Environ Sci Pollut Res DOI 10.1007/s11356-014-3953-x
RESEARCH ARTICLE
Can the origin of some metals in the seagrass Posidonia oceanica be determined by the indexes of metals pollutions? Slavka Stanković & Mihajlo Jović & Bojan Tanaskovski & Marija L. Mihajlović & Danijela Joksimović & Lato Pezo
Received: 15 August 2014 / Accepted: 4 December 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract To assess metal pollution, Fe, Mn, Cu, Zn, Pb, Ni, Co, As, Cd, and Hg contents in samples of the seagrass Posidonia oceanica and surface sediment, collected at eight locations along the Montenegrin coast, were determined. The metal pollution index (MPI) and metal enrichment factor (EF) were then calculated. MPI and EF were lower in sediment than in P. oceanica at the same locations. This was very evident for EF values of Hg and Cd. Based on the Pearson’s correlations and EF values, it was possible to conclude that the last two metals’ content in the seagrass did not originate from the crustal sources or natural weathering processes.
Keywords Heavy metals . Surface sediment . Posidonia oceanica . Metal pollution index . Enrichment factor . Correlation coefficient . Multivariate analysis
Responsible editor: Céline Guéguen S. Stanković (*) : B. Tanaskovski Faculty of Technology and Metallurgy, Department of Analytical Chemistry, University of Belgrade, 11000 Belgrade, Serbia e-mail: [email protected] M. Jović Vinča Institute of Nuclear Sciences, University of Belgrade, P. O. Box 522, 11001 Belgrade, Serbia M. L. Mihajlović Institute for Technology of Nuclear and Other Mineral Raw Materials, 86 Franchet d`Esperey St, 11000 Belgrade, Serbia D. Joksimović IBM, University of Podgorica, Dobrota bb, 85330 Kotor, Montenegro L. Pezo Institute of General and Physical Chemistry, University of Belgrade, 11000 Belgrade, Serbia
Introduction Trace elements are serious pollutants of the marine environment because of their toxicity and persistence, their poor biodegradability, and tendency to concentrate in aquatic organisms (Lafabrie et al. 2007; Conti et al. 2010). Much attention has been paid to the use of marine organisms as bioindicators of trace metal pollution in marine waters (Richir et al. 2010; Luy et al. 2012; Markovic et al. 2012). Seagrass Posidonia oceanica (L.) Delile has been studied as a bioindicator of contamination by microelements in various parts of the world, especially along the Mediterranean coast (Lafabrie et al. 2007; Conti et al. 2010; Richir et al., 2010; Tovar-Sánchez et al. 2010; Luy et al. 2012). P. oceanica meadows play a crucial role in the ecology of the Mediterranean and mostly occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. P. oceanica, which may absorb trace elements directly from the water column and/or from interstitial water in sediments (Lafabrie et al. 2007), has a high capacity to accumulate trace elements and concentrate pollutants occurring in the environment (Di Leo et al. 2013). Many microelements were found in trace amounts in sea water but often at elevated levels in seagrass (Morillo et al. 2005). Seagrasses are increasingly used as indicators of chemical contamination of coastal regions (Conti et al. 2010; Di Leo et al. 2013). In the last decade, human and industrial activities in the coastal areas of the southeastern Adriatic have increased, which has resulted in different types of contamination, including trace elements. Investigations of the southeastern Adriatic marine environment have intensified in last decade and included a number of sites from the southeastern Adriatic region, including the Albanian and Montenegrin coastal areas (Çelo et al. 1999; Çullaj et al. 2000; Rivaro et al. 2004, 2011; Joksimovic and Stankovic 2012; Jović et al. 2011, 2012; Markovic et al. 2012). However, no papers were found related
Environ Sci Pollut Res
to trace metal distribution in the surface sediment and the sediment impact on a metal bioaccumulation in P. oceanica along coastline of the eastern Adriatic Sea. Hence, the main objectives of the presented research were (1) to determine the content of trace elements (Fe, Mn, Ni, Zn, Cu, Co, Pb, As, Cd, and Hg) and to evaluate the status of the contamination level in the surface sediments and in P. oceanica; (2) to estimate the impact of the element concentrations in sediments with those found in the seagrass P. oceanica through their related correlation coefficients (r) and pollution indexes; (3) to evaluate the impact of sediment on heavy metal concentrations in P. oceanica calculating enrichment factor (EF) values and Pearson correlations for the seagrass and sediment to determine whether the metal in the seagrass had been absorbed from a sediment; and (4) to compare the obtained results with those from other parts of the Mediterranean to assess the degree of pollution in the studied area. Multivariate statistical and pattern recognition technique principal component analysis (PCA) was successfully combined with experimentally obtained metal concentrations (used as descriptors) to characterize, classify, and discriminate observed samples of surface sediments and seagrass.
