Microplastic interactions with freshwater microalgae: Hetero-aggregation and changes in plastic density appear strongly dependent on polymer type

Micro- and nano-plastics pollution in the marine environment: Progresses, drawbacks and future guidelines

Marine pollution by micro/nanoplastics (M/NPs) has emerged as a critical global issue, with widespread ecological and economic consequences. Numerous studies have investigated M/NPs pollution in marine environments, but there remains a need to assess progress, identify challenges, and propose future strategies. This review provides updated insights into marine M/NPs, including their sources, detection methods, global data from diverse marine ecosystems, and the challenges in mitigating pollution. The review reveals that the ocean harbors approximately 5.25 trillion plastic debris pieces, with a total of 50-75 trillion plastic and microplastic particles, with deep-sea regions containing up to 4 billion plastic microfibers per square kilometer. Human activities, including industrial practices and aquaculture, are major contributors to M/NPs pollution, which threatens 17% of marine species and incurs an economic loss of 6-9 billion USD. M/NPs are found across various marine habitats, including shorelines, sea floors, water columns, biota, and floating debris. Analyzing nanoplastics is particularly challenging due to their heterogeneous aggregation with other contaminants and their much lower concentrations than natural particles. Key drawbacks in addressing M/NPs pollution include inadequate funding, insufficient regulations, and a lack of policy frameworks on the prevalence, distribution, and sources of M/NPs. There is an increasing focus on utilizing innovative technologies such as artificial intelligence (AI) to monitor, assess risks, and predict the spread of M/NPs. Therefore, urgent global cooperation, involving all stakeholders and the general public, is essential. Additionally, integrating scientific and engineering methods, along with AI technologies, is crucial for monitoring and controlling M/NPs pollution and developing sustainable solutions.

Zooming in the plastisphere: the ecological interface for phytoplankton-plastic interactions in aquatic ecosystems

Phytoplankton is an essential resource in aquatic ecosystems, situated at the base of aquatic food webs. Plastic pollution can impact these organisms, potentially affecting the functioning of aquatic ecosystems. The interaction between plastics and phytoplankton is multifaceted: while microplastics can exert toxic effects on phytoplankton, plastics can also act as a substrate for colonisation. By reviewing the existing literature, this study aims to address pivotal questions concerning the intricate interplay among plastics and phytoplankton/phytobenthos and analyse impacts on fundamental ecosystem processes (e.g. primary production, nutrient cycling). This investigation spans both marine and freshwater ecosystems, examining diverse organisational levels from subcellular processes to entire ecosystems. The diverse chemical composition of plastics, along with their variable properties and role in forming the "plastisphere", underscores the complexity of their influences on aquatic environments. Morphological changes, alterations in metabolic processes, defence and stress responses, including homoaggregation and extracellular polysaccharide biosynthesis, represent adaptive strategies employed by phytoplankton to cope with plastic-induced stress. Plastics also serve as potential habitats for harmful algae and invasive species, thereby influencing biodiversity and environmental conditions. Processes affected by phytoplankton-plastic interaction can have cascading effects throughout the aquatic food web via altered bottom-up and top-down processes. This review emphasises that our understanding of how these multiple interactions compare in impact on natural processes is far from complete, and uncertainty persists regarding whether they drive significant alterations in ecological variables. A lack of comprehensive investigation poses a risk of overlooking fundamental aspects in addressing the environmental challenges associated with widespread plastic pollution.

Importance of Attachment Efficiency in Determining the Fate of PS and PVC Nanoplastic Heteroaggregation with Natural Colloids Using a Multimedia Model

Here, we assessed the heteroaggregation of polystyrene (PS) and poly(vinyl chloride) (PVC) nanoplastics with SiO2 as a model of natural colloids. Homoaggregation and heteroaggregation were evaluated as a function of CaCl2 (0-100 mM) and natural organic matter (NOM) (50 mg L-1) at a designated concentration of nanoplastics (200 μg L-1). Critical coagulation concentrations (CCC) of nanoplastics were determined in homoaggregation and heteroaggregation experiments with SiO2 and CaCl2. The attachment efficiency (α) was calculated by quantifying the number of nanoplastics in the presence of CaCl2, NOM, and SiO2 using single-particle inductively coupled plasma mass spectrometry (spICP-MS) and pseudo-first-order kinetics. The calculated α was fed into the SimpleBox4Plastics model to predict the fate of nanoplastics across air, water, soil, and sediment compartments. Nanoplastics exhibited high stability against homoaggregation, while significant heteroaggregation with SiO2 occurred at CaCl2 concentrations above 100 mM. The influence of NOM was also evaluated, showing a reduction in heteroaggregation with SiO2 for both nanoplastic types. Sensitivity analysis indicated that the degradation half-life of the tested nanoplastics had a more significant impact on persistence than did α. The results emphasize the environmental stability of nanoplastics, particularly in freshwater and soil compartments, and the critical role of NOM and emission pathways in determining their fate.

Visualization of labeled micro- and nanoplastics in interaction with algae, using super-resolution stimulated emission depletion microscopy and fluorescence lifetime imaging

In contrast to microplastics, studying the interactions of nanoplastics (NPs) with primary producers such as marine microalgae remains challenging. This is attributed to the lack of adequate visualization methods that can distinguish NPs from autofluorescent biological material such as marine algae. The aim of this study was to develop a method for labeling and visualizing nonfluorescent micro- and nanoplastics (MNPs) of various polymer types, shapes, and sizes, in interaction with marine primary producers, which are autofluorescent. A labeling technique for plastics was refined, using a swell incorporation method with the commercial dye "IDye." Comprehensive quality control measures, including toxicity, leaching, and dye longevity tests, were applied to ensure the robustness of the method. Although stimulated emission depletion (STED) microscopy successfully enabled the visualization of the diverse labeled NPs smaller than 200 nm, it could not distinguish NPs from autofluorescent organic material such as marine microalgae, due to overlapping excitation and emission spectra with the photosynthetically active molecule chlorophyll-a. This study is the first to advance the field by coupling STED with fluorescence lifetime imaging microscopy (FLIM). The FLIM technique, based on the differing lifetimes of fluorescent signals, allowed us to overcome the challenge of overlapping spectra. Our work not only refines and expands existing plastic labeling protocols to accommodate a wide range of polymer types, but also introduces a more precise method for studying interactions between MNPs and autofluorescent organisms. This combined STED-FLIM approach provides a reproducible and reliable framework for examining MNP impacts in complex, ecologically relevant environments, particularly highlighting its potential for investigating MNP-microalgae interactions.

Buoyant polyethylene rope fragments might be vehicles of migration for larval mussels (Mytilus coruscus)

The widespread use of plastics has led to ecosystem risks, which serve as ideal substrates for biofouling in aqueous environments, spreading ecological hazards. In this study, we established a simulation system incorporating Mytilus coruscus larvae and buoyant plastic rope fragments, using polyethylene rope fragments as substrates to assess the attachment behavior of the larvae and the duration of their buoyancy, in order to investigate the potential role of buoyant plastic rope fragments in facilitating larval dispersal and evaluate their ecological implications. The results demonstrated that larvae successfully attached to plastic rope fragments, showing a preference for the rougher ends, and extended their pelagic phase by up to 25 days. The average attachment count of larvae on plastic rope fragments coated with mixed microalgal biofilm (50.0 ± 23.6 ind/5 cm) was lower than on rope fragments without biofilm (70.6 ± 19.4 ind/5 cm), but the difference was not statistically significant (p > 0.05). Particle dispersal simulations indicated that the extended pelagic phase significantly increased the northward dispersal range of the larvae. Based on these findings, we suggest that the increased dispersal range may influence the genetic differentiation of M. coruscus populations. These findings enhance our understanding of the ecological impacts of plastics on M. coruscus and other sessile organisms.

