Microchemical Journal 99 (2011) 492–502

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Microchemical Journal

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A study of trace element contamination in river sediments in Serbia usingmicrowave-assisted aqua regia digestion and multivariate statistical analysis

Sanja Sakan a,⁎, Dragana Đorđević a, Gordana Dević a, Dubravka Relić b, Ivan Anđelković c, Jelena Ðuričić d

a ICTM, Chemistry Centre, University of Belgrade, Njegoševa 12, P. O. Box 815, Belgrade 11000, Serbiab Faculty of Chemistry, Applied Chemistry, University of Belgrade, P. O. Box 51, Belgrade 11000, Serbiac Innovation Centre of the Faculty of Chemistry, Belgrade 11158, Serbiad Higher Education Institution for Technology Studies, Šabac 15000, Serbia

⁎ Corresponding author at: ICTM, Chemistry CenNjegoševa 12, P. O. Box 815, Belgrade, Serbia. Tel.: +382636 061.

E-mail address: ssakan@chem.bg.ac.rs (S. Sakan).

0026-265X/$ – see front matter © 2011 Elsevier B.V. Adoi:10.1016/j.microc.2011.06.027

a b s t r a c t

a r t i c l e i n f o

Article history:Received 27 May 2011Received in revised form 30 June 2011Accepted 30 June 2011Available online 8 July 2011

Keywords:Aqua regiaRiver sedimentsContaminationDanubeSava

The aim of this study was the evaluation of the trace element contamination level in sediments of the mostimportant rivers in Serbia and their tributaries. The determination of the aqua regia soluble contents of 12micro- andmacro-elements (Ca, Cd, Co, Cr, Cu, Fe, Mn, Pb, Ni, Zn, Be and V) in sediments was developed by themicrowave digestion technique combined with inductively coupled plasma atomic emission spectrometry.Correlation analysis and principal component analysis distinguishes factors of lithogenic and anthropogenicorigins. The Fe, Mn, Be and V contents are controlled by a regional lithogenic high background factor, while Cd,Cr, Pb, Ni, Zn and Cu are recognized as tracer of pollution. For Co, mixed sources from both lithogenic andanthropogenic inputs were evidenced.The investigated sediment of the major rivers and their tributaries in Serbia showed high concentrations ofmetals, especially of Cd, Pb, Cu and Zn, which may cause serious environmental impacts. Rivers which flowinto the Danube from its entrance into Serbia significantly influence the chemical load of the water andsediments.The experimental study was conducted using two BCR standard reference materials. The calculated accuracyand precision confirmed the good performance of the adopted procedures.

tre, University of Belgrade,1 11 3336 801; fax: +381 11

ll rights reserved.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Many trace elements are often problematic environmentalpollutants, with well-known toxic effects on living systems [1].According to numerous studies, the pollution sources of heavy metalsin environment are mainly derived from anthropogenic sources [2].The accumulation of heavy metals in environmental samples such assoils and sediments causes a potential risk to human health due to thetransfer of these elements in aquatic media, their uptake by plants andtheir subsequent introduction into the food chain [3]. Largeuncontrolled metal inputs from industrial sources have contributedto increase pollution in rivers [4–10]. Sediments in rivers not only playan important role in influencing the pollution of river water, but alsocan be used to record the history of river pollution. The determinationof the total content of heavy metals in sediments is particularly usefulto collect information on the genesis of the level of sedimentcontamination. Sample digestion is often a necessary step beforedetermining metal concentrations. Around the world, many studies

have evaluated the heavy metal concentrations in sediments in soilsusing the aqua regia digestion procedure [11–13]. The aqua regia (3:1,v/v, HCl to HNO3) digestion procedure is considered adequate foranalyzing the total-recoverable heavy metals in soils and sediments.The aqua regia digestion method (USEPA Method 3050) wasdeveloped for the determination of heavy metals in the soils of theU.S.A. [14]. The DIN 38414-S7 standard method [15] was also used forthe determination of the aqua regia extractable metal content [16].This digestion procedure is so widely used that the EuropeanCommunity Bureau of Reference has certified several soil andsediment samples based on it, in addition to the total elementalconcentrations [17,18].

Microwave-assisted acid solubilization has proved to be the mostsuitable method for the digestion of complex matrices such as soilsand sediments containing oxides, clay, silicates and organic sub-stances. Microwave-assisted sample digestion techniques havebecome popular and are widely used [19]. This procedure allowsshorter digestion times and good recoveries also for very volatileelements. At present, there are various official methods which employdifferent acid mixtures and microwave heating systems: US-EPAmethod 3050B, US-EPA method 3051 and US-EPA method 3052 [11].

In this research, the content of micro- andmacro-elements in riversediments of the most important rivers which flow through Serbia as

493S. Sakan et al. / Microchemical Journal 99 (2011) 492–502

well as their tributaries was examined applying the microwave-assisted, aqua regia digestion method. Based on the results, thecontamination level of the river sediments with the examined toxicelements was evaluated and the similarity in the behavior and originof these elements were determined.

