Polystyrene nanoplastics affect growth and microcystin production of Microcystis aeruginosa

The impact of polystyrene nanoplastics (PSNPs) on physiological and biochemical parameters of the microalgae Spirulina platensis

Nanoplastics, as emerging pollutants, have harmful effects on living organisms and the environment, the mechanisms and extent of which remain unclear. Microalgae, as one of the most important biological groups in the food chain and sensitive environmental indicators to various pollutants, are considered a suitable option for investigating the effects of nanoplastics. In this study, the effects of polystyrene nanoplastics on the growth rate, dry weight, chlorophyll a and carotenoid levels, proline, and lipid peroxidation in the Spirulina platensis were examined. Three concentrations of 0.1, 1, and 10 mg L-1 of PSNPs were used alongside a control sample with zero concentration, with four repetitions in one-liter containers for 20 days under optimal temperature and light conditions. Various analyses, including growth rate, dry weight, proline, chlorophyll a and carotenoid levels, and lipid peroxidation, were performed. The results indicated that exposure to PSNP stress led to a significant decrease in growth rate, dry weight, and chlorophyll a and carotenoid levels compared to the control sample. Furthermore, this stress increased the levels of proline and lipid peroxidation in Spirulina platensis. Morphological analysis via microscopy supported these findings, indicating considerable environmental risks associated with PSNPs.

Toxicological review of micro- and nano-plastics in aquatic environments: Risks to ecosystems, food web dynamics and human health

The increase of micro- and nano-plastics (MNPs) in aquatic environments has become a significant concern due to their potential toxicological effects on ecosystems, food web dynamics, and human health. These plastic particles emerge from a range of sources, such as the breakdown of larger plastic waste, consumer products, and industrial outputs. This review provides a detailed report of the transmission and dangers of MNPs in aquatic ecosystems, environmental behavior, and interactions within aquatic food webs, emphasizing their toxic impact on marine life. It explores the relationship between particle size and toxicity, their distribution in different tissues, and the process of trophic transfer through the food web. MNPs, once consumed, can be found in various organs, including the digestive system, gills, and liver. Their consumption by lower trophic level organisms facilitates their progression up the food chain, potentially leading to bioaccumulation and biomagnification, thereby posing substantial risks to the health, reproduction, and behavior of aquatic species. This work also explores how MNPs, through their persistence and bioaccumulation, pose risks to aquatic biodiversity and disrupt trophic relationships. The review also addresses the implications of MNPs for human health, particularly through the consumption of contaminated seafood, highlighting the direct and indirect pathways through which humans are exposed to these pollutants. Furthermore, the review highlights the recommendations for future research directions, emphasizing the integration of ecological, toxicological, and human health studies to inform risk assessments and develop mitigation strategies to address the global challenge of plastic pollution in aquatic environments.

Microplastics enhanced the allelopathy of pyrogallol on toxic Microcystis with additional risks: Microcystins release and greenhouse gases emissions

Cyanobacteria blooms (CBs) caused by eutrophication pose a global concern, especially Microcystis aeruginosa (M. aeruginosa), which could release harmful microcystins (MCs). The impact of microplastics (MPs) on allelopathy in freshwater environments is not well understood. This study examined the joint effect of adding polystyrene (PS-MPs) as representative MPs and two concentrations (2 and 8 mg/L) of pyrogallol (PYR) on the allelopathy of M. aeruginosa. The results showed that the addition of PS-MPs intensified the inhibitory effect of 8 mg/L PYR on the growth and photosynthesis of M. aeruginosa. After a 7-day incubation period, the cell density decreased to 69.7 %, and the chl-a content decreased to 48 % compared to the condition without PS-MPs (p < 0.05). Although the growth and photosynthesis of toxic Microcystis decreased with the addition of PS-MPs, the addition of PS-MPs significantly resulted in a 3.49-fold increase in intracellular MCs and a 1.10-fold increase in extracellular MCs (p < 0.05). Additionally, the emission rates of greenhouse gases (GHGs) (carbon dioxide, nitrous oxide and methane) increased by 2.66, 2.23 and 2.17-fold, respectively (p < 0.05). In addition, transcriptomic analysis showed that the addition of PS-MPs led to the dysregulation of gene expression related to DNA synthesis, membrane function, enzyme activity, stimulus detection, MCs release and GHGs emissions in M. aeruginosa. PYR and PS-MPs triggered ROS-induced membrane damage and disrupted photosynthesis in algae, leading to increased MCs and GHG emissions. PS-MPs accumulation exacerbated this issue by impeding light absorption and membrane function, further heightening the release of MCs and GHGs emissions. Therefore, PS-MPs exhibited a synergistic effect with PYR in inhibiting the growth and photosynthesis of M. aeruginosa, resulting in additional risks such as MCs release and GHGs emissions. These results provide valuable insights for the ecological risk assessment and control of algae bloom in freshwater ecosystems.

