Geochemistry of major and trace elements in surface sediments of the Saronikos Gulf (Greece): Assessment of contamination between 1999 and 2018

Journal Pre-proof Geochemistry of major and trace elements in surface sediments of the Saronikos Gulf (Greece): Assessment of contamination between 1999 and 2018

A.P. Karageorgis, F. Botsou, H. Kaberi, S. Iliakis PII:

S0048-9697(20)30556-8

DOI:

https://doi.org/10.1016/j.scitotenv.2020.137046

Reference:

STOTEN 137046

To appear in:

Science of the Total Environment

Received date:

13 November 2019

Revised date:

29 January 2020

Accepted date:

30 January 2020

Please cite this article as: A.P. Karageorgis, F. Botsou, H. Kaberi, et al., Geochemistry of major and trace elements in surface sediments of the Saronikos Gulf (Greece): Assessment of contamination between 1999 and 2018, Science of the Total Environment (2018), https://doi.org/10.1016/j.scitotenv.2020.137046

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© 2018 Published by Elsevier.

Journal Pre-proof Geochemistry of major and trace elements in surface sediments of the Saronikos Gulf (Greece): assessment of contamination between 1999 and 2018 Karageorgis, A.P. 1, Botsou, F.2*, Kaberi, H. 1, Iliakis, S. 1

1

Hellenic Centre for Marine Research, Institute of Oceanography, 46.7 km Athens-

Laboratory of Environmental Chemistry, Department of Chemistry, National and

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2

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Sounio Avenue, 19013 Anavyssos, Greece

Kapodistrian University of Athens, 15784 Athens, Greece

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Corresponding author: [email protected]

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*

Abstract

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The Saronikos Gulf receives pressures from the most urbanized and industrialized areas

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in Greece, the Athens metropolitan area and Pireaus port, and as such, it is considered as

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a hot spot of pollution in the Eastern Mediterranean Sea. Decades after policies aiming to achieve clean seas have been introduced and implemented, it is currently relevant to evaluate their impact on the environmental quality. Here we propose a methodology for this topical issue to assess the distribution of major and trace elements using a 20 year (1999–2018) sedimentary record, and determine the current status, as well as contamination trends. The proposed synthesis of methods is outlined by the following major steps: establishment of background levels from dated cores, calculation of Enrichment Factors (EFs) and the multi-elemental, Modified Pollution Index (MPI), and assessment of temporal trends of MPI in a sub-regional scale. Copper, Zn, and Pb

Journal Pre-proof exhibited the highest EFs, mostly observed in the Elefsis Bay, the Inner sector, and the area parallel to the western Attica coast. The MPI classified the latter areas as moderately-heavily to severely polluted, exhibiting, however, decreasing trends in the industrialized Elefsis Bay, attributed to the decrease of land-based metal loads. No decreasing trends were detected in the other sub-regions, highlighting the need for intensifying efforts to abate pollution by designing management plans towards the

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reduction of metal contamination in the Saronikos Gulf. Finally, the present study

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illustrates that multi, regionalized background levels are necessary for effectively

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resolving elemental variations, particularly in the presence of metal-rich lithological

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complexes within the catchment areas. This finding should be taken into account when the background levels and background assessment levels are established for the Eastern

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Mediterranean’s sub-regional seas within the framework and implementation of the EU’s

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Marine Strategy Framework Directive.

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Keywords:

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Major and trace elements, background levels, contamination assessment, multi-elemental pollution indices, Saronikos Gulf, Elefsis Bay

1. Introduction During the last decades, a number of EU’s policy commitments and initiatives of international organizations have been put in place to address the use of chemicals and their emission to the environment, including marine waters (EEA, 2011). Of the most important pieces of legislation stand the WFD (Water Framework Directive, 2000/60/EC)

Journal Pre-proof for fresh, transitional, and coastal waters, the MSFD (Marine Strategy Framework Directive, 2008/56/EC) for coastal, transitional, and territorial waters, as well as the Regional Sea Conventions such as OSPAR, HELCOM and the Barcelona Conventions for the marine environment of the North-East Atlantic, the Baltic and the Mediterranean Sea, respectively. Collectively, this suite of legislative tools aims to achieve the common vision shared by the EU countries of a marine environment with close to zero

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concentrations of synthetic substances and near background levels of naturally occurring

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substances, such as heavy metals (EEA, 2011).

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Aiming to reflect on the effectiveness of legislation, the European Environment Agency (EEA) issued the assessment “Contaminants in Europe’s seas - moving towards a non-

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toxic marine environment” (EEA, 2018). Of the 1,541 assessment units, 85% have been

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classified as 'problem areas' with regard to contamination and therefore there is evidence

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of undesirable disturbance to the marine ecosystems due to inputs of contaminants. Metals have been identified as the group of substances that most often triggers the

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classification of ‘problem area’. Thus, contamination of Europe’s regional seas continues

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to be a large-scale challenge. Declining trends of some contaminants, observed mainly in the North-East Atlantic and the Baltic Sea, are encouraging, yet, the policy vision of achieving clean, non-toxic European seas is unlikely to be met within the agreed timeframe (e.g. for the Good Environmental Status (GES) of MSFD by 2020). Furthermore, the assessment recognizes that publicity and incorporation of additional data sets would permit a higher spatial coverage in future studies. Particularly for the Mediterranean region, the limited spatial coverage and temporal consistency impede regional assessments to some extent. There is also need to further explore background

Journal Pre-proof levels of metals and take into consideration sub-regional specificities in the Mediterranean basin (UNEP/MAP 2017). The present assessment focuses on the Saronikos Gulf, one of the most important coastal areas in the Eastern Mediterranean Sea in terms of contamination concern. The Saronikos Gulf and the small embayment of Elefsis Bay, represent the seaward boundary of the metropolitan areas of Athens and Piraeus port, hosting 1/3 of the current Greek

