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Interactions between microplastics and phytoplankton aggregates : Impact on their respective fates
Abstract
Plastic debris are resistant to degradation, and therefore tend to accumulate in marine environment. Nevertheless recent estimations of plastic concentrations at the surface of the ocean were lower than expected leading the communities to seek new sinks. Among the different processes suggested we chose to focus on the transport of microplastics from the surface to deeper layers of the ocean via phytoplankton aggregates that constitute most of the sinking flux. Interactions between microplastics and aggregates were studied by building a new device: the flow-through roller tank that mimics the behaviour of laboratory made aggregates sinking through a dense layer of microplastics. Three types of aggregates formed from two different algae species (the diatom Chaetoceros neogracile, the cryptophyte Rhodomonas salina and a mix) were used as model. With their frustule made of biogenic silica which is denser than the organic matter, diatom aggregates sunk faster than R. salina aggregates. Diatom aggregates were on average bigger and stickier while aggregates from R. salina were smaller and more fragile. With higher concentrations measured in R. salina aggregates, all model-aggregates incorporated and concentrated microplastics, substantially increasing the microplastic sinking rates from tenths to hundreds of metres per day. Our results clearly show that marine aggregates can be an efficient sink for microplastics by influencing their vertical distribution in the water column. Furthermore, despite the high plastic concentrations tested, our study opens new questions regarding the impact of plastics on sedimentation fluxes in oceans. As an effect of microplastic incorporation, the sinking rates of diatom aggregates strongly decreased meanwhile sinking rates of cryptophyte aggregates increased.
... [10][11][12] A key requirement for the evaluation of the risk that MP particles pose to the environment and its organisms is a thorough understanding of their transport and fate. In aquatic environments, MP particles are expected to interact with various natural particles and colloids, such as natural organic matter (NOM), 13-15 mineral particles [16][17][18] or biogenic particles [19][20][21] which may inuence the surface and transport properties of MP particles and eventually lead to heteroaggregation. As an example, coating with NOM, such as humic acids or polysaccharides, may stabilize MP particles in the aqueous phase on the one hand by enhancing electrostatic repulsion and steric hindrance. ...
... 14,15,22,23,25 Interactions of MP particles with environmental particles appear to be predominantly controlled by electrostatic attraction or repulsion forces and charge neutralization is mainly responsible for heteroaggregation 15,16,18,25 which has been shown to increase the sedimentation rate of MP particles. 16,[19][20][21] Until now, most studies investigating the interactions of MP particles with environmental particles have been conducted with pristine MP particles. 13,14,[16][17][18][19] In the environment, however, MP particles are exposed to various weathering processes, including UV-irradiation from the sun. ...
... 16 In accordance to previous ndings, heteroaggregation resulted in sedimentation of PS particles. 16,19,20,35,[47][48][49] At neutral pH, where we observed maximum heteroaggregation, we also found maximum sedimentation of PS particles in the presence of Fh (Fig. 3C). Approx. ...
Microplastic (MP) particles are ubiquitous in aquatic environments where they become exposed to UV-irradiation and environmental particles with subsequent alteration of surface properties.
... The adverse effects of MPs on phytoplankton are well described and include altered gene expression, inhibition of cell growth, reduced photosynthetic capacity, reduced chlorophyll content, formation of heteroaggregates, inhibition of biomass productivity, and reduced environmental interactions due to surface adsorption [70][71][72][73][74][75]. ...
... High concentrations and smallest particle sizes of PS particles determine a reduced photosynthetic activity and reduced growth in the marine diatom (Thalassiosira pseudonana) and marine flagellate (Dunaliella tertiolecta) [77] (Table S1). Moreover, MPs can form aggregates with some phytoplankton species; for example, Rhodomonas salina has tended to take up more microplastic aggregate [75]. ...
Microplastic contamination is rapidly becoming an increasingly worrying environmental problem and poses a real threat to marine ecosystems and human health. The aim of this research was to conduct a traditional review of the current state of the art regarding the sources of MPs in marine environment, including an assessment of their toxic effect on marine organisms and transfer within the food webs and up to humans. An extensive literature search (from 1 January 2024 to 15 February 2025) yielded a total of 1027 primary research articles on this topic. This overview revealed that MPs can be ingested by marine organisms, migrate through the intestinal wall, and spread to other organs. They can biomagnify along the food chain and can be carriers of toxic chemicals and pathogen agents. Exposure of marine organisms to MPs can lead to several risks, including tissue damage, oxidative stress, and changes in immune-related gene expression, neurotoxicity, growth retardation, and behavioural abnormalities. The toxicity of MPs depends mainly on the particle size distribution and composition/characteristics of the polymer. The main routes of human exposure to MPs have been identified as ingestion (mainly seafood), inhalation, and dermal exposure. There is strong evidence of contamination of seafood by MPs, which pose a potential risk to human health. This study provides the basis for assessing MPs’ risk to marine ecosystems and potential human health impacts.
... This means that these carriers of organic matter might remain in the water longer than previously thought, affecting the attenuation of particulate organic carbon fluxes, remineralization depths and the overall efficiency of the biological carbon pump 31,36,37 . These aggregates also serve as key vehicles for nutrients and contaminants, making our findings critical for understanding benthic-pelagic exchanges, eutrophication 38 , harmful algae blooms 39 and the source-to-sink processes of pollutants (such as microplastics and oil droplets) [40][41][42] . Given such common scenarios related to the transport of microbially colonized sediment, accounting for the morphological impacts and variances is essential. ...
The dynamic interplay between microbial communities and sediment transport shapes continental landscapes and influences particulate matter fluxes across the Earth’s surface. Microbial colonization transforms individual sediment grains into aggregates with intricate and varied morphologies, complicating sediment transport. However, current models often simplify this morphological complexity, assuming that aggregates experience fluid drag equal to that of smooth spheres or idealized shapes. Here we apply an X-ray micro-computed tomography method combined with computational fluid dynamics simulations to analyse aggregate morphology at high spatial resolution and determine the relationship with drag. Instead of aggregate size or gross shape being the primary controls on drag, we find that microbial colonization alters the fine-scale aggregate morphology and increases drag by factors of 1–3 compared with smooth surfaces. We propose a morphology-corrected drag law that accounts for this complexity, reconciling the differences in drag across diverse aggregates. Our findings suggest that a shift from focusing on gross scale variabilities (size or gross shape) to fine-scale morphologies could enable greater accuracy in transport predictions, and improve understanding of microbially colonized aggregates in fluvial, coastal and oceanic systems.
... The observed results suggest that the accumulation of Ag occurred mainly in the lysosomal compartment rather than in the gills. Mussel gills are rich in mucocytes that secrete a solution mainly composed of acidic mucopolysaccharides [67] acting as a food trap, including particles [68,69]. Those acidic mucopolysaccharides might be stimulating the extracellular dissolution of nanosilver, increasing Ag uptake by the mussels and resulting in enhanced LM destabilization. ...
With the increasing use of manufactured nanomaterials in consumer products, especially silver nanoparticles (AgNPs), concerns about their environmental impact are rising. Two AgNP formulations were tested, the commercial nanosilver product nanArgen™ and a newly eco-designed bifunctionalized nanosilver (AgNPcitLcys), using marine organisms across three trophic levels, microalgae, microcrustaceans, and bivalves. Acute toxicity was assessed on the diatom Phaeodactylum tricornutum, brine shrimp larvae Artemia franciscana, and bivalve Mytilus galloprovincialis. The behavior of the formulations in marine media, including stability across a concentration range (0.001–100 mg/L), was also evaluated. Results showed that nanArgen™ was less stable compared to AgNpcitLcys, releasing more silver ions and exhibiting higher toxicity to microalgae (100% growth inhibition at 1 mg/L) and microcrustaceans (>80% mortality at 10 mg/L). Conversely, AgNPcitLcys (10 µg/L) was more toxic to bivalves, possibly due to the smaller nanoparticle size affecting lysosomal membrane stability. This study highlights how eco-design, such as surface coating, influences AgNP behavior and toxicity. These findings emphasize the importance of eco-design in minimizing environmental impacts and guiding the development of safer, more sustainable nanomaterials.
... Otherwise, they can enter the terrestrial food chain and affect all of the organisms in the food web. 42 Microplastics are absorbed from the intestine, cross the blood−brain barrier, and accumulate in various organs, including blood clots, tumor environments, the cardiovascular region, 43 and the placenta, potentially transferring to the fetus. 44 MPs induce intestinal dysbiosis, disrupt organ function, and significantly contribute to thrombosis. ...
Chemical recycling methods for post-consumer textile waste are effective for sustainable textile waste management. However, recycling synthetic and blended (cotton and synthetic) textiles can contribute to the release of microplastic fibers (MPFs) into the environment. This study investigated MPF release across different stages of two chemical recycling approaches, acid and alkaline hydrolysis, of polyester/cotton-blended textiles. Recycling involves various stages, including dye removal, treatment stage, and product. In the treatment stage, acid hydrolysis breaks down cotton into cellulose, leaving the polyester (PET) intact, whereas alkaline hydrolysis degrades PET, allowing cotton recovery. Across all stages, dye removal generated the highest MPF count, averaging nearly 10,055 MPFs g–1 of textile waste. Statistical analysis confirmed that the recycling approach significantly affected MPF release (p < 0.05), whereas the fabric type did not (p > 0.05). Alkaline hydrolysis reduced MPF release during the treatment stage by 87.55% compared to acid hydrolysis, indicating that recovering cotton and chemically degrading PET can significantly minimize MPF emissions during recycling. Ridge regression analysis identified the reaction conditions as key factors in MPF fragmentation, with blend ratios influencing the number of released MPFs. Surface characterization revealed treatment-induced fiber alterations, raising concerns regarding MPF emissions throughout the process. These findings highlight the textile recycling industries can be a source of MPF release into the environment, but recovering PET through degradation or dissolution can help minimize this impact of the treatment stage.
... Due to their small size, microplastics can be absorbed by phytoplankton, impairing their ability to capture sunlight for photosynthesis. Additionally, microplastics may accumulate on the water's surface, blocking sunlight and hindering photosynthesis not only in the affected phytoplankton but also in nearby organisms [140]. Phytoplankton, as primary producers, form the foundation of the marine food web, supporting zooplankton, small fish, and other marine organisms. ...
The presence of micropollutants in aquatic environments is an increasing global concern due to their persistence and potential harmful effects on aquatic organisms. Among the most concerning of these micropollutants are microplastics, pharmaceutical compounds, personal care products, and industrial chemicals, posing a significant threat to human health and aquatic ecosystems. This issue is further exacerbated by the diverse sources and complex physicochemical properties of micropollutants, as well as the inability of conventional water and wastewater treatment systems to effectively remove these contaminants. The removal of micropollutants is therefore becoming increasingly important, leading to extensive research into various physicochemical, biological, and hybrid treatment methods aimed at minimizing their environmental impact. This review examines the classification, occurrence, and associated environmental and health risks of commonly detected micropollutants in aquatic systems. Additionally, it provides an overview of advanced treatment methods being developed to implement a fourth purification stage in wastewater treatment plants. Biological, chemical, physical, and hybrid purification technologies are critically reviewed, with a focus on their performance characteristics and potential applications.
