Adsorption of levofloxacin by ultraviolet aging microplastics

Characteristics of microplastics in typical poultry farms and the association of environment microplastics colonized-microbiota, waterfowl gut microbiota, and antibiotic resistance genes

Microplastics (MPs) pollution is a growing global environmental concern. MPs serve as ecological niches for microbial communities, which may accelerate the spread of antibiotic resistance genes (ARGs), posing risks to the breeding industry. While studies on MPs in aquatic organisms are common, research on farmed poultry is limited. This study investigates MPs in poultry farm environments and waterfowl intestines for the first time. MPs were isolated via density separation and analyzed for characterization in soil, pond water, and waterfowl intestines. Metagenomics was used to investigate the association between environment MPs colonized-microbiota and waterfowl gut microbiota. Our findings reveal that MPs are abundant in soil (6.75 ± 2.78 items/g d.w.), pond water (0.94 ± 0.28 items/g w.w.), and poultry intestines (45.35 ± 19.52 items/g w.w.), primarily appearing as fragmented particles sized 20-50 μm. MPs abundance in intestines correlates with environmental levels. Colonized-microbiota on MPs are linked to poultry intestinal microbiota, with greater diversity and microbial functions. Network analysis reveals that Corynebacterium plays a key role in MPs and poultry intestinal. Polymyxin resistance exhibits high clustering. Procrustes analysis reveals correlations between MPs, bacteria, and ARGs in the farming environment. Overall, MPs in poultry farms may facilitate pathogen and ARGs transmission, posing risks to animal gut health.

Fate, characteristics, and potential threat of microplastics in sludge under various dewatering treatments

Microplastics (MPs), an emerging environmental pollutant, have been found in wastewater sludge with increasing frequency. Their occurrence, surface properties, and adsorption characteristics may be altered during various sludge dewatering processes. This study explored and compared the performance of four types of sludge dewatering processes (FeCl3 + CaO, Fe2+ + H2O2 + CaO, Fe2+ + peroxymonosulfate (PMS) + CaO, and Fe2+ + CaO2 + CaO) in improving sludge dewaterability, the fate and characteristics of MPs during treatments, and their effect on the adsorption of heavy metals by aged MPs. Results showed that iron-based advanced oxidation processes (Fe-AOPs) indicated superior performance in improving sludge dewaterability compared to conventional FeCl3 + CaO treatment, as evidenced by the water content of sludge cakes being reduced to below 54.0 % (w/t) in Fe-AOPs. Fe2+ + PMS + CaO and FeCl3 + CaO effectively reduced MPs concentrations in both dewatered sludge and filtrate, thereby mitigating potential environmental risks. The potential risk associated with heavy metal adsorption onto treated MPs was greater for Fe2+ + PMS + CaO than for FeCl3 + CaO. In summary, Fe2+ + PMS + CaO offered a feasible method for sludge dewatering and MPs removal, particularly suited to sludge with low heavy metal concentrations. FeCl3 + CaO treatment effectively mitigated co-toxicity between heavy metals and MPs, proving more suitable for sludge with high heavy metal content. This study offers new insights into the selection of appropriate sludge treatments regarding MPs.

Effects of microplastics on atrazine removal in constructed wetlands: Insight into the response characteristics of microorganisms, enzyme activity, and functional genes

Constructed wetlands (CWs) technology has been widely used to treat agricultural non-point source pollution. However, knowledge about the impact mechanism and distribution characteristics of microplastics (MPs) on pesticide treatment in CWs is limited. This study employed atrazine (ATZ), a representative pesticide, as a model contaminant, to systematically investigate the impacts of polyethylene microplastics (PE MPs) on the removal of ATZ and nutrients, as well as the enzyme activity and the distribution of functional genes in vertical subsurface-flow CW microcosm. The results showed that compared to the control group (CK), CWs treated with different concentrations of MPs had no significant difference in the removal of ATZ. Moreover, in the second stage (ATZ=400 μg/L), the average removal efficiency of ATZ by CWs containing MPs was slightly higher than that of the CK group. PE MPs reduced the nitrogen removal efficiency of CWs by 1.57 %-3.03 %, but had no significant effect on TP removal. The concentration distribution of PE MPs in the substrate layer exhibited a decreasing trend from top to bottom, and the interception capacity of CWs gradually decreased with time (from 100 % to 97.4 %); When exposed to PE MPs, the activities of enzymes in substrate related to nitrogen metabolism were inhibited; Moreover, the addition of PE MPs in CWs promoted the removal of ATZ by increasing the abundance of ATZ metabolizing bacteria (Hydrogenophaga, Zoogloea, Rhizobium, etc.) and ATZ degradation key genes (atzA and trzN). These results not only provide theoretical support for the practical application of CWs in the treatment of pesticide wastewater, but also provide a theoretical basis for the environmental risk control of pesticide non-point source pollution ecological treatment technology in the presence of MPs.