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population (3.2 million people; Census 2011). More than 40% of the Greek industries are

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located in the coastal area of the Elefsis Bay, including some of the biggest plants of the

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country, such as oil refineries, steel and cement industries, and shipyards (Mavrakis and

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Salvati, 2015). Increased concentrations of trace elements in this area, resulting from the discharges of domestic and industrial effluent, have been documented since the late 1970s

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(Grimanis 1977; Scoullos et al., 1979). Later studies focused on the geochemical

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partitioning of metals (Angelidis and Grimanis, 1989; Scoullos, 1981; 1986, Voutsinou, 1981), the specific sources of Pb (Kersten et al., 1997; Prifti et al, 2015), and identified as

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major sources of pollution the sewage outfalls (WWTP), a fertilizer plant- operating in

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the Inner Saronikos Gulf until 1999 (Angelidis and Grimanis, 1989), as well as steel mills (Panagiotoulias et al., 2017) and shipyards (Pantazidou et al., 2007) in the Elefsis Bay. The contamination of the bay has resulted in the accumulation of metals in mussel tissues, which followed a spatial gradient related to land-based sources (Strogyloudi et al., 2012). Currently, the benthic community in the Saronikos Gulf presents a clear deterioration close to the Psyttaleia Island WWTP outfall, but greatly improves at a short distance (Simboura et al., 2014; Dimiza et al., 2016).

Journal Pre-proof The most recent of the above-cited studies on the distribution of trace elements have been confined, either to the Elefsis Bay, or close to point-sources of pollution in the Inner Saronikos Gulf. A large-scale geochemical mapping of sediments, however, is lacking. The present study integrates the results of 20 years of research conducted throughout the Saronikos Gulf and the Elefsis Bay. It aims to conduct a detailed geochemical mapping of the area, to explore and establish local background levels of trace elements, to estimate

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the contamination status of seafloor sediments, as well as to assess the pollution trends,

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using a multi-elemental pollution index. It also aims to propose a synthesis of methods

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that could be applied to other marine areas, in order to evaluate current environmental status, to assess pollution trends, and consequently the effectiveness of policy and

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regulatory frameworks (e.g. MSFD) aiming at reducing contaminants in Europe’s

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environment. Furthermore, such detailed and long-term analysis will serve policy makers

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and stakeholders in better understanding both the coastal and open-sea environment of

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remediation efforts.

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the area, assist future management plans, and help to assess the effectiveness of future

2. Regional setting

The study area extends between the eastern coasts of Argolis peninsula of Peloponnese and the western coasts of Attica, in central Greece (Fig. 1). The lithology of the catchment area draining into the Saronikos Gulf comprises Plio-Quaternary deposits, limestones of various ages, schists and marbles, ultra-basic ophiolite complexes, as well as volcanic outcrops at, e.g., Methana Peninsula, Aegina Island, and Soussaki, the latter representing the NW edge of the Hellenic Volcanic Arc, active from the early Pliocene to

Journal Pre-proof the present day (Nomikou et al., 2013). The Paphsanias submarine volcano lies at a distance of 1.5–2 km to the NW of Methana Peninsula, covering an area of about 12 km2 (Nomikou et al., 2013). To the west, the Saronikos Gulf incorporates the relatively deep basins of Megara (max. depth 234 m) and Epidavros (max. depth 410 m). The semi-enclosed Elefsis Bay is situated in the northern sector of the study area, with a maximum water depth ~35 m; the

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Elefsis Bay communicates to the west and to the east with Megara Basin and the Inner

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Saronikos Gulf, respectively, through narrow and shallow straits (depths 5–15 m). Since

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2012, the eastern Elefsis Bay receives treated domestic and industrial wastewaters from

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the Thriasio wastewater treatment plant, which has treatment capacity of 21,000 m3 per day. The Inner Saronikos Gulf is defined as the marine sector between the eastern coast

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of Salamis Island and Attica; the water depth varies from 15 to 97 m. The small island of

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Psyttaleia hosts the WWTP of metropolitan Athens, which has operated since 1994 and includes pre-treatment, primary and secondary treatment (since 2004) with biological

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nitrogen removal, and sludge treatment; the average supply of treated wastewater in the

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gulf is 730,000 m3 per day. Treated wastewaters discharge into the Inner Saronikos Gulf via a system of three pipelines to the south of the island, at ~62 m depth. The Outer Saronikos Gulf refers to the marine area east-southeast of Aegina Island and up to Attica coast and to Cape Sounio to the south, with water depths 90–266 m; further to the south/southeast lies the Myrtoon Sea. According to Kontoyiannis (2010), the circulation of the Saronikos Gulf has a distinct two-layer structure in the period from late spring to summer to late fall, whereas it is basically barotropic during the rest of the year (December–March). In late spring-early

Journal Pre-proof summer, cyclonic and anticyclonic flow occurs in the upper (∼0–40 m) and deeper (∼60– 100 m) layers, respectively. In summer, an anticyclonic and a cyclonic flow exists throughout the gulf, above and below the pycnocline, respectively. In winter and early spring, an anticyclonic flow prevails in the upper ∼100 m. Throughout the year, the water column is well-ventilated, except for the following areas: i) the Elefsis Bay, which displays hypoxic or intermittently anoxic conditions in its deeper, western part, during the

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stratification period; and ii) the deeper sector of the Epidavros Basin, where vertical

has

approached

nearly anoxic

conditions

(D.O.

<1

mL

L-1)

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concentration

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mixing never reached the sea bottom in the years following 1992 and dissolved oxygen

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3. Methodological approach

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m-depth was measured at 1.07 mL L-1.

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(Paraskevopoulou et al., 2014); during the March 2017 cruise, dissolved oxygen at 410

Field and laboratory methods are reported briefly in the following sections and in detail

3.1 Sampling

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in the accompanying Data in Brief paper.

