Microplastics in mangrove sediments of the Pearl River Estuary, South China: Correlation with halogenated flame retardants' levels

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.

Unveiling microplastic distribution and interactions in the benthic layer of the Yangtze River Estuary and East China Sea

Microplastics (MPs), recognized as an emerging global environmental concern, have been extensively detected worldwide, with specific attention directed towards the Yangtze River Estuary (YRE) and East China Sea (ECS) regions. Despite their critical research significance, there remains a knowledge gap concerning the distribution of MPs in the benthic layer within this area, particularly regarding interactions governing their occurrence. Here we illuminate the distribution of MPs within the benthic layer and unravel the intricate interplay between bottom water and sediment in the YRE and ECS. We find that MPs are notably more abundant in bottom water, ranging from 8 to 175 times higher than in surface water. These MPs predominantly consist of polyester fibers, exhibit a size range between 0.5 and 5.0 mm, and display distinct coloration. Co-occurrence network analysis and Principal Coordinate Analysis confirm a robust correlation between MPs in bottom water and sediment, signifying the pivotal role of bottom water in mediating the distribution and transportation of MPs within the benthic layer. Furthermore, a positive correlation between MPs in sediment and bottom water turbidity underscores the impact of surface sediment resuspension and upwelling on MPs distribution. This study clarifies the intricate interactions within the benthic layer and highlights the crucial role of bottom water as a mediator in the vertical distribution of MPs, advancing our understanding of the "source-to-sink" transport processes governing MPs within water-sediment systems.

Historical behaviors of microplastic in estuarine and riverine reservoir sediment

This study investigates the sedimentation behaviors of microplastics (MPs) within a typical meso-scale river estuary, the Yalu River Estuary (YRE) and its riverine reservoir. It analyzes sediment cores in two habitats of Yalu River, revealing changing MPs abundance over time. Results highlight significant differences in riverine and estuarine MPs deposition. Reservoir sample contains more MPs in fragments. Color variations are notable in estuarine samples but minimal in reservoir sample. After 1980, estuarine cores show an increase in coarser MPs, likely due to growth of aquaculture activities. Although sediment accumulates at 1/10 of the rate in reservoir compared to estuary, MPs in reservoir sediments exceeds estuarine level by over threefold. A possible mechanistic framework is then proposed to discuss the varying MPs behaviors in the two habitats, indicating reservoirs accumulate MPs at a higher rate due to the barrier effect of an upper-stream reservoir, stable hydrodynamics, and weak salinity-induced buoyancy.

Distribution characteristics and ecological risk assessment of microplastics in intertidal sediments near coastal water

Plastic products are widely distributed worldwide and continue to have a negative impact on the environment and organisms. Intertidal regions, which interface between upland and marine ecosystems, are regions of high ecological importance and serve as repositories for a variety of plastic wastes. However, ecological risk assessments of microplastics (MPs) in these transitional environments are still scarce. In this study, the morphological characteristics and spatial distribution of MPs in the intertidal surface sediments of Haizhou Bay were analyzed, and an ecological risk assessment framework for MPs was developed. Overall, the average abundance of MPs in the sediments was 2.31 ± 1.35 pieces/g dw. The size of the MPs was mainly less than 1 mm, and the main shape, color and polymer type of the MPs were mainly fibrous (58%), blue (30%), and PVC (22%), respectively. Cluster analyses showed that the sites could be well distinguished by size and polymer type but not by MP shape and color. According to the hazard scores, most of the sites in this area belonged to a risk level of IV, while the pollution loading index (PLI) showed that most of the sites belonged to a risk level of II. The ecological toxicity risk from the species-sensitive distribution (SSD) model showed that one-third of the sites had ecological MPs toxicity risks to marine organisms. We believe that normalized and standardized assessment methods should be implemented to monitor and manage the risk of MPs in the intertidal sediments. Particularly, the multiple dimensions, standard abundance of MPs, as well as MPs ingestion in the intertidal organisms, should be fully considered in the next step.

Probabilistic risk assessment of microplastics on aquatic biota in coastal sediments

As an emerging form of pollution, microplastic contamination of the coastal ecosystems is one of the world's most pressing environmental concerns. Coastal sediments have been polluted to varying degrees by microplastics, and their ubiquitous presence in sediments poses a threat to marine organisms. However, there is currently no ecological risk assessment of microplastics on aquatic biota in sediments. This study, for the first time, established a new procedure to evaluate the toxicity of microplastics on aquatic biota in sediments, based on the probabilistic risk assessment (PRA) concept. The choice of Zhelin Bay as the case study site was based on its severe pollution status. The average content of microplastics in the sediments of Zhelin Bay was 2054.17 items kg-1 dry weight, and these microplastics consisted of 46 different species. Microplastics in sediments exist in five different forms, with the film form being the main composition, and the majority of microplastics have particle sizes ranging from 100 to 500 μm. Correlation analysis (CA) reveals significant negative correlations between microplastic abundance, and Al2O3 and SiO2. The toxicity of microplastics, based on the PRA concept, suggests that Zhelin Bay surface sediments had a low probability (3.43%) of toxic effects on aquatic biota.

Effect of tidal current on the settling and accumulation of microplastics in the Chao Phraya River estuary, Thailand

The deposition of MPs in a water column and surface sediment during a mixed spring tidal cycle of the Chao Phraya River estuary was investigated. The settling MPs during flood and ebb tides were collected by deploying traps at 3 m below the surface, while the settled MPs throughout the tidal cycle were collected by deploying traps at 1 m above the bottom. The settling rate of MPs was 2168 pieces/m2/h during highest to low tide, and 639 pieces/m2/h during high to lowest tide. The deposition rate of MPs after the end of the tidal cycle was 3172 pieces/m2/day, while the accumulation rate of MPs in the surface sediment was 1515 pieces/m2/day. The settling MPs tended to decrease inversely to the suspended solids and salinity. The major types of the deposited MPs were polyethylene (36 %) and polyamide (33 %), while that of the surface sediment was epoxy resin (80 %).

