Authors
Keywords
Abstract
Currently, polymers have been the subject of several studies because of by-products known as microplastics (particles smaller than 5 mm). Due to the complexity of the heterogeneous soil matrix, it is difficult to study microplastics in the soil, especially considering differences in methods adopted for sampling, extraction, and quantification of the particles in various studies that analyze microplastics in soil samples.Thus, the article presents a review of studies on the analysis of microplastics in the terrestrial environment, aiming to identifythe advantages and disadvantages of methods for analyzing polymeric fragments. Theresults show substantial variation in the techniques proposed, including sieving, digestion, density separation, and filtration to extract fragments in samples. On the other hand, the methods usually adopted to identify and characterize polymers in soil refer to combinations to perform classification and spectroscopies, including Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM). In conclusion, a combination of methodologies for the characterization of polymers in soil samples seems to be more efficient for detecting and analyzing particles and overcome analytical challenges, thus providing more effective monitoring of microplastic soil contamination
Introduction
Plastics are one of the most consumed materials in the world due to theirgeneral properties of plastics, including easiness in processing, ’cost-benefit, versatility, low density, and flexibility, among others. Unfortunately, the global increase in the adoption of plastics led to increase in plastic waste generation. Approximately 6.3 thousand Mt of plastic waste has been generated since 1950, mostly discarded in landfills.
Considering the maintenance of current practices, around 12,000 Mt of plastic waste should be sent to landfills or discarded in the natural environment by 2050 1. Plastic waste represents a massive loss of valuable material and poses a significant risk to the environment and wildlife since plastic degradation takes hundreds of years 2.Considering the maintenance of current practices, around 12,000 Mt of plastic waste should be sent to landfills or discarded in the natural environment by 2050 1. Plastic waste represents a massive loss of valuable material and poses a significant risk to the environment and wildlife since plastic degradation takes hundreds of years 2.
Microplastics (MPs) are usually categorized according to origin. Primary MPs are already produced in micro-dimension 3, and secondary microplastics are plastics that have been degraded by the action of weather to micro-dimension,both with high impact on the environment4 5.Microplastics (MPs) are usually categorized according to origin. Primary MPs are already produced in micro-dimension 3, and secondary microplastics are plastics that have been degraded by the action of weather to micro-dimension,both with high impact on the environment4 5.
Thus, recent advances in the area show that MPs are widespread in diverse environments, being most studied in aquatic environments (71% of the articles surveyed),e.g., sea, lakes, and dams6. However, in terrestrial environments, its presence has been generally neglected7, is identified in only 5% of the studies’found6. However, evidence points to estimates of 4 to 23 times greater presence of MPs in soil than inwater 8. Furthermore, the ingestion of MPspotentiallyleaches toxic persistent organic pollutants (POPs) absorbed from the environment.Thus, recent advances in the area show that MPs are widespread in diverse environments, being most studied in aquatic environments (71% of the articles surveyed),e.g., sea, lakes, and dams6. However, in terrestrial environments, its presence has been generally neglected7, is identified in only 5% of the studies’ found6. However, evidence points to estimates of 4 to 23 times greater presence of MPs in soil than inwater 8. Furthermore, the ingestion of MPspotentiallyleaches toxic persistent organic pollutants (POPs) absorbed from the environment.
Therefore, the abundance of microplastics in the oceans and soil is expected to continue increasingdue to the continuous production and discard of plasticsin the environment. In addition, the ocean warming process caused by climate changestends to increase animals’’ metabolism and increase feeding rates, thus increasing exposure to microplastics9.Therefore, the abundance of microplastics in the oceans and soil is expected to continue increasingdue to the continuous production and discard of plasticsin the environment. In addition, the ocean warming process caused by climate changestends to increase animals’’ metabolism and increase feeding rates, thus increasing exposure to microplastics9.
A major concern regarding MPs in the marine environment is the impacts on the feeding and reproduction of living organisms in aquatic habitats,destabilizing the ecosystem10. However, terrestrial plastic pollution may be more hazardous due to its impacts on soil, watersheds, rivers, and lakes, thus contributing to aquatic pollution and increasing the effects of greenhouse gas, which leads to accelerated climate changes11 12.A major concern regarding MPs in the marine environment is the impacts on the feeding and reproduction of living organisms in aquatic habitats, destabilizing the ecosystem10. However, terrestrial plastic pollution may be more hazardous due to its impacts on soil, watersheds, rivers, and lakes, thus contributing to aquatic pollution and increasing the effects of greenhouse gas, which leads to accelerated climate changes11 12.A major concern regarding MPs in the marine environment is the impacts on the feeding and reproduction of living organisms in aquatic habitats, destabilizing the ecosystem10. However, terrestrial plastic pollution may be more hazardous due to its impacts on soil, watersheds, rivers, and lakes, thus contributing to aquatic pollution and increasing the effects of greenhouse gas, which leads to accelerated climate changes 11 12.
