Microplastics Alter the Properties and Sinking Rates of Zooplankton Faecal Pellets

Bioavailability and effects of microplastics on marine zooplankton: A review

Microplastics are abundant and widespread in the marine environment. They are a contaminant of global environmental and economic concern. Due to their small size a wide range of marine species, including zooplankton can ingest them. Research has shown that microplastics are readily ingested by several zooplankton taxa, with associated negative impacts on biological processes. Zooplankton is a crucial food source for many secondary consumers, consequently this represents a route whereby microplastic could enter the food web and transfer up the trophic levels. In this review we aim to: 1) evaluate the current knowledge base regarding microplastic ingestion by zooplankton in both the laboratory and the field; and 2) summarise the factors which contribute to the bioavailability of microplastics to zooplankton. Current literature shows that microplastic ingestion has been recorded in 39 zooplankton species from 28 taxonomic orders including holo- and meroplanktonic species. The majority of studies occurred under laboratory conditions and negative effects were reported in ten studies (45%) demonstrating effects on feeding behaviour, growth, development, reproduction and lifespan. In contrast, three studies (14%) reported no negative effects from microplastic ingestion. Several physical and biological factors can influence the bioavailability of microplastics to zooplankton, such as size, shape, age and abundance. We identified that microplastics used in experiments are often different to those quantified in the marine environment, particularly in terms of concentration, shape, type and age. We therefore suggest that future research should include microplastics that are more representative of those found in the marine environment at relevant concentrations. Additionally, investigating the effects of microplastic ingestion on a broader range of zooplankton species and life stages, will help to answer key knowledge gaps regarding the effect of microplastic on recruitment, species populations and ultimately broader economic consequences such as impacts on shell- and finfish stocks.

Microplastics in juvenile Chinook salmon and their nearshore environments on the east coast of Vancouver Island

Microplastics are a significant issue in the world's oceans. These small plastic particles (<5 mm in size) are becoming globally ubiquitous in the marine environment and are ingested by various fish species. Here we investigate the incidence of microplastics in juvenile Chinook salmon and their nearshore marine environments on the east coast of Vancouver Island, British Columbia. We completed a series of beach seines, plankton tows and sediment cores in nearshore areas of importance to juvenile salmon. Microplastics were extracted from fish, water and sediment samples and concentrations were quantified. Microplastics analysis, consisting predominantly of fibrous plastics, showed juvenile Chinook salmon contained 1.2 ± 1.4 (SD) microplastics per individual while water and sediment samples had 659.9 ± 520.9 microplastics m^-3 and 60.2 ± 63.4 microplastics kg^-1 dry weight, respectively. We found no differences in microplastic concentrations in juvenile Chinook and water samples among sites but observed significantly higher concentrations in sediment at the Deep Bay site compared to Nanaimo and Cowichan Bay sites. Chinook microplastic concentrations were relatively low compared to literature values and, given the size and type of microplastics we observed, are unlikely to represent an immediate threat to fish in this area. However, microplastics less than 100 μm in size were not included in the study and may represent a greater threat due to their ability to translocate through tissues.

Smells good enough to eat: Dimethyl sulfide (DMS) enhances copepod ingestion of microplastics

Marine copepods have been shown to readily ingest microplastics - a crucial first step in the transfer of plastics into the marine food chain. Copepods have also been shown to elicit a foraging behavioural response to the presence of olfactory stimuli, such as dimethyl sulfide (DMS) - a volatile compound produced by their algal prey. Here, we show that the temperate Calanoid copepod Calanus helgolandicus displays enhanced grazing rates of between 0.7 and 3-fold (72%-292%) on microplastics that have been infused in a DMS solution, compared to DMS-free controls. Environmental exposure of microplastics may result in the development of an olfactory signature that includes algal-derived compounds such as DMS. Our study provides evidence that copepods, which are known to use chemosensory mechanisms to identify and locate dense sources of palatable prey, may be at an increased risk of plastic ingestion if it mimics the scent of their prey.

Interactions between microplastics and phthalate esters as affected by microplastics characteristics and solution chemistry

Microplastics have become a major concern in recent years as they can be recognized as the transport vectors for pollutants in environment. In this study, the sorption behavior of two phthalate esters (PAEs), including diethyl phthalate (DEP) and dibutyl phthalate (DBP), onto three types of microplastics (PVC: polyvinyl chloride, PE: polyethylene, and PS: polystyrene) was investigated. The sorption isotherms of both DEP and DBP on microplastics were highly linear, suggesting that the partition was the main sorption mechanism. The K_d values of DBP were much higher than those of DEP, demonstrating that hydrophobic interaction governed the partition mechanism. Sorption of the two PAEs on the three microplastics followed the order of PS > PE > PVC, indicating that chemical properties of microplastics played an important roles in their sorption behaviors. Solution pH and natural organic matter had no significant impact on PAEs sorption by microplastics. However, the presence of NaCl and CaCl₂ enhanced the sorption of both DEP and DBP because of the salting-out effect. The findings of the present study may have significant implications for the fate and transport assessment of both PAEs and microplastics.

The interactive effects of stratospheric ozone depletion, UV radiation, and climate change on aquatic ecosystems

Summary of current knowledge about effects of UV radiation in inland and oceanic waters related to stratospheric ozone depletion and climate change.

Effects of combined exposures of fluoranthene and polyethylene or polyhydroxybutyrate microplastics on oxidative stress biomarkers in the blue mussel (Mytilus edulis)

A growing interest in developing and commercialization of new eco-friendly plastic polymers is occurring attributed to the impact of marine plastics debris and microplastics that result from the degradation of oil-based polymers as these substances adversely affect ecosystem health. Recently, polyhydroxybutyrate (PHB) has become of interest due to its biodegradability and physicochemical properties. However, biological consequences resulting from bioplastics exposure remain to be determined. Further, few data are apparently available regarding the potential for bioplastics to act as a vector for exogenous chemicals in the environment. The aim of the study was to compare the effects of polyethylene (PE MPs) and polyhydroxybutyrate (PHB MPs) microplastics administered alone or in combination with fluoranthene (Flu) on detoxifying enzymes in digestive glands and gills of Mytilus edulis. Blue mussels were exposed for 96h to eight experimental groups: control, Flu-only, PE MPs-only, PHB MPs-only, PE MPs-Flu co-exposure, PHB MPs-Flu co-exposure, Flu-incubated PE MPs, and Flu-incubated PHB MPs. Activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPx), glutathione S-transferase (GST), and glutathione reductase (GR) were found to be significantly susceptible to Flu and plastics in both tissues. Interestingly, a single exposure to PHB MPs led to decreased activity levels of CAT and GST in gills, SOD in digestive glands and SeGPx in both tissues. In co-exposure and incubation treatments, biochemical responses were generally comparable with those exerted by PE MPs or PHB MPs only, suggesting an apparent absence of combined effects of microplastics with the pollutant. Data demonstrated the ecotoxicological impact of bioplastics materials on digestive glands and gills of Mytilus edulis.

