The interaction mechanisms of algal organic matter (AOM) and various types and aging degrees of microplastics

Algal blooms can produce substantial amounts of algal organic matter (AOM). Microplastics (MPs) in aquatic environments inevitably interact with AOM. Meanwhile, the aging and type of MPs may increase the uncertainty surrounding interaction. This study focused on polyethylene (PE) and polylactic acid (PLA) to investigate their interaction with AOM before and after aging. The results shw that PLA has a stronger adsorption capacity for AOM than PE. Meanwhile, aging enhanced and weakened the adsorption of PE and PLA for AOM. Compared to unaged PE (UPE) and aged PLA (APLA), aged PE (APE) and unaged PLA (UPLA) more significantly promote the humification of AOM and alter its functional groups. 2D-IR-COS analysis reveals that the sequence of functional group changes in AOM interacting with MPs is influenced by the type and aging of MPs. After interacting with AOM, surface roughness increased for all MPs. FTIR and XPS analyses show that the addition of AOM accelerated the oxidation of MPs surfaces, especially for UPE and APLA, with oxygen content increasing by 9.32 % and 1 %. Aging enhances the interaction between PE and AOM, while weakening the interaction between PLA and AOM. These findings provide new insights into understanding the interplay between AOM and MPs.

Weak static magnetic fields facilitated highly efficient 2,4,6-trichlorophenol removal by sulfurized nanoscale zero-valent iron supported on biochar (BC-SNZVI) at neutral pH

Sulfurized nanoscale zero-valent iron supported on biochar (BC-SNZVI) has been successfully synthesized for 2,4,6-trichlorophenol (2,4,6-TCP) removal, while was only effectively under acidic conditions. To obtain highly efficient removal of 2,4,6-TCP within a broader pH range, weak static magnetic fields (WMF) was applied in BC-SNZVI/2,4,6-TCP aqueous systems. Results showed 30 mT WMF supported the most extensive 2,4,6-TCP removal, and 87.4% of 2,4,6-TCP (initial concentration of 30 mg/L) was removed by 0.5 g/L BC-SNZVI at neutral pH (pH = 6.8) within 180 min, which was increased by 54.4% compared to that without WMF. The observed rate constant (Kobs) under 30 mT WMF was 2.1-fold greater than that without WMF. Although three typical anions (NO3- (0.5-10.0 mM), H2PO4- (0.05-0.5 mM), and HCO3- (0.5-5.0 mM)) still inhibited 2,4,6-TCP removal, WMF could efficiently alleviate the inhibitory effects. Moreover, 73.1% of 2,4,6-TCP was successfully removed by BC-SNZVI under WMF in natural water. WMF remarkably boosted the dechlorination of 2,4,6-TCP, increasing the 2,4,6-TCP dechlorination efficiency from 45.2% (in the absence of WMF) to 83.8% (in the presence of WMF) by the end of 300 min. And the complete dechlorination product phenol appeared within 10 min. Force analysis confirmed the magnetic field gradient force (FB) moved paramagnetic Fe2+ at the SNZVI surface along the direction perpendicular to the external applied field, promoting the mass-transfer controlled SNZVI corrosion. Corrosion resistance analysis revealed WMF promoted the electron-transfer controlled SNZVI corrosion by decreasing its self-corrosion potential (Ecorr). With the introduction of sulfur, the magnitude of FB doubled and the Ecorr decreased comparing with NZVI. Our findings provide a facile and viable strategy for treating chlorinated phenols at neutral pH.

The structural transformation reversibility of biogas slurry derived dissolved organic matter and its binding properties with norfloxacin under temperature fluctuation

The widespread use of biogas slurry could potentially raise the environmental risk of antibiotics. Dissolved organic matter (DOM), as the most active part of biogas slurry, was able to interact with antibiotics and play a crucial role in the structure and function of soil and aquatic ecosystems. The recent shifts in global climate patterns have garnered significant attention due to their substantial impact on temperature, thereby exerting a direct influence on the characteristics of DOM and subsequently on the environmental behavior of antibiotics. However, there is limited research concerning the impact of temperature on the binding of DOM and antibiotics. Thus, this study aimed to explore the temperature-dependent structural transformation and driving factors of biogas slurry-derived DOM (BSDOM). Additionally, the binding characteristics between BSDOM and the commonly used antibiotic norfloxacin (NOR) at different temperatures were studied by using multi spectroscopic methods and two-dimensional correlation spectroscopy (2D-COS) analysis. The results suggested that the temperature-dependent structural transformation of BSDOM was reversible, with a slight lag in the transition temperature under cooling (13 °C for heating and 17 °C for cooling). Heating promoted the conversion of protein-like to humic-like substances while cooling favored the decomposition of humic-like substances. BSDOM and NOR were static quenching, with oxygen-containing functional groups such as C-O and -OH playing an important role. Temperature influenced the order of binding, the activity of the protein fraction, and its associated functional groups. At temperatures of 25 °C and 40 °C, the fluorescent components were observed to exhibit consistent binding preferences, whereby the humic-like component demonstrated a greater affinity for NOR compared to the protein-like component. However, the functional group binding order exhibited an opposite trend. At 10 °C, a new protein-like component appeared and bound preferentially to NOR, when no C-O stretch corresponding to the amide was observed. The finding will contribute to a comprehensive understanding of the interaction mechanisms between DOM and antibiotics under climate change, as well as providing a theoretical basis to reduce the environmental risks of biogas slurry and antibiotics.

