Heterogeneous aggregation between microplastics and microalgae: May provide new insights for microplastics removal

Dual impacts of elevated pCO2 on the ecological effects induced by microplastics and nanoplastics: A study with Chlamydomonas reinhardtii

Aquatic organisms face increased complexity and severity when exposed to the combined stressors of climate change and micro- and nanoplastics (MNPs), as opposed to facing these stressors individually. This study examined the effects and underlying mechanisms of elevated pCO2, which leads to freshwater acidification, as well as amino-modified polystyrene MNPs (PS-NH2 MNPs) of varying sizes (5 μm, 300 nm, 80 nm), on Chlamydomonas reinhardtii under both individual and combined conditions. The results showed a size-dependent toxicity of PS MNPs, with the smaller nanoparticles (80 nm) causing greater toxic inhibition than the larger microparticles (5 μm and 300 nm), primarily attributed to oxidative stress-related cellular damage. In contrast, freshwater acidification (FA) appeared to promote the growth of C. reinhardtii, possibly by upregulating transcripts associated with energy metabolism. However, when C. reinhardtii was exposed to both FA and MNPs simultaneously, distinct toxic effects were observed. The co-exposure to FA and NPs induced the most severe oxidative stress, implying the greatest energetic cost. This stress resulted in the downregulation of pathways involved in fatty acid biosynthesis and protein folding, ultimately causing significant damage to cellular structure and function. The increased energy from the upregulation of the TCA cycle was mainly allocated for DNA damage repair and cell division, which induced an energy deficit necessary for stress resistance. In contrast, during co-exposure to FA and MPs, energy was redirected towards DNA replication and the synthesis of anti-stress substances, facilitating recovery and promoting growth. Our study highlighted the decisive influence of climate change and particle size in assessing the ecological effects and risks associated with MNPs.

Polyethylene microplastics decrease the bioaccumulation and toxicity of picoxystrobin and azoxystrobin to microalgae Scenedesmus obliquus

Fungicide residues can interact with microplastics (MPs) in the aquatic environment leading to mixed toxicity on phytoplankton. The investigation of biological effects obtained from combined fungicide and MPs is essential for proper evaluation of the ecological risks. Until now, the mechanisms that how polyethylene (PE) MPs altered the toxicity of picoxystrobin and azoxystrobin on microalgae Scenedesmus obliquus was unknown. Here, the impacts of PE-MPs on freely dissolved concentrations (Cfree) of the 2 fungicides and their toxicity to microalgae growth were assessed after 96 h exposure. We found that the presence of PE-MPs reduced the bioaccumulation of picoxystrobin and azoxystrobin in microalgae through decreasing the fungicide Cfree. Furthermore, inhibition effects on microalgae growth and chlorophyll generation was alleviated significantly in the combination of fungicide and PE-MPs compared with the fungicide alone. Specifically, 400 mg/L of 25 μm PE induced more profound influences than other treatments in terms of decreasing Cfree, promoting growth rate, and increasing chlorophyll content that might be attributed to its higher adsorption capacity for the fungicides. Our results demonstrated the antagonism between the fungicides and PE-MPs, clarifying that PE-MPs functioned in lowering the bioavailability and acte toxicity of the 2 strobilurin fungcides to microalgae via physical adsorption especially under the small size and high level of PE-MPs. This study provides evidences that the existence of MPs is capable of influencing the toxicological behavior of fungicides in the environment, and can be a starting point for more sophisticated mechanism investigation of joint toxicity for fungicides and MPs.

Spotlight on the long-term effects of micro/nanoplastics exposure on Spirulina platensis: Algal cells, extracellular polymeric substances, and phycocyanin

Spirulina platensis (SP) provides humans with proteins and natural pigments. The effects of micro/nanoplastics (MNPs) on SP are of great interest. We focused on the effects of high concentrations (100-300 mg/L) of polystyrene MNPs on SP for 50 days. MNPs caused growth retardation, a decrease in peak concentration of algal cells, the emergence of surface cracks and pores, and stimulated the secretion of extracellular polymeric substances that promoted heterogeneous aggregation of SP. During the first 35 days, there were significant differences between the exposure groups in the phycocyanin concentration, yield and purity and the ratio of phycocyanin to phycobiliprotein, with the higher MNPs concentration resulting in lower values, whereas on day 50 there were no statistically significant differences in any of these metrics between the control or exposure groups. This study enriches the knowledge about the long-term effects of MNPs on SP for microalgae culture and food industry.

