1 Introduction

The Keratsini harbor, in the Saronikos Gulf, Greece (Fig. 1), is the commercial port of Pireaus, one of the most important ports of the Mediterranean Sea. The harbor is surrounded by the most industrialized and urbanized areas of Attica region including the greater Athens area. Until 1994, the Kerarsini bay accepted untreated waste from the greater Athens area through a central sewer outfall. Approximately 600,000 m3/day of sewage flow were discharging into the Kerarsini harbor during the central sewer operation (Theodorou and Perissoratis 1991). Now, the sewage outfall is almost entirely replaced by a new waste treatment and disposal system in Psitallia island, near Keratsini harbor.

Fig. 1
figure 1

The study area and location of the sediment samples. Isobaths are in meters

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In a previous study (Galanopoulou et al. 2005), there have been detected highly elevated concentrations of dichloro-diphenyl-trichloroethanes and other chlorinated organic pesticides and polychlorinated biphenyls in the sediments of Keratsini harbor. Elevated concentrations of aliphatic and polycyclic aromatic hydrocarbons have also been reported in the near Elefsis bay (Sklivagou et al. 2001). The present study aims to assess the pollution of the sediments of the Keratsini harbor by heavy metals and to examine their distribution and their sources.

2 Materials and Methods

Eighty-six sediment samples were collected from the seabed of the Keratsini harbor by means of a Van Veen type grab sampler. The sediments were placed in plastic bottles and were kept at −18°C until the grain size, chemical, and mineralogical analyses were carried out. Taking into account their homogeneity, their grain size, and their mineralogical composition, 30 representative sediment samples (Fig. 1) were chosen for the analysis of nine metals (Cd, Pb, W, Zn, As, Se, Cr, Cu, and As). Nearly total extraction of the metals was achieved with KNaCO3 and HCl as described by Galanopoulou (2005). The determination of metal content was carried out by applying inductively coupled plasma–atomic emission spectrometry. Accuracy of the determinations was checked by the analysis of the international standard reference material PACS-2 (National Research Council Canada). The analytical precision was generally better than 5%. Oxidable organic carbon (Corg) was also determined using the Walkley (1947) technique.

The degree of contamination of the surficial sediments of the Keratsini harbor with heavy metals was assessed on the basis of the geoaccumulation index of Müller (1979) and the corresponding sediment quality guidelines (SQGs) effects range low/effects range median (ERL/ERM; Long et al. 1995).

3 Results and Discussion

3.1 Heavy Metal Pollution

Table 1 presents the concentrations of heavy metals and Corg in the sediments of the Keratsini harbor. The results show variable concentrations of Cd (190–1,763 mg kg−1), Zn (409–6,725 mg kg−1), Pb (521–1,263 mg kg−1), Cr (264–860 mg kg−1), Cu (195–518 mg kg−1), Mn (95–1,101 mg kg−1), W (38–100 mg kg−1), As (not detectable–1,813 mg kg−1), and Se (not detectable–58 mg kg−1).

Table 1 Results of the chemical analyses of the surficial sediments of Keratsini harbor
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A comparison of the abovementioned concentrations with the corresponding values of the metals given for the shales by Wedepohl (1969, 1978) grades the values of all the considered metals in the Keratsini harbor as high to very high (Table 2). However, earlier research in the broad area of Keratsini harbor has produced lower Zn, Pb, Cr, Cu, and Mn values (Grimmanis et al. 1977; Scoullos 1981; Voutsinou-Taliadouri 1981; Scoullos 1986; Sioulas et al. 1990; Zorpas et al. 2001). According to Table 2 the concentration levels of Cd, Pb, Zn, and Cu observed in the surface sediments of Keratsini harbor are also higher than the concentrations traced in similar harbors in Greece, e.g., in the harbor of Rhodes (Angelidis and Aloupi 1995) and in the harbor of Mytilene (Cd, 0.30–0.495 μg g−1, Aloupi and Angelidis 2001) and in highly industrialized and polluted areas and harbors worldwide, e.g., Port of Bangoli, Gulf of Naples, Italy (Romano et al. 2004), Tolo harbor, Hong Kong (Owen and Sandhu 2000), Victoria harbor Hong Kong (Wong et al. 1995), Montevideo harbor, Uruguay (Muniz et al. 2004), Kaohsiung harbor, Taiwan (Chen et al. 2007), and Barcelona harbor (Guevara-Riba et al. 2004). The values of Cu measured in Victoria and Barcelona harbor are excepted. On the other hand higher Pb, Zn, and Cu concentrations have been observed in the East London harbor and Elizabeth harbor, UK (Fatoki and Mathabatha 2001).

