Effects of microplastics and mercury on manila clam Ruditapes philippinarum: Feeding rate, immunomodulation, histopathology and oxidative stress

Microplastics and copper impacts on feeding, oxidative stress, antioxidant enzyme activity, and dimethylated sulfur compounds production in Manila clam Ruditapes philippinarum

Microplastics (MPs) are widespread ocean pollutants and many studies have explored their effects. However, research on MPs combined impact with copper (Cu) on dimethylated sulfur compound production is limited. Dimethyl sulfide (DMS) is an important biogenic sulfur compound related to global temperatures. This study examined the ecotoxicological effects of polyamide 6 MPs and Cu on dimethylsulfoniopropionate (DMSP), DMS, and dimethyl sulfoxide (DMSO) production in Manila clams (Ruditapes philippinarum). Our findings showed that MPs and Cu increased oxidative stress, indicated by higher superoxide anion radical production and malondialdehyde levels while decreasing glutathione contents and increasing superoxide dismutase activities. Additionally, MPs and Cu exposure reduced DMS and dissolved DMSO (DMSOd) concentrations due to decreased grazing. These results contribute to a better understanding of the ecotoxicological effects of MPs/Cu on bivalves and their roles in the organic sulfur cycle, suggesting a need for further research on long-term impacts on them.

Comprehensive assessment of multiple biomarker mechanisms in the brackish water clam Corbicula japonica exposed to polystyrene microplastics using structural equation modeling

Using structural equation modeling (SEM), we investigated multiple biomarker mechanisms in terms of biochemical and individual marker responses in the brackish water clam Corbicula japonica following acute exposure to polystyrene microplastic (PS-MP). This study is the first to comprehensively explore multiple biomarker responses in bivalves using SEM. The model revealed that PS-MP accumulation was an independent biomarker, exhibiting significant direct effects on superoxide dismutase (SOD) and catalase (CAT) among the biochemical markers. Although CAT generally interacts closely with SOD, no significant relationship was identified between them, indicating that CAT may have independently responded to PS-MP stress. Among individual markers, significant indirect effects were observed on clearance rate (CR), reflecting feeding activity and valve open rate, indicating excretion activity via SOD and CAT. Finally, the carbon-based scope for growth was significantly influenced by CR. SEM is efficient and useful for identifying significant direct and indirect pathway relationships and for uncovering uncommon relationships in unified multiple biomarker mechanisms in aquatic studies.

Size-dependent toxic interaction between polystyrene beads and mercury on the mercury accumulation and multixenobiotic resistance (MXR) of brackish water flea Diaphanosoma celebensis

Due to their worldwide distribution and persistence, mercury (Hg), and nano- and microplastics (NMPs) pose major threats to global ocean ecosystems. Hg and NMPs co-exist in the ocean and can interact with each other. However, information on the toxicity of this interaction to marine biota remains limited. Thus, we investigated the toxicological interaction between HgCl2 (Hg) and NMPs by studying the influence of different sizes of polystyrene beads (0.05-, 0.5-, and 6-μm) on Hg accumulation in the brackish water flea Diaphanosoma celebensis. The Hg adsorption capacity of NPs (0.05-μm) was higher than that of MPs (0.5- and 6-μm). Only the group co-exposed to both Hg and NPs showed increased Hg content in D. celebensis. Multixenobiotic resistance (MXR) activity and transcriptional modulation of transporter genes (ABCBs and ABCCs) were decreased by NMP exposure, particularly by NPs, suggesting MXR disruption by NPs. However, only the activity of multidrug resistance-associated proteins (MRPs; ABCCs) increased with Hg exposure and decreased upon NP+Hg co-exposure, indicating an important role of ABCC in Hg efflux. Furthermore, in vivo toxicity tests showed a synergistic toxic interaction between Hg and NPs on the reproduction of D. celebensis. Our findings suggest that NPs have the potential to enhance the toxicity of Hg, increasing Hg accumulation not only by serving Hg as a carrier but also by disrupting MXR.

Tris(1-chloro-2-propyl) phosphate enhances the adverse effects of biodegradable polylactic acid microplastics on the mussel Mytilus coruscus

Microplastics (MPs) and organophosphate flame retardants (OPFRs) have recently become ubiquitous and cumulative pollutants in the oceans. Since OPFRs are added to or adsorbed onto MPs as additives, it is necessary to study the composite contamination of OPFRs and MPs, with less focus on bio-based PLA. Therefore, this study focused on the ecotoxicity of the biodegradable MP polylactic acid (PLA) (5 μm, irregular fragments, 102 and 106 particles/L), and a representative OPFRs tris(1-chloro-2-propyl) phosphate (TCPP, 0.5 and 50 μg/L) at environmental and high concentrations. The mussel Mytilus coruscus was used as a standardised bioindicator for exposure experiments. The focus was on examining oxidative stress (catalase, CAT, superoxide dismutase, SOD, malondialdehyde, MDA), immune responses acid (phosphatase, ACP, alkaline phosphatase, AKP, lysozyme, LZM), neurotoxicity (acetylcholinesterase, AChE), energy metabolism (lactate dehydrogenase, LDH, succinate dehydrogenase, SDH, hexokinase, HK), and physiological indices (absorption efficiency, AE, excretion rate, ER, respiration rate, RR, condition index, CI) after 14 days exposure. The results of significantly increased oxidative stress and immune responses, and significantly disturbed energy metabolism and physiological activities, together with an integrated biomarker response (IBR) analysis, indicate that bio-based PLA MPs and TCPP could cause adverse effects on mussels. Meanwhile, TCPP interacted significantly with PLA, especially at environmental concentrations, resulting in more severe negative impacts on oxidative and immune stress, and neurotoxicity. The more severe adverse effects at environmental concentrations indicate higher ecological risks of PLA, TCPP and their combination in the real marine environment. Our study presents reliable data on the complex effects of bio-based MP PLA, TCPP and their combination on marine organisms and the environment.

Merkel cells and corpuscles of Stannius as putative targets for polyethylene terephthalate microfibers in sheepshead minnow larvae

Polyethylene terephthalate (PET) fibers are contaminated in wastewater from various primary sources, such as washing textile waters. PET fibers in the environment can be degraded into microfibers because of weathering processes such as sunlight, physical wear, and heat. Although recent studies reported adverse effects of PET microfibers on aquatic organisms, the lack of information on their toxicity and mode of action hampers the risk assessment of PET microfibers. Therefore, this study aimed to investigate the biological effects of PET microfibers and their underlying mechanisms in early-staged sheepshead minnows (Cyprinodon variegatus). PET microfibers (about 13 μm diameter × 106 μm length) were prepared by cutting PET threads and treated to sheepshead minnow larvae at 10 and 100 mg/L for 10 days. No acute toxicity was found in the minnow, but PET microfibers significantly produced reactive oxygen species and reduced behavioral responses of traveled distance and maximum velocity. The transcriptomic data suggested that Merkel cells (flow sensors) and corpuscles of Stannius (calcium regulator) are putative targets, which were derived from oxidative stress, sensory neuropathy, cognitive impairment, and movement disorders. These findings underscore that although PET microfibers are not directly lethal to sheepshead minnows, they could impact their survival by damaging swimming-related key genes. This study provides new insights into how PET microfibers are toxic to aquatic organisms and disrupt ecosystems beyond survival and pathological changes.

Microplastics at an environmentally relevant dose enhance mercury toxicity in a marine copepod under multigenerational exposure: Multi-omics perspective

Here, we subjected the marine copepod Tigriopus japonicus to environmentally-relevant concentrations of microplastics (MPs) and mercury (Hg) for three generations (F0-F2) to investigate their physiological and molecular responses. Hg accumulation and phenotypic traits were measured in each generation, with multi-omics analysis conducted in F2. The results showed that MPs insignificantly impacted the copepod's development and reproduction, however, which were significantly compromised by Hg exposure. Interestingly, MPs significantly increased Hg accumulation and consequently aggravated this metal toxicity in T. japonicus, demonstrating their carrier role. Multi-omics analysis indicated that Hg pollution produced numerous toxic events, e.g., induction of apoptosis, damage to cell/organ morphogenesis, and disordered energy metabolism, ultimately resulting in retarded development and decreased fecundity. Importantly, MPs enhanced Hg toxicity mainly via increased oxidative apoptosis, compromised cell/organ morphogenesis, and energy depletion. Additionally, phosphoproteomic analysis revealed extensive regulation of the above processes, and also impaired neuron activity under combined MPs and Hg exposure. These alterations adversely affected development and reproduction of T. japonicus. Overall, our findings should offer novel molecular insights into the response of T. japonicus to long-term exposure to MPs and Hg, with a particular emphasis on the carrier role of MPs on Hg toxicity.

