Uptake and toxicity of methylmethacrylate-based nanoplastic particles in aquatic organisms

Do microbial decomposers find micro- and nanoplastics to be harmful stressors in the aquatic environment? A systematic review of in vitro toxicological research

Microbial decomposers (bacteria and fungi) are likely to interact with plastic particles introduced into natural systems, particularly micro- and nanoplastics (MNPs), exposing them to a variety of risks. In vitro testing has proven to be an accessible and viable method for gaining insights into how microbial decomposers behave individually and systemically toward MNPs. Recent advances have enhanced our understanding of MNP interactions with organisms, revealing the molecular foundations of adaptive responses as well as the biological impact and potential risks to MNPs. Despite widespread attention, this topic has not yet been reviewed. Here, we conducted a systematic review of the available research to critically assess and highlight the most recent advances in two major areas: (1) methods for in vitro evaluation of environmentally relevant microbial decomposers to MNPs; and (2) current understanding of the underlying toxicity mechanisms gained from in vitro assessments. We also addressed the key considerations throughout and proposed available opportunities in the field. Our analysis revealed that MNPs' toxicity has been studied in vitro either alone or in combination with other contaminants (e.g., antibiotics and metallic nanoparticles), with Escherichia coli and polystyrene particles receiving the most attention. Moreover, there were methodological differences in terms of MNP size, shape, polymer, surface characteristics, exposure period, and concentrations. A combination of methods, including growth-viability tests, biochemical assays, and omics profiling (metabolomics and transcriptomics), were employed to detect the effects of MNP exposure and explain its toxicity mechanism. The current literature suggests that the impacts of MNPs on microbial decomposers include alterations in the antioxidative system, gene expression levels and cell-membrane permeability and oxidative damage, all of which can be further influenced by MNPs interaction with other contaminants. This review will thus provide critical insights and up-to-date knowledge to assist novices and experts in promoting advancements and research.

Review on impacts of micro- and nano-plastic on aquatic ecosystems and mitigation strategies

The rapid proliferation of microplastics (MPs) and nanoplastics (NPs) in our environment presents a formidable hazard to both biotic and abiotic components. These pollutants originate from various sources, including commercial production and the breakdown of larger plastic particles. Widespread contamination of the human body, agroecosystems, and animals occurs through ingestion, entry into the food chain, and inhalation. Consequently, the imperative to devise innovative methods for MPs and NPs remediation has become increasingly apparent. This review explores the current landscape of strategies proposed to mitigate the escalating threats associated with plastic waste. Among the array of methods in use, microbial remediation emerges as a promising avenue for the decomposition and reclamation of MPs and NPs. In response to the growing concern, numerous nations have already implemented or are in the process of adopting regulations to curtail MPs and NPs in aquatic habitats. This paper aims to address this gap by delving into the environmental fate, behaviour, transport, ecotoxicity, and management of MPs and NPs particles within the context of nanoscience, microbial ecology, and remediation technologies. Key findings of this review encompass the intricate interdependencies between MPs and NPs and their ecosystems. The ecological impact, from fate to ecotoxicity, is scrutinized in light of the burgeoning environmental imperative. As a result, this review not only provides an encompassing understanding of the ecological ramifications of MPs and NPs but also highlights the pressing need for further research, innovation, and informed interventions.

Polystyrene nanoplastics in the marine mussel Mytilus galloprovincialis

Concerns about plastic pollution and its toxicity towards animals and people are growing. Polystyrene (PS) is a plastic polymer highly produced in Europe for packaging purposes and building insulation amongst others. Whatever their source-illegal dumping, improper waste management, or a lack of treatment for the removal of plastic debris from wastewater treatment plants-PS products ultimately end up in the marine environment. Nanoplastics (<1000 nm) are the new focus for plastic pollution, gaining broad interest. Whether primary or secondary, their small size permits nanoparticles to cross cellular boundaries, consequently leading to adverse toxic effects. An in vitro assay of Mytilus galloprovincialis haemocytes exposed to 10 μg/L of polystyrene nanoplastics (PS-NPs; 50 nm) for 24 h was used to test cellular viability along with the luminescence inhibition (LC50) of Aliivibrio fischeri bacteria to evaluate acute toxicity. Cellular viability of mussel haemocytes decreased significantly after a 24 h exposure and PS-NPs LC50 range from 180 to 217, μg/L. In addition, a 28-day exposure of the marine bivalve M. galloprovincialis to PS-NPs (10 μg/L; 50 nm) was performed to evaluate the neurotoxic effects and the uptake of these plastic particles in three bivalve tissues (gills, digestive gland, and gonads). The ingestion of PS-NPs was time- and tissue-specific, suggesting that PS-NPs are ingested through the gills and then translocated through the mussel bloodstream, to the digestive gland and gonads where the highest amount of ingested PS-NPs was reported. Ingested PS-NPs may compromise the digestive glands' key metabolic function and impair mussels' gametogenic and reproductive success. Data on acetylcholinesterase inhibition and those previously obtained on a wide range of cellular biomarkers were elaborated through weighted criteria providing a synthetic assessment of cellular hazard from PS-NPs.

The complexity of micro- and nanoplastic research in the genus Daphnia - A systematic review of study variability and a meta-analysis of immobilization rates

In recent years, the number of publications on nano- and microplastic particles (NMPs) effects on freshwater organisms has increased rapidly. Freshwater crustaceans of the genus Daphnia are widely used in ecotoxicological research as model organisms for assessing the impact of NMPs. However, the diversity of experimental designs in these studies makes conclusions about the general impact of NMPs on Daphnia challenging. To approach this, we systematically reviewed the literature on NMP effects on Daphnia and summarized the diversity of test organisms, experimental conditions, NMP properties and measured endpoints to identify gaps in our knowledge of NMP effects on Daphnia. We use a meta-analysis on mortality and immobilization rates extracted from the compiled literature to illustrate how NMP properties, study parameters and the biology of Daphnia can impact outcomes in toxicity bioassays. In addition, we investigate the extent to which the available data can be used to predict the toxicity of untested NMPs based on the extracted parameters. Based on our results, we argue that focusing on a more diverse set of NMP properties combined with a more detailed characterization of the particles in future studies will help to fill current research gaps, improve predictive models and allow the identification of NMP properties linked to toxicity.

Combined impacts of microplastics and cadmium on the liver function, immune response, and intestinal microbiota of crucian carp (Carassius carassius)

Microplastics (MPs) and the heavy metal cadmium (Cd) have attracted global attention for their toxicological interactions in aquatic organisms. The purpose of this investigation was evaluating the effect of MPs (1 mg L^-1) and Cd (5 mg L^-1) on the liver function, immune response of crucian carp (Carassius carassius) after 96 h exposure, and intestinal microbiota after 21 days, respectively. Co-exposure to MPs and Cd significantly enhanced MP accumulation in the liver of the crucian carp compared to the accumulation with exposure to MPs alone. Co-exposure to MPs and Cd triggered notable histopathological alterations accompanied by increased hepatic cell necrosis and inflammation, and was associated with higher aspartate aminotransferase and alanine aminotransferase levels, lower superoxide dismutase and catalase activity levels, but higher malondialdehyde content and total antioxidant capacity in the liver. Moreover, the combined treatment of MPs and Cd led to the up-regulated transcription of genes related to immune response, such as interleukin 8 (il-8), il-10, il-1β, tumor necrosis factor-α, and heat shock protein 70, both in the liver and spleen. Co-exposure to MPs and Cd reduced the variety and abundance of the intestinal microbiota in the crucian carp. Our research indicates that the combined exposure to MPs and Cd may exert synergistic toxic effects on crucian carp, which could impede the sustainable growth of the aquaculture industry and pose potential risks to food safety.

