Microalgal ecotoxicity of nanoparticles: An updated review

Exploring the impact of silver-based nanomaterial feed additives on green algae through single-cell techniques

Silver in its various forms, including dissolved silver ions (Ag+) and silver nanoparticles (AgNPs), is a promising alternative to traditional antibiotics, largely used in livestock as feed additives and could contribute to the decrease and avoidance of the development of antibiotic resistance. The present study aims to assess the potential ecotoxicity of a silver-based nanomaterial (Ag-kaolin), the feed supplemented with the nanomaterial and the faeces since the latter are the ones that finally reach the environment. To this end, green alga Raphidocellis subcapitata was exposed to the extracts of Ag-kaolin, supplemented feed, and pig faeces for 72 h, along with Ag+ and AgNPs as controls for comparison purposes. Given the complexity of the studied materials, single-cell techniques were used to follow the changes in the cell numbers and chlorophyll fluorescence by flow cytometry, and the accumulation of silver in the exposed cells by single cell inductively coupled plasma mass spectrometry (SC-ICP-MS). Changes in cell morphology were observed by cell imaging multimode reader. The results revealed a decrease in chlorophyll fluorescence, even at low concentrations of Ag-kaolin (10 μg L-1) after 48 h of exposure. Additionally, complete growth inhibition was found with this material like the results obtained by exposure to Ag+. For the supplemented feed, a concentration of 50 μg L-1 was necessary to achieve complete growth inhibition. However, the behaviour differed for the leachate of faeces, which released Ag2S and AgCl alongside Ag+ and AgNPs. At 50 μg L-1, inhibition was minimal, primarily due to the predominance of less toxic Ag2S in the leachate. The uptake of silver by the cells was confirmed with all the samples through SC-ICP-MS analysis. These findings demonstrate that the use of Ag-kaolin as a feed supplement will lead to a low environmental impact.

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

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

Slightly acidic electrolyzed water significantly restrains the accumulation of the microalgae Pseudokirchneriella subcapitata in hydroponic systems

AIMS

This study explored the effects of slightly acidic electrolyzed water (SAEW) on algae to exploit technologies that effectively suppress algal growth in hydroponic systems and improve crop yield.

METHODS AND RESULTS

The effects of SAEW on algal growth and the response mechanisms of algae to SAEW were investigated. Moreover, we studied whether the application of SAEW adversely affected tomato seedling growth. The results showed that SAEW significantly inhibited algal growth and destroyed the integrity of the algal cells. In addition, the intracellular oxidation-reduction system of algae was greatly influenced by SAEW. The H2O2, O2-, malondialdehyde (MDA), and reactive oxygen species (ROS) fluorescence signals were significantly induced by SAEW, and superoxide dismutase (SOD), peroxidase (POD), and glutathione reductase (GR) activities were greatly enhanced by a low SAEW concentration but significantly inhibited by SAEW with a high available chlorine concentration, which may contribute to heavy oxidative stress on algal growth and cell structure break down, eventually causing the death of algae and cell number decrease. We also found that regardless of the concentration of SAEW (from 10 to 40 mg L-1), there was no significant change in the germination index, length, or fresh weight of the hydroponic tomato seedlings.

CONCLUSIONS

Our findings demonstrate that SAEW can be used in hydroponic systems to restrain algae with no negative impact on tomato plants.

A critical review on fate, behavior, and ecotoxicological impact of zinc oxide nanoparticles on algae

The rapid inclusion of zinc oxide nanoparticles (ZnO NPs) in nanotechnology-based products over the last decade has generated a new threat in the apprehension of the environment. The massive use of zinc nanosized products will certainly be disposed of and be released, eventually entering the aquatic ecosystem, posing severe environmental hazards. Moreover, nanosized ZnO particles owing the larger surface area per volume exhibit different chemical interactions within the aquatic ecosystem. They undergo diverse potential transformations because of their unique physiochemical properties and the feature of receiving medium. Therefore, assessment of their impact is critical not only for scavenging the present situation but also for preventing unintended environmental hazards. Algae being a primary producer of the aquatic ecosystem help assess the risk of massive NPs usage in environmental health. Because of their nutritional needs and position at the base of aquatic food webs, algal indicators exhibit relatively unique information concerning ecosystem conditions. Moreover, algae are presently the most vital part of the circular economy. Hence, it is imperative to understand the physiologic, metabolic, and morphologic changes brought by the ZnO NPs to the algal cells along with the development of the mechanism imparting toxicity mechanism. We also need to develop an appropriate scientific strategy in the innovation process to restrain the exposure of NPs at safer levels. This review provides the details of ZnO NP interaction with algae. Moreover, their impact, mechanism, and factors affecting toxicity to the algae are discussed.

Physiological and transcriptomic analysis reveals the toxic and protective mechanisms of marine microalga Chlorella pyrenoidosa in response to TiO2 nanoparticles and UV-B radiation

