Periphytic biofilm: An innovative approach for biodegradation of microplastics

Research progress of electrically-enhanced membrane bioreactor (EMBR) in pollutants removal and membrane fouling alleviation

Membrane bioreactor (MBR), as a biological unit for wastewater treatment, has been proven to have the advantages of simple structure and high pollutant removal rate. However, membrane fouling limits its wide application, and it is crucial to adopt effective membrane fouling control methods. As a new type of membrane fouling control technology, electrically-enhanced MBR (EMBR) has attracted more interest recently. It uses the driving force of electric field to make pollutants flocculate or move away from the membrane surface to achieve the purpose of inhibiting membrane fouling. This paper expounds the configuration of EMBR in recent years, including the location of membrane components, the way of electric field application and the selection of electrode and membrane materials, and provides the latest development information in various aspects. The enhanced effect of electric field on the removal of comprehensive and refractory pollutants is outlined in detail. And from the perspective of sludge properties (EPS, SMP, sludge particle size, zeta potential and microbial activity), the influence of electric field on sludge characteristics and the relationship between the changes of sludge properties in EMBR and membrane fouling are discussed. Moreover, the electrochemical mechanisms of electric field alleviating membrane fouling are elucidated from electrophoresis, electrostatic repulsion, electroflocculation, electroosmosis, and electrochemical oxidation, and the regeneration and stability of EMBR are assessed. The existing challenges and future research directions are also proposed. This review could provide theoretical guidance and further studies for subsequent topic, and promoting the wide engineering applications of EMBR.

Gold nanoparticles-anchored peptides enable precise colorimetric estimation of microplastics

Microplastics (MPs, particle size < 5 mm) are an emerging contaminant in aquatic environment, which have attracted increasing attention worldwide. In this study, a colorimetric method for MPs detection was developed based on gold nanoparticles (AuNPs)-anchored peptides (LCI or TA2), which are able to specifically recognize and adhere to polypropylene (PP) or polystyrene (PS). The AuNPs-anchored peptides accumulated on the surface of MPs, rendering a color change from red to gray-blue and transforming the surface plasmon absorption intensity and wavelength. The designed method presented high selectivity, stability, and reproducibility, with a detection range of 2.5-15 μg/mL. The results demonstrated that the developed approach will be valuable in the precise, facile, and cost-effective estimation of MPs in different matrices, regulating the control over MPs pollution and its hazardous impact on health and ecosystems.

Role of organisms and their enzymes in the biodegradation of microplastics and nanoplastics: A review

Microplastic (MP) and Nanoplastic (NP) contamination have become a critical ecological concern due to their persistent presence in every aspect of the ecosystem and their potentially harmful effects. The current approaches to eradicate these wastes by burning up and dumping adversely impact the environment, while recycling has its own challenges. As a result, applying degradation techniques to eliminate these recalcitrant polymers has been a focus of scientific investigation in the recent past. Biological, photocatalytic, electrocatalytic, and, recently, nanotechnologies have been studied to degrade these polymers. Nevertheless, it is hard to degrade MPs and NPs in the environment, and these degradation techniques are comparatively inefficient and require further development. The recent research focuses on the potential use of microbes to degrade MPs and NPs as a sustainable solution. Therefore, considering the recent advancements in this important research field, this review highlights the utilization of organisms and enzymes for the biodegradation of the MPs and NPs with their probable degradation mechanisms. This review provides insight into various microbial entities and their enzymes for the biodegradation of MPs. In addition, owing to the lack of research on the biodegradation of NPs, the perspective of applying these processes to NPs degradation has also been looked at. Finally, a critical evaluation of the recent development and perspective for future research to improve the effective removal of MPs and NPs in the environment through biodegradation is also discussed.

Insights into the degradation of high-density polyethylene microplastics using microbial strains: Effect of process parameters, degradation kinetics and modeling

The extensive distribution of microplastics and their abundance around the world has raised a global concern because of the lack of proper disposal channels as well as poor knowledge of their implications on human health. Sustainable remediation techniques are required owing to the absence of proper disposal methods. The present study explores the deterioration process of high-density polyethylene (HDPE) microplastics using various microbes along with the kinetics and modeling of the process using multiple non-linear regression models. Ten different microbial strains were used for the degradation of microplastics for a period of 30 days. Effect of process parameters on the degradation process was studied with the selected five microbial strains that presented the best degradation results. The reproducibility and efficacy of the process were tested for an extended period of 90 days. Fourier-transform infrared spectroscopy (FTIR) and field emission-scanning electron microscopy (FE-SEM) were used for the analysis of microplastics. Polymer reduction and half-life were evaluated. Pseudomonas putida achieved the maximum degradation efficiency of 12.07% followed by Rhodococcus ruber (11.36%), Pseudomonas stutzeri (8.28%), Bacillus cereus (8.26%), and Brevibacillus borstelensis (8.02%) after 90 days. Out of 14 models tested, 5 were found capable of modeling the process kinetics and based on simplicity and statistical data, Modified Michaelis-Menten model (F8; R² = 0.97) was selected as superior to others. This study successfully establishes the potential of bioremediation of microplastics as the viable process.

The degradation of single-use plastics and commercially viable bioplastics in the environment: A review

Plastics have become an integral part of human life. Single-use plastics (SUPs) are disposable plastics designed to be used once then promptly discarded or recycled. This SUPs range from packaging and takeaway containers to disposable razors and hotel toiletries. Synthetic plastics, which are made of non-renewable petroleum and natural gas resources, require decades to perpetually disintegrate in nature thus contribute to plastic pollution worldwide, especially in marine environments. In response to these problems, bioplastics or bio-based and biodegradable polymers from renewable sources has been considered as an alternative. Understanding the mechanisms behind the degradation of conventional SUPs and biodegradability of their greener counterpart, bioplastics, is crucial for appropriate material selection in the future. This review aims to provide insights into the degradation or disintegration of conventional single-use plastics and the biodegradability of the different types of greener-counterparts, bioplastics, their mechanisms, and conditions. This review highlights on the biodegradation in the environments including composting systems. Here, the various types of alternative biodegradable polymers, such as bacterially biosynthesised bioplastics, natural fibre-reinforced plastics, starch-, cellulose-, lignin-, and soy-based polymers were explored. Review of past literature revealed that although bioplastics are relatively eco-friendly, their natural compositions and properties are inconsistent. Furthermore, the global plastic market for biodegradable plastics remains relatively small and require further research and commercialization efforts, especially considering the urgency of plastic and microplastic pollution as currently critical global issue. Biodegradable plastics have potential to replace conventional plastics as they show biodegradation ability under real environments, and thus intensive research on the various biodegradable plastics is needed to inform stakeholders and policy makers on the appropriate response to the gradually emerging biodegradable plastics.

Transport of microplastics in the body and interaction with biological barriers, and controlling of microplastics pollution

Microplastics (MPs) are one novel environmental pollutant sized < 5 mm that is ubiquitously present in numerous environmental media and particularly susceptible to interact with various toxic chemicals. Importantly, MPs can enter the food chain, and are bio-enriched and bio-accumulated with trophic levels, eventually endangering ecosystems and human health. However, there need to be more understanding regarding the bio-interaction of MPs with the host, particularly for biological barriers. This review aimed to summarize the latest findings regarding the main exposure routes of MPs that generated health burdens on humans. Furthermore, their interactions with biological barriers that generate adverse health effects and the underlying mechanisms were also reviewed. Additionally, we provided a comprehensive overview of recent advances regarding the removing and controlling of MPs. Finally, we discussed the future directions for MPs hazard prevention to provide helpful information for regulating decision-making and guiding safer plastics applications.

