Evaluation of data from the literature on the transport and survival of Escherichia coli and thermotolerant coliforms in aquifers under saturated conditions

Assessing the risk of E. coli contamination from manure application in Chinese farmland by integrating machine learning and Phydrus

This study aims to present a comprehensive study on the risks associated with the residual presence and transport of Escherichia coli (E. coli) in soil following the application of livestock manure in Chinese farmlands by integrating machine learning algorithms with mechanism-based models (Phydrus). We initially review 28 published papers to gather data on E. coli's die-off and attachment characteristics in soil. Machine learning models, including deep learning and gradient boosting machine, are employed to predict key parameters such as the die-off rate of E. coli and first-order attachment coefficient in soil. Then, Phydrus was used to simulate E. coli transport and survival in 23692 subregions in China. The model considered regional differences in E. coli residual risk and transport, influenced by soil properties, soil depths, precipitation, seasonal variations, and regional disparities. The findings indicate higher residual risks in regions such as the Northeast China, Eastern Qinghai-Tibet Plateau, and pronounced transport risks in the fringe of the Sichuan Basin fringe, the Loess Plateau, the North China Plain, the Northeast Plain, the Shigatse Basin, and the Shangri-La region. The study also demonstrates a significant reduction in both residual and transport risks one month after manure application, highlighting the importance of timing manure application and implementing region-specific standards. This research contributes to the broader understanding of pathogen behavior in agricultural soils and offers practical guidelines for managing the risks associated with manure use. This study's comprehensive method offers a potentially valuable tool for evaluating microbial contaminants in agricultural soils across the globe.

Transport and removal of spores of Bacillus subtilis in an alluvial gravel aquifer at varying flow rates and implications for setback distances

To guarantee proper protection from fecally transmitted pathogen infections, drinking water wells should have a sufficiently large setback distance from potential sources of contamination, e.g. a nearby river. The aim of this study was to provide insight in regards to microbial contamination of groundwater under different flow velocities, which can vary over time due to changes in river stage, season or pumping rate. The effects of these changes, and how they affect removal parameters, are not completely understood. In this study, field tracer tests were carried out in a sandy gravel aquifer near Vienna, Austria to evaluate the ability of subsurface media to attenuate Bacillus subtilis spores, used as a surrogate for Cryptosporidium and Campylobacter. The hydraulic gradient between injection and extraction was controlled by changing the pumping rate (1, 10 l/s) of a pumping well at the test site, building upon previously published work in which tracer tests with a 5 l/s pumping rate were carried out. Attachment and detachment rate coefficients were determined using a HYDRUS-3D model and ranged from 0.12 to 0.76 and 0-0.0013 h^-1, respectively. Setback distances were calculated based on the 60-day travel time, as well as a quantitative microbial risk assessment (QMRA) approach, which showed similar results at this site; around 700 m at the highest pumping rate. Removal rates (λ) in the field tests ranged from 0.2 to 0.3 log/m, with lower pumping rates leading to higher removal. It was shown that scale must be taken into consideration when determining λ for the calculation of safe setback distances.

A unified parameter model based on machine learning for describing microbial transport in porous media

The transport and retention of microorganisms are typically described using attachment/detachment and straining/liberation models. However, the parameters in the models varied significantly, posing a significant challenge to describe microbial transport under different environmental conditions. A neural network (ANN) model was developed in this study to link the parameters in the model with the factors influencing microbial transport including the properties of microorganisms such as size and surface potentials, and the properties of porous media such as grain size and porosity, and flow conditions. Exhaustive search of literature renders 420 sets of experimental data of microbial transport, which were fitted using the microbial transport model to obtain model parameters. The model parameters, together with the factors influencing microbial transport, were then used to train an ANN model to search for their relationship. An ANN-based parameter relationship was derived and was then used to simulate microbial transport. The simulated results using the relationship roughly matched with the experimental data under different environmental conditions, indicating that a unified relationship was established between the parameters of the microbial transport model and the factors influencing microbial transport, and that microbial transport can be described using the microbial transport model with the ANN-based unified relationship for model parameters.

Biomimetic Core-Shell-Structured Nanofiber Membranes for Rapid and Portable Water Purification

Rapid and portable water purification (RPWP) technologies, helping travelers survive in the wild, have attracted increasing interest due to increasing activities, such as exploration, field hiking, and excursion. Field water is usually pathogenic because of various soluble and insoluble contaminants. In this study, fish-gill-like biomimetic core-shell-structured nanofiber membranes are designed and synthesized by an in situ oxidation polymerization coating process. A polyimide nanofiber membrane and a polypyrrole (PPy) coating layer are employed as a core and shell, respectively. The biomimetic membranes exhibit dual-functional capacities: a rapid removal of insoluble contaminants owing to the highly porous network and broad-spectrum adsorption of soluble contaminants enabled by the PPy shell. Model studies confirm the excellent ability of the membranes to purify Cr(VI)-contaminated water to drinkable water with a safe capacity of ∼1415 L m^-2. Actual application tests show that the membrane can efficiently remove coliform and suspended solids in a muddy water sample taken from a river in Suzhou, China. This study provides a promising route for the design of a single-layer membrane with dual functions for highly efficient RPWP.

Spatiotemporal dynamics of Escherichia coli presence and magnitude across a national groundwater monitoring network, Republic of Ireland, 2011-2020

Groundwater is a vital drinking water resource and its protection from microbiological contamination is paramount to safeguard public health. The Republic of Ireland (RoI) is characterised by the highest incidence of verocytotoxigenic Escherichia coli (VTEC) enteritis in the European Union (EU), linked to high reliance on unregulated groundwater sources (~16% of the population). Yet, the spatio-temporal factors influencing the frequency and magnitude of microbial contamination remain largely unknown, with past studies typically constrained to spatio-temporally 'limited' sampling campaigns. Accordingly, the current investigation sought to analyse an extensive spatially distributed time-series (2011-2020) of groundwater monitoring data in the RoI. The dataset, compiled by the Environmental Protection Agency (EPA), showed 'high' contamination rates, with 66.7% (88/132) of supplies testing positive for E. coli, and 29.5% (39/132) exceeding concentrations of 10MPN/100 ml (i.e. gross contamination) at least once during the 10-year monitoring period. Seasonal decomposition analyses indicate that E. coli detection rates peak during late autumn/early winter, coinciding with increases in annual rainfall, while gross contamination peaks in spring (May) and late-summer (August), likely reflecting seasonal shifts in agricultural practices. Mixed effects logistic regression modelling indicates that monitoring sources located in karst limestone are statistically associated with E. coli presence (OR = 2.76, p = 0.03) and gross contamination (OR = 2.54, p = 0.037) when compared to poorly productive aquifers (i.e., transmissivity below 10m²/d). Moreover, 5-day and 30-day antecedent rainfall increased the likelihood of E. coli contamination (OR = 1.027, p < 0.001 and OR = 1.005, p = 0.016, respectively), with the former also being associated with gross contamination (OR = 1.042, p < 0.001). As such, it is inferred that preferential flow and direct ingress of surface runoff are the most likely ingress mechanisms associated with E. coli groundwater supply contamination. The results presented are expected to inform policy change around groundwater source protection and provide insight for the development of groundwater monitoring programmes in geologically heterogeneous regions.

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.

Review on physical and chemical factors affecting fines migration in porous media

Permeability reduction and formation damage in porous media caused by fines (defined as unconfined solid particles present in the pore spaces) migration is one of the major reasons for productivity decline. It is well accepted that particle detachment occurs under imbalanced torques arising from hydrodynamic and adhesive forces exerted on attached particles. This paper reviewed current understanding on primary factors influencing fines migration as well as mathematical formulations for quantification. We also introduced salinity-related experimental observations that contradict theoretical predictions based on torque balance criteria, such as delayed particle release and attachment-detachment hysteresis. The delay of particle release during low-salinity water injection was successfully explained and formulated by the Nernst-Planck diffusion of ions in a narrow contact area. In addition to the widely recognized explanation by surface heterogeneity and the presence of low-velocity regions, we proposed a hypothesis that accounts for the shifting of equilibrium positions, providing new insight into the interpretation of elusive attachment-detachment hysteresis both physically and mathematically. The review was finalized by discussing the quantification of anomalous salinity effect on adhesion force at low- and high-salinity conditions.

