Deep-ocean seafloor islands of plastics

Unveiling the deep-sea microplastic Odyssey: Characteristics, distribution, and ecological implications in Pacific Ocean sediments

Microplastics (MPs) in deep-sea environments are a growing concern due to their potential ecological risks and the deep sea's role in global biogeochemical cycles. This study investigated the characteristics and distribution of MPs in sediments from the Pacific Ocean at depths of 4900-7016 m across three regions: Western Pacific (WP), Central Pacific (CP), and Eastern Pacific (EP). MPs were detected at all sampling sites, with the highest abundance in WP (111.3 ± 75.1 items/kg dw) and the lowest in CP (49.4 ± 18.7 items/kg dw). Site S9 was recorded as the peak abundance (270.1 ± 107.4 items/kg dw) in WP. MPs were predominantly fibers (94.8 %) in black, gray, and blue hues, mainly composed of polyester and rayon. Statistical analysis showed significant regional variations, reflecting anthropogenic impacts and complex deposition mechanisms. Risk assessments indicated low to medium hazard levels (PLI <10, PRI ≤ III), but the potential ecological impacts remain concerning. This study highlights the significant variability in MP distribution across regions, emphasizing the importance of region-specific mitigation strategies. It calls for comprehensive, long-term research to better understand MP sources, deposition processes, and ecological impacts in deep-sea ecosystems.

Exploring the response of bacterial community functions to microplastic features in lake ecosystems through interpretable machine learning

Microplastics (MPs) are ubiquitous and have various characteristics. However, their impacts on bacterial community functions in lakes remain elusive. In this study, we identified 33 different MPs features including their abundance, shape, color, size, and polymer type, from Taihu Lake, China. These features were used to construct 48 machine learning models, utilizing four types of machine learning regression algorithms, to investigate how different MP features influence human health, carbon/nitrogen cycling, and energy source-related functions of bacterial communities. The XGBoost models provided the best performance with an average R2 of 0.85 in explaining the abundance of functions. Yellow-, fragment-, and polyethylene terephthalate (PET) MPs were the most important features by Shapley values. Yellow- and PET-MPs mainly had primarily negative impacts on human pathogens pneumonia and chemoheterotrophy, respectively. Fragment-MPs had a primarily positive impact, which shifted from positive to negative at a proportion of 0.5 for methanol oxidation. Moreover, MPs may affect community structure by filtering for functional traits. These findings are important for understanding the effects of MP pollution on bacterial community function and its role in the global carbon and nitrogen cycling and human health and help us to determine the potential impacts of MP pollution on ecosystems.

Comprehensive profiling and risk assessment of antibiotic resistomes in surface water and plastisphere by integrated shotgun metagenomics

The ever-increasing microplastics (MPs) and antibiotic-resistance genes (ARGs) in aquatic ecosystems has become a serious global challenging issue. However, the impact of different pollution sources on microbiome and antibiotic resistome in surface water (SW) and plastisphere (PS) remains largely elusive. Here, shotgun metagenomics was used to analyze microbiome structure and antibiotic resistome in SW and PS under the influence of different pollution sources. Pseudomonas were the most abundant genus, followed by Flavobacterium, Acinetobacter, Acidovorax, and Limnohabitans. However, their relative abundance varied significantly both across the sampling sites and habitats i.e. SW and PS (p < 0.05). Additionally, various ARGs were detected in SW and PS, with PS (372) having significantly more potential ARGs than SW (293). The results further showed significant variations in the relative abundance of potential pathogenic bacteria across the sampling sites and habitats (p < 0.05). Further moreover, significant differences were observed in antibiotic resistome risk scores, ARGs and MGEs across different habitats. Over all, this study suggests that pollution source and water quality parameters had a significant impact on microbiome composition and antibiotic resistome in SW and PS.

Occurrence of plastic additives in coral-reef invertebrates on natural and plastic substrates

Numerous studies have investigated the occurrence of plastic additives in marine biota. Yet, their main vector of transfer into organisms tissues remains unknown. We explored seven common additives in benthic coral reef invertebrates residing on natural/plastic substrates in a protected marine reserve versus an unprotected reef to ascertain whether additives transfer by substrate leaching. Samples of three coral-reef species were extracted and analyzed by GCMS and HPLC. Of the seven chemical additives investigated, dibenzylamine and bis(2-ethylhexyl) phthalate were detected. No significant association was found between additives and substrate type, possibly because these plastics have been submerged for years, and the majority of additives within them have leached. The marine reserve had fewer samples with additives, highlighting the importance of active management. Understanding the transfer vectors of plastic additives into biota is essential for assessing the risk they pose and devising effective management tools for protecting coral reefs.

