Co-exposure to polystyrene plastic beads and polycyclic aromatic hydrocarbon contaminants in fish gill (RTgill-W1) and intestinal (RTgutGC) epithelial cells derived from rainbow trout (Oncorhynchus mykiss)

Atlantic salmon gill epithelial cell line ASG-10, an in vitro model for studying effects of microplastics in gills

Microplastics are ubiquitous environmental pollutants frequently detected in aquatic environments. Here we used the Atlantic salmon epithelial gill cell line (ASG-10) to investigate the uptake and effects of polystyrene (PS) microplastic. The ASG-10 cell line has phagocytotic/endocytic capacities and can take up clear PS particles at 0.2 and 1.0 µm, while PS at 10 µm was not taken up. As a response to the uptake, the ASG-10 cells increased their lysosomal activity. Furthermore, no effects on the mitochondria were found, neither on the mitochondrial membrane potential nor the mitochondria morphology (branch length and diameter). Interestingly, even a very high concentration of PS (200 µg/ml) with all tested particle sizes had no effects on cell viability or cell cycle. The environmental toxin Benzo(a)pyrene (B(a)P), a known inducer of CYP1A, is highly hydrophobic and thus sticks to the PS particles. However, co-exposure of B(a)P and PS the particles did not increase the induction of CYP1A activity compared to B(a)P alone. Our study contributes to the understanding of the cellular effects of PS particles using a highly relevant Atlantic salmon gill epithelium in vitro model.

Effects of polystyrene nano- and microplastics and of microplastics with sorbed polycyclic aromatic hydrocarbons in adult zebrafish

The presence of nanoplastics (NPs) and microplastics (MPs) in the environment is recognised as a global-scale problem. Due to their hydrophobic nature and large specific surface, NPs and MPs can adsorb other contaminants, as polycyclic aromatic hydrocarbons (PAHs), and modulate their bioavailability and hazard. Adult zebrafish were exposed for 3 and 21 days to: (1) 0.07 mg/L NPs (50 nm), (2) 0.05 mg/L MPs (4.5 μm), (3) MPs with sorbed oil compounds of the water accommodated fraction (WAF) of a naphthenic crude oil (MPs-WAF), (4) MPs with sorbed benzo(a)pyrene (MPs-B(a)P), (5) 5 % WAF and (6) 21 μg/L B(a)P. Electrodense particles resembling NPs were seen in the intestine lumen close to microvilli. MPs were abundantly found in the intestine lumen, but not internalised into the tissues. After 21 days, NPs caused a significant downregulation of cat, and upregulation of gpx1a and sod1, while MPs upregulated cyp1a and increased the prevalence of liver vacuolisation. No histopathological alteration was observed in gills. In this study, contaminated MPs did not increase PAH levels in zebrafish but results highlight the potential differential impact of plastic particles depending on their size, making it necessary to urgently address the ecotoxicological impact of real environmental NPs and MPs.

Intestinal epithelial cells of Japanese flounder (Paralichthys olivaceus) as an in vitro model for studying intestine immune function based on transcriptome analysis

Japanese flounder (Paralichthys olivaceus) is an economically crucial marine species, but diseases like hemorrhagic septicemia caused by Edwardsiella tarda have resulted in significant economic losses. E. tarda infects various hosts, and its pathogenicity in fish is not fully understood. Lipopolysaccharides (LPS) are components of the outer membrane of Gram-negative bacteria and are representative of typical PAMP molecules that cause activation of the immune system. The PoIEC cell line is a newly established intestinal epithelial cell line from P. olivaceus. In order to investigate whether it can be used as an in vitro model for studying the pathogenesis of E. tarda and LPS stimulation, we conducted RNA-seq experiments for the PoIECs model of E. tarda infection and LPS stimulation. In this study, transcriptome sequencing was carried out in the PoIEC cell line after treatment with LPS and E. tarda. A total of 62.52G of high-quality data from transcriptome sequencing results were obtained in nine libraries, of which an average of 87.96% data could be aligned to the P. olivaceus genome. Data analysis showed that 283 and 414 differentially expressed genes (DEGs) in the LPS versus Control (LPS-vs-Con) and E. tarda versus Control groups (Et-vs-Con), respectively, of which 60 DEGs were shared in two comparation groups. The GO terms were predominantly enriched in the extracellular space, inflammatory response, and cytokine activity in the LPS-vs-Con group, whereas GO terms were predominantly enriched in nucleus and positive regulation of transcription by RNA polymerase II in the Et-vs-Con group. KEGG analysis revealed that three immune-related pathways were co-enriched in both comparison groups, including the Toll-like receptor signaling pathway, C-type lectin receptor signaling pathway, and Cytokine-cytokine receptor interaction. Five genes were randomly screened to confirm the validity and accuracy of the transcriptome data. These results suggest that PoIEC cell line can be an ideal in vitro model for studies of marine fish gut immunity and pathogenesis of Edwardsiellosis.

Assessment of dietary polyvinylchloride, polypropylene and polyethylene terephthalate exposure in Nile tilapia, Oreochromis niloticus: Bioaccumulation, and effects on behaviour, growth, hematology and histology

