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Separation of heavy metals using sequential extraction of heavy metals and determination of pollution indices in the Sirvan River sediments (Sanandaj)
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Maryam Rezaei1   , Hassan Nasrollah Zadeh Saravi1 , Hourieh Younesipour1 , Sharareh Firouz Kandian1 , Ahad Ahmad Nejhad1 |
| 1- Caspian Sea Ecology Research Center (CSERC), Iranian Fisheries Science Research Institute (IFSRI), Agricultural Research, Education and Extension Organization (AREEO), Sari, Iran & - |
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Abstract: (16 Views) |
Introduction
In recent decades, a broad spectrum of environmental pollution issues have arisen as by-products of enhanced and magnified human activities (Sener et al., 2023). Heavy metals, due to their strong physiological toxicity and non-degradability, pose a significant threat to environmental security and the health of humans (Zarei et al., 2023). Sediments, which are sinks of heavy metals in rivers, continuously discharge these highly toxic elements into surface waters due to their high metal transfer capacity (Kang et al., 2023). The ionic nature of heavy metals, mineral material content and size of particles in sediments, and adsorption intensity of the metals are important characteristics governing their distribution in sediments (Das et al., 2023). The Sirvan River, where the city of Sanandaj and surrounding industries are located, has a wealth of urban and industrial wastewater often pouring into the river without any treatment or exposure to environmental laws (Mashanir Electrical Engineering Services Company, 2018). Metals tend to have diverse physical and chemical properties regarding chemical reactions, toxicity, transport, and bioavailability. This reinforces the need to conduct chemical fractionation studies to ascertain the source and nature of bonding between heavy metals and sediments (Kang et al., 2017). Sequential extraction of sediments, which was conducted in five successive steps, separates resistant fractions (exchangeable, iron and manganese oxides, and organic matter), representing the product of anthropogenic metal input, from the resistant fraction (residual) responsible for the natural presence of metals in the Earth's crust (Zakir et al., 2008). Xue et al. (2023) analyzed heavy metals Zn, Cu, Cr, Cd, Ni, and Pb in sediments of the Weihe River in China. They identified the mean concentrations of As, Pb, Zn, Ni, Cr, Hg, Cu, and Cd as 15.42, 27.27, 88.05, 31.05, 75.00, 0.13, 29.47, and 1.05 mg/kg, respectively. Environmental pollution was assessed with the geo-accumulation index. Khalili et al. (2020) compared heavy metals within sediments in Haraz River with the Pollution Load Index (PLI) and the Geo-accumulation Index (Igeo). They concluded that the PLI values in summer were below one, indicating low or no sediment pollution, and PLI values in winter were above one, indicating sediment pollution in the Haraz River. The present study was conducted to determine the total, resistant, and non-resistant levels of heavy metals Zn, Cu, Ni, Pb, and Cd and to assess pollution indices in sediment samples collected from six stations in the Sirvan River of Sanandaj in summer and winter of 2023-2024.
Methodology
Sediment sampling was carried out in the Sirvan River (Gavehroud and Qeshlaq branches) at six stations. A sediment sample was collected from each station by Van Veen grab sampler in this study. In the preparation of the samples, the sediment samples were freeze-dried using a freeze dryer under a cold condition. The toxic heavy metals Zn, Cu, Ni, Pb, and Cd were analyzed using the sequential extraction procedure (Tessier et al., 1979). There are five steps in the Tessier procedure: steps 1 to 3 are the non-resistant fractions, step 4 is the resistant fraction, and step 5 is the total concentration in the sequential extraction procedure. The metals were analyzed quantitatively by Atomic Absorption Spectroscopy with flame and graphite furnace systems (D2 Thermo M5, Electron Corporation AA Series Model) in the Instrumental Analysis Laboratory of the Caspian Sea Ecology Research Institute (APHA, 2017). A control sample was taken and added to the device along with all samples. Data were normalized through the application of SPSS software version 18, and analysis of variance (ANOVA) was employed to find the difference in mean metal content over different seasons. T-test was used to find the comparison between mean metal content in resistant and non-resistant fractions (Nasiri, 2009). In addition, heavy metal pollution indices in Sanandaj Sirvan River sediments, including the Müller Geochemical Accumulation Index (Igeo), Contamination Factor (CF), Contamination Degree (CD), and Pollution Load Index (PLI), were calculated.
