Biodegradability standards for carrier bags and plastic films in aquatic environments: a critical review

Assessment of the biodegradability of polylactic acid (PLA) in freshwater using EN ISO 14851:2019: Challenges and outcomes

The biodegradability of bioplastics in natural environments remains a highly debated topic within the scientific community. It is assessed primarily using the compostability standard EN 13432, although this, however, does not accurately reflect degradation processes occurring in aquatic environments. To verify the biodegradability of polylactic acid (PLA) in freshwater, two tests, differing only in the inoculum sampling location, were conducted according to EN ISO 14851:2019, measuring oxygen demand. However, to gain a comprehensive understanding, bioplastics biodegradation should be thoroughly investigated at multiple levels beyond oxygen consumption. Additional analyses, including morphological and thermal characterization of polymers and assessment of inoculum characteristics, are fundamental in providing valuable insights into degradation mechanisms. Biodegradability tests revealed low biodegradation rates (44.04 % and 23.38 %), with no evident weight change in PLA pellets during testing. Analytical techniques (FT-IR, DSC, SEM) indicated negligible visual or structural modifications between virgin and tested pellets. Therefore, under conditions specified by the standard PLA pellets did not undergo significant biodegradation in freshwater. Discrepancies between tests α and β suggested variability due to inoculum quality. A series of challenges persist when implementing this standard, including the lack of a threshold for use in clearly classifying a bioplastic as "biodegradable" and flexibility in selecting process parameters (e.g., test material shape and size, duration, temperature, inoculum percentage). Accordingly, to facilitate a reliable assessment of the biodegradability of bioplastics in freshwater, the EN ISO 14851:2019 standard should be amended and updated.

Rayon fibre rope: A biodegradable alternative for marine use?

Rayon fibres are well-known materials that were primarily utilised as reinforcement in tyres. Today these materials are perceived as a promising substitute for synthetic fibres, exhibiting good mechanical characteristics and biodegradation in many environments. This paper investigates their potential use for marine structures. It first describes the tensile properties of the fibres and their derived yarns and ropes. These properties are then monitored during seawater ageing and the ultimate biodegradation is characterised by respirometry tests. Both material scales demonstrate rapid degradation rates under biotic conditions (90 % strength reduction after 2 weeks for yarns and 6 months for small ropes) and a relative stability in abiotic conditions. Additionally, the fibres show rapid bio-assimilation rates. The rope construction is demonstrated to have a significant impact on the degradation kinetics, suggesting possible strategies to enhance durability. The results indicate that these rayon fibre ropes may offer an attractive alternative to synthetic fibre ropes to reduce impact where there is a high risk of rope loss at sea.

An Analytical Workflow to Quantify Biodegradable Polyesters in Soils and Its Application to Incubation Experiments

Soil biodegradable polyesters are designed to undergo to microbial utilization in aerobic soils, forming carbon dioxide and microbial biomass. These polyesters are thus viable substitutes for conventional, persistent polymers (e.g., polyethylene) in specific applications for which the transfer of some of the polymers into the soil is inevitable. While polymer biodegradability is often assessed in laboratory incubations using respirometric analysis of formed CO2, approaches to accurately quantify biodegradable polyesters in soils and to track their mass loss in field incubations over time remain missing. This study first introduces an analytical workflow combining Soxhlet extraction with proton nuclear magnetic resonance spectroscopy for the accurate, high-throughput, and chemically selective quantification of eight commercially important biodegradable polyesters (i.e., poly(butylene adipate-co-terephthalate), polylactic acid, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), polycaprolactone, polybutylene adipate, polybutylene azelate, and polybutylene succinate), and the nonbiodegradable polymer polystyrene, in six soils spanning a range of types and physicochemical properties. This work introduces an effective sample deployment-retrieval approach that, combined with the analytical method, allows the biodegradation of poly(butylene adipate-co-terephthalate) and polylactic acid from a biodegradable mulch film in three agricultural soils to be monitored. In combination, the two parts of this work lay the foundation to accurately quantify and monitor biodegradable polymers in soils.

A life cycle assessment approach to minimize environmental impact for sustainable printed sensors

A printed hybrid sensor tag for applications in disposable healthcare and environmental monitoring optimized toward sustainability is presented. Following a systematic Life Cycle Assessment according to ISO 14040:2006 guidelines, the global warming potential associated with various substrate-, electrode-, and sensing materials, as well as manufacturing and end-of-life strategies, are evaluated. Results show that the utilization of bio-based polyethylene and copper inks can minimize the global warming potential most effectively by up to 39% from 42gCO2eq to 25.7gCO2eq per sensor tag. Among manufacturing methods, screen printing coupled with intense pulse light curing emerges as the most eco-efficient combination. Recycling is the most sustainable end-of-life option, although infrastructure challenges impede its full implementation. The silicon sensor chip needed for data communication has been identified as environmental hotspot. This study offers a comprehensive environmental evaluation of sustainable printed sensors and highlights critical challenges and opportunities for the electronics industry, particularly in relation to material selection, recycling strategies, and system-level considerations.

Exploring the plastic-fed Indian mealworm (Tenebrio molitor) gut bacterial strain (Bacillus subtilis AP-04) - A potential driver of polyethylene degradation

Plastic biodegradation by microbes is an environmentally friendly and sustainable approach that has no negative consequences. In this study, mealworms were fed with 9 different diets with expanded polystyrene (EPS) and polyethylene foam (PF), after 28 days of incubation mealworm survival rates were highest at 93.3 % when fed wheat bran alone whereas 83.3 % and 80 % when fed EPS and PF exclusively, indicating their adaptability to different plastics and their ability to thrive in various conditions. Histological examination revealed ingestion of EPS and PF found in the intestine confirming through cell wall disruptions. Ten bacterial isolates (AMI-1 to AMI-10) were obtained from EPS and PF-fed mealworms gut. After 30 days in mineral salt media (MSM) with low-density polyethylene (LDPE), AMI-4 showed higher turbidity and biofilm formation. Out of ten isolates seven bacterial isolates produced lipase, six produced proteases and laccases, and all exhibited positive amylase activity, with the highest zone formation in AMI-4. Morphophysical characteristics and 16S rRNA sequencing identified AMI-4 as Bacillus subtilis AP-04 (OR288581). A higher ATP value (783 ± 84.69), LDPE film Weight loss (36.55 %) and CO2 evolution (15.8 ± 0.99-22.39 ± 1.40 g/l) and the mechanical changes of LDPE film were confirmed through GSM loss 27.24 % and decrease in tensile strength (9.82 ± 0.61-7.98 ± 0.50 Mpa) by Bacillus subtilis AP-04 was recorded at 60 days of incubation. AFM, FTIR, and SEM analyses confirmed degradation in treated LDPE films compared to controls. This study reveals the potential of gut bacterial strain (Bacillus subtilis AP-04) on LDPE film, indicating their potential for bioremediation of plastic waste on a larger scale.

