Are your shoes safe for the environment? - Toxicity screening of leachates from microplastic fragments of shoe soles using freshwater organisms

Understanding the impact of nanoplastics on reproductive health: Exposure pathways, mechanisms, and implications

Microplastic pollution is a pressing global environmental concern with particular urgency surrounding the issue of nanoplastic particles. Plastic products exhibit a remarkable persistence in natural ecosystems, resisting easy degradation. Nanoplastics, characterized by their diminutive size, possess distinct properties when compared to their larger counterparts, which could potentially render them more ecologically detrimental. Microplastics themselves serve as carriers for toxic and hazardous substances, such as plastic additives, that enter and persist in the environmental cycle. Importantly, nanoplastics exhibit enhanced bioavailability upon entering the food chain. Notably, studies have demonstrated the adverse effects of nanoplastics on the reproductive function of aquatic organisms, and evidence of micro- and nanoplastics have emerged within human reproductive organs, including the placenta. However, a knowledge gap persists regarding the impacts of nanoplastics on the reproductive systems of mammals and, indeed, humans. This paper aims to elucidate the less frequently discussed sources and distribution of nanoplastics in the environment, along with the pathways of human exposure. We also emphasize the extent to which nanoplastics accumulate within the reproductive systems of organisms. Subsequently, we present an in-depth analysis of the effects of nanoplastics and their associated contaminants on mammalian and human reproductive health. The mechanisms through which nanoplastics contribute to reproductive disorders are comprehensively explored, highlighting their potential to disrupt endocrine levels in mammals and humans. Additionally, we scrutinize and discuss studies on biotoxicity of nanoplastics, offering insights into potential areas for future research.

What Are "Bioplastics"? Defining Renewability, Biosynthesis, Biodegradability, and Biocompatibility

Today, plastic materials are mostly made from fossil resources, and they are characterized by their long lifetime and pronounced persistence in the open environment. These attributes of plastics are one cause of the ubiquitous pollution we see in our environment. When plastics end up in the environment, most of this pollution can be attributed to a lack of infrastructure for appropriately collecting and recycling plastic waste, mainly due to mismanagement. Because of the huge production volumes of plastics, their merits of being cheap to produce and process and their recalcitrance have turned into a huge disadvantage, since plastic waste has become the end point of our linear economic usage model, and massive amounts have started to accumulate in the environment, leading to microplastics pollution and other detrimental effects. A possible solution to this is offered by "bioplastics", which are materials that are either (partly) biobased and/or degradable under defined conditions. With the rise of bioplastics in the marketplace, several standards and test protocols have been developed to assess, certify, and advertise their properties in this respect. This article summarizes and critically discusses different views on bioplastics, mainly related to the properties of biodegradability and biobased carbon content; this shall allow us to find a common ground for clearly addressing and categorizing bioplastic materials, which could become an essential building block in a circular economy. Today, bioplastics account for only 1-2% of all plastics, while technically, they could replace up to 90% of all fossil-based plastics, particularly in short-lived goods and packaging, the single most important area of use for conventional plastics. Their replacement potential not only applies to thermoplastics but also to thermosets and elastomers. Bioplastics can be recycled through different means, and they can be made from renewable sources, with (bio)degradability being an option for the mismanaged fraction and special applications with an intended end of life in nature (such as in seed coatings and bite protection for trees). Bioplastics can be used in composites and differ in their properties, similarly to conventional plastics. Clear definitions for "biobased" and "biodegradable" are needed to allow stakeholders of (bio)plastics to make fact-based decisions regarding material selection, application, and end-of-life options; the same level of clarity is needed for terms like "renewable carbon" and "bio-attributed" carbon, definitions of which are summarized and discussed in this paper.

Occurrence and correlation of microplastics and dibutyl phthalate in rivers from Pearl River Delta, China

Microplastics have been identified as the novel contaminants in various environments. Phthalates would be released from plasticized microplastics into a riverine environment while transporting to a marine region, but data on their relationship in rivers have been scarce. In this study, the occurrence, distribution and correlation of microplastics and dibutyl phthalate (DBP) in two rivers from the Pearl River Estuary were investigated. The elevated level of DBP in the Qianshan River (2.70 ± 0.20 μg/L) was in alignment with the presence of highest microplastic concentration at the same sampling site (15.8 ± 9.8 items/L). A positive correlation was observed between microplastics and DBP in all sampling sites (p < 0.05). The results showed that UV irradiation from sunlight was a majorly inducing factor of DBP leaching from polyethylene microplastics. The concentrations of chemical additives in some degrees reflect the microplastic pollution, but environmental factors and multidimensionality of microplastics such as residence times and types may cause spatial differences of chemical additives in aquatic systems.

