Abandoned disposable masks become hot substrates for plastisphere, whether in soil, atmosphere or water.

A large number of surgical masks (SMs) to be discarded indiscriminately during the spread of COVID-19. The relationship between the changes of masks entering the environment and the succession of the microorganisms on them is not yet clear. The natural aging process of SMs in different environments (water, soil, and atmosphere) was simulated, the changes and succession of the microbial community on SMs with aging time were explored. The results showed that the SMs in water environment had the highest aging degree, followed by atmospheric environment, and SMs in soil had the lowest aging degree. The results of high-throughput sequencing demonstrated the load capacity of SMs for microorganisms, showed the important role of environment in determining microbial species on SMs. According to the relative abundance of microorganisms, it is found that compared with the water environment, the microbial community on SMs in water is dominated by rare species. While in soil, in addition to rare species, there are a lot of swinging strains on the SMs. Uncovering the ageing of SMs in the environment and its association with the colonization of microorganisms will help us understand the potential of microorganisms, especially pathogenic bacteria, to survive and migrate on SMs.

Dissolved organic matter derived from biodegradable microplastic promotes photo-aging of coexisting microplastics and alters microbial metabolism.

Dissolved organic matter (DOM) leaching from biodegradable microplastics (BMPs) and its characteristics and corresponding environmental implication are rarely investigated. In this study, the main component of DOM leachate from the two BMPs (polyadipate/butylene terephthalate (PBAT)/polycaprolactone (PCL)) was verified by using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC). The PBAT-DOM (PBOM) was aromatized and terrestrial. Comparatively, PCL-DOM (PLOM) had low molecular weight. PBOM contained protein-like components while PLOM contained tryptophan and tyrosine components. Interestingly, both PBOM and PLOM could accelerate the decomposition and oxidation of coexisting polystyrene (PS) under light irradiation. Further, the difference in composition and the properties of BMPs-DOM significantly affected its photochemical activity. The high territoriality and protein-like component of PBOM significantly promoted the generation of 1O2 and O2•-, which caused faster disruptions to the backbone of PS. Simultaneously, the microbial community's richness, diversity, and metabolism were obviously improved under the combined pressure of aged PS and BMPs-DOM. This study threw light on the overlooked contribution of DOM derived from BMPs in the aging process of NMPs and their impact on the microbial community and provided a promising strategy for better understanding of combined MPs' fate and environmental risk.

Black carbon derived from pyrolysis of maize straw and polystyrene microplastics affects soil biodiversity.

Understanding the environmental correlation of microbial community under external stimulation is significant for ecological restoration. However, few studies focused on the response of soil biodiversity induced by black carbon (BC) derived from pyrolysis of straw and microplastics (MPs) due to their widespread existence in natural environment. In this study, polystyrene MPs (PS) and maize straw with different mass ratios were used as raw materials to prepare BC by pyrolysis. The surface morphology, chemical composition and sequential variations of different functional groups of BC were systematically analyzed. The leachate from BC was identified by three-dimensional excitation emission matrice (3D-EEM). The corresponding results showed that yield, value of O/C and N element content of BC decreased with more PS. The changed C content and oxygen-containing functional groups occurred. The order of functional groups of BC formed by co-pyrolysis was: C=C > C-O > C-H > Si-O-Si. The main component of leaching from BC was humic-like and fulvic-like acid. Simultaneously, the input of exogenous BC into soil affected abundance, composition and metabolic pathways of microorganisms. The study helps to understand environmental implication of BC which was pyrolyzed from maize straw and MPs, providing an idea for improving biogeochemical cycle process in soil.

Biofilm-Colonized versus Virgin Black Microplastics to Accelerate the Photodegradation of Tetracycline in Aquatic Environments: Analysis of Underneath Mechanisms.

