Long-term immersion of compostable plastics in marine aquarium: Microbial biofilm evolution and polymer degradation

Biodegradation of poly(butylene adipate terephthalate) and poly(vinyl alcohol) within aquatic pathway

Understanding the environmental fate of biodegradable plastics in aquatic systems is crucial, given the alarming amount of plastic waste and microplastic particles transported through aquatic pathways. In particular, there is a need to analyze the biodegradation of commercialized biodegradable plastics upon release from wastewater treatment plants into natural aquatic systems. This study investigates the biodegradation behaviors of poly(butylene adipate terephthalate) (PBAT) and poly(vinyl alcohol) (PVA) in wastewater, freshwater, and seawater. Biodegradation of PBAT and PVA assessed through biochemical oxygen demand (BOD) experiments and microcosm tests revealed that the type of aquatic system governs the biodegradation behaviors of each plastic, with the highest biodegradation rate achieved in wastewater for both PBAT and PVA (25.6 and 32.2 % in 30 d, respectively). Plastic release pathway from wastewater into other aquatic systems simulated by sequential incubation in different microcosms suggested that PBAT exposed to wastewater and freshwater before reaching seawater was more prone to degradation than when directly exposed to seawater. On the other hand, PVA displayed comparable biodegradation rate regardless of whether it was directly exposed to seawater or had passed through other environments beforehand. Metagenome amplicon sequencing of 16S rRNA genes revealed distinct community shifts dependent on the type of plastics in changing environments along the simulated aquatic pathway. Several bacterial species putatively implicated in the biodegradation of PBAT and PVA are discussed. Our findings underscore the significant influence of pollution routes on the biodegradation of PBAT and PVA, highlighting the potential for wastewater treatment to facilitate rapid degradation compared to direct exposure to pristine aquatic environments.

Carbon Recycling of High Value Bioplastics: A Route to a Zero-Waste Future

Today, 98% of all plastics are fossil-based and non-biodegradable, and globally, only 9% are recycled. Microplastic and nanoplastic pollution is just beginning to be understood. As the global demand for sustainable alternatives to conventional plastics continues to rise, biobased and biodegradable plastics have emerged as a promising solution. This review article delves into the pivotal concept of carbon recycling as a pathway towards achieving a zero-waste future through the production and utilization of high-value bioplastics. The review comprehensively explores the current state of bioplastics (biobased and/or biodegradable materials), emphasizing the importance of carbon-neutral and circular approaches in their lifecycle. Today, bioplastics are chiefly used in low-value applications, such as packaging and single-use items. This article sheds light on value-added applications, like longer-lasting components and products, and demanding properties, for which bioplastics are increasingly being deployed. Based on the waste hierarchy paradigm-reduce, reuse, recycle-different use cases and end-of-life scenarios for materials will be described, including technological options for recycling, from mechanical to chemical methods. A special emphasis on common bioplastics-TPS, PLA, PHAs-as well as a discussion of composites, is provided. While it is acknowledged that the current plastics (waste) crisis stems largely from mismanagement, it needs to be stated that a radical solution must come from the core material side, including the intrinsic properties of the polymers and their formulations. The manner in which the cascaded use of bioplastics, labeling, legislation, recycling technologies, and consumer awareness can contribute to a zero-waste future for plastics is the core topics of this article.

Biodegradation of microplastics derived from controlled release fertilizer coating: Selective microbial colonization and metabolism in plastisphere

