Design and quantitative evaluation of 'Aerosol Bio-Containment Device (ABCD)' for reducing aerosol exposure during infectious aerosol-generating events.

The Coronavirus Disease 2019 (COVID-19) pandemic renewed interest in infectious aerosols and reducing risk of airborne respiratory pathogen transmission, prompting development of devices to protect healthcare workers during airway procedures. However, there are no standard methods for assessing the efficacy of particle containment with these protective devices. We designed and built an aerosol bio-containment device (ABCD) to contain and remove aerosol via an external suction system and tested the aerosol containment of the device in an environmental chamber using a novel, quantitative assessment method. The ABCD exhibited a strong ability to control aerosol exposure in experimental and computational fluid dynamic (CFD) simulated scenarios with appropriate suction use and maintenance of device seals. Using a log-risk-reduction framework, we assessed device containment efficacy and showed that, when combined with other protective equipment, the ABCD can significantly reduce airborne clinical exposure. We propose this type of quantitative analysis serves as a basis for rating efficacy of aerosol protective enclosures.

Fluid dynamic simulations at the interface of the blue-green sharpshooter functional foregut and grapevine xylem sap with implications for transmission of Xylella fastidiosa.

Xylella fastidiosa is a multi-continental, lethal, plant pathogenic bacterium that is transmitted by sharpshooter leafhoppers (Insecta: Hemiptera: Cicadellidae: Cicadellinae) and adult spittlebugs (Hemiptera: Aphrophoridae). The bacterium forms biofilms in plant xylem and the functional foregut of the insect. These biofilms serve as sources of inoculum for insect acquisition and subsequent inoculation to a healthy plant. In this study, 3D fluid dynamic simulations were performed for bidirectional cibarial propulsion of xylem sap through tube-like grapevine xylem and an anatomically accurate model of the functional foregut of the blue-green sharpshooter, Graphocephala atropunctata. The analysis supports a model of how fluid dynamics influence X. fastidiosa transmission. The model supports the hypothesis that X. fastidiosa inoculation is mostly driven by detachment of bacteria from the foregut due to high-velocity flow during egestion (outward fluid flow from the stylets). Acquisition occurs by fluid dynamics during both egestion and ingestion (fluid uptake through the stylets and swallowing). These simulation results are supported by previously reported X. fastidiosa colonization patterns in the functional foregut and sharpshooter stylet probing behaviors. The model indicates that xylem vessel diameter influences drag forces imposed on xylem wall-adherent bacteria; thus, vessel diameter may be an important component of the complex transmission process. Results from this study are directly applicable to development of novel grapevine resistance traits via electropenetrographic monitoring of vector acquisition and inoculation behaviors.

Disrupting Irreversible Bacterial Adhesion and Biofilm Formation with an Engineered Enzyme.

Biofilm formation is often attributed to postharvest bacterial persistence on fresh produce and food handling surfaces. In this study, a predicted glycosyl hydrolase enzyme was expressed, purified, and validated for the removal of microbial biofilms from biotic and abiotic surfaces under conditions used for chemical cleaning agents. Crystal violet biofilm staining assays revealed that 0.1 mg/ml of enzyme inhibited up to 41% of biofilm formation by Escherichia coli O157:H7, E. coli 25922, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes. Furthermore, the enzyme was effective at removing mature biofilms, providing a 35% improvement over rinsing with a saline solution alone. Additionally, a parallel-plate flow cell was used to directly observe and quantify the impact of enzyme rinses on E. coli O157:H7 cells adhering to spinach leaf surfaces. The presence of 1 mg/liter enzyme resulted in nearly 6-times-higher detachment rate coefficients than a deionized (DI) water rinse, while the total cells removed from the surface increased from 10% to 25% over the 30-min rinse time, reversing the initial phases of biofilm formation. Enzyme treatment of all 4 cell types resulted in significantly reduced cell surface hydrophobicity and collapse of negatively stained E. coli 25922 cells imaged by electron microscopy, suggesting potential polysaccharide surface modification of enzyme-treated bacteria. Collectively, these results point to the broad substrate specificity and robustness of the enzyme for different types of biofilm stages, solution conditions, and pathogen biofilm types and may be useful as a method for the removal or inhibition of bacterial biofilm formation. IMPORTANCE In this study, the ability of an engineered enzyme to reduce bacterial adhesion and biofilm formation of several foodborne pathogens was demonstrated, representing a promising option for enhancing or replacing chlorine and other chemical sanitizers in food processing applications. Specifically, significant reductions of biofilms of the pathogens Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes are observed, as are reductions in initial adhesion. Enzymes have the added benefits of being green, sustainable alternatives to chemical sanitizers, as well as having a minimal impact on food properties, in contrast to many alternative antimicrobial options such as bleach that aim to minimize food safety risks.

