Microplastic (1 and 5 μm) exposure disturbs lifespan and intestine function in the nematode Caenorhabditis elegans

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.

Short-term microplastic effects on marine meiofauna abundance, diversity and community composition

Background

Due to the copious disposal of plastics, marine ecosystems receive a large part of this waste. Microplastics (MPs) are solid particles smaller than 5 millimeters in size. Among the plastic polymers, polystyrene (PS) is one of the most commonly used and discarded. Due to its density being greater than that of water, it accumulates in marine sediments, potentially affecting benthic communities. This study investigated the ingestion of MP and their effect on the meiofauna community of a sandy beach. Meiofauna are an important trophic link between the basal and higher trophic levels of sedimentary food webs and may therefore be substantially involved in trophic transfer of MP and their associated compounds.

Methods

We incubated microcosms without addition of MP (controls) and treatments contaminated with PS MP (1-µm) in marine sediments at three nominal concentrations (103, 105, 107particles/mL), for nine days, and sampled for meiofauna with collections every three days. At each sampling time, meiofauna were collected, quantified and identified to higher-taxon level, and ingestion of MP was quantified under an epifluorescence microscope.

Results

Except for Tardigrada, all meiofauna taxa (Nematoda, turbellarians, Copepoda, Nauplii, Acari and Gastrotricha) ingested MP. Absorption was strongly dose dependent, being highest at 107 particles/mL, very low at 105 particles/mL and non-demonstrable at 103 particles/mL. Nematodes accumulated MP mainly in the intestine; MP abundance in the intestine increased with increasing incubation time. The total meiofauna density and species richness were significantly lower at the lowest MP concentration, while at the highest concentration these parameters were very similar to the control. In contrast, Shannon-Wiener diversity and evenness were greater in treatments with low MP concentration. However, these results should be interpreted with caution because of the low meiofauna abundances at the lower two MP concentrations.

Conclusion

At the highest MP concentration, abundance, taxonomic diversity and community structure of a beach meiofauna community were not significantly affected, suggesting that MP effects on meiofauna are at most subtle. However, lower MP concentrations did cause substantial declines in abundance and diversity, in line with previous studies at the population and community level. While we can only speculate on the underlying mechanism(s) of this counterintuitive response, results suggest that further research is needed to better understand MP effects on marine benthic communities.

Source-specific probabilistic risk assessment of microplastics in soils applying quality criteria and data alignment methods

The risk characterization of microplastics (MP) in soil is challenging due to the non-alignment of existing exposure and effect data. Therefore, we applied data alignment methods to assess the risks of MP in soils subject to different sources of MP pollution. Our findings reveal variations in MP characteristics among sources, emphasizing the need for source-specific alignments. To assess the reliability of the data, we applied Quality Assurance/Quality Control (QA/QC) screening tools. Risk assessment was carried out probabilistically, considering uncertainties in data alignments and effect thresholds. The Hazardous Concentrations for 5% (HC5) of the species were significantly higher compared to earlier studies and ranged between 4.0 × 107 and 2.3 × 108 particles (1-5000 µm)/kg of dry soil for different MP sources and ecologically relevant metrics. The highest risk was calculated for soils with MP entering via diffuse and unspecified local sources, i.e., "background pollution". However, the source with the highest proportion of high-risk values was sewage, followed by background pollution and mulching. Notably, locations exceeding the risk threshold obtained low scores in the QA/QC assessment. No risks were observed for soils with compost. To improve future risk assessments, we advise to primarily test environmentally relevant MP mixtures and adhere to strict quality criteria.

Polyethylene microplastics induced gut microbiota dysbiosis leading to liver injury via the TLR2/NF-κB/NLRP3 pathway in mice

Microplastics (MPs) are ubiquitous environmental contaminants that have negative impacts on health and safety. The gut microbiota plays multiple roles as a newly discovered virtual metabolic organ. The objective of this study was to investigate the potential of MPs to cause liver injury by disrupting the balance of gut microbiota. The results indicated that exposure to MPs resulted in liver damage and disrupted the homeostasis of gut microbiota. MPs significantly reduced the liver organ coefficient, leading to liver cell injury and impaired function. Additionally, there was an increase in the expression of fibril-related proteins, which positively correlated with MPs concentration. Furthermore, MPs increased the relative abundances of Desulfovibrio, Clostridia, Enterorhabdus, Bacteroides, and Gemella while decreasing the abundance of Dubosoella. Different concentrations of MPs exhibited varying effects on specific bacterial groups, however, both concentrations resulted in an increase in pathogenic bacteria and a decrease in beneficial bacteria, as well as alterations in microbial structure. Moreover, MPs induced oxidative stress, inflammation, apoptosis and necrosis in liver cells. The study found that MPs disrupted gut microbiota homeostasis and activated TLR2/NF-κB/NLRP3 pathway in the liver, providing a new insight into the mechanism underlying MPs-induced liver injury. These findings serve as a warning regarding environmental pollution caused by MPs.

Comparison of reproductive toxicity between pristine and aged polylactic acid microplastics in Caenorhabditis elegans

Caenorhabditis elegans was employed as model to compare reproductive toxicity between pristine and aged polylactic acid microplastics (PLA-MPs). Aged PLA-MPs induced by UV irradiation showed degradation reflected by decrease in size and alteration in morphological surface. Aged PLA-MPs also exhibited some certain changes of chemical properties compared to pristine PLA-MP. Compared with pristine PLA-MPs, more severe toxicity on reproductive capacity and gonad development was detected in 1-100 μg/L aged PLA-MPs. Meanwhile, aged PLA-MPs caused more severe enhancement in germline apoptosis and alterations in expressions of ced-9, ced-4, ced-3, and egl-1 governing cell apoptosis. In addition, aged PLA-MPs resulted in more severe increase in expression of DNA damage related genes (cep-1, mrt-2, hus-1, and clk-2) compared to pristine PLA-MPs, and the alterations in expression of ced-9, ced-4, ced-3, and egl-1 in pristine and aged PLA-MPs could be reversed by RNAi of cep-1, mrt-2, hus-1, and clk-2. Besides this, enhanced germline apoptosis in pristine and aged PLA-MPs exposed animals was also suppressed by RNAi of cep-1, mrt-2, hus-1, and clk-2. Therefore, our results suggested the more severe exposure risk of aged PLA-MPs than pristine PLA-MPs in causing reproductive toxicity, which was associated with the changed physicochemical properties and DNA damage induced germline apoptosis.

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.

Polystyrene Nanoplastics Activate Autophagy and Suppress Trophoblast Cell Migration/Invasion and Migrasome Formation to Induce Miscarriage

Nanoplastics (NPs), as emerging pollutants, have attracted global attention. Nevertheless, the adverse effects of NPs on female reproductive health, especially unexplained miscarriage, are poorly understood. Defects of trophoblast cell migration and invasion are associated with miscarriage. Migrasomes were identified as cellular organelles with largely unidentified functions. Whether NPs might affect migration, invasion, and migrasome formation and induce miscarriage has been completely unexplored. In this study, we selected polystyrene nanoplastics (PS-NPs, 50 nm) as a model of plastic particles and treated human trophoblast cells and pregnant mice with PS-NPs at doses near the actual environmental exposure doses of plastic particles in humans. We found that exposure to PS-NPs induced a pregnant mouse miscarriage. PS-NPs suppressed ROCK1-mediated migration/invasion and migrasome formation. SOX2 was identified as the transcription factor of ROCK1. PS-NPs activated autophagy and promoted the autophagy degradation of SOX2, thus suppressing SOX2-mediated ROCK1 transcription. Supplementing with murine SOX2 or ROCK1 could efficiently rescue migration/invasion and migrasome formation and alleviate miscarriage. Analysis of the protein levels of SOX2, ROCK1, TSPAN4, NDST1, P62, and LC-3BII/I in PS-NP-exposed trophoblast cells, villous tissues of unexplained miscarriage patients, and placental tissues of PS-NP-exposed mice gave consistent results. Collectively, this study revealed the reproductive toxicity of nanoplastics and their potential regulatory mechanism, indicating that NP exposure is a risk factor for female reproductive health.

