Mimicking filtration and transport of rotavirus and adenovirus in sand media using DNA-labeled, protein-coated silica nanoparticles

DNA-labeled chitosan nanoparticles: A potential new surrogate for assessing rotavirus attenuation and transport in sand filtration water treatment

Despite being a model in waterborne risk assessment, rotavirus attenuation and transport in sand filtration water treatment remains poorly understood due to a lack of representative surrogates. We investigated the suitability of DNA-labeled chitosan nanoparticles (DCNPs) to mimic rotavirus attenuation and transport in coastal and alluvial sands. Chitosan nanoparticles were synthesized and coupled with a DNA tracer. Compared to rotavirus, DCNPs had similar size (79 ± 7.2 nm vs. 72.5 nm) and buoyant density (1.65 ± 0.07 g/cm³ vs. 1.36-1.40 g/cm³) but a less negative zeta potential (-20.61 ± 1.94 mV vs. -29.77 ± 0.86 mV) and lower hydrophobicity (0% vs. 44%). Filtration experiments (flow rate 1.26-1.27 ml/min, pH 6.0, electrical conductivity 224-226 μs/cm) showed that DCNPs approximated rotavirus attenuation in coastal and alluvial sands (p ≥ 0.07). Repeated dosing of rotavirus and DCNPs caused removal efficiencies to decline in the sand media. Both entities displayed faster and less dispersive transport than a nonreactive solute tracer (NaCl) in sand media. This preliminary study suggested that DCNPs can approximately mimic rotavirus attenuation and transport in coastal and alluvial sands. However, further validation under diverse experimental conditions is necessary. This includes varying flow rates, pH levels, ionic strengths, and the presence of multivalent cations (e.g., Ca2+ and Mg2+) and organic matter. DCNPs, made from a nontoxic, biocompatible, and biodegradable natural biopolymer, hold promise as a safe tool for assessing rotavirus attenuation and transport in sand filtration water treatment and aquifer filtration processes.

Membrane-Nanoparticle Interactions: The Impact of Membrane Lipids

The growing field of nanotechnology presents opportunity for applications across many sectors. Nanostructures, such as nanoparticles, hold distinct properties based on their size, shape, and chemical modifications that allow them to be utilized in both highly specific as well as broad capacities. As the classification of nanoparticles becomes more well-defined and the list of applications grows, it is imperative that their toxicity be investigated. One such cellular system that is of importance are cellular membranes (biomembranes). Membranes present one of the first points of contact for nanoparticles at the cellular level. This review will address current studies aimed at defining the biomolecular interactions of nanoparticles at the level of the cell membrane, with a specific focus of the interactions of nanoparticles with prominent lipid systems.

Revealing the infiltration process and retention mechanisms of surface applied free DNA tracer through soil under flood irrigation

It has been recently demonstrated that free DNA tracers have the potential in tracing water flow and contaminant transport through the vadose zone. However, whether the free DNA tracer can be used in flood irrigation area to track water flow and solute/contaminant transport is still unclear. To reveal the infiltration process and retention mechanisms of surface applied free DNA tracer through soil under flood irrigation, we tested the fate and transport behavior of surface applied free DNA tracers through packed saturated sandy soil columns with a 10 cm water head mimicking flood irrigation. From the experimental breakthrough curves and by fitting a two-site kinetic sorption model (R2 = 0.83-0.91 and NSE = 0.79-0.89), adsorption/desorption rates could be obtained and tracer retention profiles could be simulated. Together these results revealed that 1) the adsorption of free DNA was dominantly to clay particles in the soil, which took up 1.96 % by volume, but took up >97.5 % by surface area and densely cover the surface of sand particles; and 2) at a pore water pH of 8.0, excluding the 4.9 % passing through and 3.1 % degradation amount, the main retention mechanisms in the experimental soil were ligand exchange (42.0 %), Van der Waals interactions (mainly hydrogen bonds), electrostatic forces and straining (together 44.7 %), and cation bridge (5.3 %). To our knowledge, this study is the first to quantify the contribution of each of the main retention mechanisms of free synthetic DNA tracers passing through soil. Our findings could facilitate the application of free DNA tracer to trace vadose zone water flow and solute/contaminant transport under flood irrigation and other infiltration conditions.

