Hydrobiologia 506–509: 359–364, 2003.© 2003 Kluwer Academic Publishers. Printed in the Netherlands.

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Crustaceans as biological indicators of heavy metal pollution in LakeBalaton (Hungary)

Anna Farkas, Janos Salanki & Istvan VarankaBalaton Limnological Research Institute of the Hungarian Academy of Sciences, Tihany, HungaryE-mail: farkas@tres.blki.hu

Key words: biomonitoring, zooplankton, heavy metals, Lake Balaton

Abstract

Trace metals (Cd, Cu, Pb, Zn) were measured in mixed zooplankton samples collected from the open water of LakeBalaton (Hungary) in order to assess spatial and seasonal changes in the heavy metal load of different sites, during1996–2000.Samplings were performed usually twice a year in different seasons (spring, summer and autumn). Theheavy metal concentrations of zooplankton biomass were determined by atomic absorption spectrophotometry.Additionally, for some of the sampling sites – Western- and Eastern basins – the correlations between the heavymetal load of Crustaceans and the element concentrations of the water recorded monthly by the TransdanubianEnvironmental Protection Agency were also analyzed.The average metal concentrations in zooplankton variedin the following ranges: Cd: 0.25 – 3.91; Cu: 5.9 – 26.4; Pb: 1.59 – 12.84; Zn: 37.6 – 180.5 mg kg−1 dryweight. Significant spatial and seasonal variations with occasionally outstanding differences in the heavy metalload of samples could be observed during the investigated period. The heavy metal load of the Crustacea planktonbiomass in summer and autumn proved to be usually higher than in spring. During the investigated period an overallsignificant increase in the cadmium, copper and lead load of the Crustacea plankton populating the lake could beobserved. Pearson correlation analysis performed between the heavy metal concentration of Crustacea planktonbiomass and that of the water in the two outlying basins of the lake revealed strong relationship for Cd, Cu and Zn,while for lead the correlation proved to be not significant.

Introduction

The long-term monitoring of anthropogenic pollutionin aquatic ecosystems is of environmental and humanhealth concern even nowadays, when numerous effect-ive measures were undertaken to reduce the pollutionimpact of natural water bodies. In these studies aquaticorganisms are widely used for biological monitoringof variations in the environmental levels of anthro-pogenic pollutants (Phillips, 1980; Hellawell, 1986).Among aquatic indicator organisms a significant roleis assigned to zooplankton assemblages due to theirsignificant capacity to accumulate heavy metals, andtheir essential role in the enrichment of anthropogeniccompounds in food chains (Prosi, 1981; Stemberger &Chen, 1998).

Interest in monitoring the anthropogenic pollutionof Lake Balaton is justified, because the lake andits watershed are loaded by a moderate nutrient load

and a slight pollution of heavy metal, caused besidesnatural, geological sources mainly by industrial andagricultural works located in the catchment (Müller,1981; Czégény et al., 1984; Herodek et al., 1995; V.-Balogh et al., 2003). The anthropogenic heavy metalinput originates mainly from local municipal sources,waste deposits, the heavy road and rail traffic along the210 km long lakeshore, from boating and atmosphericdeposition (Hlavay et al., 1999).

On average, the concentration of dissolved heavymetals of inflow waters, which provide more than halfof the water budget of the lake, vary nowadays in thefollowing ranges: Cd 0.1 – 2.8; Cu 1.1 – 8.9; Pb 0.5– 8.3; Zn 12 – 74 µg l−1. The total heavy metal con-centration of aerosols in the catchment measured forexample in 1997 was as follows: Cd 0.55 – 0.74; Cu3.8 – 4.9; Pb 26.4 – 29.8; Zn 8.7 – 37 ng m−3 (Hlavayet al., 1999).

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Figure 1. Geographical position of Lake Balaton and the locationof sampling sites.

In this paper we present the spatial and seasonalvariations in the load of four heavy metals (Cd, Cu, Pb,Zn) in zooplankton samples during 1996 – 2000, andthe links detected between metal levels in zooplank-ton and metal concentrations in the water of two studyareas: the Eastern-, and Western-basin of Lake Balaton(Fig. 1). The heavy metal concentrations in the waterwere measured by the Transdanubian EnvironmentalProtection Agency in a parallel study within a timeinterval not longer than 3 weeks.

