The impact of nanoparticle aggregation on their size exclusion during transport in porous media: One- and three-dimensional modelling investigations

Transport of polystyrene microplastics in bare and iron oxide-coated quartz sand: Effects of ionic strength, humic acid, and co-existing graphene oxide

This research explored the effects of widely utilized nanomaterial graphene oxide (GO) and organic matter humic acid (HA) on the transport of microplastics under different ionic solution strengths in bare sand and iron oxide-coated sand. The results found transport of polystyrene microplastics (PS) did not respond to the presence of HA in sand that contains large amounts of iron oxide. Compared to bare quartz sand, ionic strength had little effect: <20 % of PS passed through Fe sand columns. There was a significant promotion of PS transport in the presence of GO, however, which can be attributed to the increased surface electronegativity of PS and steric hindrance. Moreover, GO combined with HA significantly promoted the transport of PS in the Fe sand, and transport further increased when the concentration of HA increased from 5 to 10 mg/L. Interestingly, the degree of this increase exactly corresponded to the change in the surface charge of the microplastics, demonstrating that electrostatic interaction dominated the PS transport. Further results indicated that co-existing pollutants had significant impacts on the transport of microplastics under various conditions by altering the surface characteristics of the plastic particles and the spatial steric hindrance within porous media. This research will offer insights into predicting the transport and fate of microplastics in complex environments.

Dispersion of silica-encapsulated DNA magnetic particles in a homogeneous sand tank

In this study, we focused on the 3D dispersion of colloids. To our knowledge, we were the first to do so. Thereto, we injected silica encapsulated DNA tagged superparamagnetic particles (SiDNAmag) in a homogeneous coarse grain sand tank. At four downstream locations, SiDNAmag concentrations were determined as a function of time. Longitudinal and transverse dispersivity values and associated uncertainties of SiDNAmag were determined using Monte Carlo modelling approach. The parameter associated uncertainties of hydraulic conductivity as well as of the effective porosity estimated from SiDNAmag breakthrough curves were statistically similar to those estimated from salt tracer breakthrough curves. Further, the SiDNAmag dispersivity uncertainty ranges were then statistically compared with the salt tracer (NaCl, and fluorescein) dispersivities. Our results indicated that time to rise, time of peak concentration and shape of the breakthrough curves of SiDNAmag were similar to those of the salt tracer breakthrough curves. Despite the size difference between the salt tracer molecules and SiDNAmag, size exclusion did not occur, probably due to the large pore throat diameter to SiDNAmag diameter ratio. The median longitudinal dispersivity (αL) of salt tracer and SiDNAmag were 4.9 and 5.8 × 10-4 m, respectively. The median ratio of horizontal and vertical transverse dispersivities to αL, (αTH /αL and αTV /αL, respectively), for salt tracer and SiDNAmag ranged between 0.52 and 0.56. Through the statistical tests, we concluded that the longitudinal and traverse dispersivities of SiDNAmag were not statistically significantly different from salt tracer in 3 dimensions and could be used to characterize the dispersive properties of the medium we used. Our work contributes to a better understanding of 3D dispersion of SiDNAmag in saturated porous media.

Enhanced sinks of polystyrene nanoplastics (PSNPs) in marine sediment compared to freshwater sediment: Influencing factors and mechanisms

The difference in the transport behaviors of nanoplastics consistently assistant with their toxicities to benthic and other aquatic organisms is still unclear between freshwater and marine sediments. Here, the mobilities of polystyrene nanoplastics (PSNPs) and key environmental factors including salinity and humic acid (HA) were systematically studied. In the sand column experiments, both tested PSNPs in the freshwater system (100 nm NPs (100NPs): 90.15 %; 500 nm NPs (500NPs): 54.22 %) presented much higher penetration ratio than in the marine system (100NPs: 8.09 %; 500NPs: 19.04 %). The addition of marine sediment with a smaller median grain diameter caused a much more apparent decline in NPs mobility (100NPs: from 8.09 % to 1.85 %; 500NPs: from 19.04 % to 3.51 %) than that containing freshwater sediment (100NPs: from 90.15 % to 83.56 %; 500NPs: from 54.22 % to 41.63 %). Interestingly, adding HA obviously led to decreased and slightly increased mobilities for NPs in freshwater systems, but dramatically improved performance for NPs in marine systems. Electrostatic and steric repulsions, corresponding to alteration of zeta potential and hydrodynamic diameter of NPs and sands, as well as minerals owing to adsorption of dissolved organic matter (DOM) and aggregations from varied salinity, are responsible for the mobility difference.

