Biofilm growth on buoyant microplastics leads to changes in settling rates: Implications for microplastic retention in the Great Lakes

Microfibre ingestion by the Asian Clam (Corbicula fluminea) is dependent on fibre type and biofilm development

Fibrous microplastics represent an anthropogenic pollutant affecting aquatic systems globally. However, fibres formed from natural materials (e.g., cotton or wool) have only recently been recognised as potentially posing similar ecological threats as their synthetic counterparts. In this study we employed a laboratory-based aquarium experiment to examine the ingestion of preselected anthropogenic (polyester - microplastic) and 'natural' (cotton) microfibres by the Asian Clam (Corbicula fluminea). We considered how the ingestion, retention, and rejection of preselected microfibres (specific, distinctive colours), differed associated with fibre type (cotton vs polyester), biofilm development (control - no biofilm/uncultured, 1-week culturing and 4-week culturing) and time (1-48 h). We found that the ingestion of microfibres was complex, dependent on the interaction of culturing and fibre type. Greater retention of synthetic microfibres was recorded compared to 'natural' microfibres as the duration of culturing increased. We also observed that ingestion of microfibres was immediate but that microfibres were rejected and visually observed in pseudofaeces. Our results suggest that the time microfibres spend within the environment, allowing biofilm to develop on their surface, influences the ingestion of microfibres and we call for further studies to consider this in the future.

Non-degradable microplastic promote microbial colonization: A meta-analysis comparing the effects of microplastic properties and environmental factors

Microplastics serve as favorable substrates for microbial colonization, promoting biofilm formation, which consequently facilitates the accumulation of pollutants and aids in the degradation of microplastics. Hence, obtaining a thorough comprehension of the factors that influence the development of microplastic biofilms is imperative. Nevertheless, there have been conflicting responses concerning biofilm formation in conjunction with microplastic characteristics and environmental conditions. As a result, a meta-analysis was conducted to quantitatively evaluate the impact of microplastic properties and environmental factors on biofilm formation. The findings indicated that the type and size of microplastics significantly influence biofilm growth on their surfaces. Non-degradable microplastics, particularly polyvinyl chloride (PVC) and polystyrene (PS), exhibited higher surface biomass and biodiversity in microplastic-attached biofilms compared to degradable microplastics. Furthermore, it was observed that smaller microplastics were more conducive to microbial colonization. Model selection and correlation analysis further indicated that the environment acts as a substantial predictor of biofilm formation, with prolonged exposure significantly enhancing microbial diversity within biofilms as opposed to short-term exposure. Moreover, meta-regression analysis illustrated a positive correlation between biofilm biomass and alpha-diversity with temperature, while salinity exhibited a negative correlation in diverse aquatic settings. Notably, the ease of biofilm formation on microplastics was observed to be greater in oceans compared to lakes, yet biofilms exhibited a higher diversity increment in lakes than their oceanic counterparts. In the long-term growth of biofilms, initial biomass and diversity are influenced by microplastic characteristics and the surrounding environment, although environmental influences may assume more significance as time progresses.

Sensitivity analysis of a one-dimensional microplastic transport model in turbulent rivers: Intrinsic properties and hydrodynamics

Since rivers are major transport routes for microplastics, developing novel modeling approaches has become a subject of research to better understand the transport behavior of these particles in river systems. This study aims to model the vertical transport of microplastics at selected sites of the Ergene River, Türkiye, simulate the concentration dynamics of these particles in water and sediment under different hydrodynamic and morphological conditions, and determine the sensitivity of the model results to parameters related to the physical characteristics of microplastics, as well as river hydrodynamics and morphology. A mechanistic model was developed using data on microplastics, river hydrodynamics and morphology. Mass-balance and hydrodynamic equations were utilized for model construction in GoldSim to predict the transport of microplastics between the water column and sediment. The model results revealed that the residence time of microplastics in water was directly related to flow characteristics and river hydraulics, while the initial concentration of particles in water dominated other parameters in influencing the settling and resuspension fluxes of microplastics. Turbulent conditions affected both flow rate and particle resuspension, suggesting that turbulence can either increase or decrease microplastic concentrations and their residence time in the water column and sediment. The model results for both compartments were most sensitive to changes in water and plastic density, whereas Nikuradse sand roughness was the least significant parameter affecting the model outcomes for both compartments.

Microplastics Settling in Turbid Water: Impacts of Sediments-Induced Flow Patterns on Particle Deposition Rates

When microplastics (MPs) enter water bodies, they undergo various transport processes, including sedimentation, which can be influenced by factors such as particle size, density, and interactions with other particles. Surface waters contain suspended natural particles (e.g., clay and silt), which may impact MP settling rates. Here, we investigated how the presence of suspended sediments (SS) influenced the deposition patterns and rates of MPs in turbid waters. We systematically analyzed the settling velocities of particles, including different MP sizes and SS concentrations, in a plexiglass column with a camera array. For each experimental variant, we collected data on thousands of individual MPs, strengthening the statistical analysis of the particles' velocities. Simultaneous measurements of the SS flow and MPs trajectories revealed that the SS induced complex flow patterns, with MPs spending more time in downwelling flow regions, thereby accelerating MPs sedimentation. This effect was more pronounced when SS were aggregated. Additionally, we found that smaller MP fragments were more affected by the fluctuations than spheres or larger fragments. Collectively, our results provide valuable data for future MP fate models and help to understand the sedimentation processes of MPs in natural waters, which is crucial for assessing their environmental transport and impact.

The effects of plastisphere on the physicochemical properties of microplastics

The plastisphere is the microbial communities that grow on the surface of plastic debris, often used interchangeably with plastic biofilm or biofouled plastics. It can affect the properties of the plastic debris in multiple ways. This review aims to present the effects of the plastisphere on the physicochemical properties of microplastics systematically. It highlights that the plastisphere modifies the buoyancy and movement of microplastics by increasing their density, causing them to sink and settle out. Smaller and film microplastics are likely to settle sooner because of larger surface areas and higher rates of biofouling. Biofouled microplastics may show an oscillating movement in waterbodies when settling due to diurnal and seasonal changes in the growth of the plastisphere until they come close to the bottom of the waterbodies and are entrapped by sediments. The plastisphere enhances the adsorption of microplastics for metals and organic pollutants and shifts the adsorption mechanism from intraparticle diffusion to film diffusion. The plastisphere also increases surface roughness, reduces the pore size, and alters the overall charge of microplastics. Charge alteration is primarily attributed to changes in the functional groups on microplastic surfaces. The plastisphere introduces carbonyl, amine, amide, hydroxyl, and phosphoryl groups to microplastics, causing an increase in their surface hydrophilicity, which could alter their adsorption behaviors for heavy metals. The plastisphere may act as a reactive barrier that enhances the leaching of polar additives. It may anchor bacteria that can break down plastic additives, resulting in decreased crystallinity of microplastics. This review contributes to a better understanding of how the plastisphere alters the fate, transport, and environmental impacts of microplastics. It points to the possibility of engineering the plastisphere to improve microplastic biodegradation.

Settling and rising velocities of microplastics: Laboratory experiments and lattice Boltzmann modeling

Microplastics (MPs) have become pervasive in marine ecosystems, potentially causing environmental degradation, impacting ecological function, and posing a serious public health risk. Despite the widespread distribution of MPs, their vertical transport within a water column has limited understanding, representing a key knowledge gap in the development of water quality models to minimize these risks. In this study, 6152 individual particles of six common types of MPs were observed through water column experiments to examine a range of drivers of the vertical velocity of MPs, including particle density and size, biofilm growth, water temperature, and salinity. The experimental results revealed that the vertical velocity of MPs obeyed Stokes' law under laminar conditions; increasing salinity decreased the settling tendency of the particles. Moreover, biofilm attachment induced notable alterations in particle characteristics within 60 days, resulting in slower settling velocities (up to a 21.9% change for non-buoyant MPs) and even a reversed vertical direction (up to several times for buoyant particles). Furthermore, a lattice Boltzmann model could predict the vertical velocity of MPs with reasonable accuracy, especially for small particles. This work facilitates the development of sophisticated models/formulas that integrate particle morphology, hydrodynamics, and biological factors to enhance the understanding of MP transport through the river-to-coastal continuum.

