The total concentration and the speciation of heavy metals (Pb, Cd, Cu, Zn, Ni, and Cr) in surface sediments of Rades-Hamam Lif coast were determined, with particular focus on the effect that urban and industrial waste in the Meliane river has on the estuary and coastal surface sediments of the Rades-Hamam Lif coast, off the Mediterranean Sea. Several geochemical indices were applied to assess the risk of contamination and the environmental risks of heavy metals on surface sediments. The total concentrations of these heavy metals are influenced by runoff, industrial, and urban wastewater. The Cd, Pb, Zn, and Ni are affected by anthropogenic sources, especially at the mouth of the Meliane river. The sequential extraction of Cd was presented dominantly in the exchangeable fraction and thus the high potential bioavailability. In contrast, Cr and Cu were mostly bound to the residual fraction indicating their low toxicity and bioavailability. The order of migration and transformation sequence was Cd > Pb > Ni > Zn > Cr > Cu, and the degree of pollution was Cd > Pb > Ni > Zn > Cr > Cu.
Coastal sediments are generally exposed to heavy metal pollution from urban and industrial activities, especially in river mouth [
Tunisia has about 1300 km of coastline on the Mediterranean Sea, which is of important environmental, economic, and touristic value. Some of the Tunisian coastal areas of the Mediterranean Sea (in particular, in front of the large cities) receive different types of pollution sources, such as the Rades-Hamam Lif coast, a part of a Gulf of Tunis, which is under the pressure of a rapidly growing population due to a major industrial concentration and plenty of touristic and port activity.
The Meliane river, located in the eastern shore of the Gulf of Tunis, characterized by an intensive industrial and urban activity in its watershed appears to be a good subject for study especially with all the discharges that the Meliane river sends to the Tunis bay. The Rades-Hamam Lif coast (Gulf of Tunis) has experienced, since the past few years, major environmental problems due to urban and industrial discharge on the Meliane river, which has led the Tunisian authorities to close this coast for summer visitors.
The main objectives of this study were to (1) quantify and explain the spatial distribution of chemical fractions of metal (Pb, Cu, Cr, Zn, Ni, and Cd) in surface sediments of the Rades-Hamam Lif coast and (2) assess the degree of heavy metal pollution using different contamination indices (geoaccumulation index, contamination factor, pollution load index, and biological assessment of surface sediments).
The Meliane river, with its delta located on the eastern shore of the Gulf of Tunis, is the second longest river in Tunisia after Medjerda River (Figure
Location map of surface sediment samples along the Rades-Hamam Lif coast around the mouth of the Meliane river.
Location of several industries along the Meliane river.
Since the Gulf of Tunis is a semienclosed basin, the movement of water essentially controls the sediment distribution, where a large fraction of fine sediments is transported by the main Mediterranean currents to settle in the central zone of the Gulf. Those coarse sediments are found along the west coast of the gulf. This coastal transport is particularly under the action of waves and swell [
Surface sediment samples were collected from 21 stations along the coastal area of Rades-Hamam Lif around the mouth of Meliane river, through six profiles to the beach (Figure
For the determination of the total trace metals, the surface samples were digested by adding to 1 g of sediment a mixture of three concentrated solutions: 15 mL of HClO2, 15 mL HF, and 20 mL HNO3. The resulting solutions were analyzed for Ni, Pb, Cu, Cr, Cd, and Zn by atomic absorption spectrometry (Thermo Scientific, ICE 3,000 series). The procedure used for trace metals analysis was checked for accuracy using the IAEA-405 certified reference material (Table
Accuracy of heavy metal analysis (%).