Consistent microplastic ingestion by deep-sea invertebrates over the last four decades (1976-2015), a study from the North East Atlantic

Although evidence suggests the ubiquity of microplastics in the marine environment, our knowledge of its occurrence within remote habitats, such as the deep sea, is scarce. Furthermore, long term investigations of microplastic abundances are even more limited. Here we present a long-term study of the ingestion of microplastics by two deep-sea benthic invertebrates (Ophiomusium lymani and Hymenaster pellucidus) sampled over four decades. Specimens were collected between the years 1976-2015 from a repeat monitoring site >2000 m deep in the Rockall Trough, North East Atlantic. Microplastics were identified at a relatively consistent level throughout and therefore may have been present at this locality prior to 1976. Considering the mass production of plastics began in the 1940s - 50s our data suggest the relatively rapid occurrence of microplastics within the deep sea. Of the individuals examined (n = 153), 45% had ingested microplastics, of which fibres were most prevalent (95%). A total of eight different polymer types were isolated; polyamide and polyester were found in the highest concentrations and in the majority of years, while low-density polystyrene was only identified in 2015. This study provides an assessment of the historic occurrence of microplastics on the deep seafloor and presents a detailed quantification and characterisation of microplastics ingested by benthic species. Furthermore these data advance our knowledge on the long-term fate of microplastic in marine systems.

Rainbow Trout Maintain Intestinal Transport and Barrier Functions Following Exposure to Polystyrene Microplastics

Ingestion has been proposed as a prominent exposure route for plastic debris in aquatic organisms, including fish. While the consequences of ingestion of large plastic litter are mostly understood, the impacts resulting from ingestion of microplastics (MPs) are largely unknown. We designed a study that aimed to assess impacts of MPs on fish intestinal physiology and examined integrity of extrinsic, physical and immunological barriers. Rainbow trout were exposed to polystyrene (PS) MPs (100-400 μm) via feed for a period of 4 weeks. Fish were fed four types of diets: control, diets containing virgin PS particles, or particles exposed to two different environmental matrices (sewage or harbor effluent). Extrinsic barrier disturbance in intestinal tissue was evaluated via histology. The paracellular permeability toward ions and molecules was examined using Ussing chambers and mRNA expression analysis of tight junction proteins. Active transport was monitored as transepithelial potential difference, short-circuits current and uptake rate of amino acid ³H-lysine. Immune status parameters were measured through mRNA expression level of cytokines, lysozyme activity, and hematological analysis of immune cells. We could not show that PS MPs induced inflammatory responses or acted as physical or chemical hazards upon ingestion. No measurable effects were exerted on fish intestinal permeability, active transport or electrophysiology.

Occurrence and distribution of microplastics in an urban river: A case study in the Pearl River along Guangzhou City, China

Microplastics, as emerging contaminants in the global environment, have become a cause for concern for both academics and the public. The present understanding of microplastic pollution is primarily focused on marine environments, and less attention has been given to freshwater environments, in particular, to urban rivers. In this study, microplastics were sampled from surface water and sediments in 14 sites located in the lower course of the Pearl River. These sampling sites are located along Guangzhou of South China, with built-up areas being the dominant land use. The abundances of microplastics in surface water and sediments ranged from 379 to 7924 items·m^-3 and 80 to 9597 items·kg^-1, respectively. Polyethylene and polypropylene were the common types of microplastics, together accounting for 64.3% and 73.8% of surface water and sediment samples, respectively. Fibers were the dominant microplastic shapes in both water and sediment samples. The abundances of microplastics varied in surface water and sediments with each site, which might be affected by multiple factors. Our results indicated that wastewater treatment plants (WWTP) could reduce microplastics from municipal sewage which was finally discharged into the Pearl River along Guangzhou.

Microplastics integrating the coastal planktonic community in the inner zone of the Río de la Plata estuary (South America)

This study explores in plankton samples the abundance, distribution, size, types (fibres and fragments), colours of the microplastics (MPs) and its relation with the characteristics of the plankton (size and morphology) of the Río de la Plata estuary. Water samples were collected in triplicate in freshwater-mixohaline tidal zone of the estuary, in ten sampling sites located along 150 km of coast, in two periods (September-November 2016 and April-June 2017). The results revealed the presence of MPs in all the samples analysed, with a dominance of fibres and sizes >500 ≤ 1000 μm, and blue colour being more frequent. The MPs distribution was significantly different among sampling sites, being more abundant in the most urbanized sites, sewage discharges and near the maximum turbidity front. The mean density, in the two samplings analysed, were 164 and 114 MPs m^-3. The fibres amount was significantly different among sites. The MPs integrated a planktonic community dominated by pico-microphytoplankton, mainly conformed by filaments/chains and solitary forms and by micro-mesozooplankton. The comparative analysis of plankton and MPs demonstrated that a fraction of the latter showed a frequency range of size that coincides with the most common sizes of plankton (≤500 μm). The mean percentage of MPs items in relation to zooplankton was 0.36% (sampling 1) and 1.20% (sampling 2) and for phytoplankton was 0.0002% (sampling 1) and 0.0005% (sampling 2). The correlations between the MPs concentration and habitat quality (IHRPlata index) were statistically significant, on the contrary correlations between the MPs concentration and measured environmental variables were not found. The findings of this study emphasises the need for a better treatment of urban waste, which would contribute to reducing the entry of this pollutant into the ecosystem. The presence of microplastics in plankton samples on the coast of the Río de la Plata estuary.

Microplastic in marine organism: Environmental and toxicological effects

Microplastics are tiny ubiquitous plastic particles present in marine environments. They are not an individual entity, but constitute a cocktail of polymers and additives that can absorb substances from the surrounding environment, including living substances, nutrients and marine pollutants. Given their small size (< 5 μm), microplastics can be ingested by a wide range of marine organisms with the potential to cause harms. Microplastics are a growing threat for marine biota and ecosystem. For organisms, the risks associated with microplastic ingestion are not only due to the material itself, but also to its ability to absorb and concentrate environmental contaminants in seawater and subsequently transfer them through food chains. Moreover, microplastics could influence ecological processes. Recently, plastic debris are recognized as emerging pollutants and represent a great risk for marine biodiversity worldwide. Here, we summarize the main effects of plastics and microplastics on some marine organisms and ecosystem.

