Characteristics of microplastic-derived dissolved organic matter and its binding with pharmaceuticals unveiled by fluorescence spectroscopy and two-dimensional correlation spectroscopy

Molecular fractionation on ferrihydrite eroded the disinfection byproduct formation potential of dissolved organic matter derived from microplastics and biochar

Dissolved organic matter derived from microplastics (MPDOM) and biochar (BDOM), as examples of anthropogenic DOM, have received significant attention. Nonetheless, molecular fractionation particularly the detailed "kinetic architecture" and sequential assembly of MPDOM and BDOM at the mineral-water interface remains elusive, which significantly alters DOM composition and subsequent disinfection byproducts (DBPs) formation. This work systematically investigated these issues using FT-ICR MS, 2D-COS, PARAFAC analysis, and kinetic assays. For MPDOM, polyphenolics-like from plastic additives and breakdown products were rapidly adsorbed onto ferrihydrite, while combustion-derived condensed aromatics-like in BDOM exhibited priority adsorption. These results aligned with the equilibrium adsorption capacity for phenolics and condensed aromatics calculated by the Folin-Ciocalteu and benzenepolycarboxylic acid methods, 13.93 mg g-1 and 0.93 mgC g-1 for MPDOM, 3.66 mg g-1 and 7.16 mgC g-1 for BDOM, respectively. It suggested that mineral affinity of specific compounds relied on both molecular state and origin. The molecular fractionation driven by the co-action of "mineral-OM" and "OM-OM" interactions consequently eroded DBPs formation potential (21.77 % for MPDOM and 23.05 % for BDOM) by preferentially sequestering unsaturated and aromatic substances with higher chlorine reactivity. Our findings highlight molecular fractionation on minerals is a vital geochemical behavior regulating solid-liquid distribution and chlorine reactivity, advancing our understanding of anthropogenic carbon sequestration and cycling.

Influence of different food matrices on the abundance, characterization, migration kinetics and hazards of microplastics released from plastic packaging (PP and PET)

The effect of food matrix on the release of microplastics from plastic packaging was investigated by treating plastic samples with various food simulants. MPs were released during simulated conditions, and their main source was the separation of plastic samples subjected to ageing. Acidic high oil simulants resulted in the greatest abundance of MPs (1311.33 ± 262.22 and 1414.00 ± 214.52 items/piece). Dual constant kinetic model and Elovich kinetic model described the process well (R2 > 0.9019), indicating the release rate of MPs was mainly controlled by characteristics of plastics and environment. Characterization showed the morphology of plastics became rougher, carbonyl index increased, crystalline shapes changed and proportion of O increased. The release mechanism was deduced to be deterioration of the plastic by oxidative reactions. Finally, hazard assessment methodologies were developed, the results showed these MPs are hazardous to humans. It is hoped that this study will draw more attention to the harmful effects of MPs.

Influence of the source and molecular weights on sulfathiazole/sulfadiazine binding in sedimentary dissolved organic matter

Sedimental dissolved organic matter (DOM) plays a crucial role in the migration of antibiotics in a lake environment, which is strongly associated with its physicochemical properties influenced by temporal and spatial variations. This study systematically investigated the binding behavior of sulfathiazole (ST) and sulfadiazine (SD) to DOM across different molecular weights (MWs) in sediments from Poyang Lake using multiple spectroscopic techniques. Results showed that the MW fractions of DOM from the onset of the dry season were higher than those before flooding. Additionally, key carbon parameters, including dissolved organic carbon and fluorescent components, were present in greater proportion in the truly dissolved phase and the low MW fraction of DOM. These properties of the low MW fraction of DOM enhanced its binding capacity for the two sulfonamides, with the partitioning coefficient (logKcoc) values of 5.20 and 5.06 for ST and SD, respectively. Dialysis experiments investigating the interaction between different concentrations of DOM and sulfonamides indicated that humic-like and protein-like components significantly influenced the migration of ST and SD, respectively. Moreover, protein-like components exerted a more substantial impact on the migration of sulfonamides in heavily polluted sampling sites, while the humic-like substances played a more significant role for the samples from the wetland protection area. The results enhanced the understanding of the significance of DOM sources and MW in influencing the environmental fate of antibiotics in lake ecosystems.

Changes in Fluorescence of Aquatic Dissolved Organic Matter Induced by Plastic Debris

Water contamination with plastic materials represents one of the most pressing environmental problems that the modern world is facing. In this context, the present paper aims to investigate the influence of fluorescent dissolved organic matter (FDOM) released by plastic materials on the aquatic bacterial fraction and evaluate the efficiency of fluorescence spectroscopy in identifying plastic FDOM in freshwater. To this purpose, river and tap water samples were contaminated in a controlled manner in the laboratory, and the water quality parameters and bacterial occurrence for these samples were determined using standard physico-chemical characterization methods: fluorescence spectroscopy, dynamic light scattering, and flow cytometry. The results revealed that plastic debris influenced the dissolved-particulate organic matter continuum, also affecting bacterial cell proliferation in both the river and tap samples. The study highlights that the impact of plastic FDOM on bacterial proliferation should not be taken lightly, while fluorescence spectroscopy proved to be an effective method for identifying the presence of plastic FDOM in water samples of various origins.

