Tackling the Challenge of Extracting Microplastics from Soils: A Protocol to Purify Soil Samples for Spectroscopic Analysis

Plastic Quantification and Polyethylene Overestimation in Agricultural Soil Using Large-Volume Pyrolysis and TD-GC-MS/MS

Quantification of microplastics in soil is needed to understand their impact and fate in agricultural areas. Often, low sample volume and removal of organic matter (OM) limit representative quantification. We present a method which allows simultaneous quantification of microplastics in homogenized, large environmental samples (>1 g) and tested polyethylene (PE), polyethylene terephthalate (PET), and polystyrene (PS) (200-400 μm) overestimation by fresh and diagenetically altered OM in agricultural soils using a new combination of large-volume pyrolysis adsorption with thermal desorption-gas chromatography-tandem mass spectrometry (TD-GC-MS/MS). Characteristic MS/MS profiles for PE, PET, and PS were derived from plastic pyrolysis and allowed for a new mass separation of PET. Volume-defined standard particles (125 × 125 × 20 μm3) were developed with the respective weight (PE: 0.48 ± 0.12, PET: 0.50 ± 0.10, PS: 0.31 ± 0.08 μg), which can be spiked into solid samples. Diagenetically altered OM contained compounds that could be incorrectly identified as PE and suggest a mathematical correction to account for OM contribution. With a standard addition method, we quantified PS, PET, and PEcorrected in two agricultural soils. This provides a base to simultaneously quantify a variety of microplastics in many environmental matrices and agricultural soil.

Unveiling the impact of microplastics and nanoplastics on vascular plants: A cellular metabolomic and transcriptomic review

With increasing plastic manufacture and consumption, microplastics/nanoplastics (MP/NP) pollution has become one of the world's pressing global environmental issues, which poses significant threats to ecosystems and human health. In recent years, sharp increasing researches have confirmed that MP/NP had direct or indirect effects on vegetative growth and sexual process of vascular plant. But the potential mechanisms remain ambiguous. MP/NP particles can be adsorbed and/or absorbed by plant roots or leaves and thus cause diverse effects on plant. This holistic review aims to discuss the direct effects of MP/NP on vascular plant, with special emphasis on the changes of metabolic and molecular levels. MP/NP can alter substance and energy metabolism, as well as shifts in gene expression patterns. Key aspects affected by MP/NP stress include carbon and nitrogen metabolism, amino acids biosynthesis and plant hormone signal transduction, expression of stress related genes, carbon and nitrogen metabolism related genes, as well as those involved in pathogen defense. Additionally, the review provides updated insights into the growth and physiological responses of plants exposed to MP/NP, encompassing phenomena such as seed/spore germination, photosynthesis, oxidative stress, cytotoxicity, and genotoxicity. By examining the direct impact of MP/NP from both physiological and molecular perspectives, this review sets the stage for future investigations into the complex interactions between plants and plastic pollutants.

A method for the extraction of microplastics from solid biowastes including biosolids, compost, and soil for analysis by µ-FTIR

Few methods exist detailing the extraction of microplastics from organic matrices. A validated method for the successful extraction of microplastics from solid biowastes including biosolids, compost, and soil for spectroscopic analysis by micro-Fourier transform infrared spectroscopy (µ-FTIR) was developed. Solid dry biowastes were first digested with a wet peroxide oxidation (WPO) with iron (II) solution and 30% hydrogen peroxide followed by sequential density separations with ultra-pure water and 1.8 g cm-3 NaI in an optimised sediment-microplastic isolation (SMI) unit. The average recoveries for spiked microplastics were 92, 95 and 98% for bagged compost, biosolids, and soil, respectively. This method ensures a high microplastic recovery by first chemically disintegrating biowaste aggregates without employing destructive methods like milling and allows for successful density separations where the settled fraction is isolated off from the supernatant, allowing thorough rinsing of the equipment and thus a greater transferal of particles into the vacuum filtering device. Minimal processing steps reduce the instance of introducing contamination and particle loss.•Digestion as a first step to disintegrate aggregates to release entrapped microplastics•Density separation with SMI unit with the method adapted for biowastes•Minimal steps to reduce contamination and particle loss.

