Heavy Metal Accumulation of Danube River Aquatic Plants – Indication of Chemical Contamination

Cent. Eur. J. Biol. • 3(3) • 2008 • 285–294 DOI: 10.2478/s11535-008-0017-6

Central European Journal of Biology

Heavy metal accumulation of Danube river aquatic plants – indication of chemical contamination

Research Article Slobodanka Pajević*, Milan Borišev, Srđan Rončević, Dragana Vukov, Ružica Igić

Department of Biology and Ecology, Faculty of Natural Sciences, 21 000 Novi Sad, Serbia

Received 2 November 2007; Accepted 14 February 2008

Abstract: In this paper, the ecological status of a section of the Danube River flowing through Serbia from Bezdan to Djerdap was evalutated. Using the chemical composition of water, sediment samples from the littoral zone and dominant aquatic macrophytes, the level of chemical pollution was ascertained. Chemical analyses of the water and sediment indicated that the tributaries flowing into the Danube significantly influenced the chemical load of the water and as a direct consequence, the sediment. The concentration of heavy metals including Cu, Mn and Cd found in plants of the Potamogeton genus, further indicated significant chemical pollution, establishing a clear link between the chemical composition of plant tissues and the chemical composition of water and sediment. This paper therefore describes how the chemical composition of aquatic plants can be used as a reliable indicator for heavy metal pollution of aquatic ecosystems. Keywords: Macrophytes • The Danube River • Potamogeton sp. • Bioindication • Heavy metals

1. Introduction aquatics plants and also, the effect of accumulated metals persistent in plant metabolism have been widely studied [9-11]. Most macrophytes which are primarily Macrophytes are important in the biological monitoring submersed and floating, have the ability to tolerate of aquatic ecosystems, as changes in the composition moderately high levels of heavy metal contamination of the aquatic vegetation are considered a reliable by forming chelates (by binding metal ions to organic biological indicator of the quality of water [1-3]. molecules) and by subcellular compartmentation. In such Seasonal dynamics of macrophyte associations, as aquatic plants, phytochelatines and metalothionines well as the distribution according to structure (species are the main cytoplasmic chelators of heavy metals number, population density), represent important [12]. In addition, the increased activity of metabolic indicators of general ecological circumstances which pathways giving rise to glutathione and organic acids are dominant in aquatic ecosystems [4,5]. Pollution of which act as intracellular ligands of metals and organic aquatic ecosystems may also be estimated based on acids, is important for growth in water and/or sediment the accumulation rate of nutrients and heavy metals. contaminated with heavy metals [13]. Many studies had researched the use of macrophytes While macrophytes accumulate and filter out as indicators of metals bioaccumulation [6-8]. chemical elements from the surrounding environment, However, while macrophytes are useful biomonitors, the physical presence of macrophytes in water systems the bioconcentration of metals in macrophytes may increases the stability of sediment, and, reduces be the result of the exposure to metals in both water eutrophication. In addition, macrophytes are involved in and/or sediments, making it difficult to directly compare bioremediation due to their high tolerance to metals and between the concentrations measured in plants and in the affect on ion solubility through the release of O from the environment (i.e., water or sediments). 2 their roots [14]. Consequently, macrophytic vegetation Chemical, biochemical, and biophysical mechanisms may be used in purification of natural aquatic resources, of uptake and accumulation of heavy metals into various

* E-mail: [email protected] 285 Heavy metal accumulation of Danube river aquatic plants – indication of chemical contamination

