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The environmental fate and toxic effects of antibiotics such as tetracycline (TC) could be influenced by the ubiquitous dissolved organic matter (DOM). However, DOM from different origins has different hydrophilic and hydrophobic properties. It is still unknown the effects of hydrophilic and hydrophobic DOM on the toxic effect of TC. In this study, DOM with hydrophilicity and hydrophobicity was separated and used to investigate their roles in affecting TC toxicity to the photosynthesis of green algae Chlorella vulgaris. Results showed that 10 mg L -1 TC inhibited the efficiency of photosystem II (PSII) of C. vulgaris using light by hindering electron transfer from Q A - to Q B /Q B - , and the O 2 release rate of C. vulgaris decreased by a third after 12-h treatment of 10 mg L -1 TC, while both hydrophilic and hydrophobic DOM (20 mg L -1 TOC) alleviated TC toxicity to the photosynthesis of C. vulgaris. In the presence of hydrophilic or hydrophobic DOM, stable complex of TC-hydrophilic DOM or TC-hydrophobic DOM was formed immediately, due to the good affinity of both DOM for TC. Fourier transform infrared spectroscopy result showed that both hydrophilic and hydrophobic DOM could reduce C=O in TC to C-O, and isothermal titration calorimetry result suggested that reactions of both DOM with TC were exothermic (△H < 0) and spontaneous (△G < 0). Thereinto, the reaction constant (K a ) of TC reacting with hydrophobic DOM (K a =9.70) was higher than that with hydrophilic DOM (K a =8.93), indicating hydrophobic DOM with more chemical binding sites and accessible fractions for TC. The present study suggests that DOM, especially the hydrophobic DOM, is an important consideration in the environmental impact assessment of antibiotics., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Photodemethylation is the major pathway of methylmercury (MeHg) demethylation in surface water before uptake by the food chain, whose mechanisms and influence factors are still not completely understood. Here, we review the current knowledge on photodemethylation of MeHg and divide MeHg photolysis into three pathways: (1) direct photodemethylation, (2) free radical attack, and (3) intramolecular electron or energy transfer. In aquatic environments, dissolved organic matter is involved into all above pathways, and due to its complex compositions, properties and concentrations, DOM poses multiple functions during the PD of MeHg. DOM-MeHg complex (mainly by sulfur-containing molecules) might weaken the C–Hg bond and enhance PD through both direct and indirect pathways. In special, synergistic effects of both strong binding sites and chromophoric moieties in DOM might lead to intramolecular electron or energy transfer. Moreover, DOM might play a role of radical scavenger; while triplet state DOM, which is generated by chromophoric DOM under light, might become a source of free radicals. Apart from DOMs, transition metals, halides, NO 3 −, NO 2 −, and carbonates also act as radical initialaters or scavengers, and significantly pose effects on radical demethylation, which is generally mediated by hydroxyl radicals and singlet oxygen. Environmental factors such as pH, light wavelength, light intensity, dissolved oxygen, salinity, and suspended particles also affect the PD of MeHg. This study assessed previously published works on three major mechanisms, with the goal of providing general estimates for photodemethylation under various environment factors according to know effects, and highlighting the current uncertainties for future research directions. [Display omitted] • Photodemethylation of MeHg in aquatic environments proceeds via three pathways. • The ligands of MeHg species are critical for photodemethylation. • Dissolved organic matter is the key factor for the photochemical behaviors of MeHg. • Ions, pH, wavelength, oxygen and suspended solids affect the photodemethylation. • Advanced analysis methods on organic matters are highly urged for future research. [ABSTRACT FROM AUTHOR]

