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The use of various methods for the study of metal pollution in marine sediments, the case of Euvoikos Gulf, Greece
Applied Geochemistry 18 (2003) 781–794 www.elsevier.com/locate/apgeochem
The use of various methods for the study of metal pollution in 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 is affected by a strong tidal current. A sequential extraction schema and two single-step methods were used for the determination 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 the evolution of pollution in the area and the effectiveness of analytical methods. It has been confirmed that a significant part of the pollution load remains in coastal localities in the vicinity of the land based pollution sources, whereas there are also some more remote sites where small polluted particles are transported, deposited and accumulated. The sedimentology regime of the area affects the concentration of metals in a rather complex way depending also on its content of carbonates, organic C and clay minerals. The study of sediment cores has indicated elevated metal concentrations in recent surface sediments. On the other hand, some environmentally positive trends were also observed (i.e. the reduction of mobile metals). A systematic monitoring is needed in the marine environment coupled with some reduction in pollution inputs and integrated management on the coastal zone because the overall hydrological characteristics of the area favour its rapid self-restoration. # 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction The study of coastal sediments provides useful information in marine, environmental and geochemical research about marine pollution. Urban and industrial activities contribute to the introduction of significant amounts of pollutants (among them trace metals) into the marine environment and affect directly the coastal systems where they are quite often deposited. Heavy metals, pesticides and other toxic substances can be absorbed from the water column onto surfaces of fine particles and move thereafter with the sediments.Trace
* Corresponding author. E-mail address: [email protected] (M. Scoullos).
metals participate in various biogeochemical mechanisms, have significant mobility and can affect the ecosystems through bioaccumulation and bio-magnification processes. (GESAMP/UNESCO, 1987, 1994; Salomons and Fo¨rstner, 1984). A variety of analytical methods have been developed in order to study metals in marine sediments in an attempt to determine their concentrations and their impacts. (Sulcek et al., 1977; Fo¨rstner and Wittman, 1979; Quevauviller et al., 1993) These methods can be divided into single and multiple step schemes. Most geochemical studies concerning metals in sediments deal with total concentrations. They are usually determined by single step methods employing treatment of sediments with mixtures of concentrated, strong acids i.e. HNO3, HCl, HF etc. in high temperature and,
0883-2927/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0883-2927(02)00186-5
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eventually, high pressure (UNEP, 1985; Clark and Vlets, 1981). Single step techniques are used also for the determination of the portion of metals that is considered to have anthropogenic origin or is more readily bioavailable, often using dilute acids at lower temperatures (Agemian and Chau, 1976; Sinex et al., 1980; Tack and Verloo, 1993). Multiple step methods, better known as sequential extractions, offer a useful tool for the deduction of information about the various types of metal associations in sediments. They can also inform us about the potential availability of metals to biota, their mobilisation, transport and eventually, in a few cases, about the origin of certain metal species. Use of a series of special leaching reagents could, theoretically, separate the various metal forms in the sample. The sequential extraction schemes are designed after a series of investigations on combinations of ‘‘single-step’’ methods. (Tessier et al., 1979; Scoullos, 1979; Aualitia and Pickering, 1988; Latouche et al., 1993; Davidson et al., 1994; Kersten and Fo¨rstner, 1995). Following the increasing interest in these techniques, the ‘‘Bureau of Reference’’ of the Commission of the E.U. (BCR) has proposed a sequential extraction scheme suitable for preparation of a Certified Reference Material (CRM) (Ure et al., 1993; Quevauviller et al., 1994) because sequential extraction methods are still considered to have rather low reproducibility due to trace metal redistribution in the sediment samples and non-selective behaviour of reagents (Rapin et al., 1986; Martin et al., 1987; Kheboian and Bauer, 1987; Fiedler et al., 1994; Usero et al., 1998). The CRM-601 was used in this study. For the better understanding of the effects of pollution activities on the distribution of metals in marine sediments 3 procedures are combined in the study of heavy metals in Euvoikos gulf where the authors have carried out pollution research both during 1980 and 1993. Reference material is used for the evaluation of these techniques. 1.1. The study area Euvoikos gulf is a shallow embayment of the Aegean Sea formed by the eastern coasts of Attica and Boeotia and 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 the straits should be considered as a separate section of particular interest due to the significant tidal phenomena that are observed there. The morphology of the area causes the development of a strong tidal current (about 12 km/h at the narrowest part) that changes its direction every 6 h (Livieratos, 1979; Vlachakis and Tsiblis, 1993). Such currents are very scarce in the non tidal Mediterranean Sea and
have been noted and described previously by ancient Greek writers among which was Aristotle. Usual current velocities 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 dispersion of pollutants but also affects the sedimentation processes mainly in the immediate vicinity of the Euripos straits, where the fine grained sediment fraction is eliminated. In the rest of the area the seabed is covered mainly by sand, silt and mud and at certain localities, near the coast, by pebbles. Fig. 2 presents 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 (which is included in Fig. 1 but not in Fig. 2)the composition of sediments is for Station 1: clay 51.5%, silt 38.7%, sand 9.8%, 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 waste water treatment plant of the city of Chalkis with a resident population of about 51 000 inhabitants, according to the inventory of 1991, is located on a small island in the gulf (see Fig. 1) and the treated effluents are disposed to the sea. Several industries such as cement, textile, paint, food, metal-forming and ceramic factories, shipyards etc. are located along the coastal zone. Consequently, significant alteration of the coastline, as well as construction of harbors and other interventions, has taken place in their neighborhood. Several industries have wastewater treatment plants but either because of improper operations or total lack of treatment facilities, still a significant amount of industrial effluents is disposed virtually untreated or poorly treated, directly into the sea. There is also significant air-borne pollution due to various emissions of metal enriched dust deriving from the cement factory, the shipyard etc. Transport (navigation and road traffic) is also a significant source of pollution in the area. Finally some drainage canals from cultivated agricultural lands also contribute to the pollution through runoff. It is noteworthly that industrial and urban pollution activities in the area have remained practically at the same level during the last 30 years whereas wastewater treatment plants were introduced only during the last decade. Although many problems concerning the quality of seawater have been reported in the last few years, there is neither sufficient chemical monitoring in the area nor a coastal zone management plan. Data available on trace metal levels and distributions refer to the years 1980 (Angelidis et al., 1980; Scoullos and Dassenakis, 1982, 1983) and 1993 (Dassenakis and Kloukiniotou, 1994; Dassenakis et al., 1996) only.
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Fig. 1. The studied area and the sampling stations.
2. Materials and methods Sediment samples were collected during 1997 in the area of Central Euvoikos Gulf by a grab sampler. Sampling stations are shown in Fig. 1 and are described in Table 1. A Mackereth corer (Smith, 1959) was used for the collection of 4 sediment cores, at stations 1, 2, 6 and 8. In Table 1 are also presented the values of salinity, pH and dissolved O2 in the near bottom water layer. In the studied area, due to the tidal current, no strong stratification is observed even during summer, the water is well oxygenated and there are no 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 C in a closed fan-assisted oven. It is a common procedure for the normalization of the results (Kersten and Smedes, 2002). The metal analyses were performed in the silt and clay fraction (<61 mm), because the metals are usually associated with the small grains. This fraction is also easily homogenized for better reproducibility in metal measurements (Rabbiti et al., 1983; Fo¨rstner 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 organic compounds of the sediment in strong acidic conditions (Gaudette et al., 1974).
The samples were treated by the following ‘‘singlestep’’ methods: Shaking overnight at room temperature with dilute (0.5N) HCl, to extract the ‘‘metal fraction weakly bound to the sediment’’ (W), which appears to be of ‘‘anthropogenic origin’’ (Agemian and Chau, 1976). The weight difference in this treatment represents the carbonate content of the sample. Overnight treatment with concentrated HF– HNO3–HClO4 (1:3:1) in covered PTFE beakers on 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 technique, based on the method proposed by BCR (Ure et al., 1993; Quevauviller et al., 1994) outlined below: 1. Shaking overnight with acetic acid (0.11M) at room temperature, to extract the ‘‘exchangeable fraction, soluble to water and acid’’ (E). 2. Shaking overnight with hydroxylammonium chloride (0.1M), to extract the ‘‘reducible fraction (mainly oxides) of the metal content’’ (R).
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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 2 3 4 5 6 7 8 9 10 11 13 14
Center of the small gulf Ceramics factory (50 m from the coast) Agios Stefanos bay Chalkis waste treatment plant (near the outfall pipe) Cement industry (50 m from the coast) Shipyard (50 m from the coast) Entry of the bay (in the middle) Chemical industries (50 m from the coast) Center of the gulf Faros area (100m from the west coast) Burtzi area (100m from east coast) Reference station Chipboard industry (50 m from the coast)
12 4 4 10 5 10 5 4 12 5 5 30 15
8.21 8.27 8.20 8.22 8.19 8.28 8.30 8.25 8.26 8.25 8.13 8.24 8.28
38.2 36.4 38.0 35.6 38.6 38.2 38.3 38.6 38.6 38.7 38.7 38.4 37.0
92 97 99 90 95 93 100 91 102 102 101 99 90
3. Treatment with hydrogen peroxide (8.8M) twice in a special microwave oven (Prolabo ‘‘Microdigest 40100 ) for 10 min, to extract the ‘‘oxidizable fraction (mainly sulphides and organometallic complexes)’’ (O) and shaking with ammonium acetate (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, to extract the ‘‘residual metallic fraction strongly associated with the sediment’’ (L).