Effects of variable-sized polyethylene microplastics on soil chemical properties and functions and microbial communities in purple soil

Microplastic contamination of soil has drawn increased attention due to the ecological harm it poses to the soil ecosystem. However, little is known about how microplastic particle sizes affect soil chemical properties and microbial communities, particularly in purple soil. In this study, a four-week incubation experiment was conducted to evaluate the effect of polyethylene microplastics (PE MPs) with different particle sizes (i.e., 300 and 600 μm) on soil properties, extracellular polymeric substances (EPS), enzyme activities, and microbial communities in purple soil. When compared to 600 μm-PE MPs, 300 μm-PE MPs reduced contents of dissolved organic matter (DOM), EPS, and β-1,4-N-acetylglucosaminidase (NAG) activity, but increased the cation exchange capacity (CEC). High-throughput 16S rRNA gene sequencing revealed that the 300 μm-PE MPs resulted in an increase in the phylum Nitrospirae, which is associated with microplastic degradation. The data implied that smaller PE MPs improved the growth of polyethylene-degrading bacteria by adsorbing more EPS and DOM, resulting in the degradation of microplastics. Co-occurrence network analysis revealed that smaller PE MPs had lower toxicity to microbial populations than larger PE MPs, increasing the stability of the network. CEC and β-1,4-glucosidase (BG) were found to be the two major factors affecting the microbial communities by redundancy analysis (RDA). The study highlighted how microplastic particle sizes affect soil bacterial communities and soil functions.

Monitoring of biofilm development and physico-chemical changes of floating microplastics at the air-water interface

Microplastics in the aquatic environment serve as a habitat for microbial life, on which they can form biofilms. However, how the development of the biofilm alters the properties of floating microplastics that are at the air-water interface and, therefore, not fully submerged, is not well understood. In this context, an aging experiment was conducted to monitor biofilm formation and changes in physico-chemical properties of low-density polyethylene (floating) microplastics over time. The growth of the biofilm followed the typical bacterial/biofilm growth phases and reached about 30% of the total mass of the microplastics, while the concentration of extracellular polymeric substances within the biofilm remained stable. Presence of chlorophyll a and urease activity indicated presence of photosynthetic microrganisms within the biofilm which was also confirmed by analysis of the biofilm composition. Chemical characterization by FTIR showed the formation of additional functional groups attributed to the formed biofilm, and SEM imaging showed cracks on the surface of the aged microplastics, indicating incipient degradation of the polyethylene. Moreover, the adsorption capacity of the aged particles for metals (Pb(II)) was 52% higher compared to the pristine ones. Aging increased the density and size of the particles; however, it did not lead to the submersion of the aged particles even after 12 weeks of aging, suggesting that additional environmental processes may influence the transport of microplastics from the air-water interface into the water body.

Response of occurrence in microplastics and its adsorped cadmium capacity to simulated agricultural environmental scenarios in sludge-amended soil

Large amounts of microplastics (MPs) enter the soil along with the amendment of sludge to soil. However, it is still unclear about the response of MPs occurrence and the adsorption behaviors of cadmium (Cd)on MPs to typical agricultural environmental scenarios. In present work, three kinds of MPs (polyethylene, polypropylene, and polystyrene) were chosen to investigate that response in three agricultural environmental scenarios with sludge-amended soil, including dry-wet alteration (7 d, five cycles), microbial addition (Bacillus subtilis, 0.05 g/g soil), and Ultraviolet (UV) irradiation (340 nm, 4 × 15 W, 4 d). The results showed that there was the highest adsorption capacity of Cd on MPs (36.21, 45.15, 12.43 μg/g for PE, PP, PS, respectively) after UV irradiation exceeding those from MPs triggered by other two scenarios). UV irradiation caused an increase in the abundance of Streptomyces, an expansion in specific surface area, a significant change in surface morphologies, an improvement in crystallinity or the formation of new crystals, and an enhancement in C-O and CO content, and then resulted in the incremental adsorption capacity of Cd on MPs. The findings are important of significance for controlling the environmental risks from sludge MPs via carrying heavy metals in the soil-plant systems.

A high-throughput expression and screening platform for applications-driven PETase engineering

The environmental consequences of plastic waste have impacted all kingdoms of life in terrestrial and aquatic ecosystems. However, as the burden of plastic pollution has increased, microbes have evolved to utilize anthropogenic polymers as nutrient sources. Of depolymerase enzymes, the best characterized is PETase, which hydrolyzes aromatic polyesters. PETase engineering has made impressive progress in recent years; however, further optimization of engineered PETase toward industrial application has been limited by lower throughput techniques used in protein purification and activity detection. Here, we address these deficiencies through development of a higher-throughput PETase engineering platform. Secretory expression via YebF tagging eliminates lysis and purification steps, facilitating production of large mutant libraries. Fluorescent detection of degradation products permits rapid screening of depolymerase activity in microplates as opposed to serial chromatographic methods. This approach enabled development of more stable PETase, semi-rational (SR) PETase variant containing previously unpublished mutations. SR-PETase releases 1.9-fold more degradation products and has up to 7.4-fold higher activity than wild-type PETase over 10 days at 40°C. These methods can be adapted to a variety of chemical environments, enabling screening of PETase mutants in applications-relevant conditions. Overall, this work promises to facilitate advancements in PETase engineering toward industrial depolymerization of plastic waste.

Bioremediation of microplastics in freshwater environments: A systematic review of biofilm culture, degradation mechanisms, and analytical methods

Microplastics, defined as particles <5 mm in diameter, are emerging environmental pollutants that pose a threat to ecosystems and human health. Biofilm degradation of microplastics may be an ecologically friendly approach. This review systematically summarises the factors affecting biofilm degradation of microplastics and proposes feasible methods to improve the efficiency of microplastic biofilm degradation. Environmentally insensitive microorganisms were screened, optimized, and commercially cultured to facilitate the practical application of this technology. For strain screening, technology should focus on microorganisms/strains that can modify the hydrophobicity of microplastics, degrade the crystalline zone of microplastics, and metabolise additives in microplastics. The biodegradation mechanism is also described; microorganisms secreting extracellular oxidases and hydrolases are key factors for degradation. Measuring the changes in molecular weight distribution (MWD) enables better analysis of the biodegradation behaviour of microplastics. Biofilm degradation of microplastics has relatively few applications because of its low efficiency; however, enrichment of microplastics in freshwater environments and wastewater treatment plant tailwater is currently the most effective method for treating microplastics with biofilms.

Microbial engineering strategies for synthetic microplastics clean up: A review on recent approaches

Microplastics are the small fragments of the plastic molecules which find their applications in various routine products such as beauty products. Later, it was realized that it has several toxic effects on marine and terrestrial organisms. This review is an approach in understanding the microplastics, their origin, dispersal in the aquatic system, their biodegradation and factors affecting biodegradation. In addition, the paper discusses the major engineering approaches applied in microbial biotechnology. Specifically, it reviews microbial genetic engineering, such as PET-ase engineering, MHET-ase engineering, and immobilization approaches. Moreover, the major challenges associated with the plastic removal are presented by evaluating the recent reports available.

Biotechnological methods to remove microplastics: a review

Microplastics pollution is major threat to ecosystems and is impacting abiotic and biotic components. Microplastics are diverse and highly complex contaminants that transport other contaminants and microbes. Current methods to remove microplastics include biodegradation, incineration, landfilling, and recycling. Here we review microplastics with focus on sources, toxicity, and biodegradation. We discuss the role of algae, fungi, bacteria in the biodegradation, and we present biotechnological methods to enhance degradation, e.g., gene editing tools and bioinformatics.

