The joint toxicity of polyethylene microplastic and phenanthrene to wheat seedlings

The promoting effects of soil microplastics on alien plant invasion depend on microplastic shape and concentration

Both alien plant invasions and soil microplastic pollution have become a concerning threat for terrestrial ecosystems, with consequences on the human well-being. However, our current knowledge of microplastic effects on the successful invasion of plants remains limited, despite numerous studies demonstrating the direct and indirect impacts of microplastics on plant performance. To address this knowledge gap, we conducted a greenhouse experiment involving the mixtures of soil and low-density polyethylene (LDPE) microplastic pellets and fragments at the concentrations of 0, 0.5 % and 2.0 %. Additionally, we included Solidago decurrens (native plant) and S. canadensis (alien invasive plant) as the target plants. Each pot contained an individual of either species, after six-month cultivation, plant biomass and antioxidant enzymes, as well as soil properties including soil moisture, pH, available nutrient, and microbial biomass were measured. Our results indicated that microplastic effects on soil properties and plant growth indices depended on the Solidago species, microplastic shapes and concentrations. For example, microplastics exerted positive effects on soil moisture of the soil with native species but negative effects with invasive species, which were impacted by microplastic shapes and concentrations, respectively. Microplastics significantly impacted catalase (P < 0.05) and superoxide dismutase (P < 0.01), aboveground biomass (P < 0.01), and belowground/aboveground biomass (P < 0.01) of the native species depending on microplastic shapes, but no significant effects on those of the invasive species. Furthermore, microplastics effects on soil properties, nutrient, nutrient ratio, and plant antioxidant enzyme activities contributed to plant biomass differently among these two species. These results suggested that the microplastics exerted a more pronounced impact on native Solidago plants than the invasive ones. This implies that the alien invasive species displays greater resistance to microplastic pollution, potentially promoting their invasion. Overall, our study contributes to a better understanding of the promoting effects of microplastic pollution on plant invasion.

Effect of cadmium on polystyrene transport in parsley roots planted in a split-root system and assessment of the combined toxic effects

Micro and nanoplastics (MPs/NPs) coupled with heavy metals are prevalent in both aquatic and terrestrial ecosystems. Their ecological toxicity and combined adverse effects have obtained significant concern. Past studies primarily focused on how MPs/NPs influence the behavior of heavy metals. Yet, the possible effects of heavy metals on MP/NP transport and toxicity within co-contaminated systems are still not well-understood. In this study, we conducted split-root experiments to explore the transport and toxicity of polystyrene (PS) particles of varying sizes in parsley seedlings, both with and without the addition of cadmium (Cd). Both the PS-NPs (100 nm) and PS-MPs (300 nm) traveled from the PS-spiked roots (Roots-1) to the non-PS-spiked roots (Roots-2), with or without Cd, possibly because of phloem transport. Furthermore, the presence of Cd reduced the accumulation and movement of PS-NP/MP in the roots, likely due to the increased positive charge (Cd2+) on the PS surface. PS-NPs/MPs in both Roots-1 and Roots-2 were observed using transmission electron microscopy (TEM). When Cd was added to either Roots-1 (PS + Cd|H) or Roots-2 (PS|Cd), there was a minor reduction in the chlorophyll a and carotenoids content in leaves with PS|H. The adverse impacts of MPs|H on both indicators were influenced by the MP concentration. However, chlorophyll b significantly increased in the PS|H, PS + Cd|H, and PS|Cd treatments. Consequently, the chlorophyll a/b ratio declined, indicating inhibition of photosynthesis. The dehydrogenase content showed a minor change in Roots-1 and Roots-2 without Cd stress, whereas it significantly decreased on the Cd-spiked side and subsequently inhibited root growth. In contrast, the marked rise in glutathione (GSH) levels within Cd-spiked roots suggested, based on Gaussian analysis, that GSH and Cd chelation were instrumental in mitigating Cd toxicity. When Cd was introduced to both Roots-1 and Roots-2 simultaneously (PS + Cd|Cd), the aforementioned index showed a notable decline.

Biodeterioration of polyethylene by Bacillus cereus and Rhodococcus equi isolated from soil

Polyethylene (PE), a non-biodegradable plastic, is widely used in agriculture as a mulch material, which causes serious plastic pollution when it is discarded. Recent studies have described the biodeterioration of PE by bacteria, but it is difficult for a single bacterial species to effectively degrade PE plastic. We isolated two strains with PE-degrading ability, Bacillus cereus (E1) and Rhodococcus equi (E3), from the soil attached to plastic waste on the south side of Mount Tai, China, using a medium with PE plastic as the only carbon source. By clear zone area analysis, we found that E1 mixed with E3 could improve the degradation of PE plastics. The mixture of E1 and E3 was incubated for 110 days in a medium containing PE and mulch film as the only carbon source, respectively. After 110 days, a decrease in pH and mass was observed. Obvious slits and depressions were observed on the surface of the PE film and the mulch films using scanning electron microscopy. The surface hydrophobicity of both films decreased, and FTIR revealed the formation of new oxidation groups on their surfaces during the degradation process and the destruction of the original CH2 long chains of PE. Besides, we found that surface of the mulch films contained more viable bacteria than the liquid medium. In conclusion, we identified two PE-degrading strains whose mixture can effectively degrade mulch film than pure PE film. Our results provide a reference for understanding PE plastic degradation pathways and their associated degradation processes.

Effect of microplastics used in agronomic practices on agricultural soil properties and plant functions: Potential contribution to the circular economy of rural areas

The extensive use of plastic materials and their improper disposal results in high amounts of plastic waste in the environment. Aging of plastics leads to their breakdown into smaller particles, such as microplastics (MPs) and nanoplastics. This research investigates plastics used in agricultural practices as they contribute to MP pollution in agricultural soils. The distribution and characteristics of MPs in agricultural soils were evaluated. In addition, the effect of MPs on soil properties, the relationship between MPs and metals in soil, the effect of MPs on the fate of pesticides in agricultural soils and the influence of MPs on plant growth were analysed, discussing legume, cereal and vegetable crops. Finally, a brief description of the main methods of chemical analysis and identification of MPs is presented. This study will contribute to a better understanding of MPs in agricultural soils and their effect on the soil-plant system. The changes induced by MPs in soil parameters can lead to potential benefits as it is possible to increase the availability of micronutrients and reduce plant uptake of toxic elements. Furthermore, although plastic pollution remains an emerging threat to soil ecosystems, their presence may result in benefits to agricultural soils, highlighting the principles of the circular economy.

Tire additives: Evaluation of joint toxicity, design of new derivatives and mechanism analysis of free radical oxidation

N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) is one of the most widely used antioxidant agents in tire additives. Its ozonation by-product 6PPD-quinone has recently been recognized as inducing acute mortality in aquatic organisms such as coho salmon. In this study, we aimed to develop an in-silico method to design environmentally friendly 6PPD derivatives and evaluate the joint toxicity of 6PPD with other commonly used tire additives on coho salmon through full factorial design-molecular docking and molecular dynamic simulation. The toxicity mentioned in this study is represented by the binding energy of chemical(s) binding to the coho salmon growth hormone. The recommended formula for tire additives with relatively low toxicity was then proposed. To further reduce the toxicity of 6PPD, 129 6PPD derivatives were designed based on the N-H bond dissociation reaction, and three of these derivatives showed improved antioxidant activity and 6PPD-106 was finally screened as the optimum alternative with lower toxicity to coho salmon. Besides, the mechanism of free radical oxidation (i.e., antioxidation and ozonation metabolic pathway) for 6PPD-106 was also analyzed and found that after ozonation, the toxicity of 6PPD-106's by-products is much lower than that of 6PPD's by-products. This study provided a molecular modelling-based examination of 6PPD, which comprehensively advanced the understanding of 6PPD's environmental behaviors and provided more environmentally friendly 6PPD alternatives with desired functional property and lower ecological risks.

