Microplastics in Sewage Sludge: Effects of Treatment

Decreased particle size enhances the aging behavior of microplastics during sewage sludge composting: Physicochemical properties and cadmium loading

Although aerobic composting is capable of aging microplastics (MPs), the influence of size on MPs aging during composting and loading of cadmium (Cd) remains unclear. Therefore, we investigated variations in the physicochemical properties of polyethylene terephthalate microplastics (PET-MPs) with different sizes (1.0 -5.0, 0.2 -1.0, and 0.05 -0.2 mm) during composting and the concentration of Cd accumulated on the surface of different-sized aged PET-MPs. The results indicated that PET-MPs exhibited size-dependent as they aged during composting, with smaller sizes aging faster. After composting, the 0.05 -0.2 mm PET-MPs had the greatest increase in specific surface area (205.5 %), compared with the 1.0 -5.0 mm (18.7 %) and 0.2 -1.0 mm (95.6 %) PET-MPs. The greatest increase in the carbonyl index/oxygen-to-carbon atom ratio was also observed for the 0.05 -0.2 mm PET-MPs, which were 2.25 / 3.27 and 0.02 / 2.11 times higher than those of the 1.0 -5.0 mm and 0.2-1.0 mm PET-MPs, respectively. Similarly, size-dependent accumulation of Cd on the aged PET-MPs was also observed: 0.05-0.2 mm (5.37 mg/kg Cd) > 0.2 -1.0 mm (2.90 mg/kg Cd) > 1.0-5.0 mm (0.78 mg/kg Cd). These findings demonstrate that the aging behavior of polymer is closely related to their size, emphasizing the role of size in the fate and pollutant loading of polymer.

Microplastics accumulation in leaf litter: Field evidence for microplastic ingestion and transfer through prey-predatory relationships

Microplastics (MP) contamination of the terrestrial environment is a global concern. The contamination level of MPs in leaf litter and soil fauna that feed on it has not been reported. Moreover, the interspecific relationships among field soil fauna at different trophic levels and their effects on MP loads remain unclear. Thus, we selected a model food chain including a prey-isopod and predatory-spider relationship to evaluate the role of this relationship in the MPs body burden. The results showed that MP concentrations in the fallen leaf litter ranged from 5340 ± 336.15 particles/kg to 10920 ± 432.43 particles/kg dry weight during different seasons of the monitoring year. However, we found MP particles ranged from 1.17 ± 0.25 to 10.11 ± 1.02 particles/ind in isopods and 2.25 ± 0.35 to 4.25 ± 0.35 particles/ind in spiders. All extracted MPs were colored and blue was the most prevalent one. Fiber-shaped polyester (≤500 μm) and (501-1000 μm) were the most common MPs size in tested fauna and leaf litter, respectively. Our findings indicate that MP ingestion by isopods pose a significant risk for higher trophic levels in the terrestrial food chain. Magnification of MPs was observed in the predatory spider with MP concentration increasing from 46.45 ± 16.68 particles/gm wet weight in isopod to 147.51 ± 54.4 particles/gm wet weight in spider, annually. Furthermore, the results indicate that these soil invertebrates may represent a source of MPs to other organisms in the environment.

Smaller sizes of polyethylene terephthalate microplastics mainly stimulate heterotrophic N2O production in aerobic granular sludge systems

Widespread polyethylene terephthalate microplastics (PET MPs) have played unintended role in nitrous oxide (N2O) turnovers (i.e., production and consumption) at wastewater treatment plants (WWTPs). Mainstream aerobic granular sludge (AGS) systems possess potentially strong N2O-sink capability, which may be reduced by PET MPs stress through altering N2O-contributing pathways, electron transfer, and microbial community structures. In this study, the effects of PET MPs with two common particle sizes of effluent from WWTPs (0.1 and 0.5 mm) on N2O turnovers, production pathways and N2O-sink capability were systematically disclosed in AGS systems by a series of biochemical tests and molecular biological means to achieve the goal of carbon neutrality. The results indicated that 0.1 mm PET MPs could more significantly stimulate N2O production in AGS systems by inhibiting denitrifying metabolism, compared with control and 0.5 mm PET MPs systems. Specifically, 0.1 mm PET MPs slightly increased the relative abundance of Nitrosomonas, reducing N2O yields via promoting the hydroxylamine (NH2OH) oxidation pathway during nitrification. Also, 0.1 mm PET MPs inhibited the electron transport system activities and the relative abundance of N2O reductase, hindering N2O reduction during denitrification. Most importantly, 0.1 mm PET MPs more apparently reduced the N2O-sink capability based on the ratio of N2O reductase gene and nitrite reductase gene.

Microplastics in agricultural soils following sewage sludge applications: Evidence from a 25-year study

Sewage sludges applied to agricultural soils are sources of microplastic pollution, however, little is known about the accumulation, persistence, or degradation of these microplastics over time. This is the first study to provide long-term, high temporal resolution quantitative evidence of microplastics in agricultural soils following sewage sludge application. The abundance and degradation of microplastics was assessed in soils sampled biennially from an experimental field over a 25-year period managed under an improved grassland regime following the application of five different sewage sludges. The sludges contained different microplastic compositions reflecting the different sources of the sludges. Microplastic abundance increased by 723-1445% following sewage sludge applications (p < 0.05) and remained constant over time (22 years and possibly beyond) (p > 0.05). All sludges predominantly added white/transparent microfibres to soil. Microfilms, microfibres, and fragments were most susceptible to degradation, potentially creating micro(nano)plastics. Of note was the discoloration of coloured microfibres, which may be environmentally hazardous due to the toxicity of textile dyes in soil ecosystems. We also found that plastic composition could be used to trace its source. This evidence is useful in informing regulation on sewage sludge use and management, and in assessing the fate and impact of microplastics in soil.

Tackling microplastic contamination in sewage sludge: Optimizing organic matter degradation, quantifying microplastic presence, and evaluating ecological risks for sustainable agriculture

The omnipresence of Microplastics (MPs) is a growing global concern. Using sewage sludge as fertilizer for soil amendment can be a potential source of MPs in agricultural soil if sludge contains MPs. Sludge is a complex matrix rich in organic matter, which hinders MPs separation. For maximal organic matter degradation, in this study, the application of Fenton reagents optimized for (Fe2+/H2O2) molar ratios, i.e., 1/2, 1/4, 1/6, 1/8, and 1/10. The results show that a molar ratio of 1/2 of Fe2+/H2O2 can remove 86.6 % of the organic matter in the sewage sludge. The greenness of the optimized method was assessed and compared to available methods using AGREEprep software. The method achieved a greenness score of 0.61, significantly higher than the highest score of 0.45 among the previously reported optimized methods. This optimized method was used in the analysis of MPs in sewage sludge from 14 sewage treatment plants in Ahmedabad. Also, the ecological risks due to the application of such sludge in agriculture were assessed. MPs analysis reveals variability in MPs contamination ranging from 2.43 to 22.72 × 103 units/kg of sludge. Small-sized MPs (0.05-0.25 mm) constitute the highest proportion (65 %), predominantly comprising fibers and fragments. From a chemical composition point of view, six different types of MPs are identified, among which PU, Nylon, HDPE, and PP are the most abundant. Ecological risk assessment indicated extreme hazards in terms of the potential ecological risk index being higher than 1200 for all the sludge samples due to the abundance of MPs, specifically of PU and Nylon.

Microplastics in the European native oyster, Ostrea edulis, to monitoring pollution-related patterns in the Solent region (United Kingdom)

Microplastics (MPs) are the most abundant type of debris in the marine environment, creating a significant threat to aquatic ecosystems due to their persistence, ability to absorb organic pollutants and potential ingestion by marine fauna. Shellfish are particularly vulnerable to MPs accumulation as they filter large volumes of seawater, and they become an important route for human exposure to these particles. This study, the first to examine MPs in European flat oyster (Ostrea edulis) populations, aimed to quantify these particles in the gill and digestive tissues of oysters from the Solent region (southern England). Enzymatic digestion using Proteinase-K was used in this study and MPs were identified in every oyster sampled to determine whether differences in abundance, type and size of MPs exist between locations. Oysters near urban areas contained significantly more MPs than those near rural areas. Fibres were the most prevalent type of MPs, with sizes varying across locations. The study found no significant differences in MPs presence between gills and digestive tissues, and an inverse correlation between the size of MPs and oyster size. The presence of MPs in wild O. edulis could be an additional threat to the survival of an already threatened species and may pose health risks for predatory species and human consumers of seafood. The use of O. edulis as a biomonitoring species for marine MPs pollution could help determine the extent, distribution and sources of MPs, potentially informing management strategies to reduce pollution.

