Uptake and retention of metallic nanoparticles in the Mediterranean mussel (Mytilus galloprovincialis)

Extreme heat event influences the toxic impacts of nano-TiO2 with different crystal structures in mussel Mytilus coruscus

The wide use of nano‑titanium dioxide (nano-TiO2) and its ubiquitous emission into aquatic environments are threatening environmental health. Ambient temperature can affect the aggregation state of nano-TiO2 in seawater, thus influencing the intake and physiological effects on marine species. We studied the physiological effects of mixed nano-TiO2 (a mixture of anatase and rutile crystals with an average particle size of 25 nm, P25) on mussels. Subsequently, we investigated the oxidative stress, immunotoxicity, neurotoxicity, and detoxification in Mytilus coruscus exposed to two different crystal structures of nano-TiO2 (anatase and rutile) at 100 μg/L concentration under marine heatwaves (MHWs, 28 °C). MHWs and nano-TiO2 exposure induced neurotoxicity and immune damage and caused dysregulation of redox balance in the gills. Moreover, MHWs exposure disturbed the glutathione system and detoxification function of mussels, resulting in enhanced toxicity of nano-TiO2 under co-exposure. Anatase exposure significantly impaired the antioxidant system and downregulated the relative expression of antioxidant-related genes (Nrf2 and Bcl-2), HSP-90, and immune parameters under MHWs, while producing higher ROS levels compared to rutile. Based on integrated biomarker response (IBR), mussels co-exposed to anatase and MHW showed the highest value (19.29). However, there was no significant difference in bioaccumulation of titanium between anatase (6.07 ± 0.47 μg/g) and rutile (5.3 ± 0.44 μg/g) exposures under MHWs. These results indicate that MHWs would elevate the potential hazard of nanoparticles to marine organisms.

Effect of TiO2 Nanoparticle on Bioaccumulation of ndl-PCBs in Mediterranean Mussels (Mitilus galloprovincialis)

The interaction of nanomaterials with pollutants in the marine environment might alter bioavailability, as well as toxicity, of both nanomaterials and pollutants, representing a risk, not only for marine organisms, but also for consumers through the marine food chain.The aim of this study was to evaluate the effect of titanium dioxide nanoparticles (TiO2NPs) in terms of bioaccumulation and toxicity on Mediterranean mussels (Mytilus galloprovincialis) exposed to six-indicator non-dioxin-like polychlorinated biphenyls (ndl-PCBs). Mussels were exposed to ndl-PCBs (20 µg/mL) (groups 3–4) or to a combination of ndl-PCBs (20 µg/mL) and TiO2NPs (100 µg/mL) (groups 5–6) for four consecutive days. TiO2NPs was detected in groups 5–6 (3247 ± 567 and 1620 ± 223 µg/kg respectively), but their presence did not affect ndl-PCBs bioaccumulation in mussels. In fact, in groups 3–4, the concentration of ndl-PCBs (ranging from 3818.4 ± 166.0–10,176 ± 664.3 µg/kg and 2712.7 ± 36.1–9498.0 ± 794.1 µg/kg respectively) was not statistically different from that of groups 5–6 (3048.6 ± 24.0–14,635.9 ± 1029.3 and 5726.0 ± 571.0–9931.2 ± 700.3 µg/kg respectively). Histological analyses showed alterations to the structure of the gill tissue with respect to the control groups, with more severe and diffuse dilatation of the central hemolymphatic vessels of the gill lamellae in groups 5–6 (treated with TiO2NPs and ndl-PCBs concurrently) compared to groups 3–4 (ndl-PCBs only). Finally, in mussels submitted to a seven-day depuration process, most TiO2NPs were eliminated, and NPs had a synergistic effect on ndl-PCBs elimination; as a matter of fact, in groups 5–6, the percentage of concentration was statically inferior to the one observed in groups 3–4. In any case, consumers might be exposed to TiO2NPs and ndl-PCBs (both concurrently and separately) if edible mussels, harvested in a contaminated environment, are consumed without a proper depuration process.

