The fate of missing ocean plastics: Are they just a marine environmental problem?

Quantification of ocean microplastic fragmentation processes in the Sea of Japan using a combination of field observations and numerical particle tracking model experiments

This study estimated the fragmentation rate of microplastics (MiPs) in the Sea of Japan by analyzing MiP size over time following their generation from macroplastics (MaPs). A 5-year particle-tracking model was used to simulate the MaP and MiP motions driven by ocean currents, Stokes drift, the windage of MaPs, beaching, re-drifting, the conversion process from MaPs to MiPs, and the removal of MiPs from the upper ocean. MiP sizes decreased downstream in the Tsushima Current flowing northeastward. The highest correlation between MiP size and elapsed time occurred in the simulation where MiP fragmentation also occurred in the ocean, at 20 % of the rate on beaches. The apparent fragmentation rate in nature was estimated to approximately 1.0 mm/100 days. This study demonstrated that incorporating spatiotemporal information from the simulation into observed size results could further our understanding of fragmentation of MiPs degraded in marine environments.

Fate and mass budget of microplastic in the Beibu Gulf, the northern South China sea

This study investigated the distribution, abundance, and mass budget of microplastics (MPs) in the Beibu Gulf, Northern South China Sea, focusing on their ecological significance and anthropogenic influence. Microplastics were found in all water and sediment samples, with concentrations in surface water ranging from 0.10 to 0.89 items/m³, and in bottom water from 0 to 0.85 items/m³. Sediment samples exhibited higher levels, ranging from 13.12 to 155.59 items/kg. The spatial distribution revealed higher concentrations along the northern Gulf and Guangxi Province, suggesting significant human influence from coastal activities, such as mariculture and industrial discharges. The study utilized both field data and a mass balance box model to estimate the MPs mass budget, revealing that oceanic flow and riverine discharge are major contributors, accounting for 49% and 52% of MPs, while Atmospheric deposition and sedimentation represents 8% and 1%, respectively. The inventory estimation calculated that 0.24 tons of MPs exist in the water column, and 137 tons in the sediment, emphasizing the substantial environmental burden posed by these pollutants. The significance of this research lies in its comprehensive assessment of MPs in a semi-enclosed gulf, providing critical insight into the role of coastal and hydrodynamic processes in MP distribution. This study highlights the urgent need for better waste management practices in coastal regions to mitigate microplastic pollution and its detrimental effects on marine ecosystems.

Hormesis of black soldier fly larva: Influence and interactions in livestock manure recycling

Black soldier fly larvae (BSFL) are considered important organisms, utilized as tools to transform waste including manure into valuable products. The growth and cultivation of BSFL are influenced by various factors, such as the presence of toxic substances in the feed and parasites. These factors play a crucial role in hormesis, and contributing to regulate these contaminants hermetic doses to get sustainable byproducts. This review aims to understand the effects on BSFL growth and activities in the presence of compounds like organic and inorganic pollutants. It also assesses the impact of microbes on BSFL growth and explores the bioaccumulation of pharmaceutical compounds, specifically focusing on heavy metals, pesticides, pharmaceuticals, indigenous bacteria, insects, and nematodes. The review concludes by addressing knowledge gaps, proposing future biorefineries, and offering recommendations for further research.

Reduction scenarios of plastic waste emission guided by the probability distribution model to avoid additional ocean plastic pollution by 2050s

Marine plastic pollution is progressing worldwide and will become increasingly serious if plastic waste emissions continue at the current rate or increase with economic growth. Here, we report a particle tracking-based probability distribution model for predicting the abundances of marine macroplastics and microplastics, which undergo generation, transport, and removal processes in the world's upper ocean, under various scenarios of future land-to-sea plastic waste emissions. To achieve the Osaka Blue Ocean Vision, which aims to reduce additional pollution by marine plastic litter to zero by 2050, plastic waste emission in ∼2035 should be reduced by at least 32 % relative to 2019. It is necessary to take stringent measures such as 'system change scenario' or 'improve waste management scenario' proposed in previous studies to reduce the marine plastic pollution by 2050.

Critical reassessment of microplastic abundances in the marine environment

Microplastics (MPs) pose a growing concern in the marine environment, but their global prevalence remains largely unknown due to the absence of precise and standardized detection methods. This review critically evaluates existing techniques for quantifying MP abundances in marine field studies, addressing inaccuracies resulting from the exclusion of particle sizes, polymer types, or limitations in identification methods. These traced inaccuracies were considered to recalculate MP abundances for particle sizes from 10 to 5000 μm, providing the first corrected global overview of MP distribution that enables quality assessment and reliable comparisons between adjusted data. The recalculations indicate that MP abundances are up to 15 times higher in marine waters (average (1.5 ± 36.2) × 105 items m-3) and up to 11 times higher in the marine sediments (average (2.7 ± 117.9) × 105 items kg-1) than previously reported in the literature. The Australasian Mediterranean Sea (average (1.2 ± 10.6) × 106 items m-3) and the North Atlantic (average (2.1 ± 37.6) × 105 items kg-1) emerged as the most polluted regions in marine waters and sediments, respectively, with primary contributors being the coasts of Southeast Asia and East America. This review demonstrates that previous field studies, global estimates, and models have significantly underestimated MP levels in marine environments in many cases, which could result in misinterpretations of both local and global pollution levels. This work highlights the critical need for precise handling of microplastic samples and urges future researchers to adopt standardized protocols for MP analysis to avoid inaccurate and misleading outcomes.