Table 2 Heavy metal pollution levels in marine surface sediments of different areas in the world (in mg kg−1)
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The Mn values of the sediments in the study area are comparable with those of the East London harbor and Port Elizabeth harbor, UK (Fatoki and Mathabatha 2001; Table 2) as well as with those of Victoria harbor, Hong Kong (Wong et al. 1995; Table 2) and Portovesme harbor, Sardinia (Schintu and Deggetto 1999). However, the W concentrations of the sediments of the Keratsini harbor are lower in comparison to the ones observed in Portovesme, Sardinia (0.04–0.10%, Schintu and Deggetto 1999; Table 2), while the concentrations of As detected in the seven samples of the study area are higher than the corresponding values in other ports in the world polluted by arsenic, e.g., the Copenhagen harbor (3.4–15 mg kg−1 dry sample; Andersen et al. 1998).

These high values of heavy metals observed in the sediments of the study area are due probably to the central Athens sewage outfall as well as to pollutants from the ships (paint, etc.) and the industries. As a matter of fact, high Pb, Cu, and other heavy metal concentrations have been usually identified near the outlets of drainpipes (Förstner and Wittman 1983).

Figure 2 shows a spatial distribution of Cd, Zn, Pb, Cr, Cu, Mn, W, As, and Se (obtained by Arcinfo GIS 8.3 software Inverse Distance Weighting). It seems a tendency in the distribution of certain metals showing maximum values of Zn, Pb, Cr, Mn, W, and As in the northeast and in the southeast part of the harbor, in the most protected areas from the open sea, where the hydraulic regime is rather weak. On the other hand, maximum values of Cd, Cu, and Se appeared, respectively, in the west and central part, in the central and northeast part, and at the entrance and in the central and northeast part of the harbor. It seems that the hydraulic regime within the harbor as well as the turbulence of the seabed caused by the ship engines are significant agents in the deposition of the contaminants in the Keratsini harbor.

Fig. 2
figure 2

Spatial distribution of Cd, Zn, Pb, Cr, Cu, Mn, W, As, and Se in the Keratsini harbor

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Table 3 presents the Pearson correlation coefficient matrix between the various heavy metals and Corg. Zn, Pb, Cr, W, and As were significantly correlated with each other, indicating common origin, probably the Athens sewage outfall. Furthermore, the good correlation between W, As, Zn, Pb, and Cr with Mn probably reflects adsorption of the above metals by Mn oxides. Similarly, the positive correlation of Cr with Corg probably indicates that a part of the Cr content was adsorbed by the organic matter.

Table 3 Pearson correlation coefficient matrix between the trace elements and Corg
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3.2 Organic Carbon

The concentrations of organic carbon are relatively high and vary between 0.69% and 4.41% (Table 1). These values are a little bit lower in comparison to previous studies in the area, like at the shore of Keratsini, close to the central sewer conduct (6.22%) and the Piraeus harbor (4.5%; Voutsinou-Taliadouri 1981). It appears that the biological purification plant that is operating in Psitallia island has restricted the organic pollution in the area.

It should be noted that in the wider Saronic gulf area, there have been measured significantly lower values of Corg that vary between 0.9% and 1.86% (Voutsinou-Taliadouri 1981). Lower concentrations have been determined also in other commercial ports in Greece, such as the commercial port of Rhodes (0.46–0.84%) and the Mandraki port in Rhodes (1.90–2.74%; Angelidis and Aloupi 1995). On the other hand, higher concentrations of Corg are found in other polluted areas, such as the surficial sediments of the Mediterranean shores of Israel close to the sludge outlet from the biological sewage treatment system (0.18–10.3%, Kress et al. 2004).

3.3 Geochemical Strain of the Sediments with Toxic Heavy Metals

The elements that show the highest I geo values are Cd, Pb, W, Zn, As, and Se (Table 4).

Table 4 I geo index values for heavy metals of the surficial sediments of Keratsini harbor
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Concerning Cd, the whole port is characterized as heavily polluted, with the I geo being at very high levels (8.72–11.94) and the I geo class being equal to 6. The comparison of the Cd concentrations in the sediments of the research area (190–1,763 mg kg−1) to the corresponding values SQGs ERL-ERM, according to Long et al. (1995), shows that all the sediments of the Keratsini harbor have toxic Cd concentrations, since they exceed both ERL (1.2 mg kg−1) and ERM (9.6 mg kg-1) guidelines.

