Abundance and characteristics of microplastics in different zones of waste landfill site: A case study of Hamadan, Iran

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Case Studies in Chemical and Environmental Engineering 8 (2023) 100494

Available online 21 September 2023

Case Report

Abundance and characteristics of microplastics in different zones of waste landfill site: A case study of Hamadan, Iran

Alireza Rahmani

^a

, Malihe Nasrollah Boroojerdi

^b^,^**

, Abdolmotaleb Seid-mohammadi

^a

, Amir Shabanloo

^a^,^*

, Solmaz Zabihollahi

^b

, Dostmorad Zafari

^c

aDepartment of Environmental Health Engineering, Faculty of Health and Research Center for Health Sciences, Hamadan University of Medical Sciences, Hamadan, Iran

bStudent Research Committee, Department of Environmental Health Engineering, Hamadan University of Medical Sciences, Hamadan, Iran

cDepartment of Plant Protection, Faculty of Agriculture, Bu-Ali Sina University, Hamedan, Iran

A R T I C L E I N F O Keywords:

Hamadan landfill Abundance of microplastics Leachate lagoon zone Municipal waste Waste management

A B S T R A C T

Microplastics are an emerging environmental concern that threatens the lives of humans and other organisms.

Landfills are reservoirs for the production and accumulation of microplastics because the plastic waste disposed in them turns into microplastics over time under the influence of environmental and chemical conditions. This study is the first report on the abundance and characteristics of microplastics based on size, shape, color, and chemical composition in different old and active zones of the Hamadan landfill. The results clearly showed that the abundance of microplastics is significantly higher in leachate lagoon zone and old waste sites than active and virgin sites. Accordingly, the abundance of microplastics in the leachate lagoon zone, the old municipal and medical waste site, and the active municipal and medical waste site were found to be 76513, 39813, 26900, 16940, and 18766 items/kg dry soil, respectively. The abundance of microplastics in sizes 0.45 μm–25 μm and 25 μm to 5 mm was 59.32% and 40.68%, respectively. In addition, black microplastics were identified as the most abundant color (49%). In terms of shape classification, fiber microplastics were the most abundant (71%). Also, the most abundant chemical composition among microplastics belonged to LDPE (35%) and HDPE (33%) polymers. The findings of this study showed that the abundance and characteristics of microplastics in different landfill zones are quite diverse, which will have an important impact on proper waste management and pre- vention of environmental pollution.

1. Introduction

Plastics are found in almost every material in human daily life due to their low density and electrical conductivity, good flexibility, resistance to corrosion and chemical decomposition, and low cost. As a result, the main problem facing the use of these synthetic polymers is the over- production of waste and the resulting environmental pollution [1].

Microplastics are plastic particles smaller than 5 mm in size that is constantly fragmented in the environment to become nano plastic particles [2]. Since these particles have many negative effects on human health, they have attracted increasing attention recently [3]. According to the origin of production, microplastics are divided into two cate- gories: primary and secondary. Primary microplastics are produced in microscopic dimensions for industrial and domestic applications [4], and secondary microplastics are obtained from the fragmentation of

macroplastics into smaller particles [5]. Microplastics have the ability to adsorb and transport persistent organic pollutants and heavy metals in the environments [6]. Many studies have been done on the presence of microplastics in aqueous media [7,8] and sediments [9]. Studies on microplastics in terrestrial ecosystems, particularly landfills, are limited, although it is estimated that microplastics may contaminate 4–23 times more terrestrial than aquatic environments [10]. The disposal of used plastics and plastic packaging materials has become a global concern due to their very high strength and durability in the environment [11]. It is estimated that global plastic production in 2050 will be approximately 1800 million tons [12] and by this year, there will be 12,000 million tons of plastic waste in the environment [13]. Due to the poor classification of waste and the low rate of recycling of solid waste, plastic waste is a large amount of municipal waste, and this situation is worse in devel- oping countries [14] and is estimated to account for 20% of waste in

* Corresponding author.

