Microplastic pollution in landfill soil: Emerging threats the environmental and public health
Article information
Abstract
Insufficient knowledge about the decomposition of microplastics from plastic waste in landfills hinders community involvement in waste management and sorting, posing a new threat to the environment and public health. The present study identifies, characterizes, and quantifies the microplastics in landfills soil sample to determine the latest threats posed by microplastics in the environment, particularly in landfills that are close to residential areas. This research is a descriptive study, with soil samples taken from six points in landfill site in Depok City. The abundance and shape of microplastics were characterized using a microscope, while the microplastic types were identified using Fourier Transform Infrared Spectroscopy (FTIR). The results showed that the abundance of microplastics in the Depok City landfill soil was 60,111.67 particles/kg, with the largest percentage being fragments at 63 %. FTIR functional group characterization showed the presence of plastic types, such as Polyethylene (PE), Polyvinyl Chloride (PVC), Polystyrene (PS), Polypropylene (PP), Polyethylene Terephthalate (PET), and Polyamide. The differences in waste types entering the Depok Landfill caused variations in the number, shape, and type of microplastic samples, and this study provides a foundation for mitigating and biodegrading microplastics in the landfill to minimize environmental impact and protect public health.
Introduction
The production of plastics and plastic-based products from crude oil derivatives has increased in the last six decades because of growing technology and relatively low production costs [1, 2]. With the increase in production, plastic waste has become a problem of environmental pollution in various parts of the world, starting from the emergence of plastic waste that is difficult to decompose, pollution of plastic waste on land and in the ocean, to microplastics that are dangerous and invisible to the naked eye, in the air, water and soil [2, 3].
According to research in 2010, about 275 million tons of plastic waste was produced in 192 coastal countries, with 4.8 to 12.7 million tons of waste polluting the oceans. Indonesia, as the second-largest contributor of plastic waste after China, produces 3.2 million tons of unmanaged plastic waste, with 1.29 million tons ending up in the ocean as microplastics [4]. Like many other cities around the world, Depok is facing the issue of microplastic pollution. Although there has not been extensive research on the abundance of microplastic in Depok, studies have found microplastics in Lake Kenanga and Agathis at the University Indonesia in Depok, which is located near residential areas [5]. Other studies have also found microplastic content in tap water samples from Depok, with an average of 3.23 particles per liter [6]. This highlights the urgent need for effective measures to address microplastic pollution in Depok because this condition can impact ecosystems and humans [7]. The detected microplastics can originate from various sources, including primary and secondary sources. Primary microplastics originate from industries that produce microplastics for cosmetic scrubs, polymer materials, and others. Secondary microplastics are produced by the fragmentation of larger plastic waste due to exposure to ultraviolet light [8].
Landfill, as the ultimate storage sites for plastic waste, have the potential to become a source of microplastics that have undergone decomposition. The duration of time that the landfill has been in operation and type of plastic waste that has degraded may impact the quantity, shape, and type of microplastics. The existence of pre-existing microplastics could present a new hazard to both the environment and the health of communities residing near landfills. Ingesting microplastics in a certain amount could also increase the risk of health issues such as cancer, birth defects, weakened immune systems, endocrine disruption, and developmental and reproductive disorders [9].
Although the government has implemented policies to manage plastic waste and decrease its impact, plastic pollution continues to increase. The active participation of the community in policies with regulations and the implementation of the 3R concept (Reduce, Reuse, Recycle) is still lacking, as evidenced by the fact that 50.8 % of the population in Indonesia does not sort waste, resulting in a significant amount of plastic waste being sent to landfills without treatment [10, 11]. In addition, plastic waste treatment through incineration is a commonly used method, but produces smoke containing CO2, CO, NOx, and SOx, which can cause acid rain [12]. Another approach that is often used is to process plastic waste into fuel oil, however not all plastic waste can be used, so it is still possible to produce microplastics [13].
Currently, there is still a lack of information about the presence of microplastics that break down from plastic waste and their impact on the environment and public health. Therefore, this study identified microplastic types in landfill to determine the latest threat posed by the presence of microplastics in the environment, particularly in landfills located near residential areas.
