Interactions between nano/micro plastics and suspended sediment in water: Implications on aggregation and settling

Hyporheic exchange processes of pore-scale microplastics

The transport of microplastics in the hyporheic zone remains poorly understood with few studies attempting to quantify microplastic hyporheic exchange processes. A laboratory scale erosimeter was utilized in combination with fluorometric techniques to experimentally quantify the dispersion of 3D pore-scale microplastics across the hyporheic zone. Rhodamine WT dye, Polypropylene (PP), polyethylene (PE), and polymethyl methacrylate (PMMA) were well-mixed within the riverbed and individually tested using solute transport theory for three sediment diameters and five bed shear velocities (u∗) common in the natural environment. Effective dispersion coefficients for solutes significantly differed from that of PE and PMMA in most cases, where their critical sinking velocity within sediment pore water was observed and a method for predicting polymer dispersion was proposed. When u∗ ≥ 0.0304 m/s, PMMA followed similar pathways to solutes and the effective dispersion scaling model was successfully implemented to predict its fate. PP near the riverbed interface ascended to the surface but was immobilized deeper in the riverbed, likely due to aggregation and flocculation processes. When polymer buoyancy became the dominant process, high concentrations of lighter than water microplastics ascended into the water column and high concentrations of denser than water microplastics descended through pore water, which is concerning for real-world groundwater systems. These findings provide valuable insights to guide future policy and mitigation strategies of microplastic contamination in fluvial systems by advancing our understanding of microplastic transport. Further data collection will enhance our ability to accurately quantify these transport processes and strengthen mitigation efforts, especially within high permeability sediments.

How hydrodynamic conditions dominate the microplastic footprint in the largest freshwater lake in China

Understanding the migration and diffusion process of microplastics (MPs) in lakes is of great significance to the cumulative assessment of controlling land-based MP pollution. The MPs in the surface water of Poyang Lake were identified to be mainly composed of three representative particles (>91 %): polyethylene (PE) fiber, polypropylene (PP) fragment and PE film, and this study explored the migration process of different types of MPs in three flow regimes. The results show that MP particles migrate northward under the gravity flow and jacking flow. The average time required for MPs to reach the northern lakes in jacking flow was 21.29 % shorter than that in gravity flow. Instead, MPs undergo reverse movement driven by back flow. The difference in migration rates due to MPs physical properties can reach up to 36 % in the same flow regime. The average concentration of PE fiber in the lake area is 30.61 % and 68.68 % higher than both, PP fragment and PE film. In addition, the accumulation hotspots of MPs under three flow regimes were investigated, and MP monitoring in the corresponding areas based on the flow regime can effectively reduce the ecological risk. In terms of ecological risk, the PLI reached Level IV in hotspot areas, indicating severe ecological risk. If considering that the MP type of Poyang Lake is dominated by PE and PP, only the PSL of the Hukou area reaches level II. This study provides reference and warning for tracking the paths and risks of land-based MPs entering freshwater lakes.

Enhanced retention of small-sized microplastics by iron-containing sand filtration system: Effectiveness and mechanisms

This study explores the enhanced retention of small-sized microplastics (MPs) in sand filtration systems using iron-loaded sand (IS). Conventional sand filtration has limited efficiency in removing MPs smaller than the pore size of the filter media, which presents a significant challenge for drinking water treatment plants (DWTPs). To address this issue, quartz sand was modified with iron (hydro)oxide coatings to alter the surface charge, enabling a strong electrostatic attraction with negatively charged MPs. In a 10 mmol/L NaCl solution at a flow rate of 1.5 mL/min, the effluent mass percentages (Meff) of polystyrene 200 nm MPs (MP200) and 1000 nm MPs (MP1000) decreased from 53.52% and 39.40% in bare sand (BS) to 0.79% and 2.81%, respectively. Additionally, IS maintained complete retention of MPs at various ionic strengths and valences. In binary system, while competitive attachment caused an 8.42% increase in the Meff of MP1000 in IS, series-connected columns achieved complete retention. Operational stability tests under realistic conditions, such as variable flow rates, 24-hour interruptions, and back-flushing cycles, demonstrated that IS consistently outperformed BS, with minimal MPs release. Moreover, IS achieved near-total MPs removal in the presence of humic acid and natural pond water, emphasizing its durability under complex environmental conditions. By addressing the challenges of limited retention in traditional systems and competitive attachment in mixed MPs systems, this study highlights IS as a scalable and effective solution for mitigating MPs pollution in drinking water. These findings offer crucial insights into enhancing filtration efficiency across a range of environmental and operational scenarios.

Plastic additives alter the influence of photodegradation on biodegradation of polyethylene/polypropylene polymers in natural rivers

The biodegradation of microplastics in river sediments was subject to the prior photodegradation in surface water and can be greatly affected by polymers and additives. However, the understanding of the effects of additives on the cascade photo- and biodegradation processes remains limited. In this study, the characteristics of morphology, functional groups, and indictive degrading bacteria of polyethylene (PE) and polypropylene (PP) were detected to analyze the effects of Dioctyl phthalate (DOP), Bisphenol A (BPA) and Benzotriazole (BTA), on the single and cascade photo- and biodegradation processes of PP/PE films (PP/PEP, PP/PEB, PP/PEPB). The results showed that photodegradation enhanced the biodegradation, by creating smaller fractions which induced the proliferation of new PP/PE-degrading bacteria (P-bacteria). Compared to the general PP/PE-degrading bacteria, P-bacteria displayed higher standard betweenness centrality and carbon metabolism. Among the three additives, DOP most obviously promoted photo- and biodegradation processes, followed by BPA. BTA inhibited the photodegradation to biodegradation by absorbing UV light. Overall, these findings provide insights into the nonnegligible joint influence of photodegradation and additives on the biodegradation of PP/PE resins in natural rivers.

Quantitative assessment of microplastics in fish from the Gulf of Guinea, Ghana, using LDIR spectroscopy: Implications for marine food safety and health risk evaluation

In this study, microplastic (MP) contamination was investigated in 24 marine fish species from 3 environmental hotspots- Labadi, Teshie, and Jamestown, along Ghana's Gulf of Guinea coastline. Specific fish species studied included Pseudotolithus senegalensis, Sphyraena guachancho, Brachydeuterus auratus, Chloroscombrus chrysurus, and Ethmalosa frimbriata. Fifty-eight percent of the total MPs were detected in the gastrointestinal tracts, and 42% detected in gills of 177 individual fish tested in this study. Labadi showed the highest contamination levels [mean MP concentration: 22 ± 19 (items fish)-1]. Omnivorous fish species had the highest mean ingestion rate of MPs (19.4), surpassing both carnivorous (17.7) and herbivorous species (13.5), and indicating dietary habits as a significant factor in MP bioaccumulation. White-coloured MP films (60%) of sizes: 100-1000 µm were the dominant ingested shape. Other MP shapes included fragments (26.3%), fibres (10.5%), beads (1.05%), and foam (0.61%). Using advanced spectroscopic technique such as Laser Direct Infrared (LDIR) Imaging, 16 MP polymers were characterized with polyvinyl chloride (PVC) being the prevalent MP polymer type (80%). The study observed a strong positive correlation between carnivorous demersal and omnivorous pelagic-neritic fish for specific MP polymers, suggesting that factors other than polymer density influence MP consumption patterns for fish habitats within the water column. The annual MP exposure to Ghanaian adults via fish consumption [(194-29,239 MP items (person year)-1] significantly exceeded the European Safety guidelines [518-3078 (items year)-1], emphasizing dietary habits and environmental pollution as key factors. This study provides a critical baseline on MP pollution in Ghanaian marine ecosystems, highlighting the urgent need for interventions to mitigate plastic pollution, protect marine biodiversity, safeguard marine food, and public health in West Africa.

Synergistic effects of nanoplastics and graphene oxides on microbe-driven litter decomposition in streams

The increasing production and release of plastics and graphene nanomaterials pose risks to the ecological environment. However, little is known regarding the interactive effects of nanoplastics (NPs) and graphene oxide (GO) on ecological processes in aquatic ecosystems. To address this knowledge gap, we conducted an indoor experiment to investigate the effect of NPs and GO alone, as well as their combined effects on litter decomposition and associated microbial community structure and function in streams. The combined treatments with GO and NPs significantly increased the relative abundance of Enterobacter (47.42-61.72 %), and the activities of leucine arylamidase and cellobiose hydrolase. Specifically, the combination of GO and NPs exerted a stronger impact on bacterial α-diversity and degradation function than on fungi, challenging the popular view. Importantly, this combination of NPs and GO inhibited litter decomposition at 5 days but promoted it at 40 days, indicating a time-dependent effect. Structural equation modeling revealed that NPs, GO, and their combined effects promoted litter carbon loss through direct breakdown and indirectly increased bacterial diversity and extracellular enzyme activities related to carbon cycling and depolymerisation. The results obtained in this study highlight the importance of considering the characteristics of pollutants interacting with NPs and their time-dependent effects when evaluating the ecotoxicological effects of NPs in aquatic ecosystems.

