Dissolved Organic Matter Enhanced the Aggregation and Oxidation of Nanoplastics under Simulated Sunlight Irradiation in Water

Exacerbated interfacial impacts of nanoplastics and 6:2 chlorinated polyfluorinated ether sulfonate by natural organic matter in adult zebrafish: Evidence through histopathology, gut microbiota, and transcriptomic analysis

Nanoplastics (NPs) interact with cooccurring chemicals and natural organic matter (NOM) in the environment, forming complexes that can change their bioavailability and interfacial toxicity in aquatic organisms. This study aims to elucidate the single and combined impacts of 21-day chronic exposure to low levels of polystyrene NPs (size 80 nm) at 1 mg/L and 6:2 chlorinated polyfluorinated ether sulfonate (Cl-PFAES or F53B) at 200 μg/L in the presence and absence of NOM (humic acid-HA and bovine serum albumin-BSA at 10 mg/L) in adult zebrafish (Danio rerio). Our findings through multiple bioassays, revealed that the mixture group (M), comprising of NPs, F53B, HA, and BSA, caused a higher level of toxicity compared to the single NPs (AN), single F53B (AF), and combined NPs+F53B (ANF) groups. The mixture exposure caused the highest level of vacuolization and nuclear condensation in hepatocytes, and most of the intestinal villi were fused and highly reduced in villi length and crypt depth. Further, the T-AOC levels were significantly lower (p < 0.05), while the MDA levels in the liver and intestine were significantly higher (p < 0.05) in the M group with downregulation of nfkbiaa, while upregulation of prkcda, csf1ra, and il1b apoptosis genes in the liver. Pairwise comparison of gut microbiota showed significantly higher (p < 0.05) abundances of various genera in the M group, including Gordonia, Methylobacterium, Tundrisphaera, GKS98, Pedomicrobium, Clostridium, Candidatus and Anaerobacillus, as well as higher abundance of genera including pathogenic strains, while control group showed higher abundance of probiotic genus ZOR0006 than exposed group (p < 0.01). The transcriptomic analysis revealed highest number of DEGs in the M group (2815), followed by the AN group (506) and ANF group (206) with the activation of relaxin signaling pathway-RSP (slc9a1, slc9a2) and AMP-activated protein kinase (AMPK) pathway (plin1), and suppression of the toll-like receptor (TLR) pathway (tlr4a, tlr2, tlr1), cytokine-cytokine receptor interaction (CCRI) pathway (tnfb, il21r1, il21, ifng1), and peroxisome proliferator-activated receptors (PPAR) pathway (pfkfb3). Overall, toxicity in the M group was higher, indicating that the HA and BSA elevated the interfacial impacts of NPs and F53B in adult zebrafish after chronic environmentally relevant exposure, implying the revisitation of the critical interaction of NOM with co-occurring chemicals and associated impacts.

Enhanced sinks of polystyrene nanoplastics (PSNPs) in marine sediment compared to freshwater sediment: Influencing factors and mechanisms

The difference in the transport behaviors of nanoplastics consistently assistant with their toxicities to benthic and other aquatic organisms is still unclear between freshwater and marine sediments. Here, the mobilities of polystyrene nanoplastics (PSNPs) and key environmental factors including salinity and humic acid (HA) were systematically studied. In the sand column experiments, both tested PSNPs in the freshwater system (100 nm NPs (100NPs): 90.15 %; 500 nm NPs (500NPs): 54.22 %) presented much higher penetration ratio than in the marine system (100NPs: 8.09 %; 500NPs: 19.04 %). The addition of marine sediment with a smaller median grain diameter caused a much more apparent decline in NPs mobility (100NPs: from 8.09 % to 1.85 %; 500NPs: from 19.04 % to 3.51 %) than that containing freshwater sediment (100NPs: from 90.15 % to 83.56 %; 500NPs: from 54.22 % to 41.63 %). Interestingly, adding HA obviously led to decreased and slightly increased mobilities for NPs in freshwater systems, but dramatically improved performance for NPs in marine systems. Electrostatic and steric repulsions, corresponding to alteration of zeta potential and hydrodynamic diameter of NPs and sands, as well as minerals owing to adsorption of dissolved organic matter (DOM) and aggregations from varied salinity, are responsible for the mobility difference.

Attenuation of phenylnaphthenic acids related to oil sands process water using solar activated calcium peroxide: Influence of experimental factors, mechanistic modeling, and toxicity evaluation

Refractory naphthenic acids (NAs) are among the primary toxic compounds in oil sands process water (OSPW), a matrix with a complex chemical composition that poses challenges to its remediation. This study evaluated the effectiveness of calcium peroxide (CaO2) combined with solar radiation (solar/CaO2) as an advanced water treatment process for degrading model NAs (1,2,3,4-tetrahydronaphthalene-2-carboxylic acid, pentanoic acid, and diphenylacetic acid) in synthetic water (STW) and provide preliminary insights in treating real OSPW. Solar light and CaO2 acted synergistically to degrade target NAs in STW (>67 of synergistic factor) following a pseudo-first-order kinetic (R2 ≥ 0.95), with an optimal CaO2 dosage of 0.1 g L-1. Inorganic ions and dissolved organic matter were found to hinder the degradation of NAs by solar/CaO2 treatment; however, the complete degradation of NAs was reached in 6.7 h of treatment. The main degradation mechanism involved the generation of hydroxyl radicals (•OH), which contributed ∼90% to the apparent degradation rate constant (K), followed by H2O2 (4-5%) and 1O2 (0-5%). The tentative transformation pathways of three NAs were proposed, confirming an open-ring reaction and resulting in short-chain fatty acid ions as final products. Furthermore, a reduction in acute microbial toxicity and genotoxic effect was observed in the treated samples, suggesting that solar/CaO2 treatment exhibits high environmental compatibility. Furthermore, the solar/CaO2 system was successfully applied as a preliminary step for real-world applications to remove natural NAs, fluorophore organic compounds, and inorganic components from OSPW, demonstrating the potential use of this technology in the advanced treatment of oil-tailing-derived NAs.

