The combined effects of phenanthrene and micro-/nanoplastics mixtures on the cellular stress responses of the thick-shell mussel Mytilus coruscus

Fate of microplastics and emerging contaminants: Mechanisms of interactions, bioaccumulation and combined toxicity to aquatic organisms

Microplastics (MPs) pose a major environmental challenge owing to their persistence and interactions with emerging contaminants (ECs). Their co-occurrence raises concerns about combined effects on aquatic ecosystems. MPs transport hydrophobic pollutants, affecting water quality. Studies show MPs can adsorb ECs at concentrations up to 106 times higher than their natural levels, increasing bioavailability. MPs and ECs accumulate in aquatic organisms, with evidence of trophic transfer. Their combined toxicity is often greater than their individual effects, causing physiological stress, reduced survival rates and microbial alterations, including enhanced antibiotic resistance. Beyond aquatic ecosystems, MPs and ECs pose risks to human health via bioaccumulation in the food chain. This review analyzes the mechanisms of interactions between MPs and ECs, including uptake, accumulation, and toxicity in aquatic organisms. These findings highlight the need for an integrated environmental impact assessment. Finally, future research directions are proposed, emphasizing key parameters to advance understanding in this field.

Unraveling the toxic trio: Combined effects of thifluzamide, enrofloxacin, and microplastics on Mytilus coruscus

The presence of pesticides, antibiotics, and microplastics in aquatic environments poses a significant threat because of their persistence and potential harm to aquatic life and human health. However, few studies have explored their combined effects on bioaccumulation and toxicity in edible bivalves. This study examined the bioaccumulation and toxicological impacts of thifluzamide (TF) and enrofloxacin (ENR) on oxidative stress, neurotoxicity, detoxification, and metabolism in Mytilus coruscus after 4 weeks of exposure at the environmental level. The findings indicated that coexposure to TF and ENR or the presence of microplastic polystyrene (PS) increased TF and ENR accumulation in mussels and caused oxidative damage, as evidenced by elevated catalase and glutathione transferase activities and increased malondialdehyde (MDA) levels. Notably, compared with single exposures, coexposure to PS+TF, PS+ENR, or TF+ENR generally increased the MDA content, reduced acetylcholinesterase activity, and increased detoxification gene expression. Metabolomic analysis revealed that TF, ENR, and PS, either alone or combined, significantly disrupted multiple metabolic pathways by altering levels of glycerophospholipids, eicosanoids, amino acids, and nucleotides. Coexposure particularly worsened glycerophospholipid and arachidonic acid metabolism disturbances. These results suggest that combined exposure to TF, ENR or PS exacerbated the ecotoxicological effects of TF and ENR on M. coruscus. Taken together, the results of the present study could enhance our understanding of the environmental effects resulting from multipollutant interactions and their potential risks to seafood security.

Diurnal temperature variation exacerbates the effects of phenanthrene on Trochus pyramis Born in a warmer ocean

Under global change scenarios, rising seawater temperature could affect the toxicity of chemical pollutants on marine organisms. Tropical species inhabiting coastal areas are especially vulnerable to diurnal temperature variation (DTV), yet the impacts of DTV on pollutant toxicity remains obscured. This study evaluated how a 4℃ DTV affects the toxicity of phenanthrene (PHE) on the physiological traits of Trochus pyramis, a key herbivorous gastropod in coral reef ecosystems, under both control (28°C) and elevated temperature (31°C) conditions. T. pyramis were exposed to PHE (1 and 10 μg/L) across different temperature scenarios for 14 days. Subsequently, PHE bioaccumulation, heat tolerance, antioxidant responses, and energy budgets of T. pyramis were assessed. The results showed that PHE had minimal effect on T. pyramis under DTV at 28°C, likely due to enhanced antioxidant responses and adaptive energy supply strategies induced by DTV. Conversely, DTV exacerbated the deleterious effect of PHE at 31°C, particularly under exposure to high-concentration PHE (10 μg/L), leading to reduced heat tolerance, suppressed antioxidant responses, and disturbed energy metabolism. These results underscore the necessity of incorporating DTV into PHE risk assessments for coral reef ecosystems in the context of global warming.

Could Mussel Populations Be Differentially Threatened by the Presence of Microplastics and Related Chemicals?