Unveiling the molecular mechanisms of size-dependent effect of polystyrene micro/nano-plastics on Chlamydomonas reinhardtii through proteomic profiling

Microplastics have become a prevalent environmental pollutant due to widespread release and production. Algae, as primary producers, play a crucial role in maintaining the ecological balance of freshwater environments. Despite reports on the inhibition of microalgae by microplastics, the size-dependent effects on microalgae and associated molecular mechanism remain poorly understood. This study investigates the impacts of three polystyrene micro/nano-plastics (PS-MNPs) with different sizes (100 nm, 350 nm, and 6 μm) and concentrations (25-200 mg/L) on Chlamydomonas reinhardtii (C. reinhardtii) throughout its growth period. Results reveal size- and concentration-dependent growth inhibition and induction of oxidative stress by PS-MNPs, with microalgae exhibiting increased vulnerability to smaller-sized and higher-concentration PS-MNPs. Proteomics analysis elucidates the size-dependent suppression of proteins involved in the photosynthesis process by PS-MNPs. Photosynthetic activity assays demonstrate that smaller PS-MNPs more significantly reduce chlorophyll content and the maximal photochemical efficiency of photosystem II. Finally, electron microscope and Western blot assays collectively confirm the size effect of PS-MNPs on microalgae growth is attributable to suppressed protein expression rather than shading effects. This study contributes to advancing our understanding of the intricate interactions between micro/nano-plastics and algae at the molecular level, emphasizing the efficacy of proteomics in dissecting the mechanistic aspects of microplastics-induced biological effects on environmental indicator organisms.

The photosynthetic toxicity of nano-polystyrene to Microcystis aeruginosa is influenced by surface modification and light intensity

It is known that nanoplastics can cause membrane damage and production of reactive oxygen species (ROS) in cyanobacteria, negatively impacting their photosynthetic reactions and growth. However, the synergistic effect of light intensity on nanoplastics' toxicity to cyanobacteria is rarely investigated. Here, we investigated the impact of nano-polystyrene particles (PS) and amino-modified nano-polystyrene particles (PS-NH2) on cyanobacterium Microcystis aeruginosa cultivated under two light intensities. We discovered that PS-NH2 was more toxic to M. aeruginosa compared to PS with more damage of cell membranes by PS-NH2. The membrane damage was found by scanning electron microscope and atomic force microscopy. Under low light, PS-NH2 inhibited the photosynthesis of M. aeruginosa by decreasing the PSII quantum yield, photosynthetic electron transport rate and pigment content, but increasing non-photochemical quenching and Car/chl a ratio to cope with this stress condition. Moreover, high light appeared to increase the toxicity of PS-NH2 to M. aeruginosa by increasing its in vitro and intracellular ROS content. Specifically, on the one hand, high visible light (without UV) and PS-NH2 induced more in vitro singlet oxygen, hydroxyl radical and superoxide anion measured by electron paramagnetic resonance spectrometer in vitro, which could be another new toxic mechanism of PS-NH2 to M. aeruginosa. On the other hand, high light and PS-NH2 might increase intracellular ROS by inhibiting more photosynthetic electron transfer and accumulating more excess energy and electrons in M. aeruginosa. This research broadens our comprehension of the toxicity mechanisms of nanoplastics to cyanobacteria under varied light conditions and suggests a new toxic mechanism of nanoplastics involving in vitro ROS under visible light, providing vital information for assessing ecotoxicological effects of nanoplastics in the freshwater ecosystem.

