Showing papers in "Environmental Science and Technology Letters in 2014"

Predicted Releases of Engineered Nanomaterials: From Global to Regional to Local

Abstract: A key question for industry, regulators, toxicologists, and risk assessors working with nanomaterials is what relevant environmental engineered nanomaterial (ENM) concentrations should be considered. Answering this question requires ENM material flow estimates at the local level. Using a life-cycle approach, global ENM production and application data were used to estimate releases at global, regional, national, and local levels. Local level emissions were then used to estimate releases to water (direct and from wastewater treatment effluent), soils (direct and from runoff and biosolids), and air (direct and from incineration of ENM-containing products). Waste management data for dozens of countries were used to estimate the flow of 10 major ENMs through eight world regions. A national and local release example was conducted with data from the United States, providing predicted wastewater effluent concentrations for the San Francisco Bay area, ranging from low nanograms per liter to micrograms per liter de...

Thin-Film Composite Polyamide Membranes Functionalized with Biocidal Graphene Oxide Nanosheets

Abstract: Fouling of membranes by microorganisms is a major limiting factor in membrane separation processes. Novel strategies are therefore required to decrease the extent of bacterial growth on membranes. In this study, we confer strong antimicrobial properties to thin-film composite polyamide membranes by a simple graphene oxide surface functionalization. Using amide coupling between carboxyl groups of graphene oxide and carboxyl groups of the polyamide active layer, graphene oxide is irreversibly bound to the membrane. Surface binding of graphene oxide is demonstrated by scanning electron microscopy and Raman spectroscopy. Direct contact of bacteria with functionalized graphene oxide on the membrane surface results in 65% bacterial inactivation after 1 h of contact time. This bactericidal effect is imparted to the membrane without any detrimental effect to the intrinsic membrane transport properties. Our results suggest that functionalization of thin-film composite membranes with graphene oxide nanosheets is a ...

Biochar as an Electron Shuttle between Bacteria and Fe(III) Minerals

Abstract: Biochar influences soil fertility, N2O emissions, and atmospheric CO2 budgets, and because of its quinone and aromatic structures, it is redox-active. Here we demonstrate that biochar concentrations of 5 and 10 g L–1 stimulate both the rate and the extent of microbial reduction of the Fe(III) oxyhydroxide mineral ferrihydrite (15 mM) by Shewanella oneidensis MR-1, while lower biochar concentrations (0.5 and 1 g L–1) have a negative effect on ferrihydrite reduction. Control experiments showed that biochar particles and not biochar-derived water-soluble organic compounds are responsible for the stimulating and inhibiting effect. We also found that biochar changed the mineral product of ferrihydrite reduction from magnetite (Fe3O4) to siderite (FeCO3). Our study suggests that biochar can influence soil biogeochemistry not only indirectly by changing the soil structure and chemistry but also by directly mediating electron transfer processes, i.e., by functioning as an electron shuttle.

An Integrated Framework for Optimizing CO2 Sequestration and Enhanced Oil Recovery

Abstract: CO2-enhanced oil recovery (CO2-EOR) is a technique for commercially producing oil from depleted reservoirs by injecting CO2 along with water. Because a large portion of the injected CO2 remains in place, CO2-EOR is an option for permanently sequestering CO2. This study develops a generic integrated framework for optimizing CO2 sequestration and enhanced oil recovery based on known parameter distributions for a depleted oil reservoir in Texas. The framework consists of a multiphase reservoir simulator coupled with geologic and statistical models. An integrated simulation of CO2–water–oil flow and reactive transport is conducted, followed by a global sensitivity and response surface analysis, for optimizing the CO2-EOR process. The results indicate that the reservoir permeability, porosity, thickness, and depth are the major intrinsic reservoir parameters that control net CO2 injection/storage and oil/gas recovery rates. The distance between injection and production wells and the sequence of alternating CO2...

Omniphobic Membrane for Robust Membrane Distillation

Abstract: In this work, we fabricate an omniphobic microporous membrane for membrane distillation (MD) by modifying a hydrophilic glass fiber membrane with silica nanoparticles followed by surface fluorination and polymer coating. The modified glass fiber membrane exhibits an anti-wetting property not only against water but also against low surface tension organic solvents that easily wet a hydrophobic polytetrafluoroethylene (PTFE) membrane that is commonly used in MD applications. By comparing the performance of the PTFE and omniphobic membranes in direct contact MD experiments in the presence of a surfactant (sodium dodecyl sulfate, SDS), we show that SDS wets the hydrophobic PTFE membrane but not the omniphobic membrane. Our results suggest that omniphobic membranes are critical for MD applications with feed waters containing surface active species, such as oil and gas produced water, to prevent membrane pore wetting.

Physical Disintegration of Biochar: An Overlooked Process

Abstract: Data collected from both artificially and field (naturally) weathered biochar suggest that a potentially significant pathway of biochar disappearance is through physical breakdown of the biochar structure. Via scanning electron microscopy, we characterized this physical weathering that increased the number of structural fractures and yielded higher numbers of liberated biochar fragments. This was hypothesized to be due to the graphitic sheet expansion accompanying water sorption coupled with comminution. These fragments can be on the microscale and the nanoscale but are still carbon-rich particles with no detectable alteration in the oxygen:carbon ratio from that of the original biochar. However, these particles are now easily dissolved and could be moved by infiltration. There is a need to understand how to produce biochars that are resistant to physical degradation to maximize long-term biochar C sequestration potential within soil systems.