Concerns have been raised regarding the adverse effects of nanoparticles (NPs) on marine organisms, as an increasing number of NPs inevitably enter the marine environment with the development of nanotechnology. Owing to the photocatalytic properties, TiO2 NPs' toxicity may be aggravated by enhanced UV-B resulting from stratospheric ozone depletion. However, the molecular mechanisms of phytoplankton in response to TiO2 NPs under UV-B remains poorly understood. In this study, we integrated whole transcriptome analysis with physiological data to provide understanding on the toxic and protective mechanisms of marine Chlorella pyrenoidosa in response to TiO2 NPs under UV-B. The results indicated that the changes in gene expression could be related to the growth inhibition and TiO2 NP internalization in C. pyrenoidosa, and several molecular mechanisms were identified as toxicity response to TiO2 NPs and UV-B. Differential expression of genes involved in glycerophospholipids metabolism indicated that cell membrane disruption allowed TiO2 NPs to enter the algal cell under UV-B exposure, although the up-regulation of genes involved in the general secretory dependent pathway and the ATP-binding cassette transporter family drove cellular secretion of extracellular polymeric substances, acting as a barrier that prevent TiO2 NP internalization. The absence of changes in gene expression related to the antioxidant system may be responsible for the severe oxidative stress observed in algal cells following exposure to TiO2 NPs under UV-B irradiation. Moreover, differential expression of genes involved in pathways such as photosynthesis and energy metabolism were up-regulated, including the light-harvesting, photosynthetic electron transport coupled to photophosphorylation, carbon fixation, glycolysis, pentose phosphate pathway, tricarboxylic acid cycle, and oxidative phosphorylation, indicating that more energy and metabolites were supplied to cope with the toxicity of TiO2 NPs and UV-B. The obtained results provide valuable information on the molecular mechanisms of response of marine phytoplankton exposed to TiO2 NPs and UV-B.

Interaction of Fe2O3 nanoparticles with marine microalga Chlorella sorokiniana: Analysis of growth, morphological changes and biochemical composition

The wide utilization of iron-based nanoparticles (NPs) based on their preferential properties has led to the discharge and accumulation of these materials into the aquatic environment. In this regard, a comparative study of different concentrations of α-Fe2O3 NPs and their micro form was conducted using microalga Chlorella sorokiniana up to the stationary growth phase. This study revealed that high concentrations of NPs (100 and 200 mg L-1) imposed a stressful condition on algal cells documented by a reduction in microalga growth, including cell number and specific growth rate. The physical contact between the algal cells and NPs resulted in a shading effect as well as morphological changes validated by scanning electron microscope results. The biochemical composition of C. sorokiniana exposed to high levels of Fe2O3 NPs was also evaluated. The increase in total carbohydrate content of algal cells along with a significant reduction in unsaturated fatty acids was found. Moreover, Fe2O3 NPs exposure induced oxidative stress evidenced by an increase in lipid peroxidation. To cope with oxidative stress, superoxide dismutase activity and antioxidant potential of microalga as defensive mechanisms increased in the culture with high concentrations of NPs. Besides, due to the interactions, microalga tended to form a protective layer from further cell-NP interactions through the secretion of extracellular polymeric substances. Nonetheless, the nano form of Fe2O3 was more toxic than its micro form due to its small size. Overall, this trial may provide additional insight into the toxicological mechanism and safety assessments of Fe2O3 NPs in the aquatic environment.

Toxic effects of nSiO2 and mPS on diatoms Nitzschia closterium f. minutissima

To investigate the toxic mechanism of SiO2 nanoparticles (nSiO2) and polystyrene microplastics (mPS) on microalgae Nitzschia closterium f. minutissima, growth inhibition tests were carried out. The growth and biological responses of the algae exposed to nSiO2 (0.5, 1, 2, 5, 10, 30 mg L-1) and mPS (1, 5, 10, 30 and 75 mg L-1) were explored in f/2 media for 96 h. Both micro-/nano-particles (MNPs) inhibited the growth of N. closterium f. minutissima in a concentration- and time-dependent manner. The toxic effect of mPS on N. closterium f. minutissima is higher than that of nSiO2, because silicon is essential for diatoms to maintain cell wall integrity, and the addition of appropriate amounts of nSiO2 can be absorbed and used as a nutrient to promote diatom growth and protect the integrity of the siliceous shell to some extent. Both MNPs induce the production of excess oxidation and activate the cellular antioxidant defense system, leading to increased SOD and CAT activity as a means to resist oxidative damage to the cell, and eliminating excess ROS and maintaining normal cell morphology and metabolism. SEM is consistent with the results of MDA, showing that mPS with high concentrations attach to the surface of algal cells to produce heterogeneous aggregates and disrupt the cell wall and cell membrane, causing the cells to expand and rupture. This study contributes to the understanding of the size effect of MNPs on the growth of marine diatom.

Application of Nanomaterials in the Production of Biomolecules in Microalgae: A Review

Nanomaterials (NMs) are becoming more commonly used in microalgal biotechnology to empower the production of algal biomass and valuable metabolites, such as lipids, proteins, and exopolysaccharides. It provides an effective and promising supplement to the existing algal biotechnology. In this review, the potential for NMs to enhance microalgal growth by improving photosynthetic utilization efficiency and removing reactive oxygen species is first summarized. Then, their positive roles in accumulation, bioactivity modification, and extraction of valuable microalgal metabolites are presented. After the application of NMs in microalgae cultivation, the extracted metabolites, particularly exopolysaccharides, contain trace amounts of NM residues, and thus, the impact of these residues on the functional properties of the metabolites is also evaluated. Finally, the methods for removing NM residues from the extracted metabolites are summarized. This review provides insights into the application of nanotechnology for sustainable production of valuable metabolites in microalgae and will contribute useful information for ongoing and future practice.