Intergenerational transfer of micro(nano)plastics in different organisms

Micro(nano)plastics (MNPs), widely distributed in the environment, can be ingested and accumulated by various organisms. Recently, the transgenerational transport of MNPs from parental organisms to their offspring has attracted increasing attention. In this review, we summarize the patterns, specific pathways, and related mechanisms of intergenerational transfer of MNPs in plants, non-mammals (zooplankton and fish) and mammals. The knowledge gaps are also discussed. For plant, MNPs can accumulate in fruits and seeds by intercellular and cellular internalization pathways after uptake by roots or leaves. In zooplankton (e.g., Daphnia magna), MNPs are capable of maternal transfer via two different pathways: gut-ovary-egg and brood chamber-embryo. Intergenerational transfer of MNPs in egg-laying fish can occur through direct maternal transfer. However, MNPs may be transported through follicular pseudoplacenta, surface epithelia, and trophotaeniae pathways in ovoviviparous fish. In mammals, the maternal-fetal transport of MNPs primarily occurs through the placenta, amniotic fluid, and breastfeeding. The placental barrier is the main limitation to transfer, and the ability of MNPs to cross this barrier largely depends on the trophoblast cells via internalization and intercellular pathways. Additionally, we discuss the physicochemical properties (e.g., size, shape, and ageing) of MNPs and environmental factors (e.g., salinity, minerals, organic matter) that influence intergenerational transfer. Current challenges regarding the transfer pathways and related mechanisms, as well as future perspectives, are also addressed. This review provides valuable information for assessing the fate of MNPs in organisms and potential risks to population, community, ecosystems, and human health.

Microplastic contamination in sediments: Analytical techniques and case-based evaluations

Microplastics (MPs) pollution in sediments has gained critical attention due to its pervasive presence and potential ecological risks. This review synthesizes the latest advancements in analytical techniques, providing a comprehensive overview of separation and identification methods tailored to complex sedimentary matrices. Density-based approaches, such as ZnCl2 or NaI solutions, and enzymatic digestions are increasingly refined to isolate MPs of varying sizes, yet discrepancies in mesh sizes, reagent concentrations, and digestion protocols continue to complicate cross-study comparisons. Meanwhile, cutting-edge spectroscopic tools-μFTIR, Raman imaging, thermal analyses-have greatly enhanced polymer identification down to the tens-of-micrometers scale. Case studies spanning urban estuaries to remote deep-sea basins underscore the pervasive nature of MPs worldwide, with fibers and fragments frequently dominating sediment samples. Factors such as polymer density, hydrodynamics, and biofouling contribute to the diverse distribution patterns, revealing that even ostensibly pristine environments are not exempt from contamination. Although the precise ecological and toxicological consequences of long-term sediment-bound MPs remain partly unclear, growing evidence points to intricate interactions with co-occurring contaminants and potential trophic transfer. To address these knowledge gaps, this review emphasizes the urgent need for methodological standardization and collaborative initiatives, particularly for emerging challenges like nanoplastic detection. By integrating robust sampling approaches, advanced analytical tools, and interdisciplinary research, scientists and policymakers can more accurately map and mitigate the impacts of sediment-associated MPs on aquatic ecosystems.

UV-weathering affects heteroaggregation and subsequent sedimentation of polystyrene microplastic particles with ferrihydrite

Microplastic (MP) particles are ubiquitous in aquatic environments where they become exposed to UV-irradiation with subsequent alteration of surface properties. Such particles will interact with naturally occurring colloids being subject to processes like heteroaggregation that affect both MP surface properties and their removal rates from the water column. In this study, we investigated heteroaggregation and subsequent sedimentation of 1 μm polystyrene (PS, pristine and UV-weathered) with ferrihydrite (Fh), an iron (oxy)hydroxide commonly found in nature. Heteroaggregation of pristine PS with Fh was controlled by electrostatic attraction. At neutral pH values, strong heteroaggregation was observed which led to the sedimentation of almost all PS particles. UV-weathering of PS led to lower negative surface charge, decrease of particle size, and formation of degradation products. Changes in surface properties of PS resulted in a different aggregation behavior with Fh. With increasing weathering time, the isoelectric point (pHIEP) of suspensions with PS and Fh shifted to lower pH values. Furthermore, we observed aggregation and subsequent sedimentation of weathered PS and Fh for a wider pH range (pH 3-7) compared to pristine PS (pH 6.5-7.5). We attribute this observation to increased surface reactivity of PS due to the formation of functional groups on the surface through UV-weathering. In addition, degradation products (e.g. oligomers) formed during weathering might have also interacted with PS and Fh and therefore further affected the surface properties of the particles. Overall, UV-weathering but also interactions of MP particles with environmental particles cause changes of MP surface properties, which influence its environmental behavior in water and might lead to a removal from the water column and accumulation in sediments.

Cell Response to Nanoplastics and Their Carrier Effects Tracked Real-Timely with Machine Learning-Driven Smart Surface-Enhanced Raman Spectroscopy Slides

Research on nanoplastic (NP) toxicity and their "carrier effects" on human health remains nascent, especially for real-time, in situ monitoring of metabolic reactions in live cells. Herein, we developed smart surface-enhanced Raman spectroscopy (SERS) slides using a cyclic centrifugation-enhanced electrostatic loading (CCEL) method to facilitatively track live-cell metabolic signals. The designed core-shell polystyrene NPs (mPS) with embedded Raman probes successfully identified intracellular accumulation via a distinct Raman-silent peak. The smart SERS slide effectively monitored the metabolic changes induced by mPS at the molecular level, distinguishing different stages of membrane interaction, the endocytosis process, endosomal aggregation, and cell apoptosis. Besides, this platform was employed to perform a real-time, in situ comparison of cell cycle alterations induced by bare NPs and their "carrier effects", revealing that NPs extended both the S and G2 phases in BEAS-2B cells, while the "carrier effects" further prolonged G2 and disrupted S-phase progression. Additionally, we integrated machine learning algorithms to accurately predict the cell cycle impacts associated with mPS and their "carrier effects". This study provides a label-free, in situ, real-time method for monitoring NP-induced metabolic changes in live cells, laying the groundwork for further investigation into cytotoxic behaviors and strategies to mitigate NP toxicity.

Revealing the removal behavior of polystyrene nanoplastics and natural organic matter by AlTi-based coagulant from the perspective of functional groups

The interactions of nanoplastics (NPs) with natural organic matter (NOM) are influenced by their surface functional groups. In this study, the effects of representative functional groups on the interactions among polystyrene nanoplastics (PS-COOH and PS-NH2), hydrophilic low molecular weight (LMW) substances (salicylic acid (SA), phthalic acid (PA), and gluconic acid (GA)), and a novel AlTi-based coagulant were investigated. We found that PS-NH2 (83.02 % - 93.38 %) was easier to remove over a wider pH range than PS-COOH (6.94 % - 91.07 %). PS-COOH and PS-NH2 were both able to interact with SA (-OH, -COO-, and benzene ring) through hydrogen bonding, π-π conjugation, and n-π electron donor-acceptor interactions. However, the binding of PS-COOH/PS-NH2 with SA has no effect on the interaction strength between SA and PATC due to the preferential occupation of the coagulant binding sites by SA. The lower SA removal in the PS-COOH@SA system was attributed to its stronger electrostatic repulsion and hydrophilicity. PATC could form carboxylate outer and C-O inner complexes with SA and carboxylate inner complexes with PA. In this study, the analysis of the interaction mechanisms among metal-based coagulants, NPs, and LMW substances lays a theoretical foundation for further research and understanding of coagulation theory.

Perinatal exposure to polystyrene nanoplastics alters socioemotional behaviors via the microbiota-gut-brain axis in adult offspring mice

Polystyrene nanoplastics (PS-NPs), ubiquitous environmental contaminants, have been detected in various tissues of humans and animals, raising significant concerns regarding their potential health hazards. The long-term consequences of PS-NPs exposure during early developmental stages remain inadequately characterized. In this study, we established a murine model to investigate the chronic oral administration of PS-NPs via drinking water during the perinatal period, with a focus on elucidating the impact of PS-NPs ingestion on the social behaviors of adult offspring and the underlying mechanisms, particularly those involving the gut-brain axis. Our findings revealed that perinatal PS-NPs exposure elicited depression-like behaviors, diminished social dominance, and reduced social interactions in adult offspring. Additionally, we observed a decrease in dendritic spine density within hippocampal neurons, along with ultrastructural damage to hippocampal neurons and synapses in the adult offspring. PS-NPs exposure also led to a reduction in the richness and evenness of gut microbiota species composition in both male and female mice, with gut dysbiosis being particularly pronounced in adult males. Furthermore, alterations in metabolite abundance and metabolic pathways were detected in the hippocampus of both male and female adult offspring. Notably, a significant correlation was identified between the relative abundance of intestinal microorganisms and hippocampal metabolites. These results offer new insights into the association between early-life PS-NPs exposure and adult social behaviors, mediated through the microbiota-gut-brain axis.

