Sediment Texture, Geochemical Variation, and Ecological Risk Assessment of Major Elements and Trace Metals in the Sediments of the Northeast Persian Gulf

Abstract

This study presents a comprehensive analysis of sediment texture along with geochemical variation, potential sources, and ecological risk assessment of major elements and trace metals in the bottom sediments of Iranian territorial waters situated in the northeast Persian Gulf. To achieve this, diverse laboratory methods, GIS techniques, statistical analyses, and index analysis approaches were employed. Over 50% of the sediment particles are mud, while one-third are sand-sized particles, primarily composed of skeletal fragments. The sediment’s elements concentrations were ranked in descending order as Ca > Al > Fe > Sr > Mn > Ba > Cr > Ni > V > Zn > Cu > Pb > As > Co > Mo > Cd. Cluster analysis revealed strong correlations among Al-Ni-Cr-V, Cd-Cu-Zn-Pb, Ba-Fe, silt-clay, and Ca-Sr. Calcium and strontium showed extremely severe enrichment due to high content of carbonate matter. Arsenic and Mo were significantly enriched, while Ba, V, Co, Zn, and Cu demonstrated moderate enrichment. Nevertheless, all the sampling stations were classified as having zero to very low levels of contamination, indicating a low potential ecological risk. Arsenic emerged as the primary contributor to the ecological risk index. Notably, no strong correlation was found between As, Mo, and other elements, indicating that As and Mo likely originate from distinct sources.

1. Introduction

The Persian Gulf is a foreland basin and a marginal sea known for its rich biodiversity and fishery resources, despite its extreme salinity and high temperature [1]. The ecological importance of this semi-enclosed and shallow basin has made it one of the most remarkable marine ecosystems in the world [2]. However, the region is subjected to severe threats from pollutants, including potentially toxic elements (PTEs), due to having about two-thirds of the world’s oil sources [3,4,5].

The northeast Persian Gulf is exposed to diverse sources of pollution by PTEs, which pose risks to the health of both humans and ecosystems [6]. Due to limited circulation, shallow depth, and high temperature and salinity [7,8], regional environmental and ecological contamination can be considerable. Industrial activities such as oil and gas production, petrochemical plants, power plants, and shipyards are among the primary sources of PTEs in this region [9,10]. These industries may release PTEs such as Cd, Cr, Cu, Ni, Pb, V, and Zn into surrounding water bodies via direct effluent discharge or atmospheric deposition [11]. Furthermore, crude oil and natural gas deposits may contain PTEs such as Pb, Cd, and Cu, which can be mobilized during drilling, transportation, and refining processes [12]. The discharge of wastewater from petroleum production facilities can also contribute to PTEs pollution in nearby marine environments [13]. Agriculture runoff from neighboring farms and untreated sewage discharge from populated areas are additional contributors to PTEs pollution in the region [14]. In addition, natural geological processes, including erosion and weathering of rock formations, can lead to the release of PTEs into nearby water bodies [15].

PTEs are contaminants found in both terrestrial and aquatic environments [16,17,18] that have gained widespread attention due to their toxic, persistent, and bioaccumulative nature in ecosystems [19,20,21]. These contaminants can enter the environment from natural and anthropogenic sources [12,22] and can be adsorbed into particles or re-mineralized via various biogeochemical cycles [20,23]. PTEs accumulate in the bottom sediments of aquatic environments and can disrupt the balance of aquatic ecosystems [24,25]. Therefore, aquatic sediments have been recognized as sensitive indicators for monitoring environmental contamination [23,26,27].

Studies on the geochemical variation and ecological risk assessment of major elements and trace metals have primarily been confined to the northwestern region of the Persian Gulf [2,28,29,30,31,32]. These studies are limited in their scope due to their reliance on a small number of sampling stations and a restricted range of elements [33]. As such, they offer only a narrow understanding of the spatial distribution, enrichment, and accumulation of major elements and trace metals in addition to pollution levels [33,34]. Moreover, these studies fail to provide an adequate overview of the northeastern segment of this valuable water body.

