Sinking characteristics of microplastics in the marine environment

Seasonal distribution of microplastics and associated ecological risks in a semi-arid freshwater ecosystem in India

Microplastics are persistent contaminants across all environmental matrices. However, there is a paucity of studies conducted in semi-arid aquatic environments. The present study investigated the seasonal variations in the distribution and characteristics of microplastics in water samples of Man Sagar Lake in northwestern India. The findings revealed that the average abundance of microplastics in samples was notably lower during the pre-monsoon season (42.93 ± 29.72 particles/L) compared to the post-monsoon season (70.54 ± 36.53 particles/L). A significant difference in microplastic abundance across different sampling locations was observed between the two seasons (F = 7.82, p < 0.0001). The majority of microplastics present in the samples during both seasons measured less than 500 μm in size, with fragments and fibers being the predominant shapes, and transparent being the most common-colored microplastic. The most abundant polymers detected were polyethylene, polypropylene, and polystyrene. Microplastic contamination factor (MCf) and Pollution Load Index (PLI >1) indicated a moderate to high level of microplastic contamination across all the sampling locations in both seasons. Furthermore, the potential ecological risk index (PERI) indicated that nearly 70 % of the lake area falls under the category of very high ecological risk in both seasons. Additionally, Spearman's correlation and PCA were employed to assess the interactions of microplastics with water quality parameters and potential source identification, respectively. The study's findings could help in developing region-specific remediation and prevention strategies by identifying high-risk areas and potential sources contributing to microplastic contamination.

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.

Microplastics in coral from three Mascarene Islands, Western Indian Ocean

Little is known about microplastics (MPs) in corals from the Indian Ocean. We compared MP concentrations, morphotypes, size, colours, and polymer compositions in six coral genera from three remote Mascarene islands (Rodrigues, St. Brandon's Atoll, and Agalega) of the Republic of Mauritius, on a 1200 km transect located in the South Equatorial Current (SEC). The mean MP concentration was 0.78 n/g (53 % fibres) with no significant differences between islands. Polymers were polypropylene (78 %) and polyethylene (18 %). We conclude that the SEC's MP concentrations and compositions have homogenized over thousands of kilometres across the Indian Ocean. We discuss the lack of hazardous polyurethane MPs in coral samples given obvious sources on St Brandon. To the best of our knowledge, this study is the first to report on MPs in coral from the Western Indian Ocean and the Mascarene Islands providing a baseline for further research, monitoring, mitigation, and policy development.

Microplastic contamination of intertidal sediment and cockles (Cerastoderma edule)

Microplastic pollution represents a new threat to both marine environments and the species that reside within them. This study examined the temporal concentrations of microplastics found in the commercially and ecologically important bivalve, Cerasastoderma edule and the presence of microplastics in intertidal sediment from the Special Area of Conservation (SAC) and Special Protected Area (SPA) of Dundalk Bay, Ireland. A microplastic range of 1.55 ± 1.38 to 1.92 ± 1.00 g-1 and 3.43 ± 2.47 to 6.90 ± 3.68 ind-1 was reported between seasons. Microfibres dominated the shape of microplastics present in both sediment and cockles. While a wider range of polymers were identified in cockles than in sediment, microplastic concentrations recovered from both intertidal sites studied were approximately double the estimated safe loading levels for this pollutant. The potential of cockles to perform as shallow environment biomonitors of microplastic pollution was identified as they presented buoyant microplastics that were not identified in sediment samples.

Identification Tools of Microplastics from Surface Water Integrating Digital Image Processing and Statistical Techniques

The primary objective of this study was to demonstrate the potential of digital image analysis as a tool to identify microplastic (MP) particles in surface waters and to facilitate their characterisation in terms of 2D and 3D morphology. Digital image analysis preceded by microscopic analysis was used for an exhaustive quantitative and qualitative evaluation of MPs isolated from the Vistula River. Using image processing procedures, 2D and 3D shape descriptors were determined. Principal Component Analysis was used to interpret the relationships between the parameters studied, characterising MP particle geometry, type and colour. This multivariate analysis of the data allowed three or four main factors to be extracted, explaining approximately 90% of the variation in the data characterising MP morphology. It was found that the first principal component for granules, flakes and films was largely represented by strongly correlated with 2D shape descriptors (area, perimeter, equivalent area diameter) and 3D shape descriptors (Corey Shape Factor, Compactness, Dimensionality). Considering the scraps, principal component PC1 was represented by only five of the above descriptors, and the Compactness variable had the largest contribution to principal component PC2. In addition, for granules, flakes and films, a relationship between 2D shape and the colour of their particles could be observed. For the most numerous MP group identified of multicoloured scraps, no such association was found. The results of our study can be used for further multivariate analysis regarding the presence of microplastic floating on the river surface, with a particular focus on particles of secondary origin. This is of key importance for optimising future efforts in conducting small-scale and multidimensional monitoring of and reducing plastics in the aquatic environment.

