− Peatlands can be considered as effective geo-archives of Microplastics

− Ombrotrophic peatlands must be preferred over minerotrophic ones while assessing Microplastics

− ²¹⁰Pb dating can be viewed as the appropriate age dating method when it comes to assessing Microplastics in peat sequences

− Optimum sampling method depends on the characteristics of the peatland.

Plastic has become one of the most extensively utilized materials in contemporary society. The excessive production of plastics, coupled with their low recycling rates and high environmental persistence, has rendered them a significant emerging environmental concern, characterized by their rapid accumulation in natural ecosystems (Eerkes-Medrano et al., 2015). Although plastics exhibit high durability upon disposal in the environment, they are subjected to a range of processes, including chemical weathering, photoxidation, biodegradation, and mechanical degradation, which induce structural modifications over time. The term “microplastic” was initially introduced by Thompson et al. (2004). The scientific community has not yet reached consensus on a complete and comprehensive definition of the term “microplastic.” The National Oceanic and Atmospheric Administration (NOAA) researchers define microplastics as plastic fragments measuring less than 5 mm in diameter (Arthur et al., 2009). Microplastics can be defined as polymeric particles, either regular or irregular in shape, with dimensions ranging from 1 μm to 5 mm.

Microplastics are recognized as one of the most significant emerging pollutants in all environmental compartments. Microplastics can be introduced into various environmental compartments through numerous sources, including synthetic textiles, tire wear (particularly from automobiles and trucks), household items, waste incineration, construction materials, sewage sludge, landfills, 3D printing processes, and the resuspension of polymer particles in urban dust (Osman et al., 2023). The widespread presence of microplastics in natural environments, coupled with their potential impacts on human health and living organisms, has raised significant concerns among researchers. Considering the presence of microplastic particles in the atmosphere and their deposition influenced by various factors, identifying a natural environment capable of preserving the deposition records of such particles can be important in assessing the extent of plastic pollution over time and presenting optimal strategies to mitigate future pollution levels. Furthermore, these pollutants have been used as “technofossils” in sedimentary cores to evaluate the evolution of plastic types and create a microplastic chronological sequence in the sedimentary record (Chen et al., 2022).

Peatlands are considered as the most widespread wetlands that are formed due to the decay of plant residues under water saturation (Minayeva et al., 2018). There is no consensus on a specific definition for peatlands and peats. According to Joosten and Clarke (2002), peatlands are ecosystems rich in carbon that have a layer of peat that is more than 30 cm deep and contains at least 30% dry mass of decomposed organic matter. On the contrary, Peat was defined by Burton and Hodgson (1987) as a type of soil that contains at least 50% organic materials. In addition, histosols which are described as soils consisting of at least 20% organic substances or include at least 18% organic materials under water-saturated conditions for 30 consecutive days, are also classified as peatlands in some regions (Michéli et al., 2006). These ecosystems play a significant role in global carbon cycling since they store massive amounts of C in form of peat. According to IPCC (Intergovernmental Panel on Climate Change) (2007), boreal and subarctic peatlands store 270–370 Tg C in form of peat (equivalent to 34%–36% of atmospheric C in the form of CO₂). Moreover, tropical peatlands are approximated to retain 52 Tg C (Hooijer et al., 2006). Thus, peatlands not only can be considered as reservoirs of atmospheric CO₂, with a crucial influence on the atmospheric fluxes of CO₂ and CH₄, but also they exert influence on dissolved carbon (DC) fluxes into rivers due to destabilization of peatlands because of global warming (Limpens et al., 2008). Approximately 12% of global peatlands have been drained and damaged, resulting in significant carbon loss (Smith et al., 2024).

The estimation of peatland extent across the globe encompasses huge uncertainties. Based on a meta-analysis (Xu et al., 2018), we created a new GIS map showing the distribution of peatlands worldwide (Figure 1). According to the recently released map of peatlands, there are an estimated 4.23 million km² of peatlands worldwide, or 2.84% of all land area. The obtained result is consistent with the current Parish et al. (2008) approximation of 4 million km². Peatlands can be classified based on various parameters such as the nature of water supply, vegetation and hydromorphological structure.