This study investigates the distribution, ecological risk assessment, and potential sources of major elements and trace metals in conjunction with sediment texture and particle size analysis in the bottom sediments of Iranian territorial waters. Specifically, this study analyzed 140 sediment samples using inductively coupled plasma optical emission spectroscopy to determine the concentrations of 16 elements, including Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sr V, and Zn. The data was then utilized to generate interpolated maps using GIS techniques, followed by statistical analyses such as cluster analysis, Pearson coefficient, and correlation coefficient to identify similarities among various elements and particle size fractions in surface sediments. An index analysis approach employing the enrichment factor, modified degree of contamination, and potential ecological risk index (RI) was employed to classify the degree of contamination at the tested stations.

2. Geographical Setting

The Persian Gulf is a crescent-shaped marginal sea located in a foreland basin, hemmed in by the Arabian Peninsula to its south and west and the Zagros Mountains to its north and east [35]. It is connected to the Oman Sea and the Indian Ocean via the Strait of Hormuz [36]. The average water depth of the Persian Gulf stands at 35 m, with its maximum depth reaching up to 100 m near the Strait of Hormuz in the northeast [37].

The sedimentary deposits in the region consist of detrital riverine, biogenic, as well as loess materials [36]. Sediments from riverine sources are sourced from the Shatt-al-Arab and small rivers along the northern coasts, while aeolian sediments mainly originate from southwestern winds [38,39]. These dust storms bring fine-grain detrital materials from coastal plains, northern deserts, Iraq, and the Arabian Desert to the Persian Gulf [38,39]. The presence of rivers such as Kol and Shoor (Minab) in the northern part of the Persian Gulf contributes to a lower production of carbonate sediments [40] compared to the southern part of the Gulf due to their detrital components [37].

Surface sediments in the northern Persian Gulf contain high organic-biogenic components such as Gastropoda, Ostracoda, echinoderm, bryozoan, and benthonic-planktonic foraminifera, while detrital components including quartz, feldspar, mica, clay minerals, and rock fragments are derived from the Anatolia–Zagros mountain belt via inlet rivers that flow into the northern part of the Persian Gulf [37]. The entrapment of sediments in the delta results in Arvand flooding conditions, which have a slight impact on sediment supply to the Persian Gulf. Only about 10% of material reaches the Gulf due to this process [33].

Near Bandar-e-Abbas in shallow waters, the average sedimentation rate was found to be 1.04 mm per year, with a maximum sedimentation rate of 1.2 mm/year [34]. Studies conducted in the region have reported an average bottom-dissolved oxygen level of 6.5 ppm in shallow waters up to 25 m in depth and 3.5 ppm in deeper areas [37,41].

Tidal currents are a dominant factor in the Persian Gulf’s hydrodynamics, typically flowing parallel to the catchment. Maximum tidal current velocities near the Strait of Hormuz have been estimated at around 90 cm/s, while the central part of the Khoran Strait between the ports of Pohl (Bandar-e-Abbas) and Laft (Qeshm Island) may experience maximum tide speeds of up to 137 cm/s [37,42]. High tide heights in the Persian Gulf vary from 1 to 5 m [37].

3. Materials and Methods

3.1. Sampling

The Geological Survey of Iran conducted a comprehensive study on physical, chemical, and biological parameters in the northern Persian Gulf. Sampling was carried out during the MG-2008-PG cruise, where 140 surface samples were collected from the bottom sediments of the marine boundary of Iranian coastal territory in the northeastern Persian Gulf using a Van Veen Grab Sampler (Figure 1). The sampling points’ location was recorded using the Universal Transverse Mercator coordinate system (UTM) and later converted to decimal degrees using the World Geodetic System 1984 (WGS84). The top 10 cm of sediment was subsampled using plastic syringes and stored at a temperature of 4 °C. To ensure homogeneity, mechanical shaking was applied to the samples before being separated for various analyses such as grain size and chemical composition.