Microplastics (MPs) have been recognized as emerging aquatic pollutants receiving major concern due to their detrimental effects on aquatic life. Nile Tilapia, Oreochromis niloticus is a model species considered in toxicological studies to address the effects of pollutants in freshwater animals. However, comprehensive knowledge comparing the impacts on fish across various MPs polymers is scarce. Therefore, the overarching aim of the current study was to examine the bioconcentration of MPs polymers: polyvinylchloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET), and their toxic effects on growth, and behavioral responses, hematology, and histology of gills, liver, and intestine in O. niloticus. Fishes were subjected to a 21-day dietary exposure to MPs by assigning them into six treatment groups: T1 (4% of PVC), T2 (4% of PP), T3 (4% of PET), T4 (8% of PVC), T5 (8% of PP), T6 (8% of PET), and control (0% of MPs), to assess the effects on fish across the polymers and dosage. Results showed several abnormalities in anatomical and behavioral parameters, lower growth, and high mortality in MPs-exposed fish, indicating a dose-dependent relationship. The elevated dosage of polymers raised the bioavailability of PVC, PP, and PET in gills and gut tissues. Noteworthy erythrocyte degeneration referred to cytotoxicity and stress imposed by MPs, whereas the alterations in hematological parameters were possibly due to blood cell damage, also indicating mechanisms of defense against MPs toxicity. Histopathological changes in the gills, liver, and intestine confirmed the degree of toxicity and associated dysfunctions in fish. A higher sensitivity of O. niloticus to PET-MPs compared to other polymers is likely due to its chemical properties and species-specific morphological and physiological characteristics. Overall, the present study reveals valuable insights into the emerging threat of MPs toxicity in freshwater species, which could be supportive of future toxicological research.

Cytotoxicity of 19 Pesticides in Rainbow Trout Gill, Liver, and Intestinal Cell Lines

The rainbow trout gill cell line (RTgill-W1), via test guideline 249 of the Organisation for Economic Co-operation and Development, has been established as a promising New Approach Methodology, although to advance confidence in the method more case studies are needed that: 1) expand our understanding of applicability domains (chemicals with diverse properties); 2) increase methodological throughput (96-well format); and 3) demonstrate biological relevance (in vitro to in vivo comparisons; gill vs. other cells). Accordingly, the objective of our study was to characterize the cytotoxicity of 19 pesticides against RTgill-W1 cells, and also liver (RTL-W1) and gut epithelial (RTgutGC) cell lines, and then to compare the in vitro and in vivo data. Of the 19 pesticides tested, 11, 9, and 8 were cytotoxic to the RTgill-W1, RTL-W1, and RTgutGC cells, respectively. Six pesticides (carbaryl, chlorothalonil, chlorpyrifos, dimethenamid-P, metolachlor, and S-metolachlor) were cytotoxic to all three cell lines. Aminomethylphosphonic acid, chlorantraniliprole, dicamba, diquat, imazethapyr, and permethrin exhibited cell-line-specific toxicity. No cytotoxic responses were observed for three herbicides (atrazine, glyphosate, and metribuzin) and four insecticides (clothianidin, diazinon, imidacloprid, and thiamethoxam). When cytotoxicity was measured, there was a strong correlation (rs  = 0.9, p < 0.0001) between in vitro median effect concentration (EC50) values (based on predicted concentrations using the In Vitro Mass Balance Model Equilibrium Partitioning (IV-MBM EQP) Ver. 2.1) derived from RTgill-W1 and RTL-W1 cells with in vivo median lethal concentration (LC50) values from 96-h acute toxicity studies with trout. In all 28 cases, the in vitro EC50 was within 18-fold of the in vivo LC50. These data help increase our understanding of the ecotoxicological domains of applicability for in vitro studies using cultured rainbow trout cells, while also demonstrating that these assays performed well in a 96-well format and have promise to yield data of biological relevance. Environ Toxicol Chem 2024;00:1-13. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Biological interactions of polystyrene nanoplastics: Their cytotoxic and immunotoxic effects on the hepatic and enteric systems

As emerging pollutants in the environment, nanoplastics (NPs) can cross biological barriers and be enriched in organisms, posing a greatest threat to the health of livestock and humans. However, the size-dependent toxic effects of NPs in higher mammals remain largely unknown. To determine the size-dependent potential toxicities of NPs, we exposed mouse (AML-12) and human (L02) liver cell lines in vitro, and 6-week-old C57BL/6 mice (well-known preclinical model) in vivo to five different sizes of polystyrene NPs (PS-NPs) (20, 50, 100, 200 and 500 nm). We found that ultra-small NPs (20 nm) induced the highest cytotoxicity in mouse and human liver cell lines, causing oxidative stress and mitochondrial membrane potential loss on AML-12 cells. Unexpectedly in vivo, after long-term oral exposure to PS-NPs (75 mg/kg), medium NPs (200 nm) and large NPs (500 nm) induced significant hepatotoxicity, evidenced by increased oxidative stress, liver dysfunction, and lipid metabolism disorders. Most importantly, medium or large NPs generated local immunotoxic effects via recruiting and activating more numbers of neutrophils and monocytes in the liver or intestine, which potentially resulted in increased proinflammatory cytokine secretion and the tissue damage. The discrepancy in in vitro-in vivo toxic results might be attributed to the different properties of biodistribution and tissue accumulation of different sized NPs in vivo. Our study provides new insights regarding the hepatotoxicity and immunotoxicity of NPs on human and livestock health, warranting us to take immense measures to prevent these NPs-associated health damage.

Establishment of an In Vitro Model to Study Viral Infections of the Fish Intestinal Epithelium

