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

Estuarine plastic dynamics: Analyzing export patterns from a typical semi-enclosed bay in Asia

Semi-enclosed estuarine systems are recognized as hotspots for microplastic (MP) pollution, yet their export dynamics remain poorly understood. This study investigates the distribution of microplastics (<5 mm) and macroplastics (>5 mm) in Sanya Bay, a typical semi-enclosed bay in southern China. Based on 45 surface water samples, MP concentrations ranged from 0.298 to 4.010 items/m³ (mean: 1.628 ± 1.055), significantly higher than macroplastics (mean: 0.109 ± 0.338 items/m³). Most particles were fragments smaller than 5 mm, dominated by white, green, and transparent colors. The main polymers identified were polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET). A "dual-center" pattern was observed: low-density plastics (e.g., PP, PE) accumulated near river mouths and offshore islands, while high-density plastics (e.g., PET, PVC) settled in estuarine zones. Principal Coordinate Analysis (PCoA) revealed spatial clustering across estuarine, coastal, and offshore areas, influenced by land-based inputs, human activity, and hydrodynamic transport. This study provides new insights into plastic transport mechanisms in semi-enclosed bays and highlights the importance of integrating plastic properties with environmental forces. The findings support targeted pollution management in similar coastal environments.

Modeling the spatiotemporal distribution, bioaccumulation, and ecological risk assessment of microplastics in aquatic ecosystems: A review

Microplastic (MP) pollution poses a significant threat to aquatic ecosystems. Numerical modeling has emerged as an effective tool for predicting the distribution, accumulation, and risk assessment of MPs in aquatic ecosystems. However, published work has not systematically assessed the strengths and weaknesses of various modeling approaches. Therefore, we conducted a thorough review of the main modeling approaches for MPs over the past six years. We classified the approaches into three categories as: spatial and temporal distribution, bioaccumulation, and systematic ecological risk assessment. The review analyzed application scenarios, modeling methods, and the advantages and disadvantages of models. The results indicate that the accurate simulation of MPs spatial and temporal distribution requires reasonable parameterization and comprehensive transport considerations. Meanwhile, it is important to focus on coupling process models with other types of models. To enhance risk assessment models, expanding the relevant evaluation indicators is essential.

Microplastic distribution and risk assessment in estuarine systems influenced by traditional villages and artisanal fishery activities

Microplastics (MPs) are widespread in oceans worldwide, posing a significant threat to aquatic ecosystems. The abundance of these particles in water is related to population density and urban development, functioning as a sink for MPs. However, the pollution levels due to the accumulation of MPs in the estuarine in Amazonian mangrove areas remain unknown. Here, we show that population density and fishing activities influence the distribution of MP pollution in these waters. We found the highest abundance of MPs in the inner (1.03 items/m3) and outer (0.82 items/m3) portions of the estuary, corresponding to the areas with the highest population density and fishing activity, respectively. The main morphological characteristics of MPs are fibers (89.8%), blue color (55.2%), and size of 1000-2000 μm (31.7%). The risk analysis showed a low level of danger, suggesting that the potential impact on the ecosystem is still small. Our results demonstrate that the presence of human populations and their fishing activities significantly influence the accumulation of MPs in the estuarine waters on the Amazon coast. Based on our findings, more sophisticated analysis using MPs' spatial distribution models can be associated with hydrodynamic processes, aiming to define pollution hotspots and support the mitigation of their emerging negative effects. In addition, monitoring and generating valuable information are the main targets for developing comprehensive strategies to preserve biodiversity and sustainability in the Amazon coastal zone.

Spatial distribution and risk assessment of microplastics in surface waters of the St. Lawrence Estuary