Surface sediments (0-1 cm) were collected with a stainless steel box corer operated aboard R/V Aegaeo during thirteen oceanographic cruises spanning from January 1999 to January 2018 (1999: n=25; 2001: n=21; 2009: n=12; 2010: n=14; 2012: n=12; 2013: n=13; 2014: n=4; 2016: n=14; 03/2017: n=13; 09/2017: n=22; 10/2017: n=15; 11/2017: n= 23; 01/2018: n=28). In total, 216 surface sediment samples were collected and analyzed using the same analytical methods that are described in detail in Data in Brief

Journal Pre-proof and briefly hereafter. Several samples were obtained over the same network of stations serving the diachronic monitoring of the Saronikos Gulf with respect to grain-size, organic carbon, major and trace elements contents (Table S1 in Data in BriefSupplement). In order to present the latest picture of the gulf in terms of spatial distribution maps of sedimentological and geochemical variables, the most recently analyzed sediment

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samples from each sector of the study area were selected (total 68 samples) (Fig. 1 and

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Table S2 in Data in Brief-Supplement). Moreover, core sediments were dated in the Inner

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Saronikos Gulf and the Elefsis Bay using the 210Pb method, and additional core samples

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retrieved from the western basin, the Inner, and Outer Saronikos Gulf were dated by 14C accelerator mass spectrometer (AMS) analyses at the laboratory of Beta Analytic Inc.

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3.2 Laboratory analyses

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(Florida, USA).

Particles grain-size was assessed by wet-sieving and the X-ray absorption technique,

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whereas size classes are named after Folk (1974). Organic carbon content was determined by CHN elemental analyzer type EA-1108. The precision of the method is within 5%. For the geochemical analyses, samples were sieved through a 1 mm sieve, oven dried at 40 °C and then ground to a fine powder. Major (SiO2, Al2O3, TiO2, Fe2O3, K2O, Na2O, CaO, MgO, P2O5) and trace elements (V, Cr, Mn, Co, Ni, Cu, Zn, As, Pb) were determined by X-ray Fluorescence in a PW-2400 PANalytical (former Philips) spectrometer under the experimental conditions described in Data in Brief. For the

Journal Pre-proof purposes of the present paper we present only Si, Al, Mg and Ca contents and corresponding spatial distributions. Loss on ignition (LOI) was determined after burning 1 g of sample for 1 h at 1000 °C. Analytical accuracy was checked by parallel analysis of the certified sediment standard PACS-2 and was found to be better than 7% for all elements analyzed. Analytical precision was checked in sample replicates and was always better than 0.5%. Detection limits were below 5 mg kg-1 (V, Co, Ni, As), 5-10 mg kg-1

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(Cr, Cu, Pb), and 10-12 mg kg-1 (Mn, Zn) for the elements determined. To check long-

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term repeatability in the framework of the present study, archived powder samples were

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re-scanned.

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Recent sediment accumulation rates were determined using the Constant Rate of Supply model (CRS) (Sanchez-Cabeza and Ruiz Fernádez, 2012) after total dissolution of

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sediments following the method of Sanchez-Cabeza et al. (1998) Profiles of 210Pbexcess are

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shown in Fig. 2 in Data in Brief. More details about the methods employed, analytical

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conditions and instrumentation are given in Data in Brief.

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3.3 Statistical Analysis

Major and trace element interrelations, together with grain-size parameters and organic carbon contents were studied by Factor Analysis (FA). Prior to the analysis, data were transformed (Karageorgis et al., 2009) to meet the requirements of normality (Reimann et al., 2002). After Box-Cox transformation followed by a z-transformation, all variables but sand and silt were normally distributed (Table 1 in Data in Brief). These two variables were removed from further analysis and grain-size variations are therefore explained by

Journal Pre-proof the clay fraction variability. Subsequently, Principal Factor Analysis with Varimax rotation was conducted in order to group clay, organic carbon and geochemical elements. Temporal trend analysis was performed using the sampling sites with available data for more than 5 years (n=14). The analysis was run for the he multi–elemental pollution index (MPI) The changes of the yearly MPI values during the period 1999–2018 were assessed by using the MAKENENS application for trend calculation (Salmi et al., 2002).

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The model performs two statistical tests: first, the non-parametric Mann-Kendall for the

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presence of a monotonic, increasing or decreasing trend, and secondly, the non-

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parametric Sen’s method for estimating the slope of the linear trend (Salmi et al., 2002;

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Gilbert, 1987). These methods are suitable for missing, and/or non-normally distributed data, and have been successfully used for detecting pollution trends (Olstrup et al., 2018).

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More information about the tests is given in Data in Brief.

4. Results and discussion

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4.1 Sediment grain-size and organic carbon content

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Surface sediments of the Saronikos Gulf are rich in sand (median 44%), followed by silt and clay (median values 31% and 22%, respectively) (Table 1). Their composition is primarily muddy, with varying proportions of sand, silt, and clay, thus they encompass the entire range from sand to muddy sand, sandy mud, and mud (Fig. 2a). Sand’s spatial distribution (Fig. 2b) is characterized by high values (>80%) around Aegina Island and the western coasts of Attica, whereas Elefsis Bay, Megara Basin, and Epidavros Basin exhibit low sand contents (<20%). Silt dominates the marine sector between Salamis Island and Attica, whereas high values are observed in the Elefsis Bay and both western

Journal Pre-proof basins (Fig. 2c). Clay, the finest sediment fraction, exhibits maxima in the Megara and Epidavros Basins, as well as elevated values in the Elefsis Bay (Fig. 2d). Silt and clay show elevated values SE of Aegina Island. Grain-size distribution patterns are largely explained by depth variations, with coarser sediments being observed in shallow waters (around Aegina Island, and near the coast of Attica) and finer sediments in the deeper sectors (Megara and Epidavros Basins, Outer Saronikos-SE of Aegina Island). Coarse-

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grained, sandy sediments found on the shelf at depths 80–110 m (e.g. NE of Aegina

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Island) may be also associated with relict deposits of the latest marine transgression, as it

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has been recorded in the south Evoikos and Thermaikos Gulfs (Karageorgis et al., 2000;

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2001). Similar measurements in the Saronikos Gulf have been conducted by Schwartz and Tziavos (1975); despite methodological differences, the main features identified in

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the present work confirm previous investigations. Grain size varies greatly among the

differences.

