Review of the artificially-accelerated aging technology and ecological risk of microplastics

Application of FTIR two-dimensional correlation spectroscopy (2D-COS) analysis in characterizing environmental behaviors of microplastics: A systematic review

Microplastics (MPs) are ubiquitous in the environment, continuously undergo aging processes and release toxic chemical substances. Understanding the environmental behaviors of MPs is critical to accurately evaluate their long-term ecological risk. Generalized two-dimensional correlation spectroscopy (2D-COS) is a powerful tool for MPs studies, which can dig more comprehensive information hiding in the conventional one-dimensional spectra, such as infrared (IR) and Raman spectra. The recent applications of 2D-COS in analyzing the behaviors and fates of MPs in the environment, including their aging processes, and interactions with natural organic matter (NOM) or other chemical substances, were summarized systematically. The main requirements and limitations of current approaches for exploring these processes are discussed, and the corresponding strategies to address these limitations and drawbacks are proposed as well. Finally, new trends of 2D-COS are prospected for analyzing the properties and behaviors of MPs in both natural and artificial environmental processes.

Acute inhibitory effects of tire wear particles on the removal of biological phosphorus：The critical role of aging in improving environmentally persistent free radicals

A comparative study explored how photoaging, ozonation aging, and Fenton aging affect tire wear particles (TWPs) and their phosphorus (P) removal in activated sludge. Aging altered TWPs' properties, increasing surface roughness, porosity, and generating more small particles, especially environmental persistent free radicals (EPFRs) in ozonation and Fenton aging. Post-aging TWPs (50 mg/L) inhibited sludge P removal significantly (p < 0.05), with rates of 44.3% and 59.6% for ozonation and Fenton aging, respectively. In addition, the metabolites involved in P cycling (poly-β-hydroxyalkanoates: PHA and glycogen) and essential enzymes (Exopolyphosphatase: PPX and Polyphosphate kinase: PPK) were significantly inhibited (p < 0.05). Moreover, TWPs led to a decrease in microbial cells within the sludge and altered the community structure, a situation exacerbated by the aging of TWPs. P-removing bacteria decreased (e.g., Burkholderia, Candidatus), while extracellular polymeric substance-secreting bacteria increased (e.g., Pseudomonas, Novosphingobium). Pearson correlation analysis highlighted EPFRs' role in TWPs' acute toxicity to microbial cells, yet, emphasizing particle size's impact on the sludge system's purification and community structure.

Surface characteristics and adsorption properties of polypropylene microplastics by ultraviolet irradiation and natural aging

The vast application and deep integration of plastic commodity with our human lives raise a great concern about the ubiquitous microplastics (MPs) in nature, yet the environmental behavior of MPs remain unclear. As a main type and candidate of MPs, pristine polypropylene MPs (PP-MP-Pris), as well as the influence of ultraviolet (UV) irradiation on the degree of aging and surface characteristics, were characterized quantitatively by Fourier infrared spectroscopy, scanning electron microscopy, contact angle meter, automatic specific surface area and pore analyzer and laser particle analyzer, with natural aged PP-MPs (PP-MP-Age) as comparison. The carbonyl index (CI) of UV aged PP-MPs (PP-MP-U) was increased with extension of exposure time, while biofilm with abundant functional groups and the maximum CI value were the characteristics of PP-MP-Age. Moreover, the adsorption capacity of PP-MP-U for crystal violet (CV) was increased and reached the maximum after 30 days, while that of PP-MP-Age was weakened, probably due to the enhanced hydrophilicity and the shedding of calcium carbonate (CaCO3) during the natural aging process, which was demonstrated by hydrochloric acid treatment, indicating the vital involvement of CaCO3. Moreover, the better fitting to PSO kinetics and Freundlich isotherm models indicated that the multilayered and non-homogeneous surface adsorption was acted as the rate-controlling step. Furthermore, the positive values of ΔGθ, ΔHθ and ΔSθ indicated that the adsorption was a non-spontaneous, endothermic process with increased degree of the freedom on the interface of PP-MPs and CV solution. The presence of divalent salts inhibited CV adsorption, demonstrating that electrostatic attraction played a major role in CV capture. The hydrophobic interaction, micropore filling, hydrogen bonding, and π - π conjugation were possible involved. This study is of great significance for better understanding the complex pollution of MPs and its potential environmental risks in the future.

Selection of engineered degradation method to remove microplastics from aquatic environments

Microplastics (MPs) in the aquatic environment are difficult to degrade naturally due to their hydrophobicity and structure. A variety of engineered degradation methods were developed to treat MPs contamination in the aquatic environment. Current reviews of MPs degradation methods only provided an inventory but lacked systematic comparisons and application recommendations. However, selecting suitable degradation methods for different types of MPs contamination may be more effective. This work examined the present engineered degradation methods for MPs in the aquatic environment. They were categorized into chemical degradation, biodegradation, thermal degradation and photodegradation. These degradation methods were systematically summarized in terms of degradation efficiency, technical limitations and production of environmental hazards. Also, the potential influences of different environmental factors and media on degradation were analyzed, and the selection of degradation methods were suggested from the perspectives of contamination types and degradation mechanisms. Finally, the development trend and challenges for studying MPs engineered degradation were proposed. This work will contribute to a better selection of customized degradation methods for different types of MPs contamination scenarios in aquatic environments.

Aged polystyrene microplastics exposure affects apoptosis via inducing mitochondrial dysfunction and oxidative stress in early life of zebrafish

In recent years, the toxic effects of microplastics (MPs) on aquatic organisms have been increasingly recognized. However, the developmental toxicity and underlying mechanisms of photoaged MPs at environmental concentrations remain unclear. Therefore, the photodegradation of pristine polystyrene (P-PS) under UV irradiation was used to investigate, as well as the developmental toxicity and underlying mechanisms of zebrafish (Danio rerio) exposed to P-PS and aged polystyrene (A-PS) at environmentally relevant concentrations (0.1-100 μg/L). Mortality, heart rate, body length, and tail coiling frequency of zebrafish larvae were the developmental toxicity endpoints. A-PS had increased crystallinity, the introduction of new functional groups, and higher oxygen content after UV-photoaging. The toxicity results showed that exposure to A-PS resulted in more adverse developmental toxicity than exposure to P-PS. Exposure to A-PS induced oxidative damage, as evidenced by elevated production of reactive oxygen species (ROS) and DNA damage, and led to decreased mitochondrial membrane potential (MMP) and causes the release of cytochrome c (cyt c) from the mitochondria. The caspase-3/-9 activation signaling pathways may cause developmental toxicity via mitochondrial apoptosis. Significant changes in the expression of genes were further explored linking with oxidative stress, mitochondria dysfunctions and apoptosis pathways following A-PS exposure. These findings underscore the importance of addressing the environmental applications of aged MPs and call for further research to mitigate their potential risks on aquatic ecosystems and human health.

Aged polystyrene microplastics cause reproductive impairment via DNA-damage induced apoptosis in Caenorhabditis elegans

Although polystyrene microplastics (PS-MPs) could induce toxic effects on environmental organisms, the toxicity of aged PS-MPs with H2O2 on soil organisms remains unclear. Our study utilized Caenorhabditis elegans as model organism to examine the reproductive toxicity of pristine PS-MPs (pPS-MPs) and aged PS-MPs (aPS-MPs) at environmentally relevant concentrations (0.1-100 μg/L). Acute exposure to aPS-MPs could induce greater reproductive impairment compared to pPS-MPs, as evidenced by changes in brood size and egg release. Assessment of gonad development using the number of mitotic cells, length of gonad arm, and relative area of gonad arm as parameters revealed a high reproductive toxicity caused by aPS-MPs exposure. Furthermore, aPS-MPs exposure promoted substantial germline apoptosis. Additionally, exposure to aPS-MPs (100 μg/L) markedly altered the expression of DNA damage-induced apoptosis-related genes (e.g., egl-1, cep-1, clk-2, ced-3, -4, and -9). Alterations in germline apoptosis caused by aPS-MPs were observed in mutants of cep-1, hus-1, egl-1, ced-3, -4, and -9. Consequently, the augmentation of reproductive toxicity resulting from aPS-MPs exposure was attributed to DNA damage-triggered cellular apoptosis. Additionally, the EGL-1-CEP-1-HUS-1-CED-3-CED-4-CED-9 signaling pathway was identified as a key regulator of germline apoptosis in nematodes. Our study provides insights into potential environmental risk of aPS-MPs with H2O2 on environmental organisms.