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.

Spatial distribution and characteristics of plastic pollution in the salt marshes of Bahía Blanca Estuary, Argentina

This study delves into the magnitude and attributes of plastic pollution in the salt marshes of the Bahía Blanca Estuary, Argentina, with a specific focus on its spatial distribution. The investigation included the evaluation of microplastics (1-5 mm), mesoplastics (5-25 mm) and macroplastics (25-100 mm), discovering elevated levels along the high salt marsh strandline compared to low salt marsh and mudflat areas. Notably, the abundance of plastic reached staggering levels, reaching up to 20,060 items/m2 in the vicinity of an illegal dumpsite. Microplastics, particularly in the 2-4 mm range, were dominant, and the main plastic components were high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), and polystyrene (PS). Plastic films emerged as the predominant plastic type, while the presence of pellets hinted at potential sources such as illegal dumping and port-related activities. This contamination could be largely attributed to inappropriate waste management practices and urban runoff, which pose a substantial ecological threat to these ecosystems. Urgent remedial action is essential to protect these marshes, underscoring the critical need for comprehensive wetland management and educational initiatives to ensure their long-term sustainability.

An overview of microplastic pollution in the environment over the megacity of Shanghai during 2013-2022

Microplastics (MPs) are emerging pollutants that have been globally found in the environment, and have become a focus of intensive management for the Shanghai government in China. Although there are several studies reporting the abundance of microplastics (MPs) in different matrices in Shanghai city, the general data are still limited. This work comprehensively reviews microplastic (MP) pollution in the water, sediment, atmosphere, and soil of Shanghai during 2013-2022. A summary of characteristics such as the abundance, shape, and polymer composition of MPs is presented. Additionally, the pollution trends, traceability, and ecological risks of MPs are analyzed and evaluated. Based on the analytical results, we find that the inland water in Shanghai city is the most contaminated with the highest abundance of MPs at 14.76 × 103 particles/m3 on average, while the abundances of MPs in the external water, inland sediment, external sediment, indoor atmosphere, outdoor atmosphere, inland soil, and external soil are 2.78 × 103 particles/m3, 0.80 × 103 particles/kg, 1.37 × 103 particles/kg, 0.03 × 103 particles/m3, 0.08 × 103 particles/m3, 0.27 × 103 particles/kg, and 0.18 × 103 particles/kg, respectively. Polyethylene and polypropylene are the top two detected polymer compositions of MPs. Results of ecological risk assessment using risk index and pollution load index models indicate that the risks of MPs in the water and sediment of the Yangtze Estuary are high. It is noteworthy that the abundances of MPs at the junction site of Suzhou Creek and the Huangpu River as well as in the Yangtze Estuary exhibited an increasing trend between 2017 and 2019. This work contributes to a comprehensive overview of MPs in the environment of Shanghai city during 2013-2022 and provides important data for local governments to develop urgent strategies for the management of MP pollution. However, more investigations are increasingly needed for better understand the production, migration, ecological risk, and management of MPs in the environment of Shanghai city.

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.

Microplastic contamination in water and sediments of Mahanadi River, India: An assessment of ecological risk along rural-urban area

Worldwide, environmental concerns about MPs pollution have increased. Microplastic contamination that pollutes the ocean is mostly caused by terrestrial transfer from close proximity locations. A study of MPs pollution near coastal locations becomes necessary to address the MPs transit, fate, and mitigation. In the current study MPs pollution in the surface water and sediment of the Mahanadi River estuary was assessed during Pre-MS and MS. The size, shape, and colour of the MPs were determined using a stereomicroscope, and the MPs polymer composition was identified by Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) spectroscopy. The mean concentration of MPs that were potentially discovered in water was 16.6 ± 5.2 and sediments 197.3 ± 5.4 during Pre-MS. In the MS observed mean abundance of MPs was 15.1 ± 5.4 in water and 164.6 ± 76.9 in sediments. The highest abundant size was smaller than 1 mm; the most prevalent shape were fibers followed by film and fragments; black and white was a prominent colour in water and sediments respectively. Polyesters (PEs), polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), polyamide (PA), Polystyrene (PS), and Polycarbonates (PC) were found in the analysis of the chemical composition of MPs in water and sediments samples. The calculated PLI value shows pollution load at category I, with polymer hazard levels at categories III, IV, and V, indicating very high risk. The current research results show that river inflows and fishing-related actions are probably the main causes of MPs pollution.

Microplastics distribution in river side bars: The combined effects of water level and wind intensity

Rivers are the main pathway for microplastics (MP) transport toward the ocean. However, the understanding of the processes involved in the deposition and mobilization of MP in rivers, specifically in sediment side bars (SB), remains very limited. The objectives of this study were: (i) to examine the effect of hydrometric fluctuations and wind intensity on the distribution of microplastics (MP < 5 mm) in the SB of large river (the Paraná River), (ii) to determine the characteristics of MP to infer their origin and fate, and (iii) to discuss potential similarities or differences between MP suspended in the water column and MP found in sediment. The SB and water column were sampled during the autumn, winter, and spring of 2018, and the summer of 2019 at different river discharges and wind intensities. >90 % of the MP items found were fiber of polyethylene terephthalate (PET; FT-IR analysis), the most common MP color was blue, and most were in the 0.5-2 mm size range. The concentration/composition of MP varied according to the river discharge and wind intensity. During the falling limb of the hydrograph when discharge is decreasing and sediments are exposed for short periods (13-30 days), MP particles transported by the flow were deposited on temporarily exposed SB, accumulating there in high densities (309-373 items/kg). However, during the drought, when sediments remained exposed for a long time (259 days), MP were mobilized and transported by the wind. During this period (no influence of the flow), MP densities significantly decreased on SB (39-47 items/kg). In conclusion, both hydrological fluctuations and wind intensity played a significant role in MP distribution in SB.

