Oxidative stress induced by titanium dioxide nanoparticles increases under seawater acidification in the thick shell mussel Mytilus coruscus

Diving into the metabolic interactions of titanium dioxide nanoparticles in "Sparus aurata" and "Ruditapes philippinarum"

The biological response to nanomaterials exposure depends on their properties, route of exposure, or model organism. Titanium dioxide nanoparticles (TiO2 NPs) are among the most used nanomaterials; however, concerns related to oxidative stress and metabolic effects resulting from their ingestion are rising. Therefore, in the present work, we addressed the metabolic effects of citrate-coated 45 nm TiO2 NPs combining bioaccumulation, tissue ultrastructure, and proteomics approaches on gilthead seabream, Sparus aurata and Japanese carpet shell, Ruditapes philippinarum. Sparus aurata was exposed through artificially contaminated feeds, while R. philippinarum was exposed using TiO2 NPs-doped microalgae solutions. The accumulation of titanium and TiO2 NPs in fish liver is associated with alterations in hepatic tissue structure, and alteration to the expression of proteins related to lipid and fatty acid metabolism, lipid breakdown for energy, lipid transport, and homeostasis. While cellular structure alterations and the expression of proteins were less affected than in gilthead seabream, atypical gill cilia and microvilli and alterations in metabolic-related proteins were also observed in the bivalve. Overall, the effects of TiO2 NPs exposure through feeding appear to stem from various interactions with cells, involving alterations in key metabolic proteins, and changes in cell membranes, their structures, and organelles. The possible appearance of metabolic disorders and the environmental risks to aquatic organisms posed by TiO2 NPs deserve further study.

Bio-based microplastic polylactic acid exerts the similar toxic effects to traditional petroleum-based microplastic polystyrene in mussels

Microplastics (MPs) have accumulated in the oceans, causing adverse effects on marine organisms and the environment. Biodegradable polylactic acid (PLA) is considered as an excellent substitute for traditional petroleum-based plastics, but it is difficult to degrade completely and easily become MPs in the marine environment. To test the ecological risk of bio-based PLA, we exposed thick-shelled mussels (Mytilus coruscus) to bio-based PLA and petroleum-based polystyrene (PS) (at 102, 104, and 106 particles/L) for 14 days. The significant increase in enzyme activities related to oxidative stress and immune response showed that mussels were under physiological stress after MP ingestion. While enzyme activities of nerve conduction and energy metabolism were significantly disturbed after exposure. Meanwhile, normal physiological activities in respiration, ingestion and assimilation were also suppressed in association with enzyme changes. The negative effects of PS and PLA in mussels were not differentiated, and further integration analysis of integrated biomarker response (IBR) and principal component analysis (PCA) also showed that PLA would induce adverse effects in mussels and ecological risks as PS, especially at environmental concentrations. Therefore, it is necessary to pay more attention to the environmental and ecological risk of bio-based MP PLA accumulating in the marine environment.

Differential toxic effects of nano-titanium dioxide on clams (Meretrix meretrix) with various individuality

Nano-TiO2 is inevitably released into aquatic environment with increasing of nanotechnology industries. Study pointed that different individuality showed divergent behavioral and physiological response when facing environmental stress. However, the effects of nano-TiO2 on tolerance of bivalves with different individualities remain unknown. In the study, clams were divided into two types of individuality - proactive and reactive by post-stress recovery method. It turned out that proactive individuals had quicker shell opening level, stronger burrowing behavior, faster feeding recovery, higher standard metabolic rate and more rapid ammonia excretion ability than reactive individuals after exposed to air. Then, the survival rate, hemocytes response and oxidase activity of classified clams were evaluated after nano-TiO2 exposure. Results showed that after 30 d exposure, proactive individuals accelerated burrowing behavior with higher survival rate. Moreover, proactive clams had better adaptability and less hemocytes response and oxidative damage than reactive clams. The study highlights the individualities of marine shell fish determine individual capacity to adapt to environmental changes, play important roles in aquaculture and coastal ecosystem health.

Antioxidant-related enzymes and peptides as biomarkers of metallic nanoparticles (eco)toxicity in the aquatic environment

Increased awareness of the impact of human activities on the environment has emerged in recent decades. One significant global environmental and human health issue is the development of materials that could potentially have negative effects. These materials can accumulate in the environment, infiltrate organisms, and move up the food chain, causing toxic effects at various levels. Therefore, it is crucial to assess materials comprising nano-scale particles due to the rapid expansion of nanotechnology. The aquatic environment, particularly vulnerable to waste pollution, demands attention. This review provides an overview of the behavior and fate of metallic nanoparticles (NPs) in the aquatic environment. It focuses on recent studies investigating the toxicity of different metallic NPs on aquatic organisms, with a specific emphasis on thiol-biomarkers of oxidative stress such as glutathione, thiol- and related-enzymes, and metallothionein. Additionally, the selection of suitable measurement methods for monitoring thiol-biomarkers in NPs' ecotoxicity assessments is discussed. The review also describes the analytical techniques employed for determining levels of oxidative stress biomarkers.

Cytotoxicity and Genotoxicity Effects of a Magnetic Zeolite Composite in Daphnia magna (Straus, 1820)

Zeolite type 5A combined with the magnetic properties of maghemite nanoparticles facilitate the rapid absorption of heavy metals, which makes them an interesting proposal for the remediation of water contaminated with lead and arsenic. However, the physicochemical analysis related to concentration and size for the use of this magnetic zeolite composite (MZ0) in water bodies and the possible toxicological effects on aquatic fauna has not yet been carried out. The main objective of the research work is to determine lethal concentrations that cause damage to Daphnia magna based on LC50 tests, morphology, reproductive rate, and quantification of the expression of three genes closely involved in the morphological development of vital structures (Glass, NinaE, Pph13). To achieve this objective, populations of neonates and young individuals were used, and results showed that the LC50 for neonates was 11,314 mg L-1, while for young individuals, it was 0.0310 mg L-1. Damage to morphological development was evidenced by a decrease in eye size in neonates, an increase in eye size in young individuals, variations in the size of the caudal spine for both age groups, and slight increases in the heart size, body, and antenna for both age groups. The reproductive rate of neonates was not affected by the lower concentrations of MZ0, while in young individuals, the reproductive rate decreased by more than 50% from the minimum exposure concentration of MZ0. And for both ages, Glass gene expression levels decreased as the MZ0 concentration increased. Also, the MZ0 evidenced its affinity for the exoskeleton of D. magna, which was observed using both light microscopy and electron microscopy. It is concluded that MZ0 did not generate significant damage in the mortality, morphology, reproductive rate, or gene expression in D. magna at lower concentrations, demonstrating the importance of evaluating the possible impacts on different life stages of the cladoceran.

Assessing the in vivo toxicity of titanium dioxide nanoparticles in Schmidtea mediterranea: uptake pathways and (neuro)developmental outcomes

Titanium dioxide nanoparticles (TiO2-NPs) in aquatic environments, originating from urban run-off, product use and post-consumer degradation, interact with aquatic organisms through water and sediments. Thorough toxicity assessment requires comprehensive data across all ecosystem compartments especially the benthic zone, which is currently lacking. Moreover, a proper physicochemical characterization of the particles is needed before and during toxicity assessment. In the present work, we used the planarian Schmidtea mediterranea to investigate the effects of TiO2-NPs (5 mg/L and 50 mg/L). Planarians are benthic organisms that play an important role in the food chain as predators. Our study integrated particle characterization with toxicokinetic and toxicodynamic parameters and showed that the uptake of TiO2-NPs of 21 nm occurred through the epidermis and intestine. Epidermal irritation and mucus production occurred immediately after exposure, and TiO2-NPs induced stronger effects in regenerating organisms. More specifically, TiO2-NPs interfered with neuroregeneration, inducing behavioral effects. A delay in the formation of the anterior commissure between the two brain lobes after seven and nine days of exposure to 50 mg/L was observed, probably as a result of a decrease in stem cell proliferation. Our findings underscore the need to incorporate multiple exposure routes in toxicity screenings. Additionally, we highlight the vulnerability of developing organisms and recommend their inclusion in future risk assessment strategies.

