Size-dependent adverse effects of microplastics on intestinal microbiota and metabolic homeostasis in the marine medaka (Oryzias melastigma)

Derivatives of Plastics as Potential Carcinogenic Factors: The Current State of Knowledge

Simple Summary

Nowadays, micro- and nanoplastic particles can be found almost everywhere, being especially harmful for humans. Their absorption, primarily via inhalation and digestive routes, might lead to a particularly dangerous accumulation of those substances within the human body. Due to the alarming increase in contamination worldwide and excessive production of plastics and synthetic materials, there is an urgent need to investigate the effects of those substances on human health. So far, it has been observed that nano- and microplastics might be extremely harmful, leading to serious health conditions, such as cancers of various human body systems.

Abstract

Micro- and nanoplatics have been already reported to be potential carcinogenic/mutagenic substances that might cause DNA damage, leading to carcinogenesis. Thus, the effects of micro- and nanoplastics exposure on human health are currently being investigated extensively to establish clear relationships between those substances and health consequences. So far, it has been observed that there exists a definite correlation between exposure to micro- and nanoplastic particles and the onset of several cancers. Therefore, we have conducted research using PubMed, Web of Science, and Scopus databases, searching for all the research papers devoted to cancers that could be potentially related to the subject of exposure to nano- and microplastics. Ultimately, in this paper, we have discussed several cancers, including hepatocellular carcinoma, pancreatic cancer, pancreatic ductal adenocarcinoma, biliary tract cancer, and some endocrine-related cancers.

Multiple perspectives reveal the gut toxicity of polystyrene microplastics on Eisenia fetida: Insights into community signatures of gut bacteria and their translocation

The gut is the primary pathway by which soil animals are exposed to microplastics (MPs). However, the gut toxicity of MPs has not been elucidated in earthworms. Herein, we aimed to study the gut toxicity (e.g., gut barrier dysfunction, gut bacterial translocation, and pathogen invasion) of polystyrene microplastics (PS-MPs) on Eisenia fetida and its relationship with gut bacteria. We found that PS-MPs exposure caused gut barrier damage to Eisenia fetida. This damage included apparent injury of gut epithelial cells and significantly lower transcription levels of genes coding for gut tight junction (TJ)-related proteins. We then observed significantly increased levels of bacterial lipopolysaccharide (LPS) and gut bacterial load, indicating the occurrence of gut bacterial translocation and related barrier damage. Subsequently, antibacterial immune responses were activated and accompanied by a failure of the antioxidant defense system, indicating that pathogen invasion might occur. Gut barrier damage could weaken host selective pressures (deterministic process) on gut bacteria, such as particular pathogens. Indeed, members of Proteobacteria, e.g., Aeromonas and Escherichia/Shigella, regarded as potential opportunistic pathogens, were remarkable signatures of groups exposed to PS-MPs. These potential opportunistic gut bacteria were pivotal contributors to gut TJ damage and gut bacterial translocation resulting from PS-MPs exposure. In addition, the gut bacterial networks of PS-MPs exposure groups were more uncomplicated than those of the control group, but more negative interactions were easy to observe. In conclusion, our work sheds light on the molecular mechanism of earthworm gut toxicity caused by PS-MPs exposure and provides a prospective risk assessment of MPs in soil ecosystems.

Oxidative stress mediated by the TLR4/NOX2 signalling axis is involved in polystyrene microplastic-induced uterine fibrosis in mice

Microplastics (MPs), as a new environmental pollutant, have received widespread attention worldwide. Uterine fibrosis is one of the main factors of female reproductive disorders. However, it is unclear whether the female reproductive disorders caused by MPs are related to uterine fibrosis. Therefore, in this study, we constructed female mouse models exposed to polystyrene microplastics (PS-MPs). We found that PS-MP exposure resulted in endometrial thinning and severe collagen fibre deposition in female mice. Further mechanistic studies found that PS-MP exposure increased the expression of high mobility group Box 1 (HMGB1) and acetyl-HMGB1, further activating the Toll-like receptor 4/NADPH oxidase 2 (TLR4/NOX2) signalling axis and eventually causing oxidative stress. Afterwards, oxidative stress elicited the activation of Notch and the transforming growth factor β (TGF-β) signalling pathway, leading to increased levels of fibrotic proteins and collagen. Correspondingly, PS-MP treatment upregulated the expression of TLR4 and NOX2 and the level of reactive oxygen species (ROS) and increased the levels of fibrotic protein and collagen in mouse endometrial epithelial cells cultured in vitro. Conversely, inhibition of the TLR4/NOX2 signalling pathway effectively reduced the level of ROS in cells, weakened the upregulation of Notch and TGF-β signalling by PS-MPs, and efficiently reduced the expression of fibrotic and collagen genes. In summary, we demonstrated a new mechanism by which MPs induce uterine fibrosis in mice, that is, by inducing oxidative stress to activate the Notch and TGF-β signalling pathways by triggering the TLR4/NOX2 signalling axis. Targeting TLR4/NOX2 signalling may consequently prove to be an innovative therapeutic option that is effective in alleviating the reproductive toxicity of PS-MPs. Our study sheds new light on the reproductive toxicity of MPs and provides suggestions and references for comparative medicine and clinical medicine.