Quantification of litter in cities using a smartphone application and citizen science in conjunction with deep learning-based image processing

Cities are a major source of litter pollution. Determination of the abundance and composition of plastic litter in cities is imperative for effective pollution management, environmental protection, and sustainable urban development. Therefore, here, a multidisciplinary approach to quantify and classify the abundance of litter in urban environments is proposed. In the present study, litter data collection was integrated via the Pirika smartphone application and conducted image analysis based on deep learning. Pirika was launched in May 2018 and, to date, has collected approximately one million images. Visual classification revealed that the most common types of litter were cans, plastic bags, plastic bottles, cigarette butts, cigarette boxes, and sanitary masks, in that order. The top six categories accounted for approximately 80 % of the total, whereas the top three categories accounted for more than 60 % of the total imaged litter. A deep-learning image processing algorithm was developed to automatically identify the top six litter categories. Both precision and recall derived from the model were higher than 75 %, enabling proper litter categorization. The quantity of litter derived from automated image processing was also plotted on a map using location data acquired concurrently with the images by the smartphone application. Conclusively, this study demonstrates that citizen science supported by smartphone applications and deep learning-based image processing can enable the visualization, quantification, and characterization of street litter in cities.

Physio-chemical degradation of single-use plastics in natural weather and marine environments

Plastic pollution has reached concerning levels globally, with single-use plastic products (SUPs) comprising at least 50% of plastic waste. This study investigates the physical and chemical degradation of frequently used SUPs, including petroleum-based and bio-based plastics, in natural Northern European coastal weather and marine environments over a three-year period from 2019 to 2022. Addressing a critical knowledge gap, this research was based on a hypothesis that real-world ageing studies on SUPs would produce more accurate time- and process-lines for their transformation from macro-to microplastics than are available today based on the modeling studies more frequently used. The study employs optical examination, mechanical testing, Fourier Transform Infrared (FTIR) spectroscopy, and Gas Chromatography-Mass Spectrometry (GC-MS) to determine and relate physical and chemical changes with time. The results indicate that SUPs undergo significantly faster degradation in natural weather than predicted to date. Photooxidation emerges as the primary degradation pathway for all SUPs, emphasizing the role of light in plastic breakdown. Importantly, physical degradation to microplastics in natural environments is not always associated with significant chemical changes such as breaking chemical bonds. Black SUPs exhibit greater resistance to visible light and ultraviolet radiation than equivalent white and transparent examples. In marine environments, SUPs degrade measurably slower than in air, their degradation slowing with increasing distance from the water surface. Our findings indicate the urgent need for strategies that mitigate the impacts of photo-oxidation of SUPs. Such strategies may include a focus on the removal of post-use SUPs from pavements, roads, beaches, and water surfaces where photo-oxidation is faster than underwater and underground. Preferential use of black SUPs over white or transparent should also be considered.

Vertical Flux of Microplastics in the Deep Subtropical Pacific Ocean: Moored Sediment-Trap Observations within the Kuroshio Extension Recirculation Gyre

The Kuroshio Extension recirculation gyre in the western North Pacific is an accumulation site of plastic litter transported by the Kuroshio Current. A sediment trap was moored at a depth of 4900 m at Station KEO within the Kuroshio Extension recirculation gyre, and the vertical flux of microplastics in sinking particles of size <1 mm was observed. Forty-one sediment-trap samples collected from July 1, 2014, to October 2, 2016, were analyzed with a micro-Fourier transform infrared spectrometer and microplastics were detected in all samples. Seventeen polymer types were identified, and 90% of the microplastics were less than 100 μm in size. Microplastic sinking was driven by the action of the biological pump, which was in turn driven by seasonal variations in solar radiation and increased surface primary production typical of the spring season. Microplastic mass flux varied from 4.5 × 10-3 to 0.38 mg m-2 day-1 during the sampling period, with a mean and standard deviation of 0.054 ± 0.075 mg m-2 day-1. Extrapolating the annual microplastic mass flux at Station KEO to the entire Kuroshio Extension recirculation gyre, it is estimated that 0.028 million metric tons of microplastics are transported annually to 4900 m depth in this area.

Use of pelagic tunicate Salpa fusiformis as biological sampler to estimate in-situ density of microplastics smaller than 330 μm

While microplastics (MPs) have emerged as a significant threat, information on MPs <330 μm (SMPs) is limited by the lack of simple quantification methods. We examined the potential application of salps, non-selective filter-feeding tunicates, to estimate in-situ SMP densities. After collection, salp guts were dissected, dissolved, and filtered to analyze MPs using μFTIR. The results showed each gut samples contained 1.96 ± 1.49 MP particles; their polymer composition and size were consistent with those in ambient seawater. When the SMP quantity in salp gut was converted to in-situ densities using previously published feeding parameters, SMP densities ranged between 235 and 1209 particles/m3; they were strongly correlated with those in seawater. Importantly, this method, which is less labor intensive than other methods, could easily characterize in-situ SMP distribution of different marine environments, thus improve the monitoring of their pollution. Furthermore, it could be applied to examine historical contributions of SMPs using archived salp samples.