Human exposure to microplastics via the consumption of nonalcoholic beverages in various packaging materials: The case of Hong Kong

There is growing concern over microplastics in food and beverages, with potential implications for human health. However, little is known about microplastics in nonwater, nonalcoholic packaged beverages. This study addresses this research gap by implementing a dual-method approach that includes laboratory analysis to quantify microplastics in 50 packaged nonalcoholic beverages sold in Hong Kong, coupled with a beverage frequency questionnaire survey to provide a more accurate estimate of microplastic intake from these beverages. The beverages analysed spanned five categories-juice drinks, ready-to-drink teas, soda waters, soft drinks, and sports and energy drinks-and were packaged in four forms: aluminium cans, aseptic cartons, plastic bottles and glass bottles. The results showed that all beverage samples contained microplastics, with an average abundance of 42.1 ± 41.2 n/L (interquartile range [IQR]: 17.8-54.1 n/L), and these particles were predominantly smaller than 150 µm in size. Additionally, based on an annual beverage consumption rate of 157.3 ± 209.7 L/capita (IQR: 42.9-183.0 L/capita), it is estimated that Hong Kong adults ingest approximately 6200 microplastics per capita each year. The potential primary sources of these microplastics are atmospheric fallout and the packaging materials that endure mechanical stresses during the manufacturing and transportation of beverages. Compared to other known routes of exposure, including air, seafood, sugar, salt and honey, packaged nonalcoholic beverages present a comparable level of microplastic exposure, being lower than the first three but higher than the latter two. Nevertheless, the high prevalence of smaller microplastics in the samples is concerning. This study is considered to be important for food safety and human health, as it not only raises public awareness about microplastic contamination in packaged beverages but also serves as a call to action for the beverage industry to adopt more robust safety measures and for policymakers to revise packaging standards to reduce microplastic contamination and safeguard public health.

Plastic waste management in recycling facilities: Intentionally generated MPs as an emerging contaminant

There is little knowledge about microplastic (MP) pollution in plastic recycling facility (PRF) wastewater. In this study, MPs in the wastewaters of four PRFs located in Türkiye were characterized for size, shape, color, and polymer types after sieving from 5,000 µm to the lowest 75 µm with seven sieves. The wet peroxide oxidation procedure was applied before attenuated total reflectance fourier transform infrared spectroscopy analysis for polymer identification. Polyethylene, and polypropylene were the dominant (75 % of total count) MP types within 22 polymer types. Average hit qualities of polymers increased from 69 % to above 84 % for the device software (OPUS) and open software (OpenSpecy). The abundance of MPs was determined as 53,987 MPs/L and 0.8 g MP/L for mixed PRFs 7,582 MPs/L and 4.6 g/L for the LDPE recycling facility, and 2,196 MPs/L and 0.06 g MPs/L for the granulation cooling water by count and weight, respectively. Small-sized MPs are found in the bottom sample much more than the surface and effluent samples in the washing tank. This indicated that MPs adsorbed the pollutants settled in the washing tank due to adsorbed pollution/biofilm. A maximum of 4.6 kg MP/ton of plastic recycled can be discharged as MPs that can be recovered. Considering the plastics recycling capacity, discharged MPs in these PRFs are possibly above 30,000 tons.

The distribution of sediment microplastics assemblages is driven by location and hydrodynamics, not sediment characteristics, in the Gulf of Maine, USA

Microplastics (MP) are found in marine sediments across the globe, but we are just beginning to understand their spatial distribution and assemblages. In this study, we quantified MP in Gulf of Maine, USA sediments. MP were extracted from 20 sediment samples, followed by polymer identification using Raman spectroscopy. We detected 27 polymer types and 1929 MP kg-1 wet sediment, on average. Statistical analyses showed that habitat, hydrodynamics, and station proximity were more important drivers of MP assemblages than land use or sediment characteristics. Stations closer to one another were more similar in their MP assemblages, tidal rivers had higher numbers of unique plastic polymers than open water or embayment stations, and stations closer to shore had higher numbers of MP. There was little evidence of relationships between MP assemblages and land use, sediment texture, total organic carbon, or contaminants.

Analysis of micro(nano)plastics based on automated data interpretation and modeling: A review

The widespread presence of micro(nano)plastics (MNPs) in the environment threatens ecosystem integrity, and thus, it is necessary to determine and assess the occurrence, characteristics, and transport of MNPs between ecological components. However, most analytical approaches are cost- and time-inefficient in providing quantitative information with sufficient detail, and interpreting results can be difficult. Alternative analyses integrating novel measurements by imaging or proximal sensing with signal processing and machine learning may supplement these approaches. In this review, we examined published research on methods used for the automated data interpretation of MNPs found in the environment or those artificially prepared by fragmenting bulk plastics. We critically reviewed the primary areas of the integrated analytical process, which include sampling, data acquisition, processing, and modeling, applied in identifying, classifying, and quantifying MNPs in soil, sediment, water, and biological samples. We also provide a comprehensive discussion regarding model uncertainties related to estimating MNPs in the environment. In the future, the development of routinely applicable and efficient methods is expected to significantly contribute to the successful establishment of automated MNP monitoring systems.

Settling of microplastics in mucus-rich water column: The role of biologically modified rheology of seawater

Non-buoyant microplastics (MPs) sink through the marine water column, adversely affecting the ecosystem. The manner in which MPs influence the water environment depends to a large extent on their settling dynamics, driven by their properties and the physio-chemical characteristics of water column. However, some properties of seawater remain elusive, limiting our ability to fully explain the sinking processes of MPs. One of the gaps in our understanding relates to the elevated content of exopolymers (EPSs) secreted by algae and bacteria, which locally transform seawater into a non-Newtonian liquid, altering the hydrodynamics of particle transport. In this study, we present a series of lab-scale experiments on the dynamics of isometric (spheres and irregular particles) and anisometric (disks, rods, and blades) MPs settling in artificial seawater with the addition of polysaccharides. We find that upon the appearance of EPSs in seawater, the sinking velocity of MPs diminishes and may fluctuate, the orientation pattern changes in a non-intuitive way, and MPs may tumble. As measured in rheological tests, these consequences result from seawater gaining viscoelastic and shear-thinning properties. Our findings raise concerns that mucus-rich seawater may favor the aggregation of MPs with organic matter, interaction with biota, and biofouling, which can affect the biogeochemistry of the marine ecosystem. Based on these findings, we recommend that seawater rheology, modified by excessive amounts of EPSs during algal blooms, should be considered in biogeochemical and microplastic transport models.