Materials and Methods
This research was a quantitative and qualitative descriptive study. Quantitative descriptive research aims to determine the amount and shape of microplastic particles obtained from landfill soil samples. Meanwhile, qualitative descriptive research aims to determine the type of microplastic polymer in the sample. Sampling was conducted at six soil sample points at a depth of 0-20 cm using a stainless shovel at the landfill in Depok City. Data collection on new (< 5 years) and old (> 5 years) waste generation was conducted in November 2022.
The selection of six sampling points within the landfill site in Depok City is a preliminary sample strategy to provide a comprehensive understanding of the presence of microplastics in various sections of the landfill, which is crucial for drawing accurate conclusions about the overall contamination levels, and as a representative assessment of microplastics in the complex environmental setting. In various research, the depth at which soil samples were collected to analyze microplastics varied between 0-40 cm, with the sampling process involving either a single stratum or several soil strata, extending up to 20 cm above ground level [14]. In this research, soil sample at a depth of 0-20 cm were chosen for this research because they can quickly assess the current level of contamination from microplastic in landfill, which is driven by aim of assessing the immediate and direct impacts of landfill operations on microplastic pollution [15].
This methodological choice is based on premise that the soil sample at a depth of 0-20 cm is the primary recipient of microplastics through surface runoff, atmospheric deposition, and the breakdown of larger plastic items under environmental conditions such as ultraviolet (UV) exposure. Soil sample at a depth of 0-20 cm analysis offers insights into recent contaminant inputs, facilitating the evaluation of current waste management practice and their effectiveness in controlling microplastic release. Additionally, because soil sample at a depth of 0-20 cm is more accessible and interacts dynamically with both the landfill material and the external environment, it serves as a critical indicator for microplastic transfer to adjacent ecosystems and to identify immediate risks to soil health, public health and biodiversity [14, 16–18]. Figure 1 and Table 1 shows the locations and coordinate point of the landfill soil sample collection.
Sample location
Sample collection points
The tools and materials used in this research were an oven, analytical balance, 50 ml, 100 ml, and 500 ml beakers, glass stirring rod, 250 ml glass bottle, dropping pipette, mortar pestle, and Sodium Chloride (NaCl). The amount and shape of microplastics were characterized using microscope at the Marine Biology Laboratory of Faculty of Mathematics and Natural Sciences University of Indonesia, and the type of microplastics was identified using Fourier Transform Infrared Spectroscopy (FTIR) in the Integrated Laboratory and Research Center (ILRC) University of Indonesia Laboratory. The sampling method was conducted with reference to previous research. Notably, owing to the absence of standardized methods for sample collection, we drew upon insights from prior studies to guide our sampling protocol. Given the current lack of established protocols for microplastic quantification in soil, leveraging methodologies from existing research is instrumental in ensuring a systematic and informed approach throughout the sampling process until sample analysis [15, 19–24].
Due to the absence of standardized methods for sample collection, the sampling method until sample analysis in Figure 2 was carried out with reference to previous research to guide the sampling protocol, starting from [19]:
Sampling method and analysis
1. Sample collection: In any research, the sampling method is crucial to ensure a statistically significant population. For this study, soil samples were taken from designated locations using standard sample collection protocols, namely soil attached to plastic waste a depth of 0-20 cm from the soil surface [20, 21]. Then, 500 grams of soil was placed in a 500 ml glass bottle and stored in an icebox filled with dry ice at 4 °C until transported to the laboratory. Environmental factors, such as temperature, soil moisture, and soil pH, were measured in situ [22].
2. Sample preparation: Soil samples were dried at 60 °C for 72 hours, and then ground by pestle and mortar and sieved to separate larger particles. Subsequently, density separation was performed to remove various organic minerals through microplastic extraction stages in the soil samples by adding saturated NaCl [19]. Density separation techniques are widely used to extract microplastics from different environmental samples. These approaches typically involve the use of saturated salt solutions, such as sodium chloride (NaCl), to facilitate separation [23]. The separation of microplastic density from soil samples can use several other solutions, such as Hydrogen Peroxide (H2O2), Nitric Acid (HNO3), Sodium Iodide (NaI), Zinc Chloride (ZnCl2), and Calcium Chloride (CaCl2), but the price is relatively expensive and dangerous, which makes handling and disposal difficult, and can affect the degradation of microplastic and cause discoloration of the microplastics to be tested [14, 25].
3. Quantification: The number and shape of microplastics in soil samples were determined using a microscope at a magnification of 10 x 10 [20].