Mechanistic insight into the role of typical microplastics in chlorination disinfection: Precursors and adsorbents of both MP-DOM and DBPs

Microplastics (MPs) in drinking water are predominantly < 10 µm. The leaching of MPs derived dissolved organic matters (MP-DOM) from 5 µm polypropylene MPs (PP-MPs) and polystyrene MPs (PS-MPs) and the formation of MP-DOM derived disinfection byproducts during chlorination disinfection were first investigated. Comparably, PS-MPs are more vulnerable to chlorination and the primary attacks are on para C in aromatic side-chains via electrophilic Cl-substitution and oxidation by two-electron transfer. The O/C and Cl/C ratio of polystyrene MPs was linear and exponential versus initial available Cl2 concentrations, respectively. The significant PS-DOM leaching was observed with initial available Cl2 of 4.0 mg/L (USEPA recommended upper dose). As the initial available Cl2 concentration increased to 8.0 mg/L, the adsorption of chloro-phenolic-components of 200 Daltons in PS-DOM by 5 µm PS-MPs was observed for the first time. Trichloromethane (TCM) was identified as the dominant disinfection byproduct with a formation potential of 60.3 ± 7.8 and 73.7 ± 9.8 μg/mg for PS-DOM and PP-DOM, respectively. The derived TCM could adsorb onto PS-MPs followed the pseudo-second-order kinetic and Langmuir isotherm models. Extreme chlorination could reduce the maximal adsorption capacity of TCM on 5 µm PS-MPs from 196.68 ± 48.66 to 146.02 ± 32.98 μg/g. Thus, PS-MPs act as precursors and carriers of TCM in chlorination.

Estimated microplastic stress and potential affiliated toxic elements on phytoplankton in a floodplain-lake system

Hazards associated with microplastics (MPs) and the pollutants they absorb in freshwater lake ecosystems have become a hot research topic in academia. In this study, in order to investigate potential affiliated MP hazards, lake MP samples were collected from a typical subtropical freshwater lake system in China (Poyang Lake) during the dry season (here, you should show the specific months) to explore their potential toxic element (PTE) response (i.e., exposure to Cu, Pb, and Zn) respective to the ecological environment and resident phytoplankton. Results show that average MP abundance in surface water can reach up to 1800 items m-3, which higher in the Nanjishan Wetland National Nature Reserve (NWNNR) (1175 items m-3). Polyester (i.e., purified terephthalic acid [PTA]) and polyethylene (PE) were the main polymer types found in surface water, fiber was the main MP shape, and most of the MP particle sizes are greater than 100 μm. Moreover, phytoplankton biomass was significantly higher in the NWNNR compared to Poyang Lake's retention basin and water channel. It indicated that MP pollutant status of Poyang Lake is mild; however, the ecological risks that MPs pose should not be ignored. The significant positive correlation between MPs and PTEs indicated that PTE absorption and desorption by MPs may cause potential ecological stress. Although we anticipate no direct link between ecotoxicity and phytoplankton, MPs may have indirect effects on phytoplankton through their regulatory effects on PTE levels in water.

Insight into the effect of microplastics on the adsorption and degradation behavior of thiamethoxam in agricultural soils

Thiamethoxam and microplastics are both common pollutants in farmland soil; however, few studies have focused on the interaction between thiamethoxam and microplastics in soil. Here, a batch experiment and soil incubation experiment were performed to explore the mechanism and effects of microplastics on the adsorption and degradation behaviors of thiamethoxam in soil, respectively. First, the batch experimental results indicated that the adsorption process of thiamethoxam on the microplastic/soil mixtures and soil-only systems mainly relies on chemical interactions. All sorption processes had moderate intensities of adsorption, and the sorption process occurred on the heterogeneous surface. In addition, the particle size and dose of microplastics could both affect the adsorption behavior of thiamethoxam onto microplastics/soil systems. The sorption capacity of thiamethoxam in soil decreases as the particle size of microplastics increases, but the sorption capacity increases as the dose of microplastics increases. Second, the results of the soil incubation experiment showed that the half-lives of thiamethoxam ranged from 57.7 d to 86.6 d, from 86.6 d to 173.3 d, and 115 d in the biodegradable microplastic/soil systems, nondegradable microplastic/soil systems, soil-only systems, respectively. These results indicate that biodegradable microplastics promoted the degradation of thiamethoxam, while nondegradable microplastics delayed the degradation process of thiamethoxam in soil. Overall, microplastics could change the degradation behaviors, sorption capacity and adsorption efficiency, and then affect the mobility and persistence of thiamethoxam in the soil environment. These findings contribute to understanding the influence of microplastics on the environmental fate of pesticides in the soil environment.

Competitive adsorption of lead and cadmium onto nanoplastics with different charges: Two-dimensional correlation spectroscopy study

The competitive adsorption ability and mechanisms of lead (Pb²⁺) and cadmium (Cd²⁺) by nanoplastics (NPs) with positive charges (PS-NH₂) and negative charges (PS-SO₃H) were investigated by using batch adsorption experiments coupled with the two-dimensional correlation spectroscopy (2D-COS) method. The adsorption isotherm results showed that PS-SO₃H exhibited a higher adsorption capacity for Pb²⁺ or Cd²⁺ compared to PS-NH₂. The adsorption affinity of NPs for Pb²⁺ was higher than that of Cd²⁺. The competitive adsorption results showed that Pb²⁺ had a more pronounced negative effect on the adsorption of Cd²⁺. The adsorption capacities of NPs were affected by the surface charge and solution pH. Electrostatic force was the main factor influencing PS-SO₃H to capture Pb²⁺ and Cd²⁺, while chelation was the main mechanism between PS-NH₂ and metals. The functional groups of NPs played significant roles in the sorption of Pb²⁺ or Cd²⁺ according to the FTIR spectra and 2D-COS analysis. This study provided new insights into the impact of NPs on the transport of other pollutants.

