Transcriptome alterations in zebrafish gill after exposure to different sizes of microplastics

The effects of microplastics on ionoregulatory processes in the gills of freshwater fish and invertebrates: A prospective review

From review of the very few topical studies to date, we conclude that while effects are variable, microplastics can induce direct ionoregulatory disturbances in freshwater fish and invertebrates. However, the intensity depends on microplastic type, size, concentration, and exposure regime. More numerous are studies where indirect inferences about possible ionoregulatory effects can be drawn; these indicate increased mucus production, altered breathing, histopathological effects on gill structure, oxidative stress, and alterations in molecular pathways. All of these could have negative effects on ionoregulatory homeostasis. However, previous research has suffered from a lack of standardized reporting of microplastic characteristics and exposure conditions. Often overlooked is the fact that microplastics are dynamic contaminants, changing over time through degradation and fragmentation and subsequently exhibiting altered surface chemistry, notably an increased presence and diversity of functional groups. The same functional groups characterized on microplastics are also present in dissolved organic matter, often termed dissolved organic carbon (DOC), a class of substances for which we have a far greater understanding of their ionoregulatory actions. We highlight instances in which the effects of microplastic exposure resemble those of DOC exposure. We propose that in future microplastic investigations, in vivo techniques that have proven useful in understanding the ionoregulatory effects of DOC should be used including measurements of transepithelial potential, net and unidirectional radio-isotopic ion flux rates, and concentration kinetic analyses of uptake transport. More sophisticated in vitro approaches using cultured gill epithelia, Ussing chamber experiments on gill surrogate membranes, and scanning ion selective electrode techniques (SIET) may also prove useful. Finally, in future studies we advocate for minimum reporting requirements of microplastic properties and experimental conditions to help advance this important emerging field.

Increased ingestion and toxicity of polyamide microplastics in Nile tilapia with increase of salinity

Microplastics pollution and salinity intrusion in freshwater ecosystem is one of the worldwide climate change consequences those have negative impacts on the physiology of aquatic organisms. Hence, a 15-day experiment was carried out where Nile tilapia (Oreochromis niloticus) was exposed to different salinity gradients i.e. 0 ‰, 3 ‰, 6 ‰, 9 ‰, and 12 ‰ alone and along with 10 mg/L polyamide microplastics (PA-MP) in order to measure its effects on the hematology, gill, and intestinal morphology. The results exhibited that all the fish treated with PA-MP ingested microplastics and the quantity of accumulation was significantly greater in higher salinity gradients (9 ‰ and 12 ‰). In addition, the PA-MP treated fish showed increased glucose level and at the same time reduced hemoglobin concentration with the increase of salinity. The percentages of abnormalities in erythrocytes both cellular (twin, teardrop and spindle shaped) and nuclear (notched nuclei, nuclear bridge and karyopyknosis) significantly enhanced with PA-MP exposure again in higher salinity treatments (9 ‰ and 12 ‰). The principal component analysis (PCA) exhibited that the addition of 10 mg/L PA-MP negatively affected the hematology of Nile tilapia than that of salinity treatments alone. Besides, the exposure of PA-MP in 9 ‰ and 12 ‰ salinity gradients escalated the severity of histological damages in gills and intestine. Overall, this experiment affirms that the increase of salinity enhanced the microplastics ingestion and toxicity in Nile tilapia, therefore, PA-MP possibly is addressed as additional physiological stressors along with increased salinity gradients in environment.

