Anticyclonic eddies increase accumulation of microplastic in the North Atlantic subtropical gyre

Frontal processes as drivers of floating marine debris in coastal areas

The influence of floating marine debris (FMD) on coastal and marine communities and ecosystems is undeniable, and attention is increasingly focused on ecologically and biologically important coastal areas. To protect marine life and valuable resources from FMD pollution, identifying FMD accumulation zones is recognized as a priority. One of the coastal ocean processes found governing the distribution of FMD is water convergence (frontal zones). These fronts are driven by various oceanographical factors. To date, the transport and accumulation of FMD in relation to fronts in coastal areas is poorly understood. To address this knowledge gap, we reviewed various types of ocean fronts as well as FMD accumulation along frontal zones in coastal areas defined as the region between the coastline and the shelf break. Frontogenesis (physical processes related to frontal formation) were reviewed alongside studies on FMD accumulation in frontal zones to identify physical factors that drive the pathways and accumulation in these areas. This review will contribute to our understanding of accumulation hotspots of FMD within ocean fronts and identify gaps for further research on developing a proxy for FMD hotspot identification in ecologically important coastal areas.

Unveiling high concentrations of small microplastics (11-500 μm) in surface water samples from the southern Weddell Sea off Antarctica

Recent studies have highlighted the prevalence of microplastic (MP) pollution in the global marine environment and these pollutants have been found to contaminate even remote regions, including the Southern Ocean south of the polar front. Previous studies in this region have mostly focused on MPs larger than 300 μm, potentially underestimating the extent of MP pollution. This study is the first to investigate MPs in marine surface waters south of the polar front, with a focus on small MPs 500-11 μm in size. Seventeen surface water samples were collected in the southern Weddell Sea using an in-house-designed sampling system. The analysis of the entire sample using micro-Fourier transform infrared spectroscopy (μFTIR) with focal plane array (FPA) detection revealed the presence of MPs in all samples, with the vast majority of the MPs detected being smaller than 300 μm (98.3 %). The mean concentration reached 43.5 (± 83.8) MPs m-3, with a wide range from 0.5 to 267.2 MPs m-3. The samples with the highest concentrations differed from the other samples in that they were collected north of the continental slope and the Antarctic Slope Current. Sea ice conditions possibly also influenced these varying concentrations. This study reports high concentrations of MPs compared to other studies in the region. It emphasizes the need to analyze small MPs, down to a size of 11 μm or even smaller, in the Antarctic Treaty Area to gain a more comprehensive understanding of MP pollution and its potential ecological impacts.

Does water column stratification influence the vertical distribution of microplastics?

Microplastic pollution has been confirmed in all marine compartments. However, information on the sub-surface microplastics (MPs) abundance is still limited. The vertical distribution of MPs can be influenced by water column stratification due to water masses of contrasting density. In this study, we investigated the vertical distribution of MPs in relation to the water column structure at nine sites in the Kattegat/Skagerrak (Denmark) in October 2020.A CTD was used to determine the stratification and pycnocline depth before sampling. Plastic-free pump-filter sampling devices were used to collect MPs from water samples (1-3 m3) at different depths. MPs concentration (MPs m-3) ranged from 18 to 87 MP m-3 (Median: 40 MP m-3; n = 9) in surface waters. In the mid waters, concentrations ranged from 16 to 157 MP m-3 (Median: 31 MP m-3; n = 6), while at deeper depths, concentrations ranged from 13 to 95 MP m-3 (Median: 34 MP m-3; n = 9). There was no significant difference in the concentration of MPs between depths. Regardless of the depth, polyester (47%), polypropylene (24%), polyethylene (10%), and polystyrene (9%) were the dominating polymers. Approximately 94% of the MPs fell within the size range of 11-300 μm across all depths. High-density polymers accounted for 68% of the MPs, while low-density polymers accounted for 32% at all depths. Overall, our results show that MPs are ubiquitous in the water column from surface to deep waters; we did not find any impact of water density on the depth distribution of MPs despite the strong water stratification in the Kattegat/Skagerrak.

Relationship between floating marine debris accumulation and coastal fronts in the Northeast coast of the USA

Floating marine debris (FMD) is one of the world's most concerning issues due to its potential impact on biodiversity, communities, and ecosystem services. FMD transport and concentrations are driven by fronts, generated by oceanographic processes, and the accumulation of FMD has been reported in gyres, eddies, tidal fronts, salinity fronts, and coastal fronts. This study explores the relationship between fronts and FMD accumulation in the Gulf of Maine (GoM) and the surrounding coastal areas (USA). Frontal edge detection algorithms were applied to sea surface temperature (SST) imagery from the Moderate-resolution Imaging Spectroradiometer (MODIS) between 2002 and 2012. Frontal location is spatially correlated with FMD concentrations collected by the Sea Education Association. Higher concentrations of FMD are associated with frontal frequencies (FF) of 5-10 %. FMD is trapped between fronts and the coastline in accumulation zones. These results highlight the need to consider coastal FMD hotspots, given these are areas of high biodiversity value.

Does the mouth size influence microplastic ingestion in fishes?

This study investigated microplastic (MP) contamination in six tropical fish species of different mouth sizes and trophic levels from Saint Martin's Island, Bay of Bengal. A total of 309 microplastics (MPs) were extracted from the gastrointestinal tract (GT) of these selected fishes, where the presence of MPs was 100 %. The mean abundance of MPs was significantly varied among the species and ranged from 4.38 to 10 MPs/GT (p < 0.05). This study revealed that MP incidence was strongly correlated with the mouth-to-body ratio of the selected fishes (r = 0.424, p = 0.003) and trophic levels (r = 0.458, p = 0.002). Results suggest that fish with larger mouths are more likely to ingest MPs, intentionally or unintentionally, compared to those with smaller mouths.

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.

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

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

Global distribution of marine microplastics and potential for biodegradation

Microplastics are a growing marine environmental concern globally due to their high abundance and persistent degradation. We created a global map for predicting marine microplastic pollution using a machine-learning model based on 9445 samples and found that microplastics converged in zones of accumulation in subtropical gyres and near polar seas. The predicted global potential for the biodegradation of microplastics in 1112 metagenome-assembled genomes from 485 marine metagenomes indicated high potential in areas of high microplastic pollution, such as the northern Atlantic Ocean and the Mediterranean Sea. However, the limited number of samples hindered our prediction, a priority issue that needs to be addressed in the future. We further identified hosts with microplastic degradation genes (MDGs) and found that Proteobacteria accounted for a high proportion of MDG hosts, mainly Alphaproteobacteria and Gammaproteobacteria, with host-specific patterns. Our study is essential for raising awareness, identifying areas with microplastic pollution, providing a prediction method of machine learning to prioritize surveillance, and identifying the global potential of marine microbiomes to degrade microplastics, providing a reference for selecting bacteria that have the potential to degrade microplastics for further applied research.

Quantification and characterization of microplastics in surface water samples from the Northeast Atlantic Ocean using laser direct infrared imaging

15 filtration samples were collected at eight locations onboard the RV Sonne (cruise SO279 in 2020) from 6 m water depth using a fractionated stainless-steel filtration unit. The size fraction > 300 μm was visually examined and potential microplastic particles were analyzed by ATR-FTIR spectroscopy. The treatment of size class 20 μm < d < 300 μm was based on enzymatic-oxidative microwave-assisted "one-pot" matrix digestion in conjunction with analysis of the microplastics by time-efficient LDIR imaging. Total number concentrations ranged from 47 to 2154 microplastic particles per m³ (average for all stations: 500 ± 700 microplastic particles m^-3 (1 SD; n = 8)). In total, 20 polymer types were identified. The most common polymer types were polyethylene terephthalate (20 %) and acrylates/polyurethane/varnish (15 %). 93 % of the detected microplastics were smaller than 100 μm in length. Analysis of sample replicates indicates high spatio-temporal variations in microplastic pollution within the investigated region.