Surface functionalization, particle size and pharmaceutical co-contaminant dependent impact of nanoplastics on marine crustacean - Artemia salina

Despite a significant amount of research on micronanoplastics (MNPs), there is still a gap in our understanding of their function as transporters of other environmental pollutants (known as the Trojan horse effect) and the combined effects of ingestion, bioaccumulation, and toxicity to organisms. This study examined the individual effects of polystyrene nanoplastics (PSNPs) with various surface functionalizations (plain (PS), carboxylated (PS-COOH), and aminated (PS-NH2)), particle sizes (100 nm and 500 nm), and a pharmaceutical co-contaminant (metformin hydrochloride (MH), an anti-diabetic drug) on the marine crustacean - Artemia salina. The study specifically aimed to determine if MH alters the detrimental effects of PSNPs on A. salina. The potential toxicity of these emerging pollutants was assessed by examining mortality, hatching rate, morphological changes, and biochemical changes. Smaller nanoparticles had a more significant impact than larger ones, and PS-NH2 was more harmful than PS and PS-COOH. Exposure to the nanoparticle complex with MH resulted in a decrease in hatching rate, an increase in mortality, developmental abnormalities, an increase in reactive oxygen species, catalase, and lipid peroxidase, and a decrease in total protein and superoxide dismutase, indicating a synergistic effect. There were no significant differences between the complex and the individual nanoparticles. However, accumulating these particles in organisms could contaminate the food chain. These results highlight the potential environmental risks associated with the simultaneous exposure of aquatic species to plastics, particularly smaller PS, aminated PS, and pharmaceutical complex PS.

Effects of micro-sized biodegradable plastics on Microcystis aeruginosa

Plethora of plastics are being used in current society, generating huge amounts of plastic waste. Non-biodegradability of conventional plastics is one of the main challenges to treat plastic waste. In an effort to increase the efficiency of plastic waste treatment, biodegradable plastics have gained attention. Although the use of biodegradable plastics has been increased, their potential effects on the environments are not fully elucidated yet. In this study, the impacts of micro-sized non-biodegradable plastic (i.e., polystyrene (PS)) and micro-sized biodegradable plastics (i.e., polycaprolactone (PCL) and polylactic acid (PLA)) on Microcystis aeruginosa were investigated. Regardless of microplastic (MP) types, MP treatments inhibited the growth of M. aeruginosa at the beginning (4 days) while significant dose-dependent effect was not observed in the range of 0.1 to 10 mg/L. However, after long-term exposure (12 days), micro-sized biodegradable plastics stimulated the growth of M. aeruginosa (up to 73 % increase compared to the control). The photosynthetic activity showed a similar trend to the cell growth. The MP treatments induced the production of extracellular polymeric substances (EPS). Indeed, micro-sized PCL and PLA stimulated the production of protein compounds in EPS. These might have affected the releases of chemicals from PCL and PLA, suggesting that the chemicals in biodegradable plastic leachates would promote the growth of M. aeruginosa in long-term exposure. The MP treatments also induced cyanotoxin (microcystin-LR) productions. Our results give a new insight into the cyanobacterial blooming and suggest a novel relationship between harmful algal blooms (HABs) and biodegradable plastics.

Polystyrene nanoplastics alter the ecotoxicological effects of diclofenac on freshwater microalgae Scenedesmus obliquus

Due to the escalating risk of plastic pollution, nanoplastics have attracted considerable attention in the recent past. They can co-exist and interact with other contaminants like pharmaceuticals in the aquatic environment. Therefore, it is pertinent to understand how these pollutants interact with one another in the ecosystem. The current study examined the individual and combined effects of fluorescent polystyrene nanoplastics (FNPs) and diclofenac (DCF) on Scenedesmus obliquus using a full factorial design. The toxicity of S. obliquus significantly increased in a dose-dependent manner upon exposure to pristine forms of DCF and FNPs. The major cause of individual toxicity of DCF and FNPs in S. obliquus was oxidative stress. In the combined toxicity tests when FNPs (0.01, 0.1, and 1 mg L-1) and DCF (1 mg L-1) were mixed, a synergistic effect was noted compared to the respective pristine FNPs. However, when the DCF concentration in the mixture was decreased to 0.25 mg L-1, the combined toxicity with FNPs (0.01, 0.1, and 1 mg L-1) reduced indicating an antagonistic effect. The independent action model also showed an antagonistic effect for low-dose combinations of DCF and a synergistic effect for high-dose combinations. The estimation of oxidative stress parameters, antioxidant enzyme activity, and photosynthetic pigment content in the algae further validated the cytotoxicity data. The mean hydrodynamic diameter and surface charge analyses further indicated that the colloidal stability of the FNPs in the medium was affected when they were combined with DCF. The key reason for differences in the cytotoxicity of combinations could be observed variations in the aggregation of FNPs and differential adsorption patterns of DCF on the FNPs. These factors efficiently altered cell-particle interactions in the mixture demonstrating a hormesis effect. Thus, this current study highlighted the hazardous nature of the nanoplastics and their co-exposure risks with pharmaceuticals on microalgae in freshwater environments.

