Introduction

All living organisms need a specific amount of trace metals in order to perform their vital functions. However, any increase in these proportions more than the permissible limits will lead to high risk to their health (Chapman 2007; Qing et al. 2015). Sediments can accumulate and store trace metals for a long time, which can cause negative effects on ecosystems and human health (Kaushik et al. 2009; Shang et al. 2012). Recently, the environmental researchers have done collective efforts to save our planet from the risk of contamination. They became interested in environmental monitoring studies of the marine environment, which are based on the detailed study of a specific area, either by evaluating the quality of coastal sediments (Chen et al. 2007; Özseker and Erüz 2011; Wang et al. 2018, Nour 2019a), seashells (Ziko et al. 2001; Ali et al. 2011; El-Sorogy et al. 2012,2013; Abdo et al. 2017), and/or water (Brewer et al. 1969; Wu et al. 2015; Nour 2015; El-Sorogy and Attiah 2015).

However, the present work is a general insight which aims to establish a comprehensive environmental assessment of the potentially toxic metals and their sources in several sites within the four major cities along the Egyptian Red Sea coast through the use of several important environmental indicators. Moreover, the current pollution status of the studied area will be compared along with other worldwide coasts and also compare them to the geochemical background of metal content. The periodic monitoring of the concentration of trace elements in the sediments of the Egyptian beaches is very important because it indicates the environmental status of these beaches, and these results may indicate the necessity of conducting more detailed studies for some sites that may be suffering from the presence of more pollutants. In addition, this data is a basic for continuous monitoring of environment because of its crucial importance to the health of the marine ecosystem and also to human health.

Several environmental monitoring studies have demonstrated the importance of the environmental indicators in assessing the impacts and the sources of pollutants, and it confirmed that these indicators are the ideal way to monitor environmental pollution (Yu et al. 2011; Dung et al. 2013; Nour 2019b). These environmental indicators depend on the geochemical background in their assessment of the degree of pollution, which may be the average concentration of the elements in shale in the Earth’s crust (Turekian and Wedepoh 1961) as in the case of measuring the geo-accumulation index, the enrichment factor, contamination factor, and potential contamination index, whereas in the case of soil pollution index, the permissible levels of metals in sediments (USEPA 1983) were used as geochemical background.

The Egyptian Red Sea coast extends for almost 1250 km from Suez to the Sudanese border. Marine environment is very important to humans because it provides them food resources and ecosystem services. However, human activities usually result in negative impacts on the marine ecosystem. Therefore, the periodic monitoring processes have become very important to predict and provide solutions. The sources of pollution along the Red Sea coast vary from natural to anthropogenic sources. Industrial activities, petroleum industries, urban development, tourism activities, fishing, shipping, resorts, and harbor activities are the common pollution sources. In addition, the erosion of rocks for the hinterland mountains, especially during the periods of flooding is considered a remarkable cause of such a problem. The distribution of the potentially toxic metals in sediments of the Red Sea coast can provide us with valuable information about the environmental condition of the ecosystem (Mansour et al. 2011; Attia and Ghrefat 2013; Nour et al. 2018). Certainly, surface sediments in each site contain different proportions of trace metals, which can indicate the degree of pollution and its sources, and also the related effects on the ecosystem (Zhang et al. 2014). Therefore, the study of the distribution of potentially toxic metal concentrations and their related ecological risk in the sediments is pivotal to recognize the degree of trace metal pollution in the environment which is directly related to human activities (Song et al. 2014; Nour et al. 2019).

Materials and methods

Study area

The present study is concerned with four major cities on the Egyptian Red Sea coast, including 22 sampling sites with a total length of 290 km, extending from Hurghada youth hostel to 30 km south Marsa Alam. These sites were specifically selected to cover the most important localities along the western coast of Red Sea (Figs. 1 and 2). Moreover, this area has shown extensive development in the recent decades on the eastern coast of Egypt. Sampling locations were identified with the global positioning system (GPS).

