the use of various methods for the study of metal pollution in marine

The use of various methods for the study of metal pollutionin marine sediments, the case of Euvoikos Gulf, Greece

M. Dassenakis, H. Andrianos, G. Depiazi, A. Konstantas, M. Karabela,A. Sakellari, M. Scoullos*

University of Athens, Department of Chemistry, Laboratory of Environmental Chemistry, Panepistimiopolis, 15771 Athens, Greece

Received 24 January 2001; accepted 5 July 2002

Editorial handling by M. Kersten

Abstract

This study presents the results on heavy metal (Mn, Fe, Cu, Zn) analyses of sediments taken from Euvoikos Gulf,

Greece, which is a semi-enclosed system receiving pollution loads from several urban and industrial sources and isaffected by a strong tidal current. A sequential extraction schema and two single-step methods were used for thedetermination of trace metals. The data of the 1997 period are compared with data from previous studies carried out in

the authors’ laboratory in the area (1980, 1993) using various analytical techniques, in an attempt to evaluate both theevolution of pollution in the area and the effectiveness of analytical methods. It has been confirmed that a significantpart of the pollution load remains in coastal localities in the vicinity of the land based pollution sources, whereas thereare also some more remote sites where small polluted particles are transported, deposited and accumulated. The sedi-

mentology regime of the area affects the concentration of metals in a rather complex way depending also on its contentof carbonates, organic C and clay minerals. The study of sediment cores has indicated elevated metal concentrations inrecent surface sediments. On the other hand, some environmentally positive trends were also observed (i.e. the reduc-

tion of mobile metals). A systematic monitoring is needed in the marine environment coupled with some reduction inpollution inputs and integrated management on the coastal zone because the overall hydrological characteristics of thearea favour its rapid self-restoration.

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1. Introduction

The study of coastal sediments provides useful infor-

mation in marine, environmental and geochemicalresearch about marine pollution. Urban and industrialactivities contribute to the introduction of significant

amounts of pollutants (among them trace metals) intothe marine environment and affect directly the coastalsystems where they are quite often deposited. Heavy

metals, pesticides and other toxic substances can beabsorbed from the water column onto surfaces of fineparticles and move thereafter with the sediments.Trace

metals participate in various biogeochemical mechan-isms, have significant mobility and can affect the eco-systems through bioaccumulation and bio-magnification

processes. (GESAMP/UNESCO, 1987, 1994; Salomonsand Forstner, 1984).A variety of analytical methods have been developed

in order to study metals in marine sediments in anattempt to determine their concentrations and theirimpacts. (Sulcek et al., 1977; Forstner and Wittman,

1979; Quevauviller et al., 1993) These methods can bedivided into single and multiple step schemes.Most geochemical studies concerning metals in sedi-

ments deal with total concentrations. They are usually

determined by single step methods employing treatmentof sediments with mixtures of concentrated, strong acidsi.e. HNO3, HCl, HF etc. in high temperature and,

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Applied Geochemistry 18 (2003) 781–794

www.elsevier.com/locate/apgeochem

* Corresponding author.

E-mail address: [email protected] (M. Scoullos).

mailto:[email protected]

eventually, high pressure (UNEP, 1985; Clark andVlets, 1981). Single step techniques are used also for thedetermination of the portion of metals that is consideredto have anthropogenic origin or is more readily bioa-

vailable, often using dilute acids at lower temperatures(Agemian and Chau, 1976; Sinex et al., 1980; Tack andVerloo, 1993).

Multiple step methods, better known as sequentialextractions, offer a useful tool for the deduction ofinformation about the various types of metal associ-

ations in sediments. They can also inform us about thepotential availability of metals to biota, their mobilisa-tion, transport and eventually, in a few cases, about the

origin of certain metal species. Use of a series of specialleaching reagents could, theoretically, separate the var-ious metal forms in the sample. The sequential extrac-tion schemes are designed after a series of investigations

on combinations of ‘‘single-step’’ methods. (Tessier etal., 1979; Scoullos, 1979; Aualitia and Pickering, 1988;Latouche et al., 1993; Davidson et al., 1994; Kersten

and Forstner, 1995).Following the increasing interest in these techniques,

the ‘‘Bureau of Reference’’ of the Commission of the

E.U. (BCR) has proposed a sequential extractionscheme suitable for preparation of a Certified ReferenceMaterial (CRM) (Ure et al., 1993; Quevauviller et al.,

1994) because sequential extraction methods are stillconsidered to have rather low reproducibility due totrace metal redistribution in the sediment samples andnon-selective behaviour of reagents (Rapin et al., 1986;

Martin et al., 1987; Kheboian and Bauer, 1987; Fiedleret al., 1994; Usero et al., 1998). The CRM-601 was usedin this study.