Nanoplastics increase the adverse impacts of lead on the growth, morphological structure and photosynthesis of marine microalga Platymonashelgolandica

Nanoplastics and heavy metals are common pollutants in coastal environments with high concerns, but their joint ecological risk to marine primary productivity remains unclear. In this study, the effects of 7, 70, 700 μg/L lead (Pb) single exposure and in combination with 200 μg/L polystyrene nanoplastics (NPs, 70 nm) on marine microalga Platymonas helgolandica were investigated. Pb single exposure induced a dose-dependent inhibition on the growth of P. helgolandica, which was associated with the reduced photosynthetic efficiency and nutrient accumulation. Compared to Pb single exposure, the addition of NPs significantly reduced the photosynthetic efficiency and aggravated the damage to cell structure. Reduced esterase activity and increased membrane permeability also indicated that NPs exacerbated the adverse effects of Pb on P. helgolandica. Thus, co-exposure to NPs and Pb induced more severe impacts on marine microalgae, suggesting that the joint ecological risk of NPs and heavy metals to marine primary productivity merits more attention.

Combined effects of P25 TiO2 nanoparticles and disposable face mask leachate on microalgae Scenedesmus obliquus: analysing the effects of heavy metals

Disposable surgical face masks extensively used during the COVID-19 outbreak would release microplastics into the aquatic environment. The increasing usage of titanium dioxide nanoparticles (nTiO2) in various consumer items has led to its ubiquitous presence in freshwater systems. This study determined the quantity and kind of microplastics discharged from disposable surgical face masks. The mask-leached microplastics were identified to be polypropylene of varying shapes and sizes, spanning from 1 μm to 15 μm. In addition, heavy metals like Cd, Cr, and Hg leached from the face masks were quantified. Four concentrations of nTiO2, 0.5, 1, 2, and 4 mg L-1, were mixed with leached solution from the face masks to perform the combined toxicity test on freshwater algae, Scenedesmus obliquus. A dose-dependent decrease in algal cell viability was observed upon treatment with various concentrations of nTiO2 individually. The mixtures of nTiO2 and the leached solution from the face masks exhibited significantly more toxicity in the algal cells than in their pristine forms. nTiO2 promoted increased production of oxidative stress and antioxidant enzyme activities resulting in cellular damage and decreased photosynthesis. These impacts were elevated when the algal cells were treated with the binary mixture. Furthermore, the heavy metal ions leached from face masks also contributed to the toxic effects. Our study shows that the leachates from disposable surgical face masks, combined with nTiO2, may pose a severe environmental threat.

Unmasking effects of masks: Microplastics released from disposable surgical face masks induce toxic effects in microalgae Scenedesmus obliquus and Chlorella sp

During the COVID-19 pandemic billions of face masks were used since they became a necessity in everyone's lives. But these were not disposed properly and serve as one of the most significant sources of micro and nano plastics in the environment. The effects of mask leached plastics in aquatic biota remains largely unexplored. In this work, we quantified and characterized the released microplastics from the three layers of the mask. The outer layer of the face mask released more microplastics i.e., polypropylene than middle and inner layers. We investigated and compared the acute toxic effects of the released microplastics between Scenedesmus obliquus and Chlorella sp. The results showed a decrease in cell viability, photosynthetic yield, and electron transport rate in both the algal species. This was accompanied by an increase in oxidative stress markers such reactive oxygen species (ROS) and malondialdehyde (MDA) content. There was also a significant rise of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) in both the algal cells. Furthermore, morphological changes like cell aggregation and surface chemical changes in the algae were ascertained by optical microscopy and FTIR spectroscopy techniques, respectively. The tests confirmed that Scenedesmus obliquus was more sensitive than Chlorella sp. to the mask leachates. Our study clearly revealed serious environmental risk posed by the released microplastics from surgical face masks. Further work with other freshwater species is required to assess the environmental impacts of the mask leachates.

