The effects of zinc nanooxide on cellular stress responses of the freshwater mussels Unio tumidus are modulated by elevated temperature and organic pollutants

Surviving global change: a review of the impacts of drought and dewatering on freshwater mussels

The increase in the frequency and intensity of droughts and heatwaves caused by climate change poses a major threat to biodiversity. In aquatic systems, sedentary species such as freshwater mussels are generally considered more vulnerable to changes in habitat conditions than mobile species such as fish. As mussels provide important ecosystem services, understanding the impacts of drought on freshwater mussels is of particular importance for the management of overall functioning of aquatic ecosystems. We used a comprehensive literature search to provide a systematic overview of direct and indirect effects of drought on freshwater mussels (Bivalvia: Unionida) and an evaluation of mitigation strategies. We found that drought studies were concentrated mostly in the USA, with a focus on the Unionidae family. Topics ranged from the physiological effects of high temperatures, emersion, and hypoxia/anoxia to behavioural and reproductive consequences of drought and the implications for biotic interactions and ecosystem services. Studies spanned all levels of biological organization, from individual responses to population- and community-level impacts and ecosystem-wide effects. We identified several knowledge gaps, including a paucity of trait-based evaluation of drought consequences, limited understanding of thermal and desiccation tolerance at the species level, and the synergistic effects of multiple drought stressors on mussels. Although we found many studies provided suggestions concerning management of populations, habitat conditions, and anthropogenic water use, a systematic approach and testing of recommended mitigation strategies is largely lacking, creating challenges for managers aiming to conserve freshwater mussel communities and populations in light of climate change.

Does the anesthetic tricaine methanesulfonate (MS-222) distort oxidative status parameters in tadpoles?

The effect of anesthesia/euthanasia with ethyl 3-aminobenzoate methanesulfonate (MS-222) on the oxidative status of Hyla arborea tadpoles was examined to determine whether the use of the anesthetic can confound the experimental results of the oxidative stress-based investigation. The experiment was conducted on two groups of tadpoles reared at different temperatures to produce differences in antioxidant capacity between the groups. After development at different temperatures (20 °C and 25 °C), the animals were exposed to different concentrations of MS-222 (0, 0.1, 1, and 5 g/L) for 15 min. The higher temperature decreased catalase activity, glutathione and protein carbonyl levels and increased glutathione reductase activity. The glutathione level and glutathione/thiol-related parameters were significantly changed after MS-222 exposure. However, individuals from the different temperature groups responded differently to the tested anesthetic, pointing to the possible influence of the initial levels of antioxidant capacity. The analysis of the interaction between the factors (temperature and MS-222) confirmed that the anesthetic can confound the results regarding the effects of temperature on the oxidative status parameters. The concentration of 0.1 g/L MS-222 had the lowest influence on the alterations in oxidative status and the results of the effect of temperature. A brief review of the current literature on the use of MS-222 in tadpoles made clear the absence of precise information on anesthetic concentration and exposure time. Similar studies should be repeated and extended to other amphibian species and other factors of interest to provide better guidance on tadpole anesthesia/euthanasia for future experiments that consider oxidative status parameters.

Ecotoxicological effects of zinc oxide nanoparticles (ZnO-NPs) on aquatic organisms: Current research and emerging trends

The rapid advancement of nanotechnology has contributed to the development of several products that are being released to the consumer market without careful analysis of their potential impact on the environment. Zinc oxide nanoparticles (ZnO-NPs) are used in several fields and are applied in consumer products, technological innovations, and biomedicine. In this sense, this study aims to compile existing knowledge regarding the effects of ZnO-NPs on non-target organisms, with the goal of ensuring the safety of human health and the environment. To achieve this objective, a systematic review of the available data on the toxicity of these nanomaterials to freshwater and marine/estuarine aquatic organisms was carried out. The findings indicate that freshwater invertebrates are the most commonly used organisms in ecotoxicological tests. The environmental sensitivity of the studied species was categorized as follows: invertebrates > bacteria > algae > vertebrates. Among the most sensitive species at each trophic level in freshwater and marine/estuarine environments are Daphnia magna and Paracentrotus lividus; Escherichia coli and Vibrio fischeri; Scenedesmus obliquus and Isochrysis galbana; and Danio rerio and Rutilus caspicus. The primary mechanisms responsible for the toxicity of ZnO-NPs involve the release of Zn2+ ions and the generation of reactive oxygen species (ROS). Thus, the biosynthesis of ZnO-NPs has been presented as a less toxic form of production, although it requires further investigation. Therefore, the synthesis of the information presented in this review can help to decide which organisms and which exposure concentrations are suitable for estimating the toxicity of nanomaterials in aquatic ecosystems. It is expected that this information will serve as a foundation for future research aimed at reducing the reliance on animals in ecotoxicological testing, aligning with the goal of promoting the sustainable advancement of nanotechnology.

Subchronic toxicity of iron-selenium nanoparticles on oxidative stress response, histopathological, and nuclear damage in amphibian larvae Rana saharica

In this work, we evaluated the subchronic toxicity of FeSe nanoparticles (NPs) in tadpoles of Rana saharica. Tadpoles were exposed for 1-3 weeks to FeSe NPs at 5 mg/L and 100 mg/L rates. Parameters of oxidative stress were measured in whole larvae, and the micronucleus test was performed on circulating blood erythrocytes. We noted a disturbance of the detoxification systems. Enzymatic and non-enzymatic data showed that exposure to FeSe NPs involved a highly significant depletion of GSH, a significant increase in GST activity, and a lipid peroxidation associated with a highly significant increase in MDA. We also noted a neurotoxic effect characterized by a significant inhibition of AChE activity. A micronucleus test showed concentration-dependent DNA damage. This research reveals that these trace elements, in their nanoform, can cause significant neurotoxicity, histopathologic degeneration, cellular and metabolic activity, and genotoxic consequences in Rana larvae.

Ecotoxicological, ecophysiological, and mechanistic studies on zinc oxide (ZnO) toxicity in freshwater environment

The world has faced climate change that affects hydrology and thermal systems in the aquatic environment resulting in temperature changes, which directly affect the aquatic ecosystem. Elevated water temperature influences the physico-chemical properties of chemicals in freshwater ecosystems leading to disturbing living organisms. Owing to the industrial revolution, the mass production of zinc oxide (ZnO) has been led to contaminated environments, and therefore, the toxicological effects of ZnO become more concerning under climate change scenarios. A comprehensive understanding of its toxicity influenced by main factors driven by climate change is indispensable. This review summarized the detrimental effects of ZnO with a single ZnO exposure and combined it with key climate change-associated factors in many aspects (i.e., oxidative stress, energy reserves, behavior and life history traits). Moreover, this review tried to point out ZnO kinetic behavior and corresponding mechanisms which pose a problem of observed detrimental effects correlated with the alteration of elevated temperature.

Co-exposure of environmental contaminants with unfavorable temperature or humidity/moisture: Joint hazards and underlying mechanisms

In the context of global climate change, organisms in their natural habitats usually suffer from unfavorable climatic conditions together with environmental pollution. Temperature and humidity (or moisture) are two central climatic factors, while their relationships with the toxicity of contaminants are not well understood. This review provides a synthesis of existing knowledge on important interactions between contaminant toxicity and climatic conditions of unfavorable temperature, soil moisture, and air humidity. Both high temperature and low moisture can extensively pose severe combined hazards with organic pollutants, heavy metal ions, nanoparticles, or microplastics. There is more information on the combined effects on animalia than on other kingdoms. Prevalent mechanisms underlying their joint effects include the increased bioavailability and bioaccumulation of contaminants, modified biotransformation of contaminants, enhanced induction of oxidative stress, accelerated energy consumption, interference with cell membranes, and depletion of bodily fluids. However, the interactions of contaminants with low temperature or high humidity/moisture, particularly on plants and microorganisms, are relatively vague and need to be further revealed. This work emphasizes that the co-exposure of chemical and physical stressors results in detrimental effects generally greater than those caused by either stressor. It is necessary to take this into consideration in the ecological risk assessment of both environmental contamination and climate change.

