Surface Of Microplastics Research Articles

Adsorption of As(III) by microplastics coexisting with antibiotics

Although recent studies have been conducted on the pollution and toxicity of microplastics with heavy metals or antibiotics, it is necessary to further investigate the coexistence of antibiotics and heavy metals on the surface of microplastics. In this study, the mechanisms of As(III) adsorption by polystyrene (PS) and polyamide (PA) microplastics in the presence of antibiotics (ciprofloxacin, CIP) were investigated. Adsorption behavior was investigated using kinetic and isotherm models, and the effects of microplastic particle size, aging, ion concentration, pH, xanthic acid (FA), and tannic acid (TA) were considered. Adsorption kinetics and isotherm models showed that the kinetics of As(III) adsorption on PS were consistent with a pseudo-first-order model; the kinetics of adsorption on PA were more consistent with segmented linear regression. The Freundlich model is consistent with the adsorption isotherms of As(III) on PS and PA. The smaller the microplastic particle size and the longer the aging time, the better the adsorption of As(III). Increasing NO3−significantly inhibited the adsorption of As(III) by PS, while it first promoted and then inhibited the adsorption by PA. The effect of pH was similar to that ofNO3−. The adsorption of As(III) by PS was significantly promoted by FA and TA, regardless of the presence of CIP; the adsorption of As(III) by PA was inhibited. Scanning electron microscopy (SEM) was used to characterize microscopic morphology of pristine and aged PS and PA microplastics; Fourier transform infrared (FTIR) and X-ray absorption spectroscopy (XPS) revealed changes in surface functional groups of PS and PA, while demonstrating the importance of different functional groups in exogenous additives (CIP and dissolved organic matter, DOM) in the adsorption of As(III). This study provides new insight into adsorption behaviors and interaction mechanisms between ternary pollutants.

With spatial distribution, risk evaluation of heavy metals and microplastics to emphasize the composite mechanism in hyporheic sediments of Beiluo River

This study aimed to assess the hazardous impacts of heavy metals (HMs) enrichment on the surface of microplastics (MPs) in the hyporheic zone. The present work analyzed the spatial distribution and risk evaluation of HMs (V, Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Pb) and MPs and the mechanism of HMs enrichment on MPs in the sediments. The highest rates of contamination were for Cd, Pb, and As. The main types of MPs were fiber, blue, and a size smaller than 500 µm. The lower reaches of the Beiluo River had the most serious HMs and MPs pollution, especially BL-10 (HMs: CF-Cd, 41.91; EF-Cd, 50.87; Igeo-Cd, 4.80; RI, 1291; PN, 29.83; MPs: abundance, 890 ± 18 items/kg). Meanwhile, the principal component analysis showed that natural, industrial activities, and agricultural production and transportation were primary HMs sources in sediments, and Cd, Co, and Pb were the main enriched metals on the surface of MPs. More importantly, regarding the interaction mechanism of these composite pollutants, we concluded that electrostatic adsorption and biofilm mediation were the main mechanisms of the synergistic effect. Overall, our findings provide a theoretical basis for further research on the ecotoxicity of composite pollutants in aquatic environments.

Alteration of microbial mediated carbon cycle and antibiotic resistance genes during plastisphere formation in coastal area

Microorganisms can attach on the surface of microplastics (MPs) through biological fouling process to form a diverse community called the "plastisphere", which has attracted extensive attention. Although the microbial structure and composition of biofilm have been studied, the knowledge of its microbial function and ecological risk is still limited. In this study, we investigated how the surface properties of MPs affect the biofilm communities and metabolic features under different environmental conditions, and explored the biofilm enrichment of antibiotic resistance genes (ARGs). The results showed that the incubation time, habitat and MPs aging state significantly influenced the structure and composition of biofilm microbial communities, and a small amount of pathogens have been found in the MPs-attached biofilm. The microbial carbon utilization capacity of the biofilm in different incubation habitats varies greatly with highest metabolism capacity appear in the river. The utilization efficiency of different carbon sources is polymer > carbohydrate > amino acid > carboxylic acids > amine/amide, which indicates that the biofilm communities have selectivity between different types of carbon sources. More importantly, ARGs were detected in all the MPs samples and showed a trend of estuary > river > marine. The aged MPs can accumulate more ARGs than the virgin items. In general, MPs in the aquatic environment may become a carrier for pathogens and ARGs to spread to other environment, which may enhance their potential risks to the ecosystem and human health.

