Distribution of Chemical Elements in Surface Waters from the Crn Drim River Basin, Republic of Macedonia

Silvana Vasilevska1, Trajče Stafilov1, Robert Šajn2

 

1 Institute of Chemistry, Faculty of Natural Sciences and Mathematics, Ss. Cyril and Methodius University, Arhimedova 5, 1000 Skopje, Republic of Macedonia; E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

2 Geological Survey of Slovenia, Dimičeva ulica 14, 1000 Ljubljana, Slovenia

 

Abstract

A systematic study was carried out to investigate the distribution of chemical elements in the water samples collected from the Crn Drim River Basin, Republic of Macedonia. In total, 37 samples of surface water from the Crn Drim River and 11 samples of urban water from the towns of Debar, Ohrid, Resen and Struga were collected. The determination of the concentration of 22 elements was performed by ICP-AES. Cluster and factor analysis were applied in order to show the associations of chemical elements. The highest correlation coefficients of the elements were obtained for: Fe-Al (0.79), Na-K (0.94), Mn-Fe (0.70), P-Na (0.74), Sr-Li (0.70) and P-K (0.71). Applying factor analysis, three factors were obtained: Factor 1 (Al, Fe, Cr, K, Na and Mn), Factor 2 (Sr, Li, Ca and Mg) and Factor 3 (Zn, Ba and Cu). The results show that the highest concentrations of heavy metals were found in urban waters.

Keywords: water, heavy metals, urban water, Crn Drim River Basin, Republic of Macedonia.

Introduction

 

Water is one of the most important and most widespread medium of the environment. It is a source of life on this planet, and its quality and integrity are of essential importance for all life forms. The chemical composition of natural water on earth exhibit both temporal and spatial variations. The increase of the world's population, the development of industry, agriculture and food technology, as well as urbanization requires increasing quantities of water. Under such conditions along with higher water consumption, the degree of water pollution increases. If the quality of natural water changes due to natural or anthropogenic impacts, the contaminated water may present a threat for humans, animals and plants (Bartram and Balance, 1996).

The quality of water determines its suitability for use for various purposes that have specific requirements for the physical, chemical or biological properties of the water. The quantity and quality should fulfill the requirements for its intended use in different applications. The composition of surface waters depends on natural factors in the watershed and seasonal changes, the amount of water runoff, weather conditions and water levels. Human interventions also have a significant effect on water quality. Major changes in water quality lead to changes in the entire natural ecosystem. Apart from human activities some natural processes, such as heavy rains and strong winds, may lead to excessive erosion and landslides, resulting in an increased content of suspended particles in rivers and lakes (Meybeck and Helmer, 1992).

The problem of today's environmental pollution is closely related to heavy metal contamination that plays a significant role in the environment. Heavy metals are naturally present in soil and water. As a consequence of anthropogenic activities their concentrations can be significantly increased (Barakat et al., 2012; Ahmad et al., 2014). Contamination of water with heavy metals is a particular problem in developing countries. Major sources of heavy metals contamination in the Republic of Macedonia are mines and metallurgical activities (Stafilov, 2014; Ilić Popov et al., 2014; Balabanova et al., 2016), industrial activities, motor vehicles and urban waste. The developing industry, agricultural activities, the creation of illegal landfills, uncontrolled discharge of fecal waters and untreated waters into the rivers in the Republic of Macedonia lead to pollution of the aquatic ecosystems (Dimitrovska et al., 2012; Stafilov, 2014).

The aim of this work is to present data about the spatial distribution of chemical elements in samples of surface water collected from different locations in the Crn Drim River Basin, Republic of Macedonia, as well as urban water samples collected from the sewerage systems in the towns of Resen, Ohrid, Struga and Debar from this water basin. By determining the concentration of chemical elements in the water samples, their interpretation and correlation will provide information on the presence of anthropogenic pollutants/contaminants in the form of various chemical elements in the Crn Drim River Basin.

 

Materials and Methods

Description of the Investigation Region

The investigated region includes the basin of the Crn Drim River located in the southwestern part of the Republic of Macedonia (Figure 1). It includes the natural lakes Ohrid and Prespa, through which the border of the Republic of Macedonia with Albania and Greece passes. Two artificial lakes, Debar and Globočica were built along the Crn Drim River, and Lake Mavrovo in the northern part of the investigated region.

 

fig01
Figure 1: Location of the investigated region within the territory of the Republic of Macedonia.

