Surface Of Microplastics Research Articles

Weathering influences the ice nucleation activity of microplastics.

Microplastics are being increasingly detected in the atmosphere at altitudes relevant to mixed-phase cloud formation. However, the extent to which microplastics, along with their dynamic surface properties resulting from environmental weathering, could influence atmospheric microphysical processes remains largely unexplored. Here, through a series of ice nucleation experiments and droplet freezing assays, we highlight the capability of model polyethylene microplastics to induce heterogeneous ice nucleation via immersion freezing under atmospherically relevant conditions. We find that sunlight-induced weathering of the microplastic surface influences the structure of surface-bound water molecules and dictates the ice nucleation activity of the microplastics. Using polyethylene, polypropylene, polystyrene, and polyethylene terephthalate as models, we demonstrate that the ice nucleation ability of microplastics is intrinsically linked to their underlying chemistry. Our findings underscore the need to establish a connection between microplastics and atmospheric processes, as the behavior of microplastic pollutants in the atmosphere holds the potential to influence their environmental transport as well as atmospheric microphysical processes.

Enhancing Microplastic Degradation through Synergistic Photocatalytic and Pretreatment Approaches.

Microplastics (MPs) pollution has emerged as a pressing environmental concern in recent years. Owing to their minute dimensions, conventional plastic remediation approaches are inadequate for addressing the challenges posed by MPs. Herein, spherical (BOC-S) and nanosheet (BOC-N) BiOCl photocatalysts were prepared and applied to the degradation of poly(ethylene terephthalate) (PET) MPs after hydrothermal pretreatment. The results indicated that the degradation efficiency of pretreated PET MPs using BOC-S and BOC-N photocatalysts was 8.8 and 6.9 times that of the unpretreated MPs under the same conditions. Comparative experiments confirmed the excellent performance of the photocatalysis-pretreatment system. The creation of pores on the surface of pretreated PET MPs facilitates the entry of active substances into the interior to cause damage, while the enhancement of hydrophilicity and specific surface area facilitates the contact between the catalyst and PET MPs, thus increasing the degradation efficiency. Free radical trapping experiments revealed that hydroxyl radicals (·OH) produced by photocatalysis had the greatest influence on the degradation performance of pretreated PET MPs. Finally, a possible photocatalytic degradation mechanism for PET MPs was proposed. This research offers a novel perspective on MPs degradation, providing valuable insights for advancing the efficacy of the process.

Microplastics–biofilm in aquatic ecosystem: Formation, pollutants complexation, greenhouse gas emission and ecotoxicology

The omnipresent microplastics (MPs) have gradually become a significant environmental problem due to its adverse consequences for ecological systems. MPs serve as substrates for biofilms colonization, which enhances adsorption of harmful contaminants on MPs surface in the aquatic ecosystem. The present study provides a critical discussion on the mechanism involved in MPs–biofilm formation, microbial colonization and the robust factors influencing the process in the aquatic ecosystem. Subsequently, the impact of MPs–biofilm on adsorption of inorganic and organic contaminants is explored. The ecological significance of MPs–biofilm associated pollutant complex for promoting greenhouse gases (GHGs) emissions from aquatic ecosystem is extensively discussed for understanding the climatic risk. Furthermore, the discussion is extended over ecotoxicological impact of MPs–biofilm on aquatic biodiversity and humans. The protective extracellular polymeric substances secreted by colonised bacteria over MPs during biofilm formation creates sticky MPs surface for heteroaggregates formation with swift adsorption of chemical compounds and microorganisms. MPs with functional aromatic groups facilitate the bacterial adhesion on the surface, but affect formation of biofilm. Alternatively, MPs–biofilm promotes the Mn and Fe hydrous oxides formation that can co–precipitate with heavy metal ions and facilitate in remediation measures. However, MPs biodegradation generates GHGs emission per unit mass, comparably more from freshwater than marine ecosystem. Considering the toxicity, MPs–biofilm induces the oxidative response in fishes, causing painful death and thus, destroys aquatic biodiversity. This study will be useful to address MPs–biofilm associated pollution scenario via trace, test and treat strategy involving future engineering research framework for ecological restoration.

