Photo-Oxidative Degradation Mitigated the Developmental Toxicity of Polyamide Microplastics to Zebrafish Larvae by Modulating Macrophage-Triggered Proinflammatory Responses and Apoptosis

Decoding the molecular concerto: Toxicotranscriptomic evaluation of microplastic and nanoplastic impacts on aquatic organisms

The pervasive and steadily increasing presence of microplastics/nanoplastics (MPs/NPs) in aquatic environments has raised significant concerns regarding their potential adverse effects on aquatic organisms and their integration into trophic dynamics. This emerging issue has garnered the attention of (eco)toxicologists, promoting the utilization of toxicotranscriptomics to unravel the responses of aquatic organisms not only to MPs/NPs but also to a wide spectrum of environmental pollutants. This review aims to systematically explore the broad repertoire of predicted molecular responses by aquatic organisms, providing valuable intuitions into complex interactions between plastic pollutants and aquatic biota. By synthesizing the latest literature, present analysis sheds light on transcriptomic signatures like gene expression, interconnected pathways and overall molecular mechanisms influenced by various plasticizers. Harmful effects of these contaminants on key genes/protein transcripts associated with crucial pathways lead to abnormal immune response, metabolic response, neural response, apoptosis and DNA damage, growth, development, reproductive abnormalities, detoxification, and oxidative stress in aquatic organisms. However, unique challenge lies in enhancing the fingerprint of MPs/NPs, presenting complicated enigma that requires decoding their specific impact at molecular levels. The exploration endeavors, not only to consolidate existing knowledge, but also to identify critical gaps in understanding, push forward the frontiers of knowledge about transcriptomic signatures of plastic contaminants. Moreover, this appraisal emphasizes the imperative to monitor and mitigate the contamination of commercially important aquatic species by MPs/NPs, highlighting the pivotal role that regulatory frameworks must play in protecting all aquatic ecosystems. This commitment aligns with the broader goal of ensuring the sustainability of aquatic resources and the resilience of ecosystems facing the growing threat of plastic pollutants.

Preparation of fluorescent polyurethane microspheres and their applications as reusable sensor for 4-nitrophenol detection and as microplastics model for visualizing polyurethane in cells and zebrafish

Fluorescent microspheres are of significant interests due to their wide applications in biotechnology fields. However, their preparation presents several challenges, such as the need for dye labeling, the complexity of materials and often sophisticated preparation conditions. Here a simple process for hydrophilic and crosslinked polyurethane (CPU) microspheres, with carboxyl groups on the surface via one-step precipitation polymerization in 40 min, is presented. The microsphere size is easily adjusted by varying experimental conditions. CPU microspheres exhibit high thermal and pH stability with good redispersibility in water, and emit fluorescence without any modification or dye labeling. The emission mechanism is discussed. CPU microspheres are used as fluorescent probe to detect 4-nitrophenol (4-NP) based on their emission in UV light region, with excellent selectivity and sensitivity. In addition, they are reusable with detection limit unchanged after 7 cycles of reuses, a significant feature of this work. The mechanism of fluorescence detection is thoroughly explored and ascribed to the internal filtration effect. Based on the emission in visible light region, CPU microspheres are used as a model of PU microplastics (MPs) to visualize their biodistribution in HeLa and macrophage cells, as well as in zebrafish larvae, providing a reliable tracer for the visualization and tracking of PU MPs in organisms.

Acute exposure to tris(2,4-di-tert-butylphenyl)phosphate elicits cardiotoxicity in zebrafish (Danio rerio) larvae via inducing ferroptosis

Tris(2,4-di-tert-butylphenyl)phosphate (AO168 =O), a novel organophosphate ester, is prevalent and abundant in the environment, posing great exposure risks to ecological and public health. Nevertheless, the toxicological effects of AO168 =O remain entirely unknown to date. The results in this study indicated that acute exposure to AO168 =O at 10 and 100 μg/L for 5 days obviously impaired cardiac morphology and function of zebrafish larvae, as proofed by decreased heartbeat, stroke volume, and cardiac output and the occurrence of pericardial edema and ventricular hypertrophy. Transcriptomics, polymerase chain reaction, and molecular docking revealed that the strong interaction of AO168 =O and transferrin receptor 1 activated the transportation of ferric iron into intracellular environment. The release of free ferrous ion to cytoplasmic iron pool also contributed to the iron overload in heart region, thus inducing ferroptosis in larvae via generation of excessive reactive oxygen species, glutathione peroxidase 4 inhibition, glutathione depletion and lipid peroxidation. Ferroptosis inhibitor (Fer-1) co-exposure effectively relieved the cardiac dysfunctions of zebrafish, verifying the dominant role of ferroptosis in the cardiotoxicity caused by AO168 =O. This research firstly reported the adverse impact and associated mechanisms of AO168 =O in cardiomyogenesis of vertebrates, underlining the urgency of concerning the health risks of AO168 =O.

Interactive impacts of photoaged micro(nano)plastics and co-occurring chemicals in the environment

In the environment, sunlight or ultraviolet (UV) radiation is considered to be the primary cause of plastic aging, leading to their fragmentation into particles, including micro(nano)plastics (MNPs). Photoaged MNPs possess diverse interactive properties and ecotoxicological implications substantially different from those of pristine plastic particles. This review aims to highlight the mechanisms and implications of UV-induced photoaging of MNPs, with an emphasis on various UV sources and their interactions with co-occurring organic and inorganic chemicals, as well as the associated ecological and health impacts and factors affecting those interactions. Compared to UV-B, UV-A and UV-C were more widely used in laboratory studies for MNP degradation. Photoaged MNPs act as vectors for the transportation of organic pollutants, organic matter, and inorganic chemicals in the environment. Literature showed that photoaged MNPs exhibit a higher sorption capacity for PPCPs, PAHs, PBDEs, pesticides, humic acid, fulvic acid, heavy metals, and metallic nanoparticles than pristine MNPs, potentially causing significant changes in associated ecological and health impacts. Combined exposure to photoaged MNPs and organic and inorganic pollutants significantly altered mortality rate, decreased growth rate, histological alterations, neurological impairments, reproductive toxicity, induced oxidative stress, thyroid disruption, hepatotoxicity, and genotoxicity in vivo, both in aquatic and terrestrial organisms. Limited studies were reported in vitro and found decreased cellular growth and survival, induced oxidative stress, and compromised the permeability and integrity of the cell membrane. In addition, several environmental factors (temperature, organic matter, ionic strength, time, and pH), MNP properties (polymer types, sizes, surface area, shapes, colour, and concentration), and chemical properties (pollutant type, concentration, and physiochemical properties) can influence the photoaging of MNPs and associated impacts. Lastly, the research gaps and prospects of MNP photoaging and associated implications were also summarized. Future research should focus on the photoaging of MNPs under environmentally relevant conditions, exploiting the polydisperse characteristics of environmental plastics, to make this process more realistic for mitigating plastic pollution.

Culture dependent analysis of bacterial activity, biofilm-formation and oxidative stress of seawater with the contamination of microplastics under climate change consideration

Temperature changes due to climate change and microplastic contamination are worldwide concerns, creating various problems in the marine environment. Therefore, this study was carried out to discover the impact of different temperatures of seawater exposed to different types of plastic materials on culture dependent bacterial responses and oxidative characteristics. Seawater was exposed to microplastics obtained from various plastic materials at different temperature (-18, +4, +20, and +35 °C) for seven days. Then microplastics were removed from the suspension and microplastic-exposed seawater samples were analyzed for bacterial activity, biofilm formation and oxidative characteristics (antioxidant, catalase, glutathione, and superoxide dismutase) using Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus. The results showed that the activity and biofilm formation of Pseudomonas aeruginosa and Staphylococcus aureus were affected through oxidative stress by catalase, glutathione, and superoxide dismutase due to the microplastic deformation by temperature changes. This study confirms that temperature changes as a result of climate change might influence microplastic degradation and their contamination impact in seawater in terms of bacterial metabolic and oxidation reactions.

