Impacts of microplastics and carbamazepine on the shell formation of thick-shell mussels and the underlying mechanisms of action

Omics insights in responses of bivalves exposed to plastic pollution

Plastic pollution, particularly microplastics and nanoplastics, poses a significant threat to marine ecosystems. Bivalves, vital filter feeders that accumulate plastic particles, underscore the necessity for advanced omics technologies to grasp their molecular reactions to plastic exposure. This review delves into the impact of microplastics and nanoplastics on bivalves utilizing advanced omics technologies. Through an examination of omics data, this review sheds light on how bivalves react to plastic pollution, informing strategies for conservation and food safety. Furthermore, theoretical pathways have been formulated to decipher how bivalves respond to environmental stressors from microplastics or nanoplastics through the integration of diverse biological fields. In this review, we report that microplastics and nanoplastics in marine ecosystems primarily stem from human activities on land and in marine domains. Bivalves are negatively influenced by plastic contamination, impacting their health and economic worth. Exposure to plastic particles disrupts bivalve behavior, metabolism, and reproduction, precipitating health concerns. Integration of omics data is instrumental in unraveling molecular interactions and devising biomarkers for monitoring purposes. Ingestion of plastics by bivalves poses risks to human health. Additionally, mitigation tactics involve bans, levies, and advocating for biodegradable alternatives to curtail plastic pollution. The amalgamation of omics findings aids in the comprehension of bivalve responses and effectively addressing plastic pollution. Moreover, addressing plastic pollution necessitates a multidisciplinary approach encompassing scientific inquiry, regulatory frameworks, and collaboration with stakeholders. These strategies are paramount in safeguarding bivalves, marine ecosystems, food safety, and human health.

Genes of filter-feeding species as a potential toolkit for monitoring microplastic impacts

Microplastics (MPs) are ubiquitous in the marine environment and impact organisms at multiple levels. Understanding their actual effects on wild populations is urgently needed. This study develops a toolkit to monitor changes in gene expression induced by MPs in natural environments, focusing on filter-feeding and bioindicator species from diverse ecological and taxonomic groups. Six candidate genes -Caspase, HSP70, HSP90, PK, SOD, and VTG- and nine filter-feeding species -two branchiopods, one copepod, five bivalves and one fish- were selected based on differential expression in response to MPs exposure (mainly the widely used polystyrene and polyethylene polymers) reported in over 30 publications. Some genes are particularly determinant, such as HSP70 and HSP90 (key to managing a wide range of stressors) and SOD (critical for addressing oxidative stress), as they are more directly related to stress. PK is related to carbohydrate metabolism (alterations in energy metabolism); VTG is associated with reproductive problems; Caspase mediates in apoptosis. Each gene in the toolkit plays a role depending on the type of stress assessed, and their combination provides a comprehensive understanding of the impacts of MPs. Differences in gene expressions between species and the exposure thresholds were found. These genes were examined in various scenarios with different types, concentrations, and sizes of MPs, alone or with other stressors. The toolkit offers significant advantages, allowing a comprehensive study of the impact of MPs and focusing on filtering bioindicator species, thus enabling pollution assessment and long-term monitoring. It will outperform traditional methods like tissue counts of MPs where only physical damage is visible, providing a deeper understanding. To our knowledge, this is the first toolkit of its kind.

Plastic pollution and marine mussels: Unravelling disparities in research efforts, biological effects and influences of global warming

The ever-growing contamination of the environment by plastics is a major scientific and societal concern. Specifically, the study of microplastics (1 μm to 5 mm), nanoplastics (< 1 μm), and their leachates is a critical research area as they have the potential to cause detrimental effects, especially when they impact key ecological species. Marine mussels, as ecosystem engineers and filter feeders, are particularly vulnerable to this type of pollution. In this study, we reviewed the 106 articles that focus on the impacts of plastic pollution on marine mussels. First, we examined the research efforts in terms of plastic characteristics (size, polymer, shape, and leachates) and exposure conditions (concentration, duration, species, life stages, and internal factors), their disparities, and their environmental relevance. Then, we provided an overview of the effects of plastics on mussels at each organisational levels, from the smaller scales (molecular, cellular, tissue and organ impacts) to the organism level (functional, physiological, and behavioural impacts) as well as larger-scale implications (associated community impacts). We finally discussed the limited research available on multi-stressor studies involving plastics, particularly in relation to temperature stress. We identified temperature as an underestimated factor that could shape the impacts of plastics, and proposed a roadmap for future research to address their combined effects. This review also highlights the impact of plastic pollution on mussels at multiple levels and emphasises the strong disparities in research effort and the need for more holistic research, notably through the consideration of multiple stressors, with a specific focus on temperature which is likely to become an increasingly relevant forcing factor in an era of global warming. By identifying critical gaps in current knowledge, we advocate for more coordinated interdisciplinary and international collaborations and raise awareness of the need for environmental coherence in the choice and implementation of experimental protocols.