The impact of building uses on microplastic pollution and its implications for environmental education

Rivers are major sources of marine microplastics. To investigate the influence of building use on river microplastic pollution, this study focused on the Chongqing section of the main stream of the Yangtze River. Surface water and sediment microplastic samples were collected and analyzed alongside building use data to explore the relationship between microplastic abundance and building use at different spatial scales. The results showed that: (1) The abundance of microplastics in surface water and sediment in the Chongqing section of the Yangtze River exhibited an inverse distribution pattern. In the upper reaches, the central urban area of Chongqing showed significantly higher microplastic levels in surface water (6,811 ± 3,101 n/m ³) compared to the lower reaches, confirming the direct input effect of high-intensity human activities. The accumulation of microplastics in sediment was greater in the northeastern section of Chongqing compared to the lower reaches (89.6 ± 69 vs. 45.4 ± 28 n/kg), indicating a hydrodynamic-driven sedimentation lag effect. (2) The influence of building use on microplastic abundance in surface water was significantly scale-dependent. Industrial buildings within a 2 km buffer zone explained up to 61.16% of the observed variance, suggesting cross-medium migration through atmospheric sedimentation and sewage pipe network. (3) Compared to land use types, building uses dominate the abundance distribution of microplastics in surface water at larger buffer radius (1-2 km), indicating that high-intensity human activities have a greater impact on spatial differentiation of microplastic pollution. It is recommended to implement hierarchical control measures along the Chongqing section of the Yangtze River. A 2-km ecological buffer zone is set up in industrial agglomeration areas to strictly supervise wastewater discharge from plastic products enterprises. Rainwater bioretention facilities are built within 1 km of densely populated areas to intercept microplastics from domestic sources, such as laundry fibers. This study explores the mechanism by which building use affects river microplastic pollution, providing valuable insights for microplastics control in large river basins worldwide.

A How-To Approach to Estimating Surface Charge Density of Nano/Micro Particles through Aggregation Experiments Considering the Specific Ion Effect

Accurate estimation of the surface charge density of nano/micro particles is crucial for regulating their environmental fate and bioavailability in the fields of environmental science and materials engineering. However, existing analytical methods for accurately estimating surface charge density remain significant challenges. In this study, we proposed a method for estimating the surface charge density of nano/micro particles through aggregation experiments using dynamic light scattering technology. The specific ion effect had a significant effect on the accuracy of these estimations. Without considering the specific ion effect, this led to significantly different and unacceptable surface charge densities for montmorillonite particles with permanent charges. Conversely, when considering the specific ion effect, similar surface charge densities were obtained (0.1974, 0.1930, and 0.1718 C/m2), with a mean value of 0.1874 ± 0.0136 C/m2, which aligned well with the literature-reported values. Furthermore, the surface charge density of various nano/micro particles, such as microplastic polymers, graphene oxide, and nanosilver, was also estimated using this method. The migration behavior of these particles was determined by electrostatic repulsion between them, which was controlled by their surface charge density. The surface analysis method proposed herein provides a solid foundation for the directed adjustment and control of the migration dynamics of nano/micro particles in environmental systems.

Comparison of microplastics heteroaggregation with MoS2 and graphene oxide nanosheets: Dependence on the configuration and impacts on aquatic transport

Understanding the behavior and fate of microplastics (MPs) in aquatic environment is crucial for assessing their potential risks. This study investigated the heteroaggregation behaviors of MPs with representative 2D nanosheets, MoS2 and graphene oxide (GO), under various conditions, focusing on the transport behavior of the resulting aggregates. It was found that the destabilization capabilities of 2D nanosheets are notably stronger than those of well-reported nanoparticles. More importantly, the deposition and transport of MPs are highly dependent on the configuration of the resulting aggregates. MoS2 nanosheets conformally coat MPs, forming compact and colloidally stable complexes that completely alter the MPs' surface to the negatively charged MoS2. The interaction resulted in high mobility and minimal deposition in environmental matrices. In contrast, GO nanosheets bridge MPs into large clusters, reducing transport and increasing deposition. This difference in aggregate configuration is attributed to the distinct interactions between the nanosheets and MPs: rigid MoS2 nanosheets adhere via strong van der Waals forces, while GO, with oxygen functional groups on its edges and surfaces, folds and crosslinks between particles upon adsorption. These findings underscore the critical role of 2D materials in shaping the environmental fate of MPs, advancing our knowledge on the aggregation process.

Towards A universal settling model for microplastics with diverse shapes: Machine learning breaking morphological barriers

Accurately predicting the settling velocity of microplastics in aquatic environments is a prerequisite for reliably modeling their transport processes. An increasing number of settling models have been proposed for microplastics with fragmented, filmed, and fibrous morphologies, respectively. However, none of the existing models demonstrates universal applicability across all three morphologies. Scientists now have to rely on the predominate microplastic morphology extracted from filed samples to determine the appropriate settling model used for transport modeling. Given the spatiotemporal variability in morphologies and the coexistence of diverse morphologies of microplastics in natural aquatic environments, the extracted morphological information poses significant challenges in reliably determining the appropriate model. Evidently, to reliably model the transport of microplastics in aquatic environments, a universal settling model for microplastics with diverse shapes is warranted. To develop such a universal model, a unique shape factor, which can explicitly distinguish between the distinct morphologies of microplastics, was first proposed in this study by using a specifically-modified machine learning method. Using this newly-proposed shape factor, a universal model for predicting the settling velocity of microplastics with distinct morphologies was developed by using a physics-informed machine learning algorithm and then systematically evaluated against independent data sets. The newly-developed model enables reasonable predictions of the settling velocity of microplastic fragments, films, and fibers. In contrast to purely data-driven models, the newly-developed model is characterized by its transparent formulaic structure and physical interpretability, which is conducive to further expansion and improvement. This study can serve as a paradigm for future studies, inspiring the adoption of machine learning techniques in the development of physically-based models to investigate the transport of microplastics in aquatic environments.

Colloid and Interface Science for Understanding Microplastics and Developing Remediation Strategies

Microplastics (MPs) originate from industrial production of <1 mm polymeric particles and from the progressive breakdown of larger plastic debris. Their environmental behavior is governed by their interfacial properties, which dominate due to their small size. This Perspective highlights the complex surface chemistry of MPs under environmental stressors and discusses how physical attributes like shape and roughness could influence their fate. We further identify wastewater treatment plants (WWTPs) as critical hotspots for MP accumulation, where the MPs are inadvertently transferred to sewage sludge and reintroduced into the environment. We emphasize the potential of colloid and interfacial science not only to improve our fundamental understanding of MPs but also to advance mitigation strategies in hotspots such as WWTPs.

Distribution and Biological Response of Nanoplastics in Constructed Wetland Microcosms: Mechanistic Insights into the Role of Photoaging

Concern over nanoplastic contamination of wetland ecosystems has been increasing. However, little is known about the effect of photoaging on the distribution and biological response of the nanoplastics. Here, palladium-labeled polystyrene nanoplastics (PS-Pd NPs) at 0.05-50 mg/L were exposed to constructed wetland microcosms containing floating (Eichhornia crassipes) and submerged (Vallisneria natans) macrophytes. Results demonstrate that PS-Pd NPs' concentration in surface water after 2-4 weeks of exposure was decreased by over 98.4% as compared with that in the 1st week. Photoaging enhanced the surface charge and colloidal stability of PS-Pd NPs, with a subsequent increase of the content of PS-Pd NPs in surface and middle layer water by 264.6 and 207.4%, respectively. Additionally, photoaging significantly enhanced the accumulation of PS-Pd NPs in E. crassipes roots by 6.9-65.0% and significantly decreased it in V. natans shoots by 59.7-123.0%. PS-Pd NPs inhibited the growth of V. natans by 43.8% at 50 mg/L. Mechanistically, PS-Pd NPs induced oxidative stress in V. natans, leading to the disruption of the metabolic pathway. Interestingly, PS-Pd NP exposure inhibited nitrification in wetland ecosystems due to the alteration of the related bacterial community (Ellin6067 decreased by 13.19%). These findings deepen our understanding of the environmental fate and risk of plastic particles in wetland ecosystems.