Perspectives on using marine species as bioindicators of plastic pollution

The ever-increasing level of marine pollution due to plastic debris is a globally recognized threat that needs effective actions of control and mitigation. Using marine organisms as bioindicators of plastic pollution can provide crucial information that would better integrate the spatial and temporal presence of plastic debris in the sea. Given their long and frequent migrations, numerous marine species that ingest plastics can provide information on the presence of plastic debris but only on large spatial and temporal scales, thus making it difficult to identify quantitative correlations of ingested plastics within well-defined spatio-temporal patterns. Given the complex dynamics of plastics in the sea, the biomonitoring of marine plastic debris should rely on the combination of several bioindicator species with different characteristics that complement each other. Other critical aspects include the standardization of sampling protocols, analytical detection methods and metrics to evaluate the effects of ingested plastics in marine species.

Horizontal and Vertical Distribution of Microplastics in Korean Coastal Waters

This is the first survey to investigate the vertical distribution and composition of microplastics >20 μm at the surface (0-0.2 m; bulk sample) and in the water column (3-58 m depth; pump) of six semi-enclosed bays and two nearshore areas of South Korea. The average microplastic abundance of 41 stations at all sampling depths was 871 particles/m³, and the microplastic abundance near urban areas (1051 particles/m³) was significantly higher than that near rural areas (560 particles/m³). Although the average microplastic abundances in the midcolumn (423 particles/m³) and bottom water (394 particles/m³) were approximately 4 times lower than that of surface water (1736 particles/m³), microplastics prevailed throughout the water column in concentrations of 10-2000 particles/m³. The average sizes of fragment and fiber type microplastics were 197 and 752 μm, respectively. Although the polymer composition differed by depth depending on the particle size and density, polypropylene and polyethylene predominated throughout the water column regardless of their low density and particle size. Finally, the middle and bottom water samples contained higher abundances of microplastics than predicted by a model based on physical mixing, indicating that biological interactions also influence the downward movement of low-density microplastics.

Size-selective feeding of Arenicola marina promotes long-term burial of microplastic particles in marine sediments

Despite of their ubiquitous distribution in marine sediments, the role of benthic fauna in microplastic transport at the sea floor has received little attention yet. The present study investigated the influence of bioturbation activity of the polychaete Arenicola marina on microplastic transport and burial in marine sediments. Sediment ingestion was assessed in a long term mesocosm experiment with exposure times ranging from 106 to 240 days, using three particle tracers with different particle diameters (microplastic: 500 and 1000 μm, respectively; luminophores: 130 μm). Sediment grain size distributions were assessed after experiment termination in all feeding layers at 8-12 cm depth to determine the influence of size-selective feeding of A. marina on median grain size and microplastic retention. Burial of microplastic occurred in all mesocosms up to a depth of 20 cm and was strongly dependent on individual sediment feeding rates. For low bioturbation conditions, both microplastic and luminophore concentrations exhibited an exponential decrease with increasing sediment depth, indicating particle burial via feeding funnel transport. Particle concentrations remained high in the uppermost 4 cm of the sediment. At high bioturbation rates, no microplastic particles remained in near-surface sediment layers, but a distinct accumulation of microplastic was observed in the feeding layer, suggesting the discrimination of plastic particles during feeding. In contrast, luminophores displayed a similar accumulation, but additionally showed uniform distributions above feeding layers, indicating ingestion and defecation by polychaetes. In accordance with these findings, an overall coarsening of median grain sizes was observed in all feeding layers, indicating the retention of large microplastic due to size-selective feeding. These findings demonstrate the ability of the conveyor belt-feeding polychaete A. marina to promote unidirectional transports of microplastic ≥500 μm and the potential for the long-term retention of these particles in marine sediments.

Microplastics in seawater and zooplankton from the Yellow Sea

Marine plastic pollution is a worldwide problem. Microplastics (MPs) are the predominant form of marine plastic debris, a form small enough to be ingested by and potentially harm marine organisms. It is urgent to develop ecologically relevant metrics for the risk assessment of MPs based on in situ data, especially for coastal areas. For the first time, we performed a comprehensive study of the characteristics of MPs in seawater and zooplankton in the Yellow Sea. For MPs in seawater, the average concentration is 0.13 ± 0.20 pieces/m³, dominated by fragments (42%). The average size is 3.72 ± 4.70 mm, with the most frequent size appearing at 1200 μm. The major polymer types are polypropylene and polyethylene, accounting for 88.13% in total. The distribution of MPs in seawater is patchy, with high MP concentrations close to the coastal cities. The average concentration of MPs in 11 total zooplankton groups is 12.24 ± 25.70 pieces/m³. The average size is 154.62 ± 152.90 μm, with 90% being <500 μm. Fiber is the dominant shape of MPs found in zooplankton, accounting for 46%, but the composition of the polymer type is diverse. The retention of MPs in zooplankton depends on the taxa and their abundance in the Yellow Sea. Siphonophorea, Copepoda, Euphausiacea and Amphipoda are the main repositories compared to other groups, achieving 3.57, 2.44, 1.41 and 1.36 pieces/m³, respectively. The high concentration area of MPs in zooplankton appeared near the adjacent waters of the Yangtze estuary. These results prove that zooplankton act as a repository for MPs in coastal waters. The retention of MPs in zooplankton is recommended as a key index for further ecological risk assessment of MPs.

Retention and characteristics of microplastics in natural zooplankton taxa from the East China Sea

The ubiquitous presence and persistence of microplastics (MPs) in aquatic environments have become of particular concern in recent years. Biological interactions are among the key processes that affect the impact and fate of MPs in the oceans. Zooplankton is one of the most sensitive taxa because their prey is approximately the same size as MPs. However, the status of MPs in zooplankton within natural marine environments remains largely unknown. By focusing on zooplankton in the East China Sea, the characteristics, bioaccumulated concentration, and retention of MPs for 10 zooplankton groups were systematically studied. Three types of MPs were found in zooplankton: fibres, pellets, and fragments. The fibres (54.6%) were more common than the other two types. The average lengths of the fibres, pellets, and fragments were 295.2 ± 348.6 μm, 20.3 ± 11.0 μm, and 82.4 ± 80.5 μm, respectively. Nineteen polymers were detected in the zooplankton via the Thermo Scientific Nicolet iN10 Infrared Microscope. Polymerized oxidized organic material and polyester were dominant, accounting for 35.9% and 25.6% of the polymers, respectively. The bioaccumulated concentration of MPs in the 10 zooplankton taxa varied from 0.13 pieces/zooplankton for Copepoda to 0.35 pieces/zooplankton for Pteropoda. The bioaccumulated concentration was negatively correlated with the abundance of zooplankton, showing a significant biological dilution effect. The bioaccumulated concentration was also influenced by the feeding mode of zooplankton, showing a trend of omnivorous > carnivorous > herbivorous. High retention of MPs was found in the zooplankton community of the East China Sea, achieving 19.7 ± 22.4 pieces/m³. This is much higher than the MP retention in zooplankton from other reported sea areas. By revealing the characteristics and retention of MPs in the natural zooplankton taxa from the East China Sea, this research identified the influence that MPs have on zooplankton in a typical coastal environment. This information can be utilized for subsequent controlled experiments and risk assessments.

