Attachment of positively and negatively charged submicron polystyrene plastics on nine typical soils

Association of tetrabromobisphenol A (TBBPA) with micro/nano-plastics: A review of recent findings on ecotoxicological and health impacts

Despite the diverse research into the environmental impact of plastics, several stones have yet to be unraveled in terms of their ecotoxicological potential. Moreover, their detrimental impacts have become terrifying in recent years as the understanding of their tendency to associate and form cohorts with other emerging contaminants grew. Despite the hypothesis that microplastics may potentially adsorb organic pollutants, sequestering and making them not bioavailable for enhanced toxicity, evidence with pollutants such as Tetrabromobisphenol A (TBBPA) defers this assertion. TBBPA, one of the most widely used brominated flame retardants, has been enlisted as an emerging contaminant of serious environmental and human health concerns. Being also an additive to plasticware, it is not far to suspect that TBBPA could be found in association with micro/nanoplastics in our environment. Several pieces of evidence from recent studies have confirmed the micro/nanoplastics-TBBPA association and have exposed their compounded detrimental impacts on the environment and human health. This study, therefore, presents a comprehensive and up-to-date review of recent findings regarding their occurrence, factors that foster their association, including their sorption kinetics and isotherms, and their impacts on aquatic/agroecosystem and human health. The way forward and prospects for future studies were presented. This research is believed to be of significant interest to the readership due to its relevance to current environmental challenges posed by plastics and TBBPA. The study not only contributes valuable insights into the specific interaction between micro/nanoplastics and TBBPA but also suggests the way forward and prospects for future studies in this field.

Influencing mechanisms of microplastics existence on soil heavy metals accumulated by plants

Microplastics (MPs) and heavy metals often coexist in soil, drawing significant attention to their interactions and the potential risks of biological accumulation in the soil-plant system. This paper comprehensively reviews the factors and biochemical mechanisms that influence the uptake of heavy metals by plants, in the existence of MPs, spanning from rhizospheric soil to the processes of root absorption and transport. The paper begins by introducing the origins and current situation of soil contamination with both heavy metals and MPs. It then discusses how MPs alter the physicochemical properties of rhizospheric soil, with a focus on parameters that affect the bioavailability of heavy metals such as aggregates, pH, Eh, and soil organic carbon (SOC). The paper also examines the effect of this pollution on soil organisms and plant growth and reviews the mechanisms by which MPs affect the bioavailability and movement-transformation of heavy metals in rhizospheric soil. This examination emphasizes the roles of rhizospheric microbes, soil fauna, and root physiological metabolism. Finally, the paper outlines the research progress on the mechanisms by which MPs influence the uptake and transport of heavy metals by plant roots. Through this comprehensive review, this paper provides aims to provide environmental managers with a detailed understanding of the potential impact of the coexistence of MPs and heavy metals on the soil-plant ecosystem.

Attachment of various-shaped polystyrene microplastics to silica surfaces: Experimental validation of the equivalent Cassini oval extended DLVO model

Microplastics (MPs) vary in shape and surface characteristics in the environment. The attachment of MPs to surfaces can be studied using the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. However, this theory does not account for the shape MPs. Therefore, we investigated the attachment of spherical, pear-shaped, and peanut-shaped polystyrene MPs to quartz sand in NaCl and CaCl2 solutions using batch tests. The attachment of MPs to quartz sand was quantified using the attachment efficiency (alpha). Subsequently, alpha behaviors were interpreted using energy barriers (EBs) and interaction minima obtained from extended DLVO calculations, which were performed using an equivalent sphere model (ESM) and a newly developed equivalent Cassini model (ECM) to account for the shape of the MPs. The ESM failed to interpret the alpha behavior of the three MP shapes because it predicted high EBs and shallow minima. The alpha values for spherical MPs (0.62-1.00 in NaCl and 0.48-0.96 in CaCl2) were higher than those for pear- and peanut-shaped MPs (0.01-0.63 in NaCl and 0.02-0.46 in CaCl2, and 0.01-0.59 in NaCl and 0.02-0.40 in CaCl2, respectively). Conversely, the ECM could interpret the alpha behavior of pear- and peanut-shaped MPs either by changes in EBs or interaction minima as a function of orientation angles and electrolyte ionic strength. Therefore, the particle shape must be considered to improve the attachment analyses.

