Toxicity evaluation of iron oxide nanoparticles and accumulation by microalgae Coelastrella terrestris

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.

Metal nanoparticles to improve the heat resilience in wheat (Triticum aestivumL.)

This study evaluated the efficacy of phytogenic silver and zinc nanoparticles in improving heat resilience in various wheat varieties. The silver and zinc nanoparticles were synthesized using plant leaf extract and characterized using various techniques. Four wheat varieties (DBW187, Black Wheat, DBW 50, and PBW 621) were subjected to field trials. The random block design was used, and nanoparticles in different concentrations were applied at various growth stages and morphologically, and yield parameters were recorded. UV-vis spectroscopy spectral analysis showed peaks for Ag nanoparticles at 420 nm wavelength and Zn nanoparticles at 240 and 350 nm wavelength, depicting the preliminary confirmation of nanoparticle synthesis. Electron microscopic analysis (TEM and SEM) provided morphological insights and confirmed synthesis of fine-sized particle mostly in a range between 10 and 60 nm. Energy dispersive x-ray analysis confirmed the elemental composition of the synthesized nanoparticles, with Ag and Zn elements detected in their respective samples. It also confirmed the oxide nature of synthesized ZnNPs. Dynamic light scattering analysis provided size distribution profiles, indicating average sizes of approximately 61.8 nm for Ag nanoparticles and 46.5 nm for Zn nanoparticles. The concentrations of Ag and Zn nanoparticles in the samples were found to be 196.3 ppm and 115.14 ppm, respectively, through atomic absorption spectroscopic analysis. Fourier transform infrared spectroscopy analysis revealed characteristic functional groups present in the nanoparticles. The results of field experiments established that Ag nanoparticles at 75 ppm concentration exhibited the most significant enhancements in plant growth. Conversely, Zn nanoparticles at a 100 ppm concentration demonstrated the most substantial improvements in the growth and yield of heat-stressed wheat varieties. The study concludes that optimized concentrations of silver and zinc nanoparticles can effectively improve heat stress resilience in wheat. These findings are promising to enhance abiotic stress resilience in crops.

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.

Characterization of a uranium-tolerant green microalga of the genus Coelastrella with high potential for the remediation of metal-polluted waters

Uranium (U) contamination of terrestrial and aquatic ecosystems poses a significant threat to the environment and human health due to the chemotoxicity of this actinide. The characterization of organisms that tolerate and accumulate U is crucial to decipher the mechanisms evolved to cope with the radionuclide and to propose new effective strategies for the bioremediation of U-contaminated environments. Here, we isolated a unicellular green microalga of the genus Coelastrella from U-contaminated wastewater. We showed that Coelastrella sp. PCV is much more tolerant to U than Chlamydomonas reinhardtii and Chlorella vulgaris. Coelastrella sp. PCV is able to accumulate U very rapidly and then gradually release it into the medium, behaving as an excluder to limit the toxic effects of U. The ability of Coelastrella sp. PCV to accumulate U is remarkably high, with up to 240 mg of tightly bound U per g of dry biomass. Coelastrella sp. PCV is able to grow and maintain high photosynthesis in natural metal-contaminated waters from a wetland near a reclaimed U mine. In a single one-week growth cycle, Coelastrella sp. PCV is able to capture 25-55 % of the U from the contaminated waters and shows lipid droplet accumulation. Coelastrella sp. PCV is a very promising microalga for the remediation of polluted waters with valorization of algal biomass that accumulates lipids.

Adaptive laboratory evolution empowers lipids and biomass overproduction in Chlorella vulgaris for environmental applications