The literature review by Qi et al. (2020) found microplastics in plantation, handling, and cultivation of fruits, and vegetables, reaching households through food consumption.Foods with higher contamination rates among fruits and vegetables were carrots, apples, pineapples, and cabbage13. In the study by Barboza et al. (2018), MPs and other types of synthetic products were found in foods and ingredients intended for human consumption (e.g., canned sardines, salt, beer, honey, and sugar) and water distributed in plastic bottles14.
Based on this finding, researchers investigated the potential consequences of microplastics ingested or aspirated by humans, noting that human epithelial and brain cells showedcytotoxic effects related to oxidative stress, which reinforces speculations on further impacts caused by MPs contamination in human health 14.
Studies have shown that most residues originate from terrestrial anthropogenic activities15 16 17. According to theevidence, MPs found in the environment are primarily caused by anthropogenic activities, particularlyurbanization linked to population density, even though sea cycles, storms, and floods also contribute to their dispersion 8.Studies have shown that most residues originate from terrestrial anthropogenic activities15 16 17. According to theevidence, MPs found in the environment are primarily caused by anthropogenic activities, particularlyurbanization linked to population density, even though sea cycles, storms, and floods also contribute to their dispersion8.
According to Ren et al. (2020), the influence of plastic fragments in the soil tends to reduce the microbial community's diversity and richness.In addition,it seriously impactsthe terrestrial biogeochemical cycles due to changesin soil nutrients (resources necessary for microorganisms). The process alters metabolic functions in the environment, e.g., circulation of carbon dioxide18, such as in Figure 1.
Figure 1-Carbon cycle in the presence of plastics in terrestrial and aquatic environments. Based on Dees et al., 2020.
Figure1 shows the microplastics dissemination, penetrating the soil and potentially releasing chemical products (environmental contaminants, additives, heavy metals, monomers, etc.) adsorbed on them to the surrounding environment19. The main substances usually released in the environment include bioavailable heavy metals, which may act as catalysts for undesirable reactions20. Thus, the adsorption/absorption properties ofplastic fragments favor the carriage of harmful substances that alter the physical properties of the soil. MPs can increase porosity, and change the aggregate structure, abruptly altering the microbial activity of the soil, for example21.
Another concern regarding MPs refers to the actions of weather (rain, wind, atmospheric deposition, and ocean waves) in spreading to distant places, like the Arctic22 23. MPs were also found in 98% of wet and dry samples examined from remote protected areas in the USA24 causing changes in living organisms' behavior and food chain interaction6.
Furthermore, soils carry out carbon sequestration and promote biological heterogeneity, and substances that alter the fundamental properties of the soil affect the physical and biological environment, like structure, consistency, porosity, magnetic ores, carbonates, manganese, sulfides, among others. Thus, changes in alkalinity levels affect soil fertility and lead to a deficiency of several essential nutrients. The decomposition processes of organic matter in the soil are influenced by the presence of MPs due to changes in soil temperature, affectingthermal degradationthat would support the reproduction of microorganisms. In addition, humidity ensuresthe proliferation of bacteria and fungi and generates an appropriate environment for germinating microorganism spores. Finally, oxygen plays a key role in allowing cells to breathe, helping aerobic decomposers.In sum, plastic pollution generates by-products that become severe threats to the soil biota due to changes in the terrestrial habitat25.Álvarez-Hernández et al. (2019) indicated that Polyethylene (PE) is the
most common MP found in terrestrial systems. Other studies covered a more comprehensive array of polymers, finding significant plastic pollution in agricultural soils: PE - 62.50%, Polypropylene (PP) 52.50% and, to a lesser extent, Polyamide (PA) - with 32.50% 26 27 28 29. Furthermore, it seems that agricultural coverings (mulching - usually made of PE) and application of sewage sludge comprises some of the main routes of entry of MPsinto the soil30 31. According to Bläsing and Amelung (2018), other access routes would be through landfills, flooding, bioturbation, and atmospheric deposition 32.
Yet, there are still considerable gaps in the processes and pathways of microplastics in soils. Considering the various protocols usually adopted for sampling, extraction, and analysis of plastic fragments in the soil, it is challenging to compare evidence from studies conducted on the characterization of soil pollution by MPs.After soil extraction, there are diverse techniques applicable for MPs analysis, including the main methods of polymer identification:Fourier transforms infrared spectroscopy (FTIR), Raman spectroscopy, and scanning electron microscopy (SEM).
Alternative analyzes performed to prove the existence of microplastics in soil samples include thermal desorption coupled with automated mass spectrometry for Pyrolysis-gas chromatography-mass spectrometry (pyrolysis GC-MS), which comprises a multifunctional tool for comprehensive characterization range of polymers and their degradation products33.
There is a lack of studies synthesizing the main characteristics of studies on the identification, characterization, and estimation ofmicroplastics flows of soils, especially towards the methodological standardization that may support further analysis of its environmental impacts.Therefore, to allow an improved understanding of MPs in the soil, we propose to compile methodological characteristics of studies published within the last five years on soil microplastics.