The authors’ method, compared to the BCR one, introduced the following modifications: (a) Microwave digestion was used instead of heating beakers on a hot plate (Mahan et al., 1987; Florian et al., 1998). (b) The metal content of the residual fraction was also measured. All metal determinations, following both the singlestep and the sequential extractions, were performed by
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M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794 Table 2 Measurements of metals in of reference sediments (all values in mg/g ppm) IAEA/SD-M-2 T/M (total content)
Cu Zn Mn Fe
IAEA/SD-M-1 T/M (total content)
Certified values
Found
Certified values
Found
32.7 1.2 74.8 3.1 1170100 271301800
33.6 82 1060 26 600
25.1 3.8 191 17176 513 25551 30 000 1500
28.1
31 150
BCR/ CRM- 601 (Sequential extractions) BCR method Metal Fraction
Certified values Found
Metal Fraction
Certified values Found
Cu
10.50.8 72.84.9 78.68.9 60.44.9 23015
Zn
26113 26617 10611 1614 83317
Exchangeable Reducible Organic Residue (aqua regia) Pseudo Total (aqua regia)
1979, 1986, Scoullos method EE NLI NLO L
10.30.4 65.91.8 75.83.7 56.52.2 2176
4.60.8 84.811.1 14.80.9 95.37.3
flame or graphite furnace atomic absorption spectrometry (Varian SpectrAA-100/ Varian SpectrAA-640 Zeeman). 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) were analyzed for their total metal content (UNEP, 1991). The BCR CRM-601 sediment that is certified for the BCR sequential method was also analyzed. The results are 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 having mainly geological origin (Fe and Mn). 3.1. Single step techniques It is clear from Table 3 that the organic C concentrations are reduced from the northern (1, 2) to the southern (10, 11, 13) stations probably because the main sources of TOC in the area are near the city of Chalkis. The tidal current in the area prevents the development of water column stratification and the formation of intermittently anoxic conditions, which could have lead
Exchangeable Reducible Organic Residue (aqua regia) Pseudo Total (aqua regia)
298 11 301 9 114 3 133 4 838 15
0.94.4 518 10.3 29.3 1.2 350.410.6
to high concentrations of organic C. This phenomenon has 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 content was observed in sediments of near shore stations (e.g. 14, 8, 5), that are affected by polluting activities. As the carbonates are not included in the industrial effluents, probable reasons for this phenomenon could be either the dredging of near shore sediments due to the waterway maintenance near the industrial facilities, or the contribution of atmospheric deposition of cement dust, or even biogenic carbonates in areas of apparently increased productivity due to higher nutrient content. The finegrained sediments near the cement industry (st. 5) are significantly enriched in metals, probably due to a significant cement dust deposition. The high values of Fe and Mn support the terrestrial origin of metals, and the high W fraction percentages (> 50% for Cu, Zn, Mn ) indicate increased mobility and bioavailability. Elevated concentrations of Cu, were observed at stations 7 and 8 in Vathy bay. This distribution is similar to the one observed in 1993 (Dassenakis and Kloukiniotou, 1994) which is an indication that the neighbouring industries continue to enrich the marine environment in these metals. High W fraction percentages were observed at station 7 (64.5% for Cu, 62% for
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Table 3 Metals, organic C and carbonates after ‘‘single-step’’ extractions. W: Weakly bound, T: Total (all values in ppm mg/g) Stations
1 2 3 4 5 6 7 8 9 10 11 13 14 Shipyard (inside)
%TOC
1.7 1.5 1.4 1.1 1.2 1.3 1.1 1.4 1.3 0.6 0.7 0.9 1.0
%CO3
14 26 34 32 39 18 35 43 35 27 25 27 60
Cu
Zn
Mn
Fe
W
T
W
T
W
T
W
T
14.2 14.0 9.60 20.7 23.6 5.10 48.9 45.9 23.5 10.5 9.90 11.5 12.7
40.5 37.7 29.9 41.5 36.8 38.5 75.9 83.9 36.1 38.7 41.4 63.5 55.5 240
62.4 85.8 34.6 63.8 93.8 12.7 50.1 86.6 35.1 22.8 41.3 26.4 74.7
108 141 90.2 102 150 66.5 81.0 114 99.5 179 77.7 99.0 161 435
270 262 393 285 393 176 322 253 332 243 258 308 214
383 446 702 482 611 341 561 309 547 320 506 455 379 536
3940 3870 2380 4890 7840 2620 4000 4770 3320 2370 4710 3750 7780
23 22 36 38 34 23 18 18 35 14 28 39 16 35
Zn, 21% for Fe). These observations, in combination with the sedimentation pattern of Fig. 2, indicate that the fines transported from various sources in the area of station 7 are enriched in metals, which are potentially harmful for the local ecosystems due to their enhanced mobility. In the case of station 6 near the shipyard, the total metal concentrations were much lower than the ones determined in samples collected within the shipyard. Probably heavy metal enriched particles, originated from the operations in the shipyard, are too coarse 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 outfall of the City of Chalkis (st. 4) probably because they are not removed effectively through the treatment applied there. The significant chipboard industry near station 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 central part of the area (st.13 and 10) which is far from pollution sources (27 and 18% for Cu, 12.5 and 26.5% for Zn, 17 and 9% for Fe). As is the case with TOC, the metal pollution from land based sources remains 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 of Mn 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 contribution of the lattice-held fraction of the metal.
710 500 420 380 210 460 680 450 500 040 940 680 700 600
An overall increase of Mn concentrations was noted at stations 3 and 5, probably due to the existence of increased 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) but not at stations 6, 7, 8 and 14 (near main pollution sources). The comparison of the results of the 3 sampling periods (1980, 1993, 1997) revealed a continuous increase of pollution levels near the cement industry (st. 5), the waste water treatment plant, which had not been established during 1980, (st. 4) but also in the central area (st. 9) relatively far from pollution discharges. On the other hand, the percentages of weakly bound Cu were considerably higher during 1980 (stations 3, 4, 5) and 1993 (stations 6, 7, 8) in comparison to the 1997 campaign,
Table 4 Weakly bound and Total concentrations of Cu and Zn during 1980 and 1993 periods (all values in ppm mg/g) Stations
3 4 5 6 7 8 9
Cu 1980
Cu 1993
Zn 1980
Zn 1993
W
T
W
T
W
T
W
T
15.3 14.4 11.3
16.0 15.0 14.0
59.5 67.0 51.5
12.2
28.4 53.9 55.3 44.9 80.4 37.8
42.8 40.2 21.3
11.7
5.8 10.8 41.8 36.3 52.5 1.3
20.3
46.0
29.8 54.2 55.2 126 200 23.9
76.9 81.7 129 136 377 83.1
W, weakly, T, total. Scoullos and Dassenakis, 1983; Dassenakis et al., 1996.