Terminal settling and rising velocity prediction of macroplastics: Medical face masks as newly emerged objects of concern

The widespread use of medical face masks during the SARS-CoV-2 pandemic has significantly increased plastic waste, with a considerable proportion of these masks ending up in the environment. As these masks are transported through wind and surface runoff, they accumulate in water bodies, leading to pollution and potential environmental risks. Understanding the transport behavior of these macroplastic items is crucial for addressing the pollution problem effectively. This study focuses on predicting the terminal settling and rising velocities of medical face masks, considering their unique shape and composition, aiding upcoming research with base data for, e.g., numerical transport simulations. Three different mask types, including surgical face masks, FFP2-standard face masks, and non-medical reusable face masks, were investigated in various shapes, and modified transport formulas that take into account the shape factor and sphere-equivalent radius of the masks to accurately predict their terminal settling and rising velocities were tested for applicability. The results reveal that the unique shapes of masks influence the terminal settling and rising velocity to a greater extent than their density difference to water. The absolute mean terminal velocities ranged from 0.05 to 0.3 m/s. Understanding the transport behavior of the studied face masks provides valuable insights for managing and mitigating the pollution caused by discarded face masks in water bodies and helps to develop effective strategies for environmental protection. Furthermore, the findings highlight the need for comprehensive laboratory studies to investigate the rising and settling velocities of common macroplastic items, as they are expected to vary in their hydrodynamic behavior significantly.

Effects of near-bed turbulence on microplastics fate and transport in streams

Quantifying the impact of hyporheic exchange is crucial for understanding the transport and fate of microplastics in streams. In this study, we conducted several Computational Fluid Dynamics (CFD) simulations to investigate near-bed turbulence and analyze vertical hyporheic exchange. Different arranged spheres were used to represent rough and permeable sediment beds in natural rivers. The velocities associated with vertical hyporheic flux and the gravitational force were compared to quantify the susceptibility of microplastics to hyporheic exchange. Four scenario cases representing different channel characteristics were studied and their effects on microplastics movements through hyporheic exchange were quantitatively studied. Results show that hyporheic exchange flow can significantly influence the fate and transport of microplastics of small and light-weighted microplastics. Under certain conditions, hyporheic exchange flow can dominate the behavior of microplastics with sizes up to around 800 μm. This dominance is particularly evident near the sediment-water interface, especially at the top layer of sediments. Higher bed porosity enhances the exchange of microplastics between water and sediment, while increased flow conditions extend the vertical exchange zone into deeper layers of the bed. Changes in the bedform lead to the most pronounced vertical hyporheic exchange, emphasizing the control of morphological features on microplastics transport. Furthermore, it is found that sweep-ejection events are prevailing near the bed surface, serving as a mechanism for microplastics transport in rivers. As moving from the water column to deeper layers in the sediment bed, there's a shift from sweeps dominance to ejections dominance, indicating changes of direction in microplastics movement at different locations.

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

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

Extreme weather events as an important factor for the evolution of plastisphere but not for the degradation process

Marine plastics, with their negative effects on marine life and the human health, have been recently recognized as a new niche for the colonization and development of marine biofilms. Members of the colonizing communities could possess the potential for plastic biodegradation. Thus, there is an urgent need to characterize these complex and geographically variable communities and elucidate the functionalities. In this work, we characterize the fungal and bacterial colonizers of 5 types of plastic films (High Density Polyethylene, Low Density Polyethylene, Polypropylene, Polystyrene and Polyethylene Terepthalate) over the course of a 242-day incubation in the south-eastern Mediterranean and relate them to the chemical changes observed on the surface of the samples via ATR-FTIR. The 16s rRNA and ITS2 ribosomal regions of the plastisphere communities were sequenced on four time points (35, 152, 202 and 242 days). The selection of the time points was dictated by the occurrence of a severe storm which removed biological fouling from the surface of the samples and initiated a second colonization period. The bacterial communities, dominated by Proteobacteria and Bacteroidetes, were the most variable and diverse. Fungal communities, characterized mainly by the presence of Ascomycota, were not significantly affected by the storm. Neither bacterial nor fungal community structure were related to the polymer type acting as substrate, while the surface of the plastic samples underwent weathering of oscillating degrees with time. This work examines the long-term development of Mediterranean epiplastic biofilms and is the first to examine how primary colonization influences the microbial community re-attachment and succession as a response to extreme weather events. Finally, it is one of the few studies to examine fungal communities, despite them containing putative plastic degraders.