Integrative assessment of biomarker responses in Mytilus galloprovincialis exposed to seawater acidification and copper ions

The interactive effects of ocean acidification (OA) and copper (Cu) ions on the mussel Mytilus galloprovincialis are not well understood. The underlying mechanisms also remain obscure. In this study, individuals of M. galloprovincialis were exposed for 28 days to 25 μg/L and 50 μg/L Cu ions at two pH levels (ambient level - pH 8.1; acidified level - pH 7.6). The mussels were then monitored for 56 days to determine their recovery ability. Physiological parameters (clearance rate and respiration rate), oxidative stress and neurotoxicity biomarkers (activities of superoxide dismutase, lipid peroxidation, catalase, and acetylcholinesterase), as well as the recovery ability of these parameters, were investigated in two typical tissues (i.e., gills and digestive glands). Results showed that (1) OA affected the bioconcentration of Cu in the gills and digestive glands of the mussels; (2) both OA and Cu can lead to physiological disturbance, oxidative stress, cellular damage, energy metabolism disturbance, and neurotoxicity on M. galloprovincialis; (3) gill is more sensitive to OA and Cu than digestive gland; (4) Most of the biochemical and physiological alternations caused by Cu and OA exposures in M. galloprovincialis can be repaired by the recovery experiments; (5) integrated biomarker response (IBR) analysis demonstrated that both OA and Cu ions exposure caused survival stresses to the mussels, with the highest effect shown in the co-exposure treatment. This study highlights the necessity to include OA along with pollutants in future studies to better elucidate the risks of ecological perturbations. The work also sheds light on the recovery of marine animals after short-term environmental stresses when the natural environment has recovered.

Molecular biomarker responses in the freshwater mussel Anodonta anatina exposed to an industrial wastewater effluent

Using a selection of molecular biomarkers, we evaluated responses in freshwater mussels (Anodonta anatina) exposed to effluent from an industrial wastewater treatment facility. The aims of this work were to (1) assess biomarkers of general toxicity under sublethal exposure to an anthropogenic mixture of chemicals, represented by an arbitrary effluent, and (2) evaluate the potential of A. anatina as a bioindicator of pollution. Adult mussels (n = in total 32; 24 males and 8 females) were exposed (96 h) in the laboratory to a fixed dilution of effluent or to a control treatment of standardized freshwater. Metal concentrations were in general higher in the effluent, by an order of magnitude or more, compared to the control. Toxic unit estimates were used as proxies of chemical stress, and Cu, Ni, and Zn were identified as potential major contributors (Cu> Ni > Zn). Six transcriptional (cat, gst, hsp70, hsp90, mt, sod) and two biochemical (AChE, GST) biomarkers were analyzed in two tissues, gills, and digestive glands. Out of the 16 responses (eight biomarkers × two tissues), 14 effect sizes were small (within ± 28 % of control) and differences non-significant (p > 0.05). Results did however show that (1) AChE activity increased by 40% in gills of exposed mussels compared to control, (2) hsp90 expression was 100% higher in exposed female gills compared to control, and (3) three marker signals (AChE in both tissues, and hsp70 in gills) differed between sexes, independent of treatment. Results highlight a need for further investigation of molecular biomarker variability and robustness in A. anatina.

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.

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.

Bioaccumulation and in vivo formation of titanium dioxide nanoparticles in edible mussels

The aim of this study was to evaluate the bioaccumulation of titanium dioxide nanoparticles (TiO2NPs) in edible mussels bred in polluted artificial seawater. An in vivo study was conducted by exposing mussels to different concentrations of TiO2NPs (0.25 mg/L and 2.5 mg/L) or ionic titanium (1.6 mg/L) for 4 days. Inductively coupled plasma mass spectrometry (ICP-MS) showed titanium presence in all groups proportional to exposure levels (concentration range: 209-1119 µg/kg). Single particle ICP-MS revealed NPs in both TiO2NP treated mussels (concentration range: 231-1778 µg/kg) and in ionic titanium treated mussels (concentration 1574 µg/kg), suggesting potential nanoparticle formation in vivo. These results were confirmed by transmission electron microscopy with energy dispersive X-ray detection. Nonetheless, mussels eliminated more than 70% of the TiO2NPs after 3 days' depuration. These results show the potential for consumer exposure to TiO2NPs when contaminated mussels are consumed without a proper depuration process.

Assessing cadmium-based quantum dots effect on the gonads of the marine mussel Mytilus galloprovincialis

This study assesses the sex-specific effects induced by CdTe QDs, on the marine mussel Mytilus galloprovincialis in comparison to its dissolved counterpart. A 14 days exposure to CdTe QDs and dissolved Cd was conducted (10 μg Cd L^-1), analysing Cd accumulation, oxidative stress, biotransformation, metallothionein and oxidative damage in the gonads. Both Cd forms caused significant antioxidant alterations, whereby QDs were more pro-oxidant, leading to oxidative damage, being females more affected. Overall, biochemical impairments on gonads of M. galloprovincialis demonstrate that the reproductive toxicity induced by CdTe QDs in mussels are sex-dependent and mediated by oxidative stress and lipid peroxidation. It is crucial to acknowledge how gametes are affected by metal-based nanoparticles, such as Cd-based QDs. As well as understanding the potential changes they may undergo at the cellular level during gametogenesis, embryogenesis and larval development potentially leading to serious impacts on population sustainability and ecosystem health.

