 6548; https://doi.org/10.3390/app15126548
Submission received: 16 April 2025 / Revised: 4 June 2025 / Accepted: 5 June 2025 / Published: 10 June 2025
(This article belongs to the Section Environmental Sciences)
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Versions Notes

Abstract

The continuing anthropogenic pollution of the Ile River occurs both by transboundary runoff and as a result of discharges of industrial, agricultural, and domestic wastewater on the territory of Kazakhstan. With this amount of pollution, the river’s capacity for self-purification is very limited, and in some cases practically exhausted. Hydrochemical and toxic indicators in the Ile River basin were analyzed based on water sampling from the Chinese–Kazakh border station to 37 km downstream of the hydroelectric power plants (HPPs). Heavy metals were determined by flame AAS methods. The self-purification capacity (SPC) was determined for cadmium by 28–81%, copper 15–66%, zinc 22–37%, and cobalt 5–9% while the nickel self-purification of water did not occur. The SPC was influenced by the Kapshagai reservoir. The identified main regularities of the anthropogenic transformation of water quality and self-purification capacity of the river will help both in solving the problems of river pollution and in the development of necessary measures aimed at the protection of water resources from pollution and depletion.

1. Introduction

Many of the major problems facing humanity in the XXI century are related to water quality issues [1]. These problems will be aggravated in the future by climate change due to rising water temperatures, melting glaciers, etc., and will further cause an inverse relationship with the deterioration of the water environment worldwide [2,3]. Thus, the most acute problem of the Ile River basin has become water quality change and, as a consequence, the state of the aquatic ecosystem under the influence of economic activities and transboundary influences. Transboundary problems for Kazakhstan become acute not only in the field of preserving the optimal volume of river water inflow into the water basins of the country but also in the fact that transboundary rivers carry the inflow of various toxic compounds since the territory of Kazakhstan occupies the lower reaches of all transboundary watercourses. A large volume of river flow comes from China. In China, industrialization, urban development, and intensive agriculture are the main factors of water quality degradation [4].
Environmental security is an important part of Kazakhstan’s security. In this regard, particular concern is caused by the continuing anthropogenic pollution of the main water basins of Kazakhstan, both by transboundary runoff and as a result of industrial, agricultural, and domestic wastewater discharged into them. In this regard, there is no exception to the Chinese–Kazakh transboundary Ile River, which is the main water artery of the Lake Balkash basin.
According to the World Health Organization (WHO) in 2019, one third of the world’s population does not have access to safe drinking water [5]. That is why understanding water chemistry and river quality is important for both society and ecosystems [6]. The retreat of glaciers due to global warming has had a marked impact on the water chemistry and heavy metal pollution levels in rivers [7]. Pollution by various toxic and biogenic compounds of transboundary waters flowing from the territory of China along the Ile River has been considered in a number of scientific publications for many years [4,5,6,7,8,9,10,11,12].
The primary mechanism for the development of river water chemistry is based on natural processes including the weathering of rocks, soil erosion, and the input of dissolved substances from groundwater, which are also characterized by the geological background and regional water cycle [13]. In particular, soluble substances from soil have been shown to be critical factors dominating stream water chemistry, especially in small watersheds [14,15,16]. In addition, detailed information on hydrochemical processes would be useful in order to study and understand the formation, migration, transformation, and enrichment of heavy metals in river water. Among pollutants, heavy metals pose a significant threat to aquatic biota because in contrast to organic pollutants, metals do not suffer degradation but can only be redistributed among the components of the aquatic ecosystem.
Studies [17,18] have shown that heavy metal concentrations in rivers in the Tibetan Plateau are not only affected by rock weathering and water–rock interaction but also by artificial activities such as inputs of geothermal resources [19], domestic wastewater discharge [13], vehicle discharges [20], and mining activities [21,22]. There are a growing number of studies showing that natural geologic processes must be considered as the sources of pollution in some water bodies [23,24,25]. Rock minerals (e.g., serpentine, spinel, pyroxene, and olivine minerals) contain large amounts of heavy metals [23]. Heavy metals in minerals are released on the exposure of rocks to water, which, in turn, causes the contamination of the aquatic environment [24,25]. In this regard, it is crucial to identify various sources of heavy metal pollution and quantify their contribution to the pollution of the Ile River.
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 sewerage 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.