... Microplastics in surface waters can descend into deeper layers of the water column under the influence of vertical forces, such as vertical currents, biofouling, and biological transport (Kooi et al., 2017;Long et al., 2015). As such, the water column is considered a key sink for microplastics that have been lost from surface waters. ...
Microplastic pollution has emerged as an undeniable marine environmental issue. While a distribution map of microplastics in the upper ocean has been established, the patterns of microplastics within the water column remain unclear. In this study, a large-volume in situ filtration device with filtration efficiency of 30 m³/h was employed to investigate microplastics in the deep waters of the South China Sea. The abundance of microplastics ranged from 0.2 to 1.5 items per cubic meter (n/m³), with an average of 0.56 ± 0.40 n/m³. Microplastics are primarily fragments (72.58%) and fibers (20.97%), with the predominant polymer types being polypropylene (PP) and polyethylene terephthalate (PET). The average size of microplastics is 0.91 ± 0.97 mm, with no statistically significant differences observed across different water layers from 50 to 1000 meter (m). Non-metric Multidimensional Scaling (NMDS) analysis indicated that microplastics in the water column primarily originated from surface waters in the studied region. The occurrence of microplastics in the marine water column is a complex environmental process, influenced by a range of oceanographic mechanisms, including biological, chemical, and physical interactions. Our results provided reliable baseline data on microplastics in the water column of the South China Sea, contributing a better understanding to the vertical transport and fate of microplastics in this region.
... Studies have suggested that low-density MPs, such as PP and PE, are susceptible to long-term biofouling and biofilm formation, as well as attachment to natural inorganic and organic particles present in sediment. This can ultimately lead to changes in the density pattern of MPs, causing them to settle in the sediment (Long et al. 2015). In addition, weathering can create conditions for the formation of biofilms on the surfaces of MPs, increasing their susceptibility to biofouling and the accumulation and absorption of various organic and inorganic substances (Luo et al. 2022). ...
Water and sediment samples were collected from 20 sampling sites within two major river systems within the world’s largest mangrove ecosystem. The primary objectives of the study were to determine MPs’ abundance, composition, and potential ecological risks and to identify the factors influencing their distribution and characteristics. Results revealed MP abundances, ranging from 2 to 53 items/m³ in water and 17 to 177 items/kg in sediment. The most prevalent types of MPs were films, fragments, foams, and fibers, with the most abundant fragments. Transparent MPs of various colors, such as red, green, blue, white, and yellow, were commonly observed. Additionally, sizes of MPs ranged from < 0.5 to 5 mm, with particles < 0.5 mm dominating in water and 4–5 mm particles prevailing in sediment. Six major polymers were identified, including polystyrene (PS), polyamide (PA), Polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and ethylene propylene diene monomer (EPDM), with PS being the most abundant in both river systems. Linear mixed effect models showed that factors, such as distance from Mongla port and water velocity impacted MP abundance in water, while distance from Mongla port, total organic carbon (TOC), and total phosphorus (TP) contents affected their distribution in sediment. The Shannon–Weaver Index revealed a higher MP diversity in the Shela River compared to the Pasur. Overall, the pollution load index (PLI) and polymeric hazard index (PHI) indicated that MPs impacted both river systems, but the finding from the ecological risk index (ERI) was negligible at the individual sites. Our study recommends the long-term monitoring of MP abundance and implementation of strict regulations to reduce MPs in aquatic environments and proposes various engineering and biotechnological approaches for effective MP remediation. Further research is needed to identify both point and non-point sources of MPs and develop comprehensive strategies and policies to mitigate plastic pollution in the mangrove ecosystem.
... According to Koelmans et al. [18,19], MPs are defined as particles with size lesser than 5 mm [12]; pieces of a size smaller than 1 mm are called small microplastics, while particles < 100 nm are termed as nanoplastics. MPs are often found in marine phytoplankton aggregates [22]. MPs of different types and sizes have now been identified in the seawater worldwide, inducing adverse effects on most aquatic animals [11,16,29]. ...
Environmental pollution by micro and nanoplastics (MPs) is becoming an imminent danger for the environment in the 21st century. However, the effect of the MPs of different sizes is still poorly understood. In this contribution, we compare the effect of fluorescently labelled polystyrene (PS) MPs of sizes between 20 nm and 2000 nm. Spectrally-resolved confocal microscopy and fluorescence lifetime imaging was employed to study the interaction of PS MPs with algae Chlorella sp. We observed differential effect between the smaller and the bigger-sized beads. MPs sized 20–500 nm created “corona-like” structures around algae and induced lowering of the chlorophyll fluorescence, indicating an effect on the cell photosynthesis. In addition, the 20 nm MPs induced shortening of the chlorophyll fluorescence lifetimes, pointing to the effect on the chlorophyll molecular environment. However, MPs of bigger sizes, 1000–2000 nm, rather acted as a “nucleus” for clustering of a number of neighbouring algae without affecting the chlorophyll fluorescence. Understanding the interaction of living organisms with MPs of different sizes is crucial to assess the impact of this environmental pollution on live organisms in their natural environment.
... Long et al. (2017) exposed Chaetoceros neogracile to PS microbeads at a concentration of (10 4 MPs/mL). Their results indicated that PS microbeads had no effect on the fluorescence, growth, and morphology of this phytoplankton, but when C. neogracile was exposed to a concentration of 10 5 and 10 7 MPs/mL of the same type of MP, negative effects on photosynthesis, growth, and morphology appeared [38]. Table 1 shows the abundance and characteristics of MPs in plankton samples from different studies. ...
... This is consistent with others who found that changes in surface charge of micro-and nanoplastics enhances their ability to aggregate with algae (Wang et al. 2023;Zhao et al. 2023). It has also been reported that algae excrete polysaccharides, either at high cell concentrations or when they are stressed, increasing agglomeration (Long et al. 2015). Without further investigation, it is assumed that most of these agglomerates are external to the cell (as shown in Fig. 1), because of their size. ...
Environmental context
Plastic pollution is widespread and continues to be a major concern, both for the environment and human health. Identifying nanoplastics is challenging but is important to understand how they behave once in the environment. It is shown that a combination of single particle (SP) and single cell (SC) inductively coupled plasma mass spectrometry (ICP-MS) can be used to quantify nanoplastics on a per cell basis after exposure to algal cells.
Abstract
The effects of plastic pollution on human health and the environment are not well known but there are significant concerns. Although research has increased in recent years, there remain many obstacles to the quantification of nanoplastics. This rapid communication demonstrates that combined single particle (SP)– and single cell (SC)–inductively coupled plasma–mass spectrometry (ICP-MS) provide a novel means to quantify pre-formed core–shell metal–plastic composite nanoparticles when exposed to two freshwater algal cells, Cryptomonas ovata (C. ovata) and Cryptomonas ozolini (C. ozolini). It is shown that individual palladium plastic nanoparticles (Pd NPPs) exposed to algal cells form agglomerates in the cell suspension respectively consisting of 165 and 157 (±3.8) individual Pd NPPs for C. ozolini and C. ovata cells, and that the agglomerates are also cell-associated with 1.75–1.85 agglomerates per cell.
... Second, the build-up of intracellular reactive oxygen species (ROS) inside the cells, damages chloroplasts and prevents chlorophyll synthesis (Geoffroy et al., 2003;Wu et al., 2019). Third, NPs may have a shading effect on microalgae cells preventing microalgae from accessing light and hindering their ability to photosynthesis (Long et al., 2015;Garrido et al., 2019). In addition, NPs can adversely affect thylakoids and result in reduced photosynthesis rate. ...
The acute toxicity of graded concentrations of polysterene nanoplastic (PS NPs) spheres (Size 0.1 µm) was evaluated to ascertain the effects of NPs on growth, vital photosynthetic pigments, protein and oxidative stress enzymes. The findings show that PS NPs inhibited the growth of microalgae (Chlorella vulgaris and Spirulina (Arthrospira) platensis) in a dose-dependent manner. The growth inhibition percentage reached 40.12% for C. vulgaris and 42.57% for S. platensis, compared to the control. Additionally, pigment content decreased by 31.62% to 35.06%, while protein content dropped by 37.27% to 48.48% of both the tested microalgae as the concentration of PS NPs in the medium increased. The oxidative stress created by PS NPs was evident from an increase in catalase and peroxidase activity. The findings conclusively endorse that NPs pollution in the aquatic environment will disrupt the functioning of ecosystems through its detrimental effects on microalgae forming the base of the food chain and supporting the successive trophic levels in the aquatic environment. This research will give a deeper insight into the ecotoxicological impacts of NPs in aquatic environments and the baseline information will be helpful in developing an effective strategy for mitigation of plastic pollution with a greater emphasis on nanoplastics.
... Following PET, the most abundant polymers are polypropylene, polyethylene, and polyethylene-vinylacetate. Numerous studies have highlighted these polymers as being frequently found in aquatic environments worldwide (AbidLi et al., 2018;Bayo et al., 2020;De Felice et al., 2021). These polymers are extensively used in various household items, such as packaging, long-lasting fabrics, pipes, bottles, and bags (AbidLi et al., 2018;Andrady, 2011;Long et al., 2015). The distribution of MPs is not only influenced by their density and shape. ...
Microplastic (MP) pollution is a worldwide concern and represents an ecological threat to the aquatic environment, particularly freshwater ecosystems. It can pose risks to the health of organisms and potentially lead to bioaccumulation of these tiny particles in the food chain. This study focused in MP determination on three species of freshwater mussels (Unio gibbus, Unio ravoisieri, and Unio dureui) as potential models for ecological assessment in the Sejenane stream in Northern Tunisia. To achieve this, we assessed ingested microplastics in the gills and digestive gland tissues of these mussels. Raman microspectroscopy was used to examine and identify microparticles with size ranges under 5,000 μm. Our results indicated that the microparticles are categorized into three sequential size ranges: S1 (< .45–1.2 μm), S2 (< 1.2–3 μm), and S3 (≥ 3 μm). Over 50% of the S1 class was found in Unio gibbus. Our findings showed a higher occurrence of the S3 size class of microplastics (≥ 3 µm) in the gills of all studied mussels. More than 60% of the S3 class was identified in Unio durieui, followed by S2 (< 3–1.2 µm) and S1 (< 1.2–.45 µm). Polyethylene-vinyl acetate, polypropylene, low-density polyethylene, polyethylene terephthalate, high-density polyethylene, and polyethylene are the six different types of polymers that were found. Polyethylene terephthalate emerged as the dominant polymer type in Unio dureui, accounting for up to 59% of the gills and 55% of the digestive gland. Overall, it seems that freshwater mussels are capable of accumulating microplastics from environmental contamination. However, further studies in diverse freshwater ecosystems are necessary to validate the findings of this study.