Weathering alters the profile of trace metals and organic compounds in leachates and bioavailability extracts from microplastics of trail running shoes

Microplastics (MPs) from rubber outsoles of trail running shoes may contribute significantly to contamination in protected areas. In the natural environment, weathering processes can damage MP molecular structure and alter the mobility of inorganic and organic compounds used as additives in rubber. In this study, we characterised changes in the surface morphology, functional groups, and thermal stability of MPs weathered on and below the soil surface over 12 weeks, and analysed inorganic and organic additives in leachates (0.01M CaCl2) and bioaccessibility extracts (ethyl acetate). Weathering conditions included UVC irradiation at 25 °C and 80% soil moisture. Microplastics on the soil surface exhibited cracking, fragmentation, and increased extractability of zinc, sulphur, titanium and fatty acids. Microplastics below the soil surface were not significantly physically or chemically altered, however zinc leachability increased following extended weathering by up to 155%. Bioaccessibility of thiol, aromatic and cyclic organic additives decreased from both surface and sub-surface MPs over the 12 week weathering period, but there was evidence of an increase in transformation by-products. Microplastic toxicity may be significantly altered by environmental conditions and MP weathering. It is critical ecotoxicological studies use weathered MPs to assess impacts on rare and endemic species found in protected spaces.

Microplastics leachate may play a more important role than microplastics in inhibiting microalga Chlorella vulgaris growth at cellular and molecular levels

The leaching of microplastics (MPs) additives and their negative effects on aquatic organisms remain to be systematically elucidated. In this study, the toxicological effects of MPs leachate (micro-sized polyethylene (mPE) and micro-sized polyvinyl chloride (mPVC) acceleratedly leached by UVA for 15, 90, and 180 days in seawater) on microalga Chlorella vulgaris in terms of cell growth inhibition, oxidative stress, and transcriptomes were investigated. The leachate components of MPs aged for 90 days were further identified to elucidate the corresponding toxicity mechanisms of MPs on microalgal cells. The results revealed that both leachates of mPE and mPVC inhibited cell growth and increased oxidative stress in C. vulgaris, accompanied by a growth inhibition rate to microalgal cells of 4.0%-36.2% and 7.1%-48.2%, respectively. At the same mass concentration, the toxicological effects on C. vulgaris followed the order of mPVC leachate > mPE > mPE leachate > mPVC, whereas MPs leaching time indicated no change in MPs leaching toxicity. Furthermore, the gene functions of "translation, ribosomal structure and biogenesis" were mostly affected by MPs leachate. Compared to mPE leachate and pure MPs, the stronger inhibitory effects of mPVC leachate on microalgal cells may be attributed to the fact that more substances were leached from the polymer of mPVC, including Zn, farnesol isomer a, 2,6-di-tert-butyl-4-methylphenol, and acetyl castor oil methyl ester. In summary, this study provides a better understanding of the ecotoxicological influences of MPs and MPs leachate, and offers a warning on the ecological risk caused by plastic additives.

Microplastic pollution on hiking and running trails in Australian protected environments

Microplastics (MPs) are ubiquitous worldwide, present even in remote areas of the natural environment. Hiking and trail running are a source of MPs on recreational trails in protected environments, which are characterised by high biodiversity and natural, ecological or cultural significance. Our understanding of the risks of microplastic pollution is impeded however by a lack of information on MPs present in the soil environment in such areas. This study characterised the quantity and physicochemical characteristics of MPs in two conservation areas in south-eastern Australia: 1) the adjacent Duval Nature Reserve and Dumaresq Dam Reserve, and 2) the Washpool and Gibraltar Range National Parks. We measured atmospheric deposition over a six-month period in the Reserves, and baseline amounts of MPs on recreational trails in the Reserves and National Parks. Atmospheric deposition averaged 17.4 MPs m^-2 day^-1 and was dominated by fibres, comprising 84 % of MPs. Microplastics detected on trail surfaces ranged from 162.5 ± 41.6 MPs/linear metre to 168.7 ± 18.5 MPs/linear metre and exhibited a very wide range of physical and chemical characteristics. The majority of MPs on the trail surfaces comprised polyurethane, polyethylene terephthalate and polystyrene, and 47-71 % were fibres. Microplastics were attributed to clothing, footwear, litter, and diffuse sources. Minimising and preventing MP pollution, however, is complex given there are multiple direct and diffuse sources, and several factors influencing increased MP deposition and retention in the environment.