Prediction of the aggregation rate of nanoparticles in porous media in the diffusion-controlled regime

The fate and aggregation of nanoparticles (NPs) in the subsurface are important due to potentially harmful impacts on the environment and human health. This study aims to investigate the effects of flow velocity, particle size, and particle concentration on the aggregation rate of NPs in a diffusion-limited regime and build an equation to predict the aggregation rate when NPs move in the pore space between randomly packed spheres (including mono-disperse, bi-disperse, and tri-disperse spheres). The flow of 0.2 M potassium chloride (KCl) through the random sphere packings was simulated by the lattice Boltzmann method (LBM). The movement and aggregation of cerium oxide (CeO2) particles were then examined by using a Lagrangian particle tracking method based on a force balance approach. This method relied on Newton's second law of motion and took the interaction forces among particles into account. The aggregation rate of NPs was found to depend linearly on time, and the slope of the line was a power function of the particle concentration, the Reynolds (Re) and Schmidt (Sc) numbers. The exponent for the Sc number was triple that of the Re number, which was evidence that the random movement of NPs has a much stronger effect on the rate of diffusion-controlled aggregation than the convection.

Aggregation of nanoparticles and morphology of aggregates in porous media with computations

HYPOTHESIS

The main hypothesis is that the aggregation process for nanoparticles (NPs) propagating in porous media is affected by the structure of the flow field as well as by the properties of the primary NPs. If this were true, then the aggregation could be predicted and controlled. However, to obtain reliable results from computations, one needs to account for the interactions between the NPs as well as the details of the fluid velocity, thus making advances over prior efforts that either ignored the aggregation of NPs, or used probabilistic methods to model aggregation.

EXPERIMENTS

Computational experiments were conducted using the lattice Boltzmann method in conjunction with Lagrangian particle tracking (LPT). The LPT accounted for the physicochemical interaction forces among NPs. Computationally obtained aggregation kinetics and fractal dimensions of Cerium oxide (CeO2) particles, suspended in potassium chloride (KCl) solutions with different concentration, were verified against experimental results. The model was then employed to investigate the effects of ionic strength, fluid velocity, and particle size on the aggregation kinetics and the aggregate morphology, as NPs propagated in the pore space between randomly packed spheres.

FINDINGS

The aim of this study was to develop a computational model to simulate the aggregation of NPs and obtain the morphology of aggregates in confined geometries, based on the physics of NP interactions and the flow field. The most important factor that impacted both the aggregation process and the aggregate structure was found to be the concentration of the electrolyte. The pore velocity influenced the aggregation kinetics and the NP fractal dimension, especially in diffusion-limited aggregation. The primary particle size affected the diffusion-limited aggregation kinetics and the fractal dimension of reaction-limited aggregates noticeably.

Multifunctional lipid-based nanoparticles for wound healing and antibacterial applications: A review

Wound healing primarily involves preventing severe infections, accelerating healing, and reducing pain and scarring. Therefore, the multifunctional application of lipid-based nanoparticles (LBNs) has received considerable attention in drug discovery due to their solid or liquid lipid core, which increases their ability to provide prolonged drug release, reduce treatment costs, and improve patient compliance. LBNs have also been used in medical and cosmetic practices and formulated for various products based on skin type, disease conditions, administration product costs, efficiency, stability, and toxicity; therefore, understanding their interaction with biological systems is very important. Therefore, it is necessary to perform an in-depth analysis of the results from a comprehensive characterization process to produce lipid-based drug delivery systems with desired properties. This review will provide detailed information on the different types of LBNs, their formulation methods, characterisation, antimicrobial activity, and application in various wound models (both in vitro and in vivo studies). Also, the clinical and commercial applications of LBNs are summarized.