2. Materials and Methods

2.1. 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 flows through mountainous terrain; in the middle part of the flow, it crosses plains; and in the lower part, the river passes through the Saryesik–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 their seasonal variability. This stage provided an opportunity to detail the behavior of heavy metals in the aquatic ecosystem and trace the processes of their accumulation and transformation.
This system of sampling and observation points provided full coverage of the main river sections in Kazakhstan and allowed monitoring the spatial and temporal dynamics of heavy metals there.

2.2. Sampling and Analysis

Water sampling and analysis were carried out according to generally accepted classical methods in ST RK GOST R 51592-2003 “Water” and according to general requirements for sampling 2003 [30] and GOST 17.1.5.01-80 “Nature Conservation Hydrosphere”, which are in accordance with WMO Guidelines and Recommendations [31]. Water samples were taken monthly at established points within the study area, considering the impact of both natural and anthropogenic factors. Samples were collected in 1 L plastic bottles, which were pre-washed with the water to be sampled, at a depth of 0.5 m, in accordance with the methods and GOST standards. The samples were then delivered to the laboratory. Water samples were delivered to the laboratory; 250 mL was filtered through a paper filter with white tape for the determination of heavy metals.

2.3. Analytical Methods

Heavy metals in filtered water samples were determined using the flame atomic absorption spectrometric method with an AA-7000 spectrophotometer (Shimadzu, Kyoto, Japan), equipped with a hollow cathode lamp and a titanium burner operating on an acetylene–air mixture, following the procedure described by G. Fellenberg [32]). The analysis was carried out in accordance with ST RK ISO 8288-2005 “Water Quality”, which was harmonized with ISO 8288:1986 [33]. The elements analyzed included cobalt, nickel, copper, zinc, cadmium, and lead.
Prior to analysis, water samples were filtered through 0.45 µm membrane filters and acidified with concentrated nitric acid to pH < 2 to preserve the samples. The filtered and preserved samples were stored in clean 1 L polyethylene bottles, which had been pre-rinsed with deionized water.
Calibration was performed using certified standard solutions of heavy metals and each element was measured in triplicate to ensure accuracy. The detection limits of the AA-7000 instrument were as follows: Cu—0.001 mg/L; Zn—0.001 mg/L; Pb—0.003 mg/L; Cd—0.0005 mg/L; Co—0.001 mg/L; Ni—0.001 mg/L.
The measurement accuracy ranged from ±5% to ±10%, depending on concentration. All samples were delivered to the laboratory within 24 h after sampling, and analyses were completed within 72 h.
Maximum permissible concentration (MPCf) values of heavy metals were used as criteria for assessing the degree of water pollution by heavy metals. They were determined on the basis of sanitary rules, norms [34,35,36,37,38], on the “Unified system of classification of water quality in water bodies”, approved by the Order of the Chairman of the Committee of Water Management of the Ministry of Water Resources and Irrigation of the Republic of Kazakhstan from 20 March 2024, N° 70 [39] (Table 2). We used the MPC for water bodies and watercourses of fishery significance, i.e., the MPCf.
To calculate and assess the self-purification capacity or the degree of self-purification (SPC) of water bodies or their sections from specific pollutants, the approaches specified in [38] were used.
The degree of self-purification, expressed as a percentage of the decrease in the concentration of a pollutant relative to its original value, is calculated thus:
SP = C i − C f C i 100 %
Here, Ci and Cf are concentrations of pollutants in the initial and final sites, respectively, in mg/L.
In this study, the assessment of self-purification capacity was based on a relative scale commonly used in hydroecological research. According to this classification, values below 30% indicate a low level of self-purification, values between 30% and 60% correspond to a satisfactory level, and values exceeding 60% indicate the high self-purification capacity of the water body. If the concentration of pollutants at the lower cross-section exceeds the initial concentration, the value of the SP for these sections will be marked with a minus sign. Accordingly, for these components, the self-purification process does not occur.