Recycling and Degradation of Polyamides

As one of the five major engineering plastics, polyamide brings many benefits to humans in the fields of transportation, clothing, entertainment, health, and more. However, as the production of polyamide increases year by year, the pollution problems it causes are becoming increasingly severe. This article reviews the current recycling and treatment processes of polyamide, such as chemical, mechanical, and energy recovery, and degradation methods such as thermal oxidation, photooxidation, enzyme degradation, etc. Starting from the synthesis mechanism of polyamide, it discusses the advantages and disadvantages of different treatment methods of polyamide to obtain more environmentally friendly and economical treatment schemes. Finding enzymes that can degrade high-molecular-weight polyamides, exploring the recovery of polyamides under mild conditions, synthesizing environmentally degradable polyamides through copolymerization or molecular design, and finally preparing degradable bio-based polyamides may be the destination of polyamide.

Polystyrene microplastics effects on zebrafish embryological development: Comparison of two different sizes

Microplastics have become a great worldwide problem and it's therefore important to study their possible effects on human and environmental health. In this study, zebrafish embryos were used to compare two different sizes of polystyrene microplastics (PS-MPs), 1 µm and 3 µm respectively, at 0.01, 0.1, 1.0 and 10.0 mgL-1, and were monitored up to 72 h. Toxicity tests demonstrated that neither of the PS-MPs altered the embryos' survival and the normal hatching process. Instead, higher concentrations of both sizes caused an increase of the heart rate and phenotypic changes. The PS-MPs of both sizes entered and accumulated in the larvae at the concentration of 10.0 mgL-1 and the same concentration caused an increase of apoptotic processes correlated to redox homeostasis changes. The reported results give a realistic view of the negative effects of exposure to PS-MPs and provide new information on their toxicity, also considering their sizes.

Microplastics induced apoptosis in macrophages by promoting ROS generation and altering metabolic profiles

The ubiquitous presence of Microplastics (MPs) in various environments documented in recent years has recently raised significant concerns about their toxic effects. While macrophages serve as the first line of defense against toxic substances and pathogens, the impact and mechanisms of microplastics on these immune cells remain unclear. This study aims to explore whether MPs induce macrophage apoptosis through the promotion of reactive oxygen species (ROS) generation and alterations in metabolic profiles. The viability of RAW264.7 cells decreased as the concentration of 0.5 µm or 5 µm MPs ranged from 0.2 to 1.5 mg/mL, with a more pronounced effect observed in the 0.5 µm MPs group. Zebrafish exposed to 0.5 µm or 5 µm MPs at a concentration of 0.5 mg/mL exhibited decreased macrophage abundance and increased apoptosis, accompanied by alterations in the expression of inflammatory and apoptosis-related genes. While 0.5 µm MPs were observed to enter macrophages, 5 µm MPs only adhered to the cell membrane surface. Both particle sizes induced ROS generation and disrupted cellular metabolism in RAW264.7 cells. Notably, macrophages exhibited a more pronounced response to 0.5 µm MPs, characterized by heightened ROS generation, increased secretion of pro-inflammatory mediators, and a significant decrease in sphingolipid metabolism. These findings suggest that the adverse effects on macrophages are greater with 0.5 µm MPs compared to 5 µm MPs, possibly attributed to particle size effects. This study contributes additional evidence on the impact of MPs on human immune cells.

Ecotoxicity of polylactic acid microplastic fragments to Daphnia magna and the effect of ultraviolet weathering

Biodegradable plastics (BPs) are widely used as alternatives to non-BPs due to their inherent ability to undergo facile degradation. However, the ecotoxicological impact of biodegradable microplastics (MPs) rarely remains scientific documented especially to aquatic ecosystem and organisms compared to conventional microplastics. Therefore, this study aimed to investigate the ecotoxicity of biodegradable polylactic acid (PLA) MPs to Daphnia magna with that of conventional polyethylene (PE) MPs with and without ultraviolet (UV) treatment (4 weeks). The acute toxicity (48 h) of PLA MPs was significantly higher than that of PE MPs, potentially attributable to their elevated bioconcentration resulting from their higher density. UV treatment notably reduced the particle size of PLA MPs and induced new hydrophilic functional groups containing oxygen. Thus, the acute lethal toxicity of PLA MPs exhibited noteworthy increase, compared to before UV treatment after UV treatment, which was greater than that of UV-PE MPs. In addition, UV-PLA MPs showed markedly elevated reactive oxygen species concentration in D. magna compared to positive control. However, there was no significant increase in the level of lipid peroxidation, possibly due to successful defense by antioxidant enzymes (superoxide dismutase and catalase). These findings highlight the ecotoxicological risks of biodegradable MPs to aquatic organisms, which require comprehensive long-term studies.

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

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

Environmental impacts of chlorpyrifos: Transgenerational toxic effects on aquatic organisms cannot be ignored

Chlorpyrifos (CPF) has been extensively used in the world and frequently found in natural environments, might cause a range of environmental issues and pose a health risk to aquatic species. However, investigation of its toxic effects on offspring after parental exposure has been neglected, especially for aquatic organisms such as fish. In the current study, the effects of chronic CPF exposure (3 and 60 μg/L) on adult zebrafish (F0) was investigated to determine its influence on adult reproductive capacity and offspring (F1 and F2). The results showed the existence of CPF both in F0 ovaries and F1 embryos and larvae, indicating that CPF could be transferred directly from the F0 adult fish to F1 offspring. After 90 d exposure, we observed that F0 female fish showed increased proportion of perinucleolar oocyte in the ovaries, decreased proportion of mature oocyte, and decreased egg production, but not in F1 adult. The transcriptomic analysis revealed that the disruption of metabolism during oocyte maturation in the CPF treatment zebrafish might interfere with F0 oocytes development and quality and ultimately influence offspring survival. For the larvae, the parental CPF exposure distinctly inhibited heart rate at 72 and 120 hpf and increased the mortality of F1 but not F2 larvae. The changes of biochemical indicators confirmed a disturbance in the oxidative balance, induced inflammatory reaction and apoptosis in F1 larvae. Furthermore, the changing profiles of mRNA revealed by RNA-seq confirmed an increased susceptibility in F1 larvae and figured out potential disruptions of ROS metabolism, immune system, apoptosis, and metabolism pathways. Taken together, these results show that chronic CPF treatment can induce reproductive toxicity, and parental transfer of CPF occurs in fish, resulting in transgenerational alters in F1 generation survival and transcription that raising concerns on the ecological risk of CPF in the natural 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.

Microplastic polyamide toxicity: Neurotoxicity, stress indicators and immune responses in crucian carp, Carassius carassius

This study aimed to determine the toxicity standard and potential risks and effects of polyamide (PA) exposure on neurotoxicity, stress indicators, and immune responses in juvenile crucian carp Carassius carassius. Numerous microplastics (MPs) exists within aquatic environments, leading to diverse detrimental impacts on aquatic organisms. The C. carassius (mean weight, 23.7 ± 1.6 g; mean length, 13.9 ± 1.4 cm) were exposed to PA concentrations of 0, 4, 8, 16, 32 and 64 mg/L for 2 weeks. Among the neurotransmitters, the acetylcholinesterase (AChE) activity in the liver, gill, and intestine of C. carassius was significantly inhibited by PA exposure. Stress indicators such as cortisol and heat shock protein 70 (HSP70) in the liver, gill, and intestine of C. carassius were significantly increased, while immune responses to lysozyme and immunoglobulin M (IgM) were significantly decreased. Our study demonstrates the toxic effects of MP exposure on crucian carp's neurotoxicity, stress indicators, and immune responses.

