Impacts of organic matter on the toxicity of biosynthesized silver nanoparticles to green microalgae Chlorella vulgaris

Advancements in Nano-Enhanced microalgae bioprocessing

Microalgae are promising sources of valuable compounds: carotenoids, polyunsaturated fatty acids, lipids, etc. To overcome the feasibility challenge due to low yield and attain commercial potential, researchers merge technologies to enhance algal bioprocess. In this context, nanomaterials are attractive for enhancing microalgal bioprocessing, from cultivation to downstream extraction. Nanomaterials enhance biomass and product yields (mainly lipid and carotenoids) through improved nutrient uptake and stress tolerance during cultivation. They also provide mechanistic insights from recent studies. They also revolutionize harvesting via nano-induced sedimentation, flocculation, and flotation. Downstream processing benefits from nanomaterials, improving extraction and purification. Special attention is given to cost-effective extraction, showcasing nanomaterial integration, and providing a comparative account. The review also profiles nanomaterial types, including metallic nanoparticles, magnetic nanomaterials, carbon-based nanomaterials, silica nanoparticles, polymers, and functionalized nanomaterials. Challenges and future trends are discussed, emphasizing nanomaterials' role in advancing sustainable and efficient microalgal bioprocessing, unlocking their potential for bio-based industries.

Effects of dissolved organic matter on the environmental behavior and toxicity of metal nanomaterials: A review

Metal nanomaterials (MNMs) have been released into the environment during their usage in various products, and their environmental behaviors directly impact their toxicity. Numerous environmental factors potentially affect the behaviors and toxicity of MNMs with dissolved organic matter (DOM) playing the most essential role. Abundant facts showing contradictory results about the effects of DOM on MNMs, herein the occurrence of DOM on the environmental process change of MNMs such as dissolution, dispersion, aggregation, and surface transformation were summarized. We also reviewed the effects of MNMs on organisms and their mechanisms in the environment such as acute toxicity, oxidative stress, oxidative damage, growth inhibition, photosynthesis, reproductive toxicity, and malformation. The presence of DOM had the potential to reduce or enhance the toxicity of MNMs by altering the reactive oxygen species (ROS) generation, dissolution, stability, and electrostatic repulsion of MNMs. Furthermore, we summarized the factors that affected different toxicity including specific organisms, DOM concentration, DOM types, light conditions, detection time, and production methods of MNMs. However, the more detailed mechanism of interaction between DOM and MNMs needs further investigation.

Unraveling the mysteries of silver nanoparticles: synthesis, characterization, antimicrobial effects and uptake translocation in plant-a review

MAIN CONCLUSION

The study thoroughly investigates nanosilver production, properties, and interactions, shedding light on its multifaceted applications. It underscores the importance of characterizing nanosilver for predicting its behavior in complex environments. Particularly, it highlights the agricultural and environmental ramifications of nanosilver uptake by plants. Nowadays, silver nanoparticles (AgNPs) are a very adaptable nanomaterial with many uses, particularly in antibacterial treatments and agricultural operations. Clarification of key elements of nanosilver, such as its synthesis and characterization procedures, antibacterial activity, and intricate interactions with plants, particularly those pertaining to uptake and translocation mechanisms, is the aim of this in-depth investigation. Nanosilver synthesis is a multifaceted process that includes a range of methodologies, including chemical, biological, and sustainable approaches that are also environmentally benign. This section provides a critical evaluation of these methods, considering their impacts on repeatability, scalability, and environmental impact. The physicochemical properties of nanosilver were determined by means of characterization procedures. This review highlights the significance of analytical approaches such as spectroscopy, microscopy, and other state-of the-art methods for fully characterizing nanosilver particles. Although grasp of these properties is necessary in order to predict the behavior and potential impacts of nanosilver in complex biological and environmental systems. The second half of this article delves into the intricate interactions that plants have with nanosilver, emphasizing the mechanisms of absorption and translocation. There are significant ramifications for agricultural and environmental problems from the uptake of nanosilver by plants and its subsequent passage through their tissues. In summary, by summarizing the state-of-the-art information in this field, this study offers a comprehensive overview of the production, characterization, antibacterial capabilities, and interactions of nanosilver with plants. This paper contributes to the ongoing conversation in nanotechnology.

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.