3. Research and Results

Among pollutants, heavy metals pose a significant danger to aquatic biota, as unlike organic pollutants, metals do not undergo degradation but can only be redistributed among the ecosystem components. Studies of heavy metals in the Ile River basin were conducted monthly from November 2023 to September 2024. The average seasonal concentrations are presented in Table 3.
The dynamics of heavy metals (Cu, Zn, Pb, Cd, Co, Ni) in the transboundary flow of the Ile River at the Dobyn hydrological point (HP) for the period from November 2023 to September 2024 showed a significant exceeding of the concentration for the five studied elements out of six established levels of MPCf [39], except for lead.
The exceedance of normative norms for copper ranged from 4.7 (March 2024) to 27.2 MPCf (November 2023); the lowest excess of cobalt was recorded in April 3.3 MPCf and then, with increasing temperatures until September, rose to 7.5 MPCf. Small norm exceedances were observed for cadmium 1.2–2.4 MPCf, the zinc concentration in September exceeded the MPCf value up to 6.7, and the nickel concentration in spring months was up to 7.5 MPCf. Concentrations of measured heavy metals in the border zone are given in Figure 2.
Downstream of the Kapshagai reservoir hydrological power plant (HPP), water sampling was carried out at the site 164 km upstream of the HPP. The highest exceedances of maximum concentrations in this area in spring were recorded for copper—7.9 MPCf and cobalt—7.4 MPCf; nickel exceeded the MPCf by 4.2; zinc—1.2 MPCf; lead and cadmium remained below MPCf. The highest MPCf exceedance in summer was observed for cadmium—6.3; the cobalt concentration was 4.3 times higher than the MPCf norm; and insignificant exceedances were detected for copper and zinc, with values of 1.8 and 1.4, respectively. During fall, concentrations of five metals out of the six considered were as high as in the border crossing except for lead. Copper exceeded the norm up to 11.9 MPCf, cobalt—7.1, zinc—4.4, and cadmium and nickel—2.3–2.4 MPCf. In wintertime, the content of cobalt in this area was maximally high, exceeding the MPCf up to 7.6. Insignificant exceedances were recorded for nickel (1.9 MPCf) and lead (1 MPCf), and zinc and cadmium were within the norm. Concentrations of heavy metals in water upward to the Kapshagai reservoir are given in Figure 3.
In the transformation dynamics of the considered metals up to the reservoir, the increase from the level of the border post was noted in spring for copper, cobalt, and nickel; significant decreases in the concentration of these trace elements were recorded for copper in winter and summer.
Characteristic regularities in fluctuations in temporal and spatial aspects (upward to the Kapshagai reservoir) of trace elements were not observed (Figure 2 and Figure 3), obviously associated with the presence in the catchment area of the river basin sources of anthropogenic pollution by these compounds. Consequently, the growth of toxicant concentrations in transboundary runoff occurs mainly due to contributed pollutants and the inflow of metals from the Sharyn River to the point at 164 km. The role of denudation processes in the basin, obviously, has a subordinate position.
Within the Kapshagai reservoir, samples were taken to identify the distribution of heavy metals in the water area during the spring period of 2024. The spatial distribution of heavy metals is given in Figure 4, Figure 5 and Figure 6. Exceedances of the MPCf for copper were observed from 1.8 times in the central part to 11.4 times in the dam zone of the reservoir during spring. The lowest copper MPCf exceedances were observed in the area of the Yesik River confluence and in the central part of the reservoir. The highest MPCf exceedances were recorded around the confluence of the Shengeldy River on the right side of the reservoir; on the left side of the Turgen, Baltabai, and Kaskelen rivers; and in the upstream zone due to return water inflow.
The concentrations of both cobalt as well as copper exceeded the MPCf over the whole water area of the reservoir, ranging from 4 to 5.8 MPCf. The highest cobalt exceedances of MPCf were registered in points 6 and 8, in the central part (point 9), in the water of the dam zone (point 1), and near the mouths of the Shengeldi (point 3) and Kaskelen and Kishi Almaty rivers (point 2). Figure 5 shows the distribution of cobalt in the aquatic area of the reservoir. The cobalt accumulation in the water of these sites can be explained by the influence of small rivers flowing into the reservoir.
The MPCf exceedances of nickel concentrations were also recorded in all samples taken in the water area (Figure 6), from 1.5 to 3.8 MPCf. In the inflow areas of the rivers Shengeldi (point 3) and Esik (point 5), and in the central part (point 7), this was justified with runoffs of nearby settlements and agricultural lands, which discharge their runoffs to filtration fields, ponds of terrain lowering, which subsequently fall into water bodies.
The concentrations of zinc and cadmium in the reservoir water exceeded the MPCf insignificantly up to 1.3 and 2.6 MPCf, the content of lead in the reservoir water, and the upper river gauges remained within the norm.
