How mangrove plants affect microplastic distribution in sediments of coastal wetlands: Case study in Shenzhen Bay, South China

Preliminary assessment of microplastic in rhizosphere and non-rhizosphere region of mangrove at four locations along Karachi coast, Pakistan

Mangrove ecosystem faces significant threats from the various pollutants including microplastic (MPs). The aim of this study was to assess variations in MP distribution in mangrove sediments of rhizosphere (R) and non-rhizosphere (NR) regions. A total of 14,960 MP particles were identified from Sandspit backwater (SS-1 & SS-2) and Creek areas (PQ & KC). Notably, the NR showed higher MP counts (7848) compared to the R region (7112). Analysis revealed variations in MP types, with beads being predominant in both R and NR, followed by film, fiber, and fragments. KC exhibited highest MP contamination, followed by PQ, SS-2, and SS-1. Fourier-transform infrared (FTIR) analysis confirmed the presence of polyethylene terephthalate and polyethylene in sediments samples. This first detailed report on MP in mangrove sediments and other limited studies from Pakistan establishes the widespread distribution of MPs in the coastal area and provide a baseline for further elaboration in future.

Charting the microplastic menace: A bibliometric analysis of pollution in Malaysian mangroves and polypropylene bioaccumulation assessment in Anadara granosa

According to a bibliometric analysis, studies on microplastic pollution in Malaysia are still incomprehensive. This study found microplastic contamination in sediment (97 particles/kg) and water (10,963 particles/m3) samples from Malaysian mangroves. Sediment from Matang and water from Kuala Selangor recorded the highest microplastic concentrations at 140 ± 5.13 particles/kg and 13,350 ± 37.95 particles/m3, respectively. Fragmented, blue, rayon and particles of <0.1 mm microplastic were the most abundant in sediment and water. In an experiment of polypropylene microplastic uptakes, Anadara granosa was found to uptake more 0.1 mm fiber particles. The uptake is strongly correlated to the presence of microplastics in sediment and water. The estimated dietary intake (EDI) indicates that a consumer could ingest 507 microplastic particles/year by consuming contaminated A. granosa. Therefore, mitigating measures are crucial to safeguard aquatic systems and humans from microplastic pollution.

Ecological assessment of microplastic contamination in surface water and commercially important edible fishes off Kadalundi estuary, Southwest coast of India

This study focuses on the Kadalundi estuary, Kerala's first community reserve, investigating the prevalence and impacts of microplastics on both the estuarine environment and selected fish species. This study presents the initial evidence indicating the consumption of microplastic particles by 12 commercially important edible fish species inhabiting the Kadalundi estuary. Analysis revealed significant accumulations of microplastic fibers within the surface water. In examining 12 fish species from demersal and pelagic habitats, microplastics were found in both the gastrointestinal tracts and gills. In the digestive tracts, microplastic fragments constituted the highest proportion (46%), while in the gills, microplastic fibers were dominant (52.4%). This study observed a prevalence of blue microplastics over other colors in both water and fish samples. Notably, demersal species showed a higher incidence of ingested microplastics. Polymer analysis identified Polypropylene (PP), Nylon, Low-Density Polyethylene (LDPE), Polyethylene (PE), Polypropylene isotactic (iPP), PE 1 Octene copolymer, and Rayon in water samples, while fish samples predominantly contained LDPE, PP, PE, and Nylon. Risk assessment utilizing the Polymer Hazard Index (PHI) categorized certain polymers as posing minor to moderate risks. Pollution Load Index (PLI) computations indicated moderate to high levels of microplastic contamination across various sampling sites in the estuary. Principal Component Analysis (PCA) revealed a lack of correlation between fish size and microplastic ingestion, underscoring environmental factors' influence on microplastic intake. The study emphasizes the implications of microplastic pollution on the fragile ecosystem of the Kadalundi estuary, posing potential risks to biodiversity and human health.

Comprehensive risk assessment of microplastics in tidal channel sediments in amazonian mangroves (northern Brazil)

Pollution by microplastics (MPs) in mangroves is a growing concern, given its potential ecological and human health impacts. The characteristics of microplastic pollution and a risk assessment of MPs in the Amazon region's coastal sediments are still insufficient, and information about MP pollution in the benthic component of the mangrove ecosystem is lacking. We analyzed MP concentrations in the surface sediment of 9 stations in three tidal channels along the Ajuruteua Peninsula connected to the Caeté River estuary, aiming to assess the hazard level on the environment based on the Pollution Load Index (PLI). Raman and Fourier transform infrared spectroscopy determined the MP's chemical composition. The results showed that the abundance of sediment MPs ranged from 100 to 1200 items kg-1, with an average of 433 ± 261.6 items kg-1. The MPs were mainly composed of transparent and blue fragments and fibers, ranging in size from 100 to 5000 μm. Six types of polymers were identified, including alkyd varnish (AV), resin dispersion (RD), chlorinated polyethylene (CPE), polyethylene-polypropylene (PE-PP), low-density polyethylene (LDPE), and hostaperm blue (HB). Hydrodynamic processes within estuaries and tidal channels play a crucial role in explaining the concentrations found, as circulation determines the pattern of sediment deposition and the particles adhered to it. PLI risk assessment showed that all sampling sites were at hazard level I: a low level of contamination in the mangrove sediments. However, a more comprehensive and systematic monitoring campaign is needed to expand our knowledge about pollution and contamination by MPs in Amazon mangrove areas.

Non-negligible impact of microplastics on wetland ecosystems

There has been much concern about microplastic (MP) pollution in marine and soil environments, but attention is gradually shifting towards wetland ecosystems, which are a transitional zone between aquatic and terrestrial ecosystems. This paper comprehensively reviews the sources of MPs in wetland ecosystems, as well as their occurrence characteristics, factors influencing their migration, and their effects on animals, plants, microorganisms, and greenhouse gas (GHG) emissions. It was found that MPs in wetland ecosystems originate mainly from anthropogenic sources (sewage discharge, and agricultural and industrial production) and natural sources (rainfall-runoff, atmospheric deposition, and tidal effects). The most common types and forms of MPs identified in the literature were polyethylene and polypropylene, fibers, and fragments. The migration of MPs in wetlands is influenced by both non-biological factors (the physicochemical properties of MPs, sediment characteristics, and hydrodynamic conditions) and biological factors (the adsorption and growth interception by plant roots, ingestion, and animal excretion). Furthermore, once MPs enter wetland ecosystems, they can impact the resident microorganisms, animals, and plants. They also have a role in global warming because MPs act as unique exogenous carbon sources, and can also influence GHG emissions in wetland ecosystems by affecting the microbial community structure in wetland sediments and abundance of genes associated with GHG emissions. However, further investigation is needed into the influence of MP type, size, and concentration on the GHG emissions in wetlands and the underlying mechanisms. Overall, the accumulation of MPs in wetland ecosystems can have far-reaching consequences for the local ecosystem, human health, and global climate regulation. Understanding the effects of MPs on wetland ecosystems is essential for developing effective management and mitigation strategies to safeguard these valuable and vulnerable environments.

Microplastic shape influences fate in vegetated wetlands

Coastal areas are prone to plastic accumulation due to their proximity to land based sources. Coastal vegetated habitats (e.g., seagrasses, saltmarshes, mangroves) provide a myriad of ecosystem functions, such as erosion protection, habitat refuge, and carbon storage. The biological and physical factors that underlie these functions may provide an additional benefit: trapping of marine microplastics. While microplastics occurrence in coastal vegetated sediments is well documented, there is conflicting evidence on whether the presence of vegetation enhances microplastics trapping relative to bare sites and the factors that influence microplastic trapping remain understudied. We investigated how vegetation structure and microplastic type influences trapping in a simulated coastal wetland. Through a flume experiment, we measured the efficiency of microplastic trapping in the presence of branched and grassy vegetation and tested an array of microplastics that differ in shape, size, and polymer. We observed that the presence of vegetation did not affect the number of microplastics trapped but did affect location of deposition. Microplastic shape, rather than polymer, was the dominant factor in determining whether microplastics were retained in the sediment or adhered to the vegetation canopy. Across the canopy, microfibre concentrations decreased from the leading edge to the interior which suggests that even on a small-scale, vegetation has a filtering effect. The outcome of this study enriches our understanding of coastal vegetation as a microplastics sink and that differences among microplastics informs where they are most likely to accumulate within a biogenic canopy.