... In this study, polyethylene (a low-density polymer) was the most dominant. This predominance is likely due to its low density and its tendency to undergo weathering and biofouling, leading to changes in density and eventual deposition in sediments (Long et al., 2015). The widespread presence of these polymers can be attributed to their extensive use in everyday life. ...
This study quantified microplastics (MPs) in six zones of the Mumbai mangrove ecosystem through random sampling at 30 sites using the density separation method for extraction and analysis. A total of 2,035 particles were identified based on their shape, color, and size using a stereomicroscope. The results revealed a high abundance of MPs in mangrove sediments, averaging 6,730.2 ± 2,063.9 particles/kg dry weight. The highest average was recorded in the Versova region (7,885.7 particles/kg d.w.), while the lowest was in Sewri (5,785.7 particles/kg d.w.). Fibers (56.1%), particles < 100 µm (38.5%), and translucent/transparent items (30.8%) were the predominant types. Micro-Fourier transform infrared spectroscopy analysis indicated that the most common plastic polymer was polyethylene (36.91%), followed by polyester (21.33%) and polyamide (13.47%). This study provides critical estimates of MPs abundance in Mumbai's mangrove sediments, highlighting the urgent need for management plans and 3 policies to address microplastic production and release into coastal waters, thereby protecting marine organisms.
... The formation of biofilms on the surfaces of algae may cause the particles to aggregate, thereby altering their vertical distribution in the water column. Long et al. (2015) showed that algae biofilm promotes the aggregation of MP particles, affecting their oceanic dispersal and deposition patterns. Once algae aggregates with MPs, the microbeads impacted aggregate sinking rates reached several hundred meters per day compared to the sinking rate of free beads (< 4 mm day −1 ). ...
Microplastics and nanoplastics pose a severe threat to organisms and the environment. Algae are important primary producers in aquatic ecosystems, providing nutrients for a wide range of species, so the toxic effects of pollutants on algae have negative effects on organisms at higher trophic levels. The toxic effects of micro/nanoplastics (MNPs) on algae have been the subject of many studies, with varying conclusions due to differences in experimental design. Thus, the objective of this review is to summarize the effects of MNPs on algal populations considering algal growth, pigments, photosynthesis, and oxidative stress parameters. Moreover, we provide insight into how MNPs affect algae based on the current studies. Removing MNPs has been a much less popular research topic than describing the MNPs. Algae is a promising eco-friendly method to remove MNPs. Algae have many advantages over conventional methods. Microalgal cells adsorb MNPs and are used as a source of nutrients to regulate metabolic processes to produce biomass. Therefore, this review provides methods for removing MNPs using algae. This approach will promote the development of methods to remove MNPs and contribute towards sustainability for the development of an algal-based future.
... Due to their polymer nature, plastic particles have the possibility to form homogeneous aggregates as well as heterogeneous aggregates with living organisms, sediments, metal oxides, proteins, etc [101]. Several experiments have revealed that microplastics can rapidly coagulate with biogenic particles [102][103][104], when in weak concentrations compared to biogenic one. Indeed, biofilm leads also to a reduction in hydrophobicity, which could increase the aggregation rate of the particle with phytoplankton [100,105], ultimately leading to the alteration of the settling properties of flocs or marine snow [97]. ...
... This process facilitates the movement of MPs beyond surface currents, deeper into the ocean, thereby extending their reach to new areas 166 . Surface biofouling, a common occurrence in oceans where microorganisms colonize the surfaces of MPs, alters the density of the clusters, hastening their descent to greater depths [167][168][169] . ...
... According to Koelmans et al. [2015Koelmans et al. [ , 2015b, MPs are de ned as particles with size lesser than 5 mm [Galgani et al., 2013]; pieces of a size smaller than 1 mm are called small microplastics, while particles < 100 nm are termed as nanoplastics. MPs are often found in marine phytoplankton aggregates [Long et al., 2015]. MPs of different types and sizes have now been identi ed in the seawater worldwide, inducing adverse effects on most aquatic animals [Wright et al., 2013;Della Torre et al., 2014;Ivar do Sul et al., 2014]. ...
Environmental pollution by micro and nanoplastics (MPs) is becoming an imminent danger for the environment in the 21st century. However, the effect of the MPs of different sizes is still poorly understood. In this contribution, we compare the effect of fluorescently labelled polystyrene (PS) MPs of sizes between 20 nm and 2000 nm. Spectrally-resolved confocal microscopy and fluorescence lifetime imaging was employed to study the interaction of PS MPs with algae Chlorella sp . We observed differential effect between the smaller and the bigger-sized beads. MPs sized 20–500 nm created “corona-like” structures around algae and induced lowering of the chlorophyll fluorescence, indicating an effect on the cell photosynthesis. In addition, the 20 nm MPs induced shortening of the chlorophyll fluorescence lifetimes, pointing to the effect on the chlorophyll molecular environment. However, MPs of bigger sizes, 1000–2000 nm, rather acted as a “nucleus” for clustering of a number of neighbouring algae without affecting the chlorophyll fluorescence. Understanding the interaction of living organisms with MPs of different sizes is crucial to assess the impact of this environmental pollution on live organisms in their natural environment.
... Another size range included two types of MPs: blue and black fragments (which occurrence was >15 % and >50 % of sites respectively) and fibres (with occurrence not exceeded 21 %). The presence of MPs of sizes less than the mesh size of the net is explained by the attachment of MPs to the plankton (Long et al., 2015). After fixation and processing of the samples the microparticles is separated from the organic compounds and may be found in the samples. ...
The ability of planktonic and neustonic organisms to feed on microplastics and subsequently transfer it through the marine food web has been studied extensively. However, there are no studies on microplastic in the Northwestern Black Sea. The present study assesses the diversity and spatial distribution of microplastics and ichthyoplankton in two surface layers: 0–5 cm (neuston surface layer; NL) and 5–20 cm (hyponeuston layer; HL). The sampling was undertaken in June 2020 – October 2021 in the coastal (CW) and open (OW) waters of the Northwestern Black Sea. Microplastics was observed at all studied sites and was composed of fibres (75 %) and fragments (25 %). Black and red fibres were the most abundant type of fibre, and black particles dominated the fragments. Four types of polymers were identified by Raman spectroscopy: polyethylene, polyester, polyurethane, polypropylene. The concentration of microplastics near the coast significantly exceeded that of open waters; the average microplastics concentration in the CW reached 136±74 (±SE) and 46±30 particles.m-3 in the NL and HL, respectively, whereas it reached 18±3 and 2±0.8 particles.m-3 in the NL and HL of the OW, respectively. In the NL, ichthyoplankton was found only at 31 % of the sites, and at only 24 % of sites in the HL. In total, 6 species of fish were recorded. The most abundant species was the European anchovy, one of the main commercial species in the Black Sea. The ratio of microplastics to ichthyoplankton was 0.34 (or 1:2.87) for both layers, where ichthyoplankton was present. When considering all studied sites, the ratio of microplastics to ichthyoplankton was 1.07 (or 1:0.93). As ichthyoplankton is an ephemeral component of the neuston community, but microplastics is omnipresent, we may consider that comparable densities of microplastics:ichthyoplankton favour their interrelation, negative effect, and transport through the food web.
... Density-enhancing interactions, biofilm accumulation, and adherence influence the fate of MPs. These interactions lead to their transition from the water column to deeper ocean areas or sediments influenced by water flow and tidal effects (Fischer et al., 2015;Long et al., 2015;Kaiser et al., 2017;Lebreton et al., 2017). Hydrological features and turbulence generated by waves, wind, and tides in coastal zones significantly influence the residence time of MPs in these environments (Chubarenko et al., 2016;Cai et al., 2022). ...
Microplastic (MP) contamination is becoming a major worldwide concern, affecting
terrestrial and aquatic ecosystems. This study investigated the source, distribution, and abundance of MPs
in sediments from Dongshan Bay, Fujian, South China, emphasizing particularly the coastline region’s
susceptibility to tidal impacts in four study sites. The concentrations of MPs in the sediments in the four
sites were high from 7.4 to 283.1 items/kg (dry weight). There were notable differences in abundance
between the locations and tide levels. Tides influenced the distribution of MPs greatly; however, the
estuary areas showed greater MPs abundance during high tide, due possibly to enhanced water turbulence
and riverine inputs. Low tide indicated higher concentrations in coastal locations owing to accumulation.
Popular varieties, including nylon, polypropylene, and polyethylene, were identified by polymer research,
pointing to the origins from fishing, packaging, and mariculture industries. Potential sources were
determined using the PCA-K-means statistical analysis, by linking the origins of MPs to domestic
activities, fishing, mariculturing, shipping, and packing. Fishing and packing were shown in the Sankey
diagram as the two main sources, but their effects varied with research locations and tidal regimes. This
study clarified the intricate dynamics of MPs pollution, highlighting the impact of tides on its dispersal
and the variety of sources that contribute to this widespread environmental problem in coastal areas.
Keyword: microplastic (MP); tide; source; sediment; Dongshan Bay
Microplastics originate from the fragmentation of large plastic litter or environmental emissions. These new emerging pollutants not only cause physical harm but also serve as a substrate for other contaminants that adhere to and/or are adsorbed in microplastics. Consumption of these fine particles by organisms may lead to bioaccumulation and bioamplification. Conventional wastewater treatment using inorganic and organic polymeric flocculants is nonbiodegradable and toxic to ecosystem. Plant-derived polysaccharides can provide a highly efficient, nontoxic, and ecofriendly substitute to synthetic flocculants. The microplastic removal efficiency of polysaccharides derived from fenugreek, okra, and the combination of okra and fenugreek in the ratio of 1:1 was studied in simulated and water samples collected from various sources under bench-scale laboratory conditions. Water samples used for the study were collected from surface, ocean, and groundwater sources. A combination of optical microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy was used to study the microplastic removal efficiency of the plant-derived polysaccharides. ζ-Potential measurements and scanning electron microscopy were used to confirm the mechanism and capture of microplastic from water samples. The effect of varying polymer concentrations and contact time was also studied. The best concentration was found to be 1 g/L, with fenugreek showing the best microplastic removal in 30–60 min as the optimum contact time. It was found that fenugreek was the most efficient with an ∼89% microplastic removal from groundwater samples. A combination of okra and fenugreek was the most efficient for freshwater samples with an ∼77% microplastic removal. For the ocean water, okra showed the best removal efficiency of ∼80%. The mechanism of microplastic removal using plant-based polysaccharides as flocculant was found to be bridging. Both experimental and statistical analyses demonstrated that plant-based polysaccharides showed better microplastic removal efficiency than polyacrylamide, which is commercially used for water treatment.