Tire wear particles (TWPs) exposed to the aquatic environment are rapidly colonized by microorganisms and provide unique substrates for biofilm formation, which potentially serve as vectors for tetracycline (TC) to influence their behaviors and potential risks. To date, the photodegradation capacity of TWPs on contaminants due to biofilm formation has not been quantified. To accomplish this, we examined the ability of virgin TWPs (V-TWPs) and biofilm-developed TWPs (Bio-TWPs) to photodegrade TC when exposed to simulated sunlight irradiation. V-TWPs and Bio-TWPs accelerated the photodegradation of TC, with rates (kobs) of 0.0232 ± 0.0014 and 0.0152 ± 0.0010 h-1, respectively (kobs increased by 2.5-3.7 times compared to that for only TC solution). An important factor of increased TC photodegradation behavior was identified and linked to the changed reactive oxygen species (ROS) of different TWPs. The V-TWPs were exposed to light for 48 h, resulting in more ROS for attacking TC, with hydroxyl radicals (•OH) and superoxide anions (O2•-) playing a dominant role in TC photodegradation measured using scavenger/probe chemicals. This was primarily due to the greater photosensitization effects and higher electron-transfer capacity of V-TWPs in comparison to Bio-TWPs. In addition, this study first sheds light on the unique effect and intrinsic mechanism of the crucial role of Bio-TWPs in TC photodegradation, enhancing our holistic understanding of the environmental behavior of TWPs and the associated contaminants.

Mechanistic insights into the detoxification of Cr(VI) and immobilization of Cr and C during the biotransformation of ferrihydrite-polygalacturonic acid-Cr coprecipitates.

Coupled reactions among chromium (Cr), organic matter (OM), and iron (Fe) minerals play significant roles in Cr and carbon (C) cycling in Cr-contaminated soils. Although the inhibitory effects of Cr or polysaccharides acid (PGA) on ferrihydrite transformation have been widely studied, mechanistic insights into detoxification of Cr(VI) and immobilization of Cr and C during the microbially mediated reductive transformation of ferrihydrite remain unclear. In this study, underlying sequestration mechanisms of Cr and C during dissimilatory Fe reduction at various Cr/Fe ratios were investigated. Solid-phase analysis showed that reductive transformation rates of ferrihydrite were impeded by high Cr/Fe ratio and more magnetite was found at low Cr loadings. Microscopic analysis showed that formed Cr(III) was immobilized by magnetite and goethite through isomorphous substitution, whereas PGA was adsorbed on the crystalline Fe mineral surface. Spectroscopic results uncovered that binding of Fe minerals and PGA was achieved by surface complexation of structural Fe with carboxyl functional groups, and that the adhesion order of PGA functional groups and Fe minerals was influenced by the Cr/Fe ratios. These findings have significant implications for remediating Cr contaminants, realizing C fixation, and developing a quantitative model for Cr and C cycling by coupling reductive transformation in Cr-contaminated environments.

Hematite-mediated Mn(II) abiotic oxidation under oxic conditions: pH effect and mineralization.

Interactions between manganese (Mn) and iron (Fe) are widespread processes in soils and sediments, however, the abiotic transformation mechanisms are not fully understood. Herein, Mn(II) oxidation on hematite were investigated at various pH under oxic condition. Mn(II) oxidation rates increased from 3 × 10-4 to 8 × 10-2 h-1 as pH increased from 7.0 to 9.0, whereas hematite enhanced Mn(II) oxidation rates to 1 h-1. During oxidation process, high pH could promote the oxidation of Mn(II) into Mn minerals, resulting in the rapid consumption of the newly-formed H+, and high pH facilitated Mn(II) adsorption and oxidation by altering Mn(II) reactivity and speciation. Only granule-like hausmannite was found on the hematite surface at pH 7.0, whereas hausmannite particles and feitknechtite and manganite nanowires were formed at pH from 7.5 to 9.0. Moreover, a co-shell structured nanowire composed of manganite and feitknechtite was observed owing to autocatalytic reactions. Specifically, electron transfers between Mn(II) and O2 occurred on the surface or through bulk phase of hematite, and direct electron transfers in the O2-Mn(II) complex and indirect electron transfers in the O2-Fe(II/III)-Mn(II) complex may both have contribution to the overall reactions. The findings provide a comprehensive interpretation of Fe-Mn interaction and have implications for the formation of soil Fe-Mn oxyhydroxides with unique properties in controlling element cycling.