Potential synergy of microplastics and nitrogen enrichment on plant holobionts in wetland ecosystems

Wetland ecosystems are global hotspots for environmental contaminants, including microplastics (MPs) and nutrients such as nitrogen (N) and phosphorus (P). While MP and nutrient effects on host plants and their associated microbial communities at the individual level have been studied, their synergistic effects on a plant holobiont (i.e., a plant host plus its microbiota, such as bacteria and fungi) in wetland ecosystems are nearly unknown. As an ecological entity, plant holobionts play pivotal roles in biological nitrogen fixation, promote plant resilience and defense chemistry against pathogens, and enhance biogeochemical processes. We summarize evidence based on recent literature to elaborate on the potential synergy of MPs and nutrient enrichment on plant holobionts in wetland ecosystems. We provide a conceptual framework to explain the interplay of MPs, nutrients, and plant holobionts and discuss major pathways of MPs and nutrients into the wetland milieu. Moreover, we highlight the ecological consequences of loss of plant holobionts in wetland ecosystems and conclude with recommendations for pending questions that warrant urgent research. We found that nutrient enrichment promotes the recruitment of MPs-degraded microorganisms and accelerates microbially mediated degradation of MPs, modifying their distribution and toxicity impacts on plant holobionts in wetland ecosystems. Moreover, a loss of wetland plant holobionts via long-term MP-nutrient interactions may likely exacerbate the disruption of wetland ecosystems' capacity to offer nature-based solutions for climate change mitigation through soil organic C sequestration. In conclusion, MP and nutrient enrichment interactions represent a severe ecological risk that can disorganize plant holobionts and their taxonomic roles, leading to dysbiosis (i.e., the disintegration of a stable plant microbiome) and diminishing wetland ecosystems' integrity and multifunctionality.

Mangrove plants are promising bioindicator of coastal atmospheric microplastics pollution

Plastics are commonly used by society and their break down into millimeter-sized bits known as microplastics (MPs). Due to the possibility of exposure, reports of them in atmospheric deposition, indoor, and outdoor air have sparked worry for public health. In tropical and subtropical regions all throughout the world, mangroves constitute a distinctive and significant type of coastal wetlands. Mangrove plants are considered to have the effect of accumulating sediment MPs, but the sedimentation of atmospheric MPs has not been reported. In this study, we illustrated the characteristics, abundance and spatial distribution of MPs in different species of mangrove leaves along the Seagull Island in Guangzhou. MPs samples from leaves in five species showed various shapes, colors, compositions, sizes and abundance. Acanthus ilicifolius had an average fallout rate of 1223 items/m2/day which has the highest abundance of MPs in all samples. Four shapes of MPs were found in all leaves surfaces including fiber, fragment, pellet, and film, with fiber is the most. The dominant types of MPs in all leaves were cellulose and rayon. Most of the total MPs size were smaller than 2 mm. Clearly, the microstructures of each species leaf surfaces had an impact on its ability to retain MPs. The plants rough blade surfaces and big folds or gullies caused more particles to accumulate and had a higher MPs retention capacity. Overall, our study contributes to a better knowledge of the condition of MPs pollution in atmosphere and the connection between leaves structure and the retention of MPs, which indicates that mangrove plants are promising bioindicator of coastal atmospheric MPs pollution.

Prioritising plastic pollution research in blue carbon ecosystems: A scientometric overview

The Blue Carbon Ecosystems (BCEs), comprising mangroves, saltmarshes, and seagrasses, located at the land-ocean interface provide crucial ecosystem services. These ecosystems serve as a natural barrier against the transportation of plastic waste from land to the ocean, effectively intercepting and mitigating plastic pollution in the ocean. To gain insights into the current state of research, and uncover key research gaps related to plastic pollution in BCEs, this study conveyed a comprehensive overview using bibliometric, altmetric, and literature synthesis approaches. The bibliometric analysis revealed a significant increase in publications addressing plastic pollution in BCEs, particularly since 2018. Geographically, Chinese institutions have made substantial contributions to this research field compared to countries and regions with extensive BCEs and established blue carbon science programs. Furthermore, many studies have focused on mangrove ecosystems, while limited attention was given to exploring plastic pollution in saltmarsh, seagrass, and multiple ecosystems simultaneously. Through a systematic analysis, this study identified four major research themes in BCE-plastics research: a) plastic trapping by vegetated coastal ecosystems, b) microbial plastic degradation, c) ingestion of plastic by benthic organisms, and d) effects of plastic on blue carbon biogeochemistry. Upon synthesising the current knowledge in each theme, we employed a perspective lens to outline future research frameworks, specifically emphasising habitat characteristics and blue carbon biogeochemistry. Emphasising the importance of synergistic research between plastic pollution and blue carbon science, we underscore the opportunities to progress our understanding of plastic reservoirs across BCEs and their subsequent effects on blue carbon sequestration and mineralisation. Together, the outcomes of this review have overarching implications for managing plastic pollution and optimising climate mitigation outcomes through the blue carbon strategies.

Microplastics strengthen nitrogen retention by intensifying nitrogen limitation in mangrove ecosystem sediments

Mangrove wetlands are hotspots of the global nitrogen (N) cycle and important sinks of microplastics (MPs) due to their ecotone location between terrestrial and marine ecosystems. However, the effects of MPs on N cycle processes in mangrove ecosystems are still poorly understood. Thus, the present study assessed the impacts by adding MPs to mangrove sediments in a microcosm incubation experiment. The results showed that MPs increased dissolved organic carbon and nitrate but reduced ammonium contents in the sediments. MPs increased C:N stoichiometric and N:C-acquiring enzymatic ratios, indicating an intensified N limitation in mangrove sediments following exposure of MPs. MPs decreased microbial community diversity and shifted sediment microbial communities from r- to K-strategists, consistent with the intensified N limitation. In response, dissimilatory nitrate reduction to ammonium (DNRA) rates increased while nitrous oxide (N2O) production reduced suggesting more efficient N utilization in MPs treatments. The MPs with heteroatoms such as PLA- and PVC-MPs, increased DNRA rates by 67.5-78.7%, exhibiting a stronger impact than PE-MPs. The variation partitioning analysis revealed that the variances of DNRA rates and N2O production could be attributed to synergistic effects of physicochemical properties, nutrient limitation, and microbial community in mangrove sediments. Overall, this study provides pertinent insights into the impacts of MPs as a new carbon source on nutrient limitation and N turnover in mangrove ecosystems.

Prevalence of microplastics in Peruvian mangrove sediments and edible mangrove species

Mangrove ecosystems have been hypothesised as a potential sink of microplastic debris, which could pose a threat to mangrove biota and ecological function. In this field-study we establish the prevalence of microplastics in sediments and commercially-exploited Anadara tuberculosa (black ark) and Ucides occidentalis (mangrove crab) from five different zones in the mangrove ecosystem of Tumbes, Peru. Microplastic were evident in all samples, with an average of 726 ± 396 microplastics/kg for the sediment, although no differences between the different zones of the mangrove ecosystem were observed. Microplastic concentrations were 1.6± 1.1 items/g for the black ark and 1.9 ± 0.9 microplastics/g for the mangrove crab, with a difference in the microplastic abundance between species (p < 0.05), and between the gills and stomachs of the crab (p < 0.01). Human intake of microplastics from these species, for the population in Tumbes, is estimated at 431 items per capita per year. The outcomes of this work highlight that the mangrove ecosystem is widely contaminated with microplastics, presenting a concern for the marine food web and food security.

Microplastic retention in marine vegetation canopies under breaking irregular waves

The present study provides indications and underlying drivers of wave-induced transport and retention potential of microplastic particles (MP) in marine vegetation canopies having different densities. The anthropogenic occurrence of MP in coastal waters is well documented in the recent literature. It is acknowledged that coastal vegetation can serve as a sink for MP due to its energy dissipating features, which can mimic a novel ecosystem service. While the transport behavior of MP in vegetation has previously been investigated to some extent for stationary flow conditions, fundamental investigations for unsteady surf zone flow conditions under irregular waves are still lacking. Herein, we demonstrate by means of hydraulic model tests that a vegetation's retention potential of MP in waves increases with the vegetation shoot density, the MP settling velocity and decreasing wave energy. It is found that particles migrating by traction (predominantly in contact with the bed) are trapped in the wake regions around a canopy, whereas suspended particles are able to pass vegetated areas more easily. Very dense canopies can also promote the passage of MP with diameters larger than the plant spacing, as the canopies then show characteristics of a solid sill and avoid particle penetration. The particle migration ability through a marine vegetation canopy is quantified, and the key drivers are described by an empirical expression based on the particle settling velocity, the canopy length and density. The findings of this study may contribute to improved prediction and assessment of MP accumulation hotspots in vegetated coastal areas and, thus, may help in tracing MP sinks. Such knowledge can be considered a prerequisite to develope methods or new technologies to recover plastic pollutants and rehabilitate valuable coastal environments.