4. Polymer identification: The type of microplastics concentrated in the soil samples was identified using Fourier Transform Infrared Spectroscopy (FTIR) technique, especially Attenuated Total Reflection (ATR-FTIR) [24]. ATR-FTIR technique is employed for microplastics identification due to its capacity to generate a unique molecular spectrum for each polymer, offering simple, quick, and non-destructive analysis. This technique excels in analyzing irregular, thick, or opaque microplastic samples across various polymer by comparing them to a reference spectral library [26].
Results
Microplastic shape
Based on the analysis results, the shape of microplastics discovered in the landfill soil samples from Depok City is shown in Figure 3. The analysis categorized microplastics into four shapes: fibers, fragments, films, and pellets. Fibers are thin and thread-like, whereas fragments are rectangular pieces of plastic with irregular shapes. Microplastic films are described as thin plastic sheets, while pellets are round in shape. The percentages of microplastic shapes were 63.39 % fragments, 21.07 % films, 12.57 % fibers, and 2.96 % pellets. These shapes are common for microplastics and are often the result of plastic waste breaking down over time due to environmental factors, such as weathering, UV exposure, and microbial activity. It’s worth noting that microplastics can also came in other shapes and sizes that were not identified in this study.
Microplastics shape in soil samples from Depok City’s landfill: a) Fragment, b) Film, c) Fiber, d) Pellet
The abundance of microplastics
Soil samples 1 to 3 were collected from waste piles that were less than 5 years old, while samples 4 to 6 were obtained from piles that were over 5 years old. As shown in Figure 4, the largest average abundance of microplastics was found in sample 1 (88,000 particles/kg), while the lowest was found in sample 5 (48,670 particles/kg). The overall average abundance of microplastics in the soil samples at the Depok City Landfill was 60,111.67 particles/kg. In this study, pH and soil moisture range from 6.1-7 and wet to dry respectively from all sample.
The average abundance of microplastic at Depok City’s Landfill.
The abundance of each type of microplastic found is presented in the chart bar shown in Figure 5. For each sample, the most common type of microplastics was fragments. In sample 1, the abundance of fragments was 26,666.67 particles/kg, in sample 2 it was 21,333.33 particles/kg, in sample 3 it was 15,666.67 particles/kg, in sample 4 it was 17,666.67 particles/kg, in sample 5 it was 14,000 particle/kg, and in sample 6 it was 19,000 particle/kg.
The average abundance of microplastic by type
FTIR test result
The type of microplastic polymer based on the functional groups of the compounds can be identified using the FTIR tool. The principle of FTIR is to determine the functional groups in a compound through infrared absorbance analysis. The identification results for the types of microplastic polymer found in each sample are shown in Figure 6. The identification results show that there are several wavelength peaks indicating the bonding of a compound (Table 2). Based on the readings of the wavelength peaks, it can be identified that there are suspected to be 6 types of microplastic polymers in TPA Depok City, namely polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyamide.
The identification results for the types of microplastic polymer
The identification result of FTIR test
Discussion
The accumulation of plastic waste in the environment has become a concern for both countries that import plastic waste and those with high levels of plastic usage. Plastic waste that is not recycled, whether illegally dumped or disposed of in landfills, can pollute the environment, including soil and water, through macro, micro, and nano-plastics. Approximately 75 % of the plastic waste disposed of in landfills has the potential to threaten the soil and other environments through microplastic contamination [33, 34]. Microplastics in landfills can originate from various sources, including household waste, industry, and transportation. Some consumer products, such as synthetic clothing and personal care products, can also generate microplastics when used and disposed of [20].
Based on the results, it is known that the type of microplastic fragment with the highest concentration is found in soil samples from landfill site. This could be caused by the disposal of plastic products, such as bottles, food and beverage containers, broken water jugs, pipe fragments, or ruptured plastic bags that become fragmented [35]. Film-type of microplastic were also found in the soil samples because of the presence of plastic food packaging bags and shopping bags that degraded over time. This process occurs slowly, with the plastic breaking down into smaller particles with the help of heat from sunlight, physical processes such as friction and movement of waste during stacking and compaction, as well as chemical and biological processes [36, 37]. The sources of the fiber-type microplastics in the samples were synthetic fabrics and textiles. Pellet or granule-type microplastics generally come from factories that use plastic in beauty and cleaning products, also known as microbeads [36]. The dominant type of microplastics in the landfill site may be due to differences in the plastic waste composition and decomposition processes in landfill [38]. Referring to previous studies at the Laogang landfill, it was also found that the dominant type of microplastic was fragments [39].