Polystyrene nanoplastics mediate skeletal toxicity through oxidative stress and the BMP pathway in zebrafish (Danio rerio)

The widespread presence of micro(nano)plastics (MNPs) has generated public concern. Studies have indicated that MNPs can accumulate in mammalian bones; however, research on the skeletal toxicity and underlying molecular mechanisms of MNPs in aquatic organisms remains limited. We subjected zebrafish embryos to three varying levels (1, 10, 100 μg/mL) of polystyrene nanoplastics (PSNPs) exposure over a period of 7 days in our research. The results revealed that PSNPs significantly reduced the body length and hatching rate of zebrafish, leading to skeletal deformities. mRNA level analysis showed significant upregulation of sp7, sparc, and smad1 genes transcription by PSNPs. Moreover, PSNPs markedly downregulated the mRNA levels associated with runx2a, bmp2a, and bmp4. Further investigations demonstrated that PSNPs dramatically increased ROS levels in zebrafish larvae, with significant downregulation of transcription levels of sod1 and cat genes, resulting in a sharp increase in transcription levels of apoptosis-related regulatory genes bcl-2 and bax. Furthermore, PSNPs led to a marked rise in Caspase 3 activity in zebrafish larvae, suggesting the initiation of apoptosis. PSNPs also notably inhibited alkaline phosphatase (AKP) activity. Compared to a 4-day exposure, a 7-day exposure to PSNPs intensified abnormalities across multiple indicators. In summary, our research indicates that PSNPs cause significant oxidative stress in zebrafish larvae, resulting in apoptosis. Moreover, PSNPs disrupt the transcription of genes related to skeletal development through the bone morphogenetic protein (BMP) pathway, further disrupting skeletal development processes and ultimately resulting in skeletal deformities in zebrafish larvae. This study provides new insights into the skeletal toxicity of MNPs.

Interaction of Micro- and Nanoplastics with Enzymes: The Case of Carbonic Anhydrase

Microplastics (MPs) and nanoplastics (NPs) have emerged as significant environmental pollutants with potential detrimental effects on ecosystems and human health. Several studies indicate their interaction with enzymes; this topic represents a multifaceted research field encompassing several areas of interest from the toxicological and ecotoxicological impact of MPs and NPs on humans and wildlife to the biodegradation of plastics by microbial enzymes. This review aims to provide a critical analysis of the state-of-the-art knowledge of the interaction of MPs and NPs on the enzyme carbonic anhydrase (CA), providing recent insights, analyzing the knowledge gaps in the field, and drawing future perspectives of the research and its application. CA is a widespread and crucial enzyme in various organisms; it is critical for various physiological processes in animals, plants, and bacteria. It catalyzes the reversible hydration of CO2, which is essential for respiration, acid-base balance, pH homeostasis, ion transport, calcification, and photosynthesis. Studies demonstrate that MPs and NPs can inhibit CA activity with mechanisms including adsorption to the enzyme surface and subsequent conformational changes. In vitro and in silico studies highlight the role of electrostatic and hydrophobic interactions in these processes. In vivo studies present mixed results, which are influenced by factors like particle type, size, concentration, and organism type. Moreover, the potentiality of the esterase activity of CA for plastic degradation is discussed. The complexity of the interaction between CA and MPs/NPs underscores the need for further research to fully understand the ecological and health impacts of MPs and NPs on CA activity and expression and glimpses of the potentiality and perspectives in this field.

Pentachlorophenol impairs the antimicrobic capability of blood clam via undermining humoral immunity and disrupting humoral-cellular crosstalk