substratum and littoral zone. Permanent monitoring of chemical composition of water and monitoring of the distribution and abundance of aquatic plant species are useful tools in outlining programs for the sustainable development of aquatic ecosystems. The Danube, like other river systems, is affected by human activities resulting in contamination of the water and its littoral zone. Pollution stemming from power plants, oil refineries and fertilizer plants can cause contamination of surrounding air and waterways. Consequently, in order to cultivate effected areas of once arable land, one must address not only the contamination of the Danube but also contamination coming from other tributaries. Figure 1. The Danube flow portion through Serbia. While commercial use of phytoremediation is a area, representing a part of the Deliblato Sands. This plauisble way to purify contaminated areas, the role of protected area has no pollution sources to deplete its macrophytes in the complex pathways of nutrient and aquatic ecosystems. The Smederevo metal smelter (11) heavy metal cycling, in aquatic ecosystems must first and the Kostolac thermal power plant (13) are a serious be understood. industrial threat declining water quality of the Danube. Our objective was to determine the ecological On each sampling location, three patches of each status of littoral zone of the Danube River in Serbia, plant species were collected and pooled into one by assessing the heavy metal content of dominant uniformed sample. Only vegetative parts of plants were macrophytes. The flow section of the Danube River selected (leaves with stems). Plant material was rinsed utilised in this study starts at 1433 river kilometers in deionised water, dried and prepared for analyses (rkm) on the state border with Hungary and Croatia following standard methods for the examination of water and ends at 845 rkm on the state border with Romania and wastewater [16]. The concentrations of heavy metals and Bulgaria. The results obtained, form the basis of an were determined after drying at 450ºC and treatment ecological monitoring system for this aquatic area and with 25% HCl. Concentrations of Fe, Mn, Cu and Cd highlight the importance of macrophytic vegetation in were determined from prepared solutions by employing remediation - removing chemical pollutants from water the atomic absorption spectrophotometry (AAS). and sediments in particular. Statistical analyses was conducted on plant samples using Duncan’s Multiple Range Test, at the level of significance P<0.05, using 1-way factor analyses. 2. Experimental Procedures At each location sediment was collected using a van Veen grab (36 x 28 cm) in three replicates in the vicinity Concentration of heavy metals (Fe, Mn, Cu and Cd) in of plants. Water was also sampled in the zone of plant water and sediment was determined by flame atomic growth, at a depth of 0.5 m, using 0.5 l samplers, in absorption spectrophotometry [15]. three replicates. To determine which macrophytes were dominant A t-test (one-population) was performed to test at the littoral zone samples were collected by using a the differences between concentrations of metals random block system in the period of a maximal organic in water and sediment. All statistical analyses were production (July 2006). The same plant species from conducted with computer software Origin 5.0 in order to different sites were collected to facilitate the comparison determine whether the location had an effect on metal of results (Table 1). concentration. Each metal was analyzed individually. A Djerdap I hydroelectric power plant is located at level of 0.05 alpha was used to determine significance. nd 942 river kilometer, while Djerdap II hydroelectric All data shown in tables are mean values. power plant is located at 863rd river kilometer (Figure 1). Differences in water levels on these damns can reach up to 30 meters. Prahovo (35) and Radujevac (36) represent the last two urban sites at the Danube in Serbia,with Prahovo also housing a number of chemical plants. The Mlava mouth (14), Dubovac (15,16), and Ram (17) belong to the Labuduvu Okno Protected

