Formation of Nano- and Microplastics and Dissolved Chemicals During Photodegradation of Polyester Base Fabrics with Polyurethane Coating.

Polyurethane (PU) synthetic leathers possess an intricate plastic composition, including polyester (PET) base fabrics and upper PU resin, but the release of fragments from the complexes is unclear. Therefore, we investigated the photodegradation trends of PET base fabrics with PU coating (PET-U) as a representative of composite plastics. Attention was paid to the comparison of the photoaging process of PET-U with that of pure PET base fabric (PET-P). To reveal the potential for chain scission, physical and chemical changes (e.g., surface morphology, molecular weight, and crystallinity) of the two fabrics were explored. The generation of microplastic fibers (MPFs) and microplastic particles (MPPs) was distinguished. Compared with PET-P, PET-U showed a similar but delayed trend in various characteristics and debris release rate as the photoaging time prolonged. Even so, after 360 h of illumination, the generated number of MPs (including MPFs and MPPs) rose considerably to 9.32 × 107 MPs/g, and the amount of released nanoplastics (NPs) increased to 2.70 × 1011 NPs/g from PET-U. The suppression of MP formation from PET-U was potentially directed by the physical shielding of the upper PU layer and the dropped MPs, which resisted the photochemical radical effect. The components of dissolved organic matter derived from plastics (P-DOM) were separated by molecular weight using a size-exclusion chromatography-diode array detector-organic carbon detector/organic nitrogen detector (SEC-DAD-OCD/OND), and the results showed that a larger amount of carbon- and nitrogen-containing chemical substances were generated in PET-U, accompanied by more aromatic and fluorescent compounds. The results provided theoretical bases and insights for future research on the risks of plastic debris from PU synthetic leathers on aquatic organisms and indicated feasible directions for exploring combined pollution studies of plastics.

Humic Acid and Fulvic Acid Hinder Long-Term Weathering of Microplastics in Lake Water.

We investigated the photoaging of polypropylene (PP) microplastics (MPs) in lake water. The results showed that photoaging of PP MPs was significantly inhibited in lake water compared with ultrapure water after 12 d of ultraviolet (UV) irradiation, and humic acid and fulvic acid, rather than carbonate (CO32-), nitrate (NO3-), or chloride (Cl-) ions, were identified as the primary contributors to the observed inhibition. Mechanisms for the roles of humic acid (Suwannee River humic acid) and fulvic acid (Pony Lake fulvic acid) in reducing the rates of photodegradation showed that humic acid and fulvic acid acted as both reactive oxygen species (ROS) scavengers (e.g., of •OH) (dominant contribution) and optical light filters. As ROS scavengers, humic acid and fulvic acid significantly decreased the capacity for the formation of •OH and O2•- by PP MPs under irradiation. In addition, the chromophores in humic acid and fulvic acid competed for photons with MPs through the light-shielding effect, thereby causing less fragmentation of PP particles and changes in other properties (melting temperature, contact angle, and surface zeta potential). The proposed mechanisms for inhibition by humic acid and fulvic acid will aid our efforts to assess the duration of aging and alterations of MP properties during long-term weathering in natural waters.

New Insights into the Aging Behavior of Microplastics Accelerated by Advanced Oxidation Processes.

In the environment, microplastics are subjected to multiple aging processes; however, information regarding the impact of aging on the environmental behavior of microplastics is still lacking. This study investigated the alteration properties of polystyrene and high-density polyethylene microplastics by heat-activated K2S2O8 and Fenton treatments to improve the understanding of their long-term natural aging in aquatic environments. Our results indicated that the O/C ratio was an alternative parameter to the carbonyl index (CI) to quantitatively describe the surface alteration properties of microplastics. The correlation model of the O/C ratio or CI versus alteration time was developed and compared by natural alteration of microplastics in freshwater samples. Moreover, the regression equation of the equilibrium adsorption capacity of altered microplastics versus the O/C ratio and average size was proposed. This study is the first effort in differentiating the relationships between the alteration properties and alteration time/adsorption capacity of microplastics, which would be helpful for predicting the weathering degree and accumulation of hydrophilic antibiotics onto aged microplastics in aquatic environments. This research develops promising strategies to accelerate the aging reactions using advanced oxidation processes, which would provide further information to assess the microplastic pollution in actual environments.