Genotoxicity and metabolic changes induced via ingestion of virgin and UV-aged polyethylene microplastics by the freshwater fish Perca fluviatilis

The present study aims to compare and assess the toxicity induced by aged (irradiated with ultraviolet radiation for 120 days) polyethylene microplastics (PE-MPs) in comparison to virgin (non-irradiated) ones, after feeding the freshwater fish Perca fluviatilis. To this end, MPs mediated genotoxicity was assessed by the investigation of micronucleus nuclear abnormalities frequency in fish blood, and the degree of DNA damage in the liver and muscle tissues, while metabolic alterations were also recorded in both tissues. Results showed that both virgin and aged PE-MPs induced signaling pathways leading to DNA damage and nuclear abnormalities, as well as metabolites changes in all tissues studied. Metabolic changes revealed that the metabolism of nucleic acids, energy, amino acids, and neurotransmitters was more disrupted in the liver and by aged PE-MPs compared to muscles. Fish fed with aged PE-MPs exhibited greater DNA damage, while blood cells of fish fed with virgin PE-MPs seemed to be more vulnerable to nuclear abnormalities in relation to those fed with aged PE-MPs. Moreover, aged PE-MPs induced more acute overall effects on the metabolic profiles of fish tissues, and initiated stronger stress responses, inflammation, and cellular damages in fish tissues in relation to virgin ones. Characterization of both virgin and aged MPs revealed that the latter exhibited lower crystallinity and melting point, more irregular shapes and higher moiety of oxygen and carbonyl groups, which could be attributed for their observed higher toxicity. The research outcomes provide significant insights for advancing toxicological investigations in this field.

Environmentally relevant concentrations of microplastics from agricultural mulch and cadmium negatively impact earthworms by triggering neurotoxicity and disrupting homeostasis

Recent research has highlighted the ecological risk posed by microplastics (MPs) from mulching film and heavy metals to soil organisms. However, most studies overlooked real environmental levels of MPs and heavy metals. To address this gap, pristine and aged polyethylene (PE) mulching film-derived MPs (PMPs, 500 mg/kg; AMPs, 500 mg/kg) were combined with cadmium (Cd, 0.5 mg/kg) to assess the acute toxicity to earthworms and investigate associated molecular mechanisms (oxidative stress, osmoregulation pressure, gut microbiota, and metabolic responses) at environmentally relevant concentrations. Compared to Cd alone and Cd + PMPs treatments (11.15 ± 4.19 items/g), Cd + AMPs treatment resulted in higher MPs bioaccumulation (23.73 ± 13.14 items/g), more severe tissue lesions, and increased cell membrane osmotic pressure in earthworms' intestines. Cd + AMPs induced neurotoxicity through elevated levels of glutamate and acetylcholinesterase. Earthworm intestines (0.98 ± 0.49 to 3.33 ± 0.37 mg/kg) exhibited significantly higher Cd content than soils (0.19 ± 0.01 to 0.51 ± 0.06 mg/kg) and casts (0.15 ± 0.01 to 0.25 ± 0.05 mg/kg), indicating PE-MPs facilitated Cd transport in earthworms' bodies. Metabolomic analysis showed Cd + AMPs exposure depleted energy and nucleotide metabolites, disrupted cell homeostasis more profoundly than Cd and Cd + PMPs treatments. Overall, co-exposure to AMPs + Cd induced more severe neurotoxicity and disruption of homeostasis in earthworm than Cd and PMPs + Cd treatments. Our study, using Cd and MPs with environmental relevance, underscores MPs' role in amplifying Cd accumulation and toxicity in earthworms.

Effect of ultraviolet aged polytetrafluoroethylene microplastics on copper bioavailability and Microcystis aeruginosa growth

Microplastics (MPs) are ubiquitous in aquatic environments, which can act as carriers to affect the bioavailability of heavy metals. The aging process in the environment changes the physicochemical properties of MPs, thereby affecting their environmental behavior and co-toxicity with other pollutants. However, relevant research is limited. In this study, we compared the properties and Cu2+ adsorption capacity of pristine and aged polytetrafluoroethylene (PTFE) MPs and further explored the influence on copper bioavailability and bio-effects on Microcystis aeruginosa. Aging process induced surface oxidation and cracks of PTFE MPs, and decreased the stability of MPs in water by increasing zeta potential. PTFE MPs had a strong adsorption capacity for Cu2+ and increased the bioavailability of copper to microalgae, which was not affected by the aging process. Pristine and aged PTFE MPs adhered to cyanobacterium surfaces and caused shrinkage and deformation of cells. Inhibition of cyanobacterium growth, photosynthesis and reduction of total antioxidant capacity were observed in the treatment of PTFE MPs. Combined exposure of pristine MPs and Cu2+ had stronger toxic effects to cyanobacterium, and increased Microcystin-LR release, which could cause harm to aquatic environment. Aging reduced the toxic effects of PTFE MPs on microalgae. Furthermore, soluble exopolysaccharide (EPS) content was significantly higher in co-exposure of aged MPs and Cu2+, which could reduce the toxicity to cyanobacterium cells. These results indicate that aging process alleviates the toxicity to microalgae and environmental risks caused by PTFE MPs. This study improves understanding of the combined toxicity of aged MPs and metals in freshwater ecosystems.

Insights into the effect of crystallinity on the sorption of organic pollutants to microplastics

The environmental behavior of microplastics (MPs) has attracted global attention. Research has confirmed that MPs can strongly absorb almost every kind of pollutant and can serve as vectors for pollutant transport. In this research, the sorption isotherms of six organic pollutants with different structure on four virgin plastic particles with different crystallinity were determined. Results indicated that the hydrophobicity (KOW) of organic pollutants and the crystallinity of MPs were the two key factors that affected the sorption process of organic pollutants on MPs. Strong correlations were observed between KOW and the partition coefficient. Hydrophobic partition was one of the major mechanisms regardless of the type of organic chemical (hydrophobic, polar, or dissociable). What is more, the influence of the crystallinity of MPs on the sorption process increased with increasing hydrophobicity of the chemical. Combining this result with analyzing the related literature on the effect of crystallinity, it was concluded that the effect of crystallinity on the sorption of chemicals with strong hydrophobicity was obvious, whereas this effect was negligible for chemicals with weak hydrophobicity. The influence of the crystallinity of MPs on sorption could even exceed the influence of MPs type, so crystallinity should be considered carefully when discussing the sorption capacity of MPs. This study enhances the understanding of the sorption of organic pollutants by MPs.

Photoaged polystyrene microplastics result in neurotoxicity associated with neurotransmission and neurodevelopment in zebrafish larvae (Danio rerio)

Microplastics (MPs) are emerging pollutants widely distributed in the environment, inducing toxic effects in various organisms. However, the neurotoxicity and underlying mechanisms of simulated sunlight-aged MPs have rarely been investigated. In this study, zebrafish (Danio rerio) were exposed to environmentally relevant concentrations (0, 0.1, 1, 10, and 100 μg/L) of virgin polystyrene (V-PS) and aged polystyrene (A-PS) for 120 hpf to evaluate the neurotoxicity. The results demonstrated that simulated sunlight irradiation altered the physicochemical properties (morphology, functional groups, and chemical composition) of V-PS. Exposure to A-PS causes greater toxicity on locomotor ability in larval zebrafish than V-PS. Motor neuron development was disrupted by transgenic (hb9-GFP) zebrafish larvae exposed to A-PS, with significant alterations in neurotransmitter levels (ACh, DA, 5-HT, and GABA) and enzyme activity (AChE, ChAT, and ChE). Further investigation found that exposure to A-PS had a significantly impact on the expression of neurotransmission and neurodevelopment-related genes in zebrafish. These findings suggest that A-PS induces neurotoxicity by its effects on neurotransmission and neurodevelopment. This study highlights the neurotoxic effects and mechanisms of simulated sunlight irradiation of MPs, providing new insights for assessing the ecological risks of photoaged MPs in the environment.

A systematic review of microplastics emissions in kitchens: Understanding the links with diseases in daily life

The intensification of microplastics (MPs) pollution has emerged as a formidable environmental challenge, with profound global implications. The pervasive presence of MPs across a multitude of environmental mediums, such as the atmosphere, soil, and oceans, extends to commonplace items, culminating in widespread human ingestion and accumulation via channels like food, water, and air. In the domestic realm, kitchens have become significant epicenters for MPs pollution. A plethora of kitchen utensils, encompassing coated non-stick pans, plastic cutting boards, and disposable utensils, are known to release substantial quantities of MPs particles in everyday use, which can then be ingested alongside food. This paper conducts a thorough examination of contemporary research addressing the release of MPs from kitchen utensils during usage and focuses on the health risks associated with MPs ingestion, as well as the myriad factors influencing the release of MPs in kitchen utensils. Leveraging the insights derived from this analysis, this paper proposes a series of strategic recommendations and measures targeted at mitigating the production of MPs in kitchen settings. These initiatives are designed not solely to diminish the release of MPs but also to enhance public awareness regarding this pressing environmental concern. By adopting more informed practices in kitchens, we can significantly contribute to the reduction of the environmental burden of MPs pollution, thus safeguarding both human health and the ecological system.