Optimization of microplastic removal based on the complementarity of constructed wetland and microalgal-based system

As one of the emblematic emerging contaminants, microplastics (MPs) have aroused great public concern. Nevertheless, the global community still insufficiently acknowledges the ecological health risks and resolution strategies of MP pollution. As the nature-based biotechnologies, the constructed wetland (CW) and microalgal-based system (MBS) have been applied in exploring the removal of MPs recently. This review separately presents the removal research (mechanism, interactions, implications, and technical defects) of MPs by a single method of CWs or MBS. But one thing with certitude is that the exclusive usage of these techniques to combat MPs has non-negligible and formidable challenges. The negative impacts of MP accumulation on CWs involve toxicity to macrophytes, substrates blocking, and nitrogen-removing performance inhibition. While MPs restrict MBS practical application by making troubles for separation difficulties of microalgal-based aggregations from effluent. Hence the combined strategy of microalgal-assisted CWs is proposed based on the complementarity of biotechnologies, in an attempt to expand the removing size range of MPs, create more biodegradable conditions and improve the effluent quality. Our work evaluates and forecasts the potential of integrating combination for strengthening micro-polluted wastewater treatment, completing the synergistic removal of MP-based co-pollutants and achieving long-term stability and sustainability, which is expected to provide new insights into MP pollution regulation and control.

Psychrobacter species enrichment as potential microplastic degrader and the putative biodegradation mechanism in Shenzhen Bay sediment, China

Microplastic (MP) pollution has emerged as a pressing environmental concern due to its ubiquity and longevity. Biodegradation of MPs has garnered significant attention in combatting global MP contamination. This study focused on MPs within sediments near the sewage outlet of Shenzhen Bay. The objective was to elucidate the microbial communities in sediments with varying MPs, particularly those with high MP loads, and to identify microorganisms associated with MP degradation. The results revealed varying MP abundance, ranging from 211 to 4140 items kg-1 dry weight (d. w.), with the highest concentration observed near the outfall. Metagenomic analysis confirmed the enrichment of Psychrobacter species in sediments with high MP content. Psychrobacter accounted for ∼16.71% of the total bacterial community and 41.71% of hydrocarbon degrading bacteria at the S3 site, exhibiting a higher abundance than at other sampling sites. Psychrobacter contributed significantly to bacterial function at S3, as evidenced by the Kyoto Encyclopedia of Genes and Genomes pathway and enzyme analysis. Notably, 28 enzymes involved in MP biodegradation were identified, predominantly comprising oxidoreductases, hydrolases, transferases, ligases, lyases, and isomerases. We propose a putative mechanism for MP biodegradation, involving the breakdown of long-chain plastic polymers and subsequent oxidation of short-chain oligomers, ultimately leading to thorough mineralization.

Microplastic contamination in Thai vinegar crabs (Episesarma mederi), giant mudskippers (Periophthalmodon schlosseri), and their surrounding environment from the Bang Pu mangrove forests, Samut Prakan province, Thailand

The mangrove ecosystem becomes the receptacle for both land- and marine-based plastic waste. This study examines MPs contamination in the Bang Pu mangrove forests (BPMFs) in the inner Gulf of Thailand. For this, Thai vinegar crabs (TVCs) (Episesarma mederi) and giant mudskippers (GMs) (Periophthalmodon schlosseri) were investigated with their surrounding environment in both rainy and dry seasons. Two-step digestion was employed for biota samples. MPs abundance ranged from 7.5 ± 3.8 to 15.9 ± 6.7 items/individual in TVCs and 6.2 ± 5.0 to 10.6 ± 2.6 items/individual in GMs. MPs in small-size ranges (<0.5 mm) were predominant. Fiber MPs were mostly detected in the rainy season. Most MPs were transparent with polyethylene and polypropylene as dominant polymers in all samples. Bioaccumulation was not observed in GMs. The results indicated the imperiled status of MPs contamination in TVCs and GMs with contaminated surrounding environments.

Microplastics in mangroves with special reference to Asia: Occurrence, distribution, bioaccumulation and remediation options

Microplastics (MPs) are a new and lesser-known pollutant that has intrigued the interest of scientists all over the world in recent decades. MP (<5mm in size) can enter marine environments such as mangrove forests in a variety of ways, interfering with the health of the environment and organisms. Mangroves are now getting increasingly exposed to microplastic contamination due to their proximity to human activities and their position as critical transitional zones between land and sea. The present study reviews the status of MPs contamination specifically in mangrove ecosystems situated in Asia. Different sources and characteristics of MPs, subsequent deposition of MPs in mangrove water and sediments, bioaccumulation in different organisms are discussed in this context. MP concentrations in sediments and organisms were higher in mangrove forests exposed to fishing, coastal tourism, urban, and industrial wastewater than in pristine areas. The distribution of MPs varies from organism to organism in mangrove ecosystems, and is significantly influenced by their morphometric characteristics, feeding habits, dwelling environment etc. Mangrove plants can accumulate microplastics in their roots, stem and leaves through absorption, adsorption and entrapment helping in reducing abundance of microplastic in the surrounding environment. Several bacterial and fungal species are reported from these mangrove ecosystems, which are capable of degrading MPs. The bioremediation potential of mangrove plants offers an innovative and sustainable approach to mitigate microplastic pollution. Diverse mechanisms of MP biodegradation by mangrove dwelling organisms are discussed in this context. Biotechnological applications can be utilized to explore the genetic potential of the floral and faunal species found in the Asian mangroves. Detailed studies are required to monitor, control, and evaluate MP pollution in sediments and various organisms in mangrove ecosystems in Asia as well as in other parts of the world.

Depth profiles of microplastics in sediments from inland water to coast and their influential factors

Microplastics, plastic particles with a size smaller than 5 mm, are widely observed in the global environments and pose a growing threat as they accumulate and affect the environments in numerous ways. These particles can be transported from inland water to coast and disperse from surface water to deep sediments, especially the latter, while knowledge of the hidden microplastics in sediment layers is still lacking. Understanding the characteristics and behavior of microplastics in deep sediments from inland water to coast is crucial for estimating the present and future global plastic budget from land to seas. Herein, present knowledge of microplastic sedimentation from inland water to coast is reviewed, with a focus on the physical characteristics of microplastics and environmental factors that affect sedimentation. The abundance, shape, composition, and timeline of microplastics in sediment layers in rivers, floodplains, lakes, estuaries and coastal wetlands are presented. The abundance of microplastics in sediment layers varies across sites and may exhibit opposite trends along depth, and generally the proportion of relatively small microplastics increases with depth, while less is known about the vertical trends in the shape and composition of microplastics. Timeline of microplastics is generally linked to the sedimentation rate, which varies from millimeters to centimeters per year in the reviewed studies. The spatiotemporal characteristics of microplastic sedimentation depend on the settling and erosion of microplastics, which are determined by two aspects, microplastic characteristics and environmental factors. The former aspect includes size, shape and density influenced by aggregation and biofouling, and the latter includes dynamic forces, topographic features, bioturbation and human activities. The comprehensive review of these factors highlights the needs to further quantify the characteristics of microplastic sedimentation and explore the role of these factors in microplastic sedimentation on various spatiotemporal scales.

