Introduction
Today, considerations related to the protection and prevention of marine environment pollution are vital for the marine environment planning of most countries. Among the main sources of pollution in the Oman Sea, the activities related to chemical industries and the presence of oil and gas reserves are important (Uddin et al., 2021). Benefiting from these reserves has caused the marine ecosystem to release petroleum compounds in various stages of drilling activities, construction of oil facilities, exploration, extraction and refining, loading and handling operations (Zahedi, 2016). The entry of chemical pollutants is also through the release of effluents from coastal chemical industries and desalination plants, which depending on the type of operation, contain inorganic and organic compounds with a long half-life, and high bio-accumulation property, and affect the health of the aquatic and human consumers (Bashir et al., 2020). In this regard, understanding the state of pollutants in marine ecosystems and the ecological health of marine waters and the health of aquatic consumers is essential. Also, following the process of environmental changes and creating the basic information needed in the plans and processes of the fishing activities development, is very important. In this regard, the current research was conducted to determine the status and ecological risk of heavy metals (Pb, Cr, Cd, Ni, V, and Fe) and total petroleum compounds (TPHs) in the sediments of Jask Bay, in the west of the Hormozgan province.
Methodology
Surface sediment samples were collected in spring and winter of 2023 and from 24 stations located in the western and eastern parts of Jask Bay. Extraction of petroleum components from dried sediments was performed with a 50:50 mixture of hexane and dichloromethane solvents and using a microwave radiation device (Ethos Plus model). The concentration of total petroleum hydrocarbons was determined using the ultraviolet fluorescence method (UVF) by wavelengths of excitation 310 nm and emission 360 nm and calculated according to the dry weight of the sediment (MOOPAM, 2010). Heavy metals were measured by chemical digestion with a mixture of nitric acid and hydrochloric acid (MOOPAM, 2010) under Ethos1 model laboratory microwave conditions and instrumental analysis using an atomic absorption spectrophotometer (KSL-AA320 model). The ecological risk caused by TPHs was evaluated using standard sediment quality indices (SQGs) and contamination factor (CF) (Massoud et al., 1996). The Ecological risk of heavy metals was studied by pollution factor (CF), pollution degree (CD), pollution change degree (MCD), pollution loading index (PLI), potential ecological risk index (PERI) and accumulation-land index (Igeo) (Sharifnia et al., 2018, Tomlinson et al., 1980, Hakanson, 1980). The normality of pollutant concentrations was determined using the Kolmogorov-Smirnov test. Parametric tests (Tukey's posthoc, One-Way ANOVA, F coefficient, and t-test) were used for parameters with normal distribution and non-parametric tests (Kruskal-Wallis, chi-square (χ2), Mann-Whitney) were applied for non-normal parameters.
Results
The total average concentration of TPHs in sediments from the eastern part of Jask Bay was 0.53±0.24 μg/kg dry weight, ranging from a minimum of 0.2 to a maximum of 1.07. In the western area of Jask Bay, the range of change was more limited (from 0.05 to 0.33 μg/kg dry weight) with an average of 0.2±0.09. The overall average of TPHs for Jask Bay sediments in the spring season was measured as 0.37±0.24 μg/kg dry weight. The sediments of the western and eastern parts of Jask Bay in winter showed a lower range of changes in TPHs concentration with a minimum of 0.09 to a maximum of 0.35 μg/kg and the overall average was 0.18±0.07 μg/kg of dry weight. The calculated toxicity indices and pollution coefficient for TPHs showed that the PELq values were much lower than 0.1, which means the absence of adverse biological effects. The calculated pollution factor was less than one with the range of 0.01 to 0.72.
No significant difference was observed in the concentration of cadmium in each season between the western and eastern parts of Jask Bay (p>0.05) and average cadmium concentration in spring and winter seasons was measured as 0.54 ± 0.06 and 0.29±0.04 μg/kg, respectively. These values were 6.77±2.6 and 6.45±2.22 µg/kg for Pb in spring and winter, respectively. Ni in spring and winter had total averages of 34.16±3.6 and 34.48 ±4.92 μg/kg, respectively. In spring, the concentration of chromium in the eastern part of the bay with an average of 28.69 ± 2.3 was lower than the western part with an average of 36.68 ± 5.4 μg/kg (p<0.05). In the winter season, the average of 37.62±5.9 and 32.44±4.6 was recorded in the eastern and western parts, respectively. Fe in the western and eastern parts of the bay and also the sampling seasons did not have significant changes (p>0.05) and the range of concentration changes was measured from 1.16 to 1.37 μg/kg. In spring, the concentration of V in the eastern part (26.69 ± 13.4) was significantly lower than the western part (43.05±20.3) (p<0.05), but in winter the difference between eastern and western parts was not significant and the total average in this season was 41.28 ± 17.7 μg/kg.
