Environmental Risk Assessment and Sources of Potentially Toxic Elements in Seawater of Jazan Coastal Area, Saudi Arabia

Abstract

High levels of potentially toxic elements (PTEs) in water bodies negatively affect the biota of aquatic ecosystems and surrounding environments. A risk assessment investigation of the levels and distribution of PTEs in the seawater of the Jazan coastal area, southwest Saudi Arabia, was conducted. Thirty-two surface seawater samples were collected, and contamination (C_d) and heavy metal pollution (HPI) indices, as well as multivariate statistics, were applied. The average PTE levels (µg/L), in descending order of magnitude, were Cu (2.56), Pb (2.27), Ni (1.30), Cr (1.28), Zn (1.04), Sb (0.36), Co (0.22), and Cd (0.06). A fluctuating pattern without a fixed direction was detected in the spatial distribution of these metals, with increased pollution being linked to high metal levels as shown by some samples. The HPI indicated low pollution in 50% of the samples and medium pollution in the remaining 50%, whereas the C_d indicated low contamination with PTEs. The absence of significant correlations between pairs of metals indicated different sources of metal pollution. Lithogenic sources are implicated in the supply of Co, Ni, Pb, and Sb, whereas Cr was mainly derived from an anthropogenic source, and combined lithogenic and anthropogenic sources are believed to have contributed Cu and Zn to the area. It is proposed that urbanization, agriculture, and industry are among the potential anthropogenic sources of pollutants on the Jazan coastline. Soils generated on the undifferentiated Quaternary rocks along the investigated area are the main lithogenic sources.

1. Introduction

The rapid population growth and urbanization and associated industrial activities of the past decade have produced contamination-level quantities of liquid and solid wastes in the form of potentially toxic elements (PTEs), which impose a critical threat to aquatic ecosystems and human health alike [1,2,3]. For example, marine biota such as fish and crustaceans are sensitive to changes in their environment and are thus, negatively impacted by the release of PTEs into the seawater by industrial and domestic effluent dumping [4,5,6]. Furthermore, PTEs are nonbiodegradable and, therefore, can reach toxic levels fairly rapidly. Left undetected and untreated, toxic levels of these trace elements may lead to serious illnesses [7]. Naturally sourced PTEs are released from sediments into seawater via different mechanisms such as the alteration of pH and redox potentials, resuspension of sediments, and movement of benthic biota [8,9,10,11,12].

PTEs circulate in nature through rock weathering, dust, and volcanic eruptions by which heavy metals are transferred from rivers to oceans. PTEs are adsorbed onto particle surfaces and are buried with deposited sediments [13,14,15]. Coastal areas are particularly prone to contamination due to bioaccumulation and the long-term persistence of metals and their associated toxicity [16,17,18,19]. This PTE contamination has the capacity to change seawater properties, affects the function of marine dwellers, and negatively impacts marine ecosystems and resources as well as humans who depend on these resources [17,20,21,22]. Seafood contaminated with PTEs has become an important global concern for human health, especially in developing countries [23].

Spectacular modern and Pleistocene fringing coral reefs rim the Red Sea coasts [24,25]. These Pleistocene coral reefs have been the subject of many studies from different points of view [26,27,28,29,30,31,32,33] However, the Red Sea waters are experiencing increasing pollution of various PTEs, especially in the northwestern areas, due to urbanization expansion and industrial and agricultural activities [18,19,34,35]. Kahal et al. [19] investigated the ecological risk assessment of PTEs in the Jazan area and reported enrichment in Cd, Cr, Cu, Ni, Sb, and Zn in the coastal sediments of the area. The authors related this enrichment to combined anthropogenic and lithogenic sources.

Monitoring and mitigating marine pollution is thus crucial for conserving resources, particularly shellfish and fisheries, and for improving coastal zone management in general. Accordingly, the current investigation aims to quantify the spatial distribution of PTEs in seawater for the first time and highlight their possible sources in the Jazan coastal area of southwest Saudi Arabia, which is an important fisheries area.

