With spatial distribution, risk evaluation of heavy metals and microplastics to emphasize the composite mechanism in hyporheic sediments of Beiluo River

Co-occurrence of microplastics and heavy metals to urban river sediments: The vertical distribution characterization and comprehensive ecological risk assessment

Microplastics (MPs) and heavy metals (HMs) are deemed to pose ecological risks in river ecosystems. The vertical distribution of these pollutants is more conducive to reflecting pollution status and monitoring trends in the sediment. This work analyzed the horizontal and vertical distribution, carried out a risk assessment of HMs and MPs in urban river sediment, and further optimized the two-dimensional comprehensive index (TPI) model for MPs-HMs combined pollution. The highest rates of contamination were for Zn, As, and Cd, and MP abundance in sediment ranged from 20.00 ± 8.82-1933.33 ± 141.42 items·kg-1, mainly characterized by PE and fragments. Moreover, the mean potential ecological risk index for MPs (PRI) at different depths of sediment were 197.21 ± 247.14, 176.79 ± 293.86, and 246.98 ± 538.38, respectively, indicating a moderate risk and the highest PRI value is at the bottom. The TPI exhibited that the average TPI at different depths is 324.10 ± 138.63, 368.30 ± 157.13, and 481.88 ± 296.05, indicating that the comprehensive pollution risk level belongs to considerable, the TPI increases with the depth of the sediment. The results further improved the objectivity and accuracy of the research on the ecotoxicity of compositive pollutants and provided an in-depth understanding of MPs and HMs in urban freshwater basins from a vertical perspective.

Combined pollution of soil by heavy metals, microplastics, and pesticides: Mechanisms and anthropogenic drivers

Soil is the foundation of terrestrial ecosystems and a critical resource for agricultural activities. This study investigated internal mechanism and interaction of heavy metals, pesticides (atrazine, pyrimazole and chlorpyrifos) and microplastics in soil. Specifically, certain sampling points exhibited elevated levels of individual heavy metals (Cd, Cr, Zn), exceeding the screening values, while both microplastics and pesticides demonstrated high variability, increasing the potential ecological risks. The interaction between microplastics, heavy metals, and pesticides is complex, involving electrostatic adsorption, surface complexation, biofilm mediation, and physical absorption. From a broader perspective, both heavy metals and microplastics were found to exacerbate the ecological risks posed by pesticides. Further, structural equation model and geographical weighted regression were used to reveal the driving mechanism behind complex pollution, with economic development emerging as a significant factor influencing pollution levels. These findings enhance our understanding of the combined pollution of heavy metals, microplastics, and pesticides.

Plastic debris accumulated on Sargassum algae stranded biomass are vectors for different As(V) and As(III) forms

This work shows that the plastic debris accumulated along with stranded Sargassum biomass in Guadeloupe's beaches contains different forms of arsenic. Results from synchrotron nano X-ray Fluorescence (nanoXRF) and nano X-ray Absorption Near Edge Structure (nanoXANES) show that arsenate (As(V) in a tetrahedral coordination) present in seawater is complexed in the algae cell walls in an octahedral As(V) form, which is subsequently reduced to As(III) within the algae. Inorganic As(III) is either excreted or may undergo methylation and/or binding to glutathione, which is then stored in the algal cells or excreted. The areas where As is colocalized with a variety of metals (Si, K, Ca, Fe, Ni Cu and Zn) may correspond with areas in which algae tissues remain adhered to the surface of the plastics. On the opposite, the areas in which As is found together with Ti or Cl may correspond with areas in which the algae has been decomposed or in which As has been adsorbed after being secreted by the algae. Results from this study should be taken into account to assess the ecotoxicological impacts of Sargassum biomass accumulated on beaches, as well as for the planning of its valorization. Plastics within the Sargassum biomass can act as vectors for arsenic, facilitating its transfer to other environmental compartments where the biomass is used or when it is ingested by various organisms. In a context of a growing problem of plastic pollution and a more and more frequent algae blooms, these results are particularly relevant.