The impact of riverine particles on the vertical velocities of large microplastics

Microplastics interact with other suspended particles in aquatic systems, which may impact their environmental fate. Little is known about aggregation between suspended sediment and larger microplastics (1-5 mm), and how this impacts the vertical velocities of microplastics, although it was hypothesised these are size limited. Consumer items made of five common polymers: polypropylene (PP), high density polyethylene (HDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and polystyrene (PS), were fragmented by cryomilling and their vertical velocities (rising/settling) measured experimentally before and after 24-hours of aggregation with riverine particles. Microplastic size (microscopy), zeta potential and density (density gradient column) were measured, with aggregation quantified using microscopy. PP had an experimental density of 1052 kg·m-3, and sank in river water, although it is often stated as being buoyant based on literature density values. Aggregation occurred with all five polymers: 39 %-72 % of microplastics were observed to have sediment and/or organic particles adhered, depending on the polymer type. PVC had the least negative zeta potential, -8.0 ± 3.0, and showed a much higher number of adhered sediment particles than all other polymers: on average 4.55 particles, compared with <1.72 particles for other polymers. For four polymers, aggregation did not significantly change vertical velocities. However, PP particles showed a significantly slower settling velocity after aggregation: a decrease of 6.3 % based on mean averages, from 9.7 × 10-3 to 9.1 × 10-3 m·s-1. Theoretical calculations showed the amount of adsorbed sediment or biofilm required to induce a microplastic density change of ∼50 kg·m-3 was much higher than observed experimentally. Overall, this study indicates that the vertical velocities of larger microplastics are less influenced by interactions with natural particles than smaller microplastics.

Effects of weathering on the properties and fate of secondary microplastics from a polystyrene single-use cup

In this work, we probed the changes to some physicochemical properties of polystyrene microplastics generated from a disposable cup as a result of UV-weathering, using a range of spectroscopy, microscopy, and profilometry techniques. Thereafter, we aimed to understand how these physicochemical changes affect the microplastic transport potential and contaminant sorption ability in model freshwaters. Exposure to UV led to measured changes in microplastic hydrophobicity (20-23 % decrease), density (3% increase), carbonyl index (up to 746 % increase), and microscale roughness (24-86 % increase). The settling velocity of the microplastics increased by 53 % after weathering which suggests that UV aging can increase microplastic deposition to sediments. This impact of aging was greater than the effect of the water temperature. Weathered microplastics exhibited reduced sorption capacity (up to 52 % decrease) to a model hydrophobic contaminant (triclosan) compared to unaged ones. The adsorption of triclosan to both microplastics was slightly reversible with notable desorption hysteresis. These combined effects of weathering could potentially increase the transport potential while decreasing the contaminant transport abilities of microplastics. This work provides new insights on the sorption capacity and mobility of a secondary microplastic, advances our knowledge about their risks in aquatic environments, and the need to use environmentally relevant microplastics.

One-year variation in quantity and properties of microplastics in mussels (Mytilus galloprovincialis) and cockles (Cerastoderma edule) from Aveiro lagoon

As filter feeders, marine bivalves inhabiting estuarine and coastal areas are directly exposed to microplastics (MPs) in water. To assess whether MPs number, and their shape, size, colour, and polymer type present in mussels (Mytilus galloprovincialis) and cockles (Cerastoderma edule) varied over one year, bivalves were collected over the year of 2019 in the lower part of the coastal Aveiro lagoon, Portugal. After extraction from the bivalve's whole-body soft tissues, a subset of the visually inspected particles was randomly separated for identification using the Fourier-transform mid-infrared (FT-MIR) spectroscopy. A fraction of the inspected particles, 26-32% of particles >100 μm, and 59-100% of smaller ones were confirmed as MPs. Concentrations varied within the intervals of 0.77-4.3 items g-1 in mussels and 0.83-5.1 items g-1 in cockles, with the lowest values observed in January. In winter, the accumulation of large-sized fibers was composed of a mixture of plastic types, which contrasted against the most abundant MPs in summer consisting mainly of polyethylene of diverse size classes and shapes. Temperature decrease registered in winter might have triggered a lower filtration rate, resulting in lower MPs concentrations in the whole-soft body tissues of organisms. Different properties of MPs found in bivalves between January-February and August-September appear to reflect changes in the characteristics of MPs available in the Aveiro lagoon.

Settling processes of cylindrical microplastics in quiescent water: A fully resolved numerical simulation study

The settling process of marine microplastics (MPs) is crucial research concerning the transport and movement of MPs. The settling processes of MP fibers that possess a cylindrical geometry are affected by environmental factors and properties. In this study, a three-dimensional numerical model for the still water settling of MPs with complex shapes was constructed using the lattice Boltzmann method (LBM) and the immersed boundary method (IBM). The fully resolved settling simulation of cylindrical MPs was achieved, and the model results demonstrated good agreement with the semi-empirical settling velocity formulas. Based on the simulation results, the critical aspect ratio of the cylindrical MP was found to be between 0.93 and 0.94. Near this critical aspect ratio, there is a decline in the drag force. Additionally, it was found that the angular displacement and aspect ratio influence horizontal movement but not the vertical settling velocity, while the density only affects vertical movement.

A review of methods for modeling microplastic transport in the marine environments

Microplastic (MP) pollution is ubiquitous in the oceans and poses serious threats to the marine ecosystems. Nowadays numerical modeling has become one of the widely used tools for monitoring and predicting the transport and fate of MP in marine environments. Despite the growing body of research on numerical modeling of marine MP, the advantages and disadvantages of various modeling methods have not received systematic evaluation in published works. Important aspects such as parameterization schemes for MP behaviors, factors influencing MP transport, and proper configuration in beaching are essential for guiding researchers to choose proper methods in their work. For this purpose, we comprehensively reviewed the current knowledge on factors influencing MP transport, classified modeling approaches according to the governing equations, and summarized up-to-date parameterization schemes for MP behaviors. Critical factors such as vertical velocity, biofouling, degradation, fragmentation, beaching, and washing-off were reviewed in the frame of MP transport processes.

