Insights into the pH-dependent mechanism of peracetic acid activation by biochar-supported zero-valent iron/cobalt bimetallic nanoparticles: The shift of reactive sites and the dual role of hydrogen peroxide.

The peracetic acid (PAA)-based water purification process is often controlled by the solution pH. Herein, we explored the usage of biochar (BC) supported zero-valent iron/cobalt nanoparticles (Fe/Co@BC) for triggering PAA oxidation of sulfamethazine (SMT), and discovered the PAA activation mechanisms at different pHs. Fe/Co@BC exhibited extraordinary PAA activation efficiency over the pH range of 3.0-8.2, effectively broadening the working pH of the zero-valent iron nanoparticles (NZVI)-PAA process. Specifically, the SMT removal efficiency increased by 8.3 times in Fe/Co@BC-PAA system compared to the NZVI-PAA system at pH 8.2. Besides, the leaching and recycling experiments indicated the improved stability and reusability of the materials. For the mechanism study, the main reactive species was •OH under acidic conditions and R-O•/Fe(IV) under neutral/alkaline conditions. More interestingly, the reactive sites on Fe/Co@BC shifted from Fe species to Co species as pH increased, and the role of H2O2 in this reaction system also shifted from a radical precursor to a radical scavenger with increasing pH. This study highlights the distinct mechanism of PAA activation by bimetallic composites under different pH conditions and provides a new efficient approach for PAA activation to degrade organic contaminants.

Enhanced Degradation of Micropollutants in a Peracetic Acid/Mn(II) System with EDDS: An Investigation of the Role of Mn Species.

Extensive research has been conducted on the utilization of a metal-based catalyst to activate peracetic acid (PAA) for the degradation of micropollutants (MPs) in water. Mn(II) is a commonly employed catalyst for homogeneous advanced oxidation processes (AOPs), but its catalytic performance with PAA is poor. This study showed that the environmentally friendly chelator ethylenediamine-N,N'-disuccinic acid (EDDS) could greatly facilitate the activation of Mn(II) in PAA for complete atrazine (ATZ) degradation. In this process, the EDDS enhanced the catalytic activity of manganese (Mn) and prevented disproportionation of transient Mn species, thus facilitating the decay of PAA and mineralization of ATZ. By employing electron spin resonance detection, quenching and probe tests, and 18O isotope-tracing experiments, the significance of high-valent Mn-oxo species (Mn(V)) in the Mn(II)-EDDS/PAA system was revealed. In particular, the involvement of the Mn(III) species was essential for the formation of Mn(V). Mn(III) species, along with singlet oxygen (1O2) and acetyl(per)oxyl radicals (CH3C(O)O•/CH3C(O)OO•), also contributed partially to ATZ degradation. Mass spectrometry and density functional theory methods were used to study the transformation pathway and mechanism of ATZ. The toxicity assessment of the oxidative products indicated that the toxicity of ATZ decreased after the degradation reaction. Moreover, the system exhibited excellent interference resistance toward various anions and humid acid (HA), and it could selectively degrade multiple MPs.

Metabolomics reveals how spinach plants reprogram metabolites to cope with intense stress responses induced by photoaged polystyrene nanoplastics (PSNPs).

While land-based sources have been recognized as significant long-term sinks for micro- and nanoplastics, there is limited knowledge about the uptake, translocation, and phytotoxicity of nanoplastics (NPs) in terrestrial environments, especially aged NPs. In this study, we investigated the impact of aged polystyrene nanoplastics (PSNPs) on the uptake, physiology, and metabolism of spinach. Our findings revealed that both pristine and aged PSNPs can accumulate in the roots and subsequently translocate to the aboveground tissues, thereby influencing numerous key growth indicators in spinach plants. A more pronounced impact was observed in the treatment of aged PSNPs, triggering more significant and extensive changes in metabolite levels. Furthermore, alterations in targeted pathways, specifically aminoacyl-tRNA biosynthesis and phenylpropanoid biosynthesis, were induced by aged PSNPs, while pristine PSNPs influenced pathways related to sulfur metabolism, biosynthesis of unsaturated fatty acids, and tryptophan metabolism. Additionally, tissue-specific responses were observed at the metabolomics level in both roots and leaves. These results highlight the existence of diverse and tissue-specific metabolic responses in spinach plants exposed to pristine and aged PSNPs, providing insights into the mechanisms of defense and detoxification against NP-induced stress.