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No. Location River km Sampled species 1. Bezdan 1 425 Juncus compressus Jacq. 2. Bogojevo 1 366 Rorippa amphibia L. 3. Bačka Palanka 1 298 Rorippa amphibia L. 4. Beočin 1 269 Rorippa amphibia L. 5. Sremski Karlovci 1 244 Rorippa amphibia L. 6. Stari Slankamen 1 215 P. pectinatus L., P. perfoliatus L. 7. Mouth of the Tisza River 1 214 Ceratophyllum demersum L. 8. Zemun 1 173 Juncus compressus Jacq. 9. Mouth of the Sava River 1 170 Rorippa amphibia L. 10. Vinča 1 144 P. pectinatus L., P. perfoliatus L., P. lucens L. 11. Smederevo 1 116 P. pectinatus L., P. lucens L. 12. Mouth of the Morava River 1 104 P. pectinatus L. 13. Kostolac 1 095 P. pectinatus L., P. perfoliatus L. 14. Mouth of the Mlava River 1 091 P. pectinatus L., P. gramineus L. 15. Dubovac right bank 1 085 P. pectinatus L., P. perfoliatus L. 16. Dubovac left bank 1 085 P. pectinatus L., P. perfoliatus L., P. lucens L. 17. Ram 1 076 P. perfoliatus L., P. lucens L. 18. Mouth of the DTD canal 1 076 P. lucens L. 19. Veliko Gradište 1 059 P. pectinatus L., P. x fluitansRoth., P. lucens L. 20. Golubac 1 044 Ceratophyllum demersum L., P. perfoliatus L. 21. Golubačka Tvrđava 1 040 Elodea canadensis Michx., P. pectinatus L., P. perfoliatus L., P. lucens L. – Djerdap National Park 22. Mouth of the Brnjička river 1 032 P. perfoliatus L., P. lucens L., – Djerdap National Park Myriophyllum spicatum L. 23. Dobra 1 020 P. perfoliatus L., Myriophyllum spicatum L. – Djerdap National Park 24. Djerdap National Park 1 010 P. pectinatus L., P. perfoliatus L. 25. Greben – entry into lake “Djerdap” of the Djerdap 999 P. perfoliatus L., P. lucens L. National Park 26. Donji Milanovac 990 P. lucens L. – Djerdap National Park 27. Mouth of the Porecka river 988 P. x fluitansRoth., P. pectinatus L. – Djerdap National Park 28. Malo Golubinje 980 P. perfoliatus L., P. lucens L. – Djerdap National Park 29. Veliki Kazan 970 P. x fluitansRoth. – Djerdap National Park 30. Djerdap National Park 960 P. lucens L. 31. Tekija 955 Nymphoides peltata (S.G.Gmelin) O. Kuntze., – Djerdap National Park P. perfoliatus L., P. lucens L. 32. Kladovo 933 P. perfoliatus L., P. lucens L. 33. Brza Palanka 883 P. perfoliatus L., Ceratophyllum demersum L. 34. Kusjak 863 P. pectinatus L. 35. Prahovo 861 Scirpus palustris L. 36. Radujevac 852 Scirpus palustris L.

Table 1. Location of test sites and plant species sampled along the Danube River in Serbia.

287 Heavy metal accumulation of Danube river aquatic plants – indication of chemical contamination

Sampling Fe Mn Cu Cd site water sediment water sediment water sediment water sediment mg ∙ l-1 mg ∙ g-1 μg ∙ l-1 μg ∙ g-1 μg ∙ l-1 μg ∙ g-1 μg ∙ l-1 μg ∙ g-1 1 930.3 17.4 38.0 271.3 8.1 18.0 0.3 1.4 2 589.7 24.4 33.7 129.7 21.7 38.0 1.9 1.5 3 730.3 12.6 51.7 154.3 2.7 8.8 1.1 1.2 4 390.7 30.6 22.7 373.7 4.1 26.1 1.1 1.7 5 239.0 23.4 24.3 203.7 9.6 21.0 1.1 1.4 6 981.3 - 34.3 - 8.1 - 1.1 - 7 241.7 34.8 28.7 678.3 6.8 72.4 0.8 3.2 8 240.1 23.8 26.7 294.7 4.2 36.1 0.3 1.5 9 1608.7 44.5 44.7 358.7 16.3 45.0 1.7 3.6 10 1510.3 36.1 74.3 554.3 42.7 43.7 1.7 2.8 11 242.0 7.9 25.3 154.3 8.2 5.4 0.8 0.7 12 289.3 38.7 28.7 664.3 34.7 43.0 1.7 2.4 13 489.7 - 58.3 - 31.7 - 0.7 - 14 241.0 32.5 18.3 608.0 14.3 51.0 0.3 2.5 15,16 289.0 38.4 23.3 593.3 6.7 77.7 1.5 3.2 17 1022.0 39.2 78.7 467.3 4.1 56.3 0.6 2.8 18 389.0 19.3 33.3 201.3 9.6 13.7 0.3 1.1 19 341.0 - 30.3 - 0.0 - 0.3 - 20 340.3 14.2 25.3 310.3 11.7 30.3 0.6 2.2 21 182.3 5.9 18.3 224.0 9.5 14.1 1.1 2.5 22 34.0 23.1 9.5 193.3 1.6 20.7 0.8 2.1 23 539.3 41.8 47.3 373.3 6.8 72.8 0.3 1.9 24 389.0 18.1 43.3 650.7 4.2 70.1 0.6 2.5 25 290.7 20.7 26.3 397.3 2.7 43.1 0.6 2.4 26 440.5 38.4 51.3 483.3 31.1 70.9 1.7 2.9 27 240.1 31.6 25.3 389.7 2.8 24.0 0.8 1.0 28 390.3 45.7 35.3 389.7 5.5 37.1 1.1 1.1 29 209.9 36.6 14.3 580.3 446 74.0 0.6 2.6 30 290.7 - 27.3 - 5.5 - 0.6 - 31 56.6 51.6 16.2 726.0 0.0 92.0 0.6 3.2 32 181.3 18.0 23.7 232.3 4.3 16.0 1.1 1.1 33 239.7 - 25.3 - 5.4 - 1.4 - 34 290.3 45.1 49.2 500.3 5.4 81.9 0.8 2.5 35 24.0 11.2 16.3 156.3 8.2 33.0 0.6 0.7 36 391.3 12.0 38.3 171.3 8.1 106.1 0.6 1.2

