Analytical methods and environmental processes of nanoplastics

High sensitivity in quantitative analysis of mixed-size polystyrene micro/nanoplastics in one step

As emerging environmental pollutants, microplastics (MPs) and nanoplastics (NPs) pose a serious threat to human health. Owing to the lack of feasible and reliable analytical methods, the separation and identification of MPs and NPs of different sizes remains a challenge. In this study, a hyphenated method involving filtration and surface-enhanced Raman spectroscopy (SERS) for the separation and identification of MPs and NPs is reported. This method not only avoids the loss of MPs and NPs during the transfer process but also provides an excellent SERS substrate. The SERS substrate was fabricated by electrochemically depositing silver particles onto the reduced graphene oxide layer coated on stainless steel mesh. Results show that polystyrene (PS) MPs and NPs are efficiently separated on the SERS substrate via vacuum filtration, resulting in high retention rates (74.26 % ± 1.58 % for 100 nm, 81.06 % ± 1.49 % for 500 nm, and 97.73 % ±0.11 % for 5 μm) and low limit of detection (LOD). The LOD values of 100 nm, 500 nm, and 5 μm PS are 8.89 × 10-5, 3.39 × 10-5, and 1.57 × 10-4 μg/mL, respectively. More importantly, a linear relationship for uniform quantification of 100 nm, 500 nm, 3 μm and 5 μm PS was established, and the relationship is Y = 225.61 lgX + 1076.36 with R2 = 0.980. The method was validated for the quantitative analysis of a mixture of 100 nm, 500 nm PS NPs, 3 μm and 5 μm PS MPs in a ratio of 1:1:1:1, which successfully approaches the evaluation of evaluated PS NPs in the range of 10-4-10 μg/mL with an LOD value of approximately 7.82 × 10-5 μg/mL. Moreover, this method successfully detected (3.87 ± 0.06) × 10-5 μg MPs and NPs per gram of oyster tissue.

Material-specific binding peptides empower sustainable innovations in plant health, biocatalysis, medicine and microplastic quantification

Material-binding peptides (MBPs) have emerged as a diverse and innovation-enabling class of peptides in applications such as plant-/human health, immobilization of catalysts, bioactive coatings, accelerated polymer degradation and analytics for micro-/nanoplastics quantification. Progress has been fuelled by recent advancements in protein engineering methodologies and advances in computational and analytical methodologies, which allow the design of, for instance, material-specific MBPs with fine-tuned binding strength for numerous demands in material science applications. A genetic or chemical conjugation of second (biological, chemical or physical property-changing) functionality to MBPs empowers the design of advanced (hybrid) materials, bioactive coatings and analytical tools. In this review, we provide a comprehensive overview comprising naturally occurring MBPs and their function in nature, binding properties of short man-made MBPs (<20 amino acids) mainly obtained from phage-display libraries, and medium-sized binding peptides (20-100 amino acids) that have been reported to bind to metals, polymers or other industrially produced materials. The goal of this review is to provide an in-depth understanding of molecular interactions between materials and material-specific binding peptides, and thereby empower the use of MBPs in material science applications. Protein engineering methodologies and selected examples to tailor MBPs toward applications in agriculture with a focus on plant health, biocatalysis, medicine and environmental monitoring serve as examples of the transformative power of MBPs for various industrial applications. An emphasis will be given to MBPs' role in detecting and quantifying microplastics in high throughput, distinguishing microplastics from other environmental particles, and thereby assisting to close an analytical gap in food safety and monitoring of environmental plastic pollution. In essence, this review aims to provide an overview among researchers from diverse disciplines in respect to material-(specific) binding of MBPs, protein engineering methodologies to tailor their properties to application demands, re-engineering for material science applications using MBPs, and thereby inspire researchers to employ MBPs in their research.

Surface-Enhanced Raman Spectroscopy Sensor Integrated with Ag@ZIF-8@Au Core-Shell-Shell Nanowire Membrane for Enrichment, Ultrasensitive Detection, and Inactivation of Bacteria in the Environment

A core-shell-shell sandwich material is developed with silver nanowires as the core, ZIF-8 as an inner shell, and gold nanoparticles as the outer shell, namely, Ag@ZIF-8@Au nanowires (AZA-NW). Then, the synthesized AZA-NW is transformed into a surface-enhanced Raman spectroscopy (SERS) sensor (named M-AZA) by the vacuum filtration method and used to enrich, detect, and inactivate traces of bacteria in the environment. The M-AZA sensor has three main functions: (1) trace bacteria are effectively enriched, with an enrichment efficiency of 91.4%; (2) ultrasensitive detection of trace bacteria is realized, with a minimum detectable concentration of 1 × 101 CFU/mL; (3) bacteria are effectively killed up to 92.4%. The shell thickness of ZIF-8 (5-75 nm) is controlled by adjusting the synthesis conditions. At an optimum shell thickness of 15 nm, the effect of gold nanoparticles and ZIF-8 shell on the sensor's stability, SERS activity, and antibacterial performance is investigated. The simulation of the SERS sensor using the finite difference time domain (FDTD) method is consistent with the experimental results, theoretically demonstrating the role of the gold nanoparticles and the ZIF-8 shell. The sensor also shows excellent stability, safety, and generalizability. The campus water sample is then tested on-site by the M-AZA SERS sensor, indicating its potential for practical applications.

Efficient Extraction and Analysis of Nanoplastics by Ionic Liquid-Assisted Cloud-Point Extraction Coupled with Electromagnetic Heating Pyrolysis Mass Spectrometry

Nanoplastics have attracted much attention due to their potential hazards. However, analysis of nanoplastics remains challenging. In this study, ionic liquid-assisted cloud-point extraction (IL-assisted CPE) was developed to enrich nanoplastics in the aqueous environment and further coupled with electromagnetic heating pyrolysis mass spectrometry. The use of trace ILs improves the extraction efficiency of CPE for nanoplastics. The effects of ILs (types, contents), nanoplastic properties (type, size), and environmental factors (aging time, humic acid content) were systematically investigated to evaluate the applicability. The limits of detection of poly(methyl methacrylate) (PMMA) and polystyrene (PS) were determined to be 1.78 and 2.67 μg/L, respectively. Real environmental samples including lake water, rainwater, and influent and effluent from wastewater treatment plant were analyzed with good accuracy (79.58-116.87%) and satisfactory precision (RSD ≤ 11.99%). A possible mechanism for ILs being absorbed into the ordered surfactant micellar and generating larger micelles to synergically enclose hydrophobic nanoplastics was proposed. This work provides a simple and efficient approach to the extraction and analysis of nanoplastics in aqueous environments.

Exposure to polystyrene nanoplastics induced physiological and behavioral effects on the brittle star Ophiactis virens

Nanoplastic contamination has become an issue of environmental concern but the information on the potential adverse effects of nanoplastics on marine ecosystems is still limited. Therefore, the aim of this work was to investigate the effects of the exposure to polystyrene nanoplastics (PS-NPs; 0.05, 0.5 and 5 μg/mL) on the brittles star Ophiactis virens. Diverse endpoints at different levels of biological organization were considered, including behavior, arm regeneration capacity and oxidative stress. PS-NPs were observed on the brittle star body surface but not in inner tissues. Accumulation of PS-NPs was observed in the pre-buccal cavity of animals exposed to 5 μg/mL PS-NPs which also displayed delayed righting activity and an oxidative stress condition. Nevertheless, no effect was observed on arm regeneration efficiency at any tested PS-NPs concentration. Overall, our results highlighted that prolonged exposure to high amounts of PS-NPs could interfere at least partially with the physiology of O. virens.