Occurrence Characteristics and Ecotoxic Effects of Microplastics in Environmental Media: a Mini Review

The issue of environmental pollution caused by the widespread presence of microplastics (MPs) in environmental media has garnered significant attention. However, research on MPs pollution has mainly focused on aquatic ecosystems in recent years. The sources and pollution characteristics of MPs in the environment, especially in solid waste, have not been well-described. Additionally, there are few reports on the ecotoxicity of MPs, which highlights the need to fill this gap. This review first summarizes the occurrence characteristics of MPs in water, soil, and marine environments, and then provides an overview of their toxic effects on organisms and the relevant mechanisms. This paper also provides an outlook on the hotspots of research on pollution characterization and ecotoxicity of MPs. Finally, this review aims to provide insights for future ecotoxicity control of MPs. Overall, this paper expands our understanding of the pollution characteristics and ecological toxicity of MPs in current environmental media, providing forward-looking guidance for future research.

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

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

Seawater Accelerated the Aging of Polystyrene and Enhanced Its Toxic Effects on Caenorhabditis elegans

Microplastics (MPs) are emerging pollutants and pose a significant threat to marine ecosystems. Although previous studies have documented the mechanisms and toxic effects of aging MPs in various environments, the impact of the marine environment on MPs remains unclear. In the present study, the aging process of polystyrene (PS) in seawater was simulated and the changes in its physicochemical properties were investigated. Our results showed that the surface of the PS eroded in the seawater, which was accompanied by the release of aged MPs with a smaller size. In situ optical photothermal infrared microspectroscopy revealed that the mechanism of PS aging was related to the opening of the carbonyl group and breaking of the bond between carbon and benzene removal. To verify the toxic effects of aged PS, Caenorhabditis elegans was exposed to PS. Aged PS resulted in a greater reduction in locomotion, vitality, and reproduction than virgin PS. Mechanistically, aged PS led to oxidative stress, high glutathione s-transferase activity, and high total glutathione in worms. Together, our findings provided novel information regarding the accelerated aging of PS in seawater and the increased toxicity of aged PS, which could improve our understanding of MPs' ecotoxicity in the marine environment.

Polystyrene microplastics biodegradation by gut bacterial Enterobacter hormaechei from mealworms under anaerobic conditions: Anaerobic oxidation and depolymerization

Synthetic plastic is used throughout daily life and industry, threatening organisms with microplastic pollution. Polystyrene is a major plastic polymer and also widely found sources of plastic wastes and microplastics. Here, we report that Enterobacter hormaechei LG3 (CP118279.1), a facultative anaerobic bacterial strain isolated from the gut of Tenebrio molitor larvae (mealworms) can oxidize and depolymerize polystyrene under anaerobic conditions. LG3 performed biodegradation while forming a biofilm on the plastic surface. PS biodegradation was characterized by analyses of surface oxidation, change in morphology and molecular weights, and production of biodegraded derivative. The biodegradation performance by LG3 was compared with PS biodegradation by Bacillus amyloliquefaciens SCGB1 under both anaerobic and aerobic conditions. In addition, through nanopore sequencing technology, we identified degradative enzymes, including thiol peroxidase (tpx), alkyl hydroperoxide reductase C (ahpC) and bacterioferritin comigratory protein (bcp). Along with the upregulation of degradative enzymes for biodegradation, changes in lipid A and biofilm-associated proteins were also observed after the cells were incubated with polystyrene microplastics. Our results provide evidence for anaerobic biodegradation by polystyrene-degrading bacteria and show alterations in gene expression patterns after polystyrene microplastics treatment in the opportunistic pathogen Enterobacter hormaechei.

The concentration-dependent physiological damage, oxidative stress, and DNA lesions in Caenorhabditis elegans by subacute exposure to landfill leachate

The leakage of landfill leachate (LL) into environmental media would be happened even in the sanitary/controlled landfill, due to the deterioration of geomembrane and the blockage of drainage system after long-term operation. Considering the complex composition and high concentration of pollutants in LL, its toxicity assessment should be conducted as a whole liquid contaminant. Therefore, the impacts of LL on Caenorhabditis elegans (C. elegans) were investigated under the condition of different exposure time and exposure volume fraction (EVF). The stimulating effects on locomotion behavior and growth of C. elegans were observed after acute (24 h) exposure to LL, which were increased firstly and then decreased with the increase of EVF. Meanwhile, the intestinal barrier was not affected by LL, and levels of reactive oxygen species (ROS) and cell apoptosis significantly decreased. However, stimulation and inhibition effects on locomotion behavior and growth of C. elegans were observed when subacute (72 h) exposure to 0.25%-0.5% and 1%-4% of LL, respectively. The intestinal injury index and levels of ROS and cell apoptosis significantly increased when EVF were 2% and 4%. Although the acute exposure of LL had resulted in obviously biological adaptability and antioxidant defense in C. elegans, the protective mechanisms failed to be induced as the exposure time increased (subacute exposure). The toxic effects were confirmed by the down-regulation of genes associated with antioxidant defense and neurobehavior, accompanied by the up-regulation of intestinal injury and cell apoptosis related genes. Moreover, the disturbance of metabolic pathways that associated with locomotion behaviors, growth, and antioxidant defense provided good supplementary evidence for the confirmation of oxidative stress in C. elegans. The research results verified the potential of C. elegans as model organism to determine the complex toxic effects of LL.

Microbial colonization of microplastics in wastewater accelerates the aging process associated with oxidative stress and the insulin/IGF1 signaling pathway

Although polystyrene (PS)-induced toxicity in organisms has been documented, adverse effects on lifespan and molecular mechanisms underlying microbial colonization of PS remain elusive. Herein, physicochemical properties of biofilm-developed PS (B-PS) incubated in wastewater were altered compared with virgin PS (V-PS). Bacterial community adherence to the B-PS surface were also impacted. Acute exposure to V-PS (100 μg/L) and B-PS (10 μg/L) significantly altered the mean lifespan and lipofuscin accumulation of Caenorhabditis elegans, suggesting that B-PS exposure at environmentally relevant concentrations could more severely accelerate the aging process than V-PS. Generation of ROS, gst-4::GFP expression, and oxidative stress-related gene expression were significantly altered following B-PS exposure. Moreover, B-PS exposure increased the nucleus-cytoplasm translocation of DAF-16 and altered the expression of genes encoding the insulin/IGF1 signaling (IIS) pathway. Compared with wild-type nematodes, the daf-16 mutation markedly enhanced lipofuscin accumulation and reduced mean lifespan, whereas daf-2, age-1, pdk-1, and akt-1 mutants could recover lipofuscin accumulation and mean lifespan. Accordingly, B-PS exposure accelerated the aging process associated with oxidative stress and the IIS pathway, and the DAF-2-AGE-1-PDK-1-AKT-1-DAF-16 signaling cascade may play a critical role in regulating the lifespan of C. elegans. This study provides new insights into the potential risks associated with microbial colonization of microplastics.

Biochemical and physiological effects of multigenerational exposure to spheric polystyrene microplastics in Caenorhabditis elegans

Although studies have already shown the effects of exposure to microplastics (MP) in different species, the effects over generations in these individuals remain poorly understood. Therefore, the present study aimed to evaluate the effect of polystyrene MP (spherical, 1 μm) on the responses of the free-living nematode Caenorhabditis elegans in a multigenerational approach over five subsequent generations. MP concentrations of both 5 and 50 μg/L induced a detoxification response, increasing glutathione S-transferase (GST) activity and inducing the generation of reactive oxygen species (ROS) and lipid peroxidation (TBARS). MP also demonstrated the ability to accumulate in the animal's body during the 96 h of each generational exposure, and possibly, this constant interaction was the main reason for the decreased response in physiological parameters as in the exploratory behavior (body bending) of nematodes, and in the reproduction, being this last parameter most negatively affected during the five exposed generations, with a reduction of almost 50% in the last generation. These results emphasize the importance of multigenerational approaches, highlighting their advantage in the assessment of environmental contaminants.