Interplay of compound pollutants with microplastics transported in saturated porous media: Effect of co-existing graphene oxide and tetracycline

Co-existence of microplastics, nanomaterials, and antibiotics may lead to intensified multifaceted pollution, which may influence their fate in soils. This study investigated the co-transport behavior of polystyrene microplastics (PS) and compound pollutants of graphene oxide (GO) and tetracycline (TC). Packed column experiments for microplastic with or without combined pollutants were performed in KCl (10 and 30 mM) and CaCl2 solutions (0.3 and 1 mM). The results showed transport of PS was facilitated at low ionic strengths and inhibited at high ionic strengths by GO with or without TC under examined conditions. Carrier effect of GO as well as the aggregation of PS in the presence of co-exiting GO or GO-TC could be the contributor. Although the existence of TC relieved the ripening phenomenon of PS and GO deposition due to enhanced electronegativity of sand media, the effect of GO on the PS transport has not been significantly impacted, indicating the dominant role of GO during cotransport process. Furthermore, the transport of PS was increased by TC owing to competition for deposition sites on sand surfaces. In turn, the transport of TC was mainly affected by PS whether graphene was present or not. The increase in electrostatic repulsive force (transport-promoting) and addition adsorption sites (transport-inhibiting) may be responsible for the observations. Our findings could improve understandings of complex environmental behaviors of microplastics and provide insight into investigation on cotransport of emerging contaminants under various conditions relevant to the subsurface environment.

Effect of Salinity on Hydroxyapatite Nanoparticles Flooding in Enhanced Oil Recovery: A Mechanistic Study

Fluid-fluid interactions can affect any enhanced oil recovery (EOR) method, including nanofluid (NF) brine-water flooding. Flooding with NFs changes wettability and lowers oil-water interfacial tension (IFT). Preparation and modification affect the nanoparticle (NP) performance. Hydroxyapatite (HAP) NPs in EOR are yet to be properly verified. HAP was synthesized in this study using co-precipitation and in situ surface functionalization with sodium dodecyl sulfate in order to investigate its impact on EOR processes at high temperatures and different salinities. The following techniques were employed, in that sequence, to verify its synthesis: transmission electron microscopy, zeta potential, thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, particle size analysis, and energy-dispersive X-ray spectra. The outcomes showed the production of HAP, with the particles being evenly dispersed and stable in aqueous solution. The particles' surface charge increased from -5 to -27 mV when the pH was changed from 1 to 13. The HAP NFs at 0.1 wt % altered the wettability of sandstone core plugs from oil-wet at 111.7 to water-wet at 9.0 contact angles at salinity ranges of 5000 ppm to 30,000 ppm. Additionally, the IFT was reduced to 3 mN/m HAP with an incremental oil recovery of 17.9% of the initial oil in place. The HAP NF thus demonstrated excellent effectiveness in EOR through IFT reduction, wettability change, and oil displacement in both low and high salinity conditions.

Antibiofilm and cytotoxic potential of extracellular biosynthesized gold nanoparticles using actinobacteria Amycolatopsis sp. KMN

This study intends to biosynthesize gold nanoparticles (AuNPs) using Amycolatopsis sp. KMN and to investigate its potential antibiofilm, cytotoxic and antioxidant activities. The physicochemical characterization of biosynthesize AuNPs was identified by UV-Visible, energy-dispersive X-ray, and Fourier transform infrared spectroscopy, as well as high-resolution transmission electron microscopy, X-ray diffraction, zeta potential, and dynamic light scattering methods. Crystal violet assay and scanning electron microscopy showed that the AuNPs with a particle size of 44.4 nm have a strong antibiofilm activity (at 750 µg/ml concentration) against bacteria strains viz Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853. The result also demonstrated strong cytotoxic activity against two cell lines, MCF-7 and HT-29. The MTT test result displayed that over a period of 48 hr, the IC₅₀ of AuNPs was 600 and 300 µg/ml for MCF-7 and HT-29 cell lines, respectively. The IC₅₀ of AuNPs against DPPH was 46.87 µg/ml. This is the first report that examines Amycolatopsis sp. strain KMN-mediated synthesis of AuNPs is rapid and in situ with antibiofilm and cytotoxicity activities. Moreover, it has the potential for an effective antibiofilm and cytotoxic activity that could be used in future therapeutic applications.