Effect and mechanism of microplastics exposure against microalgae: Photosynthesis and oxidative stress

The occurrence of microplastics (MPs) within aquatic ecosystems attracts a major environmental concern. It was demonstrated MPs could cause various ecotoxicological effects on microalgae. However, existing data on the effects of MPs on microalgae showed great variability among studies. Here, we performed a meta-analysis of the latest studies on the effects of MPs on photosynthesis and oxidative stress in microalgae. A total of 835 biological endpoints were investigated from 55 studies extracted, and 37 % of them were significantly affected by MPs. In this study, the impact of MPs against microalgae was concentration-dependent and size-dependent, and microalgae were more susceptible to MPs stress in freshwater than marine. Additionally, we summarized the biological functions of microalgae that are primarily affected by MPs. Under MPs exposure, the content of chlorophyll a (Chl-a) was reduced and electron transfer in the photosynthetic system was hindered, causing electron accumulation and oxidative stress damage, which may also affect biological processes such as energy production, carbon fixation, lipid metabolism, and nucleic acid metabolism. Finally, our findings provide important insights into the effects of MPs stress on photosynthesis and oxidative stress in microalga and enhance the current understanding of the potential risk of MPs pollution on aquatic organisms.

Adverse effects of silver nanoparticles on aquatic plants and zooplankton: A review

With the rapid development of nanotechnology in the past decades, AgNPs are widely used in various fields and have become one of the most widely used nanomaterials, which leads to the inevitable release of AgNPs to the aquatic environment through various pathways. It is important to understand the effects of AgNPs on aquatic plants and zooplankton, which are widely distributed and diverse, and are important components of the aquatic biota. This paper reviews the effects of AgNPs on aquatic plants and zooplankton at the individual, cellular and molecular levels. In addition, the internal and external factors affecting the toxicity of AgNPs to aquatic plants and zooplankton are discussed. In general, AgNPs can inhibit growth and development, cause tissue damage, induce oxidative stress, and produce genotoxicity and reproductive toxicity. Moreover, the toxicity of AgNPs is influenced by the size, concentration, and surface coating of AgNPs, environmental factors including pH, salinity, temperature, light and co-contaminants such as NaOCl, glyphosate, As(V), Cu and Cd, sensitivity of test organisms, experimental conditions and so on. In order to investigate the toxicity of AgNPs in the natural environment, it is recommended to conduct toxicity evaluation studies of AgNPs under the coexistence of multiple environmental factors and pollutants, especially at natural environmental concentrations.

Bioinspired and Green Synthesis of Silver Nanoparticles for Medical Applications: A Green Perspective

Silver nanoparticles (AgNPs) possess unmatched chemical, biological, and physical properties that make them unique compounds as antimicrobial, antifungal, antiviral, and anticancer agents. With the increasing drug resistance, AgNPs serve as promising entities for targeted drug therapy against several bacterial, fungal, and viral components. In addition, AgNPs also serve as successful anticancer agents against several cancers, including breast, prostate, and lung cancers. Several works in recent years have been done towards the development of AgNPs by using plant extracts like flowers, leaves, bark, root, stem, and whole plant parts. The green method of AgNP synthesis thus has several advantages over chemical and physical methods, especially the low cost of synthesis, no toxic byproducts, eco-friendly production pathways, can be easily regenerated, and the bio-reducing potential of plant derived nanoparticles. Furthermore, AgNPs are biocompatible and do not harm normally functioning human or host cells. This review provides an exhaustive overview and potential of green synthesized AgNPs that can be used as antimicrobial, antifungal, antiviral, and anticancer agents. After a brief introduction, we discussed the recent studies on the development of AgNPs from different plant extracts, including leaf parts, seeds, flowers, stems, bark, root, and whole plants. In the following section, we highlighted the different therapeutic actions of AgNPs against various bacteria, fungi, viruses, and cancers, including breast, prostate, and lung cancers. We then highlighted the general mechanism of action of AgNPs. The advantages of the green synthesis method over chemical and physical methods were then discussed in the article. Finally, we concluded the review by providing future perspectives on this promising field in nanotechnology.