Transport characteristics of DNA-tagged silica colloids as a colloidal tracer in saturated sand columns; role of solution chemistry, flow velocity, and sand grain size

In recent years, DNA-tagged silica colloids have been used as an environmental tracer. A major advantage of this technique is that the DNA-coding provides an unlimited number of unique tracers without a background concentration. However, little is known about the effects of physio-chemical subsurface properties on the transport behavior of DNA-tagged silica tracers. We are the first to explore the deposition kinetics of this new DNA-tagged silica tracer for different pore water chemistries, flow rates, and sand grain size distributions in a series of saturated sand column experiments in order to predict environmental conditions for which the DNA-tagged silica tracer can best be employed. Our results indicated that the transport of DNA-tagged silica tracer can be well described by first order kinetic attachment and detachment. Because of massive re-entrainment under transient chemistry conditions, we inferred that attachment was primarily in the secondary energy minimum. Based on calculated sticking efficiencies of the DNA-tagged silica tracer to the sand grains, we concluded that a large fraction of the DNA-tagged silica tracer colliding with the sand grain surface did also stick to that surface, when the ionic strength of the system was higher. The experimental results revealed the sensitivity of DNA-tagged silica tracer to both physical and chemical factors. This reduces its applicability as a conservative hydrological tracer for studying subsurface flow paths. Based on our experiments, the DNA-tagged silica tracer is best applicable for studying flow routes and travel times in coarse grained aquifers, with a relatively high flow rate. DNA-tagged silica tracers may also be applied for simulating the transport of engineered or biological colloidal pollution, such as microplastics and pathogens.

Controlling pore-scale processes to tame subsurface biomineralization

Microorganisms capable of biomineralization can catalyze mineral precipitation by modifying local physical and chemical conditions. In porous media, such as soil and rock, these microorganisms live and function in highly heterogeneous physical, chemical and ecological microenvironments, with strong local gradients created by both microbial activity and the pore-scale structure of the subsurface. Here, we focus on extracellular bacterial biomineralization, which is sensitive to external heterogeneity, and review the pore-scale processes controlling microbial biomineralization in natural and engineered porous media. We discuss how individual physical, chemical and ecological factors integrate to affect the spatial and temporal control of biomineralization, and how each of these factors contributes to a quantitative understanding of biomineralization in porous media. We find that an improved understanding of microbial behavior in heterogeneous microenvironments would promote understanding of natural systems and output in diverse technological applications, including improved representation and control of fluid mixing from pore to field scales. We suggest a range of directions by which future work can build from existing tools to advance each of these areas to improve understanding and predictability of biomineralization science and technology.

Upscaling Transport of Bacillus subtilis Endospores and Coliphage phiX174 in Heterogeneous Porous Media from the Column to the Field Scale

Groundwater contamination and transport of viruses and bacteria in aquifers are a major concern worldwide. To ascertain the ability of these aquifers to remove pathogens, tracer tests with microbial surrogates are carried out. These tests are laborious and may require special permits, and therefore, column tests are often done instead. Unfortunately, results from column tests tend to grossly overestimate removal rates when compared to the field scale, which can lead to an underestimation of groundwater contamination risks. Scale is an important consideration when examining pathogen transport through porous media, as pathogen removal is rarely a linear process. In this study, field tests were carried out with endospores of Bacillus subtilis and coliphage phiX174 over a distance of 25 m in an alluvial gravel aquifer near Vienna, Austria. The sandy gravel material from the field site was also used in column tests with the same tracers. Both attachment-detachment and colloid filtration theory were used to model these tests, as well as log-removal rates per meter. The results show that the spatial removal rate (log/m) is approximately 2 orders of magnitude higher on the column scale, when compared to the field. A comparison with the literature showed a correlation between the heterogeneity of the porous media and the difference in removal rates between the column and field scale.

Groundwater pollution assessment in a coastal aquifer in Cape Coast, Ghana

This work presents an assessment of the chemico-physical and microbial quality of water samples from hand-dug wells in the shallow aquifer of three communities neighbouring the University of Cape Coast, Ghana. Sanitary risk inspection was undertaken at each well location and the physical parameters including electrical conductivity, pH, Dissolved Oxygen (DO) and etc. were measured in situ via probes. Microbial groundwater quality was analysed using membrane filtration method. Samples of water were analysed for the pollution indicator anions including chloride and nitrate. In addition, the possible persistence of bacteria in groundwater environments in the absence of predator organisms were studied and results fitted with exponential, second-order polynomial and linear distribution models. Sanitary risk inspection and microbial quality results indicate that all the wells were at risk and polluted with total coliforms from on-site sanitation. Twenty-five percent (7 out of 28) of the wells recorded DO concentration within acceptable limits of drinking water standards (> 5 mg/L). Average chloride concentration, 360.5 mg/L (range: 46 mg/L to 844 mg/L) and average electrical conductivity value of 1.5 mS/cm (range: 213 μS/cm to 2.7 mS/cm) were both higher than WHO recommended limits. Acidic conditions (pH < 6.5) were observed in water samples, indicating mineralisation of the aquifer. The high EC values and chloride content in groundwater were attributable to dry atmospheric aerosol deposition and possible mineral dissolution in the aquifer. Bacteria re-growth experiment results indicate that second-order polynomial distribution best describes bacteria inactivation rates in the absence of antagonist predators in our work. Extrapolation of time for complete inactivation of bacteria under groundwater environment ranged from 0.1 to 4 years indicating bacteria can persist in aquifers for long period of time. It was concluded that all the wells are at risk of pollution and polluted with faecal matter and atmospheric aerosols.

Estimation of Saprolite Thickness Needed to Remove E. coli from Wastewater

Saprolite, weathered bedrock, is being used to dispose of domestic sewage through septic system drainfields, but the thickness of saprolite needed to remove biological contaminants is unknown for most saprolites. This study developed and tested a simple method for estimating the thickness of saprolite needed below septic drainlines to filter E. coli from wastewater using estimates of the volume of pores that are smaller than the length of the coliform (≤10 μm). Particle size distribution (texture) and water retention data were obtained for 12 different saprolites from the Piedmont and Mountain regions of North Carolina (N.C.). Saprolite textures ranged from clay loam to coarse sand. The volume of pores with diameters ≤10 μm were determined by water retention measurements for each saprolite. The data were used in an equation to estimate the saprolite thickness needed to filter E. coli. The estimated saprolite thicknesses ranged from 36 cm in the clay loam to 113 cm for the coarse sand. The average thickness across all samples was 58 cm. Saprolite thickness estimates increased as silt percentage decreased and as sand percentage and in situ saturated hydraulic conductivity increased. Silt percentage may be most useful for estimating appropriate saprolite thicknesses in the field.

Deposition and mobilization of viruses in unsaturated porous media: Roles of different interfaces and straining

The vadose zone is the first natural layer preventing groundwater pollution. Understanding virus transport and retention in the vadose zone is necessary. The effects of different interfaces and mechanisms on virus transport and retention were investigated by studying Escherichia coli phage migration in laboratory-scale columns under unsaturated conditions. The E. coli phage was used as a model virus. Colloid filtration theory, extended Derjagin-Landau-Verwey-Overbeek theory and two-site kinetic deposition model were used to calculate fitted parameters and interaction energies to assess virus retention at different interfaces. The collector diameters and the size of E. coli phages in the influent and effluent were compared to assess the effect of straining. The results indicated that the roles of solid-water interfaces (SWIs) and air-water interfaces (AWIs) in retaining E. coli phages are strongly controlled by the moisture content and hydrochemical conditions. Decreasing the moisture content and increasing the ionic strength (IS) of the suspension increased E. coli phage retention. At suspension ISs of 0.01 or 0.03 M and various moisture contents, E. coli phages were mainly retained at the SWIs rather than AWIs. When the IS was increased to 0.06 M, the viruses were strongly retained by becoming attached to both SWIs and AWIs. The role of straining in virus retention could not be ignored. Viruses were retained more at the SWIs and less straining occurred under acidic conditions than under neutral or alkaline conditions. This was mainly because of the effects of the pH and IS on surface charges and the model virus particle size. This study has important implications for modeling and predicting virus transport in soil affected by rainfall, snowmelt, and human activities (e.g., irrigation and artificial groundwater recharging).

