Polystyrene microplastics reduce abundance of developing B cells in rainbow trout (Oncorhynchus mykiss) primary cultures

Incidence of microplastic translocation in freshwater fish eggs

The issue of microplastic contamination in seafood is progressively recognised as a significant global issue. This study presents novel findings regarding the detection of microplastics within the eggs of commercially available fish intended for consumption by humans. Eggs of Ompok bimaculatus, Heteropneustes fossilis, Mystus vittatus and Anabas testudineus collected from the Periyar River, Kerala, India were subjected to analysis for the potential presence of microplastics. Out of the 91 fishes (containing eggs) examined, microplastics were observed in the eggs of 2 species, i.e., Ompok bimaculatus and Mystus vittatus. The polymers recorded were polyethylene and polypropylene. Fish eggs are commonly consumed by humans and are highly esteemed as a delectable food. Considering the widespread consumption of fish eggs as a delicacy among humans, there exists a potential route for human exposure to microplastics, which raises concerns regarding public health.

Effect of polypropylene microplastics on virus resistance in spotted sea bass (Lateolabrax maculatus)

Microplastics (MPs) pollution is a hot issue of global concern. Polypropylene microplastics (PP-MPs) age quickly in the marine environment and break down into smaller particles because of their relatively low temperature resistance, poor ultraviolet resistance, and poor antioxidant capacity, making them one of the major pollutants in the ocean. We assessed whether long-term exposure to micron-sized PP-MPs influences fish susceptibility to viral diseases. We found that exposure to PP-MPs (1-6 μm and 10-30 μm) at concentrations of 500 and 5000 μg/L resulted in uptake into spleen and kidney tissues of Lateolabrax maculatus. Increased activation of melanomacrophage centers was visible in histopathological sections of spleen from fish exposed to PP-MPs, and greater deterioration was observed in the spleen of fish infected by largemouth bass ulcerative syndrome virus after PP-MPs exposure. Additionally, exposure to PP-MPs led to significant cytotoxicity and a negative impact on the antiviral ability of cells. PP-MPs exposure had inhibitory or toxic effects on the immune system in spotted sea bass, which accelerated virus replication in vivo and decreased the expression of the innate immune- and acquired immune related genes in spleen and kidney tissues, thus increasing fish susceptibility to viral diseases. These results indicate that the long-term presence of micron-sized PP-MPs might impact fish resistance to disease, thereby posing a far-reaching problem for marine organisms.

Polystyrene microplastics induce size-dependent multi-organ damage in mice: Insights into gut microbiota and fecal metabolites

Particle size is one of the most important factors in determining the biological toxicity of microplastics (MPs). In this study, we attempted to examine the systemic toxicity of polystyrene MPs of different sizes (0.5 µm MP1 and 5 µm MP2) in C57BL/6 J mice. After the mice were given oral gavage of MPs for 8 consecutive weeks, histopathology and molecular biology assays, 16 S rRNA sequencing of the gut microbiota, and untargeted metabolomics were performed. The results showed that MPs were distributed in the organs in a size-dependent manner, with smaller particles demonstrating greater biodistribution. Further analysis indicated that exposure to MPs caused multi-organ damage through distinct toxicity pathways. Specifically, exposure to 0.5 µm MP1 led to excessive accumulation and induced more serious inflammation and mechanical damage in the spleen, kidney, heart, lung, and liver. However, 5 µm MP2 led to more severe intestinal barrier dysfunction, as well as gut dysbiosis and metabolic disorder in association with neuroinflammation. These results are helpful in expanding our knowledge of the toxicity of MPs of different sizes in mammalian models.