Microplastics impacts the toxicity of antibiotics on Pinellia ternata: An exploration of their effects on photosynthesis, oxidative stress homeostasis, secondary metabolism, the AsA-GSH cycle, and metabolomics

Antibiotics and microplastics (MPs) are two new types of contaminants that are widely existent in agricultural systems. MPs could act as carriers of antibiotics, and affect the bioavailability and degradation of antibiotics, causing a combined effect on plant growth. The aim of the present experiment was to explore the effects of the treatments of oxytetracycline (OTC, 100 mg kg-1) alone and in combination with polyethylene microplastics (PE-MPs, 0.1 %, 1 %, 3 %) on P. ternata phenotypic parameters, photosynthetic system, reactive oxygen species (ROS), secondary metabolism, ascorbate-glutathione (AsA-GSH) cycle, and metabolomics. Results demonstrated that exposure to OTC alone reduced P. ternata fresh weight by causing oxidative damage, reducing photosynthetic pigment and secondary metabolite contents. OTC + MP0.1 group alleviated OTC stress to P. ternata by increasing photosynthetic pigment contents and antioxidant enzyme activities. OTC + MP3 group significantly reduced plant height of P. ternata. In addition, metabolomics analysis showed that OTC treatment interfered with pantothenate and CoA biosynthesis. The OTC + MP0.1 group activated pantothenate and CoA biosynthesis and glutathione metabolism. The significance of this study lies in clarifying the effects of OTC on medicinal plants and whether its influence mechanism is regulated by the concentration of MPs.

Insights into combined stress mechanisms of microplastics and antibiotics on anammox: A critical review

The microplastic and antibiotic pollution poses a major threat to human health and natural ecology. Wastewater treatment systems act as a link between human societies and natural ecosystems. Microplastics (MPs) and antibiotics (ATs) in wastewater endanger the stabilization of the anaerobic ammonium oxidation (anammox) system. However, most existing studies have primarily concentrated on the effects and stress mechanisms of either MPs-induced or ATs-induced stress on anammox. A comprehensive and holistic overview of the effects and underlying mechanisms of the combined stress exerted on anammox by both MPs and ATs is currently lacking. This review concludes the effects of MPs and ATs on anammox bacteria (AnAOB) and describes the mechanisms of the effects of these two emerging contaminants on AnAOB. Subsequently, the effects that the combined stress of MPs and ATs can have on the anammox system are reviewed. The adsorption of ATs by MPs, an indispensable mechanism affecting the combined stress, is explained. Additionally, the effect of MPs' aging on their ability to adsorb ATs is presented. Finally, this paper proposes to alleviate the combined stress of MPs and ATs by enriching biofilms and points out the risk of propagation of ARGs under the combined stress. This review sheds light on valuable insights into the combined stress of MPs and ATs on anammox and points out future research directions for this combined stress.

Potential impact and mechanism of aged polyethylene microplastics on nitrogen assimilation of Lactuca sativa L

Nitrogen (N) is the driving factor for crop yield and quality, and more research is needed on the mechanisms of aged micro/nano plastics (MNPs) on N assimilation in edible crops. In this study, pot experiments were conducted to investigate the potential effect of aged polyethylene (PE) microplastic addition (particle sizes: 20 and 0.1 µm, addition levels: 0.5 % [w/w], referred to as the control (CK), P20 (20-µm PE), AP20 (20-µm aged PE), P0.1 (0.1-µm PE), AP0.1 (0.1-µm aged PE) on MNPs accumulation and N assimilation in romaine lettuce (Lactuca sativa L.). The results showed that the particle size of MNPs accumulated in lettuce decreased from root > stem > leaf. Compared to CK, the fresh plant weight significantly decreased by 40.84 and 51.62 % in AP20 and AP0.1, respectively. The results indicated that MNPs could affect lettuce growth via soil nutrient availability, and aged 100-nm PE decreased soil NH4+ and plant TN concentrations by 9.10 and 21.99 %, respectively, compared to that in CK. N assimilation in lettuce was significantly inhibited by aged MNPs, which manifested as the soluble protein content in lettuce under AP20 and AP0.1 treatments being significantly reduced by 30.59 and 42.11 %, respectively (P < 0.01). Possible mechanisms included inhibition of carbon assimilation, photosynthesis, and Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). The toxic effect of aged MNPs on growth and N assimilation in lettuce was much greater than that of the particle size, which was attributed to the carbonyl and hydroxyl groups caused by aging. Structural equation modeling showed that soil nitrogen positively affected total nitrogen (TN) (0.359), chlorophyll (0.665), Rubisco (0.441), soluble protein (0.383), and biomass (0.460), and negatively affected phosphoenolpyruvate carboxylase (PEPC) (-0.325), soluble sugar (-0.134). This study enhances current understandings of the effects of microplastics on N assimilation in edible crops. The findings indicated that aged MNPs accumulation in vegetables may negatively affect agricultural sustainability and food safety.

