How micro-/nano-plastics influence the horizontal transfer of antibiotic resistance genes - A review.

Plastic debris such as microplastics (MPs) and nanoplastics (NPTs), along with antibiotic resistance genes (ARGs), are pervasive in the environment and are recognized as significant global health and ecological concerns. Micro-/nano-plastics (MNPs) have been demonstrated to favor the spread of ARGs by enhancing the frequency of horizontal gene transfer (HGT) through various pathways. This paper comprehensively and systematically reviews the current study with focus on the influence of plastics on the HGT of ARGs. The critical role of MNPs in the HGT of ARGs has been well illustrated in sewage sludge, livestock farms, constructed wetlands and landfill leachate. A summary of the performed HGT assay and the underlying mechanism of plastic-mediated transfer of ARGs is presented in the paper. MNPs could facilitate or inhibit HGT of ARGs, and their effects depend on the type, size, and concentration. This review provides a comprehensive insight into the effects of MNPs on the HGT of ARGs, and offers suggestions for further study. Further research should attempt to develop a standard HGT assay and focus on investigating the impact of different plastics, including the oligomers they released, under real environmental conditions on the HGT of ARGs.

Phthalocyanine blue leaching and exposure effects on Microcystis aeruginosa (cyanobacteria) of photoaged microplastics.

Light-stabilizing additives may contribute to the overall pollution load of microplastics (MPs) and potentially enter the food chain, severely threatening aquatic life and human health. This study investigated the variation between polystyrene (PS) MPs and phthalocyanine blue (CuPC)-containing MPs before and after photoaging, as well as their effects on Microcystis aeruginosa. The presence of PS-MPs increased cell mortality, antioxidant enzyme activity, and the variation in extracellular components, while the presence of CuPC exacerbated these variations. CuPC-containing MPs caused different increasing trends in superoxide dismutase and malondialdehyde activities due to electron transfer across the membrane. Transcriptomic analysis revealed that the MPs and CuPC affected various cellular processes, with the greatest impact being on cell membranes. Compared with MPs, CuPC negatively affected ribosome and polysaccharide formation. These findings provide insights into the molecular mechanisms underlying the cellular response to MPs and their associated light-stabilizer pollution and imply the necessity for mitigating the pollution of both MPs and light-stabilizers.

Extraction of lipase and protease and characterization of activated sludge from pulp and paper industry.

Hydrolytic enzymes released by the microorganisms in activated sludge are responsible for the organic matter degradation there; however, the optimal extraction procedure of this valuable resource has not been well established until now. In this study protease and lipase were extracted from activated sludge using ultrasound disintegration combined with a nonionic detergent (Triton X-100) and cation-exchange resin (CER) in combination for the extraction of protease and lipase. It was observed that the concentration of 0.1% and 1% Triton X-100 has a strong influence for the extraction of lipase and protease respectively. Closer study of the enzyme extraction process is essential for different enzymes from activated sludge process.

Distinct soil microplastic distributions under various farmland-use types around Urumqi, China.

Very little is known about the occurrence of microplastics in the soils of various land uses, especially their distributional characteristics in the soils of arid areas. In this study, 24 sampling sites across three soil layers were investigated for three different farmland-use types (greenhouses, crop fields and vegetable fields) in the main agricultural and pastoral areas around Urumqi, China. The results demonstrated that the dominant sizes of soil microplastics were 0.2-0.5 and 0.5-1.0 mm, the main shape was film (85.93 %), the main color was white, and the main polymer was polyethylene (93.1 %), indicating that most microplastics derive from the damage to residual mulches. The microplastics abundance was highest in the greenhouse plots (7763 ± 2773 items/kg), followed by the vegetable plots (4128 ± 2235 items/kg) and then the crop fields (3178 ± 3172 items/kg). No significant differences were observed among the abundances of microplastics in the 0-10 cm (1822 ± 1345 items/kg), 10-20 cm (1566 ± 1139 items/kg) and 20-30 cm (1309 ± 1028 items/kg) layers, suggesting that microplastics can migrate to the deeper soil layer and are strongly influenced by tillage disturbance. The abundance of microplastics in the north of Urumqi was found to be higher than in the south, which is closely related to the division of agricultural functional zones and the intensity of agricultural management practices. It was found that different cropping characteristics and modes of agricultural use affect the abundance and migration of microplastics in various farmland-use types, and thus their distribution. This study provides important data for follow-up research on microplastics in arid terrestrial ecosystems, and corresponding policy-making on the management of these materials.