Comparative toxicity assessment of individual, binary and ternary mixtures of SiO2, Fe3O4, and ZnO nanoparticles in freshwater microalgae, Scenedesmus obliquus: Exploring the role of dissolved ions

Metal oxide nanoparticles (NPs) are considered among the most prevalent engineered nanomaterials. To have a deeper understanding of the mode of action of multiple metal oxide nanoparticles in mixtures, we have used a unicellular freshwater microalga Scenedesmus obliquus as a model organism. The toxicity of silicon dioxide (SiO2), iron oxide (Fe3O4), and zinc oxide (ZnO) NPs was studied individually as well as in their binary (SiO2 + Fe3O4, Fe3O4 + ZnO, and ZnO + SiO2) and ternary (SiO2 + Fe3O4 + ZnO) combinations. The effects of metal ions from ZnO and Fe3O4 were investigated as well. The results observed from the study, showed that a significant amount of toxicity was contributed by the dissolved ions in the mixtures of the nanoparticles. Decreases in the cell viability, ROS generation, lipid peroxidation, antioxidant enzyme activity, and photosynthetic efficiency were analyzed. Among all the individual particles, ZnO NPs showed the maximum effects and increased the toxicities of the binary mixtures. The binary and ternary mixtures of the NPs clearly showed increased toxic effects in comparison with the individual entities. However, the ternary combination had lesser toxic effects than the binary combination of Fe3O4 + ZnO. The decline in cell viability and photosynthetic efficiency were strongly correlated with various oxidative stress biomarkers emphasizing the crucial role of reactive oxygen species in inducing the toxic effects. The findings from this study highlight the importance of evaluating the combinatorial effects of various metal oxide NPs as part of a comprehensive ecotoxicity assessment in freshwater microalgae.

A phyco-nanobionics biohybrid system for increased carotenoid accumulation in C. sorokiniana UUIND6

Recent advancements in "phyco-nanobionics" have sparked considerable interest in the ability of microalgae to synthesize high-value natural bioactive compounds such as carotenoid pigments, which have been highlighted as an emergent and vital bioactive compound from both industrial and scientific perspectives. Such bioactive compounds are often synthesized by either altering the biogenetic processes existing in living microorganisms or using synthetic techniques derived from petroleum-based chemical sources. A bio-hybrid light-driven cell factory system was established herein by using harmful macroalgal bloom extract (HMBE) and efficient light-harvesting silver nanoparticles (AgNPs) to synthesize HMBE-AgNPs and integrating the synthesized HMBE-AgNPs in various concentrations (1, 2.5, 5 and 10 ppm) into the microalgae C. sorokiniana UUIND6 to improve the overall solar-to-chemical conversion efficiency in carotenoid pigment synthesis in microalgae. The current study findings found high biocompatibility of 5 ppm HMBE-AgNP concentration that can serve as a built-in photo-sensitizer and significantly improve ROS levels in microalgae (6.75 ± 0.25 μmol H2O2 g-1), thus elevating total photosynthesis resulting in a two-fold increase in carotenoids (457.5 ± 2.5 μg mL-1) over the native microalgae without compromising biomass yield. NMR spectroscopy was additionally applied to acquire a better understanding of pure carotenoids derived from microalgae, which indicated similar peaks in both spectra when compared to β-carotene. Thus, this well-planned bio-hybrid system offers a potential option for the cost-effective and long-term supply of these natural carotenoid bio-products.

The Comparative Toxic Impact Assessment of Carbon Nanotubes, Fullerene, Graphene, and Graphene Oxide on Marine Microalgae Porphyridium purpureum

The growing production and application of carbon-based nanomaterials (CNMs) represent possible risks for aquatic systems. However, the variety of CNMs with different physical and chemical properties and different morphology complicate the understanding of their potential toxicity. This paper aims to evaluate and compare the toxic impact of the four most common CNMs, namely multiwalled carbon nanotubes (CNTs), fullerene (C60), graphene (Gr), and graphene oxide (GrO) on the marine microalgae Porphyridium purpureum. The microalgae cells were exposed to the CNMs for 96 h and measured by flow cytometry. Based on the obtained results, we determined no observed effect level (NOEL), and calculated EC10 and EC50 concentrations for growth rate inhibition, esterase activity, membrane potential, and reactive oxygen species (ROS) generation changes for each tested CNM. According to the sensitivity (growth rate inhibition) of P. purpureum, the used CNMs can be listed in the following order (EC50 in mg/L, 96 h): CNTs (2.08) > GrO (23.37) > Gr (94.88) > C60 (>131.0). The toxicity of CNTs was significantly higher than the toxic effect of the other used CNMs, and only this sample caused an increase in ROS generation in microalgae cells. This effect was apparently caused by the high affinity between particles and microalgae associated with the presence of exopolysaccharide coverage on P. purpureum cells.

Toxicity Effects of Polystyrene Nanoplastics with Different Sizes on Freshwater Microalgae Chlorella vulgaris

The ubiquitous nature of plastics, particularly nanoplastics, raises concern about their potential effects on primary producer microalgae. Currently, the impacts and potential mechanisms of nanoplastics on microalgae are not fully understood. In this study, the effects of two plain commercial polystyrene nanoplastics (PS-NPs) with different sizes (50 nm and 70 nm) on C. vulgaris were assessed in a concentration range of 0-50 mg/L during 72 h exposure periods. Results revealed that both PS-NPs have dose-dependent toxicity effects on C. vulgaris, as confirmed by the decrease of growth rates, chlorophyll a and esterase activities, and the increase of ROS, MDA, and membrane damage. The membrane damage was caused by the agglomeration of PS-NPs on microalgae and may be the key reason for the toxicity. Compared with 70 nm PS-NPs (72 h EC₅₀ >50 mg/L), 50 nm PS-NPs posed greater adverse effects on algae, with an EC_50-72h of 19.89 mg/L. FTIR results also proved the stronger variation of macromolecules in the 50 nm PS-NPs treatment group. This phenomenon might be related to the properties of PS-NPs in exposure medium. The lower absolute zeta potential value of 50 nm PS-NPs induced the stronger interaction between PS-NPs and algae as compared to 70 nm PS-NPs, leading to severe membrane damage and the loss of esterase activity as well as settlement. These findings emphasized the importance of considering the impacts of commercial PS-NPs properties in toxicity evaluation.