Due to past massive usage and persistent nature, pentachlorophenol (PCP) residues are prevalent in environments, posing a potential threat to various organisms such as sessile filter-feeding bivalves. Although humoral immunity and its crosstalk with cellular one are crucial for the maintaining of robust antimicrobic capability, little is known about the impacts of PCP on these critical processes in bivalve mollusks. In this study, pathogenic bacterial challenge and plasma antimicrobic capability assays were carried out to assess the toxic effects of PCP on the immunity of a common bivalve species, blood clam (Tegillarca granosa). Moreover, the impacts of PCP-exposure on the capabilities of pathogen recognition, hemocyte recruitment, and pathogen degradation were analyzed as well. Furthermore, the activation status of downstream immune-related signalling pathways upon PCP exposure was also assessed. Data obtained illustrated that 28-day treatment with environmentally realistic levels of PCP resulted in evident declines in the survival rates of blood clam upon Vibrio challenge along with markedly weakened plasma antimicrobic capability. Additionally, the levels of lectin and peptidoglycan-recognition proteins (PGRPs) in plasma as well as the expression of pattern recognition receptors (PRRs) in hemocytes were found to be significantly inhibited by PCP-exposure. Moreover, along with the downregulation of immune-related signalling pathway, markedly fewer chemokines (interleukin 8 (IL-8), IL-17, and tumor necrosis factor α (TNF-α)) in plasma and significantly suppressed chemotactic activity of hemocytes were also observed in PCP-exposed blood clams. Furthermore, compared to that of the control, blood clams treated with PCP had markedly lower levels of antimicrobic active substances, lysozyme (LZM) and antimicrobial peptides (AMP), in their plasma. In general, the results of this study suggest that PCP exposure could significantly impair the antimicrobic capability of blood clam via undermining humoral immunity and disrupting humoral-cellular crosstalk.

Polystyrene nanoplastics exert cardiotoxicity through the Notch and Wnt pathways in zebrafish (Danio rerio)

The ubiquity of micro(nano)plastics has raised significant concerns among people. Their accumulation in the cardiovascular system necessitates attention to their cardiotoxicity. However, research on the cardiotoxicity of micro(nano)plastics remains scarce. Our study exposed zebrafish embryos to four different concentrations (0, 1, 10, 100 μg/mL) of polystyrene nanoplastics (PSNPs) for a period of 7 days. The results indicated that PSNPs noticeably decreased the hatching and survival rates of zebrafish and also induced cardiac developmental abnormalities. The mRNA level analysis revealed significant upregulations of heart development-related genes nkx2.5, cmlc-2, and myh-7 in response to PSNPs. Additionally, PSNPs significantly up-regulated the mRNA level associated with the Notch signaling pathway (notch-1a, jag-1a, and her-7) while remarkably suppressing the expression of the Wnt signaling pathway gene (wnt-3a). Further research showed that PSNPs significantly increased the expression of endoplasmic reticulum stress genes atf-6 and chop, while noticeably inhibiting mitochondrial copy numbers. Moreover, PSNPs were found to decrease calcium ion level and superoxide dismutase (SOD) activity in zebrafish larvae. Additionally, prolonged exposure to PSNPs for 7 days exacerbated abnormalities in various indicators compared to a 4-day exposure. In conclusion, our study demonstrates that PSNPs induce oxidative stress in zebrafish larvae, thereby activating endoplasmic reticulum stress and inhibiting mitochondrial activity, ultimately disrupting the Notch and Wnt signaling pathways. These disruptions result in abnormalities in cardiac developmental genes, ultimately leading to cardiac developmental abnormalities in zebrafish. The present research contributes to a novel understanding of the cardiotoxicity of PSNPs.

Interfacial effects of perfluorooctanoic acid and its alternative hexafluoropropylene oxide dimer acid with polystyrene nanoplastics on oxidative stress, histopathology and gut microbiota in Crassostrea hongkongensis oysters

The increasing interfacial impacts of polystyrene nanoplastics (PS) and per- and polyfluoroalkyl substances (PFAS) complex aquatic environments are becoming more evident, drawing attention to the potential risks to aquatic animal health and human seafood safety. This study aims to investigate the relative impacts following exposure (7 days) of Crassostrea hongkongensis oysters to the traditional PFAS congener, perfluorooctanoic acid (PFOA) at 50 μg/L, and its novel alternative, hexafluoropropylene oxide dimer acid (HFPO-DA), also known as GenX at 50 μg/L, in conjunction with fluorescent polystyrene nanoplastics (PS, 80 nm) at 1 mg/L. The research focuses on assessing the effects of combined exposure on oxidative stress responses and gut microbiota in the C. hongkongensis. Comparing the final results of PS + GenX (PG) and PS + PFOA (PF) groups, we observed bioaccumulation of PS in both groups, with the former causing more pronounced histopathological damage to the gills and intestines. Furthermore, the content of antioxidant enzymes induced by PG was higher than that of PF, including Superoxide Dismutase (SOD), Catalase (CAT), Glutathione Reductase (GR) and Glutathione Peroxidase (GSH). Additionally, in both PG and PF groups, the expression levels of several immune-related genes were significantly upregulated, including tnfα, cat, stat, tlr-4, sod, and β-gbp, with no significant difference between these two groups (p > 0.05). Combined exposure induced significant changes in the gut microbiota of C. hongkongensis at its genus level, with a significant increase in Legionella and a notable decrease in Endozoicomonas and Lactococcus caused by PG. These shifts led to beneficial bacteria declining and pathogenic microbes increasing. Consequently, the microbial community structure might be disrupted. In summary, our findings contribute to a deeper understanding of the comparative toxicities of marine bivalves under combined exposure of traditional and alternative PFAS.