- Sampling, pre-treatment, and analysis
Sampling
The improper disposal of plastics generates degradation under environmental weather conditions, changing physical and chemical properties like crystallinity, sorption capacity, color, etc. The conversion into microplastics in the soil may cause further fragmentation and dissemination due to biotic and abioticfactors34. However, studies of characterization of soil plastic pollution are currently limited by the lack of adequate methods to quantify microplastics in soils19. In general, there is the absence of standard operating procedures to quantify microplastics in the environment, particularly in soil.
Soils are heterogeneous solid mixtures composed of minerals with a wide variety of particle size distributions and organic matter at various stages of decomposition35. The complexity inorganomineral interactions and the variability of soil media pose a challenge to soil sampling procedures for microplastic characterization, although it is recognized as an important emerging issue. Considering the complexity and the heterogeneity of soil components, the extraction and the separation of MPs may be complicated. Therefore, it is necessary to sample, measure, and quantify the amount of microplastics in the terrestrial environment at a wide range of spatial and temporal scales to determine the risk of adverse effects.
The selection of an adequate sampling method comprises an appropriate step of the process, involving considerations on the distribution of fragments in the field, their potential sources, and the site's geomorphology.Mölleret al. (2020) recently indicated common sampling strategies and, in accordance with the ISO 18400-102 standard, the sampling depth must be defined byconsidering the soil profile and management practices. Sampling in agricultural fields,for example, is limited to 5 cm depth in most studies29; however, a Federal Ordinance on Soil Protection and Contaminated Sites in Germany imposes a minimum depth of 30cm for soil sampling36.
Soil samples are usually collected using an auger in a predetermined area37. The variety of sampling ranges from randomly replicated samples38 27to selected land strips 39 38 29and stratified random sampling39. About the volume of soil collected, there is wide variation in practices adopted by researchers in knowledge: some collect composite samples, whilst others carry out samples in a larger volume box, which are later reduced. The quartering method,for example, maybe performed according to the ASTM-C702 standard. The reduction increases the sampling efficiency and avoids disturbing the concentrations of MPs when achieved adequatelyin the field or the laboratory, thus preventing bias in measuring plastic concentrations40. The amount of samples collected fromeach location is dependent on the size of the area under analysis: some researchers collect only one sample41 although most adopt composite samples39.
A further difficulty relies on the choice of procedures for soil preparationto analysis:someresearchers determine 50 g of clean soil (without organic matter) for sample analysis42 28, and others adopt 250g36. However, none of the studies mentions reasons,protocols, or standards that guided theadoption of the procedures described in the studies.
Soil characterization
Considering that MPs accumulate in the soil, they become part of the complex mixture with minerals and organic materials, making it difficult to remove particles for separation35. Thus, some authors believe that it is relevant to know in advance the soil characteristics,like pH, soil texture, and othersafter density separation when there is high organic matter in the soil, influencing sample preparation and other stages of analysis, since these elements may reduce the MPs recovery rate27. Other authors,like Zhang et al. (2018), attributed a higher rate of MPs recovery to intrinsic characteristics of sandy soilsthandifferent types of soil. However, other studies could not identify any reason for high MPs recovery rates in a given soil, considering the absence of differentiating characteristics in relation to other studies 43 39.
Sample ’ s pre-treatment
The first step to extract MPs from the soil is to dry the samples in a greenhouse to eliminate moisture, hinderingthe separation of organic matter7. Studies like Thomas et al., 2020 used the recommendation of ISO 11464, which recommends drying the soil at 40ºC for 72 hours,whileother authors like Liu et al. (2018) placed samples 24 hours at a temperature of 70ºC. However, some authors urged caution in the process 43, considering that temperatures above 40ºC could change the structural and physical properties of MPs due to degradation, melting, and eventually glass transition, e.g., in polybutylene terephthalate (40°C) and polyamide (50-75°C). After the drying process, sieving is recommended since it removes excess organic matter and fractionates granulometrically, facilitating the removal of particles larger than 5 mm7. Then, considering that the organic matter has excess debris, one study reported the need to sift the samples to analyze MPs size-frequency distribution using several stacked sieves meshes with aperture sizes set to 2.0, 1.0, 0.5, and 0.25 mm44. However, there is no consensus in the studies analyzed during the review.
Following, solutions of sodium chloride (NaCl), sodium bromide (NaBr), sodium iodide (NaI), and zinc chloride (ZnCl2) are used41 to take advantage of the difference in densities of plastics and soil particles36 43 35for the elimination of organic matter, which interferes in the chemical analysis for the identification of MPs45, ismost recommended the NaI46 7. However, the authors warn that NaI is expensive and relatively toxic to the biota;thus, cost-benefit and disposal procedures must be assessed before adopting NaI. Thus, several aqueous solutions with different densities isolate the fragments, depending on type and size27 37.
In addition, some researchers adopted an additional step through combination with other extraction methods to increase the efficiency of organic matter removal, such as KOH47 or Fenton Reagent38. Present in several publications, Fenton’s reagent is composed of the oxidizer H2O2 and is a strong ferrous ion catalyst (Fe2+) used as a cleaner of complex environmental samples due to its effectiveness in removing organic composite materials48 41. There was a combination of flotation with NaCl and digestion in other studies, which is a widely used technique to eliminate organic matter from samples; however, the reagent or temperature can degrade the polymers partially or even totally7.
