Sorption of tetracycline onto hexabromocyclododecane/polystyrene composite and polystyrene microplastics: Statistical physics models, influencing factors, and interaction mechanisms

Microplastic interactions with co-existing pollutants in water environments: Synergistic or antagonistic roles on their removal through current remediation technologies

Composite water pollution, caused by microplastics (MPs) and co-occurring pollutants, is an emerging issue that induces synergistic toxicity. Multidimensional interactions occur between MPs and co-existing pollutants in a composite system, which alter the behavior of each component, resulting in unpredictable effects on the treatment processes. However, significant gaps exist in current review papers regarding MP‒pollutant interaction mechanisms and the corresponding synergistic or antagonistic effects on their removal processes. This review comprehensively describes the latest research in composite water pollution caused by MPs and various other pollutants with different compositions and states, systematically discusses their interaction mechanisms, and critically evaluates the impact of co-existing contaminants on the treatment performance of current remediation technologies. Based on current research progress and gaps, opportunities, challenges, and perspectives for future research directions are proposed. This review highlights state-of-the-art research related to composite water pollution caused by MPs and various pollutants, which is expected to inspire new strategies for the effective removal of multiple contaminants from the aquatic environment.

Combined pollution of tetracyclines and microplastics in the aquatic environment: Insights into the occurrence, interaction mechanisms and effects

Tetracyclines, a widely used class of antibiotics, and synthetic plastic products are both prevalent in the environment. When released into water bodies, these pollutants can pose significant risks due to their daily influx into aquatic ecosystems. Microplastics can adsorb tetracyclines, acting as a transport vector that enhances their impact on aquatic species. Understanding the co-exposure effects of microplastics and tetracyclines is crucial. This review comprehensively examines the occurrence and distribution of microplastics and tetracyclines across various environmental contexts. The interactions between these two contaminants are primarily driven by electrostatic interactions, hydrophobic effects, hydrogen bonding, π-π interactions, and others. Factors such as the presence of heavy metals, ions, and dissolved organic matter can influence the adsorption and desorption of tetracyclines onto microplastics. The stability of microplastic-tetracycline complexes is highly dependent on pH conditions. The combined pollution tetracyclines and microplastics leads to negative impacts on marine species. Future research should focus on understanding the adsorption behavior of tetracyclines on microplastics and developing effective treatment techniques for these contaminants in aquatic environments.

Binding between Cu2+/Zn2+ and aged polyethylene and polyethylene terephthalate microplastics in swine wastewaters: Adsorption behavior, and mechanism insights

Microplastics (MPs) have aroused growing environmental concerns due to their biotoxicity and vital roles in accelerating the spread of toxic elements. Illuminating the interactions between MPs and heavy metals (HMs) is crucial for understanding the transport and fate of HM-loaded MPs in specific environmentally relevant scenarios. Herein, the adsorption of copper (Cu2+) and zinc (Zn2+) ions over polyethylene (PE) and polyethylene terephthalate (PET) particulates before and after heat persulfate oxidation (HPO) treatment was comprehensively evaluated in simulated and real swine wastewaters. The effects of intrinsic properties (i.e., degree of weathering, size, type) of MPs and environmental factors (i.e., pH, ionic strength, and co-occurring species) on adsorption were investigated thoroughly. It was observed that HPO treatment expedites the fragmentation of pristine MPs, and renders MPs with a variety of oxygen-rich functional groups, which are likely to act as new active sites for binding both HMs. The adsorption of both HMs is pH- and ionic strength-dependent at a pH of 4-6. Co-occurring species such as humic acid (HA) and tetracycline (TC) appear to enhance the affinity of both aged MPs for Cu2+ and Zn2+ ions via bridging complexation. However, co-occurring nutrient species (e.g., phosphate and ammonia) demonstrate different impacts on the adsorption, improving uptake of Cu2+ by precipitation while lowering affinity for Zn2+ owing to the formation of soluble zinc-ammonia complex. Spectroscopic analysis indicates that the dominant adsorption mechanism mainly involves electrostatic interactions and surface complexation. These findings provided fundamental insights into the interactions between aged MPs and HMs in swine wastewaters and might be extended to other nutrient-rich wastewaters.