Effects of microplastics on the environmental behaviors of the herbicide atrazine in soil: Dissipation, adsorption, and bioconcentration

As an emerging contaminant in soil, the impact of microplastics (MPs) on the environmental behavior of other organic pollutants remains uncertain, potentially threatening the sustainability of agricultural production. In this study, the impact of two kinds of MPs on the environmental behaviors of herbicide atrazine in soil-plant system was investigated. The results showed that MPs significantly reduced the half-life 17.69 ∼ 21.86 days of atrazine in the soil, compared to the control group. Meanwhile, the introduction of MPs substantially increased atrazine adsorption. Additionally, MPs substantially enriched the diversity and functionality of soil microbiome, and the soil metabolic activity was stimulated. Regarding the crop growth, the accumulation of atrazine in maize were significantly decreased by approximately 48.4-78.5 % after exposure to MPs. In conclusion, this study reveals the impact of MPs on atrazine's environmental behaviors in soil and highlights their less effect on maize growth, providing valuable insights for managing MPs contamination in sustainable agriculture.

An Atomic-Level Perspective on the interactions between Organic Pollutants and PET particles: A Comprehensive Computational Investigation

Microplastics (MPs) have recently attracted a lot of attention worldwide due to their abundance and potentially harmful effects on the environment and on human health. One of the factors of concern is their ability to adsorb and disperse other harmful organic pollutants in the environment. To properly assess the adsorption capacity of MP for organic pollutants in different environments, it is pivotal to understand the mechanisms of their interactions in detail at the atomic level. In this work, we studied interactions between polyethylene terephthalate (PET) MP and small organic pollutants containing different functional groups within the framework of density functional theory (DFT). Our computational outcomes show that organic pollutants mainly bind to the surface of a PET model via weak non-bonding interactions, mostly hydrogen bonds. The binding strength between pollutant molecules and PET particles strongly depends on the adsorption site while we have found that the particle size is of lesser importance. Specifically, carboxylic sites are able to form strong hydrogen bonds with pollutants containing hydrogen bond donor or acceptor groups. On the other hand, it is found that in such kind of systems π-π interactions play a minor role in adsorption on PET particles.

Microplastics alter the equilibrium of plant-soil-microbial system: A meta-analysis

Microplastics (MPs) are widely identified as emerging hazards causing considerable eco-toxicity in terrestrial ecosystems, but the impacts differ in different ecosystem functions among different chemical compositions, morphology, sizes, concentrations, and experiment duration. Given the close relationships and trade-offs between plant and soil systems, probing the "whole ecosystem" instead of individual functions must yield novel insights into MPs affecting terrestrial ecosystems. Here, a comprehensive meta-analysis was employed to reveal an unambiguous response of the plant-soil-microbial system to MPs. Results showed that in view of plant, soil, and microbial functions, the general response patterns of plant and soil functions to MPs were obviously opposite. For example, polyethylene (PE) and polyvinyl chloride (PVC) MPs highly increased plant functions, while posed negative effects on soil functions. Polystyrene (PS) and biodegradable (Bio) MPs decreased plant functions, while stimulating soil functions. Additionally, low-density polyethylene (LDPE), PE, PS, PVC, Bio, and granular MPs significantly decreased soil microbial functions. These results clearly revealed that MPs alter the equilibrium of the plant-soil-microbial system. More importantly, our results further revealed that MPs tended to increase ecosystem multifunctionality, e.g., LDPE and PVC MPs posed positive effects on ecosystem multifunctionality, PE, PS, and Bio MPs showed neutral effects on ecosystem multifunctionality. Linear regression analysis showed that under low MPs size (<100 µm), ecosystem multifunctionality was gradually reduced with the increased size of MPs. The response of ecosystem multifunctionality showed a concave shape pattern along the gradient of experimental duration which was lower than 70 days. More importantly, there was a threshold (i.e., 5% w/w) for the effects of MPs concentration on ecosystem multifunctionality, i.e., under low concentration (< 5% w/w), ecosystem multifunctionality was gradually increased with the increased concentration of MPs, while ecosystem multifunctionality was gradually decreased under high concentration (i.e., > 5% w/w). These findings emphasize the importance of studying the effects of MPs on plant-soil-microbial systems and help us identify ways to reduce the eco-toxicity of MPs and maintain environmental safety in view of an ecology perspective.

Micro/nanoplastics: Critical review of their impacts on plants, interactions with other contaminants (antibiotics, heavy metals, and polycyclic aromatic hydrocarbons), and management strategies

Microplastic/nanoplastics (MPs/NPs) contamination is not only emerging threat to the agricultural system but also constitute global hazard to the environment worldwide. Recent review articles have addressed the environmental distribution of MPs/NPs and their single-exposure phytotoxicity in various plant species. However, the mechanisms of MPs/NPs-induced phytotoxicity in conjunction with that of other contaminants remain unknown, and there is a need for strategies to ameliorate such phytotoxicity. To address this, we comprehensively review the sources of MPs/NPs, their uptake by and effects on various plant species, and their phytotoxicity in conjunction with antibiotics, heavy metals, polycyclic aromatic hydrocarbons (PAHs), and other toxicants. We examine mechanisms to ameliorate MP/NP-induced phytotoxicity, including the use of phytohormones, biochar, and other plant-growth regulators. We discuss the effects of MPs/NPs -induced phytotoxicity in terms of its ability to inhibit plant growth and photosynthesis, disrupt nutrient metabolism, inhibit seed germination, promote oxidative stress, alter the antioxidant defense system, and induce genotoxicity. This review summarizes the novel strategies for mitigating MPs/NPs phytotoxicity, presents recent advances, and highlights research gaps, providing a foundation for future studies aimed at overcoming the emerging problem of MPs/NPs phytotoxicity in edible crops.

Microplastic contamination in the agricultural soil-mitigation strategies, heavy metals contamination, and impact on human health: a review

Microplastic pollution has emerged as a critical global environmental issue due to its widespread distribution, persistence, and potential adverse effects on ecosystems and human health. Although research on microplastic pollution in aquatic environments has gained significant attention. However, a limited literature has summarized the impacts of microplastic pollution the agricultural land and human health. Therefore, In the current review, we have discussed how microplastic(s) affect the microorganisms by ingesting the microplastic present in the soil, alternatively affecting the belowground biotic and abiotic components, which further elucidates the negative effects on the above-ground properties of the crops. In addition, the consumption of these crops in the food chain revealed a potential risk to human health throughout the food chain. Moreover, microplastic pollution has the potential to induce a negative impact on agricultural production and food security by altering the physiochemical properties of the soil, microbial population, nutrient cycling, and plant growth and development. Therefore, we discussed in detail the potential hazards caused by microplastic contamination in the soil and through the consumption of food and water by humans in daily intake. Furthermore, further study is urgently required to comprehend how microplastic pollution negatively affects terrestrial ecosystems, particularly agroecosystems which drastically reduces the productivity of the crops. Our review highlights the urgent need for greater awareness, policy interventions, and technological solutions to address the emerging threat of microplastic pollution in soil and plant systems and mitigation strategies to overcome its potential impacts on human health. Based on existing studies, we have pointed out the research gaps and proposed different directions for future research.

Pesticide bioaccumulation in radish produced from soil contaminated with microplastics

The aging of microplastics (MPs) in soils may affect crop bioaccumulation of coexisting contaminants. We examined the bioaccumulation of pesticides (chlorpyrifos (CPF), difenoconazole (DIF) and their mixture) in radish (Raphanus sativus) planted in soils contaminated with MPs (low-density polyethylene or biodegradable MPs). The experiment was conducted with different contamination scenarios taking into account the use of aged MPs and pesticide mixtures. Radish root biomass was negatively affected in the scenarios with aged MPs. CPF bioaccumulation in radishes appears to be enhanced by the presence of MPs, especially aged MPs, and the pesticide mixture. The results show that food safety risks associated with the bioaccumulation of individual pesticides and their mixtures are increased in soils polluted by MPs, particularly MP after aging.