 

The Crn Drim River flows through two valleys, the Ohrid-Struga and the Debar-Rekanska. Lake Prespa is located at the bottom of the Prespa Valley at an altitude of 856.45 m (Jordanoski et al., 2003). The water from Lake Prespa has no surface runoff, but runs through the limestone composition of the Galičica and Suva Gora mountains through the underground water flows into Lake Ohrid (Anovski et al., 1991; Matzinger et al., 2007; Sarafiloska and Patceva, 2012; Wagner et al., 2014). The Prespa-Ohrid hydrological area lies below 41˚16' northern latitude and extends from 18˚11' to 18˚56' east of Greenwich. It belongs to the Prespa and Ohrid Valleys. At the bottom of these valleys are the eponymous Prespa and Ohrid Lakes (Matzinger et al., 2007; Wagner et al., 2014). Although they do not have a surface hydrographic connection, these valleys and lakes within them constitute an independent hydrological region, which lies predominantly within the borders of the Republic of Macedonia (Sibinović, 1987).

The area from the north is enclosed with high mountains, and through its low mountain plains from the south and west, it is exposed to a slight influence of the Mediterranean climate. Its eastern part covers the Prespa Valley with the Small Prespa and Large Lake Prespa. Lake Prespa has a surface area of 319.9 km2, 189.2 km2 of which belongs to the Republic of Macedonia, and the remainder to Greece and Albania. The Great Lake Prespa has a mean depth of 14.93 m and is about 10 times livelier than Lake Ohrid. The largest depth of water in it is 55.5 m near the east coast, at the entrance to Mala Prespa (Sibinović, 1987).

The rivers Golema, Istočka, Kranska and Brajčinska are the main tributaries in the Macedonian section of the Great Lake Prespa. The most significant of Lake Prespa's surface flows, is the inflow of water from the north side through the Golema River and the Brajčinska and Krajnska mountain rivers flowing through the eastern side of the basin (Veljanoska-Sarafiloska, 2011).

Lake Ohrid is the largest and most important natural lake in Macedonia and probably, from a biological point of view, the most significant stagnant aquatic ecosystem in Europe. It is characterized by rich history, culture, archaeological sites and natural beauty, and in 1980 Lake Ohrid and the city of Ohrid were proclaimed as World Heritage Sites under the protection of UNESCO (Popovska and Bonacci, 2007; Jordanoski et al., 2009). Lake Ohrid has a proper elliptical shape and a meridian extension. It separates Mount Galičica from Lake Prespa. The greatest depth of 287.4 m, is in the region of the village of Peštani. It covers an area of 353.9 km2 of which 248.08 km2 are in the territory of the Republic of Macedonia, and the rest belongs to Albania. Crn Drim flows from Lake Ohrid to the city of Struga, after which its waters flow into the Adriatic Sea (Sibinović, 1987).

Lake Ohrid and Lake Prespa, which belong to the Prespa-Ohrid lake system, are of tectonic origin. The two lakes represent the remains of the pool of the former Desaret Lake from which they originated by means of geotectonic depression during the Pliocene 5.3-1.8 million years ago (Sibinović, 1987; Veljanoska-Sarafiloska, 2011). The geological age of Lake Ohrid is estimated at about 2-3 million years, which is why it is included in the group of old, long-standing lakes (Popovska and Bonacci 2007; Vogel et al., 2010).

In the southern part of Lake Ohrid, below the monastery St. Naum, there are springs (a group of karst springs) that supply this ecosystem with pure spring water. More than 56% of the water in the springs originates from Lake Prespa, which is about 150 m above the level of Lake Ohrid. With the exception of the sources that are the main aorta for supplying Lake Ohrid with water in the Lake Ohrid Watershed, there are 40 rivers, of which 23 are in Albanian and 17 in Macedonian territory. Larger tributaries of Lake Ohrid on the Macedonian side are the rivers Koselska, Čerava, Velgoška and Sateska (Lokoska et al., 2006).

Crn Drim flows from Lake Ohrid to the city of Struga at a height of 695 m, north, first flowing through Struga Field to Taš Maruništa, from where it penetrates into Drimkol Canyon and flows into Lake Globočica. Below the Globočica Dam, a short river course is formed and after it gets into the Debar Lake. The river leaves Debar Lake at Špilje Bridge and continues 12 km along the border, and then, in Debar Valley, west of the village of Spas, at an elevation of 746 m, it continues its course into the Republic of Albania.

