Structure-dependent surface catalytic degradation of cephalosporin antibiotics on the aged polyvinyl chloride microplastics

Presence of microplastic particles increased abundance of pathogens and antimicrobial resistance genes in microbial communities from the Oder river water and sediment

High abundance of microplastic particles (MPs) in the water environment could be a factor in spreading of pathogens and antimicrobial resistance genes (AMR), especially antibiotic resistance genes (ARGs). The aim of our study was to assess changes in the microbial community developing on microplastic surfaces incubated in water from the Oder River-one of Central Europe's major rivers, flowing through three countries (Czechia, Germany, and Poland)-whose diverse, 20,000-km2 catchment area (encompassing industrial, agricultural, and urban regions) ensures a relatively high abundance of microbial communities.Samples of water and sediment were taken from river in Wroclaw area. Then the water was poured into disinfected glass liquid containers and pre-drained sediment was added. Control samples of water and sediment were collected on day 0. Then microplastic particles were added (500 mg; ~ 1 mm). Subsequent sampling was performed after incubation on 7th and 14th day. From each group, samples of sediment and water were collected after the incubation period (n = 5/group), for extraction of microbial DNA and library preparation. Sequencing was performed, using MinION sequencer with 10.4.1 Flow cell. Galaxy Europe platform and R program (v 4.3.3), alpha diversity and PERMANOVA with Benjamini-Hochberg p-value correction for multiple comparisons were used. For identification of biomarker taxa being different between groups, ANCOMBC (Analysis of Compositions of Microbiomes with Bias Correction) was performed. Obtained results shown higher abundance of pathogenic bacteria such as Aeromonas salmonicida Vibrio spp., Escherichia coli or Salmonella after 7 days of incubation in water and sediment. Additionally, after 7 days of incubation numbers of ARGs was higher compared to control group.

Aquatic photochemistry for different dissociation forms of cephalosporin antibiotics: Degradation kinetics, products and photo-modified toxicity

Cephalosporin antibiotics (CFs) with ionizable groups (-COOH and -NHn) are widely detected as emerging micropollutants that pose potential environmental risks to aquatic systems, but few studies have revealed their multivariate photochemical transformation behavior in sunlight-irradiated surface waters. In this study, the apparent photodegradation, photo-oxidation towards reactive oxygen species (ROS, •OH and 1O2), and photo-modified toxicity were investigated for the four ionizable CFs: cefoxitin (CFX), cephalothin (CEF), cefoperazone (CFP) and cefazolin (CFZ). Under simulated sunlight irradiation (λ > 290 nm), their multivariate photo-transformation kinetics varied as a function of pHs and the dominant protonated states of the CF in question (H2CFs+, HCFs0 and CFs-). Based on competition kinetics and matrix deconvolution methods, the apparent photolytic rate constants (ki) of different dissociation forms were found to decrease gradually from H2CFs+ to CFs- then to HCFs0, which was dominated by the changing cumulative light absorption (∑(Lλελ,i)) for the different dissociated forms. Interestingly, it was observed that the H2CFs+ or CFs- exhibited higher reactivities towards •OH, while CFs- demonstrated the fastest reaction with 1O2. Using the theoretical derivation, the determined environmental half-lives of the CFs in sunlight-irradiated surface waters were closely dependent on the water pHs and multiple photochemical reaction types. In most cases, apparent photodegradation contributes more than ROS mediated photooxidation to the overall photo-transformation of CFs. The product identification using HPLC-MS/MS indicated that the photodegradation pathways mainly involved photoinduced hydrolysis of the β-lactam ring, cleavage of the side-chain, and decarboxylation. Based on the bioassay to Vibrio fischeri, the most CFs showed photo-enhanced toxicity, which was verified by the ECOSAR assessment, raising concerns about the formation and accumulation of more toxic intermediates. These results are of significance to better assessing the photochemical persistence and risk of the CFs in the aquatic systems and wastewater treatment.