Preferential accumulation of small (<300 μm) microplastics in the sediments of a coastal plain river network in eastern China

Microplastics are a global concern for their threat to marine ecosystems. Recent studies report a lack of smaller microplastics (<300 μm) in oceans attributed to a "loss in ocean". Several hypotheses have been proposed to explain the absence of smaller microplastics, but their fate and transport remain an enigma. Our study recovered high concentrations of microplastics (32947 ± 15342 items kg^-1 dry sediment) from sediments of a coastal plain river network in eastern China, with the <300 μm fraction accounting for ∼85% of total microplastic particles. Microplastic concentrations were generally higher in sediments from tributary streams and streams surrounded by industrial land use. The high variability of microplastics within the watershed indicates that the distribution of microplastics is regulated by several factors, such as distance to source(s), river flow characteristics, buoyancy behavior, degradation, etc. Fragment and foam forms dominated the small microplastics, while fibers were less prevalent in the <300 μm fraction and more abundant in downstream sites. The dominance of small microplastics in riverine sediments in this study provides a possible mechanism to explain the relative absence of small microplastics in the ocean, and advocates for quantification of the whole size spectrum of microplastics in future studies of riverine microplastic fluxes.

Double trouble in the South Pacific subtropical gyre: Increased plastic ingestion by fish in the oceanic accumulation zone

Fish are an important food source for South Pacific (SP) island countries, yet there is little information on contamination of commercial marine fish species by plastic. The aim of our study was to perform a broad-scale assessment of plastic ingestion by fish common in the diet of SP inhabitants. We examined 932 specimens from 34 commercial fish species across four SP locations, and some of the prey they ingested, for the presence of marine plastics. Plastic was found in 33 species, with an average ingestion rate (IR) of 24.3 ± 1.4% and plastic load of 2.4 ± 0.2 particles per fish. Rapa Nui fish exhibited the greatest IR (50.0%), significantly greater than in other three locations. Rapa Nui is located within the SP subtropical gyre, where the concentration of marine plastics is high and food is limited. Plastic was also found in prey, which confirms the trophic transfer of microplastics.

Polymer Identification of Plastic Debris Ingested by Pelagic-Phase Sea Turtles in the Central Pacific

Pelagic Pacific sea turtles eat relatively large quantities of plastic (median 5 g in gut). Using Fourier transform infrared spectroscopy, we identified the polymers ingested by 37 olive ridley, 9 green, and 4 loggerhead turtles caught as bycatch in Hawaii- and American Samoa-based longline fisheries. Unidentifiable samples were analyzed using high-temperature size exclusion chromatography with multiple detectors and/or X-ray photoelectron spectroscopy. Regardless of species differences in dive depths and foraging strategies, ingested plastics were primarily low-density, floating polymers (51% low-density polyethylene (LDPE), 26% polypropylene (PP), 10% unknown polyethylene (PE), and 5% high-density PE collectively). Albeit not statistically significant, deeper diving and deeper captured olive ridley turtles ate proportionally more plastics expected to sink (3.9%) than intermediate-diving green (1.2%) and shallow-diving loggerhead (0.3%) turtles. Spatial, but no sex, size, year, or hook depth differences were observed in polymer composition. LDPE and PP, some of the most produced and least recycled polymers worldwide, account for the largest percentage of plastic eaten by sea turtles in this region. These novel data inform managers about the threat of plastic ingestion to sea turtles and may motivate development of more environmentally friendly practices for plastic production, use, and waste management.

Polystyrene microplastics increase microbial release of marine Chromophoric Dissolved Organic Matter in microcosm experiments

About 5 trillion plastic particles are present in our oceans, from the macro to the micro size. Like any other aquatic particulate, plastics and microplastics can create a micro-environment, within which microbial and chemical conditions differ significantly from the surrounding water. Despite the high and increasing abundance of microplastics in the ocean, their influence on the transformation and composition of marine organic matter is largely unknown. Chromophoric dissolved organic matter (CDOM) is the photo-reactive fraction of the marine dissolved organic matter (DOM) pool. Changes in CDOM quality and quantity have impacts on marine microbial dynamics and the underwater light environment. One major source of CDOM is produced by marine bacteria through their alteration of pre-existing DOM substrates. In a series of microcosm experiments in controlled marine conditions, we explored the impact of microplastics on the quality and quantity of microbial CDOM. In the presence of microplastics we observed an increased production of CDOM with changes in its molecular weight, which resulted from either an increased microbial CDOM production or an enhanced transformation of DOM from lower to higher molecular weight CDOM. Our results point to the possibility that marine microplastics act as localized hot spots for microbial activity, with the potential to influence marine carbon dynamics.

Phytoplankton response to polystyrene microplastics: Perspective from an entire growth period

Microplastics are widely identified in aquatic environments, but their impacts on phytoplankton have not been extensively studied. Here, the responses of Chlorella pyrenoidosa under polystyrene (PS) microplastics exposure were studied across its whole growth period, with microplastic sizes of 0.1 and 1.0 μm and 3 concentration gradients each, which covered (10 and 50 mg/L) and exceeded (100 mg/L) its environmental concentrations, respectively. PS microplastics caused dose-dependent adverse effects on Chlorella pyrenoidosa growth from the lag to the earlier logarithmic phases, but exhibited slight difference in the maximal inhibition ratio (approximately 38%) with respect to the two microplastic sizes. In addition to the reduced photosynthetic activity of Chlorella pyrenoidosa, unclear pyrenoids, distorted thylakoids and damaged cell membrane were observed, attributing to the physical damage and oxidative stress caused by microplastics. However, from the end of the logarithmic to the stationary phase, Chlorella pyrenoidosa could reduce the adverse effects of microplastics jointly through cell wall thickening, algae homo-aggregation and algae-microplastics hetero-aggregation, hence triggering an increase of algal photosynthetic activity and its growth, and cell structures turned to normal. Our study confirmed that PS microplastics can impair but then enhance algae growth, which will be helpful in understanding the ecological risks of microplastics.

The impact of nanoplastics on marine dissolved organic matter assembly

The environmental impact of nanoplastics (NPs) released into natural aquatic surroundings is an increasing concern. NPs are widely generated from our daily waste disposal and eventually reach the ocean, wherein consequent influences on aquatic environments remain unclear. In this regard, there are few studies investigating NP-related ecological impacts. Comprising one of Earth's major carbon pools, marine dissolved organic matter (DOM) serves an essential role in global carbon dynamics. The spontaneous assembly of DOM into particulate organic matter (POM) plays important roles in the marine carbon cycle, and is involved in hemostasis of various ecological communities. Here, we report that 10 ppb NPs (polystyrene/polymethyl methacrylate, 25 nm) appeared in a water column accelerate the kinetic assembly rate of DOM-POM transition. NPs with various characteristics show similar influences on DOM assembly, and seawater samples collected from disparate sites were used to further confirm this unanticipated phenomenon. In this study, we demonstrated that hydrophobic interactions contribute to the facilitation of NP-DOM aggregations. Our results illustrate that NPs alter DOM-POM assembly, which may potentiate unanticipated perturbation to the largest marine carbon pool. Such effects would warrant increased vigilance on current practices of plastic usage and disposal.