The abundance of microplastics in landfills can be caused by the volume of plastic waste, waste and leachate management in the landfill, the age of the landfill, and environmental factors, such as temperature and humidity [34,40]. The waste generated in Depok City landfill, which has been operating since 1992, is known to have reached more than 850 ton/day, with the largest composition being organic waste (62.95 %), followed by inorganic waste such as plastic waste (21.36 %), disposable diapers (7.24 %), paper (96.10 %), glass bottles (0.57 %), fabric/textile wood (0.57 %), rubber and leather (0.50 %), and metal/cans (0.14 %) [41]. This indicates that plastic waste is the second largest contributor to the total waste entering the landfill, thus increasing the abundance of microplastic in the landfill. In the practice of waste and leachate management in landfills, it is still not considered optimal in the plastic waste recycling process, causing accumulation, which then increases the possibility of degradation and release of microplastics [34,40]. The abundance of microplastics in the Depok City landfill is also in line with the abundance of microplastics in the South China landfills, where the abundance of microplastic ranges from 590 to 10,308 particle/kg [38].
In addition, several previous studies have mentioned that the abundance and characteristics of microplastics in landfills also depend on the age of the waste generation in the landfill, where newer waste generation tends to have higher microplastic abundance, while older waste generation has high secondary microplastic abundance due to environmental degradation processes [34]. This condition is in line with the results of the study where samples 1, 2, and 3, which originated from newer waste generation, had higher microplastic abundance value compare to samples 4, 5, and 6, which came from older waste generation.
Similarly, the type of polymer found in landfills can vary depending on regional factors, type of waste disposed, and consumer habits. Several studies have shown that the most common polymer types in microplastic samples in landfills are polyethylene (PE) and polypropylene (PP), followed by polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polystyrene (PS) [38-40, 42], which is not significantly different from the type of polymer microplastics found in the Depok City Landfill.
All types of microplastic polymers can have negative impacts on the environment and public health, especially if they accumulate in the environment and the food chain. Some types of microplastic polymers are considered more hazardous than others, especially if they contain harmful chemicals such as Bisphenol A (BPA), polyvinyl chloride (PVC), and polystyrene (PS). However, the presence of several types of microplastic polymers in the Depok City landfill, such as PE, PVC, PS, PP PET, and polyamide, can cause environmental and health problems, as they can accumulate in soil and water, pollute ecosystems, and potentially be consumed by living organism, including humans. PE, PP, and PET are relatively inert, can persist in the environment for a long time, and are difficult to biodegrade naturally. PVC contains toxic additives, such as cadmium and lead, which can be released into the environment for years and damage the ecosystem. Although this study shows the presence of microplastics in the Depok City Landfills, this condition is still the basis for further research.
Conclusions
The discovery of microplastic abundance in all samples indicates an average microplastic abundance in the soil samples at the Depok City landfill of 60,111.67 particles/kg. the analysis of microplastic shape in this study was divided into four categories: fiber, fragments, films, and pellets, with fragments being the most identified shape at 63.39 %. based on the peak wavelength value readings, it is suspected that there are six types of microplastic polymers in the Depok City Landfill: polyethylene (PE), polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), and polyamide. The degradation and release of microplastics in landfills are influenced by the composition of plastic waste and decay processes in landfills. Better waste management is needed to prevent the accumulation of plastic waste in landfills and reduce microplastic abundance, which can pollute the environment and cause health problems.
Acknowledgements
This research is funded by Directorate of Research and Development, University of Indonesia under Hibah PUTI Pascasarjana 2022 (Grant No. NKB-268/UN2.RST/HKP.05.00/2022).
Notes
The authors declare no conflict of interest.
CRediT author statement
OAP: Conceptualization, Methodology, Software, Validation, Formal Analysis, Investigation, Resources, Data Curation, Writing-Original Draft Preparation, Writing-Review and Editing, Visualization, Project Administration; UAP: Conceptualization, Validation, Data Curation, Writing-Review and Editing, Supervision, Funding Acquisition; RK: Software, Validation, Investigation, Data Curation, Writing-Review and Editing, Visualization