Are mixtures of micro/nanoplastics more toxic than individual micro or nanoplastic contamination in the clam Ruditapes decussatus?

The abundance of micro (MPs) and nano (NPs) sized plastic particles in the ocean is concerning due to their harmful effects on marine life. The interactions between MPs and NPs in the marine environment and their impact on marine biota remain not fully understood. This study contributes with new insights into the interaction between polystyrene NPs (PSNPs) and polyethylene MPs (PEMPs) on the clam Ruditapes decussatus. Results showed ingestion of MPs and NPs by clams, with PSNPs demonstrating higher toxicity in hemolymph. While no genotoxicity was observed, clams treated with MPs and the mixture showed increased acetylcolinesterase (AchE) activity over time. Additionally, the antioxidant defense system mitigated oxidative stress, suggesting effective neutralization of reactive oxygen species. Hazard assessment indicated the greatest impact on clam digestive glands after ten days of exposure, with an antagonistic interaction between MPs and NPs noted.

Microplastics as a Threat to Aquatic Ecosystems and Human Health

The threat posed by microplastics has become one of the world's most serious problems. Recent reports indicate that the presence of microplastics has been documented not only in coastal areas and beaches, but also in water reservoirs, from which they enter the bodies of aquatic animals and humans. Microplastics can also bioaccumulate contaminants that lead to serious damage to aquatic ecosystems. The lack of comprehensive data makes it challenging to ascertain the potential consequences of acute and chronic exposure, particularly for future generations. It is crucial to acknowledge that there is still a substantial need for rapid and effective techniques to identify microplastic particles for precise evaluation. Additionally, implementing legal regulations, limiting plastic production, and developing biodegradation methods are promising solutions, the implementation of which could limit the spread of toxic microplastics.

The multistressor effect of pH reduction, microplastic and lanthanum on sea urchin Arbacia lixula

pH reduction (Low pH), microplastic (MP), and lanthanum (La) are substantial stressors due to their increasing trends in marine ecosystems and having adverse effects on marine species. This study investigates the single and combined effects of those stressors (Low pH: 7.45, polyethylene MP: 26 μg L-1, and La: 9 μg L-1) on the physiology and histology of sea urchin Arbacia lixula. Regarding physiological results, while the coelomocytes' quantity was slightly affected by stressors, their viability was significantly affected. The coelomocyte count and viability were suppressed most in Low pH-MP-La treatment. The stressors did not impact the respiration rate. According to the histological examination results, the crypt (villi-like structure) was shorter, and epithelial layers were thinner in single and dual stress treatments like MP, Low pH, Low pH-La, and MP-La. Overall, we suggest that the combination of variable types of those stressors causes negative effects on sea urchin's physiology and histology.

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.

Seasonality of mercury and its fractions in microplastics biofilms -comparison to natural biofilms, suspended particulate matter and bottom sediment

Biofilms can enhance the sorption of heavy metals onto microplastic (MP) surfaces. However, most research in this field relies on laboratory experiments and neglects metal fractions and seasonal variations. Further studies of the metal/biofilm interaction in the aquatic environment are essential for assessing the ecological threat that MPs pose. The present study used in situ experiments in an environment conducive to biofouling (Vistula Lagoon, Baltic Sea). The objective was to investigate the sorption of mercury and its fractions (thermodesorption technique) in MP (polypropylene-PP, polystyrene-PS, polylactide-PLA) biofilms and natural matrices across three seasons. After one month of incubation, the Hg concentrations in MP and natural substratum (gravel grains-G) biofilms were similar (MP: 145 ± 45 ng/g d.w.; G: 132 ± 23 ng/g d.w.) and approximately twofold those of suspended particulate matter (SPM) (63 ± 27 ng/g d.w.). Hg concentrations in biofilms and sediments were similar, but labile fractions dominated in biofilms and stable fractions in sediments. Seasonal Hg concentrations in MP biofilms decreased over summer>winter>spring, with significant variation for mineral and loosely bound Hg fractions. Multiple regression analysis revealed that hydrochemical conditions and sediment resuspension played a crucial role in the observed variability. The influence of polymer type and morphology (pellets, fibres, aged MP) on Hg sorption in biofilms was visible only in high summer temperatures. In this season, PP fibres and aged PP pellets encouraged biofilm growth and the accumulation of labile Hg fractions. Additionally, high concentrations of mineral (stable and semi-labile) Hg fractions were found in expanded PS biofilms. These findings suggest that organisms that ingest MPs or feed on the biofilms are exposed to the adverse effects of Hg and the presence of MPs in aquatic ecosystems may facilitate the transfer of mercury within the food chain.

Toxic effects of fragmented polyethylene terephthalate particles on the marine rotifer Brachionus koreanus: Based on ingestion and egestion assay, in vivo toxicity test, and multi-omics analysis

Microplastics (MPs) are a major concern in marine ecosystem because MPs are persistent and ubiquitous in oceans and are easily consumed by marine biota. Although many studies have reported the toxicity of MPs to marine biota, the toxicity of environmentally relevant types of MPs is little understood. We investigated the toxic effects of fragmented polyethylene terephthalate (PET) MP, one of the most abundant MPs in the ocean, on the marine rotifer Brachionus koreanus at the individual and molecular level. No significant rotifer mortality was observed after exposure to PET MPs for 24 and 48 h. The ingestion and egestion assays showed that rotifers readily ingested PET MPs in the absence of food but not when food was supplied; thus, there were also no chronic effects of PET MPs. In contrast, intracellular reactive oxygen species levels and glutathione S-transferase activity in rotifers were significantly increased by PET MPs. Transcriptomic and metabolomic analyses revealed that genes and metabolites related to energy metabolism and immune processes were significantly affected by PET MPs in a concentration-dependent manner. Although acute toxicity of PET MPs was not observed, PET MPs are potentially toxic to the antioxidant system, immune system, and energy metabolism in rotifers.

Methylmercury exposure of the sponge O. lobularis induces strong tissue and cell defects

Mediterranean marine biota suffers from various anthropogenic threats. Among them, pollutants such as mercury (Hg) represent important environmental issues that are exacerbated by bioaccumulation and bioamplification along food webs via its organic form, monomethylmercury (MMHg). To date, very little is known regarding the impact of mercury on Porifera and the few available studies have been exclusively focused on Demospongiae. This work studies the effect of MMHgCl at different biological levels of Oscarella lobularis (Porifera, Homoscleromorpha). Bioaccumulation assays show that MMHgCl significantly accumulated in sponge tissues after a 96-h exposure to 0.1 μg L-1. Toxicity assays (LC5096h) show a sensibility that depends on life-stage (adult vs bud). Additionally, we show that the exposure to 1 μg L-1 MMHgCl negatively impacts the epithelial integrity and the regeneration process in buds, as shown by the loss of cell-cell contacts and the alteration of osculum morphogenesis. For the first time in a sponge, a whole set of genes classically involved in metal detoxification and in antioxidant response were identified. Significant changes in catalase, superoxide dismutase and nuclear factor (erythroid-derived 2)-like 2 expressions in exposed juveniles were measured. Such an integrative approach from the physiological to the molecular scales on a non-model organism expands our knowledge concerning sensitivity and toxicity mechanisms induced by MMHg in Porifera, raising new questions regarding the possible defences used by marine sponges.

The physiological response of the clam Ruditapes philippinarum and scallop Chlamys farreri to varied concentrations of microplastics exposure

Microplastics (MPs) pollution's impact on the marine ecosystem is widely recognized. This study compared the effects of polyethylene (PE) and polyethylene terephthalate (PET) on two bivalve species, Ruditapes philippinarum (clam) and Chlamys farreri (scallop), at two particle concentrations (10 and 1000 μg/L). MPs were found in the digestive glands and gills of both species. Although clearance rates showed no significant changes, exposure to different MPs caused oxidative stress, energy disruption, and lipid metabolism disorders in both clam and scallop. Histopathological damage was observed in gills and digestive glands. IBR values indicated increasing toxicity with concentration, with PET being more toxic than PE. WOE model suggested increasing hazard with concentration, highlighting higher PET toxicity on clam digestive glands. In contrast, PE hazard increased in gills, showing different species responses. R. philippinarum exhibited higher sensitivity to MPs than C. farreri, providing insights for assessing ecological risk under realistic conditions and stress conditions.

