New Insights into the Microplastic Enrichment in the Blue Carbon Ecosystem: Evidence from Seagrass Meadows and Mangrove Forests in Coastal South China Sea

Anthropogenic microparticles accumulation in small-bodied seagrass meadows: The case of tropical estuarine species in Brazil

Seagrass meadows have recently been highlighted as potential hotspots for microplastic and anthropogenic microparticles (APs). This study assessed AP accumulation in shallow sediments vegetated by small-bodied seagrass species (Halodule wrightii, Halophila decipiens, and H. baillonii) and in the adjacent unvegetated area in a tropical estuary on the East Coast of South America, Brazil, over the seasonal cycle. Anthropogenic microparticles were detected in 80 % of the samples, with a mean abundance of 142 ± 140 particles kg-1 dw (N = 80). Particles were predominantly blue (51 %), fiber (73 %), and smaller than 1 mm (80 %). We observed that seagrass sediments retained APs, although no significant variation was observed between seagrass and the unvegetated area, nor between the dry and rainy seasons. A positive correlation was found between sediment grain size and AP abundance. This study represents the first record of AP contamination in seagrasses from the Tropical Southwestern Atlantic bioregion.

Occurrence and migration patterns of microplastics in different tidal zones of tourist beaches: A case study in the Bohai Bay, North China

Coastal areas are acknowledged to be significant reservoirs of microplastics, while limited research on their presence and migration in the intertidal zones. This study investigated in a tourist beach in northern China, to reveal the occurrence of microplastics at different intertidal heights, elucidates their migration patterns, and discusses the impact of tourist activities on microplastics. Results showed that the mean microplastic abundance was 2114.8 ± 933.2 items/kg in sediments and 30,670.8 ± 15,094.9 items/m3 in seawater. Fibers were the most common shape; transparent, blue, green and black prevailed in color; and cellulose and PET were the most common components. Microplastic abundances decreased from high tide zone to low tide zone, and the abundances of microplastics in seawater were positively correlated with those in the high tide zone and negatively correlated with those in the low tide zone. Compared to wave disturbance, human activities have a relatively limited impact on microplastic abundance. However, intensive tourist activities contribute to a higher diversity of microplastic types on tourist beaches. This study enhances the understanding of the occurrence and migration patterns of microplastics in tourist beaches, and provides a valuable dataset and theoretical basis for subsequent research on microplastic pollution in coastal areas.

Rhizospheric bacterial communities against microplastics (MPs): Novel ecological strategies based on the niche differentiation

Considerable amounts of microplastics (MPs) are stocked in plant rhizospheres, yielding adverse effects on rhizospheric microorganisms and threatening plant health. However, the adaptation of the rhizospheric microbiota for MPs remains largely unknown. Here, to evaluate the adaptive strategies of rhizospheric bacterial communities against MPs, we characterized the spatial dissimilarities in MPs properties and bacterial communities from mangrove non-rhizosphere to rhizosphere to root hair sediments. Consequently, two strategies were uncovered: (1) Bacterial communities showed significant niche differentiation induced by the increasingly enriched MPs evaluated by piecewise structural equation modeling (piecewise SEM), as increasing specialization (10.2 % to 19.4 % to 23.0 % of specialists) and decreasing generalization (10.4 % to 10.2 % to 8.7 % of generalists). (2) A self-remediation strategy of enhancing microbial plastic-degrading potentials was determined in bacterial communities, tightly coupled to the increase of specialists (linear regression analysis, R2 = 0.54, P < 0.001) and increasing MPs weathering degrees visualized by the scanning electron microscopy (SEM) from non-rhizosphere to rhizosphere to root hair regions. Our study provides a novel insight into the ecological strategies that rhizospheric microbes utilize against MPs, and broadens our knowledge of the interaction between soil microbes and global MPs pollution.

Effects of biodegradable microplastics on the crustacean isopod Idotea balthica basteri Audouin, 1826

Plastic pollution is a notable environmental issue, being plastic widespread and characterized by long lifetime. Serious environmental problems are caused by the improper management of plastic end-of-life. In fact, plastic litter is currently detected in any environment. Biodegradable Polymers (BPs) are promising materials if correctly applied and managed at their end of life, to minimize environmental problems. However, poor data on the fate and toxicity of BPs on marine organisms still limit their applicability. In this work we tested the effects of five biodegradable polymers (polybutylene succinate, PBS; polybutylene succinate-co-butylene adipate, PBSA; polycaprolactone, PCL; poly (3-hydroxybutyrates, PHB; polylactic acid, PLA) widely used for several purposes. Adult individuals of the isopod Idotea balthica basteri were fed on these polymers for twenty-seven days by adding biodegradable microplastic polymers (BMPs) to formulated feeds at two concentrations, viz. 0.84 and 8.4 g/kg feed. The plastic fragments affected the mortality rates of the isopods, as well as the expression levels of eighteen genes (tested by Real Time qPCR) involved in stress response and detoxification processes. Our findings confirmed that I. balthica basteri is a convenient model organism to study the response to environmental pollution and emerging contaminants in the aquatic environment, and highlighted the need for the correct use of BMPs.

Fate and drivers of mariculture-derived microplastics from ponds to mangrove forests

Due to the combined influences of marine and terrestrial disturbances, the sources of microplastics (MPs) in mangrove ecosystems are complex and diverse. Previous studies have inferred the possible involvement of mariculture activities as a potential source of mangrove MPs based on the characteristics of MPs. However, the direct contributions of mariculture-derived MPs to mangrove MPs remain largely unknown. In this study, we systematically investigated the fate of MPs in the discharge of mariculture wastewater by quantifying the source contributions of mariculture-derived MPs to rivers and mangroves. The majority of detected MPs were transparent fibers, with their composition primarily comprising materials commonly used in mariculture activities such as polyvinylpyrrolidone (PVP), polyethylene terephthalate (PET), and nylon. The partial least squares path model elucidated the relationships among the composition of MPs in ponds, rivers, and mangroves, indicating that ponds exert a substantial direct effect on mangroves, particularly significant in the sediments (63.68%). Water turbidity, sediment carbon content, and sediment particle size are key ecological factors influencing the abundance of mariculture-derived MPs. This study provides compelling evidence regarding the sources of mangrove MPs and novel insights into mitigating the dissemination of MPs.