Polystyrene microplastic exposure induces insulin resistance in mice via dysbacteriosis and pro-inflammation

Microplastics (MPs) as emerging contaminants have become a global environmental problem. However, studies on the effects of MPs on metabolic diseases remain limited. Here, we evaluated the effects of polystyrene (PS), one of the most prominent types of MPs, on insulin sensitivity in mice fed with normal chow diet (NCD) or high-fat diet (HFD), and explained the underlying mechanisms. Mice fed with NCD or HFD both showed insulin resistance (IR) after PS exposure accompanied by increased plasma lipopolysaccharide and pro-inflammatory cytokines such as tumor necrosis factor-α and interleukin-1β. Exposure to PS also resulted in a significant decrease in the richness and diversity of gut microbiota, particularly an increase in the relative abundance of Gram-negative bacteria such as Prevotellaceae and Enterobacteriaceae. Additionally, PS with a small particle size (5 μm) accumulated in the liver, kidneys and blood vessels of mice. Further analyses showed inhibition of the insulin signaling pathway in the liver of PS exposed mice, such as inhibition of IRS1 and decreased expression of PI3K. Hence, the mechanism of PS exposure to induce IR in mice might be mediated through regulating gut microbiota and PS accumulation in tissues, stimulating inflammation and inhibiting the insulin signaling pathway. In conclusion, PS might be a potential environmental contaminant that causes metabolic diseases associated with IR.

Integrated Transcriptome and 16S rDNA Analyses Reveal That Transport Stress Induces Oxidative Stress and Immune and Metabolic Disorders in the Intestine of Hybrid Yellow Catfish (Tachysurus fulvidraco♀ × Pseudobagrus vachellii♂)

Live fish are often transported in aquaculture. To explore the effects of transport stress, hybrid yellow catfish (Tachysurus fulvidraco♀ × Pseudobagrus vachellii♂) were subjected to simulated transport treatments (0–16 h) with 96 h of recovery after the 16-h transport treatment, and intestinal biochemical parameters, the transcriptome, and gut microbiota were analyzed. Transportation affected the number of mucus cells and led to oxidative stress in the intestine, which activated immune responses. Changes in lipid metabolism reflected metabolic adaptation to oxidative stress. Toll-like receptor signaling, peroxisome proliferator-activated receptor signaling, and steroid biosynthesis pathways were involved in the transport stress response. Gene expression analyses indicated that transport-induced local immune damage was reversible, whereas disordered metabolism recovered more slowly. A 16S rDNA analysis revealed that transport stress decreased the alpha diversity of the gut microbiota and disrupted its homeostasis. The dominant phyla (Fusobacteria, Bacteroidetes) and genera (Cetobacterium, Barnesiellaceae) were involved in the antioxidant, immune, and metabolic responses of the host to transportation stress. Correlation analyses suggested that gut microbes participate in the transport stress response and the host–microbiota interaction may trigger multiple events in antioxidant, immune, and metabolic pathways. Our results will be useful for optimizing transport processes.

