Interaction of TiO2 nanoparticles with the marine microalga Nitzschia closterium: growth inhibition, oxidative stress and internalization

The impact of nTiO2 and GO (graphene oxide), and their combinations, on freshwater Chlorella sp.: a comparative study in lake water and BG-11 media

Titanium dioxide nanoparticles (nTiO2) and graphene oxide (GO) are extensively used nanomaterials in various products and applications. Freshwater ecosystems are a crucial sink for these pollutants, posing severe threats to aquatic organisms. Although multiple studies have investigated the pristine toxicity of nTiO2 and GO in freshwater organisms, the combined toxicity of these materials remains unexplored. Interaction media is a crucial factor in evaluating toxicity nanomaterial toxicity towards algae. In this study, we have investigated the comparative effect of sterilized and filtered freshwater and BG-11 medium on the pristine and combined toxicity of nTiO2 and GO on freshwater algae Chlorella sp. Results indicated that the combination of nTiO2 and GO showed more toxicity when compared to their respective pristine forms. This could be due to the additive effect exhibited by nTiO2 and GO on Chlorella sp. The enhanced growth inhibition for the combined toxicity was in the order of 1 mg L-1 nTiO2 + 1 mg L-1 GO > 1 mg L-1 nTiO2 + 0.1 mg L-1 GO > 0.1 mg L-1 nTiO2 + 1 mg L-1 GO > 0.1 mg L-1 nTiO2 + 0.1 mg L-1 GO. All test groups that interacted in BG-11 media exhibited less toxicity when compared to corresponding groups in the lake water medium. This could be attributed to the cushioning effect of BG-11 medium, providing supplementary nutrition to the algal cells. This signifies that the environmentally relevant conditions could be more detrimental than the laboratory conditions. This study elucidates valuable insights into the potential detrimental effects associated with the combination of nTiO2 and GO on freshwater algae. Furthermore, we have evaluated the growth inhibition, oxidative stress, and photosynthetic activity of Chlorella sp. in both environmentally relevant interaction medium and well-defined culture medium.

TiO2 nanoparticle photoactivation and oxidation reactions in freshwater and marine systems: The role of radical scavengers

Titanium dioxide nanoparticles (TiO2-NP) present in wastewater effluent are discharged into freshwater and saltwater (i.e., marine) systems. TiO2-NP can be solar-driven photoactivated by ultraviolet (UV)-light producing reactive oxygen species including hydroxyl radicals (·OH). ·OH are non-selective and react with a broad range of species in water. In other studies, photoactivation of TiO2-NP has been correlated with oxidative stress and ecotoxicological impacts on plant and animal biota. This study examined the photoactivation of TiO2-NP in freshwater and saltwater systems, and contrasted the oxidation potential in both systems using methylene blue (MB) as a reaction probe. Maximum MB loss (51.9%, n = 4; 95% confidence interval 49.4-54.5) was measured in salt-free, deionized water where ·OH scavenging was negligible; minimum MB loss (1%) was measured in saltwater due to significant ·OH scavenging, indicating the inverse correlation between MB loss and radical scavenging. A kinetic analysis of scavenging by seawater constituents indicated Cl- had the greatest impact due to high concentration and high reaction rate constant. Significant loss of MB occurred in the presence of Br- relative to other less aggressive scavengers present in seawater (i.e., HCO3-, HSO4-). This result is consistent with the formation of Bromate, a strong oxidant that subsequently reacts with MB. In freshwater samples collected from different water bodies in Oklahoma (n = 12), the average MB loss was 13.4%. Greater MB loss in freshwater systems relative to marine systems was due to lower ·OH scavenging by various water quality parameters. Overall, TiO2-NP photoactivation in freshwater systems has the potential to cause greater oxidative stress and ecotoxicological impacts than in marine systems where ·OH scavenging is a dominant reaction.

Activation of stress reactions in the dinophyte microalga Prorocentrum cordatum as a consequence of the toxic effect of ZnO nanoparticles and zinc sulfate

According to the results of the experimental study, the main regularities of changes in morphological, structural-functional and fluorescent indices of P. cordatum were established when zinc oxide nanoparticles ZnO NPs (0.3-6.4 mg L-1) and Zn in form of salt (0.09-0.4 mg L-1) were added to the medium. The studied pollutants have cytotoxic (growth inhibition, development of oxidative stress, destruction of cytoplasmic organelles, disorganization of mitochondria) and genotoxic (changes in the morphology of nuclei, chromatin condensation) effects on microalgae, affecting almost all aspects of cell functioning. Despite the similar mechanism of action of zinc sulfate and ZnO NPs on P. cordatum cells, the negative effect of ZnO NPs is also due to the inhibition of photosynthetic activity of cells (significant decrease in the maximum quantum yield of photosynthesis and electron transport rate), reduction of chlorophyll concentration from 3.5 to 1.8 pg cell-1, as well as mechanical effect on cells: deformation and damage of cell membranes, aggregation of NPs on the cell surface. Apoptosis-like signs of cell death upon exposure to zinc sulfate and ZnO NPs were identified by flow cytometry and laser scanning confocal microscopy methods: changes in cell morphology, cytoplasm retraction, development of oxidative stress, deformation of nuclei, and disorganization of mitochondria. It was shown that the first signs of cell apoptosis appear at 0.02 mg L-1 Zn and 0.6 mg L-1 ZnO NPs after 72 h of exposure. At higher concentrations of pollutants, a dose-dependent decrease in algal enzymatic activity (up to 5 times relative to control) and mitochondrial membrane potential (up to 4 times relative to control), and an increase in the production of reactive oxygen species (up to 4-5 times relative to control) were observed. The results of the presented study contribute to the disclosure of fundamental mechanisms of toxic effects of pollutants and prediction of ways of phototrophic microorganisms reaction to this impact.

Using single-species and algal communities to determine long-term adverse effects of silver nanoparticles on freshwater phytoplankton

The physical and chemical properties of silver nanoparticles (AgNPs) have led to their increasing use in various fields such as medicine, food, and industry. Evidence has proven that AgNPs cause adverse effects in aquatic ecosystems, especially when the release of Ag is prolonged in time. Several studies have shown short-term adverse effects of AgNPs on freshwater phytoplankton, but few studies have analysed the impact of long-term exposures on these populations. Our studies were carried out to assess the effects of AgNPs on growth rate, photosynthesis activity, and reactive oxygen species (ROS) generation on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa, and additionally on microcystin (MC-LR) generation from these cyanobacteria. The tests were conducted both in single-species cultures and in phytoplanktonic communities exposed to 1 ngL-1 AgNPs for 28 days. The results showed that cell growth rate of both single-species cultures decreased significantly at the beginning and progressively reached control-like values at 28 days post-exposure. This effect was similar for the community-cultured cyanobacteria, but not for the green algae, which maintained a sustained decrease in growth rate. While gross photosynthesis (Pg) increased in both strains exposed in single cultures, dark respiration (R) and net photosynthesis (Pn) decreased in S. armatus and M. aeruginosa, respectively. These effects were mitigated when both strains were exposed under community culture conditions. Similarly, the ROS generation shown by both strains exposed in single-species cultures was mitigated when exposure occurred in community cultures. MC-LR production and release were significantly decreased in both single-species and community exposures. These results can supply helpful information to further investigate the potential risks of AgNPs and ultimately help policymakers make better-informed decisions about their utilization for environmental restoration.

Differential intestinal effects of water and foodborne exposures of nano-TiO2 in the mussel Mytilus coruscus under elevated temperature

With the wide use of nanomaterials in daily life, nano-titanium dioxide (nano-TiO2) presents potential ecological risks to marine ecosystems, which can be exacerbated by ocean warming (OW). However, most previous studies have only centered around waterborne exposure, while there is a scarcity of studies concentrating on the impact of trophic transfer exposure on organisms. We investigated the differences in toxic effects of 100 μg/L nano-TiO2 on mussels via two pathways (waterborne and foodborne) under normal (24 °C) and warming (28 °C) conditions. Single nano-TiO2 exposure (waterborne and foodborne) elevated the superoxide dismutase (SOD) and catalase (CAT) activities as well as the content of glutathione (GSH), indicating activated antioxidatant response in the intestine. However, depressed antioxidant enzymes and accumulated peroxide products (LPO and protein carbonyl content, PCC) demonstrated that warming in combination with nano-TiO2 broke the prooxidant-antioxidant homeostasis of mussels. Our findings also indicated that nano-TiO2 and high temperature exhibited adverse impacts on amylase (AMS), trypsin (PS), and trehalase (THL). Additionally, activated immune function (lysozyme) comes at the cost of energy expenditure of protein (decreased protein concentration). The hydrodynamic diameter of nano-TiO2 at 24 °C (1693-2261 nm) was lower than that at 28 °C (2666-3086 nm). Bioaccumulation results (range from 0.022 to 0.432 μg/g) suggested that foodborne induced higher Ti contents in intestine than waterborne. In general, the combined effects of nano-TiO2 and warming demonstrated a more pronounced extent of interactive effects and severe damage to antioxidant, digestive, and immune parameters in mussel intestine. The toxicological impact of nano-TiO2 was intensified through trophic transfer. The toxic effects of nano-TiO2 are non-negligible and can be exerted together through both water- and foodborne exposure routes, which deserves further investigation.

