The bioadhesion and effects of microplastics and natural particles on growth, cell viability, physiology, and elemental content of an aquatic macrophyte Elodea canadensis

Molecular mechanisms by which polyethylene terephthalate (PET) microplastic and PET leachate promote the growth of benthic cyanobacteria

Toxic blooms of benthic cyanobacteria greatly threaten freshwater ecological health and drinking water safety. Meanwhile, microplastic pollution is becoming increasingly severe and microplastics accumulate in large quantities at the bottom of lakes and rivers, widely coexisting with algae. However, impacts of microplastics on benthic cyanobacteria are still unknown. This study investigated effects of microplastic polyethylene terephthalate (PET) - which is commonly found at the bottom of lakes and rivers - and its leachate at environmentally relevant concentration (0.3 mg/L) and high exposure concentration (3.0 mg/L) on typical benthic cyanobacteria (Oscillatoria sp. and Pseudanabaena sp.), and clarified the related molecular mechanisms through transcriptomic analysis. Results show that PET or PET leachate (PET-L) can promote benthic cyanobacterial growth and promotive effect of PET-L is more obvious than that of PET system. Promotion effect of PET or PET-L is more significant at environmentally relevant concentration (39-63 % increase compared with the control) compared with high exposure concentration (21-58 % increase compared with the control). In the presence of PET or PET-L, due to an increase in the number of cyanobacterial cells, concentrations of harmful metabolites (cylindrospermopsin, geosmin, and 2-methylisoborneol) in water also increased. Although PET particles may not be conducive to benthic cyanobacterial growth due to shading effect and mechanical damage, photosynthetic efficiency of algae was improved and dysregulated genes related to photosynthesis and extracellular transport of glycolipid were upregulated according to transcriptome analysis. Moreover, PET decomposition components, such as terephthalic acid and ethylene glycol, may be able to serve as carbon sources for cyanobacterial growth. Upregulation of genes associated with glycolysis, oxidative phosphorylation, and translation revealed that PET can promote the growth of benthic cyanobacteria. This study has important value in evaluating the impact of benthic cyanobacteria on aquatic ecological health and drinking water safety with the coexistence of microplastics.

Effects of microplastics and heavy metal stress on the growth and physiological characteristics of pioneer plant Avicennia marina

Mangrove plants grow in muddy and swampy areas where the land and sea meet and are threatened by various pollutants. In the present study, Avicennia marina (Forsk.) Vierh. (A.marina), the pioneer species in mangrove, was selected as model plant. A composite pollution model of microplastics (polypropylene [PP], polyethylene [PE], and polyamide [PA]) and multiple heavy metals (Cr, Cu, Pb, Zn, Cd, Mn, Co, Hg, As, and Ni) at environmental concentrations was constructed to explore the effects of dual stress on seedling growth and metabolism. Over the 65-days co-exposure, no lethal effects were observed among any contaminant treatments. In contrast, the PP and heavy metal (PPH) and PA and heavy metal (PAH) groups promoted the growth and development of the seedlings. The PPH and PAH treatments increased the soluble protein content of seedling leaves to 4.4 and 3.1 times of the heavy metal (H) treatment, respectively. Free proline content was approximately 58 % higher in the PPH treatment group than in the H group. PE and heavy metal (PEH) exposure significantly inhibited enzyme activities related to nitrogen uptake and transformation in the root and leaf tissues of seedlings. In addition, higher concentrations and frequencies of reactive oxygen species accumulation were observed in root tissues of seedlings grown in sediment added PEH and PAH. These findings provide critical evidences to elucidate the toxicological effects of microplastics and heavy metals combined stress on mangrove plant.

