Sample Preparation Techniques for the Analysis of Microplastics in Soil—A Review

Matrix preparation and workflow for microplastics analysis in soil

One of the main difficulties in microplastic (MP) research is the lack of standardized, real-world methods such as matrix blank and simultaneous tracking of polymer particles for enumeration. Building on a previous study, a matrix preparation and experimental workflow for soil matrices is presented that addresses the challenges of purification to allow subsequent analysis using Nile Red-stained MPs as a surrogate. Key steps include peroxide digestion and density separation (NaI) followed by centrifugation for low density polyethylene (LDPE) and polyvinyl chloride (PVC) surrogates to assess recoveries in terms of number and size, based on fluorescence microscopy and Raman spectroscopy. The results yielded false positive recoveries greater than 100% for stained MPs and overall mean recovery around 80% for virgin MPs. Staining reflected the effect of pretreatment on the morphological and fluorescence characteristics of PE and PVC particles. An instrumental approach for fast Raman measurements is also presented, which facilitates counting up to 83%. Although particles down to 21 μm have been tested, this approach appears promising down to single microns due to its traceable and reliable nature for MP particles <300 μm in soil or terrestrial environments. In conclusion, the MP research community should strive to address small polymeric particles that pose an obstacle by agglomerating and interfering with particle-based quantification by spectroscopic techniques.

Determination of polystyrene nanospheres and other nanoplastics in water via binding with organic dyes by capillary electrophoresis with laser-induced fluorescence detection

The purpose of this research work was to develop a new method for the quantitative analysis of water samples containing nanoplastics in the presence of microplastics and other colloidal particles. Our approach involved a mixture of fluorescent organic dyes that was added to each water sample for binding with the target nanoplastics. Binding was proven by zeta potential measurements that revealed the point of zero charge shifting from pH 4 for polystyrene nanoparticles, to pH 6.13 after binding with the dye mixture. Centrifugation effectively separated the free dyes from all dye-bound particles in the heterogeneous mixture, thus eliminating any potential interference. Electrokinetic injection of the free dyes in the supernatant allowed efficient separation by capillary electrophoresis (CE), for accurate quantitation individually with laser-induced fluorescence detection. A diode laser was operated at λex of 450 nm to induce fluorescence from the dyes, and an optical interference filter to collect only emission photons with λem of 520 nm. The fluorescence peak intensity decreased for each dye, thereby determining the total binding activity of all plastics and other particles. This new method enables high-throughput screening of water samples for nanoplastics, based on their fast binding with organic dyes in 5 min, rapid analytical separation of dyes by capillary electrophoresis within 10 min, and instantaneous fluorescence intensity measurement of individual dye peaks. Binding percentages as high as 149(±2) %/μg of 9.5-nm polystyrene nanoparticles were attained when using a concentration of 125 μg/mL for each dye. The binding mechanism was mainly attributed to hydrophobic interaction and modified by electrostatic forces. Binding of the four dyes with polystyrene microparticles, casein micelles, and transition metal oxide nanoparticles was verified to demonstrate minimal interference. The method was successfully applied to rapid testing of water samples from various sources, ranging from drinking fountains and household faucets to flowing rivers. The method also applied to a decontamination study wherein a removal of 94 % polystyrene nanospheres (diameter = 80 nm) was achieved by adding only 20 mg of casein powder into 1.6 mL of water containing 36 mg of the nanoplastics initially.

Optimising microplastic polyethylene terephthalate fibre extraction from sediments: Tailoring a density-separation procedure for enhanced recovery and reliability

Despite the presence of microplastics in sediments being widely acknowledged, the absence of standardised processing methods in extracting microplastics can compromise reliable and comparable results. Density separation is a predominant method for extracting microplastics from sediments. In this study, Sodium Polytungstate (ρ = 1.6 g cm-3) was selected as the density separation agent for three key factors: i) optimal density for extracting common plastic polymers, ii) low toxicity, and iii) recycling potential of the solution. It is therefore cost-effective, and the risk of solution dispersal is minimal. The solution was tested through four separation procedures, extracting PET fibres from three artificial sediment mixtures (i.e., pure sand, pure mud, and 50 % sand and 50 % mud). The results indicate that the solution employed in this work is highly effective for extracting microplastic fibres from sediments, with recovery rates up to 99 %. However, the results highlight differences in the recovery among the four procedures and in terms of the sediment characteristics. Specifically, extracting microplastics was easier in sandy sediment samples than in mud-rich ones. The complexity of extracting microplastics from mud-rich sediments results from i) the creation of microplastic-sediment aggregates forming denser structures, that settle down trapping microplastics in sediments; ii) the development of a clay sediment cap that hinders the rise of microplastics to the surface. Reducing the risk of underestimation of microplastic content in mud-rich samples can be accomplished by applying a procedure that involves placing the samples with the Sodium Polytungstate solution on a stirring plate while progressively lowering the rotation velocity. Using this method, cohesive sediments lose their ability to trap microplastics while aggregating, consequently reducing their ability to drag microplastics to the bottom. This facilitated microplastics to reach the liquid surface, thereby enabling an efficient retrieval even in mud-rich samples.

A systematic review to assess current surface water and sediment microplastic sampling practices in seagrass and mangrove ecosystems

Global plastic production is estimated to be 400 million tonnes per annum, with ~ 5.25 trillion fragments floating in our oceans. Microplastics (< 5 mm) have the potential to disproportionately accumulate and become trapped in mangroves and seagrass meadows, creating plastic 'sinks'. This is concerning as these ecosystems are of great ecological and economic importance, with microplastics causing harm to inhabiting flora and fauna. However, accurately measuring microplastic abundance, comparing findings, and determining potential impacts are difficult due to a lack of standardised sampling protocols. Therefore, a systematic literature review was completed to review currently adopted microplastic sampling methods in surface water and sediment in seagrass and mangrove ecosystems. These were compared with recommendations from existing governmental and institutional groups as a first step to standardising methods for future sampling procedures in seagrasses and mangroves.

Seabirds as biovectors in the transport of plastic debris across ecosystem borders: A case study from the Humboldt Current Upwelling System

Seabirds have become biovectors of plastic pollutants between marine and terrestrial ecosystems, and transport of plastics to their nesting sites becomes relevant due to increasing levels of pollution. To determine the pathways by which plastic reaches their colonies, we analysed the abundance of plastics at the nesting sites of five seabird species (Humboldt penguin Spheniscus humboldti, Peruvian booby Sula variegata, kelp gull Larus dominicanus, grey gull Leucophaeus modestus, Markham's storm-petrel Hydrobates markhami) nesting in northern Chile. Seabirds were primarily grouped according to their nesting behaviour, but two species foraging in contrasting habitats (kelp gull and Markham's storm-petrel) were also compared directly. The abundance, type, and polymer of macro-, meso- and microplastics were analysed in the soil of colonies and control sites, and microplastic ingestion was evaluated for selected species. Densities of plastics in colonies of surface-nesting seabirds ranged from 0 to 21.4 items m-2 (mainly plastic bags and thin films), and 0.002 to 19.7 items m-2 (mainly hard fragments) in colonies of burrow-nesting seabirds. Mean microplastic loads in the stomachs of seabirds were between 3.7 ± 4.2 plastic items individual-1. Overall, the abundances of plastic items in all seabird colonies were low, suggesting a limited transfer of plastics from sea to land. For kelp gulls, the results indicate transfer of macroplastic items to colonies, reaching the colony via regurgitates, with landfills considered as the main plastic source. Our results suggest that contrasting nesting behaviour and foraging habitats among species can explain differential plastic accumulation in seabird colonies, but also other factors, such as wind, contribute to the accumulation of plastic debris in colonies. Proper management of sanitary landfills are key to reduce plastic contamination of coastal seabirds and their colonies.

Microplastic pollution unveiled: the consequences of small unregulated dumping in villages, spanning from soil to water

Microplastic contamination in soil ecosystems is a major environmental concern in the world. The current study aims to explore the extent of microplastic pollution in unregulated village dumpsites in India, focusing on the movement of these pollutants from soil to aquatic environments. Soil samples from eight distinct sites (A to H) in six villages were analyzed for various properties, including pH, bulk density, porosity, water retention capacity, hydraulic conductivity, and particle size distribution. The attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR) method was used to identify prevalent plastic types. The research classifies microplastics by their shape and color, identifying a wide range of particles such as sheets, fibers, foams, fragments, and films. The study also examines the presence and concentration of microplastics in both soil and sediment samples. It was found that PE and PP microplastics are significantly present across different size fractions. Sample A contains a variety of items in the 1-5 mm size range, mainly PE, while the 0.3-1 mm fraction is largely PP. Samples B to H are mostly composed of PE microplastics in different forms. Sample F is unique with a mix of PE, EPS, and a higher amount of red and blue foam particles in the 0.3-1 mm fraction. Microplastics were quantified using stereomicroscopy, revealing concentrations between 80 and 840 numbers per kilogram in soil and 20 to 60 numbers per kilogram in sediments. The findings emphasize the widespread nature of microplastic pollution across ecosystems and the importance of developing effective strategies for monitoring and mitigating their impact on environmental health and human well-being.

