Presence of humic acid in the environment holds promise as a potential mitigating factor for the joint toxicity of polystyrene nanoplastics and herbicide atrazine to Chlorella vulgaris: 96-H acute toxicity.

Increasing amounts of amino-functionalized polystyrene nanoplastics (PS-NH2) are entering aquatic ecosystems, raising concerns. Hence, this study investigated 96-h acute toxicity of PS-NH2 and its combination with the pesticide atrazine (ATZ) in the absence/presence of humic acid (HA) on the microalgae Chlorella vulgaris (C. vulgaris). Results showed that both PS-NH2 and PS-NH2+ATZ reduced algal growth, photosynthetic pigments, protein content, and antioxidant capacity, while increasing enzymatic activities. Gene expression related to oxidative stress was altered in C. vulgaris exposed to these treatments. Morphological and intracellular changes were also observed. The combined toxicity of PS-NH2+ATZ demonstrated a synergistic effect, but the addition of environmentally relevant concentration of HA significantly alleviated its toxicity to C. vulgaris, indicating an antagonistic effect due to the emergence of an eco-corona, and entrapment and sedimentation of PS-NH2+ATZ particles by HA. This study firstly highlights the role of HA in mitigating the toxicity of PS-NH2 when combined with other harmful compounds, enhancing our understanding of HA's presence in the environment.

Alleviating binary toxicity of polystyrene nanoplastics and atrazine to Chlorella vulgaris through humic acid interaction: Long-term toxicity using environmentally relevant concentrations.

In this study, microalgae Chlorella vulgaris (C. vulgaris) were simultaneously exposed to environmental concentrations of amino-functionalized polystyrene nanoplastics (PS-NH2; 0.05, 0.1, 0.2, 0.3 and 0.4 mg/L) and the world's second most used pesticide, the herbicide atrazine (ATZ; 10 µg/L), in the absence and presence of humic acid (HA; 1 mg/L) for 21 days. Due to the low concentrations of PS-NH2, the majority of them could not cause a significant difference in the end-points of biomass, chlorophylls a and b, total antioxidant, total protein, and superoxide dismutase and malondialdehyde compared to the control group (p > 0.05). On the other hand, by adding ATZ to the PS-NH2, all the mentioned end-point values showed a considerable difference from the control (p < 0.05). The exposure of PS-NH2+ATZ treatments to the HA could remarkably reduce their toxicity, additionally, HA was able to decrease the changes in the expression of genes related to oxidative stress (e.g., superoxide dismutase, glutathione reductase, and catalase) in the C. vulgaris in the most toxic treatment group (e.g., PS-NH2+ATZ). The synergistic toxicity of the PS-NH2+ATZ group could be due to their enhanced bioavailability for algal cells. Nevertheless, the toxicity alleviation in the PS-NH2+ATZ treatment group after the addition of HA could be due to the eco-corona formation, and changes in their zeta potential from positive to negative value, which would increase their electrostatic repulsion with the C. vulgaris cells, in such a way that HA also caused a decrease in the formation of C. vulgaris-NPs hetero-aggregates. This research underscores the complex interplay between PS-NH2, ATZ, and HA in aquatic environments and their collective impact on microalgal communities.

Combined toxic effects of polystyrene nanoplastics and lead on Chlorella vulgaris growth, membrane lipid peroxidation, antioxidant capacity, and morphological alterations.

