Microplastic retention in marine vegetation canopies under breaking irregular waves

The present study provides indications and underlying drivers of wave-induced transport and retention potential of microplastic particles (MP) in marine vegetation canopies having different densities. The anthropogenic occurrence of MP in coastal waters is well documented in the recent literature. It is acknowledged that coastal vegetation can serve as a sink for MP due to its energy dissipating features, which can mimic a novel ecosystem service. While the transport behavior of MP in vegetation has previously been investigated to some extent for stationary flow conditions, fundamental investigations for unsteady surf zone flow conditions under irregular waves are still lacking. Herein, we demonstrate by means of hydraulic model tests that a vegetation's retention potential of MP in waves increases with the vegetation shoot density, the MP settling velocity and decreasing wave energy. It is found that particles migrating by traction (predominantly in contact with the bed) are trapped in the wake regions around a canopy, whereas suspended particles are able to pass vegetated areas more easily. Very dense canopies can also promote the passage of MP with diameters larger than the plant spacing, as the canopies then show characteristics of a solid sill and avoid particle penetration. The particle migration ability through a marine vegetation canopy is quantified, and the key drivers are described by an empirical expression based on the particle settling velocity, the canopy length and density. The findings of this study may contribute to improved prediction and assessment of MP accumulation hotspots in vegetated coastal areas and, thus, may help in tracing MP sinks. Such knowledge can be considered a prerequisite to develope methods or new technologies to recover plastic pollutants and rehabilitate valuable coastal environments.

Vertical connectivity of microbiome and metabolome reveals depth-dependent variations across a deep cold-seep water column

Deciphering the vertical connectivity of oceanic microbiome and metabolome is crucial for understanding the carbon sequestration and achieving the carbon neutrality. However, we lack a systematic view of the interplay among particle transport, microbial community, and metabolic trait across depths. Through integrating the biogeochemical, microbial, and metabolic characteristics of a deep cold-seep water column (∼1989 m), we find the altered connectivity of microbial community and dissolved organic matter (DOM) across depths. Both the microbial communities (bacteria and protists) and DOM show a clear compositional connectivity from surface to the depth of 1000 m, highlighting the controls of sinking particle over microbial connectivity from the epipelagic to mesopelagic zone. However, due to the biological migration and ocean mixing, the fecal-associated bacteria and protistan consumers unexpectedly emerge and the degradation index of DOM substantially alters around 1000-1200 m. Collectively, we unveil the significance of multi-faceted particle dispersion, which supports the connectivity and variability of deep ocean microbial communities.

Geomorphological changes in young soils with sparse vegetation: Mathematical modeling and numerical simulation

This article presents an improved mathematical model and numerical simulation for weathering of large areas with complex topography. It uses the equations of momentum, temperature, and humidity in turbulent air and for heat and water infiltration into soils. A mathematical model is also presented to calculate the soil porosity fraction produced by physical rock weathering in areas where soil is produced from intrusive rocks (batholiths). An algorithm based on air velocity, humidity (rainfall), temperature variation, and soil topography was developed to quantify soil erosion and change of relief at each point and time step in air, at the ground surface, and within the soil. This results in a complete air-soil model based on conservation laws that have not previously been applied to large areas of the earth's surface. The mathematical model is solved using large-scale numerical simulations applied to an area of 6.6 km2 in the Sierra Nevada batholith of California, USA. The results show that the wind velocity and resulting erosion is greater in areas with steeper slopes and that moisture accumulates mainly in low and flat areas; therefore, erosion is not uniform throughout the study area. In addition, computer simulations localized calculations to discrete grid cells within the porous (saprolite) fraction of the soil produced by freezing and thawing of water in rock. Results indicate that this physical mechanism is the primary contributor to weathering of rock at the study area.

Hydrodynamics and effect of velocity on particle filtration due to bridging in water-saturated porous media using CFD-DEM simulation

Particle bridging owing to the confinement of the pore structure affects the transport and retention of particles in porous media. Particle motion driven by gravities were well investigated, whose filtration is mainly affected by the ratio of the particle diameter to the pore throat size of the medium. However, particles whose motions are driven by the fluid is essential to be investigated for particle separation from the carrying fluid. In this study, the motion of particles was driven by the liquid when passing through a water-saturated porous medium. The fluid-particle flow in a porous medium was modeled using computational fluid dynamics-discrete element method. The motion of particles in the slurry was traced in the porous medium, which enabled particle clogging to be directly precited by the interaction between the particles and pore surfaces by assessing the exact location of each particle. The pressure and flow field of the liquid were investigated, and the variation in flow path owing to particle clogging was predicted. The hydrodynamic study also showed that the Stokes number and particle concentration determined the particle clogging at the pore throats of the porous medium. Increasing the fluid velocity of particles such that the Stokes number was almost equal to 1 increased the separation efficiency of particles. Further increasing the fluid velocity reduced the residence time, which reduced the separation efficiency of the particles.