Functional foregut anatomy of the blue-green sharpshooter illustrated using a 3D model.

Sharpshooter leafhoppers (Hemiptera: Cicadellidae: Cicadellinae) are important vectors of the plant pathogenic bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae). This pathogen causes economically significant diseases in olive, citrus, and grapes on multiple continents. Bacterial acquisition and inoculation mechanisms are linked to X. fastidiosa biofilm formation and fluid dynamics in the functional foregut of sharpshooters, which together result in egestion (expulsion) of fluids likely carrying bacteria. One key X. fastidiosa vector is the blue-green sharpshooter, Graphocephala atropunctata (Signoret, 1854). Herein, a 3D model of the blue-green sharpshooter functional foregut is derived from a meta-analysis of published microscopy images. The model is used to illustrate preexisting and newly defined anatomical terminology that is relevant for investigating fluid dynamics in the functional foregut of sharpshooters. The vivid 3D illustrations herein and supplementary interactive 3D figures are suitable resources for multidisciplinary researchers who may be unfamiliar with insect anatomy. The 3D model can also be used in future fluid dynamic simulations to better understand acquisition, retention, and inoculation of X. fastidiosa. Improved understanding of these processes could lead to new targets for preventing diseases caused by X. fastidiosa.

Aggregation morphology of planar engineered nanomaterials.

In this investigation, the utility of a static light scattering (SLS) technique to characterize aggregate morphology of two-dimensional engineered nanomaterials (2D ENMs) was systematically evaluated. The aggregation of graphene oxide (GO) and lithiated-molybdenum disulfide (Li-MoS2) were measured and compared to that of a spherical reference colloid, carboxylate-modified latex (CML) nanoparticles. The critical coagulation concentration (CCC) for all dispersions was determined via analysis of aggregation kinetics using time-resolved dynamic light scattering. This technique allowed for the elucidation of the transition from the reaction-limited aggregation (RLA) regime to diffusion-limited aggregation (DLA). The findings of this study support the aggregation trends predicted by Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and recent computer simulations of aggregation kinetics. For all nanomaterials, as ionic strength increased towards the respective the CCC, fractal dimension decreased; any increase in ionic strength beyond the CCC did not yield significant change in fractal dimension. Across comparable primary particle sizes and using both carbonaceous (GO) and inorganic (Li-MoS2) 2D ENMs, this study further supports the use of SLS for the measurement of fractal dimension for 2D materials. To further support this claim, the aggregate morphology of GO in both RLA and DLA regimes was measured via cryogenic transmission electron microscopy.

Escherichia coli O157:H7 and Salmonella Typhimurium adhesion to spinach leaf surfaces: Sensitivity to water chemistry and nutrient availability.

This study investigated the effects of solution chemistry and growth conditions on bacterial deposition on spinach leaf surfaces using a parallel plate flow cell. Two food safety pathogens of concern and two non-pathogen bacterial surrogates (environmental E. coli isolates) were grown in ideal (LB media) and nutrient-restricted (M9 media) conditions. Bacterial attachment was quantified as mass transfer rate coefficients for cells suspended in 10 mM KCl, CaCl2 and artificial groundwater, and cell and leaf surfaces were extensively characterized (zeta potential, hydrophobicity, extracellular polymer (EPS) composition). Between the pathogens, E. coli O157:H7 attachment was greater than that of Salmonella Typhimurium, attributed to measurable variability in cell surface charge and hydrophobicity. When grown in M9 media, both pathogens were significantly more adhesive to spinach surfaces (p < 0.01) than when grown in LB media. Surrogates did not follow this trend and showed minimal changes in adhesion kinetics and surface properties between growth conditions. EPS sugar/protein ratios were reduced in some of the highest attachment scenarios, suggesting that changes in EPS composition in favor of proteins may play a role. These results show the importance of growth conditions and solution complexities in understanding mechanisms of aqueous bacterial adhesion to food surfaces.

