The diverse toxic effect of SiO₂ and TiO₂ nanoparticles toward the marine microalgae Dunaliella tertiolecta

Unraveling the toxicity mechanisms of nanoplastics with various surface modifications on Skeletonema costatum: Cellular and molecular perspectives

Nanoplastics are ubiquitous in marine environments, exhibiting high bioavailability and potential toxicity to marine organisms. However, the impacts of nanoplastics with various surface modifications on marine microalgae remain largely unexplored. This study explored the toxicity mechanisms of two nanoplastic types-polystyrene (PS) and polymethyl methacrylate (PMMA)-with distinct surface modifications on Skeletonema costatum at cellular and molecular levels. Results showed that nanoplastics significantly impaired the growth of microalgae, particularly PS-NH2, which caused the most pronounced growth inhibition, reaching 56.99 % after a 96-h exposure at 50 mg/L. Transcriptomic profiling revealed that nanoplastics disrupted the expression of genes predominantly involved in ribosome biogenesis, aminoacyl-tRNA biosynthesis, amino acid metabolism, and carbohydrate metabolism pathways. The integrated biochemical and transcriptomic evidence highlighted that PS-NH2 nanoplastics had the most adverse impact on microalgae, affecting fundamental pathways such as ribosome biogenesis, energy metabolism, photosynthesis, and oxidative stress. Our findings underscore the influence of surface-modified nanoplastics on algal growth and contribute new understanding to the toxicity mechanisms of these nanoplastics in marine microalgae, offering critical information for assessing the risks of emerging pollutants.

Influence of algal-extracellular polymeric substances (EPS) on the pristine and combined toxicity of TiO2 NPs and PSNPs in Artemia salina: Eco-corona enhances the toxic effects

The study on the influence of Natural Organic Matter (NOM) over the individual and combined effects of different nanomaterials on marine species is pertinent. The current study explores the role of Extracellular Polymeric Substances (EPS) in influencing the individual and combined toxic effects of polystyrene nanoplastics (PSNPs) viz. aminated (NH2-PSNPs), carboxylated (COOH-PSNPs), and plain PSNPs and TiO2 NPs in the marine crustacean, Artemia salina. A. salina was interacted with pristine PSNPs, pristine TiO2 NPs, EPS incubated PSNPs, EPS incubated TiO2 NPs, binary mixture of PSNPs and TiO2 NPs, and EPS adsorbed binary mixture of PSNPs and TiO2 NPs for 48 h. The present study proves that, when compared to the pristine toxicity of PSNPs and TiO2 NPs, the coexposure of TiO2 NPs with PSNPs resulted in increased toxicity. The adsorption of algal EPS on the NMs (both in their pristine and combined forms) significantly increased the toxic nature of the NMs against A. salina. It was observed that with an increase in the hydrodynamic diameter of the particles, the mortality, oxidative stress, and ingestion of the NMs by A. salina increased. The uptake of Ti by A. salina from 8 mg/L TiO2 NPs, EPS adsorbed 8 mg/L TiO2 NPs, 8 mg/L TiO2 NPs + NH2-PSNPs and the EPS adsorbed mixture of 8 mg/L TiO2 NPs, 8 mg/L TiO2 NPs + NH2-PSNPs was observed to be 0.043, 0.047, 0.186, and 0.307 mg/g of A. salina. The adsorption of algal EPS on the NMs (both in their pristine and combined forms) significantly increased the toxic nature of the NMs against A. salina. The major outcomes from the current study highlight the role of EPS in exacerbating the toxicity of NMs in marine crustaceans.

Humic acid-mediated reduction in toxicity of Co3O4 NPs towards freshwater and marine microalgae in surfactant mixed medium

The ever-increasing applications of Co3O4 nanoparticles (NPs) have posed a serious concern about their discharge in the aquatic environment and ecotoxic implications. Being toxic towards aquatic species, the impact of other aquatic components such as dissolved organic matter (DOM), salinity, and surfactants are not studied sufficiently for their effect on the stability and ecotoxicity of Co3O4 NPs. The present study aims at the influence of humic acid (HA) on the toxicity of Co3O4 NPs in freshwater (C. minutissima) and marine (T. suecica) microalgae under surfactants mixed medium. The measure of % reduction in biomass and photosynthetic pigment were used as toxicity endpoints. Among various tested concentrations of HA, 25 mg/L HA was found suitable to minimize the NP's toxicity with or without the presence of surfactants. Co3O4 NPs mediated reduction in biomass of C. minutissima was significantly minimized by the cumulative effect of HA with T80 (51.68 ± 4.55%) followed by CTAB (46.23 ± 5.62%) and SDS (42.60 ± 2.46%). Similarly, HA with T80 (26.93 ± 6.38%) followed by SDS (17.02 ± 6.64%) and CTAB (13.01 ± 3.81%) were found to minimize the growth inhibitory effect of Co3O4 NPs in T. suecica. The estimation of chlorophyll - a content also indicated that microalgae treated with HA could maintain their photosynthetic ability more than control even in the co-presence of surfactants. Also, the reduced toxicity of Co3O4 NPs were attributed to an increase in hydrodynamic sizes of HA-treated Co3O4 NPs in both marine media (f/2) and freshwater media (BG11) due to increased aggregation and faster sedimentation of Co3O4 NPs.

Differential toxicity of various mineral nanoparticles to Synechocystis sp.: With and without ciprofloxacin

Mineral nanoparticles (M-NPs) are ubiquitous in aquatic environments, but their potential harms to primary producers and impacts on the toxicity of coexisting pollutants are largely unknown. Herein, the toxicity mechanisms of various M-NPs (i.e., SiO2, Fe2O3, Al2O3, and TiO2 NPs) to Synechocystis sp. in absence and presence of ciprofloxacin (CIP) were comprehensively investigated. The heteroaggregation of cells and M-NPs can hinder substrate transfer or light acquisition. The attraction between Synechocystis sp. and M-NPs increased in the order of SiO2 < Fe2O3 < Al2O3 ≈ TiO2 NPs. Therefore, SiO2 and Fe2O3 NPs exerted slight effects on physiology and proteome of Synechocystis sp.. Al2O3 NPs with the rod-like shape caused physical damage to cells. Differently, TiO2 NPs with photocatalytic activities provided photogenerated electrons for Synechocystis sp., promoting photosynthesis and the Calvin cycle for CO2 fixation. SiO2, Fe2O3, and Al2O3 NPs alleviated the toxicity of CIP in an adsorption-depended manner. Conversely, the combination of CIP and TiO2 NPs exerted more pronounced toxic effects compared to their individuals, and CIP disturbed the extracellular electron transfer from TiO2 NPs to cells. The findings highlight the different effects of TiO2 NPs from other M-NPs on cyanobacteria, either alone or in combination with CIP, and improve the understanding of toxic mechanisms of M-NPs.

Nanopesticide risk assessment based on microbiome profiling - Community structure and functional potential as biomarkers in captan@ZnO35-45 nm and captan@SiO220-30 nm treated orchard soil

Nanoformulation should minimise the usage of pesticides and limit their environmental footprint. The risk assessment of two nanopesticides with fungicide captan as an active organic substance and ZnO35-45 nm or SiO220-30 nm as nanocarriers was evaluated using the non-target soil microorganisms as biomarkers. The first time for that kind of nanopesticides next-generation sequencing (NGS) of bacterial 16 S rRNA and fungal ITS region and metagenomics functional predictions (PICRUST2) was made to study structural and functional biodiversity. During a 100-day microcosm study in soil with pesticide application history, the effect of nanopesticides was compared to pure captan and both nanocarriers. Nanoagrochemicals affected microbial composition, especially Acidobacteria-6 class, and alpha diversity, but the observed effect was generally more substantial for pure captan. As for beta diversity, the negative impact was detected only in response to captan and still observed on day 100. Fungal community in the orchard soil showed only a decrease in phylogenetic diversity in captan set-up since day 30. PICRUST2 analysis confirmed several times lower impact of nanopesticides considering the abundance of functional pathways and genes encoding enzymes. Furthermore, the overall data indicated that using SiO220-30 nm as a nanocarrier speeds up a recovery process compared to ZnO35-45 nm.