Few studies have reported filtration, which may help retain MPs, depending on the pore size (ideal porosityreportedbetween 10µm and 20µm), although it is a slow process is49. In addition, some authors strongly recommend using the filter to remove particles that can contaminate the samples50 22. The filtersusually reported to perform filtration in studies, which present low interference with the identification of microparticles by the FTIR,are aluminum oxide and polycarbonate (PC)43. After filtration, the soil samples must be kept in the oven until dry, avoiding moisture interference in the analysis51 7.
MPs c haracterization
Recently, studies reported the use of dyes (like Nile Red or Evans Blue) to allow the visual identification of MPs by contrast with the surrounding matrix52 53 and the application of thecomplementary techniqueto avoid error rates in visual identification classification35,like Fourier transform infrared (FTIR) spectroscopy (Figure 2).
Figure 2 - Illustration showing methods used in previous studies on the detection and characterization of microplastics in soil and their impacts.
In general, the FTIR encompasses the technique usually adopted in the current MPs literature, confirming the identification, type, shape, and size of the fragments with a resolution of up to 20 µm54. FTIR spectroscopy qualitatively assesses MPs due to recognition of the spectra of the type of polymer in comparison to the spectra of known plastics and allows the identification of functional groups in the fragments19, the occurrence of structural changes in MPs55, and the presence of substances absorbed/adsorbed by the polymers that may have been released into the soil56 57.
The detection of extra peaks witha low percentage of similarity aboutthe characteristic spectrum of a pure polymerin FTIR spectroscopy indicates the need for further investigation on the possibility of polymer degradation, supporting the identification of secondary origin fragments7. Furthermore, FTIR analysis is widely adopted because it does not destroy polymeric samples 58.
Raman spectroscopy is also usedfrequently, and the combination of the electron microscope and spectroscopic investigation (either Raman or FTIR) improves analytical results59. Raman spectroscopy coupled to microscopy may identify MPs below 1 µm.In addition,there is less interference of humidity in the analysis, surpassing the limits of the FTIR. However, it requires precise technical skills to achieve spectral images60, and the high intense energy of the laser may destroy polymeric fragments50. The use of pigments and dyes introduces higher complexity in Raman analysis due to changes in the cations of the spectra in the technique, therefore, the use of Raman is not recommended in certain cases7. Another disadvantage of Raman is the Raman spectrum's obstruction due to additives used in plastics found in synthetic polymers617. Another disadvantage of Raman is the Raman spectrum's obstruction due to additives used in plastics found in synthetic polymers7.Raman spectroscopy is also usedfrequently, and the combination of the electron microscope and spectroscopic investigation (either Raman or FTIR) improves analytical results59. Raman spectroscopy coupled to microscopy may identify MPs below 1 µm.In addition,there is less interference of humidity in the analysis, surpassing the limits of the FTIR. However, it requires precise technical skills to achieve spectral images60, and the high intense energy of the laser may destroy polymeric fragments50. The use of pigments and dyes introduces higher complexity in Raman analysis due to changes in the cations of the spectra in the technique, therefore, the use of Raman is not recommended in certain cases. Another disadvantage of Raman is the Raman spectrum's obstruction due to additives used in plastics found in synthetic polymers 61.
According to Ruggeroet al. (2020), an alternative technique to identify MPs would be using the hot needle test, which may be used directly in a global sample or among residues that have undergone previous treatment. The technique is based on the contact of a hot needle, handled with tweezers,with the fragments suspected of being microplastics. The needle's heat makes the plastic sticky, leaving a mark on its surface, while other particles will not present a reaction to the heat. However, theadoption of the method is highly questioned due to the absence of validation in matrices like the soil with biota diversity and the lack of tests on its reliability regarding the size of the MPs that could be detected with this technique46.
Some researchers also use thermogravimetric analysis (TGA) to complement images acquired by FTIR or Raman, in addition to analyzing the thermal decomposition of the analyzed MPs. TGA analyzes the thermal stability of polymer samples and their fragments44, being a technique valuable for detecting the degradation level of the particles and evaluating theprimary or secondary origin of the fragments24. Furthermore, considering that plastics degradation is a long process, their permanence in the environment makes them suitable “habitats” for microorganisms62. Thus,another method adopted for thermoanalysis of fragments would be chromatography, which can identify and quantifyseveral polymers,e.g., polyethylene (PE), polystyrene (PS), polypropylene (PP), and polyethylene terephthalate (PET), in organic sediments63.
Photomicroscope, obtained by optical (OM), and scanning (SEM) microscopy provide high magnification images of microplastic surfaces,being useful to reveal the effects of degradations on the surfaces of microplastics since degradation by photo-oxidation occurs in the presence of light sources and air.The most common degradation process occurs through the appearance of microcracks arising from the splitting of polymer chains55. In addition, the analysis also helpsto determine the size of the fragments64 and verifying the existence of microorganisms on the surface of the microplastics65.