Insight into the Photodegradation of Microplastics Boosted by Iron (Hydr)oxides.

Iron (hydr)oxides as a kind of natural mineral actively participate in the transformation of organic pollutants, but there is a large knowledge gap in their impacts on photochemical processes of microplastics (MPs). This study is the first to examine the degradation of two ordinary plastic materials, polyethylene (PE) and polypropylene (PP), mediated by iron (hydr)oxides (goethite and hematite) under simulated solar light irradiation. Both iron (hydr)oxides significantly promoted the degradation of MPs (particularly PP) with a greater effect by goethite than hematite, related to hydroxyl radical (•OH) produced by iron (hydr)oxides. Under light irradiation, the surface Fe(II) phase catalyzed the production of H2O2 and promoted the release of Fe2+, leading to the subsequent light-driven Fenton reaction which produced a large amount of •OH. As the iron (hydr)oxides were modified with NaF at various concentrations, the activity of the surface Fe(II) as well as the release of Fe2+ were greatly reduced, and thus the •OH formation and MP degradation were depressed remarkably. It is worth noting that the surface hydroxyl groups (especially ≡FeOH) affected the reaction kinetics of •OH by regulating the activity of Fe species. These findings unveil the distinct impacts and intrinsic mechanisms of iron (hydr)oxides in influencing the photodegradation of MPs.

A case study of distribution and characteristics of microplastics in surface water and sediments of the seas around Shenzhen, southern coastal area of China.

Microplastics (MPs), known to cause environmental pollution, is attracting a growing attention worldwide owing to their extensive existence and potential risks to biota. The marginal sea areas are suspected to be especially susceptible to MPs pollution. Unfortunately, data on MPs in the surface water and sediments ecosystems are still limited, particularly in the southern coastal areas of China. The study was successfully utilized to explore the distribution and characteristics of MPs below 5 mm collected from 14 sites in the seas around Shenzhen, a typical special economic zone of China. MPs were detected in both surface water and sediments with concentrations ranging from 3.8 to 7.8 items per liter and 2.6 × 103 to 10.0 × 103 items per kilogram, respectively. The highest abundance of MPs appeared in S5/S9 and S14 in surface water and sediments, respectively. Fiber and film with small particle size (<0.5 mm) were identified as typical and abundant MPs type among all samples. In addition, polyethylene (PE) was considered as dominant forms of MPs in surface water and sediment samples. Results from this study indicated a positive correlation with abundance of MPs and urbanization rate, which also showed an evident difference of MPs in different urban functional areas. Based on the types and quantity of detected MPs, we assessed the risk of MPs pollution in this study area, and the ecological risk category of MPs was at a high level. Importantly, our work might be employed as a potential information so as to better understand MPs pollution, source tracing and ecological risk assessment, which enhances the possibility of achieving effective control and supervision of MPs pollution in southern coastal aera of China.

Exposed facets mediated interaction of polystyrene nanoplastics (PSNPs) with iron oxides nanocrystal.

Nanoplastics (NPs), which are often detected in the natural environment, are regarded as a group of emerging pollutants. Hematite is a substance that exists widely in the surface environment and has an important impact on the environmental behavior of pollutants. Clarifying the migration of NPs requires an in-depth understanding of intrinsic interaction mechanisms of NPs with iron-containing minerals. The interaction process of polystyrene nanoplastics (PSNPs) on the hematite exposed facets was systematically studied by experiments under different conditions, adsorption isotherm curves, Fourier Transform infrared (FTIR) spectroscopy and two-dimensional correlation spectroscopy (2D-COS) analyses. We found that PSNPs were adsorbed on the three exposed faces of hematite ({001}, {012}, and {100}) by electrostatic interaction, respectively, but the capacities for PSNPs were different. Adsorption models were established to explore the preferred interaction surface dependent on the exposed facets, and it was found that {012} surfaces were more favorable for PSNPs adsorption, while {001} surface has better adsorption capacity for PSNPs than {100} surface, which is due to the different density and proportion of hydroxyl groups on the exposed facets of hematite. These findings elucidated the dependence of PSNPs adsorption on the hematite facets, and illustrated t the effect of hematite on the migration of PSNPs in the environment.