Unlocking the combined impact of microplastics and emerging contaminants on fish: A review and meta-analysis

Microplastics (MPs) possess unique adsorptive properties that render their surfaces prone to absorbing other contaminants. When interacting with these emerging contaminants, MPs may have unpredictable negative impacts on fish. Prior studies have primarily concentrated on the impact of single contaminants, while investigations into combined pollution have not received adequate attention. Therefore, research on combined pollution holds greater practical significance. The physiological indicators of fish affected by emerging contaminants and the mechanisms behind these effects are not yet fully clear. To address this issue, a meta-analysis was performed to evaluate the impact of combined pollution of MPs-containing emerging contaminants on various aspects of fish health, encompassing behavior, consumption, development, and reproduction, along with the assessment of oxidative stress and neurotoxicity of fish. The results of the meta-analysis indicated that combined pollution adversely impacted fish reproduction, development, oxidative stress, and neurotoxicity. Importantly, significant differences were observed between fish species regarding their susceptibility to function and oxidative stress. Further investigation into the mechanisms of the impact of combined pollution on fish revealed that the magnitude of this impact is closely associated with the characteristics of the MPs themselves. MPs with higher adsorption capacities tend to lead to more severe consequences, while the impact of MPs with lower adsorption capacities relies more on their toxicity. Nevertheless, a close correlation between the duration of exposure to combined pollution and the level of oxidative stress in fish was not identified. Through a systematic analysis of existing studies, this review not only explored the cumulative effects of combined pollution on fish but also highlighted the intricate nature of such pollution within aquatic ecosystems. It contributes to the growing body of knowledge on the subject and emphasizes the need for further research to unravel the complexities associated with the combined impact of MPs-containing emerging contaminants on aquatic life.

Insight into the effect of natural aging of polystyrene microplastics on the sorption of legacy and emerging per- and polyfluorinated alkyl substances in seawater

Microplastics (MPs) are abundant in aquatic environments and due to their small size, surface properties, and strong hydrophobicity, they can easily sorb chemicals, thus potentially acting as pollutant carriers. To date, most studies investigating the sorption of chemicals on MPs have principally focused on virgin MPs. However, MPs in the environment undergo aging effects, which changes their physical-chemical properties and aptitude to interact with chemicals, such as per- and polyfluorinated alkyl substances (PFAS) referred to as "forever chemicals". In this study, we compared the sorption behavior of nine PFAS, exhibiting different physical-chemical properties, on virgin and naturally aged polystyrene microplastic (PS-MPs) to explore to what extent the environmental aging affects the sorption behavior of the PS-MPs for different legacy and emerging PFAS in seawater. Differences in the morphology and surface properties of aged PS-MPs were examined by infrared spectroscopy, surface area analysis, scanning electron microscopy, and X-ray diffraction. Results revealed that compared to virgin PS-MPs, aged PS-MPs exhibited morphological changes (e.g. cavities, pits, and rough surfaces) with biofilm development and signs of oxidation on the MPs surface. PFAS sorption on PS-MPs was enhanced for the aged PS-MPs compared to virgin PS-MPs with Kd values ranging from 327 L kg-1 for PFOA to 3247 L kg-1 for PFOS in aged PS-MPs. The difference in sorption capacity was mainly attributed to the physical-chemical changes and the adhered biofilm observed in aged PS-MPs. Results also showed that virgin PS-MPs adsorb PFAS mainly through steric hindrance, while the aged PS-MPs may involve more complex sorption mechanisms. This research provides additional insights into the ability of aged MPs as potential carriers of legacy and emerging contaminants in the marine environment.