Review of Techniques for the Detection, Removal, and Transformation of Environmental Microplastics and Nanoplastics

Plastic residues have emerged as a significant challenge in the environmental sector. Microplastics, which are plastic fragments smaller than 5 mm, have the ability to disperse through the atmosphere, oceans, and land, posing a serious threat to human health by accumulating in the food chain. However, their minuscule size makes it difficult to effectively remove them from the environment using the current technologies. This work provides a comprehensive overview of recent advancements in microplastic detection and removal technologies. For detection methods, we discuss commonly used techniques such as microscopic analysis, thermal analysis, mass spectrometry, spectroscopic analysis, and energy spectrometry. We also emphasize the importance of integrating various analytical and data-processing techniques to achieve efficient and nondestructive detection of microplastics. In terms of removal strategies, we explored innovative methods and technologies for extracting microplastics from the environment. These include physical techniques like filtration, adsorption, and magnetic separation; chemical techniques such as coagulation-flocculation-sedimentation and photocatalytic conversion; and bioseparation methods such as activated sludge and biodegradation. We also highlight the promising potential for converting microplastic contaminants into high-value chemicals. Additionally, we identify current technical challenges and suggest future research directions for the detection and removal of microplastics. We advocate for the development of unified and standardized analytical methods to guide further research on the removal and transformation of microplastics.

Microplastic removal, identification and characterization in Chennai sewage treatment plants

Sewage treatment plants (STPs) act as either sinks or sources of microplastic (MP) contamination in the environment. This study examined and assessed the occurrence, removal efficiencies, abundance and characteristics of MPs in two STPs in Chennai, India. Large volumes of influent and effluent water were collected and filtered on site via a filter in a series system. The samples were later treated in the laboratory to isolate the MPs from other organic and inorganic particles. The MPs were analysed via Fourier Transform Infra-Red (FTIR) spectroscopy and Raman spectroscopy to analyse the chemical composition of the isolated microplastics. Pollution load index (PLI) and EU classification, labelling and packaging (CLP) standard was incorporated to assess the pollution risk of MPs in STP. According to the results obtained from this research work, the MP concentrations in the influent waters were high for both STPs (5443 MPs/L and 4800 MPs/L). Although the MP removal efficiency of the STPs were quite high (~96 % and ~93 %), the pollution load indices at Kodungaiyur and Koyambedu STPs were observed to be 0.272 and 0.208 respectively, which were moderately contaminated. PORI scores revealed that Kodungaiyur Plant is in danger level I with the hazard score of 9.25 and Koyambedu plant is in danger level II with the hazard score of 12.78. The estimated quantity of the MPs discharged from the monitored STPs was approximately 28.4 & 28.2 billion MPs/day.

Sewage treatment plants as a potential source of microplastics in the environment: A preliminary study in Central India

The presence of microplastics in various environmental matrices is a reality. Besides, sewage treatment plants (STPs) play a crucial role in further adding to the microplastic pool of the environment, especially in water and soil resources. As conventional STPs are not primarily meant to remove microplastics, treated effluent and sludge contain a significant amount of microplastic items which are ultimately discharged into the surface water/soil. The present study investigated the role of selected STPs of Central India in contributing microplastics to the environment. Inlet, outlet, and sludge samples were collected from seven STPs and analyzed for the presence of microplastics. Microplastics were found in all samples with higher amounts in the inlet samples (3-35.5 items/L) compared to the outlet samples (2-13.5 items/L). Nevertheless, sludge samples showed the highest amount of microplastics (16-389 items/kg) for all the STPs under study. Size, shape, color, and chemical composition of microplastics was varied with considerable presence of polyethylene, polypropylene, polyethylene-terephthalate, polyvinylchloride, polystyrene, polyamide, polyacrylamide, polyester, and polyurethane. Discharge of these microplastic items in the surface water and terrestrial ecosystems may result in serious consequences for ecology and human health. Therefore, advanced technological development for effective microplastics' removal in STPs is inevitable.

Microplastics in freshwater and marine ecosystems: Occurrence, characterization, sources, distribution dynamics, fate, transport processes, potential mitigation strategies, and policy interventions

Most of the literature on microplastics (MPs) focuses on freshwater or terrestrial ecosystems, frequently overlooking their interconnections with the marine environments. This oversight is worrying given that both ecosystems serve as primary pathways for the introduction of MPs into marine environments. This review synthesizes existing literature on MPs in both freshwater and marine ecosystems across all six continents. The most commonly produced plastic polymers in industry are polyethylene (36 %) and polypropylene (21 %), and studies revealed that these two materials are the most abundant in aquatic ecosystems. Primary and secondary MPs originate from a range of sources including land-based disposal, the ocean, airborne deposition, wastewater treatment facilities, automobiles, pharmaceuticals and personal care products, synthetic textiles, and insect repellents. Notably, secondary MPs, which are formed from the breakdown of larger plastic items comprise approximately 69-81% of marine debris, especially in urbanized, densely populated areas. The inconsistencies of the methodologies (sampling, extraction, and quantification) and the units employed for result presentations are part of the major limitations in MPs research. Environmental phenomena such as heteroaggregation, weathering, adsorption, leaching, and fragmentation are the major factors influencing the behavior, fate, and degradation process of plastic particles. The physicochemical properties of plastic polymers, such as density, crystallinity, as well as bioturbation, meteorological forces, and wind actions, including currents, waves, and tides, are responsible for biofouling, aggregation, sinking into the bottom sediment, resuspension, and the vertical, horizontal, and spatiotemporal distributions and transport of MPs. The potential solutions to mitigate plastic pollution are grounded in the 3Rs framework, which includes reducing production and consumption, advancing the biotechnological, chemical and microbial development of degradable polymers, promoting reusable plastic products with lower environmental impacts over their lifetimes, and recycling waste into new products. The regulatory policies on single-use plastics commonly involve permanent bans and financial penalties for violators. In addition, nations such as the United States, the Netherlands, and northern Europe have introduced economic incentives to encourage the return of reusable materials to reduce plastic waste and the resulting envrionmental pollution.

Microplastics in an anaerobic digester treating sewage sludge: Occurrence and factors affecting their identification with Raman spectroscopy

Significant share of microplastics entering wastewater treatment is accumulated in sewage sludge, which is commonly treated by anaerobic digestion. The digestate is typically separated to solid and liquid fractions, and the solid fraction is often land-applied. However, the division of microplastics between these fractions is poorly understood. Thus, we investigated the occurrence of microplastics (>20 μm) at an anaerobic digester and the subsequent solid-liquid separation. Sewage sludge and digestate exhibited 7600 ± 6800 and 7200 ± 1100 microplastics per g dry weight, respectively, indicating that anaerobic digestion can decrease the fluctuation in microplastics' occurrence in sewage sludge. The microplastic flow was predominantly directed to the solid fraction, while the liquid fraction carried about 1 % of the microplastics, mostly polymers with low density (polyethylene and polypropylene). We also investigated factors affecting microplastics' identification by Raman spectroscopy. Microplastic degradation and presence of organic matter after oxidative digestion in the sample preparation, and anaerobic digestion of sewage sludge affected the spectra of different microplastics. For polyethylene and polypropylene, these changes did not interfere with recognizing their characteristic peaks, allowing high-certainty identification. In contrast, polyamide identification was notably compromised as signal-to-noise ratio can be deteriorated and natural organic matter can be misidentified as polyamide.

In situ formed sulfide-mediated aging of polystyrene microplastics and its impact on the fate of heavy metals in anaerobic digestion

Microplastics (MPs) entering wastewater treatment plants accumulate in sludge and are subsequently introduced into anaerobic digesters, a key sludge treatment process. However, little is known about how MPs undergo transformation during anaerobic digestion (AD). This study investigated the mechanism underlying the aging of polystyrene (PS) MPs in AD and its effect on heavy metal adsorption. In the AD batches containing an initial sulfate concentration of 5.1 mM, significant sulfate reduction (96.1 %) was observed, with reduced sulfur species accounting for 74 % of the total sulfur species deposited on the PS surface, as revealed by X-ray photoelectron spectroscopy. A positive correlation between sulfide formation and the selective proliferation of sulfur-reducing bacteria, particularly Desulfovibrio aminophilus, indicated the involvement of microorganisms in sulfur aging. The decomposition of in situ hydrogen peroxide (H2O2) and formation of hydroxyl radicals (∙OH) under sulfidogenic conditions were more pronounced, suggesting that reactive oxygen species may induce structural changes in PS MPs and potentially facilitate sulfur aging. Finally, isothermal titration calorimetry results showed that sulfur-aged PS had higher binding constants for Pb²⁺ and Cu²⁺ compared to pristine PS, due to the presence of sulfur-containing functional groups and a more negative surface charge. These findings provide valuable insights into the fate of MPs during the sludge treatment and their potential environmental impacts.

