Microplastics affect rice (Oryza sativa L.) quality by interfering metabolite accumulation and energy expenditure pathways: A field study

Exposure pathways, environmental processes and risks of micro (nano) plastics to crops and feasible control strategies in agricultural regions

Micro/nanoplastics (MPs/NPs) pollution may adversely impact agricultural ecosystems, threatening the sustainability and security of agricultural production. This drives an urgent need to comprehensively understand the environmental behavior and effects of MPs/NPs in soil and atmosphere in agricultural regions, and to seek relevant pollution prevention strategies. The rhizosphere and phyllosphere are the interfaces where crops are exposed to MPs/NPs. The environmental behavior of MPs/NPs in soil and atmosphere, especially in the rhizosphere and phyllosphere, determines their plant accessibility, bioavailability and ecotoxicity. This article comprehensively reviews the transformation and migration of MPs/NPs in soil, transportation and deposition in the atmosphere, environmental behavior and effects in the rhizosphere and phyllosphere, and plant uptake and transportation pathways. The article also summarizes the key factors controlling MPs/NPs environmental processes, including their properties, biotic and abiotic factors. Based on the sources, environmental processes and intake risks of MPs/NPs in agroecosystems, the article offers several feasible pollution prevention and risk management options. Finally, the review highlights the need for further research on MPs/NPs in agro-systems, including developing quantitative detection methods, exploring transformation and migration patterns in-situ soil, monitoring long-term field experiments, and establishing pollution prevention and control systems. This review can assist in improving our understanding of the biogeochemistry behavior of MPs/NPs in the soil-plant-atmosphere system and provide a roadmap for future research.

Current studies on the degradation of microplastics in the terrestrial and aquatic ecosystem

Soil and water are two important basic ecosystems for the survival of different organisms. The excessive microplastic pollutants in soil have been directly discharged into the terrestrial ecosystems. Microplastic pollutants (MPs) constitute a ubiquitous global menace due to their durability, flexibility, and tough nature. MPs posed threat to the sustainability of the ecosystem due to their small size and easy transportation via ecological series resulting in the accumulation of MPs in aquatic and terrestrial ecosystems. After being emitted into the terrestrial ecosystem, the MPs might be aged by oxidative degeneration (photo/thermal), reprecipitation (bioturbation), and hetero-accumulation. The mechanism of adsorption, degradation, and breakdown of MPs into unaffected plastic debris is accomplished by using several biological, physical, and chemical strategies. This review presents the importance of ecosystems, occurrence and sources of MPs, its toxicity, and the alteration in the ecology of the ecosystems. The inhibitory impact of MPs on the ecosystems also documents to unveil the ecological hazards of MPs. Further research is required to study the immobilization and recovery efficiency of MPs on a larger scale.

Effect of polylactic acid microplastics and lead on the growth and physiological characteristics of buckwheat

Microplastics (MPs) and heavy metals are common, often co-existing pollutants, that threaten crop growth and productivity worldwide. We analysed the adsorption of lead ions (Pb2+) to polylactic acid MPs (PLA-MPs) and their single factor and combined effects on tartary buckwheat (Fagopyrum tataricum L. Gaertn.) in hydroponics by measuring changes in the growth characteristics, antioxidant enzyme activities and Pb2+ uptake of buckwheat in response to PLA-MPs and Pb2+. PLA-MPs adsorbed Pb2+, and the better fitting second-order adsorption model implied that Pb2+ was adsorbed by chemisorption. However, the similar Pb2+ contents in the plants treated with Pb2+ only and those treated with the combined PLA-MPs-Pb2+ suggested that the adsorption played no role in the uptake of Pb2+. Low concentrations of PLA-MPs promoted shoot length. At high concentrations of both PLA-MPs and Pb2+, buckwheat growth was inhibited, and leaf peroxidase (POD), superoxide dismutase (SOD) and catalase (CAT) activities and malondialdehyde (MDA) contents were higher than in the control. No significant differences were observed in seedling growth between exposure to Pb2+ only and combined exposure to PLA-MPs with Pb2+, implying that PLA-MPs did not increase the toxicity of Pb2+ at macroscopic level. POD activity was higher and chlorophyll content was lower with PLA-MPs in the low Pb2+ dose treatments, suggesting that PLA-MPs may increase the toxicity of naturally occurring Pb2+. However, the conclusions must be verified in controlled experiments in natural soil conditions over the whole cultivation period of buckwheat.

Microplastic and natural sediment in bed load saltation: Material does not dictate the fate

Microplastic (MP) pollution is a well document threat to our aquatic and terrestrial ecosystems, however, the mechanisms by which MPs are transported in river flows are still unknown. The transport of MPs and natural sediment in aquatic flows could be somewhat comparable, as particles are similar in size. However, it is unknown how the lower density of MPs, their shape and their different material properties impact transport dynamics. To answer this, novel laboratory experiments on bed load saltation dynamics in an open-channel flow, using high-speed camera imaging and the detection of 11,035 individual saltation events were used to identify the similarities and differences between spherical MPs and spherical natural sediments transport. The tested MPs and sediment varied in terms of size and material properties (density and elasticity). Our analysis shows that the Rouse number accurately describes saltation length, height, transport velocity and collision angles equally well for both MPs and natural sediments. Through statistical inference, the distribution functions of saltation trajectory characteristics for MPs were analogous to natural sediment with only one sediment experiment (1.4% of cases) differing from all other plastic experiments. Similarly, only nine experiments (9.3% of cases) showed that collision angles for MPs differed from those of natural sediment experiments. Differences observed in terms of restitution become negligible in overall transport dynamics as turbulence overcomes the kinetic energy lost at particle-bed impact, which keeps particle motion independent from impact. Overall, spherical MP particles behave similarly to spherical natural sediments in aquatic environments under the examined experimental conditions. This is significant because there is an established body of knowledge for sediment transport that can serve as a foundation for the study of MP transport.