Immobilization mechanisms of Sr(II), Ni(II), and Cd(II) on glomalin-related soil protein in mangrove sediments at the microscopic scale

Glomalin-related soil protein (GRSP) is a significant component in the sequestration of heavy metal in soils, but its mechanisms for metal adsorption are poorly known. This study combined spectroscopic data with molecular docking simulations to reveal metal adsorption onto GRSP's surface functional groups at the molecular level. The EXAFS combined with FTIR and XPS analyses indicated that the adsorption of Cd(II), Sr(II), and Ni(II) by GRSP occurred mainly through the coordination of -OH and -COOH groups with the metal. The -COOH and -OH groups bound to the metal as electron donors and the electron density of the oxygen atom decreased, suggesting that electrostatic attraction might be involved in the adsorption process. Two-dimensional correlation spectroscopy revealed that preferential adsorption occurred on GRSP for the metal in sequential order of -COOH groups followed by -OH groups. The presence of the Ni-C shell in the Ni EXAFS spectrum suggested that Ni formed organometallic complexes with the GRSP surface. However, Sr-C and Cd-C were absent in the second shell of the Sr and Cd spectra, which was attributed to the adsorption of Sr and Cd ions with large hydration ion radius by GRSP to form outer-sphere complexes. Through molecular docking simulations, negatively charged residues such as ASP151 and ASP472 in GRSP were found to provide electrostatic attraction and ligand combination for the metal adsorption, which was consistent with the spectroscopic analyses. Overall, these findings provided new insights into the interaction mechanisms between GRSP and metals, which will help deepen our understanding of the ecological functions of GRSP in metal sequestration.

Understanding Interface Exchanges for Assessing Environmental Sorption of Additives from Microplastics: Current Knowledge and Perspectives

Although the impacts of plastic pollution have long been recognized, the presence, pervasiveness, and ecotoxicological consequences of microplastic-i.e., plastic particles < 5 mm-contamination have only been explored over the last decade. Far less focus has been attributed to the role of these materials and, particularly, microplastics, as vectors for a multitude of chemicals, including those (un)intentionally added to plastic products, but also organic pollutants already present in the environment. Owing to the ubiquitous presence of microplastics in all environmental matrices and to the diverse nature of their chemical and physical characteristics, thoroughly understanding the mechanistic uptake/release of these compounds is inherently complex, but necessary in order to better assess the potential impacts of both microplastics and associated chemicals on the environment. Herein, we delve into the known processes and factors affecting these mechanisms. We center the discussion on microplastics and discuss some of the most prominent ecological implications of the sorption of this multitude of chemicals. Moreover, the key limitations of the currently available literature are described and a prospective outlook for the future research on the topic is presented.

Microplastic pollution in terrestrial ecosystems: Global implications and sustainable solutions

Microplastic (MPs) pollution has become a global environmental concern with significant impacts on ecosystems and human health. Although MPs have been widely detected in aquatic environments, their presence in terrestrial ecosystems remains largely unexplored. This review examines the multifaceted issues of MPs pollution in terrestrial ecosystem, covering various aspects from additives in plastics to global legislation and sustainable solutions. The study explores the widespread distribution of MPs worldwide and their potential antagonistic interactions with co-occurring contaminants, emphasizing the need for a holistic understanding of their environmental implications. The influence of MPs on soil and plants is discussed, shedding light on the potential consequences for terrestrial ecosystems and agricultural productivity. The aging mechanisms of MPs, including photo and thermal aging, are elucidated, along with the factors influencing their aging process. Furthermore, the review provides an overview of global legislation addressing plastic waste, including bans on specific plastic items and levies on single-use plastics. Sustainable solutions for MPs pollution are proposed, encompassing upstream approaches such as bioplastics, improved waste management practices, and wastewater treatment technologies, as well as downstream methods like physical and biological removal of MPs. The importance of international collaboration, comprehensive legislation, and global agreements is underscored as crucial in tackling this pervasive environmental challenge. This review may serve as a valuable resource for researchers, policymakers, and stakeholders, providing a comprehensive assessment of the environmental impact and potential risks associated with MPs.