The objectives of the study were to: (1) determine the contents ofthe element Cd, Co, Cr, Cu, Fe, Mn, Pb, Ni, Zn, Be and V; (2) define theirnatural or anthropogenic source using principal component analysis(PCA) and correlation analysis (CA); (3) identify risks of toxicity fromthe sedimentary metals by comparison with Quality Guidelines forSediments and (4) determine the Ca, C and H concentrations inthe sediments to ascertain the substrates of the investigated traceelements.

Since three international rivers (the Tisa, Sava and Danube) flowthrough Serbia and the fact that the Tisa and the Sava flow into theDanube in Serbia, examination of the quality of the water andsediments of these rivers is very important for all European countriesthese rivers flow through. The investigations that were the subject ofthis study are the first systematic investigations realized in Serbia asthey include, together with those of the Tisa, Sava and Danube,sediments from their tributaries. Methods for which their calculatedaccuracy and precision confirmed their good performance wereapplied for the determination of the elements. The results of thisinvestigation have implications for the regional management of theTisa, Sava and Danube Rivers and should be used for comparison withfuture sediment quality data. In addition, such scientific andpreventive approaches based on a better understanding of the source,fate and effects of metallic contaminants in an aquatic system are alsoof great interest for the development of pollution control andsediment-remediation strategies and for an estimation of the qualityof the other polluted rivers systems in Europe and the World.

2. Materials and methods

2.1. Study region

The Danube is Europe's second longest river after the Volga. TheDanube River (Fig. 1) flows through or functions as part of the bordersof ten countries: Germany, Austria, Slovakia, Hungary, Croatia, Serbia,Bulgaria, Moldova, the Ukraine and Romania, and it empties into theBlack Sea via the Danube Delta in Romania and the Ukraine.

The Sava is a river located on the southern fringe of Central Europe,a right side tributary of the Danube River at Belgrade. It flows throughthree countries: Slovenia, Croatia and Serbia.

The Tisa is one of the main rivers of Central Europe. It flowsroughly along the Romanian border and enters Hungary at Tiszabecs;downstream, it marks the Slovak–Hungarian border, passes throughHungary and flows into the Danube in northern Serbia (Vojvodina).

Numerous industrial installations located on the banks of theDanube or its tributaries have contributed to important anthropo-genic contamination. Pollution stemming from power plants, oilrefineries and fertilizer plants can cause contamination of surround-ing air and waterways.

The Danube drainage Basin, particularly the lower Danubecomprising Hungary, Serbia, Bulgaria and Romania, has a long historyof base and precious metal mining and metallurgy that have releasedcontaminant metals into the riverine environment [20]. The potentialenvironmental implications of the mining activities in the Danubedrainage Basin were highlighted by the dam failure of the Aurultailings, which occurred in Maramures County in north-westernRomania in January 2000 [21]. The release and subsequent dispersal of100,000 m3 ofmetal and CN-richwater and sediment through the Tisaand Danube River systems caused widespread ecological damage [22]and highlighted the issues related to transboundary dispersal ofcontaminants [20]. In addition, in the Tisa Basin are the MatraMountains of eastern Hungary, which comprise magmatic exceptions

to Hungary's sedimentary-dominated geology [20]. Mining in theMatra Mountains has focused on the Cu/Au and the Pb/Zn deposits.Metal mining in Serbia is mainly focused on the Bor and MadjanpekCu deposits [23] and the Trepča deposits.

2.2. Sampling and sample preservation

The sampling was performed during the year 2008. For thisinvestigation, 35 samples of river sediment from 15 rivers in Serbia(the Danube, Sava, Tisa, Ibar, Great Morava, West Morava, SouthMorava, Nišava, and Tamiš, the canal DTD, the Topčiderska River, thePorečka River, the Kolubara, Pek and Toplica) were taken. From thelarger rivers, sampling was conducted at several locations (Fig.1). Thesediment samples were stored at 4 °C in order to prevent changes inthe chemical composition of the sediments. The contents of themicro-and macro-elements were determined in the granulometric fractionb63 μm of the bottom sediment samples (“grab” — the sample), afterair drying for 8 days [24].

The moisture content of each sample was determined by drying aseparate 1 g sample in an oven (105±2 °C) to constant weight. Fromthis, a correction to dry mass was obtained, which was applied to allreported metal concentrations.

2.3. Chemical analyses

2.3.1. InstrumentationMicrowave digestion was performed in a pressurized microwave

oven (Ethos 1, Advanced Microwave Digestion System, Milestone,Italy) equipped with a rotor holding 10 microwave vessels (PTFE).

The analytical determination of Ca, Cd, Co, Cr, Cu, Fe, Mn, Pb, Ni, Zn,Be and V was realized with an atomic emission spectrometer with aninductively coupled plasma iCAP-6500 Duo (Thermo Scientific, UnitedKingdom). The detector was a RACID86 Charge injector device (CID).In the iCAP 6000 Series of spectrometers, the following componentshave been thoroughly optimized and implemented: robust instru-ment optics based on 3 castings, ergonomic design, optical systemwith aspherical concave and convex mirrors, high-performancedetector with CID86 chip, compact solid state generator and torchdesign.