The environmental risk assessment of nanoparticles (NPs) relies on the adaptation of toxicity protocols originally conceived for contaminants having their predominant bioavailable form in the soluble one. While protocols to describe NP characteristics, behaviour and transformations in exposure media are available, no substantial update of traditional test guidelines has been proposed concerning toxicity endpoints and tests duration. Besides the eventual release of toxic metal ions, nano-ecotoxicity occurrence necessarily involve the physical contact between NPs and aquatic organisms. This relies on the onset of nano-bio interfacial interactions, driven by the properties of both NPs and biological surfaces. Superficial adhesion to the organism exterior (cell membrane/wall or body surface) and ingestion are usually the first outcomes of NP exposure but are rarely followed by dramatic outcomes in the short-term exposures. However, when prolonged exposures are performed, these side-effects can turn into more severe outcomes, with consequences also at the behavioural and ecological level. This chapter wants to highlight the importance of observing and reporting sub-lethal effects in NP acute exposures, such as adhesion and ingestion, and use them as early-warning signs of toxicity to look for to determine the need to perform a chronic exposure. The complex interplay of factors behind the occurrence of nano-ecotoxicity makes the environmental risk assessment of NP less straightforward compared to that of soluble compounds and may require a dedicated approach. This will help to obtain more environmentally relevant data and avoid the risk of underestimating the potential threat posed by NPs to aquatic ecosystems.
The increasing prevalence of microplastics in the environment has raised concerns about their potential environmental and health implications. Biofilms readily colonize microplastics upon their entry into the environment, altering their surface characteristics. While most studies have explored how biofilms influence the adsorption and transportation of other contaminants by microplastics, the reciprocal interplay between microplastics and biofilms and the resulting ecological risks remain understudied. This review comprehensively reviews the impact of microplastic properties on biofilm formation and composition, including the microbial community structure. We then explore the dynamic interactions between microplastics and biofilms, examining how biofilms alter the physicochemical properties, migration, and deposition of microplastics. Furthermore, we emphasize the potential of biofilm-colonized microplastics to influence the environmental fate of other pollutants. Lastly, we discuss how biofilm–microplastic interactions may modify the bioavailability, biotoxicity, and potential health implications of microplastics.
This study examines the impact of polyethylene and polypropylene microplastics on the growth and pigment production of Scenedesmus sp. at three different concentrations (50, 100, and 150 mg L-1). The findings demonstrate that microplastic exposure negatively impacts microalgae growth and photosynthetic pigments, irrespective of polymer type, size, and concentration. The findings indicate that the reduction in total chlorophyll percentage and the suppression of microalgal development were more pronounced for particles smaller than 500 μm and at a concentration of 150 mg L-1. The percentage reduction in carotenoid levels remained consistent at 50 and 100 mg L-1 but decreased considerably at 150 mg L-1. In addition, phthalate release from the microplastics was studied for a mixture of polypropylene and polyethylene microplastics. Several phthalates were detected in the samples namely diethyl phthalate (4.43 ng mL-1), dibutyl phthalate (389.38 ng mL-1), benzyl butyl phthalate (0.81 ng mL-1), and diisobutyl phthalate (3.92 ng mL-1), each of which presents ecological hazards. We recommend further studies to investigate the long-term environmental impacts of these interactions.
Microplastics have received increased attention due to their negative impacts on the environment and human health. To minimize these impacts, mitigation strategies that are efficient and cost‐effective for a range of plausible conditions need to be developed. Models can be used to support these mitigation‐related decisions. However, modeling studies related to the export of microplastics from terrestrial to aquatic systems have been limited. Here, we review such modeling studies, the trends over time and geography of focus, and discuss pertinent concepts and the underlying physical, chemical, and biological processes. We categorize the published modeling studies, discuss their limitations, and provide recommendations for future research to fill key knowledge gaps. Future modeling efforts should focus on collecting more comprehensive field data for validation, developing continuous models over event‐based, conducting experimental studies to better understand the fundamental processes, developing hybrid modeling frameworks, adopting sediment transport modeling approaches, incorporating land management practices in the models, integrating surface and sub‐surface processes at the watershed scale, and utilizing advanced data‐driven models like foundation models.
Microplastics (MPs) are produced from various primary and secondary sources and pose multifaceted environmental problems. They are of non-biodegradable nature and may stay in aquatic environments for a long time period. The present review has covered novel aspects pertaining to MPs that were not covered in earlier studies. It has been observed that several methods are being employed for samples collection, extraction and identification of MPs and polymer types using various equipment, chemicals and instrumental techniques. Aquatic species mistakenly ingest MPs, considering them prey and through food-chain, and then suffer from various metabolic disorders. The consumption of seafood and fish may consequently cause health implications in humans. Certain plasticizers are added during manufacturing to provide colour, durability, flexibility, and strength to plastics, but they leach out during usage, storage, and transport, as well as after entering the bodies of aquatic species and human beings. The leached chemicals (bisphenol-A, triclosan, phthalates, etc.) act as endocrine disrupting chemicals (EDCs), which effect on homeostasis; thereby causing neurotoxicity, cytotoxicity, reproductive problems, adverse behaviour and autism. Negative influence of MPs on carbon sequestration potential of water bodies is also observed, however more studies are required to understand it with a detail mechanism under natural conditions. The wastewater treatment plants are found to remove a large amount of MPs, but in turn, also act as significant sources of their release in sludge and effluents. Further, it is covered that how advanced oxidation processes, thermal- and photo-oxidation, fungi, algae and microbes degrade the plastics and increase their numbers in the surrounding environment. The management strategy comprising recovery of energy and other valuable by-products from plastic wastes, recycling and regulatory framework; are also described in detail. The future perspectives can be of paramount importance to control MPs generation and their abundance in the aquatic and other types of environments. The studies in future need to focus on advanced filtration techniques, advanced oxidation processes, energy recovery from plastic wastes and influences of MPs on carbon sequestration in aquatic environment and human health.
In contrast to microplastics, studying the interactions of nanoplastics (NPs) with primary producers such as marine microalgae remains challenging. This is attributed to the lack of adequate visualization methods that can distinguish NPs from autofluorescent biological material such as marine algae. The aim of this study was to develop a method for labeling and visualizing non-fluorescent micro and nanoplastics (MNPs) of various polymer types, shapes and sizes, in interaction with marine primary producers, which are autofluorescent. A labelling-technique for plastics was refined, using a swell incorporation method with the commercial dye ‘IDye’. Comprehensive quality control measures, including toxicity, leaching and dye longevity tests, were applied to ensure the robustness of the method. While STimulated Emission Depletion (STED) microscopy successfully enabled the visualization of the diverse labeled NPs smaller than 200 nm, it could not distinguish NPs from autofluorescent organic material (OM) such as marine microalgae, due to overlapping excitation and emission spectra with the photosynthetically active molecule chlorophyll-a. This study is the first to advance the field by coupling STED with Fluorescence Lifetime Imaging Microscopy (FLIM). The FLIM technique, based on the differing lifetimes of fluorescent signals, allowed us to overcome the challenge of overlapping spectra. Our work not only refines and expands existing plastic labeling protocols to accommodate a wide range of polymer types, but also introduces a more precise method for studying interactions between MNPs and autofluorescent organisms. This combined STED-FLIM approach provides a reproducible and reliable framework for examining MNP impacts in complex, ecologically relevant environments, particularly highlighting its potential for investigating MNP-microalgae interactions.
Plastic cannot decompose entirely in natural ecosystems due to its persistent covalent bonds, hydrophobicity, and resistant functional groups. It disintegrates into micro or nano form due to certain physical, chemical, or biological factors. Plastic's micro and nano forms can readily enter the food chain, resulting in the bioaccumulation and biomagnification of harmful substances. In view of the facts concerning plastic degradation, this review article aims to provide a comprehensive understanding of microplastic degradation processes, degradation mechanism, uptake and translocation, and toxicity mechanism. A prominent search in Google Scholar used the keywords microplastics, degradation mechanisms, biotoxicity, and toxicity mechanism to strengthen and identify the concepts related to MPs and their effect on ecosystems. Plastics, with a lifespan of 100–1000 years, undergo degradation due to environmental weathering. Degradation processes include chemical, thermal, photochemical, and biological. Factors like composition, structure, and additives influence degradation. Advanced oxidation methods are popular for chemical degradation, showing UV radiation can degrade 7–22% of floating plastic. The eradication of microplastics from the ecosystem has become a significant challenge for protecting humans and other organisms. Future research should identify environmental parameters affecting plastic degradation, predict plastic fate, and develop technologies for pollution reduction, mainly focusing on microplastics and nanoplastics' formation and degradation.
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Microplastics (MPs) contamination was investigated along a freshwater-seawater continuum from Chumphon River to the Gulf of Thailand. The vertical distribution in the water column and contamination in green mussels were also studied. MPs were detected in all water samples and sediment samples. Furthermore, MPs were detected in 75% of the green mussels. A higher abundance of MPs was observed in the river system than in the coastal region, indicating that river runoff associated with inland human activities is the major sources of MPs in the coastal regions and cultured green mussels. In the water column, a polymer gradient varying with depth existed where low-density particles decreased from surface to subsurface and sediment while high-density particles exhibited the opposite pattern. Polymers in surface and subsurface water were predominantly composed of low-density polyethylene, polypropylene, and polystyrene particles. However, sediment samples were equally dominated by those mentioned low-density polymers and high-density polyethylene terephthalate, polyamide, rayon, and cotton particles. Furthermore, fibers were the most common shape found in water, sediment, and mussel samples representing 95% of all particles in river water samples and were evenly distributed throughout the water column regardless of density. However, only shorter fiber (mostly < 1 mm) was detected in green mussel samples similar to their living environment. Blue, black and white particles dominated all samples. During the tidal cycle, half of the MPs entering the Gulf of Thailand returned to the river during high tide. This backflow predominantly comprised small fibers and low-density polymer MPs. The average daily load of MPs from Chumphon River to the Gulf of Thailand was 3.33 × 102 million items/day.
Bacteria assume a pivotal role in mitigating environmental issues associated with heavy metals, microplastics, and pesticides. Within the domain of heavy metals, bacteria exhibit a wide range of processes for bioremediation, encompassing biosorption, bioaccumulation, and biotransformation. Toxigenic metal ions can be effectively sequestered, transformed, and immobilized, hence reducing their adverse environmental effects. Furthermore, bacteria are increasingly recognized as significant contributors to the process of biodegradation of microplastics, which are becoming increasingly prevalent as contaminants in marine environments. These microbial communities play a crucial role in the colonization, depolymerization, and assimilation processes of microplastic polymers, hence contributing to their eventual mineralization. In the realm of pesticides, bacteria play a significant role in the advancement of environmentally sustainable biopesticides and the biodegradation of synthetic pesticides, thereby mitigating their environmentally persistent nature and associated detrimental effects. Gaining a comprehensive understanding of the intricate dynamics between bacteria and anthropogenic contaminants is of paramount importance in the pursuit of technologically advanced and environmentally sustainable management approaches.
