Interactive effects of microplastics and selected pharmaceuticals on red tilapia: Role of microplastic aging

A critical review of microplastics in aquatic ecosystems: Degradation mechanisms and removing strategies

Plastic waste discarded into aquatic environments gradually degrades into smaller fragments, known as microplastics (MPs), which range in size from 0.05 to 5 mm. The ubiquity of MPs poses a significant threat to aquatic ecosystems and, by extension, human health, as these particles are ingested by various marine organisms including zooplankton, crustaceans, and fish, eventually entering the human food chain. This contamination threatens the entire ecological balance, encompassing food safety and the health of aquatic systems. Consequently, developing effective MP removal technologies has emerged as a critical area of research. Here, we summarize the mechanisms and recently reported strategies for removing MPs from aquatic ecosystems. Strategies combining physical and chemical pretreatments with microbial degradation have shown promise in decomposing MPs. Microorganisms such as bacteria, fungi, algae, and specific enzymes are being leveraged in MP remediation efforts. Recent advancements have focused on innovative methods such as membrane bioreactors, synthetic biology, organosilane-based techniques, biofilm-mediated remediation, and nanomaterial-enabled strategies, with nano-enabled technologies demonstrating substantial potential to enhance MP removal efficiency. This review aims to stimulate further innovation in effective MP removal methods, promoting environmental and social well-being.

Triclosan-loaded aged microplastics exacerbate oxidative stress and neurotoxicity in Xenopus tropicalis tadpoles via increased bioaccumulation

Microplastics and chlorine-containing triclosan (TCS) are widespread in aquatic environments and may pose health risks to organisms. However, studies on the combined toxicity of aged microplastics and TCS are limited. To investigate the toxic effects and potential mechanisms associated with co-exposure to TCS adsorbed on aged polyethylene microplastics (aPE-MPs) at environmentally relevant concentrations, a 7-day chronic exposure experiment was conducted using Xenopus tropicalis tadpoles. The results showed that the overall particle size of aPE-MPs decreased after 30 days of UV aging, whereas the increase in specific surface area improved the adsorption capacity of aPE-MPs for TCS, resulting in the bioaccumulation of TCS under dual-exposure conditions in the order of aPE-TCS > PE-TCS > TCS. Co-exposure to aPE-MPs and TCS exacerbated oxidative stress and neurotoxicity to a greater extent than a single exposure. Significant upregulation of pro-symptomatic factors (IL-β and IL-6) and antioxidant enzyme activities (SOD and CAT) indicated that the aPE-TCS combination caused more severe oxidative stress and inflammation. Molecular docking revealed the molecular mechanism of the direct interaction between TCS and SOD, CAT, and AChE proteins, which explains why aPE-MPs promote the bioaccumulation of TCS, causing increased toxicity upon combined exposure. These results emphasize the need to be aware of the combined toxicity caused by the increased ability of aged microplastics to carry contaminants.

Microplastic-stressor responses are rarely synergistic in freshwater fishes: A meta-analysis

Microplastic exposure can cause a range of negative effects on the biochemistry, condition and ecology of freshwater fishes depending on aspects of the exposure and the exposed fish. However, fishes are typically exposed to microplastics and additional multiple stressors simultaneously, for which the combined effects are poorly understood and may have important management consequences. Additive effects are those where the combined effect is equal to the sum, antagonistic where combined effects are less than the sum and for synergistic effects the combined effect is greater to the sum of the individual effects. Here, we performed a meta-analysis of studies recording freshwater fish responses to microplastic-stressor exposures to test if interactions were primarily non-additive (synergistic or antagonistic), and factors impacting the net response. Individual responses were classified (antagonistic/additive/synergistic) and the fit of net responses to a null additive model determined for 838 responses (36 studies) split by categorical variables for the microplastic exposure (environmental relevance, interacting stressor, microplastic morphology and response category measured), as well as the exposed fish (lifestage, ecology and family). Most responses were classified as antagonistic (48 %) and additive (34 %), with synergistic effects least frequent (17 %). Net responses fitted null additive models for all levels of interacting stressor, fish family and microplastic morphology. In contrast, net antagonism was present for biochemical responses, embryo lifestages, environmentally relevant microplastic exposures and fish with benthopelagic ecology, while synergism was identified for fishes with demersal ecology. While substantial knowledge gaps remain and are discussed, the data thus far suggest microplastic-stressor responses in freshwater fishes are rarely synergistic and, therefore, addressing either or both stressors will likely result in positive management and biological outcomes.

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.

Immunotoxicity of microplastics in fish

Plastic waste degrades slowly in aquatic environments, transforming into microplastics (MPs) and nanoplastics (NPs), which are subsequently ingested by fish and other aquatic organisms, causing both physical blockages and chemical toxicity. The fish immune system serves as a crucial defense against viruses and pollutants present in water. It is imperative to comprehend the detrimental effects of MPs on the fish immune system and conduct further research on immunological assessments. In this paper, the immune response and immunotoxicity of MPs and its combination with environmental pollutants on fish were reviewed. MPs not only inflict physical harm on the natural defense barriers like fish gills and vital immune organs such as the liver and intestinal tract but also penetrate cells, disrupting intracellular signaling pathways, altering the levels of immune cytokines and gene expression, perturbing immune homeostasis, and ultimately compromising specific immunity. Initially, fish exposed to MPs recruit a significant number of macrophages and T cells while activating lysosomes. Over time, this exposure leads to apoptosis of immune cells, a decline in lysosomal degradation capacity, lysosomal activity, and complement levels. MPs possess a small specific surface area and can efficiently bind with heavy metals, organic pollutants, and viruses, enhancing immune responses. Hence, there is a need for comprehensive studies on the shape, size, additives released from MPs, along with their immunotoxic effects and mechanisms in conjunction with other pollutants and viruses. These studies aim to solidify existing knowledge and delineate future research directions concerning the immunotoxicity of MPs on fish, which has implications for human health.

Single and combined toxicity of tadalafil (Cilais) and microplastic in Tilapia fish (Oreochromis niloticus)

The joint impact of tadalafil (Cilais) as a pharmaceutical residue and microplastics on fish is not well comprehended. The current study examined haematological, biochemical, and antioxidant parameters, along with immunohistochemical and histological indications in tilapia (Oreochromis niloticus) after being exposed to tadalafil, polyethylene microplastics (PE-MPs), and their mixtures for 15 days. The fish were distributed into 1st group control group (The fish was maintained in untreated water without any supplements); 2nd group exposed to 10 mg/L PE-MPs;3rd group exposed to 20 mg/l tadalafil (Cilais); 4th group exposed to 20 mg/l tadalafil (Cilais) + 10 mg/LPE-MPs (in triplicate). The levels of creatinine, uric acid, glucose, AST, ALT, and albumin in fish treated with tadalafil alone or in combination with PE-MPs were significantly higher than those in the control group. Fish exposed to PE-MPs, tadalafil, and tadalafil plus PE-MPs showed significantly lower levels of RBCs, Hb, Ht, neutrophils, and lymphocytes compared to the control group. Serum levels of total antioxidant capacity and reduced glutathione (GSH) were notably lowered in fish groups subjected to PE-MPs, tadalafil, and tadalafil + PE-MPs combinations in comparison to the control group. Malondialdehyde (MDA) serum levels were notably elevated in fish groups subjected to PE-MPs, tadalafil, and tadalafil + PE-MPs combinations compared to the control group. The most severe impact was observed in the tadalafil + PE-MPs combination group. Interleukin-6 (IL-6) levels were significantly increased in liver tissues following exposure to both tadalafil and microplastics compared to tissues exposed to only one substance or the control group. Changes in the gills, liver, and renal tissues were seen following exposure to PE-MPs, tadalafil, and tadalafil + PE-MPs combination in comparison to the control group of fish. Ultimately, the mixture of tadalafil and PE-MPs resulted in the most detrimental outcomes. Tadalafil and PE-MPs exhibited showed greater adverse effects, likely due to tadalafil being absorbed onto PE-MPs.

