Vertical Distribution of Microplastics in the Water Column and Surficial Sediment from the Milwaukee River Basin to Lake Michigan

Molecular mechanisms by which polyethylene terephthalate (PET) microplastic and PET leachate promote the growth of benthic cyanobacteria

Toxic blooms of benthic cyanobacteria greatly threaten freshwater ecological health and drinking water safety. Meanwhile, microplastic pollution is becoming increasingly severe and microplastics accumulate in large quantities at the bottom of lakes and rivers, widely coexisting with algae. However, impacts of microplastics on benthic cyanobacteria are still unknown. This study investigated effects of microplastic polyethylene terephthalate (PET) - which is commonly found at the bottom of lakes and rivers - and its leachate at environmentally relevant concentration (0.3 mg/L) and high exposure concentration (3.0 mg/L) on typical benthic cyanobacteria (Oscillatoria sp. and Pseudanabaena sp.), and clarified the related molecular mechanisms through transcriptomic analysis. Results show that PET or PET leachate (PET-L) can promote benthic cyanobacterial growth and promotive effect of PET-L is more obvious than that of PET system. Promotion effect of PET or PET-L is more significant at environmentally relevant concentration (39-63 % increase compared with the control) compared with high exposure concentration (21-58 % increase compared with the control). In the presence of PET or PET-L, due to an increase in the number of cyanobacterial cells, concentrations of harmful metabolites (cylindrospermopsin, geosmin, and 2-methylisoborneol) in water also increased. Although PET particles may not be conducive to benthic cyanobacterial growth due to shading effect and mechanical damage, photosynthetic efficiency of algae was improved and dysregulated genes related to photosynthesis and extracellular transport of glycolipid were upregulated according to transcriptome analysis. Moreover, PET decomposition components, such as terephthalic acid and ethylene glycol, may be able to serve as carbon sources for cyanobacterial growth. Upregulation of genes associated with glycolysis, oxidative phosphorylation, and translation revealed that PET can promote the growth of benthic cyanobacteria. This study has important value in evaluating the impact of benthic cyanobacteria on aquatic ecological health and drinking water safety with the coexistence of microplastics.

The Three Gorges Dam alters the spatial distribution and flux of microplastics in the Yangtze River

The construction of dams disrupts the natural connectivity of rivers, potentially altering the distribution and movement of pollutants. However, the impacts of dams on microplastic (MP) flux are scarcely considered. By integrating previous findings and conducting supplementary sampling, we mapped the distribution of MPs in the Three Gorges Reservoir (TGR), covering surface water, sediment, the hydro-fluctuation belt, and the riparian zone. The TGR serves as a significant accumulation zone for MPs, with a notably higher concentration of MPs in its water compared to the upstream river water. In the reservoir, MPs are concentrated in the upstream and downstream sections of the water column, the hydro-fluctuation belt and sediment, whereas in the riparian zone, concentrations are higher in the downstream section. The distribution of MPs in reservoir water is strongly correlated (R2 > 0.9) with regional gross domestic product (GDP) and sewage discharge, whereas the factors influencing MPs in sediment, the hydro-fluctuation belt, and the riparian zone are more complex. Human activities, particularly wastewater discharge in populated areas, predominantly contributed 49.89 % to the MPs load in the reservoir. The TGR captures approximately 11,091 ± 6,998 tons of MPs annually, constituting 28.18 % of the MPs flux from the upper Yangtze River.

Insights into suspended sediment and microplastic budget of a lowland river: integrating in-situ measurements, Sentinel-2 imagery, and machine learning

The calculations on fluvial microplastic load (MPL) provide dynamic and actionable metrics for understanding microplastic (MP) particle emissions to the downstream environment. However, most of the concentration data reported in the literature do not reflect the total amount of transported MPs. This study aims to quantify the MPLs in the Middle and Lower Tisza River, Hungary by combining multiscale, frequent in-situ measurements of MP concentration (MPC) and suspended sediment concentration (SSC) in the river with Sentinel-2 and ANN-based models. MPC data were integrated with daily water discharge, applying correction factors to account for vertical variability in the water column. The results indicate the crucial role of hydrology in suspended sediment (SS) and MP transport. During floods SS load (SSL) (6706 ± 7449 ton/day) and MPL (1.71 × 109 ± 1.40 × 109 item/day) were 6.5 and 5.1 times higher than at low stage (SSL: 1031 ± 755 ton/day; MPL: 0.339 × 109 ± 0.399 × 109 item/day), respectively. Vertical measurements indicated a generally increasing SSC trend toward the riverbed, amplifying the SSL correction factor, while decreasing MPC led to attenuation for MPL correction factors. Satellite-derived estimates at four sites in the Middle and Lower Tisza revealed an increasing downstream trend in SSL and MPL, although natural and anthropogenic factors slightly influence this trend. Rating curves were established at the four sites with an R2 range of 0.55 (Mindszent) to 0.82 (Zenta) for SSL and 0.53 (Mindszent) for MPL. Although the accuracy of the rating curves is moderate to very strong, they still offer practical predictions based solely on water discharge data.

Factors influencing the vertical distribution and transport of plastics in riverine environments: Theoretical background and implications for improved field study design

Rivers have been widely recognized as important conduits and accumulation sites for plastics. Accurately describing plastic fate and transport in these systems is essential for the development of numerical models, estimating loads to oceans, and implementing effective management strategies. However, plastic transport mechanisms within fluvial environments are not well understood, and field studies often do not provide sufficient information to test analytical models of transport. Sediment transport has dynamical similarities to plastics transport in water bodies, enough to warrant further investigation into how principles from sediment transport can be used to guide the study of plastics. In this review, we summarize fundamentals from sediment transport research and their application to plastics, then use these to make suggestions of clarifying research questions and riverine field study design with the goal of generating more insightful data that can be used to understand and predict plastic fate and transport. We focus specifically on factors influencing plastic vertical distribution and movement in the water column, as variations in this direction have historically been overlooked or oversimplified in rivers.

Comprehensive analysis of microplastics at typical outlets around Hainan Island: From spatial distribution to flux estimation and correlation analysis

Previous studies on microplastics (MPs) distribution have predominantly focused on water bodies within specific regions, with limited emphasis on the contributions of MPs directly discharged from functional zones surrounding isolated island. This study addressed this gap by investigating the occurrence and distribution of MPs in water and sediment directly discharged into the adjacent coast of Hainan Island, a geographically isolated and ecologically sensitive region in the South China Sea. Based on the sampling from 40 typical sewage outlets (affiliated to five functional zones, i.e., wastewater treatment plants (WWTP), industrial area (ID), residential area (RA), aquaculture area (QA), estuary (EST)) around the Hainan Island, we analyzed the MPs abundance and composition in water and sediment. Our findings revealed significant contributions of land-derived MPs, with an average abundance of 15,900 items/m3 in water and 3171 items/kg in sediment. Annually, approximately 61.6 trillion MPs were discharged into the South China Sea via rivers from Hainan Island, highlighting its role as a major land-derived source of MPs pollution in this critical marine ecosystem. Risk assessments indicated the H and PLI level of Hainan Island as II and I, respectively, with H-water level highest in WWTP and EST as III and H-sediment level highest in WWTP, RD and QA as II, and this indicated the critical function of WWTP to control the release of land-derived MPs and reduce the environmental risks. Correlation analysis underscored the influence of natural factors (currents, tides, waves, and drifts), socio-economic factors (population density, regional area, and agricultural output), and anthropogenic activity (tourism development) on coastal MPs pollution. On the basis of existing timely MPs prevention and control measures in Hainan province, such as intercepting the MPs via WWTP and prohibiting the direct discharge of aquaculture wastewater to the surrounding sea, this study re-underscored the urgency of MPs management on the protection of the South China Sea's eco-environmental quality in view of the pivotal role of Hainan Island on the isolated geographic position and the South China Sea's ecological health. Overall, this study offered scientific insights to support source-oriented strategies for coastal MPs pollution control by providing fundamental data for predicting land-derived MPs contributions on an island-scale.

Risk-based integrated framework for evaluating effects of microplastics to aquatic ecosystems and human health

The widespread presence of microplastics (MPs) in environments and the food web is a serious concern for both aquatic ecosystems and human health. Most studies have used single tool to assess risks primarily to organisms and humans, leaving gaps in comprehensive risk assessments. This study conducted an investigation of MP abundances in surface water and wild oysters from natural estuaries of major rivers in Taiwan. Additionally, the data also used to develop an integrated risk-based framework for evaluating potential risks from organisms to human MP exposure to seafood consumption. We assessed aquatic ecological risk quotients (RQ), oyster mortality exceedance risk (ER), human MP intake exposure, and human liver damage ER. Our data showed that MP abundances ranged from 0.025 to 4.701 items/m3 and 0.015-2.374 items/g (wet weight) in water and oysters, respectively. Although RQ values indicate negligible risk for aquatic ecosystems, but oyster mortality ER results from oysters exposed to MPs showed a 6 % increase in mortality (10 % risk). The probabilistic representation of risk curves of MPs for alanine aminotransferase (ALT) levels in human serum was found to be low, indicating minimal health risk to humans. Overall, our data suggest that relying on a single risk indicator may underestimate potential risks, multi-faceted tools are recommended for assessing organism and human health.