Peatlands can be identified in different ways. “Ombrotrophic” and “minerotrophic” peatlands are the two main classes of peatlands considering the existing water source (Lindsay, 2016). Ombrotrophic peatlands are defined as peatlands that are segregated from all sources of surface or groundwater and fed explicitly by atmospheric wet and dry deposition like ash, dust, rain, snow, and fog (Allen et al., 2021). Sphagnum species predominate in their vegetation, which also includes other bryophytes, monocotyledons, and dwarf shrubs; however, their vegetation varies greatly in other parts of the world, like the southeast Asian tropical peat swamp forests. Sphagnum-dominated peatlands have been investigated more than any other types (Gilbert and Mitchell, 2006; Hughes et al., 2013; Marcisz et al., 2020). These types of peatlands are usually acidic and their pH ranges from 3 to 5.5 (Wheeler and Proctor, 2000). For instance, Aukštumala raised bog, which is located inside the Curonian freshwater lagoon is suspected to contain high levels of plastic pollution. The contamination of plastic particles in the surface beach sand of the Curonian Spit National Park has already been indicated (Esiukova et al., 2020).

In recent years the two terms “Bog” and “Fen” have also been utilized in order to describe the two main classes of peatlands. The former refers to peatlands that are uniquely fed by direct precipitation (ombrotrophic), and the latter is attributed to peatlands that have been saturated by groundwater or surface water (minerotrophic). Minerotrophic peatlands may receive inputs from either groundwater or surface water as well as the atmosphere (Lindsay, 2016) and have a highly diverse range of vegetation types. For instance, the vegetation of certain minerotrophic in northwest Europe is characterized by lack of Sphagnum and an abundance of species such as Molinia caerulea, Menyanthes trifoliata, Carex species, and Equisetum species (Charman, 2002), whereas Sphagnum species and sedges predominate in others (Lamentowicz et al., 2007).

This study aims to advance our understanding of the current status of research on the presence of micro (nano) plastics (MnPs) in peatlands. It attempts to assess the potential of peatlands as natural archives of microplastics. The current study presents a state-of-the-art, comprehensive perspective and benefits and drawbacks concerning to use of peatlands as a geo-archives for atmospheric MnPs. Moreover, it has been tried to comprehensively discuss the key aspects of using peatlands as natural archives of microplastics such as optimum sampling and age dating methods. Additionally, it serves as a valuable resource for researchers, to provide a framework for conducting studies in this field. To our best knowledge, no systematic review article has yet been published on the subject of MnPs occurrence in peatlands and their potential as MnP records.

In order to acquire adequate information relevant scientific studies have been gathered through online searches in the databases of Science Direct, and Google Scholar. The searched keywords included “microplastic” and “peatlands” or “peatland areas”, or “ombrotrophic peatlands”, or “peat cores” were examined. Moreover, the keywords “nanoplastic” and “peatlands” or “peat cores”, or “ombrotrophic peatlands”, or “peatland areas” were also considered. “Peatlands” and “plastic pollution”, or “plastic accumulation” were also searched. Furthermore, “peatlands” or “ombrotrophic peatlands” and “atmospheric deposition” or “atmospheric microplastics” were investigated as well. At the next stage, non-English articles were omitted. A total of 6 published studies during 2021-2023 were opted and scrutinized. Details about each stage are going to be explained in the next sections of the paper.

When conducting paleoenvironmental research, ombrotrophic peatlands should always be chosen over minerotrophic ones since they can be considered as effective atmospheric particle traps, which makes them a great archive of past events except at high latitudes such as sub-Arctic and Arctic regions, where ombrotrophic peatlands can scarcely found. Consequently, at high latitudes, minerotrophic peat deposits can serve as archives of atmospheric deposits despite being fed by both terrestrial and atmospheric inputs. For example, Shotyk et al. (2003) examined the collected peat cores from a minerotrophic peatland to evaluate the contributions of humans to the accumulation of Pb, Hg, and As in the atmosphere in southern Greenland and Denmark. Ideally, the dome (ombrotrophic peatland) of a bog is its most valuable component since due to the higher elevation, it is exclusively fed by rainfall and provides us with information on atmospheric deposition. Neither surface water runoff from surrounding areas nor groundwater can reach the higher section of the bog since it is above the local groundwater table.