Characteristics and adsorption behavior of typical microplastics in long-term accelerated weathering simulation

Microplastics can function as carriers in the environment, absorbing various toxins and spreading to diverse ecosystems. Toxins accumulated in microplastics have the potential to be re-released, posing a threat. In this study, two typical plastics, namely polyethylene (PE) and polystyrene (PS), along with the degradable plastic poly(butylene adipate-co-terephthalate) (PBAT), were subjected to a long-term ultraviolet alternating weathering experiment. The study investigated the variations in the weathering process and pollutant adsorption of microplastics of different particle sizes. Furthermore, the adsorption capacity of microplastics for various pollutants was assessed. The findings indicate that particle size significantly influences weathering, leading to variations in adsorption capacity. The weathered PE displays a higher adsorption capacity for azo dyes. Additionally, the adsorption capacity of PBAT for neutral red is double that of antibiotics. Importantly, the maximum adsorption capacity of PBAT for pollutants after aging is approximately 10 times greater than that of PE. Consequently, degradable plastics undergoing weathering in the natural environment may pose a higher ecological risk than traditional plastics.

Co-impacts of cation type and humic acid on migration of polystyrene microplastics in saturated porous media

The aging process of microplastics (MPs) could significantly change their physical and chemical characteristics and impact their migration behavior in soil. However, the complex effects of different cations and humic acids (HA) on the migration of aged MPs through saturated media are not clear. In this research, the migration and retention of pristine/aged PSMPs (polystyrene microplastics) under combined effects of cations (Na+, Ca2+) (ionic strength = 10 mM) and HA (0, 5, 15 mg/L) were investigated and analyzed in conjunction with the two-site kinetic retention model and DLVO theory. The findings showed that the aging process accelerated PSMPs migration under all tested conditions. Aged PSMPs were less susceptible to Ca2+ than pristine PSMPs. Under Ca2+ conditions, pristine/aged PSMPs showed higher retention than under Na+ conditions in the absence of HA. Furthermore, under Na+ conditions, the migration of aged PSMPs significantly increased at higher concentrations of HA. However, under Ca2+ conditions, the migration of aged PSMPs decreased significantly at higher concentrations of HA. In higher HA conditions, HA, Ca2+, and PSMPs interact to cause larger aggregations, resulting in the sedimentation of aged PSMPs. The DLVO calculations and two-site kinetic retention models' results showed the detention of PSMPs was irreversible under higher HA conditions (15 mg/L) with Ca2+, and aged PSMPs were more susceptible to clogging. These findings may help to understand the potential risk of migration behavior of PSMPs in the soil-groundwater environment.

An insight decipher on photocatalytic degradation of microplastics: Mechanism, limitations, and future outlook

Plastic material manufacturing and buildup over the past 50 years has significantly increased pollution levels. Microplastics (MPs) and non-biodegradable residual plastic films have become the two most pressing environmental issues among the numerous types of plastic pollution. These tiny plastic flakes enter water systems from a variety of sources, contaminating the water. Since MPs can be consumed by people and aquatic species and eventually make their way into the food chain, their presence in the environment poses a serious concern. Traditional technologies can remove MPs to some extent, but their functional groups, stable covalent bonds, and hydrophobic nature make them difficult to eliminate completely. The urgent need to develop a sustainable solution to the worldwide contamination caused by MPs has led to the exploration of various techniques. Advanced oxidation processes (AOPs) such as photo-catalytic oxidation, photo-degradation, and electrochemical oxidation have been investigated. Among these, photocatalysis stands out as the most promising method for degrading MPs. Photocatalysis is an environmentally friendly process that utilizes light energy to facilitate a chemical reaction, breaking down MPs into carbon dioxide and water-soluble hydrocarbons under aqueous conditions. In photocatalysis, semiconductors act as photocatalysts by absorbing energy from a light source, becoming excited, and generating reactive oxygen species (ROS). These ROS, including hydroxyl radicals (•OH) and superoxide ions ( [Formula: see text] ), play a crucial role in the degradation of MPs. This extensive review provides a detailed exploration of the mechanisms and processes underlying the photocatalytic removal of MPs, emphasizing its potential as an efficient and environmentally friendly approach to address the issue of plastic pollution.

Toxicological assessment of dietary exposure of polyethylene microplastics on growth, nutrient digestibility, carcass and gut histology of Nile Tilapia (Oreochromis niloticus) fingerlings

This study was conducted to ascertain the negative effects of dietary low-density polyethylene microplastics (LDPE-MPs) exposure on growth, nutrient digestibility, body composition and gut histology of Nile tilapia (Oreochromis niloticus). Six sunflower meal-based diets (protein 30.95%; fat 8.04%) were prepared; one was the control (0%) and five were incorporated with LDPE-MPs at levels of 2, 4, 6, 8 and 10% in sunflower meal-based diets. A total of eighteen experimental tanks, each with 15 fingerlings, were used in triplicates. Fish were fed at the rate of 5% biomass twice a day for 60 days. Results revealed that best values of growth, nutrient digestibility, body composition and gut histology were observed by control diet, while 10% exposure to LDPE-MPs significantly (P < 0.05) reduced weight gain (WG%, 85.04%), specific growth rate (SGR%, 0.68%), and increased FCR (3.92%). The findings showed that higher level of LDPE-MPs (10%) exposure in the diet of O. niloticus negatively affects nutrient digestibility. Furthermore, the results revealed that the higher concentration of LDPE-MPs (10%) had a detrimental impact on crude protein (11.92%) and crude fat (8.04%). A high number of histological lesions were seen in gut of fingerlings exposed to LDPE-MPs. Hence, LDPE-MPs potentially harm the aquatic health.

Toxic effects on ciliates under nano-/micro-plastics coexist with silver nanoparticles

Owing to the degradation of plastics, microplastics (MPs) and nanoplastics (NPs) have remained the focus of global attention. Silver nanoparticles (AgNPs) could adversely affect marine organisms due to their broad application. So far, the combined effects of MPs/NPs (strong adsorbents) with AgNPs on marine organisms are scant. Thus, four sizes polystyrene beads (80 nm, 220 nm, 1.07 µm, and 2.14 µm) combined with AgNPs (30 nm) were assessed using ciliated protozoa Uronema marinum. Results showed that MPs/NPs dramatically decrease the abundance, biovolume, and carbon biomass of U. marinum. And, exposure could cause changes of antioxidant enzyme activity and antioxidant content on U. marinum. The combined toxicity of MPs/NPs with AgNPs to ciliates showed an enhanced effect compared to exposure alone. Additionally, the negative effects under exposure of NPs plus AgNPs were more significant than those of MPs plus AgNPs. Transcriptome sequencing showed that co-exposure could affect the energy metabolism and lipid metabolism of ciliates, even cause DNA and protein damage. Our study provided a novel insight and first-hand basic data for the understanding of combined toxicity of MPs /NPs with AgNPs on the basic trophic level ciliated protozoa in marine ecosystems.

Are we underestimating stormwater? Stormwater as a significant source of microplastics in surface waters

Stormwater represent a critical pathway for transporting microplastics (MPs) to surface waters. Due to complex dynamics of MPs in stormwater, its dispersion, weathering, risk, and transport are poorly understood. This review bridges those gaps by summarizing the latest findings on sources, abundance, characteristics, and dynamics involved in stormwater MP pollution. Weathering starts before or after MPs enter stormwater and is more pronounced on land due to continuous heat and mechanical stress. Land use patterns, rainfall intensity, MPs size and density, and drainage characteristics influence the transport of MPs in stormwater. Tire and road wear particles (TRWPs), littering, and road dust are major sources of MPs in stormwater. The concentrations of MPs varies from 0.38-197,000 particles/L globally. Further MP concentrations showed regional variations, highlighting the importance of local monitoring efforts needed to understand local pollution sources. We observed unique signatures associated with the shape and color of MPs. Fibers and fragments were widely reported, with transparent and black being the predominant colors. We conclude that the contribution of stormwater to MP pollution in surface waters is significantly greater than wastewater treatment plant effluents and demands immediate attention. Field and lab scale studies are needed to understand its behavior in stormwater and the risk posed to the downstream water bodies.

