Use of fluorescent-labelled nanoplastics (NPs) to demonstrate NP absorption is inconclusive without adequate controls

Foliar Exposure of Deuterium Stable Isotope-Labeled Nanoplastics to Lettuce: Quantitative Determination of Foliar Uptake, Transport, and Trophic Transfer in a Terrestrial Food Chain

Nanoplastics (NPs) are widely detected in the atmosphere and are likely to be deposited on plant leaves. However, our understanding of their foliar uptake, translocation, and trophic transfer profiles is limited due to a lack of quantitative analytical tools to effectively probe mechanisms of action. Here, using synthesized deuterium (2H) stable isotope-labeled polystyrene nanoplastics (2H-PSNPs), the foliar accumulation and translocation of NPs in lettuce and the dynamics of NP transfer along a lettuce-snail terrestrial food chain were investigated. Raman imaging and scanning electron microscopy demonstrated that foliar-applied NPs aggregated on the leaf surface, entered the mesophyll tissue via the stomatal pathway, and eventually translocated to root tissues. Quantitative analysis showed that increasing levels of foliar exposure to 2H-PSNPs (0.1, 1, and 5 mg/L in spray solutions, equivalent to receiving 0.15, 1.5, and 7.5 μg/d of NPs per plant) enhanced NP accumulation in leaves, with concentrations ranging from 0.73 to 15.6 μg/g (dw), but only limited translocation (<5%) to roots. After feeding on 5 mg/L 2H-PSNP-contaminated lettuce leaves for 14 days, snails accumulated NPs at 0.33 to 10.7 μg/kg (dw), with an overall kinetic trophic transfer factor of 0.45, demonstrating trophic dilution in this food chain. The reduced ingestion rate of 3.18 mg/g/day in exposed snails compared to 6.43 mg/g/day can be attributed to the accumulation of 2H-PSNPs and elevated levels of chemical defense metabolites in the lettuce leaves, which decreased the palatability for snails and disrupted their digestive function. This study provides critical quantitative information on the characteristics of airborne NP bioaccumulation and the associated risks to terrestrial food chains.

Fluorescent carbon dot embedded polystyrene: an alternative for micro/nanoplastic translocation study in leguminous plants

Micro/nanoplastics are widespread in terrestrial ecosystem. Even though many studies have been reported on the effects of these in marine environment, studies concerning their accumulation and impact on terrestrial ecosystem have been scanty. The current study was designed to determine how terrestrial plants, especially legumes, interact with micro/nanoplastics to gain insights into their uptake and translocation. The paper describes the synthesis of fluorescent carbon dot embedded polystyrene (CDPS) followed by its characterization. Translocation studies at different concentrations from 2 to 100% (v/v) for tracking the movement and accumulation of microplastics in Vigna radiata and Vigna angularis were performed. The optical properties of the synthesized CDPS were investigated, and their translocation within the plants was visualized using fluorescence microscopy. These findings were further validated by scanning electron microscopy (SEM) imaging of the plant sections. The results showed that concentrations higher than 6% (v/v) displayed noticeable fluorescence in the vascular region and on the cell walls, while concentrations below this threshold did not. The study highlights the potential of utilizing fluorescent CDPS as markers for investigating the ecological consequences and biological absorption of microplastics in agricultural systems. This method offers a unique technique for monitoring and analyzing the routes of microplastic accumulation in edible plants, with significant implications for both food safety and environmental health.

Ants avoid food contaminated with micro- and nanoplastics

Micro- and nanoplastics (MNP) have recently received particular attention in freshwater and marine ecosystems, but less is known about their impact on terrestrial species. Ants can be used as biological indicators for many types of pollutants and are therefore a good candidate to explore the effects of MNP pollution. In the present study, we investigated the ability of workers from seven colonies of the acrobat ant Crematogaster scutellaris to detect MNP in their food. After two days of starvation, groups of ten ants were tested for their preference toward control and polyethylene-treated solutions. Every 5 min over a total 20 min period, the number of workers feeding on either solution was counted. The results showed that C. scutellaris workers could detect and avoid contaminated food, feeding more often on the uncontaminated solution in the first 10 min. However, after 10 min the food preference was no longer significant between the groups, likely owing to feeding satiation. We then assessed whether this feeding behaviour is sufficient to cause the accumulation of MNP in the ant. We thereby provided a solution containing fluorescent MNP (fMNP) at the same concentration as in the previous experiments. Observation of the ants' mouthparts using fluorescent light microscopy showed that after 10 min dense aggregations of fMNP were visible. Further investigations are needed to understand the mechanisms of detection of MNP by ants, and the accumulation dynamics in ants' bodies. Moreover, the effects of MNP on the integrity and fitness of ant colonies, as well as the potential transfer across terrestrial trophic chains should be explored.

An insight decipher on photocatalytic degradation of microplastics: Mechanism, limitations, and future outlook

Plastic material manufacturing and buildup over the past 50 years has significantly increased pollution levels. Microplastics (MPs) and non-biodegradable residual plastic films have become the two most pressing environmental issues among the numerous types of plastic pollution. These tiny plastic flakes enter water systems from a variety of sources, contaminating the water. Since MPs can be consumed by people and aquatic species and eventually make their way into the food chain, their presence in the environment poses a serious concern. Traditional technologies can remove MPs to some extent, but their functional groups, stable covalent bonds, and hydrophobic nature make them difficult to eliminate completely. The urgent need to develop a sustainable solution to the worldwide contamination caused by MPs has led to the exploration of various techniques. Advanced oxidation processes (AOPs) such as photo-catalytic oxidation, photo-degradation, and electrochemical oxidation have been investigated. Among these, photocatalysis stands out as the most promising method for degrading MPs. Photocatalysis is an environmentally friendly process that utilizes light energy to facilitate a chemical reaction, breaking down MPs into carbon dioxide and water-soluble hydrocarbons under aqueous conditions. In photocatalysis, semiconductors act as photocatalysts by absorbing energy from a light source, becoming excited, and generating reactive oxygen species (ROS). These ROS, including hydroxyl radicals (•OH) and superoxide ions ( [Formula: see text] ), play a crucial role in the degradation of MPs. This extensive review provides a detailed exploration of the mechanisms and processes underlying the photocatalytic removal of MPs, emphasizing its potential as an efficient and environmentally friendly approach to address the issue of plastic pollution.

Exploring the potential and challenges of developing physiologically-based toxicokinetic models to support human health risk assessment of microplastic and nanoplastic particles

Microplastics (MPs) and nanoplastics (NPs) pollution has emerged as a significant and widespread environmental issue. Humans are inevitably exposed to MPs and NPs via ingestion, inhalation, and dermal contacts from various sources. However, mechanistic knowledge of their distribution, interaction, and potency in the body is still lacking. To address this knowledge gap, we have undertaken the task of elucidating the toxicokinetic (TK) behaviors of MPs and NPs, aiming to provide mechanistic information for constructing a conceptual physiologically based toxicokinetic (PBTK) model to support in silico modeling approaches. Our effort involved a thorough examination of the existing literature and data collation on the presence of MPs in the human body and in vitro/ex vivo/in vivo biodistribution across various cells and tissues. By comprehending the absorption, distribution, metabolism, and excretion mechanisms of MPs and NPs in relation to their physicochemical attributes, we established a foundational understanding of the link between external exposure and internal tissue dosimetry. We observed that particle size and surface chemistry have been thoroughly explored in previous experimental studies. However, certain attributes, such as polymer type, shape, and biofilm/biocorona, warrant attention and further examination. We discussed the fundamental disparities in TK properties of MPs/NPs from those of engineered nanoparticles. We proposed a preliminary PBTK framework with several possible modeling approaches and discussed existing challenges for further investigation. Overall, this article provides a comprehensive compilation of existing TK data of MPs/NPs, a critical overview of TK processes and mechanisms, and proposes potential PBTK modeling approaches, particularly regarding their applicability to the human system, and outlines future perspectives for developing PBTK models and their integration into human health risk assessment of MPs and NPs.