Characterization of microplastics in soil, leachate and groundwater at a municipal landfill in Rayong Province, Thailand

Recent years have witnessed a dramatic increase in global plastic production, leading to heightened concerns over microplastics (MPs) contamination as a significant environmental challenge. MP particles are ubiquitously distributed across both continental and marine ecosystems. Given the paucity of research on MPs in Thailand, particularly regarding MPs contamination in terrestrial environments, this study focused on investigating the distribution and characteristics of MPs in a landfill area. We collected 15 soil samples, 2 leachate samples, and 7 groundwater samples from both inside and outside a municipal landfill situated in the urbanized coastal region of Rayong Province. Our findings revealed variability in MPs concentration across different sample types. In soil, the MP count ranged from 240 to 26,100 pieces per kg of dry soil, 58.71 % of all sample sizes are lower than 0.5 mm. Similarly, the size found in the leachate sample, and the average MP in the leachate samples was 139 pieces per liter of MPs. The groundwater samples showed a fluctuation in MPs count from 18 to 94 pieces per liter, and the size of MPs ranged mostly from 0.5 to 1 mm. The predominant forms of MPs identified were sheets, followed by fragments, fibers, and granules. According to μ-FTIR analysis, the majority of the MPs were composed of polyethylene and polypropylene, commonly used in plastic packaging and ropes. The observed high concentrations and extensive distribution of MP contamination underscore the urgency for further studies and effective management strategies to mitigate the adverse impacts of this pollution on various organisms and ecosystems.

Micro-Nanoparticle Characterization: Establishing Underpinnings for Proper Identification and Nanotechnology-Enabled Remediation

Microplastics (MPLs) and nanoplastics (NPLs) are smaller particles derived from larger plastic material, polymerization, or refuse. In context to environmental health, they are separated into the industrially-created "primary" category or the degradation derivative "secondary" category where the particles exhibit different physiochemical characteristics that attenuate their toxicities. However, some particle types are more well documented in terms of their fate in the environment and potential toxicological effects (secondary) versus their industrial fabrication and chemical characterization (primary). Fourier Transform Infrared Spectroscopy (FTIR/µ-FTIR), Raman/µ-Raman, Proton Nuclear Magnetic Resonance (H-NMR), Curie Point-Gas Chromatography-Mass Spectrometry (CP-gc-MS), Induced Coupled Plasma-Mass Spectrometry (ICP-MS), Nanoparticle Tracking Analysis (NTA), Field Flow Fractionation-Multiple Angle Light Scattering (FFF-MALS), Differential Scanning Calorimetry (DSC), Thermogravimetry (TGA), Differential Mobility Particle [Sizing] (DMPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Scanning Transmission X-ray Microspectroscopy (STXM) are reviewed as part of a suite of characterization methods for physiochemical ascertainment and distinguishment. In addition, Optical-Photothermal Infrared Microspectroscopy (O-PTIR), Z-Stack Confocal Microscopy, Mueller Matrix Polarimetry, and Digital Holography (DH) are touched upon as a suite of cutting-edge modes of characterization. Organizations, like the water treatment or waste management industry, and those in groups that bring awareness to this issue, which are in direct contact with the hydrosphere, can utilize these techniques in order to sense and remediate this plastic polymer pollution. The primary goal of this review paper is to highlight the extent of plastic pollution in the environment as well as introduce its effect on the biodiversity of the planet while underscoring current characterization techniques in this field of research. The secondary goal involves illustrating current and theoretical avenues in which future research needs to address and optimize MPL/NPL remediation, utilizing nanotechnology, before this sleeping giant of a problem awakens.

From Sea Water to Salt Crystals: An Onsite Investigation of Microplastics in a Conventional Sea Salt Farming System

This study investigated microplastic (MP) contamination in conventional sea salt farming systems. Various crude sea salt samples (n = 22) that were traditionally produced were collected from salt farms and local vendors. Salt water (n = 15), macroalgae (n = 6), and clay of pond floors (n = 6) were collected from ponds subjected to different production (stabilization, evaporation, and concentration and crystallization concentration) processes. All samples were analyzed for MP abundance and characteristics. The potential sources of MP contamination in the salt were also investigated. The mean abundance of MPs in the salt water and clay of pond floor increased progressively throughout the production process and reached its highest level in the concentration and crystallization ponds (7400 MP particles/m3 in salt water and 19,336 MP particles/m2 in the clay of the pond floor). A maximum of 26,500 MP particles/kg of macroalgal material indicated the potential sink of MPs on the surface of the algae. Approximately 34-2377 MP particles/kg salt were found in the crude sea salt samples. However, the mean abundance (378 MP particles/kg of salt) indicated nonsignificant impacts of different harvesting processes on MP contamination. Most MP size distributions, shapes and polymer types in the salts were similar to those found in the salt water, macroalgae and clay of the pond floor. Approximately 99% of the MPs were fragments that were suspected to be decomposed from larger plastic debris and plastic machinery and tools used at the salt farm. Similar patterns of polymer distribution, in which PP > PE > PET > PS, were found for all samples studied.

Nano(micro)plastic mobility in soil: Metallic additives and Sr isotopes as potential tracers

Metal contaminants were found in a soil amended with a compost produced from household waste that included plastic debris. A strong correlation between the microplastics (MPs) distribution and the metal concentrations in the soil profile. Metals in the highest concentrations corresponded to the most significant plastic additives. As the total amount of plastic debris and the loss of metals and plastic particles were unknown, it was not possible to conclude that plastic debris is responsible for all of the metal contamination. Amount of calcium (Ca) in MPs (24.5 g kg-1 of MPs) are high in response to it use as filler in plastic formulation. As strontium (Sr) is an analogous of Ca, the potential of 87Sr/86Sr ratios to quantify MPs and nanoplastics (NPs) was tested. Elemental concentrations (Ca, Cd, Cr Pb, Ni and Sr) coupled with Sr isotopic ratios were compared in both amended soil and a reference soil without amendment. The 87Sr/86Sr ratios of the amended soil were less radiogenic than for the reference soil (0.724296 ± 0.000010 against 0.726610 ± 0.00009 for the 0-5 cm soil layer, respectively). The Sr isotopic ratio of MPs was also significantly less radiogenic (0.711527 ± 0.000010 for the 0-5 cm soil layer) than for soils. The MPs< 2 mm occurred in the ploughed soil depth with concentration varying from 1.19 to 0.09 mg kg-1. The NPs concentration stayed quite constant from 0 to 55 cm at around 0.25 µg kg-1. The presence of NPs until 55 cm soil depth was attested by the detection of polypropylene NPs by Py-GCMS in the soil solution < 0.8 µm. These results highlighted, for the first time, the NPs mobility throughout the soil depth and their ability to reach hydrosystems. It also demonstrated that Sr could be a potential tracer of the MPs< 2 mm and NPs amount occurring in soils.

A modified methodology for extraction and quantification of microplastics in soil

The ubiquitousness of microplastics (<5 mm) has become a pressing environmental concern globally due to the extensive use of plastics. Microplastics have been well-studied in aquatic environments but not well-characterized in soils. Present analytical processes to quantify microplastics accurately in soil samples are quite challenging and require improved and validated analytical steps to eliminate the obscurities and biases. We aimed to develop an effective method for the extraction and quantification of microplastics from soil samples. Different ratios of low-(NaCl) and high-density solutions (ZnCl2/ NaBr) were tested to determine the most efficient combination for density-dependent separation of microplastics from soil. The combination of low- (1:6) and high-density (1:3) solutions {as weight of soil(g)/volume of density solution(ml)} accounted for 95% recovery of the spiked microplastic particles from soil samples. Likewise, different soil-to-solution ratios of H2O2 were tested for the removal of soil organic matter with heating and non-heating steps. Prior removal of organic matter from soil samples achieved a clear supernatant that facilitated 99% recovery of microplastic particles. The validation of individually spiked microplastic particles of small (10-100 μm) and large scale (100-5000 μm) resulted in recovery ranging from 88 to 99%. A validated modified method with prior digestion followed by density-dependent separation was further tested using the field samples with microplastic contamination. The microplastics of different shapes, sizes, colours and polymeric compositions were reported efficiently and well characterized in the field-collected soil samples using this method.