Interactive effects of polyethylene microplastics and cadmium on growth of Glycine max

The interaction of microplastics (MPs) and heavy metals (HMs) can lead to aggravation of detrimental effects in the plants, animals, and even human beings. Keeping this in view, the present study was designed to assess the combined toxic effects of polyethylene MPs (PE-MPs) and cadmium (Cd) on germination indices and seedling growth of soybean (Glycine max). Particle sizes of 13 and 6.5 μm and six treatments (control, Cd, 6.5 μm PE, 6.5 μm PE + Cd, 13 μm PE, and 13 μm PE + Cd) were set to simulate the effects of PE-MPs and Cd on the growth of soybean when used alone or in combined form. As compared to the control, 6.5 μm PE treatment showed significant effect on most of the germination indices, i.e., decrease in the germination index by 31%, 44% decrease in the vigor index, and 28% decrease in germination rate whereas mean germination time showed no significant differences. Treatment of smaller-size PE-MPs and Cd significantly inhibited both dry and fresh weights. All treatment groups resulted in significant effect on catalase, peroxidase, and superoxide dismutase activities of seedlings depicting adverse effects of interaction of PE-MPs and Cd. Our findings demonstrated the phyto-toxicity of PE-MPs and Cd in G. max, and it would lead to serious implications in human beings. Our study is important as it provides preliminary information regarding MP absorption and their accumulation in different levels of food chain. It can also form the basis for future research on single the combined effects of different types and sizes of MPs and heavy metals on the terrestrial plants.

Microplastic stress in plants: effects on plant growth and their remediations

Microplastic (MP) pollution is becoming a global problem due to the resilience, long-term persistence, and robustness of MPs in different ecosystems. In terrestrial ecosystems, plants are exposed to MP stress, thereby affecting overall plant growth and development. This review article has critically analyzed the effects of MP stress in plants. We found that MP stress-induced reduction in plant physical growth is accompanied by two complementary effects: (i) blockage of pores in seed coat or roots to alter water and nutrient uptake, and (ii) induction of drought due to increased soil cracking effects of MPs. Nonetheless, the reduction in physiological growth under MP stress is accompanied by four complementary effects: (i) excessive production of ROS, (ii) alteration in leaf and root ionome, (iii) impaired hormonal regulation, and (iv) decline in chlorophyll and photosynthesis. Considering that, we suggested that targeting the redox regulatory mechanisms could be beneficial in improving tolerance to MPs in plants; however, antioxidant activities are highly dependent on plant species, plant tissue, MP type, and MP dose. MP stress also indirectly reduces plant growth by altering soil productivity. However, MP-induced negative effects vary due to the presence of different surface functional groups and particle sizes. In the end, we suggested the utilization of agronomic approaches, including the application of growth regulators, biochar, and replacing plastic mulch with crop residues, crop diversification, and biological degradation, to ameliorate the effects of MP stress in plants. The efficiency of these methods is also MP-type-specific and dose-dependent.

Recent advances towards micro(nano)plastics research in wetland ecosystems: A systematic review on sources, removal, and ecological impacts

In recent years, microplastics/nanoplastics (MPs/NPs) have received substantial attention worldwide owing to their wide applications, persistence, and potential risks. Wetland systems are considered to be an important "sink" for MPs/NPs, which can have potential ecological and environmental effects on the ecosystem. This paper provides a comprehensive and systematic review of the sources and characteristics of MPs/NPs in wetland ecosystems, together with a detailed analysis of MP/NP removal and associated mechanisms in wetland systems. In addition, the eco-toxicological effects of MPs/NPs in wetland ecosystems, including plant, animal, and microbial responses, were reviewed with a focus on changes in the microbial community relevant to pollutant removal. The effects of MPs/NPs exposure on conventional pollutant removal by wetland systems and their greenhouse gas emissions are also discussed. Finally, current knowledge gaps and future recommendations are presented, including the ecological impact of exposure to various MPs/NPs on wetland ecosystems and the ecological risks of MPs/NPs associated with the migration of different contaminants and antibiotic resistance genes. This work will facilitate a better understanding of the sources, characteristics, and environmental and ecological impacts of MPs/NPs in wetland ecosystems, and provide a new perspective to promote development in this field.

Dissolved organic matter transformation mechanisms and process optimization of wastewater sludge hydrothermal humification treatment for producing plant biostimulants

Understanding the composition, transformation and bioactivity of dissolved organic matter (DOM) at the molecular level is crucial for investigating the hydrothermal humification process of wastewater sludge and producing ecological fertilizers. In this study, DOM transformation pathways under alkali-thermal humification treatment (AHT) were characterized by Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) in conjunction with molecular reaction network analysis. The effects of DOM on plant growth were examined using hydroponics and transcriptomic analysis. In the wastewater sludge humification process, AHT produced maximum amounts of protein (3260.56 mg/L) and humic acid (5788.24 mg/L) after 12 h. FT-ICR MS results indicated that protein-like structures were prone to continuous oxidation and were ultimately transformed into aromatic N-containing compounds resembling humic substances. Several reactive fragments (such as -C₂H₂O₂, -C₃H₄O₂, and -C₄H₆O₂) formed by the Maillard reaction (MR) were identified as potential precursors to humic acid (HA). In terms of biological effects, DOM_12h showed the highest rice germination and growth activity, whereas that produced by AHT for a longer period (> 12 h) displayed phytotoxicity owing to the accumulation of toxic substances. Plant biostimulants (such as amino acids and HAs) in DOM improved energy metabolism and carbohydrate storage in rice seedlings by upregulating the "starch and sucrose metabolism" pathways. Toxic substances (such as pyrrole, pyridine, and melanoidin) in DOM can activate cell walls formation to inhibit abiotic stimuli in rice seedlings through the biosynthesis of phenylpropanoid pathway. These findings provide a theoretical basis for optimizing sludge hydrothermal humification and recovering high-quality liquid fertilizers.