Machine learning models with innovative outlier detection techniques for predicting heavy metal contamination in soils

Machine learning (ML) models for accurately predicting heavy metals with inconsistent outputs have improved owing to dataset outliers, which influence model reliability and accuracy. A comprehensive technique that combines machine learning and advanced statistical methods was applied to assess data outlier's effects on ML models. Ten ML models with three outlier detection methods predicted Cr, Ni, Cd, and Pb in Narayanganj soils. XGBoost with density-based spatial clustering of applications with noise (DBSCAN) improved model efficacy (R2). The R2 of Cr, Ni, Cd, and Pb was considerably enhanced by 11.11 %, 6.33 %, 14.47 %, and 5.68 %, respectively, indicating that outliers affected the model's HM prediction. Soil factors affected Cr (80 %), Ni (72.61 %), Cd (53.35 %), and Pb (63.47 %) concentrations based on feature importance. Contamination factor prediction showed considerable contamination for Cr, Ni, and Cd. LISA revealed Cd (55.4 %), Cr (49.3 %), and Pb (47.3 %) as the significant pollutant (p < 0.05). Moran's I index values for Cr, Ni, Cd, and Pb were 0.65, 0.58, 0.60, and 0.66, respectively, indicating strong positive spatial autocorrelation and clusters with similar contamination. Finally, this work successfully assessed the influence of data outliers on the ML model for soil HM contamination prediction, identifying crucial regions that require rapid conservation measures.

Interaction and bacterial effects of microplastics pollution on heavy metals in hyporheic sediments of different land-use types in the Beiluo River Basin

Microplastics (MPs) pollution is ubiquitous, causing serious ecological damage by threatening the growth and health of living organisms. This study investigated the vertical and horizontal distribution of MPs, MPs-heavy metals (MPs-HMs) accumulation, contamination assessment and microbial biodiversity in hyporheic sediments of different land-use types. MPs abundance in shallow sediments (0-30 cm) was significantly higher than that in deep sediments (30-60 cm), with fewer large MPs in the deep sediments. Blue, fiber, and <500 μm were the dominant MPs types, and polystyrene, polylactic acid, and polyvinyl chloride were the dominant polymers in the Beiluo River Basin. The average concentrations of HMs detected in MPs were all much higher than the same metals in the sediments. The pollution loading index of MPs was higher in areas with a greater proportion of anthropogenic land use, and MP-HM were present to varying degrees in the vertical distribution (PN > 1). Critically, bacterial diversity of anthropogenic land use was smaller than that of natural land use. High MP-HM concentrations reduced the abundance of cyanobacteria, nitrospirota, acidobacteriota, and planctomycetota, whereas desulfobacterota, chloroflexi, myxococcota, actinobacteriota, and proteobacteria have developed tolerance to MP-HM. Overall, our findings contribute to the understanding of the relationship between different land-use types and the spatial distribution of MPs and MP-HM, which is critical to manage and mitigate the hyporheic zone pollution.

Polystyrene Microplastics Induce Photosynthetic Impairment in Navicula sp. at Physiological and Transcriptomic Levels

The rising concentration of microplastics (MPs) in aquatic environments poses increasing ecological risks, yet their impacts on biological communities remain largely unrevealed. This study investigated how aminopolystyrene microplastics (PS-NH2) affect physiology and gene expression using the freshwater alga Navicula sp. as the test species. After exposing Navicula sp. to high PS-NH2 concentrations for 24 h, growth was inhibited, with the most significant effect seen after 48 h. Increasing PS-NH2 concentrations reduced chlorophyll content, maximum photochemical quantum yield (Fv/Fm), and the photochemical quenching coefficient (Qp), while the non-photochemical quenching coefficient (NPQ) increased, indicating a substantial impact on photosynthesis. PS-NH2 exposure, damaged cell membrane microstructures, activated antioxidant enzymes, and significantly increased malondialdehyde (MDA), glutathione peroxidase (GPX), and superoxide dismutase (SOD) activities. Transcriptomic analysis revealed that PS-NH2 also affected the gene expression of Navicula sp. The differentially expressed genes (DEGs) are mainly related to porphyrin and chlorophyll metabolism, carbon fixation in photosynthesis, endocytosis, and glycolysis/gluconeogenesis. Protein-protein interaction (PPI) analysis revealed significant interactions among DEGs, particularly within photosystem II. These findings shed insights into the toxic mechanisms and environmental implications of microplastic interactions with phytoplankton, deepening our understanding of the potential adverse effects of microplastics in aquatic ecosystems.