Micro- and nano-plastics in the atmosphere: A review of occurrence, properties and human health risks

The ubiquitous occurrence of micro/nano plastics (MNPs) poses potential threats to ecosystem and human health that have attracted broad concerns in recent decades. Detection of MNPs in several remote regions has implicated atmospheric transport as an important pathway for global dissemination of MNPs and hence as a global health risk. In this review, the latest research progress on (1) sampling and detection; (2) origin and characteristics; and (3) transport and fate of atmospheric MNPs was summarized. Further, the current status of exposure risks and toxicological effects from inhaled atmospheric MNPs on human health is examined. Due to limitations in sampling and identification methodologies, the study of atmospheric nanoplastics is very limited today. The large spatial variation of atmospheric MNP concentrations reported worldwide makes it difficult to compare the overall indoor and outdoor exposure risks. Several in vitro, in vivo, and epidemiological studies demonstrate adverse effects of immune response, apoptosis and oxidative stress caused by MNP inhalation that may induce cardiovascular diseases and reproductive and developmental abnormalities. Given the emerging importance of atmospheric MNPs, the establishment of standardized sampling-pretreatment-detection protocols and comprehensive toxicological studies are critical to advance environmental and health risk assessments of atmospheric MNPs.

Adsorption and desorption of Hg(II) by four aged microplastics and its effects on gaseous elemental mercury production in seawater

Microplastics (MPs) weather after entering the environment gradually, and the interaction with metal ions in the aqueous environment has received extensive attention. However, there are few studies on Hg(Ⅱ), especially the effect of MPs on the release of Hg0(DEM) in water after entering the aqueous environment. In this study, four types of MPs (PP, PE, PET, PVC) were selected to study the adsorption and desorption behavior of Hg(Ⅱ) after photoaging and to explore the influence of MPs on the release of DEM in seawater under different lighting conditions. The results showed that the specific surface area, negative charges, and oxygen-containing functional group of MPs increased after aging. The adsorption capacity of aged MPs for Hg(Ⅱ) was significantly improved, which was consistent with the pseudo-first-order and pseudo-second-order model, indicating that the adsorption process was a chemical and physical adsorption. The fitting results of the in-particle diffusion model indicated that the adsorption was controlled by multiple steps. Hg(Ⅱ) was easier to desorb in the simulated gastric fluid environment. Because the aged MPs had the stronger binding force to Hg(Ⅱ), their desorption rate is lower than new MPs. Under visible light and UVA irradiation, MPs inhibited the release of Hg0. Under UVA, the mass of DEM produced in seawater with aged PE and PVC was higher than that of new PE and PVC. The aged PE and PVC could produce more ·O2-, which was conducive to the reduction of mercury. However, in UVB irradiation, the addition of MPs promoted the release of DEM, and ·O2- also played an important contribution in affecting the photochemical reaction of mercury. Therefore, the presence of aged MPs will significantly affect the water-air exchange of Hg in water. Compared with new MPs, aged MPs improved the contribution of free radicals in Hg transformation by releasing reactive oxygen species. This study extends the understanding of the effects of MPs on the geochemical cycle of Hg(Ⅱ) in seawater, better assesses the potential combined ecological risks of MPs and Hg(Ⅱ), and provides certain guidance for the pollution prevention and control of MPs.

Aging microplastics enhances the adsorption of pharmaceuticals in freshwater

Plastic pollution is an increasing environmental concern. Pollutants such as microplastics (< 5 mm) and pharmaceuticals often co-exist in the aquatic environment. The current study aimed to elucidate the interaction of pharmaceuticals with microplastics and ascertain how the process of photo-oxidation of microplastics affected the adsorption of the pharmaceuticals. To this end, a mixture containing ibuprofen, carbamazepine, fluoxetine, venlafaxine and ofloxacin (16 μmol L-1 each) was placed in contact with one of six either virgin or aged microplastic types. The virgin microplastics were acquired commercially and artificially aged in the laboratory. Polypropylene, polyethylene, polyethylene terephthalate, polyamide, polystyrene, and polyvinyl chloride microparticles at two sizes described as small (D50 < 35 μm) and large (D50 95-157 μm) were evaluated. Results demonstrated that the study of virgin particles may underestimate the adsorption of micropollutants onto microplastics. For virgin particles, only small microparticles of polypropylene, polyethylene, polyvinyl chloride, and both sizes of polyamide adsorbed pharmaceuticals. Aging the microplastics increased significantly the adsorption of pharmaceuticals by microplastics. Fluoxetine adsorbed onto all aged microplastics, from 18 % (large polyethylene terephthalate) to 99 % (small polypropylene). The current investigation highlights the potential of microplastics to act as a vector for pharmaceuticals in freshwater, especially after aging.

Various additive release from microplastics and their toxicity in aquatic environments

Additives may be present in amounts higher than 50% within plastic objects. Additives in plastics can be gradually released from microplastics (MPs) into the aquatic environment during their aging and fragmentation because most of them do not chemically react with the polymers. Some are known to be hazardous substances, which can cause toxicity effects on organisms and pose ecological risks. In this paper, the application of functional additives in MPs and their leaching in the environment are first summarized followed by their release mechanisms including photooxidation, chemical oxidation, biochemical degradation, and physical abrasion. Important factors affecting the additive release from MPs are also reviewed. Generally, smaller particle size, light irradiation, high temperature, dissolved organic matter (DOM) existence and alkaline conditions can promote the release of chemicals from MPs. In addition, the release of additives is also influenced by the polymer's structure, electrolyte types, as well as salinity. These additives may transfer into the organisms after ingestion and disrupt various biological processes, leading to developmental malformations and toxicity in offspring. Nonetheless, challenges on the toxicity of chemicals in MPs remain hindering the risk assessment on human health from MPs in the environment. Future research is suggested to strengthen research on the leaching experiment in the actual environment, develop more techniques and analysis methods to identify leaching products, and evaluate the toxicity effects of additives from MPs based on more model organisms. The work gives a comprehensive overview of current process for MP additive release in natural waters, summarizes their toxicity effects on organisms, and provides recommendations for future research.

Effect of oxygen-containing functional groups on the micromechanical behavior of biodegradable plastics and their formation of microplastics during aging

Biodegradable plastics (BPs) are more prone to generate harmful microplastics (MPs) in a short time, which have always been ignored. Oxygenated functional group formation is considered to be a key indicator for assessing microplastic formation, while it is difficult to characterize at a very early stage. The micromechanical properties of the aging plastic during the formation of the MPs are highly influenced by the evolution of oxygen-containing functional groups, however, their relationship has rarely been revealed. Herein, we compared changes in the physicochemical properties of BPs and non-degradable plastic bags during aging in artificial seawater, soil, and air. The results showed that the oxidation of plastics in the air was the most significant, with the most prominent oxidation in BPs. The accumulation of carbonyl groups leads to a significant increase in the micromechanical properties and surface brittleness of the plastic, further exacerbating the formation of MPs. It was also verified by the FTIR, 2D-COS, AFM, and Raman spectroscopy analyses. Furthermore, the increased adhesion and roughness caused by oxygen-containing functional groups suggest that the environmental risks of BPs cannot be ignored. Our findings suggest that the testing of micromechanical properties can predicate the formation of the MPs at an early stage.

Application of a genetically engineered macrophage cell line for evaluating cellular effects of UV/US-treated poly(ethylene terephthalate) microplastics

Microplastic (MP) pollution is a global environmental problem. To understand the biological effects of MPs on humans, it is essential to evaluate the response of human cells to model plastic particles that mimic environmental MPs in a sensitive and non-invasive manner. In this study, we investigated the preparation of poly(ethylene terephthalate) (PET) fragments with properties similar to those of environmental MPs by combining photo-oxidative degradation via ultraviolet (UV) irradiation with mechanical pulverization and hydrolysis via ultrasound (US) exposure. Combination of UV and US treatments decreased the particle size of PET fragments to 10.2 µm and increased their crystallinity and Young's modulus to 35.7 % and 0.73 GPa, respectively, while untreated PET fragments showed the particle size of 18.9 µm, the crystallinity of 33.7 %, and Young's modulus of 0.48 GPa. In addition, an increase in negative surface potential and O/C ratio were observed for UV/US-treated PET fragments, suggesting surface oxidation via UV/US treatment. Cytokine secretion from human macrophages was evaluated by a highly sensitive inflammation evaluation system using the HiBiT-based chemiluminescence detection method developed by genome editing technology. UV/US-treated PET fragments induced a 1.4 times higher level of inflammatory cytokine secretion on inflammatory macrophages than untreated ones, suggesting that the biological responses of PET fragments could be influenced by changes in material properties via oxidation. In conclusion, UV/US treatment enables efficient preparation of model plastic particles and is expected to provide new insights into the evaluation of biological effects using human cells. (240 words).