Microplastic separation and enrichment in microchannels under derivative electric field gradient by bipolar electrode reactions

The decomposed plastic products in the natural environment evolve into tiny plastic particles with characteristics such as small size, lightweight, and difficulty in removal, resulting in a significant pollution issue in aquatic environments. Significant progress has been made in microplastic separation technology benefiting from microfluidic chips in recent years. Based on the mechanisms of microfluidic control technology, this study investigates the enrichment and separation mechanisms of polystyrene particles in an unbuffered solution. The Faraday reaction caused by the bipolar electrodes changes the electric field gradient and improves the separation efficiency. We also propose  an evaluation scheme to measure the separation efficiency. Finite element simulations are conducted to parametrically analyze the influence of applied voltages, channel geometry, and size of electrodes on plastic particle separation. The numerical cases indicate that the electrode-installed microfluidic channels separate microplastic particles effectively and precisely. The electrodes play an important role in local electric field distribution and trigger violent chemical reactions. By optimizing the microchannel structure, applied voltages, and separation channel angle, an optimal solution for separating microplastic particles can be found. This study could supply some references to control microplastic pollution in the future.

Identification of microplastics extracted from field soils amended with municipal biosolids

Microplastic particles in arable soil are expected to impact the environment and potentially human health. The application of municipal biosolids (MBs) to agricultural land presents a further dilemma in that biosolids act as a fertilizer for crop growth, and a disposal pathway for wastewater treatment plants. They are also a direct path for emerging contaminants, such as microplastics to enter the terrestrial environment. Reliable methods are needed to identify and quantify microplastics, found in agricultural soils to determine how microplastics are being cycled in the terrestrial environment. In this study, we developed a method for extracting microplastics from soil, and characterized their composition and identity for particles sized 5 μm to 2 mm. Method development was initially completed using natural soils spiked with microplastics and MBs, followed by the analyses of soil sampled from an agricultural field where MBs were recently applied at a rate of 13 tons dw/ha. The procedures that used the spiked samples showed that microplastics can be reliably extracted from soil in a laboratory setting, and identified and semi-quantified by thermogravimetric analysis combined with Fourier-transform infrared spectroscopy (TGA-FTIR). However, when the same methods were applied to the soil samples collected from the agricultural field, reproducibility became a challenge, as the number and type of microplastics changed even within the same soils (i.e., collected the same day from the same exact location). The variation in reproducibility observed between laboratory and field samples underscores the significant heterogeneity present in the environment. This heterogeneity, in turn, affects the identification and quantity of microplastics detected, a phenomenon observed even when comparing different fields within a single treatment regimen.

A critical review of the recent trends in source tracing of microplastics in the environment

Microplastics are found across the globe because of their size and ability to transport across environments. The effects of microplastics on the micro- and macro-organisms have brought out concern over the potential risk to human health and the need to regulate their distribution at the source. Control of microplastic pollution requires region-specific management and mitigation strategies which can be developed with the information on sources and their contributions. This review provides an overview of the sources, fate, and distribution of microplastics along with techniques to source-trace microplastics. Source-tracing approaches provide both qualitative and quantitive information. Since better outcomes have been produced by the integration of techniques like backward trajectory analysis with cluster analysis, the significance of integrated and multi-dimensional approaches has been emphasized. The scope of the plastisphere, heavy metal, and biofilm microbial community in tracing the sources of microplastics are also highlighted. The present review allows the researchers and policymakers to understand the recent trends in the source-tracing of microplastics which will help them to develop techniques and comprehensive action plans to limit the microplastic discharge at sources.