Strategies for the Remediation of Micro- and Nanoplastics from Contaminated Food and Water: Advancements and Challenges

Micro- and nanoplastic (MNP) pollution is a significant concern for ecosystems worldwide. The continuous generation and extensive utilization of synthetic plastics have led to the widespread contamination of water and food resources with MNPs. These pollutants originate from daily-use products and industrial waste. Remediation of such pollutants is essential to protect ecosystems and human health since these ubiquitous contaminants pose serious biological and environmental hazards by contaminating food chains, water sources, and the air. Various remediation techniques, including physical, chemical, sophisticated filtration, microbial bioremediation, and adsorption employing novel materials, provide encouraging avenues for tackling this worldwide issue. The biotechnological approaches stand out as effective, eco-friendly, and sustainable solutions for managing these toxic pollutants. However, the complexity of MNP pollution presents significant challenges in its management and regulation. Addressing these challenges requires cross-disciplinary research efforts to develop and implement more efficient, sustainable, eco-friendly, and scalable techniques for mitigating widespread MNP pollution. This review explores the various sources of micro- and nanoplastic contamination in water and food resources, their toxic impacts, remediation strategies-including advanced biotechnological approaches-and the challenges in treating these pollutants to alleviate their effects on ecosystems and human health.

Investigating the sorption of Zinc-Oxide nanoparticles on Tire-wear particles and their toxic effects on Chlorella vulgaris: Insights from toxicological models and physiological analysis

This study investigated the interaction of Tire-wear particles (TWPs) with Zinc-Oxide nanoparticles (ZNPs) and studied their individual and combined toxic effects on Chlorella vulgaris in the co-presence of Humics. Physiological parameters, including growth, photosynthetic pigments, oxidative stress, and membrane damage, were analysed using Flow cytometry. Adsorption experiments exhibited that ZNPs were significantly absorbed by TWPs (qmax= 312.49 mg/g). A positive dose-response relation concerning inhibition in growth was observed in all treatment groups, and it was associated with reduced chlorophyll levels and damaged cell membranes. A negative impact of increased concentrations of TWPs and ZNPs was observed on anti-oxidant enzymes CAT and SOD; however, the impact was more severe when combined with exposure to both contaminants. Elevated concentrations of ZNPs and TWPs led to increased ROS production, lipid peroxidation and membrane damage, which could be contributing to the observed inhibition in growth. In the combined exposure groups, the Independent Action and the Abbott toxicity models revealed a synergistic effect on growth rates, which agreed with the Integrated Biomarker model results. The current study could enhance our understanding of the interaction between TWPs and metal nanoparticles in aquatic systems and offer novel understandings of the mechanisms underlying their combined toxic effects on microalgae.

Size-specific mediation of the physiological responses and degradation ability of microalgae to sulfamerazine by microplastics

Antibiotics and microplastics (MPs) are two classes of emerging contaminants that are commonly found in various water environments. However, how different sized MPs affect the toxicity and biodegradation of antibiotics remains poorly understood. We investigated the effects of polystyrene (PS) MPs with different particle sizes (100 nm and 30 μm) on the physiological responses and degradation behavior of Phaeodactylum tricornutum to sulfamerazine (SMR). Results showed that microalgae growth was inhibited by SMR, and MPs especially those of smaller size exacerbated the inhibitory effects of SMR on microalgae, including decreasing the content of chlorophyll a, carotenoids, malondiadehyde and superoxide dismutase activity. MPs exhibited low adsorption towards SMR, and MPs especially 30 μm MPs strengthened SMR photodegradation through leaching more organic chemicals. In comparison, 100 nm MPs obstructed the light, resulting in insignificant effects on photodegradation. Apart from photodegradation, SMR could be bioaccumulated and biodegraded by microalgae, and biodegradation was the main removal mechanism. The overall influence of MPs on SMR degradation by microalgae was a balance of the promotion on photodegradation and negative effects on microalgae growth, with the degradation efficiency and rate of SMR significantly lower in treatment of 100 nm MPs (0.0128 ± 0.0012 day-1, 30.13 ± 0.36 %) than treatments without MPs (0.0155 ± 0.0011 day-1, 32.90 ± 3.11 %) or with 30 μm MPs (0.0165 ± 0.0013 day-1, 34.46 ± 2.52 %). Overall, this study reveals the size-specific effects of MPs on the toxicity and degradation behavior of SMR, providing novel insights into the combined effects of SMR and MPs.

Limited effects of microplastics on size-fractionated phytoplankton booming in estuarine system

Despite the extensive presence and long-term exposure risks of marine microplastics (MPs), their impact on phytoplankton at the community level is still not very clear, especially considering the various size classes of phytoplankton. To address this issue, we investigated the spatial load of MPs in Linhong Estuary and conducted in-situ experiments of algal culture with added MPs. Our investigation showed that the abundance of MPs varied from 8 n/L to 50 n/L, with an average of 21.76 ± 12.31 n/L. A high loading of MPs was spatially identified outside Linhong Estuary, and clear decreasing trend from land to sea was not observed. Further microscopic examination revealed fiber-shaped MPs dominated in all collections, reaching a proportion of 93%. The chlorophyll a concentrations were 2.69-25.50 μg/L (9.14 ± 6.59 μg/L), 0.68-3.13 μg/L (1.48 ± 0.67 μg/L) and 0.14-0.65 μg/L (0.27 ± 0.14 μg/L) for microphytoplankton (20-200 μm), nanophytoplankton (2-20 μm) and picophytoplankton (0.2-2 μm), respectively. The correlation analysis between MP abundance and chlorophyll a of phytoplankton and the in-situ experiment at an environmentally realistic level both indicated a negative relationship between MP abundance and microphytoplankton with respect to chlorophyll a content, but no adverse effects of MPs were found for nanophytoplankton and picophytoplankton with smaller sizes. Our findings indicate that exposure to realistic levels of MPs only cause a limited impact on size-specific phytoplankton communities studied, but long-term interactions between MPs and these species merit further field-based assessment in real-world scenarios beyond lab-based incubation.

Impact of microplastics on aquatic flora: Recent status, mechanisms of their toxicity and bioremediation strategies

The accumulation of microplastics (MPs) in aquatic environments has occurred pervasively. The MPs affect almost all the aquatic plants including the aquatic microorganisms, ultimately disturbing the food chain. Aquatic flora attracts MPs due to the formation of several chemical bonds and interactions, including hydrogen bonds, electrostatic, hydrophobic, and van der Waals. Consequently, they hinder plant growth when adsorbed to the plant surfaces. Moreover, the major metabolic processes, including photosynthesis, reproduction, and nutrient uptake, get affected due to the pore-filling of plant tissues and the blockage of sunlight. Subsequently, prolonged exposure to MPs inflicts excessive generation of reactive oxygen species (ROS), ultimately accelerating programmed cell death. However, it has been realized that bioremediation techniques, including phytoremediation, can effectively mitigate MPs pollution by adsorbing or accumulating MPs by 25-80% at the laboratory scale. In this connection, several microorganisms are vital in deteriorating MPs due to their ability to form biofilm over the MPs' surface. Additionally, the secretion of extracellular enzymes such as styrene monooxygenase, styrene oxide isomerase, phenylacetaldehyde dehydrogenase, PETase, etc., facilitates the degradation of MPs. Moreover, the inherent ability of plants to adsorb and accumulate MPs can be utilized to manage the MPs in aquatic ecosystems. However, there is a dearth of literature and comprehensive reviews highlighting the potential of bioremediation strategies. Therefore, apart from addressing the impact of MPs on aquatic flora, this article attempts to elucidate the physical and chemical basis of plant-plastic interaction and the potential strategies aquatic flora including microorganisms employ to mitigate plastic pollution.

