Microplastics Alter the Properties and Sinking Rates of Zooplankton Faecal Pellets

Weathering Plastics as a Planetary Boundary Threat: Exposure, Fate, and Hazards

We described in 2017 how weathering plastic litter in the marine environment fulfils two of three criteria to impose a planetary boundary threat related to "chemical pollution and the release of novel entities": (1) planetary-scale exposure, which (2) is not readily reversible. Whether marine plastics meet the third criterion, (3) eliciting a disruptive impact on vital earth system processes, was uncertain. Since then, several important discoveries have been made to motivate a re-evaluation. A key issue is if weathering macroplastics, microplastics, nanoplastics, and their leachates have an inherently higher potential to elicit adverse effects than natural particles of the same size. We summarize novel findings related to weathering plastic in the context of the planetary boundary threat criteria that demonstrate (1) increasing exposure, (2) fate processes leading to poorly reversible pollution, and (3) (eco)toxicological hazards and their thresholds. We provide evidence that the third criterion could be fulfilled for weathering plastics in sensitive environments and therefore conclude that weathering plastics pose a planetary boundary threat. We suggest future research priorities to better understand (eco)toxicological hazards modulated by increasing exposure and continuous weathering processes, to better parametrize the planetary boundary threshold for plastic pollution.

Response of sediment-dwelling bivalves to microplastics and its potential implications for benthic processes

Sediments are considered an ultimate sink for microplastic (MPs) but knowledge on MPs impacts on the benthic organisms is still limited. A microcosm experiment was performed to assess the effect of MPs on two sediment-dwelling bivalve species that differ in terms of their life¬styles and feeding behaviors (the cockle Cerastoderma glaucum and the Baltic clam Limecola balthica). Fitness of both bivalves, their vertical distribution in the sediment and activity at the sediment-water interface were studied following addition of PE microspheres of three different size fractions (63-75, 150-180 and 250-300 μm) in two concentrations (0.1 and 0.5% sediment dwt) to the sediment surface. Bivalve survival was generally high and did not vary significantly among treatments. Both bivalve species captured MPs but no significant effect on their body conditions and energy reserves was observed. However, some behavioural alterations were found. The near-surface-dwelling C. glaucum emerged from the sediment less often and in lower numbers suggesting lower activity in sediments amended with large and medium MPs served in higher concentration. Also vertical distribution of deeper-dwelling L. balthica differed among treatments. The clam penetrated deeper sediment layers in microcosms treated with MPs than in the control (on average 62% of the total number of bivalves found in the sediment layer 2-4 cm vs. 65% in the upper 2 cm) which may suggest an avoidance behaviour or escape reaction in response to MPs addition to the topmost sediment. Total sediment community oxygen consumption was significantly higher in MPs-amended sediments than in the control, with the highest rates in treatment with the largest microspheres. However, oxygen uptake increase seemed to be unrelated to addition of MPs per se, suggesting rather an interaction between MPs and bivalves. The need for future studies on MPs effects on benthic community structure and functioning is highlighted.

Influence of dissolved black carbon on the aggregation and deposition of polystyrene nanoplastics: Comparison with dissolved humic acid

Dissolved black carbon (DBC), widely found in soil and water environments is likely to affect the transport of nanoplastics in aquatic environments. The aggregation and deposition behaviors of fresh and aged polystyrene nanoplastics (PSs) with and without DBC in NaCl solution were investigated by time-resolved dynamic light scattering (DLS) and quartz crystal microbalance with dissipation monitoring equipment (QCM-D) techniques. The results suggest that DBC can screen the surface charges of PSs by interacting with PSs through hydrogen bonding, hydrophobic interactions and π-π interactions, although they were negatively charged. DBC promoted the aggregation of PSs under relatively low ionic strengths, and it minimally affected the stability of PSs under high ionic strength. Deposition experiments showed that both DBC in salt solution and DBC adsorption on silica surface facilitated the deposition of fresh PSs while HA inhibited both deposition processes. After aging, PSs were more stable, and the effects of DBC and HA were weakened. This study investigated the influence mechanism of DBC on the aggregation and deposition behaviors, which provides new insights into the stability and transport of PSs in complex aquatic environments.

Zooplankton grazing of microplastic can accelerate global loss of ocean oxygen

Global warming has driven a loss of dissolved oxygen in the ocean in recent decades. We demonstrate the potential for an additional anthropogenic driver of deoxygenation, in which zooplankton consumption of microplastic reduces the grazing on primary producers. In regions where primary production is not limited by macronutrient availability, the reduction of grazing pressure on primary producers causes export production to increase. Consequently, organic particle remineralisation in these regions increases. Employing a comprehensive Earth system model of intermediate complexity, we estimate this additional remineralisation could decrease water column oxygen inventory by as much as 10% in the North Pacific and accelerate global oxygen inventory loss by an extra 0.2–0.5% relative to 1960 values by the year 2020. Although significant uncertainty accompanies these estimates, the potential for physical pollution to have a globally significant biogeochemical signal that exacerbates the consequences of climate warming is a novel feedback not yet considered in climate research.

Microplastic pollution is a major threat to marine food webs, but the wider ranging impacts on global ocean biogeochemistry are poorly understood. Here the authors use an Earth system model to determine that zooplankton grazing on microplastics could exacerbate trends in ocean oxygen loss.

Detection and removal of microplastics in wastewater: evolution and impact

The pervasiveness of microplastics in aquatic ecosystems has become a major environmental issue in recent years. The gradual dumping of plastic wastes, inadequate standard detection methods with specific removal techniques, and slow disposal rate of microplastics make it ubiquitous in the environment. Evidence shows that microplastics act as a potential vector by adsorbing different heavy metals, pathogens, and other chemical additives widely used in different raw plastic production. Microplastics are ingested by aquatic creatures such as fish and different crustaceans, and finally, people ingest them at the tertiary level of the food chain. This phenomenon is responsible for blocking the digestion tracts, disturbing the digestive behavior, finally decreasing the reproductive growth of entire living organisms. Because of these consequences, microplastics have become an increasing concern as a newly emerging potential threat, and therefore, the control of microplastics in aquatic media is required. This paper provides a critical analysis of existing and newly developed methods for detecting and separating microplastics from discharged wastewater, which are the ultimate challenges in the microplastic treatment systems. A critical study on the effect of microplastics on aquatic organisms and human health is also discussed. Thus, this analysis provides a complete understanding of entire strategies for detecting and removing microplastics and their associated issues to ensure a waste discharge standard to minimize the ultimate potential impact in aquatic environments.

Global Modeled Sinking Characteristics of Biofouled Microplastic

Microplastic debris ending up at the sea surface has become a known major environmental issue. However, how microplastic particles move and when they sink in the ocean remains largely unknown. Here, we model microplastic subject to biofouling (algal growth on a substrate) to estimate sinking timescales and the time to reach the depth where particles stop sinking. We combine NEMO-MEDUSA 2.0 output, that represents hydrodynamic and biological properties of seawater, with a particle-tracking framework. Different sizes and densities of particles (for different types of plastic) are simulated, showing that the global distribution of sinking timescales is largely size-dependent as opposed to density-dependent. The smallest particles we simulate (0.1 μm) start sinking almost immediately around the globe and their trajectories take the longest time to reach their first sinking depth (relative to larger particles). In oligotrophic subtropical gyres with low algal concentrations, particles between 1 and 0.01 mm do not sink within the simulation time of 90 days. This suggests that in addition to the comparatively well-known physical processes, biological processes might also contribute to the accumulation of floating plastic (of 1-0.01 mm) in subtropical gyres. Particles of 1 μm in the gyres start sinking largely due to vertical advection, whereas in the equatorial Pacific they are more dependent on biofouling. The qualitative impacts of seasonality on sinking timescales are small, however, localized sooner sinking due to spring algal blooms is seen. This study maps processes that affect the sinking of virtual microplastic globally, which could ultimately impact the ocean plastic budget.