Microplastic distribution in large shallow lake sediments: Variations with offshore distance and implications for microbial communities

Microplastics (MPs) are ubiquitous in global ecosystems and pose potential threats to the environment and biodiversity. However, the impact of MPs on microorganisms in real environments remains unclear. Our study focuses on the composition and distribution of MPs in sediments at different offshore distances in Taihu Lake. Our results indicated that MP abundance ranged from 240 to 1120 items/kg and decreased linearly with increasing offshore distance. Fibres dominated, with an average proportion of 47.58 %, and MPs within a particle size range of 0.5-1 mm (53.88 %) had the highest content. PA and PVC were the most abundant polymer types, accounting for 55.85 % and 17.94 %, respectively. The abundance of MPs in sediments was significantly positively correlated (P < 0.01) with the abundance of Firmicutes and significantly negatively correlated with the abundance of Planctomycetota. MPs account for 0.49 % of the variation in microbial alpha diversity and 1.88 % of the variation in microbial community composition. Our study demonstrates that environmental factor and MPs significantly affect microbial diversity and species composition. In summary, our research reveals the distribution patterns of MPs in sediments at different offshore distances in Taihu Lake, confirming the potential impact of MPs on microbial communities.

Surface Water Microplastics in the St. Lawrence River and Estuary in Canada

Microplastics (MPs) are synthetic or semisynthetic polymers that are widely distributed throughout most ecosystems and have the potential to be harmful to living organisms. In this study, we assessed the MP fraction in the top 40 cm of surface water in response to varying salinity levels at 11 distinct sites across the St. Lawrence River and Estuary (SLRE). We employed two sampling nets of different mesh size to collect MPs (100 and 300 µm). These nets were simultaneously towed in parallel from a vessel during three separate sampling events at each designated site. Filtrates collected from these samples underwent analysis of plastic fibers, fragments and spheres utilizing Fourier Transform Infrared Spectroscopy (FTIR). Data unequivocally confirmed the presence of MPs at 100% of the sites sampled within the SLRE. The most abundant categories of MPs identified were the fibers, followed by fragments and spheres. The FTIR analysis revealed the predominant materials to be polyester, polyethylene, polypropylene, nylon, and polystyrene. Notably the findings also suggest MPs are more likely aggregating when salinity increases. This work offers valuable insights into the distribution and behavior of MPs contributing to the preservation and management of water resources.

Investigating the adsorption of organic compounds onto microplastics via experimental, simulation, and prediction methods

Exploring the adsorption of organic compounds onto microplastics (MPs) is of great significance for understanding their environmental fate and evaluating their ecological risks. To date, various techniques, e.g., experiments, simulations, and prediction models, have been utilized for exploring the adsorption of different organic compounds onto MPs. In this review, we systematically introduce the sources of MPs, the interactions between MPs and organic compounds, the factors influencing the adsorption of organic compounds onto MPs, and research advances in investigating the adsorption of organic compounds by microplastics with different techniques. We also point out that the structures of MPs and environmental factors can have distinct effects on the adsorption mechanisms, and the adsorption mechanisms for numerous organic compounds onto MPs are still unclear. Besides, there is a paucity of multi-dimensional models for predicting the adsorption of organic compounds by MPs under different environmental conditions with a single click. We hope that our review can provide insights into the environmental behavior and fate of organic compounds and microplastics, as well as also guiding future research on the adsorption of organic compounds onto microplastics.

Typical migration patterns and fates of microplastics with varying properties in bays and their impacts on coastal ecologically sensitive areas

Rapid urbanization has intensified microplastic pollution in many global bays, yet the mechanisms driving microplastic behavior in these environments remain unclear. This study utilized field surveys, statistical analysis, and modeling methods to address this issue. The findings revealed three typical migration patterns of microplastics in bays. Microplastics less dense than seawater were easily transported by currents, drifting extensively throughout the bay, with about 37.2 % temporarily hovering in tidal channels and low-lying areas, ultimately leaving with ebb tides. Spherical microplastics denser than seawater were predominantly concentrated near the shore, primarily lingering in the subsurface layers. In contrast, fibrous microplastics, which are denser than seawater and the most prevalent type in human-impacted bays, displayed a unique behavior. The combined effects of their density and shape resulted in over 80 % being trapped in intertidal ecologically sensitive areas (ESAs). As a result, local ESAs, such as mangroves, bird habitats, and aquaculture, faced significant threats from fibrous microplastics and their sorption complexes associated with Cu, Pb, Cd, and Hg. Additionally, bay sediments acted as a source-sink community for microplastics. In Shenzhen Bay, China, approximately 27.1 × 1011 microplastic items were buried annually in sediments under normal hydrological conditions. However, if annual rainfall exceeded a threshold, these microplastics could be washed into ocean, serving as a source. Coastal raft aquaculture emerged as a significant contributor to marine microplastics, releasing about 3 %-8 % of terrestrial sources in Shenzhen Bay. This study enhances our understanding of microplastic behaviors and risks in bays.

Patterns and implications of plastic accumulation in mangrove ecosystems and sandy beaches in Western and Central regions of Ghana, West Africa

Plastic pollution has become increasingly apparent in sandy beach zones and aquatic environments, creating more than just visual pollution. Impacts are observed in many environmental and social levels, including the fishing communities that depend on the coastal environment for their livelihoods. Plastic pollution was assessed on the sandy beaches and mangroves of Ghana's Western and Central regions. The study's objective was to determine the composition, abundance and sources of plastic litter at four different sites during the wet and dry seasons. Samples were collected from within 50 cm2 quadrats placed randomly along four transects at each site. Plastic litter was classified according to the OSPAR guide. A total of 1895 plastic litter items with a combined weight of ~ 3000 g, representing 30 plastic categories, were collected. The average number and weight of plastic litter items were 19.73 ± 31.37 number of plastics per 50 cm2 and 32.59 ± 45.47 g per 50 cm2. The minimum and maximum plastic litter items were 0 to 159/50 cm2. The highest amount of plastic litter was found in Ghana's Central region. The total plastic litter weight is the variable that present statistical difference between the wet and dry season period. Bags, bottles, and fragments were the most common plastic items found, with 70% of the plastic litter being land-based, with the most frequent polymer types found in this study being polyethylene (~ 54%) and polypropylene (~ 20%). Mangrove regions act as sinks, specifically trapping plastic bags, contrary to the sandy beach areas, which mainly comprise plastic bottles that accumulate in these regions. Regions that have numerous communities, or are urbanised centres, tend to have higher levels or plastic litter. West Africa generally has poor waste management, absence of safe drinking water, and high levels of single-use plastics which are some of the main reasons for increased levels of plastic litter specifically in Ghana. Urgent actions are needed to prevent, mitigate and control plastic pollution in Ghana and the wider region.

Numerical plastic transport modelling in fluvial systems: Review and formulation of boundary conditions

In recent years, it has become clear that plastic pollution poses a significant threat to aquatic environments and human health. Rivers act as entry points for land-based plastic waste, while a certain fraction of entrained plastics is carried into marine environments. As such, the accurate modelling of plastic transport processes in riverine systems plays a crucial role in developing adequate remediation strategies. In this paper, we review the two main multiphase flow numerical approaches used in plastic transport modelling, comprising Lagrangian Transport Models (LTMs) and Eulerian Transport Models (ETMs). Although LTMs and ETMs can be regarded as complementary and equivalent approaches, LTMs focus on the transport trajectories of individual particles, whereas ETMs represent the behaviour of particles in terms of their mass or volume concentrations. Similar results of the two approaches are expected, while our review shows that plastic transport models are yet to be improved, specifically with respect to the formulation and implementation of boundary conditions, comprising plastic interactions with the channel bed, river bank, and the free surface, as well as interactions with biota. We anticipate that an implementation of these boundary conditions will allow for a better representation of different plastic transport modes, including bed load, suspended load, and surface load. Finally, we provide suggestions for future research directions, including a novel threshold formulation for free surface detachment of plastics, and we hope that this review will inspire the plastic research community, thereby triggering new developments in the rapidly advancing field of numerical plastic transport modelling.

Surface Texture of Macroplastic Pollution in Streams Alters the Physical Structure and Diversity of Biofilm Communities

Biofilms can develop on nearly any surface, and in aquatic ecosystems they are essential components of biogeochemical cycles and food webs. Plastic waste in waterways is a new type of surface for biofilm colonisation. To analyse the influence of plastic pollution on the development and diversity of microbial freshwater biofilms that colonised them, we incubated 388 cm2 veneers of high-density polyethylene (HDPE) with two veneer textures, smooth and rough, and tulip tree wood (Liriodendron tulipifera), in three rural headwater streams at the Savannah River Site (Aiken, SC, USA). We collected biofilms from veneers after 14, 28 and 56 days of incubation and analysed 16S rRNA genes and biofilm properties. We found that plastic negatively affected species richness of biofilms compared with wood, but that evenness was greatest on rough textured HDPE. Beta diversity was primarily influenced by stream site. Beta diversity differed more between wood and plastic veneers than with plastic surface texture and became more different over time. Wood had nine times more biomass than rough HDPE and 40 times more biomass than smooth HDPE. Given the projected increase of macroplastic pollution in aquatic ecosystems, our findings emphasise the need to further understand its effects on biofilm characteristics.

