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

E. coli phage transport in porous media: Response to colloid types and water saturation

Because of its long survival time, high migration ability and high pathogenicity, the migration of the virus in the subsurface environment deserves in-depth exploration and research. In this study we investigated the migration behavior of E. coli phage (VI) with organic colloids (HA) or inorganic colloids (SiO2) in the saturated or unsaturated bands and compared the differences in their migration mechanisms.The effects of different colloids on the surface characteristics of VI were analyzed according to particle size and zeta potential. Column experiments were conducted to simulate their migration in the subsurface environment. The results show that HA enhances the stability of VI-HA, promotes VI migration and plays a dominant role in its migration process under both saturated and unsaturated conditions. In contrast, SiO2 puts VI-SiO2 in an unstable state and is easily separated in the unsaturated state, thus promoting VI migration. Based on migration experiments, the extent of influence factors on VI migration was quantified and compared. The effect of colloids on VI migration is greater than that of moisture content, where the effect of HA is greater than that of SiO2. This study provides an experimental research idea to determine the dominant factors affecting virus migration, and provides a general direction and theoretical basis for the biological risk assessment of pathogenic microorganisms in complex underground environments, in order to enable the decision makers to make a response in time, accurately, and efficiently.

Superiority of UV222 radiation by in situ aquatic electrode KrCl excimer in disinfecting waterborne pathogens: Mechanism and efficacy

Microbial safety in water has always been the focus of attention, especially during the COVID-19 pandemic. Development of green, efficient and safe disinfection technology is the key to control the spread of pathogenic microorganisms. Here, an in situ aquatic electrode KrCl excimer radiation with main emission wavelength 222 nm (UV222) was designed and used to disinfect model waterborne virus and bacteria, i.e. phage MS2, E. coli and S. aureus. High inactivation efficacy and diversity of inactivation mechanisms of UV222 were proved by comparision with those of commercial UV254. UV222 could totally inactivate MS2, E. coli and S. aureus with initial concentrations of ∼10⁷ PFU or CFU mL^-1 within 20, 15, and 36 mJ/cm², respectively. The UV dose required by UV254 to inactivate the same logarithmic pathogenic microorganism is at least twice that of UV222. The protein, genomic and cell membrane irreparable damage contributed to the microbial inactivation by UV222, but UV254 only act on nucleic acid of the target microorganisms. We found that UV222 damage nucleic acid with almost the same or even higher efficacy with UV254. In addition, free base damage of UV222 in similar ways with UV254(dimer and hydrate). But due to the quantum yield of free base degradation of UV222 was greater than UV254, the photolysis rates of UV222 to A, G, C and U four bases were 11.5, 1.2, 3.2 and 1 times as those of UV254, respectively. Excellent disinfection performance in UV222 irradiation was also achieved in real water matrices (WWTP and Lake). In addition, it was proved that coexisting HCO₃^- or HPO₄^{2 -} in real and synthetic water matrices can produce • OH to promote UV222 disinfection. This study provided novel insight into the UV222 disinfection process and demonstrated its possibility to take place of the conventional ultraviolet mercury lamp in water purification.

Physiological characteristics, geochemical properties and hydrological variables influencing pathogen migration in subsurface system: What we know or not?

The global outbreak of coronavirus infectious disease-2019 (COVID-19) draws attentions in the transport and spread of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in aerosols, wastewater, surface water and solid wastes. As pathogens eventually enter the subsurface system, e.g., soils in the vadose zone and groundwater in the aquifers, they might survive for a prolonged period of time owing to the uniqueness of subsurface environment. In addition, pathogens can transport in groundwater and contaminate surrounding drinking water sources, possessing long-term and concealed risks to human society. This work critically reviews the influential factors of pathogen migration, unravelling the impacts of pathogenic characteristics, vadose zone physiochemical properties and hydrological variables on the migration of typical pathogens in subsurface system. An assessment algorithm and two rating/weighting schemes are proposed to evaluate the migration abilities and risks of pathogens in subsurface environment. As there is still no evidence about the presence and distribution of SARS-CoV-2 in the vadose zones and aquifers, this study also discusses the migration potential and behavior of SARS-CoV-2 viruses in subsurface environment, offering prospective clues and suggestions for its potential risks in drinking water and effective prevention and control from hydrogeological points of view.

Potential SARS-CoV-2 contamination of groundwater as a result of mass burial: A mini-review

The recent COVID-19 disease has highlighted the need for further research around the risk to human health and the environment because of mass burial of COVID-19 victims. Despite SARS-CoV-2 being an enveloped virus, which is highly susceptible to environmental conditions (temperature, solar/UV exposure). This review provides insight into the potential of SARS-CoV-2 to contaminate groundwater through burial sites, the impact of various types of burial practices on SARS-CoV-2 survival, and current knowledge gaps that need to be addressed to ensure that humans and ecosystems are adequately protected from SARS-CoV-2. Data available shows temperature is still likely to be the driving factor when it comes to survival and infectivity of SARS-CoV-2. Research conducted at cemetery sites globally using various bacteriophages (MS2, PRD1, faecal coliforms) and viruses (TGEV, MHV) as surrogates for pathogenic enteric viruses to study the fate and transport of these viruses showed considerable contamination of groundwater, particularly where there is a shallow vadose zone and heterogeneous structures are known to exist with very low residence times. In addition, changes in solution chemistry (e.g., decrease in ionic strength or increase in pH) during rainfall events produces large pulses of released colloids that can result in attached viruses becoming remobilised, with implications for groundwater contamination. Viruses cannot spread unaided through the vadose zone. Since groundwater is too deep to be in contact with the interred body and migration rates are very slow, except where preferential flow paths are known to exist, the groundwater table will not be significantly impacted by contamination from SARS-CoV-2. When burial takes place using scientifically defensible methods the possibility of infection will be highly improbable. Furthermore, the SARS-CoV-2 pandemic has helped us to prepare for other eventualities such as natural disasters where mass fatalities and subsequently burials may take place in a relatively short space of time.

Removal of bacterial plant pathogens in columns filled with quartz and natural sediments under anoxic and oxygenated conditions

Irrigation with surface water carrying plant pathogens poses a risk for agriculture. Managed aquifer recharge enhances fresh water availability while simultaneously it may reduce the risk of plant diseases by removal of pathogens during aquifer passage. We compared the transport of three plant pathogenic bacteria with Escherichia coli WR1 as reference strain in saturated laboratory column experiments filled with quartz sand, or sandy aquifer sediments. E. coli showed the highest removal, followed by Pectobacterium carotovorum, Dickeya solani and Ralstonia solanacearum. Bacterial and non-reactive tracer breakthrough curves were fitted with Hydrus-1D and compared with colloid filtration theory (CFT). Bacterial attachment to fine and medium aquifer sand under anoxic conditions was highest with attachment rates of max. k_att1 = 765 day^-1 and 355 day^-1, respectively. Attachment was the least to quartz sand under oxic conditions (k_att1 = 61 day^-1). In CFT, sticking efficiencies were higher in aquifer than in quartz sand but there was no differentiation between fine and medium aquifer sand. Overall removal ranged between < 6.8 log₁₀ m^-1 in quartz and up to 40 log₁₀ m^-1 in fine aquifer sand. Oxygenation of the anoxic aquifer sediments for two weeks with oxic influent water decreased the removal. The results highlight the potential of natural sand filtration to sufficiently remove plant pathogenic bacteria during aquifer storage.

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.