Revealing the characteristics of biofilms on different polypropylene plastic products: Comparison between disposable masks and takeaway boxes.

The increasingly severe plastic pollution issue was intensified by the enormous plastic emissions into ecosystems during the Covid-19 pandemic. Plastic wastes entering the environment were swiftly exposed to microorganisms and colonized by biofilms, and the plastic-biofilm combined effects further influenced the ecosystem. However, the non-woven structure of disposable masks discarded carelessly during the COVID-19 pandemic was different from those of plastics with flat surface. To reveal the potential effects of plastic structure on colonized biofilms, white disposable surgical masks (DM) and transparent takeaway boxes (TB), both made of polyethylene, were selected for the incubation of organic conditioning films and biofilms. The results indicated that the non-woven structure of disposable mask was destroyed by the influence of water infiltration and biofilm colonization. The influence of surface structure on conditioning films led to a relatively higher proportion of tryptophan-like substances on DM than those on TB samples. Therefore, biofilms with significantly higher microbial biomass and carbon metabolic capacity were formed on DM than those on TB samples owing to the combined effects of their differences in surface structure and conditioning films. Moreover, abundant functional microorganisms associated with stress tolerance, carbon metabolism and biofilm formation were observed in biofilms on disposable mask. Combining with the results of partial least squares regression analysis, the selective colonization of functional microorganisms on disposable masks with uneven surface longitudinal fluctuation was revealed. Although the predicted functions of biofilms on disposable masks and takeaway boxes showed more similarity to each other than to those of free-living aquatic microorganisms owing to the existence of the plastisphere, biofilms on disposable masks may potentially trigger environmental risks different from those of takeaway boxes by unique carbon metabolism and abundant biomass.

Interactions between methyl octabromo ether flame retardant and expanded polystyrene microplastics in the photoaging process.

Expanded polystyrene (EPS) plastic is widely used because of its low density and lightweight properties, enabling it to float on water and increase its exposure to sunlight. In this study, we simulated the photoaging process of flame retardant-added EPS (FR-EPS) and common original EPS (OR-EPS) microplastic (MP) particles with and without methyl octabromoether flame retardant (MOBE) in the laboratory to explore the effect of MOBE on the photodegradation of EPS. Results showed that MOBE accelerated size reduction and surface hole formation on the particles, hastening the shedding and replacement of particle surfaces. FR-EPS particles exhibited a weight loss exceeding that of OR-EPS, reaching 40.85 ± 3.72% after 36 days of irradiation. Moreover, rapid physical peeling of the FR-EPS surface was accompanied by continuous chemical oxidation and fluctuations of the carbonyl index and O/C ratio. A diffusion model based on Fick's second law fitted well for the concentration of MOBE remaining in FR-EPS particles. MOBE's sensitivity to direct photochemical reactions inhibited the early-stage photoaging of EPS MP particles by competing for photons. However, MOBE as chromophores could absorb photons and produce •OH to promote the aging of EPS. Moreover, the capacity of EPS to absorb light energy also accelerated MOBE degradation. These findings suggested that the photoaging behavior of commercial EPS products containing flame retardants in the environment is quite different from that of pure EPS, indicating that additive-plastic interactions significantly alter MP fate and environmental risks.

Microplastics exhibit lower carrying effects on the bioaccessibility and cytotoxicity of lead than montmorillonite clay particles.

Microplastics (MPs) in the environment are always colonized by microbes, which may have implications for carrying effect of pollutants and exposure risk in organisms. We present the crucial impacts and mechanisms of microbial colonization on the bioaccessibility and toxicity of Pb(II) loaded in disposable box-derived polypropylene (PP) and polystyrene (PS) MPs and montmorillonite (MMT) clay particles. After 45 d incubation, higher biomass measured by crystal violet staining were detected in MMT (1.23) than in PP and PS (0.400 and 0.721) indicating preferential colonization of microbes in clay particles. Microbial colonization further enhanced the sorption ability toward Pb(II), but inhibited the desorption and bioaccessibility of enriched Pb(II) in zebrafish and decreased the toxicity to gastric epithelial cells in an order of MMT > PS ≈ PP. The crucial effects were mainly because microbe-colonized substrates possessed higher oxygen functional groups and specific surface area and exhibited stronger interactions with Pb(II) and digestive component (i.e., pepsin) than pure substrates. This decreased the available soluble pepsin for complexing with sorbed Pb(II). The findings highlight the role of microbial colonization in modulating the exposure risks of artificial and natural substrate-associated pollutants and suggest that the risks of MPs may be overestimated compared to clay particles.