Impacts of pristine, aged and leachate of conventional and biodegradable plastics on plant growth and soil organic carbon

Plastic is an essential component of agriculture globally, becoming a concerning form of pollution. Biodegradable alternatives are gaining attention as a potential replacement for commonly used, non-degradable plastics, but there is little known about the impacts of biodegradable plastics as they age and potential leachates are released. In this study, different types (conventional: polyethylene and polypropylene and biodegradable: polyhydroxybutyrate and polylactic acid) of micro- and meso-films were added to soil at 0.1% (w/w) prior to being planted with Lolium perenne (perennial ryegrass) to evaluate the plant and soil biophysical responses in a pot experiment. Root and shoot biomass and chlorophyll content were reduced when soil was exposed to plastics, whether conventional or biodegradable, pristine, aged or when just their leachate was present. The pH and organic matter content of soil exposed to these plastics and their leachates was significantly reduced compared to control samples; furthermore, there was an increase in CO2 respiration rate from soil. In general, meso (> 5 mm) and micro (< 5 mm) plastic films did not differ in the impact on plants or soil. This study provides evidence that conventional and biodegradable plastics have both physical and chemical impacts on essential soil characteristics and the growth of L. perenne, potentially leading to wider effects on soil carbon cycling.

Natural aging and adsorption/desorption behaviors of polyethylene mulch films: Roles of film types and exposure patterns

Polyethylene (PE) mulch films are an important source of microplastics (MPs) in agricultural soils, which may further affect the bioavailability of coexisting pollutants. In this study, white (WM), black (BM), and silver-black (SM) PE mulch films were aged on the soil surface and under soil burial to simulate the two exposure patterns of abandoned mulch films in the field. Results indicated that the soil-surface exposure induced more pronounced aging characteristics, and WM seemed the most susceptible. Serious surface deterioration by aging led to a drastic decrease in the tensile properties of the films, suggesting the tendency to fragment. Oxygen-containing functional groups were generated on the film surfaces, with oxygen/carbon ratios increasing by up to 29 times, which contributed to the prominent increase in Pb adsorption on the film-derived MPs. Additionally, the film surface became more hydrophobic when exposed to the soil surface but more hydrophilic in the soil-burial exposure, which was in agreement with the change in triclosan adsorption, i.e., promotion and suppression, respectively. Aging generally decreased the desorption potential of the adsorbed pollutants in simulated gastrointestinal solutions due to increased interactions. By comparison, exposure patterns were revealed to be the critical factor for these changes, regardless of film types.

Aging of plastics in aquatic environments: Pathways, environmental behavior, ecological impacts, analyses and quantifications

The ubiquity of plastics in our environment has brought about pressing concerns, with their aging processes, photo-oxidation, mechanical abrasion, and biodegradation, being at the forefront. Microplastics (MPs), whether originating from plastic degradation or direct anthropogenic sources, further complicate this landscape. This review delves into the intricate aging dynamics of plastics in aquatic environments under various influential factors. We discuss the physicochemical changes that occur in aged plastics and the release of oxidation products during their degradation. Particular attention is given to their evolving environmental interactions and the resulting ecotoxicological implications. A rigorous evaluation is also conducted for methodologies in the analysis and quantification of plastics aging, identifying their merits and limitations and suggesting potential avenues for future research. This comprehensive review is able to illuminate the complexities of plastics aging, charting a path for future research and aiding in the formulation of informed policy decisions.

Environmental fate, aging, toxicity and potential remediation strategies of microplastics in soil environment: Current progress and future perspectives

Microplastics (MPs) are small plastic debris (<5 mm) that result from the fragmentation of plastic due to physical and physiochemical processes. MPs are emerging pollutants that pose a significant threat to the environment and human health, primarily due to their pervasive presence and potential bioaccumulation within the food web. Despite their importance, there is a lack of comprehensive studies on the fate, toxicity, and aging behavior of MPs. Therefore, this review aims to address this gap by providing a cohesive understanding of several key aspects. Firstly, it summarizes the sources and fate of MPs, highlighting their ubiquitous presence and the potential pathways through which they enter ecosystems. Secondly, it evaluates the aging process of MPs and the factors influencing it, including the morphological and physiological changes observed in crops and the release of pollutants from aged MPs, which can have detrimental effects on the environment and human health. Furthermore, the impacts of aging MPs on various processes are discussed, such as the mobilization of other pollutants in the environment. The influence of aged MPs on the soil environment, particularly their effect on heavy metal adsorption, is examined. Finally, the review explores strategies for the prevention technologies and remediation of MPs, highlighting the importance of developing effective approaches to tackle this issue. Overall, this review aims to contribute to our understanding of MPs, their aging process, and their impacts on the environment and human health. It underscores the urgency of addressing the issue of MPs and promoting research and remediation efforts to mitigate their adverse effects.

Leaching and transformation of chemical additives from weathered plastic deployed in the marine environment

Plastic pollution causes detrimental environmental impacts, which are increasingly attributed to chemical additives. However, the behaviour of plastic additives in the marine environment is poorly understood. We used a marine deployment experiment to examine the impact of weathering on the extractables profile, analysed by liquid chromatography-mass spectrometry, of four plastics at two locations over nine months in Aotearoa/New Zealand. The concentration of additives in polyethylene and oxo-degradable polyethylene were strongly influenced by artificial weathering, with deployment location and time less influential. By comparison, polyamide 6 and polyethylene terephthalate were comparatively inert with minimal change in response to artificial weathering or deployment time. Non-target analysis revealed extensive differentiation between non-aged and aged polyethylene after deployment, concordant with the targeted analysis. These observations highlight the need to consider the impact of leaching and weathering on plastic composition when quantifying the potential impact and risk of plastic pollution within receiving environments.

Plastic residues alter soil microbial community compositions and metabolite profiles under realistic conditions

Wide usage of plastic coupled with mismanagement has created a humongous environmental hazard threatening entire ecosystems. To date, the potential effects of plastic debris-induced soil nutrition substance changes and the relevant microbial metabolic behavior remain unclear. Here, we studied the effect of plastic films polyethylene and polylactic acid in differential soil environments (farmland, woodland, and wetland) for 120 days. Soil enzyme activities (urease, neutral phosphatase, and catalase) and nutrition substance (NH4+-N, available P, available K, and soil organic matter) present obvious variations in polylactic acid groups compared to polyethylene-treated samples. 16S rRNA gene sequencing indicates that several bacteria abundance such as Bacteroidales, Actinobacteriota, Nitrososphaeraceae, Pyrinomonadalcs, Muribaculaceae, exhibited obvious up-regulation or down-regulation, and simultaneously, the carbon, nitrogen, and phosphorus cycling relevant species Bryobacter, Bradyrhizobium, and Sphingomonas, expressed wider margin of down-regulation in abundance in plastic treatment soil samples. As a result, the abundance of metabolites including sugar, amino acid, and fatty acids, which may associated with nutrition substance metabolic pathways, were significantly altered in the stress of plastic. These findings provide valuable information on the environmental effects of plastics, and the relationships of subsequent nutrition substance changes and microbial metabolic behavior.

