Effects of environmental aging on the adsorption behavior of antibiotics from aqueous solutions in microplastic-graphene coexisting systems

Impact of the hydrated functional zone on the adsorption of ciprofloxacin to microplastics under the influence of UV aging

The inevitable UV aging of microplastics (MPs) is one of the key factors affecting their interaction with antibiotics. In this study, polyethylene (PE) and polystyrene (PS) MPs were aged with UV irradiation. The adsorption isotherms and kinetics of ciprofloxacin (CIP) to virgin and aged MPs were investigated through various models, and the effects of pH on the adsorption amount were explored. Characterization revealed that the surfaces of aged MPs became rougher, and the hydrophilicity increased. These aged MPs were still in the early stage of aging on the basis of their carbonyl index (CI) (<0.2) and O/C (<0.04) values. The adsorption isotherms indicated that the adsorption mechanism of aged PE was different from that of virgin PE. Compared with virgin PE, the adsorption amount of aged PE increased by 87.80-95.45%, and the adsorption rate decreased by 65.52-80.74%. However, aging did not significantly affect the equilibrium adsorption amount or adsorption rate of aged PS. The external diffusion rate (Kext) (about 2.29-0.36 h-1) was almost 30 times greater than the internal diffusion rate (Kint) in the film-pore mass transfer (FPMT) model, indicating that CIP adsorption rate was dominated by external diffusion. A hydrated functional zone is thought to form around aged MPs, thus changing the adsorption mechanism and adsorption amount of aged PE. Therefore, more attention should be given to alterations in the hydrated functional zone in the early stage of MPs aging.

Polyamide 6 microplastics as carriers led to changes in the fate of bisphenol A and dibutyl phthalate in drinking water distribution systems: The role of adsorption and interfacial partitioning

Microplastics (MPs) co-exist with plastic additives and other emerging pollutants in the drinking water distribution systems (DWDSs). Due to their strong adsorption capacity, MPs may influence the occurrence of additives in DWDSs. The article investigated the occurrence of typical additives bisphenol A (BPA) and dibutyl phthalate (DBP) in DWDSs under the influence of polyamide 6 (PA6) MPs and further discussed the partitioning of BPA/DBP on PA6s, filling a research gap regarding the impact of adsorption between contaminants on their occurrence within DWDSs. In this study, adsorption experiments of BPA/DBP with PA6s and pipe scales were conducted and their interaction mechanisms were investigated. Competitive adsorption experiments of BPA/DBP were also carried out with site energy distribution theory (SEDT) calculations. The results demonstrated that PA6s might contribute to the accumulation of BPA/DBP on pipe scales. The adsorption efficiencies of BPA/DBP with both PA6s and pipe scales were 26.47 and 2.61 times higher than those with only pipe scales. It was noteworthy that BPA had a synergistic effect on the adsorption of DBP on PA6s, resulting in a 26.47 % increase in DBP adsorption. The article provides valuable insights for the compounding effect of different types of additives in water quality monitoring and evaluation.

Effect of Biofouling on the Sorption of Organic Contaminants by Microplastics

Microplastics in the aquatic environment are susceptible to colonization by surrounding microorganisms, which form biofilms over the microplastic's surface. These biofilm-laden microplastics can then interact with a diverse array of contaminants. In the present study, biofilms were grown on microplastics in a laboratory setting using Pseudomonas aeruginosa as a model biofilm-forming bacterium for periods of 5 to 15 days. The sorption of three organic compounds representing different levels of hydrophobicity, namely methylene blue (MB), phenanthrol, and phenanthrene, was used to evaluate the effect of biofilm biomass on the adsorption of organic contaminants to microplastics. The sorption of MB and phenanthrol was found to increase with biofouling time, indicating affinity between these contaminants and the biofilm biomass on the particle. However, the presence of a biofilm did not influence the sorption of phenanthrene on the microplastics. These results suggest that the hydrophobicity of organic contaminants plays a major role in how biofouling of microplastics will influence contaminant sorption by microplastics. For some contaminants, biofilm can enhance the role of microplastics as contaminant vectors. These findings emphasize the need to understand the biomass load on environmental microplastics and the contaminants that associate with it for an accurate representation of the risk associated with microplastics in the environment. Environ Toxicol Chem 2024;43:1973-1981. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Ecotoxicological Effects of Microplastics Combined With Antibiotics in the Aquatic Environment: Recent Developments and Prospects