Formulation Controls the Potential Neuromuscular Toxicity of Polyethylene Photoproducts in Developing Zebrafish

Sunlight transforms plastic into water-soluble products, the potential toxicity of which remains unresolved, particularly for vertebrate animals. We evaluated acute toxicity and gene expression in developing zebrafish larvae after 5 days of exposure to photoproduced (P) and dark (D) leachates from additive-free polyethylene (PE) film and consumer-grade, additive-containing, conventional, and recycled PE bags. Using a "worst-case" scenario, with plastic concentrations exceeding those found in natural waters, we observed no acute toxicity. However, at the molecular level, RNA sequencing revealed differences in the number of differentially expressed genes (DEGs) for each leachate treatment: thousands of genes (5442 P, 577 D) for the additive-free film, tens of genes for the additive-containing conventional bag (14 P, 7 D), and none for the additive-containing recycled bag. Gene ontology enrichment analyses suggested that the additive-free PE leachates disrupted neuromuscular processes via biophysical signaling; this was most pronounced for the photoproduced leachates. We suggest that the fewer DEGs elicited by the leachates from conventional PE bags (and none from recycled bags) could be due to differences in photoproduced leachate composition caused by titanium dioxide-catalyzed reactions not present in the additive-free PE. This work demonstrates that the potential toxicity of plastic photoproducts can be product formulation-specific.

Trail running events contribute microplastic pollution to conservation and wilderness areas

Clothing and footwear designed for trail running shed microplastics (MPs) during use. Trail running events may therefore present a significant source of MP pollution in conservation and wilderness areas. Microplastics may present long-term risks to biodiversity and endemic plant and animal species in such areas. In this study, we used a before-after-control-impact approach to quantify and characterise MP emissions from clothing and shoe outsoles during trail running events. Microplastic deposition on trail surfaces was assessed using both a controlled study and during two public trail running events in New South Wales, Australia (the Duval Dam Buster and the Washpool World Heritage Trail Race). Microplastics were present on trails after all events and included fibres and rubber fragments. Microplastic counts varied considerably depending on trail surface hardness and gradient, and clothing and footwear properties. The controlled study showed running tights (leggings) and shoes with soft rubber outsoles produced more MPs than shirts and hard rubbers. In the trail running events, abrasive wear to shoe outsoles produced an average of 0.3 ± 0.1 to 0.9 ± 0.2 MPs/linear metre/runner, and clothing produced 0.7 ± 0.3 to 2.0 ± 0.3 fibres/linear metre/runner, with fibres accounting for 63-69% of MPs. Microplastic deposition from both footwear and clothing was higher on sloped and rock trail surfaces than flat and soil surfaces. Laser Direct Infrared (LDIR) Imaging indicated the main types of MPs present on trails were polyurethane, polyethylene terephthalate and polyamide. Trail running is increasing in popularity and large-scale events may cause a rapid and significant input of MPs in protected areas. Land managers, event coordinators and outdoor apparel manufacturers could mitigate MP impacts however, by diverting foot traffic around ecologically sensitive areas, capping participant numbers, and developing abrasion resistant clothing and footwear.

Toxic effects of pristine and aged polystyrene and their leachate on marine microalgae Skeletonema costatum

The acute toxic effects of pristine and aged polystyrene (P-PS and A-PS) and their leaching solutions (L-PS) on microalgae Skeletonema costatum were investigated by measuring algal density and growth inhibition rate (IR), chlorophyll concentration and photosynthetic efficiency (Fv/Fm) over 96 h. Total protein (TP), superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) were measured to analyze the oxidative damage to microalgae by microplastics and their leachates. Hydrodynamic diameter of microplastics in seawater, FITR and SEM images were used to study the changes of polystyrene during aging. The interaction of algae cell with microplastics and the cellular ultrastructure changes of cells were analyzed combined with electron microscopy for a comprehensive and systematic understanding on the mechanisms of microplastic toxicity to microalgae. Both high concentration and small size of PS had significant inhibitory effect on the growth of microalgae, and the inhibitory effect was greater with increasing exposure time. The inhibition effect of aged microplastics was more obvious, which was speculated to be caused by the synergistic effect of aged PS itself and leaching solution. The negative effect of leaching solution on microalgae was due to the release of some additives during the aging process. The content of MDA reached the highest value of 54.41 nmol/mgprot in 1.0 μm 50 mg/L A-PS treatment group, and A-PS were found to be more prone to heterogeneous aggregation with algae cells by SEM.

Soil microplastic characteristics and the effects on soil properties and biota: A systematic review and meta-analysis

