Uptake of microplastics by marine worms depends on feeding mode and particle shape but not exposure time

Microplastic pollution in the water and sediment of the Karnaphuli River, Bangladesh: An ecological risk assessment

Microplastics (MPs) have emerged as a new global pollutant, endangering marine ecosystems. Nonetheless, research on MP pollution in Bangladesh's estuaries and coastal environments is scare. Here, we carried out the experiment to evaluate the spatial and temporal variations of MPs along both bank of the Karnaphuli River in Chattogram city of Bangladesh, encompassing nearly all locations where the river traverses the city, while also accounting for the ecological risk assessment. The findings revealed that the potential MP content in surface water and bottom sediment varied from 14.24 to 26. 68 items m-3 and 75.63 to 272.45 items kg-1, respectively. MPs were detected in higher levels in sediment in winter but not in water until early summer. Furthermore, MPs were found at elevated levels in downstream surface water and sediment. MPs ranging from 0.3 to 0.5 mm were widespread, with fibers and fragments being the most common shapes and black and blue being the most common colors. The MPs' chemical composition includes polyethylene terephthalate (PET), high-density polyethylene (HDPE), acrylonitrile butadiene styrene (ABS), cellulose acetate (CA), ethylene-vinyl acetate (EVA), polystyrene (PS), and polyamide (PA). Surface water and bottom sediment showed a moderate correlation with MP abundance. The MP pollution's ecological danger in the Karnaphuli River was rated as Category I, suggesting a significant pollution load caused by MPs. This study sheds new light on the prevalence of MPs in the surface water and bottom sediment of the Karnaphuli River estuary, establishing the framework for future research and management of MP pollution.

Plastic pollution in mangrove ecosystems: A global meta-analysis

Mangrove ecosystems play a crucial role in blue carbon sequestration, coastal flood protection, and biodiversity conservation, while also serving as nursery habitats for threatened and economically important species. Due to their complex root structures, mangroves act as natural plastic traps, making them vulnerable to marine plastic contamination. In this study, we conducted a meta-analysis synthesising available global data on macroplastic and microplastic pollution in mangrove ecosystems, assessing their prevalence and the environmental partitioning of plastics both within and outside Marine Protected Areas (MPAs). We reviewed 44 primary studies and conducted statistical analyses to compare plastic abundance in the sediment, water, and biota. Our results show that mangrove ecosystems experience significant plastic pollution. Macroplastic abundance within the studied mangroves varied by five orders of magnitude, averaging 23.73 ± 8.80 items m-2, comparable to the highest levels recorded on beaches and underscoring the plastic-trapping capacity of mangroves. Mangroves globally had a mean contamination of 1122.98 ± 150.17 microplastics kg-1 in sediment and 16.00 ± 11.04 microplastics L-1 in seawater, both approximately double estimated safe limits. Our analyses found a 45.5 % reduction in microplastic within mangrove sediments and an 83.3 % reduction in macroplastic contamination in protected mangrove ecosystems. However, seawater microplastic levels were higher within MPAs, particularly near urbanized areas. These findings emphasize the need for integrated mitigation strategies that combine MPAs with targeted plastic waste reduction measures. Our analyses also highlight that the ecological impacts of this plastic accumulation within mangrove ecosystems remains a key knowledge gap.

Evaluating microplastic contamination in Omani mangrove habitats using large mud snails (Terebralia palustris)