Adsorption of neonicotinoid insecticides by mulch film-derived microplastics and their combined toxicity

Mulch films allow for efficient crop production, yet their low recovery after use causes severe microplastics (MPs) pollution in agricultural soils. MPs in agricultural environments undergo complex ageing processes, which can alter their interactions with coexisting neonicotinoids and result in unpredictable ecological risks. Here, polyethylene (PE) and polybutylene adipate terephthalate (PBAT), typical mulch films, were chosen for the preparation of PE-MPs and PBAT-MPs. The adsorption of two common neonicotinoids, imidacloprid and dinotefuran, by the two MPs and their joint toxicity were examined. We found that the specific surface area of PBAT-MPs (7.59 m2 g-1) is greater than that of PE-MPs (2.83 m2 g-1), which results in a greater adsorption capacity for neonicotinoids. Additionally, ageing increased the adsorption capacity of MPs for neonicotinoids by 37.50-40.68 % for PBAT-MPs and 44.23-72.34 % for PE-MPs. This enhancement is attributed to the introduction of additional oxygen-containing functional groups on the MPs' surfaces, which can form hydrogen bonds with the amino groups in imidacloprid and dinotefuran. Furthermore, compared to single MPs and neonicotinoids, stronger inhibition in the growth of Escherichia coli and the germination of lettuce seeds was observed when they coexisted. This study highlights the importance of assessing the interactions between MPs and neonicotinoids and their joint toxicity, thereby improving our understanding of the potential risks of MPs towards the agricultural ecosystems.

Adsorption and desorption of parachlormetaxylenol by aged microplastics and molecular mechanism

The addition of active ingredients such as antibacterial agent and non-active ingredients such as plastic microspheres (MPs) in personal care products (PCPs) are the common pollutants in the aquatic environment, and their coexistence poses potential threat to the aquatic ecosystem. As a substitute for the traditional antibacterial ingredients triclosan and triclocarban, the usage of parachlormetaxylenol (PCMX) is on the rise and is widely used in PCPs. In this study, the adsorption and desorption behaviors of PCMX were investigated with two typical MPs, polyvinyl chloride (PVC) and polyethylene (PE), and the effects of different aging modes and molecular mechanisms were explored through batch experiments and density functional theory calculation. Both laboratory aging and field aging resulted in surface wrinkles of MPs, along with an increased proportion of oxygen-containing functional groups (CO, -OH). At the same aging time, the degree of laboratory aging was stronger than that of field aging, and the aging degree of PVC was greater that of PE. The aging process enhanced the adsorption capacity of MPs for PCMX. The equilibrium adsorption capacity of PVC increased from 3.713 mg/g (virgin) to 3.823 mg/g (field aging) and 3.969 mg/g (laboratory aging), while that of PE increased from 3.509 mg/g to 3.879 mg/g and 4.109 mg/g, respectively. Meanwhile, aging also resulted in an increase in the desorption capacity of PCMX from PVC and PE. Oxygen-containing functional groups in aged MPs could serve as adsorption sites for PCMX and improved the electrostatic adsorption capacity. Oxygen-containing groups generated on the surface of aged MPs formed hydrogen bonding with the phenolic hydroxyl groups of PCMX, which became the main driving force for adsorption. Our results reveal the potential impact and mechanism of aging on the adsorption of PCMX by MPs, which provides new insights for the interaction mechanism between environmental MPs and associated contaminants.

Aged Microplastics and Antibiotic Resistance Genes: A Review of Aging Effects on Their Interactions

Background: Microplastic aging affects the dynamics of antibiotic resistance genes (ARGs) on microplastics, yet no review presents the effects of microplastic aging on the associated ARGs. Objectives: This review, therefore, aims to discuss the effects of different types of microplastic aging, as well as the other pollutants on or around microplastics and the chemicals leached from microplastics, on the associated ARGs. Results: It highlights that microplastic photoaging generally results in higher sorption of antibiotics and ARGs due to increased microplastic surface area and functional group changes. Photoaging produces reactive oxygen species, facilitating ARG transfer by increasing bacterial cell membrane permeability. Reactive oxygen species can interact with biofilms, suggesting combined effects of microplastic aging on ARGs. The effects of mechanical aging were deduced from studies showing larger microplastics anchoring more ARGs due to rough surfaces. Smaller microplastics from aging penetrate deeper and smaller places and transport ARGs to these places. High temperatures are likely to reduce biofilm mass and ARGs, but the variation of ARGs on microplastics subjected to thermal aging remains unknown due to limited studies. Biotic aging results in biofilm formation on microplastics, and biofilms, often with unique microbial structures, invariably enrich ARGs. Higher oxidative stress promotes ARG transfer in the biofilms due to higher cell membrane permeability. Other environmental pollutants, particularly heavy metals, antibacterial, chlorination by-products, and other functional genes, could increase microplastic-associated ARGs, as do microplastic additives like phthalates and bisphenols. Conclusions: This review provides insights into the environmental fate of co-existing microplastics and ARGs under the influences of aging. Further studies could examine the effects of mechanical and thermal MP aging on their interactions with ARGs.