Microplastic pollution in the water column and benthic sediment of the San Pedro Bay, California, USA

The concentration, character, and distribution of microplastics in coastal marine environments remain poorly understood, with most research focusing on the abundance of microplastics at the sea surface. To address this gap, we conducted one of the first comprehensive assessments of microplastic distribution through the marine water column and benthic sediment during the wet and dry season in the coastal waters of the San Pedro Bay Southern California, USA. Microplastic concentrations in the water column did not vary significantly across season but were significantly higher in nearshore environments and at the surface of the water column. Sediment samples contained significantly more microplastics in the wet season and in offshore environments. Black particles were the most dominant color, while fibers were the most abundant morphology, accounting for over 50% of both water column and sediment microplastics. Polyethylene and polypropylene were identified as the most abundant polymers in the water column regardless of morphology type. Tire and road wear particles were found through the study domain. Average microplastic concentrations in the San Pedro Bay were estimated to be 8.65 × 105 ± 7.60 × 105 particles/km2 and 3.19 ± 2.96 particles/m³. This study highlights the complexity of microplastic concentration, character, and distribution in marine environments and demonstrates that surface only sampling strategies significantly underestimate microplastic concentrations. Our findings underscore the need for continued and expanded research into microplastic distribution and transport dynamics across the marine environment to aid in understanding, managing, and mitigating plastic pollution in coastal marine systems.

Microplastic characterization and transport mode -A flow-integrated approach to sampling urban waterways

Concentrations of microplastics are both temporally and spatially variable in streamflow. Yet, an overwhelming number of published field studies do not target a range of flow conditions and fail to adequately capture particle transport within the full flow field. Since microplastic flux models rely on the representativeness of available data, current predictions of riverine exports contain substantial error. In an effort to capture more representative concentrations in streamflow, we implemented a flow-integrated fluvial monitoring program for microplastics within two channels draining an urbanized watershed in Southern California, USA. Concentrations ranged up to 5 orders of magnitude between low flow and stormflow conditions. Tire road wear particle concentrations were significantly higher for the stormwater control channel draining a smaller but more densely developed watershed. Additionally, we leveraged each site's hydrologic conditions and the physical characteristics of particles extracted from depth-integrated samples, in order to compare microplastic Rouse number distributions relative to transport mode. Results indicated that full wash load transport capable of encompassing all types of microplastics was not achieved at either site. Additionally, for the channel with the larger drainage area and less uniform cross-section, the proportion of microplastics transported as wash load was approximately 10-30% lower near the bank compared to the thalweg. The results of this study indicate the importance of considering flow field transport variability when designing fluvial microplastics studies to improve the accuracy of both monitoring and modeling efforts.

Remediation of Micro- and Nanoplastics by Membrane Technologies

Micro- and nanoplastics (NPs) cannot be completely removed from water/wastewater in conventional wastewater treatment plants (WWTPs) and drinking water treatment plants (DWTPs). According to the literature analysis, membrane processes, one of the advanced treatment technologies, are the most effective and promising technologies for the removal of microplastics (MPs) from water and wastewater. In this article, firstly, the properties of MPs commonly found in water and wastewater treatment and their removal efficiencies are briefly reviewed. In addition, research on the use of microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), and membrane bioreactors (MBR) for the remediation of MPs and NPs from water/wastewater is reviewed, and the advantages/disadvantages of each removal method are discussed. Membrane filtration is also compared with other methods used to remove MPs. Furthermore, the problem of membrane fouling by MPs during filtration and the potential for MPs to be released from the polymeric membrane structure are discussed. Finally, based on the literature survey, the current status and gaps in research on MPs removal by membrane technologies are identified, and recommendations for further research are made.

Accumulation of microplastics in various organs of fiddler crabs and sea cucumbers across the coastal habitats in Singapore

Microplastics (or MPs) are an emergent threat to marine organisms. This study assessed MP contamination in the major organs of four species from Singapore's coastal habitats: Orange Fiddler Crab (Gelasimus vocans) and Porcelain Fiddler Crab (Austruca annulipes) from mangroves, Garlic Bread Sea Cucumber (Holothuria scabra) from seagrass beds and Synaptid Sea Cucumber (Synaptula recta) from coral reefs. MPs were prevalent in all species and their organs. Mean MP concentrations in fiddler crabs were 6.63 ± 0.97 MP individual-1 in G. vocans and 12.18 ± 3.38 MP individual-1 in A. annulipes, where their female crabs had significantly more MPs than males. This study also confirmed the translocation of MPs to the crabs' hepatopancreas, which had the highest MP concentrations compared to gills and digestive tracts. These observations suggest that the fiddler crabs' sexual dimorphism could influence feeding efficiency and behaviour. In contrast, the sea cucumbers had lower MP concentrations in their organs, where the average MP concentrations were 10.00 ± 2.32 MP individual-1 in H. scabra and 6.33 ± 0.69 MP individual-1 in S. recta. For H. scabra only, their respiratory trees showed the highest MP levels compared to their digestive tracts. Across the species, MPs were predominantly <1,000 μm in size, in fibre shape and polyethylene (PE). These findings provide critical baseline data on MP contamination across different organs in marine organisms, serving as proxies for MP pollution levels in the environment.

Phytoremediation of microplastics by water hyacinth

Microplastics have emerged as pervasive environmental pollutants, posing significant risks to both terrestrial and aquatic ecosystems worldwide. Current remediation strategies-including physical, chemical, and microbial methods-are inadequate for large-scale, in situ removal of microplastics, highlighting the urgent need for alternative solutions. Phytoremediation, an eco-friendly and cost-effective technology, holds promise in addressing these challenges, though its application to microplastic pollution remains underexplored. Here we show the capacity of Eichhornia crassipes (water hyacinth), a fast-growing, floating aquatic plant, to remove microplastics from contaminated water. Our results show that within 48 h, water hyacinth achieved removal efficiencies of 55.3 %, 69.1 %, and 68.8 % for 0.5, 1, and 2 μm polystyrene particles, respectively, with root adsorption identified as the primary mechanism. Fluorescence microscopy revealed that the extremely large and abundant root caps, featuring a total surface area exceeding 150,000 mm2 per plant, serve as the principal sites for the entrapment of microplastics. Furthermore, a unique "vascular ring" structure within the stem prevents the translocation of microplastics to aerial tissues, safeguarding leaves for potential downstream applications. This study offers the first microstructural insight into the mechanisms underpinning water hyacinth's exceptional microplastic adsorption capacity and resilience, providing a promising framework for developing phytoremediation strategies to mitigate microplastic pollution in aquatic ecosystems.

Distribution and risks of microplastics and phthalate esters in the transition from inland river systems to estuarine and nearshore regions of the Yellow Sea, China

Microplastics (MPs) and phthalate esters (PAEs) are emerging pollutants of significant environmental and health concern. The Yellow Sea, a semi-enclosed marginal sea with dense coastal populations and industrial activities, serves as a critical region for studying MP and PAE pollution due to its ecological sensitivity, role in pollutant transport, and relevance to global marine pollution challenges. The distribution and characteristics of MPs and PAEs in surface water and sediment transitioning from an inland river system to estuarine and nearshore regions of the Yellow Sea in China were investigated. MP concentrations in water samples ranged from 0.89 ± 0.15 to 11.47 ± 1.80 items/L and in sediments from 93.33 ± 23.09 to 653.33 ± 50.33 items/kg dw. The main colors of MPs found in water and sediment samples were white and transparent, with fibers being the predominant shape. The primary size range was 0-0.5 mm, and the main polymer components were rayon and polyethylene. The characteristics of MPs in clams were similar to those in water and sediment, except that their predominant colors were black and blue. The total of six PAEs (Σ6 PAEs) was detected at concentrations between 0.30 and 1.29 μg/L in water and 25.75-163.61 ng/g in sediments. The concentrations of both pollutants demonstrated a distinct spatial gradient, with the highest levels observed in upstream urban areas, followed by progressively decreasing levels in downstream rural zones, and reaching their minimum concentrations in nearshore regions. Variations in the morphological characteristics (color, shape, and size) and polymer composition of MPs were observed between the aquatic phase and sediment phase along the direction of water flow. A significant correlation was found between MP abundance and Σ6 PAEs across both matrices. Ecological risk assessments revealed substantial risks associated with the presence of these pollutants, particularly in urban areas where contamination peaked. Clams collected from the nearshore regions exhibited MP counts of 1.91 ± 0.47 to 2.49 ± 0.63 items/individual and PAEs from 0.51 to 0.91 μg/g, posing high polymer risk from MPs yet no significant health risk from PAEs for human consumers. This study underscores the transition of MP and PAE pollution from riverine to marine environments, providing valuable insights into the critical sources and potential risks associated with marine MPs and PAEs.