For the better understanding of the effects of pollu-tion activities on the distribution of metals in marinesediments 3 procedures are combined in the study of

heavy metals in Euvoikos gulf where the authors havecarried out pollution research both during 1980 and1993. Reference material is used for the evaluation ofthese techniques.

1.1. The study area

Euvoikos gulf is a shallow embayment of the AegeanSea formed by the eastern coasts of Attica and Boeotiaand the western coast of Euvoia island (Fig. 1). The gulf

is naturally divided by the narrow straits of Euripos,having a width of about 40 m. The restricted area of thestraits should be considered as a separate section of

particular interest due to the significant tidal phenom-ena that are observed there.The morphology of the area causes the development

of a strong tidal current (about 12 km/h at the nar-

rowest part) that changes its direction every 6 h (Livier-atos, 1979; Vlachakis and Tsiblis, 1993). Such currentsare very scarce in the non tidal Mediterranean Sea and

have been noted and described previously by ancientGreek writers among which was Aristotle. Usual currentvelocities in the area are 6–18 cm/s and occasionally 20–30 cm/s (Leodaris et al., 1994).

The current causes the quick transport and disper-sion of pollutants but also affects the sedimentationprocesses mainly in the immediate vicinity of the

Euripos straits, where the fine grained sediment frac-tion is eliminated. In the rest of the area the seabedis covered mainly by sand, silt and mud and at cer-

tain localities, near the coast, by pebbles. Fig. 2 pre-sents the sedimentological regime of the area(Leodaris et al., 1994). In the small bay between the

city of Chalkis and the large bridge of Evripos (whichis included in Fig. 1 but not in Fig. 2)the composition ofsediments is for Station 1: clay 51.5%, silt 38.7%, sand9.8%, and for Station 2: clay 50.2%, silt 30.1%, sand

19.7%The southern part of the strait is significantly

affected by anthropogenic activities as it receives large

amounts of domestic and industrial wastes. The wastewater treatment plant of the city of Chalkis with aresident population of about 51 000 inhabitants,

according to the inventory of 1991, is located on asmall island in the gulf (see Fig. 1) and the treatedeffluents are disposed to the sea. Several industries

such as cement, textile, paint, food, metal-formingand ceramic factories, shipyards etc. are located alongthe coastal zone. Consequently, significant alteration ofthe coastline, as well as construction of harbors and

other interventions, has taken place in their neighbor-hood. Several industries have wastewater treatmentplants but either because of improper operations or

total lack of treatment facilities, still a significantamount of industrial effluents is disposed virtuallyuntreated or poorly treated, directly into the sea. There

is also significant air-borne pollution due to variousemissions of metal enriched dust deriving from thecement factory, the shipyard etc.Transport (navigation and road traffic) is also a sig-

nificant source of pollution in the area. Finally somedrainage canals from cultivated agricultural lands alsocontribute to the pollution through runoff.

It is noteworthly that industrial and urban pollu-tion activities in the area have remained practically atthe same level during the last 30 years whereas was-

tewater treatment plants were introduced only duringthe last decade. Although many problems concerningthe quality of seawater have been reported in the last

few years, there is neither sufficient chemical mon-itoring in the area nor a coastal zone managementplan. Data available on trace metal levels and distribu-tions refer to the years 1980 (Angelidis et al., 1980;

Scoullos and Dassenakis, 1982, 1983) and 1993 (Dasse-nakis and Kloukiniotou, 1994; Dassenakis et al., 1996)only.