Radika is the largest tributary of the Crn Drim and the only river in Macedonia, which gives water to two watersheds, the Adriatic watershed and the Aegean watershed. The Radika River springs under Vratsa at 2200 m above sea level. From the spring to the mouth of the Debar Lake it is 67 km long. On this route, it receives water from four tributaries: Ribnica, Mavrovska, Žirovnička and Mala Reka. Radika has clean, clear and cool water with a dark green color which is a consequence of calcium carbonate content. The valley of Radika is one of the most attractive and most picturesque canyon valleys. The canyon is a few million years old, passing through the mountains of Bistra and Stogovo in the east and Korab and Dešat to the west. After passing the villages of Dolno Kosovrasti, Dolno Melničani, Gorenci and Rajčica, Radika flows into the Crn Drim (Debar Lake), south of the city of Debar.

According to the Decree on the categorization of rivers, lakes, accumulations and surface waters of the Republic of Macedonia, the waters in the Crn Drim River Basin belong to the first and second class of waters (Official Gazette, 1999).

A geological map of the investigated area is shown in Figure 2. In the northern part of the investigated area, downstream of the river Radika, the geological formations are dominated by Mesozoic cliffs and Paleozoic metamorphic sediments, and rarely Mesozoic carbonate rocks. In the central part of the investigated area, similar formations are predominant with certain parts in which Mesozoic magnetic rocks are represented. The mountains of Karaorman, Kopanica and part of Mount Plačanska. are composed of Paleozoic metamorphic rocks with the presence of Mesozoic magmatic rocks. Mount Galičica is mainly made up of Mesozoic carbonate rocks, while in the western part of the mountain of Baba there are Paleozoic metamorphic rocks, Paleozoic magmatic rocks and Mesozoic magmatic rocks. The Debar, Ohrid, Resen and Struga fields are built from quaternary alluvial and diluvial/proluvial sediments, while the upper zones of the respective valleys are built of Neogene clastic sediments.

In the investigated region, the largest part is forested with a small part consisting of heterogeneous agricultural areas (Figure 3), while the mountains of Ničpurska, Bistra, and Stogovo on the eastern side and of Mt. Galičica are mostly represented by natural pastures. The areas close to the towns of Struga, Debar, Resen and Ohrid are predominantly agricultural areas.

 

fig02
Figure 2: Geological map of the investigated region.

 

Sampling

In the period from June to September 2015, 37 samples of surface water were collected from the Crn Drim River Basin and 11 samples of urban water from the sewage systems in the towns of Debar, Ohrid, Resen and Struga (Figure 4). Depending on the location conditions and availability, samples were taken near the vicinity of the specified locations. When collecting samples, the geographical coordinates were recorded using a global positioning system and each sample was inscribed with the sample mark, sample type and date of sampling. From each location, one sample of water was taken in a sterile plastic bottle with a plastic closure.

Surface water and urban water samples (1 L each) were prepared immediately upon arrival in the laboratory, filtered through a Whatman membrane filter with a pore sizes <0.45 μm using a vacuum pump (Merck) and acidified with 1 mL of concentrated nitric acid (HNO3, 69%, ultra pure).

The preserved samples were stored in the refrigerator until analysis. The reagent blank was prepared by filtering MilliQ water through the filter and acidified the sample.

 

fig03
Figure 3: Map of the investigated region according to land use.

 

fig04
Figure 4: Map of locations of water and urban water samples.

 

Instrumentation

The analysis of water samples was performed using an atomic emission spectrometry analysis with the inductively coupled plasma – atomic emission spectrometry, ICP-AES (Varian, 715ES). For greater sensitivity adjustment for most of the analyzed elements in the moss digests, an ultrasonic nebulizer CETAC (ICP/U-5000AT?) was used. In all samples, a total of 22 chemical elements were analyzed: Ag, Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, P, Pb, Sr, V and Zn. Standard solutions of metals were prepared by dilution of 1000 mg/L solutions (11355-ICP multi-element standard solution). The method of standard additions was applied, and it was found that the recovery of the investigated elements ranged between 98.5 and 101.2 % for ICP-AES and 96.9 and 103.2 % for ETAAS. The optimal instrumental parameters for these techniques are given in our previously published paper (Balabanova et al. 2010). All data for concentrations of the tested elements were statistically processed using Stat Soft 11.0 software. For 37 water samples the basic descriptive statistical analysis of the values for element concentration was performed.