Impact of Heterosigma akashiwo on the environmental behavior of microplastics: Aggregation, sinking, and resuspension dynamics

Aggregation processes of microalgae have significant effects on the vertical distribution of microplastics (MPs) in the marine environment. This study explored how the harmful microalga Heterosigma akashiwo affects the aggregation and sinking characteristics of four types of MPs: low and high-density polyethylene (PE) spheres, and small and large polypropylene (PP) fragments. The aggregation of MPs was primarily driven by extracellular polymeric substances (EPS) rather than direct attachment to the cells, contributing to their sinking. The sinking of low-density PE spheres followed a logistic function, saturating at 28 % with a half-saturation time of 9 days. In contrast, small PP fragments sank minimally (under 2 %) and large PP fragments showed almost no sinking, indicating the varying impacts of MP density and size. The sinking velocity of the MP aggregates was significantly lower for low-density PE spheres (0.63 mm∙s-1) than for high-density PE spheres (0.81 mm∙s-1), despite no significant differences in aggregate size or MP particle number. This result may suggest that low-density MPs could potentially affect marine carbon cycle. Furthermore, no clear evidence was found for the resuspension of the settled aggregates due to bacterial decomposition under dark and cold conditions. As the first experimental study to explore the aggregation, sinking, and resuspension of different MPs in the presence of H. akashiwo, these findings, when integrated with field observations and modeling studies, provide valuable insights for predicting MP distribution in marine environments.

When microplastics meet microalgae: Unveiling the dynamic formation of aggregates and their impact on toxicity and environmental health

Microplastics (MPs) commonly coexist with microalgae in aquatic environments, can heteroaggregate during their interaction, and potentially affect the migration and impacts of MPs in aquatic environments. The hetero-aggregation may also influence the fate of other pollutants through MPs' adsorption or alter their aquatic toxicity. Here, we explored the hetero-aggregation process and its key driving mechanism that occurred between green microalga Chlorella vulgaris (with a cell size of 2-10 μm) and two types of MPs (polystyrene and polylactide, 613 μm). Furthermore, we investigated the environmental impacts of the microplastics-microalgae aggregates (MPs-microalgae aggregates) by comparing their adsorption of Cu(II) with that of pristine MPs and evaluating the effects of hetero-aggregation on MPs aging and their toxicity to microalgae. Our results indicated that microalgal colonization occurred on the surface of MPs, possibly through electrostatic interactions, hole-filling, hydrophilic interactions, and algae-bacteria symbiosis. The hetero-aggregation led to a stronger Cu(II) adsorption by MPs-microalgae aggregates than pristine MPs due to electrostatic interactions, coordination, complexation, and ion exchange. Exposure to either MPs (pristine or aged) or Cu(II) inhibited the cell growth of C. vulgaris, while the integrated biomarker response (IBR) showed more pronounced inhibitory effects resulting from aged MPs compared to pristine MPs and an antagonistic effect on microalgae was caused by the co-exposure to MPs and Cu(II). These findings suggest that the hetero-aggregation of MPs and microalgae may alter their environmental fates and co-pollutant toxicity.