Heterogenous bioluminescence patterns, cell viability, and biofilm formation of Photobacterium leiognathi strains exposed to ground microplastics

Microplastics (MPs) have been detected in various aquatic environments and negatively affect organisms, including marine luminous bacteria. This study investigated the differences in bioluminescence patterns, cell viability, and biofilm formation of Photobacterium leiognathi strains (LB01 and LB09) when exposed to various concentrations of ground microplastics (GMPs; 0.25%, 0.50%, 1%, or 2% [w/v] per mL) at 22°C or 30°C for 3.1 days (75 h) and 7 days. The strains exhibited heterogenous responses, including variable bioluminescence patterns, cell viability, and biofilm formation, due to the GMPs having effects such as hormesis and bioluminescence quenching. Moreover, the bioluminescence and cell viability differed between the two strains, possibly involving distinct cellular mechanisms, suggesting that GMPs affect factors that influence quorum sensing. Furthermore, the biofilm formation of LB01 and LB09 was observed following exposure to GMPs. Both strains showed increased biofilm formation at higher GMP concentrations (1% and 2%) after 3.1 days at 30°C and 22°C. However, in the 7-day experiment, LB01 significantly (p < 0.05) increased biofilms at 22°C, while LB09 significantly (p < 0.05) produced biofilms at 30°C. These findings highlight the strain-specific responses of Phb. leiognathi to MP pollutants. Therefore, this study underscores the importance of evaluating MPs as environmental stressors on marine microorganisms and their role in the ecophysiological repercussions of plastic pollution in aquatic environments.

Shear induced remobilization of buried synthetic microfibers

Microplastics are known to accumulate in sediment beds of aquatic environments where they can be buried. Once buried they can remobilize due to high energetic events, entering the water column again. Here, turbulence induced by an oscillating grid device was used to investigate the remobilization of microfibers (MF) buried into the sediment bed. Four different types of plastic fibers commonly used for several industrial applications (PET, PP, PA and LDPE) and two types of soils (cohesive and non-cohesive) were investigated. Particles were in depth characterized via 3D reconstruction to estimate important parameters like the Corey shape factor and the settling velocity. Experimental runs explored a wide range of shear stresses. Measurements were taken at different time steps (between 15 min and 240 min from the start of each run). The results have shown that the remobilization of MFs is directly proportional to the value of the shear rate and the duration of the disturbance. Also, buoyant MFs were found more prone to remobilize respect to the denser ones. Drawing from experimental observations of the key parameters affecting MF remobilization, a non-dimensional predictive model was developed. A comparison with previous studies was performed to validate the model in order to predict MF remobilization in aquatic environments.

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.

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.

Why biofouling cannot contribute to the vertical transport of small microplastic

In contrast to expectations, even buoyant microplastics like polyethylene and polypropylene are found at high concentrations in deep sediment traps and deep-sea sediments. To explain the presence of such buoyant microplastic particles at great ocean depths, several vertical transport mechanisms are under discussion with biofouling as one of the most referred. Biofouling is thought to increase the density of microplastic particles to the point that they sink to the deep sea, but this has mostly been shown on large microplastic particles ≥ 1 mm. However, although microplastics are defined as particles between 1 and 5000 μm, most microplastics are < 100 μm. In the ocean plastic particles continuously fragment, converting each "large" particle into several "small" particles, and particle abundance increases drastically with decreasing size. We argue that biofouling is not a reasonable transport mechanism for small microplastic particles ≤ 100 μm, which form the majority of microplastics. Biofilm density depends on its community and composition. A biofilm matrix of extracellular polymeric substances and bacteria has a lower density than seawater, in contrast to diatoms or large organisms like mussels or barnacles. We suggest that a small microplastic particle cannot host a biofilm community consisting of the heavy organisms required to induce sinking. Furthermore, to reach the deep sea within a reasonable timespan, a microplastic particle needs to sink several meters per day. Therefore, the excess density has to not only exceed that of seawater, but also be large enough to enable rapid sinking. We thus argue that biofouling cannot be an efficient vertical transport mechanism for small microplastic. However, biofouling of small microplastic may promote the likelihood of its incorporation into sinking marine snow and increase the probability of its ingestion, allowing its transport to depth.

Evaluation of the migration behaviour of microplastics as emerging pollutants in freshwater environments

Microplastics, as an emerging pollutant, are widely distributed in freshwater environments such as rivers and lakes, posing immeasurable potential risks to aquatic ecosystems and human health. The migration behaviour of microplastics can exacerbate the degree or scope of risk. A complete understanding of the migration behaviour of microplastics in freshwater environments, such as rivers and lakes, can help assess the state of occurrence and environmental risk of microplastics and provide a theoretical basis for microplastic pollution control. Firstly, this review presents the hazards of microplastics in freshwater environments and the current research focus. Then, this review systematically describes the migration behaviours of microplastics, such as aggregation, horizontal transport, sedimentation, infiltration, stranding, resuspension, bed load, and the affecting factors. These migration behaviours are influenced by the nature of the microplastics themselves (shape, size, density, surface modifications, ageing), environmental conditions (ionic strength, cation type, pH, co-existing pollutants, rainfall, flow regime), biology (vegetation, microbes, fish), etc. They can occur cyclically or can end spontaneously. Finally, an outlook for future research is given.

Distribution, flux, and risk assessment of microplastics at the Anzali Wetland, Iran, and its tributaries

Microplastic pollution has raised significant concerns among scientific communities and society in recent years due to its increase and lesser-known effects on the environment. To improve the knowledge of microplastic pollution in freshwater, we investigated microplastics in Anzali Wetland, a Ramsar site in northern Iran, as well as its nine main entering rivers. The extracted microplastics were characterized via visual identification, SEM-EDX, and μ-Raman methods. Microplastics (size range: 50-5000 μm) were found in all water and sediment samples with concentration of fibrous particles as well as polypropylene and polyethylene polymers. The mean concentration of microplastics in bottom sediment and surface water samples of the wetland was 301 ± 222 particles∙kg-1 d.w. and 235 ± 115 particles∙m-3 (0.23 particles∙L-1), respectively. The microplastic concentration in the central and eastern parts of the wetland was higher than in other areas; however, the mean concentrations revealed homogeneity across the wetland area. Water properties (dissolved oxygen, pH, temperature, electrical conductivity, and salinity in water) did not affect the concentration of microplastic particles, though correlational analysis revealed a strong positive association between microplastic quantity and turbidity. There was a significant positive relationship between microplastic concentration and the percentage of clay in sediment samples. The quantity of microplastics in river water was higher than in wetland water, but the difference between the results was not significant. However, the quantity of microplastics in the river's littoral sediment was higher than in the bottom sediment of the wetland where the difference between the results was significant. Microplastic ecological risk assessment showed high potential ecological risk. The findings underscore the importance of effective management strategies and the implementation of policies to mitigate the negative impact of MP pollution on ecosystems and human health.