Mussels serve as indicators of anthropogenic chemical pollution; however, the effects of microplastics and plastic-related chemicals on their health performance remain an emerging issue. In this study, mussels were exposed to a polyamide (PA; 5 μg/L) and tricresyl phosphate (TCP; 1 μg/L) for 28 days. The exposures to the two contaminants were performed independently or in combination and lasted 28 days. The results showed that the independent exposure altered enzyme activities more significantly than the combined one. Exposure to the PA significantly (p < 0.05) inhibited the antioxidant enzyme catalase (CAT) by 43.5% and the neurotransmitter enzyme acetylcholinesterase (AChE) by 40.6%, while TCP specifically inhibited carboxylesterase (CE) activity by 38.5%, all in respect to the solvent control. When both pollutants were combined, most biomarker responses were similar to control levels. To further investigate if the mussels' response to contaminants (here, chemical compounds only) could be population-specific, a comparative study between Atlantic and Mediterranean mussels was included. Firstly, baseline detoxification defenses were contrasted in the digestive glands of each mussel population, followed by an assessment of in vitro responses to a wide range of plastic additives. The results revealed that Mediterranean mussels expressed higher baseline activities for most detoxification enzymes, although the in vitro sensitivity to the targeted chemicals was similar in both populations. Of all the plastic additives tested, TCP significantly inhibited CE activity both in vivo and in vitro. The in vitro screening also indicated that other plastic additives could act as strong inhibitors of CE. However, additional in vivo exposures in mussels are needed to confirm CE suitability as a biomarker of these chemical exposures. All together, these results also suggest critical population-level differences in susceptibility to microplastic pollution, highlighting a need for targeted conservation efforts.

Mixtures of polystyrene micro and nanoplastics affects fat and glucose metabolism in 3T3-L1 adipocytes and zebrafish larvae

Microplastics (MPs) and nanoplastics (NPs) are pervasive pollutants that pose a hazard to human health. Although most previous studies have investigated the effects of MPs and NPs on digestion, oxidative stress, and inflammation in diverse models, the combined effect of plastic mixtures (PM) containing MPs and NPs on obesity and type 2 diabetes mellitus (T2DM) remains unknown. The hypothesis of our study is to verify the association between PM exposure and clinical features of metabolic diseases such as lipogenesis and insulin resistance. Therefore, we investigated the effects of PM on fat and glucose metabolism in 3T3-L1 cells and high-fat diet (HFD)-induced zebrafish larvae. PM exposure increased cell viability, differentiation, adipogenesis (PPARγ and C/EBPα), and lipogenesis (FAS and SREBP-1c), while it decreased glucose uptake and inhibited insulin signal (IRS1, PI3K, AKT, and GLUT4) expression 3T3-L1 cells. In zebrafish larvae, PM mainly bioaccumulated in the intestine and pancreatic tissue, reducing glucose uptake and increasing body weight and blood glucose compared to controls. Moreover, PM significantly increased adipogenic differentiation (PPARγ) and synthesis (FASN and FABP), proinflammatory cytokines (TNF-α and IL-6), and gluconeogenesis (PCK1 and G6Pase). Conversely, energy and fat metabolism (AMPKα and adiponectin), insulin production (INSα), signaling pathway (IRS1, AKT, and GLUT2), and anti-inflammatory cytokines (IL-10 and IL-4) were suppressed. Overall, this study sheds light on the mechanisms responsible for the detrimental effects of PM exposure on fat and glucose metabolism, providing insights into metabolic disorders, like type 2 diabetes, in both in vitro and in vivo models.

Effects of microplastics on typical macrobenthos in sargassum ecosystems

Recently, microplastics (MPs) have attracted extensive attention to their wide distribution and potential toxicity in ecosystems. However, there was a lack of research focused on MPs in seaweed bed ecosystems. This study investigated the distribution and toxicity of MPs in macrobenthos in Sargassum ecosystem. According to the in-situ investigation results, the abundance of MPs in the sediment was 0.9-2.3 items/g, the indoor microcosmic experiment was constructed. After exposure to MPs (0, 2, and 20 items/g) for 30 days, the abundance of MPs in macrobenthos exhibits a concentration-dependent increase. However, there was no significant bioaccumulation of MPs at the trophic level. The indoor toxicity test revealed that MPs induced oxidative stress and altered intestinal microflora composition in macrobenthos, even at actual environmental concentrations (2 items/g). It may result in a perturbation of the organism's homeostatic equilibrium. High-concentration (20 items/g) MPs had a greater impact on alkaline phosphatase (AKP) in Mollusks. The increase in AKP activity could be indicative of an adaptive mechanism in some macrobenthos while the decline in AKP activity might signal a decrease in their survival. These results elucidated the fate of MPs in ecosystem and the ecological risks of MPs to large benthic animals on model environmental conditions.