Combined cytotoxicity of ZnO nanoparticles and chlorpyrifos in the rainbow trout, Oncorhynchus mikyss, gonadal cell line RTG-2

The toxicity of ZnO nanoparticles (ZnO NPs) in aquatic organisms has been extensively studied, but little information is available on the effects associated with their interaction with other contaminants. In this context, the in vitro effects of co-exposure of chlorpyrifos (CPF) and ZnO NPs on fish-derived cells were investigated. A selection of concentrations was tested in single and binary exposures: CPF (0.312 - 75 mg/L) and ZnO NPs (10 - 100 mg/L). Cytotoxicity was measured using commonly used cellular endpoints: Alamar Blue/CFDA-AM for viability and plasma membrane integrity, NRU for lysosomal disruption and MTT for mitochondrial function. In addition, specific mechanisms of toxicity for CPF and ZnO NPs were tested: acetylcholinesterase (AChE) activity and ROS generation, respectively. AChE was by far the most sensitive assay for single exposure to CPF. There was no concentration-response relationship for ROS after single exposure to ZnO NPs, but 10 mg/L produced significant effects only for this cellular endpoint. Co-exposure of CPF with 10 m/L of ZnO NPs produced significant effects in almost all endpoints tested, which were enhanced by co-exposure with 100 mg/L of ZnO NPs. AChE testing of additional co-exposures with bulk ZnO, together with the application of the Independent Action (IA) prediction model, which allowed us to draw more in-depth conclusions on the toxicological behavior of the mixture. Synergism was observed at 0.625 mg/L CPF concentration and antagonism at 5 mg/L CPF in mixtures containing 100 mg/L of both ZnO NPs and bulk ZnO. However, more cases of synergism between CPF and ZnO NPs occurred at intermediate CPF concentrations, demonstrating that nano-sized particles have a more toxic interaction with CPF than bulk ZnO. Therefore it can be argued that in vitro assays allow the identification of interaction profiles of NP-containing mixtures by achieving multiple endpoints with a large number of concentration combinations.

Elevated temperature decreases cardiovascular toxicity of nanoplastics but adds to their lethality: A case study during zebrafish (Danio rerio) development

To highlight the key role of global warming on the toxicity of contaminants, the cardiovascular toxicity of nanoparticles (NPs) was estimated in developing zebrafish (Danio rerio) at different exposure temperatures, and the toxicity mechanisms were explored via multi-omic analyses. Polystyrene NPs (50 nm) at 0.1 mg·L^-1 entered zebrafish embryos at 24 h post-fertilization and caused cardiovascular toxicity in the developing zebrafish at 27 ℃. This was explained by the down-regulation of the branched-chain amino acid and insulin signaling pathways owing to induced oxidative stress. Elevated exposure temperatures promoted the accumulation of NPs in developing zebrafish, increased the levels of oxidative stress and enhanced the oxidative phosphorylation rate in mitochondria, thus resulting in an additive effect on the mortality of zebrafish larvae. Notably, elevated exposure temperatures reduced the cardiovascular toxicity of NPs, as the effective concentration of NPs for inhibiting embryonic heartbeat rate increased from 0.1 mg·L^-1 at 27 ℃ to 1.0 mg·L^-1 at 30 ℃. Experiments of transgenic zebrafish Tg(myl7:GFP) and multi-omic analyses revealed that elevated temperatures enhanced the myocardial contractility of larvae, thus reducing the cardiovascular toxicity of NPs. However, the health risks of enhanced myocardial contraction caused by NP exposure at elevated temperatures requires further consideration.

Effects of different oxygen regimes on ecological performance and bioenergetics of a coastal marine bioturbator, the soft shell clam Mya arenaria

Benthic species are exposed to oxygen fluctuations that can affect their performance and survival. Physiological effects and ecological consequences of fluctuating oxygen are not well understood in marine bioturbators such as the soft-shell clam Mya arenaria. We explored the effects of different oxygen regimes (21 days of exposure to constant hypoxia (~4.1 kPa P_O2), cyclic hypoxia (~2.1-~10.4 kPa P_O2) or normoxia (~21 kPa P_O2)) on energy metabolism, oxidative stress and ecological behaviors (bioirrigation and bioturbation) of M. arenaria. Constant hypoxia and post-hypoxic recovery in cyclic hypoxia led to oxidative injury of proteins and lipids, respectively. Clams acclimated to constant hypoxia maintained aerobic capacity similar to the normoxic clams. In contrast, clams acclimated to cyclic hypoxia suppressed aerobic metabolism and activated anaerobiosis during hypoxia, and strongly upregulated aerobic metabolism during recovery. Constant hypoxia led to decreased lipid content, whereas in cyclic hypoxia proteins and glycogen accumulated during recovery and were broken down during the hypoxic phase. Digging of clams was impaired by constant and cyclic hypoxia, and bioirrigation was also suppressed under constant hypoxia. Overall, cyclic hypoxia appears less stressful for M. arenaria due to the metabolic flexibility that ensures recovery during reoxygenation and mitigates the negative effects of hypoxia, whereas constant hypoxia leads to depletion of energy reserves and impairs ecological functions of M. arenaria potentially leading to negative ecological consequences in benthic ecosystems.

Effects of temperature on the toxicity of waterborne nanoparticles under global warming: Facts and mechanisms

Global climate change is predicted to increase the average temperature of aquatic environments. Temperature changes modulate the toxicity of emerging chemical contaminants, such as nanoparticles (NPs). However, current hazard assessments of waterborne NPs seldom consider the influence of temperature. In this review, we gathered and analyzed the effects of temperature on the toxicity of waterborne NPs in different organisms. There was a general decrease in bioavailability with increasing temperature in algae and plants due to NPs aggregation, thus, reducing their toxicities. However, the agglomerated large particles caused by the increase in temperature induce a shading effect and inhibit algal photosynthesis. The toxicity of NPs in microorganisms and aquatic animals increases with increasing temperature. This may be due to the significant influence of high temperature on the uptake and excretion of chemicals across membranes, which increase the production of reactive oxygen species and enhance oxidative damage to organisms. High temperature also affect the formation and composition of a protein corona on NPs, altering their toxicity. Our results provide new insights into the toxicity of NPs in the context of global warming, and highlight the deficiencies of current research on NPs.

Toxicity evaluation of pyraclostrobin exposure in farmland soils and co-exposure with nZnO to Eisenia fetida

Although the toxicity of pyraclostrobin (PYRA) to earthworms in artificial soil is well known, the toxicity of PYRA in farmland soils is yet to be explored in detail. Additionally, with more zinc oxide nanoparticles (nZnO) entering the soil environment, the risk of PYRA co-exposure with nZnO is increasing alarmingly. However, toxicity caused by this co-exposure of PYRA and nZnO is still unknown. Therefore, we assessed the biomarkers responses to reveal the toxicity of PYRA (0.1, 1, 2.5 mg/kg) on earthworms in farmland soils (black soil, fluvo-aquic soil, and red clay) and evaluated the biomarkers responses of Eisenia fetida exposed to PYRA (0.5 mg/kg)/PYRA+nZnO (10 mg/kg). Moreover, transcriptomic analysis was performed on E. fetida exposed to PYRA/PYRA+nZnO for 28 days to reveal the mechanism of genotoxicity. The Integrated Biomarker Responses (IBR) showed PYRA induced more severe oxidative stress and damage to E. fetida in farmland soils than that in artificial soil. The oxidative stress and damage induced by PYRA+nZnO were greater than that induced by PYRA. Transcriptomic analysis showed that PYRA and PYRA+nZnO significantly altered gene expression of both biological processes and molecular functions. These results provided toxicological data for PYRA exposure in three typical farmland soils and co-exposure with nZnO.