This instrument operates sequentially with both radial and axialtorch configurations. The analytical performance of the iCAP 6000Series is demonstrated by improved detection limits, enhancedlinearity, superior long-term stability and high resolution images.

External standard solutions were prepared from 1000 mg L− 1

stock metal solutions. For minimized interferences, a multi-elementstandard stock solution was prepared in which the ratios of themetalsin this multiple element calibration standard were analogous to theirratios in samples. These multi-element standards and blanks wereprepared in the same matrix as the extracting reagents to minimizematrix effects and for background correction. The instrumentalcalibration was checked every 10–12 samples.

2.3.2. Aqua regia procedureAbout 500 mg of sample and 12 ml of aqua regia (9 ml HCl and

3 ml HNO3) were transferred into a microwave vessel [15,25]. Duringthe digestion, the temperature of the microwave oven was raised firstto 165 °C in 10 min. (holding time 0 s), then to 175 °C in 3 min, atwhich temperature it was kept for 10 min (max power 1200 W) [26].One control vessel per rack contained a temperature and pressureprobe. The vessels were removed from the oven when thetemperature was less than 50 °C and pressure less than 69 kPa. Atthe end of a digestion cycle the vessels were cooling at roomtemperature before proceeding in sample preparation to assuresecurity rules in operating steps and avoid a leak of volatilesubstances. After cooling, the sample digests were filtered with aWhatman No. 42 filter paper, since microwave digestion left solid

Fig. 1. Map of the Danube River with sample locations map.

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residues in the digests; then they were transferred into a 100 ml flaskand brought to volume.

For each digestion, reagent blanks were obtained. The blanks wereprepared in the same way as the samples without the sediments andCRMs. Blank samples, reflecting blank values for the sampling bottles,reagents, digestion vessels, filtration and any contamination duringthe whole procedure were prepared and digested in parallel with thebatch of samples, by the same procedure, by the use of the samequantities of all the reagents as in the determination but omitting thetest portion. The filtered residue was rinsed twice with 5 ml of waterand the solution was made up to 100 ml. All solutions were preparedwith Milli-Q deionised water. The above procedure was also used toobtain blank samples and all samples were blank-corrected. Theconcentrations obtained for all metals in the blanks were close to thedetection limit of themethod, indicating that contaminationwas not aproblem in the digestion and filtration.

The digests and the blanks were analyzed with the ICP-OESspectrometer. Each element's analytical wavelength was optimizeddaily before calibrating the instrument. The ICP was calibrated usingan acid blank and metal standard. All calibration curves for tracemetals had a correlation coefficient of R2≥0.995.

The acidmatrix baseline correctionwavelengths for eachmetalwereselected by comparing the observed signal intensities for the acid blank,analyte standard, and sediment digestion solutions. The followinganalysis sequencewas applied:first the blank, then the standards and attheendof the sequence, the samples. Theblank intensitywas subtractedfrom both the standard and the sample intensities. The wavelengthsused in this analysis were: 214.4 nm for Cd, 266.6 nm for Cr, 220.3 nmfor Pb, 257.6 nm for Mn, 231.6 nm for Ni, 213.8 nm for Zn, 235.3 nm forCo, and 217.8 nm for Cu. We didn't use the internal standards.

All the chemicals used in this work were of analytical reagentgrade. All glassware and plastic material used were previously treated

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for 1 week in 2 M nitric acid and rinsed with distilled water and thenwith ultrapure water.

2.3.3. Certified reference materialsCertified reference materials were supplied by The Community

Bureau of Reference Sample (BCR): BCR-143R ‘Sewage sludgeamended soil’ and BCR-146R ‘Sewage sludge from industrial origin’.The materials were handled according to the supplier's specifications.

2.3.4. Determination of C and H contentThe total carbon content and hydrogen content in the investigated

sediments were determined by elemental analysis, using a Vario EL IIIC,H,N,S/O elemental analyzer (Elementar). The total carbon content inthis research represents the sum of the inorganic and organic carbon.

2.4. Statistical analysis

To identify the relationships among the investigated elements inthe sediments and their possible sources, Pearson's correlationcoefficient analysis and principal component analysis (PCA, R and Qmodes) were performed using the commercial statistics softwarepackage SPSS version 11.5 for Windows.

3. Results

The results of the calculations of the accuracy and precision for theapplied method are given in Table 1, from which it can be seen thatthe measured concentration values are in excellent agreement withthe certified values of the BCR 143 and BCR 146 reference materials(the accuracy ranged from 81.8 to 117%). The precision is expressed asthe relative standard deviations. The relative standard deviations ofthe means of duplicate measurement were less than 10% (from 0.3 to7.2%).

In many investigations, in which were applied the same methodand same or similar certified materials as well as in this study, theresearchers obtained similar results for the accuracy of the deter-mined elements. The European Standard Bt/TF151 WI CSS 99025A(2007) [27] specifies methods for digestion of sludge, treatedbiowaste and soil by the use of aqua regia. The obtained accuracyfor the BCR 146R digestionwithmicrowave assistedwith aqua regia inclosed vessel for most of elements were in range of 80–90% (Cr, Co, Pb,Mn, and Ni) and these results are similar with our results. In thisstandard is concluded that recovery rates for CRM-sewage sludge BCR146 are in generally high and that with aqua regiawill not necessarilyrelease elements completely.