The SEM provides information on particle size, composition, and morphology, in addition to detecting patterns of degradation like fractures, grooves,etc.66, based on monitoring of the MPs surface througha high-intensity electron beam, which generates high-resolution images and allows the identification of mechanical stress67 59. The technique has also been used to identify plastic additives of inorganic origin,like metals, since it is possible to verify the morphological characteristics of these microplastics68 59. In addition, optical and electron microscopy allows the identification of evidence particle morphology and size 69 70. Nevertheless, although most researchers adopt the latest techniques, there are still studies being carried out with the use of an optical microscope and visual identification of MPs without equipment; however, errors or false positives may occur depending on the subjective attitude of the operator, the color and shape of the plastics, and the environmental matrix,considering the difficulty in differentiating MPs from the other materials within a global sample 46.
Conclusions
Currently, the research on the origin,characteristics, and impacts of microplastics is relatively recent. Thus, methods for extracting microplastics, especially fibers, from soil samples need further investigation. Furthermore, there is the absence of qualitative and quantitative methodssuitable for real-time monitoring to detectmicroplastics in effluent treatment plants. Techniques like FTIR are expensive, while lower-cost processes (like visual inspection) are time-consuming. Therefore, there is a need for research targeting the development of innovative,cost-effective qualitative and quantitative methods for the accurate determination of microplastics in the environment, especially soil pollution. Nowadays, methods require extensive pre-treatment methods to filter samples with moisture to facilitate the extraction of microplastics. The analytical methodsdescribed present requirements and limitations due to the complexity of heterogeneous soil matrices. The authors suggest combining methods to obtain comprehensive sampling, identification, characterization, and quantification of microplastics in different samples. On the other hand, the suggestion also highlights the disadvantages of some methods designed to encompass sample preparation until characterization, since they may generate divergent results and hinder comparison of evidence from different studies since there is no standard protocol for sample collection, treatment, or analysis. Different analytical methodologies will lead to discrepant results regarding properties, concentration, and other characteristics of MPs. The present article shows an inventory of the main methods for sample collection, identification, and quantification of MPs adopted in the literature recently published worldwide on plastic soil pollution.It is important to the point that the research of MPs in terrestrial environments is complex due to the heterogeneity of the soil samplesand the difficulties in removing organic matter, leading to the need foracombination of techniques for higher reliability in the characterization, according to the specific properties of the soil. There is high variability in the procedures for removal of the matrix to conserve the microplastics.Techniques are often adapted to try to ensure the efficient removal of organic materials. The use of vibrational spectroscopy (like FTIR) to confirm polymer characteristics enhances the reliability of the quantification process,whilst the use of Raman spectroscopy with fluorescent demarcation dyes should be avoideddue to potential bias in the analysis. Thus, there is urgent need for standardization of methodologies for investigation of MPs to ensure higher reliability of theresearch and provide consistency of comparisons of results in different environments.
ACKNOWLEDGMENTS
This research was funded by CNPq (#305819/2017-8, #306401/2013-4, and #420217/2016-9) and FAPESP (#2020/12208-9, and #2018/11277-7). The authors thank the UFABC, CAPES (Code 001), REVALORES Strategic Unit, CAPES (001), and Multiuser Central Facilities (CEM - UFABC).Conflicts of 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.
Reference s
2. Geyer R, Jambeck JR, Law KL. Production, use, and fate of all plastics ever made. Sci Adv. 2017;3(7):25-29. doi:10.1126/sciadv.1700782
3. Gong J, Xie P. Research progress in sources, analytical methods, eco-environmental effects, and control measures of microplastics. Chemosphere. 2020;254:126790. doi:10.1016/j.chemosphere.2020.126790