Strategies for robust and accurate experimental approaches to quantify nanomaterial bioaccumulation across a broad range of organisms

One of the key components for environmental risk assessment of engineered nanomaterials (ENMs) is data on bioaccumulation potential. Accurately measuring bioaccumulation can be critical for regulatory decision making regarding material hazard and risk, and for understanding the mechanism of toxicity. This perspective provides expert guidance for performing ENM bioaccumulation measurements across a broad range of test organisms and species. To accomplish this aim, we critically evaluated ENM bioaccumulation within three categories of organisms: single-celled species, multicellular species excluding plants, and multicellular plants. For aqueous exposures of suspended single-celled and small multicellular species, it is critical to perform a robust procedure to separate suspended ENMs and small organisms to avoid overestimating bioaccumulation. For many multicellular organisms, it is essential to differentiate between the ENMs adsorbed to external surfaces or in the digestive tract and the amount absorbed across epithelial tissues. For multicellular plants, key considerations include how exposure route and the role of the rhizosphere may affect the quantitative measurement of uptake, and that the efficiency of washing procedures to remove loosely attached ENMs to the roots is not well understood. Within each organism category, case studies are provided to illustrate key methodological considerations for conducting robust bioaccumulation experiments for different species within each major group. The full scope of ENM bioaccumulation measurements and interpretations are discussed including conducting the organism exposure, separating organisms from the ENMs in the test media after exposure, analytical methods to quantify ENMs in the tissues or cells, and modeling the ENM bioaccumulation results. One key finding to improve bioaccumulation measurements was the critical need for further analytical method development to identify and quantify ENMs in complex matrices. Overall, the discussion, suggestions, and case studies described herein will help improve the robustness of ENM bioaccumulation studies.

Relationship between levels of the heavy metals lead, cadmium and mercury, and metallothionein in the gills and stomach of Crassostrea iredalei and Crassostrea glomerata

Background: The objective of this study was to compare the levels of heavy metals (Pb, Hg, and Cd) and metallothionein (MT) in the gills and stomach of two species of mussels ( Crassostrea iredalei and Crassostrea glomerata), and to observe the ability of the mussels to absorb the heavy metals Pb, Hg and Cd present in the water. Methods: The mussels were obtained from Mayangan, Kenjeran and Gresik ports, East Java, Indonesia. MT levels were determined using ELISA. Heavy metal levels of Pb, Hg and Cd were assayed using atomic absorption spectrophotometry. Results: The levels of Pb and Cd in water were below the maximum permissible levels for local water quality standards. By contrast, the level of Hg in the water was above the maximum permissible levels for water quality standards. At Mayangan Port (Station 1), the level of Pb was higher than Hg and Cd. Levels of MT and heavy metals varied greatly among of C. iredalei and C. glomerata individuals, but were always higher in the gills than in the stomach. The highest MT level (160,250 ng/g) was observed at Kenjeran Port (Station 2). MT levels were shown to be significantly associated with heavy metal level ( P<0.0001). Conclusions: This result indicates that MT may be responsible for the sequestration of these heavy metals, as has already been observed in terrestrial animals.

Synergistic Effects of Nano-ZnO and Low pH of Sea Water on the Physiological Energetics of the Thick Shell Mussel Mytilus coruscus

In order to investigate the ecotoxicological effects of nano-ZnO particles and seawater acidification on marine bivalves, the thick shell mussels, Mytilus coruscus were subjected to joint treatments with different nano-ZnO concentrations (0 [control], 2.5 [medium] and 10 mg L^-1 [high]) under two pH levels (7.7 [low]and 8.1 [control]) for 14 days. The results showed that respiration rate (RR), absorption efficiency (AE), clearance rate (CR), O:N ratio and scope for growth (SFG) were significantly reduced with nano-ZnO concentration increase, but ammonium excretion rate (ER) was increased. Low pH significantly reduced CR, RR, SFG, and O:N ratio of the mussels especially under high nano-ZnO conditions, and significantly increased ER. Principal component analysis (PCA) showed consistent relationships among most tested parameters, especially among SFG, RR, O:N ratio and CR under the normal pH and 0 nano-ZnO conditions. Therefore, seawater acidification and nano-ZnO interactively impact the ecophysiological responses of mussels and cause more severe effects when they appear concurrently.

