Preparation and application of metal-modified biochar in the purification of micro-polystyrene polluted aqueous environment

Microplastic pollution inhibits the phagocytosis of E. coli by earthworm immune cells in soil

It has not been known how immune responses in soil invertebrates occur against microplastics (MPs). This study aims to investigate the effects of MPs on endocytosis, including phagocytosis and pinocytosis, of immune cells of soil invertebrates in the soil ecosystem in the process of bacterial infection. We employed polystyrene microplastics (∼ 1 μm PS MPs) to treat earthworm Eisenia andrei during the infection of Escherichia coli for in vitro (1, 5, 10, and 50 mg/L) and in vivo (1, 10, and 1000 mg/kg dry soil) assays. The results of in vitro migration assay revealed that MPs caused inhibitory effects on the phagocytosis, pinocytosis and oxidative stress in coelomocytes. Soil bioassay also confirmed that endocytosis of coelomocytes and mitochondrial damages in the intestinal epithelium were significantly altered in the polluted soil with MPs. Thus, MPs induced adverse effects to inhibit bacterial endocytosis, which may disturb the immune system of soil invertebrates. This study is the first report on the inhibition of phagocytosis in the soil invertebrates by MPs. These findings contribute to understanding the response of soil invertebrates, which play important roles in the soil food web with cellular level towards microplastic pollution in soil.

Micro(nano)plastics (< 4 μm): An important but ignored concern during intravenous infusion

Micro(nano)plastics (MNPs) have been observed in human blood, and atheroma, and they are associated with cardiovascular events. However, their sources remain poorly understood. Intravenous infusion products (IVIPs) might introduce MNPs directly into the human blood, which threatens health, but they remain unknown. Herein, simulated intravenous therapy was performed to detect multiple MNPs with sizes < 4 μm released from commonly used IVIPs through established analytical methods such as modified Raman spectroscopy and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDS). Results showed that polypropylene- and polyvinyl chloride- MNPs were identified from six different IVIPs during intravenous therapy via modified Raman spectroscopy. Furthermore, SEM-EDS analysis observed irregular or near-spherical MNPs ranging from 10 nm to 3.6 μm, with a number concentration of (5.82 ± 0.86) × 104 items/L during intravenous therapy. These MNPs could directly enter the human blood with infusion fluids via intravenous therapy, posing serious risks to human health and affecting the safe use of IVIPs. Overall, these findings revealed that intravenous therapy could introduce MNPs, especially nanoplastics, directly into the human blood, highlighting the importance of considering MNPs in evaluating the safety of IVIPs.

Size-matching effects in quantitative detection of PS nanoplastics using controllable and reusable Ag nanoarrays SERS substrates

This study proposes a strategy for the highly sensitive detection of polystyrene nanoplastics (PS NPs) with varying particle sizes. Ag nanoarrays (AgNAs) with different inter-column spacings and heights are fabricated via thermal deposition of Ag in anodized aluminum oxide (AAO) templates. The size-matching effects between PS NPs and the parameters of the AgNAs (inter-column spacing and height) are investigated. Utilizing this size-matching effect, the AgNAs substrate enables sensitive detection of PS NPs with particle sizes of 130 nm, 180 nm, and 230 nm, with limits of detection (LODs) of 10 μg/mL. In real water samples (river water, rainwater, and tap water), the AgNAs substrate also demonstrates good performance, achieving a LOD of 10 μg/mL for detecting 130 nm PS NPs. Additionally, toluene is used to remove PS NPs from the AgNAs surface, allowing the substrate to be reused across multiple cycles. After at least 30 detection cycles, the surface-enhanced Raman scattering (SERS) performance of the AgNAs shows no significant decline, with a relative standard deviation (RSD) of 6.8 %. The AgNAs exhibit excellent stability and reusability in detecting PS NPs, indicating strong potential for practical applications.