Impact of heteroaggregation between microplastics and algae on particle vertical transport

Understanding the impacts of microplastics (MPs) on aqueous environments requires understanding their transport dynamics and how their presence affects other natural processes and cycles. In this context, one aspect to consider is how MPs interact with freshwater snow (FWS), a mixture of algae and natural particles. FWS is one of the primary drivers of the flux of organic matter from the water surface to the bottom sediment, where zooplankton, diurnal migration, fish faecal pellets settling and turbulent mixing can also play prominent roles. Understanding how MPs and FWS heteroaggregation affects their respective settling velocities is important to assess not only MPs fate and transport but also their ecological impacts by altering FWS deposition and thereby nutrient cycling. In this present study, we obtained a mechanistic understanding of the processes controlling MPs settling dynamics and heteroaggregation with FWS and the subsequent impacts on the settling rates of both MPs and ballasted FWS. Here we used a plexiglass column equipped with a stereoscopic camera system to track the settling velocities of (1) MPs of various compositions, densities and morphologies, (2) FWS flocs and (3) MP-FWS agglomerates. For each experimental set, thousands of particles were tracked over a series of image sequences. We found that agglomerates with high-density MPs settled at least twofold faster than FWS alone, implying a much smaller residence time in the water column, except for cases with MP fibres or low-density plastics. These findings will help to refine MP fate models and, while contingent on MPs number, may impact biogeochemical cycles by changing the flux of nutrients contained in FWS to the sediment.

Informing the Exposure Landscape: The Fate of Microplastics in a Large Pelagic In-Lake Mesocosm Experiment

Understanding microplastic exposure and effects is critical to understanding risk. Here, we used large, in-lake closed-bottom mesocosms to investigate exposure and effects on pelagic freshwater ecosystems. This article provides details about the experimental design and results on the transport of microplastics and exposure to pelagic organisms. Our experiment included three polymers of microplastics (PE, PS, and PET) ranging in density and size. Nominal concentrations ranged from 0 to 29,240 microplastics per liter on a log scale. Mesocosms enclosed natural microbial, phytoplankton, and zooplankton communities and yellow perch (Perca flavescens). We quantified and characterized microplastics in the water column and in components of the food web (biofilm on the walls, zooplankton, and fish). The microplastics in the water stratified vertically according to size and density. After 10 weeks, about 1% of the microplastics added were in the water column, 0.4% attached to biofilm on the walls, 0.01% within zooplankton, and 0.0001% in fish. Visual observations suggest the remaining >98% were in a surface slick and on the bottom. Our study suggests organisms that feed at the surface and in the benthos are likely most at risk, and demonstrates the value of measuring exposure and transport to inform experimental designs and achieve target concentrations in different matrices within toxicity tests.

Settling Velocities of Small Microplastic Fragments and Fibers

There is only sparse empirical data on the settling velocity of small, nonbuoyant microplastics thus far, although it is an important parameter governing their vertical transport within aquatic environments. This study reports the settling velocities of 4031 exemplary microplastic particles. Focusing on the environmentally most prevalent particle shapes, irregular microplastic fragments of four different polymer types (9-289 μm) and five discrete length fractions (50-600 μm) of common nylon and polyester fibers are investigated, respectively. All settling experiments are carried out in quiescent water by using a specialized optical imaging setup. The method has been previously validated in order to minimize disruptive factors, e.g., thermal convection or particle interactions, and thus enable the precise measurements of the velocities of individual microplastic particles (0.003-9.094 mm/s). Based on the obtained data, ten existing models for predicting a particle's terminal settling velocity are assessed. It is concluded that models, which were specifically deduced from empirical data on larger microplastics, fail to provide accurate predictions for small microplastics. Instead, a different approach is highlighted as a viable option for computing settling velocities across the microplastics continuum in terms of size, density, and shape.

From pollution to solutions: Insights into the sources, transport and management of plastic debris in pristine and urban rivers

River systems are important recipients of environmental plastic pollution and have become key pathways for the transfer of mismanaged waste from the land to the ocean. Understanding the sources and fate of plastic debris, including plastic litter (>5 mm) and microplastics (MPs) (<5 mm), entering different riverine systems is essential to mitigate the ongoing environmental plastic pollution crisis. We comprehensively investigated the plastic pollution in the catchments of two rivers in the Yangtze River basin: an urban river, the Suzhou section of the Beijing-Hangzhou Grand Canal (SZ); and a pristine rural river, the Jingmen section of the Hanjiang River (JM). The abundance of plastic pollutants in SZ was significantly higher than in JM: 0.430 ± 0.450 items/m3 and 0.003 ± 0.003 items/m3 of plastic litter in the water; 23.47 ± 25.53 n/m3 and 2.78 ± 1.55 n/m3 MPs in the water; and 218.82 ± 77.40 items/kg and 5.30 ± 1.99 items/kg of MPs in the sediment, respectively. Plastic litter and MPs were closely correlated in abundance and polymer composition. Overall, the polymer type, shape and color of MPs were dominant by polypropylene (42.5%), fragment (60.4%) and transparent (40.0%), respectively. Source tracing analysis revealed that packaging, shipping, and wastewater were the primary sources of plastic pollutants. The mantel analysis indicated that socio-economic and geospatial factors play crucial roles in driving the hotspot formation of plastic pollution in river networks. The composition of the MP communities differed significantly between the sediments and the overlying water. The urban riverbed sediments had a more pronounced pollutant 'sink' effect compared with the pristine rivers. These findings suggested that the modification of natural streams during urbanization may influence the transport and fate of plastic pollutants in them. Our results offer pivotal insights into effective preventive measures.

Global occurrence characteristics, drivers, and environmental risk assessment of microplastics in lakes: A meta-analysis

Microplastic (MP) pollution in lakes has received much attention as an increasing amount of plastic waste enters aquatic ecosystems. However, there is still a lack of comprehensive understanding of the global distribution patterns, environmental hazards, factors driving their presence, and the relationships between sources and sinks of MPs. In this study, we conducted a meta-analysis of drivers of lake MP pollution based on 42 articles on MP pollution from three different aspects: geographical distribution, driving factors and environmental risks. The results revealed differences in the MP pollution levels across the different sampling sites in the global lakes. Moreover, there is significant heterogeneity in the abundance of MPs among various lakes, whose distribution pattern is affected by geographical location, sampling method and extraction method. The size of the MPs differed significantly between water and sediment, and the proportion of small (<1 mm) MPs in sediment was significantly greater than that in water (72% > 46%). Environmental risk assessment reveals that the risk level of MP pollution in most lakes worldwide is low, and the environmental risk of pollution in lake water is higher than that in sediment. Based on the risk assessment and geographical location of the lake, the risk of MP pollution is related not only to human activities and economic development but also to local waste management practices, which directly impact the accumulation of MPs. Therefore, we suggest that the production of biodegradable low-risk polymer plastics instead of high-risk materials, and plastic solid waste recycling management should be strengthened to effectively mitigate the presence of MPs in the environment.

Fate, abundance and ecological risks of microcystins in aquatic environment: The implication of microplastics

Microcystins are highly toxic cyanotoxins and have been produced worldwide with the global expansion of harmful cyanobacterial blooms (HABs), posing serious threats to human health and ecosystem safety. Yet little knowledge is available on the underlying process occurring in the aquatic environment with microcystins. Microplastics as vectors for pollutants has received growing attention and are widely found co-existing with microcystins. On the one hand, microplastics could react with microcystins by adsorption, altering their environmental behavior and ecological risks. On the other hand, particular attention should be given to microplastics due to their implications on the outbreak of HABs and the generation and release of microcystins. However, limited reviews have been undertaken to link the co-existing microcystins and microplastics in natural water. This study aims to provide a comprehensive understanding on the environmental relevance of microcystins and microplastics and their potential interactions, with particular emphasis on the adsorption, transport, sources, ecotoxicity and environmental transformation of microcystins affected by microplastics. In addition, current knowledge gaps and future research directions on the microcystins and microplastics are presented. Overall, this review will provide novel insights into the ecological risk of microcystins associated with microplastics in real water environment and lay foundation for the effective management of HABs and microplastic pollution.