Reviewing the role of microplastics as carriers for microorganisms in absorbing toxic trace elements

The pervasive presence of microplastics in various settings, such as freshwater and marine ecosystems, has sparked serious concerns. Microplastics can operate as possible transporters for hazardous trace elements or microbes, even though they are not naturally able to actively absorb these compounds. The binding sites on the plastic's surface or the complexes that are formed with the organic material on the plastic are how this adsorption process takes place. Microplastics' surfaces also seem to be attractive to microorganisms, such as bacteria and algae. Microorganisms can adhere to the rough surface of microplastics, which facilitates their colonization and formation of biofilms. Numerous bacteria, including ones that have the ability to absorb hazardous trace elements, can be found in these biofilms. Microplastics and microbes can interact in ways that are advantageous and detrimental. Microplastics have the ability to act as a substrate for microbial growth, which could lead to an increase in the quantity of microorganisms in the surrounding environment. On the other hand, microplastics may make it easier for microbes to spread to new areas, which could help dangerous or deadly species proliferate. Research is still ongoing to determine the degree to which microplastics serve as carriers of microbes and hazardous trace elements. Comprehending the implications of microplastics, pollutants, and microorganisms in a variety of environmental conditions is difficult due to their complex interplay. This review provides a detailed description of the complexity of the problem and used the examples related to microplastics, its environmental effects, and impacts on human health.

Harmful effects of microplastics on respiratory system of aquatic animals: A systematic review and meta-analysis

The presence of microplastics in the aquatic environment has attracted widespread attention. A large number of studies have assessed the effects of microplastics on the respiratory system of aquatic animals, but the results are not directly comparable across studies due to inconsistent evaluation criteria. Therefore, we adopted an integrated research approach that can integrate and parse complex data to improve reliability, conducted a systematic review and meta-analysis of 35 published studies, and elucidated the mechanisms of microplastic damage to cells. The results showed that PE had the greatest impact on aquatic animals, and fish were the most sensitive to the effects caused by microplastics, with oxidative stress induced by exposure concentrations exceeding 1000 µg/L or exposure times exceeding 28 days, leading to depletion of antioxidant defenses, cellular damage, inflammatory responses, and behavioral abnormalities. As this review is based on existing studies, there may be limitations in terms of literature quality, data availability and timeliness. In conclusion, we suggest to combat microplastic pollution by limiting plastic use, promoting plastic substitution and recycling, and enhancing microplastic capture degradation technologies.

Effects of sodium dodecylbenzene sulfonate (SDBS) on zebrafish (Danio rerio) gills and blood

Sodium dodecylbenzene sulfonate (SDBS) is an important surfactant used as a cleaning agent and industrial additive to remove unwanted chemicals which have been detected in the aquatic environment. The aim of this study was to examine the toxicological potential of SDBS on the gills of adult male zebrafish (Danio rerio) exposed to this chemical. For the 96 hr acute exposure, fish were divided into three groups: control, 0.25 mg/L, and 0.5 mg/L of SDBS. After the experiment, morphophysiological analyses (gill histopathology and histochemistry), oxidative stress (determination of gill activities of superoxide dismutase (SOD) and catalase (CAT)), and hematological analyses (leukocyte differentiation) were conducted. Data demonstrated that SDBS at both tested concentrations altered the histopathological index and initiated circulatory disturbances, as well as adverse, progressive, and immunological changes in the gills. In the 0.5 mg/L group, SOD activity decreased significantly, but CAT activity was not altered. Prominent blood changes observed in this group were neutrophilia and lymphocytosis. The number of mucous and chloride cells increased significantly in both groups. Taken together, our findings demonstrated that exposure of D. rerio to SDBS, even for 96 hr, produced adverse morphological and hematological effects associated with a reduction in SOD activity. Our findings indicate that exposure of aquatic species to the anionic surfactant SDBS may lead to adverse consequences associated with oxidative stress. Therefore, this study highlights the risks that this substance may pose to aquatic ecosystems and emphasizes the need for further investigations and strict regulations on its disposal.