3.2. Grain-Size Analysis

Prior to granulometry and chemical analysis, the sediments were dried at 75 °C for 24 h. The wet sieving method (Fritch model) was used for grain size analysis up to 63 μm, while the laser grain size test (Analysette 22 compact) was used for sizes less than 63 μm. To assess the precision of the method, several samples were subjected to repeated measurements, which yielded a relative standard deviation of <5%. Sediment description was carried out using the Folk classification method [43]. According to this system, clay particles are smaller than 2 microns; silt particles range from 2 to 63 microns; sand particles range from 63 microns to 2 mm; and gravel particles are larger than 2 mm.

3.3. Sediment Constituent Analysis

After drying, samples from different fractions, including 2 mm, 1 mm, 500 μ, 250 μ, and 125 μ, were selected for analysis of mineralogy, morphometry, and morphoscopy. The sediment particles were examined using an Binocular microscope (SMZ 1500 Nikon, USA) to evaluate their shape, roundness, and granularity within each sediment class. Specific and essential cases were photographed using a DS-Fi1 Nikon camera after studying the sediment particles under the microscope.

3.4. Elemental Analyses

To determine the composition of the sediment sample, 0.5 g of bulk sediments were weighed and placed in Teflon vessels. Next, 7 mL of aqua-regia solution (1:3 HCl: HNO₃) was added to each vessel [44,45]. Digestion was carried out using a Milestone Ethos1 microwave digester, with the samples being heated to 185 °C for 30 min and then held for 15 min. Subsequently, the samples were diluted with deionized distilled water up to 50 mL and analyzed for major and trace elements using an ICP-MS (Agilent 7700x, USA) device at the Iranian Geological Survey and mineral exploration.

It is important to note that the analysis focused on the “pseudo-total composition” rather than the “total composition” due to aqua-regia’s limitations in fully digesting the sample. As such, the analysis only reflects the amount of element that has been extracted which is ideal for environmental purposes.

To ensure measurement accuracy and precision, procedural blanks, duplicates, and a standard sample (MESS-1) were used. The accuracy was found to be within ±5% of the suggested values in the standard.

3.5. Estimation of Sediment Contamination

The assessment and evaluation of sediment contamination have been addressed through the utilization of several reliable pollution indices [2,46]. Specifically, this study employed the enrichment factor (EF), modified degree of contamination (mC_d), and potential ecological risk index (RI) as the chosen indices for pollution assessment and evaluation.

3.5.1. Enrichment Factor

The Enrichment Factor (EF) is a helpful indicator that reflects the status of environmental contaminants, particularly heavy elements, in marine environments [47,48]. The following equation expresses the EF Equation (1) [40,41].

$$\mathrm{EF}=(\left. [\left({\mathrm{M}}_{\mathrm{c}}\right)/\left({\mathrm{M}}_{\mathrm{r}}\right){]}_{\mathrm{s}}\right)/(\left. [\left({\mathrm{M}}_{\mathrm{c}}\right)/\left({\mathrm{M}}_{\mathrm{r}}\right){]}_{\mathrm{b}}\right)$$

(1)

Here, M_c represents the concentration of metals; M_r represents the concentration of the reference element, which in this study is aluminum (Al); s denotes the studied sample; and b indicates the background used in this study, which was the element concentration in the Upper Continental Crust (UCC; [49]). Six contamination classes were defined based on the EF values (

Table 1. Categories of sediment pollution based on the calculated indices.

EF	State of Pollution	mCd	State of Pollution	Eri	State of Pollution	RI	Ecological Risk
<1	No enrichment	<1.5	Zero to the very low degree of contamination	<40	Low	<150	Low
1–2	Deficiency to minimal enrichment	1.5–2	Low degree of contamination	40–80	Moderate	150–300	Moderate
2–5	Moderate enrichment	2–4	Moderate degree of contamination	80–160	High	300–600	High
5–20	Significant enrichment	4–8	High degree of contamination	160–320	Serious	>600	Very high
20–40	Very high enrichment	8–16	Very high degree of contamination	>320	Severe
>40	Extremely high enrichment	16–32	Extremely high degree of contamination
		≥32	Ultra-high degree of contamination

; [43]).