A bibliometric analysis of global research hotspots and progress on microplastics in soil‒plant systems

Plastic pollution has become a global and persistent challenge, posing threats to ecosystems and organisms. In recent years, there has been a rapid increase in scientific research focused on understanding microplastics in the soil‒plant system. This surge is primarily driven by the direct impact of microplastics on agricultural productivity and their association with human activities. In this study, we conducted a comprehensive bibliometric analysis to provide an overview of the current research on microplastics in soil‒plant systems. We systematically analysed 192 articles and observed a significant rise in research interests since 2017. Notably, China has emerged as a leading contributor in terms of published papers, closely followed by Germany and the Netherlands. Through co-authorship network analysis, we identified 634 different institutions that participated in publishing papers in this field, with the Chinese Academy of Sciences having the most collaborations. In the co-occurrence keyword network, we identified four clusters focusing on the diversity of microplastics within the agroecosystem, transportation, and quantification of microplastics in soil, analysis of plastic contamination type and impact, and investigation of microplastic phytotoxicity. Furthermore, we identified ten research priorities, categorized into the effects of microplastics in "soil" and "plant". The research hotspots were found to be the effect of microplastics on soil physicochemical properties and the synergistic phytotoxicity of microplastics with other pollutants. Overall, this bibliometric analysis holds significant value, serving as an important reference point and offering valuable suggestions for future researchers in this rapidly advancing field.

Impact of microplastic particle size on physiological and biochemical properties and rhizosphere metabolism of Zea mays L.: Comparison in different soil types

The effect of microplastics (MPs) on plant growth has received increasing attention. However, whether soil texture and MPs size influence the toxicological effects of MPs on plants is unknown. To address this knowledge gap, two soils with different physical structures (lime concretion black and silty loam soils) were selected to explore the potential toxicity of MPs of different particle sizes to maize growth. The results showed that, in both soils, the harm caused by small MPs on maize growth was greater than that caused by large MPs. Low MPs concentrations had no significant effect on maize growth between two soil types; however, when exposed to a concentration of 1 % large MPs, the dry biomass of maize was promoted in lime concretion black soil but inhibited in silty loam soil. All MPs-exposed treatments resulted in a high level of superoxide anions in maize roots, resulting in an increase in the root aerenchyma area and reducing the metabolic activity of maize roots. Metabolomics showed that MPs exposure affected multiple amino acid metabolic pathways, including phenylalanine and tyrosine metabolism, and inhibited lignin biosynthesis in roots. This study provides a theoretical basis for a more comprehensive assessment of the effect of MPs pollution on agricultural production.

Micro (nano)plastics and phthalate esters drive endophytic bacteria alteration and inhibit wheat root growth

Endophytes play an important role in plant growth and stress tolerance, but limited information is available on the complex effects of micro (nano)plastics and phthalate esters (PAEs) on endophytes in terrestrial plants. To better elucidate the ecological response of endophytic bacteria on exogenous pollutants, a hydroponic experiment was conducted to examine the combined impact of polystyrene (PS) and PAEs on endophyte community structure, diversity, and wheat growth. The findings revealed that wheat roots were capable of absorbing and accumulating PS nanoparticles (PS-NPs, 0.1 μm), whereas PS microparticles (PS-MPs, 1 and 10 μm) merely adhered to the root surface. The addition of PAEs resulted in a stronger accumulation of fluorescent signal from PS-NPs in the roots. The dibutyl phthalate (DBP) and di(2-ethylhexyl) phthalate (DEHP) were identified in wheat roots, and they could be metabolized to form minobutyl phthalate and phthalic acid, and mono-(2-ethylhexyl) phthalate, respectively. Compared to single PAEs, the concentration of PAEs and their metabolites in the roots treated with PS-NPs showed a great increase, while they exhibited a significant decline in the presence of PS-MPs. Principal coordinate analysis and permutational multivariate analysis of variance demonstrated that PS size were the major factor that induced oxidative damage, and altered the endogenous homeostasis of wheat roots. The increase in PS size positively promoted the relative abundance of dominant endophytes. Specifically, Proteobacteria. Proteobacteria were the most important in the symbiosis survival, which had a great impact on the microbial community and diversity. Therefore, PS and PAEs could affect the endophytes directly and indirectly. Structural equation modeling further implied that these endophytic bacteria, along with antioxidant enzymes such as superoxide dismutase which were regulated by non-enzymatic mechanisms, promoted root biomass increase. These results indicated a synergistic resistance mechanism between antioxidant enzymes and endophytic bacteria in response to environmental stress.

Environmental fate, aging, toxicity and potential remediation strategies of microplastics in soil environment: Current progress and future perspectives

Microplastics (MPs) are small plastic debris (<5 mm) that result from the fragmentation of plastic due to physical and physiochemical processes. MPs are emerging pollutants that pose a significant threat to the environment and human health, primarily due to their pervasive presence and potential bioaccumulation within the food web. Despite their importance, there is a lack of comprehensive studies on the fate, toxicity, and aging behavior of MPs. Therefore, this review aims to address this gap by providing a cohesive understanding of several key aspects. Firstly, it summarizes the sources and fate of MPs, highlighting their ubiquitous presence and the potential pathways through which they enter ecosystems. Secondly, it evaluates the aging process of MPs and the factors influencing it, including the morphological and physiological changes observed in crops and the release of pollutants from aged MPs, which can have detrimental effects on the environment and human health. Furthermore, the impacts of aging MPs on various processes are discussed, such as the mobilization of other pollutants in the environment. The influence of aged MPs on the soil environment, particularly their effect on heavy metal adsorption, is examined. Finally, the review explores strategies for the prevention technologies and remediation of MPs, highlighting the importance of developing effective approaches to tackle this issue. Overall, this review aims to contribute to our understanding of MPs, their aging process, and their impacts on the environment and human health. It underscores the urgency of addressing the issue of MPs and promoting research and remediation efforts to mitigate their adverse effects.

Revealing the metabolomics and biometrics underlying phytotoxicity mechanisms for polystyrene nanoplastics and dibutyl phthalate in dandelion (Taraxacum officinale)

Micro/nanoplastics (M/NPs) and phthalates (PAEs) are emerging pollutants. Polystyrene (PS) MPs and dibutyl phthalate (DBP) are typical MPs and PAEs in the environment. However, how dandelion plants respond to the combined contamination of MPs and PAEs remains unclear. In this study, we evaluated the individual and combined effects of PS NPs (10 mg L-1) and DBP (50 mg L-1) on dandelion (Taraxacum officinale) seedlings. The results showed that compared to control and individual-treated plants, coexposure to PS NPs and DBP significantly affected plant growth, induced oxidative stress, and altered enzymatic and nonenzymatic antioxidant levels of dandelion. Similarly, photosynthetic attributes and chlorophyll fluorescence kinetic parameters were significantly affected by coexposure. Scanning electron microscopy (SEM) results showed that PS particles had accumulated in the root cortex of the dandelion. Metabolic analysis of dandelion showed that single and combined exposures caused the plant's metabolic pathways to be profoundly reprogrammed. As a consequence, the synthesis and energy metabolism of carbohydrates, amino acids, and organic acids were affected because galactose metabolism, the citric acid cycle, and alanine, aspartic acid and glutamic acid metabolism pathways were significantly altered. These results provide a new perspective on the phytotoxicity and environmental risk assessment of MPs and PAEs in individual or coexposures.

The role of microplastics in the process of laccase-assisted phytoremediation of phenanthrene-contaminated soil

Polycyclic aromatic hydrocarbons (PAHs) are highly toxic organic pollutants widely distributed in terrestrial environments and laccase was considered as an effective enzyme in PAHs bioremediation. However, laccase-assisted phytoremediation of PAHs-contaminated soil has not been reported. Moreover, the overuse of plastic films in agriculture greatly increased the risk of co-existence of PAHs and microplastics in soil. Microplastics can adsorb hydrophobic organics, thus altering the bioavailability of PAHs and ultimately affecting the removal of PAHs from soil. Therefore, this study aimed to evaluate the efficiency of laccase-assisted maize (Zea mays L.) in the remediation of phenanthrene (PHE)-contaminated soil and investigate the effect of microplastics on this remediation process. The results showed that the combined application of laccase and maize achieved a removal efficiency of 83.47 % for soil PHE, and laccase significantly reduced the accumulation of PHE in maize. However, microplastics significantly inhibited the removal of soil PHE (10.88 %) and reduced the translocation factor of PHE in maize (87.72 %), in comparison with PHE + L treatment. Moreover, microplastics reduced the laccase activity and the relative abundance of some PAHs-degrading bacteria in soil. This study provided an idea for evaluating the feasibility of the laccase-assisted plants in the remediation of PAHs-contaminated soil, paving the way for reducing the risk of secondary pollution in the process of phytoremediation.

