Plastic Bag Derived-Microplastics as a Vector for Metal Exposure in Terrestrial Invertebrates

Diet preference of zebrafish (Danio rerio) for bio-based polylactic acid microplastics and induced intestinal damage and microbiota dysbiosis

The ingestion of petroleum-based microplastics (MPs) by aquatic animals and their toxicological effects are of wide concern. However, the ecological risks of bio-based MPs to aquatic animals remain largely unknown. In the present study, zebrafish (Danio rerio) were exposed to MPs of polylactic acid (PLA), the most widely used bio-based plastic, and polyethylene terephthalate (PET), a high-production volume petroleum-based plastic. PLA MPs were more actively ingested by fish than PET MPs. The abundance of PLA MPs in fish intestines was approximately 170 times greater than that of PET MPs after one day of exposure. The ingestion of PLA MPs caused gastrointestinal damage in zebrafish. In addition, the ingestion of PLA MPs induced specific changes in the diversity of intestinal microbiota and promoted species closely linked with energy metabolism, cellular processes, and fish diseases. This might have been related to the depolymerization of PLA in the digestive tract, which decreased the intestinal pH and changed the carbon source structure. Overall, bio-based MPs may have different ecological effects on aquatic animals than traditional petroleum-based MPs.

Polyvinylchloride and polypropylene as adsorbents of the pesticide monocrotophos enhance oxidative stress in Eudrillus eugeniae (Kinberg)

The use of plastics has increased significantly with consequent rise in the generation of wastes. Microplastics (MPs) with particle size <5 mm are produced in natural terrestrial habitats by weathering of the discarded plastic debris and therefore are likely to impact soil biota. Earthworms are the dominant soil fauna which play vital role in soil formation and decomposition of organics. Since these animals are soil feeders, MP particles contaminating soil are likely to enter in to the gut of these animals affecting their physiology. MPs have been shown to be potent adsorbents of various other pollutants such as heavy metals and agrochemicals. This study reports the effects of two MPs, polyvinyl chloride (PVC) and polypropylene (PP) alone and in combination with the pesticide monocrotophos in soil on tissue protein, lipid peroxidation (LPX), activities of lactate dehydrogenase (LDH) and catalase (CAT) of an epigeic earthworm Eudrillus eugeniae over an exposure period of 48h. Results from molecular docking and laboratory experiment confirmed that both the MPs are potent adsorbents of the pesticide and enhanced oxidative stress on the animal with significant reduction in protein, increased LPX level and enzyme activities. PP indicated significantly higher pesticide adsorption relative to PVC.

Two types of microplastics (polystyrene-HBCD and car tire abrasion) affect oxidative stress-related biomarkers in earthworm Eisenia andrei in a time-dependent manner

Microplastics are small plastic fragments that are widely distributed in marine and terrestrial environments. While the soil ecosystem represents a large reservoir for plastic, research so far has focused mainly on the impact on aquatic ecosystems and there is a lack of information on the potentially adverse effects of microplastics on soil biota. Earthworms are key organisms of the soil ecosystem and are due to their crucial role in soil quality and fertility a suitable and popular model organism in soil ecotoxicology. Therefore, the aim of this study was to gain insight into the effects of environmentally relevant concentrations of microplastics on the earthworm Eisenia andrei on multiple levels of biological organization after different exposure periods. Earthworms were exposed to two types of microplastics: (1) polystyrene-HBCD and (2) car tire abrasion in natural soil for 2, 7, 14 and 28d. Acute and chronic toxicity and all subcellular investigations were conducted for all exposure times, avoidance behavior assessed after 48 h and reproduction after 28d. Subcellular endpoints included enzymatic biomarker responses, namely, carboxylesterase, glutathione peroxidase, acetylcholinesterase, glutathione reductase, glutathione S-transferase and catalase activities, as well as fluorescence-based measurements of oxidative stress-related markers and multixenobiotic resistance activity. Multiple biomarkers showed significant changes in activity, but a recovery of most enzymatic activities could be observed after 28d. Overall, only minor effects could be observed on a subcellular level, showing that in this exposure scenario with environmentally relevant concentrations based on German pollution levels the threat to soil biota is minimal. However, in areas with higher concentrations of microplastics in the environment, these results can be interpreted as an early warning signal for more adverse effects. In conclusion, these findings provide new insights regarding the ecotoxicological effects of environmentally relevant concentrations of microplastics on soil organisms.

A review of microplastic fibres: generation, transport, and vectors for metal(loid)s in terrestrial environments

The laundering of synthetic fabrics has been identified as an important and diffuse source of microplastic (<5 mm) fibre contamination to wastewater systems. Home laundering can release up to 13 million fibres per kg of fabric, which end up in wastewater treatment plants. During treatment, 72-99% of microplastics are retained in the residual sewage sludge, which can contain upwards of 56 000 microplastics per kg. Sewage sludge is commonly disposed of by application to agricultural land as a soil amendment. In some European countries, application rates are up to 91%, representing an important pathway for microplastics to enter the terrestrial environment, which urgently requires quantification. Sewage sludge also often contains elevated concentrations of metals and metalloids, and some studies have quantified metal(loid) sorption onto various microplastics. The sorption of metals and metalloids is strongly influenced by the chemical properties of the sorbate, the solution chemistry, and the physicochemical properties of the microplastics themselves. Plastic-water partition coefficients for the sorption of cadmium, mercury and lead onto microplastics are up to 8, 32, and 217 mL g^-1 respectively. Sorptive capacities of microplastics may increase over time, due to environmental degradation processes increasing the specific surface area and surface density of oxygen-containing functional groups. A range of metal(loid)s, including cadmium, chromium, and zinc, have been shown to readily desorb from microplastics under acidic conditions. Sorbed metal(loid)s may therefore become more bioavailable to soil organisms when the microplastics are ingested, due to the acidic gut conditions facilitating desorption. Polyester (polyethylene terephthalate) should be of particular focus for future research, as few quantitative sorption studies currently exist, it is potentially overlooked from density separation studies due to its high density, and it is by far the most widely used fibre in apparel textiles production.

Distinct lipid membrane interaction and uptake of differentially charged nanoplastics in bacteria

Background

Nanoplastics have been recently found widely distributed in our natural environment where ubiquitously bacteria are major participants in various material cycles. Understanding how nanoplastics interact with bacterial cell membrane is critical to grasp their uptake processes as well as to analyze their associated risks in ecosystems and human microflora. However, little is known about the detailed interaction of differentially charged nanoplastics with bacteria. The present work experimentally and theoretically demonstrated that nanoplastics enter into bacteria depending on the surface charges and cell envelope structural features, and proved the shielding role of membrane lipids against nanoplastics.

Results

Positively charged polystyrene nanoplastics (PS-NH₂, 80 nm) can efficiently translocate across cell membranes, while negatively charged PS (PS-COOH) and neutral PS show almost no or much less efficacy in translocation. Molecular dynamics simulations revealed that the PS-NH₂ displayed more favourable electrostatic interactions with bacterial membranes and was subjected to internalisation through membrane penetration. The positively charged nanoplastics destroy cell envelope of Gram-positive B. subtilis by forming membrane pore, while enter into the Gram-negative E. coli with a relatively intact envelope. The accumulated positively charged nanoplastics conveyed more cell stress by inducing a higher level of reactive oxygen species (ROS). However, the subsequently released membrane lipid-coated nanoplastics were nearly nontoxic to cells, and like wise, stealthy bacteria wrapped up with artifical lipid layers became less sensitive to the positively charged nanoplastics, thereby illustrating that the membrane lipid can shield the strong interaction between the positively charged nanoplastics and cells.