This study investigated microplastic pollution in the large mud snail Terebralia palustris (Linnaeus, 1767) (Gastropoda: Potamididae) inhabiting the Avicennia marina mangrove ecosystems along the Sea of Oman. A modified digestion protocol, combining two methods, was employed to improve the detection of microplastics within the snail tissue. Results indicated that 50 % of the examined snails contained microplastics, with significant variability observed among different lagoons. Snails from the polluted Shinas lagoon exhibited higher levels of microplastics compared to those from the lowest polluted Al-Qurum Natural Reserve (MPA). The most prevalent type of microplastic in snail tissues was fibers, making up 75.7 % of the total. Fragments constituted about 24.2 %. Using portable Raman spectrometry, Polyurethane (PU) was identified as the predominant polymer, accounting for 50 % of the total. This was followed by Acrylic and Polyethylene, each representing 18.75 %, and Polyethylene Vynil Acetate (PEVA) at 12.50 %. Overall, it is clear that while snails do reflect the presence of microplastics (MPs) in their environment, their physical attributes do not strongly correlate with the levels or types of MPs they contain. Additionally, the significant difference between the abundance of MPs in sediment and in snails illustrates that, while snails may serve as general indicators of microplastic pollution, they may not be reliable as precise bioindicators or sentinel species for quantifying the extent of this pollution. Further studies are needed to explore other potential bioindicators in mangrove habitats.

Methylmercury sorption to polyethylene terephthalate (PET) fibers and relevance to environmental exposure

Considerable amounts of polyethylene terephthalate (PET) microplastic fibers are released into the environment by the laundering of polyester clothing. Microplastic fibers can be ingested by organisms in the environment. Therefore, it has been suggested that microplastic fibers act as vectors for adsorbed contaminants, which are subsequently desorbed in the gut of the organism. We undertook sorption isotherm experiments at pH 6, 7, and 8 to quantify the sorption of methylmercury (MeHg) to PET fibers. Sorption isotherms were fit to Langmuir, Freundlich, and Brunauer-Emmett-Teller models. Sorption decreased with increasing pH, which can be explained by physisorption on the negatively charged PET surfaces and the greater presence of neutral or negatively charged MeHg species at higher pH. We used the parameters obtained by the model fits to predict the likely concentration of MeHg on PET microplastic fibers in aquatic ecosystems with environmentally realistic MeHg concentrations. We calculated MeHg concentrations on PET microplastic fibers to be four orders of magnitude lower than previously observed concentrations of MeHg in seston (suspended particles comprising algae and bacteria) at the base of the aquatic food web. The results indicate that the presence of PET microplastic fibers in the environment do not elevate the MeHg exposure to organisms that ingest fibers in the environment.

Sediment contamination in two German estuaries: A biomarker-based toxicity test with the ragworm Hediste diversicolor under intermittent oxygenation

Toxicity testing is an important tool for risk assessment of sediment contamination in estuaries. However, there has been a predominant focus on fitness parameters as toxic endpoints and on crustaceans as test organisms, while effects at the sub-organismal level and on other benthic taxa have received less attention. Also, interactions between sediment contamination and natural stressors such as oxygen are often neglected in traditional toxicity tests. Here we conducted a toxicity test of sediments from the Elbe and Oder (Odra) estuaries under three weeks of continuous and intermittent oxygenation, using biomarkers in an annelid, the ragworm Hediste diversicolor. Contaminated sediments affected worm survival and some biomarkers of antioxidant defense, electrophilic stress, and energy status with response ratios of above 20%. Toxic effects were most pronounced in sediments from the upper Elbe estuary, which contained high levels of heavy metals and organic chemicals. Oxygen regimes hardly changed the sediment effects, suggesting the robustness of the biomarker-based toxicity test with ragworms.

Microplastics alter toxicity of the insecticide Bacillus thuringiensis israelensis to chironomid larvae in different ways depending on particle size