The relationship between microplastics in eastern oysters (Crassostrea virginica) and surrounding environmental compartments in Long Island Sound

Microplastics (MP, <5 mm) are found in coastal waters across various environmental compartments (biota, water, marine snow, sediment). The eastern oyster (Crassostrea virginica) is a commercially important species that ingests MP; however, oysters are discriminant suspension feeders that do not consume all particles to which they are exposed. This study explored the relationship between MP in oysters on a recreational oyster bed and the surrounding environmental compartments in Long Island Sound (LIS; USA). The quantity and types of MP in oysters, water, marine snow, and sediment samples were determined. Precautions were taken to minimize and monitor MP contamination in the field and laboratory to improve the quality of data collected. Microplastics were isolated from samples via chemical digestion, and any suspected particles were identified using micro-Fourier transform infrared spectroscopy. A total of 86 MP were identified out of 885 suspected particles across environmental media. The highest MP count in an individual oyster was nine, indicating low concentrations of MP in oysters and the surrounding environment. Few polymers, except polyethylene terephthalate, were shared between oysters and the surrounding environmental compartments. Sediments contained the highest number of MP across all environmental compartments (42 total). These data aid in determining the types of MP (polymer composition, shape, size) to which oysters are exposed and identified those ingested. The low numbers of MP recorded, coupled with the lack of alignment of polymers between oysters and their surrounding environment, demonstrates further that oysters are a poor bioindicator species for MP pollution.

Intertwined synergistic abiotic and biotic degradation of polypropylene pellets in marine mesocosms

The accumulation of plastic waste in the oceans has caused growing concern for its effects on marine life. The interactions of plastics with environmental factors have been linked to fragmentation to micro- and nanoparticles with different properties and consequences, but the mechanism of fragmentation has not been fully understood yet. In this work, we investigate the combined effect of marine communities and ultraviolet (UV) radiation towards the degradation of virgin and artificially weathered polypropylene (PP) pellets after a long-term incubation period in marine mesocosms. The surface chemical alterations and deterioration of the polymer, in conjunction with the attachment and evolution of marine bacterial communities, the development of biofilm and exopolymeric substances (EPS), as well as the colloidal properties (zeta-potential and hydrodynamic diameter) of the mesocosms were studied. The surface area of both types of pellets decreased over time, despite no concrete weight change being observed. Cell growth, EPS production and colloid particle size were correlated to the loss of area. Therefore, we propose that surface area could be effectively monitored, instead of weight loss, as an alternative indicator of polymer degradation in biodegradation experiments. Changes in the chemical structure of the polymer, in addition to the evolution of the biological factors, implied that a complex degradation process alternated between two phases: an abiotic phase, when UV irradiation contributes to the deterioration of the polymer surface layers and a biotic phase, when marine communities degrade the weathered polymer surface to reveal the underlying layer of virgin polymer. Finally, microscopic particles, produced as a result of the decrease in pellet area, promoted the aggregation of colloidal particles. The role and impacts of these colloidal particles in marine ecosystems are yet as unidentified as that of micro- and nano-sized plastic particles and call for further investigation.

Low-Density Plastic Debris Dispersion beneath the Mediterranean Sea Surface

Plastic is a widespread marine pollutant, with most studies focusing on the distribution of floating plastic debris at the sea surface. Recent evidence, however, indicates a significant presence of such low density plastic in the water column and at the seafloor, but information on its origin and dispersion is lacking. Here, we studied the pathways and fate of sinking plastic debris in the Mediterranean Sea, one of the most polluted world seas. We used a recent Lagrangian plastic-tracking model, forced with realistic parameters, including a maximum estimated sinking speed of 7.8 m/d. Our simulations showed that the locations where particles left the surface differed significantly from those where they reached the seafloor, with lateral transport distances between 119 and 282 km. Furthermore, 60% of particles deposited on the bottom coastal strip (20 km wide) were released from vessels, 20% from the facing country, and 20% from other countries. Theoretical considerations furthermore suggested that biological activities potentially responsible for the sinking of low density plastic occur throughout the water column. Our findings indicate that the responsibility for seafloor plastic pollution is shared among Mediterranean countries, with potential impact on pelagic and benthic biota.

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

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

Determination of Microplastics' Vertical Concentration Transport (Rouse) Profiles in Flumes

The transport behavior of microplastics (MPs) in the fluvial environment is scarcely researched. Besides settling velocities and critical shear stress for erosion, only a few investigations aim at MPs' vertical concentration profile and the underlying theory required. Therefore, this paper's experiments investigate vertical concentration profiles of approximately spherical MP particles (d = 1-3 mm) with densities close to water (0.91-1.13 g/cm³) in flow channels, coupling them with fundamental theory for the first time. The experiments were conducted in a tiling flume (slope of 0-2.4%) at 67 and 80 mm water depth, with a turbulent flow, velocities ranging from 0.4 to 1.8 m/s, and turbulence kinetic energy from 0.002 to 0.08 m²/s². The measured profiles confirm the assumption that the concentration profile shapes of settling plastics are similar to those of sediments and running reversed for buoyant plastics. Furthermore, the hypothesis of the Rouse formula's applicability for floating and sinking plastics could be confirmed for approximately uniform flows. Future studies tying in with this research should increase particle properties and hydraulic parameter variation.