Seasonal variations of microplastic pollution in the German River Weser

Rivers play a major role in the distribution of microplastics (MPs) in the environment, however, research on temporal variations in these highly dynamic systems is still in its infancy. To date, most studies dealing with the seasonality of MP contamination in rivers focus on bi-yearly analysis, while temporal fluctuations over the course of the year are rarely studied. To shed more light on seasonal variability of MP abundance and potential driving factors, we have thus sampled the water surface of one location in the Weser River in Germany monthly over one entire year. In our study, we targeted MP in the size range 10-5000 μm, using two different state-of-the-art sampling methods (manta net for large MP (l-MP; 500-5000 μm) and a filtration system for small MP (s-MP; 10-500 μm)) and analysis techniques (ATR-FTIR and FPA-μFTIR) for chemical identification. Our findings show a strong size-dependent positive correlation of the MP concentration with discharge rates (specifically direct runoff) and suspended particulate matter (SPM) for s-MPs, specifically in the size range 10-149 μm. L-MPs, however, show a different environmental behaviour and do not follow these patterns. With our study, we were able to deliver a much higher temporal resolution, covering a broader size range of MPs compared to most studies. Our findings point towards an interplay of two possible mechanisms: a) the riverbeds play an important role in large-scale MP and SPM release via resuspension during high discharge events, and b) precipitation-driven soil erosion and runoff from urban surfaces (e.g. rain sewers) introduce MP and SPM. Hence, our study serves as a basis for more detailed investigations of MP transport in and between ecosystems.

When microplastics meet electroanalysis: future analytical trends for an emerging threat

Microplastics are a major modern challenge that must be addressed to protect the environment, particularly the marine environment. Microplastics, defined as particles ≤5 mm, are ubiquitous in the environment. Their small size for a relatively large surface area, high persistence and easy distribution in water, soil and air require the development of new analytical methods to monitor their presence. At present, the availability of analytical techniques that are easy to use, automated, inexpensive and based on new approaches to improve detection remains an open challenge. This review aims to outline the evolution and novelties of classical and advanced methods, in particular the recently reported electroanalytical detectors, methods and devices. Among all the studies reviewed here, we highlight the great advantages of electroanalytical tools over spectroscopic and thermal analysis, especially for the rapid and accurate detection of microplastics in the sub-micron range. Finally, the challenges faced in the development of automated analytical methods are discussed, highlighting recent trends in artificial intelligence (AI) in microplastics analysis.

Microplastics and biobased polymers to combat plastics waste

Microplastics (MPs) have become the major global concern due to their adverse effects on the environment, human health, and hygiene. These complex molecules have numerous toxic impacts on human well-being. This review focuses on the methods for chemically quantifying and identifying MPs in real-time samples, as well as the detrimental effects resulting from exposure to them. Biopolymers offer promising solutions for reducing the environmental impact caused by persistent plastic pollution. The review also examines the significant progress achieved in the preparation and modification of various biobased polymers, including polylactic acid (PLA), poly(ε-caprolactone) (PCL), lignin-based polymers, poly-3-hydroxybutyrate (PHB), and poly(hydroxyalkanoates) (PHA), which hold promise for addressing the challenges associated with unplanned plastic waste disposal.

Extraction of Common Small Microplastics and Nanoplastics Embedded in Environmental Solid Matrices by Tetramethylammonium Hydroxide Digestion and Dichloromethane Dissolution for Py-GC-MS Determination

Determination of microplastics and nanoplastics (MNPs), especially small MPs and NPs (<150 μm), in solid environmental matrices is a challenging task due to the formation of stable aggregates between MNPs and natural colloids. Herein, a novel method for extracting small MPs and NPs embedded in soils/sediments/sludges has been developed by combining tetramethylammonium hydroxide (TMAH) digestion with dichloromethane (DCM) dissolution. The solid samples were digested with TMAH, and the collected precipitate was washed with anhydrous ethanol to eliminate the natural organic matter. Then, the MNPs in precipitate were extracted by dissolving in DCM under ultrasonic conditions. Under the optimized digestion and extraction conditions, the factors including sizes and concentrations of MNPs showed insignificant effects on the extraction process. The feasibility of this sample preparation method was verified by the satisfactory spiked recoveries (79.6-91.4%) of polystyrene, polyethylene, polypropylene, poly(methyl methacrylate), polyvinyl chloride, and polyethylene terephthalate MNPs in soil/sediment/sludge samples. The proposed sample preparation method was coupled with pyrolysis gas chromatography-mass spectrometry to determine trace small MPs and NPs with a relatively low detection limit of 2.3-29.2 μg/g. Notably, commonly used MNPs were successfully detected at levels of 4.6-51.4 μg/g in 6 soil/sediment/sludge samples. This proposed method is promising for evaluating small solid-embedded MNP pollution.