Transformation of microplastics by oxidative water and wastewater treatment processes: A critical review

Microplastics (MPs) are contaminants of emerging concern that accumulate in various environments, where they pose threats to both the ecosystem and public health. Since MPs have been detected in drinking water resources and wastewater effluents, more efficient treatment is needed at wastewater treatment plants (WWTPs) and drinking water treatment plants (DWTPs). This review discusses the potential of biological, photochemical, Fenton (-like) systems, ozonation, and other oxidation processes in the treatment of MPs in terms of their indicators of oxidation such as mass loss and surface oxidation. The oxidation processes were further analyzed in terms of limitations and environmental implications. Most previous studies examining MPs degradation using conventional treatments-such as UV disinfection, ozonation, and chlorination-employed significantly higher doses than the common doses applied in DWTPs and WWTPs. Owing to such dose gaps, the oxidative transformation of MPs observed in many previous studies are not likely to occur under practical conditions. Some novel oxidation processes showed promising MPs treatment efficiencies, while many of them have not yet been applied on a larger scale due to high costs and the lack of extensive basic research. Health and environmental impacts related to the discharge of oxidized MPs in effluents should be considered carefully in different aspects: the role as vectors of external pollutants, release of organic compounds (including organic byproducts from oxidation) and fragmentation into smaller particles as MPs circulate in the ecosystem as well as the possibility of bioaccumulation. Future research should also focus on ways to incorporate developed oxidation processes in DWTPs and WWTPs to mitigate MPs contamination.

Recent approaches and advanced wastewater treatment technologies for mitigating emerging microplastics contamination - A critical review

Microplastics have been identified as an emerging pollutant due to their irrefutable prevalence in air, soil, and particularly, the aquatic ecosystem. Wastewater treatment plants (WWTPs) are seen as the last line of defense which creates a barrier between microplastics and the environment. These microplastics are discharged in large quantities into aquatic bodies due to their insufficient containment during water treatment. As a result, WWTPs are regarded as point sources of microplastics release into the environment. Assessing the prevalence and behavior of microplastics in WWTPs is therefore critical for their control. The removal efficiency of microplastics was 65 %, 0.2-14 %, and 0.2-2 % after the successful primary, secondary and tertiary treatment phases in WWTPs. In this review, other than conventional treatment methods, advanced treatment methods have also been discussed. For the removal of microplastics in the size range 20-190 μm, advanced treatment methods like membrane bioreactors, rapid sand filtration, electrocoagulation and photocatalytic degradation was found to be effective and these methods helps in increasing the removal efficiency to >99 %. Bioremediation based approaches has found that sea grasses, lugworm and blue mussels has the ability to mitigate microplastics by acting as a natural trap to the microplastics pollutants and could act as candidate species for possible incorporation in WWTPs. Also, there is a need for controlling the use and unchecked release of microplastics into the environment through laws and regulations.

Microplastic dynamics in a free water surface constructed wetland

This study investigates microplastic (MPs) dynamics of a recently established surface flow 2100 population equivalent polishing constructed wetland (CW) receiving 1.4 ML per day of secondary treated wastewater. MPs type, size ranges and concentrations were measured along the CW at a 2-months sampling campaign. The CW received an average of 5·10⁶ MPs per day (6 MPs per liter), mostly 100-1000 μm-sized synthetic fibers followed by fragments in the same size range. 95 % of MPs were retained, resulting in 0.30 ± 0.09 MPs per liter in CW effluent. Most MPs (97 %) were trapped within the first 20 % of the CW which consisted of a settling pond and shallow vegetated treatment cells and provided an areal removal rate > 4000 MP m^-2 d^-1. Data and microscopic analysis indicate MPs erosion and fragmentation in the CW. Turbidity and suspended solids were no indicator for MP removal due to water fowl activity, algal growth, and preferential flow conditions. This is the first study on MP dynamics in an independently operating full scale free water surface CW incorporated into a municipal wastewater treatment scheme. Surface flow CWs can retain MPs effectively but accumulation in CW sediments and substrate needs to be considered when further utilized or recycled.

Plastic-microbe interaction in the marine environment: Research methods and opportunities

Approximately 9 million metric tons of plastics enters the ocean annually, and once in the marine environment, plastic surfaces can be quickly colonised by marine microorganisms, forming a biofilm. Studies on plastic debris-biofilm associations, known as plastisphere, have increased exponentially within the last few years. In this review, we first briefly summarise methods and techniques used in exploring plastic-microbe interactions. Then we highlight research gaps and provide future research opportunities for marine plastisphere studies, especially, on plastic characterisation and standardised biodegradation tests, the fate of "environmentally friendly" plastics, and plastisphere of coastal habitats. Located in the tropics, Southeast Asian (SEA) countries are significant contributors to marine plastic debris. However, plastisphere studies in this region are lacking and therefore, we discuss how the unique environmental conditions in the SEA seas may affect plastic-microbe interaction and why there is an imperative need to conduct plastisphere studies in SEA marine environments. Finally, we also highlight the lack of understanding of the pathogenicity and ecotoxicological effects of plastisphere on marine ecosystems.

Roles of extracellular polymeric substances on Microcystis aeruginosa exposed to different sizes of polystyrene microplastics

Extracellular polymeric substances (EPS) are important shields for microalgae when confronting with external stresses. However, the underlying roles of EPS in the interactions between microplastics (MPs) and microalgae remain poorly understood. In this study, three sizes of polystyrene (PS) MPs (20 nm, 100 nm, and 1 μm) were chosen for evaluating the compositions of EPS, secreted by Microcystis aeruginosa during exposure. The results indicated that the EPS compositions were different when M. aeruginosa was exposed to PS MPs of different sizes. The presence of EPS is helpful for alleviating the adverse effects of PS MPs on M. aeruginosa cell growth, photosynthesis, and oxidative stress. With the exception of the shading effect, insufficient EPS cause direct adsorption of unstable 1 μm PS MPs to the algal surface, which could destroy the cell wall. In contrast, aromatic proteins and fulvic acids are representative EPS components stimulated by 100 nm PS MPs, contributing to the self-aggregation and encapsulation of algal cells and availability of nutrients for algal growth, respectively. High amounts of polysaccharides were secreted by M. aeruginosa along with humic acids during exposure to 20 nm PS MPs, both of which are crucial in the homo-aggregation of 20 nm PS MPs toward minimize its adverse effects on M. aeruginosa. Together, these findings revealed the differences in EPS under the stimulation of PS MPs of different sizes and clarified the roles of different EPS components in resisting the adverse effects of PS MPs on M. aeruginosa.

Removing microplastics from aquatic environments: A critical review

As one of the typical emerging contaminants, microplastics exist widely in the environment because of their small size and recalcitrance, which has caused various ecological problems. This paper summarizes current adsorption and removal technologies of microplastics in typical aquatic environments, including natural freshwater, marine, drinking water treatment plants (DWTPs), and wastewater treatment plants (WWTPs), and includes abiotic and biotic degradation technologies as one of the removal technologies. Recently, numerous studies have shown that enrichment technologies have been widely used to remove microplastics in natural freshwater environments, DWTPs, and WWTPs. Efficient removal of microplastics via WWTPs is critical to reduce the release to the natural environment as a key connection point to prevent the transfer of microplastics from society to natural water systems. Photocatalytic technology has outstanding pre-degradation effects on microplastics, and the isolated microbial strains or enriched communities can degrade up to 50% or more of pre-processed microplastics. Thus, more research focusing on microplastic degradation could be carried out by combining physical and chemical pretreatment with subsequent microbial biodegradation. In addition, the current recovery technologies of microplastics are introduced in this review. This is incredibly challenging because of the small size and dispersibility of microplastics, and the related technologies still need further development. This paper will provide theoretical support and advice for preventing and controlling the ecological risks mediated by microplastics in the aquatic environment and share recommendations for future research on the removal and recovery of microplastics in various aquatic environments, including natural aquatic environments, DWTPs, and WWTPs.