In recent years, there has been a significant rise in the utilization of amino-functionalized polystyrene nanoplastics (PS-NH2). This surge in usage can be attributed to their exceptional characteristics, including a substantial specific surface area, high energy, and strong reactivity. These properties make them highly suitable for a wide range of industrial and medical applications. Nevertheless, there is a growing apprehension regarding their potential toxicity to aquatic organisms, particularly when considering the potential impact of heavy metals like lead (Pb) on the toxicity of PS-NH2. Herein, we examined the toxic effects of sole PS-NH2 (90 nm) at five concentrations (e.g., 0, 0.125, 0.25, 0.5, and 1 mg/L), as well as the simultaneous exposure of PS-NH2 and Pb2+ (using two environmental concentrations, e.g., 20 µg/L for Pb low (PbL) and 80 µg/L for Pb higher (PbH)) to the microalga Chlorella vulgaris. After a 96-h exposure, significant differences in chlorophyll a content and algal growth (biomass) were observed between the control group and other treatments (ANOVA, p < 0.05). The algae exposed to PS-NH2, PS-NH2 + PbL, and PS-NH2 + PbH treatment groups exhibited dose-dependent toxicity responses to chlorophyll a content and biomass. According to the Abbott toxicity model, the combined toxicity of treatment groups of PS-NH2 and PbL,H showed synergistic effects. The largest morphological changes such as C. vulgaris' size reduction and cellular aggregation were evident in the medium treated with elevated concentrations of both PS-NH2 and Pb2+. The toxicity of the treatment groups followed the sequence PS-NH2 < PS-NH2 + PbL < PS-NH2 + PbH. These results contribute novel insights into co-exposure toxicity to PS-NH2 and Pb2+ in algae communities.

Heavy metals (copper and iron) and nutrients (nitrate and phosphate) removal from aqueous medium by microalgae Chlorella vulgaris and Scendesmus obliquus, and their biofilms.

Microalgae have been discovered as an environmental-friendly and cost-effective solution for heavy metal treatment issues. This study illustrated the bioremediation of two heavy metals (e.g. copper and iron) and nutrients (e.g. nitrate and phosphate) uptake by freshwater microalgae Chlorella vulgaris (C. vulgaris) and Scendesmus obliquus (S. obliquus), and their 50-50% mix culture under the suspension and biofilm conditions. After one week of culture in 1L Erlenmeyer flasks, under the Organization for Economic Co-operation and Development (OECD) guideline, various concentrations of copper and iron were added to the culture bioreactors and their concentrations changes were studied. The results obtained showed that C. vulgaris, S. obliquus, and mix culture removed 98.25-99.9%, 98.75-99.1%, and 98.61-99.9% of copper and 90.22-94.05%, 85.68-99.19%, and 91.67-97.85% of iron, respectively. The results suggested that copper has more toxicity effects than iron. C. vulgaris showed to be the most vulnerable among cultures. S. obliquus showed to be more resistant to copper and iron stress situations. Mix culture showed better efficiency in iron uptake. It also demonstrated that there is a limit to nitrate uptake. Increasing heavy metal concentrations may increase nutrient uptake as long as it doesn't reach a toxic amount. Also, biofilm structure showed an effective role in heavy metal resistance.

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

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

Interfacial Design of Mixed Matrix Membranes via Grafting PVA on UiO-66-NH2 to Enhance the Gas Separation Performance.

In this study, defect-free facilitated transport mixed matrix membrane (MMM) with high loading amount of UiO-66-NH2 nanoparticles as metal-organic frameworks (MOFs) was fabricated. The MOFs were covalently bonded with poly (vinyl alcohol) (PVA) to incorporate into a poly (vinyl amine) (PVAm) matrix solution. A uniform UiO-66-NH2 dispersion up to 55 wt.% was observed without precipitation and agglomeration after one month. This can be attributed to the high covalent interaction at interfaces of UiO-66-NH2 and PVAm, which was provided by PVA as a functionalized organic linker. The CO2 permeability and CO2/N2 and selectivity were significantly enhanced for the fabricated MMM by using optimal fabrication parameters. This improvement in gas performance is due to the strong impact of solubility and decreasing diffusion in obtained dense membrane to promote CO2 transport with a bicarbonate reversible reaction. Therefore, the highest amount of amine functional groups of PVAm among all polymers, plus the abundant amount of amines from UiO-66-NH2, facilitated the preferential CO2 permeation through the bicarbonate reversible reaction between CO2 and -NH2 in humidified conditions. XRD and FTIR were employed to study the MMM chemical structure and polymers-MOF particle interactions. Cross-sectional and surface morphology of the MMM was observed by SEM-EDX and 3D optical profilometer to detect the dispersion of MOFs into the polymer matrix and explore their interfacial morphology. This approach can be extended for a variety of polymer-filler interfacial designs for gas separation applications.