Ecological and Health Risk Mediated by Micro(nano)plastics Aging Process: Perspectives and Challenges

Aged micro(nano)plastics (MNPs) are normally the ultimate state of plastics in the environment after aging. The changes in the physical and chemical characteristics of aged MNPs significantly influence their environmental behavior by releasing additives, forming byproducts, and adsorbing contaminants. However, a systematic review is lacking on the effects of aged MNPs on ecological and human health regarding the increasing but scattered studies and results. This Review first summarizes the unique characteristics of aged MNPs and methods for quantifying their aging degree. Then we focused on the potential impacts on organisms, ecosystems, and human health, including the "Trojan horse" under real environmental conditions. Through combining meta-analysis and analytic hierarchy process (AHP) model, we demonstrated that, compared to virgin MNPs, aged MNPs would result in biomass decrease and oxidative stress increase on organisms and lead to total N/P decrease and greenhouse gas emissions increase on ecosystems while causing cell apoptosis, antioxidant system reaction, and inflammation in human health. Within the framework of ecological and human health risk assessment, we used the risk quotient (RQ) and physiologically based pharmacokinetic (PBK) models as examples to illustrate the importance of considering aging characteristics and the degree of MNPs in the process of data acquisition, model building, and formula evaluation. Given the ecological and health risks of aged MNPs, our urgent call for more studies of aged MNPs is to understand the potential hazards of MNPs in real-world environments.

The wheel of time: The environmental dance of aged micro- and nanoplastics and their biological resonance

The aging of micro- and nanoplastics (MNPs) significantly affects their environmental behavior and ecological impacts in both aquatic and terrestrial ecosystems. This review explored the known effects of aging on MNPs and identified several key perspectives. Firstly, aging can alter the environmental fate and transport of MNPs due to changes in their surface properties. This alteration accelerates their accumulation in specific habitats like oceans and soils, resulting in increased bioaccumulation by organisms. In addition, aged MNPs interact differently with living organisms than their pristine counterparts by influencing the attachment of biofilms and other microorganisms in aquatic ecosystems. Moreover, the aging processes of MNPs exhibit adverse effects on aquatic and terrestrial organisms via increasing the bioavailability and potential toxicity of MNPs as degradation products are released. Last but not least, the biodegradation potential of MNPs can be altered by the aging process, thus affecting their degradation rates and pathways in the environment. However, there are still knowledge gaps regarding the natural aging behaviors of MNPs, such as the aging mechanisms of different types of plastic, the influence of environmental factors, the release of pollutants, and even the effects of aging on their transformation in different ecosystems. Therefore, a great contribution can be made to sustainable plastic use and environmental preservation by studying the natural aging of common MNPs and their subsequent biological effects.

Aging of Polystyrene Micro/Nanoplastics Enhances Cephalosporin Phototransformation via Structure-Sensitive Interfacial Hydrogen Bonding

Beyond their roles in adsorbing and transporting pollutants, microplastics (MPs) and nanoplastics (NPs), particularly polystyrene variants (PS-M/NPs), have emerged as potential accelerators for the transformation of coexisting contaminants. This study uncovered a novel environmental phenomenon induced by aged PS-M/NPs and delved into the underlying mechanisms. Our findings revealed that the aged PS-M/NP particles significantly amplified the photodegradation of common cephalosporin antibiotics, and the extent of enhancement was tightly correlated to the molecular structures of cephalosporin antibiotics. Notably, the results confirmed that the hydroxyl radical (OH•) acted as the primary agent to drive the accelerated degradation. Furthermore, in-depth analysis utilizing in situ Fourier transform infrared spectroscopy, batch adsorption experiments, and theoretical calculations underscored that the structure-dependent enhancement stemmed from the specific hydrogen bonding sites, rather than mere adsorption capacity. Specifically, the -OOH group (hydroperoxyl group) on the PS surface exhibited a greater potential to generate OH• compared to the -OH group. Therefore, cephalosporins that formed hydrogen bonds with -OOH moieties on the aged PS surfaces, as opposed to -OH, would experience a more pronounced degradation enhancement. Thus, the unique interaction pattern between contaminants and PS-M/NPs transforms aged PS into a selective reactor, facilitating the targeted degradation of pharmaceuticals in aquatic ecosystems.

