Characteristics analysis of plastisphere biofilm and effect of aging products on nitrogen metabolizing flora in microcosm wetlands experiment

Toxicological evaluation and metabolic profiling of earthworms (Eisenia fetida) after exposure to microplastics and acetochlor

In recent years, microplastic (MPs) and pesticide pollution have become prominent issues in the field of soil pollution. This research endeavored to assess the impact of ultraviolet radiation (UV) on the characteristics of microplastics, as well as investigating the toxicological effect on earthworms (Eisenia fetida) when subjected to the dual stressors of microplastics and acetochlor (ACT). This research found that microplastics aged under UV were more prone to wear and tear in the environment, and produced more oxygen-containing functional groups. Chronic exposure experiments were conducted on ACT and aged-MPs. The results revealed that aged-MPs and ACT inhibited earthworm growth, induced oxidative stress, and caused damage to both the body cavity muscles and the intestinal lumen. Compared with individual exposure, combined exposure increased the oxidative products (superoxide dismutase (SOD) and catalase (CAT)) and altered the expression levels of related genes (TCTP and Hsp70) significantly. PE inflicted more significant harm to the earthworm intestinal tissue compared to PBAT. By 1H-NMR metabolomics, the investigation delved into the repercussions of PE and ACT on the metabolic pathways of earthworms. Exposure to ACT and PE can disrupt the stability of intestinal membranes stability, amino acid metabolism, neuronal function, oxidative stress and energy metabolism. Overall, the research revealed that combined exposure of MPs and ACT exacerbated the negative effects on earthworms significantly, and contributed valuable insights to environmental risk assessment of the combined toxicity of microplastics and pesticides.

Ecological and Health Risk Mediated by Micro(nano)plastics Aging Process: Perspectives and Challenges

Aged micro(nano)plastics (MNPs) are normally the ultimate state of plastics in the environment after aging. The changes in the physical and chemical characteristics of aged MNPs significantly influence their environmental behavior by releasing additives, forming byproducts, and adsorbing contaminants. However, a systematic review is lacking on the effects of aged MNPs on ecological and human health regarding the increasing but scattered studies and results. This Review first summarizes the unique characteristics of aged MNPs and methods for quantifying their aging degree. Then we focused on the potential impacts on organisms, ecosystems, and human health, including the "Trojan horse" under real environmental conditions. Through combining meta-analysis and analytic hierarchy process (AHP) model, we demonstrated that, compared to virgin MNPs, aged MNPs would result in biomass decrease and oxidative stress increase on organisms and lead to total N/P decrease and greenhouse gas emissions increase on ecosystems while causing cell apoptosis, antioxidant system reaction, and inflammation in human health. Within the framework of ecological and human health risk assessment, we used the risk quotient (RQ) and physiologically based pharmacokinetic (PBK) models as examples to illustrate the importance of considering aging characteristics and the degree of MNPs in the process of data acquisition, model building, and formula evaluation. Given the ecological and health risks of aged MNPs, our urgent call for more studies of aged MNPs is to understand the potential hazards of MNPs in real-world environments.

Vacancy-rich NiFe-LDH/carbon paper as a novel self-supporting electrode for the electro-Fenton degradation of polyvinyl chloride microplastics

Electrochemically upcycling polyvinyl chloride (PVC) into high-value small molecules represents a sustainable strategy for mitigating plastic pollution. Herein, a cost-effective self-supporting electrode with abundant vacancies, i.e., NiFe-layered double hydroxide nanoarrays in-situ grown on the surface of carbon paper (denoted as NiFeV-LDH/CP), is developed for the electro-Fenton degradation of PVC microplastics (MPs). The NiFeV-LDH catalyst shows a high selectivity of 76 % towards H2O2 production via two-electron oxygen reduction reaction (2e- ORR). Density functional theory (DFT) calculations reveal that the energy barrier of rate-determining step (*H2O2 desorption) decreases over the vacancy-enriched NiFeV-LDH related to the pristine NiFeZn-LDH. The influence of vacancy concentration, reaction temperature and initial concentration of PVC MPs were systematically investigated. Under optimized conditions, the NiFeV-LDH/CP electrode exhibits an outstanding degradation performance of PVC MPs via direct cathodic reduction and oxidation by hydroxyl radicals. This work demonstrates that the electro-Fenton technology using LDH-based self-supporting electrodes is a promising and environmentally-friendly approach for waste plastic treatment.