Table 1 shows the results obtained from the calculation of ecological risk assessment indices of heavy metals. The accumulation-ground index (Igeo) with the highest value of 0.46 was measured for Cd.
Table 1: Values of toxicity index and pollution factor for TPHs in sediments of Jask Bay and comparison with standard values
| Contamination Factor |
Toxicity Index |
| Limited value |
Variation range in current study |
Limited value |
Variation range in current study |
|
CF <1
No effect |
0.01 - 0.72 |
PELq <0.1
No effect |
0 - 0.01 |
|
Discussion and conclusion
The results of the present study showed that the sediments of the eastern part of Jask Bay contain higher amounts of TPHs. The stations in the eastern part were closer to the coast and were less affected by surface currents, which may explain the relatively high TPHs concentration in this area (Ololade et al., 2009; Maktoof et al., 2014). The maximum measured concentration of total petroleum hydrocarbons in the dry sediments of Jask Bay is 1.07 μg/kg, which is substantially lower than the background concentration of 10 µg/g, and thus it can be concluded that TPHs concentrations in the sediments of the Jask Bay are within the background range and are unlikely to cause adverse biological effects. A review study of TPHs distribution in Persian Gulf sediments (Iraq, Iran, Kuwait, Saudi Arabia, Bahrain, Qatar, United Arab Emirates, and Oman) reported a range from 0.134 to 48018 μg/g dry weight, compared with the background concentration range of 10-15 µg/g as the background concentration in Persian Gulf sediments, it is clear that in some areas the concentration is significantly higher than the standard limits. Most of the places that had a high level of pollution were located near point sources such as oil facilities and ports (Uddin et al., 2021). As the results showed, most of the studied metals did not show significant differences between the western and eastern parts of Jask Bay. It has been reported that in the sediments from west of Hormozgan province, the range of Ni changes was from 21.24 to 27.83 μg/kg dry weight (Mortazavi et al., 2022). Cd concentration ranged from 1.24 to 1.3 and for Cr from 38.1 to 46.5 μg/kg (Mortazavi et al., 2022). For all elements, the reported values were higher than the concentrations measured in the present study. Cd in the western part of Jask Bay in spring had a pollution factor value of 2.06, which indicates the moderate pollution of sediments. Also, the accumulation-ground index (Igeo) confirmed that the sediments had been polluted with Cd. Some physicochemical characteristics of Cd, such as high accumulation in aquatic organisms and high toxicity potential, cause concern about ecological health (Mirzaei et al., 2020). High concentrations of Cd in Nakhilo Bushehr region (Arfaeinia et al., 2019), Chabahar Bay area (Agah, 2021), Strait of Hormuz (including Tiab, Lark and Hengam estuaries) (Mortazavi et al., 2022), coral reef islands of the Persian Gulf (Ranjbar et al., 2017), Khor Khamir and Tiab (Sharifinia et al., 2018), mangroves of Qeshm, Khamir and Khor Azini (Ghasemi et al., 2018) have also been reported. Cadmium is generally used in electroplating, pigments, plastic stabilizers and nickel-cadmium batteries, anti-fouling coatings, power stations, heating systems, and enters the marine ecosystem through sewage (Jumbe and Nandini, 2009). According to industrial and urban national development programs in Makran region, temporal and spatial monitoring of cadmium pollution in different environmental matrices, including water, sediment and biota is essential.
Conflict of Interest
The authors declare that they have no conflict of interest.
Acknowledgment
The authors would like to thank the Hormozgan Department of Environment for its cooperation in the analysis of oil pollutants.
Keywords
Oil pollution, Heavy metals, Jask Bay, Hormozgan, Oman Sea
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