Fig. 1
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The location and sampling map of the studied sites

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Fig. 2
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Different sources of pollutants along the Red Sea coast. a Tourist activity (Hurghada area), b industrial sewage (Safaga area), c urban activities (Quseir area), and d rock fragments (Marasa Alam)

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(1) The Hurghada area was a small fishing city. Nowadays, it can be considered the largest Egyptian resort city in the Red Sea. It includes five sampling sites: youth hostel site which has a rocky and sandy beach surrounded by Pleistocene raised reefs; the Marine Museum, which has a sandy beach rich in a different collection of marine shells; the Public beach site that has about 20 m of raised reef and intensive landfill in addition to the common marine fauna; Magawish village site which has a sandy beach with some plastic rubbish; and Makadi bay site having a fine sandy beach. This bay was partially separated from the open sea by a sand bar in addition to few landfills of tourist buildings. (2) Safaga city is located 60 km south Hurghada. It is a tourist and industrial area on the Red Sea coast where it has several tourist resorts, marine port, and phosphate port. The Safaga area includes six sampling sites: Suma bay site has three units of raised reefs on the beach with highly calcareous sand formed from reef debris; North Safaga bay site has a sandy beach poor in marine skeletons; South Safaga bay site has a shoreline delineated by ill-sorted gravels, angular basement fragments, and overlaid by a landfill of older raised reefs in the west; Umm El Huweitat site has a sandy beach rich in Sorites tests; Wadi Jasus site has some raised reefs on the beach with sands. Lastly, Kalawy bay site has a reefal beach, characterized by high diversity of recent gastropod shells. (3) Quseir City located 135 km south of Hurghada. It is a tourist city, where scuba diving and snorkeling are popular. This area includes five sampling sites: 25 km north Quseir site has sandy beach; El-Hamrawein port site has raised reefal beach and this site is a phosphate ore shipping port; Quseir City site has sandy beach; 9 km south Quseir site has a muddy reefal beach and large numbers of live Chama sp., which can distinguish this shore especially during the low tide. In the end, 24 km south Quseir site has raised reef beach with many tidal channels. (4) Marsa Alam city is located 265 km south Hurghada. It is a tourist area and includes six sampling sites: 30 km north Marsa Alam site has flattened recent raised reefs covered by thin sands and characterized by enormous amounts of living Modiulus sp. which arranged around older heads of coral reefs; 19 km north Marsa Alam site has open sea beach with consolidated rocky shore overlaying the young raised reefs; Marsa Alam city site has a sandy beach with some variety of rock fragments; 8 km south Marsa Alam site has a sandy beach; 20 km south Marsa Alam site has a sandy beach; and 32 km south Marsa Alam site has a rocky coralline flattened beach.

Geology of the study area

There are several geological studies on the Egyptian Red Sea coast (El-Akkad and Dardir 1966; Said 1990; Khalil and McClay 2009). The sedimentary rocks of the Hurghada area consist of Quaternary deposits found as recent gravels and Pleistocene coral reefs (Hume 1916), while the rocks on the coastal plain of the Safaga area range in age from Miocene to Quaternary (El-Asmar and Abel-Fattah 2000). The Quseir area contains sedimentary beds of Miocene evaporite series, Pliocene Clypeaster-Laganum series, and oyster and Pleistocene terraces raised beaches (Said 1990). El Bassyony (1982) studied the exposed sedimentary rocks in the area between Quseir and Mersa Alam and subdivided the sequence into recent coral reefs, gravel terraces and Wadi alluvial deposits, Pleistocene Um Gheig and Wizr formations, Pliocene Shagra and Gabir formations, and Middle Miocene Samh, Abu Dabbab, and Gebel El-Rusas formations.

The main sources of sediments to the Egyptian Red Sea coast are the terrigenous rock fragments transported from the hinterland mountains during the occasional runoffs through the numerous wadis and from skeletal carbonates from the sea (El Mamoney and Rifaat 2001). The type and composition of rocks nearby the sea coast, wave movement and coastal currents, and the conditions of sedimentation environment have been controlling the distribution of sediments in the coastal area (EL-Wekeil et al. 2012). The beach sediments in the studied area are poorly sorted and consist of marine shells, coarse sand, rock fragments, sea grass, and mud. These sediments are mineralogically composed of a mixture of carbonates and siliciclastic grains (Mansour et al. 2000). The coastal plain in the studied area varies from place to place in width, sediments, and topography. Coastal plain in the Hurghada area averages about 30 km, then it narrows till reaching less than 5 km in the area from Safaga to the south of Marsa Alam.

