Early microbial biofilm formation on marine plastic debris

Microplastics profile along the Rhine River

Microplastics result from fragmentation of plastic debris or are released to the environment as pre-production pellets or components of consumer and industrial products. In the oceans, they contribute to the ‘great garbage patches’. They are ingested by many organisms, from protozoa to baleen whales, and pose a threat to the aquatic fauna. Although as much as 80% of marine debris originates from land, little attention was given to the role of rivers as debris pathways to the sea. Worldwide, not a single great river has yet been studied for the surface microplastics load over its length. We report the abundance and composition of microplastics at the surface of the Rhine, one of the largest European rivers. Measurements were made at 11 locations over a stretch of 820 km. Microplastics were found in all samples, with 892,777 particles km ⁻² on average. In the Rhine-Ruhr metropolitan area, a peak concentration of 3.9 million particles km ⁻² was measured. Microplastics concentrations were diverse along and across the river, reflecting various sources and sinks such as waste water treatment plants, tributaries and weirs. Measures should be implemented to avoid and reduce the pollution with anthropogenic litter in aquatic ecosystems.

Screening for microplastic particles in plankton samples: How to integrate marine litter assessment into existing monitoring programs?

Microplastics (MPs) are a newly recognized type of environmental pollution in aquatic systems; however no monitoring of these contaminants is conducted, mostly due to the lack of routine quantification. In the net samples collected with a 90-μm WP2 net, pelagic MP abundance was quantified by light microscopy and evaluated as a function of inshore-offshore gradient, depth, and season; the same samples were used for zooplankton analysis. The MP abundance was ∼10(2)-10(4)particlesm(-3), with no significant inshore-offshore gradient during summer but increasing offshore in winter. MP abundance in deeper layers was positively affected by zooplankton abundance in the upper layers and significantly lower during winter compared to summer. These findings indicate heterogeneity of MP distribution due to biotic and abiotic factors and suggest that samples collected for other purposes can be used for quantification of MPs in the Baltic Sea, thus facilitating integration of MP assessment into existing monitoring schemes.

Microplastics in sediments: A review of techniques, occurrence and effects

Microplastics are omnipresent in the marine environment and sediments are hypothesized to be major sinks of these plastics. Here, over 100 articles spanning the last 50 year are reviewed with following objectives: (i) to evaluate current microplastic extraction techniques, (ii) to discuss the occurrence and worldwide distribution of microplastics in sediments, and (iii) to make a comprehensive assessment of the possible adverse effects of this type of pollution to marine organisms. Based on this review we propose future research needs and conclude that there is a clear need for a standardized techniques, unified reporting units and more realistic effect assessments.

Detection of Anthropogenic Particles in Fish Stomachs: An Isolation Method Adapted to Identification by Raman Spectroscopy

Microplastic particles (MP) contaminate oceans and affect marine organisms in several ways. Ingestion combined with food intake is generally reported. However, data interpretation often is circumvented by the difficulty to separate MP from bulk samples. Visual examination often is used as one or the only step to sort these particles. However, color, size, and shape are insufficient and often unreliable criteria. We present an extraction method based on hypochlorite digestion and isolation of MP from the membrane by sonication. The protocol is especially well adapted to a subsequent analysis by Raman spectroscopy. The method avoids fluorescence problems, allowing better identification of anthropogenic particles (AP) from stomach contents of fish by Raman spectroscopy. It was developed with commercial samples of microplastics and cotton along with stomach contents from three different Clupeiformes fishes: Clupea harengus, Sardina pilchardus, and Engraulis encrasicolus. The optimized digestion and isolation protocol showed no visible impact on microplastics and cotton particles while the Raman spectroscopic spectrum allowed the precise identification of microplastics and textile fibers. Thirty-five particles were isolated from nine fish stomach contents. Raman analysis has confirmed 11 microplastics and 13 fibers mainly made of cellulose or lignin. Some particles were not completely identified but contained artificial dyes. The novel approach developed in this manuscript should help to assess the presence, quantity, and composition of AP in planktivorous fish stomachs.

Biofilm and Diatom Succession on Polyethylene (PE) and Biodegradable Plastic Bags in Two Marine Habitats: Early Signs of Degradation in the Pelagic and Benthic Zone?