Exposure of the amphipod Hyalella azteca to microplastics. A study on subtoxic responses and particle biofragmentation

Microplastics are widespread pollutants in the environment and are considered a global pollution problem. Microplastics mostly originate from larger plastics and due to environmental conditions are undergoing constant fragmentation processes. It is important to understand the fragmentation pathways, since they play a key role in the fate of the particles, and also directly influence toxicity. Amphipods are potential inducers of plastic debris fragmentation. Here, Hyalella azteca was exposed to different concentrations (540, 2700, 5400 items/L) of 24.5 µm polystyrene microplastics (PS-MP) for 7 days. After exposure, oxidative stress, particle size reduction, and mortality were checked. No significant mortality was seen in any of the treatments, although changes were recorded in all enzymatic biomarkers analyzed. It was observed that throughout the ingestion and egestion of PS-MP by H. azteca, particles underwent intense fragmentation, presenting a final size up to 25.3% smaller than the initial size. The fragmentation over time (24, 72, 120, 168 h) was verified and the results showed a constant reduction in average particle size indicating that H. azteca are able to induce PS-MP fragmentation. This process may facilitate bioaccumulation and trophic particle transfer.

Aging process does not necessarily enhance the toxicity of polystyrene microplastics to Microcystis aeruginosa

Microplastic (MP) pollution in aquatic systems has attracted increasing attention in recent years. MPs will inevitably encounter aging process in the environment. However, research on the effects of aged MPs on freshwater ecosystems remains limited. This study compared the properties of pristine and aged polystyrene (PS) MPs of different sizes (20 nm, 200 nm, 2000 nm) and determined the effects of aging on the toxicity of PS MPs to typical freshwater cyanobacteria, Microcystis aeruginosa. Aging process induced significant changes to the properties of the MPs, especially their microstructures and surface functional groups. Aging process also influenced zeta potential, which could further affect stability and toxicity of PS MPs. After 96 h exposure, increase of algal growth and photosynthetic activity was observed in the treatment of pristine 200 nm, aged 20 nm and aged 200 nm PS MPs. In addition, pristine 20 nm, pristine 200 nm, pristine 2000 nm, aged 20 nm and aged 200 nm PS MPs were adsorbed on algal cell surface, which could influence the cell permeability. Pristine PS MPs promoted microcystin synthesis and release, which could do harm to drinking water safety and freshwater ecosystems. However, there was no significant increase in aged PS MPs treatments. Furthermore, the increased ¹³C content of algal cells in all pristine PS MPs treatments indicated that M. aeruginosa assimilated more CO₂ and generate more energy to resist the stress of pristine PS MPs when compared with aged PS MPs. These results indicate that aging process did not necessarily enhance the toxicity and biological risk of PS MPs to freshwater ecosystems. Findings of this study fill the knowledge gap in understanding the effects and risks of aged MPs on freshwater ecosystems.

Tracking nanoplastics in freshwater microcosms and their impacts to aquatic organisms

In this work, we used palladium-doped polystyrene NPLs (PS-NPLs with a primary size of 286 ± 4 nm) with an irregular surface morphology which allowed for particle tracking and evaluation of their toxicity on two primary producers (cyanobacterium, Anabaena sp. PCC7120 and green algae, Chlamydomonas reinhardtii) and one primary consumer (crustacean, Daphnia magna). the concentration range for Anabaena and C. reinhardtii was from 0.01 to 1000 mg/L and for D. magna, the range was from 7.5 to 120 mg/L.EC_50 s ranged from 49 mg NPLs/L for D. magna (48hEC_50 s) to 248 mg NPLs/L (72hEC_50 s for C. reinhardtii). PS-NPLs induced dose-dependent reactive oxygen species overproduction, membrane damage and metabolic alterations. To shed light on the environmental fate of PS-NPLs, the short-term distribution of PS-NPLs under static (using lake water and sediments) and stirring (using river water and sediments) conditions was studied at laboratory scale. The results showed that most NPLs remained in the water column over the course of 48 h. The maximum percentage of settled particles (∼ 30 %) was found under stirring conditions in comparison with the ∼ 10 % observed under static ones. Natural organic matter increased the stability of the NPLs under colloidal state while organisms favored their settlement. This study expands the current knowledge of the biological effects and fate of NPLs in freshwater environments.