Co-transport of Microplastics and a surrogate for Human Enteric Viruses in a saturated column packed with Quartz Sand

Groundwater can be contaminated with infective human enteric viruses from various sources, such as wastewater treatment plant discharge, landfills, septic tanks, agricultural practices, and artificial groundwater recharge. Anthropogenic pollutants, such as microplastics, may exhibit an affinity to transport biocolloids (bacteria, viruses) further and reduce their degradation rates in the natural environment. Human enteric viruses (poliovirus, hepatitis A, rotavirus, and adenovirus) can adsorb to the abiotic surface of microplastics and are simultaneously present in wastewater discharge. These newly formed clumps of pathogens and microplastics could penetrate deeper into soils as vectors for preferential flow and threaten groundwater systems, triggering a higher risk for drinking water and possibly followed by a disease outbreak. The mechanisms behind the adsorption of human enteric viruses on microplastic surfaces and their potential role in prolonging virus survival and promoting environmental transport remain unclear. This study aims to explore the possibility of co-transport of microplastics and human enteric viruses in saturated porous media, using PRD1 bacteriophage as a surrogate. PRD1 bacteriophages have been widely used as surrogates of rotavirus because they share many fundamental properties and features. Column experiments were performed using quartz sand (soil grain size: 0.60 - 1.30 mm) as a porous media in a 30 cm long and 7 cm diameter column. The column experiments were conducted by maintaining Darcy velocity of 2.65 m/day. Three different influent solution scenarios were considered in the experiments: PRD1 mixed with microplastics, PRD1 alone, and microplastics alone. The enumeration of PRD1 in the effluent solution was performed using quantitative polymerase chain reaction (qPCR) as well as the culture method, in order to differentiate between infective and inactive virus transport. Microplastics were quantified using Solid-Phase Cytometry (SPC). Results were analyzed by calculating the collision and sticking efficiencies of the microplastics and PRD1 using the classical colloid filtration theory and Hydrus 1D modeling tool. There was no evidence of interference or inhibition of microplastics on the performance of qPCR and DNA extraction in the methodological setup. Additionally, the efficacy of qPCR and DNA extraction methods did not yield significantly different results across any of the influent solution conditions. Preliminary results suggest that the presence of microplastics enhanced the transport of PRD1, which led to reduced attachment of PRD1 in the porous media. The concentration of infective phages showed a delayed sharp increase, indicating that there may be a sorption mechanism that delays their breakthrough. It is possible that a portion of the active phages possess a higher sticking efficiency and that population heterogeneity contributes to this phenomenon. A comprehensive understanding of the processes that govern virus transport with globally distributed microplastics is crucial for protecting public health.

The bioaccessibility of adsorped heavy metals on biofilm-coated microplastics and their implication for the progression of neurodegenerative diseases.