Seasonal distribution of microplastics in surface waters of the Northern Indian Ocean

Seven expeditions were carried out during pre-monsoon, monsoon and post monsoon in 2018-2019 for marine plastic collection in surface waters of Northern Indian Ocean. PE and PP (83 %) is the dominant type of polymer found in the surface waters. Colored particles account for 67 % of all particles, with fibre/line accounting for 86 %. The average (Mean ± SD) microplastics concentration in the Northern Indian Ocean during pre-monsoon is 15,200 ± 7999 no./km², Monsoon is 18,223 ± 14,725 no./km² and post monsoon is 72,381 ± 77,692 no./km². BoB during pre-monsoon and post monsoon the microplastic concentration remains same except in the northern BoB this change is caused due to weak winds. Microplastics concentration varied both spatially, temporal and heterogeneity in nature. These differences are caused by effect of wind and seasonal reversal of currents. Microplastics collected in the anticyclonic eddy are 129,000 no./km².

Exploring the presence and distribution of microplastics in subterranean estuaries from southwest India

Rivers, surface runoff, and the wind all transport microplastics (MPs) to the ocean. There is a knowledge gap concerning the distribution of microplastics in transitional subterranean estuaries. Here, we report the presence of microplastics in the pore water, groundwater, and sea water from four locations in southwest India. Pore water, groundwater, and seawater had mean MP abundances (± standard deviations) of 0.75 (±0.66), 0.15 (±0.1), and 0.11 (±0.07) MPs/l, respectively. Fibres were the dominant category of MPs found. Fourier-transformed infrared spectroscopy revealed the presence of polymers like polyester, low-density polyethylene, and polystyrene. Possible sources of microplastic are fishing activities, tourism, and coastal residents. The microplastics-derived risk assessment scores indicate severe risk to the ecosystems. Fibrous microplastics in pore water indicate that these linear particles can migrate vertically through sandy sediments, reaching subterranean estuaries. We believe submarine groundwater discharge can act as a possible pathway for microplastics to enter the oceans.

Feasibility Study for the Development of a Low-Cost, Compact, and Fast Sensor for the Detection and Classification of Microplastics in the Marine Environment

The detection and classification of microplastics in the marine environment is a complex task that implies the use of delicate and expensive instrumentation. In this paper, we present a preliminary feasibility study for the development of a low-cost, compact microplastics sensor that could be mounted, in principle, on a float of drifters, for the monitoring of large marine surfaces. The preliminary results of the study indicate that a simple sensor equipped with three infrared-sensitive photodiodes can reach classification accuracies around 90% for the most-diffused floating microplastics in the marine environment (polyethylene and polypropylene).

Microplastics trigger the Matthew effect on nitrogen assimilation in marine diatoms at an environmentally relevant concentration

Microplastics (MPs, diameter <5 mm) are widely distributed on Earth, especially in the oceans. Diatoms account for ∼40% of marine primary productivity and affect the global biogeochemical cycles of macroelements. However, the effects of MPs on marine nitrogen cycling remain poorly understood, particularly comparisons between nitrogen-replete and nitrogen-limited conditions. We found that MPs trigger the Matthew effect on nitrogen assimilation in diatoms, where MPs inhibited nitrogen assimilation under nitrogen-limited conditions while enhancing nitrogen metabolism under nitrogen-replete conditions in Phaeodactylum tricornutum. Nitrate reductase (NR) and nitrite reductase (NIR) are upregulated, but nitrate transporter (NRT) and glutamine synthetase (GS) are downregulated by MPs under nitrogen-limited conditions. In contrast, NR, NIR, and GS are all upregulated by MPs under nitrogen-replete conditions. MPs accelerate nitrogen anabolic processes with an increase in the accumulation of carbohydrates by 80.7 ± 7.9% and enhance the activities of key nitrogen-metabolizing enzymes (8.20-44.90%) under nitrogen-replete conditions. In contrast, the abundance of carbohydrates decreases by 22.0-34.4%, and NRT activity is inhibited by 79.0-86.5% in nitrogen-limited algae exposed to MPs. Metabolomic and transcriptomic analyses were performed to further explore the molecular mechanisms of reprogrammed nitrogen assimilation, including carbon metabolism, nitrogen transport and ammonia assimilation. The aforementioned spatial redistribution (e.g., the Matthew effect between nitrogen-replete and -limited conditions) of nitrogen assimilation highlights the potential risks of MP contamination in the ocean.

Plastic waste discharge to the global ocean constrained by seawater observations

Marine plastic pollution poses a potential threat to the ecosystem, but the sources and their magnitudes remain largely unclear. Existing bottom-up emission inventories vary among studies for two to three orders of magnitudes (OMs). Here, we adopt a top-down approach that uses observed dataset of sea surface plastic concentrations and an ensemble of ocean transport models to reduce the uncertainty of global plastic discharge. The optimal estimation of plastic emissions in this study varies about 1.5 OMs: 0.70 (0.13-3.8 as a 95% confidence interval) million metric tons yr-1 at the present day. We find that the variability of surface plastic abundance caused by different emission inventories is higher than that caused by model parameters. We suggest that more accurate emission inventories, more data for the abundance in the seawater and other compartments, and more accurate model parameters are required to further reduce the uncertainty of our estimate.

Horizontal distribution of surface microplastic concentrations and water-column microplastic inventories in the Chukchi Sea, western Arctic Ocean

The recent influx of microplastics into the Arctic Ocean may increase environmental stress on the western Arctic marine ecosystem, which is experiencing significant sea-ice loss due to global warming. Quantitative data on microplastics in the western Arctic Ocean are very limited, and the microplastic budget of the water column is completely unknown. To fill in gaps in our knowledge of Arctic microplastics, we observed surface concentrations (number of particles per unit volume of seawater) of meso- and microplastics using a neuston net, and we observed wind speeds and significant wave heights in the Chukchi Sea, Bering Strait, and Bering Sea. From these observations, we estimated the total number (particle inventory) and mass (mass inventory) of microplastics in the entire water column by taking into account the effect of vertical mixing. The particle inventory of microplastics in the Chukchi Sea ranged from 0 to 18,815 pieces km^-2 with a mean and standard deviation of 5236 ± 6127 pieces km^-2. The mass inventory ranged from 0 to 445 g km^-2 with a mean and standard deviation of 124 ± 145 g km^-2. Mean particle inventories for the Chukchi Sea were one-thirtieth of those for the Arctic Ocean on the Atlantic side and less than one-tenth of the average for the global ocean, suggesting that the Chukchi Sea is less polluted. However, the annual flux of microplastics from the Pacific Ocean into the Chukchi Sea, estimated from microplastic concentrations in the Bering Strait, was about 5.5 times greater than the total amount of microplastic in the entire Chukchi Sea water. This suggests that microplastic inflows from the Pacific Ocean are accumulating in large amounts in reservoirs other than the Chukchi Sea water (e.g., sea ice and seafloor sediments) or in the downstream regions of the Pacific-origin water.