Carbon cycle of polyhydroxyalkanoates (CCP): Biosynthesis and biodegradation

Carbon neutrality of bioactive materials is vital in promoting sustainable development for human society. Polyhydroxyalkanoates (PHAs) is a class of typical carbon-cycle bio-polyesters synthesized by microorganisms using sugars, organic acids, and even carbon dioxide. PHAs first degrade into 3-hydroxybutyrate (3HB) before further breaking down into carbon dioxide and water, aligning with carbon-neutral goals. Due to their diverse molecular structures and material properties, excellent biocompatibility, and controlled biodegradability, PHAs have found widespread applications in environmental protection and biomedicine. However, challenges persist in achieving cost-effective PHA production and reusing degradation products. Additionally, understanding the carbon pathways in PHA synthesis and degradation remains limited. In this review, we first introduce the concept of the Carbon Cycle of Polyhydroxyalkanoates (CCP) and describe the biosynthetic pathways of aromatic monomers, carbon conversion processes, and PHA degradation in compost, soil, and marine environments. This will help us fully understand the sustainable utilization value of PHA as a biomaterial. Future trends point to integrating synthetic biology with emerging technologies to produce low-cost, high-value PHAs, supporting global green and low-carbon development.

Microplastic pollution in the marine environment: Distribution factors and mitigation strategies in different oceans

As the COVID-19 pandemic began in 2020, plastic usage spiked, and microplastic (MP) generation has increased dramatically. It is documented that MP can transfer from the source to the ocean environment where they accumulate as the destination. Therefore, it is essential to understand their transferring pathways and effective environmental factors to determine the distribution of MPs in the marine environment. This article reviews the environmental factors that affect MP distribution in the oceans including abiotic such as ocean currents and wind direction, physical/chemical and biological reactions of MPs, natural sinking, particle size and settling velocity, and biotic including biofouling, and incorporation in fecal material. It was found that velocity and physical shearing are the most important parameters for MP accumulation in the deep ocean. Besides, this review proposes different research-based, national-level, and global-level strategies for the mitigation of MPs after the pandemic. Based on the findings, the level of MP pollution in the oceans is directly correlated to coastal areas with high populations, particularly in African and Asian countries. Future studies should focus on establishing predictive models based on the movement and distribution of MPs to mitigate the levels of pollution.

Increased adsorption of diflubenzuron onto polylactic acid microplastics after ultraviolet weathering can increase acute toxicity in the water flea (Daphnia magna)

The ultraviolet (UV) weathering of microplastics (MPs) can lead to higher adsorption of harmful contaminants, thus increasing the potential risks of their combined effects. Because biodegradable MPs are more susceptible to UV weathering than conventional MPs, concerns have arisen about their ecological toxicity and environmental impact. Therefore, this study investigated the mechanisms associated with the adsorption of the pesticide diflubenzuron (DFB) onto polylactic acid (PLA) MP particles after UV weathering and the acute effects (48 h) of their combination on the water flea Daphnia magna. These effects were also compared with those of the conventional MP polyethylene terephthalate (PET). UV weathering led to a greater number of cracks and pores in the PLA particles compared to PET, as well as a higher number of oxygen-based functional groups and a larger surface area. These surface changes in UV-weathered PLA particles promoted higher DFB adsorption, which in turn led to stronger acute toxicity for D. magna compared to UV-weathered PET particles. Combined exposure to 25 ng L-1 DFB and both UV-weathered and non-UV-weathered MPs significantly reduced the chitin content in D. magna, while combined exposure to 12.5 ng L-1 DFB and the MPs increased the chitin content. This effect was more pronounced for UV-weathered PLA exposure than UV-weathered PET exposure. The expression of the genes for chitinase and endocrine glycoprotein, both of which are closely associated with the toxic mechanisms of DFB, showed no significant changes with the combination of 25 ng L-1 DFB and non-UV-weathered MPs but were significantly downregulated after UV weathering. Overall, the UV weathering of PLA promoted the adsorption of DFB, thus increasing its toxic effects. Our findings demonstrate the importance of considering the effects of UV weathering and interactions with environmental pollutants when assessing the ecological risks associated with biodegradable MPs.

Polymer material biodegradation in the deep sea. A review

The phenomenon of marine plastic pollution is now well-established, with documented impacts on marine biodiversity and biogeochemical cycles. In order to mitigate this environmental impact, a significant amount of research has been conducted in recent years with the objective of developing biodegradable alternatives to conventional polymers and their composites in marine environments. The findings of this research significantly enhanced our understanding of biodegradation mechanisms and identified promising candidates. However, the majority of these studies have been conducted in coastal marine environments, which represent a minor component of the marine ecosystem. Recent models on the transport of plastic debris in the oceans indicate that deep-sea environments are likely to be the ultimate sink for a significant proportion of plastics entering the oceans. The aim of this review is to provide an overview of the processes of biodegradation of polymers in these deep-sea environments. The diversity and specific characteristics of these environments with respect to degradation mechanisms are discussed. While the majority of deep-sea conditions are not conducive to biodegradation, studies on organic falls (wood and whale carcasses) and a few investigations into materials previously shown to be biodegradable in coastal marine environments demonstrate mechanisms that are similar to those observed in shallow waters. Nevertheless, further research is necessary to reach definitive conclusions. It is essential to extend these studies to a broader range of deep-sea environments. Additionally, new methodologies that integrate microbiology and polymer science are required to accurately assess the process of assimilation of these materials in these environments.

Microbial degradation of polyethylene polymer: current paradigms, challenges, and future innovations

Polyethylene (PE) is the second most commonly used plastic worldwide, mainly used to produce single-use items such as bags and bottles. Its significant resistance to natural biodegradation results in the accumulation of PE in landfills, leading to various ecological and toxicological consequences. Despite extensive research on the microbial degradation of PE, achieving complete biodegradation remains a challenge. Comparing experimental outcomes is complicated by the diverse array of microbes involved in PE biodegradation, variations in culture conditions, and differences in assessment tools. This review discusses the critical hurdles in PE biodegradation experiments, including the chemical complexity of PE substrates and the challenges of isolating effective microbes and forming stable consortia. The review also delves into the difficulties in accurately assessing microbial metabolic activity and understanding the biochemical pathways involved in PE degradation. Furthermore, it addresses the pressing issues of metabolic byproducts, slow degradation rates, scalability concerns, and the challenges in measuring biodegradation levels effectively. In addition to outlining the technical challenges associated with PE experiments, this review offers recommendations for future research directions to enhance PE biodegradation outcomes. Overcoming these challenges and implementing the proposed future strategies will improve the reliability, comparability, and practicality of current PE biodegradation experiments, ultimately contributing to better comprehension and management of PE waste in the environment.