Molecular properties of dissolved organic matter leached from microplastics during photoaging process

The occurrence of dissolved organic matter (DOM) derived from microplastics (MPs) and its effect on aquatic systems has attracted great interest recently. However, the photoaging effect on the molecular structure of MP-derived DOM (MP-DOM) remains unclear. This paper presents the characteristics of DOM leached from three commercial MPs, i.e., polyethylene (PE), polypropylene (PP) and polyethylene terephthalate (PET) under UV irradiation. With prolonged aging periods, the surface roughness and oxygen-containing groups on the surface of MPs increase as more DOM leachate is generated. Moreover, the dissolved organic carbon (DOC) content of the leached DOM from PET MPs varies from 0.52 mg/L to 2.25 mg/L, which is higher than PE and PP MPs, due to the larger increased surface reaction area and the cleavage of the benzene ring. According to the excitation-emission matrix and parallel factor analysis (EEM-PARAFAC), the plastic-derived protein/phenolic-like components (C1 and C3) in MP-DOM were changed into photo-induced humic-like components (C2), which were closely related to the intermediates during photo-oxidation. High-performance liquid chromatography-mass spectrometry (HPLC−MS) analysis further identified that the highest proportion of antioxidants (24.8 %∼34.6 %) was contained in MP-DOM. Plasticizers, intermediate additives, and antimicrobial agents were also detected in DOM leachate. Correlation analysis identified that the composition of leached DOM was positively correlated with the surface roughness, the carbonyl index (CI), and the chemical groups of MPs. Moreover, a partial least square structural equation model (PLS−SEM) analysis further verified that the change of morphology and the chemical structure of MPs could affect the DOM structures and fractions directly. This study provides an in-depth understanding of the composition of MP-derived DOM during the aging process, as well as a comprehensive environmental impact assessment of MPs.

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.

Efficient photocatalytic degradation of microplastics by constructing a novel Z-scheme Fe-doped BiO2−x/BiOI heterojunction with full-spectrum response: Mechanistic insights and theory calculations

Recently, microplastics (MPs) have garnered significant attention as a challenging emerging pollutant to address. Here, a full-spectrum light-driven Fe-doping BiO2−x/BiOI (FBI) Z-scheme heterojunction was constructed for efficiently degrading MPs in waters. Compared with BiO2−x, Fe doping BiO2−x, and BiOI, the optimal photocatalyst (40-FBI) can cause deep cracks in the polyethylene terephthalate (PET) within 10 h under the irradiation of full-spectrum light. Meanwhile, FT-IR characterization revealed that the absorption peak intensities of the C-O group, CO group, -CH stretching vibration, and -OH group on the MPs surface gradually increased with degradation time. A series of experiments and theory calculations revealed that the introduction of Fe creates impurity levels, accelerating the separation of photo-generated carriers and reducing the work function of BiO2−x, thereby enhancing the transport of photo-generated carriers between Z-scheme heterojunctions. This study offers a valuable idea for designing an efficient photocatalyst by simultaneously introducing ion doping and constructing heterojunctions for enhancing MPs degradation.

Microplastic pollution in the surface waters of the zuari river, goa, india.

Limited research has been conducted on microplastic (MP) contamination in the rivers of Goa. To address this gap, this study examines the levels of MP contamination in the surface water of the Zuari River, Goa. We investigate the abundance, characteristics (size, shape, colour, and polymer composition), and risk assessment of MPs. MPs were detected at all sampling stations in the Zuari River, with concentrations varying from 0.01 particles/L (S3) to 1.38 particles/L (S13). The average abundance of MPs in the water samples was 0.28 ± 0.35 particles/L. MPs were more common in the 0.3-1mm size range (51.70%) than in the 1-5mm range (48.30%). The most common MP shapes observed were fibers (37.88%) and fragments (29.66%). FTIR analysis confirmed the presence of polyethylene terephthalate, high-density polyethylene, polypropylene, and polyacrylamide carboxyl-modified MPs. The Pollution Load Index (PLI) showed an average value of 3.8, indicating significant contamination (PLI > 1). Scanning electron microscopy (SEM) revealed various degradation features such as pits, scratches, grooves, and cracks on the MPs surfaces, while energy dispersive X-ray spectroscopy (EDS) detected metals on the MP's surfaces. This study provides key insights into MP pollution in the Zuari River's surface water and lays the groundwork for future research and management strategies in the region.