The suspension stability of nanoplastics in aquatic environments revealed using meta-analysis and machine learning

Nanoplastics (NPs) aggregation determines their bioavailability and risks in natural aquatic environments, which is driven by multiple environmental and polymer factors. The back propagation artificial neural network (BP-ANN) model in machine learning (R2 = 0.814) can fit the complex NPs aggregation, and the feature importance was in the order of surface charge of NPs > dissolved organic matter (DOM) > functional group of NPs > ionic strength and pH > concentration of NPs. Meta-analysis results specified low surface charge (0 ≤ |ζ| < 10 mV) of NPs, low concentration (< 1 mg/L) and low molecular weight (< 10 kg/mol) of DOM, NPs with amino groups, high ionic strength (IS > 700 mM) and acidic solution, and high concentration (≥ 20 mg/L) of NPs with smaller size (< 100 nm) contribute to NPs aggregation, which is consistent with the prediction in machine learning. Feature interaction synergistically (e.g., DOM and pH) or antagonistically (e.g., DOM and cation potential) changed NPs aggregation. Therefore, NPs were predicted to aggregate in the dry period and estuary of Poyang Lake. Research on aggregation of NPs with different particle size,shapes, and functional groups, heteroaggregation of NPs with coexisting particles and aging effects should be strengthened in the future. This study supports better assessments of the NPs fate and risks in environments.

Natural organic small molecules promote the aging of plastic wastes and refractory carbon decomposition in water

Microplastics and nanoplastics are ubiquitous in rivers and undergo environmental aging. However, the molecular mechanisms of plastic aging and the in-depth effects of aging on ecological functions remain unclear in waters. The synergies of microplastics and nanoplastics (polystyrene as an example) with natural organic small molecules (e.g., natural hyaluronic acid and vitamin C related to biological tissue decomposition) are the key to producing radicals (•OH and •C). The radicals promote the formation of bubbles on plastic surfaces and generate derivatives of plastics such as monomer and dimer styrene. Nanoplastics are easier to age than microplastics. Pristine plastics inhibit the microbial Shannon diversity index and evenness, but the opposite results are observed for aging plastics. Pristine plastics curb pectin decomposition (an indicator of plant-originated refractory carbon), but aging plastics promote pectin decomposition. Microplastics and nanoplastics undergoing aging processes enhance the carbon biogeochemical cycle. For example, the increased carbohydrate active enzyme diversity, especially the related glycoside hydrolase and functional species Pseudomonas and Clostridium, contributes to refractory carbon decomposition. Different from the well-studied toxicity and aging of plastic pollutants, this study connects plastic pollutants with biological tissue decomposition, biodiversity and climate change together in rivers.

Spectroscopic studies of the role of dissolved organic matter in acenaphthene photodegradation in liquid water and ice

The effect of concentration and origin of dissolved organic matter (DOM) on acenaphthene (Ace) photodegradation in liquid water and ice was investigated, and the components in DOM which were involved in Ace photodegradation were identified. The DOM samples included Suwannee River fulvic acid (SRFA), Elliott soil humic acid (ESHA), and an effluent organic matter (EfOM) sample. Due to the production of hydroxyl radical (•OH) and triplet excited-state DOM (3DOM*) which react with Ace, DOM had promotion effects on Ace photodegradation. However, the promotion effects of DOM were prevailed over by their suppressing effect of DOM including screening light effect, intermediates reducing effect and RS quenching effect, and thus, the photodegradation rates of Ace decreased in the presence of the three DOM with concentrations of 0.5-7.5 mg C/L in liquid water and ice. ESHA had higher light absorption and thus had higher screening light effect on Ace photodegradation in liquid water than SRFA and EfOM. At each DOM concentration, ESHA exhibited higher promotion effect on Ace photodegradation than SRFA and EfOM, in liquid water and ice. The binding of Ace with DOM was indicated by decreases in fluorescence intensity of Ace when coexisted with DOM. However, the binding of Ace to DOM played an unimportant role in suppressing Ace photodegradation. The photodegradation behavior of fluorophores in Ace with DOM present in ice was not similar to that in liquid water. C-O, C═O, carboxyl groups O-H and aliphatic C-H functional groups in DOM were involved in the interaction of DOM with Ace. The presence of Ace seemed to have no influence on the photodegradation behavior of functional groups in DOM.

