Concentration of Heavy Metals in Sediment and Water of Përlepnica Lake, Kosovo

Gjilan is a city located in southeast Kosovo. The main supplier of drinking water for the city is the Përlepnica Lake where heavy metals in sediment and water, and physicochemical parameters were analysed. Average concentrations of metals in soil sediment were found in the following order: Mn (708.65 mg kg −1 ) > Zn (604.55 mg kg −1 ) > Pb (264.26 mg kg −1 ) > Cr (71.43 mg kg −1 ) > Cu (61.08 mg kg −1 ) > Ni (37.27 mg kg −1 ) > Cd (6.32 mg kg −1 ) > Fe (1.83 mg kg −1 ). Average concentrations of metals in water were found in the following order: Fe (0.295 mg l −1 ) > Zn (0.066 mg l −1 ) > Cu (0.020 mg l −1 ) > Cr (0.035 mg l −1 ) > Cd (0.003 mg l −1 ) > Mn (0.003 mg l −1 ). The concentrations of heavy metals in sediment, such as Cd, Cu, Mn, Pb, and Zn, were not in accordance with the “New Dutch List” (soil and ground water criteria used in The Netherlands for contaminated land), and the concentration of Fe and Cu in water was not in accordance with EU Directive 75/440.


Introduction
Gjilan is one of the seven largest cities in Kosovo. 1 Most of the municipality uses groundwater as drinking water 2 and the other half of the citizens in this municipality are supplied by Lake Përlepnica.
The quality of sediments influences the water quality in the aquatic environment. 3 The behaviour of metals in natural waters is determined by the water chemistry and sediment composition. 4 The total heavy metal content in the sediment, related to toxicity and mobility, provides incomplete information, but can be considered as pollution indicator. 5 Heavy metals (HMs) are one of the most serious environmental pollutants due to their toxic effects. They are persistent and abundant, and can accumulate in aquatic ecosystems. 6 Monitoring and assessment of water quality is a crucial sustainability issue for surface waters. 7,8 HMs pollution of drinking water is a critical issue affecting numerous countries worldwide. The reason for studying the Përlepnica Lake was to determine the concentration of heavy metals in the sediment, and whether the HMs, present in the sediment, can penetrate the lake water. During the study, chemical analyses expressed high concentration of HMs in the sediment as well as the penetration of the heavy metals into the water. In addition, the physicochemical parameters of the lake were analysed which, in some samples, had a change in concentrations compared to the allowed concentrations for water quality. This work aimed to determine the heavy metals in water, sediment, and physicochemical parameters of Përlepnica Lake (Fig. 1). The following HMs were determined in the water of Përlepnica Lake: Fe > Zn > Cu > Cr > Cd > Mn, while the following Concentration of Heavy Metals in Sediment and Water of Përlepnica Lake, Kosovo HMs were determined in the sedimentation of the lake: Mn > Zn > Pb > Cr > C u > Ni > Cd > Fe. The conducted analysis of the water of Përlepnica Lake showed the presence of toxic metals (Fe, Zn, and Cu) that were not in accordance with EU Directive 75/440, while in the sediment of Përlepnica Lake there was a high concentration of the following HMs: Fe, Pb, Cd, Cu, Mn, and Zn. Based on these data, this study focused on the analysis of sediment and water in Përlepnica Lake, and the main objective of this study was to assess the quality of water and sediment as well as to show the levels of heavy metals in the water and sediments.

Location of sample collection
Përlepnica Lake is a small lake in the western part of Kosovo, surrounded by the Gollak mountains where the water springs. It lies northeast of the city of Gjilan from which water is supplied. A branch of Morava e Binçës (South Morava) flows through this lake, which is otherwise considered to be the largest lake in eastern Kosovo. Përlepnica Lake was built in 1966, and it is used for drinking as well as irrigation of 350 ha of arable land. The accumulation of Përlepnica Lake is formed in the river of the same name. Its water volume is 4.2 million m 3 . It has an area of 1.634 km 2 and a flow of 16.32 m 3 of water per second. Fig. 2 shows the water and sediment, and water sampling points.