Impact of soil clay minerals on growth, biofilm formation, and virulence gene expression of Escherichia coli O157:H7.

Soil, composed mainly of minerals, plays a central role in the circulation of microbial pathogens in the environment. Herein, the growth, biofilm formation, and virulence gene expression of the pathogenic bacteria Escherichia coli O157:H7 were monitored following exposure to montmorillonite, kaolinite, and goethite, three common soil minerals in the clay size fraction. E. coli O157:H7 growth was notably promoted (P < 0.05), while biofilm formation was inhibited in the presence of montmorillonite (P < 0.05), which is attributed to the suppression of colanic acid (CA) production and an increase in bacterial motility. Kaolinite not only promoted bacterial growth (P < 0.05), but also contributed to biofilm formation upon stimulating CA production. Upon exposure to goethite, notably slower bacterial growth and higher biomass of biofilm were observed as compared to the control (P < 0.05). Goethite stimulated the synthesis of CA to encase cells in a protective biofilm in response to the tight association between bacteria and goethite, which could cause bacterial death. Additionally, the transcription of virulence factors (stxA-1 and stxA-2) was significantly decreased in goethite or kaolinite system (P < 0.05). These findings indicate that minerals play important roles in the physiological state of bacteria and ultimately govern the fate of this pathogen in soils.

Coupling hydrothermal liquefaction and membrane distillation to treat anaerobic digestate from food and dairy farm waste.

Increased demand for water, energy and food requires new ways to produce fertilizers, fuels and reusable water. Recovery of resources from wastes could lead to an additional source of energy and nutrients, and also reduce the waste to be disposed. In this work, we used hydrothermal liquefaction to produce a biocrude oil product, followed by membrane distillation of the aqueous effluents to concentrate a nutrient-rich stream that can be used as fertilizer. The motivation for this work is that residual heat from the hydrothermal liquefaction process could be utilized to drive the membrane distillation process, which would improve the efficiency and reduce the cost of the distillation process. The membrane distillation system was demonstrated to be able to recover 75% of the water. The membrane distillation retentate had very high ammonium and phosphate concentrations, making it suitable as a fertilizer. Membrane permeate contained high concentrations of volatile organics.

Influence of septic system wastewater treatment on titanium dioxide nanoparticle subsurface transport mechanisms.

Engineered nanomaterials (ENMs) are commonly incorporated into food and consumer applications to enhance a specific product aspect (i.e., optical properties). Life cycle analyses revealed ENMs can be released from products during usage and reach wastewater treatment plants (WWTPs), with titanium dioxide (TiO2) accounting for a large fraction. As such, food grade (FG) TiO2, a more common form of TiO2 in wastewater, was used in this study. Nanomaterials in WWTPs have been well characterized, although the problematic septic system has been neglected. Elution and bioaccumulation of TiO2 ENMs from WTTPs in downriver sediments and microorganisms has been observed; however, little is known about mechanisms governing the elution of FG TiO2 from the septic drainage system. This study characterized the transport behavior and mechanisms of FG TiO2 particles in porous media conditions after septic waste treatment. FG and industrial grade (IG) TiO2 (more commonly studied) were introduced to septic tank effluent and low-ionic strength electrolyte solutions prior to column transport experiments. Results indicate that FG TiO2 aggregate size (200-400 nm) remained consistent across solutions. Additionally, elution of FG and IG TiO2 was greatest in septic effluent at the higher nanoparticle concentration (100 ppm). FG TiO2 was well retained at the low (2 ppm) concentration in septic effluent, suggesting that particles that escape the septic system may still be retained in drainage field before reaching the groundwater system, although eluted particles are highly stabilized. Findings provide valuable insight into the significance of the solution environment at mediating differences observed between uniquely engineered nanomaterials. Graphical abstract.