Sequestration of strontium, nickel, and cadmium on glomalin-related soil protein: Interfacial behaviors and ecological functions

Glomalin-related soil protein (GRSP) is a widespread recalcitrant soil protein complex that promotes the immobilization of metals in soils. Herein, we combined indoor simulation and field investigation to reveal the interfacial behaviors and ecological functions of GRSP to the three typical metals (Sr(II), Ni(II), and Cd(II)). The kinetic and isotherm data suggested that GRSP had a strong ability to adsorb the metals, which was closely related to the Hard-Soft-Acid-Base theory and the film diffusion mechanisms. Regarding environmental factors, the higher solution pH was beneficial to the adsorption of the metals onto GRSP, while the adsorption capacity decreased at lower or higher salinity due to the salting-out and Na⁺ competition effects. Moreover, Sr(II), Ni(II), and Cd(II) showed competitive adsorption onto GRSP, which was associated with the spatial site resistance effect. By comparing the retention factors of seven natural and artificial particles, GRSP had elevated distribution coefficients in high metal concentration, while its retention factors showed a relatively lower decrease, suggesting that GRSP had excellent buffer performance for a potential metal pollution emergency. Through the continental-scale coastal regions investigation, GRSP sequestered 1.05-3.11 μmol/g Ni, 0.31-1.49 μmol/g Sr, and 0.01-0.06 μmol/g Cd with 0.54-0.91 % of the sediment mass, demonstrating its strong ability to adsorb the metals. Therefore, we advocate that GRSP, as a recalcitrant protein complex, can be considered an effective tool for buffering capacity of metal pollution and environmental capacity within coastal wetlands.

Adsorption behavior of aniline pollutant on polystyrene microplastics

Microplastic contamination is ubiquitous in aquatic environments. As global plastic production increases, the abundance of microplastic contaminants released into the environment has also continued to soar. The hydrophobic surfaces of plastic particles can adsorb a variety of chemical pollutants, and could therefore facilitate toxin accumulation through the food chain. In this study, the adsorption behavior of aniline, a priority environmental pollutant from industrial production, on the surface of polystyrene microplastics (mPS) was investigated. The results showed that the maximum adsorption capacity of mPS was 0.060 mg/g. Adsorption equilibrium was reached after 24 h, and the pseudo-second-order model was employed to explain the adsorption kinetics of aniline on the mPS particles. The Freundlich models could describe the adsorption isotherms. The potential adsorption mechanisms may include π-π interactions and hydrophobic interactions. pH, ionic strength, and ambient temperature of the solution played important roles in the adsorption process.

Multispectroscopic Characterization of Surface Interaction between Antibiotics and Micro(nano)-sized Plastics from Surgical Masks and Plastic Bottles

Recent studies have shown that plastic particles can sorb antibiotics, and these sorption properties have been examined in various studies; however, the possible mechanism responsible for the interactions requires a deeper investigation in terms of further interaction with living systems. Moreover, the usage of disposable surgical masks and plastic bottles has increased the plastic pollution risk for living systems like humans. Therefore, this study aimed to examine the sorption characteristics between antibiotics (amoxicillin and spiramycin) and plastic particles from surgical masks and plastic bottles through batch sorption experiments. In the study, their surface interactions were characterized using multispectroscopic approaches including FTIR, Raman spectrometry, and SEM-EDX, and various surface indicators (e.g., surface oxidation, deformation, and biological potential) were examined. The sorption results showed that adsorption kinetics and the isotherm of amoxicillin and spiramycin on micro(nano)plastics from surgical masks and plastic bottles closely fit the pseudo-second-order kinetic model and Langmiur isotherm. These results indicated that the evidence for the antibiotic interaction with particles was changes in the surface functional group intensities and up-shifting, and this correlated with the sorption of antibiotics on micro(nano)-sized plastics. The C/N ratio of the plastic particles before and after antibiotic treatment was used as an indicator for the surface biological interaction, and the results showed that C/N ratios of surgical mask particles increased with both types of antibiotic sorption. However, the C/N of the particles from plastic bottles showed antibiotic type-dependence. The surface deformation indicators (e.g., O/C, C=O, C=C, and O-H indices) showed that the O/C ratios of micro(nano)plastics from surgical masks were higher with the amoxicillin and spiramycin sorption, and the C=O indices were positively linked with the amoxicillin sorption stages, whereas the C=C and O-H had a negative correlation with the amoxicillin sorption stages. Moreover, amoxicillin sorption influenced the O/C ratio and indices of O-H and C=C of micro(nano)plastics from plastic bottles in a limited manner. The C=O groups of the micro(nano)plastics from plastic bottles were positively influenced by the spiramycin sorption stages, whereas it was negatively linked with amoxicillin sorption stages. Overall, the findings from surface indicators indicated that the micro(nano)plastics from surgical masks can be more influenced with antibiotic sorption compared to plastic bottles.