Atmospheric conditions in the village of Përlepnica
Kosovo has quite different climates in the four seasons of the year. According to the data of the Hydrometeorological Institute in Kosovo, temperatures during the summer season reach an average of 35 °C, while temperatures during the winter average reach −15 °C. The summer season in the city of Gjilan is quite dry and in the absence of atmospheric rain (Fig. 3). The city of Gjilan has only one artificial lake, the Përlepnica Lake. The water in the lake is still used for drinking, but this lake dries almost completely during the summer, because the water requirements consume almost 90 % of the water in the lake.

Sampling
According to the standard methods (APHA/AWWA/WEF, 2012), 9 the water samples were collected and transported to the laboratories 10,11 (Fig. 4). Samples intended for chemical analysis had to be collected during normal operating hours, 15 to 30 cm below the surface of the water, 12 and the volume of the water samples was 1 dm 3 . A day before use, all glassware was washed with 1-2 % HCl solution, rinsed with distilled water, and oven-dried. 7 Water samples were taken at three different times in 2020 (March, April, June), while sediment samples were taken in January 2020. The weight of the sediment samples was approximately 1 kg. Sediment samples were collected by hand with a stainless-steel shovel at sampling depth of 30 cm. The sediment samples were wet, and, before being analysed, the samples were oven-dried at 105 °C. Water and sediment samples were stored in the laboratory at 20 °C until usage. 13 Samples were taken at the coordinates presented in Ta

Determination of heavy metals in water and sediments
AAS is one of the most used methods in analytical practice. It is used for the quantitative analysis of most metals in the periodic table of elements, and approximately 70 elements can be defined. 15 The AAS instrument defined the following HMs in the water: Mn, Zn, Pb, Cr, Ni, Cd, Fe, Hg, and Cu.
Chemical analysis of HMs in sediment was performed in the commercial laboratory "Agrovet" using Perkin Elmer "Optima 2100 DV ICP Optical Emission Spectrometer". 16 The ICP-OES (Method: ISO 12914, EPA 6010C) instrument defined the following HMs in the sediment: Mn, Zn, Pb, Cr, Ni, Cd, Fe, Hg, and Cu.
The HACH ® Model DR/2010 Spectrophotometer is a microprocessor-controlled single beam instrument for color- imetric testing in the laboratory or in the field. 17 The pH was determined using a portable multi-parameter analyser, WTW 3010. The conductivity of water (CW), also known as specific conductivity, represents the ability of water to convey electricity and is related to the concentration of ionized substances in water. CW was determined with WTW Cond 3110, DO was determined with WTW Oxi 315i, and NTU with 2100N ISC Turbidimeter (ISO Method 7027). 1 Sulphate (SO 4 2-) concentration was determined using Sulfa Ver 4 (0-70 mg l −1 ), method 8051, and the absorbance level was then measured using a spectrophotometer (HACH ® DR/2010) at λ = 450 nm. Nitrite (NO 2 -N) concentration was determined using Nitri Ver 3 reagent (test 0-0.300 mg l −1 , method 8507), and the absorbance level was measured using a spectrophotometer (HACH ® DR/2010) at λ = 507 nm. 17 General hardness (GH) was analysed by adding 2-5 ml of buffer and indicator (black erythromycin) in very small quantities to a sample of 100 ml of water. Following the addition of the indicator, the solution became red or light red, and the titration was done with complexon III or ethylenediaminetetraacetic acid (EDTA) until the solution changed its colour to intensive blue. 1 The calculation was based on Eq. (1).
V EDTA is titration volume of EDTA (ml), c EDTA is the EDTA concentration (0.01 mol l −1 ), and V s is the volume of the used sample (ml).
Carbonate strength (CS) is defined as the alkalinity of methyl-orange. A volume of 100 ml water sample was transferred to 500-ml Erlenmeyer flask and 2-3 drops of methylene chloride were added. The titration was performed with standard solution HCl (c = 0.01 mol l −1 ) until the colour changed to orange. 1 The analysis results were calculated in the German degrees (°dH) of water hardness according to Eq. (2).
V HCl is consumed volume of HCl solution in concentration c HCl = 0.01 mol l −1 .
Calcium (Ca 2+ ) or CaO equivalent can be determined by titration with standard EDTA solution in the presence of murexide (ammonium purpurate). First, 5 ml of NaOH in concentration 2 mol l −1 was added to 100 ml of water sample and the sample was titrated with EDTA until the colour changed from red to purple. The determination of Ca 2+ (in mg l −1 ) was calculated by Eq. (3). 11 Ca V EDTA is volume (ml) of EDTA solution in concentration c EDTA = 0.01 mol l −1 and V s is the volume of sample used, M CaO = 56 g mol −1 . The content of Mg 2+ or MgO equivalent (mg l −1 ) was calculated using Eq. (4). 1 Mg 2+ (mg l −1 ) Water sample alkalinity (A-HCl) is the measurement of its capacity to neutralize acids. Four drops of phenolphthalein were added to 100 ml of the sample. If the 100-ml solution becomes purple, the pH of water contained bases is above 8.30, and if the solution does not turn purple, 2-3 drops of methyl-orange are added, which turns the solution yellow. The solution was then titrated with HCl (c = 0.01 mol l −1 ) until it turned orange, and the amount of titre used was recorded.
Determination of chlorides (Cl − ) was carried out in an Erlenmeyer flask containing 100 ml of water sample (adjust pH to 7-10 if necessary). With the addition of 1 ml of K 2 CrO 4 0.257 mol l −1 , the sample turned yellowish. Titration was done with silver nitrate AgNO 3 (c = 0.01 mol l −1 ), and stopped when the solution turned light red. 1 The value of chlorides (mg l −1 ) in the sample was calculated according to Eq. (5).
V 1 is volume of titre for sample (ml), V 2 is volume of titre for blind sample (ml), c= 0.01 mol l −1 is molar concentration of AgNO 3 , and V s is the volume of sample used (100 ml in our research).