Selective elimination of organic pollutants and analysis of effects and novel mechanisms of aged microplastics on wavelength-dependent UV-LED/H2O2 system

The selective removal of organic pollutants and potential impact of aged microplastics (MPs) as emerging pollutants in wavelength-dependent UV-LED/H2O2 system are not fully understood. This study found that cefalexin (CFX) degradation efficiency in UV-LED alone system was highly correlated with its UV molar absorbance (R2=0.994), while in UV-LED/H2O2 system, it was correlated with ·OH yield (R2=0.991) across various wavelengths. Quantitative structure-activity relationship (QSAR) analysis showed selective degradation of six pollutants based on their e--donating capabilities (R2=0.748-0.916). The coexistence of aged MPs, introducing C-O/C=O groups and rearranging their surface e-, potentially affected the elimination efficiency of CFX. Aged polystyrene (PS) decreased the degradation efficiency of CFX by shorting the O-O bond length (lO-O) in H2O2 and capturing e- from H2O2, whereas aged polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) had negligible effects as the lO-O elongation balanced the e--donating effect of H2O2. Additionally, phenol released from aged PS, with strong nucleophilicity, competing with CFX for ·OH, further decreasing CFX degradation efficiency. This study provides valuable insights into organic pollutant selective removal and reveals a novel inhibitory mechanism of aged PS on the performance of UV-LED/H2O2 technology.

Photochemical Transformation of Ibuprofen and Chlorophene Induced by Dissolved Organic Matter

Both ibuprofen (IBP) and chlorophene (CP) are frequently detected contaminants in surface aqueous environment. Dissolved organic matter (DOM) is an important component in water with high photo-reactivity, playing an important role in the transformation processes of various organic pollutants. This study systematically studied the influence of DOM on the photochemical transformation of IBP and CP by using humic acid as model DOM. In addition, the effect of inorganic salts on this process is also considered due to the high salt content in the ocean. Further quenching experiments and reactive oxygen species (ROSs) detection were also conducted to explore the reactive species acting on the IBP and CP transformation. Based on the products analysis and theoretical calculation, we proposed the IBP and CP transformation mechanism. Overall, this study provides some new insights into the transformation of organic pollutants in natural surface water, which is significant for assessing the fate of pollutants.

Unveiling the fast adsorption and desorption of heavy metals on/off nanoplastics by real-time in-situ potentiometric sensing

Nanoplastics (<1 μm) can serve as a transport vector of environmental pollutants (e.g., heavy metals) and change their toxicities and bioavailabilities. Up to date the behaviors of adsorption and desorption heavy metals on/off nanoplastics are largely unknown. Herein, polymeric membrane potentiometric ion sensors are proposed for in-situ assessment of the real-time kinetics of heavy metal adsorption and desorption on/off nanoplastics. Results show that nanoplastics can adsorb and release heavy metals in a fast manner, indicating their superior ability in transferring heavy metals. The adsorption behaviors are closely related to the characteristics of nanoplastics and background electrolytes. Particle aggregation and increases in salinity and acidity suppress the adsorption of heavy metals on nanoplastics. The desorption efficiencies of different heavy metals are Pb2+ (31 %) < Cu2+ (40 %) < Cd2+ (97 %). Our proposed method is applicable for the detection of the plastic pollutants with size <100 nm and of the samples with high salinities (e.g., seawater). This work would provide new insights into the assessment of environmental risks posed by nanoplastics and heavy metals.

Co-photoaging inhibited the heteroaggregation between polystyrene nanoplastics and different titanium dioxide nanoparticles