Microplastics in the seagrass ecosystems: A critical review

Marine microplastic (MP) pollution represents a global environmental issue that has ignited considerable apprehension within the international community. Seagrass beds, which serve as nearshore marine ecosystems, have emerged as focal points of plastic and MP contamination due to the pronounced density of anthropogenic activities and the hydrological mitigating effects of submerged vegetation. Nevertheless, our comprehension of MPs within seagrass ecosystems remains constrained. In this study, we employed bibliometric analyses and comprehensive data exploration to summarize the historical progression of the development, pivotal areas of interest, and research deficiencies, followed by proposing future research directions for MP pollution in seagrass beds. The 37 selected papers were sourced from the Web of Science Core Collection scientific database as of December 31st, 2022. Based on the current evaluation, MPs are ubiquitously discovered within seagrass canopies, sediments, and marine organisms, while less than 15 % of seagrass species worldwide have been investigated. Moreover, methodological inconsistencies in sampling, processing and visualization between studies hindered the fusion and comparison of data. MPs in upper sediments and seagrass blades were the most widely investigated, with an average abundance of 263.4 ± 309.2 n/kg and 0.09 ± 0.03 n/blade. In all environmental compartments, the prevalent forms of MPs comprise fibrous and fragmented particles, encompassing the dominant polymers such as polypropylene, polyethylene and polyethylene terephthalate. However, the source of MPs in seagrass beds based on MP characteristics and local hydrodynamics has not been comprehensively analyzed in previous studies. The evidence for MPs acting as pollutants and contaminant carries impacting the growth and decline of seagrass is also weak. Currently, the precise implications of MPs on submerged vegetation, organisms, and the broader seagrass ecosystem remain inconclusive. However, considering the persistent accumulation of MPs, it is imperative to explore the ecological hazards they may pose within the foreseeable future.

Microplastics in aquaculture systems: Occurrence, ecological threats and control strategies

With the intensification of microplastic pollution globally, aquaculture environments also face risks of microplastic contamination through various pathways such as plastic fishing gear. Compared to wild aquatic products, cultured aquatic products are more susceptible to microplastic exposure through fishing tackle, thus assessing the impacts of microplastics on farmed species and human health. However, current research on microplastic pollution and its ecological effects in aquaculture environments still remains insufficient. This article comprehensively summarizes the pollution characteristics and interrelationships of microplastics in aquaculture environments. We analyzed the influence of microplastics on the sustainable development of the aquaculture industry. Then, the potential hazards of microplastics on pond ecosystems and consumer health were elucidated. The strategies for removing microplastics in aquaculture environments are also discussed. Finally, an outlook on the current challenge and the promising opportunities in this area was proposed. This review aims to evaluate the value of assessing microplastic pollution in aquaculture environments and provide guidance for the sustainable development of the aquaculture industry.

Microplastic in mangroves: A worldwide review of contamination in biotic and abiotic matrices

This review presents the spatial distribution (where) and the methods applied (how) in assessing Microplastics (MPs) contamination in sediments, water, and organisms in mangrove areas. We analyzed 53 articles on MPs in Asia, America, and Africa and produced by 359 authors, although very localized, lacking wide-scale coverage of mangrove coasts around the world. The results showed that most of studies provided MP's bulk characteristics (type, size, color, form), along with global gross reserves of MPs in the mangrove compartments. Investigations in mangrove areas are still relatively limited. Therefore, for future research, it is relevant to enhance spatial and temporal sampling of MP contamination and to establish standardized protocols to enable effective comparisons between mangrove areas, rivers, beaches, and coastal seas. In addition, it is crucial to investigate the role of MPs as carriers or vectors of other pollutants.

Microplastics in coastal blue carbon ecosystems: A global Meta-analysis of its distribution, driving mechanisms, and potential risks

Microplastics, as emerging pollutants, have become a global environmental concern. Blue carbon ecosystems (BCEs) are threatened by microplastics. Although substantial studies have explored the dynamics and threats of microplastics in BCEs, the fate and driving factors of microplastics in BCEs on a global scale remain largely unknown. Here, the occurrence, driving factors, and risks of microplastics in global BCEs were investigated by synthesizing a global meta-analysis. The results showed that the abundance of microplastics in BCEs has notable spatial differences worldwide, with the highest microplastic concentrations in Asia, especially in South and Southeast Asia. Microplastic abundance is influenced by the vegetation habitat, climate, coastal environment, and river runoff. The interaction of geographic location, ecosystem type, coastal environment, and climate enhanced the effects of microplastic distribution. In addition, we found that microplastic accumulation in organisms varied according to feeding habits and body weight. Significant accumulation was observed in large fish; however, growth dilution effects were also observed. The effect of microplastics on the organic carbon content of sediments from BCEs varies by ecosystem; microplastic concentrations do not necessarily increase organic carbon sequestration. Global BCEs are at a high risk of microplastic pollution, with high microplastic abundance and toxicity driving the high pollution risk. Finally, this review provides scientific evidence that will form the basis for future microplastic research, focusing on the transport of microplastics in BCEs; effects on the growth, development, and primary productivity of blue carbon plants; and soil biogeochemical cycles.

Microplastics occurrence and fate in full-scale treatment wetlands

Treatment wetlands (TWs) are an efficient technology for removing microplastics (MPs) from wastewater, according to previous studies. This study investigates the dynamics and fate of MPs in two wastewater treatment plants (WWTPs) using TWs, one with horizontal subsurface flow (HF) and another with a floating plant system (FS). Special attention is paid to the retention produced in the sludge and the role of macrophyte roots. The abundance of MPs in the influent to the WWTPs was on average 20.3 ± 0.85 MP/L and 8.4 ± 1.13 MP/L in HF and FS respectively, while the effluent had 0.58 ± 0.07 MP/L and 0.17 ± 0.06 MP/L, thus giving overall efficiencies of 97.42% and 98.13%, respectively. In the HF wetland, sludge samples near the inlet and the outlet were taken, distinguishing between sludge adhered to gravel and sludge attached to roots. In the floating macrophytes, sludge samples from secondary and tertiary treatments were taken. The results indicate that roots play a significant role in MPs retention. In the HF wetland, the complex formed by roots and gravel attached more MPs than gravel alone in the final zone of the wetland. In the FS, roots retained a significant quantity of MPs, both in the secondary and tertiary treatments, thus giving rise to a sludge less concentrated in MPs. This study aims to improve the knowledge of MPs behavior and fate in full-scale TWs, providing valuable information to enhance retention efficiency.

Distribution and risk assessment of microplastics in typical ecosystems in the South China Sea

Microplastic pollution in the marine environment has attracted worldwide attention. The South China Sea is considered a hotspot for microplastic pollution due to the developed industries and high population density around the South China Sea. The accumulation of microplastics in ecosystems can adversely affect the health of the environment and organisms. This paper reviews the recent microplastic studies conducted in the South China Sea, which novelty summarizes the abundance, types, and potential hazards of microplastics in coral reef ecosystems, mangrove ecosystems, seagrass bed ecosystems, and macroalgal ecosystems. A summary of the microplastic pollution status of four ecosystems and a risk assessment provides a more comprehensive understanding of the impact of microplastic pollution on marine ecosystems in the South China Sea. Microplastic abundances of up to 45,200 items/m³ were reported in coral reef surface waters, 5738.3 items/kg in mangrove sediments, and 927.3 items/kg in seagrass bed sediments. There are few studies of microplastics in the South China Sea macroalgae ecosystems. However, studies from other areas indicate that macroalgae can accumulate microplastics and are more likely to enter the food chain or be consumed by humans. Finally, this paper compared the current risk levels of microplastics in the coral reef, mangrove, and seagrass bed ecosystems based on available studies. Pollution load index (PLI) ranges from 3 to 31 in mangrove ecosystems, 5.7 to 11.9 in seagrass bed ecosystems, and 6.1 to 10.2 in coral reef ecosystems, respectively. The PLI index varies considerably between mangroves depending on the intensity of anthropogenic activity around the mangrove. Further studies on seagrass beds and macroalgal ecosystems are required to extend our understanding of microplastic pollution in marine environments. Recent microplastic detection in fish muscle tissue in mangroves requires more research to further the biological impact of microplastic ingestion and the potential food safety risks.

The factors influencing the vertical transport of microplastics in marine environment: A review

There have been numerous studies that have identified the presence of low-density microplastics (MPs) in the water column and sediments. The focus of current MPs research has shifted towards the interaction of MPs with marine organisms and their potential hazards, including the uptake characteristics, biological transport and toxicological effects of MPs, but the processes involved in the deposition behavior of MPs are still poorly understood. In this review, we summarize the current state of knowledge on the vertical transport of MPs influenced by their physicochemical properties and marine organisms, and discuss their potential impact on MPs deposition. The physicochemical properties of MPs determine their initial distribution. The density, shape, and size of MPs influence their settling state in the marine environment. Marine biota play a key role in the transport of MPs to deep marine environment, mainly by changing the density and adsorption of MPs. Biofouling can alter the surface properties of MPs and increase the overall density, thus affecting the vertical flux of the plastic. Macroalgae may trap MPs particles by producing chemicals or by using electrostatic interactions. Marine swimming organisms ingest MPs and excrete them encapsulated in fecal particles, while the activity of marine benthic organisms may contribute to the transfer of MPs from surface sediments to deeper layers. In addition, MPs may be incorporated into organic particles produced by marine organisms such as marine snow or marine aggregates, increasing the vertical flux of MPs. However, due to the complexity of different sea areas and MPs properties, the deposition behavior of MPs may be the result of the interaction of multiple factors. Thus, the effects of MPs properties, marine organisms and the natural environment on MPs deposition in marine environment needs further research to fill this gap.

