Introduction

The microplastics (MPs) phenomenon in the environment is currently researched all over the world. Previous studies were oriented on the identification of the sources and determination of the MPs in the aquatic environment, primarily in the oceans and seas. Investigation on the presence of microplastics in the drinking water, landfill leachate, ambient air and sediment is still in the initial phase (Eerkes-Medrano et al. 2019; Koelmans et al. 2019; Liu et al. 2019a; Guo et al. 2020).

The microplastics (size below 5 mm) can be divided into 2 groups: directly produced MPs (primary microplastics) and microplastics originated from macroplastics fragmentation (secondary microplastics) (Koelmans et al. 2019; Irfan et al. 2020). Their entry routes into the landfill leachate mainly come from dumping of waste (personal care products, synthetic textiles, industrial raw materials) and landfills’ poor management practice (absence of a surrounding fence on the landfill sites and the appropriate synthetic material for the waste covering) (Duis and Coors 2016; Li et al. 2020; Meng et al. 2020; Sturm et al. 2020).

Significant amount of different kind of waste in landfills where complex physical, chemical and biochemical reactions influenced by environmental conditions leads to fragmentation of plastics to microplastics (Pramila and Ramesh 2017; Imhof et al. 2013; Zettler et al. 2013). Landfill leachate can be the emission source of hazardous organic substances, such as bisphenol A (BPA), as well. According to the previous studies, BPA could be released from various plastic products through diffusion processes, hydrolysis and decomposition depending of physico-chemical properties (Liu et al. 2019b; Ficociello et al. 2020).

Van Praagh et al. (2018) monitored 11 landfills in Finland, Ireland and Norway in order to collect data on the quantities of microplastics in leachate. The main goals of this study were to determine the influence of different treatment methods on removal efficiency of microplastics and to assess the potential sources of emission. The study of He et al. (2019) was focused on determination of microplastics in 12 leachate samples from four active and two closed landfill sites in China. Kilponen (2016) conducted a pilot study to assess the occurrence of plastics and pollutants in urban atmospheric waters and leachate from closed landfill located near the coastal area. Microplastics and harmful substances, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and phthalates, were detected in all collected samples as well.

In addition to these organic micropollutants, a wide range of other emerging organic compounds (EOCs) such as personal care products and pharmaceuticals (PPCPs) were detected in landfill leachate. In review study conducted by Yu et al. (2020), a detailed summary of PPCPs occurrence in landfill leachate, existing landfill leachate treatment systems and environmental risk assessment on groundwater quality was presented. The most common reported PPCPs in different landfill leachate media were diethyltoluamide (DEET), caffeine, carbamazepine and ibuprofen, belonging to different pharmaceutical groups.

Talsness et al. (2009) have identified several studies that demonstrate that BPA is leaching from products that have been disposed at landfills. Yamamoto et al. (2001) researched 10 landfill sites in Japan and found concentrations of BPA in the range from 1.3 to 17,200 μg L−1.

After introduction into the aquatic ecosystem, microplastic pollutants may be subject to various phenomena due different environmental conditions such as decomposition or degradation causing the emission of emerging pollutants such as co-polymers, additives or plasticizers (Alimi et al. 2018). According to previous published study (Crawford and Quinn 2017; Chen et al. 2019), it has been proven that emerging microcontaminats such as nonylphenol, phthalate acids and bisphenol A can leach from plastic materials after weathering or aging of microplastic particles. These types of chemicals are defined as endocrine disruptors; thus, they have a negative impact on water quality. Because of their hydrophobic nature and high surface area, they can interact with other present pollutants in water media (Chen et al. 2020). Bisphenol A belongs to the group of plasticizers which is used as raw material for the production of many industrial and consumer products due to unique physico-chemical properties. BPA represents one of the chemicals which is produced in large volumes worldwide. Sources of BPA in environmental media are diverse due to anthropogenic activity. BPA is introduced into aquatic matrix through wastewater discharge or through landfill leakage (Huang et al. 2012). Waste management in Serbia and Bosnia and Herzegovina is based on landfills, which receive over 90% of total waste. The waste is disposed at sanitary landfills, controlled unsanitary municipal landfills and dumpsites (Vujić et al. 2011; Stanisavljević et al. 2012). The absence of source separation, as well as of adequate practice for plastic waste disposal, is the reason why most of it ends up on landfills.