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sub-regions, thus, the variability of metal contents may be partly obscured by grain-size

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Historic data on Corg content (1999-2017) show high variability, with a minimum value of

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0.12%, maximum value of 4.29% (identified as flyer), and median value of 1.00% (Table 1); the highest Corg content values (up to 3.01%) are routinely observed in the intermittently anoxic, western sector of the Elefsis Bay. The spatial distribution patterns of Corg content (Fig. 2e) reveal another area of local maxima, which is situated south of the WWTP of the Psyttaleia Island (2.62%). The overall pattern is characterized by decreasing trends from north to south, with the area south of Salamis Island exhibiting Corg contents <1% or further to the south <0.75%.

Journal Pre-proof 4.2 Geochemistry of major elements The geochemistry of the surface sediments of Saronikos Gulf can be expressed as a mixture of two end members: allochthonous (terrigenous) aluminosilicates (mainly feldspars and clay minerals) and autochthonous biogenic carbonates, such as foraminifera, bivalves, gastropod shells, and their fragments (Fig. 3a), supported also by microscopic observations. Aluminosilicates of typical ‘average shale’ composition

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(Wedepohl, 1995) are heavily diluted by biogenic carbonates; the carbonate content

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estimated from Ca, assuming all Ca is associated with biogenic CaCO3, ranges from

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of the sediment consists of biogenic remains.

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23.0% to 87.7% (median 52.815.8, n=210), denoting that on average more than one half

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The spatial distributions of Si and Al contents (Fig. 3b, c) show similar characteristics: i) high values (max. Si: 16.9%, max. Al: 7.31%) are observed in the Elefsis Bay, attributed

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to the terrigenous inputs from ephemeral streams discharging into the bay; ii) high values

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are recorded at both basins of the western Saronikos Gulf as well as the outer gulf, related to the settling of finer aluminosilicates in deeper waters; and iii) relatively lower values in

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the Inner Saronikos Gulf and the western coast of Attica, where sediments are coarser. Calcium distribution (Fig. 3d) exhibits inverse trends in comparison to the previous elements, with maxima along the western Attica coast and the sectors south and west of Salamis Island. Magnesium spatial distribution (Fig. 3e) shows substantially different characteristics, with maxima appearing in the NW sector of the Megara Basin, offshore Soussaki, which represent the weathering of ultramafic rocks and their metamorphic equivalents, such as serpentinites and peridotites, frequently traversed by magnesite veins

Journal Pre-proof (Kelepertsis et al., 2001; Georgopoulos et al., 2018); their subsequent influence on the trace elements contents (e.g. Cr, Co, Ni) will be discussed below.

4.3 Trace elements spatial distribution patterns The spatial distribution of trace elements is illustrated in Fig. 4. Certain elements exhibit

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similar spatial distribution patterns indicating their common origin. Vanadium, Cr, Co, and Ni (Fig. 4a, b, d, e) show distinct local maxima in the northwestern and western

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sectors of the Saronikos Gulf, and in particular offshore Soussaki, with a decreasing trend

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from west to east. Relatively elevated element contents are recorded in the Elefsis Bay

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(V, Cr, Co), whereas the Inner Saronikos Gulf and the western Attica coast exhibit

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relatively low metal contents. The Outer Saronikos Gulf exhibits low metal contents, with an increasing trend to the south, towards deeper waters. Finally, Cr is locally enriched

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around the Psyttaleia Island (Fig. 4b).

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Another group of elements showing similarities in their distribution patterns consists of Cu, Zn, As, and Pb, which exhibit maximum contents in the Elefsis Bay and the

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Psyttaleia Island region (Fig. 4f-i), with N-S decreasing trends. The Inner and the Outer Saronikos Gulf, as well as the Megara and Epidavros Basins exhibit low elements contents, whilst minor enrichment is recorded for As and Pb at the deeper sector of the Outer Saronikos Gulf. Manganese exhibits low contents all over the study area, with the exception of the Epidavros Basin, where the maximum value of 5736 mg kg-1 is recorded at a depth of 415 m.

Journal Pre-proof 4.4 Controlling mechanisms of trace element interrelations and distribution patterns The most recent data set of major and trace elements contents is examined by means of Pearson correlation coefficients (Table 2; n=68). The fine-grained sediments, represented by clay and major elements Si and Al, representing terrigenous aluminosilicates are positively and significantly correlated, whereas they are negatively correlated to Ca, which represents the (coarse-grained) biogenic carbonates (see also Figs. 2b, 3d). All

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trace elements and As are markedly associated with Al, suggesting their common origin

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from lithogenic sources or their common transport pathway. Organic carbon and several

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trace elements are significantly correlated outlining the anthropogenic impact on the area.

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Magnesium, which is found enriched in the ultrabasic rocks of Soussaki-NW Saronikos

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Gulf (see also Fig. 3e), is strongly correlated to Ni, Co, Cr, Mn, and V, thus elevated contents of those elements are lithogenic in origin.