Acute effects of three surface-modified nanoplastics against Microcystis aeruginosa: Growth, microcystin production, and mechanisms

As plastic pollution continues to increase and plastic waste is shredded to form smaller plastic particles, there is growing concern about the potential impact of nanoplastics (NPs) on freshwater ecosystems. In this work, the effects of three surface-modified NPs, including polystyrene (PS), PS-NH₂, and PS-COOH, on the growth, photosynthetic activity, oxidative damage, and microcystins (MCs) production/release of Microcystis aeruginosa (M. aeruginosa) were investigated. Results indicated that all three NPs significantly inhibited the growth of M. aeruginosa after a 96 h exposure, and the growth inhibition followed the order of PS-NH₂ > PS > PS-COOH (p < 0.05). Meanwhile, all three NPs at the concentration of 100 mg/L significantly increased the content of intra-MCs (115 %, 147 %, and 121 % higher than the control, respectively) and extra-MCs (142 %, 175 %, and 151 % higher than the control, respectively) after a 96 h exposure (p < 0.05). Moreover, our findings also suggested that the potential mechanisms of surface-modified PS NPs on M. aeruginosa growth and MCs production/release were associated with physical constraints, photosynthetic activity obstruct, and oxidative damage. Our findings provided direct evidence for different kinds of surface modifications of PS NPs on freshwater algae and improve the understanding of the potential risk of NPs in aquatic ecosystems.

Polystyrene nanoplastics promote the apoptosis in Caco-2 cells induced by okadaic acid more than microplastics

Microplastics (MPs) are widespread in the environment and can be ingested through food, water, and air, posing a threat to human health. In addition, MPs can have a potential combined effect with other toxic compounds. Polystyrene (PS) has been shown to enhance the cytotoxicity of okadaic acid (OA). However, it remains unclear whether this enhancement effect is related to the size of PS particles. In this study, we investigated the mechanism of the combined effect of PS microplastics (PS-MPs) or PS nanoplastics (PS-NPs) and OA on Caco-2 cells. The results indicated that PS-NPs enhanced the cytotoxicity of OA and induced endoplasmic reticulum (ER) stress-mediated apoptosis in Caco-2 cells, compared to PS-MPs. Specifically, PS-NPs and OA cause more severe oxidative stress, lactate dehydrogenase (LDH) release, and mitochondrial membrane depolarization. Furthermore, it induced intracellular calcium overload through store-operated channels (SOCs) and activated the PERK/ATF-4/CHOP pathway to cause ER stress. ER stress promoted mitochondrial damage and finally activated the caspase family to induce apoptosis. This study provided an indirect basis for the assessment of the combined toxicity of MPs or NPs with OA.

The environmental fate of nanoplastics: What we know and what we need to know about aggregation

The presence of nanoplastics in the environment has been proven. There is now an urgent need to determine how nanoplastics behave in the environment and to assess the risks they may pose. Here, we examine nanoplastic homo- and heteroaggregation, with a focus on environmentally relevant nanoplastic particle models. We made a systematic analysis of experimental studies, and ranked the environmental relevance of 377 different solution chemistries, and 163 different nanoplastic particle models. Since polymer latex spheres are not environmentally relevant (due to their monodisperse size, spherical shape, and smooth surface), their aggregation behavior in natural conditions is not transferable to nanoplastics. A few recent studies suggest that nanoplastic particle models that more closely mimic incidentally produced nanoplastics follow different homoaggregation pathways than latex sphere particle models. However, heteroaggregation of environmentally relevant nanoplastic particle models has seldom been studied. Despite this knowledge gap, the current evidence suggests that nanoplastics may be more sensitive to heteroaggregation than previously expected. We therefore provide an updated hypothesis about the likely environmental fate of nanoplastics. Our review demonstrates that it is essential to use environmentally relevant nanoplastic particle models, such as those produced with top-down methods, to avoid biased interpretations of the fate and impact of nanoplastics. Finally, it will be necessary to determine how the heteroaggregation kinetics of nanoplastics impact their settling rate to truly understand nanoplastics' fate and effect in the environment.

Roles of extracellular polymeric substances on Microcystis aeruginosa exposed to different sizes of polystyrene microplastics

Extracellular polymeric substances (EPS) are important shields for microalgae when confronting with external stresses. However, the underlying roles of EPS in the interactions between microplastics (MPs) and microalgae remain poorly understood. In this study, three sizes of polystyrene (PS) MPs (20 nm, 100 nm, and 1 μm) were chosen for evaluating the compositions of EPS, secreted by Microcystis aeruginosa during exposure. The results indicated that the EPS compositions were different when M. aeruginosa was exposed to PS MPs of different sizes. The presence of EPS is helpful for alleviating the adverse effects of PS MPs on M. aeruginosa cell growth, photosynthesis, and oxidative stress. With the exception of the shading effect, insufficient EPS cause direct adsorption of unstable 1 μm PS MPs to the algal surface, which could destroy the cell wall. In contrast, aromatic proteins and fulvic acids are representative EPS components stimulated by 100 nm PS MPs, contributing to the self-aggregation and encapsulation of algal cells and availability of nutrients for algal growth, respectively. High amounts of polysaccharides were secreted by M. aeruginosa along with humic acids during exposure to 20 nm PS MPs, both of which are crucial in the homo-aggregation of 20 nm PS MPs toward minimize its adverse effects on M. aeruginosa. Together, these findings revealed the differences in EPS under the stimulation of PS MPs of different sizes and clarified the roles of different EPS components in resisting the adverse effects of PS MPs on M. aeruginosa.