Detection of enteric viruses and SARS-CoV-2 in beach sand

Beach sand harbors a diverse group of microbial organisms that may be of public health concern. Nonetheless, little is known about the presence and distribution of viruses in beach sand. In this study, the first objective was to evaluate the presence of seven viruses (Aichi virus, enterovirus, hepatitis A virus, human adenovirus, norovirus, rotavirus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)) in sands collected at public beaches. The second objective was to assess the spatial distribution of enteric viruses in beach sand. To that end, 27 beach sand samples from different beaches in Portugal were collected between November 2018 and August 2020 and analyzed for the presence of viruses. At seven beaches, samples were collected in the supratidal and intertidal zones. Results show that viruses were detected in 89 % (24/27) of the sand samples. Aichi virus was the most prevalent (74 %). Noroviruses were present in 19 % of the samples (norovirus GI - 15 %, norovirus GII - 4 %). Human adenovirus and enterovirus were detected in 48 % and 22 % of the samples, respectively. Hepatitis A virus and rotavirus were not detected. Similarly, SARS-CoV-2 in beach sand collected during the initial stages of the pandemic was also not detected. The detection of three or more viruses occurred in 15 % of the samples. Concentrations of viruses were as high as 7.2 log copies (cp)/g of sand. Enteric viruses were found in higher prevalence in sand collected from the supratidal zone compared to the intertidal zone. Human adenovirus was detected in 43 % of the supratidal and 14 % in the intertidal samples and Aichi virus in 57 % and 86 % of the intertidal and supratidal areas, respectively. Our findings suggest that beach sand can be a reservoir of enteric viruses, suggesting that it might be a vehicle for disease transmission, particularly for children, the elderly, and immunocompromised users.

A Simple Method for Synthesis of Chitosan Nanoparticles with Ionic Gelation and Homogenization

Chitosan nanoparticles (CNPs) are known to have great utility in many fields (pharmaceutical, agricultural, food industry, wastewater treatment, etc.). In this study we aimed to synthesize sub-100 nm CNPs as a precursor of new biopolymer-based virus surrogates for water applications. We present a simple yet efficient synthesis procedure for obtaining high yield, monodisperse CNPs with size 68-77 nm. The CNPs were synthesized by ionic gelation using low molecular weight chitosan (deacetylation 75-85%) and tripolyphosphate as crosslinker, under rigorous homogenization to decrease size and increase uniformity, and purified by passing through 0.1 μm polyethersulfone syringe filters. The CNPs were characterized using dynamic light scattering, tunable resistive pulse sensing, and scanning electron microscopy. We demonstrate reproducibility of this method at two separate facilities. The effects of pH, ionic strength and three different purification methods on the size and polydispersity of CNP formation were examined. Larger CNPs (95-219) were produced under ionic strength and pH controls, and when purified using ultracentrifugation or size exclusion chromatography. Smaller CNPs (68-77 nm) were formulated using homogenization and filtration, and could readily interact with negatively charge proteins and DNA, making them an ideal precursor for the development of DNA-labelled, protein-coated virus surrogates for environmental water applications.

Internal microstructure of spray dried particles affects viral vector activity in dry vaccines

To maintain the activity of sensitive biologics during encapsulation by spray drying, a better understanding of deactivation pathways in dried particles is necessary. The effect of solid-air interfaces within dried particles on viral deactivation was examined with three binary excipient blends, mannitol/dextran (MD), xylitol/dextran (XD), and lactose/trehalose (LT). Particles encapsulating human serotype 5 adenovirus viral vector (AdHu5) were produced via both spray drying and acoustic levitation. The particles' internal microstructure was directly visualized, and the location of a viral vector analogue was spatially mapped within the particles by volume imaging using focused ion beam sectioning and scanning electron microscopy. The majority of the viral vector analogue was found at, or near, the solid-air interfaces. Peclet number and crystallization kinetics governed the internal microstructure of the particles: XD particles with minimal internal voids retained the highest viral activity, followed by MD particles with a few large voids, and finally LT particles with numerous internal voids exhibited the lowest viral activity. Overall, AdHu5 activity decreased as the total solid-air interfacial area increased (as quantified by nitrogen sorption). Along with processing losses, this work highlights the importance of surface area within particles as an indicator of activity losses for dried biologics.

Simulation of experimental synthetic DNA tracer transport through the vadose zone

Although multiple experimental studies have proven the use of free synthetic DNA as tracers in hydrological systems, their quantitative fate and transport, especially through the vadose zone, is still not well understood. Here we simulate the water flow and breakthrough of deuterium (D) and one free synthetic DNA tracer from a 10-day experiment conducted in a transient variably saturated 1m³ 10° sloped lysimeter using the HYDRUS-2D software package. Recovery and breakthrough flux of D (97.78%) and the DNA tracer (1.05%) were captured well with the advection-dispersion equation (R² = 0.949, NSE = 0.937) and the Schijven and Šimůnek two-site kinetic sorption model recommended for virus transport modeling (R² = 0.824, NSE = 0.823), respectively. The degradation of the DNA tracer was very slow (estimated to be 10% in 10 days), because the "loamy sand" porous media in our lysimeter was freshly crushed basaltic tephra (i.e., crushed rocks) and the microbes and DNase that could potentially degrade DNA in regular soils were rare in our "loamy sand". The timing of the concentration peaks and the HYDRUS-2D simulated temporal and spatial distribution of DNA in the lysimeter both revealed the role of the solid-water-air contact lines in mobilizing and carrying DNA tracer under the experimental variably saturated transient flow condition. The free DNA was nearly non-selectively transported through the porous media, and showed a slightly early breakthrough, possibly due to a slight effect of anion exclusion or size exclusion. Our results indicate that free DNA have the potential to trace vadose zone water flow and solute/contaminant transport, and to serve as surrogates to trace viral pathogen pollution in soil-water systems. To our knowledge, this study is the first to simulate transport mechanisms of free synthetic DNA tracers through real soil textured porous media under variably saturated transient flow condition.