Microalgal strain improvement with commercial features is needed to generate green biological feedstock to produce lipids for bioenergy. Hence, improving algal strain with enhanced lipid content without hindering cellular physiological parameters is pivotal for commercial applications of microalgae. In this report, we demonstrated the adaptive laboratory evolution (ALE) by hypersaline conditions to improve the algal strains for increasing the lipid overproduction capacity of Chlorella vulgaris for environmental applications. The evolved strains (namely E2 and E2.5) without notable impairment in general physiological parameters were scrutinized after 35 cycles. Conventional gravimetric lipid analysis showed that total lipid accumulation was hiked by 2.2-fold in the ALE strains compared to the parental strains. Confocal observation of algal cells stained with Nile-red showed that the abundance of lipid droplets was higher in the evolved strains without any apparent morphological aberrations. Furthermore, evolved strains displayed notable antioxidant potential than the control cells. Interestingly, carbohydrates and protein content were significantly decreased in the evolved cells, indicating that carbon flux was redirected into lipogenesis in the evolved cells. Altogether, our findings demonstrated a potential and feasible strategy for microalgal strain improvement for simultaneous lipids and biomass hyperaccumulation.

Spinel ferrite nanoparticles as potential materials in chlorophenol removal from wastewater

Persistent organic pollutants (POPs) including chlorophenols (CPs) are increasing in water effluents, creating serious problems for both aquatic and terrestrial lives. Several research attempts have considered the removal of CPs by functionalised nanomaterials as adsorbents and catalysts. Besides the unique crystal structure, spinel ferrite nanomaterials (SFNs) own interesting optical and magnetic properties that give them the potential to be utilised in the removal of different types of CPs. In this review, we highlighted the recent research work that focused on the application of SFNs in the removal of different CP substances based on the number of chlorine atom attached to the phenolic compound. We have also discussed the structure and properties of SFN along with their numerous characterisation tools. We demonstrated the importance of identifying the structure, surface area, porosity, optical properties, etc. in the efficiency of the SFN during the CP removal process. The reviewed research efforts applied photocatalysis, wet peroxide oxidation (WPO), persulfate activated oxidation and adsorption. The studies presented different paths of enhancing the SFN ability to remove the CPs including doping (ion substitution), oxide composite structure and polymer composite structure. Experimental parameters such as temperature, dosage of CPs and SFN structure have shown to have a major effect in the CP removal efficiency. More attention is needed to investigate the different properties of SFN that can be tailored through different techniques and expected to have major role in the removal mechanism of CPs.

Nanoremediation strategies to address environmental problems

A rapid rise in population, extensive anthropogenic activities including agricultural practices, up-scaled industrialization, massive deforestation, etc. are the leading causes of environmental degradation. Such uncontrolled and unabated practices have affected the quality of environment (water, soil, and air) synergistically by accumulating huge quantities of organic and inorganic pollutants in it. Environmental contamination is posing a threat to the existing life on the Earth, therefore, demands the development of sustainable environmental remediation approaches. The conventional physiochemical remediation approaches are laborious, expensive, and time-consuming. In this regard, nanoremediation has emerged as an innovative, rapid, economical, sustainable, and reliable approach to remediate various environmental pollutants and minimize or attenuate the risks associated with them. Owing to their unique properties such as high surface area to volume ratio, enhanced reactivity, tunable physical parameters, versatility, etc. nanoscale objects have gained attention in environmental clean-up practices. The current review highlights the role of nanoscale objects in the remediation of environmental contaminants to minimize their impact on human, plant, and animal health; and air, water, and soil quality. The aim of the review is to provide information about the applications of nanoscale objects in dye degradation, wastewater management, heavy metal and crude oil remediation, and mitigation of gaseous pollutants including greenhouse gases.

Elevated nano-α-Fe2O3 enhances arsenic metabolism and dissolved organic carbon release of Microcystis aeruginosa under a phytate environment