Elements | IEAE 405 | This study | RSD (%) |
---|---|---|---|
Pb | 72.6–77.0 | 76.8 | 2.9 |
Cd | 0.68–0.78 | 0.9 | 6.4 |
Zn | 272–286 | 287.5 | 2.5 |
Cu | 46.5–48.9 | 41.1 | 2.51 |
Cr | 80–88 | 88.0 | 4.76 |
Ni | 31.1–33.9 | 34.4 | 4.3 |
The sequential extraction procedures were applied in order to identify metal distribution in five sediment fractions: the exchangeable fraction (F1), bound to carbonates (F2), the reducible fraction (F3) (oxides Fe/Mn), oxidizable (F4) (organic matter and sulfides), and the residual fraction (F5) (remaining, nonsilicate bound metals) fractions of heavy metals in sediments [
Heavy metals sequential procedures.
Fractions | Methods |
---|---|
F1: exchangeable fraction | Exchangeable fraction from sediment sample with MgCl2 solutions |
F2: metals bound to carbonates | The metals bound to carbonates were extracted with a NaOAc solution from the residue of the previous fraction |
F3: Fe/Mn oxides fraction (reducible fraction) | The metals bound to this fraction were extracted from the residue of the previous fraction with NH2OH, HCl, and HOAc solutions |
F4: organic matter and/or sulfide fraction (oxidizable fraction) | Metals bound to this fraction were extracted from the residue of stage (2) with HNO3, H2O2, and NH4OAc solutions |
F5: residual fraction | Metals were extracted by digestion of the remaining residue of the previous stages by HF and HClO4 |
Grain size analysis of the surface sediment samples was performed using a series of eight sieves ranging from 1000 mm to 20
In order to evaluate the state of contamination of the surface sediments of the Rades-Hamam Lif coast by heavy metals, various indices can be calculated. Different authors have used these indices [
Pollutants indicators: sediment quality indexes.
Sediment quality index | |
---|---|
Contamination factor: Cf = C heavy metal/C background [ | |
If: | Cf < 1, low factor |
1 ≤ Cf < 3, moderate factor | |
3 ≤ Cf < 6, considerable factor | |
Cf ≥ 6, very high factor | |
Geoaccumulation index: Igeo = log 2 (Cn/1.5 Bn) [ | |
If: | Igeo ≤ 0, uncontaminated |
0 < Igeo ≤ 1, uncontaminated to moderately contaminated | |
1 < Igeo ≤ 2, moderately contaminated | |
2 < Igeo ≤ 3, moderately to strongly contaminated | |
3 < Igeo ≤ 4, strongly contaminated | |
4 < Igeo ≤ 5, strongly to extremely contaminated | |
Igeo > 5, extremely contaminated | |
Pollution load index: PLI = (Cf1 |
|
If: | PLI ≤ 1, no pollution |
PLI > 1, pollution |
In this study, to avoid overestimating or underestimating Igeo values, it was necessary to define the values of a local geochemical background specific to the Rades-Hamam Lif coast for each studied metal. For this, the five lowest concentrations were measured for each ETM for the totality of the results was averred [
The data obtained by the chemical analysis of the Rades-Hamam Lif surface sediments were analyzed using principal component (PCA) techniques (XLSAT 2013) in order to establish the relationship between the different variables and identify the most common sources of pollution.
Grain size distribution and TOC concentration were determined to obtain the general characteristics of the surface sediment samples from the Rades-Hamam Lif coast. The studied surface sediments were characterized by heterogeneous concentration of TOC. That constituted 0.75–3.02% of the dry weight the sediment (Table
Textural parameters and total heavy metals for surface sediments of the Rades-Hamam Lif coast.