Development of effective prevention and mitigation strategies for marine plastic pollution requires a better understanding of the pathways and transport mechanisms of plastic waste. Yet the role of estuaries as a key interface between riverine inputs of plastic pollution and delivery to receiving marine environments remains poorly understood. This study quantified the concentration and distribution of microplastics (MPs) (50-3200 μm) in surface waters of the St. Lawrence Estuary (SLE) in eastern Canada. Microplastics were identified and enumerated based on particle morphology, colour, and size class. Fourier Transform Infrared (FTIR) spectroscopy was used on a subset of particles to identify polymers. Generalized linear models (Gamma distribution with log-link) examined the relationship between MP concentrations and oceanographic variables and anthropogenic sources. Finally, a risk assessment model, using MP concentrations and chemical hazards based on polymer types, estimated the MP pollution risk to ecosystem health. Mean surface MP concentration in the SLE was 120 ± 42 SD particles m-3; MP concentrations were highest in the fluvial section and lowest in the Northwest Gulf of St. Lawrence. However, MP concentrations exhibited high heterogeneity along the length and width of the SLE. Microplastics were elevated at stations located closer to wastewater treatment plant outflows and downstream sites with more agricultural land. Black, blue, and transparent fibers and fragments ≤250 μm were most commonly encountered. Predominant polymer types included polyethylene terephthalate, regenerated cellulose, polyethylene, and alkyds. While the overall risk to ecosystem health in the entire estuary was considered low, several stations, particularly near urban centres were at high or very high risk. This study provides new insights into the quantification and distribution of MPs and first estimates of the risk of MP pollution to ecosystem health in one of the world's largest estuaries.

Microplastic contamination in three environmental compartments of a coastal lagoon in the southern Gulf of Mexico

The Sontecomapan lagoon (Mexico) is a Ramsar site within the Los Tuxtlas Biosphere Reserve, facing the Gulf of Mexico. Although the site has a protected area status, it is vulnerable to microplastic contamination, whose long-term effects are uncertain. This study gives the first approach to the degree of contamination by microplastics in surface waters, zooplankton, and sediments in the lagoon. The samples in these three environmental compartments were collected in June 2018 and analyzed in the laboratory to extract and quantify the microplastics. The microplastics sampled were classified into fibers, fragments, and foams and identified as polyester, acrylic, and rayon, among others. In the surface waters, the mean concentration of microplastics was 7.5 ± 5.3 items/L, which is higher than the values registered in other protected coastal systems, perhaps because of differences in the methods used. Zooplankton, represented by copepods, luciferids, and chaetognaths, showed concentrations of 0.002 ± 0.005, 0.011 ± 0.011, and 0.019 ± 0.016 items/individual, respectively. These values were low compared to systems with high anthropic influence, and the differences between the three kinds of organisms were attributed to their feeding habits. In the sediments, the mean concentration was 8.5 ± 12.5 items/kg, lower than the values registered in sites of high human impact; the maximum value here found (43 items/kg) was recorded in the internal part of a lagoon arm of almost stagnant water. In general, the degree of contamination by microplastics in the lagoon was low; however, their presence indicates a potential risk to the biota.

Microplastics in riverine systems: Recommendations for standardized sampling, separation, digestion and characterization

Microplastic (MP) pollution has emerged as a global concern, prompting numerous studies on MP detection. Due to the remaining methodological challenges, it affects the accuracy and reliability of MP's impact assessment on river systems. To address this, the establishment of standardized operating protocols is crucial, encompassing sampling, separation, digestion, and characterization methods. This study evaluates the current tools used for identifying and quantifying MPs in riverine ecosystems, aiming to offer harmonized guidelines for future protocols. Recommendations include adopting a consistent format for reporting MP concentrations and providing improved information on sampling, separation, and digestion for enhanced cross-study comparisons. The importance of quality assurance and quality control is also discussed. Furthermore, we highlight unresolved issues, proposing avenues for further investigation. Suggestions encompass standardizing river sampling methods, optimizing technical steps and analysis processes, and enhancing the accuracy, reliability, and comparability of detection data to advance our understanding of MPs in river environments.

First-of-Its-Kind: Nationwide meta-analysis of microplastic pollution and risk assessment in Thailand

Thailand ranks as the sixth largest contributor to global microplastic pollution, which is exacerbated by extensive plastic use. Despite rising concerns, no comprehensive review is available on microplastic contamination and its potential risk in Thailand. This review synthesised data on microplastic abundance and characteristics within the country from 118 peer-reviewed publications (2017-2024). We found predominant microplastic presence in crustaceans (1.69-160.15 items/g), followed by Mollusca (0.03-9.5 items/g) and fishes (0.01-28.17 items/g), with higher abundances in wastewater (4 × 102 to 6.09 × 105 items/m3) compared to that in freshwater (1.44-2.92 × 106 items/m3) and seawater (2.70 × 10-1 to 6.25 × 104 items/m3). Marine sediments (48.3-2.13 × 104 items/kg) also showed significantly higher microplastic concentrations than terrestrial sediments (3-2.92 × 103 items/kg). Predominant microplastics were identified as fibers (59.36% and 35.05% for biological and environmental samples, respectively) and fragments (24.14%, 30.68%) in blue (25.95%, 18.64%), and colourless/transparent (20.01%, 14.47%), primarily composed of polyethylene terephthalate (19.46%, 9.19%), nylon (3.23%, 9.99%), polypropylene (19.78%, 24.23%), and polyethylene (14.81%, 11.66%). The potential ecological risk was low in all ecosystems except for wastewater. Shrimp and fish were more susceptible to microplastics compared to other studies in the region. Additionally, the sources, transport, and pathways of microplastic pollution in Thailand's aquatic territories and the current measures and policies implemented by the government to address plastic pollution are discussed. This review has compiled up-to-date insights into the prevalence, distribution, and risks associated with microplastics, which is instrumental in formulating effective strategies for contaminant control and ultimately reducing plastic pollution.