Uptake and Effects of Nanoplastics on the Dinoflagellate Gymnodinium corollarium

Plastic nanoparticles (NPs) are the final state of plastic degradation in the environment before they disintegrate into low-molecular-weight organic compounds. Unicellular organisms are highly sensitive to the toxic effects of nanoplastics, because they are often capable of phagotrophy but are unable to consume a foreign material such as synthetic plastic. We studied the effect of polystyrene, poly(vinyl chloride), poly(methyl acrylate), and poly(methyl methacrylate) NPs on the photosynthetic dinoflagellate Gymnodinium corollarium Sundström, Kremp et Daugbjerg. Fluorescent tagged particles were used to visualize plastic capture by dinoflagellate cells. We found that these dinoflagellates are capable of phagotrophic nutrition and thus should be regarded as mixotrophic species. This causes their susceptibility to the toxic effects of plastic NPs. Living cells ingest plastic NPs and accumulate in the cytoplasm as micrometer-level aggregates, probably in food vacuoles. The action of nanoplastics leads to a dose-dependent increase in the level of reactive oxygen species in dinoflagellate cells, indicating plastic degradation in the cells. The introduction of a methyl group into the main chain in the α-position in the case of poly(methyl methacrylate) causes a drastic reduction in toxicity. We expect that such NPs can be a tool for testing unicellular organisms in terms of heterotrophic feeding ability. We suggest a dual role of dinoflagellates in the ecological fate of plastic waste: the involvement of nanoplastics in the food chain and its biochemical destruction. Environ Toxicol Chem 2023;42:1124-1133. © 2023 SETAC.

Organismal response to micro(nano)plastics at environmentally relevant concentrations: Toxicity and the underlying mechanisms

The toxic effects of micro(nano)plastics are long-standing, flourishing and fadeless as a research topic because of its' underlying threats to the ecology and human health. Nevertheless, in most of the existing studies, some model organisms are exposed to micro(nano)plastics at a high concentration unlikely to occur in the real environment, and there is limited data available on the impact of micro(nano)plastics at environmentally relevant concentrations (ERC) on environmental organisms. To gain a better insight into micro(nano)plastic toxicity to the environmental organisms, here we integrate the related publications of micro(nano)plastic research at ERC in the past 10 years using a bibliometric analysis, and focus on the analysis of publication trends, research focuses, collaborations, and research status. In addition, we further analyze the 33 final filtered literature, and elucidate the organismal response to micro(nano)plastics at ERC from the perspective of in vivo toxic effects and mechanisms involved. This paper also puts forward some limitations of the current study and some suggestions for future research. Our study may be of great significance in further understanding the ecotoxicity of micro(nano)plastics.

Tracking nanoplastics in freshwater microcosms and their impacts to aquatic organisms

In this work, we used palladium-doped polystyrene NPLs (PS-NPLs with a primary size of 286 ± 4 nm) with an irregular surface morphology which allowed for particle tracking and evaluation of their toxicity on two primary producers (cyanobacterium, Anabaena sp. PCC7120 and green algae, Chlamydomonas reinhardtii) and one primary consumer (crustacean, Daphnia magna). the concentration range for Anabaena and C. reinhardtii was from 0.01 to 1000 mg/L and for D. magna, the range was from 7.5 to 120 mg/L.EC_50 s ranged from 49 mg NPLs/L for D. magna (48hEC_50 s) to 248 mg NPLs/L (72hEC_50 s for C. reinhardtii). PS-NPLs induced dose-dependent reactive oxygen species overproduction, membrane damage and metabolic alterations. To shed light on the environmental fate of PS-NPLs, the short-term distribution of PS-NPLs under static (using lake water and sediments) and stirring (using river water and sediments) conditions was studied at laboratory scale. The results showed that most NPLs remained in the water column over the course of 48 h. The maximum percentage of settled particles (∼ 30 %) was found under stirring conditions in comparison with the ∼ 10 % observed under static ones. Natural organic matter increased the stability of the NPLs under colloidal state while organisms favored their settlement. This study expands the current knowledge of the biological effects and fate of NPLs in freshwater environments.

Critical gaps in nanoplastics research and their connection to risk assessment

Reports of plastics, at higher levels than previously thought, in the water that we drink and the air that we breathe, are generating considerable interest and concern. Plastics have been recorded in almost every environment in the world with estimates on the order of trillions of microplastic pieces. Yet, this may very well be an underestimate of plastic pollution as a whole. Once microplastics (<5 mm) break down in the environment, they nominally enter the nanoscale (<1,000 nm), where they cannot be seen by the naked eye or even with the use of a typical laboratory microscope. Thus far, research has focused on plastics in the macro- (>25 mm) and micro-size ranges, which are easier to detect and identify, leaving large knowledge gaps in our understanding of nanoplastic debris. Our ability to ask and answer questions relating to the transport, fate, and potential toxicity of these particles is disadvantaged by the detection and identification limits of current technology. Furthermore, laboratory exposures have been substantially constrained to the study of commercially available nanoplastics; i.e., polystyrene spheres, which do not adequately reflect the composition of environmental plastic debris. While a great deal of plastic-focused research has been published in recent years, the pattern of the work does not answer a number of key factors vital to calculating risk that takes into account the smallest plastic particles; namely, sources, fate and transport, exposure measures, toxicity and effects. These data are critical to inform regulatory decision making and to implement adaptive management strategies that mitigate risk to human health and the environment. This paper reviews the current state-of-the-science on nanoplastic research, highlighting areas where data are needed to establish robust risk assessments that take into account plastics pollution. Where nanoplastic-specific data are not available, suggested substitutions are indicated.

Review on the ecotoxicological impacts of plastic pollution on the freshwater invertebrate Daphnia

The environmental impacts of plastic pollution have recently attracted universal attention, especially in the aquatic environment. However, research has mostly been focused on marine ecosystems, even though freshwater ecosystems are equally if not more polluted by plastics. In addition, the mechanism and extent to which plastic pollution affects aquatic biota and the rates of transfer to organisms through food webs eventually reaching humans are poorly understood, especially considering leaching hazardous chemicals. Several studies have demonstrated extreme toxicity in freshwater organisms such Daphnia. When such keystone species are affected by ambient pollution, entire food webs are destabilized and biodiversity is threatened. The unremitting increase in plastic contaminants in freshwater environments would cause impairments in ecosystem functions and structure, leading to various kinds of negative ecological consequences. As various studies have reported the effects on daphnids, a consolidation of this literature is critical to discuss the limitations and knowledge gaps and to evaluate the risk posed to the aquatic environment. This review was undertaken due to the evident need to evaluate this threat. The aims were to provide a meaningful overview of the literature relevant to the potential impact of plastic pollution and associated contaminants on freshwater daphnids as primary consumers. A critical evaluation of research gaps and perspectives is conducted to provide a comprehensive risk assessment of microplastic as a hazard to aquatic environments. We outlined the challenges and limitations to microplastic research in hampering better-focused investigations that could support the development of new plastic materials and/or establishment of new regulations.

Plastics in scene: A review of the effect of plastics in aquatic crustaceans

Plastic pollution in aquatic environments is present in all compartments from surface water to benthic sediment, becoming a topic of emerging concern due to the internalization, retention time, and its effects on aquatic biota. Crustacea with nearly 70,000 species, broad distribution and different roles in the trophic webs is a significant target of the increasing plastic pollution. At least 98 publications in the last 10 years report the impact of plastics in crustaceans, all suggesting that this taxon is at high risk for ecosystem disadvantage by plastic contamination loads. This review compiles the current knowledge on physiological effects (endpoints) by plastic contamination analyzed in crustaceans in the last 10 years, highlighting their use as model species for ecotoxicological tests, sentinels species and bioindicators. Plastic contamination analyzed in this review includes macroplastic, microplastic, and nanoplastic, in a wide variety of types. The studies were focused on 38 marine species with an economic interest in fisheries and aquaculture; 14 freshwater with a higher frequency in standard test species and 4 estuarial and 3 mangrove species with ecological interest. The publications reviewed were divided into studies describing plastic presence in crustaceans without reporting toxic effects and those with analysis of plastic toxicity. Publications describing the plastic presence in the organisms show that the ingestion in individual effects and food-web transfer in ecological effects were the most frequent endpoints. The publications that analyzed plastic toxicity through survival, nutrition-metabolism-assimilation, and reproduction in individual effects, and bioaccumulation in ecological effects were the most frequent endpoints. This review gathers the available information on the use of crustaceans as model species in environmental impact for toxicity screening and hazard assessment. Besides, identifying knowledge gaps will let us propose some future directions in research and the effects on target fisheries species which involves a possible effect on human health.