In the paper Chen and Ma [28] stated that satisfactory precisionand accuracy were required to be within±20% and between 80 and120%, respectively. For Method 3501a for trace metal analysis usingcertified and Florida soils it is shown that recoveries of Ag, As, Cd, Cu,Hg, Mg, Mn, Pb, Zn, Fe, Ca, and P (80–106%) fell within the totalrecoverable target criteria. However, recoveries of Sb, Ba, Cr, Mo, Ni,

Table 1Accuracy and precision of applied methods.

Cd Cr Pb

BCR 143Certified value (mg kg−1) 72.0 426 174Concentration found (mg kg−1) 70.5 469 156Accuracy (%) 97.9 110 89.7t values (calculated)a 3.357 6.569 3.589

BCR 146Certified value (mg kg−1) 18.4 174 583Concentration found (mg kg−1) 16.4 148 494Accuracy (%) 89.2 85.0 84.7t values (calculated)a 4.434 7.112 11.839

a Confidence level of 95%.

Se, K, and Al (22–78%) did not fall within the target criteria. There wasalso shown problem with low recoveries of Cr, which have beenreported in the literature. In this paper is summarized that differencesin acid types and concentrations, temperatures, and pressures duringdigestion, and in matrices for the digestate and total dissolved solidafter digestion could also have caused bias and low recoveries.

In the paper [29] it was shown that that recovery for elements forthe BCR 176 was in range of 81% to 105%, which is acceptable in termsof quality assurance and quality control criteria. In the EPA Method302.0 [30] as a requirement for accuracy is demanded that averagerecovery must be within±20% of the true value.

In general, it can be concluded that different factors, such asapplied methods, certified materials, differences in acid types andconcentrations, temperatures, and pressures during digestion, and inmatrices for the digestion and total dissolved solid after digestionmaycause low recoveries. These factors may be the reason for the lowaccuracy for the BCR 146. More reproducible and accurate analyticaldata were obtained for BCR 143 in this paper. Different resultsobtained for BCR 143 and BCR 146 with same parameters of pressure,temperature, digestion time and power, showed that themajor sourceof variability in this analysis of certified materials could be due tocomplex matrix of materials (sewage sludge amended soil andsewage sludge from industrial origin) in which the elements inquestion are widely distributed. This matrix is thus difficult todecompose. Since that obtained values for analytical accuracywhich isdefined as percentage recovery for both of BCR materials were inagreement with required quality control criteria (80–120%), andcalculated precision was within ±20%, it can be concluded that theproposed method is precise and accurate.

A variety of Student's t-test can be utilized to evaluate methods forpurposes of method development or quality control. In order tocompare an experimental value with a CRM value to validate amethod/procedure, the following t-test is utilized:

� t = sqrt Nð Þ· μ – xð Þ = s;

where μ is the value of the certified reference material, x is defined asthe mean or average of a limited number of samples drawn from apopulation of experimental data, t is the Student's t-value, obtainedfor N−1 degrees of freedom, at a pre-selected confidence interval,typically a 95% confidence interval and s is standard deviation [31].Consulting the t-table at 95% confidence interval at N−1, the t-valueis 12.706 (N=2 in this case). The concentrations obtained for the twocertified materials in this paper are shown in confidence level of95%. In this case, the calculated t-values are lower than the tabulatedt-value and there is not statistical difference. Therefore, the appliedmethod is considered a valid procedure.

The contents of the elements in the investigated sediments (asmin, max, AM and SD), values for the MAQ (Maximum AllowedQuantity) for soil [32], background values calculated for theinvestigated locality, the element concentrations in the continental

Mn Ni Zn Co Cu

858 296 1063 11.8 128822 272 960 12.0 11195.8 92.0 90.4 102 86.44.488 5.091 3.622 0.244 5.029

298 65.0 3040 6.5 831270 54.0 2622 7.6 68090.7 83.1 86.2 117 81.812.654 10.444 5.800 0.918 12.097

Table 2Element content in the investigated elements (mg kg−1) and quality guidelines for sediments.

Min Max AM SD MAQa BV b Crustc Canada SQGd CSSTg

ISQGe PELf TECh MECi PECj

Cd 0.30 9.01 2.43 1.81 2 0.003–1.967 0.1 0.6 3.5 0.99 3.0 5.0Co 5.29 26.66 18.40 4.27 ndk 9.852–26.948 24 nd nd nd nd ndCr 26.69 119.5 53.62 23.08 100 13.80–86.22 126 37.3 90.0 43 76.5 110Cu 21.80 675.8 78.02 109.1 100 16.84–90.63 25 35.7 197 32 91 150Fe 20,299 50,230 40,281 6076 nd 28,128–52,433 43,200 nd nd 20,000 30,000 40,000Mn 507.1 3184 1113 469.5 nd 441.5–1662.4 716 nd nd 460 780 1100Pb 16.58 322.9 67.67 55.95 100 16.87–82.997 14.8 35.0 91.3 36 83 130Ni 32.04 283.6 83.19 61.60 50 28.56–51.40 56 nd nd 23 36 49Zn 67.58 1207 342.5 235.6 300 74.86–325.5 65 123 315 120 290 460Be 0.28 2.18 1.36 0.36 nd 0.634–2.091 2.4 nd nd nd nd ndV 40.28 110.0 87.34 14.53 nd 58.28–116.4 98 nd nd nd nd ndCa 8492 82,977 39,806 21,132 nd nd 38,500 nd nd nd nd nd