Convergence zones of coastal waters as hotspots for floating microplastic accumulation

This study examines microplastic (MP, 1-5 mm) densities in convergence zones in a coastal sea, the Seto Inland Sea, comparing them to those of non-convergence zones and other areas. Notably, Seto convergence zones exhibit MP densities 40 to 300 times higher than non-convergence zones, with an extraordinary density of 3.7 ± 6.3 pieces m-3, similar to densities found in Tokyo Bay as known a MP hotspot. The predominant polymer found was expanded polystyrene, varying seasonally and peaking in summer. Juvenile fish associated with driftweed in these convergence zones face a risk of long-term MP exposure, potentially up to four months. This large number of MPs found in coastal convergence zones is similar to accumulation zones formed in the gyres of open oceans, with strong implications for detrimental effects on coastal marine life. However, these MPs are autochthonous, and may be manageable through local marine plastic waste management.

Migration and accumulation patterns of plastic waste in the environment: A comprehensive simulation study

Plastic waste is commonly littered in the environment due to insufficient waste management practices. Mismanaged plastic waste may migrate and accumulate in terrestrial and aquatic environments. Plastic waste in the terrestrial environment is our topic of interest, as it can significantly contribute to the broader issue of plastic waste pollutants. Wind and surface runoff are the main factors affecting plastic movement in the terrestrial environment. On the other hand, land surfaces, as the resisting factors, have a role in facilitating the unique movement patterns. Our objectives are to simulate the motion rate and pattern of plastic movement by exposing five varieties of plastics to these driving and resisting variables. As foundational data, this study can be utilized to ascertain the probability of migration and accumulation in the terrestrial environment. Each plastic travels differently across different ground surfaces at various wind speed thresholds. For example, a plastic bag can be moved at 0.8 m/s on paved and bare terrain, while it requires 1.6 m/s to move a plastic bag on cutting grass. A plastic by surface runoff may already be in motion when driven at a 1 L/s rate. However, wind power will be more frequently encountered in the environment than runoff, which only occurs on rainy days. The data also shows varied patterns across various ground surfaces, i.e., how plastic waste is retained in vegetated regions, travels with soil particles in bare terrain, and is easily transported on paved terrain.

Open dumping site as a point source of microplastics and plastic additives: A case study in Thailand

Microplastics (MPs) and plastic additive chemicals are emerging pollutants of great concerns around the world. Open dumping sites can be important sources of those pollutants in emerging countries, but little is known about their occurrence, distribution, transport pathway, and remediation approach. This study aimed to obtain the comprehensive dataset on plastic pollution in an open dumping site in Thailand, including (1) the polymer types and organic/inorganic plastic additives in plastic garbage, (2) horizontal distribution of MPs and plastic additives in the surface soil, (3) the effects of soil-capping treatment, and (4) the vertical transport. First, thirty-two plastic garbage collected from the dumping site were analyzed, and a total of 40 organic chemicals (mean: 1400,000 ng/g dw) and 7 heavy metals (mean: 2,030,000 ng/g dw) were identified. The burdens stored in the dumping site were estimated to reach to 3.3-18 tons for organic additives and 4.9-26 tons for heavy metals. In the surface soil analysis, 13 types of polymers in MPs, 20 elements, and 37 organic plastic additives were detected. The pollution levels were significantly higher near the dumping site than at control sites, indicating that the open dumping site is a point source of MPs and plastic additives. Interestingly, a significantly positive correlation was found between the concentrations of MPs and organic additives in soil. This suggests that MPs act as carriers of plastic-derived chemicals. Soil-capping treatment (including removal of some trash) drastically mitigated the contaminant levels in the surface soil, indicating this treatment is one of the effective approaches to control the horizontal distribution of MPs and plastic additives. However, soil core analyzes implied that the vertical transport is still continued even after soil-capping treatment. Our findings provided the comprehensive dataset to support for understanding plastic pollution in the open dumping site.

Beach litter composition, distribution patterns and annual budgets on Novaya Zemlya archipelago, Russian Arctic

Beached macrolitter (>2,5 cm) abundance and composition in the Russian (Eastern) part of the Barents Sea and the adjacent part of the Kara Sea was assessed for 2021-2023. Average densities of beach litter on the coasts are 675 items/100 m and 37 kg/100 m (0.27 items/m2 and 0.015 kg/m2). Annual litter budgets for Cape Zhelaniya beaches are 0.49 items/m2 per year and 0.023 kg/m2 per year. The northernmost tip of Novaya Zemlya is shown to be a beach litter accumulation hot-spot on Novaya Zemlya archipelago, where litter is brought by surface currents and trapped by sea ice margins. Up to 80 % of beached marine macrolitter is made of plastics, originating from vessels. A certain accumulation strip of a beach was identified (14 m - 27.5 m distance from the waterline), and significance of the beach backshore was shown in litter accumulation. Beach litter accounting methodologies on the Arctic beaches are discussed.