The response of bacterial community to UVB was significantly different between immature periphyton and mature periphyton, but not for physiological indicators

Periphyton has important ecological functions. It can even exist in environments with strong ultraviolet radiation. However, knowledge of periphyton under ultraviolet is limited, which limits the understanding and application of periphyton in environments with high ultraviolet radiation. In this study, immature periphyton (IMP) and mature periphyton (MP) under ultraviolet B (UVB) irradiation were investigated and compared in terms of physiological characteristics and bacterial community. Analysis of the physiological characteristics showed that the response patterns of IMP and MP to UVB were similar. IMP and MP could adapt to UVB of 1 W/m² well. However, high-intensity UVB (2 and 3 W/m²) reduced the periphyton biomass, inhibited photosynthesis and antioxidant enzyme activity and caused severe lipid peroxidation in both IMP and MP. Integrated Biological Response (IBR) analysis and toxicological model fitting showed that the ED₅₀ values of UVB for IMP and MP were 1.25 and 1.50 W/m², respectively. 16 S rRNA gene analysis showed that in both IMP and MP, bacterial community composition, assembly and function were affected by UVB. In addition, the response of the bacterial community in IMP to UVB was stronger than that in MP. The diversity of the IMP community was inhibited by UVB, but that of the MP community was not. Proteobacteria and Deinococcus-Thermus are key microorganisms responsible for tolerance to UVB stress. Neutral community model fitting showed that both UVB and the development process caused the determinism of bacterial succession. However, UVB may weaken the deterministic process caused by development. Functional prediction showed that many metabolic functions of periphyton were inhibited by UVB in IMP and MP. However, UVB caused different changes (enhancement or inhibition) of some ecological functions in them. This study provides valuable information for understanding periphyton in environments with UVB radiation, which may be used to improve the application of periphyton in these environments.

Optimization of Polystyrene Biodegradation by Bacillus cereus and Pseudomonas alcaligenes Using Full Factorial Design

Microplastics (MP) are a global environmental problem because they persist in the environment for long periods of time and negatively impact aquatic organisms. Possible solutions for removing MP from the environment include biological processes such as bioremediation, which uses microorganisms to remove contaminants. This study investigated the biodegradation of polystyrene (PS) by two bacteria, Bacillus cereus and Pseudomonas alcaligenes, isolated from environmental samples in which MPs particles were present. First, determining significant factors affecting the biodegradation of MP-PS was conducted using the Taguchi design. Then, according to preliminary experiments, the optimal conditions for biodegradation were determined by a full factorial design (main experiments). The RSM methodology was applied, and statistical analysis of the obtained models was performed to analyze the influence of the studied factors. The most important factors for MP-PS biodegradation by Bacillus cereus were agitation speed, concentration, and size of PS, while agitation speed, size of PS, and optical density influenced the process by Pseudomonas alcaligenes. However, the optimal conditions for biodegradation of MP-PS by Bacillus cereus were achieved at γ_MP = 66.20, MP size = 413.29, and agitation speed = 100.45. The best conditions for MP-PS biodegradation by Pseudomonas alcaligenes were 161.08, 334.73, and 0.35, as agitation speed, MP size, and OD, respectively. In order to get a better insight into the process, the following analyzes were carried out. Changes in CFU, TOC, and TIC concentrations were observed during the biodegradation process. The increase in TOC values was explained by the detection of released additives from PS particles by LC-MS analysis. At the end of the process, the toxicity of the filtrate was determined, and the surface area of the particles was characterized by FTIR-ATR spectroscopy. Ecotoxicity results showed that the filtrate was toxic, indicating the presence of decomposition by-products. In both FTIR spectra, a characteristic weak peak at 1715 cm⁻¹ was detected, indicating the formation of carbonyl groups (−C=O), confirming that a biodegradation process had taken place.

Tracking microplastics biodegradation through CO2 emission: Role of photoaging and mineral addition

Once microplastics (MPs) enter the terrestrial ecosystem, they may affect the assessment of soil carbon storage and the fluxes of greenhouse gases. This study showed microbial incubation diminished the size and dissolved organic carbon (DOC) content of MPs and introduced more oxygen-containing functional groups to MPs potentially through microbial colonization. The aged MPs generally showed higher carbon mineralization ratio (0.010-0.876 %) than the pristine MPs (0.007-0.189 %), which was supported by their higher enzyme activities and DOC content. Interestingly, four model minerals increased the DOC release and CO₂ emission from MPs by altering MPs physicochemical properties and shaping the habitat for microbial growth. The higher enzyme activities in mineral artificial soils, except for montmorillonite, served as a potential valid explanation for their higher mineralization. The high CO₂ emission but low enzyme activity in montmorillonite artificial soil was due to most DOC being already mineralized. Aging and minerals altered the microflora and enhanced the expression of some C metabolism- and N-related functional genes, which supplemented the cause of higher CO₂ and N₂O emissions from the corresponding artificial soils. Overall, the increased biomineralization of MPs carbon by minerals was divergent from the protective role of minerals on soil organic carbon.

Ecotoxicological and health implications of microplastic-associated biofilms: a recent review and prospect for turning the hazards into benefits

Microplastics (MPs), over the years, have been regarded as a severe environmental nuisance with adverse effects on our ecosystem as well as human health globally. In recent times, microplastics have been reported to support biofouling by genetically diverse organisms resulting in the formation of biofilms. Biofilms, however, could result in changes in the physicochemical properties of microplastics, such as their buoyancy and roughness. Many scholars perceived the microplastic-biofilm association as having more severe consequences, providing evidence of its effects on the environment, aquatic life, and nutrient cycles. Furthermore, other researchers have shown that microplastic-associated biofilms have severe consequences on human health as they serve as vectors of heavy metals, toxic chemicals, and antibiotic resistance genes. Despite what is already known about their adverse effects, other interesting avenues are yet to be fully explored or developed to turn the perceived negative microplastic-biofilm association to our advantage. The major inclusion criteria for relevant literature were that it must focus on microplastic association biofilms, while we excluded papers solely on biofilms or microplastics. A total of 242 scientific records were obtained. More than 90% focused on explaining the environmental and health impacts of microplastic-biofilm association, whereas only very few studies have reported the possibilities and opportunities in turning the microplastic biofilms association into benefits. In summary, this paper concisely reviews the current knowledge of microplastic-associated biofilms and their adverse consequences and further proposes some approaches that can be developed to turn the negative association into positive.

Microbial degradation of polyethylene terephthalate: a systematic review

Plastic pollution levels have increased rapidly in recent years, due to the accumulation of plastic waste, including polyethylene terephthalate (PET). Both high production and the lack of efficient methods for disposal and recycling affect diverse aquatic and terrestrial ecosystems owing to the high accumulation rates of plastics. Traditional chemical and physical degradation techniques have caused adverse effects on the environment; hence, the use of microorganisms for plastic degradation has gained importance recently. This systematic review was conducted for evaluating the reported findings about PET degradation by wild and genetically modified microorganisms to make them available for future work and to contribute to the eventual implementation of an alternative, an effective, and environmentally friendly method for the management of plastic waste such as PET. Both wild and genetically modified microorganisms with the metabolic potential to degrade this polymer were identified, in addition to the enzymes and genes used for genetic modification. The most prevalent wild-type PET-degrading microorganisms were bacteria (56.3%, 36 genera), followed by fungi (32.4%, 30 genera), microalgae (1.4%; 1 genus, namely Spirulina sp.), and invertebrate associated microbiota (2.8%). Among fungi and bacteria, the most prevalent genera were Aspergillus sp. and Bacillus sp., respectively. About genetically modified microorganisms, 50 strains of Escherichia coli, most of them expressing PETase enzyme, have been used. We emphasize the pressing need for implementing biological techniques for PET waste management on a commercial scale, using consortia of microorganisms. We present this work in five sections: an Introduction that highlights the importance of PET biodegradation as an effective and sustainable alternative, a section on Materials and methods that summarizes how the search for articles and manuscripts in different databases was done, and another Results section where we present the works found on the subject, a final part of Discussion and analysis of the literature found and finally we present a Conclusion and prospects.