Tracking the micro- and nanoplastics in the terrestrial-freshwater food webs. Bivalves as sentinel species

Micro- (MPs) and nanoplastics (NPs) are currently ubiquitous in the ecosystems, and freshwater biota is still insufficiently studied to understand the global fate, transport paths, and consequences of their presence. Thus, in this study, we investigated the role of bivalves and a trophic transfer of MPs and NPs in an experimental food chain. The food chain consisted of terrestrial non-selective detritivore Dendrobaena (Eisenia) sp., freshwater benthic filter feeder Unio tumidus, and freshwater benthic detritivore-collectors Asellus aquaticus or Gammarus sp. Animals were exposed to different fluorescently labeled micro- and nanoplastics (PMMA 20 μm, nanoPS 15-18 nm, and 100 nm, PS 1 μm and 20 μm, PE from cosmetics) as well as to the faeces of animals exposed to plastics to assess their influence on the environmental transportation, availability to biota, and bioaccumulation of supplied particles. Damaged and intact fluorescent particles were observed in the faeces of terrestrial detritivores and in the droppings of aquatic filter feeders, respectively. They were also present in the guts of bivalves and of crustaceans which were fed with bivalve droppings. Bivalves (Unio tumidus, and additionally Unio pictorum, and Sphaerium corneum) produced droppings containing micro- and nanoparticles filtered from suspension and deposited them onto the tank bottom, making them available for broader feeding guilds of animals (e.g. collectors, like crustaceans). Finally, the natural ageing of PS and its morphological changes, leakage of the fluorescent labelling, and agglomeration of particles were demonstrated. That supports our hypothesis of the crucial role of the characterization of physical and chemical materials in adequately understanding the mechanisms of their interaction with biota. Microscopical methods (confocal, fluorescent, scanning electron) and Raman and FT-IR spectroscopy were used to track the particles' passage in a food web and monitor structural changes of the MPs' and NPs' surface.

Implications of exposure route for the bioaccumulation potential of nanopolystyrene particles

Microplastics and nanoplastics are found in marine biota across a wide range of trophic levels and environments. While a large portion of the information about plastic exposure comes from gastrointestinal (GI) data, the relevance of particle accumulation from an oral exposure compared with other types of exposure (e.g. dermal, respiratory) is unknown. To address this gap in knowledge, larval zebrafish (7 days post fertilization) were exposed to two different sizes of nanoplastics through either oral gavage or a waterborne exposure. Larvae were tracked for 48 h post exposure (hpe) to assess the migration and elimination of plastics. Larvae eliminated orally gavaged nanoplastics within 48 hpe. Oral gavage showed limited particle movement from the GI tract into other tissues. In contrast, waterborne nanoplastic-exposed larvae displayed notable fluorescence in tissues outside of the GI tract. The 50 nm waterborne-exposed larvae retained the particles past 48 hpe, and showed accumulation with neuromasts. For both sizes of plastic particles, the nanoplastics were eliminated from non-GI tract tissues by 24 hpe. Our results suggest that waterborne exposure leads to greater accumulation of plastic in comparison to oral exposure, suggesting that plastic accumulation in certain tissues is greater via routes of exposure other than oral consumption.

Labelling of micro- and nanoplastics for environmental studies: state-of-the-art and future challenges

Studying microplastics and nanoplastics (MNP) in environmental matrices is extremely challenging, and recent developments in labelling techniques may hold much promise to further our knowledge in this field. Here, we reviewed MNP labelling techniques and applications to provide the first systematic and in-depth insight into MNP labelling. We classified all labelling techniques for MNP into four main types (fluorescent, metal, stable isotope and radioisotope) and discussed per type the synthesis methods, detection methods, influencing factors, and the current and future applications and challenges. Direct labelling of environmental MNP with fluorescent dyes and metals enables simple visualisation and selective detection of MNP to improve detection efficiency. However, it is still an open question how to avoid co-labelling of non-plastic (i.e. non-target, matrix) materials. Labelling of MNP that are intentionally added in the environment may allow semi-automatic detection of MNP particles with high accuracy and sensitivity during studies on e.g. transport and degradation. The detection limit of labelled MNP largely depends on particle size and the type of matrix. Fluorescent labelling allows efficient detection of microplastics, whereas metal labelling is preferred for nanoplastics research due to a potentially higher sensitivity. A major challenge for fluorescent and metal labelling is to develop techniques that do not alter the inherent MNP properties or only do so minimally, in particular the surface properties. Stable and radioactive isotope labelling (13C and 14C, but also 15N, 2H) of the polymer itself allows to preserve inherent MNP properties, but have been largely ignored. Overall, labelling of MNP holds great promise for advancing our fundamental understanding of the behaviour of plastics, notably the smallest fractions, in the environment.

A plasmonic gold nano-surface functionalized with the estrogen receptor for fast and highly sensitive detection of nanoplastics

Nanoplastics are a global emerging environmental problem whose effects might pose potential threats to the human's health. Despite the relevance of the issue, fast, reliable and quantitative in situ analytical approaches to determine nanoplastics are not yet available. The aim of this work was to devise an optical sensor with the goal of direct detecting and quantifying nanoplastics in seawater without sample pre-treatments. To this purpose, a nano-plasmonic biosensor was developed by exploiting an Estrogen Receptor (ER) recognition element grafted onto a polymer-based gold nanograting (GNG) plasmonic platform. The ER-GNG biosensor required just minute sample volumes (2 μL), allowed rapid detection (3 min) and enabled to determine nanoplastics in simulated seawater with a linear dynamic concentrations range of 1-100 ng/mL, thus encompassing the expected environmental loads. The nanostructured grating (GNG) provided remarkable performance enhancements, extending the measurement range across five orders of magnitude, thanks to the both the SPR and the localized SPR phenomena occurring at the GNG chip. At last, the ER-GNG biosensor was tested on real seawater samples collected in the Naples area and the results (∼30 ng/mL) were verified by a conventional approach (filtration and evaporation), confirming the ER-GNG sensor offers a straightforward and highly sensitive method for the direct in-field nanoplastics monitoring.

Organ-specific distribution and size-dependent toxicity of polystyrene nanoplastics in Australian bass (Macquaria novemaculeata)

Micro- and nano-plastics (MNPs) are emerging contaminants found in air, water, and food. Ageing and weathering processes convert aquatic plastics into MNPs which, due to their small size, can be assimilated by organisms. The accumulation of MNPs in aquatic life (e.g., fish, oysters, and crabs) will, in turn, pose risks to the health of ecosystems and human. This study focuses on the uptake, biodistribution, and size-dependent toxicity of polystyrene nano-plastics (PS-NPs) in a commercially important food web, the Australian Bass (Macquaria novemaculeata). Fish were fed artemia containing PS-NPs of various sizes (ranging from 50 nm to 1 μm) for durations of 5 and 7 days. The findings revealed that smaller NPs (50 nm) accumulated in the brain and muscle tissues at higher concentrations, whereas larger NPs (1 μm) were primarily found in the gills and intestines. In addition, an inverse correlation was observed between the size of NPs and the rate of trophic transfer, with smaller PS-NPs resulting in a higher transfer rate from artemia to fish. Polystyrene NPs caused both activation of the enzyme superoxide dismutase and damage to the DNA of fish tissues. These effects were size dependent. Metabolomic analysis revealed that indirect exposure to different-sized PS-NPs resulted in altered metabolic profiles within fish intestines, potentially impacting lipid and energy metabolism. These results offer novel perspectives on the size-specific toxic impacts of NPs on fish and the transfer of plastics through the food chain.