Tide-driven microplastics transport in an elongated semi-closed bay: A case study in Xiangshan Bay, China

Coastal bays are important containers for plastic wastes before they enter the ocean. Based on field samples, this study presents the main characteristics of microplastics and uses a numerical model to study the distribution and movement of microplastics as they are driven by tidal flows in an extended semi-closed bay in Xiangshan Bay, China. The laboratory analyses of microplastic samples from 27 pollutant source samples collected in three batches provided fundamental data on microplastics. Our results show that the local microplastics are prevalent (mean abundance: 890.6 ± 419.4 particles/m³) in the water. A higher quantity of fibre- and fragment-type microplastics was identified and compared to other plastic types. The detected microplastics varied in colour and composition. The simulation suggests that the bay can trap microplastics inside it, with only 16.92 % discharged into the open ocean. A series of single-source numerical tests at nine typical observation sites were conducted to examine tide-driven microplastic transport. Our results suggest that the release location is crucial to microplastic distribution. Specifically, the microplastics tended to accumulate near the bay mouth and the Tie inlet; the microplastics released from the north shore generally evacuated the bay more easily; and the inner harbour tended to accumulate microplastics during spring tide, as opposed to the departure of microplastics at the outer bay, while the effect was reversed during neap tide. We further considered the deposit effect, which significantly reduces the discharging rate to 0.04 % with a settling velocity of 0.05 mm/s. These results may have great importance to decision-making, management, and control of microplastic pollution.

Seasonal variation in microplastics and zooplankton abundances and characteristics: The ecological vulnerability of an oceanic island system

The ingestion of microplastics (MPs - plastic particles <5 mm) by planktivorous organisms represents a significant threat to marine food webs. To investigate how seasonality might affect plastic intake in oceanic islands' ecosystems, relative abundances and composition of MPs and mesozooplankton samples collected off Madeira Island (NE Atlantic) between February 2019 and January 2020 were analysed. MPs were found in all samples, with fibres accounting for 89 % of the particles. MPs and zooplankton mean abundance was 0.262 items/m³ and 18.137 individuals/m³, respectively. Their monthly variations follow the seasonal fluctuation of environmental parameters, such as currents, chlorophyll-a concentration, sea surface temperature and precipitation intensity. A higher MPs/zooplankton ratio was recorded in the warm season (May-Oct), reaching 0.068 items/individual when considering large-sized particles (1000-5000 μm). This is the first study to assess the seasonal variability of MPs in an oceanic island system providing essential information respecting its ecological impact in pelagic environments.

Marine plastics in Mediterranean islands: Evaluating the distribution and composition of plastic pollution in the surface waters along four islands of the Western Sea Basin

To study the spatial distribution of sea surface plastics in marine protected and non-protected areas, 65 sea surface trawls were carried out using a Hydro-bios manta net coupled with a 335-μm mesh. A total of 19 sampling sites along the coastal waters of Mallorca, the "Parque Nacional Marítimo-Terrestre del Archipiélago de Cabrera" and Menorca in the Balearic Islands as well as along coastal waters of The Natural Park of Columbretes Islands (NW Mediterranean Sea) were sampled. A total of 10,637 plastic items were identified and a subset of these items was categorized by shape, color, size and polymer composition. Plastic particles were found at each sampling site and in all samples. No microscale nor mesoscale variability in floating marine plastics abundance (particles/m²) was encountered throughout the study area where similar values were found in protected areas with no local land-based contamination sources, such as Columbretes [0.04 (±0.03) particles/m²], and in high anthropized areas, such as the island of Mallorca [0.04 (±0.07) particles/m²]. However, differences were found in characteristics of plastic items (shape, polymer, and size range), with the protected area of Columbretes characterized by the presence of the highest density of very small plastic items composed mainly of fragments (93%). Quantified plastics from the marine environment were composed mainly of polyethylene (PE, 63.3%), polypropylene (PP; 24.9%), polycarbonate (PC; 4.6%) and polystyrene (PS, 3.3%). The polymer composition showed a homogenous composition between islands and differences were detected only amongst Columbretes and the other islands. Results from this study provide further evidence of the ubiquity of plastics in the marine environment and highlight that remote and protected areas, such as Columbretes, are not exempt from plastic pollution, but receptor areas for small and aged floating plastics composed mainly by fragments, which might have potentially harmful effects on protected ecosystems.

Wastewater treatment plant effluent and microfiber pollution: focus on industry-specific wastewater

The production, use, and disposal of synthetic textiles potentially release a significant amount of microfibers into the environment. Studies performed on municipal wastewater treatment plants (WWTPs) effluent reported a higher presence of microfibers due to the mix of domestic laundry effluent through sewage. As municipal WWTPs receive influents from households and industries, it serves as a sink for the microfibers. However, research on textile industry WWTPs that primarily treat the textile fabric processing wastewater was not explored with the concern of microfibers. Hence, the review aims to analyze the existing literature and enlighten the impact of WWTPs on microplastic emission into the environment by specifically addressing textile industry WWTPs. The results of the review confirmed that even after 95-99% removal, municipal WWTPs can emit around 160 million microplastics per day into the environment. Microfiber was the dominant shape identified by the review. The average microfiber contamination in the WWTP sludge was estimated as 200 microfibers per gram of sludge. As far as the industry-specific effluents are analyzed, textile wet processing industries effluents contained > 1000 times higher microfibers than municipal WWTP. Despite few existing studies on textile industry effluent, the review demonstrates that, so far, no studies were performed on the sludge obtained from WWTPs that handle textile industry effluents alone. Review results pointed out that more attention should be needed to the textile wastewater research which is addressing the textile wet processing industry WWTPs. Moreover, the sludge released from these WWTPs should be considered as an important source of microfiber as they contain more quantity of microfibers than the effluent, and also, their routes to the environment are huge and easy.

Weathering indices of microplastics along marine and coastal sediments from the harbor of Cartagena (Spain) and its adjoining urban beach

Marine and coastal sediments from the harbor of Cartagena (Spain) and its adjoining beach were investigated regarding their microplastic burden. Fibers accounted for 47.62% and 61.66% in marine and coastal sediments, respectively, followed by films (31.43% and 18.76%) and fragments (20.95% and 18.65%). Polyvinyl (36.07%), polypropylene (21.31%), and polyethylene (18.03%) were isolated for marine sediments, and low-density polyethylene (40.71%), polypropylene (20.16%), and acrylate (11.37%) for coastal sediments. Highest concentrations were found in the deepest marine sediments (24.0 m) and in the furthest zone from the seashore for coastal sediments (18 m). Carbonyl index increased in the intermediate area (12.5 m) for marine sediments (0.51), whilst vinyl index was maximum for the deepest samples (1.94), reporting Norrish type I and II reactions, respectively. Coastal sediments collected close to the high tide line displayed the highest average values for both indices, 1.57 and 1.29, respectively, indicating a higher exposition to weathering variables.

Large quantities of small microplastics permeate the surface ocean to abyssal depths in the South Atlantic Gyre

Hundreds of studies have surveyed plastic debris in surface ocean gyre and convergence zones, however, comprehensive microplastics (MPs, ≤5 mm) assessments beneath these surface accumulation areas are lacking. Using in situ high-volume filtration, Manta net and MultiNet sampling, combined with micro-Fourier-transform-infrared imaging, we discovered a high abundance (up to 244.3 pieces per cubic meter [n m^-3 ]) of small microplastics (SMPs, characteristically <100 μm) from the surface to near-sea floor waters of the remote South Atlantic Subtropical Gyre. Large horizontal and vertical variations in the abundances of SMP were observed, displaying inverse vertical trends in some cases. SMP abundances in pump samples were more than two orders of magnitude higher than large microplastics (LMPs, >300 μm) concurrently collected in MultiNet samples. Higher-density polymers (e.g., alkyd resins and polyamide) comprised >65% of the total pump sample count, highlighting a discrepancy between polymer compositions from previous ocean surface-based surveys, typically dominated by buoyant polymers such as polyethylene and polypropylene. Contrary to previous reports stating LMP preferentially accumulated at density gradients, SMP with presumably slower sinking rates are much less influenced by density gradients, thus resulting in a more even vertical distribution in the water column, and potentially longer residence times. Overall, our findings suggest that SMP is a critical and largely underexplored constituent of the oceanic plastic inventory. Additionally, our data support that weak current systems contribute to the formation of SMP hotspots at depth, implying a higher encounter rate for subsurface particle feeders. Our study unveils the prevalence of plastics in the entire water column, highlighting the urgency for more quantification of the deep-ocean MP, particularly the smaller size fraction, to better understand ecosystem exposure and to predict MP fate and impacts.