Changes in metallothionein transcription levels in the mussel Mytilus galloprovincialis exposed to CdTe quantum dots

Quantum dots (QDs) are a class of engineered nanoparticles (ENPs) with several biomedical, industrial and commercial applications. However, their metabolism and detoxification process in aquatic invertebrates and environmental health hazards remain unclear. This study investigate the transcriptional changes of metallothioneins (MTs) isoforms (mt10IIIa and mt20IV) induced by CdTe QDs, in comparison with its dissolved counterpart, in the marine mussel Mytilus galloprovincialis. Mussels were exposed to CdTe QDs and to the same Cd concentration (10 µg Cd L^-1) of dissolved Cd for 14 days and mt transcription levels were measured by real time quantitative PCR (qPCR). Tissue specific mt transcription patterns were observed in mussels exposed to both Cd forms, wherein the gills were a more sensitive organ compared to the digestive gland. No significant changes were observed in mt10IIIa transcription levels in mussels exposed to both Cd forms. In contrast, transcription of mt20IV was tissue and exposure time dependent, with higher mt20IV mRNA levels in mussels exposed to QDs and dissolved Cd when compared to unexposed mussels. Multivariate analysis indicates particle-specific effects after 14 days of exposure and a dual role of MTs in the QD metabolism and in the protection against oxidative stress in mussels exposed to Cd-based ENPs.

Toxic metals biomonitoring based on prey-predator interactions and environmental forensics techniques: A study at the Romanian-Ukraine cross border of the Black Sea

Marine cross-border areas are ideal for monitoring pollutants so as to increase ecosystems protection. This study was conducted at the Romanian-Ukraine border of the Black Sea to reveal evidence of contamination with toxic metals based on biomonitoring of: cadmium, lead, total chromium, nickel and copper at different water depths and prey-predator interactions, combined with environmental forensics techniques of biological sampling and separation in witnesses size groups. The species used were Mytilus galloprovincialis L. and Rapana venosa V. collected at 17.5m, 28m and 35m depth. An atomic absorption spectrometer with a high-resolution continuum source and graphite furnace was used for toxic metals quantification in various samples: sediments, soft tissue, stomach content, muscular leg, hepatopancreas. The best sample type, based on the pathology of metal location and bioaccumulation, is the hepatopancreas from R. venosa that proved a significant decrease of cadmium and lead at lower depths.

Blue mussels (Mytilus edulis spp.) as sentinel organisms in coastal pollution monitoring: A review

The blue mussel (Mytilus spp.) is widely used as a bioindicator for monitoring of coastal water pollution (mussel watch programs). Herein we provide a review of this study field with emphasis on: the suitability of Mytilus spp. as environmental sentinels; uptake and bioaccumulation patterns of key pollutant classes; the use of Mytilus spp. in mussel watch programs; recent trends in Norwegian mussel monitoring; environmental quality standards and background concentrations of key contaminants; pollutant effect biomarkers; confounding factors; particulate contaminants (microplastics, engineered nanomaterials); climate change; harmonization of monitoring procedures; and the use of deployed mussels (transplant caging) in pollution monitoring. Lastly, the overall state of the art of blue mussel pollution monitoring is discussed and some important issues for future research and development are highlighted.

Effects of nanoparticles in species of aquaculture interest

Recently, it was observed that there is an increasing application of nanoparticles (NPs) in aquaculture. Manufacturers are trying to use nano-based tools to remove the barriers about waterborne food, growth, reproduction, and culturing of species, their health, and water treatment in order to increase aquaculture production rates, being the safe-by-design approach still unapplied. We reviewed the applications of NPs in aquaculture evidencing that the way NPs are applied can be very different: some are direclty added to feed, other to water media or in aquaculture facilities. Traditional toxicity data cannot be easily used to infer on aquaculture mainly considering short-term exposure scenarios, underestimating the potential exposure of aquacultured species. The main outputs are (i) biological models are not recurrent, and in the case, testing protocols are frequently different; (ii) most data derived from toxicity studies are not specifically designed on aquaculture needs, thus contact time, exposure concentrations, and other ancillary conditions do not meet the required standard for aquaculture; (iii) short-term exposure periods are investigated mainly on species of indirect aquaculture interest, while shrimp and fish as final consumers in aquaculture plants are underinvestigated (scarce or unknown data on trophic chain transfer of NPs): little information is available about the amount of NPs accumulated within marketed organisms; (iv) how NPs present in the packaging of aquacultured products can affect their quality remained substantially unexplored. NPs in aquaculture are a challenging topic that must be developed in the near future to assure human health and environmental safety. Graphical abstract ᅟ.