Little information is available on the effects of nano-α-Fe2O3 on arsenic (As) metabolism of algae and potential associated carbon (C) storage in As-contaminated water with dissolved organic phosphorus (DOP) as a phosphorus (P) source. In this study, Microcystis aeruginosa (M. aeruginosa) was used to investigate impacts of nano-α-Fe2O3 on cell growth and As metabolism of algae under a phytate (PA) environment as well as potential associated C storage. Results showed that nano-α-Fe2O3 had a subtle influence on algal cell growth in a PA environment. Herein, algal cell density (OD680) and chlorophyll a (Chla) were inhibited at elevated nano-α-Fe2O3 levels, which simultaneously limited the decrease of Yield. As suggested, the complexation of PA with nano-α-Fe2O3 could alleviate the negative influence on algal cell growth. Furthermore, the elevated nano-α-Fe2O3 increased As methylation in the PA environment due to higher monomethylarsenic (MMA) and dimethylarsenic (DMA) concentrations in the test media. Additionally, microcystins (MCs) in the media changed consistently with UV254, both of which were relatively lower at 10.0 mg·L-1 nano-α-Fe2O3. Enhanced As(V) methylation of algal cells was found to simultaneously reduce the release risk of As(III) and MC while increasing dissolved organic carbon (DOC) content in media, suggesting unfavorable C storage. Three-dimensional fluorescence analysis revealed that the main DOC constituent was the tryptophan-like component in aromatic proteins. Correlation analysis showed that decreases in pH and the zeta potential and an increase in Chla may lead to metabolic As improvements in M. aeruginosa. The obtained findings highlight the need for greater focus on the potential risks of DOP combined with nano-α-Fe2O3 on algal blooms as well as the biogeochemical cycling processes of As and C storage in As-contaminated water with DOP as the P source.

Enhancing arsenate metabolism in Microcystis aeruginosa and relieving risks of arsenite and microcystins by nano-Fe2O3 under dissolved organic phosphorus conditions

Little information is available on how nano-Fe₂O₃ substituted iron ions as a possible iron source impacting on algal growth and arsenate (As(V)) metabolism under dissolved organic phosphorus (DOP) (D-glucose-6-phosphate (GP)) conditions. We investigated the growth of Microcystis aeruginosa and As(V) metabolism together with their metabolites in As(V) aquatic environments with nano-Fe₂O₃ and GP as the sole iron and P sources, respectively. Results showed that nano-Fe₂O₃ showed inhibitory effects on M. aeruginosa growth and microcystin (MCs) release under GP conditions in As(V) polluted water. There was little influence on As species changes in GP media under different nano-Fe₂O₃ concentrations except for obvious total As (TAs) removal in 100 mg L^-1 nano-Fe₂O₃ levels. As(V) metabolism dominated with As(V) biotransformation in algal cells was facilitated and arsenite (As(III)) releasing risk was relieved clearly by nano-Fe₂O₃ under GP conditions. The dissolved organic matter (DOM) in media exhibited more fatty acid analogs containing -CO, -CH₂ =CH₂, and -CH functional groups with increasing nano-Fe₂O₃ concentrations, but the fluorescent analogs were relatively reduced especially for the fluorescent DOM dominated by aromatic protein-like tryptophan which was significantly inhibited by nano-Fe₂O_3. Thus, As methylation that was facilitated in M. aeruginosa by nano-Fe₂O₃ in GP environments also caused more organic substances to release that absorb infrared spectra while reducing the release risks of As(III) and MCs as well as protein-containing tryptophan fractions. From ¹H-NMR analysis, this might be caused by the increased metabolites of aromatic compounds, organic acid/amino acid, and carbohydrates/glucose in algal cells. The findings are vital for a better understanding of nano-Fe₂O₃ role-playing in As bioremediation by microalgae and the subsequent potential aquatic ecological risks.

Toxicity of boron nitride nanoparticles influencing bio-physicochemical responses in freshwater green algae

Boron nanoparticles have emerged as promising nanomaterials with a wide array of applications in the biomedical, industrial, and environmental fields. However, the potential impact of these nanoparticles on aquatic organisms is not yet known. In the present study, the comparative impact of boron nitride nanoparticles and its bulk form is investigated on two freshwater algae. For this purpose, the effect on the physiological index, cellular morphology, and biochemistry profiles are examined. In Chlorella vulgaris, nano form of boron nitride is found to reduce the growth more (40%) than its bulk form (with ~ 25% growth reduction) at 50 mgl^-1 treatment level. While in case of Coelastrella terrestris, 40% reduction under nano form and 33.33% reduction under bulk form is observed at 100 mgl^-1 of boron nitride. Chlorophyll and carotenoid levels were also reduced under nanoparticles compared to the bulk. Proline, lactate dehydrogenase, and malondialdehyde assay were found significantly high under nanoparticle exposure. Additionally, increased catalase and superoxide dismutase enzyme activity under nanoparticle exposure revealed that the antioxidant system was activated in both the algae to eliminate the adverse influence of reactive oxygen species. The shading effect and aggregation of nanoparticles over the surface of algal cells are also important factors in attributing toxicity which are confirmed through the compound, TEM, and SEM micrographs. The study suggests that the nano form is more toxic than the bulk form and toxicity is concentration-dependent.