Pretreated polystyrene is degraded by a microbial consortium enriched from wetland plastic waste

The biodegradation of polystyrene (PS), a type of plastic with aromatic rings in its polymer chain, is a critical environmental goal worldwide. Microbial degradation of PS has been reported, but the underlying mechanisms are poorly understood. Here, we constructed a microcosm wetland containing PS plastic. We isolated six highly efficient PS plastic-degrading bacterial strains and created a microbial consortium (MCs) consisting of these strains. After a 30-day incubation period, MCs-treated PS exhibited hallmarks of degradation, including -CO- formation, reduced hydrophobicity, surface porosity, and 20 % weight loss. The efficiency of PS degradation was enhanced by using a combination of physical-chemical pretreatment and biological methods, increasing the microbial degradation rate by 20 %. Antioxidant 2246 (C23H32O2) was detected in the culture supernatant via GC-MS. Metatranscriptomic sequencing analysis provided insight into the possible metabolic pathway of PS degradation by the composite bacteria. We identified 31 highly expressed genes encoding proteins that function in carbon metabolism pathways and 34 unique proteases which catalyze the cleavage of long polymer chains. The resulting small molecules are absorbed and further degraded intracellularly by enzymes such as coenzyme synthase, hydratase, transferase, carboxylase, and dehydrogenase. These findings lay the foundation for the efficient and sustainable degradation of PS.

Mechanisms underpinning microplastic effects on the natural climate solutions of wetland ecosystems

Wetland ecosystems are vital carbon dioxide (CO2) sinks, offering significant nature-based solutions for global climate mitigation. However, the recent influx of microplastic (MP) into wetlands substantially impacts key drivers (e.g., plants and microorganisms) underpinning these wetland functions. While MP-induced greenhouse gas (GHG) emissions and effects on soil organic carbon (SOC) mineralization potentially threaten the long-term wetland C-climate feedbacks, the exact mechanisms and linkage are unclear. This review provides a conceptual framework to elaborate on the interplay between MPs, wetland ecosystems, and the atmospheric milieu. We also summarize published studies that validate possible MP impacts on natural climate solutions of wetlands, as well as provide extensive elaboration on underlying mechanisms. We briefly highlight the relationships between MP influx, wetland degradation, and climate change and conclude by identifying key gaps for future research priorities. Globally, plastic production, MP entry into aquatic systems, and wetland degradation-related emissions are predicted to increase. This means that MP-related emissions and wetland-climate feedback should be addressed in the context of the UN Paris Climate Agreement on net-zero emissions by 2050. This overview serves as a wake-up call on the alarming impacts of MPs on wetland ecosystems and urges a global reconsideration of nature-based solutions in the context of climate mitigation.

Genome-Centric Metagenomics Insights into the Plastisphere-Driven Natural Degradation Characteristics and Mechanism of Biodegradable Plastics in Aquatic Environments

Biodegradable plastics (BPs) are pervasively available as alternatives to traditional plastics, but their natural degradation characteristics and microbial-driven degradation mechanisms are poorly understood, especially in aquatic environments, the primary sink of plastic debris. Herein, the three-month dynamic degradation process of BPs (the copolymer of poly(butylene adipate-co-terephthalate) and polylactic acid (PLA) (PBAT/PLA) and single PLA) in a natural aquatic environment was investigated, with nonbiodegradable plastics polyvinyl chloride, polypropylene, and polystyrene as controls. PBAT/PLA showed the weight loss of 47.4% at 50 days and severe fragmentation within two months, but no significant decay for other plastics. The significant increase in the specific surface area and roughness and the weakening of hydrophobicity within the first month promoted microbial attachment to the PBAT/PLA surface. Then, a complete microbial succession occurred, including biofilm formation, maturation, and dispersion. Metagenomic analysis indicated that plastispheres selectively enriched degraders. Based on the functional genes involved in BPs degradation, a total of 16 high-quality metagenome-assembled genomes of degraders (mainly Burkholderiaceae) were recovered from the PBAT/PLA plastisphere. These microbes showed the greatest degrading potential at the biofilm maturation stage and executed the functions by PLA_depolymerase, polyesterase, hydrolase, and esterase. These findings will enhance understanding of BPs' environmental behavior and microbial roles on plastic degradation.

Insights into soil autotrophic ammonium oxidization under microplastics stress: Crossroads of nitrification, comammox, anammox and Feammox

Microplastics (MPs) are widespread in agroecosystems and profoundly impact soil microbiome and nutrient cycling. However, the effects of MPs on soil autotrophic ammonium oxidization processes, including nitrification, complete ammonium oxidation (comammox), anaerobic ammonium oxidation (anammox), and anaerobic ammonium oxidation coupled to iron reduction (Feammox), remain unclear. These processes are the rate-limiting steps of nitrogen cycling in agroecosystems. Here, our work unveiled that exposures of polyethylene (PE), polypropylene (PP), polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT) MPs significantly modulated ammonium oxidization pathways with distinct type- and dose-dependent effects. Nitrification remained the main contributor (56.4-70.7 %) to soil ammonium removal, followed by comammox (11.7-25.6 %), anammox (5.0-20.2 %) and Feammox (3.3-11.6 %). Compared with conventional nonbiodegradable MPs (i.e., PE and PP), biodegradable MPs (i.e., PLA and PBAT) exhibited more pronounced impacts on soil nutrient conditions and functional microbes, which collectively induced alterations in soil ammonium oxidation. Interestingly, low-dose PLA and PBAT remarkably enhanced the roles of anammox and Feammox in soil ammonium removal, contributing to the mitigation of soil acidification in agroecosystems. This study highlights the diverse responses of ammonium oxidization pathways to MPs, further deepening our understanding of how MPs affect biogeochemical cycling and enriching strategies for agricultural managements amid increasing MPs pollution.

