Microplastics In Soils Research Articles

What is the most effective analytical method for quantification and identification of microplastics in contaminated soils?

The increasing concern over microplastics (MPs) contamination in agricultural soils due to excessive plastic use is a worldwide concern. The objective of this study was to determine which analytical technique is most effective for the analysis of MPs in agricultural soils. Near-infrared spectroscopy (NIR), scanning electron microscopy (SEM), multispectral analysis, and X-ray diffractionwere usedto analyze sections of clay soil containing varying percentages of virgin white MPs from 0 to 100%. X-ray analysis only detected MPs at high concentrations (20%). However, NIR at 2.300nm and multispectral analysis at 395nm demonstrated greater accuracy and sensitivity in distinguishing between all MPs levels. SEM revealed that MPs have an amorphous structurethat isdistinct from crystalline soil, potentially influencing their interactions with other soil constituents. These findings highlight the value of NIR and multispectral analysis in accurately identifying and measuring MPs in soil. Efficient management plans rely on increased awareness of MPs' environmental impact.

Microplastic Analysis in Soil Using Ultra-High-Resolution UV–Vis–NIR Spectroscopy and Chemometric Modeling

The study of microplastics (MPs) in soils is impeded by similarities between plastic and non-plastic particles and the misidentification of MP by current analytical methods such as visual microscopic examination. Soil MPs pose serious ecological and public health risks because of their abundance, persistence, and ubiquity. Thus, reliable identification methods are badly needed for scientific study. One possible solution is UV–Vis–NIR spectroscopy, which has the ability to rapidly identify and quantify concentrations of soil microplastics. In this study, a full-range, field portable spectrometer (350–2500 nm) with ultra-high spectral resolution (1.5 nm, 3.0 nm, and 3.8 nm) identified three types of common plastics: low-density polyethylene (LDPE), polyvinyl chloride (PVC), and polypropylene (PP). Three sets of artificially MP-treated vermiculite soil samples were prepared for model prediction testing and validation: 150 samples for model calibration and 50 samples for model validation. A partial least square regression model using the spectral signatures for quantification of soil and MP mixtures was built with all three plastic polymers. Prediction R2 values of all three polymers showed promising results: polypropylene R2 = 0.943, polyvinyl chloride R2 = 0.983, and polyethylene R2 = 0.957. Our study supports previous work showing that combining ultra-high-resolution UV–Vis–NIR spectrometry with quantitative modeling can improve the accuracy and speed of MP identification and quantification in soil.

Problems caused by microplastics in soil: Personal perspective

In this perspective, I focus on problems caused by plastics or microplastics in soil that are based on my knowledge. I point out that contacts that I have had from lawyers and policy makers show that plastics in soil are going to become important legal and regulatory issues. I describe an experiment that I did with the microplastic, polyethylene glycol, added to soil, which showed that it caused ponding of water on the soil surface and reduced infiltration, probably due to the participation of the polymers of the microplastic in a process called solvation. The large, hydrated molecules apparently clogged the soil pores, preventing aeration. I also showed in the same experiment that polyethylene glycol increased the uptake of the toxic heavy metal, cadmium, into wheat plants. I end the perspective by describing a recent experiment that indicates that the Casparian strip is a likely barrier for the uptake by lettuce of polystyrene microplastics that are 200 nm in diameter. However, smaller particles might penetrate it, and we need more studies to determine the size of nanoparticles that can move through the Casparian strip and up to the shoot.

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.