A review on the remediation of microplastics using constructed wetlands: Bibliometric, co-occurrence, current trends, and future directions

Massive prevalence of microplastics (MPs) in the environment has become one of the world's most serious environmental concerns. Human dependence on plastics has created a constant flow of MPs from different sources into natural environment, which has raised public concern regarding consequences of MPs coming into contact with the natural environment. Deploying constructed wetlands (CWs) to reduce MPs pollution is considered a promising method, however there are still barriers for breakthroughs in this technology, particularly knowledge gaps in the mechanisms affect removal process. Recognising this, we provide a comprehensive summary of current advances and theories regarding the mechanisms of occurrence in this research area. In this work, the bibliometric methods were first used to identify annual publication trends and topical topics of research interest. The selected documents were then statistically analyzed using VOSviewer and the 'bibliometrix' package in R to derive the annual productivity of countries or organizations, the most relevant affiliations, the most relevant authors, the most relevant sources, textual analysis, co-occurrence analysis, and cluster analysis of keywords. Finally, detailed information concerning the removal of MPs by CWs was summarised, covering the most common operational and design parameters (i.e., structure types, wetland plants, substrate materials, and microbial communities), to reveal how these parameters can be adjusted for more efficient MPs removal rate. Challenges and future directions were additionally proposed. It is hoped that the review will help identify current research trends, provide insight into the mechanisms of the removal process, and contribute further to the development of this important area.

Recent advances in the breakdown of microplastics: strategies and future prospectives

Microplastics pollution is becoming a major environmental issue, and exposure to microplastics has been associated with numerous adverse results to both the ecological system and humans. This work summarized the state-of-the-art developments in the breakdown of microplastics, including natural weathering, catalysts-assisted breakdown and biodegradation. Characterization techniques for microplastic breakdown involve scanning electron microscopy, Fourier infrared spectroscopy, X-ray photoelectron spectroscopy, etc. Bioavailability and adsorption capacity of microplastics may change after they are broken down, therefore leading to variety in microplastics toxicity. Further prospectives for should be focused on the determination and toxicity evaluation of microplastics breakdown products, as well as unraveling uncultivable microplastics degraders via cultivation-independent approaches. This work benefits researchers interested in environmental studies, particularly the removal of microplastics from environmental matrix.

Oxidative degradation of pre-oxidated polystyrene plastics by dye decolorizing peroxidases from Thermomonospora curvata and Nostocaceae

Biodegradation of PS has attracted lots of public attentions due to its environmental friendliness. However, no specific PS degrading enzyme has been identified yet. Dye decolorizing peroxidases (DyPs) are heme-containing peroxidases named for the ability to degrade a variety of organic dyes. Herein, the abilities of two DyPs from Thermomonospora curvata (TcDyP) and Nostocaceae (AnaPX) to degrade PS were evaluated. Preoxidation methods by ultraviolet (UV) irradiation and chemical oxidants were developed to initially activate C-C bonds in the PS skeleton. DyPs degradation caused obvious etching and enhanced hydrophilicity of UV-PS films, and also generated new CO and C-OH groups. The cleavage of activated C-C bonds by DyPs was experimentally proven by analyzing the degradation products of UV-PS and model substrates. Furthermore, better pre-oxidation was obtained by using chemical oxidants KMnO₄/H₂SO₄ and ^mCPBA to oxidize PS materials in dissolved state. And AnaPX exhibited stronger degradation effects on KMnO₄/H₂SO₄-PS and ^mCPBA-PS by causing greater changes in functional groups CO, C-O, -OH groups and substituted benzenes and higher molecular weight reductions of 19.7% and 31.0%, respectively. To our knowledge, this is the first report on the identification of PS-degrading enzymes that provides experimental evidence.

pH-responsive magnetic artificial melanin with tunable aggregation-induced stronger magnetism for rapid remediation of plastic fragments

The global occurrence of plastic fragment pollutants in water resources has raised concerns about food safety, drinking water security, and long-term ecological impacts worldwide. The different chemical nature, the persistence, and the smaller size make micro-plastics accumulators for toxins that pose a potential threat to human health. Generally, the smaller the size of the plastic fragments is, the more difficult it is to remove them from the aquatic environment. Methods to remove plastics from water or other media are highly needed. Here, we develop core-shell superparamagnetic melanin nanoparticles, which can put magnetism on nano-/micro-plastics within 30 s and then rapidly remove them from water by applying an external magnetic field. The shell material (artificial nano-melanin) provides simultaneously attractive electrostatic, hydrophobic interaction, and van der Waals' forces to attract nano-/micro-plastics, which plays a key role in the rapid remediation of the plastic fragments. With this principle applied to a simple method, the average removal efficiency achieves 89.3%. We show a method for high-throughput remediation of various micro-plastics with simple materials and processes, which have the potential for rapid, green, and large-scale remediation in the future.

Effects of Selenium in Different Valences on the Community Structure and Microbial Functions of Biofilms

With the wide application of selenium (Se) in industrial production, different Se-based compounds (selenate and selenite) are produced and released into aquatic environments. The potential impacts of such Se compounds on the biofilms (a complex microbial aggregate in aquatic systems) need to be substantially explored. Herein, we investigated the responses of bacterial community diversity, composition and structure, and function of biofilms after 21 days of exposure to low concentrations (100 µg/L) and high concentrations (1 mg/L) of sodium selenate and sodium selenite, respectively. Distinct effects of selenium in different valences on the community structure and microbial functions of biofilms were observed. Compared with the controls, the addition of selenate and selenite solutions altered the richness of biofilms but not the diversity, which is dependent on the concentration and valences, with sodium selenite (1 mg/L) exhibiting a strong inhibition effect on community richness. Significant changes of community composition and structure were observed, with a significant increase in Proteobacteria (31.08–58.00%) and a significant decrease in Bacteroidetes (32.15–11.45%) after exposure to sodium selenite with high concentration. Also, different responses of gamma-Proteobacteria and alpha-Proteobacteria were observed between the sodium selenite and sodium selenate treatments. Moreover, results showed that sodium selenite could strengthen the function of the metabolism of biofilms, and the higher the concentration is, the more apparent the enhancement effect is. All these results suggested that the effects of different valence states of selenium were obvious, and sodium selenite with high concentration strongly changed the diversity, structure and function of biofilms.