Heteroaggregation between nanoplastics (NPs) and titanium dioxide nanoparticles (TiO2NPs) determines their environmental fates and ecological risks in aquatic environments. However, the co-photoaging scenario of NPs and TiO2NPs, interaction mechanisms of TiO2NPs with (aged) NPs, as well as the dependence of their heteroaggregation on TiO2NPs facets remain elusive. We found the critical coagulation concentration (CCC) of polystyrene nanoplastics (PSNPs) with coexisting RTiO2NPs was 1.9 - 2.2 times larger than that with coexisting ATiO2NPs, suggesting a better suspension stability of PSNPs+RTiO2NPs. In addition, CCC of TiO2NPs with coexisting photoaged PSNPs (APSNPs) was larger 1.7 - 2.2 times than that with PSNPs coexisting, indicating photoaging inhibited their heteroaggregation due to increasing electrostatic repulsion derived from increased negative charges on APSNPs and the polymer-derived dissolved organic carbon. Coexisted TiO2NPs promoted oxidation of PSNPs with the action of HO· and O2·- under UV light, leading to inhibited heteroaggregation. Moreover, Van der Waals and Lewis-acid interaction dominated the formation of primary heteroaggregates of PSNPs-TiO2NPs (ESE = ‒2.20 ∼ ‒2.78 eV) and APSNPs-TiO2NPs (ESE = ‒3.29 ∼ ‒3.67 eV), respectively. The findings provide a mechanistic insight into the environmental process of NPs and TiO2NPs, and are significant for better understanding their environmental risks in aquatic environments.

A QSAR prediction model for adsorption of organic contaminants on microplastics: Dubinin-Astakhov plus linear solvation energy relationships

Numerous pharmaceuticals and personal care products (PPCPs) co-exist with various types of microplastics (MPs) in the environment, making it extremely hard to experimentally measure all their adsorption interactions. Thus, a precise prediction model is on demand. In this study, we combined the commonly used Dubinin-Astakhov (DA) model and the linear solvation energy relationships (LSERs) model to predict the adsorption capacity (Q0) and adsorption affinity (E) of MPs for PPCPs, including the key parameters of MP (specific surface area, oxygen-containing functional groups), and the Kamlet-Taft solvation parameters of organic contaminants. The model was validated with the experimental data of 8 PPCPs and 8 MPs (i.e. pristine and aged PE, PET, PS, PVC) plus some published adsorption data. This new model also indicated that the adsorption of PPCPs on those MPs was primarily governed by hydrophobic interaction and hydrogen bonding. The developed model can predict the adsorption of PPCPs onto MPs with a high accuracy and can also provide insights into the understanding of interaction forces in the adsorption process.

Selective enrichment of virulence factor genes in the plastisphere under antibiotic and heavy metal pressures

The growing accumulation of plastic waste in the environment has created novel habitats known as the "plastisphere", where microorganisms can thrive. Concerns are rising about the potential for pathogenic microorganisms to proliferate in the plastisphere, posing risks to human health. However, our knowledge regarding the virulence and pathogenic potential of these microorganisms in the plastisphere remains limited. This study quantified the abundance of virulence factor genes (VFGs) in the plastisphere and its surrounding environments (water and soil) to better assess pathogenic risks. Our findings revealed a selective enrichment of VFGs in the plastisphere, which were attributed to the specific microbial community assembled. The presence of arsenic and ciprofloxacin in the plastisphere exerted additional co-selective pressures, intensifying the enrichment of VFGs. Notably, VFGs that encoded multiple functions or enhanced the survival of host microorganisms (e.g., encoding adherence functions) tended to accumulate in the plastisphere. These versatile and environmentally adaptable VFGs are more likely to be favored by bacteria in the environment, warranting increased attention in future investigations due to their potential for widespread dissemination. In terms of virulence and pathogenicity, this research offers new insights into evaluating pathogen-related risks in the plastisphere.

Deciphering fluorescent and molecular fingerprint of dissolved organic matter leached from microplastics in water