Dietary intake of microplastics impairs digestive performance, induces hepatic dysfunction, and shortens lifespan in the annual fish Nothobranchius guentheri

Microplastics (MPs) are ubiquitous in aquatic and terrestrial ecosystem, increasingly becoming a serious concern of human health. Many studies have explored the biological effects of MPs on animal and plant life in recent years. However, information regarding the effects of MPs on aging and lifespan is completely lacking in vertebrate species to date. Here we first confirm the bioavailability of MPs by oral delivery in the annual fish N. guentheri. We then show for the first time that administration of MPs not only shortens the lifespan but also accelerates the development of age-related biomarkers in N. guentheri. We also demonstrate that administration of MPs induces oxidative stress, suppresses antioxidant enzymes, reduces digestive enzymes, and causes hepatic dysfunction. Therefore, we propose that administration of MPs reduces lifespan of N. guentheri via induction of both suppressed antioxidant system and digestive disturbance as well as hepatic damage. Our results also suggest that smaller MPs appear more toxic to digestion, metabolism and growth of animals.

Organismal response to micro(nano)plastics at environmentally relevant concentrations: Toxicity and the underlying mechanisms

The toxic effects of micro(nano)plastics are long-standing, flourishing and fadeless as a research topic because of its' underlying threats to the ecology and human health. Nevertheless, in most of the existing studies, some model organisms are exposed to micro(nano)plastics at a high concentration unlikely to occur in the real environment, and there is limited data available on the impact of micro(nano)plastics at environmentally relevant concentrations (ERC) on environmental organisms. To gain a better insight into micro(nano)plastic toxicity to the environmental organisms, here we integrate the related publications of micro(nano)plastic research at ERC in the past 10 years using a bibliometric analysis, and focus on the analysis of publication trends, research focuses, collaborations, and research status. In addition, we further analyze the 33 final filtered literature, and elucidate the organismal response to micro(nano)plastics at ERC from the perspective of in vivo toxic effects and mechanisms involved. This paper also puts forward some limitations of the current study and some suggestions for future research. Our study may be of great significance in further understanding the ecotoxicity of micro(nano)plastics.

The growth toxicity and neurotoxicity mechanism of waterborne TBOEP to nematodes: Insights from transcriptomic and metabolomic profiles

Tris(2-butoxy) ethyl phosphate (TBOEP) is a typical organophosphorus flame retardant (OPFR), which has been detected in natural water bodies and drinking water and has reached a certain concentration. As a new type of organic pollutant, the environmental health risk of TBOEP needs to be assessed urgently. Here, Caenorhabditis elegans were exposed to 0, 50, 500, and 5000 ng/L TBOEP in water for 72 h. The results showed that TBOEP exposure caused concentration-dependent inhibition to the growth of nematodes, while exposure to 5000 ng/L TBOEP significantly inhibited the locomotor behavior of nematodes. Transcriptomic and metabolomic analysis showed that the disturbances in neurotransmitter transmission and amino acid, carbohydrate, and lipid metabolism were the reason for the neurotoxicity and growth toxicity of TBOEP to nematodes. These results provide basic data and a theoretical basis for evaluating the environmental health risks of organophosphorus flame retardants.

Combined effect of microplastic, salinomycin and heating on Unio tumidus

Microplastic (MP) and heating (T) suspected to modulate biological effects of aquatic contaminants. Salinomycin (Sal) is veterinary antibiotic and anticancer agent. The goal of this study was to examine the multistress effect of MP, Sal and T on the bioindicator bivalve mollusc. The Unio tumidus were treated with MP (1 mg L^-1), Sal (0.6 µg L^-1), their combination under 18° C (Mix) and 25° C (MixT) for 14 days. The digestive glands were analyzed. MP and Sal did not cause changes of Mn- and Cu,Zn-SOD, lipid peroxidation and Cyp-450-depended EROD levels, whereas catalase, GST and protein carbonyls (Sal-group) increased compared to control. In the Mix-group, enzymes, particularly EROD and GST (by 34% and 115% respectively) were up-regulated. However, in the MixT-group, they were corresponding to control or lesser (EROD, catalase). Our findings emphasize the need to take into account multistress interactions in the MP environmental risk assessment.

Microplastic pollution in soils, plants, and animals: A review of distributions, effects and potential mechanisms

Increasing production of synthetic plastics and poor management of plastic wastes have dramatically increased the amount of plastics in the environment. In 2014, at the first United Nations Environment Assembly, marine plastic waste pollution was listed as one of the 10 most pressing environmental issues. In addition, there is much plastic waste in terrestrial ecosystems due to substantial residues from agricultural mulching and packing. As a recently recognized pollutant, microplastics (MPs) have attracted significant attention from the public and various governments. Concentrations of MPs in the environment vary among locations, from <100 to >1 × 10⁶ particles per cubic meter. Many studies have addressed the impacts and potential mechanisms of MPs on the environment and organisms. Humans and other organisms can ingest or carry MPs in a variety of passive ways and these MPs can have a range of negative effects on metabolism, function, and health. Additionally, given their large surface area, MPs can sorb various pollutants, including heavy metals and persistent organic pollutants, with serious implications for animals and human wellbeing. However, due to their complexity and a lack of accurate determination methods, the systematic impacts of MP pollution on whole foodwebs are not clearly established. Therefore, this review summarizes current research advances in MP pollution, particularly the impact of MPs on soils, plants, and animals, and proposes potential future research prospects to better characterize MPs.

Effects of Polystyrene Microplastics on Human Kidney and Liver Cell Morphology, Cellular Proliferation, and Metabolism

Microplastics have gained much attention due to their prevalence and abundance in our everyday lives. They have been detected in household items such as sugar, salt, honey, seafood, tap water, water bottles, and food items wrapped in plastic. Once ingested, these tiny particles can travel to internal organs such as the kidney and liver and cause adverse effects on the cellular level. Here, human embryonic kidney (HEK 293) cells and human hepatocellular (Hep G2) liver cells were used to examine the potential toxicological effects of 1 μm polystyrene microplastics (PS-MPs). Exposing cells to PS-MPs caused a major reduction in cellular proliferation but no significant decrease in cell viability as determined by the trypan blue assay in both cell lines. Cell viability remained at least 94% for both cell lines even at the highest concentration of 100 μg/mL of PS-MPs. Phase-contrast imaging of both kidney and liver cells exposed to PS-MPs at 72 h showed significant morphological changes and uptake of PS-MP particles. Confocal fluorescent microscopy confirmed the uptake of 1 μm PS-MPs at 72 h for both cell lines. Additionally, flow cytometry experiments verified that more than 70% of cells internalized 1 μm PS-MPs after 48 h of exposure for both kidney and liver cells. Reactive oxygen species (ROS) studies revealed kidney and liver cells exposed to PS-MPs had increased levels of ROS at each concentration and for every time point tested. Furthermore, quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis at 24 and 72 h revealed that both HEK 293 and Hep G2 cells exposed to PS-MPs lowered the gene expression levels of the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), and antioxidant enzymes superoxide dismutase 2 (SOD2) and catalase (CAT), thus reducing the potential of SOD2 and CAT to detoxify ROS. These adverse effects of PS-MPs on human kidney and liver cells suggest that ingesting microplastics may lead to toxicological problems on cell metabolism and cell-cell interactions. Because exposing human kidney and liver cells to microplastics results in morphological, metabolic, proliferative changes and cellular stress, these results indicate the potential undesirable effects of microplastics on human health.