Transcriptomic and physiological effects of polyethylene microplastics on Zea mays seedlings and their role as a vector for organic pollutants

The widespread employment of plastics in recent decades has resulted in the accumulation of plastic residues in all ecosystems. Their presence and degradation into small particles such as microplastics (MPs) may have a negative effect on plant development and therefore on crop production. In this study, the effects of two types of polyethylene MPs on Zea mays seedlings cultured in vitro were analysed. In addition, four organic pollutants (ibuprofen, simazine, sertraline, and amoxicillin) were adsorbed by the MPs to evaluate their capacity as other contaminant vectors. The development of the plants was negatively affected by MPs alone or with the organic compounds. The strongest effect was observed in the W-MPs treatments, with a reduction in leaf and root length near 70%. Chlorophyll content was also differentially affected depending on the treatment. Transcriptome analysis showed that MPs affected gene expression in the roots of maize seedlings. As observed in the physiological parameters analysed, some gene expression changes were associated with specific treatments, such as changes in sugar transport genes in the B-MIX treatment. These results contribute to a better understanding of the molecular mechanisms of plants in regard to plastic stress responses.

Microplastics and Nanoplastics Effects on Plant-Pollinator Interaction and Pollination Biology

Microplastics and nanoplastics (MNPs) contamination is an emerging environmental and public health concern, and these particles have been reported both in aquatic and terrestrial ecosystems. Recent studies have expanded our understanding of the adverse effects of MNPs pollution on human, terrestrial, and aquatic animals, insects, and plants. In this perspective, we describe the adverse effects of MNPs particles on pollinator and plant health and discuss the mechanisms by which MNPs disrupt the pollination process. We discuss the evidence and integrate transcriptome studies to investigate the negative effects of MNPs on the molecular biology of pollination, which may cause delay or inhibit the pollination services. We conclude by addressing challenges to plant-pollinator health from MNPs pollution and argue that such harmful effects disrupt the communication between plant and pollinator for a successful pollination process.

Microplastics trigger the Matthew effect on nitrogen assimilation in marine diatoms at an environmentally relevant concentration

Microplastics (MPs, diameter <5 mm) are widely distributed on Earth, especially in the oceans. Diatoms account for ∼40% of marine primary productivity and affect the global biogeochemical cycles of macroelements. However, the effects of MPs on marine nitrogen cycling remain poorly understood, particularly comparisons between nitrogen-replete and nitrogen-limited conditions. We found that MPs trigger the Matthew effect on nitrogen assimilation in diatoms, where MPs inhibited nitrogen assimilation under nitrogen-limited conditions while enhancing nitrogen metabolism under nitrogen-replete conditions in Phaeodactylum tricornutum. Nitrate reductase (NR) and nitrite reductase (NIR) are upregulated, but nitrate transporter (NRT) and glutamine synthetase (GS) are downregulated by MPs under nitrogen-limited conditions. In contrast, NR, NIR, and GS are all upregulated by MPs under nitrogen-replete conditions. MPs accelerate nitrogen anabolic processes with an increase in the accumulation of carbohydrates by 80.7 ± 7.9% and enhance the activities of key nitrogen-metabolizing enzymes (8.20-44.90%) under nitrogen-replete conditions. In contrast, the abundance of carbohydrates decreases by 22.0-34.4%, and NRT activity is inhibited by 79.0-86.5% in nitrogen-limited algae exposed to MPs. Metabolomic and transcriptomic analyses were performed to further explore the molecular mechanisms of reprogrammed nitrogen assimilation, including carbon metabolism, nitrogen transport and ammonia assimilation. The aforementioned spatial redistribution (e.g., the Matthew effect between nitrogen-replete and -limited conditions) of nitrogen assimilation highlights the potential risks of MP contamination in the ocean.

Integrated effects of residual plastic films on soil-rhizosphere microbe-plant ecosystem

Intensive application of low-density polyethylene mulch films has resulted in substantial accumulation of residual plastics in agricultural soil. Although considerable concerns have been raised on the residual plastic pollution, their impacts on the soil-rhizosphere microbe-plant ecosystem have not been fully elucidated. In this study, we used a pot experiment to determine the effects of residual plastic films with different sizes (La, Ma, Mi and Mx) on properties, enzyme systems and nutrients of soil, composition of rhizosphere microbial community, and physiology, growth and stress response of rice plants. Residual plastic films significantly decreased soil bulk density and increased soil porosity, leading to the alteration of extracellular enzyme activities, and accumulation of dissolved nitrogen (NO₃-N + NH₄-N). The structures of both bacterial and fungal communities were significantly changed by residual plastic films with rhizosphere microbes more sensitive to small-sized plastics. Plant growth was inhibited to different extents by residual plastic films with different sizes. The weighted gene co-expression network analysis (WGCNA) showed that photosynthesis and carbon fixation of rice plants were repressed by residual plastic films, due to the reduced chlorophyll content and rubisco activity. In addition, the endogenous jasmonic acid and antioxidant enzyme system were induced to activate tolerant responses in rice plants to the stress imposed by residual plastic films. The partial least squares path models (PLS-PMs) revealed that residual plastic films had direct and/or indirect effects on the soil-rhizosphere microbe-plant system.