Laser Ablation as a Versatile Tool To Mimic Polyethylene Terephthalate Nanoplastic Pollutants: Characterization and Toxicology Assessment

The presence of micro- and nanoplastics in the marine environment is raising strong concerns since they can possibly have a negative impact on human health. In particular, the lack of appropriate methodologies to collect the nanoplastics from water systems imposes the use of engineered model nanoparticles to explore their interactions with biological systems, with results not easily correlated with the real case conditions. In this work, we propose a reliable top-down approach based on laser ablation of polymers to form polyethylene terephthalate (PET) nanoplastics, which mimic real environmental nanopollutants, unlike synthetic samples obtained by colloidal chemistry. PET nanoparticles were carefully characterized in terms of chemical/physical properties and stability in different media. The nanoplastics have a ca. 100 nm average dimension, with significant size and shape heterogeneity, and they present weak acid groups on their surface, similarly to photodegraded PET plastics. Despite no toxic effects emerging by in vitro studies on human Caco-2 intestinal epithelial cells, the formed nanoplastics were largely internalized in endolysosomes, showing intracellular biopersistence and long-term stability in a simulated lysosomal environment. Interestingly, when tested on a model of intestinal epithelium, nano-PET showed high propensity to cross the gut barrier, with unpredictable long-term effects on health and potential transport of dispersed chemicals mediated by the nanopollutants.

Microplastics in Small Waterbodies and Tadpoles from Yangtze River Delta, China

Although microplastic (MP) pollution in freshwater systems is gaining attention, our knowledge of its distribution in small waterbodies is scarce. Small waterbodies are freshwater habitats to many species, including amphibians, that are vulnerable to MP pollution. This study analyzed the distribution and characteristics of MPs in 25 small waterbodies from the Yangtze River Delta, China. MPs were detected in surface water, sediment, and tadpoles with abundances ranging from 0.48 to 21.52 items L^-1, 35.76 to 3185.33 items kg^-1, and 0 to 2.73 items individual^-1 (0 to 168.48 items g^-1), respectively. The dominant shape and polymer of MPs in water and tadpole samples were polyester (PES) fibers, and polypropylene (PP) fibers and fragments were dominant in sediment samples. In addition, MPs were primarily <0.5 mm in length in all samples. Tadpole length was positively correlated to the number of MPs detected. The abundance, shape, and polymer distribution of MPs in tadpoles resembled that of water rather than sediment, suggesting that tadpoles likely take up MPs from the surrounding water. This study demonstrated that MPs are abundant in these small waterbodies and are ingested by resident tadpoles. This may suggest a pathway of MP entry into aquatic and terrestrial food webs.

Microplastic pollution in China's inland water systems: A review of findings, methods, characteristics, effects, and management

The pollution of marine environments and inland waters by plastic debris has raised increasing concerns worldwide in recent years. China is the world's largest developing country and the largest plastic producer. In this review, we gather available information on microplastic pollution in China's inland water systems. The results show that microplastics are ubiquitous in the investigated inland water systems, and high microplastic abundances were observed in developed areas. Although similar sampling and analytical methods were used for microplastic research in inland water and marine systems, methods of investigation should be standardized in the future. The characteristics of the detected microplastics suggest secondary sources as their major sources. The biological and ecological effects of microplastics have been demonstrated, but their risks are difficult to determine at this stage due to the discrepancy between the field-collected microplastics and microplastics used in ecotoxicological studies. Although many laws and regulations have already been established to manage and control plastic waste in China, the implementation of these laws and regulations has been ineffective and sometimes difficult. Several research priorities are identified, and we suggest that the Chinese government should be more proactive in tackling plastic pollution problems to protect the environment and fulfill international responsibilities.

Degradation of plastics and plastic-degrading bacteria in cold marine habitats

Synthetic plastics present in everyday materials constitute the main anthropogenic debris entering the Earth’s oceans. The oceans provide important and valuable resources such as food, energy, and water. They are also the main way of international trade and the main stabilizer of the climate. Hence, changes in the marine ecosystem caused by anthropogenic influences such as plastic pollution can have a dramatic impact on a global scale. Although the problem of plastics still remains unsolved, different ways are being considered to reduce their impact on the environment. One of them is to use microorganisms capable of degradation of plastic. A particularly interesting area is the application of microorganisms isolated from cold regions in view of their unique characteristics. Nevertheless, the interactions between plastic and microorganisms are still poorly known. Here, we present a review of current knowledge on plastic degradation and plastic-microorganism interactions in cold marine habitats. Moreover, we highlight the advantages of microorganisms isolated from this environment for eliminating plastic waste from ecosystems.

Role of Marine Snows in Microplastic Fate and Bioavailability

Microplastics contaminate global oceans and are accumulating in sediments at levels thought sufficient to leave a permanent layer in the fossil record. Despite this, the processes that vertically transport buoyant polymers from surface waters to the benthos are poorly understood. Here we demonstrate that laboratory generated marine snows can transport microplastics of different shapes, sizes, and polymers away from the water surface and enhance their bioavailability to benthic organisms. Sinking rates of all tested microplastics increased when incorporated into snows, with large changes observed for the buoyant polymer polyethylene with an increase in sinking rate of 818 m day^-1 and for denser polyamide fragments of 916 m day^-1. Incorporation into snows increased microplastic bioavailability for mussels, where uptake increased from zero to 340 microplastics individual^-1 for free microplastics to up to 1.6 × 10⁵ microplastics individual^-1 when incorporated into snows. We therefore propose that marine snow formation and fate has the potential to play a key role in the biogeochemical processing of microplastic pollution.

Exposure to polystyrene nanoplastic leads to inhibition of anaerobic digestion system

In this study, impacts of nanoplastic on the pure and mixed anaerobic digestion systems were investigated. Results showed the growth and metabolism of Acetobacteroides hydrogenigenes were partly inhibited by nanoplastic existed in the pure anaerobic digestion system. The anaerobic digestion of sewage sludge was also obviously inhibited by nanoplastic existed in the mixed anaerobic digestion system. Both the methane yield and methane production rate of the mixed anaerobic digestion system showed negative correlation with the nanoplastic concentration. Compared with anaerobic digestion system without nanoplastic, methane yield and maximum daily methane yield at the nanoplastic concentration of 0.2g/L decreased for 14.4% and 40.7%, respectively. In addition, the start-up of mixed anaerobic digestion system was prolonged by addition of nanoplastic. Microbial community structure analysis indicated the microbial community structures were also affected by nanoplastic existed in the system. At the nanoplastic concentration of 0.2g/L, the relative abundances of family Cloacamonaceae, Porphyromonadaceae, Anaerolinaceae and Gracilibacteraceae decreased partly. Conversely, the relative abundances of family Anaerolinaceae, Clostridiaceae, Geobacteraceae, Dethiosulfovibrionaceae and Desulfobulbaceae improved partly.