Development and validation of a novel suspended particulate matter sampling device for analysis of particle-bound microbial communities

Biotic and abiotic materials attachment to suspended particulate matter in aquatic systems can increase their toxicity and health impacts and has led to an increased need for consistent sampling across various compartments. Sedimentation traps and continuous flow centrifuges are the traditional tools for sampling suspended particulate matter, while manta trawls have been widely used for surface water sampling of suspended or floating microplastics. Limitations, however, exist in the cost of sampling and infrastructure needed to deploy such devices. Here we report on the construction and usage of a novel suspended particulate matter sampling device, the microParticle Obtaining Trap (mPOT). Quality control testing of the mPOT showed suspended particle recovery rates of >90% for particles 100 µm and larger, while field sampling of groundwater, lake and river water shows consistent, size-fractionated recovery of particulate matter. The mPOT is well suited to sample systems not easily accessible by boat or for particles not commonly recovered by common suspended particulate matter sampling and for collection of particles smaller than 300 µm in size.

Predicting microplastic dynamics in coral reefs: presence, distribution, and bioavailability through field data and numerical simulation analysis

Understanding distribution and bioavailability of microplastics is vital for conducting ecological risk assessments (ERA) and developing mitigation strategies in marine environments. This study couples in situ data from Lizard Island (Great Barrier Reef) and numerical modelling and simulations to determine microplastic abundances in abiotic (water and sediment) and biotic (planktivorous fish, sea squirts, sponges, corals, and sea cucumbers) compartments and predict their trajectories within this ecosystem. Results show microplastics predominantly (75%) originate from beached plastics from nearby islands and coastal areas, dispersing northward without local entrapment and settlement likely occurring on northern beaches (> 50%), including Papua New Guinea. Concentrations increased by three orders of magnitude with depth, with distinct profiles: surface waters contained more fragments and low-density polymers at concentrations of < 1 microplastics m-3, and deeper layers more fibres and high-density polymers, with concentrations peaking at the seafloor at > 100 microplastics m-3. Reflecting ecological and physiological traits of each taxon, fish exhibited microplastic contamination levels nearly twice that observed in invertebrates, and while polymers and colours had no stronger evidences on influencing bioavailability, shape and size did, with fish more susceptible to contamination by microplastic fibres and all taxa to smaller-sized microplastic particles.

Microcontaminants and microplastics in water from the textile sector: a review and a database of physicochemical properties, use in the textile process, and ecotoxicity data for detected chemicals

Microcontaminants (MCs) and microplastics (MPs) originating from the textile sector are today receiving a great deal of attention due to potential environmental concerns. Environmental pressures and impacts related to the textile system include not only the use of resources (e.g., water) but also the release of a wide variety of pollutants. This review's main objective is to highlight the presence of textile MCs and MPs in water, in their full path from textile factories (from raw materials to the final product) to wastewater treatment plants (WWTPs), and finally to the receiving surface waters. Their environmental fate and ecotoxicity were also addressed. Overall, more than 500 compounds were found, many of which are so called "contaminants of environmental concern" such as per- and polyfluoroalkyl substances (PFAS) and alkylphenol compounds. A database of physicochemical properties, ecotoxicity, and place of detection (specific textile process, WWTP, surface water or sediment) (classification by several international agencies) was compiled for the chemical detected. Preliminary risk assessment was conducted for those MCs for which the reported environmental concentrations exceeded the Predicted No Effect Concentration (PNEC). These chemicals were some nonylphenols, nonylphenol ethoxylates and organophosphate esters. Among MPs, polyester and nylon fibres were the most abundant. The highest concentration of MPs was reported in sludge (about 1.4 × 106 MPs per kg) compared to wastewater and surface water which showed MP concentrations at least two orders of magnitude lower. The role of transboundary contamination due to the release of chemicals from imported textile products was also assessed.

The transport and vertical distribution of microplastics in the Mekong River, SE Asia

Rivers are primary vectors of plastic debris to oceans, but sources, transport mechanisms, and fate of fluvial microplastics (<5 mm) remain poorly understood, impeding accurate predictions of microplastic flux, ecological risk and socio-economic impacts. We report on microplastic concentrations, characteristics and dynamics in the Mekong River, one of the world's largest and polluting rivers, in Cambodia and Vietnam. Sampling throughout the water column at multiple localities detected an average of 24 microplastics m-3 (0.073 mg l-1). Concentrations increased downstream from rural Kampi, Cambodia (344 km from river mouth; 2 microplastics m-3, 0.006 mg l-1), to Can Tho, Vietnam (83 km from river mouth; 64 microplastics m-3, 0.182 mg l-1) with most microplastics being fibres (53 %), followed by fragments (44 %) and the most common polymer being polyethylene terephthalate (PET) or polyester. Pathways of microplastic pollution are expected to be from urban wastewater highlighting the need for improved wastewater treatment in this region. On average, 86 % of microplastics are transported within the water column and consequently we identified an optimum sampling depth capturing a representative flux value, highlighting that sampling only the water surface substantially biases microplastic concentration predictions. Additionally, microplastic abundance does not linearly follow discharge changes during annual monsoonal floods or mirror siliciclastic sediment transport, as microplastic concentrations decrease rapidly during higher monsoon flows. The findings reveal complex microplastic transport in large rivers and call for improved sampling methods and predictive models to better assess environmental risk and guide policy.

Plastic transport in rivers: Bridging the gap between surface and water column

Rivers act as an important transportation pathway for land-based plastic litter to the ocean. Recently, rivers have also been identified as potential sinks and reservoirs for plastics. Knowledge of plastic transport over different depth profiles in rivers remains limited. In this study, we evaluated the vertical distribution of macro- and mesoplastics, using a larvae net and a trawl net in the river Rhine and its two major branches, i.e. Waal and IJssel. Subsequently, to estimate the relationship between the surface transport of plastic items, i.e., floating items, compared to the transport in deeper layers in the water column, including suspended and bed-transported plastic, an extrapolation factor was derived per day for the middle and bottom nets divided by those found in the surface net. The observed macro- and mesoplastic OSPAR categories collected in different layers in the water column were rather consistent between different sampling techniques. Fragments of soft mesoplastic falling under the category "Plastic film plastics 0-2.5 cm (soft)" were recorded most frequently in the investigated rivers with our monitoring techniques. During larvae net monitoring, hard plastics were more frequently found at the river surface than at the middle or bottom of the river for both macroplastic and mesoplastics, while soft plastics were more frequently detected near the bottom. For larvae net monitoring, the extrapolation factor, reflecting the concentration ratio of macroplastic items transport at different depths, i.e., from the surface downwards to the middle and the bottom ranged between 0.38 to 2.2 and 0.36 to 5.7, respectively. The extrapolation factor of mesoplastic transport from the surface downwards to the middle and the bottom ranged between 0.70 to 1.84 and 0.69 to 2.57. During trawl net monitoring, the extrapolation factor, reflecting the concentration ratio, for macroplastic ranged between 0.82 and 1.30, and for mesoplastic between 0.52 and 1.40. Overall, the findings of this study show that estimates of plastic concentrations solely based on surface transport could result in an under- or overestimation of riverine plastic transport.

Microplastics influencing aquatic environment and human health: A review of source, determination, distribution, removal, degradation, management strategy and future perspective

Microplastics (MPs) are produced from various primary and secondary sources and pose multifaceted environmental problems. They are of non-biodegradable nature and may stay in aquatic environments for a long time period. The present review has covered novel aspects pertaining to MPs that were not covered in earlier studies. It has been observed that several methods are being employed for samples collection, extraction and identification of MPs and polymer types using various equipment, chemicals and instrumental techniques. Aquatic species mistakenly ingest MPs, considering them prey and through food-chain, and then suffer from various metabolic disorders. The consumption of seafood and fish may consequently cause health implications in humans. Certain plasticizers are added during manufacturing to provide colour, durability, flexibility, and strength to plastics, but they leach out during usage, storage, and transport, as well as after entering the bodies of aquatic species and human beings. The leached chemicals (bisphenol-A, triclosan, phthalates, etc.) act as endocrine disrupting chemicals (EDCs), which effect on homeostasis; thereby causing neurotoxicity, cytotoxicity, reproductive problems, adverse behaviour and autism. Negative influence of MPs on carbon sequestration potential of water bodies is also observed, however more studies are required to understand it with a detail mechanism under natural conditions. The wastewater treatment plants are found to remove a large amount of MPs, but in turn, also act as significant sources of their release in sludge and effluents. Further, it is covered that how advanced oxidation processes, thermal- and photo-oxidation, fungi, algae and microbes degrade the plastics and increase their numbers in the surrounding environment. The management strategy comprising recovery of energy and other valuable by-products from plastic wastes, recycling and regulatory framework; are also described in detail. The future perspectives can be of paramount importance to control MPs generation and their abundance in the aquatic and other types of environments. The studies in future need to focus on advanced filtration techniques, advanced oxidation processes, energy recovery from plastic wastes and influences of MPs on carbon sequestration in aquatic environment and human health.