Source, distribution and emerging threat of micro- and nanoplastics to marine organism and human health: Socio-economic impact and management strategies

The nature of micro- and nanoplastics and their harmful consequences has drawn significant attention in recent years in the context of environmental protection. Therefore, this paper aims to provide an overview of the existing literature related to this evolving subject, focusing on the documented human health and marine environment impacts of micro- and nanoplastics and including a discussion of the economic challenges and strategies to mitigate this waste problem. The study highlights the micro- and nanoplastics distribution across various trophic levels of the food web, and in different organs in infected animals which is possible due to their reduced size and their lightweight, multi-coloured and abundant features. Consequently, micro- and nanoplastics pose significant risks to marine organisms and human health in the form of cytotoxicity, acute reactions, and undesirable immune responses. They affect several sectors including aquaculture, agriculture, fisheries, transportation, industrial sectors, power generation, tourism, and local authorities causing considerable economic losses. This can be minimised by identifying key sources of environmental plastic contamination and educating the public, thus reducing the transfer of micro- and nanoplastics into the environment. Furthermore, the exploitation of the potential of microorganisms, particularly those from marine origins that can degrade plastics, could offer an enhanced and environmentally sound approach to mitigate micro- and nanoplastics pollution.

Preferential grazing and repackaging of small polyethylene microplastic particles (≤ 5 μm) by the ciliate Sterkiella sp

Microplastic (MP) particles are pollutants of global concern and are ubiquitously distributed in the ocean by physical and biological processes. It has been shown that zooplankton can ingest MP yet the interaction between ciliates and MP is still poorly understood. The discrimination and preferential uptake of MP rather than algal prey by ciliates was assessed in this study. The ciliate Sterkiella sp. was fed a diet that consisted of only Isochrysis galbana or a mixture of the same algae and similarly sized polyethylene beads in a 1:3 ratio. Significant, preferential MP grazing was observed in the Plastic-Algae treatment, which is the first reported evidence of proto-zooplankton preferentially ingesting MP over algal food. The mixed treatment contained fecal pellets with embedded MP. Preferential uptake of MP suggests that Sterkiella sp. is capable of ingesting and then "repackaging" MP that would otherwise be too small for larger taxa. This process would thus offer a mechanism for the reintroduction of MP into different compartments of the marine food web. As a consequence, it is necessary to account for small-sized MP (<5 μm) particles, that may have additional and yet unknown, impacts on marine food webs.

Microplastic changes the sinking and resuspension rates of marine mussel biodeposits

Microplastic (MP; < 5 mm) is ubiquitous in marine environments and is likely transported by biotic benthic-pelagic coupling. Mussels are key benthic-pelagic couplers, concentrating particles from the water column into dense and nutrient rich biodeposits. This study examined how MP affects benthic-pelagic coupling processes of mussels exposed to feeding regimes with and without MP by measuring four attributes of biodeposits: 1) morphology, 2) quantity of algal and MP particles, 3) sinking rate, and 4) resuspension velocity. We found interacting effects of particle treatment and biodeposit type on biodeposit morphology. Biodeposits from the algae treatment contained more algal cells on average than biodeposits from the MP treatment. Biodeposits from the MP treatment sank 34-37% slower and resuspended in 7-22% slower shear velocities than biodeposits from the algae treatment. Decreases in sinking and resuspension velocities of biodeposits containing MP may increase dispersal distances, thus decreasing in-bed nutrient input and increasing nutrient subsidies for other communities.

Microplastics in the Black Sea sediments

In this study the occurrence, morphology and identification of microplastics in Black Sea sediments collected at different depths (range 22-2131 m) were determined for the first time. The study explored the advantages and limitations of using a non-invasive method consisting of filtration of the supernatant from the mixture of sediment with saturated NaCl solution followed by FTIR 2D imaging for the identification of natural and synthetic polymers. The proposed method confirmed its potential for clear identification of polyethylene, polypropylene, acrylonitrile, polyamides and cellulose-based fibers, but more difficulties when the filter substrate neighboring the fibers exhibits intense absorptions in the 1800-1000 cm^-1 range. Microplastics (MPs) were determined in 83% of the investigated sediment samples. The average abundance in all samples was 106.7 items/kg. The highest pollution occurred on the North-Western shelf where the abundance of MPs was 10 times higher than in sediments from the deep sea. The most abundant plastic polymers were polyethylene and polypropylene, followed by acrylate and acrylonitrile copolymers. Polyamide and cellulose-based textile fibers were also found. The most frequent microplastic colors observed were black, blue and clear/transparent, while fibers represented the dominant microplastics in sediments.

The fate of plastic in the ocean environment - a minireview

The presence of plastics in the marine environment poses a threat to ocean life and has received much scientific and public attention in recent years. Plastics were introduced to the market in the 1950s and since then, global production figures and ocean plastic littering have increased exponentially. Of the 359 million tonnes (Mt) produced in 2018, an estimated 14.5 Mt has entered the ocean. In particular smaller plastic particles can be ingested by marine biota causing hazardous effects. Plastic marine debris (PMD) is exposed to physical, chemical and biological stressors. These cause macro and microplastic to break down into smaller fragments, including sub micrometre sized nanoplastic particles, which may account for an important but so far unevaluated fraction of the ocean plastic budget. Physicochemical and biological deterioration of PMD also leads to the release of more volatile compounds and the terminal oxidation of PMD, which most likely accounts for an important but also unevaluated fraction in the ocean plastic budget. This minireview provides an overview on (1) the quantity of plastic production and waste, pathways for plastics to enter the marine realm, the inventory of PMD and the negative effects of PMD to ocean life. (2) We discuss plastic degradation mechanisms in the ocean, expanding on the processes of photodegradation and biodegradation. (3) This review also highlights the emerging topic of nanoplastics in the sea and provides an overview on their specific physical and chemical properties, potential harm to ocean life, and nanoplastic detection techniques.

From source to sink: Review and prospects of microplastics in wetland ecosystems

The source, distribution, migration, and fate of microplastics (MPs) in aquatic and terrestrial ecosystems have received much attention. However, the relevant reports in wetland ecosystems, the boundary area between water and land, are still rare. Where are the sources and sinks of MPs in the wetland? The latest researches have shown that the sources of MPs in wetlands include sewage discharge, surface runoff, and plastic wastes from aquaculture. Fibers and fragments are the most common shapes, and PE, PP, PS can be detected in water or sediment matrices, and biota of wetlands. The distribution is affected by hydrodynamic conditions, sediment properties, and vegetation coverage. Factors affecting the vertical migration of MPs include their own physical and chemical properties, the combination of substances that accelerate deposition (mineral adsorption and biological flocculation), and resuspension. Minerals tend to adsorb negatively charged MPs while algae aggregates have a preference for positively charged MPs. The wetlands vegetation can trap MPs and affect their migration. In water matrices, MPs are ingested by organisms and integrated into sediments, which makes them seem undetectable in the wetland ecosystem. Photodegradation and microbial degradation can further reduce the MPs in size. Although recent research has increased, we are still searching for a methodological harmonization of the detection practices and exploring the migration rules and fate patterns of MPs. Our work is the first comprehensive review of the source, distribution, migration, and fate of MPs in wetland ecosystems. It reveals the uniqueness of wetland habitat in the research of MPs and indicates the potential of wetlands acting as sources or sinks for MPs.