Both microplastics and antibiotics are commonly found contaminants in aquatic ecosystems. Microplastics have the ability to absorb antibiotic pollutants in water, but the specific adsorption behavior and mechanism are not fully understood, particularly in relation to the impact of microplastics on toxicity in aquatic environments. We review the interaction, mechanism, and transport of microplastics and antibiotics in water environments, with a focus on the main physical characteristics and environmental factors affecting adsorption behavior in water. We also analyze the effects of microplastic carriers on antibiotic transport and long-distance transport in the water environment. The toxic effects of microplastics combined with antibiotics on aquatic organisms are systematically explained, as well as the effect of the adsorption behavior of microplastics on the spread of antibiotic resistance genes. Finally, the scientific knowledge gap and future research directions related to the interactions between microplastics and antibiotics in the water environment are summarized to provide basic information for preventing and treating environmental risks. Environ Toxicol Chem 2024;43:1950-1961. © 2024 SETAC.

Assessing microplastics-antibiotics coexistence induced ciprofloxacin-resistant Pseudomonas aeruginosa at a water region scale

Microplastics (MPs) waste is widespread globally in water systems. The opportunistic human pathogen Pseudomonas aeruginosa can cause serious acute and chronic infections that are notoriously difficult to treat. Ciprofloxacin (CIP) is broadly applied as an anti-P. aeruginosa drug. A growing evidence reveals that antibiotic-resistance genes-carrying Pseudomonas aeruginosa were detected on MPs forming plastisphere due to their adsorbability along with high occurrence of CIP in water environments. The MPs-niched CIP-resistant P. aeruginosa has been likely to emerge as an unignorable public health issue. Here, we offered a novel approach to assess the development of CIP-resistant P. aeruginosa under MPs-antibiotic coexistence at a water region scale. By combing the adsorption isotherm models used to estimate CIP condensation around MPs and a pharmacokinetic/pharmacodynamic-based microbial population dynamic model, we predicted the P. aeruginosa development on CIP-adsorbed MPs in waters. Our assessment revealed a high antibiotic resistance in the P. aeruginosa populations (∼50 %) with a wider range of waterborne total cell counts (∼10-2-104 cfu mL-1) among water regions in that the resistance proportion was primarily determined by CIP pollution level and relative abundance of various polymer type of MPs. We implicate that water region-specific MPs were highly likely to provide media for P. aeruginosa propagation. Our results highlight the importance of antibiotic-resistant pathogen colonization-emerging environmental medium interactions when addressing global threat from MPs pollution, in the context of MPs-antibiotics co-contamination assessment and for the continued provision of water system management.

Regulation of ARGs abundance by biofilm colonization on microplastics under selective pressure of antibiotics in river water environment

Interactions of microplastics (MPs) biofilm with antibiotic resistance genes (ARGs) and antibiotics in aquatic environments have made microplastic biofilm an issue of keen scholarly interest. The process of biofilm formation and the degree of ARGs enrichment in the presence of antibiotic-selective pressure and the impact on the microbial community need to be further investigated. In this paper, the selective pressure of ciprofloxacin (CIP) and illumination conditions were investigated to affect the physicochemical properties, biomass, and extracellular polymer secretion of polyvinyl chloride (PVC) microplastic biofilm. In addition, relative copy numbers of nine ARGs were analyzed by real-time quantitative polymerase chain reaction (qPCR). In the presence of CIP, microorganisms in the water and microplastic biofilm were more inclined to carry associated ARGs (2-3 times higher), which had a contributing effect on ARGs enrichment. The process of pre-microplastic biofilm formation might have an inhibitory effect on ARGs (total relative abundance up to 0.151) transfer and proliferation compared to the surrounding water (total relative abundance up to 0.488). However, in the presence of CIP stress, microplastic biofilm maintained the abundance of ARGs (from 0.151 to 0.149) better compared to the surrounding water (from 0.488 to 0.386). Therefore, microplastic biofilm act as abundance buffer island of ARGs stabilizing the concentration of ARGs. In addition, high-throughput analyses showed the presence of antibiotic-resistant (Pseudomonas) and pathogenic (Vibrio) microorganisms in biofilm under different conditions. The above research deepens our understanding of ARGs enrichment in biofilm and provides important insights into the ecological risks of interactions between ARGs, antibiotics, and microplastic biofilm.