Distribution characteristics and integrated ecological risks evaluation modelling of microplastics and heavy metals in geological high background soil

The microplastics (MPs), a novel pollutant, and heavy metals (HMs) significantly affect soil ecology. The study investigated HMs and MPs in Qianxi's high geological background soil, established a model for risk evaluation with MPs types and shapes, and proposed a two-dimensional comprehensive index model for MPs-HMs combined pollution and risk evaluation criterion. The results revealed a high soil Cd concentration, with a mean value of 0.38 mg·kg−1. Additionally, soils from soybean–wheat intercropping–potato–corn rotation (SWI-PCR) exhibited significantly higher concentrations of Hg, As, and Pb compared with those from soybean–wheat intercropping-corn rotation (SWI-CR). Moreover, the soil exhibited a high abundance of MPs (8667.66 ± 3864.26 items·kg−1), mainly characterized by PS and fiber. The mean of adjusted ecological risk index (ARI) for MPs in soil was 525.27, indicating a grade 3 risk. The two-dimensional combined index (TPI) was used to assess the ecological risk of MPs–HMs combined pollution, exhibiting an exceedance rate of 56 % with a mean of 445.07. The risk level of the combined pollution was graded as 6, indicating high risk. The microplastic risk evaluation model and the comprehensive evaluation method of combined pollution established in this study provide a reference for the future risk evaluation of multi-pollutant combined pollution.

Soil Microplastic Pollution and Microbial Breeding Techniques for Green Degradation: A Review.

Microplastics (MPs), found in many places around the world, are thought to be more detrimental than other forms of plastics. At present, physical, chemical, and biological methods are being used to break down MPs. Compared with physical and chemical methods, biodegradation methods have been extensively studied by scholars because of their advantages of greenness and sustainability. There have been numerous reports in recent years summarizing the microorganisms capable of degrading MPs. However, there is a noticeable absence of a systematic summary on the technology for breeding strains that can degrade MPs. This paper summarizes the strain-breeding technology of MP-degrading strains for the first time in a systematic way, which provides a new idea for the breeding of efficient MP-degrading strains. Meanwhile, potential techniques for breeding bacteria that can degrade MPs are proposed, providing a new direction for selecting and breeding MP-degrading bacteria in the future. In addition, this paper reviews the sources and pollution status of soil MPs, discusses the current challenges related to the biodegradation of MPs, and emphasizes the safety of MP biodegradation.

A bibliometric perspective on the occurrence and migration of microplastics in soils amended with sewage sludge.

The land application of sewage sludge from wastewater treatment plants has been recognized as a major source of microplastic contamination in soil. Nevertheless, the fate and behavior of microplastics in soil remain uncertain, particularly their distribution and transport, which are poorly understood. This study does a bibliometric analysis and visualization of relevant research publications using the CiteSpace software. It explores the limited research available on the topic, highlighting the potential for it to emerge as a research hotspot in the future. Chinese researchers and institutions are paying great attention to this field and are promoting close academic cooperation among international organizations. Current research hot topics mainly involve microplastic pollution caused by the land application of sewage sludge, as well as the detection, environmental fate, and removal of microplastics in soil. The presence of microplastics in sludge, typically ranging from tens of thousands to hundreds of thousands of particles (p)/kg, inevitably leads to their introduction into soil upon land application. In China, the estimated annual accumulation of microplastics in the soil due to sludge use is approximately 1.7 × 1013 p. In European countries, the accumulation ranges from 8.6 to 71 × 1013 p. Sludge application has significantly elevated soil microplastic concentrations, with higher application rates and frequencies resulting in up to several-fold increases. The primary forms of microplastics found in soils treated with sludge are fragments and fibers, primarily in white color. These microplastics consist primarily of components such as polyamide, polyethylene, and polypropylene. The vertical transport behavior of microplastics is influenced by factors such as tillage, wind, rainfall, bioturbation, microplastic characteristics (e.g., fraction, particle size, and shape), and soil physicochemical properties (e.g., organic matter, porosity, electrical conductivity, and pH). Research indicates that microplastics can penetrate up to 90 cm into the soil profile and persist for decades. Microplastics in sewage sludge-amended soils pose potential long-term threats to soil ecosystems and even human health. Future research should focus on expanding the theoretical understanding of microplastic behavior in these soils, enabling the development of comprehensive risk assessments and informed decision-making for sludge management practices. PRACTITIONER POINTS: Microplastics in sewage sludge range from tens to hundreds of thousands per kilogram. Sludge land application contributes significantly to soil microplastic pollution. The main forms of microplastics in sludge-amended soils are fragments and fibers. Microplastics are mainly composed of polyamide, polyethylene, and polypropylene. Microplastics can penetrate up to 90 cm into the soil profile and persist for decades.

