Perfluorooctanoate and nano titanium dioxide impair the byssus performance of the mussel Mytilus coruscus

Perfluorooctanoate (PFOA) is widely used as a surfactant and has metabolic, immunologic, developmental, and genetic toxicity on marine organisms. However, the effects of PFOA on individual defense functions in mussels in the presence of titanium dioxide nanoparticles (nano-TiO2) are poorly understood. To investigate the defense strategies and regulatory mechanisms of mussels under combined stressors, the thick-shell mussels Mytilus coruscus were exposed to different PFOA concentrations (0, 2 and 200 μg/L) and nano-TiO2 (0 and 0.1 mg /L, size: 25 nm) for 14 days. The results showed that, compared to the control group, PFOA and nano-TiO2 significantly reduced the number of byssal threads (NBT), byssal threads length (BTL), diameter of proximal threads (DPB), diameter of middle threads (DMB), diameter of distal byssal threads (DDB), adhesive plaque area (BPA), and breaking force of byssal threads (N). Under the influence of PFOA and nano-TiO2, the morphological surface smoothness of the fractured byssal threads surface increased, concurrently inducing an increased surface roughness in the adhesive plaques. Additionally, under the presence of PFOA and nano-TiO2, the foot displayed dispersed tissue organization and damaged villi, accompanied by an increased incidence of cellular apoptosis and an upregulation of the apoptosis gene caspase-8. Expression of the adhesion gene mfp-3 and byssal threads strength genes (preCOL-D, preCOL-NG) was upregulated. An interactive effect on the performance of byssal threads is observed under the combined influence of PFOA and nano-TiO2. Under co-exposure to PFOA and nano-TiO2, the performance of the byssal threads deteriorates, the foot structure is impaired, and the genes mRNA expression of byssal thread secretory proteins have compensated for the adhesion and byssal threads strength by up-regulation. Within marine ecosystems, organic and particulate contaminants exert a pronounced effect on the essential life processes of individual organisms, thereby jeopardizing their ecological niche within community assemblages and perturbing the dynamic equilibrium of the overarching ecosystem. ENVIRONMENTAL IMPLICATION: Perfluorooctanoic acid (PFOA) is prone to accumulate in marine organisms. TiO2 nanoparticles (nano-TiO2) are emerging environmental pollutants frequently found in marine environment. The effects of PFOA and nano-TiO2 on marine mussels are not well understood, and their toxic mechanisms remain largely unknown. We investigated the impacts of PFOA and nano-TiO2 on mussel byssus defense mechanisms. By assessing byssus performance indicators, morphological structures of the byssus, subcellular localization, and changes in byssal secretion-related genes, we revealed the combined effects and mechanisms through which these two types of pollutants may affect the functional capabilities and survival of mussels in the complex marine ecosystem.

Nano-TiO2 aggravates immunotoxic effects of chronic ammonia stress in zebrafish (Danio rerio) intestine

Ammonia and nano-TiO₂ are commonly found pollutants in aquatic environments around the world. NH₃ has been proved to be absorbed on nano-TiO₂ surface, therefore, the biosafety and environmental effects of ammonia and co-occurring nano-TiO₂ in aquatic environments has increased considerably in recent years. To explore the potential interactive effects and mechanisms of ammonia and nano-TiO₂ on the intestinal immune system, three-month-old female zebrafish were exposed to total ammonia nitrogen (TAN; 0, 3, 30 mg/L) with or without nano-TiO₂ (1 mg/L) for 60 d. The results showed that intestinal ammonia levels increased with the increase of TAN exposure concentration in the presence of nano-TiO₂. Histopathological analysis demonstrated that both TAN and nano-TiO₂ caused cell vacuolation, lymphocyte infiltration and goblet cells hyperplasia in the intestine mucosa. Our study also found that the contents and gene expression levels of lysozyme (lys) and β-defensin (def-β) in the intestine of zebrafish exposed to TAN alone or combined with nano-TiO₂ were significantly reduced, suggesting a decline in the intestinal innate immunity of fish. A broad upregulation of TLRs-related genes indicated that TAN and nano-TiO₂ could activate TLR4/5-mediated MyD88-dependent pathway, and eventually induce intestinal inflammation. It should be noted that TAN combined with nano-TiO₂ had more significant inhibitory effects on the intestinal structure and innate immune responses than TAN alone. Current data suggested that ammonia and nano-TiO₂ had a synergistic inhibitory effect on intestinal mucosal immunity, and their associated health risk to aquatic animals and the water ecosystem should not be underestimated.