Plastic contamination in the Southern Ocean is a growing issue. This study provides the first comprehensive analysis of marine microplastics (MPs) (0.1–5 mm) in surface sediments in Potter Cove and nearby areas around Argentina's Carlini station (25 de Mayo/King George Island, South Shetlands). Sediment samples from 31 sites (2020−2022) were collected to examine whether MP pollution originates from station activities or ocean currents. All samples contained MPs, averaging 0.18 ± 0.12 MPs/g of sediment, mainly microfibers (MFs) and irregular microfragments (MFRs) (0.11–6.23 mm) and irregular microfragments (MFRs) (0.09–4.57 mm). Infrared spectroscopy identified 13 polymer types, including cellulosic materials, polyester, and polyamide, with most MPs < 1 mm, showing aging signs, similar to laundry wear. This widespread distribution suggests contamination may stem from both local activities and external sources. Findings underscore the urgent need for MP pollution management and further research to identify sources and develop effective mitigation strategies.
Microplastic pollution in freshwater ecosystems has emerged as a significant environmental concern, warranting comprehensive investigation, and understanding. This study employs bibliometric analysis to systematically review and synthesize the existing literature on microplastic pollution in freshwater environments from 2013 to 2023. The exponential growth in research output was uncovered by analyzing 885 documents sourced from the Web of Science database, with an average annual growth rate of 73.13% and an average document citation of 30.17. Our findings highlight the dominance of primary and secondary microplastics as pollutants, their ecological consequences, and the resultant socio-economic implications. Notably, the Science of the Total Environment and Environmental Pollution journals emerge as leading publication venues, while China, Germany, and the USA lead in research contributions, underlining the global nature of microplastic pollution research. The analysis further outlines the most commonly cited works, identifying pivotal studies that have shaped current understanding and future research directions. This bibliometric analysis provides a comprehensive overview of the research landscape on microplastic pollution in freshwater ecosystems, helping researchers to identify knowledge gaps and emerging trends. These insights can guide future research directions and inform policymakers and stakeholders on where scientific efforts should be concentrated to better understand and address the impacts of microplastic pollution.
Microplastics (MPs) are an important component of suspended particulate matter in aquatic environments with two main transport modes, that is, as individual entities or in flocs. Despite its importance to MP pollution management, understanding and predicting MP flocculation remains a challenge. In this Article, we combined a meta-analysis of published data (>2,000 measurements) with new experimental data (>4,000 measurements) to investigate which size fraction of MPs can be incorporated into and transported by flocs in the aquatic environment. The size relationship between MPs and flocs can be used to predict the flocculation of MPs in various aquatic environments, and we have proposed a mathematical model to show that small MPs (<162 µm) are predominantly transported as flocs, regardless of the physicochemical characteristics of the MPs or water body. This provides valuable information to predict the transport modes of MPs, presenting a critical insight for multiple environmental settings and future pollution control strategies.
The present study analyzes the potential propagation trajectories and fate of floating microplastic particles released on the Kara Sea shelf. The transport of microplastics is described using a Lagrangian model based on daily 2016–2020 data obtained from numerical modeling of Arctic Ocean dynamics. A particle biofouling model is used to simulate the submergence of floating microplastic particles in the water column. The model includes a parameterization of the processes of biofilm accumulation (via collision with algae in surrounding water, algae growth) and degradation (via respiration, mortality). The behavior of microplastic particles of different sizes (0.5 and 0.01 mm) during the sinking process and subsequent rising due to biofilm degradation is examined. The simulation results reveal that particles of 0.01 mm in size display a tendency to sink immediately during the process of biofouling. However, when the biofilm degraded, the particles exhibited a rising velocity, comparable to the current vertical velocity, and the particles remained submerged in the water for long periods. In contrast, the 0.5 mm particles remained at the surface for a longer period before sinking, accumulating biofilm. Subsequently, their behavior was oscillatory in response to changes in the biofilm, rising rapidly when the biofilm decayed and sinking rapidly again as a result of biomass accumulation. In winter, the 0.5 mm particles were mostly frozen into the ice. The phenomenon of biofouling, whereby microplastic particles of various sizes sink at different depths, results in considerable variation in the subsequent pathways of these particles in the Arctic Ocean.
Photosynthetic organisms have an enormous influence on our environment through their effects on the development of other life on Earth and the way they alter the planet's geology and geochemistry. This book takes a unique approach by examining the evolutionary history of the major groups of aquatic photoautotrophs in the context of the ecophysiological characteristics that have allowed them to adapt to the challenges of life in water and thrive under past and present environmental conditions. The important role played by aquatic photoautotrophs on a planet undergoing unprecedented anthropogenic-induced change is also highlighted, in chapters on their critical function in mitigating environmental change through their physiological processes, and on the role of algae in biotechnology. This invaluable resource will be appreciated by researchers and advanced students interested in the biodiversity and evolutionary physiology of the full range of aquatic photoautotrophs, and their interaction with the environment.
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?
Plastic pollution is ubiquitous throughout the marine environment, yet estimates of the global abundance and weight of floating plastics have lacked data, particularly from the Southern Hemisphere and remote regions. Here we report an estimate of the total number of plastic particles and their weight floating in the world’s oceans from 24 expeditions (2007–2013) across all five sub-tropical gyres, costal Australia, Bay of Bengal and the Mediterranean Sea conducting surface net tows (N5680) and visual survey transects of large plastic debris (N5891). Using an oceanographic model of floating debris dispersal calibrated by our data, and correcting for wind-driven vertical mixing, we estimate a minimum of 5.25 trillion particles weighing 268,940 tons. When comparing between four size classes, two microplastic ,4.75 mm and meso- and macroplastic .4.75 mm, a tremendous loss of microplastics is observed from the sea surface compared to expected rates of fragmentation, suggesting there are mechanisms at play that remove ,4.75 mm plastic particles from the ocean surface.
Significance
High concentrations of floating plastic debris have been reported in remote areas of the ocean, increasing concern about the accumulation of plastic litter on the ocean surface. Since the introduction of plastic materials in the 1950s, the global production of plastic has increased rapidly and will continue in the coming decades. However, the abundance and the distribution of plastic debris in the open ocean are still unknown, despite evidence of affects on organisms ranging from small invertebrates to whales. In this work, we synthetize data collected across the world to provide a global map and a first-order approximation of the magnitude of the plastic pollution in surface waters of the open ocean.
There is compelling evidence that phytoplankton growth is limited by
iron availability in the subarctic Pacific, and equatorial Pacific and
Southern oceans. A lack of iron prevents the complete biological
utilization of the ambient nitrate and influences phytoplankton species
composition in these open-ocean `high-nitrate, low-chlorophyll' (HNLC)
regimes. But the effects of iron availability on coastal primary
productivity and nutrient biogeochemistry are unknown. Here we present
the results of shipboard seawater incubation experiments which
demonstrate that phytoplankton are iron-limited in parts of the
California coastal upwelling region. As in offshore HNLC regimes, the
addition of iron to these nearshore HNLC waters promotes blooms of large
chain-forming diatoms. The silicic acid:nitrate (Si:N) uptake ratios in
control incubations are two to three times higher than those in iron
incubations. Diatoms stressed by a lack of iron should therefore deplete
surface waters of silicic acid before nitrate, leading to a secondary
silicic acid limitation of the phytoplankton community. Higher Si:cell,
Si:C and Si:pigment ratios in diatoms in the control incubations suggest
that iron limitation leads to more silicified, faster-sinking diatom
biomass. These results raise fundamental questions about the nature of
nutrient-limitation interactions in marine ecosystems,
palaeoproductivity estimates based on the sedimentary accumulation of
biogenic opal, and the controls on carbon export from some of the
world's most productive surface waters.
Correlation between particulate organic carbon (POC) and calcium
carbonate sinking through the deep ocean has led to the idea that
ballast provided by calcium carbonate is important for the export of POC
from the surface ocean. While this idea is certainly to some extent
true, it is worth considering in more nuance, for example, examining the
different effects on the aggregation and sinking of POC of small,
non-sinking calcite particles like coccoliths and large, rapidly sinking
calcite like planktonic foraminiferan tests. We have done that here in a
simple experiment carried out in roller tanks that allow particles to
sink continuously without being impeded by container walls. Coccoliths
were efficiently incorporated into aggregates that formed during the
experiment, increasing their sinking speed compared to similarly sized
aggregates lacking added calcite ballast. The foraminiferan tests, which
sank as fast as 700 m d-1, became associated with only very
minor amounts of POC. In addition, when they collided with other,
larger, foraminferan-less aggregates, they fragmented them into two
smaller, more slowly sinking aggregates. While these effects were
certainly exaggerated within the confines of the roller tanks, they
clearly demonstrate that calcium carbonate ballast is not just calcium
carbonate ballast- different forms of calcium carbonate ballast have
notably different effects on POC aggregation, sinking, and export.
With knowledge of typical hydrodynamic behavior of waste plastic material, models predicting the dispersal of benthic plastics from land sources within the ocean are possible. Here we investigated the hydrodynamic behavior (density, settling velocity and resuspension characteristics) of non-buoyant preproduction plastic pellets in the laboratory. From these results we used the MOHID modelling system to predict what would be the likely transport and deposition pathways of such material in the Nazaré Canyon (Portugal) during the spring/summer months of 2009 and the autumn/winter months of 2011.
Model outputs indicated that non-buoyant plastic pellets would likely be transported up and down canyon as a function of tidal forces, with only a minor net down canyon movement resulting from tidal action. The model indicated that transport down canyon was likely greater during the autumn/winter, primarily as a result of occasional mass transport events related to storm activity and internal wave action. Transport rates within the canyon were not predicted to be regular throughout the canyon system, with stretches of the upper canyon acting more as locations of pellet deposition than conduits of pellet transport. Topography and the depths of internal wave action are hypothesized to contribute to this lack of homogeneity in predicted transport.
One of the primary threats to ocean ecosystems from plastic pollution is ingestion by marine organisms. Well-documented in seabirds, turtles, and marine mammals, ingestion by fish and sharks has received less attention until recently. We suggest that fishes of a variety of sizes attack drifting plastic with high frequency, as evidenced by the apparent bite marks commonly left behind. We examined 5518 plastic items from random plots on Kamilo Point, Hawai'i Island, and found 15.8% to have obvious signs of attack. Extrapolated to the entire amount of debris removed from the 15km area, over 1.3tons of plastic is attacked each year. Items with a bottle shape, or those blue or yellow in color, were attacked with a higher frequency. The triangular edges or punctures left by teeth ranged from 1 to 20mm in width suggesting a variety of species attack plastic items. More research is needed to document the specific fishes and rates of plastic ingestion.