Viral infections are still a major concern for the aquaculture industry. For salmonid fish, even though breeding strategies and vaccine development have reduced disease outbreaks, viral diseases remain among the main challenges having a negative impact on the welfare of fish and causing massive economic losses for the industry. The main entry port for viruses into the fish is through mucosal surfaces including that of the gastrointestinal tract. The contradictory functions of this surface, both creating a barrier towards the external environment and at the same time being responsible for the uptake of nutrients and ion/water regulation make it particularly vulnerable. The connection between dietary components and viral infections in fish has been poorly investigated and until now, a fish intestinal in vitro model to investigate virus-host interactions has been lacking. Here, we established the permissiveness of the rainbow trout intestinal cell line RTgutGC towards the important salmonid viruses-infectious pancreatic necrosis virus (IPNV), salmonid alphavirus (subtype 3, SAV3) and infectious salmon anemia virus (ISAV)-and explored the infection mechanisms of the three different viruses in these cells at different virus to cell ratios. Cytopathic effect (CPE), virus replication in the RTgutGC cells, antiviral cell responses and viral effects on the barrier permeability of polarized cells were investigated. We found that all virus species infected and replicated in RTgutGC cells, although with different replication kinetics and ability to induce CPE and host responses. The onset and progression of CPE was more rapid at high multiplicity of infection (MOI) for IPNV and SAV3 while the opposite was true of ISAV. A positive correlation between the MOI used and the induction of antiviral responses was observed for IPNV while a negative correlation was detected for SAV3. Viral infections compromised barrier integrity at early time points prior to observations of CPE microscopically. Further, the replication of IPNV and ISAV had a more pronounced effect on barrier function than SAV3. The in vitro infection model established herein can thus provide a novel tool to generate knowledge about the infection pathways and mechanisms used to surpass the intestinal epithelium in salmonid fish, and to study how a virus can potentially compromise gut epithelial barrier functions.

Detrimental effects of individual versus combined exposure to tetrabromobisphenol A and polystyrene nanoplastics in fish cell lines

The potential interactions between the diverse pollutants that can be released into the environment and the resulting outcomes are a challenging issue that needs to be further examined. This in vitro study was aimed to assess potential toxic effects caused by combined exposure to tetrabromobisphenol A, a flame retardant widely used and frequently detected in aquatic matrices, and commercially available polystyrene nanoparticles as reference material to evaluate nanoplastics risks. Our results, using freshwater fish cell lines and a set of relevant cytotoxicity endpoints including cell viability, oxidative stress, and DNA damage, provide additional mechanistic insights that could help to fully characterize the toxicity profiles of tetrabromobisphenol A and polystyrene nanoparticles. Furthermore, we describe subtle changes in cell viability as well as the generation of oxidative DNA damage after coexposure to subcytotoxic concentrations of the tested pollutants.

Recent consequences of micro-nanaoplastics (MNPLs) in subcellular/molecular environmental pollution toxicity on human and animals

Microplastics and Nanoplastics (MNPLs) pollution has been recognized as the important environmental pollution caused by human activities in addition to global warming, ozone layer depletion and ocean acidification. Most of the current studies have focused on the toxic effects caused by plastics and have not actively investigated the mechanisms causing cell death, especially at the subcellular level. The main content of this paper focuses on two aspects, one is a review of the current status of MNPLs contamination and recent advances in toxicological studies, which highlights the possible concentration levels of MNPLs in the environment and the internal exposure of humans. It is also proposed to pay attention to the compound toxicity of MNPLs as carriers of other environmental pollutants and pathogenic factors. Secondly, subcellular toxicity is discussed and the modes of entry and intracellular distribution of smaller-size MNPLs are analyzed, with particular emphasis on the importance of organelle damage to elucidate the mechanism of toxicity. Importantly, MNPLs are a new type of environmental pollutant and researchers need to focus not only on their toxicity, but also work with governments to develop measures to reduce plastic emissions, optimize degradation and control plastic aggression against organisms, especially humans, from multiple perspectives.

In vitro toxicity assessment of polyethylene terephthalate and polyvinyl chloride microplastics using three cell lines from rainbow trout (Oncorhynchus mykiss)

The RTgill-W1 (gill), RTG-2 (gonad), and RTL-W1 (liver) cell lines derived from a freshwater fish rainbow trout (Oncorhynchus mykiss), were used to assess the toxicity of polyethylene terephthalate (PET) and two forms of polyvinyl chloride (PVC). Two size fractions (25-μm and 90-μm particles) were tested for all materials. The highest tested concentration was 1 mg/ml, corresponding to from 70 000 ± 9000 to 620 000 ± 57 000 particles/ml for 25-μm particles and from 2300 ± 100 to 11 000 ± 1000 particles/ml for 90-μm particles (depending on the material). Toxicity differences between commercial PVC dry blend powder and secondary microplastics created from a processed PVC were newly described. After a 24-h exposure, the cells were analyzed for changes in viability, 7-ethoxyresorufin-O-deethylase (EROD) activity, and reactive oxygen species (ROS) generation. In addition to the microplastic suspensions, leachates and particles remaining after leaching resuspended in fresh exposure medium were tested. The particles were subjected to leaching for 1, 8, and 15 days. The PVC dry blend (25 μm and 90 μm) and processed PVC (25 μm) increased ROS generation, to which leached chemicals appeared to be the major contributor. PVC dry blend caused substantially higher ROS induction than processed PVC, showing that the former is not suitable for toxicity testing, as it can produce different results from those of secondary PVC. The 90-μm PVC dry blend increased ROS generation only after prolonged leaching. PET did not induce any changes in ROS generation, and none of the tested polymers had any effect on viability or EROD activity. The importance of choosing realistic extraction procedures for microplastic toxicity experiments was emphasized. Conducting long-term experiments is crucial to detect possible environmentally relevant effects. In conclusion, the tested materials showed no acute toxicity to the cell lines.