The role of turbulence in the deposition of intrinsically buoyant MPs

Intrinsically floating microplastics (MP) such as polyethene (PE) or polypropylene (PP) are among the most common MPs found in aquatic sediments. There must hence be mechanisms that cause lighter-than-water MPs to deposit despite them being buoyant. How these MPs end up in the sediment bed is only partly understood. This study explores how turbulence in the water can affect the vertical movement of buoyant MP and bring them in contact with the bed. The deposition of PE (995 kg m-3) in slow-flowing water (average flow velocities of 1.85 and 4.17 cm s-1) was measured by tracking them and analyzing their motion in an open, rectangular, glass-sided flume. Flow characteristics in terms of turbulent kinetic energy and shear velocity were measured by particle image velocimetry. Experiments were conducted at a water depth of 27 cm and at various hydraulic conditions created by adjusting inflow speeds and using different bed materials: medium gravel, fine gravel, medium sand, cohesive sediment, and glass. The results showed that the vertical velocity of the MPs in the turbulent flow regimes varied over 4 orders of magnitude from their predicted rising velocity in quiescent water (laminar flow). Turbulence mixing resulted in distribution throughout the water column with a substantial quantity consistently subject to downward vertical transport, which in turn increased the chance of the PE particles encountering the bed and potentially getting immobilized. This work provides a plausible explanation and further experimental validation for the concept of mixing induced transfer of MPs from the water surface to the sediments of shallow waters.

Microplastic-specific biofilm growth determines the vertical transport of plastics in freshwater

Understanding the sinking behavior of microplastics in freshwater is essential for assessing their environmental impact, guiding research efforts, and formulating effective policies to mitigate plastic pollution. Sinking behavior is a complex process driven by plastic density, environmental factors and particle characteristics. Moreover, the growth of biological entities on the plastic surface can affect the total density of the microplastics and thus influence the sinking behavior. Yet, our understanding of these processes in freshwater is still limited. Our research thus focused on studying biofilm growth on microplastics in freshwater. Therefore, we evaluated biofilm growth on five different polymer types (both microplastic particles and plates) which were incubated in freshwater for 63 days in a controlled laboratory setting. Biofilm growth (mass-based) was used to compare biofilm growth between polymer types, surface roughness and study the changes over time. Understanding the temporal aspect of biofilm growth enabled us to refine calculations on the predicted effect of biofilm growth on the settling behavior in freshwater. The results showed that biofilm formation is polymer-specific but also affected by surface roughness, with a rougher surface promoting biofilm growth. For PET and PS, biofilm tended to grow exponentially during 63 days of incubation. Based on our calculations, biofilm growth did affect the sinking behavior differently based on the polymer type, size and density. Rivers can function as sinks for some particles such as large PET particles. Nevertheless, for others, the likelihood of settling within river systems appears limited, thereby increasing the probability of their transit to estuarine or oceanic environments under hydrometeorological influences. While the complexity of biofilm dynamics on plastic surfaces is not fully understood, our findings help to elucidate the effect of biofilms on the vertical behavior of microplastics in freshwater systems hereby offering knowledge to interpret observed patterns in environmental plastic concentrations.

Assessing the Settling Velocity of Biofilm-Encrusted Microplastics: Accounting for Biofilms as an Equivalent to Surface Roughness

While it is well established that a biofilm contributes to the sinking of plastics, the underlying mechanisms of how it influences the vertical transport of plastics have not been well explained. In this context, our study dives into the intricate effects of biofouling on the settling velocity (Ws) of microplastics (MPs) within the fluid. We adopt the perspective that the biofilm is a form of surface roughness impacting the drag coefficient (Cd) and vertical settling of MPs. By advancing the biofouling process model, we simulate the temporal variations of density and biofilm thickness of biofouled floating MPs, accounting for realistic parameters and assuming a layer-by-layer growth of biofilm on plastisphere surfaces. MPs of polyethylene (PE) exhibit a quicker initiation of descent compared to their polypropylene (PP) counterparts. Furthermore, leveraging computational fluid dynamics (CFD) simulation, the method to predict the Cd of spherical MPs with surface roughness is established. By treating the thickness of the biofilm as roughness height, an explicit method to predict the Ws of biofouled MPs is derived. The settling experiments for biofouled MPs conducted not only support the combination of the biofouling model and the explicit method to predict the Ws of biofouled MPs but also enhance the prediction accuracy by introducing a ratio parameter Co to better relate the equivalent surface roughness height (k) to the biofilm thickness (σ), i.e., k = Co·σ, where the recommended value of Co for spherical PP and PE MPs is between 0.5 to 0.8. This study, thus, provides new insights into the dynamics of biofouled MPs in hydraulic ecosystems.

What is hiding below the surface - MPs including TWP in an urban lake

Inland lakes play an important role as habitats for local species and are often essential drinking water reservoirs. However, there is limited information about the presence of microplastics (MPs) in these water bodies. Thirteen sediment samples were collected across a Danish urban lake to map MPs, including tyre wear particles (TWP). The lower size detection limit was 10 µm. MPs were quantified as counts, size, and polymer type by Fourier-transform infrared microspectroscopy (µFTIR) and mass estimated from the 2D projections of the MPs. As TWP cannot be determined by µFTIR, counts and sizes could not be quantified by this technique. Instead, TWP mass was determined by pyrolysis gas chromatography mass spectrometry (Py-GC/MS). The average MP abundance was 279 mg kg-1 (µFTIR), of which 19 mg kg-1 (Py-GC/MS) were TWP. For MPs other than tyre wear, the average MP count concentration was 11,312 counts kg-1. Urban runoff from combined sewer overflows and separate stormwater outlets combined with outflow from a wastewater treatment plant were potential point sources. The spatial variation was substantial, with concentrations varying several orders of magnitude. There was no pattern in concentration across the lake, and the distribution of high and low values seemed random. This indicates that large sampling campaigns encompassing the entire lake are key to an accurate quantification. No preferential spatial trend in polymer characteristics was identified. For MPs other than TWP, the size of buoyant and non-buoyant polymers showed no significant difference across the lake, suggesting that the same processes brought them to the sediment, regardless of their density. Moreover, MP abundance was not correlated to sediment properties, further indicating a random occurrence of MPs in the lake sediments. These findings shed light on the occurrence and distribution of MPs, including TWP, in an inland lake, improving the basis for making mitigation decisions.

The potential of Lecane rotifers in microplastics removal

Dealing with hard-to-degrade plastics pollution of terrestrial and aquatic environments is one of the most urgent problems of the modern world. The smallest fraction (<5 mm) called micro-plastics (MP) has been found everywhere from ice in Greenland, streams, rivers, soil and even in the human placenta. The goal of our research was to assess the ability of rotifers Lecane inermis to remove micro-plastics suspended in the water column. In the experiments we investigated specific interactions between MP, biofilm and rotifers specialized in feeding on biofilm. We hypothesized that MP adhere to the biofilm and after ingestion by rotifers could be extracted from the water in the form of compact conglomerates excreted with fecal pellets. In these experiments, we demonstrated that: (i) the rotifers preferentially ingest microplastics embedded in biofilm, (ii) the presence of microplastics does not affect growth and fecundity of rotifers, and (iii) that MP aggregation is significantly improved by the presence of biofilm, additionally enhanced in the presence of rotifers. Our findings will help to understand the role of micro-grazers, such as L. inermis feeding on biofilm, in the fate of MP in nature. In the longer term, our results could help to develop biotechnological tools for MP removal from the aquatic environment.