At 37 km downstream of the Kapshagai HPP, the river water content of all metals considered was lower than that before entering the reservoir, although concentrations of copper, zinc, cobalt, and nickel were above the MPCf. For comparative analyses, points in the upstream (point 10) and downstream zone (point 1) of the Kapshagai reservoir were considered. Figure 7 shows clearly that the content of metals is significantly affected by reservoir activity. The accumulated large volume and the process of agitation during water discharge from the HPP affects the reduction of trace elements concentration in water.
Downstream the river from the reservoir to the top of the Ile River delta, the concentration of trace elements changed insignificantly for the whole period. But the content of most metals remained above the normative values. Figure 8 shows the heavy metal concentrations downstream of the Kapshagai reservoir.
In the water of the Ile River, downstream of the Kapshagai reservoir, maximum exceedances of copper (11.2–12.9 MPCf), zinc (5.5–8.2 MPCf), and cobalt (7.4–8.4 MPCf) were recorded during the autumn period. The cadmium concentration exceeded the MPCf only during autumn from 2.1 to 2.3 MPCf. The main reason for such growth was the inflow of collector-drainage water from the Akdala irrigation massif, which was characterized by increased concentrations of heavy metal salts in the collected drainage water. The highest exceeding of the MPCf of nickel concentrations up to 7.2 MPCf was probably related to the low-water period during the summer period.
From the analysis, it was revealed that in all samples taken along the Ile River, MPCf normative flow exceedances of fishery standards were recorded for copper, cobalt, and nickel. The concentrations of other trace elements periodically exceed the MPCf. Thus, in terms of heavy metal content, the river water does not meet sanitary standards for fisheries, which is due to the characteristic presence of heavy metals in the Ile River as a result of discharges from industrial and agricultural production, as well as from municipal and domestic wastewater. Generally, the self-purification of water bodies from sewage liquid occurs only due to dilution with natural water, as well as by the processes of substance transformation (chemical, biological, physicochemical, physical, etc.) running in rivers.
The calculation of the self-purification capacity (SPC) of the Ile River was made at the sites before the Kapshagai reservoir, after the reservoir, taking into account the influence of the Kapshagai reservoir and in the Kazakhstan part of the Ile River. In many cases, the concentration of pollutants in the downstream section exceeded the initial one. That was why the indicators of SPC of these areas were obtained with negative signs, which meant a lack of self-purification ability. The self-purification process was calculated for six heavy metals (Table 4). The obtained values of SPC with a negative sign were associated with anthropogenic impact, with sewage or collector water inflow occurring at these areas.
The self-purification of water masses upward to the Kapshagai reservoir occurs to a greater extent from copper (77–99%) in the summer and winter periods. During the spring period, the process of self-purification from copper does not occur, probably caused by the arrival of pollutants from adjacent lands with melt water and humic layer erosion influences. The self-purification of water from cadmium during the year is 14–49%, only during spring, and for copper, it does not occur. The self-purification of zinc during the year is low, from 7 to 26%. The lowest self-purification of water masses occurs for cobalt and nickel, 6–9%, probably because of the higher total concentrations.
The self-purification of river water from heavy metals after the Kapshagai reservoir to the delta top occurred in separate seasons in different ways during the observed period. For example, self-purification of water from cadmium in spring reached 90%, and in the rest of the year, the SPC had negative indicators. The self-purification process from cobalt was 54% and from copper, 32%, during summer, while from nickel, it was 46% in winter, and from zinc, it was 33% in autumn.
To identify the effect of reservoir activity on water self-purification capacity, SPC calculations were performed between Dobyn and 37 km downstream from the HPP. Compared to previous calculations, the self-purification of water masses in this section was much more intensive. During the period under review, the SPC from cadmium was 28–81%, that of copper was 15–66%, and that of zinc was 22–37%. The self-purification of cobalt was low, at 5–9%, while the nickel self-purification of water did not occur.
In general, from the Chinese border to the closing gauging station, the self-purification of water masses for cadmium and zinc was satisfactory at up to 93%. A low self-purification capacity in this section was manifested for copper (up to 33%), and zinc (29%) except during the autumn period, when it amounted to 2–11%, with a negative sign. During the winter period, the self-purification from nickel amounted to 27% while the other seasons had a negative sign, apparently, due to the fact that in addition to the river water transport from the upper station, there was an additional inflow of pollutants from China, which indicates water pollution rather than the self-purification of water.