A numerical study on microfluidic devices to maintain the concentration and purity of dielectrophoresis-induced separated fractions of analyte

Determining the physical and chemical properties of biologically important particles such as cells, organelles, viruses, exosomes, complexes, nucleotides, and proteins is needed to understand their function. These properties are determined with common analytical tools (mass spectrometry, cryo-EM, NMR, various spectroscopies, nucleotide sequencing, etc.) whose function can be improved when samples are pure and concentrated. Separations science plays a central role in conditioning samples, ranging from low-resolution benchtop operations like precipitations or extractions to higher-resolution chromatography and electrophoresis. In the last two decades, gradient insulator-based dielectrophoresis (g-iDEP) has emerged as a high-resolution separation technique capable of highly selective enrichment of cells, viruses, exosomes, and proteins. Specific evidence has been shown that pure homogeneous and concentrated fractions of cells and exosomes can be generated from complex mixtures. However, recovering those fractions for analysis has not been developed, limiting the technique to an analytical rather than a preparative one. Here, a finite element analysis was undertaken to identify geometries and operational parameters to efficiently remove the enriched fraction while retaining maximum concentration and providing total mass transfer. Geometric factors (e.g., side channel width and distance from the gradient-inducing gap) were studied, along with the addition of a second inlet side channel. Two flow-generating mechanisms-electroosmosis and hydrostatic pressure-were evaluated for semi-optimized device designs, including a comparison of the one- and two-inlet designs. Simulations indicate effectively one hundred percent mass transfer and a concentration increase by an order of magnitude for several device configurations and operational parameters.

Holographic generation of arbitrary ultrasonic fields by simultaneous modulation of amplitude and phase

Acoustic holograms have been used widely to generate desired acoustic fields. Following the rapid development of 3D printing technology, the use of holographic lenses has become an efficient method to produce acoustic fields with high resolution and low cost. In this paper, we demonstrate a technique to modulate the amplitude and phase of ultrasonic waves simultaneously using a holographic method with high transmission efficiency and high accuracy. On this basis, we generate an Airy beam with high propagation invariance. We then discuss the advantages and disadvantages of the proposed method when compared with the conventional acoustic holographic method. Finally, we design a sinusoidal curve with a phase gradient and a constant pressure amplitude and realize transport of a particle on a water surface along a curve.

Effects of porous media thickness and its hydraulic gradient history on the formation of sand boils: Experimental investigation

Sand boils occur where groundwater discharges to the land surface under sufficient hydraulic gradient to cause internal erosion and the upward transport of particles. A proper understanding of sand boil processes is essential in evaluating a wide range of geomechanical and sediment transport situations under which groundwater seepage occurs, such as the effects of groundwater discharge on beach stability. Although various empirical methods have been developed to estimate the critical hydraulic gradient (i_cr) leading to sand liquefaction, a prerequisite for sand boil occurrence, the effect of sand layer thickness and the implications of driving head fluctuations on the formation and reformation of sand boils have not been explored previously. This paper uses laboratory experiments to study sand boil formation and reformation for various sand thicknesses and hydraulic gradients to fill this knowledge gap. Sand layer thicknesses of 90 mm, 180 mm and 360 mm were adopted in evaluating sand boil reactivation, which was created by imposing hydraulic head fluctuations. While the first experiment (i.e., 90 mm sand layer) yielded a value for i_cr smaller (by 5%) than Terzaghi's (1922) value, the same theory underestimated i_cr by 12% and 4% for 180 mm and 360 mm sand layers, respectively. Moreover, i_cr needed for the reformation of sand boils decreased by 22%, 22% and 26% (relative to i_cr applicable to the initial sand boil) for the 90 mm, 180 mm and 360 mm sand layer thicknesses, respectively. We conclude that the formation of sand boils requires consideration of sand depth and the history of sand boil formation, particularly in relation to sand boils that form (and potentially reform) under oscillating pressures (e.g., tidal beaches).

Transport and accumulation of plastic particles on the varying sediment bed cover: Open-channel flow experiment

Contamination of sea bottom sediments by microplastics is widely confirmed, but the reasons for its patchiness remain poorly understood. Laboratory experiments are reported where combined sets of various plastic particles, different by shape, size, density, and flexibility, were transported by the step-wise increasing open-channel flow over the bottom covered with natural sediment of increasing grain size. For every particular flow velocity, observations revealed the recurrent formation of relatively narrow retention areas, where plastic particles lingered for some time in their motion. These areas follow the line of change of the sediment type from finer to coarser grains. It is shown that contact friction drives the retention of a particle at finer sediments, while particle/sediment-grain interaction becomes of importance when particles and sediment grains are of similar sizes. The presence of this effect can be expected for a relatively wide range of natural conditions.