According to the type of shore materials, the shoreline in the studied area could be classified into the following types: (i) Reefal beaches, which are composed of hard, massive algal coralline limestone of the youngest Pleistocene coral reef as in Soma bay, 24 km south Quseir, 30 km northern Mersa Alam, 19 km north Mersa Alam, and 32 km south Mersa Alam. (ii) Gravelly beaches have been formed of non-consolidated pebbles to cobbles of different origin (basement and sedimentary rocks). These clasts are transported to the shore from the hinterland mountains as in Safaga area. It is noted that the gravelly beaches of basement origin decrease southwards. (iii) Sandy beaches are mostly present along the entrances of large wadis and formed friable sandy and locally gravelly sediments as well as shell fragments. They are drifted by storms and high tide above these beaches as 25 km north Quseir, Quseir City, and 19 km north Mersa Alam. (iv) Man-made beaches are local landfill beaches formed of moderate to huge concrete masses, rock fragments, mining products, and sands. They are present around the main cities as a wave break to protect buildings from high storms. Also, they are used to make artificial lagoons and pools in tourist villages and resorts and as platforms in harbors. There are also some man-made modifications in many parts of the studied shore, e.g., construction remnants and waste accumulation of different origins, shapes, and sizes (plastic, wood, metals, concrete, tar balls, and sheets). These wastes change locally the nature of the shoreline, as the presence of local hard substrates in a sandy shoreline affects the structure of the natural community. Man-made beaches are represented along the coast by the following localities: Magawish village, Makadi bay and El-Hamrawein.

Analytical procedures

Samples of 44 surface beach sediments were collected by using a plastic box (0–10 cm) depth from the beach of four major cities (10 samples from Hurghada area, 12 samples from Safaga area, 10 samples from Quseir area, and 12 samples from Marsa Alam area) along the Egyptian Red Sea coast from lat. 27° 17′ 09″ N, long. 33° 46′ 07″ E to lat. 24° 4′ 16″ N, long. 35° 04′ 02″ E, whereas two surface sediment samples were collected from each site. Each time the plastic box was washed with distilled water before taking the sample to prevent mixing of the samples. Each sediment sample was placed in a separate plastic bag and the site data were written on it. In the laboratory, sediment samples were washed with distilled water and dried at room temperature. About 5 g of each sample was grounded in an agate mortar. According to Oregioni and Astone (1984), an acidic mixture of 15 ml nitric acid, 10 ml perchloric acid, and 5 ml hydrofluoric acid was used to digest about 0.2 g of each powder sample. This solution was diluted to double with distilled water and then filtered. The mentioned solution was then ready to measure trace metal concentrations (Fe, Mn, Cu, Zn, Pb, Ni, Cd, and Co) by using the atomic absorption spectrophotometer (AAS, GBC 932A Ver. 1.1). To verify the accuracy of these chemical measurements, duplicated samples were measured and revealed the same measured values, which reflects the high accuracy of the equipment and reagent blanks. In addition, the detection limits of measured metals were as follows: Fe 0.05 μg/g, Mn 0.02 μg/g, Cu 0.033 μg/g, Zn 0.01 μg/g, Pb 0.07 μg/g, Ni 0.05 μg/g, Cd 0.013 μg/g, and Co 0.06 μg/g.

Statistical analysis

In order to assess the trace metal content in sediments, two methods were used. The first method was to compare the average measured metal content of each studied area with the sediment quality guidelines (SQGs) such as the effect range low (ERL) (Long et al. 1995) and lowest effect level (LEL) (Persaud et al. 1993). The second method was measuring the values of the environmental parameters such as the enrichment factor (EF), which is used according to Sinex and Helz (1981) to assess the anthropogenic impacts on sediments. To estimate the intensity of trace metals pollution in sediments, the geo-accumulation index (Igeo) is measured according to Muller (1979) based on matching present situation with the background levels. To assess the extent of trace metals in sediment samples, the contamination factor (CF) is calculated according to Hakanson (1980) and the potential contamination index (Cp) is calculated according to Hakanson (1980). To assess the degree of trace metal pollution in surface sediments, the potential ecological risk index (PERI) is measured according to Hakanson (1980). To identify single-element contamination indices in the sediment sample, soil pollution index (SPI) is calculated according to Kabata-Pendias and Pendias (2001). All equations for calculating these environmental parameters and their categories are presented in Table 1.