The production of biodegradable plastic is increasing. Given the augmented littering of these products an increasing input into the sea is expected. Previous laboratory experiments have shown that degradation of plastic starts within days to weeks. Little is known about the early composition and activity of biofilms found on biodegradable and conventional plastic debris and its correlation to degradation in the marine environment. In this study we investigated the early formation of biofilms on plastic shopper bags and its consequences for the degradation of plastic. Samples of polyethylene and biodegradable plastic were tested in the Mediterranean Sea for 15 and 33 days. The samples were distributed equally to a shallow benthic (sedimentary seafloor at 6 m water depth) and a pelagic habitat (3 m water depth) to compare the impact of these different environments on fouling and degradation. The amount of biofilm increased on both plastic types and in both habitats. The diatom abundance and diversity differed significantly between the habitats and the plastic types. Diatoms were more abundant on samples from the pelagic zone. We anticipate that specific surface properties of the polymer types induced different biofilm communities on both plastic types. Additionally, different environmental conditions between the benthic and pelagic experimental site such as light intensity and shear forces may have influenced unequal colonisation between these habitats. The oxygen production rate was negative for all samples, indicating that the initial biofilm on marine plastic litter consumes oxygen, regardless of the plastic type or if exposed in the pelagic or the benthic zone. Mechanical tests did not reveal degradation within one month of exposure. However, scanning electron microscopy (SEM) analysis displayed potential signs of degradation on the plastic surface, which differed between both plastic types. This study indicates that the early biofilm formation and composition are affected by the plastic type and habitat. Further, it reveals that already within two weeks biodegradable plastic shows signs of degradation in the benthic and pelagic habitat.

Hidden plastics of Lake Ontario, Canada and their potential preservation in the sediment record

Microplastics are a source of environmental pollution resulting from degradation of plastic products and spillage of resin pellets. We report the amounts of microplastics from various sites of Lake Ontario and evaluate their potential for preservation in the sediment record. A total of 4635 pellets were sampled from the Humber Bay shoreline on three sampling dates. Pellet colours were similar to those from the Humber River bank, suggesting that the river is a pathway for plastics transport into Lake Ontario. Once in the lake, high density microplastics, including mineral-polyethylene and mineral-polypropylene mixtures, sink to the bottom. The minerals may be fillers that were combined with plastics during production, or may have adsorbed to the surfaces of the polymers in the water column or on the lake bottom. Based on sediment depths and accumulation rates, microplastics have accumulated in the offshore region for less than 38 years. Their burial increases the chance of microplastics preservation. Shoreline pellets may not be preserved because they are mingled with organic debris that is reworked during storm events.

Bacterial Community Profiling of Plastic Litter in the Belgian Part of the North Sea

Bacterial colonization of marine plastic litter (MPL) is known for over four decades. Still, only a few studies on the plastic colonization process and its influencing factors are reported. In this study, seafloor MPL was sampled at different locations across the Belgian part of the North Sea to study bacterial community structure using 16S metabarcoding. These marine plastic bacterial communities were compared with those of sediment and seawater, and resin pellets sampled on the beach, to investigate the origin and uniqueness of plastic bacterial communities. Plastics display great variation of bacterial community composition, while each showed significant differences from those of sediment and seawater, indicating that plastics represent a distinct environmental niche. Various environmental factors correlate with the diversity of MPL bacterial composition across plastics. In addition, intrinsic plastic-related factors such as pigment content may contribute to the differences in bacterial colonization. Furthermore, the differential abundance of known primary and secondary colonizers across the various plastics may indicate different stages of bacterial colonization, and may confound comparisons of free-floating plastics. Our studies provide insights in the factors that shape plastic bacterial colonization and shed light on the possible role of plastic as transport vehicle for bacteria through the aquatic environment.

