Effects of polystyrene nanoplastics on the physiological and biochemical characteristics of microalga Scenedesmusquadricauda

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

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

The freeze-thaw cycle exacerbates the ecotoxicity of polystyrene nanoplastics to Secale cereale L. seedlings

In the context of global climate change, recurrent freeze-thaw cycles (FTC) and concurrent exposure to polystyrene nanoplastics (PSNPs) directly impact crop growth and indirectly affect resilience to abiotic stress. In January 2023, experiments at the Environmental Biology Laboratory, Jilin University, Changchun, China, exposed rye seedlings to 100 nm PSNPs at concentrations of 0, 10, 50, and 100 mg/L for seven days, followed by three FTC. Scanning electron microscopy (SEM) demonstrated that PSNPs migrated from the roots to the leaves, with FTC significantly exacerbating their accumulation within plant tissues. Transmission electron microscopy (TEM) observations showed that FTC disrupted normal cell division, and combined stress from NPs damaged plant organs, particularly chloroplasts, thereby substantially inhibiting photosynthesis. FTC delayed plant phenological stages. Under combined stress, malondialdehyde (MDA) accumulation in plant tissues increased by 15.6%, while hydrogen peroxide (H2O2) content decreased. Simultaneously, the activities of peroxidase (POD) and catalase (CAT) increased by 34.2% and 38.6%, respectively. Molecular docking unveiled that PSNPs could bind to the active center of POD/CAT through hydrogen bonding or hydrophobic interactions. The Integrated Biomarker Response (IBR) index highlighted FTC as a crucial determinant for pronounced effects. Moreover, an apparent dose-dependent effect was observed, with antioxidant enzyme activities in rye seedlings induced by low pollutant concentrations and inhibited by high concentrations. These results indicate that FTC and PSNPs can disrupt plant membrane systems and cause severe oxidative damage. Overall, this study provides compelling scientific evidence of the risks associated with NPs exposure in plants subjected to abiotic stress.

Modifying luteolin's algicidal effect on Microcystis by virgin and diversely-aged polystyrene microplastics: Unveiling novel mechanisms through microalgal adaptive strategies

Luteolin has shown great potential in inhibiting Microcystis-dominated cyanobacterial blooms (MCBs). However, widespread microplastics (MPs) in natural aquatic systems can serve as substrates for cyanobacterial growth, potentially impacting their resistance to external stress and might interfere with luteolin's algicidal effect. This study investigated the impact of virgin and diversely-aged polystyrene microplastics (PS-MPs) on the inhibitory effect of luteolin involving Microcystis growth and microcystins (MCs) content in water. Moreover, the underlying mechanism was also revealed by jointly analyzing the SEM images, oxidative stress, exopolymeric substances (EPSs) content and functional gene expression. Result suggested that 0.5, 5 and 50 mg/L virgin and diversely-aged PS-MPs almost reduced growth inhibition ratio and oxidative damage of Microcysits by both doses of luteolin by stimulating EPSs secretion and inducing cell self-aggregate or hetero-aggregate with PS-MPs. Compared to virgin PS-MPs, photo-aged PS-MPs possessed rougher flaky surfaces, and hydrothermal-aging cracks the MPs internally, which were more conducive to interacting and hetero-aggregating with cells, and exhibiting more significant protective effects to Microcystis. However, MPs further reduced MCs content in water, possibly attributed to their adsorption effect on MCs, compared to luteolin stress alone. Such toxic hetero-aggregate formed by MCs, MPs, and Microcystis cells are more likely to be consumed, thus entering the food chain and triggering toxic bioaccumulation, posing greater eco-risks. This is the first study to clarify the impact and mechanisms of virgin and diversely-aged MPs on allelopathic algicidal effects from the perspective of microalgal inherent detoxifying abilities and self-protective strategies.

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.