Enhanced chalcopyrite-catalyzed heterogeneous Fenton oxidation of diclofenac by ABTS.

The widely used 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) has gained growing attention in advanced oxidation processes (AOPs), whereas there was limited knowledge regarding the feasibility of ABTS in enhancing heterogeneous Fenton oxidation so far. Hereof, ABTS was introduced into the chalcopyrite (CuFeS2)- catalyzed heterogeneous Fenton oxidation process to degrade diclofenac (DCF), and the degradation efficiency was enhanced by 25.5% compared with CuFeS2/H2O2 process. The available reactive oxygen species (ROS) and the enhanced mechanism were elaborated. Experimental results uncovered that •OH was the dominant reactive species responsible for the DCF degradation in the CuFeS2/H2O2/ABTS process, and ABTS•+ was derived from both •OH and Fe(IV). The presence of ABTS contributed significantly to the redox cycle of surface Fe of CuFeS2, and the roles of reductive sulfur species and surface Cu(I) in promoting surface Fe cycling also could not be neglected. In addition, the effects of several influencing factors were considered, and the potential practicability of this oxidation process was examined. The results demonstrate that the CuFeS2/H2O2/ABTS process would be a promising approach for water purification. This study will contribute to the development of enhancing strategies using ABTS as a redox mediator for heterogeneous Fenton oxidation of pharmaceuticals.

Low additive peracetic acid enhanced sulfamethazine degradation by permanganate: A mechanistic study.

In this study, a novel water treatment process combining permanganate (Mn(VII)) and peracetic acid (PAA, CH3C(O)OOH) was employed to degrade sulfamethazine (SMT), a typical model contaminant. Simultaneous application of Mn(VII) and a small amount of PAA resulted in much faster oxidation of organics than a single oxidant. Interestingly, coexistent acetic acid played a crucial role in SMT degradation, while background hydrogen peroxide (H2O2) had a negligible effect. However, compared with acetic acid, PAA could better improve the oxidation performance of Mn(VII) and accelerate the removal of SMT more significantly. The mechanism of SMT degradation by Mn(VII)-PAA process was systematically evaluated. Firstly, based on the quenching experiments, electron spin resonance (EPR) results and UV-visible spectrum, singlet oxygen (1O2), Mn(III)aq and MnO2 colloids were the predominant active substances, while organic radicals (R-O•) showed negligible contribution. Then, the decay of Mn(VII) in the presence of PAA and H2O2 was investigated. It was found that the coexisting H2O2 accounted for almost all the decay of Mn(VII), PAA and acetic acid both had low reactivity toward Mn(VII). During the degradation process, acetic acid was able to acidify Mn(VII) and simultaneously acted as a ligand to form reactive complexes, while PAA mainly played a role of spontaneously decomposing to produce 1O2, they jointly promoted the mineralization of SMT. Finally, the degradation intermediates of SMT and their toxicities were analyzed. This paper reported the Mn(VII)-PAA water treatment process for the first time, which provided a promising approach for rapid decontamination of refractory organics-polluted water.

Insights into growth-affecting effect of nanomaterials: Using metabolomics and transcriptomics to reveal the molecular mechanisms of cucumber leaves upon exposure to polystyrene nanoplastics (PSNPs).