Feeding exposure and feeding behaviour as relevant approaches in the assessment of the effects of micro(nano)plastics to early life stages of amphibians

The sedimentation of micro and nanosized plastics is of considerable environmental relevance and the need to assess its sublethal effects to biota increasingly recognized. In their majority, as bottom, non-selective grazers, independent-feeding young life stages of amphibians, an already severely endangered worldwide group, may be particularly vulnerable to sedimented plastics. Alongside, they may be good model organisms for the assessment of the effects of micro(nano)plastics (MNPs) through ingestion. However, to our knowledge, few studies have assessed amphibians' exposure to MNPs through contaminated food or its effects in feeding behaviour assays. The available studies reveal a lack of consistent methodology: organisms, food type, media of exposure, or exposure conditions (temperature and light) in the assessment of effects. This perspective article, will address major differences found in the available studies, identifying type, size and concentrations of the polymers tested, species, and observed effects, aiming to highlight the importance of feeding exposure assays when attempting to evaluate the effect of MNPs in amphibians.

Identification and toxicity towards aquatic primary producers of the smallest fractions released from hydrolytic degradation of polycaprolactone microplastics

Bioplastics are thought as a safe substitute of non-biodegradable polymers. However, once released in the environment, biodegradation may be very slow, and they also suffer abiotic fragmentation processes, which may give rise to different fractions of polymer sizes. We present novel data on abiotic hydrolytic degradation of polycaprolactone (PCL), tracking the presence of by-products during 132 days by combining different physicochemical techniques. During the study a considerable amount of two small size plastic fractions were found (up to ∼ 6 mg of PCL by-product/g of PCL beads after 132 days of degradation); and classified as submicron-plastics (sMPs) from 1 μm to 100 nm and nanoplastics (NPs, <100 nm) as well as oligomers. The potential toxicity of the smallest fractions, PCL by-products < 100 nm (PCL-NPs + PCL oligomers) and the PCL oligomers single fraction, was tested on two ecologically relevant aquatic primary producers: the heterocystous filamentous nitrogen-fixing cyanobacterium Anabaena sp. PCC 7120, and the unicellular cyanobacterium Synechococcus sp. PCC 7942. Upon exposure to both, single and combined fractions, Reactive Oxygen Species (ROS) overproduction, intracellular pH and metabolic activity alterations were observed in both organisms, whilst membrane potential and morphological damages were only observed upon PCL-NPs + PCL oligomers exposure. Notably both PCL by-products fractions inhibited nitrogen fixation in Anabaena, which may be clearly detrimental for the aquatic trophic chain. As conclusion, fragmentation of bioplastics may render a continuous production of secondary nanoplastics as well as oligomers that might be toxic to the surrounding biota; both PCL-NPs and PCL oligomers, but largely the nanoparticulate fraction, were harmful for the two aquatic primary producers. Efforts should be made to thoroughly understand the fragmentation of bioplastics and the toxicity of the smallest fractions resulting from that degradation.

Nanoplastics: Status and Knowledge Gaps in the Finalization of Environmental Risk Assessments

Nanoplastics (NPs) are particles ranging in size between 1 and 1000 nm, and they are a form of environmental contaminant of great ecotoxicological concern. Although NPs are widespread across ecosystems, they have only recently garnered growing attention from both the scientific community and regulatory bodies. The present study reviews scientific literature related to the exposure and effects of NPs and identifies research gaps that impede the finalization of related environmental risk assessments (ERAs). Approximately 80 articles published between 2012 and 2021 were considered. Very few studies (eight articles) focused on the presence of NPs in biotic matrices, whereas the majority of the studies (62 articles) assessed the lethal and sublethal effects of NPs on aquatic and terrestrial organisms. Whilst many studies focused on nude NPs, only a few considered their association with different aggregates. Amongst NPs, the effects of polystyrene are the most extensively reported to date. Moreover, the effects of NPs on aquatic organisms are better characterized than those on terrestrial organisms. NP concentrations detected in water were close to or even higher than the sublethal levels for organisms. An ERA framework specifically tailored to NPs is proposed.

Investigation of acute toxicity, accumulation, and depuration of ZnO nanoparticles in Daphnia magna

Size is a key factor controlling the rate of dissolution of nanoparticles, such property can be explored for producing controlled release fertilizers. Hence, one can expect the increasing discharge of nanoparticles closer to water streams in the near future. In this study, we employed the model fresh water organism Daphnia magna to investigate the uptake, acute toxicity and depuration of ZnO nanoparticles. The present study shows that the median lethal concentration (LC₅₀) depended on particle size and the presence of surfactant. The LC₅₀ for positive control ZnSO₄ (2.15 mg L^-1), 20 nm ZnO (1.68 mg L^-1), and 40 nm ZnO (1.71 mg L^-1) were statistically the same. However, the addition of surfactant increased the LC₅₀ of 40 nm and 60 nm to 2.93 and 3.24 mg L^-1, respectively. The 300 nm ZnO was the least toxic nanoparticle presenting LC₅₀ of 6.35 mg L^-1. X-ray fluorescence chemical imaging revealed that Zn accumulated along the digestive system regardless the particle size. Finally, contrary to what have been reported by several papers, the present study did not detect any depuration of ZnO nanoparticles in the next 24 h past the exposure assays. Thus, the ability of organisms to expel ingested nanomaterials might be dependent on specific physical-chemical features of such nanomaterials.

Nanoplastic State and Fate in Aquatic Environments: Multiscale Modeling

We now know that nanoplastics can harm aquatic organisms, but understanding ecological risk starts with understanding fate. We coupled population balance and fugacity models to predict the conditions under which nanoplastics remain as single particles, aggregate, or sediment and to predict their capacity to concentrate organic pollutants. We carried out simulations across a broad range of nanoplastic concentrations, particle sizes, and particle-particle interactions under a range of salinity and organic matter conditions. The model predicts that across plastic materials and environmental conditions, nanoplastics will either remain mostly dispersed or settle as aggregates with natural colloids. Nanoplastics of different size classes respond dissimilarly to concentration, ionic strength, and organic matter content, indicating that the sizes of nanoplastics to which organisms are exposed likely shift across ecological zones. We implemented a fugacity model of the Great Lakes to assess the organic pollution payload carried by nanoplastics, generating the expectation that nanoplastics would carry nine times more pollutants than microsized plastics and a threshold concentration of 10 μg/L at which they impact pollutant distribution. Our simulations across a broad range of factors inform future experimentation by highlighting the relative importance of size, concentration, material properties, and interactions in driving nanoplastic fate in aquatic environments.

Polymethylmethacrylate nanoplastics can cause developmental malformations in early life stages of Xenopus laevis

Polymethylmethacrylate (PMMA) production has increased almost 20% over the last years. With its release into the aquatic environment, its breakdown or degradation to nano dimensions (nanoplastics-NPLs) due to biological and physical/mechanical action is, theoretically, anticipated. The occurrence of PMMA-NPLs in aquatic ecosystems may thus cause adverse effects particularly to early life stages of amphibians, which may be in contact with PMMA-NPLs suspended in the water column or deposited in upper layers of the sediments. Accordingly, this work aimed at assessing the effects of PMMA-NPLs to aquatic early life stages of the model anuran species Xenopus laevis. To attain this objective, two types of toxicity assays were carried out by exposing embryos [Nieuwkoop and Faber (NF) stage 8-11] or tadpoles (NF 45) to three concentrations of PMMA-NPLs (1, 100 and 1000 μg/L): i) 96-h embryo teratogenicity assay, where survival, malformation, and total body length (BL) of embryos were assessed; and ii) 48-h feeding rate assay, where survival, feeding (FR), malformations and growth rates (body weight-BW and BL) of tadpoles were evaluated. PMMA-NPLs exposure had no significant effects on mortality, malformations of X. laevis embryos but BL was lower at 1000 μg PMMA-NPLs/L. In tadpoles, no effects on survival or FR were observed after exposure to PMMA-NPLs, but significant changes occured in BW and BL. Moreover, anatomical changes in the abdominal region (externalization of the gut) were observed in 62.5% of the tadpoles exposed to 1000 μg PMMA-NPLs/L. Despite the lack of knowledge regarding the environmental levels of NPLs, it is expected that sediments constitute a sink for these contaminants, where they can become available for organisms that, like tadpoles, feed on the organic matter at the surface of sediments. Considering the continuous release and subsequent accumulation of PMMA, the malformations obtained in the feeding assays suggest that, in the future, these nano-polymers may constitute a risk for aquatic life stages of amphibians.