Microplastics (<5 mm) are emerging freshwater contaminants that can have a wide range of effects on aquatic biota. One concern is that combined effects of microplastics (MPs) with other stressors, such as co-occurring contaminants in urban or agricultural runoff may be significant even when the direct effects of MPs may be modest. Despite the frequent detection of both insecticides and MPs in freshwater ecosystems, there is a lack of co-exposure studies of insecticides (especially Bacillus thuringiensis israelensis (Bti)) and MPs. Here we tested the effects of ingested MPs and Bti individually and in co-exposure using the aquatic midge Chironomus riparius as a model organism. First instar larvae were fed two sizes of white polyethylene particles (34-50 and 125 μm diameter) at 106 mg/L in an artificial diet and simultaneously exposed to increasing concentrations of Bti (7, 13, 27, 53, and 89 ng/L Active Ingredient) in the water column for 21 days. For comparison, a trial was also conducted with naturally occurring kaolin clay particles (1-10 μm diameter) at 106 mg/L in the artificial diet. Bti alone reduced 7-day larval survival at higher concentrations (53, and 89 ng/L). Dietary PE-MPs and kaolin did not affect the survival of C. riparius larvae. However, when exposed in combination, PE-MPs modified the toxicity of Bti. This modification was size-dependent, with smaller particles (34-50 μm) increasing survival of Bti-exposed larvae and larger particles (125 μm) reducing survival. Our results show the potential for microplastics to alter the efficacy of an insecticide widely used to control nuisance midges and mosquitoes and add to a growing body of literature describing how the toxicological effects of microplastics are influenced by the size and shape of particles.

Fate and effects of an environmentally relevant mixture of microplastics in simple freshwater microcosms

Most studies assessing the effects of microplastics (MPs) on freshwater ecosystems use reference materials of a certain size, shape, and polymer type. However, in the environment, aquatic organisms are exposed to a mixture of different polymers with different sizes and shapes, resulting in different bioaccessible fractions and effects. This study assesses the fate and effects of an environmentally relevant mixture of high-density polyethylene (HDPE) fragments, polypropylene (PP) fragments, and polyester (PES) fibres in indoor freshwater microcosms over 28 days. The MP mixture contained common polymers found in freshwater ecosystems, had a size range between 50 and 3887 µm, and was artificially aged using a mercury lamp. The invertebrate species included in the microcosms, Lymnea stagnalis (snail) and Lumbriculus variegatus (worm), were exposed to four MP concentrations: 0.01, 0.05, 0.1 and 1 % of sediment dry weight. MPs fate was assessed by performing a balance of the MPs in the surface water, water column, and sediment after a stabilization period and at the end of the experiment. Sedimentation rates per day were calculated (2.13 % for PES, 1.46 % for HDPE, 1.87 % for PP). The maximum size of MPs taken up by the two species was determined and compared to the added mixture and their mouth size. The size range taken up by L. variegatus was smaller than L. stagnalis and significantly different from the size range in the added mixture. The No Observed Effect Concentrations (NOECs) for the reproduction factor of L. variegatus and the number of egg clutches produced by L. stagnalis were 0.01 % and 0.1 % sediment dry weight, respectively. The EC10 and EC50 for the same endpoint for L. stagnalis were 0.25 % and 0.52 %, respectively. This study shows that current MP exposure levels in freshwater sediments can result in sub-lethal effects on aquatic organisms, highlighting the importance of testing MP mixtures.

Microplastics in marine ecosystems: A comprehensive review of biological and ecological implications and its mitigation approach using nanotechnology for the sustainable environment

Microplastic contamination has rapidly become a serious environmental issue, threatening marine ecosystems and human health. This review aims to not only understand the distribution, impacts, and transfer mechanisms of microplastic contamination but also to explore potential solutions for mitigating its widespread impact. This review encompasses the categorisation, origins, and worldwide prevalence of microplastics and methodically navigates the complicated structure of microplastics. Understanding the sources of minute plastic particles infiltrating water bodies worldwide is critical for successful removal. The presence and accumulation of microplastics has far reaching negative impacts on various marine creatures, eventually extending its implications to human health. Microplastics are known to affect the metabolic activities and the survival of microbial communities, phytoplankton, zooplankton, and fauna present in marine environments. Moreover, these microplastics cause developmental abnormalities, endocrine disruption, and several metabolic disorders in humans. These microplastics accumulates in aquatic environments through trophic transfer mechanisms and biomagnification, thereby disrupting the delicate balance of these ecosystems. The review also addresses the tactics for minimising the widespread impact of microplastics by suggesting practical alternatives. These include increasing public awareness, fostering international cooperation, developing novel cleanup solutions, and encouraging the use of environment-friendly materials. In conclusion, this review examines the sources and prevalence of microplastic contamination in marine environment, its impacts on living organisms and ecosystems. It also proposes various sustainable strategies to mitigate the problem of microplastics pollution. Also, the current challenges associated with the mitigation of these pollutants have been discussed and addressing these challenges require immediate and collective action for restoring the balance in marine ecosystems.