Microplastic (MP) tiny fragments (< 5mm) of conventional and specialized industrial polymers are persistent and ubiquitous in both aquatic and terrestrial ecosystem. Breathing, ingestion, consumption of food stuffs, potable water, and skin are possible routes of MP exposure that pose potential human health risk. Various microorganisms including bacteria, cyanobacteria, and microalgae rapidly colonized on MP surfaces which initiate biofilm formation. It gradually changed the MP surface chemistry and polymer properties that attract environmental metals. Physicochemical and environmental parameters like polymer type, dissolved organic matter (DOM), pH, salinity, ion concentrations, and microbial community compositions regulate metal adsorption on MP biofilm surface. A set of highly conserved proteins tightly regulates metal uptake, subcellular distribution, storage, and transport to maintain cellular homeostasis. Exposure of metal-MP biofilm can disrupt that cellular homeostasis to induce toxicities. Imbalances in metal concentrations therefore led to neuronal network dysfunction, ROS, mitochondrial damage in diseases like Alzheimer's disease (AD), Parkinson's disease (PD), and Prion disorder. This review focuses on the biofilm development on MP surfaces, factors controlling the growth of MP biofilm which triggered metal accumulation to induce neurotoxicological consequences in human body and stategies to reestablish the homeostasis. Thus, the present study gives a new approach on the health risks of heavy metals associated with MP biofilm in which biofilms trigger metal accumulation and MPs serve as a vector for those accumulated metals causing metal dysbiosis in human body.

Adsorption/desorption of mercury (II) by artificially weathered microplastics: Kinetics, isotherms, and influencing factors

While both mercury (Hg) and microplastics (MPs) are well-studied global pollutants, comparatively little is known about the interactions between them and the mobilization of Hg from MPs into organisms. We examined the affinity of Hg(II) to artificially weathered MPs, including polyamide (w-PA), polyethylene (w-PE), polyethylene terephthalate (w-PET), polyester fibers (w-PEST), polyvinyl chloride (w-PVC), and polylactic acid (w-PLA), along with crumb rubber (CR) and PE collected from a wastewater treatment plant (WWTP-PE). WWTP-PE, CR, and w-PEST had particularly high Hg(II) affinities, which can be attributed to electrostatic interaction and pore filling. The adsorption followed a pseudo-second-order kinetic process and fitted the Freundlich model, suggesting multi-step (mass transfer and intraparticle diffusion) and heterogeneous adsorptions. Hydrochemical conditions (pH, dissolved organic matter (DOM), salinity and co-existent metal ions) all impacted Hg-MP behavior. Changes in Hg speciation and MP surface properties contributed to the different Hg(II) adsorption capacities for the MPs. Weathering of MPs generally increased the adsorption of Hg(II) onto MPs, but CR, PET and PEST did not follow this trend. Less than 3% of adsorbed Hg(II) was mobilized from the MPs in freshwater, but that increased up to 73% under simulated avian digestive conditions, suggesting increased bioavailability of Hg(II) from ingested MPs. Overall, weathered MPs adsorb and retain Hg(II) under environmentally relevant conditions but desorb much of it in simulated avian digestion fluid, suggesting that birds that ingest MPs may have increased Hg(II) exposure.

Aging in soil increases the disturbance of microplastics to the gut microbiota of soil fauna

Microplastics (MPs) in the soil environment inevitably experience aging processes. However, how aging in soil affects MP toxicity to soil fauna remains poorly understood. In this study, two types of widely distributed MPs (polypropylene and tire wear particles) were aged in different soils, and their surface properties, morphology, leaching features of additives, biofilm colonization and toxicity to the typical soil fauna Enchytraeus crypticus were investigated. Results showed that aging in soil slightly changed the surface properties and morphology for both types of MPs, but significantly affected the release of additives, especially for those MPs aged in soil amended with manure. Moreover, a distinct and less diverse microbial community than the surrounding soils was formed on the surface of MPs, and MP type was a determinant of the biofilm microbial community. Exposure experiments indicated that aged MPs, especially those aged in soil with manure significantly affected the reproduction of soil worms with a more obvious disturbance to their gut microbiota, and biofilm features and changes in the leaching properties of MPs during aging were the main factors for these shifts. This study is the first attempt to reveal the role of aging in soil in MP toxicity to soil fauna.