Particles as carriers of matter in the aquatic environment: Challenges and ways ahead for transdisciplinary research

A diverse array of natural and anthropogenic particles found in the aquatic environment, can act as carriers of co-transported matter (CTM), such as nutrients, genetic material and contaminants. Thus, understanding carrier particle transport will increase our understanding of local and global fluxes of exogenous CTM (affiliated with the particle) and endogenous CTM (an inherent part of the particle). In the present contribution, researchers from multiple disciplines collaborated to provide perspectives on the interactions between carrier particles and CTM, and the fundamentals of transport of particles found in the aquatic environment and the generic spherical smooth particles, often used to make predictions about particle behavior in suspension. Evidently, the particles in the aquatic environment show a great variety of characteristics and vary greatly from each other as well as from the generic particle. However, in spite of these differences, many fundamental concepts apply to particles in general. We emphasize the importance of understanding the basic concepts of transport of particle-associated CTM, and the main assumptions in the generic-founded models, which are challenged by the diverging characteristics of particles found in the aquatic environment, as paramount moving forward. Additionally, we identified the need for a conceptual and semantic link between different scientific fields of particle research and initiated the formation of a consistent terminology. Disciplinary and organizational (academic and funding) barriers need to be overcome to enable individual researchers to move beyond their knowledge sphere, to stimulate future interdisciplinary collaborations and to avoid research silos. Hereby, we can foster faster and better progress of evolving research fields on new and emerging anthropogenic carrier particles, and stimulate the development of solutions to the technological and environmental challenges.

Influencing factors in the simulation of airflow and particle transportation in aircraft cabins by CFD

To control the transport of particles such as the SARS-CoV-2 virus in airliner cabins, which is a significant concern for the flying public, effective ventilation systems are essential. Validated computational fluid dynamics (CFD) models are frequently and effectively used to investigate air distribution and contaminant transportation. The complex geometry and airflow characteristics in airliner cabins pose a challenge to numerical CFD validation. The objective of this investigation was to identify accurate and affordable validation processes for studying the airflow field and particulate contaminant distribution in airliner cabins during the design process for different ventilation systems. This study quantitatively evaluated the effects of ventilation system, turbulence model, particle simulation method, geometry simplification, and boundary condition assignment on airflow and particulate distributions in airliner cabins with either a mixing ventilation (MV) system or a displacement ventilation (DV) system calculated by CFD. The results showed that among four turbulence models, the standard k-ε, RNG k-ε, realizable k-ε and SST k-ω models, the prediction by the realizable k-ε model agreed most closely with the experimental data. Meanwhile, the steady Eulerian method provided a reasonable prediction of the particle concentration field with low computing cost. The computational domain should be simplified differently for the DV system and the MV system with consideration of the simulation accuracy and computing cost. For more accurate modeling results, the boundary conditions should be assigned in greater detail, taking into account the uniformity on the boundary.

Terrestrial inputs govern spatial distribution of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) in an Arctic fjord system (Isfjorden, Svalbard)

Considerable amounts of previously deposited persistent organic pollutants (POPs) are stored in the Arctic cryosphere. Transport of freshwater and terrestrial material to the Arctic Ocean is increasing due to ongoing climate change and the impact this has on POPs in marine receiving systems is unknown This study has investigated how secondary sources of POPs from land influence the occurrence and fate of POPs in an Arctic coastal marine system. Passive sampling of water and sampling of riverine suspended particulate matter (SPM) and marine sediments for analysis of polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) was carried out in rivers and their receiving fjords in Isfjorden system in Svalbard. Riverine SPM had low contaminant concentrations (<level of detection-28 pg/g dw ΣPCB₁₄, 16-100 pg/g dw HCB) compared to outer marine sediments 630-880 pg/g dw ΣPCB₁₄, 530-770 pg/g dw HCB). There was a strong spatial gradient in sediment PCB and HCB concentrations with lowest concentrations in river estuaries and in front of marine-terminating glaciers and increasing concentrations toward the outer fjord. This suggests that rather than leading to increased concentrations, inputs of SPM from land lead to a dilution of contaminant concentrations in nearshore sediments. Preliminary estimates of SPM:water activity ratios suggest that terrestrial particles (with low contaminant concentrations) may have the potential to act as sorbents of dissolved contaminants in the coastal water column, with implications for bioavailability of POPs to the marine food web. There is concern that ongoing increases in fluxes of freshwater, sediments and associated terrestrial material (including contaminants) from land to the Arctic Ocean will lead to increased mobilization and transport of POPs to coastal ecosystems. However, the results of this study indicate that on Svalbard, inputs from land may in fact have the opposite effect, leading to reduced concentrations in coastal sediments and waters.

Study of particle transport and gas amplification mechanism in proportional counters

Gas amplification is an essential feature of the proportional counter. The Boltzmann equation and the Townsend ionization coefficient are introduced to describe the behavior of electrons and the gas amplification in proportional counters, respectively. However, it is difficult to solve the Boltzmann equation completely and to obtain the critical radius at which electron avalanche begins. Therefore, we try to employ the Continuity equation and the linear stopping power to derive the distribution of particles and the critical radius. The space charge effect was also investigated to understand its influence on the gas amplification of the proportional counter. Finally, the gas amplification was calculated based on the classical theory of electron transport. The results indicate that the theoretical value is in good agreement with the experimental data. This means that the continuity equation and the linear stopping power can be used to depict the particle transport and gas amplification mechanism in proportional counters.

Role of nasal vestibule morphological variations on olfactory airflow dynamics

BACKGROUND

The conductive mechanisms of olfaction are typically given little priority in the evaluation of olfactory function. The objective of this study is to investigate the role of nasal vestibule morphological variations on airflow volume at the olfactory recess in healthy subjects.