Tracing microplastic pollution in Mahi River estuary, Gulf of Khambhat, Gujarat, and their influence on functional traits of macrobenthos

Most maritime habitats contain microplastic (MPs) contamination. The quality of the benthic ecosystem's habitat is declining as MPs accumulate in marine system. The contamination of MPs must therefore be investigated. We studied MPs pollution in the Mahi River, estuary, and macrobenthos. In the present study, the abundance of MPs fragments gradually decreased from the high tide zone to the low tide zone and muddy sediment has high MPs concentrations due to sediment characteristics and particle size. The majority of sediment and biota MPs were fibrous and black. MPs in both silt and biota have identical chemical compositions (modified cellulose), shapes, and colors. A significant source of pollutants and MPs fluxing into the ocean is well within the river system. Perinereis aibuhitensis ingested the most MPs out of 11 species, whereas Amphipods did not show any presence of MPs. Our findings showed that functional characteristics are essential for macrobenthos MPs intake. MPs in macrobenthos are high due to biological functions such as feeding, ecological groups, feeding mechanisms, body size, and bioturbation. MPs in marine sediment and organisms are tracked down to the Mahi River exceeding 50 km. The present work has investigated the idea that the macrobenthos that live in the sediment are ingesting the MPs that are building up there and this ingestion relies on the macrobenthos' functional characteristics.

The power of Posidonia oceanica meadows to retain microplastics and the consequences on associated macrofaunal benthic communities

In the coastal environment, a large amount of microplastics (MPs) can accumulate in the sediments of seagrass beds. However, the potential impact these pollutants have on seagrasses and associated organisms is currently unknown. In this study, we investigated the differences in MPs abundance and composition (i.e., shape, colour and polymer type) in marine sediments collected at different depths (-5 m, -15 m, -20 m) at two sites characterized by the presence of Posidonia oceanica meadows and at one unvegetated site. In the vegetated sites, sediment samples were collected respectively above and below the upper and lower limits of the meadow (-5 m and -20 m), out of the P. oceanica meadow, and in the central portion of the meadow (-15 m). By focusing on the central part of the meadow, we investigated if the structural features (i.e. shoots density and leaf surface) can affect the amount of MPs retained within the underlying sediment and if these, in turn, can affect the associated benthic communities. Results showed that the number of MPs retained by P. oceanica meadows was higher than that found at the unvegetated site, showing also a different composition. In particular, at vegetated sites, we observed that MPs particles were more abundant within the meadow (at - 15 m), compared to the other depths, on unvegetated sediment, with a dominance of transparent fragments of polypropylene (PP). We observed that MPs entrapment by P. oceanica was accentuated by the higher shoots density, while the seagrass leaf surface did not appear to have any effect. Both the abundance and richness of macrofauna associated with P. oceanica rhizomes appear to be negatively influenced by the MPs abundance in the sediment. Overall, this study increases knowledge of the potential risks of MPs accumulation in important coastal habitats such as the Posidonia oceanica meadows.

Towards the understanding of the uptake and depuration of microplastics in the ragworm Hediste diversicolor: Field and laboratory study