Differential developmental and proinflammatory responses of zebrafish embryo to repetitive exposure of biodigested polyamide and polystyrene microplastics

Microplastics (MPs) have attracted global concern and are at the forefront of current research on environmental pollution, whereas, little is known about the degradation of ingested MPs in the gastrointestinal environment and repetitive exposure-associated risk of egested MPs to organisms. The present study revealed that polyamide (PA) and polystyrene (PS) MPs exhibited remarkably differential biodegradations in the gastric and intestinal fluids of a model fish (Siniperca chuatsi). Significant disintegration of the skeleton structure, size reduction (from 27.62 to 9.17 µm), benzene ring scission, and subsequent biogenic corona coating and surface oxidation occurred during in vitro digestion, thus increasing the hydrophilicity and agglomeration of PS. Conversely, PA MPs exhibited high resistance to enzymolysis with slight surface erosions and protein adsorption. Relative to the pristine form, the bioaccumulation of digested PS elevated and the musculoskeletal deformity and mortality of juvenile zebrafish were obviously enhanced, but these changes were unobservable for PA. Lipopolysaccharide-triggered inflammation and apoptosis via Toll-like receptor signaling pathways and reduction of extracellular matrix secretions driven by oxidative stress contributed to the aggravated inhibitory effects of digested PS on larval development. These findings emphasize the necessity of concerning the biota digestion in MP risk assessments in natural waters.

Microplastics could be marginally more hazardous than natural suspended solids - A meta-analysis

Microplastics (MP) are perceived as a threat to aquatic ecosystems but bear many similarities to suspended sediments which are often considered less harmful. It is, therefore pertinent to determine if and to what extent MP are different from other particles occurring in aquatic ecosystems in terms of their adverse effects. We applied meta-regressions to toxicity data extracted from the literature and harmonized the data to construct Species Sensitivity Distributions (SSDs) for both types of particles. The results were largely inconclusive due to high uncertainty but the central tendencies of our estimates still indicate that MP could be marginally more hazardous compared to suspended sediments. In part, the high uncertainty stems from the general lack of comparable experimental studies and dose-dependent point estimates. We therefore argue that until more comparable data is presented, risk assessors should act precautionary and treat MP in the 1-1000 µm size range as marginally more hazardous to aquatic organisms capable of ingesting such particles.

Toxic effects of sub-acute microplastic (polyamide) exposure on the accumulation, hematological, and antioxidant responses in crucian carp, Carassius carassius

The purpose of this study is to investigate the impact of microplastics (MPs) on fish and to confirm the toxic effects of MPs on fish, as well as to clarify the standard indicators. MPs are present in a large amount in the aquatic environment and can have various adverse effects on aquatic animals. Crucian carp, Carassius carassius (mean weight, 23.7 ± 1.6 g; mean length, 13.9 ± 1.4 cm), were exposed to PA (Polyamide) concentrations of 0, 4, 8, 16, 32 and 64 mg/L for 2 weeks. The PA accumulation profile in C. carassius decreased from the intestine to the gill to the liver. Hematological parameters such as red blood cell (RBC) counts, hemoglobin (Hb), and hematocrit (Ht) notably decreased at high levels of PA exposure. Plasma components such as calcium, magnesium, glucose, cholesterol, total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) were significantly altered by PA exposure. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and glutathione (GSH) of liver, gill and intestine significantly increased following PA exposure. The results of this study suggest that MP exposure affects the hematological physiology and antioxidant responses in C. carassius as well as accumulation in specific tissues.

Size-dependent long-term weathering converting floating polypropylene macro- and microplastics into nanoplastics in coastal seawater environments

In this study, we systematically developed the long-term photoaging behavior of different-sized polypropylene (PP) floating plastic wastes in a coastal seawater environment. After 68 d of laboratory accelerated UV irradiation, the PP plastic particle size decreased by 99.3 ± 0.15%, and nanoplastics (average size: 435 ± 250 nm) were produced with a maximum yield of 57.9%, evidencing that natural sunlight irradiation-induced long-term photoaging ultimately converts floating plastic waste in marine environments into micro- and nanoplastics. Subsequently, when comparing the photoaging rate of different sized PP plastics in coastal seawater, we discovered that large sized PP plastics (1000-2000 and 5000-7000 μm) showed a lower photoaging rate than that of small sized PP plastic debris (0-150 and 300-500 μm), with the decrease rate of plastic crystallinity as follow: 0-150 μm (2.01 d-1) > 300-500 μm (1.25 d-1) > 1000-2000 μm (0.780 d-1) and 5000-7000 μm (0.900 d-1). This result can be attributed to the small size PP plastics producing more reactive oxygen species (ROS) species, with the formation capacity of hydroxyl radical •OH as follows: 0-150 μm (6.46 × 10-15 M) > 300-500 μm (4.87 × 10-15 M) > 500-1000 (3.61 × 10-15 M) and 5000-7000 μm (3.73 × 10-15 M). The findings obtained in this study offer a new perspective on the formation and ecological risks of PP nanoplastics in current coastal seawater environments.

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.

Fate and environmental behaviors of microplastics through the lens of free radical

Microplastics (MPs), as plastics with a size of less than 5 mm, are ubiquitously present in the environment and become an increasing environmental concern. The fate and environmental behavior of MPs are significantly influenced by the presence of free radicals. Free radicals can cause surface breakage, chemical release, change in crystallinity and hydrophilicity, and aggregation of MPs. On the other hand, the generation of free radicals with a high concentration and oxidation potential can effectively degrade MPs. There is a limited review article to bridge the fate and environmental behaviors of MP with free radicals and their reactions. This paper reviews the sources, types, detection methods, generation mechanisms, and influencing factors of free radicals affecting the environmental processes of MPs, the environmental effects of MPs controlled by free radicals, and the degradation strategies of MPs based on free radical-associated technologies. Moreover, this review elaborates on the limitations of the current research and provides ideas for future research on the interactions between MPs and free radicals to better explain their environmental impacts and control their risks. This article aims to keep the reader abreast of the latest development in the fate and environmental behaviors of MP with free radicals and their reactions and to bridge free radical chemistry with MP control methodology.

The detrimental effects of micro-and nano-plastics on digestive system: An overview of oxidative stress-related adverse outcome pathway

With the massive manufacture and use of plastics, plastic pollution-related environmental impacts have raised great concern in recent years. As byproducts of plastic fragmentation and degradation, microplastics (MPs) and nanoplastics (NPs) have been identified as novel pollutants that posed a threat to the ecosystem and humans. Since MPs/NPs could be transported via the food chain and retained in the water, the digestive system should be one of the major targets of MPs/NPs-related toxicity. Although considerable evidence has supported the digestive toxicity of MPs/NPs, the proposed mechanisms remained ambiguous due to the variety of study types, models, and endpoints. This review provided a mechanism-based perspective on MPs/NPs-induced digestive effects by adopting the adverse outcome pathway framework as a promising tool. The overproduction of reactive oxygen species was identified as the molecular initiating event in MPs/NPs-mediated injury to the digestive system. A series of detrimental effects including oxidative stress, apoptosis, inflammation, dysbiosis, and metabolic disorders were summarized as key events. Finally, the occurrence of these effects eventually led to an adverse outcome, suggesting a possible increase in the incidence of digestive morbidity and mortality.

