Clarke concentrations of heavy metals in surface waters of the transboundary river Yertis (Kazakhstan)

ABSTRACT The Yertis (Irtysh) river is the largest left tributary of the Ob. The river is 4.248 km long and flows through the territories of three countries: China (618 km), Kazakhstan (1.589 km), and Russia (2.041 km). The purpose of this study is to analyze the concentrations of Hg, Cd, Pb, Cu, Zn in the surface waters of the transboundary river Yertis in comparison with the clarkes of elements in the hydrosphere, their spatial distribution, and change over time. The survey was conducted at six observation points within the Republic of Kazakhstan: Boran village, Ust-Kamenogorsk city, Predgornoe village, Semey city, Aksu city, Pavlodar city. The analysis of available information has allowed obtaining heavy metals distribution in space and change in time. The increased content of Hg, Cd, Zn was determined in the surface waters of the Yertis river in relation to clarkes of the hydrosphere. At the same time, a decreased content of Pb and Cu was found. The highest values of clarke concentration of elements were Cd (7), Hg (2.6), and Zn (1.7). Consequently, heavy metals have the greatest interest because their high levels in water have toxic effects on hydrobiont and benthic communities and on human health, who use these waters for household purposes.


Introduction
The concentration of dissolved forms of chemical elements in water depends on natural and anthropogenic processes.Natural constituents, lithology, basin geomorphology, climatic conditions, subsurface water, and groundwater play a leading role in the formation of the chemical composition of water (Kyrychuk & Muzyka, 2016).The formation of the chemical composition of river water depends not only on the processes occurring in the watercourse itself but also on the processes occurring in the catchment area (Nikanorov, 2001).
Heavy metals and their salts are known to be the most common types of highly toxic substances with toxic effects on hydrobionts and benthos.The toxic effects of many heavy metals on hydrobiont and benthic communities are mainly carried out by their ions.For example, as a result of anthropogenic impact, the content of heavy metal salts in water bodies disrupts the respiratory functions of aquatic organisms.In addition, heavy metal salts also have a toxic effect on human health when using these waters for household purposes (Burlibaev, 2014;Ustaoğlu & Tepe, 2019).The release of heavy metals into the environment has both natural and anthropogenic origins.The natural sources of heavy metals in surface waters are dissolution processes of endogenous and exogenous minerals, through leaching from soils.However, the anthropogenic influence is the main factor of pollution of water bodies and arteries.River waters are transformed by intensive anthropogenic influence (Condor, Custodio, Chanamé, Cuadrado, & Peñaloza, 2021).In the context of increased anthropogenic pollution -heavy metals are traditionally regarded as a priority pollutant for river waters (Sviridenko, Murashko, Sviridenko, Efremov, & Tokar, 2017).Addressing these problems requires an integrated approach to water quality monitoring from the reservoir zone to downstream.River systems are polluted mainly in the midstream and downstream dispersion zones (Normatov, Goncharuk, Amirgaliev, Madibekov, & Normatov, 2021).To quantify the pollutants coming from the upstream part of the river, it is necessary to identify the sources of pollution at the reservoirs.
The maximum concentrations of soluble heavy metals in the Yertis river are related to the location of large cities that discharge industrial and municipal wastewater (Withanachchi, Ghambashidze, Kunchulia, Urushadze, & Ploeger, 2018) that leads to the formation of complex geochemical anomalies or is caused by the introduction of heavy metals through heavily polluted right-bank tributaries that are under the influence of major metallurgical industries of Kazakhstan (Ust-Kamenogorsk city, Predgornoe village, Pavlodar city).At these sites, the average concentration of the dissolved form of heavy metals is 2-5 times higher (Sibirkina, 1999) in comparison with the background site (Boran village).This is explained by the fact that the right tributaries of the Yertis river, especially Buktyrma, Ulba, Oba, Glubochanka, and Krasnoyarka rivers are practically "poisoned" by industrial effluents of enterprises such as Kazzinc JSC -Zyryanovsk Lead Complex, Ridder (Leninogorsk) Polymetallic Complex, Ust-Kamenogorsk Titanium and Magnesium Plant and Lead-zinc Combine JSC, Irtysh Chemical Metallurgical Plant, Ulba Metallurgical Plant JSC, Aluminium of Kazakhstan JSC, "Khimprom," etc. Besides, the valleys of right-bank tributaries are more densely populated, have more intensive economic use, and more developed agriculture.Some tributaries that are extremely polluted by industrial effluent flow into certain right-bank tributaries of the Yertis river.For example, two tributaries, Breksa and Tikhaya, containing extremely high concentrations of heavy metals flow into the Ulba River.The studies (Abramov et al., 2009;Burlibaeva et al., 2020;Burlibaeva, 2011;Kushnikova, 2010;Panin, 1997;Tatykhanova, Kabdrakhmanova, & Kudaibergenov, 2014) provide information on anthropogenic pollution and retrospective studies on the quality condition of the Yertis river (Peng, Song, & Yuan, 2009;Riza & Hoque, 2021).
Based on the above, the assessment of the condition of water bodies for the protection of surface water resources, along with restoration of surface water quality are pressing challenges now.In this regard, it is necessary to develop and apply new technologies to improve water quality in areas with extremely high and high concentrations of heavy metals.The purpose of this study is to analyze the concentrations of Hg, Cd, Pb, Cu, and Zn in the surface waters of the transboundary river Yertis in comparison with the clarkes of elements in the hydrosphere, their spatial distribution and change over time.