Disentangling the retention preferences of estuarine suspended particulate matter for diverse microplastic types

As a major source of microplastics (MPs) for global oceans, estuarine MPs pose challenges for numerical modeling due to their particle diversity, while hydrodynamics and suspended particulate matter (SPM) further exacerbate transport prediction uncertainties. This study employs a categorization framework to pinpoint 16 representative MPs types, precisely simulating their transport processes in the Yangtze River estuary (YRE). Furthermore, spatial links between SPM concentrations and MP types at 1800+ simulated sites were examined using ArcGIS and bivariate Local Indicators of Spatial Association (BI-LISA). Results indicate that low-density (≤0.95 g/cm³), small-diameter (<500 μm) fiber MPs are more prone to hetero-aggregation with estuarine SPM flocs, while MPs with opposite characteristics may move depending on their intrinsic properties. High-high BI-LISA clusters were observed both in river branches and at the confluence with the sea, the latter closely associated with the turbidity maximum zone that promote MP hetero-aggregation. The interaction of these currents and Yangtze (Changjiang) diluted water forms MPs clusters between 122.0°E and 122.5°E at the confluence of the South Branch, averaging over 870 μg/m3. Examining the trapping preferences of estuarine SPMs for various MPs through this classification framework can help to determine the bioavailability of environmental MPs to aquatic organisms and map the MPs baseline values for health risk quantification.

Phenotypic and Gene Expression Alterations in Aquatic Organisms Exposed to Microplastics

The use of plastics, valued for its affordability, durability, and convenience, has grown significantly with the advancement of industry. Paradoxically, these very properties of plastics have also led to significant environmental challenges. Plastics are highly resistant to decomposition, resulting in their accumulation on land, where they eventually enter aquatic environments, due to natural processes or human activities. Among these plastics, microplastics, which are tiny plastic particles, are particularly concerning when they enter aquatic ecosystems, including rivers and seas. Their small size makes them easily ingestible by aquatic organisms, either by mistake or through natural feeding behaviors, which poses serious risks. Moreover, microplastics readily adsorb other pollutants present in aquatic environments, creating pollutant complexes that can have a synergistic impact, magnifying their harmful effects compared to microplastics or pollutants acting alone. As a result, extensive research has focused on understanding the effects of microplastics on aquatic organisms. Numerous studies have demonstrated that aquatic organisms exposed to microplastics, either alone or in combination with other pollutants, exhibit abnormal hatching, development, and growth. Additionally, many genes, particularly those associated with the antioxidant system, display abnormal expression patterns in these conditions. In this review, we examine these impacts, by discussing specific studies that explore changes in phenotype and gene expression in aquatic organisms exposed to microplastics, both independently and in combination with adsorbed pollutants.

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.

Seabed microplastics in the European continental shelf: Unravelling physical and biological transport pathways and reciprocal fauna-Polymer relationships

Marine sediments are recognized as major sinks for microplastics, including remote areas which were previously considered "plastic-free". The understanding of microplastic dynamics in marine sediments is however limited due to the numerous pelagic and benthic pathways involved, and how these are influenced by physico-chemical interactions with the particles. European continental shelves border densely populated areas and face a high risk of microplastic contamination. In this study we quantified microplastics in soft-sediments of European coastal seas and characterized their polymer composition separating surface sediments from deeper layers. We then analyzed the influence of water column and sediment properties on spatial variability of seabed microplastics and investigated the relationship with macrofauna communities. A higher proportion of negatively buoyant polymers in surface sediments (0-1 cm) across stations was explained by seawater salinity and sediment microalgal detritus, highlighting the role of riverine input and possibly the formation of hetero-aggregates in defining polymer deposition. Additionally, we found that seawater temperature influenced polymer composition in deeper sediment layers (0-3 cm), likely together with biological activities performed by macrobenthos such as ingestion and burial. Finally, we demonstrate that seabed microplastics contribute to the spatial variability in macrobenthos, highlighting that marine ecosystem functioning effects of microplastic pollution are likely mediated via the benthos.

Exploring different effects of biofilm formation and natural organic matter adsorption on the properties of three typical microplastics in the freshwater

Microplastics entering the aqueous environment are susceptible to the surrounding environmental processes, including biofilm formation and natural organic matter (NOM) adsorption, which significantly alters their properties and environmental fate. In this study, polyethylene (PE), polyvinyl chloride (PVC) and polyethylene terephthalate (PET) microplastics were respectively incubated in the untreated and disinfected freshwater to investigate the different effects of biofilm formation and only NOM adsorption on the properties of microplastics. The results showed that the total amount of fouling biomass driven by biofilm formation was markedly higher than that of NOM adsorption. The changes in microplastic surface morphologies and special surface area dominated by biofilm formation and NOM adsorption were different; biofilm formation induced various shaped bacteria and a dense layer of extracellular polymeric substances adhering on microplastic surfaces with the decreased special surface area, whereas NOM adsorption mainly resulted in the obvious pores, cracks and winkles and the increased special surface area, indicating the initial degradation of microplastics. Moreover, both biofilm formation and NOM adsorption could reduce the hydrophobicity of three microplastics. The decreased trends of the hydrophobicity of microplastics were closely related to the amount of fouling biomass in a linear relationship with different influenced coefficients (slope a), subsequently verifying that NOM adsorption played a key role in the alternation of the hydrophobicity of microplastics. Surface chemical characterization by FTIR and 3D-EEMs presented the generation of additional functional groups and components on the microplastic surface attributed to the biofilm formation and NOM adsorption in different extent and sequence. This study provides more detailed information about the different effects of biofilm formation and NOM adsorption on the properties of microplastics in the aqueous environment.

Machine learning-based prediction and model interpretability analysis for algal growth affected by microplastics

Microplastics (MPs), the plastic debris smaller than 5 mm, are ubiquitous in waterbodies and have been shown to be toxic to aquatic organisms, especially to microalgae. The aim of this study is to use machine learning models to predict the effects of MPs on algal growth and to evaluate the relative importance of different features (MP properties, algal characteristics, and experimental conditions) through model interpretability analysis. Based on literature search, 408 samples were collected as inputs for the models. Three integrated machine learning algorithms, Random Forest (RF), Categorical Boosting (CatBoost), and Light Gradient Boosting Machine (LightGBM), were used to construct classification prediction models for algal growth. Our results show that the LightGBM model yields the best performance, with a total accuracy rate of 0.8305 and a Kappa value of 0.7165. The model interpretability analysis indicates that "Exposure time", "MP concentrations", and "MP size" are the most influential features affecting algal growth. For "Exposure time", which belongs to experimental conditions, 72-216 h of MP exposure was found to exert the greatest effects on algal growth. The impact of MPs on algal growth increases with increasing MP concentrations over the range of 0 to 300 mg/L. Smaller MPs exert more effects on algal growth, and MPs are more likely to inhibit algal growth when the ratio of algal cell size to MP size is higher. Our study successfully established prediction models for evaluating the effects of various MP properties on algal growth. This study also provides insights into the prediction of MP toxicity in organisms.

