Biosorption of sub-micron-sized polystyrene microplastics using bacterial biofilms

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.

Addressing plastic pollution: A 3D-printed porous PAC scaffold for effective nanoplastic removal

The extensive presence of nanoplastics has raised concerns about their effects on ecosystems and human health. Because of the heightened ecological and biological risks posed by nanoplastics, effective removal strategies for these particles are essential. This study focuses on the use of additive manufacturing techniques to fabricate a three-dimensional (3D) structure with integrated powdered activated carbon (PAC) as an active adsorbent for the removal of various types of polymer nanoplastics. The 3D-printed porous PAC scaffold was characterized using various analysis methods, and its adsorption kinetics and mechanisms for polystyrene (PS) nanoplastics were elucidated. The 3D PAC's versatility was verified against several other nanoplastics, including polyethylene terephthalate, low-density polyethylene, polypropylene, and polyvinyl chloride. The results demonstrated that the 3D PAC scaffold effectively adsorbs PS nanoplastics through pore filling and chemical processes and that the adsorption exhibits pseudo-first-order kinetics and conforms to the Langmuir isotherm model. The 3D PAC maintained its adsorption performance under various environmental conditions and exhibited promising results when used to remove nanoplastics from real freshwater samples. This research demonstrates the potential of 3D-printed PACs to address the growing challenge of plastic pollution.

Effect of solution pH on nanoplastic adsorption onto soil particle surface and the aggregation of soil particles

Nanoplastics (NPs) are increasingly recognized as an emerging threat to the geospheric environment, and the movement behavior of NPs in the geospheric environment should be clarified. The aggregation properties of NPs, their adsorption onto soil particle surfaces, and the aggregation properties of soil particles with adsorbed NPs are considered to affect their mobility in soil; however, these processes remain unclear. Here, polystyrene (PS) NP suspensions were agitated at pH 4, 7, and 10, and aggregate size of the PSNP was measured to clarify its homo-aggregation behavior. Additionally, batch experiments were conducted using PSNPs, fine sand, and soil in solutions of pH 4, 7, and 10 to clarify the PSNP adsorption and subsequent aggregation behaviors of the soil particles. The results demonstrated that the PSNPs used in this study did not aggregate even when the solution pH was changed because the negative value of the zeta potential was sufficiently large. The PSNPs adsorbed more onto soil particles with large specific surface areas and positive zeta potentials than that onto sand particles. The zeta potentials of the soil particles and PSNPs were influenced by the solution pH. Furthermore, the adsorption of PSNPs onto soil particles changed their aggregation properties. This study contributes to the understanding of the mobility of NPs in soil; however, further studies such as water flow experiments, simulations, and the effects of NPs on the food chain are required.

Deciphering membrane biofouling induced by micro-/nano-plastics in nanofiltration: Metagenomic insights and spacer-driven mitigations

Nanofiltration (NF) is an effective process for micro-/nano-plastics (MNPs) interception, but the impact of accumulated MNPs on the microbial community structure and metabolic pathways of biofilms on NF membranes remains unclear. This provides uncertainty with respect to membrane biofouling behavior and the risks to efficient NF operations. In this study, the size-dependent (20 nm-25 μm) and concentration-dependent (0.1-50 mg·L-1) effects of MNPs on the biofouling of a NF membrane treating secondary wastewater effluent were studied. Three MNPs-tolerant, hypermetabolic and polystyrene-degradable genera (i.e., Acinetobacter, Novosphingobium and Asticcacaulis) were detected in biofilms as dominant taxonomic compositions. MNPs led to an increase of 19.3 %-76.7 % in biomass contents and a more rapid decrease in permeate flux, with 0.1 mg·L-1 of 80 nm NPs causing the most severe membrane biofouling. Metagenomic analysis revealed that MNPs upregulated enzymes involved in exopolysaccharide (ExoA/L/M/P/Q/X/Y/Z) and tyrosine (COMT, FeaB and AOC3) biosynthesis and quorum sensing (PhzF and CiaH/R), and suppressed cell motility pathways including flagellar assembly and bacterial chemotaxis. Novel types of perforated column spacer (PCS) enhanced the hydrodynamics of the membrane feed with a lower pressure drop and higher fluid velocity, introduced micro-jets and greater mass transfer inside feed channels, thus eliminating the deposition of MNPs and mitigating membrane biofouling. Overall, a greater understanding of the interaction mechanisms between MNPs and membrane biofouling in secondary effluent filtration will help develop more effective MNPs management strategies and achieve more sustainable NF operations.

