Differences in the Plastispheres of Biodegradable and Non-biodegradable Plastics: A Mini Review

Preparation and weather-resistant study of poly(butylene adipate-co-terephthalate)/poly(butylene carbonate-co-terephthalate)/modified cotton stalk lignin composite film

The development of composites for food packaging that have good mechanical and antimicrobial characteristics is still a major challenge. In this study, lignin (VL) was grafted with vinyl triethoxysilane (VTES) via a solvothermal method in an alcohol-water system. The modified lignin (VL) was then melt-blended and co-extruded with poly(butylene adipate-co-terephthalate) (PBAT) along with various ratios of poly(butylene carbonate-co-terephthalate) (PBCT), all within a non-catalyzed system, to fabricate bio-based fully biodegradable composite films. The tensile strength and elongation at break of the specimens increased by 63.54 % and 16.34 %, and UV transmittance at 400 nm decreased by 64.28 %, while the crystallinity increased from 15.61 % to 26.87 % without significant changes in the melt temperature, and the biodegradability of the film was maintained. To assess the antibacterial adhesion effect, the E.coli adherence rate on the sample surface was determined at 24.39 %, using PBAT's bacterial resistance as a reference point. The artificial indoor accelerated aging experiments were conducted to establish a multi-factor coupled aging kinetics model for the film and perform sensitivity analyses concerning temperature, irradiance, and oxygen-to‑nitrogen ratio. The results showed that the incorporation of modified cotton stalk lignin and PBCT reduced the sensitivity of PBAT towards temperature, irradiance and oxygen‑nitrogen ratio, and significantly enhanced the weather resistance of PBAT films. Consequently, these modifications significantly broaden the range of applications in the field of plastic packaging.

Stress of polyethylene and polylactic acid microplastics on pakchoi（Brassica rapa subsp. chinensis） and soil bacteria: Biochar mitigation

It remains essential to investigate the differences in phytotoxic effects between conventional and biodegradable microplastics (MPs). Furthermore, the mechanisms by which biochar mitigates the toxic effects of MPs on crops and soil remain poorly understood. The results of this research indicated that, compared to control treatment (CK), the application of 2 % polyethylene (PE) alone led to a significant reduction in the fresh weight of pakchoi by 36.8 % (P < 0.05). In examining the activities of antioxidant, as well as the concentrations of MDA and GSH in pakchoi, the 2 % PE treatment exhibited the highest levels. In contrast, the treatment that received a mixed application of biochar and MPs did not surpass the levels observed in the microplastic-only application. The combination of 0.2 % polylactic acid (PLA) with biochar resulted in a substantial increase in Chao1 index, with improvements of 46.4 % to CK. The findings also suggested that biochar can significantly impact bacterial diversity in soil with MPs, thereby altering the functions and metabolic pathways. Consequently, this modification partly influences the growth characteristics of pakchoi. Notably, PE demonstrated a higher level of toxicity to both plants and soil microorganisms than PLA at same applied quantity. These findings open avenues for innovative sustainable agricultural practices.

Non-degradable microplastic promote microbial colonization: A meta-analysis comparing the effects of microplastic properties and environmental factors

Microplastics serve as favorable substrates for microbial colonization, promoting biofilm formation, which consequently facilitates the accumulation of pollutants and aids in the degradation of microplastics. Hence, obtaining a thorough comprehension of the factors that influence the development of microplastic biofilms is imperative. Nevertheless, there have been conflicting responses concerning biofilm formation in conjunction with microplastic characteristics and environmental conditions. As a result, a meta-analysis was conducted to quantitatively evaluate the impact of microplastic properties and environmental factors on biofilm formation. The findings indicated that the type and size of microplastics significantly influence biofilm growth on their surfaces. Non-degradable microplastics, particularly polyvinyl chloride (PVC) and polystyrene (PS), exhibited higher surface biomass and biodiversity in microplastic-attached biofilms compared to degradable microplastics. Furthermore, it was observed that smaller microplastics were more conducive to microbial colonization. Model selection and correlation analysis further indicated that the environment acts as a substantial predictor of biofilm formation, with prolonged exposure significantly enhancing microbial diversity within biofilms as opposed to short-term exposure. Moreover, meta-regression analysis illustrated a positive correlation between biofilm biomass and alpha-diversity with temperature, while salinity exhibited a negative correlation in diverse aquatic settings. Notably, the ease of biofilm formation on microplastics was observed to be greater in oceans compared to lakes, yet biofilms exhibited a higher diversity increment in lakes than their oceanic counterparts. In the long-term growth of biofilms, initial biomass and diversity are influenced by microplastic characteristics and the surrounding environment, although environmental influences may assume more significance as time progresses.