Station | Silt (%) | Clay (%) | Sand (%) | TOC (%) | Cd ( |
Cu ( |
Pb ( |
Zn ( |
Cr ( |
Ni ( | |
---|---|---|---|---|---|---|---|---|---|---|---|
Marine samples | 1 | 21.5 | 14.49 | 64.01 | 0.76 | 0.38 | 4.08 | 35.07 | 39.33 | 22.91 | 34.93 |
2 | 27.43 | 10.46 | 62.11 | 0.75 | 0.40 | 3.82 | 16.14 | 39.23 | 23.02 | 18.74 | |
3 | 33.09 | 7.72 | 59.19 | 0.96 | 0.37 | 1.53 | 43.30 | 100.70 | 55.44 | 39.11 | |
4 | 19.33 | 12.22 | 68.45 | 1.02 | 0.58 | 7.11 | 27.10 | 67.73 | 47.97 | 25.86 | |
5 | 32.29 | 20.39 | 47.32 | 1.04 | 0.34 | 7.86 | 28.60 | 58.09 | 50.74 | 26.75 | |
6 | 29.19 | 24.99 | 45.82 | 1.21 | 0.38 | 9.77 | 43.52 | 78.95 | 55.14 | 31.78 | |
7 | 23.08 | 9.77 | 67.15 | 1.23 | 0.36 | 128.82 | 50.40 | 41.74 | 25.34 | 17.85 | |
8 | 27.22 | 10.33 | 62.45 | 1.34 | 0.36 | 3.42 | 24.69 | 48.32 | 27.30 | 19.65 | |
9 | 28.3 | 1.69 | 70.01 | 1.52 | 0.32 | 2.86 | 26.23 | 50.87 | 28.13 | 20.95 | |
10 | 15.45 | 19.32 | 65.23 | 1.76 | 0.47 | 2.40 | 44.99 | 34.42 | 22.35 | 18.34 | |
11 | 27.1 | 9.89 | 63.01 | 1.69 | 0.42 | 3.49 | 54.69 | 70.16 | 34.99 | 25.43 | |
12 | 23.69 | 16.75 | 59.56 | 1.75 | 0.36 | 5.65 | 37.57 | 60.75 | 26.61 | 21.79 | |
13 | 23.89 | 22.88 | 53.23 | 2.02 | 0.35 | 2.51 | 55.14 | 46.86 | 26.98 | 18.70 | |
14 | 32.25 | 18.5 | 49.25 | 1.85 | 0.39 | 3.45 | 32.77 | 43.78 | 25.00 | 23.83 | |
15 | 36.24 | 14.74 | 49.02 | 1.99 | 0.38 | 3.80 | 28.62 | 39.29 | 23.54 | 21.06 | |
16 | 24.15 | 18.6 | 57.25 | 2.14 | 0.33 | 2.40 | 33.70 | 35.92 | 21.05 | 15.98 | |
17 | 19.88 | 20.58 | 59.54 | 2.56 | 0.35 | 2.43 | 29.66 | 57.88 | 22.78 | 22.88 | |
18 | 35.23 | 29.58 | 35.19 | 2.51 | 1.37 | 4.07 | 27.55 | 56.77 | 29.64 | 20.93 | |
19 | 31.04 | 36.77 | 32.19 | 2.78 | 0.25 | 1.87 | 38.39 | 450.68 | 15.55 | 15.66 | |
20 | 29.96 | 36.83 | 33.21 | 2.96 | 0.27 | 2.98 | 37.43 | 34.22 | 18.24 | 13.98 | |
River samples | 21 | 45.92 | 20.88 | 33.22 | 3.02 | 0.65 | 19.55 | 107.02 | 27.34 | 15.55 | 50.88 |
The lowest TOC contents were recorded at the south of the study area. The variation in TOC contents among the sediments was important. In fact, the highest TOC contents were mainly found at the estuaries stations 19,20, and 21 at the mouth of the Meliane river.
The sediment texture was characterized mainly by silt and clay in the area surrounding the Meliane river with a small fraction of sand. This suggests that the finest sediments have been transported by fluvial inputs. South of the study area, toward the city of Hamam Lif, there is reversal of the trend. In fact, the sediments are rather sandy with a small amount of clay and silt. This suggests that these coarsest sediments can originate not only from terrigenous inputs but also from offshore.