Effects of humic acids on the adsorption of Pb(II) ions onto biofilm-developed microplastics in aqueous ecosystems

Microplastics (MPs), as emerging contaminants can behave as carriers for heavy metals in the water environments. Although the adsorption performance of heavy metals on MPs has been widely investigated, the effects of humic acids (HA) on the adsorption have seldom been explored. The authors were compared the Pb(II) adsorption onto biofilm-developed polyvinyl chloride (Bio-PVC) MPs with Pb(II) adsorption onto virgin PVC MPs (V-PVC), and explored the relationship between surface characteristics and the adsorption properties in the coexistence of HA. Our results showed that due to a larger specific surface area and more oxygen containing groups, Bio-PVC had a larger adsorption capability with a value of 3.57 mg/g than original ones (1.85 mg/g) due to its huge specific surface area and more oxygen containing groups. Microbial community analysis showed that the predominate bacteria in biofilms as Proteobacteria, Acidobacteria, Cyanobacteria, Firmicutes, and Bacteroidetes. Notably, the Pb(II) adsorption onto the V-PVC surfaces was increased, but the adsorption capacities of Pb(II) on Bio-PVC were suppressed with increasing HA. With the co-existence of HA, the increasing complexation and electrostatic attraction had attributed to the increased Pb(II) adsorption ability on V-PVC. Except for its competitive ability, HA has a shield effect which decreases the sorption sites on Bio-PVC. Overall, our findings provide a better understanding of the HA effect on the adsorption mechanism of heavy metals onto MPs in aquatic ecosystems.

Interaction of Antibiotics and Humic Substances: Environmental Consequences and Remediation Prospects

The occurrence and distribution of antibiotics in the environment has received increasing attention due to their potential adverse effects on human health and ecosystems. Humic substances (HS) influence the mobility, reactivity, and bioavailability of antibiotics in the environment significantly due to their interaction. As a result, HS can affect the dissemination of antibiotic-resistance genes, which is one of the main problems arising from contamination with antibiotics. The review provides quantitative data on the binding of HS with fluoroquinolones, macrolides, sulfonamides, and tetracyclines and reports the proposed mechanisms of their interaction. The main issues of the quantification of antibiotic-HS interaction are discussed, which are a development of standard approaches and the accumulation of a dataset using a standard methodology. This would allow the implementation of a meta-analysis of data to reveal the patterns of the binding of antibiotics to HS. Examples of successful development of humic-based sorbents for fluoroquinolone and tetracycline removal from environmental water systems or polluted wastewaters were given. Data on the various effects of HS on the dissemination of antibiotic-resistance genes (ARGs) were summarized. The detailed characterization of HS properties as a key point of assessing the environmental consequences of the formation of antibiotic-HS complexes, such as the dissemination of antibiotic resistance, was proposed.

Biodegradation of tylosin in swine wastewater by Providencia stuartii TYL-Y13: Performance, pathway, genetic background, and risk assessment

Microbial bioremediation offers a solution to the problem of residual antibiotics in wastewater associated with animal farms. Efficient degradation of antibiotic residues depends upon the genetic make-up of microbial degraders, which requires a comprehensive understanding of the degradation mechanisms. In this study, a novel, efficient tylosin (TYL)-degrading bacterium, Providencia stuartii TYL-Y13 (Y13) was isolated, which could completely degrade 100 mg/L TYL within 15 h under optimal operating conditions at 40 ℃, pH 7.0 %, and 1 % (v/v) bacterial inoculation rate. Whole genome sequencing revealed that strain Y13 consists of a circular chromosome and two plasmids. A new biodegradation pathway of TYL including desugarification, hydrolysis, and reduction reactions was proposed through the analysis of biodegradation products. It was demonstrated that strain Y13 gradually decreased the biotoxicity of TYL and its metabolites based on the results of the ecological structural activity relationships (ECOSAR) model analysis and toxicity assessment. Moreover, Y13 promoted the reduction of the target macrolide resistance genes in wastewater and disappeared within 84 h. These results shed new light on the mechanism of TYL biodegradation and better utilization of microbes to remediate TYL contamination.

A Review on Heavy Metal Ion Adsorption on Synthetic Microfiber Surface in Aquatic Environments

Synthetic microfibers (SMFs), tiny particles which gets fragmented from large fragments of large synthetic fibers having less than 10 µm in diameter, have gathered ubiquitously in each and every corner of the earth. After their release into the aquatic environment, they remain there without natural degradation. Furthermore, it can be anticipated that floating units are transported along the food chain leading to bioaccumulation. It has been estimated that approximately 10-20 Mt of large fabric products as garbage enter into aquatic system per annum. Recently, these synthetic fragments have been investigated as transporters of heavy metal ions (HMs) showing different types of interactions. Yet, the underlying mechanism of these types of interaction is not known, especially the factors stimulating this process and how badly they affect biotic communities. Through this article, a detailed survey was carried out on the sources of microfibers and HMs into the aquatic environment, adsorption of different types of HMs on the SMF surface, mechanics favors these HM-MF interactions, particularly highlighting the significant roles of interaction on microbial biofilm formation. Their collaborative effects which possess harmful effects on aquatic as well as terrestrial organisms was also discussed. Lastly, the future investigations should focus on rigorous research in this field. This article to the best of our knowledge briefly describes the current research developments and emphasizes the vital function of the microorganisms on MFs-HMs interactions with the encouragement for rigorous research in this field to reveal accurate mechanisms and decrease the hazards related with MF presence.

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.