Benthic plastic debris in marine and fresh water environments

This review provides a discussion of the published literature concerning benthic plastic debris in ocean, sea, lake, estuary and river bottoms throughout the world. Although numerous investigations of shoreline, surface and near-surface plastic debris provide important information on plastic types, distribution, accumulation, and degradation, studies of submerged plastic debris have been sporadic in the past and have become more prominent only recently. The distribution of benthic debris is controlled mainly by combinations of urban proximity and its association with fishing-related activities, geomorphology, hydrological conditions, and river input. High density plastics, biofouled products, polymers with mineral fillers or adsorbed minerals, and plastic-metal composites all have the potential to sink. Once deposited on the bottoms of water basins and channels, plastics are shielded from UV light, thus slowing the degradation process significantly. Investigations of the interactions between benthic plastic debris and bottom-dwelling organisms will help shed light on the potential dangers of submerged plastic litter.

Microplastics in freshwater systems: a review of the emerging threats, identification of knowledge gaps and prioritisation of research needs

Plastic contamination is an increasing environmental problem in marine systems where it has spread globally to even the most remote habitats. Plastic pieces in smaller size scales, microplastics (particles <5 mm), have reached high densities (e.g., 100,000 items per m(3)) in waters and sediments, and are interacting with organisms and the environment in a variety of ways. Early investigations of freshwater systems suggest microplastic presence and interactions are equally as far reaching as are being observed in marine systems. Microplastics are being detected in freshwaters of Europe, North America, and Asia, and the first organismal studies are finding that freshwater fauna across a range of feeding guilds ingest microplastics. Drawing from the marine literature and these initial freshwater studies, we review the issue of microplastics in freshwater systems to summarise current understanding, identify knowledge gaps and suggest future research priorities. Evidence suggests that freshwater systems may share similarities to marine systems in the types of forces that transport microplastics (e.g. surface currents); the prevalence of microplastics (e.g. numerically abundant and ubiquitous); the approaches used for detection, identification and quantification (e.g. density separation, filtration, sieving and infrared spectroscopy); and the potential impacts (e.g. physical damage to organisms that ingest them, chemical transfer of toxicants). Differences between freshwater and marine systems include the closer proximity to point sources in freshwaters, the typically smaller sizes of freshwater systems, and spatial and temporal differences in the mixing/transport of particles by physical forces. These differences between marine and freshwater systems may lead to differences in the type of microplastics present. For example, rivers may show a predictable pattern in microplastic characteristics (size, shape, relative abundance) based on waste sources (e.g. household vs. industrial) adjacent to the river, and distance downstream from a point source. Given that the study of microplastics in freshwaters has only arisen in the last few years, we are still limited in our understanding of 1) their presence and distribution in the environment; 2) their transport pathways and factors that affect distributions; 3) methods for their accurate detection and quantification; 4) the extent and relevance of their impacts on aquatic life. We also do not know how microplastics might transfer from freshwater to terrestrial ecosystems, and we do not know if and how they may affect human health. This is concerning because human populations have a high dependency on freshwaters for drinking water and for food resources. Increasing the level of understanding in these areas is essential if we are to develop appropriate policy and management tools to address this emerging issue.

Microplastics: addressing ecological risk through lessons learned

Plastic litter is an environmental problem of great concern. Despite the magnitude of the plastic pollution in our water bodies, only limited scientific understanding is available about the risk to the environment, particularly for microplastics. The apparent magnitude of the problem calls for quickly developing sound scientific guidance on the ecological risks of microplastics. The authors suggest that future research into microplastics risks should be guided by lessons learned from the more advanced and better understood areas of (eco) toxicology of engineered nanoparticles and mixture toxicity. Relevant examples of advances in these two fields are provided to help accelerate the scientific learning curve within the relatively unexplored area of microplastics risk assessment. Finally, the authors advocate an expansion of the "vector effect" hypothesis with regard to microplastics risk to help focus research of microplastics environmental risk at different levels of biological and environmental organization.

Macrodebris and microplastics from beaches in Slovenia

The amount of marine debris in the environment is increasing worldwide, which results in an array of negative effects to biota. This study provides the first account of macrodebris on the beach and microplastics in the sediment (shoreline and infralittoral) in relation to tourism activities in Slovenia. The study assessed the quality and quantity of macrodebris and the quality, size and quantity of microplastics at six beaches, contrasting those under the influences of tourism and those that were not. Beach cleanliness was estimated using the Clean Coast Index. Tourism did not seem to have an effect on macrodebris or microplastic quantity at beaches. Over 64% of macrodebris was plastic, and microplastics were ubiquitous, which calls for classification of plastics as hazardous materials. Standard measures for marine debris assessment are needed, especially in the form of an all-encompassing debris index. Recommendations for future assessments are provided for the Adriatic region.