Coliphages as viral indicators of sanitary significance for drinking water

Coliphages are virus that infect coliform bacteria and are used in aquatic systems for risk assessment for human enteric viruses. This mini-review appraises the types and sources of coliphage and their fate and behavior in source waters and engineered drinking water treatment systems. Somatic (cell wall infection) and F+ (male specific) coliphages are abundant in drinking water sources and are used as indicators of fecal contamination. Coliphage abundances do not consistently correlate to human enteric virus abundance, but they suitably reflect the risks of exposure to human enteric viruses. Coliphages have highly variable surface characteristics with respect to morphology, size, charge, isoelectric point, and hydrophobicity which together interact to govern partitioning and removal characteristics during water treatment. The groups somatic and F+ coliphages are valuable for investigating the virus elimination during water treatment steps and as indicators for viral water quality assessment. Strain level analyses (e.g., Qβ or GA-like) provide more information about specific sources of viral pollution but are impractical for routine monitoring. Consistent links between rapid online monitoring tools (e.g., turbidity, particle counters, and flow cytometry) and phages in drinking water have yet to be established but are recommended as a future area of research activity. This could enable the real-time monitoring of virus and improve the process understanding during transient operational events. Exciting future prospects for the use of coliphages in aquatic microbiology are also discussed based on current scientific evidence and practical needs.

Evaluation of Biopolymer Materials and Synthesis Techniques to Develop a Rod-Shaped Biopolymer Surrogate for Legionella pneumophila

Biopolymer microparticles have been developed for applications that require biocompatibility and biodegradability, such as drug delivery. In this study, we assessed the production of microparticles using carnauba wax, κ-carrageenan, alginate, and poly (lactic-co-glycolic acid) (PLGA) with the aim of developing a novel, DNA-tracer-loaded, biopolymer surrogate with a size, shape, surface charge, and relative hydrophobicity similar to stationary-phase Legionella pneumophila to mimic the bacteria’s mobility and persistence in engineered water systems. We found that the type and concentration of biopolymer, reaction conditions, and synthesis methods affected the morphology, surface charge, relative hydrophobicity, and DNA tracer loading efficiency of the biopolymer microparticles produced. Carnauba wax, κ-carrageenan, and alginate (Protanal^®, and low and medium viscosity) produced highly polydisperse microspheres. In contrast, PLGA and alginate-CaCO₃ produced uniform microspheres and rod-shaped microparticles, respectively, with high DNA tracer loading efficiencies (PLGA 70% and alginate-CaCO₃ 95.2 ± 5.7%) and high reproducibilities. Their synthesis reproducibility was relatively high. The relative hydrophobicity of PLGA microspheres closely matched the cell surface hydrophobicity of L. pneumophila but not the bacterial morphology, whereas the polyelectrolyte layer-by-layer assembly was required to enhance the relative hydrophobicity of alginate-CaCO₃ microparticles. Following this surface modification, alginate-CaCO₃ microparticles represented the best match to L. pneumophila in size, morphology, surface charge, and relative hydrophobicity. This new biopolymer surrogate has the potential to be used as a mimic to study the mobility and persistence of L. pneumophila in water systems where the use of the pathogen is impractical and unsafe.

Reductions of human enteric viruses in 10 commonly used activated carbon, polypropylene and polyester household drinking-water filters

Drinking-water treatment in non-networked rural communities relies on the use of point-of-use (PoU) household filters. Source waters treated by PoU filters are often microbially contaminated, but information about human enteric virus reductions in these filters is limited. This study evaluated human rotavirus, adenovirus and norovirus reductions in 10 commonly used, new PoU carbon, polypropylene and polyester microfilters. The viruses were spiked into chlorine-free tap water (pH 8.0, ionic strength 1.22 mM), and 3 sequential challenge tests were conducted in each filter under a constant flow rate of 1 L/min. In most of the filters investigated, the norovirus and adenovirus reductions were similar (P > 0.49). Compared with the norovirus and adenovirus reductions, the rotavirus reductions were significantly lower in the carbon filters (P ≤ 0.009), which may relate to rotavirus's higher zeta potential and lower hydrophobicity. Virus reductions appeared to be dictated by the filter media type through electrostatic and hydrophobic interactions; the effects of filter media pore sizes on virus reductions via physical size-exclusion were very limited. The virus reductions in the carbon filters were significantly greater than those in the polypropylene and polyester filters (P ≤ 0.0001), and they did not differ significantly between the polypropylene and polyester filters (P > 0.24). None of the filters met the "protective" rotavirus reduction level (≥3 log10) required for household drinking-water treatment. Our study's findings highlight a critical need for additional water treatment when using PoU microfilters, for example, water boiling or ultraviolet radiation, or the use of effective surface-modified filter media to prevent drinking-waterborne infections from enteric viruses.