In this study, three landfill sites with different waste management practice, waste amounts and morphological composition; different operating period; as well as different leachate management practice were investigated in order to determine the content of MPs and BPA in landfill leachate, as the constituents of plastic waste. To date, no research has been conducted on the occurrence of microplastics nor BPA in leachate from landfill sites in Serbia and Bosnia and Herzegovina.

Materials and methods

Sampling locations

Leachate sampling was conducted at two sanitary landfill sites (Jagodina, Serbia and Bijeljina, Bosnia and Herzegovina) and one non-sanitary, controlled landfill in Novi Sad, Serbia.

During the implementation of leachate sampling procedure for all three selected landfills, plankton net with mesh size of 23 μm was used to collect a higher number of microplastic particles.

Landfill site “Brijesnica”, Bijeljina, Bosnia and Herzegovina

Sanitary landfill “Brijesnica” is located beside the old city landfill site, about 3 km to the west from the Bijeljina city centre. The landfill is built according to the modern sanitary European landfilling standards in 2010, and it is designed for a 20-year landfilling period. Brijesnica landfill has a classical designed system for leachate collection.

The leachate collection system in Bijeljina consists of the non-perforated drainage pipe which is installed at the bottom of the landfill body (Fig. S1). The leachate is transferred to the leachate treatment plant employing reverse osmosis by pump (Fig. S2).

The permeate is being discharged into the recipient, and the concentrate is being returned to the landfill.

The leachate samples from landfill site in Bijeljina were collected from receiving basin. Due to the limitation to perform sampling directly from pipe which brings landfill leachate into equalization tank, sampling was conducted by addition of pump which brings leachate back into the basin via a hose inserted into the plankton net. The flow rate of the small pump (subsequently inserted into the receiving basin) was 0.3125 L s−1 or 1.125 m3 h−1.

Landfill site “Gigoš”, Jagodina, Serbia

The sanitary landfill site “Gigoš” in Jagodina, Serbia, is located in the hills, about 10 km north of the Jagodina city centre and around 1.5 km west of the A1 (E75) highway. The total estimated capacity of the landfill is 1,500,000 m3, and its estimated disposal period is 25 years. Landfill is designed according to the modern sanitary landfilling practices. Leachate collection and treatment system consist of two lagoons with leachate recirculation system. The collection of landfill leachate implies classic gravimetric system as shown in Fig. S1 for landfill site Brijesnica. Leachate sampling was conducted from lagoon for aeration and lagoon for sedimentation.

Landfill site in Novi Sad, Serbia

The non-sanitary, controlled landfill in Novi Sad, Serbia, is located in the northern part of the city, northwest of residential area “Klisa”, about 7 km from the city centre. The area for waste disposal is divided into three fields. Landfill contains certain segments which are characteristics of controlled landfills, but it is non-sanitary. Landfill does not have leachate collection system. The leachate sampling was conducted from peripheral canals 1 and 2 and from leachate lagoon (Fig. S3). An outline of the examined landfill sites is presented in Table 1.

Table 1 The main characteristics of landfill sites surveyed
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Chemicals and reagents

Hydrogen peroxide 30% G.R (unstabilised) and iron(II) sulphate heptahydrate used in wet peroxide oxidation process were purchased from Lach:Ner company (Slovakia). Zinc chloride ACS reagent, used in density separation step, was obtained from Carl Roth (≥97%, p.a., Germany). For bisphenol A detection and quantification in leachate samples, various chemicals were used such as 85% phosphoric acid (VWR chemicals, Germany), dichloromethane (LGC Promochem, India), methanol (HPLC grade, purity ≥99.9%, Sigma-Aldrich, USA), acetic acid (Zorka Pharma, Serbia) and acetonitrile (HPLC grade, purity ≥99.9%, Fisher Chemicals, Germany). Analytical standard of bisphenol A and internal standard of bisphenol A-d16 were acquired from Sigma-Aldrich (purity ≥99%, USA). Milli-Q water was obtained using the Easypure II ultrapure water system (Thermo Fisher Scientific, specific resistance 18.2 MΩ × cm). Ethanol was obtained from Sigma-Aldrich (purity ≥99.8%, USA). Oasis HLC cartridges were obtained from Supelco (USA).