Table 2. Heavy metal concentrations in water and sediment (mud) at investigated localities. pollution. Main sources of these pollutants are industrial 3. Results and Discussion and urban waste which includes the runoff from agricultural chemicals. The ecological consequence of 3.1. Heavy metals in the Danube water and such contamination is that sediment absorbs the heavy sediment in its section through Serbia metals and then these metals may enter the food chain. Due to a lack of legislation in Serbia concerning Heavy metals are naturally found in the environment at sediment quality, the quality of the sediment was low concentrations due to the composition of the Earth’s compared to Holland’s recommendations for standard crust. However, due to lax regulations of industrial sediment quality (Anon 2000), in addition to a general ‘outputs’ and inadequate environmental monitoring, directive from the EU [17]. The water quality was water systems are now contaminated with heavy metal

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Metal content water P-value Significant difference Metal content P-value Significant difference at level 0.05 sediment at level 0.05 Cd 3.11 ·10-13 Yes Cd 4.36 ·10-18 Yes Cu 0.04642 Yes Cu 4.15 ·10-12 Yes Fe 3.11 ·10-8 Yes Fe 2.40 ·10-16 Yes Mn 7.20 ·10-20 Yes Mn 4.49 ·10-15 Yes

Table 3. Statistical analysis of the dependence of metals content on the location. compared to Serbian maximum legal concentrations 3.2. Heavy metals in macrophytes – indicators of pollutants as defined in the Book of Rules regarding of the Danube River in its section through dangerous substances [18]. Serbia Results showed that waters flowing from the mouth In formulating new “ecosystematic” decrees and of the Tisza, Sava and Morava rivers, into the Danube regulations regarding water quality, countries belonging to significantly increased the chemical load of water and the European Union follow chemical and microbiological sediment (Tables 2 and 3). parameters in addition to novel biological parameters The concentration of Cd, Cu, Fe and Mn varied which include the monitoring of living creatures [19]. greatly among sample sites (Table 3). Increased concentrations of heavy metals in aquatic An increased concentration of Fe and Cd were environments does not lead to visible plant damage as observed at the convergence of the Sava River and the plants have developed specific physiological mechanisms Danube (Table 2). Similarly at the mouth of the Tisza to survive in these polluted conditions [13,20]. The ability river, high concentrations of all researched metals to effectively remove metal ions out of solution and to was found in the sediment, whilst the increased metal accumulate high levels of these pollutants in plant tissue concentration was also noticed at Location 10 which is are dependent on plant species and metal ions. Some situated after the Tamiš mouth. Furthermore, a significant factors involved in the determining such differences increase of the Mn, Cu and Cd concentrations was include the rate of chelation, ionic exchange, chemical observed in the Danube sediment following the mouth of precipitation, translocation of metal ions and precipitation the Morava River (Location 12). These results suggest induced by root exudates or by microorganisms [21]. As