Hazard of polystyrene micro-and nanospheres to selected aquatic and terrestrial organisms

Plastics contamination in the environment is a major concern. Risk assessment of micro- and nanoplastics (MPL and NPL) poses significant challenges due to MPL and NPL heterogeneity regarding compositional polymers, particle sizes and morphologies in the environment. Yet, there exists considerable toxicological literature on commercial polystyrene (PS) micro- and nanospheres. Although such particles do not directly represent the environmental MPL and NPL, their toxicity data should be used to advance the hazard assessment of plastics. Here, toxicity data of PS micro- and nanospheres for microorganisms, aquatic and terrestrial invertebrates, fish, and higher plants was collected and analyzed. The evaluation of 294 papers revealed that aquatic invertebrates were the most studied organisms, nanosized PS was studied more often than microsized PS, acute exposures prevailed over chronic exposures, the toxicity of PS suspension additives was rarely addressed, and ∼40 % of data indicated no organismal effects of PS. Toxicity mechanisms were mainly studied in fish and nematode Caenorhabditis elegans, providing guidance for relevant studies in higher organisms. Future studies should focus on environmentally relevant plastics concentrations, wide range of organisms, co-exposures with other pollutants, and method development for plastics identification and quantification to fill the gap of bioaccumulation assessment of plastics.

Oxidative Damage in Roots of Rice (Oryza sativa L.) Seedlings Exposed to Microplastics or Combined with Cadmium

This study aimed to investigate the effect of 10-40 mg L^-1 polystyrene microplastics (PS-MPs), 0.05 mg L^-1 cadmium (Cd) and their combination on the growth and related physiological and toxicological responses in Oryza sativa L. seedling roots. Results showed that the fresh weight, dry weight and root lengths of treatments by PS-MPs, Cd single and combinative were all lower than the control, and opposite phenomenon appeared in production of superoxide radical (O₂^-.), malondialdehyde (MDA) and carbonylated protein. Superoxide dismutase (SOD) and guaiacol peroxidase (POD) activities induced by 10-40 mg L^-1 PS-MPs and combination with Cd were almost higher than those by Cd alone, expression of heat shock protein (HSP)70 and carbonylated protein slightly decreased. In compound exposure, 10-20 mg L^-1 PS-MPs alleviated Cd damage and promoted root growth by increasing SOD and POD activities, but 40 mg L^-1 PS-MPs accelerated the accumulation of Cd, MDA, and O₂^-., which was responsible for decreasing root biomass and the aggravating necrosis of root tip cells.

Nanoplastics: Detection and impacts in aquatic environments - A review

The rise in the global production of plastics has led to severe concerns about the impacts of plastics in aquatic environments. Although plastic materials degrade over extreme long periods, they can be broken down through physical, chemical, and/or biological processes to form microplastics (MPs), defined here as particles between 1 μm and 5 mm in size, and later to form nanoplastics (NPls), defined as particles <1 μm in size. We know little about the abundance and effects of NPls, even though a lot of research has been conducted on the ecotoxicological impacts of MPs on both aquatic biota. Nevertheless, there is evidence that NPls can both bypass the cell membranes of microorganisms and bioaccumulate in the tissues and organs of higher organisms. This review analyzes 150 publications collected by searching through the databases Web of Science, SCOPUS, and Google Scholar using keywords such as nanoplastics*, aquatic*, detection*, toxic*, biofilm*, formation*, and extracellular polymeric substance* as singular or plural combinations. We highlight and critically synthesize current studies on the formation and degradation of NPls, NPls' interactions with aquatic biota and biofilm communities, and methods of detection. One reason for the missing data and studies in this area of research is the lack of a protocol for the detection of, and suitable methods for the characterization of, NPls in the field. Our primary aim is to identify gaps in knowledge throughout the review and define future directions of research to address the impacts of NPls in aquatic environments. The development of consistent and standardized sets of procedures would address the gaps in knowledge regarding the formation and degradation of NPls as well as sampling and characterizing natural NPls needed to observe the full extent of NPls on aquatic biota and biofilm communities.