Zooming in the plastisphere: the ecological interface for phytoplankton-plastic interactions in aquatic ecosystems

Phytoplankton is an essential resource in aquatic ecosystems, situated at the base of aquatic food webs. Plastic pollution can impact these organisms, potentially affecting the functioning of aquatic ecosystems. The interaction between plastics and phytoplankton is multifaceted: while microplastics can exert toxic effects on phytoplankton, plastics can also act as a substrate for colonisation. By reviewing the existing literature, this study aims to address pivotal questions concerning the intricate interplay among plastics and phytoplankton/phytobenthos and analyse impacts on fundamental ecosystem processes (e.g. primary production, nutrient cycling). This investigation spans both marine and freshwater ecosystems, examining diverse organisational levels from subcellular processes to entire ecosystems. The diverse chemical composition of plastics, along with their variable properties and role in forming the "plastisphere", underscores the complexity of their influences on aquatic environments. Morphological changes, alterations in metabolic processes, defence and stress responses, including homoaggregation and extracellular polysaccharide biosynthesis, represent adaptive strategies employed by phytoplankton to cope with plastic-induced stress. Plastics also serve as potential habitats for harmful algae and invasive species, thereby influencing biodiversity and environmental conditions. Processes affected by phytoplankton-plastic interaction can have cascading effects throughout the aquatic food web via altered bottom-up and top-down processes. This review emphasises that our understanding of how these multiple interactions compare in impact on natural processes is far from complete, and uncertainty persists regarding whether they drive significant alterations in ecological variables. A lack of comprehensive investigation poses a risk of overlooking fundamental aspects in addressing the environmental challenges associated with widespread plastic pollution.

Dynamic changes of leachates of aged plastic debris under different suspended sand concentrations and their toxicity

Plastic pollution in aquatic environments poses significant ecological risks, particularly through released leachates. While traditional or non-biodegradable plastics (non-BPs) are well-studied, biodegradable plastics (BPs) have emerged as alternatives that are designed to degrade more rapidly within the environment. However, research on the ecological risks of the leachates from aged BPs in aquatic environments is scarce. This controlled laboratory study investigated the leachate release processes and associated toxicity of traditional non-BPs, i.e., polyethylene terephthalate (PET) and polypropylene (PP) and BPs, i.e., polylactic acid (PLA) combined with polybutylene adipate terephthalate (PBAT) and starch-based plastic (SBP) under different aging time and suspended sand concentrations (0, 50, 100, 250, and 500 mg/L). The results indicated that BPs release significantly higher levels of dissolved organic carbon (DOC) than those of non-BPs, particularly at elevated suspended sand concentrations. The DOC concentrations in PLA+PBAT leachate reached 2.69 mg/L, surpassing those of PET and PP. Additionally, BPs released organic matter of larger molecular weight and protein-like substances. Toxicity tests showed that leachates from BPs inhibited the activity of Daphnia magna more than those from non-BPs. At a suspended sand concentration of 500 mg/L, PLA+PBAT leachate caused a 30 % inhibitory rate of Daphnia magna. Despite enhanced degradability, leachates from BPs may pose increased environmental risks in ecosystems with high suspended sand concentrations. Comprehensive ecological risk assessments are essential for effectively managing and mitigating these hazards of plastic pollution.

Clonal expression and structural analysis of polylactic acid-degrading enzyme S8SP from Bacillus safensis

Polylactic acid (PLA) is one of the most popular biodegradable plastics favored over traditional plastics. However, it is more difficult to degrade than other biodegradable plastics probably due to the low species and number of PLA-degrading microorganisms degrading enzymes in the environment. Therefore, identifying PLA-degrading microorganisms and enzymes is of great significance for the popularization and application of PLA. This study identified a PLA-degrading enzyme, S8 serine peptidase (S8SP), from Bacillus safensis, and the heterologous expression of S8SP was conducted in Escherichia coli. PLA degradation ability of S8SP was investigated using scanning electron microscopy and water contact angle. The surface of S8SP-degraded PLA films showed obvious cracks and pits and exhibited improved hydrophilicity. The molecular weight of S8SP was about 42 kDa, and its optimum temperature and pH were 40°C and 8.0, respectively. S8SP could maintain high stability in the temperature range of 30°C-40°C and pH range of 7.0-9.0. Sodium ions (Na+), potassium ions (K+), Triton X-100, and Tween-80 promoted the enzyme activity of S8SP. S8SP had a high similarity degree to S8 serine peptidase from the genus Bacillus, and had the classical hydrolase-catalyzed triplet structure.

Enzymes offer a promising avenue for enhancing the competitiveness of biodegradable plastics in environmental restoration and the circular economy

As a promising alternative to traditional plastics, the widespread application of biodegradable plastic (BP) will help solve worsening environmental problems. Enzymes such as cutinase, lipase, protease and esterase produced by bacteria and fungi in the environment play a crucial role in the degradation, recycling and valorization of BP by degrading them into low-molecular-weight oligomers or small monomers. These enzymes offering advantages such as high efficiency, cleanliness, safety and environmental friendliness, making them more competitive in environmental restoration and circular economy. This review describes in detail the occurrence and distribution of enzymes involved in the degradation of BPs (represented by PHB, PLA and PCL). Omics methods (metagenomic and proteomic) combined with high-throughput platforms can screen out BP-degrading enzymes in different environments, and then use protein engineering to optimize the degrading enzymes to improve enzymatic degradation efficiency. Finally, we focus on the methods and strategies for the commercialization of degrading enzymes, future research prospects and challenges are also discussed. This review highlights the importance of BP-degrading enzymes in the bio-cycling of BP, and expected to drive the widespread use of BP.