Silica nanoparticles mediated insect pest management

Silicon is known for mitigating the biotic and abiotic stresses of crop plants. Many studies have proved beneficial effects of bulk silicon against biotic stresses in general and insect pests in particular. However, the beneficial effects of silica nanoparticles in crop plants against insect pests were barely studied and reported. By virtue of its physical and chemical nature, silica nanoparticles offer various advantages over bulk silicon sources for its applications in the field of insect pest management. Silica nanoparticles can act as insecticide for killing target insect pest or it can act as a carrier of insecticide molecule for its sustained release. Silica nanoparticles can improve plant resistance to insect pests and also aid in attracting natural enemies via enhanced volatile compounds emission. Silica nanoparticles are safe to use and eco-friendly in nature in comparison to synthetic pesticides. This review provides insights into the applications of silica nanoparticles in insect pest management along with discussion on its synthesis, side effects and future course of action.

Bioaccumulation of titanium dioxide nanoparticles in green (Ulva sp.) and red (Palmaria palmata) seaweed

A bioaccumulation study in red (Palmaria palmata) and green (Ulva sp.) seaweed has been carried out after exposure to different concentrations of citrate-coated titanium dioxide nanoparticles (5 and 25 nm) for 28 days. The concentration of total titanium and the number and size of accumulated nanoparticles in the seaweeds has been determined throughout the study by inductively coupled plasma mass spectrometry (ICP-MS) and single particle-ICP-MS (SP-ICP-MS), respectively. Ammonia was used as a reaction gas to minimize the effect of the interferences in the 48Ti determination by ICP-MS. Titanium concentrations measured in Ulva sp. were higher than those found in Palmaria palmata for the same exposure conditions. The maximum concentration of titanium (61.96 ± 15.49 μg g-1) was found in Ulva sp. after 28 days of exposure to 1.0 mg L-1 of 5 nm TiO2NPs. The concentration and sizes of TiO2NPs determined by SP-ICP-MS in alkaline seaweed extracts were similar for both seaweeds exposed to 5 and 25 nm TiO2NPs, which indicates that probably the element is accumulated in Ulva sp. mainly as ionic titanium or nanoparticles smaller than the limit of detection in size (27 nm). The implementation of TiO2NPs in Ulva sp. was confirmed by electron microscopy (TEM/STEM) in combination with energy dispersive X-Ray analysis (EDX).

Characterization and Behaviour of Silica Engineered Nanocontainers in Low and High Ionic Strength Media

Mesoporous silica engineered nanomaterials are of interest to the industry due to their drug-carrier ability. Advances in coating technology include using mesoporous silica nanocontainers (SiNC) loaded with organic molecules as additives in protective coatings. The SiNC loaded with the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT), i.e., SiNC-DCOIT, is proposed as an additive for antifouling marine paints. As the instability of nanomaterials in ionic-rich media has been reported and related to shifting key properties and its environmental fate, this study aims at understanding the behaviour of SiNC and SiNC-DCOIT in aqueous media with distinct ionic strengths. Both nanomaterials were dispersed in (i) low- (ultrapure water-UP) and (ii) high- ionic strength media-artificial seawater (ASW) and f/2 medium enriched in ASW (f/2 medium). The morphology, size and zeta potential (ζP) of both engineering nanomaterials were evaluated at different timepoints and concentrations. Results showed that both nanomaterials were unstable in aqueous suspensions, with the initial ζP values in UP below -30 mV and the particle size varying from 148 to 235 nm and 153 to 173 nm for SiNC and SiNC-DCOIT, respectively. In UP, aggregation occurs over time, regardless of the concentration. Additionally, the formation of larger complexes was associated with modifications in the ζP values towards the threshold of stable nanoparticles. In ASW, SiNC and SiNC-DCOIT formed aggregates (<300 nm) independently of the time or concentration, while larger and heterogeneous nanostructures (>300 nm) were detected in the f/2 medium. The pattern of aggregation detected may increase engineering nanomaterial sedimentation rates and enhance the risks towards dwelling organisms.

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.

Nanomaterial Ecotoxicology in the Terrestrial and Aquatic Environment: A Systematic Review

This systematic review analyzes the studies available on the ecotoxicity of nanomaterials (NMs) in the environment to understand where future research should be addressed for achieving Agenda 2030 goals on sustainable development and environmental safety. We discuss the status of NMs ecotoxicological effects across different organisms that are representative of all natural environments (land, air, water). A total of 1562 publications were retrieved from the Web of Science (all databases) by using the search criteria "nanomaterials" and "ecotoxicology"; among them, 303 studies were included in the systematic review because they met any of the following criteria: (i) focalize on both search criteria; (ii) deal with terrestrial, or aquatic environment; (iii) address models (organisms, cells) for the nano environmental risk assessment and exposure. The knowledge gaps are identified together with novel insights that need to be further investigated to better understand the ecotoxicological environmental impacts of NMs.

Role of Silica Nanoparticles in Abiotic and Biotic Stress Tolerance in Plants: A Review

The demand for agricultural crops continues to escalate with the rapid growth of the population. However, extreme climates, pests and diseases, and environmental pollution pose a huge threat to agricultural food production. Silica nanoparticles (SNPs) are beneficial for plant growth and production and can be used as nanopesticides, nanoherbicides, and nanofertilizers in agriculture. This article provides a review of the absorption and transportation of SNPs in plants, as well as their role and mechanisms in promoting plant growth and enhancing plant resistance against biotic and abiotic stresses. In general, SNPs induce plant resistance against stress factors by strengthening the physical barrier, improving plant photosynthesis, activating defensive enzyme activity, increasing anti-stress compounds, and activating the expression of defense-related genes. The effect of SNPs on plants stress is related to the physical and chemical properties (e.g., particle size and surface charge) of SNPs, soil, and stress type. Future research needs to focus on the “SNPs–plant–soil–microorganism” system by using omics and the in-depth study of the molecular mechanisms of SNPs-mediated plant resistance.

Aquatic ecotoxicity of manufactured silica nanoparticles: A systematic review and meta-analysis

Manufactured silica nanoparticles are used worldwide in large volumes for a variety of applications. An exposure of environmental organisms is therefore likely, and several data on the ecotoxicology of silica nanoparticles to different organisms have been published in recent years. This systematic review compiles and assesses these studies, in order to analyse the sensitivity distribution across different organisms. On this basis, maximum acceptable environmental concentrations are suggested and potential environmental risks are discussed. 1429 papers were retrieved from the scientific literature (Scopus), the U.S. ECOTOX knowledge database. 63 studies were finally included in the review and appraised according to the nanoCRED criteria. A total of 219 ecotoxicological endpoints recorded in 38 species (7 taxonomic groups) were condensed into a species sensitivity distribution. The resulting concentration that is hazardous for a maximum of 5% of exposed species (HC05) is 130 μg/L, from which a PNEC of 30 μg/L is estimated by applying an assessment factor of 5. These concentrations are 1-3 orders of magnitudes above the concentrations modelled to occur in European aquatic ecosystems. Algae and bacteria have a comparatively low sensitivity to MSNP exposure, likely because their cell wall forms a protective barrier against nanoparticle exposure. Similarly, embryonic stages of fish also show a comparatively low sensitivity due to the protection from their chorion. However, the fish species Labeo rohita and Oncorhynchus mykiss are among the most sensitive species. The ecotoxicity of silica nanoparticles is linked to the number of hydroxyl groups on their surface, corresponding to findings from human toxicological studies. It is recommended that future ecotoxicological studies use explicit concentration-response designs, use proven biocide-free testing material, comparatively apply mass and surface area as exposure metrics, and provide important metainformation in the study report.