Differential intestinal effects of water and foodborne exposures of nano-TiO2 in the mussel Mytilus coruscus under elevated temperature

With the wide use of nanomaterials in daily life, nano-titanium dioxide (nano-TiO2) presents potential ecological risks to marine ecosystems, which can be exacerbated by ocean warming (OW). However, most previous studies have only centered around waterborne exposure, while there is a scarcity of studies concentrating on the impact of trophic transfer exposure on organisms. We investigated the differences in toxic effects of 100 μg/L nano-TiO2 on mussels via two pathways (waterborne and foodborne) under normal (24 °C) and warming (28 °C) conditions. Single nano-TiO2 exposure (waterborne and foodborne) elevated the superoxide dismutase (SOD) and catalase (CAT) activities as well as the content of glutathione (GSH), indicating activated antioxidatant response in the intestine. However, depressed antioxidant enzymes and accumulated peroxide products (LPO and protein carbonyl content, PCC) demonstrated that warming in combination with nano-TiO2 broke the prooxidant-antioxidant homeostasis of mussels. Our findings also indicated that nano-TiO2 and high temperature exhibited adverse impacts on amylase (AMS), trypsin (PS), and trehalase (THL). Additionally, activated immune function (lysozyme) comes at the cost of energy expenditure of protein (decreased protein concentration). The hydrodynamic diameter of nano-TiO2 at 24 °C (1693-2261 nm) was lower than that at 28 °C (2666-3086 nm). Bioaccumulation results (range from 0.022 to 0.432 μg/g) suggested that foodborne induced higher Ti contents in intestine than waterborne. In general, the combined effects of nano-TiO2 and warming demonstrated a more pronounced extent of interactive effects and severe damage to antioxidant, digestive, and immune parameters in mussel intestine. The toxicological impact of nano-TiO2 was intensified through trophic transfer. The toxic effects of nano-TiO2 are non-negligible and can be exerted together through both water- and foodborne exposure routes, which deserves further investigation.

Reduced toxic effects of nano‑copper sulfate in comparison of bulk CuSO4 on biochemical parameters in the Rohu (Labeo rohita)

Considering the wide application of nanoparticles in various fields of life and growing concern regarding their toxic effects, the present study was designed with the aim to evaluate the potential risks of using copper sulfate nanoparticles (CuSO4-NPs) in comparison to bulk form. Nanoparticles of CuSO4, having mean size of 73 nm were prepared by ball milling method, and fingerlings of Labeo rohita were exposed to two levels, 20 and 100 μg L-1 of CuSO4 in both bulk and nano forms for 28 days and their comparative effects on the metallothioneins (MTs), heat shock proteins 70 (HSP 70), lipid profile, cholesterol (CHOL) and triglyceraldehyde (TG) levels, activities of some metabolic enzymes Alanine transaminase (ALT), Aspartate transaminase (AST) Akaline phosphatase (ALP), and genes expressions of HSP-70, TNF-α and IL1-ß were investigated. CuSO4 showed the concentration and particle type dependent effects. The over expression of HSPs and MTs, significant decreases in CHOL, TG, low density lipid (LDL) levels and ALP activity, while significant increases in high density lipid (HDL)level as well as ALT and AST activities and HSP-70, TNF-α and IL1-β expressions were observed in response to higher concentration of both bulk and nano form of copper sulfate. At lower concentration (20 μg L-1), however, only bulk form showed toxicity. Thus, low concentrations of CuSO4-NPs pose negligible threat to freshwater fish.

The physiological responses to titanium dioxide nanoparticles exposure in pearl oysters (Pinctada fucata martensii)

To evaluate the physiological responses to titanium dioxide nanoparticles exposure in pearl oysters (Pinctada fucata martensii), pearl oysters were exposed for 14 days to different levels (0.05, 0.5, and 5 mg/L) of nano-TiO2 suspensions, while a control group did not undergo any nano-TiO2 treatment. And then recovery experiments were performed for 7 days without nano-TiO2 exposure. At days 1, 3, 7, 14, 17, and 21, hepatopancreatic tissue samples were collected and used to examine the activities of protease, amylase, lipase, catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), lysozyme (LYS), alkaline phosphatase (AKP), and acid phosphatase (ACP). The microstructure of the nacreous layer in shell was also analyzed by scanning electron microscopy. Results showed that pearl oysters exposed to 5 mg/L of TiO2 nanoparticles had significantly lower protease, amylase, and lipase activities and significantly higher CAT, SOD, GPx, LYS, ACP, and AKP activities than control pearl oysters did even after 7-day recovery (P-values <0.05). Pearl oysters exposed to 0.5 mg/L or 0.05 mg/L of TiO2 nanoparticles had lower protease, amylase, and lipase activities and higher CAT, SOD, GPx, LYS, ACP, and AKP activities than control pearl oysters did during the exposure period. After 7-day recovery, no significant differences in protease, lipase, SOD, GPx, CAT, ACP, AKP, or LYS activities were observed between pearl oysters exposed to 0.05 mg/L of TiO2 nanoparticles and control pearl oysters (P-values >0.05). In the period from day 7 to day 14, indistinct and irregular nacreous layer crystal structure in shell was observed. This study demonstrates that TiO2 nanoparticles exposure influences the levels of digestion, immune function, oxidative stress, and biomineralization in pearl oysters, which can be partially and weakly alleviated by short-term recovery. These findings contribute to understanding the mechanisms of action of TiO2 nanoparticles in bivalves. However, studies should evaluate whether a longer recovery period can restore to their normal levels in the future.

Effects of elevated temperature and different crystal structures of TiO2 nanoparticles on the gut microbiota of mussel Mytilus coruscus

Coastal habitats are exposed to increasing pressure of nanopollutants commonly combined with warming due to the seasonal temperature cycles and global climate change. To investigate the toxicological effects of TiO2 nanoparticles (TiO2 NPs) and elevated temperature on the intestinal health of the mussels (Mytilus coruscus), the mussels were exposed to 0.1 mg/L TiO2 NPs with different crystal structures for 14 days at 20 °C and 28 °C, respectively. Compared to 20 °C, the agglomeration of TiO2 NPs was more serious at 28 °C. Exposure to TiO2 NPs led to elevated mortality of M. coruscus and modified the intestinal microbial community as shown by 16S rRNA sequence analysis. Exposure to TiO2 NPs changed the relative abundance of Bacteroidetes, Proteobacteria and Firmicutes. The relative abundances of putative mutualistic symbionts Tenericutes and Fusobacteria increased in the gut of M. coruscus exposed to anatase, which have contributed to the lower mortality in this group. LEfSe showed the combined stress of warming and TiO2 NPs increased the risk of M. coruscus being infected with potential pathogenic bacteria. This study emphasizes the toxicity differences between crystal structures of TiO2 NPs, and will provides an important reference for analyzing the physiological and ecological effects of nanomaterial pollution on bivalves under the background of global climate change.

Characterization of oxidative damage induced by nanoparticles via mechanism-driven machine learning approaches

The wide application of TiO₂-based engineered nanoparticles (nTiO₂) inevitably led to release into aquatic ecosystems. Importantly, increasing studies have emphasized the high risks of nTiO₂ to coastal environments. Bivalves, the representative benthic filter feeders in coastal zones, acted as important roles to assess and monitor the toxic effects of nanoparticles. Oxidative damage was one of the main toxic mechanisms of nTiO₂ on bivalves, but the experimental variables/nanomaterial characteristics were diverse and the toxicity mechanism was complex. Therefore, it was very necessary to develop machine learning model to characterize and predict the potential toxicity. In this study, thirty-six machine learning models were built by nanodescriptors combined with six machine learning algorithms. Among them, random forest (RF) - catalase (CAT), k-neighbors classifier (KNN) - glutathione peroxidase (GPx), neural networks - multilayer perceptron (ANN) - glutathione s-transferase (GST), random forest (RF) - malondialdehyde (MDA), random forest (RF) - reactive oxygen species (ROS), and extreme gradient boosting decision tree (XGB) - superoxide dismutase (SOD) models performed good with high accuracy and balanced accuracy for both training sets and external validation sets. Furthermore, the best model revealed the predominant factors (exposure concentration, exposure periods, and exposure matrix) influencing the oxidative stress induced by nTiO₂. These results showed that high exposure concentrations and short exposure-intervals tended to cause oxidative damage to bivalves. In addition, gills and digestive glands could be vulnerable to nTiO₂-induced oxidative damage as tissues/organs differences were the important factors controlling MDA activity. This study provided insights into important nano-features responsible for the different indicators of oxidative stress and thereby extended the application of machine learning approaches in toxicological assessment for nanoparticles.

