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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 04 April 2017, Vol.114(14), pp.E2802-E2803
    Description: In their recent article, Coyte et al. (1) use an innovative combination of microfluidic experiments, mechanistic models, and game theory to study the impact of physical microenvironments on the activity of bacteria in porous media. The authors find that hydrodynamics can profoundly affect how bacteria compete and evolve in these systems. They indicate that this conclusion could in principle have important implications for the management of a range of engineered and natural porous media. However, two aspects of the research significantly limit its relevance to practical applications, especially in soils and sediments.The first aspect is the premise that bacterial growth in porous media occurs within biofilms that cover pore walls uniformly. This assumption underlies the model used by Coyte et al. (1), and has clearly motivated the design of their experiments. However, biofilms are far from ubiquitous in natural porous media. In the pore space of unsaturated soils, where many bacteria live, such biofilms are typically not observed (2, 3). In saturated fine- to medium-textured porous media, numerous microscopic observations indicate that biofilms are the exception rather than the rule. Indeed, even when severe bioclogging occurs in such systems, bacterial cells are not located in continuous biofilms but instead aggregate preferentially at pore necks (4, 5). Various modeling efforts have shown conclusively that to describe the occasionally pronounced effects of bacteria on the hydrodynamics of saturated porous media, approaches assuming the presence of continuous biofilms are not satisfactory, even when biofilms are considered to be permeable, and models need to invoke the development of plugs of low permeability, obstructing the lumen of pores (6, 7). It is possible that Coyte et al.’s (1) conclusions would still stand upon consideration of such plugs, but this will need to be checked.The second aspect that decreases the appeal of Coyte et al.’s (1) results in practice is the fact that, even though their research claims to be related to microbial competition, it involves only bacteria. In real porous media, other microorganisms are unavoidably present (8) and may affect not only the competition and evolution of bacteria directly, but also the hydrodynamics of the pore space. Growing fungal hyphae (9) may transport bacteria (and archaea) from one portion of the pore space to another, as well as partially clog pores. Hydrodynamics may have a sizeable effect on the dynamics of protozoan predators (10), predatory bacteria, or viral particles (phages), all ubiquitous in natural porous media and directly influencing the fate of bacterial populations.In this context, Coyte et al.’s (1) research should be viewed as the exploration of one scenario, among several plausible ones, to account for the competition or evolution of bacteria in porous media. Their results, in particular related to the application of game theory, are interesting, but do not settle the many questions associated with what determines the level of microbial biodiversity found in subsurface environments. A complete description will require the development of more realistic models, and additional data associated with the physical, chemical, and microbial characteristics of microenvironments in real porous media.
    Keywords: Biological Evolution ; Environment
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    Language: English
    In: Water Research, January 2011, Vol.45(2), pp.839-851
    Description: Transport of manufactured nano-TiO in saturated porous media was investigated as a function of morphology characteristics, pH of solutions, flow velocity, and the presence of anionic and non-ionic surfactants in different concentrations. Surfactants enhanced the transport of nano-TiO in saturated porous media while a pH approaching the point of zero charge of nano-TiO limited their transport. The deposition process, a retention mechanism of nano-TiO in saturated porous media was impacted by surfactant and pH. In Dispersion 1 systems (pH 7), the size of the nano-TiO aggregates was directly related to the presence of surfactants. The presence of non-ionic surfactant (Triton X-100) induced a size reduction of nano-TiO aggregates that was dependent on the critical micelle concentration. In Dispersion 2 systems (pH 9), the stability provided by the pH had a significant effect on the size of nano-TiO aggregates; the addition of surfactants did impact the size of the nano-TiO aggregates but in less significance as compared to Dispersion 1 systems. The electrostatic and steric repulsion forces in connection with the size of nano-TiO aggregates and flow velocity impacted the single-collector efficiency and attachment efficiency which dictated the maximum transport distance of nano-TiO for the Dispersion 1 and Dispersion 2 systems. By doubling the flow velocity at pH 9, the No Surfactant, 50% CMC Triton X-100, 100% CMC Triton X-100 and 100% CMC SDBS dispersion systems allowed nano-TiO to attain maximum transport distances of 0.898, 2.17, 2.29 and 1.12 m, respectively. Secondary energy minima played a critical role in the deposition mechanisms of nano-TiO . Nano-TiO deposited in the secondary energy wells may be released because of changes in solution chemistry. The deposition of nano-TiO in primary and secondary energy minima, the reversibility of their deposition should be characterized to analyze the transport of nanoparticles in porous media. This is necessary to assess the risk of nanoparticles to the environment and public health.