Materials and methods Samples of surface sediment and P. oceanica were collected at eight selected locations in the Montenegrin coastal area with different geochemical, hydrological, and human impacts (Sveta Stasija, Kukuljina and Herceg Novi in the Boka Kotorska Bay, and at locations of the open Montenegrin coastal area of Mamula, Zanjice, Bigova, Budva, and Bar) (Fig. 1 and Table 1). Sediment samples were collected in the fall of 2005 and 2006, while P. oceanica in the fall 2005, spring 2006, fall Fig. 1 The investigated locations: 1 Sveta Stasija, 2 Kukuljina, 3 Herceg Novi, 4 Mamula, 5 Zanjice, 6 Bigova, 7 Budva, and 8 Bar
Table 1 Coordinates and depths of the sampling stations for sediments and P. oceanica samples: Sep. 2005; May 2006; Sep. 2006; May 2007 Station
Latitude (N)
Longitude (E)
Depth (m)
1. Sv. Stasija 2. Kukuljina 3. H. Novi 4. Mamula
42°28′04″ 42°24′54″ 42°26′93″ 42°23′76″
18°44′99″ 18°42′02″ 18°32′15″ 18°34′53″
6.0 11 7.0 18
5. Zanjice 6. Bigova 7. Budva 8. Bar
42°23′72″ 42°21′37″ 42°17′07″ 42°07′32″
18°33′64″ 18°41′88″ 18°50′14″ 19°04′08″
6.5 11 4.5 6.5
2006, and the spring 2007. All sampling operations were performed simultaneously, with three repetitions, within 1 day at all locations in the four seasons. Thirty-two samples of the seagrass and 16 sediment samples were prepared and 10 elements analyzed following a laboratory-approved QA/QC protocol in three analytical replicates. About 350 g of the fresh P. oceanica samples were collected from each location. The P. oceanica samples were washed and rinsed with ultrapure water, frozen, lyophilized, and reduced to powders. The powdered P. oceanica samples (approximately 0.5 g) were digested with a mixture of 7 ml concentrated HNO3 (65 % Merck, Suprapur) and 2 ml H2O2 (30 % Merck, Suprapur), and the resulting solutions were used for trace metal analyses. At the same time, 500 g of surface sediment was collected in the vicinity of the corresponding P. oceanica meadows. Only the top 5 cm of the sediment sample was used for this study. The sediment samples were prepared for analyses as follows: After oven drying (105 °C), grinding, homogenizing, and sieving, the quantity of elements in 1.0 g of dry sediment samples was measured in the fraction ½Mn >> ½Ni > ½Zn > ½Cu > ½Co
Sediment Several researches reported that the composition of sediment particles plays a significant role in the deposition of pollutants during the sedimentation process (Esen et al. 2010; Tavakoly Sany et al. 2011). The composition of the sediment grain size was determined on the basis of sediment sieving test and on the obtained percentage of sand (0.063–2 mm) and silt/clay ( ½Pb > ½Cd > ½Hg
The most abundant metals in the marine environment are Fe and Mn where their sources are land-based and show regional variations (Dolenc et al. 1998). Depending on the sediment composition, the levels of the connected microelements in the sediment samples are different. Since clay minerals carry more Fe than sand grains, this element is principally associated with the silt-clay fraction (Dolenc et al. 1998), while Rubio et al. (2000) found the highest levels of Mn in the sand fraction. This was the case at the locations Herceg Novi and Bar, which had the highest Mn contents, 772 and 657 mg kg−1, respectively, with a low percentage of silt and clay. This phenomenon was most probably attributable to coatings of Mn oxide on the sand grains (Shrader et al. 1977). A content of heavy metals tends to increase in association with fine-grained sediments (Tavakoly Sany et al. 2011). This was the case in the surface sediment from the location Kukuljina. The surface sediment at Kukuljina had the highest clay percentage (12.15 %) and very fine sand (67.9 %) and simultaneously the highest mean content of Fe (11, 711 mg kg −1 ), Ni (74.5 mg kg −1 ), Zn (mg kg−1 ), Cu (14.4 mg kg−1), and Pb (9.6 mg kg−1) (Table 3), as was expected from the composition of the sediment (Fig. 2). Clay has relatively high trace metal contents due to greater
Environ Sci Pollut Res Table 3
The mean contents±SD of trace metals in the surface sediments (mg kg−1 dw) and the MPI values according to sampling locations
