Biosynthesized BiFe2O4@Ag nanoparticles mediated Scenedesmus obliquus induce apoptosis in AGS gastric cancer cell line.

The use of magnetic metal nanoparticles has been considered in cancer treatment studies. In this study, BiFe2O4@Ag nanoparticles were synthesized biologically by Scenedesmus obliquus for the first time and their anticancer mechanism in a gastric cancer cell line was characterized. The physicochemical properties of the nanoparticles were evaluated by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic Light Scattering (DLS), and zeta potential analyses. Cell viability and nuclear damage were investigated by the MTT and Hoechst staining assays, respectively. Flow cytometry analysis was performed to determine the frequency of the necrotic and apoptotic cells as well as cell cycle analysis of the nanoparticles-treated cells. Physicochemical characterization showed that the synthesized particles were spherical, without impurities, in a size range of 38-83 nm, with DLS size and zeta potential of 295.7 nm and -27.7 mV, respectively. BiFe2O4@Ag nanoparticles were considerably more toxic for the gastric cancer cells (AGS cell line) than HEK293 normal cells with IC50 of 67 and 117 µg/ml, respectively. Treatment of AGS cells with the nanoparticles led to a remarkable increase in the percentage of late apoptosis (38.5 folds) and cell necrosis (13.4 folds) and caused cell cycle arrest, mainly at the S phase. Also, nuclear fragmentation and apoptotic bodies were observed in the gastric cancer cells treated with the nanoparticles. This study represents BiFe2O4@Ag as a novel anticancer candidate against gastric cancer that can induce cell apoptosis through DNA damage and inhibition of cell cycle progression.

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.

Enhanced biomethane production from Scenedesmus sp. using polymer harvesting and expired COVID-19 disinfectant for pretreatment.

This study evaluates the repurposing of expired isopropanol (IPA) COVID-19 disinfectant (64% w/w) to pretreat algal biomass for enhancing methane (CH4) yield. The impact of harvesting methods (centrifugation and polymer flocculation) and microwave pretreatment on CH4 production from Scenedesmus sp. microalgal biomass were also investigated. Results show minimal impact of harvesting methods on the CH4 yield, with wet centrifuged and polymer-harvested biomass exhibiting comparable and low CH4 production at 66 and 74 L/kgvolatile solid, respectively. However, microalgae drying significantly increased CH4 yield compared to wet biomass, attributed to cell shrinkage and enhanced digestibility. Consequently, microwave and IPA pretreatment significantly enhanced CH4 production when applied to dried microalgae, yielding a 135% and 212% increase, respectively, compared to non-pretreated wet biomass. These findings underscore the advantage of using dried Scenedesmus sp. over wet biomass and highlight the synergistic effect of combining oven drying with IPA treatment to boost CH4 production whilst reducing COVID-19 waste.

The role of algal EPS in reducing the combined toxicity of BPA and polystyrene nanoparticles to the freshwater algae Scenedesmus obliquus.

Both Bisphenol A (BPA) and polystyrene nanoplastics (PSNPs) are routinely found in several consumer products such as packaging materials, flame retardants, and cosmetics. The environment is seriously endangered by nano- and microplastics. In addition to harming aquatic life, nanoplastics (NPs) also bind to other pollutants, facilitating their dispersion in the environment and possibly promoting toxicity induced by these pollutants. The toxic effects of polystyrene nanoplastics (PS-NPs) and BPA were examined in this study, as well as the combined toxic impacts of these substances on the freshwater microalgae Scenedesmus obliquus. In addition, the exopolymeric substances (EPS) secreted by algae will interact with the pollutants modifying their physicochemical behaviour and fate. This work aimed to investigate how algal EPS alters the combined effects of BPA and PSNPs on the microalgae Scenedesmus obliquus. The algae were exposed to binary mixtures of BPA (2.5, 5, and 10 mg/L) and PSNPs (1 mg/L of plain, aminated, and carboxylated PSNPs) with EPS added to the natural freshwater medium. Cell viability, hydroxyl and superoxide radical generation, cell membrane permeability, antioxidant enzyme activity (catalase and superoxide dismutase), and photosynthetic pigment content were among the parameters studied to determine the toxicity. It was observed that for all the binary mixtures, the carboxylated PSNPs were most toxic when compared to the toxicity induced by the other PSNP particles investigated. The maximum damage was observed for the mixture of 10 mg/L of BPA with carboxylated PSNPs with a cell viability of 49%. When compared to the pristine mixtures, the EPS-containing mixtures induced significantly reduced toxic effects. A considerable decrease in reactive oxygen species levels, activity of antioxidant enzymes (SOD and CAT), and cell membrane damage was noted in the EPS-containing mixtures. Reduced concentrations of the reactive oxygen species led to improved photosynthetic pigment content in the cells.