Aging of plastics in aquatic environments: Pathways, environmental behavior, ecological impacts, analyses and quantifications

The ubiquity of plastics in our environment has brought about pressing concerns, with their aging processes, photo-oxidation, mechanical abrasion, and biodegradation, being at the forefront. Microplastics (MPs), whether originating from plastic degradation or direct anthropogenic sources, further complicate this landscape. This review delves into the intricate aging dynamics of plastics in aquatic environments under various influential factors. We discuss the physicochemical changes that occur in aged plastics and the release of oxidation products during their degradation. Particular attention is given to their evolving environmental interactions and the resulting ecotoxicological implications. A rigorous evaluation is also conducted for methodologies in the analysis and quantification of plastics aging, identifying their merits and limitations and suggesting potential avenues for future research. This comprehensive review is able to illuminate the complexities of plastics aging, charting a path for future research and aiding in the formulation of informed policy decisions.

Ecotoxicological effects of antibiotic adsorption behavior of microplastics and its management measures

Microplastics adsorb heavy metals and organic pollutants to produce combined pollution. Recently, the adsorption behavior of antibiotics on microplastics has received increasing attention. Exploring the sorption behavior of pollutants on microplastics is an important reference in understanding their ecological and environmental risk studies. In this paper, by reviewing the academic literature in recent years, we clarified the current status of research on the adsorption behavior of antibiotics on microplastics, discussed its potential hazards to ecological environment and human health, and summarized the influence of factors on the adsorption mechanisms. The results show that the adsorption behavior of antibiotics on microplastics is controlled by the physical and chemical properties of antibiotics, microplastics, and water environment. Antibiotics are adsorbed on microplastics through physical and chemical interactions, which include hydrophobic interaction, partitioning, electrostatic interaction, and other non-covalent interactions. Intensity of adsorption between them is mainly determined by their physicochemical properties. The basic physicochemical properties of the aqueous environment (e.g., pH, salinity, ionic strength, soluble organic matter content, and temperature) will affect the physicochemical properties of microplastics and antibiotics (e.g., particle size, state of dispersibility, and morphology), leading to differences in the type and strength of their interactions. This paper work is expected to provide a meaningful perspective for better understanding the potential impacts of antibiotic adsorption behavior of microplastics on aquatic ecology and human health. In the meantime, some indications for future related research are provided.

Interaction between microplastic biofilm formation and antibiotics: Effect of microplastic biofilm and its driving mechanisms on antibiotic resistance gene

As two pollutants with similar transport pathways, microplastics (MPs) and antibiotics (ATs) inevitably co-exist in water environments, and their interaction has become a topic of intense research interest for scholars over the past few years. This paper comprehensively and systematically reviews the current interaction between MPs and ATs, in particular, the role played by biofilm developed MPs (microplastic biofilm). A summary of the formation process of microplastic biofilm and its unique microbial community structure is presented in the paper. The formation of microplastic biofilm can enhance the adsorption mechanisms of ATs on primary MPs. Moreover, microplastic biofilm system is a diverse and vast reservoir of genetic material, and this paper reviews the mechanisms by which microplastics with biofilm drive the production of antibiotic resistance genes (ARGs) and the processes that selectively enrich for more ARGs. Meanwhile, the enrichment of ARGs may lead to the development of microbial resistance and the gradual loss of the antimicrobial effect of ATs. The transfer pathways of ARGs affected by microplastic biofilm are outlined, and ARGs dependent transfer of antibiotic resistance bacteria (ARB) is mainly through horizontal gene transfer (HGT). Furthermore, the ecological implications of the interaction between microplastic biofilm and ATs and perspectives for future research are reviewed. This review contributes to a new insight into the aquatic ecological environmental risks and the fate of contaminants (MPs, ATs), and is of great significance for controlling the combined pollution of these two pollutants.