Magnetic Iron Nanoparticles: Synthesis, Surface Enhancements, and Biological Challenges

This review focuses on the role of magnetic nanoparticles (MNPs), their physicochemical properties, their potential applications, and their association with the consequent toxicological effects in complex biologic systems. These MNPs have generated an accelerated development and research movement in the last two decades. They are solving a large portion of problems in several industries, including cosmetics, pharmaceuticals, diagnostics, water remediation, photoelectronics, and information storage, to name a few. As a result, more MNPs are put into contact with biological organisms, including humans, via interacting with their cellular structures. This situation will require a deeper understanding of these particles’ full impact in interacting with complex biological systems, and even though extensive studies have been carried out on different biological systems discussing toxicology aspects of MNP systems used in biomedical applications, they give mixed and inconclusive results. Chemical agencies, such as the Registration, Evaluation, Authorization, and Restriction of Chemical substances (REACH) legislation for registration, evaluation, and authorization of substances and materials from the European Chemical Agency (ECHA), have held meetings to discuss the issue. However, nanomaterials (NMs) are being categorized by composition alone, ignoring the physicochemical properties and possible risks that their size, stability, crystallinity, and morphology could bring to health. Although several initiatives are being discussed around the world for the correct management and disposal of these materials, thanks to the extensive work of researchers everywhere addressing the issue of related biological impacts and concerns, and a new nanoethics and nanosafety branch to help clarify and bring together information about the impact of nanoparticles, more questions than answers have arisen regarding the behavior of MNPs with a wide range of effects in the same tissue. The generation of a consolidative framework of these biological behaviors is necessary to allow future applications to be manageable.

Nanoplastics dominate the cotransport of small-scale plastics in seawater-saturated porous media

The transport of microplastics (MP) or nanoplastics (NP) in porous media has been widely reported. However, their mutual interaction and effect on cotransport remain unclear. Here, we investigated the colloidal interaction between NP (50 nm), submicroplastics (SP, 300 nm), and MP (1000 nm) in seawater and their cotransport in saturated natural sea sands. In the single-component suspension, the recovered mass percentage (M_eff) of colloids was as follows: MP (47.81%) > NP (24.18%) > SP (21.66%). SP and MP remained monodispersed. MP had the highest mobility due to the strongest electrostatic repulsion with sand surface, whereas NP formed homoaggregates and was characterized by ripening phenomena. In the SP-MP mixture, SP and MP kept independent mobility without mutual effect. In the NP-SP-MP mixture, the M_eff of MP was reduced by 10% because unstable NP induced MP to form heteroaggregates with SP, which could not pass through the pores. In addition, NP attached to the sand surface could form additional retention sites to retain MP. By contrast, SP showed a 13% increase in M_eff because MP became an indirect carrier of SP through the bridging of NP. Overall, this study demonstrates the dominant role of unstable NP in the cotransport of NP-SP-MP in the marine sedimentary environment.

Transport of ZIF-8 in porous media under the influence of surfactant type and nanoparticle concentration

Knowledge of the fate and transport of metal-organic frameworks (MOFs) in porous media is essential to understanding their environmental impacts. However, to date, the transport mechanisms of MOFs are not fully revealed. Meanwhile, surfactants can promote MOFs dispersion by forming a stable suspension. They also allow MOFs to migrate in the aqueous environment, which would increase the risks of MOFs being exposed to human health and the ecological environment. In this study, the effect of surfactants type and nanoparticle (NP) concentrations (50, 100, and 200 mg/L) were investigated using a sand column to study the transportability of ZIF-8 NPs in saturated porous media. Surfactants used were categorized into three groups, including cationic surfactants (CTAB, DTAB), anionic surfactants (SDBS, SDS), and nonionic surfactants (Tween 80, Tween 20). Experimental results showed that the ionic surfactants significantly increased the transportability of ZIF-8 NPs. Furthermore, a low concentration of NPs tended to break through the column under ionic surfactant conditions, and the maximum effluent recovery of ZIF-8 NPs (50 mg/L) was 87.4% in the presence of SDS. Nevertheless, ZIF-8 NPs tended to deposit in the inlet of the sand column in the presence of nonionic surfactants due to hydrodynamic bridging and straining. This research provides a comprehensive understanding of the deposition mechanism of ZIF-8 NPs as affected by surfactant types and NP concentrations. Most importantly, the study highlights those ionic surfactants had a significant impact on the mobility of ZIF-8 NPs, which arouses attention to the ecological and human health risk assessment related to the manufacturing of MOFs with the aid of various dispersing agents.