4. Discussion

One of the most pressing issues in the studied basin is the degradation of natural water quality and the state of the aquatic ecosystem due to human activities and the transboundary nature of the river. Previous studies [40,41] had revealed exceedances of permissible concentrations of heavy metals in the transboundary flow of the Ile River, which were confirmed by the results of the present research conducted between October 2023 and September 2024. This situation has persisted for several years, with a growing trend in the concentrations of certain pollutants in recent years.
Among pollutants, heavy metals pose a significant danger to aquatic biota, as unlike organic pollutants, metals do not undergo degradation but can only be redistributed among the ecosystem components. Therefore, analyses of heavy metal pollution in water bodies are very important nowadays since they are the main sources of anthropogenic pollution of aquatic ecosystems. In Kazakhstan, as well as in other countries, the main pollutants of water bodies are heavy metals because of their high stability and cumulative effect. These substances, being accumulated along trophic chains to concentrations hundreds and thousands of times higher than their contents in water, are capable of causing deep disturbances of physiological and biochemical processes in aquatic organisms [42].
The content of trace elements in water is one of the important indicators determining the ecological states of water bodies. These play a major role in the development of living organisms, regulating many biochemical processes. However, their excess in a water body, created under the influence of various anthropogenic factors, leads to the disruption of the normal functioning of aquatic ecosystems. Heavy metals are able to accumulate in various objects of the aquatic environment, including fish, without undergoing chemical and biological degradation [42,43,44].
The main causes of such anthropogenic pollution of water basins are wastewater and air emissions from large industries and the transboundary transfer of toxicants along large rivers. The Ile River also accepts these influences. It is affected by transboundary pollution and tributaries that flow through small towns and large population centers [43,44].
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 massifs, 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 (Figure 4, Figure 5 and Figure 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. 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.

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 (MPCf). 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.).

Author Contributions

Conceptualization, N.A.; methodology, A.M. (Azamat Madibekov); software, A.M. (Azamat Madibekov); validation, A.M. (Ainur Mussakulkyzy); formal analysis, L.I.; investigation, A.M. (Ainur Mussakulkyzy); resources, L.I.; data curation, A.Z.; writing—original draft preparation, A.M. (Ainur Mussakulkyzy) and A.M. (Azamat Madibekov); writing—review and editing, A.M. (Ainur Mussakulkyzy) and C.O.; visualization, A.Z.; supervision, A.M. (Azamat Madibekov); project administration, N.A.; funding acquisition, N.A. and A.M. (Azamat Madibekov). All authors have read and agreed to the published version of the manuscript.