The cellular silicon, nitrogen, and carbon content and the kinetics of silicic acid use were determined for Thalassiosira weissflogii grown under nutrient-replete, iron-deficient, and zinc-deficient conditions to assess the effect of metal deficiency on diatom silicon metabolism. Iron- and zinc-deficient T. weissflogii cells contained 40 and 66% more silicon, respectively, than their nutrient-replete counterparts. Low Zn and low Fe also increased cellular C and N content. Low Zn increased cellular carbon by 55% and cellular N by 41%. Low Fe increased cellular C and N by 68 and 45%, respectively. Fe stress did not alter cellular Si/N ratios significantly, but Si/C ratios declined by 17%. In contrast, Zn stress increased Si/C and Si/N ratios by 41 and 53%, respectively. Both Zn and Fe stress dramatically altered the kinetics of silica production by T. weissflogii. Zn deficiency increased the half saturation constant (K-s) 64% and decreased the maximum specific uptake rate (V-max) by 60%. In contrast, Fe stress did not affect the value of K-s, but decreased V-max by 66%, similar to the decrease observed under low Zn. The decrease in V-max in Zn-deficient cells was almost entirely due to the higher biogenic silica content of the metal-deficient cells. The decline in V-max under Fe stress resulted from both the increase in cellular silica content and a 50% decline in the cellular uptake rates for silicic acid. The results indicate that Fe and Zn availability can significantly alter silicification in diatoms and affect the number and efficiency of silicon transport molecules in the cell membrane.
Plastics are the most abundant form of marine debris, with global production rising and documented impacts in some marine environments, but the influence of plastic on open ocean ecosystems is poorly understood, particularly for microbial communities. Plastic Marine Debris (PMD) collected at multiple locations in the North Atlantic was analyzed with Scanning Electron Microscopy (SEM) and next-generation sequencing to characterize the attached microbial communities. We unveiled a diverse microbial community of heterotrophs, autotrophs, predators, and symbionts, a community we refer to as the "Plastisphere." Pits visualized in the PMD surface conformed to bacterial shapes as suggesting active hydrolysis of the hydrocarbon polymer. Small-subunit ribosomal RNA gene surveys identified several hydrocarbon-degrading bacteria, supporting the possibility that microbes play a role in degrading PMD. Some Plastisphere members may be opportunistic pathogens such as specific members of the genus Vibrio that dominated one of our plastic samples (the authors, unpublished data). Plastisphere communities are distinct from surrounding surface water, implying that plastic serves as a novel ecological habitat in the open ocean. Plastic has a longer half-life than most natural floating marine substrates, and a hydrophobic surface that promotes microbial colonization and biofilm formation, differing from autochthonous substrates in the upper layers of the ocean.
Fluid motion within and around sinking aggregates is an important factor in particle scavenging and solute exchange between sinking aggregates and the surrounding water and, hence, vertical fluxes and remineralization processes in the ocean. In the present study, we analyzed O2 uptake rates in >2-mm porous diatom aggregates and in model aggregates impermeable to flow by measuring, on the same aggregates, the interface diffusive uptake rates with microsensors and the total (diffusive + advective) O2 uptake rate by the Winkler method. The uptake rates were measured in a flow field similar to that experienced by sinking aggregates. The ratio of total O2 uptake rate to diffusive uptake rate was 0.97 ± 0.10 (n = 14) in model aggregates impermeable to flow. In contrast, total O2 uptake was similar to or higher than diffusive uptake rate calculated from the O2 gradients at the aggregate-water interface in 85% of all field-sampled and roller tank diatom aggregates examined. The highest ratio of total O2 uptake rate relative to diffusive uptake rate measured in <1-cm field-sampled diatom aggregates was 3.91 ± 1.39 (n = 22). Hence, diffusive O2 uptake calculated from the O2 gradients in aggregates is a conservative (minimum) estimate of total O2 uptake. The estimated average fluid velocity through the cross-sectional area of field-sampled diatom aggregates, which could explain the measured differences in O2 uptake, ranged between 5 and 40 µm s-1. The average value was 16 µm s-1, which was equal to 1.3% of aggregate sinking velocity.
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 bio-imaging 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.
We analyzed size-specific dry mass, sinking velocity, and apparent diffusivity in field-sampled marine snow,
laboratory-made aggregates formed by diatoms or coccolithophorids, and small and large zooplankton fecal
pellets with naturally varying content of ballast materials. Apparent diffusivity was measured directly inside
aggregates and large (millimeter-long) fecal pellets using microsensors. Large fecal pellets, collected in the coastal upwelling off Cape Blanc, Mauritania, showed the highest volume-specific dry mass and sinking velocities because of a high content of opal, carbonate, and lithogenic material (mostly Saharan dust), which together comprised ,80% of the dry mass. The average solid matter density within these large fecal pellets was 1.7 g cm23, whereas their excess density was 0.25 6 0.07 g cm23. Volume-specific dry mass of all sources of aggregates and fecal pellets ranged from 3.8 to 960 mg mm23, and average sinking velocities varied between 51 and 732 m d21. Porosity was .0.43 and .0.96 within fecal pellets and phytoplankton-derived aggregates, respectively. Averaged values of apparent diffusivity of gases within large fecal pellets and aggregates were 0.74 and 0.95 times that of the free diffusion coefficient in sea water, respectively. Ballast increases sinking velocity and, thus, also potential O2 fluxes to sedimenting aggregates and fecal pellets. Hence, ballast minerals limit the residence time of aggregates in
the water column by increasing sinking velocity, but apparent diffusivity and potential oxygen supply within
aggregates are high, whereby a large fraction of labile organic carbon can be respired during sedimentation.
Marine benthic diatoms excrete large quantities of extracellular polymeric substances (EPS), both as a function of their motility system and as a response to environmental conditions. Diatom EPS consists predominantly of carbohydrate-rich polymers and is important in the ecology of cells living on marine sediments. Production rates, production pathways, and monosaccharide composition of water-soluble (colloidal) carbohydrates, EPS, and intracellular storage carbohydrate (glucans) were investigated in the epipelic (mud-inhabiting) diatoms Cylindrotheca closterium (Ehrenburg), Navicula perminta (Grün.) in Van Heurck, and Amphora exigua Greg. under a range of experimental conditions simulating aspects of the natural environment. Cellular rates of colloidal carbohydrate, EPS, and glucan production were significantly higher during nutrient-replete compared with nutrient-limited growth for all three species. The proportion of EPS in the extracellular carbohydrate pool increased significantly (to 44%–69%) as cells became nutrient limited. Cylindrotheca closterium produced two types of EPS differing in sugar composition and production patterns. Nutrient-replete cells produced a complex EPS containing rhamnose, fucose, xylose, mannose, galactose, glucose, and uronic acids. Nutrient-limited cells produced an additional EPS containing mannose, galactose, glucose, and uronic acids. Both EPS types were produced under illuminated and darkened conditions. 14C-labeling revealed immediate production of 14C-glucan and significant increases in 14C-EPS between 3 and 4 h after addition of label. The glucan synthesis inhibitor 2,6-dichlorobenzonitrile significantly reduced 14C-colloidal carbohydrate and 14C-EPS. The glucanase inhibitor P-nitrophenyl β-d-glucopyranoside resulted in accumulation of glucan within cells and lowered rates of 14C-colloidal and 14C-EPS production. Cycloheximide prevented glucan catabolism, but glucan production and EPS synthesis were unaffected.
Devant le jury composé de: Paul Nival (Président du jury) France Van Wambeke (rapporteur) Robert Galois (rapporteur) Gerhard Herndl (examinateur) Fereidoun Rassoulzadegan (directeur de thèse) Maria-Luiza Pedrotti (codirecteur)
As plastic debris are becoming more and more ubiquitous in the ocean throughout the years,
plastic particles and their degradations are becoming a growing issue. Modelling their transport
and looking for hotspots of microplastics is becoming important to evaluate their impact on the
environment. But only few data are available on their repartition due to their sampling difficulties.
Most of the data on microplastics are limited to size larger than 333 µm. Scientists are
trying to modelize microplastic repartition in the ocean using data on macro and microplastics,
oceanic gyres and currents. The ocean being a complex environment with a lot of parameters
that could influence a change in microplastic repartition. Plastic particle are becoming a nonnegligible
part of the plankton with plastic which can represent six times the mass of plankton in
some oceanic gyres (MOORE et al. 2001). Taking into account these high levels, it appears important
to better identify and characterize the type of “interaction” occurring between plankton
and microplastics. As a preliminary approach we focused on phytoplankton species. The aim of
this study was thus to assess if microalgae could have an impact on microplastics distribution
within the water column.
Four di.erent species (Isochrysis galbana clone Tahitian (Prymnesiophycae), Heterocapsa triquetra
(dinophyceae), Rhodomonas salina (cryptophyceae), Chaetoceros neogracile (diatom))
of microalgae were exposed to 2µm yellow-green fluorescent polystyrene microspheres. Two
concentrations were tested (5.105 and 5.106 beads/ml). Microsphere repartition was quantified
as free beads and as beads attached to microalgae. Microspheres stuck on glassware or on the
bottom were also estimated as the di.erence between added beads to those free or attached
to microalgae. Results showed di.erent patterns of microsphere repartition depending on the
species. Interaction with the diatom C. neogracile resulted in the highest concentrations of
beads attached to microalgae while we obtained the highest levels of beads stuck to the glassware
or on the bottom with R. salina. These results highlight the importance of phytoplankton
community in microplastics distribution in the water column. Depending on blooms and species
present in the water we could observe a sink of microplastics towards the benthic compartment
or a transport of microplastics towards the surface for those stuck on microalgae. These results
also suggest a potential impact of phytoplankton community on the distribution of microplatics
within the food web as microplastics attached to microalgae are assumed to be more easily
captured by filter feeders than free microplastics in the water column.
The Goiana Estuary was studied regarding the seasonal and spatial variations of microplastics (o5 mm)
and their quantification relative to the zooplankton. The total density (n 100 m�3) of microplastics
represented half of the total fish larvae density and was comparable to fish eggs density. Soft, hard
plastics, threads and paint chips were found in the samples (n¼216). Their origins are probably the river
basin, the sea and fisheries (including the lobster fleet). In some occasions, the amount of microplastics
surpassed that of Ichthyoplankton. The highest amount of microplastics was observed during the late
rainy season, when the environment is under influence of the highest river flow, which induces the
runoff of plastic fragments to the lower estuary. The density of microplastics in the water column will
determine their bioavailability to planktivorous organisms, and then to larger predators, possibly
promoting the transfer of microplastic between trophic levels. These findings are important for better
informing researchers in future works and as basic information for managerial actions.