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.

PET nanoplastics interactions with water contaminants and their impact on human cells

In recent years, many studies are focusing on the negative effects of plastic pollution, and in particular on the nanosized plastic fragments and their implications on the environment and human health. Nanoplastics in the environment interact with a great number of substances, many of which are dangerous to humans, but the interaction mechanisms, the complexes formation processes, and their biological impact are still poorly understood. Here we report a study on the interactions of polyethylene terephthalate nanoplastics, produced by laser ablation, with three different types of contaminants: glyphosate, levofloxacin and Hg²⁺ ions, and we demonstrate that the nanoplastics form complexes with all three contaminants through their favorable binding. Most importantly, this study highlights that to demonstrate the overall effect of the nanoplastics internalized by cells in vitro, it is important to combine alternative methodologies, such as metabolomics, with standard biological assays (i.e., cell viability and ROS production). In this way it becomes possible to better understand the body's response to this new class of pollutants and their possible chronic toxicity. Summary: PET nanoplastics, fabricated by laser ablation, interact with aqueous pollutants forming nanoclusters. The nanoclusters affect the cells metabolism, suggesting long-term risks.

Nationwide monitoring of microplastics in bivalves from the coastal environment of Korea

Bivalves are useful bioindicators of microplastic contamination in the marine environment for several reasons, such as extensive filter feeding activity, broad geographical distribution, and limited movement capability. This study conducted a nationwide monitoring of microplastic pollution along the Korean coasts using filter-feeding bivalves (including oyster, mussel, and Manila clam) as bioindicators to identify the national contamination level and characteristics of microplastics. Seawater sample was collected from the same sampling stations of oyster and mussel for comparison. Microplastics were widely distributed in both coastal bivalves and waters with mean concentrations of 0.33 ± 0.23 n/g (1.21 ± 0.68 n/individual) in oyster/mussel, 0.43 ± 0.32 n/g (2.19 ± 1.20 n/individual) in Manila clam, and 1400 ± 560 n/m³ in seawater. Despite the lack of significant relationship in the abundance of microplastics, their dominant features such as size, shape, color and polymer type were similar between bivalves and seawater. Fragments (69% for oyster/mussel, 72% for Manila clam, and 77% for seawater), particles smaller than 300 μm (96% for oyster/mussel, 83% for Manila clam, and 84% for seawater) and colorless (79% for oyster/mussel, 85% for Manila clam, 75% for seawater) were the dominant shape, size and color, respectively. The major polymer types were polypropylene, polyethylene, and polyester. The microplastic level in bivalves was relatively high in urbanized areas with a wide diversity of polymer types compared with those in non-urbanized areas, and the proportion of polystyrene in the Korean samples was abundant compared with other regions due to wide use of polystyrene products in Korea. Our result suggests that microplastic contamination is widespread in the Korean coastal environment, and bivalves can reflect the microplastic pollution characteristics of the surrounding waters where they live.

Microplastics interfere with mixotrophic Ochromonas eliminating toxic Microcystis

Microplastics with different sizes exist widely in fresh waters, which may affect the interspecific dynamics between predator and prey. The flagellate Ochromonas gloeopara can efficiently eliminate Microcystis aeruginosa and degrade microcystins, which shows great potential for controlling harmful Microcystis. In order to evaluate the effects of microplastics on O. gloeopara eliminating Microcystis, we designed an experiment of O. gloeopara feeding on Microcystis under different sizes (0.07 and 3 μm) and concentrations (0, 0.4, 0.8, 1.6, and 2.0 mg L^-1) of microplastics. The results showed that maximum abundance of M. aeruginosa decreased significantly with addition of microplastics, regardless of the size and concentration. O. gloeopara can ingest the microplastics and suffer from their adverse effects. The maximum abundance of O. gloeopara decreased with enhancing concentrations of 3 μm microplastics during the process of O. gloeopara eliminating M. aeruginosa, whereas 0.07 μm microplastics did not affect the growth of O. gloeopara obviously. During the period of exposure under microplastics, clearance rate of O. gloeopara on M. aeruginosa decreased with the increasing concentrations of microplastics. Specially, 3 μm microplastics had a stronger reduction on clearance rate of O. gloeopara. The time to M. aeruginosa extinction was prolonged with the increasing concentrations of microplastics in both sizes. Comparatively speaking, 3 μm microplastics had a stronger delayed effect on the removal of Microcystis. These findings suggest that microplastics can interfere with protozoa eliminating toxic Microcystis, which may aggravate their adverse impacts on aquatic ecosystem.

Flocculation of PVC Microplastic and Fine-Grained Cohesive Sediment at Environmentally Realistic Concentrations

AbstractMicroplastic particles have become ubiquitous in aquatic environments and can be found in large numbers in riverine, estuarine, and marine settings at the surface of water, in suspension, and as particles deposited at the bed. The transport and settling behavior of small microplastic particles is likely very dependent on interactions with other suspended particles. Here we show from settling tube experiments conducted in the laboratory that fragments and threads of polyvinylchloride microplastic in the size range of 63-125 µm readily flocculated with fine-grained natural sediment under relative particle number concentrations that can be observed in nature in high-turbidity estuarine and coastal environments. The implication of this flocculation is that the microplastic particles are suspended and transported incorporated in aggregates that settle faster than the individual microplastic particles. This is causing a continuous sedimentation of microplastic particles in estuarine and marine settings, resulting in increased microplastic loading for benthic life in these environments.

Microplastics do not increase bioaccumulation of petroleum hydrocarbons in Arctic zooplankton but trigger feeding suppression under co-exposure conditions

Arctic sea ice has alarmingly high concentrations of microplastics (MPs). Additionally, sea ice reduction in the Arctic is opening new opportunities for the oil and maritime industries, which could increase oil pollution in the region. Yet knowledge of the effects of co-exposure to MPs and crude oil on Arctic zooplankton is lacking. We tested the influence of MPs (polyethylene, 20.7 μm) on polycyclic aromatic hydrocarbon (PAH) bioaccumulation and oil toxicity in the key arctic copepod Calanus hyperboreus after exposure to oil with and without dispersant. Up to 30% of the copepods stopped feeding and fecal pellet production rates were reduced after co-exposure to oil (1 μL L^-1) and MPs (20 MPs mL^-1). The PAH body burden was ~3 times higher in feeding than in non-feeding copepods. Copepods ingested both MPs and crude oil droplets. MPs did not influence bioaccumulation of PAHs in copepods or their fecal pellets, but chemical dispersant increased bioaccumulation, especially of ≥4 ring-PAHs. Our results suggest that MPs do not act as vectors of PAHs in Arctic marine food webs after oil spills, but, at high concentrations (20 MPs mL^-1), MPs can trigger behavioral stress responses (e.g., feeding suppression) to oil pollution in zooplankton.

Effect of polystyrene on di-butyl phthalate (DBP) bioavailability and DBP-induced phytotoxicity in lettuce

Hydrophobic microplastics with a relatively large surface area can act as carriers for pollutants and exert a series of indirect effects on crop plants. This study investigated the toxic effects of small polystyrene (SPS, 100-1000 nm) and large polystyrene (LPS, >10,000 nm) microplastics, on lettuce under di-butyl phthalate (DBP) stress. The results indicated that single SPS, LPS, and DBP treatments significantly decreased lettuce biomass, and induced oxidative stress and damaged lettuce leaves and roots. According to Gaussian analysis, SPS or LPS could interact with DBP through van der Waals force, thereby reducing lettuce biomass and DBP enrichment in roots and leaves under combined treatments, increasing antioxidant enzyme activities and exacerbating oxidative stress and subcellular damage, compared to single DBP treatments. Observation using scanning electron microscopy demonstrated that polystyrene (PS) adhered to the root surfaces, which, in turn, caused physical blockage of the root pores. Cell membrane and wall damage was observed during PS and/or DBP exposures, as identified by transmission electron microscopy. Molecular docking illustrated that DBP and monobutyl phthalate could interact with superoxide dismutase residues through hydrogen bonding, π-π stacking, alkyl conjugation, and van der Waals forces. Interestingly, there were no statistical differences between the phytotoxicity of nano- and microplastics to lettuce. These findings showed that PS aggravated DBP-induced phytotoxicity.