Comparison of filtration mechanisms of food and industrial grade TiO2 nanoparticles.

The removal of food and industrial grade titanium dioxide (TiO2) particles through drinking water filtration was assessed via direct visualization of an in situ 2-D micromodel. The goal of this research was to determine whether variances in surface composition, aggregate size, and ionic strength result in different transport and deposition processes in porous media. Food and industrial grade TiO2 particles were characterized by measuring their hydrodynamic diameter, zeta potential, and zero point of charge before introduction into the 2-D micromodel. The removal efficiency as a function of position on the collector surface was calculated from direct visualization measurements. Notably, food grade TiO2 had a lower removal efficiency when compared with industrial grade. The difference in removal efficiency between the two particle types could be attributed to the higher stability (as indicated by the larger zeta potential values) of the food grade particles, which lead to a reduced aggregate size when compared to the industrial grade particles. This removal efficiency trend was most pronounced in the rear stagnation point, due to the high contribution of hydrodynamic forces at that point. It could be inferred from the results presented herein that particle removal strategies should be based on particle aggregate size and surface charge. Graphical abstract ᅟ.

Using the agricultural environment to select better surrogates for foodborne pathogens associated with fresh produce.

Despite continuing efforts to reduce foodborne pathogen contamination of fresh produce, significant outbreaks continue to occur. Identification of appropriate surrogates for foodborne pathogens facilitates relevant research to identify reservoirs and amplifiers of these contaminants in production and processing environments. Therefore, the objective of this study was to identify environmental Escherichia coli isolates from manures (poultry, swine and dairy) and surface water sources with properties similar to those of the produce associated foodborne pathogens E. coli O157:H7 and Salmonella enterica serotype Typhimurium. The most similar environmental E. coli isolates were from poultry (n=3) and surface water (n=1) sources. The best environmental E. coli surrogates had cell surface characteristics (zeta potential, hydrophobicity and exopolysaccharide composition) that were similar (i.e., within 15%) to those of S. Typhimurium and/or formed biofilms more often when grown in low nutrient media prepared from lettuce lysates (24%) than when grown on high nutrient broth (7%). The rate of attachment of environmental isolates to lettuce leaves was also similar to that of S. Typhimurium. In contrast, E. coli O157:H7, a commonly used E. coli quality control strain and swine isolates behaved similarly; all were in the lowest 10% of isolates for biofilm formation and leaf attachment. These data suggest that the environment may provide a valuable resource for selection of surrogates for foodborne pathogens.

Bacillus subtilis biofilm development in the presence of soil clay minerals and iron oxides.

Clay minerals and metal oxides, as important parts of the soil matrix, play crucial roles in the development of microbial communities. However, the mechanism underlying such a process, particularly on the formation of soil biofilm, remains poorly understood. Here, we investigated the effects of montmorillonite, kaolinite, and goethite on the biofilm formation of the representative soil bacteria Bacillus subtilis. The bacterial biofilm formation in goethite was found to be impaired in the initial 24 h but burst at 48 h in the liquid-air interface. Confocal laser scanning microscopy showed that the biofilm biomass in goethite was 3-16 times that of the control, montmorillonite, and kaolinite at 48 h. Live/Dead staining showed that cells had the highest death rate of 60% after 4 h of contact with goethite, followed by kaolinite and montmorillonite. Atomic force microscopy showed that the interaction between goethite and bacteria may injure bacterial cells by puncturing cell wall, leading to the swarming of bacteria toward the liquid-air interface. Additionally, the expressions of abrB and sinR, key players in regulating the biofilm formation, were upregulated at 24 h and downregulated at 48 h in goethite, indicating the initial adaptation of the cells to minerals. A model was proposed to describe the effects of goethite on the biofilm formation. Our findings may facilitate a better understanding of the roles of soil clays in biofilm development and the manipulation of bacterial compositions through controlling the biofilm in soils.