Assessment of goethite-combined/modified biochar for cadmium and arsenic remediation in alkaline paddy soil

The opposed transformation of arsenic (As) and cadmium (Cd) in paddy soil postures numerous challenges for their simultaneous remediation. An incubation study was conducted on the immobilization of Cd and As by biochar (BC), goethite (G), goethite-combined biochar (BC + G), and goethite-modified biochar (GBC). The results showed that biochar effectively immobilized Cd while significantly increasing As mobility, whereas goethite effectively immobilized As more than Cd. BC + G treatment significantly decreased toxicity characteristics leaching procedure (TCLP) and CaCl₂-extractable Cd by 22.70% and 40.15%; meanwhile, TCLP and NaHCO₃-As were significantly reduced by 38.25% and 31.87%, respectively, compared with the control. This study found that GBC was the optimum amendment within the immobilization efficiency for CaCl₂-Cd (57.03%) and TCLP-As (61.11%). BC + G and GBC applications showed some interactions between biochar and goethite, which played an essential role in immobilizing Cd and As simultaneously. Therefore, GBC showed a great benefit in being a low-cost and efficient environmental amendment for Cd and As remediation in alkaline co-contaminated paddy soil.

Exploring the adsorption behavior of benzotriazoles and benzothiazoles on polyvinyl chloride microplastics in the water environment

As a kind of emerging pollutant, microplastics (MPs) play an important role as a carrier for pollutant migration in the water environment. Carried by the MPs, benzotriazoles, and benzothiazoles (collectively referred to as BTs)¹ are ubiquitous water contaminants. In this paper, the adsorption behavior of BTs on polyvinyl chloride (PVC) MPs was first studied systematically to explain the adsorptive mechanisms and the consequential pollution caused by the absorption-desorption process. The studies on kinetics, isotherms, and thermodynamics revealed that the adsorption of BTs on PVC MPs was a multi-rate, heterogeneous multi-layer, and exothermic process, which was affected by external diffusion, intra-particle diffusion, and dynamic equilibrium. The factors including pH, salinity, and particle size also influenced the adsorption process. In the multi-solute system, competitive adsorption would occur between different BTs. The desorption of BTs from PVC MPs was positively associated with the increase of adsorption amount. Based on the results, the adsorption mechanisms of PVC MPs were clarified, involving hydrophobic interaction, electrostatic force, and non-covalent bonds. It was demonstrated that BTs in the water environment could most probably be accumulated and migrated through MPs, and eventually carried into organisms, posing an increased risk to the ecological environment.

Behavior and mechanism of atrazine adsorption on pristine and aged microplastics in the aquatic environment: Kinetic and thermodynamic studies

Microplastics (MPs) are emerging pollutants that have gained much attention due to their potential harm to aquatic ecosystems and organisms. In particular, MP conjugates are loaded with chemical contaminants (e.g., atrazine pesticide), which may be ingested by organisms and can pose higher risks. However, the combined pollution effects and interaction mechanisms remain poorly understood. In this study, we systematically explored the adsorption behaviors and mechanisms of atrazine (ATZ) on pristine and aged MPs using kinetics, isotherms, and thermodynamic models. The target MPs included polystyrene (PS), polyethylene (PE), and polypropylene (PP) as well as the corresponding aged types. Moreover, the effects of pH, humic acid (HA), ionic strength, and ion species (Cl^-, SO₄^2-, HCO₃^-, Mg²⁺, and Ca²⁺) of aqueous factors were evaluated. The adsorption capacities of MPs under kinetic equilibrium conditions were as follows: aged PE (0.940 mg g^-1) > aged PP (0.677 mg g^-1) > aged PS (0.663 mg g^-1) > PS (0.565 mg g^-1) > PE (0.535 mg g^-1) > PP (0.410 mg g^-1). The adsorption kinetics and isotherm model results suggested a combination of physisorption and chemisorption. The aging process and pH significantly affected the intrinsic charge on the surface of the MPs and their adsorption capacities. Moreover, the presence of water medium parameters might enhance or inhibit adsorption of different MPs. Hydrophobic and electrostatic attraction mainly contributed to the adsorption of ATZ on pristine MPs, whereas complex surface diffusion and hydrogen bonding dominated the ATZ adsorption on aged MPs with more oxygen-containing groups. In addition, we examined the desorption performance of ATZ from MPs under simulated gastric and intestinal conditions of warm-blooded animals, and found that the ATZ desorption ratio of aged PE (35.3%) showed the most significant effects among the six target types of MPs. This study provides in-depth insights into the co-existence and complex behaviors of MPs and the pesticide pollutant ATZ, to attract further attention to their ecological risks in freshwater environments.

Characteristics of tylosin and enrofloxacin degradation in swine manure digested by black soldier fly (Hermetia illucens L.) larvae

Black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) larvae (BSF larvae or BSFL) offer an environmental-friendly method for degrading antibiotics, such as tylosin (TYL) and enrofloxacin (EF), in swine manure. This study examined the impact of temperature on this process, role of associated microbes, dynamics of resistant genes, and a description of the microbial community associated with the BSF larval gut, how microbes isolated from the BSF larval gut as inoculants impact the process as well as enhance antibiotic digestion, and finally a quantification of antibiotics in BSF larvae fed manure with TYL or EF. Antibiotic degradation in manure was optimized at 28 °C with at least 10% greater than 23 °C and 37 °C. More than 40% reduction in TYL and EF concentrations in the manure occurred when BSF larval gut associated microbes were present. Furthermore, DNA extracted from the gut of non-sterile BSF larvae fed manure with TYL or EF indicated at least two 2^-△△Ct fold increase in antibiotic resistance genes for TYL and EF. We identified 250, 4, and 16 unique operational taxa for larvae fed control manure and manure with either TYL or EF. Intestinal microbes isolated from non-sterile larvae fed manure with TYL or EF, were identified, cultured, and examined for their ability to degrade TYL and EF in Luria-Bertani (LB) medium. Three strains (two strains of Enterococcus faecalis and one strain of Proteus mirabilis) resulted in at least 50% TYL or EF degradation within 96 h. Sterile BSF larvae inoculated with P. mirabilis recovered >60% of the degradation ability exhibited by non-sterile larvae. Finally, no TYL residuals were found in 14-d-old larvae, prepupae, or pupae of BSF immatures fed manure containing these antibiotics. While ∼65 μg/g and ∼20 μg/g of EF were found in larval contents and pupal exoskeleton, respectively.