Plastic pollution impacts on marine carbon biogeochemistry

One of the major challenges in understanding the dynamics of the ocean's health and functioning is the potential impact of the increasing presence of plastic. Besides the verified and macroscopic effects on marine wildlife and habitats, micro and macroplastics offer potential sites for microbial activity and chemical leaching. Most marine plastic is found initially in the upper meters of the water column, where fundamental biogeochemical processes drive marine productivity and food web dynamics. However, recent findings show a continuum of potential effects of these new marine components on carbon, nutrients and microbial processes. In the present analysis, we develop a common ground between these studies and we identify knowledge gaps where new research efforts should be focused, to better determine potential feedbacks of plastics on the carbon biogeochemistry of a changing ocean.

The gut retention time of microplastics in barnacle naupliar larvae from different climatic zones and marine habitats

Microplastic ingestion has been widely documented in marine zooplankton, but the retention time of microplastics in their digestive gut are still poorly studied, especially among species from different climatic zones and marine habitats. This study evaluated the ingestion and gut retention time of four sizes of fluorescent microplastic beads (1.3, 7.3, 10.6, and 19.0 μm) in stage II naupliar larvae of nine barnacle species from different habitats (epibiotic on turtles, mangroves, coral reefs, and rocky shores) and climatic zones (subtropical/tropical and temperate). Microbeads were not lethal to all species (climatic zones/habitats) tested from the four sizes of non-fluorescent virgin microbeads (1.7, 6.8, 10.4 and 19.0 μm, each at concentrations 1, 10, 100, and 1000 beads mL^-1). Gut retention time of microplastic beads in barnacle naupliar larvae significantly increased with decreasing size. Microbeads resided in digestive tracts generally 3-4 times longer in rocky shore and coral reef barnacles than in muddy shore and epibiotic ones. However, species from different climatic zone did not differ in retention time. Our results suggested nauplius larvae from rocky shore and coral reef barnacles appear to be more susceptible to the impacts of longer retained microplastics (e.g., toxic chemicals present on the surface).

Parental exposure to polystyrene microplastics at environmentally relevant concentrations has negligible transgenerational effects on zebrafish (Danio rerio)

Waterborne exposure to highly persistent microplastic pollutants is a major concern for aquatic species worldwide. There are still gaps in knowledge on microplastics' potential transgenerational effects on offspring generation. Using zebrafish, this study investigated the survival and early development of offspring through a 21-day continuous parental treatment with polystyrene microplastics. The results showed that continuous waterborne exposure to high concentrations (>100 μg/L) of polystyrene microplastics (1 μm) for 21 days resulted in notable microplastic accumulation in adult fish intestines. Exposure at microplastic concentrations greater than 100 μg/L also induced significant changes in steroidogenic mRNA expression in zebrafish gonads. However, no significant changes in the cumulative number of eggs spawned and fertilization rate were observed at any parental exposure concentrations when compared to the control. Early development of derived offspring, in terms of hatching rate, body length, malformation rate and mortality rate, did not significantly differ from that of the control. This study showed that transgenerational effects of parental exposure to polystyrene microplastics in zebrafish might be negligible or recoverable. This study provided new results and insights on the transgenerational effects of microplastics on a freshwater fish species and can help to understand impacts of microplastics on freshwater ecosystems.

Spatial distribution of microplastics around an inhabited coral island in the Maldives, Indian Ocean

Small plastic particles are considered environmental pollutants and are highly concentrated in marine sediments. However, knowledge about plastic abundance within coral reef habitat and beach sediments surrounding remote inhabited coral islands is scarce. In this study, microplastic accumulation was investigated on a small inhabited coral island located in the Maldives. Sediments from 22 sampling sites across fore reef, reef flat, and beach environments were analysed for plastic particles <5 mm. Density separation and microscope enumeration revealed a total of 1244 individual microplastic pieces, in filamentous (49%) and fragmented (51%) forms, found across all sampling sites. High concentrations were recorded at all sites, however, there was no significant relationship between microplastic concentration or size across regions (inner atoll and outer atoll) or environments (fore reef, reef flat, and beach). Furthermore, concentrations of microplastic fragment and filament forms, total concentration, and the microplastic community, showed little correlation with sediment particle size. Our findings show microplastics are ubiquitous in marine sediments around a remote coral island, at sizes ingestible by marine organisms, raising concerns about potential effects of microplastic ingestion by coral reef species.

Effects of microplastics exposure on ingestion, fecundity, development, and dimethylsulfide production in Tigriopus japonicus (Harpacticoida, copepod)

The effects of microplastics pollution on the marine ecosystem have aroused attention. Copepod grazing stimulates dimethylsulfide (DMS) release from dimethylsulfoniopropionate (DMSP) in phytoplankton, but the effect of microplastics exposure on DMS and DMSP production during copepod feeding has not yet been revealed. Here, we investigated the effects of polyethylene (PE) and polyamide-nylon 6 (PA 6) microplastics on ecotoxicity and DMS/DMSP production in the copepod Tigriopus japonicus. The microplastics had detrimental effects on feeding, egestion, reproduction, survival, and DMS and DMSP production in T. japonicus and presented significant dose-response relationships. The 24 h-EC50 for ingestion rates (IRs) of female T. japonicus exposed to PE and PA 6 were 57.6 and 58.9 mg L^-1, respectively. In comparison, the body size of the copepods was not significantly affected by the microplastics during one generation of culture. Ingesting fluorescently labeled microplastics confirmed that microplastics were ingested by T. japonicus and adhered to the organs of the body surface. T. japonicus grazing promoted DMS release originating from degradation of DMSP in algal cells. Grazing-activated DMS production decreased because of reduced IR in the presence of microplastics. These results provide new insight into the biogeochemical cycle of sulfur during feeding in copepods exposed to microplastics.

Biodegradation and disintegration of expanded polystyrene by land snails Achatina fulica

Despite increasing evidence of widespread plastic pollution in soil, it remains largely unknown about the fate of plastic influenced by soil animals. In this study, ingestion and biodegradation capability of expanded polystyrene (PS) foam was investigated in a globally distributed soil invertebrate, Achatina fulica. After 4-week exposure, 18.5 ± 2.9 mg polystyrene was ingested per snail, and egested microplastics (1.343 ± 0.625 mm) in feces with significant mass loss of mean 30.7%. Gel permeation chromatography analysis indicated a significant increase in weight-average molecular weight (M_w) and number-average molecular weight (M_n) of feces-residual PS, indicating limited extent depolymerization. Fourier transform infrared spectroscopy and proton nuclear magnetic resonance confirmed the formation of functional groups of oxidized intermediates. Suppression of gut microbes with oxytetracycline did not affect the depolymerization, indicating the independence of gut microbes. High-throughput sequencing analysis revealed significant shifts in the gut microbiome after ingestion of PS, with an increase of family Enterobacteriaceae, Sphingobacteriaceae, and Aeromonadaceae, suggesting that gut microorganisms were associated with PS biodegradation. These findings suggest that plastic litter can be disintegrated into microplastics and partially biodegraded by A. fulica, which highlights the significance of soil animals for the fate of plastic and its biodegradation in soil environments.