The interaction of micro/nano plastics and the environment: Effects of ecological corona on the toxicity to aquatic organisms

Concerns about the micro/nano plastics (MNPs) exposure risks have risen in recent years. The ecological corona (EC), which is generated by the interaction between MNPs and environmental substances, has a significant impact on their environmental fate and ecological risks. As the largest sink of MNPs, the aquatic environment is of great significance for understanding the environmental behaviour of MNPs. Transmission Electron Microscope (TME), Fourier Transform Infra-Red (FTIR), Scanning Electron Microscope (SEM), Dynamic Light Scattering (DLS) and other analytical methods have been used as effective methods to analyse the formation process of EC and detect the existing EC directly or indirectly on the surface of MNPs. The physicochemical properties of MNPs, complex aquatic environments and ageing time have been identified as the key factors affecting EC formation in aquatic environments. Moreover, the EC absorbed on MNPs significantly changed their environmental behaviour and toxicity to aquatic organisms. This review gives a full understanding of the EC formation progress on the surface of MNPs and different analytical methods for EC have been summarised which can further assist the ecological risk assessment of MNPs in the aquatic environment.

Odor-producing response pattern by four typical freshwater algae under stress: Acute microplastic exposure as an example

Algae-induced odor problems in water have been repeatedly occurred concerns for drinking water quality. However, present researches mostly focus on the odor-producing pattern of algae in normal growth, and there is scarce discussion on those under stress. Microplastics (MPs) pollution have been global concern for their negative ecological impacts and frequently co-occurs with odor-producing algal bloom in freshwaters. Thus, this study aimed to elucidate the effects and mechanisms of MPs as an environmental stress on algal odorant production for good illustration of odor-producing response pattern under stress. Variation in MP size (polystyrene microspheres; 100 nm, 1000 nm and 10 μm) had significant effects on odorant formation (β-cycloidal, 2-methylisopropanol, 2,4-heptandienal and 2,4-decadienal) by four freshwater algae (Microcystis aeruginosa, Pseudanabaena sp., Cyclotella meneghiniana and Melosira varians). The size ratio of MPs over cells (SRMC) was proposed to categorize the size-ratio dependent effects on the algal odorant production. Interestingly, when SRMC was in the range of 0.1-1, there were always promoting effects; when SRMC < 0.1 or SRMC > 1, there exhibited inhibiting effects, and the inhibiting effects of SRMC < 0.1 were far more severe than those of SRMC > 1. The promotion on odorant production in the SRMC range of 0.1-1 was mainly attributed to the increase in cellular yield, which was related to the increased odorant precursors derived from the oxidation products of reactive oxygen species (ROS). Alternatively, the inhibition of odorant production caused by MPs with SRMC < 0.1 was the results of simultaneously inhibiting cellular density and cellular yield, which might be attributed to the cellular internalization of MPs, inducing the extensive toxic effects. This study illustrated the possibilities of MPs in impairing the esthetics of the source water and provided guidance for the future algal odor issues under stress.

Toxicity mechanism of cerium oxide nanoparticles on cyanobacteria Microcystis aeruginosa and their ecological risks

The extensive application of cerium oxide nanoparticles (CeO₂ NPs), a type of rare earth nanomaterial, led to pollution into aquatic environments. Cyanobacteria, a significant component of freshwater ecosystems, can interact with CeO₂ NPs. However, little attention has been paid as to whether CeO₂ NPs will have adverse effects on cyanobacteria. In the present study, Microcystis aeruginosa (FACHB-942) was exposed to different concentrations (0, 1, 10, and 50 mg/L) of CeO₂ NPs. Results showed 50 mg/L CeO₂ NPs inhibited algal growth (11.48% ± 5.76%), suppressed photosynthesis and induced the generation of reactive oxygen species (ROS) after 72 h exposure. The toxicity mechanism is the adsorption of CeO₂ NPs on cell surface, the ROS formation and the intracellular Ce. Additionally, the intracellular microcystins (MCs) content was significantly induced (11.84% ± 1.47%) by 50 mg/L CeO₂ NPs, while no significance was found in 1 and 10 mg/L CeO₂ NP treatments. Results indicated high concentrations of CeO₂ NPs could be toxic to algae through the adverse effects on algal growth and photosynthesis. Moreover, the promoted MCs production could also pose a threat to freshwater ecosystems due to the possible release into the environment.