A continuous reactor based on the fluidized bed technique was developed
in order to study the kinetics and the mechanisms of the initial stages
of weathering of albite. Simultaneous determination of Si, Al and Na and
the observed low concentrations of the dissolved elements which were
always at levels below saturation with respect to possible secondary
precipitates, indicate that formation of a residual layer of a few tens
of angstroms occurred at the surface of the feldspar. The composition of
this layer, enriched in Si and/or Al, is strongly dependent on the pH of
the aqueous solution. The formation of the layer is followed by the
establishment of a quasi-steady state during which the dissolution of
albite tends to become stoichiometric.
Microplastics are small plastic particles (<1 mm) originating from the degradation of larger plastic debris. These microplastics have been accumulating in the marine environment for decades and have been detected throughout the water column and in sublittoral and beach sediments worldwide. However, up to now, it has never been established whether microplastic presence in sediments is limited to accumulation hot spots such as the continental shelf, or whether they are also present in deep-sea sediments. Here we show, for the first time ever, that microplastics have indeed reached the most remote of marine environments: the deep sea. We found plastic particles sized in the micrometre range in deep-sea sediments collected at four locations representing different deep-sea habitats ranging in depth from 1100 to 5000 m. Our results demonstrate that microplastic pollution has spread throughout the world's seas and oceans, into the remote and largely unknown deep sea.
The surfaces of most pelagic diatoms are sticky at times and may therefore form rapidly settling aggregates by physical coagulation. Stickiness and aggregate formation may be particularly adaptive in upwelling systems by allowing the retention of diatom populations in the vicinity of the upwelling center. We therefore hypothesized that upwelling diatom blooms are terminated by aggregate formation and rapid sedimentation. We monitored the de- velopment of a maturing diatom (mainly Chaetoceros spp.) bloom in the Benguela upwelling current during 7 d in February. Chlorophyll concentrations remained consistently high during the observation period (-500 mg Chl m ?) and phytoplankton grew at an average specific rate of 0.25 d-l. The diatoms were extraordinarily sticky, with stickiness coefficients of up to 0.40, which is the highest ever recorded for field populations. Combined with estimates of turbulent shear in the ocean such stickiness coefficients predict very high specific coagulation rates (0.3 d-l). In situ video observation demonstrated the occurrence of abundant diatom aggregates with surface water concentrations between 1,000 and 3,000 ppm. Despite the very high concentration of aggregates, vertical fluxes of phytoplankton were very low, with fractional losses CO.005 d-l, and the aggregates thus seemed to be near neutrally buoyant. Losses due to copepod grazing were also low (-0.025 d-l). Most of the aggregates were colonized by the heterotrophic dinoflagellate Noctiluca scintilluns that feed upon diatoms in the aggregates. The system appeared to be in near steady state; specific diatom growth rate, coagulation rate, and loss rate due to N. scintillans feeding were all of the same magnitude (0.25-0.3 d-l) and the latter two varied in concert. Our observations provide only partial support for the population retention hypothesis because aggregate buoyancy and N. scintillans grazing effi- ciently reduced the vertical flux of aggregates in this system.
Large transparent exopolymer particles (TEP) are found abundantly in the ocean and play an important role in many fields of marine ecology. Quantification of TEP by light microscopy, however, is labor-intensive and slow. Here we introduce a simple, semiquantitative method to determine the concentration of TEP colorimetrically. In this method TEP are first stained with alcian blue. The dye complexed with TEP is then redissolved and measured spectrophotometrically. Several independent tests of the method show that the concentration of TEP measured spectrophotometrically compares well with parallel light microscope counts. Fractionation experiments confirm that TEP are not generated as an artifact of filtration. Field data show that the concentration of TEP in different oceanic environments ranges from 10 to 500 μg liter -1 xanthan equivalent depending on season, depth, and plankton community composition.
Large and diverse mesozooplankton communities were observed on marine snow particles collected in coastal and oceanic waters of the northern Gulf of Mexico. Mesozooplankton were collected from seven phyla, including ostracods, cladocerans, pelecypods and ascidian larvae not previously recorded as being associated with marine snow. Copepod nauplii were the most common, sometimes at concentrations >100 per aggregate. Oncaea spp, Oithona spp. and Microsetella norvegica were the most common copepod species. Total mesozooplankton abundance ranged between 2 and 278 organisms per aggregate. Organisms varied markedly in their distribution across the aggregate surface and in their behaviour towards the snow matrix. Comparison of snow communities with zooplankton abundance determined from net tows suggests that some species are concentrated on snow particles. Snow particles and their associated microbial communities may be a significant source of nutrition for these mesozooplankton. Mesozooplankton may contribute significantly to the degradation and decomposition of large snow particles as they sink through the upper water column.
LARGE, rapidly sinking organic aggregates are an important component of
the carbon flux from the ocean's surface to its depths. Marine snow, the
main type of large (<0.5 mm) aggregate, is heavily colonized by
bacteria in surface waters1, yet the carbon demand of the
attached bacteria is so small that months to years are required to
consume the aggregates' carbon2-5. This has led to the
conclusion that marine aggregates are resistant to degradation by
attached bacteria, and thus act as refractory carriers of carbon to the
deep ocean. Here we report that aggregates play host to intense
activities of hydrolytic enzymes (presumably due to cell surface bound
and released enzymes of the attached bacteria), which render the
aggregates soluble. Particulate amino acids were hydrolysed rapidly
(turnover time 0.2-2.1 days), with very little of the hydrolysate being
taken up by the attached bacteria. Our results support the
hypothesis6,7 that such 'uncoupled' hydrolysis is a
biochemical mechanism for large-scale transfer of organic matter from
sinking particles to the dissolved phase, and may supply the slowly
degradable dissolved organic matter for downward export postulated by
recent models8-10.
Fractal dimensions of aggregates can potentially be used to classify aggregate morphology as well as to identify coagulation mechanisms. An analysis of size-porosity correlations for two types of marine snow aggregates yielded fractal dimensions of 1.39 ± 0.06 and 1.52 ± 0.19, which were lower than values describing inorganic collidal aggregation. -from Authors
These pages describe relatively simple and reliable methods for the culture of marine phytoplankton species useful for feeding marine invertebrates. The methods suffice for the most fastidious algae now routinely cultivable, and simplifications indicated for less demanding species are easily made; for example, omission of silicate for plants other than diatoms. Certain modifications of techniques, ancillary methods, and precautions will be treated briefly because questions often arise concerning them, but documentation will be minimal and hopefully restricted to publications readily available.
Macroscopic aggregates of detritus, living organisms and inorganic matter known as marine snow, have significance in the ocean both as unique, partially isolated microenvironments and as transport agents: much of surface-derived matter in the ocean fluxes to the ocean interior and the sea floor as marine snow. As microhabitats, marine snow aggregates contain enriched microbial communities and chemical gradients within which processes of photosynthesis, decomposition, and nutrient regeneration occur at highly elevated levels. Microbial communities associated with marine snow undergo complex successional changes on time scales of hours to days which significantly alter the chemical and biological properties of the particles. Marine snow can be produced either de novo by living plants and animals especially as mucus feeding webs of zooplankton, or by the biologically-enhanced physical aggregation of smaller particles. By the latter pathway, microaggregates, phytoplankton, fecal pellets, organic debris and clay-mineral particles collide by differential settlement or physical shear and adhere by the action of various, biologically-generated, organic compounds. Diatom flocculation is a poorly understood source of marine snow of potential global significance. Rates of snow production and breakdown are not known but are critical to predicting flux and to understanding biological community structure and transformations of matter and energy in the water column. The greatest challenge to the study of marine snow at present is the development of appropriate technology to measure abundances and characteristics of aggregates in situ.
A comprehensive assessment of marine litter in three environmental compartments of Belgian coastal waters was performed. Abundance, weight and composition of marine debris, including microplastics, was assessed by performing beach, sea surface and seafloor monitoring campaigns during two consecutive years. Plastic items were the dominant type of macrodebris recorded: over 95% of debris present in the three sampled marine compartments were plastic. In general, concentrations of macrodebris were quite high. Especially the number of beached debris reached very high levels: on average 6429±6767 items per 100m were recorded. Microplastic concentrations were determined to assess overall abundance in the different marine compartments of the Belgian Continental Shelf. In terms of weight, macrodebris still dominates the pollution of beaches, but in the water column and in the seafloor microplastics appear to be of higher importance: here, microplastic weight is approximately 100 times and 400 times higher, respectively, than macrodebris weight.
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Weathering of plastic bottles, bags, fishing line, and other products discarded in the ocean causes tiny fragments to break off. These plastic fragments may accumulate biofilms, sink, and become mixed with sediment, where benthic invertebrates may encounter and ingest them. Here we show that four species of deposit-feeding and suspension-feeding sea cucumbers (Echinodermata, Holothuroidea) not only ingest small (0.25 mm < maximum dimension < 15 mm) nylon and polyvinyl chloride (PVC) fragments along with sediment, but also ingest significantly more plastic fragments than predicted given the ratio of plastic to sand grains in the sediment. During four-hour feeding trials, holothurians ingested between 2- and 20-fold more plastic per individual than expected for PVC fragments, and between 2- and 138-fold more for nylon line. In addition, two species ingested 4 mm diameter PVC pellets. The ecological relevance of plastic ingestion was assessed in the laboratory by counting and characterizing small plastic particles discovered in sediment samples from the same field sites where our holothurians were collected. Substantial numbers of plastic fragments (105 to 214 fragments per liter of sediment) were found in samples from three different locations along the east coast of the U.S.A. In addition, plastic collected from the sediment from two of our field sites was analyzed for polychlorinated biphenyls (PCBs). Plastic from one site tested positive for Aroclor 1254 at a concentration of 0.0106 μg g-1. While the negative effects of macroscopic marine plastic debris on a host of organisms are well documented, ingestion of small plastic debris by a wide range of benthic organisms, including both primary and secondary consumers, has received little attention. Given that plastics readily adsorb PCBs and other organic pollutants in marine environments, ingestion of plastic from sediment may provide a heretofore-undescribed pathway of exposure for benthic marine invertebrates.
We introduce a novel, simple method to measure sinking velocity of particles and aggregates in roller tanks. Using this noninvasive method, it is possible to follow changes in sinking velocities on the same aggregates during time and to make paired measurements of aggregate sinking velocity and composition. Particles and aggregates are video recorded in roller tanks, and their sinking velocity is derived from the orbital trajectories. This new method is compared with three other methods (using roller tanks, a vertical flow system, and a sedimentation column), which have not previously been inter-calibrated. Agar spheres and diatom aggregates were used as model particles in all experimental systems. No method showed significantly different sinking velocities of agar spheres compared with those calculated by theory. Paired measurements showed that sinking velocities from 70 to 700 m d -1 were linearly correlated between different methods. Highest sinking velocities were measured in a sedimentation column followed by those measured in roller tanks and in the vertical flow system, respectively. The average difference of sinking velocity measured with the different methods ranged from 8% to 11% for agar spheres, and up to 20% for diatom aggregates. © 2010, by the American Society of Limnology and Oceanography, Inc.