A cuvette-compatible Zn2+sensing tool for conventional spectrofluorometers prepared by copolymerization of macrocyclic fluoroionophores on quartz glass surface

We report here the development of a surface-modified quartz glass sheet, which affords an opportunity for converting conventional spectrofluorometers to ion-selective optochemical sensors by placing it diagonally into a photometric cuvette. Moreover, we describe a generalizable technique, which allows the usage of any polymerizable ionophores for developing multiple-use fluorescent chemosensors of various selectivity. A fluorescent bis(acridino)-crown ether containing allyl groups was photocatalytically copolymerized with a methacrylate-acrylamide-based monomer mixture to obtain an ion-selective sensor membrane layer on the surface of the cuvette-compatible glass sheet. This glass membrane-based direct optode enabled the analysis of Zn²⁺above a lower limit of detection of 2.2×10^-7mol·L^-1with an excellent reusability. Limiting factors, like pH and competing ionic or organic agents were thoroughly investigated. Moreover, spiked river-water samples were measured to demonstrate applicability. The proposed sensor placed in any conventional spectrofluorometer provides an innovative method for perturbation-free analysis of Zn²⁺for all the chemists in need of a fast, easy-to-use, portable and regenerable analyzer without the requirement of an analyte-specific instrumentation.

Immune responses to ZnO nanoparticles are modulated by season and environmental temperature in the blue mussels Mytilus edulis

Increased production and release of ZnO nanoparticles (nZnO) can cause toxic effects on marine ecosystems and aquatic organisms. However, nZnO toxicity and its modulation by common environmental stressors such as temperature are not yet fully understood. We examined the responses of immune cells (hemocytes) of the blue mussels (Mytilus edulis) exposed to different concentrations (0, 10, 100 μg l^-1) of nZnO or dissolved zinc combined with two temperatures (ambient (10 °C in winter and 15 °C in summer) and warming (+5 °C above ambient temperature)) in winter and summer for 21 days. In winter mussels, exposure to nZnO induced a strong transcriptomic response in multiple immune and inflammation-related genes, stimulated phagocytosis and hemocyte mortality yet suppressed adhesion capacity of hemocytes. In summer mussels, the immune cell responses to nZnO were blunted. The transcriptional responses of hemocytes to dissolved Zn were qualitatively similar but weaker than the responses to nZnO. In the absence of the toxic stress, +5 °C warming lead to dysregulation of the transcription of key immune-related genes in the summer but not the winter mussels. Seasonal warm acclimatization and additional warming in summer suppressed the nZnO-induced transcriptional upregulation of antimicrobial peptides, Toll-like receptors and the complement system. These findings demonstrate that nZnO act as an immunogen in M. edulis and indicate that +5 °C warming might have detrimental effect on innate immunity of the temperate mussel populations in summer when exposure to pathogens is especially high. Capsule: ZnO nanoparticles act as an immunotoxicant inducing a strong immune response in the mussels which is dysregulated by warming in summer but not in winter.

Nanoparticles: Weighing the Pros and Cons from an Eco-genotoxicological Perspective

The exponential growth of nanotechnology and the industrial production have raised concerns over its impact on human and environmental health and safety (EHS). Although there has been substantial progress in the assessment of pristine nanoparticle toxicities, their EHS impacts require greater clarification. In this review, we discuss studies that have assessed nanoparticle eco-genotoxicity in different test systems and their fate in the environment as well as the considerable confounding factors that may complicate the results. We highlight key mechanisms of nanoparticle-mediated genotoxicity. Then we discuss the reliability of endpoint assays, such as the comet assay, the most favored assessment technique because of its versatility to measure low levels of DNA strand breakage, and the micronucleus assay, which is complementary to the former because of its greater ability to detect chromosomal DNA fragmentation. We also address the current recommendations on experimental design, including environmentally relevant concentrations and suitable exposure duration to avoid false-positive or -negative results. The genotoxicity of nanoparticles depends on their physicochemical features and the presence of co-pollutants. Thus, the effect of environmental processes (e.g., aggregation and agglomeration, adsorption, and transformation of nanoparticles) would account for when determining the actual genotoxicity relevant to environmental systems, and assay procedures must be standardized. Indeed, the engineered nanoparticles offer potential applications in different fields including biomedicine, environment, agriculture, and industry. Toxicological pathways and the potential risk factors related to genotoxic responses in biological organisms and environments need to be clarified before appropriate and sustainable applications of nanoparticles can be established.

Salinity-dependent effects of ZnO nanoparticles on bioenergetics and intermediate metabolite homeostasis in a euryhaline marine bivalve, Mytilus edulis

Engineered nanoparticles including ZnO nanoparticles (nZnO) are important emerging pollutants in aquatic ecosystems creating potential risks to coastal ecosystems and associated biota. The toxicity of nanoparticles and its interaction with the important environmental stressors (such as salinity variation) are not well understood in coastal organisms and require further investigation. Here, we examined the interactive effects of 100 μg l^-1 nZnO or dissolved Zn (as a positive control for Zn²⁺ release) and salinity (normal 15, low 5, and fluctuating 5-15) on bioenergetics and intermediate metabolite homeostasis of a keystone marine bivalve, the blue mussel Mytilus edulis from the Baltic Sea. nZnO exposures did not lead to strong disturbances in energy or intermediate metabolite homeostasis regardless of the salinity regime. Dissolved Zn exposures suppressed the mitochondrial ATP synthesis capacity and coupling as well as anaerobic metabolism and modified the free amino acid profiles in the mussels indicating that dissolved Zn is metabolically more damaging than nZnO. The environmental salinity regime strongly affected metabolic homeostasis and altered physiological and biochemical responses to nZnO or dissolved Zn in the mussels. Exposure to low (5) or fluctuating (5-15) salinity affected the physiological condition, energy metabolism and homeostasis, as well as amino acid metabolism in M. edulis. Generally, fluctuating salinity (5-15) appeared bioenergetically less stressful than constantly hypoosmotic stress (salinity 5) in M. edulis indicating that even short (24 h) periods of recovery might be sufficient to restore the metabolic homeostasis in this euryhaline species. Notably, the biological effects of nZnO and dissolved Zn became progressively less detectable as the salinity stress increased. These findings demonstrate that habitat salinity must be considered in the biomarker-based assessment of the toxic effects of nanopollutants on coastal organisms.

Chemically and Green Synthesized ZnO Nanoparticles Alter Key Immunological Molecules in Common Carp (Cyprinus carpio) Skin Mucus

This study was conducted to compare the effects of commercially available (C) and green synthesized (GS) Zinc oxide nanoparticles (ZnO-NPs) on immunological responses of common carp (Cyprinus carpio) skin mucus. GS ZnO-NPs were generated using Thymus pubescent and characterized by UV–vis diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectroscopy (EDX). Fish (n = 150) were randomly allocated into five groups in triplicate and received a waterborne concentration of 0% (control), 25%, and 50% of LC50 96 h of commercially available (C1 and C2) and green synthesized ZnO-NPs (GS1 and GS2) for 21 days. Results from XRD displayed ZnO-NPs with 58 nm in size and UV-vis DRS, EDX, and FT-IR analysis showed that some functional groups from plant extract bonded to the surface of NPs. The SEM images showed that ZnO-NPs have conical morphology. Acute toxicity study showed a higher dose of LC50_96h for green synthesized ZnO-NPs (78.9 mg.L⁻¹) compared to the commercial source (59.95 mg.L⁻¹). The highest activity of lysozyme and alternative complement activity (ACH50) were found in control and GS1 groups. A significant decrease in alkaline phosphatase activity (ALP) was found in C1 and C2 groups compared to other treatments. Protease activity (P) was significantly decreased in the C2 group compared to the control and GS groups. Total immunoglobulin (total Ig) content was the highest in the control. In addition, total Ig in the GS1 group was higher than GS2. The exposure to ZnO-NPs lowered total protein content in all experimental groups when compared to control. Present findings revealed lower induced immunosuppressive effects by green synthesized ZnO-NPs on key parameters of fish skin mucus.