Occurrence status of microplastics in main agricultural areas of Xinjiang Uygur Autonomous Region, China.

A large number of plastic products are used in the process of agricultural production, and the recycling efficiency is low, which leads to the production of a large number of microplastics. Therefore, the microplastic contamination in agricultural areas requires being investigated urgently. In addition, the occurrence characteristics of microplastics are also different in agricultural areas with various land use modes. In this study, the main agricultural areas in Xinjiang are taken as the research object. The abundance of microplastics in the main agricultural areas in Xinjiang ranges from 288 to 1452 items/kg. The shape of microplastics is mainly bulks, and white microplastics account for the highest proportion, and the majority of their sizes are less than 0.5 mm. The risk assessment results show that the contamination risk index of microplastics in this area is 108.92 and the risk level is grade III. The research shows that there is little difference in the abundance of microplastics between paddy field and garden land, which may be because there are few sources of microplastics in the land of these two utilization modes, and the potential pollution sources are similar, such as the atmospheric deposition of microplastics, the falling of fibers on people's clothes during farming, and the agricultural use of sludge. This study can provide a reference for further study on the existing circumstances of microplastics in agricultural areas.

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.

Insight into interactions of polystyrene microplastics with different types and compositions of dissolved organic matter.

Microplastics (MPs), as newly emerging pollutants, may interact with dissolved organic matter (DOM) widely present in the environment after entering the environment, thereby influencing the migration and transformation of MPs. The interaction characteristics and mechanism between DOM and MPs are restricted by many factors, and the current mechanism remains unclear. Thus, we explored the combination of MP with different types and compositions of DOM (fulvic acid (FA) and humic acid (HA)). Adsorption experiments revealed that MP has high adsorption affinity for all four DOMs, particularly FA. Meanwhile, the affinity of MP-DOM was also examined using excitation-emission matrix (EEM) analyses and fluorescence quenching method (excitation emission matrix-parallel factor analysis (EEM-PARAFAC)). Aromatic substances and hydrophobic substances dominate all DOM samples. For all DOM types tested, the quenching curve varies considerably with the type and compositions of DOM. In addition, three fluorescent components exhibited significant fluorescence quenching over time. The interaction mechanism of MPs and DOM at the molecular level was further elucidated by utilizing two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (COS) analysis, which revealed that the oxygen-containing functional group in MPs was the most preferred DOM binding structure. This work was facilitated to explore the environmental behavior of MPs and formation of secondary MPs under natural conditions.

New insight into transformation of tetracycline in presence of Mn(II): Oxidation versus photolysis.

Tetracycline (TC) and Mn(II) is a common antibiotic and metal ion respectively. Nevertheless, literatures involving in the effects of Mn(II) on TC transformation are still insufficient. In this study, the kinetic experiment, spectral analysis, complexation experiment and electrochemical analysis, theoretical calculation and products detection were carried out to probe into oxidation and photolysis of TC with Mn(II). Mn(II) greatly accelerated TC oxidation, preferably tending to complex with TC at O10 - O12 or O2 - O3 site. There were a TC-Mn(II)/TC-Mn(III) redox couple and electron transfer process. Conversely, Mn(II) inhibited photolysis of TC. The photolysis of excited TC could compete with energy dissipation reactions. The electron transfer and complexation reaction easily made excited TC energy transfer, thus slowing down photolysis process. During the TC transformation, the intensity of functional groups was significantly decreased. Simultaneously, the degradation pathways mainly included eight reactions. It is a very interesting and probably overlooked phenomenon, which identifies new transformation of TC with Mn(II). This study helps to further understand fate and environmental behavior of antibiotics and metal ion.