Traversing the potential of phytoremediation and phycoremediation as pioneering technologies in microplastic mitigation - A critical review

With the advent of numerous reports related to health and environmental hazards associated with microplastics (MPs), scientists have been engrossed in developing sustainable technologies for MP mitigation. Conventional methods for the remediation of MPs have several limitations, but with the increasing demand for biological mitigation methods, the latest technologies are prioritized. Among biological-driven methods, phytoremediation and phycoremediation are the two peaking approaches that have gained momentum because of their eco-friendliness, cost-effectiveness, and recyclability options. Investigations of the mechanisms underlying phytoremediation and phycoremediation processes can provide possible insights into practical applications in the present scenario. Modern instrumentation is a prerequisite for identifying and characterizing MPs and quantifying their removal efficiency. The current investigation highlights a unique combination of elaborate discussions on the use of plants in the mitigation of MPs, bibliometric analysis of the current status of research, their relevance to the modern context, and the development of a combinatorial strategy to amalgamate the advantages of these two unique processes via the concept of constructed wetlands for synergistically mitigating MPs. Thus, this review provides fresh insights into addressing MP pollution with sustainable ideologies to achieve improved mitigation outcomes without compromising the balance of the ecosystem.

Disposable face masks into aquatic media: Chemical and biological testing of the released compounds during the leaching process

The present study investigated the fate, and the biological effects posed by the presence of Disposable Face Masks (DFMs) into fresh- and saltwater media, using both chemical and biological testing. To this end, slightly fragmented DFMs were maintained in tanks with artificial sea water (ASW) or dH2O (DFMASW and DFMdH2O, respectively) for a period of 20 days (under continuous agitation, oxygen supply, and light/dark ration 1:1) to simulate both fresh- and saltwater natural conditions. Thereafter, DFMs leaching substances were determined, before proceeding to biological testing with the use of the marine bacterium Aliivibrio fischeri (Bioluminescence Inhibition assay), the fresh- and saltwater algal species Chlorococcum sp. and Tetraselmis suecica (algal bioassays), as well as the fairy shrimp Thamnocephalus platyurus, the water flea Daphnia magna, and the rotifer Brachionus calyciflorus (acute toxicity screening tests, in terms of microbiotest). According to the results, once into aquatic media (DFMASW and DFMdH2O) DFMs are subjected to degradation, leading to the release of organic, inorganic, and polymeric compounds (PP microfibers). Considering that possible interactions of the leaching substances could differentially affect the aquatic biota, the present study showed that DFMs leaching substances could be harmful to the fairy shrimp T. platyurus, and the water flea D. magna, with slight to non-toxic effects to be observed in case of Chlorococcum sp. and Tetraselmis suecica, the marine bacterium Aliivibrio fischeri, and the rotifer B. calyciflorus. The present findings showed that the DFMs improper disposal into fresh- and/or saltwater media, followed by their degradation and leaching processes, could lead to the release of substances of great environmental concern, thus promoting awareness about their proper handling and management, as well as the long-term monitoring of their environmental risk.

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.

Tire microplastic particles and warming inhibit physiological functions of the toxic microalga Alexandrium pacificum

Previous studies have confirmed that the tire microplastic particles (TMPs) have a variety of toxic biological effects. However, the potential toxic mechanisms of TMPs remain to be elucidated, especially in the interaction between particle behavior and seawater warming. In this study, we investigated the effects of three different concentrations of TMPs suspensions (0 mg/L, 1 mg/L, and 500 mg/L) on Alexandrium pacificum in both the presence and absence of warming. Our results revealed significant differences in toxicity among different concentrations of TMPs towards A. pacificum, i.e., low concentrations promoting but high concentrations inhibiting, furthermore, warming exacerbated these toxicological responses. Specifically, under elevated temperature, high concentrations TMPs could inhibit photosynthetic pigment and chlorophyll fluorescence parameter, as well as the nutrient absorption, and induced oxidative stress. Furthermore, TMPs could adsorb onto microalgae surfaces and thus, forming heterogeneous aggregates through agglomeration with extracellular secretions. This is strongly correlated with biomarker response. Overall, these findings highlight the influence of warming on the toxicity of TMPs and provide valuable data for risk assessment.

A state-of-the-art review of environmental behavior and potential risks of biodegradable microplastics in soil ecosystems: Comparison with conventional microplastics

As the use of biodegradable plastics becomes increasingly widespread, their environmental behaviors and impacts warrant attention. Unlike conventional plastics, their degradability predisposes them to fragment into microplastics (MPs) more readily. These MPs subsequently enter the terrestrial environment. The abundant functional groups of biodegradable MPs significantly affect their transport and interactions with other contaminants (e.g., organic contaminants and heavy metals). The intermediates and additives released from depolymerization of biodegradable MPs, as well as coexisting contaminants, induce alterations in soil ecosystems. These processes indicate that the impacts of biodegradable MPs on soil ecosystems might significantly diverge from conventional MPs. However, an exhaustive and timely comparison of the environmental behaviors and effects of biodegradable and conventional MPs within soil ecosystems remains scarce. To address this gap, the Web of Science database and bibliometric software were utilized to identify publications with keywords containing biodegradable MPs and soil. Moreover, this review comprehensively summarizes the transport behavior of biodegradable MPs, their role as contaminant carriers, and the potential risks they pose to soil physicochemical properties, nutrient cycling, biota, and CO2 emissions as compared with conventional MPs. Biodegradable MPs, due to their great transport and adsorption capacity, facilitate the mobility of coexisting contaminants, potentially inducing widespread soil and groundwater contamination. Additionally, these MPs and their depolymerization products can disrupt soil ecosystems by altering physicochemical properties, increasing microbial biomass, decreasing microbial diversity, inhibiting the development of plants and animals, and increasing CO2 emissions. Finally, some perspectives are proposed to outline future research directions. Overall, this study emphasizes the pronounced effects of biodegradable MPs on soil ecosystems relative to their conventional counterparts and contributes to the understanding and management of biodegradable plastic contamination within the terrestrial ecosystem.

Selection of engineered degradation method to remove microplastics from aquatic environments

Microplastics (MPs) in the aquatic environment are difficult to degrade naturally due to their hydrophobicity and structure. A variety of engineered degradation methods were developed to treat MPs contamination in the aquatic environment. Current reviews of MPs degradation methods only provided an inventory but lacked systematic comparisons and application recommendations. However, selecting suitable degradation methods for different types of MPs contamination may be more effective. This work examined the present engineered degradation methods for MPs in the aquatic environment. They were categorized into chemical degradation, biodegradation, thermal degradation and photodegradation. These degradation methods were systematically summarized in terms of degradation efficiency, technical limitations and production of environmental hazards. Also, the potential influences of different environmental factors and media on degradation were analyzed, and the selection of degradation methods were suggested from the perspectives of contamination types and degradation mechanisms. Finally, the development trend and challenges for studying MPs engineered degradation were proposed. This work will contribute to a better selection of customized degradation methods for different types of MPs contamination scenarios in aquatic environments.

Microplastics alter toxicity of the insecticide Bacillus thuringiensis israelensis to chironomid larvae in different ways depending on particle size

Microplastics (<5 mm) are emerging freshwater contaminants that can have a wide range of effects on aquatic biota. One concern is that combined effects of microplastics (MPs) with other stressors, such as co-occurring contaminants in urban or agricultural runoff may be significant even when the direct effects of MPs may be modest. Despite the frequent detection of both insecticides and MPs in freshwater ecosystems, there is a lack of co-exposure studies of insecticides (especially Bacillus thuringiensis israelensis (Bti)) and MPs. Here we tested the effects of ingested MPs and Bti individually and in co-exposure using the aquatic midge Chironomus riparius as a model organism. First instar larvae were fed two sizes of white polyethylene particles (34-50 and 125 μm diameter) at 106 mg/L in an artificial diet and simultaneously exposed to increasing concentrations of Bti (7, 13, 27, 53, and 89 ng/L Active Ingredient) in the water column for 21 days. For comparison, a trial was also conducted with naturally occurring kaolin clay particles (1-10 μm diameter) at 106 mg/L in the artificial diet. Bti alone reduced 7-day larval survival at higher concentrations (53, and 89 ng/L). Dietary PE-MPs and kaolin did not affect the survival of C. riparius larvae. However, when exposed in combination, PE-MPs modified the toxicity of Bti. This modification was size-dependent, with smaller particles (34-50 μm) increasing survival of Bti-exposed larvae and larger particles (125 μm) reducing survival. Our results show the potential for microplastics to alter the efficacy of an insecticide widely used to control nuisance midges and mosquitoes and add to a growing body of literature describing how the toxicological effects of microplastics are influenced by the size and shape of particles.