Transport of silica encapsulated DNA microparticles in controlled instantaneous injection open channel experiments

Surface water tracing is a widely used technique to investigate in-stream mass transport including contaminant migration. Recently, a microparticle tracer was developed with unique synthetic DNA encapsulated in an environmentally-friendly silica coating (Si-DNA microparticle). Previous tracing applications of such tracers reported detection and quantification, but a massive loss of tracer mass. However, the transport behavior of these DNA-tagged microparticle tracers has not been rigorously quantified and compared with that of solute tracers. Therefore, we compared the transport behavior of Si-DNA microparticles to the behavior of solute NaCl in 6 different, environmentally representative water types using breakthrough curves (BTCs), obtained from laboratory open channel injection experiments, whereby no Si-DNA microparticle tracer mass was lost. Hereafter, we modelled the BTCs using a 1-D advection-dispersion model with one transient storage zone (OTIS) by calibrating the hydrodynamic dispersion coefficient D and a storage zone exchange rate coefficient. We concluded that the transport behavior of Si-DNA microparticles resembled that of NaCl in surface-water relevant conditions, evidenced by BTCs with a similar range of D; however, the Si-DNA microparticle had a more erratic BTC than its solute counterpart, whereby the scatter increased as a function of water quality complexity. The overall larger confidence interval of D_Si-DNA was attributed to the discrete nature of colloidal particles with a certain particle size distribution and possibly minor shear-induced aggregations. This research established a solid methodological foundation for field application of Si-DNA microparticles in surface water tracing, providing insight in transport behavior of equivalent sized and mass particles in rivers.

Validation of a diffusion-based single droplet drying model for encapsulation of a viral-vectored vaccine using an acoustic levitator

Development of thermally stable spray dried viral-vectored vaccine powders is dependent on the selection of a proper excipient or excipient blend for encapsulation, which can be a time and resource intensive process. In this work, a diffusion-based droplet drying model was developed to compute droplet drying time, size, and component distribution. The model predictions were validated using an acoustic levitator to dry droplets containing protein-coated or fluorescently labelled silica nanoparticles (as adenoviral vector analogues) and a range of excipient blends. Surface morphology of the dried particles was characterized by atomic force microscopy and the distribution of silica nanoparticles was quantified by confocal microscopy. The modelled distributions of adenovirus agreed with the microscopy results for three mannitol/dextran excipient blends with varying molecular weight dextrans, verifying the equations and assumptions of the model. Viral vector activity data for adenovirus in a range of (poly)saccharide/sugar alcohol formulations were also compared to the model outputs, suggesting that viral activity decreases when the model predicts increasing adenovirus concentrations near the air-solid interface. Using a validated model with excipient property inputs that are readily available in the literature can facilitate the development of viral-vectored vaccines by identifying promising excipients without the need for experimentation.

Attenuation and transport of human enteric viruses and bacteriophage MS2 in alluvial sand and gravel aquifer media-laboratory studies

Potable groundwater contamination by human enteric viruses poses serious health risks. Our understanding of virus subsurface transport has largely depended on studying bacteriophages as surrogates. Few studies have compared the transport behaviour of enteric viruses, especially norovirus, with phage surrogates. We conducted laboratory column experiments to investigate norovirus and bacteriophage MS2 (MS2) filtration in alluvial sand, and rotavirus, adenovirus and MS2 filtration in alluvial gravel aquifer media in 2 mM NaCl (pH 6.6-6.9) with pore velocities of 4.6-5.4 m/day. The data were analysed using colloid filtration theory and HYDRUS-1D 2-site attachment-detachment modelling. Norovirus removal was somewhat lower than MS2 removal in alluvial sand. The removal of rotavirus and adenovirus was markedly greater than MS2 removal in alluvial gravel. These findings concurred with the log₁₀ reduction values, mass recoveries, attachment efficiencies and irreversible deposition rate constants. The modelling results suggested that the MS2 detachment rates were in the same order of magnitude as norovirus, but they were 1 order of magnitude faster than those of rotavirus and adenovirus. The attachment of viruses and MS2 was largely reversible with faster detachment than attachment rates, favouring free virus transport. These findings highlight the risk associated with continual virus transport through subsurface media if viruses are not inactivated and remobilising previously attached viruses could trigger contamination events. Thus, virus attachment reversibility should be considered in virus transport predictions in subsurface media. Further research is needed to compare surrogates with enteric viruses, especially norovirus, regarding their transport behaviours under different experimental conditions.