Exposure to virgin and marine incubated microparticles of biodegradable and conventional polymers modulates the hepatopancreas transcriptome of Mytilus galloprovincialis

Biodegradable polymers have been proposed as an alternative to conventional plastics to mitigate the impact of marine litter, but the research investigating their toxicity is still in its infancy. This study evaluates the potential ecotoxicological effects of both virgin and marine-incubated microparticles (MPs), at environmentally relevant concentration (0.1 mg/l), made of different biodegradable polymers (Polycaprolactone, Mater-Bi, cellulose) and conventional polymers (Polyethylene) on Mytilus galloprovincialis by using transcriptomics. This approach is increasingly being used to assess the effects of pollutants on organisms, obtaining data on numerous biological pathways simultaneously. Whole hepatopancreas de novo transcriptome sequencing was performed, individuating 972 genes differentially expressed across experimental groups compared to the control. Through the comparative transcriptomic profiling emerges that the preponderant effect is attributable to the marine incubation of MPs, especially for incubated polycaprolactone (731 DEGs). Mater-Bi and cellulose alter the smallest number of genes and biological processes in the mussel hepatopancreas. All microparticles, regardless of their polymeric composition, dysregulated innate immunity, and fatty acid metabolism biological processes. These findings highlight the necessity of considering the interactions of MPs with the environmental factors in the marine ecosystem when performing ecotoxicological evaluations. The results obtained contribute to fill current knowledge gaps regarding the potential environmental impacts of biodegradable polymers.

Toxicological impacts of microplastics on virulence, reproduction and physiological process of entomopathogenic nematodes

Microplastics have emerged as significant and concerning pollutants within soil ecosystems. Among the soil biota, entomopathogenic nematodes (EPNs) are lethal parasites of arthropods, and are considered among the most effective biological agents against pests. Infective juveniles (IJs) of EPNs, as they navigate the soil matrix scavenging for arthropod hosts to infect, they could potentially encounter microplastics. Howver, the impact of microplastics on EPNs has not been fully elucidated yet. We addressed this gap by subjecting Steinernema feltiae EPNs to polystyrene microplastics (PS-MPs) with various sizes, concentrations, and exposure durations. After confirming PS-MP ingestion by S. feltiae using fluorescent dyes, we found that the PS-MPs reduced the survival, reproduction, and pathogenicity of the tested EPNs, with effects intensifying for smaller PS-MPs (0.1-1 μm) at higher concentrations (105 μg/L). Furthermore, exposure to PS-MPs triggered oxidative stress in S. feltiae, leading to increased reactive oxygen species levels, compromised mitochondrial membrane potential, and increased antioxidative enzyme activity. Furthermore, transcriptome analyses revealed PS-MP-induced suppression of mitochondrial function and oxidative phosphorylation pathways. In conclusion, we show that ingestion of PS-MPs by EPNs can compromise their fitness, due to multple toxicity effects. Our results bear far-reaching consequences, as the presence of microplastics in soil ecosystems could undermine the ecological role of EPNs in regulating pest populations.

Polystyrene Nano- and Microplastic Particles Induce an Inflammatory Gene Expression Profile in Rat Neural Stem Cell-Derived Astrocytes In Vitro

Microplastics are considered an emerging environmental pollutant due to their ubiquitous presence in the environment. However, the potential impact of microplastics on human health warrants further research. Recent studies have reported neurobehavioral and neurotoxic effects in marine and rodent models; however, their impact on the underlying cellular physiology in mammals remains unclear. Herein, we exposed neural stem cells and neural stem cell-derived astrocytes, oligodendrocytes, and neurons to various sizes and concentrations of polystyrene nano- and microplastics. We investigated their cellular uptake, impact on cytotoxicity, and alteration of gene expression through transcriptome profiling. The cell type most affected by decreased viability were astrocytes after 7 days of repeated exposure. Transcriptional analysis showed that 1274 genes were differentially expressed in astrocytes exposed to 500 nm microplastics, but only 531 genes were altered in astrocytes exposed to 50 nm nanoplastics. Both canonical pathway and Kyoto Encyclopedia of Genes and Genomes analysis showed that upregulated pathways were involved in neuroinflammation, innate and adaptive immunity, cell migration, proliferation, extracellular matrix remodeling, and cytoskeleton structures. The downregulated pathways were involved in lipid metabolism, specifically fatty acid oxidation and cholesterol metabolism. Our results show that neural stem cell-derived astrocytes repeatedly exposed to nano- and microplastics for 7 days undergo changes that are hallmarks of astrogliosis.