Unravelling land-based discharge of microplastics in River Basantar of Jammu & Kashmir, India: Understanding sinking behaviors and risk assessments

Microplastics (MPs) are ubiquitous and are increasing globally, but there is limited information available on their presence in freshwater ecosystems. This research work aims to investigate the abundance, sinking behavior, and risk assessment of MPs in the freshwater River Basantar, Jammu & Kashmir, India. Microplastic abundance in sediments was recorded in the range of 1-6 items g-1, with a mean abundance of 3 ± 1.594 item g-1, whereas MPs in surface water ranged from 200 to 850 items L-1 with a mean abundance of 530 ± 218.4 items L-1 among 12 sites for sediments and 10 sites for surface water. Besides, the sinking behavior of MPs was analyzed through portioning coefficients (Kd) at sediments-surface water interface, which ranges from 0.71 to 2.50 L Kg-1 for River Basantar. The most common shapes identified were fragments, fibres, and films, followed by pellets, foams, and lines. ATR-FTIR polymeric characterization reported polyethylene, polypropylene, polystyrene, polyethylene terephthalate, and polyvinyl chloride, and thus, polymeric risk assessment analysis was also evaluated and normally distributed in the River Basantar. Polymer Hazard Index was calculated across all the sites which observed to be polluted under risk categories "III" and "IV" for both the sediments and surface water samples. Pollution Load Index (PLI) calculated across all the sites was >1 depicting all the sites for both sediments and surface water sampling to be polluted. Pollution Risk Index was assessed and majority of surface water and sediment samples were observed to be under "Very high" risk category. The study, using principal component analysis and heatmap analysis, found that MPs are primarily a result of urbanization and anthropogenic actions, like industrial discharges, household wastes, and agricultural runoffs. This study highlights the significance of more investigation and coordinated efforts to solve the worldwide problem of plastic pollution in freshwater environments. Results data provide insight into the current state of MP contamination and will help government authorities implement strict rules and perform management interventions to reduce and monitor pollution levels in River Basantar. Future studies on the partitioning of MPs in sediments and surface water must be focused on aggregation, biofouling, plastic density & size, salinity, and flow behaviors to understand transport and deposition in rivers.

Spatiotemporal dynamics and tidal transport of microplastics in the tropical waters of the Gulf of Thailand

Microplastics (MPs) contamination was investigated along a freshwater-seawater continuum from Chumphon River to the Gulf of Thailand. The vertical distribution in the water column and contamination in green mussels were also studied. MPs were detected in all water samples and sediment samples. Furthermore, MPs were detected in 75% of the green mussels. A higher abundance of MPs was observed in the river system than in the coastal region, indicating that river runoff associated with inland human activities is the major sources of MPs in the coastal regions and cultured green mussels. In the water column, a polymer gradient varying with depth existed where low-density particles decreased from surface to subsurface and sediment while high-density particles exhibited the opposite pattern. Polymers in surface and subsurface water were predominantly composed of low-density polyethylene, polypropylene, and polystyrene particles. However, sediment samples were equally dominated by those mentioned low-density polymers and high-density polyethylene terephthalate, polyamide, rayon, and cotton particles. Furthermore, fibers were the most common shape found in water, sediment, and mussel samples representing 95% of all particles in river water samples and were evenly distributed throughout the water column regardless of density. However, only shorter fiber (mostly <1 mm) was detected in green mussel samples similar to their living environment. Blue, black and white particles dominated all samples. During the tidal cycle, half of the MPs entering the Gulf of Thailand returned to the river during high tide. This backflow predominantly comprised small fibers and low-density polymer MPs. The average daily load of MPs from Chumphon River to the Gulf of Thailand was 3.33 × 102 million items/day.

Microplastics versus natural mineral particles. How to create and test them while maintaining environmental relevance

Whether microplastics cause different effects than inert natural particles, and how to create relevant testing materials, are key questions in microplastics research. We prepared Environmentally Relevant Microplastic (ERMP) and Mineral Microparticle (ERMS) mixtures with similar levels of polydispersity and tested their 28-day chronic effects on the reproduction and growth of L. variegatus at two different organic matter (OM) contents (average and enriched). Additionally L. variegatus was exposed to ERMP and ERMS to study the particle egestion for 14 days. We observed no differences in growth or reproduction between ERMP and ERMS at particle concentrations of up to 10 % (v/v). In contrast, organisms exposed to enriched OM content increased their growth with 30 % and increased reproduction with 20 %. For ERMP with an enriched OM content, reproduction was reduced with an effect threshold EC50 of 13.68 ± 5.54 % (v/v). After 14 days of exposure to 5 % ERMP, the egestion of faecal pellets was higher compared to exposure to 5 % ERMS, suggesting that in order to acquire the same amount of nutrition, L. variegatus is spending more energy. With this study, we demonstrate that refinements in the manufacturing of environmentally diverse particle mixtures can contribute to a more realistic testing of particle effects.

Characteristics, Contamination Levels, and Ecosystem Risk Assessment of Microplastics in Surface Water of a Highly Urbanized River from a Developing Country

Microplastic (MP) contamination poses significant risks to ecosystems and human health. However, the absence of standardized protocols, detailed polymer identification, and sources identification hinders the development of targeted mitigation strategies, particularly in developing nations. There is a scarcity of comprehensive data on MP distribution, sources, and transport mechanisms in freshwater environments. This study aimed to fill these gaps by comprehensively characterizing MP contamination, elucidating distribution patterns, identifying sources, and assessing ecological risks in an urban river adjacent to a megacity. This was accomplished using stereomicroscopy, Fourier-transform infrared(FTIR) spectroscopy, and a range of risk assessment indices. The analyses revealed spatial variations in MP levels, ranging from 350 to 660 items/m3 across different sampling stations along the river. Analysis of variance(ANOVA) highlighted significant differences in the average number of MPs among the stations (F = 16.93, p ≪ 0.01), with station S3 exhibiting the highest count and station S4 the lowest. Factors such as point sources of domestic and municipal waste, as well as river navigation, likely contribute to these variations. The predominant types, colors, and sizes of MPs observed were fiber, transparent, and <0.5 mm, respectively. Notably, 80% of the MPs consisted of polyethylene (PE) and polypropylene (PP), commonly associated with land-based sources like packaging materials. Despite minor ecological risks indicated by ecosystem risk assessment indices such as the risk index(RI) and pollution load index (PLI), which recorded values of 9.04 and 1.87, respectively, the potential hazard index(PHI) rose to hazard category V, posing a substantial threat to the river ecosystem. PCA facilitated the identification of trends linked to specific pollution sources, while cluster analysis categorized MPs with similar characteristics, thereby enhancing the understanding of their distribution patterns. These findings provided novel insights into the pervasive presence and pathways of plastic pollution in developing nations, offering important considerations for international efforts to address public health and environmental challenges associated with MPs.

Wavelength Sensitive Plastic Photodissolution: Elucidating Quantum Yield Trends for Solar Activation Spectra

Plastic photodissolution into dissolved organic carbon (DOC) is a key proposed loss pathway for plastic in aquatic environments. However, the specific solar excitation wavelengths that drive photodissolution remain unknown, limiting our ability to model and predict photodissolution rates in natural aquatic environments. To better understand the impact of solar excitation wavelength on plastic photodissolution rates, we measured the wavelength sensitivity of photodissolution for a variety of transparent and semitransparent commercial and postconsumer plastic films with wide-spanning polymer chemistries. We irradiated plastic films using custom-built light-emitting diode (LED) photoreactors that emit light in the range of 275 to 445 nm and found that plastics exhibit a strong wavelength sensitivity, producing the highest DOC release rates for short wavelength ultraviolet (UV) light. We additionally calculated photodissolution quantum yield trends for transparent plastic films and then calculated photodissolution activation spectra. We found that solar UV light between 300-350 nm is responsible for most of the plastic photodissolution for all plastic compositions and predicted plastic photodissolution rates within water columns. Results advance our ability to model plastic photodissolution in natural aquatic environments.

Microplastic pollution in Taihu Lake: Spatial distribution from the lake inlet to the lake centre and vertical stratification in the water column

The aim of this study was to analyse the distribution characteristics of microplastics in lakes, assess their potential impacts on ecosystems, and explore effective management and control strategies. Despite a wealth of research focused on lake water, the variations in microplastics with offshore distance and their vertical distribution within the water column are not well understood. Here, we investigated the freshwater continuum from the inlet of Taihu Lake to the centre, and vertically from the surface to the bottom water. The results revealed that the distribution of microplastics (<5 mm in size) exhibited a clear spatial gradient. The microplastic abundance at the lake entrance was 2.12 times greater than that at the centre, and on the lake surface, the microplastic abundance was 1.36-1.69 times higher than that estimated from the water column. Notably, the proportion of small-sized microplastics (<0.1 mm) in the bottom water was 1.72 times higher than that in the surface water. The main types of polymers identified were polyamide (PA) and polyvinyl chloride (PVC), and their main sources may be from clothes washing and industrial activities. The Monte Carlo simulation results indicated that the overall risk of microplastics in surface water was higher than that in the water column, and the contributions of PVC and polyurethane (PU) to the ecological risk were 90.10% and 9.57%, respectively. Therefore, PVC and PU should be the priority of microplastic pollution control. This study provides the first comprehensive evaluation of the spatial ecological risk of microplastics in Taihu Lake, which improves our understanding of the distribution and environmental risks of microplastics in lake systems.