782 M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794

2. Materials and methods

Sediment samples were collected during 1997 in the area

of Central Euvoikos Gulf by a grab sampler. Samplingstations are shown in Fig. 1 and are described in Table 1. AMackereth corer (Smith, 1959) was used for the collection

of 4 sediment cores, at stations 1, 2, 6 and 8. In Table 1 arealso presented the values of salinity, pH and dissolvedO2 inthe near bottom water layer. In the studied area, due to thetidal current, no strong stratification is observed even

during summer, the water is well oxygenated and there areno anoxic surface sediments (Dassenakis et al., 1996).The samples were wet-sieved through a nylon net (size

of 61 and mm) the fine grained fraction was dried at 40 �Cin a closed fan-assisted oven. It is a common procedure forthe normalization of the results (Kersten and Smedes,

2002). The metal analyses were performed in the silt andclay fraction (<61 mm), because the metals are usuallyassociated with the small grains. This fraction is also easily

homogenized for better reproducibility in metal measure-ments (Rabbiti et al., 1983; Forstner and Salomons, 1988).The organic C content of sediment samples was

determined by titration (with Fe2+) of the K2Cr2O7 that

had not been consumed for the oxidation of the organiccompounds of the sediment in strong acidic conditions(Gaudette et al., 1974).

The samples were treated by the following ‘‘single-step’’ methods:

� Shaking overnight at room temperature withdilute (0.5N) HCl, to extract the ‘‘metal fractionweakly bound to the sediment’’ (W), which

appears to be of ‘‘anthropogenic origin’’ (Age-mian and Chau, 1976). The weight difference inthis treatment represents the carbonate contentof the sample.

� Overnight treatment with concentrated HF–HNO3–HClO4 (1:3:1) in covered PTFE beakerson a hot (300 �C) plate, to extract the ‘‘total

metal content’’ (T) (UNEP, 1985).

Single-step performance was compared against the

results obtained by applying a sequential leaching tech-nique, based on the method proposed by BCR (Ure etal., 1993; Quevauviller et al., 1994) outlined below:

1. Shaking overnight with acetic acid (0.11M) atroom temperature, to extract the ‘‘exchangeablefraction, soluble to water and acid’’ (E).

2. Shaking overnight with hydroxylammoniumchloride (0.1M), to extract the ‘‘reducible frac-tion (mainly oxides) of the metal content’’ (R).

Fig. 1. The studied area and the sampling stations.

M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794 783

3. Treatment with hydrogen peroxide (8.8M) twice

in a special microwave oven (Prolabo ‘‘Micro-digest 40100) for 10 min, to extract the ‘‘oxidizablefraction (mainly sulphides and organometallic

complexes)’’ (O) and shaking with ammoniumacetate (1M) for 16 h.

4. Heating with concentrated HF–HNO3–HCl(1.5:1:1) for 20 min in the microwave oven and

further treatment with HClO4 for 4 min, toextract the ‘‘residual metallic fraction stronglyassociated with the sediment’’ (L).

The authors’ method, compared to the BCR one,

introduced the following modifications:

(a) Microwave digestion was used instead of heat-

ing beakers on a hot plate (Mahan et al., 1987;Florian et al., 1998).

(b) The metal content of the residual fraction wasalso measured.

All metal determinations, following both the single-step and the sequential extractions, were performed by

Fig. 2. Sedimentological pattern of the area (Leodaris et al., 1994).

Table 1

The sampling stations, and the hydrological parameters in the near bottom water layer

No. Remarks Depth (m) pH Salinity (%) Dissolved O2 saturation (%)

1 Center of the small gulf 12 8.21 38.2 92

2 Ceramics factory (50 m from the coast) 4 8.27 36.4 97

3 Agios Stefanos bay 4 8.20 38.0 99

4 Chalkis waste treatment plant (near the outfall pipe) 10 8.22 35.6 90

5 Cement industry (50 m from the coast) 5 8.19 38.6 95

6 Shipyard (50 m from the coast) 10 8.28 38.2 93

7 Entry of the bay (in the middle) 5 8.30 38.3 100

8 Chemical industries (50 m from the coast) 4 8.25 38.6 91

9 Center of the gulf 12 8.26 38.6 102

10 Faros area (100m from the west coast) 5 8.25 38.7 102

11 Burtzi area (100m from east coast) 5 8.13 38.7 101

13 Reference station 30 8.24 38.4 99

14 Chipboard industry (50 m from the coast) 15 8.28 37.0 90


flame or graphite furnace atomic absorption spectro-metry (Varian SpectrAA-100/ Varian SpectrAA-640Zeeman).

The relative standard deviation of the measurements,obtained by analysis of 5 subsamples of selected samples(Carayannis, 1978), was found to be less than 5%.

Two reference sediments (from IAEA/Monaco) wereanalyzed for their total metal content (UNEP, 1991).The BCR CRM-601 sediment that is certified for the

BCR sequential method was also analyzed. The resultsare presented in Table 2.