Combining multi-isotopic and molecular source tracking methods to identify nitrate pollution sources in surface and groundwater

Nitrate (NO₃^-) pollution adversely impacts surface and groundwater quality. In recent decades, many countries have implemented measures to control and reduce anthropogenic nitrate pollution in water resources. However, to effectively implement mitigation measures at the origin of pollution,the source of nitrate must first be identified. The stable nitrogen and oxygen isotopes of NO₃^- (ẟ¹⁵N and ẟ¹⁸O) have been widely used to identify NO₃^- sources in water, and their combination with other stable isotopes such as boron (ẟ¹¹B) has further improved nitrate source identification. However, the use of these datasets has been limited due to their overlapping isotopic ranges, mixing between sources, and/or isotopic fractionation related to physicochemical processes. To overcome these limitations, we combined a multi-isotopic analysis with fecal indicator bacteria (FIB) and microbial source tracking (MST) techniques to improve nitrate origin identification. We applied this novel approach on 149 groundwater and 39 surface water samples distributed across Catalonia (NE Spain). A further 18 wastewater treatment plant (WWTP) effluents were also isotopically and biologically characterized. The groundwater and surface water results confirm that isotopes and MST analyses were complementary and provided more reliable information on the source of nitrate contamination. The isotope and MST data agreed or partially agreed in most of the samples evaluated (79 %). This approach was especially useful for nitrate pollution tracing in surface water but was also effective in groundwater samples influenced by organic nitrate pollution. Furthermore, the findings from the WWTP effluents suggest that the use of literature values to define the isotopic ranges of anthropogenic sources can constrain interpretations. We therefore recommend that local sources be isotopically characterized for accurate interpretations. For instance, the detection of MST inferred animal influence in some WWTP effluents, but the ẟ¹¹B values were higher than those reported in the literature for wastewater. The results of this study have been used by local water authorities to review uncertain cases and identify new vulnerable zones in Catalonia according to the European Nitrate Directive (91/676/CEE).

Interactions between Escherichia coli survival and manganese and iron oxides in water under freeze-thaw

Pathogenic survivals were dramatically affected by Fe³⁺ and Mn²⁺ under freeze-thaw (FT), and the dissolutions of manganese and iron oxides (MIOs) were also accelerated under FT. But the mutual influences of pathogenic bacterial survival and MIOs under FT have not been profoundly explored yet. In this work, aqueous systems containing Escherichia coli as well as synthetic ferrihydrite (Fh) and manganese dioxide (MnO₂) were experimented under simulated FT cycles to study the mutual influences of metal oxides and bacteria survival while oxide dissolutions and appearances, bacterial morphology and activities (survival number, cell surface hydrophobicity (CSH) and superoxide dismutase (SOD)) were obtained. The results showed that broken E. coli cells by ice growth were observed, but both oxides promoted E. coli survival under FT stress and prolonged bacterial survival time by 1.2-2.9 times, which were mainly attributed to the release of Fe³⁺ and Mn²⁺ caused by FT. The dissolutions of Fh and MnO₂ under FT, which took place at a low level in absence of E. coli cells, were markedly enhanced with bacterial interferences by 2-8 times and higher dissolved manganese concentrations were detected than iron. This was probably because that concentrated organic matters which were released from broken cells, rejected into unfrozen liquid layer and acted as electron donors and ligands to oxide dissolution. Compared with Fh system, more significant promotion of E. coli survival under FT in MnO₂ systems were found because of more SOD generations associated with high dissolved manganese concentrations and the stronger cellular protection by MnO₂ aggregations. The results suggested that FT significantly influenced the interactions between metal oxides and bacterial in water, resulting to changes in pathogen activity and metal element cycling.

Efficiency of saprolite for removing E. coli from simulated wastewater

Saprolite, weathered bedrock, is being used to dispose of domestic sewage through septic system drainfields, but its ability to remove coliforms is unknown. This study determined if Escherichia coli could be removed by a sandy loam saprolite material. Triplicate columns containing saprolite were prepared with lengths of 30, 45, and 60 cm. A 215-mL solution containing 1 × 10⁵ CFU/100 mL of non-toxic E. coli was applied to the top of each column for 5 days/week for 13 weeks, and selected outflow samples were analyzed for E. coli. Control columns had only tap water applied to them at the same time. Significantly higher (p ≤ 0.10 compared to controls) E. coli concentrations were only detected in samples collected at the end of week 3 for the 30-cm columns and week 4 for the 45-cm columns. E. coli concentrations were small and ranged from approximately 2 to 3 MPN/100 mL. No E. coli were detected in any outflow from the 60-cm columns. From weeks 5 to 13, E. coli concentrations from all columns were either undetectable or not significantly different from the control. The results showed that 60 cm of sandy loam saprolite was sufficient for the removal of E. coli from simulated wastewater.

Vertical distribution and affecting factors of Escherichia coli over a 0-400 cm soil profile irrigated with sewage effluents in northern China

Quantification and evaluation of the spatial distribution and the primary factors that affect Escherichia coli (E. coli) distribution in soils is important to assess soil pollution and potential contamination of groundwater. However, little information is available on distribution of E. coli in deep soil layers. To analyze the spatial distribution and factors affecting E. coli over a 0-400 cm soil profile, soil samples were collected from two land use type in the sewage irrigation fields. The primary factors dominating the spatial distribution of E. coli were quantified by the model of principal component analysis with multiple linear regression (PCA-MLR). The results indicated that the number of E. coli under cropland decreased greatly with soil depth. The average number of E. coli over the 0-400 cm profile under forestland was 49 × 10⁴ colony-forming unit/g (cfu/g), which was significantly higher than that under cropland (20 × 10⁴ cfu/g). For forestland and cropland, the average number of E. coli at depths of 300-400 cm decreased by 85% and 88%, respectively, compared to that at depths of 0-100 cm. The presence of E. coli at the depths of 300-400 cm was at high level (forestland: 3 × 10⁴ cfu/g; cropland: 2 × 10⁴ cfu/g) for the potential risks of shallow groundwater. The PCA-MLR model estimated that the factors of soil organism, soil salt and land type use contributed 28%, 29% and 43%, respectively, to the distribution of E. coli. According to the Monte Carlo simulation, the average number of E. coli over the 0-400 cm profile was 46 ± 17 × 10⁴ cfu/g in the sewage irrigated area, and the interval distribution with a probability of 95% varied between 14 × 10⁴ cfu/g and 78 × 10⁴ cfu/g. The findings of this study are useful for understanding negative effects of sewage irrigation on pathogens in deep soil and are critical to assess the potential risks of groundwater pollution.