the tributaries flowing into the Danube greatly affect the a result, hyperacumulation of heavy metals can be used heavy metal contamination of the Danube. High metal alongside other bioindicaters and phytoremediaters as values in the sediment were also noted at Location important factor to consider when defining the ecological 15 and 16 (Dubovac) which belong to the Deliblato status of aquatic ecosystems, or using macrophytes for sands Protected Area in the flooded zone. At Location purification of polluted river [22-24]. 26 (Donji Milanovac), the Danube is up to 2 km wide, Our results show that purification efficacy, uptake and the water speed is slower than regions upstream and accumulation rates of studied heavy metals, depended sediment settles down. As a consequences, increased both on plant species and sampling site. Variations of concentrations of Mn, Cu and Cd, in the sediment and concentration ratio between investigated heavy metals water was identified (Table 2). At Location 29, there in plant tissue of the same plant species were site is a great narrow spot of the Danube (Veliki Kazan), dependent. and extremely high concentration of Cu was recorded both in the sediment and in the water samples. Before the Djerdap I hydroelectric power plant at Location 31 3.3. Heavy metal concentrations in (Tekije) as well as before the Djerdap II hydroelectric Potamogeton perfoliatus power plant (Location 34, Kusjak) the water is slow, Potamogeton perfoliatus species was dominant at 16 the sediment settles down, which results in high heavy out of the 36 sites sampled, and was therefore used as metal contamination. The localities which are situated a test species for chemical analyses. The content of Fe downstream from the Smederevo smelter and the in the tissue of P. perfoliatus varied from 1280 μg ∙ g-1 Kostolac power plant also appear to be chemically (0.128%), at Location 20 (Golubac), to 5800 μg ∙ g-1 loaded. (0.58%) at Location 28 (Malo Golubinje) (Table 4). The observed concentrations of Fe (found at levels of >1%) were significantly lower than results from a previous study undertaken on the same species at similar locations along the Danube River [25]. The distibution of Fe in P. perfoliatus varied along the Danube River, with

289 Heavy metal accumulation of Danube river aquatic plants – indication of chemical contamination

Sampling site Fe Mn Cu Cd Sampling site Fe Mn Cu Cd μg ∙ g-1 μg ∙ g-1 6 2550 efg 431 fg 9.67 f 1.43 ef 6 5472 c 1060 ef 12.67 d 1.33 cde 10 4067 c 1494 b 14.11 cd 1.37 ef 10 1223 g 1371 d 9.39 fg 1.90 a 13 4361 c 1557 b 10.89 ef 1.38 ef 11 6945 b 1039 ef 14.89 c 0.93 fg 15 2294 fgh 1404 b 13.00 de 1.78 cde 12 2844 f 948 f 11.33 e 0.80 g 16 2267 fgh 2695 a 13.44 de 1.94 cd 13 2972 ef 2571 d 8.72 g 1.27 def 17 2645 efg 1064 c 13.50 de 2.00 cd 14 3272 ef 1077 ef 12.89 d 1.20 ef 20 1281 j 853 d 8.89 f 1.67 de 15 1230 g 1491 c 9.89 f 1.43 bcde 21 1602 ij 567 ef 15.11 bcd 3.44 a 16 1139 g 3929 a 9.22 fg 1.67 abc 22 3022 de 1180 c 16.44 abc 1.53 def 19 3644 e 754 g 13.17 d 1.77 ab 23 5000 b 1155 c 18.94 a 2.72 b 21 4793 d 1136 e 11.33 e 1.93 a 24 2850 def 294 g 19.00 a 2.22 c 24 9895 a 679 g 23.33 a 1.60 abcd 25 3356 d 576 ef 13.33 de 1.67 de 27 5794 c 409 h 16.06 b 0.93 fg 28 5800 a 460 fg 19.11 a 1.78 cde 34 3478 ef 1561 c 8.11 h 1.67 abc