Diel Pattern of Microplastic Residues in Zebrafish

As one of the emerging pollutants, microplastics (MPs) can be taken up by aquatic organisms through ingestion. However, little is known about the uptake pattern in organisms over time and the associated mechanisms of retention patterns. The present study aims to elucidate these patterns in fish, their relationship with light/dark conditions, and examine the uptake kinetic process of small-sized plastic pollutants, especially during the long-neglected dark period. Zebrafish were sampled every 2 h during the light and dark periods after exposure to an environmentally relevant concentration (100 items/L) of MPs. The results demonstrated that MP residues in zebrafish decreased during the dark period rather than increased over time. The MP retention rhythm and the swimming behavior of exposed zebrafish displayed a statistically significant light/dark variation. Moreover, a very strong and statistically significant positive correlation was found between the swimming speed of zebrafish and the number of MP residues in the gastrointestinal tracts of zebrafish. These results clearly demonstrate that fibrous MP residues in the fish have a discernible diel pattern. This work improves the understanding of the dynamic residual process of MPs in organisms and calls for further in-depth circadian toxicokinetic studies to better suit particle pollutants.

Dietary Microplastic Administration during Zebrafish (Danio rerio) Development: A Comprehensive and Comparative Study between Larval and Juvenile Stages

One of the main sources of MPs contamination in fish farms is aquafeed. The present study investigated, for the first time through a comparative approach, the effects of different-sized fluorescent MPs included in a diet intended for zebrafish (Danio rerio). A comparison based on fish developmental stage (larval vs. juvenile), exposure time, and dietary MPs' size and concentration was performed. Four experimental diets were formulated, starting from the control, by adding fluorescent polymer A (size range 1-5 µm) and B (size range 40-47 µm) at two different concentrations (50 and 500 mg/kg). Zebrafish were sampled at 20 (larval phase) and 60 dpf (juvenile stage). Whole larvae, intestine, liver and muscles of juveniles were collected for the analyses. Polymer A was absorbed at the intestinal level in both larvae and juveniles, while it was evidenced at the hepatic and muscular levels only in juveniles. Hepatic accumulation caused an increase in oxidative stress markers in juveniles, but at the same time significantly reduced the number of MPs able to reach the muscle, representing an efficient barrier against the spread of MPs. Polymer B simply transited through the gut, causing an abrasive effect and an increase in goblet cell abundance in both stages.

Increase in temperature increases ingestion and toxicity of polyamide microplastics in Nile tilapia

Microplastics (MP) pollution and global warming are worldwide concerns, creating various physiological problems for aquatic organisms. This study was carried out to know the effects of different temperature (30, 33 and 36 °C) on ingestion of MP along with the physiological consequences in Nile tilapia (Oreochromis niloticus) exposed to virgin polyamide (PA) (10 mg/L water; 500 μm to 4 mm in size) for 15 days. A significant difference was found in PA ingestion of the fish treated with different temperature. Fish from 36 °C temperature groups ingested highest amount of PA (136 ± 24.40 item/fish) during the exposure period. The hemoglobin (Hb) and red blood cell (RBC) decreased significantly in the highest temperature (36 °C) without PA exposure. At the same time, Hb increased, but RBC significantly reduced in all the temperature conditions with PA exposure. The number of white blood cell (WBC) and glucose level increased significantly in the highest temperature (36 °C) without PA exposure. In contrast, WBC increased and glucose decreased significantly in all the temperature conditions with PA exposure. Frequencies of various nuclear and cellular abnormalities of erythrocytes increased significantly in the fish exposed to all temperature with PA exposure, though severity increased with temperature. Similarly, histological damage of gills (hyperplasia, epithelial necrosis, deformed pillar system, epithelial lifting, telangiectasia) and intestine (epithelium breakage, enterocyte vacuolization and shortening of villi) was found to be mild to severe by the accumulation of PA, increased severity with increase of temperature. This study confirms that global warming as a consequence of climate change might influence MP ingestion hampering physiological state of fish.