Coagulation studies on photodegraded and photocatalytically degraded polystyrene microplastics using polyaluminium chloride

Microplastics are ubiquitous persistent emerging contaminants, and its presence has been detected even in the most pristine and fragile ecosystems. Advanced oxidation processes are one of the novel degradation technologies used for the elimination of microplastics from the environment. In this study, the effect of ultraviolet C (UV-C, 253.7 nm) and ultraviolet A (UV-A, 365 nm) irradiations on polystyrene (PS) microplastic properties in the presence and absence of titanium dioxide were studied along with their coagulation performances using polyaluminium chloride (PAC). The effects of solar irradiation on the chemical properties of microplastics in aqueous and dry conditions were also investigated. PS microplastics (1.5 g) in three size ranges, 300–150 μm, 150–75 μm, and <75 μm were used during this experiment. After 45 days of irradiation, samples showed discolouration, brittleness, and loss of hydrophobicity. Images obtained from scanning electron microscope revealed smoothening and melting of PS surfaces upon UV exposure. Attenuated total reflectance- Fourier transform infrared spectroscopy and X-ray photon spectroscopy of photoaged samples revealed chemical alterations, bond cleavage and formation of oxygenated functional groups on microplastic surfaces. PAC coagulation of samples before and after UV irradiation showed drastic differences in removal efficiencies, with UV-C irradiated microplastics exhibiting maximum efficiency. Large sized and photocatalytically degraded microplastics showed better removal efficiencies than small sized particles. The 300–150 μm sized PS microplastic, degraded photo catalytically under UV-C irradiation showed approximately 99 % removal efficiency, while PS < 75 μm photodegraded under UV-A irradiation showed only 74.2 % removal efficiency.

Microplastics enrichment characteristics of antibiotic resistance genes and pathogens in landfill leachate

Microplastics (MPs) pollution is a pressing environmental issue for aquatic ecosystems. Landfill leachate is an important contributor of MPs and antibiotic resistant genes (ARGs). However, there are few studies on the colonization of ARGs and pathogens on MPs in leachate. This study conducted incubation experiments with polyethylene terephthalate (PET) and polypropylene (PP) MPs in landfill leachate which were about 3–5 years old (PL) and 5–10 years old (AL). After incubation, the bacterial cells colonized and grew on the surface of MPs, inducing the increase of oxygenated oxygen functional groups (e.g., hydroxyl, carbonyl) on the MPs surface. Real-time PCR indicated that MPs selectively enriched ARGs, such as genes tetM, tetC, mcr-1, aac(6′)-Ib-cr, blaTEM and blaSHV in leachate. The diversity of bacterial communities on MPs was significantly increased in AL leachate, but decreased in PL leachate. The differences in bacterial communities in MPs biofilms were related to the type of MPs. Compared with AL leachate, the abundance of Chloroflexi increased by 15.7% on the PET, and the abundance of Acidobacteriota increased by 6.23 fold on the PP. The abundance of Firmicutes increased from 20.7% in PL leachate to 65.8% and 60.7% on PET and PP, respectively. Additionally, pathogens were observed to be more abundant on MPs compared to leachate. In particular, pathogens (Staphylococcus, Streptococcus, Enterobacter and Rhodococcus) associated with sul1 and sul2 were generally present at higher levels on MPs than in the surrounding leachate. These results provide significant implications for understanding the health risk of MPs in the environment.

Physicochemical and biological changes on naturally aged microplastic surfaces in real environments over 10 months

Microplastics (MPs) undergo aging over time, which can influence their behavior in the environment. While laboratory-simulated studies have investigated MP aging, research on natural aging in various real environments remains limited. This study aims to investigate the physical, chemical and biological changes that occur in five types of MPs after more than 10 months of natural aging in three different real environments: seawater, air and soil. Results are compared with previous laboratory experiments. The surface roughness of all types of aged MPs was found to be higher in seawater than in air and soil, which differed from previous simulated studies that showed the highest roughness in air. All aged MPs exhibited the occurrence of hydroxyl and carbonyl groups due to the oxidation processes. Interestingly, the MPs aged in soil showed the lowest level of these functional groups, while in seawater or air, some MPs demonstrated the highest. This contrasts with previous studies indicating the highest level of oxygen-containing functional groups in aged MPs in air. Bacterial analysis identified fourteen bacterial phyla on the surface of aged MPs in all three real environments, with varying abundance in specific environments. Notably, the composition of bacterial communities in the microplastisphere was determined by the surrounding environments, independent of MP types. Natural aging is more complex than laboratory simulations, and the degree of MP aging increases with the complexity of environmental factors. These findings enhance our understanding of the natural aging of MPs in different real environments.