4. Anagnosti L, Varvaresou A, Pavlou P, Protopapa E, Carayanni V. Worldwide actions against plastic pollution from microbeads and microplastics in cosmetics focusing on European policies. Has the issue been handled effectively? Mar Pollut Bull. 2021;162(November 2020):111883. doi:10.1016/j.marpolbul.2020.111883
5. Galafassi S, Nizzetto L, Volta P. Plastic sources: A survey across scientific and grey literature for their inventory and relative contribution to microplastics pollution in natural environments, with an emphasis on surface water. Sci Total Environ. 2019;693:133499. doi:10.1016/j.scitotenv.2019.07.305
6. Qi R, Jones DL, Li Z, Liu Q, Yan C. Behavior of microplastics and plastic film residues in the soil environment: A critical review. Sci Total Environ. 2020;703:134722. doi:10.1016/j.scitotenv.2019.134722
7. Dioses-Salinas DC, Pizarro-Ortega CI, De-la-Torre GE. A methodological approach of the current literature on microplastic contamination in terrestrial environments: Current knowledge and baseline considerations. Sci Total Environ. 2020;730:139164. doi:10.1016/j.scitotenv.2020.139164
8. Wong JKH, Lee KK, Tang KHD, Yap PS. Microplastics in the freshwater and terrestrial environments: Prevalence, fates, impacts and sustainable solutions. Sci Total Environ. 2020;719:137512. doi:10.1016/j.scitotenv.2020.137512
9. Rodrigues JP, Duarte AC, Santos-Echeandía J, Rocha-Santos T. Significance of interactions between microplastics and POPs in the marine environment: A critical overview. TrAC - Trends Anal Chem. 2019;111:252-260. doi:10.1016/j.trac.2018.11.038
10. Mendrik FM, Henry TB, Burdett H, et al. Species-specific impact of microplastics on coral physiology. Environ Pollut. 2021;269:116238. doi:10.1016/j.envpol.2020.116238
11. Sarker A, Deepo DM, Nandi R, et al. A review of microplastics pollution in the soil and terrestrial ecosystems: A global and Bangladesh perspective. Sci Total Environ. 2020;733:139296. doi:10.1016/j.scitotenv.2020.139296
12. Filiciotto L, Rothenberg G. Biodegradable Plastics: Standards, Policies, and Impacts. ChemSusChem. 2021;14(1):56-72. doi:10.1002/cssc.202002044
13. Oliveri Conti G, Ferrante M, Banni M, et al. Micro- and nano-plastics in edible fruit and vegetables. The first diet risks assessment for the general population. Environ Res. 2020;187(May):109677. doi:10.1016/j.envres.2020.109677
14. Barboza LGA, Dick Vethaak A, Lavorante BRBO, Lundebye AK, Guilhermino L. Marine microplastic debris: An emerging issue for food security, food safety and human health. Mar Pollut Bull. 2018;133(January):336-348. doi:10.1016/j.marpolbul.2018.05.047
15. Birch QT, Potter PM, Pinto PX, Dionysiou DD, Al-Abed SR. Sources, Transport, Measurement and Impact of Nano and Microplastics in Urban Watersheds. Vol 19. Springer Netherlands; 2020. doi:10.1007/s11157-020-09529-x
16. Yao L, Hui L, Yang Z, Chen X, Xiao A. Freshwater microplastics pollution: Detecting and visualizing emerging trends based on Citespace II. Chemosphere. 2020;245. doi:10.1016/j.chemosphere.2019.125627
17. He D, Luo Y, Lu S, Liu M, Song Y, Lei L. Microplastics in soils: Analytical methods, pollution characteristics and ecological risks. TrAC - Trends Anal Chem. 2018;109:163-172. doi:10.1016/j.trac.2018.10.006
18. Dees JP, Ateia M, Sanchez DL. Microplastics and Their Degradation Products in Surface Waters: A Missing Piece of the Global Carbon Cycle Puzzle. ACS ES&T Water. 2021;1(2):214-216. doi:10.1021/acsestwater.0c00205
19. Silva AB, Bastos AS, Justino CIL, da Costa JP, Duarte AC, Rocha-Santos TAP. Microplastics in the environment: Challenges in analytical chemistry - A review. Anal Chim Acta. 2018;1017:1-19. doi:10.1016/j.aca.2018.02.043
20. Hodson ME, Duffus-Hodson CA, Clark A, Prendergast-Miller MT, Thorpe KL. Plastic Bag Derived-Microplastics as a Vector for Metal Exposure in Terrestrial Invertebrates. Environ Sci Technol. 2017;51(8):4714-4721. doi:10.1021/acs.est.7b00635
21. Huerta Lwanga E, Gertsen H, Gooren H, et al. Incorporation of microplastics from litter into burrows of Lumbricus terrestris. Environ Pollut. 2017;220:523-531. doi:10.1016/j.envpol.2016.09.096
22. Peeken I, Primpke S, Beyer B, et al. Arctic sea ice is an important temporal sink and means of transport for microplastic. Nat Commun. 2018;9(1). doi:10.1038/s41467-018-03825-5
23. Rillig MC, Lehmann A. Microplastic in terrestrial ecosystems Research shifts from ecotoxicology to ecosystem effects and Earth system feedbacks. Science (80- ). 2020;368(6498):1430-1431. doi:10.1126/science.abb5979