Toxicity of nanoplastics to zooplankton is influenced by temperature, salinity, and natural particulate matter

Increases in temperature/salinity promote nanoplastics toxicity, while organic matter/natural colloids mitigate toxicity.

Elucidating the enhanced decomposition of alkyl hydroperoxides on oxygen vacancy rich TiO2−x surfaces using DFT for polyethylene decomposition

Oxygen vacancies in TiO2 enhance the polyethylene degradation by accelerating the decomposition of alkyl hydroperoxide decomposition rate limiting step.

Chemical composition and particle size influence the toxicity of nanoscale plastic debris and their co-occurring benzo(α)pyrene in the model aquatic organisms Daphnia magna and Danio rerio

Little is known about how particle chemical composition and size might influence the toxicity of nanoscale plastic debris (NPD) and their co-occurring chemicals. Herein, we investigate the toxicity of 3 × 10¹⁰ particles/L polyethylene (PE, 50 nm), polypropylene (PP, 50 nm), polystyrene (PS, 200 and 600 nm), and polyvinyl chloride (PVC, 200 nm) NPD and their co-occurring benzo(a)pyrene (BaP) to Daphnia magna and Danio rerio. During the 21 days of exposure to PE 50 nm and PS 200 nm, the number of broods produced by D. magna decreased compared to other treatments. Exposure to BaP alone did not produce any effects on the reproduction of the daphnids, however, the mixture of BaP with PS (200 or 600 nm) or with PE (50 nm) reduced the number of broods. Exposure of D. rerio embryos to PE 50 nm, PS 200 nm, and PS 600 nm led to a delay in the hatching. The presence of PS 200 nm and PVC 200 nm eliminated the effects of BaP on the hatching rate of zebrafish. Our findings suggest that data generated for the toxicity of one type of NPD, e.g. PVC or PS may not be extrapolated to other types of NPD.

Moving forward in microplastic research: A Norwegian perspective

Given the increasing attention on the occurrence of microplastics in the environment, and the potential environmental threats they pose, there is a need for researchers to move quickly from basic understanding to applied science that supports decision makers in finding feasible mitigation measures and solutions. At the same time, they must provide sufficient, accurate and clear information to the media, public and other relevant groups (e.g., NGOs). Key requirements include systematic and coordinated research efforts to enable evidence-based decision making and to develop efficient policy measures on all scales (national, regional and global). To achieve this, collaboration between key actors is essential and should include researchers from multiple disciplines, policymakers, authorities, civil and industry organizations, and the public. This further requires clear and informative communication processes, and open and continuous dialogues between all actors. Cross-discipline dialogues between researchers should focus on scientific quality and harmonization, defining and accurately communicating the state of knowledge, and prioritization of topics that are critical for both research and policy, with the common goal to establish and update action plans for holistic benefit. In Norway, cross-sectoral collaboration has been fundamental in supporting the national strategy to address plastic pollution. Researchers, stakeholders and the environmental authorities have come together to exchange knowledge, identify knowledge gaps, and set targeted and feasible measures to tackle one of the most challenging aspects of plastic pollution: microplastic. In this article, we present a Norwegian perspective on the state of knowledge on microplastic research efforts. Norway's involvement in international efforts to combat plastic pollution aims at serving as an example of how key actors can collaborate synergistically to share knowledge, address shortcomings, and outline ways forward to address environmental challenges.

Occurrence and characterization of microplastic content in the digestive system of riverine fishes

In the present study, the occurrence and characterization of microplastics (MPs) content in the fishes of the river was studied. Therefore, six sampling stations were considered for fishing. Then, the entire stomach of fishes was investigated by visual stereomicroscope, FTIR, SEM, and EDX to analyze the content of the samples, by MPs type, shape, color, and size. The most frequency of MPs was observed in Ghazanchi (S_iii) and Kermanshah (S_iv) stations which were close to urban and industrial areas. Most types of detected MPs included polystyrene, polyethylene, and nylon with the highest frequency observed in Luciobarbus caspius and Alburnus chalcoides fishes. Overall, the frequency of detected MPs in the caught fishes was 93.8%. Indeed, MPs with a size of 0.025-1 mm (25-1000 μm) were the most frequency of MPs in fishes. The frequency of MPs shapes was fiber (85.12%), fragment (12.32%), foam (0.77%), film (1.21%), and microbead (0.56%), respectively. The highest and lowest percentage of MPs belonged to black and green with an abundance of 63% and 2%, respectively. The result implies that lots of riverine fishes are polluted with MPs, those which can move into the food chain.

Cardiovascular toxicity assessment of polyethylene nanoplastics on developing zebrafish embryos

Environmental exposure to nanoplastics is inevitable as the application of nanoplastics in our daily life is more and more extensively. So, the adverse effects of nanoplastics on human health are also gaining greater concerns. However, the subsequent toxicological response to nanoplastics, especially on cardiovascular damage was still largely unknown. In this regard, the evaluation of cardiovascular effects of nanoplastics was performed in zebrafish embryos. The results indicated that the no observed adverse effect level (NOAEL) of nanoplastics is 50 μg/mL. The pericardial toxicity and hemodynamic changes were assessed by Albino (melanin allele) mutant zebrafish line. Severe pericardial edema was observed in zebrafish embryos after exposure to nanoplastics. At the concentration higher than NOAEL, nanoplastics significantly decreased the cardiac output (CO) and blood flow velocity. The fluorescence images manifested that the nanoplastics could inhibit the subintestinal angiogenesis of transgenic zebrafish embryos line Tg (fli-1: EGFP), which might disturb the cardiovascular formation and development. The resulting vascular endothelial dysfunction and hypercoagulable state of circulating blood further accelerated thrombosis. Reactive oxidative stress (ROS) and systemic inflammation were also found in Wild AB and Tg (mpo: GFP) zebrafish embryos, respectively. We also found many neutrophils recruiting in the tail vein where the zebrafish embryo thrombosis occurred. Our data suggested that nanoplastics could trigger the cardiovascular toxicity in zebrafish embryos, which could provide an essential clue for the safety assessment of nanoplastics.

Short-term exposure to polymethylmethacrylate nanoplastics alters muscle antioxidant response, development and growth in Sparus aurata

Polymethylmethacrylate (PMMA) plastic fragments have been found abundant in the environment, but the knowledge regarding its effects on the physiology of aquatic animals is still poorly studied. Here the short-term (96 h) effects of waterborne exposure to PMMA nanoplastics (PMMA-NPs) on the muscle of gilthead sea bream (Sparus aurata) fingerlings was evaluated at a concentration range that includes 0.001 up to 10 mg/L. The expression of key transcripts related to cell stress, tissue repair, immune response, antioxidant status and muscle development, together with several biochemical endpoints and metabolic parameters. Results indicate that exposure to PMMA-NPs elicit mildly antioxidant responses, enhanced the acetylcholinesterase (AChE) activity, and inhibited key regulators of muscle development (growth hormone receptors ghr-1/ghr-2 and myostatin, mstn-1 transcripts). However, no effects on pro-inflammatory cytokines (interleukin 1β, il1β and tumor necrosis factor α, tnfα) expression nor on the levels of energetic substrates (glucose, triglycerides and cholesterol) were found.