Characterization and source apportionment of microplastics in Indian composts

Microplastics (MP), small plastic particles under 5 mm, are pollutants known to carry heavy metals in ecosystems. Composts are a significant source of soil microplastics. This study examined MSW composts from Kochi and Kozhikode in India for microplastic concentrations and heavy metals' accumulation thereon. Microplastics were isolated using zinc chloride density separation, with Fenton's reagent used for organic matter oxidation. Resin types were identified using FTIR analysis that showed the presence of PE, PP, PS, nylon, PET, and allyl alcohol copolymer. In Kozhikode's compost, the average concentration of microplastics was 840 ± 30 items/kg, while Kochi had 1600 ± 111 items/kg, mainly polyethylene films. PE was the most prevalent resin, comprising 58.3% in Kozhikode and 73.37% in Kochi. Heavy metal analysis of MP showed significant concentrations of lead, cadmium, zinc, copper, and manganese adsorbed on the surface of microplastics. The concentrations of heavy metals in the MP before Fenton oxidation ranged from 1.02 to 2.02 times the corresponding concentrations in compost for Kozhikode and 1.23 to 2.85 times for Kochi. Source apportionment studies revealed that 64% of microplastics in Kozhikode and 77% in Kochi originated from single-use plastics. Ecological risk indices, PLI and PHI, showed that composts from both locations fall under hazard level V. The study revealed that compost from unsegregated MSW can act as a significant source of microplastics and heavy metals in the soil environment, with single-use plastics contributing major share of the issue.

Microplastics reduced bioavailability and altered toxicity of phenanthrene to maize (Zea mays L.) through modulating rhizosphere microbial community and maize growth

Due to its large specific surface area and great hydrophobicity, microplastics can adsorb polycyclic aromatic hydrocarbons (PAHs), affecting the bioavailability and the toxicity of PAHs to plants. This study aimed to evaluate the effects of D550 and D250 (with diameters of 550 μm and 250 μm) microplastics on phenanthrene (PHE) removal from soil and PHE accumulation in maize (Zea mays L.). Moreover, the effects of microplastics on rhizosphere microbial community of maize grown in PHE-contaminated soil would also be determined. The results showed that D550 and D250 microplastics decreased the removal of PHE from soil by 6.5% and 2.7% and significantly reduced the accumulation of PHE in maize leaves by 64.9% and 88.5%. Interestingly, D550 microplastics promoted the growth of maize and enhanced the activities of soil protease and alkaline phosphatase, while D250 microplastics significantly inhibited the growth of maize and decreased the activities of soil invertase, alkaline phosphatase and catalase, in comparison with PHE treatment. In addition, microplastics changed the rhizosphere soil microbial community and reduced the relative abundance of PAHs degrading bacteria (Pseudomonas, Massilia, Proteobacteria), which might further inhibit the removal of PHE from soil. This study provided a new perspective for evaluating the role of microplastics on the bioavailability of PHE to plants and revealing the combined toxicity of microplastics and PHE to soil microcosm and plant growth.

Species-dependent responses of crop plants to polystyrene microplastics

Only recently there has been a strong focus on the impacts of microplastics on terrestrial crop plants. This study aims to examine and compare the effects of microplastics on two monocotyledonous (barley, Hordeum vulgare and wheat, Triticum aestivum), and two dicotyledonous (carrot, Daucus carota and lettuce, Lactuca sativa) plant species through two complimentary experiments. First, we investigated the effects of low, medium, and high (103, 105, 107 particles per mL) concentrations of 500 nm polystyrene microplastics (PS-MPs) on seed germination and early development. We found species-dependent effects on the early development, with microplastics only significantly affecting lettuce and carrot. When acutely exposed during germination, PS-MPs significantly delayed the germination of lettuce by 24%, as well as promoted the shoot growth of carrot by 71% and decreased its biomass by 26%. No effect was recorded on monocot species. Secondly, we performed a chronic (21 d) hydroponic experiment on lettuce and wheat. We observed that PS-MPs significantly reduced the shoot growth of lettuce by up to 35% and increased its biomass by up to 64%, while no record was reported on wheat. In addition, stress level indicators and defence mechanisms were significantly up-regulated in both lettuce and wheat seedlings. Overall, this study shows that PS-MPs affect plant development: impacts were recorded on both germination and growth for dicots, and responses identified by biochemical markers of stress were increased in both lettuce and wheat. This highlights species-dependent effects as the four crops were grown under identical conditions to allow direct comparison. For future research, our study emphasizes the need to focus on crop specific effects, while also working towards knowledge of plastic-induced impacts at environmentally relevant conditions.

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.

Phytotoxic effects of polyethylene microplastics combined with cadmium on the photosynthetic performance of maize (Zea mays L.)

Microplastics (MPs) and cadmium (Cd) has attracted increasing attention due to their combined toxicity to terrestrial vegetation. Photosynthesis which utilizes light energy to synthesize organic substances is crucial for crop production. However, the plant photosynthetic response to the joint toxicity of MPs and Cd is still unknown. Here, we studied the effects of polyethylene (PE) MPs on the photosynthetic performance of two maize cultivars Xianyu 335 (XY) and Zhengdan 958 (ZD) grown in a Cd contaminated soil. Results showed that the leaf Cd concentration in XY and ZD reached 26.1 and 31.9 μg g-1, respectively. PE-MPs did not influence the leaf Cd content, but posed direct and negative effects on photosynthesis by increasing the malondialdehyde content, reducing the chlorophyll content, inhibiting photosynthetic capacity, disrupting the PSII donor side, blocking electron transfer in different photosystems, and suppressing the oxidation and reduction states of PSI. Transcriptomic analysis revealed that the inhibitory effect of combined PE-MPs and Cd on maize photosynthesis was attributed to suppressed expression of the genes encoding PSII, PSI, F-type ATPase, cytochrome b6/f complex, and electron transport between PSII and PSI. Using WGCNA, we identified a MEturquoise module highly correlated with photosynthetic traits. Hub genes bridging carbohydrate metabolism, amino acid metabolism, lipid metabolism, and translation provided the molecular mechanisms of PE-MPs and Cd tolerance in maize plants. The comprehensive information on the phytotoxicity mechanisms of Cd stress in the presence or absence of PE-MPs on the photosynthesis of maize is helpful for cloning Cd and PE-MP resistance genes in the future.

Phytotoxicity assessment of dandelion exposed to microplastics using membership function value and integrated biological response index

Microplastic (MP) pollution is a critical environmental issue. Dandelions could be used as a biomonitor of environmental pollution. However, the ecotoxicology of MPs in dandelions remains unclear. Therefore, the toxic effects of polyethylene (PE), polystyrene (PS), and polypropylene (PP) at concentrations of 0, 10, 100, and 1000 mg L-1 on the germination and early seedling growth of dandelion were investigated. PS and PP inhibited seed germination and decreased root length and biomass while promoting membrane lipid peroxidation, increasing O2•-, H2O2, SP, and proline contents, and enhancing the activities of SOD, POD, and CAT. Principal component analysis (PCA) and membership function value (MFV) analysis indicated that PS and PP could be more harmful than PE in dandelion, especially at 1000 mg L-1. In addition, according to the integrated biological response (IBRv2) index analysis, O2•-, CAT, and proline were sensitive biomarkers of dandelion contamination by MPs. Here we provide evidence that dandelion has the potential to be a biomonitor to assess the phytotoxicity of MPs pollution, especially PS with high toxicity. Meanwhile, we believe that if dandelion is to be used as a biomonitor for MPs, attention should also be paid to the practical safety of dandelion.

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.