Influence of microplastics on the availability of antibiotics in soils

Microplastics (MPs) and antibiotics, as two major types of emerging pollutants, inevitably coexist in the soil environment due to agricultural film residue, sewage irrigation and sludge application. However, the impact of MPs on antibiotic availability in soils with varying characteristics has not been extensively studied. Therefore, in this study, an interference experiment was conducted using three types of MPs (polyethylene (PE), polyvinyl chloride (PVC) and polypropylene (PP)) in red soil, paddy soil and cinnamon soil. The available antibiotics in soils were evaluated using diffusive gradients in thin-films (DGT). Results showed that MPs had a significant impact on the amount of antibiotics adsorbed on soil solid (Cs) by providing additional binding sites or altering soil characteristics (e.g., pH and dissolved organic carbon). The most significant effects on Cs were observed in cinnamon soil, and the Cs values were dependent on concentration of MPs. The available antibiotics, as measured by DGT significantly decreased after the addition of MPs. This decrease was influenced by the soil characteristics. However, the concentration of antibiotics in soil solutions (Cd) was only slightly impacted by MPs. Therefore, the influence of MPs on the migration of antibiotics was reflected by their impact on the soil/water partition coefficient (Kd), while the resupply ability (R) from the soil solid phase was less influential. Moreover, the dosage of MPs had a significant effect on the availability of antibiotics in CS by promoting the adsorption of antibiotics on the solid phase, while in RS and PS, the soil properties played a dominate role in the changes in antibiotic availability after MP addition. These results indicate that the impact of MPs on available antibiotics mainly depends on soil properties. In addition, DGT measurement is more sensitive than soil solution to investigate the effects of coexisting pollutants on the behavior of antibiotics in soil.

Degradation and potential metabolism pathway of polystyrene by bacteria from landfill site

Microplastics pollution has garnered significant attention in recent years. The unique cross-linked structure of polystyrene microplastics makes them difficult to biodegrade. In this study, we investigated the microbial community in landfill soil that has the ability to degrade polystyrene, as well as two isolated strains, named Lysinibacillus sp. PS-L and Pseudomonas sp. PS-P. The maximum weight loss of polystyrene film and microplastic in 30 days is 2.25% and 6.99% respectively. The water contact angle of polystyrene film decreased by a maximum of 35.70% during biodegradation. The increase in hydrophilicity is attributed to the oxidation reaction and formation of hydroxyl groups during the degradation of polystyrene. The carbon and oxygen element contents of polystyrene decreased and increased by a maximum of 3.81% and 0.79% respectively. The peak intensity changes at wavelengths of 3285-3648 cm-1 and 1652 cm-1 in Fourier transform infrared spectroscopy confirmed the formation of hydroxyl and carbonyl groups. Furthermore, quantitative PCR revealed the gene expression levels of alkane monooxygenase and alcohol dehydrogenase were upregulated by 8.8-fold and 8.5-fold respectively in PS biodegradation. Additionally, genome annotation of Pseudomonas sp. PS-P identified nine genes associated with polystyrene metabolism. These findings highlight Pseudomonas sp. PS-P as a potential candidate strain for polystyrene degradation enzymes or genes. Thus, they lay the groundwork for understanding the potential metabolic mechanisms and pathways involved in polystyrene degradation.