As mentioned before, micro and nano plastics are one of the emerging contaminants on our planet. The versatility, stability, lightweight, and economical production of plastics has made them indispensable in our daily lives microplastics are plastic particles equal to or greater than 1 µm and less than 5 mm in (aerodynamic) diameter (Allen D. et al., 2022). Since these microscopic plastic particles have been detected in a plethora of habitats, including soils, their presence in the environment has drawn the attention of researchers across the globe. In fact, microplastics have been spotted in soils (Hoang et al., 2024; Yang et al., 2021; Wang et al., 2020; Boots et al., 2019), marine environments (Biswas and Pal, 2024; Cole et al., 2011; Nunes et al., 2023; Chen et al., 2023), marine organisms (Terrazas-López et al., 2024; Harmon et al., 2024; Parolini et al., 2023), atmosphere (Nguyen et al., 2024; O'Brien et al., 2023; Gasperi et al., 2018; Sridharan et al., 2021) and even pristine and remote environments (Abbasi et al., 2021; Mishra et al., 2021; Trainic et al., 2020; Allen S. et al., 2022). Archiving microplastic records from the past to the present will provide us with a comprehensive understanding of changes in the abundance of microplastics, which can help policymakers adopt more efficient mitigation strategies. Table 1 compares peat samples with two common plastic archives (marine/riverine sediments and ice cores).

Temporal records of environmental changes have been obtained from a considerable range of natural archives, such as corals (Williams, 2020), ice cores (Vallelonga et al., 2021), peat sequences (Fracasso et al., 2024), etc. In addition, sporadic records from herbaria (Lavoie, 2013), museum specimens (Schmitt et al., 2019), and the teeth, antlers (Kierdorf et al., 2022), and eggs of birds (Montanari, 2018) have been collected. The ubiquity of different types of peatlands throughout the world has made them a plausible option for monitoring a wide range of environmental contaminants (Figure 1).

Peatlands have been studied extensively as natural repositories of previously deposited airborne potentially toxic elements (PTEs) as these contaminants, specifically Pb, Cd and Hg, are capable of being transferred far away from their local sources due to long-range atmospheric transport (Miszczak et al., 2020; Kylander et al., 2006; Hansson et al., 2015; Talbot et al., 2017; Coggins et al., 2006; Luo et al., 2023). A few studies have also investigated the presence of polycyclic aromatic hydrocarbon (PAHs) in peatlands (Ortiz et al., 2023; Gabov et al., 2020).

Furthermore, peat cores have also been evaluated with the aim of assessing the impacts of air pollution and climate change (Souter and Watmough, 2016; Malawska and Ekonomiuk, 2008). In recent years, peatlands have become a plausible option for archiving microplastics (Table 1; Figure 1) (Nguyen et al., 2022; Allen et al., 2021). Bandekar et al. (2022) indicated that the physicochemical characteristics of submicron microplastics and peat facilitate the adsorption of plastic particles, which implies that plastic particles may be adsorbed by peatland ecosystems. Moreover, Hagelskajaer et al. (2023a) showed the presence of microplastic particles in sphagnum moss peat cores in a number of sites across the globe. The project is still ongoing however, the recent results demonstrated an increasing trend in atmospheric deposition of airborne microplastics in recent years.

The amount of plastic particles in these ecosystems is yet unknown, and the lack of analytical procedures has made it challenging to monitor the actual level of plastic pollution in peatland areas. In fact, the adsorption of polystyrene (PS) and poly (vinyl chloride) (PVC)-SMPs (sub-micron microplastics) to peat was influenced by their chemical composition. As a result, this affected the sub-micron microplastic accumulation by Sphagnum moss as well as the variety and composition of the microbial communities in peatland. Nevertheless, the use of these natural archives for microplastic records is quite limited. Therefore, there are still serious doubts about the potential of each of these natural archives to prepare microplastic records. Table 2 demonstrates the geographical characteristics for peatland microplastics.