Microplastics aging in wastewater treatment plants: Focusing on physicochemical characteristics changes and corresponding environmental risks

Microplastics (MPs) have been frequently detected in effluent wastewater and sludge in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental MPs contamination. As important as quantitative removal is, changes of physicochemical characteristics of MPs (e.g., shapes, sizes, density, crystallinity) in WWTPs are crucial to their environmental behaviors and risks and have not been put enough attention yet. This review is therefore to provide a current overview on the changes of physicochemical characteristics of MPs in WWTPs and their corresponding environmental risks. The changes of physicochemical characteristics as well as the underlying mechanisms of MPs in different successional wastewater and sludge treatment stages that mainly driven by mechanical (e.g., mixing, pumping, filtering), chemical (e.g., flocculation, advanced oxidation, ultraviolet radiation, thermal hydrolysis, incineration and lime stabilization), biological (e.g., activated sludge process, anaerobic digestion, composition) and their combination effects were first recapitulated. Then, the inevitable correlations between physicochemical characteristics of MPs and their environmental behaviors (e.g., migration, adsorption) and risks (e.g., animals, plants, microbes), are comprehensively discussed with particular emphasis on the leaching of additives and physicochemical characteristics that affect the co-exist pollutants behavior of MPs in WWTPs on environmental risks. Finally, knowing the summarized above, some relating unanswered questions and concerns that need to be unveiled in the future are prospected. The physicochemical properties of MPs change after passing through WWTP, leading to subsequent changes in co-contaminant adsorption, migration, and toxicity. This could threaten our ecosystems and human health and must be worth investigating.

Sorption behavior of Pb(II) onto polyvinyl chloride microplastics affects the formation and ecological functions of microbial biofilms

Microplastics (MPs) are regarded as transport media for heavy metals in aquatic systems, whereas the effects of the heavy metal-enriched MPs on microbial biofilms are still unclear. In this study, Pb(II) sorption onto polyvinyl chloride (PVC) MPs and its effects on the formation and ecological functions of microbial biofilms were investigated. The results showed that the interaction between Pb(II) and PVC MPs was dominated by physisorption. The maximum sorption amount reached 1.25 mg/g. Afterward, microbial biofilms were exposed to the Pb(II)-enriched PVC particles. It is suggested that Pb(II)-enriched PVC exposure reduced productivities of polysaccharides and proteins in extracellular polymeric substances, which restricted the formation of microbial biofilms. Meanwhile, microbial community structure was reassembled accompanying the decline of capacities for nitrate and phosphate removal. Therefore, this study examines the ecological risk associated with the heavy metal-enriched MPs that can adversely affect microbial biofilms.

Long-term interactions between microplastics and floating macrophyte Lemna minor: The potential for phytoremediation of microplastics in the aquatic environment

The presence of microplastics (MPs) in the environment has raised many concerns, and therefore approaches and technologies to remove them in situ are of high interest. In this context, we investigated the interactions between polyethylene MPs (fragments with a mean size of 149 ± 75 μm) and an aquatic floating macrophyte Lemna minor in order to assess its potential use for in situ phytoremediation. We first investigated the long-term effects of a high (100 mg/L = 9600 MPs/L), but still environmentally relevant concentration of MPs on L. minor. Subsequently bioadhesion of MPs was studied and the number and strength of MPs adhering to plant biomass were assessed. MPs did not adversely affect various parameters of plants (e.g., specific growth rate, chlorophyll contents, total antioxidant capacity, electron transport system activity, and contents of energy-rich molecules) throughout the duration of the experiment (12 weeks), except for the first week of the experiment, when protein content and total antioxidant capacity were affected. On the other hand, MPs affected the root length of L. minor during the first eight weeks of the experiment, while further exposure resulted in a decrease in the effects, indicating the ability of L. minor to tolerate the presence of MPs for a long period of time. MPs adhered rapidly to the plant biomass and the average percentages of strongly and weakly adhered particles were 6.5% and 20.0%, respectively, of the total MPs applied. In summary, results of this study suggest that L. minor can tolerate hotspot concentrations of MPs and can collect MPs from the water surface. Therefore, phytoremediation using floating plants could be considered as a potential method for in situ removal of MPs from the aquatic environment.

Incubation habitats and aging treatments affect the formation of biofilms on polypropylene microplastics

Microbial colonization and biofilm formation associated with microplastics (MPs) have recently attracted wide attention. However, little is known about the effect of MP aging and different exposed habitats on biofilm formation and associated microbial community characteristics. To obtain a comprehensive understanding, virgin and aged polypropylene MPs were selected as attachment substrates and exposed to different aquatic habitats (marine, estuary, and river). The results showed that the aging process could destroy surface structure and increase oxygen-containing groups of MPs. The total biomass of the biofilms, attached-bacterial OTU numbers, and α diversities increased with exposure time. The biofilms biomass and α diversity of MPs in the river were significantly higher than those in the marine and estuary habitats, and temperature and salinity were primary factors affecting microbial colonization. Bacterial communities in MP-attached biofilms were significantly different from those in surrounding water. Microorganisms tend to adhere to aged MPs, and especially, genes related to human pathogens were significantly expressed on aged MPs, suggesting a potential ecological and health risk of aged MPs in aquatic ecosystems. Our results showed that aged MPs and different habitats have an important influence on microbial colonization, and the weathering process can accelerate biofilm formation on MPs.

Current progress on plastic/microplastic degradation: Fact influences and mechanism

Plastic pollution, particularly non-degradable residual plastic films and microplastics (MPs), is a serious environmental problem that continues to worsen each year. Numerous studies have characterized the degradation of plastic fragments; however, there is known a lack of about the state of current physicochemical biodegradation methods used for plastics treatment and their degradation efficiency. Therefore, this review explores the effects of different physicochemical factors on plastics/MPs degradation, including mechanical comminution, ultraviolet radiation, high temperature, and pH value. Further, this review discusses different mechanisms of physicochemical degradation and summarizes the degradation efficiency of these factors under various conditions. Additionally, the important role of enzymes in the biodegradation mechanism of plastics/MPs is also discussed. Collectively, the topics discussed in this review provide a solid basis for future research on plastics/MPs degradation methods and their effects.

Membrane composition and successful bioaugmentation. Studies of the interactions of model thylakoid and plasma cyanobacterial and bacterial membranes with fungal membrane-lytic enzyme Lecitase ultra

Cyanobacterial/bacterial consortia are frequently inoculated to soils to increase the soil fertility and to accelerate the biodegradation of organic pollutants. Moreover, such consortia can also be successfully applied in landfills especially for the biodegradation of plastic wastes. However, the bioaugmentation techniques turn out frequently inefficient due to the competition of the indigenous microorganisms attacking directly these inoculated or secreting to their surroundings cell wall and membrane-lytic enzymes. It can be hypothesized that the resistance of the microbial membrane to the enzymatic degradation is correlated with its lipid composition. To verify this hypothesis glycolipid and phospholipid Langmuir monolayers were applied as models of thylakoid and plasma cyanobacterial and bacterial membranes. Hybrid fungal enzyme Lecitase ultra joining the activity of lipase and phospholipase A1 was applied as the model of fungal membrane-lytic enzyme. It turned out that anionic thylakoid lipids sulfoquinovosyldiacylglycerol and phosphatidylglycerols were the main targets of Lecitase ultra in the model multicomponent thylakoid membranes. The resistance of the model plasma bacterial membranes to enzymatic degradation depended significantly to their composition. The resistance increased generally when the unsaturated lipids were exchanged to their saturated counterparts. However, most resistant turned out the membranes composed of unsaturated phosphatidylamine and saturated anionic phospholipids.