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.

Photoaging Elevated the Genotoxicity of Polystyrene Microplastics to Marine Mussel Mytilus trossulus (Gould, 1850)

Micro-sized particles of synthetic polymers (microplastics) are found in all parts of marine ecosystems. This fact requires intensive study of the degree of danger of such particles to the life activity of hydrobionts and needs additional research. It is evident that hydrobionts in the marine environment are exposed to microplastics modified by biotic and abiotic degradation. To assess the toxic potential of aging microplastic, comparative studies were conducted on the response of cytochemical and genotoxic markers in hemocytes of the mussel Mytilus trossulus (Gould, 1850) after exposure to pristine and photodegraded (UV irradiation) polystyrene microparticles (µPS). The results of cytochemical tests showed that UV-irradiated µPS strongly reduced metabolism and destabilized lysosome membranes compared to pristine µPS. Using a Comet assay, it was shown that the nuclear DNA of mussel hemocytes showed high sensitivity to exposure to both types of plastics. However, the level of DNA damage was significantly higher in mussels exposed to aging µPS. It is suggested that the mechanism of increased toxicity of photo-oxidized µPS is based on free-radical reactions induced by the UV irradiation of polymers. The risks of toxic effects will be determined by the level of physicochemical degradation of the polymer, which can significantly affect the mechanisms of toxicity.

Cytochrome P450 enzymes in the black-spotted frog (Pelophylax nigromaculatus): molecular characterization and upregulation of expression by sulfamethoxazole

Cytochrome P450 (CYP) enzymes are crucial for the detoxification of xenobiotics, cellular metabolism, and homeostasis. This study investigated the molecular characterization of CYP enzymes in the black-spotted frog, Pelophylax nigromaculatus, and examined the regulation of CYP expression in response to chronic exposure to the antibiotic sulfamethoxazole (SMX) at various environmental concentrations (0, 1, 10, and 100 μg/L). The full-length cDNA of Pn-CYP26B1 was identified. The sequence included open reading frames of 1,536 bp, encoding proteins comprising 511 amino acids. The signature motif, FxxGxxxCxG, was highly conserved when compared with a number of selected animal species. SMX significantly upregulated the expression of the protein CYP26B1 in frog livers at concentrations of 1 and 10 μg/L. SMX showed an affinity for CYP26B1 of -7.6 kcal/mol, indicating a potential mechanism for SMX detoxification or adaptation of the frog. These findings contributed to our understanding of the environmental impact of antibiotics on amphibian species and underscored the importance of CYP enzymes in maintaining biochemical homeostasis under exposure to xenobiotic stress.

New insights into changes in phosphorus profile at sediment-water interface by microplastics: Role of benthic bioturbation

Microplastics (MPs) have attracted increasing attention due to their ubiquitous occurrence in freshwater sediments and the detrimental effects on benthic invertebrates. However, a clear understanding of their downstream impacts on ecosystem services is still lacking. This study examines the effects of bio-based polylactic acid (PLA), fuel-based polyethylene terephthalate (PET), and biofilm-covered PET (BPET) MPs on the bioturbator chironomid larvae (Tanypus chinensis), and the influence on phosphorus (P) profiles in microcosms. The changes in biochemical responses and metabolic pathways indicated that MPs disrupted energy synthesis by causing intestinal blockage and oxidative stress in T. chinensis, leading to energy depletion and impaired bioturbation activity. The impairment further resulted in enhanced sedimentary P immobilization. For larval treatments, the internal-P loadings were respectively 11.4%, 8.6%, and 9.0% higher in the PLA, PET, and BPET groups compared to the non-MP control. Furthermore, the influence of bioturbation on P profiles was MP-type dependent. Both BPET and PLA treatments displayed more obvious impacts on P profiles compared to PET due to the changes in MP bioavailability or sediment microenvironment. This study connects individual physiological responses to broader ecosystem services, showing that MPs alter P biogeochemical processes by disrupting the bioturbation activities of chironomid larvae.

The aging behavior of degradable plastic polylactic acid under the interaction of environmental factors

Microplastics leaching from aging biodegradable plastics pose potential environmental threats. This study used response surface methodology (RSM) to investigate the impact of temperature, light, and humidity on the aging characteristics of polylactic acid (PLA). Key evaluation metrics included the C/O ratio, functional groups, crystallinity, surface topography, and mechanical properties. Humidity was discovered to have the greatest effect on the ageing of PLA, followed by light and temperature. The interactions between temperature and light, as well as humidity and sunlight, significantly impact the aging of PLA. XPS analysis revealed PLA underwent aging due to the cleavage of the ester bond (O-C=O), resulting in the addition of C=O and C-O. The aging process of PLA was characterized by alterations in surface morphology and augmentation in crystallinity, resulting in a decline in both tensile strength and elongation. These findings might offer insights into the aging behavior of degradable plastics under diverse environmental conditions.

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.

Characteristics of microplastic-derived dissolved organic matter and its binding with pharmaceuticals unveiled by fluorescence spectroscopy and two-dimensional correlation spectroscopy

Microplastics were an extensively detected pollutant in the environment, but microplastic-derived dissolved organic matter (MP-DOM) has received less attention, much less its impact on the binding behavior of pollutants (e.g., pharmaceuticals). In this study, DOM derived from two typical MPs, i.e., polyethylene terephthalate (PET) and polystyrene (PS) was generated by UV irradiation (a widely used way for MPs' aging treatment) and characterized by multiple spectroscopic techniques and methods. Chloramphenicol (CAP) and carbamazepine (CBZ) were selected to investigate the binding mechanism between MP-DOM and pharmaceuticals. After UV irradiation, the concentration of the dissolved organic carbon, colored DOM, and carboxyl/carbonyl groups of MP-DOM increased. Moreover, the humic-like substance released preceding and more under UV irradiation. Furthermore, the protein-like substances on PET-DOM and the humic-like substances on PS-DOM were positively correlated to the binding capacity to the pharmaceuticals, respectively. 2D-COS results revealed that the fluorescent materials having more oxygen-containing functional groups for MP-DOM preferentially interacted with the pharmaceuticals. Overall, the higher fluorescence quenching was related to the protein-like substance, CBZ, and PET-DOM as compared to the humic-like substance, CAP, and PS-DOM. It was verified by the relatively high binding ability (logKM) for them (the protein-like substance: 5.15; CBZ: 4.61; PET: 4.48). This study first proved the environmental reactivity of MP-DOM to the pharmaceuticals highlighting the significance of the spectral properties for the binding behavior of MP-DOM with pharmaceuticals and the competitive sorption role of MP-DOM to the pollutants in the natural environment.