The abundance, characteristics and distribution of microplastics (MPs) in farmland soil-Based on research in China

Microplastics (MPs) in farmland soil deteriorate soil environment and increase food toxicity, thereby threatening the agricultural production environment and human safety. However, a systematic understanding of MPs pollution in farmland soil is lacking in China. Therefore, the relevant literature was comprehensively discussed to discuss the abundance, characteristics, distribution and influencing factors of MPs in farmland soil. The conclusions are as follows: (1) The highest and lowest MPs abundance were in marginal tropical humid and plateau temperate semi-arid regions, accounting for 7579 n/kg and 48 n/kg, respectively. (2) The main shapes of MPs in farmland soil are fragment/flake and fiber, accounting for 44.0 % and 34.4 %, respectively. The MPs are mostly transparent (21.8 %) and black (21.5 %). Among the MPs types, polyethylene (PE) and polypropylene (PP) are dominant, accounting for 26.2 % and 19.0 %, respectively. The main size of MPs in farmland soil is 0.1-0.5 mm, with average proportions was 51.4 %. (3) Compared with non-fertilizing and non-mulching, the MPs abundance in the fertilizing and mulching farmland soils increased by 170 % and 232 %, respectively. (4) In the farmland soil, the MPs abundance was significantly positive with temperature, sunshine hour, and altitude. (5) In farmland soil of China, the most commonly used MPs dispersion treatment was H₂O₂ solution digestion, the extracting solution commonly used for density flotation was NaCl solution, and microscopic and spectroscopic measurements were typically used measurements. The results could provide a basis for monitoring the MP abundances in farmland soil and preventing the transfer of MPs pollution in soil.

Comparison of two rapid automated analysis tools for large FTIR microplastic datasets

One of the biggest issues in microplastic (MP, plastic items  <5 mm) research is the lack of standardisation and harmonisation in all fields, reaching from sampling methodology to sample purification, analytical methods and data analysis. This hampers comparability as well as reproducibility among studies. Concerning chemical analysis of MPs, Fourier-transform infrared (FTIR) spectroscocopy is one of the most powerful tools. Here, focal plane array (FPA) based micro-FTIR (µFTIR) imaging allows for rapid measurement and identification without manual preselection of putative MP and therefore enables large sample throughputs with high spatial resolution. The resulting huge datasets necessitate automated algorithms for data analysis in a reasonable time frame. Although solutions are available, little is known about the comparability or the level of reliability of their output. For the first time, within our study, we compare two well-established and frequently applied data analysis algorithms in regard to results in abundance, polymer composition and size distributions of MP (11-500 µm) derived from selected environmental water samples: (a) the siMPle analysis tool (systematic identification of MicroPlastics in the environment) in combination with MPAPP (MicroPlastic Automated Particle/fibre analysis Pipeline) and (b) the BPF (Bayreuth Particle Finder). The results of our comparison show an overall good accordance but also indicate discrepancies concerning certain polymer types/clusters as well as the smallest MP size classes. Our study further demonstrates that a detailed comparison of MP algorithms is an essential prerequisite for a better comparability of MP data.