A Zn/Co bimetal zeolitic imidazolate framework material as a catalyst to activate persulfates to degrade tylosin in aqueous solutions

The bimetallic catalyst ZIF-11(Zn/Co)-2 activates persulfates and has an excellent removal effect on tylosin in aqueous solutions.

Interactions Between Microplastics and Heavy Metals in Aquatic Environments: A Review

Microplastics (MPs), tiny particles broken down from larger pieces of plastics, have accumulated everywhere on the earth. As an inert carbon stream in aquatic environment, they have been reported as carriers for heavy metals and exhibit diverse interactive effects. However, these interactions are still poorly understood, especially mechanisms driving these interactions and how they pose risks on living organisms. In this mini review, a bibliometric analysis in this field was conducted and then the mechanisms driving these interactions were examined, especially emphasizing the important roles of microorganisms on the interactions. Their combined toxic effects and the potential hazards to human health were also discussed. Finally, the future research directions in this field were suggested. This review summarized the recent research progress in this field and highlighted the essential roles of the microbes on the interactions between MPs and heavy metals with the hope to promote more studies to unveil action mechanisms and reduce/eliminate the risks associated with MP presence.

Sorption of Sulfamethoxazole on Inorganic Acid Solution-Etched Biochar Derived from Alfalfa

The properties of alfalfa-derived biochars etched with phosphoric (PBC) or hydrochloric acid (ClBC) compared with raw materials (BC) were examine in this paper. SEM, FT-IR, XRD, BET and elemental analysis were performed to characterize the micromorphology and chemical structure comprehensibly. The results showed that the porous structure was enhanced, and surface area was increased via etching with inorganic acids. Batch adsorption experiments were performed for sulfamethoxazole (SMX) to biochars. The experimental data showed that modified biochars exhibited higher adsorption capacity for SMX, i.e., the adsorption quantity of ClBC and PBC had risen by 38% and 46%. The impact on pH values suggested that the physisorption, including pore-filling and electrostatic interaction, might be applied to original biochar. In addition, chemisorption also played a role, including hydrogen bonding, π-π electron donor acceptor interaction (π-π EDA), and so on. Furthermore, both pH and coexisting ions also had a certain effect on sorption. Enhancement of the electrostatic attraction between biochar and SMX might also account for the enhanced capacity of SMX at pH < 7, and coexisting ions could decrease the amount of SMX adsorbed onto biochars, mainly because of competition for adsorption sites.

Sorption of pharmaceuticals and personal care products on soil and soil components: Influencing factors and mechanisms

The sorption of pharmaceuticals and personal care products (PPCPs) on soil and soil components makes an important contribution to the fate, migration and bioavailability of PPCPs. Previous reviews have mostly focused on the sorption of PPCPs on single soil components (e.g., minerals and soil organic matter). However, the sorption of PPCPs within the whole soil system has not been systematically analyzed. This paper reviews the recent progress on PPCP sorption on soil and soil components. We have evaluated the sorption of a wide range of PPCPs in research fields that are usually considered in isolation (e.g., humic acids (HAs), montmorillonite, kaolinite, and goethite), and established a bridge between PPCPs and sorbent. The sorption mechanisms of PPCPs, e.g., cation exchange, surface complexation, electrostatic interaction and hydrogen bonding, are discussed and critically evaluated. We also assessed the influence of environmental factors (pH, ionic strength, organic matter and temperature) on sorption. This review summarizes the knowledge of PPCPs sorption on soil gained in recent years, which can provide new strategies for solving the problem of antibiotic pollution.

Adsorption of nitrification inhibitor nitrapyrin by humic acid and fulvic acid in black soil: characteristics and mechanism

The compound nitrapyrin is easily adsorbed by soil organic matter in high-organic matter soils, and this results in its effectiveness reducing significantly. In this study, the adsorption characteristics and mechanisms of nitrapyrin as an adsorptive on humic acid (HA) and fulvic acid (FA) as adsorbents were investigated. The results showed that the kinetics of adsorption of nitrapyrin on both HA and FA followed pseudo-second-order kinetic models (R² ≥ 0.925, P < 0.05) and the adsorption process included an initial fast-adsorption stage and a slow-adsorption stage thereafter. The adsorption efficiencies of nitrapyrin on HA + FA were higher than that on HA or FA alone, and that of HA was higher than that of FA. The adsorption isotherms of nitrapyrin on HA and FA could be optimally fitted with the Langmuir equation (R² ≥ 0.982, P < 0.05). The maximum adsorption capacities of nitrapyrin on HA, FA and HA + FA were 4896.49, 3173.70 and 4925.56 mg kg⁻¹, respectively. Synergistic adsorption of nitrapyrin in co-existing systems of HA and FA was also observed. The adsorption mechanism of nitrapyrin on both HA and FA involved hydrogen bonding and hydrophobic interaction. Therefore, HA and FA in the soil environment can adsorb a large amount of nitrapyrin and reduce its effectiveness, and they have a positive synergistic effect.

The compound nitrapyrin is easily adsorbed by soil organic matter in high-organic matter soils, and this results in its effectiveness reducing significantly.