Make it clean, make it safe: A review on virus elimination via adsorption

Recently, the potential dangers of viral infection transmission through water and air have become the focus of worldwide attention, via the spread of COVID-19 pandemic. The occurrence of large-scale outbreaks of dangerous infections caused by unknown pathogens and the isolation of new pandemic strains require the development of improved methods of viruses' inactivation. Viruses are not stable self-sustaining living organisms and are rapidly inactivated on isolated surfaces. However, water resources and air can participate in the pathogens' diffusion, stabilization, and transmission. Viruses inactivation and elimination by adsorption are relevant since they can represent an effective and low-cost method to treat fluids, and hence limit the spread of pathogen agents. This review analyzed the interaction between viruses and carbon-based, oxide-based, porous materials and biological materials (e.g., sulfated polysaccharides and cyclodextrins). It will be shown that these adsorbents can play a relevant role in the viruses removal where water and air purification mostly occurring via electrostatic interactions. However, a clear systematic vision of the correlation between the surface potential and the adsorption capacity of the different filters is still lacking and should be provided to achieve a better comprehension of the global phenomenon. The rationalization of the adsorption capacity may be achieved through a proper physico-chemical characterization of new adsorbents, including molecular modeling and simulations, also considering the adsorption of virus-like particles on their surface. As a most timely perspective, the results on this review present potential solutions to investigate coronaviruses and specifically SARS-CoV-2, responsible of the COVID-19 pandemic, whose spread can be limited by the efficient disinfection and purification of closed-spaces air and urban waters.

Water tracking in surface water, groundwater and soils using free and alginate-chitosan encapsulated synthetic DNA tracers

Investigating contamination pathways and hydraulic connections in complex hydrological systems will benefit greatly from multi-tracer approaches. The use of non-toxic synthetic DNA tracers is promising, because unlimited numbers of tracers, each with a unique DNA identifier, could be used concurrently and detected at extremely low concentrations. This study aimed to develop multiple synthetic DNA tracers as free molecules and encapsulated within microparticles of biocompatible and biodegradable alginate and chitosan, and to validate their field utility in different systems. Experiments encompassing a wide range of conditions and flow rates (19 cm/day-39 km/day) were conducted in a stream, an alluvial gravel aquifer, a fine coastal sand aquifer, and in lysimeters containing undisturbed silt loam over gravels. The DNA tracers were identifiable in all field conditions investigated, and they were directly detectable in the stream at a distance of at least 1 km. The DNA tracers showed promise at tracking fast-flowing water in the stream, gravel aquifer and permeable soils, but were unsatisfactory at tracking slow-moving groundwater in the fine sand aquifer. In the surface water experiments, the microencapsulated DNA tracers' concentrations and mass recoveries were 1-3 orders of magnitude greater than those of the free DNA tracers, because encapsulation protected them from environmental stressors and they were more negatively charged. The opposite was observed in the gravel aquifer, probably due to microparticle filtration by the aquifer media. Although these new DNA tracers showed promise in proof-of-concept field validations, further work is needed before they can be used for large-scale investigations.

Role of biofilm on virus inactivation in limestone aquifers: implications for managed aquifer recharge

BACKGROUND

Virus, as nano-sized microorganisms are prevalent in aquifers, which threaten groundwater quality and human health wellbeing. Virus inactivation by attachment onto the limestone surfaces is a determining factor in the transport and retention behavior of virus in carbonaceous aquifers.

METHODS

In the present study, the inactivation of MS2 -as a model virus- by attachment onto the surfaces of limestone grains was investigated in a series of batch experiments under different conditions such as limestone particle size distribution (0.25-0.50, 0.5-1 and 1-2 mm), treated wastewater and RO water, temperature (4 and 22 °C), initial MS2 concentrations (10³-10⁷ PFU/mL) and static and dynamic conditions. The experimental data of MS2 inactivation was also fitted to a non-linear kinetic model with shoulder and tailing. The characteristics of biofilm on the surfaces of limestone aquifer materials were assessed using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).

RESULTS

The inactivation rate of virus decreased with increasing the adsorbent diameter. Furthermore, virus inactivation was greater at room temperature (22 °C) than 4 °C, in both static and dynamic conditions. The inactivation of virus via attachment onto the limestone aquifer materials in dynamic conditions was higher than under static conditions. In addition, fitting the experimental data with a kinetic model showed that virus inactivation was high at higher temperature, smaller limestone grains and dynamic conditions. Moreover, the experiments with treated wastewater showed that in authentic aqueous media, the virus inactivation was considerably higher than in RO water, due to the presence of either monovalent or divalent cations and surface roughness created by biofilms.

CONCLUSION

Finally, in terms of managed aquifer recharge systems, the presence of biofilm increases bacteria and virus retention onto the aquifer surfaces. Graphical abstract.

Modeling the Transport of Human Rotavirus and Norovirus in Standardized and in Natural Soil Matrix-Water Systems

We modeled Group A Rotavirus (RVA) and Norovirus genogroup II (GII NoV) transport experiments in standardized (crystal quartz sand and deionized water with adjusted pH and ionic strength) and natural soil matrix-water systems (MWS). On the one hand, in the standardized MWS, Rotavirus and Norovirus showed very similar breakthrough curves (BTCs), showing a removal rate of 2 and 1.7 log₁₀, respectively. From the numerical modeling of the experiment, transport parameters of the same order of magnitude were obtained for both viruses. On the other hand, in the natural MWS, the two viruses show very different BTCs. The Norovirus transport model showed significant changes; BTC showed a removal rate of 4 log₁₀, while Rotavirus showed a removal rate of 2.6 log₁₀ similar to the 2 log₁₀ observed on the standardized MWS. One possible explanation for this differential behavior is the difference in the isoelectric point value of these two viruses and the increase of the ionic strength on the natural MWS.