Biochar-facilitated remediation of nanoplastic contaminated water: Effect of pyrolysis temperature induced surface modifications

"Nanoplastics- the emerging contaminants" and "agricultural waste to resource conversion" both are currently at the scientific frontiers and require solutions. This study aims to utilize sugarcane bagasse-derived biochar for the removal of nanoplastics (NPs) from aqueous environment. Three types of biochar were synthesized at three different pyrolysis temperatures, i.e. 350, 550, and 750 ℃ and evaluated for their potential in removing NPs. Effect of various environmental parameters, i.e., competing ions, pH, humic acid and complex aqueous matrices on NPs sorption was also studied. Results showed that attributing to decreased carbonyl functional groups, increased surface area and pore abundance, biochar prepared at 750 ℃ showed drastically higher NPs removal (>99%), while BC-550 and BC-350 showed comparatively lower NPs sorption (<39% and <24%, respectively). Further sorption studies confirmed instantaneous NPs removal with equilibrium attainment within 5 min of interaction and efficient NPs sorption capacity, i.e. 44.9 mg/g for biochar prepared at 750 ℃. Non-linear-kinetic modeling suggested pseudo 1st order removal kinetics while isotherm and thermodynamic modeling confirmed- monolayer instantaneous sorption of NPs sorption. Enhanced electrostatic repulsion resulted in decrease in NPs sorption at alkaline conditions, whereas steric hindrance caused limited removal (<25%) at higher humic acid concentrations.

Comprehending the complexity of microplastic organismal exposures and effects, to improve testing frameworks

Microplastics (MPs) have been identified as a threat to global ecosystems. Current projections indicate that the negative impacts of MPs will increase in the environment. Traditional toxicity testing does not account for the diversity of MP particles, the inherent diversity in potential exposure routes, and complex impacts in exposed organisms. Here we present and discuss factors influencing organismal exposure to MPs driven by fate and behavior of MPs in different environmental matrices and organisms behavioral niches. We then provide a structured classification of potential effects of MPs, chemical or particulate, generic or specific to MPs. Using these analyses, we discuss appropriateness and limitations of applying traditional, chemical-based ecotoxicity testing for the study of MPs, and propose practical recommendations and guidelines. Future laboratory based studies can be improved to increase understanding of potential real world effects of MPs by careful selection of appropriate exposure systems and conditions, test organism, MP characteristics, endpoints and required controls. We build upon recommendations provided in previous publications and complement them with a list of parameters and practical information that should be checked and/or reported in MP studies.

Quality of nanoplastics and microplastics ecotoxicity studies: Refining quality criteria for nanomaterial studies

It is becoming increasingly important to develop assessment criteria for the quality of nanoplastics studies. This study is an attempt to establish such criteria based on those developed for engineered nanomaterials, the GUIDEnano and DaNa criteria being two representatives. These criteria were applied to studies on polystyrene nanoparticles (PS NPs), which currently represent the majority of studies on nanoplastics. We compiled a list of existing nanomaterial-related criteria that are not fully relevant to PS NPs and propose additional nanoplastic-specific criteria targeting polymer chemical composition, source, production and field collection, impurities/chemical additives, density, hydrophobicity, colour, and chemical leaching. For each criterion, scientific justification is provided. We conclude that the existing study quality assessments originally developed for nano(eco)toxicity studies can, through refinements, be applied to those dealing with nanoplastics studies, with a further outlook on microplastics. The final quality criteria catalogue presented here is intended as a starting point for further elaborations considering different purposes of an assessment.

Submicro- and nanoplastics: How much can be expected in water bodies?

Plastic particles smaller than 1 μm are considered to be highly dangerous pollutants due to their ability to penetrate living cells. Model experiments on the toxicity of plastics should be correlated with actual concentrations of plastics in natural water. We simulated the natural destruction of polystyrene, polyvinyl chloride, and poly(methyl methacrylate) in experiments on the abrasion of plastics with small stones. The plastics were dyed in mass with a fluorescent dye, which made it possible to distinguish plastic particles from stone fragments. We found that less than 1% of polystyrene and polyvinyl chloride were converted to submicron size particles. In the case of more rigid poly(methyl methacrylate), the fraction of such particles reaches 11%. The concentration of particles with a diameter less than 1 μm in the model experiments was from 0.7 (polystyrene) to 13 mg/L (poly(methyl methacrylate)), and when transferring the obtained data to real reservoirs, these values should be reduced by several orders of magnitude. These data explain the difficulties associated with the search for nanoplastics in natural waters. The toxicity of such particles to hydrobionts in model experiments was detected for concentrations greater than 1 mg/L, which is unrealistic in nature. Detectable and toxic amounts of nano- and submicron plastic particles in living organisms can be expected only in the case of filter-feeding organisms, such as molluscs, krill, sponges, etc.

Induction of protective response to polystyrene nanoparticles associated with methylation regulation in Caenorhabditis elegans

The epigenetic regulation mechanisms for toxicity induction of nanoplastics in organisms remain largely unknown. In Caenorhabditis elegans, we found that prolonged exposure to 1-100 μg/L polystyrene nanoparticles (PS-NPs) decreased expression of MET-2, a H3K9 methyltransferase. Meanwhile, RNAi knockdown of met-2 suppressed the PS-NPs toxicity in inducing production of reactive oxygen species (ROS) and in decreasing locomotion behavior, which suggesting that the decrease in MET-2 expression reflected a protective response. This resistance to PS-NPs toxicity could be further detected in worms with met-2 RNAi knockdown in both intestinal cells and germline cells. In PS-NPs exposed worms, intestinal RNAi knockdown of met-2 significantly increased expressions of daf-16, bar-1, and elt-2. Intestinal RNAi knockdown of daf-16, bar-1, or elt-2 suppressed the resistance of met-2(RNAi) worms to PS-NPs toxicity, suggesting that MET-2 functioned upstream of ELT-2, BAR-1, and DAF-16 in intestinal cells to control PS-NPs toxicity. Moreover, in PS-NPs exposed worms, germline RNAi knockdown of met-2 significantly decreased expressions of wrt-3 and pat-12. RNAi knockdown of wrt-3 or pat-12 further inhibited the susceptibility of worms overexpressing germline MET-2 to PS-NPs toxicity, suggesting that MET-2 functioned upstream of PAT-12 and WRT-3 in germline cells to control PS-NPs toxicity. Therefore, our data provided an important molecular basis for MET-2-mediated methylation regulation in causing protective response to nanoplastics in organisms.

Polymethylmethacrylate nanoplastics effects on the freshwater cnidarian Hydra viridissima

The current understanding of nanoplastics (NPLs) toxicity to freshwater biota, especially the potential toxic effects of polymethylmethacrylate (PMMA), remains limited. Thus, the present work intended to add knowledge about the ecotoxicity of ∼40 nm PMMA-NPLs focusing on lethality, morphology, feeding and regeneration capacity of the freshwater cnidarian Hydra viridissima, after an exposure period of 96 h. Results showed that high concentrations of PMMA-NPLs can impair the survival of H. viridissima, with an estimated 96 h-LC₅₀ of 84.0 mg PMMA-NPLs/L. Several morphological alterations were detected at concentrations below 40 PMMA-NPLs mg/L, namely partial or total loss of tentacles, which, however, did not induce significant alterations on the feeding rates. Morphological alterations not previously reported in the literature were also found after the 96 h exposure, such as double or elbow-like tentacles. Exposure to 40 mg PMMA-NPLs/L significantly impacted hydra regeneration, with organisms exposed to PMMA-NPLs presenting significant slower regeneration rates comparatively to controls, but with no impacts on the feeding rates. Overall, this work highlights the need to assess the effects of NPLs in freshwater biota. Hydra viridissima species was sensitive in a wide range of endpoints showing its value as a biological model to study the effects of small plastic particles.