Efficient bio-cementation between silicate tailings and biogenic calcium carbonate: Nano-scale structure and mechanism of the interface.

Biogenic calcium carbonate (bio-CaCO3) cementing tailings is an efficient technology to immobilize heavy metals in waste tailings. However, the underlying mechanism of interface cementation has not yet been clearly established, which limits the technological development. In this study, we used advanced techniques, including atomic force microscopy-based Lorentz contact resonance (AFM-LCR) spectroscopy, AFM-based nanoscale infrared (AFM-IR) spectroscopy, and solid-state nuclear magnetic resonance (ssNMR) spectroscopy, to reveal the structural, mechanical, and chemical properties of the interface on the nanoscale. Ureolytic bacteria produced bio-CaCO3 to fill in pore space and to bind cement tailings particles, which prevented the formation of leachate containing heavy metals. After cementation, a strong 40-300 nm thin interface was formed between the taillings and bio-CaCO3 particles. Unlike chemically synthesized CaCO3, bio-CaCO3 is strongly negatively charged, which gives it better adhesion ability. Fourier transform infrared (FTIR), AFM-IR, and 29Si ssNMR spectra indicated that the Si-OH and Si-O-Si groups on the silicate surface were converted to deprotonated silanol groups (≡Si-O-) at a high pH and they formed strong chemical bonds of Si-O-Ca on the interface through a Ca ion bridge. In addition, hydrogen bonding with Si-OH also played a role at the cementation interface. These findings provide the nano-scale interfacial structure and mechanism of bio-CaCO3 cementing silicate tailings and accelerate the development of tailings disposal technology.

Interactions between microplastics and contaminants: A review focusing on the effect of aging process.

Microplastics (MPs) in the environment are a major global concern due to their persistent nature and wide distribution. The aging of MPs is influenced by several processes including photodegradation, thermal degradation, biodegradation and mechanical fragmentation, which affect their interaction with contaminants. This comprehensive review aims to summarize the aging process of MPs and the factors that impact their aging, and to discuss the effects of aging on the interaction of MPs with contaminants. A range of characterization methods that can effectively elucidate the mechanistic processes of these interactions are outlined. The rate and extent of MPs aging are influenced by their physicochemical properties and other environmental factors, which ultimately affect the adsorption and aggregation of aged MPs with environmental contaminants. Pollutants such as heavy metals, organic matter and microorganisms have a tendency to accumulate on MPs through adsorption and the interactions between them impact their environmental behavior. Aging enhances the specific surface area and oxygen-containing functional groups of MPs, thereby affecting the mechanism of interaction between MPs and contaminants. To obtain a more comprehensive understanding of how aging affects the interactions, this review also provides an overview of the mechanisms by which MPs interact with contaminants. In the future, there should be further in-depth studies of the potential hazards of aged MPs in different environments e.g., soil, sediment, aquatic environment, and effects of their interaction with environmental pollutants on human health and ecology.

Microplastic biodegradability dependent responses of plastisphere antibiotic resistance to simulated freshwater-seawater shift in onshore marine aquaculture zones.

MPs carrying ARGs can travel between freshwater and seawater due to intensive land-sea interaction in onshore marine aquaculture zones (OMAZ). However, the response of ARGs in plastisphere with different biodegradability to freshwater-seawater shift is still unknown. In this study, ARG dynamics and associated microbiota on biodegradable poly (butyleneadipate-co-terephthalate) (PBAT) and non-biodegradable polyethylene terephthalate (PET) MPs were investigated through a simulated freshwater-seawater shift. The results exhibited that freshwater-seawater shift significantly influenced ARG abundance in plastisphere. The relative abundance of most studied ARGs decreased rapidly in plastisphere after they entered seawater from freshwater but increased on PBAT after MPs entered freshwater from seawater. Besides, the high relative abundance of multi-drug resistance (MDR) genes occurred in plastisphere, and the co-change between most ARGs and mobile genetic elements indicated the role of horizontal gene transfer on ARG regulation. Proteobacteria was dominant phylum in plastisphere and the dominant genera, such as Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Afipia, Gemmobacter and Enhydrobacter, were significantly associated with qnrS, tet and MDR genes in plastisphere. Moreover, after MPs entered new water environment, the ARGs and microbiota genera in plastisphere changed significantly and tended to converge with those in receiving water. These results indicated that MP biodegradability and freshwater-seawater interaction influenced potential hosts and distributions of ARGs, of which biodegradable PBAT posed a high risk in ARG dissemination. This study would be helpful for understanding the impact of biodegradable MP pollution on spread of antibiotic resistance in OMAZ.