31 1856 hij 290 g 17.33 ab 2.22 c Table 5. Average Fe, Mn, Cu and Cd concentrations in Potamogeton 32 3317 d 604 ef 18.39 a 1.68 de pectinatus plants. 33 2038 ghi 654 e 8.5 f 1.60 de Data with the same letter represent statistically identical values in vertical columns (P<0.05) Table 4. Average Fe, Mn, Cu and Cd concentrations in Potamogeton -1 perfoliatus plants. Concentrations were as low as1.37 μg ∙ g (in the Vinča -1 Data with the same letter represent statistically identical values in region, loc. 10 and 13) and peaked at 3.44 μg ∙ g , in vertical columns (P<0.05) the Golubac Fortress region (Location 21). Although the higher levels of accumulation observed in the section recorded values were not extremely high, the presence around Vinča (Location 10), Kostolac (Location 13), of Cd in the plant tissue is a strong indicator of the Dobra (Location 23) and Malo Golubinje (Location 28). chemical load of the water as well as the sediment of Although there was no significant corelation between the Danube River. Fe concentrations in the water and sediment compared with Fe concentrations in the plant tissue, it can be 3.4. Heavy metal concentrations in noted that with the increase of Fe in the surroundings, Potamogeton pectinatus the levels accumulating in plant tissue was greater The aquatic species, P. pectinatus, was dominant at 13 (Tables 3 and 5). sample sites. The highest Fe concentration of nearly The highest Mn concentration in the tissue of P. 1% (9895 μg ∙ g-1) was recorded in the Djerdap National perfoliatus was recorded at Location 16 (Dubovac – left Park region (Table 5). shore). This increase of Mn concentration, is most likely The Mn content in the tissue of P. pectinatus was due to an inflow of industrial waste water from the nearby on average higher when compared to P. perfoliatus and smelter, as well as contaminated waters flowing from the P. lucens. However, a significant correlation beetwen Sava, the Morava and the Mlava Rivers. Comparisions the concentrations of Mn in water and plant tissue for between the Mn concentration in P. pectinatus and the P. perfoliatus (rxy = 0.765), for P. pectinatus (rxy = 0.672) Mn concentration in water and sediment were statistically and for P. lucens (rxy = 0.665) was obtained. Also it can significant, indicating the relevance ofP. perfoliatus as a be noted that the coefficient of linear correlation between bioindicator for heavy metal contamination. water Mn concentration and sediment Mn concentration The results shown in Table 4 demonstrate that in these localities was positive although not statistically the highest concentration of Cu was recorded was significant xy(r = 0.195). The highest registered values at Location 28 (Malo Golubinje, 19.11µg·g-1). At this of Mn was 3929 μg ∙ g-1 at Location 16 (Dubovac – left sample site, large amounts of waste water loaded with shore). These data support already noted data for P. heavy metals is discarded from the thermal power plant. perfoliatus indicating that the level of Mn contamination P. perfoliatus species also had higher amounts of Cu of the water and littoral zone in the Kostolac thermal in region 23 – Dobra (18,97µg·g-1) and region 24 – the power plant region is high (Table 4). Chemically loaded Djerdap National Park (19,0 µg/g), when compared to waste waters of the Kostolac thermal power plant could the other locations. The presence of Cd was discovered theorectically introduce significant amounts of Mn to the in the tissue of P. perfoliatus at all sample sites. river system.

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Sampling site Fe Mn Cu Cd Sampling site Fe Mn Cu Cd μg ∙ g-1 μg ∙ g-1 10 2300 gh 1134 e 12.56 fg 0.98 e 7 10822 a 4997 a 58.28 a 9.17 a 11 2522 fg 1325 d 12.78 fg 1.26 de 20 3702 b 2165 b 12.78 b 1.45 b 16 3206 de 2786 a 13.44 fg 1.67 cd 33 4083 b 4036 a 17.56 b 2.78 b