Which factors mainly drive the photoaging of microplastics in freshwater?

Light irradiation is considered as most important process for the aging of microplastics (MPs); however, which factors drive the process is still unknown. This study investigated the role of typical environmental factors including ultraviolet (UV), oxygen, temperature and physical abrasion in the photoaging of polystyrene (PS) in freshwater. Results showed that UV irradiation and abrasion were dominant factors for affecting photoaging of PS based on dynamic analysis in the property of MP itself and leachate. Especially, when both factors worked together on MPs, they caused more destructive effect. Mechanical exploration revealed that photoaging of MPs was mainly controlled by reactive oxygen species (ROS, 1O2) generated from the reaction of dissolved oxygen/water molecules with polymer radicals initiated by UV energy. As an attacker on MPs, ROS formation was significantly linked with UV intensity, highlighting the important role of UV. The fragmentation was correlated to abrasion intensity, where a higher abrasion generated stronger physical force to tear MPs into fragments. The low roles of oxygen and temperature were presumably related to multiple effects of ROS formation and UV absorption. The findings firstly clarify the drivers in the photoaging of MPs, and contribute our effort to assess their fate and pollution risk in the environment.

Bioaccessibility of polypropylene microfiber-associated tetracycline and ciprofloxacin in simulated human gastrointestinal fluids.

Microplastics residues in natural waters can adsorb organic contaminants owing to their rough surface morphology and high specific surface area, potentially harming human health when ingested. Although humans inevitably ingest microplastics, the bioaccessibility of microplastic-associated chemicals in the human gastric and intestinal fluids remains unresolved. This study investigated the mechanism and primary factor controlling the bioaccessibility of polypropylene (PP) microplastic fiber-associated tetracycline (TC) and ciprofloxacin (CIP) in simulated human gastrointestinal fluids. After mixing 0.1 g of PP microfiber with 10 mg/L of TC (or CIP) for 96 h and exposure to simulated human gastrointestinal fluids, the TC concentrations were 0.440, 0.678, and 1.840 mg/L and the CIP concentrations were 0.700, 1.367, and 3.281 mg/L CIP in the simulated human saliva, gastric, and intestinal fluids after incubation for 60 s, 4 h, and 8 h, respectively. This indicated that the antibiotics TC and CIP adsorbed onto microfiber surface are readily released into human gastrointestinal fluids upon ingestion. Gastric and intestinal fluids showed enhanced bioaccessibility to TC/CIP adhered to PP microfiber. The primary factors affecting the bioaccessibility to TC/CIP adhered to PP microfiber surfaces were found to be pepsin in human gastric fluid and trypsin in human intestinal fluid. Molecular docking and simulated molecular dynamic analyses results showed that pepsin and trypsin stablish connections with TC via hydrogen bonds (reaction sites: pepsin TC: T139, T136, S97, D94, D277 and Y251; trypsin TC: S257, H120, K235, G274, and G276) and CIP via hydrophobic interactions (reaction sites: pepsin CIP: Y137, T136, T139, F173, I362, V353, and I275; trypsin CIP: W273, I161, C253, and C277). Our findings highlight that microplastic ingestion increases the risk of microplastics and the co-contaminants adsorbed to human health; thus, these findings are helpful to assess the risk of microplastics and co-contaminants to human health.

Size-dependent long-term weathering converting floating polypropylene macro- and microplastics into nanoplastics in coastal seawater environments.