Shipping can be achieved but cargo arrives with damage - titanium dioxide nanoparticles affect the DNA of Pacific oyster sperm

Titanium dioxide nanoparticles (TiO₂ NP) were reported to be reprotoxic in humans and fish. However, the effects of these NP on the reproduction of marine bivalves, namely oysters, remain unknown. Thus, a short-term (1 h) direct exposure of sperm of the Pacific oyster (Crassostrea gigas) to two TiO₂ NP concentrations (1 and 10 mg.L-1) was performed, and sperm motility, antioxidant responses, and DNA integrity were evaluated. Although no changes occurred in sperm motility and the activities of the antioxidants, the genetic damage indicator increased at both concentrations, demonstrating that TiO₂ NP affects the DNA integrity of oyster sperm. Although DNA transfer can happen, it does not fulfill its biological mission since the transferred DNA is not intact and may compromise the reproduction and recruitment of the oysters. This vulnerability of C. gigas sperm towards TiO₂ NP highlights the importance of studying the effects of NPs exposure to broadcast spawners.

Assessment of combined algal toxicity of TiO2 nanoparticles and organochlorines in karst surface waters

The widespread use of nanoparticles (NPs) and organic pollutants increases the risk of their coexistence in the aquatic environments. It is uncertain how the combined toxicities of NPs and OCs affect aquatic organisms in surface waters. In this study, the binary combined toxicities of TiO₂ NPs with three different organochlorines (OCs)-pentachlorobenzene (PeCB), 3,3,4,4-tetrachlorobiphenyl (PCB-77), and atrazine on Chlorella pyrenoidosa in three karst surface water bodies were investigated. The correlation analysis results indicated that the toxicities of TiO₂ NPs and OCs to algae were mainly related to the total organic carbon (TOC) and ionic strength of surface water. Surface water relieved the growth inhibition of the pollutants on algae as compared with ultrapure water (UW). The combined toxic effect caused by the co-exposure of TiO₂ NPs-atrazine was synergistic and had an antagonistic effect for TiO₂ NPs-PCB-77 in four types of water bodies. However, the co-exposure of TiO₂ NPs-PeCB had an additive effect in the Huaxi Reservoir (HX) and synergistic effects in Baihua Lake (BH), Hongfeng Lake (HF), and UW. TiO₂ NPs increased the bioaccumulation of OCs by algae. Both PeCB and atrazine significantly increased the bioaccumulation of TiO₂ NPs by algae, except for PeCB in HX; however, PCB-77 reduced the bioaccumulation of TiO₂ NPs by algae. The toxic effects of TiO₂ NPs and OCs on algae in different water bodies were the result of the nature of the pollutants, bioaccumulation, hydrochemical properties, and other factors.

Combined toxic effects of TiO2 nanoparticles and organochlorines on Chlorella pyrenoidosa in karst area natural waters

With the discharge of nanoparticles (NPs) into the environment, NPs can interact with coexisting organic pollutants, resulting in combined toxic effects. In order to more realistically evaluate the potential toxic effects of NPs and coexisting pollutants on aquatic organisms. We evaluated the combined toxicities of TiO₂ nanoparticles (TiO₂ NPs) and three different organochlorines(OCs)-pentachlorobenzene (PeCB), 3,3',4,4'-tetrachlorobiphenyl (PCB-77) and atrazine to algae (Chlorella pyrenoidosa) in three karst natural waters. The results indicate that the individual toxicities of TiO₂ NPs and OCs in natural waters were less than those of OECD medium, and the combined toxicities were different from but generally similar to those of OECD medium. The individual and combined toxicities were the largest in UW. The correlation analysis showed that the toxicities of TiO₂ NPs and OCs were mainly related to TOC, ionic strength, Ca²⁺ and Mg²⁺ in natural water. The binary combined toxicities of PeCB and atrazine with TiO₂ NPs to algae were synergistic. The binary combined toxicity of TiO₂ NPs and PCB-77 to algae was antagonistic. The presence of TiO₂ NPs increased the algae-accumulations of OCs. PeCB and atrazine all increased the algae-accumulations of TiO₂ NPs, while PCB-77 showed the opposite result. The above results indicated that due to the influence of different hydrochemical properties in karst natural waters, there were differences between TiO₂ NPs and OCs in their toxic effects, structural and functional damage, and bioaccumulation.

Potential risks of CO2 removal project based on carbonate pump to marine ecosystem

The development of marine carbon sequestration project has an important potential for carbon neutralization in the short-term (several decades). Marine carbon sequestration technology is based on biological and carbonate pumps to increase particulate organic carbon and authigenic insoluble carbonates to the deep sea or seafloor, aiming to achieve permanent carbon sequestration. Particularly, chemical carbon sequestration technology based on carbonate pump is proposed and considered to achieve short-term marine carbon sequestration in recent years. This technology mainly includes alkaline mineral addition and combining CO₃^2- to insoluble carbonates to improve marine carbon fixation capacity. Potential marine ecosystem risks of chemical CO₂ removal method should be considered before being a feasible technology. We reviewed the potential effects of marine chemical carbon sequestration project on marine organisms. Marine chemical carbon sequestration had two main effects on marine organisms: released chemicals effect, and particle effect. Released chemicals in mineral weathering directly affected phytoplankton and bacteria community. Particles formed during carbon sequestration process mainly affected filter feeding organisms. The toxic effects of particles on aquatic organisms increased with decreasing sizes and increasing concentrations of particle. Algae and crustaceans were the most sensitive groups exposed to metal nanoparticles (nm-μm) in seawaters, thus could be used as target species to evaluate ecological risk of small particles generated in chemical carbon sequestration project. Embryos or larva of filter feeding organisms were more sensitive to large clay and metal microparticles (μm‑mm) than adults, thus could be used as sensitive groups to establish safety concentration of large particles. The relatively inert metal nanoparticles and microparticles had higher safety concentrations than active ones. These particle concentration thresholds could be as a reference to design concentrations and initial sizes of applied minerals in marine chemical carbon sequestration project. This will ensure that the ecological risk is minimized when carbon fixation efficiency is maximized.

Changes in energy reserves and responses of some biomarkers in freshwater mussels exposed to metal-oxide nanoparticles

In this study, responses of various biomarkers in the digestive gland and foot muscle of freshwater mussels (Unio tigridis) were investigated following exposure to Al₂O₃, CuO and TiO₂ nanoparticles (NPs) for 14 days at different concentrations (0, 1, 3 and 9 mg NP/L). Mussels were fed on unicellular algae (Chlorella vulgaris) cultured in the laboratory. NP exposures caused significant increases (p < 0.05) in the levels of total glutathione (GSH), reduced-glutathione (rGSH), oxidized-glutathione (GSSG) and malondialdehyde (MDA) in the digestive gland. Oppositely, there were significant (p < 0.05) decreases in acetylcholinesterase activity in the foot muscles. Total energy reserves of the digestive gland and foot muscle significantly (p < 0.05) decreased, but only at the highest NP exposures. Nevertheless, NP exposures did not alter (p > 0.05) the algae filtering capacity of mussels. This study demonstrated that the biomarkers belonging to different metabolic systems responded to NP exposures, suggesting their usage in the monitoring studies for freshwater systems.

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.