Microplastics impact the accumulation of metals in earthworms by changing the gut bacterial communities

Microplastics (MPs) are defined as plastic debris with particle size smaller than 5 mm, which have been frequently detected in environments. In this study, earthworms (Eisenia foetida) were exposed to three different sized polystyrene (PS; 0.1, 10 and 100 μm) at 10 and 100 mg per kg soil for 21 days. We examined the contents of metals (Cu, Zn, Ni and Pb) and gut microbial communities in earthworms exposed to MPs. Results showed that MPs reduced the accumulation of Ni and Pb in earthworms on the 21st day. The composition of gut bacterial communities was altered in earthworms exposed to MPs, especially 10 μm MPs, featuring a higher relative abundance of Proteobacteria (44.5%) and Bacteroidetes (27.1%) than the control group. Additionally, gut microorganisms including genus Paenibacillus and Achromobacter in earthworms were expected to be potential biomarkers for Cu and Zn. The microbial community networks showed that MPs affected bacterial community connections by size effect, and MPs with smaller size increased the complexity of earthworm microbial community networks. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed that metabolism was the main difference in the bacterial communities in different treatments, especially carbohydrate metabolism and amino acid metabolism, which was relevant to the survival and growth of bacteria. This study provides insight into the environmental risks of MPs on terrestrial organisms.

Study of microplastics pollution in sediments and organisms in mangrove forests: A review

Microplastics (MP) are an emerging and lesser-known pollutant that has attracted the attention of researchers around the world in recent decades. Size of PM is smaller than 5 mm and can be entered in different ways into marine environments like mangrove forests and interfere with the health of the environment and organisms. The present study reviews 53 studies in the field of microplastics in different parts (sediments and organisms) of mangrove forests. About 26% of the 53 studies was published in 2020. In most studies, MP particles were categorized based on the shape, color, size, and polymer genus. The number of microplastics per kilogram of mangrove sediments has been reported as 1.22-6390. The effect of sediment texture on the frequency of microplastic particles and the relationship between sediment pH and MP abundance were also discussed. The fiber and bright color PMs were more common in living organisms (mollusks, crustaceans, and fish). The PM particles with different genus (polypropylene, polyethylene, polystyrene, and polyethylene terephthalate) were reported for sediment samples. In sediments with smaller sizes and lower pH, microplastics have been detected more frequently. It was reported that sediments and roots of mangrove forests act as livestock and retain microplastics for a long time. The highest concentration of MP in different parts of mangrove forests (sediment and organisms) has been reported for China. Few reports were observed on microplastics in water in mangrove forests. Also, the concentration of microplastics in sediments and organisms in mangrove forests exposed to fishing, coastal tourism, urban, and industrial wastewater was higher than those in pristine areas. It is necessary to conduct comprehensive studies to monitor, control, and evaluate the MP pollution in sediments and various organisms in mangrove forests worldwide.

Brain single-nucleus transcriptomics highlights that polystyrene nanoplastics potentially induce Parkinson's disease-like neurodegeneration by causing energy metabolism disorders in mice

With the prevalence of nanoplastics in daily life, human exposure is inevitable. However, whether and how nanoplastics cause neurotoxicity in humans remains obscure. Herein, we conducted a 28-day repeated dose oral toxicity study in C57BL/6 J mice exposed to 0.25-250 mg/kg body weight (BW) polystyrene nanoplastics (PS-NPs, 50 nm). We revealed that PS-NP-caused Parkinson's disease (PD)-like neurodegeneration in mice by multiple approaches. Furthermore, a single-nucleus RNA sequencing of 62,843 brain nuclei unearthed PS-NP-induced cell-specific responses in the mouse brains. These disturbed responses among various brain cells were primarily linked with energy metabolism disorder and mitochondrial dysfunction in all brain cells, and especially in excitatory neurons, accompanied by inflammatory turbulence in astrocytes and microglia, dysfunction of proteostasis and synaptic-function regulation in astrocytes, oligodendrocytes, and endotheliocytes. These responses may synergize in PS-NP-motivated PD-like neurodegeneration pathogenesis. Moreover, we verified these single-nucleus transcriptomics findings on different brain regions and found that PS-NPs potentially caused PD-like neurodegeneration primarily by causing energy metabolism disorder in the substantia nigra pars compacta (SNc) and striatum. This manifested as decreases in adenosine triphosphate (ATP) content and expression levels of ATP-associated genes and proteins. Given nanoplastics' inevitable and growing exposure risks to humans, the neurological health risks of nanoplastic exposure warrant serious consideration.