Occurrence and distribution of microplastics in China's largest freshwater lake system

Although microplastics (MPs; < 5 mm) have been recognized as one of the most challenging environmental pollutants in the ocean, our understanding of the environmental fate of freshwater MPs falls far behind, particularly on smaller MPs (<0.1 mm). Here, we seek to reveal the latest MP pollution status in the largest freshwater lake of China, Poyang Lake, by comprehensively assessing the abundance, distribution, size, shape, polymer composition, and micro-morphology of MPs in water and sediment, covering a large geographic area of the Lake and its five main river tributaries. High levels of MPs were detected in water (up to 1064 ± 90 MP/m³) and sediment (up to 1936 ± 121 MP/kg), with the highest concentrations in the Gan River and the lowest in the national Nature Reserves. While a positive correlation was identified between MP abundance in water and sediment, the size distribution of MPs in between water and sediment was distinct. The dominant MP form in sediment and water was fragment and fiber, respectively. Infrared spectroscopy analysis confirmed the dominant polymer types including polypropylene, polyvinyl chloride, polyethylene, polystyrene, and polyvinyl alcohol. Moreover, both μ-FTIR and SEM results suggested significant features of weathering and fragmentation of MPs. This study provides comprehensive data to understand the environmental behavior and pollution magnitude of MPs in China's largest freshwater lake and highlights the significant contribution of smaller-size fractions (0.03-0.1 mm) to improve future MP studies in freshwater systems.

Degradation of polyvinyl chloride microplastics via an electro-Fenton-like system with a TiO2/graphite cathode

Nowadays, microplastic pollution has been brought into focus for its hazards to aquatic life. However, researches on the electrocatalytic treatment for efficient degradation of microplastics are still insufficient. Herein, an electro-Fenton like (EF-like) technology based on TiO₂/graphite (TiO₂/C) cathode was put forward to degrade polyvinyl chloride (PVC), a typical microplastic in water. It exhibited a remarkable performance on PVC degradation via cathodic reduction dechlorination and hydroxyl radical (OH) oxidation simultaneously. Besides, the effects of reaction temperature and initial PVC concentration were investigated. Under optimal conditions, the dechlorination efficiency of PVC reached 75 % after potentiostatic electrolysis at -0.7 V vs. Ag/AgCl for 6 h. The intermediate products were explored during the degradation of PVC microplastics. The surface morphologies and molecular weight of PVC changed accordingly. Based on these results, a possible degradation process for PVC was proposed. This work demonstrated that such a heterogeneous EF-like technology using TiO₂/C cathode was hopefully to provide an eco-friendly method for microplastic wastewater treatment.

Microplastic-associated trophic transfer of benzo(k)fluoranthene in a limnic food web: Effects in two freshwater invertebrates (Daphnia magna, Chironomus riparius) and zebrafish (Danio rerio)

The continuously growing plastic production and incomplete recycling processes open manifold entry routes for microplastic particles (MPs) into the environment. Since knowledge on trophic transfer of contaminants sorbed to MPs is still insufficient for freshwater systems, the transfer of the model pollutant benzo(k)fluoranthene (BkF) sorbed to polymethyl methacrylate (PMMA) particles in a limnic food web was investigated: Two freshwater invertebrates (Daphnia magna and Chironomus riparius larvae) were selected and either left untreated, exposed to pristine PMMA, PMMA-associated BkF, or exposed to dissolved BkF (BkF_aq). As second-level consumers, zebrafish (Danio rerio) were fed twice daily with pre-treated invertebrates over two days. Induction of hepatic cytochrome P450 by BkF was determined as 7-ethoxy-O-resorufin deethylase (EROD) activity. Both invertebrate species readily ingested PMMA particles, tracked via fluorescence microscopy and accumulated BkF_aq, measured via GC-MS. Fluorescence signals in gastrointestinal tracts of zebrafish were quantified with confocal laser scanning microscopy (CLSM). The fluorescence signal in gastrointestinal tracts of zebrafish was not altered, whereas, EROD activity was significantly induced when zebrafish were fed with Chironomus riparius, pre-exposed to BkF_aq. Trophic exposure scenarios with BkF sorbed to PMMA did not result in any alterations of investigated endpoints in both invertebrate species and zebrafish compared to controls. Given that BkF amounts were in the low ng-range, as detected by GC-MS, the transport of MP-sorbed BkF to zebrafish was less effective than direct exposure to waterborne BkF_aq, and the potential threat of trophic transfer of substances such as BkF in limnic food webs may have been overestimated.

The effect of microplastics pollution in microalgal biomass production: A biochemical study

Microplastics (MPs) are widely spread throughout aquatic systems and water bodies. Given that water quality is one of the most important parameters in the microalgal-based industry, it is critical to assess the biochemical impact of short- and long-term exposure to MPs pollution. Here, the microalga Phaeodactylum tricornutum was exposed to water contaminated with 0.5 and 50 mg L^-1 of polystyrene (PS) and/or polymethyl methacrylate (PMMA). Results show that the microalgal cultures exposed to lower concentrations of PS displayed a growth enhancement of up to 73% in the first stage (days 3-9) of the exponential growth phase. Surprisingly, and despite the fact that long-term exposure to MPs contamination did not impair microalgal growth, a steep decrease in biomass production (of up to 82%) was observed. The production of photosynthetic pigments was shown to be pH-correlated during the full growth cycle, but cell density-independent in later stages of culturing. The extracellular carbohydrates production exhibited a major decrease during long-term exposure. Still, the production of extracellular proteins was not affected by the presence of MPs. This pilot laboratory-scale study shows that the microalgal exposure to water contaminated with MPs disturbs its biochemical equilibrium in a time-dependent manner, decreasing biomass production. Thus, microalgal industry-related consequences derived from the use of MPs-contaminated water are a plausible possibility.

Mussels facilitate the sinking of microplastics to bottom sediments and their subsequent uptake by detritus-feeders

Microplastics (MP) are omnipresent contaminants in the oceans, however little is known about the MP transfer between marine compartments and species. Three connected laboratory experiments using the filter-feeding mussel Mytilus galloprovincialis and the omnivorous polichaete Hediste diversicolor were conducted to evaluate whether the filtering action by mussels affects the vertical transfer of MP of different sizes (MP_SMALL = 41 μm; MP_LARGE = 129 μm) and densities (polyamide = 1.15 g cm^-3; polypropylene = 0.92 g cm^-3) across compartments and species with different feeding modes. Mussels significantly removed MP from the water column by incorporating them into biodeposits. This effect was particularly evident for the MP_SMALL, whose deposition from the water column to the bottom was enhanced (about 15%) by the action of mussels. The incorporation of MP into faecal pellets increased the particles' sinking velocity by about 3-4 orders of magnitude. Conversely, the MP presence significantly decreased the depositional velocities of faecal pellets, and the magnitude of this effect was greater with increasing MP size and decreasing density. The MP incorporation into mussels' biodeposits also more than doubled the amount of MP uptake by H. diversicolor. We conclude that detrital pathways could be a transfer route of MP across marine compartments and food webs, potentially affecting the distribution of MP in sediments and creating hot-spots of bioavailable MP.