An important number of studies have evaluated the presence of microplastics, particles with a size below 5 mm, in aquatic organisms. Studies have shown that these fragments are widely present in the marine environment, but research on the estuarine ecosystem is still scarce. In this study, two different approaches were used to evaluate the presence and ingestion of plastic particles in the ragworm Hediste diversicolor: a field study for the environmental assessment and a laboratory experiment in controlled condition. For the environmental evaluation, ingestion of microplastics was evaluated in the ragworm H. diversicolor sampled from the mudflats of the Seine estuary (France) during March and June 2017 and 2018, on two locations: S1 and S2, both characterized by high anthropogenic pressures, and for S2 a more influential hydrodynamic component. Ingestion of microplastics was measured in ragworms tissues and in gut content (sediment) after depuration. The number of particles as well as their size, shape and color were reported and compared between sampling period and locations. Results showed the presence of a low number of particles in both worms and gut content. In gut content, 45.6% and 87.58% of samples from site S1 and S2 respectively contained plastic like particles. In worms, 41.7% (S1) and 75.8% (S2) of analysed samples contained plastic like items. The lowest mean number of particles was 0.21 ± 0.31 (S1 in June 2017) in worms' tissues, but 0.80 ± 0.90 (S1 in June 2017) in the gut content and the highest was 1.47 ± 1.41 (S2 in April 2017) while the highest number was 2.55 ± 2.06 (S2 in June 2017) in worms and gut content respectively. The majority of suspected microplastics observed were fibers (66%) and fragments (27%), but films (3.7%) foam (2.1%), and granules (0.2%) were also identified. In addition, the most polymer type observed by Raman spectroscopy was polypropylene. Furthermore, a preliminary study of the ingestion and egestion of fluorescent polyethylene (PE) microbeads in the digestive tract of ragworms was conducted after exposure through water, during 1h at 1.2 × 106 MP/mL. Results showed a rapid turnover of PE microbeads throughout the digestive tract of worms especially after exposure through water. This study revealed that microplastics are ingested by the ragworm H. diversicolor but do not seem to bioaccumulate. More research is needed to measure potential chronic effects of microplastics on physiological parameters of H. diversicolor and potential trophic transfer of microplastics.

Insights into the shape-dependent effects of polyethylene microplastics on interactions with organisms, environmental aging, and adsorption properties

The shape-dependent effects of microplastics have been studied in the context of ingestion but have not been considered in other environmental processes. Therefore, we investigated how the shape of polyethylene microplastics (spheres, fragments, and films) affects interactions with plants, aging, and their adsorption properties. The shape had no effect on the growth rate and chlorophyll content of duckweed Lemna minor, but the fragments strongly adhered to the plant biomass and reduced the root length. The adsorption process of the model organic compound (methylene blue dye) was described by the same kinetic model for all shapes-the experimental data best fit the pseudo-second order model. However, twice as much methylene blue was adsorbed on films as on fragments and spheres. During environmental aging, most biofilm developed on films. The biofilm on spheres contained significantly less photosynthetic microorganisms, but twice as much extracellular polymeric substances (EPS) as on fragments and films. This suggests that the attachment of microorganisms to spherical particles is limited and therefore more intensive production of EPS is required for stable biofilm formation. From the results of this study, it is evident that the shape of microplastics significantly affects not only ecotoxicity but also other environmentally relevant processes.

Microplastic burden in marine benthic invertebrates depends on species traits and feeding ecology within biogeographical provinces

The microplastic body burden of marine animals is often assumed to reflect levels of environmental contamination, yet variations in feeding ecology and regional trait expression could also affect a species' risk of contaminant uptake. Here, we explore the global inventory of individual microplastic body burden for invertebrate species inhabiting marine sediments across 16 biogeographic provinces. We show that individual microplastic body burden in benthic invertebrates cannot be fully explained by absolute levels of microplastic contamination in the environment, because interspecific differences in behaviour and feeding ecology strongly determine microplastic uptake. Our analyses also indicate a degree of species-specific particle selectivity; likely associated with feeding biology. Highest microplastic burden occurs in the Yellow and Mediterranean Seas and, contrary to expectation, amongst omnivores, predators, and deposit feeders rather than suspension feeding species. Our findings highlight the inadequacy of microplastic uptake risk assessments based on inventories of environmental contamination alone, and the need to understand how species behaviour and trait expression covary with microplastic contamination.