3. Results and discussion

The present research includes two metals that are

widely affected by anthropogenic inputs (Cu and Zn)(Scoullos and Constandianos, 1998) and two havingmainly geological origin (Fe and Mn).

3.1. Single step techniques

It is clear from Table 3 that the organic C concentra-tions are reduced from the northern (1, 2) to the south-ern (10, 11, 13) stations probably because the mainsources of TOC in the area are near the city of Chalkis.

The tidal current in the area prevents the developmentof water column stratification and the formation ofintermittently anoxic conditions, which could have lead

to high concentrations of organic C. This phenomenonhas been observed in several enclosed gulfs in Greece,where there is not such a current, e.g. Gulf of Elefsis,

Thermaikos, Amvrakikos etc. (Scoullos, 1983, 1986;Dassenakis et al., 2000).The same table also reveals that high carbonate con-

tent was observed in sediments of near shore stations(e.g. 14, 8, 5), that are affected by polluting activities. Asthe carbonates are not included in the industrial efflu-

ents, probable reasons for this phenomenon could beeither the dredging of near shore sediments due to thewaterway maintenance near the industrial facilities, orthe contribution of atmospheric deposition of cement

dust, or even biogenic carbonates in areas of appar-ently increased productivity due to higher nutrientcontent.

The finegrained sediments near the cement industry(st. 5) are significantly enriched in metals, probably dueto a significant cement dust deposition. The high values

of Fe and Mn support the terrestrial origin of metals,and the highW fraction percentages (>50% for Cu, Zn,Mn ) indicate increased mobility and bioavailability.

Elevated concentrations of Cu, were observed at sta-tions 7 and 8 in Vathy bay. This distribution is similarto the one observed in 1993 (Dassenakis and Klouki-niotou, 1994) which is an indication that the neigh-

bouring industries continue to enrich the marineenvironment in these metals. High W fraction percen-tages were observed at station 7 (64.5% for Cu, 62% for

Table 2

Measurements of metals in of reference sediments (all values in mg/g ppm)

IAEA/SD-M-2 T/M (total content) IAEA/SD-M-1 T/M (total content)

Certified values Found Certified values Found

Cu 32.7�1.2 33.6 25.1�3.8 28.1

Zn 74.8�3.1 82 191�17176

Mn 1170�100 1060 513�25551

Fe 27130�1800 26 600 30 000�1500 31 150

BCR/ CRM- 601 (Sequential extractions)

BCR method

Metal Fraction Certified values Found Metal Fraction Certified values Found

Cu Exchangeable 10.5�0.8 10.3�0.4 Zn Exchangeable 261�13 298�11

Reducible 72.8�4.9 65.9�1.8 Reducible 266�17 301�9

Organic 78.6�8.9 75.8�3.7 Organic 106�11 114�3

Residue (aqua regia) 60.4�4.9 56.5�2.2 Residue (aqua regia) 161�4 133�4

Pseudo Total (aqua regia) 230�15 217�6 Pseudo Total (aqua regia) 833�17 838�15

1979, 1986, Scoullos method

EE 4.6�0.8 0.9�4.4

NLI 84.8�11.1 518�10.3

NLO 14.8�0.9 29.3�1.2

L 95.3�7.3 350.4�10.6


Zn, 21% for Fe). These observations, in combination

with the sedimentation pattern of Fig. 2, indicate thatthe fines transported from various sources in the area ofstation 7 are enriched in metals, which are potentially

harmful for the local ecosystems due to their enhancedmobility. In the case of station 6 near the shipyard, thetotal metal concentrations were much lower than theones determined in samples collected within the ship-

yard. Probably heavy metal enriched particles, origi-nated from the operations in the shipyard, are toocoarse to be transported and are deposited very near the

source of their emission.Total and ‘‘weakly bound’’ concentrations of Cu and

Zn were elevated in the sediments near the sewage out-

fall of the City of Chalkis (st. 4) probably because theyare not removed effectively through the treatmentapplied there. The significant chipboard industry nearstation 14 seems to affect the marine environment with

elevated Fe and Zn. The highest W portion for Fe(47%) was observed at this station.It is clear from Table 3 that the concentrations of

weakly bound Cu, Zn and Fe were low in the centralpart of the area (st.13 and 10) which is far frompollution sources (27 and 18% for Cu, 12.5 and

26.5% for Zn, 17 and 9% for Fe). As is the casewith TOC, the metal pollution from land based sourcesremains restricted, mainly in the northern part of the

system.High W percentages in the case of Mn (generally

>50%) are probably due to the elevated association ofMn with carbonates that are dissolved by the dilute HCl

(Dassenakis et al., 1995). The low ones in the case of Fe(<20% in the most cases) are due to the increased con-tribution of the lattice-held fraction of the metal.