2. Materials and Methods

2.1. Study Area

The studied area is situated in the southwest of Saudi Arabia, along the Red Sea coast, between 42°76′36″ to 42°24′06″ E and 16°48′84″ to 17°49′91″ N (Figure 1). It is covered with sedimentary rocks and soils of the undifferentiated Quaternary units. The beach is differentiated into sand-dominated type (14 localities, 43.75%), mangrove-dominated type (12 localities, 37.50%), and rock-dominated type, which includes six localities (18.75%). Geologically, Jazan province is composed of crystalline basement rock units of Precambrian age in the eastern part and coastal plain units in the western part. The composite section, from base to top, consists of Proterozoic metavolcanics and metasediments, Cambro–Ordovician Wajid Sandstone, Jurassic Khums and Amran formations, Oligocene–Miocene Tihama Asir Magmatic Complex, and Quaternary volcanic and sedimentary rocks and sabkha deposits [36].

2.2. Sampling and Analytical Procedures

Thirty-two representative samples were collected from the subtidal zone of the Jazan coastline from depths of 10 to 35 m. Direct measurements of electrical conductivity (EC) and pH were conducted on-site using EC and pH meters (Model: EZ-9902, GoolRC, Shanghai, China) The samples were kept in acid-washed plastic containers at 4 °C in an icebox. An inductively coupled plasma mass spectrometer (ICP-MS), NexION 300 D (Perkin Elmer, Waltham, MA, USA) was used to measure the concentrations of Cr, Co, Ni, Cu, Cd, Pb, Sb, and Zn at the Department of Chemistry, King Saud University, Riyadh.

The collected seawater samples were treated with 70% grade nitric acid (HNO₃) for elemental and metal analysis, and roughly 50 mL of each treated sample was subsequently digested with concentrated nitric acid (HNO₃; 5 mL) and perchloric acid (CHlO₄; 2 mL). To achieve complete digestion, the solution was left overnight before being gradually heated from 100 to 225 °C over a 6 h period the next day. Following wastewater testing standards [37], each digested sample solution was diluted with up to 50 mL of distilled water before being filtered. The ICP-AES technique was validated in terms of linearity, limit of detection (LOD), and limit of quantification (LOQ). To ensure the accuracy of the study, three samples were analyzed in duplicate. The LOD value was three times the standard deviation of the measurements for the blank solutions divided by the slope of the calibration curve for each element, whereas the LOQ value was ten times the standard deviation of the measurements for the blank solutions divided by the slope of the calibration curve for each element [38,39].

A blank and external working standards of 0, 50, 100, and 200 µg/L (Panreac, 766333. 1208) were used to obtain the Cr, Cd, Cu, Pb, Co, and Ni calibration curves. Calibration curves for Sb and Zn were prepared from a standard solution of 1000 mg/L (Aristar grade, BDH Laboratory Supplies, Lutterworth, UK). High linearity was shown in all of the curves and for all measured elements.

Heavy metal pollution index (HPI) was used as a measure. HPI is calculated by determining the unit weight (Wi) for each selected parameter, which in turn is inversely proportional to the standard permissible value (Si) for that parameter [40]. Wi takes an arbitrary value between 0 and 1. The pollution index is calculated by the following formula [41]:

$$\mathrm{HPI}=\frac{\sum \mathrm{W}\mathrm{i}\mathrm{Q}\mathrm{i}}{\sum \mathrm{W}\mathrm{i}}$$

(1)

where Qi is the subindex of the ith parameter and Wi is the unit weight for the ith parameter.

$${\mathrm{Q}}_{\mathrm{i}}=\sum (\frac{\left[\mathrm{M}\mathrm{i}\left(-\right)\mathrm{L}\mathrm{i}\right]}{\mathrm{S}\mathrm{i}-\mathrm{L}\mathrm{i}})$$

(2)

where Mi, Li, and Si are the monitored heavy metal, ideal, and standard values of the ith parameter, respectively. World Health Organization [42] standards of permissible values (Si) and highest desirable values (Ii) are adopted here. Three categories are yielded by the HPI [39]: HPI < 5 (low pollution), HPI = 5–10 (medium pollution), and HPI > 10 (high pollution).