Analyzing the impacts of cadmium alone and in co-existence with polypropylene microplastics on wheat growth

Heavy metals typically coexist with microplastics (MPs) in terrestrial ecosystems. Yet, little is known about how the co-existence of heavy metals and MPs affect crops. Therefore, this study aimed to evaluate the impact of cadmium (Cd; 40 mg/L) alone and its co-existence with polypropylene (PP)-MPs (50 and 100 µm) on seed germination, root and shoot growth, seedling dry weight (DW), and antioxidant enzyme activities of wheat. The study demonstrated that the germination rate of wheat did not vary significantly across treatment groups. Yet, the inhibitory impact on wheat seed germination was strengthened under the co-existence of Cd and PP-MPs, as the effect of a single treatment on seed germination was non-significant. The germination index and mean germination time of wheat seeds were not affected by single or combined toxicity of Cd and PP-MPs. In contrast, Cd and PP-MPs showed synergistic effects on germination energy. Wheat root and shoot length were impeded by Cd alone and in combination with PP-MPs treatments. The DW of wheat seedlings showed significant change across treatment groups until the third day, but on the seventh day, marginal differences were observed. For example, on third day, the DW of the Cd treatment group increased by 6.9% compared to CK, whereas the DW of the 100 µm PP-MPs+Cd treatment group decreased by 8.4% compared to CK. The co-occurrence of Cd and PP-MPs indicated that 50 μm PP-MPs+Cd had an antagonistic impact on wheat seedling growth, whereas 100 μm PP-MPs+Cd had a synergistic impact due to the larger size of PP-MPs. The antioxidant enzyme system of wheat seeds and seedlings increased under single Cd pollution, while the activities of superoxide dismutase, catalase, and peroxidase were decreased under combined pollution. Our study found that Cd adversely affects wheat germination and growth, while the co-existence of Cd and PP-MPs have antagonistic and synergistic effects depending on the size of the PP-MPs.

Mechanism of growth inhibition mediated by disorder of chlorophyll metabolism in rice (Oryza sativa) under the stress of three polycyclic aromatic hydrocarbons

Photosynthesis mediated by chlorophyll metabolism is the basis for plant growth, and also the important regulatory mechanism of carbon pool in cropland ecosystems. Soil organic pollutants induced growth inhibition in crop plants, herein, we conducted an in-depth investigation on the effects of three representative polycyclic aromatic hydrocarbons (PAHs), including phenanthrene (PHE), pyrene (PYR), and benzo[a]pyrene (BaP) on rice (Oryza sativa) growth and photosynthesis. PAHs were absorbed via root uptake and accumulated in leaves, causing the swelling of thylakoids and the increase of osmiophilic granules in chloroplasts. The actual quantum efficiency of PSII was significantly decreased under the stress of PHE, PYR, and BaP by 29.9%, 11.9%, and 24.1% respectively, indicating the inhibition in photon absorption and transfer, which was consistent with the decrease of chlorophyll a (22.3%-32.2% compared to the control) in rice leaves. Twenty-two encoding genes involved in chlorophyll metabolism were determined and the results indicated that the expression of chlorophyll synthetases was downregulated by over 50% whereas the degradation process was promoted. Consequently, the production of carbohydrates and the carbon fixation were inhibited, which revealed by the downregulation of intermediate metabolites in Calvin cycle and the declined carboxylation rate. The disturbed photosynthesis resulted in the decrease of the biomasses of both roots (21.0%-42.7%) and leaves (6.4%-22.1%) under the tested PAH stresses. The findings of this study implied that the photosynthetic inhibition was possibly attributed to the disorder of chlorophyll metabolism, thus providing novel insights into the mechanism of growth inhibition induced by organic pollutants and theoretical basis for the estimation of cropland carbon sequestration potential.

Microplastics change the leaching of nitrogen and potassium in Mollisols

Nowadays, the dynamics of nutrients leaching from the soils and their driving mechanism have been focused on, however, it is still unclear how microplastics (MPs) influence the nutrients' leaching in soils. In this study, five concentrations (w/w, 0.0 %, 0.5 %, 1 %, 2 %, 3 %) and three sizes of MPs of polyethylene (PE) (0.15-0.36 mm, 0.36-0.60 mm and 0.60-1.00 mm) influencing the leaching of NO₃^--N and water-soluble potassium (WSK) was simulated by a column method in Mollisols, and both the pre-fertilization and post-fertilization were considered. The results showed that, before KNO₃ addition, there was a negative power function relationship between the NO₃^--N concentration and the leaching solution volume/leaching time. The amount and concentration of NO₃^--N leaching was higher in the early leaching stage. Compared with the CK, PE_0.5% significantly reduced the leaching amount of WSK, while increased the leaching amount of NO₃^--N but not significantly. The leaching amount of WSK decreased with the increasing size of PEMP when the PEMP concentration was the same, while NO₃^--N was opposite. PE_0.60-1.00 increased the leaching amount of NO₃^--N, while reduced the leaching amount of WSK. After KNO₃ addition, compared with CK, PE_1% significantly reduced the leaching amount of NO₃^--N, and PE_1% had the lowest leaching amount of WSK. However, when the PEMP concentration in the soil reached a certain threshold (w/w, >1 %), the leaching amount of NO₃^--N and WSK increased gradually with PEMP increasing. PE_0.60-1.00 reduced the leaching amount of NO₃^--N and WSK most obviously. In general, low concentrations (w/w, <1 %) and large sizes (0.60-1.00 mm) of PEMP promoted NO₃^--N leaching and inhibited the WSK leaching from the soil before the addition of KNO₃, however, they both inhibited the leaching of NO₃^--N and WSK from the soil after addition of KNO₃.

Species sensitivity distributions of micro- and nanoplastics in soil based on particle characteristics

Micro- and nanoplastics are released into the soil through various anthropogenic activities; however, research on ecological risk assessment (ERA) of soil microplastics is limited. In this study, the species sensitivity distributions (SSDs) of representative groups of soil biota were analyzed to determine their sensitivity to microplastic properties. A total of 411 datasets from apical endpoint data within 74 studies were classified and utilized in SSD estimation. The hazardous concentrations for 5% of species for microplastics was 88.18 (40.71-191.00) mg/kg soil. It has been established that small-sized microplastics are more toxic to soil organisms than larger microplastics. Most microplastics were spherical and polystyrene, exhibiting the most adverse effects among all the microplastic types assessed herein. The results suggest that physical characteristics of microplastics are important toxicity determinants in soil ecosystems. Given the potential for adverse environmental effects, further effective management strategies should urgently be employed in these areas. This study provided an integrated perspective of microplastic ecotoxicity in soil. In addition, SSDs were estimated using larger datasets and for more species than in previous studies. This is the first study to consider microplastic properties for estimating SSD.

Effects of biodegradable and non-biodegradable microplastics on bacterial community and PAHs natural attenuation in agricultural soils

Anthropogenic activities such as in situ straw incineration and the widespread use of agricultural film led to the accumulation of polycyclic aromatic hydrocarbons (PAHs) and microplastics (MPs) in agricultural soils. In this study, four biodegradable MPs (BPs), including polylactic acid (PLA), polybutylene succinate (PBS), poly-β-hydroxybutyric acid (PHB) and poly (butylene adipate-co-terephthalate) (PBAT) and non-biodegradable low-density polyethylene (LDPE) were selected as representative MPs. The soil microcosm incubation experiment was conducted to analyze MPs effects on PAHs decay. MPs did not influence PAHs decay significantly on day 15 but showed different effects on day 30. BPs reduced PAHs decay rate from 82.4% to 75.0%- 80.2% with the order of PLA < PHB < PBS < PBAT while LDPE increased it to 87.2%. MPs altered beta diversity and impacted the functions to different extents, interfering in PAHs biodegradation. The abundance of most PAHs-degrading genes was increased by LDPE and decreased by BPs. Meanwhile, PAHs speciation was influenced with bioavailable fraction elevated by LDPE, PLA and PBAT. The facilitating effect of LDPE on 30-d PAHs decay can be attributed to the enhancement of PAHs-degrading genes and PAHs bioavailability, while the inhibitory effects of BPs were mainly due to the response of the soil bacterial community.

Do differentially charged nanoplastics affect imidacloprid uptake, translocation, and metabolism in Chinese flowering cabbage?