An overall increase of Mn concentrations was noted

at stations 3 and 5, probably due to the existence ofincreased percentages of clay minerals there (Fig. 2).An increase of total Fe was observed at stations 3, 4,

9 and 13 (attributed to the geological origin of Fe) butnot at stations 6, 7, 8 and 14 (near main pollution sour-ces).The comparison of the results of the 3 sampling peri-

ods (1980, 1993, 1997) revealed a continuous increase ofpollution levels near the cement industry (st. 5), thewaste water treatment plant, which had not been estab-

lished during 1980, (st. 4) but also in the central area (st.9) relatively far from pollution discharges. On the otherhand, the percentages of weakly bound Cu were con-

siderably higher during 1980 (stations 3, 4, 5) and 1993(stations 6, 7, 8) in comparison to the 1997 campaign,

Table 3

Metals, organic C and carbonates after ‘‘single-step’’ extractions. W: Weakly bound, T: Total (all values in ppm mg/g)

Stations %TOC %CO3 Cu Zn Mn Fe

W T W T W T W T

1 1.7 14 14.2 40.5 62.4 108 270 383 3940 23 710

2 1.5 26 14.0 37.7 85.8 141 262 446 3870 22 500

3 1.4 34 9.60 29.9 34.6 90.2 393 702 2380 36 420

4 1.1 32 20.7 41.5 63.8 102 285 482 4890 38 380

5 1.2 39 23.6 36.8 93.8 150 393 611 7840 34 210

6 1.3 18 5.10 38.5 12.7 66.5 176 341 2620 23 460

7 1.1 35 48.9 75.9 50.1 81.0 322 561 4000 18 680

8 1.4 43 45.9 83.9 86.6 114 253 309 4770 18 450

9 1.3 35 23.5 36.1 35.1 99.5 332 547 3320 35 500

10 0.6 27 10.5 38.7 22.8 179 243 320 2370 14 040

11 0.7 25 9.90 41.4 41.3 77.7 258 506 4710 28 940

13 0.9 27 11.5 63.5 26.4 99.0 308 455 3750 39 680

14 1.0 60 12.7 55.5 74.7 161 214 379 7780 16 700

Shipyard (inside) 240 435 536 35 600

Table 4

Weakly bound and Total concentrations of Cu and Zn during

1980 and 1993 periods (all values in ppm mg/g)

Stations Cu 1980 Cu 1993 Zn 1980 Zn 1993

W T W T W T W T

3 15.3 16.0 42.8 59.5

4 14.4 15.0 5.8 28.4 40.2 67.0 29.8 76.9

5 11.3 14.0 10.8 53.9 21.3 51.5 54.2 81.7

6 41.8 55.3 55.2 129

7 36.3 44.9 126 136

8 52.5 80.4 200 377

9 11.7 12.2 1.3 37.8 20.3 46.0 23.9 83.1

W, weakly, T, total. Scoullos and Dassenakis, 1983; Dassenakis

et al., 1996.


indicating an environmentally positive trend. The per-centages of W metal fraction at station 7 (centre ofVathy bay) have remained higher than in coastal st. 8 inall the periods studied (Table 4)

The changes that have occurred in the area through-out the last decades, as it concerns production rates andintroduction of new technologies in industries, in com-

bination with the establishment of treatment plants forsewage and industrial effluents, have not led yet to asignificant environmental improvement in the area at

least with respect to trace metals (in contrast e.g. toeutrophication), although in some cases (such as at sta-tions 5, 6, 9 for total Cu and at station 8 for total Zn)

the trace metal concentrations have been reduced.For the assessment of the evolution of metal pollution

throughout a period of 20 years is the trend monitoringby study of sediment cores is very useful. The results of

such a study for the area of central Euvoikos gulf arepresented in Table 5 and in Fig. 9.In the case of the ‘‘anthropogenic’’ (W) metals frac-

tion a significant downcore decrease is apparent at sta-tion 8 for all metals, at station 1 for Zn, Cu and Febelow the 10 cm ‘‘peak’’ layer and at station 2 for Zn.

This trend was not observed for Mn although char-acteristic features (such as the peak layer at 10cm depthof st.1) are visible also in the Mn vertical distribution.