** Corresponding author.

E-mail addresses: [email protected] (M. Nasrollah Boroojerdi), [email protected] (A. Shabanloo).

Contents lists available at ScienceDirect

Case Studies in Chemical and Environmental Engineering

journal homepage: www.sciencedirect.com/journal/case-studies-in-chemical- and-environmental-engineering

https://doi.org/10.1016/j.cscee.2023.100494

Received 27 August 2023; Received in revised form 14 September 2023; Accepted 16 September 2023

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landfills are plastics [15,16]. Therefore, landfills are considered the main reservoirs of microplastics that can be transferred from landfills to the surrounding environment using wind currents, which increases the potential risks if mismanaged [17]. Microplastics in landfill leachate can also act as vectors for heavy metals and organic pollutants and increase the adverse effects of discharging microplastics into the environment [18]. Studies on microplastics in landfills are few, so a comprehensive study on the identification of microplastics, their characteristics, and their fate in landfills is essential [14]. Landfilling is an organized disposal method for biodegradable and non-biodegradable wastes that is carried out in designated landfills away from municipal areas, and many countries use this method for final waste management. These dynamic systems undergo fluctuations in pH, oxygen level, and temperature over time [19]. Landfills are known as primary reservoirs for the collection of plastic waste, and usually most landfill processes involve anaerobic conditions that facilitate the breaking of plastics and microplastics [20].

Due to the fact that landfills are the primary reservoirs of plastic waste and can pose many hazards to the environment, the purpose of this study is to identify and determine the characteristics of microplastics in different parts of the soil landfill. Hamadan is one of the big cities of Iran in the western and mountainous region of the country. One of the main components of waste in Hamadan is plastic. According to the latest physical analysis of waste in the city of Hamadan in 2017, 4.58% by weight of the waste in this city is made of plastic. In this study, the abundance and characteristics of microplastics, including the morphology and composition of polymers, have been investigated for the first time in different old and active parts of the Hamadan landfill.

2. Materials and method

2.1. Location of the Hamadan landfill and sampling

The geographic location of the Hamadan landfill site and the sampling method are presented in Text S1 and Fig. S1.

2.2. Extraction of microplastics from soil

There is no standardized method to determine microplastics in the soil samples. The microplastics in the soil samples were extracted using density separation method as described method in previous studies with slightly modifications. The prepared soil samples were first dried in an oven at 60 ^◦C for 24 h. The soil samples were then sieved using a 2 mm steel sieve. 5 g of sifted soil were stirred for 15 min in 150 mL of ZnCl₂ solution with a density of 1.7 g mL⁻¹and then settled for 2 h. The su- pernatant was finally filtered by a vacuum filtration unit using a cellu- lose nitrate membrane filter (Whatman WME, 47 mm ×25 μm and 0.45

μm). The extraction was conducted in triplicate, and all the extracts were collected in filter papers. The filter papers in the vacuum filtration unit were then washed with distilled water to remove any salt residues.

The filter papers were dried in an oven at 60 ^◦C overnight. 30 ml of 35%

H2O2 solution was added to the dried filters for chemical digestion and then dried in an oven at 60 ^◦C for 1 h. Then the filtration was performed again as mentioned in the previous step and the filters were placed in an oven at 60 ^◦C overnight to dry [21–24].

2.3. Microplastics characterization

The surface of the filters was observed using a stereo microscope and then they were identified and counted. Pictures were also taken using a camera. Classification of microplastics based on size was in two ranges:

0.45 μm–25 μm and 25 μm to 5 mm. Also, microplastics were classified as colorless (white), red, green, blue, black, and other colors [24].

Microplastics were classified into fibers, films, fragments, pellets, and others based on their shape (morphological characteristics). The polymer type of microplastics was identified using Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy analysis (WQF-510A Rayleigh, China). The spectra were obtained as the average of 15 scans in the wavenumber range of 4000− 400 cm⁻¹with a resolution of 4 cm⁻¹[14].