Unveiling the residual plastics and produced toxicity during biodegradation of polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC) microplastics by mealworms (Larvae of Tenebrio molitor)

Evidence for plastic degradation by mealworms has been reported. However, little is known about the residual plastics derived from incomplete digestion during mealworm-mediated plastic biodegradation. We herein reveal the residual plastic particles and toxicity produced during mealworm-mediated biodegradation of the three most common microplastics, i.e., polyethylene (PE), polystyrene (PS), and polyvinyl chloride (PVC). All three microplastics are effectively depolymerized and biodegraded. We discover that the PVC-fed mealworms exhibit the lowest survival rate (81.3 ± 1.5%) and the highest body weight reduction (15.1 ± 1.1%) among the experimental groups by the end of the 24-day experiment. We also demonstrate that the residual PVC microplastic particles are more difficult to depurate and excrete for the mealworms compared to the residual PE and PS particles by using laser direct infrared spectrometry. The levels of oxidative stress responses, including reactive oxygen species, antioxidant enzyme activities, and lipid peroxidation, are also highest in the PVC-fed mealworms. Sub-micron microplastics and small microplastics are found in the frass of mealworms fed with PE, PS, and PVC, with the smallest particles detected at diameters of 5.0, 4.0, and 5.9 µm, respectively. Our findings provide insights into the residual microplastics and microplastic-induced stress responses in macroinvertebrates under micro(nano)plastics exposure.

Multi-biomarkers hazard assessment of microplastics with different polymers by acute embryo test and chronic larvae test with zebrafish (Danio rerio)

Microplastics as emerging contaminants show various composition features in the environment. However, influence of polymer types on the toxicity of microplastics is still unclear, thus affecting evaluation of their toxicity and ecological risks. In this work, toxic effects of microplastics (fragment, 52-74 μm) with different polymer types including polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP) and polystyrene (PS) to zebrafish (Danio rerio) were studied using acute embryo test and chronic larvae test. Silicon dioxide (SiO₂) was used as a control representing natural particles. Results showed microplastics with different polymers had no influence on embryonic development at environmental relevant concentration (10² particles/L), but could lead to accelerated heartbeat rate and increased embryonic death when exposed to SiO₂, PE and PS at higher concentrations (10⁴ and 10⁶ particles/L). Chronic exposure for zebrafish larvae indicated different polymers of microplastics did not affect zebrafish larvae' feeding and growth, nor induce oxidative stress. But larvae' locomotion level and AChE (acetylcholinesterase) activities could be inhibited by SiO₂ and microplastics at 10⁴ particles/L. Our study demonstrated negligible toxicity of microplastics at environmental relevant concentration, while different polymers of microplastics have similar toxic effects as SiO₂ at high concentrations. We suggest that microplastic particles may have the same biological toxicity as natural particles.

The role of microplastic aging on chlorpyrifos adsorption-desorption and microplastic bioconcentration

Microplastics (MPs) in soil undergo different aging processes such as photoaging, mechanical abrasion and biodegradation, leading to alterations in the surface properties of MPs. In this study, we investigated the adsorption-desorption of chlorpyrifos (CPF) on pristine and UV light-aged low-density polyethylene (LDPE) and biodegradable (Bio) MPs that were derived from plastic mulch films. We also tested the bioconcentration of pristine and aged MPs (LDPE- and Bio-MPs aged under UV light and LDPE-MPs aged in three different soils) associated with CPF by earthworms (Lumbricus terrestris). The results showed that UV-aged MPs showed higher CPF adsorption capacities than pristine MPs, with the adsorption capacities at 184.9 ± 5.3, 200.5 ± 1.8, 193.0 ± 8.7, and 215.9 ± 1.1 μg g^-1 for pristine LDPE-, UV-aged LDPE-, pristine Bio- and UV-aged Bio-MPs, respectively. The desorption rate of CPF from UV-aged LDPE-MPs within 48 h was lower than the desorption from pristine ones (28.8 ± 7.7% vs. 40.0 ± 3.9%), while both pristine and UV-aged Bio-MPs showed very low CPF desorption rates. A 4-day Petri dish experiment showed that UV-aged MPs were significantly less concentrated in earthworm casts than pristine counterparts (52% and 36% lower for UV-aged LDPE- and Bio-MPs), while UV-aged MPs with adsorbed CPF were concentrated significantly more than UV-aged MPs without CPF. Interestingly, LDPE-MPs aged in soil with a high carbon, nitrogen, and carbon-to-nitrogen ratio were significantly more concentrated in earthworm casts than pristine LDPE-MPs. In conclusion, UV-aged MPs acted as stronger vectors for CPF than pristine MPs. The bioconcentration of MPs differed significantly due to microplastic aging, as well as the combined effect with CPF. Moreover, LDPE-MPs aged in soil with enriched carbon and nitrogen were significantly concentrated in earthworm casts. Further studies on the environmental behaviours of aged MPs associated with other pollutants in soil, especially soils high in carbon and nitrogen, are needed.

UV-aged microplastics induces neurotoxicity by affecting the neurotransmission in larval zebrafish

Microplastics (MPs) are nearly ubiquitous in aquatic ecosystems and may affect aquatic organisms. In this study, virgin and aged polystyrene MPs (PS-MPs) of size 1 μm were selected to analyze their adverse effects on larvae zebrafish. Exposure to PS-MPs significantly reduced the average swimming speed of zebrafish, and the behavioral effects caused by aged PS-MPs on zebrafish were more pronounced. Fluorescence microscopy revealed that 10-100 μg/L of PS-MPs accumulated in tissues of zebrafish. As an endpoint of neurotransmitter concentration, exposure to aged PS-MPs at doses ranging from 0.1 to 100 μg/L significantly increased the dopamine (DA), 5-hydroxytryptamine (5-HT), γ-aminobutyric acid (GABA), and acetylcholine (ACh) levels in zebrafish. Similarly, exposure to aged PS-MPs significantly altered the expression of genes related to these neurotransmitters (e.g., dat, 5ht1aa, and gabral genes). According to Pearson correlation analyses, neurotransmissions was significantly correlated with neurotoxic effects of aged PS-MPs. Thus, aged PS-MPs cause neurotoxicity in zebrafish through their effects on DA, 5-HT, GABA, and ACh neurotransmissions. The results highlight the importance of the neurotoxicity of aged PS-MPs in zebrafish, which has important implications for the risk assessment of aged MPs and the conservation of aquatic ecosystems.

Characteristics and behaviors of microplastics undergoing photoaging and Advanced Oxidation Processes (AOPs) initiated aging

The fact that 94% of microplastics (MPs) ubiquitous in the environment are subject to natural weathering makes the aging study currently a research hotspot. This review summarized the physicochemical characteristics of MPs undergoing natural and artificial aging and evaluated current analytical methods used in aging studies. Besides, the differences in photoaging and aging induced by advanced oxidation processes (AOPs) were discussed, leading to a conclusion that AOPs composed of oxidant and ultraviolet (UV) irradiation can better facilitate the alteration of MPs compared to UV irradiation alone. In addition, the environmental behavior of aged MPs was outlined and their adsorption properties for organics and metals were highlighted as a result of combined effects of hydrophobic, π-π, diffusion, and hydrogen bond interaction. Furthermore, the mechanisms of photoaging and AOPs-initiated aging were analyzed, mainly the role of reactive oxygen species (ROS) and environmentally persistent free radicals (EPFRs). Finally, the applications of two-dimensional correlation spectroscopy (2D-COS) and three-dimensional fluorescence spectra using excitation emission matrix-parallel factor analysis (EEM-PARAFAC) were discussed for the aging process analysis. This overview plays an important role in explaining the aging characteristics of MPs and provides a theoretical foundation for further investigations into their toxicity and removal.