Microplastics in sub-surface waters of the Arctic Central Basin

Polar oceans, though remote in location, are not immune to the accumulation of plastic debris. The present study, investigated for the first time, the abundance, distribution and composition of microplastics in sub-surface waters of the Arctic Central Basin. Microplastic sampling was carried out using the bow water system of icebreaker Oden (single depth: 8.5 m) and CTD rosette sampler (multiple depths: 8-4369 m). Potential microplastics were isolated and analysed using Fourier Transform Infrared Spectroscopy (FT-IR). Bow water sampling revealed that the median microplastic abundance in near surface waters of the Polar Mixed Layer (PML) was 0.7 particles m^-3. Regarding the vertical distribution of microplastics in the ACB, microplastic abundance (particles m^-3) in the different water masses was as follows: Polar Mixed Layer (0-375) > Deep and bottom waters (0-104) > Atlantic water (0-95) > Halocline i.e. Atlantic or Pacific (0-83).

Microplastics Affect Energy Balance and Gametogenesis in the Pearl Oyster Pinctada margaritifera

Plastic pollution in the environment is increasing at global scale. Microplastics (MP) are derived from degradation of larger plastic items or directly produced in microparticles form (< 5 mm). Plastics, widely used in structures and equipment of pearl farming, are a source of pollution to the detriment of the lagoon ecosystem. To evaluate the impact of MP on the physiology of Pinctada margaritifera, a species of ecological and commercial interests, adult oysters were exposed to polystyrene microbeads (micro-PS of 6 and 10 μm) for 2 months. Three concentrations, 0.25, 2.5, and 25 μg L^-1, and a control were tested. Ingestion and respiration rate and assimilation efficiency were monitored on a metabolic measurement system to determine the individual energy balance (Scope For Growth, SFG). Effects on reproduction were also assessed. The assimilation efficiency decreased significantly according to micro-PS concentration. The SFG was significantly impacted by a dose-dependent decrease from 0.25 μg L^-1 ( p < 0.0001), and a negative SFG was measured in oysters exposed to 25 μg L^-1. Gonads may have provided the missing energy to maintain animals' metabolism through the production of metabolites derived from germ cells phagocytosis. This study shows that micro-PS significantly impact the assimilation efficiency and more broadly the energy balance of P. margaritifera, with negative repercussions on reproduction.

Effects of inorganic ions and natural organic matter on the aggregation of nanoplastics

The aggregation of nanoplastics (NPs) is a key issue in understanding the dynamic nature of NPs in the environment. The aggregation of NPs under various environmental conditions has not yet been studied. We investigated the influences of inorganic ions and natural organic matter (NOM) on polystyrene (PS) NPs aggregation in solutions. Results showed that PS NPs remained stable in wide ionic strength solutions of NaCl (1-100 mM) and CaCl₂ (0.1-15 mM), and only in low ionic strength FeCl₃ solutions (0.01 mM). However, obvious PS NPs aggregation was observed in FeCl₃ solutions with an increase in ionic strength (0.1 and 1 mM). Moreover, NOM had a negligible effect on PS NPs aggregation in all ionic strengths of NaCl and CaCl₂ solutions and in low ionic strength FeCl₃ solutions (0.01 mM). However, NOM reduced PS NPs aggregation in an intermediate ionic strength FeCl₃ (0.1 mM) solution and increased aggregation in a high ionic strength FeCl₃ (1 mM) solution. Based on the theoretical analysis of interaction forces among PS NPs, the Derjaguin-Landau-Verwey-Overbeek force was a contributor governing PS NPs aggregation either in the absence or presence of NOM. In addition, other factors, including electrostatic heterogeneity of PS NPs surfaces, steric repulsion induced by NOM, and clusters formed via bridging effect in the presence of NOM also contributed to altered PS NPs aggregation under selected conditions. The PS NPs-NOM clusters were directly observed using a cryogenic scanning electron microscope.

Microplastic pollution identified in deep-sea water and ingested by benthic invertebrates in the Rockall Trough, North Atlantic Ocean

Microplastics are widespread in the natural environment and present numerous ecological threats. While the ultimate fate of marine microplastics are not well known, it is hypothesized that the deep sea is the final sink for this anthropogenic contaminant. This study provides a quantification and characterisation of microplastic pollution ingested by benthic macroinvertebrates with different feeding modes (Ophiomusium lymani, Hymenaster pellucidus and Colus jeffreysianus) and in adjacent deep water > 2200 m, in the Rockall Trough, Northeast Atlantic Ocean. Despite the remote location, microplastic fibres were identified in deep-sea water at a concentration of 70.8 particles m^-3, comparable to that in surface waters. Of the invertebrates examined (n = 66), 48% ingested microplastics with quantities enumerated comparable to coastal species. The number of ingested microplastics differed significantly between species and generalized linear modelling identified that the number of microplastics ingested for a given tissue mass was related to species and not organism feeding mode or the length or overall weight of the individual. Deep-sea microplastics were visually highly degraded with surface areas more than double that of pristine particles. The identification of synthetic polymers with densities greater and less than seawater along with comparable quantities to the upper ocean indicates processes of vertical re-distribution. This study presents the first snapshot of deep ocean microplastics and the quantification of microplastic pollution in the Rockall Trough. Additional sampling throughout the deep-sea is required to assess levels of microplastic pollution, vertical transportation and sequestration, which have the potential to impact the largest global ecosystem.

Aging of microplastics promotes their ingestion by marine zooplankton

Microplastics (<5 mm) are ubiquitous in the marine environment and are ingested by zooplankton with possible negative effects on survival, feeding, and fecundity. The majority of laboratory studies has used new and pristine microplastics to test their impacts, while aging processes such as weathering and biofouling alter the characteristics of plastic particles in the marine environment. We investigated zooplankton ingestion of polystyrene beads (15 and 30 μm) and fragments (≤30 μm), and tested the hypothesis that microplastics previously exposed to marine conditions (aged) are ingested at higher rates than pristine microplastics. Polystyrene beads were aged by soaking in natural local seawater for three weeks. Three zooplankton taxa ingested microplastics, excluding the copepod Pseudocalanus spp., but the proportions of individuals ingesting plastic and the number of particles ingested were taxon and life stage specific and dependent on plastic size. All stages of Calanus finmarchicus ingested polystyrene fragments. Aged microbeads were preferred over pristine ones by females of Acartia longiremis as well as juvenile copepodites CV and adults of Calanus finmarchicus. The preference for aged microplastics may be attributed to the formation of a biofilm. Such a coating, made up of natural microbes, may contain similar prey as the copepods feed on in the water column and secrete chemical exudates that aid chemodetection and thus increase the attractiveness of the particles as food items. Much of the ingested plastic was, however, egested within a short time period (2-4 h) and the survival of adult Calanus females was not affected in an 11-day exposure. Negative effects of microplastics ingestion were thus limited. Our findings emphasize, however, that aging plays an important role in the transformation of microplastics at sea and ingestion by grazers, and should thus be considered in future microplastics ingestion studies and estimates of microplastics transfer into the marine food web.

