Monitoring of heavy metal pollution by using populus nigra and cedrus libani

Abstract

Keywords: Biomonitor; cedrus libani; copper; lead; nickel; populus nigra.

Introduction

In recent years, heavy metals emanating from different anthropogenic sources have had a direct or indirect negative impact on the environment. As a result, atmospheric pollution has increased significantly [1, 2]. The prominent increase of heavy metals such as Cd, Ni, Cu, Cr, Zn, Pb, Al and Mn as principal air pollutants in the atmosphere causes significant dangers for the environment and human health in the long term [3–5]. Many heavy metals bind to sulfur, nitrogen, and other functional groups that are found in biomolecules and thereby, disrupt their functions [6]. Consequently, exposure of living things to these metals can result in DNA mutations, cell cycle malfunctions, neurological problems, liver and kidney damage, impairment of endocrine systems, cardiovascular dysfunction [7], tumor progression, or apoptosis with carcinogenic effects [8]. In many ecological systems, high levels of heavy metals can also degrade air and water quality, causing degradation of biodiversity and biota systems, thereby posing a severe threat to biodiversity [2, 9, 10]. Due to the effects of these pollutants on human health and the environment, it has become necessary to monitor and control them. In recent years, the use of biomonitors, as an alternative analytical procedure to other conventional procedures, for air quality monitoring has increased [2, 11, 12]. “Biomonitoring is known as the methodology that takes into account the use of living organisms to monitor and evaluate the impact of different contaminants in a known area” [2, 13]. Thus, information about levels of toxic metals in soil, water, and air can be obtained by analyzing the parts of biomonitor plants, such as root, stem, shell, and leaf [14]. This type of monitoring is relatively inexpensive and easy to implement; it is a viable alternative in the absence of infrastructure/tools for conventional air quality monitoring. The aim of this study was investigate whether and Cedrus libani plants can serve as useful bioindicators in monitoring heavy metal pollution occurring in the casting factory. This was evaluated by monitoring heavy metal pollution in Kırşehir province with these plant samples collected from the vicinity of casting factory (Casting factory station) and the region where there is no casting factory (Boztepe station). The levels of Ni, Pb, and Cu in the needles and leaves of the plants as well as in the soil samples were determined by using High Resolution-Continuum Source Flame Atomic Absorption Spectrometer (HR-CS FAAS). This is the first study monitoring the pollution caused by the casting factory in the central Anatolian region in Turkey. The study will contribute to the literature from this aspect.

Material And Methods

Chemicals and Apparatus Chemicals and reagents of analytical quality and high purity were used in all experiments in this study. The stan-

Figure 1. Geographical location of the study plant samples. dard stock solutions of the metals (1000 mg/L) were obtained from Merck (Germany). Calibration standards and aqueous working standards were prepared by diluting these stock solutions. All aqueous solutions were prepared with ultrapure water that had been obtained by Milli-Qwater purification system (Millipore, Corporation, MA, USA). Analytik Jena ContrAA Model 300 series High Resolution-Continuum Source Flame Atomic Absorption Spectrometer (GLE, Berlin, Germany) was used for the analysis of metals. All absorption lines of an element in the spectral range of 185–900 nm can be analytically evaluated by using a xenon (Xe) short-arc lamp as a continuum lamp in the HR-CS FAAS [15]. The working conditions of HR-CS FAAS for the analysis of the metals are given in Table 1. Samples and Analytical Procedure For Elemental Analyses The leaves and needles of plant species poplar () and cedar (Cedrus libani) were collected from Kirsehir city of Turkey (1; Boztepe station: 39°15’05.8”N 34°15’40.4”E; 2; CFS: 39°14’55.1”N 34°07’27.3”E; Fig. 1) during June and July. The identifications of plant species were performed by plant systematic expert at Kirşehir Ahi Evran University. The collected needle and leaf samples were taken from different parts of the trees and then the samples were mixed to ensure sample homogeneity. The samples were carried to the laboratory in plastic vessels and were thoroughly washed with tap water and ultrapure water to remove impurities. Thereafter, the samples were dried in an oven at 60°C (20–24 h) till a stable weight was attained.