Materials and methods

Lake Balaton located at the western part of Hungaryis the largest shallow lake in Central Europe (Fig. 1).The surface area is 596 km2, the mean depth 3.25 mand the volume 1.9 109 m3. The inflow waters andthe processes taking place within the lake control thechemical features of the lake water. Limestone anddolomitic rocks predominate in the catchment area,so that the waters discharged to the lake carry Ca2+,Mg2+ and HCO3

− in high concentrations. Owing toCO2 exchange with the atmosphere and to photosyn-thesis, large volumes of CaCO3 are present in the lake.Due to its high alkalinity and carbonate content thelake water does not contain heavy metals in ionic form.However in unfiltered water detectable toxic heavymetal concentrations can be measured due to theirpresence in inorganic and organic forms or adsorbedto colloid particles.

Samplings of Crustacea plankton were performedusually twice a year in different seasons (spring, sum-mer and autumn) at 15 sampling sites designated alongfive transects of the lake (Fig. 1). Plankton were col-

lected by towing a plankton net (mesh size 200-µm)from about 0.5 – 1 m depth to the water surface.This sampling technique was chosen to ensure thecollection of crustacean plankton consisting almostexclusively of mature stages of copepods (>95%). Thespecies composition of zooplankton samples were ran-domly checked by sampling sites, i.e. in one of thethree replicates prepared from each sample.

Zooplankton samples designated for heavy metalanalysis were briefly rinsed with double-distilled wa-ter, dried on good quality filter paper and cleaned ofsolid impurities (paint particles, tar lumps, rust) underclose visual examination. Subsequently, the sampleswere dried at 60 ◦C, weighed, and subjected to wetdigestion in an open system with a mixture of 65%HNO3 and 30% H2O2 (Krishnamurty et al., 1976;Farkas, 1993). Metal concentrations of zooplanktonsamples were determined with a Perkin-Elmer 5100PC atomic absorption spectrophotometer equippedwith an HGA 60 graphite furnace and using deuteriumarc background correction.

Multiple spatial and seasonal contrasts of meanmetal concentrations in zooplankton were studied withthe Student-Newman-Keuls test, while Pearson correl-ation test was used to check for significant relation-ships between metal levels in zooplankton and metalconcentrations in the water.

Results

Copepods were generally numerically predominant inthe crustacean community of Lake Balaton during thewhole investigation period. Their relative proportionin the open water varied between 81 – 92% and 93– 97% in the littoral zone. Mainly four copepod spe-cies, 1 Calanoida sp. Eudiaptomus gracilis (Sars) and3 Cyclopoida spp.: Cyclops vicinus [Uljanin], Meso-cyclops leuckarti (Claus) and Acanthocyclops robustusf. limnetica [Petkovski] were present in the samples.Our results agree well with those of previous studiesdealing with the species composition of the zooplank-ton community of Lake Balaton (Ponyi, 1975; Zánkai& Ponyi, 1986; Ponyi 1991; Parpala et al., 2003).

Metal concentrations detected in the zooplanktonbiomass were generally consistent with values previ-ously reported for uncontaminated systems (Yan &Mackie, 1989; Chen et al., 2000), but elevated levelsdetected at some sampling areas were indicative ofcontamination (Table 1). In general Cd concentrations(0.37–1.85 µg g−1 dry weight) were rather low, except

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Figure 2. Elevated levels of heavy metals in zooplankton at different sampling sites of Lake Balaton. Sampling sites: a – close to the northernshoreline; b – along the middle line; c – close to the southern shoreline.

Table 1. Metal concentrations (arithmetical mean) in zooplankton (µg g−1 dry weight) and standard deviation (SD) during 1996 – 2000

Sampling No of µg g−1

occasions samples [arithmetical mean ± SD]