Total trace metals composition of surface sediments of the Rades-Hamam Lif coast is shown in Table
Ranges of heavy metals in sediments are 16.14–107.02
All surface sediments collected exceed the upper continental crust (UCC) for Pb and Cd [
Concerning spatial distribution, all of Pb, Cd, Zn, Cr, Ni, and Cu showed a significant decrease in concentrations with increasing distance from the coast. The higher value is recorded in station 20, at the mouth of the Meliane river. This behavior may suggest a seawater role in metal concentration after drifting of beach sediment away.
The values of Zn and Pb in Rades-Hamam Lif coastal sediments were significantly higher than those recorded in coastal sediments of Rosetta coast beach (Egypt), the north of Morocco, Mediterranean Spain coast. On the other hand, the values of the lead recorded opposite the Meliane river are higher than those recorded at the north of this coast in front of the Mejerda River despite the proximity of this river to lead and zinc mines. The total zinc concentration in the sediments of Rades-Hamam Lif is lower than those recorded at the mouth of the Mejerda River [
Comparison between heavy metals in the studied sediments and other worldwide localities.
Locations | Cd | Cu | Zn | Cr | Pb | Ni | Reference |
---|---|---|---|---|---|---|---|
Rades-Hamam Lif Coast | 0.25–1.37 | 1.53–19.55 | 27.34–450.68 | 15.55–55.44 | 16.14–107.2 | 13.98–50.88 | Present study |
Rosetta coast beach | 21–37 | 7.6–42.7 | 53–388 | 0.10–0.29 | 214–476 | 114–894 | El Sorogy et al. [ |
North Morocco | 0.1–0.3 | 2.8–29.11 | 63.7–115.3 | 88.4–161 | 35.4–447.8 | 34.2–79.9 | Omar et al. [ |
Spain | 0.003–0.28 | 4.4–29.2 | 22.3–103.2 | 31.8–394.7 | 7.7–30.4 | 0.1–11.6 | Diaz de Alba et al. [ |
Mouth of Mejerda River (Gulf of Tunis) | — | 62 | 209 | — | 25 | 72 | Zaaboub et al. [ |
UCC: crust average | 0.2 | 32 | 127 | 71 | 16 | 49 | Martin and whitefield [ |
Background shale | 0.3 | 45 | 95 | 90 | 20 | 68 | Turkian and Wedpohl [ |
Background continental crust | 0.2 | 55 | 70 | 100 | 12.5 | 75 | Taylor [ |
In general, the average values of Cd, Zn, and Pb are much higher than background shale [
In this study, the background value was calculated from five of the lowest values measured for each element [
The calculated results for Igeo indicate that the surface sediments could be considered “moderately to strongly contaminated” for Pb, Cr, Cd, and Ni. The geoaccumulation index for Zn showed that all samples were strongly contaminated. The Igeo values for copper indicated that all samples were uncontaminated except the river station (Table
Geoaccumulation index (Igeo), contamination factor (Cf), and pollution load index (PLI) values in surface sediments from the Rades-Hamam Lif coast.