Occurrence, potential sources, and ecological risk assessment of microplastics in the inland river basins in Northern China

Microplastics (MPs) are the pollutants, found widely across various environmental media. However, studies on the MP pollution in urban rivers and the necessary risk assessments remain limited. In this study, the abundance and characteristics of microplastics in a typical urban river were examined to evaluate their distribution, sources, and ecological risks. It was observed that the abundance of MPs in sediments (220-2840 items·kg-1 dry weight (DW)) was much higher than that in surface water (2.9-10.3 items·L-1), indicating that the sediment is the "sink" of river MPs. Surface water and sediment were dominated by small particle size MPs (< 0.5 mm). Fiber and debris were common shapes of MPs in rivers and sediments. The microplastics in river water and sediments were primarily white and transparent, respectively. Polypropylene (PP) and polyethylene (PE) were the major polymers found.

The ecological risk and fate of microplastics in the environmental matrices of marine ranching area in coastal water

The debate surrounding "source" and "sink" of microplastics (MPs) in coastal water has persisted for decades. While the transportation of MPs is influenced by surface runoff and currents, the precise transport patterns remain inadequately defined. In this study, the typical coastal habitat - marine ranching in Haizhou Bay (Jiangsu Province, China) were selected as a case study to assess the ecological risk of MPs. An enhanced framework was employed to assess the entire community characteristics of MPs in various environmental compartments, including surface water (SW), middle water (MW), bottom water (BW), sea bottom sediment (SS), and intertidal sediment (IS). The results of the assessment showed a low risk in the water column and a high risk in the sediment. PERMANOVA based on size and polymer of MPs revealed significant differences between IS and other compartments (SW, MW, BW, and SS) (P < 0.001). The co-occurrence network analysis for MP size indicated that most sites occupied central positions, while the analysis for MP polymer suggested that sites near the marine ranching area held more central positions, with sites in MW, BW, and SS being somewhat related to IS. Generalized additive model (GAM) demonstrated that MP concentration in the water correlated with Chla and nutrients, whereas MPs in sediment exhibited greater susceptibility to dissolved oxygen (DO) and salinity. We believe that except for the natural sedimentation and re-suspension of MPs in the vertical direction, MPs in bottom water may migrate to the surface water due to upwelling mediated by artificial reefs. Additionally, under the combined influence of surface runoff, currents, and tides, MPs may migrate horizontally, primarily occurring between middle and bottom water and sediments. The study recommends limiting and reducing wastewater and sewage discharge, as well as regulating fishing and aquaculture activities to control the sources and sinks of MPs in coastal water. Moreover, it advocates the implementation and strengthening of marine monitoring activities to gain a better understanding of the factors driving MP pollution in marine ranching area.

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.

Modeling the transport of microplastics along river networks

The excessive use of plastics in modern life has led to a significant increase in production and a corresponding rise in plastic waste generation. The slow degradation of plastics results in the introduction and accumulation of microplastics (MP) in the environment, posing environmental and health risks. River networks, acting as conduits between terrestrial and marine environments, play a crucial role in controlling the transport of MP. Predicting the complex processes of MP pathways in these environments is an ongoing challenge. To address this issue, we propose a model that integrates the advection-dispersion equation with anthropogenic MP loads and hydraulic river network characteristics. The validity of the model was assessed using literature data from three river networks worldwide. Model results show a good agreement between predictions and field observations (R2=0.72). Consequently, predicted MP data was used to perform a potential pollution assessment through the pollution load index, revealing in most cases higher MP contamination in headwaters stream and a dilution effect along the river network. The structure of the proposed model allows its further implementation to account for other transport mechanisms, interactions with other emerging contaminants (i.e., pharmaceuticals), and connections with other riverine environments, making it a valuable tool for understanding and mitigating MP pollution.