Abstract Molecular weight (MW) heterogeneity is a fundamental property of dissolved organic matter (DOM) in soil, which has been demonstrated to influence the binding behaviour between DOM and engineered nanoparticles. In the present study, DOM, extracted from black soil, was dialyzed into four fractions: above 10,000 Da, 3500–10,000 Da, 1000–3500 Da and 100–1000 Da. Homoaggregation and fluorescence quenching titration of selenium nanoparticles (SeNPs) was examined in the presence of the different DOM fractions, as well as the consequences for immobilization of elemental mercury. It was found that the intermediate MW fraction (3500–10,000 Da) rather than the high MW DOM fraction was likely to adsorb to SeNPs. Generally, low MW DOM was expected to adsorb initially due to faster diffusion and these compounds would be displaced by high MW DOM over longer time period. However, the electrostatic barrier imparted by adsorbed DOM limited such displacement, leading to preferential adsorption of the intermediate MW fraction over the high MW fraction. Adsorbed DOM fractions, especially that of intermediate MW, enhanced the stability of SeNPs which favoured immobilization of elemental mercury. These findings show that MW exerts an important impact on DOM binding with SeNPs which, in consequence, governs the fate of SeNPs and mercury bioremediation performance. Graphical abstract Unlabelled Image Highlights • Dissolved organic matter (DOM) affects Hg removal by selenium nanoparticles (SeNPs). • Intermediate molecular weight DOM preferentially adsorbed to SeNPs. • Intermediate molecular weight DOM limited its displacement by other DOM fractions. • Intermediate molecular weight DOM enhanced the stability of SeNPs and Hg removal. [ABSTRACT FROM AUTHOR]

Mercury pollution has become one of the serious ecological and health problems in developing countries. In aquatic environments, widespread dissolved organic matter ( DOM) affects the physical transfer, chemical transformation and bioavailability of heavy metal ions. In the arid inland lakes, water salinity has been increasing due to close hydrological system and much higher vaporization than precipitation, and thus there are usually salinity gradients in these inland lakes. The change of salinity may exert influences on complexation of DOM with heavy metals. However, response of the metal complexation of DOM to the salinity is still unclear. In this study, three-dimensional molecule fluorescence spectroscopy (3D-EEM) was used to examine the interaction of Hg(II) and DOM in sediment along a salinity gradient of the Bosten Lake, the biggest inland freshwater lake in China. Three fluorescence peaks were identified in the EEM fluorescence spectra of all DOM samples. All the three fluorescence peaks could be quenched by Hg(II), indicating the formation of stable nonluminous DOM-Hg complexes. The conditional stability constant and binding constant for DOM-Hg(II) were 3.82-4.34 and 3.76-5.54, respectively. Conditional stable constants and binding constants for the system of Hg(II) and protein-like substances were higher than those for the humic substances-Hg(II) system. The ligand ratio of fluorophore to Hg(II) correlated well with the salinity. The strong complexation of Hg(II) and DOM and its responses to salinity change may significantly influence transport, transformation and ecological risk of Hg in Bosten Lake. [ABSTRACT FROM AUTHOR]

Abstract: The three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy was employed to investigate the interaction of extracellular polymeric substances (EPS) from natural biofilm with Hg(II). The EEM spectra demonstrated that EPS with molecular weight over 14kDa had two protein-like fluorescence peaks. The fluorescence intensity at both peaks was strongly dependent on the solution pH in the absence and presence of Hg(II), with the maximal fluorescence intensity at neutral pH. Fluorescence of both protein-like peaks was significantly quenched by Hg(II). The values of conditional stability constants (log K a =3.28–4.48) derived from modified Stern–Volmer equation are approximate to those for humic substances and dissolved organic matter (DOM), indicating that fluorescent components in EPS have strong binding capacity for Hg(II). Our findings suggest that EPS from biofilm is a class of important organic ligands for complexation with Hg(II) and may significantly affect the chemical forms, mobility, bioavailability and ecotoxicity of heavy metals in the aquatic environment. [Copyright &y& Elsevier]

Abstract Particulate organic matter (POM), composed of fine root fragments and other organic debris, is an important fraction of soil organic matter which can affect the fate of nanoparticles and influence their performance in nanoparticle-based remediation technologies due to aggregation. Effects of POM are not well studied compared with those of dissolved organic matter. In this research, POM was extracted from black soil by sieving, and heteroaggregation of selenium nanoparticles (SeNPs) with POM and consequences for elemental mercury (Hg0) immobilization were investigated. It was found that low concentrations of more negatively charged POM (0–60 mg L−1) inhibited homoaggregation as well as heteroaggregation with SeNPs which had a lower negative charge through electrostatic repulsion. In the presence of high concentrations of POM (80–100 mg L−1), SeNPs were more likely to attach to POM with more Hg0 remaining in the POM since a larger concentration of nanoparticles would lead to more effective collisions. However, Hg0 immobilization efficiency using SeNPs was not significantly influenced by the addition of POM. This work is helpful to further understand the nanoparticle's behaviour in the environment and consequences for toxic metal remediation. Graphical abstract Image 102269 Highlights • POM can affect the fate of SeNPs in the environment. • POM (0–60 mg L−1) inhibited its homoaggregation and heteroaggregation with SeNPs. • Hg0 immobilization efficiency by SeNPs was not inhibited in the presence of POM. [ABSTRACT FROM AUTHOR]

