As a result of technological development, heavy metal pollution has become a threat to life. Many adverse effects of metal pollution on the aquatic environment have been identified. Heavy metal pollution in the aquatic environment derives from natural sources such as air, soil, and dissolved mineral rocks (Adamu et al. 2015; Skordas et al. 2015), as well as anthropogenic sources such as domestic, industrial, and agricultural effluents (Wei & Yang 2010; Mohiuddin et al. 2010).
The discharge, storage, and precipitation of heavy metals occur in marine and oceanic sediments (Fujita et al. 2014; Machado et al. 2016). Sediments are a good indicator of heavy metals from anthropogenic sources due to the hydrophobic properties of the latter and their tendency to accumulate with precipitation. Sediment analysis provides information on total accumulation (Anderson Abel et al. 2016). Sedimentation is very important for the accumulation of heavy metals in the hydrological cycle in the aquatic environment. Heavy metals are not completely immobilized in the surface sediment, which is a biological, physicochemical, hydrological, and geological interaction area in a complex system. Instead, they migrate and sometimes accumulate (Dhanakumar et al. 2015; Chen et al. 2019).
In order to determine metal contamination sources in the aquatic environment, it is important to examine changes in natural and anthropogenic trace elements (Bing et al. 2013). For this purpose, indices such as the enrichment factor (
Pollution has become a serious issue in countries bordering the Mediterranean Sea. The semi-enclosed structure of this ecosystem and the increase in population density along the Mediterranean coastline have caused considerable water pollution. In order to mitigate this problem, a comprehensive pollution prevention and control program (Mediterranean Action Plan), organized and supported by the United Nations and various international agencies, has been implemented by the Mediterranean countries since 1975. A number of researchers have reported that many trace metals, from either natural or anthropogenic sources, enter the Mediterranean Sea in different parts of this ecosystem (Cubadda et al. 2001).
Previous studies investigated the presence and effects of heavy metals on seawater and sediment in Iskenderun Bay (Türkmen & Aras 2011) focusing on sediment and benthos (Dural and Göksu 2006; Türkmen & Aras 2011), marine algae (Olgunoğlu & Polat 2007), aquatic vertebrates (Kargın et al. 2006; Kalay et al. 1999), and aquatic invertebrates (Duysak et al. 2013; Duysak & Ersoy 2014).
The objectives of this study were to determine the accumulation and distribution of ten heavy metals (i.e. Cu, Pb, Zn, Ni, Mn, Fe, As, Cd, Cr and Hg) in sediments collected from eight sites located in different regions of Iskenderun Bay. Furthermore, we calculated the contamination factor, the pollution load index, and the potential ecological risk index (
Two-period sampling was performed to cover the Iskenderun, Yumurtalık, and Arsuz regions in the northern and southern parts of the study area, i.e. Iskenderun Bay (Fig. 1).
Surface sediment samples were collected at the selected sites in the study area on 8 April 2018 and 8 June 2019, using a van Veen grab sampler (Table 1). Samples were homogenized and placed in plastic bags before being transferred to Petri dishes pre-washed with acid and RO purified water in the laboratory. Samples in Petri dishes were then dried at 60°C for 24 h. The concentrations of Cu, Pb, Zn, Ni, Mn, Fe, As, Cd, Cr, and Hg were measured in the digested phase by inductively coupled plasma mass spectrometry (ICP-MS; ACME Analytical Labs, Vancouver, BC, Canada). The prepared sample was digested with a modified aqua regia solution with equal parts of concentrated HCl, HNO3, and DI H2O for 1 h in a heating block. The sample was made up to volume with dilute HCl. Quality control was performed using duplicates, blanks, and internal standard reference material (DS 9) obtained from ACME Analytical Labs. The values obtained (mg kg−1) from the analysis of this sample were as follows:
Element | Observed | Permissible | Detection limits |
---|---|---|---|
Cu | 104 | 108 | 0.01 |
Pb | 118 | 126 | 0.01 |
Zn | 319.6 | 317 | 0.1 |
Ni | 38.7 | 40.3 | 0.1 |
Mn | 575 | 575 | 1 |
Fe | 23.000 | 23.300 | 100 |
As | 25 | 25.5 | 0.1 |
Cd | 2.41 | 2.40 | 0.01 |
Cr | 110.7 | 121 | 0.5 |
Hg | 0.0203 | 0.0200 | 0.005 |
Iskenderun Bay sampling sites
Sites | Coordinates | General characteristics | Depth (m) | |
---|---|---|---|---|
1 | 36°39′39″N | 36°12′46″E | The site is located in an industrial zone, 11 km from Iskenderun. The region is located near heavy industrial facilities. | 2.5 |
2 | 36°38′06″N | 36°12′10″E | The site is located 8 km from Iskenderun. | 3 |
3 | 36°27′12″N | 35°55′35″E | The region is located near agricultural land and tourist activities. In the western part of the site there is a small stream that drains into the sea. | 2 |
4 | 36°21′40″N | 35°49′23″E | The site is located 48 km from Iskenderun and 11 km from Arsuz, and away from the industrial area. | 3 |
5 | 36°51′00″N | 35°54′41″E | The site is located in the Yumurtalık Gölovası region, which is located near a thermal power plant and a terminal where oil transporta on is carried out. | 11 |
6 | 36°51′08″N | 35°54′54″E | The site is located near a thermal power plant and a terminal where oil transportation is carried out. | 8 |
7 | 36°50′40″N | 35°55′12″E | The site is located near a thermal power plant and a terminal where oil transportation is carried out. | 25 |
8 | 36°51′16″N | 35°54′43″E | The site is located near a thermal power plant and a terminal where oil transportation is carried out. | 7 |
Two indices,
To determine environmental quality of the sediment, an integrated Pollution Load Index (
Further, the
In addition, Pearson’s correlation analysis was used to analyze the relationships between the variables. Further, CA was used to determine the distance between the variables. PCA was employed to identify the main sources of variation between the study sites in the bay.
The concentration of heavy metals in the sediments is presented in Table 2 (mg kg−1). According to the results, the concentrations are in the following order: Fe > Ni > Mn > Cr > Zn > Cu > As > Pb > Cd > Hg.
Heavy metal concentrations (mg kg−1)
Site No. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
---|---|---|---|---|---|---|---|---|
Cu | 12.68 | 11.32 | 10.32 | 11.47 | 11.15 | 11.28 | 25.39 | 9.66 |
Pb | 10.40 | 9.80 | 2.11 | 2.73 | 5.57 | 5.81 | 12.93 | 5.20 |
Zn | 39.7 | 39.8 | 26.3 | 23.9 | 31.0 | 30.8 | 70.6 | 27.6 |
Ni | 797.7 | 848.0 | 1673.6 | 1460 | 115.7 | 132.9 | 252.6 | 104.8 |
Mn | 494 | 535 | 738 | 504 | 699 | 750 | 649 | 719 |
Fe | 31300 | 32000 | 38800 | 36700 | 19900 | 19900 | 30200 | 17300 |
As | 6.9 | 7.5 | 13.3 | 16.7 | 15.3 | 16.0 | 10.0 | 14.3 |
Cd | 0.14 | 0.13 | 0.03 | 0.03 | 0.10 | 0.10 | 0.17 | 0.12 |
Cr | 478.4 | 515.8 | 224.6 | 353.5 | 68.2 | 73.3 | 138.5 | 70 |
Hg | 0.034 | 0.028 | 0.005 | 0.005 | 0.012 | 0.014 | 0.045 | 0.01 |
Ni, Mn, As, Cd, and Cr were found to be present in concentrations higher than their corresponding values in the upper layer of the Earth’s crust. In addition, the concentrations of As, Ni, and Cr were higher than those in other study areas (Yalcin et al. 2019). All As and Cd concentrations, except for the shale value, are higher than the values for sand sediment, sandstone, and the upper crust of the Earth (Table 3). According to the United States Environmental Protection Agency (EPA 1995), the sediment values indicate moderate Cu pollution, heavy Ni and Fe pollution, and moderate to heavy As and Cr pollution (Table 4).