(Bio)degradation of biopolymer and biocomposite in deep-sea environments

In order to reduce the contamination of marine ecosystems by plastic materials, the scientific community is engaged in the development of biodegradable substitutes for conventional plastics. While certain candidates have been successfully tested in coastal marine environments, the degradation process in deep-sea environments remains poorly understood. This study examined the degradation of two industrial biopolyesters, a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and a polybutylene-succinate (PBS), in two deep marine environments of the Middle and Eastern Atlantic, at depths of 780 and 1740 m, as well as under laboratory conditions under hydrostatic pressure and without micro-organisms. The findings reveal a considerable biodeterioration of PHBV and a pronounced influence of flax fibre reinforcement on the degradation mechanisms. Conversely, PBS exhibits minimal to no indications of degradation. Additionally, the results confirm that biotic factors are the primary determinants of the degradation processes, with no degradation observed under abiotic conditions.

Bacterial degradation of polyethylene and polypropylene microplastics in a mangrove ecosystem

Microplastics (MPs) contamination presents a major environmental challenge, with accumulation of thousands of tons of MPs in ecosystems worldwide posing significant risks to human health and biodiversity. Identifying bacteria capable of degrading MPs offers a promising long-term solution to this issue. While several bacterial strains have demonstrated varying degrees of plastic degradation, the mechanisms underlying these processes remain poorly understood. In this study, 16S rDNA analysis was used to screen ten bacterial strains isolated from mangrove water samples for their potential to degrade MPs. Among these, Bacillus cereus strain ZRY and Pseudochrobactrum saccharolyticum strain ZRY emerged as the most effective candidates. The degradation of polyethylene (PE) and polypropylene (PP) was monitored through weight loss measurements over a 60-day incubation period. B. cereus strain ZRY achieved weight losses of 1.1% for PE and 1.0% for PP, while P. saccharolyticum strain ZRY recorded losses of 0.6% for PE and 0.4% for PP. Morphological and structural changes during degradation were analyzed using scanning electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy, which also identified key enzymes produced by both bacterial strains that facilitate the degradation of MPs. Additionally, the effect of pH, salt concentrations, inorganic ions, and incubation duration on degradation efficiency were evaluated. Our findings demonstrate the potential of these bacterial strains for MPs degradation, underscoring their potential for future applications in addressing MP pollution. This research lays the foundation for optimizing conditions to enhance bioremediation efforts utilizing these microbial candidates.

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.

Biodegradability of bioplastics in different aquatic environments: A systematic review

Bioplastics were first introduced as environmentally friendly materials, with properties similar to those of conventional plastics. A bioplastic is defined as biodegradable if it can be decomposed into carbon dioxide under aerobic degradation, or methane and CO2 under anaerobic conditions, inorganic compounds, and new cellular biomass, by the action of naturally occurring microorganisms. This definition however does not provide any information on the environmental conditions, timescale and extent at which decomposition processes should occur. With regard to the aquatic environment, recognized standards have been established to assess the ability of plastics to undergo biodegradation; however, these standards fail to provide clear targets to be met to allow labelling of a bioplastic as biodegradable. Moreover, these standards grant the user an extensive leeway in the choice of process parameters. For these reasons, the comparison of results deriving from different studies is challenging. The authors analysed and discussed the degree of biodegradability of a series of biodegradable bioplastics in aquatic environments (both fresh and salt water) using the results obtained in the laboratory and from on-site testing in the context of different research studies. Biochemical Oxygen Demand (BOD), CO2 evolution, surface erosion and weight loss were the main parameters used by researchers to describe the percentage of biodegradation. The results showed a large variability both in weight loss and BOD, even when evaluating the same type of bioplastics. This confirms the need for a reference range of values to be established with regard to parameters applied in defining the biodegradability of bioplastics.

Sustainable struggling: decoding microplastic released from bioplastics-a critical review

This comprehensive review delves into the complex issue of plastic pollution, focusing on the emergence of biodegradable plastics (BDPs) as a potential alternative to traditional plastics. While BDPs seem promising, recent findings reveal that a large number of BDPs do not fully degrade in certain natural conditions, and they often break down into microplastics (MPs) even faster than conventional plastics. Surprisingly, research suggests that biodegradable microplastics (BDMPs) could have more significant and long-lasting effects than petroleum-based MPs in certain environments. Thus, it is crucial to carefully assess the ecological consequences of BDPs before widely adopting them commercially. This review thoroughly examines the formation of MPs from prominent BDPs, their impacts on the environment, and adsorption capacities. Additionally, it explores how BDMPs affect different species, such as plants and animals within a particular ecosystem. Overall, these discussions highlight potential ecological threats posed by BDMPs and emphasize the need for further scientific investigation before considering BDPs as a perfect solution to plastic pollution.

Biodegradable plastic formulated from chitosan of Aristeus antennatus shells with castor oil as a plasticizer agent and starch as a filling substrate

Biodegradable plastics are those subjected easily to a degradation process, in which they can be decomposed after disposal in the environment through microbial activity. 30 bioplastic film formulations based only on chitosan film were used in the current investigation as a positive control together with chitosan film recovered from chitin-waste of locally obtained Aristeus antennatus. Additionally, castor oil was used as a plasticizer. While the yield of chitosan was 18% with 7.65% moisture content and 32.27% ash in the shells, the isolated chitin had a degree of deacetylation (DD) of 86%. The synthesized bioplastic films were characterized via numerous criteria. Firstly, the swelling capacity of these biofilms recorded relatively high percentages compared to polypropylene as synthetic plastic. Noticeably, the FTIR profiles, besides DSC, TGA, and XRD, confirmed the acceptable characteristics of these biofilms. In addition, their SEM illustrated the homogeneity and continuity with a few straps of the chitosan film and showed the homogeneous mixes of chitosan and castor oil with 5 and 20%. Moreover, data detected the antibacterial activity of different bioplastic formulas against some common bacterial pathogens (Enterococcus feacalis, Kelbsiella pnumina, Bacillus subtilis, and Pseudomonas aeruginosa). Amazingly, our bioplastic films have conducted potent antimicrobial activities. So, they may be promising in such a direction. Further, the biodegradability efficacy of bioplastic films formed was proved in numerous environments for several weeks of incubation. However, all bioplastic films decreased in their weights and changed in their colors, while polypropylene, was very constant all the time. The current findings suggest that our biofilms may be promising for many applications, especially in the field of food package protecting the food, and preventing microbial contamination, consequently, it may help in extending the shelf life of products.