Sigma J Eng Nat Sci, Vol. 39, Issue. 4, pp. 367–373, December 2021

Dried and homogenized samples weighing 0.50–1.50 g were transferred into a flask (Pyrex) and digested using the dry ashing method. For this, dried samples were heated in stages in an oven at 150°C for 15 min, 350°C for 15 min, 450°C for 10 min, and ashed at 500°C for 8 h, in sequence. A mixture of 2 mL of 65% concentrated nitric acid (HNO3) and 1 mL of 30% hydrogen peroxide (H2O2) were added to the ashed samples and evaporated to near dryness. This procedure was repeated until a clean sample was obtained. Subsequently, samples were cooled, 6.0 mL of 0.2 mol/L HNO3 was added and filtered (Fig. 2). Blank samples were also prepared using the same method [16]. Soil samples were taken from the places where these plant species were grown on the same date. Approximately 500 g soil samples were taken from the surface at a depth of 50–80 cm. These samples were brought to the laboratory in plastic nylon, dried in an oven at 75°C for 20–24 h, milled in a porcelain mortar, and passed through a 2-mm sieve (200 mesh). The acid extraction method as recommended by Environmental Protection Agency (EPA, Method 3050B) [17] for the decomposition of soil samples was used. 2.0 g of the powdered samples were weighed and transferred in 250 mL flask (Pyrex) for digestion. 10 mL of 50% HNO3 was added and heated to 95°C. Thereafter, the samples were cooled and 65% HNO3 was added until brown fumes disappeared. The solution was then evaporated to near dryness. Subsequently, 10 mL of 30% H2O2 and 10 mL of 37% HCl were added. This mixture was refluxed at 95°C for 15 min, cooled, filtered with a 0.45-µm membrane paper, and the total volume was maintained at 50 mL with ultrapure water (Fig. 3). Statistical Analysis The statistical analysis of the sample results were performed using the variance analysis by ANOVA (SPSS, v.13.0) for comparison between the groups. Least significant difference (LSD) test was performed to compare the results from the different-area groups. Statistical data processing was carried out at a level of reliability of 95%. p-value of less than 0.05 was considered to be meaningful.

Results And Discussion

High heavy metal content in parts of plants taken from above ground tissues is considered as an indicator of air and soil pollution levels. The monitoring of atmospheric pollution by using leaves of trees has gained considerable attention in recent years. Due to the low cost of leaves, it has been suggested in the literature that leaves can be used for monitoring air pollution [14, 18–22]. The commonly investigated species among the wide variety of trees used as biomonitors of atmospheric pollution are some of the fast-growing trees belonging to the genera Cedrus and Populus. Many studies have shown that various species of Populus and Cedrus can tolerate

Figure 2. Analysis procedure of plant samples for HR-CS FAAS analyses.

Figure 3. Analysis procedure of soil samples for HR-CS FAAS analyses. and accumulate high concentrations of heavy metals in above grounds tissues [23–28]. In this study, and Cedrus libani have been utilized because of they are the dominant tree species in Kırşehir. In addition, Cedrus species are also among the preferred biomonitors for atmospheric pollution, as they are evergreen trees [23]. Two stations were selected, one is the casting factory, which is a source of metal pollution, and the other is the Boztepe station, which has no factory and no urban area. The concentrations of Ni, Pb, and Cu in the samples of each station are shown in Table 2 and Table 3. The levels of heavy metals in the plant samples were evaluated statistically. The levels of Ni, Pb, and Cu in samples collected from the Boztepe station were determined to be in the range of 0.87 to 1.43 μg/g (mean, 1.16 µg/g), 0.55 to 0.75 μg/g (mean, 0.67 μg/g), and 2.27 to 9.66 μg/g (mean, 5.53 μg/g), respectively. On the other hand, the levels of Ni, Pb, and Cu in samples collected from the CFS were determined to be in the range of 2.40 to 2.59 μg/g (mean, 2.49 μg/g), 0.40 to 0.66 μg/g (mean, 0.50 μg/g), and 5.83 to 8.12 μg/g (mean, 6.73 μg/g), respectively. From the analysis, it was observed that the levels of Ni in the samples collected from the CFS were higher than that in the samples collected from the Boztepe station (p<0.05). However, the levels of Pb and Cu in the samples collected from the CFS and Boztepe stations were not significant (p>0.05).

Sigma J Eng Nat Sci, Vol. 39, Issue. 4, pp. 367–373, December 2021

Table 2. Concentrations of trace elements in the plant samples (N=4, µg/g) Plant samples

*: The significant difference in metal content of plants in CFS according to Boztepe p<0.05. SD: Standard deviation; CI: Confidence Intervals.

Table 3. Concentrations of trace elements in the soil samples (N=3, µg/g) Station

The levels of Ni, Pb, and Cu in Cedrus libani samples collected from the Boztepe station were determined to be in the range of 0.93 to 1.12 µg/g (mean, 1.03 µg/g), 0.84 to

Conclusions

We argued that if the levels of metals in the plants at the CFS are higher than the Boztepe stations and they exhibit statistically significant differences (p<0.05), these plants may have biomonitoring potential. The levels of Ni, Pb and Cu were not significant in soil samples taken from different stations (p>0.05). For this reason, we think that the changes in heavy metal levels observed in plants mostly effected by the parameters in the air for the studied elements. In this perspective, we suggest that Cedrus libani (for Pb and Cu) and Populus nigra plant (for Ni) have biomonitoring potential. Therefore, Populus nigra and Cedrus libani can be used as an economic tool for monitoring long-term pollution and accumulation of impurities. Other heavy metals can be studied in the tree species we work as a biomonitor. In addition, researches can be conducted on residential centers with high traffic and other centers.

Acknowledgements

This work was supported by Kirsehir Ahi Evran University Scientific Research Projects Coordination Unit. Project Number: FBA-10-12.

Data Availability Statement

The published publication includes all graphics and data collected or developed during the study.

Conflict Of Interest

The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Ethics

There are no ethical issues with the publication of this manuscript.

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