Ecotoxicological effects of DBPs on freshwater phytoplankton communities in co-culture systems.

Intensive disinfection of wastewater during the COVID-19 pandemic might elevate the generation of toxic disinfection byproducts (DBPs), which has triggered global concerns about their ecological risks to natural aquatic ecosystems. In this study, the toxicity of 17 DBPs typically present in wastewater effluents on three representative microalgae, including Scenedesmus sp. (Chlorophyta), Microcystis aeruginosa (Cyanophyta), and Cyclotella sp. (Bacillariophyta) was investigated. The sensitivities of the three microalgae to DBPs varied greatly from species to species, indicating that DBPs may change the structure of phytoplankton communities. Later, co-cultures of these phytoplankton groups as a proxy of ecological freshwater scenario were conducted to explore the impacts of DBPs on phytoplankton community succession. M. aeruginosa became surprisingly dominant in co-cultures, representing over 50% after dosing with monochloroacetic acid (MCAA, 0.1-10 mg/L). The highest proportion of M. aeruginosa was 70.3% when exposed to 2 mg/L MCAA. Although Scenedesmus sp. dominated in monochloroacetonitrile (MCAN) exposure, M. aeruginosa accounted for no less than 30% even at 40 mg/L MCAN. In this study, DBPs disrupted the original inter-algal relationship in favor of M. aeruginosa, suggesting that DBPs may contribute to the outbreak of cyanobacterial blooms in aquatic ecosystems.

Effects of leachates from UV-weathered microplastic on the microalgae Scenedesmus vacuolatus.

Plastics undergo successive fragmentation and chemical leaching steps in the environment due to weathering processes such as photo-oxidation. Here, we report the effects of leachates from UV-irradiated microplastics towards the chlorophyte Scenedesmus vacuolatus. The microplastics tested were derived from an additive-containing electronic waste (EW) and a computer keyboard (KB) as well as commercial virgin polymers with low additive content, including polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), and polystyrene (PS). Whereas leachates from additive-containing EW and KB induced severe effects, the leachates from virgin PET, PP, and PS did not show substantial adverse effects in our autotrophic test system. Leachates from PE reduced algae biomass, cell growth, and photosynthetic activity. Experimental data were consistent with predicted effect concentrations based on the ionization-corrected liposome/water distribution ratios (Dlip/w) of polymer degradation products of PE (mono- and dicarboxylic acids), indicating that leachates from weathering PE were mainly baseline toxic. This study provides insight into algae toxicity elicited by leachates from UV-weathered microplastics of different origin, complementing the current particle- vs. chemical-focused research towards the toxicity of plastics and their leachates.

Acute effects of CH3NH3PbI3 perovskite on Scenedesmus obliquus and Daphnia magana in aquatic environment.