Invasion of Trifolium repens L. aggravated by biodegradable plastics: adjustable strategy for foraging N and P

The invasion of alien plant and the pollution caused by soil microplastics have emerged as significant ecological threats. Recent studies have demonstrated aggravating effect of non-biodegradable microplastics on plant invasion. However, the impact of biodegradable microplastics (BMPs) on plant invasion remains unclear. Therefore, it is imperative to explore the impact of BMPs on plant invasion. In this study, a 30-day potting experiment with Trifolium repens L. (an invasive plant) and Oxalis corniculata L. (a native plant) was conducted to evaluate the influence of BMPs on T. repens's invasion. The findings revealed that BMPs results in a reduction in available N and P contents, thereby facilitating the colonization of arbuscular mycorrhizal fungi on T. repens 's roots. Consequently, T. repens adjusted its N and P foraging strategy by increasing P absorption ratio, and enhancing the accumulation of N and P in leaves. This ultimately led to the decrease of relative neighbor effect index of T. repens, indicating an aggravated invasion by T. repens. This study significantly enhances and expands the understanding of mechanisms by which microplastics aggravate plant invasion.

Occurrence characteristics and potential risk of microplastics under different land conditions

Microplastics (MPs) pollution has caused widespread concern, more researchers have focused on MPs in farmland soil. However, the distribution of MPs in different land use types, land restoration years and crop types remained largely unexplored. Therefore, the study investigated the distribution characteristics and evaluated ecological risk of MPs in soil of northern Shaanxi Province, China. The abundance, particle size, morphology and polymer types of MPs in soil were analyzed by sample collection, Raman spectroscopy and laser direct infrared spectroscopy (LDIR). The ecological risk index (H) and pollution load index (PLI) were employed to assess the risks posed by MPs in the soil. It was shown that the concentration of MPs in farmland soil was the highest (4483 items·kg−1) among the different land use types. The average abundance of microplastics in farmland soil was 1.98 times than that in industrial park soil. An increase in restoration years corresponded with a decrease in MPs abundance and an increase in smaller-sized MPs. In addition, the content of MPs in the soil of perennial crops was more stable, with fluctuations less than 25%, and the size of MPs was smaller than that of the annual crops. The main types of MPs in the soil of the study area were PP (28.5%) and PET (24.1%), MPs with size between 20 and 40 μm were dominated. Based on the pollution load index (PLI), 51.9% of the sampling sites were categorized as moderately polluted, and the MPs pollution risk of farmland soil was the highest. Mild and moderate pollution caused fewer adverse impact, while extremely strong pollution was detrimental to ecosystems and human health. In general, the study would provide a foundational understanding of MPs pollution levels and environment risk associated with different land use types, land restoration years and crop types.

Investigating the distribution of microplastics in soils from e-waste dismantling sites and their adsorption of heavy metals.

Microplastics are characterized by strong hydrophobicity, large specific surface area. In addition to the pollutant they contain, the heavy metals adsorbed on the surface of microplastics can migrate or be transformed with them into the environmental medium, which is potentially harmful to humans. The distribution characteristics of microplastics in contaminated soil at the e-waste dismantling site were studied. The study investigated the adsorption characteristics of polyvinyl chloride (PVC), polypropylene (PP) and acrylonitrile-butadiene-styrene (ABS) on copper (Cu), zinc (Zn) and lead (Pb). It analysed the influence of various factors on the adsorption process of heavy metals, the adsorption law of microplastics on some of the heavy metals in the environment, and the risk of heavy metal release from microplastics to soil. The results showed that ABS and PP were the main microplastics in the contaminated soil. Among them, black, white and transparent microplastics accounted for 89.91%. The shape of microplastics is mainly granular, and microplastics with a particle size of 1-2 mm accounted for the largest proportion. Further studies showed that plastic particles made of ABS, PP and PVC also have the adsorption capacity for different types of heavy metals in soil, and the trends of adsorption capacity are: PP>PVC>ABS. When PP does not reach adsorption equilibrium in the adsorption process, the smaller the particle size and the more added amount, the greater the adsorption capacity. This is because the smaller the particle size of the microplastic is, the more adsorption points it can provide, increasing its ability to adsorb heavy metal ions.