In natural environments, inorganic mercury (Hg2+) can be converted to the neurotoxin methylmercury (MeHg) mainly via the microbial Hg methylation process with anaerobic microorganisms. This process is a cellular reaction, and is influenced by cellular activity of Hg methylating microorganisms and by cellular Hg2+ uptake. In the present article, we review research progress of Hg bio-methylation, which includes: sites for Hg bio-methylation, Hg methylating microorganisms, mechanisms of Hg bio-methylation, and factors affecting Hg bio-methylation. Microbial Hg methylation occurs in a variety of sites such as the freshwater and marine environments as well as some unrecognized habitats. Sulfate-reducing bacteria using sulfate as their terminal electron acceptors are a group of the most extensively studied Hg methylators, followed by iron-reducing bacteria. The cellular uptake of Hg2+ before methylation may proceed via passive and/or active transport. Most Hg methylators have a pivotal gene pair encoding proteins required for methylation process. The cellular activity and bioavailable Hg2+ concentration for methylation can be determined primarily by many environmental factors i.e., temperature, redox potentials, pH value, existence of dissolved organic matter (DOM) and sulfur-containing organic compounds. A comprehensive understanding of methylation habitat, methylator, mechanism, and influencing factor is urgently required and will provide guidance for regulating net MeHg production within natural environments. [Display omitted] [ABSTRACT FROM AUTHOR]

• Bacteria removal by functionalized microbubbles is an interface-dependent process. • Adhesion-related VFs may facilitate cell capture by functionalized microbubbles. • Motility-related VFs weaken bubble performance unless motility structure is damaged. • Membrane structure related to antibiotic resistance impacts microbubble performance. • Organic matter in municipal wastewater enhances cell capture but consumes O 3 -CCMBs. The frequent occurrence of epidemics around the world gives rise to increasing concerns of the pollution of pathogens and antibiotic resistant bacteria in water. This study investigated the impacts of virulence factors (VFs) on the removal of antibiotic resistant and pathogenic bacteria from municipal wastewater by ozone-free or ozone-encapsulated Fe(III)-coagulant-modified colloidal microbubbles (O 3 _free-CCMBs or O 3 -CCMBs). The highly interface-dependent process was initiated with cell-capture on the microbubble surface where the as-collected cells could be further inactivated with the bubble-released ozone and oxidative species if O 3 -CCMBs were used. The microbiome sequencing analyses denote that the O 3 _free-CCMB performance of antibiotic resistant and pathogenic bacteria removal was dependent on the virulence phenotypes related to cell-surface properties or structures. The adhesion-related VFs facilitated the effective attachment between cells and the coagulant-modified bubble-surface, which further enhanced cell inactivation by bubble-released ozone. On the contrary, the motility-related VFs might help cells to escape from the bubble capture by locomotion; however, this could be overcome by O 3 -CCMB-induced oxidative demolition of the movement structures. Besides, the microbubble performance was also impacted with the cell-membrane structure related to antibiotic resistance (i.e., efflux pumps) and the dissolved organic matter through promoting the surface-capture and decreasing the oxidation efficacy. The ozone-encapsulated microbubbles with surface functionalization are robust and promising tools in hampering antibiotic resistance and pathogenicity dissemination from wastewater to surface water environment; and awareness should be raised for the influence of virulence signatures on its performance. [Display omitted] [ABSTRACT FROM AUTHOR]