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

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

Molecular mechanisms of toxicity and detoxification in rice (Oryza sativa L.) exposed to polystyrene nanoplastics

Nanoplastics (NPs) are an emerging threat to higher plants in terrestrial ecosystems. However, the molecular of NP-related phytotoxicity remains unclear. In the present study, rice seedlings were exposed to polystyrene (PS, 50 nm) NPs at 0, 50, 100, and 200 mg/L under hydroponic conditions to investigate the induced physiological indices and transcriptional mechanisms. We found that 50, 100, and 200 mg/L PS significantly reduced root (53.05%, 49.61%, and 57.58%, respectively) and shoot (54.63%, 61.56%, and 62.64%, respectively) biomass as compared with the control seedlings. The activities of antioxidant enzymes, including catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), and ascorbate peroxidase (APX), were significantly activated in all PS treatment groups, indicating that PS inhibited plant growth and induced oxidative stress. Transcriptome analyses showed that PS modulated the expression of the genes involved in cell detoxification, active oxygen metabolism, mitogen-activated protein kinase (MAPK), and plant hormone transduction pathways. Our study provides new insights into phytotoxicity by demonstrating the potential underlying toxicity of PS NPs in higher plants.

Microplastics in human food chains: Food becoming a threat to health safety

While versatile application of plastics has generated huge benefits in our life, the 'plastic end-of-life' comes with downsides of emerging concern is plastic particles within all parts of environments. Plastics are highly resistant to degradation and sustain in the environment for a prolonged period resulting in easy access of microplastics into human food chain. Microplastic exposure to humans is caused by foods of both animal and plant origin, food additives, drinks, and plastic food packaging. Living organisms can accumulate microplastics in cells and tissues which results in threats of chronic biological effects and potential health hazards for humans including body gastrointestinal disorders, immunity, respiratory problem, cancer, infertility, and alteration in chromosomes. Because of the threat of microplastics on human health, it is essential to ensure food safety as well as control plastic use with strict regulation of proper management. This study aims to enlighten future research into the core component of microplastics, their exposure to human food, prevention to human food chain, and biological reactions in human body. Finally, it is recommended to consider the presence of microplastics in different foods, as most of the existing research mainly focused on sea foods. And it is important to study the mechanism of toxicity with pathways in the human body based on the different types, shapes, and sizes of plastic particles.

Environmental microplastics: Classification, sources, fates, and effects on plants

Microplastic (MP) pollution has become a global concern due to the generation of extensive plastic waste and products (370 million metric tons in 2020) that are difficult to biodegrade. Therefore, MPs have attracted a great deal of research attention, and many new findings regarding MPs (over 9000 papers published in the last 3 years) have been reported. MPs generally exert adverse effects on plants. As MPs accumulate in agricultural ecosystems, many studies have sought to understand the sources and fates of MPs and their effects on various plants. However, there have been few reviews of the properties of MPs, their effects on plants, and their interactions with other factors (e.g., drought, heat, ultraviolet light, plant hormones, heavy metals, and other pollutants) remain poorly understood. In this review, we performed scientometrics analyses of research papers (January 1, 2019, to September 30, 2022) in this field. We focused on the recent progress in the classification of MPs and their sources, circulation, and deposition in agricultural ecosystems. We review MP uptake and transport in plants, as well as factors (size, type, and environmental factors) that affect MP uptake, the positive and negative effects of MPs on plants, and the mechanisms of MP impacts on plants. We discuss current issues and future perspectives concerning research into plant interactions with MPs, along with some promising methods to manage the MP issue.

Effects of biochar on the phytotoxicity of polyvinyl chloride microplastics

Polyvinyl chloride microplastics (PVC-MPs) are toxic to crops, resulting in economic losses during agricultural production. Owing to its strong adsorption capacity, biochar can effectively remove MPs from water. It is presumed that biochar can alleviate the phytotoxicity of PVC-MPs. To verify this hypothesis, the effects of different concentrations of corncob biochar (CCBC) on the phytotoxicity of PVC-MPs were investigated using hydroponic experiments. The results showed that PVC-MPs attached to lettuce roots substantially inhibited the growth and quality of lettuce. The tested CCBC adsorbed the PVC-MPs. At appropriate concentrations, CCBC alleviated the inhibitory effect of PVC-MPs on lettuce yield; however, it decreased some quality indicators. The single PVC-MPs induced oxidative damage to lettuce, as demonstrated by the increased hydrogen peroxide (H2O2) and malondialdehyde (MDA) content. Addition of CCBC considerably decreased the contents of H2O2 and MDA in the lettuce shoots but increased the H2O2 content in the roots. These findings indicate that CCBC may alleviate the adverse effects caused by PVC-MPs to the lettuce shoots but aggravate the toxic effects on the lettuce roots. This study provides a basis for understanding the removal of the phytotoxicity of MPs.

Effects of microplastics on cadmium accumulation by rice and arbuscular mycorrhizal fungal communities in cadmium-contaminated soil

Both microplastics (MPs) and cadmium (Cd) are common contaminants in soil-rice systems, but their combined effects remain unknown. Thereby, we explored the effects of three MPs, i.e., polyethylene terephthalate (PET), polylactic acid (PLA), and polyester (PES), on Cd accumulation in rice and the community diversity and structure of arbuscular mycorrhizal fungi (AMF) in soil spiked with or without Cd. Results showed that 2% PLA decreased shoot biomass (-28%), but PET had a weaker inhibitive effect. Overall, Cd alone did not significantly change shoot and root biomass and increased root biomass in combination with 0.2% PES. MPs generally increased soil Cd availability but decreased Cd accumulation in rice tissues. Both MPs and Cd improved the bioavailability and uptake of Fe and Mn in rice roots. MPs altered the diversity and community composition of AMF, depending on their type and dose and co-existing Cd. Overall, 2% PLA caused the most distinct changes in soil properties, plant growth and Cd accumulation, and AMF communities, but showed no synergistic interactions with Cd. In conclusion, MPs can mediate rice performance and Cd accumulation via altering soil properties, nutrient uptake, and root mycorrhizal communities, and biodegradable PLA MPs thought environment-friendly can exhibit higher phytotoxicity than conventional MPs.