Using waste biomass to produce 3D-printed artificial biodegradable structures for coastal ecosystem restoration

The loss of ecosystem functions and services caused by rapidly declining coastal marine ecosystems, including corals and bivalve reefs and wetlands, around the world has sparked significant interest in interdisciplinary methods to restore these ecologically and socially important ecosystems. In recent years, 3D-printed artificial biodegradable structures that mimic natural life stages or habitat have emerged as a promising method for coastal marine restoration. The effectiveness of this method relies on the availability of low-cost biodegradable printing polymers and the development of 3D-printed biomimetic structures that efficiently support the growth of plant and sessile animal species without harming the surrounding ecosystem. In this context, we present the potential and pathway for utilizing low-cost biodegradable biopolymers from waste biomass as printing materials to fabricate 3D-printed biodegradable artificial structures for restoring coastal marine ecosystems. Various waste biomass sources can be used to produce inexpensive biopolymers, particularly those with the higher mechanical rigidity required for 3D-printed artificial structures intended to restore marine ecosystems. Advancements in 3D printing methods, as well as biopolymer modifications and blending to address challenges like biopolymer solubility, rheology, chemical composition, crystallinity, plasticity, and heat stability, have enabled the fabrication of robust structures. The ability of 3D-printed structures to support species colonization and protection was found to be greatly influenced by their biopolymer type, surface topography, structure design, and complexity. Considering limited studies on biodegradability and the effect of biodegradation products on marine ecosystems, we highlight the need for investigating the biodegradability of biopolymers in marine conditions as well as the ecotoxicity of the degraded products. Finally, we present the challenges, considerations, and future perspectives for designing tunable biomimetic 3D-printed artificial biodegradable structures from waste biomass biopolymers for large-scale coastal marine restoration.

Bioplastic degradation and assimilation processes by a novel bacterium isolated from the marine plastisphere

Biosourced and biodegradable plastics offer a promising solution to reduce environmental impacts of plastics for specific applications. Here, we report a novel bacterium named Alteromonas plasticoclasticus MED1 isolated from the marine plastisphere that forms biofilms on foils of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Experiments of degradation halo, plastic matrix weight loss, bacterial oxygen consumption and heterotrophic biosynthetic activity showed that the bacterial isolate MED1 is able to degrade PHBV and to use it as carbon and energy source. The likely entire metabolic pathway specifically expressed by this bacterium grown on PHBV matrices was shown by further genomic and transcriptomic analysis. In addition to a gene coding for a probable secreted depolymerase, a gene cluster was located that encodes characteristic enzymes involved in the complete depolymerization of PHBV, the transport of oligomers, and in the conversion of the monomers into intermediates of central carbon metabolism. The transcriptomic experiments showed the activation of the glyoxylate shunt during PHBV degradation, setting the isocitrate dehydrogenase activity as regulated branching point of the carbon flow entering the tricarboxylic acid cycle. Our study also shows the potential of exploring the natural plastisphere to discover new bacteria with promising metabolic capabilities.

Biodegradation of plastics in the pelagic environment of the coastal zone - Proposed test method under controlled laboratory conditions

The increasing quantities of plastic litter accumulated in the oceans, including microplastics, represent a serious environmental threat. Despite the recent legislative actions, the plastic littering problem will not disappear in a short time. It may, however be ameliorated by replacing conventional non-degradable plastics with bio-based materials biodegradable in marine environment (targeting the non-recycled or mismanaged plastic waste). Although priority is set to prevention of plastic litter by means of the circular economy principles, biodegradability is a means of controlling unintentional plastic pollution. In this effort, the development of reliable test methods that would be used along with standard specifications for determining the biodegradability of novel polymeric materials or plastics in marine environments, is a necessary complementary component of the whole strategy to control the marine plastic litter and micro-, nano-plastics threat. The present work focuses on identifying gaps and improving available laboratory test methods for measuring the aerobic biodegradation of plastics in the seawater column within the coastal zone (pelagic environment). The research work followed a methodology that is based on recommendations of ASTM D6691:2017 concerning biodegradation of plastics in the seawater and the similar ISO 23977-1:2020. Three different implementation schemes of the test method were applied using different experimental setups and measuring techniques for monitoring the evolved CO2. The effect of critical parameters affecting nutrient adequacy (concentration in inoculum) and oxygen adequacy (bioreactor size, sample size, frequency of aeration) on the biodegradation of four tested materials was explored, and optimal values are proposed. The results allowed for the refinement of the proposed test method to improve reliability and reproducibility.

Marine biodegradation of tailor-made polyhydroxyalkanoates (PHA) influenced by the chemical structure and associated bacterial communities

Over recent years, biodegradable polymers have been proposed to reduce environmental impacts of plastics for specific applications. The production of polyhydroxyalkanoates (PHA) by using diverse carbon sources provides further benefits for the sustainable development of biodegradable plastics. Here, we present the first study evaluating the impact of physical, chemical and biological factors driving the biodegradability of various tailor-made PHAs in the marine environment. Our multidisciplinary approach demonstrated that the chemical structure of the polymer (i.e. the side chain size for short- vs. medium-chain PHA) which was intrinsically correlated to the physico-chemical properties, together with the specificity of the biofilm growing on plastic films (i.e., the associated 'plastisphere') were the main drivers of the PHA biodegradation in the marine environment.

Assessment of biodegradation of lignocellulosic fiber-based composites - A systematic review

Lignocellulosic fiber-reinforced polymer composites are the most extensively used modern-day materials with low density and better specific strength specifically developed to render better physical, mechanical, and thermal properties. Synthetic fiber-reinforced composites face some serious issues like low biodegradability, non-environmentally friendly, and low disposability. Lignocellulosic or natural fiber-reinforced composites, which are developed from various plant-based fibers and animal-based fibers are considered potential substitutes for synthetic fiber composites because they are characterized by lightweight, better biodegradability, and are available at low cost. It is very much essential to study end-of-life (EoL) conditions like biodegradability for the biocomposites which occur commonly after their service life. During biodegradation, the physicochemical arrangement of the natural fibers, the environmental conditions, and the microbial populations, to which the natural fiber composites are exposed, play the most influential factors. The current review focuses on a comprehensive discussion of the standards and assessment methods of biodegradation in aerobic and anaerobic conditions on a laboratory scale. This review is expected to serve the materialists and technologists who work on the EoL behaviour of various materials, particularly in natural fiber-reinforced polymer composites to apply these standards and test methods to various classes of biocomposites for developing sustainable materials.

Microbial colonization patterns and biodegradation of petrochemical and biodegradable plastics in lake waters: insights from a field experiment

Introduction

Once dispersed in water, plastic materials become promptly colonized by biofilm-forming microorganisms, commonly known as plastisphere.

Methods

By combining DNA sequencing and Confocal Laser Scanning Microscopy (CLSM), we investigated the plastisphere colonization patterns following exposure to natural lake waters (up to 77 days) of either petrochemical or biodegradable plastic materials (low density polyethylene - LDPE, polyethylene terephthalate - PET, polylactic acid - PLA, and the starch-based MaterBi® - Mb) in comparison to planktonic community composition. Chemical composition, water wettability, and morphology of plastic surfaces were evaluated, through Transform Infrared Spectroscopy (ATR-FTIR), Scanning Electron Microscopy (SEM), and static contact angle analysis, to assess the possible effects of microbial colonization and biodegradation activity.