Simultaneous detection and removal of mercury (II) using multifunctional fluorescent materials

Environmental problems caused by mercury ions are increasing due to growing industrialization, poor enforcement, and inefficient pollutant treatment. Therefore, detecting and removing mercury from the ecological chain is of utmost significance. Currently, a wide range of small molecules and nanomaterials have made remarkable progress in the detection, detoxification, adsorption, and removal of mercury. In this review, we summarized the recent advances in the design and construction of multifunctional materials, detailed their sensing and removing mechanisms, and discussed with emphasis the advantages and disadvantages of different types of sensors. Finally, we elucidated the problems and challenges of current multifunctional materials and further pointed out the direction for the future development of related materials. This review is expected to provide a guideline for researchers to establish a robust strategy for the detection and removal of mercury ionsin the environment.

Modeling the effect of fish migration on the horizontal distribution of microplastics in freshwater and ecological risks in the food web: Influence of habitat

Microplastics (MPs < 5 mm) pollution is a widespread phenomenon in freshwater ecosystems. While the role of physiochemical factors in the migration and distribution of MPs is understood, the impact of biological migration remains less clear. The influence of nekton migration determined by habitat suitability on the distribution of MPs and the consequent ecological risks to the regional food web is investigated in the freshwater environment by using Baiyangdian Lake (China) as a case study. The key findings reveal that fish migration significantly alters the horizontal distribution of MPs in the water environment, with a higher degree of fish aggregation in high suitability habitats leading to an increased presence of MPs due to their ingestion and excretion behaviors. In both high and low suitability habitats, MPs are found to bioconcentrate in fish, suggesting a significant risk to aquatic ecosystems. Despite the lack of evidence supporting MPs biomagnification, the results indicate that MPs are more likely to be biomagnified within the food web of high suitability habitats due to the enhanced foraging capabilities of aquatic organisms. These findings highlight the critical need to consider biological factors, such as nekton migration, in understanding and addressing MPs pollution in freshwater ecosystems.

The role of marine pollution on the emergence of fish bacterial diseases

Marine pollution and bacterial disease outbreaks are two closely related dilemmas that impact marine fish production from fisheries and mariculture. Oil, heavy metals, agrochemicals, sewage, medical wastes, plastics, algal blooms, atmospheric pollutants, mariculture-related pollutants, as well as thermal and noise pollution are the most threatening marine pollutants. The release of these pollutants into the marine aquatic environment leads to significant ecological degradation and a range of non-infectious disorders in fish. Marine pollutants trigger numerous fish bacterial diseases by increasing microbial multiplication in the aquatic environment and suppressing fish immune defense mechanisms. The greater part of these microorganisms is naturally occurring in the aquatic environment. Most disease outbreaks are caused by opportunistic bacterial agents that attack stressed fish. Some infections are more serious and occur in the absence of environmental stressors. Gram-negative bacteria are the most frequent causes of these epizootics, while gram-positive bacterial agents rank second on the critical pathogens list. Vibrio spp., Photobacterium damselae subsp. Piscicida, Tenacibaculum maritimum, Edwardsiella spp., Streptococcus spp., Renibacterium salmoninarum, Pseudomonas spp., Aeromonas spp., and Mycobacterium spp. Are the most dangerous pathogens that attack fish in polluted marine aquatic environments. Effective management strategies and stringent regulations are required to prevent or mitigate the impacts of marine pollutants on aquatic animal health. This review will increase stakeholder awareness about marine pollutants and their impacts on aquatic animal health. It will support competent authorities in developing effective management strategies to mitigate marine pollution, promote the sustainability of commercial marine fisheries, and protect aquatic animal health.

Adsorption/desorption of mercury (II) by artificially weathered microplastics: Kinetics, isotherms, and influencing factors

While both mercury (Hg) and microplastics (MPs) are well-studied global pollutants, comparatively little is known about the interactions between them and the mobilization of Hg from MPs into organisms. We examined the affinity of Hg(II) to artificially weathered MPs, including polyamide (w-PA), polyethylene (w-PE), polyethylene terephthalate (w-PET), polyester fibers (w-PEST), polyvinyl chloride (w-PVC), and polylactic acid (w-PLA), along with crumb rubber (CR) and PE collected from a wastewater treatment plant (WWTP-PE). WWTP-PE, CR, and w-PEST had particularly high Hg(II) affinities, which can be attributed to electrostatic interaction and pore filling. The adsorption followed a pseudo-second-order kinetic process and fitted the Freundlich model, suggesting multi-step (mass transfer and intraparticle diffusion) and heterogeneous adsorptions. Hydrochemical conditions (pH, dissolved organic matter (DOM), salinity and co-existent metal ions) all impacted Hg-MP behavior. Changes in Hg speciation and MP surface properties contributed to the different Hg(II) adsorption capacities for the MPs. Weathering of MPs generally increased the adsorption of Hg(II) onto MPs, but CR, PET and PEST did not follow this trend. Less than 3% of adsorbed Hg(II) was mobilized from the MPs in freshwater, but that increased up to 73% under simulated avian digestive conditions, suggesting increased bioavailability of Hg(II) from ingested MPs. Overall, weathered MPs adsorb and retain Hg(II) under environmentally relevant conditions but desorb much of it in simulated avian digestion fluid, suggesting that birds that ingest MPs may have increased Hg(II) exposure.

A study on managing plastic waste to tackle the worldwide plastic contamination and environmental remediation

Over the past 50 years, the emergence of plastic waste as one of the most urgent environmental problems in the world has given rise to several proposals to address the rising levels of contaminants associated with plastic debris. Worldwide plastic production has increased significantly over the last 70 years, reaching a record high of 359 million tonnes in 2020. China is currently the world's largest plastic producer, with a share of 17.5%. Of the total marine waste, microplastics account for 75%, while land-based pollution accounts for responsible for 80-90%, and ocean-based pollution 10-20% only in overall pollution problems. Even at small dosages (10 μg/mL), microplastics have been found to cause toxic effects on human and animal health. This review examines the sources of microplastic contamination, the prevalent reaches of microplastics, their impacts, and the remediation methods for microplastic contamination. This review explains the relationship between the community composition and the presence of microplastic particulate matter in aquatic ecosystems. The interaction between microplastics and emerging pollutants, including heavy metals, has been linked to enhanced toxicity. The review article provided a comprehensive overview of microplastic, including its fate, environmental toxicity, and possible remediation strategies. The results of our study are of great value as they illustrate a current perspective and provide an in-depth analysis of the current status of microplastics in development, their test requirements, and remediation technologies suitable for various environments.

Pathway-dependent toxic interaction between polystyrene microbeads and methylmercury on the brackish water flea Diaphanosoma celebensis: Based on mercury bioaccumulation, cytotoxicity, and transcriptomic analysis

Given their worldwide distribution and toxicity to aquatic organisms, methylmercury (MeHg) and microplastics (MP) are major pollutants in marine ecosystems. Although they commonly co-exist in the ocean, information on their toxicological interactions is limited. Therefore, to understand the toxicological interactions between MeHg and MP (6-μm polystyrene), we investigated the bioaccumulation of MeHg, its cytotoxicity, and transcriptomic modulation in the brackish water flea Diaphanosoma celebensis following single and combined exposure to MeHg and MP. After single exposure to MeHg for 48-h, D. celebensis showed high Hg accumulation (34.83 ± 0.40 μg/g dw biota) and cytotoxicity, which was reduced upon co-exposure to MP. After transcriptomic analysis, 2, 253, and 159 differentially expressed genes were detected in the groups exposed to MP, MeHg, and MeHg+MP, respectively. Genes related to metabolic pathways and the immune system were significantly affected after MeHg exposure, but the effect of MeHg on these pathways was alleviated by MP co-exposure. However, MeHg and MP exhibited synergistic effects on the expression of gene related to DNA replication. These findings suggest that MP can reduce the toxicity of MeHg but that their toxicological interactions differ depending on the molecular pathway.