Microplastic abundance and accumulation patterns in eelgrass (Zostera marina L.) meadows throughout coastal Massachusetts, USA

Microplastics are fast-emerging as another potential threat to already globally declining seagrass ecosystems, but there is a paucity of in situ surveys showing their accumulations. Here, we surveyed multiple Zostera marina L. meadows in 2020 and 2021 across Massachusetts, USA, for microplastic contamination, as well as identified factors related to patterns of accumulation. We found that microplastics were ubiquitous throughout all sites regardless of proximity to human development, with fibers being the most common microplastic type. In addition, we showed that accumulation of microplastics within seagrass meadows was related to epiphytic cover on leaves, plant morphology, and bulk-density in sediments. The results of this study provide the first in situ baseline microplastic concentrations on Z. marina plants and sediments for the temperate western North Atlantic. Additionally, we identify specific biotic and abiotic factors related to patterns of microplastic accumulation in these ecosystems.

Mangrove mud clam as an effective sentinel species for monitoring changes in coastal microplastic pollution

The worldwide mangrove shorelines are experiencing considerable contamination from microplastics (MPs). Finding an effective sentinel species in the mangrove ecosystem is crucial for early warning of ecological and human health risks posed by coastal microplastic pollution. This study collected 186 specimens of the widely distributed mangrove clam (Geloina expansa, Solander, 1786) from 18 stations along the Leizhou Peninsula, the largest mangrove coast in Southern China. This study discovered that mangrove mud clams accumulated a relatively high abundance of MPs (2.96 [1.61 - 6.03] items·g-1) in their soft tissue, wet weight, as compared to previously reported levels in bivalves. MPs abundance is significantly (p < 0.05 or 0.0001) influenced by coastal urban development, aquaculture, and shell size. Furthermore, the aggregated MPs exhibit a significantly high polymer risk index (Level III, H = 353.83). The estimated annual intake risk (EAI) from resident consumption, as calculated via a specific questionnaire survey, was at a moderate level (990 - 2475, items·g -1·Capita -1). However, the EAI based on suggested nutritional standards is very high, reaching 113,990 (79,298 - 148,681), items·g -1·Capita -1. We recommend utilizing the mangrove mud clam as sentinel species for the monitoring of MPs pollution changing across global coastlines.

Beneath the surface: Exploring microplastic intricacies in Anadara granosa

Anadara granosa or blood cockles have been reported to be a candidate for biomonitoring agents due to their sedimentary nature and their nutrient uptake mechanisms. Yet, this bivalve is still regarded as a delicacy in Asian cuisine. Malaysia is the largest exporter of this sea product that contaminated cockles may also be experienced by the importing countries. However, the bioaccumulation of microplastics in A. granosa cultivated in Malaysia has not been extensively studied. It is crucial to comprehend the risk posed to humans by consuming A. granosa in their diet. Therefore, the purpose of this research is to investigate the levels of microplastic accumulation in A. granosa from major exporters in Peninsular Malaysia, to evaluate the associated risk of microplastics on the species, and to estimate daily human consumption of microplastics through the consumption of A. granosa. The abundance of microplastics was quantified through the use of a stereo microscope, and the polymer type was determined using FTIR and micro-FTIR. Findings from this investigation revealed that all samples of A. granosa were contaminated with microplastics, with the highest levels of accumulation found in bivalves collected from the west coast (0.26 ± 0.15 particles/g) of Peninsular Malaysia. Fragment and fiber microplastics, measuring between 0.05 and 0.1 mm in size, were found to be the most prevalent in A. granosa, with blue being the dominant identified colour and rayon being the most common polymer type. Microplastic risk assessment due to the presence of polyacrylate, polycarbonate (PC), and polymethyl methacrylate (PMMA) resulted in a high risk of contamination for A. granosa. It was further determined that the current estimated dietary intake (EDI) suggests that consumers of A. granosa uptake approximately 21.8-93.5 particles/person/year of microplastics. This study highlights that A. granosa accumulates microplastics, which could potentially result in bioaccumulation and biomagnification in humans through consumption.

Biodegradable microplastics pose greater risks than conventional microplastics to soil properties, microbial community and plant growth, especially under flooded conditions

Biodegradable plastics (bio-plastics) are often viewed as viable option for mitigating plastic pollution. Nevertheless, the information regarding the potential risks of microplastics (MPs) released from bio-plastics in soil, particularly in flooded soils, is lacking. Here, our objective was to investigate the effect of polylactic acid MPs (PLA-MPs) and polyethylene MPs (PE-MPs) on soil properties, microbial community and plant growth under both non-flooded and flooded conditions. Our results demonstrated that PLA-MPs dramatically increased soil labile carbon (C) content and altered its composition and chemodiversity. The enrichment of labile C stimulated microbial N immobilization, resulting in a depletion of soil mineral nitrogen (N). This specialized environment created by PLA-MPs further filtered out specific microbial species, resulting in a low diversity and simplified microbial community. PLA-MPs caused an increase in denitrifiers (Noviherbaspirillum and Clostridium sensu stricto) and a decrease in nitrifiers (Nitrospira, MND1, and Ellin6067), potentially exacerbating the mineral N deficiency. The mineral N deficit caused by PLA-MPs inhibited wheatgrass growth. Conversely, PE-MPs had less effect on soil ecosystems, including soil properties, microbial community and wheatgrass growth. Overall, our study emphasizes that PLA-MPs cause more adverse effect on the ecosystem than PE-MPs in the short term, and that flooded conditions exacerbate and prolong these adverse effects. These results offer valuable insights for evaluating the potential threats of bio-MPs in both uplands and wetlands.