Dynamic characteristics of microplastics under tidal influence and potential indirect monitoring methods

Rivers are an important channel for the transport of microplastics from inland areas to the ocean. It is of great significance to explore the dynamic changes in microplastic pollution characteristics under tidal fluctuations to understand the exchange of microplastics between rivers and oceans. In this study, the occurrence of microplastics in typical tidal channels in the lower reaches of the Dong River was investigated during the wet and dry weather seasons, and high frequency continuous dynamic monitoring of microplastics was carried out in a typical tidal cross section during a tidal cycle. The abundances of microplastics during wet and dry weather seasons were 3.97-102.87 ± 28.63 item/m³ and 5.43-56.43 ± 14.32 item/m³, respectively. The microplastics generally exhibited a fluctuating growth pattern, with low contents in the upstream area and high contents in the downstream area, and the abundance of microplastics differed greatly in the different functional zones. The dynamic monitoring results showed that the abundance of microplastics was clearly affected by the tides, in that it increased during the flood tide and decreased during the ebb tide, with abundances ranging from 11.15 to 95.26 item/m³. In addition, there was a significant linear relationship between the abundance of microplastics and flow in the typical tidal cross section. The relationship between the response of microplastic pollution characteristics and tides combined with local hydrometeorological factors may be a potentially effective real-time monitoring method for assessing microplastic pollution indirectly.

Microplastic occurrence in finfish and shellfish from the mangroves of the northern Gulf of Oman

This study was conducted to assess microplastic (MP) pollution in some aquatic animals inhabiting planted and natural mangrove swamps in the northern Gulf of Oman. The KOH-NaI solution was used to retrieve MPs from the gastrointestinal tracts of animals. The highest MP prevalence was recorded in crabs (41.65 %) followed by fish (33.89 %) and oysters (20.8 %). The abundance of MPs in examined animals varied from zero in Sphyraena putnamae to 11 particles in a Rhinoptera javanica specimen. When polluted-only animals were considered, the mean abundance of MPs significantly varied among species and between locations. The mean density of ingested MPs was higher in the planted mangrove animals (1.79 ± 2.89 vs. 1.21 ± 2.25 n/individual; mean ± SD). Among the examined fish species, R. javanica ingested the highest number of MPs (3.83 ± 3.93 n/individual; mean ± SD). The polyethylene/ polypropylene fragments or fibers of average 1900 μm size were recorded as predominant (>50 % occurrence) MP particles.

Responses of mangrove (Kandelia obovata) growth, photosynthesis, and rhizosphere soil properties to microplastic pollution

In this study, we used Kandelia obovata to explore the toxicities of three typical MPs in mangroves: polyethylene, polypropylene, and polyvinylchloride. MPs were mixed into soils at 5 % (w/w) for cultivation in mangrove tide-tank system. Plant growth and soil characteristics were determined after 12 months. The results showed that MPs multiply restricted root growth, leaf ionome, chlorophyll concentration, and photosynthetic efficiency, changed leaf photochemical efficiency and excited energy distribution. Polyethylene and polypropylene MPs with 150 μm sizes significantly reduced leaf and root biomass. As for soil properties, all MPs mainly reduced bulk density but improved porosity, with 600 μm polyethylene resulting in 1.4 g cm^-3 bulk density and 55.1 % porosity. This study represent the first paper highlighting that MPs negatively affect mangrove plants by affecting plant growth, leaf ionome, and photosynthesis, which may be related with the changed soil properties, especially reduced bulk density and improved porosity.

GIS-based approach and multivariate statistical analysis for identifying sources of heavy metals in marine sediments from the coast of Hong Kong

Hong Kong is an urbanized coastal city which experiences substantially different metal loads from anthropogenic activities. This study was aimed at analyzing the spatial distribution and pollution evaluation of ten selected heavy metals (As, Cd, Cr, Cu, Pb, Hg, Ni, Zn, Fe, V) in the coastal sediments of Hong Kong. The distribution of heavy metal pollution in sediments has been analyzed using the geographic information system (GIS) technique, and their pollution degrees, corresponding potential ecological risks and source identifications, have been studied by applying the enrichment factor (EF) analysis, contamination factor (CF) analysis, potential ecological risk index (PEI), and integrated multivariate statistical methods, respectively. Firstly, the GIS technique was used to access the spatial distribution of the heavy metals; the result revealed that pollution trend of these metals was decreased from the inner to the outer coast sites of the studied area. Secondly, combining the EF analysis and CF analysis, we found that the pollution degree of heavy metals followed the order of Cu > Cr > Cd > Zn > Pb > Hg > Ni > Fe > As > V. Thirdly, the PERI calculations showed that Cd, Hg, and Cu were the most potential ecological risk factors compared to other metals. Finally, cluster analysis combined with principal component analysis showed that Cr, Cu, Hg, and Ni might originate from the industrial discharges and shipping activities. V, As, and Fe were mainly derived from the natural origin, whereas Cd, Pb, and Zn were identified from the municipal discharges and industrial wastewater. In conclusion, this work should be helpful in the establishment of strategies for contamination control and optimization of industrial structures in Hong Kong.

Occurrence of antibiotic resistance genes carried by plastic waste from mangrove wetlands of the South China Sea

Plastic waste can carry organisms such as bacterial pathogens and antibiotic resistance genes (ARGs) over long distances. However, only few studies have been conducted on the occurrence of ARGs in plastic waste from mangrove wetlands. This study evaluated the distribution characteristics and ecological risks of plastic waste from mangroves in the coastal areas of the South China Sea. The correlation between anthropogenic activity levels and abundance of ARGs in mangroves was evaluated. Transparent and white were the common colors of plastic waste in mangroves. The main shapes of plastic waste were foam and film. The predominant types of plastic waste order were as follows: polyethylene (30.18 %) > polypropylene (27.51 %) > polystyrene (23.59 %). The living area (LA) mangroves had the highest polymer hazard and pollution load indices of 329.09 and 10.03, respectively. The abundance of ARGs (5.08 × 10⁸ copies/g) on the plastic surface in LA mangroves was significantly higher than that of the other mangrove areas. Furthermore, there was a significant correlation between ARGs and intI1 on the plastic surface in mangroves. Correlation analysis between the ARGs and intI1 showed that most of the ARGs were correlated with intI1 except for msbA. In LA mangroves, sociometric and environmental factors showed significant correlations with the absolute abundances of the four ARGs and intI1, indicating that anthropogenic activities may lead to changes in the amount of ARGs on plastic surfaces. Furthermore, the ARG storage of plastic waste from different mangroves was as follows: protected areas (3.12 × 10¹⁷ copies) > living areas (2.99 × 10¹⁷ copies) > aquaculture pond areas (2.88 × 10¹⁷ copies). The higher ARG storage of LA mangroves, with the smallest area, greatly increased its ecological risk. The results of this study can provide basic data for processes that influence the distribution of plastic waste and ARGs in mangroves.

Role of mangrove forest in interception of microplastics (MPs): Challenges, progress, and prospects

Mangroves receive microplastics (MPs) from terrestrial, marine and atmospheric sources, acting as a huge filter for environmental MPs between land and sea. Due to the high primary production and complex hydrodynamic conditions in mangroves, MPs are extensively intercepted in various ways while flowing through mangroves, leading to a long-standing but fiercely increasing MPs accumulation. However, current researches mainly focused on the occurrence, source and fate of MPs pollution in mangroves, ignoring the role of mangrove forests in the interception of MPs. Our study firstly demonstrates that mangrove ecosystems have significantly greater MPs interception capacity than their surrounding environments. Then, the current status of studies related to the interception of MPs in mangrove ecosystems is comprehensively reviewed, with the main focus on the interception process and mechanisms. At last, the most pressing shortcomings of current research are highlighted regarding the intercepted flux, interception mechanisms, retention time and ecological risks of MPs in mangrove ecosystems and the relevant future perspectives are provided. This review is expected to emphasize the critical role of mangrove forests in the interception of MPs and provide the foundational knowledge for evaluating the MPs interception effect of mangrove forests globally.