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.

Hydrostatic pressure drives microbe-mediated biodegradation of microplastics in surface sediments of deep reservoirs: Novel findings from hydrostatic pressure simulation experiments

Microplastics originate from the physical, chemical, or biological degradation of plastics in the environment. Once ingested by organisms at the bottom of the food chain, microplastics are passed on to organisms at higher trophic levels, posing a threat to human health. The distribution of microplastics and the metabolic pathways involved in their microbial degradation in surface sediments of drinking water reservoirs are still poorly understood. This study analyzed the occurrence patterns of microplastics and microbial community structure associated with microplastic biodegradation in surface sediments from a deep reservoir at various hydrostatic pressures. Based on the results of Fourier-transform and laser direct infrared spectroscopy, elevating the pressure resulted in altered sizes and shapes of microplastics in sediment samples with the presence of microorganisms. The influence of hydrostatic pressure on small-sized microplastics (20-500 μm) was pronounced. For instance, high pressure accelerated the breakdown of fibers, pellets, and fragments into smaller-sized microplastics. In particular, the mean size of polyethylene terephthalate microplastics decreased from 425.78 μm at atmospheric pressure to 366.62 μm at 0.7 Mpa. Metagenomic analysis revealed an increase in the relative abundances of plastic-degrading genera, such as Rhodococcus, Flavobacterium, and Aspergillus, in response to elevated pressures. Eight functional genes for biodegradation of polystyrene, polyethylene, and polyethylene terephthalate microplastics were annotated, including paaK, ladA, tphA3. Of these, tphA3 gene abundance was negatively influenced by hydrostatic pressure, providing direct evidence for the pathway by which microbial metabolism of polyethylene terephthalate led to decreased microplastic size under high pressure conditions. This study presents novel insights into hydrostatic pressure-driven microbial community structure, functional gene abundance, and key metabolic pathways associated with biodegradation of microplastics in reservoir sediments.

Distribution and characteristics of microplastics in sediment at representative dredged material ocean dumping sites, China

Dredged material ocean dumping activities are likely an important source of microplastics (MPs) in coastal areas but have received little attention globally. In this study, we investigated the spatiotemporal distribution and characteristics of MPs in sediments at eight dredged material dumping sites of China. MPs were separated from sediment through density flotation, and polymer types were identified using μ-FTIR. The results showed that the average MP abundance was 112.82 ± 109.68 items/kg d.w. The MPs were more abundant at nearshore dumping sites than at distant dumping sites. Dumping activities may be the main contributor of MPs to Site BD1, the farthest dumping site from shore, but only a minor source of MPs at the other dumping sites. The characteristics of MPs were dominated by transparent PET fibers <1 mm. Overall, sediments at the dumping sites exhibited relatively low to moderate concentrations of MPs in comparison to most other coastal sediments.

Impact of persistent rain on microplastics distribution and plastisphere community: A field study in the Pearl River, China

Microplastic contamination is a global problem which has been threatening human health and the environment. There is still a knowledge gap about the effect of persistent rain on microplastics distribution and plastisphere community in fluvial environments. In this study, the abundance and composition of microplastics in the sediment and surface water from the Pearl River was investigated. Thirty polymers (10-500 μm) were identified from thirty-eight samples collected at ten sites using the newly developed laser direct infrared (LDIR) technique. The average concentrations of microplastics in the sediment and surface water were 1974 particles kg^-1 and 290 particles L^-1, respectively. Abnormally high concentrations of polyurethanes (PU) were possibly due to particulate pollution from ship antifouling. The persistent rain increased the abundance and diversity of microplastics in the surface water, whereas an opposite trend was observed in the sediment. Sediments could temporarily switch from microplastics sinks to potential sources under the effect of violent hydrodynamic disturbances. Additionally, plastisphere communities and predicted functional profiles indicated significant differences before and after the rain. Our study highlights the important impact of persistent rain on microplastic contamination in the environment.

Recent advances towards micro(nano)plastics research in wetland ecosystems: A systematic review on sources, removal, and ecological impacts

In recent years, microplastics/nanoplastics (MPs/NPs) have received substantial attention worldwide owing to their wide applications, persistence, and potential risks. Wetland systems are considered to be an important "sink" for MPs/NPs, which can have potential ecological and environmental effects on the ecosystem. This paper provides a comprehensive and systematic review of the sources and characteristics of MPs/NPs in wetland ecosystems, together with a detailed analysis of MP/NP removal and associated mechanisms in wetland systems. In addition, the eco-toxicological effects of MPs/NPs in wetland ecosystems, including plant, animal, and microbial responses, were reviewed with a focus on changes in the microbial community relevant to pollutant removal. The effects of MPs/NPs exposure on conventional pollutant removal by wetland systems and their greenhouse gas emissions are also discussed. Finally, current knowledge gaps and future recommendations are presented, including the ecological impact of exposure to various MPs/NPs on wetland ecosystems and the ecological risks of MPs/NPs associated with the migration of different contaminants and antibiotic resistance genes. This work will facilitate a better understanding of the sources, characteristics, and environmental and ecological impacts of MPs/NPs in wetland ecosystems, and provide a new perspective to promote development in this field.