Microcosmic mechanism analysis of the combined pollution of aged polystyrene with humic acid and its efficient removal by a composite coagulant

The composite pollutants formed by aged polystyrene (APS) and natural organic matter are complex and harmful, which lead to the deterioration of water quality. In this work, the interaction mechanism between humic acid (HA) and APS was discussed by investigating the changes in their functional groups. Besides, a novel polyaluminum-titanium chloride composite coagulant (PATC) was prepared, and its binding behaviors with HA@APS under different pH conditions were analyzed from a microscopic perspective. It was found that at pH 4, π-π conjugation was the dominant interaction between HA and APS. And the main removal mechanism of HA@APS by PATC was surface complexation. With the increase of pH, π-π conjugation, n-π electron donor-acceptor interaction (EDA), and hydrogen bonding gradually dominated the interaction between APS and HA. At pH 7, PATC hydrolyzed to form various polynuclear Al-Ti species, which could meet the demand for different binding sites of HA@APS. Under alkaline conditions, HB and n-π EDA in HA@APS were weakened, while π-π conjugation held a dominant position again. At this time, the main coagulation mechanism of PATC changed from charge neutralization to sweeping action, accompanied by hydrogen bonding. ENVIRONMENTAL IMPLICATION: Microplastics (MPs) have attracted the public's attention due to their potential toxicity to humans. The combined pollution of aged microplastics and humic acid (HA) will bring great harm to aquatic environment. The development of novel composite coagulants is hopeful to efficiently remove MPs and their combined pollutants. Elucidating the interactions between HA and aged MPs is helpful to understand the transformation and fate of MPs in actual environments, and to reveal the removal mechanism of composite pollutants by coagulation. The findings presented here will provide theoretical guidance for addressing the challenges of coagulation technology in treating new pollutants in practice.

The fate and risk of microplastic and antibiotic sulfamethoxazole coexisting in the environment

With huge amount of plastic entering to the environment, microplastic pollution has become a great concern. Microplastic behavior in the environment is important to evaluate its harm to ecosystem and human beings. It has been found that microplastic can be used as a carrier to adsorb and enrich heavy metals or organic pollutants in water or soil. With the development of industry and medicine, antibiotics are improperly used in many countries and most of them end up in wastewater. This study investigates the adsorption behavior of sulfamethoxazole (SMX) antibiotic onto virgin and aged polyamide 6 (PA6) microplastics. The maximum adsorption amount was 0.089 mg SMX/g PA6 at 25 °C and pH 7 with initial SMX concentration of 2 mg/L. Results reveal that the adsorption was mainly due to the chemical bounding. The impact of pH, salinity, and humic acid on the adsorption have been studied, and it was found that the pH has significant impact on the adsorption. At pH 5, the adsorption amount was 0.27 mg/g which is two times higher than that at pH 7. The SMX adsorbed on PA6 tends to be more likely desorbed in reservoir water than in ultrapure water. For instance, the desorption amount of SMX from virgin PA6 was 0.15 mg/L in reservoir water but 0.10 mg/L in ultrapure water. The study indicates that microplastics have great threat to environment.

Removal of pristine and aged microplastics from water by magnetic biochar: Adsorption and magnetization

Adsorption is an efficient and eco-friendly removal technique for small pristine microplastics in water. However, small pristine microplastics are not representative of those large microplastics in natural water with different aging levels. Whether the adsorption technique is effective in removing large aged microplastics from water remained unknown. To this end, the removal efficiency of large polyamide (PA) microplastics with different aging time by magnetic corncob biochar (MCCBC) was evaluated under different experimental conditions. After treated by heated-activated potassium persulfate, the physicochemical properties of PA have changed dramatically, as evidenced by rough surface, decreased particle size and crystallinity, and increased oxygen-containing functional groups, which enhanced with aging time. These changes promoted the combination of aged PA and MCCBC, thereby resulting in a higher removal efficiency of aged PA (~97 %) than that of pristine ones (~25 %). It is supposed that the adsorption process was a result of complexation, hydrophobic interaction, and electrostatic interaction. Increased ionic strength inhibited the removal of both pristine and aged PA, and neutral pH conditions favored PA removal. Furthermore, particle size played a great role in the removal of aged PA microplastics. When the particle size of aged PA was smaller than 75 μm, their removal efficiency was significantly increased (p < 0.01). The small PA microplastics were removed by adsorption, whereas the large ones were removed by magnetization. These research findings highlight magnetic biochar as promising technique for removing environmental microplastics.