Characteristics of Initial Attachment and Biofilm Formation of Pseudomonas aeruginosa on Microplastic Surfaces

The toxic effect of microplastics on living organisms is emerging as a serious environmental issue nowadays. The biofilm formed on their surface by microorganisms can further increase the toxicity, but the mechanism of biofilm formation on microplastics is not yet fully understood because of the complexities of other factors. This study aimed to identify the factors with an important influence on biofilm formation on microplastic surfaces. The microtiter plate assay was used to evaluate the biofilms formed by Pseudomonas aeruginosa PAO1, a model microorganism, on four types of microplastics, including polyethylene, polystyrene, polypropylene, and polytetrafluoroethylene. The density of microplastics was found to be a key factor in determining the amount of biofilm formation because the density relative to water has a decisive effect on the behavior of microplastics. Biofilm formation on plastics with densities similar to that of water showed remarkable differences based on surface characteristics, whereas biofilm formation on plastics with a higher density was significantly influenced by particle movement in the experimental environment. Furthermore, biofilm formation was inhibited by adding a quorum quenching enzyme, suggesting that QS is critical in biofilm formation on microplastics. This study provides useful information on biofilm formation on microplastic surfaces.

Enhanced periphyton biodegradation of endocrine disrupting hormones and microplastic: Intrinsic reaction mechanism, influential humic acid and microbial community structure elucidation

Endocrine-disrupting compounds (EDCs), as well as microplastics, have drawn global attention due to their presence in the aquatic ecosystem and persistence in wastewater treatment plants (WWTPs). In the present study, for simultaneous bio-removal of two EDCs, 17α-ethinylestradiol (EE2), bisphenol A (BPA), and a microplastic, polypropylene (PP) four kinds of periphytic biofilms were employed. Additionally, the effect of humic acid (HA) on the removal efficacy of these biofilms was evaluated. It was observed that EE2 and BPA (0.2 mg L^-1 each) were completely (∼100%) removed within 36 days of treatment; and the biodegradation of EE2, BPA, and PP was significantly enhanced in the presence of HA. Biodegradation of EE2 and BPA was evaluated through Ultra-high performance liquid chromatography (UHPLC), and Gas chromatography coupled with tandem mass spectrometry (GC-MS/MS) was used to determine the mechanism of degradation. Gel permeation chromatography (GPC) and SEM had validated the biodegradation of PP (5.2-14.7%). MiSeqsequencing showed that the community structure of natural biofilm changed after the addition of HA, as well as after the addition of EDCs and PP. This change in community structure might be a key factor regarding variable biodegradation percentages. The present study revealed the potential of periphytic biofilms for the simultaneous removal of pollutants of different chemical natures, thus provides a promising new method for wastewater treatment applications.

Aquatic Biofilms-Sink or Source of Microplastics? A Critical Reflection on Current Knowledge

The scientific understanding regarding sources, occurrence, and effects of microplastics in the aquatic environment has advanced rapidly, leaving some meaningful knowledge gaps virtually untouched. One of them is the interactions of microplastics and biofilms, microbial communities ubiquitous in aquatic ecosystems and fundamental for a range of ecosystem-level processes. It is evident that biofilms can quickly develop on the microplastic surface and consequently change particle properties and, as such, its fate and ecotoxicity. Moreover, microplastics interact with ubiquitous biofilms that are developed on any surfaces in aquatic ecosystems. Although the knowledge about these interactions is at best limited, it is expected that microplastics attach to the water-biofilm interface or penetrate the biofilm matrix. Microplastics can accumulate and ab- or adsorb to those biofilms where they are subjected to transformation processes such as fragmentation. Thus, biofilms may function as a sink. Changes in environmental conditions may, however, stress biofilms initiating their dieback and microplastic release, which could turn biofilms into a source of microplastics. We argue that the accumulation and release dynamics are a largely overlooked but potentially important piece to the puzzle that is a comprehensive understanding of microplastic fate in the environment and thus under the influence of multiple interacting factors. Environ Toxicol Chem 2022;41:838-843. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Biodegradation performance and anti-fouling mechanism of an ICME/electro-biocarriers-MBR system in livestock wastewater (antibiotic-containing) treatment

Livestock wastewater is an important reservoir of antibiotic resistance genes (ARGs) and antibiotic residues. Membrane fouling is one of the most challenging problems confining the operation and application of membrane bioreactor (MBR). In this work, a novel iron-carbon micro-electrolysis (ICME)/electro-biocarriers-MBR system was established to explore the performance of pollutant removal and anti-fouling for an actual livestock wastewater. A light-weight porous ceramsite (bulk density 0.98 g/cm³) was used as the MBR biocarriers. The electrons generated from iron corrosion in the ICME tank traveled through external wires to the stainless steel membrane modules of MBR and the protons were transferred from the MBR tank to the ICME tank through a salt bridge, thus producing a spontaneous electric field. Under the optimized conditions, the system exhibited chemical oxygen demand removal of 76.0%, total suspended solids removal of 100%, antibiotic removal of 86.4%, NH₄⁺-N removal of 91.1%, and ARGs reduction of 6-8 orders of magnitude. The quality of the final effluent can reach the national Class I-A discharge criteria. Adding ceramsite could not only effectively improve biodegradation performance but also alleviate membrane fouling through the migration and enrichment of microbial flora to the ceramsite. The self-generated electric field had no significant improvement effect on pollutant removal, but exhibited good anti-membrane fouling behavior which could be ascribed to (i) oxidization of membrane foulants by the electrochemical products (such as H₂O₂ and •OH radicals), and (ii) electrostatic repulsion of negatively charged foulants and bacterial cells. The bacterial community structure and diversity were studied using high-throughput pyrosequencing, and the results demonstrated the roles of electric field and biocarriers in enrichment of anti-fouling communities and repulsion of biofouling-creating communities.

Comparative Analysis of Selective Bacterial Colonization by Polyethylene and Polyethylene Terephthalate Microplastics

In this study, we report the biodiversity and functional characteristics of microplastic-attached biofilms originating from two freshwater bacterial communities. Even though the microplastic-biofilm (MPB) diversities are mostly determined by original bacteria instead of microplastic types, the results from 16S rRNA amplicon sequencing still showed that the dynamic biofilm successions on different microplastics were highly dissimilar. Furthermore, the analysis of biomarkers indicated distinct bacterial species with significant dissimilarities between different MPBs, which further determined the associated functions. The co-occurrence networks showed distinct interconnective characteristics in different MPBs: The structure of MPB incubated in the lake water sample was more robust under environmental stresses, and bacteria in the tap water MPB interacted more cooperatively. Regarding this cooperative interaction, the analysis of functional prediction, in this study, also showed that more symbionts and parasites colonized on microplastics in the tap water than in the lake water. Moreover, it was suggested that MPBs were more easily formed in the tap water sample. The overall results revealed significant dissimilarities in bacterial diversity, succession, and associated functions between MPBs, in which bacterial species with specific functions should be taken seriously.

Accelerated biodegradation of polyethylene terephthalate by Thermobifida fusca cutinase mediated by Stenotrophomonas pavanii

Polyethylene terephthalate (PET) is a general plastic that produces a significant amount of waste due to its non-biodagradable properties. We obtained four bacteria (Stenotrophomonas pavanii JWG-G1, Comamonas thiooxydans CG-1, Comamonas koreensis CG-2 and Fulvimonas soli GM-1) that utilize PET as a sole carbon source through a novel stepwise screening and verification strategy. PET films pretreated with S. pavanii JWG-G1 exhibited weight loss of 91.4% following subsequent degradation by Thermobifida fusca cutinase (TfC). S. pavanii JWG-G1 was able to colonize the PET surface and maintain high cell viability (over 50%) in biofilm, accelerating PET degradation. Compared with PET films with no pretreatment, pretreatment with S. pavanii JWG-G1 caused the PET surface to be significantly rougher with greater hydrophilicity (contact angle of 86.3 ± 2° vs. 96.6 ± 2°), providing better opportunities for TfC to contact and act on PET. Our study indicates that S. pavanii JWG-G1 could be used as a novel pretreatment for efficiently accelerating PET biodegradation by TfC.