An In Situ Experiment to Evaluate the Aging and Degradation Phenomena Induced by Marine Environment Conditions on Commercial Plastic Granules

In this paper, we present two novel experimental setups specifically designed to perform in situ long-term monitoring of the aging behaviour of commercial plastic granules (HDPE, PP, PLA and PBAT). The results of the first six months of a three year monitoring campaign are presented. The two experimental setups consist of: (i) special cages positioned close to the sea floor at a depth of about 10 m, and (ii) a box containing sand exposed to atmospheric agents to simulate the surface of a beach. Starting from March 2020, plastic granules were put into the cages and plunged in seawater and in a sandboxe. Chemical spectroscopic and thermal analyses (GPC, SEM, FTIR-ATR, DSC, TGA) were performed on the granules before and after exposure to natural elements for six months, in order to identify the physical-chemical modifications occurring in marine environmental conditions (both in seawater and in sandy coastal conditions). Changes in colour, surface morphology, chemical composition, thermal properties, molecular weight and polydispersity, showed the different influences of the environmental conditions. Photooxidative reaction pathways were prevalent in the sandbox. Abrasive phenomena acted specially in the sea environment. PLA and PBAT did not show significant degradation after six months, making the possible reduction of marine pollution due to this process negligible.

Impact of intensive mariculture activities on microplastic pollution in a typical semi-enclosed bay: Zhanjiang Bay

Microplastic (MP) was investigated in Zhanjiang Bay, a semi-enclosed bay in south China and famous for considerable mariculture industry, to evaluate whether mariculture activities accelerated MP pollution. The MP abundances ranged from 0 to 2.65 n/m³ (number/m³), showing seasonal variances with higher levels in May and September and lower levels in January. In the inner part of the bay, a significantly high MP abundance and predominance of foam were found during the oyster breeding period, and pollution sources were prone to be single and extensive. This suggested that MPs were strongly influenced by the intensive plastic products for oyster culturing, especially during breeding. Moreover, plastic cages used for culturing were the main source of MPs in the central part of the bay. By conducting statistical analysis for eight representative bays, the economic growth, social development, agriculture structure, and aquaculture development were supposed to influence the local MP pollution level.

Zonal Distribution Characteristics of Microplastics in the Southern Indian Ocean and the Influence of Ocean Current

As a new type of pollutant, microplastics widely exist in the marine environment and have attracted a lot of attention from the international community. In order to study the distribution of microplastics and the influence of ocean current, microplastic samples in seawater of the southern Indian Ocean were collected using a peristaltic pump equipped on-board and concentrated on site. Qualitative and quantitative analyses of microplastics were performed using a stereo-microscope and a micro-Fourier transform infrared spectroscope attenuated total reflection. The results showed that the average abundance of microplastics in seawater of the southern Indian Ocean was 2.3 ± 2.1 items/m3, which was consistent with that in other oceans. Polyethylene terephthalate (PET), polyethylene (PE), Rayon, polyamide (PA), and polyvinylidene chloride (PVDC) were the main polymers of microplastics in the southern Indian Ocean. The size range of all detected microplastics was 108.2–4703.0 µm. All microplastics had different colors, such as black, red, yellow, gray, blue, green, purple, and transparent. Fiber was the dominant shape of microplastics. The abundance distribution of microplastics fluctuated in the latitudinal direction. The abundance of microplastics from the present study area was higher in the coastal region of the South Africa continent and the Indian Ocean garbage patch, with an average abundance of 4.0 items/m3. The average abundance of microplastics was relatively high in the convergence area of the circulation, which revealed that the ocean current facilitated the agglomeration and transportation of microplastics.

Microplastic pollution in sublittoral coastal sediments of a North Atlantic island: The case of La Palma (Canary Islands, Spain)

In this work, the microplastic content of sediments collected in July 2020 between 5 and 7 m depth was studied in four locations of La Palma island (Canary Islands, Spain). At each sampling location, three samples were taken parallel to the shoreline. The microplastic content in each sampling corer was studied every 2.5 cm depth after digestion with a H₂O₂ solution followed by flotation in a saturated NaCl solution. Visualization of the final filtrates under a stereomicroscope revealed that all the sediment samples evaluated contained mostly microfibers (98.3%) which were mainly white/colorless (86.0%) and blue (9.8%), with an average length of 2423 ± 2235 (SD) mm and an average concentration of 2682 ± 827 items per kg of dry weight, being the total number of items found 1,019. Fourier Transform Infrared microscopy analysis of 13.9% (n = 139) of the microfibers also showed that they were mainly cellulosic (81.3%). No significant differences were found between the depths of the sediment. However, significant differences were found between the number of fibers from the sampling sites at the east and west of the island. Such variability could be driven by the winds and ocean mesoscale dynamics in the area. This study confirms the wide distribution of microfibers in sediments from an oceanic island like La Palma, providing their first report in marine sediments of the Canary Islands.

Neustonic microplastics and zooplankton in coastal waters of Cabrera Marine Protected Area (Western Mediterranean Sea)

The high abundance of microplastics in marine environments is becoming a growing threat for Marine Protected Areas (MPAs). Recent studies have identified microplastics (MP) as having multiple effects on biota, and it is of special interest to highlight their effects on zooplanktonic organisms. These organisms play a key role on local food web structures and there is a need to better understand the accumulation of MPs and associated contaminants within the food web. The present study addresses MP distribution and composition within Cabrera MPA as well as its effects on local zooplanktonic community composition. Neustonic microplastic and zooplankton abundance and composition were determined in the shallow coastal waters of Cabrera MPA during the summer season of 2019. Samples were taken using a sea surface manta-net, with a mesh size of 335 μm. MPs were found in all manta trawl samples for a total of 7047 MP with an overall mean abundance (± SD) of 3.52 (± 8.81) items/m³, a value higher than those reported for the majority of Western Mediterranean Sea basins. Qualitative and semi-quantitative analyses of the local zooplankton community suggest that its composition could be sensitive to MP abundances. Although no correlation was found between overall mean abundance of MP and zooplankton, a positive correlation was found between MP abundance and the abundance of the planktonic stage of the foraminifer Rosalina globularis (Tretomphalus). This species seems to be able to use MP for its dispersion. On the other hand, a negative correlation between MP abundance and Copepoda abundance was detected. This work confirms that the coastal zooplankton community composition within the MPA of Cabrera are not exempt from MP pollution and suggests important and complex interactions between MP and zooplankton organisms in coastal waters.