Aged polyamide microplastics enhance the adsorption of trimethoprim in soil environments

Microplastics (MPs) in the environment typically age. However, the influence of aged MPs on the adsorption of antibiotics in soil remains unknown. In this study, the adsorption behavior of trimethoprim (TMP) on soil and soil containing aged polyamide (PA) was investigated using batch and stirred flow chamber experiments. The adsorption of TMP on the tested soil with and without PA was fast, with the k_a values ranging from 50.5 to 55.6 L (mg min)^-1. The adsorption of TMP on aged PA was more than 20 times larger than that on the tested soil, which resulted in an "enrichment effect." Furthermore, aged PA altered the pH of the reaction system, thereby enhancing the adsorption of TMP. Consequently, the K_d values of TMP for soil, soil containing 5%, and 10% aged PA were 5.64, 12.38, and 23.65 L kg^-1, respectively. The effect of aged PA on the adsorption of TMP on soil depended on pH values. However, TMP adsorption on soil containing 10% aged PA was constantly higher (p < 0.01) than that on soil with NaCl concentrations ranging from 0 to 50 mmol L^-1. These findings provide new insights into the effect of environmental MPs on the fate and transport of antibiotics in soil environments.

Sulfide- and UV-induced aging differentially affect contaminant-binding properties of microplastics derived from commercial plastic products

Microplastics in the environments can undergo various aging processes that alter their physicochemical properties and consequently their affinities for environmental contaminants. Here, we compare the effects of sulfide-induced aging (a common process in anoxic environments) and UV-induced aging on contaminant binding of polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET) microplastics derived from commercial plastic products. The two aging processes differentially affect adsorption of pyrene (a model nonionic, nonpolar organic) and ciprofloxacin (CIP, a zwitterion under the conditions tested) by modulating the hydrophobicity, surface charges and polarity of the microplastics to different extents. The effects of the two treatments on Cd(II) adsorption correlate well with their modulation on ζ potential and surface (O + S)/C ratio of the microplastics. For all three microplastics sulfide treatment results in stronger adsorption of Cr(VI) and its subsequent conversion to Cr(III) than does UV treatment, as the thiol groups formed during sulfide treatment strongly regulate the complexation and reduction of Cr(VI). Notably, both sulfide and UV treatments result in the flattening of the PET microplastics, significantly enhancing the adsorption of all four contaminants, by increasing surface area for adsorption. The findings of this study further underline the importance of understanding environmental aging/weathering processes of microplastics, particularly, those readily occur in anoxic environments but were previously not well studied.

Characteristics and behaviors of microplastics undergoing photoaging and Advanced Oxidation Processes (AOPs) initiated aging

The fact that 94% of microplastics (MPs) ubiquitous in the environment are subject to natural weathering makes the aging study currently a research hotspot. This review summarized the physicochemical characteristics of MPs undergoing natural and artificial aging and evaluated current analytical methods used in aging studies. Besides, the differences in photoaging and aging induced by advanced oxidation processes (AOPs) were discussed, leading to a conclusion that AOPs composed of oxidant and ultraviolet (UV) irradiation can better facilitate the alteration of MPs compared to UV irradiation alone. In addition, the environmental behavior of aged MPs was outlined and their adsorption properties for organics and metals were highlighted as a result of combined effects of hydrophobic, π-π, diffusion, and hydrogen bond interaction. Furthermore, the mechanisms of photoaging and AOPs-initiated aging were analyzed, mainly the role of reactive oxygen species (ROS) and environmentally persistent free radicals (EPFRs). Finally, the applications of two-dimensional correlation spectroscopy (2D-COS) and three-dimensional fluorescence spectra using excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were discussed for the aging process analysis. This overview plays an important role in explaining the aging characteristics of MPs and provides a theoretical foundation for further investigations into their toxicity and removal.