3.5.2. Degree of Contamination

The contamination factor (C_f) defined by [50] is proposed by dividing the concentration of each element in the sediment sample by the background concentration (UCC). The modified degree of contamination (mC_d) was proposed by [51] and consists of seven classes (Table 1) for an overall assessment of sediment pollution.

$${\mathrm{C}}_{\mathrm{f}}=\frac{{\mathrm{C}}_{ \mathrm{metal}}}{{\mathrm{C}}_{ \mathrm{background}}}$$

(2)

$${\mathrm{mC}}_{\mathrm{d}}=\frac{{\sum }_{\mathrm{i}=1}^{\mathrm{n}}{\mathrm{C}}_{\mathrm{f}}^{\mathrm{i}}}{\mathrm{n}}$$

(3)

3.5.3. Potential Ecological Risk Index

The potential ecological risk index (RI) is a measure of contamination levels based on the adverse ecological impact of each potentially toxic element [52]. It is calculated using Equations (4)–(6) as follows:

$${\mathrm{Cf}}^{\mathrm{i}}=\frac{{\mathrm{C}}_{\mathrm{sample}}^{\mathrm{i}}}{{\mathrm{C}}_{\mathrm{background}}^{\mathrm{i}}}$$

(4)

$${\mathrm{Er}}^{\mathrm{i}}={\mathrm{Tr}}^{\mathrm{i}}\times {\mathrm{Cf}}^{\mathrm{i}}$$

(5)

$$\mathrm{RI}=\sum _{\mathrm{i}=1}^{\mathrm{n}}{\mathrm{Er}}^{\mathrm{i}}$$

(6)

In these equations, the contamination factor (Cfⁱ) represents the concentration of each element in the sample relative to the background level. The toxicity coefficient (Trⁱ) of a particular element indicates the relative harm it poses, with Cd, As, Pb, Ni, Cu, Cr, and Zn having coefficients of 30, 10, 5, 5, 5, 2, and 1, respectively [52]. Higher toxicity coefficients indicate greater harm caused by the potentially toxic element due to its higher toxicity, persistence, and bioaccumulation in ecosystems [53]. Erⁱ represents the potential ecological risk of each PTE as determined by [50]. Five categories are defined for Erⁱ, and four categories are defined for RI, as shown in Table 1.

3.5.4. Cluster Analysis

Cluster analysis (CA) is a statistical method commonly used in identifying groups of samples that exhibit similar behavior [54,55]. To determine the degree of similarity between various elements and particle size fractions present in the surface sediments of the northeastern part of the Persian Gulf, we utilized the multivariate statistical package analytical software (MVSP 3.1). In our study, we employed the weighted pair group method and Pearson’s correlation coefficient since these widely used methods are effective in identifying clustering tendencies [27,55,56]. By utilizing these methods, we created a cluster tree by joining alternatives of the same weight to form larger clusters.

4. Results and Discussion

4.1. Sediments Texture

The surface sediments in the study area are soft and have not undergone diagenesis, likely due to their young age [40]. These sediments appear gray in color and were deposited in water with a pH greater than 7, as determined by physicochemical analysis.

Table 2. Descriptive statistics for major and trace elements, textural properties, mean enrichment factors (EF), mean contamination factor (Cf), and potential ecological risk associated with these elements and metals in bottom sediments located in the northeastern Persian Gulf. The contents of these elements and metals in Upper Continental Crust and Earth’s shale are also included for comparative purposes.