Toxic effects of polystyrene nanoplastics and polycyclic aromatic hydrocarbons (chrysene and fluoranthene) on the growth and physiological characteristics of Chlamydomonas reinhardtii

While the toxicity of nano-microplastics and polycyclic aromatic hydrocarbons (PAHs) to aquatic organisms is well-studied, their joint impact on microalgae is less explored. This study focused on single and combined effects of PS-NPs (30 nm; concentrations: 2, 5, 10, and 25 mg/L) and two PAHs (chrysene and fluoranthene at 10, 100 µg/L) for 96 h on the accumulation, growth, photosynthetic parameters, and oxidative stress in the Chlamydomonas reinhardtii. The findings revealed that exposure to increasing concentrations of PS-NPs significantly reduced the growth inhibition ratio and chlorophyll-a content after 96 h. Both PAHs (100 µg/L) + PS-NPs (25 mg/L), significantly reduced the growth inhibition ratio and chlorophyll-a levels. Individual and combined exposures of PS-NPs and PAHs can prompt antioxidant responses like SOD, GPx, and GST, as well as an unaffected level of non-enzymatic antioxidant GSH and diminished CAT activity. Furthermore, both PAHs + PS-NPs triggered ROS levels, resulting in cell membrane damage. However, the reduced oxidative effect of LPO of combined exposures can be attributed to the activation of antioxidant defenses. In addition, the microscopic visualization data shows that PS-NPs adhered to the surface of microalgae. Also, PS-NPs reduced the adsorption of PAHs on the surface of C. reinhardtii. Altogether, this study implied that the influence of coexistent PS-NPs should be considered in the environmental risk assessment of PAHs in aquatic environments.

Dissemination of antibiotic resistance genes is regulated by iron oxides: Insight into the influence on bacterial transformation

The transportation of antibiotic resistance genes (ARGs) in manure-soil-plant continuums poses risks to human health. Horizontal gene transfer, particularly for bacterial transformation, is an important way for ARG dissemination. As crucial components in soils, iron oxides impacted the fates of various abiotic and biotic contaminants due to their active properties. However, whether they can influence the transformation of ARGs is unknown, which waits to be figured out to boost the assessment and control of ARG spread risks. In this study, we have investigated the effects of goethite, hematite, and magnetite (0-250 mg/L, with sizes < 100 nm and > 100 nm) on the transfer of ampicillin resistance genes to Escherichia coli cells. At lower iron oxide concentrations, the transformation of ARGs was first facilitated (transformation frequency reached up to 3.38-fold higher), but the facilitating effects gradually weakened and eventually disappeared as concentrations further increased. Particle size and iron oxide type were not the universal determinants controlling the transformation. At lower concentrations, iron oxides interacted with proteins and phospholipids in E. coli envelope structures, and induced the overgeneration of intracellular reactive oxygen species. Consequently, they led to pore formation and permeability enhancement on the cell membrane, thus promoting the transformation. The facilitation was also associated with the carrier-like effect of iron oxides for antibiotic resistance plasmids. At higher concentrations, the weakened facilitations were attributed to the aggregation of iron oxides. In this study, we highlight the crucial roles of the concentrations (contents) of iron oxides on the dissemination of ARGs in soils; this study may serve as a reference for ARG pollution control in future agricultural production.

Integrated physiological and transcriptomic analyzes reveal the duality of TiO2 nanoparticles on alfalfa (Medicago sativa L.)

Alfalfa (Medicago sativa L.) is a feed crop due to its rich nutrition and high productivity. The utilization of titanium oxide nanoparticles (TiO2 NPs) brings benefits to agricultural production but also has potential hazards. To investigate the duality and related mechanism of TiO2 NPs on alfalfa, its different doses including 0, 50, 100, 200, 500, and 1000 mg L- 1 (CK, Ti-50, Ti-100, Ti-200, Ti-500, and Ti-1000) were sprayed on leaves. The results showed that greater doses of TiO2 NPs (500 and 1000 mg L-1) negatively affected the physiological parameters, including morphology, biomass, leaf ultrastructure, stomata, photosynthesis, pigments, and antioxidant ability. However, 100 mg L-1 TiO2 NPs revealed an optimal positive effect; compared with the CK, it dramatically increased plant height, fresh weight, and dry weight by 22%, 21%, and 41%, respectively. Additionally, TiO2 NPs at low doses significantly protected leaf tissue, promoted stomatal opening, and enhanced the antioxidant system; while higher doses had phytotoxicity. Hence, TiO2 NPs are dose-dependent on alfalfa. The transcriptomic analysis identified 4625 and 2121 differentially expressed genes (DEGs) in the comparison of CK vs. Ti-100 and CK vs. Ti-500, respectively. They were mainly enriched in photosynthesis, chlorophyll metabolism, and energy metabolism. Notably, TiO2 NPs-induced phytotoxicity on photosynthetic parameters happened concurrently with the alterations of the genes involved in the porphyrin and chlorophyll metabolism and carbon fixation in photosynthetic organisms in the KEGG analysis. Similarly, it affected the efficiency of alfalfa energy transformation processes, including pyruvate metabolism and chlorophyll synthesis. Several key related genes in these pathways were validated. Therefore, TiO2 NPs have positive and toxic effects by regulating morphology, leaf ultrastructure, stomata, photosynthesis, redox homeostasis, and genes related to key pathways. It is significant to understand the duality of TiO2 NPs and cultivate varieties resistant to nanomaterial pollution.

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.

Less is more: The hormetic effect of titanium dioxide nanoparticles on plants

Titanium dioxide nanoparticles have attracted considerable attention due to their extensive applications; however, their multifaceted influence on plant physiology and the broader environment remains a complex subject. This review systematically synthesizes recent studies on the hormetic effects of TiO2 nanoparticles on plants - a phenomenon characterized by dual dose-response behavior that impacts various plant functions. It provides crucial insights into the molecular mechanisms underlying these hormetic effects, encompassing their effects on photosynthesis, oxidative stress response and gene regulation. The significance of this article consists in its emphasis on the necessity to establish clear regulatory frameworks and promote international collaboration to standardize the responsible adoption of nano-TiO2 technology within the agricultural sector. The findings are presented with the intention of stimulating interdisciplinary research and serving as an inspiration for further exploration and investigation within this vital and continually evolving field.

Mechanistic understanding on the uptake of micro-nano plastics by plants and its phytoremediation

Contaminated soil is one of today's most difficult environmental issues, posing serious hazards to human health and the environment. Contaminants, particularly micro-nano plastics, have become more prevalent around the world, eventually ending up in the soil. Numerous studies have been conducted to investigate the interactions of micro-nano plastics in plants and agroecosystems. However, viable remediation of micro-nano plastics in soil remains limited. In this review, a powerful in situ soil remediation technology known as phytoremediation is emphasized for addressing micro-nano-plastic contamination in soil and plants. It is based on the synergistic effects of plants and the microorganisms that live in their rhizosphere. As a result, the purpose of this review is to investigate the mechanism of micro-nano plastic (MNP) uptake by plants as well as the limitations of existing MNP removal methods. Different phytoremediation options for removing micro-nano plastics from soil are also described. Phytoremediation improvements (endophytic-bacteria, hyperaccumulator species, omics investigations, and CRISPR-Cas9) have been proposed to enhance MNP degradation in agroecosystems. Finally, the limitations and future prospects of phytoremediation strategies have been highlighted in order to provide a better understanding for effective MNP decontamination from soil.