Microplastics and nanoplastics: Exposure and toxicological effects require important analysis considerations

Microplastics (MPs) and nanoplastics (NPs) pervade both the environment and the food chain, originating from the degradation of plastic materials from various sources. Their ubiquitous presence raises concerns for ecosystem safety, as well as the health of animals and humans. While evidence suggests their infiltration into mammalian and human tissues and their association with several diseases, the precise toxicological effects remain elusive and require further investigation. MPs and NPs sample preparation and analytical methods are quite scattered without harmonized strategies to exist at the moment. A significant challenge lies in the limited availability of methods for the chemical characterization and quantification of these contaminants. MPs and NPs can undergo further degradation, driven by abiotic or biotic factors, resulting in the formation of cyclic or linear oligomers. These oligomers can serve as indicative markers for the presence or exposure to MPs and NPs. Moreover, recent finding concerning the aggregation of oligomers to form NPs, makes their analysis as markers very important. Recent advancements have led to the development of sensitive and robust analytical methods for identifying and (semi)quantifying these oligomers in environmental, food, and biological samples. These methods offer a valuable complementary approach for determining the presence of MPs and NPs and assessing their risk to human health and the environment.

Vertical distribution of microplastics in an agricultural soil after long-term treatment with sewage sludge and mineral fertiliser

Sewage sludge applications release contaminants to agricultural soils, such as potentially toxic metals and microplastics (MPs). However, factors determining the subsequent mobility of MPs in long-term field conditions are poorly understood. This study aimed to understand the vertical distribution of MPs in soils amended with sewage sludge in comparison to conventional mineral fertiliser for 24 years. The depth-dependent MP mass and number concentrations, plastic types, sizes and shapes were compared with the distribution of organic carbon and metals to provide insights into potentially transport-limiting factors. Polyethylene, polypropylene and polystyrene mass concentrations were screened down to 90 cm depth via pyrolysis-gas chromatography/mass spectrometry. MP number concentrations, additional plastic types, sizes, and shapes were analysed down to 40 cm depth using micro-Fourier transform-infrared imaging. Across all depths, MP numbers were twice and mass concentrations 8 times higher when sewage sludge was applied, with a higher share of textile-related plastics, more fibres and on average larger particles than in soil receiving mineral fertiliser. Transport of MPs beyond the plough layer (0-20 cm) is often assumed negligible, but substantial MP numbers (42 %) and mass (52 %) were detected down to 70 cm in sewage sludge-amended soils. The initial mobilization of MPs was shape- and size-dependent, because the fractions of fragmental-shaped and relatively small MPs increased directly below the plough layer, but not at greater depths. The sharp decline of total MP concentrations between 20 and 40 cm depth resembled that of metals and organic matter suggesting similar transport limitations. We hypothesize that the effect of soil management, such as ploughing, on soil compactness and subsequent transport by bioturbation and via macropores drives vertical MP distribution over long time scales. Risk assessment in soils should therefore account for considerable MP displacement to avoid underestimating soil exposure.

Interaction of titanium dioxide nanoparticles with PVC-microplastics and chromium counteracts oxidative injuries in Trachyspermum ammi L. by modulating antioxidants and gene expression

The emergence of polyvinyl chloride (PVC) microplastics (MPs) as pollutants in agricultural soils is increasingly alarming, presenting significant toxic threats to soil ecosystems. Ajwain (Trachyspermum ammi L.), a plant of significant medicinal and culinary value, is increasingly subjected to environmental stressors that threaten its growth and productivity. This situation is particularly acute given the well-documented toxicity of chromium (Cr), which has been shown to adversely affect plant biomass and escalate risks to the productivity of such economically and therapeutically important species. The present study was conducted to investigate the individual effects of different levels of PVC-MPs (0, 2, and 4 mg L-1) and Cr (0, 150, and 300 mg kg-1) on various aspects of plant growth. Specifically, we examined growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress responses, antioxidant compound activity (both enzymatic and nonenzymatic), gene expression, sugar content, nutritional status, organic acid exudation, and Cr accumulation in different parts of Ajwain (Trachyspermum ammi L.) seedlings, which were also exposed to varying levels of titanium dioxide (TiO2) nanoparticles (NPs) (0, 25, and 50 µg mL-1). Results from the present study showed that the increasing levels of Cr and PVC-MPs in soils significantly decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. Conversely, increasing levels of Cr and PVC-MPs in the soil increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, and also increased organic acid exudation pattern in the roots of T. ammi seedlings. Interestingly, the application of TiO2-NPs counteracted the toxicity of Cr and PVC-MPs in T. ammi seedlings, leading to greater growth and biomass. This protective effect is facilitated by the NPs' ability to sequester reactive oxygen species, thereby reducing oxidative stress and lowering Cr concentrations in both the roots and shoots of the plants. Our research findings indicated that the application of TiO2-NPs has been shown to enhance the resilience of T. ammi seedlings to Cr and PVC-MPs toxicity, leading to not only improved biomass but also a healthier physiological state of the plants. This was demonstrated by a more balanced exudation of organic acids, which is a critical response mechanism to metal stress.

Comprehensive assessment of microplastics in Australian biosolids: Abundance, seasonal variation and potential transport to agroecosystems

Striving towards a circular economy, the application of treated sewage sludge (biosolids) to land is an opportunity to improve the condition of the soil and add essential nutrients, in turn reducing the need for fertilisers. However, there is an increasing concern about microplastic (MP) contamination of biosolids and their transport to terrestrial ecosystems. In Australia, agriculture is the largest biosolids end-user, however, there is limited understanding of MPs in Australian biosolids. Also, while the method to isolate MPs from biosolid is established, a need to extract and analyse MPs more efficiently is still pressing. In this study, we comprehensively quantified and characterised MPs in 146 biosolids samples collected from thirteen wastewater treatment plants (WWTPs) including different seasons. We have optimised an oxidative-enzymatic purification method to overcome current limitations for MP identification in complex samples and accurately report MPs in biosolids. This method enabled removal of >93 % of dry weight of organic material and greatly facilitated the MPs instrumental analysis. The concentration of MPs (>20 µm) in all biosolids samples ranged from 11 to 150 MPs/g dry weight. Abundance of MPs was affected by seasons with higher abundance of MPs usually found during cold and wet seasons. Despite seasonal variations, polyethylene terephthalate, polyurethane and polymethyl methacrylate were the most abundant polymers. Smaller MPs (20 to 200 µm) comprised >70 % of all detected MPs with a clear negative linear relationship observed between MP size and abundance. Per capita concentration of MPs in biosolids across all studied WWTPs was 0.7 to 21 g MPs per person per year. Therefore, biosolids are an important sink and source of MPs to agroecosystems, emphasising the need to more comprehensively understand the fate, impact and risks associated with MPs on agricultural soils.

An evaluation on microplastic accumulations in Turkish soils under different land uses

Microplastic (MP) pollution is now widely reported in soil ecosystems. However, the level of this pollution in soil ecosystems has not been sufficiently elucidated. Moreover, there is little understanding of how land use conditions affect the occurrence and distribution of MPs in soils. Therefore, this study examined 55 soil samples (44 agricultural and 11 urban) from the Mediterranean, Aegean, and Marmara regions of Türkiye, representing both agricultural and urban land uses. The samples were analyzed for MP distribution characteristics, such as abundance, shape, size, color, and type. Different types of MPs were detected in the soil samples, and their averages in agricultural and urban soils were 192.7 ± 14.2 and 127.3 ± 21.6 particles kg-1, respectively. MP abundance in the soil exhibited variations between different land uses, with agricultural areas showing higher levels compared to urban areas. In agricultural soils, MPs were predominantly blue-colored (44.6 %), in the form of fibers (74.9 %), smaller than 1000 μm (66.1 %), and primarily constituted polyethylene (90.8 %). In urban areas, MPs were also blue-colored (54.7 %), had a fiber shape (64.2 %), smaller than 1000 μm (70.6 %), and mostly belonged to the polyethylene category (78.5 %). A significant difference in MP concentrations was observed between agricultural and urban areas, reflecting the influence of distinct land uses on MP levels. Moreover, Principal Component Analysis (PCA) revealed that soil properties, including pH, electrical conductivity, organic matter, aggregate stability, average weight diameter, sand, clay, and silt, emerged as the primary determinants influencing the abundance and size of MPs within the soil. These findings contribute valuable insights into the origins of soil MPs and the intricate connections between MPs and varying soil characteristics across diverse land use categories.