• Polypropylene microplastics (PP-MPs) mainly interacted with aromatic structure of humic acid (HA). • Surface roughness of PP-MPs before and after the interaction changed significantly. • HA addition increased oxygen-containing functional groups on the surface of PP-MPs. • PP-MPs after aging interacted more strongly with HA and there was a higher affinity. As an emerging pollutant, microplastics (MPs) may interact with dissolved organic matter (DOM) which is prevalent in the aqueous environment. Meanwhile, the aging of MPs in the actual environment increases the uncertainty of their environmental fate. Here, the interaction mechanisms between pristine and aged polypropylene microplastics (PP-MPs) and humic acid (HA) at pH 7.0 were explored. Microstructural changes of HA were examined by fluorescence and Fourier transformation infrared (FT-IR) spectroscopy. Atomic force microscopy coupled with infrared (AFM-IR) and micro-Raman techniques were used to characterize and analyze the interacted PP-MPs. The addition of HA increased the surface roughness of both pristine and aged PP-MPs. Results of AFM-IR and Raman spectra showed that the interaction of PP-MPs with HA accelerated their surface oxidation and enhanced the characteristic signals. XPS spectra showed that the oxygen content ratio of pristine and aged PP-MPs increased by 0.95% and 1.48% after the addition of HA, respectively. PP-MPs after aging interacted more strongly with HA and there was a higher affinity between them. Two-dimensional correlation spectroscopy (2D-COS) combined with FT-IR spectra further elucidated the interaction mechanism at the molecular level. This work will help to evaluate the environmental impact of MPs in ecosystems and understand their interactions with DOM. [Display omitted] [ABSTRACT FROM AUTHOR]

The spread of antibiotic resistance in the aquatic environment severely threatens the public health and ecological security. This study investigated simultaneously capturing and inactivating/oxidizing the antibiotic resistant bacteria (ARB) and cell-free antibiotic resistance genes (ARGs) in waters by flexibly-functionalized microbubbles. The microbubbles were obtained by surface-modifying the bubbles with coagulant (named as coagulative colloidal gas aphrons, CCGAs) and further encapsulating ozone in the gas core (named as coagulative colloidal ozone aphrons, CCOAs). CCGAs removed 92.4–97.5% of the sulfamethoxazole-resistant bacteria in the presence of dissolved organic matter (DOM), and the log reduction of cell-free ARGs (particularly, those encoded in plasmid) reached 1.86–3.30. The ozone release from CCOAs led to efficient in-situ oxidation: 91.2% of ARB were membrane-damaged and inactivated. In the municipal wastewater matrix, the removal of ARB increased whilst that of cell-free ARGs decreased by CCGAs with the DOM content increasing. The ozone encapsulation into CCGAs reinforced the bubble performance. The predominant capture mechanism should be electrostatic attraction between bubbles and ARB (or cell-free ARGs), and DOM enhanced the sweeping and bridging effect. The functionalized microbubble technology can be a promising and effective barrier for ARB and cell-free ARGs with shortened retention time, lessened chemical doses and simplified treatment unit. [Display omitted] • Coagulative colloidal gas aphrons (CCGAs) remove 97.5% of ARB and 3.30 log of ARGs. • Cell-free ARG removal by CCGAs follow "plasmid >short linear DNA >long linear DNA". • Coagulative colloidal ozone aphrons (CCOAs) inactivate 91.2% of ARB within 3 min. • CCGAs or CCOAs tend to capture DOM, DOM-associated ARB and cell-free ARGs in MWW. • CTAB (cationic) induces more robust CCGAs/CCOAs than BS-12 (zwitterionic). [ABSTRACT FROM AUTHOR]

• O 3 micro-bombs were surface- and core-modified by coagulant and O 3 , respectively. • Removing cells and in situ degrading microcystin-LR were achieved simultaneously. • Coated coagulant helped to effectively capture cells and dissolved organic matter. • Micro-bombs exploded, released oxidant and facilitated microcystin-LR degradation. • Re-growth of cells was inhibited after the ozone micro-bomb treatment. Aiming at effectively controlling the worldwide proliferation of cyanobacterial blooms, this study proposed a novel microbubble system – ozone micro-bombs for simultaneously fast removing cyanobacterial cells and in situ oxidatively degrading cyanotoxins. For producing the surface- and core-functionalized microbubbles – ozone micro-bombs, the zwitterionic surfactant-based bubble generation solution was modified with inorganic polymeric coagulant, and meanwhile, the bubble generation method was improved by injecting ozone during bubble creation. Featured as high gas holdup (>38%) and large specific surface area (<90 µm in diameter), the ozone micro-bombs efficiently eliminated Microcystis aeruginosa cells (>93.2%) within 3–5 min; and simultaneously, approximately 88.9–98.4% and 66.1–79.1% of intracellular and extracellular microcystin-LR (MC-LR) were removed, respectively. The efficient performance of cell separation by ozone micro-bombs ensured the high total MC-LR removal in spite of the cell lysis and the intracellular MC-LR release. During the treatment process, the surface-coated coagulant reinforced the capacity of microbubbles in capturing cells and dissolved organic matter; the ozone encapsulation in microbubbles enhanced the ozone transfer in water; the explosion of those micro-bombs released the oxidant of ozone and facilitated the degradation of MC-LR. Moreover, the cell re-growth was inhibited and the dissolved organic carbon got apparently decreased after treatment. With high feasibility and sound performance, the ozone micro-bomb technology is of great potential in in situ and thoroughly treating cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