Diet preference of zebrafish (Danio rerio) for bio-based polylactic acid microplastics and induced intestinal damage and microbiota dysbiosis

The ingestion of petroleum-based microplastics (MPs) by aquatic animals and their toxicological effects are of wide concern. However, the ecological risks of bio-based MPs to aquatic animals remain largely unknown. In the present study, zebrafish (Danio rerio) were exposed to MPs of polylactic acid (PLA), the most widely used bio-based plastic, and polyethylene terephthalate (PET), a high-production volume petroleum-based plastic. PLA MPs were more actively ingested by fish than PET MPs. The abundance of PLA MPs in fish intestines was approximately 170 times greater than that of PET MPs after one day of exposure. The ingestion of PLA MPs caused gastrointestinal damage in zebrafish. In addition, the ingestion of PLA MPs induced specific changes in the diversity of intestinal microbiota and promoted species closely linked with energy metabolism, cellular processes, and fish diseases. This might have been related to the depolymerization of PLA in the digestive tract, which decreased the intestinal pH and changed the carbon source structure. Overall, bio-based MPs may have different ecological effects on aquatic animals than traditional petroleum-based MPs.

Polystyrene microplastics induce gut microbiome and metabolome changes in Javanese medaka fish (Oryzias javanicus Bleeker, 1854)

Microplastics (MPs) have become emerging pollutants of public health concern, due to their impact on aqua-terrestrial ecosystems and integration into the food web, with evidence of human exposure and unrevealed health implications. There is a paucity of information regarding the effects of MPs exposure on the gut system using metagenomic and metabolomic approaches. In this study, Javanese medaka fish was exposed to 5 µm beads of polystyrene microplastics (PS-MPs) suspensions, at concentrations of 100 μg/L (MP-LOW), 500 μg/L (MP-MED), and 1000 μg/L (MP-HIGH), for a duration of 21 days, and evaluated for gut microbiome and metabolome responses. The results revealed a significant reduction (p < 0.05) in richness and diversity of the gut microbiome in the MP-HIGH group, and identification of 7 bacterial genera as differential features by the Linear discriminant analysis Effect Size (LEfSe). The gut metabolic profile revealed upregulation of 9 metabolites related to energy metabolism, via tricarboxylic acid cycle (TCA), creatine pathway, and urea cycle, as determined by the pathway analysis. Furthermore, positive correlation was found between the genus Aeromonas and glucose, lactate, and creatine metabolites. The study revealed that PS-MPs exposure resulted in altered bacterial microbiome and metabolic disorder related to energy metabolism. It further provided additional data on gut bacterial genera and metabolites associated with MPs toxicity in aquatic organism, which will inevitably enable its future health risks assessment in animals and possibly humans.

Exposure to microplastics reduces the bioaccumulation of sulfamethoxazole but enhances its effects on gut microbiota and the antibiotic resistome of mice

Microplastics (MPs) have aroused a global health concern and their coexistence with antibiotics is inevitable. However, how MPs would affect the bioaccumulation and risks of antibiotics in humans remains poorly understood. Here a mouse model was used, and through dietary exposure, we observed that while the relative distributions of sulfamethoxazole (SMX) in tissues were relatively stable, MPs significantly reduced the bioaccumulation of SMX in mice tissues (liver, lung, spleen, heart and kidney). Notably, while SMX and MPs showed a differential effect, MPs could exacerbate the effects of SMX on gut microbiota and antibiotic resistance gene (ARG) profile, with the relative abundances of sulfonamide resistance genes and multidrug genes being significantly increased. We further identified that shifts in gut microbiota contributed to the changes in ARG profiles in mice. Combined, our results demonstrate that MPs reduced the bioaccumulation of SMX, but they enhanced its effects on gut microbiota and the antibiotic resistome of mice, indicating they might have high risks to humans.

Adapting to Novel Environments Together: Evolutionary and Ecological Correlates of the Bacterial Microbiome of the World's Largest Cavefish Diversification (Cyprinidae, Sinocyclocheilus)