Effects of exposure to nanoplastics on the gill of mussels Mytilus galloprovincialis: An integrated perspective from multiple biomarkers

The pervasive presence of nanoplastics (NPs) in marine environments poses a threat to marine organisms. Gills, as the organ in direct contact with the environment in marine invertebrates, maybe the first to accumulate NPs. To date, the toxic effects of NPs on the gills of marine invertebrates are still largely unknown. In this study, the response of multiple biomarkers (i.e., total antioxidant capacity, the activity of acetylcholine, ion content and transport enzyme, metabolic enzymes, and lipids content) in mussels Mytilus galloprovincialis exposed to polystyrene nanoplastics (PS-NPs) for 7 days were evaluated. Significant inductions of total antioxidant capacity (T-AOC) and inhibition of acetylcholine (AChE) activity were detected after 7 days of PS-NPs exposure. PS-NPs also triggered significant alteration in ion content (Na+ and K+) and suppressed the activities of the ion transport enzyme (Na+/K+-ATPase). Moreover, we found the activity of metabolic enzymes (succinate dehydrogenase and pyruvate kinase) and lipids content (triacylglycerol and cholesterol) were significantly altered, suggesting the interference of PS-NPs on energy metabolism and lipid metabolism. This investigation provides substantial information to understand the physical responses of invertebrate gills to PS-NPs exposure. Given the crucial ecological roles of invertebrates, the presence of PS-NPs in the marine environment may have far-reaching impacts on population abundance, biodiversity, and stability of the marine ecosystem.

Metabolomic analysis of combined exposure to microplastics and methylmercury in the brackish water flea Diaphanosoma celebensis

Owing to their widespread distribution and high bioaccumulation, microplastics (MPs) and mercury (Hg) are considered major threats to the ocean. MP interacts with Hg because of its high adsorption properties. However, their toxicological interactions with marine organisms, especially combined effects at the molecular level, are poorly understood. This study investigated the single and combined effects of MP and Hg on the metabolic profile of the brackish water flea Diaphanosoma celebensis. A total of 238 metabolites were significantly affected by MP, Hg, or MP + Hg. Metabolite perturbation patterns showed that toxicity of Hg and MP + Hg was similar and that of MP was not significant. Among the 223 metabolites affected by Hg, profiles of 32 unannotated metabolites were significantly different from those of MP + Hg, and combined effects of MP + Hg decreased the effect of Hg on 25 of these metabolites. Only 11 annotated metabolites were significantly affected by Hg or MP + Hg and were related to carbohydrate, lipid, vitamin, and ecdysteroid metabolism. Ten metabolites were decreased by Hg and MP + Hg and were not significantly different between the exposure groups. Enrichment analysis showed that galactose, starch, and sucrose metabolism were the most affected pathways. These findings suggest that MP has negligible toxic effect, and Hg can induce energy depletion, membrane damage, and disruption of growth, development, and reproduction. Although the impact of MP was negligible, the combined effects of MP + Hg could be metabolite specific. This study provides better understanding of the combined effects of MP and Hg on marine organisms.

Impact of polyethylene microplastics on the clam Ruditapes decussatus (Mollusca: Bivalvia): examination of filtration rate, growth, and immunomodulation

The present study was conducted to assess, for the first time, the effects of a 14 days experimental exposure to polyethylene (PE) based MPs (40-48 µm) on the clam Ruditapes decussatus. Clams were exposed to three different concentrations of MPs in controlled laboratory conditions: 10 µg/L (low), 100 µg/L (medium), and 1000 µg/L (high). The effects of MPs were assessed using a multi-marker approach, including the filtration rate, growth, and the integrity of immune cells (such as haemocyte numbers, viability, and lysosomal membrane destabilization). The results revealed that as the concentration of PE-MPs increased, the filtration rate decreased, indicating that PE-MPs hindered the clams' ability to filter water. Furthermore, there was a noticeable decrease in the overall weight of the clams, particularly in the group exposed to 1000 µg/L. This decrease could be attributed to the impairment of their nutrient filtration function. In terms of immune system biomarkers, exposure to PE-MPs led to immune system disruption, characterized by a significant increase in the number of haemocytic cells, especially in the group exposed to the high concentration. Additionally, there was a notable reduction in the viability of haemocytes, resulting in the destabilization of their lysosomal membranes, particularly in the groups exposed to medium and high PE-MPs concentrations. The findings of this study indicate that the sensitivity of hemolymph parameter changes and filtration rate in R. decussatus exposed to PE-MPs (100 and 1000 µg/L), surpasses that of growth performance and can serve as reliable indicators to assess habitat conditions and contaminant levels.

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.

Toxicity of mixture of polyethylene microplastics and Up Grade® pesticide on Oreochromis niloticus juvenile: I. Hemato-biochemical and histopathological alterations

Acute toxicity experiments were conducted to determine the lethal concentration 50 (LC50) of the Up Grade®46% SL for Oreochromis niloticus. Our results showed that the 96-h LC50 value of UPGR for O. niloticus was 29.16 mg L-1. To study hemato-biochemical effects, fish were exposed for 15 days to individual UPGR at 2.916 mg L-1, individual polyethylene microplastics (PE-MPs) at 10 mg L-1, and to their combinations UPGR+PE-MPs. UPGR exposure induced significant decrease in account of red blood cells (RBCs) and white blood cells (WBCs), platelets, monocytes, neutrophils, eosinophils, and the concentrations of hemoglobin (Hb), hematocrit (Hct), and mean corpuscular hemoglobin concentration (MCHC) than other treatments, compared to the control group. Sub-acute UPGR exposure significantly increase lymphocytes, mean corpuscular volume (MCV), and mean corpuscular hemoglobin (MCH), compared to the control group. In conclusion, UPGR and PE-MPs displayed antagonistic toxic effects due to maybe the sorption of UPGR onto PE-MPs.

The combined effects of polyethylene microplastics and benzoanthracene on Manila clam Ruditapes philippinarum

Microplastic (MP) toxicity has recently been explored in various marine species. Along with the toxicity of plastics polymer itself, additional substances or pollutants that are absorbed onto it may also be harmful. In the present study, we investigated the combined impacts of polyethylene microplastics (PE MPs) and an organic pollutant (Benzo(a)anthracene, BaA) on Manila clam Ruditapes philippinarum during a one-week exposure. Two PE MPs concentrations (26 μg L^-1 and 260 μg L^-1) and one BaA concentration (3 μg L^-1) were tested. The clams were exposed to BaA and PE MPs either alone or in combination. BaA and PE MPs were incubated before the combined exposure. The biological effects of PE MPs and BaA on the clams were evaluated by considering several assays such as feeding rate, anti-oxidant enzyme activities, and the expression levels of stress-related genes. The feeding rate significantly decreased in individual PE MPs and individual BaA groups while it remained unchanged in combined groups. Superoxide dismutase (SOD) was the most affected among the biochemical parameters. Malondialdehyde (MDA), and glutathione peroxidase (GPx) activities were slightly affected, whereas no changes were observed in glutathione s-transferase (GST) activities. CYP1A1, CYP3A4, and HSP70 gene expressions displayed slightly significant changes. Considering all stressor groups, high PE MPs exposure (260 μg L^-1 PE MPs) more effectively altered the biological parameters in the clams compared to individual low PE MPs and BaA exposure, and their combination. The results also indicated the negligible vector role of PE MPs to transport BaA into the clam tissues.

Silver nanoparticles and silver ions indistinguishably decrease sperm motility in Pacific oysters (Magallana gigas) after short-term direct exposure

The present study aimed to evaluate the reprotoxicity of environmental (0.25μg.L^-1) and supra-environmental (25μg.L^-1 and 250μg.L^-1) levels of silver nanoparticles (Ag NP) on the Pacific oyster (Magallana gigas), by determining sperm quality. For that, we evaluated sperm motility, mitochondrial function and oxidative stress. To determine whether the Ag toxicity was related to the NP or its dissociation into Ag ions (Ag⁺), we tested the same concentrations of Ag⁺. We observed no dose-dependent responses for Ag NP and Ag⁺, and both impaired sperm motility indistinctly without affecting mitochondrial function or inducing membrane damage. We hypothesize that the toxicity of Ag NP is mainly due to adhesion to the sperm membrane. Blockade of membrane ion channels may also be a mechanism by which Ag NP and Ag⁺ induce toxicity. The presence of Ag in the marine ecosystem is of environmental concern as it may affect reproduction in oysters.