Translocation of 14C-polystyrene nanoplastics into fish during a very-low concentration dietary exposure

Assessing the dietary accumulation of nanoplastics in animals following very-low exposure concentrations is restricted due to analytical limitations. This study adapted a method for synthesising semi-stable 14C-PS NPs (through styrene polymerisation) in small volumes for deployment in environmental studies. The method was developed with non-labelled material where the final polystyrene product had a primary particle size of 35 ± 8 nm (as measured by transmission electron microscopy). This method was then applied to 14C-labelled styrene to produce radiolabelled polystyrene nanoplastics (14C-PS NPs). The 14C-PS NPs were added (top-dressed) to a commercially available fish feed, with a measured concentration of 27.9 ± 2.1 kBq kg-1 (n = 5), equating to 5.9 μg polystyrene kg-1 feed. Fish (rainbow trout; Oncorhynchus mykiss) were fed this diet at a ration of 2% body weight per day for a period of two weeks. On day 3, 7 and 14, the fish were sampled for the mid intestine, hind intestine, kidney and liver, and measured for tissue radioactivity (determined by liquid scintillation counting). Some background activity was detected in the control samples (e.g., 1-16 and 4-11 Bq g-1 in the hind intestine and liver, respectively) which is due to natural background fluorescence. By the end of the experiment, the hind intestine and liver had significantly elevated radioactivity (25.3 and 15.0 Bq g-1, respectively) compared to the control, indicating the accumulation of nano polystyrene. In the liver, this equated to 1.8 μg polystyrene g-1 dry weight. This study confirms the accumulation of nano particles in vertebrates at low, environmentally relevant concentration, and highlights radiolabelling as a methodological approach suitable for exploring the bioaccumulation of nanoplastics and potential impacts.

New Fluorophore and Its Applications in Visualizing Polystyrene Nanoplastics in Bean Sprouts and HeLa Cells

In the domain of environmental science, pollutants of nanoscale plastic dimensions are acknowledged as subjects of intricate significance. Such entities, though minuscule, present formidable challenges to ecological systems and human health. The diminutive dimensions of these contaminants render their detection arduous, thus demanding the inception of avant-garde methodologies. The present manuscript postulates the employment of the tetraphenylethylene functional group with a fused xanthene (TPEF), a distinguished fluorophore, as an exemplary system for the discernment of nanoplastic particulates. The synthesis and characterization of TPEF have been exhaustively elucidated, revealing its paramount fluorescence attributes and inherent affinity for interaction with nanoplastics. When subjected to comparison with TPEF, nanoplastics are observed to manifest a more pronounced fluorescent luminescence than when associated with the conventional Nile Red (NR). Particularly, the TPEF has shown exceptional affinity for polystyrene (PS) nanoplastics. Further, the resilience of nanoplastics within the hypocotyl epidermis of soybeans, as well as their persistence in mung bean sprouts subsequent to rigorous rinsing protocols, has been meticulously examined. Additionally, this investigation furnishes empirical data signifying the existence of nano-dimensional plastic contaminants within HeLa cellular structures. The urgency of addressing the environmental ramifications engendered by these diminutive yet potent plastic constituents is emphatically highlighted in this manuscript. TPEF paves the way for prospective explorations, with the aspiration of devising efficacious mitigation strategies. Such strategies might encompass delineating the trajectories undertaken by nanoplastics within trophic networks or their ingress into human cellular architectures.

Near-Infrared-II In Vivo Visualization and Quantitative Tracking of Micro/Nanoplastics in Fish

As emerging contaminants, micro/nanoplastics (MNPs) are widely present in aquatic environments and are often ingested by aquatic organisms. However, the in vivo trafficking and fate of MNPs remain largely unknown. Here, we developed near-infrared (NIR) aggregated-induced emission (AIE) fluorophore-labeled microplastics (2 μm) and nanoplastics (100 nm) as models of MNPs. This model was based on the NIR-AIE technique with strong emission at the second near-infrared (NIR-IIII) window, which overcomes the interference of autofluorescence and observation artifacts in the detection of commercial fluorescent-labeled particles. Due to its deep tissue penetration and noninvasiveness, the dynamic process of accumulation and transport of MNPs in individuals can be tracked with NIR imaging. We then directly visualized and quantified the uptake and depuration processes of MPs and NPs in zebrafish. The results showed that the MPs and NPs were mainly accumulated in the fish gut, and the distribution was heterogeneous. MPs tended to accumulate more in the fore and mid areas of the gut compared with NPs. Besides, both MPs and NPs could accumulate in large quantities locally in the gut and might cause intestinal obstruction. MNPs accumulated slowly during the initial exposure followed by rapid and sustained accumulation in gut. Based on these kinetic accumulation and depuration, we developed a refined toxicokinetic (TK) model to describe the dynamic changes in the uptake and depuration of MNPs. Overall, this study proposed a MNP model based on the NIR-AIE technique, which provided a reliable tracer technology for the visualization, tracking and quantification of MNPs in vivo.

Accumulation of polystyrene nanoplastics and triclosan by a model tooth-carp fish, Aphaniops hormuzensis (Teleostei: Aphaniidae)

The presence and effects of nanoplastics (NPs; <1 μm) in the aquatic environment are a growing concern. In this study, a model tooth-carp fish, Aphaniops hormuzensis, has been exposed to different concentrations of fluorescent polystyrene nanoplastics (PS-NP) in its diet (up to 5 mg kg-1) over periods of 28 d and the particle accumulation in different tissues determined. Accumulation was observed in both digestive and non-digestive organs, with concentrations greater in the gut, liver and gill (up to 400 μg kg-1 dw) than in the skin and muscle (<180 μg kg-1 dw), but no dependency on exposure time or dose was evident. The presence of the organic contaminant, triclosan (TCS), in the diet and at concentrations up to 0.5 μg kg-1 did not affect PS-NP uptake by A. hormuzensis, while TCS accumulation in the whole body increased with time (up to 10 μg kg-1) and, likewise, appeared to be unaffected by the presence of PS-NPs. These observations suggest that the two contaminants do not interact with each other or that any interactions have no impact on accumulation. The results of this study add to the growing body of evidence that NPs can be translocated by aquatic organisms after ingestion, and reveal that, for the species and conditions employed, nanoplastics are accumulated more readily than a widely used organic chemical.

Core-Shell Au@Nanoplastics as a Quantitative Tracer to Investigate the Bioaccumulation of Nanoplastics in Freshwater Ecosystems

Studies on the adverse effects of nanoplastics (NPs, particle diameter <1000 nm) including physical damage, oxidative stress, impaired cell signaling, altered metabolism, developmental defects, and possible genetic damage have intensified in recent years. However, the analytical detection of NPs is still a bottleneck. To overcome this bottleneck and obtain a reliable and quantitative distribution analysis in complex freshwater ecosystems, an easily applicable NP tracer to simulate their fate and behavior is needed. Here, size- and surface charge-tunable core-shell Au@Nanoplastics (Au@NPs) were synthesized to study the environmental fate of NPs in an artificial freshwater system. The Au core enables the quantitative detection of NPs, while the polystyrene shell exhibits NP properties. The Au@NPs showed excellent resistance to environmental factors (e.g., 1% hydrogen peroxide solution, simulating gastric fluid, acids, and alkalis) and high recovery rates (>80%) from seawater, lake water, sewage, waste sludge, soil, and sediment. Both positively and negatively charged NPs significantly inhibited the growth of duckweed (Lemna minor L.) but had little effect on the growth of cyanobacteria (Microcystis aeruginosa). In addition, the accumulation of positively and negatively charged NPs in cyanobacteria occurred in a concentration-dependent manner, with positively charged NPs more easily taken up by cyanobacteria. In contrast, negatively charged NPs were more readily internalized in duckweed. This study developed a model using a core-shell Au@NP tracer to study the environmental fate and behavior of NPs in various complex environmental systems.

Toxicological impact of microplastics and nanoplastics on humans: understanding the mechanistic aspect of the interaction

Plastic is a pervasive material that has become an indispensable part of our daily lives and is used in various commercial products. However, plastic waste has significantly impacted the environment, accumulating in water and land ecosystems and harming all forms of life. When plastic degrades, it breaks down into smaller particles called microplastics (MPs), which can further breakdown into nanoplastics (NPs). Due to their small size and potential toxicity to humans, NPs are of particular concern. During the COVID-19 pandemic, the production of plastic had reached unprecedented levels, including essential medical kits, food bags, and personal protective equipment (PPE), which generate MPs and NPs when burned. MPs and NPs have been detected in various locations, such as air, food, and soil, but our understanding of their potential adverse health effects is limited. This review aims to provide a comprehensive overview of the sources, interactions, ecotoxicity, routes of exposure, toxicity mechanisms, detection methods, and future directions for the safety evaluation of MPs and NPs. This would improve our understanding of the impact of MPs and NPs on our health and environment and identify ways to address this global crisis.