Conclusions

Our findings elucidated the molecular mechanism of nanoplastics’ interaction and accumulation within bacteria, and implied the shielding and internalization effect of membrane lipid on toxic nanoplastics could promote bacteria for potential plastic bioremediation.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01321-z.

Microplastics in plant-microbes-soil system: A review on recent studies

Microplastics (MPs) and nanoplastics (NPs) have been widely studied, mostly focusing on the methods of separation, detection, and adsorption or the ecological effects in aquatic ecosystems. When different sources and types of MPs/NPs enter the soil, they can affect the biogeochemical cycle in terms of the direct impacts on soil physicochemical properties and soil organisms, and the indirect impact on soil biota through changes in soil material cycling. To date, a few studies have focused on the effects of MPs/NPs on soil ecosystems, including soil properties, microbial communities, soil fauna, and plants, as well as the potential or affirmed correlations among them. In this review, we summarized the recent literature on soil MPs/NPs focusing on their types, sources, separation, and ecological impacts on soil properties, microbes, and plants. We attempted to establish an overall relationship between MPs/NPs and soil plant system. Based on existing studies, we also highlight the research gaps and propose several directions for future studies.

Review of Current Issues and Management Strategies of Microplastics in Groundwater Environments

Microplastic contamination has become widespread in natural ecosystems around the globe as a result of the tremendous rise in plastic production over the last 70 years. However, microplastic pollution in marine and riverine habitats has received more attention than that of terrestrial environments or even groundwater. This manuscript reviews the current issues, potential occurrences, and sources of the emerging problem of microplastic contamination in groundwater systems. The most prevalent types of plastic detected in groundwater are polyethylene and polyethylene terephthalate, and fibers and fragments represent the most commonly found shapes. The vertical transportation of microplastics in agricultural soils can affect groundwater aquifer systems, which is detrimental to those who use groundwater for drinking as well as to microorganisms present in the aquifers. Moreover, this review sheds light on the interlinkage between sustainable development goals and groundwater microplastic contamination issues as part of the strategies for the management of microplastic contamination in groundwater. Overall, this review reveals a lack of interest and a gap in knowledge regarding groundwater microplastic pollution and highlights future perspectives for research in this area.

Dietary exposure of copper and zinc oxides nanoparticles affect the fitness, enzyme activity, and microbial community of the model insect, silkworm Bombyx mori

Copper and Zinc oxides nanoparticles (CuO and ZnO NPs, respectively) are among the most produced and commonly used engineered nanomaterials. They can be released into the environment, thereby causing health concerns and risks to biodiversity that indicate a need to evaluate their toxicological effects in a complex situation. Here, we used the insect model organism silkworm Bombyx mori to address the concerns about the biological effects associated with dietary exposure of CuO and ZnO NPs. ICP-MS analysis revealed significant accumulation of Cu and Zn (the latter being more accumulated) in silkworms' tissues (gut, fat body, silk gland, and malpighian tubule), and some elimination through feces in the respective NPs-exposed groups. NPs-exposures led to a decrease in larval body mass, survivorship, and cocoon production, where the effects of ZnO NPs were more pronounced. We also found that NPs-exposure induced gene expression changes (Attacin, lysozyme, SOD, and Dronc) and altered the activities of antioxidant enzymes (SOD, GST, and CAT), as well as impaired nutrient metabolism (alpha-amylase). Given their antibacterial property, CuO and ZnO NPs decreased species richness and diversity of the gut bacterial community and shifted their configuration to overt microbiome i.e., decreased abundance of probiotics (e.g., Acetobacter) and increased pathobionts (e.g., Pseudomonas, Bacillus, Escherichia, Enterococcus, Ralstonia, etc.) proportions. Overall, this integrated study revealed the unintended negative effects of CuO and ZnO NPs on silkworms and highlighted the potential to inevitably affect all living things due to intensive and possible mishandling of nanomaterials.

Co-exposure of polystyrene microplastics and iron aggravates cognitive decline in aging mice via ferroptosis induction

The objective of this study was to investigate the effects of co-exposure of iron and microplastics (MPs) on the cognitive function of aged humans and animals. It was already known that individual iron or MPs exposure can initiate potential neurotoxicity. However, the combined effect of MPs and iron remained to be elucidated. In this study, the toxicity of iron, MPs, co-treatment of MPs & iron, and the underlying mechanisms were evaluated in vivo. Our findings suggest that 5 µm MPs could enter the aging mice brain and accumulate in cortex and hippocampus. In addition, MPs and iron have a good binding ability, therefore, co-exposure of MPs & iron cause significant iron overload and cognitive deficits as compared to control and individual treatments of iron and MPs. Moreover, the lipid peroxidation and inflammation, which are involved in ferroptosis, get significantly elevated by co-exposure of iron and MPs. Taken together, our results provide compelling evidence that co-exposure of iron and MPs could aggravate the cognitive impairment via disturbing brain iron homeostasis and inducing ferroptosis in cognitive-related brain areas, what's more, the results warn that MPs may act as vectors of pollutants (mostly heavy metals) increasing the health burden on body.

Influence of Different Microplastic Forms on pH and Mobility of Cu2+ and Pb2+ in Soil

Microplastics, due to their surface properties, porosity and electrostatic interactions have a high affinity for cations sorption from the aqueous phase. As soil is a complex matrix, interactions between microplastics, soil constituents and heavy metals (HM) may modify the soil microenvironment for heavy metal mobilization/immobilization processes. In order to better understand the problem, three commonly found forms of microplastics in soil (fibers, fragments and microbeads) were mixed with Cu²⁺- or Pb²⁺-contaminated soil and incubated at 22 °C for 180 days. In soil samples pH and the content of water and acid exchangeable species of metals were analyzed. The results of this study showed that the presence of microplastics in HM-contaminated soil affected metal speciation, increasing the amount of easily exchangeable and potentially bioavailable forms of Cu²⁺ or Pb²⁺ in the tested soil. Soil pH also increased, confirming that microplastic particles affect soil properties relevant to the sorption/desorption process of metal cations. Overall, the smallest microplastic particles (≤1 mm), such as fibers or glitter microbeads, had a greater impact on the change in the sorption and desorption conditions of metals in tested soil than larger particles. The findings of our study show that microplastic form, shape and size should be considered as important factors that influence the soil properties and mobility of heavy metals in soil.

Seasonal variations and feedback from microplastics and cadmium on soil organisms in agricultural fields

Plastic film mulching is an important agricultural technology that plays a critical role in increasing crop yield and maintaining soil moisture. However, long-term coverage and untimely recovery lead to a large amount of plastic residues in soils. This decomposes into smaller plastics over time, which can reduce sowing quality, destroy the soil structure, and have adverse effects on soil organisms. In this study, the seasonal variations and correlations of microplastics and cadmium (Cd) in Wuxi farmland soils of Taihu Lake, China, were investigated in the spring and winter. The microplastics were mainly in the form of films, fibers, and debris and were mainly transparent and black in color. Microplastic abundance reached 890 particles/kg soil, with the majority of microplastics (>72.5%) being 0-500 μm. Polyethylene microplastics were the main polymers, accounting for >54.65%. In addition, the abundance of soil microplastics in the winter was significantly correlated with Cd, indicating that microplastics and heavy metals present a risk of coexposure to soil organisms. Furthermore, the response of in situ earthworms to microplastic-Cd pollution revealed that microplastics can be used as a vector to transfer heavy metals in the soil environment and may accumulate in the bodies of soil organisms. Multiomics techniques demonstrated bacterial community structure dysbiosis and metabolic changes of in situ earthworms under microplastic heavy metal-contaminated soils. The abundance of microplastics in earthworm casts and intestines was higher than that in the soil samples. These results reveal the potential risks from microplastics entering the soil environment and heavy metal pollution in soil ecosystems.