Studies on adsorption and synergistic biological effects induced by microplastic particles and the Platanus pollen allergenic protein 3(Pla a3)

Microplastics (MPs) are pervasive as emerging pollutants in ambient particles and may pose a potential threat to human health through respiratory exposure. Especially, impact of climate change has led to an extended blooming period for many plants, resulting in elevated pollen levels in the air, and leading to a continuous increase in the number of individuals suffering from allergenic diseases. However, the interactions between the MPs and allergenic proteins, remain largely unexplored. In this study, we investigated cellular toxicity of the MPs and Platanus pollen allergenic protein (Pla a3) based on the characterization of two typical microplastics (polystyrene, PS and polyethylene, PE). Our results indicated that UV irradiation could make surface alterations of the MPs, including breakage, particle size reduction, and an increase in surface oxygen-containing functional groups. These changes significantly enhanced the adsorption of the Pla a 3 protein. The 'protein coronas' formed by the MPs and the Pla a3 caused more damage to the A549 cells than Pla a3 alone. Reactive oxygen species (ROS) generation and elevated superoxide dismutase (SOD) levels increased significantly after the A549 cells were exposure to the protein coronas. This excessive oxidative stress led to significant inflammation and cytokine production increase, with IL-1β, IL-4, IFN-γ, and TNF-α levels rising by 1.84 ± 0.01, 2.37 ± 0.04, 1.94 ± 0.09, and 2.19 ± 0.05-fold times respectively compared to that of the Pla a 3 exposure alone. This study provided a fundamental data for further research for the allergenicity induced by the pollen proteins.

The dual impact of tire wear microplastics on the growth and ecological interactions of duckweed Lemna minor

Tire wear microplastics (TWMs) are continuously generated during driving and are subsequently released into the environment, where they pose potential risks to aquatic organisms. In this study, the effects of untreated, hydrated, and aged (in stream water) TWMs on the growth, root development, photosynthesis, electron transport system (ETS) activity, and energy-rich molecules of duckweed Lemna minor were investigated. The results indicated that untreated and aged TWMs have the most pronounced negative effects on Lemna minor, as evidenced by reduced growth and impaired root development. In contrast, the effects of hydrated TWMs were less pronounced compared to untreated and aged TWMs. The negative effects associated with untreated and hydrated TWMs are primarily attributed to the abrasive nature of these particles, which physically damage the plant tissue. On the other hand, aged TWMs showed a different mode of action as they serve as transport vectors for algae. Once introduced into a new environment via aged TWMs, these algae competed with Lemna minor for available nutrients and space, further impairing the growth, root length, photosynthetic efficiency, and carbohydrate content of Lemna minor. This study revealed the dual threat posed by TWMs: direct physical damage from newly released particles and indirect ecological disruption from aged particles that facilitate the spread of algae.

Rising temperature impacts the trace metal uptake and toxicity in aquatic plants - A case study of Ni and Co in Elodea canadensis Michx

The global warming and environmental pollution are two crucial contemporary concerns. As both are strongly connected with urbanisation and anthropogenic impact on the environment, they often affect the ecosystem simultaneously. Aquatic habitats are particularly susceptible to thermal and chemical pollution. Temperature influences nearly all physical and chemical features of water bodies and trace metals are known for their toxicity to aquatic organisms. However, effects of multiple stressors, cumulative effects as well as response and possible adaptations of organisms are still open questions. Thus, the aim of this study was to characterize the combined effect of temperature and two trace metals (Co and Ni) on the metal bioaccumulation and viability of a model aquatic macrophyte Elodea canadensis Michx. We exposed shoots of E. canadensis to three temperatures and four metal concentrations (together and separately) applied at environmentally relevant levels. Shoot growth and metal concentration in plants were measured after 120 h. Moreover, after 24, 72 and 120 h the changes in leaf cell morphology and viability were analysed. The results showed that metal accumulation was dose-dependent and was not affected by temperature. The growth of plants was not affected by temperature nor metals. On the other hand, the exposure to Co and Ni and the elevated temperature negatively affected cell viability of E. canadensis leaves which manifested by increased permeability of plasma membranes and visible necroses. The greatest damaged leaf areas were determined after 120 h in the highest concentration of both metals and the highest temperature which indicates synergistic impact of trace metals and temperature on performance of macrohydrophytes. The observed phenomena suggest that global warming and/or thermal pollution may have implications for the performance of aquatic macrophytes in chemically polluted waters, their ability to spread and colonize polluted habitats and their suitability in phytoremediation.

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.