Synthesis and characterisation of quantum dots coupled to mycolic acids as a water-soluble fluorescent probe for potential lateral flow detection of antibodies and diagnosis of tuberculosis

This work explores the potential use of cadmium-based quantum dots (QDs) coupled to mycolic acids (MAs) as a fluorescent probe to detect anti-MA antibodies which are biomarkers for tuberculosis (TB). The use of free MAs as antigens for the serodiagnosis of TB is known but has not been developed into a point of care test. This study focuses on the synthesis, solubility, and lateral flow of QDs coupled to MAs. Water-soluble CdSe/ZnS QDs capped with l-cysteine were synthesised and covalently coupled to MAs via amide linkages to form a water-soluble fluorescent probe: MA-CdSe/ZnS QDs. The MA-CdSe/ZnS QDs showed broad absorption bands and coupling, confirmed by the presence of amide bonds in the Fourier-transform infrared (FTIR) spectrum, resulting in a blue shift in fluorescence. Powder X-ray diffraction (XRD) revealed a shift and increase in the number of peaks for MA-CdSe/ZnS QDs relative to the L-cys-CdSe/ZnS QDs, suggesting that coupling changed the crystal structure. The average particle size of MA-CdSe/ZnS QDs was ~3.0 nm. Visual paper-based lateral flow of MA-CdSe/ZnS QDs was achieved on strips of nitrocellulose membrane with both water and membrane blocking solution eluents. The highly fluorescent MA-CdSe/ZnS QDs showed good water solubility and lateral flow, which are important properties for fluorescence sensing applications.

Investigation of SiO2 Nanoparticle Retention in Flow Channels, Its Remediation Using Surfactants and Relevance of Artificial Intelligence in the Future

In this study, the effect of these variables on commercial silica NP retention was presented in a fabricated flow model considering only the physical adsorption aspects of silica NP retention. From our observations, it was established that while silica NP concentration, flow rate and salt are key variables in influencing silica NP agglomeration and retention, the effect of temperature was highly subdued. The effect of salt-induced agglomeration was particularly severe at moderate salinity (≈4 wt% NaCl). To mitigate the effect of salt-induced agglomeration, a commonly used anionic surfactant, sodium dodecyl sulfate (SDS) was added to the solution and the silica NP retention was tabulated. An amount of 0.3 wt% SDS was found to negate salt-induced agglomeration significantly, paving the way for use of silica NP solutions, even in the presence of saline conditions. A section on the prospective use of artificial intelligence for this purpose has been included. This study is useful for understanding NP retention behaviour, especially in the presence of salinity and its mitigation using surfactants, in flow applications.

Benchtop X-ray fluorescence imaging as a tool to study gold nanoparticle penetration in 3D cancer spheroids

The use of nanomaterials to improve medical diagnostics and therapeutics has been rapidly increasing. Among these materials are gold nanoparticles, which can be functionalized to target specific cells, acting as nanovectors for drug delivery, enhanced contrast agents as well as other targeted therapies. Au nanoparticles are very useful as they selectively accumulate in tumour sites due to the enhanced permeability-retention effect. There is however little information about the spatial distribution of the nanoparticles within tumours, which might hinder efficient therapies. In this study, X-ray fluorescence was used to investigate the diffusion of gold nanoparticles in cancer cell spheroids mimicking true tumour growth. Functionalization of the nanoparticles has the effect of allowing better diffusion into and out of the spheroid, while those nanoparticles that are only partially covered rapidly formed aggregates. This clustering led to size exclusion during transport within the tumour, changing its distribution profile while greatly increasing the nanoparticle concentration.