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indicating an environmentally positive trend. The percentages of W metal fraction at station 7 (centre of Vathy bay) have remained higher than in coastal st. 8 in all the periods studied (Table 4) The changes that have occurred in the area throughout the last decades, as it concerns production rates and introduction of new technologies in industries, in combination with the establishment of treatment plants for sewage and industrial effluents, have not led yet to a significant environmental improvement in the area at least with respect to trace metals (in contrast e.g. to eutrophication), although in some cases (such as at stations 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 monitoring by study of sediment cores is very useful. The results of such a study for the area of central Euvoikos gulf are presented in Table 5 and in Fig. 9. In the case of the ‘‘anthropogenic’’ (W) metals fraction a significant downcore decrease is apparent at station 8 for all metals, at station 1 for Zn, Cu and Fe below the 10 cm ‘‘peak’’ layer and at station 2 for Zn. This trend was not observed for Mn although characteristic features (such as the peak layer at 10cm depth of st.1) are visible also in the Mn vertical distribution. For total metals (T) a similar trend is clearly observed at station 8 (for Cu and in a more complicated manner for Zn) and station 2 (for Zn). Although the sedimentation rate in that area is not known and it is expected to vary significantly from one locality to another due to the complex tidal regime, the
decreasing downcore trend is a clear indication that the industrial polluting activities have enriched the surface marine sediments with metals. The decrease in surface concentrations at station 1 which is not near the main sources, and where the clay–silt sediment fraction is about 90%, is probably (if the contribution of erosion is not high) an encouraging indication about the beneficial results of the establishment and operation of wastewater treatment plants in the area. Sediment Enrichment Factor (EF), defined as [(C0/ Al0)(Cd/Ald)]/[Cd/Ald] where C0 is the concentration of the metal determined in the surface layer, Cd the concentration of the same metal in a reference depth and Al0Ald the corresponding concentrations of Al which is considered to have mainly geological origin, could be used for the assessment of anthropogenic metal enrichment (Kemp et al., 1976). The deepest sample of each core was used as reference. Two EF were determined, one concerning the total (EFt) and one concerning the concentrations of the weakly held metal (EFw). In both cases the same (total) Alt value was used since it is known that Al as a basic element of the aluminosilicate lattice of minerals has a negligible W fraction (Fo¨rstner and Wittman, 1979). The results show that there is a significant pollution enrichment at station 8 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 is that 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 27–32 62–67
40.5 40.4 41.6
23 710 26 180 30 480
383 429 529
108 110 81.0
2
0–5 20–25 35–40
37.7 40.2 38.6
22 500 26 180 28 400
446 426 494
141 94.0 78.5
6
0–2 5–10 24–29
38.5 17.9 35.2
23 460 24 040 23 860
341 389 259
66.5 63.7 110
8
0–1 5–6 10–15 15–20 20–25 30–35 40–45
83.9 62.2 60.4 65.2 76.3 51.1 22.2
18 20 23 32 28 20 23
309 326 291 386 327 281 512
114 68.8 107 160 61.1 57.5 64.6
450 750 980 450 760 720 170
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environment related to the increased bioavailable metal proportions. 3.2. Multiple step procedures The main conclusions one could extract from the results 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 known close association of Mn with carbonates that are dissolved by the reagent of the first step of the sequential process. The highest proportions of MnE values among the sampling stations were
observed in the southern part of the gulf, in areas with a relatively high percentage of sand (Fig. 2). In the case of Mn elevated values of the reducible (R) fraction were also observed (13–45%) due to known high mobility of reducible forms of Mn. In contrast to the E fraction, the highest R values were observed in the northern part of the system at stations with a relatively high percentage of clay and organic C. The previous observations are in good agreement with the behaviour of Mn in the single step methods by the use of dilute HCl. In the case of Fe, the percentages of E and R fractions 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.
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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.
indication the geological origin of the element in the study area. Some relatively high values of the FeR fraction near pollution sources at stations 5 (cement), 6 (shipyard) and 7 (chemicals) indicate that human activities could also contribute to an enrichment of coastal sediments with Fe. The fluctuation of the percentage of Fe that was extracted by dilute HCl, follow those of the E+R+O fractions. There is however an exception to this trend observed at station 14 where 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 station 1. There is no certain explanation for this
exception. The existence of complex oxide– hydroxide forms of Fe with low solubility in the reagents used in the first 3 steps of the sequential extraction, might be a possible reason for this difference, in combination with the fact that station 14 is located in a site apart from the other stations and its sediments are connected to a somewhat different catchment area. Alternatively some recent dredging activities might have exposed near surface underlying sediments of a different nature to those of the rest of the region. In the case of Al, E, R and O fraction percentages were indeed very low to negligible, a fact
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which justifies its use for the determination of EF. Elevated percentages of organic fraction (O) were measured for Cu (11–30%). This is probably due to the well-known tendency of Cu to form organic complexes e.g. with humic acids and various metabolites deriving from algal biomass decomposition and other biochemical reactions (Salomons and Fo¨rstner, 1984; Kaberi and Scoullos, 1996; Leal et al., 1999). A relative increase of organic Zn was observed at station 4 near the outlets of the waste treatment plant, obviously due to the availability of many suitable organic ligands in the area, and at station 8 near some chemical industries. 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, the presence of R is combined with the increased percentage of the W fraction (64–62%). At the same station the lowest residual (L) values were measured. These observations support the hypothesis of the transport and accumulation of small polluted particles from various parts of the 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%), probably due 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 stations 6 and 8 was not very successful as no clear trend was observed in the vertical distribution of the various metal fractions.
A comparison of the results of sequential extractions with the percentages of weakly bound metals (W), indicates that the use of dilute HCl is a very good simple method for the determination of mobile metals because effectively it includes the E and R fractions, without affecting the aluminosilicate lattice. Only in the case of Fe was a limited attack observed. On the other hand dilute HCl is strong enough to dissolve carbonate minerals. If the sediment contains a high percentage of such minerals, which are frequently biogenic, the results of the method may become difficult to interpret because the metal content will not correspond to metals of anthropogenic origin at least with regard to metals that are closely associated to carbonates (e.g. Mn or Zn).
The ability of HCl to extract the organic fraction depends on the relative stability of the organic compounds. In some cases the W fraction of the single-step technique 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 at stations 6, 7, 8, 10). In cases of sediments with high organic 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 by Scoullos (1979, 1986). That sequential extraction was based on a combination of schemes suggested by Chester (1978) and Gibbs (1973) and follows the steps described below (Figs. 7–9): 1. Treatment with 1M MgCl2 for 16 h at room temperature, to extract the ‘‘easily exchangeable metal 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 presented in Figs. 7 and 8 in the same manner done for the 1997 period. This method was also used on the CRM 601 reference sediment of the BCR, which was analysed by 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 corresponds to the EE+NLI fraction of the Scoullos (1979, 1986) method if the two reagents are applied in sequence to the same sediment sample. In both cases we have the easily extractable inorganic fraction, which is not held by the aluminosilicate lattice, the fraction held in carbonates and the easily reducible fraction. If the truly ‘‘easily extractable fraction’’ (EE) determined by the use of MgCl2 in the Scoullos (1979,1986) method is of interest, an additional initial first step should be added to the BCR method. 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 sediment from the overlying waters. It also represents the very small portion of the dried interstitial waters.
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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 NLI represents metal species that are associated with Fe and Mn oxides and carbonate minerals together with those adsorbed onto all mineral surfaces. In fact this does not include metal associated with authigenic sulphides and a few other complexes. As for the O fraction, the BCR method apparently always reflects higher extactions than the NLO of the Scoullos (1979, 1986) method. This is due to the fact that the O fraction includes theoretically the entire oxidizable fraction, practically all the sulphides as well as complexes with organic ligands, while NLO includes the latter and only a small part of the former. In both periods studied (1993, 1997) the percentages of 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 sediments have occurred.
4. Conclusions In the area of the central Euvoikos gulf, the tidal current of the Evripos straits which disperses the metals together with the improvement in the operation and technology used by local industries and the discontinuation of certain polluting activities (e.g. shipyards were shut down for several months due to financial problems) makes it very difficult to properly assess the evolution of the state of the environment of the gulf in any detail.
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Fig. 9. Vertical distributions of weakly bound (W) metal concentrations in sediment cores at stations 1, 2, 6, 8.
The comparison of the results of single and multiple step (sequential extraction) methods that were used for the study of the marine sediments has given very interesting results for the determination of pollution associated with the various fractions. It has been shown that a significant portion of the pollution load deriving from land based sources settles in the immediate vicinity, whereas there are some more remote localities of suitable geomorphology (such as around st. 7) to which small metal-rich particles are transported and deposited under favourable hydrodynamic conditions. The study of sediment cores has indicated the impact of polluting activities in recent surface sediments. At the same time an increase of metal concentrations was observed in comparison with previous periods.On the other hand some environmentally positive signs, such as the 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 more details about the nature of metal associations in the sediment, and the chemical behavior and potential environmental impacts of metals in sediments, the use of sequential extractions such as those suggested by the BCR method (including eventually the determination of the 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 order to elaborate an appropriate integrated environmental management plan for the region towards sustainability. The overall hydrological regime of the area favours its rapid restoration by allowing nature to act for the selfpurification of the system. However ‘‘dilution should not be the only solution to pollution’’. We are confident that environmental management including drastic reduction of the pollution loads at the source and proper implementation of the EU and national legislation could result in a rapid full recovery of this ecologically and economically important marine environment.
Acknowledgements The authors would like to thank Professor Dr Michael Kersten for his variable suggestions and comments in the preparation of this work. References Agemian, F., Chau, A.S.Y., 1976. Evaluation of extraction techniques for the determination of metals in aquatic sediments. Analyst 101, 761–767. Angelidis, M., Grimanis, A.P., Zafiropoulos, D., VassilakiGrimani, M., 1980. Trace elements in sediments of Evoikos Gulf, Greece. Ves J. Etud Pollut. 5, 413–418.