17 3761 cd 1797 c 13.33 fg 1.49 cd Table 7. Average Fe, Mn, Cu and Cd concentrations in Ceratop- 18 7405 a 1110 e 14.06 ef 1.37 cde hyllum demersum plants. 19 1828 hi 1842 bc 13.06 fg 0.33 f Data with the same letter represent statistically identical values in vertical columns (P<0.05) 21 793 j 695 g 11.33 g 2.61 a tissues were very similar. High accumulation of Cu in 22 2917 efg 1896 b 17.33 d 1.43 cd both species was at Location 28 (Malo Golubinje), and 25 3811 cd 642 g 19.78 c 1.33 cde Mn at Location 16 (Dubovac – left shore). 26 2911 efg 348 i 16.06 de 1.63 cd The presence of Cd was detected in P. lucens 28 4078 c 517 h 26.44 a 1.70 cd plant tissue at all researched localities. Following the 30 1423 i 406 i 23.33 b 1.73 bc distibution of Cd in P. lucens, a distinctive load of the 31 2961 ef 381 i 22.61 b 1.63 cd water and the sediment around the Golubac Fortress 32 5889 b 840 f 20.00 c 2.11 b section (Location 21- 2.61 μg∙g-1) and Kladovo (Location -1 Table 6. Average Fe, Mn, Cu and Cd concentrations in Potamogeton 32 - 2.11 μg ∙ g ) was observed. lucens plants. Based on the content of the examined heavy metals in Data with the same letter represent statistically identical values in Potamogeton spp., the chemical composition of aquatic vertical columns (P<0.05) plants is a reliable indicator of the heavy metal pollution It can also be concluded that the distribution of of the aquatic ecosystems supporting researched Cu and Mn in plants per localities was similar for all conducted by Mikryakova [26]. The metal content in three species. The Cu concentration in P. perfoliatus plants, water and sediment clearly indicated which areas ranged from 8.11 μg ∙ g-1, at Location 34 (Kusjak), to of the Danube are ecologically endangered. 23.33 μg ∙ g-1, at Location 24 (the Djerdap National Park). The presence of Cd was also detected in P. 3.6. Heavy metal concentrations in pectinatus samples from all researched locations, which Ceratophyllum demersum clearly implies chemical pollution of the water, the littoral Ceratophyllum demersum is a well known zone and the bottom. The highest concentration of hyperaccumulator and consequently plays a large role in this heavy metal of 1.93 μg ∙ g-1 was registered at the the monitoring aquatic ecosystems [7]. In our research, Golubac fortress (Location 21). C. demersum was only found at three localities, where the Danube flows slowly (Table 7). 3.5. Heavy metal concentrations in Heavy metal concentrations greater than 1% were Potamogeton lucens recorded at Location 7 (the mouth of the Tisza River) which Surprisingly, our results showed that the content of Fe in indicates that the Tisza River is under obvious chemical the dry matter of P. lucens varied significantly between pressure from industrial waters, as well as runoff from sample sites, ranging from 793 μg ∙ g-1 to 7405 μg ∙ g-1 dry surrounding agricultural areas. The highest concentrations matter. The highest concentration of this microelement of other researched heavy metals were also registered was observed in the plant tissue from Location 18 at the at this site. Furthermore, the Cd uptake of C. demersum mouth of the DTD channel (Table 6). plants at the mouth of the Tisza River was extremely high, All three examined species of the Potamogeton 9.17 μg ∙ g-1. genus, had extremely high accumulation of Fe in the section of the lower flow of the Danube around the 3.7. Heavy metal concentrations in Rorippa Djerdap National Park, the mouth of the DTD channel amphibia and Smederevo. The highest concentration of Fe The heavy metal content in helophytes is also used in was recorded in the P. pectinatus tissue. This kind of biomonitoring as an indicator of chemical contamination distibution of Fe in the tissue of the examined species, of aquatic ecosystems. These plants function as a filter positive corelated with the load of the water and the for toxic substances and aid the natural purification of sediment containing this heavy metal. waste waters from agricultural, urban and industrial According to our results, the distribution of the Cu areas [27,28]. The high accumulation of nutrients and and Mn contents in the P. perfoliatus and P. lucens plant heavy metals in aerial parts is not characteristic in these