Ecotoxic effects of microplastics and contaminated microplastics - Emerging evidence and perspective

The high prevalence and persistence of microplastics (MPs) in pristine habitats along with their accumulation across environmental compartments globally, has become a matter of grave concern. The resilience conferred to MPs using the material engineering approaches for outperforming other materials has become key to the challenge that they now represent. The characteristics that make MPs hazardous are their micro to nano scale dimensions, surface varied wettability and often hydrophobicity, leading to non-biodegradability. In addition, MPs exhibit a strong tendency to bind to other contaminants along with the ability to sustain extreme chemical conditions thus increasing their residence time in the environment. Adsorption of these co-contaminants leads to modification in toxicity varying from additive, synergistic, and sometimes antagonistic, having consequences on flora, fauna, and ultimately the end of the food chain, human health. The resulting environmental fate and associated risks of MPs, therefore greatly depend upon their complex interactions with the co-contaminants and the nature of the environment in which they reside. Net outcomes of such complex interactions vary with core characteristics of MPs, the properties of co-contaminants and the abiotic factors, and are required to be better understood to minimize the inherent risks. Toxicity assays addressing these concerns should be ecologically relevant, assessing the impacts at different levels of biological organization to develop an environmental perspective. This review analyzed and evaluated 171 studies to present research status on MP toxicity. This analysis supported the identification and development of research gaps and recommended priority areas of research, accounting for disproportionate risks faced by different countries. An ecological perspective is also developed on the environmental toxicity of contaminated MPs in the light of multi-variant stressors and directions are provided to conduct an ecologically relevant risk assessment. The presented analyses will also serve as a foundation for developing environmentally appropriate remediation methods and evaluation frameworks.

Interactions of microplastics with organic, inorganic and bio-pollutants and the ecotoxicological effects on terrestrial and aquatic organisms

As emerging contaminants, microplastics (MPs) have attracted global attention. They are a potential risk to organisms, ecosystems and human health. MPs are characterized by small particle sizes, weak photodegradability, and are good environmental carriers. They can physically adsorb or chemically react with organic, inorganic and bio-pollutants to generate complex binary pollutants or change the environmental behaviors of these pollutants. We systematically reviewed the following aspects of MPs: (i) Adsorption of heavy metals and organic pollutants by MPs and the key environmental factors affecting adsorption behaviors; (ii) Enrichment and release of antibiotic resistance genes (ARGs) on MPs and the effects of MPs on ARG migration in the environment; (iii) Formation of "plastisphere" and interactions between MPs and microorganisms; (iv) Ecotoxicological effects of MPs and their co-exposures with other pollutants. Finally, scientific knowledge gaps and future research areas on MPs are summarized, including standardization of study methodologies, ecological effects and human health risks of MPs and their combination with other pollutants.

Transcriptomic Points of Departure Calculated from Rainbow Trout Gill, Liver, and Gut Cell Lines Exposed to Methylmercury and Fluoxetine

Ethical and resource limitation concerns are pushing chemicals management to develop alternatives to animal testing strategies. The objective of our study was to determine whether transcriptomic point of departure (tPOD) values could be derived from studies that followed Organisation for Economic Co-operation and Development (OECD) Test No. 249 (rainbow trout gill cell line), as well as from studies on trout liver and gut cells. Gill, liver, and gut cell lines were exposed to methylmercury and fluoxetine. Concentrations causing 50% cytotoxicity (LC50) were derived, the whole transcriptome was sequenced, and gene tPOD and pathway benchmark dose (BMD) values were derived from transcriptomic dose-response analysis. Differences in LC50 and transcriptomic responses across the cell lines were noted. For methylmercury, the tPOD_mode values were 14.5, 20.5, and 17.8 ppb for the gill, liver, and gut cells, respectively. The most sensitive pathway (pathway BMDs in parentheses) was ferroptosis in the gill (3.1 ppb) and liver (3.5 ppb), and glutathione metabolism in the gut (6.6 ppb). For fluoxetine, the tPOD_mode values were 109.4, 108.4, and 97.4 ppb for the gill, liver, and gut cells, respectively. The most sensitive pathway was neurotrophin signaling in the gill (147 ppb) and dopaminergic signaling in the gut (86.3 ppb). For both chemicals, the gene tPOD and pathway BMD values were lower than cytotoxic concentrations in vitro, and within 10-fold below the in vivo LC50s. By bringing together transcriptomics and dose-response analysis with an OECD test method in three cell lines, the results help to establish an in vitro method yielding tPOD values that are hypothesized to be protective of in vivo concentrations associated with adverse outcomes, and also give insights into mechanisms of action. Environ Toxicol Chem 2022;41:1982-1992. © 2022 SETAC.

Genotoxicity of Particles From Grinded Plastic Items in Caco-2 and HepG2 Cells

Large plastic litters degrade in the environment to micro- and nanoplastics, which may then enter the food chain and lead to human exposure by ingestion. The present study explored ways to obtain nanoplastic particles from real-life food containers. The first set of experiments gave rise to polypropylene nanoplastic suspensions with a hydrodynamic particle size range between 100 and 600 nm, whereas the same grinding process of polyethylene terephthalate (PET) produced suspensions of particles with a primary size between 100 and 300 nm. The exposure did not cause cytotoxicity measured by the lactate dehydrogenase (LDH) and water soluble tetrazolium 1 (WST-1) assays in Caco-2 and HepG2 cells. Nanoplastics of transparent PET food containers produced a modest concentration-dependent increase in DNA strand breaks, measured by the alkaline comet assay [net induction of 0.28 lesions/10⁶ bp at the highest concentration (95% CI: 0.04; 0.51 lesions/10⁶ base pair)]. The exposure to nanoplastics from transparent polypropylene food containers was also positively associated with DNA strand breaks [i.e., net induction of 0.10 lesions/10⁶ base pair (95% CI: −0.04; 0.23 lesions/10⁶ base pair)] at the highest concentration. Nanoplastics from grinding of black colored PET food containers demonstrated no effect on HepG2 and Caco-2 cells in terms of cytotoxicity, reactive oxygen species production or changes in cell cycle distribution. The net induction of DNA strand breaks was 0.43 lesions/10⁶ bp (95% CI: 0.09; 0.78 lesions/10⁶ bp) at the highest concentration of nanoplastics from black PET food containers. Collectively, the results indicate that exposure to nanoplastics from real-life consumer products can cause genotoxicity in cell cultures.