Torrefaction of sewage sludge: An approach to nutrient recycling and contaminant reduction in agriculture

The disposal of sewage sludge, a byproduct of wastewater treatment, presents both opportunities and challenges in agricultural applications due to its rich nutrient content and potential pollutant load. This study investigates the effects of torrefaction, a low-temperature thermochemical treatment, on the elemental composition and organic pollutant content of sewage sludge and its impact on maize (Zea mays L.). Sewage sludge from a municipal wastewater treatment plant was torrefied at 320 °C for 3 h, then applied to soil in a field experiment. The torrefaction process concentrated mineral nutrients such as phosphorus and potassium but reduced nitrogen and sulfur content. The content of available phosphorus and potassium decreased by only 28°% and 24°%, respectively. Importantly, torrefaction significantly decreased the concentrations of pharmaceuticals, synthetic musk compounds, and endocrine-disrupting compounds in the sludge, with reductions of over 90°% for most compounds. Persistent organic pollutants, including polychlorinated biphenyls and organochlorine pesticides, also showed significant reductions (99 and 95°%, respectively), although polycyclic aromatic hydrocarbons (PAHs) increased by 20°% due to torrefaction. Despite this, the PAH content in torrefied sludge (Σ16 PAH <3 mg/kg) remained below regulatory limits set for soil application. At higher application doses, the effect of torrefied sludge on agronomic performance of maize did not differ from that of dried sewage sludge. Torrefaction has demonstrated promising results in improving the safety and efficacy of sewage sludge as a fertilizer by reducing organic contaminants and increasing phosphorus and potassium contents without significantly diminishing their availability. However, the limited effectiveness of torrefaction in reducing PAH content must be carefully considered when evaluating its suitability for soil applications. Furthermore, the condensate produced during the torrefaction process was not analyzed in this study and may represent a potentially hazardous by-product due to its pollutant content.

Aluminum and microplastic release from reflective agricultural films disrupt microbial communities and functions in soil

Reflective agricultural films are widely used in vegetable production and orchards to repel pests, accelerate fruit ripening, and boost yields. These films, composed of a plastic base metallized with aluminum (Al), degrade over time in soil, releasing Al and microplastics. This study investigated the aging and weathering of Al-coated reflective films (polyethylene terephthalate, PET-based) under UV radiation, simulated rainfall, and soil burial for up to 120 days, assessing the effects of released Al and microplastics on soil chemistry and microbial communities. Weathering was confirmed by the formation of C-O/CO functional groups, an increasing carbonyl index, and the oxidation of Al to Al₂O₃, as shown by Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). Faster Al-coated shedding and PET oxidation were observed in the soil environment. Microplastics (0.5 % w/w) from the films reduced soil micronutrient availability (Fe, Mn, Cu), suppressed functional genes involved in carbon, nitrogen, and phosphorus cycling, and shifted microbial communities towards oligotrophic bacteria enrichment (e.g., RB41, Candidatus_Udaeobacter, Gemmatimonadetes, and Chloroflexi) while reducing copiotrophic bacteria (e.g., Sphingomonas, Ellin6067, Dongia, Puia, and Flavisolibacter). Therefore, these findings highlight that reflective film weathering strongly alters soil nutrient content and microbial community composition, with potential implications for soil health and agricultural sustainability.

Distribution and characteristics of Microplastics in leachate and underneath soil of two informal landfills

Microplastics (MPs), an emerging pollutant, have garnered global attention as significant environmental concerns. Landfills are the major sources of MPs. However, research on the distribution and characteristics of MPs in leachate and underneath soil of informal landfills remains limited. This study investigated the abundance, polymer type, size, and morphology of MPs in 6 leachate samples and 18 underneath soil samples at different depths from two informal landfills. The ranges of MPs abundance in leachate and underneath soil from landfills were 4,010-33,213 items/Land 592-870 to 47,819 items/kg, related to the landfilled waste composition. MPs size between 20 and 100 µm accounted for the highest proportion (70 %). The fragmentation coefficient α in the underneath soil was higher than that in the leachate, indicating smaller MPs were more likely to migrate into underneath soil after filtration. The fibrous MPs proportion was below 22 %, while the fragmented MPs was more than 78 %. Large fibrous MPs were detected in the underneath soil in landfill A. Polyethylene Terephthalate (PET), Polyurethane (PU) and Polystyrene (PS) were the predominant MPs polymers types in leachate and underneath soil. Polypropylene (PP) was primarily concentrated in the upper and middle underneath soil layers, and Polyurethane (PU) was predominantly in the middle and lower layers. Principal component analysis (PCA) results indicated that geographical factors significantly influenced the distribution and characteristics of MPs. This study revealed the distribution of MPs in leachate and underneath soil at different depths, providing a valuable reference for the risk assessment of MPs pollution.

The fate of biodegradable polylactic acid microplastics in maize: impacts on cellular ion fluxes and plant growth

The widespread application of biodegradable microplastics (MPs) in recent years has resulted in a significant increase in their accumulation in the environment, posing potential threats to ecosystems. Thus, it is imperative to evaluate the distribution and transformation of biodegradable MPs in crops due to the utilization of wastewater containing MPs for irrigation and plastic films, which have led to a rising concentration of biodegradable MPs in agricultural soils. The present study analyzed the uptake and transformation of polylactic acid (PLA) MPs in maize. Seed germination and hydroponic experiments were conducted over a period of 5 to 20 days, during which the plants were exposed to PLA MPs at concentrations of 0, 1, 10, and 100 mg L-1. Low concentrations of PLA MPs (1 mg L-1 and 10 mg L-1) significantly enhanced maize seed germination rate by 52.6%, increased plant shoot height by 16.6% and 16.9%, respectively, as well as elevated aboveground biomass dry weight by 133.7% and 53.3%, respectively. Importantly, depolymerization of PLA MPs was observed in the nutrient solution, resulting in the formation of small-sized PLA MPs (< 2 μm). Interestingly, further transformation occurred within the xylem sap and apoplast fluid (after 12 h) with a transformation rate reaching 13.1% and 27.2%, respectively. The enhanced plant growth could be attributed to the increase in dissolved organic carbon resulting from the depolymerization of PLA MPs. Additionally, the transformation of PLA MPs mediated pH and increase in K+ flux (57.2%, 72 h), leading to acidification of the cell wall and subsequent cell expansion. Our findings provide evidence regarding the fate of PLA MPs in plants and their interactions with plants, thereby enhancing our understanding of the potential impacts associated with biodegradable plastics.

Interaction of micro and nanoplastics (MNPs) with agricultural stored products and their pests

Micro and nanoplastics (MNPs) pose significant environmental concerns due to their potential implications for ecosystems and human health. While previous research has primarily focused on the environmental impacts (aquatic ecosystem, soil health) of MNPs, this review investigates their interactions with agricultural stored products, specifically their effects on stored product pests and grain quality. MNPs can infiltrate grains through various pathways, including atmospheric deposition, plastic residues from cultivation, and pest activity. These contaminants may influence pest feeding and behavioral patterns, reproductive cycles, and development. Simultaneously, MNPs have the potential to alter grain properties, including mineral content, protein composition, and starch synthesis, potentially compromising nutritional quality. Understanding these interactions is critical for developing strategies to mitigate the dual threats of MNP pollution and pest infestations to stored agricultural products.

Impact and mechanism of polyethylene terephthalate microplastics with different particle sizes on sludge anaerobic digestion

Municipal wastewater treatment plants (WWTPs) are important sinks for microplastics, and the vast majority of microplastics entering WWTPs are trapped in residual sludge. In order to investigate the effect of microplastics on anaerobic digestion of sludge, polyethylene terephthalate (PET) microplastics with common particle size and physical aging were selected to conduct a comparative study. Regardless of aging, the addition of 300 and 500 μm PET microplastics inhibited methane production, with their cumulative methane production reduced by 11.3-24.9% compared to the control group. In contrast, when 100 μm microplastics were added, the raw PET promoted methane production, yielding 337 L CH4/kg VS, while the aged experimental group showed similar yields to the control group. For the 800 μm microplastics treatment group, aged microplastics facilitated methane production while raw microplastics inhibited it, with methane production of 91.0% and 111% of the control group, respectively. The effects were also investigated by model fitting, stage discussion, and microbial community structure analysis. The results discovered that the main rate-limiting steps of adding microplastics with smaller or larger particle sizes (100, 800 μm) to methane production were solubilization and hydrolysis, while the main rate-limiting step of microplastics with medium particle sizes (300, 500 μm) was methanogenesis. Physically aged PET microplastics with smaller or larger sizes showed a more significant effect on methane production. Furthermore, PET microplastics altered the microbial community structure, shifting methanogens from acetotrophic pathways to hydrotrophic pathways. This study offers new insights into the performance analysis of sludge anaerobic digestion in practical WWTPs.

