Introduction

There are several sources of heavy metals that can enter the environment: firstly, weathering processes of rocks that are rich in different metals in their chemical composition. Secondly, anthropogenic activities such as sewage, shipping, industrial activities, mining, tourist services, painting, renewable boats, and others (Chen et al. 2007; Nour et al. 2018). Marine sediments are a reservoir and a repository of these metals where they are transported directly from the source of pollution or by precipitate from seawater (Selvaraj et al. 2004; Wang 2018).

Sharm El-Sheikh city is one of the most famous tourist cities in Egypt on the Gulf of Aqaba. It is located about 385 km from Suez city (Fig. 1). It is warm in winter and has a hot weather in summer. This city is characterized by a very large number of resorts, hotels, and diving clubs. In view of the significant increase in the rate of development of Sharm El-Sheikh and the continuous increase in hotel and resort construction operations, as well as the increase in the rates of tourism activities, especially diving and boats. This study aims to determine the distribution of toxic heavy metal concentrations in the beach sediments of the most important sites in the city. Moreover, it aims to assess the potential environmental pollution risk and to identify the potential sources of these pollutants.

Fig. 1
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Location map and sampling sites

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To evaluate the status of the environmental risk of the studied area, the metal concentrations were compared with those in other world regions as the Red Sea coast, Mediterranean Sea coast, and the Caspian Sea coast. Moreover, another comparison was made with the background levels, according to the international environmental organizations such as sediment quality guidelines (SQG) (Long et al. 1995), interim sediment quality guideline (ISQG), probable effect level (PEL) (ISQG 1995), background shale (Turekian and Wedepoh 1961), and background continental crust (Taylor 1964).

Material and methods

Study area and sampling

A total of 24 recent beach sediments were collected from Sharm El-Sheikh area at the southern coast of the Sinai Peninsula on the Gulf of Aqaba (Fig. 1). Two sites were selected to the study: the first one is Sharm El-Sheikh harbor, which is located at the entrance of the city as a small bay. It is located between latitudes (27° 50′ 46″ & 27° 51′ 24″ N) and longitudes (34° 16′ 32″ & 34° 16′ 45″ E). This bay is bounded on the northwest side of Gabal El-Safra (Fig. 2a) which consists of basement rocks and Miocene sedimentary rocks (Steckler et al. 1988; Sellwood and Netherwood 1984). Gabal El-Safra contains high concentrations of Fe, Mn, and Ni (Abu El-Enain and El-Sorogy 1994). In addition, some basement rocks also existed in the hinterlands which are scattered in many parts around the studied area. This bay is semi-circular in shape and occupies an approximate area of 1.4 km2 with a narrow entrance to the sea in the southward by about 1000 m in width. This site is a tourist harbor of the city and it is always crowded with boats and yachts. The second site is Sharm El-Maya bay which is located to the east of the first site and located between latitudes (27° 51′ 21.13″ N & 27° 51′ 45.19″ N) and longitudes (34° 17′ 20.57″ E & 34° 17′ 54.42″ E). This bay is smaller than the first one by about 0.387 km2. It is a semi-circular shaped bay and located away of Gabal El-Safra (Fig. 1). It seems closer than the other site by about 310 m to the entrance of the Gulf of Aqaba. It is surrounded by two headlands, Ras Umm-Sid in the northeast and the other in the southwest (Fig. 2b), which separates Sharm El-Maya bay from the neighboring Sharm El-Sheikh harbor bay (Morsy et al. 2010).

Fig. 2
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Close view of the study area

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Sampling sites were determined by GPS (Table 1). Samples were collected randomly using stainless-steel box sampler during winter 2019. They were transported to the laboratory into cloth bags in iceboxes. They were washed with distilled water and then left to dry in the room temperature. About 5 g of each sample was pulverized in an agate mortar for 15 min and sieved to 63 μm then dried in an oven at 80c. Two grams of this powder was digested in Teflon cups for 2 h in a mixture of (1 HF, 2 HClO4, & 3 HNO3). This solution was diluted with distilled water and was prepared for calculation. The atomic absorption spectrophotometer (AAS) was used to measure the heavy metal concentrations in the studied samples. The results were measured in micrometer. All standard precautions were taken when conducting the analyses and the accuracy of the analysis was verified by replicating the measurement of some samples.