Differences in sensitivity of human lymphocytes and fish lymphocytes to polyvinyl chloride microplastic toxicity

Polyvinyl chloride (PVC) microplastics are emerging contaminants affecting biological wastewater treatment processes. So far, the toxicological investigation of PVC microplastics usually focused on the anaerobic and denitrifying bacteria. It seems that the primary lymphocytes isolated from peripheral blood are more sensitive than most other organ cell types in vitro; therefore, the aim of this study was to assess the cytotoxicity of PVC microplastic on human and fish blood lymphocytes as a useful ex vivo model for accelerated human toxicity studies. Using biochemical analyses, we showed human lymphocytes are more sensitive to toxic effects of PVC microplastic than fish lymphocytes. Our result showed that addition of PVC microplastic at 24, 48, and 96 μ g/ml for 3 h to human blood lymphocytes induced cytotoxicity. The PVC microplastic-induced cytotoxicity on human blood lymphocytes was associated with intracellular reactive oxygen species (ROS) formation, lysosomal membrane injury, mitochondrial membrane potential (MMP) collapse, depletion of glutathione, and lipid peroxidation. According to our results, PVC microplastic particles induce oxidative stress and organelle damage in human lymphocytes, while these significant alterations in toxicity parameters in PVC microplastic-treated fish lymphocytes were not observed. Finally, our findings suggest that human lymphocytes are more sensitive to PVC microplastic toxicity compared with fish lymphocytes.

Interactive effects of environmental microplastics and 2,4-dichlorophenoxyacetic acid (2,4-D) on the earthworm Eisenia andrei

Given the wide use of plastic and pesticides in agriculture, microplastics (MP) and the herbicide 2,4 dichloro-phenoxy-acetic acid (2-4-D) can be present simultaneously in soil. Nevertheless, little is known about their combined toxicity. In this study, Eisenia andrei was exposed to environmental MP (100 µg kg^-1 soil) and 2,4-D (7 mg kg^-1 soil) for 7 and 14 days. Bioaccumulation, genotoxicity, oxidative stress and gene expression level were assessed. Results revealed that MP increased 2,4-D bioaccumulation in earthworms. Simultaneous exposure to both these pollutants caused a significant reduction in lysosomal membrane stability (LMS) and an increase in micronuclei (MNi) frequency. Biochemical analysis revealed oxidative alterations in earthworms exposed to all treatments; being very pronounced in earthworms exposed to the mixture in terms of increase in glutathione-S-Transferase (GST), catalase (CAT) and malondialdehydes accumulation (MDA). Furthermore, an up-regulation in cat and gst expression level was recorded in worms exposed to single or mixture treatment, except MP in case of gst. Our data highlight the toxicity of the combined exposure to MP and 2,4-D and afford new insights into the potential ecological risks posed by MP in terrestrial ecosystems.

Microplastics change soil properties, heavy metal availability and bacterial community in a Pb-Zn-contaminated soil

Microplastics (MPs) co-occur widely with diverse contaminants in soils. However, few data are available on their impacts on soil chemical and microbial properties of heavy metal-contaminated soils. For the first time, we investigated the changes in chemical and microbial properties of a Pb-Zn-contaminated soil as induced by six different MPs, including polyethylene (PE), polystyrene (PS), polyamide (PA), polylactic acid (PLA), polybutylene succinate (PBS), and polyhydroxybutyrate (PHB), at two doses (0.2% and 2%, w/w). After 120 days of soil incubation, significant changes were observed in soil pH, dissolved organic carbon (DOC), NH₄⁺-N, NO₃^--N, available P, the availability of Zn and Pb, and the activities of soil enzymes. Overall, MPs especially at the dose of 2% decreased the richness and diversity of bacterial communities and altered microbial community composition, causing special enrichments of specific taxa. MPs increased predicted functional genes involved in xenobiotics biodegradation and metabolism. Generally, impacts were dependent on MPs' type and dose. Changes in soil properties and heavy metal availability had significant correlations with bacterial community diversity and composition. Our findings imply that MPs co-occurring with heavy metals may change metal mobility, soil fertility, and microbial diversity and functions, thus causing a potential threat to soil ecosystem multifunctionality.

Speciation and release risk of heavy metals bonded on simulated naturally-aged microplastics prepared from artificially broken macroplastics

The negative impact of microplastics (MPs) act as metals vectors to environment and ecosystem have been paid more and more attention, and the accumulation risk of them to human body through the food chains and food webs needs to attract attention. In addition, the MPs bonded with heavy metals transport from river into the sea with high salinity may also have metals release risk. Herein, natural aged microplastics prepared from artificially broken macroplastics adsorbed with heavy metals accumulated from the natural environment were tested for their states and release risk in several simulated solution (NaCl and gastrointestinal solutions) to understand their effects on environment and human health. The adsorption capacity of different heavy metals on MPs was different during natural aging process proved by four-acid digestion method. Metals with high accumulation (including Pb, As, Cr, Mn, Ni, Zn, Co, Cu and Cd) on NAMPs were selected for further study. Results obtained via three-step extraction method showed that these heavy metals were mainly present as acid-extractable and reducible ions, which were characterized by high bioavailability. Release experiments suggested the notable Mn, Zn, As, Cr, Cu and Ni release in NaCl solution, and significant release of Mn, Zn, As, Cr, Cu, Pb and Ni in gastrointestinal solutions. The high metal release ratio in the simulated gastric solution was attributed to the weak binding of metal ions to NAMPs in acidic environment. This study will play a vital rule in assessing the ecological risks associated with MPs in natural environment.

A critical review of microplastics in the soil-plant system: Distribution, uptake, phytotoxicity and prevention

Microplastics (MPs) are creating an emerging threat on the soil ecosystems and are of great global concern. However, the distribution in soil-plant system, as well as the phytotoxicity and impact mechanisms of MPs remain largely unexplored so far. This study introduced the diverse sources of MPs and showed the significant spatial variation in the global geographic distribution of MPs contamination based on data collected from 116 studies (1003 sampling sites). We systematically discussed MPs phytotoxicity, such as plant uptake and migration to stems and leaves, delaying seed germination, impeding plant growth, inhibiting photosynthesis, interfering with nutrient metabolism, causing oxidative damage, and producing genotoxicity. We further highlighted the alterations of soil structure and function by MPs, as well as their self and load toxicity, as potential mechanisms that threaten plants. Finally, this paper provided several preventive strategies to mitigate soil MPs pollution and presented research gaps in the biogeochemical behavior of MPs in soil-plant systems. Meanwhile, we recommended that methods for the quantitative detection of MPs accumulated in plant tissues should be explored and established as soon as possible. This review will improve the understanding of the environmental behavior of MPs in soil-plant systems and provide a theoretical reference to better assess the ecological risk of MPs.

Effects of microplastics on soil properties: Current knowledge and future perspectives

Microplastics (MPs) are a type of emerging contaminants that pose a potential threat to global terrestrial ecosystems, including agroecosystems. In recent years, MPs in soil and their adverse effects on soil health and fertility have attracted increasing concern. Based on the current knowledge, this review begins with a summary of the occurrence and characteristics of MPs in various soil environments, and then highlights the impacts of MPs on soil physical, chemical, and microbiological properties. Data show that MPs occur widely in all surveyed soil types, such as agricultural soils, industrial soils, urban soils, and unused soils, but show variation in their abundance, type, shape, and size. In most cases, MPs can change soil physical, chemical, and microbiological properties, but the effects vary, and are dependent on polymer type, shape, dose, and size. MPs-induced changes in soil fertility and the availability of pollutants may pose a potential threat to plant performance and crop productivity and safety. Particularly, MPs influence the emission of greenhouse gases from soil, ultimately leading to uncertain consequences for global climate change. More comprehensive and in-depth studies are required to fill large knowledge gaps.