A review of microplastic pollution in aquaculture: Sources, effects, removal strategies and prospects

As microplastic pollution has become an emerging environmental issue of global concern, microplastics in aquaculture have become a research hotspot. For environmental safety, economic efficiency and food safety considerations, a comprehensive understanding of microplastic pollution in aquaculture is necessary. This review outlines an overview of sources and effects of microplastics in aquaculture. External environmental inputs and aquaculture processes are sources of microplastics in aquaculture. Microplastics may release harmful additives and adsorb pollutants in aquaculture environment, cause deterioration of aquaculture environment, as well as cause toxicological effects, affect the behavior, growth and reproduction of aquaculture products, ultimately reducing the economic benefits of aquaculture. Microplastics entering the human body through aquaculture products also pose potential health risks at multiple levels. Microplastic pollution removal strategies used in aquaculture in various countries are also reviewed. Ecological interception and purification are considered to be effective methods. In addition, strengthening aquaculture management and improving fishing gear and packaging are also currently feasible solutions. As proactive measures, new portable microplastic monitoring system and remote sensing technology are considered to have broad application prospects. And it was encouraged to comprehensively strengthen the supervision of microplastic pollution in aquaculture through talent exchange and strengthening the construction of laws and regulations.

The role of bio-geomorphic feedbacks in shaping microplastic burial in blue carbon habitats

Coastal sediments are considered as hotspots of microplastics (MPs), with substantial MPs stocks found in blue carbon habitats such as mangroves and tidal marshes, where wave-damping vegetation reduces sediment erosion and enhances accretion. Here, we examined the effects of such bio-geomorphic feedbacks in shaping MPs burial, through a year-round field study in a mangrove habitat along the coast of South China. The results revealed that MPs abundance decreased significantly with the increase of cumulative sediment erosion as the strength of bio-geomorphic feedbacks declined. More shapes and colors of MPs were found at locations with weaker waves and less sediment erosion, where the average particle size was also higher. Our findings highlight the importance of bio-geomorphic feedbacks in affecting both the abundance and characteristics of the buried MPs. Such knowledge extends our understanding of MPs transport and burial from the perspective of bio-geomorphology, which is essential to assess and predict MPs accumulation patterns as well as its impacts on ecosystem functioning of the blue carbon habitats.

Distribution of microplastics in the catchment region of Pallikaranai marshland, a Ramsar site in Chennai, India

Microplastics are persistent toxic pollutants, detected in different environmental compartments. Numerous studies on the characteristics and distribution of microplastics present in different environmental matrices are being carried out. However, limited studies have been performed in environmental systems like eco-sensitive freshwater marshlands. Therefore, to enrich the existing knowledge and understanding, this current study has analysed the distribution and characteristics of microplastics present in the catchment region of Pallikaranai marshland, Chennai, India. Both surface water and sediment samples were contaminated with microplastics in the range of 740-2826 items/m³and 700 to 5833 items/kg of dry sediment, respectively. Compared to other shapes, fibrous microplastics were predominant in most of the surface water (n = 11) and sediment (n = 8) samples. The abundant presence of smaller microplastics (<1 mm) in the surface water suggests elevated impacts on the aquatic species owing to their higher bioavailability. Elevated anthropogenic activities and frequent movement of people in urban and residential areas were noted to possibly influence the spatial distribution of microplastics. Furthermore, heavy metals' occurrence on microplastics was investigated using X-Ray Fluorescence Analyser (XRF) and Zn, Fe, Ti, and Ni are the commonly detected (>50% of the samples) elements. The estimated average pollution load index of 2.5 indicates the polluted state of Pallikaranai catchment region.

Environmental microplastics: Classification, sources, fates, and effects on plants

Microplastic (MP) pollution has become a global concern due to the generation of extensive plastic waste and products (370 million metric tons in 2020) that are difficult to biodegrade. Therefore, MPs have attracted a great deal of research attention, and many new findings regarding MPs (over 9000 papers published in the last 3 years) have been reported. MPs generally exert adverse effects on plants. As MPs accumulate in agricultural ecosystems, many studies have sought to understand the sources and fates of MPs and their effects on various plants. However, there have been few reviews of the properties of MPs, their effects on plants, and their interactions with other factors (e.g., drought, heat, ultraviolet light, plant hormones, heavy metals, and other pollutants) remain poorly understood. In this review, we performed scientometrics analyses of research papers (January 1, 2019, to September 30, 2022) in this field. We focused on the recent progress in the classification of MPs and their sources, circulation, and deposition in agricultural ecosystems. We review MP uptake and transport in plants, as well as factors (size, type, and environmental factors) that affect MP uptake, the positive and negative effects of MPs on plants, and the mechanisms of MP impacts on plants. We discuss current issues and future perspectives concerning research into plant interactions with MPs, along with some promising methods to manage the MP issue.

The occurrence, speciation, and ecological effect of plastic pollution in the bay ecosystems

Bay is a unique part of the ecosystem, acting as the intersection for marine and terrestrial systems and hosting diverse biological organisms. The ubiquitous application of plastics has resulted in a massive amount of plastic waste released and accumulated in the bay ecosystem, posing significant ecological effects. Thus, thoroughly understanding plastic pollution's occurrence, speciation, and ecological effect in the bay ecosystems is of vital importance. We conducted a comprehensive review on the sources and distribution of plastics in the bay ecosystem, and the associate ecological effects, from individual toxicity to trophic transfer in ecosystems. Among bay areas around the world, the concentrations of microplastics vary from 0.01 to 3.62 × 10⁵ item/m³ in seawater and 0 to 6.75 × 10⁵ item/kg in sediment. Small-sized plastic particles (mostly <2 mm) were widely reported in bay organisms with the concentration range of 0 to 22.5 item/ind. Besides, the toxicity of plastics on marine organisms has been documented in terms of mortality, growth, development, reproduction, enzyme activity and transcription. Since abundance of small plastic particles (e.g., micro- and nano-scale) is far greater than large plastic debris in the bay ecosystems, in-depth risk assessment of small-sized plastics needs to be conducted under environmentally realistic conditions. Our review could provide a better understanding on the occurrence, speciation, and ecological effect of plastic pollution in the bay ecosystems.

Stable Isotopic and Metagenomic Analyses Reveal Microbial-Mediated Effects of Microplastics on Sulfur Cycling in Coastal Sediments

Microplastics are readily accumulated in coastal sediments, where active sulfur (S) cycling takes place. However, the effects of microplastics on S cycling in coastal sediments and their underlying mechanisms remain poorly understood. In this study, the transformation patterns of different S species in mangrove sediments amended with different microplastics and their associated microbial communities were investigated using stable isotopic analysis and metagenomic sequencing. Biodegradable poly(lactic acid) (PLA) microplastics treatment increased sulfate (SO₄^2-) reduction to yield more acid-volatile S and elementary S, which were subsequently transformed to chromium-reducible S (CRS). The S isotope fractionation between SO₄^2- and CRS in PLA treatment increased by 9.1‰ from days 0 to 20, which was greater than 6.8‰ in the control. In contrast, recalcitrant petroleum-based poly(ethylene terephthalate) (PET) and polyvinyl chloride (PVC) microplastics had less impact on the sulfate reduction, resulting in 7.6 and 7.7‰ of S isotope fractionation between SO₄^2- and CRS from days 0 to 20, respectively. The pronounced S isotope fractionation in PLA treatment was associated with increased relative abundance of Desulfovibrio-related sulfate-reducing bacteria, which contributed a large proportion of the microbial genes responsible for dissimilatory sulfate reduction. Overall, these findings provide insights into the potential impacts of microplastics exposure on the biogeochemical S cycle in coastal sediments.