CO2-induced pH reduction increases physiological toxicity of nano-TiO2 in the mussel Mytilus coruscus

The increasing usage of nanoparticles has caused their considerable release into the aquatic environment. Meanwhile, anthropogenic CO₂ emissions have caused a reduction of seawater pH. However, their combined effects on marine species have not been experimentally evaluated. This study estimated the physiological toxicity of nano-TiO₂ in the mussel Mytilus coruscus under high pCO₂ (2500-2600 μatm). We found that respiration rate (RR), food absorption efficiency (AE), clearance rate (CR), scope for growth (SFG) and O:N ratio were significantly reduced by nano-TiO₂, whereas faecal organic weight rate and ammonia excretion rate (ER) were increased under nano-TiO₂ conditions. High pCO₂ exerted lower effects on CR, RR, ER and O:N ratio than nano-TiO₂. Despite this, significant interactions of CO₂-induced pH change and nano-TiO₂ were found in RR, ER and O:N ratio. PCA showed close relationships among most test parameters, i.e., RR, CR, AE, SFG and O:N ratio. The normal physiological responses were strongly correlated to a positive SFG with normal pH and no/low nano-TiO₂ conditions. Our results indicate that physiological functions of M. coruscus are more severely impaired by the combination of nano-TiO₂ and high pCO₂.

Exposure of juvenile turbot (Scophthalmus maximus) to silver nanoparticles and 17α-ethinylestradiol mixtures: Implications for contaminant uptake and plasma steroid hormone levels

Combined exposure to engineered nanoparticles (ENPs) and anthropogenic contaminants can lead to changes in bioavailability, uptake and thus effects of both groups of contaminants. In this study we investigated effects of single and combined exposures of silver (Ag) nanoparticles (AgNPs) and the synthetic hormone 17α-ethinylestradiol (EE2) on tissue uptake of both contaminants in juvenile turbot (Scophthalmus maximus). Silver uptake and tissue distribution (gills, liver, kidney, stomach, muscle and bile) were analyzed following a 14-day, 2-h daily pulsed exposure to AgNPs (2 μg L^-1 and 200 μg L^-1), Ag⁺ (50 μg L^-1), EE2 (50 ng L^-1) and AgNP + EE2 (2 or 200 μg L^-1+50 ng L^-1). Effects of the exposures on plasma vitellogenin (Vtg) levels, EE2 and steroid hormone concentrations were investigated. The AgNP and AgNP + EE2 exposures resulted in similar Ag concentrations in the tissues, indicating that combined exposure did not influence Ag uptake in tissues. The highest Ag concentrations were found in gills. For the Ag⁺ exposed fish, the highest Ag concentrations were measured in the liver. Our results show dissolution processes of AgNPs in seawater, indicating that the tissue concentrations of Ag may partly originate from ionic release. Plasma EE2 concentrations and Vtg induction were similar in fish exposed to the single contaminants and the mixed contaminants, indicating that the presence of AgNPs did not significantly alter EE2 uptake. Similarly, concentrations of most steroid hormones were not significantly altered due to exposures to the combined contaminants versus the single compound exposures. However, high concentrations of AgNPs in combination with EE2 caused a drop of estrone (E1) (female fish) and androstenedione (AN) (male and female fish) levels in plasma below quantification limits. Our results indicate that the interactive effects between AgNPs and EE2 are limited, with only high concentrations of AgNPs triggering synergistic effects on plasma steroid hormone concentrations in juvenile turbots.

Environmental behaviour and ecotoxicity of quantum dots at various trophic levels: A review

Despite the wide application of quantum dots (QDs) in electronics, pharmacy and nanomedicine, limited data is available on their environmental health risk. To advance our current understanding of the environmental impact of these engineered nanomaterials, the aim of this review is to give a detailed insight on the existing information concerning the behaviour, transformation and fate of QDs in the aquatic environment, as well as on its mode of action (MoA), ecotoxicity, trophic transfer and biomagnification at various trophic levels (micro-organisms, aquatic invertebrates and vertebrates). Data show that several types of Cd-based QDs, even at low concentrations (<mgCdL^-1), induce different toxic effects compared to their dissolved counterpart, indicating nano-specific ecotoxicity. QD ecotoxicity at different trophic levels is highly dependent on its physico-chemical properties, environmental conditions, concentration and exposure time, as well as, species, while UV irradiation increases its toxicity. The state of the art regarding the MoA of QDs according to taxonomic groups is summarised and illustrated. Accumulation and trophic transfer of QDs was observed in freshwater and seawater species, while limited biomagnification and detoxification processes were detected. Finally, current knowledge gaps are discussed and recommendations for future research identified. Overall, the knowledge available indicates that in order to develop sustainable nanotechnologies there is an urgent need to develop Cd-free QDs and new "core-shell-conjugate" QD structures.