Discovery and solution for microplastics: New risk carriers in food

Microplastics (MPs), as a kind of plastic particles with an equal volume size of less than 5 mm, similar to PM2.5 in the air, are causing severe contamination issues in food. Along with the food chain accumulation, they have been confirmed to appear in daily foods and cause serious health risks to the organisms. However, there were no unifying national and local policies on separating, extracting, and detecting MPs in food, which is an essential and imperative early-warning strategy. This review carefully and comprehensively summarized the validated contaminated food, physical and chemical characteristics, extraction methods, traditional and rapid detection techniques, as well as degradation methods of MPs. We thoroughly analyzed the differences among these traditional strategies, and innovatively generalized the existing rapid detection techniques for MPs. Finally, the shortcomings of existing research were discussed, and the possibility of novel rapid and intelligent detection techniques for MPs in food was proposed.

Identification and biodegradation characterization of high-density polyethylene using marine bacteria isolated from the coastal region of the Arabian Sea, at Gujarat, India

High-Density Polyethylene (HDPE) PE is one of the primary contributors of long-lasting and prolonged pollution in the environment. In this study, more than three hundred marine isolates collected off the Gujarat Sea coast were tested for HDPE plastic utilizing ability. Among fifty-one positive noted isolates, RS124 as a potential strain was identified as Micrococcus flavus (accession is PP858228) based on 16 S rRNA gene sequencing and total cellular fatty acid profiling. Initial bacterial adherence on the film surface was shown in a scanning electron microscopy (SEM) image as a key step to biodegradation. Moreover, atomic force microscopy (AFM) shows that the film surface became more fragile, damaged, and rougher than untreated films. Shifts and alterations in peak transmittance with emergence of two new shouldered peak in degraded HDPE observed by fourier transform infrared spectroscopy (FTIR) was associated to chemical and mechanical alteration. Thermogravimetric analysis (TGA) analysis designated larger difference in percent weight loss provisions thermal instability. In the enzymatic study, the highest activity of peroxidase and dehydrogenase was recorded on the 3rd and 4th weeks of treatment with strain, respectively, during co-incubation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis disclosed the presence of a distinct 19 kDa size protein, uncovering its role in the colonization of bacteria on the hydrophilic HDPE surfaces. About 1.8% weight reduction in HDPE was recorded as a result after 30 days of bio-treatment with M. flavus. Hence, the entire observed results reveal that the M. flavus RS124 could be effectively applied for the degradation of HDPE. This is the first report on M. flavus that it exhibits plastic degrading characteristic ever, which may allow for green scavenging of plastic waste.

Dose-Dependent Responses of Escherichia coli and Acinetobacter sp. to Micron-Sized Polystyrene Microplastics

Microplastics are ubiquitous environmental contaminants that can cause significant ecological damage because of their resistance to biodegradation. We evaluated the toxic effects of 1,040 nm polystyrene (PS) microplastics in two representative bacteria, Escherichia coli and Acinetobacter sp. In particular, we examined the effects of these PS microplastics on bacterial growth and viability, parameters related to oxidative stress (reactive oxygen species [ROS], lactate dehydrogenase [LDH], and malondialdehyde [MDA]), membrane integrity, and biofilm formation. An increasing concentration of PS microplastics decreased cell growth and viability in both species. These PS microplastics also decreased cell membrane integrity and increased biofilm formation in both species. Although both species exhibited adverse overall effects from PS microplastics, they had significant differences in specific indicators of oxidative stress. Correlation analysis demonstrated different correlations among measured experimental parameters (cell viability, ROS, LDH, MDA, and biofilm formation) in these two species. These results suggest that 1,040 nm PS microplastics decreased cell growth and viability by different mechanisms in E. coli and Acinetobacter sp.