Micro(nano)plastics are ubiquitous in the environment. Among the microplastics, imidacloprid (IMI) concentration has been increasing in some intensive agricultural regions, thus receiving increased attention. However, only a few studies have investigated the interaction of nanoplastics (polystyrene (PS)) and IMI in vegetable crops. We studied the effects of positively (PS-NH₂) and negatively (PS-COOH) charged nanoplastics on the uptake, translocation, and degradation of IMI in Chinese flowering cabbage grown in Hoagland solution for 28 days. PS-NH₂ co-exposure with IMI inhibited plant growth, resulting in decreased plant weight, height, and root length. Translocation of IMI from the roots to the shoots was significantly lower in the presence of PS-NH₂, whereas PS-COOH accelerated the accumulation and translocation of IMI in plants, thus potentially affecting IMI metabolism in plants. Notably, IMI-NTG and 5-OH-IMI were the two dominant metabolites. PS-NH₂ co-exposure with IMI induced significant oxidation stress and considerably affected the activities of superoxide dismutase (SOD) and peroxidase (POD), indicating that the antioxidant defense system was the main mechanism for reducing oxidative damage. Notably, both positively and negatively charged nanoplastics can accumulate in Chinese flowering cabbage. Plants in the PS-COOH alone treatment group had the highest concentration of nanoplastics in both roots and shoots. The accumulation of nanoplastics, IMI, and its metabolites in plants raises concerns about their combined potential toxicity because it compromises food safety.

Impact of biochar coexistence with polar/nonpolar microplastics on phenanthrene sorption in soil

Microplastics and biochar normally coexist in soil. In this study, two microplastics of different polarities (nonpolar polyethylene (PE) and polar polybutylene adipate-co-terephthalate (PBAT)) and two wheat straw biochars produced at 400 (W4) and 700 °C (W7) were selected to investigate the sorption behaviors of phenanthrene in soil where microplastics and biochar coexisted. The results showed that the presence of PE more significantly weakened the adhesion of soil particles onto biochar than the presence of PBAT. Meanwhile, the presence of biochar enhanced the soil particle attachment on the microplastic surface. As a result, the sorption behavior of phenanthrene was significantly different in soil where biochar coexisted with microplastics of different polarities. The K_oc values of PE-biochar-soil mixtures at C_e= 0.005 C_s were up to 42 % lower than those of PBAT-biochar-soil mixtures, which is related to lower micropore area of particles isolated from the former. However, at C_e = 0.05 C_s and 0.5 C_s, the K_oc values of PE-biochar-soil mixtures were up to 1.4 times higher than those of PBAT-biochar-soil mixtures because of a more significant reduction in biochar surface polarity when it coexisted with nonpolar PE.

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.

A Systematic Review of Nano- and Microplastic (NMP) Influence on the Bioaccumulation of Environmental Contaminants: Part I-Soil Organisms

Nano- and microplastics (NMPs) are a group of contaminants that cause concern due to their abundance in the environment, high persistence, and interaction with other contaminants. This review aims to understand the role of NMP in the bioaccumulation of environmental contaminants. For that, a comprehensive literature search was conducted to identify publications that compared the uptake of contaminants in the presence and absence of NMP. In this part I, twenty-eight publications of the terrestrial compartment were analyzed. Two main taxonomic groups were studied, namely, earthworms and terrestrial plants. In earthworms, most studies observed an increase in the bioaccumulation of the contaminants, while in plants, most studies observed a decrease in the bioaccumulation. Changes in bioavailable fractions of contaminants due to NMP presence was the main reason pointed out by the authors for their outcomes. Moreover, biological aspects were also found to be important in defining how NMPs affect bioaccumulation. Dermal damage and changes in contaminant-degrading bacteria in the gut of earthworms caused an increase in bioaccumulation, and root pore blockage was a common reason for the decrease in the bioaccumulation of contaminants in plants. Nevertheless, such effects were mainly observed at high, unrealistic NMP concentrations. Finally, knowledge gaps were identified, and the limitations of this systematic review were presented.

Phytotoxic Effects of Polystyrene and Polymethyl Methacrylate Microplastics on Allium cepa Roots

Plastic contamination has become one of the most pressing environmental issues due to rapidly increasing production of disposable plastic products, their fragmentation into smaller pieces, and long persistence in the environment, which affects all living organisms, including plants. In this study, Allium cepa roots were exposed to 0.01, 0.1, and 1 g L^-1 of commercial polystyrene (PS-MPs) and polymethyl methacrylate microparticles (PMMA-MPs) for 72 h. Dynamic light scattering (DLS) analyses showed high stability of both types of MPs in ultrapure water used for A. cepa treatment. Morphometric analysis revealed no significant change in root length compared to control. Pyrolysis hyphenated to gas chromatography and mass spectrometry (Py-GC-MS) has proven PS-MPs uptake by onion roots in all treatments, while PMMA-MPs were recorded only upon exposure to the highest concentration. Neither MPs induced any (cyto)toxic effect on root growth and PMMA-MPs even had a stimulating effect on root growth. ROS production as well as lipid and protein oxidation were somewhat higher in PS-MP treatments compared to the corresponding concentrations of PMMA-MP, while neither of the applied MPs induced significant damage to the DNA molecule assayed with a Comet test. Significantly elevated activity of H₂O₂ scavenging enzymes, catalase, and peroxidases was measured after exposure to both types of MPs. Obtained results suggest that onion roots take up PS-MPs more readily in comparison to PMMA-MPs, while both types of MPs induce a successful activation of antioxidant machinery in root cells that prevented the occurrence of toxic effects.

Distribution and weathering characteristics of microplastics in paddy soils following long-term mulching: A field study in Southwest China

Agricultural plastic-film residues have been considered as one of the important sources of microplastics in the agroecosystem. However, limited researches were conducted on the accumulation of microplastics in long-term film-mulched paddy soil. This study aims to investigate the distribution and the weathering characteristics of filmy microplastics in a mulched paddy field (non-mulch, four years of mulched, and ten years of continuous mulched soil were investigated) in Southwest China. More than 50 % of the microplastics in the mulched soil were 1-3 mm, whereas the largest percentage of the microplastics in the non-mulched soil was <1 mm (55.3 %). Microplastic compositions in this field mainly consist of polyester (PES) and polyethylene (PE) (82.1 %). The abundance of microplastics increases with the film mulching time, which were 76.2 ± 18.4, 118.6 ± 44.8, and 159.6 ± 23.5 items kg^-1 in soil with non-mulching, four years of mulching, and ten years of continuous mulching, respectively. The filmy microplastics accumulated annually in the plough layer is estimated at 18.1 million items ha^-1. Weathering characteristics of filmy microplastics extracted from paddy soil were characterized using FTIR, SEM-EDS, AFM, and contact angle meter. The vinyl, carbonyl, and hydroxyl indices calculated from FTIR results showed that the degradation degree of microplastics incereased as mulching time rose; compared with commercial PE films, the oxygen-containing functional groups of soil-extracted PE films were increased. This study revealed the status of microplastic pollution in paddy soil with long-term mulching. It provided primary data and a scientific basis for further study on environmental behavior and ecological impacts of microplastics in agricultural soils.

Comparison of metabolome profiles in zebrafish (Danio rerio) intestine induced by polystyrene microplastics with different sizes

Microplastics (MPs) are widespread in aquatic environments. They could induce intestinal toxicity in the fish. However, research on the metabolic toxicity of polystyrene microplastics (PS-MPs) with different particle sizes to the zebrafish intestine is still limited. Here, metabolomics using ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was applied to characterize the metabolic disorders in zebrafish intestine after exposure to 500 μg/L PS-MPs with different sizes (100 nm, 5 μm, and 200 μm) for 21 days. Results showed that the 100 nm PS-MPs group increased glutathione content. A total of 35, 165, and 87 metabolites were significantly altered in zebrafish intestines of 100 nm, 5 μm, and 200 μm groups under positive ion mode, respectively. In comparison, 31, 115, and 45 metabolites were changed in the 100 nm, 5 μm, and 200 μm groups under negative ion mode, respectively. Metabolic pathway analysis indicated that carbohydrate metabolism, amino acid metabolism, and nucleotide metabolism were changed in all three groups. The greatest changes were found in the 5 μm group. Moreover, treatment with micro-sized PS-MP groups specifically changed lipid metabolism, which might be related to pathogenic bacteria (Streptococcus and Moraxella). In the 100 nm PS-MP group, S-adenosyl-L-methionine (SAM) was found to be markedly related to the intestinal microbiota. SAM level was significantly increased, which might account for the elevated glutathione content. To sum up, the mechanisms of nano-sized MPs (oxidative stress) and micro-sized MPs (lipid metabolism disorder) were distinct. This study provides novel insight into the toxicity mechanism of MPs in the zebrafish intestine.