Dynamics of plastic debris and its density change between river compartments in the Tuul River system, Mongolia

Plastic pollution in river environments has become an emerging global concern. However, the migration of plastic and changes in its properties between river compartments are less understood. This study demonstrates the plastic debris aging and the dynamics between floodplain, surface water, and sediment compartments of the Tuul River, Mongolia. Plastic occurrence is evaluated in terms of their abundance, size, shape, polymer type, and photodegradation in each compartment. Photodegradation stages were calculated using the carbonyl index (CI). Plastic abundance was 5.46 ± 3.53 items m-2 in the floodplain, 155 ± 100.7 items m-3 in the surface water, and 128.4 ± 76.3 items kg-1 in the sediment. Microplastics dominated in the size category in all compartments, while macro- and megaplastics were found only in the floodplain. Polyethylene and polypropylene dominated the surface water and sediment, while polystyrene was the predominant plastic in the floodplain. A positive correlation was found between the distributed polymer types in the surface water and sediment compartments. The similar composition in size and polymer type suggests vertical plastic migration from water to sediment. Although CI values showed that the plastic aging was significantly different between water and sediment (water, 0.61 ± 0.26, and sediment, 0.90 ± 0.68), the dominance of low-density plastics with high CI in the sediment suggests that the aged plastic density changed during the vertical transport in the river system.

Impact of weathered and virgin polyethylene terephthalate (PET) micro- and nanoplastics on growth dynamics and the production of extracellular polymeric substances (EPS) of microalgae

The ever-increasing plastic waste accumulation in the marine environment necessitates a deeper understanding of microalgae interactions with micro- and nanoplastics (MNP), and the role of extracellular polymeric substances (EPS). EPS, known for its adhesive properties and produced as an algal stress response, may facilitate aggregation of both algae and MNPs, thereby impacting ecological and hydrodynamic processes such as the trophic transfer or vertical transport of MNPs. Moreover, gaining a deeper understanding of the impact of weathering processes on the potential toxicological effects of plastic particles, and the comparative significance of plastic-specific effects relative to those of naturally occurring particles such as kaolin clay, is imperative. Therefore, this study investigated the impact of fragmented, polydisperse virgin polyethylene terephthalate (PET, Daverage = 910 nm) and weathered PET (Daverage = 1700 nm) on the growth and the production of EPS of Rhodomonas salina. Algae were exposed to a range of low MNP concentrations (10, 100 and 1000 and 10,000 MNPs ml-1) for 11 days. A natural particle control (kaolin, Daverage = 1600 nm) was deployed to differentiate particle effects from plastic effects. It was observed that exposure to both weathered PET and virgin PET resulted in initially increased growth rates (7.80 % and 7.28 % respectively), followed by significant decreases in algae cell density (-30.1 % and -11.2 % respectively). Furthermore, exposure to weathered PET caused a simultaneous elevation in cellular EPS production (76.51 %). The effects of plastics were significantly larger than the effect of kaolin. Also, the observed effects were amplified by the weathering of the plastics. These observations underscore the interactions between particle type, age and concentration, and their distinct impacts on algae density and growth inhibition. The observations indicate a role for EPS as an algal protection mechanism, potentially affecting the environmental fate of MNP - microalgae aggregates.

Determination of microplastics in sediment, water, and fish across the Orange-Senqu River basin

Microplastics are increasingly recognised as posing a significant environmental threat across systems. Their pervasive presence in freshwater poses a serious concern, given the heavy reliance of both humans and biodiversity on healthy, functioning freshwater ecosystems. Acknowledgment of the potential risks led the transboundary Orange-Senqu River Commission (ORASECOM) to include sampling for microlitter (primarily microplastics) in riverine sediment, surface water, and fishes, across Southern Africa as part of the third Joint Basin Survey (JBS3) in 2021. The aim was to establish a first, basin-wide estimate of microlitter contamination across compartments, setting a baseline for further monitoring. The survey showed that the abundance of microlitter in riverine sediment (0 - 4000 particles.kg-1 dry weight (dw)) and riverine water (1.00 ± 0.71 - 69.75 ± 68.55 SD items.L-1) varied considerably between sample sites, with no correlation between the two. The abundance of microlitter in fishes was low (average of 0.7 ± 0.4 items.individual-1). Course resolution analyses suggested that microlitter concentrations in riverine sediment and riverine water at each site did not correlate with land use directly upstream, though variation in microlitter abundance did isolate some hotspots of contamination. Discharge data collected from nine gauging stations near sampling sites confirmed that low flows prevailed in the system during the study, with high flows occurring approximately 5 months prior during the summer months. There is some variation in river flow across the catchment which is a likely driver of microlitter transport. This was evident in the polymer composition for sediment and water samples. Based on the average discharge at each gauging station and microlitter concentrations measured in riverine water, the estimated microlitter load ranged from ∼889 particles.s-1 to ∼17.9 million particles.s-1, with a substantial amount ending likely up in the mudbelt adjacent to the Orange River mouth. This assessment provides a first insight into the characterisation and distribution of microlitter in multiple compartments across the Orange-Senqu River basin. Overall, the findings highlight the need for continued monitoring across compartments at catchment scales to improve our understanding of microplastic pathways into and within riverine systems.

The role of algae in regulating the fate of microplastics: A review for processes, mechanisms, and influencing factors

As an important emerging pollutant, the fate of microplastics (MPs) in ecosystems is of growing global concern. In addition to hydrodynamics and animals, algae can also affect the transport of MPs in aquatic environments, which could potentially remove MPs from the water column. Although researchers have conducted many studies on the sink of MPs regulated by algae in both marine and freshwater environments, there is still a lack of comprehensive understanding coupled with the increasingly scattered study contents and findings. This review aims to provide a systematic discussion of the processes, mechanisms, and influencing factors, which are coupled with the sink of MPs changes by algae. The main processes identified include retention, flocculation, deposition, and degradation. The retention of MPs is achieved by adhesion of MPs to algae or embedment/encrustation of MPs within the epibiont matrix of algae, thereby preventing MPs from migrating with water currents. The extracellular polymeric substances (EPS) and enzymes produced by algal metabolic activities can lead not only to the formation of aggregates containing MPs but also to the biodegradation of MPs. The processes that algae alter the fate of MPs in aquatic environments are very complex and can be influenced by various factors such as algal attributes, microplastic characteristics and environmental conditions. This review provides insights into recent advances in the fate of aquatic MPs and highlights the need for further research on MPs-algae interactions, potentially shortening the knowledge gap in the sink of MPs in aquatic ecosystems.