A metabolomics perspective on the effect of environmental micro and nanoplastics on living organisms: A review

The increasing trend regarding the use of plastics has arisen an exponential concern on the fate of their derived products to the environment. Among these derivatives, microplastics and nanoplastics (MNPs) have been featured for their associated environmental impact due to their low molecular size and high surface area, which has prompted their ubiquitous transference among all environmental interfaces. Due to the heterogenous chemical composition of MNPs, the study of these particles has focused a high number of studies, as a result of the myriad of associated physicochemical properties that contribute to the co-transference of a wide range of contaminants, thus becoming a major challenge for the scientific community. In this sense, both primary and secondary MNPs are well-known to be adscribed to industrial and urbanized areas, from which they are massively released to the environment through a multiscale level, involving the atmosphere, hydrosphere, and lithosphere. Consequently, much research has been conducted on the understanding of the interconnection between those interfaces, that motivate the spread of these contaminants to biological systems, being mostly represented by the biosphere, especially phytosphere and, finally, the anthroposphere. These findings have highlighted the potential hazardous risk for human health through different mechanisms from the environment, requiring a much deeper approach to define the real risk of MNPs exposure. As a result, there is a gap of knowledge regarding the environmental impact of MNPs from a high-throughput perspective. In this review, a metabolomics-based overview on the impact of MNPs to all environmental interfaces was proposed, considering this technology a highly valuable tool to decipher the real impact of MNPs on biological systems, thus opening a novel perspective on the study of these contaminants.

Macroplastic and Microparticle Pollution in Beach Sediments from Urias Coastal Lagoon (Northwest Mexico)

This study investigates the occurrence and characteristics of macroplastic and polymer microparticles in the Urias coastal lagoon's beach sediments, in northwest Mexico. Coastal lagoons, productive and vulnerable ecosystems, are impacted significantly by anthropogenic activities, leadings to their pollution by various contaminants, including plastics. Our research involved sampling sediments from four sites within the lagoon that were influenced by different human activities such as fishing, aquaculture, thermoelectric power plant operations, industrial operations, and domestic wastewater discharge. Our methodology included collecting macroplastics and beach sediment samples, followed by laboratory analyses to identify the plastic debris' size, shape, color, and chemical composition. The results indicated a notable presence of macroplastic items (144), predominantly bags, styrofoam, and caps made of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). The polymer microparticles were mainly fibers, with cotton and polyester as the most common polymers, suggesting a significant contribution from clothing-related waste. The dominant colors of the microparticles were blue and transparent. High densities were observed in areas with slower water exchange. Our findings highlight the urgent need for better waste management practices to mitigate plastic pollution in coastal lagoons, preserving their ecological and economic functions.

Marine litter along the shores of the Persian Gulf, Iran

Plastic wastes -including cigarette butts (CBs)- are dangerous for marine ecosystems not only because they contain hazardous chemicals but also because they can finally turn into micro- or even nano-particles that may be ingested by micro- and macro-fauna. Even large pieces of plastics can trap animals. In this research, the pollution status of macroplastics (abundance, size, type, and colour) and cigarette butts (CBs, number/m2) on the northern coasts of the Persian Gulf has been investigated. A total of 19 stations were explored in Bushehr province (Iran), which covers a length equivalent to 160 km of the Persian Gulf coastline. Among the collected plastic waste (2992 items), disposable mugs were the most frequent (18 %). Plastics with sizes 5-15 cm were the most abundant, and the most common type of plastic was PET (P-value <0.05). The origin of most macroplastics was domestic (2269 items). According to the Index of Clean Coasts (ICC), most surveyed beaches were extremely dirty. The average number and density of CBs in this study were 220 and 2.45 items/m2, respectively. Household litter was the most abundant type of waste in the studied beaches, and this problem can be better managed by training and improving the waste disposal culture. In general, it is suggested that an integrated and enhanced management for fishing, sewage and surface water disposal, and sandy recreational beaches be implemented in Bushehr to control plastic waste.

Influence of monsoon seasonality and tidal cycle on microplastics presence and distribution in the Upper Gulf of Thailand

Southeast Asian countries are recognized as significant contributors to the discharge of abundant plastic waste into the ocean. In this study, we conducted neuston net surveys on Si Chang Island of the Gulf of Thailand, a coral reef conservation area, to determine the presence of microplastic (MP) pollution. The survey, conducted during the wet (southwesterly monsoon), transition, and dry seasons (northeasterly monsoon), revealed that the MP abundance was in the range of 0.02-42.46 particles m-3. The precipitation, wind, and current direction induced by monsoons influenced the abundance and distribution of MP, presenting a significant seasonality. The cluster analysis for colors and polymer types of MPs suggested that the origin of plastic particles is diverse. Based on our results, a proposal for the generation, sources, and pathways for MPs in the Gulf of Thailand is presented: 1) plastic wastes exposed to strong UV light during the dry season get fragmented around the river, and 2) heavy rains wash away the particles during the wet season. This proposal is applicable to tropical regions, including the Gulf of Thailand. Therefore, this paper concluded that ocean currents induced by monsoons and the unique climate, resulting in the generation of MPs on land, increase MP presence and distribution in the ocean surrounding Southeast Asia countries. Furthermore, coral reef ecosystems can be particularly threatened by MPs in these areas. So, an increase in MP monitoring on coral ecosystems from Thailand and the world is highly recommended.