The microplastics exposure induce the kidney injury in mice revealed by RNA-seq

Microplastics (MPs) may pollute drinking water, accumulate in the food chain, and release toxic chemicals that may cause a variety of diseases. The detrimental effects of MPs on kidney injury and fibrosis under long-term accumulation have not been fully documented. In this study, mice were exposed to MPs with three different diameters (80 nm, 0.5 µm, and 5 µm) to investigate the detrimental influences of MPs on the kidney. The results showed that MPs of different diameters caused varying degrees of injury to the murine kidney. MPs exposure can induce an inflammatory response, oxidative stress, and cell apoptosis in the kidney and induce kidney injury, which ultimately promotes kidney fibrosis. Furthermore, transcriptome data revealed that chronic exposure to MPs could alter the expressions of multiple genes related to immune response (80 nm) and circadian rhythm (0.5 µm, and 5 µm). Overall, our data provide new evidence and potential research for investigating the harm of MPs to kidney of mammals and even humans.

Modification of sedimentation and bioaccumulation behavior as an efficient strategy to modulate the toxicity of pyraclostrobin to zebrafish (Danio rerio)

The behavior of pesticide particles or droplets might significantly influence their environmental risks. However, studies on the risk of different pesticide formulations in aqueous environments have rarely been reported. In this study, we prepared three types of pyraclostrobin formulations to evaluate their behavior in the aqueous environment and toxicological risks to zebrafish. The results showed that pyraclostrobin emulsifiable concentrate (EC) sank faster in water with increasing hydrophilicity and density of the solvent. The particles also sank faster with increasing particle size and particle density for suspension concentrate (SC) and microcapsules (MCs). Diverse behavior in water results in different temporal and spatial distributions of the active ingredient. EC-EGDA, SC-5 μm, CS-Large and EC-MO sink or float over time, therefore reducing the effective dose suspended in water. Lower toxicological risks of the pesticides were also observed by reducing the enrichment of pyraclostrobin in zebrafish. In addition to the direct toxicity of the active ingredient, the type of pesticide formulations and their specific compositions might also influence the integrated toxicity. The environmental behavior of pesticide formulations should also be considered for their systematic assessment of environmental risks to ensure the scientific application of pesticides in different scenarios.

Disturbing ion regulation and excretion in medaka (Oryzias melastigma) gills by microplastics: Insights from the gut-gill axis

The accumulation of microplastics (MPs) in fish gills has been widely recognized, however, whether such stress could thereby impact the physiological responses of fish gills is still unknown. Here, we investigated the impacts of three sizes (400 nm, 4 μm, 20 μm) of polystyrene (PS) MPs on (Na⁺, K⁺, Cl^-) ions regulation and ammonia excretion in medaka Oryzias melastigma. Significantly increased net Na⁺ and K⁺ flux rates were observed transiently during 0-3 h and 3-9 h, but not during 9-24 h. Such results suggest that the physiological resilience of fish gills regarding Na⁺ and K⁺ regulation was unaffected upon the exposure to PS-MPs, probably evidenced by the increased secretion of mucus. However, Cl^- regulation and ammonia excretion were significantly impaired, partly in consistent with the damages of ionocytes. The adverse impacts of PS-MPs on Cl^- regulation and ammonia excretion were size-dependent, with significant disturbances observed in 4 μm and 20 μm treated group for Cl^- regulation, but only in 20 μm treated group for ammonia excretion. The specific enrichment of Shinella and lower abundance of function profiles related to ion transport and metabolism might be responsible for the specific disturbance of Cl^- regulation found in the 4 μm treated group. The enrichment of Gemmobacter also accounted for the disturbances of ammonia excretion in 20 μm treated group. Our results highlighted the impacts of PS-MPs on the physiological functions in fish gills.