M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794 Aualitia, T.U., Pickering, W.F., 1988. Sediment analysis— lability of selectively extracted fractions. Talanta 35, 559– 566. Carayannis, M.I., 1978. Evaluation, Processing and Presentation of Analytical Data. Athens, pp. 188–194. Chester, R., 1978. The Partitioning of Trace Elements in Sediments. Monograph. Comitato Nazionale Energia Nucleare, La Spezia, Italy. Clark, J.R., Vlets, J.G., 1981. Multielement extraction system for the determination of 18 trace elements in geochemichal samples. Anal. Chem. 53, 61–65. Dassenakis, M., Kloukiniotou, M., 1994. Cu and Zn in sediments of southern Euripos straits, Greece. In: Proc. 6th Internat. Conf. Environmental Contamination, Delphi, Greece, pp. 368–370. Dassenakis, M., Degaita, A., Scoullos, M., 1995. Trace metals in sediments of a Mediterranean estuary affected by human activities: Acheloos river estuary, Greece. Sci. Total Environ. 168, 19–31. Dassenakis, M., Kloukiniotou, M., Pavlidou, A., 1996. The effects of long existing pollution to trace metal levels in a small tidal Mediterranean bay. Mar. Poll. Bull. 32, 275–282. Dassenakis, M., Kapiris, K., Pavlidou, A., 2000. Aegean sea. In: Sheppard, C. (Ed.), Seas at the Millenium: An Environmental Evaluation, Vol. 1. Pergamon/An Imprint of Elsevier Science, pp. 233–252. Davidson, C.M., Thomas, R.P., McVey, S.E., Perala, R., Littlejohn, D., Ure, A.M., 1994. Evaluation of a sequential extraction procedure for the speciation of heavy metals in sediments. Anal. Chim. Acta 20 (291), 277–286. Fo¨rstner, U., Wittman, G., 1979. Metal Pollution in the Aquatic Environment. Springer, Berlin. Fo¨rstner, U., Salomons, W., 1988. Trace metals analysis on polluted sediments. I. Assessment of sources and intensities. Environ. Technol. Lett. 1, 494–505. Fiedler, H.D., Lopez-Sanchez, J.F., Rubio, R., Rauret, G., Quevauviller, P., Ure, A.M., Muntau, H., 1994. Study of the stability of extractable trace metal contents in a river sediment using sequential extraction. Analyst 119, 1109– 1114. Florian, D., Barnes, R.M., Knapp, G., 1998. Comparison of microwave-assisted acid leaching techniques for the determination of heavy metals in sediments, soils and sludges, Fres. J. Anal. Chem. 362, 558–565. Gaudette, H.E., Flight, W., Tones, L., Folger, D., 1974. An inexpensive titration method for the determinations of organic carbon in recent sediments. J. Sed. Petrol. 44, 249– 253. GESAMP/UNESCO, 1987. Land/sea boundary flux of contaminants: contributions from rivers. Rep. Studies 32, 67–81. GESAMP/UNESCO, 1994. Anthropogenic influences on sediment discharge to the coastal zone and Environmental Consequences. Rep. Studies 52, 4–30. Gibbs, R.J., 1973. Metal transport from rivers. Science 180, 71. Kaberi, H., Scoullos, M., 1996. The role of the green algae Ulva sp. in the cycling of copper in marine coastal ecosystems. MAP/UNEP Tech. Rep. Ser. 104, 83–96. Kheboian, C., Bauer, C.F., 1987. Accuracy of selective extraction procedures for metal speciation in model aquatic sediments. Anal. Chem. 59, 1417–1423. Kemp, A.L.W., Thomas, R.C., Dell, C.I., Jequet, J.M., 1976.
793
Cultural impact on the geochemistry of sediments in lake Erie. J. Fish. Res. Board Can. 33, 440–462. Kersten, M., Fo¨rstner, U., 1995. Speciation of trace metals in sediments and combustion waste. In: Ure, A.M., Davidson, C.M. (Eds.), Chemical Speciation in the Environment. Blackie Academic & Professional, UK, pp. 234–275. Kersten, M., Smedes, F., 2002. Normalization procedures for sediment contaminants in spatial and temporal trend monitoring. J. Environ. Monit. 4, 109–115. Latouche, C., Dumon, J.C., Lavaux, G., Pedemay, P., 1993. Trace metal speciation and research in marine geochemistry. Internat. J. Environ. Anal. Chem. 51, 177–185. Leodaris, S., Maroukian, X., Dassenakis, M., Poulos, S., Paulopoulos, K., Kloukiniotou, M., 1994. Environmental Study in the Avlida Coastal Zone (South Euvoikos Gulf). Depart. of Geology, Univ. Athens, pp. 16–24. Leal, M.F.C., Vaconcelos, M.T.S.D., Van der Berg, C.M.G., 1999. Copper induced release of complexing ligands similar to thiols by Emiliana puxlegi in seawater cultures. Limnol. Oceanog. 44, 1750–1762. Livieratos, E., 1979. The M2 Sea-Tidal propagation in the Euvoikos Bay. Technika Chronika 3, 49–55. Mahan, K.I., Foderaro, T.A., Garza, T.L., Martinez, R.M., 1987. Microwave digestion techniques in the sequential extraction of calcium, iron, chromium, manganese, lead and zinc in sediments. Anal. Chem. 59, 938–945. Martin, J.-M., Nirel, P., Thomas, A.G., 1987. Sequential extractions techniques: promises and problems. Mar. Chem. 22, 313–341. Quevauviller, P., Rauret, G., Griepink, B., 1993. Conclusions of the workshop. Single and sequential extraction in sediments and soils. Internat. J. Environ. Anal. Chem. 51, 231– 235. Quevauviller, P., Rauret, G., Muntau, H., Ure, A.M., Rubio, R., Lopez-Sanchez, J.F., Fiedler, H.D., Griepink, B., 1994. Evaluation of a sequential extraction procedure for the determination of extractable trace metals contents in sediments. Fres. J. Anal. Chem. 349, 808–814. Rabbiti, S., Blodrin, A., Menegazzo-Vitturi, L., 1983. Relationships between surface area and grain size in bottom sediments. J. Sed. Petrol. 53, 665–667. Rapin, F., Tessier, A., Campell, P.G.C., Carignan, R., 1986. Potential artifacts in the determination of metal partitioning in sediment by a sequential extraction procedure. Environ. Sci. Technol. 20, 836–840. Salomons, W., Fo¨rstner, U., 1984. Metals in the Hydrocycle. Springer-Verlag, Berlin. Scoullos, M., 1979. Chemical Studies of the Gulf of Elefsis, Greece. PHD Thesis, Dept Oceanography, Univ. Liverpool. Scoullos, M., 1983. Trace metals in a landlocked intermittently anoxic basin. In: Wong, C., Boyle, E., Bruland, K., Burton, J., Goldberg, E. (Eds.), Trace Metals in Seawater. Plenum Press, New York, pp. 351–366. Scoullos, M., 1986. Lead in coastal sediments: the case of the Elefsis Gulf, Greece. Sci. Total Environ. 49, 199–219. Scoullos, M., Dassenakis, M., 1982. Trace metal level in seawater and sediments of Euvoikos Gulf, Greece. VIes J. Etud. Pollut. 6, 425–429. Scoullos, M., Dassenakis, M., 1983. Trace metals in a tidal Mediterranean embayment. Mar. Pollut. Bull. 14, 24–29. Scoullos, M., Constandianos, E. Assessment of the State of
794
M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794
Pollution of the Mediterranean Sea by Zinc, Copper and Other Compounds. MAP technical Reports Series, No. 105. Sinex, S.A., Cantillo, A.Y., Helz, G.R., 1980. Accuracy of acid extraction methods for trace metals in sediments. Anal. Chem., Dec 52, 2342–2346. Smith, A.J., 1959. Description of the Mackereth portable core sampler. J. Sed. Petrol. 29, 246–250. Sulcek, Z., Povondra, P., Dolezal, J., 1977. Decomposition techniques in inorganic analysis. Crit. Rev. Anal. Chem. 255–321. Tack, F.M.G., Verloo, M.G., 1993. Leaching behavior and solid-phase fractionation of selected metals as affected by thermal treatment of a polluted sediment. Internat. J. Environ. Anal. Chem. 51, 167–175. Tessier, A., Campbell, G.C., Bisson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51, 844–850. UNEP, 1985. Reference Methods for Marine Pollution Studies, Nos. 31–39.
UNEP, 1991. In: Mee, L., Oregioni, P. (Eds.), Worldwide intercomparison of Trace Elements Measurements in Marine Sediments. IAEA/AL/053,IAEA/MEL/49,SD-M-2/TM, Report No. 49. Ure, A.M., Quevauviller, P., Muntau, H., Griepink, B., 1993. Speciation of heavy metals in soils and sediments. An account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the Commission of the European Communities. Internat. J. Environ. Anal. Chem. 51, 135–151. Usero, J., Gamero, M., Morillo, J., Gracia, I., 1998. Comparative study of three sequential extraction procedures for metals in marine sediments. Environ. Internat. 24, 487– 496. Vlachakis, G.N., Tsimblis, M.N., 1993. Euripus problem: review and a proposal. In: Proc. 4th Nat. Symp. Oceanography and Fisheries, National Centre for Marine Research, pp. 156–159.