Key adsorbents and influencing factors in the adsorption of micro- and nanoplastics: A review

Microplastics and nanoplastics (MNPs) are emerging contaminants in drinking water sources that pose serious risks to human health and ecosystems. Several removal strategies, such as adsorption, exist but present challenges for their industrial scalability. This review provides a concise overview of MNP adsorption mechanisms and highlights the limited but critical exploration of column adsorption in the literature, emphasizing its importance for large-scale applications. Special attention is given to carbon-based materials due to their cost-effectiveness, environmental friendliness and sustainability. Other adsorbents (e.g., metal-organic frameworks, clays) are also discussed for their promising performance in realistic water matrixes. To predict and optimize the efficiency of adsorbents, leading simulation models are reviewed. Taken together, this work provides a comprehensive overview of the fundamental factors, such as adsorption mechanisms, adsorbent selection and experimental conditions, to optimize MNP adsorption. By highlighting the underexplored area of column-based processes, it provides valuable information to advance adsorption as a viable industrial-scale solution for MNP contamination.

Significant microplastic accumulation and burial in the intertidal sedimentary environments of the Yellow River Delta

Estuarine intertidal habitats provide a dynamic and distinctive environment for the transport of microplastics, yet their migration and accumulation in these areas remain poorly understood. Herein, the spatial distribution patterns of microplastics in the estuarine sedimentary environment of the Yellow River Delta were investigated across elevation and depth gradients. Compared to the subtidal and supratidal zones, the estuarine intertidal zone exhibited the highest microplastic abundance in sediment (1027 ± 29 items/kg). Sediment cores revealed that the highest microplastic abundance occurred at a depth of 5-10 cm. The evolution of microplastic size and morphology characteristics with sediment depth indicates vertical transport of microplastics in estuarine sediments. The strong correlations between organic matter, silt content, and microplastics abundance in estuarine sediments suggested significant impacts of tidal hydrodynamics and sediment characteristics on microplastic migration processes. Estimates indicated that microplastic burial in the deeper sediments (638.7 tons in the 5-30 cm layer) was 1.96 times greater than that in the upper layers. Distinct variations in the carbonyl index across habitats suggested that tidal-induced dynamic redox conditions in the intertidal zone promoted both biotic and abiotic aging processes of microplastics. This study provides new insights into the environmental behavior and long-term fate of microplastics in estuarine intertidal sedimentary environments.

Efficient removal performance of polystyrene microplastics from strongly acidic solutions by two functionalized nanosized biochars derived from low-cost sustainable sources

Microplastic pollution in aquatic systems and other environments has garnered significant concern due to its persistence, widespread environmental migration, and detrimental impact on entire ecosystems. Such pollution type poses severe threats to human life quality, as well as flora and fauna. In response to this pressing global issue, the current research explores a simple, sustainable, and cost-effective solution by employing two newly modified nanobiochar materials with oxalic acid, for the adsorptive removing of polystyrene microplastics (PSMPs) from aquatic systems. The two nanobiochars were derived from sustainable and low-cost feedstocks, specifically pineapple and artichoke wastes via pyrolysis at 300 °C and 350 °C, yielding NBP and NBA, respectively. These were subsequently modified with oxalic acid (OA) to create OA@NBP and OA@NBA nanobiosorbents. The EDX analysis confirmed the primary elemental composition of carbon, oxygen, nitrogen, calcium, and magnesium. TEM analysis revealed distinct differences in particle size and morphology of OA@NBA which displayed small particles ranging from 9.81 to 16.15 nm, while OA@NBP exhibited larger particles with size ranging from 68.86 to 105.12 nm, highlighting their structural differences. OA@NBP and OA@NBA nanobiosorbents were evaluated in PSMPs removing from aquatic systems providing the optimum conditions 30-50 mg nanobiosorbent, 40 min time and pH 2.0. The adsorption and binding mechanisms were best fitted to pseudo-second-order kinetics and Langmuir-Freundlich models. Thermodynamic analysis revealed that the adsorption process was non-spontaneous and endothermic. The loaded PSMPs on OA@NBA and OA@NBP nanobiosorbents were successfully regenerated and successively used to remove PSMPs with 86.8 % and 89.5 %, respectively, after the first regeneration step. Additionally, the two nanobiosorbents demonstrated excellent PSMPs removal efficiencies in simulated seawater samples adjusted to pH 2.0, achieving removal rates of 93.4 % (OA@NBA) and 87.4 % (OA@NBP). Therefore, the characterized PSMPs removal performance at pH 2.0 can afford a good avenue for potential application of the two explored nanobiosorbents in effective removal of PSMPs pollutant from other acidic industrial wastewater matrices.