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.

Structure, mechanism, and toxicity in antibiotics metal complexation: Recent advances and perspectives

Antibiotic-metal complexes (AMCs) formed by antibiotics and metal ions have attracted considerable attentions in recent years. Although different removal methods for AMCs have been reported in the literature, very few investigations have focused on the mechanisms and toxic effects of antibiotic-metal coordination. This review briefly describes the structural characteristics of various commonly used antibiotics and the coordination mechanisms with metal ions. Considering the complexity of the real environment, various environmental factors affecting AMC formation are highlighted. The effects of AMCs on microbial community structure and the role of metal ions in influencing resistant genes from the molecular perspective are of interest within this work. The toxicities and mechanisms of AMCs on different species of biota are also discussed. These findings underline the need for more targeted detection and analysis methods and more suitable toxicity markers to verify the combination of antibiotics with metal ions and reveal environmental toxicities in future. This review presents an innovative idea that antibiotics combined with metal ions will change the toxicity and environmental behavior of antibiotics.

Adsorption of tetracycline and Cd(II) on polystyrene and polyethylene terephthalate microplastics with ultraviolet and hydrogen peroxide aging treatment

Microplastics (MPs) could serve as vectors of antibiotics and heavy metals through sorption and desorption. However, the combined adsorption process of antibiotics and heavy metals on aged MPs has rarely been studied. In this study, combined adsorption/desorption of tetracycline (TC) and Cd(II) on/from polystyrene (PS) and polyethylene terephthalate (PET) MPs, as well as ultraviolet (UV) and H₂O₂ aged MPs, was investigated. The specific surface areas of the MPs increased after UV and H₂O₂ aging. Adsorption experiments showed that the pseudo-second-order kinetic model and Freundlich model fitted adsorption of TC and Cd(II) on all of the MPs. The adsorption capacities of TC and Cd(II) were higher on aged MPs than on the pristine MPs, especially on H₂O₂ treated MPs. TC adsorption on the MPs was hardly affected by Cd(II), and Cd(II) adsorption was not significantly affected by TC when the solution pH value was below 8.0. Cd(II) slightly enhanced TC adsorption on the MPs at pH 8.0, especially on the aged MPs. The TC adsorption capacities increased with increasing pH, reaching a maximum at pH 5.0 or 6.0, and they then decreased, while the largest level of Cd(II) adsorption was at approximately pH 6.0. Adsorption of TC and Cd(II) on the pristine and aged MPs was thermodynamically favorable and spontaneous. The trend of the desorption rates of TC and Cd(II) from the MPs in different background solutions was ultrapure water < surface water < simulated gastric fluid. The desorption rates of TC and Cd(II) from the aged MPs were lower than those from the pristine MPs. The results revealed the mechanism of the TC and Cd(II) combined adsorption process on aged MPs, which will provide insight for understanding the aging process and its potential effects on sorption and desorption of antibiotics and heavy metals in the real environment.

Enhanced heavy metal adsorption on microplastics by incorporating flame retardant hexabromocyclododecanes: Mechanisms and potential migration risks

Microplastics (MPs) are known to act as carriers of heavy metals; however, little is known about the intrinsic chemical additives of MPs, such as hexabromocyclododecane (HBCD), in terms of the adsorption behaviors and migration risks of heavy metals on MPs. Here, we reported the potential mechanisms and risks of HBCD inherent in polystyrene (PS) MPs with Cu(II), Ni(II), and Zn(II) adsorption/desorption. A comparison of the adsorption capacity of the metals onto HBCD/PS composites (HBCD/PS) MPs (10.31-20.76 μmol/g), pure MPs (0-3.60 μmol/g), and natural minerals (0.11-13.88 μmol/g) showed that the addition of HBCD significantly promoted the metals adsorption onto the HBCD/PS MPs, and even exceeded that of natural particles. Isotherms and thermodynamic data suggested that the adsorption process of the metals onto the HBCD/PS MPs was spontaneous and endothermic, and that the adsorption was a mainly multi-ion process with an inclined direction. Furthermore, the results of SEM-EDS, FTIR, and XPS analyses, as well as density functional theory well explained that the metals were mainly adsorbed on the -O and -Br groups of the HBCD/PS MPs via electrostatic interactions and surface complexation. More importantly, by comparing the desorption activity with natural river water and seawater, HBCD inherent in MPs can enhance the long-range transfer of metals carried by the HBCD/PS MPs from contamination sources to potential sink like oceans. Thus, the HBCD/PS MPs with high loading of Cu(II), Ni(II), and Zn(II) could be potential secondary sources of these metals in seawater. Overall, these findings revealed the potential risks of flame retardant in MPs associated with metal migration, and advocated that flame retardant-related waste MPs should be included in coastal sustainable development.