METHODS

Anatomically realistic three-dimensional nasal airway models were constructed from computed tomography scans in five subjects. Each individual's unilateral nasal cavity (10 total) was classified according to the shape of their nasal vestibule: Standard, Notched, or Elongated. Nasal airflow simulations were performed using computational fluid dynamics modeling at two inspiratory flow rates (15 L/min and 30 L/min) to reflect resting and moderate breathing rates. Olfactory airflow volume and cross-sectional flow resistance were computed.

FINDINGS

Average olfactory airflow volumes (and percent airflow in olfactory) were: 0.25 L/min to 0.64 L/min (3.0%-7.7%; 15 L/min simulations) and 0.53 L/min to 1.30 L/min (3.2%-7.8%; 30 L/min simulations) for Standard; 0.13 L/min - 0.47 L/min (2.0%-6.8%; 15 L/min simulations) and 0.06 L/min - 0.82 L/min (1.7%-6.1%; 30 L/min simulations) for Notched; and 0.07 L/min - 0.39 L/min (1.2%-5.4%; 15 L/min simulations) and 0.30 L/min - 0.99 L/min (2.1%-6.7%; 30 L/min simulations) for Elongated. On average, relative difference in olfactory resistance between left and right sides was 141.5% for patients with different unilateral phenotypes and 82.2% for patients with identical unilateral phenotype.

INTERPRETATION

Olfactory cleft airflow volume was highest in the Standard nasal vestibule phenotype, followed by Notched phenotype for 15 L/min simulations and Elongated phenotype for 30 L/min simulations. Further, intra-patient variation in olfactory cleft airflow resistance differs greatly for patients with different unilateral phenotypes compared to patients with identical unilateral phenotype.

Experimental study of perturbative particle transport in the HL-2A tokamak

Perturbative particle transport experiment has been performed in the HL-2A tokamak by using supersonic molecular beam injection (SMBI) as an external particle source. The spatiotemporal evolution of edge density perturbation is traced and the particle source and the flux-gradient relation are obtained experimentally. The flux-gradient relation is found to be far from the diffusive model and three different transport processes are revealed, including pinch-dominant process, diffusion-pinch process and intermittent decays.

Comparison of the colloidal stability, mobility, and performance of nanoscale zerovalent iron and sulfidated derivatives

Nanoscale zerovalent iron (nZVI) and sulfidated nanoscale zerovalent iron (S-nZVI) have been increasingly studied for heavy metal removal in the subsurface. However, a comprehensive comparison of the effectiveness of the technologies and the stability of derived metal-adsorbed composites is lacking. In this study, we evaluated the colloidal stability and transport of nZVI, S-nZVI and S-nZVI modified with nanosized silica (FeSSi). Furthermore, we monitored the metal immobilization performance of the three nanoparticles (NPs) under anoxic conditions in synthetic groundwater for 30 days. The NP-metal composites were thereafter discharged into a river water and metal remobilization was monitored for 20 days. Sulfidation improved the colloidal stability of nZVI in both simple media and in natural waters, although a lower initial agglomeration rate constant (k_a) was observed in unmodified nZVI at acidic pH. The transport of nZVI in saturated soil column was enhanced with sulfidation due to decreased electrostatic attraction between the NPs and sand. The three NPs sequestered more than 80 % of Cu²⁺, Zn²⁺, Cd²⁺ and Cr₂O₇^2- from groundwater. Among the three NPs tested, S-nZVI had a slightly higher removal capacity for metals than nZVI in synthetic groundwater and the chemical stability of metal-S-nZVI composites upon discharge into river water was the highest.

A laboratory study of the expiratory airflow and particle dispersion in the stratified indoor environment

Understanding the role of human expiratory flows on respiratory infection in ventilated environments is useful for taking appropriate interventions to minimize the infection risk. Some studies have predicted the lock-up phenomenon of exhaled flows in stratified environments; however, there is a lack of high-quality experimental data to validate the theoretical models. In addition, how thermal stratification affects the transport of exhaled particles has not been explored so far. In this study, a water tank experiment was conducted according to the similarity protocols to mimic how the expiratory airflow and particles behaved in both uniform and stratified environments. The lock-up phenomenon was visualized and compared with the predicted results by an integral model. Results showed that our previously developed theoretical model of a respiratory airflow was effective to predict the airflow dispersion in stratified environments. Stratification frequency (N) of the background fluid and the Froude Number F r 0 of the thermal flow jointly determined the lock-up layer in a power law. For the particle dispersion, it indicated that small particles such as fine droplets and droplet nuclei would be 'locked' by indoor thermal stratification, and disperse with the thermal flow over a long distance, potentially increasing the long-range airborne infection risk. Large particles such as large droplets can deposit within a short distance, hardly affected by thermal stratification, however, droplet infection could happen to the susceptible people at a close contact with the infector. This study could give some guidance in view of cross-infection control indoors for stratified environment.