Size-dependent selectivity and quantification on detecting PS nanoplastics particles in a mixed solution with different diameters by using periodic Ag nanocavities SERS substrates with high sensitivity

Nanoplastic particles (NPPs) have attracted lots of attention due to their toxicity. In this study, a Surface-enhanced Raman scattering (SERS)-based category on selectivity and quantification detecting the polystyrene (PS) NPPs has been presented. Firstly, the size-dependent SERS relationship between the diameter of Ag nanocavities (AgNCAs) and the diameter of the PS NPPs is studied. By continuously dripping the PS NPPs on proposed AgNCAs substrates, AgNCAs exhibit excellent enrichment capability with a promoted limit of detection (LOD) of 0.001 mg/mL. Secondly, thermally evaporated Ag nanoparticles (AgNPs) as an enhancement layer are used to form the AgNPs/PS NPPs/AgNCAs sandwich structure with a SERS enhancement of 300 %. Thirdly, a SERS microfluidic chip constructed by integrating two kinds of pore size (87 nm and 356 nm) AgNCAs is fabricated to selectivity quantifying absolute concentration of the mixed PS NPPs with different diameters in a mixed solution. It shows excellent performance. This novel category proves a good method for identifying plastic nanoparticles and analyzing their size distribution existing in the surroundings indicating good practical applications.

Biochar in the Remediation of Organic Pollutants in Water: A Review of Polycyclic Aromatic Hydrocarbon and Pesticide Removal

This review explores biochar's potential as a sustainable and cost-effective solution for remediating organic pollutants, particularly polycyclic aromatic hydrocarbons (PAHs) and pesticides, in water. Biochar, a carbon-rich material produced from biomass pyrolysis, has demonstrated adsorption efficiencies exceeding 90% under optimal conditions, depending on the feedstock type, pyrolysis temperature, and functionalization. High surface area (up to 1500 m2/g), porosity, and modifiable surface functional groups make biochar effective in adsorbing a wide range of contaminants, including toxic metals, organic pollutants, and nutrients. Recent advancements in biochar production, such as chemical activation and post-treatment modifications, have enhanced adsorption capacities, with engineered biochar achieving superior performance in treating industrial, municipal, and agricultural effluents. However, scaling up biochar applications from laboratory research to field-scale wastewater treatment poses significant challenges. These include inconsistencies in adsorption performance under variable environmental conditions, the high cost of large-scale biochar production, logistical challenges in handling and deploying biochar at scale, and the need for integration with existing treatment systems. Such challenges impact the practical implementation of biochar-based remediation technologies, requiring further investigation into cost-effective production methods, long-term performance assessments, and field-level optimization strategies. This review underscores the importance of addressing these barriers and highlights biochar's potential to offer a sustainable, environmentally friendly, and economically viable solution for large-scale wastewater treatment.

Efficient removal of nanoplastics by iron-modified biochar: Understanding the removal mechanisms

Tiny plastic particles, particularly nanoplastics, are becoming major threats to aquatic and biotic life owing to their unique physico-chemical characteristics. Thus, in the present work, biochar (BC) was fabricated using "Ulva prolifera green tide" as a biowaste raw material by slow pyrolysis technique to examine its potential in removing nanoplastics from the environment. The findings depicted that nanoplastics removal efficiency by BC was V-shaped with initial pH increased from 2 to 11, and the main removal mechanism changed from adsorption to heterogeneous aggregation between nanoplastics, biochar colloids, and leached substances from BC. When the solution pH crossed the pHpzc of BC (2.3), the aggregation kinetics were well-fitted by the logistic model and displayed as an S-shaped curve with a lag period. Characterization results indicated that biochar colloids were the key enabler with a critical concentration of 72.01 mg L-1 at neutral pH. Keeping in mind the removal mechanisms and contribution of biochar colloids, iron-modified biochar (Fe-BC) was produced to enhance the overall removal efficiency. The Fe-BC demonstrated a two-phase removal process of pre-adsorption and post-aggregation, successfully realized to minimize lag time and enhance aggregation performance. The theoretical removal capacity of Fe-BC against nanoplastics could reach up to 1626.3 mg g-1, which was three-fold higher than that of BC. Further, the Fe-BC was suggested to be recycled and reused at least three times by ultrasound, followed by co-pyrolysis for green and efficient degradation of nanoplastics. Overall, the findings offer a promising approach for removing and recycling nanoplastics in the environment.