Enrofloxacin exposure undermines gut health and disrupts neurotransmitters along the microbiota-gut-brain axis in zebrafish

The environmental prevalence of antibiotic residues poses a potential threat to gut health and may thereby disrupt brain function through the microbiota-gut-brain axis. However, little is currently known about the impacts of antibiotics on gut health and neurotransmitters along the microbiota-gut-brain axis in fish species. Taking enrofloxacin (ENR) as a representative, the impacts of antibiotic exposure on the gut structural integrity, intestinal microenvironment, and neurotransmitters along the microbiota-gut-brain axis were evaluated in zebrafish in this study. Data obtained demonstrated that exposure of zebrafish to 28-day environmentally realistic levels of ENR (6 and 60 μg/L) generally resulted in marked elevation of two intestinal integrity biomarkers (diamine oxidase (DAO) and malondialdehyde (MDA), upregulation of genes that encode inter-epithelial tight junction proteins, and histological alterations in gut as well as increase of lipopolysaccharide (LPS) in plasma, indicating an evident impairment of the structural integrity of gut. Moreover, in addition to significantly altered neurotransmitters, markedly higher levels of LPS while less amount of two short-chain fatty acids (SCFAs), namely acetic acid and valeric acid, were detected in the gut of ENR-exposed zebrafish, suggesting a disruption of gut microenvironment upon ENR exposure. Along with corresponding changes detected in gut, significant disruption of neurotransmitters in brain indicated by marked alterations in the contents of neurotransmitters, the activity of acetylcholin esterase (AChE), and the expression of neurotransmitter-related genes were also observed. These findings suggest exposure to environmental antibiotic residues may impair gut health and disrupt neurotransmitters along the microbiota-gut-brain axis in zebrafish. Considering the prevalence of antibiotic residues in environments and the high homology of zebrafish to other vertebrates including human, the risk of antibiotic exposure to the health of wild animals as well as human deserves more attention.

Microplastics weaken the exoskeletal mechanical properties of Pacific whiteleg shrimp Litopenaeus vannamei

The ubiquitous presence of microplastics (MPs) in aquatic environments poses a significant threat to crustaceans. Although exoskeleton quality is critical for crustacean survival, the impact of MPs on crustacean exoskeletons remains elusive. Our study represents a pioneering effort to characterize the effects of MPs exposure on crustacean exoskeletons. In this study, the mechanical properties of whiteleg shrimp Litopenaeus vannamei exoskeletons were analyzed after exposure to environmentally realistic levels of MPs. Nanoindentation data demonstrated that MPs exposure significantly increased the hardness and modulus of both the carapace and abdominal segments of L. vannamei. Moreover, fractures and embedded MPs were detected on the exoskeleton surface using SEM-EDS analysis. Further analysis demonstrated that the degree of chitin acetylation (DA) in the shrimp exoskeleton, as indicated by FTIR peaks, was reduced by MPs exposure. In addition, exposure to MPs significantly inhibited the muscle Ca2+-ATPase activity and hemolymph calcium levels. Transcriptome and metabolome analyses revealed that the expression levels of genes encoding key enzymes and metabolites in the chitin biosynthetic pathway were significantly affected by MPs exposure. In conclusion, MPs at environmentally relevant concentrations may affect the exoskeletal mechanical properties of L. vannamei through a comprehensive mechanism involving the disruption of the crystalline structure of chitin, assimilation into the exoskeleton, and dysregulation of exoskeleton biosynthesis-related pathways.