Earthworms improve the rhizosphere micro-environment to mitigate the toxicity of microplastics to tomato (Solanum lycopersicum)

Microplastics (MPs) are widespread in agricultural soil, potentially threatening soil environmental quality and plant growth. However, toxicological research on MPs has mainly been limited to individual components (such as plants, microbes, and animals), without considering their interactions. Here, we examined earthworm-mediated effects on tomato growth and the rhizosphere micro-environment under MPs contamination. Earthworms (Eisenia fetida) mitigated the growth-inhibiting effect of MPs on tomato plant. Particularly, when exposed to environmentally relevant concentrations (ERC, 0.02% w/w) of MPs, the addition of earthworms significantly (p < 0.05) increased shoot and root dry weight by 12–13% and 13–14%, respectively. MPs significantly reduced (p < 0.05) soil ammonium (NH4+-N) (0.55–0.69 mg/kg), nitrate nitrogen (NO3−-N) (7.02–8.65 mg/kg) contents, and N cycle related enzyme activities (33.47–42.39 μg/h/g) by 37.7–50.9%, 22.6–37.2%, and 34.2–48.0%, respectively, while earthworms significantly enhanced (p < 0.05) inorganic N mineralization and bioavailability. Furthermore, earthworms increased bacterial network complexity, thereby enhancing the robustness of the bacterial system to resist soil MPs stress. Meanwhile, partial least squares modelling showed that earthworms significantly influenced (p < 0.01) soil nutrients, which in turn significantly affected (p < 0.01) plant growth. Therefore, the comprehensive consideration of soil ecological composition is important for assessing MPs ecological risk.

Impact on sulfadiazine bio-accessibility in soils through organic diffusive gradients in thin films (o-DGT): Differentiation based on microplastic polymers, aging, and soil properties

Due to the similar sources of swage irrigation, organic fertilizer, and sludge application, microplastics (MPs) and antibiotics coexist inevitably in the agriculture soils. However, the impacts of MPs with different polymer types and aging status on the bio-accessibility of co-existing antibiotics in soils remained unclear. Therefore, we using the diffusive gradients films for organic compounds devices (o-DGT) to evaluated the distribution of sulfadiazine (SDZ) in both paddy soil and saline soil amended with 0.5 % (w/w) MPs. Four polymer types (polyethylene: PE, polypropylene: PP, polyamide: PA, and polyethylene terephthalate: PET) and two aging statuses (aged PE and aged PP) of MPs were used in this study. Results showed that soil properties significantly influence the partition of SDZ in soil and soil solution, and SDZ gained a lower degradation rate but higher mobility in saline soil. MPs pose different impacts on partition of SDZ between paddy soil and saline soil. Notably, PP reduced the labile solid phase-solution phase partition coefficient (Kdl) by 17.7 % in paddy soil, while PE, PP, and aPE increased the Kdl value by 2.00, 1.62, and 2.81 times in saline soil. Besides, in saline soil, all the MPs reduced the SDZ concentration in the soil solution, while significantly increased the SDZ in o-DGT phase. Conversely, MPs did not impact the SDZ's o-DGT concentration in paddy soil. Additionally, MPs increased the R value of SDZ in two soils, especially in saline soil. It suggested that MPs could potentially enhance the resupply of SDZ from soil to plants, particularly under saline conditions. Furthermore, aged MPs had a more pronounced effect on these indicators compared to virgin MPs in saline soil. Therefore, MPs in soil poses a potential risk for biota's uptake of SDZ, particularly in fragile environment. Moreover, the risk intensifies with aged MPs.