Microplastic polyamide toxicity: Neurotoxicity, stress indicators and immune responses in crucian carp, Carassius carassius

This study aimed to determine the toxicity standard and potential risks and effects of polyamide (PA) exposure on neurotoxicity, stress indicators, and immune responses in juvenile crucian carp Carassius carassius. Numerous microplastics (MPs) exists within aquatic environments, leading to diverse detrimental impacts on aquatic organisms. The C. carassius (mean weight, 23.7 ± 1.6 g; mean length, 13.9 ± 1.4 cm) were exposed to PA concentrations of 0, 4, 8, 16, 32 and 64 mg/L for 2 weeks. Among the neurotransmitters, the acetylcholinesterase (AChE) activity in the liver, gill, and intestine of C. carassius was significantly inhibited by PA exposure. Stress indicators such as cortisol and heat shock protein 70 (HSP70) in the liver, gill, and intestine of C. carassius were significantly increased, while immune responses to lysozyme and immunoglobulin M (IgM) were significantly decreased. Our study demonstrates the toxic effects of MP exposure on crucian carp's neurotoxicity, stress indicators, and immune responses.

Microplastic ingestion by invasive Prussian carp (Carassius gibelio) used in fishmeal production in Türkiye

MP contamination in the gastrointestinal tract (GIT) of Prussian carp (Carassius gibelio) used in fishmeal production was examined. The samples were collected from Balık Lake, Karaboğaz Lake, and Liman Lake located in Kızılırmak Delta, Türkiye. The overall average abundance was 3.20±0.18 MP per fish and 0.036±0.002 MP per g. No significant correlation was determined between the MP abundance in the fish, fish length, and fish weight. The polymers were composed of 56.91% PET, 25.20% PP, 9.76% PE, and 8.13% PA. The determined shapes were fiber (78.0%), fragment (13.46%), and film (8.54%). The size ranged between 112 and 4775 μm with an average of 1341.41±66.07 μm. Depending on the occurrence frequency and abundance, it can be concluded that Carassius gibelio can be considered a MP vector in fishmeal. The results provide an essential baseline for future MP studies on the potential effects of MPs on aquatic organisms, fate, and impact on the fishmeal production process, aquaculture practices, and human health.

Hematological Consequences of Polyethylene Microplastics Toxicity in Male Rats: Oxidative stress, Genetic, and Epigenetic links

Microplastics (MPs) pollution is a newly emerging environmental issue. MPs can accumulate within animals and humans, which can pose a serious health threat. Petroleum-based polyethylene (PE) is one of the most popular plastics. Accordingly, its exposure rates have steadily increased over the years. This study aimed to analyze the effects of PE-MPs on the hematological system of albino rats and the epigenetic effect. Five groups of adult male eight-weeks-old rats received either distilled water, corn oil, 3.75mg/kg PE-MPs, 15mg/kg PE-MPs, or 60mg/kg of PE-MPs, daily by oral gavage for 35 days. PE-MPs significantly increased the body weights of the rats and lipid peroxidation, with concomitant reduction of superoxide dismutase activity and depletion of reduced glutathione, thus adversely affecting oxidants/antioxidants balance. Moreover, PE-MPs increased the % of abnormal RBCs, irregular cells, tear drop cells, Schistocyte cells, and folded cells. The genotoxic effects on DNA were evident by increased DNA damage, confirmed by the comet assay, in addition to increased DNA methylation. The effects of PE-MPs have been shown to be dose correlated. In conclusion, this study provides evidence of dose-related PE-MPs-induced hematological, genotoxic, and epigenetic effects in mammals, and thus emphasizes the potentially hazardous health effects of environmental PE-MPs.

Unveiling the noxious effect of polystyrene microplastics in aquatic ecosystems and their toxicological behavior on fishes and microalgae

Microplastic (MP) particles are considered noxious pollutants due to their presence in aquatic habitats at almost every level of the food chain. Thus, the entry of MP particles into marine waterbodies has triggered a common research interest. Until recently, the toxicity of polystyrene towards aquatic creatures in comparison to other polymers has not been widely investigated. This article provides an extensive overview of the occurrence of microplastic particles, the route of polystyrene (PS) in the aquatic ecosystem, the PS properties characterization, and its noxious effects on the aquatic biota, particularly fishes and microalgae. Alarming high levels of polystyrene were found in urban, coastal, and rural surface waters and sediments. The fast-screening technique began with a stereoscope to determine the polystyrene particles' shape, size, and color on the organism. SEM and complemented by micro FTIR or Raman spectroscopy were used to evaluate MP's polymer structures. The findings present evidence suggesting that polystyrene buildup in fish can have long-term and unknown consequences. Meanwhile, the presence of polystyrene on microalgae causes a decrease in chlorophyll concentration and photosynthetic activity, which may disrupt photosynthesis by interfering with the electron characters and leading to the production of reactive oxygen species (ROS).