Quantification, characterization and risk assessment of microplastics from five major estuaries along the northern Bay of Bengal coast

Microplastics (MPs) as hazardous contaminants has drawn the rapid attention of the general public due to their omnipresence and adverse impacts on ecosystems and human health. Despite this, understanding of MPs contamination levels in the estuarine ecosystems along the Bay of Bengal coast remains very limited. This research focused on the presence, spatial distribution, morpho-chemical characteristics and ecological implications of MPs in water and sediment from five key estuaries (Meghna, Karnaphuli, Matamuhuri, Bakkhali, and Naf rivers) within the Bengal delta. Out of the five estuaries, the Meghna exhibited the least amount of MPs in both surface water (150.00 ± 65.62 items/m3) and sediment (30.56 ± 9.34 items/kg). In contrast, the highest occurrence of MPs was recorded in Karnaphuli river water (350.00 ± 69.22 items/m3) and Matamuhuri river sediment (118.33 ± 26.81 items/kg). ANOVA indicated a statistically significant distinction (p < 0.01) among the examined estuaries. Most identified MPs were fibers and < 0.5 mm in size in both water and sediment samples. Transparent MPs were dominant in both water (42.28%) and sediment (45.22%). Besides violet, red, blue, pink and green colored MPs were also observed. Various polymer types, including PE, PP, PET, PS, Nylon, EVA, and ABS, were detected, with PE being the dominant one. Based on the polymer risk index (PHI), the estuaries were classified as hazard level V, signifying a severe level of MP contamination. However, the potential ecological hazardous index (PHI), potential ecological risk index (RI), and pollution load index (PLI) indicated moderate pollution levels. This study offers initial insights into the pollution caused by MPs in major estuaries of Bengal delta, which policymakers can utilize to implement suitable management strategies.

Review: Mitigation measures to reduce tire and road wear particles

The generation of tire wear is an inevitable outcome of the friction between the road and the tire which is necessary for the safe operation of vehicles on roadways. Tire wear particles form agglomerates with road surface material. These agglomerates are called tire and road wear particles (TRWP). Due to their persistence in the environmental compartments and their potentially harmful effects, research on preventative and end-of-pipe mitigation strategies for TRWP is essential. The major goal of this study is to summarize and assess the state of the art in science and technology of mitigation measures for TRWP as the basis for further research activities. Approximately 500 literature sources were found and analyzed in terms of the efficiency, maturity, implementation, and impact of the mitigation measures. Generally, technological and management mitigation measures to reduce the generation of TRWP are beneficial since they prevent TRWP from entering the environment. Once released into environmental compartments, their mobility and dispersion would increase, making removing the particles more challenging. Technological and management mitigation measures after the release of TRWP into the environment are mainly well established in industrialized countries. Street cleaning and wastewater technologies show good removal efficiencies for TRWP and microplastics. In any case, no individual measure can solely solve the TRWP issue, but a set of combined measures could potentially be more effective. The absence of fully-developed and standardized methods for tire abrasion testing and measuring TRWP in the environment makes it impossible to reliably compare the tire abrasion behavior of different tire types, determine thresholds, and control mitigation actions. Field tests and pilot studies are highly needed to demonstrate the effectiveness of the abatement measures under real conditions.

Status, characteristics, and ecological risks of microplastics in farmland surface soils cultivated with different crops across mainland China

Microplastics (MPs) in agricultural soils could affect the safety of food crops. However, most relevant studies have paid scant attention to the crop fields and focused more on MPs in farmlands with or without film mulching in different regions. To detect MPs, we investigated farmland soils with >30 typical crop species from 109 cities in 31 administrative districts across mainland China. The relative contributions of different MP sources in different farmlands were estimated in detail based on a questionnaire survey, and we also assessed the ecological risks of MPs. Our results indicated the order of MP abundances in farmlands with different crop types, namely fruit fields > vegetable fields > mixed crop fields > food crop fields > cash crop fields. For the detailed sub-types, the highest MP abundance was detected in grape fields, which was significantly higher than that in solanaceous & cucurbitaceous vegetable fields (ranked second, p < 0.05), whereas the MP abundance was lowest in cotton and maize fields. The total contributions of three potential sources, namely livestock and poultry manure, irrigation water, and atmospheric deposition to MPs, varied depending on the crop types in the farmlands. Owing to exposure to MPs, the potential ecological risks to agroecosystems across mainland China were not negligible, particularly in fruit fields. The results of the current study could provide basic data and background information for future ecotoxicological studies and relevant regulatory strategies.