Regioselective enzymatic depolymerization of aromatic-aliphatic polyester revealed by computational modelling

Poly(butylene adipate-co-terephthalate) (PBAT) is widely utilized in the production of food packaging and mulch films. Its extensive application has contributed significantly to global solid waste, posing numerous environmental challenges. Recently, enzymatic recycling has emerged as a promising eco-friendly solution for the management of plastic waste. Here, we systematically investigate the depolymerization mechanism of PBAT catalyzed by cutinase TfCutSI with molecular docking, molecular dynamics simulations, and quantum mechanics/molecular mechanics calculations. Although the binding affinities for acid ester and terephthalic acid ester bonds are similar, a regioselective depolymerization mechanism and a "chain-length" effect on regioselectivity were proposed and evidenced. The regioselectivity is highly associated with specific structural parameters, namely Substrate@O4-Met@H7 and Substrate@C1-Ser@O1 distances. Notably, the binding mode of BTa captured by X-ray crystallography does not facilitate subsequent depolymerization. Instead, a previously unanticipated binding mode, predicted through computational analysis, is confirmed to play a crucial role in BTa depolymerization. This finding proves the critical role of computational modelling in refining experimental results. Furthermore, our results revealed that both the hydrogen bond network and enzyme's intrinsic electric field are instrumental in the formation of the final product. In summary, these novel molecular insights into the PBAT depolymerization mechanism offer a fundamental basis for enzyme engineering to enhance industrial plastic recycling.

An archaeal lid-containing feruloyl esterase degrades polyethylene terephthalate

Polyethylene terephthalate (PET) is a commodity polymer known to globally contaminate marine and terrestrial environments. Today, around 80 bacterial and fungal PET-active enzymes (PETases) are known, originating from four bacterial and two fungal phyla. In contrast, no archaeal enzyme had been identified to degrade PET. Here we report on the structural and biochemical characterization of PET46 (RLI42440.1), an archaeal promiscuous feruloyl esterase exhibiting degradation activity on semi-crystalline PET powder comparable to IsPETase and LCC (wildtypes), and higher activity on bis-, and mono-(2-hydroxyethyl) terephthalate (BHET and MHET). The enzyme, found by a sequence-based metagenome search, is derived from a non-cultivated, deep-sea Candidatus Bathyarchaeota archaeon. Biochemical characterization demonstrated that PET46 is a promiscuous, heat-adapted hydrolase. Its crystal structure was solved at a resolution of 1.71 Å. It shares the core alpha/beta-hydrolase fold with bacterial PETases, but contains a unique lid common in feruloyl esterases, which is involved in substrate binding. Thus, our study widens the currently known diversity of PET-hydrolyzing enzymes, by demonstrating PET depolymerization by a plant cell wall-degrading esterase.

Chlorinated Paraffin Pollution in the Marine Environment

Chlorinated paraffins (CPs) are ubiquitous in the environment due to their large-scale usage, persistence, and long-range atmospheric transport. The oceans are a critical environment where CPs transformation occurs. However, the broad impacts of CPs on the marine environment remain unclear. This review describes the sources, occurrence and transport pathways, environmental processes, and ecological effects of CPs in the marine environment. CPs are distributed in the global marine environment by riverine input, ocean currents, and long-range atmospheric transport from industrial areas. Environmental processes, such as the deposition of particle-bound compounds, leaching of plastics, and microbial degradation of CPs, are the critical drivers for regulating CPs' fate in water columns or sediment. Bioaccumulation and trophic transfer of CPs in marine food webs may threaten marine ecosystem functions. To elucidate the biogeochemical processes and environmental impacts of CPs in marine environments, future work should clarify the burden and transformation process of CPs and reveal their ecological effects. The results would help readers clarify the current research status and future research directions of CPs in the marine environment and provide the scientific basis and theoretical foundations for the government to assess marine ecological risks of CPs and to make policies for pollution prevention and control.