Evaluation of growth and antioxidant responses of freshwater microalgae Chlorella sorokiniana and Scenedesmus dimorphus under exposure of moxifloxacin

As one of the fourth-generation fluoroquinolone antibiotics, moxifloxacin (MOX) has been frequently released to the aquatic environment, threatening local organisms. However, researches on its ecotoxicity to aquatic organisms are still limited. This study analyzed effects of MOX on the growth, photosynthesis and oxidative stress of two common types of freshwater microalgae, Chlorella sorokiniana and Scenedesmus dimorphus. The 96 h-EC₅₀ values of MOX for C. sorokiniana and S. dimorphus were 28.42 and 26.37 mg/L, respectively. Although variations of specific indicators for photosynthetic fluorescence intensity were different, photosystems of two types of microalgae were irreversibly damaged. The malondialdehyde content and superoxide dismutase of C. sorokiniana and S. dimorphus evidently increased, indicating that the exposure of MOX caused serious oxidative stress. Chlorophyll a, b and carotenoids contents of C. sorokiniana increased, probably resulting from the resistance to oxidative stress, whereas they were inhibited due to oxidation damage as for S. dimorphus. Risk quotients (RQs) of MOX for C. sorokiniana and S. dimorphus in wastewater were 7.882 and 8.495, respectively, which demonstrated that MOX had a considerable risk to aquatic environment, especially in the context of its increasing use in practice.

Carbon nanomaterial-treated cell cultures of Nostoc flagelliforme produce exopolysaccharides with ameliorative physio-chemical properties

The feasibility and efficiency of carbon nanomaterials (CNMs) in algal biotechnology are less known. In this study, the influences of four CNMs, graphene (G), graphene oxide (GO), multiwalled carbon nanotube (MWCNT), and aminated multiwalled carbon nanotube (MWCNT-NH₂), on cell growth and exopolysaccharide (EPS) production, as well as the physiochemical properties of EPS, were investigated in cell culture of Nostoc flagelliforme. A proper concentration (15 mg L^-1) of four CNMs was chosen for use after a preliminary test. Upon GO treatment, the biomass was improved by 11.1 % and the EPS production was increased by 36.1 % on day 16 compared to the nontreated control. Four CNM treatments significantly improved cellular O₂·^- and H₂O₂ levels as well as superoxide dismutase and catalase activities. The monosaccharide compositions and functional groups of the EPSs were obviously altered by the CNM treatments. Particularly, the GO treatment-resulting EPS showed obviously improved flocculating ability, water absorption ability, and reactive oxygen species scavenging ability. In general, four CNMs exerted distinct influences on the production and physio-chemical property alteration of the EPS in N. flagelliforme culture. This work expands our understanding of the application of CNMs in the induced production and functional modification of polysaccharides during algal cultivation.

Preparation, Characterization, and Environmental Safety Assessment of Dithiocarbazate Loaded Mesoporous Silica Nanoparticles

Dithiocarbazates comprise an important class of Schiff bases with remarkable biological applications due to the imine group present in their structure. However, full exploitation of the biological activity of 3-methyl-5-phenyl-pyrazoline-1-(S-benzyldithiocarbazate) (DTC) is limited due to its easy degradation and poor solubility in aqueous solutions. The loading of DTC into mesoporous silica nanoparticles (MSiNPs) can be an excellent strategy to improve the solubility of DTC in the aqueous medium. Therefore, the main goal of the present work was to design MSiNP-DTC and to evaluate the success of the loading process by measuring its physicochemical properties and evaluating the environmental safety of the new DTC formulation using different aquatic organisms, such as the microalgae Raphidocelis subcapitata, the macrophyte Lemna minor, and the marine bacterium Aliivibrio fischeri. DTC, MSiNP, and MSiNP-DTC concentrations ranging from 8.8 to 150 mg L^-1 were tested for all the species, showing low toxicity against aquatic organisms. Loading DTC into MSiNPs caused a slight increase in the toxicity at the concentrations tested, only allowing for the estimation of the effect concentration causing a 20% reduction in bioluminescence or growth rate (EC₂₀). Therefore, despite the potential of MSiNPs as a drug delivery system (DDS), it is of utmost importance to assess its impact on the safety of the new formulations.

The comprehensive effects of aluminum oxide nanoparticles on the physiology of freshwater microalga Scenedesmus obliquus and it's phycoremediation performance for the removal of sulfacetamide

Nanoparticles are inevitable byproducts of modern industry. However, the environmental impacts arising from industrial applications of nanoparticles are largely under-reported. This study evaluated the ecotoxicological effects of aluminum oxide nanoparticles (Al₂O₃NP) and its influence on sulfacetamide (SA) biodegradation by a freshwater microalga, Scenedesmus obliquus. Although Al₂O₃NP showed limited toxicity effect on S. obliquus, we observed the toxicity attenuation aspect of Al₂O₃NP in a mixture of sulfacetamide on microalgae. The addition of 100 mg L^-1 of Al₂O₃NP and 1 mg L^-1 of SA reduced total chlorophyll by 23.3% and carotenoids by 21.6% in microalgal compared to control. The gene expression study demonstrated that ATPF0C, Lhcb1, HydA, and psbA genes responsible for ATP synthesis and the photosynthetic system were significantly downregulated, while the Tas gene, which plays a major role in biodegradation of organic xenobiotic chemicals, was significantly upregulated at 1 and 100 mg L^-1 of Al₂O₃NP. The S. obliquus removed 16.8% of SA at 15 mg L^-1 in 14 days. However, the removal was slightly enhanced (18.8%) at same concentration of SA in the presence of 50 mg L^-1 Al₂O₃NP. This result proves the stability of sulfacetamide biodegradation capacity of S. obliquus in the presence of Al₂O₃NP co-contamination. The metabolic analysis showed that SA was degraded into simpler byproducts such as sulfacarbamide, sulfaguanidine, sulfanilamide, 4-(methyl sulfonyl)aniline, and N-hydroxy-benzenamine which have lower ecotoxicity than SA, demonstrating that the ecotoxicity of sulfacetamide has significantly decreased after the microalgal degradation, suggesting the environmental feasibility of microalgae-mediated wastewater technology. This study provides a deeper understanding of the impact of nanoparticles such as Al₂O₃NP on aquatic ecosystems.