Intestinal response of mussels to nano-TiO2 and pentachlorophenol in the presence of predator

With the development of industry, agriculture and intensification of human activities, a large amount of nano-TiO₂ dioxide and pentachlorophenol have entered aquatic environment, causing potential impacts on the health of aquatic animals and ecosystems. We investigated the effects of predators, pentachlorophenol (PCP) and nano titanium dioxide (nano-TiO₂) on the gut health (microbiota and digestive enzymes) of the thick-shelled mussel Mytilus coruscus. Nano-TiO₂, as the photocatalyst for PCP, enhanced to toxic effects of PCP on the intestinal health of mussels, and they made the mussels more vulnerable to the stress from predators. Nano-TiO₂ particles with smaller size exerted a larger negative effect on digestive enzymes, whereas the size effect on gut bacteria was insignificant. The presence of every two of the three factors significantly affected the population richness and diversity of gut microbiota. Our findings revealed that the presence of predators, PCP, and nano-TiO₂ promoted the proliferation of pathogenic bacteria and inhibited digestive enzyme activity. This research investigated the combined stress on marine mussels caused by nanoparticles and pesticides in the presence of predators and established a theoretical framework for explaining the adaptive mechanisms in gut microbes and the link between digestive enzymes and gut microbiota.

Toxicity enhancement of nano titanium dioxide to Brachionus calyciflorus (Rotifera) under simulated sunlight and the underlying mechanisms

Nano titanium dioxide (nTiO₂) generally shows low toxicity to organisms under light-emitting diode (LED) light. However, nTiO₂ can induce production of reactive oxygen species (ROS) under ultraviolet (UV) light due to its photocatalytic activity. Therefore, it is reasonable to expect the enhancement of nTiO₂ toxicity under sunlight. To test this hypothesis, we compared the toxicity of nTiO₂ to Brachionus calyciflorus under simulated sunlight and LED light. The results showed that the 24 h-LC₅₀ of nTiO₂ to B. calyciflorus under LED light and simulated sunlight were 24.32 (95% CI: 14.54-46.81 mg/L) and 10.44 mg/L (95% CI: 6.74-17.09 mg/L), respectively. Compared with the blank control, treatments with nTiO₂ significantly affected life-table demographic parameters, population growth parameters and swimming linear speed under both simulated sunlight and LED light. However, life expectancy, net reproductive rate, average lifespan, maximal population density, and swimming linear speed in the treatments of nTiO₂ at 0.1, 1, and/or 10 mg/L showed markedly lower values under simulated sunlight than those under LED light, suggesting that simulated sunlight could enhance the toxicity of nTiO₂. In addition, markedly higher catalase (CAT) activity and malondialdehyde (MDA) content but lower glutathione (GSH) content were observed in treatment with 10 mg/L nTiO₂ under simulated sunlight than that under LED light. The results showed that compared with LED light, simulated sunlight significantly induced more oxidative stress in the presence of nTiO₂, and the ROS production was mainly localized to the corona and digestive tract of rotifers by confocal laser scanning microscope. Exposure to 10-50 μM of vitamin C, that is an effective ROS scavenger, could rescue the swimming linear speed of rotifers to the normal level in the blank control. These results suggested that oxidative damages on cell membrane might be the vital mechanism underlying the toxicity enhancement of nTiO₂ to rotifers under simulated sunlight. Thus, the previous publications under LED light may underestimate the real toxicity and environmental risk of nTiO₂ in natural conditions.

Differential in vivo hemocyte responses to nano titanium dioxide in mussels: Effects of particle size

Titanium dioxide nanoparticles (TiO₂ NPs) are widely used in various products and inevitably released with different sizes and forms into aquatic environment. The purpose of this study was to assess the differential immune toxicity of TiO₂ NPs with size difference on mussel hemocytes using flow cytometry (FCM) assays. Hemocyte parameters, including total hemocyte count (THC), hemocyte mortality (HM), phagocytosis activity (PA), lysosomal content (LC), esterase activity (EA), mitochondrial number (MN), mitochondrial membrane potential (MMP) and reactive oxygen species content (ROS) were evaluated in the mussels Mytilus coruscus exposed to two types of TiO₂ NPs (25nm & 100nm: 0.1, 1, 10 mg/L, respectively). In general, size- and concentration-dependent toxicity was pronounced with 25nm-NP and highest concentration (10mg/L) being the most toxic. Alhough a slight recovery from the TiO₂ exposure was observed, significant carry-over effects were still detected. These results highlight the importance of differential size effects of metal oxide NPs on toxicity mechanisms in aquatic animals.

Functional, thermal, and antimicrobial properties of soluble soybean polysaccharide biocomposites reinforced by nano TiO2

This study describes a new polysaccharide-based bionanocomposite developed through solvent casting. Different concentrations (i.e., 0%, 1%, 3%, and 5% (w/w)) of nano titanium dioxide (TiO2-N) were incorporated into soluble soybean polysaccharide (SSPS), and the functional properties of the resultant SSPS films were estimated. Incorporation of TiO2-N into the SSPS matrix decreased water vapor permeability from 7.41 to 4.44 × (10(-11)gm(-1) s(-1) Pa(-1)) and oxygen permeability from 202 to 98 (cm(3)μmm(-2) d(-1) atm(-1)). Moisture content also decreased, the glass transition temperature increased, and the mechanical properties and heat seal strength of the SSPS films improved. SSPS bionanocomposite films showed excellent antimicrobial activity against Escherichia coli and Staphylococcus aureus. In summary, TiO2-N shows potential use as a filler in SSPS-based films for the food and non-food industries.