Article
10.5504/bbeq.2012.0027
A&EB
Accumulation of Heavy Metals in THE Macrozoobenthos of THE Luda River, Bulgaria Teodora Stoyanova, Ivan Traykov, Ivanka Yaneva, Valentin Bogoev Sofia University “St. Kliment Ohridski”, Faculty of Biology, Sofia, Bulgaria Correspondence to: Teodora Stoyanova E-mail:
[email protected]
Abstract
Heavy metals are among the most common environmental pollutants. Their long-term environmental chronic stress leads to negative impacts on the diversity and abundance of benthic invertebrates. The Luda River, a left tributary to the Struma River, flows through the north-western slopes of Pirin Mountain. An abandoned uranium mine is located in the upper parts of the watershed. The aim of this study was to assess the accumulation of heavy metals in the macrozoobenthos of the river. Four sites were sampled for river state assessment and from two of them additional macrozoobenthic samples were collected for heavy metal analysis in October 2011. In the lower reaches, the reduction of potential habitats, due to sand deposition, and the diversion of river waters showed stronger effect on the benthic communities than the abandoned mine. The benthic invertebrates bellow the mine were characterized with increased contents of Cr, Ni, Co, Zn, Cd, Pb and Cu. The results suggested that the metals accumulated in benthic organisms originate mostly from the water, whereas the accumulated Cd, Cu, Zn and Ni originate from the sediments. Supposedly, there is also biomagnification in the food web. Biotechnol. & Biotechnol. Eq. 2012, 26(3), 2981-2986 Keywords: accumulation, heavy metals, macrozoobenthos, mining, river state, uranium
Introduction
Uncontrolled discharge of water contaminated with heavy metals from the mining industry poses a major environmental problem (2, 24). Heavy metals have negative impacts on the structure and stability of water ecosystems due to long-term environmental chronic stress. Some metals, such as Fe, Al and Zn, are essential trace metals for living organisms, while others, such as Cr and Ni, can cause high toxicity to living organisms. At higher concentrations, however, even essential metals are known to have toxic potential (28). Metals contained in the water, substratum, and food resources may produce various toxic effects in benthic organisms (7, 11, 12, 20, 21). These toxic effects may be both direct (reduced diversity and abundance of benthic invertebrates) and/or indirect (modifications of species interactions and reductions in food quality) (5, 9, 10). The sediments in freshwater ecosystems are a habitat for various benthic macroinvertebrates and can serve as an important storage location for heavy metals. The burrowing activity of some benthic organisms leads to their chronic exposure to sediments contaminated with heavy metals (29). In Bulgaria, uranium mining and the processing of the ore ceased in 1990, but the lack of biomonitoring programs prevents the assessment of their impacts on the environment. Some researchers (3, 16, 17, 18, 19, 25, 26, 27, 30) have assessed the impact of the abandoned uranium mines on the terrestrial and freshwater communities in Bulgaria, but, to Biotechnol. & Biotechnol. Eq. 26/2012/3
the best of our knowledge, none of them has investigated the accumulation of metals in the food chain. The aim of this study was to assess the accumulation of heavy metals in the macrozoobenthos of the Luda River (northwestern Pirin Mountain, Bulgaria).
Materials and Methods
Uranium mining in the watershed of the Luda River (Pirin Mountain, Bulgaria) started in 1988 and continued until 1991 by combination of open pit and in-situ leaching methods. In the beginning of the 90’s the mine was rehabilitated, but the lack of maintenance has led to intense surface erosion of the protective layer and washout of radioactive materials and accompanying heavy metals toward the Luda River. The river is a left tributary to the Struma River – one of the biggest rivers in Bulgaria (Fig. 1). The predominant substrate on the river bed is sand and gravel.
Fig. 1. Scheme of the Luda River basin and sample sites.