Table 1 Heavy metal concentrations and metal pollution index values in studied sediments
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Environmental statistical analysis

Some environmental factors and statistical analysis were used to evaluate the assessment of the extent of the environmental pollution of the study area and identify the expected sources responsible for the presence of pollutants in the environment such as metal pollution index (MPI), the contamination factor (CF), sediments pollution index (SPI), the geo-accumulation index (Igeo), ecological risk factor (ERI), the potential contamination index (Cp), and the enrichment factor (EF) according to their pollution indicators classification in Table 2. In addition to correlation coefficients, hierarchal cluster analysis (HCA) and principal component analysis (PCA) were calculated by using SPSS program.

Table 2 Classification of some environmental factors was used in the present work
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Results and discussions

Special heavy metal distributions and worldwide comparison

The complete data analysis of the heavy metal concentrations was obtained in Table 1. Metal concentrations showed an irregular distribution pattern in the two studied sites. Sharm El-Sheikh harbor site contains different concentrations of metals ranged from the minimum to the maximum values as follows: Fe (1358–5467 μm); Mn (308–743 μm); Cu (17.25–39.21 μm); Zn (27.74–51.08 μm); Pb (22.14–42.15 μm); Ni (27.68–75.61 μm); Cd (1.78–3.12 μm); and Co (1.21–3.21 μm). On the other hand, Sharm El-Maya bay contains various heavy metal concentrations ranging from the minimum to the maximum values as follows: Fe (1223–3274 μm); Mn (158–564 μm); Cu (22.35–36.24 μm); Zn (29.24–48.24 μm); Pb (21.25–38.24 μm); Ni (20.68–64.25 μm); Cd (1.34–3.25 μm); and Co (0.89–3.11 μm).

The beach sediments of Sharm El-Sheikh harbor (Fig. 3) have a higher content of most of the studied heavy metals (Fe, Mn, Ni, and Cd) in comparison with Sharm El-Maya bay. These results are due to the fact that the Sharm El-Sheikh harbor is exposed to human pollutants represented by navigation movement of boats, plastics and wood rubbish, and fuel combustion products on the adjacent road which is very close to the shore (Fig. 4). In addition, metals transported by natural weathering of nearby mountain rocks (Gabal El-Safra) could be classified as potential sources as well. On the other hand, Sharm El-Maya bay is also affected mainly by human pollutants and decreased natural weathering effects as it is further away from Gabal El-Safra. At the same time, the presence of some basement rocks in certain places cannot be neglected. However, the differences in heavy metal concentrations in both bays are not very large and this may be attributed to the nature of each bay. Sharm El-Sheikh harbor is larger and connected to the sea by a wide entrance that may reach up to 1000 m in width, making water renewal much faster than Sharm El-Maya bay, where the later bay has an entrance of just 310 m, making the water movement more sluggish.

Fig. 3
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The comparison of heavy metal contents in sediments of both studied bays

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Fig. 4
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Some human pollutants in Sharm El-sheikh harbor: a plastics and wood rubbish; b the navigation movement of boats; c fuel combustion products on the adjacent road

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Figure 5 explains the comparison of the average concentrations of heavy metal distributions in the sediments of the two studied sites and other worldwide localities. These results explained that the study area contains metal concentrations higher than those in other worldwide coasts, such as Fe, Mn, Cu, Zn, Ni, Cd, and Co of Hurghada (Nour et al. 2018); Mn, Cu, Pb, Ni, and Cd of Shalateen (Nour et al. 2019); Fe, Mn, Cu, Ni, and Cd of the Red Sea of Saudi Arabia (Youssef and El-Sorogy 2016); Cu, Zn, Pb, Ni, and Co of the Egyptian Mediterranean coast (Okbah et al. 2014); Fe, Mn, Cu, Zn, Pb, Ni, and Cd of the Libyan Mediterranean coast (Nour and El-Sorogy 2017); and Mn, Cu, Zn, Pb, Ni, and Cd of the Russian Caspian Sea (de Mora et al. 2004).

Fig. 5
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The comparison of the average heavy metal concentrations in the sediments of the studied area and other worldwide localities

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Assessment of sediment contamination

The results of the environmental indicators (Table 3) have been used to assess the heavy metal contaminations in the studied area. MPI values have been used to assess the degree of pollution and have been calculated according to Masoud et al. (2007) as MPI = (C1 × C2 × C3 × Cn)1/n, where C is the concentration of metal in the sample and n is the number of metals. Metal pollution index (Table 1) showed that Sharm El-Sheikh harbor has a higher degree of pollution (43.4) than Sharm El-Maya bay (38.2). Samples H12, H10, and H7 have the highest MPI value (53.6, 50.1, and 49.97) respectively. This may be attributed to anthropogenic activities as heavy tourist activities, rubbish, navigation of boats’ movements, and the nearby mountain hinterland. In addition, the natural weathering of Gabal El-Safra which contains high concentrations of Fe, Mn, and Ni (Abu El-Enain and El-Sorogy 1994). Lastly, the presence of many basement rocks scattered in the surrounding highlands can be described as a possible cause of such findings.