The contamination index measures different quality parameters and their combined effects [43,44], and is obtained by the following equation:

C_d = ∑CF

(3)

CF = C (heavy metal)/C (Background)

(4)

where CF is the contamination factor, C (heavy metal) is the analytical value, and C (Background) is the upper permissible value for the ith component. Calculation of C_d yields three categories [45]: low contamination (C_d < 4), medium contamination (C_d = 4–8), and high contamination (C_d > 8).

In order to identify the possible sources of PTEs in Jazan coastal waters, statistical analyses (dendrogram using average linkage, Pearson’s correlation coefficient, principal component analysis) were performed using SPSS 16.0 and Microsoft Excel 2016.

3. Results and Discussion

3.1. Distribution of Potentially Toxic Elements

Results of PTE analyses of the 32 surface seawater samples from the Jazan coastline are presented in

Table 1. Concentrations of PTEs (μg/L), C_d, and HPI compared to the maximum admissible concentration (MAC). Also listed are the coordinates of the sampling sites (see Figure 1 for location map).

S.N.	Latitudes	Longitudes	Cr	Co	Ni	Cu	Zn	Cd	Sb	Pb	HPI	Cd
S1	16°48′84″	42°76′36″	1.50	0.13	1.60	3.50	1.30	0.08	0.52	4.20	7.95	3.69
S2	16°50′08″	42°74′03″	1.20	0.21	1.40	2.30	1.20	0.06	0.44	3.10	6.55	2.94
S3	16°53′35″	42°72′63″	1.00	0.30	0.90	2.50	1.30	0.05	0.48	2.50	6.05	2.72
S4	16°55′40″	42°72′48″	1.10	0.38	1.90	3.10	1.00	0.08	0.52	2.10	6.45	2.74
S5	16°60′26″	42°71′63″	1.40	0.32	1.60	3.00	0.50	0.04	0.48	3.20	6.97	3.31
S6	16°70′45″	42°70′90″	1.60	0.35	1.70	0.90	0.60	0.06	0.34	3.80	8.21	3.51
S7	16°76′79″	42°67′81″	1.20	0.29	1.30	2.60	0.80	0.06	0.42	2.90	6.67	2.99
S8	16°78′56″	42°67′40″	1.40	0.08	0.80	0.70	0.50	0.04	0.31	2.10	4.10	1.76
S9	16°80′93″	42°64′51″	1.00	0.09	1.00	0.90	0.70	0.04	0.42	1.00	2.71	1.08
S10	16°81′98″	42°63′51″	1.20	0.30	1.20	3.20	0.90	0.06	0.32	2.50	6.16	2.81
S11	16°82′26″	42°60′96″	1.40	0.25	0.80	2.80	1.10	0.05	0.50	1.60	4.59	2.05
S12	16°83′96″	42°58′97″	1.60	0.32	1.50	2.70	1.50	0.04	0.28	2.20	5.62	2.62
S13	16°83′49″	42°57′43″	1.20	0.17	1.20	2.10	1.20	0.07	0.34	2.80	6.03	2.62
S14	16°87′36″	42°54′89″	1.30	0.26	1.00	2.00	1.00	0.06	0.28	1.50	4.58	1.91
S15	16°90′38″	42°54′42″	1.10	0.18	1.20	3.10	1.40	0.08	0.42	1.80	4.92	3.69
S16	16°93′52″	42°54′50″	1.00	0.32	1.50	2.80	0.60	0.06	0.36	2.40	6.13	2.11
S17	16°95′40″	42°53′80″	1.40	0.18	1.40	3.30	0.80	0.05	0.30	1.80	4.43	2.74
S18	17°01′17″	42°53′31″	1.50	0.20	1.30	2.60	0.80	0.04	0.41	2.10	4.83	2.12
S19	17°02′75″	42°52′68″	1.60	0.23	1.00	2.40	1.00	0.07	0.28	1.80	4.99	2.27
S20	17°04′12″	42°47′90″	1.20	0.18	0.90	2.00	1.20	0.06	0.38	1.60	4.32	2.10
S21	17°07′56″	42°44′10″	1.00	0.08	1.40	3.20	1.00	0.08	0.42	1.20	3.56	1.81
S22	17°14′74″	42°42′07″	1.30	0.13	1.50	3.50	1.40	0.05	0.22	1.80	4.17	1.52
S23	17°36′70″	42°31′50″	1.50	0.16	1.50	2.50	1.10	0.05	0.28	1.50	3.94	2.06
S24	17°37′84″	42°32′10″	1.20	0.18	1.00	3.00	1.20	0.04	0.36	2.50	5.23	1.80
S25	17°39′51″	42°32′47″	1.40	0.28	1.20	2.20	0.80	0.04	0.40	3.60	7.26	2.54
S26	17°40′96″	42°32′53″	1.00	0.25	1.40	2.90	0.80	0.06	0.28	1.80	4.93	3.38
S27	17°42′84″	42°32′31″	1.20	0.32	0.90	3.50	1.20	0.04	0.24	2.80	6.34	2.21
S28	17°44′33″	42°29′62″	1.20	0.20	1.00	3.20	1.00	0.06	0.35	2.40	5.49	3.07
S29	17°45′02″	42°76′36″	1.00	0.18	1.60	2.00	1.20	0.04	0.40	2.50	5.27	2.54
S30	17°46′06″	42°27′26″	1.30	0.21	1.80	2.60	1.50	0.06	0.28	1.80	4.79	2.44
S31	17°47′81″	42°25′85″	1.50	0.25	1.40	2.80	1.40	0.04	0.24	1.50	4.27	2.13
S32	17°49′91″	42°24′06″	1.40	0.17	1.50	3.10	1.20	0.05	0.16	1.70	4.22	2.01
Minimum			1.00	0.08	0.80	0.70	0.50	0.04	0.16	1.00	2.71	1.08
Maximum			1.60	0.38	1.90	3.50	1.50	0.08	0.52	4.20	8.21	3.69
Average			1.28	0.22	1.30	2.56	1.04	0.06	0.36	2.27	5.37	2.38
Std. Deviation			0.20	0.80	0.30	0.73	0.29	0.01	0.09	0.76	1.28	0.64
MAC			50.0	5.00	20.0	2000	40.0	3.00	20.0	10.0