The mechanism of nanoparticle toxicity to cyanobacteria

The demand for nanoparticles is increasing tremendously, and so is the risk of their foreseeable discharge into the environment. Nanoparticles contain a variety of features, including anti-microbial properties, and have been shown to have toxic effects on aquatic organisms previously. However, the causes of nanoparticle toxicity under environmental conditions are still unknown. Exposure to nanoparticles in the environment is unavoidable as nanomaterials are used more prevalent in our daily lives, and as a result, nanotoxicity research is gaining traction. To understand the impact of nanoparticle toxicity on aquatic biota, cyanobacteria (blue-green algae) are an ideal model system. The cyanobacteria play an important role in ecological balance, nutrient cycling, energy flow, biological nitrogen fixation, and environmental remediation, and their susceptibility to nanoparticles can help in making a wise strategy for the mitigation of possible nano-pollution. This article presents an analysis of recent research findings on the toxicological influences of nanoparticles on the growth rate, biochemical changes, ultra-structural changes as well as the nanoparticle toxicity mechanisms in cyanobacteria. The finding suggests that the shading effect, generation of reactive oxygen species, membrane damage and disintegration of pigments are the main reasons for nanoparticle toxicity to the cyanobacteria.

Decreasing arsenic accumulation but promoting arsenate biotransformation in Microcystis aeruginosa regulated by nano-Fe2O3

Iron oxide nanoparticles (nano-Fe₂O₃) widely distribute in waters with low toxicity to aquatic organisms. But it is unclear for nano-Fe₂O₃ to affect the fate of coexisting arsenic (As) with its bioaccumulation and biotransformation. In this study, we thus mainly investigated arsenate (As(V)) toxicity, uptake kinetics, biotransformation and subcellular distribution in Microcystis aeruginosa influenced by nano-Fe₂O₃. The results showed that M. aeruginosa was more sensitive to As(V) associated with nano-Fe₂O₃. Due to the exaggerated increase of efflux rate constants of As compared with the uptake rate constants in algal cells affected by different levels of nano-Fe₂O₃, the As(V) bioconcentration factor decreased with nano-Fe₂O₃ increasing correspondingly, indicating that As bioaccumulation was diminished by nano-Fe₂O_3. The decreased As accumulation in M. aeruginosa could be supported by the evidential As(V) sequestration through high adsorption of nano-Fe₂O₃, which resulted in decreasing free As level for algae uptake in media. Meanwhile, As subcellular distribution was adjusted by nano-Fe₂O₃ with decreasing in cell walls and rising in cytoplasmic organelles compared with nano-Fe₂O₃ free. As(V) reduction and methylation were enhanced with increasing nano-Fe₂O₃, stimulating by its sensitivity to the interaction of nano-Fe₂O₃ and As(V) as well as the rising level of As in cytoplasmic organelles of this algae. It is confirmed by the higher relative gene expression levels of arsC and arsM in elevated nano-Fe₂O₃. Accordingly, it is highlighted to be deserved more attention that the changing behavior of As(V) by nano-Fe₂O₃ that reduce As bioaccumulation and accelerate its biotransformation in algae in As contaminated water.

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.