Seeking for a perfect (non-spherical) microplastic particle - The most comprehensive review on microplastic laboratory research

In recent decades, much attention has been paid to microplastic pollution, and research on microplastics has begun to grow exponentially. However, microplastics research still suffers from the lack of standardized protocols and methods for investigation of microplastics under laboratory conditions. Therefore, in this review, we summarize and critically discuss the results of 715 laboratory studies published on microplastics in the last five years to provide recommendations for future laboratory research. Analysis of the data revealed that the majority of microplastic particles used in laboratory studies are manufactured spheres of polystyrene ranging in size from 1 to 50 µm, that half of the studies did not characterize the particles used, and that a minority of studies used aged particles, investigated leaching of chemicals from microplastics, or used natural particles as a control. There is a large discrepancy between microplastics used in laboratory research and those found in the environment, and many laboratory studies suffer from a lack of environmental relevance and provide incomplete information on the microplastics used. We have summarized and discussed these issues and provided recommendations for future laboratory research on microplastics focusing on (i) microplastic selection, (ii) microplastic characterization, and (iii) test design of laboratory research on microplastics.

Microplastic pollution on the soil and its consequences on the nitrogen cycle: a review

Microplastics (MPs) correspond to plastics between 0.1 μm and 5 mm in diameter, and these can be intentionally manufactured to be microscopic or generated from the fragmentation of larger plastics. Currently, MP contamination is a complicated subject due to its accumulation in the environment. They are a novel surface and a source of nutrients in soils because MPs can serve as a substrate for the colonization of microorganisms. Its presence in soil triggers physical (stability of aggregates, soil bulk density, and water dynamics), chemical (nutrients availability, organic matter, and pH), and biological changes (microbial activity and soil fauna). All these changes alter organic matter degradation and biogeochemical cycles such as the nitrogen (N) cycle, which is a key predictor of ecological stability and management in the terrestrial ecosystem. This review aims to explore how MPs affect the N cycle in the soil, the techniques to detect it in soil, and their effects on the physicochemical and biological parameters, emphasizing the impact on the main bacterial groups, genes, and enzymes associated with the different stages of the N cycle.

The phytotoxicity of microplastics to the photosynthetic performance and transcriptome profiling of Nicotiana tabacum seedlings

Microplastics (MPs), as emerging "new generation" organic contaminants, have attracted extensive attention regarding their severe toxicity to aquatic and terrestrial organisms. However, the responses of plant photosynthesis to soil MP pollution are unclear. In this study, Nicotiana tabacum seedlings were grown in soils containing 0~1000 g·kg-1 polyethylene (PE)-MPs for 48 days. PE-MPs significantly increased the superoxide anion content by 15.3~44.8% but decreased the chlorophyll content and Rubisco activity by 4.3~14.0% and 4.23~30.9%, respectively. PE-MPs also inhibited RuBP carboxylation activation and regeneration, restrained light use efficiency, and prevented dark respiration, thereby reducing the light-saturated photosynthesis rate. The changed shape of OJIP transients indicated that PE-MP toxicity inhibited not only the primary photochemistry rate but also photoelectrochemical quenching, resulting in decreased quantum yields. RNA-Seq revealed thousands of differentially expressed genes (DEGs), among which 79 highly expressed DEGs were enriched in photosynthesis-related processes. Functional annotation revealed that the reduction in environment stress was mainly due to the repressed expression of light harvesting-, electron transport- and photosystem-related genes in chloroplasts. This study regarding the physiological and molecular responses of photosynthetic performance to soil PE-MP pollution provides a new viewpoint for exploring the plant photosynthesis regulating and protective mechanisms under soil MP stresses.

Microplastics reduce the bioaccumulation and oxidative stress damage of triazole fungicides in fish

Microplastics (MPs) and pesticides are typical representatives of harmful chemicals in polluted waters. It is understood that the combined toxicity may differ from that of a single toxic substance. Although their combined toxicities on aquatic organisms have practical significance and research value, they have received little attention due to their complicated interaction, and the mechanism has rarely been reported. In this paper, we designed a study to investigate the single and combined effects of polystyrene microplastics (PS-MPs) and the triazole fungicide difenoconazole on zebrafish, and to explore the mechanism of this effect. The results showed that PS-MPs could reduce the bioaccumulation of difenoconazole in zebrafish to a certain extent and alleviate the oxidative stress damage of difenoconazole in the zebrafish liver. The transcriptome and qRT-PCR data revealed the association of multiple pathways in the difenoconazole response, while the presence of PS-MPs ameliorated this effect in gene expression changes. Due to the properties of PS-MPs and the interaction between them, the toxic effect of difenoconazole when combined with PS-MPs is more prominent. These results provide a novel aspect to understand the environmental behavior of MPs and to evaluate the combined effect of MPs and pesticides on aquatic food.

Photo-transformation of microplastics and its toxicity to Caco-2 cells

In recent years, microplastics (MPs) pollution, as a global environmental problem, has been widely concerned by countries all over the world. However, the research on the impact of MPs on human health is still limited. In this study, we studied the photo-transformation behavior of polystyrene microplastics (PS-MPs) under ultraviolet light and its toxicity to Caco-2 cells. Our results showed that the surface of PS-MPs was roughened by light, and cracks and pits appeared. UV-vis spectra showed that the opening of phenyl ring and the formation of carbonyl group might exist in this process. Based on FTIR and 2D-COS analysis, we observed the formation of carbonyl group and hydroxyl group, and preliminarily determined that the order of photo-transformation of PS-MPs was 698 (CH) > 752 (CH) > 1030 (CO) > 3645 (OH/OOH) > 1740 (CO). XPS showed that the photo-transformation of PS-MPs was a process in which carbon-containing functional groups were gradually partially transformed into oxygen-containing functional groups. Finally, the toxicity results showed that with the increase of PS-MPs concentration and the extension of light irradiation time, the survival rate of Caco-2 cells gradually decreased and the integrity of cell membrane was destroyed. The increased cytotoxicity can be explained at least in part by the fact that the toxicity of oxygen-containing functional groups is greater than that of carbon-containing functional groups, but how these functional groups affect the cytotoxicity of cells still needs sustained research in the future. This study can provide new insights for understanding the environmental behavior and ecological effects of PS-MPs in the environment.

Investigating impact of physicochemical properties of microplastics on human health: A short bibliometric analysis and review

Microplastics (MPs) are contaminants of emerging concern that attracted the attention of researchers over the last decade. They can occur in saliva and stool, and on scalp hair together with skin. Further, MPs can end up in the human diet through seafood, honey, salt, and mineral water. They can be taken up into the plants' roots and lead to the occurrence of MPs in fruits and vegetables. Concentration of the airborne MPs was also reported in the environment. These pieces of evidence clarify that introduction of MPs to the human body through ingestion and inhalation routes should not be overlooked. Following oral exposure to MPs, hazardous chemicals can be released in the gastrointestinal tract leading to toxicity. Inhalation route deserves more attention due to the oxidative potential of the inhaled plastic particles. Although the major characteristics of MPs are being investigated, there are currently few regulations to control concentration of MPs in the environment and their human health impacts remained unclear indicating the need for further investigation. For instance, it is not clear if the present air quality limits for PM_2.5 and PM₁₀ can be used for the areas with high suspended plastic particles. Without comprehensive knowledge about the retention and egestion rates of field populations, it is difficult to deduce the ecological and human health consequences. In general, more information about MP contamination in various species and the consequences of MP uptake and retention is required to gain a better idea of MPs in the food web and their environmental fate. The finer details on the MP translocation between tissues and the fate of the small plastic particles might be obtained when considering the existing information about the application of MPs in the pharmaceutical industry. In this review article, we presented a short bibliometric analysis and investigated the link between physicochemical properties of MPs and human health.