Surface characteristics and adsorption properties of polypropylene microplastics by ultraviolet irradiation and natural aging

The vast application and deep integration of plastic commodity with our human lives raise a great concern about the ubiquitous microplastics (MPs) in nature, yet the environmental behavior of MPs remain unclear. As a main type and candidate of MPs, pristine polypropylene MPs (PP-MP-Pris), as well as the influence of ultraviolet (UV) irradiation on the degree of aging and surface characteristics, were characterized quantitatively by Fourier infrared spectroscopy, scanning electron microscopy, contact angle meter, automatic specific surface area and pore analyzer and laser particle analyzer, with natural aged PP-MPs (PP-MP-Age) as comparison. The carbonyl index (CI) of UV aged PP-MPs (PP-MP-U) was increased with extension of exposure time, while biofilm with abundant functional groups and the maximum CI value were the characteristics of PP-MP-Age. Moreover, the adsorption capacity of PP-MP-U for crystal violet (CV) was increased and reached the maximum after 30 days, while that of PP-MP-Age was weakened, probably due to the enhanced hydrophilicity and the shedding of calcium carbonate (CaCO3) during the natural aging process, which was demonstrated by hydrochloric acid treatment, indicating the vital involvement of CaCO3. Moreover, the better fitting to PSO kinetics and Freundlich isotherm models indicated that the multilayered and non-homogeneous surface adsorption was acted as the rate-controlling step. Furthermore, the positive values of ΔGθ, ΔHθ and ΔSθ indicated that the adsorption was a non-spontaneous, endothermic process with increased degree of the freedom on the interface of PP-MPs and CV solution. The presence of divalent salts inhibited CV adsorption, demonstrating that electrostatic attraction played a major role in CV capture. The hydrophobic interaction, micropore filling, hydrogen bonding, and π - π conjugation were possible involved. This study is of great significance for better understanding the complex pollution of MPs and its potential environmental risks in the future.

Photochemically induced aging of polystyrene nanoplastics and its impact on norfloxacin adsorption behavior

The co-occurrence of nanoplastics (NPs) and antibiotics in the environment is a growing concern for ecological safety. As NPs age in natural environments, their surface properties and morphology may change, potentially affecting their interactions with co-contaminants such as antibiotics. It is crucial to understand the effect of aging on NPs adsorption of antibiotics, but detailed studies on this topic are still scarce. The study utilized the photo-Fenton-like reaction to hasten the aging of polystyrene nanoplastics (PS-NPs). The impact of aging on the adsorption behavior of norfloxacin (NOR) was then systematically examined. The results showed a time-dependent rise in surface oxygen content and functional groups in aged PS-NPs. These modifications led to noticeable physical changes, including increased surface roughness, decreased particle size, and improved specific surface area. The physicochemical changes significantly increased the adsorption capacity of aged PS-NPs for norfloxacin. Aged PS-NPs showed 5.03 times higher adsorption compared to virgin PS-NPs. The adsorption mechanism analysis revealed that in addition to the electrostatic interactions, van der Waals force, hydrogen bonding, π-π* interactions and hydrophobic interactions observed with virgin PS-NPs, aged PS-NPs played a significant role in polar interactions and pore-filling mechanisms. The study highlights the potential for aging to worsen antibiotic risk in contaminated environments. This study not only enhances the comprehension of the environmental behavior of aged NPs but also provides a valuable basis for developing risk management strategies for contaminated areas.