Anionic nanoparticle and microplastic non-exponential distributions from source scale with grain size in environmental granular media

Nanoparticle and microplastic (colloid) transport behaviors impact strategies for groundwater protection and remediation. Complex colloid transport behaviors of anionic nano- and micro-sized colloids have been previously elucidated via independent experiments in chemically-cleaned and amended granular media with grain sizes in the range of fine to coarse sand (e.g., 200-1000 μm). Such experiments show that under conditions where a repulsive barrier was present in colloid-collector interactions (unfavorable conditions), the distribution of retained colloids down-gradient from their source deviates from the exponential decrease expected from compounded loss across a series of collectors (grains). Previous experiments have not examined the impact of colloid size or granular media grain size on colloid distribution down-gradient from their source, particularly in streambed-equilibrated granular media. To address this gap, a field transport experiment in constructed wetland stream beds to distances up to 20 m were conducted for colloids ranging in size from micro to nano (60 nm-7 μm) in streambed-equilibrated pea gravel and sand (4200 and 420 μm mean grain sizes, respectively). All colloid sizes showed non-exponential (hyper-exponential) distributions from source, over meter scales in pea gravel versus cm scales reported for fine sand. Colloids in the ca. 1 μm size range were most mobile, as expected from mass transfer to surfaces and interaction with nanoscale heterogeneity. The distance over which non-exponential colloid distribution occurred increased with media grain size, which carries implications for the potential mechanism driving non-exponential colloid distribution from source, and for strategies to predict transport.

The response of nitrogen cycling and bacterial communities to E. coli invasion in aquatic environments with submerged vegetation

The effects of exogenous Escherichia coli on nitrogen cycling (N-cycling) in freshwater remains unclear. Thus, seven ecosystems, six with submerged plants-Potamogeton crispus (PC) and Myriophyllum aquaticum (MA)-and one with no plants were set up. Habitats were assessed before and after E. coli addition (10⁷ colony-forming units/mL). E. coli colonization of freshwater ecosystems had significant effects on bacterial community structure in plant surface biofilms and surface sediments (ANOVA, P < 0.05). It reduced the relative abundance of nitrosification bacteria (-70.94 ± 26.17%) and nitrifiers (-47.86 ± 23.68%) in biofilms which lead to significant reduction of ammoxidation in water (P < 0.05). The N-cycling intensity from PC systems was affected more strongly by E. coli than were MA systems. Furthermore, the coupling coefficient of exogenous E. coli to indigenous N-cycling bacteria in sediments (6.061, average connectivity degree) was significantly weaker than that in biofilms (9.852). Additionally, at the genus level, E. coli were most-closely associated with N-cycling bacteria such as Prosthecobacter, Hydrogenophaga, and Bacillus in sediments and biofilms according to co-occurrence bacterial network (Spearman). E. coli directly changed their abundance, so that the variability of species composition of N-cycling bacterial taxa was triggered, as well. Overall, exogenous E. coli repressed ammoxidation, but promoted ammonification and denitrification. Our results provided new insights into how pathogens influence the nitrogen cycle in freshwater ecosystems.

Effect of crude oil-induced water repellency on transport of Escherichia coli and bromide through repacked and physically-weathered soil columns

Knowledge of the transport and fate of pathogenic Escherichia coli, especially in the areas contaminated with crude oil, is required to assess contamination of shallow groundwater resources. The present study aims to investigate the effect of crude oil-mediated water repellency on the movement of nalidixic acid-resistant Escherichia coli strain (E. coli NAR) and bromide (Br) as an inert tracer in two soil types. The soils were contaminated at three levels of 0, 0.5 and 1% w/w of total petroleum hydrocarbons (TPHs) using crude oil. Steady-state saturated flow in the soil columns was controlled using a tension infiltrometer. Leaching experiments were conducted through the columns of repacked (un-weathered) and physically-weathered clay loam (CL) and sandy loam (SL) soils. The columns leachate was sampled at specific times for 4 pore volumes. The shape of breakthrough curves for the E. coli NAR and Br depended on soil texture and structure and the TPHs level. Preferential flow in the crude oil-mediated water-repellent soils facilitated the transport of contaminants especially E. coli NAR. Filtration coefficient and relative adsorption index of bacteria were greatest in the repacked CL soils and were lowest in the weathered SL soils. Discontinuity of soil pores and lower flow velocity resulted in greater filtration of E. coli NAR in the repacked CL soil than other treatments. Physical weathering induced the formation of aggregates which reduced soil particle surfaces available for retention of water-repellent oil and contaminants. Movement of both bacteria and Br tracer in the weathered SL soil with 1% TPHs was higher than other treatments. This finding was attributed to low specific surface area, continuity of the pores and water repellency-mediated preferential pathways in the weathered SL soil columns. Our findings implied that shallow groundwater resources could be very sensitive to microbial contamination particularly in the oil-mediated water-repellent soils.

Translocation of Phytoliths Within Natural Soil Profiles in Northeast China

Phytoliths are a reliable paleovegetation proxy and have made an important contribution to paleoclimatic studies. However, little is known about the depositional processes affecting soil phytoliths, which limits their use for paleoclimate and paleovegetation reconstructions. Here, we present the results of a study of the vertical translocation characteristics of phytoliths in 40 natural soil profiles in Northeast China. The results show that phytolith concentration decreases within the humic horizon of the soil profiles and that ∼22% of the phytoliths are translocated below the surface of the studied soils. In addition, we find that the translocation rate of phytoliths varies markedly with phytolith type and that phytolith size and aspect ratio also have a significant effect. Phytoliths with length >30 μm and with aspect ratio >2 and those with length <20 μm and aspect ratio <2 are preferentially translocated compared to those with length >25 μm and aspect ratio <2. Our results demonstrate that differential translocation of phytoliths within soil profiles should be considered when using soil phytoliths for paleoclimate and paleovegetation reconstruction.

Impact of domestic wells and hydrogeologic setting on water quality in peri-urban Dar es Salaam, Tanzania

In densely populated urban areas of many low-income countries, water scarcity, poor water quality, and inadequate wastewater management present complex challenges to ensuring health and wellbeing. This study was conducted in an impoverished peri-urban community in Dar es Salaam, Tanzania that experiences water scarcity and relies on domestic wells for drinking water. The objective of this study was to identify the sources of domestic well water contamination and assess the relationship and association of water contamination with three variables 1) the proximity of the well to a sanitation system, 2) well age, and 3) well depth. Out of the 71 wells tested, samples from >80% of wells contained Escherichia coli (E. coli) and 58% had nitrate levels above WHO guidelines. The average concentration of total dissolved solids (TDS) was 882 mg/L, which exceeded the WHO guideline of 600 mg/L. Bivariate correlation analysis showed a strong correlation between water contamination and proximity of the well to a sanitation system along with well depth. Univariate regression analysis confirmed the association of contaminants with distance of a well from a sanitation system and well depth (p < 0.05) but age of the well did not show any significant influence on water quality. Our findings indicate significant contamination of wells from nearby septic tanks and pit latrines. New regulatory mandates for the distance of domestic wells from sanitation systems are essential to prevent groundwater contamination and to protect human health.

Event-transport of beta-d-glucuronidase in an agricultural headwater stream: Assessment of seasonal patterns by on-line enzymatic activity measurements and environmental isotopes

Understanding the fate of fecal pollution in the landscape is required for microbial risk analysis. The aim of this study was to assess the patterns and dynamics of beta-d-glucuronidase (GLUC), which has been suggested as a surrogate for fecal pollution monitoring, in a stream draining an agricultural headwater catchment. Automated enzymatic on-site measurements of stream water and sediments were made over two years (2014-2016) to quantify the sources and pathways of GLUC in a stream. The event water fraction of streamflow was estimated by stable isotopes. Samples from field sediments on a hillslope, streambed sediment and stream water were analyzed for GLUC and with a standard E. coli assay. The results showed ten times higher GLUC and E. coli concentrations during the summer than during the winter for all compartments (field and streambed sediments and stream water). The E. coli concentrations in the streambed sediment were approximately 100 times those of the field sediments. Of the total GLUC load in the study period, 39% were transported during hydrological events (increased streamflow due to rainfall or snowmelt); of these, 44% were transported when the stream contained no recent rainwater. The results suggested that a large proportion of the GLUC and E. coli in the stream water stemmed from resuspended streambed sediments. Moreover, the results strongly indicated the existence of remnant populations of GLUC-active organisms in the catchment.