Funding

The work was carried out within the framework of grant funding provided by the Committee of Science of the Ministry of Science and Higher Education of the Republic of Kazakhstan, Grant No. AP19679150: «Regularities of anthropogenic transformation of water quality in transboundary basins, using the Ile River basin as an example».

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Conflicts of Interest

The authors declare no conflict of interest.

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Applsci 15 06548 g001
Figure 1. Scheme of key sampling points along the Ile River in Kazakhstan.
Figure 1. Scheme of key sampling points along the Ile River in Kazakhstan.
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Figure 2. Exceedances (above the black line) of the maximum permissible concentrations (MPCf) of heavy metals for fishery standard, recorded in the water of the Ile River in the area of the Dobyn settlement, located in the border zone of China/Kazakhstan.
Figure 2. Exceedances (above the black line) of the maximum permissible concentrations (MPCf) of heavy metals for fishery standard, recorded in the water of the Ile River in the area of the Dobyn settlement, located in the border zone of China/Kazakhstan.
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Figure 3. Seasonal heavy metal concentrations in the water of the Ile River upward to the Kapshagai reservoir based on monthly measurements.
Figure 3. Seasonal heavy metal concentrations in the water of the Ile River upward to the Kapshagai reservoir based on monthly measurements.
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Figure 4. Copper distribution in the water area of the Kapshagai reservoir during spring 2024 based on monthly measurements.
Figure 4. Copper distribution in the water area of the Kapshagai reservoir during spring 2024 based on monthly measurements.
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Figure 5. Cobalt distribution in the water area of the Kapshagai reservoir during spring 2024 based on monthly measurements.
Figure 5. Cobalt distribution in the water area of the Kapshagai reservoir during spring 2024 based on monthly measurements.
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Figure 6. Nickel distribution in the water area of the Kapshagai reservoir during spring 2024 based on monthly measurements.
Figure 6. Nickel distribution in the water area of the Kapshagai reservoir during spring 2024 based on monthly measurements.
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Figure 7. Changes in heavy metal concentrations under the influence of the Kapshagai reservoir.
Figure 7. Changes in heavy metal concentrations under the influence of the Kapshagai reservoir.
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Applsci 15 06548 g008aApplsci 15 06548 g008b
Figure 8. Seasonal heavy metal concentrations in Ile River water downstream of the Kapshagai reservoir based on monthly measurements.
Figure 8. Seasonal heavy metal concentrations in Ile River water downstream of the Kapshagai reservoir based on monthly measurements.
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Table 1. Coordinates of water sampling points in the Ile River basin.
Table 1. Coordinates of water sampling points in the Ile River basin.
Sampling PointCoordinatesDistance from Mouth, km
Latitude (N)Longitude (E)
Ile River
HP Dobyn43°45′31.27″ N80°13′53.45″ E723
164 km upstream of Kapchagay HPP43°50′15.28″ N78°49′43.07″ E607
37 km downstream of Kapchagay HPP44°7′53.69″ N76°59′5.09″ E434
HP Ushzharma43°44′14.24″ N77°8′46.62″ E264
HP Kokzhide45°5′22.43″ N75°27′3.40″ E35
Kapchagay Reservoir
Point 143°53′17.64″ N77°8′24.94″ E311
Point 243°47′45.34″ N77°8′38.58″ E320
Point 343°56′3.82″ N77°22′56.08″ E328
Point 443°51′9.43″ N77°22′3.29″ E331