    Keywords: Titanium Dioxide ; Transport ; Aggregation ; Saturated Porous Media ; Surfactant ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 3
    Language: English
    In: Environmental Pollution, March 2013, Vol.174, pp.106-113
    Description: The aggregation, transport and deposition kinetics (i.e. attachment and release) of TiO nanoparticles (nano-TiO ) were investigated as a function of ionic strength and the presence of anionic (sodium dodecylbenzene sulfonate, SDBS) and non-ionic (Triton X-100) surfactants in 100% critical micelle concentration (CMC). The electrolyte concentration of the suspensions dictated the kinetic stability of nano-TiO thus influencing the transport and retention of the nanoaggregates in the saturated porous medium. With increasing ionic strength, the interaction between approaching nano-TiO and nano-TiO already deposited onto collectors surfaces seemed to be more favorable than the interaction between approaching nano-TiO and bare collectors surfaces. The abrupt and gradual reduction in electrolyte concentration during the flushing cycles of the column experiments induced the release of previously deposited nano-TiO suggesting attachment of nano-TiO through secondary energy minimum. ► This study focuses on aggregation, transport and deposition kinetics of nano-TiO . ► Ionic strength and surfactants impact nano-TiO transport in saturated porous media. ► Previously deposited nano-TiO serve as preferential sites for subsequent deposition. ► Changes in solution chemistry cause nanodeposits to release a portion of nano-TiO . Previously deposited nano-TiO serve as preferential sites for subsequent deposition and changes in solution chemistry cause nanodeposits to release a portion of nano-TiO .
    Keywords: Titanium Dioxide ; Nanoparticle ; Ionic Strength ; Surfactant ; Transport ; Deposition ; Release ; Saturated Porous Media ; Engineering ; Environmental Sciences ; Anatomy & Physiology
    ISSN: 0269-7491
    E-ISSN: 1873-6424
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  • 4
    Language: English
    In: Environmental pollution, 2013, Vol.174, pp.106-113
    Description: The aggregation, transport and deposition kinetics (i.e. attachment and release) of TiO₂ nanoparticles (nano-TiO₂) were investigated as a function of ionic strength and the presence of anionic (sodium dodecylbenzene sulfonate, SDBS) and non-ionic (Triton X-100) surfactants in 100% critical micelle concentration (CMC). The electrolyte concentration of the suspensions dictated the kinetic stability of nano-TiO₂ thus influencing the transport and retention of the nanoaggregates in the saturated porous medium. With increasing ionic strength, the interaction between approaching nano-TiO₂ and nano-TiO₂ already deposited onto collectors surfaces seemed to be more favorable than the interaction between approaching nano-TiO₂ and bare collectors surfaces. The abrupt and gradual reduction in electrolyte concentration during the flushing cycles of the column experiments induced the release of previously deposited nano-TiO₂ suggesting attachment of nano-TiO₂ through secondary energy minimum. ; p. 106-113.