Mechanistic transcriptome comprehension of Chlamydomonas reinhardtii subjected to black phosphorus

Two-dimensional materials have recently gained significant awareness. A representative of such materials, black phosphorous (BP), earned attention based on its comprehensive application potential. The presented study focuses on the mode of cellular response underlying the BP interaction with Chlamydomonas reinhardtii as an algal model organism. We observed noticeable ROS formation and changes in outer cellular topology after 72 h of incubation at 5 mg/L BP. Transcriptome profiling was employed to examine C. reinhardtii response after exposure to 25 mg/L BP for a deeper understanding of the associated processes. The RNA sequencing has revealed a comprehensive response with abundant transcript downregulation. The mode of action was attributed to cell wall disruption, ROS elevation, and chloroplast disturbance. Besides many other dysregulated genes, the cell response involved the downregulation of GH9 and gametolysin within a cell wall, pointing to a shift to discrete manipulation with resources. The response also included altered expression of the PRDA1 gene associated with redox governance in chloroplasts implying ROS disharmony. Altered expression of the Cre-miR906-3p, Cre-miR910, and Cre-miR914 pointed to those as potential markers in stress response studies.

Two plant-growth-promoting Bacillus species can utilize nanoplastics

Plastics in agricultural soils pose a potential risk to humans because environmental plastics can enter our foods. Here, we present a first step toward developing bacteria that can both flourish in agricultural settings and bioremediate nanoplastics. We exposed two species known to promote plant growth in agricultural settings, Bacillus inaquosorum and B. velezensis, to polystyrene nanoplastic beads at various dosages. When grown in a medium with a low dosage of plastic as the only carbon source, the bacteria could oxidize the plastic, indicating the possibility of utilizing the plastic in their growth. When plastic was added to a rich medium, low and high dosages brought immediate death or inhibition to about a third of B. inaquosorum cells during 1 h. Despite the immediate harm, over the course of 24 h, the bacteria from one strain each of B. inaquosorum and B. velezensis reached higher densities at low plastic doses than with no plastic, although they reached lower densities at high plastic doses (a toxicological phenomenon known as hormesis). Microscopic studies demonstrated that the bacteria are shielded from excessive accumulation of nanoplastic particles. Because these plant-growth-promoting species can utilize polystyrene nanoplastics, strains of these species might be developed to bioremediate environmental plastic in agricultural settings. SYNOPSIS: Plastic fragments on farmlands accumulate on produce, creating a need for bioremediation. We identify bacteria that can flourish on agricultural land and utilize nanoplastics, a first step toward developing agricultural bioremediators.

A study on the mechanism of the impact of phenthoate exposure on Prorocentrum lima

Extensive application of organophosphorus pesticides such as phenthoate results in its abundance in ecosystems, particularly in waterbodies, thereby providing the impetus to assess its role in aquatic organisms. However, the impact of phenthoate on marine algal physiological and proteomic response is yet to be explored despite its biological significance. In this study, we thus ought to investigate the impact of phenthoate in the marine dinoflagellate Prorocentrum lima, which is known for synthesizing okadaic acid (OA), the toxin responsible for diarrhetic shellfish poisoning (DSP). Our results showed that P. lima effectively absorbed phenthoate in seawater, with a reduction efficiency of 90.31% after 48 h. Surprisingly, the provision of phenthoate (100 and 1000 µg/L) substantially reduced the OA content of P. lima by 35.08% and 60.28% after 48 h, respectively. Meanwhile, phenthoate treatment significantly reduced the oxidative stress in P. lima. Proteomic analysis revealed that the expression level of seven crucial proteins involved in endocytosis was upregulated, suggesting that P. lima could absorb phenthoate via the endocytic signaling pathway. Importantly, phenthoate treatment resulted in the downregulation of proteins such as polyketide synthase (PKS)- 2, Cytochrome P450 (CYP450)- 1, and CYP450-2, involved in OA synthesis, thereby decreasing the OA biosynthesis by P. lima. Our results demonstrated the potential role of P. lima in the removal of phenthoate in water and exemplified the crucial proteins and their possible molecular mechanisms underpinning the phenthoate remediation by P. lima and also the regulatory role of phenthoate in restricting the OA metabolism. Collectively, these findings uncovered the synergistic mechanisms of phenthoate and P. lima in remediating phenthoate and reducing the toxic impact of P. lima.

Physiological impact of personal care product constituents on non-target aquatic organisms

Personal care products (PCPs) are products used in cleaning, beautification, grooming, and personal hygiene. The rise in diversity, usage, and availability of PCPs has resulted in their higher accumulation in the environment. Thus, these constitute an emerging category of environmental contaminants due to the potential of its constituents (chemical and non-chemical) to induce various physiological effects even at lower concentrations (ng/L). For analyzing the impact of the PCPs constituents on the non-target organism about 300 article including research articles, review articles and guidelines were studied from 2000 to 2023. This review aims to firstly discuss the fate and accumulation of PCPs in the aquatic environment and organisms; secondly provides overview of environmental risks that are linked to PCPs; thirdly review the trends, current status of regulations and risks associated with PCPs and finally discuss the knowledge gaps and future perspectives for future research. The article discusses important constituents of PCPs such as antimicrobials, cleansing agents and disinfectants, fragrances, insect repellent, moisturizers, plasticizers, preservatives, surfactants, UV filters, and UV stabilizers. Each of them has been found to display certain toxic impact on the aquatic organisms especially the plasticizers and UV filters. These continuously and persistently release biologically active and inactive components which interferes with the physiological system of the non-target organism such as fish, corals, shrimps, bivalves, algae, etc. With a rise in the number of toxicity reports, concerns are being raised over the potential impacts of these contaminant on aquatic organism and humans. The rate of adoption of nanotechnology in PCPs is greater than the evaluation of the safety risk associated with the nano-additives. Hence, this review article presents the current state of knowledge on PCPs in aquatic ecosystems.

Evaluation of the toxic effects of fluindapyr, a novel SDHI fungicide, to the earthworms Eisenia fetida

The emergence of resistance to existing succinate dehydrogenase inhibitor fungicides (SDHIs) calls for the urgent innovation of novel formulations, but also results in an increase information gap on the ecological risks of novel SDHIs especially to non-target organisms. Herein, the environmental behavior and toxicological effects of a novel SDHI, fluindapyr (FIP), were evaluated using earthworm as model non-target organism. Results showed that FIP had a relatively shorter half-live (about 28 days) in artificial soil compared with traditional SDHIs. Besides, FIP exhibited a rapid uptake and bioaccumulation trend in earthworms. For the toxicological effects, FIP suppressed earthworm growth (≥ 5 mg/kg) and reproduction (≥ 1 mg/kg) whereas no lethal effects were observed up to the highest tested concentration of 25 mg/mg. FIP of high exposure concentrations also induced serious epidermis and intestines damage as well as oxidative stress to earthworms after 28-day exposure. In addition, expression of oxidative damage related genes (CAT, CRT, GST, HSP70, SOD) was further verified after FIP exposure. The earthworm Tier 1 RQ also indicated a potential risk for earthworm reproduction. Data presented here may be useful for the risk assessments of FIP in soil ecosystems and help to set appropriate precautions to ensure protection against novel SDHIs.

Toxicological Impacts of TiO2 Nanoparticles on Growth, Photosynthesis Pigments, and Protein and Lipid Content of the Marine Microalga Tetraselmis Suecica

Regarding the widespread use of titanium dioxide nanoparticles (TiO2NPs) in industry, many concerns have been raised about the risks of their potential release into aquatic ecosystems. Among the marine primary producers, Tetraselmis suecica is an ecologically important microalgae species used also as live feed in the shrimp culture industry. In the present study, the impacts of TiO2NPs on growth performance, photosynthetic pigments, lipid and protein content and its interaction with the cells of T. suecica were assessed. Based on the preliminary tests and OECD suggestion, concentrations of 5, 10, 50, 100, 200 and 400 mg/L TiO2NPs were applied to algal cells for 10 days. With increasing concentration, a decrease in T. suecica cell density was observed each day. TiO2NPs induced a half-maximal inhibitory concentration (IC50) of 106.26 mg/L on algal cells on the 3rd day. Chlorophyll a and b contents of the microalga decreased up to 56.08% and 52.74%, respectively following the exposure to TiO2NPs at 400 mg/L. TiO2NPs also decreased the algal contents of protein and lipid up to 7.21% and 50.64%, respectively at the highest concentration. Based on FTIR, FESEM with EDS and mapping analyses, the interaction of TiO2NPs with the T. suecica cells was revealed. The stocks of T. suecica could be damaged by the toxic effects of the released TiO2NPs affecting their application as live feed in mariculture.