Point 543°46′25.57″ N77°21′22.46″ E334
Point 643°51′15.97″ N77°42′43.07″ E350
Point 743°47′57.07″ N77°41′1.26″ E353
Point 843°44′29.07″ N77°40′36.31″ E358
Point 943°47′37.82″ N77°55′19.78″ E367
Point 1043°49′37.26″ N78°6′3.65″ E377
Table 2. Maximum permissible concentrations of heavy metals in water for fishery purposes (MPCf) [37].
Table 2. Maximum permissible concentrations of heavy metals in water for fishery purposes (MPCf) [37].
№Heavy MetalUnit For Fishery Purposes
(MPCf)
1Copper (Cu)mg/L0.001
2Zinc (Zn)mg/L0.01
3Lead (Pb)mg/L0.01
4Cadmium (Cd)mg/L0.005
5Cobalt (Co)mg/L0.01
6Nickel (Ni)mg/L0.01
Table 3. Average heavy metal concentrations in Ile River water from October 2023 to September 2024 based on monthly measurements.
Table 3. Average heavy metal concentrations in Ile River water from October 2023 to September 2024 based on monthly measurements.
Season of SamplingSampling SiteCuZnPbCdCoNi
mg/L
Winter Dobyn0.01310.00810.0010.00720.07080.021
164 km above HPP0.00010.00750.00990.00370.07560.0191
37 km below HPP0.00790.00620.00830.00370.06430.0285
Ushzharma0.00960.00730.00680.00250.06590.0191
Kokzhide0.01050.00710.00520.00410.06590.0154
Spring Dobyn0.00620.01580.00780.00290.06430.0285
164 km above HPP0.00790.01170.00420.00250.0740.0416
37 km below HPP0.00530.010.00310.00210.06110.0416
Ushzharma0.00440.01040.00470.00290.05950.0191
Kokzhide0.00530.01210.00420.00020.04810.0341
Summer Dobyn0.00790.01560.00940.00020.04160.0611
164 km above HPP0.00180.01350.00990.00010.04340.0627
37 km below HPP0.00270.01210.00940.00000.04530.0724
Ushzharma0.00180.01210.00890.00000.0210.0578
Kokzhide0.00530.0110.00680.00010.03970.0675
Autumn Dobyn 0.01250.05540.00620.01180.07560.0098
164 km above HPP0.01190.04440.00520.01220.07080.0228
37 km below HPP0.01120.08040.00620.01030.0740.0098
Ushzharma0.01290.08230.00520.01140.07890.0079
Kokzhide0.01270.05480.00470.01140.08370.0154
MPCpx0.0010.010.010.0050.010.01
Table 4. Degrees of self-purification capacity (SPC) of the Ile River water at selected river sections.
Table 4. Degrees of self-purification capacity (SPC) of the Ile River water at selected river sections.
PeriodInitialFinalCuZnPbCdCoNi
In the territory of the Republic of Kazakhstan
Winter DobynKokzhide2012−42043727
Spring 1523469325−20
Summer 332928385−10
Autumn −21243−11−57
Before the Kapshagai reservoir
Winter Dobyn164 km above HPP997−89049−79
Spring −27264614−15−46
Summer 7713−541−4−3
Autumn52016−36−133
Taking into account the influence of the Kapshagai reservoir
Winter Dobyn37 km below HPP4023−730499−36
Spring 153760285−46
Summer 6622081−9−18
Autumn 6622081−9−18
After the Kapshagai reservoir
Winter 37 km below HPPKokzhide−33−1537−11−246
Spring 0−21−35902118
Summer 3305−135420
Autumn −133224−11−13−57
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Mussakulkyzy, A.; Opp, C.; Amirgaliev, N.; Madibekov, A.; Ismukhanova, L.; Zhadi, A. Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River. Appl. Sci. 2025, 15, 6548. https://doi.org/10.3390/app15126548

AMA Style

Mussakulkyzy A, Opp C, Amirgaliev N, Madibekov A, Ismukhanova L, Zhadi A. Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River. Applied Sciences. 2025; 15(12):6548. https://doi.org/10.3390/app15126548

Chicago/Turabian Style

Mussakulkyzy, Ainur, Christian Opp, Nariman Amirgaliev, Azamat Madibekov, Laura Ismukhanova, and Askhat Zhadi. 2025. "Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River" Applied Sciences 15, no. 12: 6548. https://doi.org/10.3390/app15126548

APA Style

Mussakulkyzy, A., Opp, C., Amirgaliev, N., Madibekov, A., Ismukhanova, L., & Zhadi, A. (2025). Transmission of Heavy Metals in River Water and Self-Purification Capacity of Ile River. Applied Sciences, 15(12), 6548. https://doi.org/10.3390/app15126548

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