Table 3 The results of the environmental indicators in the studied area
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CF values were used to estimate the amplitude of metal contamination in sediments and calculated as CF = Cm/Cb (Hakanson 1980), where Cm is the concentration of metals in the sample and Cb is the concentration of metals in the earth’s crust. The results of CF (Table 3) illustrated that both of the studied sites are very high contamination with Cd (CF > 6) and moderately contaminated with Pb (CF = 1–3).

SPI values were used to identify single metal contamination indices and calculated as SPI = Cm/Cp (Kabata-Pendias and Pendias 2001), where Cm is the concentration of metals in the sample and Cp is the concentration of metals according to the permissible metal levels in sediments according to USEPA (1983). SPI results (Table 3) revealed that the both studied sites are highly contaminated with Cd, whereas Sharm El-Sheikh harbor was moderately contaminated with Cu, Pb, and Ni, and Sharm El-Maya bay was moderately contaminated with Pb and Ni.

Igeo values were used to determine the heavy metal pollution intensity in sediment and calculated as Igeo = log2 (Cm/1.5 × Mb) according to Muller (1981), where Cm is the metal concentration in the sample and Mb is the metal concentration of shale (Turekian and Wedepoh 1961). Igeo values (Table 3) showed that the both studied sites were moderate to strongly contaminated with Cd.

The ecological risk factor was used to assess the contamination of metals in sediments (Hakanson 1980) and calculated as Eir = Tir × Cif, where Tir is a toxic response factor for metals according to Hakanson (1980) and Cif is the contamination factor of the metal. Therefore, the potential ecological risk index (PERI) can be calculated as the sum of Eir. These results demonstrated that the studied area is a highly contaminated risk with Cd where PERI value recorded (290 and 246) in Sharm El-Sheikh harbor and Sharm El-Maya bay respectively.

The potential contamination index (Cp) was calculated by the following method: Cp = Cmax/Cb (Hakanson 1980), where Cmax is the maximum concentration of metal in the sample and Cb is the concentration of metal in the earth’s crust (Turekian and Wedepoh 1961). Cp values clarified that Sharm El-Sheikh harbor and Sharm El-Maya bay were very severely contaminated with Cd and moderately contaminated with (Pb and Ni) in Sharm El-Sheikh harbor and (Pb) in Sharm El-Maya bay.

To evaluate the toxicity guidelines of heavy metals in the recent beach sediment of the studied area, the studied metal concentrations were compared with international background values as well as with those in some regions around the world (Table 4 and Fig. 5). These results revealed that Cd content in the studied area is higher than its average concentration in the shale background (8.3 times), earth’s crust (12.5 times), SQG (2.1 times), and ISQG (3.6 times). In spite of these results, Cd content in the study area is still under the probable effect level (PEL). Simultaneously, Pb and Ni metal contents in the study area showed higher concentrations than shale background, earth’s crust, and ISQG, and SQG, ISQG, and PEL respectively.

Table 4 The comparison of the average metal concentrations in the studied area with international background values
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Estimate the pollution sources

The enrichment factor was used to determine the potential source of pollutants, whether it is natural or anthropogenic. EF can be calculated as (Cm/CFe)/(Cmb/CbFe) according to Sinex and Helz (1981), where Cm is the concentration of metal in sample, CFe is the concentration of Fe in sample, Cmb is the concentration of metal in shale, and CbFe is the concentration of Fe in shale (Turekian and Wedepoh 1961). EF values (Table 3) revealed that Sharm El-Sheikh harbor is extremely enriched with Cd; very severely enriched with Pb; severely enriched with Mn, Cu, and Ni; and moderately severely enriched with Zn. On the other hand, Sharm El-Maya bay is extremely enriched with Cd and Pb, and severely enriched with Mn, Cu, Zn, and Ni. These results indicated that all studied metals were derived from anthropogenic sources where EF value > 1.5 according to Zhang and Liu (2002). The boat navigation, tourist activities, repainting boats, plastic wastes, and combustion of gasoline in motor vehicles are the possible sources of pollutants. In addition, wastewater may be one of the most important sources of certain metals such as Cd, Pb, and Co (Nour 2019).