Co-transport of biogenic nano-hydroxyapatite and Pb(II) in saturated sand columns: Controlling factors and stochastic modeling

Biogenic nano-hydroxyapatite (bio-nHAP) has recently gained great interest in many domains, especially in the remediation of heavy metal-contaminated soil, due to its high reactivity, low cost, and eco-friendly nature. The co-transport and reaction of bio-nHAP with Pb(II) in saturated porous media, however, are not well understood. This work investigated the effects of ionic strength (IS), ionic composition (IC), dissolved organic matter (DOM), and flow velocity on transport-reaction dynamics of Pb(II) and bio-nHAP by combining column breakthrough experiments and model simulations. Results showed that the mobility of Pb(II) was significantly enhanced with increasing IS/IC but less affected by flow velocity during the transport-reaction process of bio-nHAP and Pb(II) in the saturated sand column; while the transport of bio-nHAP was restricted by increasing IS/IC but facilitated by increasing velocity. IC, IS, and velocity only slightly affected the reaction kinetics between Pb(II) and bio-nHAP, likely due to the fast reaction rate between Pb(II) and bio-nHAP and precipitation of pyromorphite. The transport dynamics of bio-nHAP and Pb(II) were significantly changed by DOM, and this effect depended strongly on the type of DOM with different molecular weights. Breakthrough curves of Pb(II) and bio-nHAP exhibited apparent "anomalous", sub-diffusive transport behaviors, which could be well quantified by a novel tempered fractional derivative bimolecular reaction equation (T-FBRE). Our findings highlighted the accurate simulation of the co-transport and reaction of bio-nHAP with Pb(II) using T-FBRE and had a great benefit for risk assessment and remediation strategy development for Pb(II) contaminated soil.

Adsorptive Removal of Cd, Cu, Ni and Mn from Environmental Samples Using Fe3O4-Zro2@APS Nanocomposite: Kinetic and Equilibrium Isotherm Studies

In this study, Fe₃O₄-ZrO₂ functionalized with 3-aminopropyltriethoxysilane (Fe₃O₄-ZrO₂@APS) nanocomposite was investigated as a nanoadsorbent for the removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions from aqueous solution and real samples in batch mode systems. The prepared magnetic nanomaterials were characterized using X-ray powder diffraction (XRD), scanning electron microscopy/energy dispersion x-ray (SEM/EDX) Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Factors (such as adsorbent dose and sample pH) affecting the adsorption behavior of the removal process were studied using the response surface methodology. Under optimized condition, equilibrium data obtained were fitted into the Langmuir and Freundlich isotherms and the data fitted well with Langmuir isotherms. Langmuir adsorption capacities (mg/g) were found to be 113, 111, 128, and 123 mg/g for Cd, Cu, Ni and Mn, respectively. In addition, the adsorption kinetics was analyzed using five kinetic models, pseudo-first order, pseudo-second order, intraparticle diffusion and Boyd models. The adsorbent was successfully applied for removal of Cd(II), Cu(II), Mn (II) and Ni(II) ions in wastewater samples.

Uptake of polymeric nanoparticles in a human induced pluripotent stem cell-based blood-brain barrier model: Impact of size, material, and protein corona

The blood-brain barrier (BBB) maintains the homeostasis of the central nervous system, which is one of the reasons for the treatments of brain disorders being challenging in nature. Nanoparticles (NPs) have been seen as potential drug delivery systems to the brain overcoming the tight barrier of endothelial cells. Using a BBB model system based on human induced pluripotent stem cells (iPSCs), the impact of polymeric nanoparticles has been studied in relation to nanoparticle size, material, and protein corona. PLGA [poly(lactic-co-glycolic acid)] and PLLA [poly(d,l-lactide)] nanoparticles stabilized with Tween® 80 were synthesized (50 and 100 nm). iPSCs were differentiated into human brain microvascular endothelial cells (hBMECs), which express prominent BBB features, and a tight barrier was established with a high transendothelial electrical resistance of up to 4000 Ω cm². The selective adsorption of proteins on the PLGA and PLLA nanoparticles resulted in a high percentage of apolipoproteins and complement components. In contrast to the prominently used BBB models based on animal or human cell lines, the present study demonstrates that the iPSC-based model is suited to study interactions with nanoparticles in correlation with their material, size, and protein corona composition. Furthermore, asymmetrical flow field-flow fractionation enables the investigation of size and agglomeration state of NPs in biological relevant media. Even though a similar composition of the protein corona has been detected on NP surfaces by mass spectrometry, and even though similar amounts of NP are interacting with hBMECs, 100 nm-sized PLGA NPs do impact the barrier, forming endothelial cells in an undiscovered manner.