Nanoplastics pose a greater effect than microplastics in enhancing mercury toxicity to marine copepods

Due to human activities, high abundances of nano/microplastics (N/MPs) concurrent with metal pollution have become a serious problem in the global marine environment. Because of displaying a high surface-area-to-volume ratio, N/MPs can serve as the carriers of metals and thus increase their accumulation/toxicity in marine biota. As one of the most toxic metals, mercury (Hg) causes adverse effects on marine organisms but whether environmentally relevant N/MPs can play a vector role of this metal in marine biota, as well as their interaction, is poorly known. To evaluate the vector role of N/MPs in Hg toxicity, we first performed the adsorption kinetics and isotherms of N/MPs and Hg in seawater, as well as ingestion/egestion of N/MPs by marine copepod Tigriopus japonicus, and second, the copepod T. japonicus was exposed to polystyrene (PS) N/MPs (500-nm, 6-μm) and Hg in isolation, combined, and incubated forms at environmentally relevant concentrations for 48 h. Also, the physiological and defense performance including antioxidant response, detoxification/stress, energy metabolism, and development-related genes were assessed after exposure. The results indicated N/MPs significantly increased Hg accumulation and thus its toxicity effects in T. japonicus as exemplified by decreased transcription of genes related to development and energy metabolism and increased transcriptional levels of genes functioning in antioxidant and detoxification/stress defense. More importantly, NPs were superimposed onto MPs and produced the most vector effect in Hg toxicity to T. japonicus, especially in the incubated forms. Overall, this study highlighted the role of N/MPs as a potential risk factor for increasing the adverse effects of Hg pollution, and emphasized the adsorption forms of contaminants by N/MPs should doubly be considered in the continuing researches.

Comparative toxicity of micro and nanopolystyrene particles in Mya arenaria clams

The contamination of coastal marine environments by plastics of sizes ranging from mm down to the nanoscale (nm) could pose a threat to aquatic organisms. The purpose of this study was to examine the toxicity of polystyrene nanoparticles (PsNP) of various sizes (50, 100 and 1000 nm) to the marine clams Mya arenaria. Clams were exposed to concentrations of PsPP for 7 days at 15 °C and analyzed for uptake/transformation, changes in energy metabolism, oxidative stress, genotoxicity and circadian neural activity. The results revealed that PsNP accumulated in the digestive gland was 50 nm > 100 nm > 1000 nm. All sized increased oxidative stress as follows: 50 nm (peroxidase, antioxidant potential and LPO), 100 nm (LPO and antioxidant potential) and 1000 nm (LPO). Tissue damage was also size dependent by increasing genotoxicity. The 100 nm PsPP altered the levels of the circadian metabolite melatonin. We conclude that the toxicity of plastics is size dependent in clams.

Heavy metals and metalloid in aquatic invertebrates: A review of single/mixed forms, combination with other pollutants, and environmental factors

Heavy metals (HMs) and metalloid occur naturally and are found throughout the Earth's crust but they are discharged into aquatic environments at high concentrations by human activities, increasing heavy metal pollution. HMs can bioaccumulate in higher organisms through the food web and consequently affect humans. In an aquatic environment, various HMs mixtures can be present. Furthermore, HMs adsorb on other environmental pollutants, such as microplastics and persistent organic pollutants, causing a synergistic or antagonistic effect on aquatic organisms. Therefore, to understand the biological and physiological effects of HMs on aquatic organisms, it is important to evaluate the effects of exposure to combinations of complex HM mixtures and/or pollutants and other environmental factors. Aquatic invertebrates occupy an important niche in the aquatic food chain as the main energy link between higher and lower organisms. The distribution of heavy metals and the resulting toxic effects in aquatic invertebrates have been extensively studied, but few reports have dealt with the relationship between HMs, pollutants, and environmental factors in biological systems with regard to biological availability and toxicity. This review describes the overall properties of individual HM and their effects on aquatic invertebrates and comprehensively reviews physiological and biochemical endpoints in aquatic invertebrates depending on interactions among HMs, other pollutants, and environmental factors.

Norgestrel causes digestive gland injury in the clam Mactra veneriformis: An integrated histological, transcriptomics, and metabolomics study

The potential adverse effects of progestins on aquatic organisms, especially non-target species, are of increasing concern worldwide. However, the effect and mechanism of progestin toxicity on aquatic invertebrates remain largely unexplored. In the present study, clams Mactra veneriformis were exposed to norgestrel (NGT, 0, 10, and 1000 ng/L), the dominant progestin detected in the aquatic environment, for 21 days. NGT accumulation, histology, transcriptome, and metabolome were assessed in the digestive gland. The bioconcentration factor (BCF) was 386 and 268 in the 10 ng/L NGT group and 1000 ng/L NGT group, respectively, indicating efficient accumulation of NGT in the clams. Histological analysis showed that NGT led to the swelling of epithelial cells and blurring of the basement membrane in the digestive gland. Differentially-expressed genes and KEGG pathway enrichment analysis using a transcriptomic approach suggested that NGT primarily disturbed the detoxification system, antioxidant defense, carbohydrate and amino acid metabolism, and steroid hormone metabolism, which was consistent with the metabolites analyzed using a metabolomic approach. Furthermore, we speculated that the oxidative stress caused by NGT resulted in histological damage to the digestive gland. This study showed that NGT caused adverse effects in the clams and sheds light on the mechanisms of progestin interference in aquatic invertebrates.

Microplastic sources, formation, toxicity and remediation: a review

Microplastic pollution is becoming a major issue for human health due to the recent discovery of microplastics in most ecosystems. Here, we review the sources, formation, occurrence, toxicity and remediation methods of microplastics. We distinguish ocean-based and land-based sources of microplastics. Microplastics have been found in biological samples such as faeces, sputum, saliva, blood and placenta. Cancer, intestinal, pulmonary, cardiovascular, infectious and inflammatory diseases are induced or mediated by microplastics. Microplastic exposure during pregnancy and maternal period is also discussed. Remediation methods include coagulation, membrane bioreactors, sand filtration, adsorption, photocatalytic degradation, electrocoagulation and magnetic separation. Control strategies comprise reducing plastic usage, behavioural change, and using biodegradable plastics. Global plastic production has risen dramatically over the past 70 years to reach 359 million tonnes. China is the world's top producer, contributing 17.5% to global production, while Turkey generates the most plastic waste in the Mediterranean region, at 144 tonnes per day. Microplastics comprise 75% of marine waste, with land-based sources responsible for 80-90% of pollution, while ocean-based sources account for only 10-20%. Microplastics induce toxic effects on humans and animals, such as cytotoxicity, immune response, oxidative stress, barrier attributes, and genotoxicity, even at minimal dosages of 10 μg/mL. Ingestion of microplastics by marine animals results in alterations in gastrointestinal tract physiology, immune system depression, oxidative stress, cytotoxicity, differential gene expression, and growth inhibition. Furthermore, bioaccumulation of microplastics in the tissues of aquatic organisms can have adverse effects on the aquatic ecosystem, with potential transmission of microplastics to humans and birds. Changing individual behaviours and governmental actions, such as implementing bans, taxes, or pricing on plastic carrier bags, has significantly reduced plastic consumption to 8-85% in various countries worldwide. The microplastic minimisation approach follows an upside-down pyramid, starting with prevention, followed by reducing, reusing, recycling, recovering, and ending with disposal as the least preferable option.