A novel approach to extract, purify, and fractionate microplastics from environmental matrices by isopycnic ultracentrifugation

The increasing accumulation of microplastics (MP) in the environment is considered one of the most important environmental challenges of our times. Reliable extraction and detection methods for MP in environmental samples are essential for determining the extent of pollution and assessing ecological risks. However, extraction of MP from complex environmental matrices such as soil remains technically challenging. Today, density-based extractions with saturated salt solutions are widely applied. Nevertheless, current methods do not allow for the fractionation of different MP particle types according to their specific polymer densities. Here, we present a novel isopycnic ultracentrifugation approach for the simultaneous extraction and fractionation of MP mixtures based on the particle-specific buoyant densities. In this proof-of-concept study, diffusion-based density gradients were prepared using caesium chloride media, covering a density range between 1.1 and 1.5 g mL^-1_, sufficient to resolve many common polymer densities. We selected MP particles with a low (polyamide; PA66), medium (polybutylene adipate terephthalate; PBAT), and high (polyethylene terephthalate; PET) density to validate separation performance. Both pristine and soil-incubated MP mixtures showed clear banding patterns at expected buoyant densities after isopycnic separation. μFTIR imaging of subsamples collected from resolved MP fractions showed a polymer-specific separation of ≥87.6 %. In addition, the quantitative recovery of MP particles from soil was between 86 and 99 %. The potential of isopycnic ultracentrifugation to preserve MP-associated biofilms was also assessed. Soil-incubated MP particles were inspected by confocal laser scanning microscopy before and after isopycnic separation, indicating a preservation of bioorganic structures. Hence, isopycnic ultracentrifugation offers a powerful novel approach for a polymer-specific extraction and resolution of MP particles with a wide potential for applications in MP research.

Distribution, characteristics, and risk assessments analysis of microplastics in shore sediments and surface water of Moheshkhali channel of Bay of Bengal, Bangladesh

Microplastic pollution in various ecosystems has gained significant attention across the globe. Due to ubiquitous abundance, terrestrial and aquatic ecosystems at regional scales are polluted via uncontrolled anthropogenic actions. Therefore, this study investigates microplastic pollution and distribution in sediments and surface water of the Moheshkhali channel of Bangladesh, Bay of Bengal, along with their shape, size, color, and polymeric analysis. It has been observed that both sediments and surface water are significantly contaminated with microplastics at 14 sediments and 12 surface water sampling sites. 291 particles of microplastic were observed in two quadrants, separated 10-m away from each other, across 14 sediment sampling sites, with average concentrations registered in the range of 6.66 to 138.33 particles/m². At the same time, 163 particles were observed across 12 sampling sites in the surface water, ranging from 0 to ~0.1 particles/m³. Various shapes, like films, fragments, fiber/lines, foams, and pellets (resins), were observed extensively in the Moheshkhali channel. Besides, various risk assessments, like contamination factors, polymeric risk assessment, pollution risk index, and pollution load index, were analyzed for each sampling site across the channel. Pollution load index (PLI) of shore sediments and surface water were 2.51 and 1.67, respectively, indicating significant pollution in the Moheshkhali channel. This research investigation provides insight into anthropogenic activities and baseline microplastic pollution in the Moheshkhali channel of Bangladesh, which helps to prepare robust strategies for conservation and management to deal with such environmental issues.

Efficient extraction of small microplastic particles from rat feed and feces for quantification

To date, microplastic is ubiquitously encountered in the environment. Studies analyzing microplastic in terrestrial ecosystems, including animal feces and feed, are few. Microplastic quantification method validation and harmonization are not yet far developed. For the analysis of small microplastic, approximately <0.5 mm, extraction from organic and inorganic materials is fundamental prior to quantitative and qualitative analysis. Method validation, including recovery studies, are necessary throughout the analytical chain. In this study, we developed an optimized, efficient protocol with a duration of 72 h for the digestion of laboratory rat feed and feces. A combination of a mild acidic (H₂O₂ 15%; HNO₃ 5%) and an alkaline treatment (10% KOH) dissolving the previous filter, followed by enzymatic digestion (Viscozyme®L) proved to be efficient for the extraction and identification of spiked polyamide (15-20 μm) and polyethylene (40-48 μm) from feed and feces samples from rats, showing high recovery rates. Extracted rat feces samples from an in vivo study in which Wistar rats were fed with feed containing microplastic were analyzed with pyrolysis-gas chromatography-Orbitrap™ mass spectrometry, quantifying recovered microplastic in rat feces in environmentally relevant concentrations. The presented three-step protocol provides a suitable, time and cost-effective method to extract microplastic from rat feed and feces.