Effects of nanostructure antifouling biocides towards a coral species in the context of global changes

Biofouling prevention is one of the biggest challenges faced by the maritime industry, but antifouling agents commonly impact marine ecosystems. Advances in antifouling technology include the use of nanomaterials. Herein we test an antifouling nano-additive based on the encapsulation of the biocide 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT) in engineered silica nanocontainers (SiNC). The work aims to assess the biochemical and physiological effects on the symbiotic coral Sarcophyton cf. glaucum caused by (1) thermal stress and (2) DCOIT exposure (free or nanoencapsulated forms), in a climate change scenario. Accordingly, the following hypotheses were addressed: (H1) ocean warming can cause toxicity on S. cf. glaucum; (H2) the nanoencapsulation process decreases DCOIT toxicity towards this species; (H3) the biocide toxicity, free or encapsulated forms, can be affected by ocean warming. Coral fragments were exposed for seven days to DCOIT in both free and encapsulated forms, SiNC and negative controls, under two water temperature regimes (26 °C and 30.5 °C). Coral polyp behavior and photosynthetic efficiency were determined in the holobiont, while biochemical markers were assessed individually in the endosymbiont and coral host. Results showed transient coral polyp retraction and diminished photosynthetic efficiency in the presence of heat stress or free DCOIT, with effects being magnified in the presence of both stressors. The activity of catalase and glutathione-S-transferase were modulated by temperature in each partner of the symbiosis. The shifts in enzymatic activity were more pronounced in the presence of free DCOIT, but to a lower extent for encapsulated DCOIT. Increased levels of oxidative damage were detected under heat conditions. The findings highlight the physiological constrains elicited by the increase of seawater temperature to symbiotic corals and demonstrate that DCOIT toxicity can be minimized through encapsulation in SiNC. The presence of both stressors magnifies toxicity and confirm that ocean warming enhances the vulnerability of tropical photosynthetic corals to local stressors.

A Weight of Evidence approach to classify nanomaterials according to the EU Classification, Labelling and Packaging Regulation criteria

In the context of the European Union (EU) Horizon 2020 GRACIOUS project (Grouping, Read-Across, Characterisation and classification framework for regulatory risk assessment of manufactured nanomaterials and Safer design of nano-enabled products), we proposed a quantitative Weight of Evidence (WoE) approach for hazard classification of nanomaterials (NMs). This approach is based on the requirements of the European Regulation on Classification, Labelling and Packaging of Substances and Mixtures (the CLP regulation), which implements the United Nations' Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS) in the European Union. The goal of this WoE methodology is to facilitate classification of NMs according to CLP criteria, following the decision trees defined in ECHA's CLP regulatory guidance. In the WoE, results from heterogeneous studies are weighted according to data quality and completeness criteria, integrated, and then evaluated by expert judgment to obtain a hazard classification, resulting in a coherent and justifiable methodology. Moreover, the probabilistic nature of the proposed approach enables highlighting the uncertainty in the analysis. The proposed methodology involves the following stages: (1) collection of data for different NMs related to the endpoint of interest: each study related to each NM is referred as a Line of Evidence (LoE); (2) computation of weighted scores for each LoE: each LoE is weighted by a score calculated based on data quality and completeness criteria defined in the GRACIOUS project; (3) comparison and integration of the weighed LoEs for each NM: A Monte Carlo resampling approach is adopted to quantitatively and probabilistically integrate the weighted evidence; and (4) assignment of each NM to a hazard class: according to the results, each NM is assigned to one of the classes defined by the CLP regulation. Furthermore, to facilitate the integration and the classification of the weighted LoEs, an online R tool was developed. Finally, the approach was tested against an endpoint relevant to CLP (Aquatic Toxicity) using data retrieved from the eNanoMapper database, results obtained were consistent to results in REACH registration dossiers and in recent literature.

Ecotoxicity of silica nanoparticles in aquatic organisms: An updated review

This review aims to (i) provide a current overview of the main characteristics of SiNP (physical and chemical properties, applications, and emissions), (ii) evaluate the scientific production up to date concerning SiNP, with focus on their toxic effects, through a bibliometric analysis, (iii) describe the main toxic mechanisms of SiNP, (iv) assess the current knowledge about ecotoxicity of SiNP on aquatic organisms (marine and freshwater), and (v) identify the main gaps in the knowledge of SiNP toxicity from an environmentally point of view. The scientific production of SiNP concerning their chemical and physical characteristics has increased exponentially. However, little information is available regarding their ecotoxicity. Particle functionalization is a key factor that reduces SiNP toxicity. Most of the studies employed standard species as test organisms, being the local/native ones poorly represented. Further studies employing long-term exposures and environmentally relevant concentrations are needed to deepen the knowledge about this emergent pollutant.

Effects of undissociated SiO2 and TiO2 nano-particles on molting of Daphnia pulex: Comparing with dissociated ZnO nano particles

The toxic effects of different nanoparticles (NPs) have been reported to be quite different. The present study exposed Daphnia pulex to undissociated TiO₂ NPs and SiO₂ NPs, and dissociated ZnO NPs. The acute toxicity of the three oxide NPs and their influence on D. pulex molting, as well as the expressions of genes related to molting, energy metabolism and genetic material expression were compared. The results showed that the toxicities of TiO₂ NPs and SiO₂ NPs to D. pulex were weaker than ZnO NPs. During the exposure period, agglomerates of undissociated TiO₂ NPs and SiO₂ NPs influenced movements of D. pulex, and induced their molting after attaching to the body surface. Meanwhile, gene expressions of molting (eip) and energy metabolism (scot and idh) were up-regulated. Therefore, we inferred that the adhering to the surface of daphnids, promoting their molting and improving their energy metabolism may be parts of the toxicity mechanisms of undissociated NPs to D. pulex. On the contrary, dissociated ZnO NPs inhibited molting and gene expressions of eip, scot and idh, which showed a similar trend as bulk ZnO and ZnSO₄·7H₂O under the low-dose exposure condition. This indicates that the toxic effects of dissociated ZnO NPs were primarily caused by released Zn ions. The results provided direct evidence about the effect of nanoparticles on molting and revealed that the toxicity mechanisms of dissociated NPs were different from undissociated NPs.

Toxicity evaluation of nano-TiO2 in the presence of functionalized microplastics at two trophic levels: Algae and crustaceans

The rising use of contaminants such as nanoparticles and microplastics has taken a heavy toll on the marine environment. However, their combined toxic effects on the species across various trophic levels remain quite unexplored. The aim of this study was to explore the effects of three surface-functionalized (carboxylated, plain, and aminated) polystyrene microplastics on nano-TiO₂ toxicity across two trophic levels containing Chlorella sp. as the prey and Artemia salina as the predator. The experiments carried out on Chlorella sp. include the toxicity assessment, oxidative stress determination, and uptake of nano-TiO₂ (both in the presence and absence of microplastics). Results revealed that the aminated and plain polystyrene microplastics enhanced nano-TiO₂ toxicity, while carboxylated microplastics decreased the toxic effects in Chlorella sp. On the other hand, toxicity assessment in Artemia salina was carried out using two different modes of exposure: aqueous and dietary routes. The aqueous route involving the direct exposure of nano-TiO₂ and microplastics indicated greater toxicity, uptake, and accumulation in Artemia salina than the dietary route of exposure. Since dietary exposure decreased the toxicity, uptake, and accumulation of nano-TiO₂, no change (p > 0.05) in the biomagnification factors of nano-TiO₂ was noted for all the test concentrations of nano-TiO₂ combined with and without microplastics. The computed values were less than 1, indicating negligible transfer of nano-TiO₂ from Chlorella sp. to Artemia salina. Overall, the study highlights the two-level trophic toxicity and the transfer potential of nano-TiO₂ under the influence of different microplastics.