Macrozoobenthic samples were collected by the standard method (14) from four sites in October 2011. Site 1 is located about 1 km above the mine and served as a control site; site 2 is 2981
located about 900 m bellow the stulm and after the confluence of the polluted tributaries of the river; site 3 is located after the confluence of the biggest tributary of the river; site 4 is downstream Rakitna Village. The distance between sites 1 and 4 is about 5.4 km. The samples were fixed in 4% formaldehyde and after laboratory sorting by systematic groups were kept in 70% alcohol. Margalef’s diversity index (d) (23), Biological Monitoring Working Party (BMWP), Average Score Per Taxon (ASPT) (1) and Hilsenhoff Biotic Index (HBI) (13) were used to assess the river state. Macrozoobenthic samples for heavy metal analysis were collected from sites 1 and 2, together with the samples for river state assessment. The benthic invertebrates were separated from the sand and the leaves in the field. They were transferred in polyethylene envelopes and frozen until the laboratory analyses. The analyses were done in the laboratories of Dial Ltd., Sofia, Bulgaria. The concentrations of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined according to ISO 11047/1998 (15). The ability of benthic macroinvertebrates to accumulate metals was quantified through the bioaccumulation factors (BAF) according to Klavins et al. (22) (Equations 1 and 2): (1) BAFWv = Mbenthos /Mwat BAFSv = Mbenthos /Msed (2) where: Mbenthos is the metal amount in the benthos; Mwat is the metal amount in the water, and MSED is the amount in the sediment. The physical and chemical variables of the river were measured in situ. Electrical conductivity and chemical reaction (pH) were measured by HI 98129, the temperature and oxygen by WTW 3310 oximether.
Results and Discussion
The average values of the physical and chemical variables of the Luda River water followwd a regular pattern along its course (Table 1). The water temperature was influenced by the altitude and the shading along the river. The confluence of the biggest tributary with high levels of dissolved oxygen at site 3 is the reason for the higher average values of oxygen. The increased temperature and the influence of Rakitna Village determined the lower concentration of oxygen at site 4. TABLE 1 Average values and standard deviations of abiotic variables: temperature (t), oxygen (O2), chemical reaction (pH), electrical conductivity (EC) in the Luda River Site
t (°C)
O2 (mg/l)
рН
EC (µS/cm)
1 2 3 4
10.4 ± 1.7 10.9 ± 2.9 11.4 ± 3.5 12.5 ± 4
9.6 ± 0.6 9.8 ± 1.1 10.2 ± 1.2 9.4 ± 1.2
7.1 ± 0.6 7.5 ± 0.6 7.6 ± 0.6 7.7 ± 0.6
138 ± 49 378 ± 76 344 ± 85 388 ± 56
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The chemical reaction of the water was in the range of 7.1 to 7.7. Although the mining included in situ leaching with acids for a short time, the high percentage of sedimentary rocks is responsible for the fast recovery of the chemical reaction of the drainage water from the mine (pH = 7.8). This water was also characterized with high values of lectrical conductivity (EC = 802 µS/cm), correspondingly – high content of dissolved solids. The increase of EC in the river below the mine is due to the inflow of the drainage water from the stulm. A total of 44 benthic taxa were found in the macrozoobenthic communities of the Luda River in October 2011. The following families: Lumbricidae (Olygochaeta), Baetidae (Ephemeroptera), Rhyacophilidae (Trichoptera), Elmidae (Coleoptera), Tipulidae, Chironomidae and Simulidae (Diptera) were found at all observed sites (Table 2). In the upper parts of the river, the macrozoobenthic communities were characterized with rich species diversity. Margalef’s diversity index and ASPT indicated healthy benthic communities. Although, the structural and biotic indices showed a slight change in the conditions from sites 1 to 3, they did not indicate a change in water quality (Fig. 2). The recorded changes in HBI were not a