Adsorption and migration of sulfamethoxazole driven by suspended particulate matter in water body

The extensive use of antibiotics has led to significant antibiotic pollution in water bodies, and suspended particulate matter (SPM) is known to be a key carrier of antibiotics in rivers. In this work, the adsorption characteristics of sulfamethoxazole (SMX) on SPM was investigated through batch adsorption and annular flume experiments, and the MIKE 21 model was employed to simulate the migration of SMX and SPM. Results revealed that most SMX adsorption occurred rapidly within 20 min, and 80 % of the equilibrium adsorption capacity was reached. Multilayer adsorption was confirmed by Freundlich model, and adsorption process was found to be spontaneous, endothermic, disordered, and the equilibrium adsorption amounts of SMX on SPM increased with salinity and organic matter increase. SMX desorption from SPM occurred upon the sudden changes of hydrodynamic states, nearly reaching the one-fifth of the SMX equilibrium adsorption amounts within 30 min and the re-adsorption of SMX on SPM would occur with water remained stationary or the re-disturbance time prolonged. The dynamic adsorption process of SMX related with the physicochemical property changes of SPM, which was contributed to the hydrogen bonds, π-π interactions, surface complexation, significantly influenced by the pore filling at the macropore and mesopore scales. The MIKE 21 simulations confirmed hydrodynamic states as the primary factors affecting the migration of SMX and SPM. SMX concentrations in the water would decrease in the presence of SPM, leading to the slower downstream migration of SMX.

Modeling of heteroaggregation driven buoyant microplastic settling: Interaction with multiple clay particles

The ecological risk of microplastics (MPs) has received widespread attention, but understanding ecological risk starts with understanding environmental migration. Heteroaggregation is an important process that affects the vertical migration of MPs, and the mathematical model is a common tool used to project the migration behavior of MPs. However, the mathematical model based on the aggregation of MPs with one clay particle is not applicable to simulate the migration behavior of buoyant microplastic (BMP). Hence, this study developed a model for heteroaggregation of one BMP with multiple clay particles based on the Population Balance Equation, and the main factors affecting the sedimentation of BMP are clarified through parameter sensitivity analysis and scenario simulation. The results show that neglecting the interaction of one BMP with multiple clay particles in the mathematical model can underestimate the predicted settling concentration of BMP, especially in aqueous environments with higher clay concentration and salinity. The settling process of BMP is controlled by the heteroaggregation rate, which is sensitive to environmental conditions and insensitive to particle properties. This study emphasizes the importance of considering the interaction of one BMP with multiple clay particles in the future mathematical model, which will provide a more reliable prediction of the migration of MPs in aquatic environments.

Interaction and bacterial effects of microplastics pollution on heavy metals in hyporheic sediments of different land-use types in the Beiluo River Basin

Microplastics (MPs) pollution is ubiquitous, causing serious ecological damage by threatening the growth and health of living organisms. This study investigated the vertical and horizontal distribution of MPs, MPs-heavy metals (MPs-HMs) accumulation, contamination assessment and microbial biodiversity in hyporheic sediments of different land-use types. MPs abundance in shallow sediments (0-30 cm) was significantly higher than that in deep sediments (30-60 cm), with fewer large MPs in the deep sediments. Blue, fiber, and <500 μm were the dominant MPs types, and polystyrene, polylactic acid, and polyvinyl chloride were the dominant polymers in the Beiluo River Basin. The average concentrations of HMs detected in MPs were all much higher than the same metals in the sediments. The pollution loading index of MPs was higher in areas with a greater proportion of anthropogenic land use, and MP-HM were present to varying degrees in the vertical distribution (PN > 1). Critically, bacterial diversity of anthropogenic land use was smaller than that of natural land use. High MP-HM concentrations reduced the abundance of cyanobacteria, nitrospirota, acidobacteriota, and planctomycetota, whereas desulfobacterota, chloroflexi, myxococcota, actinobacteriota, and proteobacteria have developed tolerance to MP-HM. Overall, our findings contribute to the understanding of the relationship between different land-use types and the spatial distribution of MPs and MP-HM, which is critical to manage and mitigate the hyporheic zone pollution.

Remote sensing research on plastics in marine and inland water: Development, opportunities and challenge

The accumulation of plastic waste from various sources into marine and inland water is considered a global problem due to its serious impacts on aquatic ecosystems and human health. In the past decade, remote sensing has played an important role in monitoring of plastic pollution in marine and inland water sources and has achieved a series of research results in this field. In this study, a comprehensive review was conducted on the development, opportunities, and challenges of datasets and methods in Marine and Inland Water Plastics Remote Sensing (MIWPRS) monitoring over the past decade, based on the Web of Science (WOS) core database. The results indicated that compared with traditional methods, remote sensing has attracted the attention of scholars due to its advantages. Since 2014, the number of related publications has been increasing year by year, especially in China and the United States, which have achieved tremendous development. The MIWPRS research focus mostly on the use of different satellite remote sensing data and related algorithms to obtain the distribution of plastics in marine and inland water. However, it faces the challenge of lacking subsequent systematic impact assessment models and key pollution prevention measures. In terms of data acquisition, there is a lack of continuous observation models due to the fluidity of marine and inland water. Therefore, MIWPRS has great development opportunities in developing specialized sensors and combining multi-source data with interdisciplinary knowledge such as artificial intelligence (AI) and GIS. It is necessary for us to improve the seasonal migration model of plastics in water and promote the development of MIWPRS towards broader and deeper fields.

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

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

Traversing the potential of phytoremediation and phycoremediation as pioneering technologies in microplastic mitigation - A critical review

With the advent of numerous reports related to health and environmental hazards associated with microplastics (MPs), scientists have been engrossed in developing sustainable technologies for MP mitigation. Conventional methods for the remediation of MPs have several limitations, but with the increasing demand for biological mitigation methods, the latest technologies are prioritized. Among biological-driven methods, phytoremediation and phycoremediation are the two peaking approaches that have gained momentum because of their eco-friendliness, cost-effectiveness, and recyclability options. Investigations of the mechanisms underlying phytoremediation and phycoremediation processes can provide possible insights into practical applications in the present scenario. Modern instrumentation is a prerequisite for identifying and characterizing MPs and quantifying their removal efficiency. The current investigation highlights a unique combination of elaborate discussions on the use of plants in the mitigation of MPs, bibliometric analysis of the current status of research, their relevance to the modern context, and the development of a combinatorial strategy to amalgamate the advantages of these two unique processes via the concept of constructed wetlands for synergistically mitigating MPs. Thus, this review provides fresh insights into addressing MP pollution with sustainable ideologies to achieve improved mitigation outcomes without compromising the balance of the ecosystem.

Perfluorobutanoic acid weakens the heterogeneous aggregation of microplastics and microalgae: Perspective from physicochemical properties, extracellular polymeric substances secretion and DLVO theory

Microplastics (MPs) and per- and poly-fluoroalkyl substances extensively coexist in aquatic environments and potentially endanger organisms. Microalgae may decrease the effective concentration of pollutants via hetero-aggregation with MPs and adsorption of emerging contaminants. However, the potential influence of coexistent pollutants on hetero-aggregation of MPs and microalgae remains unknown. This study investigated the hetero-aggregation process involving different sizes of polystyrene (PS, 3.0 and 50.0 μm) with Chlorella sorokiniana (C. sorokiniana) in the presence or absence of perfluorobutanoic acid (PFBA) along settling experiments, scanning electron microscope, and Derjaguin-Landau-Verwey-Overbeek (DLVO) model. We found that the hetero-aggregation between C. sorokiniana and 3 μm PS was more pronounced than with 50 μm PS, while PFBA inhibited this process. ΔOD1 values (reflected hetero-aggregation level) for 3PS-cells and 50PS-cells were 0.189 and 0.087, respectively, and PFBA decreased these values to 0.134 and 0.033. Furthermore, extracellular polymeric substances, known as inducer of hetero-aggregation, increased by 14.33% when exposed to 3 μm PS alone, whereas the co-exposure group showed a decrease of 4.52% compared to 3PS-cells group. PFBA also significantly decreased the protein/polysaccharide ratios in both MPs sizes, reducing hetero-aggregation. DLVO theory revealed that microalgae lowered the energy barrier significantly, while PFBA elevated it, indicating that hetero-aggregation was inhibited by PFBA. This study provides new perspectives for pollutant removal and toxicity variation in aquatic environments.

Impact of electrolyte and natural organic matter characteristics on the aggregation and sedimentation of polystyrene nanoplastics

Nanoplastics are increasingly pervasive in ecosystems worldwide, raising concerns about their persistence and mobility in the environment. Our study focused on the interactions between polystyrene nanoplastics (PS NPs, Do:~200 nm) and Natural Organic Matter (NOM) uniquely isolated from water bodies under different electrolyte and temperature conditions (i.e., effectively mimicking a wide range of environmental scenarios). The selected dissolved NOM (DOM) fractions of varied physical chemical characteristics and geographical origins include: the hydrophobic acid (HPOA) fraction from the South Platte River (SPR HPOA, USA), the biopolymer/colloid fractions from Cazaux Lake (CL BIOP, France), and the dissolved fraction of the biofilm recovered from a nanofiltration-fouled module at the Méry-sur-Oise drinking water treatment plant (NF BIOP, France). The biopolymers (NF BIOP and CL BIOP) clearly hindered PS NPs aggregation through steric effects, forming a protective eco-corona, enhancing PS NPs stability, and inhibiting sedimentation in the long term, compared to HPOA. The temperature impacted the homo and hetero-aggregation of PS NPs differently, illustrating the complex interplay between thermal effects and NOMs stabilizing interactions. Furthermore, the seldom-explored aspect of the sequential introduction of reactants into the solution during aggregation experiments (i.e., which simulates a realistic scenario: the transport of PS NPs from one aquatic system to another of different compositions) was also investigated. This study provides essential insights into the dynamic behavior of PS NPs in environmental matrices and crucial knowledge for predicting nanoplastic interactions in complex ecosystems.