Recent advances in micro (nano) plastics in the environment: Distribution, health risks, challenges and future prospects

Environmental micro(nano)plastics have become a significant global pollution problem due to the widespread use of plastic products. In this review, we summarized the latest research advances on micro(nano)plastics in the environment, including their distribution, health risks, challenges, and future prospect. Micro(nano)plastics have been found in a variety of environmental media, such as the atmosphere, water bodies, sediment, and especially marine systems, even in remote places like Antarctica, mountain tops, and the deep sea. The accumulation of micro(nano)plastics in organisms or humans through ingestion or other passive ways poses a series of negative impacts on metabolism, immune function, and health. Moreover, due to their large specific surface area, micro(nano)plastics can also adsorb other pollutants, causing even more serious effects on animal and human health. Despite the significant health risks posed by micro(nano)plastics, there are limitations in the methods used to measure their dispersion in the environment and their potential health risks to organisms. Therefore, further research is needed to fully understand these risks and their impacts on the environment and human health. Taken together, the challenges of micro(nano)plastics analysis in the environment and organisms must be addressed, and future research prospects need to be identified. Governments and individuals must take action to reduce plastic waste and minimize the negative impact of micro(nano)plastics on the environment and human health.

Plastic wastes and surface antibiotic resistance genes pollution in mangrove environments

Mangroves are located at the intersection of land and sea and are also heavily affected by plastic wastes. Biofilms of plastic wastes in mangroves are reservoirs for antibiotic resistance genes (ARGs). In this study, plastic wastes and ARG pollution were investigated from three typical mangrove areas in Zhanjiang, South China. Transparent was the dominant colors of plastic wastes in three mangroves. Fragment and film shape accounted for 57.73-88.23% of plastic waste samples in mangroves. In addition, 39.50% of plastic wastes in protected area mangroves are PS. The metagenomic results shows that the 175 ARGs were found on plastic wastes of the three mangroves, the abundance accounting for 91.11% of the total ARGs. The abundance of Vibrio accounted for 2.31% of the total bacteria genera in aquaculture pond area mangrove. Correlation analysis shows that a microbe can carry multiple ARGs that may improve resistance to antibiotics. Microbes are the potential hosts of most ARGs, suggesting that ARGs can be transmitted by microbes. Because the mangroves are closely related to human activities and the high abundance of ARGs on plastic increases the ecological risks, people should improve plastic waste management and prevent the spread of ARGs by reducing plastic pollution.

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.

Atmospheric microplastics at a southern China metropolis: Occurrence, deposition flux, exposure risk and washout effect of rainfall

Atmospheric microplastics (AMPs) have raised much concern for public health due to their potential for exposure. In this study, temporal distribution, characteristics and exposure risk of AMPs were studied in the urban area of Guangzhou, a metropolis in Southern China, and the washout effect of rainfall on AMPs was investigated. It was found that AMP abundances in Guangzhou were in a range of 0.01-0.44 items/m³, with higher abundance in the wet season (0.19 ± 0.01 items/m³) than in the dry season (0.15 ± 0.02 items/m³). The distribution of AMPs did not correspond to that of common air pollutants (e.g., PM_2.5 and PM₁₀), implying that their pollution sources might be distinct. In Guangzhou, a total of 1.26 × 10¹¹ items AMPs are in the air every year, and annual inhalation exposure of adults was estimated to be in the range of 79.65-3.50 × 10³ items. The annual deposition flux of AMPs is 65.94 ± 7.53 items/m²/d, and the deposition flux in the wet season (84.00 ± 6.95 items/m²/d) was much greater than that in the dry season (47.88 ± 8.35 items/m²/d). Furthermore, rainfall has an effective mechanism for removing AMPs from the atmosphere, with an average washout ratio of (19.39 ± 6.48) × 10⁴ for rainfall washing AMPs out. Compared to moderate rain (2.5-10 mm/h) and heavy rain (10-50 mm/h), light rain (rainfall intensity <2.5 mm/h) had a better washout effect. This study contributes to the evaluation of AMP exposure risk and understanding of AMP environmental behavior and fate by providing long-term monitoring data on AMPs and quantifying the washout effect of rainfall on AMPs for the first time.

Characterization of microplastic pollution in the Pasur river of the Sundarbans ecosystem (Bangladesh) with emphasis on water, sediments, and fish

An emerging concern of today's world, due to their universal dispersion worldwide, is the environment's microplastic pollution. The Sundarbans, the world's largest mangrove, have unique and dynamic environmental settings with numerous pollution risk exposures, including microplastics (MPs). Thus, the present study has focused on the MP pollution in water, sediment, and fish samples of the Sundarbans of Bangladesh for the first time. Water and sediment samples were collected (n = 30/each) from sampling locations along the Pasur river (Bangladesh). Furthermore, nine species of fish samples were collected from a local fish market situated at the Mongla port. Results show that 100 % of the analyzed samples have evidence of MPs. On average, 2.66 × 10³ plastic particles/L and 1.57 × 10⁵ particles/kg were found in water and sediment samples, respectively. Furthermore, results show a higher number of MPs in the animals' gastrointestinal tract (GIT) (10.41 particles/g), concerning the average concentration recorded in the muscles (4.68 particles/g). O. pama and H. nehereus were the species that showed the highest MPs accumulation in the GIT. In the muscles, the highest MP levels were observed in T. ilisha and L. calcarifer. Most of the particles were smaller than 1 mm; black-colored particles dominated the pool. FT-IR analysis revealed the presence of seven polymer types where polyamide was abundant in water and sediment samples. SEM analysis showed morphological structures and adsorbed particles on the surface of plastic samples, and the spatial distribution of MPs indicates that the location with high human intervention has elevated levels of MPs. Therefore, our study demonstrates that Sundarbans mangrove forests are highly contaminated with MPs and that its fisheries can be a potential source of human exposure to these pollutants.