Stress Responses and Ammonia Nitrogen Removal Efficiency of Oocystis lacustris in Saline Ammonium-Contaminated Wastewater Treatment

The increasing concern over climate change has spurred significant interest in exploring the potential of microalgae for wastewater treatment. Among the various types of industrial wastewaters, high-salinity NH4+-N wastewater stands out as a common challenge. Investigating microalgae's resilience to NH4+-N under high-salinity conditions and their efficacy in NH4+-N utilization is crucial for advancing industrial wastewater microalgae treatment technologies. This study evaluated the effectiveness of employing nitrogen-efficient microalgae, specifically Oocystis lacustris, for NH4+-N removal from saline wastewater. The results revealed Oocystis lacustris's tolerance to a Na2SO4 concentration of 5 g/L. When the Na2SO4 concentration reached 10 g/L, the growth inhibition experienced by Oocystis lacustris began to decrease on the 6th day of cultivation, with significant alleviation observed by the 7th day. Additionally, the toxic mechanism of saline NH4+-N wastewater on Oocystis lacustris was analyzed through various parameters, including chlorophyll-a, soluble protein, oxidative stress indicators, key nitrogen metabolism enzymes, and microscopic observations of algal cells. The results demonstrated that when the Oocystis lacustris was in the stationary growth phase with an initial density of 2 × 107 cells/L, NH4+-N concentrations of 1, 5, and 10 mg/L achieved almost 100% removal of the microalgae on the 1st, 2nd, and 4th days of treatment, respectively. On the other hand, saline NH4+-N wastewater minimally impacted photosynthesis, protein synthesis, and antioxidant systems within algal cells. Additionally, NH4+-N within the cells was assimilated into glutamic acid through glutamate dehydrogenase-mediated pathways besides the conventional pathway involving NH4+-N conversion into glutamine and assimilation amino acids.

Meta-analysis for systematic review of global micro/nano-plastics contamination versus various freshwater microalgae: Toxicological effect patterns, taxon-specific response, and potential eco-risks

Micro/nano-plastics (MNPs), as emerging persistent pollutants, are threatening freshwater ecosystems worldwide. Microalgae are important primary producers at the base of trophic level and susceptible to MNPs contamination, possibly resulting in further contamination in higher trophic levels and water quality. This study conducted a systematic review of 1071 observations from 63 publications, utilizing meta-analysis and subgroup analysis to investigate the toxicological effect patterns of MNPs parameters (size, concentration, and type) on microalgae. We also explored the potential eco-risks of certain specific MNPs parameters and subtle variations in the response of various microalgae taxa to MNPs. Results suggested that microplastics significantly inhibited microalgal photosynthesis, while nano-plastics induced more severe cell membrane damage and promoted toxin-release. Within a certain range of concentrations (0∼50 mg/L), rising MNPs concentration progressively inhibited microalgal growth and chlorophyll-a content, and progressively enhanced toxin-release. Among MNPs types, polyamide caused higher growth inhibition and more severe lipid peroxidation, and polystyrene induced more toxin-release, whereas polyethylene terephthalate and polymethyl methacrylate posed minimal effects on microalgae. Moreover, Bacillariophyta growth was inhibited most significantly, while Chlorophyta displayed strong tolerance and Cyanophyta possessed strong adaptive and exceptional resilience. Particularly, Komvophoron, Microcystis, Nostoc, Scenedesmus, and Gomphonema were more tolerant and might dominate freshwater microalgal communities under MNPs contamination. These results are crucial for acquiring the fate of freshwater microalgae under various MNPs contamination, identifying dominant microalgae, and reasonably assessing and managing involved eco-risks.

Nitrogen and phosphorus limitations promoted bacterial nitrate metabolism and propagation of antibiotic resistome in the phycosphere of Auxenochlorella pyrenoidosa

Despite that nitrogen (N) and phosphorus (P) play critical roles in the lifecycle of microalgae, how N and P further affect the distribution of bacteria and antibiotic resistance genes (ARGs) in the phycosphere is still poorly understood. In this study, the effects of N and P on the distribution of ARGs in the phycosphere of Auxenochlorella pyrenoidosa were investigated. Results showed that the growth and chlorophyll synthesis of microalgae were inhibited when N or P was limited, regardless of the N/P ratios, but the extracellular polymeric substances content and nitrate assimilation efficiency were enhanced in contrast. Metagenomic sequencing revealed that N or P limitation resulted in the recruitment of specific bacteria that highly contribute to the nitrate metabolism in the phycosphere. Besides, N or P limitation promoted the propagation of phycosphere ARGs, primarily through horizontal gene transfer mediated by mobile genetic elements. The enrichment of specific bacteria induced by changes in the algal physiology also contributed to the ARGs proliferation under nutrient limitation. Our results demonstrated that the reduction of algal cells caused by nutrient limitation could promote the propagation of ARGs, which provides new insights into the occurrence and spread of ARGs in the phycosphere.