MPs and NPs intake and heavy metals accumulation in tissues of Palinurus elephas (J.C. Fabricius, 1787), from NW Aegean sea, Greece

European marine waters are infested with plastic, with an average density of 1 plastic item in every four square-meters. Research relevant to MPs-NPs ingestion by wild decapods in European waters is limited, none of which regards the European spiny lobster. Totally 4102 plastic particles were extracted from the spiny lobster stomach tissues of both sexes. Out of the 63 samples analysed only three (4.8%) of them were found with no plastic particles. The range of number of MPs in stomachs was from 20 to 273 MPs individual^-1. The 98.3% were fragments. In total 3833 plastic particles were extracted from the gill tissues of both sexes. MPs were found in all samples (n = 50),99.2% of the detected particles were fragments. The MPs detected in gills ranged from 11 to 339 MPs individual^-1. The DLS method was used in order to evaluate the NPs presence. Nanoplastics were detected in 22.6% of stomachs and in the 48.1% of gills. A total of 43 polymer types were identified in both tissues. Also, our study assessed the accumulation of heavy metals at the edible tail muscle. Certain elements were detected above the EU's Maximum Residue Level, including arsenic. The present results are alarming and the potential human health implications could be serious.

Liberation of plastic nanoparticles and organic compounds from three common plastics in water during weathering under UV radiation-free conditions

A 620-day batch experiment was conducted to examine the generation of nano-sized plastic particles and migration of organic compounds derived from plastic additives and impurities during the weathering of three common plastic types in water with and without reactive oxygen species. The results show that the amount of nanoplastics plus organic compounds liberated from the tested plastic films, as indicated by total organic carbon, was in the following decreasing order: PET >PP > ABS. Hydroxyl radical generated from Fenton-like reaction significantly enhanced the generation of nanoplastics and release of organic compounds from the weathered plastic films via oxidative degradation. Over 30 organic compounds including potentially toxic organic pollutants originated from plastic additives and impurities were detected. There was a marked difference in the plastic nanoparticle size distribution between the deionized water and the water containing reactive oxygen species. The strong oxidizing capacity of hydroxyl radical resulted in rapider disintegration of the coarser nanoparticles (>500 nm) into the finer nanoparticles (<500 nm) and allowed complete decomposition of the nanoplastics with a size <50 nm or even <100 nm. Elevated level of Ca was detected on the surfaces of the ABS and PP nanoparticles. PP- and PET-derived nanoplastics contained heavy metal(loid)s while no heavy metal(loid)s was detected for the ABS nanoparticles. PET nanoparticles had a stronger capacity to bind S- and N-containing organic ligands compared to the other two plastic nanoparticles. The nanoplastics generated from the weathering were irregular in shape, which means that they had larger specific area compared to spherical engineered nanoplastics.

Microplastics contamination in bivalves from the Daya Bay: Species variability and spatio-temporal distribution and human health risks

Microplastic contamination is an emerging global threat for various marine organisms. Marine invertebrates such as bivalve mollusks are more susceptible to the widespread presence of microplastics due to their limited abilities to escape from pollution exposure and they can readily ingest environmental pollutants like microplastics through their filter-feeding behaviors. In this study, microplastic contamination in bivalves related to species, spatial, and temporal variability were conducted. Results showed that the frequency of microplastic occurrence varied from 86.7 % to 93.3 % in six species of bivalves, and the average abundance of microplastics ranged from 3.5 to 8.6 items per individual or from 0.2 to 3.1 items per gram tissues wet weight. No significant difference was observed in microplastic abundances of bivalves collected from different research regions and sampling seasons. However, the sediment-dwelling bivalves had higher microplastics abundances than the water-dwelling bivalves. Microplastic features with various shapes, colors, sizes, and polymer types detected in bivalves were similar with those in seawater and sediment environments that they are living in. The potential risk assessment of microplastics in bivalves basing on polymer hazard index (PHI) was in the risk levels of II-III, implying that microplastic contamination in bivalves may pose health risk to human via seafood consumption.

Salt marshes as the final watershed fate for meso- and microplastic contamination: A case study from Southern Brazil

Plastics pose a major threat to aquatic ecosystems especially in smaller size fractions. Salt marshes play a crucial role in maintaining the coastal zone and aquatic food web, yet their contamination, including by plastic materials, is still poorly investigated. This work investigated meso- (MEP, 5-25 mm) and microplastic (MIP, 1 μm-5 mm) contamination of a salt marsh, which reached average levels of 279.63 ± 410.12 items kg^-1, 366.92 ± 975.18 items kg^-1, and 8.89 ± 8.75 items L^-1 in surface sediment, sediment cores and water, respectively. Photomicrographs revealed a complex fouling community on plastics surface for both different salt marsh zones and plastic formats. Abundance of plastics in sediment was higher in the dryer, vegetated zones compared to flooded, unvegetated zones. This is consistent with the role of vegetation as a trap for solid litter and final fate of plastic deposition, but also with local hydrodynamics influencing deposition pattern. Plastics were detected up to 66 cm-depth, presenting higher levels at surface sediments. It was also possible to identify the main groups of microorganisms (1638 bacterial cells, 318 microalgae cells, and 20049.93 μm² of filamentous fungi) composing the Plastisphere communities on all plastic items recorded in the different zones. These results are a pioneer contribution, highlighting that regional salt marshes participate in sequestration and longstanding accumulation of plastic particles in estuarine environments, before exportation to the ocean.