Methodology for Determining the Die-Off Coefficient of Enterococci in the Conditions of Transport through the Karst Aquifer—Case Study: Bokanjac–Poličnik Catchment

This paper presents the methodology for determining the die-off coefficient of faecal indicator bacteria (enterococci) when transported in a karst environment. The main problem in exploring karst environments, which this methodology strives to cope with, is lack of field measurements, poor data on karst rock formation, fractures and channels within it, and groundwater level dynamics. The analysed karst catchment (Bokanjac–Poličnik) is situated in the hinterland of the city of Zadar (Republic of Croatia) and covers an area of 235.07 km2. In the water supply wells within the analysed catchment, a frequent occurrence of enterococci was observed. The proposed methodology consists of two basic steps. Preliminary analyses as the initial step were used in the accumulation of certain assumptions related to the detection of increased concentrations of enterococci as well as in determination of the potential source of pollution. In the second step, the analytical model was constructed with the aim of resolving processes of sorption and die-off and determining the dominant factor in the process of natural removal of enterococci when transported in karst environment. Within the model, two parts of the pollutant transport are integrated: vertical percolation and horizontal seepage flow and transport. The mean value of the total die-off coefficient by transport through the unsaturated zone in the analysed case is k t o t = 8.25. Within the saturated zone the total die-off coefficient k t o t is within the limits of 0.1 and 0.5.

Natural freeze-thaw cycles may increase the risk associated with Salmonella contamination in surface and groundwater environments

Groundwater contamination by bacteria poses a serious threat to our drinking water supplies. In cold climate regions, microorganisms introduced to upper soil layers by spreading of animal manure are subject to low temperatures and multiple cycles of freezing and thawing at the beginning of winter and during spring melt. We investigated the influence of temperature fluctuations around the freezing point, known as freeze-thaw (FT), on the inactivation rates, growth, and biofilm formation of a manure-isolated strain of Salmonella typhimurium. Moreover, the effects of FT on the transport characteristics of S. typhimurium in quartz sand were monitored in model porewater solutions of two different ionic strengths (IS: 10 and 100 mM KCl) and two different humic acid (HA) concentrations (1 and 5 mg/L). Increasing numbers of FT cycles were found to decrease the deposition of S. typhimurium onto quartz sand and increase the percentage of detached cells in sand-packed column experiments. Based on the calculated bacterial attachment efficiencies, the predicted minimum setback distances between the location of water supply wells and manure spreading activities are higher when the effects of FT are taken into consideration. While FT treatment significantly affected cell viability (in the presence of HA), most cells were in a viable but non-culturable (VBNC) state with compromised ability to form biofilm. This investigation demonstrates the effects of spring temperature variations in upper soil layers on S. typhimurium properties and the potential increased risk of bacterial contamination in representative aquifer environments in cold climate regions.

Effect of Artificial Solar Radiation on the Die-Off of Pathogen Indicator Organisms in Urban Floods

In the last decade, flooding has caused the death of over 60,000 people and affected over 900 million people globally. This is expected to increase as a result of climate change, increased populations and urbanisation. Floods can cause infections due to the release of water-borne pathogenic microorganisms from surcharged combined sewers and other sources of fecal contamination. This research contributes to a better understanding of how the occurrence of water-borne pathogens in contaminated shallow water bodies is affected by different environmental conditions. The inactivation of fecal indicator bacteria Escherichia coli was studied in an open stirred reactor, under controlled exposure to simulated sunlight, mimicking the effect of different latitudes and seasons, and different concentrations of total suspended solids (TSS) corresponding to different levels of dilution and runoff. While attachment of bacteria on the solid particles did not take place, the decay rate coefficient, k (d^-1), was found to depend on light intensity, I (W m^-2), and duration of exposure to sunlight, T (h d^-1), in a linear way (k = k _D+ 0.03·I and k = k _D+ 0.65·T, respectively) and on the concentration of TSS (mg L^-1), in an inversely proportional exponential way (k = k _D+ 14.57·e^-0.02·[TSS] ). The first-order inactivation rate coefficient in dark conditions, k _D= 0.37 d^-1, represents the effect of stresses other than light. This study suggests that given the sunlight conditions during an urban flood, and the concentration of indicator organisms and TSS, the above equations can give an estimate of the fate of selected pathogens, allowing rapid implementation of appropriate measures to mitigate public health risks.

World's Largest Mass Bathing Event Influences the Bacterial Communities of Godavari, a Holy River of India

Kumbh Mela is one of the largest religious mass gathering events (MGE) involving bathing in rivers. The exponential rise in the number of devotees, from around 0.4 million in 1903 to 120 million in 2013, bathing in small specified sites can have a dramatic impact on the river ecosystem. Here, we present the spatiotemporal profiling of bacterial communities in Godavari River, Nashik, India, comprising five sites during the Kumbh Mela, held in 2015. Assessment of environmental parameters indicated deterioration of water quality. Targeted amplicon sequencing demonstrates approximately 37.5% loss in microbial diversity because of anthropogenic activity during MGE. A significant decrease in phyla viz. Actinobacteria, Chloroflexi, Proteobacteria, and Bacteroidetes was observed, while we noted substantial increase in prevalence of the phylum Firmicutes (94.6%) during MGE. qPCR estimations suggested nearly 130-fold increase in bacterial load during the event. Bayesian mixing model accounted the source of enormous incorporation of bacterial load of human origin. Further, metagenomic imputations depicted increase in virulence and antibiotic resistance genes during the MGE. These observations suggest the striking impact of the mass bathing on river ecosystem. The subsequent increase in infectious diseases and drug-resistant microbes pose a critical public health concern.

Modeling the Impact of Land Use Change on Basin-scale Transfer of Fecal Indicator Bacteria: SWAT Model Performance

Land use change from annual crops to commercial tree plantations can modify flow and transport processes at the watershed scale, including the fate and transport of fecal indicator bacteria (FIB), such as . The Soil and Water Assessment Tool (SWAT) is a useful means for integrating watershed characteristics and simulating water and contaminants. The objective of this study was to provide a comprehensive assessment of the impact of land use change on microbial transfer from soils to streams using the SWAT model. This study was conducted for the Houay Pano watershed located in northern Lao People's Democratic Republic. Under the observed weather conditions, the SWAT model predicted a decrease from 2011 to 2012 and an increase from 2012 to 2013 in surface runoff, suspended solids, and transferred from the soil surface to streams. The amount of precipitation was important in simulating surface runoff, and it subsequently affected the fate and transport of suspended solids and bacteria. In simulations of identical weather conditions and different land uses, fate and transport was more sensitive to the initial number of than to its drivers (i.e., surface runoff and suspended solids), and leaf area index was a significant factor influencing the determination of the initial number of on the soil surface. On the basis of these findings, this study identifies several limitations of the SWAT fertilizer and bacteria modules and suggests measures to improve our understanding of the impacts of land use change on FIB in tropical watersheds.

Temporal Variability of Faecal Contamination from On-Site Sanitation Systems in the Groundwater of Northern Thailand

We investigated the impacts of on-site sanitation systems to local groundwater. In this year-long study, we monitored the response of faecal contamination levels to hydroclimatological factors including rainfall and groundwater table. Concentration of faecal indicators-E. coli (ESC), Enterococcus (ENT), nitrate-in thirteen pairs of shallow and deep wells were determined every 7-14 days. All samples from shallow wells were tested positive for faecal contamination (ESC and ENT > 1 MPN/100 mL) but concentration varies. A maximum of 24,000 MPN/100 mL were recorded in some shallow wells. Water from deep wells showed lower susceptibility to contamination with only 4 and 23% of samples tested positive for ESC and ENT, respectively. Concentrations of ESC and ENT were lower too, with a maximum of 5 MPN/100 mL and 28 MPN/100 mL, respectively. Fluctuation in contamination among the wells was described by four archetypal responses to hydroclimatological forcing: (i) flushing during the onset of wet season, (ii) dilution over the course of the wet season, (iii) concentration during the dry season, and (iv) synoptic response to storms. Previous studies attempting to link the prevalence of faecal/waterborne diseases and temporal factors (e.g., dry vs wet season) have produced differing outcomes. Our study may help explain the relevant hydrological mechanisms leading to these varying observations. Presently, most communities in Thailand have access to 'improved' sanitation systems. However, due to the unsustainable implementation of these systems, the otherwise viable drinking-water resources in the form of the abundant local groundwater has become a genuine health hazard.