result of organic pollution. They reflected the impoverishment of the habitats in the lower parts of the river. The synergetic effect of the reduction of potential habitats, due to sand deposition; the diversion of river waters to the point of almost complete dry-up of the river during the driest period of the year; and the moderate organic pollution from Rakitna Village have led to an overall deterioration of the water ecosystem at site 4. Downstream all these factors have stronger effect on the benthic communities than the abandoned mine. The average contents of heavy metals in the water and sediments of the Luda River were used to estimate the bioaccumulation factors. According to Calmano et al. (4) and Chaillou et al. (6), the main factors affecting the mobility of metals are the pH and redox potential. Our data (Table 1) suggested that the alkaline conditions in the water prevent the mobilisation of metals from the sediment. In our previous work (27) the concentrations of heavy metals in the water and sediments of the Luda River were found to increase bellow the mine. The same situation was observed with the contents of heavy metals in the macrozoobenthic communities in the present study. The benthic invertebrates bellow the mine were characterized with higher contents than those in the control site: chromium, nickel (5 times), cobalt (1.7 times), zinc (1.6 times), cadmium (1.3 times), copper, iron and lead (1.2 times) (Fig. 3). According to Chiba et al. (8) iron is often found in high concentrations in biota, without apparent toxicity. The bioaccumulation factors (BAF) of metals in the benthic macroinvertebrate from the Luda River are shown in Table 3. The water bioaccumulation factor was high at all sampling sites, indicating a high bioavailability of trace metals for benthic organisms. The high values of BAFW suggested that biomagnification of metal contaminants occurs in the food web. Together with the accumulation of heavy metals from the Biotechnol. & Biotechnol. Eq. 26/2012/3
TABLE 2 Composition of the macrozoobenthos of the Luda River in October 2011
Plecoptera Leuctridae Leuctra sp. Perlodidae Isoperla sp. Perlidae Perla marginata Nemouridae Protonemura sp. Nemoura sp. Ephemeroptera Heptageniidae Ecdyonurus sp. Rhytrogena sp. Leptophlebiidae Habroleptoides confusa Ephemeridae Ephemera danica Baetidae Baetis rhodani Trichoptera Phryganeidae sp. 1 Sericostomatidae Sericostoma sp. Philopotamidae Philopotamus montanus Rhyacophilidae Rhyacophila nubila Rhyacophila tristis Limnephilidae sp.1 Hydropsychidae Hydropsyche bulbifera Odonata Gomphidae Gomphus sp. Aeshnidae Aeshna sp. Gastropoda Lymnaeidae sp.1 Planorbidae Gyranlus albus Bivalvia
1
2
Sites
3
15.8 10.8
6.1
1.2
0.7
2.6
4
0.2 3.7 8.3
1.3 1.8
2
2.4 0.9
3.2 6.9
5.1 5.4
6.6
0.5
0.3
0.9 4.1
0.7 7.7
11.2 29.8
0.2 1.7
2.1
0.7
1.9
1.1
0.9 2.2
1.1 1.6
2.4 1.4
8.4
7.5
0.3
0.3 3.7
0.3 0.2
1.1
0.3 0.2
Biotechnol. & Biotechnol. Eq. 26/2012/3
Sites
1 2 Sphaeriidae Sphaerium sp. 0.9 Crustacea Amphipoda Gammaridae Gammarus balcanicus 11.2 Coleoptera Dytiscidae Agabus sp. 0.8 Elmidae Elmis sp. 8.9 3.4 Optioservus spp. 1.5 0.8 Chrysomelidae sp.1 0.8 Turbellaria Planariidae Crenobia alpina 1.9 Planaria torva 10.6 Hirudinea Erpobdella octoculata Diptera Tipulidae Tipula sp. 0.7 2.1 Hexatoma spp. 0.2 0.3 Simulidae 1 6.6 Tabanidae Tabanus sp. 0.8 Empididae sp. 1 0.3 Pediciidae Dicranota sp. 1 0.9 4.5 Athericidae A. marginata 0.8 Limonidae Limonium sp. 0.9 3.4 Antocha sp. 0.5 Tanyderidae sp. 1 1.7 1.8 Dixidae Dixa sp. 0.5 0.3 Ceratopogonidae sp.1 0.5 Chironomidae 3.4 21.6 Oligochaeta Lumbricidae g. sp. ju. 0.3 0.5 Σ Relative abundance 100 100 % Total number of taxa 35 32
3
4
0.7 1.4 1.4
0.3
0.3
1.4
1.2
1.7
2.1
0.3
5.8
1.4 1
0.3 41
65.5
0.3
0.3
100
100
24
9 2983
14
8
12
6
10 d
ASPT
8 6
2
4 2
0
0 1
2
3
1
4
sites
2
3
4
sites
a
175
c
6
145
5 4
115
HBI
BMWP
4
85
3 2 1
55
0
25 1
2
3
1
4
sites
2
3
sites
b
4 d
Fig. 2. Structural (a) and biotic (b, c, d) indices at different sites along the Luda River in October 2011.