a MAQ — Maximum Allowed Quantity [32].b Background value, calculated as: mean±2 SD, after the outliers were excluded.c Element concentrations in the Continental Crust [33].d Summary of existing Canadian Sediment Quality Guidelines (freshwater sediment) [34].e ISQG — interim sediment quality guideline — below which harmful effects are unlikely to be observed.f PEL — Probable effect level-above which harmful effects are likely to be observed.g Consensus-based sediment quality guidelines recommendations for use & application developed by [35].h TEC — treshold effect concentrations.i MEC — Midpoint effect concentration — concentration midway between the TEC and PEC concentrations (TEC+PEC/2=MEC).j PEC — probable effect concentrations.k nd — no data.

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crust [33], the Canadian Sediment Quality Guidelines for elements infreshwater sediments [34] and the CSST-sediment quality guidelines[35] are given in Table 2. The background values were definedusing the arithmetic mean plus or minus two standard deviations[mean±2×SD], after exclusion of the outliers.

The contents of elements in some of river sediments (Danube,Danube tributaries [36–39], Sava [40] and Tisa [41–43]) in differentcountries through which these rivers flow are shown in Table 3.

The contents of the investigated elements by location are shown inFigs. 2 and 3.

4. Discussion

4.1. Content of the elements in the investigated sediments andcomparison with standards and similar results for river sediments

Beryllium: The values for the Be content in the sediments (b than2.5 mg kg− 1) are close to calculated background concentrations andthe Be concentrations in the continental crust (Table 2), which

Table 3Content of elements (mg kg−1) in different river sediments.

Danubea Danubeb Danubec Danube-tributariesc

Cd 0.34–2.63 2.12–4.03 b1.1–25.9 b1.1–32.9Co nd nd nd ndCr 22.79–57.98 51.8–112.5 35.3–139.0 26.5–556.5Cu 27.86–338.8 17.8–57.6 31.3–662.9 31.3–8088Fe 20,994–35899.5 nd 17,600–56,700 20,000–64,400Mn 612.7–1236.4 nd 442–1379 486–1655Pb 37.77–74.99 19.4–40.9 14.7–107.6 18.1–541.8Ni 31.25–60.16 23.7–116.4 24.6–142.8 17.5–173.3Zn 156.2–406.9 49.4–389.5 83–622 78–2010

a The Danube River sediments, from Zemun to Tekija, Serbia [36].b The Danube River sediments, from Smedervo to Radujevac, Serbia (location from accumc Sediments along the entire course of the river Danube (from Neu-Ulm to the Danube Dd Danube river sediments (section through Serbia) [39].e The Sava River sediments — Sava River drainage basin within Slovenia and Croatia [40]f Tisa River, Serbia (total digestion), Sakan and Đorđević [41].g Kiss-Janosne-Holt Tisza, an oxbow lake located in the upper part of the Tisza River in Hh Average content, Tisza River sediment (Hungary) [43].

indicates a dominant geochemical origin of this element in theinvestigated sediments.

Cadmium: The highest content of Cdwas observed in the Ibar, Tisa,Sava, Morava, South Morava, Nišava, Kolubara and Pek Riversediments (Fig. 2). The Cd contents in the sediment from the Ibarand in the Sava sediment (at the location Šabac) were greater than thePEL and PEC levels. These results indicate the existence of contam-ination with Cd in most of the studied river systems. The obtainedresults are in accordance with the results for the Cd content in Savasediment in Slovenia, where higher contents were found in the upperflow [44]. The highest value for Cd in the Danube sediment was foundin the lower stretch of the River Danube near the Irongate, which isconsistent with previous results [38]. For the Ibar [45] and for the Tisain Serbia and Hungary [41–43], the existence of anthropogenic Cdsources was also shown.

Cobalt: The values of the Co contents in the sediments were closeto or somewhat higher than the background concentrations and crustconcentrations, except for the Sava, Ibar, Morava and West Moravasediments, for which contents up to 120 mg kg− 1 were observed.

Danubed Savae Tisaf KSHTg Tiszah

0.7–3.2 bgd–12.44 1.90–3.97 0.7±0.4 2.5nd 0.83–51.8 nd 21.2±2.3 ndnd 5.28–150.7 22.81–40.8 110±13.5 265.4–106.1 3.19–147.9 39.5–126 62±14 1615900–51,600 2318–69,800 25,498–41,865 nd nd129.7–726 50.33–13,700 936–2202 nd ndnd 8.19–229 31.8–89.6 48±34 261nd 7.96–172.6 24.1–47.6 70±8 36nd 11.92–2760 199–377 216±55 476

ulation of Iron Gate I, Iron Gate II, and downstream from Iron Gate II) [37].elta and the Black Sea) and in several of its main tributaries for the first time [38].