Results and Discussion

The phylogenetic composition of plastisphere and planktonic communities was notably different. Pioneering microbial colonisers, likely selected from lake waters, were found associated with all plastic materials, along with a core of more than 30 abundant bacterial families associated with all polymers. The different plastic materials, either derived from petrochemical hydrocarbons (i.e., LDPE and PET) or biodegradable (PLA and Mb), were used by opportunistic aquatic microorganisms as adhesion surfaces rather than carbon sources. The Mb-associated microorganisms (i.e. mostly members of the family Burkholderiaceae) were likely able to degrade the starch residues on the polymer surfaces, although the Mb matrix maintained its original chemical structure and morphology. Overall, our findings provide insights into the complex interactions between aquatic microorganisms and plastic materials found in lake waters, highlighting the importance of understanding the plastisphere dynamics to better manage the fate of plastic debris in the environment.

Enzyme selection, optimization, and production toward biodegradation of post-consumer poly(ethylene terephthalate) at scale

Poly(ethylene terephthalate) (PET) is one of the world's most widely used polyester plastics. Due to its chemical stability, PET is extremely difficult to hydrolyze in a natural environment. Recent discoveries in new polyester hydrolases and breakthroughs in enzyme engineering strategies have inspired enormous research on biorecycling of PET. This study summarizes our research efforts toward large-scale, efficient, and economical biodegradation of post-consumer waste PET, including PET hydrolase selection and optimization, high-yield enzyme production, and high-capacity enzymatic degradation of post-consumer waste PET. First, genes encoding PETase and MHETase from Ideonella sakaiensis and the ICCG variant of leaf-branch compost cutinase (LCCICCG ) were codon-optimized and expressed in Escherichia coli BL21(DE3) for high-yield production. To further lower the enzyme production cost, a pelB leader sequence was fused to LCCICCG so that the enzyme can be secreted into the medium to facilitate recovery. To help bind the enzyme on the hydrophobic surface of PET, a substrate-binding module in a polyhydroxyalkanoate depolymerase from Alcaligenes faecalis (PBM) was fused to the C-terminus of LCCICCG . The resulting four different LCCICCG variants (LCC, PelB-LCC, LCC-PBM, and PelB-LCC-PBM), together with PETase and MHETase, were compared for PET degradation efficiency. A fed-batch fermentation process was developed to produce the target enzymes up to 1.2 g L-1 . Finally, the best enzyme, PelB-LCC, was selected and used for the efficient degradation of 200 g L-1 recycled PET in a well-controlled, stirred-tank reactor. The results will help develop an economical and scalable biorecycling process toward a circular PET economy.

Enzymatic polyethylene biorecycling: Confronting challenges and shaping the future

Polyethylene (PE) is a widely used plastic known for its resistance to biodegradation, posing a significant environmental challenge. Recent advances have shed light on microorganisms and insects capable of breaking down PE and identified potential PE-degrading enzymes (PEases), hinting at the possibility of PE biorecycling. Research on enzymatic PE degradation is still in its early stages, especially compared to the progress made with polyethylene terephthalate (PET). While PET hydrolases have been extensively studied and engineered for improved performance, even the products of PEases remain mostly undefined. This Perspective analyzes the current state of enzymatic PE degradation research, highlighting obstacles in the search for bona fide PEases and suggesting areas for future exploration. A critical challenge impeding progress in this field stems from the inert nature of the C-C and C-H bonds of PE. Furthermore, breaking down PE into small molecules using only one monofunctional enzyme is theoretically impossible. Overcoming these obstacles requires identifying enzymatic pathways, which can be facilitated using emerging technologies like omics, structure-based design, and computer-assisted engineering of enzymes. Understanding the mechanisms underlying PE enzymatic biodegradation is crucial for research progress and for identifying potential solutions to the global plastic pollution crisis.

Sustainable Polycaprolactone Polyol-Based Thermoplastic Poly(ester ester) Elastomers Showing Superior Mechanical Properties and Biodegradability

Thermoplastic elastomers (TPEs) have attracted increasing attention for a wide variety of industrial and biomedical applications owing to their unique properties compared to those of traditional rubbers. To develop high-performance engineering TPEs and reduce the environmental pollution caused by plastic waste, α,ω-hydroxyl-terminated polycaprolactone (PCL) polyols with molecular weights of 1000-4200 g mol-1 and polydispersity index (Ð) of 1.30-1.88 are synthesized via the ring-opening polymerization of sustainable ε-caprolactone using a heterogeneous double metal cyanide catalyst. The resulting PCL polyols are employed as soft segments to produce thermoplastic poly(ester ester) elastomers and are compared to conventional thermoplastic poly(ether ester) elastomers prepared from polytetramethylene ether glycol (PTMEG). Notably, the PCL-based TPEs exhibit superior mechanical properties and biodegradability compared to PTMEG-based TPEs owing to their crystallinity and microphase separation behaviors. Accordingly, they have 39.7 MPa ultimate strength and 47.6% biodegradability, which are much higher than those of PTMEG-based TPEs (23.4 MPa ultimate strength and 24.3% biodegradability). The introduction of biodegradable PCLs demonstrates significant potential for producing biodegradable TPEs with better properties than polyether-derived elastomers.

Biocompatible and Biodegradable 3D Printing from Bioplastics: A Review

There has been a lot of interest in developing and producing biodegradable polymers to address the current environmental problem caused by the continued usage of synthetic polymers derived from petroleum products. Bioplastics have been identified as a possible alternative to the use of conventional plastics since they are biodegradable and/or derived from renewable resources. Additive manufacturing, also referred to as 3D printing, is a field of growing interest and can contribute towards a sustainable and circular economy. The manufacturing technology also provides a wide material selection with design flexibility increasing its usage in the manufacture of parts from bioplastics. With this material flexibility, efforts have been directed towards developing 3D printing filaments from bioplastics such as Poly (lactic acid) to substitute the common fossil- based conventional plastic filaments such as Acrylonitrile butadiene styrene. Plant biomass is now utilized in the development of biocomposite materials. A lot of literature presents work done toward improving the biodegradability of printing filaments. However, additive manufacture of biocomposites from plant biomass is faced with printing challenges such as warping, low agglomeration between layers and poor mechanical properties of the printed parts. The aim of this paper is to review the technology of 3D printing using bioplastics, study the materials that have been utilized in this technology and how challenges of working with biocomposites in additive manufacture have been addressed.