Vertical carbon fluxes between the surface and 2500 m depth were estimated from in situ profiles of particle size distributions and abundances me/asured off Cape Blanc (Mauritania) related to deep ocean sediment traps. Vertical mass fluxes off Cape Blanc were significantly higher than recent global estimates in the open ocean. The aggregates off Cape Blanc contained high amounts of ballast material due to the presence of coccoliths and fine-grained dust from the Sahara desert, leading to a dominance of small and fast-settling aggregates. The largest changes in vertical fluxes were observed in the surface waters (<250 m), and, thus, showing this site to be the most important zone for aggregate formation and degradation. The degradation length scale (L), i.e. the fractional degradation of aggregates per meter settled, was estimated from vertical fluxes derived from the particle size distribution through the water column. This was compared with fractional remineralization rate of aggregates per meter settled derived from direct ship-board measurements of sinking velocity and small-scale O2 fluxes to aggregates measured by micro-sensors. Microbial respiration by attached bacteria alone could not explain the degradation of organic matter in the upper ocean. Instead, flux feeding from zooplankton organisms was indicated as the dominant degradation process of aggregated carbon in the surface ocean. Below the surface ocean, microbes became more important for the degradation as zooplankton was rare at these depths.
We analyzed size-specific dry mass, sinking velocity, and apparent diffusivity in field-sampled marine snow, laboratory-made aggregates formed by diatoms or coccolithophorids, and small and large zooplankton fecal pellets with naturally varying content of ballast materials. Apparent diffusivity was measured directly inside aggregates and large (millimeter-long) fecal pellets using microsensors. Large fecal pellets, collected in the coastal upwelling off Cape Blanc, Mauritania, showed the highest volume-specific dry mass and sinking velocities because of a high content of opal, carbonate, and lithogenic material (mostly Saharan dust), which together comprised similar to 80% of the dry mass. The average solid matter density within these large fecal pellets was 1.7 g cm(-3), whereas their excess density was 0.25 +/- 0.07 g cm(-3). Volume-specific dry mass of all sources of aggregates and fecal pellets ranged from 3.8 to 960 mu g mm(-3), and average sinking velocities varied between 51 and 732 m d(-1). Porosity was >0.43 and >0.96 within fecal pellets and phytoplankton-derived aggregates, respectively. Averaged values of apparent diffusivity of gases within large fecal pellets and aggregates were 0.74 and 0.95 times that of the free diffusion coefficient in sea water, respectively. Ballast increases sinking velocity and, thus, also potential O(2) fluxes to sedimenting aggregates and fecal pellets. Hence, ballast minerals limit the residence time of aggregates in the water column by increasing sinking velocity, but apparent diffusivity and potential oxygen supply within aggregates are high, whereby a large fraction of labile organic carbon can be respired during sedimentation.
Observations of a diatom bloom by in situ photography showed that at the beginning of the bloom the diatoms occurred only as discrete cells and were limited to the surface mixed layer. Below the thermocline, suspended particulate matter concentrations were low and dominated by 200 to 350 p-~ diameter flocs composed mainly of fine-grained detritus and terrestrial sediment. Some time after the beginning of the bloom diatoms started to clump together into aggregate particles, many mm in diameter, composed of a loose network of cells. Flocculation promoted by the high particle concentra-tions and the development of normal marine surface stickiness caused the diatoms to settle through the thermocline. A progressive increase in the apparent robustness and density of the flocs occurred with depth. The macroflocs could only be detected using the in situ photographs. They did not survive normal Niskin bottle sampling, and Coulter Counter analysis produced particle spectra reflecting only the size of the constituent diatoms and sediment grains. Observations indicate that studies of particle size based on water samples give misleading results and the size of particulate matter in general has been considerably underestimated in past studies based on conventional sampling methods.
The hydrodynamic behavior of diatom aggregates has a significant influence on the interactions and flocculation kinetics of algae. However, characterization of the hydrodynamics of diatoms and diatom aggregates in water is rather difficult. In this laboratory study, an advanced visualization technique in particle image velocimetry (PIV) was employed to investigate the hydrodynamic properties of settling diatom aggregates. The experiments were conducted in a settling column filled with a suspension of fluorescent polymeric beads as seed tracers. A laser light sheet was generated by the PIV setup to illuminate a thin vertical planar region in the settling column, while the motions of particles were recorded by a high speed charge-coupled device (CCD) camera. This technique was able to capture the trajectories of the tracers when a diatom aggregate settled through the tracer suspension. The PIV results indicated directly the curvilinear feature of the streamlines around diatom aggregates. The rectilinear collision model largely overestimated the collision areas of the settling particles. Algae aggregates appeared to be highly porous and fractal, which allowed streamlines to penetrate into the aggregate interior. The diatom aggregates have a fluid collection efficiency of 10%-40%. The permeable feature of aggregates can significantly enhance the collisions and flocculation between the aggregates and other small particles including algal cells in water.
A continuous reactor based on the fluidized bed technique was developed
in order to study the kinetics and the mechanisms of the initial stages
of weathering of albite. Simultaneous determination of Si, Al and Na and
the observed low concentrations of the dissolved elements which were
always at levels below saturation with respect to possible secondary
precipitates, indicate that formation of a residual layer of a few tens
of angstroms occurred at the surface of the feldspar. The composition of
this layer, enriched in Si and/or Al, is strongly dependent on the pH of
the aqueous solution. The formation of the layer is followed by the
establishment of a quasi-steady state during which the dissolution of
albite tends to become stoichiometric.
The physical adsorption of nanosized plastic beads onto a model cellulose film and two living algal species, Chlorella and Scenedesmus, has been studied. This adsorption has been found to ubiquitously favor positively charged over negatively charged plastic beads due to the electrostatic attraction between the beads and the cellulose constituent of the model and living systems. Such a charge preference is especially pronounced for Chlorella and Scenedesmus, whose binding with the plastic beads also depended upon algal morphology and motility, as characterized by the Freundlich coefficients. Using a CO2 depletion assay, we show that the adsorption of plastic beads hindered algal photosynthesis, possibly through the physical blockage of light and air flow by the nanoparticles. Our ROS assay further indicated that plastic adsorption promoted algal ROS production. Such algal responses to plastic exposure may have implications on the sustainability of the aquatic food chain.
Marine snow is a ubiquitous feature of the ocean and an important agent in the transport of energy and nutrients through marine ecosystems. Diatom aggregates, which form during blooms and, to a lesser extent, by the resuspension of benthic biofilms, are a primary source of marine snow. Genera commonly found in diatom aggregates are: Nitzschia,
Chaetoceros,
Rhizosolenia,
Leptocylindricus,
Skeletonema and Thalassionema. Most fieldwork has been restricted to a limited number of locations in the Northern Hemisphere. To quantify the global impact of diatom aggregation there is a need to conduct fieldwork in a wider range of areas, particularly in the Southern Hemisphere. Aggregates form when particles collide and stick together. Collisions in the water column are affected by turbulence, differential settlement and animal feeding, whereas diatom stickiness is affected by extracellular polymeric substances (EPS). Laboratory experiments have demonstrated that diatoms produce more EPS under nutrient limitation, although little is known about how limitation by different nutrients affects the quantity and composition of EPS and subsequent stickiness. EPS form three pools in the environment: cell coatings, soluble EPS and transparent exopolymeric particles (TEP). There is a need to investigate the dynamics of conversion between the pools of EPS by both abiotic and biological processes and how these conversions affect aggregate concentration and structure. Processes governing disaggregation have been largely overlooked, although they are as important as aggregation in determining the dynamics of aggregate concentrations in the water column. The biogeochemical significance of diatom aggregates as a means of transporting carbon and other nutrients from the euphotic zone to the seabed is well established. However, the internal biogeochemistry of aggregates is not well understood. Aggregates contain anaerobic microsites and further work is required to establish whether aggregates are significant sinks for nitrogen in the water column through anaerobic denitrification. Several hypotheses have been proposed to explain diatom aggregation in the field, but many of these are flawed because the mechanisms and adaptive explanations proposed require natural selection to operate at the level of populations rather than genes or individuals.
The spatial distribution of chemical elements in the ocean is controlled by particles (including organisms); aggregation controls the particle properties. Coagulation is an important mechanism for controlling the size of marine particles and thereby their transport properties. Coagulation theory has provided a framework for the calculation of aggregation rates and size distributions. The use of fractal scaling to relate aggregate length to mass has been an important development that still needs to be fully incorporated into mathematical expressions for particle collision rates. In addition, disaggregation has emerged as an important process that is poorly described mathematically. Observations of particle spectra in the ocean are in general agreement with those expected for coagulation processes but tend to be for too small a size range to include the effects of particle disaggregation. Analysis of material caught in sediment traps suggests that aggregates are the dominant form of material falling through the ocean. An important aspect of the marine system is the presence of multiple particle sources that can confound fractal scaling based on single source particles. Coupled coagulation and chemical reaction models have become important tools in the interpretation of Th distributions. Further development of coagulation theory to describe marine systems promises to push the limits of our understanding of coagulation processes and their implications.
Cylindrical tanks of unfiltered seawater were rotated on a roller table until the particles in the seawater formed aggregates resembling marine snow. During the summer of 1987 comparisons were made between marine snow in field samples from two coastal sites on seven separate dates, and aggregates formed in the laboratory in seawater samples taken on the same dates. Aggregates in field and laboratory samples were photographed and their dimensions were determined. Particulate composition of the aggregates was characterized by the abundance of diatoms, benthic diatoms, diatom frustules, mineral grains, fecal pellets, and fungal spores. Laboratory-prepared aggregates had a significantly greater short axis, and significantly larger calculated volume than field aggregates. Particulate compositions of field aggregates were paralleled by similar changes in the laboratory product. Dry weights of known numbers of aggregates collected on three dates indicated no significant differences in calculated densities or porosities of marine snow formed in the field and in the laboratory. We suggest that this method of forming marine snow in the laboratory may provide researchers with a useful experimental tool.
Marine phytoplanktonic cells can achieve neutral buoyancy only if the excess density of their relatively heavy structural materials (proteins, carbohydrates, silicate) is compensated for by the incorporation of materials that have densities less than seawater. We have calculated densities and osmotic concentrations for several marine algae, based on published values of structural materials and concentrations of inorganic ions and other osmolytes. The calculations, incorporating the partial molal volume, molecular mass, concentrations and osmotic coefficients, indicate that most published listings of intracellular osmolytes in marine algae are insufficient to provide the turgor known to exist. Similarly, the density of phytoplanktonic cells, calculated on the basis of known or estimated concentrations of cellular components, generally exceeds the density of seawater, which would cause negative buoyancy (sinking) throughout. We use models of osmotic concentration and cellular density in which we supplement known concentrations of osmolytes with proxy osmolytes. In particular, concentrations of some 100 mol m-3 of quaternary ammonium derivatives can explain the deficits of both osmotic concentration and buoyancy.