Table 1 The equations of the environmental pollution indicators and their risk categories
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Moreover, to illustrate the linkage between trace metals in the surface sediments, hierarchal cluster analysis (HCA) and Pearson’s correlation coefficients were measured with the SPSS program. Regarding the estimation of the possible sources of trace metals in the studied area, a principal component analysis (PCA) was calculated.

Results and discussions

Trace metal distribution in studied sites

Sediments of the Red Sea coast are composed of varying components such as gravels, sands, and muddy sand, as well as marine skeletons of different fauna (molluscs, echinoderms, scleractinian corals, foraminifers, and ostracods). The obtained data of the mean concentrations of eight trace metals in 22 famous sites along the Egyptian Red Sea coast are shown in Table 2. The comparative data regarding the mean trace metal concentrations in sediments of the Egyptian Red Sea coast with other worldwide ones, geochemichal background, and sediment quality guidelines (SQGs) are presented in Table 3.

Table 2 The average concentration of trace metals in beach sediments of 22 sites (2 samples/site) along the Red Sea coast
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Table 3 The comparison between the mean concentrations of metals in study area and those in other worldwide, geochemical background, and sediment quality guidelines
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Iron concentration in the present work ranged from 3589 μg/g in 8 km south Marsa Alam to 1060 μg/g in the Hurghada Marine Museum. The presence of Fe in the coastal sediments relatively indicates terrigenous contamination sources (Mansour et al. 2000). The average content of Fe in the present study (2021 μg/g) was lower than the background value in shale (Turekian and Wedepoh 1961), continental crust (Taylor 1964), and the lowest effect level (LEL) (Persaud et al. 1993). Moreover, it was lower than the Red Sea coast, Saudi Arabia (Youssef and El-Sorogy 2016); the Mediterranean coast in Egypt and Libya (Okbah et al. 2014; Nour and El-Sorogy 2017); Taranto Gulf, Italy (Buccolieri et al. 2006); Arabian Gulf, Saudi Arabia (El-Sorogy et al. 2018); and Caspian Sea in Azerbaijan and Russia (De Mora et al. 2004).

The Um El Huweitat site (Safaga area) recorded the highest value of manganese (914.3 μg/g), while the Marine Museum site (Hurghada area) recorded the lowest value (76.65 μg/g). The main anthropogenic sources of Mn are landfills, marine paints, and pipeline corrosion. In addition, the higher concentrations of Mn in coastal sediments may relate to its incorporation in the crystal lattice of calcite (Nawar and Shata 1989). In the present study, the average concentration of Mn (324 μg/g) was higher than those in the Red Sea coast (Saudi Arabia), Mediterranean coast (Libya), Arabian Gulf (Saudi Arabia), and the Caspian Sea (Russia). However, the concentration of Mn in the studied area was still lower than the average background in shale, continental crust, and LEL.

Copper concentrations ranged from 64.25 μg/g in Magawish Village site (Hurghada area) to 2.47 μg/g in 19 km north Marsa Alam site with an average of 23.4 μg/g. This average content of Cu was higher than those in the Red Sea coast (Saudi Arabia), Mediterranean coast (Egypt, Libya, and France), Bengal bay (India), and the Caspian Sea (Russia). Moreover, Cu in the Hurghada area was higher than the average background in shale and SQGs (Long et al. 1995; Persaud et al. 1993). While the Safaga area recorded higher content of Cu than the LEL value. Cu can enter the marine environment by ship constructions, removing rust, and painting ships. Although copper is vital for the synthesis of hemoglobin (Underwood 1977), the exposure to a high dose of Cu can cause several health problems (Gorell et al. 1997).