No
Location
Fe
Mn
Zn
Ni
Pb
Cu
Co
As
Cd
Hg
MPI*
1
Sv.Stasija Kukuljina
3
H.Novi
4
Mamula
5
Zanjice
6
Bigova
7
Budva
8
Bar
209 ±19b 326 ±28c 772 ±64f 282 ±24c 497 ±44d 184 ±18b 132 ±12a 657 ±56e 850
25.1 ±2.2a 45.2 ±5.3de 23.8 ±1.9c 7.8 ±0.9e 19.8 ±1.9b 4.0 ±0.5e 5.1 ±0.6f 22.4 ±2.0d 95
18.2 ±1.7b 74.5 ±3.2d 32.3 ±3.3c 12.8 ±1.1e 16.3 ±1.5a 10.5 ±0.8d 2.7 ±0.2f 15.8 ±1.2d 68
7.0 ±1.2a 9.6 ±1.3d 3.7 ±0.4d 5.1 ±0.5c 3.9 ±0.5b 1.3 ±0.1e 2.6 ±0.3f 5.2 ±0.5c 20
6.6 ±0.5d 14.4 ±1.3g 11.9 ±0.9f 4.7 ±0.4b 7.7 ±0.7e 5.6 ±0.4c 3.2 ±0.3a 14.7 ±1.2g 45
3.9 ±0.3a 10.2 ±1.0de 9.0 ±0.8d 5.0 ±0.4b 6.6 ±0.7c 13.9 ±1.2f 5.2 ±0.5b 11.4 ±1.1e 19
4.9 ±0.5cd 5.2 ±0.5d 3.7 ±0.4 4.6 ±0.6bc 19.7 ±2.6e 3.5 ±0.5b 2.6 ±0.4a 3.1 ±0.5ab 13
0.75 ±0.1e 0.54 ±0.05d 0.77 ±0.11e 0.42 ±0.05c 0.87 ±0.13e 0.30 ±0.03b 0.06 ±0.01a 0.07 ±0.01a 0.30
0.024 ±0.002c 0.098 ±0.004e 0.028 ±0.002d 0.029 ±0.003d 0.009 ±0.0001a 0.029 ±0.003d 0.014 ±0.001b 0.155 ±0.009f 0.30
10.4
2
9263 ±268e 11,711 ±396g 6090 ±221d 1591 ±140c 10,507 ±363f 714 ±61a 1243 ±124b 6216 ±238d 47,200
Background values
18.2 12.6 7.0 11.8 8.2 3.4 11.6
*MPI metal pollution index; different letters (a–g) printed within the same column show significantly different means of observed data (p ½Mn >> ½Zn > ½Ni > ½Pb > ½Cu > ½Co > ½As > ½Cd > ½Hg The Fe contents in P. oceanica from the Montenegrin coastline were found to be generally lower or similar to those reported for Mediterranean French coast (Luy et al. 2012), NW Mediterranean (Marseille and Corsica) (Warnau et al. 1995) and the Aegean Sea, Greece (Sanz-Lazaro et al. 2012). Measured Cu contents were similar to the estimated natural background level for Cu in nine tropical seagrass
Environ Sci Pollut Res Table 4
The mean contents±SD of trace metals in P. oceanica (mg kg−1 dw) and the MPI values according to sampling locations
No
Location
Fe
Mn
Zn
Ni
Pb
Cu
Co
As
Cd
Hg
MPI*
1
Sv. Stasija Kukuljina
3
H. Novi
4
Mamula
5
Zanjice
6
Bigova
7
Budva
8
Bar
211 ±21c 104 ±9.4a 120 ±10.5 134 ±11b 118 ±10.2ab 137 ±14b 106 ±9.5a 385 ±31d
110 ±8.3d 82 ±5.3c 49 ±3.5b 45 ±2.5b 42 ±2.3b 44 ±3.3b 35 ±3.1a 93 ±6.1c
25 ±2.3a 33 ±3.4b 23 ±2.1a 32 ±3.0b 31 ±3.2b 39 ±4.1b 25 ±2.5a 37 ±3.6b
10.1 ±1.5d 10.5 ±2.0d 8.2 ±0.9cd 6.2 ±0.56bc 3.4 ±0.3a 6.9 ±0.7c 4.5 ±0.5b 5.1 ±0.63b
8.1 ±0.53b 6.8 ±0.44b 6.2 ±0.37ab 5.9 ±0.30a 7.5 ±0.63 5.3 ±0.43a 5.7 ±0.5a 8.9 ±0.75b
4.1 ±0.4a 4.0 ±0.3a 3.7 ±0.4a 4.3 ±0.4a 4.3 ±0.4a 4.1 ±0.4a 3.8 ±0.4a 6.5 ±0.60b
3.8 ±0.43b 7.5 ±0.5c 2.7 ±0.60b 1.2 ±0.30a 8.0 ±1.34c 2.0 ±0.31ab 2.7 ±0.3b 2.5 ±0.29b
2.2 ±0.25a 2.6 ±0.35ab 2.9 ±0.39ab 3.9 ±0.43b 2.8 ±0.46ab 2.8 ±0.41ab 2.7 ±0.4ab 3.5 ±0.52b
0.92 ±0.25b 0.40 ±0.35a 0.98 ±0.1b 0.40 ±0.03a 0.68 ±0.46a 0.54 ±0.41a 0.62 ±0.4 1.28 ±0.52b
17.0
2
1332 ±77e 1700 ±101f 825 ±69c 750 ±51bc 1075 ±109d 540 ±37a 725 ±49b 550 ±46a
16.0 13.2 11.5 13.6 11.9 11.1 17.3
*MPI metal pollution index; different letters (a–g) printed within the same column show significantly different means of observed data (p1. For visualizing the data trends and the discriminating efficiency of the used descriptors, a scatter plot of samples using the first two principal components (PCs) issued from PCA of the data matrix is obtained (Fig. 4). As can be seen, there is a neat separation of the various samples, according to metal content data. The first PC explained 40.22 % of the total variance in metal content data, and the second PC accounts for 26.02 % of variability (Fig. 4). Projection of the variables on the first factorial plane indicates that all samples and the variables contribute mostly to the first PC and thus to the total variability of the basic set. The influence of processing parameters can be observed in Fig. 4, with higher Cd, Hg, Zn, and Pb contents found at the left side of the graphic (seagrass samples) and higher As, Co, Mn, Fe, and Cu contents noticed at the right side of the PCA graphic (surface sediment content). The Ni content may be a little higher in the grass. Figure 4 also shows at which locations were the highest
4 3
Factor 2: 26.02%
2
Seagrass
6
4 7
1 4
3 0 -1
Surface sediments
7
Cd Hg
2
1 8
Zn
-2
1
5
6
5
As Co Mn Fe
Pb
3 8
Cu
Ni
-3 2 -4 -3
-2
-1
0
1
2
3