Evaluation of silver nanoparticles (AgNPs) penetration through a clay liner in landfills

Most products containing engineered nanomaterials are disposed at landfills in the final stage of their lifecycle. This study aims to assess landfill liners as a final barrier of disposed silver nanoparticles (AgNPs). Sorption and transport of AgNPs were investigated in the laboratory-scale simulation of landfill liner conditions. Field soil (silt loam) and bentonite were tested in batch sorption experiments respectively. To test transportation, 3 cm thick mixture of the field soil and the bentonite constituted the porous media to meet the criteria for compacted clay liner of landfill. Mathematical modeling in the experimental and actual landfill conditions was also conducted. The results demonstrated considerable extent of sorption by both types of sorbents. The breakthrough of AgNPs was not observed for 200 days (over 20 pore volume). In general, the experimental results indicated that AgNPs cannot easily pass through the landfill clay liner under present standards. Modeling results also showed that AgNPs could be blocked effectively. Although long-term tests are still required, these results clearly show resistance to current sanitary landfill liners against AgNP penetration. As the trial to assess the safety of landfills against AgNP migration, this work provides insights into the fate and transport of nanomaterials in the landfill environment.

Modelling the fate and transport of colloidal particles in association with BPA in river water

A simplified modelling approach for illustrating the fate of emerging pollutants can improve risk assessment of these chemicals. Once released into aquatic environments, these pollutants will interact with various substances including suspended particles, colloidal or nano particles, which will greatly influence their distribution and ultimate fate. Understanding these interactions in aquatic environments continues to be an important issue because of their possible risk. In this study, bisphenol A (BPA) in the water column of Bentong River, Malaysia, was investigated in both its soluble and colloidal phase. A spatially explicit hydrological model was established to illustrate the associated dispersion processes of colloidal-bound BPA. Modelling results demonstrated the significance of spatial detail in predicting hot spots or peak concentrations of colloidal-bound BPA in the sediment and water columns as well. The magnitude and setting of such spots were system based and depended mainly on flow conditions. The results highlighted the effects of colloidal particles' concentration and density on BPA's removal from the water column. It also demonstrated the tendency of colloidal particles to aggregate and the impact all these processes had on BPA's transport potential and fate in a river water. All scenarios showed that after 7.5-10 km mark BPA's concentration started to reach a steady state with very low concentrations which indicated that a downstream transport of colloidal-bound BPA was less likely due to minute BPA levels.

Nanomaterials and Annelid Immunity: A Comparative Survey to Reveal the Common Stress and Defense Responses of Two Sentinel Species to Nanomaterials in the Environment

Simple Summary

Nanotechnology is a dynamically developing field producing large amounts of nanocompounds that are applied in industry, daily life, and health care. During production, use, and waste these materials could end up in water or soil. Large scale contaminations of our environment are a threat to public health. Pollution can have harmful effects on the immune system, as revealed by numerous studies in humans and other vertebrates. The relative simplicity of invertebrate immune functions offers potentially sensitive and accessible means of monitoring the effects and complex interactions of nanoparticles which ultimately affect host resistance. Among terrestrial and freshwater invertebrates, earthworms and leeches are the “keystone” species to evaluate the health of our ecosystems. In this review we compare the conserved stress and immune responses of these invertebrate model organisms toward nanoparticles. The obtained knowledge provides exciting insights into the conserved molecular and cellular mechanisms of nanomaterial-related toxicity in invertebrates and vertebrates. Understanding the unique characteristics of engineered nanoproducts and their interactions with biological systems in our environment is essential to the safe realization of these materials in novel biomedical applications.

Abstract

Earthworms and leeches are sentinel animals that represent the annelid phylum within terrestrial and freshwater ecosystems, respectively. One early stress signal in these organisms is related to innate immunity, but how nanomaterials affect it is poorly characterized. In this survey, we compare the latest literature on earthworm and leeches with examples of their molecular/cellular responses to inorganic (silver nanoparticles) and organic (carbon nanotubes) nanomaterials. A special focus is placed on the role of annelid immunocytes in the evolutionarily conserved antioxidant and immune mechanisms and protein corona formation and probable endocytosis pathways involved in nanomaterial uptake. Our summary helps to realize why these environmental sentinels are beneficial to study the potential detrimental effects of nanomaterials.

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.