Combined toxicity of polyethylene microplastics and nickel oxide nanoparticle on earthworm (Eisenia andrei): oxidative stress responses, bioavailability and joint effect.

The co-occurrence of heavy metals and microplastics (MPs) is an emerging issue that has attracted considerable attention. However, the interaction of nickel oxide nanoparticle (nano-NiO) combined with MPs in soil was poorly researched. Here, experiments were conducted to study the influence of nano-NiO (200mg/kg) and polyethylene (PE) MPs with different concentrations (0.1, 1, and 10%) and sizes (13, 50, and 500µm) on earthworms for 28days. Compared to control, the damage was induced by PE and nano-NiO, which was evaluated by biomarker Integrated Biomarker Response index: version 2 (IBRv2) based on six biomarkers including SOD, POD, CAT, MDA, AChE, Na+/K+-ATPase and cellulase. The majority of the chosen biomarkers showed significant but complicated responses with increasing contaminant concentrations after 28days of exposure. Moreover, the joint effect was assessed as antagonism by the effect addition index (EAI). Overall, this work expands our understanding of the combined toxicity of PE and nano-NiO in soil ecosystems.

Qualitative and quantitative detection of microplastics in soil based on LIF technology combined with OOA-ELM/SPA-PLS

Traditional methods for detecting soil microplastics include chemical digestion, density separation, staining, etc. These methods often only provide qualitative analysis of microplastics and are difficult to accurately quantify. To address this issue, laser induced fluorescence (LIF) technology is introduced, which can achieve high sensitivity, non-destructive, and rapid detection, and improve the accuracy and efficiency of qualitative and quantitative analysis of soil microplastics. Therefore, based on LIF technology, a qualitative prediction model for optimizing Extreme Learning Machine (ELM) using Osprey Optimization Algorithm (OOA) and a quantitative prediction model combining Continuous Projection Algorithm (SPA) with Partial Least Squares Algorithm (PLS) were established. Qualitative analysis used eight types of microplastics, with AS, PA66, ABS, PS, POM, PBT, PET, and PVC as experimental samples. Initially, spectral data is obtained using LIF technology and the raw spectral data is pre-processed using polynomial smoothing algorithm (SG) and moving average (MA) methods. Subsequently, factor analysis (FA) and local linear embedding (LLE) techniques are applied to dimensionality reduction and then input into the ELM model. At the same time, the ELM parameter is optimized by using OOA algorithm. In the quantitative analysis, PA66 powder and soil are mixed in different proportions (10:0, 8:2, 5:5, 2:8, 0:10), SG and MA pre-processing are performed on the spectral data obtained by LIF technology, and SPA is used to select the spectral characteristic wavelength for the original data and the pre-processed spectral data, and then a linear regression model is established combined with PLS. In order to facilitate the comparison of data, the experimental results are reserved to 5 decimal places, the experimental results indicate that LIF technology is faster than traditional methods in extracting raw data. The convergence of the OOA-optimized ELM model is better than that of the PSO-optimized ELM model. Among all the models of qualitative analysis, SG-LLE-OOA-ELM had the best prediction effect, with mean square error (MSE) of 0.00834, coefficient of determination (R2) of 0.99841, root mean square error (RMSE) of 0.09134, and mean absolute error (MAE) of 0.07038. Among the models of quantitative analysis, the best effect is SG-SPA-PLS model with R2 of 0.99951.