A small-scale, portable method for extracting microplastics from marine sediments

Microplastics (plastic particles, 0.1 μm-5 mm in size) are widespread marine pollutants, accumulating in benthic sediments and shorelines the world over. To gain a clearer understanding of microplastic availability to marine life, and the risks they pose to the health of benthic communities, ecological processes and food security, it is important to obtain accurate measures of microplastic abundance in marine sediments. To date, methods for extracting microplastics from marine sediments have been disadvantaged by complexity, expense, low extraction efficiencies and incompatibility with very fine sediments. Here we present a new, portable method to separate microplastics from sediments of differing types, using the principle of density floatation. The Sediment-Microplastic Isolation (SMI) unit is a custom-built apparatus which consistently extracted microplastics from sediments in a single step, with a mean efficiency of 95.8% (±SE 1.6%; min 70%, max 100%). Zinc chloride, at a density of 1.5 g cm^-3, was deemed an effective and relatively inexpensive floatation media, allowing fine sediment to settle whilst simultaneously enabling floatation of dense polymers. The method was validated by artificially spiking sediment with low and high density microplastics, and its environmental relevance was further tested by extracting plastics present in natural sediment samples from sites ranging in sediment type; fine silt/clay (mean size 10.25 ± SD 3.02 μm) to coarse sand (mean size 149.3 ± SD 49.9 μm). The method presented here is cheap, reproducible and is easily portable, lending itself for use in the laboratory and in the field, eg. on board research vessels. By employing this method, accurate estimates of microplastic type, distribution and abundance in natural sediments can be achieved, with the potential to further our understanding of the availability of microplastics to benthic organisms.

The Deposition and Accumulation of Microplastics in Marine Sediments and Bottom Water from the Irish Continental Shelf

Microplastics are widely dispersed throughout the marine environment. An understanding of the distribution and accumulation of this form of pollution is crucial for gauging environmental risk. Presented here is the first record of plastic contamination, in the 5 mm-250 μm size range, of Irish continental shelf sediments. Sixty-two microplastics were recovered from 10 of 11 stations using box cores. 97% of recovered microplastics were found to reside shallower than 2.5 cm sediment depth, with the area of highest microplastic concentration being the water-sediment interface and top 0.5 cm of sediments (66%). Microplastics were not found deeper than 3.5 ± 0.5 cm. These findings demonstrate that microplastic contamination is ubiquitous within superficial sediments and bottom water along the western Irish continental shelf. Results highlight that cores need to be at least 4-5 cm deep to quantify the standing stock of microplastics within marine sediments. All recovered microplastics were classified as secondary microplastics as they appear to be remnants of larger items; fibres being the principal form of microplastic pollution (85%), followed by broken fragments (15%). The range of polymer types, colours and physical forms recovered suggests a variety of sources. Further research is needed to understand the mechanisms influencing microplastic transport, deposition, resuspension and subsequent interactions with biota.

Interactions between polystyrene microplastics and marine phytoplankton lead to species-specific hetero-aggregation

To understand the fate and impacts of microplastics (MP) in the marine ecosystems, it is essential to investigate their interactions with phytoplankton as these may affect MP bioavailability to marine organisms as well as their fate in the water column. However, the behaviour of MP with marine phytoplanktonic cells remains little studied and thus unpredictable. The present study assessed the potential for phytoplankton cells to form hetero-aggregates with small micro-polystyrene (micro-PS) particles depending on microalgal species and physiological status. A prymnesiophycea, Tisochrysis lutea, a dinoflagellate, Heterocapsa triquetra, and a diatom, Chaetoceros neogracile, were exposed to micro-PS (2 μm diameter; 3.96 μg L^-1) during their growth culture cycles. Micro-PS were quantified using an innovative flow-cytometry approach, which allowed the monitoring of the micro-PS repartition in microalgal cultures and the distinction between free suspended micro-PS and hetero-aggregates of micro-PS and microalgae. Hetero-aggregation was observed for C. neogracile during the stationary growth phase. The highest levels of micro-PS were "lost" from solution, sticking to flasks, with T. lutea and H. triquetra cultures. This loss of micro-PS sticking to the flask walls increased with the age of the culture for both species. No effects of micro-PS were observed on microalgal physiology in terms of growth and chlorophyll fluorescence. Overall, these results highlight the potential for single phytoplankton cells and residual organic matter to interact with microplastics, and thus potentially influence their distribution and bioavailability in experimental systems and the water column.

Distribution and importance of microplastics in the marine environment: A review of the sources, fate, effects, and potential solutions

The presence of microplastics in the marine environment poses a great threat to the entire ecosystem and has received much attention lately as the presence has greatly impacted oceans, lakes, seas, rivers, coastal areas and even the Polar Regions. Microplastics are found in most commonly utilized products (primary microplastics), or may originate from the fragmentation of larger plastic debris (secondary microplastics). The material enters the marine environment through terrestrial and land-based activities, especially via runoffs and is known to have great impact on marine organisms as studies have shown that large numbers of marine organisms have been affected by microplastics. Microplastic particles have been found distributed in large numbers in Africa, Asia, Southeast Asia, India, South Africa, North America, and in Europe. This review describes the sources and global distribution of microplastics in the environment, the fate and impact on marine biota, especially the food chain. Furthermore, the control measures discussed are those mapped out by both national and international environmental organizations for combating the impact from microplastics. Identifying the main sources of microplastic pollution in the environment and creating awareness through education at the public, private, and government sectors will go a long way in reducing the entry of microplastics into the environment. Also, knowing the associated behavioral mechanisms will enable better understanding of the impacts for the marine environment. However, a more promising and environmentally safe approach could be provided by exploiting the potentials of microorganisms, especially those of marine origin that can degrade microplastics.

CAPSULE

The concentration, distribution sources and fate of microplastics in the global marine environment were discussed, so also was the impact of microplastics on a wide range of marine biota.