Research progress on the role of biofilm in heavy metals adsorption-desorption characteristics of microplastics: A review

Microplastics (MPs) have been found to be widely distributed in aquatic environments, where they will interact with toxic heavy metals and result in more serious adverse effects on the aquatic environments and organisms. However, after entering the aquatic environments, MPs are quickly covered by biofilms, which significantly modify MPs properties and relevant heavy metals adsorption-desorption characteristics In order to better understand the adsorption behavior of heavy metals on biofilm developed MPs (BMPs), we comprehensively reviewed representative studies in this area. First, we summarized the formation process of biofilms on MPs. Subsequently, we reviewed the current understanding on the influence of biofilm formation on the properties of MPs and discussed the metal adsorption-desorption characteristics of MPs affected by these changes. Finally, based on the systematic literature review, some future research needs and strategies were proposed to further understand the interactions between MPs and heavy metals.

An analytical approach to confidence interval estimation of river microplastic sampling

Microplastics (MPs), plastic particles <5 mm in diameter, are emerging ubiquitous pollutants in natural environments, including freshwater ecosystems. As rivers facilitate efficient transport among landscapes, monitoring is crucial for elucidating the origin, dynamics, and fate of MPs. However, standardized methodologies for in situ sampling in freshwater environments remain undefined to date. Specifically, evaluating the sampling error of MP concentration estimates is crucial for comparing results among studies. This study proposes a novel method for computing confidence intervals (CIs) from a single estimate of numerical concentration (expressed in particles·m-3). MPs are expected to disperse according to purely random processes, such as turbulent diffusion, and to consequently exhibit a random distribution pattern that follows a Poisson point process. Accordingly, the present study introduced a framework based on the Poisson point process to compute CIs, which were validated using MP samples from two urban rivers in Chiba, Japan, obtained using a mesh with an opening size of 335 μm. Random number simulations revealed that the CIs were applicable when ≥10 MPs were present in a sample. Further, when ≥50 MPs were present in a sample, the sampling error (95% CI) was within ±30% of the concentration estimates. The proposed framework allows for the intercomparison of single river MP samples despite the lack of sample replicates. Further, the present study emphasizes that the volume of sampled river water is the only controllable parameter that can reduce the sampling error.

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.

No Effect of Realistic Microplastic Exposure on Growth and Development of Wild-caught Culex (Diptera: Culicidae) Mosquitoes

Microplastic (MP) pollution is a threat to environments around the world and mosquitoes are particularly affected because of their high chance of encountering MP as larvae. Mosquitoes have been shown to readily consume microplastics and they have a significant impact on health in society, yet we have limited knowledge on the effects of MP exposure on fitness-related traits. Additionally, the data we do have come primarily from studies that have used unrealistically high microplastic concentrations, or unrealistic methods of exposure. Here we exposed wild-type first instar Culex pipiens and Culex tarsalis larvae to two 4.8-5.8 μm polystyrene microplastic concentrations (0 particles/ml, 200 particles/ml, 20,000 particles/ml) to evaluate the effect of MP exposure on body size, development, and growth rate. We found no effect of microplastics on any of the traits in either species. These results indicate microplastic exposures comparable to levels found in nature have minimal effects on these fitness-related traits. Future directions for this work include examining whether the effects of MP exposure are exacerbated when evaluated in combination with other common stressors, such as warming temperatures, pesticides, and food limitation.

Vertical Differentiation of Microplastics Influenced by Thermal Stratification in a Deep Reservoir

Microplastics (MPs) are an emerging environmental concern. However, vertical transport of MPs remains unclear, particularly in deep reservoirs with thermal stratification (TS). In this study, the vertical variation in MP organization, stability, migration, and the driving factors of the profile in a deep reservoir were comprehensively explored. This is the first observation that TS interfaces in a deep reservoir act as a buffer area to retard MP subsidence, especially at the interface between the epilimnion and the metalimnion. Interestingly, there was a size-selection phenomenon for MP sinking. In particular, the high accumulation of large-sized MPs (LMPs; >300 μm) indicated that LMPs were more susceptible to dramatic changes in water density at the TS interfaces. Furthermore, simultaneous analysis of water parameters and MP surface characteristics showed that the drivers of MP deposition were biological to abiotic transitions during different layers, which were influenced by algae and metals. Specifically, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and microscopic Fourier transform infrared analyses implied that the occurrence of metals on the MP surface can promote MP deposition in the hypolimnion. Our findings demonstrated that TS significantly influenced the MP fate in deep reservoirs, and the hotspot of MP exposure risk for vulnerable benthic organisms on the reservoir floor deserves more attention.

First report on the toxicity of SARS-CoV-2, alone and in combination with polyethylene microplastics in neotropical fish

The COVID-19 pandemic has caused unprecedented negative impacts in the modern era, including economic, social, and public health losses. On the other hand, the potential effects that the input of SARS-CoV-2 in the aquatic environment from sewage may represent on non-target organisms are not well known. In addition, it is not yet known whether the association of SARS-CoV-2 with other pollutants, such as microplastics (MPs), may further impact the aquatic biota. Thus, we aimed to evaluate the possible ecotoxicological effects of exposure of male adults Poecilia reticulata, for 15 days, to inactivated SARS-CoV-2 (0.742 pg/L; isolated SARS.CoV2/SP02.2020.HIAE.Br) and polyethylene MP (PE MPs) (7.1 × 10⁴ particles/L), alone and in combination, from multiple biomarkers. Our data suggest that exposure to SARS-CoV-2 induced behavioral changes (in the open field test), nephrotoxic effect (inferred by the increase in creatinine), hepatotoxic effect (inferred by the increase in bilirubin production), imbalance in the homeostasis of Fe, Ca, and Mg, as well as an anticholinesterase effect in the animals [marked by the reduction of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity]. On the other hand, exposure to PE MPs induced a genotoxic effect (assessed by the comet assay), as well as an increase in enzyme activity alpha-amylase, alkaline phosphatase, and carboxylesterases. However, we did not show synergistic, antagonistic, or additive effects caused by the combined exposure of P. reticulata to SARS-CoV-2 and PE MPs. Principal component analysis (PCA) and values from the "Integrated Biomarker Response" index indicate that exposure to SARS-CoV-2 was determinant for a more prominent effect in the evaluated animals. Therefore, our study sheds light on the ecotoxicity of the new coronavirus in non-target organisms and ratifies the need for more attention to the impacts of COVID-19 on aquatic biota.

Effects of irrigation on the fate of microplastics in typical agricultural soil and freshwater environments in the upper irrigation area of the Yellow River

Agricultural activities are among the most significant sources of microplastics (MPs) in water. However, few studies have explored the effect of irrigation on the fate of MPs in agricultural systems. This study investigated the distribution of MPs in agricultural soil, surface water, and sediment of adjacent rivers, as well as the "MP communities" in various environments before and after irrigation in a typical agricultural irrigation area of the Yellow River. MPs were detected in all of the examined sites. The number of MPs in surface water and sediment increased after irrigation, whereas those in the surface soil of croplands decreased. In the vertical direction, irrigation accelerated the migration of MPs (< 100 µm) deep into the soil. The vertical mobility of fibers in soil was faster than that of other types of MPs. Moreover, irrigation decreased the correlation between soil properties and MPs in soils. MP community analysis indicated that irrigation enhanced the differences between MP communities among adjacent environments. Collectively, our findings confirmed that river water irrigation caused secondary MP pollution in the soil environment and accelerated MP pollution in deep soil. Therefore, this study provides a theoretical basis for the development of strategies for MP pollution control in agricultural soil.

Bioremediation of microplastics in freshwater environments: A systematic review of biofilm culture, degradation mechanisms, and analytical methods

Microplastics, defined as particles <5 mm in diameter, are emerging environmental pollutants that pose a threat to ecosystems and human health. Biofilm degradation of microplastics may be an ecologically friendly approach. This review systematically summarises the factors affecting biofilm degradation of microplastics and proposes feasible methods to improve the efficiency of microplastic biofilm degradation. Environmentally insensitive microorganisms were screened, optimized, and commercially cultured to facilitate the practical application of this technology. For strain screening, technology should focus on microorganisms/strains that can modify the hydrophobicity of microplastics, degrade the crystalline zone of microplastics, and metabolise additives in microplastics. The biodegradation mechanism is also described; microorganisms secreting extracellular oxidases and hydrolases are key factors for degradation. Measuring the changes in molecular weight distribution (MWD) enables better analysis of the biodegradation behaviour of microplastics. Biofilm degradation of microplastics has relatively few applications because of its low efficiency; however, enrichment of microplastics in freshwater environments and wastewater treatment plant tailwater is currently the most effective method for treating microplastics with biofilms.

