The generation of environmentally persistent free radicals on photoaged microbeads from cosmetics enhances the toxicity via oxidative stress

Photoaged nanoplastics with multienzyme-like activities significantly shape the horizontal transfer of antibiotic resistance genes

Nanoplastics (NPs), identified as emerging pollutants, pose a great risk to environment and global public health, exerting profound influences on the prevalence and dissemination of antibiotic resistance genes (ARGs). Despite evidence suggesting that nano-sized plastic particles can facilitate the horizontal gene transfer (HGT) of ARGs, it is imperative to explore strategies for inhibiting the transfer of ARGs. Currently, limited information exists regarding the characteristics of environmentally aged NPs and their impact on ARGs propagation. Herein, we investigated the impact of photo-aged NPs on the transfer of ARG-carrying plasmids into Escherichia coli (E. coli) cells. Following simulated sunlight irradiation, photo-aged nano-sized polystyrene plastics (PS NPs) exhibited multiple enzyme-like activities, including peroxidase (POD) and oxidase (OXD), leading to a burst of reactive oxygen species (ROS). At relatively low concentrations (0.1, 1 μg/mL), both pristine and aged PS NPs facilitated the transfer of pUC19 and pHSG396 plasmids within E. coli due to moderate ROS production and enhanced cell membrane permeability. Intriguingly, at relatively high concentrations (5, 10 μg/mL), aged PS NPs significantly suppressed plasmids transformation. The non-unidirectional impact of aged PS NPs involved the overproduction of ROS (•OH and •O2-) via nanozyme activity, directly degrading ARGs and damaging plasmid structure. Additionally, oxidative damage to bacteria resulted from the presence of much toxic free radicals, causing physical damage to cell membranes, reduction of the SOS response and restriction of adenosine-triphosphate (ATP) supply, ultimately leading to inactivation of recipient cells. This study unveils the intrinsic multienzyme-like activity of environmentally aged NPs, highlighting their potential to impede the transfer and dissemination of ARGs.

Environmentally persistent free radicals on photoaging microplastics shortens longevity via inducing oxidative stress in Caenorhabditis elegans

Microplastics (MPs) are ubiquitous environmental contaminants that exert multiple toxicological effects. Current studies have mainly focused on modeled or unaged MPs, which lack environmental relevance. The generation and toxicity of environmentally persistent free radicals (EPFRs) on photoaging polystyrene (PS) have not been well studied, and the role of EPFRs on the toxic effects of photoaged PS is easily ignored. Photoaging primarily produces EPFRs, followed by an increase in reactive oxygen species (ROS) content and oxidative potential, which alter the physicochemical properties of photoaged PS. The mean lifespan and lipofuscin content were significantly altered after acute exposure to photoaged PS for 45 d (PS-45) and 60 d (PS-60) in Caenorhabditis elegans. Intestinal ROS and gst-4::GFP expression were enhanced, concomitant with the upregulation of associated genes. Treatment with N-acetyl-l-cysteine by radical quenching test significantly decreased EPFRs levels on the aged PS and inhibited the acceleration of the aging and oxidative stress response in nematodes. Pearson's correlation analysis also indicated that the EPFRs levels were significantly associated with these factors. Thus, the EPFRs generated on photoaged PS contribute to the acceleration of aging by oxidative stress. This study provides new insights into the potential toxicity and highlights the need to consider the role of EPFRs in the toxicity assessment of photoaged PS.

Adverse effects and potential mechanisms of polystyrene microplastics (PS-MPs) on the blood-testis barrier

Microplastics (MPs) are defined as plastic particles or fragments with a diameter of less than 5 mm. These particles have been identified as causing male reproductive toxicity, although the precise mechanism behind this association is yet to be fully understood. Recent research has found that exposure to polystyrene microplastics (PS-MPs) can disrupt spermatogenesis by impacting the integrity of the blood-testis barrier (BTB), a formidable barrier within mammalian blood tissues. The BTB safeguards germ cells from harmful substances and infiltration by immune cells. However, the disruption of the BTB leads to the entry of environmental pollutants and immune cells into the seminiferous tubules, resulting in adverse reproductive effects. Additionally, PS-MPs induce reproductive damage by generating oxidative stress, inflammation, autophagy, and alterations in the composition of intestinal flora. Despite these findings, the precise mechanism by which PS-MPs disrupt the BTB remains inconclusive, necessitating further investigation into the underlying processes. This review aims to enhance our understanding of the pernicious effects of PS-MP exposure on the BTB and explore potential mechanisms to offer novel perspectives on BTB damage caused by PS-MPs.