Transport of microplastics in the body and interaction with biological barriers, and controlling of microplastics pollution

Microplastics (MPs) are one novel environmental pollutant sized < 5 mm that is ubiquitously present in numerous environmental media and particularly susceptible to interact with various toxic chemicals. Importantly, MPs can enter the food chain, and are bio-enriched and bio-accumulated with trophic levels, eventually endangering ecosystems and human health. However, there need to be more understanding regarding the bio-interaction of MPs with the host, particularly for biological barriers. This review aimed to summarize the latest findings regarding the main exposure routes of MPs that generated health burdens on humans. Furthermore, their interactions with biological barriers that generate adverse health effects and the underlying mechanisms were also reviewed. Additionally, we provided a comprehensive overview of recent advances regarding the removing and controlling of MPs. Finally, we discussed the future directions for MPs hazard prevention to provide helpful information for regulating decision-making and guiding safer plastics applications.

Microplastics exacerbate virus-mediated mortality in fish

Microplastics are a persistent and increasing environmental hazard. They have been reported to interact with a variety of biotic and abiotic environmental stressors, but the ramifications of such interactions are largely unknown. We investigated virus-induced mortalities in a commercially important salmonid following exposure to microplastics, plastic microfibers, and natural (non-plastic) microparticles. Microplastics or microparticles alone were not lethal. Mortality increased significantly when fish were co-exposed to virus and microplastics, particularly microfibers, compared to virus alone. This presents the unique finding that microplastics (not natural microparticulate matter) may have a significant impact on population health when presented with another stressor. Further, we found that mortality correlated with host viral load, mild gill inflammation, immune responses, and transmission potential. We hypothesize that microplastics can compromise host tissues, allowing pathogens to bypass defenses. Further research regarding this mechanism and the interplay between microplastics and infectious disease are paramount, considering microplastics increasing environmental burden.

Microplastic and oil pollutant agglomerates synergistically intensify toxicity in the marine fish, Asian seabass, Lates calcalifer

Asian seabass, Lates calcarifer frys were exposed to polystyrene (MP: 0.5 mg/l), oil (0.83 ml/l) and agglomerates (MP + oil + Corexit) as eight treatments in three replicates, and fresh synthetic marine water (control) for 15 days. The synergistic effect was confirmed (P ˂ 0.05) by bio-indicators including RBC count, total plasma protein, aspartate aminotransferase (AST), catalase (CAT), glutathione S-transferase (GST), basophils, thrombocyte and eosinophils percentages. Most of the significant and synergistic effects were observed in the highest doses (5 mg/l MP and 5 mg/l MP-oil-dispersant). Exposure to MP and a combination of MP+ oil caused tissue lesions in gill, liver and intestine. Our results suggest there are no critical health issues for Asian seabass in natural environments. However, the bioaccumulation of MPs, oil, and their agglomerates in consumers' bodies may remain a concern.