Basin scale monitoring of microplastics and phthalates in sediments from the Persian Gulf and the Gulf of Makran using GIS-based algorithms: Insights towards spatial variation and potential risk assessment

Information on sedimentary microplastics and phthalates has been restricted to the coastal regions of the Persian Gulf and the Gulf of Makran. Our basin-wide study monitored their levels, spatial behaviors, and potential risks using GIS-based techniques. Microplastics and phthalates ranged from 5 to 75 particles/kg d.w and 0.004-1.219 μg g-1 d.w, respectively. Microplastics were in the size category of 100 μm to 3 mm, and black microfibers (< 1 mm) and high-density polymers were dominant. The total number of microplastics was between 356.333 × 1012 and 469.075 × 1012 particles in the surface sediments of the studied regions (confidence interval = 99 %). Diethylhexyl phthalate (DEHP) and Di-isobutyl phthalate contributed 88 % of detected phthalates. Significant correlations among microplastic abundance, total phthalates, and DEHP were distinguished (p < 0.05). Overall, the findings reiterated the widespread presence of microplastics and a potential link between phthalates and microplastics. Semi-variogram, cluster Voronoi polygons, and Trend analysis identified spatial outliers and major deposition sites of microplastics and phthalates and consequently outlined the localities where upcoming studies should be concentrated. A hotspot of potential risks was marked using Fuzzy logic and GIS-based algorithms in the Sea of Makran, covering an area equal to 342. 99 km2.

Ingestion and adherence of microplastics by estuarine mysid shrimp

Microplastics have been reported to be present in zooplankton, yet questions persist regarding their fate and dynamics within biota. We selected the commercial mysid shrimp, Mesopodopsis orientalis, as the focal zooplankton for this study due to their crucial role in our study area, the Inner Gulf of Thailand in January 2022. We investigated the presence of microplastics in mysid bodies and fecal pellets, examining both attached microplastics on external body parts and those ingested. In addition, we conducted microplastic feeding experiments, exposing mysids to various treatments of microplastics. The results of the field investigation indicate that mysids exhibited an average of 0.12 ± 0.03 microplastic items/mysid from whole-body samples. The shape, type, and color of microplastics found in mysids were similar to those present in seawater, with blue PET microfibers being the most prevalent. Our observations on live mysids revealed that microplastics were acquired through ingestion and adherence to appendages and exoskeletons. Microplastics were observed in mysid's fecal pellets at 0.09 ± 0.03 items/mysid, while microplastics adhering to the mysid's body and appendages were observed at 0.10 ± 0.04 items/mysid. The sizes of microplastics extracted from preserved mysids ranged from 58 μm to 4669 μm, with median of 507 μm. The laboratory experiments revealed that the presence of microalgae enhanced microplastic ingestion in mysids; microplastics incubated with a cyanobacterium, Oscillatoria sp., and diatom Navicula sp. significantly increased the number of microplastic particles ingested by mysids. This study showed that microplastics can be more ingested in mysids, especially when food items are present. Microplastic fate in these animals may involve expulsion into the environment or adherence, potentially facilitating their transfer up the marine food web.

The power of Posidonia oceanica meadows to retain microplastics and the consequences on associated macrofaunal benthic communities

In the coastal environment, a large amount of microplastics (MPs) can accumulate in the sediments of seagrass beds. However, the potential impact these pollutants have on seagrasses and associated organisms is currently unknown. In this study, we investigated the differences in MPs abundance and composition (i.e., shape, colour and polymer type) in marine sediments collected at different depths (-5 m, -15 m, -20 m) at two sites characterized by the presence of Posidonia oceanica meadows and at one unvegetated site. In the vegetated sites, sediment samples were collected respectively above and below the upper and lower limits of the meadow (-5 m and -20 m), out of the P. oceanica meadow, and in the central portion of the meadow (-15 m). By focusing on the central part of the meadow, we investigated if the structural features (i.e. shoots density and leaf surface) can affect the amount of MPs retained within the underlying sediment and if these, in turn, can affect the associated benthic communities. Results showed that the number of MPs retained by P. oceanica meadows was higher than that found at the unvegetated site, showing also a different composition. In particular, at vegetated sites, we observed that MPs particles were more abundant within the meadow (at - 15 m), compared to the other depths, on unvegetated sediment, with a dominance of transparent fragments of polypropylene (PP). We observed that MPs entrapment by P. oceanica was accentuated by the higher shoots density, while the seagrass leaf surface did not appear to have any effect. Both the abundance and richness of macrofauna associated with P. oceanica rhizomes appear to be negatively influenced by the MPs abundance in the sediment. Overall, this study increases knowledge of the potential risks of MPs accumulation in important coastal habitats such as the Posidonia oceanica meadows.