Persistence of Salmonella Typhimurium in Well Waters from a Rural Area of Changchun City, China

Salmonella-contaminated well water could cause major infection outbreaks worldwide, thus, it is crucial to understand their persistence in those waters. In this study, we investigated the persistence of Salmonella enterica serovar Typhimurium in 15 well waters from a rural area of Changchun City, China. Results illustrated that the time to reach detection limit (ttd), first decimal reduction time (δ), and the shape parameter (p) ranged from 15 to 80 days, from 5.6 to 66.9 days, and from 0.6 to 6.6, respectively. Principal component analysis showed that ttds of S. Typhimurium were positively correlated with total organic carbon, pH, NH₄⁺–N, and total phosphate. Multiple stepwise regression analysis revealed that ttds could be best predicted by NH₄⁺–N and pH. Canonical correspondence analysis and variation partition analysis revealed that NH₄⁺–N and pH, and the rest of the water parameters, could explain 27.60% and 28.15% of overall variation of the survival behavior, respectively. In addition, ttds were found to be correlated (p < 0.01) with δ and p. Our results showed that the longer survival (>2.5 months) S. Typhimurium could constitute an increased health risk to the local communities, and provided insights into the close linkage between well water quality and survival of S. Typhimurium.

Microbial Groundwater Quality Status of Hand-Dug Wells and Boreholes in the Dodowa Area of Ghana

To assess the suitability of water sources for drinking purposes, samples were taken from groundwater sources (boreholes and hand-dug wells) used for drinking water in the Dodowa area of Ghana. The samples were analyzed for the presence of fecal indicator bacteria (Escherichia coli) and viruses (Adenovirus and Rotavirus), using membrane filtration with plating and glass wool filtration with quantitative polymerase chain reaction (PCR), respectively. In addition, sanitary inspection of surroundings of the sources was conducted to identify their vulnerability to pollution. The presence of viruses was also assessed in water samples from the Dodowa River. More than 70% of the hand-dug wells were sited within 10 m of nearby sources of contamination. All sources contained E. coli bacteria, and their numbers in samples of water between dug wells and boreholes showed no significant difference (p = 0.48). Quantitative PCR results for Adenovirus indicated 27% and 55% were positive for the boreholes and hand-dug wells, respectively. Samples from all boreholes tested negative for the presence of Rotavirus while 27% of the dug wells were positive for Rotavirus. PCR tests of 20% of groundwater samples were inhibited. Based on these results we concluded that there is systemic microbial and fecal contamination of groundwater in the area. On-site sanitation facilities, e.g., pit latrines and unlined wastewater drains, are likely the most common sources of fecal contamination of groundwater in the area. Water abstracted from groundwater sources needs to be treated before use for consumption purposes. In addition, efforts should be made to delineate protected areas around groundwater abstraction points to minimize contamination from point sources of pollution.

Exploring links between water quality and E. coli O157:H7 survival potential in well waters from a rural area of southern Changchun City, China

Waterborne infectious disease outbreak associated with well water contamination is a worldwide public health issue, especially for rural areas in developing countries. In the current study, we characterized 20 well water samples collected from a rural area of southern Changchun city, China, and investigated the survival potential of Escherichia coli O157:H7 in those water samples. The results showed that nitrate and ammonia concentrations in some well water samples exceed the corresponding China drinking water standards, indicating potential contamination by local agricultural farms. Our results also revealed that the average survival time (ttd) of E. coli O157:H7 in all well water samples was 30.09 days, with shortest and longest ttd being 17.95 and 58.10 days, respectively. The ttds were significantly correlated with pH and the ratio of total nitrogen to total phosphorus. In addition, it was found that the shape parameter (p) and first decimal reduction parameter (δ) were negatively (P < 0.05) and positively (P < 0.05) correlated to ttd, respectively. Our study showed that E. coli O157:H7 could survive up to two months in well water, suggesting that this pathogen could constitute a great public health risk.

The public health significance of latrines discharging to groundwater used for drinking

Faecal contamination of groundwater from pit latrines is widely perceived as a major threat to the safety of drinking water for several billion people in rural and peri-urban areas worldwide. On the floodplains of the Ganges-Brahmaputra-Meghna delta in Bangladesh, we constructed latrines and monitored piezometer nests monthly for two years. We detected faecal coliforms (FC) in 3.3-23.3% of samples at four sites. We differentiate a near-field, characterised by high concentrations and frequent, persistent and contiguous contamination in all directions, and a far-field characterised by rare, impersistent, discontinuous low-level detections in variable directions. Far-field FC concentrations at four sites exceeded 0 and 10 cfu/100 ml in 2.4-9.6% and 0.2-2.3% of sampling events respectively. The lesser contamination of in-situ groundwater compared to water at the point-of-collection from domestic wells, which itself is less contaminated than at the point-of-consumption, demonstrates the importance of recontamination in the well-pump system. We present a conceptual model comprising four sub-pathways: the latrine-aquifer interface (near-field); groundwater flowing from latrine to well (far-field); the well-pump system; and post-collection handling and storage. Applying a hypothetical dose-response model suggests that 1-2% of the diarrhoeal disease burden from drinking water is derived from the aquifer, 29% from the well-pump system, and 70% from post-collection handling. The important implications are (i) that leakage from pit latrines is a minor contributor to faecal contamination of drinking water in alluvial-deltaic terrains; (ii) fears of increased groundwater pollution should not constrain expanding latrine coverage, and (iii) that more attention should be given to reducing contamination around the well-head.

Bacterial mobilization and transport through manure enriched soils: Experiment and modeling

A precise evaluation of bacteria transport and mathematical investigations are useful for best management practices in agroecosystems. In this study, using laboratory experiments and modeling approaches, we assess the transport of bacteria released from three types of manure (cow, sheep, and poultry) to find the importance of the common manures in agricultural activities in soil and water pollution. Thirty six intact soil columns with different textures (sandy, loamy, and silty clay loam) were sampled. Fecal coliform leaching from layers of the manures on the soil surface was conducted under steady-state saturated flow conditions at 20 °C for up to four Pore Volumes (PVs). Separate leaching experiments were conducted to obtain the initial concentrations of bacteria released from the manures (Co). Influent (Co) and effluent (C) bacteria concentrations were measured by the plate-count method and the normalized concentrations (C/C0) were plotted versus PV representing the breakthrough curves (BTCs). Transport parameters were predicted using the attachment/detachment model (two-kinetic site) in HYDRUS-1D. Simulations fitted well the experimental data (R² = 0.50-0.96). The attachment, detachment, and straining coefficients of bacteria were more influenced by the soils treated with cow manure compared to the sheep and poultry manures. Influent curves of fecal coliforms from the manures (leached without soil) illustrated that the poultry manure had the highest potential to pollute the effluent water from the soils in term of concentration, but the BTCs and simulated data related to the treated soils illustrated that the physical shape of cow manure was more important to both straining and detachment of bacteria back into the soil solution. Detachment trends of bacteria were observed through loam and silty clay loam soils treated with cow manure compared to the cow manure enriched sandy soil. We conclude that management strategies must specifically minimize the effect of fecal coliform concentrations before field application, especially for the combination of poultry and cow manures, which has higher solubility and tailing behavior, respectively. Interestingly, the addition of sheep manure with all three soils had the lowest mobilization of bacteria. We also suggest studying the chemistry of soil solution affected by manures to present all relevant information which affect bacterial movement through soils during leaching.