The resistance change and stress response mechanisms of chlorine-resistant bacteria under microplastic stress in drinking water distribution system

The presence of both chlorine-resistant bacteria (CRB) and microplastics (MPs) in drinking water distribution systems (DWDS) poses a threat to water quality and human health. However, the risk of CRB bio evolution under the stress of MPs remains unclear. In this study, polypropylene (PP) and polyethylene (PE) were selected to study the adsorption and desorption behavior of sulfamethoxazole (SMX), and it was clear that MPs had the risk of carrying pollutants into DWDS and releasing them. The results of the antibiotic susceptibility test and disinfection experiment confirmed that MPs could enhance the resistance of CRB to antibiotics and disinfectants. Bacteria epigenetic resistance mechanisms were approached from multiple perspectives, including physiological and biochemical characteristics, as well as molecular regulatory networks. When MPs enter DWDS, CRB could attach to the surface of MPs and directly interact with both MPs and the antibiotics they release. This attachment process promoted changes in the composition and content of extracellular polymers (EPS) within cells, enhanced surface hydrophobicity, stimulated oxidative stress function, and notably elevated the relative abundance of certain antibiotic resistance genes (ARGs). This study elucidates the mechanism by which MPs alter the intrinsic properties of CRB, providing valuable insights into the effective avoidance of biological risks to water quality during CRB evolution.

Adsorption behavior of triazine pesticides on polystyrene microplastics aging with different processes in natural environment

The presence of microplastics in the ecological environment, serving as carriers for other organic pollutants, has garnered widespread attention. These microplastics exposed in the environment may undergo various aging processes. However, there is still a lack of information regarding how these aged microplastics impact the environmental behavior and ecological toxicity of pollutants. In this study, we modified polystyrene microplastics by simulating the aging behavior that may occur under environmental exposure, and then explored the adsorption behavior and adsorption mechanism of microplastics before and after aging for typical triazine herbicides. It was shown that all aging treatments of polystyrene increased the adsorption of herbicides, the composite aged microplastics had the strongest adsorption capacity and the fastest adsorption rate, and of the three herbicides, metribuzin was adsorbed the most by microplastics. The interactions between microplastics and herbicides involved mechanisms such as hydrophobic interactions, surface adsorption, the effect of π-π interactions, and the formation of hydrogen bonds. Further studies confirmed that microplastics adsorbed with herbicides cause greater biotoxicity to E. coli. These findings elucidate the interactions between microplastics before and after aging and triazine herbicides. Acting as carriers, they alter the environmental behavior and ecological toxicity of organic pollutants, providing theoretical support for assessing the ecological risk of microplastics in water environments.

Characteristics and adsorption behavior of typical microplastics in long-term accelerated weathering simulation

Microplastics can function as carriers in the environment, absorbing various toxins and spreading to diverse ecosystems. Toxins accumulated in microplastics have the potential to be re-released, posing a threat. In this study, two typical plastics, namely polyethylene (PE) and polystyrene (PS), along with the degradable plastic poly(butylene adipate-co-terephthalate) (PBAT), were subjected to a long-term ultraviolet alternating weathering experiment. The study investigated the variations in the weathering process and pollutant adsorption of microplastics of different particle sizes. Furthermore, the adsorption capacity of microplastics for various pollutants was assessed. The findings indicate that particle size significantly influences weathering, leading to variations in adsorption capacity. The weathered PE displays a higher adsorption capacity for azo dyes. Additionally, the adsorption capacity of PBAT for neutral red is double that of antibiotics. Importantly, the maximum adsorption capacity of PBAT for pollutants after aging is approximately 10 times greater than that of PE. Consequently, degradable plastics undergoing weathering in the natural environment may pose a higher ecological risk than traditional plastics.

Understanding microplastic aging driven by photosensitization of algal extracellular polymeric substances

The aging of microplastics (MPs) is extremely influenced by photochemically-produced reactive intermediates (PPRIs), which are mediated by natural photosensitive substances. Algal extracellular polymeric substances (EPS) can produce PPRIs when exposed to sunlight. Nonetheless, the specific role of EPS in the aging process of MPs remains unclear. This work systematically explored the aging process of polystyrene (PS) MPs in the EPS secreted by Chlorella vulgaris under simulated sunlight irradiation. The results revealed that the existence of EPS accelerated the degradation of PS MPs into particles with sizes less than 1 µm, while also facilitating the formation of hydroxy groups on the surface. The release rate of dissolved organic matter (DOM) from PS MPs was elevated from 0.120 mg·L-1·day-1 to 0.577 mg·L-1·day-1. The primary factor contributing to the elevated levels of DOM was humic acid-like compounds generated through the breakdown of PS. EPS accelerated the aging process of PS MPs by primarily mediating the formation of triplet excited states (3EPS*), singlet oxygen (1O2), and superoxide radicals (O2∙-), resulting in indirect degradation. 3EPS* was found to have the most substantial impact. This study makes a significant contribution to advance understanding of the environmental fate of MPs in aquatic environments impacted by algal blooms.