Effects of COVID-19 on coastal and marine environments: Aggravated microplastic pollution, improved air quality, and future perspective

The COVID-19 pandemic during 2020-2023 has wrought adverse impacts on coastal and marine environments. This study conducts a comprehensive review of the collateral effects of COVID-19 on these ecosystems through literature review and bibliometric analysis. According to the output and citation analysis of these publications, researchers from the coastal countries in Asia, Europe, and America payed more attentions to this environmental issue than other continents. Specifically, India, China, and USA were the top three countries in the publications, with the proportion of 19.55%, 18.99%, and 12.01%, respectively. The COVID-19 pandemic significantly aggravated the plastic and microplastic pollution in coastal and marine environments by explosive production and unproper management of personal protective equipment (PPE). During the pandemic, the estimated mismanaged PPE waste ranged from 16.50 t/yr in Sweden to 250,371.39 t/yr in Indonesia. In addition, the PPE density ranged from 1.13 × 10-5 item/m2 to 2.79 item/m2 in the coastal regions worldwide, showing significant geographical variations. Besides, the emerging contaminants released from PPE into the coastal and marine environments cannot be neglected. The positive influence was that the COVID-19 lockdown worldwide reduced the release of air pollutants (e.g., fine particulate matter, NO2, CO, and SO2) and improved the air quality. The study also analyzed the relationships between sustainable development goals (SDGs) and the publications and revealed the dynamic changes of SDGs in different periods the COVID-19 pandemic. In conclusion, the air was cleaner due to the lockdown, but the coastal and marine contamination of plastic, microplastic, and emerging contaminants got worse during the COVID-19 pandemic. Last but not least, the study proposed four strategies to deal with the coastal and marine pollution caused by COVID-19, which were regular marine monitoring, performance of risk assessment, effective regulation of plastic wastes, and close international cooperation.

Polyester microfiber impacts on coastal sediment organic matter consumption

As plastic pollution continues to accumulate at the seafloor, concerns around benthic ecosystem functionality heightens. This research demonstrates the systematic effects of polyester microfibers on seafloor organic matter consumption rates, an important benthic ecosystem function connected to multiple reactions and processes. We used a field-based assay to measure the loss of organic matter, both with and without polyester microfiber contamination. We identified sediment organic matter content, mud content, and mean grain size as the main drivers of organic matter consumption, however, polyester microfiber contamination decoupled ecosystem relationships and altered observed organic matter cycling dynamics. Organic matter consumption rates varied across horizontal and vertical spaces, highlighting that consumption and associated plastic effects are dependent on environmental heterogeneity at both small (within sites) and larger (between sites) scales. Our results emphasize the important role habitat heterogeneity plays in seafloor organic matter consumption and the associated effects of plastic pollution on ecosystem function.

The under-investigated plastic threat on seagrasses worldwide: a comprehensive review

Marine plastic pollution is a well-recognised and debated issue affecting most marine ecosystems. Despite this, the threat of plastic pollution on seagrasses has not received significant scientific attention compared to other marine species and habitats. The present review aims to summarise the scientific data published in the last decade (January 2012-2023), concerning the evaluation of plastic pollution, of all sizes and types, including bio-based polymers, on several seagrass species worldwide. To achieve this goal, a comprehensive and critical review of 26 scientific papers has been carried out, taking into consideration the investigated areas, the seagrass species and the plant parts considered, the experimental design and the type of polymers analysed, both in field monitoring and in laboratory-controlled experiments. The outcomes of the present review clearly showed that the dynamics and effects of plastic pollution in seagrass are still under-explored. Most data emerged from Europe, with little or no data on plastic pollution in North and South America, Australia, Africa and Antarctica. Most of the studies were devoted to microplastics, with limited studies dedicated to macroplastics and only one to nanoplastics. The methodological approach (in terms of experimental design and polymer physico-chemical characterisation) should be carefully standardised, beside the use of a model species, such as Zostera marina, and further laboratory experiments. All these knowledge gaps must be urgently fulfilled, since valuable and reliable scientific knowledge is necessary to improve seagrass habitat protection measures against the current plastic pollution crisis.

The occurrence of pollutants in organisms and water of inland mariculture systems: Shrimp aquaculture is a procession of Microplastics accumulation

Microplastics (MPs) pollution in the ocean was widely concerned, but the current study on MPs pollution in the mariculture system is relatively lacking. This study researched the MPs pollution characteristics in water and shrimp at different stages of the pond and industrial aquaculture. The study shows that in the same aquaculture stage, MPs abundance in shrimp and water in pond aquaculture mode is higher than that in industrial aquaculture mode. The MPs pollution characteristics in shrimp and water show significant consistency. The hazard index of MPs in pond water and industrial models are 122 (Level Ⅲ) and 540 (Level Ⅲ), respectively, indicating that industrial aquaculture models may suffer from more severe MPs stress. The aquaculture period and mode significantly affected the MPs abundance of water and shrimp, but there was no interaction between the aquaculture period and mode. MPs abundance in shrimp show a significant relationship with the length of crustacean and weight. This study further enhanced the understanding of MPs pollution of water and organisms in different aquaculture modes at different stages, and warned MPs is widely spread in mariculture systems.

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.

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.

Effects of micro(nano)plastics on soil nutrient cycling: State of the knowledge

The ecological impacts of micro(nano)plastics (MNPs) have attracted attention worldwide because of their global occurrence, persistence, and environmental risks. Increasing evidence shows that MNPs can affect soil nutrient cycling, but the latest advances on this topic have not systematically reviewed. Here, we aim to present the state of knowledge about the effects of MNPs on soil nutrient cycling, particularly of C, N, and P. Using the latest data, the present review mainly focuses on three aspects, including (1) the effects and underlying mechanisms of MNPs on soil nutrient cycling, particularly of C, N and P, (2) the factors influencing the effects of MNPs on soil nutrient cycling, and (3) the knowledge gaps and future directions. We conclude that MNPs can alter soil nutrient cycling via mediating soil nutrient availability, soil enzyme activities, functional microbial communities, and their potential ecological functions. Furthermore, the effects of MNPs vary with MNPs characteristics (i.e., polymeric type, size, dosage, and shape), chemical additives, soil physicochemical conditions, and soil biota. Considering the complexity of MNP-soil interactions, multi-scale experiments using environmental relevant MNPs are required to shed light on the effects of MNPs on soil nutrients. By learning how MNPs influence soil nutrients cycles, this review can guide policy and management decisions to safeguard soil health and ensure sustainable agriculture and land use practices.