The use of various methods for the study of metal pollution in 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 is affected by a strong tidal current. A sequential extraction schema and two single-step methods were used for the determination 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 the evolution of pollution in the area and the effectiveness of analytical methods. It has been confirmed that a significant part of the pollution load remains in coastal localities in the vicinity of the land based pollution sources, whereas there are also some more remote sites where small polluted particles are transported, deposited and accumulated. The sedimentology regime of the area affects the concentration of metals in a rather complex way depending also on its content of carbonates, organic C and clay minerals. The study of sediment cores has indicated elevated metal concentrations in recent surface sediments. On the other hand, some environmentally positive trends were also observed (i.e. the reduction of mobile metals). A systematic monitoring is needed in the marine environment coupled with some reduction in pollution inputs and integrated management on the coastal zone because the overall hydrological characteristics of the area favour its rapid self-restoration. # 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction The study of coastal sediments provides useful information in marine, environmental and geochemical research about marine pollution. Urban and industrial activities contribute to the introduction of significant amounts of pollutants (among them trace metals) into the marine environment and affect directly the coastal systems where they are quite often deposited. Heavy metals, pesticides and other toxic substances can be absorbed from the water column onto surfaces of fine particles and move thereafter with the sediments.Trace
* Corresponding author. E-mail address: [email protected] (M. Scoullos).
metals participate in various biogeochemical mechanisms, have significant mobility and can affect the ecosystems through bioaccumulation and bio-magnification processes. (GESAMP/UNESCO, 1987, 1994; Salomons and Fo¨rstner, 1984). A variety of analytical methods have been developed in order to study metals in marine sediments in an attempt to determine their concentrations and their impacts. (Sulcek et al., 1977; Fo¨rstner and Wittman, 1979; Quevauviller et al., 1993) These methods can be divided into single and multiple step schemes. Most geochemical studies concerning metals in sediments deal with total concentrations. They are usually determined by single step methods employing treatment of sediments with mixtures of concentrated, strong acids i.e. HNO3, HCl, HF etc. in high temperature and,
0883-2927/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0883-2927(02)00186-5
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eventually, high pressure (UNEP, 1985; Clark and Vlets, 1981). Single step techniques are used also for the determination of the portion of metals that is considered to have anthropogenic origin or is more readily bioavailable, often using dilute acids at lower temperatures (Agemian and Chau, 1976; Sinex et al., 1980; Tack and Verloo, 1993). Multiple step methods, better known as sequential extractions, offer a useful tool for the deduction of information about the various types of metal associations in sediments. They can also inform us about the potential availability of metals to biota, their mobilisation, transport and eventually, in a few cases, about the origin of certain metal species. Use of a series of special leaching reagents could, theoretically, separate the various metal forms in the sample. The sequential extraction schemes are designed after a series of investigations on combinations of ‘‘single-step’’ methods. (Tessier et al., 1979; Scoullos, 1979; Aualitia and Pickering, 1988; Latouche et al., 1993; Davidson et al., 1994; Kersten and Fo¨rstner, 1995). Following the increasing interest in these techniques, the ‘‘Bureau of Reference’’ of the Commission of the E.U. (BCR) has proposed a sequential extraction scheme suitable for preparation of a Certified Reference Material (CRM) (Ure et al., 1993; Quevauviller et al., 1994) because sequential extraction methods are still considered to have rather low reproducibility due to trace metal redistribution in the sediment samples and non-selective behaviour of reagents (Rapin et al., 1986; Martin et al., 1987; Kheboian and Bauer, 1987; Fiedler et al., 1994; Usero et al., 1998). The CRM-601 was used in this study. For the better understanding of the effects of pollution activities on the distribution of metals in marine sediments 3 procedures are combined in the study of heavy metals in Euvoikos gulf where the authors have carried out pollution research both during 1980 and 1993. Reference material is used for the evaluation of these techniques. 1.1. The study area Euvoikos gulf is a shallow embayment of the Aegean Sea formed by the eastern coasts of Attica and Boeotia and 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 the straits should be considered as a separate section of particular interest due to the significant tidal phenomena that are observed there. The morphology of the area causes the development of a strong tidal current (about 12 km/h at the narrowest part) that changes its direction every 6 h (Livieratos, 1979; Vlachakis and Tsiblis, 1993). Such currents are very scarce in the non tidal Mediterranean Sea and
have been noted and described previously by ancient Greek writers among which was Aristotle. Usual current velocities 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 dispersion of pollutants but also affects the sedimentation processes mainly in the immediate vicinity of the Euripos straits, where the fine grained sediment fraction is eliminated. In the rest of the area the seabed is covered mainly by sand, silt and mud and at certain localities, near the coast, by pebbles. Fig. 2 presents 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 (which is included in Fig. 1 but not in Fig. 2)the composition of sediments is for Station 1: clay 51.5%, silt 38.7%, sand 9.8%, 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 waste water treatment plant of the city of Chalkis with a resident population of about 51 000 inhabitants, according to the inventory of 1991, is located on a small island in the gulf (see Fig. 1) and the treated effluents are disposed to the sea. Several industries such as cement, textile, paint, food, metal-forming and ceramic factories, shipyards etc. are located along the coastal zone. Consequently, significant alteration of the coastline, as well as construction of harbors and other interventions, has taken place in their neighborhood. Several industries have wastewater treatment plants but either because of improper operations or total lack of treatment facilities, still a significant amount of industrial effluents is disposed virtually untreated or poorly treated, directly into the sea. There is also significant air-borne pollution due to various emissions of metal enriched dust deriving from the cement factory, the shipyard etc. Transport (navigation and road traffic) is also a significant source of pollution in the area. Finally some drainage canals from cultivated agricultural lands also contribute to the pollution through runoff. It is noteworthly that industrial and urban pollution activities in the area have remained practically at the same level during the last 30 years whereas wastewater treatment plants were introduced only during the last decade. Although many problems concerning the quality of seawater have been reported in the last few years, there is neither sufficient chemical monitoring in the area nor a coastal zone management plan. Data available on trace metal levels and distributions refer to the years 1980 (Angelidis et al., 1980; Scoullos and Dassenakis, 1982, 1983) and 1993 (Dassenakis and Kloukiniotou, 1994; Dassenakis et al., 1996) only.
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783
Fig. 1. The studied area and the sampling stations.
2. Materials and methods Sediment samples were collected during 1997 in the area of Central Euvoikos Gulf by a grab sampler. Sampling stations are shown in Fig. 1 and are described in Table 1. A Mackereth corer (Smith, 1959) was used for the collection of 4 sediment cores, at stations 1, 2, 6 and 8. In Table 1 are also presented the values of salinity, pH and dissolved O2 in the near bottom water layer. In the studied area, due to the tidal current, no strong stratification is observed even during summer, the water is well oxygenated and there are no 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 C in a closed fan-assisted oven. It is a common procedure for the normalization of the results (Kersten and Smedes, 2002). The metal analyses were performed in the silt and clay fraction (<61 mm), because the metals are usually associated with the small grains. This fraction is also easily homogenized for better reproducibility in metal measurements (Rabbiti et al., 1983; Fo¨rstner 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 organic compounds of the sediment in strong acidic conditions (Gaudette et al., 1974).
The samples were treated by the following ‘‘singlestep’’ methods: Shaking overnight at room temperature with dilute (0.5N) HCl, to extract the ‘‘metal fraction weakly bound to the sediment’’ (W), which appears to be of ‘‘anthropogenic origin’’ (Agemian and Chau, 1976). The weight difference in this treatment represents the carbonate content of the sample. Overnight treatment with concentrated HF– HNO3–HClO4 (1:3:1) in covered PTFE beakers on 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 technique, based on the method proposed by BCR (Ure et al., 1993; Quevauviller et al., 1994) outlined below: 1. Shaking overnight with acetic acid (0.11M) at room temperature, to extract the ‘‘exchangeable fraction, soluble to water and acid’’ (E). 2. Shaking overnight with hydroxylammonium chloride (0.1M), to extract the ‘‘reducible fraction (mainly oxides) of the metal content’’ (R).
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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 2 3 4 5 6 7 8 9 10 11 13 14
Center of the small gulf Ceramics factory (50 m from the coast) Agios Stefanos bay Chalkis waste treatment plant (near the outfall pipe) Cement industry (50 m from the coast) Shipyard (50 m from the coast) Entry of the bay (in the middle) Chemical industries (50 m from the coast) Center of the gulf Faros area (100m from the west coast) Burtzi area (100m from east coast) Reference station Chipboard industry (50 m from the coast)
12 4 4 10 5 10 5 4 12 5 5 30 15
8.21 8.27 8.20 8.22 8.19 8.28 8.30 8.25 8.26 8.25 8.13 8.24 8.28
38.2 36.4 38.0 35.6 38.6 38.2 38.3 38.6 38.6 38.7 38.7 38.4 37.0
92 97 99 90 95 93 100 91 102 102 101 99 90
3. Treatment with hydrogen peroxide (8.8M) twice in a special microwave oven (Prolabo ‘‘Microdigest 40100 ) for 10 min, to extract the ‘‘oxidizable fraction (mainly sulphides and organometallic complexes)’’ (O) and shaking with ammonium acetate (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, to extract the ‘‘residual metallic fraction strongly associated with the sediment’’ (L).