Characterization of polyethylene terephthalate (PET) and polyamide (PA) true-to-life nanoplastics and their biological interactions

Plastic and microplastics, including polyethylene (PE), polypropylene (PP), and polystyrene (PS), are major contributors to environmental pollution. However, there is a growing recognition of the need to investigate a wider range of plastic polymers to fully understand the extent and impacts of plastic pollution. This study focuses on the comprehensive characterization of true-to-life nanoplastics (T2LNPs) derived from polyethylene terephthalate (PET) and polyamide (PA) to enhance our understanding of environmental nanoplastics pollution. T2LNPs were produced through cryogenic mechanical fragmentation of everyday items made from these polymers. A solid methodological framework incorporating various characterization techniques was established. Attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and thermogravimetric analysis (TGA) were employed to study the chemical composition and confirm the absence of chemical modifications possibly occurring during fragmentation. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to analyze the morphology of the T2LNPs. Additionally, AFM image analysis compared to dynamic light scattering (DLS) measurements provided insights into the size distribution and the stability of the T2LNP suspensions. The results revealed the heterogeneity of T2LNPs derived from PET and PA, emphasizing the importance of studying different plastic compositions to comprehensively understand nanoplastics pollution. Lastly, the distinctive characteristics and morphology of T2LNPs were translated into the realm of biological interactions, offering initial insights into the influence of these disparities on the formation of the protein corona on the surface of T2LNPs. By proposing T2LNPs as test materials and establishing a comprehensive characterization approach, this study aims to bridge the knowledge gap regarding the behavior and toxicity of nanoplastics. Furthermore, it highlights the need for a reliable and transferable analytical package for nanoplastic characterization to facilitate future studies on the environmental impact of nanoplastics.

Does functionalised nanoplastics modulate the cellular and physiological responses of aquatic fungi to metals?

Co-contamination of freshwaters by nanoplastics (NPs; ≤ 1 μm) and metals is an emerging concern. Aquatic hyphomycetes play a crucial role as primary decomposers in these ecosystems. However, concurrent impacts of NPs and metals on the cellular and physiological activities of these fungi remain poorly understood. Here, the effects of environmentally realistic concentrations of two types of polystyrene (PS) NPs (bare and -COOH; up to 25 μg L-1) and copper (Cu; up to 50 μg L-1) individually and all possible combinations (NPs types and Cu) on Articulospora tetracladia, a prevalent aquatic hyphomycete, were investigated. Endpoints measured were intracellular reactive oxygen species accumulation, plasma membrane disruption and fungal growth. The results suggest that functionalised (-COOH) NPs enhance Cu adsorption, as revealed by spectroscopic analyses. Notably, NPs, Cu and their co-exposure to A. tetracladia can lead to ROS accumulation and plasma membrane disruption. In most cases, exposure to treatments containing -COOH NPs with Cu showed greater cellular response and suppressed fungal growth. By contrast, exposure to Cu individually showed stimulatory effects on fungal growth. Overall, this study provides novel insight that functionalisation of NPs facilitates metal adsorption, thus modulating the impacts of metals on aquatic fungi.

Teratogenic effects of environmental concentration of plastic particles on freshwater organisms

Given the widespread presence of plastics, especially in micro- and nanoscale sizes, in freshwater systems, it is crucial to identify a suitable model organism for assessing the potential toxic and teratogenic effects of exposure to plastic particles. Until now, the early life stage of freshwater organisms and the regeneration capacity in relation to plastic particles exposure is a still poorly investigated topic. In this study, we examine the teratogenic effect on diatom Cocconeis placentula and cnidarian Hydra vulgaris under controlled exposure conditions of poly(styrene-co-methyl methacrylate) (P(S-co-MMA)) particles. Significant effects were observed at the lowest concentrations (0.1 μg/L). A significant increase in the teratological frequency in C. placentula and a significant decrease in the regeneration rate in H. vulgaris were found at the lowest concentration. The delay in hydra regeneration impaired the feeding capacity and tentacles reactivity at 96 h of exposure. No effects on diatom growth were observed upon exposure to P(S-co-MMA) particles (0.1, 1, 100, 10,000 μg/L) for 28 days and these findings agree with other studies investigating algal growth. The application of the Teratogenic Risk Index, modified for diatoms, highlighted a moderate risk for the lowest concentration evaluating C. placentula and low risk at the lowest and the highest concentrations considering H. vulgaris. This study suggests the importance of testing organisms belonging to different trophic levels as diverse teratogenic effects can be found and the need to evaluate environmentally relevant concentrations of plastic particles.

A critical review on nanoplastics and its future perspectives in the marine environment

Nanoplastics (plastic particles smaller than 1 μm) are the least-known type of marine litter. Nanoplastics (NPs) have attracted much interest in recent years because of their prevalence in the environment and the potential harm they can cause to living organisms. This article focuses on understanding NPs and their fate in the marine environment. Sources of NPs have been identified, including accidental release from products or through nano-fragmentation of larger plastic debris. As NPs have a high surface area, they may retain harmful compounds. The presence of harmful additives in NPs poses unique practical challenges for studies on their toxicity. In this review, several methods specifically adapted for the physical and chemical characterization of NPs have been discussed. Furthermore, the review provides an overview of the translocation and absorption of NPs into organisms, along with an evaluation of the release of potential toxins from NPs. Further, we have provided an overview about the existing methods suggested for the possible degradation of these NPs. We conclude that the hazards of NPs are plausible but unknown, necessitating a thorough examination of NPs' sources, fate, and effects to better mitigate and spread awareness about this emerging contaminant.

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

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

Nano- and Microplastics Migration from Plastic Food Packaging into Dairy Products: Impact on Nutrient Digestion, Absorption, and Metabolism

The ongoing use of plastic polymers to manufacture food packaging has raised concerns about the presence of nano- and microplastics (NMPs) in a variety of foods. This review provides the most recent data on NMPs' migration from plastic packaging into dairy products. Also discussed are the possible effects of NMPs on nutrient digestion, absorption, and metabolism. Different kinds of dairy products, including skimmed milk, whole liquid milk, powder milk, and infant formula milk, have been found to contain NMPs of various sizes, shapes, and concentrations. NMPs may interact with proteins, carbohydrates, and fats and have a detrimental impact on how well these nutrients are digested and absorbed by the body. The presence of NMPs in the gastrointestinal tract may impact how lipids, proteins, glucose, iron, and energy are metabolized, increasing the risk of developing various health conditions. In addition to NMPs, plastic oligomers released from food packaging material have been found to migrate to various foods and food simulants, though information regarding their effect on human health is limited. Viewpoints on potential directions for future studies on NMPs and their impact on nutrient digestion, absorption, and health are also presented in this review.

Positive responses and mechanisms of nitrifying sludge to carbon quantum dots: reactor performance, microbial behavior, and antioxidant defense

Extensive application of carbon quantum dots (CQDs) enlarges its concentration in sewage treatment system. The response of nitrifying sludge to CQDs after long-term exposure was investigated. Results showed that CQD concentrations of 0-100 mg/L presented positive effect to enzymes involved in nitrification, accelerating NH4+-N degradation and NO2--N transformation. The oxidation rate of NO2--N was significantly improved from 3.14 to 7.91 mg/(L h) under the stress of 100 mg/L CQDs. Besides, CQDs stimulated the production of sludge biomass and kept the stability of sludge settleability. Additionally, CQDs were mainly captured by loosely bound extracellular polymeric substances, reducing aromatic-like protein. Microbes alleviated CQD stress by secreting tryptophan-like protein and polysaccharides. After few CQDs entered cells, intracellular antioxidant defense was activated. Total antioxidant capacity level was heightened at least 31%. The activities of superoxide dismutase and catalase were enhanced at relatively low and high CQD concentration levels. Hence, microbial metabolic pathways, microbial community, and nitrifying bacteria were not significantly affected by CQDs. The findings of this work provide new insight for understanding the environmental implication of CQDs in the biological treatment system.