Are research methods shaping our understanding of microplastic pollution? A literature review on the seawater and sediment bodies of the Mediterranean Sea

The lack of standardization on the definition and methods in microplastic (MP) research has limited the overall interpretation and intercomparison of published data. This has presented different solutions to assess the presence of these pollutants in the natural environment, bringing the science forward. Microplastics have been reported worldwide across different biological levels and environmental compartments. In the Mediterranean Sea, numerous research efforts have been dedicated to defining the MP pollution levels. The reported MP concentrations are comparable to those found in the convergence zone of ocean gyres, pointing to this basin as one of the world's greatest plastic accumulation areas. However, to what extent are the data produced limited by the methods? Here, we present the results of a systematic review of MP research methods and occurrence targeting the seawater and sediment bodies of the Mediterranean Sea. Based on this dataset, we 1) assess the discrepancies and similarities in the methods, 2) analyze how these differences affect the reported concentrations, and 3) identify the limitations of the data produced for the Mediterranean Sea. Moreover, we reaffirm the pressing need of developing a common reporting terminology, and call for international collaboration between Mediterranean countries, especially with North African countries, to provide a complete picture of the MP pollution status in this basin.

A proposed nomenclature for microplastic contaminants

Microplastics are emerging contaminants with a wide environmental distribution and potential to elicit adverse impacts on organisms. Despite this lack of consistency among reports, data obtained from different investigations are often compared, resulting in the potential for misrepresentation of global microplastic contamination. Major interlaboratory variability in quantification of microplastic levels stem from size-related differences in sampling and analysis with different density solutions to separate microplastics. Herein, we propose a nomenclature that provides key information relating to the microplastics abundance in samples. That is, the proposed nomenclature, MPs_c^{a, b}, informs on mesh or filter size used in sampling, the density of flotation solution used to separate the microplastics, and the detection limit during the analysis progress of microplastics. This proposed nomenclature would facilitate comparisons among studies to avoid over- or under-estimation of global microplastic levels. Moreover, it would also facilitate the interpretation of meta-data in future assessments.

Microplastic pollution in inshore and offshore surface waters of the southern Caspian Sea

In this study, as the first comprehensive monitoring, the occurrence of microplastics (MPs) in inshore and offshore surface waters of the southern Caspian Sea was investigated. Our data indicated that MPs, which were detected in all the samples, were widely distributed in the thirteen studied stations. Non-normally distribution of the MPs was observed among the studied stations (p<0.05). The average concentration of microplastics in the selected stations was 0.246 ± 0.020 MP/m³. In most of the transects, negative gradients of MPs from coastal waters to deeper waters were observed. The dominant size and color of MPs in the inshore and offshore water samples was 1000-5000 μm and white-transparent, respectively. Films and fibers constituted about 50% and 40% of the total number of MPs of the water samples, respectively. Also, polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) were the three main polymer types of microplastics in the inshore and offshore surface waters. Our data provide valuable evidence for the comparative assessing of future data regarding decreases or increases of MPs in the southern Caspian Sea.

Distribution and transport of microplastics in the upper 1150 m of the water column at the Eastern North Atlantic Subtropical Gyre, Canary Islands, Spain

Nowadays it is widely known that pollution by microplastics (MP) at the open ocean covers immense areas. Buoyant plastics tend to accumulate in areas of convergence at the sea surface such as subtropical gyres, while non-buoyant plastics accumulate at the seafloor. However, previous studies have revealed that the total amount of plastic in the different oceans is not well correlated with the concentrations measured at the sea surface and the sea floor, evidencing a significant amount of missing plastic in the oceans. This deviation could be related to an underestimation of the role played by small fragments of plastic and fibers in the oceans. Furthermore, microplastic fragments with a density lower than the density of seawater have been gathered hundreds of meters below the sea surface in the Pacific Ocean due to their size and shape. The main objective of this study is to carry out, for the first time, an equivalent analysis along the water column for the Atlantic Ocean. In that sense, a total number of 51 samples were collected during four different oceanographic cruises between February and December 2019, from the sea surface down to 1150 m depth at the open ocean waters of the Canary Islands region (Spain). For each sample, 72 l of seawater were filtered on board with a mesh size of 100 μm, where the presence of microplastics has been clearly observed. Our results reveal the presence of microplastics at least up to 1150 m depth, at the Northeastern Atlantic Subtropical Gyre with noticeable seasonal differences. The spatial distribution of these small fragments and fibers at the water column is mainly related to the oceanic dynamics and mesoscale convective flows, overcoming the MP motion induced by their own buoyancy. Moreover, these microplastics have being transported by the ocean dynamics as passive drifters.

Transport, weathering and pollution of plastic from container losses at sea: Observations from a spillage of inkjet cartridges in the North Atlantic Ocean

Observations of beached polypropylene inkjet cartridges, spilled from a ship container lost in the North Atlantic Ocean, have been compiled through calls on international social media. Within a period of four years from the spillage, a total of about 1500 cartridges was reported in locations as far apart as Florida and northern Norway. The distribution of cartridges reflected the principal surface currents in the ocean, with some carried by the Azores and Canary currents around the North Atlantic Gyre, and others transported northwards with the North Atlantic and Norwegian currents. Along the shorelines of the UK and Ireland, there was a clear, preferential accumulation of cartridges on west- and south-facing coasts, consistent with the direction of the North Atlantic current and the heading of the principal winds. Dates of first sightings in various regions throughout the North Atlantic (and as reported on social media) suggested that cartridges traveled on average at around 6-13 cm s^-1. These observations and estimates were largely consistent with simulations of the dispersion of free floating, neutrally buoyant particles from the spillage site derived from PlasticAdrift, an empirical model based on drifter tracking data. Microscopic and X-ray fluorescence analyses of selected cartridges revealed a high degree of exterior weathering, resulting in chalking and embrittlement of the polypropylene and the formation of microplastics rich in Ti, chemical fouling of interior ink foams (where still present) by Fe oxides, and, in some cases, the presence of an electronic chip containing Cu, Au and brominated compounds. Significantly, the latter characteristic renders cartridges as electrical and electronic waste and means that current, conventional regulations on plastic cargo lost at sea are not applicable here. More generally, the study highlights the potential usefulness of social media-led citizen science to marine research, and inadequacies in the relevance and robustness of instruments and conventions that deal with plastic waste in the ocean.

Anthropogenic particles in sediment from an Arctic fjord

The research on plastic pollution is increasing worldwide but little is known about the contamination levels in the Arctic by microplastics and other anthropogenic particles (APs) such as dyed fibres. In this study, two different sampling designs were developed to collect 68 sediment subsamples in five locations in a remote Arctic fjord, Kongsfjorden, northwest of Svalbard. Those five stations composed a transect from a sewage outlet recently installed close to the northernmost settlement, Ny-Ålesund, to an offshore site. Plastics and other APs were extracted by density separation and analysed by both Raman and Fourier Transform Infrared spectroscopy. Among the 37 APs found, 19 were microplastics. The others were classified as APs due to the presence of a dye or another additive. On average, 0.33 AP 100 g^-1 were found in the surface sediment and their sizes ranged between 0.10 and 6.31 mm. The site most polluted by APs was located at the mouth of the fjord while the less polluted ones were the offshore and the outlet sites. We believe that currents in the fjord have carried APs towards the mouth of the fjord where an eddy could retain APs which might sink the seafloor due to various reasons (ingestion & packaging, fouling-induced changes in buoyancy). In the cores, several different APs were found down to a depth of 12 cm. These APs may have been present in the sediments for decades or been transported deeper by biota. Here we provided data on plastic but also on other anthropogenic particles from a remote fjord in Svalbard.