Organosilicon and inorganic silica inhibit polystyrene nanoparticles uptake in rice

Nanoplastics (NPs) have become an emerging global environmental problem, and the toxicity of polystyrene nanoplastics (PS-NPs) in rice plants has received widespread attention. However, few studies have focused on silicon (Si)-mediated interactions between PS-NPs and rice. Thus, two forms of Si (organosilicon/inorganic silica) treated rice cells were exposure of positively or negatively charged NPs, PS-NH₂ and PS-COOH, to evaluate the effects of Si for defense against PS-NPs toxicity in rice. The result showed PS-NH₂ nanoparticles were accumulated at relatively low levels in cells compared with that of PS-COOH, but induced a higher accumulation of hydrogen peroxide (H₂O₂) and superoxide radicals (O₂^•-). However, both organosilicon and inorganic silica can generate more negative potential on the surfaces of cell wall to absorb large numbers of positively charged PS-NH₂. In addition, they can prevent the uptake of both PS-NH₂ and PS-COOH through reducing the porosity on the surface of the cell walls. These finally alleviated the toxicity of oxidative stress caused by PS-NPs and improved the viability of rice cells. Our findings demonstrated the significant contribution of Si in combating PS-NPs in rice.

Nano- and microplastics: a comprehensive review on their exposure routes, translocation, and fate in humans

Contamination of the environment with nano-and microplastic particles (NMPs) and its putative adverse effects on organisms, ecosystems, and human health is gaining increasing scientific and public attention. Various studies show that NMPs occur abundantly within the environment, leading to a high likelihood of human exposure to NMPs. Here, different exposure scenarios can occur. The most notable exposure routes of NMPs into the human body are via the airways and gastrointestinal tract (GIT) through inhalation or ingestion, but also via the skin due to the use of personal care products (PCPs) containing NMPs. Once NMPs have entered the human body, it is possible that they are translocated from the exposed organ to other body compartments. In our review article, we combine the current knowledge on the (1) exposure routes of NMPs to humans with the basic understanding of the potential (2) translocation mechanisms into human tissues and, consequently, their (3) fate within the human body. Regarding the (1) exposure routes, we reviewed the current knowledge on the occurrence of NMPs in food, beverages, personal care products and the air (focusing on indoors and workplaces) and found that the studies suggest an abundant presence of MPs within the exposure scenarios. The overall abundance of MPs in exposure matrices relevant to humans highlights the importance of understanding whether NMPs have the potential for tissue translocation. Therefore, we describe the current knowledge on the potential (2) translocation pathways of NMPs from the skin, GIT and respiratory systems to other body compartments. Here, particular attention was paid to how likely NMPs can translocate from the primary exposed organs to secondary organs due to naturally occurring defence mechanisms against tissue translocation. Based on the current understanding, we conclude that a dermal translocation of NMPs is rather unlikely. In contrast, small MPs and NPs can generally translocate from the GIT and respiratory system to other tissues. Thus, we reviewed the existing literature on the (3) fate of NMPs within the human body. Based on the current knowledge of the contamination of human exposure routes and the potential translocation mechanisms, we critically discuss the size of the detected particles reported in the fate studies. In some cases, the particles detected in human tissue samples exceed the size of a particle to overcome biological barriers allowing particle translocation into tissues. Therefore, we emphasize the importance of critically reading and discussing the presented results of NMP in human tissue samples.

Surface functionalization and size of polystyrene microplastics concomitantly regulate growth, photosynthesis and anti-oxidant status of Cicer arietinum L

Microplastics are a recent entrant in the list of environmental pollutants, exhibiting great diversity owing to different sizes, surface charges, and morphologies. The present study explores the impact of varied size, surface functionalization, and concentration of polystyrene microplastics (PS MP) on plants. For this study, Cicer seedlings were exposed to two different sizes of PS (1 μm and 12 μm) with three different surface functionalization (plain, carboxylated, and aminated) and at three distinct concentrations (10, 50, and 100 mg/L). The growth and photosynthetic parameters (like pigment content, Hill activity, etc.) along with oxidative stress marker (ROS) and anti-oxidant enzyme activities (like Superoxide dismutase, Catalase, and Peroxidase) were assessed. The results incline towards the idea that with increasing concentration of PS, there was a decline in the growth of the seedlings. There was also a dose-dependent increase in oxidative stress due to the suppression of the action of antioxidant enzymes. The effect was more prominent for 12 μm PS, perhaps due to its larger size and adherence to roots resulting in mechanical damage as deduced from MDA levels in the seedlings. Besides, MP with negative surface charge was comparatively less toxic than uncharged or positively charged PS of 1 μm. Overall, it can be concluded that the impact of MP on plants does not rely on individual characteristics of the particles alone, rather it is a concerted result of various determinants like size, charge, and concentration.