Spatial distribution of polystyrene nanoplastics and small microplastics in the Bohai Sea, China

Micro- and nano-plastic (MNP) pollution has attracted public concerns. Currently, most environmental researches focus on large microplastics (MPs), while small MNPs that have great impacts on marine ecosystems are rarely reported. Understanding the pollution levels and distribution patterns of small MNPs could help assess their potential impacts on the ecosystem. Polystyrene (PS) MNPs were often used as models to assess their toxicity, hence, we collected 21 sites in a Chinese sea area (the Bohai Sea) to analyze their pollution level and horizontal distribution in surface water samples, and vertical distributions in five sites with the water depth >25 m. Samples were filtered by glass membranes (1 μm) to trap MPs, which were frozen, ground, dried, and detected by pyrolysis-gas chromatography-mass spectrometry (pyGC-MS); while the nanoplastics (NPs) in the filtrate were captured with alkylated ferroferric oxide (Fe₃O₄) to form aggregates, which were separated by glass membrane (300 nm) filtration for pyGC-MS determination. Small PS MPs (1-100 μm) and NPs (<1 μm) were detected in 18 samples with the mass concentrations ranging from <0.015 to 0.41 μg/L, indicating that PS MNPs are widely present in Bohai Sea. Our study contributes to understanding the pollution levels and distribution patterns of MNPs (<100 μm) in the marine system and provides valuable data for their further risk assessment.

Formation, behavior, properties and impact of micro- and nanoplastics on agricultural soil ecosystems (A Review)

Micro and nanoplastics (MPs and NPs, respectively) in agricultural soil ecosystems represent a pervasive global environmental concern, posing risks to soil biota, hence soil health and food security. This review provides a comprehensive and current summary of the literature on sources and properties of MNPs in agricultural ecosystems, methodology for the isolation and characterization of MNPs recovered from soil, MNP surrogate materials that mimic the size and properties of soil-borne MNPs, and transport of MNPs through the soil matrix. Furthermore, this review elucidates the impacts and risks of agricultural MNPs on crops and soil microorganisms and fauna. A significant source of MPs in soil is plasticulture, involving the use of mulch films and other plastic-based implements to provide several agronomic benefits for specialty crop production, while other sources of MPs include irrigation water and fertilizer. Long-term studies are needed to address current knowledge gaps of formation, soil surface and subsurface transport, and environmental impacts of MNPs, including for MNPs derived from biodegradable mulch films, which, although ultimately undergoing complete mineralization, will reside in soil for several months. Because of the complexity and variability of agricultural soil ecosystems and the difficulty in recovering MNPs from soil, a deeper understanding is needed for the fundamental relationships between MPs, NPs, soil biota and microbiota, including ecotoxicological effects of MNPs on earthworms, soil-dwelling invertebrates, and beneficial soil microorganisms, and soil geochemical attributes. In addition, the geometry, size distribution, fundamental and chemical properties, and concentration of MNPs contained in soils are required to develop surrogate MNP reference materials that can be used across laboratories for conducting fundamental laboratory studies.

Nanoparticulate pollutants in the environment: Analytical methods, formation, and transformation

The wide application of nanomaterials and plastic products generates a substantial number of nanoparticulate pollutants in the environment. Nanoparticulate pollutants are quite different from their bulk counterparts because of their unique physicochemical properties, which may pose a threat to environmental organisms and human beings. To accurately predict the environmental risks of nanoparticulate pollutants, great efforts have been devoted to developing reliable methods to define their occurrence and track their fate and transformation in the environment. Herein, we summarized representative studies on the preconcentration, separation, formation, and transformation of nanoparticulate pollutants in environmental samples. Finally, some perspectives on future research directions are proposed.

Physicochemical characterization and quantification of nanoplastics: applicability, limitations and complementarity of batch and fractionation methods

A comprehensive physicochemical characterization of heterogeneous nanoplastic (NPL) samples remains an analytical challenge requiring a combination of orthogonal measurement techniques to improve the accuracy and robustness of the results. Here, batch methods, including dynamic light scattering (DLS), nanoparticle tracking analysis (NTA), tunable resistive pulse sensing (TRPS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM), as well as separation/fractionation methods such as centrifugal liquid sedimentation (CLS) and field-flow fractionation (FFF)-multi-angle light scattering (MALS) combined with pyrolysis gas chromatography mass spectrometry (pyGC-MS) or Raman microspectroscopy (RM) were evaluated for NPL size, shape, and chemical composition measurements and for quantification. A set of representative/test particles of different chemical natures, including (i) polydisperse polyethylene (PE), (ii) (doped) polystyrene (PS) NPLs, (iii) titanium dioxide, and (iv) iron oxide nanoparticles (spherical and elongated), was used to assess the applicability and limitations of the selected methodologies. Particle sizes and number-based concentrations obtained by orthogonal batch methods (DLS, NTA, TRPS) were comparable for monodisperse spherical samples, while higher deviations were observed for polydisperse, agglomerated samples and for non-spherical particles, especially for light scattering methods. CLS and TRPS offer further insight with increased size resolution, while detailed morphological information can be derived by electron microscopy (EM)-based approaches. Combined techniques such as FFF coupled to MALS and RM can provide complementary information on physical and chemical properties by online measurements, while pyGC-MS analysis of FFF fractions can be used for the identification of polymer particles (vs. inorganic particles) and for their offline (semi)quantification. However, NPL analysis in complex samples will continue to present a serious challenge for the evaluated techniques without significant improvements in sample preparation.

Complementary Analysis for Undetectable Microplastics from Contact Lenses to Aquatic Environments via Fourier Transform Infrared Spectroscopy

Although microplastics (MPs) are intrinsically toxic and function as vectors for organic micropollutants, their discharge from wastewater treatment plant effluents and human activity remains unknown owing to the limitations of detection and treatment technologies. It is imperative to quantify MPs from human activities involving the consumption of various plastic products. This study warns that contact lenses can generate MPs and nanoplastics (NPs) after being discharged into aquatic environments. Identification via micro-Fourier transform infrared spectroscopy revealed that the fragmented particles (from a few tens to a few hundred micrometres) could not be detected as poly(2-hydroxyl methacrylate), the component of contact lenses, owing to changes in its chemical properties. After the degradation process, the median size of the contact lens particles decreased from 313 to 85 µm. Approximately 300,600 g of contact lens waste is discharged into sewage systems daily in the United States of America (USA), where 45 million people wear contact lenses and throw away one-fifth of them every day. Contact lens waste (1 g) has the potential to release 5653.3-17,773.3 particles of MPs. This implies that the currently reported MP amounts in the environmental matrix exclude significant amounts of MPs and NPs from discharged contact lenses. The identification method should be examined, and a registration of the disposal process should be established.