Self-motivated photoaging of microplastics by biochar-dissolved organic matter under different pyrolysis temperatures

Dissolved organic matter (DOM) released from biochar (BDOM) can interact with microplastics (MPs) in the environment, inevitably affecting their environmental behaviour. Information regarding the influence of BDOM on MPs during photoaging and associated variations in the MP aging mechanism remains unclear. This study evaluated the effect of BDOM on the aging of polystyrene (PS) MPs. The results showed that among three pyrolysis temperatures, low-temperature BDOM significantly enhanced the photoaging process of PS MPs, with the smallest average particle size and highest carbonyl index value after 15 days of aging under light conditions. The DOM level decreased after 5 days, increased after 5-10 days, and stabilised after 15 d. BDOM accelerates PS MPs aging, leading to more DOM released from PS, which can be transformed into 1O2 via triplet-excited state (3DOM⁎ and 3PS⁎) to further enhance PS MPs aging, resulting in the realisation of the self-accelerated aging process of PS MPs. 1O2 plays a crucial role in the self-motivated accelerated aging process of PS MPs. These findings provide new insights into the effects of the DOM structure and composition on reactive oxygen species generation during MPs aging.

Effect of microplastics on urban wastewater disinfection and impact on effluent reuse: Sunlight/H2O2 vs solar photo-Fenton at neutral pH

The interference of three types of microplastics (MPs) on the inactivation of Escherichia coli (E. coli) by advanced oxidation processes (AOPs) (namely, sunlight/H2O2 and solar photo-Fenton (SPF) with Ethylenediamine-N,N'-disuccinic acid (EDDS)), in real secondary treated urban wastewater was investigated for the first time. Inactivation by sunlight/H2O2 treatment decreased as MPs concentration and H2O2 dose were increased. Noteworthy, an opposite behaviour was observed for SPF process where inactivation increased as MPs concentration was increased. Biofilm formation and microbial attachment on surfaces of post-treated MPs were observed on polyethylene (PE) and polyvinyl chloride (PVC) MPs by field emission scanning electron microscopy. In presence of PE MPs, a complete inactivation of E. Coli was achieved by SPF with EDDS (Fe:EDDS = 1:2) after 90 min treatment unlike of sunlight/H2O2 treatment (∼4.0 log reduction, 40 mg/L H2O2 dose, 90 min treatment). The lower efficiency of sunlight/H2O2 process could be attributed to the blocking/scattering effect of MPs on sunlight, which finally reduced the intracellular photo Fenton effect. A reduced E. coli regrowth was observed in presence of MPs. SPF (Fe:EDDS = 1:1) with PE MPs was less effective in controlling bacterial regrowth (∼120 CFU/100 mL) than sunlight/H2O2 (∼10 CFU/100 mL) after 48 h of post-treatment. These results provide useful information about possible interference of MPs on urban wastewater disinfection by solar driven AOPs and possible implications for effluent reuse.

Polystyrene microplastics enhance oxidative dissolution but suppress the aquatic acute toxicity of a commercial cadmium yellow pigment under simulated irradiation

Commercial cadmium yellow (CdS) pigment widely coexist with microplastics (MPs) in surface water, thus it is important to understand how MPs affect CdS pigment stability and toxicity under irradiation. Herein, the dissolution of CdS pigment (krelease = 0.118 h-1) under irradiation was visibly increased to 0.144 h-1 by polystyrene (PS) MPs, due to reactive species generation such as 1O2, •OH and 3PS* , while O2•- was unimportant to this process. The O2, humic acid, photoaging status of PS MPs could promote PS MPs-related CdS pigment dissolution rate by modifying reactive species generation. However, the CO32-, PO43- and alkaline condition significantly decreased the dissolution rate to 0.091, 0.053 and 0.094 h-1, respectively, through modifying free Cd2+ stability. Comparably, PS MPs-related CdS pigment dissolution was relatively slow in natural water samples (krelease = 0.075 h-1). PS MPs at environmental concentration can also promote CdS pigment dissolution and Cd2+ release, but suppress acute toxicity of CdS pigment to zebrafish larvae as increasing 10 h survival from 65% to 85% by adsorbing the Cd2+ and decreasing Cd2+ bioavailability. This study emphasized the environmental risks and human safety of CdS pigment should be carefully evaluated in the presence of PS MPs in aquatic environments.

Photo-oxidation of Micro- and Nanoplastics: Physical, Chemical, and Biological Effects in Environments

Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.

Adsorption behavior of triclosan on polystyrene nanoplastics: The roles of particle size, surface functionalization, and environmental factors

Nanoplastics (NPs) contribute substantially to the transport of waterborne pollutants. Triclosan (TCS) has a high potential to contact with NPs because of their prevalence in natural waters. Herein, this study investigated the adsorption behavior of TCS on differently sized and functionalized polystyrene (PS) NPs. The effects of environmental factors such as pH, salinity, and dissolved organic matter (DOM) were also evaluated. Results suggest that the adsorption equilibrium constant (kd) of TCS in pristine PSNP suspensions followed the order as: PSNPs-50 nm (4.39 L·g-1) > PSNPs-100 nm (2.78 L·g-1) > PSNPs-200 nm (2.59 L·g-1) > PSNPs-500 nm (1.36 L·g-1) ≈ PSNPs-900 nm (1.36 L·g-1). For the functionalized PSNPs (i.e., PSNPs-COOH, PSNPs-NH2), the values of specific surface area normalized kd called kd, SSA were higher than those of pristine PSNPs. Meanwhile, TCS adsorption on two functionalized PSNPs remained stable and then decreased as salinity increased, while an opposite trend was observed toward pristine PSNPs. All these suggested that physicochemical properties of PSNPs (e.g., particle size and surface functional groups) are important factors influencing their adsorption capacity. When the solution pH raised, the adsorbed amounts of TCS on all tested PSNPs prone to decline. However, DOM only affected the adsorption behavior of PSNPs-50 nm, probably owing to its aggregation with tiny PSNPs and the induced secondary adsorption.