2.4. Quality assurance and control (QA/QC) microplastics extraction To verify the accuracy of microplastics extraction method, recovery experiments with clean soil samples were performed according to the literatures [9,25]. Soil samples were prepared from remote and pristine areas, then the microplastics in them were extracted. To simulate the microplastics in the soil sample, microplastics with sizes of 300 and 850 μm made of polystyrene (PS), polypropylene (PP) and polyethylene terephthalate (PET) were prepared. After these microplastics were stained with blue markers, they were added to soil samples and the extraction of these samples was done by the mentioned method. No microplastics were detected in the control samples and the average detection rate in the soil samples was 90.2 ± 4.3%. These results confirm the validity of the modified protocol in the current study. In order to prevent the entry of microplastics into the soil samples from the environment, in all stages of microplastics extraction, all open con- tainers were covered with aluminum foil. Also, during the experiments, synthetic clothing was avoided and work surfaces were cleaned with alcohol before use. When analyzing filter papers, a control filter paper was placed in the laboratory to assess the possibility of air pollution.

Fig. 1. (a) Total abundance of microplastics in different soil areas of Hamadan landfill. (b) The abundance of microplastics in different soil areas of Hamadan landfill based on size.

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2.5. Data analysis

Statistical analyses were carried out using SPSS 22.0 software. The normality test was performed using Shapiro Wilk test, and nonpara- metric testing method (Mann-Whitney U) was adopted when the data sets did not fit the normal distribution. If the data fitted normal distribution, analysis of variance (ANOVA) was performed to determine the differences in the quantities of microplastics among different samples at the 95% confidence level. All data are shown as mean ±standard de- viation, and P <0.05 was considered as statistically significant.

3. The abundance of microplastics in Hamadan waste landfill 3.1. The abundance of microplastics based on size

Fig. 1(a) shows that microplastics have been detected in all the soil of different areas of the landfill. The highest abundance of microplastics was found in the leachate lagoon zone soil, which was 76513 items/kg dry soil and the lowest abundance was 3160 items/kg dry soil in the soil of the virgin area. Fig. 1(a) also shows that old landfill sites have more microplastics compared to active sites. Accordingly, the abundance of microplastics in the old and active municipal waste landfill soil was 39813 and 16940 items/kg dry soil, respectively. In the medical waste landfill site, the abundance of microplastics in the old and active sites was 26900 and 18766 items/kg dry soil, respectively. The results of a recent study show that the abundance of microplastics in wastewater treatment plant sludge is between 160 and 56400 particles/Kg dry sludge, which is lower than the value reported in the present study [21].

Fig. 1(b) classifies the abundance of microplastics in different Hamadan landfill sites in two size ranges including 25 μm to 5 mm and 0.45 μm–25 μm. The results clearly show that in the leachate lagoon zone, the abundance of microplastics in these two size ranges is 34947 and 41567 particles/Kg dry sludge, respectively. Also, the results of Fig. 1(b) show that the abundance of microplastics in the two size ranges of 25 μm to 5 mm and 0.45 μm–25 μm in the entire Hamadan landfill is 40.68% and 59.32%, respectively. The higher abundance of microplastics in old sites and the reduction in the size of microplastic in them can be related to the following reasons; (i) Chemical reactions and mechanical pressure on plastics cause them to turn into microplastics over time. (ii) The decomposition of polymers by various microorganisms in landfills cau- ses plastics to become microplastics. (iii) The number of buried plastics over time can also affect this issue. In other words, the more plastic has been buried in landfills in the past, the more microplastics are expected in these places [14,26]. (iv) Some environmental factors such as the photodegradation process can also increase the abundance of microplastics in old landfill sites, and on the other hand, reduce the size of microplastics over time [27].