Toxic effect of mussel Mytilus galloprovincialis exposed to Ag-TiO2 and ZnTi2O4-TiO2 bicomponent nanoparticles

Nanoparticles (NPs) are widely used in various fields, including antifouling paints for ships and industrial structures submerged in water. The potential impact of NPs on aquatic organisms, particularly their potential toxicity, is a significant concern, as their negative impact has been relatively poorly studied. In this study, we evaluated the effect of different concentrations of bimetallic Ag-TiO₂ and ZnTi₂O₄-TiO₂ NPs, which could potentially be used in antifouling coatings, on the hemocytes of the Mediterranean mussel Mytilus galloprovincialis. Hemocytes were exposed to NPs at concentrations of 0.1-1 mg/L for 1 and 2 h, and the production of reactive oxygen species (ROS), levels of DNA damage, and number of dead cells were measured. Exposure to Ag-TiO₂ NPs at 1 mg/L concentration for 1 h suppressed ROS production in hemocytes and reduced the relative number of agranulocytes in cell suspensions, without inducing DNA damage or cell death. Exposure to ZnTi2O4-TiO2 NPs did not cause changes in the ratio of granulocytes to agranulocytes in suspensions, nor did it affect other functional parameters of hemocytes. However, after a 2 h exposure period, ZnTi2O4-TiO2 NPs (1 mg/L) significantly reduced the production of ROS by hemocytes. These findings suggest that Ag-TiO2 and ZnTi2O4-TiO2 NPs have low acute toxicity for marine bivalves.

Biodegradation of polystyrene (PS) and polypropylene (PP) by deep-sea psychrophilic bacteria of Pseudoalteromonas in accompany with simultaneous release of microplastics and nanoplastics

Plastics dumped in the environment are fragmented into microplastics by various factors (UV, weathering, mechanical abrasion, animal chewing, etc.). However, little is known about plastic fragmentation and degradation mediated by deep-sea microflora. To obtain deep-sea bacteria that can degrade plastics, we enriched in situ for 1 year in the Western Pacific using PS as a carbon source. Subsequently, two deep-sea prevalent bacteria of the genus Pseudoalteromonas (Pseudoalteromonas lipolytica and Pseudoalteromonas tetraodonis) were isolated after 6 months enrichment in the laboratory under low temperature (15 °C). Both showed the ability to degrade polystyrene (PS) and polypropylene (PP), and biodegradation accelerated the generation of micro- and nanoplastics. Plastic biodegradation was evidenced by the formation of carboxyl and carboxylic acid groups, heat resistance decrease and plastic weight loss. After 80 days incubation at 15 °C, the microplastic concentration of PS and PP could be up to 1.94 × 107/L and 5.83 × 107/L, respectively, and the proportion of nanoplastics (< 1 μm) could be up to 65.8 % and 73.6 %. The film weight loss were 5.4 % and 4.5 % of the PS films, and 2.3 % and 1.8 % of the PP films by P. lipolytica and P. tetraodonis, respectively; thus after discounting the weight loss of microplastics, the only 3.9 % and 2.8 % of the PS films, and 1.3 % and 0.7 % of the PP films, respectively, were truly degraded by the two bacteria respectively after 80 days of incubation. This study highlights the role of Pseudoalteromonas in fragmentation and degradation of plastics in cold dark pelagic deep sea.

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.

Nano-scale and micron-scale plastics amplify the bioaccumulation of benzophenone-3 and ciprofloxacin, as well as their co-exposure effect on disturbing the antioxidant defense system in mussels, Perna viridis

Plastics ranging from nano-scale to micron-scale are frequently ingested by many marine animals. These particles exhibit biotoxicity and additionally perform as vectors that convey and amass adsorbed chemicals within organisms. Meanwhile, the frequency of detection of the benzophenone-3 and ciprofloxacin can be adsorbed on plastic particles, then accumulated in bivalves, causing biotoxicity. To understand their unknown accumulative kinetics in vivo affected by different plastic sizes and toxic effect from co-exposure, several scenarios were set up in which the mode organism were exposed to 0.6 mg/L of polystyrene carrying benzophenone-3 and ciprofloxacin in three sizes (300 nm, 38 μm, and 0.6 mm). The live Asian green mussels were chosen as mode organism for exposure experiments, in which they were exposed to environments with plastics of different sizes laden with benzophenone-3 and ciprofloxacin, then depurated for 7 days. The bioaccumulation and depuration kinetics of benzophenone-3 and ciprofloxacin were measured using HPLC-MS/MS after one week of exposure and depuration. Meanwhile, their toxic effect were investigated by measuring the changes in six biomarkers (condition index, reactive oxygen species, catalase, glutathione, lipid peroxidation, cytochrome P450 and DNA damage). The bioconcentration factors in mussels under different exposure conditions were 41.48-111.75 for benzophenone-3 and 6.45 to 12.35 for ciprofloxacin. The results suggested that microplastics and nanoplastics can act as carriers to increase bioaccumulation and toxicity of adsorbates in mussels in a size-dependent manner. Overproduction of reactive oxygen species caused by microplastics and nanoplastics led to increased DNA damage, lipid peroxidation, and changes in antioxidant enzymes and non-enzymatic antioxidants during exposure. Marked disruption of antioxidant defenses and genotoxic effects in mussels during depuration indicated impaired recovery. Compared to micron-scale plastic with sizes over a hundred micrometers that had little effect on bivalve bioaccumulation and toxicity, nano-scale plastic greatly enhanced the biotoxicity effect.