Microplastics in beach sediments of the Azores archipelago, NE Atlantic

Oceanic islands are exposed to plastic debris that has accumulated in the open ocean, particularly in the subtropical gyres. This study investigates the abundance and typology of microplastics (from 0.1 to 5 mm) on 19 sandy beaches spread across 8 oceanic islands of the Azores archipelago. Between January and April 2016, a total of 341 particles retrieved from all beaches, were identified as microplastics. The highest concentration (50.19 ± 21.93 particles kg-1 dw) was found in Terceira Island. Beach morphology and grain size were important factors explaining microplastic concentration. Fibres were the most dominant morphology recovered (80.9 %), followed by fragments (12.3 %). Fourier transform infrared spectroscopy (FTIR) revealed that 41 % of the fibres consisted of polyester and 60 % of the fragments were polyethylene. This research underlines the widespread contamination of microplastics in oceanic islands of the Atlantic Ocean.

Sunlight-Driven Photochemical Removal of Polypropylene Microplastics from Surface Waters Follows Linear Kinetics and Does Not Result in Fragmentation

Floating microplastics are susceptible to sunlight-driven photodegradation, which can convert plastic carbon to dissolved organic carbon (DOC) and can facilitate microplastic fragmentation by mechanical forces. To understand the photochemical fate of sub-millimeter buoyant plastics, ∼0.6 mm polypropylene microplastics were photodegraded while tracking plastic mass, carbon, and particle size distributions. Plastic mass loss and carbon loss followed linear kinetics. At most time points DOC accumulation accounted for under 50% of the total plastic carbon lost. DOC accumulation followed sigmoidal kinetics, not the exponential kinetics previously reported for shorter irradiations. Thus, we suggest that estimates of plastic lifespan based on exponential DOC accumulation are inaccurate. Instead, linear plastic-C mass and plastic mass loss kinetics should be used, and these methods result in longer estimates of photochemical lifetimes for plastics in surface waters. Scanning electron microscopy revealed that photoirradiation produced two distinct patterns of cracking on the particles. However, size distribution analyses indicated that fragmentation was minimal. Instead, the initial population of microplastics shrank in size during irradiations, indicating photoirradiation in tranquil waters (i.e., without mechanical forcing) dissolved sub-millimeter plastics without fragmentation.

Abundance and potential sources of floating polystyrene foam macro- and microplastics around Japan

Polystyrene foam is widely used due to its lightweight, impact resistance, and excellent thermal insulation properties. Meanwhile, weak adhesion between beads in polystyrene foam leads to fragmentation, generating a substantial amount of microplastics (<5 mm). Such polystyrene foam debris littered on beaches diminishes the aesthetic value of coastal areas, negatively impacting tourism. Due to its density lower than other plastics, polystyrene foam macroplastics float on the sea surface and, thus, they are significantly influenced by wind drag during oceanic transport. In contrast, polystyrene foam microplastics drifting beneath the sea surface are carried mostly by ocean currents. These properties of polystyrene foam macroplastics and microplastics hinder the elucidation of their transport, distribution, and fate in nature, despite their potential to adversely impact marine ecosystems. To elucidate the generation, transport, and fragmentation processes of polystyrene foam ocean plastics, we conducted concurrent visual observations and surface net towing from seven training vessels around Japan during 2014-2020. Overall, the abundances of polystyrene foam ocean plastics were higher in the Sea of Japan than in the North Pacific south of Japan. The average abundances of polystyrene foam microplastics and macroplastics were 0.33 pieces/m3 and 0.45 pieces/km, respectively, over the entire sea area around Japan. In the Sea of Japan, the peak abundances of polystyrene foam macroplastics occurred in upstream of the Tsushima Current, while the peak for microplastics occurred downstream, suggesting that continuous fragmentation occurred during transport between the two peaks. Backward-in-time particle tracking model experiments suggested that the sources of polystyrene foam macroplastics observed in the Sea of Japan included aquaculture buoys and styrene debris beached around the Tsushima Strait. The present study demonstrated that reducing the release of polystyrene foam aquaculture floats will likely diminish the abundance of ocean plastics in the Sea of Japan.

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.

A particle tracking model approach to determine the dispersal of riverine plastic debris released into the Indian Ocean

Although the Indian Ocean receives a large amount of land-based plastic waste, the studies on pathways of riverine plastic debris are limited to date. Therefore, a particle tracking model that included ocean surface currents, horizontal diffusion, Stokes drift, windage, and beaching/re-drifting processes was developed to reproduce the behavior of riverine plastic debris in the Indian Ocean. The modeled particles were released in the model domain based on riverine plastic debris database. The maximum abundance of beached particles occurred during the southwesterly monsoon season, particularly in the Bay of Bengal. The particles released from the rivers were trapped in the northern Indian Ocean unless both Stokes drift and windage were excluded from transportation velocity. These results suggest that the riverine plastic debris was trapped in the northern Indian Ocean until it fragmented into less buoyant small microplastics drifting in the subsurface layer, free from windage and Stokes drift at increasing depths.

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.