	Min	Max	Mean	SD	C.V. (%)	UCC 1	Shale 2	EF	CF	Er
Ca (%)	0.24	31.09	18.17	7.45	41	3.00	2.2	91.2	8.3
Al (%)	0.11	5.79	2.52	1.59	63	8.04	8.0
Fe (%)	0.09	21.14	2.18	2.30	106	3.50	4.7	4.3	0.6
Sr (mg/kg)	71	3550	1288	755	59	350	300	43.5	3.7
Mn (mg/kg)	13	3122	387	374	97	600	850	2.4	0.5
Ba (mg/kg)	2	3436	142	327	230	550	580	1.8	0.3
Cr (mg/kg)	2	228	70	45	65	85	90	3.0	0.8	1.7
Ni (mg/kg)	2	130	50	34	68	50	68	3.2	1.0	5.0
V (mg/kg)	1	142	41	26	64	110	90	1.8	0.5
Zn (mg/kg)	1	437	34	39	115	71	95	1.4	0.4	0.4
Cu (mg/kg)	1	278	13	24	178	25	45	1.1	0.3	1.5
Pb (mg/kg)	1	145	9	14	146	16	20	3.7	0.5	2.3
Co (mg/kg)	1	18	8	4	53	17	19	1.5	0.5
As (mg/kg)	1	14	4	2	54	2	13	14.6	2.7	27.3
Mo (mg/kg)	0.2	12.5	0.9	1	138	1.5	2.6	7.5	0.6
Cd (mg/kg)	0.06	1.53	0.20	0.15	75	0.10	0.30	3.7	0.7	20.4
Gravel (%)	0.0	51.7	3.9	8.8	222
Sand (%)	0.3	99.9	41.9	31.5	75
Silt (%)	0.0	69.9	32.1	21.7	67
Clay (%)	0.0	69.6	21.9	17.4	79

¹ Upper Continental Crust (UCC; [42]). ² Average contents in the Earth’s shale [57].

presents the sand content, ranging from 0.3% to 99.9%, with an average value of 41.9%. Based on Folk’s classification [43], more than 50% of the sediments consist of mud (silt and clay) particles, while sand-sized particles, primarily composed of skeletal fragments (such as benthonic and planktonic shells of carbonate composition), constitute one-third of the total bed sediments. The analysis categorized 75% of bed sediments into four major types, namely slightly gravelly sandy mud, slightly gravelly mud, slightly gravelly muddy sand, and slightly gravelly sand (Figure 2). Sedimentological studies reveal that gravel-sized sediments are mainly composed of skeletal and rock fragments. In order to provide a comprehensive understanding of the textural properties of the bottom sediments in the northeastern Persian Gulf, GIS techniques were employed to generate several interpolated maps. Figure 3 illustrates the accumulation of coarse materials such as gravel and sand in the east and west regions of the study area. This observation may be attributed to the prevailing current velocities in those areas.

Sample A-271, which represents group A in Figure 4, is located in the northeast of Qeshm Island. The sediment sample’s granulometric curve indicates a dominance of sand particles. The rock fragments present in the sedimentary basin vary between 8% to 22% in different fractions. Quartz is the most abundant mineral in this sediment sample, indicating that marine currents carried these particles from the Gulf of Oman and beaches around rivers such as Kol and Shur Rivers and deposited them in the study area. Therefore, it can be concluded that the main source of sediment in this group is detrital in nature. Calcite is also relatively abundant, suggesting that the sediment has both detrital and chemical origins.

Sample L-SL-1, which represents group B in Figure 4, is located near Larak Island. The sediment sample’s granulometric curve also indicates a dominance of sand particles. The rock fragments constitute only 3% of the 125 μ fractions. Calcite is the most abundant mineral in this sediment sample and can be related to chemical and biogenic sources. Quartz is relatively abundant after calcite, and the presence of quartz, feldspar, and clay minerals supports the idea that the part of sediment has a detrital origin.

Based on the granulometric curve, statistical parameters, and components of sediments analyzed under a binocular microscope, two main groups of sediments can be identified in the study area. The first group (A) consists of coarse-grained sediments of biogenic origin with tiny detrital particles, composed mainly of shell fragments. The large size of these sediments in the Persian Gulf belongs to shells with biogenic sources. The second group (B) belongs to mixed fine and coarse-grain, bimodal or trimodal sediments with more than one source, including detrital, chemical, biogenic, and wind origins. These sediments contain siliciclastic minerals such as quartz, feldspar, rock fragments, and clay minerals. Additionally, chemical carbonate precipitated from seawater and biogenic sediments are present.

4.2. Variations of Elemental Composition

Table 2 presents the descriptive statistics for the concentrations of major elements and trace metals, as well as the textural properties of bottom sediments in the northeastern Persian Gulf. The statistical parameters reported in Table 2 include the mean, maximum, minimum, standard deviation, and average contents in the Earth’s shale, as reported by [57].