The symbiosis between a host and its microbiome is essential for host fitness, and this association is a consequence of the host’s physiology and habitat. Sinocyclocheilus, the largest cavefish diversification of the world, an emerging multi-species model system for evolutionary novelty, provides an excellent opportunity for examining correlates of host evolutionary history, habitat, and gut-microbial community diversity. From the diversification-scale patterns of habitat occupation, major phylogenetic clades (A–D), geographic distribution, and knowledge from captive-maintained Sinocyclocheilus populations, we hypothesize habitat to be the major determinant of microbiome diversity, with phylogeny playing a lesser role. For this, we subject environmental water samples and fecal samples (representative of gut-microbiome) from 24 Sinocyclocheilus species, both from the wild and after being in captivity for 6 months, to bacterial 16S rRNA gene profiling using Illumina sequencing. We see significant differences in the gut microbiota structure of Sinocyclocheilus, reflective of the three habitat types; gut microbiomes too, were influenced by host-related factors. There is no significant association between the gut microbiomes and host phylogeny. However, there is some microbiome related structure at the clade level, with the most geographically distant clades (A and D) being the most distinct, and the two overlapping clades (B and C) showing similarities. Microbes inhabiting water were not a cause for significant differences in fish-gut microbiota, but water quality parameters were. Transferring from wild to captivity, the fish microbiomes changed significantly and became homogenized, signifying plastic changes and highlighting the importance of environmental factors (habitat) in microbiome community assembly. The core microbiome of this group, at higher taxonomic scale, resembled that of other teleost fishes. Our results suggest that divergent natural environments giving rise to evolutionary novelties underlying host adaptations, also includes the microbiome of these fishes.

Microplastic-oil-dispersant agglomerates in the marine environment: Formation mechanism and impact on oil dispersion

Microplastics (MPs) can interact with spilled oil to form MP-oil-dispersant agglomerates (MODAs) in oceans. This study investigated the MODA formation mechanism and its impact on oil dispersion during marine oil spill responses. Two types of agglomerates, MODA-1 (MP-in-oil) and MODA-2 (MP-oil droplet-embedded), were identified. The 12 µm-MPs only formed MODA-1, while 45 µm-MPs and 125 µm-MPs formed MODA-1 and MODA-2 due to the surface free energy minimization principle. Impacts of MODA on oil dispersion under different mixing energy levels and seawater salinities were explored. We found that MODA reduced oil dispersion effectiveness under different mixing energy levels. Among three MP sizes, 12 µm-MPs caused the greatest reduction in dispersion effectiveness due to the formation of MODA-1. Pristine 12 µm-MPs reduced dispersion effectiveness by 21.95% under 5.62 × 10^-1 W/kg, while pristine 45 µm-MPs and pristine 125 µm-MPs decreased it by 5.85% and 1.83%, respectively. In addition, MODA formed by pristine MPs has a larger impact on oil dispersion effectiveness than that of aged MPs under different salinities. Under 20psu, pristine 12 µm-MPs reduced dispersion effectiveness by 33.68%, while aged 12 µm-MPs decreased it by 24.61%. This study is the first report on the MODA formation mechanism, which is essential for exploring MODA transport and toxicity through marine trophic levels.

Quantifying the Colonization of Environmental Microbes in the Fish Gut: A Case Study of Wild Fish Populations in the Yangtze River

In aquatic animals, gut microbial communities shift with host development and living environments. Understanding the mechanism by which the environment impacts the gut microbial communities of aquatic animals is crucial for assessing and managing aquatic ecosystem health. Here, we proposed a simplified framework for the colonization and dynamics of gut microbial communities. Then, to quantify the colonization of environmental microbes in the wild fish gut, the current study used 16S rRNA gene amplicon sequencing to obtain the structure of the water environmental microbial community and the gut microbial community in 10 wild fish populations (Leiocassis crassilabris, Leiocassis longirostris, Pelteobagrus vachelli, Silurus asotus, Siniperca chuatsi, Coilia brachygnathus, Aristichthys nobilis, Hypophthalmichthys molitrix, Coreius heterodon, and Xenocypris argentea) from the Wuhan section of the Yangtze River, and the relationship of these microbial communities was analyzed. The results identified that in most individuals, approximately 80% of gut microbes [at the operational taxonomic unit (OTU) level] were shared with the water environmental microbial community (except for individuals of Siniperca chuatsi and Coilia brachygnathus, approximately 74%). In approximately 80% of individuals, more than 95% of microbial species (OTUs) in the gut were transient. For fish species, more than 99% of microbial species (OTUs) that were introduced into the gut were transient. Nearly 79% of OTUs and 89% of species of water environmental microbes could be introduced into the fish gut. Driven by the introduction of transient microbes, fishes with similar feeding habits had similar gut microbial communities. The results indicated that for adult wild fishes, most gut microbiota were transient from the environmental microbiota that were related to fish feeding habits. We therefore encourage future research to focus on environmental microbiota monitoring and management to promote the better conservation of aquatic animals. It was important to note that, because of various influence factors, interspecific differences and individual variations on gut microbial community characteristics, the quantification of gut microbes in the current work was approximate rather than accurate. We hope that more comparable research could be conducted to outline the quantitative characteristics of the relationship between gut microbial community and aquatic environment microbial community as soon as possible.