The hyperbenthic environment: A forgotten habitat for plastic pollution

This study investigates the abundances and composition of microplastics (MP) among the shallow layers of a coastal Mediterranean Marine Protected Area (Cabrera MPA), seafloor sediments, hyperbenthic environment, and the water column. The mid waters samples were collected mid-way between the sea surface and the seafloor and hyperbenthic samples at the water layer adjacent to the seafloor. Sampling was carried out on patchiness seafloor of Posidonia oceanica meadows. The seafloor sediments showed a mean abundance of 378,769.20 ± 508,109.11 MPs/m3, three orders of magnitude higher than the hyperbenthic (209.17 ± 117.07 MPs/m3), and the mid waters layer (106.48 ± 107.17 MPs/m3). An increasing vertical gradient in MP abundances, mainly composed of fibers was observed. Fibers were made-up mainly of polystyrene (PS, 25 %), expanded polystyrene (EPS, 18 %) and cellulose acetate (CA, 16 %). The results stress the need to increase efforts to find solutions to mitigate fiber pollution in the marine environment.

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 degradation stimulated by in-situ bioelectric field in agricultural soils

Bioelectric field is a stimulated force to degrade xenobiotic pollutants in soils. However, the effect of bioelectric field on microplastics (MPs) aging is unclear. The degradation behavior of polyvinyl chloride (PVC), polyethylene (PE) and polylactic acid (PLA) was investigated in an agricultural soil microbial electrochemical system in which bioelectric field was generated in-situ by native microbes. Based on the density function theory, the energy gaps between the highest and the lowest occupied molecular orbitals of the three polymers with periodic structure were 4.20, 7.24 and 10.09 eV respectively, and further decreased under the electric field, indicating the higher hydrolysis potential of PLA. Meanwhile, the mass loss of PLA in the closed-circuit group (CC) was the highest on day 120, reaching 8.94%, which was 3.01-3.54 times of that without bioelectric field stimulation. This was mainly due to the enrichment of plastic-degrading bacteria and a robust co-occurrence network as the deterministic assembly process, e.g., the abundance of potential plastic-degrading bacteria on the surface of PLA and PVC in the CC increased by 1.92 and 1.30 times, respectively, compared to the open-circuit group. In terms of functional genes, the xenobiotic biodegradation and metabolism capacity of plasticsphere in the CC were stronger than that in soil, and determined by the bioaccessibility of soil nitrogen and carbon. Overall, this study explored the promoting effect of bioelectric field on the degradation of MPs and reveled the mechanism from quantum chemical calculations and microbial community analysis, which provides a novel perception to the in-situ degradation of MPs.

Accumulation and re-distribution of microplastics via aquatic plants and macroalgae - A review of field studies

The aquatic plants and macroalgae are primary producers with major roles regarding the maintenance of ecosystems but their interaction with microplastics (MPs) has received less attention than animals. We summarize the methodologies used, the MPs abundances and their characteristics across the literature on MPs pollution in aquatic plants and macroalgae. The sampling and quantification of MPs still lacks consistency between studies, which increased the uncertainty in cross-comparisons. The abundance of MPs varied by orders of magnitude between species and were mostly fibers and polymers with large degrees of production and applications. Filamentous species contained more MPs than others. The average ratio of MPs between vegetated and unvegetated sites reached 3:1. The average ratio of MPs between the biotic and abiotic fractions reached 2193:1, suggesting a high level of retention in fields. Our findings supported that aquatic plants and macroalgae are critical in the plastic flux within the marine environments.

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.

First evidence of meso- and microplastics on the mangrove leaves ingested by herbivorous snails and induced transcriptional responses

Although evidence suggests the ubiquity of meso- and microplastics (MMPs) in mangrove forests, our knowledge of their bioavailability and risk on mangrove leaves is scarce. Here, we investigated MMP contamination concerning submerged mangrove leaves and herbivorous snails that mainly feed on them from the four mangrove forests located in Beibu Gulf, Guangxi Province, China. Results showed that the MMP abundance on the mangrove leaves ranged from 0.01 ± 0.00 to 0.42 ± 0.15 items cm^-2, while it ranged from 0.33 ± 0.21 to 6.20 ± 2.91 items individual^-1 in the snails. There were significant positive correlations between snails and leaves regarding the abundance of total MMPs and the proportions of MMPs with the same characteristics. Expanded polystyrene (EPS) that mainly derived from aquaculture rafts, accounted for a major component both on the leaves and in the snails in Shi Jiao (SJ). Both the detection frequency and percentage of larger EPS (2.00-17.50 mm) on the leaves in SJ were higher than other sites. Meanwhile, the detection frequency, abundance and percentage of larger EPS on the leaves had significant positive correlations with those of micro-EPS in the snails. These findings suggested that mangrove leaves may represent a viable pathway for MMPs to enter the herbivorous snails. Larger EPS with higher frequency of occurrence on mangrove leaves were more likely to be encountered and ingested by snail considering its opportunistic feeding behavior. In addition, 11 sensitive genes involved in the processes of metabolism, intestinal mucosal immune systems, and cellular transduction in the snails were significantly suppressed by MMP exposure, which may be potentially used as early biomarkers to indicate the biological effects of MMPs under realistic environmental conditions. Overall, this study provides novel insights into the fate, sources, and biological effects of MMPs on mangrove leaves.

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.