Progress on the Effects of Microplastics on Aquatic Crustaceans: A Review

It is impossible to overlook the effects of microplastics on aquatic life as they continuously accumulate in aquatic environments. Aquatic crustaceans, as both predator and prey, play an important role in the food web and energy transmission. It is of great practical significance to pay attention to the toxic effects of microplastics on aquatic crustaceans. This review finds that most studies have shown that microplastics negatively affect the life history, behaviors and physiological functions of aquatic crustaceans under experimental conditions. The effects of microplastics of different sizes, shapes or types on aquatic crustaceans are different. Generally, smaller microplastics have more negative effects on aquatic crustaceans. Irregular microplastics have more negative effects on aquatic crustaceans than regular microplastics. When microplastics co-exist with other contaminants, they have a greater negative impact on aquatic crustaceans than single contaminants. This review contributes to rapidly understanding the effects of microplastics on aquatic crustaceans, providing a basic framework for the ecological threat of microplastics to aquatic crustaceans.

Sorption and desorption of bisphenols on commercial plastics and the effect of UV aging

Plastics gradually degrade in the natural environment from the effect of irradiation, which can change the surface properties of plastics and affect the migration behaviour of pollutants. Up to now, studies on the sorption/desorption behaviour of organic pollutants on aged plastics are still limited. In this study, several types of commercial plastics (polyurethane (PU), polyamide (PA), polyvinyl chloride (PVC), expanded polystyrene (EPS)) were selected to investigate the sorption and release behaviour for four kinds of bisphenols (bisphenol-F, A, B, AP). The results from Raman spectroscopy and scanning electron microscopy (SEM) analysis showed evidence of oxidization and surface cracks of plastics after irradiation. The sorption behaviour for both fresh and aged plastics were dominated by hydrophobicity. In addition, the electrostatic force, H-bonding interaction, and π-π interaction were also the important factors impacting the sorption process. The desorption kinetics behaviour indicates that desorption becomes faster after aging. Hydrophobicity is also an important factor that affects desorption behaviour. This study showed that sorption capacity for most fresh and aged plastics was enhanced by the impact of salinity and dissolved organic matter (DOM). Increased temperature could increase the desorption of bisphenols on both fresh and aged plastics, which illustrated that warm environments would promote more pollutants be released from plastics to water bodies.

Transgenic zebrafish (Danio rerio) as an emerging model system in ecotoxicology and toxicology: Historical review, recent advances, and trends

Zebrafish (Danio rerio) is an alternative model system for drug screening, developing new products, and assessing ecotoxic effects of pollutants and biomonitor species in environmental risk assessment. However, the history and current use of transgenic zebrafish lines in ecotoxicology and toxicology studies remain poorly explored. Thus, the present study aimed to summarize and discuss the existing data in the literature about the applications of transgenic zebrafish lines in ecotoxicology and toxicology. The articles were analyzed according to publication year, journal, geographic distribution, and collaborations. Also, the bioassays were evaluated according to the tested chemical, transgenic lines, development stage, biomarkers, and exposure conditions (i.e., concentration, time, type, and route of exposure). Revised data showed that constitutive transgenic lines are the main type of transgenic used in the studies, besides most of uses embryos and larvae under static conditions. Tg(fli1: EGFP) was the main transgenic line, while the GFP and EGFP were the main reporter proteins. Transgenic zebrafish stands out in assessing vasotoxicity, neurotoxicity, systemic toxicity, hepatoxicity, endocrine disruption, cardiotoxicity, immunotoxicity, hematotoxicity, ototoxicity, and pancreotoxicity. This review showed that transgenic zebrafish lines are emerging as a suitable in vivo model system for assessing the mechanism of action and toxicity of chemicals and new biotechnology products, and the effects of traditional and emerging pollutants.

Aging relieves the promotion effects of polyamide microplastics on parental transfer and developmental toxicity of TDCIPP to zebrafish offspring

Understanding the role of microplastics (MPs) in the biological fate and toxicity of organic pollutants in food webs is vital for its risk assessment. However, contradictory results and the neglect of MP aging as a factor have led to a research gap, which needs to be filled. Our study discovered that polyamide (PA, a ubiquitous MP in water) MPs clearly facilitated bioaccumulation of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) in the F0 zebrafish gonads and parental transfer of TDCIPP to the F1 offspring. Rapid TDCIPP desorption in the gut and intestine barrier dysfunction triggered by MPs were the causes for the phenomenon. In contrast to the pristine forms, aged PA with higher hydrophilcity exhibited stronger binding and polar interactions with TDCIPP, and the intestine damage was neglectable, resulting in increased intestinal immobilization and prevented parental transfer of TDCIPP. Additionally, the aggravated body weight loss and decreased length of TDCIPP offspring were relieved after PA aging. The recovery of subintestinal venous plexus angiogenesis, yolk lipid utilization, and ATP synthesis were responsible for the mitigated transgenerational toxicity. Our results highlight the significance of aging on the role of MPs with respect to coexisting pollutants and have great implications for understanding MP-associated risks.

Developmental and reproductive toxic effects of exposure to microplastics: A review of associated signaling pathways

Microplastics (MPs), small pieces of plastic (∼5 mm), are released into the environment not only as a result of the decomposition of large-sized plastics but also from day-to-day use of plastic products. Chronic exposure to MPs has been attributed to harmful effects on aquatic organisms and rodents. Effects include gastrointestinal toxicity, hepatotoxicity, neurotoxicity, and reproductive and developmental toxicities. Exposure to MPs may also potentially affect human health. Herein, we reviewed the impact of MPs on male and female reproductive systems and the associated mechanisms involved in the reproductive and developmental toxicities of MPs. We performed a literature search in Google Scholar and PubMed using the following keywords: MPs and reproductive toxicity; MPs and developmental studies; MPs and infertility; MPs and aquatics; and MPs and rodents. Evidence of MPs accumulation has been reported in many organs of humans and experimental models. The harmful effects of MPs have been manifested in male and female reproductive systems of mammalian and aquatic animals, including developmental effects on gametes, embryos, and their offspring. This review describes various signaling pathways involved in MPs-associated male and female reproductive and developmental toxicities.

Pristine and artificially-aged polystyrene microplastic particles differ in regard to cellular response

Microplastic particles (MP), arising from the gradual decomposition of plastics in the environment, have been identified as a global problem. Most investigations of MP cytotoxicity use pristine spherical particles available from commercial sources when evaluating their impact on mammalian cells, while only limited data is available for the more relevant "weathered microplastic". In this study, we exposed murine macrophages to polystyrene MP either after up to 130 days of accelerated ageing or in pristine condition. Weathered and pristine MP were physicochemically characterized, and their cytotoxicity was investigated using biological assays, transcriptome analysis, and metabolic pathways prediction. Whereas the response to pristine MP is mainly dominated by a TNF-α release, sharp-edged weathered MP induce broader adverse cellular reactions. This study stresses the importance of including more realistic test particles (e.g., weathered particles) in combination with a broad range of biological assays when evaluating the potential risk of microplastic exposure.