From the sea to the laboratory: Characterization of microplastic as prerequisite for the assessment of ecotoxicological impact

The presence of microplastic (MP) in the aquatic environment is recognized as a global-scale pollution issue. Secondary MP particles result from an ongoing fragmentation process governed by various biotic and abiotic factors. For a reliable risk assessment of these MP particles, knowledge about interactions with biota is needed. However, extensive testing with standard organisms under reproducible laboratory conditions with well-characterized MP suspensions is not available yet. As MP in the environment represents a mixture of particles differing in properties (e.g., size, color, polymer type, surface characteristics), it is likely that only specific particle fractions pose a threat towards organisms. In order to assign hazardous effects to specific particle properties, these characteristics need to be analyzed. As shown by the testing of particles (e.g. nanoparticles), characteristics other than chemical properties are important for the emergence of toxicity in organisms, and parameters such as surface area or size distribution need consideration. Therefore, the use of "well-defined" particles for ecotoxicological testing (i.e., standard particles) facilitates the establishment of causal links between physical-chemical properties of MP particles and toxic effects in organisms. However, the benefits of well-defined particles under laboratory conditions are offset by the disadvantage of the unknown comparability with MP in the environment. Therefore, weathering effects caused by biological, chemical, physical or mechanical processes have to be considered. To date, the characterization of the progression of MP weathering based on powder and suspension characterization methods is in its infancy. The aim of this commentary is to illustrate the prerequisites for testing MP in the laboratory from 3 perspectives: (i) knowledge of particle properties; (ii) behavior of MP in test setups involving ecotoxicological test organisms; and (iii) accordingly, test conditions that may need adjustment. Only under those prerequisites will reliable hazard assessment of MP be feasible. Integr Environ Assess Manag 2017;13:500-504. © 2017 SETAC.

Microplastics Affect the Ecological Functioning of an Important Biogenic Habitat

Biological effects of microplastics on the health of bivalves have been demonstrated elsewhere, but ecological impacts on the biodiversity and ecosystem functioning of bivalve-dominated habitats are unknown. Thus, we exposed intact sediment cores containing European flat oysters (Ostrea edulis) or blue mussels (Mytilus edulis) in seawater to two different densities (2.5 or 25 μg L^-1) of biodegradable or conventional microplastics in outdoor mesocosms. We hypothesized that filtration rates of the bivalves, inorganic nitrogen cycling, primary productivity of sediment dwelling microphytobenthos, and the structure of invertebrate benthic assemblages would be influenced by microplastics. After 50 days, filtration by M. edulis was significantly less when exposed to 25 μg L^-1 of either type of microplastics, but there were no effects on ecosystem functioning or the associated invertebrate assemblages. Contrastingly, filtration by O. edulis significantly increased when exposed to 2.5 or 25 μg L^-1 of microplastics, and porewater ammonium and biomass of benthic cyanobacteria decreased. Additionally the associated infaunal invertebrate assemblages differed, with significantly less polychaetes and more oligochaetes in treatments exposed to microplastics. These findings highlight the potential of microplastics to impact the functioning and structure of sedimentary habitats and show that such effects may depend on the dominant bivalve present.

Plastics in the Marine Environment

Plastics contamination in the marine environment was first reported nearly 50 years ago, less than two decades after the rise of commercial plastics production, when less than 50 million metric tons were produced per year. In 2014, global plastics production surpassed 300 million metric tons per year. Plastic debris has been detected worldwide in all major marine habitats, in sizes from microns to meters. In response, concerns about risks to marine wildlife upon exposure to the varied forms of plastic debris have increased, stimulating new research into the extent and consequences of plastics contamination in the marine environment. Here, I present a framework to evaluate the current understanding of the sources, distribution, fate, and impacts of marine plastics. Despite remaining knowledge gaps in mass budgeting and challenges in investigating ecological impacts, the increasing evidence of the ubiquity of plastics contamination in the marine environment, the continued rapid growth in plastics production, and the evidence-albeit limited-of demonstrated impacts to marine wildlife support immediate implementation of source-reducing measures to decrease the potential risks of plastics in the marine ecosystem.

Sources and sinks of plastic debris in estuaries: A conceptual model integrating biological, physical and chemical distribution mechanisms

Micro- and macroplastic accumulation threatens estuaries worldwide because of the often dense human populations, diverse plastic inputs and high potential for plastic degradation and storage in these ecosystems. Nonetheless, our understanding of plastic sources and sinks remains limited. We designed conceptual models of the local and estuary-wide transport of plastics. We identify processes affecting the position of plastics in the water column; processes related to the mixing of fresh and salt water; and processes resulting from the influences of wind, topography, and organism-plastic interactions. The models identify gaps in the spatial context of plastic-organisms interactions, the chemical behavior of plastics in estuaries, effects of wind on plastic suspension-deposition cycles, and the relative importance of processes affecting the position in the water column. When interpreted in the context of current understanding, sinks with high management potential can be identified. However, source-sink patterns vary among estuary types and with local scale processes.

Effects of microplastics on European flat oysters, Ostrea edulis and their associated benthic communities

Plastic pollution is recognised as an emerging threat to aquatic ecosystems, with microplastics now the most abundant type of marine debris. Health effects caused by microplastics have been demonstrated at the species level, but impacts on ecological communities remain unknown. In this study, impacts of microplastics on the health and biological functioning of European flat oysters (Ostrea edulis) and on the structure of associated macrofaunal assemblages were assessed in an outdoor mesocosm experiment using intact sediment cores. Biodegradable and conventional microplastics were added at low (0.8 μg L(-1)) and high (80 μg L(-1)) doses in the water column repeatedly for 60 days. Effects on the oysters were minimal, but benthic assemblage structures differed and species richness and the total number of organisms were ∼1.2 and 1.5 times greater in control mesocosms than in those exposed to high doses of microplastics. Notably, abundances of juvenile Littorina sp. (periwinkles) and Idotea balthica (an isopod) were ∼2 and 8 times greater in controls than in mesocosms with the high dose of either type of microplastic. In addition, the biomass of Scrobicularia plana (peppery furrow shell clam) was ∼1.5 times greater in controls than in mesocosms with the high dose of microplastics. This work indicates that repeated exposure to high concentrations of microplastics could alter assemblages in an important marine habitat by reducing the abundance of benthic fauna.

Sinking rates of microplastics and potential implications of their alteration by physical, biological, and chemical factors

To follow the pathways of microplastics in aquatic environments, profound knowledge about the behaviour of microplastics is necessary. Therefore, sinking experiments were conducted with diverse polymer particles using fluids with different salinity. Particles ranged from 0.3 and 3.6mm with sinking rates between 6 and 91×10(-3)ms(-1). The sinking velocity was not solely related to particle density, size and fluid density but also to the particles shape leading to considerable deviation from calculated theoretical values. Thus, experimental studies are indispensable to get basic knowledge about the sinking behaviour and to gain representative datasets for model approaches estimating the distribution of microplastics in aquatic systems. The sinking behaviour may be altered considerably by weathering and biofouling demanding further studies with aged and fouled plastic particles. Furthermore, assumptions are made about the influence of sinking fouled microplastics on the marine carbon pump by transferring organic carbon to deeper water depths.