heavy metal concentration in surficial sediments from anzali wetland, iran

HEAVY METAL CONCENTRATION IN SURFICIAL SEDIMENTSFROM ANZALI WETLAND, IRAN

GH. AMINI RANJBARIranian Fisheries Research and Training Organization, P.O. Box 14155–6116, Iran

(Received 1 August, 1996; accepted in revised form 22 April, 1997)

Abstract. Concentrations of Cd, Pb, Cu, Zn and Ni were determined in surficial sediments from elevensampling sites in Anzali wetland. Four different methods were tested to choose the most efficientprocedure for determination of the metals. The measurement of the metal levels were performed usingatomic absorption spectroscopy. In order to interpret analytical results, several statistical methodswere applied. There were statistically significant differences among the accumulation of the metalsin sediments, while differences were not be observed among the seasons. Sampling site eight showedthe lowest similarity compared to others.

Kurtzfassung. Gehalte an Cd, Pb, Cu, Zn und Ni wurden in den oberflachliche sedimenten vonelf probestellen aus der Anzali Lagune gemessen. Vier verschiedene Methoden Wurden untersuchtum das leistungsfahigste zu wahlen. Die Messungen wurden mittles flammen-AAS vorgenommen.Zur Interpretation der Ergebnisse, mehrere statistische Methoden wurden angewendet. Es gab all-gemein statistische Signifikanz Unterschiede zwischen der Akkumulation der Metalle in Sedimente.Betrachtliche Unterschiede zwischen den Jahrezeiten Konnten dagegen nicht festgestellt werden. DieProbestelle acht wies die geringsteAhnlichkeit mit den anderen auf.

Key words: heavy metals, sediment, analysis, Anzali wetland, Iran

1. Introduction

Heavy metals are natural constituents of aquatic ecosystems. A number of theseelements are biologically essential. Trace metals introduced into the aquatic envi-ronments by various anthropogenic activities are ultimately absorbed by depositsand incorporated into sediments. Sediments represent the most concentrated phys-ical pool of metals in aquatic environments (Gerhardt, 1990; Clements, 1991;Everaartset al., 1993).

Anzali wetland is one of the most important water bodies in northern Iran. Itsopen water surface area is more than 58 km2. The wetland represents an interna-tionally important wildlife reserve which listed under Ramsar Convention (Holcik,1993; Pourang, 1995). The location of sampling sites are shown in Figure 1.

The main objectives at the present study were: (a) to determine heavy met-als concentrations in surficial sediments from different sites of the wetland andcomparison with results from other geographical regions, (b) to obtain referencevalues to be used in the future to measure the changes produced by an increase incontamination.

Water, Air, and Soil Pollution104: 305–312, 1998.c 1998Kluwer Academic Publishers. Printed in the Netherlands.

306 GH. AMINI RANJBAR

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HEAVY METAL CONCENTRATION IN SURFICIAL SEDIMENTS 307

Figure 2. Sequence of steps for preparation and analysis of sediment samples on the basis of digestionwith a mixture of HNO3/HCl.

2. Material and Methods

Surficial sediments were sampled from eleven sampling sites in various part ofthe wetland using a standard Van Veen grab with an effective grasping area of250 cm2. The samples were taken 4 times (November 1992, February, May andAugust in 1993). Each time three sub-samples were collected from each site andwere analysed separately. Initially four different analytical procedures were testedto choose the most advantageous one. Based on the results presented in Table I, itwas concluded that digestion with a mixture of HCl/HNO3 was the most efficientprocedure. Hence it is used for all samples in this study. Figure 2 shows a flowscheme of the preparation and analysis of the samples according to the chosenprocedure. Throughout analytical work, deionized double distilled water (DDDW)was used. All the reagents were of high purity. All labware was washed first withdetergent and tapwater and was then soaked in 15% HNO3 for 24 hr followed byrinsing repeatedly in DDDW. With each sample set a reference material and twoblanks were also run. All analyses were undertaken in triplicate on each sample andmean values were calculated. For eliminating of interferences a 10% Potassiumadded to all standards and sample solutions. Determinations were performed by aShimadzu model AA-670/GU-8 flame atomic absorption spectrophotometer. Deu-terium source automatic background correction was used throughout the analyticalprogram. Conditions of analyses were as recommended by the manufacturer.


Table IComparison of the results of four different analytical procedures for heavy metals determi-nation in surficial sediments. Values are means of five replicate measerments

Procedure Concentration (�g g�1 dry weight)Pb Cu Ni Zn Cd

1 Digestion with a mixture of HNO3/HCl 3.060 3.746 4.505 13.290 1.82 Digestion with HCl 1.392 1.695 2.068 9.779 1.23 Extraction with EDTA solution 2.320 3.099 3.228 10.01 1.54 Digestion with HNO3 2.243 2.187 0.898 9.258 1.4

3. Data Analysis

Three one-way ANOVAs were conducted, two of them to determine whether thedifferences among concentrations in different seasons and sampling sites could besignificant and another to examine whether concentrations of heavy metals weresignificantly different in sediments (Sokal and Rohlf, 1981). Each datum was themean of metal concentrations in three sub-samples. In the cases, there were sta-tistically significant differences between the group means, Duncan’s new multiplerange test (Zar, 1984) was employed. Hierarchical cluster analysis (Using Euclid-ian measures) was used to group different sampling sites based on concentrationsof metals in sediments (Ludwig and Reynolds, 1988; Green, 1979). All statisticalanalyses were done with the Statgraphics (version 5.0, 1991).