Extractable additives in microplastics: A hidden threat to soil fauna

Microplastics (MPs) have become an emerging threat for organisms. However, the toxicity mechanisms on biota, especially soil biota remain largely unclear. This study distinguished the effects of five types of MPs and their extractable additives on a typical soil oligochaete Enchytraeus crypticus using a traditional ecotoxicological approach combined with gut microbiota analysis. A variety of inorganic and organic compounds were screened in extractable solutions. Both MPs and their extractable additives decreased the growth and survival rates of the worms and shifted the gut microbiota, and the effects were type-specific. The differences between the effects of MPs and their extractable additives on traditional ecotoxicological parameters were insignificant, suggesting that extractable additives were the main toxicity pathways on soil fauna. The type-specific effects of MPs were attributed to the varied chemical compositions of extractable additives, and the compounds responsible for the shift of gut microbiota were further identified. The distinguishable effects on gut microbiota between MPs and their extractable additives together with the significant regressions between gut microbiota and traditional ecotoxicological parameters confirmed that gut microbiota could be a more sensitive indicator of organism's health conditions. Combined, the study provided an important insight into the toxicity mechanisms of MPs on soil fauna and extractable additives of MPs may be a hidden threat.

Polystyrene nano/microplastics induce microbiota dysbiosis, oxidative damage, and innate immune disruption in zebrafish

The toxicity of polystyrene nano/microplastics with diameter sizes of 50um and 100 nm and concentrations of 100 and 1000 μg/mL on gut microbiota, antioxidant activity and innate immune response in zebrafish was investigated. After exposure to polystyrene plastics particle, the pathological morphological changes of intestine and gills were observed, and the injury severity was related to the concentration and particle size of plastics. Significant changes in the richness and diversity of gut microbiota were observed after polystyrene plastics-exposed in zebrafish. The plastics-treated groups exhibited more substantial oxidative stress than the control group. In addition, the mRNA expression level of most pro- and anti-inflammatory factors, including IL-8, NF-κb, and IL-10, increased while the mRNA expression of TNF-α, a pro-inflammatory factor, decreased. Our results suggest that polystyrene nano/microplastics may represent a potential threat to the gut microbiota, oxidative status, and innate immunity. These results indicated that polystyrene nano/microplastics exerted size and concentration-dependent toxicity on zebrafish. The findings provide new evidence for the toxicity of polystyrene plastics on zebrafish.

Effects of secondary polyethylene microplastic exposure on crucian (Carassius carassius) growth, liver damage, and gut microbiome composition

Microplastics (MPs) have been found in the natural environment and even in the organs of fish, which is attracting worldwide attention. In this study, agricultural film was milled to simulate secondary polyethylene microplastics (PE-MPs) to evaluate their effect and toxicity on the growth, liver damage, and gut microbiome composition of crucian (Carassius carassius), a common freshwater fish, after 30 days of feed exposure. Three fish feed treatments with different PE-MPs concentrations, low, medium, and high, whose PE-MPs intake was 6.38, 12.18, and 22.33 mg MPs/fish/day, respectively, were used. The results indicated that crucian growth was promoted in the low and medium PE-MPs groups due to the increase in Firmicutes and decrease in Bacteroidetes, probably resulting in obesity and lipid accumulation, while the growth rate of crucians in the high PE-MPs group showed a clear downward trend. Severe liver damage was observed in PE-MPs-treated groups. Disordered liver tissue and necrosis of pancreatic acinar epithelial cells were observed in the medium and high PE-MPs groups compared with those of the control group. The gut microbiome composition of crucians showed significant alteration, and some harmful bacteria were found in the gut following PE-MPs exposure. Alpha diversity indices revealed that the diversity of the gut microbiome rose markedly in the low, medium, and high PE-MPs groups. This study suggests that MPs adversely affect crucian growth and health, with increased disease risk.