The deep sea is a major sink for microplastic debris

Marine debris, mostly consisting of plastic, is a global problem, negatively impacting wildlife, tourism and shipping. However, despite the durability of plastic, and the exponential increase in its production, monitoring data show limited evidence of concomitant increasing concentrations in marine habitats. There appears to be a considerable proportion of the manufactured plastic that is unaccounted for in surveys tracking the fate of environmental plastics. Even the discovery of widespread accumulation of microscopic fragments (microplastics) in oceanic gyres and shallow water sediments is unable to explain the missing fraction. Here, we show that deep-sea sediments are a likely sink for microplastics. Microplastic, in the form of fibres, was up to four orders of magnitude more abundant (per unit volume) in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean than in contaminated sea-surface waters. Our results show evidence for a large and hitherto unknown repository of microplastics. The dominance of microfibres points to a previously underreported and unsampled plastic fraction. Given the vastness of the deep sea and the prevalence of microplastics at all sites we investigated, the deep-sea floor appears to provide an answer to the question-where is all the plastic?

Rapid bacterial colonization of low-density polyethylene microplastics in coastal sediment microcosms

Background

Synthetic microplastics (≤5-mm fragments) are emerging environmental contaminants that have been found to accumulate within coastal marine sediments worldwide. The ecological impacts and fate of microplastic debris are only beginning to be revealed, with previous research into these topics having primarily focused on higher organisms and/or pelagic environments. Despite recent research into plastic-associated microorganisms in seawater, the microbial colonization of microplastics in benthic habitats has not been studied. Therefore, we employed a 14-day microcosm experiment to investigate bacterial colonization of low-density polyethylene (LDPE) microplastics within three types of coastal marine sediment from Spurn Point, Humber Estuary, U.K.

Results

Bacterial attachment onto LDPE within sediments was demonstrated by scanning electron microscopy and catalyzed reporter deposition fluorescence in situ hybridisation (CARD-FISH). Log-fold increases in the abundance of 16S rRNA genes from LDPE-associated bacteria occurred within 7 days with 16S rRNA gene numbers on LDPE surfaces differing significantly across sediment types, as shown by quantitative PCR. Terminal-restriction fragment length polymorphism (T-RFLP) analysis demonstrated rapid selection of LDPE-associated bacterial assemblages whose structure and composition differed significantly from those in surrounding sediments. Additionally, T-RFLP analysis revealed successional convergence of the LDPE-associated communities from the different sediments over the 14-day experiment. Sequencing of cloned 16S rRNA genes demonstrated that these communities were dominated after 14 days by the genera Arcobacter and Colwellia (totalling 84–93% of sequences). Attachment by Colwellia spp. onto LDPE within sediments was confirmed by CARD-FISH.

Conclusions

These results demonstrate that bacteria within coastal marine sediments can rapidly colonize LDPE microplastics, with evidence for the successional formation of plastisphere-specific bacterial assemblages. Although the taxonomic compositions of these assemblages are likely to differ between marine sediments and the water column, both Arcobacter and Colwellia spp. have previously been affiliated with the degradation of hydrocarbon contaminants within low-temperature marine environments. Since hydrocarbon-degrading bacteria have also been discovered on plastic fragments in seawater, our data suggest that recruitment of hydrocarbonoclastic bacteria on microplastics is likely to represent a shared feature between both benthic and pelagic marine habitats.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-014-0232-4) contains supplementary material, which is available to authorized users.