In this study, we systematically developed the long-term photoaging behavior of different-sized polypropylene (PP) floating plastic wastes in a coastal seawater environment. After 68 d of laboratory accelerated UV irradiation, the PP plastic particle size decreased by 99.3 ± 0.15%, and nanoplastics (average size: 435 ± 250 nm) were produced with a maximum yield of 57.9%, evidencing that natural sunlight irradiation-induced long-term photoaging ultimately converts floating plastic waste in marine environments into micro- and nanoplastics. Subsequently, when comparing the photoaging rate of different sized PP plastics in coastal seawater, we discovered that large sized PP plastics (1000-2000 and 5000-7000 µm) showed a lower photoaging rate than that of small sized PP plastic debris (0-150 and 300-500 µm), with the decrease rate of plastic crystallinity as follow: 0-150 µm (2.01 d-1) > 300-500 µm (1.25 d-1) > 1000-2000 µm (0.780 d-1) and 5000-7000 µm (0.900 d-1). This result can be attributed to the small size PP plastics producing more reactive oxygen species (ROS) species, with the formation capacity of hydroxyl radical •OH as follows: 0-150 µm (6.46 × 10-15 M) > 300-500 µm (4.87 × 10-15 M) > 500-1000 (3.61 × 10-15 M) and 5000-7000 µm (3.73 × 10-15 M). The findings obtained in this study offer a new perspective on the formation and ecological risks of PP nanoplastics in current coastal seawater environments.

Remarkable characteristics and distinct community of biofilms on the photoaged polyethylene films in riverine microcosms.

Recalcitrant plastics in the environment are gradually fragmented into weathered debris distinguished from their original state by the integrative action of influencing factors, such as UV light, heating and physical abrasion. As new artificial carbon-source substrates in aquatic ecosystems, plastic products can be colonized by biofilms and even utilized by microorganisms. To investigate the influences of weathering of plastics on the colonized biofilms, freshwater samples from the Yangtze River (Nanjing, China) were collected for biofilm incubation. Based on the characterization of plastics and biofilms, the effects of plastic surface properties on biofilm characteristics were revealed by the analysis of partial least squares regression (PLSR). Roughness was the principal influencing factor, while rigidity had the opposite effect to it. 16S rRNA gene high-throughput sequencing results indicated the high relative abundance of Cyanobacteria and rising proportion of harmful components (e.g., Flavobacterium) on photoaged polyethylene plastics. The microbial functional profiles (KEGG) predicted by Tax4Fun showed that the functions (e.g., membrane transport, energy metabolism, etc.) of biofilm on photoaged plastics were dissimilar with those on original ones. These findings suggested that the distinct microbial community and the adverse functional changes in biofilms on photoaged plastics potentially enhanced their environmental risks. On the other hand, 28-day cultured biofilms on original low-density polyethylene (LDPE) films were dominated by Exiguobacterium. The previously ignored potentials of this microorganism in rapidly accommodating to a hydrophobic substrate and its plastic degrading ability were both worthy of attention. Therefore, it is necessary to consider the weathering process of plastics in exploring the "plastisphere", and to give further insights into the double-edged nature of the "plastisphere".

Contribution of aged polystyrene microplastics to the bioaccumulation of pharmaceuticals in marine organisms using experimental and model analysis.

Microplastics (MPs) in the environment would undergo extensive weathering, which can act as a vector affecting the accumulation of pollutants in organisms. However, the risk of organic pollutants adsorbed on aged MPs to marine organisms is poorly understood. This study revealed the contribution of aged polystyrene (PS) MPs to the total bioaccumulation of atorvastatin (ATV) and amlodipine (AML), and assessed the environmental risks via experimental and model analysis. The results showed that pharmaceuticals were more easily released in gastrointestinal fluids from aged MPs relative to that in simulated seawater. The hydrophobic pharmaceuticals were more bioaccessible than hydrophilic ones by organisms. Model analysis showed that ingestion of water and food were the most important uptake routes for pharmaceuticals in marine fish and seabirds, while aged PS MPs could decrease the bioaccumulation of pharmaceuticals (contributed for -2.9% and -1.2% for the total uptake of ATV, and -25.8% and -4.4% for AML), indicating the cleaning effect of aged MPs, and the potential higher exposure risks of pharmaceuticals in warm-blooded organisms than that in cold-blooded ones via ingested MPs. The study revealed the effect of aged MPs to the bioaccumulation of pharmaceuticals in marine organisms, and highlighted the combined risks of aged MPs and pharmaceuticals in the environment.