Removal of microplastics by algal biomass from aqueous solutions: performance, optimization, and modeling

Microplastics (MPs) are emerging pollutants that pose significant risks to ecosystems due to their inherent toxicity, capacity to accumulate various pollutants, and potential for synergistic impacts. Given these concerns, the focus of this research is on the critical need for effective MPs removal from aquatic environments. Using BBD method, this study aimed to identify the key parameters affecting the removal of MPs by algal biomass from aqueous solutions. The investigation specifically analyzed the effects of varying initial PS concentrations (100 to 900 mg/L), pH values (4 to 10), reaction durations (20 to 40 min), and C. vulgaris dosages (50 to 400 mg/L). Data analysis indicated that QM best described the experimental findings, leading to the identification of optimal conditions for PS removal: a pH of 7.5, a reaction time of 31.90 min, a C. vulgaris dosage of 274.05 mg/L, and a PS level of 789.37 mg/L. Under these conditions, the study achieved a maximum removal efficiency of 73.01% for PS. These outcomes demonstrate the significant potential of C. vulgaris in efficiently removing PS from water. Furthermore, using algae as a green, eco-friendly alternative to conventional chemical coagulants offers a practical and sustainable approach to addressing MPs pollution in our water systems.

Perfluorobutanoic acid weakens the heterogeneous aggregation of microplastics and microalgae: Perspective from physicochemical properties, extracellular polymeric substances secretion and DLVO theory

Microplastics (MPs) and per- and poly-fluoroalkyl substances extensively coexist in aquatic environments and potentially endanger organisms. Microalgae may decrease the effective concentration of pollutants via hetero-aggregation with MPs and adsorption of emerging contaminants. However, the potential influence of coexistent pollutants on hetero-aggregation of MPs and microalgae remains unknown. This study investigated the hetero-aggregation process involving different sizes of polystyrene (PS, 3.0 and 50.0 μm) with Chlorella sorokiniana (C. sorokiniana) in the presence or absence of perfluorobutanoic acid (PFBA) along settling experiments, scanning electron microscope, and Derjaguin-Landau-Verwey-Overbeek (DLVO) model. We found that the hetero-aggregation between C. sorokiniana and 3 μm PS was more pronounced than with 50 μm PS, while PFBA inhibited this process. ΔOD1 values (reflected hetero-aggregation level) for 3PS-cells and 50PS-cells were 0.189 and 0.087, respectively, and PFBA decreased these values to 0.134 and 0.033. Furthermore, extracellular polymeric substances, known as inducer of hetero-aggregation, increased by 14.33% when exposed to 3 μm PS alone, whereas the co-exposure group showed a decrease of 4.52% compared to 3PS-cells group. PFBA also significantly decreased the protein/polysaccharide ratios in both MPs sizes, reducing hetero-aggregation. DLVO theory revealed that microalgae lowered the energy barrier significantly, while PFBA elevated it, indicating that hetero-aggregation was inhibited by PFBA. This study provides new perspectives for pollutant removal and toxicity variation in aquatic environments.

Evaluating physiological responses of microalgae towards environmentally coexisting microplastics: A meta-analysis

Microplastics (MPs) are abundantly present in aquatic environments, where the phytoplankton-microalgae, are now inevitably bound to a long-term coexistence with them. While numerous studies have focused on the toxicological effects of high-concentration MPs exposure, there remains controversy over whether and how MPs affect microalgae at environmentally relevant concentrations. This study aims to draw conclusions that narrow the gap from 52 studies with varying results. Overall, MPs can inhibit growth and photosynthesis, induce oxidative damage, from which microalgae can recover after an appropriate period. Cyanobacteria exhibit greater vulnerability than chlorophyta. The relative size of MPs to algal cells potentially governs their coexistence behavior, thereby altering the mechanisms of impact. Pristine MPs may increase the production of extracellular polymeric substances (EPS) and microcystins (MCs), while aged MPs have the opposite effect. Additionally, relevant factors are systematically discussed, offering insights for future research.