Photocatalytic degradation of (micro)plastics using TiO2-based and other catalysts: Properties, influencing factor, and mechanism.

(Micro)plastics pollution has raised global concern because of its potential threat to the biota. The review on recent developments of photocatalytic degradation of (micro)plastics is still insufficient. In this study, we have discussed various bare and composites photocatalysts involved in the photocatalytic degradation of (micro)plastics. The photocatalytic mechanisms and factors affecting the degradation were also discussed. To improve the performance of photocatalysts, their surface is modified with metal or non-metal dopants. These doped photocatalysts are then compounded with a variety of environmentally friendly and nontoxic polymers to prepare multifunctional composites. The generation of reactive oxygen species (ROS) plays an important role in the photocatalytic degradation of (micro)plastics, and superoxide ions (O2-) and hydroxyl radicals (OH) participate in the photocatalytic degradation, leading to the breaking of the polymer chain and the production of some intermediates. Although satisfactory progress has been achieved in the photodegradation of (micro)plastics, most photocatalytic degradation technologies investigated to date cannot realize the complete mineralization of (micro)plastics. Furthermore, based on the current challenges of the existing photocatalytic degradation technologies, perspectives for future research directions have been proposed. This review presents a systematic summary of the progress made in the photocatalytic degradation of (micro)plastics and offers a comprehensive reference for future research on improving the (micro)plastics photocatalytic degradation efficiency.

The photodegradation processes and mechanisms of polyvinyl chloride and polyethylene terephthalate microplastic in aquatic environments: Important role of clay minerals.

It is well known that microplastics (MPs) may experience weathering and aging under ultraviolet light (UV) irradiation, but it remains unclear if these processes are impacted by natural components, such as clay minerals. In this study, we systematically investigated the photodegradation behaviors of polyvinyl chloride (PVC) and poly (ethylene terephthalate) (PET), two utmost used plastics, in the presence of clay minerals (kaolinite and montmorillonite). The results demonstrated that the clay minerals, particularly kaolinite, significantly promoted the MPs photodegradation, and the aging of PET was more prominent. The photodegradation was the most distinct at pH 7.0, regardless of the presence or absence of the clay minerals. The results of electron paramagnetic resonance and inhibition experiments of reactive oxygen species indicated that the minerals, particularly kaolinite, remarkably facilitated production of •OH, which was the key species contributing to the photodegradation of MPs. Specifically, UV irradiation facilitated the photo-ionization of MPs, producing hydrated electrons and MP radical cations (MP+). The Lewis base sites prevalent on the clay siloxane surfaces could stabilize the MP radical cations and prevent their recombination with hydrated electrons, which promoted the generation of •OH under aerobic conditions, and facilitated the degradation of MP. Two-dimensional (2D) Fourier transformation infrared (FTIR) correlation spectroscopy (COS) analysis and ultra-high-performance liquid chromatography coupled to a Q Exactive Orbitrap HF mass spectrometer were used to identify the sequential changes of functional groups, and the degradation products of the MPs. This study improves our understanding on the aging of MPs in the complex natural environment.

The aging behavior of polyvinyl chloride microplastics promoted by UV-activated persulfate process.

Microplastics (MPs) experienced different aging processes in environment. Literatures about effect of artificially-accelerated aging on MPs behavior are still insufficient. The accelerated process induced by ultraviolet(UV)-activated persulfate (PS) is a promising technology for obtaining different aged MPs to understand long-term aging behavior. In the work, the aging behavior of polyvinyl chloride (PVC) accelerated by UV/PS system were investigated. It exhibited a dechlorination with 58.495 ± 6.090 mg/L Cl- release after 35 h UV-activated PS (0.01 M) process. The treatment led to significant alternations on surface morphology and chemical feature of PVC. The crystallinity was increased, and average size was reduced from 154.11 µm to 119.28 µm with aging time. Subsequently, many smaller size particles were produced. Furthermore, the process induced the breaking of backbone. Simultaneously, more oxygen-containing functional groups were identified. The oxidation reaction accelerated by sulfate radical (SO4•-) and reactive oxygen species (ROS) was predominant, which immensely promoted aging process. Sustained high levels of free radical contributed to production of alcohols and carboxylic acids short chain organics. The study explored aging behavior of PVC accelerated by UV/PS system, which could be helpful for understanding environmental behavior and providing further information to assess potential risks of MPs.