The results of the correlation coefficient for the studied heavy metals (Table 5) illustrated that a strong positive correlation between Cd and each of Fe, Pb, and Mn (r = 0.64**, r = 0.59**, and r = 0.55** respectively) could be found. In addition, there is a good correlation between Cu and Zn (r = 0.51**) and Fe with Ni and Mn (r = 0.5** and 0.45*). The presence of this positive correlation between metals indicates that they may come from similar sources.

Table 5 Heavy metal correlation coefficients in the studied area
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The results of dendrogram of hierarchal cluster analysis (HCA) and the principal component analysis (PCA) of heavy metals in the study area (Fig. 6 and Table 6) supported the results of the correlation matrix. The studied heavy metals divided into two clusters: cluster 1 consists of four sub-clusters (Fe-Cd, Mn, Pb, and Ni). While cluster 2 included two sub-clusters (Cu-Zn and Co). To emphasize that, PCA has arranged metals in three components with 72.973% of cumulative percentage: PC1 explains 43.616 % of the variance and clarified positive loading for Cd (0.821), Fe (0.723), Pb (0.695), Cu (0.662), Zn (0.654), Mn (0.614), Co (0.54), and Ni (0.524). PC2 demonstrated 15.8 % of the variance and showed positive loading for Co and Cu (0.591 and 0.45) respectively. Moreover, it shows negative loading for Mn, Fe, Cd, Ni, and Pb. PC3 revealed that 13.557 % of the variance and showed positive loading for Ni (0.697) and negative loading for Pb, Mn, Cu, and Cd. This result reveals that Cd, Fe, Pb, Cu, Zn, Mn, Co, and Ni may be derived from anthropogenic sources as boat navigation, repainting of boats, and the supply of fuel and tourist activities. Furthermore, the presence of Co, Ni, and Fe in PC2 and PC3 points to natural weathering especially from Gabal El-Safra and basement fragments.

Fig. 6
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The results of dendrogram of hierarchal cluster analysis in studied sediments

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Table 6 Three principal component loadings for metals in the study area
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Conclusions

The present study states that the sediments in the vicinity of the beach of Sharm El-Sheikh harbor contain concentrations of metals (Fe, Mn, Ni, and Cd) slightly higher than those in Sharm El-Maya bay. The environmental pollution indicators report that Sharm El-Sheikh harbor has a higher degree of pollution (MPI = 43.4) than Sharm El-Maya bay (MPI = 38.2). Both studied sites are very highly contaminated with Cd according to CF, Cp, EF, and SPI. The results of the ecological risk factor clarified that the studied area have a high risk of being contaminated with Cd where PERI value recorded (290 and 246) in Sharm El-Sheikh harbor and Sharm El-Maya bay respectively. In addition, they are moderately to highly contaminated with Pb, Mn, Cu, and Zn.

The studied area suffers from obvious human impacts due to heavy tourist activity, heavy boat navigation, large numbers of anchored tourist boats, the activity of vacationers, diving operations, and the car fuel combustion products on the main road which is very close to the beach. In addition, all these sources of natural pollution due to the weathering of the rocks of Gabal El-Safra and basement rocks play a role. However, the distribution of heavy metal concentrations in the both studied bays does not show significant differences between them, although Sharm El-Sheikh harbor is exposed to an increase in pollutants due to the natural weathering of the rocks of Gabal El-Safra that is rich in Fe, Mn, and Ni, which surrounds the bay by the West. This is mostly due to the nature and location of each of them, where Sharm El-Sheik harbor is characterized by a larger space and openness to the sea with a wide entrance up to 1000 m, while Sharm El-Maya bay has a smaller area and narrowing entrance to the sea by only 310 in width. The area of a given body of water and the breadth of the connection to the sea are important factors in speeding up water renewal process, wave movements, and the rates of sedimentation or erosion of the beach.

The present study shows that the studied area is enriched in Mn, Cu, Ni, and Cd of its counterparts in the Hurghada coast, the Shalateen coast, Red Sea of Saudi Arabia, and the Russian Caspian Sea. In addition, Cd, Pb, and Ni contents in the studied area are higher than its average in the shale background, earth’s crust, SQG, and ISQG.