New Horizons in Micro/Nanoplastic-Induced Oxidative Stress: Overlooked Free Radical Contributions and Microbial Metabolic Dysregulations in Anaerobic Digestion

Excessive production of reactive oxygen species (ROS) induced by micro/nanoplastics (MPs/NPs) is highly toxic to microbes. However, the mechanisms underlying ROS generation and metabolic regulation within anaerobic guilds remain poorly understood. In this study, we investigated the effects of environmentally relevant levels of polypropylene (PP)-MPs/NPs on oxidative stress and microbial ecology during anaerobic digestion (AD). Electron paramagnetic resonance spectroscopy revealed that PP-MPs/NPs elevated the concentrations of environmentally persistent free radicals (EPFRs) and derived hydroxyl radicals (•OH). EPFRs were identified as the primary contributors to •OH generation, as evidenced by a high Spearman correlation coefficient (r = 0.884, p < 0.001) and free radical-quenching studies. The formation of •OH enhanced ROS production by 86.2-100.9%, resulting in decreased cellular viability and methane production (by 37.5-50.5%) at 100 mg/g TS PP-MPs/NPs. Genome-centric metagenomic and metatranscriptomic analyses suggested that PP-MPs/NPs induced the reassembly of community structures, re-evolution of functional traits, and remodeling of interspecies interactions. Specifically, PP-MPs/NPs induced a shift in methanogen consortia from hydrogenotrophic Methanofollis sp. to acetoclastic and hydrogenotrophic Methanothrix soehngenii, primarily because of the latter's diverse ingestion patterns, electron bifurcation complexes, and ROS-scavenging abilities. Downregulation of genes associated with antioxidative defense systems (i.e., sodN, katA, and osmC) and ROS-driven redox signal transduction pathways (c-di-AMP and phosphorylation signaling pathways) provided insights into the mechanisms underlying ROS-induced microbial metabolic dysregulation. Our findings enhance the understanding of microbial ecological and metabolic traits under MPs/NPs stressors, facilitating the control of MPs/NPs toxicity and the stabilization of AD processes.

Evaluation of the migration behaviour of microplastics as emerging pollutants in freshwater environments

Microplastics, as an emerging pollutant, are widely distributed in freshwater environments such as rivers and lakes, posing immeasurable potential risks to aquatic ecosystems and human health. The migration behaviour of microplastics can exacerbate the degree or scope of risk. A complete understanding of the migration behaviour of microplastics in freshwater environments, such as rivers and lakes, can help assess the state of occurrence and environmental risk of microplastics and provide a theoretical basis for microplastic pollution control. Firstly, this review presents the hazards of microplastics in freshwater environments and the current research focus. Then, this review systematically describes the migration behaviours of microplastics, such as aggregation, horizontal transport, sedimentation, infiltration, stranding, resuspension, bed load, and the affecting factors. These migration behaviours are influenced by the nature of the microplastics themselves (shape, size, density, surface modifications, ageing), environmental conditions (ionic strength, cation type, pH, co-existing pollutants, rainfall, flow regime), biology (vegetation, microbes, fish), etc. They can occur cyclically or can end spontaneously. Finally, an outlook for future research is given.

Combined effects of microplastics and pharmaceutical and personal care products on algae: A critical review

Microplastics (MPs) and pharmaceuticals and personal care products (PPCPs) are ubiquitous in aquatic environments. Algae play an important role in aquatic environments. Thus, it is important to study the response of algae to combined exposure of MPs and PPCPs. Here, we review the effects of MPs and PPCPs on algae. First, the individual effects of MPs and PPCPs on algae were summarized. Second, the combined effects of MPs and PPCPs on algae were systematically analyzed. (1) Antagonism: ① when the MPs are too large to enter the algal cells, the adsorption of PPCPs onto MPs results in decreased the contact of MPs and PPCPs with algae; ② PPCPs and MPs have opposing actions on the same biological target; ③ MPs increase the activity of metabolic enzymes in algae, thus promoting the PPCP degradation. (2) Synergy: ① when the MPs are small enough to enter algal cells, the adsorption of PPCPs on MPs promotes the entry of PPCPs; ② when MPs are negatively charged, the adsorption of positively charged PPCPs by MPs decreases the electrostatic repulsion, increasing the interaction between algae and MPs; ③ complementary modes of action between MPs and PPCPs show combined effects on the same biological target. Third, the relative importance of the factors that impact the combined effects are evaluated using the random forest model decreased in the following order: PPCP types > algal species > MP size > MP concentration > MP types > exposure time. Finally, future directions for the combined effects of MPs and PPCPs are proposed, which will facilitate a better understanding of the environmental fate and risks of both MPs and PPCPs.