    Keywords: Collectors ; Porous Media ; Titanium Dioxide ; Surfactants ; Octoxynol ; Electrolytes ; Sodium ; Nanoparticles ; Energy ; Micelles ; Ionic Strength
    ISSN: 0269-7491
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 5
    Language: English
    In: Journal of Hydrology, March 2018, Vol.558, pp.72-89
    Description: In the hydrological cycle, the infiltration process is a critical component in the distribution of water into the soil and in the groundwater system. The nonlinear dynamics of the soil infiltration process yield preferential flow which affects the water distribution in soil. Preferential flow is influenced by the interactions between water, soil, plants, and microorganisms. Although the relationship among the plant roots, their rhizodeposits and water transport in soil has been the subject of extensive study, the effect of microbial exudates has been studied in only a few cases. Here the authors investigated the influence of two artificial microbial exudates–catechol and riboflavin–on the infiltration process, particularly unstable fingered flow, one form of preferential flow. Flow experiments investigating the effects of types and concentrations of microbial exudates on unstable fingered flow were conducted in a two-dimensional tank that was filled with ASTM graded silica sand. The light transmission method (LTM) which is based on capturing the light intensity transmitted through a sand-water system and then converting it into degree of water saturation was used to visualize and characterize the flow of water in porous media as well as to image and measure the spatial and temporal distribution of water in porous media. Flow patterns, vertical and horizontal profiles of the degree of water saturation of the fingers, as well as measurements of the fingers dimension (width), number, and velocity were determined using the light transmission method. Interfacial experiments exploring the influence of microbial exudates on the wettability behavior of water were performed by measuring the contact angle and the interfacial tension of the (solid)-gas-microbial exudate solution systems. Unstable wetting front generating fingered flow was observed in all infiltration experiments. The experimental results showed that the microbial exudate addition affected the infiltration process, as the measurements of the degree of saturation profiles and widths of the fingers differed from those of the control NaCl solution. These differences may be due to an improved water holding capacity in the presence of the microbial exudates. The lowest catechol solution concentration (10 μM) produced the largest finger width (9.69 cm) among the tested catechol solution concentrations and all the other solutions including the control solution (7.24 cm). Moreover, the wettability of the medium for the catechol solution increased with an increase in concentration. The highest riboflavin solution concentration (1000 μM) generated the highest finger width (7.75 cm) among the tested riboflavin solution concentrations. However, the wettability of the medium for the riboflavin solution decreased with an increase in concentration. Our study demonstrated that the microbial exudates which are biochemical compounds produced and released by microbes in the environment are capable of influencing the soil infiltration process. The results of this study also demonstrated that the influence of the contact angle expressed as should be integrated in the scaling of the finger dimension, i.e., finger width, when the Miller and Miller (1956) scaling theory is applied for the hydrodynamic scaling in porous media.
    Keywords: Preferential Flow ; Fingered Flow ; Wetting Front Instability ; Unsaturated Porous Media ; Microbial Exudates ; Light Transmission Method (Ltm) ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 6
    Language: English
    In: Journal of Geotechnical and Geoenvironmental Engineering, Feb, 2014, Vol.140(2), p.04013013(1)
    Keywords: Nanoparticles -- Research ; Porous Materials -- Usage ; Lactates -- Analysis ; Magnetic Susceptibility -- Analysis
    ISSN: 1090-0241
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Journal of Microbiological Methods, 15 February 2013, Vol.92(2), pp.135-144
    Description: Traditional microscopy methods for the detection and quantification of in soil matrices are time-consuming, labor-intensive, and lack sensitivity and specificity. This research focused on developing a qPCR protocol for the sensitive and specific detection and quantification of in natural soil matrices and soil–water extracts. The physico-chemical parameters — lysis media, number of thermal shocks and thawing temperatures — controlling DNA extraction efficiency were investigated. Experimental results identified oocyst age as a critical parameter affecting oocyst disruption and quantification. The most efficient oocyst disruption method for oocysts regardless of their age was established as 5 thermal shocks with thawing at 65 °C in Tris-EDTA (TE) buffer. In addition to the purification columns used to remove PCR inhibitors present in environmental matrices, a combination of 3 mM MgCl and 600 ng/μl BSA yielded the highest amplicon yield for both young and aged oocysts. Sucrose flotation was determined to be a better oocyst isolation method than two-phase flotation. The optimized parameters for DNA extraction and the qPCR assay resulted in very specific and sensitive detection of . Minimum detection limits were 0.667 for young oocysts and 6.67 for aged oocysts per PCR reaction. The accuracy of the detections and quantifications was 0.999. Protocol performance was tested in contrasting soil samples and soil–water extract samples on the basis of percentage of recovery (PR) values. Depending on the number of oocysts used to inoculate the samples, the average PR values ranged from 7.2 to 43.5%, 29.3–52.5%, and 11.5–60.8% for Trenton, Greenson, and Sparta soil–water extracts, respectively, and 12.1–77% for DI water. PR values ranged from 4.3% to 107.8% for Trenton, Greenson and Sparta soil samples. ► qPCR method developed to quantify in soil and soil–water extract samples. ► Sucrose flotation is better than two-phase flotation for isolating oocysts from soil. ► Oocyst age has a significant effect on DNA extraction, purification and quantification.