Levels, spatial distributions, and provision of petroleum hydrocarbons and phthalates in sediments from Obhur lagoon, Red Sea coast of Saudi Arabia

The levels, spatial distribution, and sources of petroleum hydrocarbons and phthalates were assessed in surface sediment samples from the urban lagoon of Obhur near Jeddah, the largest city on the Red Sea coast of Saudi Arabia. The lagoon was divided into the inner zone, middle zone, and outer zone based on its geomorphological features and developmental activities. n-Alkanes, hopane and sterane biomarkers, and unresolved complex mixture were the major petroleum hydrocarbon compounds of the total extractable organic matter. Phthalates were also measured in the sediment samples. In the three zones, n-alkanes ranged from 89.3 ± 88.5 to 103.2 ± 114.9 ng/g, whereas the hopane and sterane biomarkers varied from 69.4 ± 75.3 to 77.7 ± 69.9 ng/g and 72.5 ± 77.9-89.5 ± 82.2 ng/g, respectively. The UCM concentrations ranged from 821 ± 1119 to 1297 ± 1684 ng/g and phthalates from 37.4 ± 34.5 65 ± 68 ng/g. The primary origins of these anthropogenic hydrocarbons in the lagoon sediments were petroleum products (boat engine discharges, boat washing, lubricants, and wastewater flows) and plasticizers (plastic waste and litter). The proportions of anthropogenic hydrocarbons derived from petroleum products in the sediment's TEOM ranged from 43 ± 33 to 62 ± 15%, while the percentages for plasticizers varied from 2.9 ± 1.2 to 4.0 ± 1.6%. The presence and inputs of these contaminants from petroleum and plastic wastes in the lagoon's sediments will eventually have an impact on its habitats, including the benthic nursery and spawning areas.

Three-dimensional evaluation of beaches of oceanic islands as reservoirs of plastic particles in the open ocean

The quantification of plastic debris on beaches has been extensively used as an indicator of plastic pollution in the marine environment. However, most efforts have focused on surface layers, with few investigations looking deeper into the substrate, thus underestimating total standing stocks. Such information is crucial to improve our understanding of where plastic accumulates in the oceans. In this study, we investigated the three-dimensional distribution of plastic (>1 mm) in three sandy beaches located in oceanic islands of the North Atlantic (Azores and the Canary Islands) that are known to accumulate significant quantities of small plastic debris at the surface layer. On each beach, we collected a total of 16 sediment cores down to 1 m depth, from the high tide line up to the backshore following a stratified random sampling design spread across four different levels across the beach. Samples were taken every 10 cm down to 1 m into the sand. Our results revealed the presence of plastic items in the deepest layers with subsurface layers accounting for 84 % of the total plastic abundance and with a similar pattern in terms of size, shape, colour and composition. Furthermore, we found increasing plastic concentrations towards the upper levels of the beach, indicating longer term accumulation in the backshore. Collectively, this study suggests that the plastic items reaching sandy beaches of the Macaronesia are being incorporated into its deepest layers, acting as reservoirs of plastic in the open ocean.

Sediment-driven plastisphere community assembly on plastic debris in tropical coastal and marine environments

Coastal habitats have been suggested to serve as a sink for unaccounted plastic debris, i.e., "missing plastic" in the sea, and hence, a hotspot of plastic pollution in the marine and coastal environments. Although the accumulation of plastic debris may pose significant threats to coastal ecosystems, we know little about the fate of these plastic debris and their ecological impacts due to the lack of studies on plastic-microbe interactions in coastal habitats, especially for the tropical marine and coastal environments. In this study, we collected plastic debris from 14 sites consisting of various coastal ecosystems (seagrass meadows, mangrove forests, and beaches), and marine ecosystem (coral reef) around Singapore and characterized the prokaryotic and eukaryotic microbial communities colonized on them. Our results showed that the composition of plastisphere communities in these intertidal ecosystems was predominantly influenced by the sediment than by the plastic materials. Compared with surrounding sediment and seawater, the plastic debris enriched potential plastic degraders, such as Muricauda, Halomonas, and Brevundimonas. The plastic debris was also found to host taxa that play significant roles in biogeochemical cycles (e.g., cyanobacteria, Erythrobacter), hygienically relevant bacteria (e.g., Chryseobacterium, Brevundimonas), and potential pathogens that may negatively impact the health of coastal ecosystems (e.g., Thraustochytriaceae, Labyrinthulaceae, Flavobacterium). Taken together, our study provides valuable insights into the plastic-microbe interactions in tropical coastal and marine ecosystems, highlighting the urgent need for plastisphere studies to understand the fate and ecological impacts of plastic debris accumulated in coastal habitats.