Attenuation of rotavirus, MS2 bacteriophage and biomolecule-modified silica nanoparticles in undisturbed silt loam over gravels dosed with onsite wastewater

Contamination of potable groundwater by pathogenic viruses from on-site wastewater treatment systems (OWTS) poses a serious health risk. This study investigated the attenuation and transport of rotavirus, bacteriophage MS2 and DNA-labelled-glycoprotein-coated silica nanoparticles (DGSnp) in 2 intact cores of silt loam over gravels dosed with wastewater from an OWTS at 3.53 L/day. To simulate a worst-case scenario, experiments were conducted under saturated conditions. The results from 6 experiments demonstrated that the rotavirus and DGSnp reductions were very similar and markedly greater than the MS2 reduction. This was reflected in the peak concentrations, relative mass recoveries, and temporal and spatial reduction rates. For a given log₁₀ reduction, the estimated soil depth required for MS2 was over twice that required for rotavirus and DGSnp. This is the first study in which DGSnp was used as a rotavirus surrogate in soil under wastewater applications. Consistent with previous studies, DGSnp showed promise at mimicking rotavirus attenuation and transport in porous media. The results suggest DGSnp could be used to assess the attenuation capacity of subsurface media to rotavirus. However, DGSnp is not conservative and will underestimate the setback distances required for rotavirus reductions by 3%. On the other hand, separation distances determined using the rotavirus parameters and criteria but based on MS2 attenuation, can be too conservative in some subsurface media. To determine safe and realistic separation distances, it would be beneficial and complementary to apply both conservative virus surrogate using MS2 bacteriophage and representative but non-conservative new virus surrogates using biomolecule-modified silica nanoparticles.

Fecal source tracking methods to elucidate critical sources of pathogens and contaminant microbial transport through New Zealand agricultural watersheds - A review

In New Zealand, there is substantial potential for microbial contaminants from agricultural fecal sources to be transported into waterways. The flow and transport pathways for fecal contaminants vary at a range of scales and is dependent on chemical, physical and biological attributes of pathways, soils, microorganisms and landscape characteristics. Understanding contaminant transport pathways from catchment to stream can aid water management strategies. It is not practical, however to conduct direct field measurement for all catchments on the fate and transport of fecal pathogens due to constraints on time, personnel, and material resources. To overcome this problem, fecal source tracking can be utilised to link catchment characteristics to fecal signatures identifying critical sources. In this article, we have reviewed approaches to identifying critical sources and pathways for fecal microorganisms from agricultural sources, and make recommendations for the appropriate use of these fecal source tracking (FST) tools.

Cotransport of human adenoviruses with clay colloids and TiO2 nanoparticles in saturated porous media: Effect of flow velocity

This study focuses on the effects of two clay colloids (kaolinite, KGa-1b and montmorillonite, STx-1b) and titanium dioxide (TiO₂) nanoparticles (NPs) on human adenovirus transport and retention in water saturated porous media at three different pore water velocities (0.38, 0.74, and 1.21cm/min). Transport and cotransport experiments were performed in 30-cm long laboratory columns packed with clean glass beads with 2mm diameter. The experimental results suggested that the presence of KGa-1b, STx-1b and TiO₂ NPs increased human adenovirus inactivation and attachment onto the solid matrix, due to the additional attachment sites available. Retention by the packed column was found to be highest (up to 99%) in the presence of TiO₂ NPs at the highest pore water velocity, and lowest in the presence of KGa-1b. The experimental results suggested that adenoviruses would undergo substantial aggregation or heteroaggregation during cotransport. However, no distinct relationships between mass recoveries and water velocity could be established from the experimental cotransport data. Note that for the cotransport experiments, collision efficiency values were shown to be higher for the higher flow rate examined in this study.

Applying Quantitative Molecular Tools for Virus Transport Studies: Opportunities and Challenges

Bacteriophages have been used in soil column studies for the last several decades as surrogates to study the fate and transport behavior of enteric viruses in groundwater. However, recent studies have shown that the transport behavior of bacteriophages and enteric viruses in porous media can be very different. The next generation of virus transport science must therefore provide more data on mobility of enteric viruses and the relationship between transport behaviors of enteric viruses and bacteriophages. To achieve this new paradigm, labor intensity devoted to enteric virus quantification method must be reduced. Recent studies applied quantitative polymerase chain reaction (qPCR) to column filtration experiments to study the transport behavior of human adenovirus (HAdV) in porous media under a variety of conditions. A similar approach can be used to study the transport of other enteric viruses such as norovirus. Analyzing the column samples with both qPCR and culture assays and applying multiplex qPCR to study cotransport behavior of more than one virus will provide information to under-explored areas in virus transport science. Both nucleic acid extraction kits and one-step lysis protocols have been used in these column studies to extract viral nucleic acid for qPCR quantification. The pros and cons of both methods are compared herein and solutions for overcoming problems are suggested. As better understanding of the transport behavior of enteric viruses is clearly needed, we strongly advocate for application of rapid molecular tools in future studies as well as optimization of protocols to overcome their current limitations.