Particle transport and deposition correlation with near-wall flow characteristic under inspiratory airflow in lung airways

Exposure of lung airways to detrimental suspended aerosols in the environment increases the vulnerability of the respiratory and cardiovascular systems. In addition, recent developments in therapeutic inhalation devices magnify the importance of particle transport. In this manuscript, particle transport and deposition patterns in the upper tracheobronchial (TB) tree were studied where the inertial forces are considerable for microparticles. Wall shear stress divergence (WSSdiv) is proposed as a wall-based parameter that can predict particle deposition patterns. WSSdiv is proportional to near-wall normal velocity and can quantify the strength of flow towards and away from the wall. Computational fluid dynamics (CFD) simulations were performed to quantify airflow velocity and WSS vectors for steady inhalation in one case-control and unsteady inhalation in six subject-specific airway trees. Turbulent flow simulation was performed for the steady case using large eddy simulation to study the effect of turbulence. Magnetic resonance velocimetry (MRV) measurements were used to validate the case-control CFD simulation. Inertial particle transport was modeled by solving the Maxey-Riley equation in a Lagrangian framework. Deposition percentage (DP) was quantified for the case-control model over five particle sizes. DP was found to be proportional to particle size in agreement with previous studies in the literature. A normalized deposition concentration (DC) was defined to characterize localized deposition. A relatively strong correlation (Pearson value > 0.7) was found between DC and positive WSSdiv for physiologically relevant Stokes (St) numbers. Additionally, a regional analysis was performed after dividing the lungs into smaller areas. A spatial integral of positive WSSdiv over each division was shown to maintain a very strong correlation (Pearson value > 0.9) with cumulative spatial DC or regional dosimetry. The conclusions were generalized to a larger population in which two healthy and four asthmatic patients were investigated. This study shows that WSSdiv could be used to predict the qualitative surface deposition and relative regional dosimetry without the need to solve a particle transport problem.

Plutonium production and particles incorporation into the human body

Plutonium is one of the most toxic radioactive substances known. The isotope ²³⁹Pu gained attention when it had become known as a potential explosive material for atomic bombs. This paper describes the main problems encountered during the early years of operation of the first plutonium production plant in the former Soviet Union, the Mayak Production Association (Mayak PA). Mayak PA caused severe radioactive contamination of the environment and exposure personnel and population living in the vicinity areas to high radiation doses. The authors focus on key findings of large-scale studies on the internal dosimetry of workers for use in assessment of radiological risks from exposure to plutonium. This work presents an overview of the important issues for inhalation dose assessments such as generation of plutonium particles, plutonium intake, dissolution of plutonium particles, distribution of plutonium in humans, related exposures and health effects. Understanding the relationship between health effects, radiation dose and route of exposure helps quantify the health risks associated with occupational exposure in the nuclear industry and validate the radiation protection standards used in the Russian Federation and worldwide.

Improved understanding of particle transport in karst groundwater using natural sediments as tracers

Colloids and particles act as vectors for contaminant transport. In karst aquifers, particle transport is particularly efficient and plays critical roles in soil erosion and in the process of karstification. However, available techniques for particle tracing are either expensive or not representative for the transport of natural colloids and particles. We developed a new method for particle tracing, using natural sediments as artificial tracers, and first applied this method at a karst experimental site in the Alps. Suspended particles were injected into a swallow hole together with a conservative solute tracer for comparison. Breakthrough curves for 32 different particle size classes between 0.8 and 450 μm were recorded at a karst spring 230 m away using a mobile particle counter that allows quantitative detection at high temporal resolution. Results show that (i) sediments can be used as efficient particle tracers in karst groundwater; (ii) recoveries are similar for particles and solutes; (iii) mean velocity increases with increasing particle size; (iv) dispersion decreases with increasing particle size; (v) these observations point to exclusion processes. As a conclusion, this new experimental technique allows new insights into the transport and fate of colloids and particles in groundwater at affordable costs.

Study on performance of electrostatic precipitator under multi-physics coupling

A wire-plate electrostatic precipitator (ESP) is developed to analyze the particle transport characteristics and the influence of various factors on the performance of ESP. Above all, an experimental device is built to measure the current density distribution of the plates and obtain good consistency with the numerical simulation results, taking the ESP model established by COMSOL/Multiphysics as the numerical simulating object. Firstly, the electric field is solved by finite element method(FEM) to obtain the potential and charge density distribution. Then, the influence of secondary flow on the main flow at different flow velocities is explored. Finally, multi-physics coupling calculations show the influence of dust particle properties, electrode configuration, and operating conditions on ESP performance. The study found that the particle diameter is positively correlated with its charge, force, and motion, and the relative permittivity of the particles affects the collecting efficiency by affecting its charge difficulty. The wire-to-wire spacing is not proportional to collecting efficiency, when the spacing is 80 mm, the efficiency and the corona current can be maximized. Average electric field strength, corona current density, and current density distribution standard deviation satisfy the cubic function relationship. In addition, the effect of airflow velocity on collecting efficiency and particle precipitation is revealed. It provides a valuable basis for design and performance optimization of ESP.