Despite extensive research into the presence and behavior of microplastics (MPs) in the environment, limited attention has been given to the investigation of the characteristics of dissolved organic matter (DOM) that leaches from MPs (MPs-DOM). Herein, two frequently encountered plastic particles in aquatic environments, specifically polyethylene terephthalate (PET)- and polyethylene (PE)-MPs, were subjected to leaching in the aquatic settings for seven days, both in the absence of light and under UV irradiation. Measurements of dissolved organic carbon (DOC) indicated that UV exposure enhanced the liberation of DOM from PET-MPs, while PE-MPs did not exhibit such leaching. After UV treatment for seven days, the DOM released from PET-MPs increased by 25 times, while that from PE-MPs remained almost unchanged. Then, the molecular diversity and the evolving formation of DOM originating from different MPs were comprehensively analyzed with fluorescence excitation-emission matrix (EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Specifically, both PET- and PE-DOM exhibited three fluorescence signatures, with the predominant C1 (tryptophan-like) component showing a decline in PET-DOM and a rise in PE-DOM during aging. The FT-ICR-MS analysis unveiled that PET-DOM grew more recalcitrant under UV exposure, while PE-DOM became increasingly labile. In brief, UV irradiation influences MPs-DOM release and transformation differently, depending on the plastic composition. This highlights the significance of exploring MPs-DOM transformation in securing environmental safety.

Photo-oxidation of Micro- and Nanoplastics: Physical, Chemical, and Biological Effects in Environments

Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.

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.

Microplastics in cultivated soil environment: Construction of toxicity grading evaluation system, development of priority control checklist, and toxicity mechanism analysis

The present study aimed to comprehensively evaluate the toxicological effects of microplastics (MPs) on cultivated soil quality. Based on improved G1 evaluation method, we first constructed a grading evaluation system comprising of the indicators of toxicological effects of cultivated soil quality under MPs exposure, while focusing on types of MPs that had significant/non-significant toxicity effects. Furthermore, we verified reliability of screening results of significance-links at each level, using several data processing methods. Then, using natural breakpoint classification method, a priority control checklist of toxicological effects of 18 types of MPs on cultivated soil was developed to determine the types of MPs having significant toxicity risks and cultivated soil quality links significantly affected by the toxicity of MPs exposure. Finally, quantum-mechanics/molecular-mechanics (QM/MM) methods were used to carry out the differential toxicity mechanism analysis. The results showed that MPs with higher non-polar surface area may lead to stronger toxicity effect to the cultivated soil quality. Notably, the MPs that have abundant binding sites enhance the binding affinity, and less polar MPs bind more strongly to the non-polar amino acids of target receptors. Our study provides a new theoretical perspective for multi-dimensional analysis toxicological effects of different MPs exposure on cultivated soil quality.

Cation-π mechanism promotes the adsorption of humic acid on polystyrene nanoplastics to differently affect their aggregation: Evidence from experimental characterization and DFT calculation

Multiple water-chemistry factors determine nanoplastics aggregation and thus change their bioavailability and ecological risks in natural aquatic environments. However, the dominant factors and their interactive mechanisms remain elusive. In this study, polystyrene nanoplastics (PSNPs) showed greater colloidal stability in Li Lake water compared to ultrapure water. The RDA and PARAFAC results suggested that dissolved organic carbon, humic acid (HA) in particular, Ca2+, and pH are critical factors influencing PSNPs aggregation. Batch experiments showed that the critical coagulation concentration (CCC) of PSNPs was increased with pH increase; HA increased the CCC of PSNPs in NaCl by 2.6-fold but decreased that in CaCl2 by 1.8-fold. Moreover, cations increased the adsorption of HA on PSNPs. The DFT results suggested that HA-cations complexes (EAE = -1.10 eV and -0.51 eV for HA-Ca2+ and HA-Na+, respectively) but not HA alone (EAE = -0.33 eV) are the main scenarios for their adsorption on PSNPs, and a cation-π mechanism between PSNPs and HA-cations complexes dominates PSNPs aggregation in this scenario. The findings are significant for better understanding the environmental process and fate of nanoplastics in aquatic environments. ENVIRONMENTAL IMPLICATION: Nanoplastics are kinds of emerging contaminants. Nanoplastic aggregation determines their bioavailability and toxic risks to ecological health. Herein, the hydrodynamic sizes of PSNPs in local Li Lake water was tested and a redundancy analysis was performed to examine the key water-chemistry factors driving PSNPs aggregation. Moreover, the mechanisms in PSNPs aggregation driven by multiple dominant water-chemistry factors including cations, pH, and DOC were firstly unveiled by combining experimental characterization and theoretical computations. This work improves our understanding of the environmental fate of nanoplastics and provides a theoretical basis for the risk assessment and control of nanoplastics in real aquatic environments.