Environmental Health and Safety Implications of the Interplay Between Microplastics and the Residing Biofilm

The increasing prevalence of microplastics in the environment has raised concerns about their potential environmental and health implications. Biofilms readily colonize microplastics upon their entry into the environment, altering their surface characteristics. While most studies have explored how biofilms influence the adsorption and transportation of other contaminants by microplastics, the reciprocal interplay between microplastics and biofilms and the resulting ecological risks remain understudied. This review comprehensively reviews the impact of microplastic properties on biofilm formation and composition, including the microbial community structure. We then explore the dynamic interactions between microplastics and biofilms, examining how biofilms alter the physicochemical properties, migration, and deposition of microplastics. Furthermore, we emphasize the potential of biofilm-colonized microplastics to influence the environmental fate of other pollutants. Lastly, we discuss how biofilm-microplastic interactions may modify the bioavailability, biotoxicity, and potential health implications of microplastics.

Biodegradable and conventional mulches inhibit nitrogen fixation by peanut root nodules - potentially related to microplastics in the soil

Mulching has been demonstrated to improve the soil environment and promote plant growth. However, the effects of mulching and mulch-derived microplastics (MPs) on nitrogen fixation by root nodules remain unclear. In this study, we investigated the effects of polyethylene (PE) and polylactic acid-polybutylene adipate-co-terephthalate (PLA-PBAT) film mulching on nitrogen fixation by root nodules after 4 years of continuous mulching using 15N tracer technology. Additionally, we examined the relationship between nitrogen fixation and MPs. We found a reduction in the proportion of nitrogen fixation by nodules (54.3 %-58.7 %) due to mulching. This decrease may be attributed to reduced dinitrogenase activity and flavonoid content at the seedling stage caused by mulching, and mulching with PLA-PBAT films significantly decreased the abundance of Bradyrhizobium at maturity. Furthermore, combined analysis of nitrogen-fixing bacteria (nifH) and metabolomes indicated that N-lauroylethanolamine may act as a regulatory signal influencing the root nodule nitrogen fixation process and that mulching resulted in significant changes in its content. The mantel test and PLS-PM suggest that microplastic from mulching may harm root nodule nitrogen fixation. This study reveals the influence of mulching on plant nitrogen uptake and the potential threat of mulch-derived microplastics, with a special focus on root nodule nitrogen fixation.

Research progress on degradation of biodegradable micro-nano plastics and its toxic effect mechanism on soil ecosystem

Biodegradable plastics (BPs) are known to decompose into micro-nano plastics (BMNPs) more readily than conventional plastics (CPs). Given the environmental risks posed by BMNPs in soil ecosystems, their impact has garnered increasing attention. However, research focusing on the toxic effects of BMNPs on soils remains relatively limited. The degradation process and duration of BMNPs in soil are influenced by numerous factors, which directly impact the toxic effects of BMNPs. This highlights the urgent need for further research. In this context, this review delineates the classification of BPs, investigates the degradation processes of BPs along with their influencing factors, summarizes the toxic effects on soil ecosystems, and explores the potential mechanisms that underlie these toxic effects. Finally, it provides an outlook on related research concerning BMNPs in soil. The results indicate that specific BMNPs release additives at a faster rate during decomposition, degradation, and aging, with certain compounds exhibiting increased bioavailability. Importantly, a substantial body of research has shown that BMNPs generally manifest more pronounced toxic effects in comparison to conventional micro-nano plastics (CMNPs). The toxic effects associated with BMNPs encompass a decline in soil quality and microbial biomass, disruption of nutrient cycling, inhibition of plant root growth, and negative impacts on invertebrate reproduction, survival, and fertilization rates. The rough and complex surfaces of BMNPs contribute to increased mechanical damage to tested organisms, enhance absorption by microorganisms, and disrupt normal physiological functions. Notably, the toxic effects of BMNPs on soil ecosystems are influenced by factors including concentration, type of BMNPs, exposure conditions, degradation products, and the nature of additives used. Therefore, it is crucial to standardize detection technologies and toxicity testing conditions for BMNPs. In conclusion, this review provides scientific evidence that supports effective prevention and management of BMNP pollution, assessment of its ecological risks, and governance of BMNPs-related products.

High-altitude aquatic ecosystems offer faster aging rate of plastics

While research on the aging behavior of plastics in aquatic systems is extensive, studies focusing on high-altitude ecosystems, characterized by higher solar radiation and lower temperatures, remain limited. This study investigated the long-term aging behavior of non-biodegradable plastics (non-BPs), namely polyethylene terephthalate (PET) and polypropylene (PP) and biodegradable plastics (BPs), specifically polylactic acid plus polybutylene adipate-co-terephthalate (PLA + PBAT) and starch-based plastic (SBP), in a tributary of the Yarlung Zangbo River on the high-altitude Tibetan Plateau. Over 84 days of field aging, all four types of plastics exhibited initial rapid aging followed by deceleration. This aging process can be divided into two phases: rapid surface oxidation aging and an aging plateau phase. Notably, PP aged at a rate comparable to BPs, contrary to expectations of faster aging for BPs. Compared to low-altitude aquatic ecosystems, plastics in this study showed a faster aging rate. This was primarily due to intense ultraviolet radiation causing severe photoaging. Furthermore, the lower temperatures contributed to the formation of thinner biofilms. These thinner biofilms exhibited a reduced capacity to block light, further exacerbating the photoaging process of plastics. Statistical analysis results indicated that temperature, total nitrogen TN, and total phosphorus TP were likely the main water quality parameters influencing plastic aging. The varying effects of water properties and nutrients underscore the complex interaction of water quality parameters in high-altitude environments. Given the delicate nature of the high-altitude environment, the environmental impact of plastics, especially BPs, warrants careful consideration.