Effects of tire wear particle on growth, extracellular polymeric substance production and oxidation stress of algae Chlorella vulgaris: Performance and mechanism

Tire wear particles (TWP) represent a distinctive form of microplastics (MPs) that are widely distributed in aquatic ecosystems. However, the toxicity of various types of TWP on phytoplankton remain to be further explored. Thus, three different TWPs originating from replaced bicycle, car, and electro-mobile tire (marked as BTWP, CTWP, and ETWP) were selected and their long-term biological influences on Chlorella vulgaris were investigated. Results demonstrated TWPs showed a concentration-dependent growth promotion of Chlorella vulgaris, with a maximum promotion rate reached to 40.51 % (10 mg/L, 10 d), 23.5 % (80 mg/L, 12 d), and 28.7 % (20 mg/L, 12 d) in the presence of BTWP, CTWP and ETWP, respectively. Meanwhile, TWPs could stimulate the secretion of EPS and induce oxidative stress. EPS analysis revealed the increase of polysaccharides could protect the cell from the direct contact with TWP particles. Moreover, the increased concentration of EPS also helps to induce the settlement of TWP and reduce the leachate release. The release of TWP into the environment could act as an accelerator for the growth of Chlorella vulgaris, which might further change the normal physicochemical behaviors of algae colony in aquatic system. Our findings provide new insights into the toxicity mechanism of TWPs on freshwater algae and valuable data on environmental risk assessment of TWPs.

Impacts of nano- and micro-plastics exposure on zooplankton grazing, bacterial communities, and dimethylated sulfur compounds production in the microcosms

Dimethyl sulfide (DMS) is a prevalent volatile organic sulfur compound relevant to the global climate. Ecotoxicological effects of nano- and microplastics (NPs and MPs) on phytoplankton, zooplankton, and bacteria have been investigated by numerous studies. Yet, the influences of NPs/MPs on dimethylated sulfur compounds remains understudied. Herein, we investigated the impacts of polystyrene (PS) NPs/MPs (80 nm, 1 μm, and 10 μm) on zooplankton grazing, chlorophyll a (Chl a) concentration, bacterial community, dimethylsulfoniopropionate (DMSP), and DMS production in the microcosms. Our findings revealed that rotifer grazing increased the production of DMS in the absence of NPs/MPs but did not promote DMS production when exposed to NPs/MPs. The ingestion rates of the rotifer and copepod exposed to NPs/MPs at high concentrations were significantly reduced. NPs/MPs exposure significantly decreased DMS levels in the treatments with rotifers compared to the animal controls. In the bacterial microcosms, smaller NPs/MPs sizes were more detrimental to Chl a concentrations compared to larger sizes. The study revealed a stimulatory effect on Chl a concentrations, DMSPd concentrations, and bacterial abundances when exposed to 10 μm MP with low concentrations. The effects of NPs/MPs on DMS concentrations were both dose- and size-dependent, with NPs showing greater toxicity compared to larger MPs. NPs/MPs led to changes in bacterial community compositions, dependent on both dosage and size. NPs caused a notable decrease in the alpha diversities and richness of bacteria compared to MPs. These results provide insights into the influences of NPs/MPs on food webs, and subsequently organic sulfur compounds cycles.

Microalgae separation in MP-PVC contaminated wastewater using plant-based coagulant over different extraction methods in Bauru, Brazil

This study investigates the effectiveness of coagulation-flocculation and sedimentation (CFS) for separating microalgae, focusing on the use of various Moringa oleifera extracts as natural coagulants. We examined photobioreactor effluent (PBR) both with and without microplastic PVC (MP-PVC) contamination, referred to as PBR R2 and PBR R1, respectively. Utilising response surface methodology, we identified optimal conditions for the removal of microalgae and MP-PVC. Validation tests demonstrated that the aqueous extract of delipidated Moringa oleifera powder (AEDMOP) achieved high removal efficiencies, with coagulant dosages of 630 mg L-1 for PBR R1 and 625 mg L-1 for PBR R2. Both conditions showed microalgae removal efficiencies exceeding 83% for turbidity, colour, OD540 nm, OD680 nm, and OD750 nm, and 63% for OD254 nm. Interestingly, the optimised conditions for PBR R2 required slightly less coagulant, likely due to the additional particulate matter from MP-PVC. While extracellular polymeric substances (EPS) exhibited a marginal effect on flocculation, further investigation into their role in CFS is necessary. Our findings highlight the potential of AEDMOP for efficient microalgae separation, even in the presence of microplastics.

Polyethylene microplastic modulates the toxicity of pentachlorophenol to the microalgae Isochrysis galbana, clone t-ISO

Pentachlorophenol (PCP) and polyethylene microplastic (PE-MP) have been designated as emerging and persistent pollutants, respectively. The combined effects of those pollutants are still unknown, especially to organisms like phytoplankton that may adsorb to their surface. Therefore, the purpose of this study was to investigate for the first time the effects of PE-MP alone and in combination with PCP on the microalgae Isochrysis galbana, clone t-ISO following 72 h of exposure. Photosynthetic pigments amounts, carotenoid, protein, carbohydrate and fatty acids have been assessed. Acute toxicity test showed that the 72 h median inhibition concentration (72 h-EC50) was 148.2, 0.66 and 087 mg L-1 for PE-MP, PCP and their mixture. The utmost effects in growth inhibition rates were noted with 0.5 and 1.25 mg L-1 PCP (23% and 85%, respectively), and 100 and 300 mg L-1 PE-MP (49% and 64%, respectively). Moreover, it was found that those concentrations had a major impact on the photosynthetic pigments, protein, carbohydrate, and fatty acids amounts in algal cells. Furthermore, levels of H2O2 and Malondialdehyde (MDA), as well as the activities of catalase (CAT), superoxide dismutase (SOD), and ascorbate peroxidase (APX), indicated the induction of an oxidative stress in algal cells. It appears that adding PE-MP at a no-effect concentration (25 mg L-1) reduces the toxicity caused by PCP due to its adsorption to polyethylene microplastics.

Temporal changes in microalgal biomass and species composition on different plastic polymers in nutrient-enriched microcosm experiments

Marine plastic debris (MPD) is a potential threat to marine ecosystems, but its function as a vector for the transportation of harmful microalgae and its impact on the habitats of other marine organisms are uncertain. To address this gap in knowledge, we performed month-long experiments in 30 L microcosms that contained plates made of six different plastic polymers (polypropylene [PP], low-density polyethylene [LDPE], high-density polyethylene [HDPE], polyvinyl chloride [PVC], polyethylene terephthalate [PET], and polystyrene [PS]), and examined the time course of changes in planktonic and periphytic microalgae. There were no significant differences in the composition of periphytic microalgae or biomass among the different plastic polymers (p > 0.05). Nutrient depletion decreased the abundance of planktonic microalgae, but increased the biomass of attached periphytic microalgae (p < 0.05). In particular, analysis of the plastic plates showed that the abundance of benthic species that are responsible for harmful algal blooms (HABs), such as Amphidinium operculatum and Coolia monotis, significantly increased over time (days 21-28; p < 0.05). Our findings demonstrated that periphyton species, including benthic microalgae that cause HABs, can easily attach to different types of plastic and potentially spread to different regions and negatively impact these ecosystems. These observations have important implications for understanding the potential role of MPD in the spread of microalgae, including HABs, which pose a significant threat to marine ecosystems.

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.

Biofilms in plastisphere from freshwater wetlands: Biofilm formation, bacterial community assembly, and biogeochemical cycles

Microorganisms can colonize to the surface of microplastics (MPs) to form biofilms, termed "plastisphere", which could significantly change their physiochemical properties and ecological roles. However, the biofilm characteristics and the deep mechanisms (interaction, assembly, and biogeochemical cycles) underlying plastisphere in wetlands currently lack a comprehensive perspective. In this study, in situ biofilm formation experiments were performed in a park with different types of wetlands to examine the plastisphere by extrinsic addition of PVC MPs in summer and winter, respectively. Results from the spectroscopic and microscopic analyses revealed that biofilms attached to the MPs in constructed forest wetlands contained the most abundant biomass and extracellular polymeric substances. Meanwhile, data from the high-throughput sequencing showed lower diversity in plastisphere compared with soil bacterial communities. Network analysis suggested a simple and unstable co-occurrence pattern in plastisphere, and the null model indicated increased deterministic process of heterogeneous selection for its community assembly. Based on the quantification of biogeochemical cycling genes by high-throughput qPCR, the relative abundances of genes involving in carbon degradation, carbon fixation, and denitrification were significantly higher in plastisphere than those of soil communities. This study greatly enhanced our understanding of biofilm formation and ecological effects of MPs in freshwater wetlands.