Interactions of microplastics with organic, inorganic and bio-pollutants and the ecotoxicological effects on terrestrial and aquatic organisms

As emerging contaminants, microplastics (MPs) have attracted global attention. They are a potential risk to organisms, ecosystems and human health. MPs are characterized by small particle sizes, weak photodegradability, and are good environmental carriers. They can physically adsorb or chemically react with organic, inorganic and bio-pollutants to generate complex binary pollutants or change the environmental behaviors of these pollutants. We systematically reviewed the following aspects of MPs: (i) Adsorption of heavy metals and organic pollutants by MPs and the key environmental factors affecting adsorption behaviors; (ii) Enrichment and release of antibiotic resistance genes (ARGs) on MPs and the effects of MPs on ARG migration in the environment; (iii) Formation of "plastisphere" and interactions between MPs and microorganisms; (iv) Ecotoxicological effects of MPs and their co-exposures with other pollutants. Finally, scientific knowledge gaps and future research areas on MPs are summarized, including standardization of study methodologies, ecological effects and human health risks of MPs and their combination with other pollutants.

Co-occurence of antibiotics and micro(nano)plastics: a systematic review between 2016-2021

Pollution by plastics and antibiotics are emerging issues in the areas of the environment and human health. In recent years, several studies have documented the widespread occurrence of plastic particles in various environmental, as well as human, systems, and much research has focused on possible interactions of contaminants with microplastics. Thus, the co-occurrence of plastics and antibiotics has caused another global problem for the environment and human health. Therefore, we focused on the current knowledge in the field of the co-occurrence of plastics and antibiotics to summarize the available studies. In this review, categorization of the topics, contaminants details, such as polymer type, size and source, antibiotic type, and other experimental parameters were summarized and discussed. This study indicated that the sorption of antibiotics on plastics, antibiotic susceptibility in the presence of plastics, and antibiotic resistance gene onto plastics were the most frequently examined categories in this field. Moreover, the variability in the procedures and the processes, and the heterogeneity data of reporting between different studies on similar topic make it difficult to bring all results together and produce a comprehensive picture of the current knowledge. Therefore, it is suggested that further research should be done using this systematic study.

Post COVID-19 pandemic: Disposable face masks as a potential vector of antibiotics in freshwater and seawater

With the outbreak and widespread of the COVID-19 pandemic, large numbers of disposable face masks (DFMs) were abandoned in the environment. This study first investigated the sorption and desorption behaviors of four antibiotics (tetracycline (TC), ciprofloxacin (CIP), sulfamethoxazole (SMX), and triclosan (TCS)) on DFMs in the freshwater and seawater. It was found that the antibiotics in the freshwater exhibited relatively higher sorption and desorption capacities on the DFMs than those in the seawater. Here the antibiotics sorption processes were greatly related to their zwitterion species while the effect of salinity on the sorption processes was negligible. However, the desorption processes were jointly dominated by solution pH and salinity, with greater desorption capacities at lower pH values and salinity. Interestingly, we found that the distribution coefficient (K_d) of TCS (0.3947 L/g) and SMX (0.0399 L/g) on DFMs was higher than those on some microplastics in freshwater systems. The sorption affinity of the antibiotics onto the DFMs followed the order of TCS > SMX > CIP > TC, which was positively correlated with octanol-water partition coefficient (log K_ow) of the antibiotics. Besides, the sorption processes of the antibiotics onto the DFMs were mainly predominated by film diffusion and partitioning mechanism. Overall, hydrophobic interaction regulated the antibiotics sorption processes. These findings would help to evaluate the environmental behavior of DFMs and to provide the analytical framework of their role in the transport of other pollutants.