Materials and methods
The object of study is the transboundary river Yertis, the largest left tributary of the Ob.The river is 4.248 km long and flows through the territories of three countries: China (618 km), Kazakhstan (1.589 km), and Russia (2.041 km).The total area of the basin is 1.65 million km2.The watercourse originates on the western slopes of the Mongolian Altai, at an altitude of 2.500 m, where it is called the "Black Irtysh" ("Kara Yertis").From China, under the name "Kara Yertis," the river crosses the border with Kazakhstan, passes through the Zhaisan basin, and flows into drainage Lake Zhaisan (Zhaisan, Kazakhstan).Flowing from Lake Zhaisan, the Yertis river runs northwest across the West Siberian Plain, and the Yertis flows into the Ob near Khanty-Mansiysk (Russia).
The annual monitoring data National report (2019) of the Ministry of Ecology, Geology, and Natural Resources of the Republic of Kazakhstan was used as an information base.Studies were conducted for heavy metals of Hazard Class 1, 2, and 3 (Hg, Cd, Pb, Cu, and  Zn).The year 2003 was taken as the basis of the study, being the most representative for the highest concentrations of Hg, Cd, Pb, Cu, and Zn in the surface waters of the Yertis River and their spatial distribution.To obtain information on the change in dynamics, the following years were selected: Hg (2003-2006), Cd (2010-2014), Cu, and Zn (2017).
Six observation points (sites) were examined from the upper Yertis river to the boundary-crossing: To analyze comparisons of the occurrence of heavy metals in water, the concept of clarke concentration (C c ) was used as a formalized universal indicator of the relative abundance of chemical elements in natural bodies with respect to the clarkes of elements in the hydrosphere.
The clarke concentration value is always greater than one (C c > 1), which indicates the accumulation (concentration) of the chemical element in the natural object under study compared to the crust (hydrosphere).When C c = 1, the content of the elements in the natural object and the Earth's crust is similar.Clarke is the average content of an element in the Earth's crust expressed as a weight percentage (mg/ kg/l).The unit was proposed by AE Fersman after American scientist FW Clarke (Dobrovolskaya, 2007).Clarkes of elements in the hydrosphere are shown Table 1 (Perelman, 1982).