Different sampling techniques can be used while sampling peats in paleoenvironmental studies. Basically, the optimum technique depends on the depth in which sampling occurs. Superficial layers (50–100 cm) must be cored cautiously in order to obtain a perfectly shaped core, which is a significant foundation for next stages such as the exact approximation of subsample volume. François et al. (2010) described two methods for sampling superficial layers. For coring of the first 50–100 cm (acrotelm and the subjacent part of catotelm) a stainless steel Wardenaar peat corer can be utilized. The purpose of this double-bladed cutter corer is to extract intact peat monoliths. The full description has been provided by Wardenaar (1987). Allen et al. (2021) used a Wardenaar corer to collect a peat core from the selected peat site in order to evaluate the potential of an ombrotrophic peatland for archiving microplastics deposition. Another peat corer that functions on the same principles is known as Malcolm sampler, which has been fully depicted by Cuttle and Malcolm (1979). Despite the Wardenaar sampler, in this apparatus one of the blades is smaller than the other, functioning as a lid that can be removed to reveal the core upon retrieval. It must be noticed that the Wardenaar or Malcolm blades’ cutting edges need to be sharpened, particularly if there are fibrous layers or roots that are difficult to cut through. If such material is not cut efficiently before pushing, the core will be compressed (François et al., 2010).

For deeper layers, another device which is referred to as Belarus corer is typically used. Actually, two versions of this corer are in use: titanium and stainless steel. The same alloy that was used to make the Wardenaar corer was also used to make the titanium corer, which is significantly lighter. Based on different circumstances, other peat corers may also be used during the investigation of peats. For example, Permafrost can be found worldwide in the organic soils of high altitudes and polar regions. In these areas, the thickness of ice is usually more than 1 m. There are extra difficulties when it comes to coring frozen peat, and the aforementioned corers are not appropriate to sample frozen peats. Tommy Nørnberg created and constructed a special peat sampler to collect continuous samples of frozen peat in the Arctic (Nørnberg et al., 2004). The device produced cores that were 70 cm long and 9.7 cm in diameter (Nørnberg et al., 2004). The cores that were recovered using this apparatus were successfully used to evaluate atmospheric mercury deposition in the Arctic on Bathurst Island, Nunavut (Givelet et al., 2004a). Later, to make the extraction of peat cores easier, Teflon was sprayed onto the core barrel. Using peat from the Carey Islands in Greenland, the updated version was utilized to replicate atmospheric mercury and cadmium deposition in the Arctic (Outridge et al., 2016).

Overall, it is rational to prefer ombrotrophic peatlands over minerotrophic ones while conducting research on the presence of microplastics in peatland areas except for regions that are located at high latitudes. The elimination of the inputs from surface or groundwater will not only facilitate the assessment but also provide us with a more accurate understanding of atmospheric deposition. We suggest that both surface and deep sampling are needed while investigating the presence of microplastics in peatlands since small-size microplastics are capable of migrating to deeper layers. For surface sampling modified version of the Wardenaar sampler is proposed which is commercially available in the market since it has shown great success in the uppermost 1 m of surface peat layers, yielding extensive, undamaged monoliths that make precise environmental reconstructions easier. For deep sampling, Belarus corer will be effective.

Moreover, the effects of core compression during the sampling must also be considered. Although some degrees of compression are inevitable during the sampling process (especially when the surface of the bog is dry), it must be prevented as much as possible. Givelet et al. (2004b) mentioned the effects of core compression on anthropogenic Pb concentrations and the age-depth relationship. The results indicated that the aging or magnitude of changes in anthropogenic Pb concentrations will not be impacted by the compression of the peat core alone. However, in terms of the effect of core compression on microplastic concentration further investigations are needed. Finally, the importance of covering the monoliths with foil bags, while transporting them to the laboratory to avoid any plastic pollution. Figure 2 illustrates the different peat sampling methods.