Predicting aqueous sorption of organic pollutants on microplastics with machine learning

Microplastics (MPs) are ubiquitously distributed in freshwater systems and they can determine the environmental fate of organic pollutants (OPs) via sorption interaction. However, the diverse physicochemical properties of MPs and the wide range of OP species make a deeper understanding of sorption mechanisms challenging. Traditional isotherm-based sorption models are limited in their universality since they normally only consider the nature and characteristics of either sorbents or sorbates individually. Therefore, only specific equilibrium concentrations or specific sorption isotherms can be used to predict sorption. To systematically evaluate and predict OP sorption under the influence of both MPs and OPs properties, we collected 475 sorption data from peer-reviewed publications and developed a poly-parameter-linear-free-energy-relationship-embedded machine learning method to analyze the collected sorption datasets. Models of different algorithms were compared, and the genetic algorithm and support vector machine hybrid model displayed the best prediction performance (R2 of 0.93 and root-mean-square-error of 0.07). Finally, comparison results of three feature importance analysis tools (forward step wise method, Shapley method, and global sensitivity analysis) showed that chemical properties of MPs, excess molar refraction, and hydrogen-bonding interaction of OPs contribute the most to sorption, reflecting the dominant sorption mechanisms of hydrophobic partitioning, hydrogen bond formation, and π-π interaction, respectively. This study presents a novel sorbate-sorbent-based ML model with a wide applicability to expand our capacity in understanding the complicated process and mechanism of OP sorption on MPs.

Microplastics degradation stimulated by in-situ bioelectric field in agricultural soils

Bioelectric field is a stimulated force to degrade xenobiotic pollutants in soils. However, the effect of bioelectric field on microplastics (MPs) aging is unclear. The degradation behavior of polyvinyl chloride (PVC), polyethylene (PE) and polylactic acid (PLA) was investigated in an agricultural soil microbial electrochemical system in which bioelectric field was generated in-situ by native microbes. Based on the density function theory, the energy gaps between the highest and the lowest occupied molecular orbitals of the three polymers with periodic structure were 4.20, 7.24 and 10.09 eV respectively, and further decreased under the electric field, indicating the higher hydrolysis potential of PLA. Meanwhile, the mass loss of PLA in the closed-circuit group (CC) was the highest on day 120, reaching 8.94%, which was 3.01-3.54 times of that without bioelectric field stimulation. This was mainly due to the enrichment of plastic-degrading bacteria and a robust co-occurrence network as the deterministic assembly process, e.g., the abundance of potential plastic-degrading bacteria on the surface of PLA and PVC in the CC increased by 1.92 and 1.30 times, respectively, compared to the open-circuit group. In terms of functional genes, the xenobiotic biodegradation and metabolism capacity of plasticsphere in the CC were stronger than that in soil, and determined by the bioaccessibility of soil nitrogen and carbon. Overall, this study explored the promoting effect of bioelectric field on the degradation of MPs and reveled the mechanism from quantum chemical calculations and microbial community analysis, which provides a novel perception to the in-situ degradation of MPs.

Natural Solar Irradiation Produces Fluorescent and Biodegradable Nanoplastics

Nanoplastics (NPs) have raised global concern owing to their potential health effects. Herein, after simulated and natural solar irradiation, polyethylene, polypropylene, polystyrene, and poly(vinyl chloride) nanoplastics (PVC NPs) were observed to exhibit enhanced fluorescence, particularly PVC NPs. Furthermore, the role of photoaged NPs as a potential fluorescence indicator was evaluated by exposing a model aquatic organism Daphnia magna to these NPs. Our results revealed that photoaged NPs exhibited strong fluorescence owing to the generation of conjugated π bonds, which can achieve π-π* electron transition with low energy consumption. Photogenerated fluorescence also enabled the photoaged NPs to act as efficient fluorescent tracers, which can help track NP migration in various organisms. The results of two-photon laser confocal scanning microscopy revealed that the photoaged NPs could translocate across biological barriers and accumulate in extraintestinal tissues in addition to being ingested and excreted. Moreover, compared with pristine NPs, the photoaged NPs underwent biodegradation more easily, probably because of increased hydrophilicity due to photogenerated oxygen-containing moieties. Therefore, in addition to producing fluorescent NPs without the attachment of external fluorescent dyes, the natural photoaging process can promote the migration and degradation of photoaged NPs in food chains.