Vertical and seasonal variations in biofilm formation on plastic substrates in coastal waters of the Black Sea

Plastic contamination of the marine environment is an increasing concern worldwide. Therefore, it is important to understand the kinetics of biofilms on plastics to study their behavior, fate, and transport pathways in the ocean. In this study, the vertical and seasonal variations in biofouling formation on transparent polyethylene terephthalate (PET) plastic fragments in the Southwest Crimea coastal waters of the Black Sea were investigated. Biofilms were identified in the transient light as 'dark spots' on the plastic surface, for which the numbers, size, and area were measured using specialized software. The rate of biofouling in the surface water layer was lower than those found in the middle and near-bottom water column, which could be due to a damaging effect of turbulent mixing on the biofilm. The highest rates of biofouling and diverse community were observed during the summer. The epibiotic assembly was represented by diatoms (11 taxa), dinoflagellates (3 taxa), green algae, filamentous cyanobacteria, small flagellates, and ciliates. Significant differences between the biofouling rates observed in different seasons made it difficult to estimate the period of time the plastic substrate has been in the marine environment. It was proposed to use the green alga Phycopeltis arundinacea (Montgn) De Tender et al., 2015 as a bioindicator to study the age of the biofouling community. Discoid thalli were identified at all stages of colonization of the plastic fragments in different seasons. Results obtained in this study demonstrate that biofouling organisms may be good model organisms in revealing age of biofilm formation and longevity of plastic debris in the ocean. Consequently, it is proposed that such biofouling organisms could be used as target species to monitor the biodegradation of plastic debris.

Buoyant microplastics in freshwater sediments - How do they get there?

The accumulation of microplastics (MPs) in the sediments of a stormwater treatment pond was studied to gain knowledge on how these facilities protect the natural environment against this emerging pollutant. Thirteen sediment samples were analyzed for MPs down to 10 μm, mapping the pattern of accumulation in the pond. The average abundance in terms of MP-number and mass was 11.8 μg kg^-1 and 44,383 item kg^-1, respectively. They were rather unevenly distributed, with concentrations varying up to two orders of magnitude within the pond, showing that a trustworthy quantification of MPs retained by such units must rely on many and well-distributed subsamples. Buoyant MPs made up 95.4 % of the MP-mass and 83.5 % of the MP-number and in most of the sampled locations, polypropylene dominated the polymer fingerprint, followed by polyethylene. No spatial pattern in the distribution of MPs in the pond was identified. Instead, the MP content correlated to the organic matter and silt content, indicating that the processes leading to deposition could be similar. A computational fluid dynamics model was set up and used to simulate the transport mechanisms governing the conveyance of MPs in the pond from water to sediments. The results showed that the combination of advection and dispersion were likely the driving mechanism for buoyant (and non-buoyant) MPs to get in contact with the sediment bed and spread over the pond. Once in contact with the sediments, the MPs would have some probability of being permanently incorporated and hereby preventing them from entering the downstream aquatic environment.

Fate and effects of microplastics in combination with pharmaceuticals and endocrine disruptors in freshwaters: Insights from a microcosm experiment

Microplastic contamination of freshwater ecosystems has become an increasing environmental concern. To advance the hazard assessment of microplastics, we conducted a microcosm experiment in which we exposed a simplified aquatic ecosystem consisting of moss and caddisflies to microplastics (polyethylene, polystyrene and polypropylene) and pharmaceuticals and personal care products (1H-benzotriazole, bisphenol A, caffeine, gemfibrozil, ketoprofen, methylparaben, estriol, diphenhydramine, tris (1-chloro-2-propyl) phosphate) over the course of 60 days. We monitored the flux of microplastics within the microcosm, as well as the metabolic and total protein variation of organisms. This study offers evidence highlighting the capacity of moss to act as a sink for free-floating microplastics in freshwater environments. Moss is also shown to serve as a source and pathway for microplastic particles to enter aquatic food webs via caddisflies feeding off of the moss. Although most ingested microparticles were eliminated between caddisflies life stages, a small fraction of microplastics was transferred from aquatic to terrestrial ecosystem by emergence. While moss exhibited a mild response to microplastic stress, caddisflies ingesting microplastics showed stress comparable to that caused by exposure to pharmaceuticals. The molecular responses that the stressors triggered were tentatively identified and related to phenotypic responses, such as the delayed development manifested through the delayed emergence of caddisflies exposed to stress. Overall, our study provides valuable insights into the adverse effects of microplastics on aquatic species, compares the impacts of microplastics on freshwater biota to those of pharmaceuticals and endocrine disrupting compounds, and demonstrates the role aquatic organisms have in redistributing microplastics between aquatic and terrestrial ecosystems.

Microplastic pollution in aquatic environments may facilitate misfeeding by fish

Numerous recent studies have documented ingestion of microplastics (MPs) by many aquatic animals, yet an explanation for misfeeding by fish remains unexplained. Here we tested the hypothesis that biofilm (biofouling) on MP surfaces due to exposure in the aquatic environment facilitates misfeeding in fish. Spherical polystyrene (PS) was cultured for 0-22 weeks in a freshwater environment to grow a biofilm on the MPs. Goldfish were employed in a simple feeding experiment with and without provision of genuine food at ecologically relevant MP concentrations. Absorbance (ABS), which is a proxy for biofilm formation, increased exponentially within three weeks of initiation and reached a plateau after approximately five weeks. Although fish did not swallow the MPs, "capture" occurred when food pellets were in the vicinity and significantly increased in probability with aging. Duration of capture also increased significantly with increasing aging. These results suggest that drifting of MPs in aquatic environments may facilitate fish misidentification of MPs as edible prey.

A critical review of microplastic degradation and material flow analysis towards a circular economy

The resilience and low cost of plastics has made their usage ubiquitous, but is also the cause of their prevalence and longevity as waste. Plastic pollution has become a great concern to the health and wellbeing of ecosystems around the world; microplastics are a particular threat, due to their high mobility, ease of ingestion by wildlife, and ability to adsorb and carry toxic contaminants. Material flow analysis has been widely applied to examine stocks and flows of materials in other industries, and has more recently been applied to plastics to examine areas where waste can reach the environment. However, while much research has gone into the environmental fate of microplastics, degradation strategies have been a lesser focus, and material flow analysis of microplastics has suffered from lack of data. Furthermore, the variety of plastics, their additives, and any contaminants pose a significant challenge in degrading (and not merely fragmenting) microplastic particles. This review discusses the current degradation strategies and solutions for dealing with existing and newly-generated microplastic waste along with examining the status of microplastics-based material flow analysis, which are critical for evaluating the possibility of incorporating microplastic waste into a circular economy. The degradation strategies are critically examined, identifying challenges and current trends, as well as important considerations that are frequently under-reported. An emphasis is placed on identifying missing data or information in both material flow analysis and degradation methods that could prove crucial in improving understanding of microplastic flows, as well as optimizing degradation strategies and minimizing any negative environmental impact.