.

ungary [42].

Fig. 2. Content of Be, Cd, Co, Cr, Cu and Ni in investigated sediments (I1, I2 — Ibar, V1, V2 — Great Morava, Z1, Z2 — West Morava, JM — South Morava, N1, N2 — Nišava, Ta — Tamiš,DT — canal DTD, Tr — Topčiderska River, Pr — Porečka River, Ko — Kolubara, Pe — Pek, To — Toplica). Explanation: BV — background value, Cr — continental crust, PEL — probableeffect level, and PEC — probable effect concentrations.

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Chromium: Higher contents of Cr were found in the sediments ofthe Sava, Ibar, and Great andWest Morava in respect to the other riversediments (Fig. 2). These results indicate the existence of local sourcesof Cr contamination. In the West Morava River Basin Cr ore exists,

which can be the cause of the increased content of chromium insediments. The other values for the Cr content in the sediments arewithin the range of background concentrations and crust concentra-tions (Table 2).

Fig. 3. Content of Fe, Mn, Pb, V and Zn in investigated sediments (I1, I2 — Ibar, V1, V2 — Great Morava, Z1, Z2 — West Morava, JM — South Morava, N1, N2 — Nišava, Ta — Tamiš,DT — canal DTD, Tr — Topčiderska River, Pr — Porečka River, Ko — Kolubara, Pe — Pek, To — Toplica). Explanation: BV — background value, Cr — continental crust, PEL — probableeffect level, and PEC — probable effect concentrations.

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Copper: In most of the sediments, the content of Cu was lessthan 100 mg kg− 1 (Fig. 2), except in the sediment samples of theWest Morava and Porečka River (Fig. 1) and very high concentra-tions of Cu in the Pek (more than 600 mg kg− 1). Higher values ofCu in these three river systems indicate the existence of anthropo-genic sources of Cu. The source of the Pek River is near toMajdanpek, and since there is a Cu mine in Majdanpek, it isjustifiable to assume that the origin of the Cu is associated with theexistence of this mine.

Nickel: In some of the sediment samples, the Ni content wasgreater than 50 mg kg− 1 (Sava, Ibar, Great Morava, Morava West,South Morava, Topčiderska River, Kolubara and Toplica, Fig. 2). Theseresults indicate the existence of anthropogenic sources of Ni in thewatersheds of these rivers.

Iron: Tidily uniform distribution of the Fe content, with a highercontent in the sediments of the Tisa, Sava, Ibar, Great, West and SouthMorava River, as well as in Tamiš, Kolubara, Pek and Toplica (Fig. 3).The increased Fe contents in the sediments can be associated with

Table 5Rotated component matrix.

PC1 PC2 PC3 PC4 Communalities

ln Cd 0.704 0.697ln Co 0.657 0.637 0.911ln Cr 0.864 0.909ln Cu 0.935 0.915ln Fe 0.729 0.949ln Mn 0.545 0.533ln Pb 0.898 0.873ln Ni 0.887 0.900ln C 0.948 0.931ln H 0.568 0.563 0.885ln Zn 0.768 0.864ln Be 0.857 0.746ln V 0.839 0.936ln Ca 0.672 0.713Variance 4.248 3.330 2.205 1.979% Variance 30.344 23.784 15.748 14.137

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anthropogenic sources and may also indicate the existence ofminerals with increased Fe contents in the basins of the rivers.

Manganese: The Mn contents in the studied sediments were tidilyuniform in most of the samples, except in the South Morava Riversediment, where the Mn content was somewhat higher (around3000 mg kg− 1).

Lead: In most of the studied sediments, the content of Pb wasabout 50 mg kg− 1 (Fig. 3). In the sediments of the Ibar, Great MoravaandWestMorava River, the Pb content was higher than 100 mg kg− 1.Since that Ibar River is in the watershed of the West Morava, and theWest Morava is in the watershed of the Great Morava river Basin(Fig. 1), it is possible to conclude that the cause of the lead pollution oftheWest and Great Morava is mainly the contaminated Ibar River. Thelandfill Trepča has the greatest influence on the lead and zincpollution of the Ibar, since in this area are located a large number ofproduction and manufacturing capacities of the mining–metallurgicalsystem Trepča — nine lead and zinc mines, three flotations, two ofmetallurgy, the chemical industry and a battery factory. The influenceof the landfill Trepča (nine huge industrial landfills) on river pollutionwas shown previously [46].

Vanadium: The V contents were neatly uniform in the sedimentsamples and ranged from 60 to 100 mg kg− 1. The content of V in thesediments is close to calculated background concentrations and the Vconcentrations in continental crust.

Zinc: Higher contents of Zn were found in the sediment samples ofthe Ibar, Pek, Great Morava andWest Morava River, Tisa and Kolubara(Fig. 1), whereby the Zn content in the Ibar River sediment was over1000 mg kg− 1 (Fig. 3). These results indicate significant anthropo-genic sources of Zn in these rivers. For the Ibar River, Great and WestMorava, the sources of pollution are the same as for lead, i.e., theimpact of the proximity to the landfill and the production andmanufacturing capacities of the mining–metallurgical systems resortof Trepča. The Zn pollution of the Tisa was previously observed and itsorigin was associated with the recent mining accidents in Romania[41–43].