Differences in microplastic abundances within demersal communities highlight the importance of an ecosystem-based approach to microplastic monitoring

Plastic pollution is prevalent in all habitats and microplastic ingestion has been recorded in several different species examined to date. However, most studies have focused solely on commercial species. This study investigates microplastics (MPs) by assessing the levels present in a mixed demersal trawl at two sites in a coastal embayment. MPs were recovered from species' gastrointestinal tracts and polymers identified with μFTIR spectroscopic analysis. Particles recovered comprised 20% natural fibres. The majority of MPs were identified as PE, PVDF, and PETE. Results show an average MP range of 0.11-4.67 MPs individual^-1. Fluctuating trendlines for MPs within species suggest that their bioavailability is influenced by several factors. Individual species show significant differences in ingested MP between trawls; however, when the entire trawl community is assessed there is no significant difference between sites. These results suggest that future studies should follow an ecosystem-based approach to monitor MPs.

Ingestion and impact of microplastics on arctic Calanus copepods

Microplastics (MPs) are contaminants of emerging concern in the Arctic, but knowledge of their potential effects on Arctic plankton food webs remains scarce. We experimentally investigated ingestion and effects of MPs (20 μm polyethylene spheres) on the arctic copepods Calanus finmarchicus, C. glacialis and C. hyperboreus. These species dominate arctic zooplankton biomass and are relevant target species to investigate the potential impacts of MPs on the Arctic marine ecosystem. Females of each species were exposed to two concentrations of MPs (200 and 20,000 MPs L^-1) in combination with different food (diatom) concentrations, reflecting high (3000-5000 cells mL^-1, spring phytoplankton bloom) and low (50-500 cells mL^-1, pre/post bloom) food conditions. MPs did not affect negatively fecal pellet production rates in any of the species at the studied exposure concentrations. However, egg production rates of copepods exposed to MPs were 8 times higher compared with the controls, which suggests that MP exposure can cause stress-induced spawning in arctic copepods. Microscopic examination of the fecal pellets confirmed ingested MPs in the three species (up to aprox. 1000 MPs cop^-1 d^-1). The number of MPs per pellet decreased exponentially with increasing food concentration. The daily ingestion of MPs per copepod was higher at low- food concentrations (250-500 cells mL^-1). At our exposure conditions, the presence of MPs inside C. hyperboreus fecal pellets did not affect their sinking rates. Overall, our experimental research show that 1) acute exposure to virgin polyethylene MPs has a low impact on arctic Calanus species at environmentally relevant MP concentrations, independent of food availability, and 2) arctic copepods influence the environmental fate of plankton-sized MPs by exporting buoyant MPs from the surface layer to the sea floor via fecal pellets.

Low level of microplastic contamination in wild fish from an urban estuary

Microplastic accumulation in estuarine environments is considered the dominant input of land-based plastics into the oceans. In this study, the level of microplastic contamination was evaluated in 26 species of wild fish from the Pearl River Estuary, South China. Results showed that microplastics abundance ranged from 0.17 items individual^-1 (Boleophthalmus pectinirostris & Acanthogobius flavimanus) to 1.33 items individual^-1 (Plectorhynchus cinctus) among different species. The distribution of microplastic abundance in the gills and gastrointestinal tracts was not significantly different. Microplastics in gills are strongly related to the filtration area of gills in 15 fish species. Fibers were the dominant shapes accounting for 93.45% of the total shapes. The majority of microplastics were <3 mm in size. The most common polymer composition was polyethylene terephthalate (38.2%) and the most common color was black (30.36%). The findings of this study provide baseline data for microplastic contamination in wild fish from an urban estuary.

The global biological microplastic particle sink

Every year, about four percent of the plastic waste generated worldwide ends up in the ocean. What happens to the plastic there is poorly understood, though a growing body of evidence suggests it is rapidly spreading throughout the global ocean. The mechanisms of this spread are straightforward for buoyant larger plastics that can be accurately modelled using Lagrangian particle models. But the fate of the smallest size fractions (the microplastics) are less straightforward, in part because they can aggregate in sinking marine snow and faecal pellets. This biologically-mediated pathway is suspected to be a primary surface microplastic removal mechanism, but exactly how it might work in the real ocean is unknown. We search the parameter space of a new microplastic model embedded in an earth system model to show that biological uptake can significantly shape global microplastic inventory and distributions and even account for the budgetary “missing” fraction of surface microplastic, despite being an inefficient removal mechanism. While a lack of observational data hampers our ability to choose a set of “best” model parameters, our effort represents a first tool for quantitatively assessing hypotheses for microplastic interaction with ocean biology at the global scale.

Marine Plastic Debris: A New Surface for Microbial Colonization

Plastics become rapidly colonized by microbes when released into marine environments. This microbial community-the Plastisphere-has recently sparked a multitude of scientific inquiries and generated a breadth of knowledge, which we bring together in this review. Besides providing a better understanding of community composition and biofilm development in marine ecosystems, we critically discuss current research on plastic biodegradation and the identification of potentially pathogenic "hitchhikers" in the Plastisphere. The Plastisphere is at the interface between the plastic and its surrounding milieu, and thus drives every interaction that this synthetic material has with its environment, from ecotoxicity and new links in marine food webs to the fate of the plastics in the water column. We conclude that research so far has not shown Plastisphere communities to starkly differ from microbial communities on other inert surfaces, which is particularly true for mature biofilm assemblages. Furthermore, despite progress that has been made in this field, we recognize that it is time to take research on plastic-Plastisphere-environment interactions a step further by identifying present gaps in our knowledge and offering our perspective on key aspects to be addressed by future studies: (I) better physical characterization of marine biofilms, (II) inclusion of relevant controls, (III) study of different successional stages, (IV) use of environmentally relevant concentrations of biofouled microplastics, and (V) prioritization of gaining a mechanistic and functional understanding of Plastisphere communities.

Nanoplastics affect moulting and faecal pellet sinking in Antarctic krill (Euphausia superba) juveniles

Plastic debris has been identified as a potential threat to Antarctic marine ecosystems, however, the impact of nanoplastics (<1 μm) is currently unexplored. Antarctic krill (Euphausia superba) is a keystone species of Southern Ocean pelagic ecosystems, which plays a central role in the Antarctic food webs and carbon (C) cycle. Krill has been shown to rapidly fragment microplastic beads through the digestive system, releasing nanoplastics with unknown toxicological effects. Here we exposed krill juveniles to carboxylic (COOH, anionic) and amino- (NH₂, cationic) polystyrene nanoparticles (PS NPs) and we investigated lethal and sub-lethal endpoints after 48 h. The analysis of PS NP suspensions in Antarctic sea water (SW) media showed that PS-COOH formed large agglomerates (1043 ± 121 nm), while PS-NH₂ kept their nominal size (56.8 ± 3 nm) during the exposure time. After 48 h, no mortality was found but increase in exuviae production (12.6 ± 1.3%) and reduced swimming activity were observed in juveniles exposed to PS-NH₂. The microbial community composition in SW supports the release of krill moults upon PS NP exposure and stimulates further research on the pivotal role of krill in shaping Southern Ocean bacterial assemblages. The presence of fluorescent signal in krill faecal pellets (FPs) confirmed the waterborne ingestion and egestion of PS-COOH at 48 h of exposure. Changes in FP structure and properties were also associated to the incorporation of PS NPs regardless of their surface charge. The effects of PS NPs on krill FP properties were compared to Control 0 h as a reference for full FPs (plastic vs food) and Control 48 h as a reference for more empty-like FPs (plastic vs lack of food). Exposure to PS NPs led to a FP sinking rate comparable to Control 48 h, but significantly lower than Control 0 h (58.40 ± 23.60 m/d and 51.23 ± 28.60 m/d for PS-COOH and PS-NH₂; 168.80 ± 74.58 m/d for Control 0 h). Considering the important role played by krill in the food web and C export in the Southern Ocean, the present study provides cues about the potential impact of nanoplastics on Antarctic pelagic ecosystems and their biogeochemical cycles.