Aquatic organisms modulate the bioreactivity of engineered nanoparticles: focus on biomolecular corona

The increased use of nanoparticle (NP)-enabled materials in everyday-life products have raised concerns about their environmental implications and safety. This motivated the extensive research in nanoecotoxicology showing the possibility that NPs could cause harm to the aquatic organisms if present at high concentrations. By contrast, studies dealing with influence that organisms could exert on the fate and thus effects of NPs are still very rare. Drawing on the existing up-to-date knowledge we critically discuss the formation of biomolecular corona as one of the mechanisms by which organisms exerted control on the NPs fate in the aquatic and biotic environments. We focused the formation of corona by exogeneous and endogenous biomolecules and illustrated the discussion with the specific example of phytoplankton and aquatic invertebrate species. We highlighted the necessity to incorporate the concept of biomolecular corona within more general framework considering the feedback of aquatic organisms and the control they exert in shaping the fate and impact of NPs in the aquatic and biological environment. In our view such broader perspective will contribute to get novel insights into the drivers of environmental transformations of NPs and their mechanisms, which are important in environmental risk assessment.

Mechanism of MnO2 nanorods toxicity in marine microalgae Chlorella sorokiniana during long-term exposure

Due to the increasing production and use of nanomaterials (NMs), their potential toxic impacts on the environment should be considered for a safe application of NMs. In this regard, the potential hazards of MnO₂ nanorods (NRs) on the green microalgae Chlorella sorokiniana during long-term exposure were investigated. Exposure to the high concentration of MnO₂ NRs (100 and 200 mg L^-1) significantly reduced the cell number of C. sorokiniana over 20 days of the experiment. The different concentrations of MnO₂ NRs (25-200 mg L^-1) induced the remarkable increase in the chlorophyll (a+b) content of algal cells due to the shading effect of NRs. For more than 72 h, the chlorophyll content of microalgae decreased due to the aggregation of NRs and the possible effects of oxidative stress. Long-term exposure to high concentrations of NRs caused a significant decrease in the primary and secondary metabolites of microalgae, including carotenoids, phenolic compounds, proteins, lipids, and carbohydrates. Oxidative stress was one of the possible toxic mechanisms of MnO₂ NRs to microalgae validated by an increase in lipid peroxidation induced by exposure to NRs. The algal cells increased the catalase activity and the amount of extracellular polymeric substances in response to NRs toxicity. The low level of Mn ions in the culture media indicated that MnO₂ NRs dissolution was not the cause of the observed reduction in the microalgae growth. Moreover, the bulk form of MnO₂ was not involved in the toxic impact of MnO₂, which was documented by an insignificant decrease in the growth, pigment, and lipid peroxidation of C. sorokiniana. These results may provide an additional insight into the potential hazards of MnO₂ NRs on the aquatic ecosystem.

Attitudes, Barriers, Motivations to Sun Protection in Reunion Island’s Schools: Qualitative Study

The incidence of melanoma in Reunion Island is on the rise and is now one of the highest worldwide. Although the main risk factor of melanoma is sun exposure during childhood, sun protection measures remain insufficient in Reunionese schools. From November 2019 to November 2020, we conducted a qualitative study to explore the attitudes, barriers, and motivations to sun protection among the main actors of children’s protection in Reunion Island. Individual semi-directive interviews were performed with 14 children aged 6 to 10 years, 13 parents, and 13 teachers. The interviews were recorded and transcribed. Relevant data were coded, triangulated, analyzed, and then modeled following the methodology of grounded theory. Sufficiency of the data was sought. All 40 participants described their sun protection habits. Protection was lower during school activities than during leisure activities. Parents identified several practical and financial barriers to sun protection. Teachers pointed out the lack of adequate infrastructure and sun protection training. Responsibility for children’s protection was a point of disagreement between parents and teachers. Children limited their use of protection, mainly for reasons of comfort. Children’s sun protection in schools is the responsibility of educational staff, parents, and society at large. Improving communication between these various actors is necessary. Sun safety campaigns and reorganization of the school environment would allow for better protection of the child population.

Toxicity Effects of Combined Mixtures of BDE-47 and Nickel on the Microalgae Phaeodactylum tricornutum (Bacillariophyceae)

Nickel and 2,2’,4,4’-tetrabromodiphenyl ether (BDE-47) are two environmental pollutants commonly and simultaneously present in aquatic systems. Nickel and BDE-47 are individually toxic to various aquatic organisms. However, their toxicity mechanisms are species-dependent, and the toxic effects of combined mixtures of BDE-47 and nickel have not yet been investigated. The present study investigated the toxic effects of combined mixtures of BDE-47 and nickel in the diatom Phaeodactylum tricornutum. BDE-47 and nickel mixtures significantly decreased cell abundance and photosynthetic efficiency, while these cells’ reactive oxygen species (ROS) production significantly increased. The EC₅₀-72 h for BDE-47 and mixtures of BDE-47 and nickel were 16.46 ± 0.93 and 1.35 ± 0.06 mg/L, respectively. Thus, combined mixtures of the two pollutants enhance their toxic effects. Interactions between BDE-47 and nickel were evaluated, revealing synergistic interactions that contributed to toxicity in P. tricornutum. Moreover, transcriptomic analyses revealed photosynthesis, nitrogen metabolism, the biosynthesis of amino acids, the biosynthesis of secondary metabolites, oxoacid metabolism, organic acid metabolism, carboxylic acid metabolism, and oxidation-reduction processes were considerably affected by the mixtures. This study provides evidence for the mechanisms of toxicity from combined BDE-47 and nickel exposure while also improving our understanding of the ecological risks of toxic chemicals on microalgae.