Millimeter-sized marine plastics: a new pelagic habitat for microorganisms and invertebrates

Millimeter-sized plastics are abundant in most marine surface waters, and known to carry fouling organisms that potentially play key roles in the fate and ecological impacts of plastic pollution. In this study we used scanning electron microscopy to characterize biodiversity of organisms on the surface of 68 small floating plastics (length range = 1.7–24.3 mm, median = 3.2 mm) from Australia-wide coastal and oceanic, tropical to temperate sample collections. Diatoms were the most diverse group of plastic colonizers, represented by 14 genera. We also recorded ‘epiplastic’ coccolithophores (7 genera), bryozoans, barnacles (Lepas spp.), a dinoflagellate (Ceratium), an isopod (Asellota), a marine worm, marine insect eggs (Halobates sp.), as well as rounded, elongated, and spiral cells putatively identified as bacteria, cyanobacteria, and fungi. Furthermore, we observed a variety of plastic surface microtextures, including pits and grooves conforming to the shape of microorganisms, suggesting that biota may play an important role in plastic degradation. This study highlights how anthropogenic millimeter-sized polymers have created a new pelagic habitat for microorganisms and invertebrates. The ecological ramifications of this phenomenon for marine organism dispersal, ocean productivity, and biotransfer of plastic-associated pollutants, remains to be elucidated.

The present and future of microplastic pollution in the marine environment

Recently, research examining the occurrence of microplastics in the marine environment has substantially increased. Field and laboratory work regularly provide new evidence on the fate of microplastic debris. This debris has been observed within every marine habitat. In this study, at least 101 peer-reviewed papers investigating microplastic pollution were critically analysed (Supplementary material). Microplastics are commonly studied in relation to (1) plankton samples, (2) sandy and muddy sediments, (3) vertebrate and invertebrate ingestion, and (4) chemical pollutant interactions. All of the marine organism groups are at an eminent risk of interacting with microplastics according to the available literature. Dozens of works on other relevant issues (i.e., polymer decay at sea, new sampling and laboratory methods, emerging sources, externalities) were also analysed and discussed. This paper provides the first in-depth exploration of the effects of microplastics on the marine environment and biota. The number of scientific publications will increase in response to present and projected plastic uses and discard patterns. Therefore, new themes and important approaches for future work are proposed.

Marine plastic pollution in waters around Australia: characteristics, concentrations, and pathways

Plastics represent the vast majority of human-made debris present in the oceans. However, their characteristics, accumulation zones, and transport pathways remain poorly assessed. We characterised and estimated the concentration of marine plastics in waters around Australia using surface net tows, and inferred their potential pathways using particle-tracking models and real drifter trajectories. The 839 marine plastics recorded were predominantly small fragments (“microplastics”, median length = 2.8 mm, mean length = 4.9 mm) resulting from the breakdown of larger objects made of polyethylene and polypropylene (e.g. packaging and fishing items). Mean sea surface plastic concentration was 4256.4 pieces km⁻², and after incorporating the effect of vertical wind mixing, this value increased to 8966.3 pieces km⁻². These plastics appear to be associated with a wide range of ocean currents that connect the sampled sites to their international and domestic sources, including populated areas of Australia's east coast. This study shows that plastic contamination levels in surface waters of Australia are similar to those in the Caribbean Sea and Gulf of Maine, but considerably lower than those found in the subtropical gyres and Mediterranean Sea. Microplastics such as the ones described here have the potential to affect organisms ranging from megafauna to small fish and zooplankton.

The plastic-associated microorganisms of the North Pacific Gyre

Microorganisms likely mediate processes affecting the fate and impacts of marine plastic pollution, including degradation, chemical adsorption, and colonization or ingestion by macroorganisms. We investigated the relationship between plastic-associated microorganism communities and factors such as location, temperature, salinity, plankton abundance, plastic concentration, item size, surface roughness, and polymer type. Small plastic items from the surface of the North Pacific Gyre in 2011 were examined using scanning electron microscopy. Bacillus bacteria (mean 1664 ± 247 individuals mm(-2)) and pennate diatoms (1097 ± 154 mm(-2)) were most abundant, with coccoid bacteria, centric diatoms, dinoflagellates, coccolithophores, and radiolarians present. Bacterial abundance was patchy, but increased on foamed polystyrene. Diatom abundance increased on items with rough surfaces and at sites with high plastic concentrations. Morphotype richness increased slightly on larger fragments, and a biogeographic transition occurred between pennate diatom groups. Better characterizing this community will aid in understanding how it interacts with plastic pollution.