Microplastics pollution in the soils of various land-use types along Sheshui River basin of Central China

Very little information is now available about the occurrence of microplastics in the soils of various land-use types. In this study, 18 sampling sites with two soil layers were investigated for four different land-use types (grassland, dry land, paddy field, and plastic greenhouses) in Sheshui River basin of central China. The results demonstrated that the total abundance of microplastics in all sites lied within the range of 875 ± 229-6075 ± 865 n kg^-1, and had an average value of 2522 ± 1276 n kg^-1 ('n' being the number of microplastics). The abundance of microplastics in dry land had the highest value, whereas the greenhouse had the lowest value. There were no significant differences in the number of microplastics among the four land-use types. Except for four sites, no significant difference was observed in the abundance of microplastics between 0-10 cm and 10-20 cm layers. Fiber and fragment were the leading shapes of the microplastics along with brown color and the size of less than 1 mm. Combined with the site survey, the potential sources of microplastics in the studied region were mainly the wastewater irrigation, application of organic fertilizer, and plastic mulching film. Multivariate analysis and principal component analysis demonstrated that the carbon and nitrogen in soil samples were positively correlated with the abundance of microplastics, whereas a significantly negative correlation was observed between the soil δ¹³C and the abundance of microplastics. It was inferred that the transformation and degradation of aging microplastics were primarily associated with the turnover of soil's carbon and nitrogen. The results of the current study contribute towards an in-depth understanding of the level of microplastics pollution for various land-use types and corresponding policy-making regarding the management of microplastics.

Impact of microplastics on bioaccumulation of heavy metals in rape (Brassica napus L.)

Microplastics have become a global environmental problem due to the ubiquitous existence. The impacts of microplastics on heavy metals behaviors in aquatic environment are widely investigated, however, the impacts of microplastics on bioaccumulation of heavy metals in vegetables in terrestrial environment are seldom investigated. Herein, batch experiments were carried out, the microplastics (0.001%, 0.01%, 0.1%) and heavy metal (50, 100 mg/kg Cu²⁺ or 25, 50 mg/kg Pb²⁺) were single or combined spiked into soil to cultivate rapes (Brassica napus L.) in greenhouse. Copper and lead contents of rapes in MP0.1+Cu100 and MP0.1+Pb50 treatments reached 38.9 mg/kg and 9.4 mg/kg, which were significantly (p < 0.05) higher than those of Cu100 (35.3 mg/kg) and Pb50 (8.7 mg/kg) treatments, respectively. Results showed that microplastics in soil would facilitate heavy metals entering rape plants. In addition, contents of total chlorophyll, soluble sugar, vitamin C, malondialdehyde contents, activities of superoxide dismutase and guaiacol peroxidase, as well as related gene expression were analyzed to investigate the toxic effects of these pollutants (microplastics, Cu, and Pb) to rape plants. Malondialdehyde contents of rapes in MP0.1+Cu50, MP0.1+Cu100, MP0.1+Pb25, and MP0.1+Pb50 treatments reached 0.102 mmol/mg Protein, 0.123 mmol/mg Protein, 0.101 mmol/mg Protein, and 0.119 mmol/mg Protein, which were 1.42, 1.37, 1.46, and 1.45 times of those in Cu50, Cu100, Pb25, and Pb50 treatments, respectively. The changes of malondialdehyde content, activities of superoxide dismutase and guaiacol peroxidase, as well as contents of sugar and vitamin C indicated that microplastics in soil would bring severer damage and deteriorate quality of rape plants. The data in this study indicated that microplastics would increase the bioaccumulation of heavy metals in vegetables and damage to vegetables.

Micro/nano-plastics occurrence, identification, risk analysis and mitigation: challenges and perspectives

Micro/nanoplastics (MP/NPs) are emerging global pollutants that garnered enormous attention due to their potential threat to the ecosystem in virtue of their persistence and accumulation. Notably, United Nations Environment Programme (UNEP) yearbook in 2014 proposed MPs as one among ten emergent issues that the Earth is facing today. MP/NPs can be found in most regularly used products (primary microplastics) or formed by the fragmentation of bigger plastics (secondary microplastics) and are inextricably discharged into the environment by terrestrial and land-based sources, particularly runoff. They are non-degradable, biologically incompatible, and their presence in the air, soil, water, and food can induce ecotoxicological issues and also a menace to the environment. Due to micro size and diverse chemical nature, MP/NPs easily infiltrate wastewater treatment processes. This communication reviews the current understanding of MP/NPs occurrence, mobility, aggregation behavior, and degradation/assimilation in terrestrial, aquatic (fresh & marine), atmospheric depositions, wetlands and trophic food chain. This communication provide current perspectives and understanding on MP/NPs concerning (1) Source, occurrence, distribution, and properties (2) Impact on the ecosystem and its services, (3) Techniques in detection and identification and (4) Strategies to manage and mitigation.

Micro-Nano Plastic in the Aquatic Environment: Methodological Problems and Challenges

Microplastic research has become a buzz word. It is seen as one of the most pressing issues of Anthropocene contamination. There is certainly no doubt about the ubiquitous presence of microplastic (MP) in almost all environmental matrices. However, the validity of considering them as a vector for contaminants needs some reconsideration, there are other more potent pathways. Their effect on marine biota also calls for some realistic experiments with environmental concentrations of MP and nanoplastic (NP). It has been observed that in most published literature, polymer characterization is performed. Is it necessary to do, or will merely finding and confirming the particle as plastic suffice for environmental research? Harmonization of protocols is necessary, and there is likely a need for some inter-laboratory comparison exercises in order to produce comparable data and reliable assessments across regions. Samples collected from the same area using different techniques show an order of magnitude difference in MP concentration. The issue of nanoplastic is more contentious; are we technologically ready to identify NP in environmental samples?

Microplastics and environmental pollutants: Key interaction and toxicology in aquatic and soil environments

Nowadays, a growing number of microplastics are released into the environment due to the extensive use and inappropriate management of plastic products. With the increasing body of evidence about the pollution and hazards of microplastics, microplastics have drawn major attention from governments and the scientific community. As a kind of emerging and persistent environmental pollutants, microplastics have recently been detected on a variety of substrates in the world. Therefore, this paper reviews the recent progress in identifying the sources of microplastics in soil, water, and atmosphere and describing the transport and fate of microplastics in the terrestrial, aquatic and atmospheric ecosystems for revealing the circulation of microplastics in the ecosystem. In addition, considering the persistence of microplastics, this study elucidates the interactions of microplastics with other pollutants in the environment (i.e., organic pollutants, heavy metals) with emphasis on toxicity and accumulation, providing a novel insight into the ecological risks of microplastics in the environment. The negative impacts of microplastics on organisms and environmental health are also reviewed to reveal the environmental hazards of microplastics. The knowledge gaps and key research priorities of microplastics are identified to better understand and mitigate the environmental risks of microplastics.

Key factors controlling transport of micro- and nanoplastic in porous media and its effect on coexisting pollutants

Environmental behavior of micro- and nanoplastics (M&NPs) pollution is an emerging topic in environmental research. The strong adsorption capacities of microplastics and nanoplastics to other substances is a concern. As a carrier, M&NPs probably transfer certain hazardous pollutants over long distance and pose risks to ecosystem and human health. Therefore, understanding the interaction and cotransport of M&NPs with coexisting pollutants is designed and becomes popular for many researchers. This paper introduced the carrier function of M&NPs firstly. Then literature on cotransport of M&NPs with potential coexisting contaminants has been reviewed and discussed. Interacting with micro and nanoplastics, the transport of coexisting matter may be facilitated or inhibited. In reverse, transport and deposition of M&NPs influenced by changed external environment and properties of plastics particles. Finally, limitations of existing studies on cotransport of M&NPs in porous media and directions for future studies were given. This review could serve as a useful reference for predicting the transport of microplastics and coexisting pollutants in natural porous media.