Using Data-Driven Methods and Aging Information to Quantitatively Identify Microplastic Environmental Sources and Establish a Comprehensive Discrimination Index

The global distribution of microplastics (MPs) across various environmental compartments has garnered significant attention. However, the differences in the characteristics of MPs in different environments remain unclear, and there is still a lack of quantitative analysis of their environmental sources. In addition, the inclusion of aging in source apportionment is a novel approach that has not been widely explored. In this study, we conducted a meta-analysis of the literature from the past 10 years and extracted conventional and aging characteristic data of MPs from 321 sampling points across 7 environmental compartments worldwide. We established a data-driven analysis framework using these data sets to identify different MP communities across environmental compartments, screen key MP features, and develop an environmental source analysis model for MPs. Our results indicate significant differences in the characteristics of MP communities across environments. The key features of differentiation were identified using the LEfSe method and include the carbonyl index, hydroxyl index, fouling index, proportions of polypropylene, white, black/gray, and film/sheet. These features were screened for each environmental compartment. An environmental source identification model was established based on these features with an accuracy of 75.1%. In order to accurately represent the single/multisource case in a more probabilistic manner, we proposed the MP environmental source index (MESI) to provide a probability estimation of the sample having multiple sources. Our findings contribute to a better understanding of MP migration trends and fluxes in the plastic cycle and inform effective prevention and control strategies for MP pollution.

Holes on surfaces of the weathered plastic fragments from coastal beaches

The surface morphology of weathered plastics undergoes a variety of changes. In this study, 3950 plastic fragments from 26 beaches around the world, were assessed to identify holes. Holes were identified on 123 fragments on 20 beaches, with the highest frequency (10.3 %) being identified at Qesm AL Gomrok Beach in Egypt. The distribution of holes could be divided into even, single-sided, and random types. The external and internal holes were similar in size (37 ± 15 μm) of even type fragments. The external holes were larger than the internal holes in single-sided (516 ± 259 μm and 383 ± 161 μm) and random (588 ± 262 μm and 454 ± 210 μm) fragment types. The external hole sizes were positively correlated with the internal hole sizes for each type. This study reports a novel deformation phenomenon on the surface of weathered plastics and highlights their potential effects on plastics.

Polyvinyl chloride microplastics induce changes in gene expression and organ histology along the HPG axis in Cyprinus carpio var. larvae

The negative consequences of microplastics pollution on the health of aquatic species have garnered extensive attention. However, the mechanisms through which microplastics may cause harm in the reproductive processes of fish remain unknown. For this study, Cyprinus carpio var. was subjected to four treatments with various concentrations of PVC microplastics for 60 days, through food rationed diets (no plastic control, 10%, 20% and 30%). The gonadosomatic indices, gonad and brain histologies, sex hormone levels, and transcriptional and translational genes in the hypothalamic-pituitary-gonadal (HPG) axes of both sexes were observed. According to the results, the gonadosomatic indices were significantly decreased, gonadal development was delayed, and the level of estradiol (E2) in the females was significantly elevated. In addition, the expression levels of genes associated with the HPG axis in the brains and gonads (gnrh, gtha1, fshβ, cyp19b, erα, vtg1, dmrt1, sox9b, and cyp19a) and the transcription levels of apoptosis-related genes in the brains and gonads (caspase3, bax, and bcl-2) exhibited significant changes. Further investigation revealed that the translation levels of genes linked to sex differentiation and sex steroid hormone (cyp19b and dmrt1) were significantly altered. These findings indicated that PVC likely microplastics may have a negative impact on the reproductive system of Cyprinus carpio var. by inhibiting gonadal development, affecting the gonad and brain structures, and altering the levels of steroid hormones and the expression of HPG axis-related genes. This work provides new insights into the toxicity of microplastics in aquatic organisms by revealing that PVC microplastics are a potential threat against the reproduction of fish populations.