Characterizing export of land-based microplastics to the estuary - Part I: Application of integrated geospatial microplastic transport models to assess tire and road wear particles in the Seine watershed

Human and ecological exposure to micro- and nanoplastic materials (abbreviated as MP, < 5 mm) occurs in both aquatic and terrestrial environments. Recent reviews prioritize the need for assessments linking spatially distributed MP releases with terrestrial and freshwater transport processes, thereby providing a better understanding of the factors affecting MP distribution to the sea. Tire and road wear particles (TRWP) have an estimated generation rate of 1 kg tread inhabitant^-1 year^-1 in Europe, but the fate of this MP source in watersheds has not been systematically assessed. An integrated temporally and geospatially resolved watershed-scale MP modeling methodology was applied to TRWP fate and transport in the Seine (France) watershed. The mass balance considers TRWP generation and terrestrial transport to soil, air, and roadways, as well as freshwater transport processes including particle heteroaggregation, degradation and sedimentation within subcatchments. The per capita TRWP mass release estimate in the Seine watershed was 1.8 kg inhabitant^-1 yr^-1. The model estimates indicated that 18% of this release was transported to freshwater and 2% was exported to the estuary, which demonstrated the potential for appreciable capture, degradation, and retention of TRWP prior to export. The modeled pseudo-steady state sediment concentrations were consistent with measurements from the Seine watershed supporting the plausibility of the predicted trapping efficiency of approximately 90%. The approach supported the efficient completion of local and global sensitivity analyses presented in Part II of this study, and can be adapted to the assessment of other MPs.

Modeling of the transport and deposition of polydispersed particles: Effects of hydrodynamics and spatiotemporal evolution of the deposition rate

A time-distance-dependent deposition model is built to investigate the effects of hydrodynamic forces on the transport and deposition of polydispersed particles and the evolution of deposition rates with time and distance. Straining and the heterogeneity of the particle population are considered to play important roles in the decreasing distribution of deposition rates. Numerical simulations were applied in a series of sand column experiments at different fluid velocities for three different porous media. The effects of hydrodynamics forces are elaborated with the systematic variations of deposition dynamic parameters of the proposed model. With retention distributions with particle size as well as temporal and spatial evolutions of deposition rates, the transport and deposition mechanisms of polydispersed particles will be elucidated through the interplay of the variation of the particle size distribution of mobile particle populations and the geometrical change of the porous medium due to retention (straining and blocking).

Fate of nano- and microplastic in freshwater systems: A modeling study

Riverine transport to the marine environment is an important pathway for microplastic. However, information on fate and transport of nano- and microplastic in freshwater systems is lacking. Here we present scenario studies on the fate and transport of nano-to millimetre sized spherical particles like microbeads (100 nm-10 mm) with a state of the art spatiotemporally resolved hydrological model. The model accounts for advective transport, homo- and heteroaggregation, sedimentation-resuspension, polymer degradation, presence of biofilm and burial. Literature data were used to parameterize the model and additionally the attachment efficiency for heteroaggregation was determined experimentally. The attachment efficiency ranged from 0.004 to 0.2 for 70 nm and 1050 nm polystyrene particles aggregating with kaolin or bentonite clays in natural freshwater. Modeled effects of polymer density (1-1.5 kg/L) and biofilm formation were not large, due to the fact that variations in polymer density are largely overwhelmed by excess mass of suspended solids that form heteroaggregates with microplastic. Particle size had a dramatic effect on the modeled fate and retention of microplastic and on the positioning of the accumulation hot spots in the sediment along the river. Remarkably, retention was lowest (18-25%) for intermediate sized particles of about 5 μm, which implies that the smaller submicron particles as well as larger micro- and millimetre sized plastic are preferentially retained. Our results suggest that river hydrodynamics affect microplastic size distributions with profound implications for emissions to marine systems.

The role of anisotropic expansion for pulmonary acinar aerosol deposition

Lung deformations at the local pulmonary acinar scale are intrinsically anisotropic. Despite progress in imaging modalities, the true heterogeneous nature of acinar expansion during breathing remains controversial, where our understanding of inhaled aerosol deposition still widely emanates from studies under self-similar, isotropic wall motions. Building on recent 3D models of multi-generation acinar networks, we explore in numerical simulations how different hypothesized scenarios of anisotropic expansion influence deposition outcomes of inhaled aerosols in the acinar depths. While the broader range of particles acknowledged to reach the acinar region (dp=0.005-5.0μm) are largely unaffected by the details of anisotropic expansion under tidal breathing, our results suggest nevertheless that anisotropy modulates the deposition sites and fractions for a narrow band of sub-micron particles (dp~0.5-0.75μm), where the fate of aerosols is greatly intertwined with local convective flows. Our findings underscore how intrinsic aerosol motion (i.e. diffusion, sedimentation) undermines the role of anisotropic wall expansion that is often attributed in determining aerosol mixing and acinar deposition.