Macro- and microplastics as complex threats to coral reef ecosystems

The impacts of macroplastics (macro-), microplastics (MPs, <5mm), and nanoplastics (NPs, <100 nm) on corals and their complex reef ecosystems are receiving increased attention and visibility. MPs represent a major, contemporary, sustainability challenge with known and unknown effects on the ocean, and coral reef ecosystems worldwide. However, the fate and transport processes of macro-, MPs, and NPs and their direct and indirect impacts on coral reef ecosystems remains poorly understood. In this study, we verify and briefly summarize MPs distribution and pollution patterns in coral reefs from various geographical regions and discuss potential risks. The main interaction mechanisms show that MPs may substantially affect coral feeding performance, proper skeletal formation, and overall nutrition and, thus, there is an urgent need to address this rapidly growing environmental problem. From a management perspective, macro-, MPs, and NPs should, ideally, all be included in environmental monitoring frameworks, as possible, to aid in identifying those geographical areas that are most heavily impacted and to support future prioritization of conservation efforts. The potential solutions to the macro-, MP, and NP pollution problem include raising public awareness of plastic pollution, developing robust, environmental, conservation efforts, promoting a circular economy, and propelling industry-supported technological innovations to reduce plastic use and consumption. Global actions to curb plastic inputs, and releases of macro-, MP, and NP particles, and their associated chemicals, to the environment are desperately needed to secure the overall health of coral reef ecosystems and their inhabitants. Global scale horizon scans, gap analyses, and other future actions are necessary to gain and increase momentum to properly address this massive environmental problem and are in good accordance with several relevant UN sustainable development goals to sustain planetary health.

A Novel Strategy to Directly Quantify Polyethylene Microplastics in PM2.5 Based on Pyrolysis-Gas Chromatography-Tandem Mass Spectrometry

The broad application of plastic products has resulted in a considerable release of microplastics (MPs) into the ecosystem. While MPs in other environmental matrices (e.g., soil and water) have been studied for a long time, the atmospheric fine particulate matter (PM_2.5)-bound MPs are rarely investigated due to the lack of an appropriate analytical approach. The prevalently used visual and spectroscopic means (e.g., optical microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy) suffer from obvious drawbacks that cannot precisely detect MPs of tiny sizes and provide quantitative information. In the present study, a novel strategy that does not require sample pretreatment was developed to first effectuate accurate quantification of polyethylene MP (PE-MP) in PM_2.5 based on pyrolysis-gas chromatography-tandem mass spectrometry (Pyr-GC-MS/MS). It featured acceptable recoveries (97%-110%), high sensitivity (LOD = 1 pg), and qualified precisions (RSD of 3%-13%). Employing this approach, for the first time, exact atmospheric concentrations of PE-MPs in PM_2.5 from megacities in North (Zhengzhou and Taiyuan) and South (Guangzhou) China were obtained, and relatively serious pollution was found in Taiyuan. The 100% sample detection rates also suggested the widespread occurrence and possible human exposure risks of PM_2.5-bound PE-MPs. In brief, the new strategy could conduct direct, sensitive, and accurate quantification of PE-MP in PM_2.5, favoring further studies of environmental fates, distributions, and toxicities of atmospheric MPs.

Metabolomics as a Tool to Understand Nano-Plant Interactions: The Case Study of Metal-Based Nanoparticles

Metabolomics is a powerful tool in diverse research areas, enabling an understanding of the response of organisms, such as plants, to external factors, their resistance and tolerance mechanisms against stressors, the biochemical changes and signals during plant development, and the role of specialized metabolites. Despite its advantages, metabolomics is still underused in areas such as nano-plant interactions. Nanoparticles (NPs) are all around us and have a great potential to improve and revolutionize the agri-food sector and modernize agriculture. They can drive precision and sustainability in agriculture as they can act as fertilizers, improve plant performance, protect or defend, mitigate environmental stresses, and/or remediate soil contaminants. Given their high applicability, an in-depth understanding of NPs' impact on plants and their mechanistic action is crucial. Being aware that, in nano-plant interaction work, metabolomics is much less addressed than physiology, and that it is lacking a comprehensive review focusing on metabolomics, this review gathers the information available concerning the metabolomic tools used in studies focused on NP-plant interactions, highlighting the impact of metal-based NPs on plant metabolome, metabolite reconfiguration, and the reprogramming of metabolic pathways.

Nanoplastics in the soil environment: Analytical methods, occurrence, fate and ecological implications

Soils play a very important role in ecosystems sustainability, either natural or agricultural ones, serving as an essential support for living organisms of different kinds. However, in the current context of extremely high plastic pollution, soils are highly threatened. Plastics can change the chemical and physical properties of the soils and may also affect the biota. Of particular importance is the fact that plastics can be fragmented into microplastics and, to a final extent into nanoplastics. Due to their extremely low size and high surface area, nanoplastics may even have a higher impact in soil ecosystems. Their transport through the edaphic environment is regulated by the physicochemical properties of the soil and plastic particles themselves, anthropic activities and biota interactions. Their degradation in soils is associated with a series of mechanical, photo-, thermo-, and bio-mediated transformations eventually conducive to their mineralisation. Their tiny size is precisely the main setback when it comes to sampling soils and subsequent processes for their identification and quantification, albeit pyrolysis coupled with gas chromatography-mass spectrometry and other spectroscopic techniques have proven to be useful for their analysis. Another issue as a consequence of their minuscule size lies in their uptake by plants roots and their ingestion by soil dwelling fauna, producing morphological deformations, damage to organs and physiological malfunctions, as well as the risks associated to their entrance in the food chain, although current conclusions are not always consistent and show the same pattern of effects. Thus, given the omnipresence and seriousness of the plastic menace, this review article pretends to provide a general overview of the most recent data available regarding nanoplastics determination, occurrence, fate and effects in soils, with special emphasis on their ecological implications.

Polystyrene nanoplastics aggravates lipopolysaccharide-induced apoptosis in mouse kidney cells by regulating IRE1/XBP1 endoplasmic reticulum stress pathway via oxidative stress

Nanoplastics (NPs) pollution poses a huge threat to the ecosystem and has become one of the environmental pollutants that have attracted much attention. There is increasing evidence that both oxidative stress and endoplasmic reticulum stress (ERS) are associated with polystyrene nanoplastics (PS-NPs) exposure. Lipopolysaccharide (LPS) has been shown to induce apoptotic damage in various tissues, but whether PS-NPs can aggravate LPS-induced apoptosis in mouse kidneys through oxidative stress-regulated inositol-requiring enzyme 1 (IRE1)/X-box binding protein 1 (XBP1) ERS pathway remains unclear. In this study, based on the establishment of in vitro and in vivo PS-NPs and LPS exposure models alone and in combination in mice and HEK293 cells, the effects and mechanisms of PS-NPs on LPS-induced renal cell apoptosis were investigated. The results showed that PS-NPs could aggravate LPS-induced apoptosis. PS-NPs/LPS can induce ERS through oxidative stress, activate the IRE1/XBP1 pathway, and promote the expression of apoptosis markers (Caspase-3 and Caspase-12). Kidney oxidative stress, ERS, and apoptosis in PS-NPs + LPS combined exposure group were more severe than those in the single exposure group. Interestingly, 4-phenylbutyric acid-treated HEK293 cells inhibited the expression of the IRE1/XBP1 ERS pathway and apoptotic factors in the PS-NPs + LPS combined exposure group. N-acetyl-L-cysteine effectively blocked the activation of the IRE1/XBP1 ERS pathway, suggesting that PS-NPs-induced oxidative stress is an early event that triggers ERS. Collectively, these results confirmed that PS-NPs aggravated LPS-induced apoptosis through the oxidative stress-induced IRE1/XBP1 ERS pathway. Our study provides new insights into the health threats of PS-NPs exposed to mammals and humans.