Photoaging of Typical Microplastics as Affected by Air Humidity: Mechanistic Insights into the Important Role of Water Molecules

Recent studies showed that land is the most important sink for microplastics (MPs); however, limited information is available on the photoaging processes of land surface MPs that are exposed to the air. Herein, this study developed two in situ spectroscopic methods to systematically explore the effect of air humidity on MP photoaging using a microscope of Fourier transform infrared spectroscopy and a laser Raman microscope, which were equipped with a humidity control system. Polyethylene microplastics, polystyrene microplastics, and poly(vinyl chloride) microplastics (PVC-MPs) were used as model MPs. Our results showed that relative humidity (RH) could significantly influence the MP surface oxygen-containing moieties generated from photo-oxidation, especially for PVC-MPs. As the RH level varied from 10 to 90%, a decrease in the photogenerated carbonyl group and an increase in the hydroxyl group were observed. This could be attributed to the involvement of water molecules in the production of hydroxyl groups, which subsequently inhibited carbonyl generation. Moreover, the adsorption of coexisting contaminants (i.e., tetracycline) on photoaged MPs exhibited strong RH dependence, which could be assigned to the varied hydrogen bonding between tetracycline carbonyls and aged MP surface hydroxyls. This study reveals a ubiquitous but previously overlooked MP aging route, which may account for the changed MP surface physiochemical properties under solar irradiation.

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.

Digestion of plastics using in vitro human gastrointestinal tract and their potential to adsorb emerging organic pollutants

Excessive plastic use has inevitably led to its consumption by organisms, including humans. It is estimated that humans consume 20 kg of plastic during their lifetime. The presence of microplastics in the human body can carry serious health risks, such as biological reactions e.g. inflammation, genotoxicity, oxidative stress, apoptosis, as well toxic compounds leaching of unbound chemicals/monomers, free radicals or adsorbed organic pollutants, which mainly depend on the properties of the ingested plastic. Plastics are exposed to different substances (e.g., enzymes and acids) in the digestive system, which potentially affects their properties and structure. By stimulating the human digestive system and applying a set of advanced analytical tools, we showed that the surface of polystyrene and high-density polyethylene plastics frequently in contact with food undergoes fundamental changes during digestion. This results in the appearance of additional functional groups, and consequent increase in the plastic adsorption capacity for hydrophobic ionic compounds (such as triclosan and diclofenac) while reducing its adsorption capacity for hydrophobic non-ionic compounds (such as phenanthrene). Micro- and nanostructures that formed on the flat surface of the plastics after digestion were identified using scanning electron microscopy. These structures became defragmented and detached due to mechanical action, increasing micro- and nanoplastics in the environment. Due to their size, the release of plastic nanostructures after digestion can become an "accidental food source" for a wider group of aquatic organisms and ultimately for humans as the last link in the food chain. This, combined with improved adsorption capacity of digested plastics to hydrophobic ionic pollutants, can pose a serious threat to the environment including human health and safety.

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 behavior of aged polybutylece terephthalate microplastics coexisting with Cd(II)-tetracycline