Enhancing aggregation of microalgae on polystyrene microplastics by high light: Processes, drivers, and environmental risk assessment

Microplastics (MPs) are emerging pollutants, causing potential threats to aquatic ecosystems and serious concern in aggregating with microalgae (critical primary producers). When entering water bodies, MPs are expected to sink below the water surface and disperse into varying water compartments with different light intensities. However, how light influences the aggregation processes of algal cells onto MPs and the associated molecular coupling mechanisms and derivative risks remain poorly understood. Herein, we investigated the aggregation behavior between polystyrene microplastics (mPS, 10 µm) and Chlorella pyrenoidosa under low (LL, 15 μmol·m-2·s-1), normal (NL, 55 μmol·m-2·s-1), and high light (HL, 150 μmol·m-2·s-1) conditions from integrated in vivo and in silico assays. The results indicated that under LL, the mPS particles primarily existed independently, whereas under NL and HL, C. pyrenoidosa tightly bounded to mPS by secreting more protein-rich extracellular polymeric substances. Infrared spectroscopy analysis and density functional theory calculation revealed that the aggregation formation was driven by non-covalent interaction involving van der Waals force and hydrogen bond. These processes subsequently enhanced the deposition and adherence capacity of mPS and relieved its phytotoxicity. Overall, our findings advance the practical and theoretical understanding of the ecological impacts of MPs in complex aquatic environments.

Micro/nano-plastics and microalgae in aquatic environment: Influence factor, interaction, and molecular mechanisms

Micro/nano-plastics, as emerging persistent pollutant, are frequently detected in aquatic environments together with other environmental pollutants. Microalgae are the major primary producers and bear an important responsibility for maintaining the balance of aquatic ecosystems. Numerous studies have been conducted on the influence of micro/nano-plastics on the growth, photosynthesis, oxidative stress, gene expression and metabolites of microalgae in laboratory studies. However, it is difficult to comprehensively evaluate the toxic effects of micro/nano-plastics on microalgae due to different experimental designs. Moreover, there is a lack of effective analysis of the aforementioned multi-omics data and reports on shared biological patterns. Therefore, the purpose of this review is to compare the acute, chronic, pulsed, and combined effect of micro/nano-plastics on microalgae and explore hidden rules in the molecular mechanisms of the interaction between them. Results showed that the effect of micro/nano-plastics on microalgae was related to exposure mode, exposure duration, exposure size, concentration, and type of micro/nano-plastics. Meanwhile, the phenomenon of poisoning and detoxification between micro/nano-plastics and microalgae was found. The inhibitory mechanism of micro/nano-plastics on algal growth was due to the micro/nano-plastics affected the photosynthesis, oxidative phosphorylation, and ribosome pathways of algal cells. This brought the disruption of the functions of chloroplasts, mitochondria, and ribosome, as well as impacted on energy metabolism and translation pathways, eventually leading to impairment of cell function. Besides, algae resisted this inhibitory effect by regulating the alanine, aspartate, and glutamate metabolism and purine metabolism pathways, thereby increasing the chlorophyll synthesis, inhibiting the increase of reactive oxygen species, delaying the process of lipid peroxidation, balancing the osmotic pressure of cell membrane.

Impacts of microplastic and seawater acidification on unicellular red algae: Growth response, photosynthesis, antioxidant enzymes, and extracellular polymer substances

