Combined toxic effects of perfluorooctanoic acid and microcystin-LR on submerged macrophytes and biofilms

Phytoremediation of perfluoroalkyl and polyfluoroalkyl substances (PFAS): Insights on plant uptake, omics analysis, contaminant detection and biomass disposal

The unique properties of per- and polyfluoroalkyl substances (PFAS) have driven their pervasive use in different industrial applications, leading to substantial environmental pollution and raising critical concerns about the long-term impacts on ecosystem and human health. To tackle the global challenge of PFAS contamination, there is an urgent need for sustainable and efficient remediation strategies. Phytoremediation has emerged as a promising eco-friendly approach with the potential to mitigate the spread of these persistent contaminants. However, addressing this complex issue requires interdisciplinary cutting-edge research to develop comprehensive and scalable solutions for effective PFAS management. This review highlights recent advancements in the detection, quantification, and monitoring of PFAS uptake by plants, providing a detailed description of PFAS accumulation in several plant species. Besides, the physiological and molecular responses elicited by these pollutants are described. Leveraging omic technologies, including genomics, transcriptomics, and proteomics, provides unprecedented insights into the plant-PFAS interaction. Novel approaches based on artificial intelligence to predict this interaction and up to date disposal and valorization methods for PFAS-contaminated plant biomass, are discussed here. This review offers an interdisciplinary approach to explore what has been discovered so far about PFAS phytoremediation, covering the entire process from contaminant uptake to sustainable disposal, providing a roadmap for future research.

Calcium peroxide treatment of cyanobacterial blooms: Ecological safety assessment on submerged macrophyte Vallisneria natans

The outbreak of cyanobacterial blooms poses an increasingly serious ecological challenge. Our previous study found that calcium peroxide (CaO2) has a high inhibitory effect on cyanobacteria, along with a practical application potential in cyanobacteria-dominated lakes. In order to explore the sensitivity of aquatic ecosystems to CaO2 treatment, we conducted this study to elucidate the ecological impact of CaO2 on Vallisneria natans (V. natans) when inhibiting cyanobacterial bloom. This study firstly optimized the performance of CaO2 by preparing alginate-encapsulated CaO₂ (CaO2-Bead), which prolonged the release time of reactive oxygen species (ROS). Subsequently, the sensitivity of submerged plant V. natans and its biofilm was explored. After adding 100 mg L-1 CaO2-Bead, significant inhibitory effect on cyanobacteria was found, and the inhibition rate of cyanobacterial biomass reached 93.5 %. More importantly, CaO2-Bead can alleviate the oxidative stress, effects of Extracellular Polymeric Substances (EPS) structure and microbial community on the surface of leaf biofilm caused by cyanobacteria. At the same time, it decreased the damage of photosynthesis, mitochondrial transport, plant-pathogen interaction, mitogen-activated protein kinases (MAPK), and ubiquitin-mediated protein degradation in pathways in V. natans under inhibition of cyanobacteria. Our research provides a theoretical basis for evaluating the safety of CaO2 on the aquatic environment when treating cyanobacterial blooms.

Uncovering toxin production and molecular-level responses in Microcystis aeruginosa exposed to the flame retardant Tetrabromobisphenol A

Tetrabromobisphenol A (TBBPA) poses significant ecological risks owing to its toxicity; however, its specific effects on toxin-producing cyanobacteria in aquatic environments remain poorly understood. This study systematically investigated the effects of TBBPA at concentrations ranging from 100 ng/L to 100 mg/L on Microcystis aeruginosa (M. aeruginosa) by examining growth, photosynthesis, toxin production, antioxidant responses, and molecular-level changes. The results indicated that low levels of TBBPA (0.1-1000 μg/L) induced stimulatory effects on the growth and microcystin-leucine-arginine (MC-LR) production of M. aeruginosa. Metabolomic analysis revealed that low levels of TBBPA significantly upregulated metabolites associated with energy metabolism, xenobiotic biodegradation, oxidative stress responses, and protein biosynthesis in M. aeruginosa, potentially contributing to the observed hormetic effect. Conversely, higher doses (40-100 mg/L) inhibited growth and significantly increased MC-LR release by compromising cellular structural integrity. Proteomic analysis revealed that toxic levels of TBBPA significantly affected the expression of proteins associated with energy harvesting and utilization. Specifically, TBBPA disrupted electron flow in oxidative phosphorylation and the photosynthetic system (PS) by targeting PSI, PSII, and Complex I, impairing energy acquisition and causing oxidative damage, ultimately leading to algal cell death. Additionally, proteins involved in the biosynthesis and metabolism of cysteine, methionine, phenylalanine, tyrosine, and tryptophan were upregulated, potentially enhancing M. aeruginosa resistance to TBBPA-induced stress. This study offers insights into the effects of TBBPA on M. aeruginosa and its potential risks to aquatic ecosystems.