Evaluation of Maghemite Nanoparticles-Induced Developmental Toxicity and Oxidative Stress in Zebrafish Embryos/Larvae

Maghemite nanoparticles ([Formula: see text] NPs) have a wide array of applications in various industries including biomedical field. There is an absence of legislation globally for the regulation of the production, use, and disposal of such NPs as they are eventually dumped into the environment where these NPs might affect the living systems. This study evaluates the effect of the [Formula: see text] NP-induced developmental toxicity in zebrafish embryos/larvae. The commercially available Fe₂O₃ NPs were purchased, and zebrafish embryos toxicity test was done by exposing embryos to various concentrations of [Formula: see text] NPs at 1 hpf and analyzed at 96 hpf. Based on the LC₅₀ value (60.17 ppm), the sub-lethal concentrations of 40 and 60 ppm were used for further experiments. Hatching, lethality, developmental malformations, and heartbeat rate were measured in the control and treated embryos/larvae. The ionic Fe content in the media, and the larvae was quantified using ICP-MS and AAS. The biomolecular alterations in the control and treated groups were analyzed using FT-IR. The Fe ions present in the larvae were visualized using SEM-EDXS. In situ detection of AChE and apoptotic bodies was done using staining techniques. Biochemical markers (total protein content, AChE, and Na⁺ K⁺-ATPase) along with oxidants and antioxidants were assessed. A significant decrease in the heartbeat rate and hatching delay was observed in the treated groups affecting the developmental processes. Teratogenic analysis showed increased developmental deformity incidence in treated groups in a dose-dependent manner. The accumulation of Fe was evidenced from the ICP-MS, AAS, and SEM-EDXS. Alterations in AChE and Na⁺ K⁺-ATPase activity were observed along with an increment in the oxidants level with a concomitant decrease in antioxidant enzymes. These results show [Formula: see text] NP exposure leads to developmental malformation and results in the alteration of redox homeostasis.

A review on the diverse interactions between microalgae and nanomaterials: Growth variation, photosynthetic performance and toxicity

Vast improvements in nanotechnology have led to the wide usage of nanomaterials (NMs) in daily products. This study reviews the interactions between NMs and microalgae in terms of impacts on growth and photosynthetic efficiency, and their toxicity on microalgae. All types of NMs such as carbon-based NMs (CNMs), metal oxide-based NMs (MONMs) and noble metal-based NMs (NMNMs) improve microalgal growth and photosynthetic efficiency at low concentration, typically ranging between 1 and 15 mg/L depending on the type of NMs, due to hormetic responses by microalgae. Higher concentrations of NMs have been found to reduce photosynthetic efficiency and subsequent growth inhibition of microalgae. MONMs-microalgae and NMNMs-microalgae interactions focus on membrane alteration, whereas carbon-based NMs-microalgae focus more on shading effect. The toxicity of each type of NMs on microalgae is in the order rGO > GO > MG > CNT for carbon-based NMs, ZnO > TiO₂ > CuO > Fe₂O₃ for MONMs and Ag > Au > Pt for NMNMs. Incorporation of NMs in microalgae are seen to have promising future on producing higher microalgae yield with increased economic efficiency.

Effects of Metal Oxide Nanoparticles in Zebrafish

Metal oxide nanoparticles (MO NPs) are increasingly employed in many fields with a wide range of applications from industries to drug delivery. Due to their semiconducting properties, metal oxide nanoparticles are commonly used in the manufacturing of several commercial products available in the market, including cosmetics, food additives, textile, paint, and antibacterial ointments. The use of metallic oxide nanoparticles for medical and cosmetic purposes leads to unavoidable human exposure, requiring a proper knowledge of their potentially harmful effects. This review offers a comprehensive overview of the possible toxicity of metallic oxide nanoparticles in zebrafish during both adulthood and growth stages, with an emphasis on the role of oxidative stress.

Zero-Valent Iron Nanoparticles Induce Reactive Oxygen Species in the Cyanobacterium, Fremyella diplosiphon