Building the Bridge From Aquatic Nanotoxicology to Safety by Design Silver Nanoparticles

Nanotechnologies have rapidly grown, and they are considered the new industrial revolution. However, the augmented production and wide applications of engineered nanomaterials (ENMs) and nanoparticles (NPs) inevitably lead to environmental exposure with consequences on human and environmental health. Engineered nanomaterial and nanoparticle (ENM/P) effects on humans and the environment are complex and largely depend on the interplay between their peculiar properties such as size, shape, coating, surface charge, and degree of agglomeration or aggregation and those of the receiving media/body. These rebounds on ENM/P safety and newly developed concepts such as the safety by design are gaining importance in the field of sustainable nanotechnologies. This article aims to review the critical characteristics of the ENM/Ps that need to be addressed in the safe by design process to develop ENM/Ps with the ablility to reduce/minimize any potential toxicological risks for living beings associated with their exposure. Specifically, we focused on silver nanoparticles (AgNPs) due to an increasing number of nanoproducts containing AgNPs, as well as an increasing knowledge about these nanomaterials (NMs) and their effects. We review the ecotoxicological effects documented on freshwater and marine species that demonstrate the importance of the relationship between the ENM/P design and their biological outcomes in terms of environmental safety.

Double-dose responses of Scenedesmus capricornus microalgae exposed to humic acid

Dissolved organic matter (DOM) has been found to attenuate the ecotoxicity of various environmental pollutants, but research on its own toxic effects in aquatic ecosystems has been very limited. Herein, the toxic effects of humic acid (HA), a represent DOM typically found in natural waters, on the freshwater alga Scenedesmus capricornus were investigated. As result, HA exerted a double-dose effect on the growth of Scenedesmus capricornus. At HA concentrations below 2.0 mgC/L, the growth of Scenedesmus capricornus was slightly promoted, as was the synthesis of chlorophyll and macromolecules in the algae. Moreover, S. capricornus can maintain its growth by secreting fulvic acid as a nutrient carbon source. However, the growth of Scenedesmus capricornus was significantly inhibited when HA was beyond 2.0 mgC/L. The main mechanisms of humic acid's toxicity were membrane damage and oxidative stress. Particularly, when the oxidative stress exceeds the algae's carrying capacity, the synthesis of EPS is greatly inhibited and HA damage results. Taken together, DOM may have both positive and negative effects on aquatic ecosystems.

The effects of copper ions and copper nanomaterials on the output of amino acids from marine microalgae

In this study, the marine microalgae Skeletonema costatum and Nitzschia closterium were exposed to different forms of copper, such as a metal salt (Cu²⁺), a nano-metal (nano-Cu), and nano-metal oxide (nano-CuO). During a 96-h exposure to nanoparticles (NPs) and salt, the cell number, Cu²⁺ concentration in the culture medium, morphology, and intracellular amino acids were measured to assess the toxicity of the copper materials and the toxicity mechanism of the NPs. As results, the toxicity of Cu²⁺, nano-Cu, and nano-CuO to marine phytoplankton decreased in order. The EC₅₀ values of Cu²⁺ and nano-Cu for S. costatum and N. closterium ranged from 0.356 to 0.991 mg/L and 0.663 to 2.455 mg/L, respectively. Nano-Cu inhibits the growth of marine phytoplankton by releasing Cu²⁺; however, nano-CuO is harmful to microalgae because of the effect of NPs. The secretion of extracellular polymeric substances by microalgae could also affect the toxicity of nano-Cu and nano-CuO to microalgae. S. costatum was more sensitive to copper than N. closterium. Cu²⁺, nano-Cu, and nano-CuO all reduced per-cell amino acids and the total output of algae-derived amino acids by affecting the growth of the phytoplankton. This study helps to understand the risk assessment of nano-Cu and nano-CuO to marine microalgae.

Individual and Binary Mixture Toxicity of Five Nanoparticles in Marine Microalga Heterosigma akashiwo

The investigation of the combined toxic action of different types of nanoparticles (NPs) and their interaction between each other and with aquatic organisms is an important problem of modern ecotoxicology. In this study, we assessed the individual and mixture toxicities of cadmium and zinc sulfides (CdS and ZnS), titanium dioxide (TiO₂), and two types of mesoporous silicon dioxide (with no inclusions (SMB3) and with metal inclusions (SMB24)) by a microalga growth inhibition bioassay. The counting and size measurement of microalga cells and NPs were performed by flow cytometry. The biochemical endpoints were measured by a UV-VIS microplate spectrophotometer. The highest toxicity was observed for SMB24 (EC50, 3.6 mg/L) and CdS (EC50, 21.3 mg/L). A combined toxicity bioassay demonstrated that TiO₂ and the SMB3 NPs had a synergistic toxic effect in combinations with all the tested samples except SMB24, probably caused by a “Trojan horse effect”. Sample SMB24 had antagonistic toxic action with CdS and ZnS, which was probably caused by metal ion scavenging.