Adsorption of Per- and Polyfluoroalkyl Substances (PFAS) and Microcystins by Virgin and Weathered Microplastics in Freshwater Matrices.

Microplastics and per- and polyfluoroalkyl substances (PFAS) both represent persistent groups of environmental contaminants that have been associated with human health risks. Microcystin toxins are produced and stored in the cells of cyanobacteria and may be released into sources of drinking water. Recent concerns have emerged regarding the ability of microplastics to adsorb a range of organic contaminants, including PFAS and microcystins. This study examined the adsorption of two long-chain and two short-chain PFAS, as well as two common microcystins, by both virgin and weathered microplastics in freshwater. Natural weathering of microplastic surfaces may decrease adsorption by introducing hydrophilic oxygen-containing functional groups. Up to 50% adsorption of perfluorooctanesulfonic acid (PFOS) was observed for virgin PVC compared to 38% for weathered PVC. In contrast, adsorption capacities for microcystins by virgin LDPE were approximately 5.0 µg/g whereas no adsorption was observed following weathering. These results suggest that adsorption is driven by specific polymer types and dominated by hydrophobic interactions. This is the first known study to quantify PFAS and microcystins adsorption when considering environmentally relevant concentrations as well as weathered microplastics.

Interaction and mechanistic studies of thiram and common microplastics in food and associated changes in hazard

Microplastics (MPs), an emerging pollutant in the environment and food, may adsorb other contaminants such as pesticide due to particles’ properties. The adsorption behavior and their hazardous changes of four common types of MPs to thiram was investigated. The adsorption kinetics and isotherm models were fitted well using the pseudo-second-order model and the Langmuir model respectively, indicating forces such as van der Waals forces dominate, and the maximum adsorption capacity at pH values of 6–7 also indicates that electrostatic forces play a smaller role. The adsorption thermodynamic studies showed that the adsorption was a spontaneous and exothermic process. The decrease in the adsorption capacity as the concentration of MPs increases and more adsorption by aged MPs demonstrate that the adsorption process is related to the sites on the surface of MPs. Due to the influence of ionic strength, the adsorption capacity of MPs for thiram increases significantly when the adsorption process takes place in solutions with salinity or in orange and apple juices. The bioavailability of thiram adsorbed by PVC and PET increased significantly. This study highlights the strong role of MPs in food as carriers of pesticide residues in food systems and that the combined hazard should also be of concern.

Microplastics contamination in fish feeds: Characterization and potential exposure risk assessment for cultivated fish of Bangladesh

Fish feed is becoming an increasingly vital source of nourishment for farmed fish, which are mainly coming from marine fish and agricultural sources. Anthropogenic particles, such as microplastics, are abundant in both marine fish and agricultural byproducts that are utilized to make fish feed. This study investigated whether fish feed could be a source of microplastic contamination, and revealed that a 20 weeks adult farmed tilapia fish might consume up to 268.45 ± 1.438 microplastic particles via fish feed where finisher type feeds were found to be mostly contributory in this number. The microplastics were initially observed with a stereomicroscope and FESEM-EDS. Polymeric composition of microplastics was determined to be polypropylene (PP), nylon-6 (NY-6), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl alcohol (PVA), polyethylene (PE), high- and low-density polyethylene (HDPE, LDPE), ethylene vinyl acetate (EVA), polycarbonate (PC), poly vinyl acetate (PVAc), poly urethane (PU) and polyvinyl chloride (PVC) by FTIR. Results also revealed that the size of microplastic particles in all fish feed ranged from 14 μm to 4480 μm, with 550 ± 45.45 to 11,600 ± 56.1 microplastic particles/kg of fish feed. The FESEM-EDS data demonstrated to overlook the microplastic surface along with attachment of heavy metals onto that surface such as Pb, Ni, and Co in finisher type feed that could create additional health risks.