Tracking effluent discharges in undisturbed stony soil and alluvial gravel aquifer using synthetic DNA tracers

With the intensification of human activities, fresh water resources are increasingly being exposed to contamination from effluent disposal to land. Thus, there is a greater need to identify the sources and pathways of water contamination to enable the development of better mitigation strategies. To track discharges of domestic effluent into soil and groundwater, 10 synthetic double-stranded DNA (dsDNA)³ tracers were developed in this study. Laboratory column experiment and field groundwater and soil lysimeter studies were carried out spiking DNA with oxidation-pond domestic effluent. The selected DNA tracers were compared with a non-reactive bromide (Br) tracer with respect to their relative mass recoveries, speeds of travel and dispersions using the method of temporal moments. In intact stony soil and gravel aquifer media, the dsDNA tracers typically showed earlier breakthrough and less dispersion than the Br tracer, and underwent mass reduction. This suggests that the dsDNA tracers were predominantly transported through the network of larger pores or preferential flow paths. Effluent tracking experiments in soil and groundwater demonstrated that the dsDNA tracers were readily detectable in effluent-contaminated soil and groundwater using quantitative polymerase chain reaction. DNA tracer spiked in the effluent at quantities of 36μg was detected in groundwater 37m down-gradient at a concentration 3-orders of magnitude above the detection limit. It is anticipated it could be detected at far greater distances. Our findings suggest that synthetic dsDNA tracers are promising for tracking effluent discharges in soils and groundwater but further studies are needed to investigate DNA-effluent interaction and the impact of subsurface environmental conditions on DNA attenuation. With further validation, synthetic dsDNA tracers, especially when multiple DNA tracers are used concurrently, can be an effective new tool to track effluent discharge in soils and groundwater, providing spatial estimation on the presence or absence of contamination sources and pathways.

Abundance and Distribution of Enteric Bacteria and Viruses in Coastal and Estuarine Sediments-a Review

The long term survival of fecal indicator organisms (FIOs) and human pathogenic microorganisms in sediments is important from a water quality, human health and ecological perspective. Typically, both bacteria and viruses strongly associate with particulate matter present in freshwater, estuarine and marine environments. This association tends to be stronger in finer textured sediments and is strongly influenced by the type and quantity of clay minerals and organic matter present. Binding to particle surfaces promotes the persistence of bacteria in the environment by offering physical and chemical protection from biotic and abiotic stresses. How bacterial and viral viability and pathogenicity is influenced by surface attachment requires further study. Typically, long-term association with surfaces including sediments induces bacteria to enter a viable-but-non-culturable (VBNC) state. Inherent methodological challenges of quantifying VBNC bacteria may lead to the frequent under-reporting of their abundance in sediments. The implications of this in a quantitative risk assessment context remain unclear. Similarly, sediments can harbor significant amounts of enteric viruses, however, the factors regulating their persistence remains poorly understood. Quantification of viruses in sediment remains problematic due to our poor ability to recover intact viral particles from sediment surfaces (typically <10%), our inability to distinguish between infective and damaged (non-infective) viral particles, aggregation of viral particles, and inhibition during qPCR. This suggests that the true viral titre in sediments may be being vastly underestimated. In turn, this is limiting our ability to understand the fate and transport of viruses in sediments. Model systems (e.g., human cell culture) are also lacking for some key viruses, preventing our ability to evaluate the infectivity of viruses recovered from sediments (e.g., norovirus). The release of particle-bound bacteria and viruses into the water column during sediment resuspension also represents a risk to water quality. In conclusion, our poor process level understanding of viral/bacterial-sediment interactions combined with methodological challenges is limiting the accurate source apportionment and quantitative microbial risk assessment for pathogenic organisms associated with sediments in aquatic environments.

Adsorption of Rotavirus, MS2 Bacteriophage and Surface-Modified Silica Nanoparticles to Hydrophobic Matter

Adsorption to aquifer media is an important process in the removal of viruses from groundwater. Even though hydrophobic interactions have been shown to contribute to adsorption, little is known about the hydrophobicity of viruses found in groundwater. In this study, the hydrophobicity of rotavirus, MS2 bacteriophage and DNA-labelled silica nanoparticles (SiNPs) coated with glycoprotein, protein A and alpha-1-microglobulin/bikunin precursor (AMBP) was investigated. The hydrophobicity was experimentally determined by using a modified microbial adhesion to hydrocarbons (MATH) assay. The results were compared with the theoretical hydrophobicity of the viral capsid proteins and the proteins used to coat the nanoparticles, and with the results of adsorption tests with unmodified and organosilane-coated (hydrophobic) silica sand. While most theoretical protein hydrophobicity values were similar, the results of the MATH assay suggested fundamental differences in the hydrophobicity of the viruses and the SiNPs. MS2 was found to be highly hydrophobic as based on the MATH hydrophobicity and a significantly enhanced adsorption to hydrophobic sand, whereas rotavirus was relatively hydrophilic. The MATH assay revealed that protein-coating of SiNP introduced some degree of hydrophobicity to hydrophilic SiNPs, enabling them to more closely mimic viral hydrophobicity. Our study also demonstrated that the protein-coated SiNPs better mimicked rotavirus adsorption to sand media (coated or not coated with hydrophobic organic matter) than the MS2. This further supports previous findings that these surface-modified SiNPs are useful surrogates in mimicking rotavirus retention and transport in porous media.