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.

Insights into the accumulation, distribution and toxicity of pyrene associated with microplastics in rice (Oryza sativa L.) seedlings

Microplastic and polycyclic aromatic hydrocarbons (PAHs) can be introduced into agroecosystems through various agricultural activities and may threaten food safety and human health. However, little research has focused on the behavior of microplastics-associated PAHs and their toxicity effects in agroecosystems, especially in crops. In the present study, we investigated the accumulation, distribution and toxicity of pyrene associated with polyethylene (PE) microplastics in rice (Oryza sativa L.). With quantitative analysis using 14C isotope labelling, the total accumulation efficiency of 14C-pyrene in rice seedlings was 22.4 ± 1.2% and 14.5 ± 0.3% when exposed to freely dissolved pyrene and PE-associated pyrene, respectively. The translocation of 14C-pyrene was significantly decreased by microplastics adsorption even when the amount of pyrene in the rice roots had no significant difference. Subcellular distribution of 14C-pyrene in rice suggested that PE microplastics-associated pyrene located more on cell walls than free dissolved pyrene. Furthermore, results showed free pyrene, but not PE-associated pyrene, significantly decreased the length and biomass of rice roots as well as increased the activities of antioxidant enzymes (superoxide dismutase and catalase). It indicated that the association with microplastics alleviated the phytotoxicity of pyrene in rice seedlings. These findings shed new light on the environmental behavior and effects of PAHs associated with microplastics in crops and will be helpful to its comprehensive risks assessment.

Polystyrene microplastics protect lettuce (Lactuca sativa) from the hazardous effects of Cu(OH)2 nanopesticides

Copper-based nanopesticides are released into the environment during foliar spray application, and they could, on their own or in combination with microplastics (MPs), pose threats to environmental safety and human health. In this study, Cu(OH)₂ nanowires greatly decreased the vigor of lettuce seeds (p< 0.01) and the root length of lettuce seedlings (p< 0.01) and significantly altered the lettuce antioxidant defence system and MDA content (p< 0.05). Released Cu²⁺ played a critical role in the toxicity mechanism of Cu(OH)₂ nanowires in lettuce seedlings, as evidenced by the substantial accumulation of Cu in the seedling roots (p< 0.01) rather than in the leaves. Polystyrene (PS) MPs (1 mg/L) stimulated lettuce seedling growth, as shown by the (highly) significant increase in root and leaf length and in the seed vigor index (p< 0.01 or 0.05). Notably, PS MPs (1 mg/L) neutralized the hazardous effects of 1 mg/L Cu(OH)₂ nanowire treatment on lettuce growth, as reflected by the vitality and root length of the seedlings returning to normal levels. The PS MPs (1 mg/L) absorbed on middle root surfaces and strongly hindered Cu accumulation in lettuce roots, which was the predominant mechanism by which PS MPs suppressed the hazardous effects of the Cu(OH)₂ nanowires. This study strengthens the understanding of the toxicity and toxicity mechanisms of Cu(OH)₂ nanowires with or without PS MPs in the environment.

Responses of cherry radish to different types of microplastics in the presence of oxytetracycline

Croplands have become a hotspot for antibiotic and microplastic (MP) pollution. However, little is known regarding their combined effects on crops. In this study, the individual and combined effects of oxytetracycline (OTC) and three MPs (i.e., polypropylene (PP), polyamide (PA), and polyvinylchloride (PVC)) on cherry radish were investigated using pot experiments. Individually, OTC (50 mg kg^-1), PA (2%, w/w), and PP (2%, w/w) induced negligible effects on cherry radish biomass and the root/shoot ratio. However, PVC (2%, w/w) significantly inhibited cherry radish growth; that is, its shoot and root fresh weight decreased by 46.2% and 81.1%, respectively. In the combined exposure groups, OTC alleviated the adverse effects of PVC on the cherry radish leaf number and shoot fresh weight. This was linked to that OTC increased the content of photosynthetic pigments. Superoxide dismutase activity in cherry radish roots was inhibited to different extents in all treatment groups except for the PA and PVC treatments. Malondialdehyde (MDA) content in cherry radish roots increased in all treatment groups, suggesting that both OTC and MPs caused oxidative damage to cherry radish root cells, therefore inhibiting cherry radish root growth. However, the presence of OTC non-significantly changed the effects of MPs on cherry radish roots. Irrespective of OTC presence, MPs induced a reduction in the root/shoot ratio of cherry radish, suggesting that the inhibitory effect of MPs on cherry radish roots was stronger than that on shoots. These findings contribute to the evaluation of the phytotoxicity of antibiotics and MPs in soil-vegetable systems.

Microplastic/nanoplastic toxicity in plants: an imminent concern

The toxic impact of microplastics/nanoplastics (MPs/NPs) in plants and the food chain has recently become a top priority. Several research articles highlighted the impact of MPs/NPs on the aquatic food chain; however, very little has been done in the terrestrial ecosystem. A number of studies revealed that MPs/NPs uptake and subsequent translocation in plants alter plant morphological, physiological, biochemical, and genetic properties to varying degrees. However, there is a research gap regarding MPs/NPs entry into plants, associated factors influencing phytotoxicity levels, and potential remediation plans in terms of food safety and security. To address these issues, all sources of MPs/NPs intrusion in agroecosystems should be revised to avoid these hazardous materials with special consideration as preventive measures. Furthermore, this review focuses on the routes of accumulation and transmission of MPs/NPs into plant tissues, related aspects influencing the intensity of plant stress, and potential solutions to improve food quality and quantity. This paper also concludes by providing an outlook approach of applying exogenous melatonin and introducing engineered plants that would enhance stress tolerance against MPs/NPs. In addition, an overview of inoculation of beneficial microorganisms and encapsulated enzymes in soil has been addressed, which would make the degradation of MPs/NPs faster.

Polystyrene nanoplastic contamination mixed with polycyclic aromatic hydrocarbons: Alleviation on gas exchange, water management, chlorophyll fluorescence and antioxidant capacity in wheat

Polycyclic aromatic hydrocarbons (PAHs) constitute a significant environmental pollution group that reaches toxic levels with anthropogenic activities. The adverse effects of nanoplastics accumulating in ecosystems with the degradation of plastic wastes are also a growing concern. Previous studies have generally focused on the impact of single PAH or plastic fragments exposure on plants. However, it is well recognized that these contaminants co-exist at varying rates in agricultural soil and water resources. Therefore, it is critical to elucidate the phytotoxicity and interaction mechanisms of mixed pollutants. The current study was designed to comparatively investigate the single and combined effects of anthracene (ANT, 100 mg L^-1), fluorene (FLU, 100 mg L^-1) and polystyrene nanoplastics (PS, 100 mg L^-1) contaminations in wheat. Plants exposed to single ANT, FLU and PS treatments demonstrated decline in growth, water content, high stomatal limitations and oxidative damage. The effect of ANT + FLU on these parameters was more detrimental. In addition, ANT and/or FLU treatments significantly suppressed photosynthetic capacity as determined by carbon assimilation rate (A) and chlorophyll a fluorescence transient. The antioxidant system was not fully activated (decreased superoxide dismutase, peroxidase and glutathione reductase) under ANT + FLU, then hydrogen peroxide (H₂O₂) content (by 2.7-fold) and thiobarbituric acid reactive substances (TBARS) (by 2.8-fold) increased. Interestingly, ANT + PS and FLU + PS improved the growth, water relations and gas exchange parameters. The presence of nanoplastics recovered the adverse effects of ANT and FLU on growth by protecting the photosynthetic photochemistry and reducing oxidative stress. PAH plus PS reduced the ANT and FLU accumulation in wheat leaves. In parallel, the increased antioxidant system, regeneration of ascorbate, glutathione and glutathione redox status observed under ANT + PS and FLU + PS. These findings will provide an information about the phytotoxicity mechanisms of mixed pollutants in the environment.

