Higher toxicity induced by co-exposure of polystyrene microplastics and chloramphenicol to Microcystis aeruginosa: Experimental study and molecular dynamics simulation

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.

Effect of ultraviolet aged polytetrafluoroethylene microplastics on copper bioavailability and Microcystis aeruginosa growth

Microplastics (MPs) are ubiquitous in aquatic environments, which can act as carriers to affect the bioavailability of heavy metals. The aging process in the environment changes the physicochemical properties of MPs, thereby affecting their environmental behavior and co-toxicity with other pollutants. However, relevant research is limited. In this study, we compared the properties and Cu2+ adsorption capacity of pristine and aged polytetrafluoroethylene (PTFE) MPs and further explored the influence on copper bioavailability and bio-effects on Microcystis aeruginosa. Aging process induced surface oxidation and cracks of PTFE MPs, and decreased the stability of MPs in water by increasing zeta potential. PTFE MPs had a strong adsorption capacity for Cu2+ and increased the bioavailability of copper to microalgae, which was not affected by the aging process. Pristine and aged PTFE MPs adhered to cyanobacterium surfaces and caused shrinkage and deformation of cells. Inhibition of cyanobacterium growth, photosynthesis and reduction of total antioxidant capacity were observed in the treatment of PTFE MPs. Combined exposure of pristine MPs and Cu2+ had stronger toxic effects to cyanobacterium, and increased Microcystin-LR release, which could cause harm to aquatic environment. Aging reduced the toxic effects of PTFE MPs on microalgae. Furthermore, soluble exopolysaccharide (EPS) content was significantly higher in co-exposure of aged MPs and Cu2+, which could reduce the toxicity to cyanobacterium cells. These results indicate that aging process alleviates the toxicity to microalgae and environmental risks caused by PTFE MPs. This study improves understanding of the combined toxicity of aged MPs and metals in freshwater ecosystems.

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.

When antibiotics encounter microplastics in aquatic environments: Interaction, combined toxicity, and risk assessments

Antibiotics and microplastics (MPs), known as emerging pollutants, are bound to coexist in aquatic environments due to their widespread distribution and prolonged persistence. To date, few systematic summaries are available for the interaction between MPs and antibiotics in aquatic ecosystems, and a comprehensive reanalysis of their combined toxicity is also needed. Based on the collected published data, we have analyzed the source and distribution of MPs and antibiotics in global aquatic environments, finding their coexistence occurs in a lot of study sites. Accordingly, the presence of MPs can directly alter the environmental behavior of antibiotics. The main influencing factors of interaction between antibiotics and MPs have been summarized in terms of the characteristics of MPs and antibiotics, as well as the environmental factors. Then, we have conducted a meta-analysis to evaluate the combined toxicity of antibiotics and MPs on aquatic organisms and the related toxicity indicators, suggesting a significant adverse effect on algae, and inapparent on fish and daphnia. Finally, the environmental risk assessments for antibiotics and MPs were discussed, but unfortunately the standardized methodology for the risk assessment of MPs is still challenging, let alone assessment for their combined toxicity. This review provides insights into the interactions and environment risks of antibiotics and MPs in the aquatic environment, and suggests perspectives for future research.

Unraveling the nexus: Microplastics, antibiotics, and ARGs interactions, threats and control in aquaculture - A review

In recent years, aquaculture has expanded rapidly to address food scarcity and provides high-quality aquatic products. However, this growth has led to the release of significant effluents, containing emerging contaminants like antibiotics, microplastics (MPs), and antibiotic resistance genes (ARGs). This study investigated the occurrence and interactions of these pollutants in aquaculture environment. Combined pollutants, such as MPs and coexisting adsorbents, were widespread and could include antibiotics, heavy metals, resistance genes, and pathogens. Elevated levels of chemical pollutants on MPs could lead to the emergence of resistance genes under selective pressure, facilitated by bacterial communities and horizontal gene transfer (HGT). MPs acted as vectors, transferring pollutants into the food web. Various technologies, including membrane technology, coagulation, and advanced oxidation, have been trialed for pollutants removal, each with its benefits and drawbacks. Future research should focus on ecologically friendly treatment technologies for emerging contaminants in aquaculture wastewater. This review provided insights into understanding and addressing newly developing toxins, aiming to develop integrated systems for effective aquaculture wastewater treatment.