Impacts of climatic stressors on dissolved organic matter leaching from microplastics and their effects on biogeochemical processes: A review

This review explores the potential impact of microplastic-derived dissolved organic matter (MP-DOM) on biogeochemical processes associated with global carbon and nitrogen cycles, with consideration given to the possible influence of irregular climate changes. We synthesize literature on MP-DOM leaching behaviors during various natural aging processes, such as heavy rainfall, heat waves, and UV irradiation, which may be intensified by climate change. MP-DOM release varies with plastic type and conditions, with organic additives significantly influencing leaching under UV exposure. Increased turbulence from hydrological events and rising temperatures also enhances MP-DOM release. While most research has focused on specific additive releases, the broader effects of polymer degradation and subsequent impacts on microbial communities and biogeochemical cycles are only recently recognized. These disruptions may affect cellular processes in algae and plant roots, enhance microbial utilization of dissolved organic carbon, and potentially increase greenhouse gas production. Our review highlights overlooked roles of MP-DOM exacerbated by climatic stressors and calls for further research to understand its broader biogeochemical impacts. We also emphasize the importance of distinguishing between polymers and commercial plastics when assessing MP-DOM's effects on biogeochemical processes associated with carbon and nitrogen cycles and recommend investigating additional aging processes influencing MP-DOM release.

Preliminary insights into the photosensensitivity of bio-based plastics: Release of microplastic-derived organic matter in water under UV irradiation

This is the first study to investigate the possible release of microplastic-derived dissolved organic matter (MP-DOM) in water from three major types of bio-based MPs, namely, polylactic acid (PLA), polyhydroxyalkanoate (PHA) and PLA-PHA mixtures, under ultraviolet (UV) irradiation conditions. At an initial MP concentration of approximately 5 g per liter, the release of MP-DOM from the studied MPs ranged from 1.55 to 6.68 mg of dissolved organic carbon per g of MP after 30 days of exposure. The results from the measured MP-DOM, along with changes in spectral measurements obtained from shortwave infrared spectroradiometer (SWIR) and micro Fourier-transform infrared spectrometer (μFT-IR), confirmed that the bio-based polymers appeared to be photosensitive due to the observed possible formation of carbonyl bonds with increased carbonyl index on the UV-irradiated surface. Additionally, the fluorescence excitation-emission spectra of the MP-DOM revealed narrow fluorescence peaks, suggesting the presence of organic matter with structural features similar to those of humic substances. These findings on bio-based MPs provide insights into their fate and potential impacts on water environments.

Insights into the photoaging behavior of biodegradable and nondegradable microplastics: Spectroscopic and molecular characteristics of dissolved organic matter release

Biodegradable plastics are increasingly used as a potential alternative to nondegradable plastics to tackle plastic pollution. However, recent studies have raised concerns about the ecological risks posed by biodegradable microplastics (MPs), which mainly focused on the risks generated by MPs themselves, neglecting the risks associated with the MPs derived dissolved organic matter (DOM). Therefore, this study selected polylactic acid (PLA) MPs with 50 µm particle size and polystyrene (PS) MPs with 50 µm and 500 nm particle sizes as representatives of biodegradable and nondegradable MPs, respectively, to comparative investigate their photoaging behavior, particularly the differences in DOM release. The results showed that both PLA-MPs and PS-MPs exhibited considerable photoaging under ultraviolet irradiation, accompanied by different color changes (PS turned yellow and PLA turned grayish brown), which were attributed to the different functional groups produced on their surfaces after photoaging (PS-MPs: CO, PLA-MPs: terminal -COOH). Additionally, excitation-emission matrix characterization combined with parallel factor analysis revealed that 50 µm PLA-MPs (16-23 %) released more protein-like low molecular weight DOM during photoaging than that of both 50 µm PS-MPs (7-13 %) and 500 nm PS-MPs (8-18 %). Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) further confirmed that PLA-MPs (41.4 %) produced more unstable DOM easily utilized by microorganisms than that of 50 µm PS-MPs (6.3 %) and 500 nm PS-MPs (7.9 %). These results together suggested that biodegradable MPs with small particle size derived DOM may have a greater impact on microbial activity and carbon cycle than that of nondegradable MPs.

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.

Photodegradation Processes and Weathering Products of Microfibers in Aquatic Environments

Microplastics, particularly microfibers (MFs), pose a significant threat to the environment. Despite their widespread presence, the photochemical reactivity, weathering products, and environmental fate of MFs remain poorly understood. To address this knowledge gap, photodegradation experiments were conducted on three prevalent MFs: polyester (POL), nylon (NYL), and acrylic (ACR), to elucidate their degradation pathways, changes in surface morphology and polymer structure, and chemical and colloidal characterization of weathering products during photochemical degradation of MFs. The results showed that concentrations of dissolved organic carbon, chromophoric dissolved organic matter (DOM), and fluorescent components consistently increased during weathering, exhibiting a continuous release of DOM. Scanning electron microscopy and Raman spectroscopy revealed changes in the surface morphology and polymer spectra of the MFs. During the weathering experiments, DOM aromaticity (SUVA254) decreased, while spectral slope increased, indicating concurrent DOM release and degradation of aromatic components. The released DOM or nanoplastics were negatively charged with sizes between 128 and 374 nm. The production rate constants of DOM or the photochemical reactivity of MFs followed the order ACR > NYL ≥ POL, consistent with their differences in chemical structures. These findings provide an improved understanding of the photochemical reactivity, degradation pathways, weathering products, and environmental fate of microfibers in the environment.