Photocatalytic Degradation of Polyamide 66; Evaluating the Feasibility of Photocatalysis as a Microfibre-Targeting Technology

Wastewater treatment plants (WWTPs) have been identified as main contributors to releasing microfibres into the environment, however, WWTPs do not have microfibre-targeting technologies. In this study, photocatalysis is evaluated as a potential technology to treat microfibres in WWTPs by studying the degradation of polyamide 66 (PA66) microfibres using ultraviolet (UV) and titanium dioxide (TiO2). PA66 microfibres suspended in deionised water were exposed to different combinations of UV and TiO2. The degradation of the PA66 microfibres was monitored by changes in mass, carbonyl index and morphology using microbalance, infrared spectroscopy, and scanning electron microscopy. The formation of by-products from the degradation of the fibres was evaluated by measuring the chemical oxygen demand (COD) of the treated water. The degradation efficiency was optimised under UVC with a dose of 100 mg TiO2/L. Under these conditions, the PA66 microfibres presented a 97% mass loss within 48 h. The photocatalytic conditions applied generated a relatively low level of by-products (<10 mg/L of COD). Therefore, photocatalysis with TiO2 an UVC could potentially be a feasible technology to treat microfibres in WWTPs, although more investigation is required to establish if this treatment leads to the formation of nanofibres. Further work is needed to translate the present optimised conditions to WWTPs.

Application of Zn/Al layered double hydroxides for the removal of nano-scale plastic debris from aqueous systems

Nano-scale plastic debris (NPDs) are emerging as potential contaminants as they can be easily ingested by aquatic organisms and carry many pollutants in the environment. This study is aimed to remove NPDs from aqueous environment for the first time by using eco-friendly adsorption techniques. Initially, the interaction between NPDs and synthesized Zn-Al layered double hydroxide (LDH) was confirmed by pH titration of Zn-Al LDH against NPDs at varying mass ratio (50:1 to 50:7) and FTIR analysis for both before and after 2 h of contact time. Fast removal was observed in deionized water and synthetic freshwater with maximum sorption capacity (Q_max) of 164.49 mg/g,162.62 mg/g, respectively, according to Sips isotherm. Whereas, removal was least in synthetic hard water having a Q_max value of 53 mg/g. For 2 mM concentration of SO₄^2- and PO₄^3-, the adsorption capacity significantly decreased to 2%. The removal efficiency was found 100 % at pH 4, while at pH 9, it reached 37 % due to increased competitive binding and destabilization of LDH under alkaline conditions. The process of sorption was spontaneous in different types of water studied. The study reveals that Zn-Al LDH can be used as potential adsorbent for the removal of NPDs from freshwater systems.

Nano-plastics and their analytical characterisation and fate in the marine environment: From source to sea

Polymer contamination is a major pollutant in all waterways and a significant concern of the 21st Century, gaining extensive research, media, and public attention. The polymer pollution problem is so vast; plastics are now observed in some of the Earth's most remote regions such as the Mariana trench. These polymers enter the waterways, migrate, breakdown; albeit slowly, and then interact with the environment and the surrounding biodiversity. It is these biodiversity and ecosystem interactions that are causing the most nervousness, where health researchers have demonstrated that plastics have entered the human food chain, also showing that plastics are damaging organisms, animals, and plants. Many researchers have focused on reviewing the macro and micro-forms of these polymer contaminants, demonstrating a lack of scientific data and also a lack of investigation regarding nano-sized polymers. It is these nano-polymers that have the greatest potential to cause the most harm to our oceans, waterways, and wildlife. This review has been especially ruthless in discussing nano-sized polymers, their ability to interact with organisms, and the potential for these nano-polymers to cause environmental damage in the marine environment. This review details the breakdown of macro-, micro-, and nano-polymer contamination, examining the sources, the interactions, and the fates of all of these polymer sizes in the environment. The main focus of this review is to perform a comprehensive examination of the literature of the interaction of nanoplastics with organisms, soils, and waters; followed by the discussion of toxicological issues. A significant focus of the review is also on current analytical characterisation techniques for nanoplastics, which will enable researchers to develop protocols for nanopolymer analysis and enhance understanding of nanoplastics in the marine environment.

Nanoplastics in the oceans: Theory, experimental evidence and real world

This review critically analyses >200 papers collected by searching on Pubmed the word "nanoplastics", a group of emerging contaminants which are receiving growing attention. The present review intends to provide an overview of current knowledge on nanoplastic pollution starting with the theory of polymer degradation, passing to laboratory confirmation of nanoplastic formation and ending with the possible occurrence in sea water samples. Most of the observations proposed focus the attention on polystyrene (PS) because the majority of research knowledge is based on this polymer. Moreover, we thoroughly describe what effects have been observed on different organisms tested in controlled conditions. Nanoplastics formation, fate and toxicity seem to be a very dynamic phenomenon. In light of this, we identify some aspects retained crucial when an ecotoxicological study with nanoplastics is performed and which elements of nanoplastics toxicity could be deeper covered.

Interfacial interaction between diverse microplastics and tetracycline by adsorption in an aqueous solution

The accumulation of microplastics in offshore aquaculture waters has gradually become a threat to the survival of marine life, and the combined pollution of microplastics and other pollutants is attracting widespread attention. In this paper, tetracycline (TC) was selected as a typical antibiotic, and its adsorption behavior on the surface of diverse type and different sizes of microplastics was studied to explore their combined pollution in an aqueous solution. The results of isotherm fitting showed that the maximum adsorption capacity and coefficient of polyethylene (PE) were the largest, and the adsorption capacity of PE was the strongest among the three microplastics: polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC). With increasing PE particle size, the maximum adsorption capacity and adsorption coefficient of TC showed a significant decreasing trend, with a slight fluctuation in the middle. The presence of Pb²⁺, Cr³⁺, Cd²⁺, and Zn²⁺ markedly enhanced the adsorption of TC to PE, and Cu²⁺ could reduce the adsorption of TC to PE. The presence of chloride ions did not affect the adsorption process, which indicated that the adsorption mechanism between TC and microplastics is mainly an ion exchange mechanism. These results showed that the surface properties of microplastics and the chemical properties of the aqueous solution played an important role in the adsorption of TC. This study provides important scientific guidance and a theoretical basis for the study of the interfacial behavior, migration and transformation of marine microplastics.

Immunotoxicity of polystyrene nanoplastics in different hemocyte subpopulations of Mytilus galloprovincialis

Plastic represents 60-80% of litter in the ocean. Degradation of plastic to small fragments leads to the formation of microplastics (MPs <5 mm) and nanoplastics (NPs <1 µm). One of the most widely used and representative plastics found in the ocean is polystyrene (PS). Among marine organisms, the immune system of bivalves is recognized as suitable to assess nanomaterial toxicity. Hemocyte subpopulations [R1 (large granular cells), R2 (small semi-granular cells) and R3 (small agranular or hyaline cells)] of Mytilus galloprovincialis are specialized in particular tasks and functions. The authors propose to examine the effects of different sizes (50 nm, 100 nm and 1 μm) PS NPs on the different immune cells of mussels when they were exposed to (1 and 10 mg·L−1) of PS NPs. The most noteworthy results found in this work are: (i) 1 µm PS NPs provoked higher immunological responses with respect to 50 and 100 nm PS NPs, possibly related to the higher stability in size and shape in hemolymph serum, (ii) the R1 subpopulation was the most affected with respect to R2 and R3 concerning immunological responses and (iii) an increase in the release of toxic radicals, apoptotic signals, tracking of lysosomes and a decrease in phagocytic activity was found in R1.

PET microplastics toxicity on marine key species is influenced by pH, particle size and food variations

This study aims to evaluate effects induced by the exposure of key marine species to leachates and suspensions of different particle-size of PET microparticles, a plastic polymer that is actually considered safe for the environment. Leachates and suspensions of small (5-60 μm); medium (61-499 μm) and large (500-3000 μm) PET were tested on bacteria (V. fischeri; UNI EN ISO 11348-3:2009), algae (P. tricornutum; UNI EN ISO 10253:2016E), and echinoderms (P. lividus; EPA 600/R-95-136/Section 15) species both under standard (8.0) and acidified (7.5) pH conditions. Results obtained show that: i) conversely to larval stage of P. lividus, bacterial and algal tested species are not sensitive to PET pollution under all tested conditions; ii) different tested particle-sizes of PET produce effects that are not always related to their particle-size; iii) differences comparing acidified and standard pH conditions were recorded; iv) concerning echinoderms, food availability produce significant differences compared to fasting conditions; v) special attention on the possible interactions between MPs and other stressors (e.g., food and pH) is needed in order to give a better picture of natural occurring dynamics on marine ecosystems especially in the future frame of global changes.