CH3NH3PbI3 is one of the most widely studied and most promising photoelectric conversion materials for large-scale application. However, once it is discharged into the aquatic environment, it will release a variety of lethal substances to the aquatic organisms. Herein, two typical aquatic pollution indicators, Scenedesmus obliquus (a typical phytoplankton) and Daphnia magna (a typical zooplankton), were used to assess the acute effects of CH3NH3PbI3 perovskite on aquatic organisms. The results showed that, when the initial CH3NH3PbI3 perovskite level (CPL) was 40 mg L-1 or higher, the growth of S. obliquus would be remarkably inhibited with significant decreases of chlorophyll content and protein content. And when the CPL was over 5 mg L-1, the survival of D. magna would be notably threatened. Specifically, the 72 h EC-50 of CH3NH3PbI3 perovskite to S. obliquus was calculated as 37.21 mg L-1, and the 24 h LC-50 of this perovskite to D. magna adults and neonates were calculated as 37.53 mg L-1 and 18.55 mg L-1, respectively. Moreover, remarkably solution pH declination and large amounts of lead bio-accumulation was observed in the both acute experiments, which could be the main reasons causing the above acute effects. Considering the strong acute effects of these CH3NH3PbI3 perovskite materials and their attractive application prospect, more attentions should be paid on their harmness to the environment.

The effects of exogenous cerium on photosystem II as probed by in vivo chlorophyll fluorescence and lipid production of Scenedesmus obliquus XJ002.

Cerium is the most abundant rare earth metal in the earth's crust, and it has deleterious effects on aquatic ecosystems from fertilizer runoff. Scenedesmus obliquus is an oil-rich microalga that grows rapidly and is sensitive to many kinds of toxins. Given that microalgae are useful indicators of eutrophication and toxic stress, it was found that lower concentrations of cerium (0.50-5.00 mg·L-1 ) stimulated algal growth and increased chlorophyll a content, whereas higher concentrations (above 50.00 mg·L-1 ) had an inhibitory effect on algal growth and chlorophyll a content. The algal growth rate and chlorophyll a content peaked at a cerium concentration of 5.00 mg·L-1 . Both the donor and acceptor sides of photosystem II (PSII) reaction centers were sensitive to cerium-induced stress. Specifically, high concentrations of cerium damaged the oxygen evolving complex and PSII reaction center and suppressed electron transport at the donor and receptor side of the reaction center, influencing the absorption, transfer, and application of light energy in S. obliquus XJ002. In addition, we established a simple method to quantify the intracellular lipid content of S. obliquus XJ002, and the optimum staining conditions for Nile red were as follows: volume percentage of dimethyl sulfoxide was 2%, the concentration of Nile red was 2.0 µg·mL-1 , and the staining time of Nile red was 5 min. The addition of cerium resulted in a significant increase in the total lipid content of XJ002. When the concentration of cerium was 50 mg·L-1 , the total lipid content was 16.26% higher than the control group. This information will enhance our ability to utilize microelement fertilizer in biomass accumulation programs and will help to further reveal the key regulatory factors in the lipid metabolism, and would lay the foundation for promoting the research of microalgae bioenergy.

Chemical- and species-specific toxicity of nonylphenol and octylphenol to microalgae Chlorella pyrenoidosa and Scenedesmus obliquus.

As typical endocrine disrupters, nonylphenol (NP) and octylphenol (OP) are emerging pollutants that have attracted wide attention. This study investigated the toxicity effects of NP and OP on microalgae Chlorella pyrenoidosa and Scenedesmus obliquus, particularly on their growth inhibition, photosynthetic pigment, chlorophyll fluorescence, and superoxide dismutase and malondialdehyde levels. Results showed that the 96 h EC50 of NP and OP was 2.89 and 5.21 mg/L on C. pyrenoidosa, respectively, and 1.54 and 8.48 mg/L on S. obliquus, respectively. NP exerted a stronger inhibitory effect on cell growth, photosynthesis, and PSII activity, and it contributed more oxidative stress on C. pyrenoidosa than on S. obliquus. By contrast, OP exerted a stronger inhibitory effect on S. obliquus than on C. pyrenoidosa. Furthermore, the toxicity of OP to the tested microalgae was lower than that of NP. Principal component analysis (PCA) and Pearson's correlation indicate that the accumulation of reactive oxygen species is the dominant mechanism of NP and OP cellular toxicity. The principal components of NP and OP affecting microalgae are distinct in the PCA plot, and different endocrine disrupters have varying chemical-specific influences on algal cells. This study confirmed that the toxicity of NP and OP to microalgae C. pyrenoidosa and S. obliquus is chemical- and species-specific. These findings should be considered when assessing the health risk of environmental pollution.