Phytotoxicity of 6PPD and its uptake by Myriophyllum verticillatum: Oxidative stress and metabolic processes

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), a widely utilized antioxidant in automobile tires and rubber goods, is frequently detected in aquatic ecosystems and poses a potential threat to aquatic organisms. However, research on the impact of 6PPD on aquatic plants is still scarce. Here, we investigated the bioaccumulation of 6PPD in Myriophyllum verticillatum (M. verticillatum) (watermilfoil), and its impacts on biochemical characteristics and metabolomics. 6PPD (10,100 mg/L) significantly inhibited the growth and photosynthetic pigment content of M. verticillatum. After 14 days of exposure to 100 μg/L 6PPD, accumulation levels of 6PPD and its metabolite 6PPDQ in M. verticillatum reached 0.52 mg/kg and 0.09 mg/kg, respectively. Moreover, 6PPD significantly induced the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) enzymes and glutathione (GSH), reducing the levels of reactive oxygen species (ROS) and malondialdehyde (MDA), thereby mitigating oxidative damage in M. verticillatum. Furthermore, metabolic pathway analysis revealed that 6PPD has remarkable effects on amino acid and sugar metabolism. This study provides data support for understanding the toxic effects of 6PPD on aquatic plants and evaluating its potential risks.

Response of Ceratophyllum demersum L. and its epiphytic biofilms to 6PPD and 6PPD-Q exposure: Based on metabolomics and microbial community analysis

The emerging contaminant N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and its ozone conversion product N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine quinone (6PPD-Q) pose a threat to aquatic ecosystems. Aquatic animals and plants exhibit vigorous responses at very low ambient concentrations. However, studies of submerged macrophytes, key producers in aquatic ecosystems, are limited and the full extent of their toxic effects and feedback mechanisms is unknown. To investigate the phytotoxicity of 6PPD and 6PPD-Q, we modeled plant responses to abiotic stress using Ceratophyllum demersum L. (C. demersum) as a representative submerged plant. Our findings indicate that 6PPD and 6PPD-Q disrupt physiological and biochemical processes in C. demersum, encompassing growth inhibition, reduction in photosynthetic pigments, induction of oxidative damage, and metabolic alterations. Moreover, unfavorable modifications to biofilms induced were also discernible supported by confocal laser scanning microscopy (CLSM) images and microbial community profiling. More importantly, we found a robust correlation between differentially expressed metabolites (DEMs) and dominant genera, and 6PPD and 6PPD-Q significantly altered their correlation. Overall, our results imply that even though C. demersum is a resilient submerged macrophyte, the toxic effects of 6PPD and 6PPD-Q cannot be disregarded.

Concentration-dependent cellular responses of coontail (Ceratophyllum demersum) during the substitutions to perfluorooctanoic acid by its two alternatives

The substitutions of alternatives to legacy per- and polyfluoroalkyl substances (PFASs) may lead to unknown and variational joint toxicity on ecosystems. To comprehensively understand the effects of substitutions on aquatic ecosystems, the single and joint effects of perfluorooctanoic acid (PFOA) and its alternatives (perfluorobutanoic acid, PFBA; 2,3,3,3-tetrafluoro-2-(1,1,2,2,3,3,3,heptafluoropropoxy)propanoic acid, GenX) with various concentrations and compositions on a primary producer, coontail (Ceratophyllum demersum), were investigated at cellular level. Results showed that the substitutions of PFBA/GenX could alleviate the inhibition of PFOA on plant length, hydrogen peroxide accumulation, and chlorophyll b, due to the shifts of reactive oxygen species and their less toxicity to antioxidants. Significant up-regulations of superoxide dismutase, glutathione, and carotenoid implied their primary roles in defensing against PFASs (p < 0.05). Catalase/peroxidase was significantly up-regulated in PFBA/GenX substitutions (p < 0.05) to help alleviate stress. PFBA substitutions reduced 23.9 % of PFOA in organelle and GenX reduced the subcellular concentrations of PFOA by 1.8-17.4 %. Redundancy analysis suggested that PFOA, PFBA, and GenX in cell wall and organelle, as well as GenX in soluble fractions, were responsible for the cellular responses. These findings were helpful to understand the integrated effects on aquatic ecosystems during the substitutions to legacy PFASs by alternatives.