TiO2 nanoparticles in the marine environment: Physical effects responsible for the toxicity on algae Phaeodactylum tricornutum

Nanoscale titanium dioxide (nTiO2) has been widely used in cosmetics, catalysts, varnishes, etc., which is raising concerns about its potential hazards to the ecosystem, including the marine environment. In this study, the toxicological effect of nTiO2 on the marine phytoplankton Phaeodactylum tricornutum was carefully investigated. The results showed that nTiO2 at concentrations ≥20mg/L could significantly inhibit P. tricornutum growth. The 5-day EC50 of nTiO2 to P. tricornutum growth is 167.71mg/L. Interestingly, nTiO2 was found to exert its most severe inhibition effects on the first day of exposure, at a lower EC50 of 12.65mg/L. During the experiment, nTiO2 aggregates were found to entrap algae cells, which is likely responsible for the observed toxic effects. Direct physical effects such as cell wall damage from the algae entrapment were confirmed by flow cytometry and TEM imaging. Moreover, low indirect effects such as shading and oxidative stress were observed, which supported the idea that direct physical effects could be the dominant factor that causes nTiO2 toxicity in P. tricornutum. Our research provides direct evidence for the toxicological impact of nTiO2 on marine microalgae, which will help us to build a good understanding of the ecological risks of nanoparticles in the marine environment.

Histopathological assessment and inflammatory response in the digestive gland of marine mussel Mytilus galloprovincialis exposed to cadmium-based quantum dots

Although tissue-level biomarkers have been widely applied in environmental toxicology studies, the knowledge using this approach in marine invertebrates exposed to engineered nanomaterials (ENMs) remains limited. This study investigated histopathological alterations and inflammatory responses induced by Cd-based quantum dots (QDs), in comparison with their dissolved counterparts, in the marine mussel Mytilus galloprovincialis. Mussels were exposed to CdTe QDs and dissolved Cd at the same concentration (10μg Cd L(-1)) for 14days and a total of 15 histopathological alterations and 17 histomorphometric parameters were analysed in the digestive gland along with the determination of histopathological condition indices (Ih). A multivariate analysis showed that the mussel response to QDs was more related to exposure time, inflammatory conditions (frequency of haemocytic infiltration and granulocytomas) and changes of cell-type composition (especially the rate between basophilic and digestive cells) when compared to dissolved Cd, while the response to dissolved Cd was associated with histomorphometric parameters of the epithelium and lumen of digestive tubules and increase of the atrophic tubule frequency. Both Cd forms induced higher Ih compared to unexposed mussels indicating a significant decrease in the health status of digestive gland in a Cd form and time-dependent pattern. Results indicate that the multiparametric tissue-level biomarkers in the digestive gland provide a suitable approach to assess the ecotoxicity and mode of action of metal-based ENMs in marine bivalves.

Toxicity assessment and comparison between two types of iron oxide nanoparticles in Mytilus galloprovincialis

Nanoparticles (NPs), due to their increased application and production, are being released into the environment with unpredictable impact on the physiology of marine organisms, as well as on entire ecosystems and upcoming effects on human health. The aim of the present study was to evaluate and compare the oxidative responses of the mussel Mytilus galloprovincialis after exposure to iron oxide NPs and to iron oxide NPs incorporated into zeolite for 1, 3 and 7 days. Our results showed that both effectors induced changes on animal physiology by causing oxidative stress in hemocytes of exposed mussels compared to control animals. This was shown by the significant increase in reactive oxygen species (ROS) production, protein carbonylation, lipid peroxidation, ubiquitin conjugates and DNA damage. In addition an increase in prooxidant levels as measured by the prooxidant-antioxidant balance (PAB) assay was observed in exposed mussels' hemolymph. The results show that ROS, DNA damage, protein and lipid oxidation, ubiquitin conjugates and PAB could constitute, after further investigation, reliable biomarkers for the evaluation of pollution or other environmental stressors. In addition, more studies are needed in order to ensure the safety of these NPs on various biomedical applications, since it is critical to design NPs that they meet the demands of application without causing cellular toxicity.