Seeking for a perfect (non-spherical) microplastic particle - The most comprehensive review on microplastic laboratory research

In recent decades, much attention has been paid to microplastic pollution, and research on microplastics has begun to grow exponentially. However, microplastics research still suffers from the lack of standardized protocols and methods for investigation of microplastics under laboratory conditions. Therefore, in this review, we summarize and critically discuss the results of 715 laboratory studies published on microplastics in the last five years to provide recommendations for future laboratory research. Analysis of the data revealed that the majority of microplastic particles used in laboratory studies are manufactured spheres of polystyrene ranging in size from 1 to 50 µm, that half of the studies did not characterize the particles used, and that a minority of studies used aged particles, investigated leaching of chemicals from microplastics, or used natural particles as a control. There is a large discrepancy between microplastics used in laboratory research and those found in the environment, and many laboratory studies suffer from a lack of environmental relevance and provide incomplete information on the microplastics used. We have summarized and discussed these issues and provided recommendations for future laboratory research on microplastics focusing on (i) microplastic selection, (ii) microplastic characterization, and (iii) test design of laboratory research on microplastics.

Polystyrene nanoplastics change the functional traits of biofilm communities in freshwater environment revealed by GeoChip 5.0

There is an increasing concern regarding the potential effects of nanoplastics (NPs) on freshwater ecosystems. Considering the functional values of biofilms in freshwater, knowledge on whether and to what extent NPs can influence the ecosystem processes of biofilms were still limited. Herein, the freshwater biofilms cultured in lab were exposed to 100 nm polystyrene NPs (PS-NPs) of different dosages (1 and 10 mg/L) for 14 days. Confocal laser scanning microscope observation indicated that biofilms were dominated by filamentous, and spiral algae species and the intensity of extracellular polymeric substances increased under PS-NPs exposure. GeoChip 5.0 analysis revealed that PS-NPs exposure triggered a significant increase in functional genes α diversity (p < 0.05) and altered biofilms' functional structure. Furthermore, the abundance of genes involved in the total carbon and nitrogen cycling were increased under PS-NPs exposure. The abundance of nitrogen fixation genes experienced the most pronounced increase (24.4%) under 1 mg/L PS-NPs treatment, consistent with the increase of ammonium in overlying water. Whereas antibiotic resistance genes and those related to photosynthetic pigments production were suppressed. These results provided direct evidence for PS-NPs' effects on the biofilm functions in terms of biogeochemical cycling, improving our understanding of the potentials of NPs on freshwater ecosystems.

Method for rapid biofilm cultivation on microplastics and investigation of its effect on the agglomeration and removal of microplastics using organosilanes

Since microplastics were recognized as a global environmental problem in the early 2000s, research began on possible solutions such as the removal of microplastics from waters. A novel and promising approach for this purpose is microplastics agglomeration-fixation using organosilanes. In this study, it is investigated how biofilm coverage of microplastics affects this process. The biofilm was grown on the microplastics by cultivating it for one week in a packed bed column operated with biologically treated municipal wastewater enriched with glucose. The biofilm was characterized using confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and Fourier-Transform infrared spectroscopy (FT-IR). The results show a partial coverage of the microplastics with attached bacteria and extracellular polymeric substances (EPS) after 7 days of incubation. Comparing five polymer types (polyethylene, polypropylene, polyamide, polyester, and polyvinyl chloride) and three organosilanes, the biofilm coverage caused a reduced removal efficiency for all combinations tested as it changes the surface chemistry of the microplastics and therefore the interaction with the organosilanes tested in this study. Treatment of biofilm covered microplastic with ultrasound partly recovers the removal. However, the results underline the importance of simulated environmental exposure when performing experiments for microplastic removal.

On the degradation of (micro)plastics: Degradation methods, influencing factors, environmental impacts

Plastics and microplastics are difficult to degrade in the natural environment due to their hydrophobicity, the presence of stable covalent bonds and functional groups that are not susceptible to attack. In nature, microplastics are more likely to attract other substances due to their large specific surface area, which further prevents degradation from occurring. Some of these substances are toxic and harmful, and can be spread to various organisms through the food chain along with the microplastics to cause harm to them. Degradation is an effective way to eliminate plastic pollution, and a comprehensive understanding of the methods and mechanisms of plastic degradation is necessary, because it is the result of synergistic effects of several degradation methods, both in nature and in consideration of future engineering applications. The authors firstly summarize the degradation methods of (micro)plastics; secondly, review the influence of intrinsic properties and environmental factors during the degradation process; finally, discuss the environmental impact of the degradation products of (micro)plastics. It is evident that the degradation of (micro)plastics still has many challenges to overcome, and there are no mature and effective methods that can be applied in engineering practice or widely used in nature. Therefore, there is an urgent need for research on the degradation of (micro)plastics.

Effects of high-molecular-weight polyvinyl chloride on Xenopus laevis adults and embryos: the mRNA expression profiles of Myf5, Esr1, Bmp4, Pax6, and Hsp70 genes during early embryonic development

Microplastics and associated adverse effects have been on the global agenda in recent years. Because of its importance as a model organism for studies on developmental biology, Xenopus laevis has been chosen as the study animal in in vitro teratogenesis studies. FETAX test uses early-stage embryos of X. laevis to measure the potential of substances to cause mortality, malformation, and growth inhibition in developing embryos. The aim of this study was to examine the effects of high molecular weight polyvinyl chloride (HMW-PVC) on parental X. laevis frogs and their embryos using the FETAX test. To this purpose, a HMW-PVC dose of 1% of body weight/twice each week was provided to frogs by oral gavage throughout 6 weeks. After the procedure, oocytes and sperms of HMW-PVC-exposed frogs were fertilized and FETAX was applied to selected embryos. After the completion of a 96-h incubation period, tadpoles were examined, their live/dead status were determined, their lengths were measured, and their anomalies were photographed. Besides, excised organs of the parental frogs were referred to histopathology examination. On the other hand, the mRNA expression levels of Hsp70, Myf5, Bmp4, Pax6, and Esr1 genes were determined by applying real-time quantitative PCR method to cDNA which was synthesized from the total RNA of embryos. The results showed that treatment with HMW-PVC dose of 1% of body weight/twice each week caused malformations and decreased viability. Hsp70 and Pax6 gene expression levels significantly decreased in all assay groups, as compared with controls. Lung and intestine tissues showed normal appearance in histopatological examination. Further research is required to explain the whole effects of HMW-PVC exposure on X. laevis embryos.

Photocatalytic and biological technologies for elimination of microplastics in water: Current status

Water pollution by microplastics (MPs) has emerged as a significant environmental and public health concern. Several conventional technologies in drinking water and wastewater treatment facilities are capable of capturing a substantial portion of microplastics from surface water; however, only limited methods are available for actual destruction of microplastics. Rate of success is highly variable, and actual mechanisms which result in MP destruction are only partly known. Photocatalysis and microbial degradation technologies show promise at laboratory scale for the transformation of microplastics to water-soluble hydrocarbons, carbon dioxide and, in limited cases, useful fuels. Both photocatalytic and microbial technologies offer the potential for long-term water security and ecological stability and deserve further attention by scientists. Additional research is necessary, however, in identifying more effective semiconductors for photocatalysis, and optimal effective microbial consortia and environmental conditions to optimize microplastic biodegradation. Many more polymer types beyond polyethylene must be studied for degradation, and laboratory-scale research must be expanded to field-scale. This paper provides a comprehensive overview of processes and mechanisms for removing MPs by photocatalysis and microbial technologies. It provides useful data for research dedicated to improved removal of MPs from surface waters.