A systematic review on bioplastic-soil interaction: Exploring the effects of residual bioplastics on the soil geoenvironment

Growing demand for plastic and increasing plastic waste pollution have led to significant environmental challenges and concerns in today's world. Bioplastics offer exciting new opportunities and possibilities where biodegradable and bio-based plastics are expected to be more eco-friendly and rely on renewable resources. With all its promises, evaluating its real impact and fate on the geoenvironment is paramount for promoting bioplastic use. This paper presents a systematic literature review to understand current bioplastic-soil research and the effects of its residues on the geoenvironment. 632 studies related to bioplastic research in soil since 1973 were identified and categorized into different relevant topics. Publication trend showed bioplastic-soil research grew exponentially after 2010 wherein field studies accounted to 33.1 % of the total studies and only about 9.7 % studied the effects of bioplastic residues on the geoenvironment. Majority of the lab studies were on development and subsequent stability of bioplastics in soil. Short-term studies (in months) dominated the longer-term studies and studies over 4 years were almost non-existent. Lab and field experiments often gave inconsistent results with seasonal, climatic and bio-geographical factors strongly influencing the field results and bioplastic stability in soil. Most existing studies reported significant effects for microbioplastic concentrations at or above 1 % w/w. Bioplastic residues were found to substantially affect soil C/N ratio, impact soil microbial diversity by favouring certain microbial taxa and alter soil physical structure by influencing soil aggregates formation. At higher concentrations, plant health and germination success were also negatively affected. Conclusively, the review found it important to focus more on long-term field experiments to better understand the degree and extent of bioplastic residue impact on soil physico-chemical properties, mechanical properties, soil biology, soil-bioplastic-plant response, nutrients and toxicity. There are also very few studies investigating contaminant transport and migration of micro or nano-bioplastics in soil.

Effect of Polymer Properties on the Biodegradation of Polyurethane Microplastics

The release of fragments from plastic products, that is, secondary microplastics, is a major concern in the context of the global plastic pollution. Currently available (thermoplastic) polyurethanes [(T)PU] are not biodegradable and therefore should be recycled. However, the ester bond in (T)PUs might be sufficiently hydrolysable to enable at least partial biodegradation of polyurethane particles. Here, we investigated biodegradation in compost of different types of (T)PU to gain insights into their fragmentation and biodegradation mechanisms. The studied (T)PUs varied regarding the chemistry of their polymer backbone (aromatic/aliphatic), hard phase content, cross-linking degree, and presence of a hydrolysis-stabilizing additive. We developed and validated an efficient and non-destructive polymer particle extraction process for partially biodegraded (T)PUs based on ultrasonication and density separation. Our results showed that biodegradation rates and extents decreased with increasing cross-linking density and hard-segment content. We found that the presence of a hydrolysis stabilizer reduced (T)PU fragmentation while not affecting the conversion of (T)PU carbon into CO2. We propose a biodegradation mechanism for (T)PUs that includes both mother particle shrinkage by surface erosion and fragmentation. The presented results help to understand structure-degradation relationships of (T)PUs and support recycling strategies.