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.

The potential impacts of micro-and-nano plastics on various organ systems in humans

Humans are exposed to micro-and-nano plastics (MNPs) through various routes, but the adverse health effects of MNPs on different organ systems are not yet fully understood. This review aims to provide an overview of the potential impacts of MNPs on various organ systems and identify knowledge gaps in current research. The summarized results suggest that exposure to MNPs can lead to health effects through oxidative stress, inflammation, immune dysfunction, altered biochemical and energy metabolism, impaired cell proliferation, disrupted microbial metabolic pathways, abnormal organ development, and carcinogenicity. There is limited human data on the health effects of MNPs, despite evidence from animal and cellular studies. Most of the published research has focused on specific types of MNPs to assess their toxicity, while other types of plastic particles commonly found in the environment remain unstudied. Future studies should investigate MNPs exposure by considering realistic concentrations, dose-dependent effects, individual susceptibility, and confounding factors.

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.

Effects of biodegradable and conventional microplastics on the intestine, intestinal community composition, and metabolic levels in tilapia (Oreochromis mossambicus)

Despite growing interest in conventional microplastics (CMPs) and their toxicological effects on aquatic species, little is known about biodegradable microplastics (BMPs) and their corresponding implications for aquatic life. Here, tilapia (Oreochromis mossambicus) were semi-statically exposed for 14 days to the bio-based plastic polylactic acid (PLA, 100 μg/L, 2.52 ± 0.46 μm) and the petroleum-based plastic polyvinyl chloride (PVC, 100 μg/L, 1.58 ± 0.36 μm). The results showed that ingesting the above two types of microplastics (MPs) led to oxidative stress in the fish gut, and damage to gut tissues and organelles, and PLA resulted in more obvious gut tissue edema than PVC. Furthermore, PLA caused increased levels of gut microbiota dysbiosis and a decrease in the abundance of the genus Cetobacterium, which is linked to vitamin B-12 synthesis, whereas an opposite relationship was observed on PVC. Metabolomic analysis indicated that PVC caused a significant down-regulation of orotic acid, co-metabolite of folic acid with vitamin B-12, while PLA did not affect orotic acid, which may lead to the accumulation of folic acid in fish. The joint analysis found that MPs disturbed gut metabolism homeostasis, implying that abnormal gut microbiota metabolites may be a key mechanism for MPs to induce tissue damage and oxidative stress in the gut. Overall, this study systematically illustrates the differential toxic effects of BMPs and CMPs on tilapia through gut microbiota and metabolite interactions, which will contribute to assessing the risks of BMPs to organismal health.

Photoaged microplastics induce neurotoxicity associated with damage to serotonergic, glutamatergic, dopaminergic, and GABAergic neuronal systems in Caenorhabditis elegans

Microplastics (MPs) are ubiquitous environmental contaminants that cause neurotoxicity in various organisms. MPs are typically affected by light irradiation and undergo photoaging. However, the neurotoxic effects of photoaged polystyrene (P-PS) and its underlying mechanisms remain unclear. In this study, locomotion behaviors, neuronal development, neurotransmitter levels, and the expression of neurotransmission-related genes were investigated in Caenorhabditis elegans exposed to P-PS at environment-relevant concentrations (0.1-100 μg/L). The characterization results showed that photoaging accelerated the aging process and changed the physicochemical properties of the MPs. The toxicity results suggested that exposure to 1-100 μg/L P-PS caused more severe neurotoxicity than virgin polystyrene (V-PS) with endpoints of head thrashes, body bends, wavelength, and mean amplitude. Exposure to P-PS also altered the fluorescence intensity and neurodegeneration percentage of serotonergic, glutamatergic, dopaminergic, and aminobutyric acid (GABA) in transgenic nematodes. Similarly, significant reductions in the levels of these neurotransmitters were also observed. Based on Pearson's correlation, locomotion behaviors were negatively correlated with the neurotransmission of serotonin, glutamate, dopamine, and GABA. Further investigation suggested that the expression of neurotransmitter-related genes (e.g., tph-1, eat-4, and unc-46) was significantly altered in the nematodes. Collectively, the neurotoxic effects of P-PS were attributed to abnormal neurotransmission. This study highlights the potential toxicity of MPs photoaged under environmentally relevant conditions.

Interaction between antibiotics and microplastics: Recent advances and perspective

Both microplastics and antibiotics are emerging pollutants, which are ubiquitous in aquatic environments. With small size, high specific surface area, and attached biofilm, microplastics are capable of adsorbing or biodegrading antibiotic pollutants across aquatic environments. However, the interactions between them are poorly understood, especially factors that affect microplastics' chemical vector effects and the mechanisms driving these interactions. In this review, the properties of microplastics and their interaction behavior and mechanisms towards antibiotics were comprehensively summarized. Particularly, the impact of weathering properties of microplastics and the growth of attached biofilm was highlighted. We concluded that compared with virgin microplastics, aged microplastics usually adsorb more types and quantities of antibiotics from aquatic environments, whilst the attached biofilm could further enhance the adsorption capacities and biodegrade some antibiotics. This review can answer the knowledge gaps of the interaction between microplastics and antibiotics (or other pollutants), offer basic information for evaluating their combined toxicity, provide insights into the distribution of both emerging pollutants in the global water chemical cycle, and inform measures to remove microplastic-antibiotic pollution.

Aging behavior of biodegradable polylactic acid microplastics accelerated by UV/H2O2 processes

The usage of biodegradable plastics is expanding annually due to worldwide plastic limits, resulting in a substantial number of microplastics (MPs) particles formed from biodegradable plastic products entering the aquatic environment. Until now, the environmental behaviors of these plastic product-derived MPs (PPDMPs) have remained unclear. In this work, commercially available polylactic acid (PLA) straws and PLA food bags were used to evaluate the dynamic aging process and environmental behavior of PLA PPDMPs under UV/H2O2 conditions. By combining scanning electron microscopy, two-dimensional (2D) Fourier transform infrared correlation spectroscopy (COS) and X-ray photoelectron spectroscopy, it was determined that the aging process of the PLA PPDMPs was slower than that of pure MPs. The 2D-COS analysis revealed that the response orders for the functional groups on the PLA MPs differed during the aging process. The results demonstrated that the oxygen-containing functional groups of the PLA PPDMPs were the first to react. Subsequently, the -C-H and -C-C- structural responses began, and the polymer backbone was ruptured by the aging process. However, the aging of the pure-PLA MPs started with a brief oxidation process and then breakage of the polymer backbones, followed by continuous oxidation. Moreover, compared to the PLA PPDMPs, the pure-PLA MPs exhibited a greater adsorption capacity, which was increased by 88% after aging, whereas those of the two PPDMPs only increased by 64% and 56%, respectively. This work provides new insights into the behaviors of biodegradable PLA MPs in aquatic environments, which is critical for assessing the environmental risks and management policies for degradable MPs.