Nanoscale zero-valent iron nanoparticles (nZVIs) are known to boost biomass production and lipid yield in Fremyella diplosiphon, a model biodiesel-producing cyanobacterium. However, the impact of nZVI-induced reactive oxygen species (ROS) in F. diplosiphon has not been evaluated. In the present study, ROS in F. diplosiphon strains (B481-WT and B481-SD) generated in response to nZVI-induced oxidative stress were quantified and the enzymatic response determined. Lipid peroxidation as a measure of oxidative stress revealed significantly higher malondialdehyde content (p < 0.01) in both strains treated with 3.2, 12.8, and 51.2 mg L^-1 nZVIs compared to untreated control. In addition, ROS in all nZVI-treated cultures treated with 1.6-25.6 mg L^-1 nZVIs was significantly higher than the untreated control as determined by the 2',7'-dichlorodihydrofluorescein diacetate fluorometric probe. Immunodetection using densitometric analysis of iron superoxide dismutase (SOD) revealed significantly higher SOD levels in both strains treated with nZVIs at 51.2 mg L^-1. In addition, we observed significantly higher (p < 0.001) SOD levels in the B481-SD strain treated with 6.4 mg L^-1 nZVIs compared to 3.2 mg L^-1 nZVIs. Validation using transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDS) revealed adsorption of nZVIs with a strong iron peak in both B481-WT and B481-SD strains. While the EDS spectra showed strong signals for iron at 4 and 12 days after treatment, a significant decrease in peak intensity was observed at 20 days. Future efforts will be aimed at studying transduction mechanisms that cause metabolic and epigenetic alterations in response to nZVIs in F. diplosiphon.

Interaction Effect of EDTA, Salinity, and Oxide Nanoparticles on Alga Chlamydomonas reinhardtii and Chlamydomonas euryale

The interaction effects of organic ligand ethylene diamine tetra-acetic acid (EDTA) and oxide nanoparticles (magnetite Fe₃O₄-NPs and copper CuO-NPs) were investigated during a 72 h period on two green algal species-Chlamydomonas reinhardtii under freshwater conditions and Chlamydomonas euryale under saltwater conditions. Fe₃O₄-NPs had larger agglomerates and very low solubility. CuO-NPs, having smaller agglomerates and higher solubility, were more toxic than Fe₃O₄-NPs in freshwater conditions for similar mass-based concentrations, especially at 72 h under 100 mg L^-1. Furthermore, the effect of EDTA increased nanoparticle solubility, and the salinity caused a decrease in their solubility. Our results on C. euryale showed that the increase in salinity to 32 g L^-1 caused the formation of larger nanoparticle agglomerates, leading to a decrease in the toxicity impact on algal cells. In addition, EDTA treatments induced a toxicity effect on both freshwater and saltwater Chlamydomonas species, by altering the nutrient uptake of algal cells. However, C. euryale was more resistant to EDTA toxicity than C. reinhardtii. Moreover, nanoparticle treatments caused a reduction in EDTA toxicity, especially for CuO-NPs. Therefore, the toxicity impact caused by these environmental factors should be considered in risk assessment for metallic nanoparticles.

Metal- and metal/oxide-based engineered nanoparticles and nanostructures: a review on the applications, nanotoxicological effects, and risk control strategies

The production and demand of nanoparticles in the manufacturing sector and personal care products, release a large number of engineered nanoparticles (ENPs) into the atmosphere, aquatic ecosystems, and terrestrial environments. The intentional or involuntary incorporation of ENPs into the environment is carried out through different processes. The ENPs are combined with other compounds and release into the atmosphere, settling on the ground due to the water cycle or other atmospheric phenomena. In the case of aquatic ecosystems, the ENPs undergo hetero-aggregation and sedimentation, reaching different living organisms and flora, as well as groundwater. Accordingly, the high mobility of ENPs in diverse ecosystems is strongly related to physical, chemical, and biological processes. Recent studies have been focused on the toxicological effects of a wide variety of ENPs using different validated biological models. This literature review emphasizes the study of toxicological effects related to using the most common ENPs, specifically metal and metal/oxides-based nanoparticles, addressing different synthesis methodologies, applications, and toxicological evaluations. The results suggest negative impacts on biological models, such as oxidative stress, metabolic and locomotive toxicity, DNA replication dysfunction, and bioaccumulation. Finally, it was consulted the protocols for the control of risks, following the assessment and management process, as well as the classification system for technological alternatives and risk management measures of ENPs, which are useful for the transfer of technology and nanoparticles commercialization.