How plastic debris and associated chemicals impact the marine food web: A review

Contamination from plastic debris is omnipresent in marine environments, posing a substantial risk to marine organisms, food webs and the ecosystem. The overlap between the size range of marine plastic pollution with prey means that plastics are readily available for consumption by organisms at all trophic levels. Large plastic debris can directly result in the death of larger marine organisms, through entanglement, strangulation, choking and starvation through a false sense of satiation. Whereas smaller plastic debris, such as micro- and nano-plastics can have adverse impact to marine organisms due to their large surface area to volume ratio and their ability to translocate within an organism. Various physiological processes are reported to be impacted by these small contaminants, such as feeding behaviour, reproductive outputs, developmental anomalies, changes in gene expression, tissue inflammation and the inhibition of growth and development to both adults and their offspring. Micro- and nano-plastics are still relatively poorly understood and are considered a hidden threat. Plastic is a complex contaminant due to the diversity in sizes, shapes, polymer compositions, and chemical additives. These factors can each have unique and species-specific impacts. Consumption of plastics can occur directly, through ingestion and indirectly, through trophic transfer, entanglement of prey, adherence of plastics to external surfaces, and adherence of organisms to the external surfaces of plastics. This review investigated the intrusion of plastics into the marine food web and the subsequent consequences of plastic pollution to marine biota.The objective of this review was to identify the complexity of impacts to marine organisms through the food web from plastic contamination. Through a concise analysis of the available literature the review has shown that plastic pollution and their associated additives can adversely impact environmental and biological health.

Protective efficacy of dietary natural antioxidants on microplastic particles-induced histopathological lesions in African catfish (Clarias gariepinus)

Microplastic particles (MPs) are a common environmental pollutant easily ingested by fish in aquaculture. The current study evaluated the protective efficacies of some antioxidant, e.g., lycopene, citric acid, and chlorella, against the toxic effects of MP ingestion by Clarias gariepinus using histopathological biomarkers. Five experimental groups were established, a control group receiving only a standard diet, a group exposed to 500 mg/kg MP concomitant with the standard diet, and three antioxidant groups exposed to MPs plus either lycopene (500 mg/kg), citric acid (30 g/kg), or chlorella (50 g/kg) in the standard diet. After 15 days, fish were sacrificed for histological and histochemical examinations. Histological analysis of the kidney for group 2 (fed 500 mg/kg MPs alone) revealed distributed tissue dissociation, regional glomerular hypertrophy or shrinkage, melanomacrophage accumulation, and expansion of Bowman's space, while liver tissue exhibited dilation and rupture of the central vein wall, hemorrhage, cytoplasmic vacuolation, and cellular necrosis or apoptosis. Fish exposed to MPs also exhibited connective tissue fiber accumulation around renal blood vessels, renal tubules, the central hepatic vein, hepatic blood sinusoids, and serosal, muscle, and submucosal layers of the intestine. In addition, MP exposure reduced carbohydrate (mainly glycogen) contents in the brush borders and basement membranes of renal tubules, glomeruli, and intestinal tissues as well as in the cytoplasm of hepatocytes. These signs of renal, hepatic, and intestinal histopathology were fully or partially reversed by dietary lycopene, chlorella, or citric acid. Enhancing dietary antioxidants is an effective strategy for preventing MP toxicity in Clarias gariepinus in aquaculture.

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.

Polystyrene microplastics inhibit the neurodevelopmental toxicity of mercury in zebrafish (Danio rerio) larvae with size-dependent effects

Insufficient evidence exists regarding the effects of microplastics (MPs) on the neuronal toxicity of heavy metals in the early stages of organisms. Herein, the effects of micro-polystyrene (μ-PS; 157 μm) and nano-polystyrene (n-PS; 100 nm) particles on the neurodevelopmental toxicity of mercury (Hg) in zebrafish embryos were compared. Zebrafish embryos exposed to Hg at the concentration of 0.1 mg L^-1 revealed blood disorders, delayed hatching, and malformations such as pericardial oedema and tail deformity. The length of the larval head was significantly reduced (P < 0.01) and in vivo expression of atoh1a in the cerebellum of neuron-specific transgenic zebrafish Tg(atoh1a:dTomato) larvae was inhibited by 29.46% under the Hg treatment. Most of the toxic effects were inhibited by the combined exposure to μ-PS or n-PS with Hg, and n-PS decreased the neurodevelopmental toxicity of Hg more significantly than μ-PS. Metabolomic analysis revealed that in addition to inhibiting the amino acid metabolism pathway as in the μ-PS+Hg treatment, the n-PS+Hg treatment inhibited unsaturated fatty acid metabolism in zebrafish larvae, likely because of a greater reduction in Hg bioavailability, thus reducing the oxidative damage caused by Hg in the larvae. The combined effects of MPs and heavy metals differ greatly among different species and their targeted effects. We conclude that the combined toxicity mechanisms of MPs and heavy metals require further clarification.

Short-Term Exposure to MPs and DEHP Disrupted Gill Functions in Marine Bivalves

The synergistic impact of microplastics (MPs) and organic pollutants remains poorly understood in the marine environment. This study aimed to assess the toxicity of polypropylene microplastics (PS) and/or di-(2-ethylhexyl) phthalate (DEHP) on marine clams. Both Ruditapes philippinarum and Tegillarca granosa were exposed to PS and DEHP individually and combined at environmentally relevant concentrations for 48 h. The filtration rate, antioxidant enzymes activity, lipid peroxidation, reactive oxygen species accumulation, and histological alterations were evaluated. Our results show that single or co-exposure to MPs and DEHP significantly decreases the filtration rate in both type of clams, but the latter exhibited stronger inhibition effect. Close examination of accumulation of reactive oxygen species and related biomarkers revealed that combined exposure exerts greater oxidative stress in the cells, which causes more serious histopathological damage in the gills of the bivalves. Our study implies that MPs, in synergy with organic pollutants, can be more harmful for marine organisms.

The single and combined effects of mercury and polystyrene plastic beads on antioxidant-related systems in the brackish water flea: toxicological interaction depending on mercury species and plastic bead size

Plastics are considered as a major threat to marine environments owing their high usage, persistence, and negative effects on aquatic organisms. Although they often exist as mixtures in combination with other pollutants (e.g., mercury (Hg)) in aquatic ecosystems, the combined effects of plastics and ambient pollutants remain unclear. Therefore, in the present study, we investigated the toxicological interactions between Hg and plastics using two Hg species (HgCl₂ and MeHgCl) and different-sized polystyrene (PS) beads (diameter: 0.05, 0.5, and 6-μm) in the brackish water flea Diaphanosoma celebensis. The single and combined effects of Hg and PS beads on mortality were investigated, and changes in the antioxidant system and lipid peroxidation were further analyzed. After 48-h exposure to single Hg, HgCl₂ induced a higher mortality rate than MeHgCl. The combined exposure test showed that 0.05-μm PS beads can enhance the toxicity of both the Hg species. The expression of GST-mu, glutathione S-transferease (GST) activity and malondialdehyde (MDA) content increased significantly after exposure to Hg alone (HgCl₂ or MeHgCl) exposure. Combined exposure with PS beads modulated the effects of Hg on the antioxidant system depending on bead size and the Hg species. In particular, the 0.05-μm beads significantly increased the expression level of GST-mu, GST activity and MDA content, regardless of Hg species. These findings suggest that toxicological interactions between Hg and PS beads depend on the type of Hg species and the size of PS beads; nano-sized 0.05-μm PS beads can induce synergistic toxicity with Hg.

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

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

Seasonal trends of mercury bioaccumulation and assessment of toxic effects in Asian clams and microbial community from field study of estuarine sediment

This study investigated seasonal trends in bioaccumulation potential and toxic effects of mercury (Hg) in Asian clams (Corbicula fluminea) and microbial community. For this, a clam-exposure experiment was performed during summer, fall, and winter seasons in four different sites (HS1: control/clean site; HS2, HS3, and HS4: contaminated sites) of Hyeongsan River estuary, South Korea. Total mercury (THg) and methylmercury (MeHg) in whole sediments were highest at HS4 site during fall, sustained similar levels during winter, but decreased during summer. Unlike whole sediment, pore water reported higher levels in summer, and gradually declined during fall and winter. Asian clams from HS4 site collected during summer presented highest bioaccumulations of THg (521.52 μg/kg, dry weight) and MeHg (161.04 μg/kg, dry weight), which also correlated with the higher levels of Hg present in pore water in the same season. Moreover, biota-sediment-pore water accumulation factor (BSpAF) were comparatively greater in clams collected from HS2∼HS4 compared to HS1 sites, suggesting that porewater was a better indicator of accumulation of Hg. Upregulation of biomarker genes responsible for detoxifying process (gsts1), scavenging oxidative stress (cat), and protein reparation (hsp70 and hsp90) were observed in clams collected from HS2∼HS4. The overexpression of these biomarkers implied that Asian clams can be considered as promising warning tools for Hg-contamination. Both bacterial and metabolic diversities were negatively affected by higher levels of THg and MeHg. Phylum Proteobacteria was enriched in HS2∼HS4 compared to HS1. In contrast, phylum Bacteroidetes showed a reverse trend. The metabolic profile was highest in HS1 and lowest in HS4, revealing higher stress of Hg in HS4 site. Overall, the outcomes of this field study broaden the information on seasonal trends of bioaccumulation of Hg and its toxic effects. These findings may be helpful in Hg monitoring and management programs in other river systems.