4
Factor 1: 40.20%
Fig. 4 Biplot for metal content data found in surface sediments and seagrass samples
concentrations of investigated elements. So, we can see that the highest Zn content had the grass at locations 1 (Sv. Stasija 110 mg/kg) and 8 (Bar 93 mg/kg), because the direction of the Zn vector is in the direction of points 1 and 8 or the sediment at the location 2 had the highest Cu content (Kukuljina 14.4 mg/kg). Variations in the metal contents in P. oceanica can be influenced by a number of variable environmental factors such as salinity, temperature, pH, oxygen content, nutrient level, precipitation, inflow of fresh water, currents, etc., rather than a constant source of pollution (Stankovic et al. 2014). The Ni content in P. oceanica are consistent with previously reported studies (Joksimović and Stanković 2012) confirming that this type of seagrass has the ability to accumulate large amounts of this metal, suggesting that Ni concentration in P. oceanica tissues reflects the Ni concentration in sediment (Lafabrie et al. 2007, Joksimović and Stanković 2012). Enrichments of the elements in the sediment and P. oceanica To determine the crustal or natural processes’ impact of the investigated element level in the tested samples, the obtained level of each element was compared with its background level in shale and clay (Rivaro et al. 2011) and the mean EF values were calculated for the investigated elements in the surface sediments and P. oceanica (Table 5). Elements can be divided into three major groups: elements without enrichment, EFPb) or very high (Cd and Hg) EF values, indicating their enrichment from non-crustal sources in the seagrass. The EF values suggest that P. oceanica from the location Bar was the highest enriched with most of the investigated elements, especially with Cd. According to an USEPA regulation (Ligero et al. 2002), sediments with Hg contents below 0.3 mg kg−1 dw were considered as not polluted. This was the case for the analyzed sediments (Table 3), and the EF value for Hg indicated that Hg was not enriched in the sediments but was enriched in the P. oceanica samples, obviously not absorbed by P. oceanica from the surface sediment. The highest EF values were found for Cd in both the sediments and the P. oceanica samples (Table 5). For example, the Cd content in the sediment was not particularly high at the sampling site Bar (0.07 mg kg−1), but a much higher Cd content
was found in the seagrass at this location, 3.5 mg kg−1 dw, and EF values at this location were 1.77 and 1000.2, respectively. It is known that seagrass is very efficient in accumulating Cd from a water (Lee and Wang, 2001, Joksimović and Stanković 2012). If we compare metal EF values for sediments and P. oceanica on the Bigova and Bar locations (Table 5), it is evident that metal EF values for the sediment on the Bar location were lower than on Bigova, but the metal EF values for P. oceanica was opposite at the same locations: on the Bar location, metal EF values were higher than on the Bigova location. Correlation coefficients of the element contents and MPI values The correlation coefficients, r values (at p
RESEARCH ARTICLE
Can the origin of some metals in the seagrass Posidonia oceanica be determined by the indexes of metals pollutions? Slavka Stanković & Mihajlo Jović & Bojan Tanaskovski & Marija L. Mihajlović & Danijela Joksimović & Lato Pezo
Received: 15 August 2014 / Accepted: 4 December 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract To assess metal pollution, Fe, Mn, Cu, Zn, Pb, Ni, Co, As, Cd, and Hg contents in samples of the seagrass Posidonia oceanica and surface sediment, collected at eight locations along the Montenegrin coast, were determined. The metal pollution index (MPI) and metal enrichment factor (EF) were then calculated. MPI and EF were lower in sediment than in P. oceanica at the same locations. This was very evident for EF values of Hg and Cd. Based on the Pearson’s correlations and EF values, it was possible to conclude that the last two metals’ content in the seagrass did not originate from the crustal sources or natural weathering processes.