Hormetic effect of a short-chain PFBS on Microcystis aeruginosa and its molecular mechanism

Short-chain Perfluorinated compounds (PFCs), used as substitutes for highly toxic long-chain PFCs, are increasingly entering the aquatic environment. However, the toxicity of short-chain PFCs in the environment is still controversial. This study investigated the effects of short-chain perfluorobutanesulfonic acid (PFBS) at different concentrations (2.5, 6, 14.4, 36, and 90 mg/L) on M. aeruginosa growth under 12-day exposure and explored the molecular mechanism of toxicity using transcriptomics. The results showed that M. aeruginosa exhibited hormetic effects after exposure to PFBS. Low PFBS concentrations stimulated algal growth, whereas high PFBS concentrations inhibited it, and this inhibitory effect became progressively more pronounced with increasing PFBS exposure concentrations. Transcriptomics showed that PFBS promoted the pathways of photosynthesis, glycolysis, energy metabolism and peptidoglycan synthesis, providing the energy required for cell growth and maintaining cellular morphology. PFBS, on the other hand, caused growth inhibition in algae mainly through oxidative stress, streptomycin synthesis, and genetic damage. Our findings provide new insights into the toxicity and underlying mechanism of short-chain PFCs on algae and inform the understanding of the hormetic effect of short-chain PFCs, which are crucial for assessing their ecological risks in aquatic environments.

Tracking the micro- and nanoplastics in the terrestrial-freshwater food webs. Bivalves as sentinel species

Micro- (MPs) and nanoplastics (NPs) are currently ubiquitous in the ecosystems, and freshwater biota is still insufficiently studied to understand the global fate, transport paths, and consequences of their presence. Thus, in this study, we investigated the role of bivalves and a trophic transfer of MPs and NPs in an experimental food chain. The food chain consisted of terrestrial non-selective detritivore Dendrobaena (Eisenia) sp., freshwater benthic filter feeder Unio tumidus, and freshwater benthic detritivore-collectors Asellus aquaticus or Gammarus sp. Animals were exposed to different fluorescently labeled micro- and nanoplastics (PMMA 20 μm, nanoPS 15-18 nm, and 100 nm, PS 1 μm and 20 μm, PE from cosmetics) as well as to the faeces of animals exposed to plastics to assess their influence on the environmental transportation, availability to biota, and bioaccumulation of supplied particles. Damaged and intact fluorescent particles were observed in the faeces of terrestrial detritivores and in the droppings of aquatic filter feeders, respectively. They were also present in the guts of bivalves and of crustaceans which were fed with bivalve droppings. Bivalves (Unio tumidus, and additionally Unio pictorum, and Sphaerium corneum) produced droppings containing micro- and nanoparticles filtered from suspension and deposited them onto the tank bottom, making them available for broader feeding guilds of animals (e.g. collectors, like crustaceans). Finally, the natural ageing of PS and its morphological changes, leakage of the fluorescent labelling, and agglomeration of particles were demonstrated. That supports our hypothesis of the crucial role of the characterization of physical and chemical materials in adequately understanding the mechanisms of their interaction with biota. Microscopical methods (confocal, fluorescent, scanning electron) and Raman and FT-IR spectroscopy were used to track the particles' passage in a food web and monitor structural changes of the MPs' and NPs' surface.

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.