, along with the minimum, maximum, and average PTE concentrations and sampling site coordinates. The ranges of PTE concentration (µg/L) were in the following order: Cu (0.70–3.50), Pb (1.00–4.20), Ni (0.80–1.90), Cr (1.00–1.60), Zn (0.50–1.50), Sb (0.16–0.52), Co (0.08–0.38), and Cd (0.04–0.08). Arranged by their average values, the elements take the following order: Cu > Pb> Ni > Cr > Zn > Sb > Co > Cd. The average pH, electrical conductivity, and salinity of the studied seawaters were 8.34, 51.87 mS/cm, and 34 ppt, respectively. No consistent patterns in any specific direction were observed in the distribution of PTEs in seawater samples across the investigated coast (Figure 2). However, some samples exhibited higher PTE levels, such as S1 and S4 for Sb, Cu, and Cd, and S6 and S12 for Co and Cr, which were attributed to an increase in pollution sources.

The studied localities were subdivided into five clusters according to the Q mode HCA of the sample locations and the investigated metals (Figure 3). The first cluster contained samples S2–S5, S7, S10, S13, S16, S24, S25, and S27–S29. Samples from this cluster, especially S4, S16, S27, and S29, had the highest levels of Cu, Co, Ni, Cd, and Sb. The second cluster contained samples S11, S12, S14, S15, S17–S23, S26, S30, S31, and S32. Samples from this cluster had the highest levels of Cr, Zn, Cd, and Cu. The third cluster contained sample S1, which had the highest levels of Cu, Cd, Sb, and Pb. The fourth cluster contained samples S8 and S9, which had the lowest levels of Cr, Co, Ni, Cu, Zn, Cd, and Pb. The fifth cluster contained sample S6, which had the highest level of Cr.

3.2. Environmental Risk Assessment

Contamination from anthropogenic sources, such as the leakage of untreated municipal wastewater as well as the utilization of chemicals in industry and agriculture, gravely impacts the quality of surface water [15]. The comparison between PTE averages and those recorded from several neighboring and worldwide coastal seawaters is presented in

Table 2. PTE values (μg/L) of the current study compared to those reported globally.