Because slicing regulates sample thickness, which is crucial for volume estimations, it is considered as a key process. In addition, slicing a peat core with fibrous layers (such as those of Scheuchzeria and Eriophorum spp.) makes the process challenging. There are some techniques in use today, but there is no consensus on an optimum way to slice a peat monolith or core. Whichever option is selected, the greatest amount of caution should be used to reduce material loss and cross-contamination. A precise procedure is to measure the core/monolith section’s total length, freeze it, and then cut it with a band saw. This allows for very accurate measurement of the clean slice dimensions, which is necessary for the accurate derivation of bulk density (François et al., 2010). Basic tools such as titanium knives or scissors may also be practical under special circumstances. Regardless of the instruments utilized, they must be cleaned after every slice is separated. However, plastic tools must be avoided in order to prevent any additional plastic contamination.

The next step, which ensures the reconstruction of high-resolution records and is crucial to sample preparation, is subsampling the previously mentioned slices. Sub-samples must represent the characteristics of the slice from which, they have been cutted. Furthermore, the quantity of the sub-samples must be determined considering the item which is supposed to be analyzed. For instance, Allen et al. (2021) subsampled the collected peat core with 1 cm deep sections in order to examine atmospheric microplastics deposition in ombrotrophic peat.

As mentioned before, peat samples contain considerable amounts of organic matter. The presence of these organic substances may hinder the identification and quantification of microplastics as they can be mistaken for microplastics. Therefore, choosing the most efficient method to remove them is of great significance. Different protocols have been suggested to eliminate organic residues. However, no pre-treatment technique has been unanimously accepted globally. Naidoo et al. (2017) proposed acid digestion for isolation of microplastics in juvenile fish. Enzymatic digestion is another method that has been tested by a number of researchers (Courtene-Jones et al., 2017; Mbachu et al., 2021). Oxidizing is the other procedure which has been used to isolate microplastics (Ziajahromi et al., 2017). Nevertheless, not all digestion processes can eliminate organic matter without damaging polymers. HNO₃, for instance, has been shown to degrade polyamide (PA), melt polyethylene terephthalate (PET) and high-density polyethylene (HDPE), and cause polymer yellowing (Dehaut et al., 2016; Karami et al., 2017). Moreover, expense is another important factor that must be taken into account while selecting the optimum strategy. Enzymes are too expensive to be consistently incorporated into microplastic sampling protocols, regardless of their effectiveness. Furthermore, rapid digestion times are typically favored over laborious procedures. Protocols might, for instance, last anywhere from an hour to 24 or 48 h (Catarino et al., 2017; Dehaut et al., 2016; Karami et al., 2017). While thermal digestion can shorten the time required for complete digestion, it also damages polymers, so it should be considered cautiously (Munno et al., 2018).

Prata et al. (2019) investigated the digestion efficiency of five solutions (H₂O₂, H₂O₂ + Fe), pH (KOH, HNO₃) and a surfactant (SDS) for removing organic substances without damaging microplastics. In order to obtain this goal, two temperature conditions were applied to pools of six organic materials in glass flasks: room temperature (RT, average 25°C) and 50°C temperature (OasisTM Benchtop IR CO₂ Incubator, Caron) as well as two-time intervals—one and 6 h. These pools were supplemented with 10 mL of solutions or the control (H2O). Each organic matter sample was exposed to 5 mL of each of the two solutions (KOH and H₂O₂ + Fe) as well as the control (H₂O) for a single test condition: 50°C for 1 h after the results of the first test were analyzed. The next step involved testing the polymers’ resistance to the digestion protocols. Furthermore, resistance of filters on digestion protocols was also evaluated. The highest digestion efficiencies under 1 hour at 50°C were shown by the strong redox (H₂O₂ + Fe) and high pH (KOH) treatments, at 65.9% and 58.3%, respectively. These treatments were therefore selected for additional testing. When organic matter was tested separately under these circumstances, it was found that KOH was most effective when it came to removing animal tissues, but H₂O₂ Fe was better suited for removing plant material.