Distribution, biological effects and biofilms of microplastics in freshwater systems - A review

The rapidly rising output and mass use of plastics have made plastics pollution a major environmental problem. Since plastics are persistent in the environment, understanding the migration transformation characteristics of plastics is critical. Given the ever-increasing concern about the environmental risks posed by microplastics, their prevalence, fate, abundance and impact have been intensively studied. Most of these investigations focused on the marine environment, but research on freshwater microplastics is less extensive. This article aims to briefly summarize the research progress of freshwater microplastics, identify existing gaps and draw novel conclusions, so as to provide useful information for the research of freshwater microplastics. Using the statistics and analysis of freshwater microplastics studies in 2016-2021, this review systematically discusses microplastics in globally freshwater systems. The biological effects of microplastics on freshwater organisms were discussed as well. Some potential ecological effects of microplastic biofilms were shown, such as climate change and material circulation. More importantly, we present some unique conclusions. For example, the detection of freshwater microplastics is mainly concentrated in natural freshwater systems, while few are concentrated in artificial freshwater systems. In addition, polystyrene is the main mode for testing the biological effects of freshwater microplastics, and polyethene and polypropylene which are the most common in freshwater environments, have not been taken seriously. We also pointed out that studies on advanced freshwater plants in the topic of biological effects of microplastics still need strengthen.

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.

Toxicological characterization of produced water from the Permian Basin

Produced water (PW) is a hypersaline waste stream generated from the shale oil and gas industry, consisting of numerous anthropogenic and geogenic compounds. Despite prior geochemical characterization, the comprehensive toxicity assessment is lacking for evaluating treatment technologies and the beneficial use of PW. In this study, a suite of in vitro toxicity assays using various aquatic organisms (luminescent bacterium Vibrio fischeri, fish gill cell line RTgill-W1, and microalgae Scenedesmus obliquus) were developed to investigate the toxicological characterizations of PW from the Permian Basin. The exposure to PW, PW inorganic fraction (PW-IF), and PW salt control (PW-SC) at 30-50% dilutions caused significant toxicological effects in all model species, revealing the high salinity was the foremost toxicological driver in PW. In addition, the toxicity level of PW was usually higher than that of PW-IF, suggesting that organic contaminants might also play a critical role in PW toxicity. When comparing the observed toxicity with associated chemical characterizations in different PW samples, strong correlations were found between them since higher concentrations of contaminants could generally result in higher toxicity towards exposed organisms. Furthermore, the toxicity results from the pretreated PW indicated that those in vitro toxicity assays had different sensitives to the chemical components present in PW. As expected, the combination of multiple pretreatments could lead to a more significant decrease in toxicity compared to the single pretreatment since the mixture of contaminants in PW might exhibit synergistic toxicity. Overall, the current work is expected to enhance our understanding of the potential toxicological impacts of PW to aquatic ecosystems and the relationships between the chemical profiles and observed toxicity in PW, which might be conducive to the establishment of monitoring, remediation, treatment, and reuse protocols for PW.

Microplastics altered contaminant behavior and toxicity in natural waters

Microplastics (MPs) have received an increasing attention because of their ubiquitous presence and aquatic toxicity associated with MPs and MP-bound contaminants in the natural water. This review is to critically examine the chemical additives leached from MPs, the altered contaminant behaviors and the resulting changes in their aquatic ecotoxicity. Available data suggest that heavy metals Zn, Cr, Pb, and Cd regulated and present in plastics at the sub-mg g^-1 to mg g^-1 level can leach a significant amount depending on MPs size, aging, pH, and salinity conditions. MP-bound organic contaminants are primarily additive-derived (e.g., brominated diphenyl ethers, nonylphenol, and bisphenol A) at the µg g^-1 to mg g^-1 level, and secondarily pyrogenic and legacy origins (e.g., PAHs and PCBs) in the range of ng g^-1 and mg g^-1. MPs tend to have higher but more variable sorption capacities for organic compounds than metals (1.77 ± 2.34 vs. 0.82 ± 0.94 mg g^-1). MPs alter the behavior of heavy metals through the electrostatic interactions and surface complexation, while the transport of additive derived organic compounds are altered primarily through hydrophobic effect as supported by a positive correlation (R² = 0.71) between the logarithmic MPs-adsorbed concentrations and octanol/water partition coefficients (K_OW) of organic compounds. MPs constitute less than 0.01% of the total mass of aquatic particulates in typical waters, but play a discernible role in the local partitioning and long-distance movement of contaminants. MPs alone exert higher toxicity to invertebrates than algae; however, when MPs co-occur with pollutants, both synergistic and antagonistic toxicities are observed depending mainly on the ingestibility of MPs, the extent of sorption, MPs as a transport vector or a sink to scavenge pollutants. We finally suggest several key areas of future research directions and needed data concerning the role of MPs in mitigating pollutant leaching, transport and risk under conditions mimicking natural and polluted waters.

Micro/nanoplastics effects on organisms: A review focusing on 'dose'

Microplastics have become predominant contaminants, attracting much political and scientific attention. Despite the massively-increasing research on microplastics effects on organisms, the debate of whether environmental concentrations pose hazard and risk continues. This study critically reviews published literatures of microplastics effects on organisms within the context of "dose". It provides substantial evidence of the common occurrence of threshold and hormesis dose responses of numerous aquatic and terrestrial organisms to microplastics. This finding along with accumulated evidence indicating the capacity of organisms for recovery suggests that the linear-no-threshold model is biologically irrelevant and should not serve as a default model for assessing the microplastics risks. The published literature does not provide sufficient evidence supporting the general conclusion that environmental doses of microplastics cause adverse effects on individual organisms. Instead, doses that are smaller than the dose of toxicological threshold and more likely to occur in the environment may even induce positive effects, although the ecological implications of these responses remain unknown. This study also shows that low doses of microplastics can reduce whereas high doses can increase the negative effects of other pollutants. The mechanisms explaining these findings are discussed, providing a novel perspective for evaluating the risks of microplastics in the environment.