Mesophilic anaerobic digestion of mixed sludge in CSTR and AnMBR systems: A perspective on microplastics fate

Most microplastics (MPs) end up in the biosolids produced in wastewater treatment plants (WWTPs) and can pose contamination risks when the biosolids are applied to agriculture. This study evaluated the impact of mesophilic anaerobic digestion on the fate of MPs in WWTP sludge. For this, two laboratory-scale anaerobic digesters were operated in parallel, consisting of a continuous stirred tank reactor (CSTR) and a membrane bioreactor (AnMBR) equipped with an ultrafiltration membrane to decouple the hydraulic and sludge retention times. Both digesters were continuously fed with mixed sludge from a municipal WWTP. The results showed a significant reduction in the MP concentration, with the AnMBR having the higher MP removal efficiency (88.6% vs. 62.1%) and obtaining a higher percentage of biomethanisation (58.3% vs. 43.7%). Polypropylene (PP) and polyacrylonitrile were the main polymers in the mixed sludge, while PP and polyethylene were the dominant polymers in the digested samples. The MP particles in all the samples were predominantly in the 500-104 μm size range. Microbiological analysis indicates a greater species diversity in the microbial community of the AnMBR, the results also revealed a symbiotic relationship between the Firmicutes and Patescibacteria phyla in this digester.

Impacts of microplastic accumulation in aquatic environment: Physiological, eco-toxicological, immunological, and neurotoxic effects

The presence of microplastics (MPs) in aquatic ecosystem has become a pressing global concern. MPs pose a significant threat to aquatic ecosystems, with devastating consequences for both aquatic life and human health. Notably, freshwater ecosystems are particularly vulnerable to MPs pollution. MPs, characterized by their small size (< 5 mm), have emerged as a ubiquitous environmental pollutant. They exhibit diverse characteristics, including varying sizes, forms, polymer types, and colors. Two distinct categories of MPs exist: primary and secondary. Primary MPs are incorporated into industrial hard materials, cosmetics, and hand cleaners, whereas secondary MPs result from the breakdown of larger plastic products in both terrestrial and marine environments. They enter the environment through various sources, such as household products, clothing, industrial activities, sewage waste and plastic degradation. Aquatic organisms ingest these contaminants, facilitating the transfer of MPs into the food chain and potentially causing severe health problems. This review delves into the bioaccumulation of MPs in fish, highlighting the eco-toxicological, neurological and immunological effects. This review provides an in-depth analysis of innovative solutions for MPs removal and reduction. Finally, we delineate evidence-based strategies to mitigate impacts of MPs, offering valuable insights to inform policy formulations and accelerate the development of sustainable plastic technologies.

Microplastics in soils: A comprehensive review

Microplastics (MPs) have become pervasive pollutants in terrestrial ecosystems, raising significant ecological risks and human health concerns. Despite growing attention, a comprehensive understanding of their quantification, sources, emissions, transport, degradation, and accumulation in soils remains incomplete. This review synthesizes the current knowledge on the anthropogenic activities contributing to soil MP contamination, both intentional and unintentional behaviors, spanning sectors including agriculture, domestic activities, transportation, construction, and industry. Furthermore, it examines the spatial distribution, accumulation, and abundance of MPs across various land use types, alongside a critical assessment of existing quantification methodologies. While the predominant metric for MP quantification is particle number concentration, integrating mass and area concentration enhances the ability to compare pollution levels, assess fluxes, and conduct risk analyses. Additionally, the review explores the transport behavior of MPs in soil, distinguishing between external mechanisms (abiotic factors: wind, leaching, and runoff, biotic factors: soil bioturbation and food chain interactions), and internal mechanisms that are impacted by the characteristics of MPs themselves (e.g., shape, color, size, density, surface properties), soil properties (e.g., porosity, pH, ionic strength, organic matter and mineral content), coexisting substances, and soil structural dynamics. The study of MP transport in soil remains in its early stages, with substantial gaps in knowledge. Future research should focus on integrating number, mass concentration, and area concentration for the more holistic quantification of MP abundance, and prioritize the development of more accurate and efficient methodologies. In addition, the investigation of MP transport and degradation processes under varying environmental conditions and soil management practices is critical for addressing this emerging environmental challenge.

Exploring Innovative Approaches for the Analysis of Micro- and Nanoplastics: Breakthroughs in (Bio)Sensing Techniques

Plastic pollution, particularly from microplastics (MPs) and nanoplastics (NPs), has become a critical environmental and health concern due to their widespread distribution, persistence, and potential toxicity. MPs and NPs originate from primary sources, such as cosmetic microspheres or synthetic fibers, and secondary fragmentation of larger plastics through environmental degradation. These particles, typically less than 5 mm, are found globally, from deep seabeds to human tissues, and are known to adsorb and release harmful pollutants, exacerbating ecological and health risks. Effective detection and quantification of MPs and NPs are essential for understanding and mitigating their impacts. Current analytical methods include physical and chemical techniques. Physical methods, such as optical and electron microscopy, provide morphological details but often lack specificity and are time-intensive. Chemical analyses, such as Fourier transform infrared (FTIR) and Raman spectroscopy, offer molecular specificity but face challenges with smaller particle sizes and complex matrices. Thermal analytical methods, including pyrolysis gas chromatography-mass spectrometry (Py-GC-MS), provide compositional insights but are destructive and limited in morphological analysis. Emerging (bio)sensing technologies show promise in addressing these challenges. Electrochemical biosensors offer cost-effective, portable, and sensitive platforms, leveraging principles such as voltammetry and impedance to detect MPs and their adsorbed pollutants. Plasmonic techniques, including surface plasmon resonance (SPR) and surface-enhanced Raman spectroscopy (SERS), provide high sensitivity and specificity through nanostructure-enhanced detection. Fluorescent biosensors utilizing microbial or enzymatic elements enable the real-time monitoring of plastic degradation products, such as terephthalic acid from polyethylene terephthalate (PET). Advancements in these innovative approaches pave the way for more accurate, scalable, and environmentally compatible detection solutions, contributing to improved monitoring and remediation strategies. This review highlights the potential of biosensors as advanced analytical methods, including a section on prospects that address the challenges that could lead to significant advancements in environmental monitoring, highlighting the necessity of testing the new sensing developments under real conditions (composition/matrix of the samples), which are often overlooked, as well as the study of peptides as a novel recognition element in microplastic sensing.

Impact of polystyrene nanoplastics on physiology, nutrient uptake, and root system architecture of aeroponically grown citrus plants

The widespread presence of plastic pollution has become a challenge for both aquatic and terrestrial plants. Notably, nanoplastics (NPs) have been found to enter the root tissues and translocate to different organs of plants; however, most previous studies were performed using crop or vegetable seedlings, and the extent NPs accumulation in fruit tree plants, particularly citrus, and their impacts remains unclear. This study was designed to fill this gap by determining the uptake and accumulation of green, fluorescent polystyrene nanoplastics (PS-NPs) of two different sizes (20 nm and 50 nm in diameter) in citrus rootstock ('US-942') in an aeroponic system and their impact on plant growth and physiological functions, nutrient uptake, and root system architectural and anatomical traits. The 20 nm PS-NPs negatively impacted the root system architecture (total root length, root surface area, number of root forks) and nutrient contents (N, P, K, Mg, S, B, Fe, Cu, Mn) at both 15 and 30 days after treatment; however, no significant differences were recorded for growth and physiological parameters. Microscopic analysis of roots revealed that under both the PS-NPs treatments, root apoplastic barriers were fully developed near the root tips. Furthermore, PS-NPs are predominantly adhered to the root surface, and no signs of uptake and translocation were recorded in root sections. However, alterations to the external root cell layers were observed. This research sheds light on the impact of PS-NPs on plant roots and their physiology and contributes to a better understanding of these emerging pollutants on tree crop horticulture.

Comprehensive understanding of microplastics in compost: Ecological risks and degradation mechanisms

The introduction of microplastics (MPs) into soil ecosystems via compost application has emerged as a critical environmental concern. However, the ecological risks and degradation behavior of MPs in compost remain insufficiently understood. This review addresses these gaps by synthesizing recent findings on MPs in composting systems, focusing on their sources, impacts on compost quality, ecological risks, and degradation mechanisms. MP sources vary significantly across compost matrices-domestic waste, sludge, and agricultural waste‑leading to differences in their types and quantities. MPs adversely impact compost quality by disrupting its physical structure and impairing fertility, aeration, and water retention. Furthermore, their persistence after compost application can result in long-term environmental accumulation, posing risks to soil ecosystems and biological health. This review also explores the aging and degradation of MPs during composting, a complex process influenced by physical, chemical, and biological mechanisms. Finally, we propose future research directions, emphasizing the development of standardized methodologies to assess MP behavior in compost and strategies to mitigate associated risks. These insights contribute to advancing sustainable waste management and environmental protection practices.