Mechanistic study on the increase of Microcystin-LR synthesis and release in Microcystis aeruginosa by amino-modified nano-plastics

Ecological risk of micro/nano-plastics (MPs/NPs) has become an important environmental issue. Microcystin-leucine-arginine (MC-LR) produced by Microcystis aeruginosa (M. aeruginosa) is the most common and toxic secondary metabolites (SM). However, the influencing mechanism of MPs and NPs exposure on MC-LR synthesis and release have still not been clearly evaluated. In this work, under both acute (4d) and long-term exposure (10d), only high-concentration (10 mg/L) exposure of amino-modified polystyrene NPs (PS-NH2-NPs) promoted MC-LR synthesis (32.94 % and 42.42 %) and release (27.35 % and 31.52 %), respectively. Mechanistically, PS-NH2-NPs inhibited algae cell density, interrupted pigment synthesis, weakened photosynthesis efficiency, and induced oxidative stress, with subsequent enhancing the MC-LR synthesis. Additionally, PS-NH2-NPs exposure up-regulated MC-LR synthesis pathway genes (mcyA, mcyB, mcyD, and mcyG) combined with significantly increased metabolomics (Leucine and Arginine), thereby enhancing MC-LR synthesis. PS-NH2-NPs exposure enhanced the MC-LR release from M. aeruginosa via up-regulated MC-LR transport pathway genes (mcyH) and the shrinkage of plasma membrane. Our results provide new insights into the long-time coexistence of NPs with algae in freshwater systems might pose a potential threat to aquatic environments and human health.

Toxic mechanisms of the antiviral drug arbidol on microalgae in algal bloom water at transcriptomic level

Increasing antivirals in surface water caused by their excessive consumption pose serious threats to aquatic organisms. Our recent research found that the input of antiviral drug arbidol to algal bloom water can induce acute toxicity to the growth and metabolism of Microcystis aeruginosa, resulting in growth inhibition, as well as decrease in chlorophyll and ATP contents. However, the toxic mechanisms involved remained obscure, which were further investigated through transcriptomic analysis in this study. The results indicated that 885-1248 genes in algae were differentially expressed after exposure to 0.01-10.0 mg/L of arbidol, with the majority being down-regulated. Analysis of commonly down-regulated genes found that the cellular response to oxidative stress and damaged DNA bonding were affected, implying that the stress defense system and DNA repair function of algae might be damaged. The down-regulation of genes in porphyrin metabolism, photosynthesis, carbon fixation, glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation might inhibit chlorophyll synthesis, photosynthesis, and ATP supply, thereby hindering the growth and metabolism of algae. Moreover, the down-regulation of genes related to nucleotide metabolism and DNA replication might influence the reproduction of algae. These findings provided effective strategies to elucidate toxic mechanisms of contaminants on algae in algal bloom water.

Polystyrene microplastics enhance microcystin-LR-induced cardiovascular toxicity and oxidative stress in zebrafish embryos