Effects of nanoplastics exposure on ingestion, life history traits, and dimethyl sulfide production in rotifer Brachionus plicatilis

Microplastics (MPs) and nanoplastics (NPs) have gained global concern due to their detrimental effects on marine organisms. We investigated the effects of 80 nm polystyrene (PS) NPs on life history traits, ingestion, and dimethyl sulfide (DMS) and dimethylsulfoniopropionate (DMSP) production in the rotifer Brachionus plicatilis. Fluorescently labeled 80 nm PS NPs were ingested by the rotifer B. plicatilis and accumulated in the digestive tract. The lethal rates of B. plicatilis exposed to NPs were dose-dependent. High concentrations of PS NPs exposure had negative effects on developmental duration, leading to prolonged embryonic development and pre-reproductive periods, shortened reproductive period, post-reproductive period, and lifespan in B. plicatilis. High concentrations of PS NPs exposure inhibited life table demographic parameters such as age-specific survivorship and fecundity, generation time, net reproductive rate, and life expectancy. Consequently, the population of B. plicatilis was adversely impacted. Furthermore, exposure to PS NPs resulted in a reduced ingestion rate in B. plicatilis, as well as a decreased in DMS, particulate DMSP (DMSPp) concentration, and DMSP lyase activity (DLA), which exhibited a dose-response relationship. B. plicatilis grazing promoted DLA and therefore increased DMS production. PS NPs exposure caused a decline in the increased DMS induced by rotifer grazing. Our results help to understand the ecotoxicity of NPs on rotifer and their impact on the biogeochemical cycle of dimethylated sulfur compounds.

Effects of environmental microplastic exposure on Chlorella sp. biofilm characteristics and its interaction with nitric oxide signaling

Microalgal biofilm is promising in simultaneous pollutants removal, CO2 fixation, and biomass resource transformation when wastewater is used as culturing medium. Nitric oxide (NO) often accumulates in microalgal cells under wastewater treatment relevant abiotic stresses such as nitrogen deficiency, heavy metals, and antibiotics. However, the influence of emerging contaminants such as microplastics (MPs) on microalgal intracellular NO is still unknown. Moreover, the investigated MPs concentrations among existing studies were mostly several magnitudes higher than in real wastewaters, which could offer limited guidance for the effects of MPs on microalgae at environment-relevant concentrations. Therefore, this study investigated three commonly observed MPs in wastewater at environment-relevant concentrations (10-10,000 μg/L) and explored their impacts on attached Chlorella sp. growth characteristics, nutrients removal, and anti-oxidative responses (including intracellular NO content). The nitrogen source NO3--N at 49 mg/L being 20 % of the nitrogen strength in classic BG-11 medium was selected for MPs exposure experiments because of least intracellular NO accumulation, so that disturbance of intracellular NO by nitrogen availability could be avoided. Under such condition, 10 μg/L polyethylene (PE) MPs displayed most significant microalgal growth inhibition comparing with polyvinyl chloride (PVC) and polyamide (PA) MPs, showing extraordinarily low chlorophyll a/b ratios, and highest superoxide dismutase (SOD) activity and intracellular NO content after 12 days of MPs exposure. PVC MPs exposed cultures displayed highest malonaldehyde (MDA) content because of the toxic characteristics of organochlorines, and most significant correlations of intracellular NO content with conventional anti-oxidative parameters of SOD, CAT (catalase), and MDA. MPs accelerated phosphorus removal, and the type rather than concentration of MPs displayed higher influences, following the trend of PE > PA > PVC. This study expanded the knowledge of microalgal biofilm under environment-relevant concentrations of MPs, and innovatively discovered the significance of intracellular NO as a more sensitive indicator than conventional anti-oxidative parameters under MPs exposure.

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.

