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Volume 33, Issue 6 (2-2025) |
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Correlation between microplastic pollution and potentially toxic elements in the sediments of the Southwestern Caspian Sea Coastline
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Fereshteh Haji Aghaei Ghazi Mahalleh   , Javid Imanpour Namin1 |
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Abstract: (252 Views) |
Introduction
Microplastics (MPs) have garnered significant attention due to their widespread presence in the environment and the potential threats they pose to aquatic organisms (Wang et al., 2021). These particles, smaller than 5 millimeters, are classified into primary and secondary types. Primary microplastics are manufactured in micrometer sizes for use in various industries, including aerospace, medicine, and cosmetics (Alomar et al., 2016). In contrast, secondary microplastics are formed from the breakdown of larger plastic debris into smaller particles (Duis and Coors, 2016). Microplastics readily accumulate in aquatic environments and, due to their resistance to degradation, are dispersed globally (Wang et al., 2021). These particles can adversely affect aquatic organisms due to their physical and chemical properties, leading to disturbances in feeding, reproduction, and immune functions (Oliviero et al., 2019). Additionally, microplastics can adsorb pollutants such as heavy metals, exacerbating their harmful effects on aquatic ecosystems. This combination presents a significant threat to marine life health (Prunier et al., 2019). Furthermore, microplastics provide a substrate for microorganisms, facilitating the formation of biofilms. These biofilms can alter the physical and chemical properties of microplastics, influencing their ability to adsorb contaminants (Tu et al., 2020). The objective of this study is to examine the correlation between microplastic pollution and potentially toxic elements in the sediments of the southwestern Caspian Sea coast and assess their impacts on the region marine ecosystem.
Methodology
The Caspian Sea, the largest enclosed lake in the world, is significantly impacted by human activities such as oil and gas extraction, agriculture, and industrial development. Rivers such as the Volga, Kura, and Ural transport pollutants, including heavy metals, to the sea, posing a threat to the ecosystem, particularly along the southwestern coast (Efendieva, 1994; Simonett, 2006). Sediment sampling was conducted at three polluted stations in Kiashahr, Anzali, and Astara (Kostianoy et al., 2005). Sediment sampling was performed in the spring of 2022 using Van Veen grabs (20×20 cm) with three replicates at each statio (Claessens et al., 2011; Löder and Gerdts, 2015). After being transferred to glass bottles and sent to the laboratory. Microplastic extraction from sediments involves two essential stages. In the first stage, the organic materials in the sediments were digested using hydrogen peroxide (H2O2, 30%). The digestion time varies between 1 and 10 days, depending on the type and amount of organic material (Erkes-Medrano et al., 2015; Zhang et al., 2016). After digestion, the samples were dried at 60°C for 48 hours (Vianello et al., 2013). In the second stage, density separation was used to extract the microplastics. In this step, 100 g of dried sediment was placed in a glass beaker, and 800 mL of saturated NaCl solution (293 g/L) was added (Thompson et al., 2004). After shaking for five minutes, the beaker was left to stand for 45 minutes to allow the high-density particles to settle. The resulting supernatant, containing the floating particles, was filtered through a nitrocellulose filter (Hidalgo-Ruz et al., 2012; Wagner et al., 2014; Duis and Coors, 2016). This process was repeated three times, and the filters were dried at 60°C (Law et al., 2010). Finally, the microplastic particles were examined and counted using a 40x magnification loop, and the number of microplastic particles per gram of dry sediment was reported (Reddy et al., 2006; Morét-Ferguson et al., 2010). The polymer types of the extracted microplastics were identified using FT-IR spectroscopy with ATR, analyzing spectra in the 400-4000 cm⁻¹ range and comparing characteristic peaks with standard polymer databases (Veerasingam et al., 2021). Data analysis was performed using SPSS version 27. The Kolmogorov-Smirnov test was used to check for normality, and to compare pollution levels across stations, ANOVA and Kruskal-Wallis tests were applied. To examine the correlation between microplastic pollution and potentially toxic elements, Pearson and Spearman correlation coefficients were used. All analyses were conducted at a %95 confidence level. Graphs were plotted using Excel 2022.