Comparison of uptake and elimination kinetics of metallic oxide nanomaterials on the freshwater microcrustacean Daphnia magna

The widespread use and release of nanomaterials (NMs) in aquatic ecosystems is a concerning issue as well as the fate and behavior of the NMs in relation to the aquatic organisms. In this work, the freshwater microcrustacean Daphnia magna was exposed to 12 different and well-known NMs under the same conditions for 24 h and then placed in clean media for 120 h, in order to determine their different uptake and elimination behaviors. The results showed that most of the tested NMs displayed a fast uptake during the first hours arriving to a plateau by the end of the uptake phase. The elimination behavior was determined by a fast loss of NMs during the first hours in the clean media, mainly stimulated by the presence of food. Remaining NMs concentrations can still be found at the end of the elimination phase. Two NMs had a different profile (i) ZnO-NM110 exhibited increase and loss during the uptake phase, and (ii) SiO₂-NM204 did not show any uptake. A toxicokinetic model was applied and the uptake and elimination rates were found along with the dynamic bioconcentration factors. These values allowed to compare the NMs, to cluster them by their similar rates, and to determine that the TiO₂-NM102 is the one that has the fastest uptake and elimination behavior, SiO₂-NM204 has the slowest uptake and CeO₂ <10 nm has the slowest elimination. The present work represents a first attempt to compare different NMs based on their uptake and elimination behaviors from a perspective of the nano-bio interactions influence.

The effects and mechanisms of polystyrene and polymethyl methacrylate with different sizes and concentrations on Gymnodinium aeruginosum

In this study, Gymnodinium aeruginosum was exposed to polystyrene (PS) and polymethyl methacrylate (PMMA) of three particle sizes (0.1 μm, 1.0 μm and 100 μm) and two concentrations (10 mg/L and 75 mg/L) for 96 h. The density of algae cells, the endpoints that reactive oxygen species (ROS), total protein (TP), malondialdehyde (MDA), superoxide dismutase (SOD) and catalase (CAT), scanning and transmission electron microscopy (SEM and TEM) were used to explore the toxicity mechanism to the microalgae. At a concentration of 75 mg/L, the 96 h inhibition ratios (IR) with particle sizes of 0.1 μm, 1.0 μm and 100 μm on G. aeruginosum were 55.9%, 63.7% and 6.0% for PS, respectively, and 3.0%, 4.1% and -0.6% for PMMA, respectively. The most significant changes in ROS, TP, MDA, SOD and CAT were observed at 75 mg/L 1.0 μm of PS when treated for 96 h. When exposed to nanoplastics (NPs) and microplastics (MPs), the algae cells were damaged, and the antioxidant system was activated. Extracellular polymeric substance (EPS) could help to detoxify the algae. In general, PS was more toxic than PMMA. The toxicity of small MNPs (0.1 μm and 1.0 μm) was related to the concentrations, while large MNPs (100 μm) did not.

Toxicity of a Binary Mixture of TiO2 and Imidacloprid Applied to Chlorella vulgaris

Nanoparticles have applications in various fields such as manufacturing and materials synthesis, the environment, electronics, energy harvesting, and medicine. Besides many applications of nanoparticles, further research is required for toxic environmental effect investigation. The toxic effect of titanium dioxide nanoparticles on the physiology of the green alga Chlorella vulgaris was studied with a widely used pesticide, imidacloprid (IMD). Chlorella vulgaris was exposed for 120 h in Bold's basal medium to different toxic compounds, such as (i) a high concentration of TiO₂ nanoparticles, 150-2000 mg/L, usually optimised in the photocatalytic degradation of wastewater, (ii) an extremely toxic pesticide for the aquatic environment, imidacloprid, in concentrations ranging from 5 to 40 mg/L, (iii) TiO₂ nanoparticles combined with imidacloprid, usually used in a photocatalytic system. The results show that the TiO₂ nanoparticles and IMD inhibited Chlorella vulgaris cell growth and decreased the biovolume by approximately 80% when 2 g/L TiO₂ was used, meaning that the cells devised a mechanism to cope with a potentially stressful situation; 120 h of Chlorella vulgaris exposure to 40 mg/L of IMD resulted in a 16% decreased cell diameter and a 41% decrease in cell volume relative to the control sample, associated with the toxic effect of pesticides on the cells. Our study confirms the toxicity of nanoparticles through algal growth inhibition with an effective concentration (EC50) value measured after 72 h of 388.14 mg/L for TiO₂ and 13 mg/L for IMD in a single-toxic system. The EC50 of TiO₂ slowly decreased from 258.42 to 311.11 mg/L when IMD from 5 to 20 mg/L was added to the binary-toxic system. The concentration of TiO₂ in the binary-toxic system did not change the EC50 for IMD, and its value was 0.019 g/L. The photodegradation process of imidacloprid (range of 5-40 mg/L) was also investigated in the algal medium incubated with 150-600 mg/L of titanium dioxide.