Keywords Heavy metals . Surface sediment . Posidonia oceanica . Metal pollution index . Enrichment factor . Correlation coefficient . Multivariate analysis
Responsible editor: Céline Guéguen S. Stanković (*) : B. Tanaskovski Faculty of Technology and Metallurgy, Department of Analytical Chemistry, University of Belgrade, 11000 Belgrade, Serbia e-mail: [email protected] M. Jović Vinča Institute of Nuclear Sciences, University of Belgrade, P. O. Box 522, 11001 Belgrade, Serbia M. L. Mihajlović Institute for Technology of Nuclear and Other Mineral Raw Materials, 86 Franchet d`Esperey St, 11000 Belgrade, Serbia D. Joksimović IBM, University of Podgorica, Dobrota bb, 85330 Kotor, Montenegro L. Pezo Institute of General and Physical Chemistry, University of Belgrade, 11000 Belgrade, Serbia
Introduction Trace elements are serious pollutants of the marine environment because of their toxicity and persistence, their poor biodegradability, and tendency to concentrate in aquatic organisms (Lafabrie et al. 2007; Conti et al. 2010). Much attention has been paid to the use of marine organisms as bioindicators of trace metal pollution in marine waters (Richir et al. 2010; Luy et al. 2012; Markovic et al. 2012). Seagrass Posidonia oceanica (L.) Delile has been studied as a bioindicator of contamination by microelements in various parts of the world, especially along the Mediterranean coast (Lafabrie et al. 2007; Conti et al. 2010; Richir et al., 2010; Tovar-Sánchez et al. 2010; Luy et al. 2012). P. oceanica meadows play a crucial role in the ecology of the Mediterranean and mostly occur in shallow and sheltered coastal waters anchored in sand or mud bottoms. P. oceanica, which may absorb trace elements directly from the water column and/or from interstitial water in sediments (Lafabrie et al. 2007), has a high capacity to accumulate trace elements and concentrate pollutants occurring in the environment (Di Leo et al. 2013). Many microelements were found in trace amounts in sea water but often at elevated levels in seagrass (Morillo et al. 2005). Seagrasses are increasingly used as indicators of chemical contamination of coastal regions (Conti et al. 2010; Di Leo et al. 2013). In the last decade, human and industrial activities in the coastal areas of the southeastern Adriatic have increased, which has resulted in different types of contamination, including trace elements. Investigations of the southeastern Adriatic marine environment have intensified in last decade and included a number of sites from the southeastern Adriatic region, including the Albanian and Montenegrin coastal areas (Çelo et al. 1999; Çullaj et al. 2000; Rivaro et al. 2004, 2011; Joksimovic and Stankovic 2012; Jović et al. 2011, 2012; Markovic et al. 2012). However, no papers were found related
Environ Sci Pollut Res
to trace metal distribution in the surface sediment and the sediment impact on a metal bioaccumulation in P. oceanica along coastline of the eastern Adriatic Sea. Hence, the main objectives of the presented research were (1) to determine the content of trace elements (Fe, Mn, Ni, Zn, Cu, Co, Pb, As, Cd, and Hg) and to evaluate the status of the contamination level in the surface sediments and in P. oceanica; (2) to estimate the impact of the element concentrations in sediments with those found in the seagrass P. oceanica through their related correlation coefficients (r) and pollution indexes; (3) to evaluate the impact of sediment on heavy metal concentrations in P. oceanica calculating enrichment factor (EF) values and Pearson correlations for the seagrass and sediment to determine whether the metal in the seagrass had been absorbed from a sediment; and (4) to compare the obtained results with those from other parts of the Mediterranean to assess the degree of pollution in the studied area. Multivariate statistical and pattern recognition technique principal component analysis (PCA) was successfully combined with experimentally obtained metal concentrations (used as descriptors) to characterize, classify, and discriminate observed samples of surface sediments and seagrass.