Recent developments in microplastic contaminated water treatment: Progress and prospects of carbon-based two-dimensional materials for membranes separation

Micro (nano)plastics pollution is a noxious menace not only for mankind but also for marine life, as removing microplastics (MPs) is challenging due to their physiochemical properties, composition, and response toward salinity and pH. This review provides a detailed assessment of the MPs pollution in different water types, environmental implications, and corresponding treatment strategies. With the advancement in nanotechnology, mitigation strategies for aqueous pollution are seen, especially due to the fabrication of nanosheets/membranes mostly utilized as a filtration process. Two-dimensional (2D) materials are increasingly used for membranes due to their diverse structure, affinity, cost-effectiveness, and, most importantly, removal efficiency. The popular 2D materials used for membrane-based organic and inorganic pollutants from water mainly include graphene and MXenes however their effectiveness for MPs removal is still in its infancy. Albeit, the available literature asserts a 70- 99% success rate in micro/nano plastics removal achieved through membranes fabricated via graphene oxide (GO), reduced graphene oxide (rGO) and MXene membranes. This review examined existing membrane separation strategies for MPs removal, focusing on the structural properties of 2D materials, composite, and how they adsorb pollutants and underlying physicochemical mechanisms. Since MPs and other contaminants commonly coexist in the natural environment, a brief examination of the response of 2D membranes to MPs removal was also conducted. In addition, the influencing factors regulate MPs removal performance of membranes by impacting their two main operating routes (filtration and adsorption). Finally, significant limitations, research gaps, and future prospects of 2D material-based membranes for effectively removing MPs are also proposed. The conclusion is that the success of 2D material is strongly linked to the types, size of MPs, and characteristics of aqueous media. Future perspectives talk about the problems that need to be solved to get 2D material-based membranes out of the lab and onto the market.

Effect of pH on Adsorption of Tetracycline Antibiotics on Graphene Oxide

Graphene oxide (GO) has good dispersibility and adsorption capacity for antibiotics adsorption, a complex process influenced by many factors. In this work, the adsorption mechanism of GO on tetracycline antibiotics at different pH was studied to address its attenuated effects on the microbial growth. The results showed that the adsorption process of GO on three antibiotics, namely, tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC), followed the pseudo-second-order kinetic model. The maximum adsorption capacities were observed at pH5 which were 133.0 mg/g for TC, 125.4 mg/g for OTC, and 167.0 mg/g for CTC. Furthermore, the reaction was uniform adsorption with a single layer on the surface of GO, and heating was conducive to the reaction. In the microbial growth experiment, the growth of E. coli and B. subtilis senses was optimal at pH5, which was consistent with the adsorption experiment. This study analyzed the effect of pH on the adsorption of antibiotics by GO and provided a theoretical basis for the further application of GO in various aquatic environments.

Heavy metal-mediated adsorption of antibiotic tetracycline and ciprofloxacin on two microplastics: Insights into the role of complexation