Dietary exposure to nTiO2 reduces byssus performance of mussels under ocean warming

Nano‑titanium dioxide (nTiO₂) is a widely used nanomaterial posing potential ecological risk for marine ecosystems that might be enhanced by elevated temperatures such as expected during climate change. nTiO₂ may affect benthic filter feeders like mussels through waterborne exposures and via food chain due to the adsorption on/in algae. Mussel byssus are proteinaceous fibers secreted by byssal glands of the mussels for attachment. Byssus production and mechanical properties are sensitive to environmental stressors but the combined effects of warming and nTiO₂ on byssus performance of mussels are unclear hampering our understanding of the predation and dislodgement risk of mussels under the multiple stressor scenarios. We explored the effects of a short-term (14-day) single and combined exposures to warming (28 °C) and 100 μg L^-1 nTiO₂ (including food co-exposure) on the byssus performance of the thick shell mussel Mytilus coruscus. The mechanical strength (measured as the breaking force) of the byssal threads was impaired by warming and nTiO₂ (including food co-exposure), but the number and length of the byssal threads were increased. The mRNA expression levels of mussel foot proteins (mfp-3, mfp-5) and pre-collagens (preCOL-D, preCOL-P, preCOL-NG) were up-regulated to varying degrees, with the strongest effects induced by warming. This indicates that the physiological and molecular mechanisms of byssus secretion are plastic. However, downregulation of the mRNA expression of preCOL-D and preCOL-P under the combined warming and nTiO₂ exposures indicate the limits of these plasticity mechanisms and suggest that the attachment ability and survival of the mussels may be impaired if the pollution or temperature conditions further deteriorate.

Prospects of microalgae in nutraceuticals production with nanotechnology applications

Nutraceutical supplements provide health benefits, such as fulfilling the lack of nutrients in the human body or being utilized to treat or cure certain diseases. As the world population is growing, certain countries are experiencing food crisis challenges, causing natural foods are not sustainable to be used for nutraceutical production because it will require large-scale of food supply to produce enriched nutraceutics. The high demand for abundant nutritional compounds has made microalgae a reliable source as they can synthesize high-value molecules through photosynthetic activities. However, some microalgae species are limited in growth and unable to accumulate a significant amount of biomass due to several factors related to environmental conditions. Therefore, adding nanoparticles (NPs) as a photocatalyst is considered to enhance the yield rate of microalgae in an energy-saving and economical way. This review focuses on the composition of microalgal biomass for nutraceutical production, the health perspectives of nutritional compounds on humans, and the application of nanotechnology on microalgae for improved production and harvesting. The results obtained show that microalgal-based compounds indeed have better nutrients content than natural foods. However, nanotechnology must be further comprehended to make them non-hazardous and sustainable.

The Occurrence of Oxidative Stress Induced by Silver Nanoparticles in Chlorella vulgaris Depends on the Surface-Stabilizing Agent

Silver nanoparticles (AgNPs) are of great interest due to their antimicrobial properties, but their reactivity and toxicity pose a significant risk to aquatic ecosystems. In biological systems, AgNPs tend to aggregate and dissolve, so they are often stabilized by agents that affect their physicochemical properties. In this study, microalga Chlorella vulgaris was used as a model organism to evaluate the effects of AgNPs in aquatic habitats. Algae were exposed to AgNPs stabilized with citrate and cetyltrimethylammonium bromide (CTAB) agents and to AgNO₃ at concentrations that allowed 75% cell survival after 72 h. To investigate algal response, silver accumulation, ROS content, damage to biomolecules (lipids, proteins, and DNA), activity of antioxidant enzymes (APX, PPX, CAT, SOD), content of non-enzymatic antioxidants (proline and GSH), and changes in ultrastructure were analyzed. The results showed that all treatments induced oxidative stress and adversely affected algal cells. AgNO₃ resulted in the fastest death of algae compared to both AgNPs, but the extent of oxidative damage and antioxidant enzymatic defense was similar to AgNP-citrate. Furthermore, AgNP-CTAB showed the least toxic effect and caused the least oxidative damage. These results highlight the importance of surface-stabilizing agents in determining the phytotoxicity of AgNPs and the underlying mechanisms affecting aquatic organisms.

Insights into roles of triclosan in microalgal-bacterial symbiosis system treating wastewater

Triclosan (TCS) is an antimicrobial agent and frequently detected in wastewater or water body. This study investigated the role of TCS in microalgal-bacterial symbiosis (MABS) system treating wastewater. The results showed that the removal efficiencies of NH₄⁺-N, total nitrogen, and total phosphorus decreased under increased TCS stress, with decrease ratios of 32.0%, 28.9%, and 46.1%. The activities of microalgae were more affected than that of bacteria. The secretion of extracellular polymeric substances (EPSs) and activity of superoxide dismutase firstly increased and then decreased with aggravated TCS stress, while the accumulation of malondialdehyde increased, leading to increased permeability of cytomembrane and bioaccumulation of TCS. In addition, the aggregation properties of microalgae and bacteria were enhanced with TCS loading increasing, and the migration of TCS was affected by enhanced EPSs secretions and MABS aggregates. This work may provide some new insights into the roles of TCS in MABS system.

Combined analysis of transcriptomics and metabolomics on the cumulative effect of nano-titanium dioxide on mulberry seedlings

Introduction

Titanium dioxide nanoparticles (TiO₂ NPs) are among the most widely used inorganic nanomaterials in industry, medicine and food additives. There are increasing concerns regarding their potential risks to plants and the environment. Mulberry trees are widely grown in China due to their high survival rate and ability to aid ecological recovery.

Methods

Herein, the effects of TiO₂ NPs with different concentrations (100, 200, 400 and 800 mg/L) on the growth and physiology of the mulberry tree were systematically evaluated in aspects of physiology, transcriptomics and metabolomics.

Results

Results showed that TiO₂ NPs could be absorbed by the mulberry sapling root system and be transferred to the plant shoot. This results in the destruction of mulberry sapling root and leaf tissue. Furthermore, the number of chloroplasts and their pigment contents were reduced and the homeostasis of metal ions was disrupted. The toxic effects of TiO₂ NPs attenuated the mulberry sapling's stress resistance, the contents of malondialdehyde in 100 mg/L, 200 mg/L 400 mg/L and 800 mg/L treatment groups increased by 87.70%, 91.36%, 96.57% and 192.19% respectively compared with the control group. The transcriptomic data showed that TiO₂ NPs treatment mainly affected the expression of genes related to energy synthesis and transport, protein metabolism, and response to stress. Meanwhile, the results of metabolomics showed that 42 metabolites produced significant differences in mulberry, of which 26 differential metabolites were up-regulated in expression and 16 differential metabolites were down-regulated, mainly including metabolic pathways such as secondary metabolite biosynthesis, citric acid cycle, and tricarboxylic acid cycle, and was not conducive to the seed germination and or growth of the mulberry sapling.

Discussion

This study enriches the understanding of the effects of TiO₂ NPs on plants and provides a reference for the comprehensive scientific assessment of the potential risks of nanomaterials on plants.

Harmonizing nanomaterial exposure methodologies in ecotoxicology: the effects of two innovative nanoclays in the freshwater microalgae Raphidocelis subcapitata

Layered double hydroxides (LDHs) are innovative nanomaterials (NMs) with a typical nanoclay structure (height <40 nm) consisting of layers of metallic cations and hydroxides stabilized by anions and water molecules. Upon specific triggers, anions can exchange by others in the surrounding environment. Due to this stimuli-responsive behavior, LDHs are used as carriers of active ingredients in the industrial or pharmaceutical sectors. Available technical guidelines to evaluate the ecotoxicity of conventional substances do not account for the specificities of NMs, leading to inaccuracies and uncertainty. The present study aimed to assess two different exposure methodologies (serial dilutions of the stock dispersion vs. direct addition of NM powder to each concentration) on the ecotoxicological profile of different powder grain sizes of Zn-Al LDH-NO3 and Cu-Al LDH-NO3 (bulk, <25, 25-63, 63-125, 125-250, and >250 µm) in the growth of the freshwater microalgae Raphidocelis subcapitata. Results revealed that the serial dilutions methodology was preferable for Zn-Al LDH-NO3, whereas for Cu-Al LDH-NO3 both methodologies were suitable. Thus, the serial dilutions methodology was selected to assess the ecotoxicity of different grain sizes for both LDHs. All Zn-Al LDH-NO3 grain sizes yielded similar toxicity, while Cu-Al LDH-NO3 powders with smaller grain sizes caused a higher effect on microalgae growth; thus, grain size separation might be advantageous for future applications of Cu-Al LDH-NO3s. Considering the differences between exposure methodologies for the Zn-Al LDH-NO3, further research involving other NMs and species must be carried out to achieve harmonization and validation for inter-laboratory comparison.