Location	Pb	Cd	Zn	Ni	Co	Cr	Cu	Reference
Red Sea, Saudi Arabia	2.27	0.06	1.04	1.30	0.22	1.28	2.56	Present study
Al-Uqair Coastline, Arabian Gulf	0.26	0.05	6.72	3.01	-	9.64	2.48	[15]
Arabian Gulf, Saudi Arabia	0.48	0.03	0.97	-	2.06	12.95	2.65	[16]
Yanbu, Red Sea, Saudi Arabia	0.28	0.31	1.67	4.42	0.14	0.72	2.45	[17]
North Atlantic	125	5.5	0.15	-	159	3.5	1.15	[46]
North Pacific	32	5.5	0.15	-	27	3	0.9
Gulf of Aqaba, Saudi Arabia	0.20	0.03	3.32	-	0.24	0.96	6.18	[47]
Average oceanic concentration	0.001	0.07	0.4	-	-	0.33	0.12	[48]
Arabian Gulf, Bahrain	0.16	0.11	0.84	0.31	-	-	0.20	[49]
Abu Ali Island, Arabian Gulf	0.15	0.08	11.44	3.49	0.27	-	3.77	[50]
Arabian Gulf, Saudi Arabia	0.04	0.11	16.21	4.36	0.36	1.38	5.24	[51]
Arabian Gulf, Saudi Arabia	0.28	0.07	1.53	4.40	0.23	2.44	2.44	[52]
Gulf of Aqaba	0.32	0.57	0.24	0.22	0.17	-	0.14	[53]
Red Sea Coast, Egypt	0.03	0.06	5.5	0.76	0.03	0.18	0.97	[54]
Oman Sea, Oman	2.22	0.13	11.7	10.9	-	15.51	2.77	[55]
Mediterranean Sea, Egypt	0.426	-	1.694	1.92	-	0.133	-	[56]
Caspian Sea Coast, Iran	1.67	0.27	16.94	9.93	1.65		5.02	[57]

. The average level of Pb was higher than the levels listed in Table 2, except in the North Pacific and North Atlantic [46], in contrast to the Cd level, which was less than the levels shown in Table 2, except for the Gulf of Aqaba and the Saudi east coasts along the Gulf [15,16,47]. The average level of Zn was higher than those from the North Atlantic, North Pacific, Arabian Gulf (Saudi Arabia and Bahrain), and Gulf of Aqaba [15,16,45,46,47,48,49].

The Ni average value reported in this study is above the values from the Arabian Gulf (Bahrain and Saudi Arabia) and the Gulf of Aqaba [16,46,48], whereas it is lower than those from the Arabian Gulf and the Red Sea coast [17,50,51,52]. Notably, the Co and Cr levels are higher than the Gulf of Aqaba and the Red Sea values reported from Egypt [17,53,54]. The average value of Cu is higher than the values reported globally (e.g., North Atlantic, North Pacific, and Arabian Gulf).

Based on heavy metal concentration, the water quality along the Jazan coastline was quantitatively assessed using HPI. This method showed that PTE average concentrations were below the maximum admissible concentrations as defined by WHO [42]. The spatial distribution of HPI fluctuated but agreed well with that of PTEs (Figure 4). HPI levels ranged from 2.71 in S9 to 8.21 in S6, with an average value of 5.37 (Table 1). Sixteen seawater samples (50%) were categorized as low pollution (HPI < 5), while the other sixteen were categorized as medium pollution (HPI = 5–10). Cd varied from 1.08 in S9 to 3.69 in S1, with an average value of 2.38, which indicated that contamination of the seawater of the Jazan area with PTEs was low (C_d < 4). The highest HPI and C_d values were seen in samples 1 and 6 and may be attributed to an increase in the concentrations of Sb, Cu, and Cd in sample 1 and an increase in the concentrations of Co and Cr in sample 6.