Microplastics released from disposable medical devices and their toxic responses in Caenorhabditis elegans

Owing to accelerated urbanization and industrialization, many plastic products have been manufactured and discharged into the environment, causing environmental and public health problems. Plastics in environmental media are further degraded by prolonged exposure to light, heat, mechanical friction, and other factors to form new pollutants called microplastics (MPs). Medical plastics have become a crucial source of plastics in environmental media. However, the release profiles of MPs from medical plastics and their potential ecological and health risks remain unclear. We used optical photothermal infrared spectroscopy to explore the release profiles of eight typical disposable medical devices under high-temperature steam disinfection (HSD). We also evaluated the toxicity of disposable medical devices-derived MPs in Caenorhabditis elegans (C. elegans). Our results showed that the changes in the surface morphology and modification of the disposable medical devices were mainly associated with the material. Polypropylene (PP) and polystyrene (PS) materials exhibited high aging phenomena (e.g., bumps, depressions, bulges and cracks), and HSD broke their oxygen-containing functional groups and carbon chains. By contrast, minor changes in the chemical and physical properties were observed in the polyvinyl chloride (PVC)-prepared disposable medical devices under the same conditions. Further physicochemical characterization indicated that the amount of MPs released from PP-prepared disposable medical devices (P4: 1.27 ± 0.34 × 106) was greater than that from PVC-prepared disposable medical devices (P7: 1.08 ± 0.14 × 105). The particle size of the released MPs was the opposite, PVC-prepared disposable medical devices (P7: 11.45 ± 1.79 μm) > PP-prepared disposable medical devices (P4: 7.18 ± 0.52 μm). Toxicity assessment revealed that disposable medical devices-released MPs significantly increased germ cell apoptosisin C. elegans. Moreover, MPs from PP-prepared disposable medical devices disrupted the intestinal barrier of worms, decreasing their lifespan. Our findings provided novel information regarding the profiles and mechanisms of MP release from disposable medical devices and revealed their potential risks to ecological environment.

Microplastics as an emerging vector of Cr(VI) in water: Correlation of aging properties and adsorption behavior

Microplastics (MPs) are emerging contaminants with growing concerns due to their potential adverse effects on the environment. However, understanding the aging properties and adsorption behavior of MPs is still limited. In this study, we investigated the correlation between the adsorption capacity, aging stages, and aging properties of polyethylene MPs using a correlation equation. Our results revealed that the trends of O/C ratio and contact angle of polyethylene MPs with aging time were fitted to be linear under xenon lamp accelerated aging conditions. Conversely, the trends of other properties such as particle size, crystallinity, and molecular weight with time were fitted to conform to the Boltzmann equation. Moreover, the aging curve data for carbonyl index and molecular weight (Mw) perfectly matched, confirming Mw play a crucial role in verifying the aging process. Additionally, the adsorption amount of polyethylene MPs increased sharply with the increase of aging ages, reaching up to 1.850 mg/g. The adsorption data fit well to the pseudo-second-order kinetics and Langmuir model, suggesting that the adsorption process is dominated by chemisorption. The low pH and low salt concentration is beneficial to the adsorption capacity of MPs onto Cr(VI). Further, a relationship equation was established to predict adsorption risk at different aging stages. These findings provide new insights into the impact of aging on pollutants transport and the fate of MPs, enabling the prediction of adsorption risk of MPs at different aging stages in water environments.

Releases of microplastics and chemicals from nonwoven polyester fabric-based polyurethane synthetic leather by photoaging

The nonwoven PET fabrics are chemically, mechanically and thermally treated fiber aggregate without weaving, knitting or braiding, which could be used as a base to make polyurethane (PU) synthetic leather through a series of processing. Our research systematically compared the photoaging behaviors of pure non-woven PET base fabric (NPET-P) and PU synthetic leather (nonwoven PET-base fabrics with PU coating, NPET-U), and their possibilities for microplastic fibers (MPFs) generation and chemical transformation in water. NPET-U was photoaged to a higher oxidation degree with higher O/C ratios and more distinct changes in chemical structures. The amount of MPFs released from NPET-U (1.98 × 107 g/fibers) was significantly lower than that from NPET-P (4.76 × 107 g/fibers) after 360 h light irradiation (p value <0.05) with a slower degradation rate and delayed MPFs release. The lengths and diameters of released MPFs from NPET-U varied within a smaller range than that from NPET-P exposed to UV light irradiation. Natural sunlight aging of fabrics for 365 days was found to be equivalent to approximately 85.3-127.2 h UV aging in the laboratory, which indicated the lab accelerated experiments was extraordinarily intense to simulate natural sunlight aging. Furthermore, abundant calcium and sulfur-contained chemicals were detected in original fabrics and the leachate of 360 h light-aged fabrics using the inductively coupled plasma optical emission spectrometer (ICP-OES). The organic components of the leachate were separated according to their molecular weight with the changes of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and the UV response over aging time. UV stimulation aggravated the role of plastic polymers as disinfection by-product (DBP) precursors. Nevertheless, although NPET-U could produce more nitrogen-contained chemicals, it had similar formation potentials of nitrogen-containing DBPs as NPET-P. The discussion lucubrated the potential risks of the production of MPFs and chemical release in the leachate with regard to combined plastic pollution.

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

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

High salinity promotes the photoaging of polystyrene microplastics with humic acid in seawater

The photoaging of microplastics (MPs) accumulated in the sea can be influenced by humic acid (HA). However, the role of salinity cannot be ignored, as it may potentially disrupt the interaction between MPs and HA, thereby altering the photoaging of MPs. Herein, this study investigated how salinity influences the effect of humic acid (HA, derived from lignite) on the photoaging of polystyrene microplastics (PS MPs) in artificial and natural seawater. The results revealed that HA promoted the photoaging of PS MPs under both low (5 PSU) and high salinity (35 PSU) in light conditions (L), reflected in the formation of fragments, the production of oxygen-containing functional groups (OH, CO, and OCO), and the increase in hydrophilicity of PS MPs. Furthermore, high salinity promoted the photoaging of PS MPs with HA more significantly, as evidenced by the similar indicators and the order of oxygen/carbon atom ratio (O/C): L-HA-High (0.15) > L-HA-Low (0.10) > Unaged (0.02). Interestingly, due to the reduction of electrostatic repulsion, the adsorption of HA on photoaged PS MPs in natural and artificial high salinity seawater was 1.77 mg/g and 0.39 mg/g, respectively, which was significantly higher than those PS MPs photoaged in the low salinity seawater. Furthermore, the electron spin resonance (ESR) results confirmed that more hydroxyl radicals (OH) were generated after adsorbing HA under high salinity conditions, thus promoting the fragmentation and oxidation of PS MPs. Overall, our findings highlight the crucial role of salinity in influencing the photoaging of MPs with HA and help to assess the marine risk of MPs accurately.

Fabrication of Polypropylene Nanoplastics Via Thermal Oxidation Reaction for Human Cells Responsiveness Studies

With the current worldwide increasing use of plastics year by year, nanoplastics (NPs) have become a global threat to environmental and public health concerns. Among plastics, polypropylene (PP) is widely used in industrial and medical applications. Owing to the lack of validated detection methods and standard materials for PP NPs, understanding the impact of PP NPs on the environmental and biological systems is still limited. Here, isotactic polypropylene (iPP) was fabricated into oxidized polypropylene micro/nanoplastics (OPPs) via a thermal oxidation using hydrogen peroxide (H2O2) under various heating temperatures. The resulting OPPs were investigated in terms of the size distribution, surface chemistry, morphology, and thermal property as well as their concentration-dependent cytotoxicity to a human intestinal epithelial cell line (Caco-2), which could be a route to uptake NPs into the body through the food chain. The average diameters of the OPPs decrease with increasing reaction temperature. The OPPs obtained at 175 °C (OPP175) were spherical in shape and had a rough surface, with size distributions of approximately 0.14 ± 0.02 μm. A significant increase in the carbonyl content of the oxidized product was confirmed by Fourier transform infrared and X-ray photoelectron spectroscopy analyses. Caco-2 cells were exposed to OPP175 in a dose-dependent manner, and a significant loss of cell viability occurred at the concentration of 100 μg/mL. Thus, this study provides a fundamental approach for the fabrication of a model of NPs for the urgently demanded in vitro and in vivo studies to assess the potential impact of NPs on biological systems.

Microplastics - Back to Reality: Impact of Pristine and Aged Microplastics in Soil on Earthworm Eisenia fetida under Environmentally Relevant Conditions

Recently, studies have highlighted the potential danger for soil organisms posed by film-derived microplastics (MPs). However, the majority of those does not accurately reflect the field conditions and the degree of MP contamination that can be found in actual settings. To fill the gap between laboratory and field scenarios, the polyethylene (PE) plastic film was made into PE-MPs and aged. Toxicity and molecular mechanisms of pristine PE-MPs (PMPs) and aged PE-MPs (AMPs) with the concentration at 500 mg/kg of dry weight were determined after 14 days of exposure by measuring the oxidative stress, osmoregulation pressure, gut microbiota, and metabolic responses in earthworms under environmentally relevant conditions. Our research showed that, when compared to PMPs (13.13 ± 1.99 items/g), AMPs accumulated more (16.19 ± 8.47 items/g), caused more severe tissue lesions, and caused a higher increase of cell membrane osmotic pressure in earthworms' intestines. Furthermore, the proportion of probiotic bacteria Lactobacillus johnsonii in the gut bacterial communities was 24.26%, 23.26%, and 12.96%, while the proportion of pathogenic bacteria of the phylum Verrucomicrobia was 2.28%, 4.79%, and 10.39% in the control and PMP- and AMP-exposed earthworms, indicating that the decrease in number of probiotic bacteria and the increase in number of pathogenic bacteria were more pronounced in the gut of AMP- rather than PMP-exposed earthworms. Metabolomic analysis showed that AMP exposure reduced earthworm energy metabolites. Consequently, the constant need for energy may result in protein catabolism, which raises levels of some amino acids, disturbs normal cell homeostasis, causes changes of cell membrane osmolarity, and destroys the cell structure. Our studies showed that aged MPs, with the same characteristics as those found in the environment, have greater toxicity than pristine MPs. The results of this study broaden our understanding of the toxicological effects of MPs on soil organisms under environmentally relevant conditions.