Microplastics pollution in China water ecosystems: a review of the abundance, characteristics, fate, risk and removal

Microplastics pollution has been a focus for researchers in recent years worldwide, for the large quantities of plastics in production and the resistance to degradation. China's microplastics pollution attracts much attention because of its long coastline, large population and rapid economic development. This review addresses the widespread microplastics pollution in China's water ecosystems through available research results from recent years and analyses the abundance, characteristics, fate and risk of microplastics. This paper also discusses the current treatment technology of microplastics. The conclusions show that estuaries are severely affected by microplastics pollution; the accumulation of microplastics and adsorption of contaminants by microplastics could also lead to serious risks besides ingestion; there are few technologies that can efficiently remove microplastics pollution in sewage treatment plants. Finally, this review suggests directions for future research trends.

Are we underestimating microplastic abundance in the marine environment? A comparison of microplastic capture with nets of different mesh-size

Microplastic debris is ubiquitous and yet sampling, classifying and enumerating this prolific pollutant in marine waters has proven challenging. Typically, waterborne microplastic sampling is undertaken using nets with a 333 μm mesh, which cannot account for smaller debris. In this study, we provide an estimate of the extent to which microplastic concentrations are underestimated with traditional sampling. Our efforts focus on coastal waters, where microplastics are predicted to have the greatest influence on marine life, on both sides of the North Atlantic Ocean. Microplastic debris was collected via surface trawls using 100, 333 and 500 μm nets. Our findings show that sampling using nets with a 100 μm mesh resulted in the collection of 2.5-fold and 10-fold greater microplastic concentrations compared with using 333 and 500 μm meshes respectively (P < 0.01). Based on the relationship between microplastic concentrations identified and extrapolation of our data using a power law, we estimate that microplastic concentrations could exceed 3700 microplastics m^-3 if a net with a 1 μm mesh size is used. We further identified that use of finer nets resulted in the collection of significantly thinner and shorter microplastic fibres (P < 0.05). These results elucidate that estimates of marine microplastic concentrations could currently be underestimated.

Microplastic in the stomachs of open-ocean and deep-sea fishes of the North-East Atlantic

The presence of microplastic in marine fishes has been well documented but few studies have directly examined differences between fishes occupying contrasting environmental compartments. In the present study, we investigated the gut contents of 390 fishes belonging to three pelagic (blue jack mackerel, chub mackerel, skipjack tuna) and two deep-sea species (blackbelly rosefish, blackspot seabream) from the Azores archipelago, North-East Atlantic for microplastic contamination. Our results revealed that pelagic species had significantly more microplastic than the deep-water species. In all of the species studied, fragments were the most common plastic shape recovered and we found a significant difference in the type of polymer between the pelagic and deep-water species. In deep-sea fish we found almost exclusively polypropylene, whereas in the pelagic fish, polyethylene was the most abundant polymer type. Overall, the proportion of fish containing plastic items varied across our study species from 3.7% to 16.7% of individuals sampled, and the average abundance of plastic items ranged from 0.04 to 0.22 per individual (the maximum was 4 items recovered in one stomach). Despite the proximity of the Azores archipelago to the North Atlantic subtropical gyre, a region of elevated plastic abundance, the proportion of individuals containing plastic (9.49%) were comparable with data reported elsewhere.

Experimental ingestion of fluorescent microplastics by pacific oysters, Crassostrea gigas, and their effects on the behaviour and development at early stages

Plastics are persistent synthetic polymers that accumulate as waste in the marine environment. Microplastics (MPs, <5 mm) can be found either as microbeads in body care and some industrial products or as plastic debris through degradation. Plastic microbeads (1-5 μm, fluorescent, Cospheric) were used to characterise the MP ingestion and determine their potential harmful effects on both the swimming behaviour and development of oyster D-larvae (Crassostrea gigas). For 24 h, embryos were first exposed to MPs at a temperature of 24 °C. In addition, 3 day-old D-larvae were exposed to the same temperature for 1, 3 and 5 h. Three concentrations of MPs were used: 0.1, 1 and 10 mg MP. L^-1. After a 24-h period of embryonic exposure, we noted that MP agglomerates were stuck to the D-larvae coat and locomotor eyelashes. We also observed a significant increase in severe malformations and developmental arrests for larvae exposed to MPs ranging from 1 mg MP. L^-1. In terms of swimming behaviour, the maximum speed recorded was lower for larvae exposed at 0.1 and 1 mg MP. L^-1. After an acute exposure to MPs, particles were found in the digestive tract of 3 dpf (days post fertilisation) D-larvae. After 1-h exposure, the concentrations tested (0.1, 1 and 10 mg MP. L^-1) resulted in respectively 38%, 86% and 98%. The larvae swimming behaviour was recorded and analysed. Unlike the results observed at the embryo-larval stage, 3-dpf larvae showed significant impacts with no dose-response effect.

How sea urchins face microplastics: Uptake, tissue distribution and immune system response

Plastic pollution represents one of the major threats to the marine environment. A wide range of marine organisms has been shown to ingest microplastics due to their small dimensions (less than 1 mm). This negatively affects some biological processes, such as feeding, energy reserves and reproduction. Very few studies have been performed on the effect of microplastics on sea urchin development and virtually none on adults. The aim of this work was to evaluate the uptake and distribution of fluorescent labelled polystyrene microbeads (micro-PS) in the Mediterranean sea urchin Paracentrotus lividus and the potential impact on circulating immune cells. Differential uptake was observed in the digestive and water vascular systems as well as in the gonads based on microbeads size (10 and 45 μm in diameter). Treatment of sea urchins with particles of both sizes induced an increase of the total number of immune cells already after 24 h. No significant differences were observed among immune cell types. However, the ratio between red and white amoebocytes, indicative of sea urchin healthy status, increased with both particles. This effect was detectable already at 24 h upon exposure to smaller micro-PS (10 μm). An increase of intracellular levels of reactive oxygen and nitrogen species was observed at 24 h upon both micro-PS exposure, whereas at later time these levels became comparable to those of controls. A significant increase of total antioxidant capacity was observed after treatment with 10 μm micro-PS. Overall data provide the first evidence on polystyrene microbeads uptake and tissue distribution in sea urchins, indicating a stress-related impact on circulating immune cells.

High concentrations of plastic hidden beneath the surface of the Atlantic Ocean

Concern over plastic pollution of the marine environment is severe. The mass-imbalance between the plastic litter supplied to and observed in the ocean currently suggests a missing sink. However, here we show that the ocean interior conceals high loads of small-sized plastic debris which can balance and even exceed the estimated plastic inputs into the ocean since 1950. The combined mass of just the three most-littered plastics (polyethylene, polypropylene, and polystyrene) of 32–651 µm size-class suspended in the top 200 m of the Atlantic Ocean is 11.6–21.1 Million Tonnes. Considering that plastics of other sizes and polymer types will be found in the deeper ocean and in the sediments, our results indicate that both inputs and stocks of ocean plastics are much higher than determined previously. It is thus critical to assess these terms across all size categories and polymer groups to determine the fate and danger of plastic contamination.

The risks posed by plastic contamination of the ocean cannot be assessed as their amount and location remain largely unknown. Here the authors show that large quantities of microplastics exist below the ocean surface over the entire Atlantic in quantities greater than previously estimated.