Microplastics (MPs) have recently become an emerging environmental concern. Nevertheless, limited information is known about the adsorption of MPs for organic contaminants under combined heavy metals pollution, with an emphasis on the role of complexation. Thus, this study aims to comprehensively compare and investigate the adsorption performance of antibiotic tetracycline (TC) and ciprofloxacin (CIP) on two polar MPs (polyamide (PA) and polyvinyl chloride (PVC)) affected by Cu(II) and Cd(II) with contrasting complexation abilities. Batch adsorption experiments were used in combination with speciation calculation, zeta potential determination, FTIR spectroscopy characterization and investigation of the affinity of MPs for heavy metals. Results showed that the sorption kinetics and isotherms of TC and CIP on PA and PVC could be well fitted to pseudo-second-order and Langmuir models, respectively, both in the absence and presence of Cu and Cd, suggesting that multiple interactions and monolayer adsorption played an important role in the adsorption process. The presence of Cu substantially improved TC and CIP adsorption and obviously changed the pH dependence of their adsorption onto both MPs, which may result from the Cu-induced strong complexation with TC and CIP. The presence of Cd slightly enhanced TC adsorption on both MPs while reduced CIP adsorption especially on PVC, which may be ascribed to the Cd-induced cationic bridging effects in TC adsorption and the competitive adsorption of Cd in CIP adsorption. Therefore, the heavy metal-mediated complexation effects may play a dominant role in antibiotic adsorption by MPs only in the presence of heavy metals with strong complexation ability while the adsorption performance in the presence of heavy metals with negligible complexation capacity may be influenced by effects other than complexation. This study helps further understand the heavy metal-mediated adsorption behavior of organic contaminants on polar MPs and the role of complexation reactions therein.

Removal and toxic forecast of microplastics treated by electrocoagulation: Influence of dissolved organic matter

In recent years, the break of COVID-19 makes the large use of disposable products, which causes the removal of microplastics become an imperative problem. Electrocoagulation is one of the effective removal technologies, but there is hardly research concentrating on the effect of substrate in the actual water on the microplastics removal with electrocoagulation. As an important role of water bodies, dissolved organic matter (DOM) has a vital and inevitable effect on the efficiency of electrocoagulation. In this study, the effect of DOM in tailwater on microplastics during electrocoagulation is elucidated by comparing the electrocoagulation treatment results between simulated wastewater and tailwater, using parallel factor analysis (PARAFAC), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrometer (FTIR) and zeta potential analyzer. Three kinds of microplastic particles (i.e. polypropylene, polyethylene, and polymethyl methacrylate) were added into each of the two kinds of wastewaters to form six electrocoagulation systems. Results show that DOM in tailwater promotes the production of flocs and free radicals during electrocoagulation process. Fe²⁺ and Fe³⁺ are adsorbed on the surface of DOM molecules and combined with •OH form flocs. Although DOM accelerates the production of free radicals and thus promotes the aging of microplastics, flocs with DOM as crystal nucleus can prevent toxic substances and small-sized microplastics from leaching into water again. Therefore, electrocoagulation is preferred to removal microplastics in water with high concentration of DOM. This study provides a significant reference for microplastics removal by electrocoagulation in actual water, and promote the practical application of electrocoagulation for microplastics removal in water treatment.

Synthesis of mesoporous-structured MIL-68(Al)/MCM-41-NH2 for methyl orange adsorption: Optimization and Selectivity

Here, we report a novel amino-modified mesoporous-structured aluminum-based metal-organic framework adsorbent, MIL-68(Al)/MCM-41-NH₂, for dye sewage treatment. The introduction of molecular sieves overcomes the inherent defects of microporous MOFs in contaminant transfer and provides more active sites to enhance adsorption efficiency. Compared with using organic amino ligands directly, this strategy is ten times cheaper. The composite was well characterized and analyzed in terms of morphology, structure and chemical composition. Batch experiments were carried out to study the influences of essential factors on the process, such as pH and temperature. In addition, their interactions and the optimum conditions were examined using response surface methodology (RSM). The adsorption kinetics, isotherms and thermodynamics were systematically elucidated. In detail, the adsorption process conforms to pseudo-second-order kinetics and follows the Sips and Freundlich isothermal models. Moreover, the maximum adsorption capacity Q_s of methyl orange (MO) was 477 mg g^-1. It could be concluded that the process was spontaneous, exothermic, and entropy-reducing. Several binary dye systems have been designed for selective adsorption research. Our material has an affinity for anionic pigments. The adsorption mechanisms were discussed in depth. The electrostatic interaction might be the dominant effect. Meanwhile, hydrogen bonding, π-π stacking, and pore filling might be important driving forces. The excellent thermal stability and recyclability of the adsorbent are readily noticed. After five reuse cycles, the composite still possesses a removal efficiency of 90% for MO. Overall, the efficient and low-cost composite can be regarded as a promising adsorbent for the selective adsorption of anionic dyes from wastewater.