Biodegradation of poly-3-hydroxybutyrate after soil inoculation with microbial consortium: Soil microbiome and plant responses to the changed environment

Biodegradable plastics play a vital role in addressing global plastics disposal challenges. Poly-3-hydroxybutyrate (P3HB) is a biodegradable bacterial intracellular storage polymer with substantial usage potential in agriculture. Poly-3-hydroxybutyrate and its degradation products are non-toxic; however, previous studies suggest that P3HB biodegradation negatively affects plant growth because the microorganisms compete with plants for nutrients. One possible solution to this issue could be inoculating soil with a consortium of plant growth-promoting and N-fixing microorganisms. To test this hypothesis, we conducted a pot experiment using lettuce (Lactuca sativa L. var. capitata L.) grown in soil amended with two doses (1 % and 5 % w/w) of P3HB and microbial inoculant (MI). We tested five experimental variations: P3HB 1 %, P3HB 1 % + MI, P3HB 5 %, P3HB 5 % + MI, and MI, to assess the impact of added microorganisms on plant growth and P3HB biodegradation. The efficient P3HB degradation, which was directly dependent on the amount of bioplastics added, was coupled with the preferential utilization of P3HB as a carbon (C) source. Due to the increased demand for nutrients in P3HB-amended soil by microbial degraders, respiration and enzyme activities were enhanced. This indicated an increased mineralisation of C as well as nitrogen (N), sulphur (S), and phosphorus (P). Microbial inoculation introduced specific bacterial taxa that further improved degradation efficiency and nutrient turnover (N, S, and P) in P3HB-amended soil. Notably, soil acidification related to P3HB was not the primary factor affecting plant growth inhibition. However, despite plant growth-promoting rhizobacteria and N2-fixing microorganisms originating from MI, plant biomass yield remained limited, suggesting that these microorganisms were not entirely successful in mitigating the growth inhibition caused by P3HB.

Synergistic preparation of a straw fiber/polylactic acid composite with high toughness and strength through interfacial compatibility enhancement and elastomer toughening

Plant fiber-reinforced polylactic acid (PLA) composites are extensively utilized in eco-friendly packaging, sports equipment, and various other applications due to their environmental benefits and cost-effectiveness. However, PLA suffers from brittleness and poor toughness, which restricts its use in scenarios demanding high toughness. To expand the application range of plant fiber-reinforced PLA-based composites and enhance their poor toughness, this study employed a two-step process involving wheat straw fiber (WF) to improve the interfacial compatibility between WF and PLA. Additionally, four elastomeric materials-poly (butylene adipate-co-terephthalate) (PBAT), poly (butylene succinate) (PBS), polycaprolactone (PCL), and polyhydroxyalkanoate (PHA)-were incorporated to achieve a mutual reactive interface enhancement and elastomeric toughening. The results demonstrated that Fe3+/TsWF/PLA/PBS exhibited a tensile strength, elongation at break, and impact strength of 34.01 MPa, 14.23 %, and 16.2 kJ/m2, respectively. These values represented a 2.4 %, 86.7 %, and 119 % increase compared to the unmodified composites. Scanning electron microscopy analysis revealed no fiber exposure in the cross-section, indicating excellent interfacial compatibility. Furthermore, X-ray diffraction and differential scanning calorimetry tests confirmed improvements in the crystalline properties of the composites. This work introduces a novel approach for preparing fiber-reinforced PLA-based composites with exceptional toughness and strength.

Accumulation and growth toxicity mechanisms of fluxapyroxad revealed by physiological, hepatopancreas transcriptome, and gut microbiome analysis in Pacific white shrimp (Litopenaeus vannamei)

Fluxapyroxad (FX), a typical succinate dehydrogenase inhibitor fungicide, is causing increased global concerns due to its fungicide effects. However, the accumulation and grow toxicity of FX to Litopenaeus vannamei (L. vannamei) is poorly understand. Therefore, the accumulation pattern of FX in L. vannamei was investigated for the first time in environmental concentrations. FX accumulated rapidly in shrimp muscle. Meanwhile, growth inhibition was observed and the mechanism derived by primarily accelerated glycolipid metabolism and reduced glycolipid content. Moreover, exposure to environmental concentrations of FX induced significant growth inhibition and oxidative stress and inhibited oxidative phosphorylation and TCA cycle in L. vannamei. The endocytosis signaling pathway genes were activated, thereby driving growth toxicity. Oxidative phosphorylation and cytosolic gene expression were further rescued in elimination experiments, demonstrating the mechanism of growth toxicity by FX exposure. The results revealed that FX persistently altered the gut microbiome of L. vannamei using gut microbiome sequencing, particularly with increased Garcinia Purple Pseudoalteromonas luteoviolacea for organic pollutant degradation. This study provided new insights into the potential toxicity of FX to marine organisms, emphasizing the need for further investigation and potential regulatory considerations.