Results
The average concentration of elements at the three stations revealed that the highest and lowest average concentrations of elements in the sediment were for manganese (Mn) with 760661.80±53.41 µg/kg dry weight at the Anzali station and cadmium (Cd) with 41.44±1.93 µg/kg dry weight at the Astara station. The results of the Kolmogorov-Smirnov test for the distribution of potentially toxic elements in the sediment samples from the stations indicated that some elements did not follow a normal distribution (p˂0.05). To compare the average concentrations of elements across the stations and examine the correlation between elements, parametric tests (one-way analysis of variance and Pearson correlation coefficient) were used for normally distributed data, while non-parametric tests (Kruskal-Wallis and Spearman correlation coefficient) were employed for non-normally distributed data. One-way analysis of variance (ANOVA) results for comparing the average concentration of elements across the stations showed that manganese and zinc had significant differences at all stations (p˂0.05). The cadmium element showed no significant difference between the Kiashahr and Astara stations, but significant differences were observed between Kiashahr and Anzali, as well as Anzali and Astara stations (p˂0.05). The Kruskal-Wallis test results also indicated significant differences for arsenic, cobalt, chromium, copper, iron, mercury, nickel, and lead among the stations (p˂0.05). The Anzali station, with 67±4 pieces per 300 grams of dry sediment, exhibited the highest contamination, while the Kiashahr station, with 45.33±2.30 pieces per 300 grams of dry sediment, showed the lowest contamination. One-way analysis of variance (ANOVA) revealed that the Anzali station had a significant difference when compared to both Kiashahr and Astara stations (p˂0.05). However, no significant difference was observed between the Kiashahr and Astara stations. The microplastics extracted from the sediment samples were categorized into two color groups: blue and red. At the Kiashahr station, red microplastics accounted for 53%, representing the highest abundance, while blue microplastics constituted 47%, representing the lowest abundance. At the Anzali station, blue microplastics were the most abundant, comprising 75%, while red microplastics represented the lowest abundance, constituting 25%. At the Astara station, red microplastics accounted for 53%, representing the highest abundance, while blue microplastics constituted 47%, representing the lowest abundance. A total of 496 microplastic pieces were extracted from the sediment samples at the three stations. All the extracted microplastics were fiber type. The microplastics found in the sediment samples were classified into seven categories: less than 0.5 mm, 0.5-1 mm, 1-2 mm, 2-3 mm, 3-4 mm, 4-5 mm and greater than 5 mm. At the Kiashahr station, the highest abundance of microplastics was found in the 4-5 mm range, followed by the 3-4 mm range. The lowest abundance was observed in the 1-2 mm particles. At the Anzali station, the highest abundance was found in particles larger than 5 mm, followed by the 4-5 mm range, while the lowest abundance was observed in particles smaller than 0.5 mm. At the Astara station, the highest abundance was found in particles larger than 5 mm, followed by the 4-5 mm range, while the lowest abundance was observed in the 1-2 mm particles. The extracted microplastics from the sediments of the southwestern Caspian Sea coast were identified using FTIR-ATR spectroscopy. Five different polymers were identified, including polyethylen (PE), polypropylene (PP), polyester, polystyrene (PS) and nylon. Overall, polyethylene was the dominant polymer in the extracted microplastics from the sediments.
The correlation analysis results between the abundance of microplastics and the concentration of potentially toxic elements in the sediments from the Kiashahr, Anzali, and Astara stations indicated no significant correlation between these two variables at the stations under study. Manganese, zinc, and cadmium had a normal distribution in all stations, thus Pearson's correlation coefficient was used to assess the correlation between microplastic pollution and potentially toxic elements. For other elements, whose data did not follow a normal distribution and successful normalization techniques were not applied, the Spearman correlation coefficient was employed.
Discussion and conclusion
In this study, the Anzali station exhibited the highest contamination, with an average of 67 ± 4 microplastic pieces per 300 grams of dry sediment. This finding is consistent with the study by Rasta et al. (2020) which reported a high concentration of microplastic contamination in the sediments of Anzali Wetland. All the microplastics extracted from the sediments in this research were of the fiber type, with blue being the most dominant color, accounting for 58%. Similar results were found in the study by Zhang et al., (2020) in the Shengsi region of China, where fiber-type microplastics were the most abundant, with blue identified as the predominant color. Microplastics at the Kiashahr station were most abundant in the 4-5 mm size range, while the Anzali and Astara stations exhibited the highest abundance in microplastics larger than 5 mm. Similar findings were reported by Kühn et al., (2018) on the coasts of the Netherlands, where microplastics in the size range of 500-2000 micrometers were predominant. In this study, no significant correlation was observed between microplastics and the concentration of elements in the sediments. This lack of correlation may be attributed to differences in the sources of microplastics and elements, the physical and chemical properties of these pollutants, and the varying environmental conditions (Napper and Thompson, 2016). Finally, it can be concluded that the Anzali station has the highest microplastic pollution, primarily composed of fiber type and secondary microplastics, with blue being the predominant color. Anthropogenic sources, such as laundry runoff, fishing gear, and the release of plastic packaging by tourists, contribute to the spread of this pollution in the marine environment. Correlation analysis revealed no significant relationship between microplastics and elements, likely due to differences in sources and the physical and chemical characteristics of these pollutants. A comparison of element concentrations with global standards indicates that the pollution levels are within safe limits; however, continued monitoring and management are crucial to mitigate pollution levels. |
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| Keywords: Caspian Sea, Microplastic, Potentially toxic elements, Sediments, Statistical correlation |
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Full-Text [PDF 1054 kb]
(50 Downloads)
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Type of Study: Research |
Subject:
آلودگي محيطهاي آبي
Received: 2025/02/2 | Accepted: 2025/02/28 | Published: 2025/03/17
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Haji Aghaei Ghazi Mahalleh F, Imanpour Namin J. Correlation between microplastic pollution and potentially toxic elements in the sediments of the Southwestern Caspian Sea Coastline. isfj 2025; 33 (6) :27-47 URL: http://isfj.ir/article-1-2864-en.html
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