Differential physiological response of marine and freshwater microalgae to polystyrene microplastics

Effects of microplastics on microalgae have not been compared from different habitat. To answer this question, three marine microalgae species (Chlorella marined, Nannochloropsis oculate, and Phaeodactylum tricornutum) and two freshwater species (Chlorella vulgaris and Tetradesmus obliquus) were selected and exposed to the environment relevant concentrations of polystyrene microplastics. The results indicated that microplastics have a significant concentration effect on the growth of microalgae. The attachment of microalgae to microplastics surface and the aggregation of microalgae with each other were observed. Under exposure of microplastics, the photosynthesis of microalgae was inhibited while the antioxidant system was activated, indicating that microplastics had a negative impact on microalgae. At the end of exposure, the oxidative stress status caused by microplastics in marine microalgae were alleviated, but the antioxidant system of freshwater microalgae was still at high levels, indicating a stress response. In addition, integrated biomarker response (IBR) indicated that the effects of microplastics on freshwater microalgae were severer than marine microalgae, which might relate to their differences in removing reactive oxygen species (ROS) effectively and membrane structure. Our study provides a reliable data for understanding the complex effects of microplastics on microalgae, and especially for comparing the differential effects of microplastics among different microalgae.

Nitrogen forms and concentration influence the impact of titanium dioxide nanoparticles on the biomass and antioxidant enzyme activities of Microcystis aeruginosa

Nanoparticles (NPs) are becoming more widely produced, used, and released into the aquatic environment. In aquatic ecosystems, these NPs affect different populations of photosynthesizing organisms, such as cyanobacteria. This study aimed to evaluate the effects of titanium dioxide (TiO₂) NPs (48 mg l^-1) combined with low (0.04 mM) and high (9 mM) concentrations of urea and nitrate on Microcystis aeruginosa. Microcystins (MCs) production and release were monitored in the cyanobacterium. The results showed that high urea concentration (9 mM) combined with TiO₂ NPs inhibited growth, pigment, and malondialdehyde (MDA) content by 82%, 63%, and 47%, respectively. The treatment also increased the reactive oxygen species (ROS) and glutathione S-transferase (GST) activity by 40.7% and 67.7%, respectively. Similarly, low nitrate (0.04 mM) combined with TiO₂ NPs inhibited growth by 40.3% and GST activity by 36.3% but stimulated pigment production and ROS concentration in M. aeruginosa. These responses suggest that high urea combined with TiO₂.NPs and high nitrate combined with TiO₂ NPs induced oxidative stress in cyanobacteria. The peroxidase (POD) activity of M. aeruginosa decreased by 17.7% with increasing urea concentrations. Our findings suggest that TiO₂ NPs combined with changing nutrient (urea and nitrate) concentrations may adversely affect cyanobacterial development and antioxidant defense enzymes.

The ecotoxicological effects of chromium (III) oxide nanoparticles to Chlorella sp.: perspective from the physiological and transcriptional responses

Extensive application of nanomaterials enlarges its concentrations in the aquatic environments and poses a threat to algae. This study comprehensively analyzed the physiological and transcriptional responses of Chlorella sp. after being exposed to chromium (III) oxide nanoparticles (nCr₂O₃). The nCr₂O₃ at 0-100 mg/L presented adverse effects on cell growth (96 h EC₅₀ = 16.3 mg/L), decreasing the photosynthetic pigment concentrations and photosynthetic activity. Moreover, more extracellular polymeric substances (EPS), especially polysaccharides in soluble EPS, were produced in algae cell, which mitigated the damage of nCr₂O₃ to cells. However, with the increase of nCr₂O₃ doses, the EPS protective responses were exhausted, accompanied by toxicity in the form of organelle damage and metabolic disturbance. The enhanced acute toxicity was closely related to the physical contact of nCr₂O₃ with cells, oxidative stress, and genotoxicity. Firstly, large amounts of nCr₂O₃ aggregated around and were attached to cells, causing physical damage. Then, the intracellular reactive oxygen species and malondialdehyde levels were significantly increased that led to lipid peroxidation, especially at 50-100 mg/L nCr₂O₃. Finally, the transcriptomic analysis further revealed that the transcription of ribosome, glutamine, and thiamine metabolism-related genes were impaired under 20 mg/L nCr₂O₃, suggesting nCr₂O₃ inhibited algal cell growth through metabolism, cell defense, and repair, etc.

Transcriptomic hallmarks of in vitro TiO2 nanotubes toxicity in Chlamydomonas reinhardtii

Recently, more accessible transcriptomic approaches have provided a new and deeper understanding of environmental toxicity. The present study focuses on the transcriptomic profiles of green microalgae Chlamydomonas reinhardtii exposed to new industrially promising material, TiO₂ nanotubes (NTs), as an example of a widely used one-dimensional nanomaterial. The first algal in vitro assay included 2.5 and 7.5 mg/L TiO₂ NTs, resulting in a dose-dependent negative effect on biological endpoints. At a working concentration of 7.5 mg/L, RNA-sequencing showed a mainly negative effect on the cells. In summary, the results indicated metabolic disruption, ^{such as ATP loss, damage to mitochondria and chloroplasts, loss of solutes due to permeated membranes,} and cell wall damage. Moreover, apoptosis-induced transcripts were detected. Interestingly, reactivation of transposons was observed. In signalling and transcription pathways, including chromatin remodelling and locking, the annotated genes were downregulated.

Potential risks of CO2 removal project based on carbonate pump to marine ecosystem

The development of marine carbon sequestration project has an important potential for carbon neutralization in the short-term (several decades). Marine carbon sequestration technology is based on biological and carbonate pumps to increase particulate organic carbon and authigenic insoluble carbonates to the deep sea or seafloor, aiming to achieve permanent carbon sequestration. Particularly, chemical carbon sequestration technology based on carbonate pump is proposed and considered to achieve short-term marine carbon sequestration in recent years. This technology mainly includes alkaline mineral addition and combining CO₃^2- to insoluble carbonates to improve marine carbon fixation capacity. Potential marine ecosystem risks of chemical CO₂ removal method should be considered before being a feasible technology. We reviewed the potential effects of marine chemical carbon sequestration project on marine organisms. Marine chemical carbon sequestration had two main effects on marine organisms: released chemicals effect, and particle effect. Released chemicals in mineral weathering directly affected phytoplankton and bacteria community. Particles formed during carbon sequestration process mainly affected filter feeding organisms. The toxic effects of particles on aquatic organisms increased with decreasing sizes and increasing concentrations of particle. Algae and crustaceans were the most sensitive groups exposed to metal nanoparticles (nm-μm) in seawaters, thus could be used as target species to evaluate ecological risk of small particles generated in chemical carbon sequestration project. Embryos or larva of filter feeding organisms were more sensitive to large clay and metal microparticles (μm‑mm) than adults, thus could be used as sensitive groups to establish safety concentration of large particles. The relatively inert metal nanoparticles and microparticles had higher safety concentrations than active ones. These particle concentration thresholds could be as a reference to design concentrations and initial sizes of applied minerals in marine chemical carbon sequestration project. This will ensure that the ecological risk is minimized when carbon fixation efficiency is maximized.

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.