The physical impacts of microplastics on marine organisms: a review

Plastic debris at the micro-, and potentially also the nano-scale, are widespread in the environment. Microplastics have accumulated in oceans and sediments worldwide in recent years, with maximum concentrations reaching 100 000 particles m(3). Due to their small size, microplastics may be ingested by low trophic fauna, with uncertain consequences for the health of the organism. This review focuses on marine invertebrates and their susceptibility to the physical impacts of microplastic uptake. Some of the main points discussed are (1) an evaluation of the factors contributing to the bioavailability of microplastics including size and density; (2) an assessment of the relative susceptibility of different feeding guilds; (3) an overview of the factors most likely to influence the physical impacts of microplastics such as accumulation and translocation; and (4) the trophic transfer of microplastics. These findings are important in guiding future marine litter research and management strategies.

Microplastic ingestion by zooplankton

Small plastic detritus, termed "microplastics", are a widespread and ubiquitous contaminant of marine ecosystems across the globe. Ingestion of microplastics by marine biota, including mussels, worms, fish, and seabirds, has been widely reported, but despite their vital ecological role in marine food-webs, the impact of microplastics on zooplankton remains under-researched. Here, we show that microplastics are ingested by, and may impact upon, zooplankton. We used bioimaging techniques to document ingestion, egestion, and adherence of microplastics in a range of zooplankton common to the northeast Atlantic, and employed feeding rate studies to determine the impact of plastic detritus on algal ingestion rates in copepods. Using fluorescence and coherent anti-Stokes Raman scattering (CARS) microscopy we identified that thirteen zooplankton taxa had the capacity to ingest 1.7-30.6 μm polystyrene beads, with uptake varying by taxa, life-stage and bead-size. Post-ingestion, copepods egested faecal pellets laden with microplastics. We further observed microplastics adhered to the external carapace and appendages of exposed zooplankton. Exposure of the copepod Centropages typicus to natural assemblages of algae with and without microplastics showed that 7.3 μm microplastics (>4000 mL(-1)) significantly decreased algal feeding. Our findings imply that marine microplastic debris can negatively impact upon zooplankton function and health.

To eat or not to eat? Debris selectivity by marine turtles

Marine debris is a growing problem for wildlife, and has been documented to affect more than 267 species worldwide. We investigated the prevalence of marine debris ingestion in 115 sea turtles stranded in Queensland between 2006–2011, and assessed how the ingestion rates differ between species (Eretmochelys imbricata vs. Chelonia mydas) and by turtle size class (smaller oceanic feeders vs. larger benthic feeders). Concurrently, we conducted 25 beach surveys to estimate the composition of the debris present in the marine environment. Based on this proxy measurement of debris availability, we modeled turtles’ debris preferences (color and type) using a resource selection function, a method traditionally used for habitat and food selection. We found no significant difference in the overall probability of ingesting debris between the two species studied, both of which have similar life histories. Curved carapace length, however, was inversely correlated with the probability of ingesting debris; 54.5% of pelagic sized turtles had ingested debris, whereas only 25% of benthic feeding turtles were found with debris in their gastrointestinal system. Benthic and pelagic sized turtles also exhibited different selectivity ratios for debris ingestion. Benthic phase turtles had a strong selectivity for soft, clear plastic, lending support to the hypothesis that sea turtles ingest debris because it resembles natural prey items such as jellyfish. Pelagic turtles were much less selective in their feeding, though they showed a trend towards selectivity for rubber items such as balloons. Most ingested items were plastic and were positively buoyant. This study highlights the need to address increasing amounts of plastic in the marine environment, and provides evidence for the disproportionate ingestion of balloons by marine turtles.

Microplastics in beaches of the East Frisian islands Spiekeroog and Kachelotplate

Microplastic particles were quantified in beach transects of the East Frisian islands Spiekeroog and Kachelotplate and in two samples from a tidal flat. Both granules and fibres were present while fragments and polystyrene pellets were completely absent. On the Kachelotplate the highest number of granules (496/10 g sediment) was observed at the high water line while on Spiekeroog a sample from the dune area had the highest value (38/10 g sediment). The tidal flat samples hat 36 and 136 granules/10 g sediment with the higher number being associated with a blue mussel bank. Fibres were more homogeneously distributed and did not show any particular enrichment. In comparison with data from the Belgian coast the total numbers are higher which might be related to the exposure situation of the island beaches.