Plastisphere-hosted viruses: A review of interactions, behavior, and effects

Microbial communities, including bacteria, diatoms, and fungi, colonize plastic surfaces, forming biofilms known as the "plastisphere." Recent research has revealed that plastispheres also host a wide range of viruses, sparking interest in microbial ecology and virology. This shared habitat allows viruses to replicate, interact, infect, and spread, potentially impacting the environment and human health. Consequently, viruses attached to microplastics are now recognized to have broad effects on cellular and immune responses. However, the ecology and implications of viruses hosted in plastisphere habitats remain poorly understood, highlighting their fundamental importance as a subject of study. This review explores various pathways for virus attachment to plastispheres, factors influencing these interactions, their impacts within plastisphere and host-associated environments, and associated issues. It also summarizes current research and identifies knowledge gaps. We anticipate that this paper will help improve our predictive understanding of plastisphere viruses in natural settings and emphasizes the need for more research in real-world environments to advance the field.

Exploring the hidden environmental pollution of microplastics derived from bioplastics: A review

Bioplastics might be an ecofriendly alternative to traditional plastics. However, recent studies have emphasized that even bioplastics can end up becoming micro- and nano-plastics due to their degradation under ambient environmental conditions. Hence, there is an urgent need to assess the hidden environmental pollution caused by bioplastics. However, little is known about the evolutionary trends of bibliographic data, degradation pathways, formation, and toxicity of micro- and nano-scaled bioplastics originating from biodegradable polymers such as polylactic acid, polyhydroxyalkanoates, and starch-based plastics. Therefore, the prime objective of the current review was to investigate evolutionary trends and the latest advancements in the field of micro-bioplastic pollution. Additionally, it aims to confront the limitations of existing research on microplastic pollution derived from the degradation of bioplastic wastes, and to understand what is needed in future research. The literature survey revealed that research focusing on micro- and nano-bioplastics has begun since 2012. This review identifies novel insights into microbioplastics formation through diverse degradation pathways, including photo-oxidation, ozone-induced degradation, mechanochemical degradation, biodegradation, thermal, and catalytic degradation. Critical research gaps are identified, including defining optimal environmental conditions for complete degradation of diverse bioplastics, exploring micro- and nano-bioplastics formation in natural environments, investigating the global occurrence and distribution of these particles in diverse ecosystems, assessing toxic substances released during bioplastics degradation, and bridging the disparity between laboratory studies and real-world applications. By identifying new trends and knowledge gaps, this study lays the groundwork for future investigations and sustainable solutions in the realm of sustainable management of bioplastic wastes.

Deterioration of single-use biodegradable plastics in high-humidity air and freshwaters over one year: Significant disparities in surface physicochemical characteristics and degradation rates

More single-use plastics are accumulating in the environment, and likewise biodegradable plastics (BPs), which are being vigorously promoted, cannot escape the fate. Currently, studies on the actual degradation of BPs in open-air and freshwaters are underrepresented despite they are potentially headmost leakage and contamination sites for disposable BPs. Herein, we compared the degradation behavior of six BP materials and non-degradable polypropylene (PP) plastics over a 1-year in situ suspension in the high-humidity air, a eutrophic river, and an oligotrophic lake. Moreover, a 3-months laboratory incubation was performed to detect the release of dissolved organic carbon (DOC) from BPs. In both air and freshwaters, poly(p-dioxanone) (PPDO) degraded significantly while PP and polylactic acid (PLA) showed no signs of degradation. The average degradation rates of three poly(butylene adipate-co-terephthalate) (PBAT)-based films varied: 100% in river, 55% in lake, and 10% in air. In addition to PLA, surface chemical groups, hydrophilicity, and thermal stability of BPs changed, and microplastics were found on their surfaces. Correspondingly, BPs with faster degradation rates released relatively higher amounts of DOC. Environmental microbial and chemical characteristics may contribute to differences in BP degradation besides polymer specificity. Altogether, our results indicate the need for appropriate monitoring of BPs.

Evaluation of bioplastics biodegradation under simulated landfill conditions

Bioplastics that are generated from renewable sources have been regarded as an alternative to conventional plastics. Polylactic acid (PLA) is one of the mostly produced bioplastics because of its long shelf life for various applications. Even though bioplastics have drawn attention recently, their ultimate fate in landfills is still unknown. In this study, a standardized laboratory-scale lysimeter experiment was performed for the simulation of landfill conditions in order to evaluate the biodegradability of PLA during municipal solid waste stabilization. The reactors were loaded with municipal solid waste (MSW) taken from an operating landfill, certified PLA cups, and seed sludge. Various phases of landfill stabilization were simulated; hence, the reactors were operated under aerobic, semi-aerobic, and anaerobic conditions, respectively. Throughout the operation, both leachate and biogas generation in the reactors were regularly monitored. At the end of each phase, bioplastic cups were removed from the reactors, gently cleaned, weighed, and examined under a scanning electron microscope (SEM). The experimental results indicated that bioplastics did not undergo significant biodegradation during the first two stabilization phases (aerobic and semi-aerobic). On the other hand, it was observed that the cups were much softer and whiter at the end of the anaerobic phase. The weight of cups decreased by 12.8% on average, and their surfaces were prominently damaged after the completion of the last phase indicating the potential signs of biodegradation.