Differential effects of ocean warming and BDE-47 on mussels with various personalities

Marine warming and polybrominated diphenyl ethers (PBDEs) pollution are two of the most concerning environmental problems in recent years. However, the impact of their co-occurrence on marine bivalves and the tolerance of bivalves with different traits remain unknown. In this study, thick shell mussels Mytilus coruscus were divided into two personalities according to individual feeding and byssus growth. The reliability of the classification was validated by respiration, self-organization, and post-stress behavior. Then, the survival rate, hemolymph immunity, and digestive glands oxidase activity of classified mussels were evaluated after 21 days of compound exposure to warming and BDE-47. The results showed that mussels could be divided into proactive and reactive types consistently. Compared to reactive mussels, proactive mussels exhibited some traits, such as faster food recovery, more byssus growth, higher metabolic rate, and more efficient clustering. Both single or combined warming and BDE-47 exposure impacted the individual survival, hemolymph, and antioxidase of mussels. Notably, the negative impacts of BDE-47 were exacerbated by warming. Moreover, proactive mussels displayed better adaptability with higher survival rates along with less damage to hemolymph immunity and antioxidant ability compared to reactive ones when facing environmental challenges. This study highlights potential risks associated with the coexistence of marine warming and PBDEs pollution while demonstrating differential fitness among individuals with distinct personalities.

Toxic effects of polystyrene nanoplastics and polycyclic aromatic hydrocarbons (chrysene and fluoranthene) on the growth and physiological characteristics of Chlamydomonas reinhardtii

While the toxicity of nano-microplastics and polycyclic aromatic hydrocarbons (PAHs) to aquatic organisms is well-studied, their joint impact on microalgae is less explored. This study focused on single and combined effects of PS-NPs (30 nm; concentrations: 2, 5, 10, and 25 mg/L) and two PAHs (chrysene and fluoranthene at 10, 100 µg/L) for 96 h on the accumulation, growth, photosynthetic parameters, and oxidative stress in the Chlamydomonas reinhardtii. The findings revealed that exposure to increasing concentrations of PS-NPs significantly reduced the growth inhibition ratio and chlorophyll-a content after 96 h. Both PAHs (100 µg/L) + PS-NPs (25 mg/L), significantly reduced the growth inhibition ratio and chlorophyll-a levels. Individual and combined exposures of PS-NPs and PAHs can prompt antioxidant responses like SOD, GPx, and GST, as well as an unaffected level of non-enzymatic antioxidant GSH and diminished CAT activity. Furthermore, both PAHs + PS-NPs triggered ROS levels, resulting in cell membrane damage. However, the reduced oxidative effect of LPO of combined exposures can be attributed to the activation of antioxidant defenses. In addition, the microscopic visualization data shows that PS-NPs adhered to the surface of microalgae. Also, PS-NPs reduced the adsorption of PAHs on the surface of C. reinhardtii. Altogether, this study implied that the influence of coexistent PS-NPs should be considered in the environmental risk assessment of PAHs in aquatic environments.

Triclosan exposure induces immunotoxic impacts by disrupting the immunometabolism, detoxification, and cellular homeostasis in blood clam (Tegillarca granosa)

Omnipresent presence of triclosan (TCS) in aqueous environment puts a potential threat to organisms. However, it's poorly understood about its immunometabolic impacts of marine invertebrates. In present study, we use a representative bivalve blood clam (Tegillarca granosa) as a model, investigating the effects of TCS exposure at 20 and 200 μg/L for 28 days on immunometabolism, detoxification, and cellular homeostasis to explore feasible toxicity mechanisms. Results demonstrated that the clams exposed to TCS resulting in evident immunotoxic impacts on both cellular and humoral immune responses, through shifting metabolic pathways and substances, as well as suppressing the expressions of genes from the immune- and metabolism-related pathways. In addition, significant alterations in contents (or activity) of detoxification enzymes and the expression of key detoxification genes were detected in TCS-exposed clams. Moreover, exposure to TCS also disrupted cellular homeostasis of clams through increasing MDA contents and caspase activities, and promoting activation of the apoptosis-related genes. These findings suggested that TCS might induce immunotoxic impacts by disrupting the immunometabolism, detoxification, and cellular homeostasis.

Exposure to polystyrene nanoplastics and PCB77 induced oxidative stress, histopathological damage and intestinal microbiota disruption in white hard clam Meretrix lyrata