Process-generated nanoparticles from ceramic tile sintering: Emissions, exposure and environmental release

The ceramic industry is an industrial sector in need of significant process changes, which may benefit from innovative technologies such as laser sintering of ceramic tiles. Such innovations result in a considerable research gap within exposure assessment studies for process-generated ultrafine and nanoparticles. This study addresses this issue aiming to characterise particle formation, release mechanisms and their impact on personal exposure during a tile sintering activity in an industrial-scale pilot plant, as a follow-up of a previous study in a laboratory-scale plant. In addition, possible particle transformations in the exhaust system, the potential for particle release to the outdoor environment, and the effectiveness of the filtration system were also assessed. For this purpose, a tiered measurement strategy was conducted. The main findings evidence that nanoparticle emission patterns were strongly linked to temperature and tile chemical composition, and mainly independent of the laser treatment. Also, new particle formation (from gaseous precursors) events were detected, with nanoparticles <30nm in diameter being formed during the thermal treatment. In addition, ultrafine and nano-sized airborne particles were generated and emitted into workplace air during sintering process on a statistically significant level. These results evidence the risk of occupational exposure to ultrafine and nanoparticles during tile sintering activity since workers would be exposed to concentrations above the nano reference value (NRV; 4×10(4)cm(-3)), with 8-hour time weighted average concentrations in the range of 1.4×10(5)cm(-3) and 5.3×10(5)cm(-3). A potential risk for nanoparticle and ultrafine particle release to the environment was also identified, despite the fact that the efficiency of the filtration system was successfully tested and evidenced a >87% efficiency in particle number concentrations removal.

Agar agar-stabilized milled zerovalent iron particles for in situ groundwater remediation

Submicron-scale milled zerovalent iron (milled ZVI) particles produced by grinding macroscopic raw materials could provide a cost-effective alternative to nanoscale zerovalent iron (nZVI) particles for in situ degradation of chlorinated aliphatic hydrocarbons in groundwater. However, the aggregation and settling of bare milled ZVI particles from suspension presents a significant obstacle to their in situ application for groundwater remediation. In our investigations we reduced the rapid aggregation and settling rate of bare milled ZVI particles from suspension by stabilization with a "green" agar agar polymer. The transport potential of stabilized milled ZVI particle suspensions in a diverse array of natural heterogeneous porous media was evaluated in a series of well-controlled laboratory column experiments. The impact of agar agar on trichloroethene (TCE) removal by milled ZVI particles was assessed in laboratory-scale batch reactors. The use of agar agar significantly enhanced the transport of milled ZVI particles in all of the investigated porous media. Reactivity tests showed that the agar agar-stabilized milled ZVI particles were reactive towards TCE, but that their reactivity was an order of magnitude less than that of bare, non-stabilized milled ZVI particles. Our results suggest that milled ZVI particles could be used as an alternative to nZVI particles as their potential for emplacement into contaminated zone, their reactivity, and expected longevity are beneficial for in situ groundwater remediation.

Effect of polyelectrolyte-surfactant complexation on Marangoni transport at a liquid-liquid interface

Complexation of surfactants and oppositely charged polyelectrolytes is expected to alter Marangoni transport at a fluid interface compared to either single component system due to altered interfacial tension isotherms and mass transfer rates as well as adsorption irreversibility effects. We investigate Marangoni transport at the oil/water interface by passing mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and cationic polyelectrolyte poly(3-(2-methylpropionamide)propyl) trimethylammonium chloride-acrylamide (poly[AM-MAPTAC]), or rinsing solutions, over an oil/water interface in a radial, stagnation point flow. The displacements of adsorbed tracer particles are recorded through optical microscopy. The net displacement, defined as the sum of the displacements occurring during the adsorption and desorption stages of one application and rinsing cycle, is up to 10 times greater for complexing surfactant/polymer mixtures compared to either single component system. The enhanced net displacement is largely determined by the enhanced transport upon adsorption, while the reverse displacement that would normally occur upon rinsing is partially suppressed by partially irreversible polymer adsorption at the oil/water interface. In addition to effects of complexation on interfacial tension gradient induced flow, complexation effects on the bulk, and possibly interfacial, viscosity also influence the interfacial transport.

Colloidal activated carbon for in-situ groundwater remediation--Transport characteristics and adsorption of organic compounds in water-saturated sediment columns

Colloidal activated carbon can be considered as a versatile adsorbent and carrier material for in-situ groundwater remediation. In analogy to other nanoremediation approaches, activated carbon colloids (ACC) can be injected into the subsurface as aqueous suspensions. Deposition of ACC on the sediment creates a sorption barrier against further spreading of hydrophobic pollutants. This study deals with the optimization of ACC and their suspensions with a focus on suspension stability, ACC mobility in saturated porous media and sorption efficiency towards organic contaminants. ACC with an appropriate particle size range (d50=0.8μm) were obtained from a commercial powdered activated carbon product by means of wet-grinding. Among the various methods tested for stabilization of ACC suspensions, addition of humic acid (HA) and carboxymethyl cellulose (CMC) showed the best results. Due to electrosteric stabilization by adsorption of CMC, suspensions remained stable even at high ACC concentrations (11gL(-1)) and conditions typical of very hard water (5mM divalent cations). Furthermore, CMC-stabilized ACC showed high mobility in a water-saturated sandy sediment column (filter coefficient λ=0.2m(-1)). Such mobility is a pre-requisite for in-situ installation of sorption or reaction barriers by simple injection-well or direct-push application of ACC suspensions. Column experiments with organic model compounds proved the efficacy of ACC deposits on sediment for contaminant adsorption and retardation under flow-through conditions.