Is hydrodynamic diameter the decisive factor? - Comparison of the toxic mechanism of nSiO2 and mPS on marine microalgae Heterosigma akashiwo

To investigate the toxic mechanism of SiO₂ nanoparticles (nSiO₂) and polystyrene microplastics (mPS) on microalgae Heterosigma akashiwo, growth inhibition tests were carried out. The growth and biological responses of the algae exposed to nSiO₂ (0.5, 1, 1.5, 2, 5, 10 and 30 mg L^-1) and mPS (1, 2, 5, 10, 30 and 75 mg L^-1) were explored in f/2 media for 96 h. It was found that the hydrodynamic diameter of the particles seems to be one of the more important factors to influence the algae. nSiO₂ and mPS with similar hydrodynamic diameters have the similar toxic mechanism on H. akashiwo, and the effects were dose- and time-dependent. High concentrations of micro-/nano-particles (MNPs) could inhibit the growth of algal cells, however, low concentrations of MNPs did not restrict or even promoted the growth of algae, known as "Hormesis" phenomenon. The 96 h-EC20 values of nSiO₂ and mPS on H. akashiwo were 2.69 and 10.07 mg L^-1, respectively, and chlorophyll fluorescence parameters indicated that the microalgal photosynthetic system were inhibited. The hydrophilic surface of nSiO₂ increased the likelihood of nSiO₂ binding to the hydrophilic functional group of microalgae, which may account for the slightly stronger toxic effect of nSiO₂ than mPS. The algae continued to produce reactive oxygen species (ROS) under stress conditions. Total protein (TP) levels reduced, and superoxide dismutase (SOD) and catalase (CAT) levels increased to maintain ROS levels in the cells. The decrease in adenosine triphosphate (ATPase) indicated an impact on cellular energy metabolism. Cell membrane damage, cytoplasm and organelle efflux under stress were confirmed by scanning and transmission electron microscopy (SEM and TEM) images. This study contributes to the understanding of the size effect of MNPs on the growth of marine microalgae.

Effect of Microplastics on the Removal of Nitrogen and Phosphorus from Synthetic Piggery Digestate by Microalgae

Microplastics (MPs) have been proven to be one of the major threats to the wastewater treatment system. However, the impact of MPs on microalgae-based wastewater treatment technology are still unknown. In this study, effects of polyvinyl chloride (PVC), polypropylene (PP), and polyethylene (PE) on the removal of nitrogen and phosphorus from synthetic piggery digestate by microalgae were investigated. Results show that the effect of PVC particle size on the growth of microalgae was significant. The effects of PVC content, PP particle size and content, PET particle size and content on the growth of microalgae were all not significant. The removal of ammonia nitrogen by microalgae was influenced significantly by PVC particle size and content, PP particle size and content, the effects of PET particle size and content on the removal of ammonia nitrogen were all not significant. The effects of particle size and content for three MPs on the removal of total phosphorus were all significant. Microalgae cells were bound together after being adsorbed by MPs, which increased the secretion of extracellular polymers and influenced the removal of ammonia nitrogen and total phosphorus.

Impact of silver nanoparticles on the nutritional properties of Arthrospira platensis

Background

Arthrospira platensis is farmed worldwide due to its nutrient-rich properties and provides multiple benefits to human health. However, the wide usage of silver nanoparticles (Ag NPs) causes pollution which may affect the nutritional quality of A. platensis. Hence, this study aimed to investigate the interaction and accumulation of Ag NPs on A. platensis, and determine the changes in biomass and nutritional value of A. platensis due to the exposure to Ag NPs.

Methods

The interaction and accumulation of Ag NPs on A. platensis were examined through Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscope (SEM). The loss in biomass together with the macromolecules, pigments, and phenolic compounds of A. platensis was investigated upon treating with various concentrations of Ag NPs (5, 10, 25, 50 and 100 µg/mL) for 24, 48, 72 and 96 h.

Results

The results showed that the treatment of A. platensis with Ag NPs caused a dose and time-dependent reduction in biomass, macronutrients, pigments and phenolic compounds. The highest detrimental effects were found at 96 h with the reported values of 65.71 ± 2.79%, 67.21 ± 3.98%, 48.99 ± 4.39% and 59.62 ± 3.96% reduction in biomass, proteins, carbohydrates and lipids, respectively, along with 82.99 ± 7.81%, 67.55 ± 2.63%, 75.03 ± 1.55%, and 63.43 ± 2.89% loss in chlorophyll-a, carotenoids, C-phycocyanin, and total phenolic compounds of A. platensis for 100 µg/mL of Ag NPs. The EDX analysis confirmed the surface accumulation of Ag NPs on Arthrospira cells, while SEM images evidenced the surface alterations and damage of the treated cells. The functional groups such as hydroxyl, amine, methyl, amide I, amide II, carboxyl, carbonyl and phosphate groups from the cell wall of the A. platensis were identified to be possibly involved in the interaction of Ag NPs with A. platensis.

Conclusion

The study confirmed that the exposure of Ag NPs is detrimental to A. platensis where the interaction and accumulation of Ag NPs on A. platensis caused reduction in biomass, macromolecules, pigments, and total phenolic compounds.

Interaction of TiO2 nanoparticles with the C. vulgaris: oxidative stress, lipid peroxidation and lipid amount

Nanoparticles are widely used in many industries such as food and cosmetics. With increasing use, its spread to environmental environments is also increasing. Microalgae have an important place in the uptake of nanoparticles into the food chain. In this study, the effect of TiO₂ nanoparticle on antioxidant enzyme activity, malondialdehyde, hydrogen peroxide, chlorophyll-a and total lipid amount in C. vulgaris microalgae has been investigated. As a result of the dose study, while the superoxide dismutase and ascorbate peroxidase enzyme activities decreased, the amount of MDA, H₂O₂ and chlorophyll-a increased. Depending on the times at different light:dark ratios, both an increase and a decrease occurred in the SOD, APX enzyme activity and the amount of MDA, H₂O₂. There was an increase in the amount of chlorophyll-a. In the time study, while the SOD and APX enzyme activities increased, the amount of MDA and H₂O₂ decreased. The amount of chlorophyll-a increased. In the total lipid study, the total lipid amount in the group with nano TiO₂ increased compared to the control group. At the same time, C18:2 T (linoleic acid) has been found as fatty acid methyl ester in both groups.

Nano-ecotoxicology in a changing ocean

The ocean faces an era of change, driven in large by the release of anthropogenic CO2, and the unprecedented entry of pollutants into the water column. Nanomaterials, those particles < 100 nm, represent an emerging contaminant of environmental concern. Research on the ecotoxicology and fate of nanomaterials in the natural environment has increased substantially in recent years. However, commonly such research does not consider the wider environmental changes that are occurring in the ocean, i.e., ocean warming and acidification, and occurrence of co-contaminants. In this review, the current literature available on the combined impacts of nanomaterial exposure and (i) ocean warming, (ii) ocean acidification, (iii) co-contaminant stress, upon marine biota is explored. Here, it is identified that largely co-stressors influence nanomaterial ecotoxicity by altering their fate and behaviour in the water column, thus altering their bioavailability to marine organisms. By acting in this way, such stressors, are able to mitigate or elevate toxic effects of nanomaterials in a material-specific manner. However, current evidence is limited to a relatively small set of test materials and model organisms. Indeed, data is biased towards effects upon marine bivalve species. In future, expanding studies to involve other ecologically significant taxonomic groups, primarily marine phytoplankton will be highly beneficial. Although limited in number, the available evidence highlights the importance of considering co-occurring environmental changes in ecotoxicological research, as it is likely in the natural environment, the material of interest will not be the sole stressor encountered by biota. As such, research examining ecotoxicology alongside co-occurring environmental stressors is essential to effectively evaluating risk and develop effective long-term management strategies.

Impacts of nano-titanium dioxide toward Vallisneria natans and epiphytic microbes

In this study, Vallisneria natans plants were exposed to 5 and 20 nm of titanium dioxide nanoparticles (TiO₂ NPs) anatase and 600-1000 nm of bulk at 5 and 20 mg/L for 30 days. SEM images and EDX spectra revealed that epiphytic biofilms were more prone to TiO₂ NPs adhesion than bare plant leaves. TiO₂ NPs injured plant leaf cells, ruptured epiphytic diatoms membranes and increased the ratio of free-living microbes. The TN, NH₄⁺-N and NO₃--N concentrations significantly decreased, respectively, by 44.9%, 33.6%, and 23.6% compared to bulk treatments after 30 days due to macrophyte damage and a decline in diversity of epiphytic bacterial community and abundance of nitrogen cycle bacteria. TiO₂ NPs size-dependent decrease in bacterial relative abundance was detected, including phylum Cyanobacteria, Planctomycetes, and Verrucomicrobia. Although TiO₂ NPs increased eukaryotic diversity and abundance, abundances of Bacillariophyceae and Vampyrellidae classes and Gastrotricha and Phragmoplastophyta phylum decreased significantly under TiO₂ NPs exposure compared to bulk and control. TiO₂ NPs reduced intensities of interaction relationships among epiphytic microbial genera. This study shed new light on the potential effects of TiO₂ NPs toxicity toward aquatic plants and epiphytic microbial communities and its impacts on nitrogen species removal in wetlands.