Quantitative Effects of Biochar Oxidation and Pyrolysis Temperature on the Transport of Pathogenic and Nonpathogenic Escherichia coli in Biochar-Amended Sand Columns

The present study quantifies the transport of Escherichia coli pathogenic O157:H7 and nonpathogenic K12 strains in water-saturated Quincy sand (QS) columns amended with oxidized (OX) or unoxidized (UO) pine wood (PW) or pine bark (PB) biochar produced at either 350 or 600 °C. Our results showed that (1) the addition of oxidized biochar into QS columns enhanced the transport of E. coli O157:H7 by 3.1 fold compared to the unoxidized counterparts, likely because of an increase in the repulsive forces due to their higher negative charge densities. (2) The retention of E. coli O157:H7 was 3.3 fold higher than that of E. coli K12 in all biochar-amended sand columns. (3) Increased application rates of unoxidized PW600 biochar from 0 to 20 wt % led to a reduction in the transport of E. coli O157:H7 and K12 from 98 to 10% and from 95 to 70%, respectively. Our data showed that mixing sand with PW350-UO at a 20 wt % application rate almost completely retained the pathogenic E. coli in the subsurface, suggesting that utilizing sand mixed with biochar can act as a promising biofilter capable of protecting natural aquafers from pathogens.

Microbial Remobilisation on Riverbed Sediment Disturbance in Experimental Flumes and a Human-Impacted River: Implication for Water Resource Management and Public Health in Developing Sub-Saharan African Countries

Resuspension of sediment-borne microorganisms (including pathogens) into the water column could increase the health risk for those using river water for different purposes. In the present work, we (1) investigated the effect of sediment disturbance on microbial resuspension from riverbed sediments in laboratory flow-chambers and in the Apies River, Gauteng, South Africa; and (2) estimated flow conditions for sediment-borne microorganism entrainment/resuspension in the river. For mechanical disturbance, the top 2 cm of the sediment in flow-chambers was manually stirred. Simulating sudden discharge into the river, water (3 L) was poured within 30 s into the chambers at a 45° angle to the chamber width. In the field, sediment was disturbed by raking the riverbed and by cows crossing in the river. Water samples before and after sediment disturbance were analysed for Escherichia coli. Sediment disturbance caused an increase in water E. coli counts by up to 7.9-35.8 times original values. Using Shields criterion, river-flow of 0.15-0.69 m³/s could cause bed particle entrainment; while ~1.57-7.23 m³/s would cause resuspension. Thus, sediment disturbance in the Apies River would resuspend E. coli (and pathogens), with possible negative health implications for communities using such water. Therefore, monitoring surface water bodies should include microbial sediment quality.

Effect of Low Energy Waves on the Accumulation and Transport of Fecal Indicator Bacteria in Sand and Pore Water at Freshwater Beaches

Elevated fecal indicator bacteria (FIB) in beach sand and pore water represent an important nonpoint source of contamination to surface waters. This study examines the physical processes governing the accumulation and distribution of FIB in a beach aquifer. Field data indicate E. coli and enterococci can be transported 1 and 2 m, respectively, below the water table. Data were used to calibrate a numerical model whereby FIB are delivered to a beach aquifer by wave-induced infiltration across the beach face. Simulations indicate FIB rapidly accumulate in a beach aquifer with FIB primarily associated with sand rather than freely residing in the pore water. Simulated transport of E. coli in a beach aquifer is complex and does not correlate with conservative tracer transport. Beaches with higher wave-induced infiltration rate and vertical infiltration velocity (i.e., beaches with higher beach slope and wave height, and lower terrestrial groundwater discharge) had greater E. coli accumulation and E. coli was transported deeper below the beach face. For certain beach conditions, the amount of FIB accumulated in sand over 5-6 days was found to be sufficient to trigger a beach advisory if eroded to surface water.

Experimental and Numerical Investigations of Silver Nanoparticle Transport under Variable Flow and Ionic Strength in Soil

Unsaturated column experiments were conducted with an undisturbed loamy sand soil to investigate the influence of flow interruption (FI) and ionic strength (IS) on the transport and retention of surfactant-stabilized silver nanoparticles (AgNP) and the results were compared to those obtained under continuous flow conditions. AgNP concentrations for breakthrough curves (BTCs) and retention profiles (RPs) were analyzed by ICP-MS. Experimental results were simulated by the numerical code HP1 (Hydrus-PhreeqC) with the DLVO theory, extended colloid filtration theory and colloid release model. BTCs of AgNP showed a dramatic drop after FI compared to continuous flow conditions. Evaporation increased due to FI, resulting in increased electrical conductivity of the soil solution, which led to a totally reduced mobility of AgNP. A reduction of IS after FI enhanced AgNP mobility slightly. Here the strongly increased Al and Fe concentration in the effluent suggested that soil colloids facilitated the release of AgNP (cotransport). The numerical model reproduced the measured AgNP BTCs and indicated that attachment to the air-water interface (AWI) occurring during FI was the key process for AgNP retention.

Evaluation of β-d-glucuronidase and particle-size distribution for microbiological water quality monitoring in Northern Vietnam

In many karst regions in developing countries, the populations often suffer from poor microbial water quality and are frequently exposed to bacterial pathogens. The high variability of water quality requires rapid assays, but the conventional cultivation-based analysis of fecal indicator bacteria, such as Escherichia coli (E. coli), is very time-consuming. In this respect, the measurement of the enzymatic activity of E. coli could prove to be a valuable tool for water quality monitoring. A mobile automated prototype device was used for the investigation of β-d-glucuronidase (GLUC) activity at a remote karst spring, connected to a sinking surface stream, in Northern Vietnam. To assess the relationship between GLUC activity, discharge dynamics and contamination patterns, multiple hydrological, hydrochemical, physicochemical and microbiological parameters, including discharge, turbidity, particle-size distributions, and E. coli, were measured with high temporal resolution during ten days of on-site monitoring. A complex contamination pattern due to anthropogenic and agricultural activities led to high E. coli concentrations (270 to >24,200 MPN/100ml) and a GLUC activity between 3.1 and 102.2 mMFU/100ml. A strong daily fluctuation pattern of GLUC activity and particle concentrations within small size classes (<10μm) could be observed, as demonstrated by autocorrelations. A Spearman's rank correlation analysis resulted in correlation coefficients of rs=0.56 for E. coli and GLUC activity and rs=0.54 for GLUC activity and the concentration of 2-3μm particles. On an event scale, correlations were found to be higher (rs=0.69 and 0.87, respectively). GLUC activity and E. coli displayed a general contamination pattern, but with significant differences in detail, which may be explained by interferences of e. g. viable but non-culturable cells. Although further evaluations are recommended, GLUC activity is a promising, complementary parameter for on-site and near real-time water quality monitoring.

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.

Impact of manure-related DOM on sulfonamide transport in arable soils

Field application of livestock manure introduces colloids and veterinary antibiotics, e.g. sulfonamides (SAs), into farmland. The presence of manure colloids may potentially intensify the SAs-pollution to soils and groundwater by colloid-facilitated transport. Transport of three SAs, sulfadiazine (SDZ), sulfamethoxypyridazine (SMPD), and sulfamoxole (SMOX), was investigated in saturated soil columns with and without manure colloids from sows and farrows, weaners, and fattening pigs. Experimental results showed that colloid-facilitated transport of SMOX was significant in the presence of manure colloids from fattening pigs with low C/N ratio, high SUVA280nm and protein C, while manure colloids from sows and farrows and weaners had little effect on SMOX transport. In contrast, only retardation was observed for SDZ and SMPD when manure colloids were present. Breakthrough curves (BTCs) of colloids and SAs were replicated well by a newly developed numerical model that considers colloid-filtration theory, competitive kinetic sorption, and co-transport processes. Model results demonstrate that mobile colloids act as carriers for SMOX, while immobile colloids block SMOX from sorbing onto the soil. The low affinity of SMOX to sorb on immobile colloids prevents aggregation and also promotes SMOX's colloid-facilitated transport. Conversely, the high affinity of SDZ and SMPD to sorb on all types of immobile colloids retarded their transport. Thus, manure properties play a fundamental role in increasing the leaching risk of hydrophobic sulfonamides.