Quantitative analysis and risk assessment to full-size microplastics pollution in the coastal marine waters of Hong Kong

Given the potential risk to the ecosystem, attention has increased in recent decades to the contamination of the aquatic environment by microplastics (MPs). Due to the limitations of conventional analysis methods of MPs, little is known about the size distribution and abundance of a full-size MPs from 1 μm to 5 mm. The present study quantified MPs with size ranges of 50 μm - 5 mm and 1-50 μm in the coastal marine waters from twelve locations in Hong Kong using fluorescence microscopy and flow cytometry respectively, during the end of wet (September 2021) and dry (March 2022) seasons. The average abundance of MPs with size ranges of 50 μm - 5 mm and 1-50 μm from twelve sampling locations marine surface waters were found ranging from 27 to 104 particles L^-1 and 43,675-387,901 particles L^-1 in the wet season respectively, and 13-36 particles L^-1 and 23,178-338,604 particles L^-1 in the dry season respectively. Significant temporal and spatial variations of small MPs abundance might be observed at the sampling locations, which were contributed by the influences of the estuary of Pearl River, sewage discharge points, land structure, and other anthropogenic activities. Based on the MPs abundance information, ecological risk assessment was conducted and revealed that the small MPs (< 10 μm) in coastal marine surface waters may pose potential health risks to aquatic organisms. Additional risk assessments are needed in order to determine whether or not the MPs exposure would cause health risks to the public.

Combined effects of salinity and polystyrene microplastics exposure on the Pacific oysters Crassostrea gigas: Oxidative stress and energy metabolism

Microplastics (MPs) pollution and salinity variation are two environmental stressors, but their combined effects on marine mollusks are rarely known. Oysters (Crassostrea gigas) were exposed to 1 × 10⁴ particles L^-1 spherical polystyrene MPs (PS-MPs) of different sizes (small polystyrene MPs (SPS-MPs): 6 μm, large polystyrene MPs (LPS-MPs): 50-60 μm) under three salinity levels (21, 26, and 31 psu) for 14 days. Results demonstrated that low salinity reduced PS-MPs uptake in oysters. Antagonistic interactions between PS-MPs and low salinity mainly occurred, and partial synergistic effects were mainly induced by SPS-MPs. SPS-MPs induced higher lipid peroxidation (LPO) levels than LPS-MPs. In digestive glands, low salinity decreased LPO levels and glycometabolism-related gene expression, which was related to salinity levels. Low salinity instead of MPs mainly affected metabolomics profiles of gills through energy metabolism and osmotic adjustment pathway. In conclusion, oysters can adapt to combined stressors through energy and antioxidative regulation.

Occurrence and risks of microplastics in the ecosystems of the Middle East and North Africa (MENA)

The ubiquitous nature of microplastics (MPs) in nature and the risks they pose on the environment and human health have led to an increased research interest in the topic. Despite being an area of high plastic production and consumption, studies on MPs in the Middle East and North Africa (MENA) region have been limited. However, the region witnessed a research surge in 2021 attributed to the COVID-19 pandemic. In this review, a total of 97 studies were analyzed based on their environmental compartments (marine, freshwater, air, and terrestrial) and matrices (sediments, water columns, biota, soil, etc.). Then, the MP concentrations and polymer types were utilized to conduct a risk assessment to provide a critical analysis of the data. The highest MP concentrations recorded in the marine water column and sediments were in the Mediterranean Sea in Tunisia with 400 items/m³ and 7960 items/kg of sediments, respectively. The number of MPs in biota ranged between 0 and 7525 per individual across all the aquatic compartments. For the air compartment, a school classroom had 56,000 items/g of dust in Iran due to the confined space. Very high risks in the sediment samples (Erⁱ > 1500) were recorded in the Caspian Sea and Arab/Persian Gulf due to their closed or semi-closed nature that promotes sedimentation. The risk factors obtained are sensitive to the reference concentration which calls for the development of more reliable risk assessment approaches. Finally, more studies are needed in understudied MENA environmental compartments such as groundwater, deserts, and estuaries.