Cd Cu Pb Zn

1996 May 45 0.55 ± 0.15 7.53 ± 2.07 2.82 ± 1.46 180.5 ± 58.4

July 45 4.22 ± 3.13 5.91 ± 1.11 2.29 ± 0.63 133.7 ± 37.2

September 45 1.30 ± 0.21 10.81 ± 1.82 1.89 ± 0.59 157.8 ± 24.7

1997 May 51 0.88 ± 0.30 10.12 ± 4.35 2.53 ± 1.14 37.6 ± 5.3

July 51 0.89 ± 0.44 11.83 ± 4.17 2.93 ± 1.12 42.4 ± 6.8

Oct. 51 3.11 ± 0.39 10.96 ± 5.33 2.08 ± 0.56 70.6 ± 5.3

1998 April 51 2.02 ± 0.66 6.7 ± 1.49 1.59 ± 0.39 56 ± 14.2

August 51 3.01 ± 1.20 18.05 ± 7.43 1.83 ± 0.41 82 ± 10.6

1999 July 51 2.85 ± 0.78 26.43 ± 17.72 3.39 ± 1.38 57.4 ± 17.4

2000 April 51 3.91 ± 2.06 12.55 ± 7.64 3.13 ± 1.54 50.9 ± 26.3

July 51 2.18 ± 0.60 13.35 ± 5.64 4.01 ± 2.63 53.5 ± 20.2

for elevated levels (7.42–36.87 µg g−1 dry weight)detected on two occasions (July 1996 and April 2000)at some sampling sites from the Eastern basin (Fig. 2A, B). Significantly higher concentrations were recor-ded for Cu (on average 3.7–12.5 µg g−1 dry weight)showing an excessive load (71.4–276.3 µg g−1 dryweight) in summer 1999 at a few sampling locationsin the Western basin (Fig. 2 C). Pb concentrationsof zooplankton varied between 0.65–2.10 µg g−1 dryweight, with somewhat higher elevation in July 2000(5.07–9.96 µg g−1 dry weight) at sampling sites situ-ated in the Western basin of the lake (Fig. 2 D). The Znconcentration of zooplankton varied usually between37.0–70.0 µg g−1 dry weight, except the significantly

higher elevation observed for the samples collected in1996 (80.5 – 157.8 µg g−1 dry weight) (Table 1).

The pattern of temporal variation in the heavymetal concentration of zooplankton was not statistic-ally similar during the studied period when comparingSITES/SPECIES, however highest elevations for allfour elements were characteristic in general in sum-mer and/or in autumn (Table 1). Mean Cd, Cu and Pbconcentrations of zooplankton averaged for the wholelake indicate a slight increasing trend during the fouryears period (Table 1). For the assessment of long termvariations of the heavy metal load of Lake Balaton, wehave compared our results with the heavy metal con-centration data of zooplankton recorded twenty years

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Figure 3. Box plots of mean heavy metal concentrations recorded in zooplankton samples during 1978–1979 and 1996–2000. The ‘box’ heightdefines the inter-quartile range. The horizontal bar in the box is located at the median. The tails define the 95% confidence limits of the metalconcentration data.

Table 2. Pearson correlation coefficients (r) and levels of signi-ficance (p) for the relationships between the main metal concen-trations in zooplankton and metal concentrations in the water

Element Western basin Eastern basin

r p r p

Cd 0.62964 0.002 0.69014 0.001

Cu 0.70368 0.001 0.64722 0.002

Pb 0.01547 n.s. –0.00557 n.s.

Zn 0.92412 <0.0001 0.88392 <0.0001

ago (Salánki et al., 1982). The sampling circumstancesfor both investigations were rather similar i.e. the samesampling technique was applied and the investigationswere performed similarly in the open water and duringthe ice-free seasons. The same sample preparation wasused, while metal levels of the digests were determ-ined during the eighties by the AAS flame technique.Despite the weaker sensitivity of this instrumentationat concentrations close to the detection limit, meas-urements in the concentration range of our samplesproved to be reliable. Based on these facts, the relevantdifferences observed in the heavy metal concentrationsof zooplankton samples recorded during the eightiesand nowadays are attributed to changes in the pollutionload of the area. Box plots of metal concentrations ofzooplankton samples indicate a significant decrease inthe Cu and Pb load between survey years (Fig. 3).