Are biosynthesized nanomaterials toxic for the environment? Effects of perlite and CuO/perlite nanoparticles on unicellular algae Haematococcus pluvialis

The properties of nanomaterials such as perlite nanoparticles and their increased application have raised concerns about their probable toxic impacts on the aquatic ecosystems and algae. Here, a novel biochemical synthesis and immobilization of CuO is reported on perlite nanoparticles (CuO/Per-NPs) and its toxic effect on alga has been compared with nanoperlites. This biosynthesis of CuO/Per-NPs performed using phytochemicals of Haematococcus pluvialis, Sargassum angustifolium, and walnut leaves in the aqueous extract. The structural, morphological, and colloidal properties of the as-synthesized nanoparticles have been confirmed by various methods. According to the obtained results, the morphology of the synthesized CuO/Per-NPs was spherical with sizes ranging from about 13 to 24 nm. Besides, the effects of Per-NPs and CuO/Per-NPs on unicellular algae H. pluvialis were studied. The changes in the amount of chlorophyll a, chlorophyll b, and Carotenoids in the presence of different concentrations of Per-NPs (25, 50, 100 mg/L) were more than CuO/Per-NPs. Also, decreased growth rate and efficiency of photosystem II confirmed the toxic effects of Per-NPs. However, the toxicity of CuO/Per-NPs appears to be lower than that of Per-NPs, which can be due to the changes in the surface and cationic charge of modified nanoperlit. These changes lead to a decrease in the interaction of nanoparticles with H. pluvilalis and a reduction in ROS production. Finally, the results of GC-MS used to evaluate volatile compounds, indicated an increase in the number of phenolic compounds in comparison to the control samples in 25, 50, and 100 mg/L treatments of nano-perlite.

Environmentally relevant concentrations of titanium dioxide nanoparticles pose negligible risk to marine microbes

Nano-sized titanium dioxide (nTiO₂) represents the highest produced nanomaterial by mass worldwide and, due to its prevalent industrial and commercial use, it inevitably reaches the natural environment. Previous work has revealed a negative impact of nTiO₂ upon marine phytoplankton growth, however, studies are typically carried out at concentrations far exceeding those measured and predicted to occur in the environment currently. Here, a series of experiments were carried out to assess the effects of both research-grade nTiO₂ and nTiO₂ extracted from consumer products upon the marine dominant cyanobacterium, Prochlorococcus, and natural marine communities at environmentally relevant and supra-environmental concentrations (i.e., 1 μg L^-1 to 100 mg L^-1). Cell declines observed in Prochlorococcus cultures were associated with the extensive aggregation behaviour of nTiO₂ in saline media and the subsequent entrapment of microbial cells. Hence, higher concentrations of nTiO₂ particles exerted a stronger decline of cyanobacterial populations. However, within natural oligotrophic seawater, cultures were able to recover over time as the nanoparticles aggregated out of solution after 72 h. Subsequent shotgun proteomic analysis of Prochlorococcus cultures exposed to environmentally relevant concentrations confirmed minimal molecular features of toxicity, suggesting that direct physical effects are responsible for short-term microbial population decline. In an additional experiment, the diversity and structure of natural marine microbial communities showed negligible variations when exposed to environmentally relevant nTiO₂ concentrations (i.e., 25 μg L^-1). As such, the environmental risk of nTiO₂ towards marine microbial species appears low, however the potential for adverse effects in hotspots of contamination exists. In future, research must be extended to consider any effect of other components of nano-enabled product formulations upon nanomaterial fate and impact within the natural environment.

Acute and chronic toxicity of amine-functionalized SiO2 nanostructures toward Daphnia magna

Silicon oxide (SiO₂) nanostructures (SiO₂NS) are increasingly being incorporated into an array of products, notably in the food, pharmaceutical, medical industries and in water treatment systems. Amorphous SiO₂NS have low toxicity, however, due to their great versatility, superficial modifications can be made and these altered structures require toxicological investigation. In this study, SiO₂NS were synthetized and amine-functionalized with the molecules (3-aminopropyl)triethoxysilane (APTMS) and 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEAEAPTMS), named SiO₂NS@1 and SiO₂NS@3, respectively. The bare SiO₂NS, SiO₂NS@1 and SiO₂NS@3 samples were characterized and the influence of the culture medium used in the toxicological assays was also evaluated. The effect of amine functionalization of SiO₂NS was investigated through acute and chronic toxicity assays with Daphnia magna. Modifications to ultrastructures of the intestine and eggs of these organisms were observed in TEM and SEM analysis. The toxicity was influenced by the surface modifications and a possible Trojan horse effect was highlighted, particularly in the case of chronic exposure. Exposure to all NSs promoted alterations in the microvilli and mitochondria of the D. magna intestine and some damage to egg cells was also observed. The results demonstrate the importance of carrying out a full characterization of these materials, since surface modifications can enhance their toxic potential.

The interactive effects of titanium dioxide nanoparticles and light on heterotrophic bacteria and microalgae associated with marine aggregates in nearshore waters

Titanium dioxide nanoparticles (n-TiO₂) are emerging contaminants and the ecological impact of these materials to the nearshore environment is largely unknown. The reactivity of n-TiO₂ increases with light exposure, and the photocatalytic effects have been shown on cultures of bacteria and microalgae in the laboratory. The purpose of this study was to assess the response of natural bacterial and microalgal communities associated with marine aggregates to n-TiO₂ under conditions similar to those found in the photic zone of nearshore waters. Nano and bulk TiO₂ particles were incorporated into marine aggregates over 4 days under two light conditions: 6:18 and 0:24 (hours light:dark). The abundance and metabolic response of heterotrophic bacteria and viability of microalgae associated with aggregates were assessed. Although the proportion of living microalgae was unchanged, the abundance, total metabolic activity and functional diversity of heterotrophic bacteria were significantly altered by irradiated n-TiO₂.

Combined effects of nano-TiO2 and hexavalent chromium towards marine crustacean Artemia salina

There has been a significant increased concern of the impact of the toxicity of multiple contaminants in the marine environment. Thus, this study was aimed at determining whether the interaction between nano-TiO₂ and Cr(VI) would modulate their toxic effects with the marine crustacean, Artemia salina. Nano-TiO₂ agglomerated in artificial sea water (ASW) and readily formed micron-sized particles that settled down in the medium. The addition of Cr(VI) to nano-TiO₂ aggravated their agglomeration through sorption of Cr(VI) onto nano-TiO₂. This was reflected by a decrease in the residual concentration of Cr in the suspension. Acute toxicity tests performed using pristine nano-TiO₂ (0.25, 0.5, 1, 2, and 4 mg/L) and Cr(VI) (0.125, 0.25, 0.5, and 1 mg/L) displayed a concentration dependent rise in the mortality of Artemia salina. To examine the effects of mixtures of nano-TiO₂ and Cr(VI) on Artemia salina, two groups of experiments were designed. The former group studied the toxic effect of nano-TiO₂ (0.5, 1, 2, and 4 mg/L) with a fixed concentration (0.125 mg/L) of Cr(VI). While the latter group studied the toxicity of Cr(VI) (0.25, 0.5, and 1 mg/L) with a fixed concentration (0.25 mg/L) of nano-TiO₂. The toxic effects of nano-TiO₂ was not significantly reduced at a fixed concentration of Cr(VI) but in contrast, a significant reduction in the Cr(VI) toxicity by fixed concentration of nano-TiO₂ was observed. Toxicity data was well supported by an independent action model that proved the mode of action between nano-TiO₂ and Cr(VI) to be antagonistic. Furthermore, ROS generation and measurement of antioxidant enzyme activities were also in line with toxicity results. From this study, the modification of Cr(VI) toxicity at fixed concentration of nano-TiO₂ could have a huge impact on the reduction in Cr(VI) toxicity across trophic levels.

Investigating the potential use of an oleaginous bacterium, Rhodococcus opacus PD630, for nano-TiO2 remediation

The occurrence of titanium dioxide nanoparticles (nTiO₂), in the effluents released from wastewater treatment plants, has raised concerns. The fate of nTiO₂ and their potential impact on organisms from different ecosystems are widely investigated. For the first time, in this work, we report the responses of an oleaginous bacteria Rhodococcus opacus PD630, belonging to an ecologically important genus Rhodococcus to environmentally relevant concentrations of nTiO_2, under dark and UV light conditions. We observed a dose-dependent increase in nTiO₂ uptake by the bacteria that reached a maximum of 1.4 mg nTiO₂ (g cell)^-1 under mid-log UV exposure, corresponding to 97% uptake. The nTiO₂ induced oxidative stress in bacteria that increased from 25.1 to a maximum of 100.3, 44.1, and 51.7 μmol ^.OH (g cell)^-1 under dark, continuous, and mid-log UV, respectively. However, nTiO₂ did not affect bacterial viability. Further, due to oxidative stress, the triacylglycerol (biodiesel) content from bacteria increased from 30% to a maximum of 54% CDW. Based on our findings, we propose an application of R. opacus PD 630 in nTiO₂ remediation due to their high nTiO₂ uptake and resistance.