Highly Branched Copolymers with Degradable Bridges for Antifouling Coatings

The antifouling properties of traditional self-polishing marine antifouling coatings are mainly achieved based on their hydrolysis-sensitive side groups or the degradable polymer main chains. Here, we prepared a highly branched copolymer for self-polishing antifouling coatings, in which the primary polymer chains are bridged by degradable fragments (poly-ε-caprolactone, PCL). Owing to the partial or complete degradation of PCL fragments, the remaining coating on the surface can be broken down and eroded by seawater. Finally, the polymeric surface is self-polished and self-renewed. The designed highly branched copolymers were successfully prepared by reversible complexation mediated polymerization (RCMP), and their primary main chains had an M_n of approximately 3410 g·mol^-1. The hydrolytic degradation results showed that the degradation of the copolymer was controlled, and the degradation rate increased with increasing contents of degradable fragments. The algae settlement assay tests indicated that the copolymer itself has some antibiofouling ability. Moreover, the copolymer can serve as a controlled release matrix for antifoulant 4,5-dichloro-2-octylisothiazolone (DCOIT), and the release rate increases with the contents of degradable fragments. The marine field tests confirmed that these copolymer-based coatings exhibited excellent antibiofouling ability for more than 3 months. The current copolymer is derived from commonly used monomers and an easily conducted polymerization method. Hence, we believe this method may offer innovative insights into marine antifouling applications.

Impact of polystyrene nanoplastics (PSNPs) on seed germination and seedling growth of wheat (Triticum aestivum L.)

Microplastics and nanoplastics are emerging pollutants of global concern. However, the understanding of their ecological effects on terrestrial plants is still limited. We conducted the systematic research to reveal the impact of polystyrene nanoplastics (PSNPs) (0.01-10 mg/L) on seed germination and seedling growth of wheat (Triticum aestivum L.). The results showed that PSNPs had no discernible effect on seed germination rate whereas significantly (p < 0.01) increased root elongation by 88.6 %-122.6 % when compared with the control. Similarly, remarkable increases in carbon, nitrogen contents, and plant biomass were also observed after exposure to PSNPs. Moreover, PSNPs could reduce the shoot to root biomass ratio (S:R ratio) of wheat seedlings. Furthermore, the imagings of a 3D laser confocal scanning microscopy (LCSM) and scanning electron microscopy (SEM) indicated that PSNPs were taken up and subsequently down-top transported to shoot. The absorption and accumulation of four micronutrients (Fe, Mn, Cu and Zn) in wheat were generally reduced in varying degrees. Notably, metabolomics analysis revealed that all PSNPs treatments altered the leaf metabolic profiles mainly by regulating energy metabolisms and amino acid metabolisms. These findings are expected to provide new insights into the effects of PSNPs on crop plants.

Nano-plastics induce aquatic particulate organic matter (microgels) formation

The pervasive presence of plastic waste in the aquatic environment is widely viewed as one of the most serious environmental challenges for current and future generations. Microplastics ultimately degrade into nano and smaller-sizes. In turn, their biological and ecological impacts become more complicated and ambiguous. Nano-plastic particles travel from freshwater systems to estuarine and oceanic regions, during which they can interact with dissolved organic matter (DOM) to form microgels. Microgel formation is ubiquitous in aquatic systems, serving as a shunt between DOM and particulate organic matter (POM), as well as playing key roles in particle aggregation/sedimentation and pollutant transport. Currently the influences and mechanisms of the aggregation behavior and environmental fate of nano-plastics in different aquatic environments is poorly understood. Here, we report that 25 nm polystyrene nano-particles in lake and river water can promote POM (microgel) formation and accelerate the DOM-POM transition. We also adjusted various salinities of water samples to simulate scenarios based on plastic transport in waters flowing from rivers to seas. The results indicate polystyrene nanoparticles can interact with organic matter to form large organic particles, which may undergo further settling in response to specific salinity levels. Polystyrene-induced microgel formation appears to involve the hydrophobic interactions between plastics and DOM. Our data provides much needed information for modeling and understanding the retention and sedimentation of nano-plastics. We show that nano-plastics alter the DOM-POM shunt to cause unanticipated perturbations in the functionality of aquatic ecosystems.

Chronic dietary exposure to polystyrene microplastics in maturing Japanese medaka (Oryzias latipes)

Fish studies report consumption of microplastics (MPs) in the field, and concern exists over associated risks. However, laboratory studies with adult fish are scarce. In this study, outbred and see-through Japanese medaka (Oryzias latipes) were fed diets amended with 500, 1000, or 2000 μg/g 10 μm fluorescent spherical polystyrene microplastics (MPs) for 10 weeks during their maturation from juveniles to spawning adults. No behavioral changes, growth differences, or mortalities occurred. In vivo examinations and histologic sections showed no evidence of translocation of MPs from the gut to other internal organs. Mature females experienced dose-dependent decreases in egg number. Scanning electron microscopic examination of gills and gut revealed MPs in both areas. Swollen enterocytes were observed on apices of gut folds only in exposed fish. These were particularly apparent in foreguts of the high exposure group. Enterocytes with eroded brush borders were found in foregut of high and medium exposure groups. Increased mucus production, in long strands and sheets, was seen over primary and secondary lamellae of gills. Histological analysis showed alteration in buccal cavity, kidney, and spleen. Thickening and roughening of epithelium in headgut and pharynx and cellular alterations in spleen occurred. Head kidney was the primary site of alteration. Glomerulopathy and nephrogenesis were observed in exposed fish, increasing in severity with exposure level.

Microplastic consumption and excretion by fathead minnows (Pimephales promelas): Influence of particles size and body shape of fish

The present study characterizes the dependence of microplastic consumption and excretion on particle size and body shape of fathead minnow (Pimephales promelas) over time that has not been studied. Specifically, the study is to answer four important questions: 1) how do P. promelas consume microplastic particles at different size ranges over time? 2) how long does it take for P. promelas to excrete microplastic particles after consumption? 3) do P. promelas reconsume microplastic particles after excretion? 4) are microplastic consumption and excretion by P. promelas dependent on the body shape? To answer these questions, larval P. promelas were exposed to polyethylene microbeads (PMBs) at two different consumable size ranges of 63-75 µm and 125-150 µm in moderately hard water. The experiments were designed to allow and to not allow fish to reconsume the particles they excreted. Results of the present study showed that P. promelas consumed significant amount of PMBs after 1 h of exposure to PMBs regardless particle size. The number of consumed PMBs per fish at smaller size range was up to 10 times higher than that at larger size range. When expressing the consumption in µg PMBs/fish, this difference was approximately 1.3 times, suggesting the importance of the measurement unit. After consuming, fish excreted PMBs over time and reconsumed excreted PMBs if reconsumption was allowed. Interestingly, it took longer for bent body fish to excrete PMBs than regular straight body fish. Our observation showed that excreted PMBs were likely coated with intestinal fluid that is denser than water, resulting in aggregation and deposition of PMBs. This result suggests that in the natural environment, the consumption and excretion of plastics by fish would enhance the movement of plastics from the water column to the waterbed and make it available for benthic organisms.