Microbial communities on plastic particles in surface waters differ from subsurface waters of the North Pacific Subtropical Gyre

The long-term fate of plastics in the ocean and their interactions with marine microorganisms remain poorly understood. In particular, the role of sinking plastic particles as a transport vector for surface microbes towards the deep sea has not been investigated. Here, we present the first data on the composition of microbial communities on floating and suspended plastic particles recovered from the surface to the bathypelagic water column (0-2000 m water depth) of the North Pacific Subtropical Gyre. Microbial community composition of suspended plastic particles differed from that of plastic particles afloat at the sea surface. However, in both compartments, a diversity of hydrocarbon-degrading bacteria was identified. These findings indicate that microbial community members initially present on floating plastics are quickly replaced by microorganisms acquired from deeper water layers, thus suggesting a limited efficiency of sinking plastic particles to vertically transport microorganisms in the North Pacific Subtropical Gyre.

Weathering and fragmentation of plastic debris in the ocean environment

Fragmentation of plastic macro-debris into secondary microplastics [MPs] is primarily the result of their extensive oxidation under exposure to solar UV radiation. The heterogeneity in the marine zones with respect to their oxidative potential for plastics, introduces a marked zonal bias in their ability to carry out weathering and fragmentation. Comparing the oxidative environments of the beach zone and the upper pelagic zone with floating plastics, it is argued that the latter tends to preclude photooxidative fragmentation. Abundant MPs found in seawater are therefore more likely to have originated on beaches or land and subsequently transferred to the water, as opposed to being generated by weathering of floating plastic stock. Laboratory-accelerated weathering of plastics in seawater obtains efficient micro-fragmentation and in some instances photo- dissolution of the plastic debris, but these results cannot be reliably extrapolated to natural weathering conditions in the ocean environment.

Effects of Biofilms and Particle Physical Properties on the Rising and Settling Velocities of Microplastic Fibers and Sheets

Vertical dynamics of microplastics (MPs) in the water column are complex and not fully understood due to the diversity of environmental MPs and the impact of weathering and biofouling on their dynamical properties. In this study, we investigate the effects of the particle properties and biofilm on the vertical (settling or rising) velocity of microplastic sheets and fibers under laboratory conditions. The experiments focus on three types of MPs (polyester PES fibers, polyethylene terephthalate PET sheets, and polypropylene PP sheets) of nine sizes and two degrees of biological colonization. Even though pristine PES fibers and PET sheets had a similar density, the sinking velocity of fibers was much smaller and independent of their length. The settling or rising velocity of sheets increased with the particle size up to a threshold and then decreased in the wake of horizontal oscillations in large particles. Biofilms had unexpected effects on vertical velocities. Irregular biofilm distributions can trigger motion instabilities that decrease settling velocities of sheets despite the increase in density. Biofilms can also modify the orientation of fibers, which may increase their settling velocity. Finally, we selected the most performant theoretical formulation for each type of particle and proposed modifications to consider the effect of biofilm distribution.

Surface properties and rising velocities of pristine and weathered plastic pellets

This study compared the surface properties and rising velocities of pristine and weathered plastic production pellets, to evaluate impacts of environmental conditions. Rising velocities were measured for 140 weathered pellets collected from a Spanish beach and compared with pristine low-density polyethylene, high-density polyethylene and polypropylene pellets. A subset of 49 weathered pellets were analysed by Fourier-transform infrared spectroscopy (FTIR), with all found to be polyethylene. Experimental rising velocities for the weathered pellets varied widely, from (2.36 ± 0.01) cm s^-1 to (10.56 ± 0.26) cm s^-1, with a mean value of (5.79 ± 0.06) cm s^-1. Theoretical rising velocities were consistently higher than experimental velocities for all pellet types: on average 136% of experimental values for weathered pellets. This discrepancy was more distinct for less spherical pellets, which were often more weathered. Flatter pellets often oscillated as they rose, which explains at least some of this finding. Atomic force microscopy (AFM) analysis revealed that the roughness of the pristine and weathered pellets was (59 ± 11) nm, and (74 ± 26) nm respectively. X-ray photoelectron spectroscopy (XPS) analysis showed that the proportion of surface oxidised carbon species were 2.3% and 4.0% of the total carbon signal for a pristine and a weathered pellet, respectively; consistent with photochemical reactions changing the surface chemistry of weathered pellets. As determined by density column, weathered pellets had slightly lower experimental densities than pristine pellets. Overall, this study illustrates why it is important that modelling studies on the environmental fate and/or movements of microplastics validate or correct predictions using experimental data.