Potential risk of co-occurrence of microplastics and chlorinated persistent organic pollutants to coastal wetlands: Evidence from a case study

Microplastic (MP) pollution in coastal wetlands is of a global concern. Little attention has been paid to the co-occurrence and corresponding risk of MPs with pollutants, especially refractory chlorinated persistent organic pollutants (CPOPs). A case study of Zhejiang, China was conducted to investigate the occurrence of MPs and targeted CPOPs in coastal wetlands. MPs were 100% detected, but with the lowest abundance in coastal wetlands (average: 666.1 ± 159.1 items kg^-1), as compared to other 6 terrestrial ecosystems (average: 1293.9 ± 163.7 items kg^-1) including paddy field, upland, facility vegetable field, forestland, urban soil, and grassland. A total of 35 kinds CPOPs were also detected in all studied coastal wetlands, with their concentration almost under 10 μg kg^-1 (90.1%). Both enrichment of MPs and CPOPs was affected by sediment TOC, wetland vegetation and land use simultaneously. Interestingly, the occurrence of MPs was significantly correlated with polychlorinated biphenyls (PCBs) but not organochlorine pesticides (OCPs). Results of co-occurrence pollution assessment of MPs and CPOPs further indicated only Hangzhou Bay showed the ecological risk among all tested wetlands. This would suggest a potential risk of co-occurrence of MPs and modern CPOPs in coastal wetland in economic development area. Possible reason may lie on strong MP vector effect to CPOPs. More attention should thus be paid to other wetlands polluted by MPs and MP-carrying CPOPs in area with relatively great environmental pressure induced by human activity. This study may provide reference for a better understanding with respect to the risk level posed by co-occurrence of MPs and CPOPs to global coastal wetlands.

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-microbe interaction in the marine environment: Research methods and opportunities

Approximately 9 million metric tons of plastics enters the ocean annually, and once in the marine environment, plastic surfaces can be quickly colonised by marine microorganisms, forming a biofilm. Studies on plastic debris-biofilm associations, known as plastisphere, have increased exponentially within the last few years. In this review, we first briefly summarise methods and techniques used in exploring plastic-microbe interactions. Then we highlight research gaps and provide future research opportunities for marine plastisphere studies, especially, on plastic characterisation and standardised biodegradation tests, the fate of "environmentally friendly" plastics, and plastisphere of coastal habitats. Located in the tropics, Southeast Asian (SEA) countries are significant contributors to marine plastic debris. However, plastisphere studies in this region are lacking and therefore, we discuss how the unique environmental conditions in the SEA seas may affect plastic-microbe interaction and why there is an imperative need to conduct plastisphere studies in SEA marine environments. Finally, we also highlight the lack of understanding of the pathogenicity and ecotoxicological effects of plastisphere on marine ecosystems.

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.

Urban mangrove ecosystems are under severe threat from microplastic pollution: a case study from Mangalavanam, Kerala, India

The prevalence of microplastics in urban mangrove ecosystems has received little scientific attention despite their immense ecological significance. An investigation was conducted to assess the microplastic abundance and characteristics in three different environmental compartments viz; soil (933 ± 564 particles/kg), sediment (1275 ± 532 particles/kg d.w.), and water (101.6 ± 24 particles/liter) of the Mangalavanam bird sanctuary, a protected mangrove forest in the Cochin city of India. Microplastic fibres were predominant in water, while soil and sediment contained a higher proportion of microplastic fragments. Importantly, surrounding urban features and tidal fluctuation were considered to be influencing microplastic metrics in the area. The colour composition of microplastics was found to be similar in all three environmental compartments and most of the identified polymers were those which are scarcely recycled. Altogether, this study highlights the importance of adopting location-specific measures to protect the area from microplastic pollution and provides the baseline data required for further assessing the impacts of microplastic pollution on mangroves, avifauna, and other components of biodiversity in the region.

How does bivalve size influence microplastics accumulation?

Microplastics (wasted plastic particles < 5 mm in diameter) are ubiquitously distributed in the marine environment. Filter-feeding and low trophic level bivalves are vulnerable to microplastics accumulation from the surrounding depositional environment, thereby threatening both ecological health and human food safety. Microplastics had been detected in lots of coastal Bivalvia species. However, the influence of biological morphology on the mechanism of microplastics accumulation is not clear. There is also a knowledge gap of which species are preferred for commercial consumption, which creates loopholes in risk identification for food safety. A survey on a commercial popular eaten but under-researched hard clam (Meretrix meretrix; Linnaeus, 1758) from a famous fishery port city in southern China was carried out to comprehensively analyze shell size influence on microplastics accumulation in bivalves and consequently, human intake risk via bivalve consumption. Detected microplastics count in per individual (MCI) was 24.64 ± 19.11 items · individual^-1, and microplastics count per gram (MCG; wet weight with shell) was 0.66 ± 0.54 items · g^-1. When the shell width grew by 1 mm, MCI increased by 1.01 times, but MCG decreased by 0.97 times. Dominant microplastics characteristics found in this study was fiber and fragment. Sizes ranged from 25 to 150 μm, and dark colors (black, red, and blue) were found. The mostly common polymers were polyethene (PE, 40%), polyethylene terephthalate (PET, 23%), and polypropylene (PP, 18%). Estimated annual intake (EAI) risk of microplastics via hard clam consumption by residents was 6652.26 ± 5327.28 items · year ^-1 · person ^-1. The microplastics in bivalves and EAI was relatively high. When shell width grew by 1 mm, EAI decreased by 0.97 times. Therefore, eating a fixed amount of larger hard clams with a relatively low amount of microplastics can reduce EAI risk for consumers. A systematic investigation of emission sources along main coast, where bivalve production is prominent will be useful for food safety control in this region.