Microplastic accumulation and transport in agricultural soils with long-term sewage sludge amendments

Land application of sewage sludge brings microplastic contamination to soil. However, studies regarding the occurrence and mobility of sludge-borne microplastics in soil are insufficient. In the present study, based on an experimental field, the effects of sludge application amount on the accumulation and migration of microplastics in 0–20 (upper) and 20–40cm (lower) soil layers were evaluated. After 16 years of continuous sludge application (36 t/ha per year), the microplastic content and migration ratio in upper soil reached 6,811 particles/kg and 148%, which was about 5 and 20 times, respectively, higher than that of the control soil without sludge. The microplastics in upper and lower soil layers, were mainly 0.2–0.5mm in size, mostly fibrous in shape, primarily transparent in color, and predominantly rayon in composition. Microplastic surfaces may persistently adsorb clay minerals and iron/titanium oxides from soil, posing potential environmental risks. Sludge application had a significant positive correlation with soil microplastic abundance, resulting in a good fit of predictive model constructed for microplastic accumulation in sludge-amended soils. These findings help to improve the knowledge on environmental behavior of microplastics in sludge-amended soil, and can provide a scientific basis for the regulation of microplastic pollution during sludge land application.

Integrated transcriptomics and proteomics analyses reveal the ameliorative effect of hepatic damage in tilapia caused by polystyrene microplastics with chlorella addition

Fish exhibit varying responses to polystyrene microplastics (MPs) depending on particle size. Previous studies suggested that microorganisms adhering to the surface of MPs can induce toxic effects. In this study, Tilapia were exposed to MPs of control (group A), 75 nm (B), 7.5 μm (C), 750 μm (D), as well as combinations of all sizes (E) and 75 nm MPs with Chlorella vulgaris addition (F) for 7, 10 and 14 days. Histopathological changes in liver of tilapia were assessed using enzyme activities, transcriptomics and proteomics. The results showed that in groups combined MPs of different particle sizes and those supplemented with chlorella, MPs were localized on the surface of goblet cells, leading to vacuoles, constricted hepatic sinuses and nuclei displacement. Exposure to 7.5 and 750 μm MPs significantly increased the contents of fatty acid synthase (FAS), adenosine triphosphate (ATP), acetyl-CoA carboxylase (ACC), lipoprotein lipase (LPL), total cholesterol (TC), total triglyceride (TG) contents at 7 and 10 days. In particular, cytochrome p450 1a1 (EROD), reactive oxygen species (ROS) and superoxide dismutase (SOD) were markedly elevated following exposure to MPs. Apoptotic markers caspase-3, and inflammatory markers, including tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β), had a similar upward trend in comparisons of group C vs A at 7 d, group D vs A at 14 d. The peroxisome proliferator activated receptor (PPAR) signaling pathway, spliceosome, was highly enriched during the 7-day exposure of medium sized MPs, while largest MPs in the comparison of group D vs A at 14 d activated pathways such as phagosome, apoptosis, salmonella infection. Transcriptomic analysis revealed that after 14 days, the kyoto encyclopedia of genes and genomes (KEGG) pathways associated with protein processing in endoplasmic reticulum and the PPAR signaling has been significantly enriched in the Chlorella-supplemented group, which was further confirmed via the proteomic analysis. Overall, the findings highlight the size-dependent effects of MPs on histopathological changes, gene and protein expression in the liver of tilapia, and C. vulgaris effectively attenuated liver damages, likely through modulation of endoplasmic reticulum protein processing and PPAR signaling pathways.

Biofilms on microplastic surfaces and their effect on pollutant adsorption in the aquatic environment

Biofilms on microplastic surfaces and their effect on pollutant adsorption in the aquatic environment

Co-accumulation characteristics and interaction mechanism of microplastics and PFASs in a large shallow lake

Microplastics (MPs) and per- and polyfluoroalkyl substances (PFASs) coexist widely in lakes and affect ecological security. The coexistence characteristics and adsorption-desorption mechanisms between MPs and typical PFASs were explored in a typical eutrophic shallow lake (Taihu Lake). Polyvinyl chloride (PVC) and polyethylene (PE) are the primary types of MPs in Taihu Lake, with average abundances in water and sediment of 18630 n/m3 and 584 n/kg, respectively. The average concentrations of PFASs in water and sediment are 288.93 ng/L and 4.33 ng/g, with short-chain PFASs (C4-C7) being the main pollutants. Perfluorobutanoic acid (PFBA) in both water and sediment contributed 38.48 % and 44.53 %, respectively, followed by hexafluoropropylene oxide dimer acid (HFPO-DA). The morphological characteristics of MPs influence the distribution of long-chain PFAS in lake water, while the presence of HFPO-DA and perfluorohexanoic acid (PFHxA) in sediment is directly linked to the concentration and size of MPs. A combination of field investigations and indoor experiments revealed that the irreversible adsorption characteristics between MPs and HFPO-DA may promote the high cumulative flux of HFPO-DA in sediment, and the biofilm on the surface of MPs significantly accelerates this accumulation process. The results provide a new perspective on the co-transport behavior of emerging pollutants in aquatic environments.