Composting-based degradation of poly (ethylene terephthalate) microplastics and its enhancement with exogenous PET hydrolase supplementation

Poly (ethylene terephthalate) (PET) constitutes an important composition of environmental microplastics (MPs). This study was to explore the degradation of PET MPs in high-temperature composting and also to make an attempt for an enhanced degradation by exogenous addition of thermophilic PET hydrolase. Herein, six 220 L composters were applied to perform the composting, with half designated enhanced group with PET hydrolase added. After 20 days, PET MPs exhibited a notable reduction (21.1%) in weight and the addition of PET hydrolase resulted in 32.8% reduction of PET MPs. This is also corroborated by the increase of terephthalic acid (one of PET degradation products) from 2.0μg/g sample in initial mixture to 3.7μg/g sample in composting group and 9.3μg/g sample in enhanced group. Besides, the particle size distribution of PET MPs shifted toward smaller sizes after composting, with the supplementation of PET hydrolase further accentuating this shift. After composting, the surface of PET MPs in both treatments exhibited conspicuous corrosion and oxidation. An analysis of publicly available compost metagenomes indicated the wide distribution of potential PET hydrolase and TPA 1,2-dioxygenase genes. These findings suggest that composting exhibited a noticeable performance in the degradation of PET MPs and enzyme-assisted composting enhanced the degradation, providing a new approach for addressing environmental microplastics pollution.

Laboratory Studies about Microplastic Aging and Its Effects on the Adsorption of Chlorpyrifos.

The constant change in microplastics (MP) due to exposure to environmental conditions leads to physical and chemical changes that enhance their ability to transport other pollutants, increasing the concern about their widespread presence in the environment. This work aimed to simulate the aging process of six MP (polyamide 6, unplasticized polyvinyl chloride, low-density polyethylene, polystyrene, polyethylene-co-vinyl acetate, polypropylene) in freshwater and seawater ecosystems at laboratory scale and evaluate its effects through optical microscope observation, Fourier transform infrared spectroscopy-Attenuated Total Reflectance (FTIR-ATR), Raman spectroscopy, and thermal gravimetric analysis (TGA). Through a combined experimental study of aged MP, the degradation by UV interaction was evidenced by the appearance of new infrared bands in the FTIR spectra assigned to ketones and hydroxyl groups. While Raman analysis and microscope images reveal the appearance of pores, wrinkles, and roughness in the MP surfaces. Variations in the temperature of the maximum weight loss of the MP were observed in the TGA analysis. The adsorption of chlorpyrifos (CPF), a common pesticide widely used in agriculture, by the pristine and aged MP was also studied. The highest affinity for CPF was observed for pristine LDPE and the lowest for PP. The batch adsorption studies revealed an increase in adsorption capacity as a consequence of the aging process for both MP. These results proved that the weathering effects caused changes in the behavior of MP, namely in the interaction with other pollutants.

Soil organic matter facilitates the transport of microplastic by reducing surface hydrophobicity