Current advances, challenges and strategies for enhancing the biodegradation of plastic waste

Due to its highly recalcitrant nature, the growing accumulation of plastic waste is becoming an urgent global problem. Biodegradation is one of the best possible approaches for the treatment of plastic waste in an environmentally friendly manner, but our current knowledge on the underlying mechanisms, as well as strategies for the development and enhancement of plastic biodegradation are still limited. This review aims to provide an updated and comprehensive overview of current research on plastic waste biodegradation, focusing on enhancement strategies with ongoing research significance, including the mining of highly efficient plastic-degrading microorganisms/enzymes, utilization of synergistic additives, novel pretreatment approaches, modification via molecular engineering, and construction of bacterial/enzyme consortia systems. Studying these strategies can (i) enrich the high-performance microbial/enzymes toolbox for plastic degradation, (ii) provide methods for recycling and upgrading plastics, as well as (iii) enable further molecular modification and functional optimization of plastic-degrading enzymes to realize economically viable biodegradation of plastics. To the best of our knowledge, this is the first review to discuss in detail strategies to enhance biodegradation of plastics. Finally, some recommendations for future research on plastic biodegradation are listed, hoping to provide the best direction for tackling the plastic waste dilemma in the future.

Research progress on the role of biofilm in heavy metals adsorption-desorption characteristics of microplastics: A review

Microplastics (MPs) have been found to be widely distributed in aquatic environments, where they will interact with toxic heavy metals and result in more serious adverse effects on the aquatic environments and organisms. However, after entering the aquatic environments, MPs are quickly covered by biofilms, which significantly modify MPs properties and relevant heavy metals adsorption-desorption characteristics In order to better understand the adsorption behavior of heavy metals on biofilm developed MPs (BMPs), we comprehensively reviewed representative studies in this area. First, we summarized the formation process of biofilms on MPs. Subsequently, we reviewed the current understanding on the influence of biofilm formation on the properties of MPs and discussed the metal adsorption-desorption characteristics of MPs affected by these changes. Finally, based on the systematic literature review, some future research needs and strategies were proposed to further understand the interactions between MPs and heavy metals.

New Horizons in Nanofiller-Based Polymer Composites II

Nanofiller-based polymer composites are a hot-topic research area with significant industrial potential [...].

Toughening Enhancement Mechanism and Performance Optimization of Castor-Oil-Based Polyurethane Cross-Linked Modified Polybutylene Adipate/Terephthalate Composites

In this study, polyol castor oil (CO) and toluene-2,4-diisocyanate (TDI) were selected to modify PBAT, and castor-oil-based polyurethane (COP) was produced in a PBAT matrix using melt-blending and hot-pressing technology to study the effect of network cross-linking structure on various properties of bio-based polyester PBAT, aiming to introduce CO and TDI to improve the mechanical properties of composite materials. The results showed that when the total addition of CO and TDI was 15%, and the ratio of the hydroxyl group of CO to the isocyanate group of TDI was 1:1, the mechanical properties were the best. The tensile strength of the composite was 86.19% higher than that of pure PBAT, the elongation at break was 70.09% higher than that of PBAT, and the glass transition temperature was 7.82 °C higher than that of pure PBAT. Therefore, the composite modification of PBAT by CO and TDI can effectively improve the heat resistance and mechanical properties of PBAT-based composites.

Surface structures changes and biofilm communities development of degradable plastics during aging in coastal seawater

Biodegradable plastics (BPs) are a suitable alternative to conventional plastics. Still, their excessive or unplanned use may disrupt the abundance and community structure of the microbial population. To this end, a 58-day experiment in which biodegradable plastic objects, such as bags and boxes, were exposed to near-coastal seawater was conducted. They also assessed how they affected the diversity and organization of bacterial populations in seawater and on the surface of BPs products. It is evident that after the exposure time, both BP's bag and box products deteriorate in the ocean to varying degrees. The results of high-throughput sequencing of bacterial communities in seawater and those colonized on BPs products reveal significant differences in microbial community structures between seawater and BPs plastic samples. These suggest that the degradation of biodegradable plastics is shadowed by microorganisms and exposure time, while BP products influence the structural characteristics of microbial communities.

Microplastic biodegradability dependent responses of plastisphere antibiotic resistance to simulated freshwater-seawater shift in onshore marine aquaculture zones