Impact of sulfhydryl ligands on the transformation of silver ions by molybdenum disulfide and their combined toxicity to freshwater algae

The transformation of silver ions (Ag⁺) mediated by engineered nanomaterials (ENMs) influences the biosafety of Ag-containing products in natural environments. Actually, modification of biomolecules to ENMs in aquatic ecosystems alters their interactions with Ag⁺. This study discovered that surface functionalization of glutathione (GSH, a sulfhydryl compound ubiquitous in natural waters) on molybdenum disulfide (MoS₂) nanoflakes suppressed the redox reaction between 1 T components and Ag⁺, inhibiting the MoS₂-mediated reduction of Ag⁺ to Ag nanoparticles (AgNPs) in aqueous phase in the dark. However, AgNPs formation (from 2.32 ± 0.35-3.25 ± 0.29 mg/L per day, pH 7.0) and oxidation of MoS₂ were remarkably accelerated after GSH binding under light conditions. The dominant electron donator of MoS₂ to Ag⁺ was transformed from the electron-hole pairs to surface ligands driven by the introduction of chromophoric groups was authenticated as the cause for the elevated Ag⁺ reduction. These processes also occurred between Ag⁺ and MoS₂ at low levels (50 μg/L). Additionally, the joint algal toxicity of GSH-modified MoS₂ with Ag⁺ was weaker than that of pristine MoS₂ due to increased retention of free Ag⁺ and AgNPs formation. Our findings improve the understanding of the interaction between ENMs and Ag⁺ in aquatic ecosystems.

Microplastics aging in wastewater treatment plants: Focusing on physicochemical characteristics changes and corresponding environmental risks

Microplastics (MPs) have been frequently detected in effluent wastewater and sludge in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental MPs contamination. As important as quantitative removal is, changes of physicochemical characteristics of MPs (e.g., shapes, sizes, density, crystallinity) in WWTPs are crucial to their environmental behaviors and risks and have not been put enough attention yet. This review is therefore to provide a current overview on the changes of physicochemical characteristics of MPs in WWTPs and their corresponding environmental risks. The changes of physicochemical characteristics as well as the underlying mechanisms of MPs in different successional wastewater and sludge treatment stages that mainly driven by mechanical (e.g., mixing, pumping, filtering), chemical (e.g., flocculation, advanced oxidation, ultraviolet radiation, thermal hydrolysis, incineration and lime stabilization), biological (e.g., activated sludge process, anaerobic digestion, composition) and their combination effects were first recapitulated. Then, the inevitable correlations between physicochemical characteristics of MPs and their environmental behaviors (e.g., migration, adsorption) and risks (e.g., animals, plants, microbes), are comprehensively discussed with particular emphasis on the leaching of additives and physicochemical characteristics that affect the co-exist pollutants behavior of MPs in WWTPs on environmental risks. Finally, knowing the summarized above, some relating unanswered questions and concerns that need to be unveiled in the future are prospected. The physicochemical properties of MPs change after passing through WWTP, leading to subsequent changes in co-contaminant adsorption, migration, and toxicity. This could threaten our ecosystems and human health and must be worth investigating.

Effect of Early-Life Exposure of Polystyrene Microplastics on Behavior and DNA Methylation in Later Life Stage of Zebrafish

Microplastic contamination has received increasing attention in recent years, and concern regarding the toxicity of microplastics to the environment and humans has increased. In this study, we investigated the neurodevelopmental toxicity of polystyrene microplastics (PSMPs) in the zebrafish Danio rerio under different exposure scenarios. Zebrafish were exposed to PSMPs during embryonic stage and then allowed the fish to recover. The neurodevelopmental toxic responses were investigated using fish behavior and behavior-related gene expression. Early-life exposure to PSMPs did not alter fish behavior at the early stage; however, it led to hyperactivity later life stage. Generally, oxidative stress (i.e., sod2 and nrf2a)- and nervous system (i.e., slc6a4b, npy, and nrbf2)-related gene expression increased in all PSMPs-exposed fish. DNA hypomethylation was observed in fish challenged for a second time using the same PSMPs. Taken together, the current results imply that PSMPs have neurodevelopmental toxic potential when introduced early in life.

Developmental toxicity of glyphosate on embryo-larval zebrafish (Danio rerio)

Glyphosate (GLY) induces developmental toxicity in fish, but research on the toxicity mechanism is limited. In this study, zebrafish embryos were exposed for 120 hpf to 0.7, 7, and 35 mg L-1 GLY. The results show that GLY treatment induced developmental toxicity in the fish, including premature hatching, reduced heartbeats, pericardial and yolk sac oedema, swim bladder deficiency, and shortened body length, which was possibly due to a significantly decreased triiodothyronine (T3)/thyroxine (T4) ratio and the abnormal expression patterns of hypothalamic-pituitary-thyroid (HPT) (crh, tshβ, tr α, tr β, and t tr ) and growth hormone/insulin-like growth factor (GH/IGF) axis-related genes (gh, ghrα, ghrβ, igf1, igf1rα, and igf1rβ) in larvae exposed to GLY. In addition, GLY exposure altered the levels of SOD and CAT, increased ROS, promoted malondialdehyde (MDA) content, and significantly altered the levels of endoplasmic reticulum (ER) stress signalling pathway factors (perk, eif2α, gadd34, atf4, ire1α, xbp1, atf6, hspa5, and chop), suggesting that GLY treatment induced oxidative injury and ER stress in the larvae. Further research showed that treatment with a higher concentration of GLY upregulated the levels of iNOS, IL-1β, and TNF-α while inhibiting the expression of IL-10 and TGF-β, suggesting that GLY causes an inflammatory reaction in the larvae. In addition, we also found that apoptosis was induced in the larvae, which was determined by acridine orange staining and abnormal expression of p53, caspase-3, -8, and -9. Taken together, our results demonstrate that GLY exposure altered the T3/T4 ratio, disturbed the expression patterns of HPT and GH/IGF axis-related genes, and induced oxidative and ER stress, inflammatory reactions, and apoptosis in the zebrafish larvae. This investigation contributes to improved understanding of the developmental toxicity mechanism of GLY in fish.

Photoaged polystyrene microplastics serve as photosensitizers that enhance cimetidine photolysis in an aqueous environment

Microplastics (MPs) have received much attention in recent years because of their continuous photoaging process in aquatic environments. However, little research has been conducted on the photochemistry of aged microplastics and the associated effects on coexisting pharmaceuticals. This study investigated the photodegradation of cimetidine via aged polystyrene microplastics (PS-MPs) with different aging times (0-7 d) under simulated sunlight irradiation (700 W/m²). PS-MPs with 5 d of aging time resulted in much faster cimetidine degradation (>99%) after 2 h of irradiation than pristine PS-MPs (<8%). The enhanced photodegradation of cimetidine by aged PS-MPs was related to the increase in chromophoric oxygenated groups (CO, C-O) followed by redshifted absorbance through the photoaging process, which induced the formation of the environmentally persistent free radicals (EPFRs) OH, ¹O₂ and ³PS*. However, only ¹O₂ and ³PS* contributed to enhanced cimetidine photodegradation, with ¹O₂ playing a more important role in our case. This work also demonstrated that other compounds that are susceptible to indirect photolysis, such as codeine and morphine, are likewise significantly degraded under irradiation in the presence of aged PS-MPs. Although previous studies have reported how MPs can increase the persistence of contaminants, this study demonstrates that MPs can serve as photosensitizers and alter the fate of coexisting pharmaceuticals in aquatic environments.

Weathering pathways and protocols for environmentally relevant microplastics and nanoplastics: What are we missing?

To date, most studies of microplastics have been carried out with pristine particles. However, most plastics in the environment will be aged to some extent; hence, understanding the effects of weathering and accurately mimicking weathering processes are crucial. By using microplastics that lack environmental relevance, we are unable to fully assess the risks associated with microplastic pollution in the environment. Emerging studies advocate for harmonization of experimental methods, however, the subject of reliable weathering protocols for realistic assessment has not been addressed. In this work, we critically analysed the current knowledge regarding protocols used for generating environmentally relevant microplastics and leachates for effects studies. We present the expected and overlooked weathering pathways that plastics will undergo throughout their lifecycle. International standard weathering protocols developed for polymers were critically analysed for their appropriateness for use in microplastics research. We show that most studies using weathered microplastics involve sorption experiments followed by toxicity assays. The most frequently reported weathered plastic types in the literature are polystyrene>polyethylene>polypropylene>polyvinyl chloride, which does not reflect the global plastic production and plastic types detected globally. Only ~10% of published effect studies have used aged microplastics and of these, only 12 use aged nanoplastics. This highlights the need to embrace the use of environmentally relevant microplastics and to pay critical attention to the appropriateness of the weathering methods adopted moving forward. We advocate for quality reporting of weathering protocols and characterisation for harmonization and reproducibility across different research efforts.