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Subsequently, grouping of variables with common geochemical behavior were identified by means of Principal Factor Analysis. A 3-factor model explains 84.0% of the total

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variance (Table 2 and Figure 4 in Data in Brief). Final communalities, a measure of how

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well an input variable is represented in the space of the canonical variables, are satisfactory (>0.73), except for As, and Mg (0.54 and 0.47, respectively). The first factor (34.1%) shows positive loadings for clay, Si, Al, V, Mn, Co, indicating the terrigenous component of the elements, i.e. fine-grained aluminosilicate minerals. All other trace elements are partly of terrigenous origin as well (in decreasing order: Pb, Ni, Zn, Co, Cr, and As). F1 exhibits high scores in the Elefsis Bay and the outer, deeper Saronikos Gulf (Fig. 5a). Factor 2 (30.6%) exhibits high positive loading for Corg, Cu, Zn, As, and Pb, and represents the anthropogenic factor that introduces organic load and trace element

Journal Pre-proof contaminants in the study area from domestic and industrial effluents, and the overall impact of the greater Athens metropolis. The spatial distribution of F2 scores indicates that the most impacted area is the Elefsis Gulf and the Inner Saronikos/Psyttaleia Island (Fig. 5b). Finally, Factor 3 (19.3%) associates Mg, Cr, Ni, Co, V, and Mn probably originating in the ultrabasic rocks of the Soussaki area and characterizes the sediment

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4.5 Establishing background concentration levels

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geochemistry of the NW, W Saronikos Gulf (Fig. 5c).

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Contamination assessments should take into consideration the local background of

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examined elements before assigning potential excess values to human interventions

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(Birch, 2017). A common approach for establishing local background levels is to use sedimentary cores of which a part of sediment layers penetrate to pre-industrial

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depositions (Förstner and Salomons, 1980; Birch et al., 2013; Birch, 2017). After

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preliminary trials using different sediment cores, it was concluded that the background levels differ significantly between the four sub-regions of the Saronikos Gulf. In order to

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distinguish the pre-industrial deposits in the different sub-regions, a set of 14C and

210

Pb-

dated cores were used (see Fig. 1 in Data in Brief for core locations). In the Elefsis Bay, the average sediment accumulation rate at station S2 was estimated at 0.26 cm y-1, in agreement with Eleftheriou et al. (2018), thus element contents below 30 cm were used as background levels. In the Inner Saronikos Gulf, the dating (Beta – 392908) of core S7 south of the WWTP showed that element contents in sediment layers below 30 cm depth represent background levels. The calculation of the sediment accumulation rate in core K4a (Keratsini), which reached an average value of 0.9 cm y-1, showed that sediments

Journal Pre-proof below 1.1 m-depth have been deposited before the industrial development of the greater Athens area; these element background levels are comparable to those obtained in core S7. In the

14

C dated (Beta – 495758) sediment core of the western basin (SARC18),

sediment accumulation rates are much lower, around 0.006 cm y-1, thus element contents in the 12.5-22.5 cm depth layer are safely used as background values. Accordingly,

14

C

dating of a box core from the Outer Saronikos Gulf (S21) led to the use of element

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contents in sediment layers below 40 cm depth as the background levels. Table 3 presents

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the pre-industrial levels of Al, metals, and As, considered as background levels for each

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sub-region. The relevant element ratios to Al, and the down-core variability of element to

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Al ratios are also presented in Table 3, and illustrated in Fig. 3a–e of Data in Brief,

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4.6 Contamination assessment

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respectively.

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4.6.1. Enrichment Factors

The assessment of the metal contamination is based on the widely, and most successfully

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used Enrichment Factor (EF) (Birch, 2017). Aluminium (Al) was used as geochemical normalizer for correcting grain-size effects and dilution by sedimentary phases such as carbonates, assuming that Al is held exclusively in terrigenous aluminosilicates (Loring 1991; Loring and Rantala 1992; Kersten and Smedes 2002). The EF is estimated according to the following equation (1):

EF=(element/Al)sample/(element/Al)background

(Eq. 1)

Journal Pre-proof Enrichment factors of 1.5–3, 3–5, 5–10 and >10 times were classified of minor, moderate, severe and very severe modification, respectively (Birch and Olmos, 2008). The EFs presented hereafter were estimated for the most recent data set (n=68) and thus represent the latest available information on the contamination status of the study area (Table 3, Data in Brief). Enrichment factors calculated for V (Fig. 6a) exhibit median values <1.5 (no human

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influence in all studied sub-regions of Saronikos Gulf, suggesting that sediments are not

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enriched in V. Similarly, low median values are observed for Cr, Co, and Ni, whereas

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elevated EF values, falling within the range of moderate (Cr, Co, Ni) or even severe (Cr)

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modifications (EF: 5–10) are restricted in small areas between the Salamis and Psyttaleia Islands (Fig. 6b, d and e) and the western coast of Attica.

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Although manganese is a vital micronutrient for marine organisms and plays a significant

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role in photosynthesis (Horsburgh et al. 2002; Kernen et al. 2002), it is also considered as an emerging contaminant (Pinsino et al., 2012) posing toxic effects in marine organisms

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(Martin et al. 2008). Enrichment factors for Mn are highly variable among the sediments

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of the Saronikos Gulf (range: 0.5–9). In the Elefsis Bay, the highest EF value (4.0) is observed at the deepest, western station (S2). Excess Mn may originate in hydrothermalism, as sediments offshore Methana are influenced by past and present hydrothermal activity as sediments offshore Methana are influenced by past and present hydrothermal activity, which is usually associated to localized enrichment in Mn, high Fe contents and elevated concentrations of As, Sb, Mn, V, Co, P and Zn (Hübner et al., 2004).