Bacillus spp. metabolites are effective in eradicating Aedes aegypti (Diptera: Culicidae) larvae with low toxicity to non-target species.

The growing spread of dengue, chikungunya and Zika viruses demand the development of new and environmentally safe control methods for their vector, the mosquito Aedes aegypti. This study aims to find novel larvicidal agents from mutualistic (endophytic and rhizospheric) or edaphic bacteria that have no action against non-target organisms. Eleven out of the 254 bacterial strains tested were able to kill Ae. aegypti larvae. Larvicidal activity did not depend on presence of cells, since culture supernatants or crude lipopeptide extracts (CLEs) killed the larvae. Bacillus safensis BacI67 and Bacillus paranthracis C21 supernatants were the best performing supernatants, displaying the lowest lethal concentrations (LC50 = 31.11 µL/mL and 45.84 µL/mL, respectively). Bacillus velezensis B64a and Bacillus velezensis B15 produced the best performing CLEs (LC50 = 0.11 mg/mL and 0.12 mg/mL, respectively). Mass spectrometry analysis of CLEs detected a mixture of surfactins, iturins, and fengycins. The samples tested were weakly- or non-toxic to mammalian cells (RAW 264.7 macrophages and VERO cells) and non-target organisms (Caenorhabditis elegans, Galleria mellonella, Scenedesmus obliquus, and Tetrahymena pyriformis) - especially B. velezensis B15 CLE. The biosynthetic gene clusters related to secondary metabolism identified by whole genome sequencing of the four best performing bacteria strains revealed clusters for bacteriocin, beta-lactone, lanthipeptide, non-ribosomal peptide synthetases, polyketide synthases (PKS), siderophores, T3PKS, type 1 PKS-like, terpenes, thiopeptides, and trans-AT-PKS. Purification of lipopeptides may clarify the mechanisms by which these extracts kill Ae. aegypti larvae.

Effects and possible mechanisms of sanguinarine on the competition between Raphidiopsis raciborskii (Cyanophyta) and Scenedesmus obliquus (Chlorophyta): A comparative toxicological study.

The phytogenic algicide sanguinarine shows strong inhibitory effects on some bloom-forming cyanobacteria and exhibits great potential in cyanobacterial bloom mitigation. To evaluate the possible ecological effects of sanguinarine on microalgae, the effects and possible mechanisms of sanguinarine on the competition between bloom-forming cyanobacterium Raphidiopsis raciborskii (formerly named Cylindrospermopsis raciborskii) and green alga Scenedesmus obliquus were investigated through co-culture competition test and comparative toxicological study including growth characteristics, chlorophyll fluorescence transients, activities of antioxidant enzymes, and lipid peroxidation. The results of Raphidiopsis-Scenedesmus co-culture competition test showed that sanguinarine decreased the competition ability of R. raciborskii, which benefitted S. obliquus in winning the competition. Toxicological studies have shown that sanguinarine exhibited high inhibitory effects on the growth and photosynthesis of R. raciborskii but no obvious toxicity on S. obliquus at concentrations of no more than 80 µg L-1. Oxidative damage partially contributed but was not the primary mechanism for the toxicity of sanguinarine on R. raciborskii. The results presented in this study indicate that sanguinarine may be a good algicidal candidate in mitigation of Raphidiopsis-based water bloom.

Anti-Biofouling and Self-Cleaning Surfaces Featured with Magnetic Artificial Cilia.