Key mechanisms of micro- and nanoplastic (MNP) toxicity across taxonomic groups

Micro- and nanoplastics (MNPs) are ubiquitous in aquatic and terrestrial environments, and detrimental biological effects have been observed on a variety of organisms, from bacteria and alga to plants and animals. A fast-growing number of toxicological studies report diverse responses and wide species-dependent sensitivity upon MNP exposure. While studies are dominated by in vivo animal tests, our understanding of cellular toxicity and the corresponding toxicity mechanisms is still limited. This challenges the proper assessment of environmental hazards and health risks of MNPs. In this review, we gathered and analyzed the up-to-date studies on humans, animals, plants, alga, and bacteria, and identified the similarities and differences in key toxicity mechanisms of MNPs across different taxonomic groups. Particularly, human cell-based studies at the cellular level provide fundamental and valuable information on the key toxicity mechanisms, which are essential to answer the question of whether and how MNPs pose health threats. In general, toxicity mechanisms of MNPs depend on their size, surface characteristics, polymer type, as well as cell type. Plausible toxicity mechanisms mainly include membrane disruption, extracellular polymeric substance disruption, reactive oxygen species generation, DNA damage, cell pore blockage, lysosome destabilization, and mitochondrial depolarization. A deeper understanding of these key mechanisms in different taxonomic groups can also improve both in vivo and in vitro models useful for predictive impact assessments of plastic pollution on the environment and human health.

Microplastic pollution in Southern Atlantic marine waters: Review of current trends, sources, and perspectives

Microplastics (MPs) are emerging and ubiquitous contaminants which have been gaining prominence since the last decade to nowadays. This is due to their possible adverse effects in aquatic ecosystems as well as the huge amount of plastic waste exponentially generated around the globe. Plastics may be introduced either directly to water bodies or indirectly to the aquatic systems by being carried by the wind, from emissions of contaminated effluents, and soil leaching, among other processes. In turn, these debris may interact with organic and inorganic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs) and trace constituents, and with microorganisms. Although the abundance of microplastics from South Atlantic waters is among the highest found worldwide, the number of studies in these marine waters regarding MP contamination is still scarce. Additionally, there still are no consensus on the best sampling conditions, which may be underestimating MPs. In this way, adequate MPs studies regarding their distribution, exposure levels, chemical and biological interactions are highly suggested in order to better understand both environmental and human health potential risks. This review assessed advances in sampling, analytical methodologies, characterization and understanding of MP sources in these marine waters in comparison to data from other regions around the globe.

Inflammatory responses associated with hyposaline stress in gill epithelial cells of the spotted scat Scatophagus argus

The molecular processes of immune responses in mucosal tissues such as fish gills under environmental stress are poorly understood. In the present study, pro-inflammatory response under hyposaline stress and its regulation by cortisol/corticosteroid receptors (CRs) in gill epithelial cells of the spotted scat Scatophagus argus were analyzed. The fish were transferred to freshwater for 6 days (144 h) of acclimation. Following freshwater exposure, the cortisol concentration increased transiently before returning to the control level over time. mRNA expression of pro-inflammatory cytokines (TNF-a, IL-1b and IL-6) was stimulated by cortisol through CR signals at early stages of acclimation, but hyposaline stress inhibited their levels by the end of the experimental period. The transcriptional profile of anti-inflammatory cytokine IL-10 was quite different from these pro-inflammatory cytokines, and its value fluctuated within a narrow range during the experimental period. Full-length cDNAs of mineralocorticoid receptor (MR) and glucocorticoid receptor 1 (GR1) (different kinds of CRs) were cloned from the gills. Our results showed that MR and GR displayed mutually antagonistic effects during hyposaline stress. MR responded quickly at early stages, and its expression decreased with the drop of cortisol concentration. By contrast, GR expression was maintained at high levels after the acclimation of freshwater exposure. The tight coordination of GR and MR helps to shape the effects of stress on the immune system, which in turn, regulates the stress response. Our results confirm the interaction between endocrine and cytokine messengers and a clear difference in the sensitivity of GR and MR during the hyposaline challenge in gill epithelial cells of the spotted scat Scatophagus argus.

Functionalized Nanoplastics (NPs) Increase the Toxicity of Metals in Fish Cell Lines

Nanoplastics (NPs) are one of the most abundant environment-threatening nanomaterials on the market. The objective of this study was to determine in vitro if functionalized NPs are cytotoxic by themselves or increase the toxicity of metals. For that, we used 50 nm polystyrene nanoparticles with distinct surface functionalization (pristine, PS-Plain; carboxylic, PS-COOH; and amino PS-NH₂) alone or combined with the metals arsenic (As) and methylmercury (MeHg), which possess an environmental risk to marine life. As test model, we chose a brain-derived cell line (SaB-1) from gilthead seabream (Sparus aurata), one of the most commercial fish species in the Mediterranean. First, only the PS-NH₂ NPs were toxic to SaB-1 cells. NPs seem to be internalized into the cells but they showed little alteration in the transcription of genes related to oxidative stress (nrf2, cat, gr, gsta), cellular protection against metals (mta) or apoptosis (bcl2, bax). However, NPs, mainly PS-COOH and PS-NH₂, significantly increased the toxicity of both metals. Since the coexistence of NPs and other pollutants in the aquatic environment is inevitable, our results reveal that the combined effect of NPs with the rest of pollutants deserves more attention.