Underappreciated microplastic galaxy biases the filter-based quantification

Long-term environmental loading of microplastics (MPs) causes alarming exposure risks for a variety of species worldwide, considered a planetary threat to the well-being of ecosystems. Robust quantitative estimates of MP extents and featured diversity are the basis for comprehending their environmental implications precisely, and of these methods, membrane-based characterizations predominate with respect to MP inspections. However, though crucial to filter-based MP quantification, aggregation statuses of retained MPs on these substrates remain poorly understood, leaving us a "blind box" that exaggerates uncertainty in quantitive strategies of preselected areas without knowing overview loading structure. To clarify this uncertainty and estimate their impacts on MP counting, using MP imaging data assembled from peer-reviewed studies through a systematic review, here we analyze the particle-specific profiles of MPs retained on various substrates according to their centre of mass with a fast-random forests algorithm. We visualize the formation of distinct galaxy-like MP aggregation-similar to the solar system and Milky Way System comprised of countless stars-across the pristine and environmental samples by leveraging two spatial parameters developed in this study. This unique pattern greatly challenges the homogeneously or randomly distributed MP presumption adopted extensively for simplified membrane-based quantification purposes and selective ROI (region of interest) estimates for smaller-sized plastics down to the nano-range, as well as the compatibility theory using pristine MPs as the standard to quantify the presence of environmental MPs. Furthermore, our evaluation with exemplified numeration cases confirms these location-specific and area-dependent biases in many imaging analyses of a selective filter area, ascribed to the minimum possibility of reaching an ideal turnover point for the selective quantitive strategies. Consequently, disproportionate MP schemes on loading substrates yield great uncertainty in their quantification processing, highlighting the prompt need to include pattern-resolved calibration prior to quantification. Our findings substantially advance our understanding of the structure, behavior, and formation of these MP aggregating statuses on filtering substrates, addressing a fundamental question puzzling scientists as to why reproducible MP quantification is barely achievable even for subsamples. This study inspires the following studies to reconsider the impacts of aggregating patterns on the effective counting protocols and target-specific removal of retained MP aggregates through membrane separation techniques.

Condition of composted microplastics after they have been buried for 30 years: Vertical distribution in the soil and degree of degradation

Microplastics in soils are a growing concern. Composting household wastes can introduce microplastics to agroecosystems, because when unsorted compost is used as a fertilizer, the plastic debris it contains degrades to microplastics. This paper examines the distribution and degradation of microplastics in agricultural soil samples to investigate their potential mobility. The source of microplastics was a household waste compost added to the soil more than 30 years before the study. The microplastics were sorted from a plot-composite soil and characterised by Attenuated Total Reflectance combined with Fourier transform infrared spectroscopy (ATR-FTIR). The microplastics are present in the cultivated depth but have not been transferred deeper (2.9 g kg-1 in the 0-5 cm soil depth against 0.9 g kg-1 in the 30-35 cm soil depth). Polyethylene (PE), polypropylene (PP), polystyrene (PS) and Polyvinylchloride (PVC) were identified in the forms of heterogeneous fragments, films, and fibres and accounted for 90% of the total microplastics. Advanced degradation observed was mainly assumed to be due to composting, though the plastic may have degraded further in the soil matrix. Highly degraded plastics are a greater danger for further leaching of contaminants into soil and our food supply.

Combined exposure of PVC-microplastic and mercury chloride (HgCl2) in sorghum (Pennisetum glaucum L.) when its seeds are primed titanium dioxide nanoparticles (TiO2-NPs)

The present work studied the impact of different levels of PVC-microplastics (PVC-MPs), namely 0 (no PVC-MPs), 2, and 4 mg L-1, along with mercury (Hg) levels of 0 (no Hg), 10, and 25 mg kg-1 in the soil, while concurrently applying titanium dioxide-nanoparticles (TiO2-NPs) at 0 (no TiO2-NPs), 50, and 100 µg mL-1 to sorghum (Pennisetum glaucum L.) plants. This study aimed to examine plant growth and biomass, photosynthetic pigments and gas exchange characteristics, oxidative stress indicators, and the response of various antioxidants (enzymatic and non-enzymatic) and their specific gene expression, proline metabolism, the AsA-GSH cycle, and cellular fractionation in the plants. The research outcomes indicated that elevated levels of PVC-MPs and Hg stress in the soil notably reduced plant growth and biomass, photosynthetic pigments, and gas exchange attributes. However, PVC-MPs and Hg stress also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H2O2), and electrolyte leakage (EL) which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression and sugar content. Furthermore, a significant increase in proline metabolism, the AsA-GSH cycle, and the pigmentation of cellular components was observed. Although, the application of TiO2-NPs showed a significant increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and their gene expression and also decreased oxidative stress. In addition, the application of TiO2-NPs enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in P. glaucum plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Macro, meso, micro and nanoplastics in horticultural soils in Argentina: Abundance, size distribution and fragmentation mechanism

Soil contamination with plastics is a major worldwide concern. However, data on plastic pollution in horticultural soils from Latin America is scarce. Furthermore, there is limited information on the fragmentation process that plastics undergo in environmental conditions. In this study, we investigated the abundance of macro, meso, micro and nano plastics in a previously studied horticultural soil (2015) from Buenos Aires, that has not been used for any productive activity since. Although the mass of macroplastics was conserved, the number of plastic fragments per square meter increased significantly, indicating a possible natural fragmentation process. Black polyethylene (PE) mulch film was the most abundant plastic found. For this material, when considering the mass of plastic fragments per square meter, the relative abundance was, in decreasing order: macroplastics (65.1-79.1 %) > mesoplastics (15.6-24.8 %) > microplastics (5.3-12.4 %) > nanoplastics (0.1 %). However, when considering the number of plastic items per square meter, the order was: microplastics (2383-3815) > mesoplastics (1019-1076) > nanoplastics (509-550) > macroplastics (25-46). The size distribution of plastic debris was analyzed using the natural logarithm of abundance versus the square root of the mean decile area, with good linear correlations (0.7749 < R2 < 0.9785). These results provide evidence for an ongoing dynamic fragmentation process (Mott model). We hypothesize that the breakdown of plastic into smaller pieces could be explained by a random fragmentation process based on soil volume changes between natural hydration/dehydration states. These data suggest that soil under natural conditions could act as an 'environmental plastic grinder'.

Determination of microplastics in agricultural soil by double-shot pyrolysis-gas chromatography combined with two-step extraction

A method for the determination of five microplastics in agricultural soil was established by double-shot pyrolysis-gas chromatography combined with two-step extraction. First, polycarbonate (PC), polystyrene (PS), polypropylene (PP), and polyethylene (PE) were extracted from soil samples using a mixed solvent of cyclohexanone and p-xylene, and then PE terephthalate was extracted with m-methylphenol. Subsequently, PC and PE terephthalate were analyzed by thermochemolysis, and PE, PP, and PS were investigated by direct pyrolysis at 600°C. The linearity of the method was satisfactory for five microplastics and the correlation coefficients were higher than 0.97 in the respective concentration range. The limits of detection and the limits of quantification were 0.2-10.0 and 0.5-20.0 μg/g, respectively. The method provided recoveries of 75.1%-141.5%, with acceptable repeatability within 20.0%. It was a supplementary method for the existing characterization of microplastics in agricultural soil.