The abundance, removal efficiency, and characteristics of microplastics in three urban wastewater treatment plants (WWTPs) on the southern coast of the Caspian Sea

Wastewater treatment plants (WWTPs) are one of the major collection points of microplastics (MPs). The MPs in influents and effluents of WWTPs were assessed for three cities on the southern coast of the Caspian Sea in the winter and spring seasons. The MP removal rate of WWTPs ranged between 71.12 and 88.13% depending on the season and treatment methods. The higher removal efficiency of MPs in the city of Sari compared to that in the other two cities might be attributed to the implementation of more effective treatment techniques at the Sari WWTP. Our findings showed that the presence of MPs in influents was greater in the spring than in the winter, attributed to the increased usage of personal care and washing products during the COVID-19 lockdown period. Conversely, in effluents, the abundance of MPs was higher in the winter than in the spring, likely due to precipitation and inadequate management of sewage overflows. On average, more than 50% of identified MPs had black/grey and white/transparent colours. The majority of the identified MPs that were found in both the influents and effluents of all three investigated WWTPs were smaller than 500 µm and had a fibre shape. Our findings indicate that removing plastics with a size smaller than 100 µm is more challenging compared to larger-sized plastics in WWTPs. Moreover, a strong correlation was observed between TSS and the abundance of MPs in influents. The predominant types of MP that were identified with spectroscopic analysis in most samples were polyamide (PA), acrylic, polyethylene (PE), polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC), and polypropylene (PP). Based on the results of our study, it can be estimated that a total of 132 × 106 and 223 × 106 MPs are discharged per day from the three investigated WWTPs into aquatic environments that ultimately reach the Caspian Sea in the spring and winter, respectively. Our findings enhance our knowledge about the load of MPs from WWTPs into the Caspian Sea, and it provides a foundation for future discussions on management strategies and the reuse of wastewater.

A review of methods for mitigating microplastic contamination in biosolids from wastewater treatment plants before agricultural soil application

Wastewater treatment plants (WWTP) are recognized as major sources of microplastic (MP) particles in terrestrial environments, particularly in agricultural soils through biosolids application. While many reviews have focused on the distribution, detection, and mitigation of MPs in wastewater effluent to limit their discharge into oceans, our understanding of methods to mitigate biosolid contamination remains limited. This review focuses on methods for mitigating MPs contamination in biosolids at various intervention points, including sources, WWTP including the primary and secondary treatment stages where sludge is generated, and post-contamination. These methods are categorized as physical, physicochemical, and biological approaches, and their advantages and limitations are discussed. For instance, physicochemical methods, especially froth flotation, are cost-effective but are hindered by contaminants and reagents. Physical methods like microfibre filtration devices (MFD) are safe but their efficiency depends on the filter pore size and design. Biological methods, particularly microbial degradation, are limited by the varying efficiencies of microorganisms in breaking down MPs and the extended time required for their effective degradation. Other physical methods including dissolved air flotation, and ultrasonication already exist in WWTPs but may require retrofitting or optimization to enhance MP removal from biosolids. As each method inherently has limitations, the key to achieving MP-free biosolids, and thus preventing their release into agricultural soil, lies in integrating these methods through multi-coupling strategies.

Effects of aging of polyethylene microplastics and polystyrene nanoplastics on antibiotic resistance gene transfer during primary sludge fermentation

The increasing presence of nano and microplastics (NPs/MPs) in wastewater treatment plants and their inevitable accumulation in the sludge has raised serious concerns in recent years. This study investigated the effects of pristine and aged polyethylene microplastics (PEMPs), polystyrene nanoplastics (PsNPs), and their mixtures on the primary sludge fermentation process. Pristine MPs/NPs (150 μg/L and 2 g/L for PsNPs and PEMPs, respectively) underwent two weeks of weathering in the presence of humic and alginic acids. The results from a batch fermentation experiment (15 days, pH 10) revealed that the exposure to aged PEMPs/PsNPs experienced greater VFA production than pristine samples. Notably, the aged PEMPs/PsNPs mixture showed a 23.12% increase in VFA production over the pristine mixture. The relative abundance and total concentration of antibiotic resistance genes (ARGs) increased in all PEMPs/PsNPs batches compared to the control, with the most significant rise in total ARGs observed in the aged PEMPs sample. Aged PEMPs exhibited a 26.22-fold increase in tetA genes, while aged mix samples showed a 19.68-fold increase in tetM genes compared to their pristine counterparts. Both pristine and aged PEMPs/PsNPs, particularly the aged PEMPs adversely affected the microbial communities at the genus level and altered the microbial structure. Microbial richness and diversity were enhanced in samples exposed to pristine PEMPs/PsNPs and aged PsNPs but decreased in aged PEMPs and in the aged mixture group, suggesting a negative impact of aged polyethylene microplastics on microbial communities. Correlation analysis suggested that phyla Planctomycetes, Proteobacteria, and TM7 are potential hosts of ARGs. These findings manifest the substantial effects of aged nano/microplastics compared to their pristine forms, emphasizing the complex interplay between various forms of PEMPs/PsNPs and microbial dynamics in sludge fermentation processes.

Behavior and flow of microplastics during sludge treatment in Japan

Microplastic (MP) pollution is a growing public and scientific concern. In urban environments, wastewater treatment plants (WWTPs) are major sources of MPs. This study sampled sludge and separated water from each sludge treatment unit in two WWTPs in Osaka, Japan. Analyzing method for MPs in sewage sludge was optimized, ultrasonic pretreatment and double digestion were introduced into the analyzing method of MPs in sewage sludge, recovering test of standard MPs proved its high efficiency. Then MPs larger than 100 μm were extracted and analyzed, their size and type were recorded, the MP concentration was calculated, and the MP flow in the sludge treatment system was estimated. MPs were detected at every step of the sludge treatment process, and 13 types of MPs were identified. The MP concentration in sludge ranged from 81 ± 48 to 6470 ± 1490 particles/kg dry sludge (DS). In the separated water, MP concentrations were much lower, ranging from 0 to 1740 ± 794 particles/kg DS. During the thickening and dewatering processes, nearly all MPs were transferred into thickened or dewatered sludge; only 5-10 % of MPs returned to the primary sedimentation pond with the separated water. The most common types of MPs were PMMA, PE, and PS. No significant differences in MP type distributions were observed among sampling batches; however, significant differences in a few types of MPs were detected between treatment units, which requires further investigation. All detected MPs were smaller than 1000 μm; larger MPs might have been removed in the grit chamber before reaching the primary or secondary sedimentation ponds. Overall, the particle size distribution did not substantially change during sludge treatment.

Sorption of metal ions onto PET-derived microplastic fibres

This study investigated microplastic polyester fibres representative of those shed during laundering as sorbents for metal ions. During sewage distribution and treatment, microplastics are exposed to elevated concentrations of metal ions, typically for several days. Cryogenic milling was used to generate polyethylene terephthalate (PET) fibres. Characterisation using optical microscopy and Raman spectroscopy revealed that milling did not cause significant chemical alteration to the fibres. Milled fibres were subsequently assessed in screening tests for their capacity to retain 12 metal ions-Sb(III), As(III), Cd(II), Cr(VI), Cu(II), Co(II), Pb(II), Hg(II), Mo(VI), Ni(II), V(V) and Zn(II)-at pH 8. All metal ions were sorbed onto PET fibres. The highest distribution coefficient (Kd) was observed for Pb2+ (939 mL g-1), followed by Cd2+ (898 mL g-1), Cu2+ (507 mL g-1), Hg2+ (403 mL g-1), and Zn2+ (235 mL g-1). The extent of sorption is largely explicable by electrostatic interactions between the PET surface (1.95 point of zero net charge) and the predicted metal ion species. The sorption behaviour of Cd2+ and Hg2+ was examined in more detail since both showed high sorption capacity and are highly toxic. Kinetic experiments revealed that the sorption of both elements was relatively fast, with a steady state reached within six hours. Experimental data from isotherm tests fitted well to the Langmuir sorption model and demonstrated that PET fibres had a much greater sorption capacity for Hg2+ (17.3-23.1 μg g-1) than for Cd2+ (4.3-5.3 μg g-1). Overall, the results indicate that retention of metal ions onto PET fibres originating from laundry is expected during full-scale sewage treatment, which facilitates the subsequent transfer of metals into the terrestrial environment, given that sewage sludge is commonly applied to agricultural land.

Utilization of AI - reshaping the future of food safety, agriculture and food security - a critical review

Artificial intelligence is an emerging technology which harbors a suite of mechanisms that have the potential to be leveraged for reaping value across multiple domains. Lately, there is an increased interest in embracing applications associated with Artificial Intelligence to positively contribute to food safety. These applications such as machine learning, computer vision, predictive analytics algorithms, sensor networks, robotic inspection systems, and supply chain optimization tools have been established to contribute to several domains of food safety such as early warning of outbreaks, risk prediction, detection and identification of food associated pathogens. Simultaneously, the ambition toward establishing a sustainable food system has motivated the adoption of cutting-edge technologies such as Artificial Intelligence to strengthen food security. Given the myriad challenges confronting stakeholders in their endeavors to safeguard food security, Artificial Intelligence emerges as a promising tool capable of crafting holistic management strategies for food security. This entails maximizing crop yields, mitigating losses, and trimming operational expenses. AI models present notable benefits in efficiency, precision, uniformity, automation, pattern identification, accessibility, and scalability for food security endeavors. The escalation in the global trend for adopting alternative protein sources such as edible insects and microalgae as a sustainable food source reflects a growing recognition of the need for sustainable and resilient food systems to address the challenges of population growth, environmental degradation, and food insecurity. Artificial Intelligence offers a range of capabilities to enhance food safety in the production and consumption of alternative proteins like microalgae and edible insects, contributing to a sustainable and secure food system.