Priorities to inform research on marine plastic pollution in Southeast Asia

Southeast Asia is considered to have some of the highest levels of marine plastic pollution in the world. It is therefore vitally important to increase our understanding of the impacts and risks of plastic pollution to marine ecosystems and the essential services they provide to support the development of mitigation measures in the region. An interdisciplinary, international network of experts (Australia, Indonesia, Ireland, Malaysia, the Philippines, Singapore, Thailand, the United Kingdom, and Vietnam) set a research agenda for marine plastic pollution in the region, synthesizing current knowledge and highlighting areas for further research in Southeast Asia. Using an inductive method, 21 research questions emerged under five non-predefined key themes, grouping them according to which: (1) characterise marine plastic pollution in Southeast Asia; (2) explore its movement and fate across the region; (3) describe the biological and chemical modifications marine plastic pollution undergoes; (4) detail its environmental, social, and economic impacts; and, finally, (5) target regional policies and possible solutions. Questions relating to these research priority areas highlight the importance of better understanding the fate of marine plastic pollution, its degradation, and the impacts and risks it can generate across communities and different ecosystem services. Knowledge of these aspects will help support actions which currently suffer from transboundary problems, lack of responsibility, and inaction to tackle the issue from its point source in the region. Being profoundly affected by marine plastic pollution, Southeast Asian countries provide an opportunity to test the effectiveness of innovative and socially inclusive changes in marine plastic governance, as well as both high and low-tech solutions, which can offer insights and actionable models to the rest of the world.

Marine litter and climate change: Inextricably connected threats to the world's oceans

The global issues of climate change and marine litter are interlinked and understanding these connections is key to managing their combined risks to marine biodiversity and ultimately society. For example, fossil fuel-based plastics cause direct emissions of greenhouse gases and therefore are an important contributing factor to climate change, while other impacts of plastics can manifest as alterations in key species and habitats in coastal and marine environments. Marine litter is acknowledged as a threat multiplier that acts with other stressors such as climate change to cause far greater damage than if they occurred in isolation. On the other hand, while climate change can lead to increased inputs of litter into the marine environment, the presence of marine litter can also undermine the climate resilience of marine ecosystems. There is increasing evidence that that climate change and marine litter are inextricably linked, although these interactions and the resulting effects vary widely across oceanic regions and depend on the particular characteristics of specific marine environments. Ecosystem resilience approaches, that integrate climate change with other local stressors, offer a suitable framework to incorporate the consideration of marine litter where that is deemed to be a risk, and to steer, coordinate and prioritise research and monitoring, as well as management, policy, planning and action to effectively tackle the combined risks and impacts from climate change and marine litter.

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.

Merging Plastics, Microbes, and Enzymes: Highlights from an International Workshop

In the Anthropocene, plastic pollution is a worldwide concern that must be tackled from different viewpoints, bringing together different areas of science. Microbial transformation of polymers is a broad-spectrum research topic that has become a keystone in the circular economy of fossil-based and biobased plastics. To have an open discussion about these themes, experts in the synthesis of polymers and biodegradation of lignocellulose and plastics convened within the framework of The Transnational Network for Research and Innovation in Microbial Biodiversity, Enzymes Technology and Polymer Science (MENZYPOL-NET), which was recently created by early-stage scientists from Colombia and Germany. In this context, the international workshop "Microbial Synthesis and Degradation of Polymers: Toward a Sustainable Bioeconomy" was held on 27 September 2021 via Zoom. The workshop was divided into two sections, and questions were raised for discussion with panelists and expert guests. Several key points and relevant perspectives were delivered, mainly related to (i) the microbial evolution driven by plastic pollution; (ii) the relevance of and interplay between polymer structure/composition, enzymatic mechanisms, and assessment methods in plastic biodegradation; (iii) the recycling and valorization of plastic waste; (iv) engineered plastic-degrading enzymes; (v) the impact of (micro)plastics on environmental microbiomes; (vi) the isolation of plastic-degrading (PD) microbes and design of PD microbial consortia; and (vii) the synthesis and applications of biobased plastics. Finally, research priorities from these key points were identified within the microbial, enzyme, and polymer sciences.

A review of microplastic impacts on seagrasses, epiphytes, and associated sediment communities

Microplastics have been discovered ubiquitously in marine environments. While their accumulation is noted in seagrass ecosystems, little attention has yet been given to microplastic impacts on seagrass plants and their associated epiphytic and sediment communities. We initiate this discussion by synthesizing the potential impacts microplastics have on relevant seagrass plant, epiphyte, and sediment processes and functions. We suggest that microplastics may harm epiphytes and seagrasses via impalement and light/gas blockage, and increase local concentrations of toxins, causing a disruption in metabolic processes. Further, microplastics may alter nutrient cycling by inhibiting dinitrogen fixation by diazotrophs, preventing microbial processes, and reducing root nutrient uptake. They may also harm seagrass sediment communities via sediment characteristic alteration and organism complications associated with ingestion. All impacts will be exacerbated by the high trapping efficiency of seagrasses. As microplastics become a permanent and increasing member of seagrass ecosystems it will be pertinent to direct future research towards understanding the extent microplastics impact seagrass ecosystems.

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.

Conjugative antibiotic-resistant plasmids promote bacterial colonization of microplastics in water environments

Both microplastic and bacterial antibiotic resistance have attracted attention worldwide. When microplastics coexist with antibiotic-resistant bacteria (ARB), which carry antibiotic resistance genes (ARGs), ARB colonize the surface of microplastics, and a unique biofilm is formed. The ARB and ARGs in biofilms are denser and more difficult to remove. However, studies on the factors influencing the formation of microplastic biofilms are limited. In this study, plasmid RP4, which appeared in wastewater treatment plants, was found to be able to promote irreversible bacterial colonization of microplastics, and the hypothetical reason was conjugative pili expression. Then, the potential conjugative pili synthesis promoter "nanoalumina" and inhibitor "free nitrous acid" (FNA) were selected to test this hypothesis. Simultaneously, nanoalumina promoted and FNA inhibited bacterial colonization when RP4 existed. Combined with the gene expression and ATP analysis results, this hypothesis was confirmed, and the mechanism of RP4 on bacterial colonization was related mainly to conjugative pili protein synthesis and intracellular ATP. In this study, the effects of plasmid RP4, nanoalumina, and FNA on the formation of microplastic biofilms were reported, which has a certain reference value for other researchers exploring microplastic biofilms.