The influence of small intestinal mucus structure on particle transport ex vivo

Mucus provides a barrier to bacteria and toxins while allowing nutrient absorption and waste transport. Unlike colonic mucus, small intestinal mucus structure is poorly understood. This study aimed to provide evidence for a continuous, structured mucus layer and assess the diffusion of different sized particles through it. Mucus structure was assessed by histology and immunohistochemistry. Ultra-structure was assessed by scanning electron microscopy. Tracking of 100 nm and 500 nm latex beads was conducted using ex vivo porcine mucus. The porcine jejunum and ileum were filled with mucus. Layered MUC2 staining was visible throughout the small intestine, covering villus tips. Scanning electron microscopy showed net-like mucin sheets covering villi (211 ± 7 nm pore diameter). Particle tracking of 100 nm latex beads, showed no inhibition of diffusion through mucus while 500 nm beads displayed limited diffusion. These results suggest a continuous mucus layer exists throughout the small intestine, which is highly stratified adjacent to the epithelium. The network observed is consistent with previous observations and correlates with stratified MUC2 staining. Mucin pore size is consistent with free diffusion of 100 nm and limited diffusion of 500 nm particles. Small Intestinal mucus structure has important implications for drug delivery systems and prevention and treatment of conditions like mucositis and inflammatory bowel disease.

Metal leaching in a highway embankment on field and laboratory scale

Increasing worldwide motor vehicle traffic leads to the question of the possible environmental consequences. This paper aims to analyse metal leaching in a highway embankment using both field and laboratory experiments. Soil, soil solution and road runoff were collected along one of the oldest highways in the world to characterize leaching of the metals Cd, Cr, Cu, Ni, Pb and Zn. Batch, column and adsorption experiments were carried out to study the reliability and transferability of laboratory approaches. Depending on the element, the ratio of particle-bound metals in road runoff varied between 15-90%. Metal levels in embankment soils were significantly higher compared to a reference site in a forest at 800 m distance (up a factor of 30). High metal concentrations in soil solution at 50 cm soil depth were not a direct result of road runoff but rather of elevated concentrations in the soil matrix. The use of batch S4 elution was found to be the best overall laboratory method to predict soil solution concentrations in field. Adsorption experiments showed a relative increase in retention capacity in roadside soil of up to a factor of 20 after nearly 100 years of operation. The input of alkaline dust and organic carbon into roadside soils increases its retention capacity in the long term.

Transport and dissolution of microscale Composition B detonation residues in porous media

The deposition of military explosive residues on training ranges has resulted in extensive contamination of land and water resources. Experiments were performed to examine the transport and dissolution of mm-sized and microscale Composition B (Comp B) residues applied to the top of sand columns under unsaturated flow conditions. Under a continuous application of artificial rainwater, greater dissolved effluent concentrations of TNT and RDX (5- and 10-fold, respectively) were observed for the columns amended with microscale residues than for the columns amended with the mm-sized residues. This difference between microscale and mm-sized residues likely was due, in part, to dissolution of microscale particles entrapped in the sand column. Elution of particulate Comp B from the columns, based on the difference between total and dissolved explosives concentrations in column effluent, indicated higher and more frequent detections of particulate explosives in the columns amended with microscale Comp B than the columns amended with mm-sized Comp B. Examination of the vertical profiles of explosives in sand indicated that particulate residues had migrated into the sand, with a greater particulate mass observed in the columns which had received the microscale Comp B compared to those which received the mm-sized Comp B. These results indicate that both mm-sized and microscale detonation residues can contribute to the undissolved (e.g., particulate) Comp B transport into to the subsurface. This particulate transport increases the effective contact time between residues and infiltrating rainwater, leading to overall increases in the dissolved mass contaminant flux.

Transport of exhaled particulate matter in airborne infection isolation rooms

The goal of this research was to examine the characteristics of the spatial velocity and concentration profiles which might result in health care workers' exposure to a pathogenic agent in an airborne infection isolation room (AIIR). Computational fluid dynamics simulations were performed for this purpose. This investigation expanded on the work of Huang and Tsao [The influence of air motion on bacteria removal in negative pressure isolation rooms. HVAC & R Research 2005; 11: 563-85], who studied how ventilation conditions impact dispersion of pathogenic nuclei in an AIIR by investigating the airflow conditions impacting dispersion of infectious agents in the AIIR. The work included a careful quality assurance study of the computed airflow, and final simulations were performed on a fine tetrahedral mesh with approximately 1.3×106 cells. The 1 μm diameter particles were released from a 0.001225 m2 area representing the nose and mouth. Two cases were investigated during the current study: continuous exhalation of pathogen-laden air from the patient and expulsion of pathogenic particles by a single cough or sneeze. Slow decay of particle concentration in the AIIR during the single cough/sneeze simulation and tendency for particle accumulation near the AIIR walls observed in the continuous breathing simulation suggest that unintended exposures are possible despite the ventilation system. Based on these findings, it is recommended that extra care be taken to assure proper functionality of personal protective equipment used in an AIIR.