Advanced Functional Nanostructures based on Magnetic Iron Oxide Nanomaterials for Water Remediation: A Review

The fast growth of industrialization combined with the increasing population has led to an unparalleled demand for providing water in a safe, reliable, and cost-effective way, which has become one of the biggest challenges of the twenty-first century faced by global society. The application of nanotechnology in water treatment and pollution cleanup is a promising alternative in order to overcome the current limitations. In particular, the application of magnetic iron oxide nanoparticles (MIONs) for environmental remediation has currently received remarkable attention due to its unique combination of physicochemical and magnetic properties. Given the broadening use of these functional engineered nanomaterials, there is a growing concern about the adverse effects upon exposure of products and by-products to the environment. This makes vitally relevant the development of green chemistry in the synthesis processes combined with a trustworthy risk assessment of the nanotoxicity of MIONs as the scientific knowledge of the potential hazard of nanomaterials remains limited. This work provides comprehensive coverage of the recent progress on designing and developing iron oxide-based nanomaterials through a green synthesis strategy, including the use of benign solvents and ligands. Despite the limitations of nanotoxicity and environmental risks of iron oxide-based nanoparticles for the ecosystem, this critical review presents a contribution to the emerging knowledge concerning the theoretical and experimental studies on the toxicity of MIONs. Potential improvement of applications of advanced iron oxide-based hybrid nanostructures in water treatment and pollution control is also addressed in this review.

Health Risk Assessment of Heavy Metals in Soils before Rice Sowing and at Harvesting in Southern Jiangsu Province, China

Rice, one of the most important staple crops in China, is easily contaminated by heavy metal pollution from industrial development. In this work, we systematically investigated the heavy metal (Cr, Cd, Pb, Zn, and Cu) and metalloid (Hg and As) concentrations in paddy soils and different rice tissues in southern Jiangsu Province, China. The potential ecological hazard index method and in vitro simulation test were used to evaluate the influence of heavy metals on local resident health. The results showed that, before rice sowing and at the harvesting period, the order of Eri values was EriCd>EriHg>EriAs>EriPb>EriCu>EriCr>EriZn. The low-risk index values (91.63 and 30.29) for the heavy metals indicated the low risk at the two stages in the study area based on the potential ecological hazard index. As determined with Tessier’s five-stage sequential extraction procedure, the proportions of the chemical speciation of the heavy metals were as follows: residual > organic matter-bound > iron-manganese oxide-bound > carbonate-bound > exchangeable. The order of the values of the accumulation and transfer factors was Cd (3.16) > Cu (0.42) > Zn (0.28) > Pb (0.25) > As (0.07) > Cr (0.04) > Cr (0.03) and root > stem > leaves, respectively. In vitro simulation tests showed that, in both adults and children, the daily amount of Pb and Cd intake through the soil-oral cavity route in the study area did not exceed the daily tolerance for Pb and Cd proposed by the WHO. In summary, although there is no obvious danger to local adults and children, it is necessary to be aware of the possibility of rice contamination from Cd in the soil.

New insights on improved growth and biogas production potential of Chlorella pyrenoidosa through intermittent iron oxide nanoparticle supplementation

In the present work, the effect of α-Fe₂O₃-nanoparticles (IONPs) supplementation at varying doses (0, 10, 20 and, 30 mg L^-1) at the intermittent stage (after 12th day of growth period) was studied on the growth and biogas production potential of Chlorella pyrenoidosa. Significant enhancements in microalgae growth were observed with all the tested IONPs doses, the highest (2.94 ± 0.01 g L^-1) being at 20 mg L^-1. Consequently, the composition of the biomass was also improved. Based on the precedent determinations, theoretical chemical oxygen demand (COD_th) as well as theoretical and stoichiometric methane potential (TMP, and SMP) were also estimated. The COD_th, TMP, SMP values indicated IONPs efficacy for improving biogas productivity. Further, the biochemical methane potential (BMP) test was done for IONPs supplemented biomass. The BMP test revealed up to a 25.14% rise in biogas yield (605 mL g^-1 VS_fed) with 22.4% enhanced methane content for 30 mg L^-1 IONPs supplemented biomass over control. Overall, at 30 mg L^-1 IONPs supplementation, the cumulative enhancements in biomass, biogas, and methane content proffered a net rise of 98.63% in biomethane potential (≈ 2.86 × 10⁴ m³ ha^-1 year^-1) compared to control. These findings reveal the potential of IONPs in improving microalgal biogas production.