Role of pH and ionic strength in the aggregation of TiO2 nanoparticles in the presence of extracellular polymeric substances from Bacillus subtilis.

Increased use of commercial titanium dioxide nanoparticles (TiO2 NPs) in consumer products most likely leads to their additional environmental release. Aggregation and disaggregation processes are expected to play an important role in the fate and transport of TiO2 NPs in natural aquatic ecosystems. Therefore, in this work, we have studied the colloidal stability of TiO2 NPs in the presence of extracellular polymeric substances (EPS) from Bacillus subtilis and the adsorption behavior of EPS on TiO2 NPs in aqueous solutions at different pH values and ionic strengths (IS). The adsorption and aggregation processes were found to depend on the solution chemistry. The mass fraction of EPS on TiO2 NPs decreased with increased pH and NaCl concentrations, which was verified by Fourier transform infrared spectroscopy. The presence of EPS can substantially influence the colloidal stability of TiO2 NPs. In deionized water, the aggregation of NPs was induced by the addition of EPS only when the pH was below the TiO2 NP point of zero charge (≈6). When the pH was equal to pHPZC, TiO2, the TiO2 NPs would rapidly form large aggregates, but the adsorption of EPS leads to partial fragmentation via electrostatic repulsion and steric hindrance. When the pH was greater than pHPZC, TiO2, the aggregation rate was minimally affected by the increased EPS concentration. In NaCl solution, the aggregation rate of TiO2 NPs obviously increased with increased NaCl concentration. The critical coagulation concentration (CCC) of TiO2 NPs is 13.9 mM in the absence of EPS and increases to 155.6, 213.7 and 316.4 mM in the presence of 1, 5 and 10 mg/L EPS in NaCl solution, respectively, which indicates that the steric hindrance occurs after the addition of EPS. This study suggests that environmental conditions and EPS concentration greatly modify the colloidal stability of TiO2 nanoparticles.

Efficacy of post-harvest rinsing and bleach disinfection of E. coli O157:H7 on spinach leaf surfaces.

Attachment and detachment kinetics of Escherichia coli O157:H7 from baby spinach leaf epicuticle layers were investigated using a parallel plate flow chamber. Mass transfer rate coefficients were used to determine the impact of water chemistry and common bleach disinfection rinses on the removal and inactivation of the pathogen. Attachment mass transfer rate coefficients generally increased with ionic strength. Detachment mass transfer rate coefficients were nearly the same in KCl and AGW rinses; however, the detachment phase lasted longer in KCl than AGW (18 ± 4 min and 4 ± 2 min, respectively), indicating that the ions present during attachment play a significant role in the cells' ability to remain attached. Specifically, increasing bleach rinse concentration by two orders of magnitude was found to increase the detachment mass transfer rate coefficient by 20 times (from 5.7 ± 0.7 × 10-11 m/s to 112.1 ± 26.8 × 10-11 m/s for 10 ppb and 1000 ppb, respectively), and up to 88 ± 4% of attached cells remained alive. The spinach leaf texture was incorporated within a COMSOL model of disinfectant concentration gradients, which revealed nearly 15% of the leaf surface is exposed to almost 1000 times lower concentration than the bulk rinse solution.

Influence of extracellular polymeric substances on the aggregation kinetics of TiO2 nanoparticles.