Common and particular biochemical responses of Unio tumidus to herbicide, pharmaceuticals and their combined exposure with heating

The priority list of freshwater pollutants is increasingly amended by pharmaceuticals. Their impact on the aquatic biota can be modulated by the presence of typical pollutants, like pesticides, and/or abnormal heating. The aim of this study was to elucidate potentially hazardous impact of combined environmental factors on the freshwater mussels by analyzing various sets of biochemical markers. We treated the bivalve molluscs of Unio tumidus with non-steroidal anti-inflammatory drug diclofenac (Dc, 2 nM), calcium antagonist and antihypertensive drug nifedipine (Nf, 2 nM) or organophosphonate glyphosate-based herbicide Roundup MAX (Rn, 79 nM of glyphosate) at 18 °C as well as with the mixture of these substances at 18 °C (Mix) or 25 °C (MixT) during 14 days. The concentrations used were correspondent to the environmentally relevant levels. The biomarkers of stress and toxicity were evaluated in digestive gland, except the lysosomal membrane stability measured in hemocytes. Exposures caused an oxidative stress due to the decreased SOD and GST activities and GSH/GSSG ratio, increased levels of thiobarbituric acid-reactive substances and protein carbonyls (with some exceptions). Dc increased cathepsin D activity in lysosomes. Nf increased lysosomal membrane stability and caspase-3 activity. Rn caused a dramatic distortion of metallo-thiolome due to increased levels of GSH and metallothionein-related thiols (MTSH) as well as depletion of Zn, Cu and Cd in the composition of metallothioneins, and decreased Zn/Cu molar ratio in the tissue. The particular toxicity of Rn was also attested by decreased lysosomal membrane stability and cholinesterase activity. Canonical discriminant analysis separated Rn-, Mix- and MixT-groups from the joint set of C-, Dc- and Nf-groups. Generally, compound-specific effects were expressed in U. tumidus responses to the mixtures, but in MixT-group some effects were particular or extremely strong. Multi-marker approach and integrative analysis proved to be a useful tool for understanding possible future risks to freshwater mussels under a combination of xenobiotics and warming climate.

Season-dependent effects of ZnO nanoparticles and elevated temperature on bioenergetics of the blue mussel Mytilus edulis

Input of ZnO nanoparticles (nZnO) from multiple sources have raised concerns about the potential toxic effects on estuarine and coastal organisms. The toxicity of nZnO and its interaction with common abiotic stressors (such as elevated temperature) are not well understood in these organisms. Here, we examined the bioenergetics responses of the blue mussel Mytilus edulis exposed for 21 days to different concentrations of nZnO or dissolved zinc (Zn²⁺) (0, 10, 100 μg l^-1) and two temperatures (ambient and 5 °C warmer) in winter and summer. Exposure to nZnO had little effect on the protein and lipid levels, but led to a significant depletion of carbohydrates and a decrease in the electron transport system (ETS) activity. Qualitatively similar but weaker effects were found for dissolved Zn. In winter mussels, elevated temperature (15 °C) led to elevated protein and lipid levels increasing the total energy content of the tissues. In contrast, elevated temperature (20 °C) resulted in a decrease in the lipid and carbohydrate levels and suppressed ETS in summer mussels. These data indicate that moderate warming in winter (but not in summer) might partially compensate for the bioenergetics stress caused by nZnO toxicity in M. edulis from temperate areas such as the Baltic Sea.

Biochemical Responses of the Bivalve Mollusk Unio tumidus Inhabiting a Small Power Plant Reservoir on the Dniester River Basin, Ukraine

Hydropower plants (HPPs) can affect the hydrological regime. However, biochemical responses of aquatic animals for the evaluation of this disturbing are not applied yet. The specimens of Unio tumidus were sampled in a reservoir (R) of a small HPP as well as downstream from the dam (DS). Biochemical indexes in the digestive gland and alkali labile phosphates (ALP) in the gonads were examined. The R-mollusks showed low cholinesterase, catalase and caspase-3 activities, and metallothionein concentration, but elevated levels of zinc and copper, oxidized glutathione and protein carbonyls. Concentrations of lactate, pyruvate and ALP, activity of superoxide dismutase and glutathione S-transferase, and lipid peroxidation level were similar in both groups. Integrated biomarker response (IBR/n) index (n = 13) was 2.17 and 0.29 in the R- and DS-groups correspondingly. We suggest that using integrative biological response based on the biochemical markers of bivalve mollusks can be a valid early warning step in assessing 'environmental flow' impact.

Interactive effects of salinity variation and exposure to ZnO nanoparticles on the innate immune system of a sentinel marine bivalve, Mytilus edulis

ZnO nanoparticles (nZnO) are released into the coastal environment from multiple sources, yet their toxicity to marine organisms is not well understood. We investigated the interactive effects of salinity (normal 15, low 5, and fluctuating 5-15) and nZnO (100 μg l-1) on innate immunity of the blue mussels Mytilus edulis from a brackish area of the Baltic Sea. Exposure to ionic Zn (100 μg l-1) was used to test whether the toxic effects of nZnO can be attributed to the potential release of Zn2+. Functional parameters and the expression of key immune-related genes were investigated in the mussels exposed to nZnO or ionic Zn under different salinity regimes for 21 days. nZnO exposures elevated hemocyte mortality, suppressed adhesion, stimulated phagocytosis, and led to an apparent increase in lysosomal volume. At salinity 15, nZnO suppressed the mRNA expression of the Toll-like receptors TLRb and c, C-lectin, and the complement system component C3q indicating impaired ability for pathogen recognition. In contrast, the mRNA levels of an antimicrobial peptide defensin increased during nZnO exposure at salinity 15. At fluctuating salinity (5-15), nZnO exposure increased expression of multiple immune-related genes in hemocytes including the complement system components C1 and C3q, and the Toll-like receptors TLRa, b and c. Low salinity (5) had strong immunosuppressive effects on the functional and molecular immune traits of M. edulis that overshadowed the effects of nZnO. The salinity-dependent modulation of immune response to nZnO cannot be attributed to the differences in the aggregation or solubility of nZnO, and likely reflects the interaction of the toxic effects of nanoparticles and physiological effects of the osmotic stress. These findings have implications for the environmental risk assessment of nanomaterials and the development of the context-specific biomarker baselines for coastal pollution monitoring.

The effects of ZnO nanostructures of different morphology on bioenergetics and stress response biomarkers of the blue mussels Mytilus edulis

Biofouling causes massive economical losses in the maritime sector creating an urgent need for effective and ecologically non-harmful antifouling materials. Zinc oxide (ZnO) nanorod coatings show promise as an antifouling material; however, the toxicity of ZnO nanorods to marine organisms is not known. We compared the toxicity of suspended ZnO nanorods (NR) with that of ZnO nanoparticles (NP) and ionic Zn²⁺ in a marine bivalve Mytilus edulis exposed for two weeks to 10 or 100 μg Zn L^-1 of ZnO NPs, NRs or Zn²⁺, or to immobilized NRs. The multi-biomarker assessment included bioenergetics markers (tissue energy reserves, activity of mitochondrial electron transport system and autophagic enzymes), expression of apoptotic and inflammatory genes, and general stress biomarkers (oxidative lesions, lysosomal membrane stability and metallothionein expression). Exposure to ZnO NPs, NRs and Zn²⁺ caused accumulation of oxidative lesions in proteins and lipids, stimulated autophagy, and led to lysosomal membrane destabilization indicating toxicity. However, these responses were not specific for the form of Zn (NPs, NR or Zn²⁺) and showed no monotonous increase with increasing Zn concentrations in the experimental exposures. No major disturbance of the energy status was found in the mussels exposed to ZnO NPs, NRs, or Zn²⁺. Exposure to ZnO NPs and NRs led to a strong induction of apoptosis- and inflammation-related genes, which was not seen in Zn²⁺ exposures. Based on the integrated biomarker response, the overall toxicity as well as the pro-apoptotic and pro-inflammatory action was stronger in ZnO NPs compared with the NRs. Given the stability of ZnO NR coatings and the relatively low toxicity of suspended ZnO NR, ZnO NR coating might be considered a promising low-toxicity material for antifouling paints.