Concurrent water- and foodborne exposure to microplastics leads to differential microplastic ingestion and neurotoxic effects in zebrafish

Organisms constantly ingest microplastics directly from the environment or indirectly via trophic transfer due to the pervasiveness of microplastic pollution. However, most previous studies have only focused on waterborne exposure at the individual level, while few studies have investigated the contribution of trophic transfer to the exposure in organisms. We comprehensively evaluated the differences in microplastic ingestion and toxic effects in zebrafish exposed to microplastics via two concurrent routes (waterborne and foodborne). The polyethylene microplastics (40-47 μm, 0.1-10 mg/L) concentration used here was set in a range closed to the environmentally relevant microplastic concentrations, especially considering the extreme high concentration scenarios in wastewater. The concentration of microplastics resulting from foodborne exposure (0.01±0.01 μg/mg; 0.1±0.1 particles/mg) was significantly lower than that through waterborne exposure (0.06±0.02 μg/mg; 0.8±0.3 particles/mg), suggesting the ingestion of microplastics in their tissues occurs mainly through direct environmental uptake rather than food chain transfer (though the initial microplastic concentration was 1000 folds lower). However, more sublethal impacts, including the significant abnormal hyperactive swimming behaviour (107±5% induction; p< 0.05), were observed in the foodborne group than waterborne group. Additionally, ingenuity pathway analysis predicted both exposure routes caused obvious nervous system interference but through opposite modes of action. This was further verified by the alteration of neurotransmitter biomarkers that neurotoxicity mechanisms were completely different for the two exposure routes. The neurotoxic effects of microplastics are non-negligible and can exert together through both water- and foodborne exposure routes, which deserves further attention.

Mercury-Induced Oxidative Stress Response in Benthic Foraminifera: An In Vivo Experiment on Amphistegina lessonii

The evaluation of the effects of pollution (e.g., Hg pollution) is a difficult task and relies mostly on biomonitoring based on bioindicators. The application of biomarkers may represent a complementary or alternative approach in environmental biomonitoring. Mercury is known to pose a significant health hazard due to its ability to cross cellular membranes, bioaccumulate, and biomagnify. In the present research, the effects of short-term (i.e., 24 h) Hg exposure in the symbiont-bearing benthic foraminiferal species Amphistegina lessonii are evaluated using several biomarkers (i.e., proteins and enzymes). Mercury leads to significant changes in the biochemistry of cells. Its effects are mainly associated with oxidative stress (i.e., production of reactive oxygen species: ROS), depletion of glutathione (GSH), and alteration of protein synthesis. Specifically, our findings reveal that exposure to Hg leads to the consumption of GSH by GPx and GST for the scavenging of ROS and the activation of antioxidant-related enzymes, including SOD and GSH-enzymes (GST, GSR, GPx, and Se-GPx), that are directly related to a defense mechanism against ROS. The Hg exposure also activates the MAPK (e.g., p-p38) and HSP (e.g., HSP 70) pathways. The observed biochemical alterations associated with Hg exposure may represent effective and reliable proxies (i.e., biomarkers) for the evaluation of stress in A. lessonii and lead to a possible application for the detection of early warning signs of environmental stress in biomonitoring.

Mercury can be transported into marine copepod by polystyrene nanoplastics but is not bioaccumulated: An increased risk?

Plastic pollution is a serious problem in the global marine environment because it can produce negative effects at the biological and ecological levels. Due to large surface-area-to-volume ratio and inherent hydrophobicity, nanoplastics can serve as carriers of contaminants, and may affect their fate and toxicity in marine environments. However, the combined effects of nanoplastics and mercury (Hg) in marine organisms have not been well characterized. In this study, after verifying the ingestion of polystyrene nano-size plastics (PS NPs, 50 nm) by the copepod Tigriopus japonicus and adsorption of Hg to PS NPs, we investigated the effects of PS NPs and Hg exposure (alone or in combination) for 48 h on the copepods. Specifically, a 72-h depuration was performed after 48 h exposure. The results showed that after 48 h exposure, the copepod's Hg concentration was significantly increased in the combined exposure group compared to that in the Hg treatment group, but these differences did not persist following 24 h of depuration. Therefore, PS NPs transported Hg into the copepods but did not promote Hg bioaccumulation. Treatment with PS NPs alone did not induce toxicity in T. japonicus, but co-exposure to PS NPs and Hg resulted in elevated transcription of genes related to energy production, antioxidant response, and detoxification/stress defense when compared with Hg treatment alone, demonstrating the synergistic interaction between PS NPs and Hg. Our findings contribute to a comprehensive understanding about the combined toxicity of nanoplastics and metals and the potential ecological risks of associated with these effects in marine environments.

Fishing in troubled waters: Limited stress response to natural and synthetic microparticles in brown shrimp (Crangon crangon)

Marine invertebrates inhabiting estuaries and coastal areas are exposed to natural suspended particulate matter (SPM) like clay or diatom shells but also to anthropogenic particles like microplastics. SPM concentrations may reach 1 g per liter and more, comprising hundreds of millions of items in the size range of less than 100 μm. Suspension feeders and deposit feeders involuntarily ingest these particles along with their food. We investigated whether natural and anthropogenic microparticles at concentrations of 20 mg L^-1, which correspond to natural environmental SPM concentrations in coastal marine waters, are ingested by the brown shrimp Crangon crangon and whether these particles induce an oxidative stress response in digestive gland tissue. Shrimp were exposed to clay, silica, TiO₂, polyvinyl chloride (PVC), or polylactide microplastics (PLA) for 6, 12, 24, and 48 h, respectively. The activities of the anti-oxidative enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR) were measured. All five particle types were ingested by the shrimp along with food. The presence of the particles in the shrimp stomach was verified by scanning electron microscopy. The activities of the anti-oxidative enzymes did not vary between animals exposed to different types of microparticles and control animals that did not receive particles. The temporal activity differed between the three enzymes. The lack of a specific biochemical response may reflect an adaptation of C. crangon to life in an environment where frequent ingestion of non-digestible microparticles is unavoidable and continuous maintenance of inducible biochemical defense would be energetically costly. Habitat characteristics as well as natural feeding habits may be important factors to consider in the interpretation of hazard and species-specific risk assessment.

In vivo oxidative stress responses of the freshwater basket clam Corbicula javanicus to microplastic fibres and particles

Microplastics have been detected in several aquatic organisms, especially bivalves such as clams, oysters, and mussels. To understand the ecotoxicological implication of microplastic accumulation in biota, it is crucial to investigate effects at the physiological level to identify knowledge gaps regarding the threat posed to the environment and assist decision-makers to set the necessary priorities. Typically, xenobiotics elicit an overproduction of reactive oxygen species in organisms, resulting in oxidative stress and cellular damage when not combated by the antioxidative system. Therefore, the present study aimed to establish the impacts of microplastic particles and fibres on the freshwater basket clam Corbicula javanicus. We measured the oxidative stress responses following microplastic exposure as the specific activities of the antioxidative enzymes glutathione S-transferase and catalase. When exposed to polyester fibres from the fleece jackets, the enzyme activities increased in the clams, while the enzyme activities decreased with high-density polyethylene microplastic fragments from bottle caps. All the exposures showed that the adverse effects on the antioxidative response system were elicited, indicating the negative ecotoxicological implications of microplastic pollution.

