Quantification of polystyrene plastics degradation using 14C isotope tracer technique

A Perspective on the Controversy over Global Emission Fluxes of Microplastics from Ocean into the Atmosphere

Since the transfer of microplastic across the sea-air interface was first reported in 2020, numerous studies have been conducted on its emission flux estimation. However, these studies have shown significant discrepancies in the estimated contribution of oceanic sources to global atmospheric microplastics, with evaluations ranging from predominant to negligible, varying by 4 orders of magnitude from 7.7 × 10-4 to 8.6 megatons per year, thereby creating considerable confusion in the research on the microplastic cycle. Here, we provide a perspective by applying the well-established theory of particulate transfer through the sea-air interface. The upper limit of global sea-air emission flux microplastics was calculated, aiming to constrain the controversy in the previously reported fluxes. Specifically, the flux of sub-100 μm microplastic cannot exceed 0.01 megatons per year, and for sub-0.1 μm nanoplastics, it would not exceed 3 × 10-7 megatons per year. Bridging this knowledge gap is crucial for a comprehensive understanding of the sea-air limb in the "plastic cycle", and facilitates the management of future microplastic pollution.

Assessing microbial plastic degradation requires robust methods

Plastics are versatile materials that have the potential to propel humanity towards circularity and ultimate societal sustainability. However, the escalating concern surrounding plastic pollution has garnered significant attention, leading to widespread negative perceptions of these materials. Here, we question the role microbes may play in plastic pollution bioremediation by (i) defining polymer biodegradability (i.e., recalcitrant, hydrolysable and biodegradable polymers) and (ii) reviewing best practices for evaluating microbial biodegradation of plastics. We establish recommendations to facilitate the implementation of rigorous methodologies in future studies on plastic biodegradation, aiming to push this field towards the use of isotopic labelling to confirm plastic biodegradation and further determine the molecular mechanisms involved.

Single-Particle Analysis of the Photodegradation of Submicron Polystyrene Particles Using Infrared Photothermal Heterodyne Imaging

Sunlight irradiation is the predominant process for degrading plastics in the environment, but our current understanding of the degradation of smaller, submicron (<1000 nm) particles is limited due to prior analytical constraints. We used infrared photothermal heterodyne imaging (IR-PHI) to simultaneously analyze the chemical and morphological changes of single polystyrene (PS) particles (∼1000 nm) when exposed to ultraviolet (UV) irradiation (λ = 250-400 nm). Within 6 h of irradiation, infrared bands associated with the backbone of PS decreased, accompanied by a reduction in the particle size. Concurrently, the formation of several spectral features due to photooxidation was attributed to ketones, carboxylic acids, aldehydes, esters, and lactones. Spectral outcomes were used to present an updated reaction scheme for the photodegradation of PS. After 36 h, the average particle size was reduced to 478 ± 158 nm. The rates of size decrease and carbonyl band area increase were -24 ± 3.0 nm h-1 and 2.1 ± 0.6 cm-1 h-1, respectively. Using the size-related rate, we estimated that under peak terrestrial sunlight conditions, it would take less than 500 h for a 1000 nm PS particle to degrade to 1 nm.

Novel bacterial taxa in a minimal lignocellulolytic consortium and their potential for lignin and plastics transformation

The understanding and manipulation of microbial communities toward the conversion of lignocellulose and plastics are topics of interest in microbial ecology and biotechnology. In this study, the polymer-degrading capability of a minimal lignocellulolytic microbial consortium (MELMC) was explored by genome-resolved metagenomics. The MELMC was mostly composed (>90%) of three bacterial members (Pseudomonas protegens; Pristimantibacillus lignocellulolyticus gen. nov., sp. nov; and Ochrobactrum gambitense sp. nov) recognized by their high-quality metagenome-assembled genomes (MAGs). Functional annotation of these MAGs revealed that Pr. lignocellulolyticus could be involved in cellulose and xylan deconstruction, whereas Ps. protegens could catabolize lignin-derived chemical compounds. The capacity of the MELMC to transform synthetic plastics was assessed by two strategies: (i) annotation of MAGs against databases containing plastic-transforming enzymes; and (ii) predicting enzymatic activity based on chemical structural similarities between lignin- and plastics-derived chemical compounds, using Simplified Molecular-Input Line-Entry System and Tanimoto coefficients. Enzymes involved in the depolymerization of polyurethane and polybutylene adipate terephthalate were found to be encoded by Ps. protegens, which could catabolize phthalates and terephthalic acid. The axenic culture of Ps. protegens grew on polyhydroxyalkanoate (PHA) nanoparticles and might be a suitable species for the industrial production of PHAs in the context of lignin and plastic upcycling.

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

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