Multiple effects of submerged plants on microplastics-heavy metals redistribution and combination in the hyporheic sediment

Submerged plants (SP) in the hyporheic sediment (HS) dynamically alter the spatial distributions of heavy metals (HMs) and microplastics (MPs). In this study, we examined the redistribution and combination of HMs and MPs in the HS surrounding the SP (SSP) and non-nearby the SP (NSP) in the Weihe River Basin. The strong bioconcentration capacity of SP directly caused a decrease of HMs in the SSP (Bioconcentration Factors: SSP>NSP, 1.07 >1.00). Algal proliferation at high nutrient concentrations strengthened the interception of MPs by SP (SSP-MPs >NSP-MPs, 495 >315 items/kg). The significant correlation between SSP-HMs and SSP-MPs indicates the formation of MPs-HMs. The concentration of SSP-HMs was greater than NSP-HMs (Mn (462.95 >437.66 mg/kg)>Zn (63.46 >60.51 mg/kg)>V (53.98 >50.67 mg/kg)>Pb (21.98 >18.47 mg/kg)>As (18.36 >15.65 mg/kg). This finding implies that the MPs trapped by the SP indirectly contribute to elevating SSP-HMs, which showed higher pollution risk (Nemerow Pollution Index: 1.37 >1.22; Contamination Factor: V, 0.87 >0.82, Zn, 0.95 >0.90, As, 1.61 >1.41, Pb, 0.98 >0.88). Furthermore, SP can reduce NSP contamination by proactively collecting pollutants into SSP, endangering the integrity of rivers through the ingesting of hydrobiont. Our study provides theoretical suggestions for the application of SP to improve ecological health in the complex environment.

Response of soil heavy metal forms and bioavailability to the application of microplastics across five years in different soil types

Microplastics (MPs) potentially alter physicochemical and transformation of heavy metals (HMs) in soils, which may depend on the specific characteristics of soil types. However, the dynamical and long-term mechanisms remain to be elucidated. A five-year incubation experiment was conducted to evaluate the influence of MPs on the chemical speciation of Pb, Ni, Cu, Cr, Cd, and As in the meadow, tidal, cinnamon, saline-alkali, and brown soils. From the first year to the fifth year, the clay value of the meadow, tidal, cinnamon, and saline-alkali soils was increased by 31.35 %, 9.63 %, 30.12 %, and 33.12 %, respectively; the pH values of the cinnamon and saline-alkali soils were increased by 15.02 % and 15.86 %, respectively. Besides, speciation distribution results suggested that the application of MPs reduced the liable available (LB) form (F2-dissolved and F3-ion exchangeable) of HMs and increased the potentially available (PB) form (F5-minerals and F6-organic-bound fraction) of HMs in all soils. Compared with other forms, F2 HMs fraction was the most responsive to MPs. Furthermore, the average bioconcentration factor (BCF) of Cr and Pb decreased by 73.75 % and 70.41 % in soils, respectively. Interestingly, soil type showed more impact on the form of HMs, which was associated with the different physicochemical parameters of soils, while application time displayed more impact on the bioavailability of HMs. Moreover, our results suggested that soils with higher clay content and pH values (such as cinnamon and saline-alkali soils) may mitigate the bioavailability of HMs more effectively in the presence of MPs, while soils with lower clay content may be more vulnerable to HMs contamination over time. This work highlights the importance of long-term monitoring of the impact of MPs on HMs dynamics for effective mitigation of soil contamination risks. Our study provides valuable guidance for soil remediation strategies and environmental quality management across different soil types.