Vertical distribution, accumulation, and characteristics of microplastics in mangrove sediment in China

Mangroves in tropical and subtropical regions worldwide are recognized as important sinks for microplastics (MPs). However, recent studies have focused on surface sediments, and in China, the vertical distribution and characteristics of MPs in mangrove sediments remain poorly understood. In this study, sediment cores of 100 cm depth were collected from six representative mangroves in China to investigate MPs via chronological analysis. Futian had the highest abundance of MPs (0-3123 n/kg), followed by Dongfang, Yunxiao, Zhanjiang, Dongzhaigang and Fangchenggang. The earliest MPs occurring in mangroves were dated back to 1955, and their abundance increased exponentially from bottom to surface sediments. MPs were mainly white in color, fiber-shaped, 1000-5000 μm in size, and of polypropylene/polyethylene polymer types. Furthermore, the MPs in the urban mangrove also showed a higher diversity in color. The results showed that the MP stocks in the urbanized Futian mangrove reached 1828 mg/m³, an order of magnitude higher than in other areas (251 ± 180 mg/m³), contributing to 0.0057 % of the carbon storage of the sediment. The abundance of MPs in mangrove sediments is expected to increase by 2.38-9.54 times by 2030, and therefore deserve further attention.

Plastic pollution of four understudied marine ecosystems: a review of mangroves, seagrass meadows, the Arctic Ocean and the deep seafloor

Plastic pollution is now a worldwide phenomenon affecting all marine ecosystems, but some ecosystems and regions remain understudied. Here, we review the presence and impacts of macroplastics and microplastics for four such ecosystems: mangroves, seagrass meadows, the Arctic Ocean and the deep seafloor. Plastic production has grown steadily, and thus the impact on species and ecosystems has increased, too. The accumulated evidence also indicates that plastic pollution is an additional and increasing stressor to these already ecosystems and many of the species living in them. However, laboratory or field studies, which provide strong correlational or experimental evidence of ecological harm due to plastic pollution remain scarce or absent for these ecosystems. Based on these findings, we give some research recommendations for the future.

Microplastics in surface sediments of a highly urbanized wetland

This study investigates the incidence of MPs in surface sediment samples, collected from the Anzali Wetland, Gillan province, North of Iran. This natural habitat receives municipal wastewater effluents and hosts industries and recreational activities that could release plastic to the wetland. There is need for studies to understand MPs pollution in wetlands. A total of 40 superficial sediment samples were taken covering potential pollution hotspots in the wetland. The average level of MPs was 362 ± 327.6 MP/kg: the highest MPs levels were near the outlet of a highly urbanized river (Pirbazar River) (1380 MP/kg), which runs through Rasht city. This was followed by 1255 MP/kg where there was intense fishing, boating and tourism activities in the vicinity of Bandar-e Anzali city. Fibers were the most common type of MPs (80% of the total MPs detected). The MPs polluting the wetland were predominantly white/transparent (42%), and about 40% of them were >1000 μm. Polypropylene (PP) and polyethylene (PE) prevailed in MPs found. MPs were characterized with polarized light microscopy, Raman spectroscopy, Scanning Electron Microscopy coupled with Energy-Dispersive X-ray spectroscopy. Microplastics levels were found to correlate significantly (p > 0.7) with electrical conductivity (EC) and sand-size fraction of the sediments. Coarse-grained sediments presented large capacity to lodge the MPs. This study can be used to establish protection policies in wetlands and newly highlights the opportunity of intercepting MPs in the Anzali Wetland, which are generally >250 μm, before they fragment further.

Distribution and retention of microplastics in plantation mangrove forest sediments

Microplastics (MPs) in ocean tides can be effectively intercepted by mangroves, especially sediments, which are considered to be effective sinks. However, the retention of plantation mangrove forests on MPs is still unclear. In this study, the spatial distribution and its implication factors of MPs in surface sediments of plantation mangrove forests were investigated for the first time. In plantation forests, MPs were detected with abundances ranging from 67 ± 21 to 203 ± 25 items/kg, and plantation forests were significantly lower than natural forests at the CJ sampling site (p < 0.05). Plantation forests had fewer fibrous MPs than natural forests (p < 0.05). Furthermore, the MPs abundance showed strong linear relationships with the sand content (p = 0.002, R² = 0.86) and Aegiceras corniculata biomass (p = 0.001, R² = 0.84). Partial least squares path modeling analysis (PLS-PM) indicated that these two factors influenced MPs abundance by retaining MPs with fibrous, fragmented, denser and larger-sized characteristics. Our results revealed the differences in MPs abundance and characteristics between plantation and natural mangrove forests, and it is necessary to monitor MPs pollution to provide significant guidance for the restoration of constructed wetlands.

Microplastic/nanoplastic toxicity in plants: an imminent concern

The toxic impact of microplastics/nanoplastics (MPs/NPs) in plants and the food chain has recently become a top priority. Several research articles highlighted the impact of MPs/NPs on the aquatic food chain; however, very little has been done in the terrestrial ecosystem. A number of studies revealed that MPs/NPs uptake and subsequent translocation in plants alter plant morphological, physiological, biochemical, and genetic properties to varying degrees. However, there is a research gap regarding MPs/NPs entry into plants, associated factors influencing phytotoxicity levels, and potential remediation plans in terms of food safety and security. To address these issues, all sources of MPs/NPs intrusion in agroecosystems should be revised to avoid these hazardous materials with special consideration as preventive measures. Furthermore, this review focuses on the routes of accumulation and transmission of MPs/NPs into plant tissues, related aspects influencing the intensity of plant stress, and potential solutions to improve food quality and quantity. This paper also concludes by providing an outlook approach of applying exogenous melatonin and introducing engineered plants that would enhance stress tolerance against MPs/NPs. In addition, an overview of inoculation of beneficial microorganisms and encapsulated enzymes in soil has been addressed, which would make the degradation of MPs/NPs faster.

Current status and trends of research on microplastic fugacity characteristics and pollution levels in mangrove wetlands

Microplastics have been widely detected in the environment, while mangrove wetlands are considered barriers to land-based plastic transport to the ocean, requiring special attention. However, the current literature is distributed and broad besides limited information on the fate characteristics and pollution levels. This study uses a systematic literature review method to analyze the current research status and future trends. In this study, the literature is summarized and concluded that Characteristics including color, shape, size, polymer chemistry and surface microstructure are the basic information for microplastic research in mangrove wetlands. Size is the key to studying distribution and convergence without international standards. The shape is vital to study its sources and environmental processes. Color affects biological predation and is important information for studying ecological risk. The chemical composition of plastics is the key to studying microplastics’ fingerprint information, source, and sink. The surface microstructure is an important basis for studying adsorption behavior and aging processes. Mangrove microplastic studies in China are mainly on the southern and southeastern coasts, and microplastic pollution is more severe in Fujian, Guangdong, and Guangxi than in Hainan. In contrast, studies on mangrove microplastics abroad are mainly concentrated in Southeast Asia, the Middle East, and South America. Overall, microplastic contamination was detected in the major distribution areas of mangroves worldwide and was correlated with mangrove density and human activities.

A case study of distribution and characteristics of microplastics in surface water and sediments of the seas around Shenzhen, southern coastal area of China

Microplastics (MPs), known to cause environmental pollution, is attracting a growing attention worldwide owing to their extensive existence and potential risks to biota. The marginal sea areas are suspected to be especially susceptible to MPs pollution. Unfortunately, data on MPs in the surface water and sediments ecosystems are still limited, particularly in the southern coastal areas of China. The study was successfully utilized to explore the distribution and characteristics of MPs below 5 mm collected from 14 sites in the seas around Shenzhen, a typical special economic zone of China. MPs were detected in both surface water and sediments with concentrations ranging from 3.8 to 7.8 items per liter and 2.6 × 10³ to 10.0 × 10³ items per kilogram, respectively. The highest abundance of MPs appeared in S5/S9 and S14 in surface water and sediments, respectively. Fiber and film with small particle size (<0.5 mm) were identified as typical and abundant MPs type among all samples. In addition, polyethylene (PE) was considered as dominant forms of MPs in surface water and sediment samples. Results from this study indicated a positive correlation with abundance of MPs and urbanization rate, which also showed an evident difference of MPs in different urban functional areas. Based on the types and quantity of detected MPs, we assessed the risk of MPs pollution in this study area, and the ecological risk category of MPs was at a high level. Importantly, our work might be employed as a potential information so as to better understand MPs pollution, source tracing and ecological risk assessment, which enhances the possibility of achieving effective control and supervision of MPs pollution in southern coastal aera of China.