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.

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.

Understanding the underestimated: Occurrence, distribution, and interactions of microplastics in the sediment and soil of China, India, and Japan

Microplastics (MPs) are non-biodegradable substances that can sustain our environment for up to a century. What is more worrying is the incapability of modern technologies to annihilate MPs from om environment. One ramification of MPs is their impact on every kind of life form on this planet, which has been discussed ahead; that is why these substances are surfacing in everyday discussions of scholars and researchers. This paper discusses the overview of the global occurrence, abundance, analysis, and remediation techniques of MPs in the environment. This paper primarily reviews the event and abundance of MPs in coastal sediments and agricultural soil of three major Asian countries, India, China, and Japan. A significant concentration of MPs has been recorded from these countries, which affirms its strong presence and subsequent environmental impacts. Concentrations such as 73,100 MPs/kg in Indian coastal sediments and 42,960 particles/kg in the agricultural soil of China is a solid testimony to prove their massive outbreak in our environment and require urgent attention towards this issue. Conclusions show that human activities, rivers, and plastic mulching on agricultural fields have majorly acted as carriers of MPs towards coastal and terrestrial soil and sediments. Later, based on recorded concentrations and gaps, future research studies are recommended in the concerned domain; a dearth of studies on MPs influencing Indian agricultural soil make a whole sector and its consumer vulnerable to the adverse effects of this emerging contaminant.

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.

Toxic effects of polystyrene microplastics on the intestine of Amphioctopus fangsiao (Mollusca: Cephalopoda): From physiological responses to underlying molecular mechanisms

Microplastics are broadly used and among the most studied environmental pollutants due to their potential impacts on organisms and human health. Amphioctopus fangsiao (Cephalopoda: Octopodidae) is an important commercial species in the Pacific Northwest and is very popular among consumers owing to its rich nutritional value and fresh flavor. However, the toxic effects of microplastic exposure on A. fangsiao, including phenotypical effect and underlying molecular mechanism, remain limited. In this study, the octopus A. fangsiao were exposed to microplastics (polystyrene microplastics, Micro-PS) at concentrations of 100 and 1000 μg/L for 21 days, and then the physiological response, histopathological analysis, biomarkers of oxidative stress and glycolipid metabolism, microbiome perturbations and transcriptomic profiles in the intestines were performed. Results demonstrated that Micro-PS exposure had distinct adverse effects on the food intake of A. fangsiao. Histological analysis revealed that Micro-PS exposure has resulted in histopathological damage, thus causing early inflammation of the intestine. Oxidative stresses, metabolic disorders and microbiome perturbations were also detected in the intestine of A. fangsiao based on physiological biomarkers and microbiome analyses. Moreover, transcriptome analysis detected the differentially expressed genes (DEGs) and significantly enriched KEGG pathways in response to oxidative stress, glycolipid metabolism, DNA damage and transmembrane transport of intestinal cells, revealing distinct toxic effects at the molecular level. In summary, Micro-PS exposure has a strong impact on the intestines of A. fangsiao. For the first time, this study uses multiple approaches based on the physiological and biochemical response as well as transcriptional regulation analysis. The first assessment of the toxic impact of this species under Micro-PS exposure is also reported.

A review of sources, status, and risks of microplastics in the largest semi-enclosed sea of China, the Bohai Sea

The largest semi-enclosed sea of China, the Bohai Sea, serves as an important sink of microplastics (MPs) originated from terrestrial and marine sources. This study summarized potential sources and migration pathways of MPs in the Bohai Sea and reviewed the abundance and characteristics of MPs in water, sediments, and organisms. Coastal anthropogenic activities (i.e., plastic production, agricultural activities, and industrial and domestic sewage discharge) and marine origins (i.e., aquaculture, marine litters, and transportation) might accelerate the MPs enrichment in the Bohai Sea. The abundance of MPs ranged from 0.07 to 5200 items/m³ in the seawater, mainly influenced by the application of different trawl nets/sieves with different sizes (0.005-0.33 mm). Sediments of coastal rivers contained the MPs ranging from 56.7 to 1795 items/kg, significantly higher than that of the Bohai Sea (6.24-461.6 items/kg). Among organisms, the average abundance of MPs was the lowest in zooplanktons (0.03 items/animal), significantly lower than that in invertebrates (1.39 items/animal) and fish (2.12 items/animal), but no biomagnification of MPs was observed. The preliminary risk assessment indicated that seawater in the Liaodong Bay had medium ecological risk of MPs while other bays of the Bohai Sea had minor risks. To make the ecological risk of MPs quantifiable and comparable, future research priorities are recommended to focus on more frequent field surveys, standardization of sampling methods, and establishment of toxicity database of common polymer types of MPs in the Bohai Sea.

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.