Polystyrene nanoplastics (PSNPs, <100nm), an artificial pollutant that is widespread in the environment, can be assimilated by plants to alter plant gene expression and its metabolic pathway; thus, interfering with physiological homeostasis and growth of plants. Recently, the biosafety and potential environmental risks of PSNPs have attracted enormous attention. However, the knowledge regarding the uptake and phytotoxicity of atmosphere PSNPs subsiding to plant leaves is still limited. Here, we separately applied 50 mg/L and 100 mg/L PSNPs on cucumber leaves to simulate the plant response to the atmosphere PSNPs. We found that the PSNPs can be accumulated on the surface of cucumber leaves and are also able to be uptake by cucumber leaf stomata. The repertoires of metabolomics and transcriptomics from cucumber leaves upon PSNPs treatment demonstrated that the deposition of PSNPs on leaves alters the biosynthesis of various metabolites and the expression of a variety of genes. The leaves exposure to low concentration (50 mg/L) of PSNPs impact the genes involved in carbohydrate metabolism and the biosynthesis of metabolites related to membrane stability maintenance, thereby, probably enhancing plant tolerance to the stress caused by PSNPs. Whereas, exposure to high concentration (100 mg/L) of PSNPs, both nitrogen and carbohydrate metabolism in cucumber leaves are affected, as well as that the photosynthetic capacity was decreased, leading to the threat to plant health. Combined omics technologies, our findings advance our understanding about how the PSNPs released to ecological environment influence the terrestrial plant growth and provide phytotoxic mechanism.

Aging significantly increases the interaction between polystyrene nanoplastic and minerals.

With the massive use and discarding of plastic products, plastic particles, including nanoplastics (NPs), which are continuously released under the action of environmental factors, are posing greater risk to the ecosystem and human health. NPs exposed to the environment experience aging, which can significantly change their physical and chemical properties and affect their environmental behavior. Here, we examined the adsorption behavior of polystyrene nanoplastic (PSNP) aging by ultraviolet (UV) exposure on different minerals (goethite, magnetite, kaolinite and montmorillonite). Aging not only changes the surface morphology of PSNP, but also increases the surface negative charge and produces a large number of oxygen-containing functional groups (OFGs). Incubation of aged PSNP with minerals indicated that iron oxides (goethite and magnetite) showed stronger interactions with aged PSNP than pristine PSNP, and there was an interaction between clay minerals and aged PSNP. The adsorption experiments and scanning electron microscopy (SEM) suggested that the higher adsorption capacity of a mineral surface to aged PSNP may be related to electrostatic attraction and ligand exchange. The Fourier transform infrared (FTIR) spectra after adsorption showed that the adsorption affinity between the functional groups was different, and two-dimensional correlation spectroscopy (2D-COS) analysis further indicated that the mineral preferentially adsorbed the aged PSNP in accordance with the order of OFGs. The findings provide a theoretical basis for scientific evaluation of ecological risks of NPs in the environment.

The characteristics of dissolved organic matter release from UV-aged microplastics and its cytotoxicity on human colonic adenocarcinoma cells.

There are a large number of microplastic (MPs) in the sea or on land, most of which undergo physical, chemical or biological processes leading to the release of dissolved organic matter (DOM). In this study, we analyzed the change of Polyurethane microplastic (PU-MPs) valence bond under different aging conditions thanks to Fourier transform infrared spectroscopy (FTIR) and its surface characteristics using scanning electron microscopy (SEM) and also described the characteristics of DOM dissolved from PU (PU-DOM) under UV aging process in two different medium (water and air), based on Dissolved organic carbon (DOC) measurements, UV-visible spectrometer and Three-dimensional excitation emission matrices (3D-EEMs). The DOC data both showed that Under UV aging of different systems, PU-DOM concentration increases with the extension of aging time, and correspondingly, its toxicity to human colon adenocarcinoma cells also increases, but the release amount of PU-DOM under air aging is higher than that of PU-DOM in water. We speculate that it may be the refraction and scattering of water, which leads to the reduction of the intensity of UV radiation. 3D-EEMs identified tryptophan-like fluorescent component and tyrosine-like component, meanwhile, the liquid chromatography-mass spectrometer (LC-MS) data further confirmed the formation of acid substances. The results further confirmed that the composition of PU-DOM in different systems is the same, but the release amount is different. The contents of the produced conjugated carbonyls and Reactive oxygen species (ROS) because of light irradiation increased likewise. The cytotoxicity of PU-DOM was consistent with the changing trend of ROS level in PU-MPs, suggesting that the produced ROS induced the in vitro toxicities. The results not only highlight the adverse health effects of photoaged PU-MPs, but also provide new perspectives for the environmental risks of MPs.