How surfactants affect the depuration of polycyclic aromatic hydrocarbons adsorbed on the mangrove leaf surfaces: insight from an in situ method

The effects of sodium dodecyl benzene sulfonate (SDBS), polyoxyethylene (20) sorbitan monolaurate (Tween 20), and their mixtures on the depuration of anthracene (Ant) and fluoranthene (Fla) individually adsorbed on the Kandelia obovata (Ko) leaf surfaces were in situ investigated. The Ko original leaf-wax microstructures have been destroyed by SDBS, Tween 20, and their mixtures at or above their critical micelle concentration (CMC). The volatilization rate constants (k_V) of the adsorbed PAHs decreased with surfactants at or above their CMC resulting from the plasticizing effect and a decrease in the polarity of the Ko leaf-waxes induced by surfactants. Moreover, the photolysis rate constants (k_P) of the adsorbed PAHs decreased with SDBS while increased with Tween 20 and their mixtures at or above their CMC, which can be attributed to effects of surfactants on the light adsorption behavior of Ko leaf-waxes. Overall, the effects of surfactants on the depuration of the adsorbed PAHs were dependent not only on the physical-chemical properties of surfactants but also on the micro-environment of the substrates adsorbed the PAHs. These results are of great significance for further understanding the accumulation of PAHs and could expand our knowledge about the migration mechanism of PAHs from the atmosphere by mangrove leaf surface micro-zones.

The Occurrence of Microplastics in Sediment Cores from Two Mangrove Areas in Southern Thailand

Mangroves are areas that connect the land and sea, and are important to the ecosystem. They are important places for food sources and the habitat of aquatic fauna in the tidal areas. However, the existence of plastic debris poses a risk to the aquatic environment. This study aimed to investigate the accumulation of microplastics (MPs) in sediment cores from two mangrove areas. The first mangrove area is in the outer section of the Songkhla lagoon (SK), while the second is in the coastal area of Pattani province (PN). Sediment core sampling was performed from SK = 8 stations and PN = 5 stations. Surface enrichment of MP was observed, especially in sediments of 0–4 cm. MPs were found throughout the depth in both areas, while fewer MPs were found in deeper sediment core layers (p < 0.05) at some stations inside the mangrove zone. Simple linear regression of the observed MPs and distance in the horizontal were found to be significant at SK within the mangrove zone with r2 = 0.79 (p < 0.05). MP fibers were the most commonly found MP type in both areas and were less than 1 mm. Blue and black MPs were the most abundant colors found in both areas. The six polymer types reported in this study comprised polyethylene, rayon, rubber, styrene, Poly (vinyl acetate), and paint. The findings of the present study suggest that long-term monitoring of marine debris along coastlines is necessary to help improve national policies and measures related to marine plastic debris.

Riparian vegetation as a trap for plastic litter

Plastic pollution represents the most widespread threaten throughout the world and, amongst aquatic habitats, freshwaters and in particular riparian zones seems to be highly disturbed. Since the plastic storage and accumulation on the riparian vegetation have not yet been deeply investigated, here, we focussed on the riparian zone's function in trapping plastic litter. To do so, we assessed the occurrence and density of plastics in different vegetated (arboreal, shrubby, herbaceous, reed, bush) and unvegetated types in 8 central Italian rivers, running in different land use contexts. Our results showed that plastic pieces, bags, bottles and food containers were the most abundant specific categories on the vegetated types, demonstrating the riparian vegetation role in trapping plastic litter. Specifically, the highest plastic density was found on the shrubby type suggesting that a tree shape retains plastics more easily than all other vegetated and unvegetated types. Shape and size classification of plastics are not significantly different between vegetated and unvegetated types. These findings allow to collect important information on how the riparian vegetation can be exploited in management activities for removing plastic litters from both freshwater and sea, being the former considered the main plastic source for the latter. This study highlights a further ecosystem service as mechanical filter provided by the riparian zone, even if further studies ought to be performed to understand the role of vegetation as plastic trap and the possible detrimental effects of plastics on the plant health status.

A review on microplastic pollution in the mangrove wetlands and microbial strategies for its remediation

Mangroves are one of the most productive ecosystems in the world harboring huge biological diversity. The prime ecological roles of mangroves are prevention of coastal erosion and shoreline protection. Mangroves face varying degrees of threats due to overexploitation, conversion of mangrove habitats for agriculture, settlement and industrial purposes, illegal encroachment, global warming, sea-level rise, El Nino, and pollution. Among them, microplastic (MP) pollution is a major concern threatening not only the mangroves per se but also the rich biodiversity that it shelters. In general, the microbial communities which are paramount to nutrient recycling and ecological dynamics undergo substantial changes upon MP exposure. If the MP pollution in the mangrove habitats continues unabated in the coming decades, there may be serious consequences on the already threatened mangrove ecosystems and the coastal communities. This review article attempts to consolidate MP pollution of mangrove wetlands, its impact on mangroves and associated microbiota, and the microbial solution for its remediation as a sustainable strategy.

Artificial light source selection in seaweed production: growth of seaweed and biosynthesis of photosynthetic pigments and soluble protein

Seaweed growth is often limited by light. Artificial light supply has been well studied in terrestrial agriculture, however, much less is known about its effect in seaweed aquaculture. In this study, the effects of four artificial light sources (white, red, green, and blue LEDs light) on a brown alga Sargassum fusiforme and a green alga Ulva pertusa were investigated. Seaweed growth, accumulation of photosynthetic pigments (chlorophyll a and carotenoid), and soluble protein were evaluated. White LED light was the optimal supplementary light when cultivating Ulva pertusa and Sargassum fusiforme, because it promoted seaweed growth while maintaining protein production. Meanwhile, red LED was unfavored in the cultivation of S. fusiforme, as it affected the seaweed growth and has a lower residual energy ratio underneath the water. LEDs would be a promising supplementary light source for seaweed cultivation.