24. Brahney J, Hallerud M, Heim E, Hahnenberger M, Sukumaran S. Plastic rain in protected areas of the United States. Science (80- ). 2020;368(6496):1257-1260. doi:10.1126/science.aaz5819
25. Lin D, Yang G, Dou P, et al. Microplastics negatively affect soil fauna but stimulate microbial activity: insights from a field-based microplastic addition experiment. Proc R Soc B Biol Sci. 2020;287(1934). doi:10.1098/rspb.2020.1268
26. Lv L, Yan X, Feng L, et al. Challenge for the detection of microplastics in the environment. Water Environ Res. 2019;93(1):5-15. doi:10.1002/wer.1281
27. Corradini F, Casado F, Leiva V, Huerta-Lwanga E, Geissen V. Microplastics occurrence and frequency in soils under different land uses on a regional scale. Sci Total Environ. 2021;752:141917. doi:10.1016/j.scitotenv.2020.141917
28. Liu M, Lu S, Song Y, et al. Microplastic and mesoplastic pollution in farmland soils in suburbs of Shanghai, China. Environ Pollut. 2018;242:855-862. doi:10.1016/j.envpol.2018.07.051
29. Piehl S, Leibner A, Löder MGJ, Dris R, Bogner C, Laforsch C. Identification and quantification of macro- and microplastics on an agricultural farmland. Sci Rep. 2018;8(1):1-9. doi:10.1038/s41598-018-36172-y
30. Kumar M, Xiong X, He M, et al. Microplastics as pollutants in agricultural soils. Environ Pollut. 2020;265:114980. doi:10.1016/j.envpol.2020.114980
31. Zhang Y, Kang S, Allen S, Allen D, Gao T, Sillanpää M. Atmospheric microplastics: A review on current status and perspectives. Earth-Science Rev. 2020;203(December 2019):103118. doi:10.1016/j.earscirev.2020.103118
32. Yang Y, Liu L, Zhang F, et al. Enhanced nitrous oxide emissions caused by atmospheric nitrogen deposition in agroecosystems over China. Environ Sci Pollut Res. 2021;28(12):15350-15360. doi:10.1007/s11356-020-11591-5
33. Dierkes G, Lauschke T, Becher S, Schumacher H, Földi C, Ternes T. Quantification of microplastics in environmental samples via pressurized liquid extraction and pyrolysis-gas chromatography. Anal Bioanal Chem. 2019;411(26):6959-6968. doi:10.1007/s00216-019-02066-9
34. Baho DL, Bundschuh M, Futter MN. Microplastics in terrestrial ecosystems: Moving beyond the state of the art to minimize the risk of ecological surprise. Glob Chang Biol. 2021;(March):1-18. doi:10.1111/gcb.15724
35. Bläsing M, Amelung W. Plastics in soil: Analytical methods and possible sources. Sci Total Environ. 2018;612:422-435. doi:10.1016/j.scitotenv.2017.08.086
36. Möller JN, Heisel I, Satzger A, et al. Tackling the Challenge of Extracting Microplastics from Soils: A Protocol to Purify Soil Samples for Spectroscopic Analysis. Environ Toxicol Chem. 2021;00(00):1-14. doi:10.1002/etc.5024
37. Yu Y, Flury M. How to take representative samples to quantify microplastic particles in soil? Sci Total Environ. 2021;784:147166. doi:10.1016/j.scitotenv.2021.147166
38. Crossman J, Hurley RR, Futter M, Nizzetto L. Transfer and transport of microplastics from biosolids to agricultural soils and the wider environment. Sci Total Environ. 2020;724:138334. doi:10.1016/j.scitotenv.2020.138334
39. Scheurer M, Bigalke M. Microplastics in Swiss Floodplain Soils. Environ Sci Technol. 2018;52(6):3591-3598. doi:10.1021/acs.est.7b06003
40. Ghimire S, Flury M, Scheenstra EJ, Miles CA. Sampling and degradation of biodegradable plastic and paper mulches in field after tillage incorporation. Sci Total Environ. 2020;703:135577. doi:10.1016/j.scitotenv.2019.135577
41. Weithmann N, Möller JN, Löder MGJ, Piehl S, Laforsch C, Freitag R. Organic fertilizer as a vehicle for the entry of microplastic into the environment. Sci Adv. 2018;4(4):1-8. doi:10.1126/sciadv.aap8060
42. Zhou B, Wang J, Zhang H, et al. Microplastics in agricultural soils on the coastal plain of Hangzhou Bay, east China: Multiple sources other than plastic mulching film. J Hazard Mater. 2020;388(December 2019):121814. doi:10.1016/j.jhazmat.2019.121814
43. Thomas D, Schütze B, Heinze WM, Steinmetz Z. Sample preparation techniques for the analysis of microplastics in soil—a review. Sustain. 2020;12(21):1-28. doi:10.3390/su12219074
44. Gimiliani GT, Fornari M, Redígolo MM, Willian Vega Bustillos JO, Moledo de Souza Abessa D, Faustino Pires MA. Simple and cost-effective method for microplastic quantification in estuarine sediment: A case study of the Santos and São Vicente Estuarine System. Case Stud Chem Environ Eng. 2020;2:100020. doi:10.1016/j.cscee.2020.100020
45. Wang X, Li C, Liu K, Zhu L, Song Z, Li D. Atmospheric microplastic over the South China Sea and East Indian Ocean: abundance, distribution and source. J Hazard Mater. 2020;389(September 2019):121846. doi:10.1016/j.jhazmat.2019.121846