Descriptive and background level values of the variables (mg kg−1)
Cu | Pb | Zn | Ni | Mn | Fe | As | Cd | Cr | Hg | |
---|---|---|---|---|---|---|---|---|---|---|
Heavy metal Av. | 12.90 | 6.81 | 36.21 | 673.26 | 636.0 | 28262 | 12.5 | 0.10 | 240.2 | 0.01 |
Iskenderun Gulf | 16.77 | 15.72 | 89.15 | 646.14 | 1166.3 | 9.75 | 0.26 | 1687.2 | ||
Ambarlı Port | 280 | 96 | 346 | 53 | 339 | |||||
Laizhou Bay | 22 | 21.9 | 60.4 | 0.12 | 60 | |||||
Liaodon Bay | 19.4 | 31.8 | 71.7 | 22.5 | 1.2 | 46.4 | ||||
Coastal Bohai Bay | 38.5 | 34.7 | 131.1 | 40.7 | 0.22 | 101.4 | ||||
Interdial Bohai Bay | 24 | 21.11 | 89.60 | 41.35 | 0.12 | 68.6 | ||||
Al-khobar Area | 330 | 9.4 | 86 | 116 | 244 | 16.73 | 3.1 | 83 | 1.61 | |
Standard error | 5.11 | 3.83 | 15.06 | 629.01 | 108.7 | 8187 | 3.85 | 0.05 | 186.1 | 0.01 |
Sand Sediment | 40.00 | 17.00 | 65.00 | 40.0 | 680.0 | 19.22 | - | - | 74.00 | 650 |
Sandstone | 9.00 | 7.00 | 16.00 | 2.00 | 90.00 | 1 | 1.00 | 0.09 | 35.00 | 240 |
Shale | 45.00 | 20.00 | 95.00 | 50.00 | 85.00 | 13.0 | 0.30 | 90.00 | ||
Upper crust | 25.00 | 16.00 | 71.00 | 50.00 | 600.0 | 1.50 | 0.001 | 85.00 | ||
Soil | 21.00 | 14.00 | 94.00 | 24.00 | 600.0 | 7.40 | 0.34 | 64.00 | ||
TEL | 19 | 30.2 | 124 | 15.9 | 7.2 | 0.68 | 52.3 | 0.70 | ||
PEL | 110 | 110 | 270 | 42.8 | 42 | 4.2 | 160 | 1.4 |
Sediment values according to EPA
Metal (mg kg−1) | Not polluted | Moderately polluted | Heavily polluted | Current study |
---|---|---|---|---|
Cu | < 25 | 25–30 | > 50 | 9.66–25.39 |
Pb | < 40 | 40–60 | > 60 | 2.11–12.93 |
Zn | < 90 | 90–200 | > 200 | 23.9–70.6 |
Ni | < 20 | 20–50 | > 50 | 104.8–1673.6 |
Mn | < 300 | 300–500 | > 500 | 494–750 |
Fe | < 17 000 | 17 000–25 000 | > 25000 | 17300–38800 |
As | < 3 | 3–8 | > 8 | 6.9–16.7 |
Cd | - | - | > 6 | 0.03–0.17 |
Cr | < 25 | 25–75 | > 75 | 68.2–515.8 |
Hg | < 1 | > −1 | > 1 | 0–0.004 |
The
Enrichment factor (
Site No. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | Ave. |
---|---|---|---|---|---|---|---|---|---|
Cu | 0.42 | 0.36 | 0.27 | 3.22 | 0.58 | 0.59 | 0.87 | 0.58 | 0.50 |
Pb | 0.78 | 0.71 | 0.12 | 0.17 | 0.65 | 0.68 | 1.00 | 0.70 | 0.60 |
Zn | 0.62 | 0.61 | 0.33 | 0.32 | 0.77 | 0.76 | 1.15 | 0.78 | 0.67 |
Ni | 17.6 | 18.3 | 29.8 | 27.5 | 4.01 | 4.61 | 5.78 | 4.18 | 13.98 |
Mn | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 | 0.00 |
As | 5.75 | 6.11 | 8.95 | 11.8 | 20.0 | 20.9 | 8.64 | 21.5 | 13.00 |
Cd | 1.05 | 0.95 | 0.18 | 0.19 | 1.18 | 1.18 | 1.32 | 1.63 | 0.96 |
Cr | 7.98 | 8.41 | 3.02 | 5.03 | 1.78 | 1.92 | 2.39 | 2.11 | 4.08 |
Hg | 0.12 | 0.10 | 0.01 | 0.01 | 0.07 | 0.08 | 0.17 | 0.06 | 0.08 |
The
Contamination factor (
Site No. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
---|---|---|---|---|---|---|---|---|
Cu | 0.28 | 0.25 | 0.22 | 0.25 | 0.24 | 0.25 | 0.56 | 0.21 |
Pb | 0.52 | 0.49 | 0.10 | 0.13 | 0.27 | 0.29 | 0.64 | 0.26 |
Zn | 0.41 | 0.41 | 0.27 | 0.25 | 0.32 | 0.32 | 0.74 | 0.29 |
Ni | 11.7 | 12.4 | 24.6 | 21.4 | 1.70 | 1.95 | 3.71 | 1.54 |
Mn | 0.58 | 0.62 | 0.86 | 0.59 | 0.82 | 0.88 | 0.76 | 0.84 |