Exposure of synthesized Co3O4 nanoparticles to Chlorella minutissima: An ecotoxic evaluation in freshwater microalgae

The current study focuses on the ecotoxicity of cobalt oxide nanoparticles (Co₃O₄ NPs) in the aquatic environment towards freshwater microalgae, Chlorella minutissima. The interaction of Co₃O₄ NPs with microalgae shows the growth suppressing effect. The 72 h EC ₅₀ (effective concentration of a chemical having 50% of its impact) values of Co₃O₄ NPs for C. minutissima was 38.16 ± 1.99 mg/L. The decline in chlorophyll a content and increase in reactive oxygen species (ROS) also indicated the compromised physiological state of microalgae. An increased LDH (lactate dehydrogenase) level in treated samples suggests membrane disintegration by Co₃O₄ NPs. Light microscopy, scanning electron microscopy (SEM) and Energy Dispersive X-Ray-Scanning electron microscopy (EDX-SEM) further confirm cell entrapment and deposition of Co₃O₄ NPs on the cell surface. Cellular internalization of NPs, as shown by Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), also contributes towards the toxicity of NPs. The findings suggest the role of extracellular as well as intracellular nanoparticles (NPs) in exerting a toxic effect on the C. minutissima.

TiO2 nanoparticles and multi-walled carbon nanotubes monitoring and bioremediation potential using ciliates Pseudocohnilembus persalinus

In recent years, the release of nanomaterials pollutants to water bodies, to a great extent, attributed to anthropogenic activities. Their impacts on aquatic organisms as well as nanomaterial monitoring and bioremediation using organism have drawn much attentions. However, studies on relationship of nano-contaminants and aquatic organisms are very scarce. Our results showed that titanium dioxide nanoparticles (TiO₂-NPs) and Multi-walled carbon nanotubes (MWCNTs) caused an obvious cell decreases on the whole, but a significant increase at 48 h TiO₂-NPs exposure, indicating a resistant mechanism in ciliates for nano-toxic. Besides, MWCNTs was more toxic to Pseudocohnilembus persalinus than that of TiO₂-NPs in terms of EC₅₀ value. It is firstly found that P. persalinus ingested and released TiO₂-NPs through cytostome and cytoproct, which might be the reason that TiO₂-NPs less toxic than MWCNTs. The significantly increased superoxide dismutase (SOD) and glutathione S-transferase (GST) enzyme activities and expression levels were evaluated by reactive oxygen species ROS generation, which demonstrated that P. persalinus antioxidant defense enzyme played roles on nano-toxic resistant in ciliates. Moreover, the integrated biomarker response (IBR) was also determined, which demonstrated that MWCNTs had comparatively higher values than those of TiO₂-NPs after higher concentration exposure to ciliates. In addition, it was confirmed by the present work that sod, gst and cat played different roles on immunity, and the sensitivity of cat gene expression to these two nanomaterials exposure was dissimilar. Damages of shrunk as well as losses of cilia on the cell surface caused by TiO₂-NPs and MWCNTs exposure in P. persalinus using SEM revealed possible physical hazards of aggregated nanomaterials. Our findings will be helpful to understand the effect mechanisms of NPs on ciliates, and also demonstrated the possibility of P. persalinus as bio-indicator of nanomaterials in aquatic and potentials on bioremediation.

Effects of suspended micro- and nanoscale particles on zooplankton functional diversity of drainage system reservoirs at an open-pit mine

Water from mining drainage is turbid because of suspensions. We tested the hypothesis that the chemical composition as well as shape and size of particles in suspensions of natural origin affect the density and functional diversity of zooplankton. The suspensions were analyzed with atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and optical microscopy. Elements found in the beidellite clays were also identified in the mineral structure of the particles. As the size of the microparticles decreased, the weight proportions of phosphorus, sulfur, and chlorine increased in the suspensions. These conditions facilitated the biomass growth of large and small microphages and raptorials. As the size of the nanoparticles decreased, the shares of silicon, aluminum, iron, and magnesium increased. These conditions inhibited raptorials the most. Ecosystem functionality was the highest with intermediate suspension parameters, which were at the lower range of the microphase and the upper range of the nanophase. The functional traits of zooplankton demonstrate their potential for use as sensitive indicators of disruptions in aquatic ecosystems that are linked with the presence of suspensions, and they facilitate gaining an understanding of the causes and scales of the impact of suspensions.

Chronic exposure of the freshwater alga Pseudokirchneriella subcapitata to five oxide nanoparticles: Hazard assessment and cytotoxicity mechanisms

The increasing use of nanoparticles (NPs) unavoidably enhances their unintended introduction into the aquatic systems, raising concerns about their nanosafety. This work aims to assess the toxicity of five oxide NPs (Al₂O₃, Mn₃O₄, In₂O₃, SiO₂ and SnO₂) using the freshwater alga Pseudokirchneriella subcapitata as a primary producer of ecological relevance. These NPs, in OECD medium, were poorly soluble and unstable (displayed low zeta potential values and presented the tendency to agglomerate). Using the algal growth inhibition assay and taking into account the respective 72 h-EC₅₀ values, it was possible to categorize the NPs as: toxic (Al₂O₃ and SnO₂); harmful (Mn₃O₄ and SiO₂) and non-toxic/non-classified (In₂O₃). The toxic effects were mainly due to the NPs, except for SnO₂ which toxicity can mainly be attributed to the Sn ions leached from the NPs. A mechanistic study was undertaken using different physiological endpoints (cell membrane integrity, metabolic activity, photosynthetic efficiency and intracellular ROS accumulation). It was observed that Al₂O_3, Mn₃O₄ and SiO₂ induced an algistatic effect (growth inhibition without loss of membrane integrity) most likely as a consequence of the cumulative effect of adverse outcomes: i) reduction of the photosynthetic efficiency of the photosystem II (Ф_PSII); ii) intracellular ROS accumulation and iii) loss of metabolic activity. SnO₂ NPs also provoked an algistatic effect probably as a consequence of the reduction of Ф_PSII since no modification of intracellular ROS levels and metabolic activity were observed. Altogether, the results here presented allowed to categorize the toxicity of the five NPs and shed light on the mechanisms behind NPs toxicity in the green alga P. subcapitata.

Differential sensitivity of marine algae Dunaliella salina and Chlorella sp. to P25 TiO2 NPs

The use of P25 TiO₂ NPs in consumer products, their release, and environmental accumulation will have harmful effects on the coastal ecosystems. The sensitivity to TiO₂ NPs may vary depending on the structural property and physiological mechanism of algal species. Therefore, the present study investigates the differences in sensitivity of two marine algae, Dunaliella salina and Chlorella sp., towards P25 TiO₂ NPs. Among the two species, Chlorella sp. was more sensitive to TiO₂ NPs than Dunaliella salina. The different working concentrations of TiO₂ NPs, 0.1, 1, and 10 mg L^-1, were selected based on the EC₅₀ value. The EC₅₀ value of TiO₂ NPs for Dunaliella salina was found to be 1.8 and 13.3 mg L^-1 under UV-A and dark conditions, respectively. The EC₅₀ value of TiO₂ NPs for Chlorella sp. was found to be 1.6 and 5.0 mg L^-1 under UV-A and dark conditions, respectively. The decrease in cell viability was significantly higher for Chlorella sp. compared to Dunaliella salina at all concentrations except 0.1 mg L^-1. The cellular viability data was in correlation with the oxidative stress markers such as total ROS and LPO. A concentration-dependent increase in ROS and lipid peroxidation was noted under UV-A exposure, which was higher in Chlorella sp. compared to Dunaliella salina. The decrease in the SOD activity with NP concentration was more in Dunaliella salina than Chlorella sp. under both conditions, whereas Chlorella sp. showed increased CAT activity with increasing concentration. The uptake of TiO₂ NPs was more in Chlorella sp. than Dunaliella salina.