Microplastics and per- and polyfluoroalkyl substances (PFAS) in landfill-wastewater treatment systems: A field study

Landfills and wastewater treatment plants (WWTP) are point sources for many emerging contaminants, including microplastics and per- and polyfluoroalkyl substances (PFAS). Previous studies have estimated the abundance and transport of microplastics and PFAS separately in landfills and WWTPs. In addition, previous studies typically report concentrations of microplastics as particle count/L or count/g sediment, which do not provide the information needed to calculate mass balances. We measured microplastics and PFAS in four landfill-WWTP systems in Illinois, USA, and quantified mass of both contaminants in landfill leachate, WWTP influent, effluent, and biosolids. Microplastic concentrations in WWTP influent were similar in magnitude to landfill leachates, in the order of 102 μg plastic/L (parts-per-billion). In contrast, PFAS concentrations were higher in leachates (parts-per-billion range) than WWTP influent (parts-per-trillion range). After treatment, both contaminants had lower concentrations in WWTP effluent, although were abundant in biosolids. We concluded that WWTPs reduce PFAS and microplastics, lowering concentrations in the effluent that is discharged to nearby surface waters. However, partitioning of both contaminants to biosolids may reintroduce them as pollutants when biosolids are landfilled or used as fertilizer.

Beach wrack as a potential microplastic hot spot in the South-Eastern Baltic Sea environment

Beach wrack is considered as a major source of nutrients to the sandy coast ecosystems in the South-East Baltic Sea, and it serves as the natural beach sediment storage and habitat formation material. However, it also could be a hot spot for microplastic and other types of marine litter accumulation. We carried out the recovery rate experiments to determine the most reliable method for a rapid and cost-effective application to extract microplastics from the beach wrack. The aeration of media in a saturated solution of sodium chloride revealed to be statistically significant and reliable, therefore was selected as a most suitable to extract the microplastics from the beach wrack. This study shows that the concentration of microplastics is significantly different between the four analyzed compartments in the coastal zone. The microplastic concentration in a beach wrack, with a mean value of 0.47 ± 0.17 items/cm3, contained 4.7 times more microplastics than observed in the surface sand samples. This study estimated that on average over 450 million microplastic items could be found during the castaway event in the South-East Baltic Sea coast.

The role of marine bacteria in modulating the environmental impact of heavy metals, microplastics, and pesticides: a comprehensive review

Bacteria assume a pivotal role in mitigating environmental issues associated with heavy metals, microplastics, and pesticides. Within the domain of heavy metals, bacteria exhibit a wide range of processes for bioremediation, encompassing biosorption, bioaccumulation, and biotransformation. Toxigenic metal ions can be effectively sequestered, transformed, and immobilized, hence reducing their adverse environmental effects. Furthermore, bacteria are increasingly recognized as significant contributors to the process of biodegradation of microplastics, which are becoming increasingly prevalent as contaminants in marine environments. These microbial communities play a crucial role in the colonization, depolymerization, and assimilation processes of microplastic polymers, hence contributing to their eventual mineralization. In the realm of pesticides, bacteria play a significant role in the advancement of environmentally sustainable biopesticides and the biodegradation of synthetic pesticides, thereby mitigating their environmentally persistent nature and associated detrimental effects. Gaining a comprehensive understanding of the intricate dynamics between bacteria and anthropogenic contaminants is of paramount importance in the pursuit of technologically advanced and environmentally sustainable management approaches.

Identification of micro- and nanoplastic particles in postnatal sprague-dawley rat offspring after maternal inhalation exposure throughout gestation

Micro-nanoplastic particulates (MNPs) have been identified in both indoor and outdoor environments. From these real-world exposures, MNPs have been identified in human fluids and organ tissues, including the placenta and breastmilk. Laboratory studies have identified MNPs are capable of crossing the placental barrier and depositing in fetal tissues; however, it remained unclear if MNPs persist in offspring tissues after birth. Six pregnant Sprague-Dawley rats were divided equally into two groups: control and exposed to polyamide-12 (PA-12) MNP aerosols (11.46 ± 3.78 mg/m3) over an average of 4.35 h ± 0.39 for 10 non-consecutive days between gestational day (GD) 6 - GD 19, in our custom rodent exposure chamber, allowing for whole-body inhalation. Two-weeks after delivery in-house, offspring tissues (i.e. lung, liver, kidney, heart, brain) from 1 male and 1 female pup per litter were fixed in 4 % paraformaldehyde, sectioned, stained with hematoxylin and eosin, and assessed using hyperspectral dark-field microscopy. PA-12 MNPs were identified in all offspring tissues of the exposed dams. No MNPs were visualized in control tissues. These findings have important implications for human MNPs translocation, deposition, maternal/fetal health, and the developmental origins of health and disease. Further research is warranted to quantify MNPs mass deposition, biological accumulation, and systemic toxicity.

Determination of microplastics in sediment, water, and fish across the Orange-Senqu River basin

Microplastics are increasingly recognised as posing a significant environmental threat across systems. Their pervasive presence in freshwater poses a serious concern, given the heavy reliance of both humans and biodiversity on healthy, functioning freshwater ecosystems. Acknowledgment of the potential risks led the transboundary Orange-Senqu River Commission (ORASECOM) to include sampling for microlitter (primarily microplastics) in riverine sediment, surface water, and fishes, across Southern Africa as part of the third Joint Basin Survey (JBS3) in 2021. The aim was to establish a first, basin-wide estimate of microlitter contamination across compartments, setting a baseline for further monitoring. The survey showed that the abundance of microlitter in riverine sediment (0 - 4000 particles.kg-1 dry weight (dw)) and riverine water (1.00 ± 0.71 - 69.75 ± 68.55 SD items.L-1) varied considerably between sample sites, with no correlation between the two. The abundance of microlitter in fishes was low (average of 0.7 ± 0.4 items.individual-1). Course resolution analyses suggested that microlitter concentrations in riverine sediment and riverine water at each site did not correlate with land use directly upstream, though variation in microlitter abundance did isolate some hotspots of contamination. Discharge data collected from nine gauging stations near sampling sites confirmed that low flows prevailed in the system during the study, with high flows occurring approximately 5 months prior during the summer months. There is some variation in river flow across the catchment which is a likely driver of microlitter transport. This was evident in the polymer composition for sediment and water samples. Based on the average discharge at each gauging station and microlitter concentrations measured in riverine water, the estimated microlitter load ranged from ∼889 particles.s-1 to ∼17.9 million particles.s-1, with a substantial amount ending likely up in the mudbelt adjacent to the Orange River mouth. This assessment provides a first insight into the characterisation and distribution of microlitter in multiple compartments across the Orange-Senqu River basin. Overall, the findings highlight the need for continued monitoring across compartments at catchment scales to improve our understanding of microplastic pathways into and within riverine systems.

Seasonal variations in microplastics in a coastal wetland in southwest India as well as their risks to Sillago sihama and Gerres filamentosus

Microplastics are minute plastic particles ranging from 1 µm to 5 mm in size. Mangroves are crucial ecosystems with roles in carbon sequestration, shoreline protection, and habitat for diverse species. Despite their significance, the extent of microplastic pollution in mangroves, especially in India, remains inadequately understood. To address this gap, we conducted a seasonal sampling in the Kota mangrove ecosystem at different water column depths. Our analysis revealed average microplastic abundances of 0.93 (monsoon), 3.71 (post-monsoon), and 2.92 MPs/L (pre-monsoon). The average microplastic abundances were 19.88 and 15.86 microplastics/individual for Gerres filamentosus and Sillago sihama, respectively. Fibrous microplastics smaller than 1 mm were dominant. Transparent microplastics dominated the water column (28.57% in monsoon, 77.45% in post-monsoon, and 49.24% in pre-monsoon), and they were also prevalent in S. sihama (49.55%) and G. filamentosus (41.51%). This points towards greater bioavailability and suggests that transparent microplastics are often mistaken for prey. Anthropogenic influence is a major factor that governs microplastic distribution than season in Kota mangroves. Fourier transform infrared spectroscopy revealed that polypropylene was the dominant polymer in both water column as well as in S. sihama and G. filamentosus. We identified aquaculture, tourism, and local activities as probable sources of microplastic pollution. The monitoring data is crucial as it provides insights into microplastics pollution in two economically important fish species that are largely consumed by the local population. Exposure to microplastics from the consumption of these fish may cause serious health issues for human beings.

The Detection and Analysis of Microplastics in a Typical Mountainous Drinking Water System in China

Microplastics (MPs) are widely detected in urban drinking water systems. However, the presence and characteristics of MPs in mountainous drinking water systems with independent and simple filtration facilities have been overlooked. In this study, we revealed the ubiquity of MPs and demonstrated that their concentrations increased along with the pipeline length in Bainitan Village, Tiantai County, China. The simple filtration facility in this village did not effectively remove most MPs. Polyethylene, polyurethane, and polyethylene terephthalate were the dominant polymers in water samples (72.32% in total), while polyvinylchloride, polyurethane, and polyethylene were the most prevalent in the sediment (74.00% in total) of the reservoir. Long fragments were the predominant shape of MPs in all samples, with the majority being smaller than 100 μm. The estimated daily intake of MPs through drinking water ingestion was highest in infants (2.14-31.26 MPs/kg bw/day), compared to children (1.41-20.67 MPs/kg bw/day) and adults (1.05-15.35 MPs/kg bw/day), highlighting their increased vulnerability. This emphasizes the need for advanced water treatment systems in mountainous regions. It also underscores the necessity for government attention to improve water safety in remote areas. Our research will contribute valuable baseline data for further research on MP exposure, particularly in mountainous communities.