Parasite infection but not chronic microplastic exposure reduces the feeding rate in a freshwater fish

Microplastics (plastics <5 mm) are an environmental contaminant that can negatively impact the behaviour and physiology of aquatic biota. Although parasite infection can also alter the behaviour and physiology of their hosts, few studies have investigated how microplastic and parasite exposure interact to affect hosts. Accordingly, an interaction experiment tested how exposure to environmentally relevant microplastic concentrations and the trophically transmitted parasite Pomphorhynchus tereticollis affected the parasite load, condition metrics and feeding rate of the freshwater fish final host chub Squalius cephalus. Microplastic exposure was predicted to increase infection susceptibility, resulting in increased parasite loads, whereas parasite and microplastic exposure were expected to synergistically and negatively impact condition indices and feeding rates. Following chronic (≈170 day) dietary microplastic exposure, fish were exposed to a given number of gammarids (4/8/12/16/20), with half of the fish presented with parasite infected individuals, before a comparative functional response experiment tested differences in feeding rates on different live prey densities. Contrary to predictions, dietary microplastic exposure did not affect parasite abundance at different levels of parasite exposure, specific growth rate was the only condition index that was lower for exposed but unexposed fish, with no single or interactive effects of microplastic exposure detected. However, parasite infected fish had significantly lower feeding rates than unexposed fish in the functional response experiment, with exposed but unexposed fish also showing an intermediate decrease in feeding rates. Thus, the effects of parasitism on individuals were considerably stronger than microplastic exposure, with no evidence of interactive effects. Impacts of environmentally relevant microplastic levels might thus be relatively minor versus other stressors, with their interactive effects difficult to predict based on their single effects.

Microplastics toxicity, detection, and removal from water/wastewater

The world has witnessed massive and preeminent microplastics (MPs) pollution in water bodies due to the inevitable continuous production of plastics for various advantageous chemical and mechanical features. Plastic pollution, particularly contamination by MPs (plastic particles having a diameter lesser than 5 mm), has been a rising environmental concern in recent years due to the inappropriate disposal of plastic trash. This study presents the recent advancements in different technologies for MPs removal in order to gain proper insight into their strengths and weaknesses, thereby orchestrating the preparation for innovation in the field. The production, origin, and global complexity of MPs were discussed. This study also reveals MPs' mode of transportation, its feedstock polymers, toxicities, detection techniques, and the conventional removal strategies of MPs from contaminated systems. Modification of conventional methods vis-à-vis new materials/techniques and other emerging technologies, such as magnetic extraction and sol-gel technique with detailed mechanistic information for the removal of MPs are presented in this study. Conclusively, some future research outlooks for advancing the MPs removal technologies/materials for practical realization are highlighted.

Polystyrene microparticles can affect the health status of freshwater fish - Threat of oral microplastics intake

Plastic waste pollution is considered one of the biggest problems facing our planet. The production and use of these materials has led to huge amounts of plastic waste entering the aquatic environment and affecting aquatic life. In our experiment, the effect of polystyrene microparticles (PS-MPs; 52.5 ± 11.5 μm) on individual juvenile rainbow trout (Oncorhynchus mykiss) was tested at three different dietary concentrations of 0.5, 2 and 5 % for six weeks. At the end of the experiment, various health parameters of exposed organisms were compared with the control group. The haematological profile revealed an immune response by a decrease in lymphocyte count with a concurrent increase in the number of neutrophil segments at the highest concentration of PS-MPs (5 %). Biochemical analysis showed significant reductions in plasma ammonia in all tested groups, which may be related to liver and gill damage, as determined by histopathological examination and analysis of inflammatory cytokines expression. In addition, liver damage can also cause a significant decrease in the plasma protein ceruloplasmin, which is synthesized in the liver. PS-MPs disrupted the antioxidant balance in the caudal kidney, gill and liver, with significant changes observed only at the highest concentration. In summary, PS-MPs negatively affect the health status of freshwater fish and represent a huge burden on aquatic ecosystems.

circRNA432 enhances the coelomocyte phagocytosis via regulating the miR-2008-ELMO1 axis in Vibrio splendidus-challenged Apostichopus japonicus