Harmful effects of metal(loid) oxide nanoparticles

Abstract

The incorporation of nanomaterials (NMs), including metal(loid) oxide (MOx) nanoparticles (NPs), in the most diversified consumer products, has grown enormously in recent decades. Consequently, the contact between humans and these materials increased, as well as their presence in the environment. This fact has raised concerns and uncertainties about the possible risks of NMs to human health and the adverse effects on the environment. These concerns underline the need and importance of assessing its nanosecurity. The present review focuses on the main mechanisms underlying the MOx NPs toxicity, illustrated with different biological models: release of toxic ions, cellular uptake of NPs, oxidative stress, shading effect on photosynthetic microorganisms, physical restrain and damage of cell wall. Additionally, the biological models used to evaluate the potential hazardous of nanomaterials are briefly presented, with particular emphasis on the yeast Saccharomyces cerevisiae, as an alternative model in nanotoxicology. An overview containing recent scientific advances on cellular responses (toxic symptoms exhibited by yeasts) resulting from the interaction with MOx NPs (inhibition of cell proliferation, cell wall damage, alteration of function and morphology of organelles, presence of oxidative stress bio-indicators, gene expression changes, genotoxicity and cell dead) is critically presented. The elucidation of the toxic modes of action of MOx NPs in yeast cells can be very useful in providing additional clues about the impact of NPs on the physiology and metabolism of the eukaryotic cell. Current and future trends of MOx NPs toxicity, regarding their possible impacts on the environment and human health, are discussed.

Key points

• The potential hazardous effects of MOx NPs are critically reviewed.

• An overview of the main mechanisms associated with MOx NPs toxicity is presented.

• Scientific advances about yeast cell responses to MOx NPs are updated and discussed.

Accumulation and cellular toxicity of engineered metallic nanoparticle in freshwater microalgae: Current status and future challenges

Metal nanoparticles (MNPs) are employed in a variety of medical and non-medical applications. Over the past two decades, there has been substantial research on the impact of metallic nanoparticles on algae and cyanobacteria, which are at the base of aquatic food webs. In this review, the current status of our understanding of mechanisms of uptake and toxicity of MNPs and metal ions released from MNPs after dissolution in the surrounding environment were discussed. Also, the trophic transfer of MNPs in aquatic food webs was analyzed in this review. Approximately all metallic nanoparticles cause toxicity in algae. Predominantly, MNPs are less toxic compared to their corresponding metal ions. There is a sufficient evidence for the trophic transfer of MNPs in aquatic food webs. Internalization of MNPs is indisputable in algae, however, mechanisms of their transmembrane transport are inadequately known. Most of the toxicity studies are carried out with solitary species of MNPs under laboratory conditions rarely found in natural ecosystems. Oxidative stress is the primary toxicity mechanism of MNPs, however, oxidative stress seems a general response predictable to other abiotic stresses. MNP-specific toxicity in an algal cell is yet unknown. Lastly, the mechanism of MNP internalization, toxicity, and excretion in algae needs to be understood carefully for the risk assessment of MNPs to aquatic biota.

Aquatic Toxicity of Photocatalyst Nanoparticles to Green Microalgae Chlorella vulgaris

In the last years, nanoparticles such as TiO2, ZnO, NiO, CuO and Fe2O3 were mainly used in wastewater applications. In addition to the positive aspects concerning using nanoparticles in the advanced oxidation process of wastewater containing pollutants, the impact of these nanoparticles on the environment must also be investigated. The toxicity of nanoparticles is generally investigated by the nanomaterials’ effect on green algae, especially on Chlorella vulgaris. In this review, several aspects are reviewed: the Chlorella vulgaris culture monitoring and growth parameters, the effect of different nanoparticles on Chlorella vulgaris, the toxicity of photocatalyst nanoparticles, and the mechanism of photocatalyst during oxidative stress on the photosynthetic mechanism of Chlorella vulgaris. The Bold basal medium (BBM) is generally recognized as an excellent standard cultivation medium for Chlorella vulgaris in the known environmental conditions such as temperature in the range 20–30 °C and light intensity of around 150 μE·m2·s−1 under a 16/8 h light/dark cycle. The nanoparticles synthesis methods influence the particle size, morphology, density, surface area to generate growth inhibition and further algal deaths at the nanoparticle-dependent concentration. Moreover, the results revealed that nanoparticles caused a more potent inhibitory effect on microalgal growth and severely disrupted algal cells’ membranes.

Long-Term Toxicity of ZnO Nanoparticles on Scenedesmus rubescens Cultivated in Semi-Batch Mode

The scope of this study was to investigate the toxic effects of zinc oxide (ZnO) nanoparticles (NPs) on freshwater microalgae, in long-term semi-batch feeding mode at two different hydraulic retention times (HRTs) (20 and 40 days). A freshwater microalgae, Scenedesmus rubescens, was employed and exposed to a semi-continuous supply of ZnO NPs at a low concentration of 0.081 mg/L for a period of 28 d. Experiments were conducted under controlled environmental conditions. Τhe impact of ZnO NPs on S. rubescens, which was assessed in terms of nutrient removal, biomass growth, and algal lipid content. Semi-batch mode cultures showed that low ZnO NP concentrations at an HRT of 40 d did not have any negative effect on microalgae growth after the fourth day of culture. In contrast, algal growth was inhibited up to 17.5% at an HRT of 20 d in the presence of ZnO NPs. This might be attributed to the higher flow rate applied and ZnO NPs load. A positive correlation between nutrient removal and microalgae growth was observed. The algal lipid content was, in most cases, higher in the presence of ZnO NPs at both HRTs, indicating that even low ZnO NPs concentration cause stress resulting in higher lipid content.

Glycan Nanobiosensors

This review paper comprehensively summarizes advances made in the design of glycan nanobiosensors using diverse forms of nanomaterials. In particular, the paper covers the application of gold nanoparticles, quantum dots, magnetic nanoparticles, carbon nanoparticles, hybrid types of nanoparticles, proteins as nanoscaffolds and various nanoscale-based approaches to designing such nanoscale probes. The article covers innovative immobilization strategies for the conjugation of glycans on nanoparticles. Summaries of the detection schemes applied, the analytes detected and the key operational characteristics of such nanobiosensors are provided in the form of tables for each particular type of nanomaterial.