Micro(nano)plastic pollution in terrestrial ecosystem: emphasis on impacts of polystyrene on soil biota, plants, animals, and humans

Pollution with emerging microscopic contaminants such as microplastics (MPs) and nanoplastics (NPs) including polystyrene (PS) in aquatic and terrestrial environments is increasingly recognized. PS is largely used in packaging materials and is dumped directly into the ecosystem. PS micro-nano-plastics (MNPs) can be potentially bioaccumulated in the food chain and can cause human health concerns through food consumption. Earlier MP research has focused on the aquatic environments, but recent researches show significant MP and NP contamination in the terrestrial environments especially agricultural fields. Though PS is the hotspot of MPs research, however, to our knowledge, this systematic review represents the first of its kind that specifically focused on PS contamination in agricultural soils, covering sources, effects, and ways of PS mitigation. The paper also provides updated information on the effects of PS on soil organisms, its uptake by plants, and effects on higher animals as well as human beings. Directions for future research are also proposed to increase our understanding of the environmental contamination of PS in terrestrial environments.

Scientific Uncertainty of Marine Microplastic Pollution and the Dilemma of Future International Unified Legislation

Several countries or regions have issued bans on microplastic pollution. This paper conducted a textual analysis on the provisions of the referenced countries or regions, and it was noticed that most of the existing bans only regulate and control microbeads instead of legal rules regarding all types of marine microplastic pollution. Existing international conventions can solve some of the problems of marine microplastic pollution, but they cannot solve all of them. Scientific uncertainty of marine microplastic pollution leads to the dilemma of future legislation. Specifically, based on the theory of legal norms, there are several issues faced by future international uniform legislation. The basic elements of legal rules are the hypothesis, disposition, and sanctions. At present, the scientific uncertainty of marine microplastic pollution cannot establish the three elements (hypothesis, disposition, and sanctions) of legal rules, so the existing bans in various countries can only target microbeads, and it is difficult to regulate other types of marine microplastic pollution. Consequently, we conclude that the time for comprehensive legislation on marine microplastics pollution is not yet ripe.

Exploration of Single and Co-Toxic Effects of Polypropylene Micro-Plastics and Cadmium on Rice (Oryza sativa L.)

The widespread application of micro-plastics (MP) and their release in the open environment has become a matter of worldwide concern. When interacting with contaminants such as heavy metals in the soil ecosystem, MPs can result in detrimental effects on the soil environment and plant growth and development. However, information based on the interaction between MPs and heavy metals and their effects on terrestrial plants is still limited. Keeping this in mind, the present study was conducted to explore the single and combined toxicity of polypropylene (PP) MPs (13 and 6.5 μm) and cadmium (Cd) on germination indices; root and stem growth; fresh and dry weight; and anti-oxidative enzyme activities of rice (Oryza sativa L.) seedlings. Our results indicated that a single application of PP MP and Cd on rice seedlings inhibited most of the germination indicators, while their co-occurrence (PP + Cd) showed a reduction in the overall toxicity to some extent. A single application of both the contaminants significantly inhibited root length, stem length, fresh weight and the activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) enzymes in rice seedling, while no significant effect on dry weight was observed. The combined toxicity of both PP and Cd revealed that 13 μm PP + Cd had an antagonistic effect on the growth of rice seedlings, while 6.5 μm PP + Cd showed a synergistic effect. The present study revealed that smaller PP MP particles (6.5 µm) prominently affected plant growth more as compared to larger particles (13 µm). Our work reported the combined effect of PP MP and Cd on the germination and growth of rice for the first time. This study can provide the basis for future research on the combined effects of different types and sizes of MPs and heavy metals on the terrestrial ecosystem.

Combined Inhibitory Effect of Canada Goldenrod Invasion and Soil Microplastics on Rice Growth

Alien plant invasion and residual soil microplastics (MPs) are growing threats to agricultural crop production. This study determined the adverse effects of Canadian goldenrod (Solidago canadensis L.) invasion and residual soil MPs on rice growth and development. The biomass, phenological indices, photosynthetic parameters, and antioxidant enzyme activities of rice were measured on the 50th and 80th day of post-plantation. Biomass and phenotypic results indicated the more harmful effects of the combination of S. canadensis invasion and residual soil MPs compared to S. canadensis invasion or residual soil MPs effects alone. Moreover, the interaction effect of S. canadensis invasion and residual soil MPs markedly reduced the ascorbate peroxidase and catalase belowground, while they increased in the aboveground parts of the rice. However, the S. canadensis invasion and residual soil MPs interactive treatments lowered the superoxide dismutase concentrations in the belowground parts of the rice plants while elevating the peroxidase and reactive oxygen species concentrations in both the belowground and aboveground parts compared to the other treatments. Among all treatments, S. canadensis invasion alone had the most negligible negative impact on rice biomass and growth indices. Our study suggests that soil MPs could negatively affect crop production with invasive alien plants, and the combined effects were more harmful than either of the single factors. Our findings will lay the groundwork for analyzing the impacts of invasive alien plants on rice crops.

Negative effects of poly(butylene adipate-co-terephthalate) microplastics on Arabidopsis and its root-associated microbiome

The degradable plastic poly(butylene adipate-co-terephthalate) (PBAT) is considered a potential replacement for low-density polyethylene (LDPE) as the main component of mulch film. However, it is not clear whether PBAT is harmful to the plant-soil system. Thus, we determined the effects of LDPE microplastics (LDPE-MPs) and PBAT microplastics (PBAT-MPs) on the growth of Arabidopsis. The inhibitory effect of PBAT-MPs was greater than that of LDPE-MPs on the growth of Arabidopsis. Transcriptome analysis showed that PBAT-MPs severely disrupted the photosynthetic system of Arabidopsis and increased the expression levels of genes in drug transport-related pathways. PBAT-MPs increased the relative abundances of Bradyrhizobium, Hydrogenophaga, and Arthrobacter in the bulk soil and rhizosphere soil. The abundances of Variovorax, Flavobacterium, and Microbacterium increased in the plant root zone only under PBAT-MPs. Functional prediction analysis suggested that microorganisms in the soil and plant root zone could degrade xenobiotics. Furthermore, the degradation products from PBAT comprising adipic acid, terephthalic acid, and butanediol were more toxic than PBAT-MPs. Our findings demonstrate that PBAT-MPs may be degraded by microorganisms to produce chemicals that are highly toxic to plants. Thus, biodegradable plastics may pose a great risk to the environment.