Physicochemical and structural features of heat treated silver-silica nanocomposite and their impact on biological properties

In the last few decades, many nanostructures with varying properties and possible applications have been developed. These materials have been intended to work in various environmental temperature conditions. In this context, the main challenge has been to comprehend the impact of synergic interaction between individual elements included in non-annealed materials in relation to systems subjected to temperature impact. Another problem has corresponded to the impact of thermal modification on organisms such as bacteria and human cells. Such problems can be solved by the fabrication of a nanocomposite with mono-dispersed 8 nm silver (Ag⁰ or Ag⁺) embedded into a silica carrier, followed by the analysis of the impact of heat treatment under various temperature conditions on its physicochemical features. Therefore, methodical studies reported in this text have shown an increase of silver particle size up to 170 nm, a decrease of its concentration, as well as the formation of sub-nanometer Ag⁺ and/or Ag²⁺ clusters as the temperature rises to 1173 K. In turn, the structurally disordered silica carrier had been entirely transformed to cristobalite and tridymite only at 1473 K as well as partial reduction of Ag²⁺ to Ag⁺. Simultaneously, inhibition of growth of Gram-positive and Gram-negative bacteria, as well as an increase in cytotoxicity towards human cells was observed as the temperature rose. As a final point, for the first time, a "pseudo" phase diagram of the structural alterations in the Ag/SiO₂ nanocomposite has been created, as well as a model of silver-silica transformation to biological systems has been developed.

The efficiency and economic aspects of phytoremediation technology using Phalaris arundinacea L. and Brassica napus L. combined with compost and nano SiO2 fertilization for the removal of PAH's from soil

The paper presents an evaluation of efficiency and economic potential of the phytoremediation technology, based on the use of energy crops (P. arundinacea L. and B. Napus L.), combined with the fertilization with compost, supported by the addition of nano SiO₂. The experiment was conducted in in-situ conditions, using two experimental blocks, divided according to used plant species. Each block included four types of plots with different fertilization treatments (control plots; treatment with nano SiO₂; treatment with compost; treatment with mixture of compost and nano SiO₂). During the studied period (three vegetation seasons), a cyclic analysis of 16 PAH's content were conducted. Furthermore, a quantitative determination of biomass production was performed as well as assessment of economic potential of different strategies. Data collected during research, shows that method based on energy crops use, due to the join effect of the dangerous pollutants removal and the production of removable energy resource, can be considered as sustainable and should be recommended for use during heavy polluted soil remediation. Moreover, it should be also noted, that the best results for both PAH's removal efficiency and biomass production, were acquired on plots with P. arundinacea L. cultivation, fertilized with mix of compost and nano SiO₂.

Influence of differently functionalized polystyrene microplastics on the toxic effects of P25 TiO2 NPs towards marine algae Chlorella sp

Increased utilization of titanium dioxide nanoparticles (TiO₂ NPs) for commercial as well as industrial purposes resulted in the accumulation of nanoparticles in the marine system. Microplastics being an emerging secondary pollutant in the marine ecosystem have an impact on the toxic effects of TiO₂ NPs which has not been evaluated up to date. So it is important to assess the toxic effects of both these pollutants on the marine environment. The present study examines the impact of differently functionalized microplastics on the toxic effects of P25 TiO₂ NPs to marine algae Chlorella sp. The tendency of nanoparticles to undergo aggregation in artificial seawater was observed with increase in time. The median effective concentration for TiO₂ NPs was found to be 81 μM which indicates higher toxic effects of NPs toward algae. In contrast, microplastics irrespective of their difference in functionalization had minimal toxic effect of about 15% at their higher concentration tested, 1000 mg L^-1. Plain and aminated polystyrene microplastics enhanced the TiO₂ NPs toxicity which was further validated with oxidative stress determination studies like reactive oxygen species and lipid peroxidation assays. Negatively charged carboxylated polystyrene microplastics decreased the TiO₂ NPs toxicity with possible hetero-aggregation between TiO₂ NPs and microplastics in the system. The toxicity data obtained for the mixture was further corroborated with Abbott's mathematical model.

Nano-fumed silica as a novel pollutant that inhibits the algicidal effect of p-hydroxybenzoic acid on Microcystis aeruginosa

Nanomaterials and/or contaminants are becoming more common in the developing world, but their effects on interspecific interactions are rarely reported, particularly in aquatic ecosystems. Thus, the present study determined the effects of the novel pollutant nano-fumed silica (NFS) on algal control by a macrophyte via the allelochemical p-hydroxybenzoic acid in a microcosm test. The allelochemical p-hydroxybenzoic acid caused significant decreases in chlorophyll a, but increased the amount of superoxide anion radicals ( O2∙- ) and the electric conductivity in Microcystis aeruginosa. The 50% inhibitory concentration (IC₅₀) for p-hydroxybenzoic acid was 0.919 mmol/L in microalga during the exponential phase. Interestingly, NFS at 100-1600 mg/L had clear stimulatory effects on M. aeruginosa. When NFS at 800 mg/L was combined with different concentrations of p-hydroxybenzoic acid, the IC₅₀ for p-hydroxybenzoic acid was 1.045 mmol/L. Thus, NFS significantly reduced the algicidal effect exhibited by p-hydroxybenzoic acid on M. aeruginosa. Furthermore, NFS might act as a silicon nutrient and enhance allelopathic resistance in M. aeruginosa to inhibit the algicidal effects of macrophytes via allelopathy. These findings suggest that before algal control is considered using macrophyte allelopathy, it is essential to remove the pollutant NFS from polluted lakes.

The impact of morphology and size of zinc oxide nanoparticles on its toxicity to the freshwater microalga, Raphidocelis subcapitata

Microalgae are key test organisms to assess the effects of chemicals on aquatic ecosystems. Zinc oxide nanoparticles (ZnO NPs) as a widely used metal oxide is considered a potential threat to these primary producers at the base of the food chain. This study investigates the toxicity of ZnO NPs, bulk ZnO, and Zn²⁺ to the representative of freshwater microalgae, Raphidocelis subcapitata. To examine the effect of shape and size of nanoparticles, two types of spherical ZnO NPs with different sizes (20 and 40 nm) and two types of rod-shaped ZnO NPs with different lengths (100 and 500 nm) were synthesized. Microalgal cells were exposed to eight concentrations of each ZnO NP type from 0.01 to 0.7 mg/L for 96 h. The results showed that 0.7 mg/L of ZnO NP could completely inhibit algal growth. Size did not interfere with toxicity in spherical ZnO NPs, but the toxicity decreased by increasing the size of rod-shaped ZnO NPs. Spherical ZnO NPs acted more destructive to microalgal cells than nanorod shape. The addition of 0.7 mg/L of ZnO nanorods to samples caused 30% cell death, while 50% cell death was observed by adding the same concentration of nanospherical ZnO. Nano ZnO revealed to be more toxic than bulk ZnO and Zn²⁺. The Zn²⁺ released from dissolution of ZnO NPs was one of the sources of toxicity, but the ZnO nanostructures were also an important factor in the toxicity.

What kind of effects do Fe2O3 and Al2O3 nanoparticles have on anaerobic digestion, inhibition or enhancement?

Fe₂O₃ and Al₂O₃ nanoparticles are widely used in products and find their way to wastewater treatment plants through the contact of water with these products. In this study, impacts of Fe₂O₃ and Al₂O₃ nanoparticles on methane potential of waste activated sludge (WAS) were investigated by comparing long and short term toxicity test results, modelling and FISH analysis. Methane production from the samples treated with the maximum concentration of Fe₂O₃ nanoparticles decreased 28.9% at the end of the long term BMP test. EC₅₀ value for BMP test of the Fe₂O₃ nanoparticles was calculated as 901.94 mg/gTS with high coefficient of determination. Methane production from the samples treated with Al₂O₃ nanoparticles increased up to 14.8% (p > 0.05) at the end of the BMP test. However, short term toxicity tests for Fe₂O₃ and Al₂O₃ nanoparticles showed no impact on anaerobic digestion of WAS. Kinetic parameters obtained from models and captured FISH images were consistent with these results. Different impacts of nanoparticles on methane production suggested that anaerobic microorganisms can be affected from nanoparticles in various mechanisms. Hydrolysis (k_H) and overall reaction rates (k_R) values were determined as 0.0277 and 0.1441 d^-1, respectively for each concentration of Al₂O₃ nanoparticles and raw WAS. Similarly, methane production from WAS containing 5, 50, 150 and 250 mgFe₂O₃/gTS were modeled with same kinetic values. However, k_H constant was calculated as 0.0149 d^-1 for 500 mgFe₂O₃/gTS. This means that Fe₂O₃ nanoparticles starting from this concentration inhibited the methanogenic consortium and caused decreased biogas production and spesific methane production rate.