Physicochemical parameters in the water of Përlepnica Lake
Water quality assessment in lakes is a widely recognized problem. In order to understand water quality conditions, monitoring the physicochemical parameters of lake water is crucial, because it provides essential information for efficient water management practices. 18 The water of Përlepnica Lake has no odour and no taste, which was determined during sampling, because this lake has no industry or urban development to cause water pollution.
The temperature of surface waters is influenced by latitude, altitude, season, time of day, air circulation, cloud cover, the flow, and the depth of the water. Water temperature varies due to atmospheric conditions during the seasons. 11 Water temperature is a good indicator of whether water is polluted or not. The acceptable limit of water temperature according to Directive 75/440 BE is 22 °C. The temperature values of all the water samples were found to be in the range between 17.5 and 18.8 °C, the average temperature value was 18.06 °C, and the samples analysed were in accordance with Directive 75/440 BE ( Table 3). The pH is classed as one of the most important water quality parameters. Measurement of pH relates to the acidity or alkalinity of the water. A sample is considered to be acidic at pH below 7.00, and alkaline at pH higher than 7.0. Acidic water can lead to corrosion of metal pipes and plumping systems. 19 The normal water pH range mentioned in Directive 75/440 BE and guidelines is between 6.50 and 8.50.
The pH values of all the water samples were found to be in the range between 7.28 and 8.25, the average pH value was 7.97, and the samples analysed were in accordance with Directive 75/440 BE (Table 3). Electrical conductivity is the ability of any medium, water in this case, to carry an electric current. The presence of dissolved solids such as calcium, chloride, and magnesium in water samples carries the electric current through water. 19 The measured CW values of all the samples are plotted in Table 3. According to Directive 75/440 BE, the maximum allowable level of conductivity is (200-800) μS cm −1 . The results showed that the measured conductivity of all water samples ranged from 382 to 406 μS cm −1 , and the average conductivity value was 392.83 μS cm −1 (Table 3). High conductivity may lead to lowering the aesthetic value of the water by giving mineral taste to the water. For industrial and agricultural activity, monitoring of the water conductivity is crucial. Water with high conductivity may cause corrosion of the metal surface of equipment such as boiler. 20 Turbidity is the cloudiness of water caused by a variety of particles, and is another key parameter in drinking water analysis. 19 The turbidity (NTU) results for all water samples studied are shown in ). NTU is usually very high in Përlepnica Lake in the winter season when rainfall is more frequent.
Dissolved oxygen (DO) is considered an important measure of water quality as it is a direct indicator of an aquatic resource's ability to support aquatic life. 21 According to Directive 75/440 BE, the maximum allowable level of DO is > 5 mg l −1 . The lowest DO value was 3.69 mg l −1 , the highest value was 5.10 mg l −1 , and the average DO value was 4.35 mg l −1 (Table 3). Based on the analysed samples, DO was not in accordance with Directive 75/440 BE, and the results of DO showed that the oxygen in the water of Përlepnica Lake was consumed by organic matter that decomposed in the water. Alkalinity (A-HCl) refers to the capability of water to neutralize the acid. 22 The acceptable limit of A-HCl in water according to Directive 75/440 BE is 10.50 ml. The results showed that the measured A-HCl of all water samples ranged from 2.80 to 3.20 ml, and the average A-HCl value was 3.01 ml ( Table 3). The value of alkalinity in water depends on the presence of bicarbonate and carbonates. 23 The low alkalinity of water in the Përlepnica Lake was due to its low concentration of bicarbonates (HCO 3 − ). The acceptable limit of HCO 3 − in water according to Directive 75/440 BE is 630 mg l −1 . The results showed that the measured conductivity of all water samples ranged from 176.90 to 195.20 mg l −1 , and the average HCO 3 − value was 184.95 mg l −1 (Table 3). General hardness (GH) is mainly contributed by bicarbonates, carbonates, sulphates, and chlorides of calcium and magnesium. Therefore, the principal hardness-causing ions are calcium and magnesium. 24 According to Directive 75/440 BE, the maximum allowable level of GH/°dH is 30 °dH. The lowest GH/°dH value was 10.2 °dH, the highest value was 11.3 °dH, and the average GH/°dH value was 10.83 °dH (Table 3). Based on the sample values, the water of Përlepnica Lake is of medium strength °dH. The reason why the water of Përlepnica Lake has medium hardness °dH is due to the low concentration of calcium and magnesium. The calcium (Ca 2+ ) results for all studied water samples of Përlepnica Lake are shown in (Table 3). According to Directive 75/440 BE, the maximum allowable level of Ca 2+ is < 200 mg l −1 . The lowest Ca 2+ value was 55.31 mg l −1 , the highest value was 64.12 mg l −1 , and the average of Ca 2+ was 61.27 mg l −1 ( Table 3). As mentioned previously, magnesium (Mg +2 ) is a contributor to the general hardness of water. The acceptable limit of Mg +2 in water according to Directive 75/440 BE is < 50 mg l −1 . The results showed that the measured Mg +2 of all water samples ranged from 8.41 to 12.10 mg l −1 , and the average Mg +2 value was 10.47 mg l −1 ( Table 3). Chloride (Cl − ) is present in all-natural waters, and its content moves to a greater extent in natural waters. 25 Dissolved Cl − in surface waters occurs naturally from the geology, but high concentrations typically result from runoff of de-icing salts. 26 According to Directive 75/440 BE, the maximum allowable level of Cl − is 200 mg l −1 . The results showed that the measured Cl − of all water samples ranged from 180 to 185 mg l −1 , and the average Cl − value was 182 mg l −1 ( Table 3). The high amount of chlorides also indicates an undesirable effect on the structure of metal pipes, causing a salty taste in the water. 23 Sulphates (SO 4