Distinct accumulation of nanoplastics in human intestinal organoids

Plastic particles, especially nanoplastics, represent an emerging concern of threat to human health, oral uptake is an important pathway for the plastic particles ingestion by human. While their fate and adverse effects in animal gastrointestinal tract are increasingly investigated, knowledge about their uptake and toxicity in human intestine is still limited. Here, by exposing human intestinal organoids to polystyrene nanoplastics (PS-NPs, ~50 nm in size) with concentrations of 10 and 100 μg/mL, we present evidence of their distinct accumulation in various type cells in intestinal organoids, then causing the cell apoptosis and inflammatory response. Our results further revealed that the effective inhibition of PS-NPs accumulation in secretive cells through co-exposure to a clathrin-mediated endocytosis inhibitor (chlorpromazine), and proved the essential role of active endocytosis in the PS-NPs uptaking into enterocyte cells. Our work not only elucidated the potential uptake and toxicity of PS-NPs in human intestinal cells and the underlying mechanism, but also provide a potential therapeutic approach to relieve the toxicity of PS-NPs to human through the endocytosis inhibition.

Cyanidin-3-O-glucoside promotes stress tolerance and lifespan extension of Caenorhabditis elegans exposed to polystyrene via DAF-16 pathway

Microplastic pollution has attracted growing attention due to its prevalent and persistent exposure to general population through the food chain, but few reports have focused on the toxicological prevention of polystyrene (PS). Using the wild-type and mutant strains, this study explored the impacts of PS and cyanidin-3-O-glucoside (C3G) on stress tolerance and lifespan of Caenorhabditis elegans (C. elegans). In N2 nematodes, PS exposure initiated the oxidative stress and subsequent lifespan reduction, while these adverse impacts could be positively improved by C3G treatment. Considering the pivotal role of DAF-16 pathway in stress tolerance and lifespan regulation, the expression of the daf-16 gene and its downstream antioxidant genes (clt-2, hsp-16.1, sod-3, sod-5) were examined, and found to be significantly enhanced by C3G. Since the sod-3 gene was up-regulated the most fold by C3G, the activity of SOD enzyme that encoded by the sod-3 was examined, and could be obviously enhanced upon C3G treatment. This explained the improved oxidative stress and delayed oxidation-associated aging after C3G intervention. Nevertheless, these positive effects of C3G were weakened in daf-16(-) mutant strain (with deleted DAF-16 gene), for which the beneficial effects of C3G in promoting stress resistance and lifespan extension were inhibited. These findings suggested that the DAF-16 gene and its downstream antioxidant genes, have participated in C3G's regulations on redox balance and lifespan that impacted by nano-polystyrene particles. This study highlighted the link between dietary components and environmentally driven disturbance.

Ecotoxicological effects of plastics on plants, soil fauna and microorganisms: A meta-analysis

The interactions of plastics and soil organisms are complex and inconsistent observations on the effects of plastics have been made in published studies. In this study, we assessed the effects of plastic exposure on plants, fauna and microbial communities, with a meta-analysis. Using a total of 2936 observations from 140 publications, we analysed how responses in plants, soil fauna and microorganisms depended on the plastic concentration, size, type, species and exposure media. We found that overall plastics caused substantial detrimental effects to plants and fauna, but less so to microbial diversity and richness. Plastic concentration was one of the most important factors explaining variations in plant and faunal responses. Larger plastics (>1 μm) caused unfavourable changes to plant growth, germination and oxidative stress, while nanoplastics (NPs; ≤ 1 μm) only increased oxidative stress. On the contrary, there was a clear trend showing that small plastics adversely affected fauna reproduction, survival and locomotion than large plastics. Plant responses were indifferent to plastic type, with most studies conducted using polyethylene (PE) and polystyrene (PS) plastics, but soil fauna were frequently more sensitive to PS than to PE exposure. Plant species played a vital role in some parameters, with the effects of plastics being considerably greater on vegetable plants than on cereal plants.

Distribution, biological effects and biofilms of microplastics in freshwater systems - A review

The rapidly rising output and mass use of plastics have made plastics pollution a major environmental problem. Since plastics are persistent in the environment, understanding the migration transformation characteristics of plastics is critical. Given the ever-increasing concern about the environmental risks posed by microplastics, their prevalence, fate, abundance and impact have been intensively studied. Most of these investigations focused on the marine environment, but research on freshwater microplastics is less extensive. This article aims to briefly summarize the research progress of freshwater microplastics, identify existing gaps and draw novel conclusions, so as to provide useful information for the research of freshwater microplastics. Using the statistics and analysis of freshwater microplastics studies in 2016-2021, this review systematically discusses microplastics in globally freshwater systems. The biological effects of microplastics on freshwater organisms were discussed as well. Some potential ecological effects of microplastic biofilms were shown, such as climate change and material circulation. More importantly, we present some unique conclusions. For example, the detection of freshwater microplastics is mainly concentrated in natural freshwater systems, while few are concentrated in artificial freshwater systems. In addition, polystyrene is the main mode for testing the biological effects of freshwater microplastics, and polyethene and polypropylene which are the most common in freshwater environments, have not been taken seriously. We also pointed out that studies on advanced freshwater plants in the topic of biological effects of microplastics still need strengthen.

Nanoplastics: Status and Knowledge Gaps in the Finalization of Environmental Risk Assessments

Nanoplastics (NPs) are particles ranging in size between 1 and 1000 nm, and they are a form of environmental contaminant of great ecotoxicological concern. Although NPs are widespread across ecosystems, they have only recently garnered growing attention from both the scientific community and regulatory bodies. The present study reviews scientific literature related to the exposure and effects of NPs and identifies research gaps that impede the finalization of related environmental risk assessments (ERAs). Approximately 80 articles published between 2012 and 2021 were considered. Very few studies (eight articles) focused on the presence of NPs in biotic matrices, whereas the majority of the studies (62 articles) assessed the lethal and sublethal effects of NPs on aquatic and terrestrial organisms. Whilst many studies focused on nude NPs, only a few considered their association with different aggregates. Amongst NPs, the effects of polystyrene are the most extensively reported to date. Moreover, the effects of NPs on aquatic organisms are better characterized than those on terrestrial organisms. NP concentrations detected in water were close to or even higher than the sublethal levels for organisms. An ERA framework specifically tailored to NPs is proposed.

Polystyrene microbeads influence lipid storage distribution in C. elegans as revealed by coherent anti-Stokes Raman scattering (CARS) microscopy

The exposure of Caenorhabditis elegans to polystyrene (PS) beads of a wide range of sizes impedes feeding, by reducing food consumption, and has been linked to inhibitory effects on the reproductive capacity of this nematode, as determined in standardized toxicity tests. Lipid storage provides energy for longevity, growth, and reproduction and may influence the organismal response to stress, including the food deprivation resulting from microplastics exposure. However, the effects of microplastics on energy storage have not been investigated in detail. In this study, C. elegans was exposed to ingestible sizes of PS beads in a standardized toxicity test (96 h) and in a multigeneration test (∼21 days), after which lipid storage was quantitatively analyzed in individual adults using coherent anti-Stokes Raman scattering (CARS) microscopy. The results showed that lipid storage distribution in C. elegans was altered when worms were exposed to microplastics in form of PS beads. For example, when exposed to 0.1-μm PS beads, the lipid droplet count was 93% higher, the droplets were up to 56% larger, and the area of the nematode body covered by lipids was up to 79% higher than in unexposed nematodes. The measured values tended to increase as PS bead sizes decreased. Cultivating the nematodes for 96 h under restricted food conditions in the absence of beads reproduced the altered lipid storage and suggested that it was triggered by food deprivation, including that induced by the dilutional effects of PS bead exposure. Our study demonstrates the utility of CARS microscopy to comprehensively image the smaller microplastics (<10 μm) ingested by nematodes and possibly other biota in investigations of the effects at the level of the individual organism.