Single and combined effects of polyethylene microplastics and acetochlor on accumulation and intestinal toxicity of zebrafish (Danio rerio)

The co-exposure of microplastics (MPs) and other contaminants has aroused extensive attention, but the combined impacts of MPs and pesticides remain poorly understood. Acetochlor (ACT), a widely used chloroacetamide herbicide, has raised concerns for its potential bio-adverse effects. This study evaluated the influences of polyethylene microplastics (PE-MPs) for acute toxicity, bioaccumulation, and intestinal toxicity in zebrafish to ACT. We found that PE-MPs significantly enhanced ACT acute toxicity. Also, PE-MPs increased the accumulation of ACT in zebrafish and aggravate the oxidative stress damage of ACT in intestines. Exposure to PE-MPs or/and ACT causes mild damage to the gut tissue of zebrafish and altered gut microbial composition. In terms of gene transcription, ACT exposure triggered a significant increase in inflammatory response-related gene expressions in the intestines, while some pro-inflammatory factors were found to be inhibited by PE-MPs. This study provides a new perspective on the fate of MPs in the environment and on the assessment of the combined effects of MPs and pesticides on organisms.

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.

Neurotoxicity of microplastics: a CiteSpace-based review and emerging trends study

Microplastics, as a currently emerging pollutant, are gaining increasing attention from researchers in various fields. The purpose of this study is to summarize research development on microplastics in the field of neurotoxicity using bibliometric tools and visualization methods and to identify current research hotspots. The Web of Science Core Collection (WoSCC) was searched under the topics of "microplastics" and "neurotoxicity." A total of 33 published articles were obtained by exclusion and analyzed using CiteSpace (V6.1.R2). It was found that microplastic neurotoxicity research is currently on the rise, with the most research results being published in China, the most collaboration occurring between Italy and other countries, and the least collaboration occurring between authors. The focus and hotspots of future research on the neurotoxicity of microplastics may revolve around "accumulation" and "integrated biomarker response." These findings demonstrate the trends and frontiers in the field of microplastic neurotoxicity research and provide valuable information for subsequent research directions and potential collaborations.

Sub-chronic exposure of Oreochromis niloticus to environmentally relevant concentrations of smaller microplastics: Accumulation and toxico-physiological responses

This study assesses the accumulation and toxic effects of environmentally relevant concentrations (0.01, 0.1 and 1 mg/L) of polystyrene MPs (1 µm) in Oreochromis niloticus (Nile tilapia) for 14 days. The results showed that 1 µm PS-MPs accumulated in the intestine, gills, liver, spleen, muscle, gonad and brain. RBC, Hb and HCT showed a significant decline, while WBC and PLT showed a significant increase after the exposure. Glucose, total protein, A/G ratio, SGOT, SGPT and ALP showed significant increments in 0.1 and 1 mg/L of PS-MPs treated groups. The increase in cortisol level and upregulation of HSP70 gene expression in response to MPs exposure indicate MPs-mediated stress in tilapia. MPs-induced oxidative stress is evident from reduced SOD activity, increased MDA levels and upregulated P53 gene expression. The immune response was enhanced by inducing respiratory burst activity, MPO activity and serum TNF-α and IgM levels. MPs exposure also led to down-regulation of CYP1A gene and decreased AChE activity, GNRH and vitellogenin levels, indicating the toxicity of MPs on the cellular detoxification mechanism, nervous and reproductive systems. The present study highlights the tissue accumulation of PS-MP and its effects on hematological, biochemical, immunological and physiological responses in tilapia with low environmentally relevant concentrations.

Microplastics in aquatic environments: A comprehensive review of toxicity, removal, and remediation strategies

The occurrence of microplastics (MPs) in aquatic environments has been a global concern because they are toxic and persistent and may serve as a vector for many legacies and emerging pollutants. MPs are discharged to aquatic environments from different sources, especially from wastewater plants (WWPs), causing severe impacts on aquatic organisms. This study mainly aims to review the Toxicity of MPs along with plastic additives in aquatic organisms at various trophic compartments and available remediation methods/strategies for MPs in aquatic environments. Occurrences of oxidative stress, neurotoxicity, and alterations in enzyme activity, growth, and feeding performance were identical in fish due to MPs toxicity. On the other hand, growth inhibition and ROS formation were observed in most of the microalgae species. In zooplankton, potential impacts were acceleration of premature molting, growth retardation, mortality increase, feeding behaviour, lipid accumulation, and decreased reproduction activity. MPs togather with additive contaminants could also exert some toxicological impacts on polychaete, including neurotoxicity, destabilization of the cytoskeleton, reduced feeding rate, growth, survivability and burrowing ability, weight loss, and high rate of mRNA transcription. Among different chemical and biological treatments for MPs, high removal rates have been reported for coagulation and filtration (>86.5 %), electrocoagulation (>90 %), advanced oxidation process (AOPs) (30 % to 95 %), primary sedimentation/Grit chamber (16.5 % to 58.84 %), adsorption removal technique (>95 %), magnetic filtration (78 % to 93 %), oil film extraction (>95 %), and density separation (95 % to 100 %). However, desirable extraction methods are required for large-scale research in MPs removal from aquatic environments.

Probing the aging process and mechanism of microplastics under reduction conditions

Microplastics (MPs) are becoming a class of pollutants with high global concerns. Research on the aging of MPs has focused on oxidative environments, it is of great interest to study the aging of MPs under reduction conditions. In this study, a reduction environment was constructed by purging nitrogen and adding reducing agents (NaBH₄, VC, Na₂S, C₂Na₂O₄) to understand the aging behavior and mechanism of MPs. The results proved that PVC occurred aging under four reduction conditions, and the aging degree was the strongest under NaBH₄ reduction condition. The aged PVC became broken, particle size decreased, and dechlorination phenomenon was observed. These phenomena were more obvious under the reduction condition in light, which was the superposition of photo-aging and reduction aging. The functional group components of PVC changed (C-C/CC increased, and oxygen-containing functional groups decreased) under reduction conditions, but photo-aging was dominant in the light system. Electron transfer occurred during the reduction process, and the EDC of PVC aged increased and EAC decreased. This study may shed light on a highly efficient aging pathway of MPs that is often overlooked in nature, contributing to understanding the aging behavior of MPs in complex environments.

The adverse impact of microplastics and their attached pathogen on hemocyte function and antioxidative response in the mussel Mytilus galloprovincialis

Microplastics (MPs) are widely distributed in marine environments, and they are easily attached by various microorganisms, including pathogenic bacteria. When bivalves mistakenly eat MPs, pathogenic bacteria attached to MPs enter their bodies through the Trojan horse effect, causing adverse effects. In this study, the mussel Mytilus galloprovincialis was exposed to aged polymethylmethacrylate MPs (PMMA-MPs, 20 μm) and Vibrio parahaemolyticus attached to PMMA-MPs to explore the effect of synergistic exposure by measuring lysosomal membrane stability, ROS content, phagocytosis, apoptosis in hemocytes, antioxidative enzyme activities and apoptosis-related gene expression in gills and digestive glands. The results showed that MP exposure alone did not cause significant oxidative stress in mussels, but after long-term coexposure to MPs and V. parahaemolyticus, the activities of antioxidant enzymes were significantly inhibited in the gills of mussels. Both single MP exposure and coexposure will affect hemocyte function. Coexposure can induce hemocytes to produce higher ROS, improve phagocytosis, significantly reduce the stability of the lysosome membrane, and induce the expression of apoptosis-related genes, causing apoptosis of hemocytes compared with single MP exposure. Our results demonstrate that MPs attached to pathogenic bacteria have stronger toxic effects on mussels, which also suggests that MPs with pathogenic bacteria might have an influence on the immune system and cause disease in mollusks. Thus, MPs may mediate the transmission of pathogens in marine environments, posing a threat to marine animals and human health. This study provides a scientific basis for the ecological risk assessment of MP pollution in marine environments.