Microplastic accumulation and transport in agricultural soils with long-term sewage sludge amendments

Land application of sewage sludge brings microplastic contamination to soil. However, studies regarding the occurrence and mobility of sludge-borne microplastics in soil are insufficient. In the present study, based on an experimental field, the effects of sludge application amount on the accumulation and migration of microplastics in 0-20 (upper) and 20-40 cm (lower) soil layers were evaluated. After 16 years of continuous sludge application (36 t/ha per year), the microplastic content and migration ratio in upper soil reached 6811 particles/kg and 148 %, which was about 5 and 20 times, respectively, higher than that of the control soil without sludge. The microplastics in upper and lower soil layers, were mainly 0.2-0.5 mm in size, mostly fibrous in shape, primarily transparent in color, and predominantly rayon in composition. Microplastic surfaces may persistently adsorb clay minerals and iron/titanium oxides from soil, posing potential environmental risks. Sludge application had a significant positive correlation with soil microplastic abundance, resulting in a good fit of predictive model constructed for microplastic accumulation in sludge-amended soils. These findings help to improve the knowledge on environmental behavior of microplastics in sludge-amended soil, and can provide a scientific basis for the regulation of microplastic pollution during sludge land application.

The effect of polyvinyl chloride microplastics on soil properties, greenhouse gas emission, and element cycling-related genes: Roles of soil bacterial communities and correlation analysis

Different shapes (membranes and particles) and concentrations (1 % (w/w) and 2 % (w/w)) of polyvinyl chloride (PVC) microplastics (MPs) were investigated to determine their impact on the soil environment. The incorporation of MPs can disrupt soil macroaggregates. Compared with 1 % (w/w) MPs, 2 % MPs resulted in a significant increase in soil organic carbon content. MP particles significantly increased soil CO2 emissions, and CH4 emissions were enhanced by both membrane and particle MPs at high concentrations. Microplastics can alter the abundance of Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteriota, and Firmicutes at the phylum level, and Nocardioides, Rhodococcus and Bacillus at the genus level. MP particles had a more significant impact on soil bacterial communities than MP membranes. The relative abundances of genes involved in the C, N, and P cycles were detected by qPCR, and more remarkable changes were observed in MP membrane treatments. The relative abundance of Vicinamibacteraceae and Vicinamibacterales exhibited a positive correlation with most C/N/P cycle-related genes, whereas Pseudarthrobacter and Nocardioides demonstrated a negative correlation. This study highlights that the influence of MPs on soil parameters is mediated by soil microorganisms, providing insight into the effects of MPs on the soil microenvironment.

Polyethylene nanoplastics, tebuconazole and cadmium affect soil-wheat system by altering rhizosphere microenvironment under single or combined exposure

Microplastics and nanoplastics (NPs) are pollutants of global concern. However, the understanding of the combined effects of NPs and other pollutants in the soil-plant system remains limited, particularly for polyethylene (PE), the primary component of agricultural films. This study investigated the effects of PE NPs (0.5 %, w/w), fungicide tebuconazole (Te, 10 mg·kg-1), and cadmium (Cd, 4.0 mg·kg-1) on the soil-wheat system under single and combined exposures. The synergistic toxicity observed between NPs and Te impacted the nutritional conditions and antioxidant mechanisms of the soil-wheat system. The NPs increased the concentration of Cd in roots and the proportion of bioavailable Cd, exacerbating oxidative stress in wheat and inhibiting biomass. The soil-wheat system responded to stress by upregulating or downregulating pathways related to carbohydrate, amino acid, and sugar metabolism under various treatments. Sixteen functional genes associated with carbohydrate metabolism, amino acid metabolism, energy utilization, and gene repair at KEGG level 3 were employed to sustain microenvironmental homeostasis. Correlation analysis between microorganisms and environmental factors showed that various PGPG played roles in maintaining the health of the soil-wheat system. These results help to elucidate the comprehensive effects of NPs with other pollutants on the soil-plant system and provide new perspectives for toxic mechanisms.

The interaction between sludge and microplastics during thermal hydrolysis of sludge

In municipal wastewater treatment plants (WWTPs), large number of microplastics (MPs) accumulated in wastewater migrated into sludge. Thermal hydrolysis of sludge (THS) was one of the most promising processes for promoting changes in molecular structure of MPs. The physicochemical properties and degradative pathways of polyethylene (PE) and polyethylene terephthalate (PET) in THS under different temperatures were studied in this paper. It was found that there was a mutual promotion relationship between sludge degradation and MPs aging. The presence of PE and PET MPs not only increased organics and nitrogen concentrations of sludge filtrate, but also enhanced the transformation of organics like proteins. Sludge accelerated the aging of PE and PET MPs. The friability of PE and PET MPs was increased with more surface fragmentation and breakage under the temperature of 120 ℃-180 ℃. Moreover, PE and PET MPs occurred thermal oxidation and reduction reactions with significant chemical structure changes at 160 °C and 140 °C, respectively. Pristine PE and PET had multiple carbon and oxygen active sites. During THS reaction, not only PE and PET reacted hydrolysis/decomposition to produce short-chain hydroxyl-terminated compounds, but also hydrothermal shear broke the polymer molecules and formed carboxyl-terminated and olefin-terminated low-carbon chains. This study provided some promising sign for in situ microplastic removal during sludge treatments.

Multifaceted effects of microplastics on soil-plant systems: Exploring the role of particle type and plant species

Microplastics have emerged as a global environmental concern, yet their impact on terrestrial environments, particularly agricultural soils, remains underexplored. Agricultural soils, due to intensive farming, may serve as significant sinks for microplastics. This study investigated the effects of different types of microplastics-polyester microfibers, polyethylene terephthalate microfragments, and polystyrene microspheres-on soil properties and radish growth, while a complementary experiment examined the impact of polyester microfibers on the growth of lettuce and Chinese cabbage. Through both horizontal and vertical comparisons, this research comprehensively evaluated the interactions between microplastic particles and plant species in soil-plant systems. The results showed that polyester microfibers significantly affected soil bulk density, with effects varying based on planting conditions (p < 0.01). Polyethylene terephthalate microfragments and polystyrene microspheres reduced the proportion of small soil macroaggregates under radish cultivation (p < 0.01). Additionally, polystyrene microspheres significantly altered the total organic carbon stock in radish-growing soil, potentially affecting the microclimate (p < 0.01). Interestingly, polyester microfibers promoted lettuce seed germination and significantly enhanced the root biomass of Chinese cabbage (p < 0.05). Overall, the environmental effects of microplastic exposure varied depending on the type of particle and plant species, suggesting that microplastics are not always harmful to soil-plant systems and may even offer benefits in certain scenarios. Given the crucial role of soil-plant systems in terrestrial ecosystems, and their direct connection to food safety, human health, and global change, further research should explore both the positive and negative impacts of microplastics on agricultural practices.

Pyrolysis-induced migration and transformation of heavy metals in sewage sludge containing microplastics

Stabilizing heavy metals (HMs) in sewage sludge is urgently needed to facilitate its recycling and reuse. Pyrolysis stands out as a promising method for not only stabilizing these metals but also producing biochar. Our research delves into the migration and transformation of specific HMs (Cr, Mn, Ni, Cu, Zn, As, and Pb) during co-pyrolysis under various conditions, including the presence and absence of microplastics (PVC and PET). We examined different concentrations of these plastics (1 %, 5 %, 10 %, and 15 %) and temperatures (300 °C, 500 °C, and 700 °C). Findings reveal that microplastics, particularly PVC, enhance the migration of Zn and Mn, leading to significant volatilization of Zn and Pb at higher temperatures, peaking at 700 °C. The increase in temperature also markedly influences HM migration, with As showcasing notable loss rates that climbed by 18.0 % and 16.3 % in systems with PET and PVC, respectively, as temperatures soared from 300 °C to 700 °C. Moreover, our speciation analysis indicates that microplastics aid in transforming certain HMs from unstable to more stable forms, suggesting their beneficial role in HM stabilization during pyrolysis. This study significantly enriches our understanding of microplastics' impact on HM behavior in sewage sludge pyrolysis, offering new avenues for pollution control and environmental management strategies.