A New Colorimetric Test for Accurate Determination of Plastic Biodegradation

As plastic waste is accumulating in both controlled waste management settings and natural settings, much research is devoted to search for solutions, also in the field of biodegradation. However, determining the biodegradability of plastics in natural environments remains a big challenge due to the often very low biodegradation rates. Many standardised test methods for biodegradation in natural environments exist. These are often based on mineralisation rates in controlled conditions and are thus indirect measurements of biodegradation. It is of interest for both researchers and companies to have tests that are more rapid, easier, and more reliable to screen different ecosystems and/or niches for their plastic biodegradation potential. In this study, the goal is to validate a colorimetric test, based on carbon nanodots, to screen biodegradation of different types of plastics in natural environments. After introducing carbon nanodots into the matrix of the target plastic, a fluorescent signal is released upon plastic biodegradation. The in-house-made carbon nanodots were first confirmed regarding their biocompatibility and chemical and photostability. Subsequently, the effectivity of the developed method was evaluated positively by an enzymatic degradation test with polycaprolactone with Candida antarctica lipase B. Finally, validation experiments were performed with enriched microorganisms and real environmental samples (freshwater and seawater), of which the results were compared with parallel, frequently used biodegradation measures such as O₂ and CO₂, dissolved organic carbon, growth and pH, to assess the reliability of the test. Our results indicate that this colorimetric test is a good alternative to other methods, but a combination of different methods gives the most information. In conclusion, this colorimetric test is a good fit to screen, in high throughput, the depolymerisation of plastics in natural environments and under different conditions in the lab.

The plastic and microplastic waste menace and bacterial biodegradation for sustainable environmental clean-up a review

Environment plastic litter accumulation is a significant concern, needing urgent advancements in plastic waste management. Recent investigations into plastic biodegradation by bacteria and their enzymes are creating exciting unique opportunities for the development of biotechnological plastic waste treatment methods. This review summarizes information on bacterial and enzymatic biodegradation of plastic in a wide range of synthetic plastics such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyurethane (PUR), polytetrafluoroethylene (PTFE) and polyvinyl chloride (PVC). Plastic biodegradation is facilitated by Acinetobacter, Bacillus, Brevibacillus, Escherichia, Pseudomonas, Micrococcus, Streptomyces, and Rhodococcus bacteria, and enzymes such as proteases, esterases, lipases, and glycosidases. Molecular and analytical procedures used to analyze biodegradation processes are outlined, as are the obstacles in verifying plastic breakdown using these methods. Taken together, the findings of this study will contribute significantly to the construction of a library of high-efficiency bacterial isolates and consortiums and their enzymes for use in plastic biosynthesis. This information is useful to researchers investigating plastic bioremediation and a supplement to the scientific and grey literature already accessible. Finally, the review focuses on expanding the understanding of bacterial capacity to break-down plastic utilizing modern biotechnological methods, bio-nanotechnological-based materials, and their future role in resolving pollution problems.

The performance and environmental impact of pro-oxidant additive containing plastics in the open unmanaged environment-a review of the evidence

Pro-oxidant additive containing (PAC) plastics is a term that describes a growing number of plastics which are designed to degrade in the unmanaged natural environment (open-air, soil, aquatic) through oxidation and other processes. It is a category that includes 'oxo-degradable' plastics, 'oxo-biodegradable' plastics and those containing 'biotransformation' additives. There is evidence that a new standard PAS 9017 : 2020 is relevant to predicting the timescale for abiotic degradation of PAC plastic in hot dry climates under ideal conditions (data reviewed for South of France and Florida). There are no reliable data to date to show that the PAS 9017 : 2020 predicts the timescale for abiotic degradation of PAC plastics in cool or wet climatic regions such as the UK or under less ideal conditions (soil burial, surface soiling etc.). Most PAC plastics studied in the literature showed biodegradability values in the range 5-60% and would not pass the criteria for biodegradability set in the new PAS 9017 : 2020. Possible formation of microplastics and cross-linking have been highlighted both by field studies and laboratory studies. Systematic eco-toxicity studies are needed to assess the possible effect of PAC additives and microplastics on the environment and biological organisms.

Characterization of dynamic plastisphere and their underlying effects on the aging of biodegradable and traditional plastics in freshwater ecosystems

Recently, biodegradable plastics (BPs) are emerging as a sustainable alternative to traditional plastics. When released into an aquatic environment, the biodegradable performance of BPs is influenced by biochemical processes, especially the developed plastisphere. However, studies addressing the biodegrading capacity of BPs and traditional plastics within the plastisphere are still limited. Here, we investigated plastisphere community variations and their capacity to biodegrade polyethylene terephthalate (PET) and starch-based plastics (SBP) for four time periods (15, 30, 45, and 80 days) in three freshwaters. Unexpectedly, there is no significant difference in the microbial communities and network structure of the plastisphere between SBP and PET. Moreover, SBP tended to age rapidly at the early stage (0-15 days), while the aging degree of SBP and PET did not display an obvious difference at 80 days. Partial least squares path modeling suggested that plastic aging was mainly dominated by keystone taxa of network and aquatic environmental factors. These results suggest that the aging rate of commercial BPs may not be as fast as we imagine in freshwaters (SBP ≈ PET), and the environmental behaviors of BPs in the aquatic environment should be paid more attention to.

Discussion about suitable applications for biodegradable plastics regarding their sources, uses and end of life

This opinion paper offers a scientific view on the current debate of the place of biodegradable plastics as part of the solution to deal with the growing plastic pollution in the world's soil, aquatic, and marine compartments. Based on the current scientific literature, we focus on the current limits to prove plastic biodegradability and to assess the toxicity of commercially used biobased and biodegradable plastics in natural environments. We also discuss the relevance of biodegradable plastics for selected applications with respect to their use and end of life. In particular, we underlined that there is no universal biodegradability of plastics in any ecosystem, that considering the environment as a waste treatment system is not acceptable, and that the use of compostable plastics requires adaptation of existing organic waste collection and treatment channels.

Effect of polyhydroxyalkanoates on the microbial reductive dechlorination of polychlorinated biphenyls and competing anaerobic respirations in a marine microbial culture

The effect of polyhydroxyalkanoates (PHAs) with different composition on the reductive dechlorination activity of a polychlorinated biphenyls (PCBs) dechlorinating marine microbial community and on the activity of sulfate-reducing (SRB) and methanogenic bacteria (MB), were investigated in marine sediment microcosms and compared with the main monomer, 3-hydroxybutyric acid (3HB). Despite PHAs were fermented more slowly than 3HB, all electron donors stimulated constantly sulfate-reduction, methanogenesis and, only transiently, PCB reductive dechlorination. No relevant differences were observed with different compositions of PHAs. According to electron balances, the majority of the supplied electrons (50 %) were consumed by SRB and to less extent by MB (9-31 %), while a small percentage (0.01 %) was delivered to OHRB. In the studied conditions PHAs were confirmed as potential slow‑hydrogen releasing compounds in marine environment but their fermentation rate was sufficiently high to mainly stimulate the competitors of organohalide respring bacteria for electron donors.

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.

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.