The results of a comparison of the metal contents in the riversediments with the Quality Guidelines for freshwater sedimentspublished by CSST [35], Environment Canada [34] and soil standardsfor Serbia [32] show that at some localities, the contents of Cd, Cr, Cu,Pb, Ni and Zn exceeded the criteria (PEL and PEC), above whichharmful effects are likely to be observed and the concentration levelsof these elements are unsafe when compared with the Serbian MAQ(Maximum Allowed Quantity). These results indicate the existence ofanthropogenic sources of Cd, Cr, Cu, Pb, Ni and Zn in the investigatedarea. The concentrations of Be, V, Co, Fe and Mn are close to thecalculated background, except for some localities where slightlyincreased contents of Fe and Mn were observed. It may be concluded

Table 4Linear correlation coefficient matrix for selected elements in sediment samples.

Cd Co Cr Cu Fe Mn Ni

Ca −0.459⁎⁎ −0.483⁎⁎ −0.640⁎⁎

Cd 0.575⁎⁎ 0.491⁎⁎ 0.544⁎⁎ 0.385⁎ 0.4Co 0.728⁎⁎ 0.362⁎ 0.904⁎⁎ 0.486⁎⁎ 0.6Cr 0.585⁎⁎ 0.9Cu 0.421⁎

Fe 0.661⁎⁎ 0.4MnNiPbCHZnBeV

⁎⁎ Correlation is significant at the 0.01 level.⁎ Correlation is significant at the 0.05 level.

that the river systems polluted with heavy metals in Serbia are: theIbar (Cd, Cr, Ni, Pb, Zn), the Tisa (Cd, Zn), the Great Morava (Ni, Pb,Zn), the West Morava (Pb, Cr, Cu), the Sava (Cd, Ni) and the Pek (Cu,Zn). The influences of the content of toxic elements in the tributarieson the contents of elements in the investigated river systems (IbarRiver, Great and West Morava, Tisa, Sava, Danube) were also shown.

4.2. Statistical analyses

4.2.1. Inter-element relationshipsInter-element relationships can provide interesting information

on element sources and pathways. The element correlations in theinvestigated sediment are listed in Table 4. The relevant data for thesediments showing significant correlations between Ni, Co, Cr, Pb, Znand Fe indicates that the Ni, Co, Cr, Pb and Zn distributions werecontrolled by the same factor, such as Fe oxides and clay minerals andhave a similar origin. Mn oxides are important substrates of Cd and Co.Cu is positively correlated with Cd, Fe, V, Zn and V, which points tosimilarities between Cu, Cd, Zn and V, with clay minerals and Feoxides as important substrates that affect the contents of theseelements in the sediments. Be is correlated with Co, Fe, Mn and V,which indicates geochemical similarities between Be, Co, V and Fe andMn with oxides as well as clay minerals as their substrates. A positivecorrelation exists between Ca and C, suggesting that the dominantnature of C in the studied sediments is carbonate. The lack of positivecorrelations between Ca and C with the other elements indicates thatcarbonates are not important substrates of the investigated elements.These results evidence mutual element dependence in sediments as

Pb C H Zn Be V

0.708⁎⁎ −0.618⁎⁎

74⁎⁎ 0.676⁎⁎ −0.390⁎ 0.795⁎⁎ 0.408⁎

73⁎⁎ 0.678⁎⁎ 0.652⁎⁎ 0.626⁎⁎ 0.531⁎⁎ 0.741⁎⁎

76⁎⁎ 0.690⁎⁎ 0.422⁎ 0.508⁎⁎ 0.371⁎

0.515⁎⁎ 0.456⁎⁎ 0.492⁎⁎

93⁎⁎ 0.577⁎⁎ −0.400⁎ 0.579⁎⁎ 0.577⁎⁎ 0.589⁎⁎ 0.893⁎⁎

−0.373⁎ 0.409⁎ 0.586⁎⁎

0.679⁎⁎ 0.349⁎ 0.495⁎⁎

0.349⁎ 0.838⁎⁎

−0.366⁎

0.378⁎ 0.425⁎ 0.626⁎⁎

0.362⁎

0.697⁎⁎

500 S. Sakan et al. / Microchemical Journal 99 (2011) 492–502

well as existence of a stronger correlation within a certain group ofelements.