Microplastics in the marine environment: a review of the methods used for identification and quantification

This review of 68 studies compares the methodologies used for the identification and quantification of microplastics from the marine environment. Three main sampling strategies were identified: selective, volume-reduced, and bulk sampling. Most sediment samples came from sandy beaches at the high tide line, and most seawater samples were taken at the sea surface using neuston nets. Four steps were distinguished during sample processing: density separation, filtration, sieving, and visual sorting of microplastics. Visual sorting was one of the most commonly used methods for the identification of microplastics (using type, shape, degradation stage, and color as criteria). Chemical and physical characteristics (e.g., specific density) were also used. The most reliable method to identify the chemical composition of microplastics is by infrared spectroscopy. Most studies reported that plastic fragments were polyethylene and polypropylene polymers. Units commonly used for abundance estimates are "items per m(2)" for sediment and sea surface studies and "items per m(3)" for water column studies. Mesh size of sieves and filters used during sampling or sample processing influence abundance estimates. Most studies reported two main size ranges of microplastics: (i) 500 μm-5 mm, which are retained by a 500 μm sieve/net, and (ii) 1-500 μm, or fractions thereof that are retained on filters. We recommend that future programs of monitoring continue to distinguish these size fractions, but we suggest standardized sampling procedures which allow the spatiotemporal comparison of microplastic abundance across marine environments.

The applicability of reflectance micro-Fourier-transform infrared spectroscopy for the detection of synthetic microplastics in marine sediments

Synthetic microplastics (≤5-mm fragments) are globally distributed contaminants within coastal sediments that may transport organic pollutants and additives into food webs. Although micro-Fourier-transform infrared (micro-FT-IR) spectroscopy represents an ideal method for detecting microplastics in sediments, this technique lacks a standardized operating protocol. Herein, an optimized method for the micro-FT-IR analysis of microplastics in vacuum-filtered sediment retentates was developed. Reflectance micro-FT-IR analyses of polyethylene (PE) were compared with attenuated total reflectance FT-IR (ATR-FT-IR) measurements. Molecular mapping as a precursor to the imaging of microplastics was explored in the presence and absence of 150-μm PE fragments, added to sediment at concentrations of 10, 100, 500 and 1000ppm. Subsequently, polymer spectra were assessed across plastic-spiked sediments from fifteen offshore sites. While all spectra obtained of evenly shaped plastics were typical to PE, reflectance micro-FT-IR measurements of irregularly shaped materials must account for refractive error. Additionally, we provide the first evidence that mapping successfully detects microplastics without their visual selection for characterization, despite this technique relying on spectra from small and spatially separated locations. Flotation of microplastics from sediments only enabled a fragment recovery rate of 61 (±31 S.D.) %. However, mapping 3-mm(2) areas (within 47-mm filters) detected PE at spiking concentrations of 100ppm and above, displaying 69 (±12 S.D.) % of the fragments in these locations. Additionally, mapping detected a potential PE fragment in a non-spiked retentate. These data have important implications for research into the imaging of microplastics. Specifically, the sensitivity and spatial resolution of the present protocol may be improved by visualizing the entire filter with high-throughput detection techniques (e.g., focal plane array-based imaging). Additionally, since micro-FT-IR analyses depend on methods of sample collection, our results emphasize the urgency of developing efficient and reproducible techniques to separate microplastics from sediments.

Microplastics as contaminants in the marine environment: a review

Since the mass production of plastics began in the 1940s, microplastic contamination of the marine environment has been a growing problem. Here, a review of the literature has been conducted with the following objectives: (1) to summarise the properties, nomenclature and sources of microplastics; (2) to discuss the routes by which microplastics enter the marine environment; (3) to evaluate the methods by which microplastics are detected in the marine environment; (4) to assess spatial and temporal trends of microplastic abundance; and (5) to discuss the environmental impact of microplastics. Microplastics are both abundant and widespread within the marine environment, found in their highest concentrations along coastlines and within mid-ocean gyres. Ingestion of microplastics has been demonstrated in a range of marine organisms, a process which may facilitate the transfer of chemical additives or hydrophobic waterborne pollutants to biota. We conclude by highlighting key future research areas for scientists and policymakers.