For total metals (T) a similar trend is clearly observed atstation 8 (for Cu and in a more complicated manner forZn) and station 2 (for Zn).Although the sedimentation rate in that area is not

known and it is expected to vary significantly from onelocality to another due to the complex tidal regime, the

decreasing downcore trend is a clear indication that theindustrial polluting activities have enriched the surfacemarine sediments with metals. The decrease in surfaceconcentrations at station 1 which is not near the main

sources, and where the clay–silt sediment fraction isabout 90%, is probably (if the contribution of erosion isnot high) an encouraging indication about the beneficial

results of the establishment and operation of wastewatertreatment plants in the area.Sediment Enrichment Factor (EF), defined as [(C0/

Al0)�(Cd/Ald)]/[Cd/Ald] where C0 is the concentrationof the metal determined in the surface layer, Cd theconcentration of the same metal in a reference depth

and Al0�Ald the corresponding concentrations of Alwhich is considered to have mainly geological origin,could be used for the assessment of anthropogenic metalenrichment (Kemp et al., 1976). The deepest sample of

each core was used as reference. Two EF were deter-mined, one concerning the total (EFt) and one con-cerning the concentrations of the weakly held metal

(EFw). In both cases the same (total) Alt value was usedsince it is known that Al as a basic element of the alu-minosilicate lattice of minerals has a negligible W frac-

tion (Forstner and Wittman, 1979). The results showthat there is a significant pollution enrichment at station8 for both Cu (EFw=29.4, EFt=4.1) and Zn

(EFw=4.9, EFt=1,4) as well as at station 1 for Cu(EFw=0.33, EFt=0.29) and at station 2 for Zn(EFw=3.2, EFt=0.15). Another interesting result isthat in most cases the values of EFw were higher than

the values of EFt, indicating problems for the marine

Table 5

Total metal concentrations in sediment cores (all values in ppm mg/g)

Station Depth (cm) Cu Fe Mn Zn

1 0–2 40.5 23 710 383 108

27–32 40.4 26 180 429 110

62–67 41.6 30 480 529 81.0

2 0–5 37.7 22 500 446 141

20–25 40.2 26 180 426 94.0

35–40 38.6 28 400 494 78.5

6 0–2 38.5 23 460 341 66.5

5–10 17.9 24 040 389 63.7

24–29 35.2 23 860 259 110

8 0–1 83.9 18 450 309 114

5–6 62.2 20 750 326 68.8

10–15 60.4 23 980 291 107

15–20 65.2 32 450 386 160

20–25 76.3 28 760 327 61.1

30–35 51.1 20 720 281 57.5

40–45 22.2 23 170 512 64.6


environment related to the increased bioavailable metalproportions.

3.2. Multiple step procedures

The main conclusions one could extract from theresults of the application of the sequential extraction

process presented in Figs. 3–6 are the following:

� Among the metals studied, the highest values of

exchangeable (E ) fraction were observed for Mn(20–66%). This is probably due to the knownclose association of Mn with carbonates that are

dissolved by the reagent of the first step of thesequential process. The highest proportions ofMnE values among the sampling stations were

observed in the southern part of the gulf, inareas with a relatively high percentage of sand(Fig. 2).

� In the case of Mn elevated values of the reduci-

ble (R) fraction were also observed (13–45%)due to known high mobility of reducible formsof Mn. In contrast to the E fraction, the highest

R values were observed in the northern part ofthe system at stations with a relatively high per-centage of clay and organic C. The previous

observations are in good agreement with thebehaviour of Mn in the single step methods bythe use of dilute HCl.

� In the case of Fe, the percentages of E and Rfractions were both very low as was the organic(O) fraction which was negligible. This is a clear

Fig. 3. Concentrations of Exchangeable (E), Reducible (R), Organic (O), and residual (L) fractions of Cu during 1997.