Massive occurrence of benthic plastic debris at the abyssal seafloor beneath the Kuroshio Extension, the North West Pacific

The abyss (3500-6500 m) covers the bulk of the deep ocean floor yet little is known about the extent of plastic debris on the abyssal seafloor. Using video imagery we undertook a quantitative assessment of the debris present on the abyssal seafloor (5700-5800 m depth) beneath the Kuroshio Extension current system in the Northwest Pacific. This body of water is one of the major transit pathways for the massive amounts of debris that are entering the North Pacific Ocean from Asia. Shallower sites (1400-1500 m depth) were also investigated for comparison. The dominant type of debris was single-use plastics - mainly bags and food packaging. The density of the plastic debris (mean 4561 items/km²) in the abyssal zone was the highest recorded for an abyssal plain suggesting that the deep-sea basin in the Northwest Pacific is a significant reservoir of plastic debris.

Is cell culture a suitable tool for the evaluation of micro- and nanoplastics ecotoxicity?

Plastic particles have been described in aquatic ecosystems worldwide. An increasing number of studies have tried to evaluate the toxic impacts of microplastics (1-5000 µm) but also nanoplastics (<1 µm) in marine and freshwater organisms. However, the wide variety of plastic particles characteristics such as various sizes, shapes, functionalization or types of polymer, makes it difficult to evaluate their impact with regular ecotoxicity testing. In this context, cell culture, mainly used in human toxicology, could be a promising tool to evaluate micro- and nanoplastics toxicity with a wide diversity of conditions allowing to generate a large set of data. This review presents the current research on micro and nanoplastics using cell culture of marine and freshwater organisms, describes the limitations of cell culture tool and defines whether this tool can be considered as a relevant alternative strategy for ecotoxic evaluation of micro and nanoplastics especially for future regulatory needs. Articles using specifically cell culture tool from aquatic organisms such as fish or bivalves were identified. The majority evaluated the toxicity of polystyrene nanobeads on immune parameters, oxidative stress or DNA damage in fish cells. Although most of the papers characterized nanoplastic particles into the cell culture media, the relevance of testing conditions is not always clear. The development of cell culture can offer many opportunities for the evaluation of plastic particles' cellular impacts, but more research is needed to develop relevant culture models, on various aquatic organisms, and with consideration of abiotic parameters especially composition of cell culture media for nanoplastic evaluation.

Microplastic Mass Concentrations and Distribution in German Bight Waters by Pyrolysis-Gas Chromatography-Mass Spectrometry/Thermochemolysis Reveal Potential Impact of Marine Coatings: Do Ships Leave Skid Marks?

In this first mass-related survey of microplastics (MPs, <1 mm) in the German Bight (North Sea, 2.5 m water depth), spatial load, temporal variations, and potential sources were examined. Relevant plastic types were detected using pyrolysis-gas chromatography-mass spectrometry/thermochemolysis (Py-GC/MS). This suitable method provides qualitative and trace-level polymer or polymer cluster-specific mass quantitative MP data. Neither MP concentration (2-1396 μg m^-3) nor type distribution was homogeneous. Concentrations appeared to be substantially influenced by meteorological and oceanographic conditions. The coastal MP-type composition showed an overprint indicating a packaging waste-related signal. Considerably different compositions were observed in central and estuarine areas. Here, a close relation to marine (antifouling) coating particles, i.e., abrased chlorinated rubber-, acryl-styrene-, and epoxide binder-containing particles are hypothesized as the main MP source, indicating ship "skid marks". They represent a dominant, toxicologically relevant but underestimated marine-based MP share, inverting the widely cited 80% terrestrial- to 20% marine-based debris ratio for MPs. In consequence of the findings, polymer clusters attributed to the basic polymers polyethylene, polypropylene, polystyrene, poly(ethylene terephthalate), poly(vinyl chloride), poly(methyl methacrylate), and polycarbonate are proposed for Py-GC/MS MPs mass determination based on specific thermal decomposition products linked to related polymer structural units.

Pelagic microplastics in surface water of the Eastern Indian Ocean during monsoon transition period: Abundance, distribution, and characteristics

Microplastics (MPs) have been documented in almost all marine environments, including coastal regions, the open ocean, and the deep sea. However, relatively little knowledge was available about MP pollution in the open ocean, especially the Indian Ocean. We conducted field observations at 36 stations in the Eastern Indian Ocean (EIO), using a typical manta trawl with a mesh size of 330 μm for surface water sampling. Ours is the first study to obtained comprehensive and comparable baseline data about MPs in the EIO, including abundance, spatial distribution and characteristics. Abundance of MPs in the EIO varied from 0.01 items m^-2 to 4.53 items m^-2, with an average concentration of 0.34 ± 0.80 item m^-2. The mean concentration of MPs in the Bay of Bengal (BoB) was 2.04 ± 2.26 items m^-2 and 0.16 ± 0.17 items m^-2 in the open ocean of the EIO. These results illustrate the high spatial heterogeneity of MPs distribution. Micro-FTIR analysis of polymer composition showed that the vast majority of MPs consisted of polypropylene (PP, 51.11%) and polyethylene (PE, 20.07%). Our data show that MP pollution in the EIO, whether in the epeiric sea or the open ocean, is among the highest of the world's oceans. The BoB is likely to become a MP hotspot due to the vast input of land-based plastics and the presence of multiscale recirculation gyres. These results are absolutely thought provoking: The EIO needs more attention on MPs.

Spatial and Temporal Distribution of Chemically Characterized Microplastics within the Protected Area of Pelagos Sanctuary (NW Mediterranean Sea): Focus on Natural and Urban Beaches

Data on the abundance and distribution of Anthropogenic Marine Debris (AMD) on the coastal areas of the northern Tyrrhenian coast are still scarce. The objective of this study is to characterize, in terms of size, color, morphology and polymeric nature, the Large Microplastics (LMPs), i.e., plastic objects within 1 and 5 mm, sampled on three beaches located within the coastal macro-area of the Pelagos Sanctuary, an international protected zone in the north-western Mediterranean. The beaches have similar morphological characteristics but different degrees of urbanization. LMPs were sampled seasonally for one year. The polymeric nature of a representative subsample of the collected LMPs was investigated using a portable Raman instrument, to assess the feasibility of in situ characterization. In this study, 26,486 items were sorted by typology (Expanded Polystyrene-EPS, fragments, and resin pellets), size, and for fragments and resin pellets, also by color and chemical nature. Statistical data on the quantity, density, type, spatial distribution, and seasonality of the sampled LMPs are presented. Differences in LMP abundance and composition were detected among sites. A seasonality trend emerges from our statistical analysis, depending on both LMP typology and urbanization degrees of the beaches. Our data do not show the existence of a relationship between the size of the investigated MPs and their color, while they suggest that the type of polymer influences the degree of fragmentation. This underlines the need to further investigate the mechanisms leading to the production and dispersion of MPs in coastal areas, taking into account both the urbanization of the beach, and therefore the possible sources of input, and the different types of MPs. Finally, a Raman portable instrument proved to be a valuable aid in performing in situ polymeric characterization of LMPs.

Spatio-temporal distribution of plastic and microplastic debris in the surface water of the Bohai Sea, China

As an emerging marine environmental issue, marine plastic debris pollution has attracted worldwide attention. Studies have covered more and more areas of the world's oceans. To further understand the sources and variation of marine plastic debris in the surface water of the Bohai Sea, in this study, plastic debris was collected during the four seasons of 2016-2017. The results showed the mean density of plastic debris over these seasons was 0.49 ± 0.18 particles/m³. Macro-, meso-, and micro- plastics accounted for 5%, 26%, and 69% of the total number of plastic debris, respectively. The density of the microplastics was 0.35 ± 0.13 particles/m³. The highest density was found in spring, followed by summer and winter, and the lowest in autumn. High distribution densities were observed in the Liaodong Bay and the Bohai Strait, which were attributed to the dynamics of the rim current, terrain, and fishery activities. CAPSULE ABSTRACT: Riverine input, dynamics of the rim current, terrain, and fishery activities contribute to the variations in marine plastic debris in the surface water of the Bohai Sea.