On the degradation of (micro)plastics: Degradation methods, influencing factors, environmental impacts

Plastics and microplastics are difficult to degrade in the natural environment due to their hydrophobicity, the presence of stable covalent bonds and functional groups that are not susceptible to attack. In nature, microplastics are more likely to attract other substances due to their large specific surface area, which further prevents degradation from occurring. Some of these substances are toxic and harmful, and can be spread to various organisms through the food chain along with the microplastics to cause harm to them. Degradation is an effective way to eliminate plastic pollution, and a comprehensive understanding of the methods and mechanisms of plastic degradation is necessary, because it is the result of synergistic effects of several degradation methods, both in nature and in consideration of future engineering applications. The authors firstly summarize the degradation methods of (micro)plastics; secondly, review the influence of intrinsic properties and environmental factors during the degradation process; finally, discuss the environmental impact of the degradation products of (micro)plastics. It is evident that the degradation of (micro)plastics still has many challenges to overcome, and there are no mature and effective methods that can be applied in engineering practice or widely used in nature. Therefore, there is an urgent need for research on the degradation of (micro)plastics.

The First Observation of the Formation of Persistent Aminoxyl Radicals and Reactive Nitrogen Species on Photoirradiated Nitrogen-Containing Microplastics

Nitrogen-containing microplastics (N-MPs) are widely present in the atmosphere, but their potential health risks have been overlooked. In this study, the formation of persistent aminoxyl radicals (PAORs) and reactive nitrogen species (RNSs) on the N-MPs under light irradiation was investigated. After photoaging, an anisotropic triplet with the g-factor of ∼2.0044, corresponding to PAORs, was detected on the nonaromatic polyamide (PA) rather than amino resin (AmR) by electron paramagnetic resonance and confirmed by density functional theory calculations. The generated amine oxide portions on the photoaged PA were identified using X-ray photoelectron spectroscopy and Raman spectroscopy, which were considered to be the main structural basis/precursors of a PAOR. Surprisingly, RNSs were also observed on the irradiated PA. The generated ·NO due to the aphotolysis of nitrone groups simultaneously reacted with peroxide radicals and O₂·^- to yield ·NO₂ and peroxynitrite, respectively, which were responsible for peroxyacyl nitrates (PAN) and CO₃·^- formation. Besides, a significantly higher oxidative potential and reductive potential were observed for the aged PA than AmR, which is assigned to the abundant RNSs, organic hydroperoxides and PANs, and a strong ability to transfer electrons from PAOR, respectively. This work provides important information for the potential risks of airborne N-MPs and may serve as a guide for future toxicological assessments.

Photoaging enhanced the adverse effects of polyamide microplastics on the growth, intestinal health, and lipid absorption in developing zebrafish

The safety of microplastics (MPs) and associated health effects has been one of the major concerns worldwide. However, the role of photoaging toward the risk of MPs in water ecosystems remains inconclusive yet. In this study, the size of polyamide (PA, ∼32.50 μm) MPs was obviously decreased after photoaging in water containing fulvic acid (FA) and humic acid (HA) (∼19.75 and ∼24.30 μm, respectively). Nanoplastics were formed (4.65% and 2.03%, respectively) and hydrophilia and colloidal stability was improved due to the formation of oxygen-containing functional groups. FA-aged PA exhibited higher inhibition on body length and weight of developing zebrafish than HA-aged and pristine PA. Photoaged MPs in intestine were more difficult to be depurated by zebrafish, leading to the disappearance of intestinal folding, shedding of more enterocytes, and emaciation of intestinal microvilli. Dietary lipid digestion in larvae was inhibited by aged PA due to oxidative stress-triggered lipid peroxidation and inhibition of lipase activities and bile acids secretion. Exposure of photoaged MPs down-regulated genes (cd36, dgat1a, dgat2, mttp, etc.) associated with triglyceride resynthesis and transportation, resulting in lipid maladsorption and growth inhibition. Our findings highlight the potential negative effects of environmentally aged MPs on diet digestion and nutrient assimilation in fish.

Prolonged oral ingestion of microplastics induced inflammation in the liver tissues of C57BL/6J mice through polarization of macrophages and increased infiltration of natural killer cells

Microplastics (< 5 mm diameter) are one of most important environmental pollutants and contaminants worldwide. However, how microplastics affect liver immune microenvironment in not well understood. Microplastics (0.5 µm) were administered orally to C57BL/6J mice for 4 consecutive weeks at the rate of 0.5 mg/day. Non-parenchymal cells were isolated from of the mice through fractionation of fresh hepatic tissues. The immune landscape for four cell populations of B cells, T cells, NK cells and macrophages in the liver tissues was then evaluated using flow cytometry. The secretion level of inflammatory cytokines and associated signaling pathway were investigated using quantitative real-time polymerase chain reaction and western blot. Oral ingestion of microplastics increases liver weight, general liver index as well as expression of serum, liver function-related indicators. Microplastics also increased the infiltration of natural killer cells and macrophages to non-parenchymal liver cells, but reduced that of B cells to the same tissues. However, microplastics had no effect on the infiltration of T cell to non-parenchymal liver cells. Ingestion of MPs also up-regulated the expression of IFN-γ, TNF-α, IL-1β, IL-6 and IL-33 mRNA, but down-regulated that of IL-4, IL-5, IL-10, IL-18 and TGF-β1. Overall, the aforementioned processes were regulated via the NF-κB pathway in the hepatic non-parenchymal cells. Microplastics disrupts inflammatory process in liver tissues via the NF-κB signaling pathway. These findings provide a strong foundation on immune processes in hepatic tissues following prolonged ingestion of microplastics.

Microplastic Contamination in Soils: A Review from Geotechnical Engineering View

Microplastic contamination is a growing threat to marine and freshwater ecosystems, agricultural production, groundwater, plant growth and even human and animal health. Disintegration of plastic products due to mainly biochemical or physical activities leads to the formation and existence of microplastics in significant amounts, not only in marine and freshwater environments but also in soils. There are several valuable studies on microplastics in soils, which have typically focused on environmental, chemical, agricultural and health aspects. However, there is also a need for the geotechnical engineering perspective on microplastic contamination in soils. In this review paper, first, degradation, existence and persistence of microplastics in soils are assessed by considering various studies. Then, the potential role of solid waste disposal facilities as a source for microplastics is discussed by considering their geotechnical design and addressing the risk for the migration of microplastics from landfills to soils and other environments. Even though landfills are considered as one of the main geotechnical structures that contribute to the formation of considerably high amounts of microplastics and their contamination in soils, some other geotechnical engineering applications (i.e., soil improvement with tirechips, forming engineering fills with dredged sediments, soil improvement with synthetic polymer-based fibers, polystyrene based lightweight fill applications), as potential local source for microplastics, are also mentioned. Finally, the importance of geotechnical engineering as a mitigation tool for microplastics is emphasized and several important research topics involving geotechnical engineering are suggested.