In fact, a considerable number of studies have utilized H₂O₂ in order to digest organic materials in the investigation of microplastic (Allen et al., 2019; Brahney et al., 2020; Radford et al., 2021). The equilibrium between the breakdown of biogenic organic matter and its inefficacy against synthetic polymers has rendered H₂O₂ a desirable substance for a number of research groups (Hagelskjær et al., 2023b). Nguyen et al. (2022) during their investigation to study the Occurrence and distribution of microplastics in a tropical peatland in the Mekong Delta, Vietnam, used H₂O₂ to digest organic matter. Allen et al. (2021) in their study to assess peatlands as a natural archive of atmospheric deposition also used H₂O₂ and density separation (ZnCL₂) to process blank samples. The use of H₂O₂ digestion in conjunction with an appropriate density separation technique may produce satisfactory results regarding the separation of atmospheric plastic particles through microscopic analysis in aerosol, rain, river, and seawater samples where the plastic-to-biogenic organic matter ratio is quite large. As mentioned before, it is well known that adding Fe²⁺ as a catalyst increases H₂O₂ digestion efficiency (Walling, 1975; Prata et al., 2019). However, Hagelskjær et al. (2023a) indicated that neither H₂O₂ nor Fenton reaction could remove enough organic materials in matrices made mostly of refractory vegetal matter. The main components of sphagnum moss and peat are polysaccharides that contain cellulose and fructose, such as galactose, glucose, mannose, arabinose, and xylose (Black et al., 1955). They offered a unique protocol to enhance the efficiency of removal of organic materials in vegetal matrices such as peat samples. NaClO (50 vol%) digested sphagnum moss to a total of 86%–96% mass, while H₂O₂ (30 vol%) only removed 24%–46% mass of the matrix (Hagelskjær et al., 2023b). The utilization of the innovative purged air-assisted digestion technique resulted in an increase in NaClO efficiency to over 99% mass and a reduction in processing time. Digestion of different synthetic polymer types showed that high concentrations (>12.5 vol%) of NaClO attack polyamide (PA) and polyethylene terephthalate (PET), but have no effect on polymer types including all strains of polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and acrylonitrile butadiene styrene (ABS), which together account for the majority of annual plastic production. Three commercial sphagnum moss samples were analyzed to show that the protocol could separate and identify aerosol-sized microplastics as small as Ø = 0.8 μm. Therefore, this method can be considered among the ideal digestion methods while preparing peat samples for further steps. Figure 3 introduces the four major techniques which have been used to digest organic matters in peat samples.

Although none of the studies, which have investigated the presence of microplastics in peatlands, have elementally examined peat samples, the addition of this stage may be beneficial as it can provide us with invaluable data about the sources of the detected microplastics. However, we highly encourage conducting elemental, mineralogical, and isotopic analysis in conjunction with the investigation of microplastics for a comprehensive understanding.

Givelet et al. (2004a) suggested that before conducting any costly and time-consuming chemical process or analysis, all peat samples can be evaluated for main and trace elements utilizing the non-destructive, rapid and cost-effective X-ray fluorescence (XRF) approach. This method offers helpful geochemical information that facilitates recording the organic geochemical processes taking place in the peat profiles., which may have an impact on the distribution of trace elements. For instance, strontium (Sr) and calcium (Ca) can be used to identify mineral weathering reactions in peat profiles, as well as redox processes involving iron (Fe) and manganese (Mn), as well as atmospheric aerosols of marine origin containing bromine (Br) and selenium (Se). In addition, Shotyk et al. (2003) showed that the distribution and abundance of the conservative lithogenic elements such as titanium (Ti) and zirconium (Zr) demonstrate variations in the concentration of mineral matter within the peat core. Mowreover, an analytical procedure for determining the total mercury (Hg) concentrations in solid peat samples was presented by Roos-Barraclough et al., 2002. They analyzed samples of solid peat using a direct mercury analyzer (LECO AMA 254). To put it briefly, three subsamples that had been previously collected from a freshly chosen section of each slice were air-dried for a whole night in a Class 100 laminar flow clean air cabinet before being evaluated for total mercury content. After that, the three subsamples’ results were averaged. Furthermore, an extensive range of trace elements can be measured for other elements in solid peat samples through instrumental neutron activation analysis (INAA). Additionally, the trace element contents have been identified through the use of ICP-MS, ICP-OES, HG-AAS, and HG-AFS (Krachler et al., 1999; Chen et al., 2003).