Effects of polymer aging on sorption of 2,2',4,4'-tetrabromodiphenyl ether by polystyrene microplastics

The sorption behavior of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on aged polystyrene (PS) microplastics via seawater soaking, ultraviolet (UV) irradiation, seawater soaking and UV irradiation together was investigated. The effects of environmental factors including salinity, pH, and dissolved organic matter (DOM) on sorption of BDE-47 by the aged PS microplastics were analyzed. The equilibrium sorption capacity of BDE-47 by virgin PS, aged PS with seawater soaking, aged PS with UV irradiation and aged PS with seawater soaking and UV irradiation was 6.16, 4.96, 3.53, and 3.75 ng/g, respectively. The decrease in sorption capacity was related to the increase of surface crystallinity and the appearance of surface oxygen-containing functional groups. The kinetic and isotherm models suggested that aging did not change the sorption mechanism of BDE-47 on PS microplastics. pH had negligible impacts on BDE-47 sorption by virgin and aged PS. Sorption capacity of BDE-47 on aged PS in water with high salinity was lower than that on virgin PS, and DOM has less effect on the sorption of BDE-47 on aged PS.

Effects of Polyester Microfibers on Microphytobenthos and Sediment-Dwelling Infauna

Microfibers often dominate sediment microplastic samples, but little is known about their ecological effects on benthic organisms and functions. Polyethylene terephthalate) (PET) microfibers were added to 36 sediment chambers at six concentrations (0-0.5 g kg^-1 sediment) to assess the effects on microphytobenthos (MPB), a key deposit-feeding bivalve, Macomona liliana, and sediment nutrient pools. MPB photosynthesis was promoted in 18 chambers through a 12 h light/dark cycle. Another 18 chambers were maintained under dark conditions to inhibit photosynthesis. After 35 days of MPB growth and stabilization, four M. liliana were added to each chamber for a further 40 days. MPB biomass and composition were examined alongside M. liliana biochemical and behavioral properties and porewater dissolved inorganic nutrient concentrations. Increasing microfibers resulted in lower MPB biomass, fewer diatom-associated fatty acids (FAs), and an increase in cyanobacteria. The changes in MPB coincided with up to 75% lower energy reserves and reduced burrowing activity in M. liliana. In the light, nitrate + nitrate (NO_x) was significantly elevated and related to M. liliana and MPB biochemical properties. Ammoniu (NH₄⁺) concentrations increased but were variable in both the light and the dark. Our results suggest that increasing microfiber concentrations influence the interactions between M. liliana and MPB and affect biogeochemical processing in coastal marine sediments.

Exposure to a microplastic mixture is altering the life traits and is causing deformities in the non-biting midge Chironomus riparius Meigen (1804)

The effect of microplastics (MP) exposure on the chironomid species Chironomus riparius Meigen, 1804 was investigated using the OECD sediment and water toxicity test. Chironomid larvae were exposed to an environmentally relevant low microplastics concentration (LC), a high microplastics concentration (HC) and a control (C). The LC was 0.007 g m^-2 on the water surface + 2 g m^-3 in the water column + 8 g m^-2 in the sediment, and the HC was 10 X higher than this for each exposure. The size of the majority of the manufactured microplastic pellets varied between 20 and 100 μm. The MP mixture consisted of: polyethylene-terephtalate (PET), polystyrene (PS), polyvinyl-chloride (PVC) and polyamide (PA) in a ratio of 45%: 15%: 20%: 20%, respectively, for the sediment exposure; 100% polyethylene for the water column exposure; and 50% polyethylene: 50% polypropylene for the water surface exposure. Different endpoints were monitored, including morphological changes in the mandibles and mentums of 4th instar larvae, morphological changes in the wings, mortality, emergence ratio, and developmental time. A geometric morphometric analysis showed a tendency toward widening of the wings, elongation of the mentums and changing the shape of the mandibles in specimens exposed to both concentrations of microplastics. The development time of C. riparius was significantly prolonged by the MP treatment: 13.8 ± 0.5; 14.4 ± 0.6; and 15.3 ± 0.4 days (mean ± SD) in the C, LC, and HC, respectively. This study indicates that even environmentally relevant concentrations of MP mixture have a negative influence on C. riparius, especially at the larval stage.

Biofouling, metal sorption and aggregation are related to sinking of microplastics in a stratified reservoir

Microplastic particles entering aquatic systems are rapidly colonized by microbial biofilms. The presence of microbial biomass may cause sinking of particles and as a consequence prevent their transport to the oceans. We studied microbial colonization of different polymer particles exposed in the epi-, meta- and hypolimnion of a freshwater reservoir during late summer for 47 days. Parameters measured included biofilm formation, metal sorption and sinking velocities. Microbial biofilms contained bacteria, cyanobacteria and algae as well as inorganic particles such as iron oxides. Regardless of biofilm thickness and biovolumes of different biofilm constituents, single polyethylene (PE) particles stayed buoyant, whereas the sinking velocity of single polystyrene (PS) and polyethylene terephthalate (PET) particles did not change significantly compared to initial values. During exposition, a mixing event occurred, by which anoxic, iron-rich water from the hypolimnion was mixed with water from upper layers. This induced aggregation and sinking of hypolimnetic PE particles together with organic matter, cyanobacteria colonies and iron minerals.

Microplastics in aquatic environments: Toxicity to trigger ecological consequences

The prevalence of microplastic debris in aquatic ecosystems as a result of anthropogenic activity has received worldwide attention. Although extensive research has reported ubiquitous and directly adverse effects on organisms, only a few published studies have proposed the long-term ecological consequences. The research in this field still lacks a systematic overview of the toxic effects of microplastics and a coherent understanding of the potential ecological consequences. Here, we draw upon cross-disciplinary scientific research from recent decades to 1) seek to understand the correlation between the responses of organisms to microplastics and the potential ecological disturbances, 2) summarize the potential ecological consequences triggered by microplastics in aquatic environments, and 3) discuss the barriers to the understanding of microplastic toxicology. In this paper, the physiochemical characteristics and dynamic distribution of microplastics were related to the toxicological concerns about microplastic bioavailability and environmental perturbation. The extent of the ecological disturbances depends on how the ecotoxicity of microplastics is transferred and proliferated throughout an aquatic environment. Microplastics are prevalent; they interfere with nutrient productivity and cycling, cause physiological stress in organisms (e.g., behavioral alterations, immune responses, abnormal metabolism, and changes to energy budgets), and threaten the ecosystem composition and stability. By integrating the linkages among the toxicities that range from the erosion of individual species to the defective development of biological communities to the collapse of the ecosystem functioning, this review provides a bottom-up framework for future research to address the mechanisms underlying the toxicity of microplastics in aquatic environments and the substantial ecological consequences.

Mitigation strategies to reverse the rising trend of plastics in Polar Regions

Plastic marine pollution in the Arctic today illustrates the global distribution of plastic waste of all sizes traveling by wind and waves, entering food chains, and presenting challenges to management and mitigation. While currents move plastics from lower latitudes into the Arctic, significant waste is also generated by remote communities, as well as maritime activities, such as shipping, fishing and tourism, which are increasing their activities as seasonal sea ice diminishes. Mitigation strategies may include monitoring programs of plastic waste abundance and distribution, improved waste management in Arctic communities, Extended Producer Responsibility (EPR) to reverse the transport of waste plastics and packaging from remote communities, incentivized gear recovery of abandoned, lost and discarded fishing gear (ALDFG), gear tagging and tracking, and restricting tourism and employing "leave no trace" policies. Here we report how these mitigation strategies are employed in the Arctic to minimize plastic waste impacts, and move Arctic communities toward better materials management and circular economic practices. The evidence of harm from waste plastics exacerbated by the ubiquity of plastic marine pollution in all biomes, and the rapid reporting of ecological and social costs, together suggest that we know enough to act quickly to manage and mitigate plastics from all sources to the Arctic.