Toxicity of synthesized silver nanoparticles in a widespread fish: A comparison between green and chemical

Metallic nanoparticles are gaining importance in various fields of life due to their large surface area to volume ratio. However, metallic nanoparticles pose different toxic effects on fish when they appear with different shapes and compositions in water. Herein the present study was designed to evaluate the median (LC₅₀) and sub-lethal (1/10th of LC₅₀) concentrations of Ag-Green NPs, 700 μg/L for Ag-Chem NPs, and 50 μg/L for Ag₂O-Chem NPs were confirmed in Hypophthalmichthys molitrix. Furthermore, exposure of H. molitrix fingerlings to 10 % of LC₅₀ concentration of these particles induced significantly higher (p < 0.05) activities of serum alanine transaminase, aspartate aminotransferase, lactate dehydrogenase, white blood cells, acetylcholinesterase and catalase, superoxide dismutase, peroxidase, relative gene expressions of antioxidant enzymes, heat shock protein (Hsp70), hypoxia- inducible factor 1-alpha (HIF-1α) and lipid peroxidase level than the control, but decreased hematological parameters with less effects of Ag-Green NPs than chemically synthesized AgNPs. Moreover, the histopathological study also indicated morphological changes in the liver and gills of treated fish groups. The comparative toxicity evaluation revealed the maximum negative effect of Ag₂O-Chem NPs followed by Ag-Chem NPs while Ag-Green NPs showed the least toxic effects. Based on our results, replacement of chemically synthesized NPs to green synthesized AgNPs can be recommended in large scale application to reduce the noxious effects to aquatic environment.

Toxicokinetics and toxicodynamics of plastic and metallic nanoparticles: A comparative study in shrimp

Nanoplastic is recognized as an emerging environmental pollutant due to the anticipated ubiquitous distribution, increasing concentration in the ocean, and potential adverse health effects. While our understanding of the ecological impacts of nanoplastics is still limited, we benefit from relatively rich toxicological studies on other nanoparticles such as nano metal oxides. However, the similarity and difference in the toxicokinetic and toxicodynamic aspects of plastic and metallic nanoparticles remain largely unknown. In this study, juvenile Pacific white shrimp Litopenaeus vannamei was exposed to two types of nanoparticles at environmentally relative low and high concentrations, i.e., 100 nm polystyrene nanoplastics (nano-PS) and titanium dioxide nanoparticles (nano-TiO₂) via dietary exposure for 28 days. The systematic toxicological evaluation aimed to quantitatively compare the accumulation, excretion, and toxic effects of nano-PS and nano-TiO₂. Our results demonstrated that both nanoparticles were ingested by L. vannamei with lower egestion of nano-TiO₂ than nano-PS. Both nanoparticles inhibited the growth of shrimps, damaged tissue structures of the intestine and hepatopancreas, disrupted expression of immune-related genes, and induced intestinal microbiota dysbiosis. Nano-PS exposure caused proliferative cells in the intestinal tissue, and the disturbance to the intestinal microbes was also more serious than that of nano-TiO₂. The results indicated that the effect of nano-PS on the intestinal tissue of L. vannamei was more severe than that of nano-TiO₂ with the same particle size. The study provides new theoretical basis of the similarity and differences of their toxicity, and highlights the current lack of knowledge on various aspects of absorption, distribution, metabolism, and excretion (ADME) pathways of nanoplastics.

Nano-ecotoxicology in a changing ocean

The ocean faces an era of change, driven in large by the release of anthropogenic CO2, and the unprecedented entry of pollutants into the water column. Nanomaterials, those particles < 100 nm, represent an emerging contaminant of environmental concern. Research on the ecotoxicology and fate of nanomaterials in the natural environment has increased substantially in recent years. However, commonly such research does not consider the wider environmental changes that are occurring in the ocean, i.e., ocean warming and acidification, and occurrence of co-contaminants. In this review, the current literature available on the combined impacts of nanomaterial exposure and (i) ocean warming, (ii) ocean acidification, (iii) co-contaminant stress, upon marine biota is explored. Here, it is identified that largely co-stressors influence nanomaterial ecotoxicity by altering their fate and behaviour in the water column, thus altering their bioavailability to marine organisms. By acting in this way, such stressors, are able to mitigate or elevate toxic effects of nanomaterials in a material-specific manner. However, current evidence is limited to a relatively small set of test materials and model organisms. Indeed, data is biased towards effects upon marine bivalve species. In future, expanding studies to involve other ecologically significant taxonomic groups, primarily marine phytoplankton will be highly beneficial. Although limited in number, the available evidence highlights the importance of considering co-occurring environmental changes in ecotoxicological research, as it is likely in the natural environment, the material of interest will not be the sole stressor encountered by biota. As such, research examining ecotoxicology alongside co-occurring environmental stressors is essential to effectively evaluating risk and develop effective long-term management strategies.

An Integrated Testing Strategy for Ecotoxicity (ITS-ECO) Assessment in the Marine Environmental Compartment using Mytilus spp.: A Case Study using Pristine and Coated CuO and TiO2 Nanomaterials

An integrated testing strategy for ecotoxicity assessment (ITS-ECO) was developed to aid in the hazard and fate assessment of engineered nanomaterials (ENMs) deposited in marine environments using the bivalve Mytilus spp. as a test species. The ENMs copper(II) oxide (CuO) and titanium dioxide (TiO₂ ), either in pristine form (core) or with functionalized coatings (polyethylene glycol [PEG], carboxyl [COOH], and ammonia [NH₃ ]) were selected as case study materials based on their production levels and use. High-throughput in vitro testing in Tier 1 of the ITS-ECO revealed CuO ENMs to elicit cytotoxic effects on lysosomes of hemocytes of mussels, with the hazard potential CuO PEG > CuO COOH > CuO NH₃  > CuO core, whereas TiO₂ ENMs were not cytotoxic. Genotoxicity in hemocytes as well as gill cells of mussels following in vivo exposure (48 h) to CuO ENMs was also seen. Longer in vivo exposures in Tier 2 (48 h-21 days) revealed subacute and chronic oxidative effects for both CuO and TiO₂ ENMs, in some cases leading to lipid peroxidation (core TiO₂ ENMs). In Tier 3 bioaccumulation studies, distinct patterns of uptake for Cu (predominantly in gills) and Ti (predominantly in digestive glands) and between the different core and coated ENMs were found. Clear NM-specific and coating-dependent effects on hazard and fate were seen. Overall, using a tiered testing approach, the ITS-ECO was able to differentiate the hazard (acute, subacute, and chronic effects) posed by ENMs of different compositions and coatings and to provide information on fate for environmental risk assessment of these ENMs. Environ Toxicol Chem 2022;41:1390-1406. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A novel molluscan TLR molecule engaged in inflammatory response through MyD88 adapter recruitment

Toll-like receptors (TLRs) mediated signaling plays a vital role in activating innate and adaptive immunity. Although TLR mediated signaling has been comprehensively investigated in mammalian species, the mechanisms underlying TLR signaling in molluscs remain obscure. In the present study, a novel TLR isoform namely McTLR-like1 was identified in the thick shell mussel Mytilus coruscus. McTLR-like1 was highly expressed in molluscan immune-related tissues, and its transcriptional levels in hemocytes were significantly increased when challenged by V. alginolyticus. McTLR-like1 activated nuclear factor κB (NF-κB) and strengthened the transcription and phosphorylation of NF-κB subunit P65 in mammalian cells. Upon the silencing of McTLR-like1, the mRNA expression levels of pro-inflammatory cytokines were down-regulated, and the animals exhibited higher levels of resistance when challenged with V. alginolyticus. McMyD88a mRNA expression was also downregulated alongside McTLR-like1. Furthermore, GST-pull down assays revealed a visible affinity between McTLR-like1 and McMyD88a. Collectively, these results demonstrated that the newly identified gene affiliated to the molluscan TLR family and plays a role in the TLR-mediated activation of inflammatory response via its affinity with MyD88. The present study enhances our knowledge of TLR signaling mechanisms in molluscs and provides new insights into the evolution of TLRs.

Biochemical response of Ficopomatus enigmaticus adults after exposure to organic and inorganic UV filters

With the increase of UV filters usage and consequent release into aquatic environments, the concerns about their potential ecological risks are also increasing. According to this, in the present study, adult polychaetes of the species Ficopomatus enigmaticus were chronically exposed to three concentrations (0.01, 0.1 and 0.5 mg/L) of organic and inorganic filters (Ethylhexyl methoxycinnamate (EHMC) and nanoparticulate Zinc oxide (nZnO), respectively) in order to analyse biochemical responses related to cellular damage, antioxidant defence, biotransformation mechanisms and, lastly, neurotoxicity. Despite major lipid peroxidation caused by EHMC was observed, both UV filters have produced the same response patterns. In details, a clear concentration-dependent activation of glutathione S-transferases and a significant decrease of acetylcholinesterase levels defined an important neurotoxic effect was observed for both contaminants. These results become important to expand the limited scientific literature on biochemical responses of marine and brackish water invertebrates to organic and inorganic UV filters.