Occurrence and distribution of microplastics and polychlorinated biphenyls in sediments from the Qiantang River and Hangzhou Bay, China

Rivers are important routes for sea-bound microplastics. Thus, this study investigated the occurrences and distributions of microplastics and polychlorinated biphenyls (PCBs) in sediment samples from the Qiantang River (QR) and Hangzhou Bay (HZ) and analyzed the correlation between microplastics and PCBs. A total of 15 sampling sites were selected, including eight from the QR (i.e., four in the Tonglu area and four in the Fuyang area), two from the Andong salt marsh (ASM; located in a hydrodynamic turning point of the HZ), and five from HZ. The mean microplastic abundance was highest in the QR, followed by HZ and ASM, with 0.23 ± 0.06, 0.18 ± 0.05, and 0.15 ± 0.03 particles/g sediment, respectively. Cluster analysis demonstrated that fragments and fibers may have originated from domestic sewage inputs to the QR. Spatially, mean PCB concentrations from Tonglu, Fuyang, and HZ were 1.47 ± 0.10, 1.65 ± 0.10, and 1.65 ± 0.09 ng/g sediment, respectively, which were higher than that from the ASM (1.13 ± 0.09 ng/g sediment). The vertical distributions (0-5 cm, 5-10 cm, and 10-15 cm) of microplastics in the sediments at Tonglu and Fuyang decreased with increasing depth, which was opposite to the depth trend of PCB concentrations. Micro-Fourier transform infrared spectroscopy analysis suggested that polyethylene was typically the dominant polymer, accounting for 60 ± 0.08% of the total suspected plastic particles. Microbeads and films showed considerable correlations with both highly and lesser chlorinated PCBs. Overall, our findings highlight the need for routine monitoring of microplastics in China in addition to measures for controlling plastic pollution on a national scale. Further study should ascertain specific sources of microplastics and analyze their adsorption capacity to organic pollutants.

Distribution, abundance and risks of microplastics in the environment

Microplastics (plastic particles < 5 mm) have received increasing attention in recent years due to their wide distribution in the environment. A bibliometric analysis was carried out using Web of Science, with significant contributions being observed by English and French research institutions in the microplastic field. Analysis of keywords revealed that the research hotspots were distribution, abundance, and risks of microplastics in the environment. Microplastics have been detected in water bodies and sediments of seven continents and four oceans. However, meaningful comparisons among studies are difficult due to the inconsistencies in sampling methods and concentration units. Moreover, studies have shown that the chemical composition of microplastics, as well as the pollutants adsorbed onto them, can have negative impacts on marine organisms. It remains unclear whether and how the consumption of aquatic products contaminated with microplastics affect human health. Therefore, it is advised that future research should focus on the transfer, accumulation, and effects of microplastics in the food chain.

Environmentally Accurate Microplastic Levels and Their Absence from Exposure Studies

Microplastics (synthetic polymers; <5 mm) are ubiquitous, in the environment and in the news. The associated effects of microplastics on flora and fauna are currently only established through laboratory-based exposure trials; however, such studies have come under scrutiny for employing excessive concentrations with little environmental relevance. This critical review is intended to summarize key issues and approaches for those who are considering the need for local microplastics research, both in terms of environmental pollution and the impacts on aquatic species. A meta-analysis of results from published experimental (n = 128) and environmental (n = 180) studies allowed us to compare the reported impacts from experiments that expose organisms to microplastics, and the concentrations of environmental microplastics found in the wild. The results of this meta-analysis highlight three issues that should be modified in future work (1) use of extreme dosages, (2) incompatible and incomparable units, and (3) the problem of establishing truly informative experimental controls. We found that 5% of exposure trials examined did not use any control treatment, and 82% use dramatically elevated dosages without reference to environmental concentrations. Early studies in this field may have been motivated to produce unequivocal impacts on organisms, rather than creating a robust, environmentally relevant framework. Some of the reported impacts suggest worrying possibilities, which can now inspire more granular experiments. The existing literature on the extent of plastic pollution also has limited utility for accurately synthesizing broader trends, as has been raised in previous reviews; environmental extraction studies use many different units, among which only 76% (139/180) could be plausibly converted for comparison. Future research should adopt the units of microparticles/kg (of sediment) or mp/L (of fluid) to improve comparability. Now that the global presence of microplastic pollution is well established, with more than a decade of research, new studies should focus on comparative aspects rather than the presence of microplastics. Robustly designed, controlled, hypothesis-driven experiments based on environmentally relevant concentrations are needed now to understand our future in the new plastic world.

A machine learning algorithm for high throughput identification of FTIR spectra: Application on microplastics collected in the Mediterranean Sea

The development of methods to automatically determine the chemical nature of microplastics by FTIR-ATR spectra is an important challenge. A machine learning method, named k-nearest neighbors classification, has been applied on spectra of microplastics collected during Tara Expedition in the Mediterranean Sea (2014). To realize these tests, a learning database composed of 969 microplastic spectra has been created. Results show that the machine learning process is very efficient to identify spectra of classical polymers such as poly(ethylene), but also that the learning database must be enhanced with less common microplastic spectra. Finally, this method has been applied on more than 4000 spectra of unidentified microplastics. The verification protocol showed less than 10% difference in the results between the proposed automated method and a human expertise, 75% of which can be very easily corrected.

The uptake and elimination of polystyrene microplastics by the brine shrimp, Artemia parthenogenetica, and its impact on its feeding behavior and intestinal histology

Microplastics are a ubiquitous contaminant of marine ecosystems that have received considerable global attention. The effects of microplastic ingestion on some marine biota have been evaluated, but the uptake, elimination, and histopathological impacts of microplastics remain under-investigated especially for zooplankton larvae. Here, we show that 10 μm polystyrene microspheres can be ingested and egested by Artemia parthenogenetica larvae, which impact their health. The results indicate that A. parthenogenetica larvae have a varying capacity to consume 10 μm polystyrene microspheres that is dependent on microplastic exposure concentrations, exposure times, and the availability of food. The lowest level of microplastics that was ingested by A. parthenogenetica was 0.15 particles/individual when exposed to 10 particles/mL and 0.05 particles/individual when exposed to 1 particle/mL over 24 h and 14 d, respectively. A. parthenogenetica larvae were able to egest feces with microplastics within 3 h of ingestion. However, ingested microplastics persisted in individuals for up to 14 days. Furthermore, microalgal feeding was significantly reduced by 27.2% in the presence of 10² particles/mL microplastics over 24 h. Histological analyses indicated that a greater abundance of lipid droplets was present among epithelia after 24 h of exposure at a concentration of 10 particles/mL. Moreover, intestinal epithelia were deformed and disorderedly arranged after 14 d of exposure. Overall, these results indicate that marine microplastic pollution could pose a threat to A. parthenogenetica health, especially that of larvae. Consequently, further research is required to evaluate the potential physiological and histopathological effects of microplastics for other marine invertebrate species.