The fouling of surfaces submerged in a liquid is a serious problem for many applications including lab-on-a-chip devices and marine sensors. Inspired by the versatility of cilia in manipulating fluids and particles, it is experimentally demonstrated that surfaces partially covered with magnetic artificial cilia (MAC) have the capacity to efficiently prevent attachment and adhesion of real biofouling agents-microalgae Scenedesmus sp. Actuation of the MAC resulted in over 99% removal of the algae for two different scenarios: (1) actuating the MAC immediately after injecting the algae into a microfluidic chip, demonstrating antifouling and (2) starting to actuate the MAC 1 week after injecting the algae into the chip and leaving them to grow in static conditions, showing self-cleaning. It is shown that the local and global flows generated by the actuated MAC are substantial, resulting in hydrodynamic shear forces acting on the algae, which are likely to be key to efficient antifouling and self-cleaning. These findings and insights will potentially lead to novel types of self-cleaning and antifouling strategies, which may have a relevant practical impact on different fields and applications including lab-on-a-chip devices and water quality analyzers.

Effects of carbon nanotubes on the toxicities of copper, cadmium and zinc toward the freshwater microalgae Scenedesmus obliquus.

Due to their unique structure and properties, carbon nanotubes (CNTs) released into the aquatic environment can potentially influence the behavior of other coexisting pollutants, thereby altering their toxicity to aquatic organisms. In this study, the toxicities of multi-walled CNTs and three heavy metals, copper (Cu), cadmium (Cd) and zinc (Zn) were determined individually. Following this, CNTs with low concentrations (1 and 5 mg/L) were co-exposed with Cu, Cd or Zn to the microalgae Scenedesmus obliquus, to investigate the effects and underlying mechanisms of CNTs on metal toxicity. Results showed that CNTs, especially at a concentration of 5 mg/L, promoted algae growth and enhanced photosynthetic efficiency via increasing exciton trap efficiency and quantum yield for electron transport. Introduction of CNTs appeared to alleviate the adverse effects of Cu, Cd or Zn on microalgae, indicated by algae growth, total chlorophyll content and photosynthetic indices. However, these effects differed greatly for different metals, depending on both the toxicity of each metal and the exposure period (4 day and 8 day). Enhancement of photosynthesis and interference of metal uptake by CNTs, have a crucial role in the effects of CNTs on metal toxicity.

Effects of nanomaterials on metal toxicity: Case study of graphene family on Cd.

The risk of heavy metal cadmium (Cd) on aquatic organisms has drawn widespread attentions, but the effects of nanomaterials (e.g. graphene (G)) on Cd toxicity are rarely clarified. It was known that mixture of contaminants may exhibit more severe impact than the individual metal. Here, we conducted a study systematically on the effects of nanomaterials on the toxicity of Cd to Scenedesmus Obliquus (S. obliquus) with or without the presence of graphene family materials (GFMs) derived from G, such as graphene oxide (GO) and amine-modified graphene (GNH). Our results showed that the influence of GFMs on the acute toxicity of Cd to S. obliquus is in the order of GO > G > GNH based on their EC50 of Cd-GFMs. The effects of GFMs on the cytotoxicity and oxidative damage of Cd to S. obliquus are varied with the concentrations of GFMs. The differences between the effects of GFMs on Cd toxicity may attribute to their different surface oxygen-containing functional groups contained in the nanomaterials. The adsorption capacity of nanomaterials on metal ions, their dispersibility in water and their interaction mode with organisms, may dominate main contributions to their effects on Cd toxicity. Our study aids to clarify the interference of nanoparticles on the ecotoxicity of metals, to avoid the misunderstanding of the potential risk of metals in the complicate water environments.

A study into the species sensitivity of green algae towards imidazolium-based ionic liquids using flow cytometry.

The sensitivity of individual organisms towards toxic agents is an important indicator of environmental pollution. However, organism-specific quantification of sensitivity towards pollutants remains a challenge. In this study, we determined the sensitivity of Chlorella vulgaris (C. vulgaris) and Scenedesmus quadricauda (S. quadricauda) towards three ionic liquids (ILs), 1-alkyl-3-methyl-imidazolium chlorides [Cnmim][Cl] (n = 4,6,8). We kept all external parameters constant to identify the biotic parameters responsible for discrepancies in species sensitivity, and used flow cytometry to determine four conventional endpoints to characterise cell viability and cell vitality. Our results demonstrate that after exposure to the ILs, cell proliferation was inhibited in both species. At the same time, the cell size, complexity and membrane permeability of both algae also increased. However, while Chl a synthesis by S. quadricauda was inhibited, that of C. vulgaris was enhanced. S. quadricauda has evolved a metabolic defense that can counteract the decreased esterase activity that has been shown to occur in the presence of ILs. While it is likely that S. quadricauda was less sensitive than C. vulgaris to the ILs because of this metabolic defense, this alga may also exhibit better membrane resistance towards ILs.