The major and trace elements present in the sediments (Table S1) were ranked in descending order as follows: Ca > Al > Fe > Sr > Mn > Ba > Cr > Ni > V > Zn > Cu > Pb > As > Co > Mo > Cd. The average concentrations of Ca, Sr, As, and Cd exceeded the upper continental crust (UCC) values. These results indicate that calcium (Ca) is the most abundant element present in the bottom sediments of the northeastern Persian Gulf, with a concentration range from 0.24 to 31.09 percent mg/kg and a mean value of 18.17 percent mg/kg. Aluminum (Al) is the second most abundant element, but significant differences were observed between the mean concentration of Al in the marine sediment of the study area and the corresponding mean values for shale and crust. The concentration of strontium (Sr) varied from 71 to 3550 mg/kg, with a mean value of 1288 mg/kg. Notably, there is a remarkable difference between the mean concentration of Ba in the sediments of the study area and the corresponding UCC values (Ba is remarkably lower).

The coefficient of variation (C.V.) is the ratio of the standard deviation to the mean. The higher the coefficient of variation, the greater the level of dispersion around the mean. It is generally expressed as a percentage. Fe, Ba, Zn, Cu, Pb, and Mo had C.V. greater than 100%, indicating considerable variability [58] in the concentrations of these elements. The lowest coefficient of variation (C.V.) belongs to Ca, indicating less variability in the concentrations of calcium in the study area.

To better visualize the concentrations of major elements and trace metals, GIS techniques were employed to generate a series of interpolated maps (Figure 5). The distribution maps of calcium and aluminum indicate that the islands of Kish, Lavan, Faro, Beni Faro, Hengam, and Hondurabi in the Persian Gulf are dominated by carbonate sediments. This inference is supported by the high levels of calcium and low levels of aluminum in these areas.

4.3. Assessment of Sediment Contamination

4.3.1. Enrichment Factor

The results indicated that Ca and Sr had the highest mean EF values, suggesting that they belong to the extremely high enrichment class (Table 2). However, it should be noted that the presence of these elements in high concentrations does not necessarily indicate anthropogenic pollution, as they can naturally occur in sediments as a result of geologic and biochemical processes. Extremely severe enrichment was observed for Ca and Sr, while As and Mo exhibited significant enrichment based on their mean EF values. Fe, Pb, Cd, Ni, Cr, and Mn were found to belong to the moderate enrichment class. Finally, Ba, V, Co, Zn, and Cu displayed EF values less than two, indicating deficiency to minimal enrichment.

4.3.2. Modified Degree of Contamination

The results of the modified degree of contamination (mC_d) values indicate that, except for three stations, all other sites fall under the category of zero to very low degree of contamination, based on the classification proposed by [50]. The remaining three stations belong to the Low degree of contamination category. Among the sampled stations, the highest mC_d values were recorded at Stations Q-R-1 (2.62) and S-252 (1.52).

4.3.3. Potential Ecological Risk Index

The potential ecological risk index (RI) of bottom sediments in the northeastern Persian Gulf was assessed based on the presence of studied potentially toxic elements. Results showed that the potential ecological risk (Erⁱ) exhibited a decreasing order as follows: As > Cd > Ni > Pb > Cr > Cu > Zn, with As being the main contributor to the RI. Specifically, As and Cd accounted for 47% and 35%, respectively, of the Eri index in bottom sediments of the northeastern Persian Gulf. The average potential ecological risk values for all elements were lower than 40 (as shown in Table 2), indicating a low potential ecological risk. The samples had an average potential ecological risk index (RI) value of 46, suggesting that they can be characterized as having a low ecological risk.

4.4. Statistical Analyses

The resulting dendrogram (Figure 6) provided us with detailed information on the similarities between these clusters, enabling us to better interpret data. The highest correlation coefficients were observed between Zn-Cu (0.95), Al-Ni (0.92), Cr-V (0.89), and Zn-Pb (0.88). The UPGMA analysis of the dendrogram revealed several significant clusters with strong correlations: (A) Al-Ni-Cr-V; (B) Cd-Cu-Zn-Pb; (C) Ba-Fe; (D) silt-clay; (E) Ca-Sr.