Impact of polystyrene microplastic exposure on gilthead seabream (Sparus aurata Linnaeus, 1758): Differential inflammatory and immune response between anterior and posterior intestine

Plastics are the most widely discharged waste into the aquatic ecosystems, where they break down into microplastics (MPs) and nanoplastics (NPs). MPs are ingested by several marine organisms, including benthic and pelagic fish species, contributing to organ damage and bioaccumulation. This study aimed to assess the effects of MPs ingestion on gut innate immunity and barrier integrity in gilthead seabreams (Sparus aurataLinnaeus, 1758) fed for 21 days with a diet enriched with polystyrene (PS-MPs; 1-20 μm; 0, 25 or 250 mg /kg b.w./die). Physiological fish growth and health status were not impacted by PS-MPs treatments at the end of experimental period. Inflammation and immune alterations were revealed by molecular analyses in both anterior (AI) and posterior intestine (PI) and were confirmed by histological evaluation. PS-MPs triggered TLR-Myd88 signaling pathway with following impairment of cytokines release. Specifically, PS-MPs increased pro-inflammatory cytokines gene expression (i.e., IL-1β, IL-6 and COX-2) and decreased anti-inflammatory ones (i.e., IL-10). Moreover, PS-MPs also induced an increase in other immune-associated genes, such as Lys, CSF1R and ALP. TLR-Myd88 signaling pathway may also lead to the mitogen-activated protein kinases (MAPK) signaling pathway activation. Here, MAPK (i.e., p38 and ERK) were activated by PS-MPs in PI, following the disruption of intestinal epithelial integrity, as evidenced by reduced gene expression of tight junctions (i.e. ZO-1, Cldn15, Occludin, and Tricellulin), integrins (i.e., Itgb6) and mucins (i.e., Muc2-like and Muc13-like). Thus, all the obtained results suggest that the subchronic oral exposure to PS-MPs induces inflammatory and immune alterations as well as an impact on intestinal functional integrity in gilthead seabream, with a more evident effect in PI.

Hazard assessment of different-sized polystyrene nanoplastics in hematopoietic human cell lines

The environmental presence of micro/nanoplastics (MNPLs) is an environmental and human health concern. Such MNPLs can result from the physicochemical/biological degradation of plastic goods (secondary MNPLs) or can result from industrial production at that size, for different commercial purposes (primary MNPLs). Independently of their origin, the toxicological profile of MNPLs can be modulated by their size, as well as by the ability of cells/organisms to internalize them. To get more information on these topics we have determined the ability of three different sizes of polystyrene MNPLs (50, 200, and 500 nm) to produce different biological effects in three different human hematopoietic cell lines (Raji-B, THP-1, and TK6). Results show that none of the three sizes was able to induce toxicity (growth ability) in any of the tested cell types. Although transmission electron microscopy and confocal images showed cell internalization in all the cases, their quantification by flow cytometry demonstrated an important uptake by Raji-B and THP-1 cells, in comparison with TK6 cells. For the first ones, the uptake was negatively associated with the size. Interestingly, when the loss of mitochondrial membrane potential was determined, dose-related effects were observed for Raji-B and THP-1 cells, but not for TK6 cells. These effects were observed for the three different sizes. Finally, when oxidative stress induction was evaluated, no clear effects were observed for the different tested combinations. Our conclusion is that size, biological endpoint, and cell type are aspects modulating the toxicological profile of MNPLs.

Tissue Clearing To Localize Microplastics via Three-Dimensional Imaging of Whole Organisms

Understanding the biological impacts of plastic pollution requires an effective methodology to detect unlabeled microplastics in environmental samples. Detecting unlabeled microplastics in an organism generally requires a digestion protocol, which results in the loss of spatial information on the distribution of microplastic within the organism and could lead to the disappearance of the smaller plastics. Fluorescence microscopy allows visualization of ingested microplastics but many labeling strategies are nonspecific and label biomass, thus limiting our ability to distinguish internalized plastics. While prelabeled plastics can be used to avoid nonspecific labeling, this approach precludes the detection of environmental microplastics in organisms. Also, using prelabeled microplastics can affect the viability of the organism and impact plastic uptake. Thus, a method was developed that employs nonspecific labeling with a tissue-clearing technique. Briefly, unlabeled microplastics are stained with a fluorescent dye after ingestion by the organism. The tissue-clearing technique then removes tissue-bound dye while rendering the structurally intact organism transparent. The internalized plastics remain stained and can be visualized in the cleared tissue with fluorescence microscopy. The technique is demonstrated using polystyrene beads in living aquatic organismsTigriopus californicusandDaphnia magnaand by spiking a model vertebrate (Cephalochordata) with different microplastics.

Natural Solar Irradiation Produces Fluorescent and Biodegradable Nanoplastics

Nanoplastics (NPs) have raised global concern owing to their potential health effects. Herein, after simulated and natural solar irradiation, polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) nanoplastics (PVC NPs) were observed to exhibit enhanced fluorescence, particularly PVC NPs. Furthermore, the role of photoaged NPs as a potential fluorescence indicator was evaluated by exposing a model aquatic organism Daphnia magna to these NPs. Our results revealed that photoaged NPs exhibited strong fluorescence owing to the generation of conjugated π bonds, which can achieve π-π* electron transition with low energy consumption. Photogenerated fluorescence also enabled the photoaged NPs to act as efficient fluorescent tracers, which can help track NP migration in various organisms. The results of two-photon laser confocal scanning microscopy revealed that the photoaged NPs could translocate across biological barriers and accumulate in extraintestinal tissues in addition to being ingested and excreted. Moreover, compared with pristine NPs, the photoaged NPs underwent biodegradation more easily, probably because of increased hydrophilicity due to photogenerated oxygen-containing moieties. Therefore, in addition to producing fluorescent NPs without the attachment of external fluorescent dyes, the natural photoaging process can promote the migration and degradation of photoaged NPs in food chains.

Evaluation of bioaccumulation of nanoplastics, carbon nanotubes, fullerenes, and graphene family materials

Bioaccumulation is a key factor in understanding the potential ecotoxicity of substances. While there are well-developed models and methods to evaluate bioaccumulation of dissolved organic and inorganic substances, it is substantially more challenging to assess bioaccumulation of particulate contaminants such as engineered carbon nanomaterials (CNMs; carbon nanotubes (CNTs), graphene family nanomaterials (GFNs), and fullerenes) and nanoplastics. In this study, the methods used to evaluate bioaccumulation of different CNMs and nanoplastics are critically reviewed. In plant studies, uptake of CNMs and nanoplastics into the roots and stems was observed. For multicellular organisms other than plants, absorbance across epithelial surfaces was typically limited. Biomagnification was not observed for CNTs and GFNs but were observed for nanoplastics in some studies. However, the reported absorption in many nanoplastic studies may be a consequence of an experimental artifact, namely release of the fluorescent probe from the plastic particles and subsequent uptake. We identify that additional work is needed to develop analytical methods to provide robust, orthogonal methods that can measure unlabeled (e.g., without isotopic or fluorescent labels) CNMs and nanoplastics.