Microplastics in coastal farmed oyster (Crassostrea angulata) shells: Abundance, characteristics, and diversity

One of the most concerning emerging pollutants is microplastics (MPs), which can infiltrate soft tissues of organisms by ingestion, adhesion, and fusing and may even become embedded in biominerals. However, very little evidence is available about MPs in biominerals found in the wild. This study detected the abundance and characteristics of MPs in the shells of farmed oysters (Crassostrea angulata) off the coast of Taiwan and discussed the distribution, accumulation, and diversity in the oyster shells. The results showed that MPs were ubiquitous in oyster shells, with an average abundance of 0.70 ± 0.40 MPs/g. MPs abundance was significantly (p < 0.01) higher in small oyster shells (shell length < 6.5 cm, weight 5-10 g) and inorganic (CaCO3) fraction (HCl digestion) than in large oyster shells (>6.5 cm, 10-25 g) and an organic fraction (H2O2 digestion), respectively. However, there was no significant difference in MPs abundance between the top and bottom shells (p > 0.05). MPs with a size <2 mm accounted for 78.5 %, fibrous MPs for 93.7 %, and rayon for 89.5 %. The MPs diversity integrated index (MPDII) in oyster shells was low (0.27), and the small and fibrous MPs seemed more easily embedded in biominerals. The findings confirm the presence of MPs in oyster shells in coastal environments. In addition, oyster shells may contain higher amounts of MPs than soft tissues 4-5 times, which needs to be confirmed. Further revealing the distribution and accumulation of MPs in water/terrestrial biominerals will help to understand the fate of MPs in the environment.

Prediction of microplastic abundance in surface water of the ocean and influencing factors based on ensemble learning

Microplastics are regarded as emergent contaminants posing a serious threat to the marine ecosystem. It is time-consuming and labor-intensive to determine the number of microplastics in different seas using traditional sampling and detection methods. Machine learning can provide a promising tool for prediction, but there is a lack of research on this. To screen high-performance models for the prediction of microplastic abundance in the marine surface water and explore the influencing factors, three ensemble learning models, random forest (RF), gradient boosted decision tree (GBDT), and extreme gradient boosting (XGBoost), were developed and compared. A total of 1169 samples were collected, and multi-classification prediction models were constructed with 16 features of the data as inputs and six classes of microplastic abundance intervals as outputs. Our results show that the XGBoost model has the best performance of prediction, with a total accuracy rate of 0.719 and an ROC AUC (Receiver Operating Characteristic curve, Area Under Curve) value of 0.914. Seawater phosphate (PHOS) and seawater temperature (TEMP) have negative effects on the abundance of microplastics in surface seawater, while the distance between the sampling point and the coast (DIS), wind stress (WS), human development index (HDI), and sampling latitude (LAT) have positive effects. This work not only predicts the abundance of microplastics in different seas but also offers a framework for the use of machine learning in the study of marine microplastics.

Estimation of the age of polyethylene microplastics collected from oceans: Application to the western North Pacific Ocean

The knowledge of microplastic (MP) age could aid the deduction of the origin and fate of a fragment carried by ocean currents over long time periods and distances. The present study developed a novel method to estimate the age of MPs (i.e., UV radiation exposure time) using the oxidation level of polyethylene (i.e., carbonyl index) from infrared spectrometry, ultraviolet erythemal radiation (UVER) data, and ambient seawater temperatures. Accelerated and outdoor exposure experiments were conducted to establish relationships among the temporally integrated UVER, ambient temperature, and carbonyl index. Thereafter, the age of MPs was computed, with Miyakojima Island serving as the reference location. The estimated ages of MPs collected from the western North Pacific Ocean ranged from 1 to 3 years, and those MPs from nearshore waters ranged from 0 to 5 years.

Modelling the transportation of marine plastics over the ocean surface by Cellular Automata

This article describes a novel Cellular Automata (CA) model to predict the transportation of buoyant marine plastics. The proposed CA model provides a simpler and more affordable approach to a field where the computationally intensive Lagrangian particle-tracking models dominate. The transportation of marine plastics was investigated using well-defined, probabilistic rules governing the advection and diffusion processes. The CA model was applied to evaluate the impact of two input scenarios, namely a "population" and a "river" scenario. Of the sub-tropical gyres, a high percentage of buoyant plastics were found in the Indian gyre (population: 5.0 %; river: 5.5 %) and North Pacific gyre (population: 5.5 %; river: 7 %). These findings show good agreement with previously published results from particle-tracking models. The CA model could be a useful rapid-scenario assessment tool for the estimation marine plastic pollution prior to more in-depth studies on effective mitigation measures to, for example, reduce plastics waste.

Role of mangrove forest in interception of microplastics (MPs): Challenges, progress, and prospects

Mangroves receive microplastics (MPs) from terrestrial, marine and atmospheric sources, acting as a huge filter for environmental MPs between land and sea. Due to the high primary production and complex hydrodynamic conditions in mangroves, MPs are extensively intercepted in various ways while flowing through mangroves, leading to a long-standing but fiercely increasing MPs accumulation. However, current researches mainly focused on the occurrence, source and fate of MPs pollution in mangroves, ignoring the role of mangrove forests in the interception of MPs. Our study firstly demonstrates that mangrove ecosystems have significantly greater MPs interception capacity than their surrounding environments. Then, the current status of studies related to the interception of MPs in mangrove ecosystems is comprehensively reviewed, with the main focus on the interception process and mechanisms. At last, the most pressing shortcomings of current research are highlighted regarding the intercepted flux, interception mechanisms, retention time and ecological risks of MPs in mangrove ecosystems and the relevant future perspectives are provided. This review is expected to emphasize the critical role of mangrove forests in the interception of MPs and provide the foundational knowledge for evaluating the MPs interception effect of mangrove forests globally.