MPs carrying ARGs can travel between freshwater and seawater due to intensive land-sea interaction in onshore marine aquaculture zones (OMAZ). However, the response of ARGs in plastisphere with different biodegradability to freshwater-seawater shift is still unknown. In this study, ARG dynamics and associated microbiota on biodegradable poly (butyleneadipate-co-terephthalate) (PBAT) and non-biodegradable polyethylene terephthalate (PET) MPs were investigated through a simulated freshwater-seawater shift. The results exhibited that freshwater-seawater shift significantly influenced ARG abundance in plastisphere. The relative abundance of most studied ARGs decreased rapidly in plastisphere after they entered seawater from freshwater but increased on PBAT after MPs entered freshwater from seawater. Besides, the high relative abundance of multi-drug resistance (MDR) genes occurred in plastisphere, and the co-change between most ARGs and mobile genetic elements indicated the role of horizontal gene transfer on ARG regulation. Proteobacteria was dominant phylum in plastisphere and the dominant genera, such as Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Afipia, Gemmobacter and Enhydrobacter, were significantly associated with qnrS, tet and MDR genes in plastisphere. Moreover, after MPs entered new water environment, the ARGs and microbiota genera in plastisphere changed significantly and tended to converge with those in receiving water. These results indicated that MP biodegradability and freshwater-seawater interaction influenced potential hosts and distributions of ARGs, of which biodegradable PBAT posed a high risk in ARG dissemination. This study would be helpful for understanding the impact of biodegradable MP pollution on spread of antibiotic resistance in OMAZ.

The plastisphere of biodegradable and conventional microplastics from residues exhibit distinct microbial structure, network and function in plastic-mulching farmland

The inhomogeneity of plastisphere and soil may result in different microbial communities, thus potentially affecting soil functions. Biodegradable plastics offer an alternative to conventional plastics, nevertheless, the inadequate end-of-life treatment of biodegradable plastics may release more microplastics. Herein, we collected PE and PBAT/PLA microplastics in plastic-mulching farmland in Hebei, China. The bacterial communities of soil, PE and PBAT/PLA plastisphere were investigated using 16 S high-throughput sequencing. We found that the structure of bacterial communities in PBAT/PLA plastisphere were significantly distinct from PE plastisphere and soil. The alpha diversities in PBAT/PLA plastisphere were significantly lower than PE plastisphere and soil. Statistical analysis of differentially ASVs suggested that PBAT/PLA microplastics act as a filter, enriching taxa with the capability to degrade plastic polymers such as Proteobacteria and Actinobacteria. Compared to PE plastisphere, PBAT/PLA plastisphere has networks of less complexity, lower modularity, and more competitive interactions. Predicted metabolic pathways involved in human diseases, carbohydrate metabolism, amino acid metabolism, and xenobiotic biodegradation and metabolism were promoted in PBAT/PLA plastisphere, along with the facilitation in abundance of genes associated with carbon and nitrogen cycling. Our results highlighted the uniqueness of plastisphere of biodegradable microplastics from conventional microplastics and their potential impact on soil functions.

Bacterial dynamics during the burial of starch-based bioplastic and oxo-low-density-polyethylene in compost soil

BACKGROUND

Plastic waste accumulation is one of the main ecological concerns in the past decades. A new generation of plastics that are easier to degrade in the environment compared to conventional plastics, such as starch-based bioplastics and oxo-biodegradable plastics, is perceived as a solution to this issue. However, the fate of these materials in the environment are unclear, and less is known about how their presence affect the microorganisms that may play a role in their biodegradation. In this study, we monitored the dynamics of bacterial community in soil upon introduction of commercial carrier bags claimed as biodegradable: cassava starch-based bioplastic and oxo-low-density polyethylene (oxo-LDPE). Each type of plastic bag was buried separately in compost soil and incubated for 30, 60, 90, and 120 days. Following incubation, soil pH and temperature as well as the weight of remaining plastics were measured. Bacterial diversity in soil attached to the surface of remaining plastics was analyzed using Illumina high-throughput sequencing of the V3-V4 region of 16SrRNA gene.

RESULTS

After 120 days, the starch-based bioplastic weight has decreased by 74%, while the oxo-LDPE remained intact with only 3% weight reduction. The bacterial composition in soil fluctuated over time with or without the introduction of either type of plastic. While major bacterial phyla remained similar for all treatment in this study, different types of plastics led to different soil bacterial community structure. None of these bacteria were abundant continuously, but rather they emerged at specific time points. The introduction of plastics into soil increased not only the population of bacteria known for their ability to directly utilize plastic component for their growth, but also the abundance of those that may interact with direct degraders. Bacterial groups that are involved in nitrogen cycling also arose throughout burial.

CONCLUSIONS

The introduction of starch-based bioplastic and oxo-LDPE led to contrasting shift in soil bacterial population overtime, which may determine their fate in the environment.

Synergistic modification of polylactic acid by oxidized straw fibers and degradable elastomers: A green composite with good strength and toughness

Polylactic acid-based (PLA) composites are widely used in biomedicine, electrical components, food packaging and other fields, but their unsatisfactory mechanical properties such as high brittleness and poor toughness, cause problems in functional applications. This work developed a green and environmentally friendly strategy to improve PLA mechanical properties. Flexible polybutylene succinate (PBS) and alkaline hydrogen peroxide (AHP) treated straw fibers (SF) synergistically modified PLA. AHP is decomposed into a large amount of HOO-, which oxidizes the hydroxyl groups in SF to carboxyl groups to obtain oxidized straw fiber (OSF), which reacts with PLA in the molten state to form new ester bonds. The tensile strength of the OSF/PLA composite is 41.78 MPa, 38 % higher than the SF/PLA composite. The impact toughness of OSF/PBS/PLA composite is 14.47 KJ/m² increased by 54 % after the adding PBS, while the tensile strength was also better than the control group. The synergistic action of PLA and PBS in OSF is attributed to the formation of new chemical bonds, efficient crystallization, and compatible interface. This study provides a new strategy to produce fiber-reinforced PLA composites with good toughness. It takes positive significance for developing degradable plastics with good performance and controllable cost.