Exploring possible controlling factors of spatial distribution of microplastics in sediments of a river segment (Loire River, France)

Microplastics (MP) have been reported in many rivers across the globe but their depositional and archiving mechanisms in sediments are not fully understood yet. The aim of this study was to identify potential controlling factors of MP spatial distribution in surface sediment after a characterisation (sediment composition, hydrological conditions, sedimentary environment) of 14 sampling sites in an 8 km2 segment of the Loire river. Samples were collected from 3 sedimentary environments (sandbars, riverbanks and semi-active channels) with diverse flooding frequencies, grain size distributions and total organic carbon (TOC) contents. After treatment of sediment samples, MP concentrations and sizes were determined and polymer types identified by μFTIR (micro Fourier transform infrared) spectroscopy. After checking the influence of sample-scaled variability over river segment-scaled variability, MP concentrations were evaluated to 867-10635 MP/kg of sediment dry weight (sed dw, size range 25-5000 μm) in the river segment. No environmental parameters were individually correlated with MP contamination in our study, possibly due to complex depositional environments in this river segment. A systemic approach however allowed to exhibit that sediment composition reflecting hydro-morpho-sedimentary conditions can help to understand MP distribution in a river segment. A higher MP contamination observed in semi-active channel samples (median contamination value of 4797 MP/kg sed dw) could indicate that MP deposition is favoured in fine-grained (FGS) and TOC-rich sediment, reflecting less energetic hydrological conditions. Moreover, increasing flooding frequency seems to favor accumulation of MP only in the case of semi-active channels. On the contrary, less MP were detected in sandbars and riverbanks (median contamination of 1296 MP/kg sed dw), formed in higher hydrodynamical energy conditions. As a 10-fold variability of MP concentration exists in the study area, the importance of multiplying replicates even at the scale of a small river segment is underlined to access representativity of MP contamination.

Microplastic Transport and Accumulation in Rural Waterbodies: Insights from a Small Catchment in East China

Microplastic (MP) pollution in agricultural ecosystems is an emerging environmental concern, with limited knowledge of its transport and accumulation in rural waterbodies. This study investigates the distribution and sources of MP in drainage ditches influenced by pond connectivity, land use, and soil properties within a small catchment in Nanjing, East China. Sediment was collected from ditches in 18 sites across forest, agricultural, horticultural, and urban areas. Using laser-directed infrared spectroscopy (LDIR), 922 MP particles were identified. Six materials were dominant: fluororubber (FR), polyethylene terephthalate (PET), polyurethane (PU), acrylonitrile (ACR), chlorinated polyethylene (CPE), and polyethylene (PE). MP concentrations varied by land use and pond connectivity, with ditches above ponds exhibiting higher counts (1700 particles/kg) than those below (1050 particles/kg), indicating that ponds act as MP sinks. The analysis revealed site-specific MP sources, with FR linked to road runoff and PET associated with agricultural practices. Correlations between MP shape and soil properties showed that more compact and filled shapes were more commonly associated with coarser soils. PE particle size was negatively correlated with organic matter. This study highlights the need for targeted strategies to reduce MP pollution in rural landscapes, such as reducing plastic use, ditch maintenance, and improved road runoff management.

Impact of COVID-19 pandemic on microplastic occurrence in aquatic environments: A three-year study in Taihu Lake Basin, China

The impact of the Coronavirus Disease 2019 (COVID-19) pandemic on microplastic (MP) occurrence in aquatic environments deserves an in-depth study. In this study, the occurrence of MPs and environmental flux of plastics before (2019) and during (2020 and 2021) the pandemic were comparatively investigated in various aquatic compartments in the Taihu Lake Basin in China. The field-based investigations from 2019 to 2021 for Taihu Lake have shown that, at the onset of the outbreak, the MP abundance declined at a rate of 62.3 %, but gradually recovered to the pre-pandemic level. However, the amount of plastics being released into aquatic environments showed a declining trend in 2020 and 2021 compared to those in 2019, with decrease rates of 13.7 % and 15.8 %, respectively. Characterization analysis of MP particles and source apportionment framework implied that while the contributions of tire abrasion and domestic waste to MP occurrence were depleted owing to the reduction in human activity during the pandemic, weathering and fragmentation of retained plastics contributed to the recovery of stored MPs. This study provides insights into the anthropogenic influences on MP occurrence, and supports policymakers in managing and controlling plastic contamination in large freshwater systems in the "new normal" phase.

Understanding the mechanism of microplastic-associated antibiotic resistance genes in aquatic ecosystems: Insights from metagenomic analyses and machine learning

The pervasive presence of microplastics (MPs) in aquatic systems facilitates the transmission of antibiotic resistance genes (ARGs), thereby posing risks to ecosystems and human well-being. However, owing to variations in environmental backgrounds and the limited scope of research subjects, studies on ARGs in MPs lack unified conclusions, particularly regarding whether different types of MPs selectively promote ARG enrichment. Analysing large-scale datasets can better encompass broad spatiotemporal scales and diverse samples, facilitating a more extensive exploration of the complex ecological relationships between MPs and ARGs. The present study integrated existing metagenomic datasets to conduct a comprehensive risk assessment and comparative analysis of resistance groups across various MPs. In addition, we endeavoured to elucidate potential associations between ARGs and bacterial taxa, as well as MP structural features, using machine learning (ML) methods. The findings of our research highlight the pivotal role of MP type in shaping plastispheres, accounting for 9.56 % of the biotic variation (Adonis index) and explaining 18.59 % of the ARG variance. Compared to conventional MPs, biodegradable MPs, such as polyhydroxyalkanoates (PHA) and polylactic acid (PLA), exhibit lower species uniformity and diversity but pose a higher risk of ARG occurrence. These ML approaches effectively forecasted ARG abundance by using the bacterial taxa and molecular structure descriptors (MDs) of MPs (average R2tra = 0.882, R2test = 0.759). Feature analysis showed that MDs associated with lipophilicity, solubility, toxicity, and surface potential significantly influenced the relative abundance of ARGs in the plastispheres. The interpretable multiple linear regression (MLR) model, particularly notable, elucidated a linear relationship between bacterial genera and ARGs, offering promise for identifying potential ARG hosts. This study offers novel insights into ARG dynamics and ecological risks within aquatic plastispheres, highlighting the importance of comprehensive MP monitoring initiatives.

Microplastics abundance and potential ecological risk assessment in sediment, water and fish of Deepor Beel-a Ramsar Wetland of the Brahmaputra plain, India

Microplastics (MPs) are increasingly recognized as environmental contaminants with complex impacts on fish and other aquatic organisms. This study determined the microplastics abundance and the induced-ecological risks of microplastics in water, sediment, and commonly harvested fishes of a Ramsar site, Deepor Beel of Assam, India. Six samples of water and sediment were collected with nine individuals of two commonly harvested fish species Puntius sophore (Pool Barb) and Gudusia chapra (Indian River Shad). The abundance of microplastics in water and sediments were analyzed through organic matter digestion using hydrogen peroxide (H2O2, 30%) and sodium chloride (NaCl) for density separation. Potassium hydroxide (KOH, 10%) was used for digestion of fish gut. The microplastics were identified visually and chemically characterized through micro-Raman spectroscopy. Total 467 microplastic particles in water and sediment, and 62 particles in fish were identified. An average concentration of 0.55 ± 0.06 particles/L in water, 4.03 ± 0.41 particles/100 g in sediment samples, 3.83 ± 2.26 particles/individual in Puntius sophore, and 6.5 ± 3.40 particles/individual in Gudusia chapra were detected. Fibers accounted to the major shape of microplastic in water (54%) and sediment (50%), whereas fragments (65%) were the major shapes detected in both fishes. The color composition includes blue, black, red, green, brown, yellow, and transparent. Fiber particles size ranged between 150 and 1782 µm, fragments within 85-325 µm, and sphere within 85-220 µm. Chemical characterization of microplastics revealed polymer types including polypropylene (PP = 27%), polyvinyl chloride (PVC = 25%), acrylonitrile-butadiene-styrene (ABS = 18%), polycarbonate (PC = 13%), polyethylene (12%), and polystyrene (PS = 5%). PHI levels were at hazard level III and V for water and sediment samples and at level IV for both fish species. The PLI at hazard level I indicated low pollution levels, whereas the PERI were within danger and extreme danger levels. This study is the first report in abundances of microplastics and the ecological risk assessment of microplastics in surface waters, sediments and fishes of Deepor Beel wetland.