Critical effect of biodegradation on long-term microplastic weathering in sediment environments: A systematic review.

Microplastic (MP) pollution in global sediment has been intensely studied and recognized as the ultimate sink for residual MPs in terrestrial and aquatic ecosystems. During MP long-term retention in sediments, plastic-degrading bacteria (i.e., Flavobacteriaceae, Bacillus, Rhodobacteraceae, and Desulfobacteraceae) can utilize those MPs as their carbon and energy sources through enzyme (hydrolase and oxidoreductase) reactions, which further alter or transform high molecular weight MP polymers into lower molecular weight biodegradation byproducts (i.e., monomers and oligomers) and release toxic additives. In other words, MPs can act as durable substrates for plastic-degrading bacteria in sediments. However, to date, the biodegradation rates of MPs in sediment environments are still poorly understood due to their limited degradation efficiency. Herein, we review the enzyme-induced biodegradation processes of MPs in sediment environments, which is important for accessing the alteration of MP properties and their potential ecological risks after undergoing long-term weathering processes. In addition, the factors associated with the MP properties (polymer type, molecular weight, crystallinity, and hydrophobicity) and sediment conditions (sediment type, temperature, pH, salinity, and oxygen content) that influence plastic degradation processes are also reviewed. The mechanisms may relate to the MP properties and sediment conditions that can influence microbial abundance, enzyme concentrations, and enzyme activities, thus altering MP biodegradation ratios. We anticipate that the observations reviewed in this study will pose a new issue to better understand the formation process, fate, and potential ecological risks associated with aged MPs in sediment environments.

Wastewater treatment plants act as essential sources of microplastic formation in aquatic environments: A critical review.

According to extensive in situ investigations, the microplastics (MPs) determined in current wastewater treatment plants (WWTPs) are mostly aged, with roughened surfaces and varied types of oxygen-containing functional groups (i.e., carbonyl and hydroxyl). However, the formation mechanism of aged MPs in WWTPs is still unclear. This paper systematically reviewed MP fragmentation and generation mechanisms in WWTPs at different treatment stages. The results highlight that MPs are prone to undergo physical abrasion, biofouling, and chemical oxidation-associated weathering in WWTPs at different treatment stages and can be further decomposed into smaller secondary MPs, including in nanoplastics (less than 1000 nm or 100 nm in size), suggesting that WWTPs can act as a formation source for MPs in aquatic environments. Sand associated mechanical crashes in the primary stage, microbes in active sewage sludge-related biodegradation in the secondary stage, and oxidant-relevant chemical oxidation processes (light photons, Cl2, and O3) in the tertiary stage are the dominant causes of MP formation in WWTPs. For MP formation mechanisms in WWTPs, external environmental forces (shear and stress forces, UV radiation, and biodegradation) can first induce plastic chain scission, destroy the plastic molecular arrangement, and create abundant pores and cracks on the MP surface. Then, the physicochemical properties (modulus of elasticity, tensile strength and elongation at break) of MPs shift consequently and finally breakdown into smaller secondary MPs or nanoscale plastics. Overall, this review provides new insights to better understand the formation mechanism, occurrence, fate, and adverse effects of aged microplastics/nanoplastics in current WWTPs.

Interaction of graphene oxide with artificial cell membranes: Role of anionic phospholipid and cholesterol in nanoparticle attachment and membrane disruption.

A mechanistic understanding of the interaction of graphene oxide (GO) with cell membranes is critical for predicting the biological effects of GO following accidental exposure and biomedical applications. We herein used a quartz crystal microbalance with dissipation monitoring (QCM-D) to probe the interaction of GO with model cell membranes modified with anionic lipids or cholesterol under biologically relevant conditions. The attachment efficiency of GO on supported lipid bilayers (SLBs) decreased with increasing anionic lipid content and was unchanged with varying cholesterol content. In addition, the incorporation of anionic lipids to the SLBs rendered the attachment of GO partially reversible upon a decrease in solution ionic strength. These results demonstrate the critical role of lipid bilayer surface charge in controlling GO attachment and release. We also employed the fluorescent dye leakage technique to quantify the role of anionic lipids and cholesterol in vesicle disruption caused by GO. Notably, we observed a linear correlation between the amount of dye leakage from the vesicles and the attachment efficiencies of GO on the SLBs, confirming that membrane disruption is preceded by GO attachment. This study highlights the non-negligible role of lipid bilayer composition in controlling the physicochemical interactions between cell membranes and GO.