Persistent versus transient, and conventional plastic versus biodegradable plastic? -Two key questions about microplastic-water exchange of antibiotic resistance genes

The ubiquitous microplastics (MPs) in water environment play an important role in the dissemination of antibiotic resistance genes (ARGs) due to their exchange between floating MPs and receiving waters. However, whether the ARG exchange is persistent or transient and what are the differences in ARG exchange between conventional plastics and biodegradable plastics are the two key issues to be addressed. In this study, biodegradable PBAT and non-biodegradable PET MPs were chosen to explore the MP-water ARG exchange after the MPs floated to the receiving waters. The results demonstrated that the active exchange of ARGs between MPs and receiving waters occurred, which, however, were transient for most of ARGs. The relative abundance of ARGs both on the MPs and in the waters rapidly decreased to the initial or lower levels within 4 weeks. Approximately 25-50% (ARG subtype number ratio) of studied ARG subtypes were introduced into the receiving waters by MPs, and 35-65% of studied ARG subtypes went through fluctuation in terms of abundance on MPs and in the receiving water. ARGs tended to converge between MPs and the receiving waters with time. Furthermore, the ARG exchange between MPs and waters facilitated horizontal gene transfer (HGT). IntI1 and tnpA05 played the crucial roles in HGT, which was indicated by their correlated change with most ARGs; in contrast, tnpA04 showed the obvious lagging responses. The biodegradable MP of PBAT generally accumulated higher levels of most ARGs including multidrug resistant genes than the non-biodegradable MP of PET. The transient exchange of most ARGs between MPs and water implies that the on-off hitchhiking of ARGs on MPs in aquatic environment may not exert significant influence on ARG transmission. However, compared with the conventional plastics, the biodegradable MPs might pose much higher ARG dissemination risks due to the higher enrichment of ARGs particularly with people's ever-increasingly usage. Enough attention must be paid to this emerging issue.

Slower antibiotics degradation and higher resistance genes enrichment in plastisphere

Microplastics (MPs) are increasingly entering the urban aquatic ecosystems, and the environmental significance and health risks of plastisphere, a special biofilm on MPs, have received widespread attention. In this study, MPs of polylactic acid (PLA) and polyvinyl chloride (PVC) and quartzite were incubated in an urban water environment, and the tetracycline (TC) degradation ability was compared. Approximatedly 24% of TC biodegraded in 28 d in the water-quartzite system, which is significantly higher than that in the water-PLA (17.3%) and water-PVC systems (16.7%). Re-incubation of microorganisms in biofilms affirmed that quartzite biofilm has a higher TC degradation capacity than the plastisphere. According to high-throughput sequencing of 16S rRNA and metagenomic analysis, quartzite biofilm contained more abundant potential TC degrading bacteria, genes related to TC degradation (eutG, aceE, and DLAT), and metabolic pathways related to TC degradation. An oligotrophic environment on the quartzite surface might lead to the higher metabolic capacity of quartzite biofilm for unconventional carbons, e.g., TC. It is also found that, compared with quartzite biofilm, the distinct microbes in the plastisphere carried more antibiotic resistance genes (ARGs). Higher affinity of MPs surface to antibiotics may lead to higher antibiotics stress on the plastisphere, which further amplify the carrying capacity for ARGs of microorganisms in the plastisphere. Compared to the nondegradable PVC MPs, surface of the biodegradable PLA plastics harbored significantly higher amounts of biomass and ARGs. Compared to the mineral particles, the capability of plastisphere has lower ability to degrade unconventional carbon sources such as the refractory organic pollutants, due to the abundance of carbon sources (adsorbed organic carbon and endogenous organic carbon) on the MPs surface. Meanwhile, the stronger adsorption capacity for pollutants also leads to higher pollutant stress (such as antibiotic stress) in plastisphere, which in turn affects the microbiological characteristics of the plastisphere itself, such as carrying more ARGs.

Research and Application of Polypropylene Carbonate Composite Materials: A Review

The greenhouse effect and plastic pollution caused by the accumulation of plastics have led to a global concern for environmental protection, as well as the development and application of biodegradable materials. Polypropylene carbonate (PPC) is a biodegradable polymer with the function of "carbon sequestration", which has the potential to mitigate the greenhouse effect and the plastic crisis. It has the advantages of good ductility, oxygen barrier and biocompatibility. However, the mechanical and thermal properties of PPC are poor, especially the low thermal degradation temperature, which limits its industrial use. In order to overcome this problem, PPC can be modified using environmentally friendly materials, which can also reduce the cost of PPC-based products to a certain extent and enhance their competitiveness in terms of improving their mechanical and thermal properties. In this paper, we present different perspectives on the synthesis, properties, degradation, modification and post-modification applications of PPC. The modification part mainly introduces the influence of inorganic materials, natural polymer materials and degradable polymers on the performance of PPC. It is hoped that this work will serve as a reference for the early promotion of PPC.