Impacts of stratigraphic heterogeneity and release pathway on the transport of bacterial cells in porous media

In order to manage and control the pathogen release from waste streams of various municipal, industrial, and agricultural pollution sources, it is crucial to investigate the impact of release pathways of such contaminants on their fate and transport in groundwater, especially in respect to natural heterogeneities encountered in aquifers. In this laboratory scale study, we investigate the impacts of different release scenarios of Escherichia coli bacteria, including spatially distributed surface recharge and single-point deep injection, as well as mono-pulse and continuous injection on the transport of Escherichia coli within both single-layered and multilayer aquifers. The results demonstrate earlier arrival of bacteria breakthrough curve (BTC) than conservative solute within a single-layer system with textural and continuum scale heterogeneities, attributed to size exclusion mechanism and preferential flow paths. Size exclusion may be responsible for multiple peaked BTCs observed in all cases of mono-pulse injection of bacteria through both single layer and multi-layer systems. The higher breakthrough of bacteria suspension introduced through a distributed source compared to the point source injection at the same flow rate (19% and 53% in middle and top layers, respectively) suggests that natural hydrologic events such as storm may be more influential in the transport of pathogens in soils than point injections of bacteria in engineering applications such as bioremediation. Moreover, our results reveal that the concentration of the semi-steady state breakthrough formed under distributed and continuous injection condition increases significantly with an increase in the recharge flow rate. This would suggest that a variation in hydrologic conditions can significantly mobilize pathogens which are already deposited in soils.

Quantitative Linking of Nanoscale Interactions to Continuum-Scale Nanoparticle and Microplastic Transport in Environmental Granular Media

Quantitative linkage of fundamental physicochemical characteristics to rate coefficients used in simulations of experimentally observed transport behaviors of nanoparticles and microplastics (colloids) in environmental granular media is an active area of research. Quantitative linkage is herein demonstrated for (i) colloids ranging from nano- to microscale; in two field-based granular media of contrasting grain size, (ii) natural fine sand at the column scale; and (ii) streambed-equilibrated commercial pea gravel at the field scale. Continuum-scale rate coefficients were linked to nanoscale interactions via mechanistic pore-scale colloid trajectory simulations that predicted and defined fast- and slow-attaching subpopulations, as well as nonattaching subpopulations that either remained in the near-surface pore water or re-entrained to bulk pore water. These subfractions of the classic collector efficiency were upscaled to continuum-scale rate coefficients that produced experimentally observed colloid breakthrough-elution concentration histories and nonexponential colloid distributions from the source. The simulations explained transition from hyperexponential to nonmonotonic colloid distributions from the source as driven accumulation of mobile near-surface colloids due to relatively strong secondary minimum interaction and weak diffusion for microscale colloids. The assumption of depletion of the fast-attaching colloid subpopulation by attachment to grain surfaces produced the experimentally observed contrasting distances across which nonexponential colloid distribution from the source occurred in the fine sand versus pea gravel. Rate coefficients were quantitatively calculated from physicochemical parameters and the following three fit parameters: (i) fractional coverage by nanoscale heterogeneity; (ii) efficiency of return to the near-surface domain; and (iii) in explicit simulations, characteristic velocity for scaling transfer to near-surface pore water.

Atlantic and Mediterranean populations of the widespread serpulid Ficopomatus enigmaticus: Developmental responses to carbon nanotubes

Ficopomatus enigmaticus was adopted as model species for ecotoxicological bioassay, with its larval development as endpoint. Two different populations of the same species, collected in areas far from each other (Mediterranean Sea and Atlantic Ocean), were exposed to multi-walled carbon nanotubes, a class of emerging pollutants with a constantly increasing relevance in the landscape of nanomaterials production. Moreover, a molecular analysis based on Cyt b amplification and sequencing, was carried out to confirm that both populations belong to the same species. The aim of the present work was to strengthen existing results about F. enigmaticus relevance in ecotoxicological bioassays, adding the variable of population effect. For both populations the concentration-response curve of effect at different toxicant concentrations was similar and, at certain concentrations, overlapping, confirming the ecological relevance of the assay. These results posed an interesting acceptance on the introduction of this species as model in ecotoxicological bioassay scenery, underlining the relevance of a widespread wild species to compare effects of chemicals and environmental samples over large distances using the same bioassay.