Molecular mechanisms and physiological responses of rice leaves co-exposed to submicron-plastics and cadmium: Implication for food quality and security

The effects of co-exposure to aged submicron particles (aSMPs) and Cd as model contaminants on rice leaves via the foliar route were investigated. Thirty-day-old rice seedlings grown in soil were exposed to Cd (nitrate) through foliar spraying at concentrations of 1, 10, 50, 100, and 500 μM, with or without aSMP at a rate of 30 μg d-1. It was observed that Cd translocated from leaves to roots via stems even without co-exposure to SMP. Co-exposure can reduce cadmium levels in leaves. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis confirmed a significant reduction (29.3 - 77.9%) in Cadmium accumulation in the leaves of rice plants during co-exposure. Exposure to Cd resulted in physiological, transcriptomic, and metabolomic changes in rice leaves, disrupting 28 metabolism pathways, and impacting crop yield and quality. Exposure to both Cd and aSMPs can interfere with the Cd distribution in plants. Rice leaves exposed solely to Cd exhibit higher toxicity and Cd accumulation, compared to those co-exposed to Cd and aSMPs. The accumulation of Cd in plant leaves is enhanced with aSMPs, which may lead to more pronounced gene expression regulation and changes in metabolic pathways, compared to Cd exposure. Our study found that the independent Cd exposure group had higher Cd accumulation and toxicity in rice leaves compared to the combined exposure of Cd and aSMPs. We hypothesize that aged negatively charged SMPs can capture Cd and reduce its exposure in the free state while jointly inhibiting Cd-induced oxidative and chloroplast damage, thereby reducing the potential risk of Cd exposure in rice plants.

Effects of microplastics pollution on plant and soil phosphorus: A meta-analysis

The widespread use of microplastics leads to environmental pollution, which threatens ecosystem functions (i.e., nutrient cycling). Some studies have focused on the impacts of microplastics on phosphorus from plants and soils. However, inconsistent responses of plant and soil phosphorus to microplastics have been observed. This work synthesized the results of 781 paired observations from 73 publications to explore the overall effects of microplastics on plant and soil phosphorus and whether the impacts depended on microplastics properties and experimental variables. We found the overall negative effects of microplastics on plant phosphorus and soil available phosphorus. Additionally, microplastics significantly inhibited neutral phosphatase activity but increased soil phosphorus leaching. Furthermore, the impacts of microplastics on plant and soil phosphorus varied depending on microplastics types, sizes, concentrations, and experimental durations. Soil total phosphorus and available phosphorus exhibited stronger negative responses to biodegradable than conventional microplastics. Acid phosphatase was more sensitive to biodegradable than conventional microplastics. In addition, soil total phosphorus, available phosphorus, and alkaline phosphatase were significantly correlated with microplastic concentrations and exposure time. Overall, our findings suggest that microplastics potentially threaten soil fertility and plant productivity. This work provides an important reference for predicting ecosystem functions in the context of microplastics pollution.

Effects of microplastic properties and dissolved organic matter on phosphorus availability in soil and aqueous mediums

Plastic mulching films and phosphate fertilizers have been widely used to improve agricultural soil productivity. Microplastics (MP) and phosphorus (P) significantly accumulate in agricultural soil and water bodies. However, the effects of residual MP on P availability in soil and aqueous mediums remain unclear. In this study, available P (Olsen-P) in soils and P adsorption capacity in aqueous medium were determined to examine the influence of MP properties on P availability in laboratory. In agricultural soils, Olsen-P was significantly affected by MP types. Conventional MP (mulching film particles), such as polyethylene (PE) and polyvinyl chloride (PVC), and biodegradable MP, such as polylactic acid (PLA), substantially reduced soil Olsen-P by 9.7-38.6% and 38.4-73.6%, respectively. The size and concentration of MP strongly affected soil Olsen-P, with smaller (25 μm) and more concentrated (5%) MP causing greater reductions in Olsen-P. In the soil contaminated with MP, increased fulvic acid content significantly increased Olsen-P levels. Microplastics exhibited strong P adsorption capacities, leading to decreased P availability in aqueous medium. Conventional MP exhibited a higher P adsorption capacity than biodegradable MP, with P distribution coefficients (Kd values) ordered as PVC (5.19 L kg-1) > PE (4.23 L kg-1) > PLA (2.48 L kg-1). Notably, the Kd values increased with decreasing sizes of conventional MP, whereas the opposite trend was observed for PLA. The presence of fulvic acid affected the adsorption of P by MP in aqueous medium. Increased fulvic acid content reduced P adsorption capacity of MP, thus enhancing P availability. Our findings contribute to a better understanding of P dynamics in MP-contaminated agricultural soil and aqueous medium, which could aid in formulating sustainable agricultural practices and effective environmental management strategies for plastic mulching films and P contamination.