Materials and methods Samples of surface sediment and P. oceanica were collected at eight selected locations in the Montenegrin coastal area with different geochemical, hydrological, and human impacts (Sveta Stasija, Kukuljina and Herceg Novi in the Boka Kotorska Bay, and at locations of the open Montenegrin coastal area of Mamula, Zanjice, Bigova, Budva, and Bar) (Fig. 1 and Table 1). Sediment samples were collected in the fall of 2005 and 2006, while P. oceanica in the fall 2005, spring 2006, fall Fig. 1 The investigated locations: 1 Sveta Stasija, 2 Kukuljina, 3 Herceg Novi, 4 Mamula, 5 Zanjice, 6 Bigova, 7 Budva, and 8 Bar
Table 1 Coordinates and depths of the sampling stations for sediments and P. oceanica samples: Sep. 2005; May 2006; Sep. 2006; May 2007 Station
Latitude (N)
Longitude (E)
Depth (m)
1. Sv. Stasija 2. Kukuljina 3. H. Novi 4. Mamula
42°28′04″ 42°24′54″ 42°26′93″ 42°23′76″
18°44′99″ 18°42′02″ 18°32′15″ 18°34′53″
6.0 11 7.0 18
5. Zanjice 6. Bigova 7. Budva 8. Bar
42°23′72″ 42°21′37″ 42°17′07″ 42°07′32″
18°33′64″ 18°41′88″ 18°50′14″ 19°04′08″
6.5 11 4.5 6.5
2006, and the spring 2007. All sampling operations were performed simultaneously, with three repetitions, within 1 day at all locations in the four seasons. Thirty-two samples of the seagrass and 16 sediment samples were prepared and 10 elements analyzed following a laboratory-approved QA/QC protocol in three analytical replicates. About 350 g of the fresh P. oceanica samples were collected from each location. The P. oceanica samples were washed and rinsed with ultrapure water, frozen, lyophilized, and reduced to powders. The powdered P. oceanica samples (approximately 0.5 g) were digested with a mixture of 7 ml concentrated HNO3 (65 % Merck, Suprapur) and 2 ml H2O2 (30 % Merck, Suprapur), and the resulting solutions were used for trace metal analyses. At the same time, 500 g of surface sediment was collected in the vicinity of the corresponding P. oceanica meadows. Only the top 5 cm of the sediment sample was used for this study. The sediment samples were prepared for analyses as follows: After oven drying (105 °C), grinding, homogenizing, and sieving, the quantity of elements in 1.0 g of dry sediment samples was measured in the fraction ½Mn >> ½Ni > ½Zn > ½Cu > ½Co
Sediment Several researches reported that the composition of sediment particles plays a significant role in the deposition of pollutants during the sedimentation process (Esen et al. 2010; Tavakoly Sany et al. 2011). The composition of the sediment grain size was determined on the basis of sediment sieving test and on the obtained percentage of sand (0.063–2 mm) and silt/clay ( ½Pb > ½Cd > ½Hg
The most abundant metals in the marine environment are Fe and Mn where their sources are land-based and show regional variations (Dolenc et al. 1998). Depending on the sediment composition, the levels of the connected microelements in the sediment samples are different. Since clay minerals carry more Fe than sand grains, this element is principally associated with the silt-clay fraction (Dolenc et al. 1998), while Rubio et al. (2000) found the highest levels of Mn in the sand fraction. This was the case at the locations Herceg Novi and Bar, which had the highest Mn contents, 772 and 657 mg kg−1, respectively, with a low percentage of silt and clay. This phenomenon was most probably attributable to coatings of Mn oxide on the sand grains (Shrader et al. 1977). A content of heavy metals tends to increase in association with fine-grained sediments (Tavakoly Sany et al. 2011). This was the case in the surface sediment from the location Kukuljina. The surface sediment at Kukuljina had the highest clay percentage (12.15 %) and very fine sand (67.9 %) and simultaneously the highest mean content of Fe (11, 711 mg kg −1 ), Ni (74.5 mg kg −1 ), Zn (mg kg−1 ), Cu (14.4 mg kg−1), and Pb (9.6 mg kg−1) (Table 3), as was expected from the composition of the sediment (Fig. 2). Clay has relatively high trace metal contents due to greater