Microplastics monitoring in freshwater systems: A review of global efforts, knowledge gaps, and research priorities

The escalating production of synthetic plastics and inadequate waste management have led to pervasive microplastic (MP) contamination in aquatic ecosystems. MPs, typically defined as particles smaller than 5 mm, have become an emerging pollutant in freshwater environments. While significant concern about MPs has risen since 2014, research has predominantly concentrated on marine settings, there is an urgent need for a more in-depth critical review to systematically summarize the current global efforts, knowledge gaps, and research priorities for MP monitoring in freshwater systems. This review evaluates the current understanding of MP monitoring in freshwater environments by examining the distribution, characteristics, and sources of MPs, alongside the progression of analytical methods with quantitative evidence. Our findings suggest that MPs are widely distributed in global freshwater systems, with higher abundances found in areas with intense human economic activities, such as the United States, Europe, and China. MP abundance distributions vary across different water bodies (e.g., rivers, lakes, estuaries, and wetlands), with sampling methods and size range selections significantly influencing reported MP abundances. Despite great global efforts, there is still a lack of harmonized analyzing framework and understanding of MP pollution in specific regions and facilities. Future research should prioritize the development of standardized analysis protocols and open-source MP datasets to facilitate data comparison. Additionally, exploring the potential of state-of-the-art artificial intelligence for rapid, accurate, and large-scale modeling and characterization of MPs is crucial to inform effective strategies for managing MP pollution in freshwater ecosystems.

Diving into the Depths: Uncovering Microplastics in Norwegian Coastal Sediment Cores

High concentrations of microplastics (MPs) have been documented in the deep-sea surface sediments of the Arctic Ocean. However, studies investigating their high-resolution vertical distribution in sediments from the European waters to the Arctic remain limited. This study examines MPs in five sediment cores from the Norwegian Coastal Current (NCC), encompassing the water-sediment interface and sediment layers up to 19 cm depth. Advanced analytical methods for MP identification down to 11 μm in size were combined with radiometric dating and lithology observations. MPs were present across all sediment cores, including layers predating the introduction of plastics, with concentrations exhibiting significant variation (54-12,491 MP kg-1). The smallest size class (11 μm) predominated in most sediment layers (34-100%). A total of 18 different polymer types were identified across all sediment layers, with polymer diversity and depth correlations varying widely between stations. Our findings suggest that differences in seafloor topography and the impact of anthropogenic activities (e.g., fishing) lead to varying environmental conditions at the sampling sites, influencing the vertical distribution of MPs. This challenges the reliability of using environmental parameters to predict MP accumulation zones and questions the use of MPs in sediment cores as indicators of the Anthropocene.

Distribution and risk assessment of microplastics in water, sediment and brine shrimps in a remote salt lake on the Tibetan Plateau, China

Microplastics (MPs) are pervasive environmental contaminants that have infiltrated even the most remote ecosystems. Despite their widespread distribution, the transfer patterns and impacts of MPs in remote lakes remain poorly understood. This study aimed to address the knowledge gap regarding the pathways and consequences of MP pollution in these isolated environments. Focusing on Kyêbxang Co, a remote salt lake in Tibet, this study investigated the transfer patterns, sources and ecological impacts of MPs, providing insights into their mobility and fate in pristine ecosystems. Water, sediment and biota (brine shrimp) samples from Kyêbxang Co, collected during the summer of 2020, were analyzed using µ-Raman spectroscopy to determine MP abundances, polymer types and potential sources. Findings indicated significant MP contamination in all examined media, with concentrations highlighting the role of runoff in transporting MPs to remote locations. The majority of detected MPs were small fragments (<0.5 mm), constituting over 93 %, with polypropylene being the predominant polymer type. The presence of a halocline may slow the descent of MPs, potentially increasing the exposure and ingestion risk to brine shrimp. Despite the currently low ecological risk estimated for MPs, this study underscores the need for long-term monitoring and development of a comprehensive ecological risk assessment model for MPs.

Solute flow and particle transport in aquatic ecosystems: A review on the effect of emergent and rigid vegetation

In-channel vegetation is ubiquitous in aquatic environments and plays a critical role in the fate and transport of solutes and particles in aquatic ecosystems. Recent studies have advanced our understanding of the role of vegetation in solute flow and particle transport in aquatic ecosystems. This review summarizes these papers and discusses the impacts of emergent and rigid vegetation on the surface flow, the advection and dispersion of solutes, suspended load transport, bedload transport, and hyporheic exchange. The two competing effects of emergent vegetation on the above transport processes are discussed. On the one hand, emergent vegetation reduces mean flow velocity at the same surface slope, which reduces mass transport. On the other hand, at the same mean flow velocity, vegetation generates turbulence, which enhances mass transport. Mechanistic understanding of these two competing effects and predictive equations derived from laboratory experiments are discussed. Predictive equations for the mean flow velocity and turbulent kinetic energy inside an emergent vegetation canopy are derived based on force and energy balance. The impacts of emergent vegetation on the advection-dispersion process, the suspended load and bedload transport, and the hyporheic exchange are summarized. The impacts of other vegetation-related factors, such as vegetation morphology, submergence, and flexibility, are briefly discussed. The role of vegetation in transporting other particles, such as micro- and macro-plastics, is also briefly discussed. Finally, suggestions for future research directions are proposed to advance the understanding of the dynamic interplays among natural vegetation, flow dynamics, and sedimentary processes.

Plastic litter is a part of the carbon cycle in an urban river: Microplastic and macroplastic accumulate with organic matter in floating debris rafts

Watershed models of plastic export from rivers to oceans have large uncertainties, and improvements require direct measurements of riverine macroplastic (>5 mm) and microplastic (<5 mm). Also, plastic represents allochthonous carbon inputs to rivers but is rarely measured as carbon mass. We quantified plastic and organic matter within floating debris rafts and open water in an urban river. Macroplastics only occurred in debris rafts. Microplastics had higher concentrations in debris rafts relative to open water. Across sites, organic matter was positively correlated with microplastics and macroplastics. Last, carbon in plastic was 40% of the carbon mass in coarse particulate organic matter in debris rafts. Floating plastic litter accumulates with particulate organic matter in debris rafts. Plastic is an overlooked and ecological meaningful component of carbon standing stocks in urban rivers. Results will inform improved carbon budget calculation in rivers and watershed models of plastic export. PRACTITIONER POINTS: Plastic particles floating on the surface of an urban river accumulate in debris rafts compared to open water in terms of count and mass. Abundance and composition of plastic particles in debris rafts were distinct from those in open water areas. Plastic litter as units of carbon mass was in the same order of magnitude as carbon mass in course particulate organic matter. Plastic litter moves in similar ways to naturally occurring organic particles and should be measured as a part of the riverine carbon cycle.

Unveiling the ecotoxicological impact of microplastics on organisms - the persistent organic pollutant (POP): A comprehensive review

Microplastics have been ubiquitous in our environment for decades, and numerous studies have revealed their extensive dispersion, reaching far beyond the surface of the land, soil, aquatic ecosystems. They have infiltrated the food-chain, the food web, even the air we breathe, as well as the water we drink. Microplastics have been detected in the food we consume, acting as vectors for hazardous chemicals that adhere to their hydrophobic surfaces. This can result in the transfer of these chemicals to the aquatic life, posing a threat to their well-being. The release of microplastics into different environmental settings can give rise to various eco-toxicological implications. The substantial body of literature has led scientists to the consensus that microplastic pollution is a global problem with the potential to impact virtually any type of ecosystem. This paper aims to discuss crucial information regarding the occurrence, accumulation, and ecological effects of microplastics on organisms. It also highlights the new and emerging disease named "Plasticosis" that is directly linked to microplastics and its toxicological effects like permanent scarring and long-term inflammation in the digestive system of the seabirds. By comprehending the behaviour of these microplastic pollutants in diverse habitats and evaluating their ecological consequences, it becomes possible to facilitate a better understanding of this toxicological issue.

Tire-derived contaminants 6PPD and 6PPD-Q: Analysis, sample handling, and reconnaissance of United States stream exposures

The environmental ubiquity of tire and road wear particles (TRWP) underscores the need to understand the occurrence, persistence, and environmental effects of tire-related chemicals in aquatic ecosystems. One such chemical is 6PPD-quinone (6PPD-Q), a transformation product of the tire antioxidant 6PPD. In urban stormwater runoff 6PPD-Q can exceed acute toxicity thresholds for several salmonid species and is being implicated in significant coho salmon losses in the Pacific Northwest. There is a critical need to understand the prevalence of 6PPD-Q across watersheds to identify habitats heavily affected by TRWPs. We conducted a reconnaissance of 6PPD and 6PPD-Q in surface waters across the United States from sites (N = 94) with varying land use (urban, agricultural, and forested) and streamflow to better understand stream exposures. A rapid, low-volume direct-inject, liquid chromatography mass spectrometry method was developed for the quantitation of 6PPD-Q and screening for 6PPD. Laboratory holding times, bottle material, headspace, and filter materials were investigated to inform best practices for 6PPD-Q sampling and analysis. Glass bottles with PTFE-lined caps minimized sorption and borosilicate glass fiber filters provided the highest recovery. 6PPD-Q was stable for at least 5 months in pure laboratory solutions and for 75 days at 5 °C with minimal headspace in the investigated surface water and stormwaters. Results also indicated samples can be frozen to extend holding times. 6PPD was not detected in any of the 526 analyzed samples and there were no detections of 6PPD-Q at agricultural or forested sites. 6PPD-Q was frequently detected in stormwater (57%, N = 90) and from urban impacted sites (45%, N = 276) with concentrations ranging from 0.002 to 0.29 μg/L. The highest concentrations, above the lethal level for coho salmon, occurred during stormwater runoff events. This highlights the importance of capturing episodic runoff events in urban areas near ecologically relevant habitat or nursery grounds for sensitive species.