The I geo for Pb varies between 4.12 and 5.40, allocating it in the I geo classes 5–6. Hence, the area is characterized as heavily contaminated up to polluted by Pb. In addition, the comparison of the Pb concentration in the sediments of the research area (521–1,263 mg kg−1) to the corresponding SQGs ERL-ERM demonstrated that all samples of the Keratsini harbor contain toxic Pb concentrations, since they exceed both ERL (46.7 mg kg−1) and ERM (218 mg kg−1).

W I geo index varying between 3.80 and 5.21 and the corresponding I geo class of 4–6 classifies the sediments as highly contaminated up to polluted.

The I geo index for As traced only in seven samples varies from 1.76 to 6.54 and is placed in the I geo classes 2–6. In view of these results, therefore, the region is described as uncontaminated to polluted in regards to As. Moreover, a comparison of the As concentration in the sediments of the research area (not detectable–1,813 mg kg−1) with the corresponding SQGs ERL/ERM established that:

  • Twenty-three of the 30 samples (76.7%) present non-toxic concentrations.

  • Two of the 30 samples (6.7%) exhibit concentrations higher than the toxic effect range ERL (8.2 mg kg−1) and lower than ERM (70 mg kg−1) and correspond to polluted marine sediments.

  • Five of the 30 samples (16.7%) exhibit toxic As concentrations, since they exceed both ERL (8.2 mg kg−1) and ERM (70 mg kg−1) and correspond to polluted marine sediments.

Similarly, the Se concentrations in the samples wherein they were traced exhibit a high fluctuation with the result that, regarding Se, the region is described from uncontaminated to polluted. The I geo classes where these samples are placed according to their indices are 1–6, with index values from 0.47 to 6, respectively.

The I geo index for Zn ranges between 1.52 and 5.56 and the I geo class from 2 to 6. The sediments are therefore classified as slightly contaminated up to polluted. A comparison of the Zn concentrations in the sediments of the research area (409–6,725 mg kg−1) to the valid SQGs ERL-ERM resulted in the following:

  • One of the 30 samples (3.3%) exhibits concentrations that are higher than the toxic effect range ERL (150 mg kg−1) and lower than ERM (410 mg kg−1) and corresponds to medium polluted marine sediments.

  • Twenty-nine of the 30 samples (96.7%) exhibit toxic concentrations of Zn, since they exceed both ERL (150 mg kg−1) and ERM (410 mg kg−1) and correspond to polluted marine sediments.

The I geo index for Cu is between 1.53 and 2.94 and the class from 2 to 3. Therefore, the sediments are described as slightly up to heavily contaminated. From comparison of the Cu sediment concentrations in the research area (195–518 mg kg−1) to the SQGs ERL-ERM, it was established that:

  • Twelve of the 30 samples (40%) exhibit concentrations that are higher than the toxic effect range ERL (34 mg kg−1) and lower than ERM (270 mg kg−1) and one sample (3.3%) is at the limit of ERM (270 mg kg−1), so they correspond to medium polluted marine sediments.

  • Seventeen of the 30 samples (56.7%) exhibit toxic Cu concentrations, since they exceed both ERL (34 mg kg−1) and ERM (270 mg kg−1) and correspond to polluted marine sediments.

The I geo index values for Cr, ranging between 0.97 and 2.67, are placed into classes 1–3, thus varying from not contaminated to slightly contaminated and from slightly contaminated to highly contaminated areas. From the comparison of the Cr sediment concentration in the research area (264–860 mg kg−1) to the SQGs ERL-ERM, it results that:

  • Nine of the 30 samples (30%) exhibit concentrations that are higher than the toxic effect range ERL (81 mg kg−1) and lower than ERM (370 mg kg−1) and correspond to medium polluted marine sediments.

  • Twenty-one of the 30 samples (70%) exhibit toxic Cr concentrations, since they exceed both ERL (81 mg kg−1) and ERM (370 mg kg−1) and correspond to polluted marine sediments.

4 Conclusions

The results of the chemical analysis of the Keratsini harbor surficial sediments showed that the sediments present highly elevated Cd, Pb, W, Zn, As, Se, Cr, and Cu concentrations. Based on the I geo indices, these sediments can be characterized as heavily polluted in regard to Cd, Pb, W, As, Se, and Zn and highly contaminated concerning Cu and Cr. Moreover, according to the SQGs as established by Long et al., the concentrations of Cd, Pb, As, Zn, Cu, and Cr of most of the sediments exceed the toxic effect range.

The enrichment of heavy metals in the sediments could be attributed to the deposition of the dissolved and particulate heavy metals and their compounds in the water column through the Athens central sewage outfall. In addition to this source, other inputs of heavy metals include inputs from the ships (cargo, fuel, paints etc.) and from the industrial activity in the wider area.