Journal Pre-proof Enrichment factors for Cu, Zn, and Pb appear to be considerably elevated in the Elefsis Bay and the Inner Saronikos Gulf (Fig. 6f, g, i), with maximum values of 13, 12.1, and 27.6, respectively, recorded at Stn. S7 south of the Psyttaleia Isl. that correspond to very severe modification. Station S3, located between the eastern tip of Salamis Isl. and Keratsini area in Piraeus (see Fig. 1 in Data in Brief) represents the second most contaminated area (EF Cu: 12.6, EF Zn: 10.1, and EF Pb: 21.4). The spatial distribution

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patterns of EFs for Cu and Zn exhibit similarities, with values 5-10 in the area between

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Salamis Island and western Attica, including the Psyttaleia area, and the Elefsis Bay with

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values in the range 3-12 (Fig. 6f, g). In a SW direction, EF values decrease progressively

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to minor modification and no modification. Lead, however, exhibits very high EFs all over the Saronikos Gulf with maxima (very severe modification) in the area between

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Salamis Island and western Attica, and some patches towards the SE, along the coast. The

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latter areas, however, do not show very high Pb contents (20-30 mg kg-1; Fig. 4i), and sediments are Ca-rich biogenic sands (Fig. 2a, 3d), with low Al contents (Fig. 3c). This

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niche highlights the importance of sediment grain-size and major element composition in

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contamination assessment applications, where relatively low element contents do not provide solid evidence for absence of modification.

4.6.2. Pollution Indices Multi-elemental pollution indices are advantageous to single-element ones, as for example EF, as they integrate the additive effect of multiple contaminants, which are often present in urbanized and industrialized environments, in sediment quality pollution assessments. In this study, the Modified Pollution Index (MPI) introduced by Brady et al.

Journal Pre-proof (2015) is used. These authors tested MPI in several study areas and concluded that it is more reliable than other single, and multi-elemental indices. This argument has been recently confirmed by Martínez-Guijarro et al. (2019). It is calculated by Eq. (2) and could be considered as an advancement of two widely-used indices: first, the Håkanson’s modified degree of contamination index (mCd) (Eq. 3) (Håkanson, 1980) in the sense that a suite of elements are combined to produce a single value, and secondly the Nemerow

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Pollution Index (PI) (Eq. 4; Nemerow, 1991), in the way that it uses the maximum

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Contamination Factor (CFmax) to develop a weighted average, hence taking into

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consideration the impact of contamination of one element, that otherwise could be

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diminished (Brady et al., 2015). The advantage of MPI over the mCd and the Nemerow PI is that the use of EF allows for correcting the grain-size effects. Sediments with MPIs

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<1, 1–2, 2–3, 3–5, 5–10 and >10 were classified as unpolluted, slightly, moderately,

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moderately-heavily, heavily, and severely polluted, respectively (Brady et al., 2015).

𝑖 ∑𝑛 𝑖=1 𝐶𝐹

𝑛

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𝑚𝐶𝐷 =

2

ur

(𝐸𝐹𝑚𝑒𝑎𝑛 )2 +(𝐸𝐹𝑚𝑎𝑥 )2

𝑀𝑃𝐼 = √

2

[𝑀𝑒]𝑠𝑎𝑚𝑝𝑙𝑒

, where 𝐶𝐹 = [𝑀𝑒]

[𝐶𝐹]2 +[𝐶𝐹𝑚𝑎𝑥]2

𝑃𝐼 = √

(Eq. 2)

𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑

(Eq. 3)

(Eq. 4)

According to Figure 7, showing the spatial distribution pattern of MPI, the Elefsis Bay, is heavily to moderately-heavily polluted in a west – east direction. In the Inner Saronikos Gulf, severely polluted sediments are found close to the Psyttaleia WWTP outfall (Stn. S7; MPI: 15.1) and the adjacent western Attica coast (Keratsini, Stn.

Journal Pre-proof S3, MPI: 11.3). Similarly to the spatial distribution of the Cu, Zn, and Pb EFs (Fig. 7f, g, i), the MPI is reducing to moderately-heavily and heavily polluted ranges in a NW-SE zone parallel to the Attica coastline (Fig. 7). This pattern is in line with the biological quality defined by integrating biotic indices (macro-invertebrates, macro-algae and phytoplankton), showing a clear gradient from poor quality in the outfall to moderate in the southwestern area of the outfall, and good-to-high in the outer part of the Saronikos

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Gulf (Simboura et al., 2014). The degradation of water and sediment quality is coherent

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with the cyclonic hydrological regime forcing the dispersion of treated wastewater

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towards the southwest area of the outfall. Finally, the elevated MPI values falling within

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the range of heavily polluted sediments found at the Epidavros basin are attributed solely

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to the elevated EF of Mn.

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5. Assessment of pollution trends

Trend analysis was conducted for sampling stations visited several times over the past 20

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years, to identify significant and sustained, increasing or decreasing trends of the MPI. Of

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the 14 stations tested, significant trends were detected only for two (Table 4 in Data in Brief). Figure 8 shows that, for the period 1999–2018, the MPI follows a downward trend at two stations of the Elefsis Bay. Several polluting industries have ceased their operation during the last decade due to the recent extreme economic crisis in Greece. Therefore, the decreasing trend of the MPI in the most industrialized part of the study area is connected to the reduction of metal discharges in the coastal environment. Furthermore, environmental policy enforcement combined with technological improvements by big

Journal Pre-proof industrial polluters, such as the steel-making industry have contributed to the improvement of sediment quality (Panagiotoulias et al., 2017). In the rest of the studied stations no trends for MPI were detected (Table 4 in Data in Brief). This holds true also for the outfall of WWTP in the inner part of the gulf, as well. The findings of this study are in line with the recently published European Environmental Agency’s report (EEA, 2018) concluding that concentrations of some well-known

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contaminants appear to be declining in Europe’s regional seas, yet, concern remains and

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it seems unlikely that the recently agreed EU targets (e.g. the descriptor on contaminants

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that is part of the MSFD’s goal of achieving good environmental status in Europe’s

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regional seas) will be met within the agreed timeframe. In this study, the encouraging result of declining pollution trends is restricted only to the small embayment of the

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Elefsis Bay. Its size, morphology, and limited water exchange with the Saronikos Gulf,

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combined with the abrupt decrease of contaminant releases into the coastal marine environment over the last decade, are the main reasons of the positive and visible impact

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on sediments quality. Further beyond into the Saronikos Gulf, more efforts are needed to

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reduce trace elements emissions from both point (e.g. WWTP) and diffuse sources.