Interactive effects of freshwater acidification and selenium pollution on biochemical changes and neurotoxicity in Oreochromis mossambicus

Effect of selenium and acidification in freshwater environment was assessed solitary but no reports are available on the impacts of both factors act together. In the present study, effects of combined simultaneous exposure to selenium (Se) and low pH were assessed in Mozambique tilapia, Oreochromis mossambicus. Responses were measured based on antioxidant defenses (enzymatic SOD, CAT, GPx and non-enzymatic GSH), biotransformation enzyme (GST), metallothionein levels (MT), oxidative damage (LPO, CP), Na⁺/K⁺-ATPase (NKA) activity in gills and liver tissues and neurotoxicity (acetylcholinesterase, AChE) response in brain tissue. Fish were exposed to combined treatment at different pH levels (7.5, control (optimum pH for tilapia growth); 5.5, low pH) and Se concentrations (0, 10, and 100 μg L^-1). Toxicity levels of Se were not significantly different under control and low pH indicating that pH did not affect Se toxicity. Levels of GSH and MT were enhanced in Se-exposed fish at both pH. Combined effects of high Se concentration and low pH decreased SOD and CAT activities and increased those of GPx and GST. However, organisms were not able to prevent cellular damage (LPO and CP), indicating a condition of oxidative stress. Furthermore, inhibition of Na⁺/K⁺-ATPase activity was showed. Additionally, neurotoxicity effect was observed by inhibition of cholinesterase activity in organisms exposed to Se at both pH conditions. As a result, the combined stress of selenium and freshwater acidification has a slight impact on antioxidant defense mechanisms while significantly inhibiting cholinesterase and Na+/K + -ATPase activity in fish. The mechanisms of freshwater acidification mediating the toxic effects of trace non-metal element on freshwater fish need to investigate further.

The cadmium toxicity in gills of Mytilus coruscus was accentuated by benzo(a)pyrene of higher dose but not lower dose

In natural environment, the existence of interactions of toxic mixtures could induce diverse biochemical pathways and consequently exert different toxicological responses in aquatic organisms. However, little information is available on the effects of combined xenobiotics on lower aquatic invertebrates. Here, we assessed the effects of cadmium (Cd, 0.31 mg/L) as well as the mixture of Cd (0.31 mg/L) and benzo(a)pyrene (Bap, 5 or 50 μg/L) on bioaccumulation, antioxidant, lipid peroxidation (LPO) and metallothionein (MT) responses in gills of thick shell mussel Mytilus coruscus. Upon exposed to single Cd, the metal bioaccumulation, antioxidant enzymes activities, LPO and MT level significantly increased in the gills, suggesting an apparent toxicity to mussels. The interaction of Cd + 5 μg/L Bap did not significantly alter these endpoints compared to single Cd. However, once the dose of Bap elevated to 50 μg/L, the induction of bioaccumulation, antioxidant system and LPO was even more pronounced while the induction of MT was remarkably inhibited, implying an accentuated toxicity. Collectively, the current results demonstrated that 0.31 mg/L Cd exposure resulted in severe toxicity to mussels despite of the induction of MT system to alleviate the metal toxicity. Once the Cd exposure combined with Bap, the lower dose of Bap could not change the Cd toxicity while the higher dose of Bap accentuated the toxicity by inhibiting metallothionein synthesis. These findings might provide some useful clues for elucidation the mechanism of the interaction of combined xenobiotics in molluscs.

Gonadal antioxidant responses to seawater acidification and hypoxia in the marine mussel Mytilus coruscus

This study investigated the combined effects of seawater acidification and hypoxia on the antioxidant response in gonads of the thick shell mussel Mytilus coruscus. Mussels were collected along the Shengsi Island, East China Sea, where oxygen and pH fluctuations frequently occur in summer. Mussels were exposed to three pH (8.1, 7.7, and 7.3) and two dissolved oxygen (DO) levels (6 and 2 mg L^-1) for 21 days followed by a 10-day recovery period (pH 8.1 and DO 6 mg L^-1). Gonad surface area (GSA) and activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), glutathione S-transferase (GST), and malondialdehyde (MDA) in gonad were measured at days 21 and 31. Complex and enzyme-specific responses were observed after the 21-day exposure period. Overall, PCA analysis revealed a stronger effect of pH than DO. Integrated biomarker response (IBR) analysis demonstrated that low pH and DO decreased mussel's antioxidant system and increased oxidative damage with potential consequences for gonad development. Mussels exposed to low pH and DO were only partly able to recover a normal enzymatic activity after 10-day recovery period. This suggests that mussels exposed to short-term pH and DO fluctuations event in the field may suffer lasting negative impacts.

Enhanced immunity and hemocytes proliferation by three immunostimulants in tri-spine horseshoe crab Tachypleus tridentatus

Tachypleus amebocyte lysate (TAL) is crucial in medical testing, but its industry in China has been restricted due to the decline of horseshoe crab population in recent years. Exploring methods of enhancing immunity and rapid hemocytes proliferation is urgent for the industrial horseshoe crab culture. In this study, β-glucan (G), peptidoglycan (P), and squalene (S) were injected to horseshoe crabs at two concentrations (5 and 10 mg/kg), in order to compare their effects on total hemocyte count (THC), reactive oxygen species (ROS), and non-specific immune enzyme activities. Results showed that the THC, superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC) were significantly increased by three immunostimulants at different points of time; ROS was significantly increased except at two squalene groups; lysozyme (LZM) and alkaline phosphatase (AKP) activity were increased except at low dose (5 mg/kg) squalene group; malondialdehyde (MDA) activity was decreased in all treatments; and hemocyanin concentration (HC) changed little during the experiment. At the 48th hour, THC, ROS, SOD, CAT, T-AOC, LZM, and AKP activities were significantly higher in the two peptidoglycan groups than those in the control group; the low dose β-glucan and squalene groups showed significantly higher SOD and CAT, but their THC and AKP were not significantly different from those of the control group. In general, all three immunostimulants stimulated the hemolymph parameters of horseshoe crabs, notably, peptidoglycan could significantly increase the THC and enzyme activities, suggesting that peptidoglycan can be developed as an efficient immunostimulant for horseshoe crabs.

Does the photocatalytic activity of nanoparticles protect the marine mussel Mytilus galloprovincialis from polycyclic aromatic hydrocarbon toxicity?

In the present study, five NPs (containing ZnO, Au-ZnO, Cu-ZnO, TiO₂, and Au-TiO₂) were characterized using dynamic light scattering and transmission electron microscopy, in order to observe their behavior under environmental change. The applicability of NPs for degradation of three polycyclic aromatic hydrocarbons (PAHs), including benzo(a)pyrene, fluoranthene, and benzanthracene, using UV irradiation showed the high photocatalytic efficiency of doped NPs for the removal of the study pollutants. To predict the environmental impact and interaction between NPs and PAHs on marine organisms, Mytilus galloprovincialis mussels were exposed to concentrations of each chemical (50 and 100 μg/L) for 14 days. The mussel's response was determined using the oxidative stress biomarker approach. Measured biomarkers in the mussel's digestive gland showed possible oxidative mechanisms in a concentration-dependent manner occurring after exposure to PAHs and NPs separately. Overall, this finding provides an interesting combination to remove PAHs in water, and the incorporation of chemical element into the crystallographic structure of NPs and the combination of two different NPs to form a binary hybrid NPs are promising materials.