Microplastics (MPs) are one of the emerging classes of pollutants that can be infiltrated into any aqueous solutions from disposed toxic metals and antibiotics, further exacerbating the potential biotoxicity of MPs. However, the research on the interaction between MPs and various pollutants is limited. Therefore, in this study, the changes in toxicity of polybutylece terephthalate (PBT) MPs were assessed following adsorption of heavy metals and antibiotics. The adsorption behavior of Cd(II) and tetracycline (TC) on ultraviolet (UV) light-aged PBT was investigated. The results demonstrated that the Cd(II) adsorption behavior could be described by the pseudo-second-order kinetic and Langmuir isothermal models, while the TC adsorption behavior has well fitted using Elovich and Sips models. The whole adsorption process occurred via either external diffusion or internal diffusion. The interactions between aged PBT and pollutants were evaluated under different environmental conditions, such as solution pH and the concentrations of dissolved organic matter and cations. The amounts of Cd(II) and TC adsorbed were higher in the competitive systems than the single solution, which might attribute to the formation of Cd(II)-TC complexes and aged PBT functional group changes. The results of two-dimensional correlation spectroscopy (2D-COS) describes the sequence of functional group transformation during the uptake of Cd(II)-TC by aged PBT in binary systems. These findings identify a strong interaction between aged PBT and contaminants, establishing the potential fate of aged MPs under natural aquatic environment conditions.

Soil plastisphere: Exploration methods, influencing factors, and ecological insights

Microplastic (MP), an emerging contaminant, is globally prevalent and poses potential environmental threats and ecological risks to both aquatic and terrestrial ecosystems. When MPs enter into natural environments, they may serve as artificial substrates for microbial colonization and plastisphere formation, providing new ecological niches for microorganisms. Recent studies of the plastisphere have focused on aquatic ecosystems. However, our understanding of the soil plastisphere e.g. its formation process, microbial ecology, co-transport of organic pollutants and heavy metals, and effects on biogeochemical processes is still very limited. This review summarizes latest methods used to explore the soil plastisphere, assesses the factors influencing the microbial ecology of the soil plastisphere, and sheds light on potential ecological risks caused by the soil plastisphere. The formation and succession of soil plastisphere communities can be driven by MP characteristics and soil environmental factors. The soil plastisphere may affect a series of ecological processes, especially the co-transport of environmental contaminants, biodegradation of MPs, and soil carbon cycling. We aim to narrow the knowledge gap between the soil and aquatic plastisphere, and provide valuable guidance for future research on the soil plastisphere in MP-contaminated soils.

Polystyrene microplastics accelerated photodegradation of co-existed polypropylene via photosensitization of polymer itself and released organic compounds

Combined pollution consisted of various types of microplastics (MPs) was extensively detected in the environment; however, little is known about their interaction on degradation behavior during exposure in sunlight. This study investigated the effects of polystyrene (PS) MPs and mechanisms on photodegradation of pure and commercial polypropylene (PP) MPs co-existed in aquatic environment. Results showed that PS MPs significantly accelerated photodegradation of co-existed PP, including faster oxidation and fragmentation. Photodegradation route of PP MPs such as the reaction priority of partial chemical bindings was even altered with the presence of PS MPs, highlighting the important role of PS in photodegradation process of PP. Analysis of leachate and free radical indicated that the critical effects were derived from photosensitization of PS polymer itself and its released dissolved organic matter (PS-DOM); here, more important role of PS itself in initial period and that of PS-DOM in later period. Among generated ROS, OH· was the key species for accelerating photodegradation of PP by PS itself and its released DOM, which were generated from the reaction of polymer radical with dissolved oxygen. The findings firstly reveal the important role of PS in photodegradation of co-existed MPs and suggested the shorter duration of (micro)plastics in combined system than that in the single, which provide useful information to assess environmental behavior and fate of MPs more holistically.

Non-Negligible Effects of UV Irradiation on Transformation and Environmental Risks of Microplastics in the Water Environment

Microplastics (MPs) are ubiquitous in environmental media, and their harmful effects on MPs on the ecosystem have attracted more and more attention. Once released into the environment, MPs can trigger oxidative degradation through ultraviolet (UV) to cause photoaging. Photoaging significantly affects the properties of MPs, which leads to changing their environmental behaviors and increasing environmental risks. In this review, the generation of MPs under UV irradiation and the influence of environmental factors on the photoaging of MPs were discussed. Photoaging of MPs is an important process affecting the migration, transformation and interaction of pollutants in water and soil. In order to fully predict the fate and environmental interaction of MPs, more researches are needed in the future to explore the photoaging behavior of different types of MPs under natural environmental conditions.