Joint effects of zinc oxide nanoparticles and chlorpyrifos on the reproduction and cellular stress responses of the earthworm Eisenia andrei

The co-exposure of soil organisms to ZnO nanoparticles (ZnO NPs) and pesticides is likely to take place in agricultural soils. However, the impacts of co-exposure on terrestrial ecosystems are virtually unknown. In this paper, Eisenia andrei was exposed for a 28-day period to serial concentrations of ZnO NPs and/or the organophosphate insecticide chlorpyrifos (CPF) in natural soil, and was evaluated for single and joint effects. Zn and CPF accumulation in earthworm tissue was also determined. In the single assay, ZnO NPs and CPF caused statistical significant effects on survival and growth, but mainly on reproduction. Significant reductions in fecundity and fertility were detected with EC50 values of 278 and 179 mg Zn/kg for ZnO NPs, and of 50.75 and 38.24 mg/kg for CPF, respectively. The most notable effect on biomarkers was the reduction in acetylcholinesterase (AChE) activity caused by CPF, which reflected the neurotoxicity of this compound. The results of the combined assay indicated that co-exposure to ZnO NPs and CPF increased adverse effects in E. andrei. According to the independent action model, the binary mixtures showed a synergism (a stronger effect than expected from single exposures) on earthworm reproduction, which became up to 84% higher than the theoretically predicted values. Zn, and especially CPF accumulation, were influenced by the co-exposure. These results underpin the need to consider the effects of mixtures of NPs and organic chemicals on soil to adequately make ecological risk assessments of NPs.

Biochemical responses of freshwater mussel Unio tumidus to titanium oxide nanoparticles, Bisphenol A, and their combination

Multiple interactions between different pollutants in the surface waters can cause unpredictable consequences. The aim of the study was to evaluate the combined effect of two widespread xenobiotics, titanium oxide nanoparticles (TiO₂) and bisphenol A (BPA), on freshwater bivalve Unio tumidus. The specimens were exposed for 14 days to TiCl₄ (Ti, 1.25 µM), TiO₂ (1.25 μM), BPA (0.88 nM), or their combination (TiO₂ + BPA). Every type of exposure resulted in a particular oxidative stress response: TiO₂ had antioxidant effect, decreasing the generation of reactive oxygen species (ROS) and phenoloxidase (PhO) activity, and doubling reduced glutathione (GSH) concentration in the digestive gland; Ti caused oxidative changes by increasing levels of ROS, PhO and superoxide dismutase; BPA decreased the GSH level by a factor of two. In the co-exposure treatment, these indices as well as lysosomal membrane stability were not affected. All Ti-containing exposures caused elevated levels of metalated metallothionein (Zn,Cu-MT), its ratio to total metallothionein protein, and lactate/pyruvate ratio. Both BPA-containing exposures decreased caspase-3 activity. All exposures, and particularly co-exposure, up-regulated CYP450-dependent oxidation, lipid peroxidation and lipofuscin accumulation, lysosomal cathepsin D and its efflux, as well as alkali-labile phosphates in gonads and caused DNA instability (except for TiO₂). To summarize, co-exposure to TiO₂ + BPA produced an overlap of certain individual responses but strengthened the damage. Development of water purification technologies using TiO₂ requires further studies of the biological effects of its mixtures. U. tumidus can serve as a sentinel organism in such studies.

The influence of surface waters on the bioavailability and toxicity of zinc oxide nanoparticles in freshwater mussels

The release of engineered nanoparticles in the aquatic environment could pose a threat to the biota. The purpose of the study was to examine the influence of surface water characteristics on zinc oxide nanoparticles (nZnO) and ZnS0₄ toxicity to the freshwater mussel Dreissena polymorpha. Mussels were exposed to an equivalent concentration of 25 μg/L Zn as either nZnO or ZnSO₄ for 96 h at 15 °C in 4 types of surface waters: green water (high conductivity and pH with low natural organic matter content), brown water (low conductivity and pH with high natural organic matter content), diluted municipal effluent (high conductivity and pH with high urban organic matter content) and aquarium water (treated green water with organic matter removed). After the exposure period, mussels were analyzed for air-time survival, total and labile Zn levels in tissues, lipid metabolism (phospholipase A2, triglycerides levels) and oxidative stress (glutathione S-transferase, arachidonate cyclooxygenase, lipid peroxidation). The data revealed that mussels exposed to ZnSO₄ in controlled aquarium water accumulated more total and labile Zn tissues, decreased oxidative stress and triglycerides and increased air time survival. While nZnO had few effects in aquarium water, oxidative stress was enhanced and total Zn in tissues were decreased in brown water and diluted municipal effluent and triglycerides were higher in nZn-exposed mussels in brown water. Air-time survival was decreased in mussels kept in green water and nZnO. It was also decreased in mussels exposed to ZnSO₄ in green water and diluted municipal effluent. In conclusion, the fate and toxic effects of Zn could be influenced by both the chemical form (nanoparticles or ionic Zn) and surface water properties in freshwater mussels.

Bioenergetic responses of freshwater mussels Unio tumidus to the combined effects of nano-ZnO and temperature regime

Bivalves from the cooling reservoirs of electrical power plants (PP) are exposed to the chronic heating and chemical pollution making them a suitable model to study the combined effects of these stressors. We investigated the effect of in situ exposures to chemical and thermal pollution in the PP cooling ponds on the metabolic responses of unionid bivalves (Unio tumidus) to a novel widespread pollutant, ZnO nanoparticles (nZnO). Male U. tumidus from the reservoirs of Dobrotvir and Burshtyn PPs (DPP and BPP) were maintained in clean water at 18 °C, or exposed for 14 days to one of the following conditions: nZnO (3.1 μM) or Zn²⁺ (3.1 μM, a positive control for Zn impacts) at 18 °C, elevated temperature (T, 25 °C), or nZnO at 25 °C (nZnO + T). Baseline levels of glycogen, lipids and ATP were similar in the two studied populations, whereas the levels of proteins, lactate/pyruvate ratio (L/P) and extralysosomal cathepsin D level were higher in the tissues of BPP mussels. The levels of glycogen and glucose declined in most experimental exposures indicating elevated energy demand except for a slight increase in the digestive gland of warming-exposed BPP mussels and in the gills of the nZnO + T-exposed DPP-mussels. Experimental exposures stimulated cathepsin D activity likely reflecting onset of autophagic processes to compensate for stress-induced energy demand. No depletion of ATP in Zn-containing exposures was observed indicating that the cellular metabolic adjustments were sufficient for such compensation. Unexpectedly, experimental warming mitigated most metabolic responses to nZnO in co-exposures. Our data thus indicate that metabolic effects of nZnO strongly depend on the environmental context of the mussels (such as temperature and acclimation history) which must be taken into account for the molecular and cellular biomarker-based assessment of the nanoparticle effects in the field.