The soil environment serves as an assembling area for microplastics, and is an important secondary source of microplastics in other environmental media. Recently, soil microplastics have been extensively studied; however, high variability is observed among the research results owing to different soil properties, and the complexity of soil microplastic composition. The present study amassed the findings of 2886 experimental groups, across 38 studies from 2016 to 2022, and used meta-analysis to quantitatively analyze the differences in the effects of microplastic exposure on soil physicochemical properties and biota. The results showed that among the existing soil microplastic research, agricultural soils maintained a higher environmental exposure distribution than other environments. Microplastic fibers and fragments were the predominant shapes, indicating that the extensive use of agricultural films are the primary influencing factor of soil microplastic pollution at present. The results of the meta-analysis found that microplastic exposure had a significant negative effect on soil bulk density (lnRR = -0.04) and aggregate stability (lnRR = -0.085), indicating that microplastics may damage the integrity of soil structure or damage the soil surface. The significant changes in plant root biomass and soil phosphatase further signified the potential impact of microplastics on soil nutrient and geochemical element cycling. We further constructed species sensitivity distribution curves, revealing that invertebrates had a higher species sensitivity to microplastics, as they can pass through the gut wall of soil nematodes, causing oxidative stress and affecting gene expression. In general, soil is an interconnected complex, and microplastic exposure can directly or indirectly interact with environmental chemical processes in the soil environment, potentially harming the soil ecosystem; however, current research remains insufficient with respect to breadth and depth in terms of the comprehensive "source-sink" mechanism of soil microplastics, the hazard of exposure, and the overall toxic effects.

Amine-modified nanoplastics promote the procoagulant activation of isolated human red blood cells and thrombus formation in rats

Background

Microplastics (MPs) and nanoplastics (NPs) formed from decomposed plastic are increasing environmental threats. Although MPs and NPs exposed through various routes enter the systemic circulation, the potential toxicity of those is largely unknown. We investigated whether polystyrene NPs (PS-NPs) promote the coagulation activity of red blood cells (RBCs).

Results

We tested several types of PS-NPs using human RBCs and found that amine-modified 100 nm PS-NPs were the most potent. We measured the uptake of PS-NPs using flow cytometry and confocal microscopy. Electron microscopy revealed morphological changes of RBCs by PS-NPs. PS-NPs induced the externalization of phosphatidylserine, generation of microvesicles in RBCs, and perturbations in the intracellular microenvironment. PS-NPs increased the activity of scramblases responsible for phospholipid translocation in RBCs. PS-NPs modulated the functional interaction to adjacent tissues and coagulation cascade, enhancing RBC adhesion and thrombin generation. Our observations in human RBCs were consistent with those in isolated rat RBCs, showing no inter-species differences. In rat venous thrombosis models, the intravenous administration of PS-NPs enhanced thrombus formation.

Conclusion

Amine-modified PS-NPs induce the prothrombotic activation of RBCs causing thrombus formation. We believe that our study will contribute to understanding the potential toxicity of amine-modified polystyrene particles in blood cells and cardiovascular systems.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12989-022-00500-y.

Toxicity assessment of tire particles released from personal mobilities (bicycles, cars, and electric scooters) on soil organisms

Tire particles are generated by the abrasion of tire treads on roads and are major contributors to microplastics in soil environments. Contamination by tire wear particles worsens annually as the use of personal mobilities increases. Tire particles (112-541 µm) were obtained from three types of personal mobility tires (bicycle, car, and electric scooter) and exposed to plants (Vigna radiata) and springtails (Folsomia candida) for 28 d to assess the toxicity of each tire-particle type. The laboratory-generated tire particles exhibit adverse effects depending on the origin of the tire or test species. Particles from bicycle or electric-scooter tires changed the soil's bulk density and water holding capacity and adversely affected plant growth. Car tire particles had leached various organic compounds and induced detrimental effects on springtails (adult and offspring growth). We concluded that laboratory-generated tire particles (frow new tires) can affect the soil environment by changing soil properties and leaching chemicals; thus, causing adverse effects on soil organisms. Since this study found tire particle toxicity on soil organisms, it would be possible to compare the various contamination levels in areas near road soil and other clean soils.

Microplastics from shoe sole fragments cause oxidative stress in a plant (Vigna radiata) and impair soil environment

Shoe sole fragments are generated by sole abrasion, which is unavoidable. These fragments can enter the soil ecosystem. However, limited studies have evaluated their effects on soils and plants. Here, we aimed to evaluate the toxicity of shoe sole fragments on a crop plant, Vigna radiata (mung bean). Shoe sole fragments (size: 57-229 µm) were obtained from four shoe types (trekking shoes, slippers, sneakers, and running shoes) and plant toxicity assessments were performed. Additionally, the fragments were leached for 30 d, and potentially toxic leachates were identified. Shoe sole fragments exhibited adverse effects depending on the shoe type. The fragments of soles from sneakers increased the bulk density of the soil but reduced its water holding capacity. Moreover, the microplastic fragments and leachates directly affected plant growth and photosynthetic activities. The fragments of slippers and running shoes boosted plant growth but changed the flavonoid content and photosynthetic factors. Trekking shoe sole fragments did not exhibit plant photoinhibition; however, their leachate inhibited photosynthesis. Overall, it was concluded that shoe sole fragments can cause adverse effects in plants and impair soil environment. Our study findings indicate that it is necessary to develop shoe soles that have less harmful environmental effects.