Toxic effects of nano-TiO2 in bivalves-A synthesis of meta-analysis and bibliometric analysis

Since the beginning of the 21st century, the increasing production and application of nano-TiO₂ in consumer products have inevitably led to its release into aquatic systems and therefore caused the exposure of aquatic organisms, resulting in growing environmental concerns. However, the safety of nano-TiO₂ in aquatic environments has not been systematically assessed, especially in coastal and estuary waters where a large number of filter-feeding animals live. Bivalves are considered around the world to be a unique target group for nanoparticle toxicity, and numerous studies have been conducted to test the toxic effects of nano-TiO₂ on bivalves. The aim of this review was to systematically summarize and analyze published data concerning the toxicological effects of nano-TiO₂ in bivalves. In particular, the toxicity of nano-TiO₂ to the antioxidant system and cell physiology was subjected to meta-analysis to reveal the mechanism of the toxicological effects of nano-TiO₂ and the factors affecting its toxicological effects. To reveal the cooperation, hot keywords and co-citations in this field, bibliometric analysis was conducted, and the results showed that the toxicological molecular mechanisms of nano-TiO₂ and the combined effects of nano-TiO₂ and other environmental factors are two major hot spots. Finally, some perspectives and insights were provided in this review for future research on nano-TiO₂ toxicology in bivalves.

Physiological effects of plastic particles on mussels are mediated by food presence

Plastic particles cause toxic effects on marine organisms but whether food particles can affect the toxic effects of plastic particles on filter feeding animals remains unknown. To evaluate the intake and physiological effects of different size particles and their exposure ways, the thick shell mussels Mytilus coruscus were exposed to polystyrene (PS) nanoplastics (NPs, 70 nm) and microplastics (MPs, 10 µm) respectively for two weeks by mixing NPs/MPs with microalgae or exposed to MNPs individually after feeding. Intake of particles and their physiological effects including energy budget, digestive enzymes and oxidative responses were assessed after exposure. Results indicated food presence mediate the effects while MPs decrease the energy budget and increase the catalase activity and malondialdehyde levels. Moreover, exposure way significantly affected energy budget and size of particle had a significant impact on enzyme activities. Our results showed MPs induce more significant effects than NPs on mussels, emphasized the importance of particle exposure way and suggested that mixture exposure with microalgae alleviate the influences on mussels caused by plastic particles alone. This study emphasized that we need to take the food particles into account for evaluating the toxic effects of plastic particles on filter feeding animals in the natural environment.

Mild Effects of Sunscreen Agents on a Marine Flatfish: Oxidative Stress, Energetic Profiles, Neurotoxicity and Behaviour in Response to Titanium Dioxide Nanoparticles and Oxybenzone

UV filters are potentially harmful to marine organisms. Given their worldwide dissemination and the scarcity of studies on marine fish, we evaluated the toxicity of an organic (oxybenzone) and an inorganic (titanium dioxide nanoparticles) UV filter, individually and in a binary mixture, in the turbot (Scophthalmus maximus). Fish were intraperitoneally injected and a multi-level assessment was carried out 3 and 7 days later. Oxybenzone and titanium dioxide nanoparticles induced mild effects on turbot, both isolated and in mixture. Neither oxidative stress (intestine, liver and kidney) nor neurotoxicity (brain) was found. However, liver metabolic function was altered after 7 days, suggesting the impairment of the aerobic metabolism. An increased motility rate in oxybenzone treatment was the only behavioural alteration (day 7). The intestine and liver were preferentially targeted, while kidney and brain were unaffected. Both infra- and supra-additive interactions were perceived, with a toxicodynamic nature, resulting either in favourable or unfavourable toxicological outcomes, which were markedly dependent on the organ, parameter and post-injection time. The combined exposure to the UV filters did not show a consistent increment in toxicity in comparison with the isolated exposures, which is an ecologically relevant finding providing key information towards the formulation of environmentally safe sunscreen products.

Do males and females respond differently to ocean acidification? An experimental study with the sea urchin Paracentrotus lividus

Seawater pH lowering, known as ocean acidification, is considered among the major threats to marine environment. In this study, post-spawning adults of the sea urchin Paracentrotus lividus were maintained at three pH values (8.0, 7.7, 7.4) for 60 days. Physiological, biochemical, cellular, behavioural and reproductive responses were evaluated in males and females. Significant differences between sexes were observed, with higher ammonia excretion and lower catalase activity in males. Respiration rate (after 21 days), catalase activity in gonads and total coelomocyte count showed the same increasing trend in males and females under low pH. Ammonia excretion, gonadosomatic index and lysozyme activity exhibited opposite responses to low pH, with an increasing trend in males and decreasing in females. Results demonstrated that exposure to low pH could result in different response strategies of male and female sea urchins at a physiological, biochemical and immunological level. Reduced female gonadosomatic index under low pH suggested decreased energy investment in reproduction.

Engineered metal nanoparticles in the marine environment: A review of the effects on marine fauna

There is an increasing awareness of how damaging pollutants in the marine environment can be, however information on the effects of metal engineered nanoparticles (ENPs) on marine biota is still insufficient, despite an exponential rising in related publications in recent years. In order to provide an integrated insight on the present state of the art on metal ENP-related ecotoxicology studies on marine fauna, this review aimed to: (i) highlight the means of toxicity of metal ENPs in the marine environment, (ii) identify the principal biotic and abiotic factors that may alter metal ENP toxicity, and (iii) analyse and categorize results of these studies, including accumulation, molecular and histological biomarkers, genotoxicity and behavioural changes. Data retrieved from Scopus yielded 134 studies that met pre-established criteria. Most often, the target ENPs were titanium, zinc, copper or silver, and most studies (61.2%) focused on the phylum Mollusca. The degree of toxicity of metal ENPs was often dependent on the concentrations tested, length of exposure and the type of tissue sampled. Effects from simple tissue accumulation to DNA damage or behavioural alterations were identified, even when concentrations below environmentally available levels were used. It is proposed that other phyla besides the traditional Mollusca (and within it Bivalvia) should be used more often in this kind of studies, that exact pathways of toxicity be further explored, and lastly that co-stressors be used in order to best mimic conditions observed in nature. In this review, the current knowledge on engineered metal nanoparticles and their effects on marine fauna was summarized, highlighting present knowledge gaps. Guidelines for future studies focusing on under-developed subjects in ENP toxicology are also briefly provided.

The Nrf2 molecule trigger antioxidant defense against acute benzo(a)pyrene exposure in the thick shell mussel Mytilus coruscus

The NF-E2-related factor 2 (Nrf2), an ubiquitous, evolutionarily conserved transcription factor, acts as a major sensor of oxidative stress in cells. In the present study, a Nrf2 homolog was newly identified in the thick shell mussel Mytilus coruscus. Accordingly, its functional role in antioxidant defense in response to acute benzo(a)pyrene (Bap) exposure was assessed. The newly identified McNrf2 affiliated to traditional Nrf2 family through Blast, multiple alignment and phylogenetic analysis. After acute exposure to Bap, antioxidants including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathine reductase (GR) were significantly induced in gills and digestive glands at both mRNA and enzymatic levels, and the expression of McNrf2 mRNA was also up-regulated. The analysis of correlating the expression of McNrf2 and the mRNA levels of these antioxidant genes showed positive ties, indicating that Nrf2 was needed for protracted induction of such genes. Further, the recombinant McNrf2 was produced through pET-32a prokaryotic system. After 50 μg/L Bap exposure, ROS generation and LPO level in gills of Nrf2 over-expressed mussels significantly decreased compared to Nrf2 wild-type mussels, as well as reduced ROS production in digestive glands. Collectively, these results show that Nrf2 pathway can provide protection from oxidative stress triggered by Bap in the thick shell mussel.

Rethinking Nano-TiO2 Safety: Overview of Toxic Effects in Humans and Aquatic Animals

Titanium dioxide nanoparticles (nano-TiO₂ ) are widely used in consumer products, raising environmental and health concerns. An overview of the toxic effects of nano-TiO₂ on human and environmental health is provided. A meta-analysis is conducted to analyze the toxicity of nano-TiO₂ to the liver, circulatory system, and DNA in humans. To assess the environmental impacts of nano-TiO₂ , aquatic environments that receive high nano-TiO₂ inputs are focused on, and the toxicity of nano-TiO₂ to aquatic organisms is discussed with regard to the present and predicted environmental concentrations. Genotoxicity, damage to membranes, inflammation and oxidative stress emerge as the main mechanisms of nano-TiO₂ toxicity. Furthermore, nano-TiO₂ can bind with free radicals and signal molecules, and interfere with the biochemical reactions on plasmalemma. At the higher organizational level, nano-TiO₂ toxicity is manifested as the negative effects on fitness-related organismal traits including feeding, reproduction and immunity in aquatic organisms. Bibliometric analysis reveals two major research hot spots including the molecular mechanisms of toxicity of nano-TiO₂ and the combined effects of nano-TiO₂ and other environmental factors such as light and pH. The possible measures to reduce the harmful effects of nano-TiO₂ on humans and non-target organisms has emerged as an underexplored topic requiring further investigation.