New insights on metal ions accelerating the aging behavior of polystyrene microplastics: Effects of different excess reactive oxygen species.

Microplastics (MPs) will coexist with various pollutants in the environment, but it is not clear whether these pollutants will affect the aging process of MPs. The aging process of polystyrene microplastics (PS-MPs) mediated by Cu2+ and Pb2+ was investigated in this study. The results showed that the aging rate of PS-MPs mediated by Cu2+ and Pb2+ were significantly higher than that of ultrapure water (After 7 days of light irradiation, the CI values of aging PS-MPs mediated by ultrapure water, Cu2+ and Pb2+ increased from 0.030 of original PS-MPs to 0.034, 0.048 and 0.086 respectively). This process may be related to the generation of a large amount of reactive oxygen species, because OH were detected in PS-MPs suspension mediated by Cu2+, which were significantly higher than those in ultrapure water, while 1O2 mediated by Pb2+ were more. However, these photo-aging effects were significantly inhibited by reactive oxygen species (ROS) quencher, which indicated that excessive ROS production was the main reason for metal ions to promote the photo-aging of PS-MPs. In addition, this study reported that excessive ROS will accelerate the formation of carbonyl group on the surface of PS-MPs, and lead to the change of physical and chemical properties of PS-MPs. This study provides new insights for the environmental behavior of MPs under the condition of combined pollution.

Photo-transformation of microplastics and its toxicity to Caco-2 cells.

In recent years, microplastics (MPs) pollution, as a global environmental problem, has been widely concerned by countries all over the world. However, the research on the impact of MPs on human health is still limited. In this study, we studied the photo-transformation behavior of polystyrene microplastics (PS-MPs) under ultraviolet light and its toxicity to Caco-2 cells. Our results showed that the surface of PS-MPs was roughened by light, and cracks and pits appeared. UV-vis spectra showed that the opening of phenyl ring and the formation of carbonyl group might exist in this process. Based on FTIR and 2D-COS analysis, we observed the formation of carbonyl group and hydroxyl group, and preliminarily determined that the order of photo-transformation of PS-MPs was 698 (CH) > 752 (CH) > 1030 (CO) > 3645 (OH/OOH) > 1740 (CO). XPS showed that the photo-transformation of PS-MPs was a process in which carbon-containing functional groups were gradually partially transformed into oxygen-containing functional groups. Finally, the toxicity results showed that with the increase of PS-MPs concentration and the extension of light irradiation time, the survival rate of Caco-2 cells gradually decreased and the integrity of cell membrane was destroyed. The increased cytotoxicity can be explained at least in part by the fact that the toxicity of oxygen-containing functional groups is greater than that of carbon-containing functional groups, but how these functional groups affect the cytotoxicity of cells still needs sustained research in the future. This study can provide new insights for understanding the environmental behavior and ecological effects of PS-MPs in the environment.

Degradation of polyethylene plastic in soil and effects on microbial community composition.

Plastics pollution in global soil systems is becoming a severely global issue and potential threat to terrestrial ecosystem serves and human health. Herein, in order to determine the degradability and ecological effects of polyethylene (PE) films, we measured the weight loss and characterization of PE films and analyzed variation in microbial community. The results of weight loss, SEM and FTIR spectra exhibited that PE films had unique degradation performance under different conditions. Simultaneously, we investigated the effects of PE films on the microbial community, and the microbiota colonizing on plastics. PE films may change the soil microbial community composition in soil, and hold the post of unique matrix for microbial colonization. These results indicate that the degradation of PE films and microbial community composition in soil can be affected by different conditions (soil layer, time and plants). By assessing the alteration of microbial community composition and PE films in soil, this work will contribute to enhance our understanding on the potential risks of plastics on soil ecosystems and provide a scientific basis for understanding the ecological effect of plastics on soil functions.