Nanoplastics: Detection and impacts in aquatic environments - A review

The rise in the global production of plastics has led to severe concerns about the impacts of plastics in aquatic environments. Although plastic materials degrade over extreme long periods, they can be broken down through physical, chemical, and/or biological processes to form microplastics (MPs), defined here as particles between 1 μm and 5 mm in size, and later to form nanoplastics (NPls), defined as particles <1 μm in size. We know little about the abundance and effects of NPls, even though a lot of research has been conducted on the ecotoxicological impacts of MPs on both aquatic biota. Nevertheless, there is evidence that NPls can both bypass the cell membranes of microorganisms and bioaccumulate in the tissues and organs of higher organisms. This review analyzes 150 publications collected by searching through the databases Web of Science, SCOPUS, and Google Scholar using keywords such as nanoplastics*, aquatic*, detection*, toxic*, biofilm*, formation*, and extracellular polymeric substance* as singular or plural combinations. We highlight and critically synthesize current studies on the formation and degradation of NPls, NPls' interactions with aquatic biota and biofilm communities, and methods of detection. One reason for the missing data and studies in this area of research is the lack of a protocol for the detection of, and suitable methods for the characterization of, NPls in the field. Our primary aim is to identify gaps in knowledge throughout the review and define future directions of research to address the impacts of NPls in aquatic environments. The development of consistent and standardized sets of procedures would address the gaps in knowledge regarding the formation and degradation of NPls as well as sampling and characterizing natural NPls needed to observe the full extent of NPls on aquatic biota and biofilm communities.

Coronas of micro/nano plastics: a key determinant in their risk assessments

As an emerging pollutant in the life cycle of plastic products, micro/nanoplastics (M/NPs) are increasingly being released into the natural environment. Substantial concerns have been raised regarding the environmental and health impacts of M/NPs. Although diverse M/NPs have been detected in natural environment, most of them display two similar features, i.e.,high surface area and strong binding affinity, which enable extensive interactions between M/NPs and surrounding substances. This results in the formation of coronas, including eco-coronas and bio-coronas, on the plastic surface in different media. In real exposure scenarios, corona formation on M/NPs is inevitable and often displays variable and complex structures. The surface coronas have been found to impact the transportation, uptake, distribution, biotransformation and toxicity of particulates. Different from conventional toxins, packages on M/NPs rather than bare particles are more dangerous. We, therefore, recommend seriously consideration of the role of surface coronas in safety assessments. This review summarizes recent progress on the eco-coronas and bio-coronas of M/NPs, and further discusses the analytical methods to interpret corona structures, highlights the impacts of the corona on toxicity and provides future perspectives.

Identification of Trace Polystyrene Nanoplastics Down to 50 nm by the Hyphenated Method of Filtration and Surface-Enhanced Raman Spectroscopy Based on Silver Nanowire Membranes

Nanoplastics are emerging pollutants that pose potential threats to the environment and organisms. However, in-depth research on nanoplastics has been hindered by the absence of feasible and reliable analytical methods, particularly for trace nanoplastics. Herein, we propose a hyphenated method involving membrane filtration and surface-enhanced Raman spectroscopy (SERS) to analyze trace nanoplastics in water. In this method, a bifunctional Ag nanowire membrane was employed to enrich nanoplastics and enhance their Raman spectra in situ, which omitted sample transfer and avoided losing smaller nanoplastics. Good retention rates (86.7% for 50 nm and approximately 95.0% for 100-1000 nm) and high sensitivity (down to 10^-7 g/L for 50-1000 nm and up to 10⁵ SERS enhancement factor) of standard polystyrene (PS) nanoplastics were achieved using the proposed method. PS nanoplastics with concentrations from 10^-1 to 10^-7 g/L and sizes ranging from 50 to 1000 nm were successfully detected by Raman mapping. Moreover, PS micro- and nanoplastics in environmental water samples collected from the seafood market were also detected at the μg/L level. Consequently, the proposed method provides more possibilities for analyzing low-concentration nanoplastics in aquatic environments with high enrichment efficiency, minimal sample loss, and high sensitivity.

Current Methods and Prospects for Analysis and Characterization of Nanomaterials in the Environment

Analysis and characterization of naturally occurring and engineered nanomaterials in the environment are critical for understanding their environmental behaviors and defining real exposure scenarios for environmental risk assessment. However, this is challenging primarily due to the low concentration, structural heterogeneity, and dynamic transformation of nanomaterials in complex environmental matrices. In this critical review, we first summarize sample pretreatment methods developed for separation and preconcentration of nanomaterials from environmental samples, including natural waters, wastewater, soils, sediments, and biological media. Then, we review the state-of-the-art microscopic, spectroscopic, mass spectrometric, electrochemical, and size-fractionation methods for determination of mass and number abundance, as well as the morphological, compositional, and structural properties of nanomaterials, with discussion on their advantages and limitations. Despite recent advances in detecting and characterizing nanomaterials in the environment, challenges remain to improve the analytical sensitivity and resolution and to expand the method applications. It is important to develop methods for simultaneous determination of multifaceted nanomaterial properties for in situ analysis and characterization of nanomaterials under dynamic environmental conditions and for detection of nanoscale contaminants of emerging concern (e.g., nanoplastics and biological nanoparticles), which will greatly facilitate the standardization of nanomaterial analysis and characterization methods for environmental samples.

Evaluating the Occurrence of Polystyrene Nanoparticles in Environmental Waters by Agglomeration with Alkylated Ferroferric Oxide Followed by Micropore Membrane Filtration Collection and Py-GC/MS Analysis

Although nanoplastics (NPs) are recognized as emerging anthropogenic particulate pollutants, the occurrence of NPs in the environment is rarely reported, partly due to the lack of sensitive methods for the concentration and detection of NPs. Herein, we present an efficient method for enriching NPs of different compositions and various sizes. Alkylated ferroferric oxide (Fe₃O₄) particles were prepared as adsorbents for highly efficient capture of NPs in environmental waters, and the formed large Fe₃O₄-NP agglomerates were separated by membrane filtration. Detection limits of 0.02-0.03 μg/L were obtained for polystyrene (PS) and poly(methyl methacrylate) (PMMA) NPs by detection with pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). When analyzing real water samples from different sources, it is remarkable that PS NPs were detected in 11 out of 15 samples with concentrations ranging from <0.07 to 0.73 μg/L, while PMMA were not detected. The wide detection of PS NPs in our study confirms the previous speculation that NPs may be ubiquitous in the environmental waters. The accurate quantification of PS NPs in environmental waters make it possible to monitor the pollution status of NPs in aquatic systems and evaluate their potential risks.

Nanoplastics: Status and Knowledge Gaps in the Finalization of Environmental Risk Assessments

Nanoplastics (NPs) are particles ranging in size between 1 and 1000 nm, and they are a form of environmental contaminant of great ecotoxicological concern. Although NPs are widespread across ecosystems, they have only recently garnered growing attention from both the scientific community and regulatory bodies. The present study reviews scientific literature related to the exposure and effects of NPs and identifies research gaps that impede the finalization of related environmental risk assessments (ERAs). Approximately 80 articles published between 2012 and 2021 were considered. Very few studies (eight articles) focused on the presence of NPs in biotic matrices, whereas the majority of the studies (62 articles) assessed the lethal and sublethal effects of NPs on aquatic and terrestrial organisms. Whilst many studies focused on nude NPs, only a few considered their association with different aggregates. Amongst NPs, the effects of polystyrene are the most extensively reported to date. Moreover, the effects of NPs on aquatic organisms are better characterized than those on terrestrial organisms. NP concentrations detected in water were close to or even higher than the sublethal levels for organisms. An ERA framework specifically tailored to NPs is proposed.