Photoaging enhanced the adverse effects of polyamide microplastics on the growth, intestinal health, and lipid absorption in developing zebrafish

The safety of microplastics (MPs) and associated health effects has been one of the major concerns worldwide. However, the role of photoaging toward the risk of MPs in water ecosystems remains inconclusive yet. In this study, the size of polyamide (PA, ∼32.50 μm) MPs was obviously decreased after photoaging in water containing fulvic acid (FA) and humic acid (HA) (∼19.75 and ∼24.30 μm, respectively). Nanoplastics were formed (4.65% and 2.03%, respectively) and hydrophilia and colloidal stability was improved due to the formation of oxygen-containing functional groups. FA-aged PA exhibited higher inhibition on body length and weight of developing zebrafish than HA-aged and pristine PA. Photoaged MPs in intestine were more difficult to be depurated by zebrafish, leading to the disappearance of intestinal folding, shedding of more enterocytes, and emaciation of intestinal microvilli. Dietary lipid digestion in larvae was inhibited by aged PA due to oxidative stress-triggered lipid peroxidation and inhibition of lipase activities and bile acids secretion. Exposure of photoaged MPs down-regulated genes (cd36, dgat1a, dgat2, mttp, etc.) associated with triglyceride resynthesis and transportation, resulting in lipid maladsorption and growth inhibition. Our findings highlight the potential negative effects of environmentally aged MPs on diet digestion and nutrient assimilation in 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.

Subchronic toxicity of dietary sulfamethazine and nanoplastics in marine medaka (Oryzias melastigma): Insights from the gut microbiota and intestinal oxidative status

Antibiotics and nanoplastics are two prevalent pollutants in oceans, posing a great threat to marine ecosystems. As antibiotics and nanoplastics are highly bioconcentrated in lower trophic levels, evaluating their impacts on marine organisms via dietary exposure route is of great importance. In this study, the individual and joint effects of dietborne sulfamethazine (SMZ) and nanoplastic fragments (polystyrene, PS) in marine medaka (Oryzias melastigma) were investigated. After 30 days of dietary exposure, 4.62 mg/g SMZ decreased the Chao1 index (60.86% for females and 26.85% for males) and the Shannon index (68.95% for females and 65.05% for males) and significantly altered the structure of gut microbial communities in both sexes. The female fish exposed to 4.62 mg/g SMZ exhibited higher intestinal sod (43.5%), cat (38.5%) and gpx (39.6%) transcripts, indicating oxidative stress in the gut. PS alone at 3.45 mg/g slightly altered the composition of the gut microbiota. Interestingly, the mixture of SMZ and PS caused more modest effects on the gut microbiota and intestinal antioxidant physiology than the SMZ alone, suggesting that the presence of PS might alleviate the intestinal toxicity of SMZ in a scenario of dietary co-exposure. This study helps better understand the risk of antibiotics and nanoplastics to marine ecosystems.

Fourier transform infrared (FTIR) analysis identifies microplastics in stranded common dolphins (Delphinus delphis) from New Zealand waters

Here we provide a first assessment of microplastics (MPs) in stomach contents of 15 common dolphins (Delphinus delphis) from both single and mass stranding events along the New Zealand coast between 2019 and 2020. MPs were observed in all examined individuals, with an average of 7.8 pieces per stomach. Most MPs were fragments (77%, n = 90) as opposed to fibres (23%, n = 27), with translucent/clear (46%) the most prevalent colour. Fourier transform infrared (FTIR) spectroscopy revealed polyethylene terephthalate (65%) as the most predominant polymer in fibres, whereas polypropylene (31%) and acrylonitrile butadiene styrene (20%) were more frequently recorded as fragments. Mean fragment and fibre size was 584 μm and 1567 μm, respectively. No correlation between total number of MPs and biological parameters (total body length, age, sexual maturity, axillary girth, or blubber thickness) was observed, with similar levels of MPs observed between each of the mass stranding events. Considering MPs are being increasingly linked to a wide range of deleterious effects across taxa, these findings in a typically pelagic marine sentinel species warrants further investigation.

Dietary lipid levels affected antioxidative status, inflammation response, apoptosis and microbial community in the intestine of juvenile turbot (Scophthalmus maximus L.)