Quantitative separation of polystyrene nanoparticles in environmental matrices with picogram detection limits using capillary electrophoresis

We developed a capillary electrophoresis method to separate polystyrene particles (PSPs) with different sizes or different surface functionalities. Separations were performed in buffer and 100 mg L-1 clay or 100 mg L-1 Suwanee River humic acid. In all solutions, PSPs were baseline or near-baseline resolved in less than 15 minutes.

Study on the mechanism of co-pyrolysed biochar on soil DOM evolution in short-term cabbage waste decomposition

Cabbage waste returned soil was studied to assess the short-term influences of the application of cabbage waste biochar (CB), pine wood biochar (PB), and co-pyrolysed biochar (PCB) on soil dissolved organic matter (DOM) evolution. The decrease in DOM and soil organic matter (SOM) content was greater in the biochar-added soils during 35 days of decomposition. The DOM and SOM content in PCB added group decreased by 26.96 mg L-1 and 4.48 g kg-1, respectively. The increase in relative abundance of humic acid-like substances in DOMs was higher in the biochar-added soils during decomposition, which increased by 4.29% in PCB added group. PCB addition also resulted in a high SOM content (initial content of 78.82 g kg-1), and mineral elements were introduced into the soil, thus increasing soil pH (7.81) and electrical conductivity (574.67 μs cm-1). Moreover, the addition of biochars attenuated the decrease in average relative abundance of Bacillaceae and promoted bacterial proliferation during decomposition. The application of biochars regulated the soil bacterial community and promoted organic matter conversion and soil DOM evolution.

Does functionalised nanoplastics modulate the cellular and physiological responses of aquatic fungi to metals?

Co-contamination of freshwaters by nanoplastics (NPs; ≤ 1 μm) and metals is an emerging concern. Aquatic hyphomycetes play a crucial role as primary decomposers in these ecosystems. However, concurrent impacts of NPs and metals on the cellular and physiological activities of these fungi remain poorly understood. Here, the effects of environmentally realistic concentrations of two types of polystyrene (PS) NPs (bare and -COOH; up to 25 μg L-1) and copper (Cu; up to 50 μg L-1) individually and all possible combinations (NPs types and Cu) on Articulospora tetracladia, a prevalent aquatic hyphomycete, were investigated. Endpoints measured were intracellular reactive oxygen species accumulation, plasma membrane disruption and fungal growth. The results suggest that functionalised (-COOH) NPs enhance Cu adsorption, as revealed by spectroscopic analyses. Notably, NPs, Cu and their co-exposure to A. tetracladia can lead to ROS accumulation and plasma membrane disruption. In most cases, exposure to treatments containing -COOH NPs with Cu showed greater cellular response and suppressed fungal growth. By contrast, exposure to Cu individually showed stimulatory effects on fungal growth. Overall, this study provides novel insight that functionalisation of NPs facilitates metal adsorption, thus modulating the impacts of metals on aquatic fungi.

Effect of polystyrene microplastics on tetracycline photoconversion under simulated sunlight: Vital role of aged polystyrene

Photoconversion of tetracycline (TC) has been widely reported. However, the effect of microplastics (MPs) on TC conversion kinetics and mechanism has rarely been discussed. In this study, we investigated the effect of (aged) MPs on TC degradation under simulated sunlight and elucidated the underlying mechanism. Our findings demonstrated that the physical and chemical properties of polystyrene (PS), such as particle size, surface groups, and morphology, were significantly altered after aging. Moreover, photoconversion efficiency of TC was suppressed with the spiking of aged PS, while virgin PS showed an opposite tendency. The photodegradation reaction for photosensitization of PS involved 1O2 and HO·. The light-screening effect of aged PS occupied predominance, weakening the direct UV-light absorption of TC and resulting in lower TC degradation efficiency. Additionally, triplet-excited state PS was generated after photon acceptance by aged PS, which could transfer energy to O2, leading to the production of 1O2. The toxicity test manifested that the direct impact of TC products on fathead minnow was ignorable, but long-term negative effects on growth deserved observation. This study enhances our understanding of the environmental fate of PS and TC under sunlight, and provides crucial reference information for better evaluating the potential risk of MPs and chemicals.

Differential Photoaging Effects on Colored Nanoplastics in Aquatic Environments: Physicochemical Properties and Aggregation Kinetics

Nanoplastics (NPs) have different colors, which could affect their photoaging processes in aquatic environments. This study investigated the effects of irradiation on physicochemical properties and aggregation kinetics of five colored NPs. Photodegradation rates and photooxidation degrees ranked white ≈ yellow > red > blue ≈ black NPs, indicating that NPs with longer color wavelengths photoaged faster. The discoloration process followed color fading (2-14 days, except for white NPs), yellowing (10-16 days), yellow fading (18 days), and turning transparent (20-22 days). White NPs exhibited a different photoaging sequence (C-H → C-OH → C═O → O-C═O) from others. Photodegradation was mainly controlled by singlet oxygen, producing 13 chemicals that were mostly organic acids. The overall colloidal stability of pristine NPs ranked blue > yellow > red > black > white. Irradiation for 16 days retarded aggregation of white and other NPs in NaCl solution, raising the critical coagulation concentration (CCC) by 82.14 and 0.85-7.90%, respectively. Contrarily, irradiation promoted aggregation in CaCl2 solution by reducing the CCC of white (67.37%) and other (33.33-37.58%) NPs. The findings demonstrate that colored NPs underwent photoaging processes different from white/transparent NPs, which were focused by previous work, highlighting the important role of color in their environmental fate and transport.