The health risks associated with combined exposure to microplastics (MPs) and cyanobacteria toxins have gained increasing attention due to the large-scale prevalence of cyanobacterial blooms and accumulation of MPs in aquatic environments. Therefore, we explored the cardiovascular toxic effects of microcystin-LR (MC-LR, 1, 10, 100 μg/L) in the presence of 5 μm polystyrene microplastics (PS-MPs, 100 μg/L) and 80 nm polystyrene nanoplastics (PS-NPs, 100 μg/L) in zebrafish models. Embryos were exposed to certain PS-MPs and PS-NPs conditions in water between 3 h post-fertilization (hpf) and 168 hpf. Compared to MC-LR alone, a significant decrease in heart rate was observed as well as notable pericardial edema in the MC-LR + PS-MPs/NPs groups. At the same time, sinus venosus and bulbus arteriosus (SV-BA) distances were significantly increased. Furthermore, the addition of PS-MPs/NPs caused thrombosis in the caudal vein and more severe vascular damage in zebrafish larvae compared to MC-LR alone. Our findings revealed that combined exposure to PS-NPs and MC-LR could significantly decreased the expression of genes associated with cardiovascular development (myh6, nkx2.5, tnnt2a, and vegfaa), ATPase (atp1a3b, atp1b2b, atp2a1l, atp2b1a, and atp2b4), and the calcium channel (cacna1ab and ryr2a) compared to exposure to MC-LR alone. In addition, co-exposure with PS-MPs/NPs exacerbated the MC-LR-induced reactive oxygen species (ROS) production, as well as the ROS-stimulated apoptosis and heightened inflammation. We also discovered that astaxanthin (ASTA) treatment partially attenuated these cardiovascular toxic effects. Our findings confirm that exposure to MC-LR and PS-MPs/NPs affects cardiovascular development through calcium signaling interference and ROS-induced cardiovascular cell apoptosis. This study highlights the potential environmental risks of the co-existence of MC-LR and PS-MPs/NPs for fetal health, particularly cardiovascular development.

Effect of luminescent materials on the biochemistry, ultrastructure, and rhizobial microbiota of Spirodela polyrhiza

Fluorescent materials and technologies have become widely used in scientific research, and due to the ability to convert light wavelengths, their application to photosynthetic organisms can affect their development by altering light quality. However, the impacts of fluorescent materials on aquatic plants and their environmental risks remain unclear. To assess the effects of luminescent materials on floating aquatic macrophytes and their rhizosphere microorganisms, 4-(di-p-tolylamino)benzaldehyde-A (DTB-A) and 4-(di-p-tolylamino)benzaldehyde-M (DTB-M) (emitting blue-green and orange-red light, respectively) were added individually and jointly to Spirodela polyrhiza cultures and set at different concentrations (1, 10, and 100 μM). Both DTB-A and DTB-M exhibited phytotoxicity, which increased with concentration under separate treatment. Moreover, the combined group exhibited obvious stress relief at 10 μM compared to the individually treated group. Fluorescence imaging showed that DTB-A and DTB-M were able to enter the cell matrix and organelles of plant leaves and roots. Peroxidation induced cellular damage, contributing to a decrease in superoxide dismutase (SOD) and peroxidase (POD) activities and malondialdehyde (MDA) accumulation. Decomposition of organelle structures, starch accumulation in chloroplasts, and plasmolysis were observed under the ultrastructure, disrupting photosynthetic pigment content and photosynthesis. DTB-A and DTB-M exposure resulted in growth inhibition, dry weight loss, and leaf yellowing in S. polyrhiza. A total of 3519 Operational Taxonomic Units (OTUs) were identified in the rhizosphere microbiome. The microbial communities were dominated by Alphaproteobacteria, Oxyphotobacteria, and Gammaproteobacteria, with the abundance and diversity varied significantly among treatment groups according to Shannon, Simpson, and Chao1 indices. This study revealed the stress defense response of S. polyrhiza to DTB-A and DTB-M exposures, which provides a broader perspective for the bioremediation of pollutants using aquatic plants and supports the further development of fluorescent materials for applications.

Interactions between biofilms and PFASs in aquatic ecosystems: Literature exploration

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) have been detected in most aquatic environments worldwide and are referred to as "forever chemicals" because of their extreme chemical and thermal stability. Biofilms, as basic aquatic bioresources, can colonize various substratum surfaces. Biofilms in the aquatic environment have to interact with the ubiquitous PFASs and have significant implications for both their behavior and destiny, which are still poorly understood. Here, we have a preliminary literature exploration of the interaction between PFASs and biofilms in the various aquatic environments and expect to provide some thoughts on further study. In this review, the biosorption properties of biofilms on PFASs and possible mechanisms are presented. The complex impact of PFASs on biofilm systems was further discussed in terms of the composition and electrical charges of extracellular polymeric substances, intracellular microbial communities, and overall contaminant purification functions. Correspondingly, the effects of biofilms on the redistribution of PFASs in the aqueous environment were analyzed. Finally, we propose that biofilm after adsorption of PFASs is a unique ecological niche that not only reflects the contamination level of PFASs in the aquatic environment but also offers a possible "microbial pool" for PFASs biodegradation. We outline existing knowledge gaps and potential future efforts for investigating how PFASs interact with biofilms in aquatic ecosystems.