Circular RNAs (circRNAs) are a kind of extensive and diverse covalently closed circular endogenous RNA, which exert crucial functions in immune regulation in mammals. However, the functions and mechanisms of circRNAs in invertebrates are largely unclarified. In our previous work, 261 differentially expressed circRNAs including circRNA432 (circ432) were identified from skin ulcer syndrome (SUS) diseased sea cucumber Apostichopus japonicus by RNA-seq. To better address the functional role of sea cucumber circRNAs, circ432 was first found to be significantly induced by Vibrio splendidus challenge and LPS exposure in this study. Knock-down circ432 could depress the V. splendidus-induced coelomocytes phagocytosis. Moreover, circ432 is validated to serve as the sponge of miR-2008, a differential expressed miRNA in SUS-diseased sea cucumbers, by Argonaute 2-RNA immunoprecipitation (AGO2-RIP) assay, luciferase reporter assay and RNA fluorescence in situ hybridization (FISH) in vitro. Engulfment and cell motility protein 1 (AjELMO1) is further demonstrated to be the target of miR-2008, and silencing AjELMO1 inhibits the V. splendidus-induced coelomocytes phagocytosis, and this phenomenon could be further suppressed by supplementing with miR-2008 mimics, suggesting that circ432 might regulate coelomocytes phagocytosis via miR-2008-AjELMO1 axis. We further confirm that the depressed coelomocytes' phagocytosis by circ432 silencing is consistent with the decreased abundance of AjELMO1, and could be recovered by miR-2008 inhibitors transfection. All our results provide the evidence that circ432 is involved in regulating pathogen-induced coelomocyte phagocytosis via sponge miR-2008 and promotes the abundance of AjELMO1. These findings will enrich the regulatory mechanism of phagocytosis in echinoderm and provide theoretical data for SUS disease prevention and control in sea cucumbers.

Acute polyethylene microplastic (PE-MPs) exposure activates the intestinal mucosal immune network pathway in adult zebrafish (Danio rerio)

Polyethylene is one of the most important plastic types with the highest consumption in the world. Plastics are prone to photodegradation and turn into microplastics, which are magnified as they move across trophic levels. Microplastics would be able to penetrate into lymph even cross cell membranes, causing harm to the lymphatic and/or circulatory systems, accumulating in secondary organs, and impacting the immune system and cell health. The objective of this study was to test that the activation of the intestinal immune network might be caused by disruption of intestinal microbiota after exposure to different polyethylene microplastics (PE-MPs) concentrations (1, 10, 100, and 1000 μg/mL) in adult zebrafish (Danio rerio) for 7 days. The concentrations of PE-MPs (100 and 1000 μg/mL) exposure decreased the goblet cell coverage. The intestinal microbial diversity index (Shannon and Simpson) was increased at 100 and 1000 μg/mL PE-MPs concentrations. The relative abundance of intestinal dominant microbiota phylum Proteobacteria and Actinobacteria increased significantly (P < 0.05); however, phylum Fusobacteria decreased significantly (P < 0.05). The relative abundance of intestinal microbiota at level of genera showed varying degrees of elevation such as Acinetobacter (6.31-fold), Plesiomonas (4.80-fold), Flavobacterium (10.54-fold) and Pseudomonas (5.17-fold) in 1000 μg/mL PE-MPs. Intestinal innate immunity-complement C3 and C4 content first increased and then declined in a dose-dependent manner. Expression of genes from the intestinal immune network for mucosal immunoglobulin production were increased also in a dose-dependent manner. The expression of immune-related genes (pigr, il10 and ighv4-5) were positively correlated with the relative abundance of genera Plesiomonas. In conclusion, PE-MPs increase the infection probability in the intestinal mucosa by altering the abundance of intestinal dominant microbiota at the level of phylum. PE-MPs exposure activated the intestinal immune network pathway for mucosal immunoglobulin production at a concentration of 100 or 1000 μg/mL for 7 days.