Untoward Effects of Micro- and Nanoplastics: An Expert Review of Their Biological Impact and Epigenetic Effects

The production of plastic has dramatically increased in the last 50 y. Because of their stability and durability, plastics are ubiquitously incorporated in both marine and terrestrial ecosystems. Plastic is acted upon by biological, chemical, and physical agents, leading to fragmentation into small pieces [i.e., microplastics (MPs) or nanoplastics (NPs)], classified depending on their size. MPs range from 0.1 to 5000 μm and NPs are fragments between 0.001 to 0.1 μm. MPs and, especially NPs, are easily incorporated into living beings via ingestion. The penetration of MPs and NPs into the food system is an important issue, for both food security and health risk assessment. Ingestion of different MPs and NPs has been associated with different issues in the intestine, such as direct physical damage, increased intestinal permeability, diminished microbiota diversity, and increases in local inflammatory response. However, the potential harmful effects of low-dose dietary plastic are still unclear. Some evidence indicates that intestinal uptake of plastic particles is relatively low and is mostly dependent on the particle's size. However, other evidence highlights that NPs dysregulate key molecular signaling pathways, modify the gut microbiota composition, and may induce important epigenetic changes, including transgenerational effects that might be involved in the onset of many different metabolic disorders. Until now, experiments have been mostly performed on marine organisms, Caenorhabditis elegans, and mouse models, but some research indicates accidental plastic dietary consumption by humans, raising the issue of detrimental health effects of MPs and NPs. This review discusses the impact that MPs and NPs could have on the intestinal tract and the biodistribution and systemic, cellular, and molecular levels. Accumulated evidence of MPs' effects on the human gut suggests that large exposure to MPs and NPs may have phenotypical untoward effects in humans, calling for urgent research in this field.

Recent advances on ecological effects of microplastics on soil environment

The mass production and wide application of plastics and their derivatives have led to the release of a large number of discarded plastic products into the natural environment, where they continue to accumulate due to their low recycling rate and long durability. These large pieces of plastic will gradually break into microplastics (<5 mm), which are highly persistent organic pollutants and attract worldwide attention due to their small particle size and potential threats to the ecosystem. Compared with the aquatic system, terrestrial systems such as soils, as sinks for microplastics, are more susceptible to plastic pollution. In this article, we comprehensively summarized the occurrence and sources of microplastics in terrestrial soil, and reviewed the eco-toxicological effects of microplastics in soil ecosystems, in terms of physical and chemical properties of soil, soil nutrient cycling, soil flora and fauna. The influence of microplastics on soil microbial community, and particularly the microbial community on the surface of microplastics, were examined in detail. The compound effects of microplastics and other pollutants, e.g., heavy metals and antibiotics, were addressed. Future challenges of research on microplastics include development of new techniques and standardization for the extraction and qualitative and quantitative analysis of microplastics in soils, toxic effects of microplastics at microbial or even molecular levels, the contribution of microplastics to antibiotic resistance genes migration, and unraveling microorganisms for the degradation of microplastics. This work provides as a better understanding of the occurrence, distribution and potential ecological risks of microplastics in terrestrial soil ecosystems.

Label-free identification of microplastics in human cells: dark-field microscopy and deep learning study

The development of an automatic method of identifying microplastic particles within live cells and organisms is crucial for high-throughput analysis of their biodistribution in toxicity studies. State-of-the-art technique in the data analysis tasks is the application of deep learning algorithms. Here, we propose the approach of polystyrene microparticle classification differing only in pigmentation using enhanced dark-field microscopy and a residual neural network (ResNet). The dataset consisting of 11,528 particle images has been collected to train and evaluate the neural network model. Human skin fibroblasts treated with microplastics were used as a model to study the ability of ResNet for classifying particles in a realistic biological experiment. As a result, the accuracy of the obtained classification algorithm achieved up to 93% in cell samples, indicating that the technique proposed will be a potent alternative to time-consuming spectral-based methods in microplastic toxicity research.

Size-dependent transgenerational toxicity induced by nanoplastics in nematode Caenorhabditis elegans

Nanoplastic exposure can potentially cause the severe transgenerational toxicity in organisms. However, the transgenerational nanoplastic toxicity and the underlying mechanisms are still largely unclear. Using Caenorhabditis elegans as an animal model, we here compared the transgenerational toxicity of two sizes of polystyrene nanoparticles (PS-NPs, 20 and 100 nm). The nematodes were exposed to PS-NPs at the P0 generation, and from the F1 generation the nematodes were grown under the normal condition. Exposure to 20 nm PS-NPs resulted in more severe transgenerational toxicity than exposure to 100 nm PS-NPs. At the concentration of 100 μg/L, the toxicity of 20 nm PS-NPs on locomotion and reproduction was detected at the F1-F6 generations, whereas the toxicity of 100 nm PS-NPs could only be observed at the F1-F3 generations. The difference in transgeneration toxicity between PS-NPs (20 nm) and PS-NPs (100 nm) was associated with the difference in transgenerational activation of oxidative stress. Based on observations on SOD-3::GFP, HSP-6::GFP, and HSP-4::GFP expressions, PS-NPs (20 nm) and PS-NPs (100 nm) further induced different transgenerational responses of anti-oxidation, mt UPR, and ER UPR. Our data suggested that the induction of transgenerational toxicity of PS-NPs was size dependent in nematodes. The results are helpful for our understanding the cellular mechanisms for the induction of transgenerational nanoplastic toxicity in organisms.

Effects of Microplastics on Immune Responses of the Yellow Catfish Pelteobagrus fulvidraco Under Hypoxia

Compared with marine organisms, research on microplastics (MPs) in freshwater organisms is still less although MPs have been widely found in the freshwater ecosystem. Hypoxia is a ubiquitous issue in freshwater aquaculture, and under such scenarios, the toxic effects of MPs on typical aquaculture fish need to be clarified. In this study, we studied the effects of MPs (polystyrene) on specific growth rate (SGR), hypoxia-inducible factor-1α (HIF-1α), tumor necrosis factor-α (TNF-α), interleukin-8 (IL-8), and interferon (IFN) in the yellow catfish (Pelteobagrus fulvidraco) under hypoxic conditions. After 15 days of exposure, the SGR was not affected by MPs or hypoxia. MPs significantly increased the expressions of HIF-1α and TNF-α but inhibited the expression of IFN at high concentration MPs under normoxia. However, hypoxia significantly inhibited the expression of IL-8 and TNF-α under high MP concentration and low MP concentration, respectively. In addition, MPs had significant concentration-dependent inhibitory effects on IFN under hypoxia. Surprisingly, a positive correction between HIF-1α and TNF-α was found in fish. Although hypoxia might alleviate the effects of MPs with low concentrations, the interaction of hypoxia and MPs aggravated the negative effects of MPs on immune factors at high concentration MPs. This study provided new insight into the complex effects of hypoxia and MPs on aquatic organisms, and future studies should focus on the cellular pathways of immune cells in fish. Given that MPs could induce the immune response in fish, considerations should be paid to the impacts of MPs on freshwater aquaculture, and hypoxia should be taken into consideration when evaluating the effects of MPs.

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

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

Microplastic pollution in freshwater systems in Southeast Asia: contamination levels, sources, and ecological impacts

Plastics are synthetic polymers known for their outstanding durability and versatility, and have replaced traditional materials in many applications. Unfortunately, their unique traits ensure that they pose a major threat to the environment. While literature on freshwater microplastic contamination has grown over the recent years, research undertaken in rapidly developing countries, where plastic production and use are increasing dramatically, has lagged behind that in other parts of the world. In the South East Asia (SEA) region, basic information on levels of contamination is very limited and, as a consequence, the risk to human and ecological health remains hard to assess. This review synthesises what is currently known about microplastic contamination of freshwater ecosystems in SEA, with a particular focus on Malaysia. The review 1) summarises published studies that have assessed levels of contamination in freshwater systems in SEA, 2) discusses key sources and transport pathways of microplastic in freshwaters, 3) outlines what is known of the impacts of microplastic on freshwater organisms, and 4) identifies key knowledge gaps related to our understanding of the transport, fate and effects of microplastic.