Systematic Review of Nano- and Microplastics' (NMP) Influence on the Bioaccumulation of Environmental Contaminants: Part II-Freshwater Organisms

Nano- and microplastic fragments (NMPs) exist ubiquitously in all environmental compartments. The literature-based evidence suggests that NMPs interact with other environmental contaminants in freshwater ecosystems through sorption mechanisms, thereby playing a vector role. Chemically bound NMPs can translocate throughout the environment, reaching long distances from the contaminant discharge site. In addition, they can be ab/adsorbed by freshwater organisms. Although many studies show that NMPs can increase toxicity towards freshwater biota through the carrier role, little is known regarding their potential to influence the bioaccumulation of environmental contaminants (EC) in freshwater species. This review is part II of a systematic literature review regarding the influence of NMPs on bioaccumulation. Part I deals with terrestrial organisms and part II is devoted to freshwater organisms. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA ScR) was used for the literature search and selection. Only studies that assessed the bioaccumulation of EC in the presence of NMPs and compared this with the bioaccumulation of the isolated EC were considered. Here, we discuss the outcome of 46 papers, considering NMPs that induced an increase, induced a decrease, or caused no effect on bioaccumulation. Lastly, knowledge gaps are identified, and future directives for this area of research are discussed.

Effects of microplastics on the toxicity of co-existing pollutants to fish: A meta-analysis

Aquatic ecosystems are among the main destination for microplastics (MPs) in the environment. MPs that enter aquatic ecosystems can contribute to pollution together with other co-existing pollutants. However, whether such pollution results in higher or lower toxicity to fish than that caused by co-existing pollutants alone remains controversial. This study aimed at closing this research gap based on 1380 biological endpoints under the background of environmental MP concentrations collected from 55 laboratory studies. Overall, MPs in co-existing pollutant solutions significantly increased the toxicity to fish. Specifically, MPs elevated negative effects on the immune system, metabolism, and oxidative damage. Subgroup analysis indicated that changes in toxicity were related to fish life stage and MP size, but not to co-existing pollutant or MP type. Meta-regression analysis indicated that changes in toxicity were not related to the logarithm of the octanol-water partition coefficient (logKow) or exposure time. Finally, the differences between laboratory research and the actual aquatic environment were discussed from four aspects: MPs, co-existing pollutants, environmental factors, and experimental objects. Our study provides a basis for further understanding the potential impact of MPs on aquatic organisms from a combined pollution perspective. Moreover, our results can provide a reference for the conservation and management of aquatic ecosystems.

Vertical Differentiation of Microplastics Influenced by Thermal Stratification in a Deep Reservoir

Microplastics (MPs) are an emerging environmental concern. However, vertical transport of MPs remains unclear, particularly in deep reservoirs with thermal stratification (TS). In this study, the vertical variation in MP organization, stability, migration, and the driving factors of the profile in a deep reservoir were comprehensively explored. This is the first observation that TS interfaces in a deep reservoir act as a buffer area to retard MP subsidence, especially at the interface between the epilimnion and the metalimnion. Interestingly, there was a size-selection phenomenon for MP sinking. In particular, the high accumulation of large-sized MPs (LMPs; >300 μm) indicated that LMPs were more susceptible to dramatic changes in water density at the TS interfaces. Furthermore, simultaneous analysis of water parameters and MP surface characteristics showed that the drivers of MP deposition were biological to abiotic transitions during different layers, which were influenced by algae and metals. Specifically, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and microscopic Fourier transform infrared analyses implied that the occurrence of metals on the MP surface can promote MP deposition in the hypolimnion. Our findings demonstrated that TS significantly influenced the MP fate in deep reservoirs, and the hotspot of MP exposure risk for vulnerable benthic organisms on the reservoir floor deserves more attention.

Aging process does not necessarily enhance the toxicity of polystyrene microplastics to Microcystis aeruginosa

Microplastic (MP) pollution in aquatic systems has attracted increasing attention in recent years. MPs will inevitably encounter aging process in the environment. However, research on the effects of aged MPs on freshwater ecosystems remains limited. This study compared the properties of pristine and aged polystyrene (PS) MPs of different sizes (20 nm, 200 nm, 2000 nm) and determined the effects of aging on the toxicity of PS MPs to typical freshwater cyanobacteria, Microcystis aeruginosa. Aging process induced significant changes to the properties of the MPs, especially their microstructures and surface functional groups. Aging process also influenced zeta potential, which could further affect stability and toxicity of PS MPs. After 96 h exposure, increase of algal growth and photosynthetic activity was observed in the treatment of pristine 200 nm, aged 20 nm and aged 200 nm PS MPs. In addition, pristine 20 nm, pristine 200 nm, pristine 2000 nm, aged 20 nm and aged 200 nm PS MPs were adsorbed on algal cell surface, which could influence the cell permeability. Pristine PS MPs promoted microcystin synthesis and release, which could do harm to drinking water safety and freshwater ecosystems. However, there was no significant increase in aged PS MPs treatments. Furthermore, the increased ¹³C content of algal cells in all pristine PS MPs treatments indicated that M. aeruginosa assimilated more CO₂ and generate more energy to resist the stress of pristine PS MPs when compared with aged PS MPs. These results indicate that aging process did not necessarily enhance the toxicity and biological risk of PS MPs to freshwater ecosystems. Findings of this study fill the knowledge gap in understanding the effects and risks of aged MPs on freshwater ecosystems.

Effect of aging on polyethylene microfiber surface properties and its consequence on adsorption characteristics of 17alpha-ethynylestradiol

This study assessed the interactive changes to the endocrine disruptor 17 alpha-ethynylestradiol (EE2) triggered by photoaging onto fibrous microplastics frequently found in the environment. The physicochemical property change of the polyethylene (PE) microfiber according to irradiation (i.e. 14 d UV-C (254 nm)) was studied through Fourier transform infrared spectroscopy, scanning electron microscope, and contact angle analysis. Additionally, the EE2 adsorption kinetics experiment was performed for the PE microfiber before and after UV irradiation to assess the change in adsorption characteristics. After UV irradiation, the PE microfiber surface roughness increased, the oxygen-containing functional group (e.g. carbonyl group) increased, and the contact angle (virgin PE: 80.02°, aged PE: 65.13°) decreased. A decrease in the surface hydrophobicity led to a decrease in the adsorption rate of EE2 (virgin PE: k = 0.0105 h-1, aged PE: not calculated). The hydrophobic interaction significantly affects the adsorption behavior of hydrophobic organic pollutants such as EE2 onto MPs, and continuous photo-aging of MPs may cause a new pattern of ecological risk. Therefore, there is a greater necessity for additional research relevant to this issue.