Micro (nano) plastics in wastewater: A critical review on toxicity risk assessment, behaviour, environmental impact and challenges

With millions of tonnes of plastic pollution generated every year, small-sized plastic particles, including micro- and nanoplastics, end up in freshwater systems. Due to the very small size and very large specific surface area of nanoplastics, they are known to be persistent and toxic in our environment. These particles are also known to react with other water-borne contaminants and cause acute toxicity in organisms. Nanoplastics are prone to biomagnification and can be transported to humans through various pathways. This study aims to contribute towards understanding the behaviour of nanoplastics in our environment, specifically through identification of various sources, detection techniques, toxicity estimation, health risk in humans, environmental fate, recovery and reuse, and future challenges and limitations. Detailed review on the toxic effects of nanoplastics on various organisms and their degradation rates in soil and water matrices are provided. The suitability of small- and large-scale separation techniques for the removal of nanoplastics in wastewater treatment plants is also discussed. Current challenges and future perspectives in understanding the fate and transport of nanoplastics in the environment are also discussed. Research gaps, including the development of quantification techniques, estimation of degradation mechanisms, transport in marine ecosystems, and development of sensors to examine nanoplastics in the environment, are explored. Finally, we can limit the release of nanoplastics to the environment through reduction, reuse and recycling (3 Rs) of bulk plastic products.

Key knowledge gaps for One Health approach to mitigate nanoplastic risks

There are increasing concerns over the threat of nanoplastics to environmental and human health. However, multidisciplinary barriers persist between the communities assessing the risks to environmental and human health. As a result, the hazards and risks of nanoplastics remain uncertain. Here, we identify key knowledge gaps by evaluating the exposure of nanoplastics in the environment, assessing their bio-nano interactions, and examining their potential risks to humans and the environment. We suggest considering nanoplastics a complex and dynamic mixture of polymers, additives, and contaminants, with interconnected risks to environmental and human health. We call for comprehensive integration of One Health approach to produce robust multidisciplinary evidence to nanoplastics threats at the planetary level. Although there are many challenges, this holistic approach incorporates the relevance of environmental exposure and multi-sectoral responses, which provide the opportunity to identify the risk mitigation strategies of nanoplastics to build resilient health systems.

Recent Advances in Spectroscopic Techniques for the Analysis of Microplastics in Food

Microplastic pollution has become a worldwide concern in aquatic and terrestrial environments. Microplastics could also enter the food chain, causing potential harm to human health. To facilitate the risk assessment of microplastics to humans, it is critically important to have a reliable analytical technique to detect, quantify, and identify microplastics of various materials, sizes, and shapes from environmental, agricultural, and food matrices. Spectroscopic techniques, mainly vibrational spectroscopy (Raman and infrared), are commonly used techniques for microplastic analysis. This review focuses on recent advances of these spectroscopic techniques for the analysis of microplastics in food. The fundamental, recent technical advances of the spectroscopic techniques and their advantages and limitations were summarized. The food sample pretreatment methods and recent applications for detecting and quantifying microplastics in different types of food were reviewed. In addition, the current technical challenges and future research directions were discussed. It is anticipated that the advances in instrument development and methodology innovation will enable spectroscopic techniques to solve critical analytical challenges in microplastic analysis in food, which will facilitate the reliable risk assessment.

Assessing the role of polyethylene microplastics as a vector for organic pollutants in soil: Ecotoxicological and molecular approaches

Microplastics (MPs), pharmaceuticals and pesticides are emerging pollutants with proposed negative impacts on the environment. Rising interest in investigations of MPs is likely related to their potential to accumulate in agricultural systems as the base of the food chain. We applied an integrated approach using classic bioassays and molecular methods to evaluate the impact associated with a mixture of three types of polyethylene (PE) microbeads, namely, white (W), blue (B), and fluorescent blue (FB), and their interactions with pollutants (OCs), including ibuprofen (IB), sertraline (STR), amoxicillin (AMX) and simazine (SZ), on different soil organisms. PE-MPs exhibited different abilities for the adsorption of each OC; W selectively adsorbed higher amounts of SZ, whereas B and FB preferably retained AMX. Standard soil was artificially contaminated with OCs and MPs (alone or combined with OCs) and incubated for 30 days. The presence of MPs or MPs and OCs (MIX) in soil did not produce any effect on Caenorhabditis elegans endpoint growth, reproduction, or survival. Inhibition of leaf growth in Zea mays was detected, but this negative effect declined over time, while the inhibition of root growth increased, especially when OCs (32%) or MIX (47%) were added. Moreover, the expression of the antioxidant genes CAT 1, SOD-1A and GST 1 on plants was affected by the treatments studied. The addition of MPs or MIX significantly affected the soil bacterial phylogenetic profile, which selectively enriched members of the bacterial community (particularly Proteobacteria). The predicted functional profiles of MP/MIX samples indicated a potential impact on the carbon and nitrogen cycle within the soil environment. Our results indicate that MPs and their capability to act as pollutant carriers affect soil biota; further studies should be carried out on the bioavailability of OCs adsorbed by microplastics and how long it takes to leach these OCs into different organisms and/or ecosystems.

Interactions between microplastics/nanoplastics and vascular plants

Microplastics and nanoplastics are distributed in the environments universally. The interrelationship between vascular plants and micro/nanoplastics began to attract attention in recent years. Based on the relevant literatures collected from various databases, this review focuses on two topics: 1) the effect of vascular plants on the fate of micro/nanoplastics; 2) the effects of micro/nanoplastics on vascular plants. The review of the available studies reveals that vascular plants can act as sinks for microplastics and nanoplastics as their surfaces can adsorb these plastics; moreover, nanoplastics can be internalized by plants. Plastics on the surfaces and in the interiors of vascular plants can cause various phytotoxicity effects, including impacts on growth, photosynthesis, and oxidative stress. Furthermore, the results and mechanisms of phytotoxicity effects caused by microplastics or nanoplastics can be very different. However, knowledge gaps still exist in the relationships between micro/nanoplastics and vascular plants based on the analysis of available studies; thus, potential subjects for future studies were proposed, including the fates, analysis methods, influencing factors, mechanisms of phytotoxicity, and further influences of microplastics and nanoplastics in the vascular plant ecosystems. This study presents a review of micro/nanoplastics-vascular plant research and reaches a basis for future research.

Toxicity of nanoplastics for zebrafish embryos, what we know and where to go next

Nanoplastics (NP) are an emerging threat to human health and there is a need to understand their toxicity. Zebrafish (ZF) is extensively used as a toxicology model due to its power to com-bine genetic, cellular, and whole organism endpoints. The present review integrates results regarding polystyrene NP effects on ZF embryo development. Study design was evaluated against NP effects. NP size, concentration, and exposure time did not affect organism responses (mortality, development, heart rate, locomotion) or cellular responses (gene expression, enzymes, metabolites). However, NP accumulation depended on size. Smaller NP can reach internal organs (brain, eyes, liver, pancreas, heart) but larger (>200 nm) accumulate mainly in gut, gills and skin. Locomotion and heart rate were commonly affected with hypoactivity and bradycardia being more prevalent. Effects on genetic/enzymatic/metabolic pathways were thoroughly analyzed. Immunity genes were generally upregulated whereas oxidative stress response genes varied. Central nervous system genes and visual related genes were generally downregulated. Results of genetic and enzymatic analyses coincided only for some genes/enzyme pairs. Reviewed studies provide a basis for understanding NP toxicity but results are hard to integrate. We propose key recommendations and future directions with regard to experimental design that may allow greater comparability across future studies.