Hazard assessment of airborne and foodborne biodegradable polyhydroxyalkanoates microplastics and non-biodegradable polypropylene microplastics

Microplastics (MP) are ubiquitous in the environment, and are toxic to various living organisms. Proper application of biodegradable plastics may alleviate the hazards of conventional non-biodegradable plastics. In the current study, multi-omics analyses were performed to compare the biodegradable polyhydroxyalkanoates (PHA) and non-biodegradable polypropylene (PP) MP for their toxicity on mouse liver and lung. Airborne PHA MP induced nasal microbiome dysbiosis, pulmonary microbiome alteration, pulmonary and serum metabolome disruption, and hepatic transcriptome disturbances, resulting in mild pulmonary toxicity. By contrast, airborne PP MP caused greater alterations in nasal and pulmonary microbiome, pulmonary and serum metabolome, and hepatic transcriptome, resulting in pulmonary and hepatic toxicity. Both foodborne PHA and PP MP caused intestinal microbiome dysbiosis, while foodborne PHA MP caused slighter intestinal and serum metabolome disruption, hepatic transcriptome disturbances and hepatotoxicity (e.g., lower serum aspartate aminotransferase and alanine aminotransferase) compared to foodborne PP MP. Some potential differential biomarkers were determined between PP and PHA MP exposures, i.e., nasal Allobaculum and pulmonary Alloprevotella for airborne PHA; nasal Lactobacillus and pulmonary Acinetobacter for airborne PP; intestinal Faecalibacterium for foodborne PHA; and intestinal unclassified_Erysipelatoclostridiaceae for foodborne PP. The results show that PHA MP can induce less pulmonary and hepatic toxicity compared to PP MP, suggesting PHA is a potential substitution for PP. The findings can benefit the hazard assessment of airborne and foodborne PHA and PP MP.

An in-depth analysis of microbial response to exposure to high concentrations of microplastics in anaerobic wastewater fermentation

The impact of microplastics (MPs) in anaerobic wastewater treatment on microbial metabolism is significant. Anaerobic granular sludge (AS) and biofilm (BF) are two common ways, and their responses to microplastics will have a direct impact on their application potential. This study investigated the microbial reactions of AS and BF to three types of MPs: polyethylene (PE), polyvinyl chloride (PVC), and a mixture of both (MIX). Results exhibited that MPs reduced methane output by 44.65 %, 55.89 %, and 53.18 %, elevated short-chain fatty acid (SCFA) levels by 95.93 %, 124.49 %, and 110.78 %, and lowered chemical oxygen demand (COD) removal by 28.77 %, 36.78 %, and 33.99 % for PE-MP, PVC-MP, and MIX-MP, respectively, with PVC-MP showing the greatest inhibition. Meanwhile, microplastics also facilitated the relative production of reactive oxygen species (ROS, 40.29 %-96.99 %), lactate dehydrogenase (LDH, 20.01 %-75.02 %), and adenosine triphosphate (ATP, 26.64 %-43.80 %), while reducing cytochrome c (cyt c, 23.60 %-49.02 %) and extracellular polymeric substances (EPS, 17.44 %-26.58 %). AS and BF displayed distinct enzymatic activities under MPs exposure. Correspondingly, 16S-rRNA sequencing indicated that AS was mainly involved in acetate generation by Firmicutes, while BF performed polysaccharide degradation by Bacteroidota. Metatranscriptomic analysis showed AS to be rich in acetogens (Bacillus, Syntrophobacter) and methanogens (Methanothrix, Methanobacterium), while BF contained more fermentation bacteria (Mesotoga, Lentimicrobium) and electroactive microorganisms (Clostridium, Desulfuromonas) under MIX-MP. Moreover, BF exhibited higher glycolysis gene expression, whereas AS was more active in methane metabolism, primarily through the acetoclastic methanogenic pathway's direct acetate conversion. This study provides new insights into understanding the microbial response produced by microplastics during anaerobic wastewater digestion.

Enhanced removal of microplastics from wastewater treatment plants by a novel magnetic filter

Microplastics (MPs) discharged from wastewater treatment plants (WWTPs) have emerged as serious pollutants in aquatic environments. Herein, a new magnetic filter (MFA) was prepared using an acidification-magnetization method with fly ash (FA) as the base material. The filter specifically targeted the removal of 1-μm polystyrene microspheres (PSMPs) because of the challenges they pose in filtration processes. The findings demonstrated that MFA filter exhibited superior PSMPs removal efficiency, with increases of 219%, 250%, and 288% compared to FA at flow rates of 1, 3, and 5 mL min-1, respectively. Scanning electron microscopy and other characterizations provided insights into the removal mechanisms of PSMPs using the MFA filter, which combined electrostatic attraction, π-electron conjugation, hydrogen bonding, and complexation. Environmental variables, such as solution pH, ionic strength, and dissolved organic matter, were identified as considerable influences in the removal process of PSMPs. The practical application confirmed that the MFA filter considerably promoted the elimination of MPs from the secondary treatment effluent of WWTPs without having any toxic effects on freshwater fish. Thus, this study provides a new approach to the resource utilization of FA, which would prominently promote its application prospects in MPs immobilization and removal from wastewater effluent.