Micro and Nano Plastics Distribution in Fish as Model Organisms: Histopathology, Blood Response and Bioaccumulation in Different Organs

Micro- and nano-plastic (MP/NP) pollution represents a threat not only to marine organisms and ecosystems, but also a danger for humans. The effects of these small particles resulting from the fragmentation of waste of various types have been well documented in mammals, although the consequences of acute and chronic exposure are not fully known yet. In this review, we summarize the recent results related to effects of MPs/NPs in different species of fish, both saltwater and freshwater, including zebrafish, used as model organisms for the evaluation of human health risk posed by MNPs. The expectation is that discoveries made in the model will provide insight regarding the risks of plastic particle toxicity to human health, with a focus on the effect of long-term exposure at different levels of biological complexity in various tissues and organs, including the brain. The current scientific evidence shows that plastic particle toxicity depends not only on factors such as particle size, concentration, exposure time, shape, and polymer type, but also on co-factors, which make the issue extremely complex. We describe and discuss the possible entry pathways of these particles into the fish body, as well as their uptake mechanisms and bioaccumulation in different organs and the role of blood response (hematochemical and hematological parameters) as biomarkers of micro- and nano-plastic water pollution.

Is cell culture a suitable tool for the evaluation of micro- and nanoplastics ecotoxicity?

Plastic particles have been described in aquatic ecosystems worldwide. An increasing number of studies have tried to evaluate the toxic impacts of microplastics (1-5000 µm) but also nanoplastics (<1 µm) in marine and freshwater organisms. However, the wide variety of plastic particles characteristics such as various sizes, shapes, functionalization or types of polymer, makes it difficult to evaluate their impact with regular ecotoxicity testing. In this context, cell culture, mainly used in human toxicology, could be a promising tool to evaluate micro- and nanoplastics toxicity with a wide diversity of conditions allowing to generate a large set of data. This review presents the current research on micro and nanoplastics using cell culture of marine and freshwater organisms, describes the limitations of cell culture tool and defines whether this tool can be considered as a relevant alternative strategy for ecotoxic evaluation of micro and nanoplastics especially for future regulatory needs. Articles using specifically cell culture tool from aquatic organisms such as fish or bivalves were identified. The majority evaluated the toxicity of polystyrene nanobeads on immune parameters, oxidative stress or DNA damage in fish cells. Although most of the papers characterized nanoplastic particles into the cell culture media, the relevance of testing conditions is not always clear. The development of cell culture can offer many opportunities for the evaluation of plastic particles' cellular impacts, but more research is needed to develop relevant culture models, on various aquatic organisms, and with consideration of abiotic parameters especially composition of cell culture media for nanoplastic evaluation.

Mucin corona delays intracellular trafficking and alleviates cytotoxicity of nanoplastic-benzopyrene combined contaminant

Nanoplastics have recently become a worldwide concern as newly emerging airborne pollutants, which can associate with polycyclic aromatic hydrocarbons (PAHs) and form combined contaminant nanoparticles (CCNPs). After being inhaled in the respiratory system, the CCNPs would first encounter the mucous gel layer being rich in mucin. Herein, polystyrene-benzopyrene (PS@Bap) NPs were prepared as CCNPs model and their interaction with mucin and the resultant biological responses were studied. It was observed that mucin corona stably attached to the CCNPs surface, which significantly altered the fate of the CCNPs in lung epithelial cells (A 549 cell line). The mucin corona would 1) stably adsorbed on PS@Bap at the early stages of endocytosis until degraded during the lysosomal transport and maturation process, 2) delay intracellular trafficking of PS@Bap and the progress of Bap detached from PS, 3) enhance uptake of PS@Bap but reduce the cytotoxicity elicited by PS@Bap, as indicated by cell viability, generation of reactive oxygen species, impairment on mitochondrial function, and further cell apoptosis. In addition, in vivo study also verified the enhanced effect of PS on the development of an acute lung inflammatory response induced by Bap. This study highlights the significance of incorporating the effects of mucin for precisely assessing the respiratory system toxicity of nanoplastics based CCNPs in atmospheric environments.

Enhanced toxicity of triphenyl phosphate to zebrafish in the presence of micro- and nano-plastics

Co-occurrence of microplastics and chemicals was a complex environmental issue, whereas little concerned on the effect of microplastics on the toxicity of chemicals. In this study, we studied the changes of toxicity of triphenyl phosphate (TPhP) to zebrafish, in the presence of micro-polystyrene (MPS, 5.8 μm) and nano-polystyrene (NPS, 46 nm). Results indicated that separate MPS and NPS had no acute toxicity and little reproductive toxicity on zebrafish. TPhP alone was a highly toxic substance with a median lethal concentration (LC₅₀) of 976 μg/L, the presence of MPS and NPS did not have significant effect on the acute toxicity of TPhP. TPhP alone stimulated the enlargement of liver and gonad of fish (except the testis) by 1.25-2.12 fold, and the presence of NPS further aggravated this stimulation by 1.23-2.84 fold, while MPS did not. The gonadal histology indicated that comparing with TPhP alone, the addition of MPS and NPS further inhibited the process of spermatogenesis and oogenesis, even causing obvious lacunas in testis and atretic follicles oocytes in ovary. Meanwhile, TPhP did not significantly disturb the hormone homeostasis (E₂/T) and vitellogenin (Vtg) content in fish, but the presence of NPS increased the E₂/T ratio and Vtg content in male fish, while slightly decreased those in female fish, which implying that effects of PS was sex-dependent. As a result, the egg production, the fertilization rate and hatchability of eggs significantly reduced after combined TPhP+PS exposure, demonstrating that co-occurrence of TPhP and PS, especially NPS, could greatly impaired the reproductive performance of zebrafish.