Mechanisms for enhanced lignin humification with reduced organic matter loss by goethite in biogas residue composting.

In this study, effects of three iron (oxyhydr)oxides on the biogas residue composting, i.e., composting with goethite (CFe1), hematite (CFe2) or magnetite (CFe3), were investigated. Results showed that composting performance of CFe1 was much better than those of CFe2 and CFe3. Addition of goethite increased temperature of CFe1 and enhanced lignin humification. More than 31.49% of Fe(III) in goethite was reduced to amorphous Fe(II) during the composting, suggesting that goethite worked as electron acceptor for microbial metabolism and heat generation. The functional bacteria Chloroflexi and Actinobacteria, and genes encoding key enzymes (AA1 family), which play essential roles in humification of lignin, were enriched in CFe1. Besides, goethite reduced 10.96% organic matter (OM) loss probably by increasing the molecular size and aggregation of OM for its protection during the composting. This study shows that adding goethite is an efficient strategy to enhancing the humification of lignin-rich biowaste.

The persistently breaking trade-offs of three-decade plastic film mulching: Microplastic pollution, soil degradation and reduced cotton yield.

Plastic mulching has been extensively used for near 40 years in China because of the commonly recognized trade-offs between economic profit and adverse impacts. Whether the trade-offs is well kept after decades of mulching usage is poorly understood. In this study, microplastic (MP) pollution, soil physical properties, as well as the root traits and yields of cotton under plastic mulching for different years (up to 32 years) in northwest China were investigated. The results showed that average abundance of MPs in soil ranged from 28.00 to 1426.67 items kg-1 and increased with time whereas size of MPs decreased with time. With respect to soil physical properties, bulk density and penetration resistance significantly increased with mulching time while saturated hydraulic conductivity and mean weight diameter of water-stable aggregates in cotton fields decreased over time, indicating that long-term plastic mulching has irreversible adverse impact on soil function. The significantly increased soil penetration resistance and decreased hydraulic conductivity substantially restricted root growth and this finally led to remarkable reduction of seed cotton yield. It is urgent for the agricultural departments to take appropriate measures to mitigate the constantly increased negative trade-offs of plastic mulching in the arid areas.

Temporospatial nano-heterogeneity of self-assembly of extracellular polymeric substances on microplastics and water environmental implications.

Environmental behavior and ecotoxicity of microplastics (MPs) are significantly influenced by the omnipresent self-assembly of microbial extracellular polymeric substances (EPS) on them. However, mechanisms of EPS self-assembly onto MPs at nanoscale resolution and effects of aging are unclear. For the first time, temporospatial nano-heterogeneity of self-assembly of EPS onto fresh and one-year aged polypropylene (PP) MPs were investigated by atomic-force-microscopy-infrared-spectroscopy (AFM-IR). Natural aging caused high degree nanoscale fragmentation of MPs physically and chemically. Self-assembly of EPS on MPs was aging-dependent. Polysaccharides were assembled on MP surface faster than proteins. Initially, regardless of the fresh or aged MPs, polysaccharides and proteins, with the former being predominant, were successively and separately assembled to different nanospaces because of their competition for binding sites. More and more proteins and polysaccharides were superimposed on each other with assembly time due to intermolecular forces. The nanochemical textural analysis showed that the nano-heterogeneity of EPS assembly to MPs was clearly correlated with the aging-induced nanochemical and nanomechanical heterogeneity of MP surface. The spontaneous self-assembly of EPS with temporospatial nano-heterogeneity on MPs have multiple impacts on behavior, ecotoxicity and fate of MPs and their associated pollutants as well as other key ecological processes in aquatic environment.