3.3. Possible Sources of PTEs

PTEs are released into the aquatic environment via anthropogenic and/or geogenic sources [58]. Three clusters of PTEs are recognized in this study using a dendrogram based on average linkages (Figure 5). Cobalt, antimony, and cadmium share considerable similarities and represent the first cluster. This cluster shows low linkage distances compared to the other two clusters. The second cluster encompasses Cr, Ni, and Zn, and the third cluster includes Cu and Pb. Pearson’s correlation coefficient did not show any significant correlations between pairs of metals. Correlations between Sb and several PTEs, for example, Cr, Cu, and Zn are mainly negative (

Table 3. PTE correlation matrix.

	Cr	Co	Ni	Cu	Zn	Cd	Sb	Pb
Cr	1
Co	0.082	1
Ni	0.114	0.214	1
Cu	−0.072	0.141	0.223	1
Zn	0.021	−0.130	0.075	0.402 *	1
Cd	−0.216	−0.035	0.233	0.241	0.143	1
Sb	−0.281	0.106	0.009	−0.037	−0.184	0.281	1
Pb	0.201	0.369 *	0.217	0.011	−0.159	0.043	0.342	1

Note: * Correlation is significant at the 0.05 level (2-tailed).

). In addition, negative correlations were recorded between Zn and Pb. This lack of positive correlations between different PTEs is an indication of the contribution of more than one pollution source [59,60,61]. Principal component analysis was used to identify the possible sources of metals in Jazan coastal waters. Three principal components were identified based on the extraction method. Each component includes various elements (variables) believed to have originated from the same source, with a total covered variance of 61.429% (

Table 4. Percentages of the three component loadings and their variance. Numbers in bold indicate a significant positive loading.

	Component
	1	2	3
Cr	−0.048	−0.235	0.763
Co	0.575	−0.291	0.312
Ni	0.582	0.187	0.338
Cu	0.393	0.668	0.196
Zn	−0.011	0.759	0.239
Cd	0.495	0.444	−0.396
Sb	0.539	−0.238	−0.617
Pb	0.669	−0.445	0.172
% of Variance	22.593	20.621	18.215
Cumulative %	22.593	43.214	61.429

). The first component represents 22.593% of the total variance and presents a significant positive loading for Co, Ni, Sb, and Pb (0.575, 0.582, 0.539, and 0.669, respectively). The second component covers 20.621% of the total variance and presents a significant positive loading for Cu and Zn (0.668 and 0.759, respectively). The third component covers the remaining 18.215% and presents a highly positive loading for Cr (0.763). The results of the principal component analysis are supported by a varimax plot of the Kaiser normalization (Figure 6).

The link between elements and PCA was used in order to differentiate between sources of lithogenic and anthropogenic origin [18,62,63] (Wang et al., 2014; Zhang et al., 2016; Kahal et al., 2018). Cobalt, nickel, antimony, and lead (first component) were derived mainly from lithogenic sources. These metals may originate from soils formed on the undifferentiated Quaternary units along the Jazan coastline. Cu and Zn from the second component, which may be derived from a combined lithogenic and anthropogenic source, are used as markers of agronomic activities in agriculture after being eroded and transported into the area. Chromium from the third component is derived mainly from anthropogenic sources. Overall, these findings indicate multiple sources of the investigated PTEs in seawaters of the Jazan coastline: natural sources (weathering of undifferentiated Quaternary units and atmospheric deposition) and anthropogenic sources (urbanization and agricultural and industrial activities).

4. Conclusions

The following order of the average PTE contents was detected: Cu > Pb> Ni > Cr > Zn > Sb > Co > Cd. These PTEs are distributed in an inconsistent pattern with no specific direction. The average values of Pb, Zn, Ni, Co, Cr, and Cu concentrations exceeded the average values reported from surface seawater globally. Based on the HPI, 50% of the seawater samples showed low pollution and 50% medium pollution, whereas C_d indicated low contamination with PTEs. Three clusters of PTEs were recognized, indicating more than one source of the pollutant elements. Co, Ni, Sb, and Pb were mainly of lithogenic origin, Cu and Zn were of both lithogenic and anthropogenic origins, and Cr was mainly from an anthropogenic source. Potential anthropogenic sources of pollutants in the Jazan coastline include agricultural and industrial sources and rapid urbanization around the study area, while sedimentary rocks and Quaternary soils represent the main lithogenic sources.