Stations | Cf (Cd) | Cf (Cu) | Cf (Cr) | Cf (Zn) | Cf (Pb) | Cf (Ni) | Igeo (Cd) | Igeo (Cr) | Igeo (Ni) | Igeo (Pb) | Igeo (Cu) | Igeo (Zn) | PLI |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | 1.2 | 1.9 | 1.2 | 1.1 | 1.3 | 2.0 | 0.31 | 2.4 | 2.5 | 2.7 | 0.8 | 2.9 | 1.4 |
2 | 1.2 | 1.7 | 1.2 | 1.1 | 0.6 | 1.1 | 0.3 | 2.4 | 2.3 | 2.4 | 0.8 | 2.9 | 1.1 |
3 | 1.2 | 0.7 | 2.9 | 2.9 | 1.7 | 2.3 | 0.31 | 2.8 | 2.6 | 2.8 | 0.6 | 3.3 | 1.7 |
4 | 1.9 | 3.3 | 2.5 | 1.9 | 1.0 | 1.5 | 0.32 | 2.7 | 2.4 | 2.6 | 1.0 | 3.1 | 1.9 |
5 | 1.0 | 3.6 | 2.7 | 1.6 | 1.1 | 1.5 | 0.31 | 2.7 | 2.4 | 2.6 | 1.1 | 3.1 | 1.7 |
6 | 1.2 | 4.5 | 2.9 | 2.3 | 1.7 | 1.8 | 0.31 | 2.8 | 2.5 | 2.8 | 1.2 | 3.2 | 2.2 |
7 | 1.1 | 60.2 | 1.3 | 1.2 | 2.0 | 1.0 | 0.31 | 2.4 | 2.3 | 2.9 | 2.2 | 2.9 | 2.5 |
8 | 1.1 | 1.5 | 1.4 | 1.4 | 0.9 | 1.1 | 0.31 | 2.5 | 2.3 | 2.6 | 0.8 | 3.0 | 1.2 |
9 | 1.0 | 1.3 | 1.5 | 1.4 | 1.0 | 1.2 | 0.31 | 2.5 | 2.3 | 2.6 | 0.7 | 3.0 | 1.2 |
10 | 1.5 | 1.1 | 1.2 | 1.0 | 1.7 | 1.0 | 0.32 | 2.4 | 2.3 | 2.8 | 0.7 | 2.8 | 1.2 |
11 | 1.3 | 1.6 | 1.8 | 2.0 | 2.1 | 1.4 | 0.31 | 2.6 | 2.4 | 2.9 | 0.8 | 3.2 | 1.7 |
12 | 1.1 | 2.6 | 1.4 | 1.7 | 1.4 | 1.2 | 0.31 | 2.5 | 2.3 | 2.8 | 1.0 | 3.1 | 1.5 |
13 | 1.1 | 1.1 | 1.4 | 1.3 | 2.1 | 1.1 | 0.31 | 2.5 | 2.3 | 2.9 | 0.7 | 3.0 | 1.3 |
14 | 1.2 | 1.6 | 1.3 | 1.2 | 1.3 | 1.4 | 0.31 | 2.4 | 2.4 | 2.7 | 0.8 | 3.0 | 1.3 |
15 | 1.2 | 1.7 | 1.2 | 1.1 | 1.1 | 1.2 | 0.31 | 2.4 | 2.3 | 2.6 | 0.8 | 2.9 | 1.2 |
16 | 1.0 | 1.1 | 1.1 | 1.0 | 1.3 | 0.9 | 0.31 | 2.4 | 2.2 | 2.7 | 0.7 | 2.9 | 1.1 |
17 | 1.1 | 1.1 | 1.2 | 1.6 | 1.1 | 1.3 | 0.31 | 2.4 | 2.4 | 2.6 | 0.7 | 3.1 | 1.2 |
18 | 4.4 | 1.9 | 1.5 | 1.6 | 1.0 | 1.2 | 0.35 | 2.5 | 2.3 | 2.6 | 0.8 | 3.1 | 1.7 |
19 | 0.8 | 0.8 | 0.8 | 13.1 | 1.5 | 0.9 | 0.31 | 2.2 | 2.2 | 2.8 | 0.6 | 4.0 | 1.4 |
20 | 0.8 | 1.3 | 0.9 | 0.9 | 1.4 | 0.8 | 0.31 | 2.3 | 2.2 | 2.7 | 0.7 | 2.8 | 1.0 |
21 | 2.1 | 9.1 | 0.8 | 0.7 | 4.2 | 2.9 | 0.32 | 2.2 | 2.7 | 3.2 | 1.4 | 2.7 | 2.3 |
The Cf of lead varied from 0.64 to 4.26 and from 0.74 to 9.13 for Cu. The Cf values of cadmium are between 0.81 and 4.43. For Cr, the Cf oscillated between 0.81 and 2.97. The calculated values of the contamination factor of Zn varied from 0.79 to 13.16. Finally, the Cf values varied between 0.82 and 2.99 for Ni. According to the classification adopted by Hankanson [
The PLI values oscillated between 1.02 and 2.51. According to Tomlinson classification [
The different pollution indices (Cf, PLI, and Igeo) show that the area around the mouth of the Meliane river is the most polluted zone. However, a downward trend has been observed from the coast to the open sea as a function of littoral drift. This is probably due to the continued discharge of urban wastewater as well as industrial discharges at the Meliane river. These discharges are then transported to the Rades-Hamam Lif coast. On the other hand, the piers of Rades channel limited the extension in the north in favor to the south of the study area.