Generation of environmentally persistent free radicals on photoaged tire wear particles and their neurotoxic effects on neurotransmission in Caenorhabditis elegans

Tire wear particles (TWP) are a prevalent form of microplastics (MPs) extensively distributed in the environment, raising concerns about their environmental behaviors and risks. However, knowledge regarding the properties and toxicity of these particles at environmentally relevant concentrations, specifically regarding the role of environmentally persistent free radicals (EPFRs) generated during TWP photoaging, remains limited. In this study, the evolution of EPFRs on TWP under different photoaging times and their adverse effects on Caenorhabditis elegans were systematically investigated. The photoaging process primarily resulted in the formation of EPFRs and reactive oxygen species (O2•-, ⋅OH, and 1O2), altering the physicochemical properties of TWP. The exposure of nematodes to 100 μg/L of TWP-50 (TWP with a photoaging time of 50 d) led to a significant decrease in locomotory behaviors (e.g., head thrashes, body bends, and wavelength) and neurotransmitter contents (e.g., dopamine, glutamate, and serotonin). Similarly, the expression of neurotransmission-related genes was reduced in nematodes exposed to TWP-50. Furthermore, the addition of free-radical inhibitors significantly suppressed TWP-induced neurotoxicity. Notably, correlation analysis revealed a significantly negative correlation between EPFRs levels and the locomotory behaviors and neurotransmitter contents of nematodes. Thus, it was concluded that EPFRs on photoaged TWP induce neurotoxicity by affecting neurotransmission. These findings elucidate the toxicity effects and mechanisms of EPFRs, emphasizing the importance of considering their contributions when evaluating the environmental risks associated with TWP.

Environmentally persistent free radicals on photoaged microplastics from disposable plastic cups induce the oxidative stress-associated toxicity

Microplastics (MPs) are ubiquitous environmental contaminants that exerting multiple toxicological effects. Most studies have focused primarily on the models of unaged MPs and lack environmental relevance. The generation and toxicity of environmentally persistent free radicals (EPFRs) on photoaging MPs from disposable plastic cups (DPC-MPs) have not been well studied. Here, the formation of EPFRs on photoaged DPC-MPs and their toxic effects in nematodes were investigated. UV irradiation generated EPFRs, which influenced the characterization of DPC-MPs. Exposure to photoaged DPC-MPs at environmentally relevant concentrations （100-1000 μg/L） reduced the locomotion behavior, body length, and brood size. The Reactive oxygen species (ROS) production, lipofuscin accumulation, malondialdehyde (MDA), and 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels were increased along with the downregulation of the expression levels of associated genes, such as clk-1, clt-1, and gst-4，in nematodes. Moreover, the toxicity and oxidative stress response of nematodes were significantly inhibited due to N-acetyl-l-cysteine (NAC). Pearson's correlation analysis revealed that the oxidative stress was significantly associated with adverse physiological effects. Therefore, EPFRs on photoaged DPC-MPs cause toxicity in nematodes, and oxidative stress is important for regulating toxicity. This study offers novel insights into the potential risks of DPC-MPs under UV irradiation, highlighting the need to consider the role of EPFRs in toxicity assessments of DPC-MPs.

Environmentally persistent free radicals on photoaged nanopolystyrene induce neurotoxicity by affecting dopamine, glutamate, serotonin and GABA in Caenorhabditis elegans

Microplastics are widely detected in the environment and induce toxic effects in various organisms. However, the properties and toxicity associated with environmentally persistent free radicals (EPFRs) in photoaged nanopolystyrene (NPS) remain largely unknown. We investigated the generation of EPFRs on photoaged NPS and their neurotoxicity and underlying mechanism in Caenorhabditis elegans. The results suggested that photoaging induces the generation of EPFRs and reactive oxygen species (O2•-, •OH, and 1O2), which altered the physicochemical properties (morphology, crystallinity, and functional groups) of NPS. Acute exposure to 1 μg/L of NPS-60 (NPS with light irradiation time of 60 d) significantly decreased locomotion behaviors and neurotransmitter contents (e.g., glutamate, serotonin, dopamine, and γ-aminobutyric acid). Treatment with N-acetyl-L-cysteine (NAC) by radical quenching test significantly reduced EPFRs levels on the aged NPS, and the toxicity of NAC-quenching NPS was decreased in nematodes compared to those in photoaged NPS. EPFRs also caused dysfunction of neurotransmission-related gene expression in C. elegans. Thus, EPFRs generated on photoaged NPS contributed to neurotoxicity by affecting dopamine, glutamate, serotonin, and γ-aminobutyric acid neurotransmission. The study highlights the potential risks of photoaged NPS and the contributions of EPFRs to toxicity.