Sustainable fabrication of hybrid silver-copper nanocomposites (Ag-CuO NCs) using Ocimum americanum L. as an effective regime against antibacterial, anticancer, photocatalytic dye degradation and microalgae toxicity

In this study, a sustainable fabrication of hybrid silver-copper oxide nanocomposites (Ag-CuO NCs) was accomplished utilizing Ocimum americanum L. by one pot green chemistry method. The multifarious biological and environmental applications of the green fabricated Ag-CuO NCs were evaluated through their antibacterial, anticancer, dye degradation, and microalgae growth inhibition activities. The morphological features of the surface functionalized hybrid Ag-CuO NCs were confirmed by FE-SEM and HR-TEM techniques. The surface plasmon resonance λ_max peak appeared at 441.56 nm. The average hydrodynamic size distribution of synthesized nanocomposite was 69.80 nm. Zeta potential analysis of Ag-CuO NCs confirmed its remarkable stability at -21.5 mV. XRD and XPS techniques validated the crystalline structure and electron binding affinity of NCs, respectively. The Ag-CuO NCs demonstrated excellent inhibitory activity against Vibrio cholerae (19.93 ± 0.29 mm) at 100 μg/mL. Anticancer efficacy of Ag-CuO NCs was investigated against the A549 lung cancer cell line, and Ag-CuO NCs exhibited outstanding antiproliferative activity with a low IC₅₀ of 2.8 ± 0.05 μg/mL. Furthermore, staining and comet assays substantiated that the Ag-CuO NCs hindered the progression of the A549 cells and induced apoptosis as a result of cell cycle arrest at the G₀/G₁ phase. Concerning the environmental applications, the Ag-CuO NCs displayed efficient photocatalytic activity against eosin yellow degradation up to 80.94% under sunlight irradiation. Microalgae can be used as an early bio-indicator/prediction of environmental contaminants and toxic substances. The treatment of the Ag-CuO NCs on the growth of marine microalgae Tetraselmis suecica demonstrated the dose and time-dependent growth reduction and variations in the chlorophyll content. Therefore, the efficient multifunctional properties of hybrid Ag-CuO NCs could be exploited as a regime against infective diseases and cancer. Further, the findings of our investigation witness the remarkable scope and potency of Ag-CuO NCs for environmental applications.

Toxic effects of pristine and aged polystyrene and their leachate on marine microalgae Skeletonema costatum

The acute toxic effects of pristine and aged polystyrene (P-PS and A-PS) and their leaching solutions (L-PS) on microalgae Skeletonema costatum were investigated by measuring algal density and growth inhibition rate (IR), chlorophyll concentration and photosynthetic efficiency (Fv/Fm) over 96 h. Total protein (TP), superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) were measured to analyze the oxidative damage to microalgae by microplastics and their leachates. Hydrodynamic diameter of microplastics in seawater, FITR and SEM images were used to study the changes of polystyrene during aging. The interaction of algae cell with microplastics and the cellular ultrastructure changes of cells were analyzed combined with electron microscopy for a comprehensive and systematic understanding on the mechanisms of microplastic toxicity to microalgae. Both high concentration and small size of PS had significant inhibitory effect on the growth of microalgae, and the inhibitory effect was greater with increasing exposure time. The inhibition effect of aged microplastics was more obvious, which was speculated to be caused by the synergistic effect of aged PS itself and leaching solution. The negative effect of leaching solution on microalgae was due to the release of some additives during the aging process. The content of MDA reached the highest value of 54.41 nmol/mgprot in 1.0 μm 50 mg/L A-PS treatment group, and A-PS were found to be more prone to heterogeneous aggregation with algae cells by SEM.

Evaluation of acute toxicity response to the algae Chlorella pyrenoidosa of biosynthetic silver nanoparticles catalysts

Biosynthetic of silver nanoparticles (AgNPs) by using fungi has attracted much attention due to its high catalytic efficiency and environmentally friendly characteristic. However, a few studies have focused on the ecological toxicity effects of biogenic AgNPs on algae. Here, we first investigated the catalytic reduction of 4-nitrophenol (4-NP) by WZ07-AgNPs biosynthesized by Letendraea sp. WZ07. WZ07-AgNPs had significant catalytic activity with 97.08% degradation of 4-NP in 3.5 min. Then, the toxic effects of WZ07-AgNPs and commercial-AgNPs were compared by Chlorella pyrenoidosa growth, chlorophyll content, protein content, physiological, and biochemical indexes. The results demonstrated that the algal cell biomass of C. pyrenoidosa was differentially inhibited after exposure to different concentrations of AgNPs, which showed concentration dependence and time dependence. The 96h-EC₅₀ values of WZ07-AgNPs and commercial-AgNPs on C. pyrenoidosa were 15.99 mg/mL and 12.69 mg/mL, respectively. With the increase concentration of AgNPs, the chlorophyll content was gradually decreased, the protein content was first increased and then decreased, the activities of superoxide dismutase (SOD) and catalase (CAT) were decreased, and the level of malondialdehyde (MDA) was increased significantly of C. pyrenoidosa. In general, AgNPs affect the growth of algae to some extent. However, compared with commercial-AgNPs, WZ07-AgNPs is less toxic to C. pyrenoidosa, which could be used as a potential and an eco-friendly catalyst. This study provides a basis for the safe application of biosynthetic AgNPs.