Wet wipes and disposable surgical masks are becoming new sources of fiber microplastic pollution during global COVID-19

The demand of wet wipes and masks has been rising worldwide since the outbreak of global COVID-19; however, with more reports about improper handling of wipes and masks, their potential threats to the environment are gradually emerging. Wipes and masks are made of a large number of plastic fibers, which are easily broken and fragmented into microplastic fibers under the influence of environmental factors. Weathered wipes or masks can release billions of microplastic fibers, which is a great challenge to the local ecological security. Wipes and masks as new microplastic pollution sources and their potential role in the ecosystem have not been fully recognized and considered. Microplastic fiber pollution is a huge environmental issue, and how to prevent a large number of discarded wipes and masks from entering the environment and how to deal with them are an important issue for all countries and regions in the world. In the post era of global COVID-19, disposable wipes and masks, as new sources of environmental microplastic fiber pollution, should be given concern. It is urgent to recognize this potential environmental threat and prevent it from becoming the next microplastic problem.

Microplastics lag the leaching of phenanthrene in soil and reduce its bioavailability to wheat

Microplastics wildly occur in soil and they can become the carriers of persistent contaminants. However, the influence of microplastics on polycyclic aromatic hydrocarbons vertical translocation in the soil system after rainfall is limitedly understood. Here, experiments were conducted to study the influence of polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) microplastics on the leaching behavior and bioavailability of phenanthrene (Phe). The adsorption capacity of phenanthrene on the microplastics followed the order of PS > PE > PVC. The Phe concentrations in the top soil layer after 15 days of leaching with water were 30.25, 28.32 and 27.25 mg kg^-1 for the treatments of Phe-PS, Phe-PE and Phe-PVC respectively, which is consistent with the adsorption capacities of microplastics. The concentrations of Phe were correlated with the microplastic adsorption capacities at soil depths of 5-45 cm. Under long-term leaching, Phe could reach the deeper soil layer. Phe concentrations significantly decreased in the leachate over time. Phe concentrations in wheat had a positive correlation with that in leachate/leached top soil layer. Our findings are beneficial to accurately evaluate the ecological risk of the combined contamination of PAHs and microplastics, and improve the understanding of the environmental behaviors of different microplastics.

Materials, surfaces, and interfacial phenomena in nanoplastics toxicology research

In response to the growing worldwide plastic pollution problem, the field of nanoplastics research is attempting to determine the risk of exposure to nanoparticles amidst their ever-increasing presence in the environment. Since little is known about the attributes of environmental nanoplastics (concentration, composition, morphology, and size) due to fundamental limitations in detection and quantification of smaller plastic particles, researchers often improvise by engineering nanoplastic particles with various surface modifications as models for laboratory toxicological testing. Polystyrene and other commercially available or easily synthesized polymer materials functionalized with surfactants or fluorophores are typically used for these studies. How surfactants, additives, fluorophores, the addition of surface functional groups for conjugation, or other changes to surface attributes alter toxicological profiles remains unclear. Additionally, the limited polymers used in laboratory models do not mimic the vast range of polymer types comprising environmental pollutants. Nanomaterials are tricky materials to investigate due to their high surface area, high surface energies, and their propensity to interact with molecules, proteins, and biological probes. These unique properties can often invalidate common laboratory assays. Extreme care must be taken to ensure that results are not artefactual. We have gathered zeta potential values for various polystyrene nanoparticles with different functionalization, in different solvents, from the reported literature. We also discuss the effects of surface engineering and solvent properties on interparticle interactions, agglomeration, particle-protein interactions, corona formation, nano-bio interfaces, and contemplate how these parameters might confound results. Various toxicological exemplars are critically reviewed, and the relevance and shortfalls of the most popular models used in nanoplastics toxicity studies published in the current literature are considered.

A review on marine plastisphere: biodiversity, formation, and role in degradation

The pollution of plastic waste has become an increasingly serious environmental crisis. Recently, plastic has been detected in various kinds of environments, even in human tissues, which is an increasing threat to the ecosystems and humans. In the ocean, the plastic waste is eventually fragmentized into microplastics (MPs) under the disruption of physical and chemical processes. MPs are colonized by microbial communities such as fungi, diatoms, and bacteria, which form biofilms on the surface of the plastic called “plastisphere”. In this review, we summarize the studies related to microorganisms in the plastisphere in recent years and describe the microbial species in the plastisphere, mainly including bacteria, fungi, and autotrophs. Secondly, we explore the interactions between MPs and the plastisphere. The depth of MPs in the ocean and the nutrients in the surrounding seawater can have a great impact on the community structure of microorganisms in the plastisphere. Finally, we discuss the types of MP-degrading bacteria in the ocean, and use the “seed bank” theory to speculate on the potential sources of MP-degrading microorganisms. Challenges and future research prospects are also discussed.

Wet wipes and disposable surgical masks are becoming new sources of fiber microplastic pollution during global COVID-19

The demand of wet wipes and masks has been rising worldwide since the outbreak of global COVID-19; however, with more reports about improper handling of wipes and masks, their potential threats to the environment are gradually emerging. Wipes and masks are made of a large number of plastic fibers, which are easily broken and fragmented into microplastic fibers under the influence of environmental factors. Weathered wipes or masks can release billions of microplastic fibers, which is a great challenge to the local ecological security. Wipes and masks as new microplastic pollution sources and their potential role in the ecosystem have not been fully recognized and considered. Microplastic fiber pollution is a huge environmental issue, and how to prevent a large number of discarded wipes and masks from entering the environment and how to deal with them are an important issue for all countries and regions in the world. In the post era of global COVID-19, disposable wipes and masks, as new sources of environmental microplastic fiber pollution, should be given concern. It is urgent to recognize this potential environmental threat and prevent it from becoming the next microplastic problem.

Size effects of polystyrene microplastics on the accumulation and toxicity of (semi-)metals in earthworms

Microplastics (MPs) are plastic fragments less than 5 mm, which may have adverse impacts on organisms. In this study, we investigated the impacts and mechanisms of polystyrene MPs (10 μm and 100 μm) and nanoplastics (NPs, 100 nm) with different concentrations (10 mg/kg and 100 mg/kg) in soil on the uptake of metal Cd and semi-metal As in earthworms, Eisenia fetida. MPs facilitated the accumulation of (semi-)metals via damaging the integrity of earthworm intestine, and earthworms accumulated more (semi-)metals in MP treatment groups than NP treatment groups, especially in group of 100 mg/kg of 10 μm MP with concentrations of 1.13 mg/kg and 32.7 mg/kg of Cd and As, respectively. Higher genotoxicity to earthworms was observed for MPs than NPs. Antioxidant enzymes activity and their mRNA gene relative expression levels indicated that MPs with high concentration induced severer damage to earthworms, thus resulting in the increased accumulation of (semi-)metals by earthworms. In addition, proteomic and metabolomic analysis revealed that MPs (100 ppm of 10 μm) disturbed the earthworm immune and metabolic systems, resulting in the highest accumulation of (semi-)metals in earthworms. This study clarifies the influence mechanisms of MPs with different sizes and levels on the accumulation of (semi-)metals by terrestrial invertebrates.