Distribution pattern and influencing factors for the microplastics in continental shelf, slope, and deep-sea surface sediments from the South China Sea

Marine microplastic pollution has become a major global concern in recent years and the fate of microplastics in the ocean is a hot issue of research. We investigated microplastic pollution in surface sediments in the northern South China Sea to explore its distribution characteristics and influencing factors across the continental shelf, continental slope, and deep-sea environments. It was found that the microplastic abundance of surface sediments was 130.56 ± 40.48 items/kg. The average abundance of microplastics in all three topographic areas gradually decreased with increasing distance offshore. However, the differences in microplastic diversity indices between the three areas were not significant and were higher than those in other seas of the world, indicating that the waters of the northern South China Sea are rich in microplastics from complex sources, with more pollution input channels. In the continental shelf, fibrous and low density microplastics accounted for the largest amount, with a low degree of microplastic aging, and were mostly transported by suspended-load. These microplastics were mainly influenced by human activities. In the deep sea, microplastics with higher density were the most abundant and the number of fibrous microplastics was fewer, while the average size was larger, mainly influenced by the bottom currents. These microplastics underwent long-term bedload transport. In the continental slope, the main factors affecting the distribution of microplastics were more complex. In addition to pollution by human activities, the slope also receives microplastic materials carried by bottom currents; therefore, the composition of microplastics in the slope combines those characteristics of microplastics in both the continental shelf and deep-sea areas. The findings of this study indicate that the South China Sea is affected by complex pollution sources under the dual effects of human activities and natural conditions; in particular, the pollution situation in the deep-sea area needs extensive attention.

Critical effect of biodegradation on long-term microplastic weathering in sediment environments: A systematic review

Microplastic (MP) pollution in global sediment has been intensely studied and recognized as the ultimate sink for residual MPs in terrestrial and aquatic ecosystems. During MP long-term retention in sediments, plastic-degrading bacteria (i.e., Flavobacteriaceae, Bacillus, Rhodobacteraceae, and Desulfobacteraceae) can utilize those MPs as their carbon and energy sources through enzyme (hydrolase and oxidoreductase) reactions, which further alter or transform high molecular weight MP polymers into lower molecular weight biodegradation byproducts (i.e., monomers and oligomers) and release toxic additives. In other words, MPs can act as durable substrates for plastic-degrading bacteria in sediments. However, to date, the biodegradation rates of MPs in sediment environments are still poorly understood due to their limited degradation efficiency. Herein, we review the enzyme-induced biodegradation processes of MPs in sediment environments, which is important for accessing the alteration of MP properties and their potential ecological risks after undergoing long-term weathering processes. In addition, the factors associated with the MP properties (polymer type, molecular weight, crystallinity, and hydrophobicity) and sediment conditions (sediment type, temperature, pH, salinity, and oxygen content) that influence plastic degradation processes are also reviewed. The mechanisms may relate to the MP properties and sediment conditions that can influence microbial abundance, enzyme concentrations, and enzyme activities, thus altering MP biodegradation ratios. We anticipate that the observations reviewed in this study will pose a new issue to better understand the formation process, fate, and potential ecological risks associated with aged MPs in sediment environments.

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.

Impact of the surrounding environment on antibiotic resistance genes carried by microplastics in mangroves

The pollution of antibiotic resistance genes (ARGs) carried by microplastics (MPs) is a growing concern. Mangroves are located at the intersection of land and sea and are seriously affected by MP pollution. However, few studies have systematic research evaluating the transmission risk of ARGs carried by MPs in mangroves. We conducted in situ experiments by burying five different MPs (polypropylene, high-density polyethylene, polystyrene, polyethylene glycol terephthalate, and polycaprolactone particles) in mangroves with different surrounding environments. A total of 10 genes in the MPs of mangroves were detected using quantitative real-time polymerase chain reactions, including eight ARGs and two mobile genetic elements (MGEs). The abundance of ARGs in Guanhai park mangroves in living areas (GH) was higher than that of Gaoqiao mangroves in protected areas (GQ) and Beiyue dike mangroves in aquaculture pond areas (BY). Pathogenic bacteria, such as Acinetobacter, Bacillus, and Vibrio were found on the MP surfaces of the mangroves. The number of ARGs carried by multiple drug-resistant bacteria in the GH mangroves was greater than that in the GQ and BY mangroves. Moreover, the ARGs carried by MPs in GH mangroves had the highest potential transmission risk by horizontal gene transfer. Sociometric and environmental factors were the main drivers shaping the distribution characteristics of ARGs and MGEs. Polypropylene and high-density polyethylene particles are preferred substrates for obtaining diffuse ARGs. This study investigated the drivers of ARGs in the MPs of mangroves and provided essential guidance on the use and handling of plastics.

Effects of microplastics on greenhouse gas emissions and microbial communities in sediment of freshwater systems

Microplastics can regulate greenhouse gas emissions from environmental systems and affect microbes in the environment. However, the effect of microplastics in freshwater sediment system is still not well studied. In this paper, polyethylene terephthalate (PET) particles with six different diameters of 5-2000 µm were added to freshwater sediment, PET exposing for 90 days was carried out and its effect on greenhouse gas emissions, nutrients cycle and microbial communities were studied. In the 5 µm experimental group, carbon dioxide (CO₂) emissions were significantly promoted in the 7-30 days and nitrogen monoxide (N₂O) emissions were significantly promoted in the 7 days after cultivation. Microplastics in the range of 300-800 µm significantly promoted CO₂ emissions after three days of culture. In addition, microplastics increased the total organic carbon (TOC) content in freshwater sediment and changed microbial diversity, especially increased the microorganisms capable of degrading complex organics such as Saprospiraceae. There was a positive correlation between N₂O emission and nitrate (NO₃^-) content in sediment after 3 days of culture, while greenhouse gas emission was mainly related to TOC content after 90 days of culture. These results showed that microplastics could affect the carbon and nitrogen cycling process of shallow lake ecosystem.

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.