Prediction of vertical transport of microplastics: Shape- and aging-dependent drag models

The prediction of vertical transport of microplastics (MPs) is essential for understanding their multidimensional transport, fate, and environmental risks, but drag models applicable to aging MPs are currently understudied. In this study, pristine and UV-aged polyethylene terephthalate (PET) and polystyrene (PS) MPs were used for settling experiments. Combining physicochemical properties and transport data, a shape-dependent drag model based on the Corey shape factor was optimized with average errors of 9.73 % and 10.42 % and coefficients of determination of 0.6878 and 0.8359 for predicting the settling terminal velocities (ut) for PET and PS MPs, respectively. Meanwhile, aging-dependent drag models were constructed by incorporating the carbonyl index as functional forms of the newly defined aging index, which can be used to differentiate the effects of shape and aging characteristics on the vertical transport of MPs. These aging-dependent models showed better predictive abilities with average errors of 3.97 % and 4.56 % in predicting ut for PET MPs, and of 5.89 % and 6.91 % for PS MPs. Additionally, the drag models in this study improved applicability to predict vertical transport of environmentally-collected weathered MPs. With the continuous improvement of the transport database of diverse MPs, this study is expected to provide scientific support for predicting the environmental behaviors of MPs and formulating targeted pollution control strategies.

A perspective on the algae-derived dissolved organic matter and its dynamic influence on the aggregation of nanoplastics in eutrophic waters

The aggregation behavior of nanoplastics (NPs) is crucial in determining their fate in aquatic environments. Dissolved organic matter (DOM), characterized by its complex molecular structure and diverse functional groups, can spontaneously absorb on the surface of NPs, thus altering their colloidal stability. In eutrophic waters, DOM primarily originates from metabolic byproducts released by phytoplankton, and its molecular composition and hydrophilic properties change dynamically as the progression of algal blooms. This perspective aims to summarize the heterogeneity of DOM during the initiation, outbreak and recession of algal blooms. And we investigate the influence of molecular-level variations in DOM composition on the aggregation behavior of NPs. Additionally, this study provides insights into the underlying mechanisms relating to the interactions between DOM and NPs. Ultimately, it tackles the challenges and future directions, highlighting the necessity for comprehensive studies to understand the fate of NPs in eutrophic waters.

A state-of-the-art review of environmental behavior and potential risks of biodegradable microplastics in soil ecosystems: Comparison with conventional microplastics

As the use of biodegradable plastics becomes increasingly widespread, their environmental behaviors and impacts warrant attention. Unlike conventional plastics, their degradability predisposes them to fragment into microplastics (MPs) more readily. These MPs subsequently enter the terrestrial environment. The abundant functional groups of biodegradable MPs significantly affect their transport and interactions with other contaminants (e.g., organic contaminants and heavy metals). The intermediates and additives released from depolymerization of biodegradable MPs, as well as coexisting contaminants, induce alterations in soil ecosystems. These processes indicate that the impacts of biodegradable MPs on soil ecosystems might significantly diverge from conventional MPs. However, an exhaustive and timely comparison of the environmental behaviors and effects of biodegradable and conventional MPs within soil ecosystems remains scarce. To address this gap, the Web of Science database and bibliometric software were utilized to identify publications with keywords containing biodegradable MPs and soil. Moreover, this review comprehensively summarizes the transport behavior of biodegradable MPs, their role as contaminant carriers, and the potential risks they pose to soil physicochemical properties, nutrient cycling, biota, and CO2 emissions as compared with conventional MPs. Biodegradable MPs, due to their great transport and adsorption capacity, facilitate the mobility of coexisting contaminants, potentially inducing widespread soil and groundwater contamination. Additionally, these MPs and their depolymerization products can disrupt soil ecosystems by altering physicochemical properties, increasing microbial biomass, decreasing microbial diversity, inhibiting the development of plants and animals, and increasing CO2 emissions. Finally, some perspectives are proposed to outline future research directions. Overall, this study emphasizes the pronounced effects of biodegradable MPs on soil ecosystems relative to their conventional counterparts and contributes to the understanding and management of biodegradable plastic contamination within the terrestrial ecosystem.

Long-term pollution status of microplastics in sediment of a typical mariculture area

Microplastics (MPs) are pervasive in various environmental media, posing a significant global issue. However, long-term data on marine MPs pollution trends are limited. This study investigates sediment samples from six stations in Sishili Bay, Yellow Sea, collected in 2015, 2018, and 2021, an area impacted by industrial, maricultural, and tourism activities. Findings reveal an annual increase in MPs abundance, with mean concentrations of 92.60 ± 23.93 items/kg.dw in 2015, 146.18 ± 14.80 items/kg.dw in 2018, and 203.21 ± 20.31 items/kg.dw in 2021. MPs distribution is spatially uniform, showing no significant seasonal changes, attributed to the bay's semi-enclosed nature. Predominant MPs are fibers (>70 %) and transparent particles (>35 %), with most particles <1000 μm. PET and Rayon are the main polymers identified. The study emphasizes the escalating MPs pollution in the mariculture area, highlighting the urgent need for targeted pollution control and mitigation strategies.

Heteroaggregation, disaggregation, and migration of nanoplastics with nanosized activated carbon in aquatic environments: Effects of particle property, water chemistry, and hydrodynamic condition

Nanosized activated carbon (NAC) as emerging engineered nanomaterials may interact with nanoplastics prevalent in aquatic environments to affect their fate and transport. This study investigated the effects of particle property (charge and concentration), water chemistry [electrolytes, pH, humic acid (HA), and sodium alginate (SA)], and hydrodynamic condition [wave (i.e., sonication) and turbulence (i.e., stirring)] on the heteroaggregation, disaggregation, and migration of NAC with positively charged amino-modified polystyrene (APS) or negatively charged bare polystyrene (BPS) nanoplastics. The homoaggregation rate of APS was slower than its heteroaggregation rate with NAC, with critical coagulation concentrations (CCC) decreasing at higher NAC concentrations. However, the homoaggregation rate of BPS was intermediate between its heteroaggregation rates under low (10 mg/L) and high (40 mg/L) NAC concentrations. The heteroaggregation rate of APS+NAC enhanced as pH increasing from 3 to 10, whereas the opposite trend was observed for BPS+NAC. In NaCl solution or at CaCl2 concentration below 2.5 mM, HA stabilized APS+NAC and BPS+NAC via steric hindrance more effectively than SA. Above 2.5 mM CaCl2, SA destabilized APS+NAC and BPS+NAC by calcium bridging more strongly than HA. The migration process of heteroaggregates was simulated in nearshore environments. The simulation suggests that without hydrodynamic disturbance, APS+NAC (971 m) may travel farther than BPS+NAC (901 m). Mild wave (30-s sonication) and intense turbulence (1500-rpm stirring) could induce disaggregation of heteroaggregates, thus potentially extending the migration distances of APS+NAC and BPS+NAC to 1611 and 2160 m, respectively. Conversely, intense wave (20-min sonication) and mild turbulence (150-rpm stirring) may further promote aggregation of heteroaggregates, shortening the migration distances of APS+NAC and BPS+NAC to 262 and 552 m, respectively. Particle interactions mainly involved van der Waals attraction, electrostatic repulsion, steric hindrance, calcium bridging, π-π interactions, hydrogen bonding, and hydrophobic interactions. These findings highlight the important influence of NAC on the fate, transport, and risks of nanoplastics in aquatic environments.