Sample processing

Prior to every conducted sampling, a detailed preparation of brown glass bottles for sampling was implemented. Prior to sampling procedure, brown glass bottles were cleaned with diluted nitric acid and rinsed several times with Milli-Q water, after which it was overnight dried in oven. The usage of plastic bottles was not applied in order to avoid contamination mitigation. All steps in sample preparation are provided under fume hood. In order to collect a larger number of microplastic particles, grab sampling was carried out from four sampling points at each sampling site by making one composite sample. All landfill leachate samples were collected in 2.5-L sampling bottles and subsequently filtered through a plankton net (880mm long bag, nylon mesh material with pore dimension size 23 μm). The additional rinsing with Milli-Q water was applied several times on plankton net and sample bottles in order to ensure that residual microplastic particles are removed. In order to examine procedural contamination, field blanks were also collected in each sampling point. Field blanks were collected by rinsing plankton net with 2.5 L Milli-Q water and collected in clean glass bottles. No microplastic particles were detected in field-controlled blanks.

Leachate samples for the determination of BPA were collected at each landfill site. In Bijeljina, leachate samples were collected from receiving basin, and in Jagodina landfill site, leachates were taken from aeration and sedimentation lagoons while in Novi Sad samples were taken from the lagoon.

Minimization of sample contamination

During the laboratory analysis of microplastic particles, several steps were conducted to avoid contamination of samples by airborne fibre and particles. The thorough cleaning of all used laboratory equipment was carried out, and washed equipment was instantly covered by aluminium foil. The decontamination procedure consists of rinsing three times all used materials with Milli-Q water and ethanol. In each stage of extraction process, all used materials and dishes were covered with aluminium foil. The clean laboratory coats from natural fabric and nitrile gloves were worn during sample preparation. The working laboratory place was cleaned with ethanol to minimize a risk of contamination. The following cleaning procedure was applied between preparations of samples. Also, the usage of plastic materials was avoided.

In addition, all work solutions such as zinc chloride and iron sulphate were filtered through 0.45 μm glass fibre filter prior to microplastic extraction.

Microplastic extraction from landfill leachates

Laboratory analysis of collected samples was performed according to the proposed method defined by NOAA Marine Debris Division with slight modification of defined procedure (Masura et al. 2015).

The collected landfill leachate samples were first filtrated through stainless steel sieve (63 μm). All retained MPs content was rinsed with distilled water and transferred into glass baker and dried overnight in the drying oven (Memmert GmbH + Co. KG, Germany) at 90°C. The total weight of dried residues in samples (organic matter and MPs) is determined, and concentration of total solids (TS) was calculated. The removal of organic matter was performed with 20 mL 30% of hydrogen peroxide and 20 mL 0.05 M iron sulphate solution. The mixture was heated at 75 °C.

The density separation was performed by addition of zinc chloride (933.3 g L−1; density 1.6 g cm−3) to the sample, and solution was heated at approximately 75 °C (Rodrigues et al. 2020). Samples were left overnight in order to achieve a flotation of MPs in samples. The settled microplastics were collected in sieve mesh size of 63 μm, covered with aluminium foil and left overnight to dry. Extracted MPs were placed to Petri dishes. The weight of extracted microplastic particles was determined by gravimetric analysis. The same procedure was repeated for all samples.

The MPs isolated from landfill leachates were observed by stereomicroscope SteREO Discovery.V8 (Carl Zeiss Microscopy GmbH, Germany) in order to provide visual sorting of particles according to their morphological characteristics. In addition, the quick and simple testing of the burning behaviour of sample was performed (Vogel et al. 2012) in order to assess if the sample consists of plastic. This test is suitable for screening of plastic materials.