Long-term aged fibrous polypropylene microplastics promotes nitrous oxide, carbon dioxide, and methane emissions from a coastal wetland soil

Microplastics (MPs) has been suggested that it can greatly affect soil greenhouse gases (GHGs) emissions via altering soil physical, chemical, and biological properties. However, the difference in GHGs emissions, especially for those from coastal wetland soils, between varied aged MPs was rarely explored and the underlying mechanisms of GHGs emissions affected by the aged MPs were poorly understood. Therefore, the implications of fibrous polypropylene MPs (FPP-MPs) exposure on N2O, CO2, and CH4 emissions were examined by a 60-day soil incubation experiment. Compared with the control, the additions of un-aged FPP-MPs with both two rates (0.2 and 2 %) and aged FPP-MPs with a low rate (0.2 %) showed an insignificant effect on N2O emission, while the aged FPP-MPs added with a high rate (2 %) resulted in a remarkably increase in N2O emission, especially for those of the 30-day-aged FPP-MPs. A significant increase in CO2 emission was only observed in the 30-day-aged FPP-MPs treatments, compared with the control, and a higher addition rate produced a higher increase of CO2 emission. Regarding CH4 emission, it was significantly increased by adding aged FPP-MPs, and a longer aging period or/and a higher addition rate generated a higher degree of promotion of CH4 emission. However, compared with the CO2 emission, the quantity of CH4 emission was extremely low. These increased GHGs emissions can be ascribed to the improvements in soil physical structure and other chemical properties (e.g., pH and contents of soil organic matter and dissolved organic carbon) and enhancements in the abundances of denitrification- and carbon mineralization-related microorganisms. Overall, our results highlight the risk of elevated GHGs emissions from the soil polluted with 30-day-aged FPP-MPs, which should not be ignored as long-term aged FPP-MPs continue to increase in coastal wetland soils.

Soil microbial community parameters affected by microplastics and other plastic residues

Introduction

The impact of plastics on terrestrial ecosystems is receiving increasing attention. Although of great importance to soil biogeochemical processes, how plastics influence soil microbes have yet to be systematically studied. The primary objectives of this study are to evaluate whether plastics lead to divergent responses of soil microbial community parameters, and explore the potential driving factors.

Methods

We performed a meta-analysis of 710 paired observations from 48 published articles to quantify the impact of plastic on the diversity, biomass, and functionality of soil microbial communities.

Results and discussion

This study indicated that plastics accelerated soil organic carbon loss (effect size = -0.05, p = 0.004) and increased microbial functionality (effect size = 0.04, p = 0.003), but also reduced microbial biomass (effect size = -0.07, p < 0.001) and the stability of co-occurrence networks. Polyethylene significantly reduced microbial richness (effect size = -0.07, p < 0.001) while polypropylene significantly increased it (effect size = 0.17, p < 0.001). Degradable plastics always had an insignificant effect on the microbial community. The effect of the plastic amount on microbial functionality followed the "hormetic dose-response" model, the infection point was about 40 g/kg. Approximately 3564.78 μm was the size of the plastic at which the response of microbial functionality changed from positive to negative. Changes in soil pH, soil organic carbon, and total nitrogen were significantly positively correlated with soil microbial functionality, biomass, and richness (R2 = 0.04-0.73, p < 0.05). The changes in microbial diversity were decoupled from microbial community structure and functionality. We emphasize the negative impacts of plastics on soil microbial communities such as microbial abundance, essential to reducing the risk of ecological surprise in terrestrial ecosystems. Our comprehensive assessment of plastics on soil microbial community parameters deepens the understanding of environmental impacts and ecological risks from this emerging pollution.

Impact of accelerated weathering on the leaching kinetics of stabiliser additives from microplastics

The release of additives from microplastics is known to harm organisms. In the environment, microplastics are exposed to weathering processes which are suspected to influence additive leaching kinetics, the extent and mechanism of which remain poorly understood. We examined the impact of weathering on stabiliser additive leaching kinetics using environmentally relevant accelerated weathering and leaching procedures. Nine binary polymer-additive formulations were specifically prepared, weathered, analysed, and evaluated for their leaching characteristics. Cumulative additive release (Ce) varied widely between formulations, ranging from 0.009 to 1162 µg/g. Values of Ce generally increased by polymer type in the order polyethylene terephthalate < polyamide 6 < polyethylene. The change in leaching kinetics after accelerated weathering was incongruous across the nine formulations, with a significant change in Ce only observed for three out of nine formulations. Physicochemical characterisation of the microplastics demonstrated that additive blooming was the primary mechanism influencing the leaching response to weathering. These findings highlight the dependency of additive fate on the polymer type, additive chemistry, and the extent of weathering exposure. This has significant implications for risk assessment and mitigation, where the general assumption that polymer weathering increases additive leaching may be too simplistic.

Toxicity assessment of microplastic (MPs); a threat to the ecosystem

Plastic is now considered part and parcel of daily life due to its extensive usage. Microplastic (MP) pollution is becoming a growing worry and has been ranked as the second most critical scientific problem in the realm of ecology and the environment. Microplastics are smaller in size than the plastic and are more harmful to biotic and as well as abiotic environments. The toxicity of microplastic depends upon its shape and size and increases with an increase in its adsorption capacity and their toxicity. The reason behind their harmful nature is their small size and their large surface area-to-volume ratio. Microplastic can get inside fruits, vegetables, seeds, roots, culms, and leaves. Hence microplastic enters into the food chain. There are different entry points for microplastic to enter into the food chain. Such sources can include polluted food, beverages, spices, plastic toys, and household (packing, cooking, etc.). The concentration of microplastic in terrestrial environments is increasing day by day. Microplastic causes the destruction of soil structure; destroys soil microbiota, cause depletion of nutrients in the soil, and their absorption by plants decreases plant growth. Apart from other environmental problems caused by microplastic, human health is also badly affected by microplastic pollution present in the terrestrial environment. The presence of microplastics in the human body has been confirmed. Microplastic enters into the body of humans in different possible ways. According to their way of entering the body, microplastics cause different diseases in humans. MPs also cause negative effects on the human endocrine system. At the ecosystem level, the impacts of microplastic are interconnected and can disrupt ecological processes. Although recently different papers have been published on several aspects of the microplastic present in the terrestrial environment but there is no complete overview that focus on the interrelationship of MPs in plants, and soil and their effect on higher animals like a human. This review provides a completely detailed overview of existing knowledge about sources, occurrences, transport, and effects of microplastic on the food chain and soil quality and their ecotoxicological effects on plants and humans.

Quantification of the redox properties of microplastics and their effect on arsenite oxidation

Microplastics have attracted global concern. The environmental-weathering processes control their fate, transport, transformation, and toxicity to wildlife and human health, but their impacts on biogeochemical redox processes remain largely unknown. Herein, multiple spectroscopic and electrochemical approaches in concert with wet-chemistry analyses were employed to characterize the redox properties of weathered microplastics. The spectroscopic results indicated that weathering of phenol-formaldehyde resins (PFs) by hydrogen peroxide (H2O2) led to a slight decrease in the content of phenol functional groups, accompanied by an increase in semiquinone radicals, quinone, and carboxylic groups. Electrochemical and wet-chemistry quantifications, coupled with microbial-chemical characterizations, demonstrated that the PFs exhibited appreciable electron-donating capacity (0.264-1.15 mmol e- g-1) and electron-accepting capacity (0.120-0.300 mmol e- g-1). Specifically, the phenol groups and semiquinone radicals were responsible for the electron-donating capacity, whereas the quinone groups dominated the electron-accepting capacity. The reversible redox peaks in the cyclic voltammograms and the enhanced electron-donating capacity after accepting electrons from microbial reduction demonstrated the reversibility of the electron-donating and -accepting reactions. More importantly, the electron-donating phenol groups and weathering-induced semiquinone radicals were found to mediate the production of H2O2 from oxygen for arsenite oxidation. In addition to the H2O2-weathered PFs, the ozone-aged PF and polystyrene were also found to have electron-donating and arsenite-oxidation capacity. This study reports important redox properties of microplastics and their effect in mediating contaminant transformation. These findings will help to better understand the fate, transformation, and biogeochemical roles of microplastics on element cycling and contaminant fate.