Biodiversity of multi-trophic biological communities within riverine sediments impacted by PAHs contamination and land use changes

River ecosystems currently face a significant threat of degradation and loss of biodiversity resulting from continuous emissions of persistent organic pollutants and human activities. In this study, multi-trophic communities were assessed using DNA metabarcoding in a relatively stable riverine sediment compartment to investigate the biodiversity dynamics in the Beiluo River, followed by an evaluation of their response to polycyclic aromatic hydrocarbons (PAHs) and land use changes. A total of 48 bacterial phyla, 4 fungal phyla, 4 protist phyla, 9 algal phyla, 31 metazoan phyla, and 12 orders of fish were identified. The total concentration of PAHs in the Beiluo River sediments ranged from 25.95 to 1141.35 ng/g, with low molecular weight PAHs constituting the highest proportion (68.67%), followed by medium (22.19%) and high (9.14%) molecular weight PAHs. Notably, in contrast to lower trophic level aquatic communities such as bacteria, algae, and metazoans, PAHs exhibited a significant inhibitory effect on fish. Furthermore, the diversity of aquatic communities displayed obvious heterogeneity across distinct land use groups. A high proportion of cultivated land reduced the biodiversity of fish communities but increased that of metazoans. Conversely, an elevated proportion of built-up land reduced metazoan biodiversity, while simultaneously enhancing that of fungi and bacteria. Generally, land use changes exert both indirect and direct effects on aquatic communities. The direct effects primarily influence the abundance of aquatic communities rather than their diversity. Nevertheless, PAHs pollution may have limited potential to disrupt community structures through complex species interactions, as the hub species identified in the co-occurrence network did not align with those significantly affected by PAHs. This study indicates the potential of PAHs and land use changes to cause biodiversity losses. However, it also highlights the possibility of mitigating these negative effects in riverine sediments through optimal land use management and the promotion of enhanced species interactions.

The interaction of microplastic and heavy metal in bioretention cell: Contributions of water-soil-plant system

The effectiveness of bioretention cells for heavy metals (HMs) and microplastics (MPs) removal from stormwater runoff has been demonstrated. Knowledge of the mechanisms that dictate the interactions between MPs and HMs would be helpful in pollution control. In this study, the performances of different water-soil-plant bioretention cells for HMs removal through the interception of polyethylene MPs (PE-MPs) were investigated. The results showed that PE-MPs bound to HMs and preferentially tended to bind to Pb (32%-44%) in the complex HMs (Cu, Zn, Cd, and Pb). This could be the reason that the concentration of Pb significantly increased in the effluent under low-intensity simulated rainfall events over a long duration. The accumulation of 1.49 g/kg PE-MPs caused a significant soil pH value decrease and a notable soil zeta potential increase in the bioretention cell, while the low sand/silt ratio media buffered this process. The retention of PE-MPs increased 138.5% in the 0-10 cm soil surface layer when the sand/silt ratio reduced from 2:1 to 1:1 and planted with Canna indica. Meanwhile, PE-MPs amplified the instability of Zn removal in bioretention cells under low-intensity rainfall events in long-duration, high silt percentage substrate and vegetation coverage. The study would contribute to developing a long-term management program for PE-MPs and HMs trapped in bioretention cells to reduce the risk of pollution transport.

Effects of microplastics on the rheological properties of sediment slurries in aquatic environments

Sediment slurries, characterized by their high concentrations of fine-grained cohesive sediment, are prevalent in various aquatic environments, including fluid mud, sediment gravity flows, and dredging slurries. Abundant microplastics have been detected in sediment slurries, which indicates that these slurries function as carriers for the transport of microplastics. However, there is a dearth of understanding on how sediment slurries transport microplastics. To ascertain the transport mechanisms, elucidating the effects of microplastics on the rheological properties of sediment slurries is a prerequisite because these properties govern the flow dynamics and mobility of such slurries. This study conducts experimental and theoretical investigations to examine, interpret, and quantify the effects of microplastics on the rheological properties of sediment slurries. Microplastics are shown to increase the yield stress and viscosity of sediment slurries via enhancing sediment aggregation. A new descriptor, specifically, the effective volume fraction, is proposed to characterize the effects of microplastics on sediment aggregation. Based on the newly-proposed descriptor, a new analytical model is proposed to predict the yield stress and viscosity of sediment slurries with microplastics. This study lays a foundation for further interpretating the flow dynamics and thus the transport processes of sediment slurries laden with microplastics.