Effect of the UV filter, Benzophenone-3, on biomarkers of the yellow clam (Amarilladesma mactroides) under different pH conditions

This work aimed to investigate effects of the ocean contamination by the sunscreen Benzophenone-3 (BP3) and acidification, caused by CO₂ enrichment, to the yellow clam, Amarilladesma mactroides. Biochemical biomarkers were analyzed in tissues (gills, digestive gland, and mantle) of clams exposed to the environmental concentration of 1 μg/L BP3, at seawater natural pH (pH 8.1) and at lower pH (pH 7.6). The tissues responded in different ways considering their physiological roles. In general, BP3 altered activity of the enzymes, glutathione-S-transferase (GST) and glutathione cysteine ligase (GCL); but mostly increased the level of glutathione (GSH). These effects were enhanced by acidification, without augmenting lipid peroxidation (LPO). Carbonic anhydrase activity (CA) increased after BP3 exposure in the digestive gland and decreased in the gills at pH 7.6, while Ca²⁺-ATPase activity was affected by acidification only. Changing levels of these enzymes can alter shell formation and affect the bivalve maintenance in impacted environments.

Environmental transformation of n-TiO2 in the aquatic systems and their ecotoxicity in bivalve mollusks: A systematic review

Over the past decades, titanium dioxide nanoparticles (n-TiO₂) have been extensively used in several industrial applications and the manufacture of novel consumer products. Although strict regulations have been put in place to limit their release into the aquatic environment, these nanoparticles can still be found at elevated levels within the environment, which can result in toxic effects on exposed organisms and has possible implications in term of public health. Bivalve mollusks are a unique and ideal group of shellfish for the study and monitoring the aquatic pollution by n-TiO₂ because of their filter-feeding behaviour and ability to accumulate toxicants in their tissues. In these animals, exposure to n-TiO₂ leads to oxidative stress, immunotoxicity, neurotoxicity, and genotoxicity, as well as behavioral and physiological changes. This review summarizes the uptake, accumulation, and fate of n-TiO₂ in aquatic environments and the possible interactions between n-TiO₂ and other contaminants such as heavy metals and organic pollutants. Moreover, the toxicological impacts and mechanisms of action are discussed for a wide range of bivalve mollusks. This data underlines the pressing need for additional knowledge and future research plans for the development of control strategies to mitigate the release of n-TiO₂ to the aquatic environment to prevent the toxicological impacts on bivalves and protect public health.

Toxic impacts of rutile titanium dioxide in Mytilus galloprovincialis exposed to warming conditions

Climate change is leading to a gradual increase in the ocean temperature, which can cause physiological and biochemical impairments in aquatic organisms. Along with the environmental changes, the presence of emerging pollutants such as titanium dioxide (TiO₂) in marine coastal systems has also been a topic of concern, especially considering the interactive effects that both factors may present to inhabiting organisms. In the present study, it has been assessed the effects of the presence in water of particles of rutile, the most common polymorph of TiO₂, in Mytilus galloprovincialis, under actual and predicted warming conditions. Organisms were exposed to different concentrations of rutile (0, 5, 50, 100 μg/L) at control (18 ± 1.0 °C) and increased (22 ± 1.0 °C) temperatures. Histopathological and biochemical changes were evaluated in mussels after 28 days of exposure. Histopathological examination revealed similar alterations on mussels' gills and digestive glands with increasing rutile concentrations at both temperatures. Biochemical markers showed that contaminated mussels have an unchanged metabolic capacity at 18 °C, which increased at 22 °C. Although antioxidant defences were activated in contaminated organisms at 22 °C, cellular damage was still observed. Overall, our findings showed that histopathological impacts occurred after rutile exposure regardless of the temperature, while biochemical alterations were only significantly noticeable when temperature was enhanced to 22 °C. Thus, this study demonstrated that temperature rise may significantly enhance the sensitivity of bivalves towards emerging pollutants.

Can water remediated by manganese spinel ferrite nanoparticles be safe for marine bivalves?

In the last few years the use of nanoparticles (NPs) such as the manganese spinel ferrite (MnFe₂O₄) has been increasing, with a vast variety of applications including water remediation from pollutants as metal(oid)s. Although an increasing number of studies already demonstrated the potential toxicity of NPs towards aquatic systems and inhabiting organisms, there is still scarce information on the potential hazard of the remediated water using NPs. The present study aimed to evaluate the ecotoxicological safety of Pb contaminated seawater remediated with MnFe₂O₄, NPs, assessing the toxicity induced in mussels Mytilus galloprovincialis exposed to contaminated seawater and to water that was remediated using MnFe₂O₄, NPs. The results obtained demonstrated that seawater contaminated with Pb, NPs or the mixture of both (Pb + NPs) induced higher toxicity in mussels compared to organisms exposed to Pb, NPs and Pb + NPs after the remediation process. In particular, higher metabolic depression, oxidative stress and neurotoxicity were observed in mussels exposed to contaminated seawater in comparison to mussels exposed to remediated seawater.

New insights on the impacts of e-waste towards marine bivalves: The case of the rare earth element Dysprosium

With the technological advances and economic development, the multiplicity and wide variety of applications of electrical and electronic equipment have increased, as well as the amount of end-of-life products (waste of electrical and electronic equipment, WEEE). Accompanying their increasing application, there is an increasing risk to aquatic ecosystems and inhabiting organisms. Among the most common elements present in WEEE are rare earth elements (REE) such as Dysprosium (Dy). The present study evaluated the metabolic and oxidative stress responses of mussels Mytilus galloprovincialis exposed to an increasing range of Dy concentrations, after a 28 days experimental period. The results obtained highlighted that Dy was responsible for mussel's metabolic increase associated with glycogen expenditure, activation of antioxidant and biotransformation defences and cellular damage, with a clear loss of redox balance. Such effects may greatly impact mussel's physiological functions, including reproduction capacity and growth, with implications for population conservation. Overall the present study pointed out the need for more research on the toxic impacts resulting from these emerging pollutants, especially towards marine and estuarine invertebrate species.

Microplastics impair digestive performance but show little effects on antioxidant activity in mussels under low pH conditions

In the marine environment, microplastic contamination and acidification may occur simultaneously, this study evaluated the effects of ocean acidification and microplastics on oxidative stress responses and digestive enzymes in mussels. The thick shell mussels Mytilus coruscus were exposed to four concentrations of polystyrene microspheres (diameter 2 μm, 0, 10, 10⁴ and 10⁶ particles/L) under two pH levels (7.7 and 8.1) for 14 days followed by a 7-day recovery acclimation. Throughout the experiment, we found that microplastics and ocean acidification exerted little oxidative stress to the digestive gland. Only catalase (CAT) and glutathione (GSH) showed a significant increase along with increased microplastics during the experiment, but recovered to the control levels once these stressors were removed. No significant effects of pH and microplastics on glutathione peroxidase (GPx) and superoxide dismutase (SOD) were observed. The responses of digestive enzymes to both stressors were more pronounced than antioxidant enzymes. During the experiment, pepsin (PES), trypsin (TRS), alpha-amylase (AMS) and lipase (LPS) were significantly inhibited under microplastics exposure and this inhibition was aggravated by acidification conditions. Only PES and AMS tended to recover during the recovery period. Lysozyme (LZM) increased significantly under microplastic exposure conditions, but acidification did not exacerbate this effect. Therefore, combined stress of microplastics and ocean acidification slightly impacts oxidative responses but significantly inhibits digestive enzymes in mussels.