Influence of titanium dioxide nanoparticles on the toxicity of arsenate in Nannochloropsis maritima

Interest is growing in the role that nanoparticles play in modifying the biological effects of contaminants. This study aimed to determine whether nano-TiO₂ exhibited pronounced influence on arsenate (As(V)) toxicity levels to the marine microalgae Nannochloropsis maritima. We compared individual and combined toxicity levels of As(V) and nano-TiO₂ by assessing the inhibition percentages of algal growth. Compared to groups treated with As(V) alone, an EC₅₀ of 53.0 mg/L decreased by 28.8% after the addition of nanoparticles. This enhanced toxicity was attributed to the inhibition of As methylation and the promotion of lipid peroxidation in the presence of nano-TiO₂. Additionally, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) also showed that algal cells exhibited different degrees of shrinkage, that cell wall were destroyed in the process, and that the photosynthetic apparatus was virtually indiscernible after the addition of nano-TiO₂. In addition, for low As(V) concentration exposure groups, nano-TiO₂ could alleviate As(V) toxicity to some extent by reducing As sorption onto algal cells and subcellular distribution in organelles, but this alleviation effect could not protect against the combined toxicity (both As(V) and nano-TiO₂) effect on N. maritima, which was verified by the higher inhibition percentage of the algal growth rate in the combined exposure group treatment compared to the As(V) exposure treatment alone. Our results suggest that more attention must be paid to the potential impact of nanoparticles on the bioavailability and biotransformation of contaminants in phytoplankton.

Functionalized and grafted TiO2, CeO2, and SiO2 nanoparticles-ecotoxicity on Daphnia magna and relevance of ecofriendly polymeric networks

Effects of functionalization and grafting of TiO₂, CeO₂, and SiO₂ nanoparticles (NPs) were investigated, and toxicity of pristine, functionalized, and grafted NP towards Daphnia magna was measured. Surface functionalization of NP with amine groups decreased hydrophobicity of NP. When NPs were hydrophilic, they were less toxic than hydrophobic NP towards D. magna. Grafting agents influenced toxicity: no toxicity of NP was observed when bio-based and hydrogenated synthetic polymers were used, whereas perfluorinated polymers induced a higher toxicity.

Physiological changes in Chlamydomonas reinhardtii after 1000 generations of selection of cadmium exposure at environmentally relevant concentrations

Cadmium (Cd) is a nonessential and toxic trace element widely existing in waters through various anthropogenic activities such as mining and waste disposal. The physiological responses of aquatic organisms to long-term Cd exposure at environmentally relevant concentrations are still not well explored. In the present study, two strains of unicellular green algae Chlamydomonas reinhardtii, a walled strain CC125 and a wall-less strain CC406 were selected to investigate the physiological changes of aquatic organisms after long-term Cd exposure at environmentally relevant concentrations (4.92 and 49.2 μg L-1). After about 1000 generations of selection, all of the two strains showed higher intracellular lipid peroxidation and lower photosynthetic activities, and failed to evolve specific adaptation to high levels of Cd (4.92 mg L-1) compared to the control. However, short-term low dose Cd exposure exerted hormetic effects on C. reinhardtii and the hormetic stimulation of growth rate, chlorophyll contents and photochemical activities at the lower concentration of Cd (4.92 μg L-1) groups were more pronounced than those at higher ones (49.2 μg L-1). Taken together, this study confirmed that long-term exposure to Cd at environmentally relevant concentrations which were regarded as nontoxic in acute experiments would produce toxic effects on C. reinhardtii and should be paid more attention.

Toxicity of Co nanoparticles on three species of marine microalgae

Cobalt nanoparticles (CoNPs) are being used in wide range of applications and may enter aquatic environments where they pose a potential threat to aquatic organisms. Algal growth inhibition tests were conducted to explore the potential toxicity of CoNPs on marine microalgae, Platymonas subcordiforus, Chaetoceros curvisetus and Skeletonema costatum. This is one of the first time to explore toxicity of CoNPs on marine algae systematically. The results showed that CoNPs induced toxicity on the three algae. The CoNP toxicity on three species microalgae was partly attributed to the Co²⁺ released by CoNPs in the f/2 seawater medium. The particle size distribution of CoNPs in seawater revealed that CoNPs were agglomerated in the seawater. The shading effect of CoNPs and scanning electron microscope (SEM) images also showed the aggregating of CoNPs and microalgae, which influenced the photosynthetic utilization and inhibited the growth of the three algae. The order of toxic sensitivity of CoNPs on the three algae was as follows: Platymonas subcordiforus < Chaetoceros curvisetus < Skeletonema costatum.

TiO2 nanoparticles in seawater: Aggregation and interactions with the green alga Dunaliella tertiolecta

Titanium dioxide nanoparticles (TiO₂ NPs) have been widely employed in industrial applications, thus rising concern about their impact in the aquatic environment. In this study we investigated the chemical behaviour of TiO₂ NPs in the culture medium and its effect on the green alga Dunaliella tertiolecta, in terms of growth inhibition, oxidative stress, ROS (Reactive Oxygen Species) accumulation and chlorophyll content. In addition, the influence of exopolymeric substances (EPS) excreted by the microalgae on the stability of NPs has been evaluated. The physicochemical characterization showed a high propensity of TiO₂ NPs to form micrometric-sized aggregates within 30min, large enough to partially settle to the bottom of the test vessel. Indeed, an increasing amount of TiO₂ particles settled out with time, but the presence of EPS seemed to mitigate this behaviour in the first 6h of exposure where the main effects in D. tertiolecta were observed. TiO₂ NPs did not inhibit the 72-h growth rate of D. tertiolecta, nor affected the cellular chlorophyll concentration in the range 0.01-10mgL^-1. The time-course of ROS production showed an initial transient increase of ROS in TiO₂ NP-exposed algae compared to the control, concomitant with an enhancement of catalase activity. Interestingly, intracellular ROS was a small fraction of total ROS, the highest amount being extracellular. The occurrence of cell-mediated chemical transformations of TiO₂ NPs in the external medium, related to the presence of EPS, has been evaluated. Our results showed that carbohydrates were the major component of EPS, whereas proteins of medium molecular weight (20-80kDa) were preferentially bound to TiO₂ NPs, likely influencing their biological fate.

Effect of Engineered Nanoparticles on Exopolymeric Substances Release from Marine Phytoplankton

Engineered nanoparticles (ENPs), products from modern nanotechnologies, can potentially impact the marine environment to pose serious threats to marine ecosystems. However, the cellular responses of marine phytoplankton to ENPs are still not well established. Here, we investigate four different diatom species (Odontella mobiliensis, Skeletonema grethae, Phaeodactylum tricornutum, Thalassiosira pseudonana) and one green algae (Dunaliella tertiolecta) for their extracellular polymeric substances (EPS) release under model ENP treatments: 25 nm titanium dioxide (TiO₂), 10-20 nm silicon dioxide (SiO₂), and 15-30 nm cerium dioxide (CeO₂). We found SiO₂ ENPs can significantly stimulate EPS release from these algae (200-800%), while TiO₂ ENP exposure induced the lowest release. Furthermore, the increase of intracellular Ca²⁺ concentration can be triggered by ENPs, suggesting that the EPS release process is mediated through Ca²⁺ signal pathways. With better understanding of the cellular mechanism mediated ENP-induced EPS release, potential preventative and safety measures can be developed to mitigate negative impact on the marine ecosystem.