Phthalocyanine blue leaching and exposure effects on Microcystis aeruginosa (cyanobacteria) of photoaged microplastics

Light-stabilizing additives may contribute to the overall pollution load of microplastics (MPs) and potentially enter the food chain, severely threatening aquatic life and human health. This study investigated the variation between polystyrene (PS) MPs and phthalocyanine blue (CuPC)-containing MPs before and after photoaging, as well as their effects on Microcystis aeruginosa. The presence of PS-MPs increased cell mortality, antioxidant enzyme activity, and the variation in extracellular components, while the presence of CuPC exacerbated these variations. CuPC-containing MPs caused different increasing trends in superoxide dismutase and malondialdehyde activities due to electron transfer across the membrane. Transcriptomic analysis revealed that the MPs and CuPC affected various cellular processes, with the greatest impact being on cell membranes. Compared with MPs, CuPC negatively affected ribosome and polysaccharide formation. These findings provide insights into the molecular mechanisms underlying the cellular response to MPs and their associated light-stabilizer pollution and imply the necessity for mitigating the pollution of both MPs and light-stabilizers.

Repeated Exposure Enhanced Toxicity of Clarithromycin on Microcystis aeruginosa Versus Single Exposure through Photosynthesis, Oxidative Stress, and Energy Metabolism Shift

Antibiotics are being increasingly detected in aquatic environments, and their potential ecological risk is of great concern. However, most antibiotic toxicity studies involve single-exposure experiments. Herein, we studied the effects and mechanisms of repeated versus single clarithromycin (CLA) exposure on Microcystis aeruginosa. The 96 h effective concentration of CLA was 13.37 μg/L upon single exposure but it reduced to 6.90 μg/L upon repeated exposure. Single-exposure CLA inhibited algal photosynthesis by disrupting energy absorption, dissipation and trapping, reaction center activation, and electron transport, thereby inducing oxidative stress and ultrastructural damage. In addition, CLA upregulated glycolysis, pyruvate metabolism, and the tricarboxylic acid cycle. Repeated exposure caused stronger inhibition of algal growth via altering photosynthetic pigments, reaction center subunits biosynthesis, and electron transport, thereby inducing more substantial oxidative damage. Furthermore, repeated exposure reduced carbohydrate utilization by blocking the pentose phosphate pathway, consequently altering the characteristics of extracellular polymeric substances and eventually impairing the defense mechanisms of M. aeruginosa. Risk quotients calculated from repeated exposure were higher than 1, indicating significant ecological risks. This study elucidated the strong influence of repeated antibiotic exposure on algae, providing new insight into antibiotic risk assessment.

Flunitrazepam and its metabolites induced brain toxicity: Insights from molecular dynamics simulation and transcriptomic analysis

Psychoactive drugs frequently contaminate aquatic environments after human consumption, raising concerns about their residues and ecological harm. This study investigates the effects of flunitrazepam (FLZ) and its metabolite 7-aminoflunitrazepam (7-FLZ), benzodiazepine-class psychoactive drugs, on brain accumulation, blood-brain barrier (BBB), and neuroinflammation of the model organism zebrafish. Molecular dynamics simulation and transcriptome sequencing were used to uncover their toxic mechanisms. Results demonstrate that both FLZ and 7-FLZ can accumulate in the brain, increasing Evans blue levels by 3.4 and 0.8 times, respectively. This increase results from abnormal expression of tight junction proteins, particularly ZO-1 and Occludin, leading to elevated BBB permeability. Furthermore, FLZ and 7-FLZ can also induce neuroinflammation, upregulating TNFα by 91% and 39%, respectively, leading to pathological changes and disrupted intracellular ion balance. Molecular dynamics simulation reveals conformational changes in ZO-1 and Occludin proteins, with FLZ exhibiting stronger binding forces and greater toxicity. Weighted gene co-expression network analysis identifies four modules correlated with BBB permeability and neuroinflammation. KEGG enrichment analysis of genes within these modules reveals pathways like protein processing in the endoplasmic reticulum, NOD-like receptor signaling pathway, and arginine and proline metabolism. This study enhances understanding of FLZ and 7-FLZ neurotoxicity and assesses environmental risks of psychoactive substances. ENVIRONMENTAL IMPLICATION: With the increasing prevalence of mental disorders and the discharge of psychoactive drugs into water, even low drug concentrations (ng/L-μg/L) can pose neurological risks. This study, utilizing molecular dynamic (MD) simulations and transcriptome sequencing, investigate the neurotoxicity and mechanisms of flunitrazepam and 7-aminoflunitrazepam. It reveals that they disrupt the blood-brain barrier in zebrafish and induce neuroinflammation primarily by inducing conformational changes in tight junction proteins. MD simulations are valuable for understanding pollutant-protein interactions. This research offers invaluable insights for the environmental risk assessment of psychoactive drugs and informs the development of strategies aimed at prevention and mitigation.