Effects of polystyrene nanoplastics on growth and hemolysin production of microalgae Karlodinium veneficum

There are few studies on the effects of nanoplastics on growth and hemolysin production of harmful algal bloom species at present. In this study, Karlodinium veneficum was exposed to different concentrations (0, 5, 25, 50, 75 mg/L) of polystyrene nanoplastics (PS-NPs, 100 nm) for 96 h. The effects of PS-NPs on growth of K. veneficum were investigated by measuring algal cell abundance, growth inhibition rate (IR), total protein (TP), malondialdehyde (MDA), glutathione reductase (GSH), superoxide dismutase (SOD), ATPase activity (Na+/K+ ATPase and Ca2+/Mg2+ ATPase). Scanning electron microscope and transmission electron microscope (SEM and TEM) images of microalgae with or without nanoplastics were also observed. The effects of PS-NPs on hemolysin production of K. veneficum were studied by measuring the changes of hemolytic toxin production of K. veneficum exposed to PS-NPs on 1, 3, 5 and 7 days. High concentrations (50 and 75 mg/L) of PS-NPs seriously affected the growth of K. veneficum and different degrees of damage to cell morphology and ultrastructure were found. Excessive free radicals and other oxidants were produced in the cells, which disrupted the intracellular redox balance state and caused oxidative damage to the cells, and the basic activities such as photosynthesis and energy metabolism were weakened. The athletic ability of K. veneficum was decreased, but the ability to produce hemolysin was enhanced. It was suggested that the presence of nanoplastics in seawater may strengthen the threat of harmful algal bloom species to aquatic ecosystems and human health.

Emergence of nanoplastics in the aquatic environment and possible impacts on aquatic organisms

Plastic production on a global scale is instrumental in advancing modern society. However, plastic can be broken down by mechanical and chemical forces of humans and nature, and knowledge of the fate and effects of plastic, especially nanoplastics, in the aquatic environment remains poor. We provide an overview of current knowledge on the environmental occurrence and toxicity of nanoplastics, and suggestions for future research. There are nanoplastics present in seas, rivers, and nature reserves from Asia, Europe, Antarctica, and the Arctic Ocean at levels of 0.3-488 microgram per liter. Once in the aquatic environment, nanoplastics accumulate in plankton, nekton, benthos through ingestion and adherence, with multiple toxic results including inhibited growth, reproductive abnormalities, oxidative stress, and immune system dysfunction. Further investigations should focus on chemical analysis methods for nanoplastics, effect and mechanism of nanoplastics at environmental relevant concentrations in aquatic organisms, as well as the mechanism of the Trojan horse effect of nanoplastics.

Are nanoplastics potentially toxic for plants and rhizobiota? Current knowledge and recommendations

Soil is now becoming a reservoir of plastics in response to global production, use/disposal patterns and low recovery rates. Their degradation is caused by numerous processes, and this degradation leads to the formation and release of plastic nanoparticles, i.e., nanoplastics. The occurrence of nanoplastics in the soil is expected to both directly and indirectly impact its properties and functioning. Nanoplastics may directly impact the physiology and development of living organisms, especially plants, e.g., by modifying their production yield. Nanoplastics can also indirectly modify the physicochemical properties of the soil and, as a result, favour the release of related contaminants (organic or inorganic) and have an impact on soil biota, and therefore have a negative effect on the functioning of rhizospheres. However all these results have to be taken carefully since performed with polymer nano-bead not representative of the nanoplastics observed in the environment. This review highlight thus the current knowledge on the interactions between plants, rhizosphere and nanoplastics, their consequences on plant physiology and development in order to identify gaps and propose scientific recommendations.

Nanoplastics impacts on Thiobacillus denitrificans: Effects of size and dissolved organic matter

The widespread distribution of nanoplastics and dissolved organic matter (DOM) in sewage raises concerns about the potential impact of DOM on the bioavailability of nanoplastics. In this study, the effects of different sizes (100 nm and 350 nm) of polystyrene nanoplastics (PS-NPs, 50 mg/L) and combined with 10 mg/L or 50 mg/L DOMs (fulvic acid, humic acid and sodium alginate) on the growth and denitrification ability of Thiobacillus denitrificans were investigated. Results showed that 100 nm PS-NPs (50 mg/L) cause a longer delay in the nitrate reduction (3 days) of T. denitrificans than 350 nm PS-NPs (2 days). Furthermore, the presence of DOM exacerbated the adverse effect of 100 nm PS-NPs on denitrification, resulting in a delay of 1-4 days to complete denitrification. Fulvic acid (50 mg/L) and humic acid (50 mg/L) had the most significant adverse effect on increasing 100 nm PS-NPs (50 mg/L), causing a reduction of 20 mmol/L nitrate by T. denitrificans in nearly 7 days. It is noteworthy that the presence of DOM did not modify the adverse effect of 350 nm PS-NPs on denitrification. Further analysis of toxicity mechanism of PS-NPs revealed that they could induce reactive oxygen species (ROS) and suppressed denitrification gene expression. The results suggested that DOM may assist in the cellular internalization of PS-NPs by inhibiting PS-NPs aggregation, leading to the increased ROS levels and accelerated T. denitrificans death. This study highlights the potential risk of nanoplastics to autotrophic denitrifying bacteria in the presence of DOM and provides new insights for the treatment of nitrogen-containing wastewater by T. denitrificans.