Insights into the response mechanisms of Tetradesmus obliquus to aged polylactic acid and tetracycline exposure via transcriptome analysis and physiological evaluations

Microplastics (MPs) and antibiotics, identified as emerging pollutants, are extensively prevalent in aquatic environments and display prolonged durability. Unlike conventional plastics, biodegradable plastics are more susceptible to decomposition in the environment, resulting in the generation of microplastics and posing potential risks to the aquatic ecosystems. In this study, we assessed growth inhibition, chlorophyll a content, malondialdehyde content (MDA), and antioxidant enzyme activities. These measurements were integrated with transcriptome analysis to explore the response mechanisms of virgin and aged polylactic acid (vPLA and aPLA) and tetracycline (TC) following 14-day exposure to Tetradesmus obliquus, either individually or in combination. The findings indicated that exposure to vPLA did not significantly impact the growth of T. obliquus. Conversely, aPLA demonstrated growth-promoting effects on T. obliquus, particularly in the latter incubation stages. Moreover, a 14-day exposure significantly increased the chlorophyll a content and the activities of superoxide dismutase (SOD), catalase glutathione (CAT) and glutathione S-transferase (GST) within the algal cells. Apart from 1 mg L-1, the TC concentrations of 2.5, 5.0, and 10 mg L-1 exhibited significant toxic effects on T. obliquus, including growth inhibition, decreased chlorophyll a content, elevated activities of SOD, CAT, and GST, and increased MDA levels. Exposure to a combination of 300 mg L-1 aPLA and 5.0 mg L-1 TC, compared to solely 5 mg L-1 TC, demonstrated a notable reduction in TC toxicity to T. obliquus in the presence of aPLA. This was indicated by elevated algal cell density and chlorophyll a content, as well as a decrease in MDA content. Transcriptome analysis indicated an enrichment of differentially expressed genes (DEGs) in pathways linked to porphyrin metabolism, photosynthesis, carbon fixation, and metabolism within the aPLA + TC combined exposure. The study aid in expanding our knowledge of the potential ecological risks posed by biodegradable plastics and accompanying pollutants in aquatic environments.

Ecotoxicological Effects of Microplastics Combined With Antibiotics in the Aquatic Environment: Recent Developments and Prospects

Both microplastics and antibiotics are commonly found contaminants in aquatic ecosystems. Microplastics have the ability to absorb antibiotic pollutants in water, but the specific adsorption behavior and mechanism are not fully understood, particularly in relation to the impact of microplastics on toxicity in aquatic environments. We review the interaction, mechanism, and transport of microplastics and antibiotics in water environments, with a focus on the main physical characteristics and environmental factors affecting adsorption behavior in water. We also analyze the effects of microplastic carriers on antibiotic transport and long-distance transport in the water environment. The toxic effects of microplastics combined with antibiotics on aquatic organisms are systematically explained, as well as the effect of the adsorption behavior of microplastics on the spread of antibiotic resistance genes. Finally, the scientific knowledge gap and future research directions related to the interactions between microplastics and antibiotics in the water environment are summarized to provide basic information for preventing and treating environmental risks. Environ Toxicol Chem 2024;43:1950-1961. © 2024 SETAC.

A critical review of microplastics in aquatic ecosystems: Degradation mechanisms and removing strategies

Plastic waste discarded into aquatic environments gradually degrades into smaller fragments, known as microplastics (MPs), which range in size from 0.05 to 5 mm. The ubiquity of MPs poses a significant threat to aquatic ecosystems and, by extension, human health, as these particles are ingested by various marine organisms including zooplankton, crustaceans, and fish, eventually entering the human food chain. This contamination threatens the entire ecological balance, encompassing food safety and the health of aquatic systems. Consequently, developing effective MP removal technologies has emerged as a critical area of research. Here, we summarize the mechanisms and recently reported strategies for removing MPs from aquatic ecosystems. Strategies combining physical and chemical pretreatments with microbial degradation have shown promise in decomposing MPs. Microorganisms such as bacteria, fungi, algae, and specific enzymes are being leveraged in MP remediation efforts. Recent advancements have focused on innovative methods such as membrane bioreactors, synthetic biology, organosilane-based techniques, biofilm-mediated remediation, and nanomaterial-enabled strategies, with nano-enabled technologies demonstrating substantial potential to enhance MP removal efficiency. This review aims to stimulate further innovation in effective MP removal methods, promoting environmental and social well-being.

Distribution and effects of microplastics as carriers of heavy metals in river surface sediments

There are few studies on microplastics (MPs) in urban river sediments compared to oceans, soils, and even rivers. In this study, the seasonal abundance of MPs, as well as their influencing factors on heavy metal adsorption in river sediments of the Ancient Canal of Zhenjiang City, China, were investigated for the first time. Through on-site sampling, microscopic observation, Raman spectroscopy, scanning electron microscopy, and high-temperature digestion, the abundance, shape, color, particle size, type, and surface characteristics of MPs in Ancient Canal sediments in different seasons, as well as the influencing factors of MPs as heavy metal carriers in different seasons, were analyzed. The results showed that the average abundance of MPs is 2049.09 ± 883.78 and 2216.36 ± 826.21 items kg-1 dry sediments in summer and winter, respectively, and different sites change significantly. In addition, particle sizes, types, colors, and shapes of MPs exhibited seasonal variations. Four MPs shapes were mainly observed: fibers, fragments, particles, and films. Among them, MPs in summer sediments are mainly fiber, and MPs in winter sediments are mainly particles. In the sediment in summer and winter, transparent MPs and small-size (<0.5 mm) MPs are the main ones, where the abundance of MPs decreased with increasing MPs size. The main MPs species are polyvinyl chloride (PVC), polystyrene (PS), polypropylene (PP), polyethylene terephthalate (PET), polycarbonate (PC), and polyethylene (PE), with PP being the predominant MPs in the sediments in different seasons. Scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) revealed that the surfaces of the MPs were characterized by rough, porous, cracked, and torn, with the attachment of various heavy metal elements, and all of the heavy metal elements accumulated to different degrees on the MPs. There was a significant positive correlation (p < 0.05) between the Mn content in the MPs and the Mn content in the sediments in winter, suggesting that the Mn in the MPs in winter may be derived from the sediments. In addition, the type, shape, size, and color of MPs affect the adsorption capacity of heavy metals. Most of the adsorption of MPs on Pb showed a significant negative correlation, and the adsorption of MPs on Cr, Zn, Cu, Cd, and Mn showed a significant positive correlation. MPs can be used as carriers of heavy metals, which will further enhance the hazards of living organisms and pose a potential threat to the safety of the urban river environment.

Fauna - Microplastics interactions: Empirical insights from benthos community exposure to marine plastic waste

Microplastic deposition in soft marine sediments raises concerns on their role in sediment habitats and unknown effects on resident macrobenthic communities. To assess the reciprocal influence that MPs and macrobenthos might have on each other, we performed a mesocosm experiment with ambient concentrations of environmental Polyethylene (PE) and a non-manipulated, natural macrobenthic community from the Belgian part of the North Sea (BPNS). Our results show that PE fragments increase mortality of abundant bivalves (specifically Abra alba) after 30 days of exposure but not for the most abundant polychaete Owenia fusiformis, possibly due to its predominant suspension feeding behavior. Fast burial of surface MPs exposes deep-dwelling burrowers to the pollutant, however reducing the amount of MPs interacting with (sub) surface living fauna. We conclude that macrobenthos promotes the sequestration of deposited MPs, counteracting resuspension, and can have cascading effects on biodiversity due to their effect on abundant and functionally important species.