Photoaged Polystyrene Nanoplastics Result in Transgenerational Reproductive Toxicity Associated with the Methylation of Histone H3K4 and H3K9 in Caenorhabditis elegans

Polystyrene nanoplastics (PS-NPs) are emerging environmental contaminants that are ubiquitously detected in various environments and have toxic effects on various organisms. Nevertheless, the transgenerational reproductive toxicity and underlying mechanisms of PS-NPs remain largely unknown, especially for photoaged PS-NPs under ultraviolet irradiation. In this study, only the parental generation (P0) was exposed to virgin and aged PS-NPs at environmentally relevant concentrations (0.1-100 μg/L), and subsequent generations (F1-F4) were cultured under normal conditions. Ultraviolet irradiation induced the generation of environmentally persistent free radicals and reactive oxygen species, which altered the physical and chemical characteristics of PS-NPs. The results of toxicity testing suggested that exposure to aged PS-NPs caused a more severe decrease in brood size, egg ejection rate, number of fertilized eggs, and hatchability than did the virgin PS-NPs in the P0, F1, and F2 generations. Additionally, a single maternal exposure to aged PS-NPs resulted in transgenerational effects on fertility in the F1 and F2 generations. Increased levels of H3K4 and H3K9 methylation were observed in the F1 and F2 generations, which were concomitant with the transgenerational downregulation of the expression of associated genes, such as spr-5, set-17, and met-2. On the basis of correlation analyses, the levels of histone methylation and the expression of these genes were significantly correlated to transgenerational reproductive effects. Further research showed that transgenerational effects on fertility were not observed in spr-5(by134), met-2(n4256), and set-17(n5017) mutants. Overall, maternal exposure to aged PS-NPs induced transgenerational reproductive effects via H3K4 and H3K9 methylation, and the spr-5, met-2, and set-17 genes were involved in the regulation of transgenerational toxicity. This study provides new insights into the potential risks of photoaging PS-NPs in the environment.

Maternal exposure to sunlight-irradiated graphene oxide induces neurodegeneration-like symptoms in zebrafish offspring through intergenerational translocation and genomic DNA methylation alterations

The physiochemical properties of graphene oxide may be affected by sunlight irradiation. However, the underlying mechanisms that alter the properties and subsequent intergenerational effects are not sufficiently investigate. Epigenetics is an early sensitive marker for the intergenerational effects of nanomaterial exposure due to the epigenetic memory. In this study, we investigate changes in the physicochemical properties and the intergenerational effects of maternal exposure to simulated sunlight-irradiated polyethyleneimine-functionalized graphene oxide (SL-PEI-GO). Results show that the physicochemical properties of polyethyleneimine-functionalized graphene oxide (PEI-GO) can be altered significantly by the oxidation of carbon atoms with unpaired electrons present in the defects and on the edges of PEI-GO by sunlight. First, the positive charges, sharp edges, defects and disordered structures of SL-PEI-GO make it translocate from maternal zebrafish to offspring, thus catalyzing the production of reactive oxygen species and damaging mitochondria directly. In addition, changes in DNA methylation reduce the expression of protocadherin1a, protocadherin19 and cadherin4, thus destroying cell membrane integrity, cell adhesion and Ca2+ binding. The alteration of DNA methylation induced by maternal exposure activates the Ca2+-CaMKK-brsk2a pathway, which catalyzes the phosphorylation of Tau and eventually results in the appearance of neurodegeneration-like symptoms, including the loss of neurons and neurobehavioral disorders. This study demonstrates that maternal exposure to SL-PEI-GO induces clear neurodegeneration-like symptoms in offspring through both the intergenerational translocation of nanomaterials and differential DNA methylation. These findings may provide new insights into the health risks of nanomaterials altered by nature conditions.

Scientific and regulatory challenges of environmentally persistent free radicals: From formation theory to risk prevention strategies

EPFRs (Environmentally Persistent Free Radicals) are a class of pollutants that have been identified as potential environmental contaminants due to their persistence and ability to generate reactive oxygen species (ROS) that can cause oxidative stress in living organisms. However, no study has comprehensively summarized the production conditions, influencing factors and toxic mechanisms of EPFRs, impeding exposure toxicity assessments and risk prevention strategies. To bridge the gap between theoretical research and practical application, a thorough literature review to summarize the formation, environmental effects, and biotoxicity of EPFRs are conducted. A total of 470 relevant papers were screened in Web of Science Core collection databases. The transfer of electrons between interfaces and the cleavage of covalent bonds of persistent organic pollutants is crucial to the generation of EPFRs, which is induced by external sources of energy, including thermal energy, light energy, transition metal ions, and others. In the thermal system, the stable covalent bond of organic matter can be destroyed by heat energy at low temperature to form EPFRs, while the formed EPFRs can be destroyed at high temperature. Light can also accelerate the production of free radicals and promote the degradation of organic matter. The persistence and stability of EPFRs are synergistically influenced by individual environmental factors such as environmental humidity, oxygen content, organic matter content, and environmental pH. Studying the formation mechanism of EPFRs and their biotoxicity is essential for fully understanding the hazards posed by these emerging environmental contaminants.