Correlation analysis among heavy metal concen-tration data of zooplankton samples and that of the wa-

ter was studied on measurement data originating fromthe two outlying basins of Lake Balaton (Western-and Eastern basins). In these areas, the concentrationof heavy metals in the water varied in the followingranges: Cd 0.23 – 0.55; Cu 4.76 – 8.45; Pb 0.60 –1.45; Zn 11.23 – 22.50 µg l−1, with somewhat highervalues characteristic in summer and autumn, than inspring. Results of statistical analysis revealed signi-ficant positive correlation among the Cd, Cu and Znconcentrations of the zooplankton biomass and that ofthe ambient water (Fig. 4; Table 2), while for lead suchlinks could not be detected.

Discussion

According to results of previous studies regardingthe species composition and biomass distribution ofplanktonic Crustacea in Lake Balaton, it has becomeapparent, that despite significant differences in theabundance of Crustaceans, the species compositionfrom spring to autumn in the two main basins ofthe lake (Western- and Eastern basin) is rather sim-ilar (Ponyi, 1975, 1991). Therefore, in our study wehave accounted first with significant variabilities in-duced by spatial and seasonal differences in the heavymetal load of the sites rather than with the effect oftaxonomic heterogeneities of zooplankton samples.

Detected differences in metal levels of the zo-oplankton proved to be remarkable, with Cu showingaccumulation factors of 3–5, and Zn of more than 10,

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Figure 4. Links between metal concentrations in zooplankton and metal concentrations of the ambient water during 1996–2000 in the outlyingbasins of Lake Balaton.

compared to the relatively low Cd and Pb concentra-tions. These differences correspond to accumulationpatterns described for copepods populating uncontam-inated freshwater systems (Chen et al., 2000), whichare related basically to the specific essentiality of mi-croelements from a biological point of view (Merian,1991), as well as to the specific way in which certainmetals are accumulated from water and food (Chen etal., 2000).

Considering the spatial variations in the Cd, Cu,Pb and Zn load of zooplankton samples, it was notpossible to discern a consistent pattern or general trendtherefore, elevated levels of trace elements detected atsome sampling sites are indicative of contamination ofpoint source origin.

For the appraisal of seasonal variations in theheavy metal load of zooplankton, the datasets of metalconcentrations in the water of the study areas recordedmonthly by the Transdanubian Environmental Protec-tion Agency were also taken into consideration. Ingeneral, a slight elevation of metal concentrations inthe water was characteristic for summer and autumn,and thus the seasonal variations in the heavy metalload of zooplankton could be related first of all tochanges in the pollution load of the sites. This hy-pothesis is supported also by the strong correlationsdetected between the Cd, Cu and Zn concentrations inzooplankton and the aqueous metal concentrations ob-served in the datasets of the two outlying basins of thelake (Western- and Eastern basins). Nevertheless, theeffect of seasonal changes in the accumulation strategy

of Crustaceans after overwintering from regulation tonet accumulation, as well as the increase in feedingrate during summer and autumn cannot be neglected(Ritterhoff & Zauke, 1997).

The Pb load of zooplankton, similarly to results ofother studies (Ritterhoff & Zauke, 1997; Stemberger& Chen, 1998), was characterized by a significantlylower variability and showed insignificant correlationwith the Pb concentration of the ambient water. Thisphenomenon, we think, is related mainly to the relat-ively shorter biological half-life of lead, compared toother heavy metals (Merian, 1991).

Conclusions

Mean metal concentrations in the zooplankton of LakeBalaton proved to be generally consistent with levelsreported for uncontaminated freshwater ecosystems.However elevated levels detected in some samplingareas are indicative of contamination.

During the studied period (1996–2000) a slightlyincreasing trend in the Cd, Cu and Pb load of zo-oplankton, and thus of Lake Balaton is outlined.Nevertheless, compared to the microelement concen-trations recorded 20 years ago, a significant decreasein the Cu and Pb pollution impact of the area can beconcluded.

In our study, unselected zooplankton samplesproved to be well-suited as indicators of Cd, Cu and Znload of the ambient water, if similar sampling, sample

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preparation and measurement protocols were applied.Nevertheless, it must be emphasized, that poorly char-acterized mixed zooplankton samples originating fromsites of highly variable ecological status should not beused in comparative biomonitoring studies, due to theuncertainty induced by the species specific affinity toaccumulate different microelements.

Acknowledgements

This research was financed by the Balaton ResearchProject through the Prime Minister’s Office. We aregrateful to the Transdanubian Environmental Protec-tion Agency for providing heavy metal concentrationdata of the water.

