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.

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.

Releases of microplastics and chemicals from nonwoven polyester fabric-based polyurethane synthetic leather by photoaging.

The nonwoven PET fabrics are chemically, mechanically and thermally treated fiber aggregate without weaving, knitting or braiding, which could be used as a base to make polyurethane (PU) synthetic leather through a series of processing. Our research systematically compared the photoaging behaviors of pure non-woven PET base fabric (NPET-P) and PU synthetic leather (nonwoven PET-base fabrics with PU coating, NPET-U), and their possibilities for microplastic fibers (MPFs) generation and chemical transformation in water. NPET-U was photoaged to a higher oxidation degree with higher O/C ratios and more distinct changes in chemical structures. The amount of MPFs released from NPET-U (1.98 × 107 g/fibers) was significantly lower than that from NPET-P (4.76 × 107 g/fibers) after 360 h light irradiation (p value <0.05) with a slower degradation rate and delayed MPFs release. The lengths and diameters of released MPFs from NPET-U varied within a smaller range than that from NPET-P exposed to UV light irradiation. Natural sunlight aging of fabrics for 365 days was found to be equivalent to approximately 85.3-127.2 h UV aging in the laboratory, which indicated the lab accelerated experiments was extraordinarily intense to simulate natural sunlight aging. Furthermore, abundant calcium and sulfur-contained chemicals were detected in original fabrics and the leachate of 360 h light-aged fabrics using the inductively coupled plasma optical emission spectrometer (ICP-OES). The organic components of the leachate were separated according to their molecular weight with the changes of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and the UV response over aging time. UV stimulation aggravated the role of plastic polymers as disinfection by-product (DBP) precursors. Nevertheless, although NPET-U could produce more nitrogen-contained chemicals, it had similar formation potentials of nitrogen-containing DBPs as NPET-P. The discussion lucubrated the potential risks of the production of MPFs and chemical release in the leachate with regard to combined plastic pollution.

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.

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.

Critical effect of iron red pigment on photoaging behavior of polypropylene microplastics in artificial seawater.

Microplastics (MPs) containing chemical additives undergo extensive aging in the environment, but the effect of additives on aging behavior of MPs is not fully understood. This study evaluated the effects of iron red pigment on the photoaging behavior of polypropylene (PP) MPs and the release kinetics of Fe(II) and Fe(III) under simulated sunlight. Based on analyses in surface property and aging products of leachate, the incorporated iron red pigment significantly decreased the photoaging rate of PP MPs. The critical effect mainly depended on the light shielding and the competition of pigment for electrons and reactive oxygen species generated from irradiated MPs. Light irradiation also caused the production of homologous series of organic products containing dicarboxylic acid end groups. Moreover, aging of pigmented MPs enhanced the release of Fe ions in leachates, and the types of released iron ions were different between dark and light conditions, where the iron ion in dark system was mainly as Fe(III), while Fe(II) was the dominant form in light irradiation, since the released Fe(III) reacted with MP-derived organic acids and reactive oxygen species in light condition. The findings highlight the critical role of inorganic pigments in the environmental fate and risk of MPs.

Simulation of natural aging property of microplastics in Yangtze River water samples via a rooftop exposure protocol.

Due to low aging rate, the environmental behavior of naturally weathered microplastics (MPs) are not fully understood. Here, we systematically investigated the surface property and adsorption behavior of polypropylene (PP), polyethylene (PE) and polystyrene (PS) MPs during outdoor exposure in Yangtze River water for 18 months, and compared their difference from those in laboratory process. Results showed that compared to PE and PS MPs, PP underwent higher changes in surface aging properties such as rapid fragmentation and surface oxidation. Outdoor exposure exhibited different effects on adsorption property of MPs for metal ions, where adsorption capacities of PE and PS MPs for Co(II) were increased with aging degrees, while few change occurred on different aged PP MPs. As for Cr(VI), aging process further decreased the overall adsorption on PP, PE and PS MPs. The difference was mainly ascribed to the surface property (e.g. oxygen-containing groups and size) and the adhered biofilm and charged minerals. We further validated that similar types of oxidation products were formed between natural and laboratory aging of MPs, whereas the reaction order of these products, fragmentation rate and the change in adsorption property of aged MPs might be different in both processes. The findings provide essential information to assess real environmental behavior of MP samples.

Review of the artificially-accelerated aging technology and ecological risk of microplastics.

After being discarded into the environment, the microplastics (MPs) will undergo weathering effects. However, the low degradation rate of MPs in natural processes greatly limits the understanding of long-term aging behavior. By critically reviewing 82 articles in Web of Science from 2015 to 2020, the paper summarized different laboratory technologies including light irradiation, chemical oxidation, heat treatment and γ-ray irradiation to simulate and accelerate the aging of MPs, and evaluated the feasibility by comparison with natural processes. The advantages of laboratory technologies are that aging conditions can be artificially controlled and that the labor and time costs can be saved, whereas the laboratory system is too simple to simulate complex aging processes in the environment. We further reviewed the potential impacts of aging process on the risks of MPs (i.e. physical injury, combined toxicity with external pollutants and chemical risk of additives and low-molecular products). The overall risks are seemingly enhanced by aging process due to the high ingestion by organisms, the strong interaction with pollutants and the release of MP-derived organic compounds. Further studies on the aging behavior of MPs should be focused on the laboratory techniques that can simulate multiple processes of natural aging, the long-term fragmentation behavior of MPs, the effect of aging on growth rate of biofilm in MPs and ingestion property by organisms, and the relationship between aging property of MPs and release rate of chemicals in leachates.

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.

Adsorption of triclosan onto different aged polypropylene microplastics: Critical effect of cations.

Adsorption of organic contaminants onto aged microplastics (MPs) may be important in understanding their transport potential and ecological risks in aquatic environment. Cations of Na+ and Ca2+ are common electrolytes in water, which can greatly influence the adsorption behavior of MPs by impacting the electrostatic interaction between MPs and organic contaminants. The results of this study showed that aged isotactic polypropylene (iPP) MPs exhibited higher adsorption capacity to triclosan (TCS) than pristine ones, and the sorption affinity was enhanced with the increase of ionic concentrations. The crucial influence of cations on the adsorption behavior of aged MPs mainly depended on the changed properties of TCS and interactions between MPs and TCS. Salting out effect induced the precipitation of TCS from water and facilitated the partition of TCS onto MPs in high salinity water. Besides, compressing electrostatic double layer of MPs via squeezing out effect and bridging effect between functional groups of aged MPs and contaminants may also be significant factors in the sorption process. These findings will be helpful for understanding the role of cations on the transport of pollutants, the fate of MPs and their associated environmental risks in aquatic ecosystems.