Microplastics in the Gulf of Mexico: A Bird’s Eye View

Microplastic debris is a persistent, ubiquitous global pollutant in oceans, estuaries, and freshwater systems. Some of the highest reported concentrations of microplastics, globally, are in the Gulf of Mexico (GoM), which is home to the majority of plastic manufacturers in the United States. A comprehensive understanding of the risk microplastics pose to wildlife is critical to the development of scientifically sound mitigation and policy initiatives. In this review, we synthesize existing knowledge of microplastic debris in the Gulf of Mexico and its effects on birds and make recommendations for further research. The current state of knowledge suggests that microplastics are widespread in the marine environment, come from known sources, and have the potential to be a major ecotoxicological concern for wild birds, especially in areas of high concentration such as the GoM. However, data for GoM birds are currently lacking regarding typical microplastic ingestion rates uptake of chemicals associated with plastics by avian tissues; and physiological, behavioral, and fitness consequences of microplastic ingestion. Filling these knowledge gaps is essential to understand the hazard microplastics pose to wild birds, and to the creation of effective policy actions and widespread mitigation measures to curb this emerging threat to wildlife.

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.

Microplastics in Freshwater Environment in Asia: A Systematic Scientific Review

Microplastics (MPs) are an emerging pollutant in the aquatic environment, and this has gradually been recognized in the Asian region. This systematic review study, using the Scopus database, provides an insightful understanding of the spatial distribution of scientific studies on MPs in freshwater conducted across the Asian region, utilized sampling methods, and a detailed assessment of the effects of MPs on different biotic components in freshwater ecosystems, with special focus on its potential risks on human health. The results of this review indicate that research on microplastics in Asia has gained attention since 2014, with a significant increase in the number of studies in 2018, and the number of scientific studies quadrupled in 2021 compared to 2018. Results indicated that despite a significant amount of research has been conducted in many Asian countries, they were not distributed evenly, as multiple studies selected specific rivers and lakes. Additionally, around two-thirds of all the papers focused their studies in China, followed by India and South Korea. It was also found that most of the studies focused primarily on reporting the occurrence levels of MPs in freshwater systems, such as water and sediments, and aquatic organisms, with a lack of studies investigating the human intake of MPs and their potential risks to human health. Notably, comparing the results is a challenge because diverse sampling, separation, and identification methods were applied to estimate MPs. This review study suggests that further research on the dynamics and transport of microplastics in biota and humans is needed, as Asia is a major consumer of seafood products and contributes significantly to the generation of plastic litter in the marine environment. Moreover, this review study revealed that only a few studies extended their discussions to policies and governance aspects of MPs. This implies the need for further research on policy and governance frameworks to address this emerging water pollutant more holistically.

Study of microplastics pollution in sediments and organisms in mangrove forests: A review

Microplastics (MP) are an emerging and lesser-known pollutant that has attracted the attention of researchers around the world in recent decades. Size of PM is smaller than 5 mm and can be entered in different ways into marine environments like mangrove forests and interfere with the health of the environment and organisms. The present study reviews 53 studies in the field of microplastics in different parts (sediments and organisms) of mangrove forests. About 26% of the 53 studies was published in 2020. In most studies, MP particles were categorized based on the shape, color, size, and polymer genus. The number of microplastics per kilogram of mangrove sediments has been reported as 1.22-6390. The effect of sediment texture on the frequency of microplastic particles and the relationship between sediment pH and MP abundance were also discussed. The fiber and bright color PMs were more common in living organisms (mollusks, crustaceans, and fish). The PM particles with different genus (polypropylene, polyethylene, polystyrene, and polyethylene terephthalate) were reported for sediment samples. In sediments with smaller sizes and lower pH, microplastics have been detected more frequently. It was reported that sediments and roots of mangrove forests act as livestock and retain microplastics for a long time. The highest concentration of MP in different parts of mangrove forests (sediment and organisms) has been reported for China. Few reports were observed on microplastics in water in mangrove forests. Also, the concentration of microplastics in sediments and organisms in mangrove forests exposed to fishing, coastal tourism, urban, and industrial wastewater was higher than those in pristine areas. It is necessary to conduct comprehensive studies to monitor, control, and evaluate the MP pollution in sediments and various organisms in mangrove forests worldwide.

Effects of Microplastics on Microbial Community in Zhanjiang Mangrove Sediments

Microplastics are easily consumed by marine animals, thereby entering the food chain and endangering animal health. However, there are few studies focusing on the effects of microplastics in mangrove sediments on microbial communities. In order to study the influence of microplastics on microorganisms, microplastics and microorganisms were extracted from Zhanjiang (Guangdong Province, China) mangrove sediments and analyzed. The results showed that there were differences in Shannon and Simpson indices of the microbial community in microplastics (p < 0.05), and there were also differences between JG30_KF_CM45 and Natranaerovirga at the genus level, indicating that microplastics may affect the diversity and composition of microorganisms in sediments. In addition, FAPROTAX function prediction analysis showed that microplastics may affect the nitrification of microbial communities. The results from this study indicate that microplastics affected the diversity and richness of microorganisms in mangrove sediments, which provides an experimental basis for the relationship between microplastics and microorganisms.

An enhanced risk assessment framework for microplastics occurring in the Westerscheldt estuary

Microplastics (MPs) pollution in the aquatic environment raises considerable concerns. Freshwater system is generally considered as an important source for MPs transformation into the marine environment, however, only limited data on the MPs pollution in global freshwater systems is available at this time. In this study, we explored the abundance, characteristics and distribution of microplastics in the Scheldt River. The investigation results indicated that the abundance of microplastics in sediments (15-413 items/kg dry weight (DW)) was much higher than that in surface water (0-113 items/m³), and small size MPs (less than 500 μm) frequently appeared in sediments. Industrial activities were regarded as the major cause of MP discharging. Risk assessment models with using data of the concentration of MPs, polymer types and toxicity of MPs exposure were developed to assess the risk of MPs pollution in both surface water and sediment of the Westerscheldt estuary. Risk assessment results revealed that MPs exposure have potentially adverse effects on the aquatic ecosystem and human health. MPs tend to be transported from "Hotspots", such as urban or industries area, to remote areas. The risk assessment of MPs serves as a baseline for better understanding the distribution and characteristics of MPs and highlights the need of intensively monitoring to limit MPs release by intensively monitoring. This research provides a perspective on the risk of MPs that could be used in future studies.