Effect of aging of microplastics on gene expression levels of the marine mussel Mytilus edulis: Comparison in vitro/in vivo exposures

In the present study, effects of aging MPs of polyethylene (PE) were investigated in the marine mussel Mytilus edulis, commonly used as bioindicator of aquatic ecosystem, using both in vitro and in vivo exposures, using concentrations found in marine waters (0.008, 10 and 100 μg.L-1). Changes in gene expression levels implicated in detoxification, immune system, cytoskeletton and cell cycle control were evaluated by quantitative RT-qPCR. Results demonstrated differential expression levels depending upon the state of plastic degradation (aged vs non-aged) and way of exposure (vitro vs vivo). This study highlighted the interest of using molecular biomarkers based on analysis of gene expression pattern in an ecotoxicological context that gives indication of relative slight changes between tested conditions as compared to other biochemical approaches (e.g. enzymatic activities). In addition, in vitro analysis could be used to generate large amount of data as regards to the toxicological effects of MPs.

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.

Impact of plastic mulching as a major source of microplastics in agroecosystems

The contamination of agroecosystems by microplastics (MPs) has raised great concerns recently. Plastic mulching has contributed a lot in the building of MP pollution in farmlands. This technique has been in use for decades worldwide because of its immense advantages, preferably in drier and colder regions. The physical extraction of plastic mulches at the end of the growing season is very laborious and ineffective, and thus small pieces of mulches are left in the field which later convert into MP particles after aging, weathering, or on exposure to solar radiation. MPs not only influence physical, chemical, or biological properties of soils but also reduce crop productivity which could be a threat to our food security. They also interact with and accumulate other environmental contaminants such as microbial pathogens, heavy metals, and persistent organic pollutants on their surfaces which increase their risk of toxicity in the environment. MPs also transfer from one trophic level to the other in the food chain and ultimately may impact human health. Because of the ineffectiveness of the recovery of plastic film fragments from fields, researchers are now mainly focusing on alternative solutions to conventional plastic mulch films such as the use of biodegradable mulches. In this review, we have discussed the issue of plastic mulch films in agroecosystems and tried to link already existing knowledge to the current limitations in research on this topic from cropland soils and future prospects have been identified and proposed.

Beyond the exposure phase: Microplastic depuration and experimental implications

Currently, most studies focus on the effect of microplastics (MPs) in the exposure phase, but pay limited attention to the depuration phase. Depuration is a promising practice to achieve safe aquaculture production, which is also helpful to understand the long-term impact of MPs. Therefore, investigating the post-exposure scenarios of MPs has great practical significance. In order to provide implications for future research, this work attempted to systematize the current findings and knowledge gaps regarding the depuration of MPs. More specifically, three methods, including direct fitting, one-compartment kinetic model and interval observation, for estimating the retention time of MPs to further determine the minimum depuration time were introduced, in which the one-compartment kinetic model could also be used to calculate the depuration rate constant and biological half-life of MPs. Moreover, the post-exposure effect of MPs generally presented three scenarios: incomplete reversal (legacy effect), return to control level (recovery) and stimulatory response (hormesis-like effect). In addition, the possible tissue translocation of MPs, the influence of food abundance and body shape on MPs egestion, and the potential interaction with environmental factors, have aroused great scientific concerns and need further exploration and clarification.

Microplastics induce neurotoxicity in aquatic animals at environmentally realistic concentrations: A meta-analysis

Microplastics (MPs) draw international attention owing to their widespread distribution in water ecosystems, but whether MPs cause neurotoxic effects in aquatic animals at environmentally realistic concentrations is still controversial. This meta-analysis recompiled 35 studies to determine whether MPs could change the levels of brain (in vivo) neurotransmitters in aquatic animals at environmentally realistic concentrations (≤1 mg/L, median = 0.100 mg/L). Then, a group comparison was conducted to compare the effects of different factors on the effect size and to explore the significant factors affecting the neurotoxicity of MPs. The results demonstrated that MP exposure could considerably decrease the levels of acetylcholinesterase (AchE) in the brain of aquatic animals by 16.2%. However, the effects of MPs on cholinesterase (CHE), acetylcholine (ACh), dopamine (DA) and γ-aminobutyric acid (GABA) were not statistically significant due to the small number of studies and samples. The neurotoxicity of MPs was closely linked with particle size and exposure time but independent of animal species, MP compositions, MP morphology and MP concentrations. Further literatures review indicated that MP-induced neurotoxicity and behavioral changes are related with multiple biological processes, including nerve damage, oxidative stress, intestinal flora disturbance and metabolic disorder. Furthermore, some factors influencing MP neurotoxicity in the real environment (e.g. the aging of MPs, the release of MP additives, and the co-exposure of MPs and pollutants) were discussed. Overall, this study preliminarily explored whether MPs induced changes in neurotoxicity-related indicators in aquatic animals through meta-analysis and provided scientific evidence for evaluating the health risks and neurotoxicity of MPs at the environmental level.

Effect of size continuum from nanoplastics to microplastics on marine mussel Mytilus edulis: Comparison in vitro/in vivo exposure scenarios

For several decades, plastic has been a global threat in terms of pollution. Plastic polymers, when introduce in the aquatic environment, are exposed to fragmentation processes into microplastics (MPs) and nanoplastics (NPs) which could potentially interact with living organisms. The objective of this work was to study the effects of plastic particles representative of those found in the environment, on the marine mussels Mytilus edulis, under two exposure scenarios: in vivo and in vitro. Whole mussels or cultured hemocytes were exposed for 24 h to NPs and MPs generated from macro-sized plastics collected in the field, but also to reference NPs, at concentrations found in the environment: 0.08, 10 μg and 100 μg·L^-1. Results showed that immune response was only activated when mussels were exposed in vivo. However, cytotoxicity (hemocyte mortality) and genotoxicity (DNA damage) parameters were induced after both types of exposure, but in a dose-dependent manner after in vitro hemocyte exposure to all tested plastic conditions. These results indicate that in vitro approaches could be considered as potential predictors of in vivo exposures.

Which factors mainly drive the photoaging of microplastics in freshwater?

Light irradiation is considered as most important process for the aging of microplastics (MPs); however, which factors drive the process is still unknown. This study investigated the role of typical environmental factors including ultraviolet (UV), oxygen, temperature and physical abrasion in the photoaging of polystyrene (PS) in freshwater. Results showed that UV irradiation and abrasion were dominant factors for affecting photoaging of PS based on dynamic analysis in the property of MP itself and leachate. Especially, when both factors worked together on MPs, they caused more destructive effect. Mechanical exploration revealed that photoaging of MPs was mainly controlled by reactive oxygen species (ROS, ¹O₂) generated from the reaction of dissolved oxygen/water molecules with polymer radicals initiated by UV energy. As an attacker on MPs, ROS formation was significantly linked with UV intensity, highlighting the important role of UV. The fragmentation was correlated to abrasion intensity, where a higher abrasion generated stronger physical force to tear MPs into fragments. The low roles of oxygen and temperature were presumably related to multiple effects of ROS formation and UV absorption. The findings firstly clarify the drivers in the photoaging of MPs, and contribute our effort to assess their fate and pollution risk in the environment.