3−
) are more commonly found in groundwater than in rivers and lakes. 26 The high concentration of SO 4 3− in water is caused by the oxidation of gypsum and the release of industrial wastewater. 24 According to Directive 75/440 BE, the maximum allowable level of SO 4 3− is 200 mg l −1 . The results showed that the measured SO 4 3− of all water samples ranged from 39.04 to 41.62 mg l −1 , and the average SO 4 3− value was 40.16 mg l −1 (Table 3). Based on the results of the analysed samples, the concentration of SO 4 3− was quite low compared to the value allowed by the Directive 75/440 BE. A high concentration of nitrate (NO 3 − ) in water is not suitable for human consumption because it increases cancer risk. 27 NO 3 − in water mostly occurs when municipal or industrial waste is discharged or wastewater is released. 23 The acceptable limit of NO 3 − in water according to Directive 75/440 BE is 25 mg l −1 . The results showed that the measured NO 3 − of all water samples ranged from 5.10 to 6.30 mg l −1 , and the average NO 3 − value was 5.06 mg l −1 ( Table 3). The value of NO 3 − in this lake is low because there is no pollution from solid waste or sewage. Nitrites (NO 2 − ) can be in very high concentrations if the water has decomposing organic matter or if an organic industry releases its wastewater into a river or lake. 23 The acceptable limit of NO 2 − in water according to Directive 75/440 BE is 0.005 mg l −1 . The results showed that the measured NO 2 − of all water samples ranged from 0.002 to 0.003 mg l −1 , and the average NO 2 − value was 0.0025 mg l −1 ( Table 3). The low nitrite concentrations in Përlepnica Lake are good result because this expresses inactivity of decomposition of organic matter in the water.
During the analysis of samples (SP 1 -SP 6 ), all physicochemical parameters of the Përlepnica Lake were in accordance with the Directive 75/440, except NTU, which was slightly higher, and DO, which was less than the permitted concentration EC 74/440 (Table 3). Based on Table 4, it can be seen that Përlepnica Lake has higher values in physicochemical parameters compared to Skadar Lake.