Tissue specific responses to cadmium-based quantum dots in the marine mussel Mytilus galloprovincialis

In recent years, Cd-based quantum dots (QDs) have generated interest from the life sciences community due to their potential applications in nanomedicine, biology and electronics. However, these engineered nanomaterials can be released into the marine environment, where their environmental health hazards remain unclear. This study investigated the tissue-specific responses related to alterations in the antioxidant defense system induced by CdTe QDs, in comparison with its dissolved counterpart, using the marine mussel Mytilus galloprovincialis. Mussels were exposed to CdTe QDs and dissolved Cd for 14 days at 10 μgCd L(-1) and biomarkers of oxidative stress [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (total, Se-independent and Se-dependent GPx) and glutathione-S-transferase (GST) activities] were analyzed along with Cd accumulation in the gills and digestive gland of mussels. Results show that both Cd forms changed mussels' antioxidant responses with distinct modes of action (MoA). There were tissue- and time-dependent differences in the biochemical responses to each Cd form, wherein QDs are more pro-oxidant when compared to dissolved Cd. The gills are the main tissue affected by QDs, with effects related to the increase of SOD, GST and GPx activities, while those of dissolved Cd was associated to the increase of CAT activity, Cd accumulation and exposure time. Digestive gland is a main tissue for accumulation of both Cd forms, but changes in antioxidant enzyme activities are smaller than in gills. A multivariate analysis revealed that the antioxidant patterns are tissue dependent, indicating nano-specific effects possibly associated to oxidative stress and changes in redox homeostasis.

Ecotoxicological impact of engineered nanomaterials in bivalve molluscs: An overview

The increasing production and application of engineered nanomaterials (ENMs) in consumer products over the past decade will inevitably lead to their release into aquatic systems and thereby cause the exposure to aquatic organisms, resulting in growing environmental and human health concern. Since bivalves are widely used in the monitoring of aquatic pollution, the aim of this review was to compile and analyse data concerning the ecotoxicity of ENMs using bivalve molluscs. The state of the art regarding the experimental approach, characterization, behaviour, fate, bioaccumulation, tissue and subcellular distribution and mechanisms of toxicity of ENMs in marine and freshwater bivalve molluscs is summarized to achieve a new insight into the mode of action of these nanoparticles in invertebrate organisms. This review shows that the studies about the toxic effects of ENMs in bivalves were conducted mainly with seawater species compared to freshwater ones and that the genus Mytilus is the main taxa used as a model system. There is no standardization of experimental approaches for toxicity testing and reviewed data indicate the need to develop standard protocols for ENMs ecotoxicological testing. In general, the main organ for ENM accumulation is the digestive gland and their cellular fate differs according to nano-specific properties, experimental conditions and bivalve species. Endosomal-lysosomal system and mitochondria are the major cellular targets of ENMs. Metal based ENMs mode of action is related mainly to the dissolution and/or release of the chemical component of the particle inducing immunotoxicity, oxidative stress and cellular injury to proteins, membrane and DNA damage. This review indicates that the aquatic environment is the potential ultimate fate for ENMs and confirms that bivalve molluscs are key model species for monitoring aquatic pollution by ENMs.

Toxicokinetics and tissue distribution of cadmium-based Quantum Dots in the marine mussel Mytilus galloprovincialis

Environmental health hazards of Quantum Dots (QDs) are of emergent concern, but limited data is available about their toxicokinetics (TK) and tissue distribution in marine bivalves. This study investigated the QDs behavior in seawater, their TK and tissue distribution in Mytilus galloprovincialis, in comparison with soluble Cd. Mussels were exposed to CdTe QDs and soluble Cd for 21 days at 10 μgCd L(-1) followed by a 50 days depuration. TK of QDs in mussels is related to the homo-aggregate uptake, surface charge, aggregation and precipitation as key factors. There were tissue- and time-dependent differences in the TK of both Cd forms, and soluble Cd is the most bioavailable form. Digestive gland is a preferential site for QDs storage and both Cd forms are not eliminated by mussels (t1/2>50 days). Results indicate that the TK model of CdTe QDs in marine mussels is distinct from their soluble counterparts.

Interactive effects of n-TiO2 and 2,3,7,8-TCDD on the marine bivalve Mytilus galloprovincialis