Recent advances on the methods developed for the identification and detection of emerging contaminant microplastics: a review

The widespread use of plastics, popular for their versatility and cost-efficiency in mass production, has led to their essential role in modern society. Their remarkable attributes, such as flexibility, mechanical strength, lightweight, and affordability, have further strengthened their importance. However, the emergence of microplastics (MPs), minute plastic particles, has raised environmental concerns. Over the last decade, numerous studies have uncovered MPs of varying sizes in diverse environments. They primarily originate from textile fibres and cosmetic products, with large plastic items undergoing degradation and contributing as secondary sources. The bioaccumulation of MPs, with potential ingestion by humans through the food chain, underscores their significance as environmental contaminants. Therefore, continuous monitoring of environmental and food samples is imperative. A range of spectroscopic techniques, including vibrational spectroscopy, Raman spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, hyperspectral imaging, and nuclear magnetic resonance (NMR) spectroscopy, facilitates the detection of MPs. This review offers a comprehensive overview of the analytical methods employed for sample collection, characterization, and analysis of MPs. It also emphasizes the crucial criteria for selecting practical and standardized techniques for the detection of MPs. Despite advancements, challenges persist in this field, and this review suggests potential strategies to address these limitations. The development of effective protocols for the accurate identification and quantification of MPs in real-world samples is of paramount importance. This review further highlights the accumulation of microplastics in various edible species, such as crabs, pelagic fish, finfish, shellfish, American oysters, and mussels, shedding light on the extreme implications of MPs on our food chain.

Does microplastic analysis method affect our understanding of microplastics in the environment?

Two analytical methods - both in active use at different laboratories - were tested and compared against each other to investigate how the procedure influences microplastic (MP) detection with micro Fourier Transform Infrared Spectroscopy (μFTIR) imaging. A representative composite water sample collected from the Danube River was divided into 12 subsamples, and processed following two different methods, which differed in MP isolation procedures, the optical substrate utilized for the chemical imaging, and the detection limit of the spectroscopic instruments. The first instrument had a nominal pixel resolution of 5.5 μm, while the second had a nominal resolution of 25 μm. These two methods led to different MP abundance, MP mass estimates, but not MP characteristics. Only looking at MPs > 50 μm, the first method showed a higher MP abundance, namely 418-2571 MP m-3 with MP mass estimates of 703-1900 μg m-3, while the second method yielded 16.7-72.1 MP m-3 with mass estimates of 222-439 μg m-3. Looking deeper into the steps of the methods showed that the MP isolation procedure contributed slightly to the difference in the result. However, the variability between individual samples was larger than the difference caused by the methods. Somewhat sample-dependent, the use of two different substrates (zinc selenide windows versus Anodisc filters) caused a substantial difference between results. This was due to a higher tendency for particles to agglomerate on the Anodisc filters, and an 'IR-halo' around particles on ZnSe windows when scanning with μFTIR. Finally, the μFTIR settings and nominal resolution caused significant differences in identifying MP size and mass estimate, which showed that the smaller the pixel size, the more accurately the particle boundary can be defined. These findings contributed to explaining disagreements between studies and addressed the importance of harmonization of methods.

Analytical challenges in detecting microplastics and nanoplastics in soil-plant systems

Microplastics (MPx) and nanoplastics (NPx) are increasingly accumulating in terrestrial ecosystems, heightening concerns about their potential adverse effects on human health via the food chain. Techniques aimed at recovering the most challenging colloidal fractions of MPx and NPx, especially for analytical purposes, are limited. This systematic review emphasises the absence of a universal, efficient, and cost-effective analytical method as the primary hindrance to studying MPx and NPx in soil and plant samples. The study reveals that several methods, including density separation, organic matter removal, and filtration, are utilized to detect MPx or NPx in soil through vibrational spectroscopy and visual identification. Instruments such as Pyrolysis Gas Chromatography Mass Spectrometry (Py-GCMS), Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), Fourier Transform Infrared (FTIR) Spectroscopy, and fluorescence microscopy are employed to identify MPx and NPx in plant tissue. In extraction procedures, organic solvents and sonication are used to isolate NPx from plant tissues, while Pyrolysis GC-MS quantifies the plastics. SEM and TEM serve to observe and characterize NPx within plant tissues. Additionally, FTIR and fluorescence microscopy are utilized to identify polymers of MPx and NPx based on their spectral characteristics and fluorescence signals. The findings from this review clarify the identification and quantification methods for MPx and NPx in soil and plant systems and provide a comprehensive methodology for assessing MPx/NPx in the environment.

Tracing microplastics in rural drinking water in Chongqing, China: Their presence and pathways from source to tap

Despite the significant attention given to microplastics in urban areas, our understanding of microplastics in rural drinking water systems is still limited. To address this knowledge gap, we investigated the presence and pathways of microplastics in rural drinking water system, including reservoir, water treatment plant (WTP), and tap water of end-users. The results showed that the treatment processes in the WTP, including coagulation-sedimentation, sand-granular active carbon filtration, and ultrafiltration, completely removed microplastics from the influent. However, the microplastic abundance increased during pipe transport from WTP to residents' homes, resulting in the presence of 1.4 particles/L of microplastics in tap water. This microplastic increase was also observed during the transportation from the reservoir to the WTP, suggesting that the plastic pipe network is a key source of microplastics in the drinking water system. The main types of polymers were PET, PP, and PE, and plastic breakdown, atmospheric deposition, and surface runoff were considered as their potential sources. Furthermore, this study estimated that rural residents could ingest up to 1034 microplastics annually by drinking 2 L of tap water every day. Overall, these findings provide essential data and preliminary insights into the fate of microplastics in rural drinking water systems.

The Microplastics Iceberg: Filling Gaps in Our Understanding

Plastic is an indispensable material in modern society; however, high production rates combined with inadequate waste management and disposal have resulted in enormous stress on ecosystems. In addition, plastics can become smaller particles known as microplastics (MPs) due to physical, chemical, and biological drivers. MP pollution has become a significant environmental problem affecting terrestrial and aquatic ecosystems worldwide. Although the topic is not entirely new, it is of great importance to the field of polymers, drawing attention to specific gaps in the existing literature, identifying future areas of research, and improving the understanding of MP pollution and its environmental impacts. Despite progress in this field, problems remain. The lack of standardized methods for MP sampling, separation, extraction, and detection makes it difficult to collect information and establish links between studies. In addition, the distribution and pathways of MPs in ecosystems remain unknown because of their heterogeneous nature and the complex matrices in which they occur. Second, toxicological tests showed that MPs can be ingested by a wide range of organisms, such as Danio rerio and Eisenia fetida, resulting in gut obstruction, physical damage, histological changes, and oxidative stress. The uptake of MP and their toxicological effects depend on their shape, size, concentration, and polymer composition. Furthermore, MPs can enter the food chain, raising concerns regarding potential contaminations for human and environmental health. This review paper sheds light on the pressing issue of MP pollution and highlights the need for interdisciplinary collaboration between scientists, policymakers, and industry leaders.

Microplastics in food - a critical approach to definition, sample preparation, and characterisation

The ubiquity of microplastics (MPs) is a more and more frequently brought up topic. The fact that such particles are present in food raises particular concern. Information regarding the described contamination is incoherent and difficult to interpret. Problems appear already at the level of the definition of MPs. This paper will discuss ways of explaining the concept of MPs and methods used for its analysis. Isolation of characterised particles is usually performed using filtration, etching and/or density separation. Spectroscopic techniques are commonly applied for analysis, whereas visual evaluation of the particles is possible thanks to microscopic analysis. Basic information about the sample can be obtained by the combination of Fourier Transform Infrared spectroscopy or Raman spectroscopy and microscopy or using the thermal method combined with spectroscopy or chromatography. The unification of the research methodology will allow a credible assessment of the influence of this pollution coming from food on health.

A Complete Guide to Extraction Methods of Microplastics from Complex Environmental Matrices

Sustainable development is a big global challenge for the 21st century. In recent years, a class of emerging contaminants known as microplastics (MPs) has been identified as a significant pollutant with the potential to harm ecosystems. These small plastic particles have been found in every compartment of the planet, with aquatic habitats serving as the ultimate sink. The challenge to extract MPs from different environmental matrices is a tangible and imperative issue. One of the primary specialties of research in environmental chemistry is the development of simple, rapid, low-cost, sensitive, and selective analytical methods for the extraction and identification of MPs in the environment. The present review describes the developments in MP extraction methods from complex environmental matrices. All existing methodologies (new, old, and proof-of-concept) are discussed and evaluated for their potential usefulness to extract MPs from various biotic and abiotic matrices for the sake of progress and innovation. This study concludes by addressing the current challenges and outlining future research objectives aimed at combating MP pollution. Additionally, a set of recommendations is provided to assist researchers in selecting appropriate analytical techniques for obtaining accurate results. To facilitate this process, a proposed roadmap for MP extraction is presented, considering the specific environmental compartments under investigation. By following this roadmap, researchers can enhance their understanding of MP pollution and contribute to effective mitigation strategies.