Coated controlled-release fertilizers (CRFs) are widely used in agriculture, and the persistent presence of residual polymer coating has raised environmental concerns. This study investigates the underlying degradation dynamics of microplastics (MPs) derived from three typical materials used in CRFs, including polyethylene (PE), epoxy (EP), and polyurethane (PU), through a soil degradation test. The formation of surface biofilm, the succession process, and metabolic characteristics of microbial community are revealed by laser scanning confocal microscope, 16S rRNA sequencing, and non-targeted metabolomics analysis. The weight loss rates of PE, EP, and PU after 807 days of degradation were 16.70 %, 2.79 %, and 4.86 %, respectively. Significant secondary MPs were produced with tears and holes appeared in the coating cross sections and pyrolysis products were produced such as ethers, acids, and esters for PE; alkanes, olefins and their branched-chain derivatives for EP; and short-chain fatty acids and benzene molecules for PU. The coating surface selectively recruited the bacteria of Chujaibacter and Ralstonia and fungus of Fusarium and Penicillium, forming biofilm composed of lipids, proteins, and living cells. The metabolism of amino acids and polymers was enhanced to protect against MP-induced stress. The metabolites or intermediates of organic acids and derivatives, oxygen-contained organic compounds, and benzenoids on CRF surface increased significantly compared with soil, but there were no significant differences among different coating types. This study provides insights to the underlying mechanisms of biodegradation and microenvironmental changes of MPs in soil.

Impacts of plastic-free materials on coral-associated bacterial communities during reef restoration

Coral propagation and out-planting based restoration approaches are increasingly being applied to assist natural recovery of coral reefs. However, many restoration methods rely on plastic zip-ties to secure coral material which is potentially problematic for the marine environment. Plastic-free biodegradable alternatives may however pose unique risks to coral-associated bacterial communities integral to coral health. Therefore, to identify whether biodegradable materials differentially impact coral-associated bacterial communities we examined Acropora millepora coral-associated bacterial communities during propagation in two experiments on the Great Barrier Reef. Coral fragments were secured to coral nurseries with conventional plastic, metal, or biodegradable (polyester and polycaprolactone) ties. Tie failure and coral-associated bacterial communities were then characterized over six months. Minimal coral mortality was observed (3.6%-8%) and all ties had low failure rates (0%-4.2%) except for biodegradable polyester ties (29.2% failure). No differences were observed between coral-associated bacterial communities of fragments secured with different ties, and no proliferation of putatively pathogenic bacteria was recorded. Overall, our findings suggest that reducing reliance on conventional plastic is feasible through transitions to biodegradable materials, without any notable impacts on coral-associated bacterial communities. However, we caution the need to examine more coral taxa of different morphologies and new plastic-free materials prior to application.

Synergistic effects of biochar derived from different sources on greenhouse gas emissions and microplastics mitigation during sewage sludge composting

This study aimed to investigate the effects of biochar derived from different sources (wheat straw, sawdust and pig manure) on greenhouse gas and microplastics (MPs) mitigation during sewage sludge composting. Compared to the control, all biochar significantly reduced the N2O by 28.91-41.23%, while having no apparent effect on CH4. Sawdust biochar and pig manure biochar significantly reduced the NH3 by 12.53-23.53%. Adding biochar decreased the global warming potential during composting, especially pig manure biochar (177.48 g/kg CO2-eq.). The concentration of MPs significantly increased in the control (43736.86 particles/kg) compared to the initial mixtures, while the addition of biochar promoted the oxidation and degradation of MPs (15896.06-23225.11 particles/kg), with sawdust biochar and manure biochar were more effective. Additionally, biochar significantly reduced the abundance of small-sized (10-100 μm) MPs compared to the control. Moreover, biochar might regulate specific microbes (e.g., Thermobifida, Bacillus and Ureibacillus) to mitigate greenhouse gas emissions and MPs degradation.

Mitigating plastic pollution at sea: Natural seawater degradation of a sustainable PBS/PBAT marine rope

This paper evaluates the use of a PBS/PBAT biodegradable rope to reduce the environmental impact of fishing gear lost at sea. The study aims to better understand the degradation mechanisms that the rope and its monofilaments may encounter due to the long term exposure to seawater. The monofilaments were immersed in natural seawater for up to 18 months, and rope samples were also immersed to study aging at a larger scale and evaluate the ability of a modelling tool to predict initial and aged states of the rope. At low temperatures, no loss of properties was observed for the monofilament and rope. However, at higher temperatures, biodegradation and hydrolysis processes were observed, leading to a faster loss of properties in the monofilament compared to the rope. The modelling tool provided conservative predictions due to severe mechanical test conditions of aged monofilament and a degradation gradient within the rope structure.