Environmental mixtures of nanomaterials and chemicals: The Trojan-horse phenomenon and its relevance for ecotoxicity

The usage of engineered nanomaterials (NM) offers many novel products and applications with advanced features, but at the same time raises concerns with regard to potential adverse biological effects. Upon release and emission, NM may interact with chemicals in the environment, potentially leading to a co-exposure of organisms and the occurrence of mixture effects. A prominent idea is that NM may act as carriers of chemicals, facilitating and enhancing the entry of substances into cells or organisms, subsequently leading to an increased toxicity. In the literature, the term 'Trojan-horse effect' describes this hypothesis. The relevance of this mechanism for organisms is, however, unclear as yet. Here, a review has been performed to provide a more systematic picture on existing evidence. It includes 151 experimental studies investigating the exposure of various NM and chemical mixtures in ecotoxicological in vitro and in vivo model systems. The papers retrieved comprised studies investigating (i) uptake, (ii) toxicity and (iii) investigations considering both, changes in substance uptake and toxicity upon joint exposure of a chemical with an NM. A closer inspection of the studies demonstrated that the existing evidence for interference of NM-chemical mixture exposure with uptake and toxicity points into different directions compared to the original Trojan-horse hypothesis. We could discriminate at least 7 different categories to capture the evidence ranging from no changes in uptake and toxicity to an increase in uptake and toxicity upon mixture exposure. Concluding recommendations for the consideration of relevant processes are given, including a proposal for a nomenclature to describe NM-chemical mixture interactions in consistent terms.

Toxic effects of multi-walled carbon nanotubes on bivalves: Comparison between functionalized and nonfunctionalized nanoparticles

Despite of the large array of available carbon nanotube (CNT) configurations that allow different industrial and scientific applications of these nanoparticles, their impacts on aquatic organisms, especially on invertebrate species, are still limited. To our knowledge, no information is available on how surface chemistry alteration (functionalization) of CNTs may impact the toxicity of these NPs to bivalve species after a chronic exposure. For this reason, the impacts induced by chronic exposure (28days) to unfunctionalized MWCNTs (Nf-MWCNTs) in comparison with functionalized MWCNTs (f-MWCNTs), were evaluated in R. philippinarum, by measuring alterations induced in clams' oxidative status, neurotoxicity and metabolic capacity. The results obtained revealed that exposure to both MWCNT materials altered energy-related responses, with higher metabolic capacity and lower glycogen, protein and lipid concentrations in clams exposed to these CNTs. Moreover, R. philippinarum exposed to Nf-MWCNTs and f-MWCNTs showed oxidative stress expressed in higher lipid peroxidation and lower ratio between reduced and oxidized glutathione, despite the activation of defense mechanisms (superoxide-dismutase, glutathione peroxidase and glutathione S-transferases) in exposed clams. Additionally, neurotoxicity was observed by inhibition of Cholinesterases activity in organisms exposed to both MWCNTs.

Early ecotoxic effects of ZnO nanoparticle chronic exposure in Mytilus galloprovincialis revealed by transcription of apoptosis and antioxidant-related genes

Recently, China became one of the largest nanomaterial markets in the world. The wide use of ZnO nanoparticles in a number of products implies an increasing release in marine environment and consequently the evaluation of the potential effects upon marine organisms largely cultured in China for commercial purposes, such as invertebrate bivalves is a current need. To this aim, survival, bioaccumulation, and transcription pattern of key genes, p53, PDRP, SOD, CAT, and GST, involved in DNA damage/repair and antioxidation, in Mytilus galloprovincialis digestive gland, exposed to ZnO NPs (<100 nm) and ZnO bulk (150-200 nm) for 4 weeks, were evaluated. ZnSO₄ was also assessed to appraise the role of zinc ions. Starting from 72 h, increasing mortality values along the exposure time were observed for all ZnO compounds. The highest difference was evident after 28 d when NPs resulted three times more toxic than bulk, (LC₅₀) = 0.78 mg Zn/L (confidence limits: 0.64, 1.00) and 2.62 mg Zn/L (confidence limits: 1.00, 4.00), respectively. For ZnSO₄ the (LC₅₀) was always the lowest reaching the minimum value at 28 d 0.25 mg Zn/L (confidence limits: 0.10-0.40). Digestive gland showed higher uptake rate of ionic Zn respect to ZnO NPs and bulk during the first three days of exposure. In particular at the end of the exposure time (28 d) at 1 mg Zn/L the rank of Zn uptake rate was Zinc ion > ZnO NPs > ZnO bulk. The relative expression of investigated genes evidenced that distinct actions of apoptosis and antioxidation occurred in M. galloprovincialis exposed to ZnO NPs with a peculiar pattern dependent on exposure time and concentration. Application of the qRT-PCR technique revealed evidence of sensitivity to the nanomaterial since the first time of exposure.

Detoxification and cellular stress responses of unionid mussels Unio tumidus from two cooling ponds to combined nano-ZnO and temperature stress

Bivalve mollusks from the cooling reservoirs of fuel power plants (PP) are acclimated to the chronic heating and chemical pollution. We investigated stress responses of the mussels from these ponds to determine their tolerance to novel environmental pollutant, zinc oxide nanoparticles (nZnO). Male Unio tumidus from the reservoirs of Dobrotvir and Burschtyn PPs (DPP and BPP), Ukraine were exposed for 14 days to nZnO (3.1 μM), Zn²⁺ (3.1 μM) at 18 °C, elevated temperature (T, 25 °C), or nZnO at 25 °C (nZnO + T). Control groups were held at 18 °C. Zn-containing exposures resulted in the elevated concentrations of total and Zn-bound metallothionein (MT and Zn-MT) in the digestive gland, an increase in the levels of non-metalated MT (up to 5 times) and alkali-labile phosphates and lysosomal membrane destabilization in hemocytes. A common signature of nZnO exposures was modulation of the multixenobiotic-resistance protein activity (a decrease in the digestive gland and increase in the gills). The origin of population strongly affected the cellular stress responses of mussels. DPP-mussels showed depletion of caspase-3 in the digestive gland and up-regulation of HSP70, HSP72 and HSP60 levels in the gill during most exposures, whereas in the BPP-mussels caspase-3 was up-regulated and HSPs either downregulated or maintained stable. BPP-mussels were less adapted to heating shown by a glutathione depletion at elevated temperature (25 °C). Comparison with the earlier studies on mussels from pristine habitats show that an integrative 'eco-exposome'-based approach is useful for the forecast of the biological responses to novel adverse effects on aquatic organisms.

A calcium channel blocker nifedipine distorts the effects of nano-zinc oxide on metal metabolism in the marsh frog Pelophylax ridibundus

Global decline of amphibian populations causes particular concern about their vulnerability to novel environmental pollutants, including engineering nanomaterials and pharmaceutical products. We evaluated the bioavailability of nanoform of zinc oxide (n-ZnO) in frog Pelophylax ridibundus and determined whether co-exposure to a common pharmaceutical, a calcium-channel blocker nifedipine (Nfd) can affect this bioavailability. Male frogs were exposed for 14 days to the tap water (Control) and n-ZnO (3.1 μM), Zn²⁺ (3.1 μM, as a positive control for n-ZnO exposures), Nfd (10 μM), and combination of n-ZnO and Nfd (n-ZnO + Nfd) in environmentally-relevant concentration. Exposure to Zn²⁺ or n-ZnO led to up-regulation of metal-binding proteins, metallothioneins (MTs) in the liver and Zn-carrying vitellogenin-like proteins in the blood plasma. Notably, upregulation of MTs by Zn²⁺ or n-ZnO exposures combined with increased binding of Zn and Cu to MTs. This was associated with the more reducing conditions in the liver tissue indicated by elevated lactate to pyruvate ratio. Nfd suppressed the binding of Zn and Cu to MTs and led to a decrease in Lactate/Pyruvate ratio and elevated protein carbonylation indicating pro-oxidant conditions. Redox status parameters were not directly related to DNA fragmentation, nuclear abnormalities or suppression of cholinesterase activity indicating that factors other than oxidative stress are involved in cytotoxicity of different pollutants and their combinations. Furthermore, activity of Phase I biotransformation enzyme (CYP450 oxidase measured as EROD) was elevated in Nfd-containing exposures and in Zn²⁺ exposed frogs. Tyrosinase-like activity in the frog liver was strongly stimulated by Zn²⁺ but suppressed by n-ZnO, Nfd and n-ZnO + Nfd. These findings show that Nfd modulates homeostasis of essential metals in amphibians and emphasize that physiological consequences of combined n-ZnO and Nfd exposures are difficult to predict based on the mechanisms of single stressors.