Spatio-temporal variation of soil microplastics as emerging pollutant after long-term application of plastic mulching and organic compost in apple orchards

Microplastics (MPs) pollution in agroecosystems have aroused great alarm and widespread concern. However, the spatial distribution and temporal variation characteristics of MPs in apple orchards with long-term plastic mulching and organic compost input are still poorly understood. This study investigated MPs accumulation characteristics and vertical distribution after applying plastic mulch and organic compost in apple orchards for 3 (AO-3), 9 (AO-9), 17 (AO-17), and 26 (AO-26) years on the Loess Plateau. The clear tillage (no plastic mulching and organic composts) area was used as a control (CK). At a soil depth of 0-40 cm, AO-3, AO-9, AO-17, and AO-26 treatments increased the abundances of MPs, and the black fibers and fragments of rayon and polypropylene were dominant. In the 0-20 cm soil layer, the abundances of MPs increased with the treatment time; the abundance was 4333 pieces kg^-1 after 26 years of treatment, gradually decreasing with soil depth. In different treatments and soil layers, the percentages of MPs <1000 μm were dominant (>50%). The AO-17 and AO-26 treatments significantly increased the MPs with the size of 0-500 μm at 0-40 cm and the abundances of pellets in 0-60 cm soil. In conclusion, the long-term (≥17 years) application of plastic mulching and organic composts increased the abundances of small particles at 0-40 cm, and plastic mulching contributed the most to MPs, while organic composts increased the complexity and diversity of MPs.

Microplastics and mesoplastics as emerging contaminants in Tehran landfill soils: The distribution and induced-ecological risk

Environmental pollution with microplastics (MPs) and mesoplastics (MEPs) and their potential risks to human health and ecosystem quality have aroused the concern of communities. Therefore, the pioneering study was conducted on Tehran landfill soil contamination with MPs and MEPs. 56 shallow and deep soil samples were collected from different landfill areas in the wet and dry seasons. The physical and chemical characteristics of MPs and MEPs were measured using a stereomicroscope and FTIR-ATR spectroscopy, respectively. The results showed that the average MP abundance in shallow and deep soil was 863 ± 681 and 225 ± 138 particles/kg soil, and for MEPs, it was 29.8 ± 6.4 and 18.1 ± 8.3 particles/kg_soil. The low-density plastic particles were separated completely by flotation with H₂O, NaCl, and ZnCl₂ solutions, but PVC was only separated by 90%. Over 90% of MPs and MEPs were LDPE, PP, and PS polymers, explained by their widespread applications in single-use products and their consumption in Iran. Films, white and black, and 0.1-0.5 mm were the dominant shapes, colors, and sizes of MPs, respectively. The prevailing MEPs were film-shaped and in white and yellow colors, with a size of 0.5-1.0 cm. Canonical correlation analysis indicated that total organic matter and moisture were highly correlated with MP shapes. The calculated polymer hazard index values have a wide range at different sampling points, and this index yielded hazard levels III-IV and II-IV for MPs and MEPs, respectively, while according to the pollution load index category, the hazard level of MPs and MEPs was I-II and I. The potential ecological risk index from combined polymers has been estimated to be of minor to extreme danger for MPs and of minor risk for MEPs. Our findings provided baseline data on MPs contamination in Tehran landfill soil and its associated ecological risk, which aids policymakers in implementing risk-reduction measures.

Digital holographic approaches to the detection and characterization of microplastics in water environments

Microplastic (MP) pollution is seriously threatening the environmental health of the world, which has accelerated the development of new identification and characterization methods. Digital holography (DH) is one of the emerging tools to detect MPs in a high-throughput flow. Here, we review advances in MP screening by DH. We examine the problem from both the hardware and software viewpoints. Automatic analysis based on smart DH processing is reported by highlighting the role played by artificial intelligence for classification and regression tasks. In this framework, the continuous development and availability in recent years of field-portable holographic flow cytometers for water monitoring also is discussed.

Research status and prospects of microplastic pollution in lakes

As an emerging pollutant, microplastics have attracted widespread concern around the world. Research on microplastics was first conducted in oceans, and in recent years, inland water, especially lakes, has gradually become a hot spot. This paper systematically reviews the sampling, separation, purification, and identification technologies used to assess microplastics in lakes and summarizes the occurrence of lake microplastics worldwide. The results show that microplastics are widespread in lake water and sediment. There are obvious geographical differences in the occurrence of microplastics. The abundance of microplastics in different lakes varies greatly. The forms are mostly fibrous and fragments, and the main polymers are polypropylene (PP) and polyethylene (PE). Previous papers have failed to comment in as much detail on the microplastic sampling techniques employed within lake systems. The sampling and analysis methods are critical to accurately evaluating contamination results. Due to the widespread presence of microplastics and the lack of uniform standards, there are various sampling methods. Trawls and grabs are most widely used in the sampling of lake water bodies and sediment, and sodium chloride and hydrogen peroxide are the most widely used media for flotation and digestion, respectively. In the future, it will be critical to establish unified standards for lake microplastic sampling and analysis technology, further explore the migration mechanism of microplastics in lake systems, and pay attention to the impact of microplastics on lake ecosystems.

Unaccounted Microplastics in the Outlet of Wastewater Treatment Plants—Challenges and Opportunities

Since the 1950s, plastic production has skyrocketed. Various environmental and human activities are leading to the formation and accumulation of microplastics (MPs) in aquatic and terrestrial ecosystems, causing detrimental effects on water, soil, plants, and living creatures. Wastewater treatment plants (WWTPs) are one of the primary MP management centers meant to check their entry into the natural systems. However, there are considerable limitations in effectively capturing, detecting, and characterizing these MPs in the inlet and outlet of WWTPs leading to “unaccounted MPs” that are eventually discharged into our ecosystems. In order to assess the holistic picture of the MPs’ distribution in the ecosystems, prevent the release of these omitted MPs into the environment, and formulate regulatory policies, it is vital to develop protocols that can be standardized across the globe to accurately detect and account for MPs in different sample types. This review will cover the details of current WWTP adoption procedures for MP management. Specifically, the following aspects are discussed: (i) several processes involved in the workflow of estimating MPs in the outlet of WWTPs; (ii) key limitations or challenges in each process that would increase the uncertainty in accurately estimating MPs; (iii) favorable recommendations that would lead to the standardization of protocols in the workflow and facilitate more accurate analysis of MPs; (iv) research opportunities to tackle the problem of ‘missing MPs’; and (v) future research directions for the efficient management of MPs. Considering the burgeoning research interest in the area of MPs, this work would help early scientists in understanding the current status in the field of MP analysis in the outlet of WWTPs.

Prevalence and implications of microplastics in potable water system: An update

Synthetic plastics, which are lightweight, durable, elastic, mouldable, cheap, and hydrophobic, were originally invented for human convenience. However, their non-biodegradability and continuous accumulation at an alarming rate as well as subsequent conversion into micro/nano plastic scale structures via mechanical and physio-chemical degradation pose significant threats to living beings, organisms, and the environment. Various minuscule forms of plastics detected in water, soil, and air are making their passage into living cells. High temperature and ambient humidity increase the degradation potential of plastic polymers photo-catalytically under sunlight or UV-B radiations. Microplastics (MPs) of polyethylene terephthalate, polyethylene, polystyrene, polypropylene, and polyvinyl chloride have been detected in bottled water. These microplastics are entering into the food chain cycle, causing serious harm to all living organisms. MPs entering into the food chain are usually inert in nature, possessing different sizes and shapes. Once they enter a cell or tissue, it causes mechanical damage, induces inflammation, disturbs metabolism, and even lead to necrosis. Various generation routes, types, impacts, identification, and treatment of microplastics entering the water bodies and getting associated with various pollutants are discussed in this review. It emphasizes potential detection techniques like pyrolysis, gas chromatography-mass spectrometry (GC-MS), micro-Raman spectroscopy, and fourier transform infrared spectroscopy (FT IR) spectroscopy for microplastics from water samples.

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.

A novel application of thermogravimetry-mass spectrometry for polystyrene quantification in the PM10 and PM2.5 fractions of airborne microplastics

Microplastics have appeared as emerging pollutants due to the diverse applications of plastics in today's world. Growing evidence points to the negative impacts that airborne microplastics have on human health, as they can enter the human body through respiration. Our aim was to quantify polystyrene airborne microplastics in smaller fractions, thoracic (PM₁₀) and alveolar (PM_2.5), as they have scarcely been studied. In this work, we proposed a methodology based on thermogravimetric analysis coupled with mass spectrometry that requires minimal sample preparation and does not limit particle size. We applied this methodology to quantify the airborne polystyrene in PM₁₀ and PM_2.5 fractions in mass units of microplastics per m³ of air in an urban and agricultural region during the summer of 2021. The mean concentrations of polystyrene found in the PM₁₀ and PM_2.5 fractions were 2.09 and 1.81 ng m^-3, respectively. Therefore, the majority of airborne polystyrene microplastics are found in the alveolar fraction which, is associated with severe cardiopulmonary and respiratory diseases. According to air mass backward trajectories, it was noted that the main sources of these emerging pollutants could be related to local agricultural practices.