4.2.2. Principal component analyses — R modeTo quantitatively evaluate the clustering behavior, PC analysis

with Varimax normalization (PCA-V) was applied and the results aregiven in Table 5 and Fig. 4. PCA was performed on the logarithmvalues of the concentrations of the elements. Four factors originatedwith a cumulative variance of 84.01% for the sediment samples(Table 5). PC1 contributed 30.34% of the total variance, showinghigher loadings for Cd, Co, Cr, Pb, Ni, and Zn. PC1 indicate the likelyinfluence from mining, industrial effluents, etc. and this PC could beconsidered to be dominated by “anthropogenic factor-mixed origin ofelements”. The fact that at some localities the contents of Cd, Cr, Cu,Pb, Ni and Zn exceed the MAQ, PEL and PEC values for the respectiveelement may confirm this assumption. PC2, loaded by Co, Fe, Mn, H,Be, and V and accounting for 23.78% of the total variances, is mainlycontrolled by the “natural factor” of the lithogenic process during theweathering process of natural parent materials, such as rocks and

Fig. 4. Results of PCA (R mode).

soils. Iron is known as an Earth element in analysis [47]. This factorcould be identified as the “high background lithogenic factor” or“natural factor”, since the Be, V and Co content in sediments wereclose to the background concentrations. Cobalt emerges in both PC1and PC2, showing that this metal has a mixed source. PC 3 (15.75%)probably represents carbonates, which are not a significant substrateof the elements studied. PC 4, with a variance loading of 14.14%,showed higher loadings for Cu and H, evidencing the main metalcontribution of Cu coming from anthropogenic sources, dominantlymining activities. This factor could be identified as the “anthropogenicfactor-mining origin”.

4.2.3. Principal component analysis — Q modeApplying the Q mode of PCA the sediments are grouped by

location, whereby four groups of sediment samples were isolated(Fig. 5). One group consists of sediments with the highest content of

Fig. 5. Results of PCA (Qmode): (a) a plot of the scores factor score 3 vs. 1 and (b) a plotof the scores factor score 4 vs. 1.

501S. Sakan et al. / Microchemical Journal 99 (2011) 492–502

toxic elements. These river sediments originated from the riversystems most polluted with heavy metals in Serbia: the Ibar, GreatMorava and West Morava. In this investigation, two samples ofsediments from the West Morava were taken. One sediment samplefrom theWestMorava (marked in the paper with ZM2) belongs to thegroup with the Great Morava and the Ibar, while the other sample(ZM1) belongs to the second group of sediments (Fig. 5). Sedimentlabeled ZM2 was sampled at a distance of 3.8 km from the confluenceof the West Morava into the Great Morava, while the sample labeledZM1 was sampled at a distance of 177.6 km from the confluence. Thisresult indicates a much greater pollution of sediments in the WestMorava River near the confluence, which is a consequence of pollutionsources in its catchment area and the contamination which is derivedfrom contaminated tributaries.

Another sediment sample group (Fig. 5) constitutes sedimentsfrom the major river systems: the Tisa, Sava and Danube, along withthe samples from smaller rivers that have a higher content of some ofthe elements as in the major rivers. The sample of Pek sedimentmakes a separate group in Fig. 5(b) as a result of very large content ofCu in this river.

5. Conclusions

The river sediment samples collected from the major rivers andtheir tributaries in Serbia, showed high concentrations of metals,especially of Cd, Pb, Cu and Zn, which may cause serious environ-mental impacts. The results of PCA and correlation analyses showedthat these statistical techniques were useful in interpreting the largedata set, and for extracting structural information. The conclusionsdrawn from this study are as follows:

1) Comparison of the metal contents in river sediments with theQuality Guidelines for freshwater sediments indicates the exis-tence of anthropogenic sources of Cd, Cr, Cu, Pb, Ni and Zn in theinvestigated area.

2) The concentrations of Be, V, Co, Fe and Mn in the sediments wereclose to the calculated background values, except for some localitieswhere slightly increased contents of Fe and Mn were observed.

3) The river systems polluted with heavy metals in Serbia are: theIbar (Cd, Cr, Ni, Pb, Zn), the Tisa (Cd, Zn), the Great Morava (Ni, Pb,Zn), the West Morava (Pb, Cr, Cu), the Sava (Cd, Ni) and the Pek(Cu, Zn). The rivers which flow into the Danube after its enteringpoint into Serbia (the Tisza, the Sava, the Great and the WestMorava) significantly influence the chemical load of its water andsediment.

4) The results of correlation analysis corroborated those of principalcomponent analysis. Principal component analysis distinguishedfactors of lithogenic and anthropogenic origins of the traceelements: the distribution of Cd, Co, Cr, Pb, Ni and Zn arecontrolled by the “anthropogenic factor-mixed origin of ele-ments”; Co, Fe, Mn, Be and V mainly represent the “highbackground lithogenic factor” or “natural factor” of lithogenicprocesses. Co emerges in two components (PC1 and PC2), showingthat this metal has a mixed source, lithogenic and anthropogenic.Ca and C represent the carbonates that are not a significantsubstrate of the elements studied. Cu and H, representing the“anthropogenic factor-mining origin” evidence that the main Cucontribution comes from the anthropogenic sources, dominantlyfrom mining activities.

5) Applying the Q mode of PCA, the sediments were grouped bylocation, and isolated four groups of sediment samples wereisolated. It can be clearly distinguished that groups consisting ofthe river systems most polluted with heavy metals in Serbia,the Ibar, the Great Morava and the West Morava, were clearlyisolated.

Acknowledgments

This research was supported by the Ministry of Science andTechnological Development of the Republic of Serbia, Grant Nos. 172001and 43007. In addition, we would like to thank the RepublicHydrometeorological Service of Serbia for the sediment samples. Theauthors are grateful to anonymous reviewers whose comments led to agreatly improved manuscript.

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