Microplastic (MP) contamination in water has garnered significantly global concerns. The MP removal particularly challenges when the particle size decreases to several microns and other contaminants co-exist. This study used the coagulative colloidal gas aphrons (CCGAs) to simultaneously remove the micron-scale MP particles (~5 µm in diameter) and dissolved organic matter (DOM). Carboxyl-modified poly-(methyl methacrylate) (PMMA) and unsurface-coated polystyrene (PS) were chosen as target MPs. Over 94% of PS particles and almost 100% of color were simultaneously removed with lower CCGA consumption than the scenarios with either contaminant in water. The PMMA removal was not as high as the PS removal since the HA polyanions could compete with the negatively-charged PMMA for CCGAs. High salinity reduced the removal of HA by changing its interfacial behaviors without impacting the MP separation. In river water or influent of wastewater treatment plant, the MP particles were almost completely eliminated whereas the DOM (tyrosine-like or tryptophan-like) was partially removed. The fluorescence quenching titration revealed that CCGAs preferably captured the free DOM and the DOM-coated MP particles through complexation interaction. The study denoted that the CCGA system could be a robust tool for efficiently and synergistically removing micron-scale MPs and DOM from different water matrixes. ga1 • Coagulant-coated bubbles simultaneously remove 5 μm-microplastics & organic matter. • Salinity may reduce humic acid removal but impact little on microplastic separation. • Inreal waters, microplastics are eliminated but organic matter removal is weakened. • Interaction between microplastics & organic matter impacts the synergistic removal. • Coagulant-modified microbubbles tend to capture organic matter before microplastics. [ABSTRACT FROM AUTHOR]

• For COAs, stability increased and air holdup dropped with salinity increasing. • Salinity impeded CGA adsorption on hydrophobic surface and PHE desorption by CGAs. • At low PHE concentrations, COA-treatment was susceptible to salinity variation. • The prevention of PHE desorption by salinity was enhanced in the presence of DNOM. • Successive COA addition improved PHE removal by river water-induced COAs. Polycyclic aromatic hydrocarbons (PAHs) tend to adsorb and accumulate on sediments owing to their hydrophobicity and persistence. Salinity is the predominant factor determining the PAH partition between aqueous and solid phases in freshwater, estuaries and seawater. This study focuses on the impact of salinity on the phenanthrene (PHE) removal from sediments using an in situ and targeted remediation technology – colloidal ozone aphrons (COAs). The ozone-encapsulated colloidal aphrons exhibited increasing air holdup but decreasing stability with the salinity increasing from 0.5‰ to 35‰. The hydrophobic attraction between Tween-20-coated bubbles and the hydrophobic solid surface weakened at high salinities. The presence of inorganic ions in the aqueous phase could lead to the salting-out of nonionic compounds (PHE, Tween-20 and even ozone), hindering detaching and degrading PHE from the solid phase. Anyhow, COAs achieved high efficiencies of washing (88.0–90.2%) and oxidative degradation (74.0–76.5%) particularly for the hydrophobic sediments with highly concentrated PHE (200.4 μg/kg) over the investigated salinities. The flushing effect imposed by the bubble flow played an important role, which was not greatly influenced by salinity. Although the dissolved natural organic matter competed with PHE for COAs and led to low PHE removal, the efficiency was improved by successive COA addition. [ABSTRACT FROM AUTHOR]