Results and discussion
The results of the study show that the increased content of Hg, Cd, Zn was found in the surface waters of the Yertis river in relation to clarkes of the hydrosphere, along with the decreased content of Pb and Cu (Figures 2,3 ,5 ,8 ,9 and 10).Accumulation of the listed chemical elements is exclusively anthropogenic.
The sites with the highest values of concentration are under the influence of the main metallurgical industries of Kazakhstan (Panin, 1997;Vinokurov, 2014).The content of Hg, Cd, Pb, Cu, and Zn in the surface waters of the Yertis river for 2003 is presented in Table 2.The results obtained during the study for the above-mentioned observation points (sites) are shown in Figures 3-12.
Mercury is a Hazard Class 1 substance.The MPC (Maximum Permissible Concentration) (GOST, 1999) of mercury is 0.0001 mg/kg for fishery water bodies.The clarke value in river water is 0.00007 mg/kg.In the study, the maximum values of mercury are established in the point (Ust-Kamenogorsk city − 0.00007 mg/kg or about 1 clarke) (Figures 2 and 11).Clarke values of mercury resulted from municipal wastewater of Ust-Kamenogorsk city, which is used in various household and industrial appliances, as well as from the Zyryanovsk mining and processing plant of Kazzinc OJSC, processing polymetallic ores, where wastewater enters the Ulba River.The Ulba River is the right tributary of the Yertis river and its main pollutant.From the point (Predgornoe village) to the point (Aksu city) the lowest concentrations are observed (below 0.00001 mg/kg) and only toward the point (Pavlodar city) mercury concentration increases and is within 0.00004 mg/kg.Variation limits of mercury do not exceed clarke values at this site (from Boran village to Pavlodar city).But we know that the site (Pavlodar city) is considered to be a hotbed of mercury     5).On an inter-annual basis, there is a widespread accumulation of mercury in the point (Pavlodar city), which is explained by the largest discharges of wastewater, which are from the enterprises of SEZ (Pavlodar Special Economic Zone).The SEZ is located on the territory where the chemical plant "Khimprom" was once located.According to data from National report (2019) of the Ministry of Ecology, Geology and Natural Resources of the Republic of Kazakhstan, no mercury concentrations were detected in the Yertis river from 2007 to 2020.
Cadmium is a Hazard Class 2 metal.The MPC of cadmium is 0.005 mg/kg for fishery water bodies.Clarke value in river water is 0.0002 mg/kg.In the point Ust-Kamenogorsk city, cadmium content is higher in comparison with the background site (Boran village) and is within 1 clarke.The highest cadmium content (0.0006 mg/kg or more than 3  clarkes) is observed in the Predgornoe village (Figure 6).There are no recorded cadmium concentrations further downstream at other points (from Semey city to Pavlodar city).Cadmium in the surface waters of the Yertis river is observed everywhere in the time period (Burlibaeva et al., 2020).
More significant cadmium concentrations can be found in the time section (2010-2014) at the points (Ust-Kamenogorsk city and Predgornoe village).2019) of the Ministry of Ecology, Geology, and Natural Resources of the Republic of Kazakhstan, cadmium was not found in the surface waters of the Yertis river in 2019.Cadmium belongs to rare, dispersed elements: it is contained as an isomorphic mixture in many minerals and always in zinc minerals.Its main applications are in the manufacture of nickelcadmium batteries, where cadmium salts are used.Cadmium is a by-product of zinc and is released into surface waters by this metal.
The lead is a Hazard Class 1-2 metal.The MPC is 0.006 mg/kg for fishery water bodies.Clarke value in river water is 0.001 mg/kg.This element belongs to the     low abundances in the surface waters of the Yertis river within the Republic of Kazakhstan.An elevation of the maximum permissible concentration of lead in water by 1-2 times is presented in the lower stream of the Yertis river (Russia) as stated in the article (Zemtsova et al., 2019).The concentration of dissolved lead was 0.004-0.009mg/kg.At the site (Predgornoe village, Kazakhstan) the maximum lead concentration is 0.0003 mg/kg or less than 1 clarke (Figures 9 and  12).Lead is not observed anywhere in the investigated sites except 2003.
Zinc is a Hazard Class 3 metal.The MPC is 0.01 mg/kg for fishery water bodies.Clarke value in river water is 0.02 mg/kg.The highest zinc concentrations in the river water of the Yertis river are found in the point (Predgornoe village, 0.0413 mg/kg or over 2 clarkes) (Figures 9 and 12).Zinc content is less than 1 clarke in Ust-Kamenogorsk point, which means it is higher compared to the background site (Boran village).Zinc content is below the norm in subsequent observation points (Semey city, Aksu city, Pavlodar city).Having the intention of comparing zinc content within 14 years (2003 and 2017), Table 3 shows the   data for 2017.According to the data in the point (Predgornoe village), zinc content is 0.034 mg/kg or 1.7 clarkes.Taking into account the above, it can be firmly stated that the trend is not changing and zinc content is not decreasing and remains in the same range.
Copper and zinc are most often released into waters from non-ferrous metallurgy plants, from mine waters and from transport.The increase in concentrations of these substances results in a slowing of the processes of self-purification of water from organic compounds and in the suppression of the biological life of the basin.Copper and zinc are not completely removed from the waters, only their forms and migration rates change.The decrease in the concentration of these substances comes only from dilution (Otyukova, 2016).The main contributor to the zinc intake at the point Predgornoe village is the right-bank tributarythe Krasnoyarka river.The Krasnoyarka river flows in the area of the Ridder mining and processing complex, which includes the Berezovsky section of polymetallic ores with high copper and zinc content.Mine waters from the Berezovsky mine flow directly into the Krasnoyarka river.
Copper is a Hazard Class 3 metal.The MPC is 0.001 mg/kg for fishery water bodies.Clarke value in river water is 0.007 mg/kg.Its concentration in all observation points (from Boran village to Pavlodar city) in river water remains at the same level (0.002-0.003 mg/kg or less than 1 clarke) (Figures 11 and 12).However, there is an elevation of the standard MPC for copper ions, and it is 2-3 times higher.Abundances of this element are recorded every year.
Copper concentrations for 2017 are presented in Table 3.