Toxicity of benzophenone-3 and its biodegradation in a freshwater microalga Scenedesmus obliquus.

Environmental contamination by benzophenone-3 has gained attention because of its frequent occurrence and adverse environmental impact. Studies investigating the toxicity and removal mechanisms, along with its degradation pathway in microalgae are still rare. In this study, the ecotoxicity of benzophenone-3 on Scenedesmus obliquus was assessed through dose-response test, risk quotient evaluation, and changes of microalgal biochemical characteristics and gene expression. The calculated risk quotients of benzophenone-3 were >1, implying its high environmental risk. Expression of the ATPF0C and Tas genes encoding ATP-synthase and oxidoreductase was significantly increased in S. obliquus after exposure to benzophenone-3, while that of Lhcb1 and HydA genes was reduced. When exposed to 0.1-3 mg L-1 benzophenone-3, 23-29 % removal was achieved by S. obliquus, which was induced by abiotic removal, bioadsorption, bioaccumulation and biodegradation. Metabolic fate analyses showed that biodegradation of benzophenone-3 was induced by hydroxylation, and methylation, forming less toxic intermediates according to the toxicity assessment of the identified products. This study provides a better understanding of the toxicity and metabolic mechanisms of benzophenone-3 in microalgae, demonstrating the potential application of microalgae in the remediation of benzophenone-3 contaminated wastewater.

Phytotoxicity, Bioaccumulation, and Degradation of Nonylphenol in Different Microalgal Species without Bacterial Influences.

Nonylphenol (NP) is a contaminant that has negative impacts on aquatic organisms. To investigate its phytotoxicity, bioaccumulation, and degradation in algae without associated bacteria, six freshwater microalgae-Ankistrodesmus acicularis, Chlorella vulgaris, Chroococcus minutus, Scenedesmus obliquus, Scenedesmus quadricauda, and Selenastrum bibraianum-in bacteria-free cultures were studied. When exposed to 0.5-3.0 mg L-1 NP for 4 days, cell growth and photosynthesis, including maximal photochemistry (Fv/Fm), were suppressed progressively. The antioxidant responses of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) showed species differences. While the antioxidant enzymes in C. vulgaris and S. obliquus were more active with the increase of NP (0-3 mg L-1), they dropped in the other four algae at concentrations of 1 and 1.5 mg L-1. Therefore, C. vulgaris and S. obliquus were designated as NP-tolerant species and showed more conspicuous and faster changes of antioxidant reactions compared with the four NP-sensitive species. All six species degraded NP, but A. acicularis was more reactive at low NP concentrations (<1 mg L-1), suggesting its possible application in sewage treatment for its potential for effective NP removal from water bodies in a suitable scope. Therefore, the conclusion is that biodegradation of NP by algae is species specific.

Photosynthetic toxicity of non-steroidal anti-inflammatory drugs (NSAIDs) on green algae Scenedesmus obliquus.