Effect of background ions and physicochemical factors on the cotransport of microplastics with Cu2+ in saturated porous media

Microplastics (MPs) in subsurface environments are migratory and can carry heavy metals, increasing the extent of MP and heavy metal pollution. This study used quartz sand-filled column experiments to investigate the adsorption and cotransport behaviours of PS-MPs, O3, UV-aged PS-MPs, and Cu2+ at different MP concentrations, ionic strengths, and ionic valences in a saturated porous medium. The results showed that when MPs migrate alone in the absence of an ionic background, higher concentrations have increased mobility. In contrast, an increase in the background ion concentration or ion valence inhibits the individual transport capacity of PS-MPs. An increase in the concentration of background ions or elevation in the valence state promotes Cu2+ transport because of the action of the double electric layer on the surface of the colloid and the electrostatic repulsive forces combined with the background ions. The adsorption capacity of aged PS-MPs was stronger than that of PS-MPs because of the binding of the aged PS-MPs to Cu2+ through complexation and electrostatic attraction. In the binary system of PS-MPs/Cu2+, PS-MPs promoted Cu2+ transport and the mobility of Cu2+ loaded by PS-MPs decreased with increasing background ion concentration. The cotransport results showed that MPs promote Cu2+ transport in the following order: O3-aged Ps > UV-aged Ps > Ps, as the increasing cation concentration in the MPs and Cu2+ occupies the PS surface adsorption sites. Overall, PS is an effective carrier for Cu2+. These findings offer fresh exploration concepts for the joint migration of MPs and heavy metals in underground settings.

Photoaging-induced variations in heteroaggregation of nanoplastics and suspended sediments in aquatic environments: A case study on nanopolystyrene

Photoaging of nanoplastics (NPs) and heteroaggregate with suspended sediments (SS) determines transport processes and ecological risks of NPs in aquatic environments. This study investigated the disruption of photoaging on the heteroaggregation behavior of polystyrene NPs (PSNPs) and SS in different valence electrolyte solutions and deduced the interaction mechanisms by integrating aggregation kinetics and molecular dynamics (MD) simulation. Increasing the electrolyte concentration significantly enhanced the heteroaggregation between PSNPs and SS, and the divalent electrolytes induced the heteroaggregation more efficiently. MD simulation at the molecular level revealed that PS and SS could spontaneously form clusters, and photoaged PS has a stronger potential to fold into a dense state with SS. Photoaging for 30 d retarded heteroaggregation due to the steric hindrance produced by the leached organic matter in NaCl solutions, and the critical coagulation concentration (CCC) increased by >85.44 %. Contrarily, photoaging caused more oxygen-containing functional groups produced on the surface of PSNPs through Ca2+ bridging promoting heteroaggregation and thus destabilizing in CaCl2 solutions, the CCC decreased by 23.53 % ∼ 35.29 %. These findings provide mechanistic insight into the environmental process of NPs and SS and are crucial for a comprehensive understanding of the environmental fate and transport of NPs in aquatic environments.

Polystyrene microplastics as carriers for nano-hydroxyapatite particles: Impact of surface functionalization and mechanistic insights

The potential of microplastics (MPs) to act as carriers for contaminants or engineered nanomaterials is of rising concern. However, directly determining the vector effect of polystyrene (PS) MPs towards nano-hydroxyapatite (nHAP) particles, a typical nano phosphorus fertilizer and soil remediation material, has been rarely studied. In this study, the interaction of differentially surface functionalized PS MPs with nHAP were investigated through batch experiments under different solution chemistry conditions. The results demonstrated that nHAP had the highest attachment/adsorption affinity onto carboxyl-functionalized PS, followed by bare PS and amino-functionalized PS under near-neutral pH conditions. Adsorption of nHAP exhibited a strong pH-dependent behavior with PS MPs, increasing under acidic-neutral pH (3-7) and decreasing at higher pH values. The presence of humic acid and NaCl hindered the adsorption of nHAP onto MPs. Scanning electron microscopy observations revealed a rod-like morphology for adsorbed nHAP, which was randomly distributed on MPs surface. Surface complexation and cation-π interaction were mainly responsible for the adsorption of nHAP as revealed by multiple spectroscopic analyses. These results provide mechanistic insights into nHAP-PS interactions and expound the effect of surface functionalization of PS on binding mechanisms, and thus bring important clues for better understanding the vector effects of MPs towards nanoparticles.

Effects of microplastics on the rheological properties of sediment slurries in aquatic environments

Sediment slurries, characterized by their high concentrations of fine-grained cohesive sediment, are prevalent in various aquatic environments, including fluid mud, sediment gravity flows, and dredging slurries. Abundant microplastics have been detected in sediment slurries, which indicates that these slurries function as carriers for the transport of microplastics. However, there is a dearth of understanding on how sediment slurries transport microplastics. To ascertain the transport mechanisms, elucidating the effects of microplastics on the rheological properties of sediment slurries is a prerequisite because these properties govern the flow dynamics and mobility of such slurries. This study conducts experimental and theoretical investigations to examine, interpret, and quantify the effects of microplastics on the rheological properties of sediment slurries. Microplastics are shown to increase the yield stress and viscosity of sediment slurries via enhancing sediment aggregation. A new descriptor, specifically, the effective volume fraction, is proposed to characterize the effects of microplastics on sediment aggregation. Based on the newly-proposed descriptor, a new analytical model is proposed to predict the yield stress and viscosity of sediment slurries with microplastics. This study lays a foundation for further interpretating the flow dynamics and thus the transport processes of sediment slurries laden with microplastics.

Modified hydrothermal method for synthesizing titanium dioxide-decorated multiwalled carbon nanotube nanocomposites for the solar-driven photocatalytic degradation of dyes

This study aimed to address the issue of rapid electron-hole recombination in photocatalysis by exploiting multi-phase TiO2 decorated on multiwalled carbon nanotubes (MWCNTs) to improve the photocatalytic degradation of dyes. A simple and eco-friendly one-pot method was utilized to create the TiO2/MWCNT nanostructure using glucose as both a structure-directing agent and a carbon source without requiring any prior covalent or non-covalent functionalization of the MWCNTs at 160 °C. Furthermore, it was found that the average width of the nanocomposites changed from 20 ± 1 and 42 ± 2 nm to 56 ± 3 nm, corresponding to MWCNT contents of 1.0, 2.0, and 3.0 (wt%), respectively. Specifically, TiO2/MWCNTs with a low content of MWCNTs demonstrated enhanced performance for the photocatalytic degradation of dyes, with the bandgap of the nanocomposites decreasing to 2.5 eV with 1.0% MWCNTs and 2.4 eV with 2.0% MWCNTs. The TiO2/MWCNT-1.0 catalyst demonstrated high photocatalytic efficiency for methylene blue (MB) degradation with a rate constant of 0.0051 min-1. TiO2/MWCNT-2.0 was more effective for rhodamine (RhB) degradation than pristine TiO2, with a rate constant of 0.0065 min-1 within 120 min of solar-light exposure. This novel modified approach can be used to synthesize nanocomposites simply and is potentially feasible for efficient dye degradation and beyond, offering a promising solution for water-pollution treatment.

Modeling the settling and resuspension of microplastics in rivers: Effect of particle properties and flow conditions

Microplastics have numerous different shapes, affecting the fate and transport of these particles in the environment. However, theoretical models generally assume microplastics to be spherical. This study aims to develop a modeling approach that incorporates the shapes of microplastics to investigate the vertical transport of microplastics in rivers and simulate the effect of particle and flow characteristics on settling and resuspension. To achieve these aims, a mechanistic model was developed utilizing the mass-balance and hydrodynamic equations. Scenario analysis was implemented assigning different values to model parameters, such as bed shear stress, shape factor and particle size to simulate the effect of flow patterns and particle properties. The model outcomes revealed that the residence time of microplastics in the water column was longest in medium bed shear stress, whilst it was shortest in low bed shear stress. This suggests that the influence of turbulence is not unidirectional; it can both increase and decrease microplastic concentrations and residence time in the water column. According to the scenario analysis, the settling flux of microplastics was the highest for near-spherical particles and increased with the size of the particles, as well as with increasing bed shear stress. However, the resuspension of particles was primarily influenced by increasing bed shear stress, but the ranking of resuspension flux values for different shaped and sized microplastics exhibited alterations with changing flow patterns. Turbulent conditions predominantly influenced the resuspension of near-spheres and large microplastics. On the contrary, the settling of fibers and small microplastics were significantly influenced by changing flow patterns, whereas near-spheres and largest particles were least affected. The model results were sensitive to changes in shape factor developed for this model, therefore this parameter should be improved in future studies.

Distribution of microplastics in Lanzhou section of the Yellow River: Characteristics, ecological risk assessment, and factors analysis

Microplastic (MP) is an emerging pollutant that has attracted attention in the environmental field, and the research of MPs in freshwater systems needs to be strengthened. To characterize the MPs in surface water and sediments of the western urban river network, water and sediment samples were collected. The results showed that the abundance of MPs in the water body of the river network ranged from 7 to 172 n/L, whereas the abundance of MPs in the sediments ranged from 7 to 144 n/kg, and the average abundance in the dry season was significantly higher than that in the rainy season. The majority of MPs (83.67 %) were < 1 mm and fibrous. The most commonly identified types of MPs were PET and PP, while the color blue was frequently observed. MPs have the potential to vertically migrate in sediments, with size, shape, density, and hydrodynamic forces being the main factors that contribute to this process. Correlation analysis results revealed that anthropogenic and meteorological factors, including precipitation, atmospheric conditions, and population density, had a discernible impact on the abundance, size, and shape of MPs. The ecological risk of MPs was assessed using the Polymer Hazardous Index (PHI), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI) methods, and the results showed that the overall ecological risk of the Lanzhou section of the Yellow River was low. This study can provide a scientific basis for monitoring and risk assessment of emerging contaminants such as MPs in the river environment.