Tracing the Century-Long Evolution of Microplastics Deposition in a Cold Seep

Microplastic (MP) pollution is one of the greatest threats to marine ecosystems. Cold seeps are characterized by methane-rich fluid seepage fueling one of the richest ecosystems on the seafloor, and there are approximately more than 900 cold seeps globally. While the long-term evolution of MPs in cold seeps remains unclear. Here, how MPs have been deposited in the Haima cold seep since the invention of plastics is demonstrated. It is found that the burial rates of MPs in the non-seepage areas significantly increased since the massive global use of plastics in the 1930s, nevertheless, the burial rates and abundance of MPs in the methane seepage areas are much lower than the non-seepage area of the cold seep, suggesting the degradation potential of MPs in cold seeps. More MP-degrading microorganism populations and functional genes are discovered in methane seepage areas to support this discovery. It is further investigated that the upwelling fluid seepage facilitated the fragmentation and degradation behaviors of MPs. Risk assessment indicated that long-term transport and transformation of MPs in the deeper sediments can reduce the potential environmental and ecological risks. The findings illuminated the need to determine fundamental strategies for sustainable marine plastic pollution mitigation in the natural deep-sea environments.

Effects of organic matter on interaction forces between polystyrene microplastics: An experimental study

The aggregation and deposition processes of marine microplastics are extremely important in marine ecosystems. The main effect of these two physical processes is the transfer of surface microplastics to the deep sea, and the underlying kinetics can be significantly affected by the organic matter in the ocean. The morphology of and interaction force on 20-μm polystyrene microplastics in the presence of organic matter were studied by using environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM), respectively. Experiments were performed using organic matter of various concentrations, and the results showed that humic acid formed a translucent organic film around polystyrene microplastics. With increasing total organic content (TOC), the average overall size of the microplastic coated with biofilm increased up to 11 % (at a TOC of 50 mg/L) and then decreased slightly. The biofilm formed by humic acid decreases the repulsion force between two particles and thus could promote the aggregation process significantly. A modified formulation of eXtended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, describing the interaction force of microplastics with the influences of biofilms was proposed based on the measured results.

Interactions of microplastics with organic, inorganic and bio-pollutants and the ecotoxicological effects on terrestrial and aquatic organisms

As emerging contaminants, microplastics (MPs) have attracted global attention. They are a potential risk to organisms, ecosystems and human health. MPs are characterized by small particle sizes, weak photodegradability, and are good environmental carriers. They can physically adsorb or chemically react with organic, inorganic and bio-pollutants to generate complex binary pollutants or change the environmental behaviors of these pollutants. We systematically reviewed the following aspects of MPs: (i) Adsorption of heavy metals and organic pollutants by MPs and the key environmental factors affecting adsorption behaviors; (ii) Enrichment and release of antibiotic resistance genes (ARGs) on MPs and the effects of MPs on ARG migration in the environment; (iii) Formation of "plastisphere" and interactions between MPs and microorganisms; (iv) Ecotoxicological effects of MPs and their co-exposures with other pollutants. Finally, scientific knowledge gaps and future research areas on MPs are summarized, including standardization of study methodologies, ecological effects and human health risks of MPs and their combination with other pollutants.

Single-particle analysis of micro/nanoplastics by SEM-Raman technique

Micro/nanoplastics (MNPs) have received global concern due to their widespread contamination, ingestion in organisms, and the ability to cross the biological barrier. Although MNPs have been detected in a variety of ecosystems, the identification of single MNPs remains an unsolved challenge. Herein, for the first time, scanning electron microscope (SEM) coupled with surface-enhanced Raman spectroscopy (SERS), which combined the advantages of ultrahigh spatial resolution of SEM and structural fingerprint of Raman spectroscopy, was proposed to identify MNPs at single-particle level. Under the optimum conditions, the polystyrene (PS) MNPs with sizes of 500 nm and 1 μm were identified by the image of SEM and fingerprint peaks of Raman spectroscopy. Additionally, the applicability of the method in different sample matrices and for other types of MNPs such as poly-methyl methacrylate (PMMA) with the sizes of 300 nm, 1 μm were validated. This method is simple, rapid and effective and is likely to provide an essential tool to identify other micro/nanoparticles in addition to MNPs.