Size-Dependent Uptake and Depuration of Nanoplastics in Tilapia (Oreochromis niloticus) and Distinct Intestinal Impacts

Nanoplastics (NPs, <1 μm) are of great concern worldwide because of their high potential risk toward organisms in aquatic systems, while very little work has been focused on their tissue-specific toxicokinetics due to the limitations of NP quantification for such a purpose. In this study, NPs with two different sizes (86 and 185 nm) were doped with palladium (Pd) to accurately determine the uptake and depuration kinetics in various tissues (intestine, stomach, liver, gill, and muscle) of tilapia (Oreochromis niloticus) in water, and subsequently, the corresponding toxic effects in the intestine were explored. Our results revealed uptake and depuration constants of 2.70-378 L kg^-1 day^-1 and 0.138-0.407 day^-1 for NPs in tilapia for the first time, and the NPs in tissues were found to be highly dependent on the particle size. The intestine exhibited the greatest relative accumulation of both sizes of NPs; the smaller NPs caused more severe damage than the larger NPs to the intestinal mucosal layer, while the larger NPs induced a greater impact on microbiota composition. The findings of this work explicitly indicate the size-dependent toxicokinetics and intestinal toxicity pathways of NPs, providing new insights into the ecological effects of NPs on aquatic organisms.

Investigating nanoplastics toxicity using advanced stem cell-based intestinal and lung in vitro models

Plastic particles in the nanometer range-called nanoplastics-are environmental contaminants with growing public health concern. As plastic particles are present in water, soil, air and food, human exposure via intestine and lung is unavoidable, but possible health effects are still to be elucidated. To better understand the Mode of Action of plastic particles, it is key to use experimental models that best reflect human physiology. Novel assessment methods like advanced cell models and several alternative approaches are currently used and developed in the scientific community. So far, the use of cancer cell line-based models is the standard approach regarding in vitro nanotoxicology. However, among the many advantages of the use of cancer cell lines, there are also disadvantages that might favor other approaches. In this review, we compare cell line-based models with stem cell-based in vitro models of the human intestine and lung. In the context of nanoplastics research, we highlight the advantages that come with the use of stem cells. Further, the specific challenges of testing nanoplastics in vitro are discussed. Although the use of stem cell-based models can be demanding, we conclude that, depending on the research question, stem cells in combination with advanced exposure strategies might be a more suitable approach than cancer cell lines when it comes to toxicological investigation of nanoplastics.

Spectro-Microscopic Techniques for Studying Nanoplastics in the Environment and in Organisms

Nanoplastics (NPs), small (<1 μm) polymer particles formed from bulk plastics, are a potential threat to human health and the environment. Orders of magnitude smaller than microplastics (MPs), they might behave differently due to their larger surface area and small size, which allows them to diffuse through organic barriers. However, detecting NPs in the environment and organic matrices has proven to be difficult, as their chemical nature is similar to these matrices. Furthermore, as their size is smaller than the (spatial) detection limit of common analytical tools, they are hard to find and quantify. We highlight different micro-spectroscopic techniques utilized for NP detection and argue that an analysis procedure should involve both particle imaging and correlative or direct chemical characterization of the same particles or samples. Finally, we highlight methods that can do both simultaneously, but with the downside that large particle numbers and statistics cannot be obtained.

Uptake, distribution and elimination of palladium-doped polystyrene nanoplastics in rainbow trout (Oncorhynchus mykiss) following dietary exposure

The ingestion of nanoplastics (NPs) by fish has led to concerns regarding fish health and food chain transfer, but analytical constraints have hindered quantitative data collection on their uptake and depuration. We used palladium-doped polystyrene nanoplastics (PS-Pd NPs, ~200 nm) to track particle fate in rainbow trout (Oncorhynchus mykiss) during a week-long dietary exposure and subsequent 7-day depuration period on a control diet (no added PS-Pd NPs). At Day 3 and 7 of the exposure, and after depuration, the mid intestine, hind intestine, liver, gallbladder, kidney, gill and carcass were sampled. All organs and the carcass were analysed for total Pd content by inductively couple plasma mass spectrometry. After 3 days of exposure, the mid (32.5 ± 8.3 ng g-1) and hind (42.3 ± 8.2 ng g-1) intestine had significantly higher total Pd concentrations compared to the liver and carcass (1.3 ± 0.4 and 3.4 ± 1.1 ng g-1, respectively). At Day 7, there was no time-related difference in any organ (or the carcass) total Pd concentrations compared to Day 3. When the total Pd content was expressed as a body distribution based on mass of tissue, the carcass contained the highest fraction with 72.5 ± 5.2 % at Day 7, which could raise concerns over transfer to higher trophic levels. The total number of particles that entered the fish over the 7 days was 94.5 ± 13.5 × 106 particles, representing 0.07 ± 0.01 % of the Pd the fish had been fed. Following depuration, there was no detectable Pd in any organ or the carcass, indicating clearance from the fish. These data indicate that these NPs are taken into the internal organs and carcass of fish, yet removal of the exposure results in substantial excretion to below the limit of detection.

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.

Hazard of polystyrene micro-and nanospheres to selected aquatic and terrestrial organisms

Plastics contamination in the environment is a major concern. Risk assessment of micro- and nanoplastics (MPL and NPL) poses significant challenges due to MPL and NPL heterogeneity regarding compositional polymers, particle sizes and morphologies in the environment. Yet, there exists considerable toxicological literature on commercial polystyrene (PS) micro- and nanospheres. Although such particles do not directly represent the environmental MPL and NPL, their toxicity data should be used to advance the hazard assessment of plastics. Here, toxicity data of PS micro- and nanospheres for microorganisms, aquatic and terrestrial invertebrates, fish, and higher plants was collected and analyzed. The evaluation of 294 papers revealed that aquatic invertebrates were the most studied organisms, nanosized PS was studied more often than microsized PS, acute exposures prevailed over chronic exposures, the toxicity of PS suspension additives was rarely addressed, and ∼40 % of data indicated no organismal effects of PS. Toxicity mechanisms were mainly studied in fish and nematode Caenorhabditis elegans, providing guidance for relevant studies in higher organisms. Future studies should focus on environmentally relevant plastics concentrations, wide range of organisms, co-exposures with other pollutants, and method development for plastics identification and quantification to fill the gap of bioaccumulation assessment of plastics.

Potential Artifacts and Control Experiments in Toxicity Tests of Nanoplastic and Microplastic Particles

To fully understand the potential ecological and human health risks from nanoplastics and microplastics (NMPs) in the environment, it is critical to make accurate measurements. Similar to past research on the toxicology of engineered nanomaterials, a broad range of measurement artifacts and biases are possible when testing their potential toxicity. For example, antimicrobials and surfactants may be present in commercially available NMP dispersions, and these compounds may account for toxicity observed instead of being caused by exposure to the NMP particles. Therefore, control measurements are needed to assess potential artifacts, and revisions to the protocol may be needed to eliminate or reduce the artifacts. In this paper, we comprehensively review and suggest a next generation of control experiments to identify measurement artifacts and biases that can occur while performing NMP toxicity experiments. This review covers the broad range of potential NMP toxicological experiments, such as in vitro studies with a single cell type or complex 3-D tissue constructs, in vivo mammalian studies, and ecotoxicity experiments testing pelagic, sediment, and soil organisms. Incorporation of these control experiments can reduce the likelihood of false positive and false negative results and more accurately elucidate the potential ecological and human health risks of NMPs.

Removal of nanoplastics in water treatment processes: A review

Nanoplastics are drawing a significant attention as a result of their propensity to spread across the environment and pose a threat to all organisms. The presence of nanoplastics in water is given attention nowadays as the transit of nanoplastics occurs through the aquatic ecosphere besides terrestrial mobility. The principal removal procedures for macro-and micro-plastic particles are effective, but nanoparticles escape from the treatment, increasing in the water and significantly influencing the society. This critical review is aimed to bestow the removal technologies of nanoplastics from aquatic ecosystems, with a focus on the treatment of freshwater, drinking water, and wastewater, as well as the importance of transit and its impact on health concerns. Still, there exists a gap in providing a collective knowledge on the methods available for nanoplastics removal. Hence, this review offered various nanoplastic removal technologies (microorganism-based degradation, membrane separation with a reactor, and photocatalysis) that could be the practical/effective measures along with the traditional procedures (filtration, coagulation, centrifugation, flocculation, and gravity settling). From the analyses of different treatment systems, the effectiveness of nanoplastics removal depends on various factors, source, size, and type of nanoplastics apart from the treatment method adopted. Combined removal methods, filtration with coagulation offer great scope for the removal of nanoplastics from drinking water with >99 % efficiency. The collected data could serve as base-line information for future research and development in water nanoplastics cleanup.