Adsorption of chlorophenols on polyethylene terephthalate microplastics from aqueous environments: Kinetics, mechanisms and influencing factors

Microplastics have received growing attention as carriers of organic pollutants in the water environment. To better understand the contribution of hydrophobic interaction, hydrogen-bonding interaction, π-π interaction and electrostatic interaction on the adsorption of hydrophilic compounds on microplastics and their adsorption behavior in natural waters, polyethylene terephthalate (PET, <150 μm) was used as an adsorbent and 4-chlorophenol (MCP), 2,4-dichlorophenol (DCP) and 2,4,6-trichlorophenol (TCP) were used as adsorbates. The results of batch adsorption experiments showed that chlorophenols (CPs) reached adsorption sites of PET through film diffusion and intra-particle diffusion. pH greatly affected the adsorption capacity. Hydrophobic interaction was the main adsorption mechanism of undissociated CPs on PET. Hydrogen-bonding interaction was also an adsorption mechanism between undissociated CPs and PET, and the contribution of hydrogen-bonding interaction to adsorption decreased with the increase of chlorine content. Meanwhile, the increase of chlorine content was favorable to the hydrophobic interaction between undissociated CPs and PET. However, higher chlorine content CPs with lower pK_a values tended to dissociate at neutral pH condition and resulted in stronger electrostatic repulsion with PET. The increase of solution ionic strength and fulvic acid content negatively affected the adsorption of DCP and TCP on PET, but did not show significant impacts on MCP adsorption. Similarly, the adsorption capacity obtained using Taihu lake water and Bohai seawater as matrices was much lower than that using laboratory water for both DCP and TCP, while the adsorption coefficient (K_d) of MCP remained at approximately 10.6 L/kg to 11.4 L/kg in the three different solution matrices. The K_d values exhibited using natural water matrices consistently followed the order of DCP > MCP > TCP. This study provides insights into the fate of CPs in the presence of microplastics and suggests that the potential risks posed by CPs and microplastics to aqueous ecosystems merit further investigation.

Cellulase modified waste biomass to remove sulfamethazine from aqueous solutions

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

Adsorption behavior and mechanism of five pesticides on microplastics from agricultural polyethylene films

Polyethylene (PE) agricultural soil films are easily embrittled and decomposed to microplastics (MPs) in environment. As widely used pesticides in vegetable farmland, carbendazim, dipterex, diflubenzuron, malathion, difenoconazole have potential environmental and human safety risks. They are often coexisting with MPs in the environment, and may cause consequential pollution to the ecosystem. Studying the adsorption behavior between pesticides and PE agricultural soil films MPs would be helpful for the risk assessment of co-exposure of pesticides and MPs. Herein, a systematic study on batch adsorption experiments was performed to determine the adsorption process of pesticides on MPs, the environmental factors on adsorption capacity were evaluated, and the adsorption mechanisms were discussed. Results suggested that all these five pesticides can adsorb on MPs, especially for diflubenzuron and difenoconazole. The adsorption kinetics and isotherm fitted to the Pseudo-second-order and Freundlich model, respectively, indicating that besides the adsorption onto surface sites, mass transfer and intraparticle diffusion were involved in the adsorption process, and the adsorption process was mostly controlled by physical and chemical interactions. The adsorption amounts of 5 pesticides on PE MPs follow the order of DIF > DIFE > MAL > CAR > DIP with K_F correlated positively with octanol-water partition coefficients (LogK_ow). The thermodynamic study indicates the adsorption of all pesticides as spontaneous and exothermic processes. The results of this study illustrated that PE MPs can be a good carrier of pesticides in agricultural field.

Pb(II) uptake onto nylon microplastics: Interaction mechanism and adsorption performance

Both heavy metals and microplastic pollutants are ubiquitous in the aquatic environment. The uptake of lead(II) ions from aqueous solutions onto aged nylon microplastics was investigated as a function of pH, contact time, temperature, supporting electrolyte concentration and fulvic acid concentration in batch studies. The effect of surface properties on the adsorption behavior of lead(II) was investigated with scanning electron microscope equipped with the energy dispersive X-ray spectroscope (SEM-EDAX), Fourier transform-infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA), X-ray diffraction (XRD) and differential scanning calorimetric (DSC). The adsorption kinetics conformed to the pseudo-second order equation, Elovich equation and intraparticle diffusion model well. The experimental data of the adsorption process was fitted to the Langmuir and Freundlich adsorption isotherms and the parameters were estimated. The lead(II) uptake on aged nylon microplastics was spontaneous and endothermic in nature. The lead(II) adsorption was significantly dependent on the sodium chloride concentrations, initial solution pH and fulvic acid concentrations. Results of this study highlight the importance of surface carboxyl function group of aged nylon microplastics in controlling lead(II) adsorption.

Sorption properties of cadmium on microplastics: The common practice experiment and A two-dimensional correlation spectroscopic study

Microplastics (MPs) that have accumulated in the environment are emerging as contaminating pollutants due to their interactions with metal ions. MPs change the migration and transformation of metal ions in the environment and afterward impact their environmental presence. Therefore, it is necessary to evaluate the interaction characteristics and mechanisms between Cd²⁺and MPs for assessing the ecological impacts of MPs. The traditional sequencing batch equilibrium test demonstrated that the sorption of Cd²⁺ onto MPs was related to the type of MPs present, the pH value of the solution, the ionic strength of the participants and the presence of humic acid. The sorption dynamics and isotherm experiment illustrated that the interactions were controlled by surface sorption and distribution effects. The specific surface area and surface charge were the main factors in managing the sorption process. FTIR spectra and a 2D-COS analysis showed that different functional groups played an important role in the sorption of Cd²⁺onto MPs. The results from this work afford new insights on how MPs may play an important role in the fate and transport of heavy metals and present a new analysis method for evaluating the environmental behavior of MPs and their role in transporting other contaminants.