Integrated metagenomic and metatranscriptomic analysis reveals actively expressed antibiotic resistomes in the plastisphere

The plastisphere is viewed as a reservoir for the antibiotic resistome in water environments and may pose health concerns. However, the expression profiles of the resistome in the plastisphere are largely unknown. Here, we profiled the occurrence, abundance, and transcriptional level of antibiotic resistance genes (ARGs), plasmid associated ARGs, microbial composition and ARG bacterial hosts in the plastisphere and urban river water using 16S rRNA gene sequencing, metagenomic sequencing, and metatranscriptomic sequencing methods. A total of 173 ARGs conferring resistance to 24 major classes of antibiotics commonly prescribed to humans and animals were detected in the plastisphere. Of these, 75 genes were observed with transcriptional activity, indicating that the antibiotic resistome in the plastisphere was not only present, but also actively expressed. Human pathogens belonging to family Enterobacteriaceae were identified as bacterial hosts of ARGs in the plastisphere. The opportunistic and multidrug resistant human pathogen Enterobacter cloacae was found to actively express tetG and confer tetracycline resistance to the plastisphere. Furthermore, 39 genes were identified as "plasmid associated ARGs" in the plastisphere, displaying a higher proportion of transcript abundance compared with water. The above results suggest that the plastisphere is a hotspot for antibiotic resistome acquisition, expression, and dissemination.

Genomic Evidence for the Recycling of Complex Organic Carbon by Novel Thermoplasmatota Clades in Deep-Sea Sediments

Thermoplasmatota have been widely reported in a variety of ecosystems, but their distribution and ecological role in marine sediments are still elusive. Here, we obtained four draft genomes affiliated with the former RBG-16-68-12 clade, which is now considered a new order, “Candidatus Yaplasmales,” of the Thermoplasmatota phylum in sediments from the South China Sea. The phylogenetic trees based on the 16S rRNA genes and draft genomes showed that “Ca. Yaplasmales” archaea are composed of three clades: A, B, and C. Among them, clades A and B are abundantly distributed (up to 10.86%) in the marine anoxic sediment layers (>10-cm depth) of six of eight cores from 1,200- to 3,400-m depths. Metabolic pathway reconstructions indicated that all clades of “Ca. Yaplasmales” have the capacity for alkane degradation by predicted alkyl-succinate synthase. Clade A of “Ca. Yaplasmales” might be mixotrophic microorganisms for the identification of the complete Wood-Ljungdahl pathway and putative genes involved in the degradation of aromatic and halogenated organic compounds. Clades B and C were likely heterotrophic, especially with the potential capacity of the spermidine/putrescine and aromatic compound degradation, as suggested by a significant negative correlation between the concentrations of aromatic compounds and the relative abundances of clade B. The sulfide-quinone oxidoreductase and pyrophosphate-energized membrane proton pump were encoded by all genomes of “Ca. Yaplasmales,” serving as adaptive strategies for energy production. These findings suggest that “Ca. Yaplasmales” might synergistically transform benthic pollutant and detrital organic matter, possibly playing a vital role in the marine and terrestrial sedimentary carbon cycle.

IMPORTANCE Deep oceans receive large amounts of complex organic carbon and anthropogenic pollutants. The deep-sea sediments of the continental slopes serve as the biggest carbon sink on Earth. Particulate organic carbons and detrital proteins accumulate in the sediment. The microbially mediated recycling of complex organic carbon is still largely unknown, which is an important question for carbon budget in global oceans and maintenance of the deep-sea ecosystem. In this study, we report the prevalence (up to 10.86% of the microbial community) of archaea from a novel order of Thermoplasmatota, “Ca. Yaplasmales,” in six of eight cores from 1,200- to 3,400-m depths in the South China Sea. We provide genomic evidence of “Ca. Yaplasmales” in the anaerobic microbial degradation of alkanes, aliphatic and monoaromatic hydrocarbons, and halogenated organic compounds. Our study identifies the key archaeal players in anoxic marine sediments, which are probably critical in recycling the complex organic carbon in global oceans.