Effects of polymethylmethacrylate nanoplastics on the polychaete Hediste diversicolor: Behavioural, regenerative, and biochemical responses

Plastics, particularly microplastics (MPs) and nanoplastics (NPs), have been regarded as pollutants of emerging concern due to their effects on organisms and ecosystems, especially considering marine environments. However, in terms of NPs, there is still a knowledge gap regarding the effects of size and polymer on marine invertebrates, such as benthic organisms. Therefore, this study aimed to understand, regarding behavioural, physiological, and biochemical endpoints (neurotransmission, energy metabolism, antioxidant status, and oxidative damage), the effects of 50 nm waterborne polymethylmethacrylate (PMMA) NPs (0.5 to 500 µg/L) on the marine benthic polychaete Hediste diversicolor, a key species in estuarine and coastal ecosystems. Results demonstrated that worms exposed to PMMA NPs had a shorter burrowing time than control organisms. Nevertheless, worms exposed to PMMA NPs (0.5 and 500 µg/L) decreased cholinesterase activity. Energy metabolism was decreased at 50 and 500 µg/L, and glycogen content decreased at all concentrations of PMMA NPs. Enzymes related to the antioxidant defence system (superoxide dismutase and glutathione peroxidase) displayed increased activities in H. diversicolor specimens exposed to concentrations between 0.5 and 500 µg/L, which led to no damage at the cell membrane and protein levels. In this study, polychaetes also displayed a lower regenerative capacity when exposed to PMMA NPs. Overall, the data obtained in this study emphasize the potential consequences of PMMA NPs to benthic worms, particularly between 0.5 and 50 µg/L, with polychaetes exposed to 50 µg/L being the most impacted by the analysed NPs. However, since sediments are considered to be sinks and sources of plastics, further studies are needed to better understand the impacts of different sizes and polymers on marine organisms, particularly benthic species.

Ingestion of microplastics and microfibers by the invasive blue crab Callinectes sapidus (Rathbun 1896) in the Balearic Islands, Spain

The blue crab Callinectes sapidus Rathbun, 1896 is native to the western coasts of the Atlantic Ocean and is currently considered an invasive species in the Mediterranean Sea. In this study, we examined the stomach contents of C. sapidus to determine the frequency of occurrence of microplastics (MPs) and microfibers (MFs) in the Balearic Islands archipelago in the western Mediterranean Sea. A total of 120 individuals were collected from six locations between 2017 and 2020. Overall, 65.8% of the individuals had MPs and/or MFs particles with an average of 1.4 ± 1.6 particles ind.-1 of which an average of 1.0 ± 1.3 items ind.-1 were MFs and an average of 0.4 ± 0.8 items ind.-1 were MPs. In terms of type, fragments were the dominant type of MPs and the most common size of items ranged from between 0.5 and 1 mm (40%) followed by 1-5 mm (31%). The most prevalent polymers were low-density polyethylene (39%) and high-density polyethylene (26%). In terms of links to human activities, MP ingestion was positively correlated with an increase in drain pipes, whereas MF ingestion was positively correlated with an increase in sewage pipelines, providing evidence of potential sources and the bioavailability of these particles in various environments. This study confirms the widespread presence of MP and MF particles, even in areas that are currently managed under different protection statuses, in the stomach contents of invasive blue crab species throughout coastal communities.

First attempt to quantify microplastics in Mediterranean Sabellaria spinulosa (Annelida, Polychaeta) bioconstructions

This work focuses on the arenaceous reefs by the polychaete Sabellaria spinulosa and addresses microplastics pollution. The main aim is to assess microplastics amount in a bioconstruction located in the Adriatic coast of Italy (Mediterranean Sea) through a comparative approach: sea-floor sediment and bioconstruction samples were analysed to quantify microplastics absolute abundance in both substrates. A total of 431 MPs were found in the investigated substrates: respectively 85 % fibers and 15 % fragments. Multivariate analysis indicates that MPs within bioconstruction occur in higher abundances and with different morphologies than in sediment samples. The analysis of bioconstruction polished sections allowed for observation of MPs agglutinated in their original position: higher concentration is reported in inter-tube areas. Results suggest that physical characteristics of MPs could play a key-role in bioconstruction inclusion processes and raise questions on effective role of sabellariid bioconstructions as a trap for this pollutant in the littoral environment.