Fe | 0.66 | 0.68 | 0.82 | 0.78 | 0.42 | 0.42 | 0.64 | 0.36 |
As | 3.83 | 4.16 | 7.38 | 9.27 | 8.50 | 8.88 | 5.55 | 7.94 |
Cd | 0.7 | 0.65 | 0.15 | 0.15 | 0.5 | 0.5 | 0.85 | 0.65 |
Cr | 5.31 | 5.73 | 2.49 | 3.92 | 0.75 | 0.81 | 1.53 | 0.77 |
Hg | 0.08 | 0.07 | 0.01 | 0.01 | 0.03 | 0.03 | 0.11 | 0.02 |
0.11 | 0.09 | 0.0 | 0.0 | 0.0 | 0.0 | 0.16 | 0.0 |
The
Further, the highest integrated
Potential ecological index (RI) for a single metal (E_f^i)
Site No. | Cu | Pb | Zn | Ni | As | Cd | Cr | Hg | |
---|---|---|---|---|---|---|---|---|---|
1 | 1.40 | 2.60 | 0.41 | 58.66 | 38.33 | 21 | 10.63 | 3.40 | 136.46 |
2 | 1.25 | 2.45 | 0.41 | 62.35 | 41.66 | 19.5 | 11.46 | 2.80 | 141.91 |
3 | 1.14 | 0.52 | 0.27 | 123.05 | 73.88 | 4.5 | 4.99 | 0.50 | 208.89 |
4 | 1.27 | 0.68 | 0.25 | 107.39 | 92.77 | 4.5 | 7.85 | 0.50 | 215.24 |
5 | 1.23 | 1.39 | 0.32 | 8.50 | 85.00 | 15.0 | 1.51 | 1.20 | 114.18 |
6 | 1.25 | 1.45 | 0.32 | 9.77 | 88.88 | 42 | 1.62 | 1.40 | 119.72 |
7 | 2.82 | 3.23 | 0.74 | 18.57 | 55.55 | 25.5 | 3.07 | 4.50 | 114.00 |
8 | 1.07 | 1.30 | 0.29 | 7.70 | 79.44 | 18 | 1.55 | 1.00 | 110.37 |
Average | 1.43 | 1.70 | 0.38 | 49.05 | 69.44 | 15.37 | 5.33 | 1.91 | 145.09 |
Geoaccumulation (Igeo) values for the sampling sites
Site No. | Igeo | |||||||||
---|---|---|---|---|---|---|---|---|---|---|
Cu | Pb | Zn | Ni | Mn | Fe | As | Cd | Cr | Hg | |
1 | 3.58 | 1.67 | 3.82 | −0.83 | 7.97 | 12.03 | 2.12 | −3.24 | −6.96 | −6.9 |
2 | 2.61 | 1.77 | 3.91 | −0.76 | 8.06 | 12.17 | 2.22 | −3.29 | −7.09 | −6.7 |
3 | 1.48 | 0.31 | 2.56 | −37.4 | 6.33 | 7.37 | 0.93 | –5.25 | −8.49 | −8.3 |
4 | 2.66 | 1.04 | 3.77 | −6.74 | 8.08 | 12.10 | 2.61 | –5.13 | −2.08 | −7.9 |
5 | 2.78 | 1.79 | 4.08 | 5.71 | 8.51 | 12.89 | 2.83 | –3.54 | 10.8 | −6.9 |
6 | 2.81 | 1.84 | 4.11 | −5.79 | 8.47 | 12.94 | 2.88 | −3.53 | −11.3 | −6.7 |
7 | 3.80 | 2.82 | 5.06 | 6.62 | 8.81 | 13.73 | 2.92 | −2.75 | −11.6 | −5.5 |
8 | 2.55 | 1.62 | 3.87 | 5.49 | 8.23 | 12.66 | 2.62 | −3.36 | −14.3 | −7.1 |
Mean | 2.78 | 1.61 | 3.90 | −2.76 | 8.06 | 11.99 | 2.39 | −3.76 | −9.10 | −7.0 |
Although Pearson’s correlation analysis carried out to determine the correlation between variables indicated that many metals are correlated, Ni, Mn, As, and Cr showed no correlation with any other metals. Fe and Mn are highly correlated with all metals except Pb and Cd, and Al is highly correlated with all metals except Pb, Cd, and Hg. This indicates that the transport mechanisms of Pb and Cd are different from those of other elements. The greatest contribution to
Pearson’s correlation coefficients between variables (boldface figures represent statistically significant correlations at 95% confidence interval)
Cu | Pb | Zn | Ni | Mn | Fe | As | Cd | Cr | Hg | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|
Cu | 1 | |||||||||||
Pb | ||||||||||||
Zn | ||||||||||||
Ni | −024 | −0.43 | −0.33 | |||||||||
Mn | −0.07 | −0.34 | −0.12 | −0.39 | ||||||||
Fe | 0.14 | −0.06 | 0.858 | −0.51 | ||||||||
As | –0.33 | −0.57 | −0.05 | 0.51 | −0.31 | |||||||