The effects of nanoplastics on marine plankton: A case study with polymethylmethacrylate

Marine biota is currently exposed to plastic pollution. The biological effects of plastics may vary according to polymer types (e.g. polystyrene, polyethylene, acrylate), size of particles (macro, micro or nanoparticles) and their shape. There is a considerable lack of knowledge in terms of effects of nanoplastics (NP) to marine biota particularly of polymers like polymethylmethacrylate (PMMA). Thus, this study aimed to assess its ecotoxicological effects using a battery of standard monospecific bioassays with four marine microalgae (Tetraselmis chuii, Nannochloropsis gaditana, Isochrysis galbana and Thalassiosira weissflogii) and a marine rotifer species (Brachionus plicatilis). The tested PMMA-NP concentrations allowed the estimation of median effect concentrations for all microalgae species. T. weissflogii and T. chuii were respectively the most sensitive (EC_50,96h of 83.75 mg/L) and least sensitive species (EC_50,96h of 132.52 mg/L). The PMMA-NP were also able to induce mortality in rotifers at concentrations higher than 4.69 mg/L with an estimated 48 h median lethal concentration of 13.27 mg/L. A species sensitivity distribution curve (SSD), constructed based on data available in the literature and the data obtained in this study, reveal that PMMA-NP appears as less harmful to marine biota than other polymers like polystyrene.

Nanopolystyrene at predicted environmental concentration enhances microcystin-LR toxicity by inducing intestinal damage in Caenorhabditis elegans

We employed nematode Caenorhabditis elegans to determine the combinational effect between nanopolystyrene at predicted environmental concentration and microcystin-LR (MC-LR). Prolonged exposure to nanopolystyrene (1 μg/L) increased MC-LR (0.1 μg/L) toxicity in reducing brood size and locomotion behavior and in inducing oxidative stress. Moreover, the adsorption of MC-LR by nanopolystyrene particles played an important role in inducing the enhancement in MC-LR toxicity by nanopolystyrene particles. Additionally, only exposure to resuspension of nanopolystyrene (1 μg/L) caused the increased intestinal permeability in MC-LR (0.1 μg/L) exposed nematodes. Our data indicates the potential of nanopolystyrene at predicted environmental concentration in enhancing MC-LR toxicity on environmental organisms.

Evaluation of the infiltration of polystyrene nanobeads in zebrafish embryo tissues after short-term exposure and the related biochemical and behavioural effects

One of the current main challenges faced by the scientific community is concerning the fate and toxicity of plastics, due to both the well-known threats made by larger plastic items spreading in ecosystems and their fragmentation into micro- and nanoparticles. Since the chemical and physical characteristics of these smaller plastic fragments are markedly different with respect to their bulk product, the potential toxicological effects in the environment need to be deeply investigated. To partially fill this gap of knowledge, the aim of this study was to evaluate the polystyrene nanobead intake in the tissues of zebrafish (Danio rerio) embryos and their related toxicity. Embryos at 72 h post fertilization (hpf) were exposed for 48 h to 0.5 μm fluorescent polystyrene nanobeads at a concentration of 1 mg L^-1. Confocal microscopy was employed to investigate nanoplastic ingestion and tissue infiltration, while potential sub-lethal effects were evaluated by measuring several endpoints, which covered the adverse effects at the molecular (protein carbonylation), cellular (P-glycoprotein, activity of several antioxidant/detoxifying enzymes) and organism levels by evaluating of possible changes in the embryos' swimming behaviour. Imaging observations clearly highlighted the nanoplastics' uptake, showing nanobeads not only in the digestive tract, but also migrating to other tissues through the gut epithelium. Biomarker analyses revealed a significant decrease in cyclooxygenase activity and an induction of superoxide dismutase. The behavioural test highlighted a significant (p < 0.05) variation in the turn angle between the control and exposed embryos. This study points out the capability of nanoplastics to infiltrate zebrafish embryo tissues, even after a short exposure, thus suggesting the need for deeper investigations following longer exposure times, and highlighting the potential of nanoplastics to cause toxicological effects on freshwater organisms, at the organism level.

Toxicological Evaluation and Quantification of Ingested Metal-Core Nanoplastic by Daphnia magna Through Fluorescence and Inductively Coupled Plasma-Mass Spectrometric Methods

There are few studies on nanoplastic that propose quantification of the amount ingested combined with evaluation of the toxic effects on aquatic organisms. We propose 2 methods to quantify the amount of polystyrene nanoplastic (PSNP) ingested by Daphnia magna: fluorescence intensity, where a fluorescent monomer (F) is added to the PSNP and quantified through fluorescence light microscopy, and total aluminum quantification, where PSNP is synthesized with Al₂ O₃ metal-core nanoparticles and used for quantification of the nanoplastic ingested by the organism Daphnia magna using inductively coupled plasma-mass spectrometry. In addition, the PSNP was functionalized with palmitic acid to simulate the environmental conditions leading to biological and chemical transformations. Acute and chronic toxicity tests were performed with fluorescent PSNP (PSNP/F) and palmitic acid-functionalized PSNP/F (PSNP/F-PA). The ingestion quantified was higher by factors of 2.8 and 3.0 for PSNP/F-PA and 1.9 and 1.7 for PSNP/F applying the fluorescence intensity and total Al quantifying methods, respectively, when compared to PSNP. These results are consistent with the data obtained in the toxicity tests, which showed an approximately 3 times increase in the adverse effect of PSNP/F-PA on the mobility and reproduction of the organisms. Thus, the strong inhibition of D. magna reproduction caused by PSNP/F-PA in the chronic toxicity tests could be associated with a greater amount of this nanoplastic being ingested by the organisms. Environ Toxicol Chem 2019;38:2101-2110. © 2019 SETAC.

Influence of nanoplastic surface charge on eco-corona formation, aggregation and toxicity to freshwater zooplankton

Concerns about possible environmental implications of nano- and micro-plastics are continuously raising. Hence, comprehensive understanding of their behaviour, bioaccumulation and toxicity potential is required. Nevertheless, systematic studies on their fate and possible effects in freshwaters, as well as the influence of particle-specific and environmental factors on their behaviour and impacts are still missing. The aims of the present study are thus two-fold: (i) to examine the role of the surface charge on nanoplastic stability and acute effects to freshwater zooplankton; (ii) to decipher the influence of the refractory natural organic matter (NOM) on the nanoplastic fate and effects. Amidine and carboxyl-stabilized polystyrene (PS) spheres of 200 nm diameter characterized by opposite primary surface charges and neutral buoyancy were selected as model nanoplastics. The results demonstrated that the surface functionalization of the polystyrene nanoplastics controls their aggregation behaviour. Alginate or Suwannee River humic acid (SRHA) modified significantly the surface charge of positively-charged amidine PS nanoplastic and the aggregation state, while had no significant influence on the negatively-charged carboxyl PS nanoplastic. Both amidine and carboxyl PS nanoplastics were ingested by the zooplankton and concentrated mainly in the gut of water flea Daphnia magna and larvae Thamnocephalus platyurus, and the stomach of rotifer Brachionus calyciflorus. Amidine PS nanoplastic was more toxic than carboxyl one. The toxicity decreased in the order D. magna (48 h -immobilization) > B. calyciflorus (24 h - lethality) > T. platyurus (24 h - lethality). Alginate or SRHA reduced significantly the toxicity of both amidine and carboxyl PS nanoplastics to the studied zooplankton representatives. The implications of this laboratory study findings to natural environment were discussed.

Hyperbranched polymeric nanomaterials impair the freshwater crustacean Daphnia magna

Hyperbranched polymers are nanomaterials belonging to the class of dendritic architectures with increasing applications in many diverse fields. We studied the toxicity of two hyperbranched polymers to the freshwater crustacean Daphnia magna. A hyperbranched hydroxyl-terminated polyester and a commercial hyperbranched polyamidoamine, Helux-3316 were tested for the acute immobilization of daphnids, the overproduction of reactive oxygen species and the activity of the antioxidant enzymes catalase and glutathione S-transferase. The effect for D. magna immobilization was higher for the hyperbranched polyamidoamine Helux-3316, which was attributed to the presence of primary amino groups on its surface. Following exposure to both hyperbranched polymers, a clear overproduction of reactive oxygen species took place accompanied by concentration-dependent enzymatic antioxidant response. Our results showed that the overproduction of reactive oxygen species activated antioxidant defence mechanisms and was responsible for the immobilization of daphnids exposed to both hyperbranched polymers. We showed evidence of the uptake of fluorescently labelled Helux-3316 that accumulated into the gastrointestinal tract of D. magna, and its removal via excretion within fecal pellets. This is the first work reporting the internalization of hyperbranched polymers in aquatic organisms.