Safe distances between groundwater-based water wells and pit latrines at different hydrogeological conditions in the Ganges Atrai floodplains of Bangladesh

BACKGROUND

Groundwater drawn from shallow tubewells in Bangladesh is often polluted by nearby pit latrines, which are commonly used toilets in rural and sub-urban areas of the country.

METHODS

To determine the minimum safe distance of a tubewell from a pit latrine in different hydrogeological conditions of Bangladesh, 20 monitoring wells were installed at three study sites (Manda, Mohanpur and Bagmara) with the vertical and horizontal distances ranging from 18-47 to 2-15 m, respectively. Water samples were collected three times in three seasons and tested for faecal coliforms (FC) and faecal streptococci (FS) as indicators of contamination. Soil samples were analysed for texture, bulk density and hydraulic conductivity following standard procedures. Sediment samples were collected to prepare lithological logs.

RESULTS

When the shallow aquifers at one of the three sites (Mohanpur) were overlained by 18-23-m-thick aquitards, the groundwater of the monitoring wells was found contaminated with a lateral and vertical distances of 2 and 31 m, respectively. However, where the aquitard was only 9 m thick, contamination was found up to lateral and vertical distances of 4.5 and 40.5 m, respectively. The soil textures of all the sites were mainly composed of loam and sandy loam. The hydraulic conductivities in the first aquifer at Manda, Mohanpur and Bagmara were 5.2-7.3, 8.2 and 1.4-15.7 m/h, respectively.

CONCLUSIONS

The results showed that the safe distance from the tubewell to the pit latrine varied from site to site depending on the horizontal and vertical distances of the tubewell as well as hydrogeological conditions of a particular area.

Evaluation of gaseous concentrations, bacterial diversity and microbial quantity in different layers of deep litter system

Objective

An experiment was conducted to investigate the environment of the deep litter system and provided theoretical basis for production.

Methods

The bedding samples were obtained from a pig breeding farm and series measurements associated with gases concentrations and the bacterial diversity as well as the quantity of Escherichia coli, Lactobacilli, Methanogens were performed in this paper.

Results

The concentrations of CO₂, CH₄, and NH₃ in the deep litter system increased with the increasing of depth while the N₂O concentrations increased fiercely from the 0 cm to the −10 cm depth but then decreased beneath the −10 cm depth. Meanwhile, the Shannon index, the dominance index as well as the evenness index at the −20 cm layer was significantly different from the other layers (p<0.05). On the other hand, the quantity of Escherichia coli reached the highest value at the surface beddings and there was a significant drop at the −20 cm layer with the increasing depth. The Lactobacilli numbers increased with the depth from 0 cm to −15 cm and then decreased significantly under the −20 cm depth. The expression of Methanogens reached its largest value at the depth of −35 cm.

Conclusion

The upper layers (0 cm to −5 cm) of this system were aerobic, the middle layers (−10 cm to −20 cm) were micro-aerobic, while that the bottom layers (below −20 cm depth) were anaerobic. In addition, from a standpoint of increasing the nitrification pathway and inhibiting the denitrification pathway, it should be advised that the deep litter system should be kept aerobic.

Quantifying Attachment and Antibiotic Resistance of from Conventional and Organic Swine Manure

Broad-spectrum antibiotics are often administered to swine, contributing to the occurrence of antibiotic-resistant bacteria in their manure. During land application, the bacteria in swine manure preferentially attach to particles in the soil, affecting their transport in overland flow. However, a quantitative understanding of these attachment mechanisms is lacking, and their relationship to antibiotic resistance is unknown. The objective of this study is to examine the relationships between antibiotic resistance and attachment to very fine silica sand in collected from swine manure. A total of 556 isolates were collected from six farms, two organic and four conventional (antibiotics fed prophylactically). Antibiotic resistance was quantified using 13 antibiotics at three minimum inhibitory concentrations: resistant, intermediate, and susceptible. Of the 556 isolates used in the antibiotic resistance assays, 491 were subjected to an attachment assay. Results show that isolates from conventional systems were significantly more resistant to amoxicillin, ampicillin, chlortetracycline, erythromycin, kanamycin, neomycin, streptomycin, tetracycline, and tylosin ( < 0.001). Results also indicate that isolated from conventional systems attached to very fine silica sand at significantly higher levels than those from organic systems ( < 0.001). Statistical analysis showed that a significant relationship did not exist between antibiotic resistance levels and attachment in from conventional systems but did for organic systems ( < 0.001). Better quantification of these relationships is critical to understanding the behavior of in the environment and preventing exposure of human populations to antibiotic-resistant bacteria.

Comparison of the occurrence and survival of fecal indicator bacteria in recreational sand between urban beach, playground and sandbox settings in Toronto, Ontario

While beach sands are increasingly being studied as a reservoir of fecal indicator bacteria (FIB), less is known about the occurrence of FIB in other recreational sands (i.e., sandboxes and playgrounds). In this study, different culture-based FIB enumeration techniques were compared and microbial source tracking assays were conducted on recreational sand samples from beaches, playgrounds and sandboxes around Toronto, ON. FIB were detected in every sand sample (n=104) with concentrations not changing significantly over the five month sampling period. Concentrations of FIB and a gull-specific DNA marker were significantly higher in foreshore beach sands, and indicated these were a more significant reservoir of FIB contamination than sandbox or playground sands. Human- and dog-specific contamination markers were not detected. All culture-based FIB enumeration techniques were consistent in identifying the elevated FIB concentrations associated with foreshore beach sands. However, significant differences between differential agar media, IDEXX and Aquagenx Compartment Bag Test were observed, with DC media and Enterolert being the most sensitive methods to detect Escherichia coli and enterococci, respectively. To better understand the elevated occurrence of E. coli in foreshore sands, microcosm survival experiments were conducted at two different temperatures (15 °C and 28 °C) using non-sterile saturated foreshore beach sands collected from two urban freshwater beaches with different sand type (fine grain and sand-cobble). Microcosms were inoculated with a mixture of eight sand-derived E. coli strains and sampled over a 28-day period. E. coli levels were found to decline in all microcosms, although survival was significantly greater in the finer sand and at the cooler temperature (15 °C). These results indicate that FIB can be widespread in any type of recreational sand and, while E. coli can survive for many weeks, it is most likely to accumulate in cooler fine-grain sand as occurs below the foreshore sand surface.

Critical role of surface roughness on colloid retention and release in porous media

This paper examines the critical role of surface roughness (both nano- and micro-scale) on the processes of colloid retention and release in porous media under steady-state and transient chemical conditions. Nanoscale surface roughness (NSR) in the order of a few nanometers, which is common on natural solid surfaces, was incorporated into extended-DLVO calculations to quantify the magnitudes of interaction energy parameters (e.g. the energy barrier to attachment, ΔΦa , and detachment, ΔΦd , from a primary minimum). This information was subsequently used to explain the behavior of colloid retention and release in column and batch experiments under different ionic strength (IS) and pH conditions. Results demonstrated that the density and height of NSR significantly influenced the interaction energy parameters and consequently the extent and kinetics of colloid retention and release. In particular, values of ΔΦa and ΔΦd significantly decreased in the presence of NSR. Therefore, consistent with findings of column experiments, colloid retention in the primary minimum was predicted to occur at some specific locations on the sand surface, even at low IS conditions. However, NSR yielded a much weaker primary minimum interaction compared with that of smooth surfaces. Colloid release from primary minima upon decreasing IS and increasing pH was attributed to the impact of NSR on the values of ΔΦd . Pronounced differences in the amount of colloid retention in batch and column experiments indicated that primary minimum interactions were weak even at high IS conditions. Negligible colloid retention in batch experiments was attributed to hydrodynamic torques overcoming adhesive torques, whereas significant colloid retention in column experiments was attributed to nano- and micro-scale roughness which would dramatically alter the lever arms associated with hydrodynamic and adhesive torques.