A mechanistic study of TiO2 nanoparticle toxicity on Shewanella oneidensis MR-1 with UV-containing simulated solar irradiation: Bacterial growth, riboflavin secretion, and gene expression

Toxicity of nanomaterials to ecological systems has recently emerged as an important field of research, and thus, many researchers are exploring the mechanisms of how nanoparticles impact organisms. Herein, we probe the mechanisms of bacteria-nanoparticle interaction by investigating how TiO₂ nanoparticles impact a model organism, the metal-reducing bacterium Shewanella oneidensis MR-1. In addition to examining the effect of TiO₂ exposure, the effect of synergistic simulated solar irradiation containing UV was explored in this study, as TiO₂ nanoparticles are known photocatalysts. The data reveal that TiO₂ nanoparticles cause an inhibition of S. oneidensis growth at high dosage without compromising cell viability, yet co-exposure of nanoparticles and illumination does not increase the adverse effects on bacterial growth relative to TiO₂ alone. Measurements of intracellular reactive oxygen species and riboflavin secretion, on the same nanoparticle-exposed bacteria, reveal that TiO₂ nanoparticles have no effect on these cell functions, but application of UV-containing illumination with TiO₂ nanoparticles has an impact on the level of riboflavin outside bacterial cells. Finally, gene expression studies were employed to explore how cells respond to TiO₂ nanoparticles and illumination, and these results were correlated with cell growth and cell function assessment. Together these data suggest a minimal impact of TiO₂ NPs and simulated solar irradiation containing UV on S. oneidensis MR-1, and the minimal impact could be accounted for by the nutrient-rich medium used in this work. These measurements demonstrate a comprehensive scheme combining various analytical tools to enable a mechanistic understanding of nanoparticle-cell interactions and to evaluate the potential adverse effects of nanoparticles beyond viability/growth considerations.

Effects of PVP/PEI coated and uncoated silver NPs and PVP/PEI coating agent on three species of marine microalgae

In the last years, applications for silver nanoparticles (Ag NPs) continue to increase together with the concerns about their potential input and hazards in aquatic ecosystems, where microalgae are key organisms. The aim of the present study was to assess the relative sensitivity of three marine microalgae species with differences in cell wall composition/structure exposed to Poly N-vinyl-2-pirrolidone/Polyethyleneimine (PVP/PEI) coated 5nm Ag NPs and uncoated 47nm Ag NP. As limited attention has been paid to the role of coating agents in NP toxicity, the effect of PVP/PEI alone was also evaluated. After 72h in artificial seawater, 47nm Ag NPs formed around 1400nm size aggregates while PVP/PEI coated 5nm Ag NPs reached around 90nm. Ag⁺ release in seawater was around 3% for 47nm Ag NPs and 30% for PVP/PEI coated 5nm Ag NPs. PVP/PEI coated 5nm Ag NP aggregates entrapped the algal cells in a network of heteroaggregates, while uncoated 47nm Ag NPs interacted to a lesser extent with algae. The concentration of PVP/PEI coated 5nm Ag NPs that exerted the median effect (EC50) on algae growth pointed out differences in algae sensitivity: T. suecica was about 10 times more sensitive than I. galbana and P. tricornutum. Further, the coating agent alone was as toxic to algae as PVP/PEI coated 5nm Ag NPs, suggesting that presence of the coating agent was the main driver of toxicity of coated NPs. Uncoated 47nm Ag NPs instead, showed similar toxicity towards algae although P. tricornutum was slightly less sensitive than T. suecica and I. galbana, which agrees with the presence of a resistant silicified cell wall in the diatom. The present work demonstrates differences in sensitivity of three marine microalgae, possibly related to their cell surface and size characteristics.

Effects of titanium dioxide nanoparticles derived from consumer products on the marine diatom Thalassiosira pseudonana

Increased manufacture of TiO₂ nanoproducts has caused concern about the potential toxicity of these products to the environment and in public health. Identification and confirmation of the presence of TiO₂ nanoparticles derived from consumer products as opposed to industrial TiO₂ NPs warrant examination in exploring the significance of their release and resultant impacts on the environment. To this end, we examined the significance of the release of these particles and their toxic effect on the marine diatom algae Thalassiosira pseudonana. Our results indicate that nano-TiO₂ sunscreen and toothpaste exhibit more toxicity in comparison to industrial TiO₂ and inhibited the growth of the marine diatom T. pseudonana. This inhibition was proportional to the exposure time and concentrations of nano-TiO₂. Our findings indicate a significant effect, and therefore, further research is warranted in evaluation and assessment of the toxicity of modified nano-TiO₂ derived from consumer products and their physicochemical properties.

Genotoxic and cytotoxic effects of ZnO nanoparticles for Dunaliella tertiolecta and comparison with SiO2 and TiO2 effects at population growth inhibition levels

The increasing use of oxide nanoparticles (NPs) in commercial products has intensified the potential release into the aquatic environment where algae represent the basis of the trophic chain. NP effects upon algae population growth were indeed already reported in literature, but the concurrent effects at cellular and genomic levels are still largely unexplored. Our work investigates the genotoxic (by COMET assay) and cytotoxic effects (by qualitative ROS production and cell viability) of ZnO nanoparticles toward marine microalgae Dunaliella tertiolecta. A comparison at defined population growth inhibition levels (i.e. 50% Effect Concentration, EC50, and No Observed Effect Concentration, NOEC) with SiO2 and TiO2 genotoxic effects and previously investigated cytotoxic effects (Manzo et al., 2015) was performed in order to elucidate the possible diverse mechanisms leading to algae growth inhibition. After 72h exposure, ZnO particles act firstly at the level of cell division inhibition (EC50: 2mg Zn/L) while the genotoxic action is evident only starting from 5mg Zn/L. This outcome could be ascribable mainly to the release of toxic ions from the aggregate of ZnO particle in the proximity of cell membrane. In the main, at EC50 and NOEC values for ZnO NPs showed the lowest cytotoxic and genotoxic effect with respect to TiO2 and SiO2. Based on Mutagenic Index (MI) the rank of toxicity is actually: TiO2>SiO2>ZnO with TiO2 and SiO2 that showed similar MI values at both NOEC and EC50 concentrations. The results presented herein suggest that up to TiO2 NOEC (7.5mg/L), the algae DNA repair mechanism is efficient and the DNA damage does not result in an evident algae population growth inhibition. A similar trend for SiO2, although at lower effect level with respect to TiO2, is observable. The comparison among all the tested nanomaterial toxicity patterns highlighted that the algae population growth inhibition occurred through pathways specific for each NP also related to their different physicochemical behaviors in seawater.

Multidisciplinary screening of toxicity induced by silica nanoparticles during sea urchin development

The aim of this study was to investigate the potential toxicity of Silica nanoparticles (SiO2 NPs) in seawater by using the sea urchin Paracentrotus lividus as biological model. SiO2 NPs exposure effects were identified on the sperm of the sea urchin through a multidisciplinary approach, combining developmental biology, ecotoxicology, biochemistry, and microscopy analyses. The following responses were measured: (i) percentage of eggs fertilized by exposed sperm; (ii) percentage of anomalies and undeveloped embryos and larvae; (iii) enzyme activity alterations (acetylcholinesterase, AChE) in the early developmental stages, namely gastrula and pluteus. Sperms were exposed to seawater containing SiO2 NPs suspensions ranging from 0.0001mg/L to 50mg/L. Fertilization ability was not affected at any concentration, whereas a significant percentage of anomalies in the offspring were observed and quantified by means of EC50 at gastrula stage, including undeveloped and anomalous embryos (EC50=0.06mg/L), and at pluteus stage, including skeletal anomalies and delayed larvae (EC50=0.27mg/L). Moreover, morphological anomalies were observed in larvae at pluteus stage, by immunolocalizing molecules involved in larval development and neurotoxicity effects - such as acetylated tubulin and choline acetyltransferase (ChAT) - and measuring AChE activity. Exposure of sea urchins to SiO2 NPs caused neurotoxic damage and a decrease of AChE expression in a non-dose-dependent manner. In conclusion, through the multidisciplinary approach used in this study SiO2 NPs toxicity in sea urchin offspring could be assessed. Therefore, the measured responses are suitable for detecting embryo- and larval- toxicity induced by these NPs.