Unveiling the impacts of microplastics on cadmium transfer in the soil-plant-human system: A review

The co-contamination of soils by microplastics (MPs) and cadmium (Cd), one of the most perilous heavy metals, is emerging as a significant global concern, posing risks to plant productivity and human health. However, there remains a gap in the literature concerning comprehensive evaluations of the combined effects of MPs and Cd on soil-plant-human systems. This review examines the interactions and co-impacts of MPs and Cd in soil-plant-human systems, elucidating their mechanisms and synergistic effects on plant development and health risks. We also review the origins and contamination levels of MPs and Cd, revealing that sewage, atmospheric deposition, and biosolid applications are contributors to the contamination of soil with MPs and Cd. Our meta-analysis demonstrates that MPs significantly (p<0.05) increase the bioavailability of soil Cd and the accumulation of Cd in plant shoots by 6.9 and 9.3 %, respectively. The MPs facilitate Cd desorption from soils through direct adsorption via surface complexation and physical adsorption, as well as indirectly by modifying soil physicochemical properties, such as pH and dissolved organic carbon, and altering soil microbial diversity. These interactions augment the bioavailability of Cd, along with MPs, adversely affect plant growth and its physiological functions. Moreover, the ingestion of MPs and Cd through the food chain significantly enhances the bioaccessibility of Cd and exacerbates histopathological alterations in human tissues, thereby amplifying the associated health risks. This review provides insights into the coexistence of MPs and Cd and their synergistic effects on soil-plant-human systems, emphasizing the need for further research in this critical subject area.

Meta-analysis reveals the combined effects of microplastics and heavy metal on plants

The combined pollution of microplastics and heavy metals is becoming increasingly serious, and its effects on toxicology and heavy metal accumulation of plants are closely related to crop yield and population health. Here, we collected 57 studies to investigate the effect of microplastics on heavy metal accumulation in plants and their combined toxicity. An assessment was conducted to discover the primary pollutant responsible for the toxicity of combined pollution on plants. The study examined the influence of microplastic characteristics, heavy metal characteristics, and experimental methods on this pollutant. The results showed that combined toxicity of plants was more similar to heavy metals, whereas microplastics interacted with heavy metals mainly by inducing oxidative stress damage. Culture environment, heavy metal type, experimental duration, microplastic concentration and microplastic size were the main factors affecting heavy metal accumulation in plants. There was a negative correlation between experimental duration, microplastic concentration and microplastic size with heavy metal accumulation in plants. The interactions among influencing factors were found, and microplastic biodegradation was the core factor of the strong interaction. These results provided comprehensive insights and guiding strategies for environmental and public health risks caused by the combined pollution of microplastics and heavy metals.

Factors influencing the distribution, risk, and transport of microplastics and heavy metals for wildlife and habitats in "island" landscapes: From source to sink

Microplastics (MPs) and heavy metals (HMs) are important pollutants in terrestrial ecosystems. In particular, the "island" landscape's weak resistance makes it vulnerable to pollution. However, there is a lack of research on MPs and HMs in island landscapes. Therefore, we used Helan Mountain as the research area. Assess the concentrations, spatial distribution, ecological risks, sources, and transport of MPs and HMs in the soil and blue sheep (Pseudois nayaur) feces. Variations in geographical distribution showed a connection between human activity and pollutants. Risk assessment indicated soil and wildlife were influenced by long-term pollutant polarization and multi-element inclusion (Igeo, Class I; PHI, Class V; RI (MPs), 33 % Class II, and 17 % Class IV; HI = 452.08). Source apportionment showed that tourism and coal combustion were the primary sources of pollutants. Meanwhile, a new coupling model of PMF/Risk was applied to quantify the source contribution of various risk types indicated transportation roads and tourism sources were the main sources of ecological and health risks, respectively. Improve the traceability of pollution source risks. Furthermore, also developed a novel tracing model for pollutant transportation, revealing a unique "source-sink-source" cycle in pollutant transportation, which provides a new methodological framework for the division of pollution risk areas in nature reserves and the evaluation of spatial transport between sources and sinks. Overall, this study establishes a foundational framework for conducting comprehensive risk assessments and formulating strategies for pollution control and management.