A novel extraction protocol of nano-polystyrene from biological samples

Toxicological data demonstrate that nanoplastics (NPs) can cause direct adverse health effects. However, a method for quantifying NPs in biological samples is lacking to date. In this study, a diatomite associated coagulation-sedimentation extraction (CSE) protocol was developed to selectively enrich polystyrene nanoplastics (PS-NP) from microplastics (PS-MP) in the digest of animal tissues, which were then analyzed using pyrolysis gas chromatography-mass spectrometry. We demonstrate that 0.02 g of 7-μm diatomite can selectively adsorb 70-nm PS-NP in 5 mL oyster digest. The method works in the range of 0.006-5 μg PS-NP per 0.5 g wet weight tissue, which has been verified via samples of environmentally contaminated oysters and chow diet PS-NP-treated C57BL/6 mice (digestive tract, kidney, and liver tissues). The particle size-dependent colloidization or buoyancy theoretically supported the general CSE procedure. This work will pave the way for assessing human exposure to NPs and associated health risks.

Influence of Microplastics on the Mobility, Bioavailability, and Toxicity of Heavy Metals: A Review

Microplastics (MPs) can pose ecological risk to the environment and have the potential to negatively affect human health, raising serious public concerns. It is recognized that MPs could act as a vector for various environmental pollutants including heavy metals and potentially influencing their mobility, fate, and bioavailabilty in the environment. However, knowledge on the mechanisms underpinning the interaction processes between MPs and heavy metals is far from clear. This review discusses the effects of MPs on the adsorption/desorption, speciation and bioavailability, and toxicity of various heavy metals. The present review also systematically identifies the environmental factors (e.g., pH, ionic strength, and organic matters) that could affect their interaction processes. This work aims to establish a meaningful perspective for a comprehensive understanding of the indirect ecological risks of MPs as vectors for contaminants. The work also provides a reference for the development of better regulatory strategies in mitigating the negative effects caused by the co-existence of MPs and heavy metals.

Separation and enrichment of nanoplastics in environmental water samples via ultracentrifugation

Nanoplastics are an emerging contaminant in aquatic environments. However, analytical methods for the separation, concentration, and identification of nanoplastics, which are essential to assess nanoplastic presence in the environment, are lacking. Here, we developed a new and easy-to-use method to separate and enrich nanoplastics in field water samples with ultracentrifugation. River water was spiked with polystyrene fragments (< 1000 nm) at an environmentally relevant concentration (10⁸-10⁹ particles/L). The polystyrene fragments were successfully separated and enriched by a factor of nearly 50 times with a high recovery rate (87.1%) after undergoing our process. Particles were then characterized using UV-vis spectroscopy, scanning electron microscopy (SEM), and enhanced darkfield microscopy with a hyperspectral imaging (HSI) spectrometer. These techniques are non-destructive and allow the assessment of plastic concentration, morphology, and polymer type. Our method can potentially be applied to other water samples to supply clean, enriched nanoplastic samples that can facilitate their identification in environmental samples.

Field-flow fractionation for nanoparticle characterization

This review presents field-flow fractionation: The elements of theory enable the link between the retention and the characteristics of the nanometer-sized analytes to be highlighted. In particular, the nature of force and its way of being applied are discussed. Four types of forces which determine four types of techniques were considered: hydrodynamic, sedimentation, thermal, and electrical; this is to show the importance of the choice of technique in relation to the characterization objectives. Then the separation performance is presented and compared with other separation techniques: field-flow fractionation has the greatest intrinsic separation capability. The characterization strategies are presented and discussed; on the one hand with respect to the characteristics needed for the description of nanoparticles; on the other hand in connection with the choice of the nature of the force, and also of the detectors used, online or offline. The discussion is based on a selection of published study examples. Finally, current needs and challenges are addressed, and as response, trends and possible characterization solutions.

Heteroaggregation of different surface-modified polystyrene nanoparticles with model natural colloids

This study investigated heteroaggregation of three surface-functionalized polystyrene nanoparticles (PSNPs), i.e. negatively charged unfunctionalized nanoparticles (Bare-PS) and carboxylated nanoparticles (COOH-PS), and positively charged amino-functionalized nanoparticles (NH₂-PS), with two model natural colloids, positively charged hematite and negatively charged kaolin, respectively. Heteroaggregation was conducted at a constant natural colloid concentration and variable NP/colloid concentration ratios. Electrostatic interaction was the main mechanism driving the formation of heteroaggregates. In binary systems containing hematite and Bare-PS/COOH-PS, a charge neutralization - charge inverse mechanism was observed with the increase of PSNP concentration. At NP/hemetite concentration ratios much smaller or larger than the full charge neutralization point, the primary heteroaggregates were stable, while full charge neutralization induced the formation of large secondary heteroaggregates. Large aggregates were not observed in suspensions containing kaolin and NH₂-PS, as highly positively charged NH₂-PS reversed surface charges of kaolin at extremely low concentrations. Heteroaggregation between PSNPs and natural colloids with the same charge is unfavorable due to strong electrostatic repulsion. In the presence of electrolytes, homoaggregation and heteroaggregation both occurred, and homoaggregation of hematite played a key role when the concentration of PSNPs was low. The presence of Suwannee River natural organic matter (SRNOM) could modify surface charges of nanoparticles, and thus affect heteroaggregation behaviors of the binary suspension. When SRNOM and electrolytes were both present, whether SRNOM inducing or hindering the stability of the binary system was a combined effect of NP/colloid concentration ratios, SRNOM concentrations, electrolyte types and ionic strength. Mechanisms extensively reported in homoaggregation such as steric hindrance and cation bridging effects between SRNOM and Ca²⁺ also stand for heteroaggregation. These results highlight the critical role of surface modification on the environmental behaviors of NPs, and will underpin our understanding of the fate and transport of NPs in the aquatic environment.

Environmental factors-mediated behavior of microplastics and nanoplastics in water: A review

The release of plastics in nature is an increasing global concern due to their degradation from microplastics (MPs) and even to nanoplastics (NPs), which are being recognized as a potential global threat to humans and environment. This paper summarizes the current knowledge on the effect of different environmental factors on the aggregation of MPs and NPs in aquatic environment. Stability (or extent of aggregation) of MPs and NPs varies with pH, ionic strength, ion type (monovalent, divalent, and trivalent), kind of minerals, and natural organic matter (NOM) of the aquatic environment. Electrostatic interactions between particles at different pH and ionic strength caused by salts of different valents govern the aggregation. In the presence of minerals (or inorganic colloids), net surface charge of mineral and surface potential of MPs and NPs (i.e., positive or negative surface functionality) play important roles in the heteroaggregation of MPs and NPs. In the presence of NOM, additional complex interactions including hydrophobic interactions and bridging are also involved in the aggregation of particles. Understanding the interactions of MPs and NPs of different surface charge with diverse environmental factors at a wide range of environmental conditions is pivotal to assess the mobility and the fate of degraded plastic particles and their risk to human health and ecological systems.