Laboratory simulated aging methods, mechanisms and characteristic changes of microplastics: A review

Microplastics (MPs) aging occurs in all environmental medias and affects the environmental behaviour and toxicity of MPs. Due to the extremely slow process of aging, laboratory simulated aging methods have had to be used to research the properties, behaviour, toxicity and effects of aged MPs. However, multiple laboratory aging methods with different mechanisms have led to divergent viewpoints on the characteristics, behavior and toxicity of aged MPs. Therefore, this paper reviewed the main laboratory MPs aging methods and mechanism, including those that involve UV, advanced oxidation processes (AOPs), sunlight or simulated sunlight, chemical treatment, heat, plasma radiation, etc. As a technology with a low time cost, AOPs have potential and are recommended. Physical, chemical, and coupled aging significantly alter MPs surface topography and functional groups, which affect MPs adsorption, migration and toxicity. However, the effects of aging on environmental behaviour and toxicity are highly uncertain. The carbonyl index (CI) and O/C ratio are generally applied to evaluate the MPs aging degree. This review highlights the need to provide adequate information on coupled simulated aging methods to allow better elucidation of the underlying mechanisms of aging and its effect on MPs environmental behaviour and toxicity.

Release of millions of micro(nano)plastic fragments from photooxidation of disposable plastic boxes

The widespread use of disposable plastic boxes is exacerbating the dangers of microplastics (MPs); however, little is known about the fragmentation behavior of MPs during aging. In this study, the dynamic evolution on the release of micro(nano)plastics and photoaging properties of two disposable plastic boxes (polypropylene (PP) and polystyrene (PS)) were investigated under light irradiation and mechanical abrasion. Results showed that the weight of PP and PS was decreased by 53 % and 100 %, respectively after 60 d of ultraviolet irradiation (UV60). Moreover, a large number of fragmented particles were produced from the combined light irradiation and abrasion, with 0.142 ± 0.006 and 0.141 ± 0.013 million micro(nano)plastics/mL particles from PP and PS boxes, respectively, and the nanometer range (<100 nm) accounted for 70.8 % and 46.8 %. The correlation model of the average size or alteration time versus carbonyl index (CI) was developed, which indicated that the fragmentation behavior was mainly related to the photooxidation, though mechanical abrasion also played a certain enhancing role. Additionally, PS was susceptible to the fragmentation and photooxidation compared to PP possibly since the phenyl ring of PS was more vulnerable to UV attack than the methyl of PP. The findings of this study clarify the dynamic fragmentation process of micro(nano)plastics of disposable plastic boxes and provide useful information to access environmental fate of MPs more holistically.

Field validated biomarker (ValidBIO) based assessment of impacts of various pollutants in water

The sensitivity of fish towards pollutants serves as an excellent tool for the analysis of water pollution. The effluents generated from various anthropogenic activities may contain heavy metals, pesticides, microplastics, and persistent organic pollutants (POPs) and ultimately find its way to aquatic environment. The enzymatic activities of fish collected from water bodies near major cities, oil spillage sites, agricultural land, and intensively industrialized areas have been reported to be significantly impacted in various field studies. These significant alterations in enzymatic activities act as a biomarker for monitoring purposes. The use of biomarkers not only helps in the identification of known and unknown pollutants and their detrimental health impacts, but also identifies the interaction between pollutants and organisms. The conventional method majorly used is physicochemical analysis, which is recognized as the backbone of the system for monitoring water quality. In physicochemical monitoring, major problems exist in assessing or predicting biological effects from chemical or physical data. Xenobiotic-induced enzymatic changes in fish may serve as an intuitive and efficient biomarker for determining contaminants in water bodies. Therefore, field validated biomarker (ValidBIO) approach needs to be integrated in water quality monitoring program for environmental health risk assessment of aquatic life impacted due to various point and non-point sources of water pollution.

Influence of ultraviolet-aging and adsorbed pollutants on toxicological effects of polyvinyl chloride microplastics to zebrafish

Microplastics (MPs) undergo various aging processes and interact with diverse pollutants in the environment. In the present study, we investigated the influence of ultraviolet (UV) aging on the adsorption of organic pollutants by polyvinyl chloride microplastics (mPVC) and explored toxicity variations among pristine, aged, and pollutant-loaded mPVCs to zebrafish. Irradiation of UV for 30 d significantly changed the physiochemical properties of mPVC, leading to more oxygen-containing groups and free radicals (¹O₂, ·O₂^-, and ·OH) on mPVC surfaces. The aging process reduced the adsorption of mPVC against a hydrophobic compound chlorpyrifos (CPF) but enhanced the adsorption against a moderately hydrophilic compound erythromycin (ERY). Ingestion of CPF- and ERY-loaded mPVCs resulted in bioaccumulation of the two compounds in zebrafish, suggesting a carrier effect of mPVCs. In toxicity tests, the aged mPVC caused severer gut damages, stronger oxidative stresses, and greater interference with the gut microbiota in zebrafish than the pristine mPVC. The CPF and ERY-loaded mPVCs produced lower oxidative stresses in zebrafish than mPVCs alone, due to fewer radicals on mPVC surfaces after the adsorption of organic contaminants. Notably, the CPF and ERY-loaded mPVCs presented greater effects on fish swimming behaviors and gut microbial compositions, which was associated with the released CPF and ERY from mPVCs within the zebrafish. Overall, the present study demonstrated significant influences of UV-aging and the adsorbed pollutants on the toxicological effects of MPs and highlighted the necessity to perform toxicity studies of MPs using more environmentally relevant MPs.

Effects of the Antidepressant Amitriptyline on Juvenile Brown Trout and Their Modulation by Microplastics

Pharmaceuticals such as antidepressants are designed to be bioactive at low concentrations. According to their mode of action, they can also influence non-target organisms due to the phylogenetic conservation of molecular targets. In addition to the pollution by environmental chemicals, the topic of microplastics (MP) in the aquatic environment came into the focus of scientific and public interest. The aim of the present study was to investigate the influence of the antidepressant amitriptyline in the presence and absence of irregularly shaped polystyrene MP as well as the effects of MP alone on juvenile brown trout (Salmo trutta f. fario). Fish were exposed to different concentrations of amitriptyline (nominal concentrations between 1 and 1000 µg/L) and two concentrations of MP (104 and 105 particles/L; <50 µm) for three weeks. Tissue cortisol concentration, oxidative stress, and the activity of two carboxylesterases and of acetylcholinesterase were assessed. Furthermore, the swimming behavior was analyzed in situations with different stress levels. Exposure to amitriptyline altered the behavior and increased the activity of acetylcholinesterase. Moreover, nominal amitriptyline concentrations above 300 µg/L caused severe acute adverse effects in fish. MP alone did not affect any of the investigated endpoints. Co-exposure caused largely similar effects such as the exposure to solely amitriptyline. However, the effect of amitriptyline on the swimming behavior during the experiment was alleviated by the higher MP concentration.