Fate, abundance and ecological risks of microcystins in aquatic environment: The implication of microplastics

Microcystins are highly toxic cyanotoxins and have been produced worldwide with the global expansion of harmful cyanobacterial blooms (HABs), posing serious threats to human health and ecosystem safety. Yet little knowledge is available on the underlying process occurring in the aquatic environment with microcystins. Microplastics as vectors for pollutants has received growing attention and are widely found co-existing with microcystins. On the one hand, microplastics could react with microcystins by adsorption, altering their environmental behavior and ecological risks. On the other hand, particular attention should be given to microplastics due to their implications on the outbreak of HABs and the generation and release of microcystins. However, limited reviews have been undertaken to link the co-existing microcystins and microplastics in natural water. This study aims to provide a comprehensive understanding on the environmental relevance of microcystins and microplastics and their potential interactions, with particular emphasis on the adsorption, transport, sources, ecotoxicity and environmental transformation of microcystins affected by microplastics. In addition, current knowledge gaps and future research directions on the microcystins and microplastics are presented. Overall, this review will provide novel insights into the ecological risk of microcystins associated with microplastics in real water environment and lay foundation for the effective management of HABs and microplastic pollution.

Aggregation behavior of polystyrene nanoplastics: Role of surface functional groups and protein and electrolyte variation

Aggregation kinetics of plastics are affected by the surface functional groups and exposure orders (electrolyte and protein) with kinds of mechanisms in aquatic environment. This study investigates the aggregation of polystyrene nanoplastics (PSNPs) with varying surface functional groups in the presence of common electrolytes (NaCl, CaCl2, Na2SO4) and bovine serum albumin (BSA). It also examines the impact of different exposure orders, namely BSA + NaCl (adding them together), BSA → NaCl (adding BSA firstly and then NaCl), and NaCl → BSA (adding NaCl firstly and then BSA), on PSNPs aggregation. The presence of BSA decreased the critical coagulation concentration in NaCl (CCCNa+) of the non-modified PS-Bare from 222.17 to 142.81 mM (35.72%), but increased that of the carboxyl-modified PS-COOH from 157.34 to 160.03 mM (1.71%). This might be ascribed to the thicker absorbed layer of BSA onto the PS-Bare surface, known from Ohshima's soft particle theory. Their aggregation in CaCl2 was both increased because of Ca2+ bridging. Different from the monotonous effects of BSA on PS-Bare and PS-COOH, BSA initially facilitated PS-NH2 aggregation via patch-charge attraction, then inhibited it at higher salt levels through steric repulsion. Furthermore, exposure orders had no significant effect on PS-Bare and PS-COOH, but had a NaCl concentration-dependent impact on PS-NH2. At the low NaCl concentrations (10 and 100 mM), no obvious influence could be observed. While, at 300 mM NaCl, the high concentrations of BSA could not totally stabilize the salt-induced aggregates in NaCl → BSA, but could achieve it in the other two orders. These might be attributed to the electrical double layer compression by NaCl, "patch-charge" force and steric hindrance by BSA. These experimental findings shed light on the potential fate and transport of nanoparticles in aquatic environments.