UV stabilizers can foster early development of biofilms on freshwater microplastics

Interactions between microbes and microplastics are important as of emerging plastic loads in the global environment. Although diverse plastic additives are used in large amounts, there are very few studies on a quantitative comparison of plastisphere on plastics with different plastic additives. We studied the effects of two widely used UV stabilizers (benzotriazole-type UV-327 and benzophenone-type UV-531 were selected based on their persistence and toxicity) in low-density polyethylene (LDPE) on freshwater microbes. This is the first study on the sole effects of UV stabilizers used as plastic additives on freshwater in situ plastisphere biofilm development. Confocal laser scanning microscopy, assisted with proper differentiating fluorochromes and threshold-based 3D segmentation of data, was used to visualize and quantify biofilm. On the first week of biofilm growth, there was very little biovolume and a negligible amount of phototrophs on pristine LDPE contrasting other substrates. Biovolumes were significantly higher on LDPE with UV stabilizers (up to 159% higher than pristine LDPE), although the biomass was mostly dead due to toxicity (>100% higher dead biovolume than live biovolume in LDPE with UV stabilizers). After the fourth week, marginally higher biovolumes along with a revival of the biomass on LDPE with UV stabilizers were observed. The ability to induce microorganismic intracellular reactive oxygen species by UV stabilizers was detected, which may stimulate biofilm growth during the primary phase of biofilm development. Atomic force microscopy analysis denoted that LDPE with UV stabilizers exhibit considerably stronger adhesion force than pristine LDPE. These observations suggest that UV stabilizers can foster the early attachment of microbes to microplastics while killing the surface contacting layer. An alive upper layer of microbes can get developed on the dead biofilm without much disruption due to the toxicity of UV stabilizers. This occurrence can eventually boost the early development of biofilms on plastics.

Influence of Particle Size and Fragmentation on Large-Scale Microplastic Transport in the Mediterranean Sea

Microplastic particles move three-dimensionally through the ocean, but modeling studies often do not consider size-dependent vertical transport processes. In addition, microplastic fragmentation in ocean environments remains poorly understood, despite fragments making up the majority of microplastic pollution in terms of the number of particles and despite its potential role in mass removal. Here, we first investigate the role of particle size and density on the large-scale transport of microplastics in the Mediterranean Sea and next analyze how fragmentation may affect transport and mass loss of plastics. For progressively smaller particle sizes, microplastics are shown to be less likely to be beached and more likely to reach open water. Smaller particles also generally get mixed deeper, resulting in lower near-surface concentrations of small particles despite their higher total abundance. Microplastic fragmentation is shown to be dominated by beach-based fragmentation, with ocean-based fragmentation processes likely having negligible influence. However, fragmentation remains a slow process acting on decadal time scales and as such likely does not have a major influence on the large-scale distribution of microplastics and mass loss over periods less than 3 years.

Anthropocene microplastic stratigraphy of Xiamen Bay, China: A history of plastic production and waste management

Microplastics (MPs) are considered one of the significant stratigraphic markers of the onset of the Anthropocene Epoch; however, the interconnections between historic plastic production, waste management as well as social-economic and timing of MP accumulation are not well understood. Here, stratigraphic data of MPs from a sediment core from Xiamen Bay, China, was used to reconstruct the history of plastic pollution. Generalized Additive Modeling indicates a complex temporal evolution of MP accumulation. The oldest MPs deposited in 1952 was 30,332 ± 31,457 items/kg•dw, coincide with the infancy of the plastic industry and onset of the Anthropocene. The Cultural Revolution (1966-1976) curtailed these initial increases. Subsequent rapid growth in MPs during the late 1970s was peaked at 189,241 ± 29,495 items/kg•dw in 1988 and was followed by a drastic decline in the late 1980s to a low value in 1996 (16,626 ± 26,371 items/kg•dw), coinciding with proliferation of MP sources, coupled with evolution of plastic production, consumption, and regulation. Increasing MPs over the past decades implies that previous mitigation measures have been compromised by the escalated influx of MPs from increasing plastics production, legacy MPs remaining in circulation and insufficient waste management for a growing population. The present methodology and results represent a conceptual advance in understanding how changes in policy and economics over time correlate to changes in MP records in Anthropocene strata, which may help make decisions on plastic pollution mitigation strategies worldwide.

Insights into behavior and mechanism of tetracycline adsorption on virgin and soil-exposed microplastics

Microplastics (MPs), as vectors of pollutants, have attracted extensive attention because of their environmental effects. However, the adsorption behavior and antibiotic mechanism of environmentally exposed MPs is limited. Here, the adsorption of tetracycline (TC) onto virgin and soil-exposed polylactic acid (PLA), polyvinyl chloride (PVC) and polyethylene (PE) MPs showed that the adsorption capacity of MPs for TC increased after soil exposure, and PLA showed the strongest increase. Soil exposure increased the time to reach equilibrium, and the adsorption rate was controlled by both intraparticle diffusion and membrane diffusion. The isothermal adsorption results of soil-exposed PE and PLA indicated that TC adsorbed on heterogeneous surfaces was affected by the physicochemical adsorption process. The equilibrium absorption capacity of MPs for TC increased by 88% (PLA), 26% (PVC) and 15% (PE) after soil exposure. Soil dissolved organic matter promoted the desorption of TC from MPs, and TC speciation changed with pH. Soil-exposed MPs have the potential to promote TC degradation in solution without the addition of biological inhibitors. Moreover, density functional theory calculations verified that PE and PVC adsorbed TC through physical interactions, while hydrogen bonds were formed on PLA with TC. These results clarified the behavior and mechanisms of TC adsorption on virgin and soil-exposed MPs, which can help in the risk assessment of concomitant pollution of MPs and antibiotics.

Enhanced settling of microplastics after biofilm development: A laboratory column study mimicking wastewater clarifiers

The settling of microplastics (MPs) is crucial for their removal from municipal wastewater treatment plants (WWTPs) and sedimentation in static waterbodies, where they can accumulate in bottom sediments. Biofilm formation on MPs enhances their aggregation with other particles, thereby changing their density and size and altering their settling rates. However, only a few studies have investigated the settling of MPs of different sizes and materials. Specifically, the settling of small-sized MPs (<150 μm) has been poorly documented. In this study, cylindrical and fragmented particles of four polymer types (high-density polyethylene (HDPE), polypropylene (PP), polystyrene (PS), and poly(ethylene terephthalate) (PET)) were used to investigate the settling or floating of reference MPs (20-130 μm) in a custom-made column that simulated a primary sedimentation tank in a typical WWTP before and after incubation in wastewater influent. The settling velocity of the reference MP particles was strongly influenced by the particle size and density. The settled fractions of all the cylindrical reference MPs increased significantly (up to 5 times) due to biofilm formation at overflow velocities of 0.15, 0.26, and 0.40 mm s^-1. This was observed even for HDPE and PP (density <1 g cm^-3) after biofilm formation. The fragmented reference MPs showed complex and rather unpredictable behavior, possibly due to their irregular shape. Generally, the settling of pristine PS and PET in the laboratory tests was consistent with the theoretical predictions obtained using Stokes' law. The experimental findings of this study can be used to develop models that predict the removal efficiencies of MPs in WWTPs and to estimate the sinking of MPs to bottom sediments of static waterbodies.

Microplastics in urban runoff: Global occurrence and fate

Public concerns on microplastic (MP) pollution and its prevalence in urban runoff have grown exponentially. Huge amounts of MPs are transported from urban environments via surface runoff to different environment compartments, including rivers, lakes, reservoirs, estuaries, and oceans. The global concentrations of MPs in urban runoff range from 0 to 8580 particles/L. Understanding the sources, abundance, composition and characteristics of MPs in urban runoff on a global scale is a critical challenge because of the existence of multiple sources and spatiotemporal heterogeneity. Additionally, dynamic processes in the mobilization, aging, fragmentation, transport, and retention of MPs in urban runoff have been largely overlooked. Furthermore, the MP flux through urban runoff into rivers, lakes and even oceans is largely unknown, which is very important for better understanding the fate and transport of MPs in urban environments. Here, we provide a critical review of the global occurrence, transport, retention process, and sinks of MPs in urban runoff. Relevant policies, regulations and measures are put forward. Future global investigations and mitigation efforts will require us to address this issue cautiously, cooperating globally, nationally and regionally, and acting locally.