Fig. 4. Concentrations of Exchangeable (E), Reducible (R), Organic (O), and residual (L) fractions of Zn during 1997.


indication the geological origin of the element in

the study area. Some relatively high values ofthe FeR fraction near pollution sources at sta-tions 5 (cement), 6 (shipyard) and 7 (chemicals)

indicate that human activities could also con-tribute to an enrichment of coastal sedimentswith Fe. The fluctuation of the percentage of Fe

that was extracted by dilute HCl, follow those ofthe E+R+O fractions. There is however anexception to this trend observed at station 14where the high value of the W fraction of Fe

does not correspond to high E+R+O fractions.This is observed to a lesser degree also at station1. There is no certain explanation for this

exception. The existence of complex oxide–

hydroxide forms of Fe with low solubility in thereagents used in the first 3 steps of the sequentialextraction, might be a possible reason for this

difference, in combination with the fact thatstation 14 is located in a site apart from theother stations and its sediments are connected to

a somewhat different catchment area. Alter-natively some recent dredging activities mighthave exposed near surface underlying sedimentsof a different nature to those of the rest of the

region.� In the case of Al, E, R and O fraction percen-

tages were indeed very low to negligible, a fact

Fig. 5. Concentrations of Exchangeable (E), Reducible (R), Organic (O), and residual (L) fractions of Fe during 1997.

Fig. 6. Concentrations of Exchangeable (E), Reducible (R), Organic (O), and residual (L) fractions of Mn during 1997.


which justifies its use for the determination ofEF.

� Elevated percentages of organic fraction (O)were measured for Cu (11–30%). This is prob-

ably due to the well-known tendency of Cu toform organic complexes e.g. with humic acidsand various metabolites deriving from algal

biomass decomposition and other biochemicalreactions (Salomons and Forstner, 1984; Kaberiand Scoullos, 1996; Leal et al., 1999).

� A relative increase of organic Zn was observedat station 4 near the outlets of the wastetreatment plant, obviously due to the avail-

ability of many suitable organic ligands in thearea, and at station 8 near some chemicalindustries.

� At station 7 the highest values of the R fraction

were measured for Cu (50.8%) and Zn (50.3%).As was observed also in the case of Mn, thepresence of R is combined with the increased

percentage of the W fraction (64–62%). At thesame station the lowest residual (L) values weremeasured. These observations support the

hypothesis of the transport and accumulation ofsmall polluted particles from various parts ofthe area to that point, due to the tidal current

and favourable geomorphology.� The highest values of L fraction were found at

the central station 13 (Cu: 73%, Zn: 68%, Mn:23%, Fe: 95%) due to minimum direct influence

from pollution sources. Also at station 14, (Cu:78%, Zn: 72%, Mn: 38%, Fe: 98%), probablydue to recent dredging activities at the port near

the industry, and at station 1 (Fe: 99%, Zn:82%).

� The application of sequential extraction to the

sediment cores that were retrieved from stations6 and 8 was not very successful as no clear trendwas observed in the vertical distribution of thevarious metal fractions.

A comparison of the results of sequential extractions

with the percentages of weakly bound metals (W), indi-cates that the use of dilute HCl is a very good simplemethod for the determination of mobile metals because

effectively it includes the E and R fractions, withoutaffecting the aluminosilicate lattice. Only in the case ofFe was a limited attack observed. On the other hand

dilute HCl is strong enough to dissolve carbonateminerals. If the sediment contains a high percentage ofsuch minerals, which are frequently biogenic, the resultsof the method may become difficult to interpret because

the metal content will not correspond to metals ofanthropogenic origin at least with regard to metals thatare closely associated to carbonates (e.g. Mn or Zn).

The ability of HCl to extract the organic fractiondepends on the relative stability of the organic com-pounds. In some cases the W fraction of the single-steptechnique was higher than E+R, including a part of O

(e.g. for Cu and Zn at stations 3, 4, 5, 13, 14 but not atstations 6, 7, 8, 10). In cases of sediments with highorganic content the extraction with dilute HCl is not

very efficient and the attribution to ‘‘anthropogenic’’fraction is uncertain.During the 1993 period a different sequential method

was used, namely a technique, proposed and used byScoullos (1979, 1986). That sequential extraction wasbased on a combination of schemes suggested by Che-

ster (1978) and Gibbs (1973) and follows the stepsdescribed below (Figs. 7–9):

1. Treatment with 1M MgCl2 for 16 h at room

temperature, to extract the ‘‘easily exchangeablemetal content’’ (EE).

2. Treatment with acetic reducing reagent (1M

acetic acid and hydroxylamine hydrochloride)for 16 h at room temperature to extract the‘‘non-exchangeable metals in the non-lattice

held inorganic fraction’’ (NLI).3. Treatment with 0.05M EDTA for 24 h at room

temperature to extract the metals held in the

‘‘non-lattice organic sediment fraction’’ (NLO).4. Treatment with a mixture of concentrated HF–

HNO3–HClO4 (1:3:1) in PTFE beakers on a hot(300 �C) plate to extract the ‘‘metal content held

in the lattice sediment fraction’’ (L). In all cases‘‘lattice’’ refers to the aluminosilicate lattice.