The authors’ method, compared to the BCR one, introduced the following modifications: (a) Microwave digestion was used instead of heating beakers on a hot plate (Mahan et al., 1987; Florian et al., 1998). (b) The metal content of the residual fraction was also measured. All metal determinations, following both the singlestep and the sequential extractions, were performed by
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M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794 Table 2 Measurements of metals in of reference sediments (all values in mg/g ppm) IAEA/SD-M-2 T/M (total content)
Cu Zn Mn Fe
IAEA/SD-M-1 T/M (total content)
Certified values
Found
Certified values
Found
32.7 1.2 74.8 3.1 1170100 271301800
33.6 82 1060 26 600
25.1 3.8 191 17176 513 25551 30 000 1500
28.1
31 150
BCR/ CRM- 601 (Sequential extractions) BCR method Metal Fraction
Certified values Found
Metal Fraction
Certified values Found
Cu
10.50.8 72.84.9 78.68.9 60.44.9 23015
Zn
26113 26617 10611 1614 83317
Exchangeable Reducible Organic Residue (aqua regia) Pseudo Total (aqua regia)
1979, 1986, Scoullos method EE NLI NLO L
10.30.4 65.91.8 75.83.7 56.52.2 2176
4.60.8 84.811.1 14.80.9 95.37.3
flame or graphite furnace atomic absorption spectrometry (Varian SpectrAA-100/ Varian SpectrAA-640 Zeeman). 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) were analyzed for their total metal content (UNEP, 1991). The BCR CRM-601 sediment that is certified for the BCR sequential method was also analyzed. The results are 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 having mainly geological origin (Fe and Mn). 3.1. Single step techniques It is clear from Table 3 that the organic C concentrations are reduced from the northern (1, 2) to the southern (10, 11, 13) stations probably because the main sources of TOC in the area are near the city of Chalkis. The tidal current in the area prevents the development of water column stratification and the formation of intermittently anoxic conditions, which could have lead
Exchangeable Reducible Organic Residue (aqua regia) Pseudo Total (aqua regia)
298 11 301 9 114 3 133 4 838 15
0.94.4 518 10.3 29.3 1.2 350.410.6
to high concentrations of organic C. This phenomenon has 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 content was observed in sediments of near shore stations (e.g. 14, 8, 5), that are affected by polluting activities. As the carbonates are not included in the industrial effluents, probable reasons for this phenomenon could be either the dredging of near shore sediments due to the waterway maintenance near the industrial facilities, or the contribution of atmospheric deposition of cement dust, or even biogenic carbonates in areas of apparently increased productivity due to higher nutrient content. The finegrained sediments near the cement industry (st. 5) are significantly enriched in metals, probably due to a significant cement dust deposition. The high values of Fe and Mn support the terrestrial origin of metals, and the high W fraction percentages (> 50% for Cu, Zn, Mn ) indicate increased mobility and bioavailability. Elevated concentrations of Cu, were observed at stations 7 and 8 in Vathy bay. This distribution is similar to the one observed in 1993 (Dassenakis and Kloukiniotou, 1994) which is an indication that the neighbouring industries continue to enrich the marine environment in these metals. High W fraction percentages were observed at station 7 (64.5% for Cu, 62% for
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Table 3 Metals, organic C and carbonates after ‘‘single-step’’ extractions. W: Weakly bound, T: Total (all values in ppm mg/g) Stations
1 2 3 4 5 6 7 8 9 10 11 13 14 Shipyard (inside)
%TOC
1.7 1.5 1.4 1.1 1.2 1.3 1.1 1.4 1.3 0.6 0.7 0.9 1.0
%CO3
14 26 34 32 39 18 35 43 35 27 25 27 60
Cu
Zn
Mn
Fe
W
T
W
T
W
T
W
T
14.2 14.0 9.60 20.7 23.6 5.10 48.9 45.9 23.5 10.5 9.90 11.5 12.7
40.5 37.7 29.9 41.5 36.8 38.5 75.9 83.9 36.1 38.7 41.4 63.5 55.5 240
62.4 85.8 34.6 63.8 93.8 12.7 50.1 86.6 35.1 22.8 41.3 26.4 74.7
108 141 90.2 102 150 66.5 81.0 114 99.5 179 77.7 99.0 161 435
270 262 393 285 393 176 322 253 332 243 258 308 214
383 446 702 482 611 341 561 309 547 320 506 455 379 536
3940 3870 2380 4890 7840 2620 4000 4770 3320 2370 4710 3750 7780
23 22 36 38 34 23 18 18 35 14 28 39 16 35
Zn, 21% for Fe). These observations, in combination with the sedimentation pattern of Fig. 2, indicate that the fines transported from various sources in the area of station 7 are enriched in metals, which are potentially harmful for the local ecosystems due to their enhanced mobility. In the case of station 6 near the shipyard, the total metal concentrations were much lower than the ones determined in samples collected within the shipyard. Probably heavy metal enriched particles, originated from the operations in the shipyard, are too coarse 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 outfall of the City of Chalkis (st. 4) probably because they are not removed effectively through the treatment applied there. The significant chipboard industry near station 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 central part of the area (st.13 and 10) which is far from pollution sources (27 and 18% for Cu, 12.5 and 26.5% for Zn, 17 and 9% for Fe). As is the case with TOC, the metal pollution from land based sources remains 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 of Mn 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 contribution of the lattice-held fraction of the metal.
710 500 420 380 210 460 680 450 500 040 940 680 700 600
An overall increase of Mn concentrations was noted at stations 3 and 5, probably due to the existence of increased 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) but not at stations 6, 7, 8 and 14 (near main pollution sources). The comparison of the results of the 3 sampling periods (1980, 1993, 1997) revealed a continuous increase of pollution levels near the cement industry (st. 5), the waste water treatment plant, which had not been established during 1980, (st. 4) but also in the central area (st. 9) relatively far from pollution discharges. On the other hand, the percentages of weakly bound Cu were considerably higher during 1980 (stations 3, 4, 5) and 1993 (stations 6, 7, 8) in comparison to the 1997 campaign,
Table 4 Weakly bound and Total concentrations of Cu and Zn during 1980 and 1993 periods (all values in ppm mg/g) Stations
3 4 5 6 7 8 9
Cu 1980
Cu 1993
Zn 1980
Zn 1993
W
T
W
T
W
T
W
T
15.3 14.4 11.3
16.0 15.0 14.0
59.5 67.0 51.5
12.2
28.4 53.9 55.3 44.9 80.4 37.8
42.8 40.2 21.3
11.7
5.8 10.8 41.8 36.3 52.5 1.3
20.3
46.0
29.8 54.2 55.2 126 200 23.9
76.9 81.7 129 136 377 83.1
W, weakly, T, total. Scoullos and Dassenakis, 1983; Dassenakis et al., 1996.