Molecular properties of dissolved organic matter leached from microplastics during photoaging process

The occurrence of dissolved organic matter (DOM) derived from microplastics (MPs) and its effect on aquatic systems has attracted great interest recently. However, the photoaging effect on the molecular structure of MP-derived DOM (MP-DOM) remains unclear. This paper presents the characteristics of DOM leached from three commercial MPs, i.e., polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) under UV irradiation. With prolonged aging periods, the surface roughness and oxygen-containing groups on the surface of MPs increase as more DOM leachate is generated. Moreover, the dissolved organic carbon (DOC) content of the leached DOM from PET MPs varies from 0.52 mg/L to 2.25 mg/L, which is higher than PE and PP MPs, due to the larger increased surface reaction area and the cleavage of the benzene ring. According to the excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), the plastic-derived protein/phenolic-like components (C1 and C3) in MP-DOM were changed into photo-induced humic-like components (C2), which were closely related to the intermediates during photo-oxidation. High-performance liquid chromatography-mass spectrometry (HPLC-MS) analysis further identified that the highest proportion of antioxidants (24.8 %∼34.6 %) was contained in MP-DOM. Plasticizers, intermediate additives, and antimicrobial agents were also detected in DOM leachate. Correlation analysis identified that the composition of leached DOM was positively correlated with the surface roughness, the carbonyl index (CI), and the chemical groups of MPs. Moreover, a partial least square structural equation model (PLS-SEM) analysis further verified that the change of morphology and the chemical structure of MPs could affect the DOM structures and fractions directly. This study provides an in-depth understanding of the composition of MP-derived DOM during the aging process, as well as a comprehensive environmental impact assessment of MPs.

Eco-friendly, stable, and high-performance biochar prepared by a twice-modification scheme: Saccharification of raw materials & thermal air oxidation of biochar

Organic pollutants, such as phenolic compounds, pose significant risks to both the environment and human health. While biochar is an effective adsorbent for removing these pollutants, its dissolved solid (DS) components can lead to the loss of functional groups, structural disintegration, unstable performance, and environmental issues. This study introduces a twice-modification scheme designed to produce a biochar (BC-M) that combines high stability with superior performance. The process begins with the preparation of a stable biochar from cellulase-treated lignocellulose. This precursor biochar is then subjected to thermal air oxidation to enhance its oxygen-containing functional groups, thereby improving its adsorption capabilities. A mathematical model was developed to explore the relationship between different thermal air oxidation conditions and the properties of BC-M, aiming to optimize both adsorption capacity and DS. The model's multi-objective optimization indicated the optimal modification conditions. Compared to unmodified biochar (BC-O), BC-M showed significant improvements: its specific surface area increased by 63.6%, pore volume by 139%, and functional groups by 50%-1271%. Notably, the DS of BC-M was reduced to just 1.08 mg/L, representing a 97.5% reduction from BC-O, with a minimal mass loss of only 0.78 ± 0.45% during modification. BC-M also demonstrated a remarkable enhancement in the adsorption of phenolic compounds, with a capacity 21%-2408% higher than BC-O. Furthermore, calculations indicated that BC-M could reduce carbon emissions by 0.70 t CO2/yr/t, outperforming activated carbon in this regard. This study offers valuable insights into biochar modification, providing a low-cost, high-stability, and high-efficiency alternative for environmental cleanup.