Concentrations of tire wear microplastics and other traffic-derived non-exhaust particles in the road environment

Tire wear particles (TWP) are assumed to be one of the major sources of microplastic pollution to the environment. However, many of the previously published studies are based on theoretical estimations rather than field measurements. To increase the knowledge regarding actual environmental concentrations, samples were collected and analyzed from different matrices in a rural highway environment to characterize and quantify TWP and other traffic-derived non-exhaust particles. The sampled matrices included road dust (from kerb and in-between wheeltracks), runoff (water and sediment), and air. In addition, airborne deposition was determined in a transect with increasing distance from the road. Two sieved size fractions (2-20 µm and 20-125 µm) were analyzed by automated Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy (SEM/EDX) single particle analysis and classified with a machine learning algorithm into the following subclasses: TWP, bitumen wear particles (BiWP), road markings, reflecting glass beads, metals, minerals, and biogenic/organic particles. The relative particle number concentrations (%) showed that the runoff contained the highest proportion of TWP (up to 38 %). The share of TWP in kerb samples tended to be higher than BiWP. However, a seasonal increase of BiWP was observed in coarse (20-125 µm) kerb samples during winter, most likely reflecting studded tire use. The concentration of the particle subclasses within airborne PM_80-1 decreases with increasing distance from the road, evidencing road traffic as the main emission source. The results confirm that road dust and the surrounding environment contain traffic-derived microplastics in both size fractions. The finer fraction (2-20 µm) dominated (by mass, volume, and number) in all sample matrices. These particles have a high potential to be transported in water and air far away from the source and can contribute to the inhalable particle fraction (PM₁₀) in air. This highlights the importance of including also finer particle fractions in future investigations.

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.

Urban mangrove ecosystems are under severe threat from microplastic pollution: a case study from Mangalavanam, Kerala, India

The prevalence of microplastics in urban mangrove ecosystems has received little scientific attention despite their immense ecological significance. An investigation was conducted to assess the microplastic abundance and characteristics in three different environmental compartments viz; soil (933 ± 564 particles/kg), sediment (1275 ± 532 particles/kg d.w.), and water (101.6 ± 24 particles/liter) of the Mangalavanam bird sanctuary, a protected mangrove forest in the Cochin city of India. Microplastic fibres were predominant in water, while soil and sediment contained a higher proportion of microplastic fragments. Importantly, surrounding urban features and tidal fluctuation were considered to be influencing microplastic metrics in the area. The colour composition of microplastics was found to be similar in all three environmental compartments and most of the identified polymers were those which are scarcely recycled. Altogether, this study highlights the importance of adopting location-specific measures to protect the area from microplastic pollution and provides the baseline data required for further assessing the impacts of microplastic pollution on mangroves, avifauna, and other components of biodiversity in the region.

Systematic development of extraction methods for quantitative microplastics analysis in soils using metal-doped plastics

The inconsistency of available methods and the lack of harmonization in current microplastics (MPs) analysis in soils demand approaches for extraction and quantification which can be utilized across a wide variety of soil types. To enable robust and accurate assessment of extraction workflows, PET MPs with an inorganic tracer (Indium, 0.2% wt) were spiked into individual soil subgroups and standard soils with varying compositions. Due to the selectivity of the metal tracer, MPs recovery rates could be quickly and quantitatively assessed using ICP-MS. The evaluation of different methods specifically adapted to the soil properties were assessed by isolating MPs from complex soil matrices by systematically investigating specific subgroups (sand, silt, clay, non-lignified and lignified organic matter) before applying the workflow to standard soils. Removal of recalcitrant organic matter is one of the major hurdles in isolating MPs for further size and chemical characterization, requiring novel approaches to remove lignocellulosic structures. Therefore, a new biotechnological method (3-F-Ultra) was developed which mimics natural degradation processes occurring in aerobic (Fenton) and anaerobic fungi (CAZymes). Finally, a Nile Red staining protocol was developed to evaluate the suitability of the workflow for non-metal-doped MPs, which requires a filter with minimal background residues for further chemical identification, e.g. by μFTIR spectroscopy. Image analysis was performed using a Deep Learning tool, allowing for discrimination between the number of residues in bright-field and MPs counted in fluorescence mode to calculate a Filter Clearness Index (FCI). To validate the workflow, three well-characterized standard soils were analyzed applying the final method, with recoveries of 88% for MPs fragments and 74% for MPs fibers with an average FCI of 0.75. Collectively, this workflow improves our current understanding of how to adapt extraction protocols according to the target soil composition, allowing for improved MPs analysis in environmental sampling campaigns.

Thermogravimetry coupled with mass spectrometry successfully used to quantify polyethylene and polystyrene microplastics in organic amendments

The global consumption of plastic is growing year by year, producing small plastic pieces known as microplastics (MPs) that adversely affect ecosystems. The use of organic amendments (compost and manure) polluted with MPs affects the quality of agricultural soils, and these MPs can be incorporated into the food chain and negatively impact human health. Current European legislation only considers large plastic particles in organic amendments. There is no information regarding MP pollution. Thus, the development of a methodology to support future legislation ensuring the quality of agricultural soils and food safety is necessary. This proposed methodology is based on thermogravimetry coupled with mass spectrometry to quantify polyethylene and polystyrene (PE and PS) MPs through their mass spectrometry signal intensity of characteristic PE (m/z 41, 43 and 56) and PS (m/z 78 and 104) ions. This method has been validated with several organic amendments where the MP content ranged from 52.6 to 4365.7 mg kg^-1 for PE-MPs and from 1.1 to 64.3 mg kg^-1 for PS-MPs. The proposed methodology is a quick and robust analytical method to quantify MPs in organic amendments that could support new legislation.

Method Development for Separation and Analysis of Tire and Road Wear Particles from Roadside Soil Samples

A comprehensive understanding of tire and road wear particles (TRWPs) and their detection and quantification in soils is still challenged by the lack of well-set standardized methods, inherent technological inconsistencies, and generalized protocols. Our protocol includes soil sampling, size separation, and organic matter removal by using hydrogen peroxide followed by density separation and analysis. In this context, roadside soil samples from different sites in Kansas and Ohio, USA, were collected and analyzed. Tire cryogrinds analogous to TRWPs were used to evaluate various density separation media, and collected particles more than 1 mm in size were then subjected to infrared spectroscopy (IR), thermogravimetric analysis (TGA), and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) to confirm TRWP presence. Particles smaller than 1 mm were Soxhlet extracted, followed by gas chromatography-mass spectrometry (GC-MS) to validate the presence of tire-related intermediates. SEM-EDX validated the presence of elemental combinations (S + Zn/Na) ± (Al, Ca, Mg, K, Si) attributed to tires. Ketones, carboxylic acids, epoxies, cyclohexane, and benzothiazole sulfenamide (BTS) intermediates were the most probable tire-related intermediates observed in the roadside soil samples. Thus, this simple, widely applicable, cost-effective sample preparation protocol for TRWP analysis can assist TRWP research advancement in terrestrial environments.

Influence of sediment texture on HDPE microplastics recovery by density separation

Microplastics (MPs) are an emerging environmental pollutant, threatening marine and terrestrial ecosystems. Because of their properties and their widely varying size (5mm-0.1 μm), it is still difficult to define a valid and efficient method for extracting MPs from solid matrices. Among the several methods proposed, density separation is the most practical and cost-effective one. Progress is still ongoing towards a deeper understanding of the advantages and limitations related to the application of density separation for MPs extraction, the recovery yields and the factors that may influence it. In this context, we introduce the following work, which provides an early-stage insight into how the sediment texture may influence the efficiency of this extraction method, and how parameters, such as sedimentation time and extraction cycles, can be modified to always achieve the best recovery. Our focus has been directed on evaluating the extraction efficiency of HDPE MPs by density separation using NaCl, from three types of sediment: sandy (SS), sandy loam (SLS) and sandy-clay loam (SCLS). We investigated the impact of sedimentation time (1, 6, 12, 24 h) and extraction cycles (3 cycles for each sedimentation time) on MPs recovery. Finally, we determined the minimum amount of MPs (MPs g/g sediment) below which it is not possible to quantify MPs with the method used. The results have shown that the recovery efficiency of MPs from sediment is structure dependent. The highest recoveries are reached after a settling time of 1 and 6 h. Furthermore, for samples with minimum clay content (SS), only one extraction cycle is needed, whereas two extraction cycles are required for SLS and SCLS. The outcomes about the detection limit (LOD) of the method, showed the existence of an interaction MPs-clay/sediment, which allowed us to understand how far this extraction method is suitable in field, thus defining the minimum grade of MPs pollution (MPs g/g sediment) below which this method is no longer capable to extract MPs from contaminated samples.