The aging of microplastics exacerbates the damage to photosynthetic performance and bioenergy production in microalgae (Chlorella pyrenoidosa)

The toxicity of microplastics (MPs) on freshwater plants has been widely studied, yet the influence of aged MPs remains largely unexplored. Herein, we investigated the influence of polyvinyl chloride (PVC) MPs, both before and after aging, at different environmentally relevant concentrations on Chlorella pyrenoidosa, a freshwater microalgae species widely recognized as a valuable biomass resource. During a 96-h period, both virgin and aged MPs hindered the growth of C. pyrenoidosa. The maximum growth inhibition rates were 32.40 % for virgin PVC at 250 mg/L and 44.72 % for aged PVC at 100 mg/L, respectively. Microalgae intracellular materials, i.e., protein and carbohydrate contents, consistently decreased after MP exposure, with more pronounced inhibition observed with aged PVC. Meanwhile, the MP aging significantly promoted the nitrogen uptake of C. pyrenoidosa, i.e., 1693.45 ± 42.29 mg/L (p < 0.01), contributing to the production of humic acid-like substances. Additionally, aged PVC induced lower chlorophyll a and Fv/Fm when compared to virgin PVC, suggesting a more serious inhibition of the photosynthesis process of microalgae. The toxicity of MPs to C. pyrenoidosa was strongly associated with intercellular oxidative stress levels. The results indicate that MP aging exacerbates the damage to photosynthetic performance and bioenergy production in microalgae, providing critical insights into the toxicity analysis of micro(nano)plastics on freshwater plants.

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.

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.

Impact of heteroaggregation between microplastics and algae on particle vertical transport

Understanding the impacts of microplastics (MPs) on aqueous environments requires understanding their transport dynamics and how their presence affects other natural processes and cycles. In this context, one aspect to consider is how MPs interact with freshwater snow (FWS), a mixture of algae and natural particles. FWS is one of the primary drivers of the flux of organic matter from the water surface to the bottom sediment, where zooplankton, diurnal migration, fish faecal pellets settling and turbulent mixing can also play prominent roles. Understanding how MPs and FWS heteroaggregation affects their respective settling velocities is important to assess not only MPs fate and transport but also their ecological impacts by altering FWS deposition and thereby nutrient cycling. In this present study, we obtained a mechanistic understanding of the processes controlling MPs settling dynamics and heteroaggregation with FWS and the subsequent impacts on the settling rates of both MPs and ballasted FWS. Here we used a plexiglass column equipped with a stereoscopic camera system to track the settling velocities of (1) MPs of various compositions, densities and morphologies, (2) FWS flocs and (3) MP-FWS agglomerates. For each experimental set, thousands of particles were tracked over a series of image sequences. We found that agglomerates with high-density MPs settled at least twofold faster than FWS alone, implying a much smaller residence time in the water column, except for cases with MP fibres or low-density plastics. These findings will help to refine MP fate models and, while contingent on MPs number, may impact biogeochemical cycles by changing the flux of nutrients contained in FWS to the sediment.

Photodegradation of Microplastics through Nanomaterials: Insights into Photocatalysts Modification and Detailed Mechanisms

Microplastics (MPs) pose a profound environmental challenge, impacting ecosystems and human health through mechanisms such as bioaccumulation and ecosystem contamination. While traditional water treatment methods can partially remove microplastics, their limitations highlight the need for innovative green approaches like photodegradation to ensure more effective and sustainable removal. This review explores the potential of nanomaterial-enhanced photocatalysts in addressing this issue. Utilizing their unique properties like large surface area and tunable bandgap, nanomaterials significantly improve degradation efficiency. Different strategies for photocatalyst modification to improve photocatalytic performance are thoroughly summarized, with a particular emphasis on element doping and heterojunction construction. Furthermore, this review thoroughly summarizes the possible fundamental mechanisms driving the photodegradation of microplastics facilitated by nanomaterials, with a focus on processes like free radical formation and singlet oxygen oxidation. This review not only synthesizes critical findings from existing studies but also identifies gaps in the current research landscape, suggesting that further development of these photocatalytic techniques could lead to substantial advancements in environmental remediation practices. By delineating these novel approaches and their mechanisms, this work underscores the significant environmental implications and contributes to the ongoing development of sustainable solutions to mitigate microplastic pollution.

Unveiling the molecular mechanisms of size-dependent effect of polystyrene micro/nano-plastics on Chlamydomonas reinhardtii through proteomic profiling

Microplastics have become a prevalent environmental pollutant due to widespread release and production. Algae, as primary producers, play a crucial role in maintaining the ecological balance of freshwater environments. Despite reports on the inhibition of microalgae by microplastics, the size-dependent effects on microalgae and associated molecular mechanism remain poorly understood. This study investigates the impacts of three polystyrene micro/nano-plastics (PS-MNPs) with different sizes (100 nm, 350 nm, and 6 μm) and concentrations (25-200 mg/L) on Chlamydomonas reinhardtii (C. reinhardtii) throughout its growth period. Results reveal size- and concentration-dependent growth inhibition and induction of oxidative stress by PS-MNPs, with microalgae exhibiting increased vulnerability to smaller-sized and higher-concentration PS-MNPs. Proteomics analysis elucidates the size-dependent suppression of proteins involved in the photosynthesis process by PS-MNPs. Photosynthetic activity assays demonstrate that smaller PS-MNPs more significantly reduce chlorophyll content and the maximal photochemical efficiency of photosystem II. Finally, electron microscope and Western blot assays collectively confirm the size effect of PS-MNPs on microalgae growth is attributable to suppressed protein expression rather than shading effects. This study contributes to advancing our understanding of the intricate interactions between micro/nano-plastics and algae at the molecular level, emphasizing the efficacy of proteomics in dissecting the mechanistic aspects of microplastics-induced biological effects on environmental indicator organisms.

Physiological and genetic responses of the benthic dinoflagellate Prorocentrum lima to polystyrene microplastics

Microplastics are well known as contaminants in marine environments. With the development of biofilms, most microplastics will eventually sink and deposit in benthic environment. However, little research has been done on benthic toxic dinoflagellates, and the effects of microplastics on benthic dinoflagellates are unknown. Prorocentrum lima is a cosmopolitan toxic benthic dinoflagellate, which can produce a range of polyether metabolites, such as diarrhetic shellfish poisoning (DSP) toxins. In order to explore the impact of microplastics on marine benthic dinoflagellates, in this paper, we studied the effects of polystyrene (PS) on the growth and toxin production of P. lima. The molecular response of P. lima to microplastic stress was analyzed by transcriptomics. We selected 100 nm, 10 μm and 100 μm PS, and set three concentrations of 1 mg L-1, 10 mg L-1 and 100 mg L-1. The results showed that PS exposure had limited effects on cell growth, but increased the OA and extracellular polysaccharide content at high concentrations. After exposure to PS MPs, genes associated with DSP toxins synthesis, carbohydrate synthesis and energy metabolism, such as glycolysis, TCA cycle and pyruvate metabolism, were significantly up-regulated. We speculated that after exposure to microplastics, P. lima may increase the synthesis of DSP toxins and extracellular polysaccharides, improve the level of energy metabolism and gene expression of ABC transporter, thereby protecting algal cells from damage. Our findings provide new insights into the effects of microplastics on toxic benthic dinoflagellates.