The toxic effects of organic pollutants and nanoplastics on fish have been extensively studied, but there is limited research available on their combined toxicity to bivalves. This research aimed to investigate the accumulation and ecotoxicological impacts such as antioxidant capacity, histopathology and intestinal microbiota in white hard clam Meretrix lyrata, resulting from 7 days of single and mixture exposure to 3,3',4,4'-tetrachlorobiphenyl (PCB77, 0.1 mg/L) and polystyrene nanoplastics (PS-NPs, 80 nm, 1 mg/L). Our findings revealed that PS-NPs accumulated in various tissues such as the intestine, gill, mantle, foot, and siphon. And when compared to the PCB-PSNPs (PP) co-exposure group, the intestinal fluorescence intensity mediated by plastic particles in the PS-NPs (PS group) was significantly higher. The gill, digestive gland, and intestine were all damaged to varying extent by single exposure to PS-NPs or PCB77, according to histopathological analysis, which was aggravated by PP group. Moreover, the co-exposure induced a higher level of oxidative stress, which reflected by increase of activities of superoxide dismutase, catalase, glutamate oxaloacetate transaminase and glutamic-pyruvic transaminase and malondialdehyde content. In addition, the intestine microbial composition was dramatically altered by the combined exposure, reducing the abundance of probiotics such as Firmicutes, thereby posing a great threat to the health and metabolism of M. lyrata. In conclusion, our findings showed that PS-NPs and PCB77 co-exposure induced a higher toxicity to M. lyrata, including histopathological changes, altered antioxidant capacity and intestinal microbiota disruption. This study provides novel insights into PCB77 and PS-NPs' combined toxicity to marine organisms and its underlying molecular mechanisms of ecotoxicological effects.

Microplastics in coral reef sediments underestimated? They may hide in biominerals

Microplastics (MPs) may be underestimated in coral reef sediments. Current pretreatments for determining MPs in the sediments are mainly density separation and organic matter removal, ignoring MPs that may be embedded or encrusted in biominerals. This could lead to discrepancies in assessing the potential risk of MPs contamination. To confirm whether MPs in coral reef sediments are underestimated, a two-step sequential digestion, including organic matter removal (H2O2 digestion) and biomineral removal (HCl digestion), was performed on sediments from the coral reef area of the South Penghu Marine National Park (SPMNP, Taiwan). The MPs abundance and characteristics of the two steps were analyzed separately. The results showed that the average MPs abundance after HCl digestion (78 ± 42 MPs/kg) was significantly higher than that of H2O2 digestion (38 ± 25 MPs/kg). The MPs diversity integrated index (MPDII) in coral reef sediments was low (MPDII = 0.35), and MPs were mainly small (<2.0 mm, 91.3 %), fibrous (93.5 %), colored (60.9 %), and rayon polymers (73.9 %). Correlation analysis showed that MPs in biominerals mainly dominated MPs in the sediments. These results confirm that current assessments of MPs contamination levels in biomineral-rich sediments may be underestimated and uncertain. In addition, the mineralization of organisms in SPMNP reef regions was affected by MPs from moderate to high levels, depending on the proportion of MPs in biominerals.

Toxic effects of four emerging pollutants on cardiac performance and associated physiological parameters of the thick-shell mussel (Mytilus coruscus)

Robust cardiac performance is critical for the health and even survival of an animal; however, it is sensitive to environmental stressors. At present, little is known about the cardiotoxicity of emerging pollutants to bivalve mollusks. Thus, in this study, the cardiotoxic effects of four emergent pollutants, carbamazepine (CBZ), bisphenol A (BPA), tetrabromobisphenol A (TBBPA), and tris(2-chloroethyl) phosphate (TCEP), on the thick-shell mussel, Mytilus coruscus, were evaluated by heartbeat monitoring and histological examinations. In addition, the impacts of these pollutants on parameters that closely related to cardiac function including neurotransmitters, calcium homeostasis, energy supply, and oxidative status were assessed. Our results demonstrated that 28-day exposure of the thick-shell mussel to these pollutants resulted in evident heart tissue lesions (indicated by hemocyte infiltration and myocardial fibrosis) and disruptions of cardiac performance (characterized by bradyrhythmia and arrhythmia). In addition to obstructing neurotransmitters and calcium homeostasis, exposure to pollutants also led to constrained energy supply and induced oxidative stress in mussel hearts. These findings indicate that although do differ somehow in their effects, these four pollutants may exert cardiotoxic impacts on mussels, which could pose severe threats to this important species and therefore deserves more attention.

Toxicities of polystyrene microplastics (MPs) and hexabromocyclododecane (HBCD), alone or in combination, to the hepatopancreas of the whiteleg shrimp, Litopenaeus vannamei