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.

Fate of microplastics in the drinking water production

Microplastics are ubiquitous and consequently enter drinking water treatment plants. Knowledge of the microplastic fate in drinking water production is still very limited, although explorative studies have shown tap water contains low contents of microplastics. In this study, we measure microplastic concentrations in drinking water sources and assess the effectiveness of various drinking water treatment facilities to reduce the microplastic concentrations in water to gain insight into the fate of microplastics. Two analytical techniques, laser direct infrared spectroscopy (LDIR) and optical microscopy, have been applied to cover the particle size range from 20 µm to 5 mm. In total five different drinking water sites were investigated using four different types of raw water (groundwater, surface water, dune filtrate and riverbank filtrate) for drinking water production. This research shows that drinking water treatment removes the majority of microplastics and that concentration of microplastics larger than 20 µm in tap water is less than 2 microplastics particles per litre. Between the different raw water sources it is found that groundwater had by far the lowest microplastics concentrations (< 1.000 microplastics per m³) and the highest concentration was found in riverine water, up to 460.000 particles per m³, specifically in the Lek Canal () (a canal connected to the river Rhine). On average the most abundant plastics found are polyamide (PA, 33%), polyethylene terephthalate (PET, 15%), rubbers (10%), polyethylene (PE, 10%) and chlorinated polyethylene (CPE, 7%). This study also showed that natural treatment steps, such as dune infiltration and sedimentation, remove microplastics effectively. However, this may introduce an adverse effect where microplastics potentially accumulate in the sediment and environment.

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.

Rapid extraction of high- and low-density microplastics from soil using high-gradient magnetic separation

Microplastics (MPs) are present in all environments, and concerns over their possible detrimental effects on flora and fauna have arisen. Density separation (DS) is commonly used to separate MPs from soils to allow MP quantification; however, it frequently fails to extract high-density MPs sufficiently, resulting in under-estimation of MP abundances. In this proof-of-concept study, a novel three-stage extraction method was developed, involving high-gradient magnetic separation and removal of magnetic soil (Stage 1), magnetic tagging of MPs using surface modified iron nanoparticles (Stage 2), and high-gradient magnetic recovery of surface-modified MPs (Stage 3). The method was optimised for four different soil types (loam, high‑carbon loamy sand, sandy loam and high-clay sandy loam) spiked with different MP types (polyethylene, polyethylene terephthalate, and polytetrafluoroethylene) of different particle sizes (63 μm to 2 mm) as well as polyethylene fibres (2-4 mm). The optimised method achieved average recoveries of 96% for fibres and 92% for particles in loam, 91% for fibres and 87% for particles in high‑carbon loamy sand, 96% for fibres and 89% for particles in sandy loam, and 97% for fibres and 94% for particles in high-clay sandy loam. These were significantly higher than recoveries achieved by DS, particularly for fibres and high-density MPs (p < 0.05). To demonstrate the practical application of the HGMS method, it was applied to a farm soil sample, and high-density MP particles were only recovered by HGMS. Furthermore, this study showed that HGMS can recover fibre-aggregate complexes. This improved extraction method will provide better estimates of MP quantities in future studies focused on monitoring the prevalence of MPs in soils.

Plastic debris in plastic-mulched soil-a screening study from western Germany

Background

Agricultural plastic mulches offer great benefits such as higher yields and lower pesticide use. Yet, plastic mulches may disintegrate over time and fragment into smaller debris. Such plastic debris is expected to remain in the field after removal of the plastic mulch and thus contributes to soil contamination with plastics.

Method

To investigate this, we collected soil samples at 0-10 cm and 10-40 cm depth from three fields covered with black mulch film for three consecutive years. Three fields without any reported plastic use served as control. Visual plastic debris > 1 cm (macroplastics) was collected from the soil surface. Mesoplastics between 2 mm and 1 cm were density separated from the sampled soil using saturated NaCl solution and analyzed by Fourier-transform infrared spectroscopy. Debris ≤ 2 mm (microplastics) was dispersed from 50 g soil using sodium hexametaphosphate solution followed by the aforementioned density separation. The separated polyethylene (PE), polypropylene (PP), and polystyrene (PS) were quantified via solvent-based pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS).

Results

With 89-206 fragments ha^-1, the majority of macroplastics were located in fields previously covered with mulch films. 80% of the collected specimen were identified as black PE film. The number of mesoplastics in plastic-mulched soil was 2.3 particles kg^-1, while only 1.0 particles kg^-1 were found in the reference fields. Py-GC/MS revealed microplastic levels of up to 13 mg kg^-1. The PE content was significantly higher in plastic-mulched fields than in reference fields.

Discussion

Although the identified plastic levels are lower than those reported in comparable studies, our results still suggest that plastic mulching functions as a source of plastic debris in agricultural systems. Due to its severely restricted degradability, these plastics are likely to accumulate in soil in the long term and further fragment into smaller and smaller debris.

Microplastics in arid soils: Impact of different cropping systems (Altay, Xinjiang)

Although microplastic pollution in the soil environment is currently an important research topic, few studies have focused on farmland soil in arid regions. This study investigated the abundances, sizes, polymer compositions, and forms of microplastics across nine agricultural plots cultivated with maize, sunflower, and potato (three of each crop) plants to determine the influences of different cropping characteristics and agricultural practices. The study area was within the arid region of the Ulungur River basin in Qinghe County, Altay, Xinjiang, China. The main forms of microplastics were fragments and fibers, and polyethylene was the dominant polymer (91.6%). The microplastic abundance ranged from 11 347 items/kg_dw to 78 061 items/kg_dw (mean of 52 081.7 items/kg_dw). The abundance and proportion of microplastics with a diameter of <0.2 mm were significantly higher in the sunflower and maize plots (i.e., tall crops) than in the potato plots (i.e., short crops) (p < 0.05). This is due to straw residues affecting the migration and recovery of the mulch. The abundance and fragmentation of microplastics were significantly higher in the sunflower and maize plots where plastic mulch was extensively used because these tall crops anchored the mulch near their stem-root systems. The mulch was then slowly aged (e.g., via wind erosion) before being fragmented due to agricultural practices (e.g., mechanical plowing and residue retention). Although microplastics sourced from mulch are probably immobilized by straw residues in the short term, fragile and easily broken pieces of mulch are eventually released into the soil due to agricultural practices. The findings suggest that different cropping characteristics can affect the abundance and fragmentation of microplastics in agricultural soils, even within the same region, and thus the level and type of microplastic pollution. Traditional plastic mulch should be replaced with biodegradable mulch to reduce microplastic pollution in agricultural fields.

Quality assessment of research studies on microplastics in soils: A methodological perspective

Microplastics have become a global concern, and soil acts as a major sink for plastic pollution. Due to rapid development of soil microplastics research, various analysis methods have been developed, but require proper consistency and standard procedures. The objective of this study was to appraise a quality assessment concerning soil microplastics from a methodological perspective. Nine studies were selected for the quality assessment exercise based on methodological investigations on soil microplastics and were evaluated based on the adapted Criteria for Reporting and Evaluating Ecotoxicity Data (CRED) method. The highest score obtained by an individual study was 21 while the lowest was 14, leaving a wide score gap which indicated inconsistency amongst the studies. Criterion with the highest average score of 2.0 was obtained for sample size and data reporting. The lowest average score of 0.89 was for the negative control. In conclusion, the total average scores for all eleven criteria were 1.56. Current quality assessment perceived that there was room for improvement and betterment of quality assurance for studies on microplastics and a form of guideline on methodological aspects of soil microplastics studies. It was suggested that future microplastics studies should methodically include quality assurance/quality control (QA/QC) protocols in every process to ensure that good quality data is produced and applied in the risk assessment process.