A principal component analysis (PCA) was also performed to identify the relationships between variables (Table
Pearson coefficient for Ni, Zn, Cr, Cd, Cu, Pb, sand, clay, silt, and TOC for surface sediments of the Rades-Hamam Lif coast.
Variables | Ni ( |
Zn ( |
Cr ( |
Cd ( |
Cu ( |
Pb ( |
Sand (%) | Silt (%) | Clay (%) | TOC (%) |
---|---|---|---|---|---|---|---|---|---|---|
Ni ( |
1 | −0.09 | 0.29 | 0.67 | −0.1 | 0.15 | −0.03 | 0.3 | −0.19 | −0.38 |
Zn ( |
1 | 0.46 | 0.1 | 0.63 | 0.41 | −0.24 | 0.11 | 0.24 | 0.04 | |
Cr |
1 | 0.63 | 0.65 | 0.72 | −0.04 | 0.14 | −0.05 | −0.31 | ||
Cd ( |
1 | 0.14 | 0.62 | −0.32 | 0.51 | 0.05 | 0.03 | |||
Cu ( |
1 | 0.48 | 0.03 | −0.05 | −0.01 | −0.11 | ||||
Pb ( |
1 | −0.44 | 0.3 | 0.38 | 0.24 | |||||
Sand (%) | 1 | −0.7 | −0.84 | −0.7 | ||||||
Silt (%) | 1 | 0.2 | 0.36 | |||||||
Clay (%) | 1 | 0.68 | ||||||||
TOC (%) | 1 |
Determining the total concentration of metals is probably the most fundamental way to assess sediment quality; but for further understanding of potential mobility, bioavailability and toxicity of metals in sediments, metal fractionation, acid volatile sulfur (AVS), and simultaneously extracted metal (SEM) can investigate the bioavailability and the toxicity of metals [
However, sequential extraction remains the most common method. Therefore, the sequential extraction procedure was performed to obtain information about the strength and ways of metal associating with sediments [
The concentration of trace elements is usually controlled by a variety of physical and chemical factors [
In this study, the distribution of different fractions of heavy metals in sediments of the Rades-Hamam Lif coast is shown in Figure
Chemical speciation of Pb, Zn, Cu, Cd, Cr, and Ni (in %).
The metals in F1 fraction are considered to be the weakest bound metals in sediments and can be defined as “the exchangeable fraction” which can migrate to the aqueous phases and therefore become the most movable fraction. The heavy metals bound to this fraction are sensitive to any environmental changes [
For Cr, though its mean proportion in the acid-soluble fraction was 16.44%, it presented a clear spatial variation from the north to the south of the study area, with a range of 9.6% and 21.56%. On average, the percentage of Zn in the acid-soluble fraction from different sampling sites was fairly constant, with ranges varying from 1.36 to 6.95% and 12.84% for the station 21 located in the mouth of the Meliane river (Figure
This sequence should reflect the relative concentrations of the metallic elements in the water since the trace metals linked to the exchangeable fraction are electrostatically adsorbed and, therefore, they are weakly bound and can therefore be released by cation exchange at near neutral pH [
The metal bound to carbonates varies significantly from one element to another. Indeed, the Cu content in the F2 fraction varies from 0.02 to 3.82% with an average of 1.08%. The highest values characterize the sediments collected at the mouth of the Meliane river. Overall, the average proportions of Pb, Zn, and Cr are relatively low, and they are of the order of 8.02%, 4.82%, and 6.28%, respectively. Ni values related to the carbonate fraction vary from 3.14% to 34.72% with an average of 11.97%. The highest value characterizes the station sampled at the mouth of the Meliane river. Cadmium (Cd) bounds to carbonate fraction with the highest proportions ranging from 12.6 to 56.31% with an average of 45.85%. The lowest proportion (12.6%) bound to carbonates corresponds to the highest percentage of cadmium in the exchangeable fraction (86.46%). The most labile fraction (exchangeable fraction and carbonate-related fraction) is greater than 95.29% for Cd, which confirms the bioavailability and mobility of this element. The order of abundance of trace metals bounded to carbonates fraction is as follows: Cd >>> Ni > Pb > Cr > Zn >> Cu.