Nanoplastics are bioaccumulated in fish liver and muscle and cause DNA damage after a chronic exposure

The extent of the widespread, planetary contamination by plastic waste is difficult to fully capture. Nanoplastics (NPs) are currently in the center of research concerning plastic litter, both for the analytical challenges they pose and for their potential to provoke hazardous effects in organisms. However, there are still many unanswered questions in this multidisciplinary field, with a crucial missing piece being the quantification of NPs in fish tissues after in vivo exposures. Another relevant question that is still greatly unexplored is how a chronic exposure to NPs will affect fish health. This study aims to provide answers to both of these relevant knowledge gaps. To this end, goldfish (Carassius auratus) were exposed to 44 nm polystyrene (PS)-NPs via water for 30 days. Following the exposure, gastrointestinal tract, liver and muscle were sampled for PS-NPs analysis by means of size exclusion chromatography coupled to high resolution mass spectrometry. PS-NPs were detected in all liver and muscle samples of exposed fish, with higher concentrations in liver than in muscle, whereas no PS-NPs were detected in the gastrointestinal tract. Nevertheless, exposure to PS-NPs did not induce changes in hematology parameters nor in cortisol and glucose levels in plasma. On the other hand, even a relatively low concentration of PS-NPs was able to cause DNA damage, measured by an increase in erythrocyte nuclear abnormalities, suggesting that PS-NPs can reach the cell nucleus and cause genotoxicity. These results show for the first time that PS-NPs find their way to fish muscle after chronic exposure, where they bioaccumulate, but do not alter fish survival nor hematological or physiological stress indicators. The accumulation of PS-NPs in fish muscle can represent a threat to human health as a possible route of exposure to small-sized plastics. The present results in a model fish species open windows for future studies in edible fish species.

Effects of polystyrene micro/nanoplastics on liver cells based on particle size, surface functionalization, concentration and exposure period

Micro/nanoplastics (MP/NP) contaminate our food and drinking water but their impact on human health has not been well-documented. The liver is one of the first organs that ingested MP/NP encounter and it has a major role in the clearance of xenobiotics. Therefore, the effects of polystyrene MP/NP on liver HepG2 cells were studied. Cellular responses to particles of various sizes (50-5000 nm) and surface functionalization (aminated, carboxylated or non-functionalized) were determined at different concentrations (0.1-100 μg/mL) and exposure periods (1-24 h). Smaller sized particles were internalized by HepG2 cells more avidly than larger particles regardless of functionalization; the highest uptake being for 50 and 100 nm aminated particles at lower concentrations. Confocal microscopy images of cells corroborated quantitative uptake results. Aminated particles were more toxic to the cells than carboxylated or non-functionalized particles. Among aminated particles smaller particles (50 and 100 nm) were more detrimental to cell viability compared to larger particles (1000 or 5000 nm) with toxicity increasing with concentration. Treatment with the particles for 4 h increased intracellular concentrations of Caspase-3 by 1.5-2.8 fold, but 24 h exposure to the particles attenuated this increase in Caspase-3 concentrations. A slight trend of higher Caspase-3 concentration in cells treated with larger particles (500-5000 nm) compared to smaller particles (50-200 nm) was observed, indicating that larger particles are more likely to direct cells toward apoptotic cell death upon 4 h exposure. Exposure of cells to large PS particles (500-5000 nm) upregulated interleukin-8 and the effect was enhanced at 24 h. Overall, the study demonstrated that smaller aminated particles were most toxic to hepatocytes, but larger particles induced apoptotic cell death or an inflammatory response depending on the length of exposure.

Fabrication of Nylon-6 and Nylon-11 Nanoplastics and Evaluation in Mammalian Cells

Microplastics (MPs) and nanoplastics (NPs) exist in certain environments, beverages, and food products. However, the ultimate risk and consequences of MPs and NPs on human health remain largely unknown. Studies involving the biological effects of small-scale plastics have predominantly used commercially available polystyrene beads, which cannot represent the breadth of globally dominant plastics. Nylon is a commodity plastic that is used across various industry sectors with substantial global production. Here, a series of well-characterized nylon-11 and nylon-6 NPs were successfully fabricated with size distributions of approximately 100 nm and 500 nm, respectively. The facile fabrication steps enabled the incorporation of fluorescent tracers in these NPs to aid the intracellular tracking of particles. RAW 264.7 macrophages were exposed to nylon NPs in a dose-dependent manner and cytotoxic concentrations and cellular uptake were determined. These well-characterized nylon NPs support future steps to assess how the composition and physicochemical properties may affect complex biological systems and ultimately human health.

Experimental evidence that polystyrene nanoplastics cross the intestinal barrier of European seabass

Plastic pollution in marine ecosystems constitutes an important threat to marine life. For vertebrates, macro/microplastics can obstruct and/or transit into the airways and digestive tract whereas nanoplastics (NPs; < 1000 nm) have been observed in non-digestive tissues such as the liver and brain. Whether NPs cross the intestinal epithelium to gain access to the blood and internal organs remains controversial, however. Here, we show directly NP translocation across the intestinal barrier of a fish, the European seabass, Dicentrarchus labrax, ex vivo. The luminal side of median and distal segments of intestine were exposed to fluorescent polystyrene NPs (PS-NPs) of 50 nm diameter. PS-NPs that translocated to the serosal side were then detected quantitatively by fluorimetry, and qualitatively by scanning electron microscopy (SEM) and pyrolysis coupled to gas chromatography and high-resolution mass spectrometry (Py-GC-HRMS). Fluorescence intensity on the serosal side increased 15-90 min after PS-NP addition into the luminal side, suggesting that PS-NPs crossed the intestinal barrier; this was confirmed by both SEM and Py-GC-HRMS. This study thus evidenced conclusively that NPs beads translocate across the intestinal epithelium in this marine vertebrate.

Polystyrene nanoplastics demonstrate high structural stability in vivo: A comparative study with silica nanoparticles via SERS tag labeling

Nanoplastics are regarded as inert particulate pollutants pose potential threat to organisms. It has been verified that they can penetrate biological barriers and accumulate in organisms; however, there is still a knowledge gap on the in vivo stability and degradation behaviors due to the lack of ideal analytical methods. Herein, a surface-enhanced Raman scattering (SERS) tag labeling technique was developed to study the in vivo behaviors of polystyrene (PS) nanoplastics by comparison with silica (SiO₂) nanoparticles (NPs). The labeled NPs were composed of gold NP core, attached Raman reporters as well as PS and silica shell, respectively, demonstrating strong SERS signals which were responsive to the compactness of the shells. The labeled NPs enabled the probing of in vivo structural stability of PS and silica in the liver, spleen and lung of mice after intravenous injection via the time-dependent evolution of SERS signal intensity and gold element content in the organs. The results indicated that both PS and silica model NPs retained in these organs without apparent excretion within 28 d. However, the structural stabilities of PS and silica differed dramatically as reflected by the SERS signal and tissue slice characterization. The silica shell completely degraded whereas the PS shell was still compact. Our results verified the long-term accumulation and in vivo inert property of nanoplastics, hinting that they were distinct from natural NPs and probably induce higher health risks from the aspect of the non-degradation property.