3.2. The abundance of microplastics based on color

The present study divided microplastics into white, red, blue, green, black, and other colors. As shown in Fig. 2, the abundance of microplastics with black and white colors is higher than other colors in all soil samples of the landfill site, respectively. Accordingly, the abundance of microplastics with black, white, blue, red, and green colors is 49%, 29%, 6%, 4%, and 1% respectively. The abundance of microplastics with other colors was also 11%. The greater abundance of black and white colors is due to the use of black and white plastics in the packaging of consumer goods, and food, and their use as garbage bags, which has also been confirmed in previous studies. In addition, the results of Fig. 2 clearly show that the abundance of microplastics with all colors is generally higher in the leachate lagoon zone compared to other zones.

Accordingly, the abundance of black and white microplastics in the leachate zone is 32600 and 30534 items/kg dry soil, respectively. Also, the results show that the abundance of colored microplastics in the municipal waste old zone is higher compared to municipal waste active zone. The results of the recent study show that 59.6%, 17.6%, 9%, 6.5%, 2.3%, and 5% of microplastics identified in sewage treatment plant sludge are white, black, red, blue, green, and other colors. The results of this study also show that most of the microplastics are white and black, which is due to the production and consumption of white and black plastics in daily life [21].

3.3. The abundance of microplastics based on shape

As shown in Fig. 3, 71% of all microplastics detected in the Hamadan landfill are fibers, 16% in the form of fragments, 12% in the form of films, and 1% in the form of pellets. The recent study shows that 59.82%

and 7.86% of the microplastics in the buried waste samples were in the form of fragments and films, respectively [14]. In another study, the abundance of microplastics identified in the waste landfill leachate in the form of fragment, flake, line, foam, and pellet was reported to be 58.62%, 22.87%, 14.81%, 3.06%, and 0.64% respectively [28]. Also, the results of another study showed that the abundance of fiber, shaft, film, flake and sphere microplastics in sewage treatment plant sludge is 62.5%, 14.9%, 14%, 7.3% and 1.3%, respectively [21]. In a study that was conducted on the water of a lake, microplastics in the form of fiber, fragments, film, beads, foam, and others were the most abundant, respectively, the results of which are in accordance with the results of the present study [29]. Fig. 3 also shows that the leachate zone has the highest abundance of microplastics with different shapes compared to other zones. Accordingly, the abundance of film microplastics in the leachate zone is around 49533 items/kg dry soil. Also, the old zones had more microplastics compared to the active zones. As seen in Fig. 3, the abundance of fiber microplastics in the municipal waste old zone, medical waste old zone, medical waste active zone, and the municipal waste active zone is about 32333, 16933, 11866, and 11266 items/kg Fig. 2. Abundance of microplastics in different soil areas of Hamadan landfill

based on color. Fig. 3.The abundance of microplastics in different soil areas of Hamadan

landfill based on shape.

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dry soil, respectively. Stereo microscope images of some shapes of microplastic identified in the Hamadan landfill are shown in Fig. 4.

3.4. The abundance of microplastics based on chemical composition ATR-FTIR analysis was used to identify the type of polymer in the chemical composition of microplastics extracted from the Hamadan landfill. ATR-FTIR spectra of different microplastics including Low density polyethylene (LDPE), High-density polyethylene (HDPE), Poly- propylene (PP), Polyester (PES), and Polyethylene terephthalate (PET) are presented in Fig. 5. The results clearly show that the abundance of LDPE (35%) and HDPE (33%) polymers is higher compared to other polymers including PP (11%), PES (8%) and PET (7%). Also, about 6%

of polymers were placed in the unknown group. The reason for the abundance of polymers identified in this study can be attributed to the fact that PE, PP, and PET polymers are often used for the production of plastic products and packaging, and these types of plastics have a short lifespan and a low recycling rate. Therefore, they constitute an important part of household waste that ends up in landfills [30]. In the study of Ren et al., the abundance and characteristics of microplastics in sewage sludge have been investigated. In their study, Poly Vinyl Chloride (PVC, 41.18%), Poly (1-butene) (PB, 23.53%), Polytetrafluoroethylene (PTFE, 11.76%), PE (11.76%), and Polyacrylonitrile (PAN, 5.88%) were the Fig. 4.Stereo microscope images of some shapes of microplastic identified in

the Hamadan landfill.