The widespread use of pharmaceuticals and personal care products (PPCPs) has raised serious concerns regarding their potential ecotoxicological effects. We examined the photosynthetic toxicity of four non-steroidal anti-inflammatory drugs (NSAIDs), i.e. ibuprofen (rac-IBU and S-(+)-IBU), aspirin (ASA) and ketoprofen (KEP) on the green alga Scenedesmus obliquus. Our results showed that NSAIDs exerted inhibitory effects on algal growth; the IC50-24h of S-(+)-IBU, rac-IBU, ASA, and KEP was 123.29, 107.91, 103.05, and 4.03 mg/L, respectively. KEP was the most toxic, ASA was slightly more toxic than rac-IBU, and S-(+)-IBU was the least toxic. NSAIDs adversely affected the cellular ultrastructure, as evident from plasmolysis, chloroplast deformation and disintegration. NSAID treatments decreased the chlorophyll and carotenoid content, and chlorophyll fluorescence parameters such as minimum fluorescence yield (F0), maximum fluorescence yield (Fm), maximum photochemical quantum yield (Fv/Fm), PSII (photosystem II) effective quantum yield [Y(II)], photosynthetic electron transfer rate (ETR), and the photochemical quenching (qP), were also adversely affected. Algal photosynthetic and respiratory rates decreased following NSAID treatments, and the expression of genes involved in photosynthetic electron transport (psaA, psaB, psbB, psbD, and rbcL) was down-regulated. Furthermore, the functioning of the photosynthetic electron transport chain from PSI (photosystem I) to PSII, carbon assimilation, and photorespiration were affected. Our results suggest that NSAIDs can exert considerable toxic effects on the photosynthetic system of S. obliquus. These results provide a basis for evaluating the environmental safety of NSAIDs.

Aluminium triggers oxidative stress and antioxidant response in the microalgae Scenedesmus sp.

Aluminium (Al) water pollution is an increasing environmental problem and comprehensive analysis of toxic responses of aquatic primary producer organisms is imperative. We characterized the antioxidant response of Scenedesmus sp. microalga to Al-induced oxidative stress. After 72 h of exposure to Al (0, 10, and 100 µM) in a modified Bold Basal Medium (pH 5.0), we observed cell aggregation and alterations in the subcellular structure, strong lipid peroxidation and oxidative stress induction (detected with the fluorescent probe 2',7'-dichlorodihydrofluorescein diacetate) in parallel with Al accumulation in cells. At the same time, Al toxicity caused depletion of important macronutrients like Ca, which is important for cell-wall structure. Analysis of antioxidant enzymatic activities in Al-treated Scenedesmus cells revealed that catalase, ascorbate peroxidase, as well as different isoforms of superoxide dismutase were inhibited especially at the highest Al dose (100 µM), cells that accumulated the highest concentration of Al. On the other hand, glutathione reductase activity increased at that Al concentration. Immunodetection after Western-blotting confirmed that only ascorbate peroxidase inhibition was apparently due to a decrease in enzyme levels. However, the inhibition of catalase and activation of glutathione reductase activities seemed related with post-translational modifications in protein function as protein expression decreased or increased, respectively under Al stress. Our results may help to understand toxic mechanisms triggered by Al in freshwater microalgae, which in turn could aid to select suitable biomarkers of Al contamination in aquatic ecosystems.

Decomplexation of Cu(II)-natural organic matter complex by non-thermal plasma oxidation: Process and mechanisms.

Heavy metals and natural organic matters (NOM) form very stable heavy metal-NOM complexes in aqueous, facilitating the migration of heavy metals and enhancing their potential risks. In this study, non-thermal plasma oxidation was attempted to destroy the heavy metal-NOM complexes, with Cu-humate (Cu-HA) as a model. The decomplexation efficiency reached 86.1 % within 50 min of plasma oxidation at 16 kV. The generated reactive species by the non-thermal plasma, including O2-, 1O2, OH, attacked the carboxyl and hydroxyl functional groups of HA, leading to cleavage of the Cu-O bonds, decomplexation of Cu-HA, and release of free Cu(II). Meanwhile, a variety of small molecular intermediates, including phenols, benzoic acids, esters, amines, ketones, acetic acid, formic acid, and oxalic acid, were generated due to attack by the oxidative species on the aromatic moiety and double bonds in Cu-HA. As a consequence of decomplexation, the residual toxicity of Cu-HA to Scenedesmus obliquus was distinctly reduced. This study provides a potential technique to decomplex heavy metal-NOM complexes, and reduces their toxicity to typical Scenedesmus obliquus.