Bioaccumulation and biomagnification effects of nano-TiO2 in the aquatic food chain

The increasing production of nano-TiO₂ has attracted extensive concerns about the ecological consequence and health risk of these compounds in natural ecosystem. However, little is known about its toxicity on zooplankton, especially its possibility to access to the food chain via dietary exposure. To address this concern, the toxic and cumulative effects of nano-TiO₂ on an aquatic food chain were explored through two trophic levels independently or jointly including producer and consumer. The results revealed that exposure to suspensions of nanomaterials had negative effects on both producers and consumers. Specifically, nanoparticles reduced the density of algal cells in a concentration-dependent way, and hatching life expectancy, average lifespan, net reproductive rate, and population intrinsic growth rate of rotifers decreased significantly with the concentration of nanomaterials increased (P < 0.05). Notably, nanoparticles accumulated in algal cells and were transferred to consumers through dietary exposure. Biomagnification of nano-TiO₂ was observed in this simplified food chain, as many of the biomagnification factor (BMF) values in this study were >1. Exposure concentration, exposure time and their interactions play a strong part in the accumulation of nanoparticles in algae and rotifers. Overall, the present findings confirmed that nano-TiO₂ was deleterious to plankton, posing a significant environmental threat to aquatic ecosystems. Graphical abstract.

Mechanism of the allelopathic effect of macroalgae Gracilaria bailiniae on Nitzschia closterium

With the rapid development of the seaweed industry in China, the scale and production of its commercial seaweed are ranked among the most significant worldwide. Consequently, the control of algal blooms, especially fouling diatoms, during macroalgae industrialisation is an important issue. Many diatom bloom studies have focused on physical and chemical controls, with limited economic and eco-friendly biological controls reported. In our study, Gracilaria bailiniae fresh thalli and aqueous extract profoundly suppressed Nitzschia closterium growth (50% inhibition concentration of the fourth day (IC_50-4 day) was 0.667 × 10^-3 g·mL^-1 and 3.889 × 10^-3 g·mL^-1, respectively). The cellular morphology changes of N. closterium exposed to the G. bailiniae aqueous extract were severe atrophies and plasmolysis and dissolution of endocellular structures. To explore more potential allelochemicals to control N. closterium, the intracellular compounds of G. bailiniae were detected and screened. Three organic acids (citrate, hydroxyethanesulfonic acid (HA) and taurine) had allelopathic potential against N. closterium. Our results showed that citrate and HA markedly suppressed N. closterium (IC_50-4 day: 1.035 mM and 1.151 mM, respectively); however, taurine poorly suppressed N. closterium (IC_50-4 day: 2.500 mM). Therefore, HA is one of the main allelopathic compounds in G. bailiniae. Further, the allelopathic mechanism of HA against the N. closterium photosynthetic system broke its photosynthetic apparatus (oxygen-evolving complex, reaction centres, the effective antenna size and the donor side of photosystem II) and hindered electron transport. The experimental results provide a new and eco-friendly strategy to control diatom blooms.

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.

Toxicity of TiO2 nanoparticles to the marine microalga Chaetoceros muelleri Lemmermann, 1898 under long-term exposure

Titanium dioxide nanoparticles (TiO₂NPs) have been extensively used in industry, raising many concerns about their release into the aquatic environments. In marine ecosystems, microalgae are major primary producers; among them, Chaetoceros muelleri is an important microalga in the aquaculture industry as live feed. The impacts of TiO₂NPs on the growth, photosynthetic pigments, protein and lipid contents, and the interaction of TiO₂NPs with the cell wall of C. muelleri were investigated in the present study. Algal cells were exposed to concentrations of 5, 10, 50, 100, 200, and 400 mg/L TiO₂NPs for 10 days. There was a significant difference in the growth between the control and TiO₂NPs treatments on each day. The half-maximal inhibitory concentration (IC₅₀) of TiO₂NPs on algal cells was found to be 10.08 and 5.01 mg/L on the 3rd and 10th days, respectively. The contents of chlorophyll a and c reduced significantly in the TiO₂NPs-treated microalgae. TiO₂NPs also reduced the protein and lipid contents in the treated microalgae, up to 13.02% and 47.6% respectively, at the highest concentration. The interaction of TiO₂NPs with the C. muelleri cells was obvious based on Fourier transform infrared spectroscopy, microscopic images, EDS, and Mapping analyses. Toxic effects of the released TiO₂NPs can damage the stocks of C. muelleri as an important live feed in mariculture.

Photocatalytic Selective Degradation of Catechol and Resorcinol on the TiO2 with Exposed {001} Facets: Roles of Two Types of Hydroxyl Radicals

Photocatalytic studies on contaminant degradation in water suspension generally suggest that the degradation reaction mainly takes place on the surface of the photocatalysts rather than in the water phase. The mechanism of selective degradation is often difficult to distinguish concerning the contribution of adsorption and radical selectivity. This study is thus designed to investigate the roles of two types of hydroxyl radicals, adsorbed hydroxyl radical (·OHa) and free hydroxyl radical (·OHf), on the selective degradation of catechol (CT) and resorcinol (RE). CT and RE are significantly different in adsorption on a TiO2 photocatalyst with a highly exposed {001} facet. CT can be selectively degraded by TiO2 and was highly correlated with adsorption. Free radical quenching experiment results showed that the degradation of CT can be identified as the combined effect of both ·OHa and ·OHf, while the degradation of RE was mainly due to the ·OHf. Electron paramagnetic resonance coupled with spin trapping agents was used to detect the relative concentration of hydroxyl radicals in all the photocatalytic degradation processes. After a series analysis, we proposed that the mechanism of selective degradation mainly depends on the concentration of ·OHf for the pollutant molecules with weak adsorption on the catalyst surface.

Mixture toxicity of TiO2 NPs and tetracycline at two trophic levels in the marine ecosystem: Chlorella sp. and Artemia salina

Increasing usage of both nanomaterials and pharmaceuticals and their unabated release to the marine ecosystem pose a serious concern nowadays. The toxicity of the mixture of TiO₂ NPs and tetracycline (TC) in the marine species are not very well covered in prior literature. The current study explores the joint toxic effects of TiO₂ NPs and TC in a simulated marine food chain: Chlorella sp. and Artemia salina. Chlorella sp. was interacted with pristine TiO₂ NPs (0.05, 05, and 5 mg/L), TC (0.5 mg/L), and their combinations for 48 h. The toxicity induced in Chlorella sp. by pristine TiO₂ NPs through oxidative stress and chloroplast damage was not significantly changed in the presence of TC. Principal component analysis for the toxicity parameters revealed a strong association between growth inhibition and adsorption/internalization. In the second trophic level (A. salina), the waterborne exposure of TC additively increased the toxicity of TiO₂ NPs. Both adsorption and degradation played a major role in the removal of TC from the suspension, resulting in additive toxic effects in both Chlorella sp. and A. salina. Compared to the waterborne exposure, the foodborne exposure of TiO₂ NPs and TC induced lesser toxic effects owing to reduced uptake and accumulation in A. salina. Biomagnification results indicate that the dietary transfer of TiO₂ NPs and TC does not pose a serious environmental threat in this two-level marine food chain.

Enhanced removal efficiency of sulfamethoxazole by acclimated microalgae: Tolerant mechanism, and transformation products and pathways

This study utilized sulfamethoxazole (SMX) acclimatization to enhance the tolerance and biodegradation capacity of Chlorella vulgaris. Compared to wild C. vulgaris, the growth inhibition and oxidative damage induced by SMX evidently decreased in acclimated C. vulgaris, and meanwhile photosynthetic and antioxidant activities were significantly promoted. The physiological analyses with the aid of principal component analysis revealed the increase of catalase and glutathione reductase activities was the critical tolerant mechanism of acclimated C. vulgaris. As the consequence, the acclimated C. vulgaris exhibited enhanced efficiency and (pseudo-first-order) kinetic rate for removal of SMX. The distribution analysis of residual SMX demonstrated the biodegradation was the major removal mechanism of SMX by C. vulgaris, while bioadsorption and bioaccumulation made pimping contributions. During the degradation process of SMX, nine transformation products (TPs) were identified. Based on the identified TPs, a possible transformation pathway was proposed.