Differences in microplastic degradation in the atmosphere and coastal water environment from two island nations: Japan and New Zealand

Microplastics are subject to environmental forces that can change polymer organization on a molecular scale. However, it is not clear to what extent these changes occur in the environment and whether microplastics in the atmospheric and water environment differ. Here we identify structural differences between microplastics in the atmosphere and water environment from Japan and New Zealand, representing two archipelagos differing in their proximity to nearby countries and highly populated areas. We first highlight the propensity for smaller microplastics to arrive via air masses from the Asian continent to the Japan Sea coastal area, while New Zealand received larger, locally derived microplastics. Analyses of polyethylene in the Japanese atmosphere indicate that microplastics transported to the Japanese coastal areas were more crystalline than polyethylene particles in the water, suggesting that the plastics arriving by air were relatively more aged and brittle. By contrast, polypropylene particles in New Zealand waters were more degraded than the microplastic particles in the air. Due to the lack of abundance, both polyethylene and polypropylene could not be analyzed for both countries. Nevertheless, these findings show the structural variation in microplastics between environments in markedly different real-world locations, with implications for the toxic potential of these particles.

Fate and environmental behaviors of microplastics through the lens of free radical

Microplastics (MPs), as plastics with a size of less than 5 mm, are ubiquitously present in the environment and become an increasing environmental concern. The fate and environmental behavior of MPs are significantly influenced by the presence of free radicals. Free radicals can cause surface breakage, chemical release, change in crystallinity and hydrophilicity, and aggregation of MPs. On the other hand, the generation of free radicals with a high concentration and oxidation potential can effectively degrade MPs. There is a limited review article to bridge the fate and environmental behaviors of MP with free radicals and their reactions. This paper reviews the sources, types, detection methods, generation mechanisms, and influencing factors of free radicals affecting the environmental processes of MPs, the environmental effects of MPs controlled by free radicals, and the degradation strategies of MPs based on free radical-associated technologies. Moreover, this review elaborates on the limitations of the current research and provides ideas for future research on the interactions between MPs and free radicals to better explain their environmental impacts and control their risks. This article aims to keep the reader abreast of the latest development in the fate and environmental behaviors of MP with free radicals and their reactions and to bridge free radical chemistry with MP control methodology.

Distribution of bound-PAH residues and their correlations with the bacterial community at different depths of soil from an abandoned chemical plant site

The situ pollutant residue and microbial characteristics in contaminated environments are crucial for ecological restoration and soil utilization. This work reported the variation of polycyclic aromatic hydrocarbon (PAH) residues and the bacterial community at different depths in an aged-abandoned site. These results unveiled that over 90% of low molecular weight (LMW) and medium molecular weight (MMW), 52.84-76.88% of high molecular weight (HMW) bound-PAH (BP) residues were sequestrated in humin (HM). The stresses of PAH and soil depth enhanced the frequency of bacteria associations, especially positive associations. We enriched and cultured PAH degradation bacteria (PDB) from the sampling site mainly consisting of Pseudomonas and Acinetobacter, which were originally 0.39-0.52% abundant in the sampling site. The abundances of PDB and PAH-degradation genes (PDGs) were higher at shallower depths and increased with high PAH concentration. Simultaneously, Pearson correlation analysis and experimental verification found that the process of PAH binding with SOM limited the further increase of PDB and PDGs in PAH-contaminated sites. These findings may illustrate possible ecological risks of contaminated soils and provide guidance for the isolation and application of PDB.

Nanoplastics impacts on Thiobacillus denitrificans: Effects of size and dissolved organic matter

The widespread distribution of nanoplastics and dissolved organic matter (DOM) in sewage raises concerns about the potential impact of DOM on the bioavailability of nanoplastics. In this study, the effects of different sizes (100 nm and 350 nm) of polystyrene nanoplastics (PS-NPs, 50 mg/L) and combined with 10 mg/L or 50 mg/L DOMs (fulvic acid, humic acid and sodium alginate) on the growth and denitrification ability of Thiobacillus denitrificans were investigated. Results showed that 100 nm PS-NPs (50 mg/L) cause a longer delay in the nitrate reduction (3 days) of T. denitrificans than 350 nm PS-NPs (2 days). Furthermore, the presence of DOM exacerbated the adverse effect of 100 nm PS-NPs on denitrification, resulting in a delay of 1-4 days to complete denitrification. Fulvic acid (50 mg/L) and humic acid (50 mg/L) had the most significant adverse effect on increasing 100 nm PS-NPs (50 mg/L), causing a reduction of 20 mmol/L nitrate by T. denitrificans in nearly 7 days. It is noteworthy that the presence of DOM did not modify the adverse effect of 350 nm PS-NPs on denitrification. Further analysis of toxicity mechanism of PS-NPs revealed that they could induce reactive oxygen species (ROS) and suppressed denitrification gene expression. The results suggested that DOM may assist in the cellular internalization of PS-NPs by inhibiting PS-NPs aggregation, leading to the increased ROS levels and accelerated T. denitrificans death. This study highlights the potential risk of nanoplastics to autotrophic denitrifying bacteria in the presence of DOM and provides new insights for the treatment of nitrogen-containing wastewater by T. denitrificans.