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indicating an environmentally positive trend. The percentages of W metal fraction at station 7 (centre of Vathy bay) have remained higher than in coastal st. 8 in all the periods studied (Table 4) The changes that have occurred in the area throughout the last decades, as it concerns production rates and introduction of new technologies in industries, in combination with the establishment of treatment plants for sewage and industrial effluents, have not led yet to a significant environmental improvement in the area at least with respect to trace metals (in contrast e.g. to eutrophication), although in some cases (such as at stations 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 monitoring by study of sediment cores is very useful. The results of such a study for the area of central Euvoikos gulf are presented in Table 5 and in Fig. 9. In the case of the ‘‘anthropogenic’’ (W) metals fraction a significant downcore decrease is apparent at station 8 for all metals, at station 1 for Zn, Cu and Fe below the 10 cm ‘‘peak’’ layer and at station 2 for Zn. This trend was not observed for Mn although characteristic features (such as the peak layer at 10cm depth of st.1) are visible also in the Mn vertical distribution. For total metals (T) a similar trend is clearly observed at station 8 (for Cu and in a more complicated manner for Zn) and station 2 (for Zn). Although the sedimentation rate in that area is not known and it is expected to vary significantly from one locality to another due to the complex tidal regime, the
decreasing downcore trend is a clear indication that the industrial polluting activities have enriched the surface marine sediments with metals. The decrease in surface concentrations at station 1 which is not near the main sources, and where the clay–silt sediment fraction is about 90%, is probably (if the contribution of erosion is not high) an encouraging indication about the beneficial results of the establishment and operation of wastewater treatment plants in the area. Sediment Enrichment Factor (EF), defined as [(C0/ Al0)(Cd/Ald)]/[Cd/Ald] where C0 is the concentration of the metal determined in the surface layer, Cd the concentration of the same metal in a reference depth and Al0Ald the corresponding concentrations of Al which is considered to have mainly geological origin, could be used for the assessment of anthropogenic metal enrichment (Kemp et al., 1976). The deepest sample of each core was used as reference. Two EF were determined, one concerning the total (EFt) and one concerning the concentrations of the weakly held metal (EFw). In both cases the same (total) Alt value was used since it is known that Al as a basic element of the aluminosilicate lattice of minerals has a negligible W fraction (Fo¨rstner and Wittman, 1979). The results show that there is a significant pollution enrichment at station 8 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 is that 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 27–32 62–67
40.5 40.4 41.6
23 710 26 180 30 480
383 429 529
108 110 81.0
2
0–5 20–25 35–40
37.7 40.2 38.6
22 500 26 180 28 400
446 426 494
141 94.0 78.5
6
0–2 5–10 24–29
38.5 17.9 35.2
23 460 24 040 23 860
341 389 259
66.5 63.7 110
8
0–1 5–6 10–15 15–20 20–25 30–35 40–45
83.9 62.2 60.4 65.2 76.3 51.1 22.2
18 20 23 32 28 20 23
309 326 291 386 327 281 512
114 68.8 107 160 61.1 57.5 64.6
450 750 980 450 760 720 170
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environment related to the increased bioavailable metal proportions. 3.2. Multiple step procedures The main conclusions one could extract from the results 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 known close association of Mn with carbonates that are dissolved by the reagent of the first step of the sequential process. The highest proportions of MnE values among the sampling stations were
observed in the southern part of the gulf, in areas with a relatively high percentage of sand (Fig. 2). In the case of Mn elevated values of the reducible (R) fraction were also observed (13–45%) due to known high mobility of reducible forms of Mn. In contrast to the E fraction, the highest R values were observed in the northern part of the system at stations with a relatively high percentage of clay and organic C. The previous observations are in good agreement with the behaviour of Mn in the single step methods by the use of dilute HCl. In the case of Fe, the percentages of E and R fractions 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.
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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.
indication the geological origin of the element in the study area. Some relatively high values of the FeR fraction near pollution sources at stations 5 (cement), 6 (shipyard) and 7 (chemicals) indicate that human activities could also contribute to an enrichment of coastal sediments with Fe. The fluctuation of the percentage of Fe that was extracted by dilute HCl, follow those of the E+R+O fractions. There is however an exception to this trend observed at station 14 where 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 station 1. There is no certain explanation for this
exception. The existence of complex oxide– hydroxide forms of Fe with low solubility in the reagents used in the first 3 steps of the sequential extraction, might be a possible reason for this difference, in combination with the fact that station 14 is located in a site apart from the other stations and its sediments are connected to a somewhat different catchment area. Alternatively some recent dredging activities might have exposed near surface underlying sediments of a different nature to those of the rest of the region. In the case of Al, E, R and O fraction percentages were indeed very low to negligible, a fact
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which justifies its use for the determination of EF. Elevated percentages of organic fraction (O) were measured for Cu (11–30%). This is probably due to the well-known tendency of Cu to form organic complexes e.g. with humic acids and various metabolites deriving from algal biomass decomposition and other biochemical reactions (Salomons and Fo¨rstner, 1984; Kaberi and Scoullos, 1996; Leal et al., 1999). A relative increase of organic Zn was observed at station 4 near the outlets of the waste treatment plant, obviously due to the availability of many suitable organic ligands in the area, and at station 8 near some chemical industries. 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, the presence of R is combined with the increased percentage of the W fraction (64–62%). At the same station the lowest residual (L) values were measured. These observations support the hypothesis of the transport and accumulation of small polluted particles from various parts of the 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%), probably due 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 stations 6 and 8 was not very successful as no clear trend was observed in the vertical distribution of the various metal fractions.
A comparison of the results of sequential extractions with the percentages of weakly bound metals (W), indicates that the use of dilute HCl is a very good simple method for the determination of mobile metals because effectively it includes the E and R fractions, without affecting the aluminosilicate lattice. Only in the case of Fe was a limited attack observed. On the other hand dilute HCl is strong enough to dissolve carbonate minerals. If the sediment contains a high percentage of such minerals, which are frequently biogenic, the results of the method may become difficult to interpret because the metal content will not correspond to metals of anthropogenic origin at least with regard to metals that are closely associated to carbonates (e.g. Mn or Zn).
The ability of HCl to extract the organic fraction depends on the relative stability of the organic compounds. In some cases the W fraction of the single-step technique 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 at stations 6, 7, 8, 10). In cases of sediments with high organic 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 by Scoullos (1979, 1986). That sequential extraction was based on a combination of schemes suggested by Chester (1978) and Gibbs (1973) and follows the steps described below (Figs. 7–9): 1. Treatment with 1M MgCl2 for 16 h at room temperature, to extract the ‘‘easily exchangeable metal 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 presented in Figs. 7 and 8 in the same manner done for the 1997 period. This method was also used on the CRM 601 reference sediment of the BCR, which was analysed by 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 corresponds to the EE+NLI fraction of the Scoullos (1979, 1986) method if the two reagents are applied in sequence to the same sediment sample. In both cases we have the easily extractable inorganic fraction, which is not held by the aluminosilicate lattice, the fraction held in carbonates and the easily reducible fraction. If the truly ‘‘easily extractable fraction’’ (EE) determined by the use of MgCl2 in the Scoullos (1979,1986) method is of interest, an additional initial first step should be added to the BCR method. 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 sediment from the overlying waters. It also represents the very small portion of the dried interstitial waters.
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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 NLI represents metal species that are associated with Fe and Mn oxides and carbonate minerals together with those adsorbed onto all mineral surfaces. In fact this does not include metal associated with authigenic sulphides and a few other complexes. As for the O fraction, the BCR method apparently always reflects higher extactions than the NLO of the Scoullos (1979, 1986) method. This is due to the fact that the O fraction includes theoretically the entire oxidizable fraction, practically all the sulphides as well as complexes with organic ligands, while NLO includes the latter and only a small part of the former. In both periods studied (1993, 1997) the percentages of 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 sediments have occurred.
4. Conclusions In the area of the central Euvoikos gulf, the tidal current of the Evripos straits which disperses the metals together with the improvement in the operation and technology used by local industries and the discontinuation of certain polluting activities (e.g. shipyards were shut down for several months due to financial problems) makes it very difficult to properly assess the evolution of the state of the environment of the gulf in any detail.
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Fig. 9. Vertical distributions of weakly bound (W) metal concentrations in sediment cores at stations 1, 2, 6, 8.
The comparison of the results of single and multiple step (sequential extraction) methods that were used for the study of the marine sediments has given very interesting results for the determination of pollution associated with the various fractions. It has been shown that a significant portion of the pollution load deriving from land based sources settles in the immediate vicinity, whereas there are some more remote localities of suitable geomorphology (such as around st. 7) to which small metal-rich particles are transported and deposited under favourable hydrodynamic conditions. The study of sediment cores has indicated the impact of polluting activities in recent surface sediments. At the same time an increase of metal concentrations was observed in comparison with previous periods.On the other hand some environmentally positive signs, such as the 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 more details about the nature of metal associations in the sediment, and the chemical behavior and potential environmental impacts of metals in sediments, the use of sequential extractions such as those suggested by the BCR method (including eventually the determination of the 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 order to elaborate an appropriate integrated environmental management plan for the region towards sustainability. The overall hydrological regime of the area favours its rapid restoration by allowing nature to act for the selfpurification of the system. However ‘‘dilution should not be the only solution to pollution’’. We are confident that environmental management including drastic reduction of the pollution loads at the source and proper implementation of the EU and national legislation could result in a rapid full recovery of this ecologically and economically important marine environment.
Acknowledgements The authors would like to thank Professor Dr Michael Kersten for his variable suggestions and comments in the preparation of this work. References Agemian, F., Chau, A.S.Y., 1976. Evaluation of extraction techniques for the determination of metals in aquatic sediments. Analyst 101, 761–767. Angelidis, M., Grimanis, A.P., Zafiropoulos, D., VassilakiGrimani, M., 1980. Trace elements in sediments of Evoikos Gulf, Greece. Ves J. Etud Pollut. 5, 413–418.