Microplastic and antibiotic proliferated the colonization of specific bacteria and antibiotic resistance genes in the phycosphere of Chlorella pyrenoidosa

Despite that the phycosphere was an important niche for the proliferation of various bacteria and antibiotic resistance genes (ARGs), the factors that affect the colonization of bacteria and ARGs in the phycosphere are still poorly understood. In this study, sterile C. pyrenoidosa co-cultured with bacteria from different sources and provided with polylactic acid microplastic (PLA MPs) and florfenicol (FF) was examined. Results showed that bacteria promoted the growth of C. pyrenoidosa and increased its chlorophyll contents. PLA MPs and FF also showed positive effects on C. pyrenoidosa due to the "Hormesis effect". The occurrence of bacteria in the phycosphere was significantly affected by their sources and the addition of PLA MPs and FF. However, the core microbiota of the phycosphere in each group was similar. Additionally, PLA MPs and FF proliferated the abundance of phenicol-related ARGs (especially floR) and mobile genetic elements in the phycosphere. Notably, PLA MPs and FF enhanced the abundance of Flavobacterium, a potential host of ARGs. Our results highlighted the important roles of bacteria in microalgae and demonstrated exogenous pollutants could promote the spread of ARGs between surrounding environments and the phycosphere, which provide new insights into the occurrence and spread of ARGs in the phycosphere.

Toxicity interaction of polystyrene nanoplastics with sulfamethoxazole on the microalgae Chlamydomonas reinhardtii: A closer look at effect of light availability

The coexistence of nanoplastics and antibiotics in the aquatic environment has raised a complicated risk for ecosystems and human health. How the environmental factors e.g., light, regulate the interaction between nanoplastics and antibiotics and the resulting combined toxicity is poorly understood. Here, we investigated the individual and combined toxicity of polystyrene nanoplastics (nPS, 100 mg L¹) and sulfamethoxazole (SMX, 2.5 and 10 mg L^-1) toward the microalgae Chlamydomonas reinhardtii under low (LL, 16 μmol m^-2·s^-1), normal (NL, 40 μmol m^-2·s^-1), and high light (HL, 150 μmol m^-2·s^-1) in terms of cellular responses. Results indicated that the joint toxicity of nPS and SMX commonly exhibited a strong antagonistic/mitigative effect under LL/NL at 24 h, and under NL at 72 h. nPS could adsorb more SMX under LL/NL at 24 h (1.90/1.33 mg g^-1) and under NL at 72 h (1.01 mg g^-1), thereby alleviating SMX toxicity to C. reinhardtii. However, the self-toxicity of nPS had a negative influence on the degree of antagonism between nPS and SMX. The experimental results coupled with computational chemistry further revealed that the adsorption capacity of SMX on nPS was stimulated by low pH under LL/NL at 24 h (∼7.5), while by less co-existing saline ions (0.83 ppt) and algae-derived dissolved organic matter (9.04 mg L^-1) under NL at 72 h. nPS toxicity that was responsible for the toxic action modes was mainly attributed to the shading effect induced by hetero-aggregation and hindrance of light transmittance (>60%), as well as being regulated by additives leaching (0.49-1.07 mg L^-1) and oxidative stress. Overall, these findings provided a critical basis for the risk assessment and management of multiple pollutants in the complex natural environment.