6. Conclusions Sediments are a useful archive for the study of anthropogenic pollution in both organic and inorganic contaminants, including metals and the metalloid As. Figure 9 conceptualizes the methodology applied here to identify contaminated areas and explore the temporal trends of contaminants. It was tested in the heavily urbanized and industrialized Saronikos Gulf and the Elefsis Bay in the Eastern Mediterranean, and can

Journal Pre-proof be broadly applied in other coastal and open sea systems. The methodology includes the following sequence of steps: 1) the buildup of the dataset; 2) the identification of controlling mechanisms that define the spatial variation of metals; 3) the establishment of the regionalized background levels of metals; and 4) the exploration of temporal trends of metals in the study area. The ultimate goal is to inform researchers, policy makers and stakeholders whether policy commitments had a positive result on the environmental

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quality of the seabed or not, so as to strengthen policy enforcement and update

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management plans. The cycle implies that the procedure is perpetual and should be in line

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with new scientific achievements with respect to contaminants that could put in risk

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human and ecosystem health, their levels, as well as amendments on relevant quality criteria.

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As far as it concerns the present case study, the Saronikos Gulf and the Elefsis Bay

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surface sediments collected from 1999 to 2018 have been analyzed for major and trace elements and basic physical and geochemical parameters. Results, in terms of element

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contents, their spatial distribution, enrichment factors, and the multi-elemental Modified

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Pollution Index, point out that the Elefsis Bay, the Inner Saronikos Gulf and some areas of the Outer Saronikos Gulf are contaminated by Cu, Zn, and Pb, exhibiting maximum EF values of 12, 12.4, and 20.6, respectively. According to the classification of Birch and Olmos (2008), such values correspond to very severe modification. However, the majority of the Outer and the Western Saronikos Gulf appear to be less modified, or not impacted at all. Also encouraging is the decreasing trend of the MPI at stations from the Elefsis Bay monitored frequently since 1999. However, it is unclear at what extent this trend is the result of environmental policies implementation or shutting down of

Journal Pre-proof industries following the economic crisis in Greece. To clarify this, continuous monitoring and updating the results of this study should be conducted, following Greece’s economic recovery. Nevertheless, more efforts should be in place to tackle pollution in the inner Saronikos Gulf, particularly at the well-known and long-existing hot spots of pollution, such as the sewage outfalls, where no temporal trends were observed. Moreover, the methodological approach followed in the assessment of the seafloor quality of the

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Saronikos Gulf illustrates that, when estimating enrichment factors, a single local

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background may not resolve effectively the background elemental variations, particularly

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in the presence of metal-rich lithological complexes within parent catchment areas. In

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such cases several local backgrounds may be required to assess potential contamination and its impact on the marine environment. This finding should be taken into account

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when background levels and background assessment levels are established for the Eastern

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Acknowledgements

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Mediterranean’s sub-regional seas within the framework of MSFD implementation.

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The officers and crew of the R/V Aegaeo are thanked for their continuous support during sampling at sea. Thanks goes to C. Anagnostou, A. Androni, G. Kambouri, T.D. Kanellopoulos, A. Papageorgiou, G. Rousakis, I. Stavrakaki and M. Taxiarchi for their support during field and laboratory work. The primary investigators of the Saronikos projects, E. Krasakopoulou, K.S. Parinos and S. Zervoudaki, are gratefully acknowledged. Finally, L. Bray in thanked for linguistic editing. The monitoring of Saronikos Gulf was financed by the Athens Water Supply and Sewerage Company (EYDAP SA). The comments of two anonymous reviewers are greatly acknowledged.

Journal Pre-proof

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Birch, G.F., Olmos, M.A., 2008. Sediment-bound heavy metals as indicators of human

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Birch, G.F., Olmos, M.A., Lu, X.T., 2012. Assessment of future anthropogenic change

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Birch, G.F., Chang, C.-H., Lee, J.-H., Churchill, L.J., 2013. The use of vintage surficial sediment data and sedimentary cores to determine past and future trends in estuarine metal contamination (Sydney estuary, Australia). Sci. Total Environ. 454–455, 542– 561. https://doi.org/https://doi.org/10.1016/j.scitotenv.2013.02.072 Brady, J.P., Ayoko, G.A., Martens, W.N., Goonetilleke, A., 2015. Development of a hybrid pollution index for heavy metals in marine and estuarine sediments. Environ. Monit. Assess. 187, 306. https://doi.org/10.1007/s10661-015-4563-x

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Acta 59, 1217–1232. https://doi.org/10.1016/0016-7037(95)00038-2

Journal Pre-proof Figure captions Figure 1. Bathymetric map of the Saronikos Gulf and sampling stations network. Figure 2. (a) Ternary diagram of sediment classification scheme after Folk (1974); (b), (c), (d) and (e) spatial distribution of sand, silt, clay, and organic carbon percentages, respectively.

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Figure 3. (a) Ternary plot of relative proportions of Al2O3 x 5, SiO2, and CaO x 2 in the Saronikos Gulf sediments; average shale data point after Turekian & Wedepohl (1961)

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and Wedephol (1995), and upper crust data point after Taylor & McLennan (1995); (b),

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(c), (d) and (e) spatial distribution of Si, Al, Ca, and Mg percentages, respectively.

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Figure 4. Spatial distribution of trace elements in the Saronikos Gulf.

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Figure 5. Spatial distribution of the 3 Factors obtained from Principal Factor Analysis; (a)

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F1: fine-grained, terrigenous aluminosilicate factor; (b) F2: anthropogenic factor; and (c) F3: ultra-basic formations factor

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Figure 6. Spatial distribution of enrichment factors calculated for trace elements.