Zn can enter the marine environment via paints, mining wastewater, agriculture, and industrial activities. In addition, Zn in the form of zinc sulfate can be found in house construction, cans, galvanized pipes, garbage, and wear of automobile tires (Cameron 1992; Mulligan et al. 2001). Hurghada public beach recorded the highest value of Zn (109.5 μg/g), while the lowest value (11.24 μg/g) was recorded in 24 km south Quseir. The average content of Zn in the present study (48.19 μg/g) was higher than the ones in Red Sea coast (Saudi Arabia), Mediterranean coast (Egypt and Libya), and the Caspian Sea (Russia). However, this concentration was lower than those in the background shale, continental crust, and SQGs.

The highest value of Pb (79.81 μg/g) was recorded in the Hurghada marine museum, while the lowest value (7.41 μg/g) was recorded in 20 km south Marsa Alam. Pb can enter the marine environment by marine paints, oil wastes, domestic sewage, and traffic exhaust (Cameron 1992). In addition, it can be naturally derived from parent rocks. In the present study, the average content of Pb (30.4 μg/g) was higher than the ones in the Mediterranean Sea (Libya), Arabian Gulf (Saudi Arabia), Bengal bay (India), and the Caspian Sea (Azerbaijan and Russia). Moreover, this average content also was higher than the background value in shale and continental crust, whereas the Hurghada area only recorded higher Pb content than SQGs. Organic matter and clay minerals play an important role to extract Pb from sea water to sediment (Irwin et al. 1997).

Nickel concentrations ranged from 85.43 μg/g in Makadi bay to 4.25 μg/g in 20 km south Marsa Alam, with an average of 40.7 μg/g. This value was higher than the ones in the Red Sea coast (Saudi Arabia), Mediterranean coast (Egypt and Libya), Bengal bay (India), and the Caspian Sea (Russia). Moreover, these average content showed lower values than the background one in shale and continental crust. In contrast to that, all studied areas recorded higher Ni content than the value of SQGs. Ni can enter the marine environment by natural dissolution of rocks and soils or by industrial processes and waste disposal.

Cadmium recorded the highest value (4.61 μg/g) in El-Hamrawein port, while the Hurghada Marine Museum site recorded the lowest value (0.11 μg/g). The average content of Cd in the present study (1.38 μg/g) was higher than those in the Red Sea coast (Saudi Arabia), Mediterranean coast (Libya and France), Naples harbor (Italy), Bengal bay (India), and the Caspian Sea (Azerbaijan and Russia). Moreover, these average contents were higher than the background value of shale and continental crust, whereas, Quseir and Marsa Alam areas recorded higher content of Cd than the background value of SQGs. Mostly, cadmium is an output of terrigenous and anthropogenic origin and it has a remarkable ability for mobility in the seawater surface (Bender and Gagner 1976). However, it is classified as a chemical hazard (EC 2001; USFDA 1993). Cd is used in several purposes as in batteries and pigments (Boehme and Panero 2003; Lin et al. 2013).

Cobalt concentrations ranged from 15.27 μg/g in the Marsa Alam City to 1.17 μg/g in youth hostel site (Hurghada area), with an average of 6.19 μg/g. This average was higher than the ones in the Red Sea coast (Saudi Arabia), Mediterranean Sea (Egypt and Libya), Naples harbor (Italy), Arabian Gulf (Saudi Arabia), and the Caspian Sea (Russia). However, this concentration was lower than those in the background shale and continental crust. Cobalt sources vary from natural weathering of basement rocks where it is enriched in mafic relative to felsic igneous rocks (Wedepohl 1978) and anthropogenic sources as steels, fertilizers and lead, iron, and silver mining (Reimann and de Caritat 1998). It is worth mentioning that cobalt is more mobile in the surface environment under acidic and reducing conditions (McBride 1994).

Generally, the trace metal distribution along the Red Sea coast (Fig. 3) revealed that the Hurghada area is enriched in Cu, Zn, Pb, and Ni and the Marsa Alam area has high concentrations of Co, Mn, and Fe compared to other sites. On the other hand, the Quseir area is enriched in Cd.