    Keywords: Cryptosporidium Parvum ; Real-Time Pcr ; Quantification ; Oocyst Disruption ; DNA Extraction ; Oocyst Isolation ; Biology
    ISSN: 0167-7012
    E-ISSN: 1872-8359
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  • 8
    Language: English
    In: Soil Science Society of America journal, 2011, Vol.75(6), pp.2037-2048
    Description: When the Soil Science Society of America was created, 75 yr ago, the USA was suffering from major dust storms, causing the loss of enormous amounts of topsoil as well as human lives. These catastrophic events reminded public officials that soils are essential to society's well-being. The Soil Conservation Service was founded and farmers were encouraged to implement erosion mitigation practices. Still, many questions about soil processes remained poorly understood and controversial. In this article, we argue that the current status of soils worldwide parallels that in the USA at the beginning of the 20th century. Dust bowls and large-scale soil degradation occur over vast regions in a number of countries. Perhaps more so even than in the past, soils currently have the potential to affect populations critically in several other ways as well, from their effect on global climate change, to the toxicity of brownfield soils in urban settings. Even though our collective understanding of soil processes has experienced significant advances since 1936, many basic questions still remain unanswered, for example whether or not a switch to no-till agriculture promotes C sequestration in soils, or how to account for microscale heterogeneity in the modeling of soil organic matter transformation. Given the enormity of the challenges raised by our (ab)uses of soils, one may consider that if we do not address them rapidly, and in the process heed the example of U.S. public officials in the 1930s who took swift action, humanity may not get a chance to explore other frontiers of science in the future. From this perspective, insistence on the fact that soils are critical to life on earth, and indeed to the survival of humans, may again stimulate interest in soils among the public, generate support for soil research, and attract new generations of students to study soils. ; p. 2037-2048.
    Keywords: Dust Storms ; Students ; Carbon Sequestration ; Topsoil ; Urban Soils ; Society ; No-Tillage ; Soil Organic Matter ; Humans ; Climate Change ; Models ; Farmers ; Soil Degradation ; Toxicity ; Soil Conservation
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Journal of Soils and Sediments, 2015, Vol.15(3), pp.634-647
    Description: Byline: Burcu UyuAur (1), Chunyan Li (2), Philippe C. Baveye (3), Christophe J. G. Darnault (2) Keywords: Geochemistry; Precipitation; Sorption; Two-site and mobile-immobile transport models; Uranyl silicates; Vadose zone Abstract: Purpose Uranium contamination of subsurface environments was once thought to be an isolated occurrence, mostly at production sites. But recent evidence has shown that the presence of uranium in phosphate fertilizers has caused massive amounts of this element to be released worldwide. Concerns are related to uranium movement to groundwater supplies and its significant toxicological risks to human populations. Information is direly needed on how geochemical processes control uranium transport in the vadose zone. Materials and methods Laboratory experiments were performed to investigate the effects of the pH of the soil solution on the reactive transport of uranium(VI) in the vadose zone. The uranium solution was prepared by dilution of a 10.sup.-3 M stock solution of uranium perchlorate, (UO.sub.2(ClO.sub.4).sub.2), with DI water. Two U(VI) solutions were prepared at concentrations of 2x10.sup.-6 M at pH 6 and 11 and were percolated under steady-state conditions through columns filled with sand. The convective-dispersion equation (CDE) was used to analyze the tracer and uranium breakthrough curves resulting from the column experiments. The program CXTFIT was used to estimate the transport parameters of equilibrium and nonequilibrium (i.e., two-site and mobile-immobile) models applied to the experimental data. Results and discussion Comparison of U(VI) breakthrough behavior at pH 6 with that of a nonreactive tracer indicated that U(VI) transport was significantly retarded, and about 52 % of the added U(VI) adsorbed to the quartz sand, likely in the cationic forms U[O.sub.2]OH.sup.