Mechanism insight into the facet-dependent photoaging of polystyrene microplastics on hematite in freshwater

Hematite, as an extensive natural mineral with multiple crystal facets, profoundly affects the migration and transformation of pollutants in the natural environment. However, little is known about the photochemical behavior of microplastics on different facets of hematite in the aquatic environment. In this work, the photoaging of polystyrene microplastics (PS-MPs) on different crystal planes ({001}, {100}, and {012} facets) and related mechanisms were studied. Two-dimensional correlation spectroscopy analysis illustrated that the reaction pathways of PS-MPs photoaging on hematite tended to preferential chemical oxidization. The stronger performance of PS-MPs photoaging, expressed by particle size reduction and surface oxidation, was observed on the {012} crystal facet. Under irradiation, {012} facet-dominated hematite with a narrower bandgap (1.93 eV) reinforced the photogenerated charge carrier separation, and the lower activation energy barrier (1.41 eV calculated from density functional theory) led to effective •OH formation from water oxidation. These findings elucidate the underlying photoaging mechanism of MPs on hematite with different mineralogical phases.

Exposure Order to Photoaging and Humic Acids Significantly Modifies the Aggregation and Transformation of Nanoplastics in Aqueous Solutions

The colloidal stability of nanoplastics in aqueous solutions is greatly regulated by photoaging and dissolved organic matter (DOM). However, how the exposure order to sunlight and DOM modifies the environmental behavior of nanoplastics is seldomly determined. Here, with two different exposure orders, we investigated the impact of molecular-weight (MW)-fractionated humic acids (HAs) derived from biochar and the Suwannee River, respectively, on the aggregation of poly(ethylene terephthalate) nanoplastics (PET-NPs) in mono- and divalent electrolyte solutions. For exposure pattern (i) (photoaging followed by HA coating), photoaged PET-NPs had more oxidized surfaces and exhibited 22-320% higher binding affinity to HAs (especially the higher MW fractions) than the pristine counterparts, which greatly improved the dispersion of PET-NPs. For exposure pattern (ii) (HA coating followed by photoaging), HA-PET assemblies were formed, the dispersion of which increased with increasing irradiation time and was significantly higher than that of the samples in the exposure pattern (i) at the end of the experiment. This high dispersion of photoaged HA-PET assemblies was ascribed to the extra oxidation of PET by reactive oxygen species generated in the PET-HA interfaces during photoaging. These findings highlight the "active nature" of HA-PET assemblies, which provide new insight into the reaction of HA with nanoplastics beyond adsorption in the natural environment.

Aging of Nanoplastics Significantly Affects Protein Corona Composition Thus Enhancing Macrophage Uptake

Nanoplastics (NPs), as emerging contaminants, have attracted increasing attention for their effects on human exposure and potential health risks. The protein corona formed on the surface of NPs affects the biological activity and fate of the NPs in vivo. However, how environmental aging, an inevitable process once NPs enter the environment, affects the formation of protein corona on NPs is still unclear. This study investigated the changes in the compositions of protein corona formed on photo-aged polystyrene (PS) NPs in human bronchoalveolar lavage fluid (BALF), corresponding to the inhalation exposure pathway. The results demonstrated that both the species and abundance of proteins in the BALF protein corona on the surface of PS NPs were altered by aging. In addition, the aged PS NPs are more hydrophilic and less electronegative than the pristine PS NPs; hence, there is an increased sorption of more negatively charged hydrophilic proteins. Moreover, aging-induced alterations in BALF protein corona enhanced the uptake of aged PS NPs by lung macrophages J774A.1 through phagocytosis and clathrin-mediated endocytosis. These findings highlight the importance of environmental aging processes in the biosafety assessment of nanoplastics.

The multiple roles of phenols in the degradation of aniline contaminants by sulfate radicals: A combined study of DFT calculations and experiments

Recent research revealed inhibition or enhancement of dissolved organic matter (DOM) to the degradation of trace organic contaminants (TrOC) in natural and engineered water systems. Phenols containing acetyl, carboxyl, formyl, hydroxy, and methoxy groups were selected as the model DOM to quantitatively study their roles in the degradation of simple anilines, sulfonamide antibiotics, phenylurea pesticides by sulfate radicals (SO₄^•-). Experimental results found that p-methoxyphenol inhibited aniline and sulfamethoxazole degradation by thermally activated peroxydisulfate (TAP), while p-acetylphenol slightly promoted aniline degradation. Quantum chemical calculations were applied to study the microscopic mechanism and kinetics of phenols affecting the degradation of aniline pollutants (AN) in three ways: competitively reacting with SO₄^•-, repairing aniline cationic radicals (AN^•+) and phenylaminyl radicals (AN(-H)^•), and generating phenoxy radicals to degrade anilines. Generally, the degradation of sulfonamides and phenylureas prefer to be inhibited by hydroxy- and methoxy-phenols with low oxidation potential (E_ox), due to their diffusion-limiting reaction with SO₄^•- and rapid back-reduction AN^•+ with the calculated rate constants of (0.02 - 6.38) × 10⁹ M^-1 s^-1. Phenols repairing AN(-H)^• through H abstraction reaction is speculated to possibly dominate the joint degradation of phenols and anilines by TAP, which has a poor correlation with E_ox. This study provides mechanistic insight into the chemical behavior of complex and heterogeneous DOM in complex aqueous environments.