A review of interactions of microplastics and typical pollutants from toxicokinetics and toxicodynamics perspective

The widespread microplastics (MPs) pollution has become a concerning environmental issue. The interactions between MPs and typical pollutants may change the bioaccumulation, and toxicity of pollutants, leading to high uncertainty in risk assessment. Still, significant gaps remain in the knowledge available to integrate these interactions in the perspectives of toxicokinetics (TK) and toxicodynamics (TD), which is also an essential part of quantitative toxicological research. This review systematically summarizes the interaction between MPs and typical pollutants in TK and TD processes. MPs can be acted as the vector or sink of pollutants to increase or decrease their bioaccumulation, and also may not affect their bioaccumulation due to no interaction. The adverse outcome pathway (AOP) framework enables novel approaches for determining the interaction between MPs and pollutants in the TD process. MPs can directly or indirectly enhance, reduce and not affect the toxicity of pollutants. A series of factors influencing the interaction in TK and TD processes are summarized, including MPs characteristics and exposure scenarios. TK-TD approach can quantitatively understand the interaction between MPs and pollutants based on the mechanism. Given the current knowledge gap in TK and TD processes, future perspectives on combined exposure research are proposed.

Quantitative assessment of in vivo distribution of nanoplastics in bivalve Ruditapes philippinarum using reliable SERS tag-labeled nanoplastic models

Nanoplastics (NPs) as emerging marine pollutants can be taken up by seafood organisms. It is crucial to quantitatively assess NP's distribution behavior in organisms to elucidate concentration dependent biological effects. Such a knowledge gap has remained due to the lack of reliable NP models and analytical methods. Herein, surface enhanced Raman scattering (SERS)-labeled NP models were developed and their bioavailability, distribution and accumulation in Ruditapes philippinarum, a typical marine bivalve, were quantitatively studied. Taking advantage of the sensitive and characteristic SERS signals of the NP models, distribution could be quickly and accurately obtained by the Raman imaging technique. Moreover, quantitative analysis of NPs could be performed by the detection of gold element contents via inductively coupled plasma mass spectroscopy (ICP-MS) detection. ICP-MS results revealed that after 3 days exposure of monodispersed NPs (100 nm, 0.2 mg L^-1), the digestive gland accumulated 86.7% of whole-body NPs followed by gill (5.2%), mantle (5.1%), foot (1.3%), exhalant siphon (1.1%), and adductor (0.6%). Upon 11 days depuration, 98.7% of NPs in the digestive gland were excreted, whereas the clearance ratios in other organs were much lower. NP aggregates (around 1.5 μm) demonstrated similar distribution and clearance trends to the monodispersed ones. However, the accumulation amount in each organ was 15.2% to 77.6% lower. Surface adherence and passive ingestion routes resulted in NP accumulation, which contributed to the comparable NP abundance in these organs. Additionally, boiling treatment (mimicking a cooking process) did not decrease the NP amount in these organs. This work provided a dual-mode and quantitative analysis protocol for NPs for the first time, and suggested the risk of NP uptake by humans via bivalve seafood diets.

Single-Particle Resolution Fluorescence Microscopy of Nanoplastics

Understanding of nanoplastic prevalence and toxicology is limited by imaging challenges resulting from their small size. Fluorescence microscopy is widely applied to track and identify microplastics in laboratory studies and environmental samples. However, conventional fluorescence microscopy, due to diffraction, lacks the resolution to precisely localize nanoplastics in tissues, distinguish them from free dye, or quantify them in environmental samples. To address these limitations, we developed techniques to label nanoplastics for imaging with stimulated emission depletion (STED) microscopy to achieve resolution at an order of magnitude superior to conventional fluorescence microscopy. These techniques include (1) passive sorption; (2) swell incorporation; and (3) covalent coupling of STED-compatible fluorescence dyes to nanoplastics. We demonstrate that our labeling techniques, combined with STED microscopy, can be used to resolve nanoplastics of different shapes and compositions as small as 50 nm. The longevity of dye labeling is demonstrated in different media and conditions of biological and environmental relevance. We also test STED imaging of nanoplastics in exposure experiments with the model worm Caenorhabditis elegans. Our work shows the value of the method for detection and localization of nanoplastics as small as 50 nm in a whole animal without disruption of the tissue. These techniques will allow more precise localization and quantification of nanoplastics in complex matrices such as biological tissues in exposure studies.

Nanoplastics and Human Health: Hazard Identification and Biointerface

Nanoplastics are associated with several risks to the ecology and toxicity to humans. Nanoplastics are synthetic polymers with dimensions ranging from 1 nm to 1 μm. They are directly released to the environment or secondarily derived from plastic disintegration in the environment. Nanoplastics are widely detected in environmental samples and the food chain; therefore, their potentially toxic effects have been widely explored. In the present review, an overview of another two potential sources of nanoplastics, exposure routes to illustrate hazard identification of nanoplastics, cell internalization, and effects on intracellular target organelles are presented. In addition, challenges on the study of nanoplastics and future research areas are summarized. This paper also summarizes some approaches to eliminate or minimize the levels of nanoplastics to ensure environmental safety and improve human health.

Effects of virgin and weathered polystyrene and polypropylene microplastics on Raphidocelis subcapitata and embryos of Danio rerio under environmental concentrations

Microplastics are ubiquitous contaminants of freshwater ecosystems. However, few ecotoxicity assays have been conducted on freshwater organisms using environmentally relevant concentrations of virgin and weathered microplastics. This work assessed the adverse effects of virgin and artificially weathered fragments of polystyrene and polypropylene on the microalga Raphidocelis subcapitata (72 h growth inhibition assay) and on embryos of the fish Danio rerio (96 h fish embryo assay) under environmentally relevant concentrations (2000-200,000 MP L^-1) and high concentrations (12.5-100 mg L^-1). Sizes of microplastics were measured as tens (polystyrene) to hundreds (polypropylene) of micrometers, while aging was assessed by measuring the carbonyl index. In the microalga, the tested high concentrations promoted growth, while environmentally relevant concentration induced either growth inhibition or promotion. In zebrafish embryos, environmentally relevant concentrations decreased body length and heart rates. No relevant effects were observed in organisms exposed to high concentrations for mortality, malformations, hatching rates, and swimming bladder inflation. Virgin microplastics presented slightly higher toxicity but direct comparison was hindered by the lack of a linear dose-response curve. Despite the lack of a clear pattern, adverse effects were often observed in the lowest environmentally relevant concentrations, raising concerns over the impacts of microplastics on freshwater ecosystems.

Enhanced microalgal toxicity due to polystyrene nanoplastics and cadmium co-exposure: From the perspective of physiological and metabolomic profiles

As important emerging contaminants, nanoplastics can act as vectors for other environmental pollutants, resulting in their migration throughout ecosystems and altering their toxicity. In this study, the fluorescent dye label aggravated the toxicity of polystyrene (PS) nanoplastics (100 nm diameter particles) to microalgae Euglena gracilis. Therefore, the toxicity of non-fluorescent labelled PS alone and in combination with divalent cadmium (Cd²⁺) on Euglena gracilis in the environmentally relevant concentrations was investigated. Results revealed that co-exposure to 50 μg/L (1.1 × 10¹⁰ particles/L) PS and 50 μg/L Cd²⁺ resulted in synergistic effects, significantly inhibiting microalgal growth by 28.76%. Superoxide dismutase, peroxidase and extracellular polymeric substances were distinctly enhanced in co-exposure treatments compared to the control, indicating that cellular antioxidant defense responses were activated. LC-MS-based metabolomic analysis suggested that PS and Cd²⁺ exposure alone or in combination induced significant disruption to carbohydrate and purine metabolism-related pathways, as compared to controls. As part of the PS and Cd²⁺ stress response, differential metabolites involved in lipid metabolism and amino acid metabolism provide antioxidants and cell membrane protective molecules. Overall, this combined physiological and metabolomic analysis approach provides a better understanding of the potential risks posed by nanoplastics and heavy metal pollution in aquatic ecosystems.