Airborne microplastics in indoor and outdoor environments of a coastal city in Eastern China

Microplastics (MPs) in marine and terrestrial environments have been intensively studied, but the dynamics of airborne MPs remains limited. Existing studies on atmospheric MPs are mostly derived from collection of atmospheric deposition, whereas direct measurements of airborne MPs are scarce. However, the abundance of airborne MPs is more relevant for evaluating human inhalation exposure risk. Herein, airborne MPs in indoor and outdoor environments from urban and rural areas of a coastal city in eastern China were investigated. MP concentrations (mean±SD) in indoor air (1583 ± 1180 n/m³) were an order of magnitude higher than outdoor air (189 ± 85 n/m³), and airborne MP concentrations in urban areas (224 ± 70 n/m³) were higher than rural areas (101 ± 47 n/m³). MPs smaller than 100 µm dominated airborne MPs, and the predominant shape of airborne MPs was fragments, as opposed to fibers. The larger MP size fractions contained a higher proportion of fibers, whereas the smaller size fractions were nearly exclusively composed of fragments. The health risk caused by ubiquitous airborne MPs should not be discounted as the maximum annual outdoor exposure of airborne MPs can reach 1 million/year, while indoor exposure may be even higher due to higher indoor airborne MP concentrations.

Forgotten but not gone: Particulate matter as contaminations of mucosal systems

A decade ago, environmental issues, such as air pollution and the contamination of the oceans with microplastic, were prominently communicated in the media. However, these days, political topics, as well as the ongoing COVID-19 pandemic, have clearly taken over. In spite of this shift in focus regarding media representation, researchers have made progress in evaluating the possible health risks associated with particulate contaminations present in water and air. In this review article, we summarize recent efforts that establish a clear link between the increasing occurrence of certain pathological conditions and the exposure of humans (or animals) to airborne or waterborne particulate matter. First, we give an overview of the physiological functions mucus has to fulfill in humans and animals, and we discuss different sources of particulate matter. We then highlight parameters that govern particle toxicity and summarize our current knowledge of how an exposure to particulate matter can be related to dysfunctions of mucosal systems. Last, we outline how biophysical tools and methods can help researchers to obtain a better understanding of how particulate matter may affect human health. As we discuss here, recent research has made it quite clear that the structure and functions of those mucosal systems are sensitive toward particulate contaminations. Yet, our mechanistic understanding of how (and which) nano- and microparticles can compromise human health via interacting with mucosal barriers is far from complete.

Microfluidic electric parallel egg-laying assay and application to in-vivo toxicity screening of microplastics using C. elegans

Environmental pollutants like microplastics are posing health concerns on aquatic animals and the ecosystem. Microplastic toxicity studies using Caenorhabditis elegans (C. elegans) as a model are evolving but methodologically hindered from obtaining statistically strong data sets, detecting toxicity effects based on microplastics uptake, and correlating physiological and behavioural effects at an individual-worm level. In this paper, we report a novel microfluidic electric egg-laying assay for phenotypical assessment of multiple worms in parallel. The effects of glucose and polystyrene microplastics at two concentrations on the worms' electric egg-laying, length, diameter, and length contraction during exposure to electric signal were studied. The device contained eight parallel worm-dwelling microchannels called electric traps, with equivalent electrical fields, in which the worms were electrically stimulated for egg deposition and fluorescently imaged for assessment of neuronal and microplastic uptake expression. A new bidirectional stimulation technique was developed, and the device design was optimized to achieve a testing efficiency of 91.25%. Exposure of worms to 100 mM glucose resulted in a significant reduction in their egg-laying and size. The effects of 1 μm polystyrene microparticles at concentrations of 100 and 1000 mg/L on the electric egg-laying behaviour, size, and neurodegeneration of N2 and NW1229 (expressing GFP pan-neuronally) worms were also studied. Of the two concentrations, 1000 mg/L caused severe egg-laying deficiency and growth retardation as well as neurodegeneration. Additionally, using single-worm level phenotyping, we noticed intra-population variability in microplastics uptake and correlation with the above physiological and behavioural phenotypes, which was hidden in the population-averaged results. Taken together, these results suggest the appropriateness of our microfluidic assay for toxicological studies and for assessing the phenotypical heterogeneity in response to microplastics.

Nano and microplastic interactions with freshwater biota - Current knowledge, challenges and future solutions

Current understanding of nano- and microplastic movement, propagation and potential effects on biota in freshwater environments is developing rapidly. Still, there are significant disconnects in the integration of knowledge derived from laboratory and field studies. This review synthesises the current understanding of nano- and microplastic impacts on freshwater biota from field studies and combines it with the more mechanistic insights derived from laboratory studies. Several discrepancies between the field and laboratory studies, impacting progress in process understanding, were identified including that the most prevalent plastic morphologies found in the field (fibres) are not those used in most of the laboratory studies (particles). Solutions to overcome these disparities are proposed to aid comparability of future studies. For example, environmental sampling and separation of biota into its constituents is encouraged when conducting field studies to map microplastic uptake preferences. In laboratory studies, recommendations include performing toxicity studies to systematically test possible factors affecting toxicity of nano- and microplastics, including morphology, chemical makeup (e.g., additives) and effects of plastic size. Consideration should be given to environmentally relevant exposure factors in laboratory studies, such as realistic exposure medium and effects of plastic ageing. Furthermore, based on this comprehensive review recommendations of principal toxicity endpoints for each of the main trophic levels (microbes, primary producers, primary consumers and secondary consumers) that should be reported to make toxicity studies more comparable in the future are given.

Transgenerational neurotoxicity of polystyrene microplastics induced by oxidative stress in Caenorhabditis elegans

Microplastics (MPs), emerging environmental contaminants, exhibit multiple toxicities in organisms. However, the transgenerational neurotoxicity of MPs has received little attention. Caenorhabditis elegans has been used as a model organism for studying transgenerational toxicity. In this study, the transgenerational neurotoxicity and oxidative stress of MPs were investigated over five generations (F0-F4) of C. elegans. The parental generation (F0) was exposed to polystyrene microplastics (PS-MPs) at concentrations of 0.1-100 μg/L, and subsequent generations (F1-F4) were cultured under toxicant-free conditions. The results indicated that exposure to PS-MPs at concentrations of 10-100 μg/L significantly decreased head thrash and body bends in nematodes, and this reduction was also observed in subsequent generations (F1-F2). This suggested that neurotoxicity induced by PS-MPs can be transferred from the parent to subsequent generations. Maternal exposure to 100 μg/L PS-MPs significantly enhanced ROS production and lipofuscin accumulation in subsequent generations (F1-F2), indicating that the induction of oxidative stress plays an important role in the transgenerational neurotoxicity in C. elegans. Moreover, maternal exposure to PS-MPs resulted in the transgenerational upregulation of genes related to oxidative stress (clk-1, ctl-1, sod-3, sod-4, and sod-5) in the F1-F3 generations, which indicated that these genes may be involved in regulating transgenerational neurotoxicity in C. elegans.