Despite the growing concern over the potential biological impact of nanoparticles (NPs) in the aquatic environment, little is known about their interactions with other pollutants. The bivalve Mytilus sp, largely utilized as a sentinel for marine contamination, has been shown to represent a significant target for different types of NP, including n-TiO2, one of the most widespread in use. In this work, the possible interactive effects of n-TiO2 and 2,3,7,8-TCDD, chosen as models of NP and organic contaminant, respectively, were investigated in Mytilus galloprovincialis. In vitro experiments with n-TiO2 and TCDD, alone and in combination, were carried out in different conditions (concentrations and times of exposure), depending on the target (hemocytes, gill cells and biopsies) and the endpoint measured. Mussels were also exposed in vivo to n-TiO2 (100 μg L(-1)) or to TCDD (0.25 μg L(-1)), alone and in combination, for 96 h. A wide range of biomarkers, from molecular to tissue level, were measured: lysosomal membrane stability and phagocytosis in hemocytes, ATP-binding cassette efflux transporters in gills (gene transcription and efflux activity), several biomarkers of genotoxicity in gill and digestive cells (DNA damage, random amplified polymorphic DNA-RAPD changes), lysosomal biomarkers and transcription of selected genes in the digestive gland. The results demonstrate that n-TiO2 and TCDD can exert synergistic or antagonistic effects, depending on experimental condition, cell/tissue and type of measured response. Some of these interactions may result from a significant increase in TCDD accumulation in whole mussel organisms in the presence of n-TiO2, indicating a Trojan horse effect. The results represent the most extensive data obtained so far on the sub-lethal effects of NPs and organic contaminants in aquatic organisms. Moreover, these data extend the knowledge on the molecular and cellular targets of NPs in bivalves.

Evaluation of cadmium, lead and metallothionein contents in the tissues of mussels (Mytilus galloprovincialis) from the Campania coast (Italy): levels and seasonal trends

The biological effect of seasonality on cadmium, lead and metallothionein contents was assessed in mussels Mytilus galloprovincialis from natural banks located along the coastline of the Gulf of Naples (Campania, Italy). Heavy metals and metallothionein concentrations were measured in digestive and reproductive glands. The results showed a clear correlation between metallothionein content and the reproductive gland status determined during the seasons; on the contrary, no correlation was found between metallothionein and metal contents. Data allow us to hypothesize that metallothionein functions go beyond metal detoxification, thus opening new scenarios for these proteins in invertebrates. The effect of seasons on metals concentration in mussel tissues showed similar seasonal patterns between the sites, regardless of their anthropogenic impacts. Cadmium content was not strictly related to seasonal periods, whereas lead content was significantly lower in summer. The results also indicate that the metal contents in mussels from the Gulf of Naples do not represent a risk to human health, even in the period of their maximum accumulation, and that the relaying of mussels before marketing could improve the animal stress conditions, but having a slight effect on metal excretion.

Impacts of metal and metal oxide nanoparticles on marine organisms

Increasing use of metal and metal oxide nanoparticles [Me(O)NPs] in products means many will inevitably find their way into marine systems. Their likely fate here is sedimentation following hetero-aggregation with natural organic matter and/or free anions, putting benthic, sediment-dwelling and filter feeding organisms most at risk. In marine systems, Me(O)NPs can absorb to micro-organisms with potential for trophic transfer following consumption. Filter feeders, especially bivalves, accumulate Me(O)NPs through trapping them in mucus prior to ingestion. Benthic in-fauna may directly ingest sedimented Me(O)NPs. In fish, uptake is principally via the gut following drinking, whilst Me(O)NPs caught in gill mucus may affect respiratory processes and ion transport. Currently, environmentally-realistic Me(O)NP concentrations are unlikely to cause significant adverse acute health problems, however sub-lethal effects e.g. oxidative stresses have been noted in many organisms, often deriving from dissolution of Ag, Cu or Zn ions, and this could result in chronic health impacts.

Zinc oxide nanoparticles toxicity to Daphnia magna: size-dependent effects and dissolution

As the production of zinc oxide nanoparticles (ZnO-NPs) and other metal oxides is exponentially increasing, it is important to investigate potential environmental and health impacts of such nanoparticles. Nanoparticles' properties (e.g., size, dissolution rate) may change in different water media, and their characterization is essential to derive conclusions about toxicity results. Therefore, an aquatic model organism, Daphnia magna, was used to investigate the effect of ZnO-NPs with 2 different particle sizes (30 nm and 80-100 nm) and then compare these effects with ZnO microsized particles (>200 nm) and the ionic counterpart (in the form of ZnCl2 ) on immobilization, feeding inhibition, and reproduction endpoints. The 48-h median lethal concentration (LC50) for immobilization ranged between 0.76 mg Zn L(-1) for the ionic zinc and 1.32 mg Zn L(-1) for ZnO-NPs of 80 nm to 100 nm. For the chronic exposures, the reproduction output was impaired similarly among zinc exposures and possibly driven mainly by the zinc ionic form. The concentrations used showed a total dissolution after 48 h. On the other hand, feeding activity was more affected by the 30 nm ZnO-NPs than by the ionic zinc, showing that the particulate form was also playing an important role in the feeding inhibition of D. magna. Dissolution and particle size in the daphnia test media were found to be essential to derive conclusions on toxicity. Therefore, they can possibly be considered critical for evaluating nanoparticles' toxicity and fate.