A multivariate analysis of microplastics in soils along the headwaters of Yangtze river on the Tibetan Plateau

Microplastics (MPs) are among the most widespread anthropogenic pollutants of natural environments, while limited research has focused on the fate of MPs in soils along the Plateau rivers. In this study, we investigated MPs in soils along the source areas of the Yangtze River on the Qinghai–Tibet Plateau. The results showed mean MP abundance values of (89.4 ± 51.0) and (64.4 ± 24.5) items/kg of dry soils around the tributary and mainstream areas, respectively. Film, transparent colors, and polyethylene were common shape, color, and compositions, respectively. The correlation analysis and PCA revealed that MP abundance was related to soil heavy metals (Cr and Ni) and nutrients (TOC and TP) (p < 0.05). Structural equation modeling also revealed that population density was the dominant driving factor contributing to MPs, with a total effect coefficient of 0.45. In addition, the conditional fragmentation model further distinguished the differences in MP sources from upstream to downstream along the Jinsha River. The significant sources of MPs in the bare land and grasslands from the upper reaches of the Jinsha River included traffic, tourism, and atmospheric transport. In contrast, MP transport during farming activities mainly contributed to MPs in the agricultural soil in the lower reaches.

The microplastics distribution characteristics and their impact on soil physicochemical properties and bacterial communities in food legumes farmland in northern China

Microplastics (MPs) pose a threat to farmland soil quality and crop safety. MPs exist widely in food legumes farmland soil due to the extensive use of agricultural film and organic fertilizer, but their distribution characteristics and their impact on soil environment have not been reported. The abundance and characteristics of MPs, soil physical and chemical properties, and bacterial community composition were investigated in 76 soil samples from five provinces in northern China. The results showed that the abundance of MPs ranged from 1600 to 36,200 items/kg. MPs in soil were mostly fibrous, less than 0.2 mm, and white. Rayon, polyester and polyethylene were the main types of MPs. The influences of MPs on soil physicochemical properties and bacterial communities mainly depended on the type of MPs. Notably, polyethylene significantly decreased the proportion of silt particles, and increased the nitrate nitrogen content as well as the abundance of MPs-degrading bacteria Paenibacillus (p < 0.05). Moreover, bacteria were more sensitive to polyesters in soil with low concentration of organic matter. This study indicated that MPs in food legumes farmland soil presented a higher-level. And, they partially altered soil physicochemical properties, and soil bacteria especially in soil with low organic matter.

Experimental Study on the Migration and Distribution of Microplastics in Desert Farmland Soil Under Drip Irrigation.

The microplastics (MPs) formed by broken plastic film may migrate in the soil under drip irrigation. To investigate the migration distribution of MPs in desert farmland soil under drip irrigation conditions, our study was conducted on farmland in Xinjiang (China). A MP drip irrigation penetration migration testing device was set up in combination with Xinjiang farmland irrigation methods to conduct a migration simulation experiment. The results showed that the migration amount of MPs in soil was significantly positively correlated with the amount of drip irrigation, and significantly negatively correlated with the soil depth; in addition, the relationship between the migration amount of MPs in different types of soil was: clay < sandy loam < sandy soil. Under drip irrigation conditions, the migration rates of MPs were 30.51%, 19.41%, and 10.29% in sandy soil, sandy loam soil, and clay, respectively. The migration ability of these three particle sizes of polyethylene MPs in soil was ranked as follows: 25 to 147 μm > 0 to 25 μm > 147 to 250 μm. When the drip irrigation volume was 2.6 to 3.2 L, horizontal migration distances of MPs exceeded 5 cm, and vertical migration distances reached more than 30 cm. Our findings provide reference data for the study of soil MP migration. Environ Toxicol Chem 2024;43:1250-1259. © 2024 SETAC.

Examining Soil Microplastics: Prevalence and Consequences Across Varied Land Use Contexts

In an extensive exploration of microplastics within soil environments, our study aims to investigate the presence, spread, and ecological impact of microplastics in soil, focusing on Makassar City, Indonesia. Using a Sinher binocular digital microscope, we visually examined soil samples in Petri dishes, measuring microplastic sizes with Image-J software. Fourier-transform infrared (FTIR) spectroscopy was also employed for additional identification and analysis of polymer compositions. Our research uncovered a widespread presence of microplastics across diverse soil types and land uses, including residential, fishpond, agricultural, landfill, coastal, and bareland areas. The concentration of these microplastics was found to be between 16.6 to 21.9 particles/gram, showing consistency across most land uses, with some variations in coastal areas. We noted a significant variety in microplastic forms, predominantly fragments and films, across the different land uses. A wide range of colors was observed, including blue, green, red, and transparent. Polyethylene (PE) and polypropylene (PP) were identified as the predominant polymers. Our study highlights the non-uniform distribution of microplastics in soil, suggesting potential significant impacts on soil organisms and the wider ecosystem. These findings underscore the critical need for more comprehensive research on the ecological implications of microplastics in soil environments. Doi: 10.28991/CEJ-2024-010-04-017 Full Text: PDF