Aggregation behavior of polyethylene microplastics in the nearshore environment: The role of particle size, environmental condition and turbulent flow

Estuary and coastal waters are hotspot areas for microplastics (MPs) pollution. MPs of varying sizes converge in this complex nearshore environment. Aggregation is an important process that affects the transport and fate of MPs in the aqueous environment. Nevertheless, the influence of different factors on the aggregation behavior and the aggregates structure of MPs is unclear. In this study, the aggregation behavior and the aggregates structure of polyethylene microplastics (PEs) of different sizes under the impact of nearshore environmental conditions (i.e., salinity gradient, dissolved organic matter-DOM, turbulent flow) were investigated. The results show that particle size was the dominant factor affecting the stability of PEs in the aqueous environment, and the critical coagulation concentration (CCC) of PEs shifts to the right with increasing size. It was also found that the size of PEs stable aggregates is negatively correlated with the turbulent kinetic energy dissipation rate. The particle size of PEs can significantly affect the fractal dimension (FD) of stable aggregates, and the smaller the particle size, the more compact the aggregates formed. Moreover, salinity and DOM control the size and FD of PEs stable aggregates through different mechanisms. The findings of this study will be helpful for the prediction of the transport and fate of MPs in the aqueous environment.

Immune and inflammatory responses of human macrophages, dendritic cells, and T-cells in presence of micro- and nanoplastic of different types and sizes

Environmental pollution by microplastics (MPs) is a growing concern regarding their impact on aquatic and terrestrial systems and human health. Typical exposure routes of MPs are dermal contact, digestion, and inhalation. Recent in vitro and in vivo studies observed alterations in immunity after MPs exposure, but systemic studies using primary human immune cells are scarce. In our investigation, we addressed the effect of polystyrene (PS) and poly methyl methacrylate (PMMA) in three different sizes (50-1100 nm) as well as amino-modified PS (PS-NH2; 50 nm) on cells of the adaptive and innate immune system. T-cells isolated from human peripheral blood mononuclear cells (PBMCs) were least affected regarding the cytotoxicity but displayed increased activation marker expression after 72 h, and strongly modulated cytokine secretion patterns. Conversely, phagocytic dendritic cells and macrophages derived from isolated monocytes were highly sensitive to pristine MPs. Their marker expression suggested a downregulation of the inflammatory phenotypes indicative of M2 macrophage induction after MPs exposure for 24 h. Our results showed that even pristine MPs affected immune cell function and inflammatory phenotype dependent on MPs polymers, size, and immune cell type.

Adsorption behaviors and bioavailability of tetrabromobisphenol A in the presence of polystyrene microplastic in soil: Effect of microplastics aging

Microplastics, a kind of emerging pollutant, have become a global environmental research hotspot in recent years due to its wide distribution in soil and its impact on soil ecosystems. However, little information is available on the interactions between microplastics and organic contaminants in soil, especially after microplastic aging. The impact of polystyrene (PS) microplastic aging on the sorption of tetrabromobisphenol A (TBBPA) in soil and the desorption characteristics of TBBPA-loaded microplastics in different environments were studied. The results showed a significant increase of 76.3% in adsorption capacity of TBBPA onto PS microplastics after aging for 96 h. Based on the results of characterization analysis and density functional theory (DFT) calculation, the mechanisms of TBBPA adsorption changed mainly from hydrophobic and π-π interactions on pristine PS microplastics to hydrogen bond and π-π interactions on aged PS microplastics. The presence of PS microplastics increased the TBBPA sorption capacity onto soil-PS microplastics system and significantly altered the distribution of TBBPA on soil particles and PS microplastics. The high TBBPA desorption over 50% from aged PS microplastics in simulated earthworm gut environment suggested that TBBPA contamination combined with PS microplastics might pose a higher risk to macroinvertebrates in soil. Overall, these findings contribute to the understanding of impact of PS microplastic aging in soil on the environmental behaviors of TBBPA, and provide valuable reference for evaluating the potential risk posed by the co-existence of microplastics with organic contaminants in soil ecosystems.