Separation of Microplastic Particles from Sewage Sludge Extracts Using Magnetic Seeded Filtration

Microplastic particles (MP) are efficiently retained in wastewater treatment plants and enriched in sewage sludge. For monitoring MP contents in wastewater systems, sewage sludge is thus well suited, but also requires an isolation of MP from the sludge matrix, as other sewage sludge components may interfere with the MP identification and quantification. Although organic matter in sludge samples can be removed through acid and enzymatic digestion procedures, cellulose - mainly from toilet paper - remains in the digests, due to its high chemical resistivity and similar density to MP. We apply the separation concept of magnetic seeded filtration to isolate MP through selective hetero-agglomeration with magnetic seed particles. MP and cellulose differ in their hydrophobic properties and we investigate to what extent these differences can be exploited to selectively form MP-magnetite hetero-agglomerates in the presence of cellulose. These hetero-agglomerates are subsequently separated using a magnet. Five MP types (Polyethylene terephthalate (PET), polypropylene (PP), low density polyethylene (LDPE), polyvinyl chloride (PVC) and polystyrene (PS)) and cellulose particles were mixed in different combinations with both hydrophilic and hydrophobic (silanized) magnetite particles. PET, PP, LDPE and PS only poorly agglomerated with pristine (hydrophilic) magnetite, but efficiently formed hetero-agglomerates with hydrophobic magnetite and were successfully removed from suspensions ( 80 - 100 % ). PVC agglomerated more efficiently with pristine than with hydrophobic magnetite and cellulose only agglomerated to a limited extent with either hydrophilic or hydrophobic magnetite, resulting in a high process selectivity. Results from experiments conducted at different ionic strengths and with hydrophilic and hydrophobic magnetite suggests that the agglomeration process was dominated by hydrophobic interactions. Enzymatic and oxidative treatment of the MP only marginally affected the separation efficiencies and (treated) MP spiked to sewage sludge extracts were successfully recovered using magnetic seeded filtration.

Comparison of different salt solutions for density separation of conventional and biodegradable microplastic from solid sample matrices

Microplastics are the new emerging pollutants ubiquitously detectable in aquatic and terrestrial ecosystems. Fate and behavior, as well as ecotoxicity, are of increasing environmental concern, particularly in sediments and soils as natural sinks. For a global environmental risk assessment, reliable and easy to apply analytical methods are mandatory to obtain comparable data. This is based on the isolation of microplastics out of the solid sample matrices prior to instrumental detection. Thus, this study provides an easy to apply approach for density separation. The technique emerged from a comparative study using different salt solutions to isolate conventional, and for the first time biodegradable, microplastics from different solid sample matrices, i.e., sand, artificial soil, and compost. Four solutions (water, sodium chloride, sodium hexametaphosphate, and sodium bromide) of different densities were applied followed by oxidizing digestion. Finally, the impact of the procedures on size and surface properties of microplastics was tested. Dependent on the sample matrix, the highest recovery rates of 87.3-100.3% for conventional polymers, and 38.2-78.2% for biodegradable polymers, were determined with sodium bromide. It could be shown that the type of solid sample matrix influences the recovery rates and has to be considered when choosing a sample preparation technique.

Spatial distribution of microplastics in the tropical Indian Ocean based on laser direct infrared imaging and microwave-assisted matrix digestion

Suspended particulate matter was collected from subsurface (6 m) water along an E-W transect through the tropical Indian Ocean using a specialized inert (plastic free) fractionated filtration system. The samples were subjected to a new microwave-assisted "one-pot" matrix removal (efficiency: 94.3% ± 0.3% (1 SD, n = 3)) and microplastic extraction protocol (recovery: 95% ± 4%). The protocol enables a contamination-minimized digestion and requires only four filtration steps. In comparison, classical sample processing approaches involve up to eight filtration steps until the final analysis. Microplastics were identified and physically characterized by means of a novel quantum cascade laser-based imaging routine. LDIR imaging facilitates the analysis of up to 1000 particles/fibers (<300 μm) within approximately 1-2 h. In comparison to FTIR and Raman imaging, it can help to circumvent uncertainties, e. g. from subsampling strategies due to long analysis and post-processing times of large datasets. Over 97% of all particles were correctly identified by the automated routine - without spectral reassignments. Moreover, 100% agreement was obtained between ATR-FTIR and LDIR-based analysis regarding particles and fibers >300 μm. The mean microplastic concentration of the analyzed samples was 50 ± 30 particles/fibers m^-3 (1 SD, n = 21). Number concentrations ranged from 8 to 132 particles/fibers m^-3 (20-300 μm). The most abundant polymer clusters were acrylates/polyurethane/varnish (49%), polyethylene terephthalate (26%), polypropylene (8%), polyethylene (4%) and ethylene-vinyl acetate (4%). 96% of the microplastic particles had a diameter <100 μm. Though inter-study comparison is difficult, the investigated area exhibits a high contamination with particulate plastics compared to other open ocean regions. A distinct spatial trend was observed with an increasing share of the size class 20-50 μm from east to west.