Microplastics (MPs) pollution and seawater acidification have increasingly become huge threats to the ocean ecosystem. Their impacts on microalgae are of great importance, since microalgae are the main primary producers and play a critical role in marine ecosystems. However, the impact of microplastics and acidification on unicellular red algae, which have a unique phycobiliprotein antenna system, remains unclear. Therefore, the impacts of polystyrene-MPs alone and the combined effects of MPs and seawater acidification on the typical unicellular marine red algae Porphyridium purpureum were investigated in the current study. The result showed that, under normal seawater condition, microalgae densities were increased by 17.75-41.67 % compared to the control when microalgae were exposed to small-sized MPs (0.1 μm) at concentrations of 5-100 mg L-1. In addition, the photosystem II and antioxidant enzyme system were not subjected to negative effects. The large-sized MPs (1 μm) boosted microalgae growth at a low concentration of MPs (5 mg L-1). However, it was observed that microalgae growth was significantly inhibited when MPs concentration increased up to 50 and 100 mg L-1, accompanied by the remarkably reduced Fv/Fm value and the elevated levels of SOD, CAT enzymes, phycoerythrin (PE), and extracellular polysaccharide (EPS). Compared to the normal seawater condition, microalgae densities were enhanced by 52.11-332.56 % under seawater acidification, depending on MPs sizes and concentrations, due to the formed CO2-enrichment condition and appropriate pH range. PE content in microalgal cells was significantly enhanced, but SOD and CAT activities as well as EPS content markedly decreased under acidification conditions. Overall, the impacts of seawater acidification were more pronounced than MPs impacts on microalgae growth and physiological responses. These findings will contribute to a substantial understanding of the effects of MPs on marine unicellular red microalgae, especially in future seawater acidification scenarios.

Recent progress on the toxic effects of microplastics on Chlorella sp. in aquatic environments

Microplastics (MPs) are emerging contaminants that have harmful effects on ecosystems. Microalgae are important primary producers in aquatic environments, providing nutrients for various organisms. These microorganisms may be affected by MPs. Therefore, it is important to investigate the toxicity aspects of different MPs on Chlorella species. It can be seen that the BG-11 culture medium was the most commonly used medium in 40 % of the studies for the growth of Chlorella sp. Chlorella sp. grows optimally at a temperature of 25 °C and a pH of 7. Most studies show that Chlorella sp. can grow in the range of 3000-6000 lux. Moreover, various techniques have been used to analyze the morphological properties of MPs in different studies. These techniques included scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and transmission electron microscopy (TEM), which were used in 65 %, 35 %, and 27 % of the studies, respectively. 53 % of the research has focused on the toxic effects of PS on Chlorella sp. Findings show that 41 % of the studies investigated MPs concentrations in the range of 10-100 mg/L, followed by 32 % of the studies in the range of 100-1000 mg/L. The studies found that MPs were used in a spherical shape in 45 % of the cases. The enzymes most affected by MPs were superoxide dismutase (SOD) and Malondialdehyde (MDA), accounting for 48 % of the studies each. Additionally, exposure to MPs increased the activity of enzymes such as SOD and MDA. In general, it can be concluded that MPs had a relatively high negative effect on the growth of Chlorella sp.

Reactive oxygen species mediated extracellular polymeric substances production assisting the recovery of Thalassiosira pseudonana from polystyrene micro and nanoplastics exposure

As emerging pollutants in the aquatic environments, micro- and nano-plastics (MNPs) aroused widespread environmental concerns for their potential threats to the ecological health. Previous research has proved that microalgae growth could recover from the MNPs toxicities, in which the extracellular polymeric substances (EPS) might play the key role. In order to comprehensively investigate the recovery process of microalgae from MNPs stress and the effecting mechanisms of EPS therein, this study conducted a series of experiments by employing two sizes (0.1 and 1 μm) of polystyrene (PS) MNPs and the marine model diatom Thalassiosira pseudonana during 14 days. The results indicated: the pigments accumulations and photosynthetic recovery of T. pseudonana under MPs exposure showed in the early stage (4-5 days), while the elevation of reactive oxygen species (ROS) and EPS contents lasted longer time period (7-8 days). EPS was aggregated with MNPs particles and microalgal cells, corresponding to the increased settlement rates. More increase of soluble (SL)-EPS contents was found than bound (B)-EPS under MNPs exposure, in which the increase of the protein proportion and humic acid-like substances in SL-EPS was found, thus facilitating aggregates formation. ROS was the signaling molecule mediating the overproduction of EPS. The transcriptional results further proved the enhanced EPS biosynthesis on the molecular level. Therefore, this study elucidated the recovery pattern of microalgae from MNPs stress and linked "ROS-EPS production changes-aggregation formation" together during the growth recovery process, with important scientific and environmental significance.