Noncovalent interactions between fluoroquinolone antibiotics with dissolved organic matter: A 1H NMR binding site study and multi-spectroscopic methods

Fluoroquinolone antibiotics (FQs) are considered to be emerging environmental contaminants that have been detected extensively in aquatic environment. It is of quite importance to explore FQs interacting with dissolved organic matter (DOM). The interactions of FQs with DOM were examined by nuclear magnetic resonance (NMR) spectroscopy, fluorescence quenching, UV-vis, Fourier transform infrared (FT-IR) spectroscopic techniques. The bindings of FQs to DOM had one single binding site and their quenching mechanisms were static, which were evaluated by the Stern-Volmer and Site-binding equations. Addition of DOM could result in micro-environmental changes of fluorophores groups in FQs. The location adjacent oxygen right of Ofloxacin (OFL) and the aromatic ring (the adjacency replaced by two nitrogen-containing groups) of Ciprofloxacin (CIP), Enrofloxacin (ENR), Norfloxacin (NOR) might be highly affected by DOM molecule. The negative enthalpy change (ΔH⁰), negative entropy change (ΔS⁰) and the positive Gibbs' energy change (ΔG⁰) figured out that the binding processes were exothermic but not thermodynamic favorable, the formation of HA-FQs complexes would be powered chiefly by the ΔS⁰. H-bonding, electrostatic effect, van der Waals force were the acting force in the binding reactions and the π-π stacking effect was the major binding force under alkaline conditions. Moreover, the protonated, deprotonated, or partially protonated state of FQs were found to have different binding capacity to DOM, and the binding reactions for FQs-HA system were suppressed as the ionic strength increased. Meanwhile, alterations of FQs conformation in the presence of DOM were evaluated by FT-IR and UV-vis spectra.

Sorption properties of tylosin on four different microplastics

After oxidation, abrasion and crushing, microplastics (MPs) can enter the aqueous environment and may adsorb surrounding organic pollutants, altering its migration and spatial distribution. Therefore, an investigation of the sorption properties and mechanism of organic pollutant on MPs can offer a theoretical basis for scientific evaluation of their ecological risks. Using tylosin (TYL) as a model pollutant, the sorption performance of MPs was examined via a series of batch equilibrium experiments which resulted the sorptive removal of TYL on MPs reached equilibrium at 36 h, and the sorption ability of TYL on the MPs followed the order of PE (polyethylene) < PP (polypropylene) < PS (polystyrene) < PVC (polyvinyl chloride). The pseudo-second-order model well fit for the sorption kinetics data, and the adsorption isotherms could be better described by Freundlich equation rather than Langmuir model. Additionally, the initial solution pH and ionic strength played important roles across the adsorption. The sorption procedure of TYL on MPs was dominated by electrostatic interaction, surface complexation and hydrophobic interaction.

Iron and manganese oxides modified maize straw to remove tylosin from aqueous solutions

Maize straw modified by iron and manganese oxides was synthesized via a simple and environmentally friendly method. Three maize straw materials, the original maize straw, maize straw modified by manganese oxides and maize straw modified by iron and manganese oxides, were detected by SEM, BET, XPS, XRD and FTIR. The results showed that maize straw was successfully modified and maize straw modified by iron and manganese oxides has a larger surface area than MS. According to the experimental data, the sorption trend could conform to the pseudo-second-order kinetic model well, and the sorption ability of tylosin on sorbents followed the order of original maize straw < maize straw modified by manganese oxides < maize straw modified by iron and manganese oxides. The study indicated that manganese oxides and iron-manganese oxides could significantly enhance the sorption capacity of original maize straw. The sorption isotherm data of tylosin on original maize straw fit a linear model well, while Freundlich models were more suitable for maize straw modified by manganese oxides and maize straw modified by iron and manganese oxides. The pH, ionic strength and temperature can affect the sorption process. The sorption mechanisms of tylosin on iron and manganese oxides modified maize straw were attribute to the surface complexes, electrostatic interactions, H bonding and hydrophobic interactions.

Maize straw decorated with sulfide for tylosin removal from the water

MS-ZnS and MS-ZnS:Mn complexes were synthesized via a simple method. The results showed that sulfide was successfully loaded on the maize straw. The results of fitting the experimental data showed that the sorption conforms to the pseudo-second-order kinetics, and the TYL sorption on MS fit the Henry model well, but the Freundlich model was more suited to MS-ZnS and MS-ZnS:Mn. In addition, the k_f values of MS-ZnS (206.0(mg/kg)/(mg/L)ⁿ) and MS-ZnS:Mn (382.5(mg/kg)/(mg/L)ⁿ) were significantly greater than that of MS (72.2(mg/kg)/(mg/L)ⁿ), indicating that ZnS and ZnS:Mn could improve the sorption capacity of TYL on MS. The pH, ionic strength and temperature influence the sorption process, and the sorption ability of TYL on MS-ZnS and MS-ZnS:Mn showed little change when the solution pH was > 5; the amount of TYL sorption on the adsorbents gradually decreased with the increasing concentration of KNO₃. Electrostatic interactions, H bonding and hydrophobic interactions are involved in the sorption of TYL on MS, MS-ZnS and MS-ZnS:Mn, and compared with MS, the main mechanism is surface complexation. This research can provide technical support for the utilization of biomass and the restoration of water polluted by antibiotics.