Microplastic in the coral reef environments of the Gulf of Mannar, India - Characteristics, distributions, sources and ecological risks

Microplastics (MPs; particles <5 mm) are widely distributed in various habitats from the land to the oceans. They have even reached the remotest of places, including the deep seas and Polar Regions. Although research on MPs pollution in the marine environment has received widespread attention in recent years, the distribution, sources and ecological risks of MPs in coastal areas remain unclear. This study assessed the abundance, characteristics, sources and ecological risk of MPs in surface waters and sediment of the mainland coast and four island groups comprising the coral reef environment of the Gulf of Mannar (GoM), southeast India. Mean MPs abundance across all 95 sampling sites ranged from 28.4 to 126.6 items L^-1 in water and from 31.4 to 137.6 items kg^-1 in sediment. MP fibers <2 mm dominated the water, while fragments >3 mm were predominant in sediments. Polyethylene (PE) and polypropylene (PP) were the most common polymers in both matrices. The major proportion of MPs in the GoM derived from land-based sources, with distance to the mainland, coastal population density and improper handling of solid waste being the main factors influencing the abundance of MPs. Polymer Hazard Index (PHI), Pollution Load Index (PLI) and Potential Ecological Risk Index (PERI) were used to assess current levels of MPs. While the GoM has high PHI values (>1000) resulting from MPs with high hazard scores (e.g. polyamide, polystyrene, polyvinyl chloride), the PLI values (1.46 and 1.51) indicate low MPs pollution levels in GoM waters and sediments, and the PERI values (31.7 and 24.4) indicate that this represents a minor ecological risk. The results from the current study enhance our understanding of the characteristics, sources, and associated environmental risks of MPs to marine ecosystems. This data may provide a baseline for future monitoring and the formulation of environmental policy.

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.

Microplastics in equatorial coasts: Pollution hotspots and spatiotemporal variations associated with tropical monsoons

Microplastics (MP < 5 mm) are eroding oceanic health and coastal development at a planetary scale. Coastlines in Southeast Asia (SEA) are plagued with plastic litters, but how MP are dispersed within SEA region is poorly understood, which can vary dramatically under the tropical climate. We systematically quantified MP in equatorial Singapore, to assess how prevailing Monsoons and other factors impact MP distributions in beaches and mangroves. Data highlighted spatial preponderance differed broadly by seasons (p < 0.05) and were strongly modulated by wind speediness (p < 0.05; r = 0.6-0.7) and promoted transboundary migrations of MP. Conversely, an inverse relationship existed between sediment MP and rainfall (r = -0.54) possibly due to re-entrainment of surficial MP. Elevated concentrations in mangrove's compartments (p < 0.05) suggest effective repository hotspots. Coastal MP consisted assorted morphologies and commonest polymers including 34% polypropylene (PP), 26% polyethelene (PE), and 23% Low Density PE. Further comparisons revealed coastal MP in Singapore accelerated by two orders of magnitude since 2014, implying cumulative pollution which is not reversible. We synthesized the first seasonal coastal MP report in SEA which is useful for source apportionment, prediction study, and mitigation planning under tropical circumstances.

Distribution, characteristics, and human exposure to microplastics in mangroves within the Guangdong-Hong Kong-Macao Greater Bay Area

In this study, three mangroves in the Guangdong-Hong Kong-Macao Greater Bay Area- Qi'ao Island in Zhuhai, Nansha in Guangzhou, and Futian in Shenzhen-were selected for investigating the distribution of microplastics and their characteristics The average microplastic abundance in each descended in the order: Futian (1600 n/kg) > Nansha (1100 n/kg) > Qi'ao Island (440 n/kg), with values from the forest fringe being significantly higher than those in the forest interior. The microplastics were mainly fibers, 1-5 mm in size, and white/black in color; they consisted of polypropylene and polyethylene, with foam and polystyrene accounting for a high proportion in Nansha. The exposure of humans to microplastics in the Futian forest fringe reached 35.95 ng/d·kg; it was one order of magnitude higher than the exposures in Qi'ao Island and Nansha. Furthermore, ingestion accounted for approximately 74% of the total exposure to the human body, dermal contact constitutes 25%, and sediment inhalation accounted for less than 1%.

Prevalence of microplastic fibers in the marginal sea water column off southeast China

Microplastic (MP) fibers are present in all environmental media, yet little is known about their distribution, sources, and transport in the water column of marginal seas. In this study, we conducted an intensive sampling campaign in the marginal sea water column off southeast China, which is an area that is greatly influenced by high MP emissions. We found that hydrological effects largely regulated the spatial variations of MP fiber distribution and that MP fibers likely were not entering the South China Sea through terrestrial input from southeast China during the summer monsoon. Polyethylene terephthalate (PET) fibers were pervasive in the surface water (SW) (89.47%), subsurface chlorophyll maximum layer (SCML) (92.65%), and bottom water (BW) (94.29%) of the water column during the sampling period. Approximately 32% of MP fibers in the samples were smaller than 330 μm. The abundance of MP fibers in SW was significantly lower than that in the SCML and BW. Based on this observation, we estimated the inventory of MP fibers in the SW, SCML, and BW of the sampling area to be 1.377-1.378, 2.820-2.825, and 2.627-2.629 metric tons, respectively. These results improved our understanding of the source-to-sink process of MP fiber contamination in the water column of marginal seas.