In general, volume reduction is an important stage in preparing samples for chemical analysis. A number of methods are usually used in ordr to reduce the volume of the collected samples including filtration, lyophilisation, nitrogen condensing and desiccation. However, since peat samples contain considerable amounts of organic materials, eliminating them is prior to chemical analysis. Various methods have been suggested for the removal of organic matters, among them utilization of H₂O₂, KOH, NaOH and Fenton Reagent as digestive agents at maximum 55°C are the most common ones. Munno et al. (2018) examined the effect of temperature and digestion method on microplastics. They deduced that temperatures above 60°C during digestion process can have detrimental impacts on microplastics. They reported that in order to minimize the loss of any constituent microplastics, especially microbeads from personal care products, temperatures must be controlled to avoid temperature spikes during reactions. At or below 60°C, wet peroxide oxidation is still an effective method for digesting samples containing plant matter in freshwater and marine samples (water, sediment), and it may also be applicable to tissues. Evaluations of the prevalence, varieties, origins, and consequences of microplastics could be lacking if some materials are excluded from method-processing conditions. Identification of microplastics is another significant stage, which includes a variety of methods. In general, identification methods can be divided in three categories: visual identification, which encompasses the use of microscope (amongst Nile Red microscopy) for the identification of microplastics, spectroscopy methods, which includes various methods such as Raman spectroscopy (micro-Raman, surface enhanced Raman, Tip-enhanced Raman), FTIR (micro-FTIR, nano-FTIR, atomic force microscopy infrared spectroscopy) and a number of novel methods which have recently been applied by researchers and thermal degradation (pyrolysis, laser desorption/ionization, thermal desorption, etc.). Each of the mentioned methods has its own pros and cons. For instance, thermal degradation may alter the molecular structure of microplastics, resulting in alteration in the chemical composition of detected microplastics. Instead of taking many minutes, the majority of FTIR measurements are completed in a couple of seconds. Furthermore, FTIR significantly increases sensitivity for a variety of reasons. Because of the substantially increased optical throughput and far more sensitive detectors used, there is a significant reduction in noise levels (Dutta, 2017). Besides, the likelihood of a mechanical failure is relatively low. On the other side, Dispersive instruments typically have two beams, while FTIR instruments only have one. When it comes to the non-destructive identification of extremely small microplastics (less than 20 µm), µ-Raman stands out as the preferred technique. It is possible to get over some of the commonly mentioned limitations of Raman techniques, like poor signal and fluorescence interference, by employing more effective detectors, adhering to the proper cleaning protocols, and using baseline removal algorithms. With less operator time required, plastic particle identification is now possible because to the introduction of automated Raman mapping procedures.

A crucial component of paleoenvironmental research is creating high-quality chronologies, particularly for the last several centuries that have seen a great deal of change. In fact, reconstructing the historical rate of organic matter accumulation and exogenous material deposition flux requires accurate peat dating. Furthermore, an authentic and comprehensive chronology is required if peat samples are going to be collated with other natural archives such as polar ice, lake sediments, and bryophytes, including specimens from herbariums. It must be noted that since the peat deposition process is characterized by constant decomposition and compression changes, the relationship between depth and age in a peat core is typically non-linear (Oldfield et al., 1990). Due to developments in dating techniques, particularly ²¹⁰Pb dating, making use of peat samples, the modern history of atmospheric deposition may now be recreated covering the last 200 years or so. It is of great significance when it comes to probing the presence of microplastics in peatlands. Peat chronologies can be produced using a wide range of techniques, including the examination of fly-ash particles, historical pollen, tephra layers, chronostratigraphic markers, and short-lived radioisotopes (²¹⁰Pb, ¹³⁷Cs, ²⁴¹Am, and ¹⁴C bomb pulse). However, the two main procedures are radiocarbon age dating and radiometric age dating.