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.

Abundance and characteristics of microplastics in the surface water and sediment of parks in Xi'an city, Northwest China.

Microplastics (MPs), as a new type of pollutants, have attracted wide attention especially in recent years, but there was insufficient research on the distribution and characteristics of MPs in urban park water body. In this study, the pollution of MPs in water and sediment of Xi'an, the largest city in northwest China, was investigated. The MPs concentration in the surface water and sediment was 2900-6970 items/m3 and 940-3560 items/kg, respectively. According to the urban functions, the parks were divided into residential areas, commercial areas, tourism areas and industrial areas, and the highest abundance of MPs was observed in the tourism and residential areas, suggesting the impacts of human activities. MPs in these parks were mainly in four kinds of shapes, namely fiber, pellet, fragment and film, and dominated by fibers and fragments. Most of the extracted MPs were small in size, and 63-92% of them were smaller than 0.5 mm. Polypropylene and polyethylene terephthalate were the main polymer types in surface water and sediments, respectively. This study showed that the park water and sediment can be used as an important "sink" in MPs, which is of great significance for monitoring and alleviating the pollution of urban MPs. This study provided important reference for better understanding MPs levels in inland freshwaters.

Photodegradation of microplastics mediated by different types of soil: The effect of soil components.

Microplastics (MPs) have attracted considerable attention due to its worldwide distribution, environmental persistence, and ecological risks. In this work, the photodegradation of MPs mediated by five different types of soils were investigated. The results showed: after 20 d of xenon lamp irradiation, significant degradation of MP was observed on Harbin (S1), Huainan (S2), Jiangxi (S3), Shaanxi (S4) and Hainan (S5). The order of photodegradation rate of MP was S2 > S5 > S4 > S1 > S3. The components of the soil have some correlations with MPs photodegradation. The photodegradation of MP mediated by soil components (specifically, the clay, the iron oxides and MnO2) displayed positive effect, while the photodegradation of MPs mediated by organic carbon showed inhibition trend. It is worth noting that electrostatic interaction may be the dominant factor affecting the interaction between MPs photodegradation rate and different soils surfaces. This study is helpful to deepen the understanding of the photochemical behavior of MP in soil, and is of great significance to evaluate the environmental fate and mechanism mediated by MP in soil.

Mechanistic insights into the environmental fate of tetracycline affected by ferrihydrite: Adsorption versus degradation.

Tetracycline (TC), a widely used antibiotic, is frequently detected in soil environments. It has a strong tendency to form complexes with metals, including iron (oxyhydr)oxide. In this study, ferrihydrite (Fh), a representative iron oxyhydroxide of the iron plaques on the surface of plant roots, was chosen to study the contributions of iron oxyhydroxide on the environmental fate of TC in the rhizosphere environment. Fh adsorption isotherm of TC showed good fitting to the Freundlich model, and the Fh adsorption capacity of TC was found much larger than the other iron oxyhydroxide of high crystallinity. The adsorption mechanisms mainly included electrostatic interaction, H-bonding, and complexation. The results of FTIR and XPS spectra revealed that tricarbonylamide, dimethylamino, and the hydroxyl in the B ring of TC were mainly responsible for the complexation with Fh surface hydroxyl groups. Furthermore, it should be noted that the adsorbed TC on Fh could be degraded and the degradation kinetics of TC better fitted to the pseudo-second-order model. Fh could promote electron transfer from TC to Fe(III) on the Fh surface, which led to the degradation of TC and the formation of Fe(II) ions. The degradation pathways of TC mainly involved three reactions: hydroxylation, dealkylation, and deamination. This study provides mechanistic insights on TC-Fh interaction, which improves the understanding of TC fate in the rhizosphere environment.