Effects of mycogenic silver nanoparticles on organisms of different trophic levels

Biogenic silver nanoparticles (AgNPs) are considered a promising alternative to their synthetic versions. However, the environmental impact of such nanomaterials is still scarcely understood. Thus, the present study aims at assessing the antimicrobial action and ecotoxicity of AgNPs biosynthesized by the fungus Aspergillus niger IBCLP20 towards three freshwater organisms: Chlorella vulgaris, Daphnia similis, and Danio rerio (zebrafish). AgNPs IBCLP20 showed antibacterial action against Klebsiella pneumoniae between 5 and 100 μg mL^-1, and antifungal action against Trichophyton mentagrophytes in concentrations ranging from 20 to 100 μg mL^-1. The cell density of the microalgae Chlorella vulgaris decreased 40% after 96 h of exposure to AgNPs IBCLP20, at the highest concentration analysed (100 μg L^-1). The 48 h median lethal concentration for Daphnia similis was estimated as 4.06 μg L^-1 (2.29-6.42 μg L^-1). AgNPs IBCLP20 and silver nitrate (AgNO₃) caused no acute toxicity on adult zebrafish, although they did induce several physiological changes. Mycosynthetized AgNPs caused a significant increase (p < 0.05) in oxygen consumption at the highest concentration studied (75 μg L^-1) and an increase in the excretion of ammonia at the lower concentrations, followed by a reduction at the higher concentrations. Such findings are comparable with AgNO₃, which increased the oxygen consumption on low exposure concentrations, followed by a decrease at the high tested concentrations, while impairing the excretion of ammonia in all tested concentrations. The present results show that AgNPs IBCLP20 have biocidal properties. Mycogenic AgNPs induce adverse effects on organisms of different trophic levels and understanding their impact is detrimental to developing countermeasures aimed at preventing any negative environmental effects of such novel materials.

Toxicity of silver nanoparticles on Achromobacter denitrificans: effect of concentration, temperature and coexisting anions

The indoor culture method was carried out to study the toxic effect of silver nanoparticles (AgNPs) on Achromobacter denitrificans. Specifically, the effects of AgNPs concentration, temperature and coexisting anions were analyzed. The results showed that AgNPs exerted significant inhibition on the bacteria, which was closely correlated with its concentration and temperature. Both the ammonia oxidation and generation capacity of Achromobacter denitrificans decreased significantly with an increase in AgNPs concentration. Compared with the inhibition performance at 30 °C, NH₄⁺-N generation rates decreased by 45.31% at 20 °C and 17.58% at 40 °C, respectively, revealing that too low or too high temperature induced to reduce the nitrogen conversion ability of Achromobacter denitrificans. While compared with temperature, the effect of coexisting ions (Cl^- and SO₄^2-) was not significant (P > 0.05). Electron microscopy observations found that AgNPs non-specifically bound to the cells (content ranging from 0.04% to 0.10%) and acted on the cell surface structure, causing wrinkles, depressions, and ruptures on the surface of cell membranes, and leakage of substances in the membranes. AgNPs increased the rate of cell apoptosis and decreased the cell body volume mainly with short-term acute effects.

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.

Nano-sized polystyrene plastics toxicity to microalgae Chlorella vulgaris: Toxicity mitigation using humic acid

Polystyrene nanoplastics (PS-NPs) can cause toxicity in aquatic organisms, but presence of natural organic matter (NOM) may alter toxicity of PS-NPs. To better understand effects of NOM on acute toxicity of PS-NPs, humic acid (HA) as a model of NOM was added to green microalga Chlorella vulgaris medium in the presence of amino-functionalized polystyrene nanoplastics (PS-NH₂). Acute toxicity tests of PS-NH₂ to C. vulgaris biomass and chlorophyll a content showed statistical differences between media treated with different concentrations of PS-NH₂ and control groups (p<0.05). HA significantly mitigated PS-NH₂ toxicity to C. vulgaris biomass and chlorophyll a end-points (p<0.05). Additionally, high HA concentration was more effective than low concentration (10 vs 5 mg/L), showing a greater ameliorative effect on PS-NH₂ acute toxicity (p<0.05). Algae exposed to higher PS-NH₂ concentrations showed greater morphological changes (i.e., diminution of photosynthetic pigments, reduction of algal size and formation of more cellular aggregates). Formation of high amounts of algal aggregates under influence of PS-NH₂ was presumably related to the high electrostatic tendency of these particles (with positively charged surfaces) to C. vulgaris polysaccharide walls (having negative charge). Formation of aggregates was significantly reduced in the presence of HA. HA with dominant negatively charged functional groups (following sorption by PS-NH₂ via reduction of PS-NH₂ zeta potential), could decrease electrostatic attraction between PS-NH₂ and algae, thereby substantially ameliorating cellular aggregation and cell size reduction.