Microplastic sample purification methods - Assessing detrimental effects of purification procedures on specific plastic types

In search of effective, fast, and cheap methods to purify environmental samples for microplastic analysis, scientific literature provides various purification protocols. However, while most of these protocols effectively purify the samples, some may also degrade the targeted polymers. This study was conducted to systematically compare the effects of purification protocols based on acidic, alkaline, oxidative, and enzymatic digestion and extraction via density separation on eight of the most relevant plastic types. It offers insights into how specific purification protocols may compromise microplastic detection by documenting visible and gravimetric effects, analyzing potential surface degradation using Fourier transform infrared spectroscopy (FTIR) and bulk erosion on a molecular level using gel permeation chromatography (GPC). For example, protocols using strong acids and high temperatures are likely to completely dissolve or cause strong degradation to a wide range of polymers (PA, PC, PET, PS, PUR & PVC), while strong alkaline solutions may damage PC and PET. Contrarily, Fenton's reagent, multiple enzymatic digestion steps, as well as treatment with a zinc chloride solution frequently used for density-separation, do not degrade the eight polymers tested here. Therefore, their implementation in microplastic sample processing may be considered an essential stepping-stone towards a standardized protocol for future microplastics analyses.

A review of microplastics in soil: Occurrence, analytical methods, combined contamination and risks

Microplastics (MPs) pollution is becoming a serious environmental issue of global concern. Currently, the effects of MPs on aquatic ecosystems have been studied in detail and in depth from species to communities. However, soils, the largest reservoir of MPs, have been less studied, and little is known about the occurrence, environmental fate and ecological impacts of MPs. Therefore, based on the existing knowledge, this paper firstly focused specifically on the main sources of soil MPs pollution and explored the main reasons for their strong heterogeneity in spatial distribution. Secondly, as a primary prerequisite for evaluating MPs contamination, we systematically summarized the analytical methods for soil MPs and critically compared the advantages and disadvantages of the different methods in the various operational steps. Furthermore, this review highlighted the combined contamination of MPs with complex chemical contaminants, the sorption mechanisms and the associated factors in the soil. Finally, the risks posed by MPs to soil, plants, the food chain and even humans were outlined, and future directions for soil MPs research were proposed, while the urgent need for a unified approach to MPs extraction and identification was emphasized. This study provides a theoretical reference for a comprehensive understanding of the separation of soil MPs and their ecological risk as carriers of pollution.

Municipal biowaste treatment plants contribute to the contamination of the environment with residues of biodegradable plastics with putative higher persistence potential

Biodegradable plastics (BDP) are expected to mineralize easily, in particular under conditions of technical composting. However, the complexity of the sample matrix has largely prevented degradation studies under realistic conditions. Here composts and fertilizers from state-of-the-art municipal combined anaerobic/aerobic biowaste treatment plants were investigated for residues of BDP. We found BDP fragments > 1 mm in significant numbers in the final composts intended as fertilizer for agriculture and gardening. Compared to pristine compostable bags, the recovered BDP fragments showed differences in their material properties, which potentially renders them less prone to further biodegradation. BDP fragments < 1 mm were extracted in bulk and came up to 0.43 wt% of compost dry weight. Finally, the liquid fertilizer produced during the anaerobic treatment contained several thousand BDP fragments < 500 µm per liter. Hence, our study questions, if currently available BDP are compatible with applications in areas of environmental relevance, such as fertilizer production.