Microplastics and heavy metal contamination along a land-use gradient in a Himalayan foothill river: Prevalence and controlling factors

The co-occurrence of microplastics (MPs) and heavy metals in aquatic systems has raised significant concerns, yet their relationship in freshwater ecosystems remains poorly understood. This study aims to evaluate the prevalence of MPs and factors controlling their distribution in both water and sediment in the Markanda River, Northwest India. MPs were extracted from sediment and water samples using density separation and classified through fluorescence microscopy and Raman spectroscopy. Metal concentrations in river water samples were analyzed using ICP-MS, and their correlation with MP abundance was explored. The results indicated the widespread occurrence of MP pollution across the Markanda River basin, with particle concentrations ranging from 10 to 530 particles L-1 in surface water and 1330-4330 particles kg-1 dry weight (dw) in sediment samples. The variability in MP abundance at sampling sites along the Markanda River courses results from factors such as the proximity of industrial establishments and human habitation, while the influence of grain size on MP distribution appears to be limited. Pellets (88.5 %) and fragments (8.5 %) were the most abundant types of MPs, with polyethylene (45.45 %) and polystyrene (30.9 %) being the dominant forms in water samples. The ICP-MS analysis of heavy metals in water samples indicated elevated levels of As (1.67 to 32.31 ppb) in downstream areas of the river system, influenced by human activities. While metals exhibited correlation with each other, there was a weak association, except for As, with the levels of MPs in the Markanda River. The SEM-EDX analyses to characterize chemical elements absorbed onto the surface of MP showed distinct variations in upstream and downstream sites, with the presence of elements such as Mn, Ni, Cr, Zn, As, Se, and Cu found in downstream areas. We conclude that MPs contaminated with heavy metals potentially threaten the ecological security of freshwater aquatic systems and highlight the importance of management action to reduce plastic pollution worldwide.

Distribution characteristics and ecological risk analysis of microplastics in sediments and effluents related to offshore oil and gas activities in the Bohai Sea, China

Oil and gas activities are sources of marine microplastics (MPs) but have received less attention globally. This study assessed the distribution characteristics and ecological risks of MPs in 31 sediment samples and effluent samples of 5 oil and gas platforms related to offshore oil and gas activities in the Bohai Sea. The results showed that the mean abundance of MPs in sediment, produced water, and domestic sewage was 205.7 ± 151.5 items/kg d.w., 18 ± 11 items/L, and 26 ± 39 items/L, respectively. The MPs in sediments and effluents were dominated by transparent, rayon, and fibers <1 mm. Oil and gas activities may influence the abundance of MPs in the sediments. The sediments in the area were at a low level of risk, but some samples exhibited indexes beyond low levels. The mass of MPs carried by the effluents from oil and gas platforms in the Bohai Sea was less than that of other sources.

Are mixtures of micro/nanoplastics more toxic than individual micro or nanoplastic contamination in the clam Ruditapes decussatus?

The abundance of micro (MPs) and nano (NPs) sized plastic particles in the ocean is concerning due to their harmful effects on marine life. The interactions between MPs and NPs in the marine environment and their impact on marine biota remain not fully understood. This study contributes with new insights into the interaction between polystyrene NPs (PSNPs) and polyethylene MPs (PEMPs) on the clam Ruditapes decussatus. Results showed ingestion of MPs and NPs by clams, with PSNPs demonstrating higher toxicity in hemolymph. While no genotoxicity was observed, clams treated with MPs and the mixture showed increased acetylcolinesterase (AchE) activity over time. Additionally, the antioxidant defense system mitigated oxidative stress, suggesting effective neutralization of reactive oxygen species. Hazard assessment indicated the greatest impact on clam digestive glands after ten days of exposure, with an antagonistic interaction between MPs and NPs noted.

Response of microbial communities and biogeochemical cycling functions to sediment physicochemical properties and microplastic pollution under damming and water diversion projects

Understanding the interactions among flow-sediment, microorganisms, and biogeochemical cycles is crucial for comprehending the ecological response mechanisms of dams and water diversion. This study focused on the spatial patterns of carbon, nitrogen, phosphorus, and sulfur (CNPS) cycle functional genes in the water resource for the middle route of the South-to-North Water Diversion Project in China, specifically the Danjiangkou Reservoir (comprising the Han and Dan reservoirs). The investigation incorporated sediment physicochemical properties and microplastic pollution. Numerous microbial species were identified, revealing that microbial communities demonstrated sensitivity to changes in sedimentary mud content. The communities exhibited greater β diversity due to finer sediment particles in the Han Reservoir (HR), whereas in the Dan Reservoir (DR), despite having higher sediment nutrient content and MPs pollution, did not display this pattern. Regarding the composition and structure of microbial communities, the study highlighted that sediment N and P content had a more significant influence compared to particle size and MPs. The quantitative microbial element cycling (QMEC) results confirmed the presence of extensive chemolithotrophic microbes and strong nitrogen cycle activity stemming from long-term water storage and diversion operations. The denitrification intensity in the HR surpassed that of the DR. Notably, near the pre-dam area, biological nitrogen fixation, phosphorus removal, and sulfur reduction exhibited noticeable increases. Dam construction refined sediment, fostering the growth of different biogeochemical cycling bacteria and increasing the abundance of CNPS cycling genes. Furthermore, the presence of MPs exhibited a positive correlation with S cycling genes and a negative correlation with C and N cycling genes. These findings suggest that variations in flow-sediment dynamics and MPs pollution have significant impact the biogeochemical cycle of the reservoir.

Differences of microplastics and nanoplastics in urban waters: Environmental behaviors, hazards, and removal

Microplastics (MPs) and nanoplastics (NPs) are ubiquitous in the aquatic environment and have caused widespread concerns globally due to their potential hazards to humans. Especially, NPs have smaller sizes and higher penetrability, and therefore can penetrate the human barrier more easily and may pose potentially higher risks than MPs. Currently, most reviews have overlooked the differences between MPs and NPs and conflated them in the discussions. This review compared the differences in physicochemical properties and environmental behaviors of MPs and NPs. Commonly used techniques for removing MPs and NPs currently employed by wastewater treatment plants and drinking water treatment plants were summarized, and their weaknesses were analyzed. We further comprehensively reviewed the latest technological advances (e.g., emerging coagulants, new filters, novel membrane materials, photocatalysis, Fenton, ozone, and persulfate oxidation) for the separation and degradation of MPs and NPs. Microplastics are more easily removed than NPs through separation processes, while NPs are more easily degraded than MPs through advanced oxidation processes. The operational parameters, efficiency, and potential governing mechanisms of various technologies as well as their advantages and disadvantages were also analyzed in detail. Appropriate technology should be selected based on environmental conditions and plastic size and type. Finally, current challenges and prospects in the detection, toxicity assessment, and removal of MPs and NPs were proposed. This review intends to clarify the differences between MPs and NPs and provide guidance for removing MPs and NPs from urban water systems.

Heteroaggregation kinetics of oppositely charged nanoplastics in aquatic environments: Effects of particle ratio, solution chemistry, and interaction sequence

Interactions between positively charged amino-modified (APS) and negatively charged bare (BPS) polystyrene nanoplastics may cause heteroaggregation in aquatic environments. This study investigated the effects of particle concentration ratio, solution chemistry [electrolytes, pH, and natural organic matter (NOM)], and interaction sequence on their heteroaggregation kinetics. In the absence of electrolytes and NOM, the APS/BPS ratio for attaining maximum heteroaggregation rate (khetero) increased from APS/BPS= 3/7 to APS/BPS= 1/1 as pH increased from 4 to 10, indicating that electrostatic interactions dominated heteroaggregation. In the absence of NOM, khetero ranked APS/BPS= 2/3 > APS/BPS= 1/1 > APS/BPS= 3/2. Colloidal stability decreased linearly as pH increased from 4 to 8 at APS/BPS= 1/1, while diffusion-limited heteroaggregation persisted at pH 10. In NaCl solution, humic acid (HA) retarded heteroaggregation more effectively than sodium alginate (SA) via steric hindrance and weakening electrostatic interactions, following the modified Derjaguin-Landau-Verwey-Overbeek (MDLVO) theory. Compared with simultaneous interactions among APS, BPS, NaCl, and NOM, the NOM retardation effects on heteroaggregation weakened if delaying its interaction with others. In CaCl2 solution, the effects of NOM on heteroaggregation depended on counterbalance among charge screening, steric hindrance, and calcium bridging. These findings highlight the important role of heteroaggregation between oppositely charged nanoplastics on their fate and transport in aquatic environments.