M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794 Aualitia, T.U., Pickering, W.F., 1988. Sediment analysis— lability of selectively extracted fractions. Talanta 35, 559– 566. Carayannis, M.I., 1978. Evaluation, Processing and Presentation of Analytical Data. Athens, pp. 188–194. Chester, R., 1978. The Partitioning of Trace Elements in Sediments. Monograph. Comitato Nazionale Energia Nucleare, La Spezia, Italy. Clark, J.R., Vlets, J.G., 1981. Multielement extraction system for the determination of 18 trace elements in geochemichal samples. Anal. Chem. 53, 61–65. Dassenakis, M., Kloukiniotou, M., 1994. Cu and Zn in sediments of southern Euripos straits, Greece. In: Proc. 6th Internat. Conf. Environmental Contamination, Delphi, Greece, pp. 368–370. Dassenakis, M., Degaita, A., Scoullos, M., 1995. Trace metals in sediments of a Mediterranean estuary affected by human activities: Acheloos river estuary, Greece. Sci. Total Environ. 168, 19–31. Dassenakis, M., Kloukiniotou, M., Pavlidou, A., 1996. The effects of long existing pollution to trace metal levels in a small tidal Mediterranean bay. Mar. Poll. Bull. 32, 275–282. Dassenakis, M., Kapiris, K., Pavlidou, A., 2000. Aegean sea. In: Sheppard, C. (Ed.), Seas at the Millenium: An Environmental Evaluation, Vol. 1. Pergamon/An Imprint of Elsevier Science, pp. 233–252. Davidson, C.M., Thomas, R.P., McVey, S.E., Perala, R., Littlejohn, D., Ure, A.M., 1994. Evaluation of a sequential extraction procedure for the speciation of heavy metals in sediments. Anal. Chim. Acta 20 (291), 277–286. Fo¨rstner, U., Wittman, G., 1979. Metal Pollution in the Aquatic Environment. Springer, Berlin. Fo¨rstner, U., Salomons, W., 1988. Trace metals analysis on polluted sediments. I. Assessment of sources and intensities. Environ. Technol. Lett. 1, 494–505. Fiedler, H.D., Lopez-Sanchez, J.F., Rubio, R., Rauret, G., Quevauviller, P., Ure, A.M., Muntau, H., 1994. Study of the stability of extractable trace metal contents in a river sediment using sequential extraction. Analyst 119, 1109– 1114. Florian, D., Barnes, R.M., Knapp, G., 1998. Comparison of microwave-assisted acid leaching techniques for the determination of heavy metals in sediments, soils and sludges, Fres. J. Anal. Chem. 362, 558–565. Gaudette, H.E., Flight, W., Tones, L., Folger, D., 1974. An inexpensive titration method for the determinations of organic carbon in recent sediments. J. Sed. Petrol. 44, 249– 253. GESAMP/UNESCO, 1987. Land/sea boundary flux of contaminants: contributions from rivers. Rep. Studies 32, 67–81. GESAMP/UNESCO, 1994. Anthropogenic influences on sediment discharge to the coastal zone and Environmental Consequences. Rep. Studies 52, 4–30. Gibbs, R.J., 1973. Metal transport from rivers. Science 180, 71. Kaberi, H., Scoullos, M., 1996. The role of the green algae Ulva sp. in the cycling of copper in marine coastal ecosystems. MAP/UNEP Tech. Rep. Ser. 104, 83–96. Kheboian, C., Bauer, C.F., 1987. Accuracy of selective extraction procedures for metal speciation in model aquatic sediments. Anal. Chem. 59, 1417–1423. Kemp, A.L.W., Thomas, R.C., Dell, C.I., Jequet, J.M., 1976.
793
Cultural impact on the geochemistry of sediments in lake Erie. J. Fish. Res. Board Can. 33, 440–462. Kersten, M., Fo¨rstner, U., 1995. Speciation of trace metals in sediments and combustion waste. In: Ure, A.M., Davidson, C.M. (Eds.), Chemical Speciation in the Environment. Blackie Academic & Professional, UK, pp. 234–275. Kersten, M., Smedes, F., 2002. Normalization procedures for sediment contaminants in spatial and temporal trend monitoring. J. Environ. Monit. 4, 109–115. Latouche, C., Dumon, J.C., Lavaux, G., Pedemay, P., 1993. Trace metal speciation and research in marine geochemistry. Internat. J. Environ. Anal. Chem. 51, 177–185. Leodaris, S., Maroukian, X., Dassenakis, M., Poulos, S., Paulopoulos, K., Kloukiniotou, M., 1994. Environmental Study in the Avlida Coastal Zone (South Euvoikos Gulf). Depart. of Geology, Univ. Athens, pp. 16–24. Leal, M.F.C., Vaconcelos, M.T.S.D., Van der Berg, C.M.G., 1999. Copper induced release of complexing ligands similar to thiols by Emiliana puxlegi in seawater cultures. Limnol. Oceanog. 44, 1750–1762. Livieratos, E., 1979. The M2 Sea-Tidal propagation in the Euvoikos Bay. Technika Chronika 3, 49–55. Mahan, K.I., Foderaro, T.A., Garza, T.L., Martinez, R.M., 1987. Microwave digestion techniques in the sequential extraction of calcium, iron, chromium, manganese, lead and zinc in sediments. Anal. Chem. 59, 938–945. Martin, J.-M., Nirel, P., Thomas, A.G., 1987. Sequential extractions techniques: promises and problems. Mar. Chem. 22, 313–341. Quevauviller, P., Rauret, G., Griepink, B., 1993. Conclusions of the workshop. Single and sequential extraction in sediments and soils. Internat. J. Environ. Anal. Chem. 51, 231– 235. Quevauviller, P., Rauret, G., Muntau, H., Ure, A.M., Rubio, R., Lopez-Sanchez, J.F., Fiedler, H.D., Griepink, B., 1994. Evaluation of a sequential extraction procedure for the determination of extractable trace metals contents in sediments. Fres. J. Anal. Chem. 349, 808–814. Rabbiti, S., Blodrin, A., Menegazzo-Vitturi, L., 1983. Relationships between surface area and grain size in bottom sediments. J. Sed. Petrol. 53, 665–667. Rapin, F., Tessier, A., Campell, P.G.C., Carignan, R., 1986. Potential artifacts in the determination of metal partitioning in sediment by a sequential extraction procedure. Environ. Sci. Technol. 20, 836–840. Salomons, W., Fo¨rstner, U., 1984. Metals in the Hydrocycle. Springer-Verlag, Berlin. Scoullos, M., 1979. Chemical Studies of the Gulf of Elefsis, Greece. PHD Thesis, Dept Oceanography, Univ. Liverpool. Scoullos, M., 1983. Trace metals in a landlocked intermittently anoxic basin. In: Wong, C., Boyle, E., Bruland, K., Burton, J., Goldberg, E. (Eds.), Trace Metals in Seawater. Plenum Press, New York, pp. 351–366. Scoullos, M., 1986. Lead in coastal sediments: the case of the Elefsis Gulf, Greece. Sci. Total Environ. 49, 199–219. Scoullos, M., Dassenakis, M., 1982. Trace metal level in seawater and sediments of Euvoikos Gulf, Greece. VIes J. Etud. Pollut. 6, 425–429. Scoullos, M., Dassenakis, M., 1983. Trace metals in a tidal Mediterranean embayment. Mar. Pollut. Bull. 14, 24–29. Scoullos, M., Constandianos, E. Assessment of the State of
794
M. Dassenakis et al. / Applied Geochemistry 18 (2003) 781–794
Pollution of the Mediterranean Sea by Zinc, Copper and Other Compounds. MAP technical Reports Series, No. 105. Sinex, S.A., Cantillo, A.Y., Helz, G.R., 1980. Accuracy of acid extraction methods for trace metals in sediments. Anal. Chem., Dec 52, 2342–2346. Smith, A.J., 1959. Description of the Mackereth portable core sampler. J. Sed. Petrol. 29, 246–250. Sulcek, Z., Povondra, P., Dolezal, J., 1977. Decomposition techniques in inorganic analysis. Crit. Rev. Anal. Chem. 255–321. Tack, F.M.G., Verloo, M.G., 1993. Leaching behavior and solid-phase fractionation of selected metals as affected by thermal treatment of a polluted sediment. Internat. J. Environ. Anal. Chem. 51, 167–175. Tessier, A., Campbell, G.C., Bisson, M., 1979. Sequential extraction procedure for the speciation of particulate trace metals. Anal. Chem. 51, 844–850. UNEP, 1985. Reference Methods for Marine Pollution Studies, Nos. 31–39.
UNEP, 1991. In: Mee, L., Oregioni, P. (Eds.), Worldwide intercomparison of Trace Elements Measurements in Marine Sediments. IAEA/AL/053,IAEA/MEL/49,SD-M-2/TM, Report No. 49. Ure, A.M., Quevauviller, P., Muntau, H., Griepink, B., 1993. Speciation of heavy metals in soils and sediments. An account of the improvement and harmonization of extraction techniques undertaken under the auspices of the BCR of the Commission of the European Communities. Internat. J. Environ. Anal. Chem. 51, 135–151. Usero, J., Gamero, M., Morillo, J., Gracia, I., 1998. Comparative study of three sequential extraction procedures for metals in marine sediments. Environ. Internat. 24, 487– 496. Vlachakis, G.N., Tsimblis, M.N., 1993. Euripus problem: review and a proposal. In: Proc. 4th Nat. Symp. Oceanography and Fisheries, National Centre for Marine Research, pp. 156–159.