The F3 fraction is the part of the heavy metals represented by Fe/Mn oxide or hydroxide precipitation. Metals bound to Fe/Mn oxides would be released under reductive conditions and, therefore, are unstable under anaerobic condition [
The percentages of cadmium and copper in the reducible fraction are the lowest and the average values being, respectively, 0.91% and 4.41%, suggesting the order of abundance of heavy metals in the oxide and hydroxide fraction of Fe and Mn as follows: Ni >> Cr > Pb > Zn >>> Cu >> Cd.
In the oxidizable fraction (F4), heavy metals tend either to associate with reactive groups of organic matter or to generate water-insoluble materials with sulfur ions, that is why it is difficult to release under normal and moderate reduction or weak oxidizing environment [
The results showed that the most chrome and copper in all the sediments were strongly retained in the residual fraction (F5). Their average percentage in this fraction was 64.42% and 43.09%, respectively. A high proportion of this fraction was also observed for Ni and Zn in some sites. These facts suggested that these metals are strongly associated with the aluminosilicates lattice of minerals [
The heavy metals bound to the exchangeable and carbonate fraction are the most moveable fraction, followed by reducible and oxidizable fractions, which are easier to be released into the water column and are considered to have high bioavailability and toxicity. The sum of these four fractions is called the extractable fraction [
In order to be able to explain the risk posed by sediment to organisms, it is essential to know the bioavailable fraction of contaminants [
According to Cai et al. [
Biological assessment index values
Range | Average | |
---|---|---|
Pb | 0.59–10.57 | 4.72 |
Cu | 0.006–12.06 | 1.13 |
Cd | 27.72–513.72 | 113.14 |
Cr | 0.44–3.11 | 1.55 |
Zn | 0.63–7.92 | 2.43 |
Ni | 0.96–7.65 | 3.02 |
Different useful tools, indices, and approaches such as chemometric indices, sequential extraction, and multivariate statistical analysis have been carried out for the evaluation of sediments contamination of the Rades-Hamam Lif coast.
The total concentrations of Cd, Cr, Cu, Zn, Pb, and Ni showed significant spatial variation. The highest concentrations of heavy metals were recorded at the mouth of the Meliane river, and they tend to decrease with increasing distance from the coast. The total concentration of trace metals was influenced by runoff, industrial wastewater, and wastewater discharged into the Meliane river. Cd, Pb, Cr, and Ni were mainly bound to an exchangeable fraction with a very high percentage for Cd indicating its high mobility and toxicity. Ni was bound to Fe/Mn oxide, suggesting that this element is difficult to release in the environment. Zn is bound to oxidizable fraction. The Cr and Cu in all sediment samples were strongly retained in the residual fraction. The north-south shoreline drift appears to extend the influence and to increase the transfer of hazardous pollutants toward the southern and offshore areas, to be accumulated by marine species and integrated into food chains and to end in humans. This study suggests that the surface sediments of the Rades-Hamam Lif coast are polluted by high concentrations of several pollutants due essentially to several industrial and urban discharges in the Meliane river which is mainly close to the coast. The state of contamination of the sediments of the Rades-Hamam Lif coast requires the concern of competent authorities.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors wish to confirm that there are no known conflicts of interest associated with this publication.