Microplastics and Co-pollutants in soil and marine environments: Sorption and desorption dynamics in unveiling invisible danger and key to ecotoxicological risk assessment

Microplastics (MPs) and their co-pollutants pose significant threats to soil and marine environments, necessitating understanding of their colonization processes to combat the plastic pandemic and protect ecosystems. MPs can act as invisible carriers, concentrating and transporting pollutants, leading to a more widespread and potentially toxic impact than the presence of either MPs or the pollutants alone. Analyzing the sorption and desorption dynamics of MPs is crucial for understanding pollutants amplification and predicting the fate and transport of pollutants in soil and marine environments. This review provides an in-depth analysis of the sorption and desorption dynamics of MPs, highlighting the importance of considering these dynamics in ecotoxicological risk assessment of MPs pollution. The review identifies limitations of current frameworks that neglect these interactions and proposes incorporating sorption and desorption data into robust frameworks to improve the ability to predict ecological risks posed by MPs and co-pollutants in soil and marine environments. However, failure to address the interplay between sorption and desorption can result in underestimation of the true impact of MPs and co-pollutants, affecting livelihoods and agro-employments, and exacerbate poverty and community disputes (SDGs 1, 2, 3, 8, 9, and 16). It can also affect food production and security (SDG 2), life below water and life on land (DSGs 14 and 15), cultural practices, and natural heritage (SDG 11.4). Hence, it is necessary to develop new approaches to ecotoxicological risk assessment that consider sorption and desorption processes in the interactions between the components in the framework to address the identified limitations.

Revealing the Freezing-Induced Alteration in Microplastic Behavior and Its Implication for the Microplastics Released from Seasonal Ice

Ice can serve as a significant temporary repository and conveyance mechanism for microplastics (MPs). MPs present in the water column can become entrapped within developing ice formations, subsequently being sequestered and transported by ice floes. With changing temperatures, MPs stored in ice can be released back into the environment, while freezing conditions can alter the properties of MPs, ultimately affecting the fate of MPs in the environment. Freezing of MPs in freshwater ice results in the aggregation of MP particles due to physical compression, leading to an increase in particle size once the MPs are released from the ice. The freezing-induced aggregation enhances buoyancy effects, accelerating the settling/rising velocity of MPs in water. Additionally, freezing can lead to enhanced surface wetting alterations, thus improving the dispersion of hydrophobic MPs. The presence of salt in the water can mitigate the effect of freezing on MPs due to the formation of a brine network within the ice structure, which reduces the pressure on MPs entrapped by ice. In cold regions, numerous MPs undergo freezing and thawing, re-entering the water column.

Confocal Surface-Enhanced Raman Imaging of the Intestinal Barrier Crossing Behavior of Model Nanoplastics in Daphnia Magna

Nanoplastics (nP) pose hazards to aquatic animals once they are ingested. Significant knowledge gaps exist regarding the nP translocation across the animal intestine, which is the first barrier between the ingested nP and the animal body. We examined the intestinal barrier crossing behavior of nP in an aquatic animal model (Daphnia magna) and determined the translocation mechanism with the help of model "core-shell" polystyrene nanoplastics (nPS) and confocal surface-enhanced Raman spectroscopy (SERS). The Raman reporter (4-mercaptobenzoic acid)-tagged gold "core" of the model nPS enables sensitive and reliable particle imaging by confocal SERS. This method detected SERS signals of model nPS concentration as low as 4.1 × 109 particles/L (equivalent to 0.27 μg/L PS "shell" concentration). The translocation was observed with the help of multilayer stacked Raman maps of SERS signals of the model nPS. With a higher concentration or longer exposure time of the model nPS, uptake and translocation of the plastic particles increased. In addition, we demonstrated that clathrin-dependent endocytosis and macropinocytosis were two major mechanisms underlying the translocation. This study contributes to a mechanistic understanding of nP translocation by using the pioneering model nPS and an analytical toolkit, which undergird further investigations into nP behavior and health effects in aquatic species.

Comparative study of polystyrene microplastic transport behavior in three different filter media: Quartz sand, zeolite, and anthracite

Microplastics (MPs) are emerging contaminants that are attracting increasing interest from researchers, and the safety of drinking water is greatly affected by their transportation during filtration. Polystyrene (PS) was selected as a representative MPs, and three filter media (quartz sand, zeolite, and anthracite) commonly found in water plants were used. The retention patterns of PS-MPs by various filter media under various background water quality conditions were methodically investigated with the aid of DLVO theory and colloidal filtration theory. The results show that the different structures and elemental compositions of the three filter media cause them to exhibit different surface roughnesses and surface potentials. A greater surface roughness of the filter media can provide more deposition sites for PS-MPs, and the greater surface roughness of zeolite and anthracite significantly enhances their ability to inhibit the migration of PS-MPs compared with that of quartz sand. However, surface roughness is not the only factor affecting the migration of MPs. The lower absolute value of the surface potential of anthracite causes the DLVO energy between it and PS-MPs to be significantly lower than that between zeolite and PS-MPs, which results in stronger retention of PS-MPs by anthracite, which has a lower surface roughness, than zeolite, which has a higher surface roughness. The transport of PS-MPs in the medium is affected by the combination of the surface roughness of the filter media and the DLVO energy. Under the same operating conditions, the retention efficiencies of the three filter materials for PS-MPs followed the order of quartz sand < zeolite < anthracite. Additionally, the conditions of the solution markedly influenced the transport ability of PS-MPs within the simulated filter column. The transport PS-MPs in the simulated filter column decreased with increasing solution ionic strength and cation valence. Naturally, dissolved organic matter promoted the transfer of PS-MPs in the filter layer, and humic acid had a much stronger facilitating impact than fulvic acid. The study findings might offer helpful insight for improving the ability of filter units ability to retain MPs.

Understanding microplastic presence in different wastewater treatment processes: Removal efficiency and source identification

Municipal effluents discharged from wastewater treatment plants (WWTPs) are a considerable source of microplastics in the environment. The dynamic profiles of microplastics in treatment units in WWTPs with different treatment processes remain unclear. This study quantitatively analyzed microplastics in wastewater samples collected from different treatment units in two tertiary treatment plants with distinct processes. The influents contained an average of 15.5 ± 3.5 particles/L and 38.5 ± 2.5 particles/L in the two WWTPs with in the oxidation ditch process and the integrated fixed-film activated sludge process, respectively. Interestingly, microplastic concentrations in the influent were more influenced by the population density in the served area than sewage volume or served population equivalent. Throughout the treatment process, concentrations were reduced to 1.5 ± 0.5 particles/L and 1.0 ± 1.0 particles/L in the final effluents, representing an overall decrease of 90% and 97%, in WWTPs with the oxidation ditch process and integrated fixed-film activated sludge process, respectively. A significant proportion of the microplastics were removed during the primary treatment stage in both WWTPs, with better performance for foam, film, line-shaped and large-sized microplastics. Most microplastics were accumulated in activated sludge, indicating its key role as the primary sink in WWTPs. The multiple correspondence analysis identified laundry washing and daily necessities such as packaging and containers as the major contributors to microplastics in WWTPs. The study proposed recommendations for upgrading WWTPs, modifying designs, and implementing strategies to reduce microplastic sources, aiming to minimize the release of microplastics into the environment. These findings can shed lights on the sources of microplastics in WWTPs, and advance our understanding of the mechanisms for more effective microplastic removals in wastewater treatment technologies in future applications.

Toxicological review of micro- and nano-plastics in aquatic environments: Risks to ecosystems, food web dynamics and human health

The increase of micro- and nano-plastics (MNPs) in aquatic environments has become a significant concern due to their potential toxicological effects on ecosystems, food web dynamics, and human health. These plastic particles emerge from a range of sources, such as the breakdown of larger plastic waste, consumer products, and industrial outputs. This review provides a detailed report of the transmission and dangers of MNPs in aquatic ecosystems, environmental behavior, and interactions within aquatic food webs, emphasizing their toxic impact on marine life. It explores the relationship between particle size and toxicity, their distribution in different tissues, and the process of trophic transfer through the food web. MNPs, once consumed, can be found in various organs, including the digestive system, gills, and liver. Their consumption by lower trophic level organisms facilitates their progression up the food chain, potentially leading to bioaccumulation and biomagnification, thereby posing substantial risks to the health, reproduction, and behavior of aquatic species. This work also explores how MNPs, through their persistence and bioaccumulation, pose risks to aquatic biodiversity and disrupt trophic relationships. The review also addresses the implications of MNPs for human health, particularly through the consumption of contaminated seafood, highlighting the direct and indirect pathways through which humans are exposed to these pollutants. Furthermore, the review highlights the recommendations for future research directions, emphasizing the integration of ecological, toxicological, and human health studies to inform risk assessments and develop mitigation strategies to address the global challenge of plastic pollution in aquatic environments.