A data normalization test was made using the Box-Cox Transformation method (Box and Cox 1964). By using bivariate statistics with a p<0.05; p>0.01 level of significance the degree of correlation of the values of the concentrations of the chemical elements in the samples was estimated, and the coefficients of correlation are presented in the correlation matrix. From numerous variables, the factor analysis derives a smaller number of new, synthetic variables. The factor analysis was performed on variables standardized to zero mean and unit of standard deviation (Reimann et al., 2002). The universal kriging method with linear variogram interpolation was applied for construction of the areal distribution maps of the elements and the factor scores (Snedecor, 1976).

 

Results and Discussion

The investigated region is divided into seven zones in order to easily notice the differences that would arise between the concentrations of the analyzed elements, as follows: the first zone covers the tributaries of Lake Prespa; the second zone covers Lake Prespa; the third zone covers the tributaries of Lake Ohrid ; the fourth zone Lake Ohrid; the fifth zone covers the Crn Drim River; the sixth zone covers the Radika River and the seventh zone covers the urban waters of the cities of Resen, Ohrid, Struga and Debar. The average concentration values of 14 elements of samples taken from various areas of the River Basin, as well as the average concentration of elements in urban water samples from the towns of Debar, Struga, Ohrid and Resen are presented in Table 1.

The obtained results for element concentration in 37 samples of surface water were used for statistical analysis shown in the Table 2. It contains the values for the arithmetic mean, the Box-Cox transformed mean, the median, the minimum, the maximum, the 10th, the 25th, the 75th and the 90th percentile, the arithmetic standard deviation, the standard deviation, the coefficient of variation and asymmetry of the elements in the surface water samples. The highest values for statistical parameters are obtained for Ca. While the values of the statistical parameters for phosphorus in river and lake waters are below the detection limit, i.e. below 0.1 mg/L.

 

tab01

 

tab02

 

The concentrations of Ag, As, Cd, Co, Mo, Ni, Pb and V were analyzed below their limit of detection in most of the samples (Table 3). The mean values of the concentrations of elements in urban water samples are higher than the average values of the elements in surface water samples.

In addition, to determine the concentration of chemical elements in surface and urban water samples, the correlation relations of these elements were analyzed. For this purpose, a matrix of correlation coefficients is made, which is shown in Table 4. Statistical significance occurs at p> 0.05 and those correlation coefficients are written in red in the matrix. The highest correlation coefficients were obtained for the relations: Fe-Al (0.79), Na-K (0.94), Mn-Fe (0.70), P-Na (0.74), Sr-Li (0.70) and P-K (0.71).

 

tab03

 

A multivariate factor analysis was applied in order to gain a better understanding of the interdependence of the analyzed elements. Table 5 presents the matrix of load factors. Factor 1 (F1) has a load value of 5.46 and a variability of 33.6% of the total variability, which is 78.3%. This factor associates the chemical elements Al, Fe, Cr, K, Na and Mn. The highest load value in this geochemical association of elements was obtained for aluminum and iron (0.90), and the lowest for sodium and manganese (0.70). Factor 2 (F2) has a load value of 2.80 with a variability of 27.1% and associates the following chemical elements Sr, Li, Ca and Mg. Factor 3 (F3) comprises 17.6% of the total variability of the matrix with the lowest load value of 1.93. F3 associates Zn, Ba and Cu with the highest load value for Zn of 0.85.

Using the multivariate cluster analysis, the significance of the factor analysis and the stability of the association of the elements was checked. The dendrogram of the interdependence of the analyzed elements in the surface and urban water samples from the Crn Drim River Basin is shown in Figure 5. An identical result is obtained with those using the multivariate factor analysis. In the dendrogram, three clusters with sub-clusters are formed that correspond to the three factors obtained by factor analysis.

 

tab04

 

tab05

 

fig05
Figure 5: Dendrogram of the mutual dependence of the analyzed elements in the surface and urban water samples.

 

The spatial distributions of factor scores of each factor (F1, F2 and F3) the average factor values for each zone and the towns presented by histograms are given in Figures 6-8.

The geochemical association of F1 (Al, Fe, Cr, K, Na and Mn) has a trend of increasing from left to right, with the exception of their value in the water samples from the tributaries of Lake Ohrid, and this is the result of the geological composition of the investigated region. The values of this geochemical association are higher in urban waters, especially in urban water from the town of Struga (Figure 6).