Ecotoxic effects of microplastics and contaminated microplastics - Emerging evidence and perspective

The high prevalence and persistence of microplastics (MPs) in pristine habitats along with their accumulation across environmental compartments globally, has become a matter of grave concern. The resilience conferred to MPs using the material engineering approaches for outperforming other materials has become key to the challenge that they now represent. The characteristics that make MPs hazardous are their micro to nano scale dimensions, surface varied wettability and often hydrophobicity, leading to non-biodegradability. In addition, MPs exhibit a strong tendency to bind to other contaminants along with the ability to sustain extreme chemical conditions thus increasing their residence time in the environment. Adsorption of these co-contaminants leads to modification in toxicity varying from additive, synergistic, and sometimes antagonistic, having consequences on flora, fauna, and ultimately the end of the food chain, human health. The resulting environmental fate and associated risks of MPs, therefore greatly depend upon their complex interactions with the co-contaminants and the nature of the environment in which they reside. Net outcomes of such complex interactions vary with core characteristics of MPs, the properties of co-contaminants and the abiotic factors, and are required to be better understood to minimize the inherent risks. Toxicity assays addressing these concerns should be ecologically relevant, assessing the impacts at different levels of biological organization to develop an environmental perspective. This review analyzed and evaluated 171 studies to present research status on MP toxicity. This analysis supported the identification and development of research gaps and recommended priority areas of research, accounting for disproportionate risks faced by different countries. An ecological perspective is also developed on the environmental toxicity of contaminated MPs in the light of multi-variant stressors and directions are provided to conduct an ecologically relevant risk assessment. The presented analyses will also serve as a foundation for developing environmentally appropriate remediation methods and evaluation frameworks.

Interactions of microplastics with organic, inorganic and bio-pollutants and the ecotoxicological effects on terrestrial and aquatic organisms

As emerging contaminants, microplastics (MPs) have attracted global attention. They are a potential risk to organisms, ecosystems and human health. MPs are characterized by small particle sizes, weak photodegradability, and are good environmental carriers. They can physically adsorb or chemically react with organic, inorganic and bio-pollutants to generate complex binary pollutants or change the environmental behaviors of these pollutants. We systematically reviewed the following aspects of MPs: (i) Adsorption of heavy metals and organic pollutants by MPs and the key environmental factors affecting adsorption behaviors; (ii) Enrichment and release of antibiotic resistance genes (ARGs) on MPs and the effects of MPs on ARG migration in the environment; (iii) Formation of "plastisphere" and interactions between MPs and microorganisms; (iv) Ecotoxicological effects of MPs and their co-exposures with other pollutants. Finally, scientific knowledge gaps and future research areas on MPs are summarized, including standardization of study methodologies, ecological effects and human health risks of MPs and their combination with other pollutants.

Micro(nano)plastics in food system: potential health impacts on human intestinal system

Micro(nano)plastics (MNPs) in human food system have been broadly recognized by researchers and have drawn an increasing public attention to their potential health risks, particularly the risk to the intestinal system regarding the long-term exposure to MNPs through food consumption. This study aims to review the environmental properties (formation and composition) of MNPs and MNPs pollution in human food system following the order of food production, food processing and food consumption. The current analytic and identical technologies utilized by researchers are also summarized in this review. In fact, parts of commonly consumed food raw materials, processed food and the way to take in food all become the possible sources for human MNPs ingestion. In addition, the available literatures investigating MNPs-induced intestinal adverse effect are discussed from in vitro models and in vivo mammalian experiments, respectively. Particle translocation, cytotoxicity, damaged gut barrier, intestinal inflammation as well as microbial alteration are mostly reported. Moreover, the practical remediation strategies for MNPs pollution are also illustrated in the last section. This review is expected to provide a research insight for foodborne MNPs and arouse more public awareness of MNPs pollution in food and potential risk for human intestinal health.

Phytotoxicity complements chemical assessment for re-use and re-purposing of refinery wastes for soil amendment purposes after bioremediation

The objective of this study was to assess the suitability of onsite re-use of mature compost for landscaping and tree mulching, produced from the bioremediation of oily sludge from the refinery. Compost samples from the co-composting process were analysed for a range of contaminants, including a human health risk assessment fractionation (HRAF) of the remaining petroleum hydrocarbons, as well as a phytotoxicity test. The chemical characterisation demonstrated that the process removed more than 94% of the original petroleum hydrocarbons from the sludge, and the removal rates were high at 1155 mg/kg/day. The HRAF demonstrated no residual risks, posed by the petroleum hydrocarbons present in the compost to human health if used on-site when compared to the relevant Australian environmental investigation levels (ILs). However, the phytotoxicity assessment demonstrated that the compost was toxic to germinating lettuce. The gap in the literature this study addressed was to provide an estimate of the LD₅₀ and no effect concentration (NEC) for the compost using a standard plant bioassay containing a range of residual (aged) and bioremediated refinery process wastes, including petroleum hydrocarbons. The values estimated for LD₅₀ and NEC were approximately 125 and 43 mg/kg, respectively for compost containing residual petroleum hydrocarbon fractions, filling a gap in the current literature which has limited data on standard toxicity values that can be used in determining and informing commercial remediation strategies and their outcomes with aged sludges. Phytotoxicity was shown to be an important complement to conventional analyses and HRAF data when characterising the sludge, and understanding its potential for re-use. The novelty of the study is that it highlighted a gap in the complementary use of chemical and bioassay analyses for evaluating refinery waste remediation endpoints, which has potential for broader application to other projects.

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.

Microplastic particles alter wheat rhizosphere soil microbial community composition and function

The wide existence of microplastics (MPs) in the terrestrial systems is proved by -many studies, and their presence could potentially change the soil chem-physical properties and processes. Various types of microplastics may have different behaviors, inducing distinct effects on the soil ecosystems. However, the knowledge of microplastic impacts on rhizosphere soil bacterial community structure is limited. In our study, three types of microplastics, i.e., polyethylene (PE), polyvinylchloride (PVC) and polystyrene (PS), with the same particle size (200 µm) and concentration (2%) were used to investigate their influences on the rhizosphere soil bacterial communities. Results revealed that the alpha diversities (richness, evenness and diversity) of microbiota in the rhizosphere soil were variously decreased by the microplastics, especially the PE MPs. The relative abundance of some various phyla and genera related to pollution degradation was miscellaneously increased, indicating that the MPs with different characterizations may have miscellaneous biodegradation pathways. Moreover, the PICRUSt2 analysis demonstrated that PS decreased most functional category levels and led to a decrease of bacterial genus number, however, PE and PVC improved metabolic pathways and xenobiotics biodegradation and metabolism. Our findings offer important knowledge of how the microplastics with different characterizations influence rhizosphere soil bacterial communities and their related function.

Ecotoxicological effects of micro- and nanoplastics on terrestrial food web from plants to human beings

Micro- and nanoplastics (MNPs) are present in almost all environmental compartments. Terrestrial soils are major environmental reservoirs for MNPs, but the ecotoxicological effects of MNPs on terrestrial biota remain relatively understudied. In this review, we collated findings of previous research on the uptake and impact of MNPs in terrestrial organisms, including flora, fauna, and human beings. Terrestrial plants can take up MNPs via the roots or leaves and translocate them to other parts. MNPs have been detected in the gastrointestinal tracts or feces of many terrestrial animals, including some high trophic-level predators, indicating the incidence of direct ingestion or trophic transfer of MNPs. The presence of MNPs in food items and human feces combines to verify human intake of MNPs via the dietary pathway. Exposure to MNPs can cause diverse effects on terrestrial organisms, including alterations in growth performance, oxidative stress, metabolic disturbance, cytotoxicity, genotoxicity, and mortality. The biological internalization and impact of MNPs are influenced by the physicochemical properties of MNPs (e.g., particle size, polymer type, surface chemistry, and exposure concentrations) and the physiology of the species. MNPs can also affect the bioavailability of co-occurring intrinsic or extrinsic contaminants to terrestrial biota, but their specific role is under dispute. Finally, we underlined the current research gaps and proposed several priorities for future studies.

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

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