Attachment and Detachment Behavior of Human Adenovirus and Surrogates in Fine Granular Limestone Aquifer Material

The transport of human adenovirus, nanoparticles, and PRD1 and MS2 bacteriophages was tested in fine granular limestone aquifer material taken from a borehole at a managed aquifer recharge site in Adelaide, South Australia. Comparison of transport and removal of virus surrogates with the pathogenic virus is necessary to understand the differences between the virus and surrogate. Because experiments using pathogenic viruses cannot be done in the field, laboratory tests using flow-through soil columns were used. Results show that PRD1 is the most appropriate surrogate for adenovirus in an aquifer dominated by calcite material but not under high ionic strength or high pH conditions. It was also found that straining due to size and the charge of the colloid were not dominant removal mechanisms in this system. Implications of this study indicate that a certain surrogate may not represent a specific pathogen solely based on similar size, morphology, and/or surface charge. Moreover, if a particular surrogate is representative of a pathogen in one aquifer system, it may not be the most appropriate surrogate in another porous media system. This was apparent in the inferior performance of MS2 as a surrogate, which is commonly used in virus transport studies.

Interaction of human adenoviruses and coliphages with kaolinite and bentonite

Human adenoviruses (hAdVs) are pathogenic viruses responsible for public health problems worldwide. They have also been used as viral indicators in environmental systems. Coliphages (e.g., MS2, ΦX174) have also been studied as indicators of viral pollution in fecally contaminated water. Our objective was to evaluate the distribution of three viral fecal indicators (hAdVs, MS2, and ΦΧ174), between two different phyllosilicate clays (kaolinite and bentonite) and the aqueous phase. A series of static and dynamic experiments were conducted under two different temperatures (4, 25°C) for a time period of seven days. HAdV adsorption was examined in DNase I reaction buffer (pH=7.6, and ionic strength (IS)=1.4mM), whereas coliphage adsorption in phosphate buffered saline solution (pH=7, IS=2mM). Moreover, the effect of IS on hAdV adsorption under static conditions was evaluated. The adsorption of hAdV was assessed by real-time PCR and its infectivity was tested by cultivation methods. The coliphages MS2 and ΦΧ174 were assayed by the double-layer overlay method. The experimental results have shown that coliphage adsorption onto both kaolinite and bentonite was higher for the dynamic than the static experiments; whereas hAdV adsorption was lower under dynamic conditions. The adsorption of hAdV increased with decreasing temperature, contrary to the results obtained for the coliphages. This study examines the combined effect of temperature, agitation, clay type, and IS on hAdV adsorption onto clays. The results provide useful new information on the effective removal of viral fecal indicators (MS2, ΦX174 and hAdV) from dilute aqueous solutions by adsorption onto kaolinite and bentonite. Factors enabling enteric viruses to penetrate soils, groundwater and travel long distances within aquifers are important public health issues. Because the observed adsorption behavior of surrogate coliphages MS2 and ΦΧ174 is substantially different to that of hAdV, neither MS2 nor ΦΧ174 is recommended as a suitable model for adenovirus.

Transport of Human Adenoviruses in Water Saturated Laboratory Columns

Groundwater may be contaminated with infective human enteric viruses from various wastewater discharges, sanitary landfills, septic tanks, agricultural practices, and artificial groundwater recharge. Coliphages have been widely used as surrogates of enteric viruses, because they share many fundamental properties and features. Although a large number of studies focusing on various factors (i.e. pore water solution chemistry, fluid velocity, moisture content, temperature, and grain size) that affect biocolloid (bacteria, viruses) transport have been published over the past two decades, little attention has been given toward human adenoviruses (hAdVs). The main objective of this study was to evaluate the effect of pore water velocity on hAdV transport in water saturated laboratory-scale columns packed with glass beads. The effects of pore water velocity on virus transport and retention in porous media was examined at three pore water velocities (0.39, 0.75, and 1.22 cm/min). The results indicated that all estimated average mass recovery values for hAdV were lower than those of coliphages, which were previously reported in the literature by others for experiments conducted under similar experimental conditions. However, no obvious relationship between hAdV mass recovery and water velocity could be established from the experimental results. The collision efficiencies were quantified using the classical colloid filtration theory. Average collision efficiency, α, values decreased with decreasing flow rate, Q, and pore water velocity, U, but no significant effect of U on α was observed. Furthermore, the surface properties of viruses and glass beads were used to construct classical DLVO potential energy profiles. The results revealed that the experimental conditions of this study were unfavorable to deposition and that no aggregation between virus particles is expected to occur. A thorough understanding of the key processes governing virus transport is pivotal for public health protection.