Isolation of marine polyethylene (PE)-degrading bacteria and its potential degradation mechanisms

Microbial degradation of polyethylene (PE) offers a promising solution to plastic pollution in the marine environment, but research in this field is limited. In this study, we isolated a novel marine strain of Pseudalkalibacillus sp. MQ-1 that can degrade PE. Scanning electron microscopy and water contact angle results showed that MQ-1 could adhere to PE films and render them hydrophilic. Analyses using X-ray diffraction, fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy showed a decrease in relative crystallinity, the appearance of new functional groups and an increase in the oxygen-to‑carbon ratio of the PE films, making them more susceptible to degradation. The results of gel permeation chromatography and liquid chromatography-mass spectrometry indicated the depolymerization of the long PE chains, with the detection of an intermediate, decanediol. Furthermore, genome sequencing was employed to investigate the underlying mechanisms of PE degradation. The results of genome sequencing analysis identified the genes associated with PE degradation, including cytochrome P450, alcohol dehydrogenase, and aldehyde dehydrogenase involved in the oxidative reaction, monooxygenase related to ester bond formation, and esterase associated with ester bond cleavage. In addition, enzymes involved in fatty acid metabolism and intracellular transport have been identified, collectively providing insights into the metabolic pathway of PE degradation.

Microplastics increase the microbial functional potential of greenhouse gas emissions and water pollution in a freshwater lake: A metagenomic study

Aquatic ecosystems are being increasingly polluted by microplastics (MPs), which calls for an understanding of how MPs affect microbially driven biogenic element cycling in water environments. A 28-day incubation experiment was conducted using freshwater lake water added with three polymer types of MPs (i.e., polyethylene, polypropylene, polystyrene) separately or in combination at a concentration of 1 items/L. The effects of various MPs on microbial communities and functional genes related to carbon, nitrogen, phosphorus, and sulfur cycling were analyzed using metagenomics. Results showed that Sphingomonas and Novosphingobium, which were indicator taxa (genus level) in the polyethylene treatment group, made the largest functional contribution to biogenic element cycling. Following the addition of MPs, the relative abundances of genes related to methane oxidation (e.g., hdrD, frhB, accAB) and denitrification (napABC, nirK, norB) increased. These changes were accompanied by increased relative abundances of genes involved in organic phosphorus mineralization (e.g., phoAD) and sulfate reduction (cysHIJ), as well as decreased relative abundances of genes involved in phosphate transport (phnCDE) and the SOX system. Findings of this study underscore that MPs, especially polyethylene, increase the potential of greenhouse gas emissions (CO2, N2O) and water pollution (PO43-, H2S) in freshwater lakes at the functional gene level.

Plant and microbial response in constructed wetland treating tetracycline antibiotic polluted water: Evaluating the effects of microplastic size and concentration

Microplastics (MPs) and antibiotics are novel water pollutants that have attracted increasing attention. Constructed wetlands (CWs) are widely applied treating various types of polluted water. How these two new pollutants affect plants and microorganisms in CWs, especially deciphering the unknown roles of MPs size and concentration, is of great essential. Here, five CW treatments with submerged macrophyte Myriophyllum aquaticum were established to treat oxytetracycline (OTC) antibiotic-polluted water. The effects of polystyrene (PS) nanoplastics (NPs) (700 nm) and MPs (90-110 μm) on plant and microbial communities at 10 μg/L and 1 mg/L, respectively, were systematically evaluated. PS reduced the nitrogen and phosphorus removal efficiencies and inhibited OTC removal. Low doses (10 μg/L) of NPs and high doses (1 mg/L) of MPs had the greatest effects on plant and microbial responses. The overall effect of MPs was greater than that of NPs. Compared with high NPs concentration (1 mg/L), low concentrations (10 μg/L) had higher catalase (CAT), superoxide dismutase (SOD), and malondialdehyde (MDA) content. However, the activity and content of MPs at low concentrations (10 μg/L) were lower than those at high concentrations (1 mg/L). The coexistence of OTC and MPs/NPs decreased the microbial diversity and abundance. Low doses of NPs and high doses of MPs decreased the relative abundance of Abditibacteriota, Deinococccota, and Zixibacteria. Redundancy and network analyses revealed a strong correlation between pollutant removal and plant and microbial responses. NH4+-N and OTC removal was positively and negatively correlated with CAT, SOD, and MDA content, respectively. MDA positively correlated to chlorophyll content, whereas SOD showed a negative correlation with Chloroflexi. This study highlighted the scale effect of MPs in wastewater treatment via CWs. It enhances our understanding of the response of plants and microorganisms to the remediation of water co-polluted with MPs and antibiotics.