46. Ruggero F, Gori R, Lubello C. Methodologies for Microplastics Recovery and Identification in Heterogeneous Solid Matrices: A Review. J Polym Environ. 2020;28(3):739-748. doi:10.1007/s10924-019-01644-3
47. Zhou Q, Tian C, Luo Y. Various forms and deposition fluxes of microplastics identified in the coastal urban atmosphere. Kexue Tongbao/Chinese Sci Bull. 2017;62(33):3902-3909. doi:10.1360/N972017-00956
48. Tagg AS, Harrison JP, Ju-Nam Y, et al. Fenton’s reagent for the rapid and efficient isolation of microplastics from wastewater. Chem Commun. 2017;53(2):372-375. doi:10.1039/c6cc08798a
49. Talvitie J, Mikola A, Koistinen A, Setälä O. Solutions to microplastic pollution – Removal of microplastics from wastewater effluent with advanced wastewater treatment technologies. Water Res. 2017;123:401-407. doi:10.1016/j.watres.2017.07.005
50. Dehaut A, Hermabessiere L, Duflos G. Current frontiers and recommendations for the study of microplastics in seafood. TrAC - Trends Anal Chem. 2019;116:346-359. doi:10.1016/j.trac.2018.11.011
51. Simon M, van Alst N, Vollertsen J. Quantification of microplastic mass and removal rates at wastewater treatment plants applying Focal Plane Array (FPA)-based Fourier Transform Infrared (FT-IR) imaging. Water Res. 2018;142:1-9. doi:10.1016/j.watres.2018.05.019
52. Helmberger MS, Tiemann LK, Grieshop MJ. Towards an ecology of soil microplastics. Funct Ecol. 2020;34(3):550-560. doi:10.1111/1365-2435.13495
53. Nel HA, Chetwynd AJ, Kelleher L, et al. Detection limits are central to improve reporting standards when using Nile red for microplastic quantification. Chemosphere. 2021;263. doi:10.1016/j.chemosphere.2020.127953
54. Xu C, Zhang B, Gu C, et al. Are we underestimating the sources of microplastic pollution in terrestrial environment? J Hazard Mater. 2020;400(June):123228. doi:10.1016/j.jhazmat.2020.123228
55. Padervand M, Lichtfouse E, Robert D, Wang C. Removal of microplastics from the environment. A review. Environ Chem Lett. 2020;18(3):807-828. doi:10.1007/s10311-020-00983-1
56. Afrin S, Uddin MK, Rahman MM. Microplastics contamination in the soil from Urban Landfill site, Dhaka, Bangladesh. Heliyon. 2020;6(11). doi:10.1016/j.heliyon.2020.e05572
57. Hou L, Kumar D, Yoo CG, Gitsov I, Majumder ELW. Conversion and removal strategies for microplastics in wastewater treatment plants and landfills. Chem Eng J. 2021;406(April 2020):126715. doi:10.1016/j.cej.2020.126715
58. Renner G, Schmidt TC, Schram J. Analytical methodologies for monitoring micro(nano)plastics: Which are fit for purpose? Curr Opin Environ Sci Heal. 2018;1:55-61. doi:10.1016/j.coesh.2017.11.001
59. Shruti VC, Pérez-Guevara F, Elizalde-Martínez I, Kutralam-Muniasamy G. Current trends and analytical methods for evaluation of microplastics in stormwater. Trends Environ Anal Chem. 2021;30. doi:10.1016/j.teac.2021.e00123
60. Ribeiro-Claro P, Nolasco MM, Araújo C. Characterization of Microplastics by Raman Spectroscopy. Compr Anal Chem. 2017;75:119-151. doi:10.1016/bs.coac.2016.10.001
61. Karami A, Golieskardi A, Choo CK, Larat V, Karbalaei S, Salamatinia B. Microplastic and mesoplastic contamination in canned sardines and sprats. Sci Total Environ. 2018;612:1380-1386. doi:10.1016/j.scitotenv.2017.09.005
62. Laverty AL, Primpke S, Lorenz C, Gerdts G, Dobbs FC. Bacterial biofilms colonizing plastics in estuarine waters, with an emphasis on Vibrio spp. And their antibacterial resistance. PLoS One. 2020;15(8 August). doi:10.1371/journal.pone.0237704
63. Becker R, Altmann K, Sommerfeld T, Braun U. Quantification of microplastics in a freshwater suspended organic matter using different thermoanalytical methods – outcome of an interlaboratory comparison. J Anal Appl Pyrolysis. 2020;148(December 2019):104829. doi:10.1016/j.jaap.2020.104829
64. Al-Salem SM, Al-Hazza’a A, Karam HJ, Al-Wadi MH, Al-Dhafeeri AT, Al-Rowaih AA. Insights into the evaluation of the abiotic and biotic degradation rate of commercial pro-oxidant filled polyethylene (PE) thin films. J Environ Manage. 2019;250(September):109475. doi:10.1016/j.jenvman.2019.109475
65. Kim SW, An YJ. Edible size of polyethylene microplastics and their effects on springtail behavior. Environ Pollut. 2020;266:115255. doi:10.1016/j.envpol.2020.115255
66. Enyoh CE, Verla AW, Verla EN, Ibe FC, Amaobi CE. Airborne microplastics: a review study on method for analysis, occurrence, movement and risks. Environ Monit Assess. 2019;191(11). doi:10.1007/s10661-019-7842-0
67. Winkler A, Santo N, Ortenzi MA, Bolzoni E, Bacchetta R, Tremolada P. Does mechanical stress cause microplastic release from plastic water bottles? Water Res. 2019;166:115082. doi:10.1016/j.watres.2019.115082