Microplastics and bisphenol A hamper gonadal development of whiteleg shrimp (Litopenaeus vannamei) by interfering with metabolism and disrupting hormone regulation

Gonadal development is a prerequisite for the reproductive success of an organism, and might be affected by environmental factors such as emergent pollutants. Although marine crustaceans are threatened by ubiquitous emergent pollutants such as microplastics (MPs) and bisphenol A (BPA) under realistic scenarios, studies about the impacts of these pollutants on the gonadal development of crustacean species are rare. In this study, the effects of MPs and BPA, alone or in combination, on gonadal development were investigated in whiteleg shrimp (Litopenaeus vannamei). The results obtained demonstrated that whiteleg shrimp exposed to MPs and BPA had significantly smaller gonad-somatic index (GSI) and an obvious delay in the gonad developmental stage. In addition, exposure of whiteleg shrimp to pollutants tested resulted in a reduction in the oxygen consumption rate, elevation in the ammonia excretion rate, decline in the O: N ratio, and downregulation in the expression of metabolism-related genes, indicating significant disruptions of shrimp metabolism by the pollutants. Furthermore, in addition to a few exceptions, both the in vivo contents of gonadal development-related hormones (GIH and MIH) and the expression of genes encoding regulatory hormones (GIH, MIH, and CHH) were upregulated by the exposure of whiteleg shrimp to the pollutants investigated, suggesting a significant obstruction of endocrine regulation. Moreover, MP-BPA coexposure was shown to be more toxic to whiteleg shrimp than the corresponding single exposures and significantly greater amount of BPA accumulated in the gonads (both testis and ovaries) of shrimp with the coexistence of MPs, which may be caused by the Trojan horse effect and summation of the toxic impacts on common targets. In general, the data obtained in this study demonstrated that MPs and BPA at environmentally realistic concentrations significantly inhibited the gonadal development of whiteleg shrimp probably by interfering with metabolism and disrupting endocrine regulation.

Computational biotransformation of polyethylene terephthalate by depolymerase: A QM/MM approach

Despite increasing environmental concerns on ever-lasting Polyethylene Terephthalate (PET), its global production is continuously growing. Effective strategies that can completely remove PET from environment are urgently desired. Here biotransformation processes of PET by one of the most effective enzymes, leaf-branch compost cutinase (LCC), were systematically explored with Molecular Dynamics and Quantum Mechanics/Molecular Mechanics approaches. We found that four concerted steps are required to complete the whole catalytic cycle. The last concerted step, deacylation, was determined as the rate-determining step with Boltzmann-weighted average barrier of 13.6 kcal/mol and arithmetic average of 16.1 ± 2.9 kcal/mol. Interestingly, unprecedented fluctuations of hydrogen bond length during LCC catalyzed transformation process toward PET were found. This fluctuation was also observed in enzyme IsPETase, indicating that it may widely exist in other catalytic triad (Ser-His-Asp) containing enzymes as well. In addition, possible features (bond, angle, dihedral angle and charge) that influence the catalytic reaction were identified and correlations between activation energies and key features were established. Our results present new insights into catalytic mechanism of hydrolases and shed light on the efficient recycling of the ever-lasting PET.

Impact of Urbanization on Antibiotic Resistome in Different Microplastics: Evidence from a Large-Scale Whole River Analysis

Microplastics (MPs) are becoming ubiquitous in environments and viewed as carriers of antibiotic resistance genes (ARGs). Rivers connecting differently urbanized areas contribute a significant input of MPs and ARGs to the environment. However, a systematic study assessing the role of urbanization in shaping antibiotic resistome and mobilome in riverine MPs is lacking. Here, we conducted a large-scale study by placing five types of MPs (polyethylene, polypropylene, polystyrene, polyethylene-fiber, and polyethylene-fiber-polyethylene) into Beilun River with an urbanization gradient. A total of 314 ARGs and 57 mobile genetic elements (MGEs) were detected in MPs by high-throughput quantitative polymerase chain reaction (PCR). The ARGs in MPs showed a clear spatial distribution with the abundance increased by 2 orders of magnitude from rural to urban regions. A holistic analysis of 13 socioeconomic and environmental factors identified that urbanization predominantly contributed to both the abundance and potential MGE-mediated dissemination of ARGs in riverine MPs. Notably, MPs types were found to significantly affect the resistome and dissemination risk of ARGs, with polypropylene being the preferred substrates to acquire and spread ARGs. This work highlights the necessity of controlling MPs and ARGs pollution in urban areas and provides an important guide for the future usage and disposal of plastics.

Microplastic in terrestrial ecosystems

Research shifts from ecotoxicology to ecosystem effects and Earth system feedbacks