Adsorption and desorption of phenanthrene and 1-hydroxyphenanthrene by goethite-coated polyvinyl chloride

Microplastics loaded with phenanthrene and derivatives are widely detected in aquatic environments, and the coating of natural minerals or organic macromolecules may change the environmental behavior of microplastics. In this study, three kinds of composites with different coverage were prepared by coating goethite on the surface of polyvinyl chloride microplastics to investigate the adsorption and desorption behavior of phenanthrene (PHE) and 1-hydroxyphenanthrene (1-OHPHE), and the effect of mucin on desorption was investigated. The results showed that goethite promoted the adsorption of PHE and 1-OHPHE by increasing the specific surface area of the composites. With the increase of the cover degree, the adsorption of PHE decreased because of the decrease in hydrophobicity; while the adsorption of 1-OHPHE initially increased and then decreased with the contributions of hydrophobic interaction and hydrogen bond. The adsorption of 1-OHPHE could be influenced by the pH and ionic strength primarily through electrostatic interactions and Ca2+ bridging. The goethite significantly increased the desorption hysteresis for two chemicals due to the complicated pore structures and increased adsorption affinity. Mucin promoted the desorption of PHE through competitive adsorption, and inhibit the desorption of 1-OHPHE through hydrophobic interaction, hydrogen bonding and Ca2+ bridging. This study elucidated the effects of natural minerals on the adsorption and desorption behavior of organic pollutants on microplastics, briefly discussed the effects of organic macromolecules on the desorption behavior of pollutants with different properties, and emphasized the different environmental behaviors of pollutants.

Insights into the inhibitory effects of trichloroisocyanuric acid disinfectant on the phototransformation of polypropylene microplastics

The chemical components in the natural aquatic environment have the potential to be involved in phototransformation of microplastics (MPs). Little information is available regarding the mediation effects of artificially introduced chemicals on MP phototransformation, especially those used in aquaculture water that are vulnerable to human interference. Herein, this study investigated the phototransformation process and mechanism of polypropylene microplastic (PP MPs) in presence of trichloroisocyanuric acid (TCCA) disinfectant with unique properties unlike the conventional inorganic chlorine disinfectants. The results showed that the presence of TCCA inhibited the surface photooxidation of PP MPs. Analysis of PP MP surface and reaction filtrate indicated that the inhibitory effects were likely derived from TCCA derivatives and the weakening in promoting effect of polypropylene microplastic-derived dissolved organic matter (PP-DOM) as photolytic byproducts, with the more important role of free chlorine in initial period and that of other chlorine species (i.e., the adsorbed chloride ions (Cl−), newly formed carbon-chlorine (CCl) bonds, chlorinated cyanurates, and chlorinated products) in middle and later period. The study highlights for the first time the important role of chlorine species derived from TCCA in phototransformation process of co-existed PP MPs and proposes a previously unrecognized phototransformation pathway, which will provide a new understanding and knowledge for the environmental behavior of MPs in aquaculture environment.

Polystyrene microplastics as carriers for nano-hydroxyapatite particles: Impact of surface functionalization and mechanistic insights

The potential of microplastics (MPs) to act as carriers for contaminants or engineered nanomaterials is of rising concern. However, directly determining the vector effect of polystyrene (PS) MPs towards nano-hydroxyapatite (nHAP) particles, a typical nano phosphorus fertilizer and soil remediation material, has been rarely studied. In this study, the interaction of differentially surface functionalized PS MPs with nHAP were investigated through batch experiments under different solution chemistry conditions. The results demonstrated that nHAP had the highest attachment/adsorption affinity onto carboxyl-functionalized PS, followed by bare PS and amino-functionalized PS under near-neutral pH conditions. Adsorption of nHAP exhibited a strong pH-dependent behavior with PS MPs, increasing under acidic-neutral pH (3−7) and decreasing at higher pH values. The presence of humic acid and NaCl hindered the adsorption of nHAP onto MPs. Scanning electron microscopy observations revealed a rod-like morphology for adsorbed nHAP, which was randomly distributed on MPs surface. Surface complexation and cation-π interaction were mainly responsible for the adsorption of nHAP as revealed by multiple spectroscopic analyses. These results provide mechanistic insights into nHAP-PS interactions and expound the effect of surface functionalization of PS on binding mechanisms, and thus bring important clues for better understanding the vector effects of MPs towards nanoparticles.