Planting Enhances Soil Resistance to Microplastics: Evidence from Carbon Emissions and Dissolved Organic Matter Stability

Microplastics (MPs) have become a global hotspot due to their widespread distribution in recent years. MPs frequently interact with dissolved organic matter (DOM) and microbes, thereby influencing the carbon fate of soils. However, the role of plant presence in regulating MPs-mediated changes in the DOM and microbial structure remains unclear. Here, we compared the mechanisms of soil response to 3 common nonbiodegradable MPs in the absence or presence of radish (Raphanus sativus L. var. radculus Pers) plants. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis revealed that MPs reduced the chemodiversity and biodiversity of dissolved organic matter (DOM). MPs enhanced the degradation of lignin-like compounds and reduced the DOM stability. Comparative analysis showed that MPs caused less disturbance to the microbial composition and metabolism in planted soil than in unplanted soil. In unplanted soil, MPs stimulated fermentation while upregulating photoautotrophic activity in planted soil, thereby enhancing system stability. The rhizosphere effect mitigated MPs-induced CO2 emissions. Overall, our study highlights the crucial role of rhizosphere effects in maintaining ecosystem stability under soil microbe-DOM-pollutant interactions, which provides a theoretical basis for predicting the resistance, resilience, and transitions of the ecosystem upon exposure to the anthropogenic carbon source.

Leaching behavior of microplastics during sludge mechanical dewatering and its effect on activated sludge

Dewatering is an indispensable link in sludge treatment, but its effect on the microplastics (MPs) remains inadequately understood. This study investigated the physicochemical changes and leaching behavior of MPs during the mechanical dewatering of sludge, as well as the impact of MP leachates on activated sludge (AS). After sludge dewatering, MPs exhibit rougher surfaces, decreased sizes and altered functional groups due to the addition of dewatering agents and the application of mechanical force. Meanwhile, plastic additives, depolymerization products, and derivatives of their interactions are leached from MPs during sludge dewatering process. The concentration of MP-based leachates in sludge is 2-25 times higher than that in water. The enhancement of pH and ionic strength caused by dewatering agents induces the release of MP leachates enriched with protein-like, fulvic acid-like, and soluble microbial by-product-like substances. The reflux of MP leachates in sludge dewatering liquor to the wastewater treatment system negatively impacts AS, leading to a decrease in COD removal rate and inhibition of the extracellular polymeric substances secretion. More importantly, MP leachates cause oxidative stress to microbial cells and alter the microbial community structure of AS at the phylum and genus levels. These findings confirm that MPs undergo aging and leaching during sludge dewatering process, and MP leachates may negatively affect the wastewater treatment system.

The bifunctional impact of polylactic acid microplastics on composting processes and soil-plant systems: Dynamics of microbial communities and ecological niche competition

Although extensive research has been conducted on the environmental impact of microplastics (MPs), their effects on microorganisms during the composting process and on the compost-soil system remain unclear. Our research investigates the microbial response to polylactic acid microplastics (PLAMPs) during aerobic composting and examines how compost enriched with PLAMPs affects plants. Our findings reveal that PLAMPs play a dual role in the composting process, influencing microorganisms differently depending on the composting phase. PLAMPs reduce the relative abundance of sensitive bacterial ASVs, specifically those belonging to Limnochordaceae and Enterobacteriaceae, during composting, while increasing the relative abundance of ASVs belonging to Steroidobacteriaceae and Bacillaceae. The impact of PLAMPs on microbial community assembly and niche width was found to be phase-dependent. In the stabilization phase (S5), the presence of PLAMPs caused a shift in the core microbial network from bacterial dominance to fungal dominance, accompanied by heightened microbial antagonism. Additionally, these intricate microbial interactions can be transferred to the soil ecosystem. Our study indicates that composting, as a method of managing PLAMPs, is also influenced by PLAMPs. This influence is transferred to the soil through the use of compost, resulting in severe oxidative stress in plants. Our research is pivotal for devising future strategies for PLAMPs management and predicting the subsequent changes in compost quality and environmental equilibrium.

Sources, interactions, influencing factors and ecological risks of microplastics and antibiotic resistance genes in soil: A review

Microplastics (MPs) and antibiotic resistance genes (ARGs) are gaining increasing attention as they pose a threat to the ecological environment and human health as emerging contaminants. MPs has been proved to be a hot spot in ARGs, and although it has been extensively studied in water environment, the results of bibliometrics statistical analysis in this paper showed that relevant studies in soil ecological environment are currently in the initial stage. In view of this, the paper provides a systematic review of the sources, interactions, influencing factors, and ecological risks associated with MPs and ARGs in soil environments. Additionally, the mechanism and influencing factors of plastisphere formation and resistance are elaborated in detail. The MPs properties, soil physicochemical properties, soil environmental factors and agricultural activities are the primarily factors affecting the interaction between MPs and ARGs in soil. Challenges and development directions of related research in the future are also prospected. It is hoped that the review could assist in a deeper comprehension and exploration of the interaction mechanism between MPs and ARGs in soil as well as the function of MPs in the transmission process of ARGs among diverse environmental media and organisms, and provide theory basis and reference for the MPs and ARGs pollution control and remediation in soil.

Impacts of microplastics on ecosystem services and their microbial degradation: a systematic review of the recent state of the art and future prospects

Microplastics are tiny plastic particles with a usual diameter ranging from ~ 1 μ to 5 µm. Recently, microplastic pollution has raised the attention of the worldwide environmental and human concerns. In human beings, digestive system illness, respiratory system disorders, sleep disturbances, obesity, diabetes, and even cancer have been reported after microplastic exposure either through food, air, or skin. Similarly, microplastics are also having negative impacts on the plant health, soil microorganisms, aquatic lives, and other animals. Policies and initiatives have already been in the pipeline to address this problem to deal with microplastic pollution. However, many obstacles are also being observed such as lack of knowledge, lack of research, and also absence of regulatory frameworks. This article has covered the distribution of microplastics in water, soil, food and air. Application of multimodel strategies including fewer plastic item consumption, developing low-cost novel technologies using microorganisms, biofilm, and genetic modified microorganisms has been used to reduce microplastics from the environment. Researchers, academician, policy-makers, and environmentalists should work jointly to cope up with microplastic contamination and their effect on the ecosystem as a whole which can be reduced in the coming years and also to make earth clean.

Discrimination of Microplastics and Phytoplankton Using Impedance Cytometry

Both microplastics and phytoplankton are found together in the ocean as suspended microparticles. There is a need for deployable technologies that can identify, size, and count these particles at high throughput to monitor plankton community structure and microplastic pollution levels. In situ analysis is particularly desirable as it avoids the problems associated with sample storage, processing, and degradation. Current technologies for phytoplankton and microplastic analysis are limited in their capability by specificity, throughput, or lack of deployability. Little attention has been paid to the smallest size fraction of microplastics and phytoplankton below 10 μm in diameter, which are in high abundance. Impedance cytometry is a technique that uses microfluidic chips with integrated microelectrodes to measure the electrical impedance of individual particles. Here, we present an impedance cytometer that can discriminate and count microplastics sampled directly from a mixture of phytoplankton in a seawater-like medium in the 1.5-10 μm size range. A simple machine learning algorithm was used to classify microplastic particles based on dual-frequency impedance measurements of particle size (at 1 MHz) and cell internal electrical composition (at 500 MHz). The technique shows promise for marine deployment, as the chip is sensitive, rugged, and mass producible.

Differential impacts of microplastics on carbon and nitrogen cycling in plant-soil systems: A meta-analysis

Microplastics (MPs) are widely present in terrestrial ecosystems. However, how MPs impact carbon (C) and nitrogen (N) cycling within plant-soil system is still poorly understood. Here, we conducted a meta-analysis utilizing 3338 paired observations from 180 publications to estimate the effects of MPs on plant growth (biomass, nitrogen content, nitrogen uptake and nitrogen use efficiency), change in soil C content (total carbon (TC), soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass carbon (MBC)), C losses (carbon dioxide (CO2) and methane), soil N content (total nitrogen, dissolved organic nitrogen, microbial biomass nitrogen, total dissolve nitrogen, ammonium, nitrate (NO3--N) and nitrite) and nitrogen losses (nitrous oxide, ammonia (NH3) volatilization and N leaching) comprehensively. Results showed that although MPs significantly increased CO2 emissions by 25.7 %, they also increased TC, SOC, MBC, DOC and CO2 by 53.3 %, 25.4 %, 19.6 % and 24.7 %, respectively, and thus increased soil carbon sink capacity. However, MPs significantly decreased NO3--N and NH3 volatilization by 14.7 % and 43.3 %, respectively. Meanwhile, MPs significantly decreased plant aboveground biomass, whereas no significant changes were detected in plant belowground biomass and plant N content. The impacts of MPs on soil C, N and plant growth varied depending on MP types, sizes, concentrations, and experimental durations, in part influenced by initial soil properties. Overall, although MPs enhanced soil carbon sink capacity, they may pose a significant threat to future agricultural productivity.