Fig. 3
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The average concentration of trace metals (μg/g) in beach sediments of four major cities along the Red Sea coast

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Assessment of sediment contamination

For an overview of the comprehensive evaluation of the potential pollutants in the beach sediments of the Red Sea coast, the environmental indicators were calculated based on the geochemical background. To calculate the ratio between the existence of trace metal concentration in the sediment sample to that in geochemical background given by Turekian and Wedepoh (1961), contamination factor and the potential contamination index were measured (Table 4). These results show that the Hurghada area is moderately contaminated with Pb and Cu (CF = 1–3) and the Quseir area was very highly contaminated with Cd (C > 6) and moderately contamination for Pb. Also, Safaga and Marsa Alam areas showed a significant correlation with CF, where they have considerable contamination for Cd (CF = 3–6) and moderate contamination for Pb. These results confirmed by the results of Cp indicate that Quseir and Marsa Alam areas are very severely contaminated with Cd in 9 km south Quseir and 20 km south Marsa Alam sites, respectively. Moreover, Hurghada and Safaga areas are severely contaminated with Pb and Cd respectively. At the same time, the studied beaches are moderately contaminated with Cu, Zn, and Ni in the Hurghada area; Pb, Ni, Mn, and Cu in the Safaga area; Pb in the Quseir area; and Pb, Ni, and Mn in the Marsa Alam area, whereas to understand the intensity of the trace metal contamination in the studied area, geo-accumulation index was calculated (Table 5). Igeo shows that the Red Sea coast suffers from high concentrations of cadmium, especially in El-Hamrawein site which seems to be heavily contaminated with this metal that may be caused by phosphate extraction and export operations. Moreover, Quseir City, 9 km south Quseir, and 20 km south Marsa Alam sites are moderately to strongly contaminated with Cd. While the sites located 25 km north Quseir City, 19 km north Marsa Alam, and Marsa Alam City are moderately polluted with cadmium.

Table 4 Contamination factors and the potential contamination indexes for the beach sediment samples of the Egyptian Red Sea coast
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Table 5 Geo-accumulation factors data for the beach sediment samples of the Egyptian Red Sea coast
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On the other hand, to identify single-element contamination index in the studied area, soil pollution index (Table 6) showed that the Hurghada area is highly contaminated with Pb (SPI > 3) in most studied sites. In addition, it appears to be moderately contaminated by Cd, Zn, Ni, and Cu. Regarding other studied areas (Safaga, Quseir, and Marsa Alam), they highly contaminated with Cd. Moreover, they are moderately contaminated with (Ni and Pb) for Safaga and with (Co and Pb) for Quseir and Marsa Alam areas. These results fully compatible with the potential ecological risk index (Table 7). The Quseir area has a high ecological risk with Cd (160 ≤ PERI < 320) in most sampling sites, especially in El-Hamrawein port and 9 km south Quseir were very high risk (PERI ≥ 320). Safaga and Marsa Alam sites show considerable ecological risk with Cd (80 ≤ PERI < 160).

Table 6 The soil pollution index for the beach sediment samples of the Egyptian Red Sea coast
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Table 7 The potential ecological risk index for the beach sediment samples of the Egyptian Red Sea coast
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Pollution source analysis of trace metals

According to the enrichment factors (Table 8), the Hurghada area is extremely severe with Pb in the majority of sample sites and with Cu in youth hostel site. Moreover, it is very severe enriched with (Cu, Ni, and Zn) while being severely to moderately severe enriched with Cd and Mn, respectively, in most sample sites. The Safaga area is extremely severe with Cd and it is severe enriched with Pb, Ni, Cu, and Mn in most sample sites. The Quseir area is extremely severe with Cd and very severely enriched with Pb. To emphasize this point, some sampling sites such as El-Hamrawein port and Quseir City are extremely severe with Cd and Pb. In addition, the Quseir area is severely enriched with Co and Ni. The Marsa Alam area is extremely severe with Cd in most sample sites, while it is severely enriched with Pb especially in 19 km north Marsa Alam and Marsa Alam City sites. The sources of these metals in the studied area are districted according to anthropogenic sources. To emphasize that, Zhang and Liu (2002) stated that when the EF value is more than 1.5, and this would indicate that the possible source of the metals is more likely to be anthropogenic. Field observation point to the fact that the Hurghada area is subjected to different anthropogenic sources such as urbanization, tourism activities, shipyards, plastic rubbish, and landfilling processes. The Safaga area is under the effects of commercial vessels and passenger transport, tourism activities in addition to soil erosion and basement fragments. The Quseir area is related to phosphate shipping movement, fishing boats and tourism industry. The Marsa Alam area has many resorts, diving activities and rock erosion.