Comprehensive Understanding on the Aging Process and Mechanism of Microplastics in the Sediment-Water Interface: Untangling the Role of Photoaging and Biodegradation.

Microplastics (MPs) in coastal wetlands have been of great concern, but information on the aging behavior of MPs in the sediment-water interface is still lacking. In this study, the contribution of a typical abiotic (photoaging) and biotic (biodegradation) process and the underlying aging pathway of MPs with different degradabilities (including polypropylene, polyethylene terephthalate, and polylactic acid) were studied. With a quantified relative importance of photoaging (>55%) vs biodegradation, the crucial contribution of photoaging on MP aging was highlighted. This was likely attributed to more generation of reactive oxygen species (ROS) under sunlight irradiation conditions, containing O2•- and H2O2. By raising higher the level of malondialdehyde (0.5-3.5 times as high as that in the dark condition), these photochemically formed ROS caused oxidative stress and inhibited the selective attachment of plastic-degrading microbes on the MP surface, thereby weakening the effect of biodegradation. On this basis, the aging characteristics and potential pathway of different MPs were revealed. The functional group of nondegradable polypropylene tends to be broken by ROS first, while biodegradation (Arthrobacter oryzae and Bacillus sp.) played a relatively dominant role in biodegradable polylactic acid. This study provides a new sight for the understanding on the aging behaviors of MPs in the sediment-water interface.

Electron beam synergetic removal of microplastics and hexavalent chromium: Synergetic removal process and mechanism

Microplastics are ubiquitous in the environment and aged microplastics are highly susceptible to absorbing pollutants from the environment. In this study, electron beam was innovatively used to treat PVC composite Cr(VI) pollutants (Composite contaminant formed by polyvinyl chloride microplastics with the heavy metal hexavalent chromium). Experiments showed that electron beam was able to achieve synergistic removal of PVC composite Cr(VI) pollutants compared to degrading the pollutants alone. During the electron beam removal of PVC composite Cr(VI) pollutants, the reduction efficiency of Cr(VI) increased from 57% to 92%, Cl− concentration increased from 3.52 to 12.41 mg L−1, and TOC concentration increased from 16.72 to 26.60 mg L−1. The research confirmed that electron beam can effectively promote the aging degradation of PVC, alter the physicochemical properties of microplastics, and generate oxygen-containing functional groups on the surface of microplastics. Aged microplastics enhanced the adsorption capacity for Cr(VI) through electrostatic and chelation interactions, and the adsorption process followed second-order kinetics and the Freundlich model. Theoretical calculations and experiments demonstrated that PVC consumed oxidizing free radical through dechlorination and decarboxylation processes, generating inorganic ions and small organic molecules. These inorganic ions and small organic molecules further reacted with oxidizing free radical to produce reducing free radicals, facilitating the reduction of Cr(VI). Cr(VI) continuously consumed the educing free radicals to transform into Cr (Ⅲ), enhancing the system oxidative atmosphere and promoting the oxidation degradation of PVC. This study investigated the formation and synergistic removal processes of PVC composite pollutants, offering new insights for controlling microplastics composite pollution.

Tracing the Transport and Residence Times of Atmospheric Microplastics Using Natural Radionuclides.

While atmospheric microplastics are known to be transported over long distances, their residence times and transport processes lack clarity. This study utilized natural radionuclides 7Be, 210Pb, and 210Po to explore the transport of atmospheric microplastics in Tianjin, a coastal city in Northern China. Microplastic concentrations ranged from 0.03 to 0.13 particles m-3 over the course of a year. The proportion of microplastic fragments in winter was significantly higher than that in other seasons, with median microplastic sizes in autumn and winter being larger than those in spring and summer. The atmospheric microplastic surface was rough, exhibiting irregular pores and multiple depressions and cracks. Microplastics experienced vertical mixing with the upper atmosphere in April and August and were influenced by rainfall in July. The residence time of atmospheric particles ranged from 9.47 to 22.85 days throughout the year, with an average of 14.41 days. The peak residence time of atmospheric particulates in November may be correlated with increased 210Po levels from coal consumption. Their prolonged atmospheric presence and rough surface allow microplastics to act as carriers for various chemical pollutants, underscoring the complexity and potential risks associated with their presence in the atmosphere.