Neurobehavior and neuron damage following prolonged exposure of silver nanoparticles with/without polyvinylpyrrolidone coating in Caenorhabditis elegans

Silver nanoparticles (AgNPs) have become widespread in the environment with increasing industrial applications. But the studies about their potential health risks are far from enough, especially in neurotoxic effects. This study aimed to investigate the neurotoxic effects of longer-term exposure (prolonged exposure for 48 h and chronic exposure for 6 days) of 20nm AgNPs with/without polyvinylpyrrolidone (PVP) coating at low concentrations (0.01-10 mg·L^-1 ) to Caenorhabditis elegans. The results suggested that exposure to AgNPs induced damage to nematode survival, with the longest and relative average life span reduced. Exposure to AgNPs caused neurotoxicity on locomotion behaviors (head thrashes, body bends, pharyngeal pumping frequency, and defecation interval) and sensory perception behaviors (chemotaxis assay and thermotaxis assay), as well as impaired dopaminergic, GABAergic, and cholinergic neurons, except for glutamatergic, based on the alters fluorescence intensity, in a dose- and time-dependent manner. Further investigations suggested that the low-dose AgNPs (0.01-0.1 mg·L^-1 ) exposure raises receptors of GABAergic and dopamine in C. elegans at the genetic level, whereas opposite results were observed at higher doses (1-10 mg·L^-1 ), which implied that AgNPs could cause neurotoxicity by impairing neurotransmitter delivery. The PVP-AgNPs could cause a higher fatality rate and neurotoxicity at the same dose. Notably, AgNPs did not cause any deleterious effect on nematodes at the lowest dose of 0.01 mg·L^-1 . In general, these results suggested that AgNPs possess the neurotoxic potential in C. elegans and provided useful information to understand the neurotoxicity of AgNPs, which would offer an inspiring perspective on the safe application.

Induction of protective response to polystyrene nanoparticles associated with dysregulation of intestinal long non-coding RNAs in Caenorhabditis elegans

Intestinal barrier plays a crucial function during the response to polystyrene nanoparticles (PS-NPs) in nematode Caenorhabditis elegans. Long non-coding RNAs (lncRNAs) are involved in the control of various biological processes, including stress response. We here used C. elegans to determine intestinal lncRNAs dysregulated by PS-NPs (1-100 μg/L). In intestine of PS-NPs exposed worms, we found four lncRNAs (linc-61, linc-50, linc-9, and linc-2) in response to PS-NPs and with the function in controlling PS-NPs toxicity. The alteration in expressions of these four intestinal lncRNAs reflected a protective response to PS-NPs exposure. During the response to PS-NPs, limited number of transcriptional factors functioned as the downstream targets of these four lncRNAs. linc-2 acted upstream of DAF-16, linc-9 acted upstream of NHR-77, linc-50 functioned upstream of DAF-16, and linc-61 regulated the functions of DAF-16, DVE-1, and FKH-2 to control PS-NPs toxicity. The obtained data demonstrated the important role of lncRNAs in intestinal barrier to mediate a protective response to PS-NPs exposure at low concentrations.

Dysregulated mir-76 mediated a protective response to nanopolystyrene by modulating heme homeostasis related molecular signaling in nematode Caenorhabditis elegans

The underlying mechanisms of microRNAs (miRNAs) in regulating nanoplastic toxicity are still largely unclear in organisms. In nanopolystyrene (NPS) exposed Caenorhabditis elegans, the expression of mir-76 (a neuronal miRNA) was significantly decreased, and the mir-76 mutant was resistant to the toxicity of NPS. The aim of this study was to determine the molecular basis of mir-76 in controlling NPS toxicity in nematodes. The mir-76 mutation increased expression of glb-10 encoding a globin protein in NPS (1 μg/L) exposed nematodes. Exposure to NPS (1-100 μg/L) increased the glb-10 expression, and the glb-10(RNAi) worm was susceptible to NPS toxicity in inducing reactive oxygen species (ROS) production and in decreasing locomotion behavior. Using ROS production and locomotion behavior as endpoints, mutation of glb-10 inhibited resistance of mir-76 mutant to NPS toxicity, and neuronal overexpression of mir-76 inhibited the resistance to NPS toxicity in nematodes overexpressing neuronal glb-10 containing 3' untranslated region (3'UTR). Thus, GLB-10 functioned as a target of mir-76 in the neurons to regulate the NPS toxicity. Moreover, a signaling cascade of HRG-7-HRG-5 required for the control of heme homeostasis was identified to function downstream of neuronal GLB-10 to regulate the NPS toxicity. In this signaling cascade, the neuronal HRG-7 regulated the NPS toxicity by antagonizing function of intestinal HRG-5. Furthermore, in the intestine, HRG-5 controlled NPS toxicity by inhibiting functions of hypoxia-inducible transcriptional factor HIF-1 and transcriptional factor ELT-2. Our results highlight the crucial function of heme homeostasis related signaling in regulating the NPS toxicity in organisms.

Induction of Protective Response Associated with Expressional Alterations in Neuronal G Protein-Coupled Receptors in Polystyrene Nanoparticle Exposed Caenorhabditis elegans

In this study, the association of expressional alterations in neuronal G protein-coupled receptors (GPCRs) with induction of protective response to polystyrene nanoparticles (PS-NPs) was investigated in Caenorhabditis elegans. On the basis of both phenotypic analysis and expression levels, the alterations in expressions of NPR-1, NPR-4, NPR-8, NPR-9, NPR-12, DCAR-1, GTR-1, DOP-2, SER-4, and DAF-37 in neuronal cells mediated the protective response to PS-NPs exposure. In neuronal cells, NPR-9, NPR-12, DCAR-1, and GTR-1 controlled the PS-NPs toxicity by activating or inhibiting JNK-1/JNK MAPK signaling. Neuronal NPR-8, NPR-9, DCAR-1, DOP-2, and DAF-37 controlled the PS-NPs toxicity by activating or inhibiting MPK-1/ERK MAPK signaling. Neuronal NPR-4, NPR-8, NPR-9, NPR-12, GTR-1, DOP-2, and DAF-37 controlled the PS-NPs toxicity by activating or inhibiting DBL-1/TGF-β signaling. Neuronal NPR-1, NPR-4, NPR-12, and GTR-1 controlled the PS-NPs toxicity by activating or inhibiting DAF-7/TGF-β signaling. Our data provides an important neuronal basis for induction of protective response to PS-NPs in C. elegans.

A probabilistic risk assessment of microplastics in soil ecosystems

Plastics have a variety of applications due to their versatility, relative cost, and strength-to-weight ratio, and resistance to degradation. As a result, plastic waste can be found in all corners of the Earth. A class of plastic contaminants that have received increasing attention in terms of their potential impact on ecosystems is microplastics (≤5 mm). The greatest attention to date has been on their potential effect in marine ecosystems. However, a growing number of studies are examining their potential impact on soil ecosystems. The data reported in the literature on the environmentally-relevant concentrations of microplastics in soils and the concentration of microplastics that causes an adverse effect in soil biota were used to perform a probabilistic risk assessment of microplastics to soil biota. An environmental exposure distribution was constructed from the concentrations of microplastics reported in soil in the literature. Species sensitivity distributions were constructed using concentration of microplastics in soil that had no adverse effect on soil species (NOEC) or the lowest concentrations that had an adverse effect on soil species (LOEC) reported in the literature. The 95th centile of the environmental exposure distribution (8147 microplastic particles per gram of soil) was greater than 22 and 28% of the species sensitivity distribution constructed using NOECs and LOECs, respectively. The assessment concluded that environmentally relevant concentrations of microplastics reported in the literature could pose a considerable risk to soil biota. It is also important to note that due to the continued production of large quantities of plastic and the persistence of microplastics in the environment, environmentally-relevant concentrations of microplastics in soil are likely to only rise.