Tylosin sorption to diatomaceous earth described by Langmuir isotherm and Freundlich isotherm models

Tylosin, an antibiotic used for maintaining livestock health, is a macrolide structurally similar to a number of important, often prescribed human antibiotics. Because of this relationship, tylosin presents a potential threat of antimicrobial resistance from environmental buildup. This work investigated tylosin sorption to natural diatomaceous earth product (DE) and the types of physical interactions responsible for sorption. Most sorption processes were best described by the Langmuir model when compared with Freundlich model. Heat of sorption (ΔH) was 1.14 kJ mol^-1 indicating a physisorption process. Change in entropy (ΔS) was 119 J mol^-1. Sorption was evaluated from aqueous solution with various H⁺, KCl and Urea concentrations. In 0.01 M phosphate buffer (PB) pH 6.6, a maximum sorption capacity of 15 mg tylosin per g of DE was achieved. Changing the pH to 2.9 or 11.2 resulted in decreased sorption of tylosin (13 and 10 mg g^-1, respectively). Addition of 1 M KCl to 0.01 M PB pH 6.6 decreased sorption of tylosin to DE with the maximum binding capacity of 7 mg g^-1. Sorption in 1.0 M urea, 0.01 M phosphate buffer pH 6.6 showed a maximum sorption of 13 mg g^-1. Based on these results, the sorption of tylosin appears to be a physisorption process, with charge-charge interactions being the mode of sorption at neutral pH and small contributions from secondary interactions. This information will be useful for developing effective strategies for mitigating tylosin and other antimicrobial's impact on the environment.

Factors influencing adsorption and desorption of trimethoprim on marine sediments: mechanisms and kinetics

Adsorption-desorption behavior of ionic antibiotics in natural aquatic environment is complex, especially in coastal or estuary area where influencing factors such as pH and salinity usually varied in a wide range. In this study, batch-type and stirred flow chamber (SFC) experiments were carried out to simulate the sorption-desorption behavior of trimethoprim (TMP) in seawater-sediment system. Equilibrium and kinetic modeling were carried out to determine the rate and extent of TMP sorption on two marine sediments with different properties. Sediment BHB (K _d , 6.40 L kg^-1) has a greater sorption capacity compared with sediment LZB (K _d , 3.40 L kg^-1), which is related to the higher content of organic carbon and clay of sediment BHB. Adsorption of TMP varied in the pH range of 6.9 to 8.1 with maximum adsorption at pH 7.4. Increasing salinity and presence of phosphate and nitrate led to decreased TMP sorption. Attenuated total reflection Fourier transform infrared (ATR-FTIR) analysis demonstrated the formation of hydrogen bond between TMP and marine sediments. Adsorption of TMP on marine sediments was a non-equilibrium process that can be described with second-order kinetic model. Our analysis suggested that chemical non-equilibrium was the rate controlling process and intraparticle diffusion was also involved in TMP adsorption. A moderate desorption percentage (16.4-22.8% for LZB and 32.5-42.0%for BHB) was observed. Overall, the results showed that environmental factors and time-dependent processes need to be considered in modeling the fate and transport of TMP in coastal/estuarine waters.

Rates and equilibria of perfluorooctanoate (PFOA) sorption on soils from different regions of China

Understanding sorption of PFOA on soil particles is crucial to evaluate its environmental risk. Here, sorption of PFOA onto ten agricultural soils was examined. The influence of soil physico-chemical properties on PFOA sorption was investigated. The sorption rate of PFOA followed a pseudo-second-order kinetics. Isotherm data of PFOA sorption was fitted with both Freundlich and linear models and the latter fitted better. The sorption-desorption of PFOA onto ten soil samples depended on soil organic carbon content and composition of soil minerals. The sorption and desorption isotherms of PFOA on ten soils were linear, except for the sorption of PFOA onto a few soils, which was described by the Freundlich equation with the parameter N >1. The main sorption mechanism of PFOA was hydrophobic interaction between the perfluorinated carbon chain and the organic matter of soil, as evidenced by the correlation between the solid-liquid distribution coefficient and the fraction of soil organic carbon. The sorption of PFOA in soils was highly irreversible.

Adsorption of sulfamethoxazole (SMZ) and ciprofloxacin (CIP) by humic acid (HA): characteristics and mechanism

The adsorption behavior and mechanisms of single adsorption and co-adsorption of ciprofloxacin and sulfamethoxazole with HA were studied in detail.

An efficient method for tylosin removal from an aqueous solution by goethite modified straw mass

Renewable agricultural residues are produced in large quantities as waste, and their storage and management create environmental problems.

Sorption and toxicity reduction of pharmaceutically active compounds and endocrine disrupting chemicals in the presence of colloidal humic acid

This study investigated the toxicity changes and sorption of pharmaceuticals and endocrine disrupters in the presence of humic acid (HA). For the sorption experiment, a dead end filtration (DEF) system was used to separate bound and free-form target compounds. An algae growth inhibition test and E-screen assay were conducted to estimate the toxic effect of pharmaceutically active compounds (PhACs) and endocrine disrupting chemicals (EDCs), respectively. The permeate concentration was confirmed using liquid chromatography-mass spectrometry. In the sorption test, we observed significant sorption of PhACs and EDCs on colloidal HA, except for sulfamethoxazole (SMX). The values of log KCOC derived from DEF determinations ranged from 4.40 to 5.03. The removal efficiency varied with the HA concentration and the target chemical properties. Tetracycline and 4-octylphenol showed the highest sorption or removal efficiency (≈50%), even at 5 mg C/L HA. The algal growth inhibition of PhACs and the estrogenic effects of EDCs were significantly decreased in proportion to HA concentrations, except for SMX. In addition, the chemical analysis results showed a positive relationship with the bioassay results. Consequently, the sorption of PhACs and EDCs onto colloidal HA should be emphasized in natural environments because it significantly reduces bioavailable concentrations and toxicity to aquatic organisms.

The physical–biological processes of petroleum hydrocarbons in seawater/sediments after an oil spill

Physical adsorption and biodegradation processes of crude oil in a seawater–sediment system.

Sorption and photodegradation of tylosin and sulfamethazine by humic acid-coated goethite

Humic acid and mineral oxides are simultaneously present in soils and can form organomineral complexes.