References

Chen, C. Y, R. S. Stemberger, B. Klaue, J. D. Blum, P. C. Pickhardt& C. L. Folt, 2000. Accumulation of heavy metals in food webcomponents across a gradient of lakes. Limnol. Oceanogr. 45:1525–1536.

Czégény, I., I. Dévai & Gy. Dévai, 1984. Heavy metal analyses.In Dévai, Gy. (ed.), Studies of the Ecological Effects of LakeBalaton and River Zala Sediments on Chironomids (Diptera:Chironomidae). Acta Biologica Debrecina Oecologia Hungarica,Supplementum Oecologia Hungarica 1: 131–133.

Farkas, A., 1993. Preparation of samples for heavy metal analysesand measuring heavy metals. In Salánki, J. & V. Istvánovics(eds), Limnological Bases of Lake Management. Proceedings ofthe ILEC/UNEP International Training Course 24 May – 5 June1993 Tihany Hungary. ILEC Kusatsu Shiga Japan: 160–163.

Hellawell, J. M., 1986. Biological indicators of freshwater pollutionand environmental management. Elsevier Amsterdam: 546–554.

Herodek, S., V. Istvánovics, G. Jolánkai, P. Csathó, T. Németh &Gy. Várallyay, 1995. P-cycle in the Balaton catchment – a Hun-

garian case study. In Thiessen, H. (ed.), Phosphorus in the GlobalEnvironment. John Wily & Sons Ltd.: 275–300.

Hlavay, J., K. Polyák, Á. Molnár & E. Mészáros, 1999. Develop-ment of a monitoring network for the analysis of elements inaerosol samples collected at Lake Balaton. Acta Biol. Hun. 50:89–98.

Krishnamurty, K. V., E. E. Shprit & M. M. Reddy, 1976. Tracemetal extraction of soils and sediments by nitric acid-hydrogenperoxide. Atom. Absorp. Newsl. 15: 68–70.

Merian, E. (ed.), 1991. Metals and their Compounds in the Environ-ment. VCH, Weinheim.

Müller, G., 1981. Heavy metals and nutrients in sediments of LakeBalaton, Hungary. Environmental Technology Letters 2: 39–48.

Parpala, L., L.G.-Tóth, V. Zinevici, P. Németh & K. Szalontai,2003. Structure and production of metazoan zooplankton in LakeBalaton (Hungary) in summer. Hydrobiologia 506–509: ???

Phillips, D. J. H., 1980. Quantitative aquatic biological indicators.Applied Science Publishers, London: 488–493.

Ponyi, J., 1975. The biomass of zooplankton in Lake Balaton.Symposia Biologica Hungarica 15: 215–224.

Ponyi, J., 1991. Feeding, population dynamics and productionof aquatic invertebrates in Lake Balaton, with particular atten-tion to the role of biotic factors. In Lázár, G. (ed.), Advancesin Biological Research in Hungary: 1986–1990. Ecology, Bp.,AKAPRINT: 58–61.

Prosi, F., 1981. Heavy Metals in Aquatic Organisms. In Förstner,U. & G. T. W. Wittmann (eds), Metal Pollution in the AquaticEnvironment. Springer-Verlag Berlin.

Ritterhoff, J. & G. P. Zauke, 1997. Trace metals in field samplesof zooplankton from the Fram Strait and the Greenland Sea. Sci.Total Environ. 199: 255–270.

Stemberger, R. S. & C. Y. Chen, 1998. Fish tissue and zooplanktonassemblages of Northeastern U.S. lakes. Can. J. Fish. Aquat. Sci.55: 339–352.

Salánki, J., K. V.-Balogh & E. Berta, 1982. Heavy metals in animalsof Lake Balaton. Wat. Res. 16: 1147–1152.

V.-Balogh, K., L. Vörös, N. Tóth & M. Bokros, 2003. Changesof organic matter quality along the longitudinal axis of a largeshallow lake (Lake Balaton). Hydrobiologia 506–509: 67–74.

Zánkai, P. N. & J. E. Ponyi, 1986. Composition, density and feedingof crustacean zooplankton community in a shallow, temperatelake (Lake Balaton, Hungary). Hydrobiologia 135: 131–147.