The conversion of metal ions to metals particles contributes the photoaging of microplastics in aquatic environments

Metals ions enriched on the surface of Microplastics (MPs) may undergo redox reactions under UV irradiation to promote its photoaging. However, there is a paucity of information on studies of the aging behavior of MPs mediated by different metal ions. This study aims to investigate the effects of three different metal ions (Ag+, Cu2+ and Al3+) on the photoaging properties of polypropylene (PP) to enhance our comprehension of their aging in water contaminated by heavy metals. Physicochemical analyses, like the ratio of O/C and carbonyl index (CI), suggested that metal ions accelerated the aging of PP. The correlation model was established between CI and aging time to confirm that the aging sequence of PP in three metal ions solution was Ag+-PP>Cu2+-PP>Al3+-PP. Electron Paramagnetic Resonance (EPR) results showed metal ions enhanced the generation of reactive oxygen species (•O2–, HO• and 1O2) to accelerate aging through free radical pathways. Electronic exchange capability (EEC) and X-Ray Photoelectron Spectroscopy (XPS) confirmed metal particles were on PP, leading to the e-bridge for electronic relays that altered the EEC of PP and accelerated its protonation process. It needs to note the surface plasmon resonance (SPR) effect of metal nanoparticles may also accelerated the photoaging of MPs in UV–vis illumination. For the first time, the study establishes a connection between different valence states metal ion and PP aging, shedding light on interfacial and free radical aging process of MPs. The finding also proposes the potential e-bridge or SPR effect of metal particles may exist in accelerating photoaging reaction of PP in special water bodies contaminated with heavy metals. The environmental implications and ecological risks of this phenomenon warrant greater consideration.

Investigation on the adsorption mechanism of a mixture of seven pharmaceutical compounds on virgin and aged biodegradable microplastics

In this study the adsorption of a mixture of seven pharmaceutical compounds on virgin and aged polylactic acid (PLA) microplastics (MPs) was investigated. PLA MPs were aged under UV radiation and simulated solar light (SSL) creating three types of MPs: i) virgin, ii) UV-aged and iii) SSL-aged PLA-MPs. The different PLA-MPs were characterized with various characterization techniques (FTIR, SEM, TGA) which revealed modifications on the surface of the aged MPs like cracks and pits, creating more adsorption sites. Pseudo-first, pseudo-second and the intraparticle diffusion model were applied to explore the mechanism and the rate limiting step of the adsorption mechanism. Isothermal study was also conducted and revealed better fitting with the Freundlich model indicating a multi-layer coverage on the MPs surface. Aging appears to enhance the adsorption capacity of the target compounds on the PLA-MPs for both types of aged MPs however the UV-aged showed higher uptake. Finally, the effect of other parameters, like the pH or the type of the water matrix were also investigated offering a deeper insight on the adsorption mechanism of the target compounds.

Adsorption and Desorption Behavior of PAEs Plasticizer on PVC and Rubber Particles After Natural Environment Aging

Microplastics （MPs） coexist with plasticizers in the aqueous environment to form composite pollution, but the adsorption and desorption behaviors of MPs and plasticizers under natural conditions are unknown. Polyvinyl chloride （PVC） and rubber were used as the target MPs to characterize the changes in their morphological features after aging for one anniversary in atmospheric exposure and lake sedimentary burial environments and to investigate the adsorption and desorption behavior of the MPs to the coexisting phthalate esters （PAEs） plasticizer before and after aging. The results showed that the surface of MPs was rougher after exposure to the atmospheric environment and burial in a depositional environment, showing the characteristics of porous polymers. The carbonyl index （CI） of PVC and rubber increased by 62.2% and 321.2%, respectively, in the atmospheric environment and increased by 51.1% and 223.1%, respectively, in the depositional environment. The atmospheric exposure was capable of accelerating the aging process of MPs. PAEs were adsorbed on the surface of MPs through hydrophobic interaction, and the amount of adsorption was significantly and positively correlated with their hydrophobic properties. The adsorption capacity and adsorption rate of PVC on PAEs were inhibited after aging. Aging promoted the adsorption of rubber on strongly hydrophobic PAEs plasticizers and inhibited the adsorption of weakly hydrophobic PAEs. The environmental aging process reduced the desorption of strongly hydrophobic PAEs from rubber, enhanced the reversibility of rubber adsorption of weakly hydrophobic PAEs, and increased the desorption rate of PAEs from PVC.