Microplastic Contamination in Urban, Farmland and Desert Environments along a Highway in Southern Xinjiang, China.

The different types of microplastics (MPs), including debris, fibers, particles, foams, films and others, have become a global environmental problem. However, there is still a lack of research and understanding of the pollution characteristics and main causes of MPs in the arid region of Xinjiang, China. In this survey, we focused on the occurrence and distribution of MPs in urban, farmland and desert areas along a highway in the survey area. Our results showed that the main types of MPs were polypropylene (PP) flakes, polyethylene (PE) films and both PE and PP fragments and fibers. The abundance levels of MPs in street dust of Korla, Alar and Hotan districts equaled 804, 307 and 1526 particles kg−1, respectively, and were positively correlated with the urban population. In farmland areas, there were only two types of MPs (films and fibers), of which the film particles dominated and accounted for 91% of the total on the average. The highest abundance rate of MPs reached 7292 particles kg−1 in the desert area along the highway. The minimum microplastic particle sizes were 51.8 ± 2.2 µm in urban street dust samples, 54.2 ± 5.3 µm in farmland soil samples and 67.8 ± 8.4 µm in samples from along the desert highway. Particle sizes < 500 µm were most common and accounted for 48−91% of the total in our survey. The abundance and shape distribution of the MPs were closely related to the different types of human activities.

Characteristics and distribution of microplastics in shoreline sediments of the Yangtze River, main tributaries and lakes in China-From upper reaches to the estuary.

Microplastics (MPs) pervade the environment and increasingly threaten both natural ecosystems and human health. In this study, we investigated MP particle concentrations in sediment samples collected from 54 sites along the banks of the Yangtze River and its major tributaries and on lakeshores. The main polymer types found in the samples were polypropylene (PP), polystyrene (PS) and polyethylene (PE). MP particle abundance in the various types of locations was 35-51,968 particles/kg dry weight (d.w.) on the banks of the main river, 52-1463 particles/kg (d.w.) on the banks of tributaries and 2574-23,685 particles/kg (d.w.) on lakeshores. Correlation between MP abundance and mean annual runoff of each upstream tributary was significant, which suggests that increased runoff brings more microplastic waste to streambank sediments. The most common shape of MP particles in all upstream samples was flake, and in downstream samples it was foam. Small microplastic particles (< 0.50 mm) were predominant at all sites in this study, and the minimum particle size in samples from the Yangtze river banks was 0.065 mm. Average abundance of MP particles on the shores of the source lake was 9069 particles/kg around the inlet but only 866 particles/kg around the outlet; the difference was due to interception associated with sedimentation and precipitation in the lake. Our study represents the large-scale study of MPs contamination in sediment along the Yangtze River and provides important data regarding the accumulation and distribution of MPs in shoreline sediments of the upper, middle and lower reaches of the Yangtze River, main tributaries and lakes in China.

Effects of aging on environmental behavior of plastic additives: Migration, leaching, and ecotoxicity.

Microplastics (MPs), an emerging pollutant, are of global concern due to their wide distribution and large quantities. In addition to MPs themselves, various additives within MPs (such as plasticizers, flame retardants, antioxidants and heavy metals) may also have harmful effects on the environment. Most of these additives are physically bound to plastics and can therefore be leached from the plastic and released into the environment. Aging of MPs in the actual environment can affect the migration and release of additives, further increasing the ecotoxicological risk of additives to organisms. This work reviews the functions of several commonly used additives in MPs, and summarizes the representative characterization methods. Furthermore, the migration and leaching of additives in the human environment and marine environment are outlined. As aging promotes the internal chain breaking of MPs and the increase of specific surface area, it in turn stimulates the release of additives. The hazards of additive exposure have been elucidated, and various studies from the laboratory have shown that more toxic additives such as phthalates and brominated flame retardants can disrupt a variety of biological processes in organisms, including metabolism, skeletal development and so on. Increase of MPs ecological risk caused by the leaching of toxic additives is discussed, especially under the effect of aging. This study presents a systematic summary of various functional and environmental behaviors of additives in plastics, using weathering forces as the main factor, which helps to better assess the environmental impact and potential risks of MPs.