Aquatic Biofilms-Sink or Source of Microplastics? A Critical Reflection on Current Knowledge

The scientific understanding regarding sources, occurrence, and effects of microplastics in the aquatic environment has advanced rapidly, leaving some meaningful knowledge gaps virtually untouched. One of them is the interactions of microplastics and biofilms, microbial communities ubiquitous in aquatic ecosystems and fundamental for a range of ecosystem-level processes. It is evident that biofilms can quickly develop on the microplastic surface and consequently change particle properties and, as such, its fate and ecotoxicity. Moreover, microplastics interact with ubiquitous biofilms that are developed on any surfaces in aquatic ecosystems. Although the knowledge about these interactions is at best limited, it is expected that microplastics attach to the water-biofilm interface or penetrate the biofilm matrix. Microplastics can accumulate and ab- or adsorb to those biofilms where they are subjected to transformation processes such as fragmentation. Thus, biofilms may function as a sink. Changes in environmental conditions may, however, stress biofilms initiating their dieback and microplastic release, which could turn biofilms into a source of microplastics. We argue that the accumulation and release dynamics are a largely overlooked but potentially important piece to the puzzle that is a comprehensive understanding of microplastic fate in the environment and thus under the influence of multiple interacting factors. Environ Toxicol Chem 2022;41:838-843. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Distribution Characteristics and Source Analysis of Microplastics in Urban Freshwater Lakes: A Case Study in Songshan Lake of Dongguan, China

Current studies on microplastic pollution mainly focus on marine systems. However, few studies have investigated microplastics in an urban lake. This research intends to use an urban lake (Songshan Lake) as an example to explore the pollution characteristics of microplastics and use the principal component as well as the heat map analysis to discuss the relationships between different shapes of microplastics. According to this study, the average abundance of microplastics in the surface water and surface sediments of Songshan Lake were, respectively, 2.29 ± 0.98 items/m3 and 244 ± 121 items/kg; thin films were the major microplastics in both media; transparent this type of color has the most microplastic content. The particle size of microplastics was mainly 0.18–0.6 mm (43.3%) in surface water and 1–2 mm (48.3%) in surface sediments. The composition included five polymers: polyethylene (PE), polypropylene (PP), polypropylene–polyethylene copolymer (PP–PE copolymer), polystyrene (PS), and polyvinyl chloride (PVC), among which PE (47%) and PP (36%) were the main components. Principal component analysis (PCA) showed that there was a positive correlation among the four shapes of microplastics: films, fragments, foams, and fibers. The heat map analysis showed that the same category of shape distribution features may be similar for each sampling site.

Microplastics prevalence in water, sediment and two economically important species of fish in an urban riverine system in Ghana

Urban riverine systems serve as conduits for the transport of plastic waste from the terrestrial dumpsites to marine repositories. This study presented data on the occurrence of microplastics in water, sediment, Bagrid Catfish (Chrysichthys nigrodigitatus) and Black-chinned Tilapia (Sarotherodon melanotheron) from the Densu River, an urban riverine system in Ghana. Microplastics were extracted from the samples collected from both the lentic and lotic sections of the river. The results indicated widespread pollution of the Densu River with microplastics in all the compartments studied. The average numbers of microplastic particles deposited in the Dam (2.0 ± 0.58) and Delta (2.50 ± 0.48) sections of the river were not affected by the differences in their hydrology. However, the stagnant water system of the Dam promoted the floating of larger-sized microplastics while the flowing waters of the Delta did not show any selectivity in the deposition of microplastics between sediment and the water column. The number of microplastics ingestions by the Bagrid Catfish (2.88 ± 2.11) was similar to the Black-chinned Tilapia (2.38 ± 1.66) but both species ingested lower numbers of microplastics than reported for marine fish species in coastal Ghana.

Interactions of microplastics, antibiotics and antibiotic resistant genes within WWTPs

Microplastics (MPs) have been detected in atmosphere, soil, and water and have been characterized as contaminants of emerging concern. When exposed to these environments, MPs interact with the chemical compounds as well as the (micro)organisms inhabiting these ecosystems. This paper overviews the interactions and significant factors influencing the sorption process of antibiotics on MPs since distinct interactions are developed between MPs and antibiotics. The interplay between the MPs and the antibiotic resistant genes (ARGs) microbial hosts is presented and the important factors that may shape the plastisphere resistome are discussed. The interactions of MPs, antibiotics and antibiotic resistant bacteria (ARB) and ARGs in wastewater treatment plants (WWTPs) were discussed with the aim to provide a perspective for better understanding of the role of WWTPs in bringing together MPs, antibiotics and ARB/ARGs and further as release points of MPs carrying antibiotics, and ARB/ARGs.

Investigating the Human Impacts and the Environmental Consequences of Microplastics Disposal into Water Resources

During the last decades, one of the most contentious environmental issues has been the investigation of the fate of microplastics (MPs) and detrimental consequences in natural and water resources worldwide. In this respect, it is critical research firstly to track the ways in which MPs are determined as key anthropogenic pollutants in terms of ecological risk and secondly to plan feasible policies under which the role of science and society in tackling this global issue in the future should be prioritized. In this study, a systematic theoretical, technical, and planning analysis was developed in alignment with a Scopus search deployed in the second half of the year 2021 and covering a wide chronological range (from 1970s onwards) and thematic contexts of analysis by using keywords and key phrases organized into two groups. The document results were graphically represented, revealing the main scientific focus of studies. Subsequently, our study investigated the quantitative assessment methods of MPs in marine environments, denoting the range of standard procedures applied for collecting and analyzing samples of water, bottom sediments, and coastal deposits. The technological part of the study includes the presentation of the relevant analytical techniques applied for MPs tracking and monitoring in water resources, determining the wide spectrum of plastic compounds traced. Of particular interest was the determination of environmental depletion and human implications caused, even by extremely low concentrations of MPs, for marine biota, posing potential risks to marine ecosystems, biodiversity, and food availability. Finally, the research proposed the challenges of actions needed to support scientific, industry, policy, and civil society communities to curb the ongoing flow of MPs and the toxic chemicals they contain into water resources, while rethinking the ways of plastics consumption by humanity.