Counting Nanoplastics in Environmental Waters by Single Particle Inductively Coupled Plasma Mass Spectroscopy after Cloud-Point Extraction and In Situ Labeling of Gold Nanoparticles

The globally raising concern for nanoplastics (NPs) pollution calls for analytical methods for investigating their occurrence, fates, and effects. Counting NPs with sizes down to 50 nm in real environmental waters remains a great challenge. Herein, we developed a full method from sample pretreatment to quantitative detection for NPs in environmental waters. Various NPs of common plastic types and sizes (50-1200 nm) were successfully labeled by in situ growth of gold nanoparticles and counted by single particle inductively coupled plasma mass spectrometry. Sucrose density gradient centrifugation enables the isolation of gold-labeled NPs from homogeneously nucleated Au nanoparticles, enhancing the particle number detection limit to 4.6 × 10⁸ NPs/L for 269 nm spherical polystyrene NPs. For real environmental water samples, the pretreatment of acid digestion with a mixture of 5 mM HNO₃ and 40 mM HF eliminates the coexisting inorganic nanoparticles, while the following dual cloud-point extraction efficiently isolates NPs from various matrices and thus improves the Au-labeling efficiency. The high spiked recoveries (72.9%-92.8%) of NPs in different waters demonstrated the applicability of this method in different scenarios.

Microplastics in the coral reefs and their potential impacts on corals: A mini-review

Plastic debris exists worldwide and research on microplastic pollution has gradually spread from the oceans to freshwater and terrestrial systems. Coral reefs not only serve as one of the most charismatic and biodiverse ecosystems on our planet, but also maintain the human harvesting of natural resources and livelihoods of hundreds of millions of people. However, the abundance and distribution characteristics of microplastics in coral reef systems receive little scientific attention. Meanwhile, the impacts of microplastics and nanoplastics on coral health and its potential mechanisms remain further studied. Herein, this review first summarized the current status of microplastics pollution in global coral reefs, especially included (i) abundance and distribution characteristics of microplastics in different media (e.g., seawater, sediment, corals), and (ii) possible sources of microplastics in reef regions. Furthermore, the main interaction mechanisms between microplastics and corals are highlighted. Following this, the direct or indirect impacts of microplastics on coral species are discussed. With the rapid increase of plastic consumption and background of pervasive global coral bleaching, research on marine microplastics must focus on the critical coral reef regions and include a comprehensive knowledge about the distribution, fate, and potential risks from an ecosystem perspective.

Nanoplastics in aquatic systems - are they more hazardous than microplastics?

The fragmentation of plastic materials into nanoparticles of less than 1000 nm (secondary nanoplastics) and their possible accumulation in the environment is a recent matter of concern. There are still no suitable standard methods for determining the concentrations and chemical makeup of these particles in aquatic systems and the fate and effect of nanoplastics in the aquatic environment has been little explored, although there has been research using engineered nanoparticles as models. In this review, we give a summary of the (mainly laboratory-based) studies on the influences of nanoplastics. We aim to provide an updated overview of this emerging topic, reviewing the literature mainly from 2018 onwards and considering the effects of nanoplastics on ecosystems, their uptake and transport of polluting molecules, and the challenges that are faced by workers in this area. The review includes 119 references.

Research progress of nanoplastics in freshwater

With the mass production and use of plastic products, which leads to their continuous entry into the water environment, the problem of environmental pollution has been paid more and more attention by scholars from different countries. In recent years, a large number of studies have focused on microplastics, but few on nanoplastics (NPs). However, NPs are smaller in size, have a higher affinity for cells, and surface and volume ratios are higher than those of microplastics. NPs may also enter biological tissues, blood and cells, which may cause greater potential harm to organisms. In this paper, firstly, the environmental fate of NPs accumulation and deposition is summarized, and further research is needed in the future; secondly, the current techniques for NPs extraction and characterization of NPs extraction and characterization are summarized. At present, the analytical methods of NPs are in the primary stage, and lack of standardized and accurate methods; finally, the toxic effects of NPs on biological morphology, behavior and reproduction are discussed. It has been found that the small size and high surface area of NPs make them more toxic to organisms than microplastics. However, most of the current toxicological studies of NPs on freshwater organisms could not be simulated in real environment.

Measuring particle size distribution and mass concentration of nanoplastics and microplastics: addressing some analytical challenges in the sub-micron size range

HYPOTHESIS

The implementation of the proposal from the European Chemical Agency (ECHA) to restrict the use of nanoplastics (NP) and microplastics (MP) in consumer products will require reliable methods to perform size and mass-based concentration measurements. Analytical challenges arise at the nanometre to micrometre interface, e.g., 800 nm-10 µm, where techniques applicable at the nanometre scale reach their upper limit of applicability and approaches applicable at the micrometre scale must be pushed to their lower limits of detection.

EXPERIMENTS

Herein, we compared the performances of nine analytical techniques by measuring the particle size distribution and mass-based concentration of polystyrene mixtures containing both nano and microparticles, with the educational aim to underline applicability and limitations of each technique.

FINDINGS

Light scattering-based measurements do not have the resolution to distinguish multiple populations in polydisperse samples. Nanoparticle tracking analysis (NTA), nano-flowcytometry (nFCM) and asymmetric flow field flow fractionation hyphenated with multiangle light scattering (AF4-MALS) cannot measure particles in the micrometre range. Static light scattering (SLS) is not able to accurately detect particles below 200 nm, and similarly to transmission electron microscopy (TEM) and flow cytometry (FCM), is not suitable for accurate mass-based concentration measurements. Alternatives for high-resolution sizing and concentration measurements in the size range between 60 nm and 5 µm are tunable resistive pulse sensing (TRPS) and centrifugal liquid sedimentation (CLS), that can bridge the gap between the nanometre and micrometre range.

Fate of nanoplastics in the environment: Implication of the cigarette butts

Fate, transport and accumulation of nanoplastics have attracted considerable attention in the past few years. While actual researches have been focused on nanoplastics dispersed or aggregated in different environmental system, no study have been focused on the possibility that nanoplastics are co-transported with other natural or anthropogenic materials. Therefore, the large quantity of debris released in the environment, such as cigarette butts (CGB), could be part of the nanoplastics fate and behavior. Here we show the considerable sorption capacities of cigarette filters for nanoplastics. To address this topic, we chose polystyrene-based nanoplastics with similar state of charge (according to the physico-chemical characteristic of the zeta potential -45 to -40 mV) but with different sizes (50-800 nm) and morphologies. A kinetic approach to sorption in fresh water (pH = 8.05; 179.5 μS cm^-1) at room temperature was carried out by means of the flow field flow analysis method (AF4) to determine the partition coefficients and water sampling rates between nanoplastics and cigarette butts. Using different models of, more or less environmentally relevant, nanoplastics (NPTs) and adequate analytical strategies, we found partition coefficients between the NPTs and CGBs ranged from 10² to 10⁴ in freshwater conditions. We demonstrated that the physical features of the NPTs (size and morphology) have an influence on the sorption behaviour. Asymmetrical shaped NPTs with broader size distribution seems to be mostly retained in the CGBs after longer equilibration time. This result shows the importance of the NPTs features on the mechanisms governing their transfer and fate in the environment through environmental matrices, especially when other materials are involved. We anticipate our work to be a starting point for investigating the co-transport of NPTs with other materials present in the environment (natural and anthropogenic).