Ecotoxicological and health implications of microplastic-associated biofilms: a recent review and prospect for turning the hazards into benefits

Microplastics (MPs), over the years, have been regarded as a severe environmental nuisance with adverse effects on our ecosystem as well as human health globally. In recent times, microplastics have been reported to support biofouling by genetically diverse organisms resulting in the formation of biofilms. Biofilms, however, could result in changes in the physicochemical properties of microplastics, such as their buoyancy and roughness. Many scholars perceived the microplastic-biofilm association as having more severe consequences, providing evidence of its effects on the environment, aquatic life, and nutrient cycles. Furthermore, other researchers have shown that microplastic-associated biofilms have severe consequences on human health as they serve as vectors of heavy metals, toxic chemicals, and antibiotic resistance genes. Despite what is already known about their adverse effects, other interesting avenues are yet to be fully explored or developed to turn the perceived negative microplastic-biofilm association to our advantage. The major inclusion criteria for relevant literature were that it must focus on microplastic association biofilms, while we excluded papers solely on biofilms or microplastics. A total of 242 scientific records were obtained. More than 90% focused on explaining the environmental and health impacts of microplastic-biofilm association, whereas only very few studies have reported the possibilities and opportunities in turning the microplastic biofilms association into benefits. In summary, this paper concisely reviews the current knowledge of microplastic-associated biofilms and their adverse consequences and further proposes some approaches that can be developed to turn the negative association into positive.

Mediterranean microplastic contamination: Israel's coastline contributions

This study provides an analysis of the current state of microplastic (MP) contamination along the Mediterranean coastline of Israel. Six strategic sites were monitored in this study - each representing a unique coastal environment. We conclude that Tel Aviv and Hadera, both located near stream estuaries, were highly contaminated (18,777 particles/m³) with MP compared to the other locations. The MP detected included both secondary MP and pristine polymeric pellets. In-depth characterization of the MP illustrated a large percentage of both fragmented and film MP morphologies and the most common MP polymers were polyethylene and polypropylene. Further particle analysis showed that MPs were contaminated with biofilm, including microorganisms such as diatoms, as well as metal residues. Through the spatial analysis presented herein we suggest that local rivers are significant contributors to MP contamination along the Mediterranean Sea coastline of Israel and may pose a direct threat to environment and human health.

A record of microplastic in the marine nearshore waters of South Georgia

The polar plastics research community have recommended the spatial coverage of microplastic investigations in Antarctica and the Southern Ocean be increased. Presented here is a baseline estimate of microplastics in the nearshore waters of South Georgia, the first in situ study of the north-east coast of the island. Our results show that the microplastic concentration in seawater at twelve stations in proximity to King Edward Point Research Station ranged from 1.75 ± 5.17 MP/L (mean ± SD), approximately one order of magnitude higher than similar studies of sea surface waters south of the Polar Front. Levels of microplastics in freshwater (sampled from Gull Lake) and precipitation (collected adjacent to the research station) were 2.67 ± 3.05 MP/L, and 4.67 ± 3.21 MP/L respectively. There was no significant difference in the microplastic concentration between seawater sites, and no significant bilateral relationship between concentration and distance from the research station outlets. We report an average concentration of 1.66 ± 3.00 MP/L in wastewater collected from the research station but overall, the counts of microplastics were too low to attach any statistical significance to the similarity in the microplastic assemblages of seawater and wastewater, or assemblages retrieved from penguin species in the region in other studies. Using a calculation described in contemporary literature we estimate the number of microfibres potentially being released from ships and stations annually in the region but acknowledge that further samples are needed to support the figures generated. More extensive research into microplastic distribution, characteristics, and transport in the region is recommended to fully compute the level of risk which this pollutant represents to the ecosystem health of this remote region.

Horizontal and vertical distribution of microplastics in dam reservoir after impoundment

In freshwater ecosystems, microplastics (MPs) are commonly found in reservoirs. However, limited information is available on the distribution of MPs in the reservoirs. In this study, we investigated the horizontal and vertical distribution characteristics of MPs in the Guanyingyan reservoir (the upper reaches of the Yangtze River, China) after impoundment and the influence of free-floating plant residues on the distribution of MPs. Results indicated that the MPs abundance in the horizontal distribution of the reservoir decreased significantly while the distance from the dam increased. The abundance of MPs in shoreline waters (average: 8.45 items L^-1) was significantly higher than that in central waters (average: 4.80 items L^-1). As for the vertical distribution, the percentages of fibers in the three water layers (surface, intermediate, and deep) have less variation when compared to other types of MPs. Besides, MPs who are less than 0.5 mm in size are the majority. With deeper underwater, there would be more MPs with particles smaller than 200 μm in size. At the same time, there would be fewer MPs with particles ranging from 200 to 500 μm in size. PS, PP, and PE are the main polymer types of surface water, while PVC, PE, and PET are the common type in deep water. In shoreline water, the dry weight of floating plant residues showed a positive correlation with microplastic abundance in different layers. As above said, this study confirmed that MPs in reservoirs after impoundment would tend to accumulate in the front section of the reservoir and the shoreline water. Besides, free-floating plant residues would accumulate in reservoirs, resulting in the sinking of MPs.

Integrated effects of polymer type, size and shape on the sinking dynamics of biofouled microplastics

Sinking of microplastics (MPs) after biofouling is considered an important mechanisms responsible for the downward transport/sedimentation of MPs in the ocean and freshwaters. Previous studies demonstrated MP sinking caused by an increase in the composite density of MPs after biofouling, while MPs with smaller size or shapes with higher surface area to volume ratios (SA:V), such as films, are speculated to sink faster. In this study, we designed an in situ microcosm to simulate the ambient environmental conditions experienced by floating MPs to elucidate the biofouling and sinking of polyethylene (PE), polypropylene (PP), and expanded-polystyrene (EPS) MPs of various sizes and shapes. Our results showed smaller PE and PP MP granules sank faster than large ones. Even EPS granules of 100 μm diameter, having a much lower density (0.02 mg/mm³) than water, started to sink after 2 weeks of biofouling. Moreover, PE film and fiber MPs with higher SA:V did not sink faster than PE MP granules of the same mass, implying that mechanisms other than SA:V, such as fouling contact area and drag coefficient, play a role in the regulation of biofouling and sinking of MPs.

Plastics, prawns, and patterns: Microplastic loadings in Nephrops norvegicus and surrounding habitat in the North East Atlantic

The presence of microplastics (MPs), a contaminant of emerging concern, has attracted increasing attention in commercially important seafood species such as Nephrops norvegicus. This species lend themselves well as bioindicators of environmental contamination owing to their availability, spatial and depth distribution, interactions with seafloor sediment and position in the ecosystem and food chain. This study assesses the abundance of MPs in N. norvegicus and in benthic sediments across six functional units in the North East Atlantic. Assessment of the relationship between MP abundance in N. norvegicus, their biological parameters and their surrounding environment was examined. Despite the lack of statistical significance, MP abundances, size, shape, and polymer type recorded in N. norvegicus mirrored those found in the surrounding environment samples. The three main polymers identified in both organisms and sediment were polystyrene, polyamide (nylons), and polypropylene. The level of MP contamination in N. norvegicus could be related to local sources, with relatively low abundances recorded in this study for the North East Atlantic in comparison to other regional studies. Furthermore, larger organisms contained a lower abundance of MPs, demonstrating no accumulation of MPs in N. norvegicus. Based on the results of this study, data on MP ingestion could be used to study trends in the amount and composition of litter ingested by marine animals towards fulfilling requirements of descriptor 10 of the Marine Strategy Framework Directive.