Results
The bioavailable fraction is the percentage of heavy metals that, in the most favorable reduction and pH conditions, can be released and become available to organisms for causing toxicity (Sundaray et al., 2011). Exchangeable fraction is directly absorbed by aquatic organisms, while the carbonate, reducible, and oxidizable fractions can be mobilized from sediments during environmental changes such as pH, temperature, redox conditions, and salinity shifts (Wang et al., 2015; Ma et al., 2016; Huang et al., 2017). Overall, during the summer and winter of the year (2023–2024), the mean levels of the studied metals in the resistant fraction (natural sources) were higher compared to the non-resistant fraction (anthropogenic sources). This implies that the sources of heavy metals such as Zn, Cu, Ni, and Pb are predominantly natural and geochemical with minimal contribution from human activities. Cd level during summer was higher in resistant fraction (anthropogenic sources) than in resistant fraction (natural sources), while during winter, it was nearly similar in both fractions. Besides this, the trend of average concentrations in both the resistant and non-resistant fractions was also identical in all seasons: Zn was more concentrated, and Cd was least among metals being investigated. Igeo values for Ni indicated a pollution class of zero, i.e., "unpolluted.". Zn, Cu, and Pb were assigned to pollution class one, which is an "unpolluted to moderately polluted" status. Cd, however, was assigned to pollution class four, which is a "heavily polluted" status. The results also revealed that Ni had the lowest value of Contamination Factor (CF) and Cd had the highest CF value. Similarly, Cd exhibited the highest Contamination Degree (CD) and the lowest was that of Ni. On the basis of Pollution Load Index (PLI), the total metal concentration was highest in winter, and the non-resistant metal proportion in summer was lowest. Statistical comparison by ANOVA revealed a significant difference between the mean total metal concentration in the summer and winter months (p< 0.05). There was no difference observed in the mean concentrations within stations one to six (P > 0.05). Further, a statistical difference (p<0.05) was observed between the non-resistant and resistant fractions of the discussed metals based on the t-test.
Discussion and conclusion
In the current study, sequential extraction method was used to study the natural and anthropogenic sources of metallic elements Zn, Cu, Ni, Pb, and Cd in the sediments of the Sirvan River. Environmental chemical conditions, emerging pollutants, and physical parameters are the most important influences on local sediments' heavy metal pollution (Zhang and Wang, 2020). Analysis of the total concentrations of the non-essential metals Pb and Cd in the different stations and seasons revealed that Pb registered the maximum mean concentration of the non-essential metals, particularly during winter. Anthropogenic inputs like boat traffic and urban, industrial, and agricultural wastewater discharge are primarily responsible for the elevated concentrations of Pb in the sediments (Vieira et al., 2016). Seasonal analysis of heavy metals during summer and winter sediments of (2023–2024) indicated that, excluding Cd, the residual fraction of Zn, Cu, Ni and Pb was significantly larger than others. It reflects their source is mainly natural and geochemical in origin instead of having minimal anthropogenic input. The residual fraction, due to its silicate complexation, will be environmentally stable under variable conditions and will not be bioavailable to aquatic life (Moore et al., 2015). Conventional methods are unable to detect and differentiate this contamination fraction. Therefore, in order to assess pollution and study the bioavailability of heavy metals to biological systems, it is not sufficient to strive for measurements on total concentration alone. Based on the indices of contamination, Contamination Factor (CF), Contamination Degree (CD), and Pollution Load Index (PLI), Sirvan River sediments are exposed to heavy metal pollution at low to high levels. The Igeo indicated that the heavy metals under investigation ranged from unpolluted to highly polluted conditions. Generally, semi-essential and essential components (Zn, Cu, and Ni) and non-essential component (Pb) in Sirvan River sediments are not believed to be very hazardous on average. However, Cd with the highest figures in all the indices and reflecting high human impact in the region may have deleterious effects on organisms in the study area. From the location of the study area and the diversity of land uses particularly urban, industrial, and agriculture, it is evident that the region undergoes various types of pollution, e.g., river sediment pollution with heavy metals. Therefore, efficient prevention, control, and reduction management plans for heavy metal contamination of sediments must be carried out. Estimation of the level of pollution of agricultural lands around the Sirvan River, nearby industries, and urban sewage networks will be helpful in avoiding the entry of heavy metals into the food chain and reducing the level of contamination in these areas. Generally, the Sirvan River sediments are not critical regarding heavy metal pollution by Zn, Cu, Ni, and Pb. However, the high values of Cd's Contamination Degree (13.35) and Contamination Factor (20.60) indicate a significant role of human activity in contaminating and accumulating the metal in regional sediments.
Conflict of Interest
The authors declare that they have no conflict of interest
Acknowledgment
This research was supported by the Iranian Fisheries Science Research Institute (Ministry of Agriculture Jihad). We should acknowledge the necessity of thanking the staff of the Ecology Department of the Caspian Sea Ecology Research Center for their assistance in sampling and sample analysis. |
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| Keywords: Heavy metals, Sediments, Resistant and Non-Resistant Fractions, Pollution Index, Sirvan River, Kurdistan. |
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Full-Text [PDF 1096 kb]
(7 Downloads)
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Type of Study: Research |
Subject:
آلودگي محيطهاي آبي
Received: 2025/10/1 | Accepted: 2025/12/31
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