To enhance our understanding of the behavior of microplastics in peatlands, some information is provided below regarding their color, shape, size, abundance, and polymer types in peatlands (Table 2).

To our best knowledge, only one study has investigated the consequences of the presence of microplastics in peatland areas and the details have been provided by Nguyen et al. (2023). Nguyen et al. (2023) indicated that polyvinyl chloride, polyethylene, and polypropylene are the main sources of microplastics in the peatlands of Long An province, Mekong Delta, which have been produced by human activities. The entire peatland region was categorized as being at extreme risk. Notably, the findings showed a strong positive association (r = 0.49, 0.69, and 0.43, respectively) between the degree of human activity and the ecological risk indices HI, PLI, and RI. Appropriate strategies have been put forth to address current issues and encourage long-term peatland area protection. Using alternative materials like bioplastics, cutting back on single-use plastic products (SUPs), and adhering to the 4Rs principle are important additional strategies. The SWOT framework has been used to identify obstacles in the way of removing microplastic pollution and putting specific priority actions into action.

Overall, despite some geographical limitations, ombrotrophic peatlands can be considered as efficient atmospheric microplastic deposition collectors. However, the effect of vegetation type and general characteristics of the peat on the behavior of plastic particles is still ambiguous. These parameters (vegetation type and other characteristics of the studied peatland) can be considered as limiting factors when it comes to evaluating peatlands as natural archives of airborne microplastics. Optimum sampling methods and pretreatment processes were proposed. However, the lack of an integrated sampling and treatment process may be an obstacle in preparing peat samples. Therefore, the existence of a consistent process is essential while examining peatland microplastics. The dating techniques and their importance were also discussed and the proposed technique was introduced.

Despite the fact that the availability of field studies makes it difficult to draw a comprehensive conclusion, the demonstrated efficacy of peatlands as natural archives for other pollutants, coupled with the limited number of studies on the ability of peatlands to retain microplastic particles, suggests that peatlands may serve as an ideal choice for documenting accumulation and deposition rates of microplastic particles in different time intervals. Furthermore, the global distribution and abundance of peatlands provide additional justification for their utilization as natural archives for microplastics. It is essential to consider that the regulation of inflow to peatlands significantly influences their effectiveness as natural archives. Accordingly, among the various types of peatlands, ombrotrophic peatlands appear to be a more logical option, as they are exclusively fed by atmospheric precipitation. The climatic conditions of the study area appear to significantly influence the progression of the research process. In regions characterized by lower peat depths, the application of the Wardenaar peat corer for sampling surface layers warrants consideration and further investigation. A variety of methodologies may be employed for dating. Investigations into the presence of microplastics in peatlands have utilized ²¹⁰Pb dating. Determining the optimal technique for ²¹⁰Pb dating requires further research.

It is imperative to undertake additional field studies to elucidate the distribution and dispersion mechanisms of microplastic particles within peatland ecosystems. Additionally, the role of vegetation and the diverse attributes of peatlands in influencing the adsorption and distribution of microplastic particles warrants thorough examination. The majority of existing research has predominantly focused on ombrotrophic peatlands. Investigating non-atmospheric inflow of microplastic particles in peatlands necessitates further research focusing on their presence in minerotrophic peatlands, a critical area requiring detailed examination by researchers. Addressing the aforementioned aspects necessitates conducting studies across diverse climatic conditions. Ultimately, determining the chronological framework of microplastic particles represents a pivotal component of such studies. At present, employing ²¹⁰Pb dating appears to be a logical and reliable method for establishing the temporal presence of microplastic particles within peatlands. However, an important question arises: is it feasible to utilize the microplastic particles themselves as a tool for dating peat samples? What are the most effective methodologies for dating within this area of investigation?