Impact of algal extracellular polymeric substances on the environmental fate and risk of molybdenum disulfide in aqueous media

Molybdenum disulfide (MoS₂) poses great potential in water treatment as a popular transition metal dichalcogenide, arousing considerable concern regarding its fates and risk in aquatic environments. This study revealed that the interplay with extracellular polymeric substances (EPS) of freshwater algae significantly changed the properties and toxicity of MoS₂ to aquatic fish. The predominant binding of aromatic compounds, polysaccharides, and carboxyl-rich proteins in EPS on the 1T polymorph of MoS₂ via hydrophilic effects and the preferential adsorption of carboxylic groups contributed to morphological alterations, structural disorders (band gap and phase alterations), and the attenuated aggregation of MoS₂ in aqueous solutions. Electron charge transfer and n-π* interactions with EPS decreased the catalytic activity of MoS₂ by inhibiting its capability of generating reactive intermediates. The dissolution of MoS₂ slowed down after interacting with EPS (from 0.089 to 0.045 mg/L per day) owing to rapid initial oxidation (i.e., forming Mo-O bond) and carbon grafting. Notably, the morphological and structural alterations after EPS binding alleviated the toxicity (e.g., malformation and oxidative stress) of MoS₂ to infantile zebrafish. Our findings provide insights into the environmental fate and risk of MoS₂ by ubiquitous EPS in natural waters, serving as valuable information while developing water treatment processes accordingly.

Mass Spectrometry Imaging of Low-Molecular-Weight Phenols Liberated from Plastics

The abundant and heterogeneous distribution of toxic phenol from plastics has drawn worldwide attention. However, the common analysis methods failed to identify the accurate species of these phenolic hazards from plastics in a direct and nondestructive approach. Herein, we demonstrate the layered double hydroxides (LDHs) as a novel matrix in matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) for low-molecular-weight phenols leaked from plastics. LDHs own abundant hydroxyl groups to facilitate chemoselectivity and ionization of phenols through the formation of hydrogen bonds with these phenols. More importantly, the LDH matrix could provide a distinguishable signal for the homolog and isomeride of these phenolic hazards. The developed method could realize nondestructive and in situ mapping of phenolic hazards in plastics. Our success could help to track the low-molecular-weight compounds liberated from plastics and supply spatial information for polluted plastics. We anticipated that the proposed approach could provide sufficient information to evaluate and alarm the safety of food packaging plastics.

Chronic exposure to UV-aged microplastics induces neurotoxicity by affecting dopamine, glutamate, and serotonin neurotransmission in Caenorhabditis elegans

Microplastics are ubiquitous in all environments and exert toxic effects in various organisms. However, the neurotoxicity and underlying mechanisms of long-term exposure to MPs aged under UV radiation remain largely unclear. In this study, Caenorhabditis elegans was treated with 0.1-100 μg/L virgin and aged polystyrene microplastics (PS-MPs) for 10 d, with locomotion behavior, neuronal development, neurotransmitter content, and neurotransmission-related to gene expression as endpoints. Using locomotion behavior as an endpoint, chronic exposure to aged PS-MPs at low concentrations (1 μg/L) caused more severe neurotoxicity than that to virgin PS-MPs. In transgenic nematodes, exposure to 10-100 μg/L aged PS-MPs significantly influenced the fluorescence intensity and percentage of worms with neurodegeneration of dopaminergic, glutamatergic, and serotonergic neurons compared with control. Further investigations showed that the content of glutamate, serotonin, and dopamine was significantly influenced in nematodes chronically exposed to 100 μg/L of aged PS-MPs. Similarly, neurotransmission-related gene (e.g., eat-4, dat-1, and tph-1) expression was also altered in nematodes. These results indicate that aged PS-MPs exert neurotoxicity owing to their effects on dopamine, glutamate, and serotonin neurotransmission. This study provides insights into the underlying mechanisms and potential risks of PS-MPs after UV radiation.

Plastic Formulation is an Emerging Control of Its Photochemical Fate in the Ocean

Sunlight exposure is a control of long-term plastic fate in the environment that converts plastic into oxygenated products spanning the polymer, dissolved, and gas phases. However, our understanding of how plastic formulation influences the amount and composition of these photoproducts remains incomplete. Here, we characterized the initial formulations and resulting dissolved photoproducts of four single-use consumer polyethylene (PE) bags from major retailers and one pure PE film. Consumer PE bags contained 15-36% inorganic additives, primarily calcium carbonate (13-34%) and titanium dioxide (TiO₂; 1-2%). Sunlight exposure consistently increased production of dissolved organic carbon (DOC) relative to leaching in the dark (3- to 80-fold). All consumer PE bags produced more DOC during sunlight exposure than the pure PE (1.2- to 2.0-fold). The DOC leached after sunlight exposure increasingly reflected the ¹³C and ¹⁴C isotopic composition of the plastic. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that sunlight exposure substantially increased the number of DOC formulas detected (1.1- to 50-fold). TiO₂-containing bags photochemically degraded into the most compositionally similar DOC, with 68-94% of photoproduced formulas in common with at least one other TiO₂-containing bag. Conversely, only 28% of photoproduced formulas from the pure PE were detected in photoproduced DOC from the consumer PE. Overall, these findings suggest that plastic formulation, especially TiO₂, plays a determining role in the amount and composition of DOC generated by sunlight. Consequently, studies on pure, unweathered polymers may not accurately represent the fates and impacts of the plastics entering the ocean.

Photolytic degradation elevated the toxicity of polylactic acid microplastics to developing zebrafish by triggering mitochondrial dysfunction and apoptosis

Biodegradable plastics (BPs), as alternatives to conventional plastics, are increasingly consumed, but pose potential threats to aquatic ecosystems. In addition, the impact of natural aging on the toxicity of BPs is poorly understood. In this study, the photodegradation of polylactic acid (PLA, a typical BP) microplastics (MPs) under ultraviolet irradiation in water for 90 days was investigated, and the toxicities of virgin and degraded PLA to infantile zebrafish were compared. The results revealed that the size of MPs was reduced from ~25.56 to ~11.22 µm after degradation and nanoparticles were generated with a maximum yield of 7.13%. The formation of abundant oxygen-containing groups (i.e. C˭O and C-O-C) improved the hydrophilia and stability of MPs. Compared with pristine PLA, the efflux and detoxification of degraded PLA mediated by ABC transporters and P450 enzymes were slower, leading to higher bioaccumulation and skeletal development inhibition of zebrafish. Further, oxidative stress-triggered mitochondrial structural damage, depolarization, fission inhibition, and apoptosis were identified as crucial mechanisms underlying the elevated toxicity of PLA after degradation. These findings highlight the importance and necessity of considering natural degradation of BPs and related toxicity, which poses great implications for risk assessment and management of BPs.

Weathering Plastics as a Planetary Boundary Threat: Exposure, Fate, and Hazards

We described in 2017 how weathering plastic litter in the marine environment fulfils two of three criteria to impose a planetary boundary threat related to "chemical pollution and the release of novel entities": (1) planetary-scale exposure, which (2) is not readily reversible. Whether marine plastics meet the third criterion, (3) eliciting a disruptive impact on vital earth system processes, was uncertain. Since then, several important discoveries have been made to motivate a re-evaluation. A key issue is if weathering macroplastics, microplastics, nanoplastics, and their leachates have an inherently higher potential to elicit adverse effects than natural particles of the same size. We summarize novel findings related to weathering plastic in the context of the planetary boundary threat criteria that demonstrate (1) increasing exposure, (2) fate processes leading to poorly reversible pollution, and (3) (eco)toxicological hazards and their thresholds. We provide evidence that the third criterion could be fulfilled for weathering plastics in sensitive environments and therefore conclude that weathering plastics pose a planetary boundary threat. We suggest future research priorities to better understand (eco)toxicological hazards modulated by increasing exposure and continuous weathering processes, to better parametrize the planetary boundary threshold for plastic pollution.