Table 8 Enrichment factors data for the beach sediment samples of the Egyptian Red Sea coast
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The results of the correlation matrix among the studied trace metals (Table 9) revealed that a strongly positive correlation between Cu and each of Zn, Ni, and Pb (r = 0.887**, r = 0.870**, and r = 0.540**) respectively. Zn is well correlated with Ni and Pb (r = 0.875** and r = 0.572**) respectively. Moreover, Mn is well correlated with Co and Fe (r = 0.551** and r = 0.0.526*) respectively. In addition, there are good correlations noticed between Cd and Co (r = 0.0.539**). On the contrary, there are negative correlation between Fe and each of Cu, Zn, Pb, and Ni (r = − 0.164, − 0.106, − 0.28, and − 0.143 respectively). To distinguish between the potential sources of these metals in the studied area, PCA was used on the examined metals. These results revealed two principal components have been extracted covering 69.72% of the cumulative variance (Table 10). PC1 showed positive loading for Cu (0.937), Zn (0.906), Ni (0.841), and Pb (0.677). PC2 showed positive loading for Mn, Co, and Fe (0.871, 0.727, and 0.647) respectively. This result implied that these metals may have been descended from the same sources. In addition, it shows similarity in migration under the same environmental conditions and show similar behaviors during transportation (Wang et al. 2015). Cu, Zn, Ni, and Pb metals in PC1 are mainly derived from anthropogenic sources (Simeonov et al. 2000; Thuong et al. 2013) such as ship constructions, removing rust from bodies, marine paints, oil wastes, domestic sewage, traffic exhaust, mining wastewater, garbage, galvanized pipes, and wear of automobile tires (Cameron 1992; Mulligan et al. 2001). While Mn, Co, and Fe are mainly from natural rock erosion. On the other hand, Co and Cd are from both natural and anthropogenic sources. Simultaneously, the dendrogram of HCA of trace metals in the study area (Fig. 4), confirmed the results of the correlation matrix and classified the studied trace metals into two clusters: cluster 1 includes Cu, Zn, Ni, and Pb at distance 10 which exactly matches with component one in PCA, while cluster 2 which includes Fe, Mn, Cd, and Co at distance 15 which well correlated with the second component in PCA.

Table 9 The correlation matrix among the studied trace metals in the beach sediment samples of the Egyptian Red Sea coast
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Table 10 Principal component loadings for the trace metals in the beach sediment samples of the Egyptian Red Sea coast
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Fig. 4
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The dendrogram for hierarchal cluster analysis (HCA) of trace metals in the study area

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Conclusion

The results of the various environmental pollution indicators in this work confirm that the Red Sea coast in the studied area is a considerable ecological risk with Cd, especially in the Quseir area. The Hurghada area is very severely contaminated with Pb, Zn, Ni, and Cu. Marsa Alam and Safaga areas are severely contaminated with Cd and Pb. When comparing these results to the geochemical background values, the Egyptian Red Sea coast is higher in the concentration of Cd than the background values of shale, continental crust, and SQGs. In addition, Pb concentration in the studied area is higher than in background shale and continental crust; meanwhile, it is lowered than in SQGs. Regarding Ni and Cu concentrations, they are higher than in SQGs. However, the two metal concentrations are lower than the background values of shale and continental crust.

Despite the presence of the weathering effects represented by the presence of basement fragments and phosphate in some sites along the coastal area as in the south Safaga bay and El-Hamrawein port, the anthropogenic sources of trace metals such as landfill, plastic rubbish, phosphate operations, fishing boats, shipyards, population, and tourist activities are the most fundamental factors according to the results of EF, Cp, CF, SPI, and PERI.

In the present study, the average concentrations of Cd, Pb, Cu, Zn, Ni, and Co in sediments of the Egyptian Red Sea coast are higher than the ones in Saudi Red Sea coast, Egyptian and Libyan Mediterranean Sea coast, Indian Bengal bay, and Russian Caspian Sea.