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

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

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

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

Acute toxicity of gold nanoparticles synthesized from macroalga Saccharina japonica towards Daphnia magna.

This study was performed to explore acute toxicity of biologically synthesized gold nanoparticles (AuNPs) to a model organism Daphnia magna. Hence, using aqueous extract of marine macroalga Saccharina japonica, two AuNPs including SJ-AuNPs-72 (72.6 ± 43.8 nm) and SJ-AuNPs-10 (10.8 ± 2.8 nm) were synthesized. These AuNPs were characterized by different techniques such as UV-Vis spectrophotometry, transmission electron microscopy (TEM), dynamic light scattering (DLS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and energy-dispersive X-ray spectroscopy (EDX). The 48-h LC50 values of SJ-AuNPs-72 and SJ-AuNPs-10 to D. magna were 1.57 ± 0.07 and 2.69 ± 0.12 mg/L, respectively, showing greater toxicity of SJ-AuNPs-72. After exposure of daphnids to treatments, AuNPs were accumulated in gut tract, and lipid droplets under the Daphnia carapace were also observed. Whereas studies on toxicity of biosynthesized AuNPs are still scarce, the achievements of this work are helpful for understanding the toxicity of biosynthesized AuNPs to crustacean D. magna.

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

The increasing production of eco-friendly nanoparticles like biosynthesized nanoparticles (BNPs) calls for study on their environmental and biological safety. Herein, the impact of natural organic matter on the toxicity of BNPs was studied. Using leaf extract of herbal plant Allium fistulosum, the Allium fistulosum-silver nanoparticles (AF-AgNPs) were synthesized with the yield of around 100% and used to explore the impacts of natural organic matter (Suwannee river humic acid) on their toxicity to green microalgae Chlorella vulgaris. The results showed that the as-prepared AF-AgNPs could decrease the end-points of biomass and chlorophyll a content of C. vulgaris in a dose-dependent manner. In addition, AF-AgNPs enhanced algal aggregation and decreased size of cells, especially at higher concentrations. However, organic matter showed an ameliorative effect on the toxicity of AF-AgNPs, and significant enhancement of biomass and chlorophyll a content (p < 0.05) were observed in media treated with higher contents of AF-AgNPs. Organic matter could also prevent more cellular aggregation and size reduction of C. vulgaris. Our results are helpful for understanding the effects of organic matter on the toxicity of BNPs to aquatic organisms.

A comparative study of accumulated total mercury among white muscle, red muscle and liver tissues of common carp and silver carp from the Sanandaj Gheshlagh Reservoir in Iran.

The Sanandaj Gheshlagh Reservoir (SGR) is a mercury polluted lake that is located in the West of Iran. Common carp (Cyprinus carpio) and silver carp (Hypophthalmichthys molitrix) are the most abundant fishes in the SGR. A total of 48 common and silver carps (24 each) were captured randomly, using 50×6 m gill net (mesh size: 5×5 cm) during July to December 2009. Each month, the levels of accumulated total mercury (T-Hg) in white muscle, red muscle and liver tissues of these fishes were measured using an Advanced Mercury Analyzer (Model; Leco 254 AMA, USA) on the dry weight basis. There were no statistically significant differences between T-Hg concentrations in white muscle, red muscle and liver in common carp in comparison with similar tissues in silver carp (P>0.05). The content of T-Hg in liver tissue of both species was lower than of white and red muscle tissues. Higher levels of accumulated T-Hg were observed during summer. Results showed that T-Hg concentrations in common and silver carps target tissues were strongly dependent on age, length and weight (P<0.05). The results indicated that the levels of accumulated T-Hg in tissues of all samples with weights of over 850 g were greater than those limits established by WHO and FAO (500 ng g(-1)).