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Figure 7. Spatial distribution of the Modified Pollution Index (MPI) Figure 8. Trends for MPI at stations S1 (a) and S2 (b) of the Elefsis Bay. Figure 9. Conceptual map of the proposed methodology, relevant tasks, and objectives.

Journal Pre-proof Table 1. Summary statistics (minimum, maximum, mean, standard deviation, and no. of samples) of sediment grain-size and geochemical properties. Unit

Min

Max

Median

Mean

SD

n

Sand

%

0

98

44

45

32

175

Silt

%

1

72

31

31

20

175

Clay

%

0

82

22

25

17

175

Corg

%

0.12

Si

%

1.39

Al

%

0.07

Ca

%

9.22

Mg

%

17.6 7.31 35.1

1.04

4.24

1.00 10.2 2.76 21.1 1.83

5

121

42

-1

19

544

145

-1

62

5736

334

-1

1

27

-1

9

392

-1

7

365

-1

15

982

As

-1

mg kg

2

Pb

mg kg-1

5

Cu Zn

mg kg mg kg

210

2.64

1.49

211

6.40

210

0.51

210

22.3 1.89

152

91

211

447

604

210

9

9

5

211

67

77

59

211

27

52

62

208

88

169

190

210

179

15

19

19

211

374

47

69

69

210

-p

mg kg

4.00

210

re

Ni

mg kg

9.20

29

lP

Co

mg kg

120

44

na

Mn

mg kg

ur

Cr

mg kg

Jo

V

1.00

ro

-1

1.46

of

4.29

Journal Pre-proof

Table 2. Pearson correlation coefficient matrix of clay, organic carbon, selected major and trace elements clay

Corg

Si

Al

Ca

Mg

V

Cr

Mn

Co

Ni

Cu

Zn

As

Pb

clay

1

0.429

0.663

0.760

-0.722

0.402

0.855

0.725

0.755

0.805

0.840

0.566

0.672

0.271

0.664

Corg

0.429

1

0.444

0.405

-0.546

-0.153

0.561

0.576

0.318

0.342

0.447

0.786

0.789

0.612

0.691

Si

0.663

0.444

1

0.856

-0.896

0.346

0.848

0.646

0.772

0.816

0.745

0.538

0.689

0.371

0.725

-0.942

0.387

0.917

0.602

0.871

0.879

0.795

0.604

0.745

0.410

0.796

-0.856

-0.800

-0.676

-0.788

-0.458

-0.815

0.496

0.509

0.021

0.018

-0.040

0.098

0.903

0.901

0.751

0.857

0.497

0.857

0.755

0.897

0.697

0.723

0.519

0.673

0.934

0.859

0.531

0.647

0.274

0.679

1

0.934

0.545

0.647

0.341

0.685

Al

0.760

0.405

0.856

1

Ca

-0.722

-0.546

-0.896

-0.942

1

-0.361

-0.921

-0.651

-0.833

Mg

0.402

-0.153

0.346

0.387

-0.361

1

0.345

0.377

0.433 0.875

V

0.855

0.561

0.848

0.917

-0.921

0.345

1

0.793

Cr

0.725

0.576

0.646

0.602

-0.651

0.377

0.793

1

Mn

0.755

0.318

0.772

0.871

-0.833

0.433

0.875

0.642

Co

0.805

0.342

0.816

0.879

-0.856

0.496

0.903

0.755

0.901

0.897

o r p

r P

e 0.642 1

0.934

f o

Ni

0.840

0.447

0.745

0.795

-0.800

0.509

0.859

0.934

1

0.630

0.698

0.391

0.695

Cu

0.566

0.786

0.538

0.604

-0.676

0.021

0.751

0.697

0.531

0.545

0.630

1

0.910

0.677

0.841

Zn

0.672

0.789

0.689

0.745

-0.788

0.018

0.857

0.723

0.647

0.647

0.698

0.910

1

0.701

0.965

As

0.271

0.612

0.371

0.410

-0.458

-0.040

0.497

0.519

0.274

0.341

0.391

0.677

0.701

1

0.676

Pb

0.664

0.691

0.725

0.796

-0.815

0.098

0.857

0.673

0.679

0.685

0.695

0.841

0.965

0.676

1

u o

rn

l a

Values in bold are different from 0 with a significance level alpha=0.05

J

Journal Pre-proof Table 3. Background levels of metals and As in the sub-basins of the Saronikos Gulf. Basin

Elefsis Bay

Inner Saronikos

Outer

Western

Core

Core

Core

S2

S7

K4a

S21

Core SARC-18

Al (%)

5.64

1.81

6.66

4.43

3.49

V (mg kg-1)

79

23

89

77

55

Cr (mg kg )

136

107

230

112

158

Mn (mg kg-1)

379

167

496

727

475

-1

12

5

11

15

14

-1

Ni (mg kg )

115

36

164

106

176

Cu (mg kg-1)

14

7

26

22

18

Zn (mg kg )

59

25

63

78

49

As (mg kg-1)

19

25

29

11

21

5

21

46

8

35

14

ro

-p re

Pb (mg kg )

lP

-1

na

-1

ur

Co (mg kg )

Jo

-1

of

Core

Journal Pre-proof Declaration of competing interests

☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Jo

ur

na

lP

re

-p

ro

of

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

36

Journal Pre-proof Graphical abstract

Jo

ur

na

lP

re

-p

ro

of

Highlights  A synthesis of methods is proposed to detect polluted areas and temporal trends of metals  The methodology may help evaluate policy effectiveness and guide remediation efforts  Temporal trends were analysed using a 20-year record of sedimentary metals  Local background levels are necessary to detect pollution, even in regional seas  Pollution is decreasing only in the heaviest industrialized part of the study area

37

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9