Comparative Evaluation of Analytical Techniques for Quantifying and Characterizing Polyethylene Microplastics in Farmland Soil Samples

The presence of microplastics in soil has become a significant global concern, posing a threat to environmental, agricultural, and human health. However, the use of various detection methods has led to significant discrepancies in the statistics reported for the abundance of soil microplastics across the available literature, resulting in poor comparability across the available literature. Studies have shown that plastic film residue is among the main primary sources of microplastics in farmland soils. Therefore, we manufactured and selected polyethylene microplastics (PE-MPs) from plastic film and combined them with soil samples after density separation treatment, forming a spiked test soil sample, which was subjected to density separation and extraction using a ZnCl2 solution. The experiment used visual inspection by stereo microscopy, micro-Fourier transform infrared spectroscopy, micro-Raman spectrometry, laser direct infrared imaging, and pyrolysis-gas chromatography–mass spectroscopy for the quantitative analysis of spiked soil. This study systematically assessed and compared these five common soil microplastic detection methods. The results revealed different quantitative detection accuracies across various particle size ranges. Micro-Fourier transform infrared spectroscopy showed a broader applicable particle size range (20–5000 μm) and higher detection rate (91%), while the detection range (&gt;50 μm) and rate (70%) of visual inspection through stereo microscopy were lower. For the identification of microplastic morphology, laser direct infrared imaging performed better, whereas micro-Fourier transform infrared spectroscopy had the advantage in determining the types of polymers present over micro-Raman spectrometry. The advantages, disadvantages, and detection rates of the above five detection methods were clarified during the detection process. Considering these findings and similar studies, we suggest three combinations of the evaluated methods to optimize the detection of PE-MPs.

Vis-NIR spectroscopy based rapid and non-destructive method to quantitate microplastics: An emerging contaminant in farm soil

Microplastics (MPs) is the second most important environmental issue and can potentially enter into food chain through farmland contamination and other means. There are no standardized extraction methods for quantification of MPs in soil. The embedded errors and biases generated serious problems regarding the comparability of different studies and leading to erroneous estimation. To address this gap, present study was formulated to develop an efficient method for MPs analysis suitable for a wide range of soil and organic matrices. A method based on Vis-NIR (Visible-Near Infra Red) spectroscopy is developed for four different soil belonging to Alfisol, Inceptisol, Mollisol and Vertisol and two organic matter matrices (FYM and Sludge). The developed method was found as rapid, reproducible, non-destructive and accurate method for estimation of all three-density groups of MPs (Low, Medium and High) with a prediction accuracy ranging from 1.9 g MPs/kg soil (Vertisol) to 3.7 g MPs/kg soil (Alfisol). Two different regression models [Partial Least Square Regression (PLSR) and Principal Component Regression (PCR)] were assessed and PLSR was found to provide better information in terms of prediction accuracy and minimum quantification limit (MQL). However, PCR performed better for organic matter matrices than PLSR. The method avoids any complicated sample preparation steps except drying and sieving thus saving time and acquisition of reflectance spectrum for single sample is possible within 18 s. Owing to have the minimum quantification limit ranging from 1.9–3.7 g/kg soil, the vis-NIR based method is perfectly suitable for estimation of MPs in soil samples collected from plastic pollution hotspots like landfill sites, regular based sludge amended farm soils. Additionally, the method can be adapted by small scale compost industries for assessing MPs load in product like city compost which are applied at agricultural fields and will be helpful in quantifying possible MPs at the sources itself.