Microplastics and heavy metal contamination along a land-use gradient in a Himalayan foothill river: Prevalence and controlling factors

The co-occurrence of microplastics (MPs) and heavy metals in aquatic systems has raised significant concerns, yet their relationship in freshwater ecosystems remains poorly understood. This study aims to evaluate the prevalence of MPs and factors controlling their distribution in both water and sediment in the Markanda River, Northwest India. MPs were extracted from sediment and water samples using density separation and classified through fluorescence microscopy and Raman spectroscopy. Metal concentrations in river water samples were analyzed using ICP-MS, and their correlation with MP abundance was explored. The results indicated the widespread occurrence of MP pollution across the Markanda River basin, with particle concentrations ranging from 10 to 530 particles L-1 in surface water and 1330-4330 particles kg-1 dry weight (dw) in sediment samples. The variability in MP abundance at sampling sites along the Markanda River courses results from factors such as the proximity of industrial establishments and human habitation, while the influence of grain size on MP distribution appears to be limited. Pellets (88.5 %) and fragments (8.5 %) were the most abundant types of MPs, with polyethylene (45.45 %) and polystyrene (30.9 %) being the dominant forms in water samples. The ICP-MS analysis of heavy metals in water samples indicated elevated levels of As (1.67 to 32.31 ppb) in downstream areas of the river system, influenced by human activities. While metals exhibited correlation with each other, there was a weak association, except for As, with the levels of MPs in the Markanda River. The SEM-EDX analyses to characterize chemical elements absorbed onto the surface of MP showed distinct variations in upstream and downstream sites, with the presence of elements such as Mn, Ni, Cr, Zn, As, Se, and Cu found in downstream areas. We conclude that MPs contaminated with heavy metals potentially threaten the ecological security of freshwater aquatic systems and highlight the importance of management action to reduce plastic pollution worldwide.

The competition of heavy metals between hyporheic sediments and microplastics of driving factors in the Beiluo River Basin

Both sediments and microplastics (MPs) are medias of heavy metals (HMs) in river ecosystems. This study investigated HMs (Mn, Cr, V, As, Cu, Co, Cd, Pb, and Ni) concentration and driving factors for competitive enrichment between hyporheic sediments versus MPs. The medias basic characteristics indicated that the sediments were mostly sand and rich in Fe2O3; three polymer types were identified, with blue, fragment, less than 500 µm being the main types of MPs. The results have shown that the average content of extracted HMs in MPs was much higher than that of the same metals accumulated in sediments. HMs in sediments and MPs reached heavily polluted at some points, among which As and Cd were ecological risks. Electrostatic adsorption and surface complexation, and biofilm-mediated and organic matter complexation were the interaction mechanism of HMs with sediments and MPs. Further, the driving factors affecting the distribution of HMs in the two carriers were analyzed by multivariate statistical analysis. The results demonstrated that carrier characteristics, hydrochemical factors, and the inherent metal load of MPs were the main causes of the high HMs content. These findings improved our understanding of HMs fate and environmental risks across multiple medias.

Metal pollution assessment in the surface sediments of a river system in Türkiye: Integrating toxicological risk assessment and source identification

This study investigates potentially toxic elements (PTEs) in the surface sediments of the Abdal River system, a critical water source for Samsun province, Türkiye, due to the presence of the Çakmak Dam. PTE concentrations, measured in mg/kg, show significant variability: Hg (0.03) < Cd (0.26) < As (10.98) < Pb (13.88) < Cu (48.61) < Ni (62.45) < Zn (70.97) < Cr (96.28) < Mn (1015) < Fe (38357). Seasonal variations were observed, in particular increased concentrations of As, Cd and Pb in summer (p < 0.05). Contamination and ecological risk indices (mHQ, EF, Igeo, CF, PLI, Eri, mCd, NPI, PERI, MPI, and TRI) indicate moderate to low levels of contamination, suggesting potential ecological effects. Health risk assessments suggest minimal risks to human health from sediment PTEs. Statistical analyses (PCC, PCA and HCA) improve the understanding of the sediment environment and contamination sources, while the coefficient of variation assists in source identification.