Distribution and risk assessment of microplastics in Liujiaxia Reservoir on the upper Yellow River

Microplastics (MPSs) distribution in global freshwater systems is extensively reported, but the distribution of MPSs in reservoirs of the Yellow River has rarely been studied. To fill in this gap, we systematically investigated the distribution of MPSs in surface water and bank sediments gleaned from Liujiaxia Reservoir of the upper Yellow River for the first time and conducted an ecological risk assessment in succession in this work. The results showed that the main polymer types of MPSs in the surface water and bank sediments of Liujiaxia Reservoir were polyethylene terephthalate (PET), polystyrene (PS), and polypropylene (PP), and the abundance of MPSs in the reservoir surface water and bank sediments ranged from 4.48 to 12.09 item/L and 447.27 to 1543.80 item/kg (dry weight), respectively. Further physical morphology analysis of MPSs in the samples revealed that MPSs in the surface water and bank sediments of Liujiaxia Reservoir were predominantly fibrous with small particle sizes (<1 mm), and there was abundant color, mainly exhibiting transparent, black, and blue. The results of the MPS pollution load index (PLI>1) and the hazard ranking of MPSs (H_Zone = 10.20 for surface water and H_Zone = 14.06 for bank sediments) yielded a hazard class II for MPS pollution in Liujiaxia Reservoir, the combined pollution risk index (PRI_Zone = 17.05 for surface water and PRI_Zone = 31.25 for bank sediments) stated clearly the potential ecological risk in the Liujiaxia Reservoir. Briefly, this study supplemented and enriched the data on the distribution of MPSs in the reservoirs of the Yellow River basin, and provide a benchmark for future pollution control and management in the reservoir area.

Microplastics in coastal urban sediments: Discrepancies in concentration and character revealed by different approaches to sample processing

Intertidal, silty sediment samples have been collected from three coastal locations with different uses and anthropogenic signatures in the vicinity of Plymouth, southwest England, and analysed for microplastics (MPs) by two independent means. Firstly, MPs were counted and characterised directly on unprocessed dried sediment under a stereo microscope, and secondly MPs were isolated from sediment by flotation in ZnCl₂ solution and filtration before analysis. Direct counting resulted in average (± one standard deviation) numbers of MPs per g of dry sediment of 0.77 ± 0.16 at a marina-harbour, 0.58 ± 0.30 under a busy road bridge and 0.79 ± 0.43 adjacent to country parkland. After flotation and filtration, concentrations were reduced to 0.24 ± 0.11, 0.18 ± 0.06 and 0.48 ± 0.38 MP g^-1, respectively. Observations were attributed to hetero-aggregation of small fibres with settling sediment during flotation, and the presence of MPs (including paints) that were too dense to float or that had aggregated or agglomerated with denser sediment and construction material in situ. The findings have implications for the efficacy of flotation procedures, accurate estimations of MP concentrations in sediment and the representativeness of MPs by type, and inter-site comparisons of MPs that are widely reported in the literature.

Occurrence of microplastics pollution in the Yangtze River: Distinct characteristics of spatial distribution and basin-wide ecological risk assessment

The widespread presence of microplastics (MPs) in the Yangtze River, the third longest river in the world, has drawn increasing attention. Although numerous studies have been conducted recently to investigate and analyze the MPs exposure to the surface water of the river, most merely focus on a certain part of the Yangtze River, and knowledge of MPs based on the basin-wide is still scattered. This article reveals the spatial distribution characteristics of MPs in the Yangtze River from the whole watershed scale. Among the five areas in the basin, the upstream and the midstream were demonstrated to contain more MPs (3598.6 particles/m³ and 3226.8 particles/m³). The obtained results suggested the MP presented in the entire watersheds was uneven and the 'hotspots' occurred, where the MPs concentrations were relatively higher than the surrounding. The discharging of the wastewater treatment plants along the river, the locations of dams, and the stability and fragment of MPs, were demonstrated to be the important driving factors in the spatial distribution of MPs and leading to the appearance of the MP 'hotspots' in the Yangtze River, but were previously overlooked. It is the first study to evaluate the ecological risk of MPs exposure to the surface water of the Yangtze River with multiple assessment methods, taking not only abundance but also morphological characteristics, polymer composition and toxic effect into account. More importantly, based on the multiple individual MPs risk assessment methods, we developed the BetaMP method which achieves a comprehensive assessment of MP risk in basin-wide by taking multiple MP characteristics into account for the first time. This is conducive to better understanding the environmental impacts of MPs pollution in the different regions of the river.