Recent advances in toxicological research and potential health impact of microplastics and nanoplastics in vivo

As emerging pollutants, direct and indirect adverse impacts of micro(nano)plastics (MPs/NPs) are raising an increasing environmental concern in recent years due to their poor biodegradability and difficulty in recycling. MPs/NPs can act as carriers of bacteria, viruses, or pollutants (such as heavy metals and toxic organic compounds), and may potentially change the toxicity and bioavailability of pollutants. Ingested or attached MPs/NPs can also be transferred from low-trophic level organisms to high-nutrient organisms or even the human body through the food chain transfer process. This article reviews the emerging field of micro- and nanoplastics on organisms, including the separate toxicity and toxicity of compound after the adsorption of organic pollutants or heavy metals, as well as possible mechanism of toxicological effects and evaluate the nano- and microplastics potential adverse effects on human health. The inherent toxic effects MPs/NPs mainly include the following: physical injury, growth performance decrease and behavioral alteration, lipid metabolic disorder, induced gut microbiota dysbiosis and disruption of the gut's epithelial permeability, neurotoxicity, damage of reproductive system and offspring, oxidative stress, immunotoxicity, etc. Additionally, MPs/NPs may release harmful plastic additives and toxic monomers such as bisphenol A, phthalates, and toluene diisocyanate. The vectors' effect also points out the potential interaction of MPs/NPs with pollutants such as heavy metals, polycyclic aromatic hydrocarbons, organochlorine pesticides, polychlorinated biphenyls, perfluorinated compounds, pharmaceuticals, and polybrominated diphenyl ethers. Nevertheless, these potential consequences of MPs/NPs being vectors for contaminants are controversial.

Oxidative Stress in Far Eastern Mussel Mytilus trossulus (Gould, 1850) Exposed to Combined Polystyrene Microspheres (µPSs) and CuO-Nanoparticles (CuO-NPs)

The ingress of nanoparticles of metal oxides and microfragments of synthetic polymers (microplastics) into a marine environment causes unpredictable consequences. The effects of such particles cannot be predicted due to a lack of ecotoxicological information. In this research, a series of laboratory experiments were conducted on the combined effects of CuO-nanoparticles (CuO-NPs) and polystyrene microspheres (µPSs) on the development of oxidative stress processes in the marine filter-feeder mollusk Mytilus trossulus. Biomarkers of oxidative stress, including the lysosome membrane stability of hematocytes (LMS), the index of antioxidant activity (IAA), the levels of malonaldehyde (MDA) and protein carbonyls (PCs), and DNA damage in digestive gland cells, were measured after 5 days of exposure. Based on a battery of biochemical markers, it was shown that oxidative stress was induced at varying degrees in the experimental mollusks when exposed to CuO-NPs and µPSs both separately and in combination. In contrast, the single-treatment effect on the lysosomal membrane was enhanced by the combined CuO-NPs and µPSs (from 77.14 ± 8.56 to 42 ± 4.26 min). In addition, exposure to both the compounds alone and in combination decreased the IAA (from 22.87 ± 1.25, to 19.55 ± 0.21, 10.73 ± 0.53, and 12.06 ± 1.62 nM/mg protein, respectively). The PC level significantly increased only after CuO-NP exposure (from 0.496 ± 0.02 to 0.838 ± 0.03 μM/mg protein). Furthermore, the results showed that the investigated particles, both alone and in combination, promoted DNA damage in digestive gland cells (from 2.02 ± 0.52 to 5.15 ± 0.37, 18.29 ± 2.14, and 10.72 ± 2.53%, respectively), indicating that these compounds are genotoxic. Overall, the results obtained suggest that oxidative stress is the leading factor in the negative effects of CuO-NPs and µPSs. Considering the exceptional role of genome integrity in the functioning of biological systems, the revealed damages in the DNA molecule structure should be attributed to the most important manifestations of the toxicity of these two forms of marine pollution.

The influence of salinity on the toxicity of remediated seawater

Mercury (Hg) is one of the most hazardous pollutants, due to its toxicity, biological magnification and worldwide persistence in aquatic systems. Thus, new efficient nanotechnologies (e.g. graphene oxide functionalized with polyethyleneimine (GO-PEI)) have been developed to remove this metal from the water. Aquatic environments, in particular transitional systems, are also subjected to disturbances resulting from climate change, such as salinity shifts. Salinity is one of the most relevant factors that influences the distribution and survival of aquatic species such as mussels. To our knowledge, no studies assessed the ecotoxicological impairments induced in marine organisms exposed to remediate seawater (RSW) under different salinity levels. For this, the focus of the present study was to evaluate the effects of seawater previously contaminated with Hg and remediated with GO-PEI, using the species Mytilus galloprovincialis, maintained at three different salinities (30, 20 and 40). The results obtained demonstrated similar histopathological and metabolic alterations, oxidative stress and neurotoxicity in mussels under RSW treatment at stressful salinity conditions (20 and 40) in comparison to control salinity (30). On the other hand, the present findings revealed toxicological effects including cellular damage and histopathological impairments in mussels exposed to Hg contaminated seawater in comparison to non-contaminated ones, at each salinity level. Overall, these results confirm the high efficiency of GO-PEI to sorb Hg from water with no noticeable toxic effects even under different salinities, leading to consider it a promising eco-friendly approach to remediate contaminated water.

Metabolic, cellular and defense responses to single and co-exposure to carbamazepine and methylmercury in Dreissena polymorpha

Carbamazepine (CBZ) and Hg are widespread and persistent micropollutants in aquatic environments. Both pollutants are known to trigger similar toxicity mechanisms, e.g. reactive oxygen species (ROS) production. Here, their effects were assessed in the zebra mussel Dreissena polymorpha, frequently used as a freshwater model in ecotoxicology and biomonitoring. Single and co-exposures to CBZ (3.9 μg L^-1) and MeHg (280 ng L^-1) were performed for 1 and 7 days. Metabolomics analyses evidenced that the co-exposure was the most disturbing after 7 days, reducing the amount of 25 metabolites involved in protein synthesis, energy metabolism, antioxidant response and osmoregulation, and significantly altering cells and organelles' structure supporting a reduction of functions of gills and digestive glands. CBZ alone after 7 days decreased the amount of α-aminobutyric acid and had a moderate effect on the structure of mitochondria in digestive glands. MeHg alone had no effect on mussels' metabolome, but caused a significant alteration of cells and organelles' structure in gills and digestive glands. Single exposures and the co-exposure increased antioxidant responses vs control in gills and digestive glands, without resulting in lipid peroxidation, suggesting an increased ROS production caused by both pollutants. Data globally supported that a higher number of hyperactive cells compensated cellular alterations in the digestive gland of mussels exposed to CBZ or MeHg alone, while CBZ + MeHg co-exposure overwhelmed this compensation after 7 days. Those effects were unpredictable based on cellular responses to CBZ and MeHg alone, highlighting the need to consider molecular toxicity pathways for a better anticipation of effects of pollutants in biota in complex environmental conditions.

Effects of microplastics on the accumulation and neurotoxicity of methylmercury in zebrafish larvae

Microplastics (MPs) and methylmercury (MeHg) have attracted increasing attention due to ubiquitous occurrence and toxicity. This study aimed to investigate whether MPs could absorb MeHg and thus modify its bioconcentration and neurotoxicity in the zebrafish larvae (Danio rerio). The pseudo-second-order model (R² = 0.989) was found to be suitable for describing the adsorption kinetics of MeHg onto MPs. Compared with Freundlich and Temkin models, the Langmuir isotherm model provided a better fit with the experimental data exhibiting a maximum monolayer adsorption capacity of 54.945 mg/g. These results suggested that adsorption occurs mainly by a chemical process dominated by monolayer adsorption. MPs adsorbed MeHg to form MPs/MeHg complex, which was ingested by zebrafish larvae, and promoted accumulation of MeHg. Thus, the presence of MPs aggravated the reduction of locomotor activity induced by MeHg, and downregulation of neurotransmitters related genes, such as ache, gfap and scl1A3b. Metabolome analysis also revealed disrupted glutathione (GSH) metabolism upon exposure of MeHg alone and in combination with MPs, as reflected by the increased in the ratio of GSH and oxidized glutathione. These effects were also confirmed by upregulation of oxidative stress-related genes, such as sod, sod mt and gpx4a. Collectively, these results indicated that MPs could act as a carrier of MeHg and enhance its accumulation in zebrafish, thereby disrupting locomotor activity by excessive oxidative stress. This study provides a scientific basis for improving health risk assessment of environmental pollutants, particularly those potentially able to adsorb to MPs by virtue of their chemical nature.