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.

Bioavailability and effect of α-Fe2O3 nanoparticles on growth, fatty acid composition and morphological indices of Chlorella vulgaris

The wide application of α-Fe₂O₃ nanoparticles (NPs) in different fields has resulted in release and accumulation of these materials into the aquatic ecosystem. Therefore, it is important to understand the potential impact of these NPs on aquatic organisms especially primary producers i.e., microalgae. Present study aimed to investigate the bioavailability and the effect of α-Fe₂O₃ NPs on growth of iron deprived cells of Chlorella vulgaris. Results showed that α-Fe₂O₃ NPs are not available as iron source to support the growth of C. vulgaris. Moreover，α-Fe₂O₃ NPs induced stress condition to C. vulgaris, which were reflected in its growth rates, total lipid contents, fatty acid profile and cell morphology. Specifically, low concentrations of α-Fe₂O₃ NPs (0.1, 0.5, 2.5, 5, 10 mg/L) showed similar growth profile and total lipid contents at both exponential and stationary growth phases. At 50 and 100 mg/L α-Fe₂O₃ NPs concentrations biomass reduced by 41.2% and 83.7% whereas total lipid contents increased by 39.7% and 25.5% respectively at exponential growth phase along with reduction in fatty acids. The results illustrated novel insights into the microalgal interaction with nanoparticles, providing fundamental knowledge for the development of future microalgae ecology and cultivation technology.

Algae-mediated biosystems for metallic nanoparticle production: From synthetic mechanisms to aquatic environmental applications

Driven by the growing impetus of green chemistry and environmental protection, the use of bio-based systems to produce green metallic nanomaterials used for environmental remediation has thus developed urgently. It is proposed that using algae as a living cell factory or algal extract as a natural reducing agent is a green and clean way to efficiently synthesize various metallic nanomaterials. However, studies on algal-based biological synthesis of metallic nanomaterials and their applications towards removal of toxic pollutants from wastewater are still limited, which largely discourage the sustainability. Herein, this review aims to introduce the recent advances on algae-mediated nanomaterial-producing biosystems. The corresponding synthetic mechanisms, operation parameters, and case studies on various algae-synthesized metallic nanoparticles are comprehensively discussed and summarized. More importantly, the applicability of algae-synthesized metallic nanoparticles on water treatment is introduced in-depth. To improve economic viability, the challenges and future perspectives are also considered. Taken together, this review systematically presents the achievements and current progress of algae-mediated metallic nanoparticle biosynthesis towards the aquatic pollutants treatment, which can provide new insights on promoting the algae-based nanomaterial production yield and environmental application potential.

Toxic effects of polystyrene nanoplastics on microalgae Chlorella vulgaris: Changes in biomass, photosynthetic pigments and morphology

Presence of nanoplastics within aqueous media has raised concerns about their adverse impacts on aquatic organisms. This study evaluated toxic effects of amino-functionalized polystyrene nanoplastics (PS-NH₂) with diameters of 90 (PS-NH₂-90), 200 (PS-NH₂-200) and 300 (PS-NH₂-300) nm on green microalgae Chlorella vulgaris. A dose-dependent toxicity response by PS-NH₂-90 and/or PS-NH₂-200 on biomass and photosynthetic pigment (chlorophyll a) end-points of C. vulgaris was observed. Whereas varied concentrations of PS-NH₂-300 had no significant toxic effect on biomass and chlorophyll a end-points compared to control groups (p > 0.05). A comparison of toxicity of similar concentrations of PS-NH₂-90, PS-NH₂-200 and PS-NH₂-300 showed small-sized PS-NH₂ were more toxic than large-sized PS-NH₂ (toxicity of PS-NH₂ increased in the order PS-NH₂-300 < PS-NH₂-200 < PS-NH₂-90). With decreasing PS-NH₂ size, greater morphological changes and loss of original shape were observed, so that algal density/size reduced, and cell aggregations increased. Since PS-NH₂ have high affinity to C. vulgaris due to electrostatic interaction with polysaccharide wall of algae, this could be as the main reason for formation of large aggregates at high concentrations of PS-NH₂ compared to low concentrations of PS-NH₂ used in algae medium. At high concentrations, PS-NH₂ may act as intermediaries for connection of algal cells and therefore formation of aggregates. Field emission scanning electron microscopy images confirmed that high amounts of PS-NH₂-90 were found to be embedded and adsorbed on algal cells, thereby limiting transfer of materials, gas exchange and energy between the aqueous medium and algal cells. These data may have serious ecological health implications, as C. vulgaris are important primary producers responsible for producing oxygen in aquatic environments.