Dark-field hyperspectral microscopy for label-free microplastics and nanoplastics detection and identification in vivo: A Caenorhabditis elegans study

Microplastics pollution is a serious ecological threat, severely affecting environments and human health. Tackling microplastics pollution requires an effective methodology to detect minute polymer particles in environmental samples and organisms. Here were report a novel methodology to visualise and identify nanoscale (down to 100 nm) and microscale synthetic commercially-available uniform spherical polymer particles using dark-field hyperspectral microscopy in visible-near infrared (400-1000 nm) wavelength range. Polystyrene particles with diameters between 100 nm-1 μm, polymethacrylate 1 μm and melamine formaldehyde 2 μm microspheres suspended in pure water samples were effectively imaged and chemically identified based on spectral signatures and image-assisted analysis. We succeeded in visualisation and spectral identification of pure and mixed nano- and microplastics in vivo employing optically-transparent Caenorhabditis elegans nematodes as a model to demonstrate the ingestion and tissue distribution of microplastics. As we demonstrate here, dark-field hyperspectral microscopy is capable for differentiating between chemically-different microplastics confined within live invertebrate intestines. Moreover, this optical technology allows for quantitative identification of microplastics ingested by nematodes. We believe that this label-free non-destructive methodology will find numerous applications in environmental nano- and microplastics detection and quantification, investigation of their biodistribution in tissues and organs and nanotoxicology.

Environmental fate, ecotoxicity biomarkers, and potential health effects of micro- and nano-scale plastic contamination

In recent decades, the quantity of plastic waste products has increased tremendously. As plastic wastes are released into the environment, they exert harmful effects on biota and human health. In this work, a comprehensive review is offered to describe the physical and chemical characteristics of microplastics and nanoplastics in relation to their fate, microbial ecology, transport, and ecotoxic behavior. Present discussion is expanded further to cover the biochemical, physiological, and molecular mechanisms controlling the environmental fate, ecotoxicity, and human health hazards of micro- and nanoplastics. The risks of their exposure to microbes, plants, animals, and human health are also reviewed with special emphasis. Finally, a direction for future interdisciplinary research in materials and polymer science is also discussed to help control the pollution caused by micro- and nanoplastics.

Bacterial consumption by nematodes is disturbed by the presence of polystyrene beads: The roles of food dilution and pharyngeal pumping

Microplastics (MPs; <5 mm) released into freshwaters from anthropogenic sources accumulate in sediments, where they may pose an environmental threat to benthic organisms, such as nematodes. Several studies have examined the effects of nano- and microplastics on the nematode Caenorhabditis elegans, whereas reduced food availability was suggested as a possible explanation for the observed inhibitory effects. Therefore, this study should clarify whether micro-beads of different sizes (1.0 and 6.0 μm in diameter) and materials (polystyrene PS, silica) are able to interfere with the feeding of C. elegans on its bacterial diet (Escherichia coli), and, by this, lowering its consumption rate within 7 h of exposure. Moreover, it was examined whether an inhibited bacterial consumption was caused by a reduction of the nematode's pumping rate, as a primary indicator of food ingestion. Bacterial consumption by C. elegans was significantly decreased in the presence of 1.0- and 6.0-μm PS beads (49-67% lower bacterial consumption compared to control), whereas in the presence of 1.0-μm silica beads feeding was not impeded. Interestingly, the pumping rate was significantly lower in the presence of non-ingestible 6.0-μm PS beads with 161 ± 16 pumps min-1, while it was largely unchanged for nematodes exposed to ingestible 1.0-μm PS beads with 205 ± 12 pumps min-1, compared to control conditions with 210 ± 18 pumps min-1, respectively. As reduced bacterial consumption leads to generally lower energy reserves in C. elegans, these results allow to link observed inhibitory effects of MPs on the nematodes to a lower food availability. Such indirect, food-web related, effects of MPs should raise concern of ecological consequences in natural habitats, where temporal food deficiencies can occur. Consequently, disturbances in food availability and feeding efficiency should be regarded as important parameters in environmental risk assessments focusing on MPs.

Microplastics in soils: A review of methods, occurrence, fate, transport, ecological and environmental risks

The global prevalence of microplastics (MPs) poses a potential threat and unpredictable risk to the function and health of environmental systems. However, the research progress of soil MPs is restricted by the inherent technical inconformity and difficulties in analyzing particles in complex matrices. Here, we reviewed a selection of papers and then extrapolated a tentative standardized method for such analyses. The multiple sources of soil MPs in soil need to be quantified. Global monitoring data of soil MPs is far from sufficient. The interaction between MPs and different properties and environmental factors controls the migration and retention of MPs in soil. The migration behavior and key mechanisms of MPs in real-world environments remain to be determined. The presence of MPs threatens soil microbial-plant-animal ecosystem function and health, and may enter the human body through the food chain, although the extent of these hazards is currently debated. In particular, attention should be paid to the potential transport and ecotoxicological mechanisms of contaminants derived and adsorptive from MPs and of harmful microorganisms (such as pathogens) attached as biofilms. Although there exist preliminary studies on soil MPs, it is urgent to consider the diversity of MPs as a suite of contaminants and to systematically understand the sources, flux and effects of these artificial pollutants in time and space from the perspective of plastic environmental cycle. More comprehensive quantification of their environmental fate is undertaken to identify risks to global human and ecological systems. From the perspective of controlling soil MP pollution, the responsibility assignment of government manage-producer-consumer system and the strategy of remediation should be implemented. This review is helpful for providing an important roadmap and inspiration for the research methods and framework of soil MPs and facilitates the development of waste management and remediation strategies for regional soil MP contamination.

Response of DBL-1/TGF-β signaling-mediated neuron-intestine communication to nanopolystyrene in nematode Caenorhabditis elegans

TGF-β signaling pathway is important for the regulation of stress response in organisms. We here used Caenorhabditis elegans to determine the function of DBL-1/TGF-β signaling pathway in the control of response to nanopolystyrene (100 nm). In DBL-1/TGF-β signaling pathway, exposure to 1-1000 μg/L nanopolystyrene significantly increased the expressions of dbl-1 encoding a TGF-β ligand, sma-6 encoding a TGF-β receptor, sma-4 encoding a Co-Smad, and two genes (mab-31 and sma-9) encoding transcriptional factors. DBL-1 acted in the neurons to control the response to nanopolystyrene. In the neurons, the expression and the function of DBL-1 were under the control of two signaling cascades (SMOC-1-ZAG-1 and SMOC-1-ADT-2). TGF-β receptor SMA-6 acted in the intestine to control the response to nanopolystyrene. The downstream Co-Smad/SMA-4 and two transcriptional factors (MAB-31 and SMA-9) of SMA-6 in the intestine were further identified to be required for the control of response to nanopolystyrene. In nanopolystyrene exposed nematodes, intestinal MAB-31 activated the mitochondrial Mn-SOD/SOD-3 by modulating DAF-16 activity, and intestinal SMA-9 activated the mitochondrial unfolded protein response by affecting ELT-2 activity. Therefore, the DBL-1/TGF-β signaling pathway mediated an important neuron-intestine communication in nanopolystyrene exposed nematodes.

A methodological approach of the current literature on microplastic contamination in terrestrial environments: Current knowledge and baseline considerations

Plastic pollution is one of the major challenges in the Anthropocene. A plastic waste sub-product, microplastics (<5 mm), has been regarded as contaminants of concern for its detrimental effects and widespread in the environment. Most studies assessing microplastics focused on marine environments, while terrestrial and soil systems have been overlooked. In this review, we analyzed the current knowledge regarding microplastic pollution in natural soil or agricultural ecosystems. We focused on reviewing the procedural steps for microplastic extraction and identification in detail. The heterogeneity of the methods applied, lack of standardized procedures and incompatible parameters reported, make the results incomparable among most studies. Several microplastic concentration units are needed to make studies comparable. Correctly determining and reporting microplastic morphotypes are key to understanding the sources of contamination. Minimal considerations and recommendations were stated for extraction, digestion, filtration, and polymer identification procedures. Baseline contamination prevention measures were identified as mandatory along the entire sampling, handling and identification procedures. Lastly, knowledge gaps were identified and discussed for further research.