Effect of cadmium on the sorption of tylosin by polystyrene microplastics.

Microplastics are widespread in the environment and might transport readily by ocean currents, wind and atmospheric deposition. Simultaneously, antibiotics and heavy metals could often be detected in the environment. They are both positively charged, it is necessary to clarify the interactions of these pollutants with microplastics when they were coexist. In this study, the most commonly used polystyrene (PS) was selected as a representative microplastic. This study investigated the effect of Cd(II) on the sorption of TYL by PS in different coexistence systems. The results showed that: in the composite system, when TYL and Cd(II) coexist, the presence of Cd(II) could inhibit the sorption of TYL by PS, and the inhibitory effect increases with the increase of the concentration of Cd(II), indicating that competitive sorption dominates the sorption. When PS adsorbed Cd(II) first and then adsorbed TYL, the presence of Cd(II) was conducive to the sorption of TYL, and the sorption strengthened with the increase of Cd(II) concentration, indicating that the complexation between TYL and Cd(II) enhanced the sorption of TYL. In addition, initial pH values and ionic strength were essential in the sorption process. Therefore, this study could provide an important basis for evaluating the environmental behavior and ecological risk of microplastics in the process of compound pollution.

The occurrence and abundance of microplastics in surface water and sediment of the West River downstream, in the south of China.

Microplastic pollution has aroused great concern in inland waters. Freshwater is the transport routes and potential sources for plastic fragments to the oceans. However, information especially about the occurrence of microplastics in freshwater systems is unclear in certain key areas. This work studied the distribution and characteristics for microplastics in the downstream area of West River. Both sediment and surface water detected microplastics with abundance ranging from 2560 to 10,240 items/kg and 2.99 to 9.87 items/L, respectively. Small size (<0.5 mm) and fiber were the main size and type in both surface waters and sediments. Polypropylene, polyethylene, polyethylene, polyvinyl chloride and polyethylene terephthalate were the polymer types of microplastics, as identified using a Fourier transform infrared spectrometer. In addition, findings here might be in consideration of studying about the distribution of microplastics and the degree to which they were influenced by the use of land. In descending order, the highest microplastics abundance was observed in commercial/public/recreational > residential > industrial > natural areas. Our results indicate the occurrence of high abundance microplastics in river impacted by human activities, and suggest that spatial distribution of microplastics varies between different land use areas.

Cellulase modified waste biomass to remove sulfamethazine from aqueous solutions.

The objective of this work is to find a simple and environmentally friendly way to prepare high efficiency adsorbent from maize stover by cellulase. The characteristics of the original maize cob (MC), maize husk (MH), maize straw (MS), and its cellulase modified form (MMC, MMH and MMS) were detected by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Batch adsorption experiments indicated that the adsorption followed the pseudo-second-order kinetic model, and the adsorption capacity of sulfamethazine (SMT) to adsorbents was in order of MMC > MMS > MMH > MC > MS > MH. The adsorption isotherm data of SMT on original materials were consistent with Freundlich models, while Henry models were more suitable for the modified materials. The adsorption was affected by pH and ionic strength which demonstrated the interaction between π-π EDA and H bonds might be an important factor in the adsorption of SMT on maize stover. The results of FTIR and two-dimensional correlation spectroscopy (2D-COS) analysis further demonstrated that oxhydryl and aromatic structures in the modified maize stover could interact with SMT via H bonds and π-π EDA interaction, respectively. This work provides a green way to remove SMT from aqueous solution, and new insights into the mechanisms of adsorption of SMT on stover materials.