Critical review on unveiling the toxic and recalcitrant effects of microplastics in aquatic ecosystems and their degradation by microbes

Production of synthetic plastic obtained from fossil fuels are considered as a constantly growing problem and lack in the management of plastic waste has led to severe microplastic pollution in the aquatic ecosystem. Plastic particles less than 5mm are termed as microplastics (MPs), these are pervasive in water and soil, it can also withstand longer period of time with high durability. It can be broken down into smaller particles and can be adsorbed by various life-forms. Most marine organisms tend to consume plastic debris that can be accumulated easily into the vertebrates, invertebrates and planktonic entities. Often these plastic particles surpass the food chain, resulting in the damage of various organs and inhibiting the uptake of food due to the accumulation of microplastics. In this review, the physical and chemical properties of microplastics, as well as their effects on the environment and toxicity of their chemical constituents are discussed. In addition, the paper also sheds light on the potential of microorganisms such as bacteria, fungi, and algae which play a pivotal role in the process of microplastics degradation. The mechanism of microbial degradation, the factors that affect degradation, and the current advancements in genetic and metabolic engineering of microbes to promote degradation are also summarized. The paper also provides information on the bacterial, algal and fungal degradation mechanism including the possible enzymes involved in microplastic degradation. It also investigates the difficulties, limitations, and potential developments that may occur in the field of microbial microplastic degradation.

Multi-omics analyses reveal the responses of wheat (Triticum aestivum L.) and rhizosphere bacterial community to nano(micro)plastics stress

The pervasive existence of nanoplastics (NPs) and microplastics (MPs) in soil has become a worldwide environmental concern. N/MPs exist in the environment in a variety of forms, sizes, and concentrations, while multi-omics studies on the comprehensive impact of N/MPs with different properties (e.g. type and size) on plants remain limited. Therefore, this study utilized multi-omics analysis methods to investigate the effects of three common polymers [polyethylene-NPs (PE-NPs, 50 nm), PE-MPs (PE-MPs, 10 μm), and polystyrene-MPs (PS-MPs, 10 μm)] on the growth and stress response of wheat, as well as the rhizosphere microbial community at two concentrations (0.05 and 0.5 g/kg). PS and PE exhibited different effects for the same particle size and concentration. PE-NPs had the most severe stress effects, resulting in reduced rhizosphere bacteria diversity, plant biomass, and antioxidant enzyme activity while increasing beneficial bacteria richness. N/MPs altered the expression of nitrogen-, phosphorus-, and sulfur-related functional genes in rhizosphere bacteria, thereby affecting photosynthesis, as well as metabolite and gene levels in wheat leaves. Partial least squares pathway models (PLSPMs) indicated that concentration, size, and type play important roles in the impact of N/MPs on the plant ecological environment, which could have essential implications for assessing the environmental risk of N/MPs.

Mechanistic insight into the impact of polystyrene microparticle on submerged plant during asexual propagules germination to seedling: Internalization in functional organs and alterations of physiological phenotypes

Asexual reproduction is one of the most important propagations in aquatic plants. However, there is a lack of information about the growth-limiting mechanisms induced by microplastics on the submerged plant during asexual propagule germination to seedling. Hence, we investigated the effects of two sizes (2 µm, 0.2 µm) and three concentrations (0.5 mg/L, 5 mg/L, and 50 mg/L) of polystyrene microplastics (PSMPs) on Potamogeton crispus turion germination and seedling growth. Both PSMPs sizes were found in P. crispus seedling tissues. Metabolic profile alterations were observed in leaves, particularly affecting secondary metabolic pathways and ATP-binding cassette transporters. Metal elements are indispensable cofactors for photosynthesis; however, alterations in the metabolic profile led to varying degrees of reduced concentrations in magnesium, iron, copper, and zinc within P. crispus. Therefore, the maximum quantum yield of photosystem II significantly decreased in all concentrations with 0.2 µm-PSMPs, and at 50 mg/L with 2 µm-PSMPs. These findings reveal that internalization of microplastics, nutrient absorption inhibition, and metabolic changes contribute to the negative impact on P. crispus seedlings.