Conclusions
In the present research, concentrations of heavy metals (mercury, cadmium, lead, copper, and zinc) in the surface waters of the Yertis river were studied at six locations (from point (A) to point (F)).Concentrations of mercury, cadmium, and zinc at the investigated sites were higher than their clarkes in the hydrosphere, while concentrations of lead and copper were recorded below the clarkes.But copper concentration is 0.002-0.003mg/kg, which is 2-3 times higher than MPC.
To summarize, the high content of heavy metals in the surface runoff of the Yertis river is an important issue for maintaining the sustainability of the ecosystem, which requires urgent and effective solutions.Comprehensive solutions are needed to improve water quality in the Yertis river, such as the construction of modern local treatment plants at industrial sites, also the development and application of new technologies for water treatment in extreme pollution areas, e.g.phytoremediation, and the development and achievement of environmental quality targets for East Kazakhstan and Pavlodar regions of Kazakhstan.Transboundary cooperation with neighboring countriesin particular, with the People's Republic of China and the Russian Federation, is also an important factor in maintaining the optimal ecological status of the Yertis river, as this parameter includes both quantitative and qualitative characteristics of the flow of surface water bodies.

Figure 3 .
Figure 3. Comparative characteristics of mercury concentration in surface waters of the Yertis river with clarkes of elements in the hydrosphere.

Figure 4 .
Figure 4. Comparative characteristics of mercury concentration in surface waters of the Yertis river with the clarkes of elements in hydrosphere at the point (Pavlodar city).

Figure 5 .
Figure 5. Dynamics of clarke concentrations of mercury at the point (Pavlodar city).
Figures 7-8 show the change of cadmium concentration over time.A gradual increase of cadmium concentration is observed (from C c = 0.7 up to C c = 3.8) between 2010 and 2013 at the Ust-Kamenogorsk point.The maximum value of the clarke concentration (C c = 3.8) occurred in 2013.The cadmium content is not significant in 2014-2015.Consequently, after 2013, the site (Ust-Kamenogorsk city) shows a decline in cadmium concentration in the surface waters of the Yertis river (C c = 0.005).At the observation point (Predgornoe village), no downward or upward trend is observed (Figure 8).The clarke concentration is distributed chaotically.High concentrations of clarkes were recorded in 2010 (C c = 3.75) and 2013 (C c = 4.415).Further, in 2014-2015 cadmium content was minimal (within C c = 0.01-0.005)as at the point (Ust-Kamenogorsk city).A decline was observed.According to data from the National report (

Figure 6 .
Figure 6.Comparative characteristics of cadmium concentration in surface waters of the Yertis river with the clarkes of elements in the hydrosphere.

Figure 7 .
Figure 7. Dynamics of clarke concentrations of cadmium in surface waters of the Yertis river at the point (Ust-Kamenogorsk city).

Figure 8 .
Figure 8. Dynamics of clarke concentrations of cadmium at the point (site) Predgornoe village in surface waters of the Yertis river.

Figure 9 .
Figure 9. Comparative characteristics of lead concentration in surface waters of the Yertis river with the clarkes of elements in the hydrosphere.

Figure 10 .
Figure 10.Comparative characteristics of zinc concentration in surface waters of Yertis river with the clarkes of elements in the hydrosphere.

Figure 11 .
Figure 11.Comparative characteristics of copper concentration in surface waters Yertis river with the clarkes of elements in the hydrosphere.

Figure 12 .
Figure 12.Clarke concentrations of heavy metals occurring in the effluents Yertis river in space.

Table 1 .
Clarkes of elements in the hydrosphere for mercury, lead, cadmium, copper, zinc.

Table 3 .
Heavy metal concentrations in the water of the Yertis river (mg/kg).
(A) -observation points on the Figure1.