Groundwater contamination by microplastic (MP) causes increasing concern about the critical factors that determine MP transport mechanisms in the vadose zone. Strong water repellency of native microplastic surfaces and respective attractive hydrophobic interactions with components of the soil matrix limits its mobility. However, adsorption of dissolved organic matter (DOM) onto microplastic surfaces can potentially make them more hydrophilic, enhancing their mobility. Consequently, the main objective of this study was to systematically determine the effects of DOM on both the surface properties and the mobility of polystyrene microplastic (PSP), and to use the extended DLVO theory (XDLVO) to predict PSP transport behavior with natural DOM for the first time. Breakthrough experiments were conducted in columns filled with quartz sand, through which PSP (1 µm) were percolated at either 0 or 5 mg/L dissolved organic carbon (DOC) derived from beech (Fagus sylvatica) litter at ionic strengths ranging from 0.5 to 2.5 mM CaCl2, since the cation background also affects wettability and mobility. Using sessile drop contact angle and zeta potential measurements, XDLVO interaction energy components including Lewis acid-base energies were approximated. Breakthrough curve analysis confirmed that DOM coming from natural sources strongly enhanced the mobility of PSP in the quartz sand matrix, in particular at higher ionic strength. At 2.5 mM CaCl2, the presence of DOM increased PSP breakthrough from 1 % to 60 %. Consequently, in the absence of DOM, laser microscope images showed much more pronounced formation of microplastic clusters on quartz grain surfaces than at co-percolation of PSP with DOM. This behavior could be clearly predicted with the XLDVO approach, which suggests at 0 mg/L DOC a deep primary energy minimum between individual PSP and between PSP and quartz surfaces. In contrast, repulsive hydrophilic interactions between the surfaces were predicted at 5 mg/L DOC. We conclude that even low concentrations of DOM, as usually found in subsoil, can significantly enhance the mobility of microplastic in soils via rendering the surfaces more hydrophilic. This implies potentially serious repercussions for the spread of this contaminant in the environment.

Determining the Contribution of Micro/Nanoplastics to Antimicrobial Resistance: Challenges and Perspectives.

Microorganisms colonizing the surfaces of microplastics form a plastisphere in the environment, which captures miscellaneous substances. The plastisphere, owning to its inherently complex nature, may serve as a "Petri dish" for the development and dissemination of antibiotic resistance genes (ARGs), adding a layer of complexity in tackling the global challenge of both microplastics and ARGs. Increasing studies have drawn insights into the extent to which the proliferation of ARGs occurred in the presence of micro/nanoplastics, thereby increasing antimicrobial resistance (AMR). However, a comprehensive review is still lacking in consideration of the current increasingly scattered research focus and results. This review focuses on the spread of ARGs mediated by microplastics, especially on the challenges and perspectives on determining the contribution of microplastics to AMR. The plastisphere accumulates biotic and abiotic materials on the persistent surfaces, which, in turn, offers a preferred environment for gene exchange within and across the boundary of the plastisphere. Microplastics breaking down to smaller sizes, such as nanoscale, can possibly promote the horizontal gene transfer of ARGs as environmental stressors by inducing the overgeneration of reactive oxygen species. Additionally, we also discussed methods, especially quantitatively comparing ARG profiles among different environmental samples in this emerging field and the challenges that multidimensional parameters are in great necessity to systematically determine the antimicrobial dissemination risk in the plastisphere. Finally, based on the biological sequencing data, we offered a framework to assess the AMR risks of micro/nanoplastics and biocolonizable microparticles that leverage multidimensional AMR-associated messages, including the ARGs' abundance, mobility, and potential acquisition by pathogens.

Multigenerational exposure of microplastics on the microbiota of E. affinis (copepod): a comparative study between biodegradable and nonbiodegradable microplastics