Photo aging and fragmentation of polypropylene food packaging materials in artificial seawater.

Plastic litters in marine environment usually contain varied types and contents of additives that can significantly affect the photochemical aging and fragmentation process of microplastics (MPs). This study investigated the photo aging process of two common polypropylene (PP) food packaging materials (i.e., meal box and tea cup) in artificial seawater within 12 d of ultraviolet (UV) irradiation. Results revealed that the aging of both plastic materials were critically inhibited compared with pure PP, indicating that PP food packaging materials in natural seawater may share longer aging time than pure ones. GC-MS analysis revealed that antioxidant Irgafos 168 (tris (2,4-di-tert-butylphenyl) phosphite) was the dominant additive in these plastic materials. Photo reaction between Irgafos 168 and hydroperoxide species on the surface of MPs to prevent the formation of hydroxyl radical was the possible mechanism for the inhibiting effects. After antioxidant was exhausted, its photo degradation products could become the dominant contributor to influence the aging process of MPs. This is the first work exploring the role of antioxidant on the aging process of PP MPs in simulated ocean environment. The findings could be of great help for unraveling the effect of antioxidants on the aging-related environmental risk of hydrocarbon plastics in ocean environment.

Photo aging of polypropylene microplastics in estuary water and coastal seawater: Important role of chlorine ion.

Photo aging of microplastics (MPs) in water environment are relevant to free radical associated polymer chain reaction, and various photo chemical reactive constitutes (i.e., Cl-, Br-, NO3-, CO32-, and natural organic matters) would affect the reaction, leading to a great difference in the photo aging mechanism of MPs between freshwater and seawater system. This study investigated light induced photo aging process of polypropylene (PP) MPs in ultrapure water, estuary water, and seawater. Results revealed that the aging rate of PP MPs was significantly decreased in estuary water and seawater compared with that in ultrapure water, leading to a longer resistance time after emission in marine environment. Besides, lower carbonyl index was found with the increased aqueous Cl- concentration, highlighting the important role of Cl- in the inhibitory effect for PP MPs aging process in seawater. This is due to the formation of Cl2•- in seawater which could react with HO2• and prevent the formation of O2•-, thus inhibit the photo aging process of PP MPs under light irradiation. The finding in this study clearly indicates the impact of the water matrices on the photo aging rate of MPs in natural water.

Insight into chain scission and release profiles from photodegradation of polycarbonate microplastics.

Bisphenol A polycarbonate (BPA-PC) is a kind of widely used engineering plastics. However, excessive usage causes the production of plastic wastes, following property changes of polymers and high risks of released chemicals during outdoor weathering. In this study, we systematically investigated the photoaging behavior of PC microplastics (MPs) in aquatic environment and evaluated the potential risk of released intermediates. Light irradiation along with mechanical abrasion facilitated the fragmentation of PC MPs and stimulated photooxidative modification during 640 h of ultraviolet (UV) exposure. Continuous degradation of the polymer was accompanied with dramatic decline of molecular weight. Also, BPA was released from irradiated PC MPs with a trend of an initial rapid increase followed by a decrease versus the irradiation time, and the maximum concentration of dropped BPA was detected up to 652.80 ± 72.89 µg/g (43.39% and 56.61% respectively in particles and leachates). However, the releasing amount of BPA in the leachate merely occupied 2.7% of the total organic carbon (TOC) leached out, suggesting that a great number of unknown organic products were produced other than BPA. Liquid chromatography-time-of-flight-mass spectrometry (LC-TOF-MS) analysis showed that these organic compounds forming MPs-derived dissolved organic matter (MPs DOM) were partly composed of 4,4'-dihydroxybenzophenone (DHB), p-hydroxybenzoic acid (p-HBA) and methyparaben (MeP), which would also contribute to the estrogenic activity. The degradation pathway of PC MPs was elaborated with the photolysis process of PC dimer and BPA, and the remarkable photoaging of PC MPs was mainly dominated by the generated reactive oxygen species (ROS). The findings of this study indicated that understanding the photoaging process of PC MPs was vital to evaluate their integral cumulative estrogenic activity in aquatic environment, and further highlighted the notable possible risks of plastic leachates to exposed biota.