First evidence of in vitro cytotoxic effects of marine microlitter on Merluccius merluccius and Mullus barbatus, two Mediterranean commercial fish species

Marine litter is composed mainly of plastics and is recognized as a serious threat to marine ecosystems. Ecotoxicological approaches have started elucidating the potential severity of microplastics (MPs) in controlled laboratory studies with pristine materials but no information exists on marine environmental microlitter as a whole. Here, we characterized the litter in the coastal Northern Tyrrhenian sea and in the stomach of two fish species of socio-economic importance, and exposed primary cell cultures of mucosal and lymphoid organs to marine microlitter for evaluating possible cytotoxic effects. An average of 0.30 ± 0.02 microlitter items m^-3 was found in water samples. μFT-IR analysis revealed that plastic particles, namely HDPE, polyamide and polypropylene were present in 100% and 83.3% of Merluccius merluccius and Mullus barbatus analyzed, which overall ingested 14.67 ± 4.10 and 5.50 ± 1.97 items/individual, respectively. Moreover, microlitter was confirmed as a vector of microorganisms. Lastly, the apical end-point of viability was found to be significantly reduced in splenic cells exposed in vitro to two microlitter conditions. Considering the role of the spleen in the mounting of adaptive immune responses, our results warrant more in-depth investigations for clarifying the actual susceptibility of these two species to anthropogenic microlitter.

Assessing Fish Immunotoxicity by Means of In Vitro Assays: Are We There Yet?

There is growing awareness that a range of environmental chemicals target the immune system of fish and may compromise the resistance towards infectious pathogens. Existing concepts to assess chemical hazards to fish, however, do not consider immunotoxicity. Over recent years, the application of in vitro assays for ecotoxicological hazard assessment has gained momentum, what leads to the question whether in vitro assays using piscine immune cells might be suitable to evaluate immunotoxic potentials of environmental chemicals to fish. In vitro systems using primary immune cells or immune cells lines have been established from a wide array of fish species and basically from all immune tissues, and in principal these assays should be able to detect chemical impacts on diverse immune functions. In fact, in vitro assays were found to be a valuable tool in investigating the mechanisms and modes of action through which environmental agents interfere with immune cell functions. However, at the current state of knowledge the usefulness of these assays for immunotoxicity screening in the context of chemical hazard assessment appears questionable. This is mainly due to a lack of assay standardization, and an insufficient knowledge of assay performance with respect to false positive or false negative signals for the different toxicant groups and different immune functions. Also the predictivity of the in vitro immunotoxicity assays for the in vivo immunotoxic response of fishes is uncertain. In conclusion, the currently available database is too limited to support the routine application of piscine in vitro assays as screening tool for assessing immunotoxic potentials of environmental chemicals to fish.

Prolonged oral ingestion of microplastics induced inflammation in the liver tissues of C57BL/6J mice through polarization of macrophages and increased infiltration of natural killer cells

Microplastics (< 5 mm diameter) are one of most important environmental pollutants and contaminants worldwide. However, how microplastics affect liver immune microenvironment in not well understood. Microplastics (0.5 µm) were administered orally to C57BL/6J mice for 4 consecutive weeks at the rate of 0.5 mg/day. Non-parenchymal cells were isolated from of the mice through fractionation of fresh hepatic tissues. The immune landscape for four cell populations of B cells, T cells, NK cells and macrophages in the liver tissues was then evaluated using flow cytometry. The secretion level of inflammatory cytokines and associated signaling pathway were investigated using quantitative real-time polymerase chain reaction and western blot. Oral ingestion of microplastics increases liver weight, general liver index as well as expression of serum, liver function-related indicators. Microplastics also increased the infiltration of natural killer cells and macrophages to non-parenchymal liver cells, but reduced that of B cells to the same tissues. However, microplastics had no effect on the infiltration of T cell to non-parenchymal liver cells. Ingestion of MPs also up-regulated the expression of IFN-γ, TNF-α, IL-1β, IL-6 and IL-33 mRNA, but down-regulated that of IL-4, IL-5, IL-10, IL-18 and TGF-β1. Overall, the aforementioned processes were regulated via the NF-κB pathway in the hepatic non-parenchymal cells. Microplastics disrupts inflammatory process in liver tissues via the NF-κB signaling pathway. These findings provide a strong foundation on immune processes in hepatic tissues following prolonged ingestion of microplastics.