Cd | 0.57 | 0.76* | −0.70 | −0.10 | −0.41 | −0.63 | ||||||
Cr | −0.11 | 0.26 | 001 | 0.58 | −0.87 | 0.66 | −066 | 0.0 | ||||
Hg | 0.77* | 0.91 | −0.31 | −0.36 | 0.07 | −0.79 | 0.29 |
Correlation is significant at the 0.05 level;
Correlation is significant at the 0.01 level
CA was performed to identify the relationships between the variables and clustering of the variables. According to the clustering dendrogram, three large clusters can be distinguished (Fig. 2). The first cluster contains Cu, Zn, Pb Hg, Cd, and Al. This indicates that the transport mechanisms and/or sources of these elements are similar. The second group consists of Ni, Fe, and Cr. The third one consists of Mn and As and is located further away from the two other groups (Fig. 3).
Table 10 presents the results of PCA. A total of 94.5% of the data variance was explained by three principle components: PC1 (Pb, ZN, Al, Hg) accounted for 51% of the total variance, PC2 (Fe and As) – 31% of the variance; and PC3 (Cu, Ni, and Fe) – 11.2%. Iskenderun Bay is dominated by currents coming from the coasts of Israel, Lebanon, and Syria, due to the bay’s connection with the open sea. Further, the bay is affected by two cyclonic wind systems: one of them is clockwise and the other one is counterclockwise. Recently, Iskenderun Bay has experienced serious pollution problems as a result of rapid population growth and unplanned urbanization in parallel to industrialization. Pollution is at a critical level due to large industrial plants located along the coastal areas of Iskenderun Bay. These industrial plants are iron and steel plants, fertilizer plants, industrial factories, oil transportation, liquid gas, and coal transportation (Özcan et al. 2010). In addition, agricultural pollutants and household waste transported by the Seyhan, Ceyhan and Orontes rivers reach the bay region. Further, we found that As, Ni, and Fe concentrations exceed the acceptable limits due to waste coming from iron and steel plants, agricultural land, and industrial areas.
Principal Component Analysis (PCA)
PC1 | PC2 | PC3 | |
---|---|---|---|
Cu | 0.34 | 0.02 | |
Pb | −0.06 | −0.14 | |
Zn | −0.00 | 0.27 | |
Ni | −0.20 | −0.42 | |
Mn | −0.10 | 0.15 | |
Fe | −0.03 | −0.45 | |
As | −0.27 | 0.29 | |
Cd | 0.38 | 0.09 | −0.31 |
Cr | 0.04 | −0.50 | −0.23 |
Al | 0.21 | 0.30 | |
Hg | −0.10 | −0.02 | |
Eigenvalue | 5.71 | 3.48 | 1.23 |
% Variance | 51.96 | 31.64 | 11.29 |
% Clustering | 51.96 | 83.60 | 1.23 |
The content of heavy metals and potential ecological risks were studied using sediment samples collected from eight sampling sites in Iskenderun Bay.
The content of heavy metals and potential ecological risks in Iskenderun Bay were studied based on sediment samples collected there. The enrichment and contamination factors indicated a significant moderate accumulation of the metals. Although the calculated ecological risk values for As and Ni exceeded the maximum limits at several sites, they were generally below the permissible limits. The integrated