What can we learn from studying plastic debris in the Sea Scheldt estuary?

The Sea Scheldt estuary has been suggested to be a significant pathway for transfer of plastic debris to the North Sea. We have studied 12,801 plastic items that were collected in the Sea Scheldt estuary (Belgium) during 3 sampling campaigns (in spring, summer, and autumn) using a technique called anchor netting. The investigation results indicated that the abundance of plastic debris in the Scheldt River was on average 1.6 × 10^-3 items per m³ with an average weight of 0.38 × 10^-3 g per m³. Foils were the most abundant form, accounting for >88 % of the samples, followed by fragments for 11 % of the samples and filaments, making up for <1 % of the plastic debris. FTIR spectroscopy of 7 % of the total number of plastic debris items collected in the Sea Scheldt estuary (n = 883) revealed that polypropylene (PP), polyethylene (PE), and polystyrene (PS) originating from disposable packaging materials were the most abundant types of polymers. A limited number of plastic debris items (n = 100) were selected for non-destructive screening of their mineral element composition using micro-X-ray fluorescence spectrometry (μXRF). The corresponding results revealed that S, Ca, Si, P, Al, and Fe were the predominant mineral elements. These elements originate from flame retardants, mineral fillers, and commonly used catalysts for plastic production. Finally, machine learning algorithms were deployed to test a new concept for forensic identification of the different plastic entities based on the most important elements present using a limited subset of PP (n = 36) and PE (n = 35) plastic entities.

An estimation of tire and road wear particles emissions in surface water based on a conceptual framework

Freshwater sources have been contaminated with toxic and unwanted substances worldwide. Among these toxic substances, microplastics (MPs) are becoming prominent. There is already a debate on the impact of MPs on the aquatic environment. Tire and road wear particles (TRWPs) are a dominant group among MPs, and it is vital to estimate their occurrence in the environment. This study proposed a conceptual framework to estimate the occurrence and emissions of TRWPs in the environment. The proposed framework developed a vehicle emission model combined with a previously developed freshwater transport model and was demonstrated using a region in Okanagan Valley, British Columbia, as a case study. A sensitivity analysis was performed to address the uncertainty in TRWP emissions. Furthermore, scenarios were developed considering various environmental, management, and treatment factors to forecast the TRWP emissions under different situations. The total TRWPs emission estimated on the road ranged between 25 and 167 t/year, the estimated TRWPs emission to surface water ranged between 4 and 32 t/year, and the estimated TRWPs emission entering lakebed ranged between 4 and 23 t/year. Furthermore, the scenarios analysis showed that selected management and treatment strategies under given environmental conditions can reduce the total emission on-road (from >130 t/year to <60 t/year); reduce emission to surface water (from >35 t/year to ≈ 12 t/year); and reduce lakebed emissions (from 25 t/year to <8 t/year). Therefore, these management and treatment strategies could reduce the annual per-capita TRWP emissions from >4 kg/c/year to <2 kg/c/year. The proposed framework is flexible and can be adapted to forecast TRWP emissions in different regions. The developed model and framework can be improved by collecting more data and considering other contributing factors.

Microplastic contamination and risk assessment in blue shark (Prionace glauca) from the eastern tropical Pacific Ocean

We quantified the abundance and characteristics of microplastics in the blue shark, Prionace glauca, found in the eastern tropical Pacific Ocean and investigated the potential microplastic pollution risks. Microplastics (MPs) were detected in 39.1 % of specimens, up to 0.15 ± 0.38 items/g wet weight of the posterior part of the pylorus, and were sized 45.87 to 3220.12 μm. The majority were fibrous in shape (83.3 %) and blue in color (72.2 %). Both sexes of sharks had similar MP abundance and characteristics, except for polymers, with polyethylene terephthalate and polypropylene representing the dominant type in males and females, respectively. Most individuals experienced low pollution, but one male P. glauca exhibited a high ecological risk level owing to the high MP abundance and detection of polyvinyl chloride. This study provides an important baseline for the ingestion of microplastics by pelagic shark species and is a preliminary quantitative measure that could be used in future studies of the risk of MPs.

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.