Responses of cherry radish to different types of microplastics in the presence of oxytetracycline

Croplands have become a hotspot for antibiotic and microplastic (MP) pollution. However, little is known regarding their combined effects on crops. In this study, the individual and combined effects of oxytetracycline (OTC) and three MPs (i.e., polypropylene (PP), polyamide (PA), and polyvinylchloride (PVC)) on cherry radish were investigated using pot experiments. Individually, OTC (50 mg kg^-1), PA (2%, w/w), and PP (2%, w/w) induced negligible effects on cherry radish biomass and the root/shoot ratio. However, PVC (2%, w/w) significantly inhibited cherry radish growth; that is, its shoot and root fresh weight decreased by 46.2% and 81.1%, respectively. In the combined exposure groups, OTC alleviated the adverse effects of PVC on the cherry radish leaf number and shoot fresh weight. This was linked to that OTC increased the content of photosynthetic pigments. Superoxide dismutase activity in cherry radish roots was inhibited to different extents in all treatment groups except for the PA and PVC treatments. Malondialdehyde (MDA) content in cherry radish roots increased in all treatment groups, suggesting that both OTC and MPs caused oxidative damage to cherry radish root cells, therefore inhibiting cherry radish root growth. However, the presence of OTC non-significantly changed the effects of MPs on cherry radish roots. Irrespective of OTC presence, MPs induced a reduction in the root/shoot ratio of cherry radish, suggesting that the inhibitory effect of MPs on cherry radish roots was stronger than that on shoots. These findings contribute to the evaluation of the phytotoxicity of antibiotics and MPs in soil-vegetable systems.

Quantitative assessment of interactions of hydrophilic organic contaminants with microplastics in natural water environment

The interaction between microplastics (MPs) and hydrophilic organic contaminants (HOCs) in natural water environment has recently raised great public attentions due to the potential toxicity to humans. However, the quantitative assessment is less studied. In this study, the interaction between ciprofloxacin (CIP) and ofloxacin (OFL) (two important HOCs) and virgin and aged polystyrene (PS) was investigated. The aged PS showed higher adsorption rate and capacity than the virgin PS, due to its larger surface area and more O-containing groups. The pH-dependent adsorption of CIP was higher than OFL on both virgin and aged PS; the maximum adsorption for both HOCs occurred at pH 5. The sequential orders of functional groups for the adsorption were discovered according to the study by the 2D correlation Fourier transform infrared spectroscopy. Several mechanisms existed for the interaction: (1) at 3.0 < pH < 5.0, the electrostatic attraction (EA) was inhibited while H-bond (HB) was dominant, accounting for > 60% of the total uptake; (2) at 5.0 < pH < 8.0, the contribution of EA increased to around 50-60% while HB decreased to 30-40%; (3) at 8.0 < pH < 10.0, EA, HB and π-π conjugation caused 30-40%, 25-40% and 20-45% of the total uptake, respectively; (4) at 10.0 < pH < 12.0, π-π conjugation accounted for 90-100%. Notably, higher adsorption of CIP was mainly attributed to the presence of secondary amino groups and its higher pK_a value, correspondingly leading to the additional ordinary HB and negative charge-assisted HB, and EA interactions with PS. This study further provides clear evidences on the risk of MPs and HOCs on humans and aqueous living organisms.

Adsorption of Different Pollutants by Using Microplastic with Different Influencing Factors and Mechanisms in Wastewater: A Review

The studies on microplastics are significant in the world. According to the literature, microplastics have greatly specific surface areas, indicating high adsorption capacities for highly toxic pollutants in aquatic and soil environments, and these could be used as adsorbents. The influencing factors of microplastic adsorption, classification of microplastics, and adsorption mechanisms using microplastics for adsorbing organic, inorganic, and mixed pollutants are summarized in the paper. Furthermore, the influence of pH, temperature, functional groups, aging, and other factors related to the adsorption performances of plastics are discussed in detail. We found that microplastics have greater advantages in efficient adsorption performance and cost-effectiveness. In this paper, the adsorptions of pollutants by microplastics and their performance is proposed, which provides significant guidance for future research in this field.