The early stage of aggregation of titanium oxide (TiO2) nanoparticles was investigated in the presence of extracellular polymeric substance (EPS) constituents and common monovalent and divalent electrolytes through time-resolved dynamic light scattering (DLS). The hydrodynamic diameter was measured and the subsequent aggregation kinetics and attachment efficiencies were calculated across a range of 1-500 mM NaCl and 0.05-40 mM CaCl2 solutions. TiO2 particles were significantly aggregated in the tested range of monovalent and divalent electrolyte concentrations. The aggregation behavior of TiO2 particles in electrolyte solutions was in excellent agreement with the predictions based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Divalent electrolytes were more efficient in destabilizing TiO2 particles, as indicated by the considerably lower critical coagulation concentrations (CCC) (1.3 mM CaCl2 vs 11 mM NaCl). The addition of EPS to the NaCl and low concentration CaCl2 (0.05-10 mM) solutions resulted in a dramatic decrease in the aggregation rate and an increase in the CCC values. For solutions of 11 mM NaCl (the CCC values of TiO2 in the absence of EPS) and above, the resulting attachment efficiency was less than one, suggesting that the adsorbed EPS on the TiO2 nanoparticles led to steric repulsion, which effectively stabilized the nanoparticle suspension. At high CaCl2 concentrations (10-40 mM), however, the presence of EPS increased the aggregation rate. This is attributed to the aggregation of the dissolved extracellular polymeric macromolecules via intermolecular bridging, which in turn linked the TiO2 nanoparticles and aggregates together, resulting in enhanced aggregate growth. These results have important implications for assessing the fate and transport of TiO2 nanomaterials released in aquatic environments.

Efficient Photocatalytic Disinfection of Escherichia coli O157:H7 using C70-TiO2 Hybrid under Visible Light Irradiation.

Efficient photocatalytic disinfection of Escherichia coli O157:H7 was achieved by using a C70 modified TiO2 (C70-TiO2) hybrid as a photocatalyst under visible light (λ > 420 nm) irradiation. Disinfection experiments showed that 73% of E. coli O157:H7 died within 2 h with a disinfection rate constant of k = 0.01 min(-1), which is three times that measured for TiO2. The mechanism of cell death was investigated by using several scavengers combined with a partition system. The results revealed that diffusing hydroxyl radicals play an important role in the photocatalytically initiated bacterial death, and direct contact between C70-TiO2 hybrid and bacteria is not indispensable in the photocatalytic disinfection process. Extracellular polymeric substances (EPS) of bacteria have little effect on the disinfection efficiency. Analyses of the inhibitory effect of C70-TiO2 thin films on E. coli O157:H7 showed a decrease of the bacterial concentration from 3 × 10(8) to 38 cfu mL(-1) in the solution with C70-TiO2 thin film in the first 2 h of irradiation and a complete inhibition of the growth of E. coli O157:H7 in the later 24 h irradiation.

Effects of copper particles on a model septic system's function and microbial community.

There is concern surrounding the addition of nanoparticles into consumer products due to toxicity potential and the increased risk of human and environmental exposures to these particles. Copper nanoparticles are found in many common consumer goods; therefore, the disposal and subsequent interactions between potentially toxic Cu-based nanoparticles and microbial communities may have detrimental impacts on wastewater treatment processes. This study investigates the effects of three copper particles (micron- and nano-scale Cu particles, and a nano-scale Cu(OH)2-based fungicide) on the function and operation of a model septic tank. Septic system analyses included water quality evaluations and microbial community characterizations to detect changes in and relationships between the septic tank function and microbial community phenotype/genotype. As would be expected for optimal wastewater treatment, biological oxygen demand (BOD5) was reduced by at least 63% during nano-scale Cu exposure, indicating normal function. pH was reduced to below the optimum anaerobic fermentation range during the micro Cu exposure, suggesting incomplete degradation of organic waste may have occurred. The copper fungicide, Cu(OH)2, caused a 57% increase in total organic carbon (TOC), which is well above the typical range for septic systems and also corresponded to increased BOD5 during the majority of the Cu(OH)2 exposure. The changes in TOC and BOD5 demonstrate that the system was improperly treating waste. Overall, results imply individual exposures to the three Cu particles caused distinct disruptions in septic tank function. However, it was observed that the system was able to recover to typical operating conditions after three weeks post-exposure. These results imply that during periods of Cu introduction, there are likely pulses of improper removal of total organic carbon and significant changes in pH not in the optimal range for the system.

Antimicrobial behavior of novel surfaces generated by electrophoretic deposition and breakdown anodization.

