Relative transport of human adenovirus and MS2 in porous media

Effect of Human Adenovirus Type 35 Concentration on Its Inactivation and Sorption on Titanium Dioxide Nanoparticles

Removal of pathogenic viruses from water resources is critically important for sanitation and public health. Nanotechnology is a promising technology for virus inactivation. In this paper, the effects of titanium dioxide (TiO2) anatase nanoparticles (NPs) on human adenovirus type 35 (HAdV-35) removal under static and dynamic (with agitation) batch conditions were comprehensively studied. Batch experiments were performed at room temperature (25 °C) with and without ambient light using three different initial virus concentrations. The virus inactivation experimental data were satisfactorily fitted with a pseudo-first-order expression with a time-dependent rate coefficient. The experimental results demonstrated that HAdV-35 sorption onto TiO2 NPs was favored with agitation under both ambient light and dark conditions. However, no distinct relationships between virus initial concentration and removal efficiency could be established from the experimental data.

Attachment of human adenovirus onto household paints

Attachment of human adenovirus 40 (HAdV40) onto surfaces coated with three compositionally different household paints was evaluated experimentally and interpreted based on measured physicochemical properties of the paints. Polar, dispersive and electrostatic interactions between HAdV40 and the paints were predicted using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) model. Quartz crystal microbalance (QCM-D) was used to quantify virus attachment to paints from 1 mM and 150 mM NaCl solutions, with the latter having the ionic strength of a typical respiratory fluid. Acrylic latex water-based, alkyd water-based, and alkyd oil-based paints were all determined to be highly hydrophobic (ΔG_sws < - 48 mJ/m²). XDLVO modeling and preliminary QCM-D tests evaluated virus-paint interactions within and outside pH windows of favorable virus-paint electrostatic interactions. Hydrophobic and electrostatic interactions governed virus attachment while van der Waals interactions played a relatively minor role. In higher ionic strength solutions, the extent of virus attachment correlated with the free energy of virus-paint interfacial interaction, [Formula: see text] : more negative energies corresponded to higher values of the areal mass density of attached viruses. Hydrophobicity was the dominant factor in determining virus adhesion from high ionic strength solutions where electrostatic interactions were screened out. The hydrophobicity of paints, while desirable for minimizing moisture intrusion, also facilitates attachment of colloids such as viruses. The results call for new approaches to the materials design of indoor paints with enhanced resistance to virus adhesion. Paints so formulated should help reduce human exposure to viruses.

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.

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.

Transport of Escherichia coli phage through saturated porous media considering managed aquifer recharge

Virus is one of the most potentially harmful microorganisms in groundwater. In this paper, the effects of hydrodynamic and hydrogeochemical conditions on the transportation of the colloidal virus considering managed aquifer recharge were systematically investigated. Escherichia coli phage, vB_EcoM-ep3, has a broad host range and was able to lyse pathogenic Escherichia coli. Bacteriophage with low risk to infect human has been found extensively in the groundwater environment, so it is considered as a representative model of groundwater viruses. Laboratory studies were carried out to analyze the transport of the Escherichia coli phage under varying conditions of pH, ionic strength, cation valence, flow rate, porous media, and phosphate buffer concentration. The results indicated that decreasing the pH will increase the adsorption of Escherichia coli phage. Increasing the ionic strength, either Na⁺ or Ca²⁺, will form negative condition for the migration of Escherichia coli phage. A comparison of different cation valence tests indicated that changes in transport and deposition were more pronounced with divalent Ca²⁺ than monovalent Na⁺. As the flow rate increases, the release of Escherichia coli phage increases and the retention of Escherichia coli phage in the aquifer medium reduces. Changes in porous media had a significant effect on Escherichia coli phage migration. With increase of phosphate buffer concentration, the suspension stability and migration ability of Escherichia coli phage are both increased. Based on laboratory-scale column experiments, a one-dimensional transport model was established to quantitatively describe the virus transport in saturated porous medium.

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.

Temperature dependency of virus and nanoparticle transport and retention in saturated porous media

The influence of temperature on virus (PRD1 and ΦX174) and carboxyl-modified latex nanoparticle (50 and 100nm) attachment was examined in sand-packed columns under various physiochemical conditions. When the solution ionic strength (IS) equaled 10 and 30mM, the attachment rate coefficient (k_att) increased up to 109% (p<0.0002) and the percentage of the sand surface area that contributed to attachment (S_f) increased up to 160% (p<0.002) when the temperature was increased from 4 to 20°C. Temperature effects at IS=10 and 30mM were also dependent on the system hydrodynamics; i.e., enhanced retention at a lower pore water velocity (0.1m/day). Conversely, this same temperature increase had a negligible influence on k_att and S_f values when IS was 1mM or >50mM. An explanation for these observations was obtained from extended interaction energy calculations that considered nanoscale roughness and chemical heterogeneity on the sand surface. Interaction energy calculations demonstrated that the energy barrier to attachment in the primary minimum (∆Φ_a) decreased with increasing IS, chemical heterogeneity, and temperature, especially in the presence of small amounts of nanoscale roughness (e.g., roughness fraction of 0.05 and height of 20nm in the zone of influence). Temperature had a negligible effect on k_att and S_f when the IS=1mM because of the large energy barrier, and at IS=50mM because of the absence of an energy barrier. Conversely, temperature had a large influence on k_att and S_f when the IS was 10 and 30mM because of the presence of a small ∆Φ_a on sand with nanoscale roughness and a chemical (positive zeta potential) heterogeneity. This has large implications for setting parameters for the accurate modeling and transport prediction of virus and nanoparticle contaminants in ground water systems.

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.