Microplastics in the Coral Reef Systems from Xisha Islands of South China Sea

The impacts of microplastics on coral reefs are gaining attention due to findings that microplastics affect coral health. This work investigated the distribution and characteristics of microplastics in the seawater, fish, and corals in 3 atolls from the Xisha Islands of South China Sea. In the seawater samples, microplastics were detected in the outer reef slopes, reef flats, and lagoons with abundances ranging from 0.2 to 11.2, 1.0 to 12.2, and 1.0 to 45.2 items L^-1, respectively. Microplastic abundance was 0-12.0 items individual^-1 (0-4.7 items g^-1) in fish and 1.0-44.0 items individual^-1(0.02-1.3 items g^-1) in coral. The predominant shape and polymer of microplastics in seawater, fish, and coral were fibrous rayon and polyethylene terephthalate (PET). Microplastic sizes primarily ranged from 20-330 μm in both the seawater and fish, while there were relatively more 1-5 mm microplastics in the corals. The shape, size, color, and polymer type distribution patterns of microplastics in seawater more closely resembled those in fish gills than those in fish gastrointestinal tracts or coral samples. This study shows that microplastics are abundant in these coral reef systems and they are captured by fish or "trapped" by corals.

Can plastics affect near surface layer ocean processes and climate?

Plastics in the ocean are of great concern nowadays, and are often referred to as the apocalyptic twin of climate change in terms of public fear and the problems they pose to the aquatic and terrestrial environment. The number of studies focusing on the ecological effects and toxicity of plastics has substantially increased in the last few years. Considering the current trends in the anthropogenic activities, the amount of plastics entering the world oceans is increasing exponentially, but the oceans have a low assimilative capacity for plastics and the near-surface layer of it is a finite space. If loading of the oceans with plastics continues at the current rate, the thin sea surface microlayer can have a substantial amount of plastics comparable to the distribution of phytoplankton, at least in the major oceanic gyres and coastal waters in the future. Also, processes like biofouling can cluster microplastics in dense fields in the near-surface layer. Plastics can contribute to the warming or cooling of the water column by scattering and attenuating incoming solar radiation, leading to a potential change in the optical and other physico-chemical properties of the water column. We propose a new notion that changes in solar radiation in the water column due to the plastics have the potential to affect the physical processes in the ocean surface and near-surface layers, and can induce climate feedback cycles. The future can be very different, if plastics evolve as one of the key players affecting the ocean physical processes and hence this is the time to tackle this puzzle with appropriate strategies or let the genie out of the bottle.

The Role of Ekman Currents, Geostrophy, and Stokes Drift in the Accumulation of Floating Microplastic

Floating microplastic in the oceans is known to accumulate in the subtropical ocean gyres, but unclear is still what causes that accumulation. We investigate the role of various physical processes, such as surface Ekman and geostrophic currents, surface Stokes drift, and mesoscale eddy activity, on the global surface distribution of floating microplastic with Lagrangian particle tracking using GlobCurrent and WaveWatch III reanalysis products. Globally, the locations of microplastic accumulation (accumulation zones) are largely determined by the Ekman currents. Simulations of the North Pacific and North Atlantic show that the locations of the modeled accumulation zones using GlobCurrent Total (Ekman+Geostrophic) currents generally agree with observed microplastic distributions in the North Pacific and with the zonal distribution in the North Atlantic. Geostrophic currents and Stokes drift do not contribute to large-scale microplastic accumulation in the subtropics, but Stokes drift leads to increased microplastic transport to Arctic regions. Since the WaveWatch III Stokes drift and GlobCurrent Ekman current data sets are not independent, combining Stokes drift with the other current components leads to an overestimation of Stokes drift effects and there is therefore a need for independent measurements of the different ocean circulation components. We investigate whether windage would be appropriate as a proxy for Stokes drift but find discrepancies in the modeled direction and magnitude. In the North Pacific, we find that microplastic tends to accumulate in regions of relatively low eddy kinetic energy, indicating low mesoscale eddy activity, but we do not see similar trends in the North Atlantic.

Small Microplastics As a Main Contributor to Plastic Mass Balance in the North Atlantic Subtropical Gyre

Estimates of cumulative plastic inputs into the oceans are expressed in hundred million tons, whereas the total mass of microplastics afloat at sea is 3 orders of magnitude below this. This large gap is evidence of our ignorance about the fate of plastics, as well as transformations and sinks in the oceans. One of the current challenges consists of identifying and quantifying plastic particles at the microscale, the small microplastics (SMP, 25-1000 μm). The aim of the present study is to investigate SMP concentration in count and in mass at the sea surface in the North Atlantic subtropical gyre during the sea campaign Expedition 7 ^th Continent. After isolation, SMP were characterized by micro-Fourier-transform infrared spectroscopy. Microplastic distribution was modeled by a wind-driven vertical mixing correction model taking into account individual particle properties (dimension, shape and density). We demonstrate that SMP buoyancy is significantly decreased compared to the large microplastics (LMP, 1-5 mm) and consequently more susceptible to vertical transport. The uncorrected LMP concentration in count was between 13 000 and 174 000 pieces km^-2, and was between 5 and 170 times more abundant for SMP. With a wind-driven vertical mixing correction, we estimated that SMP were 300 to 70 000 times more abundant than LMP. When discussing this in terms of weight after correction, LMP concentrations were between 50 and 1000 g km^-2, and SMP concentrations were between 5 and 14 000 g km^-2.

Microplastic and charred microplastic in the Faafu Atoll, Maldives

Microplastics are recognized as a growing threat for the marine environment that may even affect areas generally considered pristine. In this work we surveyed the microplastic contamination in the Faafu Atoll (Maldives, Indian Ocean) across twelve sampling station, located either inside or outside the reef rim. Sediments and seawater samples were collected. Despite the remoteness of the atoll, the scarce local population and low touristic annual afflux, the detected average abundance were 0.32 ± 0.15 particles/m³ in the surface water and 22.8 ± 10.5 particles/m² in the beach sediments. Polymers identified through Fourier-Transform Infrared spectroscopy were mostly polyethylene, polypropylene, polystyrene, polyvinylchloride, polyethyleneterephtalate, and polyamide. Elastomeric residues and charred microparticles were also found. In particular, the charred microparticles were prevalently located nearby the inhabited island and they might be considered a peculiarity of the area, related to local practice of burning plastic waste at the shoreline.

Microplastic contamination in benthic organisms from the Arctic and sub-Arctic regions

The seafloor is recognized as one of the major sinks for microplastics (MPs). However, to date there have been no studies reported the MP contamination in benthic organisms from the Arctic and sub-Arctic regions. Therefore, this study provided the first data on the abundances and characteristics of MPs in a total of 413 dominant benthic organisms representing 11 different species inhabiting in the shelf of Bering and Chukchi Seas. The mean abundances of MP uptake by the benthos from all sites ranged from 0.02 to 0.46 items g^-1 wet weight (ww) or 0.04-1.67 items individual^-1, which were lower values than those found in other regions worldwide. The highest value appeared at the northernmost site, implying that the sea ice and the cold current represent possible transport mediums. Interestingly, the predator A. rubens ingested the maximum quantities of MPs, suggesting that the trophic transfer of MPs through benthic food webs may play a critical role. Fibers constituted the major type (87%) in each species, followed by film (13%). The colors of fibers were classified as red (46%) and transparent (41%), and the film was all gray. The predominant composition was polyamide (PA) (46%), followed by polyethylene (PE) (23%), polyester (PET) (18%) and cellophane (CP) (13%). The most common sizes of MPs concentrated in the interval from 0.10 to 1.50 mm, and the mean size was 1.45 ± 0.13 mm. Further studies about the temporal trends and detrimental effects of MPs remain to be carried out in benthic organisms from the Arctic and sub-Arctic regions.