Accumulation of microplastics in tadpoles from different functional zones in Hangzhou Great Bay Area, China: Relation to growth stage and feeding habits.

Microplastics (MPs) are ubiquitous in freshwater ecosystems, including inland small waterbodies (e.g., ponds and ditches), which are unique habitats for tadpoles. The uptake of MPs by tadpoles is influenced by their habitat, life stage, and feeding strategy. In this study, we investigated MP levels in small waterbodies in three different functional zones from the Hangzhou Great Bay Area, China, and resident tadpoles at different stages of metamorphosis with different feeding habits. Our results indicated that MPs in all three sampling areas were predominantly fibers; and the highest abundances of MPs were observed in water (4.70 ± 2.30 items/L) and sediment (728 ± 324 items/kg) from a textile industrial area, likely the result of nearby human activities. There was no significant difference in MP number in tadpoles between areas; however, omnivorous tadpoles with labial teeth and horny beaks ingested more MPs than did filter feeders. Based on their developmental characteristics, the collected tadpoles were categorized as: pre-metamorphosis, pro-metamorphosis, and metamorphic climax. The MP levels exhibited an upward trend, and MP size gradually increased as tadpole development progressed. This suggests that MPs may accumulate in tadpoles as they grow and potentially affect their metamorphosis from larvae to frogs.

Persistent versus transient, and conventional plastic versus biodegradable plastic? -Two key questions about microplastic-water exchange of antibiotic resistance genes.

The ubiquitous microplastics (MPs) in water environment play an important role in the dissemination of antibiotic resistance genes (ARGs) due to their exchange between floating MPs and receiving waters. However, whether the ARG exchange is persistent or transient and what are the differences in ARG exchange between conventional plastics and biodegradable plastics are the two key issues to be addressed. In this study, biodegradable PBAT and non-biodegradable PET MPs were chosen to explore the MP-water ARG exchange after the MPs floated to the receiving waters. The results demonstrated that the active exchange of ARGs between MPs and receiving waters occurred, which, however, were transient for most of ARGs. The relative abundance of ARGs both on the MPs and in the waters rapidly decreased to the initial or lower levels within 4 weeks. Approximately 25-50% (ARG subtype number ratio) of studied ARG subtypes were introduced into the receiving waters by MPs, and 35-65% of studied ARG subtypes went through fluctuation in terms of abundance on MPs and in the receiving water. ARGs tended to converge between MPs and the receiving waters with time. Furthermore, the ARG exchange between MPs and waters facilitated horizontal gene transfer (HGT). IntI1 and tnpA05 played the crucial roles in HGT, which was indicated by their correlated change with most ARGs; in contrast, tnpA04 showed the obvious lagging responses. The biodegradable MP of PBAT generally accumulated higher levels of most ARGs including multidrug resistant genes than the non-biodegradable MP of PET. The transient exchange of most ARGs between MPs and water implies that the on-off hitchhiking of ARGs on MPs in aquatic environment may not exert significant influence on ARG transmission. However, compared with the conventional plastics, the biodegradable MPs might pose much higher ARG dissemination risks due to the higher enrichment of ARGs particularly with people's ever-increasingly usage. Enough attention must be paid to this emerging issue.

Interactions between polypropylene microplastics (PP-MPs) and humic acid influenced by aging of MPs.

As an emerging pollutant, microplastics (MPs) may interact with dissolved organic matter (DOM) which is prevalent in the aqueous environment. Meanwhile, the aging of MPs in the actual environment increases the uncertainty of their environmental fate. Here, the interaction mechanisms between pristine and aged polypropylene microplastics (PP-MPs) and humic acid (HA) at pH 7.0 were explored. Microstructural changes of HA were examined by fluorescence and Fourier transformation infrared (FT-IR) spectroscopy. Atomic force microscopy coupled with infrared (AFM-IR) and micro-Raman techniques were used to characterize and analyze the interacted PP-MPs. The addition of HA increased the surface roughness of both pristine and aged PP-MPs. Results of AFM-IR and Raman spectra showed that the interaction of PP-MPs with HA accelerated their surface oxidation and enhanced the characteristic signals. XPS spectra showed that the oxygen content ratio of pristine and aged PP-MPs increased by 0.95% and 1.48% after the addition of HA, respectively. PP-MPs after aging interacted more strongly with HA and there was a higher affinity between them. Two-dimensional correlation spectroscopy (2D-COS) combined with FT-IR spectra further elucidated the interaction mechanism at the molecular level. This work will help to evaluate the environmental impact of MPs in ecosystems and understand their interactions with DOM.