Risk associated with microplastics in urban aquatic environments: A critical review

The presence of microplastics (MPs) has been recognized as a significant environmental threat due to adverse effects spanning from molecular level, organism health, ecosystem services to human health and well-being. MPs are complex environmental contaminants as they bind to a wide range of other contaminants. MPs associated contaminants include toxic chemical substances that are used as additives during the plastic manufacturing process and adsorbed contaminants that co-exist with MPs in aquatic environments. With the transfer between the water column and sediments, and the migration within aquatic systems, such contaminants associated MPs potentially pose high risk to aquatic systems. However, only limited research has been undertaken currently to link the environmental risk associated with MPs occurrence and movement behaviour in aquatic systems. Given the significant environmental risk and current knowledge gaps, this review focuses on the role played by the abundance of different MP species in water and sediment compartments as well as provides the context for assessing and quantifying the multiple risks associated with the occurrence and movement behaviour of different MP types. Based on the review of past literature, it is found that the physicochemical properties of MPs influence the release/sorption of other contaminants and current MPs transport modelling studies have primarily focused on virgin plastics rather than aged plastics. Additionally, risk assessment of contaminants-associated MPs needs significantly more research. This paper consolidates the current state-of-the art knowledge on the source to sink movement behaviour of MPs and methodologies for assessing the risk of different MP species. Moreover, knowledge gaps and emerging trends in the field are also identified for future research endeavours.

Microplastics alter nitrous oxide production and pathways through affecting microbiome in estuarine sediments

Increasing microplastics (MPs) pollution in estuaries profoundly impacts microbial ecosystems and biogeochemical processes. Nitrous oxide (N₂O), a powerful greenhouse gas, is an important intermediate product of microbial nitrogen cycling. However, how MPs regulate N₂O production and its pathways remain poorly understood. Here, impacts of traditional petroleum-based and emerging biodegradable MPs on microbial N₂O production and its pathways were studied through dual-isotope (¹⁵N-¹⁸O) labeling technique and molecular methods. Results indicated that both traditional petroleum-based and emerging biodegradable MPs promoted sedimentary N₂O production, whereas pathways varied. Biodegradable polylactic acid (PLA) MPs displayed greater promotion of N₂O production than petroleum-based MPs, polyvinyl chloride (PVC) and polyethylene (PE), of which PLA promoted through nitrifier nitrification (NN) and heterotrophic denitrification (HD), PE through nitrifier denitrification and HD, and PVC through NN. By combining the analysis of N₂O production rates with sediment chemical and microbiological properties, we demonstrated that the enrichment of nitrifying and denitrifying bacteria, as well as related functional genes directly and/or indirectly increased N₂O production primarily by interacting with carbon and nitrogen substrates. Different response of nitrogen cycling microbes to MPs led to the difference in N₂O increase pathways, of which nitrifying bacteria significantly enriched in all MPs treatments due to the niches provided by MPs. However, part of denitrifying bacteria significantly enriched in treatments containing PLA and PE MPs, which may serve as organic carbon substrates. This work highlights that the presence of MPs can promote sedimentary N₂O production, and the emerging biodegradable MPs represented by PLA may have a greater potential to enhance estuarine N₂O emissions and accelerate global climate change.

Evaluation of Istanbul from the environmental components' perspective: what has changed during the pandemic?

This study aims to determine the 1-year change over the pandemic period in Istanbul, the megacity with the highest population in Turkey, based on environmental components. Among the environmental topics, water consumption habits, changes in air quality, changes due to noise elements, and most importantly, the changes in usage habits of disposable plastic materials that directly affect health have been revealed. The results obtained showed that, in Istanbul, 8.1 × 10⁸ gloves should be considered waste, and considering the population living in districts along coastal areas, the number of waste masks that are likely to end up in the sea was 325.648 pieces/day. The results of the air quality and noise measurements during the pandemic showed that reductions in parallel with human activities were recorded with the lockdown effect. The average noise values of the districts along both sides of the Bosporus, where urbanization is concentrated, were between 50 and 59 dB. The precautions taken during the pandemic have had an effective role in reducing air pollution in Istanbul. In the measurements, the parameters with effective reductions were PM₁₀ (7-47%), PM_2.5 (13-48%), NO₂ (13-38%), and SO₂ (10-56%). As a result, Istanbul's year of changes during the pandemic period, in terms of water, air, noise, and solid plastic wastes, which are the most important components of the environment, is presented.