Enhanced phototransformation of atorvastatin by polystyrene microplastics: Critical role of aging.

Reactive oxygen species (ROS) generated from light irradiation of microplastics (MPs) can potentially affect the environmental fate of organic contaminants when they coexist in the same environment. This study investigated the effect of polystyrene (PS) MPs with different aging degrees on the phototransformation of atorvastatin (ATV) under simulated sunlight. Results showed that the presence of PS MPs facilitated the phototransformation of ATV, and the degradation rate was linearly correlated with the aging degree (i.e., carbonyl index) of MPs. The enhanced effects mainly depended on the contents of oxygen-containing functional groups of PS MPs, which increased the absorption of light energy and the generation of ROS (e.g., singlet oxygen (1O2) and triplet-excited state PS (3PS*)). Quenching experiments indicated that 1O2 generated from photosensitization of PS was the major contributor to the increased phototransformation of ATV. Additionally, the role of 3PS* became more important in the photodegradation mediated by higher degree aged MPs because much more 1O2 was generated from the 3PS* . PS MPs also increased the types and yields of degradation products, especially for higher degree aged MPs, despite the low effect on leachate toxicity. The findings provide a novel insight into the critical role of MPs in the fate of organic contaminants in aquatic environments.

Desorption of pharmaceuticals from pristine and aged polystyrene microplastics under simulated gastrointestinal conditions.

Microplastics (MPs) in the environment usually undergo extensive weathering and can transport pollutants to organisms once being ingested. However, the transportation mechanism and effect of aging process are poorly understood. This study systematically investigated the desorption mechanisms of pharmaceuticals from pristine and aged polystyrene (PS) MPs under simulated gastric and intestinal conditions of marine organisms. Results showed that the increased desorption in stomach mainly depended on the solubilization of pepsin to pharmaceuticals and the competition for sorption sites on MPs via π-π and hydrophobic interactions. However, high desorption in gut relied on the solubilization of intestinal components (i.e. bovine serum albumin (BSA) and bile salts (NaT)) and the competitive sorption of NaT since the enhanced solubility increased the partition of pharmaceuticals in aqueous phase. Aging process suppressed the desorption of pharmaceuticals because aging decreased hydrophobic and π-π interactions but increased electrostatic interaction between aged MPs and pharmaceuticals, which became less affected by gastrointestinal components. Risk assessment indicated that the MP-associated pharmaceuticals posed low risks to organisms, and warm-blooded organisms suffered relatively higher risks than cold-blooded ones. This study reveals important information to understand the ecological risks of co-existed MPs and pollutants in the environment.

Effect of aging on adsorption behavior of polystyrene microplastics for pharmaceuticals: Adsorption mechanism and role of aging intermediates.

In the environment, aging obviously changes physicochemical properties of microplastics (MPs), but the effects of aging process on adsorption behavior of MPs are not fully understood. In this study, the aging of polystyrene (PS) was accelerated by photo-Fenton reaction. The adsorption mechanism of different aged PS toward atorvastatin (ATV) and amlodipine (AML) and the role of PS-derived intermediates in adsorption process were investigated. Results showed that the adsorption of pristine PS toward pharmaceuticals relied on hydrophobic and π-π interaction, while for aged PS, electrostatic interaction and hydrogen bonding controlled the adsorption. The study revealed that the intermediates released from aging process in high concentration (TOC of 10 mg/L) significantly decreased the adsorption of ATV (10 mg/L) on PS (5.0 g/L) but increased the adsorption of AML (10 mg/L). However, those intermediates at environmental concentration (0.1 mg/L) exhibited low effects on adsorption of pharmaceuticals (1.0 mg/L) on MPs (0.5 g/L of PS). The impact mainly depended on electrostatic interaction between MPs and aging intermediates. Besides, the adsorption of low-degree aged PS was more susceptible to the aging intermediates than that of high-degree aged ones. These findings highlight significant implication of MP-derived intermediates in aquatic environments.