Key issues for bio-based, biodegradable and compostable plastics governance

Among global efforts facing plastic pollution, their gradual replacement with alternative materials has gained strength during the last decade. We identified five stakeholders and their respective key participation in the chain of bio-based, biodegradable and compostable plastics (BBCP), which have contributed to several flaws on governance of these materials. The widespread unfamiliarity of the consumers about biodegradability concepts has been leading to misguided purchase decisions and disposal practices, along with possible littering behavior. Simultaneously, the adoption of greenwashing practices by stores and manufacturers contribute to disseminating misguided decisions on plastic consumption. Such issues are further aggravated by the lack of certification standards concerning the impact of littering, including the assessment of persistency and toxicity, also covering those made with biodegradable plastics.". Moreover, even though such alternative polymers were originally conceived as a strategy to minimize plastics pollution, the almost inexistence of specific regulatory frameworks in different political scales may convert them in a relevant part of the problem. Therefore, the governance systems and management strategies need to incorporate BBCP as potentially hazardous waste as they do for conventional plastics.

Rigid bioplastics shape the microbial communities involved in the treatment of the organic fraction of municipal solid waste

While bioplastics are gaining wide interest in replacing conventional plastics, it is necessary to understand whether the treatment of the organic fraction of municipal solid waste (OFMSW) as an end-of-life option is compatible with their biodegradation and their possible role in shaping the microbial communities involved in the processes. In the present work, we assessed the microbiological impact of rigid polylactic acid (PLA) and starch-based bioplastics (SBB) spoons on the thermophilic anaerobic digestion and the aerobic composting of OFMSW under real plant conditions. In order to thoroughly evaluate the effect of PLA and SBB on the bacterial, archaeal, and fungal communities during the process, high-throughput sequencing (HTS) technology was carried out. The results suggest that bioplastics shape the communities' structure, especially in the aerobic phase. Distinctive bacterial and fungal sequences were found for SBB compared to the positive control, which showed a more limited diversity. Mucor racemosus was especially abundant in composts from bioplastics' treatment, whereas Penicillium roqueforti was found only in compost from PLA and Thermomyces lanuginosus in that from SBB. This work shed a light on the microbial communities involved in the OFMSW treatment with and without the presence of bioplastics, using a new approach to evaluate this end-of-life option.

Secondary microplastics formation and colonized microorganisms on the surface of conventional and degradable plastic granules during long-term UV aging in various environmental media

Recently, biodegradable plastics (BPs) as an alternative of conventional plastics have been widely advocated and applied. However, there is still a large research gap between the formation of secondary microplastics (MPs) and colonized microorganisms on their surface under long-term aging in different environments. In this study, the generation of secondary MPs and the formation of surface biofilms on the micro-sized (3-5 mm) biodegradable plastic poly (butyleneadipate-co-terephthalate) (BP-PBAT) and conventional plastic polyvinyl chloride (CP-PVC) under long-term UV aging was investigated. The results showed that hundreds and even thousands of MPs (185.53 ± 85.73 items/g - 1473.27 ± 143.67 items/g) were generated by BP-PBAT and CP-PVC after aged for 90 days, and the abundance of MPs produced by BP-PBAT was significantly higher than that of CP-PVC. Moreover, the α diversities and detected OTU number of biofilm communities formed on MPs increased with MPs-aging. The genes related to the formation of biofilms was significantly expressed on aged MPs and the genes related to human pathogens and diseases were also detected in enriching on MPs surface. Overall, BPs may lead to greater ecological risks as it releases thousands of secondary MPs after being aged, and their environmental behavior needs to be further explored.

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.

A comprehensive review on recent advancements in biodegradation and sustainable management of biopolymers

Recent years have seen upsurge in plastic manufacturing and its utilization in various fields, such as, packaging, household goods, medical applications, and beauty products. Due to various adverse impacts imposed by synthetic plastics on the health of living well-being and the environment, the biopolymers have been emerged out an alternative. Although, the biopolymers such as polyhydroxyalkanoates (PHA) are entirely degradable. However, the other polymers, such as poly (lactic acid) (PLA) are only partially degradable and often not biosynthesized. Biodegradation of the polymers using microorganisms is considered an effective bioremediation approach. Biodegradation can be performed in aerobic and anaerobic environments. In this context, the present review discusses the biopolymer production, their persistence in the environment, aerobic biodegradation, anaerobic biodegradation, challenges associated with biodegradation and future perspectives. In addition, this review discusses the advancement in the technologies associated with biopolymer production, biodegradation, and their biodegradation standard in different environmental settings. Furthermore, differences in the degradation condition in the laboratory as well as on-site are discussed.

Enhancing the biodegradation of (bio)plastic through pretreatments: A critical review

As plastic packaging becomes nearly indispensable in the plastic economy, rigorous efforts have been made to recapture the material value form this waste stream, which is mostly composed of highly resistant plastics. Biodegradation offers an attractive alternative for conventional plastic waste treatment as this approach is environmentally friendly, has low cost and facilitates valorisation. Moreover, there is also an increasing interest in plastic pretreatments waste to enhance biodegradation. This review investigates the pretreatment methods that optimise plastic biodegradation by examining the process's mechanisms and key influencing factors, which can be categorised into: biotic factors, abiotic factors and polymer characteristics. Various types of chemical and physical pretreatments have demonstrated to effectively enhance biodegradation through oxidation and surface changes on the plastics, leading to increased bioconversion rates and biogas production. A critical evaluation of the various categories of pretreatment methods is presented. This evaluation leads to the conclusion that the category of non-thermal physical treatments is most promising, due to the relatively low energy requirements and the absence of a need for chemical additions. Moreover, non-thermal physical treatments have demonstrated application potential at large scale. Based on these conclusions, pretreatments are expected to be an integral part of the biodegradation of plastics within a circular economy approach.

Is a compostable plastic biodegradable in the sea? A rapid standard protocol to test mineralization in marine conditions

Due to environmental persistence, lack of a proper land-based waste management, and global circulation, marine ecosystems are especially threatened by plastics. The search for alternatives to conventional oil-based polymers gave rise to novel materials commercialized under different "green" labels based on compostability. However, current international standards are not effective in predicting actual biodegradability of plastic objects in natural scenarios, and degradation of these novel bioplastics in marine conditions is unwarranted. We present a simple and rapid standard protocol based on their biological oxygen demand, intended to support policy-makers and plastic industry in the search for truly marine-biodegradable plastics. Improvements include: development of an environmentally relevant nutrient formulation following Redfield ratio (106C:16 N:1P); use of a natural inoculum representative of marine habitats (sediment pore water); standardization of the test material by grinding to particles below 250 μm to shorten the incubation period, and selection of a truly biodegradable biopolymer (PHB), used as positive control. This protocol was successfully applied to show that commercial compostable plastics are not biodegradable in marine environments.