Detection of bisphenol A (BPA) in landfill leachate samples

Prior to sample preparation, the pH of the samples was adjusted to pH 3 using 85% phosphoric acid. The following procedure for determination of bisphenol A was conducted according to previous published method (Lee et al. 2017). The solid phase extraction (SPE) was carried out on Oasis HLB (60 mg/3 cc) cartridges (Supelco, USA). The column was conditioned with 5 mL of dichloromethane, 5 mL of ultrapure water and 5 mL of methanol. The 300 mL samples were loaded at flow rate of 5 mL min−1. Elution was performed with 5 mL of methanol. Afterward sample was evaporated under gentle nitrogen stream. One millilitre sample was analysed by HPLC system (HPLC DAD 1260, Agilent Technologies, Germany). Separation of BPA present in leachate samples was performed on the Zorbax Extend C18 stationary phase (150 × 4.6 mm, 5 μm, Agilent Technologies, USA) with isocratic extraction in mobile phase ratio (A-50% of 0.1% of acetic acid in ultrapure water and B-50% acetonitrile). The flow rates of the mobile phases were 0.8 mL min−1, and the maximum wavelength for BPA was 276 nm. Quantification of bisphenol A in landfill leachate was conducted based on previous formed linear curve with internal standard with ten calibration levels (correlation coefficient r2=0.999) (Fig. S4). Calibration curve was based on least square linear regression model in function of peak area of BPA and internal standard vs. concentration of BPA and BPA d16. The retention time of BPA analyte was tR=3.8 min. The detection of BPA was provided by comparing UV spectrum of target analyte with HPLC offline library.

Results and discussion

Based on the laboratory analyses, the presence of MPs in the leachate samples from all three landfill sites was determined. In Fig. 1, microscopic images of MPs identified in landfill leachate are presented.

Fig. 1
figure 1

Microscopic images of microplastics particles

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Comparing the obtained microscopic images of the MPs to the microscopic images from the available literature (Gray et al. 2018; He et al. 2019), the presence of microplastics particles could be suggested. Particles with different sizes, shapes and colours have been identified in all leachate samples (Fig. 1). Almost all MPs identified in landfill leachate were with irregular shape and rough edges (Fig. 1) indicating the fragmentation of larger plastics disposed at investigated landfill sites. The same findings were presented in the research of He et al. (2019) for microplastics from landfills in China. Fragmentation of larger plastic items leads to the formation of small MPs with high specific surface available for the high potential of organic micropollutants sorption not only from water but also from ambient air (Bouwmeester et al. 2015).

The obtained results on the quantities of total solids and MPs detected in the leachate samples from landfill sites in Bosnia and Herzegovina and Republic of Serbia are shown in Table 2. Also, the burning tests of sample indicated the presence of plastic materials with flammable properties.

Table 2 Results of the total solids and microplastics concentrations in the leachate samples from landfills in Bosnia and Herzegovina and Republic of Serbia
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The concentration values of the microplastics particles in the leachate samples from three landfills are in the same range. The total solids were measured in higher concentrations than MPs up to 25, 100 and 500 times, in leachate samples from all three landfill sites.

Table 3 presents the results (range, min-max) of microplastics particles in treated and untreated leachate from different countries.

Table 3 Results of the microplastics concentrations in treated and untreated leachate samples from landfills in different countries
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Microplastics were detected in the range from 0.42 to 24.58 particles/L in leachate samples from municipal solid waste landfills in China. In the report of van Praagh et al. (2018), wide range of MPs sizes in landfill leachates in Iceland, Finland and Norway was detected. MPs concentrations ranged from 0.0000014 to 295.1 μg L−1. The landfill sites were highlighted as source of MPs to the environment (Hou et al. 2021). PE and PP were the most dominant polymers in landfill leachates in China (Su et al. 2019), while in untreated leachates in Nordic countries, PE and polyurethene (PU) were the most commonly detected (van Praagh et al. 2018). MPs in the landfill leachate could be found in different sizes in the range of 50–5000 μm (van Praagh et al. 2018), according to various degradation processes of plastics which occur in landfills, such as aerobic biodegradation, transition from aerobic condition to anaerobic condition, hydrolysis, methane fermentation and final maturation. The most leachate treatment processes have not been designed to reduce the particles like MPs (Hou et al. 2021). However, MPs can be degraded by indirect electrochemical oxidation or by advanced oxidation processes such as photo-Fenton, O3/UV, H2O2/UV, ultrasound (US), UV/US and H2O2/US (Gewert et al. 2015; Mandal et al. 2017).