Influence of polystyrene microplastics on levofloxacin removal by microalgae from freshwater aquaculture wastewater

Chlorella vulgaris (C. vulgaris) has attracted widespread attention because of its ability to absorb, enrich, and degrade typical endocrine-disrupting antibiotics (such as levofloxacin) in aquaculture wastewater. However, microplastic pollution in wastewater, which is becoming an increasingly severe problem, will exert a toxic effect on aquatic organisms (such as C. vulgaris and other microalgae). Polystyrene microplastics (PS-MPs), which are commonly found in freshwater aquaculture wastewater, are the most harmful. Therefore, clarifying the effects of PS-MPs on the ability of C. vulgaris to degrade typical endocrine-disrupting antibiotics in freshwater aquaculture wastewater and determining the mechanism of the effect are particularly important. The results of this study showed that under the stress of PS-MPs, the growth of C. vulgaris was significantly inhibited; the EPS-polysaccharide content per algal cell, EPS adsorption, intracellular enrichment and degradation of levofloxacin, total CYP450 content, and total CYP450 activity all decreased; and the relative expression of key genes related to the metabolic activity of algal cells, such as psbA, psaB, and rbcL, was generally downregulated. PS-MPs mainly affected the removal of a typical endocrine-disrupting antibiotic by C. vulgaris by altering adsorption, enrichment, and enzyme degradation. The results provide a reference for research on the impact of microplastic pollution on the treatment of freshwater aquaculture wastewater.

Surface Coating-Modulated Phytotoxic Responses of Silver Nanoparticles in Plants and Freshwater Green Algae

Silver nanoparticles (AgNPs) have been implemented in a wide range of commercial products, resulting in their unregulated release into aquatic as well as terrestrial systems. This raises concerns over their impending environmental effects. Once released into the environment, they are prone to various transformation processes that modify their reactivity. In order to increase AgNP stability, different stabilizing coatings are applied during their synthesis. However, coating agents determine particle size and shape and influence their solubility, reactivity, and overall stability as well as their behavior and transformations in the biological medium. In this review, we attempt to give an overview on how the employment of different stabilizing coatings can modulate AgNP-induced phytotoxicity with respect to growth, physiology, and gene and protein expression in terrestrial and aquatic plants and freshwater algae.

Effects of polystyrene and triphenyl phosphate on growth, photosynthesis and oxidative stress of Chaetoceros meülleri

The toxicity of microplastics to marine organisms has attracted much attention; however, studies of their effects on marine microalgae remain limited. Here, the effects of the single and combined toxicity of polystyrene (PS) and triphenyl phosphate (TPhP) on the cell growth, photosynthesis, and oxidative stress of Chaetoceros meülleri were investigated. PS inhibited growth of the algae cells and caused a dose-dependent effect on oxidative stress. The significantly high production of reactive oxygen species (ROS) induced severe cell membrane damage, as confirmed by high fluorescence polarization. However, there was no obvious decrease in chlorophyll a content, and 80 mg/L of PS significantly promoted chlorophyll a synthesis. The TPhP also inhibited cell growth, except at low concentrations (0.2-0.8 mg/L), which stimulated algae growth over 48 h. Moreover, no obvious decrease in chlorophyll a and maximal photochemical efficiency of PSII was found in the TPhP experimental groups except for 3.2 mg/L TPhP, where the rapid light curves showed a significantly reduced photosynthetic capacity of algae. In addition, TPhP caused high ROS levels at 96 h, resulting in cell membrane damage. Using the additive index and independent action methods, the combined toxic effects of PS and TPhP on the algae were evaluated as antagonistic; however, cell membrane damage caused by high ROS levels was still noticeable. This study has shown the potential toxicity of PS and TPhP to marine microalgae, and provided insights into the combined risk assessment of TPhP and microplastics in the marine environment.

Toxic effects of benzovindiflupyr, a new SDHI-type fungicide on earthworms (Eisenia fetida)

Benzovindiflupyr has received increasing attention as a new novel succinate dehydrogenase inhibitor (SDHI)-type fungicide. Nonetheless, its traces remaining in soil potentially trigger an ecotoxicological threat to soil organisms including earthworms. This paper evaluates the eco-toxicity of different benzovindiflupyr doses (0.1, 1, 5, and 10 mg kg-1) on earthworms (Eisenia fetida) after long-term exposure. Consequently, benzovindiflupyr at higher doses significantly inhibited the activities of respiratory chain complex II and succinate dehydrogenase (SDH) in E. fetida. Besides, the reactive oxygen species (ROS) and lipid peroxidation (LPO) were significantly induced in earthworms when treated with this fungicide. After benzovindiflupyr exposure, activities of antioxidant enzymes including catalase, peroxidase, and superoxide dismutase were activated. However, glutathione S-transferase activity in E. fetida was initially induced then inhibited in earthworms after treatment. Furthermore, benzovindiflupyr exposure induced the protein carbonylation (PCO) level in cells indicating oxidative damage to the cellular protein. Due to the destruction of the normal function in the coelomocytes, the phagocytic activity was initially activated, then inhibited when earthworms were treated at 5 and 10 mg kg-1 concentrations. Additionally, DNA damage was induced (larger olive tail moment (OTM) values) with the increase of benzovindiflupyr doses and exposure time. The weight was significantly decreased after benzovindiflupyr exposure on days 21 and 28. Benzovindiflupyr at higher doses significantly decreased the reproduction (number of cocoons and juveniles) of E. fetida. These findings reveal that benzovindiflupyr potentially induces a potential toxicological risk to earthworms when applied in the mentioned above dosages.

Review of the toxic effect of microplastics on terrestrial and aquatic plants

As a new pollutant, microplastics (MPs) exhibited more and more significant influence on the organisms in the environment. Especially, the effects on the growth and development of plants by MPs attracted wide attentions in recent period. In the review article, we summarized the important influences of MPs on terrestrial and aquatic plants. The properties, including type, size and oxygen-containing group of MPs on their physical injures toward plants were critically reviewed, which were significantly correlated to the toxicity to plants. The secondary risks of MPs including the additives and MP-derived organic products and the adsorbed environmental pollutants to plants were clearly revealed. The hydrophobic organic pollutants released from MPs showed significant chemical effects on the plants. We also outlined the effects of MPs to the various regions (e.g. the seed and rhizome) of plants and compared the toxic difference of MPs on terrestrial and aquatic plants. Generally, the seed and rhizome of plants were susceptible to MPs, and the effects of MPs on terrestrial and aquatic plants were different. The review paper improves the understanding of potential toxicity of MP themselves and the released and adsorbed chemicals to plants in the environment.

Exposure-based ecotoxicity assessment of Co3O4 nanoparticles in marine microalgae

The exposure-effect study was conducted to evaluate the effect of Co₃O₄ nanoparticles on Tetraselmis suecica. The growth suppressing effect has been observed during the interaction between nanoparticles and microalgae as indicated by 72 h EC₅₀ (effective concentration of a chemical at which 50% of its effect is observed) value (45.13±3.95 mg/L) of Co₃O₄ nanoparticles for Tetraselmis suecica. Decline in chlorophyll a content also indicated the compromised photosynthetic ability and physiological state of microalgae. Further biochemical investigation such as increase in extracellular LDH (lactate dehydrogenase) level, ROS (reactive oxygen species), and levels of membrane lipid peroxidation in treated samples signifies the compromised cellular health and membrane disintegration caused by nanoparticles. Parallel to this, the cell entrapment, membrane damage, and attachment of nanoparticles on cell surface were also visualized by SEM-EDX (scanning electron microscope-energy dispersive X-ray) microscopy. The overall results of this study clearly indicated that Co₃O₄ nanoparticles might have toxic effects on growth of marine microalgae and other aquatic life forms as well. Hence, release of Co₃O₄ nanoparticles in aquatic ecosystem and resulting ecotoxic effect should be broadly addressed.