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: M acrophytes • The Danube River • Potamogeton sp. • Bioindication • Heavy metals © Versita Warsaw and Springer-Verlag Berlin Heidelberg.
1. Introduction Macrophytes are important in the biological monitoring of aquatic ecosystems, as changes in the composition of the aquatic vegetation are considered a reliable biological indicator of the quality of water [1-3]. Seasonal dynamics of macrophyte associations, as well as the distribution according to structure (species number, population density), represent important indicators of general ecological circumstances which are dominant in aquatic ecosystems [4,5]. Pollution of aquatic ecosystems may also be estimated based on the accumulation rate of nutrients and heavy metals. Many studies had researched the use of macrophytes as indicators of metals bioaccumulation [6-8]. However, while macrophytes are useful biomonitors, the bioconcentration of metals in macrophytes may be the result of the exposure to metals in both water and/or sediments, making it difficult to directly compare between the concentrations measured in plants and in the environment (i.e., water or sediments). Chemical, biochemical, and biophysical mechanisms of uptake and accumulation of heavy metals into various * E-mail:
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aquatics plants and also, the effect of accumulated metals persistent in plant metabolism have been widely studied [9-11]. Most macrophytes which are primarily submersed and floating, have the ability to tolerate moderately high levels of heavy metal contamination by forming chelates (by binding metal ions to organic molecules) and by subcellular compartmentation. In such aquatic plants, phytochelatines and metalothionines are the main cytoplasmic chelators of heavy metals [12]. In addition, the increased activity of metabolic pathways giving rise to glutathione and organic acids which act as intracellular ligands of metals and organic acids, is important for growth in water and/or sediment contaminated with heavy metals [13]. While macrophytes accumulate and filter out chemical elements from the surrounding environment, the physical presence of macrophytes in water systems increases the stability of sediment, and, reduces eutrophication. In addition, macrophytes are involved in bioremediation due to their high tolerance to metals and the affect on ion solubility through the release of O2 from their roots [14]. Consequently, macrophytic vegetation may be used in purification of natural aquatic resources,
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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. While commercial use of phytoremediation is a plauisble way to purify contaminated areas, the role of macrophytes in the complex pathways of nutrient and heavy metal cycling, in aquatic ecosystems must first be understood. Our objective was to determine the ecological status of littoral zone of the Danube River in Serbia, by assessing the heavy metal content of dominant macrophytes. The flow section of the Danube River utilised in this study starts at 1433 river kilometers (rkm) on the state border with Hungary and Croatia and ends at 845 rkm on the state border with Romania and Bulgaria. The results obtained, form the basis of an ecological monitoring system for this aquatic area and highlight the importance of macrophytic vegetation in remediation - removing chemical pollutants from water and sediments in particular.
2. Experimental Procedures Concentration of heavy metals (Fe, Mn, Cu and Cd) in water and sediment was determined by flame atomic absorption spectrophotometry [15]. To determine which macrophytes were dominant at the littoral zone samples were collected by using a random block system in the period of a maximal organic production (July 2006). The same plant species from different sites were collected to facilitate the comparison of results (Table 1). Djerdap I hydroelectric power plant is located at 942nd river kilometer, while Djerdap II hydroelectric 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 286
Figure 1.
The Danube flow portion through Serbia.
area, representing a part of the Deliblato Sands. This protected area has no pollution sources to deplete its aquatic ecosystems. The Smederevo metal smelter (11) and the Kostolac thermal power plant (13) are a serious industrial threat declining water quality of the Danube. On each sampling location, three patches of each plant species were collected and pooled into one uniformed sample. Only vegetative parts of plants were selected (leaves with stems). Plant material was rinsed in deionised water, dried and prepared for analyses following standard methods for the examination of water and wastewater [16]. The concentrations of heavy metals were determined after drying at 450ºC and treatment with 25% HCl. Concentrations of Fe, Mn, Cu and Cd were determined from prepared solutions by employing the atomic absorption spectrophotometry (AAS). Statistical analyses was conducted on plant samples using Duncan’s Multiple Range Test, at the level of significance P1%) 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 μg ∙ g
Cd
Sampling site
Mn
Cu μg ∙ g
Cd
-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
13
4361 c
1557 b
10.89 ef
1.38 ef
11
6945 b
1039 ef
14.89 c
0.93 fg
a
15
2294 fgh
1404 b
13.00 de
1.78 cde
12
2844 f
948 f
11.33 e
0.80
16
2267 fgh
2695 a
13.44 de
1.94 cd
13
2972 ef
2571 d
8.72 g
1.27 def
g
17
2645 efg
1064 c
13.50 de
2.00 cd
14
3272 ef
1077 ef
12.89 d
1.20
20
1281 j
853 d
8.89 f
1.67 de
15
1230 g
1491 c
9.89 f
1.43 bcde
ef
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
24
2850 def
294 g
19.00 a
2.22 c
24
9895 a
679 g
23.33 a
1.60 abcd
a
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
32
3317 d
604 ef
18.39 a
1.68 de
33
2038 ghi
654 e
8.5 f
1.60 de
Table 4.
Average Fe, Mn, Cu and Cd concentrations in Potamogeton perfoliatus plants.
Data with the same letter represent statistically identical values in vertical columns (P