4. Results and Discussion

In general, metal concentrations in the sediments from different sampling sites ofthe study area were found in the following order: Zn > Cu > Ni > Pb > Cd > (Figure3).

The result of one-way ANOVA present in Table IIa suggests that there werehighly significant differences in accumulation of different heavy metals. Duncan’stest shows that with the exception of Pb and Ni, there were significant differencesbetween concentration of other metals (Table II).

No significant differences could be detected between seasons from heavy metalsaccumulation in sediments point of view (Table III). As shown in Table IVa therewere no significant differences (P�0.05) between the sampling sites. HoweverTable IVb shows that heavy metals concentrations in sampling sites, 1, 6 andparticularly 8 are high as compared with other sites.

Sampling site 1 was located where there are the majority of industrial activitiesin the wetland’s watershed. The long water retention time in this region may because of relatively high concentration of heavy metals in sediments samples fromthis site.


Figure 3. Comparison of mean heavy metal levels (�g g�1 dry weight) in surficial sediments. (Cdvalues are multiplied by 20.)

Table II(a) Results of one-way ANOVA was used to determine whether significant differ-ences occurred in mean values of different metals concentrations. (b) Duncan’stest was used to compare the means (P�0.05)

(a)

Source of variation SS df MS F P

Treatment 1867586.0 4 466896.50 95.252 <.00001Error 980343.6 200 4901.72

Total 2847929.7

(b)

Metal Mean Homogeneous metals

Cd 1.26585 XPb 51.72195 XNi 52.68780 XCu 86.97317 XZn 276.77805 X


Table IIIResults of one-way ANOVA was used to examine whether there were signif-icant differences between seasons from the metal levels viewpoint


Treatment 36069.8 3 12023.279 0.859 0.4631Error 2811859.8 201 13989.352

Total 2847929.7 204

Table IV(a) Results of one-way ANOVA was used to test whether differences amongheavy metal levels in different sampling sites are significant. (b) Duncan’stest was used to compare the means (P�0.05)

(a)


Treatment 23347.0 10 23345.696 1.732 .0759Error 2614472.2 194 13476.663

Total 2847929.7 204

(b)

Sampling sites Mean Homogeneous metals

11 56.14000 X2 64.59000 X4 67.31500 X

10 69.11000 X7 75.18500 X5 85.85000 X9 90.24500 X3 94.87000 X1 107.99500 XX6 119.38500 XX8 180.23000 X

Sampling sites 6 and 8 were located along two main outlet of the wetland.Relatively high levels of heavy metals in these sites can be attributed to discharg-ing parts of Anzali city sewage effluents in the outlets near the mentioned sites.Another reason for this case may be deposition of some suspended solids becauseof flocculation during the mixing of fresh and brackish water (Duinkeret al., 1982;Sholkovitz. 1976).


Figure 4. Dendograms for hierarchical clusters analysis of eleven sampling sites based on heavymetals concentrations in sediments.

Figure 4 depicts a dendrogram drived by average linkage clustering of elevensampling sites based on all the five heavy metals concentrations in sediments. Inorder to interpret the results, arbitrary dashed lines have been used. Comparisonbetween sampling sites indicates that at a distance about 4, four distinct clusters areemerged: A (sampling sites, 2, 4, 5, 7, 10 and 11), B (sampling site 9), C (samplingsites 1, 3 and 6) and D (sampling site 8). At a higher distance (about 7), clusters Aand B fuse, forming a single cluster (E). Clusters E and C also fuse and formingcluster F. The major differences are in clustering of sampling site 8 and remainingones. The same conclusion can be drawn from the results presented in Table IVb.The main cause for the considerable differences between clustering of site 8 andother may be different kind of polluted substances arising from the market of thecity, discharging into Shanbehbazar outlet.

With respect to the data on metal concentrations in surficial sediments of fresh-water bodies in various region of the world (Table V), it can be concluded that thelevels of the all selected heavy metals in this study were relatively high.

Table 5 also shows considerably elevated levels of the heavy metals (exceptfor Ni) in the studied area as compared with world average shale. However heavymetal contents in commercially important fishes from the wetland are below therecommended levels for human consumption and it appears that the levels of noneof the selected heavy metals in this study present no danger to the wetland ecologicalequilibrium (Pourang, 1995; Sadeghi, 1995).

Acknowledgements

I am grateful to A. Shams for his cooperation in this research. I also thank N.Pourang for help in preparation of the manuscript.


Table VHeavy metal concentrations (�g g�1 dry weight) in surficial sediments(bulk) from various geographical regions. References: (1) Present study;(2) Chapman, 1992; (3) Gibbs, 1993, (4) Soechtig, 1990; (5) Young andHarvey, 1991; (6) Dave, 1991

Geographical area Cu Zn Pb Cd Ni

Anzali wetland, Iran (1) 87.5 278.5 51.8 1.2 52.6World average shale (2, 3) 45 95 20 0.3 68World average soil (3) 20 50 10 0.06 40Ecker river, Germany (4) 29.7 693.9 86.5 0.2 –Lake Goerge, Canada (5) 21.5 75.0 – 1.9 –Lake Plastic, Canada (5) n 12.7 91.1 – 6.8 –Lake Blue Chalk, Canada (5) 8.3 130.3 – 3.5 –Lake Lumsden, Canada (5) 35.8 58.9 – 5.7 –Lake Hjalmaren, Sweden (6) 40 190 42 – –

References

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heavy metal concentration in surficial sediments from anzali wetland, iran

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