The accumulation of plastic debris around the world, especially in marine environments, has been well documented during the past decades. Recent studies have found that inorganic surfaces of microplastics (MPs) can be used by microorganisms as living substrates and form an ecosystem named “plastisphere.” Some microorganisms present in MPs are capable of producing polymer-degrading enzymes. In addition, MPs can also serve as vectors and carry microorganisms (including potential pathogens) into higher trophic levels through their ingestion by animals. In this study, impacts on copepod microbiota during chronic exposure to MPs were investigated by exposing copepods to a classic single-use polymer (low-density polyethylene (LDPE)) and a biodegradable polymer (polybutylene adipate terephthalate (PBAT)). Copepods were exposed to “virgin” and “weathered” MPs during four generations at an environmentally relevant concentration of 300 µg/L, followed by one “detoxification” generation without MP exposition. Impacts of MP exposure on copepod microbiota were investigated using 16S rRNA gene high-throughput sequencing. The result of nonmetric multidimensional scaling (NMDS) analysis showed that copepods (with or without MP exposure) carried distinguishable microbiota as compared with the microbiota of water and microalgae used for maintaining copepods. According to the results of permutational analysis of variance (PERMANOVA), the microbiota of MP-exposed (both PBAT and LDPE) copepods was significantly different from the microbiota of unexposed copepods during generations one to four. After “detoxification,” however, no significant difference in microbiota composition was observed among all generation five copepods. Altogether, impacts on copepod microbiota of MP exposure for multiple generations were observed, despite plastic origin (biodegradable or not) and aging conditions. Furthermore, copepod microbiota seemed to return to their original structure as soon as the MP exposure stopped.

Fluorescence Correlation Spectroscopy Studies of Dye Diffusion on Fresh and Aged Polyethylene Terephthalate.

Microplastics accumulate a wide variety of organic pollutants and thus may serve as efficient vectors for the transport of toxic substances. Much remains to be learned about how organic molecules interact with the surfaces of plastics and how these properties evolve as the microplastics are weathered. In this Letter, we report, for the first time, the application of confocal fluorescence correlation spectroscopy (FCS) to studies of organic molecules adsorbed from aqueous solution onto the surfaces of synthetic secondary microplastics. Both fresh and artificially aged poly(ethylene terephthalate) (PET) plastics are employed. The plastics are artificially aged in a UV-ozone chamber. Raman and infrared spectra confirm the composition of the PET microplastics. Water contact angle and surface roughness measurements reveal, respectively, an increase in wettability and a change in the nature of roughness with aging, consistent with surface oxidation. Rhodamine B (RhB) dye is used as a fluorescent probe in FCS studies and serves as an analogue for organic pollutants commonly found on microplastics. The FCS results reveal the accumulation of dye on the PET surfaces as they age. Dye motion is significantly slower on the plastics than in bulk aqueous solution and occurs by anomalous subdiffusion. The rate of diffusion becomes dramatically slower and more anomalous as the plastics are aged. Surface diffusion is likely slowed by either ionic interactions or hydrogen bonding between the dye and plastic. These results provide new insights critical to the understanding of how microplastics accumulate and transport organic pollutants as they weather in the environment.

The adsorption of PAHs on microplastics and desorption in the simulated human digestive system

Plastic debris is widely distributed in the aquatic environment and interacts with other pollutants. Microplastics (MPs) have a stronger binding ability with pollutants and could unconsciously ingested by humans, thus becoming the carrier of pollutants into the human body and affecting human health. In this study, polycyclic aromatic hydrocarbons (PAHs) were selected as model pollutants, polyethylene (PE) and polymethyl methacrylate (PMMA) were selected as research objects. The adsorption of PAHs on different kinds of MPs and desorption behavior in a simulated human digestive system were systematically studied. The results indicated that PAHs with higher molecular weight were more easily adsorbed on MPs, and the adsorption efficiency of PAHs on PE was 1.4–3.8 times higher than PMMA. The desorption experiments were conducted in simulated gastrointestinal fluid, the activity of enzymes directly affected the desorption of PAHs, and the desorption efficiency of PAHs from the surfaces of PMMA (0.7–41.6 %) was significantly higher than PE (0.8–27.7 %). For 15 PAHs, the desorption efficiency from the surfaces of PE decreased gradually with the number of PAHs rings, which was opposite to PMMA. Molecular dynamics simulation showed that enzymes in digestive fluid attenuated the interaction energy between MPs and PAHs, resulting in substantial desorption of PAHs from the surfaces of MPs. The risk assessment demonstrated that the carcinogenic risk of PAHs desorption from PMMA was higher than PE. This study helps understand the adsorption of PAHs on MPs and the potential health risks of accidental ingestion by humans.