An enlarging ecological risk: Review on co-occurrence and migration of microplastics and microplastic-carrying organic pollutants in natural and constructed wetlands

Wetlands are a key hub for the accumulation of microplastics (MPs) and have great load capacity to organic pollutants (OPs), thus, have been a hot research topic. It has shown that OPs adsorbed on MPs could be transported to anywhere and MP-associated biofilms also affects the co-occurrence of MPs and OPs. This would induce the desorption of MP-carrying OPs into environment again, increasing latent migration and convergence of MPs and OPs in wetlands. Considering MPs vector effect and MP-associated biofilms, it is necessary to integrate MPs information on its occurrence characteristics and migration behavior for an improved assessment of ecological risk brought by MPs and MP-carrying OPs to whole wetland ecosystems. In this review, we studied papers published from 2010 to 2020, focused on the interaction of MPs with OPs and the role of their co-occurrence and migration on ecological risk to wetlands. Results suggested the interaction between MPs and OPs dominated by adsorption altered their toxicity and environmental behavior, and the corresponding ecological risk induced by their co-occurrence to wetlands is various and complicated. Especially, constructed wetlands as the special hub for the migration of MPs and MP-carrying OPs might facilitate their convergence between natural and constructed wetlands, posing a potential enlarging ecological risk to whole wetlands. Since the study of MPs in wetlands has still been in a primary stage, we hope to provide a new sight to set forth the potential harm of MPs and MP-carrying OPs to wetlands and useful information for follow-up study.

Microplastics distribution in different habitats of Ximen Island and the trapping effect of blue carbon habitats on microplastics

Sediments are considered to be important sinks of microplastics, but the enrichment process of microplastics by blue carbon ecosystems is poorly studied. This study analyzed the spatial distribution and temporal changes, assessed the polymer types and morphological characteristics of microplastics in sediments of five ecosystems, i.e. forests, paddy fields, mangroves, saltmarshes and bare beaches on Ximen Island, Yueqing Bay, China. The trapping effect of blue carbon (mangrove and saltmarsh) sediments on microplastic was further explored. Temporal trends in microplastic abundance showed a significant increase over the last 20 years, with the enrichment of microplastics in mangrove and saltmarsh sediments being 1.7 times as high as that in bare beach, exhibiting blue carbon vegetations have strong enrichment effect on microplastics. The dominant color, shape, size, and polymer type of microplastics in sediments were transparent, fibers and fragments, <1 mm, and polyethylene, respectively. Significant differences in the abundance and characteristics of microplastics between intertidal sediments and terrestrial soils reveal that runoff input is the main source of microplastics. This study provided the evidence of blue carbon habitats as traps of microplastics.

Urban natural wetland as a sink for microplastics: A case from Lalu Wetland in Tibet, China

Microplastics have been reported in a wide range of aquatic habitats. The wetlands are considered to be important roles in microplastic migration in water bodies. Nevertheless, knowledge about the occurrence and fate of microplastics in urban natural wetland is still limited for us to better understand how they become a sink of microplastics. In this study, the distribution and characteristics of microplastics in surface water, surface sediments, and sediment cores of the Lalu Wetland watershed, China's highest urban wetland, were investigated in August 2020 and January 2021. The abundances of microplastics in the surface water were 0.06-3.05 MPs/L. Microplastic abundance in the surface sediment and sediment core was 0.01-1.10 MPs/g and 0-16.23 MPs/g, respectively. The abundance of microplastics in the water was significantly lower in the wetland than that in the channel in the watershed. Comparing the wetland inlet and outlet water, the microplastic interception rates were 53% in January and 95% in August. The characteristics and seasonal variation of microplastics in the Lalu Wetland implied that urban natural wetlands were good at intercepting microplastics, and vegetation growth might play an important role on the interception of microplastics by the wetland. The increasing of microplastics from bottom to top in the sediment cores of Lalu Wetland also indicated that the ecological risks of microplastics accumulation in sediments of urban natural wetland required further attention.

Widespread microplastic pollution in mangrove soils of Todos os Santos Bay, northern Brazil

Microplastics have been studied in sediments from coastal and aquatic environments, but contamination of mangrove soils is still relatively unknown in most mangroves around the world. In this study, the presence of microplastics was investigated in six mangrove soils around the Todos Santos Bay (TSB), the largest and most important navigable bay on the Brazilian coast. Samples were collected at three depths (surface, 10 cm, and 30 cm) at three different distances from the lower tidal area. Ten grams of soil were sieved in a 150 μm mesh and centrifuged with ZnCl₂ solution (density of 1.5 kg dm^-3) for the extraction of microplastics. The microplastics were quantified, measured, and described using a systematic photographic method and the ImageJ program. Microplastics were abundant in all samples, with a mean of 10,782 ± 7,671 items kg^-1 (max.: 31,087 items kg^-1, only one sample <2,000 items kg^-1), higher than any other value reported worldwide. The abundances varied among the six mangroves studied, with a predominance of fibers and mean size of 196 μm. Even remote mangroves were highly polluted, reflecting a large dispersion of the pollutants. The abundance did not differ significantly between soil depths, evidencing a continuous input and burial of microplastics in the soil up to 30 cm. The investigation of the source of microplastics and their presence in water and biota is urgent in this Brazilian region, and these results emphasize the need for global actions to protect coastal ecosystems.

Macroalgal morphology mediates microplastic accumulation on thallus and in sediments

The accumulation process of microplastics (MPs) is a key to understanding their fate in the environment. However, there is limited information about the short-term accumulation of MPs on macrophytes. The ability of macrophyte to attenuate wave and reduce current velocity is potentially facilitating MPs deposition. We hypothesize that the macroalgae retain MPs with their morphologies (filamentous and non-filamentous) being one of the factors to govern retention. Our hypothesis was tested by field observation during the dry season in Hong Kong when the macroalgae communities were the most diverse. MPs per biomass, surface area, or interstitial volume were used to represent the abundances on macroalgae. We found that filamentous algae retained a 2.35 times higher number of MPs when compared with non-filamentous algae if unit per biomass was considered. Other units, however, showed insignificant differences in MPs abundances between algal morphologies. Fibre was the most dominant shape of MPs with no significant difference in their abundances between filamentous and non-filamentous algae, suggesting fibres were retained regardless of the algal morphologies. To further evaluate the potential accumulation in the environment, sediment samples were also collected under the algal mat and immediate vicinity (~50 cm) of the algal mat. We found that sediment collected under the vegetated area contained significantly higher MPs. This was 3.39 times higher than the unvegetated area. Sediment collected under/near filamentous algae retained much higher abundances of MPs than those of non-filamentous algae. Provided that the observed retention of MPs on macroalgae, we speculate macrophyte system is one of the short-term MPs accumulation hotspots where the temporal increase of MPs depends on the seasonality of macrophyte in a given region.

Linking human activity to spatial accumulation of microplastics along mangrove coasts

Microplastics (MP) in mangrove coasts are threating ecological health and seafood safety. However, quantitative evidence on the effects of different coastal human activities on microplastic accumulation in mangrove sediments is lacking, thereby impeding the policy development of evidence-based waste management. In this study, continuous geographical sampling (N = 50) was applied to collect sediments from the largest mangrove coast, namely the Leizhou Peninsula in China. Similar worldwide research data (16 mangrove coasts) were collected from the Science Citation Index Expanded (SCIE) database of the Web of Science. The connections between human drivers and microplastic accumulation were evaluated by spatial comparison, multi-correspondence analysis, and multiple differences analysis. The microplastic abundance fluctuated widely along the mangrove coasts (average value was 51.24, ranged from 6.40 to 255.57 items·kg^-1 dry weight; coefficient of variation = 97%) with a globally lower-middle concentration in sediments of the Leizhou Peninsula. Densely populated urban residents and the floating population of tourists largely contributed to the high abundance of microplastics in mangrove sediments, of which large-sized (1-5 mm) white foams were the dominant type. Although suburbs had less crowds, both onshore and offshore fishery production could cause high accumulation of microplastics in neighboring mangrove coasts, which were characterized by small-sized (<1 mm) fragments with fresh color. Small microplastics (80%) with fresh color (44%) were dominant. Weathering may break down more toxic particles in urban areas neighboring mangrove coasts. Larger mangrove patches could partly block ocean-based microplastics; however, coasts surrounded by more geographical barriers had intensified pollutant accumulation. It was suggested that foam packaging of commodities for urban residents and tourists in popular tourism areas should be reduced and restrictions of fishery waste plastics are needed along shores with mangroves, especially in coasts surrounded by more geographic barriers.