Specific dynamic action of mussels exposed to TiO2 nanoparticles and seawater acidification

Both nanoparticles (NPs) and ocean acidification (OA) pose threats to marine animals as well as marine ecosystems. The present study aims to evaluate the combined effects of NPs and OA on specific dynamic action (SDA) of mussels. The thick shell mussels Mytilus coruscus were exposed to two levels of pH (7.3 and 8.1) and three concentrations of TiO₂ NPs (0, 2.5, and 10 mg L^-1) for 14 days followed by a 7-day recovery period. The SDA parameters, including standard metabolic rate, peak metabolic rate, aerobic metabolic scope, SDA slope, time to peak, SDA duration and SDA, were measured. The results showed that TiO₂ NPs and low pH significantly affected all parameters throughout the experiment. When the mussels were exposed to seawater acidification or TiO₂ NPs conditions, standard metabolic rate, aerobic metabolic scope, SDA slope and SDA significantly decreased, whereas peak metabolic rate, time to peak and SDA duration significantly increased. In addition, interactive effects between TiO₂ NPs and pH were observed in SDA parameters except time to peak and SDA. Therefore, the synergistic effect of TiO₂ NPs and low pH can adversely affect the feeding metabolism of mussels.

Nano-TiO2 impairs digestive enzyme activities of marine mussels under ocean acidification

With the development of nanotechnology and increased nanomaterial application, TiO₂ nanoparticles have been released into the aquatic environment, causing potential ecotoxicological effects on aquatic organisms. Ocean acidification caused by anthropogenic CO₂ is one of the most common environmental stressors, occurring simultaneously with marine contaminants, e.g., nanoparticles. Marine bivalves can accumulate nanoparticles and their digestive functions may be affected. In this study, we investigated the potential influences of TiO₂ nanoparticles on the digestive enzyme activities of marine mussels Mytilus coruscus under ocean acidification. Mussels were exposed to combined treatments with three concentrations of nano-TiO₂ (0, 2.5, 10 mg/L) and two pH values (8.1, 7.3) for 14 days, and then recovered under ambient condition (pH 8.1 and no nanoparticle) for 7 days. Samples were taken on the 1st, 3rd, 7th, 14th, and 21st day, the digestive enzymes, including amylase, pepsin, trypsin, lipase, and lysozyme, were investigated. Our results showed that nano-TiO₂ and low pH had negative effects on amylase, pepsin, trypsin, and lipase, while both of them led an increase in lysozyme activity. Nano-TiO₂ showed greater effects on the digestive capacity of M. coruscus rather than low pH. Moreover, a recovery period of 7 days was not sufficient for these enzymes to fully recover.

Nanosized titanium dioxide UV filter increases mixture toxicity when combined with parabens

To address the concern about the environmental impact of engineered nanoparticles frequently used in the recently marketed personal care and hygiene products (PCPs), we conducted a toxicity assessment and determined the EC₅₀ values of the nanosized inorganic UV filter TiO₂ (nano-TiO₂), as well as those of the organic UV filter oxybenzone (BP3) and three parabens (methyl, propyl, and benzylparaben) present in most PCPs formulation. The bioassays were carried out through standardized toxicity bioassays on two environmentally relevant aquatic species i.e. Daphnia magna and Phaeodactylum tricornutum. For nano-TiO₂ 48 h EC₅₀ on D. magna was 3.09 mgL^-1 and for parabens ranged from 32.52 to 1.35 mgL^-1. The two most toxic compounds on D. magna, nano-TiO₂ and benzylparaben (BzP), were further tested with the algae. For nano-TiO₂ 72 h EC₅₀ value was 2.27 mgL^-1 and for BzP it was 10.61 mgL^-1. In addition, D. magna was exposed to selected binary mixtures of the target compounds i.e. nano-TiO₂+BP3, nano-TiO₂+BzP and BP3+BzP On the endpoint of 48 h, a synergistic action was observed for nano-TiO₂+BP3 and nano-TiO₂+BzP, but an antagonistic effect occurred in the mixture BP3+BzP. These findings suggest that nano-TiO₂ can increase the toxicity of the mixture when combined with other compounds.

A novel invertebrate toll-like receptor is involved in TLR mediated signal pathway of thick shell mussel Mytilus coruscus

Toll-like receptors (TLRs) are the most well studied pattern recognition receptors (PRRs) that play a crucial role in both innate and adaptive immunity in animals. In the present study, a novel toll-like receptor (McTLRj) was identified and characterised in thick shell mussel Mytilus coruscus. McTLRj possessed a signal peptide, a transmembrane domain, leucine-rich repeats and an intracellular Toll/interleukin-1 receptor domain that were conserved in typical TLRs. McTLRj transcripts were constitutively expressed in all of the examined tissues with high expression level in immune-related tissues, and significantly induced in haemocytes upon live Vibrio alginolyticus, lipopolysaccharide, polyinosinic-polycytidylic acid and peptidoglycans challenge. The overexpression of the McTLRj TLR fragment in Drosophila S2 cells could induce the expression of Drosophila attacin A, drosomycin, cecropin A, and metchnikowin expression. The expression of McTLRj was obviously repressed by dsRNA-mediated RNA interference, and downstream TLR pathway factors, such as MyD88a, IRAK4, and TRAF6 were significantly repressed in McTLRj-silenced mussels upon LPS challenge. These results collectively indicated that McTLRj is a TLR family member that may play a potential PRR role in TLR-mediated signalling pathway. This research contributed to the clarification of innate immune response in molluscs.

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.

A novel invertebrate toll-like receptor with broad recognition spectrum from thick shell mussel Mytilus coruscus

Toll-like receptors (TLRs) are a category of most well recognized pattern recognition molecules that act on a vital role in both innate and adaptive immunity. In the present study, a novel toll-like receptor (McTLRw) was identified and characterized in thick shell mussel Mytilus coruscus. McTLRw possesses one intracellular Toll/interleukin-1 (IL-1) receptor (TIR) domain, one transmembrane region (TM), one leucine rich repeat N-terminal domain (LRR_NT) and a few of leucine-rich repeats (LRRs), which all are common in typical TLRs. McTLRw transcripts were constitutively expressed in all examined tissues with higher expression levels in immune related tissues, and were significantly induced in haemocytes with the challenges of live Vibrio alginolyticus, lipopolysaccharide (LPS), peptidoglycans (PGN) and β-glucan (GLU), but not induced by polyinosinic-polycytidylic acid (poly I:C). rMcTLRw exhibited affinity to LPS, PGN and GLU while no affinity to poly I:C. Further, the downstream of TLR signaling pathway myeloid differentiation factor 88a (MyD88a), interleukin-1 receptor-associated kinase-4 (IRAK4) and tumor necrosis factor receptor-associated factor 6 (TRAF6) were significantly repressed in McTLRw silenced mussels while challenged with LPS. These results collectively indicated that McTLRw is one member of TLR family and involved in immune response to against invaders by taking participate in TLR mediated signaling pathway.

The impacts of warming on the toxicity of carbon nanotubes in mussels

With the increased production and research on nanoparticles, the presence of carbon nanotubes (CNTs) in aquatic systems is very likely to increase. Although it has been shown that CNTs may cause toxicity in marine organisms, to our knowledge, the possible impacts under global temperature increase is still unknown. For this reason, biochemical and physiological impacts induced in Mytilus galloprovincialis due to the presence of functionalized multi-walled CNTs (f-MWCNTs) and increased temperature were investigated in the present study. The mussels exposed to increased temperature alone presented higher metabolic capacity and expenditure of glycogen as an energy resource to fuel up defense mechanisms and thus preventing oxidative damage. Contrarily, organisms exposed to f-MWCNTs alone seemed not stressed enough to demonstrate differences in the metabolism capacity. Furthermore, f-MWCNTs seemed not able to significantly activate their antioxidant and biotransformation enzymes, which in turn may led to oxidative damage in the cells especially when organisms were exposed to a warmer temperature. In fact, at higher temperature, the antioxidant response of organisms exposed to f-MWCNTs was not effective and oxidative damage levels were observed. Nevertheless, no additive or synergetic effects were observed when mussels were exposed to both stressors simultaneously.