Aged microplastics change the toxicological mechanism of roxithromycin on Carassius auratus: Size-dependent interaction and potential long-term effects

Size effects of microplastics have received extensive attention for their influence on other pollutants and harm to organisms. In this study, we investigated the uptake, elimination, tissue distribution and potential toxicity mechanism of roxithromycin (ROX) in the presence of 0.5, 5 and 50 μm of aged microplastics (AMPs) in Carassius auratus. The results showed that AMPs promoted the ROX bioaccumulation of various tissues in a size-dependent manner. AMPs and ROX significantly induced superoxide dismutase and catalase activities of liver and gut, and inhibited acetylcholinesterase activities of brain. The coexistence of smaller AMPs exacerbated pathological abnormalities in liver, gill and brain induced by ROX, while larger AMPs caused more intestinal damage. Moreover, high-throughput 16S rRNA gene sequencing indicated that the abundance of Proteobacteria in 0.5 μm AMPs and ROX joint treatments and Firmicutes and Bacteroidota in 50 μm AMPs and ROX joint treatments were significantly raised (p < 0.05). Metabolomics revealed that AMPs and ROX had a size-dependent long-term effect on gut microbial metabolites, which was mainly related to galactose metabolism, amino acid metabolism and primary bile acid biosynthesis pathways after a 7-day elimination, respectively. These results provide important insights into the relationship between the size effect of AMPs and interaction mechanism of AMPs and coexisting pollutants on aquatic organisms.

Single and combined effects of microplastics and cadmium on juvenile grass carp (Ctenopharyngodon idellus)

Microplastics (MPs) have received extensive attention as a new type of environmental pollutants with potential ecological risks. However, there are still few studies on the physiological stress response of aquatic organisms under the interaction of MPs and heavy metals. In this study, grass carp (Ctenopharyngodon idellus) were chosen as experimental fish and were exposed to 5 μm polystyrene microplastics (PS - MPs, 700 μg/L) and cadmium (Cd, 100 μg/L) individually or in combination. The results indicated that the presence of Cd didn't affect the accumulation of MPs in the intestines of grass carp. On the contrary, the concentration of Cd in the intestines of grass carp was higher in the MPs - Cd combined exposure group than in the Cd alone exposure group. Histological analysis revealed multiple abnormalities in the intestines after acute exposure, and the damage in the MPs - Cd combined exposure group was particularly severe. After 24 h of exposure, the expression of pro-inflammatory cytokines was significantly up-regulated in all exposed groups. However, after 48 h of exposure, the expression of inflammatory cytokines was significantly down-regulated, which may be related to intestinal damage. Our results deepen the significance of toxicological studies of MPs exposure, highlight their interaction with heavy metal toxicants, and provide important data for assessing the risk of MPs and heavy metals to grass carp.

Ecotoxic effects of microplastics and contaminated microplastics - Emerging evidence and perspective

The high prevalence and persistence of microplastics (MPs) in pristine habitats along with their accumulation across environmental compartments globally, has become a matter of grave concern. The resilience conferred to MPs using the material engineering approaches for outperforming other materials has become key to the challenge that they now represent. The characteristics that make MPs hazardous are their micro to nano scale dimensions, surface varied wettability and often hydrophobicity, leading to non-biodegradability. In addition, MPs exhibit a strong tendency to bind to other contaminants along with the ability to sustain extreme chemical conditions thus increasing their residence time in the environment. Adsorption of these co-contaminants leads to modification in toxicity varying from additive, synergistic, and sometimes antagonistic, having consequences on flora, fauna, and ultimately the end of the food chain, human health. The resulting environmental fate and associated risks of MPs, therefore greatly depend upon their complex interactions with the co-contaminants and the nature of the environment in which they reside. Net outcomes of such complex interactions vary with core characteristics of MPs, the properties of co-contaminants and the abiotic factors, and are required to be better understood to minimize the inherent risks. Toxicity assays addressing these concerns should be ecologically relevant, assessing the impacts at different levels of biological organization to develop an environmental perspective. This review analyzed and evaluated 171 studies to present research status on MP toxicity. This analysis supported the identification and development of research gaps and recommended priority areas of research, accounting for disproportionate risks faced by different countries. An ecological perspective is also developed on the environmental toxicity of contaminated MPs in the light of multi-variant stressors and directions are provided to conduct an ecologically relevant risk assessment. The presented analyses will also serve as a foundation for developing environmentally appropriate remediation methods and evaluation frameworks.

The legacy effect of microplastics on aquatic animals in the depuration phase: Kinetic characteristics and recovery potential

The prevalence of microplastics (MPs) in global aquatic environments has received considerable attention. Currently, concerns have been raised regarding reports that the adverse effect of MPs on aquatic animals in the exposure phase may not be (completely) reversed in the depuration phase. In order to provide insights into the legacy effect of MPs from the depuration phase, this study evaluated the kinetic characteristics and recovery potential of aquatic animals after the exposure to MPs. More specifically, a total of 68 depuration kinetic curves were highly fitted to estimate the retention time of MPs. It was shown that the retention time ranged from 1.26 to 3.01 days, corresponding to the egestion of 90 % to 99 % of ingested MPs. The retention time decreased with the increased retention rate. Furthermore, variables potentially affecting the retention time were ranked by the decision tree-based eXtreme Gradient Boosting (XGBoost) algorithm, suggesting that the particle size and tested species were of great importance for explaining the difference in retention time of MPs. Moreover, a biomarker profile was recompiled to determine the toxic changes. Results indicated that the MPs-induced toxicity significantly reduced in the depuration phase, evidenced by the recovery of energy reserves and metabolism, hepatotoxicity, immunotoxicity, hematological parameters, neurotoxicity and oxidative stress. However, the continuous detoxification and remarkable genotoxicity implied that the toxicity was not completely alleviated. In addition, the current knowledge gaps are also highlighted, with recommendations proposed for future research.

A review on the remediation of microplastics using constructed wetlands: Bibliometric, co-occurrence, current trends, and future directions

Massive prevalence of microplastics (MPs) in the environment has become one of the world's most serious environmental concerns. Human dependence on plastics has created a constant flow of MPs from different sources into natural environment, which has raised public concern regarding consequences of MPs coming into contact with the natural environment. Deploying constructed wetlands (CWs) to reduce MPs pollution is considered a promising method, however there are still barriers for breakthroughs in this technology, particularly knowledge gaps in the mechanisms affect removal process. Recognising this, we provide a comprehensive summary of current advances and theories regarding the mechanisms of occurrence in this research area. In this work, the bibliometric methods were first used to identify annual publication trends and topical topics of research interest. The selected documents were then statistically analyzed using VOSviewer and the 'bibliometrix' package in R to derive the annual productivity of countries or organizations, the most relevant affiliations, the most relevant authors, the most relevant sources, textual analysis, co-occurrence analysis, and cluster analysis of keywords. Finally, detailed information concerning the removal of MPs by CWs was summarised, covering the most common operational and design parameters (i.e., structure types, wetland plants, substrate materials, and microbial communities), to reveal how these parameters can be adjusted for more efficient MPs removal rate. Challenges and future directions were additionally proposed. It is hoped that the review will help identify current research trends, provide insight into the mechanisms of the removal process, and contribute further to the development of this important area.

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.