A nine-week feeding trial was conducted to comprehensively investigate the effects of different levels of dietary lipid on intestinal physiology of juvenile turbot. Three diets with different lipid levels (8%, 12% and 16%) were formulated, which were designated as the low-lipid group (LL), medium-lipid group (ML) and high-lipid group (HL), respectively. Each diet was fed to six replicate tanks, and each tank was stocked with 35 fish. The results revealed that medium dietary lipid (12%) increased the activities of intestinal digestive enzymes and brush border enzymes. Excessive dietary lipid (16%) decreased the intestinal antioxidative enzyme levels and increased the lipid peroxidation pressure. In addition, HL stimulated the occurrence of intestinal inflammation and significantly up-regulated the mRNA expression level of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interferon-γ (IFN-γ) and transforming growth factor-β (TGF-β). Dietary LL and HL induced the apoptosis of intestinal epithelial cells. Sequencing of bacterial 16 s rRNA V4 region indicated that the abundance and diversity of intestinal microflora in fish fed with medium lipid diet (12%) were significantly higher than those in other groups, indicating the intestinal microflora ecology in group ML was more balanced. MetaStat analysis indicated that both low- and high-lipid diets significantly reduced the relative abundance of intestinal beneficial bacteria. In conclusion, results of this study demonstrated the sensitivity of intestinal health and microbiota to dietary lipid levels. From the perspective of microecological balance, medium dietary lipid (12%) was more conducive to maintaining the intestinal microflora stability of turbot.

Microplastics in mangroves and coral reef ecosystems: a review

Microplastic pollution has recently been identified as a major issue for the health of ecosystems. Microplastics have typically sizes of less than 5 mm and occur in various forms, such as pellets, fibres, fragments, films, and granules. Mangroves and coral reefs are sensitive and restricted ecosystems that provide free ecological services such as coastal protection, maintaining natural cycles, hotspots of biodiversity and economically valuable goods. However, urbanization and industrial activities have started contaminating even these preserved ecosystems. Here we review sources, occurrence, and toxicity of microplastics in the trophic levels of mangrove and coral reef ecosystems. We present detection methods, such as microscopic identification and spectroscopy. We discuss mitigating measures that prevent the entry of microplastics into the marine environment.

Reality Check: Experimental Studies on Microplastics Lack Realism

Environmental microplastics are gaining interest due to their ubiquity and the threat they pose to environmental and human health. Critical studies have revealed the abundance of microplastics in nature, while others have tested the impacts of these small plastics on organismal health in the laboratory. Yet, there is often a mismatch between these two areas of research, resulting in major discrepancies and an inability to interpret certain findings. Here, we focus on several main lines of inquiry. First, even though the majority of environmental microplastics are plastic microfibers from textiles, laboratory studies still largely use spherical microbeads. There are also inconsistencies between the measurements of microplastics in the environment as compared to the concentrations that tend to be used in experimental studies. Likewise, the period of exposure occurring in experimental studies and in the environment are vastly different. Lastly, although experimental studies often focus on a particular subset of toxic chemicals present on microplastics, textile microfibers carry other dyes and chemicals that are understudied. They also cause types of physical damage not associated with microspheres. This review will analyze the literature pertaining to these mismatches, focusing on aquatic organisms and model systems, and seek to inform a path forward for this burgeoning area of research.

Microplastic: A potential threat to human and animal health by interfering with the intestinal barrier function and changing the intestinal microenvironment

Plastics are widely used in many fields due to their stable physical and chemical properties, and their global production and usage increase significantly every year, which leads to the accumulation of microplastics in the entire ecosystem. Numerous studies have shown that microplastics (MPs) have harmful effects on living organisms. This review aims to provide a comprehensive conclusion of the current knowledge of the impacts of MPs on the stability of the gut microenvironment, especially on the gut barrier. Studies showed that exposure to MPs could cause oxidative damage and inflammation in the gut, as well as the destruction of the gut epithelium, reduction of the mucus layer, microbial disorders, and immune cell toxicity. Although there are few reports directly related to humans, we hoped that this review could bring together more and more evidence that exposure to MPs results in disturbances of the intestinal microenvironment. Therefore, it is necessary to investigate their threats to human health further.

Metabolomic Studies for the Evaluation of Toxicity Induced by Environmental Toxicants on Model Organisms

Environmental pollution causes significant toxicity to ecosystems. Thus, acquiring a deeper understanding of the concentration of environmental pollutants in ecosystems and, clarifying their potential toxicities is of great significance. Environmental metabolomics is a powerful technique in investigating the effects of pollutants on living organisms in the environment. In this review, we cover the different aspects of the environmental metabolomics approach, which allows the acquisition of reliable data. A step-by-step procedure from sample preparation to data interpretation is also discussed. Additionally, other factors, including model organisms and various types of emerging environmental toxicants are discussed. Moreover, we cover the considerations for successful environmental metabolomics as well as the identification of toxic effects based on data interpretation in combination with phenotype assays. Finally, the effects induced by various types of environmental toxicants in model organisms based on the application of environmental metabolomics are also discussed.