Gut microbiota, a key to understanding the knowledge gaps on micro-nanoplastics-related biological effects and biodegradation

Micro-nanoplastics (MNPs) pollution as a global environmental issue has received increasing interest in recent years. MNPs can enter and accumulate in the organisms including human beings mainly via ingestion and inhalation, and large amounts of foodborne MNPs have been frequently detected in human intestinal tracts and fecal samples. MNPs regulate the structure composition and metabolic functions of gut microbiota, which may cause the imbalance of intestinal ecosystems of the hosts and further mediate the occurrence and development of various diseases. In addition, a growing number of MNPs-degrading strains have been isolated from organismal feces. MNPs-degraders colonize the plastic surfaces and form the biofilms, and the long-chain polymers of MNPs can be biologically depolymerized into short chains. In general, MNPs are gradually degraded into small molecule substances (e.g., N2, CH4, H2O, and CO2) via a series of enzymatic catalyses, mainly including biodeterioration, fragmentation, assimilation, and mineralization. In this review, we outline the current progress of MNPs effects on gut microbiota and MNPs degradation by gut microbiota, which provide a certain theoretical basis for fully understanding the knowledge gaps on MNPs-related biological effect and biodegradation.

Nanoplastic Contamination in Freshwater Biofilms Using Gel Permeation Chromatography and Plasmonic Nanogold Sensor Approaches

The worldwide contamination of aquatic ecosystems by plastics is raising concern, including their potential impacts on the base of the food chain, which has been poorly documented. This study sought to examine, for the first time, the presence of nanoplastics (NPs) in biofilms from freshwater streams/rivers. They were collected at selected polluted sites, such as the industrial sector for plastic recycling and production, miscellaneous industries, agriculture, municipal wastewaters/effluents and road runoffs. In parallel, the functional properties of sampled biofilms were determined by proteins, lipids, esterase (lipase), viscosity and oxidative stress. The results revealed that biofilms collected at the plastic industries and road runoffs contained the highest NP levels based on size exclusion chromatography, fluorescence detection and a new nanogold sensor visualization method. Examination of the chromatographic elution profiles showed increased abundance and size of NPs in the 10-150 nm size range at the polluted sites. Biofilms from the plastic industry site had elevated levels of aldehydes (oxidative stress) and lipids compared to the other sites. Biofilms collected at the municipal sites had elevated levels of proteins and esterases/lipases, with a decrease in total lipids. Biofilms collected at agriculture sites had the lowest levels of NPs in this campaign, but more samples would be needed to confirm these trends. In conclusion, biofilms represent an important sink for plastics in freshwater environments and display signs of distress upon oxidative stress.

Using Spirulina platensis as a natural biocoagulant for polystyrene removal from aqueous medium: performance, optimization, and modeling

Microplastics (MPs) are newly recognized contaminants that result from the breakdown of plastics released into aquatic environments. This study focuses on the elimination of polystyrene (PS) using S. platensis, a natural biocoagulant, from aqueous solutions. The research investigated several crucial variables, including the initial level of PS ranging from 100 to 900 mg L-1, pH levels from 4 to 10, the contact time of 20-40 min, and doses of S. platensis ranging from 50 to 250 mg L-1. The analysis of the data revealed that the quadratic model offered the best fit for the experimental results. In the present study, we utilized S. platensis as a novel natural biocoagulant to effectively eliminate PS from aqueous solutions. Process optimization was performed using a Box-Behnken design (BBD). The best-fitting model for the data was the quadratic model. The results displayed that the highest elimination of PS (81%) was occurred at a pH of 4, with a contact time of 30 min, a dose of S. platensis at 250 mg L-1, and a PS concentration of 500 mg L-1. These findings show that S. platensis has a significant effect on removing PS from the aquatic environment. Algae can serve as a convenient and eco-friendly method, replacing chemical coagulants, to effectively remove MPs from the aquatic environment.