Effects of nanoplastics on microalgae and their trophic transfer along the food chain: recent advances and perspectives

Nanoplastics (NPs) have drawn increasing attention in recent years due to their potential threats to aquatic ecosystems. Microalgae are primary producers, which play important roles in the normal functioning of ecosystems. According to the source of production and laboratory experiments, both NPs and microalgae are likely to be widely found in various water environments, so they have a great chance of interacting with each other. Although tremendous efforts have been made to explore these potential interactions, a timely and critical review is still missing. In this paper, the effects of NPs on microalgae and their trophic transfer along the food chain are summarized. The toxic impact of NPs on microalgae is tightly associated with the concentrations, sizes and surface charge of NPs, as well as the microalgal species. In addition, NPs could also interact with many other contaminants, thus leading to combined effects on microalgae. NP exposure might block substance and energy exchange between microalgae and their surrounding environment, lead to a shading effect on microalgae, promote the production of reactive oxygen species (ROS) or induce direct physical damage on microalgae, thereby inhibiting the growth of microalgae. Moreover, NPs could also be trophically transferred along the food chain through microalgae and subsequently affect the species at a higher trophic level. Yet importantly, current understanding of the interactions between NPs and microalgae is still quite limited, and needs to be further studied.

Narrowing feedstock exemptions under the Montreal Protocol has multiple environmental benefits

The Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) can be further strengthened to control ozone-depleting substances and hydrofluorocarbons used as feedstocks to provide additional protection of the stratospheric ozone layer and the climate system while also mitigating plastics pollution. The feedstock exemptions were premised on the assumption that feedstocks presented an insignificant threat to the environment; experience has shown that this is incorrect. Through its adjustment procedures, the Montreal Protocol can narrow the scope of feedstock exemptions to reduce inadvertent and unauthorized emissions while continuing to exempt production of feedstocks for time-limited, essential uses. This upstream approach can be an effective and efficient complement to other efforts to reduce plastic pollution. Existing mechanisms in the Montreal Protocol such as the Assessment Panels and national implementation strategies can guide the choice of environmentally superior substitutes for feedstock-derived plastics. This paper provides a framework for policy makers, industries, and civil society to consider how stronger actions under the Montreal Protocol can complement other chemical and environmental treaties.

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.

Interactions and effects of microplastics with heavy metals in aquatic and terrestrial environments

Contamination of waters and soils with microplastics (MPs) is an emerging environmental issue worldwide. MPs constitute a cocktail of various additives and polymers besides adsorbing toxic heavy metals from the environment. This co-occurrence of MPs with heavy metals poses a threat to the health of organisms and is poorly understood. Ingestion of MPs contaminated with heavy metals may also result in subsequent transfer of heavy metals up in the food chain. MPs surfaces play a crucial role in the adsorption of heavy metals. Aged/biofouled MPs facilitate greater adsorption of metals and certain microplastic (MP) polymers adsorb some metals more specifically. External factors involved in the process of adsorption/accumulation of heavy metals are the solution pH, salinity, and the concentration of relevant heavy metals in the media. Desorption greatly depends upon pH of the external solution. This is more concerning as the guts/digestive systems of organisms have low pH which could enhance the desorption of toxic metals and making them accumulate in their bodies. The aim of this article is to discuss the abundance, distribution, adsorption, and desorption behavior of MPs for heavy metals, and their combined toxic effects on flora and fauna based on the limited research on this topic in the literature. There is an overarching need to understand the interactions of MPs with heavy metals in different ecosystems so that the extent of ecotoxic effects they pose could be assessed which would help in the environmental regulation of these pollutants.

Microplastic Contamination in Soils: A Review from Geotechnical Engineering View

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

Field to laboratory comparison of metal accumulation on aged microplastics in coastal waters

The ubiquity of microplastics in the environment has attracted much attention on their risks. Though newly produced plastics were considered inert to aqueous metals, a few studies suggest aged microplastics can accumulate metals. Still, knowledge gap exists on the comparability of metal accumulation in field condition and that acquired in controlled laboratory settings. Accordingly, we comparatively assessed the field accumulation and laboratory adsorption of metals on aged microplastics in coastal waters. Microplastics of different polymeric types were aged for 8 weeks at three coastal sites with different contamination levels. Microplastics accumulated metals to substantial concentrations during ageing (median concentrations, μg g^-1: Fe = 950, Mn = 94, Zn = 19, Cu = 2.8, Ni = 1.7, Pb = 1.6, and Cd = 0.005). Adsorption capacity of (aged) microplastics was evaluated in laboratory using a stable isotope tracer method. At environmentally realistic concentrations (μg L^-1, ¹¹⁴Cd = 1.7, ⁶⁵Cu = 4.4, ⁶²Ni = 5.4, ²⁰⁶Pb = 0.5, and ⁶⁸Zn = 13), the median concentrations of newly adsorbed isotopes on the aged microplastics were 0.01, 1.4, 0.07, 0.56, and 1.1 μg g^-1, respectively, one to two orders of magnitude higher than those adsorbed on pristine microplastics. However, the composition pattern of metals accumulated on aged microplastics differed from the composition of metals newly adsorbed in laboratory: the prior one reflected the contamination status of ageing sites and varied by polymeric types; whereas the laboratory newly adsorbed metals on aged microplastics were uniformly correlated to particulate Fe and Mn concentrations, suggesting Fe and Mn mineral coatings mediated the ensuing metal adsorption. Such discrepancy unveiled the complexity of metal accumulation behavior in the real environment and highlighted that cares should be taken when translating laboratory findings to risk assessment of metal contaminated microplastics in the real environment.

Battling the known unknowns: a synoptic review of aquatic plastics research from Australia, the United Kingdom and China

Plastic pollution is a global environmental and human health issue, with plastics now ubiquitous in the environment and biota. Despite extensive international research, key knowledge gaps ("known unknowns") remain around ecosystem-scale and human health impacts of plastics in the environment, particularly in limnetic, coastal and marine systems. Here we review aquatic plastics research in three contrasting geographic and cultural settings, selected to present a gradient of heavily urbanised (and high population density) to less urbanised (and low population density) areas: China, the United Kingdom (UK), and Australia. Research from each country has varying environmental focus (for example, biota-focussed studies in Australia target various bird, fish, turtle and seal species, while UK and China-based studies focus on commercially important organisms such as bivalves, fish and decapods), and uses varying methods and reporting units (e.g. mean, median or range). This has resulted in aquatic plastics datasets that are hard to compare directly, supporting the need to converge on standardised sampling methods, and bioindicator species. While all the study nations show plastics contamination, often at high levels, datasets are variable and do not clearly demonstrate pollution gradients.

Effect of (bio)plastics on soil environment: A review

The contribution of improperly disposed plastic wastes is globally evaluated at the level of 30% and these wastes make a particular threat to all living creatures. Thus, the evaluation of the possible impacts of plastic particles on the biotic part of ecosystems has become increasingly important in recent years. As a result, the growing number of publications concerning this subject has been observed since 2018. This paper aims to review the advances in studies on the effect of petroleum-derived plastic and bioplastic particles, taken together in the term (bio)plastics, on the terrestrial ecosystem, particularly on soil biota. It is the first review, in which both petroleum-derived plastics and bioplastics were analysed regarding their potential impacts on the soil compartment. Petroleum-derived plastics were more frequently studied than bioplastics and among analysed papers about 18% concern bioplastics. It was found that (bio)plastics did not affect the germination of seeds. However, they might contribute to the delay in germination processes. Both inhibitory and stimulating effects were observed in relation to the growth of roots and stems. (Bio)plastic microparticles did not inhibit the biochemical activity of nitrifiers and transformation of carbon compounds. Earthworms were predominantly used organisms to test the effect of petroleum-derived plastics on soil biota but there are hardly any data about bioplastics. Petroleum-derived microplastics present in soil at concentrations up to 1000 mg kg^-1 usually neither cause to the mortality of earthworms nor affect their reproduction. Micro- and nanoparticles of petroleum-derived plastics could be accumulated in the earthworm intestine and transferred in the food chain. Summarizing, a high variability of results and often appearing lack of dose-dependence relationships hamper the final evaluation of the ecotoxicity of (bio)plastics simultaneously creating a need to develop the ecotoxicological studies on (bio)plastics, especially including these on the effect of bioplastics on soil animals.