Metal concentration in sediment
Heavy metal pollution has been widely studied because it causes environmental and public health problems worldwide. 29 Among chemical pollutants, heavy metals are of great concern because they are known to inflict several health disorders in humans. 30 Iron (Fe) can initiate cancer mainly by the process of oxidation of DNA molecules. 31 Concentrations of Fe in all samples are very high (1.69-1.96 mg kg −1 ; Table 5) and the samples are included in a single group .
However, according to "The Dutch List", Fe has no criterion value because it is a massive element in sediments. The average concentration of Fe in Përlepnica Lake (Kosovo) was 1.83 mg kg −1 , Badovc Lake had very high concentration of 19084 mg kg −1 , while no Fe was present in Balaton Lake and Skadar Lake ( Table 6).
Cadmium (Cd) has toxic effects on the reproductive system, fertility, causes kidney damage, renal disorder, and is carcinogenic. 32 The lower and higher values of Cd are divided into two groups: (i) The first group of samples that included SP 1 , SP 3 , SP 4 , SP 5 , and SP 6 contained high concentrations of Cd (6.05-10.40 mg kg −1 ) and is presented in category B of sediment pollution (Table 5). (ii) The second group of samples that included SP 2 , SP 7 , and SP 8 contained low concentrations of Cd (3.73-4.31 mg kg −1 ), which is presented in category A of sediment unpolluted (Table 5).
Copper (Cu) causes toxic effects such as liver damage, Wilson disease, insomnia, and gastrointestinal problems. 32 The lower and higher values of Cu are divided into two groups: (i) The first group of samples that included SP 1 , SP 2 , SP 3 , SP 4 , SP 5 , SP 6 , and SP 8 contained high concentrations of Cu (52.31-89.99 mg kg −1 ), and is presented in category B of sediment pollution (Table 5). (ii) The second group of samples that included SP 7 contained a low concentration of Cu 40.24 mg kg −1 , and is presented in category A of sediment unpolluted ( Table 5).
The average concentration of Cu in Përlepnica Lake sediment was 61.08 mg kg −1 . It was almost the same value as in Badovc Lake where the average concentration of Cu was 61.21 mg kg −1 , and the concentration of these two lakes was much higher compared to Balaton and Skadar Lake ( Table 6).
Manganese (Mn) is considered an essential micronutrient for the metabolic process. Its toxicity alters physiological, biochemical, and molecular processes at the cell level. 33,34 The values of Mn in all samples were very high (505.56-930.92 mg kg −1 ) and the samples were included in a single group in category C of sediment significant pollution (Table 5).
Nevertheless, Mn according to "The Dutch List" has no criterion value because it is a massive element in soil, but the average concentration of Mn (708.65 mg kg −1 ) in Përlepnica Lake was very high compared to the Badovc Lake Mn (660 mg kg −1 ), while in Balaton Lake (Hungary) and Skadar Lake the concentration of Mn in the sediments was not present (Table 6).
Nickel (Ni) has toxic effects causing dermatitis, nausea, chronic asthma, coughing, a human carcinogen, reproductive effects, and respiratory cancer. 32 Concentrations of Ni in all samples were low (31.46-44.62 mg kg −1 ) and the samples were included in a single group in category A of sediment unpolluted (Table 5).
In Përlepnica Lake, the average concentration of Ni in sediment was 37.27 mg kg −1 , while in Badovc Lake the aver-  age concentration of Ni was 305 mg kg −1 , and this concentration was very high compared to Përlepnica, Balaton, and Skadar lakes ( Table 6).
Lead (Pb) is a highly toxic pollutant, and its effects on the human body are devastating. 35 The values of Pb in all samples were very high (123.38-346.60 mg kg −1 ) and the sam-ples were included in a single group as presented in category B of sediment significant pollution ( Table 5).
The average concentration of Pb in the sediment of Përlepnica Lake was 264.26 mg kg −1 , a very high concentration compared to Badovc, Balaton, and Skadar lakes (Table 6).
Zinc (Zn) has toxic effects on the nervous system and its fumes can cause skin problems. 36 Values of Zn in all samples were very high (300.68-927.76 mg kg −1 ) and the samples were included in a single group as presented in category C of sediment significant pollution ( Table 5).
The concentration of Zn in Përlepnica Lake was quite high, and the average concentration in sediments was 604.55 mg kg −1 , while in Badovc Lake the average concentration of Zn was 122 mg kg −1 . Balaton and Skadar lakes Zn concentration was not high ( Table 6).
Mercury (Hg) is recognized as a toxic, persistent, and mobile contaminant that does not degrade into the environment. 36 Concentration of Hg in the sediment in samples SP 1 -SP 8 was detected at the level of 1 ppb, and fortunately did not appear in the sediment of Përlepnica Lake (Table 5).
According to this study, it can be assumed that the sediment of Përlepnica Lake has higher sediment mass compared to the other lakes mentioned.