Biofilms have devastating impacts on many industries such as increased fuel consumption and damage to surfaces in maritime industries. Ideal biofouling management is inhibition of initial bacterial attachment. The attachment of a model marine bacterium (Halomonas pacfica g) was investigated to evaluate the potential of these new novel surfaces to resist initial bacterial adhesion. Novel engineered surfaces were generated via breakdown anodization or electrophoretic deposition, to modify three parameters: hydrophobicity, surface chemistry, and roughness. Mass transfer rates were determined using a parallel plate flow chamber under relevant solution chemistries. The greatest deposition was observed on the superhydrophilic surface, which had micro- and nano-scale hierarchical structures composed of titanium oxide deposited on a titanium plate. Conversely, one of the hydrophobic surfaces with micro-porous films overlaid with polydimethylsiloxane appeared to be most resistant to cell attachment.

Fate and Transport of Molybdenum Disulfide Nanomaterials in Sand Columns.

Research and development of two-dimensional transition metal dichalcogenides (TMDC) (e.g., molybdenum disulfide [MoS2]) in electronic, optical, and catalytic applications has been growing rapidly. However, there is little known regarding the behavior of these particles once released into aquatic environments. Therefore, an in-depth study regarding the fate and transport of two popular types of MoS2 nanomaterials, lithiated (MoS2-Li) and Pluronic PF-87 dispersed (MoS2-PL), was conducted in saturated porous media (quartz sand) to identify which form would be least mobile in aquatic environments. The electrokinetic properties and hydrodynamic diameters of MoS2 as a function of ionic strength and pH were determined using a zeta potential analyzer and dynamic light scattering techniques. Results suggest that the stability is significantly decreased beginning at 10 and 31.6 mM KCl, for MoS2-PL and MoS2-Li, respectively. Transport study results from breakthrough curves, column dissections, and release experiments suggest that MoS2-PL exhibits a greater affinity to be irreversibly bound to quartz surfaces as compared with the MoS2-Li at a similar ionic strength. Derjaguin-Landau-Verwey-Overbeek theory was used to help explain the unique interactions between the MoS2-PL and MoS2-Li surfaces between particles and with the quartz collectors. Overall, the results suggest that the fate and transport of MoS2 is dependent on the type of MoS2 that enters the environment, where MoS2-PL will be least mobile and more likely be deposited in porous media from pluronic-quartz interactions, whereas MoS2-Li will travel greater distances and have a greater tendency to be remobilized in sand columns.

Understanding the transformation, speciation, and hazard potential of copper particles in a model septic tank system using zebrafish to monitor the effluent.

Although copper-containing nanoparticles are used in commercial products such as fungicides and bactericides, we presently do not understand the environmental impact on other organisms that may be inadvertently exposed. In this study, we used the zebrafish embryo as a screening tool to study the potential impact of two nano Cu-based materials, CuPRO and Kocide, in comparison to nanosized and micron-sized Cu and CuO particles in their pristine form (0-10 ppm) as well as following their transformation in an experimental wastewater treatment system. This was accomplished by construction of a modeled domestic septic tank system from which effluents could be retrieved at different stages following particle introduction (10 ppm). The Cu speciation in the effluent was identified as nondissolvable inorganic Cu(H2PO2)2 and nondiffusible organic Cu by X-ray diffraction, inductively coupled plasma mass spectrometry (ICP-MS), diffusive gradients in thin-films (DGT), and Visual MINTEQ software. While the nanoscale materials, including the commercial particles, were clearly more potent (showing 50% hatching interference above 0.5 ppm) than the micron-scale particulates with no effect on hatching up to 10 ppm, the Cu released from the particles in the septic tank underwent transformation into nonbioavailable species that failed to interfere with the function of the zebrafish embryo hatching enzyme. Moreover, we demonstrate that the addition of humic acid, as an organic carbon component, could lead to a dose-dependent decrease in Cu toxicity in our high content zebrafish embryo screening assay. Thus, the use of zebrafish embryo screening, in combination with the effluents obtained from a modeled exposure environment, enables a bioassay approach to follow the change in the speciation and hazard potential of Cu particles instead of difficult-to-perform direct particle tracking.