Microplastics are transferred by soil fauna and regulate soil function as material carriers

The ecotoxicological effects of microplastics, a new and widespread ecosystem pollutant, have been extensively reported. However, it remains unclear whether soil fauna transfer microplastics and whether migration behaviours influence subsequent ecological functions in terrestrial ecosystems. We investigated the transfer patterns of microplastics and their adsorbed substances by soil animals (the springtail, Folsomia candida) and the effect of the transfer on the decomposition of soil organic matter through a standardized cotton strip assay. The results showed that springtails had a strong ability to transfer microplastics into the soil. The adsorbed nutrient (nitrogen; N), pollutant (cadmium; Cd), and green fluorescent Escherichia coli (GFP-E. coli) were also transferred with the microplastics. In addition, cotton strip decomposition was accelerated when the microplastics adsorbed N, but the adsorption of Cd decreased decomposition. These ecological effects were particularly strong for small microplastics. Microplastic transfer regulated soil bacterial communities, promoting the growth of Ascomycota fungi and inhibiting that of Basidiomycota, leading to cotton strip decomposition. Thus, microplastic pollution may occur at one site, but microplastics can be transferred anywhere in terrestrial ecosystems by soil animals and adsorb other substances, including nutrients and pollutants, that affect ecosystem function. Therefore, more studies on the migration behaviour of microplastics are necessary.

Positively Charged Microplastics Induce Strong Lettuce Stress Responses from Physiological, Transcriptomic, and Metabolomic Perspectives

Microplastics (MPs) can enter plants through the foliar pathway and are potential hazards to ecosystems and human health. However, studies related to the molecular mechanisms underlying the impact of foliar exposure to differently charged MPs to leafy vegetables are limited. Because the surfaces of MPs in the environment are often charged, we explored the uptake pathways, accumulation concentration of MPs, physiological responses, and molecular mechanisms of lettuce foliarly exposed to MPs carrying positive (MP+) and negative charges (MP-). MPs largely accumulated in the lettuce leaves, and stomatal uptake and cuticle entry could be the main pathways for MPs to get inside lettuce leaves. More MP+ entered lettuce leaves and induced physiological, transcriptomic, and metabolomic changes, including a decrease in biomass and photosynthetic pigments, an increase in reactive oxygen species and antioxidant activities, a differential expression of genes, and a change of metabolite profiles. In particular, MP+ caused the upregulation of circadian rhythm-related genes, and this may play a major role in the greater physiological toxicity of MP+ to lettuce, compared to MP-. These findings provide direct evidence that MPs can enter plant leaves following foliar exposure and a molecular-scale perspective on the response of leafy vegetables to differently charged MPs.

How do controlled-release fertilizer coated microplastics dynamically affect Cd availability by regulating Fe species and DOC content in soil?

Microplastics (MPs) affect the accumulation of heavy metals by regulating the soil environment. However, studies on the dynamic effects of microplastics on the available states of heavy metals in soil are lacking. In particular, how controlled-release fertilizer coated microplastics can synergistically change the avsilable states of heavy metals in soil by affecting soil physical and chemical properties and microbial community structure is still lacking. The dynamic effect of polyurethane (PU) MPs on the effective state of soil cadmium (Cd; DGTCd), at different particle sizes and concentrations, was studied in situ by diffusive gradient in thin-films (DGT) for the first time. The bioavailability, soil chemical properties, and microbial effects of PU MPs on Cd depend on PU particle size and concentration; high-concentration (1 %) PU MPs cause a significant increase in DGT-Cd concentration. The addition of PU MPs decreased soil pH and dissolved organic carbon (DOC), while increasing the absolute zeta value, Fe(II) and Mn(II), in a manner dependent on particle size, concentration, and culture time. Correlation analysis combined with path analysis showed that PU MPs affected the effective state of Cd by changing soil properties, among which Fe(II) content and DOC were important factors controlling the activation of Cd. Meanwhile, changes in soil properties and heavy metal availability correlated significantly with microbial community composition, suggesting that PU MPs may indirectly impact heavy metal activity by affecting microorganisms and functional genes associated with C and Fe cycling. Therefore, when the concentration of PU MPs is higher than 1 %, we should strengthen ecological risk prevention and control of the compound pollution of controlled-release fertilizer coated microplastics and heavy metals in farmland soil.