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

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

Aging behavior of microplastics accelerated by mechanical fragmentation: alteration of intrinsic and extrinsic properties

Microplastics (MPs) inevitably undergo multiple aging processes during their life cycle in the environment. However, the information regarding the mechanical fragmentation behavior of MPs remained unclear, including the changes in the intrinsic properties of aged MPs, the measurement of aging degree, the underlying mechanism, and the interaction with heavy metals. Here, MPs (PS, PP, PET) were aged by crushing (-CR) and ball-milling (-BM) to simulate mild and severe mechanical fragmentation, respectively. Our results indicated that mechanical fragmentation significantly affected the morphology of MPs. The aging degree of MP-BM was deeper compared to MP-CR owing to smaller particle size, larger specific surface area, poorer heat resistance, better hydrophilicity, and richer oxygen-containing functional groups. The carbonyl index (CI) and O/C ratio were used to measure the aging degree of the two mechanical aging treatments. Besides, the mechanism was proposed and the discrepancy between the two treatments was elaborated from three aspects including the excitation energy source, reaction interface, and reaction dynamics. Furthermore, the extrinsic properties of MPs altered with the increase of aging degree; specifically, the adsorption capacities of heavy metals were enhanced. Meanwhile, it was unveiled that the CI value and O/C ratio played a vital role in estimating the adsorption ability of heavy metals. The findings not only reveal the mechanical fragmentation behavior of MPs but also provide new insights into the assessment of the potential risks of the aged MPs via chemical indexes.

Photoaged microplastics induce neurotoxicity via oxidative stress and abnormal neurotransmission in zebrafish larvae (Danio rerio)

Microplastics (MPs) are ubiquitous environmental contaminants and cause neurotoxicity in various organisms. However, previous studies that analyzed the effects of MPs mainly focused on virgin polystyrene (V-PS) as representative models of MPs, and the mechanism underlying the neurotoxicity of photoaged polystyrene (P-PS) remains largely unknown. In this study, zebrafish (Danio rerio) were exposed to environmentally relevant concentrations (0.1-100 μg/L) of V-PS and P-PS(10 μm). The results indicated that UV radiation accelerated the aging process and changed physical and chemical properties of PS. Whereas exposure to both V-PS and P-PS at low concentrations (100 μg/L) significantly reduced the locomotor behavior of zebrafish larvae, P-PS caused more severe neurotoxicity compared to V-PS. The activity of antioxidant enzymes (SOD, CAT, and GST) and MDA content were significantly altered in zebrafish exposed to 10-100 μg/L of P-PS. Similarly, exposure to P-PS significantly increased neurotransmitter (5-HT, GABA, DA, and ACh) levels and activity of AChE, ChAT, and ChE. Star plots based on integrated biomarker response (IBR) values showed more incline toward neurotransmitter biomarkers in response to increasing P-PS concentration, and the behavioral parameters negatively correlated with the neurotransmitter biomarkers. Further investigations revealed that the expression of neurotransmission- (e.g., ache, drd3, 5th2c, and gat1) and oxidative stress- (e.g., cat1, sod1, gpx1a, and gstrl) related genes was significantly affected by PS in larval zebrafish. Thus, this study provides new insights on the potential risks of MPs into the environment.

Formation, behavior, properties and impact of micro- and nanoplastics on agricultural soil ecosystems (A Review)

Micro and nanoplastics (MPs and NPs, respectively) in agricultural soil ecosystems represent a pervasive global environmental concern, posing risks to soil biota, hence soil health and food security. This review provides a comprehensive and current summary of the literature on sources and properties of MNPs in agricultural ecosystems, methodology for the isolation and characterization of MNPs recovered from soil, MNP surrogate materials that mimic the size and properties of soil-borne MNPs, and transport of MNPs through the soil matrix. Furthermore, this review elucidates the impacts and risks of agricultural MNPs on crops and soil microorganisms and fauna. A significant source of MPs in soil is plasticulture, involving the use of mulch films and other plastic-based implements to provide several agronomic benefits for specialty crop production, while other sources of MPs include irrigation water and fertilizer. Long-term studies are needed to address current knowledge gaps of formation, soil surface and subsurface transport, and environmental impacts of MNPs, including for MNPs derived from biodegradable mulch films, which, although ultimately undergoing complete mineralization, will reside in soil for several months. Because of the complexity and variability of agricultural soil ecosystems and the difficulty in recovering MNPs from soil, a deeper understanding is needed for the fundamental relationships between MPs, NPs, soil biota and microbiota, including ecotoxicological effects of MNPs on earthworms, soil-dwelling invertebrates, and beneficial soil microorganisms, and soil geochemical attributes. In addition, the geometry, size distribution, fundamental and chemical properties, and concentration of MNPs contained in soils are required to develop surrogate MNP reference materials that can be used across laboratories for conducting fundamental laboratory studies.

Sunlight and marine weathering of poly(oxymethylene): Evolution of the physico-chemical properties

Plastic pollution is now an environmental problem that affects all environmental compartments. The study of plastic degradation in terrestrial, marine and other freshwater environments is emerging. Research is mainly focused on plastic fragmentation into microplastics. In this contribution, an engineering polymer, poly(oxymethylene) (POM), was studied under different weathering conditions using physico-chemical characterization techniques. A POM homopolymer and a POM copolymer were characterized by electron microscopy, tensile tests, DSC, infrared spectroscopy and rheometry tests after climatic and marine weathering or artificial UV/water spray cycles. Natural climatic conditions were the most favorable for POM degradation, especially under solar UV, as evidenced by the strong fragmentation into microplastics when subjected to artificial UV cycles. The evolution of properties with exposure time was found to be non-linear under natural conditions, in contrast to artificial conditions. Two main stages of degradation were evidenced by the correlation between strain at break and carbonyl indices.

Natural Solar Irradiation Produces Fluorescent and Biodegradable Nanoplastics

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

Desorption behavior of antibiotics by microplastics (tire wear particles) in simulated gastrointestinal fluids

Microplastics (MPs) are widely distributed throughout the environment. Upon ingesting MPs, the pollutants that they carry are then desorbed into organisms. This results in the accumulation of various chemicals within the organism. This study systematically examined the mechanism of antibiotic desorption using tire wear particles (TWP) as a carrier of antibiotics in simulated human gastrointestinal fluid and fish intestinal fluid. The findings of this study revealed the formation of cracks, pores, and depressions on the surface of photoaged TWP in an aquatic environment, as well as additional adsorption sites that are more favorable for the attachment of pollutants. Furthermore, the simulated human gastric fluid had a higher desorption rate than that of the fish intestinal fluid. The competition for TWP adsorption sites in the gastrointestinal fluid and the potential dissolution of antibiotics were the primary drivers of the increase in the desorption rate. The desorption rate in the simulated human gastrointestinal fluid was greater than that in the simulated fish intestinal fluid due to the composition of the gastrointestinal fluid. However, the carrying of pollutants by MPs poses a potential threat to human health. This study improves our understanding of TWP toxicity and has significant implications for the development of risk assessments.

Spherical DNA for Probing Wettability of Microplastics

Wettability of microplastics may change due to chemical or physical transformations at their surface. In this work, we studied the adsorption of spherical nucleic acids (SNAs) with a gold nanoparticle core and linear DNA of the same sequence to probe the wettability of microplastics. Soaking microplastics in water at room temperature for 3 months resulted in the enhancement of SNA adsorption capacity and affinity, whereas linear DNA adsorption was the same on the fresh and soaked microplastics. Drying of the soaked microplastics followed by rehydration decreased the adsorption of the SNA, suggesting that the effect of soaking was reversible and related to physical changes instead of chemical changes of the microplastics. Raman spectroscopy data also revealed no chemical transformations of the soaked microplastics. Heating of microplastics over a short period induced a similar effect to long-term soaking. We propose that soaking or heating removes air entrapped in the nanosized pores at the water-plastic interface, increasing the contact surface area of the SNA to afford stronger adsorption. However, such wetted porosity would not change the adsorption of linear DNA because of its much smaller size.