Metal concentration in water
Sediments have one of the most important roles in the water environment, as they are usually the main collector of contaminants and pollutants introduced into water systems -substances dissolved in water are bonded on the solid particles over time, and finally trapped in bottom deposits. 38 The amount of available ecological water is a key factor that determines the function of the ecosystem. 39 Also, the monitoring of heavy metals is extremely important in an aquatic environment used by the population for drinking water. The concentrations of HMs in this lake with the analysed samples SP 1 -SP 6 were in accordance with EC 75/440: Mn 0.002-0.004 mg l −1 , Zn 0.051-0.091 mg l −1 , Cr 0.033-0.038 mg l −1 , Cd 0.002-0.004 mg l −1 , Pb < 1 ppb, and Ni < 1 ppb ( Table 7).
The concentration of Cu in some samples was above the concentration permitted by Directive EC 75/440. Thus, they were divided into two groups: (i) samples SP 3 and SP 4 were in accordance with EC Directive 75/440 (Table 7). (ii) samples SP 1 , SP 2 , SP 5 , and SP 6 were not in accordance with EC directive 75/440 (Table 7) From the analysed water and sediment samples, the concentration of heavy metals in the sediments is beginning to penetrate the water of Përlepnica Lake. This will affect the consumers of this water. Table 8 shows the comparison of HMs concentrations in the water of Përlepnica, Badovc, and Batlava Lakes.

Conclusions
In the current study, several HMs (Fe, Cd, Cr, Cu, Mn, Ni, Pb, Zn, and Hg) were determined to cause future prob-lems for the aquatic environment and the inhabitants of this municipality. In the water, the average concentration of Fe was 0.29-0.31 mg l −1 , Cu was above 0.02 mg l −1 , and Zn was 0.06-0.07 mg l −1 . The water analyses of Përlepnica Lake showed that the concentrations of Fe, Cu, and Zn in the water are not in the accordance with EU Directive 75/440.
In addition, sediment analysis showed that the average content of the HMs was as follows: Pb -264.26 mg kg −1 , Fe -1.83 mg kg −1 , Cd -6.32 mg kg −1 , Cu -61.08 mg kg −1 , Mn -708.65 mg kg −1 , and Zn -604.55 mg kg −1 , which exceeded the permissible limits according to the instructions of the New Dutch List. From the results obtained in sediment and water, it is preferable to continuously monitor the lake, because many HMs are too close to penetrate the water and thus start water pollution of Përlepnica Lake. In addition, according to the results obtained in the analytical laboratory for heavy metals in water and sediments, the authors propose that the bed (bottom) of Përlepnica Lake should be cleaned or the sediment mechanically removed, as it contains many heavy metals and can cause serious problems soon.