Exploring specific biomarkers regarding neurobehavioral toxicity of lead dioxide nanoparticles in medaka fish in different water matrices

Nano-scale lead dioxide (nPbO₂) is an industrial metal oxide nanoparticle that can be also formed as a corrosion by-product from chlorination of Pb-containing plumbing materials. nPbO₂ governs release of toxic lead ion in drinking water and receiving organisms; however, its modes of toxic action regarding neurobehavioral toxicity remain unclear. This study evaluated the toxicity mechanism of nPbO₂ (10 and 20 mg/L) versus its released Pb(II)_aq (100 μg/L) in terms of aqueous chemistry, bioavailability and neurobehavioral toxicity to medaka fish in different water matrices. In very hard water (VHW), dissolved salts enhanced the aggregation and sedimentation of nPbO₂, resulting in higher bioavailability and altered locomotion of treated fish than those fish exposed to nPbO₂ in soft water with humic acid (SW + HA). Transcriptomic results identified six differentially expressed genes with greater altered expression with nPbO₂ than the control or Pb(II)_aq exposure. With VHW exposure, nPbO₂ caused greater altered expression of genes involved in cell adhesion (nlgn1 and epd), cell cytoskeleton (α1-tubulin), and relevant apoptosis (c-fos, birc5.1-a and casp3), as compared with SW + HA or Pb(II)_aq exposure. This study provides novel molecular mechanistic insights into the neurobehavioral nanotoxicity using nPbO₂ and medaka fish as surrogates, suggesting nPbO₂ promotes neurobehavioral dysfunction, leading to adverse outcomes from gene alteration to the organismal level. The identified biomarkers responded specifically to the nPbO₂-induced neurotoxicity in different water matrices can be used for evaluating toxicity risks of small metal oxide particulates on human or aquatic life under environmentally relevant exposures.

An inevitable but underestimated photoaging behavior of plastic waste in the aquatic environment: Critical role of nitrate

Photoaging is an important reaction for waste plastics in the aquatic environment and plays a key role in the lifetime of plastics. Nevertheless, when natural photosensitive substances such as nitrate participate in this process, the physiochemical changes in plastics and the corresponding reaction mechanisms are not well-understood. In this work, the photochemical behavior of polyethylene terephthalate (PET) bottles in deionized water and nitrate solution was systematically investigated under ultraviolet (UV) irradiation. The analyses of the surface physicochemical properties of the photoaged PET bottles indicated that, after 20 days of photo-irradiation, the presence of nitrate reduced the contact angle from 69.8 ± 0.9° to 60.0 ± 0.3°, and increased the O/C ratio from 0.23 to 0.32, respectively. The leaching rate of dissolved organic carbon (DOC), which was 0.0193 mg g^-1·day^-1 in nitrate solution, was twice that of 0.00941 mg g^-1·day^-1 in deionized water. Furthermore, fluorescence spectroscopy revealed that the increasing DOC had aromatic rings with hydroxyl on the side-chain formed after UV irradiation. The positive effect of nitrate on the degradation of PET bottles was mainly through the generation of hydroxyl radicals that were produced through the photolysis of nitrate. In addition, two-dimensional correlation spectroscopy analysis showed that the chain scission of PET plastics could be initiated by nitrate-induced ·OH attacking the carbon-oxygen bonds instead of forming peroxides with oxygen. This work elucidates the mechanism of photodegradation of plastics that was induced by nitrate and highlights the important role of natural photosensitive substances in the photoaging process of plastics.

Nanoplastics: Detection and impacts in aquatic environments - A review

The rise in the global production of plastics has led to severe concerns about the impacts of plastics in aquatic environments. Although plastic materials degrade over extreme long periods, they can be broken down through physical, chemical, and/or biological processes to form microplastics (MPs), defined here as particles between 1 μm and 5 mm in size, and later to form nanoplastics (NPls), defined as particles <1 μm in size. We know little about the abundance and effects of NPls, even though a lot of research has been conducted on the ecotoxicological impacts of MPs on both aquatic biota. Nevertheless, there is evidence that NPls can both bypass the cell membranes of microorganisms and bioaccumulate in the tissues and organs of higher organisms. This review analyzes 150 publications collected by searching through the databases Web of Science, SCOPUS, and Google Scholar using keywords such as nanoplastics*, aquatic*, detection*, toxic*, biofilm*, formation*, and extracellular polymeric substance* as singular or plural combinations. We highlight and critically synthesize current studies on the formation and degradation of NPls, NPls' interactions with aquatic biota and biofilm communities, and methods of detection. One reason for the missing data and studies in this area of research is the lack of a protocol for the detection of, and suitable methods for the characterization of, NPls in the field. Our primary aim is to identify gaps in knowledge throughout the review and define future directions of research to address the impacts of NPls in aquatic environments. The development of consistent and standardized sets of procedures would address the gaps in knowledge regarding the formation and degradation of NPls as well as sampling and characterizing natural NPls needed to observe the full extent of NPls on aquatic biota and biofilm communities.