Differences, links, and roles of microbial and stoichiometric factors in microplastic distribution: A case study of five typical rice cropping regions in China

Microplastics (MPs), as new pollutants in agroecosystems, have already attracted widespread attention from scientists. However, our understanding of MP geographic distribution and its influencing factors across spatial scales remains poor. Here, a regional-scale field investigation was conducted to assess the distribution characteristic of MPs in five major rice-growing regions of China, and we explored the roles of biological and abiotic factors, especially stoichiometry and microbial influences on MP distribution. MPs were observed in all sampling sites, averaging 6,390 ± 2,031 items⋅kg^–1. Sizes less than 0.5 mm and black and transparent MPs dominated. Fiber, classified as one of the MP shapes, occurred most frequently. MP community analysis, firstly used in paddy soil, revealed more black MPs abundance in Henan (HE), more rayon, blue, and other colors MPs in Hunan (HN), more transparent MPs in Tianjing (TJ), and more PE MPs in Heilongjiang (DB). Higher MP community diversity was found in most south paddy soils of this study, due to a broader range of sources. C/N showed a positive relationship with pellet-shaped MP abundance and MPs of size between 2 and 5 mm (P < 0.05). Chao1 index of soil microbial communities was positively correlated with the MP abundance, MPs of size less than 0.5 mm, and fiber abundance. The minimum temperature was positively correlated with MP abundance (P < 0.05), implying the potential effects of the freeze-thaw process might exist. The regression analysis highlighted the important role of population quantity in determining MP abundance (R = 0.421, P = 0.02). This study confirmed the wide distribution of MPs in different soil depths of paddy lands in China and demonstrated that its distribution was influenced by population quantity and environmental variables, such as microbiology. These findings could provide a basis for the toxicological behavior of MPs and the potential risk to human health.

Phytotoxicity of polystyrene, polyethylene and polypropylene microplastics on tomato (Lycopersicon esculentum L.)

Despite the fact that microplastic pollution in terrestrial ecosystems has received increasing attention, there are few studies on the potential effects of different microplastics on terrestrial plants. In this study, the toxicity of polystyrene (PS), polyethylene (PE) and polypropylene (PP) microplastics with different concentrations (0, 10, 100, 500 and 1000 mg/L) to tomato (Lycopersicon esculentum L.) were studied by a hydroponic experiment. The results showed that the three microplastics had inhibitory effects on seed germination when the concentration was less than or equal to 500 mg/L, and the inhibition rate ranged from 10.1% to 23.6%. Interestingly, the inhibition effect was alleviated under 1000 mg/L microplastic treatment. Generally, PE was more toxic to seedling growth than PS and PP. Additionally, it was confirmed that microplastics could cause oxidative stress in plants, and PP was relatively less toxic to antioxidant enzymes than PS and PE. These results can provide a theoretical basis and data support for further investigation on the toxicity of microplastics to tomatoes, and contribute to understanding the type specificity of microplastics' toxic effects on plants.

Translocation and chronic effects of microplastics on pea plants (Pisum sativum) in copper-contaminated soil

Microplastics (MPs) released into soil environments, along with the existing pollutants in soil, may have adverse effects on plants. However, the chronic effects of MPs in soils contaminated with heavy metals on crop plants remain unidentified. This study aimed to investigate the chronic effects of MPs (polystyrene, 20 nm) on the reproductive and nutritional status of pea crop plant (Pisum sativum) grown in Cu- (40 mg/kg) and MP-contaminated soils (40, 20 mg/kg). The crop yield reduced in all groups, with an evident decrease in the complex exposure group (comprising MPs and Cu). Moreover, significant changes in plants were identified regarding the weight, color, amino acids, and protein content of peas. Nutrient content in beans increased by MP exposure in single and complex exposure groups. Cu accumulation did not differ in the presence and absence of MPs. Additionally, MPs that infiltrated into incomplete casparian strips during root formation translocated into aerial parts via the apoplast pathway along the cell walls of the vascular bundle. Therefore, long-term exposure to MPs in soil can significantly affect plants while collective application of Cu and MPs imposed severe damage. The changes in the crop quality and nutrient contents may in turn affect human health through the food chain.

Effects of polyethylene and polylactic acid microplastics on plant growth and bacterial community in the soil

Microplastics (MPs), especially biodegradable MPs (BMPs) have attracted increasing attention in recent years. However, the effects of MPs with different biodegradability on the soil-plant systems are not well explored. In this study, the effects of polyethylene MPs (PEMPs) and polylactic acid MPs (PLAMPs) on physio-biochemical performance and metabolomic profile of soybean (Glycine max), as well as the bacterial communities in soil were investigated. Our results showed that PEMPs had no noticeable toxicity on the plant growth, while 0.1% PLAMPs significantly decreased the root length by 27.53% when compared with the control. The peroxidase (POD) activity was reduced and catalase (CAT) activity was increased by MPs in plant leaves. The metabolomics study suggested that the significantly affected metabolic pathway is amino acid metabolism. Additionally, Shannon and Simpson indices of rhizosphere soil were changed only under 0.1% PLAMPs. The key bacteria involved in the dinitrogen fixation were also altered. This study provides a novel insight into the potential effects of MPs with different biodegradability on soil-plant systems and highlights that BMPs might have stronger negative effects for terrestrial ecosystem, which needs to be further explored in future research.