Overview of the environmental risks of microplastics and their controlled degradation from the perspective of free radicals

Owing to the significant environmental threat posed by microplastics (MPs) of varying properties, MPs research has garnered considerable attention in current academic discourse. Addressing MPs in river-lake water systems, existing studies have seldom systematically revealed the role of free radicals in the aging/degradation process of MPs. Hence, this review aims to first analyze the pollution distribution and environmental risks of MPs in river-lake water systems and to elaborate the crucial role of free radicals in them. After that, the study delves into the advancements in free radical-mediated degradation techniques for MPs, emphasizing the significance of both the generation and elimination of free radicals. Furthermore, a novel approach is proposed to precisely govern the controlled generation of free radicals for MPs' degradation by interfacial modification of the material structure. Hopefully, it will shed valuable insights for the effective control and reduction of MPs in river-lake water systems.

Microplastic-derived dissolved organic matter: Generation, characterization, and environmental behaviors

Microplastics (MPs) represent a substantial and emerging class of pollutants distributed widely in various environments, sparking growing concerns about their environmental impact. In environmental systems, dissolved organic matter (DOM) is crucial in shaping the physical, chemical, and biological processes of pollutants while significantly contributing to the global carbon budget. Recent findings have revealed that microplastic-derived dissolved organic matter (MP-DOM) constitutes approximately 10 % of the DOM present on the ocean surface, drawing considerable attention. Hence, this study's primary objective is to explore, the generation, characterization, and environmental behaviors of MP-DOM. The formation and characteristics of MP-DOM are profoundly influenced by leaching conditions and types of MPs. This review delves into the mechanisms of the generation of MP-DOM and provides an overview of a wide array of analytical techniques, including ultraviolet-visible (UV-Vis) spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), and mass spectroscopy, used to assess the MP-DOM characteristics. Furthermore, this review investigates the environmental behaviors of MP-DOM, including its impacts on organisms, photochemical processes, the formation of disinfection by-products (DBPs), adsorption behavior, and its interaction with natural DOM. Finally, the review outlines research challenges, perspectives for future MP-DOM research, and the associated environmental implications.

The environmental effects of microplastics and microplastic derived dissolved organic matter in aquatic environments: A review

Currently, microplastics (MPs) have ubiquitously distributed in different aquatic environments. Due to the unique physicochemical properties, MPs exhibit a variety of environmental effects with the coexisted contaminants. MPs can not only alter the migration of contaminants via vector effect, but also affect the transformation process and fate of contaminants via environmental persistent free radicals (EPFRs). The aging processes may enhance the interaction between MPs and co-existed contaminants. Thus, it is of great significance to review the aging mechanism of MPs and the influence of coexisted substances, the formation mechanism of EPFRs, environmental effects of MPs and relevant mechanism. Moreover, microplastic-derived dissolved organic matter (MP-DOM) may also influence the elemental biogeochemical cycles and the relevant environmental processes. However, the environmental implications of MP-DOM are rarely outlined. Finally, the knowledge gaps on environmental effects of MPs were proposed.

Effect of pyrolysis temperature and molecular weight on characterization of biochar derived dissolved organic matter from invasive plant and binding behavior with the selected pharmaceuticals

A comprehensive understanding of the characteristics of biochar released-dissolved organic matter (BDOM) derived from an invasive plant and its impact on the binding behavior of pharmaceuticals is essential for the application of biochar, yet has received less attention. In this study, the binding behavior of BDOM pyrolyzed at 300-700 °C with sulfathiazole, acetaminophen, chloramphenicol (CAP), and carbamazepine (CMZ) was investigated based on a multi-analytical approach. Generally, the pyrolysis temperature exhibited a more significant impact on the spectral properties of BDOM and pharmaceutical binding behavior than those of the molecular weight. With increased pyrolysis temperature, the dissolved organic carbon decreased while the proportion of the protein-like substance increased. The highest binding capacity towards the drugs was observed for the BDOM pyrolyzed at 500 °C with the molecular weight larger than 0.3 kDa. Moreover, the protein-like substance exhibited higher susceptive and released preferentially during the dialysis process and also showed more sensitivity and bound precedingly with the pharmaceuticals. The active binding points were the aliphatic C-OH, amide II N-H, carboxyl CO, and phenolic-OH on the tryptophan-like substance. Furthermore, the binding affinity of the BDOM pyrolyzed at 500 °C was relatively high with the stability constant (logKM) of 4.51 ± 0.52.