Fig. 5.ATR-FTIR spectra of polymers identified in Hamadan landfill and The abundance of microplastics in different soil areas of Hamadan landfill based on shape.

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dominant polymers identified in the chemical composition of microplastics [31]. The results of the present study are compared with previous studies in Table 1.

4. Conclusion

This study presents the first report of the abundance and characteristics of microplastics in different zones of the landfill site in Hamadan, Iran. The abundance and characteristics of microplastics was reported based on size (0.45 μm–25 μm and 25 μm to 5 mm), color (black, white, blue, red, green and other colors) and shape (fiber, fragment, film and pellet) and chemical composition (LDPE, HDPE, PP, PES, PET and other polymers). The results showed that the abundance of microplastics in the leachate lagoon zone (76513 items/kg dry soil) is significantly higher than in other landfill zones. In addition, the old waste sites had a higher abundance of microplastics compared to the active sites. The results showed that 59.32% of microplastics are in the size range of 0.45 μm–25 μm and 40.68% were also in the size range of 25 μm to 5 mm. The abundance of microplastics with black, white, blue, red, and green colors is 49%, 29%, 6%, 4%, and 1% respectively. In addition, the abundance of fiber, fragment, film and pellet microplastics was 71%, 16%, 12% and 1% respectively. Analysis of the chemical composition of Hamadan landfill microplastics showed that PE polymer (LDPE +HDPE) is about 67%, which was significantly higher compared to PP (11%), PES (8%) and PET (7%). The results of this study can be a starting point for investigating the impact of the life of different landfill zones and its relationship with the abundance and concentration of microplastics. The fact that as the landfill ages, the abundance of microplastics increases and their size decreases can improve the understanding of health offi- cials for better waste management and control of environmental pollution with microplastics. The findings of this study showed that different landfill zones are a great source of microplastics that threaten the health of the environment. Therefore, it is suggested to study in detail the role of different landfill zones in the contamination of groundwater and air with microplastics in future studies.

CRediT authorship contribution statement

Alireza Rahmani: Resources, Supervision, Project administration.

Malihe Nasrollah Boroojerdi: Methodology, Investigation, Data cura- tion, Writing – review & editing. Abdolmotaleb Seid-mohammadi: Data analysis and Investigation. Amir Shabanloo: Investigation, Writing – review & editing. Solmaz Zabihollahi: Data analysis and Investigation.

Dostmorad Zafari: Data analysis and Investigation.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Data availability

Data will be made available on request.

Acknowledgments

The work was financially supported by the Hamadan University of Medical Sciences (Project No. 9912058770, Ethical approval No. IR.

UMSHA.REC.1399.985)

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.

org/10.1016/j.cscee.2023.100494.

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Table 1

Comparison of the results of the present study with similar previous studies.

Sample type Concentration Microplastic particle color Microplastic particle

shape Microplastic particle

size Polymer type Ref.

Leachate 0.42–24.58 items/L – Lines (fiber) =

14.81%

≥5000 μ =4.35% PE =34.94% [28]

Flake (film) =

22.87% 1000-5000 μ =20.77% PP =34.94%

Fragment =58.62% 100-1000 μ =74.88% PET =5.96%

Pellet =0.64% PS =4.99%

Foam =3.06% Others =19.17%

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45.12% [14]

Fragment =15.38% PE =9.67%

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Film =20% PP =32.4%

Fiber =20% Others =34.4%

Bead =6%

Refuse samples 590-103080 items/Kg Transparent predominant Fiber >Film >

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abundant PE =29.8% [30]

PP =19.4%

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Blue =6% Film =12% PP =11%

Red =4% Pellet =1% PES =8%

Green =1% PET =7%

Other =11%.

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