 

fig06afig06b         
(a)                                                                                              (b)
Figure 6: Spatial distribution of factor scores of F1(Al-Fe-Cr-K-Na-Mn) (a) and their average values according to the zones and urban waters in the towns (b).

 

The concentration of Al in urban waters, especially from Resen, Struga and Ohrid, is higher than that in surface water, its sources are waste waters from industries and households, as well as from atmospheric waters (Tables 1 and 2). However, the determined concentrations of Al in the surface water samples are below the maximum allowable concentration of Al for the first and second class of water (1500 μg/L) according to the Decree on Classification of Waters (Official Gazette, 1999) in which the waters from the investigated region are classified (Table 6). A higher concentration of Al is recorded in water samples from Mavrovo Lake, especially in area near the villages of Leunovo (93 μg/L) and from Lake Prespa, which is a result of drainage waters from surrounding mountains, the soils of which have a high content of Al as a results of their geological origin (Stafilov and Šajn 2016).

 

tab06

 

Higher concentrations of Fe were obtained in urban water from the city of Debar, and then in urban waters from Struga, which is probably the result of pollution in urban waters from urban activities (Tables 1 and 2). A higher concentration of Fe is recorded in water samples from Lake Prespa due to the presence of Fe in the geological composition of the environment. The lowest concentration of Fe is determined in the tributaries of Lake Ohrid (18 μg/L). All of the obtained Fe concentration values are below the maximum permissible concentrations.

Cr was determined in all water samples, but with higher concentrations in urban waters (Tables 1 and 2). The highest Cr concentration was found in urban water from the city of Ohrid of 6.8 μg/L, due to the discharge of untreated industrial wastewater into the sewage system. The Cr concentration in the water samples is below the maximum allowable concentration for Cr of 50 μg/L for the first and second class of surface waters (Table 6).

The highest mean value for Mn concentration was obtained in water samples taken from the tributaries of Lake Prespa with a value of 1592 μg/L, and the lowest average value was obtained in water samples from the river Radika, 6.86 μg/L (Tables 1 and 2). The average value of Mn concentration in urban water samples was obtained from the city of Debar is 828 μg/L. Although concentrations of Mn in urban waters are high, they do not exceed the limit value for Mn concentration in urban water of 2000 μg/L. The maximum allowable concentration of Mn in surface waters of the first and second class is 50 μg/L, which means that the specified concentrations of Mn in the surface water samples from the tributaries of Lake Prespa exceed the maximum allowable concentration for Mn. Its presence in water samples is probably due to an increased content of manganese in the soil from the southwestern part of the Republic of Macedonia which is of lithological origin with an average content of 910 mg/kg (Stafilov and Šajn, 2016).

Elements of F2 (Sr, Ca, Mg, Li) are characteristic of carbonate rocks. It is most present in the urban waters from the town of Resen, and there are also their high concentrations in the urban water samples from the town of Debar (Figure 7). In the town of Resen, the water is naturally rich in carbonates, while in Debar it is a result of the rinsing of the remains of construction activities and wastewaters from the gypsum factory. The lowest concentrations of these elements are found in the surface water samples from the river Radika, while a fairly high concentration were found in the surface water samples from the tributaries of Lake Prespa due to the high content of earth-alkaline elements in the surrounding soil dominated by quaternary alluvial and deluvian formations (Stafilov and Šajn, 2016).

 

fig07afig07b
(a)                                                                                              (b)
Figure 7: Spatial distribution of factor scores of F2 (Sr-Li-Ca-Mg) (a) and their average values according to the zones and urban waters in the towns (b).

 

The Ca concentrations in some water samples are higher in urban waters as a result of the discharge of its compounds in urban waters from industries, households and storm-water. The Ca concentration of 110 mg/L in urban water from Debar is the highest, resulting from atmospheric waters that have passed calcium from the current construction activities in the nearby environment, as well as the discharge of wastewater from the gypsum factory.

Lithium is present in low concentrations in surface water samples but higher in urban waters especially in urban water from the city of Resen as a result of inflow of waste water from industries and atmospheric waters. Mg is present in the water samples, with the lowest concentration in the water from the Radika River (4 mg/L) because the area along the Radika River there are small quantities of carbonate rocks. A fairly high concentration of Mg is determined in urban water from Resen (13 mg/L), which is probably due to the rinsing of soils rich in lithium and magnesium.