Occurrence, distribution and affecting factors of microplastics in agricultural soils along the lower reaches of Yangtze River, China

Microplastics become one of the serious persistent pollutants in terrestrial environments, and thus may represent a threat to the quality of soil and inhabiting organisms. It is imperative to understand occurrence and distribution of microplastics in soils. In this study, a large-scale field survey encompassing 85 locations along the lower reaches of Yangtze River and estuary was performed to investigate the microplastics abundance in agricultural soils. Microplastics were isolated from all the samples and all depths (0-80 cm). The microplastics abundance in soils ranged from 4.94 items/kg to 252.70 items/kg, with an average of 37.32 items/kg. The most common microplastic type detected was Polypropylene (PP) occurring as white fragments with sizes ranging from 0.1 mm to 0.5 mm. Abiotic parameters such as soil pH and texture were the general factors being associated with microplastic abundance. Meantime, traffic was indicated as one important factor to affect the microplastic abundance. Overall, the road input seems to be the main source of microplastic pollution in agricultural areas along the Yangtze River and estuary. Further studies should elucidate the original of the plastic fragments in order to establish a baseline for regulative initiatives securing environmental protection.

Effects of chemical and natural ageing on the release of potentially toxic metal additives in commercial PVC microplastics

Various chemical substances, such as potentially toxic trace metals, are used as plastic additives to improve the performance of polymers and extend the service life of plastic products. However, these added trace metals are likely released from plastic into the environment when the plastic becomes a pollutant, although the process is poorly understood. In this study, chemical ageing of commercial polyvinyl chloride (PVC) microplastics using hydrogen peroxide (H₂O₂) and natural ageing of PVC that had been added to an alkaline paddy soil were undertaken to evaluate the potential release of trace metals from PVC. Enhanced release of trace metals from PVC with the increasing H₂O₂ concentrations was observed, in which the released Pb was 1-2 orders of magnitude higher than other metals (p < 0.01). The released Cr, Ni, Pb, Cu, Zn, Cd and Mn accounted for 87.37%, 79.27%, 22.02%, 20.93%, 17.06%, 15.11%, and 11.02% of their total concentrations (0.28 ± 0.03, 0.08 ± 0.01, 13.67 ± 0.18, 1.07 ± 0.02, 2.20 ± 0.18, 0.05 ± 0.00 and 1.26 ± 0.08 mmol kg^-1) in PVC after ageing with 30% H₂O₂, respectively. Compared with the control treatment without PVC addition, the concentrations of CaCl₂-extractable Cu, Mn, Ni, Pb, and Zn in the soil treated with 5% PVC are significantly increased after incubation for 60 days (p < 0.01). In conclusion, chemical and natural ageing have the potential to lead to the release of Cu, Mn, Ni, Pb, and Zn from the commercial PVC into aquatic and terrestrial environments.

Estimation of soil microplastic input derived from plastic gauze using a simplified model

Plastic gauzes have been widely used in the BTH region against haze events and for agricultural practices. The breakage of plastic gauzes would lead to the release of microplastics into soils, but it is difficult to estimate the inputs due to their wide implementation. In this study, we have conducted an estimation model based on the remote sensing technology for plastic gauze identification and the data from field experiments and literature. This model first managed to interpret the distribution of plastic gauzes from the Landsat8 images with the average overall accuracy at 0.92 and the average kappa at 0.77. By deeming the implementation duration of plastic gauzes from their distribution and using the breakage rates of plastic materials in soils reported in the literature, the model estimated that on average 1629.68 tons of microplastics have been released to soils from plastic gauze annually in the BTH region. Comparing with the microplastics released from other sources (e.g., personal care products, household dusts, laundry, and tire wear), plastic gauze could be a considerable contributor to soil microplastics.

Structure-dependent surface catalytic degradation of cephalosporin antibiotics on the aged polyvinyl chloride microplastics

Microplastics (MPs) have been recognized as a global concern due to their potential health effect, as MPs could adsorb and carry various pollutants in aquatic environment. In the present study, a new environmental behavior related to polyvinyl chloride microplastics (PVC-MPs) and the underlying mechanism were described. Our results showed that the photo-aged PVC-MPs could affect the transformation of cephalosporin antibiotics. For instance, the presence of altered PVC-MPs significantly accelerated the hydrolysis of cefazolin (CFZ), but exhibited negligible effect on the degradation of cephalexin (CFX). As indicated by in situ Fourier transform infrared spectra and theoretical calculations, hydrogen bonds could be formed between β-lactam carbonyl of CFZ and the oxygen-containing moieties on the aged PVC-MP surfaces. The hydrogen-bonding was able to significantly increase the positive atomic Mulliken charge on the β-lactam carbonyl carbon, thus narrowing the energy gap of CFZ hydrolysis and subsequently enhancing the disruption of β-lactam ring. While for CFX, instead of the β-lactam carbonyl, the amide amino group was involved in the hydrogen-bonding due to the structural difference. Therefore, in addition to increasing the adsorption capacity, the aged PVC-MPs could act as the catalyst to mediate the transformation of antibiotics. Our study would help improve the understanding for interactions between contaminants and MPs in natural environments.

Interaction of plastic particles with heavy metals and the resulting toxicological impacts: a review

Interactions of plastic particles with different organic/inorganic pollutants including heavy metals impact their ecotoxicological potential, and proper understanding in this regard is important for their ecological risk assessment. However, many studies have reported the interactions between micro-/nanoplastics (MNPs) and heavy metals (HMs), but the most prevalent interactive forces and factors monitoring their interactions are still not clear. So, the present review represents the mechanisms of interactions with special emphasis on major interactive forces and biophysicochemical and environmental factors influencing trace element's adsorption onto the surface of MNPs. Electrostatic interaction and pore-filling mechanism can best explain the HMs adsorption to MNPs. A number of biophysicochemical factors (such as biofilm, size, crystallinity, and surface charge) and environmental factors (such as pH, salt, and temperature) act together for mediating interactions and ecotoxicities of MNPs and HMs in the real environment. From a toxicological point of view, the synergistic mode of action may be more active in animals, whereas the antagonistic activity may be prevalent in plants. Besides polymer density, biofilm formation and agglomeration property of MNPs can control the vertical distribution of MNPs along the water column. Finally, the ecotoxicological potential of MNPs in the natural environment can be considered as a function of spatiotemporal variation in abiotic (including MNPs and heavy metals) and biotic components. This review will be helpful in the detail understanding of ecotoxicological risk assessment of MNPs in relation to their interaction with heavy metals.

Electrostatic attraction of cationic pollutants by microplastics reduces their joint cytotoxicity

Microplastic (MP) pollution causes global concerns regarding the consequential impacts on human health. In particular, MPs may act as vectors for various contaminants to induce adverse effects in human. In this work, the joint cytotoxicity of two different MPs co-exposed with diverse ionic pollutants was investigated in two cell lines from human digestive system: human gastric epithelium (GES-1) and colorectal mucosa (FHC) cell lines. The results indicated that the cytotoxicity of cationic pollutants was alleviated by MPs more significantly than that of anionic pollutants in both culture medium and river water. The electrostatic attraction between the negatively charged MPs and cations was a key factor in determining the ultimate joint toxicity. Our findings indicate that the joint cytotoxicity of MP-pollutant mixtures may be proactively reduced by modulating the surface charge of MPs.