Toxicity of polystyrene nanoplastics in Ctenopharyngodon idella juveniles: A genotoxic, mutagenic and cytotoxic perspective

The increased contamination of surface water with plastic waste is proportional to the increased consumption of products that use them as raw material. However, the impact of these residues on aquatic biota remains limited, mainly when it comes to nanoplastics (NPs). Thus, the aim of the current study is to test the hypothesis that the exposure of Ctenopharyngodon idella juveniles to polystyrene nanoplastics (PS NPs) at low concentrations (0.04 ng/L, 34 ng/L and 34 μg/L), for 20 days, leads to DNA damage and has mutagenic and cytotoxic effects on their erythrocytes. Comet assay enabled observing that DNA damage (inferred from the greater tail length, DNA percentage in the tail and Olive tail moment) induced by PS NPs has increased as the pollutant concentrations have increased, as well as that the formation of micronuclei and other nuclear abnormalities was equitable in animals exposed to this pollutant. On the other hand, there were significant changes in erythrocyte shape and size, oxidative stress generation (NO levels, lipid peroxidation, hydrogen peroxide), antioxidant system inhibition (mediated by total hepatic glutathione) and PS NPs accumulation in the liver and brain of animals exposed to higher concentrations of it. Therefore, the current study has confirmed the initial hypothesis and enhanced the knowledge about the genotoxic, mutagenic and cytotoxic potential of PS NPs in freshwater fish at early developmental stage, relating these effects to biochemical changes and significant accumulation of these nanomaterials. Besides, it is a warning about the (eco) toxicological risk represented by these nanopollutants in aquatic environments. CAPSULE: Polystyrene nanoplastics are capable of inducing DNA damage, mutagenic and cytotoxicity changes in fish.

Antioxidants and molecular damage in Nile Tilapia (Oreochromis niloticus) after exposure to microplastics

Recently, research on the biological effects of microplastics (MPs) has grown exponentially. However, effects of MPs on freshwater fishes and the mechanisms of the biological effects of MPs were limited. So, the purpose of the current study was to clarify the effects of microplastics on oxidative stress response, DNA fragmentation, and proteinogram of the early juvenile stage of Nile Tilapia (Oreochromis niloticus). The fishes were assigned into four groups: one control, three MPs-exposed groups as 1 mg/L of MPs, 10 mg/L of MPs, and 100 mg/L of MPs respectively for 15 days and 15 days of recovery. The activities of superoxide dismutase, catalase, total peroxides, and oxidative stress index (OSI), as well as lipid peroxidation and DNA fragmentation, increased in groups exposed to MPs compared to the control group in a dose-dependent manner. In contrast, the activity of total antioxidant capacity decreased in groups exposed to MPs compared to the control group in a dose-dependent manner. The electrophoretic pattern of muscle proteins revealed alteration in the proteinogram in the MPs-exposed groups compared to control. After the recovery period, the activities of superoxide dismutase, catalase, total peroxides, total antioxidant capacity, lipid peroxidation, DNA fragmentation, and the electrophoretic pattern of muscle proteins returned to normal levels in 1 mg/L of MPs-exposed group. Combined with our previous work, these results suggest that MPs cause the overproduction of reactive oxygen species (ROS) and alters the antioxidants parameters, resulting in oxidative stress and DNA damage. The present study fosters a better understanding of the toxic effects of MPs on Tilapia as a freshwater model. Graphical Abstract.

Effects of polystyrene microbeads on cytotoxicity and transcriptomic profiles in human Caco-2 cells

Microplastics (MPs) pollution is a global paradigm that raises concern in relation to environment and human health. In order to investigate the molecular toxicity mechanisms of MPs, transcriptomic analyses were performed on in vitro Caco-2 cell model. After observing that polystyrene microplastics (PS-MPs) decreased cell viability in a dose-dependent manner, the responsible genes and involved pathways that might make contribution to PS-MBs-induced toxicity to Caco-2 cells were identified with Illumina RNA seq. A total of 442 genes including, 210 up-regulated ones and 232 down-regulated ones, showed differential expression after treatment by PS-MPs with a concentration of 12.5 mg L^-1 or 50.0 mg L^-1 for 24 hours. Gene Ontology (GO) annotation enriched unigenes can be grouped into three separated clusters: cellular component (CC), biological process (BP), and molecular function (MF). The dominate pathways related to NF-κB, MAPK signaling, cytokine-cytokine receptor interaction, and toll-like receptor were strongly influenced by PS-MBs. These pathways are involved in modulating cell inflammatory and proliferation. The qPCR were applied to investigate the transcriptional level of five proliferation related genes (Ras, ERK, MER, CDK4, Cyclin D1) and four inflammation related genes (TRPV1, iNOS, IL-1β, IL-8), and the results were consistent with RNA-seq data. This study has provided new insight into the understanding of the toxicity effects of PS-MBs-induced intestinal inflammatory diseases.

A critical viewpoint on current issues, limitations, and future research needs on micro- and nanoplastic studies: From the detection to the toxicological assessment

Increasing scientific attention on the presence of micro- and nanoplastics (MNPs) in the environments and their potential toxic effects on humans and the ecosystems is evident. Accordingly, the number of publications on this topic has increased substantially from only 5 in 2010 to more than 850 in 2019. Thus, this critical review aimed at providing state-of-the-art information on the existing methods for characterization and detection of MNPs in various matrices, as well as the reported toxic effects of MNPs in both in vivo and in vitro systems, anticipating challenges and providing future needs to improve the current scientific knowledge. We performed a systematic search of recent literature on available methodologies for the characterization/detection of MNPs in different samples, and the summary of such protocols is provided. Also, the existing procedures for in vitro and in vivo toxicity evaluation of MNPs were critically described. The results of our search revealed that quite a great deal of effort had been made to detect, characterize, and quantify the fate and effect of MNPs. However, we are still far from a complete understanding of behaviors of MNPs in the environments and biological systems. Thus, there is a need to advance the existing protocols to improve data accuracy. Besides, more studies that focus on uptake kinetics, accumulation, and biodistribution of MNPs in biological systems are required.