Enrichment of Nanoplastics in Waters Using Magnetic Solid Phase Extraction With Magnetic Biochar Adsorbents and Their Determination by Pyrolysis Gas Chromatography-Mass Spectrometry

Nanoplastics (NPs) are emerging water contaminants that threaten human health and ecological security. Developing a method for detecting NPs is significant because of their biological toxicity and mobility. In this study, magnetic solid-phase extraction (MSPE) combined with pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) was used for the pretreatment and qualitative detection of NPs in complex matrices to avoid sample dissolution and eluent usages. The developed methodology can quickly achieve low detection limits in tap and river water, with 0.7283 and 0.6474 µg/L, respectively. To enrich NPs in water, magnetic biochars derived from cornstalks (Fe3O4/BCs, i.e., Fe3O4/YMG and Fe3O4/YMG-ZnCl2) were conveniently fabricated using activation and coprecipitation methods and employed as adsorbents for MSPE. The results indicated that the incorporation of Fe3O4 into BC not only rendered it magnetic but also enhanced the diversity of its surface functional groups and adsorption sites, making it suitable for MSPE. Fe3O4/YMG-ZnCl2 demonstrated excellent extraction and enrichment capacity for polystyrene NPs (PSNPs) over various competitive species. Additionally, it exhibited good resistance to pH and anions, and its reaction mechanism was verified using adsorption kinetics and isothermal models. In addition, after extracting PSNPs from tap and river water using Fe3O4/YMG-ZnCl2, they were successfully qualitatively analyzed by Py-GC/MS.

Effective removal of microplastics by filamentous algae and its magnetic biochar: Performance and mechanism

In recent years, filamentous algae blooms and microplastics (MPs) pollution have become two major ecological and environmental problems in urban water systems. In order to solve these two problems at the same time, this study explored the loading capacity of MPs on fresh filamentous algae, and successfully synthesized magnetic filamentous algae biochar loading with Fe3O4 by hydrothermal method, with the purpose of removing MPs from water. The magnetic filamentous algal biochar was characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and so on. Experiments on adsorption kinetics, adsorption isotherms and optimum pH were carried out to explore the adsorption mechanism of MPs on magnetic filamentous algal biochar. The adsorption kinetics and adsorption isotherm models were evaluated, and the selection criterion for the appropriate model was determined by using the residual sum of squares (RSS) and Bayesian information criterion (BIC). Microscope images revealed that fresh filamentous algae could interact with MPs in the form of entanglement, adhesion and encapsulation. The average load of MPs in filamentous algae samples was 14.1 ± 5 items/g dry weight. The theoretical maximum adsorption capacities of polystyrene MPs (PS-MPs) by raw biochar (A500) and magnetic biochar with Fe3O4 (M2A500) were 176.99 mg/g and 215.58 mg/g, respectively. The adsorbent materials gave better reusability because they could be reused up to five times. Overall, these findings have provided new insights into the use of filamentous algae for in situ remediation of fluvial MPs pollution, as well as feasible strategies for the recycling of algal waste.

Microplastic pollutants in water: A comprehensive review on their remediation by adsorption using various adsorbents

Microplastics (MPs), as emerging pollutants, have attracted the attention of environmentalists, statespersons, and the scientific community over the last few decades. To address the spread of MPs in the environment, it is imperative to develop various removal techniques and materials that are effective, scalable, and ecologically benign. However, to the best of our knowledge, no review has systematically examined the removal of MPs using adsorption or provided an in-depth discussion on various adsorbents. Adsorption is an inexpensive and effective technology for wastewater treatment. Recently, many researchers have conducted studies on MP remediation using diverse adsorbent materials, such as biochar, activated carbon, sponges, carbon nanotubes, metal-layered oxides, metal-organic frameworks (MOFs), and zeolites. Each adsorbent has advantages and disadvantages. To overcome their disadvantages, researchers have been designing and developing hybrid adsorbents for MP remediation. This review provides insights into these individual adsorbents and also discusses hybrid adsorbents for MP removal. Finally, the review elaborates on future possibilities and ways to enable more efficient, scalable, and environmentally friendly MP cleanup. Overall, this review bridges the gap between contemporary MP remediation using adsorption techniques and adsorbent development.