site 1
site 2 contents of heavy metals, mg/kg
contents of heavy metals, mg/kg
75 60 45 30 15 0 Cd
Co
Cr
Cu
Ni
Pb
Zn
4270
site 1
site 2
3570 2870 2170 1470 770 70 Mn
Fe
Fig. 3. Contents of heavy metals (cadmium Cd, cobalt Co, chromium Cr, copper Cu, nickel Ni, lead Pb, zinc Zn, manganese Mn and iron Fe) in macrozoobenthic invertebrates of sites 1 and 2 of the Luda River in October 2011.
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water into benthic invertebrates, there was also accumulation of metals from the sediments into benthic organisms (Cd, Cu, Zn – at site 1 and Cd, Cu, Zn, Ni at site 2). TABLE 3 Water (BAFW) and sediment (BAFS ) bioaccumulation factors of metals in the macrozoobenthos of sites 1 and 2 of the Luda River Site 1 Cd Co Cr Cu Fe Mn Ni Pb Zn
BAFW 9300 266 878 1884 14891 10859 654 1855 2324
Site 2 BAFS 1.36 0.49 0.02 1.65 0.18 0.72 0.24 0.59 1.23
BAFW 12100 1135 4368 1048 3008 2673 3490 973 2074
BAFS 2.27 0.95 0.09 1.11 0.40 0.75 1.36 0.61 1
At site 2, the values of BAFW for Cu, Fe, Mn, Pb, Zn and those of BAFS for Cu and Zn decreased. The increased values of the mentioned metals in the water and sediments of site 2 together with almost the unchanged values of these metals in macrozoobenthic communities (in comparison to their contents in the benthic communities at site 1) led to decreased BAF. On the other hand, the absence of some species such as Gammarus balcanicus and Planaria torva, which composed approximately 22% of the total number of the control site, could contribute to the observed changes in BAF at site 2.
Conclusions
The abandoned uranium mine continues to affect the benthic communities of the Luda River, resulting in slight decrease in the values of structural and biotic indices downstream. In the lower reaches, the lack of potential habitats, due to sand deposition, and the diversion of river waters have a stronger effect on the benthic communities than the abandoned mine. The contents of Cd and Ni in benthic invertebrates bellow the mine are 5 times higher than those in the control site; the content of Co is increased 1.7 times; of Zn, 1.6 times; of Cd, 1.3 times; of Cu, Fe and Pb, 1.2 times. According to BAF, the benthic communities of the Luda River mostly accumulate heavy metals from the water, whereas the accumulation of Cd, Cu, Zn and Ni occurs from the sediments. According to our results the benthic communities below the mine do not show signs of acute toxicity, but the high values of BAFw suggest possible biomagnification of metals in the higher trophic levels.
Acknowledgements
This study was partly supported by the Sofia University Fund for Scientific Investigations, Projects 69/2011 and 215/2010, and the National Science Fund of the Bulgarian Ministry Biotechnol. & Biotechnol. Eq. 26/2012/3
of Education and Science, Projects DO12-131/2008 and BG051PO001-3.3.04/41.
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