Environ Sci Pollut Res Table 3
The mean contents±SD of trace metals in the surface sediments (mg kg−1 dw) and the MPI values according to sampling locations
No
Location
Fe
Mn
Zn
Ni
Pb
Cu
Co
As
Cd
Hg
MPI*
1
Sv.Stasija Kukuljina
3
H.Novi
4
Mamula
5
Zanjice
6
Bigova
7
Budva
8
Bar
209 ±19b 326 ±28c 772 ±64f 282 ±24c 497 ±44d 184 ±18b 132 ±12a 657 ±56e 850
25.1 ±2.2a 45.2 ±5.3de 23.8 ±1.9c 7.8 ±0.9e 19.8 ±1.9b 4.0 ±0.5e 5.1 ±0.6f 22.4 ±2.0d 95
18.2 ±1.7b 74.5 ±3.2d 32.3 ±3.3c 12.8 ±1.1e 16.3 ±1.5a 10.5 ±0.8d 2.7 ±0.2f 15.8 ±1.2d 68
7.0 ±1.2a 9.6 ±1.3d 3.7 ±0.4d 5.1 ±0.5c 3.9 ±0.5b 1.3 ±0.1e 2.6 ±0.3f 5.2 ±0.5c 20
6.6 ±0.5d 14.4 ±1.3g 11.9 ±0.9f 4.7 ±0.4b 7.7 ±0.7e 5.6 ±0.4c 3.2 ±0.3a 14.7 ±1.2g 45
3.9 ±0.3a 10.2 ±1.0de 9.0 ±0.8d 5.0 ±0.4b 6.6 ±0.7c 13.9 ±1.2f 5.2 ±0.5b 11.4 ±1.1e 19
4.9 ±0.5cd 5.2 ±0.5d 3.7 ±0.4 4.6 ±0.6bc 19.7 ±2.6e 3.5 ±0.5b 2.6 ±0.4a 3.1 ±0.5ab 13
0.75 ±0.1e 0.54 ±0.05d 0.77 ±0.11e 0.42 ±0.05c 0.87 ±0.13e 0.30 ±0.03b 0.06 ±0.01a 0.07 ±0.01a 0.30
0.024 ±0.002c 0.098 ±0.004e 0.028 ±0.002d 0.029 ±0.003d 0.009 ±0.0001a 0.029 ±0.003d 0.014 ±0.001b 0.155 ±0.009f 0.30
10.4
2
9263 ±268e 11,711 ±396g 6090 ±221d 1591 ±140c 10,507 ±363f 714 ±61a 1243 ±124b 6216 ±238d 47,200
Background values
18.2 12.6 7.0 11.8 8.2 3.4 11.6
*MPI metal pollution index; different letters (a–g) printed within the same column show significantly different means of observed data (p ½Mn >> ½Zn > ½Ni > ½Pb > ½Cu > ½Co > ½As > ½Cd > ½Hg The Fe contents in P. oceanica from the Montenegrin coastline were found to be generally lower or similar to those reported for Mediterranean French coast (Luy et al. 2012), NW Mediterranean (Marseille and Corsica) (Warnau et al. 1995) and the Aegean Sea, Greece (Sanz-Lazaro et al. 2012). Measured Cu contents were similar to the estimated natural background level for Cu in nine tropical seagrass
Environ Sci Pollut Res Table 4
The mean contents±SD of trace metals in P. oceanica (mg kg−1 dw) and the MPI values according to sampling locations
No
Location
Fe
Mn
Zn
Ni
Pb
Cu
Co
As
Cd
Hg
MPI*
1
Sv. Stasija Kukuljina
3
H. Novi
4
Mamula
5
Zanjice
6
Bigova
7
Budva
8
Bar
211 ±21c 104 ±9.4a 120 ±10.5 134 ±11b 118 ±10.2ab 137 ±14b 106 ±9.5a 385 ±31d
110 ±8.3d 82 ±5.3c 49 ±3.5b 45 ±2.5b 42 ±2.3b 44 ±3.3b 35 ±3.1a 93 ±6.1c
25 ±2.3a 33 ±3.4b 23 ±2.1a 32 ±3.0b 31 ±3.2b 39 ±4.1b 25 ±2.5a 37 ±3.6b
10.1 ±1.5d 10.5 ±2.0d 8.2 ±0.9cd 6.2 ±0.56bc 3.4 ±0.3a 6.9 ±0.7c 4.5 ±0.5b 5.1 ±0.63b
8.1 ±0.53b 6.8 ±0.44b 6.2 ±0.37ab 5.9 ±0.30a 7.5 ±0.63 5.3 ±0.43a 5.7 ±0.5a 8.9 ±0.75b
4.1 ±0.4a 4.0 ±0.3a 3.7 ±0.4a 4.3 ±0.4a 4.3 ±0.4a 4.1 ±0.4a 3.8 ±0.4a 6.5 ±0.60b
3.8 ±0.43b 7.5 ±0.5c 2.7 ±0.60b 1.2 ±0.30a 8.0 ±1.34c 2.0 ±0.31ab 2.7 ±0.3b 2.5 ±0.29b
2.2 ±0.25a 2.6 ±0.35ab 2.9 ±0.39ab 3.9 ±0.43b 2.8 ±0.46ab 2.8 ±0.41ab 2.7 ±0.4ab 3.5 ±0.52b
0.92 ±0.25b 0.40 ±0.35a 0.98 ±0.1b 0.40 ±0.03a 0.68 ±0.46a 0.54 ±0.41a 0.62 ±0.4 1.28 ±0.52b
17.0
2
1332 ±77e 1700 ±101f 825 ±69c 750 ±51bc 1075 ±109d 540 ±37a 725 ±49b 550 ±46a
16.0 13.2 11.5 13.6 11.9 11.1 17.3
*MPI metal pollution index; different letters (a–g) printed within the same column show significantly different means of observed data (p1. For visualizing the data trends and the discriminating efficiency of the used descriptors, a scatter plot of samples using the first two principal components (PCs) issued from PCA of the data matrix is obtained (Fig. 4). As can be seen, there is a neat separation of the various samples, according to metal content data. The first PC explained 40.22 % of the total variance in metal content data, and the second PC accounts for 26.02 % of variability (Fig. 4). Projection of the variables on the first factorial plane indicates that all samples and the variables contribute mostly to the first PC and thus to the total variability of the basic set. The influence of processing parameters can be observed in Fig. 4, with higher Cd, Hg, Zn, and Pb contents found at the left side of the graphic (seagrass samples) and higher As, Co, Mn, Fe, and Cu contents noticed at the right side of the PCA graphic (surface sediment content). The Ni content may be a little higher in the grass. Figure 4 also shows at which locations were the highest