The results of this method for Cu and Zn are pre-sented in Figs. 7 and 8 in the same manner done for the

1997 period. This method was also used on the CRM601 reference sediment of the BCR, which was analysedby the BCR method of sequential extractions as well.The results are presented in the second part of Table 2.

The conclusions taken from the comparison of data are:The E and R fraction of the BCR method broadly cor-

responds to the EE+NLI fraction of the Scoullos (1979,

1986) method if the two reagents are applied in sequenceto the same sediment sample. In both cases we have theeasily extractable inorganic fraction, which is not held by

the aluminosilicate lattice, the fraction held in carbonatesand the easily reducible fraction. If the truly ‘‘easilyextractable fraction’’ (EE) determined by the use of MgCl2in the Scoullos (1979,1986) method is of interest, an addi-tional initial first step should be added to the BCRmethod.It should be stressed that the EE represents those

metal species which occur on the surfaces of minerals

and which may have been incorporated into the sedi-ment from the overlying waters. It also represents thevery small portion of the dried interstitial waters.


The NLI represents metal species that are associatedwith Fe and Mn oxides and carbonate minerals together

with those adsorbed onto all mineral surfaces. In factthis does not include metal associated with authigenicsulphides and a few other complexes.

As for the O fraction, the BCR method apparentlyalways reflects higher extactions than the NLO of theScoullos (1979, 1986) method. This is due to the fact

that the O fraction includes theoretically the entire oxi-dizable fraction, practically all the sulphides as well ascomplexes with organic ligands, while NLO includes thelatter and only a small part of the former.

In both periods studied (1993, 1997) the percentagesof the mobile metal fraction at station 7 are elevated.This observation indicates that at least during the last

decade no significant changes in the nature of the sedi-ments have occurred.

4. Conclusions

In the area of the central Euvoikos gulf, the tidalcurrent of the Evripos straits which disperses the metals

together with the improvement in the operation andtechnology used by local industries and the dis-continuation of certain polluting activities (e.g. ship-yards were shut down for several months due to

financial problems) makes it very difficult to properlyassess the evolution of the state of the environment ofthe gulf in any detail.

Fig. 7. Concentrations of Easily Exchangeable (EE), Non-Lattice held Inorganic, (NLI) Non-Lattice held Organic (O) and Lattice

held (L) fractions of Cu during 1993.

Fig. 8. Concentrations of Easily Exchangeable (EE), Non-Lattice held Inorganic, (NLI) Non-Lattice held Organic (O) and Lattice

held (L) fractions of Zn during 1993.


The comparison of the results of single and multiplestep (sequential extraction) methods that were used for

the study of the marine sediments has given very inter-esting results for the determination of pollution asso-ciated with the various fractions. It has been shown that

a significant portion of the pollution load deriving fromland based sources settles in the immediate vicinity,whereas there are some more remote localities of sui-

table geomorphology (such as around st. 7) to whichsmall metal-rich particles are transported and depositedunder favourable hydrodynamic conditions.The study of sediment cores has indicated the impact

of polluting activities in recent surface sediments. At thesame time an increase of metal concentrations wasobserved in comparison with previous periods.On the

other hand some environmentally positive signs, such asthe reduction of mobile metals were also observed.The single step extraction method of using dilute HCl

seems to be useful for a monitoring system but for moredetails about the nature of metal associations in thesediment, and the chemical behavior and potential

environmental impacts of metals in sediments, the use ofsequential extractions such as those suggested by theBCR method (including eventually the determination ofthe very easily extractable and the residual fractions)

could provide very interesting and useful information.A systematic monitoring is needed in the study area

(including sediments, seawater and organisms) by using

both simple and more sophisticated techniques in orderto elaborate an appropriate integrated environmental

management plan for the region towards sustainability.The overall hydrological regime of the area favours itsrapid restoration by allowing nature to act for the self-

purification of the system. However ‘‘dilution shouldnot be the only solution to pollution’’. We are confidentthat environmental management including drastic

reduction of the pollution loads at the source andproper implementation of the EU and national legisla-tion could result in a rapid full recovery of this ecologi-cally and economically important marine environment.

Acknowledgements

The authors would like to thank Professor DrMichael Kersten for his variable suggestions and com-

ments in the preparation of this work.

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