Moderate ocean warming mitigates, but more extreme warming exacerbates the impacts of zinc from engineered nanoparticles on a marine larva

There is growing concern about the combined effects of multiple human-induced stressors on biodiversity. In particular, there are substantial knowledge gaps about the combined effects of existing stressors (e.g. pollution) and predicted environmental stress from climate change (e.g. ocean warming). We investigated the impacts of ocean warming and engineered nanoparticles (nano-zinc oxide, nZnO) on larvae of a cosmopolitan tropical sea urchin, Tripneustes gratilla. Larval T. gratilla were exposed to all combinations of three temperatures, 25, 27 and 29 °C (current SST and near-future predicted warming of +2 and + 4 °C) and six concentrations of nZnO (0, 0.001, 0.01, 0.1, 1 and 10 mg nZnO·L^-1). These stressors had strong interactive effects on fertilization, gastrulation and normal development of 5 day old larvae. High concentrations of nZnO had a negative effect, but this impact was less pronounced for sea urchins reared at their preferred temperature of 27 °C compared to 25 or 29 °C. Larval growth was also impacted by combined stress of elevated temperature and nZnO. Subsequent measurement of the dissolution and aggregation of nZnO particles and the direct effect of Zn²⁺ ions on larvae, suggest the negative effects of nZnO on larval development and growth were most likely due to Zn²⁺ ions. Our results demonstrate that marine larvae may be more resilient to stressors at optimal temperatures and highlight the potential for ocean warming to exacerbate the effects of pollution on marine larvae.

Genotoxicity of metal based engineered nanoparticles in aquatic organisms: A review

Engineered nanoparticles (ENPs) are an emerging class of environmental contaminants, but are generally found in very low concentrations and are therefore likely to exert sub-lethal effects on aquatic organisms. In this review, we: (i) highlight key mechanisms of metal-based ENP-induced genotoxicity, (ii) identify key nanoparticle and environmental factors which influence the observed genotoxic effects, and (iii) highlight the challenges involved in interpreting reported data and provide recommendations on how these challenges might be addressed. We review the application of eight different genotoxicity assays, where the Comet Assay is generally preferred due to its capacity to detect low levels of DNA damage. Most ENPs have been shown to cause genotoxic responses; e.g., DNA or/and chromosomal fragmentation, or DNA strand breakage, but at unrealistic high concentrations. The genotoxicity of the ENPs was dependent on the inherent physico-chemical properties (e.g. size, coating, surface chemistry, e.tc.), and the presence of co-pollutants. To enhance the value of published genotoxicity data, the role of environmental processes; e.g., dissolution, aggregation and agglomeration, and adsorption of ENPs when released in aquatic systems, should be included, and assay protocols must be standardized. Such data could be used to model ENP genotoxicity processes in open environmental systems.

The impacts of emergent pollutants on Ruditapes philippinarum: biochemical responses to carbon nanoparticles exposure

Multi-walled carbon nanotubes (MWCNTs) are one of the most important carbon Nanoparticles (NPs). The production and use of these NPs are increasing rapidly and, therefore, the need to assess their presence in the environment and associated risks has become of prime importance. Recent studies demonstrated the impacts of different NPs on bivalves, a taxonomic group where species tolerance to anthropogenic stressors, such as pollutants, is widely variable. The Manila clam Ruditapes philippinarum is one of the most commonly used bivalve species in environmental monitoring studies and ecotoxicology tests, however, to our knowledge, no information is available on biochemical alterations on this species due to MWCNTs exposure. Thus, the present study aimed to assess the toxic effects of different MWCNT concentrations (0.01; 0.10 and 1.00mg/L) in R. philippinarum biochemical (energy reserves, metabolic capacity, oxidative status and neurotoxicity) performance, after 28days of exposure. The results obtained revealed that exposure to MWCNTs altered energy-related responses, with higher metabolic capacity and lower glycogen and protein concentrations in clams exposed to these carbon NPs. Moreover, R. philippinarum exposed to MWCNTs showed oxidative stress expressed in higher lipid peroxidation and lower ratio between reduced and oxidized glutathione, despite the activation of defence mechanisms in exposed clams. Additionally, neurotoxicity was observed by inhibition of cholinesterases activity in organisms exposed to MWCNTs. The present study provides valuable information regarding how these emerging pollutans could become a potential risk for the environment and living organisms.

Endocrine and cellular stress effects of zinc oxide nanoparticles and nifedipine in marsh frogs Pelophylax ridibundus

Freshwater organisms including amphibians experience increasing exposures to emerging pollutants such as nanoparticles and pharmaceuticals, which can affect their fitness and performance. We studied the effects of two common pollutants extensively used in industry, pharmaceutical and personal care products, nano-zinc oxide (nZnO) and a Ca-channel blocker nifedipine (Nfd), on endocrine status and cellular stress markers of the marsh frog Pelophylax ridibundus. Males were exposed for 14days to nZnO (3.1μM), Zn²⁺ (3.1μM, as a positive control for nZnO exposures), Nfd (10μM), and combination of nZnO and Nfd (nZnO+Nfd). Exposure to nZnO and Zn²⁺ led to an increase in Zn burdens, elevated concentrations of the metal-bound metallothioneins (MT-Me) in the liver and increased vitellogenin in the serum, whereas exposures to Nfd and nZnO+Nfd resulted in the metal release from MTs and a significant increase in the ratio of total to metal-bound MTs. This likely reflects oxidative stress caused by Nfd exposures as manifested in the elevated levels of oxyradical production, upregulation of superoxide dismutase activity (SOD) and increase in the total and oxidized glutathione concentrations in Nfd-exposed frogs. Zn-containing exposures upregulated activity of deiodinase (in nZnO and nZnO+Nfd exposures) and serum thyrotropin level (in the case of Zn²⁺). All exposures caused an increase in DNA fragmentation, lipofuscin accumulation as well as upregulation of caspase-3 and CYP450 levels reflecting cytotoxicity of the studied compounds in the liver. Across all experimental treatments, nZnO exposures in the absence of Nfd had the least impact on the cellular stress traits or redox status in frogs. This indicates that at the low environmentally relevant levels of pollution, pharmaceuticals such as Nfd and free metals (such as Zn²⁺) may represent a stronger threat to the health of the frogs than nZnO particles.

In vivo exposure of the marine clam Ruditapes philippinarum to zinc oxide nanoparticles: responses in gills, digestive gland and haemolymph

Potential nanoparticle (NP) toxicity poses a growing concern in marine coastal environments. Among NPs, zinc oxide nanoparticles (nZnO) are widely used in many common products that ultimately become deposited in coastal habitats from multiple non-point sources. In this study, we evaluated the in vivo effects of nZnO in the clam Ruditapes philippinarum. Animals were exposed to nZnO (1 and 10 μg/L) and ZnCl2 (10 μg/L) for 7 days. ZnCl2 was used to compare the effects of the NPs to those of Zn(2+) and to ascertain whether nZnO toxicity is attributable to the release of ions into the aquatic medium. At differing time intervals during the exposure, several biochemical and cellular responses were evaluated in the clam gills, digestive gland, and haemolymph. The results showed that nZnO, at concentrations close to the predicted environmental levels, significantly affected various parameters in clam tissues. Significant increases in catalase and superoxide dismutase activities and a decreasing trend of glutathione S-transferase activity indicated the involvement of oxidative stress in nZnO toxicity. In clams exposed to ZnCl2, slight variations in antioxidant enzyme activities were detected with respect to nZnO-treated clams. However, no damage to lipids, proteins or DNA was revealed in all exposure conditions, suggesting a protection of antioxidant enzymes in the tissues. Of the various haemolymph parameters measured, haemocyte proliferation increased significantly, in ZnCl2-treated clams in particular. Under nZnO (10 μg/L) and ZnCl2 exposure, DNA damage in haemocytes was also revealed, but it was lower in clams exposed to ZnCl2. A decreasing trend in gill AChE activity of treated clams proposed a possible role of zinc ions in nZnO toxicity. However, the dissimilar modulation of the responses in the nZnO- and ZnCl2-exposed clams suggested different mechanisms of action, with nZnO toxicity possibly depending not only on the release of zinc ions but also on NP-specific features. Changes in the biological parameters measured in the clams were consistent with Zn accumulation in their gills and digestive glands.