A comprehensive risk assessment of microplastics in soil, water, and atmosphere: Implications for human health and environmental safety

Microplastics (MPs) are pervasive across ecosystems, likely posing significant environmental and health risks based on more and more evidence. In this study, we searched through the Web of Science Core Collection and obtained 1039 papers for visualization and analysis. In order to discuss the chemical composition, migration, transformation and potential risk of MPs, 135 sets of relevant data in soil, water, and atmosphere were collected in China as a typical region, which is a hotspot region for investigation of MPs. The results showed that the primary polymer categories of MPs in the environment to be polypropylene, polyethylene, and polystyrene. The soil contains a significant quantity of MPs, averaging at 12,107.42 items·kgdw-1, while water contains averaging at 97,271.18 items m-3. The total pollution load indexes for all three environments are at risk level I. Based on current risk assessment methods, the potential ecological risk of MPs is low. However, based on the polymer components, migration and transformation patterns, and especially the complexes with other pollutants, it indicates an increasing indirect risk. Interactions with some other pollutants are likely amplify the ecological and health risks associated with MPs. Aggregative results showed that the present risk assessment models could not assess the risks of MPs well. Thus, we suggested develop a risk assessment methodology for MPs based on relevant research progress. Some factors such as the size and form of MPs, sources and distribution, bioaccumulation, social acceptance and economic costs could be considered adding in the present risk assessment models. Finally, promotion of development and application of green chemically synthesized bioplastics such as using synthetic biology to help degrade plastics would be an alternative and sustainable option to relieve the adverse environmental and health concerns of MPs.

Effects of Polyethylene Terephthalate Microplastics on Anaerobic Mono-Digestion and Co-Digestion of Fecal Sludge from Septic Tank

Anaerobic digestion (AD) is one of the most significant processes for treating fecal sludge. However, a substantial amount of microplastics (MPs) have been identified in septic tanks, and it remains unclear whether they impact the resource treatment of feces. To investigate this, polyethylene terephthalate (PET) was used as an indicator of MPs to study their effect on the anaerobic digestion of fecal sludge (FS). Two digestion systems were developed: FS mono-digestion and FS co-digestion with anaerobic granular sludge. The results indicated that the effects of PET varied between the two systems. PET inhibited volatile fatty acid synthesis in both systems, but the inhibition period differed. During mono-digestion, PET slightly increased gas and methane production, in contrast to the co-digestion system, where PET reduced methane production by 75.18%. Furthermore, in the mono-digestion system, PET increased soluble chemical oxygen demand and ammonia nitrogen concentrations while blocking phosphorus release, whereas the co-digestion system showed the opposite effects. Ultimately, the choice of digestion method is crucial for the resource utilization of septic tank sludge, and the impact of MPs on AD cannot be ignored.

Characteristics and aging of microplastics in waste activated sludge under persulfate and hydrothermal co-treatment: Impact of solid content and temperature

Activated persulfate and hydrothermal treatment (HTT) are often employed to treat waste activated sludge, which can improve the efficiency of subsequent sludge treatment and change the distribution of pollutants in the sludge. However, the impact of sludge solid content and temperature on the occurrence and aging of microplastics (MPs) during HTT remains poorly understood. This study investigated the effects of persulfate-HTT (SPS-HTT) co-treatment on the migration, occurrence, and aging of MPs in sludge with different solid contents (2% and 5% solid content). The results indicated that SPS-HTT co-treatment triggers both the disruption of sludge flocs and the melting deformation of MPs at high temperatures, leading to variations in the increasing trend of MP concentration in the solid-liquid phase at different solid contents. 5% solid content sludge showed a weak release of MPs from the solid phase. The proportion of fiber MPs first increased and then decreased with increasing temperature, while no significant changes were observed in the color and type of MPs. Higher temperature and solid content induced the melting deformation of MPs, exacerbated the aging of polypropylene MPs, and resulted in rough surfaces, higher carbonyl index, and variations in crystallinity. Moreover, the correlation between the carbonyl index and aging indicators increased with increasing solid content. The MP-derived dissolved organic matter under HTT primarily comprised soluble microbial by-products and humic acid-like substances. These findings underscore the significance of sludge solid content in affecting the migration and aging of MPs during HTT, and offer novel insights into the application of HTT to MP management in sludge treatment.

Integrated approaches for plastic waste management

Plastic pollution is the challenging problem of the world due to usage of plastic in daily life. Plastic is essential for packaging food and other goods and utensils to avoid the risk of microbial attack. Due to its hydrophobic nature, it is used for wrapping as laminates or packaging liquid substances in pouches and sachets. The tensile strength of the plastic is more therefore it is used for manufacturing carrying bags that can bear heavy loads. Plastic is available in various forms as per the requirements in our daily life. Annually millions to trillions of polyethene carry bags are being manufactured and utilized throughout the world. The plastic requires millions of years for natural degradation. The physical and chemical processes are able to degrade plastic material at the meager level by 200 to 500 years in natural conditions. Many industries focus on recycling of plastic. Biodegradation is a comparatively slow and cheaper process that involves microbes. To dispose of plastic completely there is a need of an integrated process in which all the possible methods of disposal are involved and used sustainably so that minimum depletion occurs to the livestock and the environment. In the current review, we could try to emphasize the intricate nature of plastic polymers, pollution caused by it and possible mitigation strategies for plastic waste management.

Microplastics monitoring in freshwater systems: A review of global efforts, knowledge gaps, and research priorities

The escalating production of synthetic plastics and inadequate waste management have led to pervasive microplastic (MP) contamination in aquatic ecosystems. MPs, typically defined as particles smaller than 5 mm, have become an emerging pollutant in freshwater environments. While significant concern about MPs has risen since 2014, research has predominantly concentrated on marine settings, there is an urgent need for a more in-depth critical review to systematically summarize the current global efforts, knowledge gaps, and research priorities for MP monitoring in freshwater systems. This review evaluates the current understanding of MP monitoring in freshwater environments by examining the distribution, characteristics, and sources of MPs, alongside the progression of analytical methods with quantitative evidence. Our findings suggest that MPs are widely distributed in global freshwater systems, with higher abundances found in areas with intense human economic activities, such as the United States, Europe, and China. MP abundance distributions vary across different water bodies (e.g., rivers, lakes, estuaries, and wetlands), with sampling methods and size range selections significantly influencing reported MP abundances. Despite great global efforts, there is still a lack of harmonized analyzing framework and understanding of MP pollution in specific regions and facilities. Future research should prioritize the development of standardized analysis protocols and open-source MP datasets to facilitate data comparison. Additionally, exploring the potential of state-of-the-art artificial intelligence for rapid, accurate, and large-scale modeling and characterization of MPs is crucial to inform effective strategies for managing MP pollution in freshwater ecosystems.

Tracing the Transport and Residence Times of Atmospheric Microplastics Using Natural Radionuclides

While atmospheric microplastics are known to be transported over long distances, their residence times and transport processes lack clarity. This study utilized natural radionuclides 7Be, 210Pb, and 210Po to explore the transport of atmospheric microplastics in Tianjin, a coastal city in Northern China. Microplastic concentrations ranged from 0.03 to 0.13 particles m-3 over the course of a year. The proportion of microplastic fragments in winter was significantly higher than that in other seasons, with median microplastic sizes in autumn and winter being larger than those in spring and summer. The atmospheric microplastic surface was rough, exhibiting irregular pores and multiple depressions and cracks. Microplastics experienced vertical mixing with the upper atmosphere in April and August and were influenced by rainfall in July. The residence time of atmospheric particles ranged from 9.47 to 22.85 days throughout the year, with an average of 14.41 days. The peak residence time of atmospheric particulates in November may be correlated with increased 210Po levels from coal consumption. Their prolonged atmospheric presence and rough surface allow microplastics to act as carriers for various chemical pollutants, underscoring the complexity and potential risks associated with their presence in the atmosphere.

Impact of polystyrene nanoplastics on primary sludge fermentation under acidic and alkaline conditions: Significance of antibiotic resistance genes

As a part of industrial or commercial discharge, the influx of nanoplastics (NPs) to the wastewater treatment plants is inevitable. Consequently, it has become a must to understand the effects of these NPs on different unit processes. This study aimed to investigate the impact of three different concentrations of polystyrene nanoplastics (PsNPs) on the fermentation of primary sludge (PrS), implemented in batch anaerobic bioreactors, at pH 5 and 10, considering the pH-dependent nature of the fermentation process. The results showed that PsNPs stimulated hydrogen gas production at a lower dose (50 μg/L), while a significant gas suppression was denoted at higher concentrations (150 μg/L, 250 μg/L). In both acidic and alkaline conditions, propionic and acetic acid predominated, respectively, followed by n-butyric acid. Under both acidic and alkaline conditions, exposure to PsNPs boosted the propagation of various antibiotic resistance genes (ARGs), including tetracycline, macrolide, β-lactam and sulfonamide resistance genes, and integrons. Notably, under alkaline condition, the abundance of sul2 gene in the 250 μg PsNPs/L batch exhibited a 2.4-fold decrease compared to the control batch. The response of the microbial community to PsNPs exposure exhibited variations at different pH values. Bacteroidetes prevailed at both pH conditions, with their relative abundance increasing after PsNPs exposure, indicating a positive impact of PsNPs on PrS solubilization. Adverse impacts, however, were detected in Firmicutes, Chloroflexi and Actinobacteria. The observed variations in the survival rates of various microbes stipulate that they do not have the same tolerance levels under different pH conditions.