Optimization of microplastic removal based on the complementarity of constructed wetland and microalgal-based system

As one of the emblematic emerging contaminants, microplastics (MPs) have aroused great public concern. Nevertheless, the global community still insufficiently acknowledges the ecological health risks and resolution strategies of MP pollution. As the nature-based biotechnologies, the constructed wetland (CW) and microalgal-based system (MBS) have been applied in exploring the removal of MPs recently. This review separately presents the removal research (mechanism, interactions, implications, and technical defects) of MPs by a single method of CWs or MBS. But one thing with certitude is that the exclusive usage of these techniques to combat MPs has non-negligible and formidable challenges. The negative impacts of MP accumulation on CWs involve toxicity to macrophytes, substrates blocking, and nitrogen-removing performance inhibition. While MPs restrict MBS practical application by making troubles for separation difficulties of microalgal-based aggregations from effluent. Hence the combined strategy of microalgal-assisted CWs is proposed based on the complementarity of biotechnologies, in an attempt to expand the removing size range of MPs, create more biodegradable conditions and improve the effluent quality. Our work evaluates and forecasts the potential of integrating combination for strengthening micro-polluted wastewater treatment, completing the synergistic removal of MP-based co-pollutants and achieving long-term stability and sustainability, which is expected to provide new insights into MP pollution regulation and control.

Integrating transcriptomics and biochemical analysis to understand the interactive mechanisms of the coexisting exposure of nanoplastics and erythromycin on Chlorella pyrenoidosa

Nanoplastics and antibiotics frequently co-exist in water polluted by algal blooms, but little information is available about interaction between substances. Erythromycin, as a representative of antibiotics, has been frequently detected in aquatic environments. This investigation attempted to reveal the interaction mechanism of nanoplastics and erythromycin on Chlorella pyrenoidosa. Results demonstrated that the joint toxicity of erythromycin and nanoplastics was dynamic and depended on nanoplastics concentration. Antagonistic effects of 1/2 or 1 EC50 erythromycin and nanoplastic concentration (10 mg/L) on the growth of C. pyrenoidosa was observed. The joint toxicity of 1/2 or 1 EC50 erythromycin and nanoplastic concentration (50 mg/L) was initially synergistic during 24-48 h and then turned to antagonistic during 72-96 h. Consequently, antagonistic effect was the endpoint for joint toxicity. Integration of transcriptomics and physiological biochemical analysis indicated that the co-existence of nanoplastics and erythromycin affected the signal transduction and molecular transport of algal cell membrane, induced intracellular oxidative stress, and hindered photosynthetic efficiency. Overall, this study provided a theoretical basis for evaluating the interactive mechanisms of nanoplastics and antibiotics.

Using Spirulina platensis as a natural biocoagulant for polystyrene removal from aqueous medium: performance, optimization, and modeling

Microplastics (MPs) are newly recognized contaminants that result from the breakdown of plastics released into aquatic environments. This study focuses on the elimination of polystyrene (PS) using S. platensis, a natural biocoagulant, from aqueous solutions. The research investigated several crucial variables, including the initial level of PS ranging from 100 to 900 mg L-1, pH levels from 4 to 10, the contact time of 20-40 min, and doses of S. platensis ranging from 50 to 250 mg L-1. The analysis of the data revealed that the quadratic model offered the best fit for the experimental results. In the present study, we utilized S. platensis as a novel natural biocoagulant to effectively eliminate PS from aqueous solutions. Process optimization was performed using a Box-Behnken design (BBD). The best-fitting model for the data was the quadratic model. The results displayed that the highest elimination of PS (81%) was occurred at a pH of 4, with a contact time of 30 min, a dose of S. platensis at 250 mg L-1, and a PS concentration of 500 mg L-1. These findings show that S. platensis has a significant effect on removing PS from the aquatic environment. Algae can serve as a convenient and eco-friendly method, replacing chemical coagulants, to effectively remove MPs from the aquatic environment.