4 3
Factor 2: 26.02%
2
Seagrass
6
4 7
1 4
3 0 -1
Surface sediments
7
Cd Hg
2
1 8
Zn
-2
1
5
6
5
As Co Mn Fe
Pb
3 8
Cu
Ni
-3 2 -4 -3
-2
-1
0
1
2
3
4
Factor 1: 40.20%
Fig. 4 Biplot for metal content data found in surface sediments and seagrass samples
concentrations of investigated elements. So, we can see that the highest Zn content had the grass at locations 1 (Sv. Stasija 110 mg/kg) and 8 (Bar 93 mg/kg), because the direction of the Zn vector is in the direction of points 1 and 8 or the sediment at the location 2 had the highest Cu content (Kukuljina 14.4 mg/kg). Variations in the metal contents in P. oceanica can be influenced by a number of variable environmental factors such as salinity, temperature, pH, oxygen content, nutrient level, precipitation, inflow of fresh water, currents, etc., rather than a constant source of pollution (Stankovic et al. 2014). The Ni content in P. oceanica are consistent with previously reported studies (Joksimović and Stanković 2012) confirming that this type of seagrass has the ability to accumulate large amounts of this metal, suggesting that Ni concentration in P. oceanica tissues reflects the Ni concentration in sediment (Lafabrie et al. 2007, Joksimović and Stanković 2012). Enrichments of the elements in the sediment and P. oceanica To determine the crustal or natural processes’ impact of the investigated element level in the tested samples, the obtained level of each element was compared with its background level in shale and clay (Rivaro et al. 2011) and the mean EF values were calculated for the investigated elements in the surface sediments and P. oceanica (Table 5). Elements can be divided into three major groups: elements without enrichment, EFPb) or very high (Cd and Hg) EF values, indicating their enrichment from non-crustal sources in the seagrass. The EF values suggest that P. oceanica from the location Bar was the highest enriched with most of the investigated elements, especially with Cd. According to an USEPA regulation (Ligero et al. 2002), sediments with Hg contents below 0.3 mg kg−1 dw were considered as not polluted. This was the case for the analyzed sediments (Table 3), and the EF value for Hg indicated that Hg was not enriched in the sediments but was enriched in the P. oceanica samples, obviously not absorbed by P. oceanica from the surface sediment. The highest EF values were found for Cd in both the sediments and the P. oceanica samples (Table 5). For example, the Cd content in the sediment was not particularly high at the sampling site Bar (0.07 mg kg−1), but a much higher Cd content
was found in the seagrass at this location, 3.5 mg kg−1 dw, and EF values at this location were 1.77 and 1000.2, respectively. It is known that seagrass is very efficient in accumulating Cd from a water (Lee and Wang, 2001, Joksimović and Stanković 2012). If we compare metal EF values for sediments and P. oceanica on the Bigova and Bar locations (Table 5), it is evident that metal EF values for the sediment on the Bar location were lower than on Bigova, but the metal EF values for P. oceanica was opposite at the same locations: on the Bar location, metal EF values were higher than on the Bigova location. Correlation coefficients of the element contents and MPI values The correlation coefficients, r values (at p