Effects of Microplastics on Higher Plants: A Review

Microplastics pose great risks to terrestrial systems owing to their large quantity and strong persistence. Higher plants, an irreplaceable part of the terrestrial ecosystem, are inevitably exposed to microplastics. This review highlights the effects of microplastics on higher plant growth and performance. The tested microplastics, plant species, and cultural methods used in existing studies were summarized. We discussed the reasons why these microplastics, plants, and methods were selected. The various responses of higher plants to microplastics in both soils and waters were critically reviewed. We also highlighted the influencing mechanisms of microplastics on higher plants. Conclusively, more than 13 types of common microplastics and more than 30 species of higher plants have been selected and studied by the published literatures. Soil culture tests and hydroponic experiments are almost equally divided. The effects of microplastics on higher plants varied among microplastic properties, plant species, and environmental factors. Microplastics had no or positive effects on higher plants under certain experimental conditions. However, more studies showed that microplastics can inhibit higher plant growth and performance. We reduced the inhibitory mechanisms into direct and indirect mechanisms. The direct mechanisms include blocking pores or light, causing mechanical damage to roots, hindering genes expression, and releasing additives. The indirect mechanisms contain changing soil properties, affecting soil microbes or soil animals, and affecting bioavailability of other pollutants. This review improves the understanding of effects and influencing mechanisms of microplastics on higher plants.

Impact of microplastics from polyethylene and biodegradable mulch films on rice (Oryza sativa L.)

Extensive use of plastic film mulch has resulted in accumulation of a large amount of residual plastic, which will eventually fragment into microplastics in agricultural soils. However, it is unclear how microplastics from plastic mulch film affect crops. To address this issue, rice plants exposed to microplastics derived from poly(butyleneadipate-co-terephthalate) (PBAT)-based biodegradable mulch film (BM) and polyethylene (PE) mulch film (PM) were investigated for plant growth, physio-biochemical processes, and gene expressions. Both types of microplastics significantly reduced the height and dry weight of rice plant. Oxidative stress was induced by microplastics in rice shoot and root, with levels of ROS relatively higher under treatment PM than that under treatment BM. Transcriptomic data showed that more genes were down-regulated by treatment PM than that by treatment BM. Genes encoding ammonium and nitrate transporters were down-regulated by both types of microplastics in rice roots at vegetative stage, whereas up-regulated at reproductive stage, as compared to their respective treatment with no microplastics (CK). Similar results regarding phenylpropanoid biosynthesis pathway and lignin content were also observed in rice roots. Net photosynthetic rate and SPAD value were significantly inhibited by treatments BM and PM in rice shoot, and the expression of genes involved in light reaction was reduced at vegetative stage, whereas there were no differences of them at reproductive stage, as compared to their respective treatment CK. Our study suggests that microplastics from BM and PM both affect the growth of rice plants via nitrogen metabolism and photosynthesis. The negative effects imposed by both types of microplastics on rice plant can be mitigated with the growth of plants, and the negative effects of microplastics from PE mulch film on rice plant are relatively stronger than that from the PBAT-based biodegradable film.

Adverse Effects of Arsenic Uptake in Rice Metabolome and Lipidome Revealed by Untargeted Liquid Chromatography Coupled to Mass Spectrometry (LC-MS) and Regions of Interest Multivariate Curve Resolution

Rice crops are especially vulnerable to arsenic exposure compared to other cereal crops because flooding growing conditions facilitates its uptake. Besides, there are still many unknown questions about arsenic’s mode of action in rice. Here, we apply two untargeted approaches using liquid chromatography coupled to mass spectrometry (LC-MS) to unravel the effects on rice lipidome and metabolome in the early stages of growth. The exposure is evaluated through two different treatments, watering with arsenic-contaminated water and soil containing arsenic. The combination of regions of interest (ROI) and multivariate curve resolution (MCR) strategies in the ROIMCR data analyses workflow is proposed and complemented with other multivariate analyses such as partial least square discriminant analysis (PLS-DA) for the identification of potential markers of arsenic exposure and toxicity effects. The results of this study showed that rice metabolome (and lipidome) in root tissues seemed to be more affected by the watering and soil treatment. In contrast, aerial tissues alterations were accentuated by the arsenic dose, rather than with the watering and soil treatment itself. Up to a hundred lipids and 40 metabolites were significantly altered due to arsenic exposure. Major metabolic alterations were found in glycerophospholipids, glycerolipids, and amino acid-related pathways.

Phytotoxic effects of plastic pollution in crops: what is the size of the problem?

Plastic pollution is one of the most impactful human interferences in our planet. Fragmentation of plastic leads to nano- and microplastics (NP/MP) formation, which accumulate in agricultural lands, representing an increasing risk for crop production and food safety. It has been shown that MP promote damage in plant tissues by several direct and indirect ways, and that NP can enter the tissues/cells and accumulate in edible organs. Investigation of the phytotoxic effects of NP/MP in plants started only in 2016, with most of the studies performed with crops. Since contradictory results are often observed, it is important to review the literature in order to identify robust effects and their possible mechanisms. In this review, we discuss the potential of NP/MP in damaging crop species, with focus on the physiological changes described in the literature. We also performed scientometrics analyses on research papers in this field during 2016-2021, to reveal the research situation of phytotoxic effects of plastic pollution in crops. Our review is as a starting point to help identify gaps and future directions in this important, emerging field.