The photochemical behaviors of microplastics through the lens of reactive oxygen species: Photolysis mechanisms and enhancing photo-transformation of pollutants

The photoaging mechanisms of various polymers have been explored based on the basic autoxidation scheme (BAS) before 10 years ago, however current research verified some defects in the BAS in both thermodynamic and dynamics. These defects are troublesome because they are associated with the hydrogen abstraction which is central to continuously perform the photooxidation process of microplastics. These found indicated that we might wrongly inferred photo-oxidation process of some microplastics. In addition, the important role of reactive oxygen species (ROS) in the type-dependent photoaging process of various microplastics has been revealed recently. In this case, fully and accurately understanding the photoaging mechanisms of different microplastics in environment is a priority to further manage the ecological risk of microplastics. Herein, this review aims to revise and update the degradation process of microplastics based on the revised BAS and in the perspective of ROS. Specifically, the modification of BAS is firstly discussed. The photoaging mechanisms of representative microplastics (i.e., polyethylene, polystyrene and polyethylene terephthalate) are then updated based on the corrected BAS. Additionally, the role of ROS in their photolysis process and the possibility of microplastics as photosensitizers/mediators to regulate the fate of co-existent pollutants are also analyzed. Finally, several perspectives are then proposed to guide future research on the photoaging behaviors of microplastics. This review would pave the way for the understanding of microplastic photoaging and the management of plastic pollution in environments.

Wastewater preinteraction accelerates the photoaging of disposable box-derived polystyrene microplastics in water

Before being discharged into natural environment, almost all of microplastics (MPs) interact with wastewater constituents in wastewater treatment plants (WWTPs). This study investigated the photoaging of disposable box-derived polystyrene (PS) mediated by real wastewater by simulating the case flowing from WWTPs to natural water. Results showed that wastewater influent pretreatment significantly enhanced the photoaging of PSMPs through the sorption of wastewater constituents, e.g., 2.02 times of increase in photooxidation after 30 d of ultraviolet irradiation. Fulvic acid was identified as the leading contributor for the enhancing effect of wastewater relative to other wastewater constituents such as Cl, CO₃^2-, NO₃^- and clay particles. In-depth mechanism analysis showed that the observed enhancement was critically controlled by the photosensitization effect of wastewater itself and the enhanced utilization of PSMPs for ultraviolet energy. Specifically, various sorbed wastewater constituents can not only generate higher concentrations of •OH and O₂^⋅- than clean MPs without constituents, but also reinforce the utilization of PSMPs for light energy due to the increased dispersion in solution by increasing hydrophilicity and surface charges. Also, the light-shielding effect was induced by wastewater, but was less important. This study bridges wastewater source and MP aging and fate and suggests the shortened lifetime of (micro)plastic samples via WWTP input to deepen our understanding of MP pollution in the environment.

Combined effects of photoaging and natural organic matter on the colloidal stability of nanoplastics in aquatic environments

The transport and fate of nanoplastics (NPs) in aquatic environments are closely associated with their colloidal stability, which is affected by aging and natural organic matter (NOM) adsorption. This study systematically investigated the combined effects of photoaging and NOM (e.g. humic acids, HA; and a model protein, bovine serum albumin, BSA) on the aggregation kinetics of NPs (polystyrene, PS) in NaCl and CaCl₂ solutions. Our results showed that photoaged NPs adsorbed less HA than pristine NPs due to weaker hydrophobic and π-π interactions. In return, HA showed weaker impacts on NPs' stability after photoaging. Differently, photoaged NPs absorbed more BSA than pristine NPs due to stronger hydrogen bonding and electrostatic attraction. Thus, the inhibitory effects of BSA on the aggregation kinetics of NPs were enhanced after photoaging. Regarding the effects of NOM on the aging of NPs, our results showed that HA competed with NPs for photons and underwent photo-degradation. Subsequently, the destruction/reconstruction of adsorbed HA increased (in NaCl) or decreased (in CaCl₂) the stability of NPs. Notably, light radiation-induced flocculation of BSA molecules, which wrapped and integrated NPs and lead to their destabilization. Overall, this study provided new insights into the aggregation behavior of NPs in aquatic systems, which have significant implications for predicting the transport and fate of NPs in complex real-world environments.

Removal of microplastics and nanoplastics from urban waters: Separation and degradation

The omnipresent micro/nanoplastics (MPs/NPs) in urban waters arouse great public concern. To build a MP/NP-free urban water system, enormous efforts have been made to meet this goal via separating and degrading MPs/NPs in urban waters. Herein, we comprehensively review the recent developments in the separation and degradation of MPs/NPs in urban waters. Efficient MP/NP separation techniques, such as adsorption, coagulation/flocculation, flotation, filtration, and magnetic separation are first summarized. The influence of functional materials/reagents, properties of MPs/NPs, and aquatic chemistry on the separation efficiency is analyzed. Then, MP/NP degradation methods, including electrochemical degradation, advanced oxidation processes (AOPs), photodegradation, photocatalytic degradation, and biological degradation are detailed. Also, the effects of critical functional materials/organisms and operational parameters on degradation performance are discussed. At last, the current challenges and prospects in the separation, degradation, and further upcycling of MPs/NPs in urban waters are outlined. This review will potentially guide the development of next-generation technologies for MP/NP pollution control in urban waters.