Environmental behaviors of microplastics in aquatic systems: A systematic review on degradation, adsorption, toxicity and biofilm under aging conditions.

Microplastics (MPs, < 5 mm) in the environment have attracted worldwide attention due to their wide distribution and difficulty in handling. Aging processes such as UV irradiation, biodegradation, physical abrasion and chemical oxidation can affect the environmental behavior of MPs. This review article summarizes different aging processes of MPs and subsequent effects on the adsorption of pollutants, the leaching of additives, and the toxicity of MPs. In addition, the formation process of biofilm on the surface of MPs and the interactions between biofilm and aged MPs are revealed. MPs can accumulate different environmental pollutants (organic pollutants, heavy metals, microorganisms, etc.) through surface adsorption, pore filling and distribution. Moreover, the aging of MPs affects their adsorption performance toward these pollutants due to a series of changes in their specific surface area and oxygen-containing functional groups. The release of some toxic additives such as phthalates after aging can enhance the toxic effects of MPs. Aging also changes the shape and size of MPs, which can affect the eating habits of the organisms and further increase the potential toxicity of MPs. This article conducts a systematical analysis and summary of the environmental behavior and physicochemical properties of MPs as well as the changes due to MPs aging, which helps to better understand the impact of aging on MPs in the environment. Future research on MPs aging should reduce the knowledge gap between laboratory simulation and actual conditions and increase the environmental relevance.

Biofilm enhances the copper (II) adsorption on microplastic surfaces in coastal seawater: Simultaneous evidence from visualization and quantification.

Microplastics (MPs) exposed to the urban coastal seawater could form biofilms, which facilitate the adsorption and transportation of hazardous contaminants. However, influence of biofilms on the metal adsorption of MPs, especially the co-existence of biofilm and metals on MPs, is still less known. In this study, the adsorption of copper (Cu) on biofilm-coated MPs (BMPs) was visually analyzed and quantified. The results of scanning electron microscopy in combination with energy dispersive X-ray showed that biofilm and metals co-occurred on MPs in seawater. The nanoscale secondary ion mass spectrometry images further exhibited that the distribution of Cu, chlorine (Cl) and biofilm on MP surfaces was highly consistent. Moreover, the adsorption of Cu(II) on BMPs was enhanced as quantified by inductively coupled plasma-mass spectrometer. Furthermore, different species on BMPs with and without Cu were identified, and their potential functions of metal or Cl metabolism were predicted based on KEGG pathway database. Overall, for the first time, this study provides visual and quantified evidences for the enhancement of Cu(II) adsorption on BMPs based on co-localization, and it may shed a light on the development of methodologies for investigating the interaction among MPs, biofilms and pollutants in marine environment.

Microplastics distribution in different habitats of Ximen Island and the trapping effect of blue carbon habitats on microplastics.

Sediments are considered to be important sinks of microplastics, but the enrichment process of microplastics by blue carbon ecosystems is poorly studied. This study analyzed the spatial distribution and temporal changes, assessed the polymer types and morphological characteristics of microplastics in sediments of five ecosystems, i.e. forests, paddy fields, mangroves, saltmarshes and bare beaches on Ximen Island, Yueqing Bay, China. The trapping effect of blue carbon (mangrove and saltmarsh) sediments on microplastic was further explored. Temporal trends in microplastic abundance showed a significant increase over the last 20 years, with the enrichment of microplastics in mangrove and saltmarsh sediments being 1.7 times as high as that in bare beach, exhibiting blue carbon vegetations have strong enrichment effect on microplastics. The dominant color, shape, size, and polymer type of microplastics in sediments were transparent, fibers and fragments, <1 mm, and polyethylene, respectively. Significant differences in the abundance and characteristics of microplastics between intertidal sediments and terrestrial soils reveal that runoff input is the main source of microplastics. This study provided the evidence of blue carbon habitats as traps of microplastics.