Zeolite facilitates sequestration of heavy metals via lagged Fe(II) oxidation during sediment aeration

Aeration of sediments could induce the release of endogenous heavy metals (HMs) into overlying water. In this study, experiments involving FeS oxygenation and contaminated sediment aeration were conducted to explore the sequestering role of zeolite in the released HMs during sediment aeration. The results reveal that the dynamic processes of Fe(II) oxidation play a crucial role in regulating HMs migration during both FeS oxygenation and sediment aeration in the absence of zeolite. Based on the release of HMs, Fe(II) oxidation can be delineated into two stages: stage I, where HMs (Mn2+, Zn2+, Cd2+, Ni2+, Cu2+) are released from minerals or sediments into suspension, and stage II, released HMs are partially re-sequestered back to mineral phases or sediments due to the generation of Fe-(oxyhydr) oxide. In contrast, the addition of zeolite inhibits the increase of HMs concentration in suspension during stage I. Subsequently, the redistribution of HMs between zeolite and the newly formed Fe-(oxyhydr) oxide occurs during stage II. This redistribution of HMs generates new sorption sites in zeolite, making them available for resorbing a new load of HMs. The outcomes of this study provide potential solutions for sequestering HMs during the sediment aeration.

Effects of biodegradable microplastics on arsenic migration and transformation in paddy soils: a comparative analysis with conventional microplastics

The combined pollution of microplastics (MPs) and arsenic (As) in paddy soils has attracted more attention worldwide. However, there are few comparative studies on the effects of biodegradable and conventional MPs on As migration and transformation. Therefore, conventional (polystyrene, polyethylene, polyvinyl chloride) and biodegradable (polybutadiene styrene, polylactic acid, polybutylene adipate terephthalate) MPs were selected to explore and demonstrate their influences and mechanism on As migration from paddy soils to overlying water and As speciation transformation through microcosmic experiment with measuring the changes of As chemical distribution, physicochemical indexes and microbial community in paddy soils. The results showed that biodegradable MPs enhanced As migration and transformation more effective than conventional MPs during 60 d. Biodegradable MPs indirectly increased the content of As(Ⅲ) and bioavailable As by changing the microbial community structure and affecting the biogeochemical cycles of carbon, nitrogen, sulfur and iron in soils, and promoted the As migration and transformation. PBS showed the strongest promoting effect, transforming to more As(Ⅲ) (11.43%) and bioavailable As (4.28%) than control. This helps to a better understanding of the effects of MPs on As biogeochemical cycle and to clarify the ecological and food safety risks of their combined pollution in soils.

New insights into the role of sediments in microplastic inputs from the Northern Dvina River (Russia) to the White and Barents Seas

The Northern Dvina River is one of the main sources of microplastic pollution entering to the White and Barents Seas. The coastal and bottom sediments of this river play an important role as a transfer link of microplastics. With Py-GC/MS and μFT-IR methods, it was found that the sediments contain up to 350 mg/kg or 650 particles/kg of microplastic (dry weight). The unique hydrologic conditions of the river branching area contribute to the formation of a microplastic pollution hotspot. The hotspot accumulates >30 % of microplastic pollution, mainly ABS plastic particles smaller than 0.3 mm with roughness and cracks, which increases the hazard class (from II to IV) of microplastic pollution. Obtained data and high annual variability of pollution indicates that this area acts as a place of accumulation, degradation and gradual release of microplastics into the White and Barents Seas, i.e. into the Arctic region.

Biological effects of perfluoroalkyl substances on running water ecosystems: A case study in Beiluo River, China

Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are emerging contaminants that pose a threat to the biodiversity of the Beiluo River, a polluted watercourse on the Loess Plateau impacted by diverse human activities. However, the occurrence, spatial distribution, and substitution characteristics of PFASs in this region remain unclear. This study aimed to unravel PFAS distribution patterns and their impact on the aquatic ecosystems of the Beiluo River Basin. The total PFAS concentration in the area ranged from 16.64-35.70 ng/L, with predominantly perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), collectively contributing 94%. The Mantel test revealed threats to aquatic communities from both legacy long-chain (perfluorooctanoic acid and sodium perfluorooctane sulfonic acid) and emerging (6:2 fluorotelomer sulfonic acid, 2-Perfluorohexyl ethanoic acid, and hexafluoropropylene oxide dimer acid (Gen-X)) PFSAs. The canonical correspondence analysis ordination indicated that trace quantities of emerging PFASs, specifically 2-Perfluorohexyl ethanoic acid and hexafluoropropylene oxide dimer acid (Gen-X), significantly influenced geographical variations in aquatic communities. In conclusion, this study underscores the importance of comprehensively exploring the ecological implications and potential risks associated with PFASs in the Beiluo River Basin.