Acute toxicity and accumulation of ZnO NPs in Ceriodaphnia dubia: Relative contributions of dissolved ions and particles

Although the ecotoxicological effects of various metal oxide nanoparticles on aquatic organisms are being actively studied, the contributions of particles and dissolved ions towards toxicity are still not well understood. The current study aims to assess the contribution of ZnO NP(particle) and ZnO NP(ion) to the overall toxicity and accumulation of ZnO NP(total) in Ceriodaphnia dubia. The aggregation and dissolution kinetics were studied for three different sizes (50nm, 100nm and bulk) of ZnO particles at 0.05, 0.12, 0.25 and 0.5mg/L concentrations in the sterile lake water medium at 6, 12, 24, and 48h intervals. The 48h LC50 of ZnO NP(total) was found to be 0.431, 0.605 and 0.701mg/L for 50, 100nm and bulk particles exposure. However, LC50 of Zn(ion) was found to be 1.048, 1.343 and 2.046mg/L for dissolved ions from different sizes (50nm, 100nm, and bulk) of ZnO particles. At LC50 concentration, the accumulation of 90-95% was noted for the NP(particles) across the sizes employed, while only about 4-5% contribution was from the NP(ion) to the overall accumulation NP(total). The relative contribution of ZnO NP(ion) to overall toxicity and accumulation was found to be lesser than that of ZnO NP(particles) across the sizes used in the study.

Effect of temperature on oxidative stress parameters and enzyme activity in tissues of Cape River crab (Potamanautes perlatus) following exposure to silver nanoparticles (AgNP)

Biomarkers of oxidative stress have been widely used in environmental assessments to evaluate the effects of exposure of aquatic organisms to contaminants from various anthropogenic sources. Silver nanoparticles (AgNP), the most produced NP worldwide and used in several consumer products, are known to produce oxidative stress in aquatic organisms. Similarly, temperature is also known to affect reactive oxygen species (ROS) by influencing the inputs of contaminants into the environment, as well as altering behavior, fate, and transport. Aquatic ecosystems are affected by both anthropogenic releases of contaminants and increased temperature. To test this hypothesis, the influence of AgNP and temperature in the response to multiple biomarkers of oxidative stress was studied in the gills and hepatopancreas of the Cape River crab Potamonautes perlatus. Responses were assessed through activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and the nonenzymatic antioxidant glutathione S-transferase (GST). The response of the oxidative stress biomarkers analyzed was always higher in hepatopancreas than in gills. Elevated temperatures (28°C) induced oxidative stress by increasing SOD, CAT, and GST activities, particularly at 100 µg/ml AgNP. These data indicate that AgNP-mediated toxicity to P. perlatus is modulated by elevated temperatures, but this relationship is not linear. Co-effects of AgNP and temperature are reported for the first time in P. perlatus.

Inhibition of the oxidative stress response by heat stress in Caenorhabditis elegans

It has long been recognized that simultaneous exposure to heat stress and oxidative stress shows a synergistic interaction that reduces organismal fitness, but relatively little is known about the mechanisms underlying this interaction. We investigated the role of molecular stress responses in driving this synergistic interaction using the nematode Caenorhabditis elegans. To induce oxidative stress, we used the pro-oxidant compounds acrylamide, paraquat, and juglone. As expected, we found that heat stress and oxidative stress interact synergistically to reduce survival. Compared to exposure to each stressor alone, during simultaneous, sub-lethal exposure to heat stress and oxidative stress the normal induction of key oxidative stress response (OxSR) genes was generally inhibited while the induction of key heat shock response (HSR) genes was not. Genetically activating the SKN-1 dependent OxSR increased a marker for protein aggregation and decreased whole-worm survival during heat stress alone, with the latter being independent of HSF-1. In contrast, inactivating the HSR by HSF-1 knockdown, which would be expected to decrease basal heat shock protein expression, increased survival during oxidative stress alone compared to wild- type worms. Taken together, these data suggest that in C. elegans the HSR and OxSR cannot be simultaneously activated to the same extent that each can be activated during a single stressor exposure. We conclude that the observed synergistic reduction in survival during combined exposure to heat stress and oxidative stress is due, at least in part, to inhibition of the OxSR during activation of the HSR.

The influence of zinc chloride and zinc oxide nanoparticles on air-time survival in freshwater mussels

The purpose of this study was to determine the cumulative effects of exposure to either dissolved zinc or nanozinc oxide (nanoZnO) and air-time survival in freshwater mussels. Mussels were exposed to each forms of zinc for 96h then placed in air to determine survival time. A sub-group of mussels before and after 7days of exposure to air were kept aside for the determination of the following biomarkers: arachidonate-dependent cyclooxygenase (COX) and peroxidase (inflammation and oxidative stress), lipid metabolism (total lipids, esterases activity, HO-glycerol, acetyl CoA and phospholipase A2) and lipid damage (lipid peroxidation [LPO]). The results showed that air-time survival was decreased from a mean value of 18.5days to a mean value of 12days in mussels exposed to 2.5mg/L of nanoZnO although it was not lethal based on shell opening at concentrations below 50mg/L after 96h. In mussels exposed to zinc only, the median lethal concentration was estimated at 16mg/L (10-25 95% CI). The air-time survival did not significantly change in mussels exposed to the same concentration of dissolved Zn. Significant weight losses were observed at 0.5mg/L of nanoZnO and at 2.5mg/L for dissolved zinc chloride, and were also significantly correlated with air-time survival (r=0.53; p<0.01). Air exposure significantly increased COX activity in control mussels and in mussels exposed to 0.5mg/L of nanoZnO and zinc chloride. The data also suggested fatty acid breakdown and β-oxidation. Mussels exposed to contaminants are more susceptible to prolonged exposure to air during low water levels.

Hepatic metallothioneins in molecular responses to cobalt, zinc, and their nanoscale polymeric composites in frog Rana ridibunda

Despite numerous studies suggesting a dramatic decline of amphibians, the biochemical mechanisms of adaptation in these animals to polluted environment are poorly studied. The aim of this study was to elucidate the ability to release cobalt (Co) and zinc (Zn) from their nanoscale complexes (NCs) derived from the polymeric substance of N-vinylpyrrolidone (PS) in the liver of amphibian (Rana ridibunda). Frog males were subjected to 14days exposure to waterborne Co(2+) (50μg/L), Zn(2+) (100μg/L), as well as corresponding concentrations of Co-NC, Zn-NC or PS. Main attention was paid to MT's interrelations with indices of stress and toxicity. Only Co(2+) and Zn(2+) caused elevation of the correspondent metal in MTs. Co(2+) caused down-regulation of cathepsin D activity, while Zn(2+), Zn-NC and the PS up-regulated this activity. Zn(2+) provoked 1.6 times increase of metal-bounded form of the MT (MT-Me), while all other exposures caused the elevation of the ratio of MT total protein concentration (MT-SH) and concentrations of the MT-Me and/or immunoreactive (MTi) form (up to ~10 times) accompanied by a decrease in the levels of oxyradicals. The increased DNA fragmentation and down-regulation of caspase-3 activity in relation to the redox state of glutathione and/or lactate/pyruvate were shown at all exposures. These data indicate the vulnerability of the redox state of cellular thiols and inability to release Co and Zn from NCs in frog's liver.