The hepatopancreas is one of the largest organs playing crucial roles in metabolism and detoxification in crustacean invertebrates. Although toxicities have been increasingly documented for the two ubiquitous pollutants, hexabromocyclododecane (HBCD) and microplastics (MPs), in model animals, little is known about their impacts on the hepatopancreas of crustaceans. To fill this knowledge gap, the effects of MPs and HBCD, alone or in combination, on the hepatopancreas were evaluated in a commercially important crustacean species (the whiteleg shrimp) by histological observation as well as quantification of hepatic lesion-, metabolism-, and detoxification-related parameters. In addition, to reveal potential mechanisms underlying the hepatoxicity observed, the accumulation of HBCD in the shrimp and the status of oxidative stress were also investigated. Our results demonstrated that exposure of the whiteleg shrimp to MPs and HBCD for 4 weeks resulted in evident histological injury in the hepatopancreas and marked elevation in hepatic lesion markers (alanine aminotransferase and aspartate aminotransferase) in the hemolymph. Moreover, both metabolism (activity of phosphofructokinase, contents of lactic acid and adenosine triphosphate, and expression of metabolism-related genes) and detoxification (contents of cytochrome P450, UDP-glucuronosyltransferase, and glutathione, activity of glutathione S-transferase, and expression of detoxification-related genes) were found to be disrupted by the pollutants tested. In addition, exposure to MPs and HBCD also led to alterations in the contents and/or activities of antioxidant enzymes and resulted in oxidative damage to the hepatopancreas (indicated by marked elevation in malondialdehyde content). Furthermore, a significant amount of HBCD accumulated in shrimp treated with HBCD-containing seawater. The data also illustrated that HBCD-MP coexposure was more toxic than single exposure to these pollutants. These findings suggest that MPs and HBCD may exert hepatotoxic impacts on whiteleg shrimp by accumulating in vivo and inducing oxidative stress, which could pose a severe threat to the health of this important crustacean species.

Tris(2-chloroethyl) Phosphate Exerts Hepatotoxic Impacts on Zebrafish by Disrupting Hypothalamic-Pituitary-Thyroid and Gut-Liver Axes

The ubiquitous environmental presence of tris(2-chloroethyl) phosphate (TCEP) poses a potential threat to animals; however, little is known about its hepatotoxicity. In this study, the effects of TCEP exposure (0.5 and 5.0 μg/L for 28 days) on liver health and the potential underlying toxification mechanisms were investigated in zebrafish. Our results demonstrated that TCEP exposure led to hepatic tissue lesions and resulted in significant alterations in liver-injury-specific markers. Moreover, TCEP-exposed fish had significantly lower levels of thyrotropin-releasing hormone and thyroid-stimulating hormone in the brain, evidently less triiodothyronine whereas more thyroxine in plasma, and markedly altered expressions of genes from the hypothalamic-pituitary-thyroid (HPT) axis in the brain or liver. In addition, a significantly higher proportion of Bacteroidetes in the gut microbiota, an elevated bacterial source endotoxin lipopolysaccharide (LPS) in the plasma, upregulated expression of LPS-binding protein and Toll-like receptor 4 in the liver, and higher levels of proinflammatory cytokines in the liver were detected in TCEP-exposed zebrafish. Furthermore, TCEP-exposed fish also suffered severe oxidative damage, possibly due to disruption of the antioxidant system. These findings suggest that TCEP may exert hepatotoxic effects on zebrafish by disrupting the HPT and gut-liver axes and thereafter inducing hepatic inflammation and oxidative stress.

Combined exposure of polystyrene microplastics and carbamazepine induced transgenerational effects on the reproduction of Daphnia magna

Polystyrene microplastics (PS MPs) and carbamazepine (CBZ) are frequently detected in freshwater ecosystems. However, the transgenerational effects of PS MPs and CBZ on the reproduction of aquatic organisms and the corresponding mechanisms are still unclear. In the present study, Daphnia magna was used to evaluate the reproductive toxicity in two consecutive generations (F0, F1). The molting and reproduction parameters, the expression of reproduction, and the toxic metabolism genes were examined after 21-day exposure. A significantly enhanced toxicity was observed in the presence of 5 μm PS MPs and CBZ. Chronic exposure results showed that the 5 μm PS MPs alone, CBZ alone, and their mixtures exerted significant reproductive toxicity of D. magna. The results of RT-qPCR showed transcripts of genes related to reproduction (cyp314, ecr-b, cut, vtg1, vtg2, dmrt93b) and toxic metabolism (cyp4, gst) were altered in both the F0 and F1. In addition, for the F0, gene transcriptional changes of reproduction were not fully translated into physiological performance, probably due to the compensatory responses caused by the low dose of PS MPs alone, CBZ alone, and their mixtures. Whereas for the F1, the trade-off between reproduction and toxic metabolism at gene levels was observed, which translated into a significant reduction in the total neonate number of F1. These findings suggest that long-term exposure to MPs and CBZ can cause serious reproduction damage to aquatic animals, which needs to be given sufficient attention.