+ and UO .sub.2 .sup.2+ . The adsorption was reversible upon the addition of deionized water. At pH 11, the U(VI) breakthrough curve increased gradually and reached a plateau value C/C .sub.0 oscillating between 72 and 82 %. Upon reaction, Si was released from the dissolution of quartz sand, which allowed the possible transport of U(VI) following precipitation of a U(VI) containing solid, such as uranyl-silicate minerals, or sorption of U(VI) onto silica colloids. Two-site and mobile-immobile (MIM) models suggested an influence of either rate-limited mass transfer processes or immobile/mobile water partitioning in U(VI) reactive transport. Conclusions The reactive transport of U(VI) governed by adsorption-desorption processes, precipitation, and complexation reactions in which kinetic behaviors are controlled by pH, solution chemistry, and heterogeneous flow regime impacts the mobility of U(VI). The column transport experiments indicated that under geochemical conditions and vadoze zone processes (preferential flow) that favor the mobility of U(VI), dissolved- and colloidal-phase associations of U(VI) may be transported rapidly and in high concentrations from the soil surface to the groundwater. Author Affiliation: (1) Tubitak Marmara Research Center, P.K. 21 41470, Gebze, Kocaeli, Turkey (2) Department of Environmental Engineering and Earth Sciences, L.G. Rich Environmental Laboratory, Clemson University, 342 Computer Court, Anderson, SC, 29625, USA (3) Laboratory of Soil and Water Engineering, Department of Civil and Environmental Engineering, Rensselaer Polytechnic University, 319 Materials Research Center, 110 Eighth St., Troy, NY, 12180, USA Article History: Registration Date: 31/10/2014 Received Date: 19/05/2014 Accepted Date: 31/10/2014 Online Date: 20/11/2014 Article note: Responsible Editor: Dong-Mei Zhou
    Keywords: Geochemistry ; Precipitation ; Sorption ; Two-site and mobile-immobile transport models ; Uranyl silicates ; Vadose zone
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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  • 10
    Language: English
    In: Water, 2017, Vol.9(6), p.433
    Description: Surfactants released into the terrestrial environment in large amounts can potentially alter the physical, chemical and biological properties of soils, particularly the saturated hydraulic conductivity (Ks). Unfortunately findings regarding this process are quite limited. In this study, column tests were used to analyze the effects of Aerosol 22, a widely used anionic surfactant, on Ks of loamy sand and sandy loam soils. Solutions were injected into columns from the bottom with controlled pressure heads. Both the overall Ks of columns and the Ks of 6 layers at distances of 0–1 cm, 1–3 cm, 3–5 cm, 5–7 cm, 7–9 cm, and 9–10 cm from the bottom, were continuously monitored before and after the surfactant injections. Results showed that the overall Ks of all columns decreased after 2–4 pore volumes of the surfactant injections. However, stabilization and even increase at the beginning of the surfactant injection was also observed due to the different Ks variations in different layers. Specifically, a surfactant injection of 2–4 pore volumes continuously decreased the Ks of the 0–1 cm layers which yielded a Ks reduction of two orders of magnitude and dominated the Ks variations of the column. In contrast, an increase in the Ks of the 1–3 cm and 3–5 cm layers was more likely, while Ks variation of the 5–10 cm layers was less likely. We hypothetically attributed the Ks variations to the swelling of clay, the collapse of soil aggregates and subsequent particle displacements from surfactant adsorption, which caused pore clogging in the bottom 0–1 cm layer and higher porosities in the layers above. The adsorption of the surfactant aggregates and crystallization were also possibly thought to cause a pore clogging in the bottom layer thus decrease the surfactant concentration from the inlet, the severity of which affects these layers less at greater distances from the inlet. In view of the uncertainty showed by the experimental results, we also suggest to include more replicate columns in future studies, so as to increase the repeatability of the measurements.
    Keywords: Life Sciences ; Adsorption ; Soil ; Clogging ; Surfactant ; Hydraulic Conductivity ; Engineering
    ISSN: 2073-4441
    E-ISSN: 2073-4441
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