The geochemical association of F3 (Zn-Ba-Cu) has high factor values in the surface water samples taken from the rivers Crn Drim, Radika and the tributaries of Lake Ohrid, but much higher values in urban waters from the towns of Struga, Debar and Ohrid (Figure 8). This geochemical association has the lowest values in the samples of water taken from Lake Ohrid.

 

fig08afig08b
(a)                                                                                              (b)
Figure 8: Spatial distribution of factor scores of F3 (Zn-Ba-Cu) (a) and their average values according to the zones and urban waters in the towns (b).

 

Zn concentrations in surface water samples ranged from 7.3 to 2200 μg Zn/L. The highest was found in urban waters from the towns of Struga (300 μg Zn/L) and Ohrid (240 μg Zn/L) as a result of pollution from industrial waste waters (Figure 9). However, all of the determined concentrations of Zn in the surface lake and river waters are below the maximum permissible concentrations (100 μg Zn/L for the surface waters of I and II class), while the concentration of Zn in urban waters from Struga and Ohrid exceed the maximum permissible concentrations for II and IV class (200 μg Zn/L) (Table 6).

Barium also has higher concentrations in urban water samples resulting from waste or drainage water rich in barium that ends up in urban waters. The concentrations of Ba were, in general, below the maximum permitted concentrations of Ba in surface and wastewaters (1000 μg/L for the waters of I and II class and 4000 μg/L for the waters of III and IV class) (Table 6).

Significantly higher concentrations of Cu are determined in urban waters, especially from the towns of Struga and Ohrid, as a result of wastewater from industries, wastewater containing copper chemicals and agricultural drainage waters (Tables 1 and 2). The determined concentration of Cu in water samples taken from the Crn Drim River is above the maximum allowable concentration of Cu (10 μg/L), which is probably due to the inflow of untreated urban waters from the city of Struga (Figure 10).

 

fig09afig09b
(a)                                                                                              (b)
Figure 9: Spatial distribution of Zn in samples of surface and urban water (a) and their average values according to the zones and urban waters in the towns (b).

 

fig10afig10b
(a)                                                                                              (b)
Figure 10: Spatial distribution of Cu in samples of surface and urban water (a) and their average values according to the zones and urban waters in the towns (b).

 

In most of the samples analysed, the concentration of lead was bellow the limit of detection of 10 µg/L. In measurable concentrations (20 µg/L), Pb was found in the surface water samples from Lake Globočica. Its origin is most probably that of anthropogenic activities. The Pb concentration in the water sample taken from Lake Mavrovo was even higher (140 µg/L) due to its lithological origin from the area of the Bistra Mountain (Stafilov and Šajn 2016). Lead was also determined in the urban water samples from the towns of Ohrid (150 µg/L) and Struga (13 µg/L).

Comparative statistics have been applied in order to check if there is a certain difference in the distribution of chemical elements in surface and urban water samples taken from the whole Crn Drim River Basin. The results are given in Table 7. As evident, appreciably higher concentrations of analyzed elements (2 to 9 times) were found in urban as opposed to surface waters. The high enrichment factors confirmed that the urban waters are under anthropogenic pressure that leads to elevated concentrations of toxic elements, which have a potentially harmful effect on the environment.

 

tab07

 

Conclusions

The aim of this study is the systematic investigation of the spatial distribution of 22 chemical elements in 37 samples of surface water and 11 samples of urban water from 47 locations in the Crn Drim River Basin, Republic of Macedonia. The analyses were performed with atomic emission spectroscopy with inductively coupled plasma. The basic descriptive statistics and matrix of correlation coefficients have been developed. Factor analysis with the multivariate R-method is applied in order to show the associations of chemical elements in the samples. Тhe significance of the factor analysis and the stability of the association of the elements was verified by cluster analysis. Three factors were obtained and it was found that the distribution of associations is mostly a result of the complex geology and lithology of the Crn Drim River Basin. Тhe results for the analyzed elements in the urban water samples from the towns of Struga, Ohrid, Resen and Debar indicate that the sewage systems in the towns are under anthropogenic influence. The high concentrations of potentially toxic elements, present as contaminants in untreated waste waters from the sewage system in the cities of Ohrid and Struga, pose a potential source of pollution for Lake Ohrid and the Crn Drim River. For this reason, it is necessary to undertake protective measures that would include effective urban and industrial waste waters treatment.

 

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