Microbial biodegradation of plastics: Challenges, opportunities, and a critical perspective

The abundance of synthetic polymers has increased due to their uncontrolled utilization and disposal in the environment. The recalcitrant nature of plastics leads to accumulation and saturation in the environment, which is a matter of great concern. An exponential rise has been reported in plastic pollution during the corona pandemic because of PPE kits, gloves, and face masks made up of single-use plastics. The physicochemical methods have been employed to degrade synthetic polymers, but these methods have limited efficiency and cause the release of hazardous metabolites or by-products in the environment. Microbial species, isolated from landfills and dumpsites, have utilized plastics as the sole source of carbon, energy, and biomass production. The involvement of microbial strains in plastic degradation is evident as a substantial amount of mineralization has been observed. However, the complete removal of plastic could not be achieved, but it is still effective compared to the preexisting traditional methods. Therefore, microbial species and the enzymes involved in plastic waste degradation could be utilized as eco-friendly alternatives. Thus, microbial biodegradation approaches have a profound scope to cope with the plastic waste problem in a cost-effective and environmental-friendly manner. Further, microbial degradation can be optimized and combined with physicochemical methods to achieve substantial results. This review summarizes the different microbial species, their genes, biochemical pathways, and enzymes involved in plastic biodegradation.

Degradation of Cellulose Derivatives in Laboratory, Man-Made, and Natural Environments

Biodegradable polymers complement recyclable materials in battling plastic waste because some products are difficult to recycle and some will end up in the environment either because of their application or due to wear of the products. Natural biopolymers, such as cellulose, are inherently biodegradable, but chemical modification typically required for the obtainment of thermoplastic properties, solubility, or other desired material properties can hinder or even prevent the biodegradation process. This Review summarizes current knowledge on the degradation of common cellulose derivatives in different laboratory, natural, and man-made environments. Depending on the environment, the degradation can be solely biodegradation or a combination of several processes, such as chemical and enzymatic hydrolysis, photodegradation, and oxidation. It is clear that the type of modification and especially the degree of substitution are important factors controlling the degradation process of cellulose derivatives in combination with the degradation environment. The big variation of conditions in different environments is also briefly considered as well as the importance of the proper testing environment, characterization of the degradation process, and confirmation of biodegradability. To ensure full sustainability of the new cellulose derivatives under development, the expected end-of-life scenario, whether material recycling or "biological" recycling, should be included as an important design parameter.

Mesocosm trials reveal the potential toxic risk of degrading bioplastics to marine life

If biodegradable plastics tackle the marine plastic pollution problem sufficiently remains questionable. To gain more insight in degradability, performance, and the impact of degradation on the toxicity, commercial bags made from two biodegradable plastics and one conventional plastic (PE) were exposed for 120 days in a mesocosm featuring benthic, pelagic, and littoral habitat simulations. Degradability was assessed as weight loss, and specimens were tested for toxicity using Paracentrotus lividus sea-urchin larvae after different exposure times. Both biodegradable bags showed degradation within 120 days, with the littoral simulation showing the highest and the pelagic simulation the lowest decay. Disregarding habitat, the home-compostable plastic showed higher marine degradation than the industrial-compostable material. The relevant initial toxicity of both biopolymers was lost within 7 days of exposure, pointing towards easily leachable chemical additives as its cause. Interestingly, littoral exposed specimens gained toxicity after 120 days, suggesting UV- induced modifications that increase biopolymer toxicity.

Experimental evaluation of microplastic consumption by using a size-fractionation approach in the planktonic communities

The increasing amount of plastic particles introduced into continental aquatic environments has drawn the attention of researchers around the globe. These particles can be assimilated by a wide range of aquatic organisms, from microorganisms to fish, causing detrimental effects on trophic webs. Using an experimental approach, we investigated the effect of microplastic particles of different sizes on the planktonic trophic chain by sampling natural plankton communities from a lake located in the Upper Paraná River floodplain, Brazil. Zooplankton samples were collected at the beginning of the experiment and after 36 h of incubation. Microplastic particles (MP) samples were taken every 12 h. The effect of MP particle consumption from the control and treatment groups indicates significant effects by all plankton size fractions (p < 0.05). We demonstrated that the presence of MP particles can significantly affect the trophic web, furthermore, we detected the effect of higher consumption effect of smaller size MP particles. This study suggest that the largest MP consumption effects come from the lower trophic levels of the trophic chain, such as protists. The competitive effect of large predators is a crucial factor in controlling the abundance of populations, and although they did not directly consume MP particles, they ingest them indirectly through prey capable of absorbing these compounds in the environment. Our findings warn that MP particles enter the food webs of tropical regions when exposed to these pollutants, and that the presence of these particles should not be neglected when studying freshwater ecosystems.

Biodegradation Behavior of Degradable Mulch with Poly (Butylene Adipate-co-Terephthalate) (PBAT) and Poly (Butylene Succinate) (PBS) in Simulation Marine Environment

Poly (butylene adipate-co-terephthalate) (PBAT) and poly (butylene succinate) (PBS) are polyester materials with excellent biodegradability under soil and compost conditions. However, the research on their degradation process in the marine environment is scarce. In this study, a more realistic simulation marine environment with sediment and marine organisms was developed, followed by investigation of the biodegradation behavior of PBAT and PBS mulch in it. The effect of aromatic structure, carboxyl end group content, molecular weight, and inorganic fillers on the degeneration of mulch was characterized by the changes in appearance, chemical structure, thermal properties, and crystallinity via Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, gel permeation chromatography, element analysis, and X-ray photoelectron spectroscopy. The molecular weight of polyester blends decreased, while the content of the C-O bond in the composites increased, indicating that the samples indeed degraded. The degradation rate was measured with the CO₂ release amount. The aliphatic polyester structure, lower molecular weight, higher carboxyl end group content, and the involvement of inorganic fillers facilitate the disintegration of polyester in the marine environment, which provides an effective method to construct materials with controllable biodegradable performance.

Methodologies to Assess the Biodegradability of Bio-Based Polymers—Current Knowledge and Existing Gaps

Our society lives in a time of transition where traditional petroleum-based polymers/plastics are being replaced by more sustainable alternative materials. To consider these bioproducts as more viable options than the actual ones, it is demanded to ensure that they are fully biodegradable or compostable and that there is no release of hazardous compounds to the environment with their degradation. It is then essential to adapt the legislation to support novel specific guidelines to test the biodegradability of each biopolymer in varied environments, and consequently, establish consistent data to design a coherent labeling system. This review work aims to point out the current standards that can serve as a basis for the characterization of biopolymers’ biodegradation profile in different environments (soil, compost, and aquatic systems) and identify other laboratory methodologies that have been adopted for the same purpose. With the information gathered in this work, it was possible to identify remaining gaps in existing national and international standards to help establish new validation criteria to be introduced in future research and policies related to bioplastics to boost the sustainable progress of this rising industry.