The concentration of Cr, Ni, and V in the area is partly from geogenic sources, as confirmed by their high correlation with aluminum. Furthermore, the low levels of these elements in the sediments around the islands can be attributed to a relatively lower amount of detrital sediment input. This leads us to believe that the origin of these particular elements in the sediments of the Persian Gulf is predominantly geogenic in nature. However, there are also some amounts of these elements that have a secondary anthropogenic origin. These results are consistent with previous research by [2] who found high similarity coefficients between Ni, Cr, and Total Petroleum Hydrocarbons in sediment from Mahshahr Bay in the northwest Persian Gulf. Other studies suggest that some of these elements in the mangroves located in the northwest Qeshm and Asalouye region may have a partly anthropogenic origin [59].

Cu, Zn, Pb, and Cd also showed a relatively high correlation coefficient indicative of a common origin. The next cluster, consisting of Ca-Sr-Sand, showed a relatively low correlation compared to the previous ones. Thus, Ca and Sr that accumulated in coarse sediments most likely have biogenic sources. As mentioned above, calcite is the most abundant sediment mineral related to chemical, biogenic, and detrital sources. Lastly, a strong negative correlation coefficient between Al and Ca showed that Al has a non-carbonate source.

Notably, no strong correlation was found between As and other elements. The significant enrichment of As suggests that it likely originated from a different source. The same argument can be done for Mo. The distribution map of arsenic and molybdenum clearly indicates that the elevated concentrations of these elements in the northeast section of the study area are closely linked to the presence of numerous industries in Bandar-e-Abbas and Qeshm cities, as shown in Figure 1. Previous studies have recorded high amounts of arsenic in dust particles in Iran [60]. Therefore, it is possible that some of the high concentration of arsenic may have originated from wind.

5. Conclusions

The Persian Gulf is a globally significant body of water that plays a vital role in maintaining the ecological balance of the region. In recent years, there has been growing concern about the impact of human activities on the Gulf, and particularly on the bottom sediments in Iranian territorial waters located in the northeast region. To address this concern, this study presented a comprehensive analysis of sediment texture, geochemical variation, potential sources, and ecological risk assessment of major elements and trace metals in the bottom sediments of Iranian territorial waters situated in the northeast Persian Gulf region.

The samples underwent an analysis utilizing granulometric curve, statistical parameters, and binocular microscope components, which resulted in the identification of two distinct sediment groups. The first group was composed of coarse-grained sediments of biogenic origin, primarily consisting of shell fragments with small detrital particles. The second group included mixed fine and coarse-grain, bimodal or trimodal sediments originating from multiple sources, such as detrital, chemical, biogenic, and wind origins. These sediments contained siliceous minerals like rock fragments, quartz, feldspar, and clay minerals. Additionally, they featured chemical carbonate precipitated from seawater and biogenic sediments.

Additionally, calcium is the most abundant element present in the bottom sediments, followed by aluminum and iron. Arsenic and molybdenum exhibit extremely high enrichment, while iron, lead, cadmium, nickel, chromium, and manganese belong to the moderate enrichment class. Other elements were classified as deficient to minimal enrichment (Ba > V > Co > Zn > Cu). Stations were classified as having a low degree of contamination based on modified degree of contamination values.

The distribution maps of calcium and aluminum in the Persian Gulf suggest that carbonate sediments dominate around several islands in the region. The low levels of Cr, Ni, and V around these islands imply that the origin of these elements in the sediments is predominantly geogenic. On the other hand, the distribution map of arsenic and molybdenum shows high concentrations of these elements in the northeast section of the study area, which can be attributed to industrial activities in Bandar-e-Abbas and Qeshm cities. As previous studies have recorded high amounts of arsenic in dust particles in Iran, it is possible that some of the elevated concentration of arsenic may have originated from wind transport. The findings of this study provide valuable information for continued research in this ecologically sensitive region, particularly regarding the potential sources of pollution and their impact on the marine ecosystem.