Enrofloxacin exposure induces anxiety-like behavioral responses in zebrafish by affecting the microbiota-gut-brain axis

The ubiquitous presence of antibiotic residues in aqueous environments poses a great potential threat to aquatic organisms. Nevertheless, the behavioral effects of environmentally realistic levels of antibiotics remain poorly understood in fish species. In this study, the behavioral impacts of enrofloxacin, one of typical fluoroquinolone antibiotics that is frequently detected in aquatic environments, were evaluated by the classic light-dark test (LDT) and novel tank task (NTT) in zebrafish. Furthermore, the effects of enrofloxacin exposure on the microbiota-gut-brain axis were also assessed to reveal potential affecting mechanisms underlying the behavioral abnormality observed. Our results demonstrated that zebrafish exposed to 60 μg/L enrofloxacin for 28 days took significantly longer to enter the stressful area of the testing tank and spent significantly less time there in both the LDT and NTT, indicating abnormal anxiety-like behaviors induced by the exposure. In addition, exposure to enrofloxacin at 6 and 60 μg/L resulted in a significant elevation in Bacteroidetes and a marked decline in the Firmicutes/Bacteroidetes ratio of the gut microbiota. Moreover, the intestinal contents of interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), glucagon-like peptide 1 (GLP-1), and 5-hydroxytryptamine (5-HT) in zebrafish were significantly upregulated, whereas those of plasma adrenocorticotropic hormone (ACTH) and cortisol (COR) were markedly downregulated upon enrofloxacin exposure. Incubation of zebrafish with a high dose of enrofloxacin (60 μg/L) also resulted in evident increases in the contents of corticotropin-releasing hormone (CRH), brain-derived neurotrophic factor (BDNF), and neuropeptide Y (NPY) in the brain. Fortunately, no significant alteration in the expression of glial fibrillary acidic protein (GFAP) was detected in the brain after enrofloxacin exposure. Our findings suggest that the disruption of the microbiota-gut-brain axis may account for enrofloxacin-induced anxiety-like behaviors in zebrafish. Since the disruption of microbiota-gut-brain axis may give rise to various clinical symptoms, the health risk of antibiotic exposure deserves more attention.

Elucidating the consequences of the co-exposure of microplastics jointly to other pollutants in bivalves: A review

The marine environment has numerous impacts related to anthropogenic activities including pollution. Abundances of microplastics (MPs) and other pollutants are continuously increasing in the marine environment, resulting in a complex mixture of contaminants affecting biota. In order to understand the consequences, a review of studies analyzing combined effects of MPs and other types of pollutants in bivalves has been conducted as species in this group have been considered as sentinel and bioindicators. Regarding studies reviewed, histological analyses give evidence that MPs can be located in the haemolymph, gills and gonads, as well as in digestive glands in the intestinal lumen, epithelium and tubules, demonstrating that the entire body of bivalves is affected by MPs. Moreover, DNA strand breaks represent the most relevant form of damage caused by the enhanced production of reactive oxygen species in response to MPs exposure. The role of MPs as vectors of pollutants and the ability of polymers to adsorb different compounds have also been considered in this review highlighting a high variability of results. In this sense, toxic impacts associated to MPs exposure were found to significantly increase with the co-presence of antibiotics or petroleum hydrocarbons amongst other pollutants. In addition, bioaccumulation processes of pollutants (PAHs, metals and others) have been affected by the co-presence with MPs. Histological, genetic and physiological alterations are the most reported damages, and the degree of harm seems to be correlated with the concentration and size of MP and with the type of pollutant.

Tetracycline adsorption trajectories on aged polystyrene in a simulated aquatic environment: A mechanistic investigation

Microplastics (MPs) have attracted widespread attention as an organic class of pollutants as well as pollutant carriers in recipient aquatic ecosystems. In this study, tetracycline (TC) adsorption by polystyrene (PS), with multiple aging-based temporal changes in the adsorption mechanism, was observed. The results revealed that the pseudo-second-order model accurately predicted the TC adsorption kinetics for different types of PS. In addition, the isothermal adsorption processes fit the Freundlich model; however, their interactions were drastically weakened at lower temperatures or increasing salinities. Corresponding to the electrostatic interactions, adsorption TC was largely pH-dependent, with the maximum adsorbed TC content on the PS surface at a pH of 5 in an aqueous environment. More importantly, mechanistic studies have revealed that, compared to virgin PS, TC complexes with aged PS are principally controlled by hydrogen bonding and ionic interactions, followed by π-π, polar-polar, and van der Waals interactions. These findings will aid in understanding the insights of TC and aged PS interactions and the underlying interactive molecular forces, which will be advantageous for comprehending the real case scenario of inter-pollutant interactions and related environmental pollution.