Plant-Extract-Mediated Synthesis of Metal Nanoparticles

Metal nanoparticles (MNPs) have been widely used in several fields including catalysis, bioengineering, photoelectricity, antibacterial, anticancer, and medical imaging due to their unique physical and chemical properties. In the traditional synthesis method of MNPs, toxic chemicals are generally used as reducing agents and stabilizing agents, which is fussy to operate and extremely environment unfriendly. Based on this, the development of an environment-friendly synthesis method of MNPs has recently attracted great attention. The use of plant extracts as reductants and stabilizers to synthesize MNPs has the advantages of low cost, environmental friendliness, sustainability, and ease of operation. Besides, the as-synthesized MNPs are nontoxic, more stable, and more uniform in size than the counterparts prepared by the traditional method. Thus, green preparation methods have become a research hotspot in the field of MNPs synthesis. In this review, recent advances in green synthesis of MNPs using plant extracts as reductants and stabilizers have been systematically summarized. In addition, the insights into the potential applications and future development for MNPs prepared by using plant extracts have been provided.

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.

Toxicity of biosynthesized silver nanoparticles to aquatic organisms of different trophic levels

Although biosynthesized nanoparticles are regarded as green products, research on their toxicity to aquatic food chains is scarce. Herein, biosynthesized silver nanoparticles (Alcea rosea-silver nanoparticles, AR-AgNPs) were produced by the reaction of Ag ions with leaf extract of herbal plant Alcea rosea. Then, the toxic effects of AR-AgNPs and their precursors such as Ag⁺ ions and coating agent (A. rosea leaf extract) on organisms of different trophic levels of a freshwater food chain were investigated. To the three studied aquatic organisms including phytoplankton (Chlorella vulgaris), zooplankton (Daphnia magna) and fish (Danio rerio), the coating agents of AR-AgNPs showed no toxic effects, and Ag⁺ ions were more toxic in comparison to AR-AgNPs. Further investigations revealed that the release of Ag⁺ ions from AR-AgNPs to the test media were not considerable due to the high stability of AR-AgNPs, thus the toxicity stemmed mainly from the particles of AR-AgNPs in all the three trophic levels. Based on values of 72-h EC₅₀ for C. vulgaris, 48-h LC₅₀ for D. magna and 96-h LC₅₀ for D. rerio, the most sensitive organism to AR-AgNPs exposure was D. magna (the second trophic level).

Green biomimetic silver nanoparticles utilizing the red algae Amphiroa rigida and its potent antibacterial, cytotoxicity and larvicidal efficiency

The present investigation reports a simple, rapid, inexpensive, and eco-friendly approach for synthesizing Amphiroa rigida-mediated silver nanoparticles (AR-AgNPs) for the first time. The biomimetic synthesized AR-AgNPs were characterized by both spectral and microscopic analysis. The UV-visible spectrum showed the surface plasmon peak at 420 nm, which indicated the formation of AR-AgNPs. X-ray diffraction characterization of AR-AgNPs showed a face-centered cubic crystal (25 nm) and the transmission electron microscope micrograph showed spherical shape. The functional group of polysaccharide that plays a major role as a stabilizing and reducing agent is confirmed by Fourier-transform infrared spectroscopy. The biomimetic synthesized AR-AgNPs showed antibacterial activity against Staphylococcus aureus (21 ± 0.2 mm) and Pseudomonas aeruginosa (15 ± 0.2 mm). Further, the cytotoxic effects of AR-AgNPs against MCF-7 human breast cancer cells were observed through acridine orange-ethidium bromide and Hoechst staining. Besides, AR-AgNPs are found to be inhibit the growth of 3rd and 4th instar larvae of Aedes aegypti in a dose-dependent manner.