Microbial Enzyme Biotechnology to Reach Plastic Waste Circularity: Current Status, Problems and Perspectives

The accumulation of synthetic plastic waste in the environment has become a global concern. Microbial enzymes (purified or as whole-cell biocatalysts) represent emerging biotechnological tools for waste circularity; they can depolymerize materials into reusable building blocks, but their contribution must be considered within the context of present waste management practices. This review reports on the prospective of biotechnological tools for plastic bio-recycling within the framework of plastic waste management in Europe. Available biotechnology tools can support polyethylene terephthalate (PET) recycling. However, PET represents only ≈7% of unrecycled plastic waste. Polyurethanes, the principal unrecycled waste fraction, together with other thermosets and more recalcitrant thermoplastics (e.g., polyolefins) are the next plausible target for enzyme-based depolymerization, even if this process is currently effective only on ideal polyester-based polymers. To extend the contribution of biotechnology to plastic circularity, optimization of collection and sorting systems should be considered to feed chemoenzymatic technologies for the treatment of more recalcitrant and mixed polymers. In addition, new bio-based technologies with a lower environmental impact in comparison with the present approaches should be developed to depolymerize (available or new) plastic materials, that should be designed for the required durability and for being susceptible to the action of enzymes.

The use of microplastics as a reliable chronological marker of the Anthropocene onset in Southeastern South America

Microplastics (MPs) represent an emergent contamination marker. For this reason, we analyzed the vertical distribution of MPs in six sediment cores retrieved from the Patos-Mirim System, the world's largest coastal lagoonal system. The sediment cores span from mid Holocene to present times according to both radiocarbon and lead dating and are located close to both urban/industrial and agricultural regions. We identified a basal pre-disturbance MP-free zone in all cores and an uppermost contaminated 70-cm-zone, where a general increasing trend in MPs content resembling the human anthropization process was recorded. The predominant format of MPs was fiber, followed by fragments. The most commonly identified polymers were rayon, PVC, acrylate, polycarbonate and cellophane. Urban/industrial and agricultural activities were shown as clear sources of MPs, leading to comparable MPs concentration values in the sediment cores. Thus, MPs are collectively a reliable indicator of the Anthropocene onset, and in the Patos-Mirim System the most appropriate chronology can be assigned to the beginning of 1970s, matching the intensification of anthropogenic activities in the area.

A growing plastic smog, now estimated to be over 170 trillion plastic particles afloat in the world's oceans-Urgent solutions required

As global awareness, science, and policy interventions for plastic escalate, institutions around the world are seeking preventative strategies. Central to this is the need for precise global time series of plastic pollution with which we can assess whether implemented policies are effective, but at present we lack these data. To address this need, we used previously published and new data on floating ocean plastics (n = 11,777 stations) to create a global time-series that estimates the average counts and mass of small plastics in the ocean surface layer from 1979 to 2019. Today's global abundance is estimated at approximately 82-358 trillion plastic particles weighing 1.1-4.9 million tonnes. We observed no clear detectable trend until 1990, a fluctuating but stagnant trend from then until 2005, and a rapid increase until the present. This observed acceleration of plastic densities in the world's oceans, also reported for beaches around the globe, demands urgent international policy interventions.

Contamination of sea surface water offshore the Tokai region and Tokyo Bay in Japan by small microplastics

A nested double neuston net was prepared and used to collect samples from the surface of coastal waters around Japan to obtain information about the properties of both small microplastics (SMPs; <350 μm) and large microplastics (LMPs; >350 μm). The SMP concentrations ranged from 1000 to 5900 pieces m^-3 in the open ocean and averaged approximately 3000 pieces m^-3 in the inner part of Tokyo Bay. The SMP concentrations were around 20-60 times greater than the LMP concentrations. By analyzing the seawater, we obtained a microplastic size distribution that spanned 50-5000 μm. The LMPs mainly comprised packaging-related plastics, such as polyethylene (PE) and polypropylene, while the SMPs were dominated by paint-related plastics. SMPs derived from packaging materials (e.g., PE) may have gradually sank down from the sea surface when they were smaller than 600 μm.

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.

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.

Pelagic distribution of plastic debris (> 500 µm) and marine organisms in the upper layer of the North Atlantic Ocean

At present, the distribution of plastic debris in the ocean water column remains largely unknown. Such information, however, is required to assess the exposure of marine organisms to plastic pollution as well as to calculate the ocean plastic mass balance. Here, we provide water column profiles (0–300 m water depth) of plastic (0.05–5 cm in size) concentration and key planktonic species from the eastern North Atlantic Ocean. The amount of plastic decreases rapidly in the upper few meters, from ~ 1 item/m³ (~ 1000 µg/m³) at the sea surface to values of ~ 0.001–0.01 items/m³ (~ 0.1–10 µg/m³) at 300 m depth. Ratios of plastic to plankton varied between ~ 10^–5 and 1 plastic particles per individual with highest ratios typically found in the surface waters. We further observed that pelagic ratios were generally higher in the water column below the subtropical gyre compared to those in more coastal ecosystems. Lastly, we show plastic to (non-gelatinous) plankton ratios could be as high as ~ 10²–10⁷ plastic particles per individual when considering reported concentrations of small microplastics < 100 μm. Plastic pollution in our oceans may therefore soon exceed estimated safe concentrations for many pelagic species.