Results in other studies (van Praagh et al. 2018; Swedish Waste Association 2018) indicated that treatment processes decreased concentration of microparticles from 3 to 100% depending on the treatment technique. In our study, aeration decreased the microparticle and total solids concentration in leachate from sanitary landfill in Jagodina, Serbia, for 2% and 90%, respectively. Also, the ranges in our study were three orders of magnitude higher than in Nordic countries (Finland, Iceland and Norway). This could be the consequence of better waste management practice in developed countries compared to developing countries such as Republic of Serbia and Bosnia and Herzegovina, where the plastic recycling and waste sorting are not completely applied. The detection of microplastic particles conducted in developing countries in the South East Europe region presents the basis for further detailed investigation on MPs type and quantity, as well as on transport phenomena and life cycle assessment in different aged landfills with different waste management practice.

The obtained results of bisphenol A in leachate samples are presented in Table 4.

Table 4 Results of bisphenol A in the leachate samples from landfills in Bosnia and Herzegovina and Republic of Serbia
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The obtained results show that concentration of bisphenol A in leachate from the lagoon on non-sanitary landfill Novi Sad was 700 μg L−1, while significant higher concentrations were determined in leachate samples from sanitary landfills in Jagodina and Bijeljina. The concentrations of BPA in aeration and sedimentation lagoon in Jagodina were 2.72 mg L−1 and 2.78 mg L−1, respectively. The concentration level of BPA in leachate sample from Bijeljina was 1.52 mg L−1. Obtained results indicate the high concentration of BPA comparing to the previous studies: 67 μg L−1 (Shindo et al. 1998), 1–100 μg L−1 (Yasuhara et al. 1999), 0.6–31 μg L−1 (Sakamoto et al. 2000) and 0.13 μg L−1 (Behnisch et al. 2001) in landfills in Japan. The reason for this could be the higher amount of plastic waste which could be the source of BPA leaching (Xu et al. 2011) and MPs as well.

The BPA and MPs concentrations were measured in the same range at all selected landfill sites in Serbia and Bosnia and Herzegovina and indicate the same trend, which could be noticed in Fig. 2. The data were statistical processed via Microsoft Excel program (Microsoft Office 365) and presented as mean values (the red and blue bars) with standard deviations (±SD) (error bars) (n=3).

Fig. 2
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BPA vs. MPs concentrations in water samples at landfills in Serbia and Bosna and Herzegovina

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This first scientific research of microplastics in leachate samples from landfills sites in the South East Europe present the basis for further research activities which will include the more precise MPs identification methodologies, the identification of the entire pathway of MPs from the landfill body to its final recipient as well as the identification of MPs types and compositions from different aged and managed landfills.

Conclusion

The relatively high concentration levels of BPA in leachate samples, 7 to 20.000 times higher than in the other studies, from all investigated landfills indicate the presence of significant amounts of plastic waste as the main source of this hazardous substance and MPs as well. The preliminary amounts of MPs have been determined on two sanitary landfills and one non-sanitary controlled landfill site. The concentration ranges of MPs were higher than in the other studies of landfill leachates which highlight landfill sites especially in developing countries without waste sorting as potential sources of MPs to the environment. Similar trend in the concentrations of MPs and BPA occurrence in the landfill leachates was noticed. Further studies could be conducted to investigate correlation between MPs and BPA concentrations in leachate samples. Standardization of leachate sampling techniques and methods for MPs quantification methodologies with recovery rates of MPs during extraction process is important for validated results. The sorption effects of MPs as potential transporters of hazardous organic pollutants from landfills to recipients should be investigated as well.