The effect of adsorption on the fate of colloidal polystyrene microplastics in drinking water distribution system pipe scales

With microplastics (MPs) being continuously found in various environments, the pollution of water supply systems by MPs is receiving increasing attention. As the sediment in drinking water distribution systems (DWDSs), pipe scales act as the interface for complex reactions between bulk water and pipe surfaces. Consequently, the fate of MPs in pipe scales requires exploration, especially colloidal MPs. In this study, MPs were detected in different pipe scale layers, with concentrations of 0.32-3.10 items g^-1. Subsequently, the adsorption interaction mechanisms between pipe scales and colloidal polystyrene microplastics (PSMPs) were investigated through batch adsorption experiments. The findings indicated that pipe scales showed a potential adsorption capacity for PSMPs. The adsorption kinetics and isotherms results demonstrated that the PSMP adsorption process was physically dominant and complicated. van der Waals and electrostatic interactions, hydrogen bonding, and pore filling were the main adsorption mechanisms. These results verify that colloidal MPs can be adsorbed by pipe scales, demonstrating that pipe scales play an essential role in the fate of colloidal MPs in DWDSs and the quality and security of drinking water. The secondary release of MPs from pipe scales is also worthy of attention due to the environmental and health risks.

Microplastics can affect soil properties and chemical speciation of metals in yellow-brown soil

Although the influence of microplastics (MPs) in different soil environments has been investigated, their effects on the physiochemical properties and chemical speciation of heavy metals in yellow-brown soil remains unknown. This study aimed to determine the effects of various concentrations of linear low-density polyethylene (LLDPE), polyamide (PA), polyurethane (PU), polystyrene (PS), and low-density polyethylene (LDPE) MPs on the yellow-brown soil environment and chemical speciation of the heavy metals cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). MPs influenced the physicochemical properties and chemical speciation of heavy metals in yellow-brown soil. The physicochemical properties of yellow-brown soil can be altered by changing the concentrations of LDPE MP. The relationship between changes in field capacity (FC) and LDPE concentrations was approximately linear. The physiochemical properties of yellow-brown soil containing added PA, PU, and LDPE MPs were substantially improved (control vs. MPs): FC, 39 % vs. 42.50 % for PU, cation exchange capacity (CEC) 45.77, 56.65, and 57.44 cmol.kg^-1 for PA, PU, and LDPE respectively, and organic matter (OM) content, 40.16 vs. 51.68 g.kg^-1 for PA. The LLDPE and PU MPs also simultaneously affected the chemical speciation of heavy metals in yellow-brown soil. The LLDPE MPs increased the acid-soluble (45.17-54.67 % (Cd-F1), 7.24-11.30 % (Cu-F1), 4.20-7.23 % (Pb-F1), 21.21-31.47 % (Zn-F1)) and reducible (24.02-29.41 % (Cd-F2), 25.69-34.95 % (Cu-F2), 74.29-81.07 % (Pb-F2), 28.77-34.19 % (Zn-F2)) fractions of heavy metals, which increased their bioavailability. However, PU MPs reduced the ecological risk of heavy metals in yellow-brown soil by increasing the content of the residual fraction (26.11-40.21 % (Cd-F4), 47.63-59.67 % (Cu-F4), 17.25-26.76 % (Pb-F4), 32.63-50.46 % (Zn-F4)). Changes in the properties of yellow-brown soil and the impact of MPs on heavy metals, might change the chemical speciation of heavy metals. The impact of MPs on heavy metals in yellow-brown soil requires further investigation.