Surface-enhanced Raman scattering labeled nanoplastic models for reliable bio-nano interaction investigations

Nanoplastics (NPs) have attracted great attention as an emerging pollution. To date, their interaction with biological systems has been studied mostly by using fluorescent-labeled NPs, which suffered from serious drawbacks such as biological autofluorescence interference and false-positive results. Reliable optically labeled NP models are eagerly desired until now. Herein, a novel near-infrared (NIR) surface-enhanced Raman scattering (SERS) labeled NP model was proposed, which gained single-particle ultra-sensitivity, deep tissue detection, multiplex labeling ability, and anti-interference property. More importantly, the NP demonstrated satisfactory in vivo signal stability which completely prevented the positive-false problems. The advantages of the NPs enabled direct, dynamic in vivo behavior imaging study in living zebrafish embryo, adult zebrafish and green vegetable Brassica rapa. It was found for the first time that NPs entered blood circulation system of zebrafish larva via dermal uptake route, which only occurred in a short 48 h-window post-hatch. NPs widely distributed in roots, shoots and leaves of Brassica rapa seedlings germinating and growing in the NP-containing hydroponic culture. Different depths of one root showed varied adsorption capabilities towards NPs with fulvic acid, lipid and sodium dodecyl sulfate eco-coronas. This work provided an ideal tool for reliable bio-NP interaction study for a variety of organisms, which could promote the research of NPs.

Immunotoxic effects of metal-based nanoparticles in fish and bivalves

There is a global research interest in metal nanoparticles (MNPs) due to their diverse applications, rapidly increasing use, and increased presence in the aquatic environment. Currently, most MNPs in the environment are at levels unlikely to cause overt toxicity. Sub-lethal effects that MNPs may induce, notable immunotoxicity, could however have significant health implications. Thus, deciphering the immunological interactions of MNPs with aquatic organisms constitutes a much-needed area of research. In this article, we critically assess the evidence for immunotoxic effects of MNPs in bivalves and fish, as key wildlife sentinels with widely differing ecological niches that are used as models in ecotoxicology. The first part of this review details the properties, fate, and fundamental physicochemical behavior of MNPs in the aquatic ecosystem. We then consider the toxicokinetics of MNP uptake, accumulation, and deposition in fish and bivalves. The main body of the review then focuses on immune reactions in response to MNPs exposure in bivalves and fish illustrating their immunotoxic potential. Finally, we identify major knowledge gaps in our current understanding of the implications of MNPs exposure for immunological functions and the associated health consequences for bivalves and fish, as well as the general lessons learned on the immunotoxic properties of the emerging class of nanoparticulate contaminants in fish and bivalves.

Physical and chemical threats posed by micro(nano)plastic to sea urchins

The awareness of the plastic issue is rising in recent years. Our seas and coastal seawaters are investigated with the aim to evaluate the possible fate, behavior and the impact of these novel contaminants upon marine biota. In particular, benthic organisms are exposed to micro(nano)plastics that sink and accumulated on the seabed. Sea urchins can be prone to the plastic impact for all their lifespan with effect that can be extended upon the trophic cascade since their key role as grazer organisms. Moreover, they are largely used in the assessment of contaminant impact both as adult individuals and as early larval stages. This review analyzes the recent literature about the chemical and physical hazards posed by diverse polymers to sea urchins, in relation to their peculiar characteristics and to their size. The search was based on a query of the keyword terms: microplastic _ OR nanoplastic_AND Sea urchins in Web of Science and Google Scholar. The effects provoked by exposure of different sea urchin biological form are highlighted, considering both laboratory exposure and collection in real world. Additional focus has also been given upon the exposure methods utilized in laboratory test and in the existing limitations in the testing procedures. In conclusion, the micro(nano)plastics major impact seemed to be attributable to leaching compounds, however variability and lacking of realisms in the procedures do not allow a full understanding of the hazard posed by micro(nano)plastics for sea urchins. Finally, the work provides insights into the future research strategies to better characterize the actual risk for sea urchins.

Distribution and translocation of micro- and nanoplastics in fish

Microplastics (MPs) and nanoplastics (NPs) are regarded as emerging particulate contaminants. Here, we first summarize the distribution of plastic particles in fish. Field investigations verify the presence of various kinds of fibrous, spherical, and fragmentary MPs in fish gastrointestinal tract and gills, and specifically in muscle and liver. Laboratory works demonstrate that NPs even penetrate into blood vessels of fish and pass onto next generations. Second, we systematically discuss the translocation ability of MPs and NPs in fish. MPs can enter early-developing fish through adherence, and enter adult fish internal organs by intestine absorption or epidermis infiltration. NPs can not only penetrate into fish embryo blastopores, but also reach adult fish internal organs through blood circulation. Third, the cellular basis for translocation of plastic particles, NPs in particular, into cells are critically reviewed. Endocytosis and paracellular penetration are two main pathways for them to enter cells and intercellular space, respectively. Finally, we compare the chemical and physical properties among various particular pollutants (MPs, NPs, settleable particulate matters, and manufactured nanomaterials) and their translocation processes at different biological levels. In future studies, it is urgent to break through the bottleneck techniques for NPs quantification in field environmental matrix and organisms, re-confirm the existence of MPs and NPs in field organisms, and develop more detailed translocating mechanisms of MPs and NPs by applying cutting-edge tracking techniques.

Size Effects of Microplastics on Embryos and Observation of Toxicity Kinetics in Larvae of Grass Carp (Ctenopharyngodon idella)

Microplastics have caused great concern in recent years. However, few studies have compared the toxicity of different sizes of microplastics in fishes, especially commercial fishes, which are more related to human health. In the present study, we revealed the effects of varying sizes of microplastics on grass carp embryos and larvae using scanning electron microscopy (SEM) and fluorescence imaging. Embryos were exposed to 80 nm and 8 μm microplastics at concentrations of 5, 15, and 45 mg/L. Toxicity kinetics of various sizes of fluorescent microplastics were analyzed through microscopic observation in the larvae. Results found that nanoplastics could not penetrate the embryo’s chorionic membrane, instead they conglutinated or aggregated on the chorion. Our results are the first to explore the defense mechanisms of commercial fish embryos against microplastics. Larvae were prone to ingesting their own excrement, resulting in microplastic flocculants winding around their mouth. For the first time, it was found that excreted microplastics could be reconsumed by fish and reaccumulated in the oral cavity. Microplastics of a certain size (1 μm) could be accumulated in the nasal cavity. We speculate that the presence of a special groove structure in the nasal cavity of grass carp larvae may manage to seize the microplastics with a particular size. As far as we know, this is the first report of microplastics being found in the nasal passages of fish. Fluorescence images clearly recorded the toxicity kinetics of microplastics in herbivorous fish.

A comparative investigation of toxicity of three polymer nanoparticles on acorn barnacle (Amphibalanus amphitrite)

Pollution from plastic waste is increasingly prevalent in the environment and beginning to generate significant adverse impact on the health of living organisms. In this study, we investigate the toxicity of polymer nanoparticles exposed to Acorn Barnacle (Amphibalanus amphitrite) nauplii, as an animal model. Highly stable aqueous dispersion of luminescent nanoparticles from three common polymers: polymethylmethacrylate (PMMA), polystyrene (PS), and polyvinylchloride (PVC), were prepared via nanoprecipitation and fully characterised. Exposure studies of these polymer particles to freshly spawned barnacle nauplii were performed within a concentration range from 1 to 25 mg/L under laboratory-controlled conditions. The exposure to PMMA and PS nanoparticles did not show detrimental toxicity and did not cause sufficient mortality to compute a LC₅₀ value. However, PVC nanoparticles were significantly toxic with a mortality rate of up to 99% at 25 mg/L, and the calculated LC₅₀ value for PVC nanoparticles was 7.66 ± 0.03 mg/L, 95% CI. Interestingly, PVC nanoparticle aggregates were observed to adhere to the naupliar carapace and appendages at higher concentrations and could not be easily removed by washings. To explore the possibility of chemical toxicity of polymer nanoparticles, analysis of the polymer powders which was used to prepare the nanoparticles was conducted. The presence of low molecular weight oligomers such as dimers, trimers and tetramers were observed in all polymer samples. The chemical nature and concentration of such compounds are likely responsible for the observed toxicity to the barnacle nauplii. Overall, our study shows that care should be exercised in generalising the findings of exposure studies performed using one type of plastic particles, as the use of different plastic particles may elicit different responses inside a living organism.