291 Heavy metal accumulation of Danube river aquatic plants – indication of chemical contamination

Sampling site Fe Mn Cu Cd dissolved metals and toxins. These aquatic plants μg ∙ g-1 are useful indicators when monitoring of ecological status of ecosystems. Consequently, this study aimed 2 10170 a 203 b 18.61 a 1.10 b at understanding the importance of macrophytes 3 3783 c 95 d 9.06 c 1.02 b in bioindication and bioremediation of toxic metals 4 7594 b 170 c 6.61 c 0.56 c and controlling the heavy metal pollution – thereby 5 8978 a 327 a 13.83 b 1.06 b suggesting the remedial measures for the preservation 9 7305 b 249 b 17.11 ab 1.46 a and restoration of Danube river ecosystem. Our results Table 8. Average Fe, Mn, Cu and Cd concentrations in Rorippa amp- show that purification efficacy, uptake and accumulation hibia plants. rates of studied heavy metals, depended both on plant Data with the same letter represent statistically identical values in species and sampling site. vertical columns (P<0.05) All three examined species of the Potamogeton species, however, very high concentration of metals can genus, had extremely high accumulation of Fe in the often be noted in roots and rhizoma. section of the lower flow of the Danube around the Rorippa amphibia was used as a test species in this Djerdap National Park, the mouth of the DTD channel research. The chemical analysis of the upper part of the and the metal smelter. The highest concentration of Fe plant was done. was noted in the P. pectinatus. The distribution of Fe in The highest accumulation of Fe in R. amphibia tissue tissues of the examined species positively reflected the -1 was registered at the Bogojevo site (10170 μg ∙ g ) degree contamination in the water and sediment. (Table 8). Also, relatively high concentrations of Fe The increase in Mn concentrations in the plants -1 was noted in Sremski Karlovci (8979 μg ∙ g ), while the may be the result of the industrial waste waters inflow lowest levels were recorded at the Bačka Palanka site from the smelter, as well as the inflows from other -1 (3783 μg ∙ g ). Based on these results, it can be noted rivers. A statistically significant correlation between that there is a distinctive chemical load in the water and Mn concentration in P. pectinatus tissue and Mn sediment in the Bogojevo and Sremski Karlovci sections. concentration in water and sediment was observed The concentration of Cd in Rorippa amphibia which confirms the role of this plant as an indicator plant tissue was recorded at all localities where this of the environmental chemical load. It can also be species was identified and concentrations ranged from concluded that the distribution of Cu and Mn in plants -1 -1 0.56 μg ∙ g to 1.46 μg ∙ g . Although samples were not at specific locations was similar for all three species collected from more locations, it still can be concluded of Potamogeton. The correlation coefficient of Mn that the chemical composition of R. amphibia can also site distribution between P. perfoliatus and P. lucens serve as an indicator of chemical load of the littoral zone. was highly significant xy(r = 0.906). Also, significant correlations of Mn distributions were recorded between

P. pectinatus and P. lucens (rxy = 0.783) and between

4. Conclusions P. pectinatus and P. perfoliatus (rxy = 0.921). Significant correlations of Cu distributions were recorded between In aquatic ecosystems, water and sediment quality P. perfoliatus and P. lucens (rxy = 0.737) and between P. may vary depending anthropogenic origin as well as pectinatus and P. perfoliatus (rxy = 0.715). natural parameters including various biogeochemical Based on the heavy metals concentrations in processes. Results obtained from our study showed that Potamogeton spp., it can be concluded that the chemical the rivers which flow into the Danube from its entering composition of macrophytes is a reliable indicator of point in Serbia (the Tisza, the Sava, the Morava, and the heavy metal pollution of the aquatic ecosystems. the Tamiš) significantly influence the chemical load of Furthermore, these macrophytes may potentially be water and sediment. Where the Sava River converges useful in purifying natural aquatic resources as part with the Danube, increased concentrations of Fe and Cd of program for sustainable development of aquatic were recorded. At the mouth of the Tisza River, higher ecosystems. concentrations of all researched metals were registered in the sediment, while the increased metal concentration was also noticed at the site situated after the Tamiš Acknowledgements mouth. The sample sites situated downstream from the smelter and the power plant were also chemically loaded. This study was supported by Ministry of Science and Macrophytes are biological filters that purify Environment Protection of the Republic of Serbia as part water bodies and littoral zones by accumulating of project number 143037.

292 S. Pajević et al.

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