Toward Resource Recovery from Wastewater: Extraction of Phosphorus from Digested Sludge Using a Hybrid Forward Osmosis–Membrane Distillation Process

Abstract: We demonstrate the simultaneous extraction of phosphorus and clean water from digested sludge centrate using a forward osmosis (FO)–membrane distillation (MD) hybrid process. In this FO–MD hybrid process, FO concentrates orthophosphate and ammonium for subsequent phosphorus recovery in the form of struvite (MgNH4PO4·6H2O), while MD is used to recover the draw solution and extract clean water from the digested sludge centrate. A decline in water flux was observed during the FO process, but fouling was largely reversible after a brief, simple membrane flushing using deionized water. The FO process also provides an effective pretreatment capacity to the subsequent MD process, which exhibited stable water flux. The use of MgCl2 as the draw solute for the FO process is another novel aspect of the system. The reverse salt flux of magnesium to the concentrated digested sludge across the FO membrane and the diffusion of protons away from the digested sludge create favorable conditions for the formation of struvit...

Recovery of Electrical Energy in Microbial Fuel Cells

Abstract: Recovery of electrical energy is a key parameter for evaluating the performance of microbial fuel cells (MFCs). In this brief review, we analyze energy data in the sampled publications on continuously operated MFCs from the past 12 years and present a rough picture of energy recovery in MFCs. We observe that most MFCs produce a normalized energy recovery (NER) lower than 1.5 kWh/m3 or 1.0 kWh/kg of chemical oxygen demand (COD). The small MFCs (<100 mL) that produce high power densities do not exhibit any obvious advantage in NER compared with the larger MFCs. Pure substrates lead to better performance in both power and energy recovery. MFCs seem to be able to extract more energy (kilowatt hour per kilogram of COD) from low-strength substrates. The separator/membrane does not significantly affect NER. To establish an energy balance in MFCs and gain a better understanding of the MFC application niche, NER should be properly presented in future studies.

High Levels of Organophosphate Flame Retardants in the Great Lakes Atmosphere

Abstract: Levels of 12 organophosphate flame retardants (OPs) were measured in particle phase samples collected at five sites in the North American Great Lakes basin from March 2012 to December 2012 (inclusive). The target compounds were three chlorinated OPs [tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP), and tris(1,3-dichloro-2-propyl) phosphate (TDCPP)], three alkyl phosphates [tri-n-butyl phosphate (TnBP), tris(butoxyethyl) phosphate (TBEP), and tris(2-ethylhexyl) phosphate (TEHP)], and six aryl phosphates [triphenyl phosphate (TPP), tri-o-tolyl phosphate (TOTP), tri-p-tolyl phosphate (TPTP), tris(3,5-dimethylphenyl) phosphate (TDMPP), tris(2-isopropylphenyl) phosphate (TIPPP), and tris(4-butylphenyl) phosphate (TBPP)]. Total OP (ΣOP) atmospheric concentrations ranged from 120 ± 18 to 2100 ± 400 pg/m3 at the five sites, with the higher ΣOP levels detected at Cleveland and Chicago. ΣOP concentrations at these urban sites were dominated by the chlorinated OPs (TCEP, TCPP, and TDCP...

Compressible Carbon Nanotube–Graphene Hybrid Aerogels with Superhydrophobicity and Superoleophilicity for Oil Sorption

Abstract: Spilled oil represents a menace to the aquatic ecosystem and the whole environment in general and requires timely cleanup. Among all the avaliable technologies, oil sorption has attracted the most attention because of its simplicity and high level of effectiveness. The key for the development of this technology is convenient fabrication of high-performance oil sorbents that can be used repeatedly. In this work, a fast microwave irradiation-mediated approach has been proposed for manufacturing multiwall carbon nanotube (MWCNT)–graphene hybrid aerogels, in which MWCNTs are vertically anchored on the surface of cell walls of graphene aerogels. The hybrid monoliths show superhydrophobicity and superoleophilicity, a large pore volume, a large pore size, and excellent compressibility, demonstrating outstanding performance for recyclable oil sorption.

Transport of gold nanoparticles through plasmodesmata and precipitation of gold ions in woody poplar.

Abstract: Poplar plants (Populus deltoides × nigra, DN-34) were used as a model to explore vegetative uptake of commercially available gold nanoparticles (AuNPs) and their subsequent translocation and transport into plant cells. AuNPs were directly taken up and translocated from hydroponic solution to poplar roots, stems and leaves. Total gold concentrations in leaves of plants treated with 15, 25 and 50 nm AuNPs at exposure concentrations of 498±50.5, 247±94.5 and 263±157 ng/mL in solutions were: 0.023±0.006, 0.0218±0.004 and 0.005±0.0003 µg/g dry weight, respectively, which accounted for 0.05, 0.10 and 0.03%, respectively, of the total gold mass added. The presence of total gold in plant tissues was measured by inductively coupled plasma mass spectrometry, while AuNPs were observed by transmission electron microscopy in plant tissues. In solution, AuNPs were distinguished from Au(III) ions by membrane separation and centrifugation. AuNPs behaved conservatively inside the plants and were not dissolved into gold ions. On the other hand, Au(III) ions were taken up and reduced into AuNPs inside whole plants. AuNPs were observed in the cytoplasm and various organelles of root and leaf cells. A distinct change in color from yellow to pink was observed as Au(III) ions were reduced and precipitated in hydroponic solution. The accumulation of AuNPs in the plasmodesma of the phloem complex in root cells clearly suggests ease of transport between cells and translocation throughout the whole plant, inferring the potential for entry and transfer in food webs.

A Novel Electro-Fenton Process with H2O2 Generation in a Rotating Disk Reactor for Organic Pollutant Degradation

Abstract: The feasibility of the electrogeneration of H2O2 and degradation of an organic pollutant by a novel electro-Fenton (EF) process was demonstrated using dual rotating graphite felt disks to supply oxygen instead of the traditional aeration method, with methyl orange (MO) as the model pollutant. The effects of rotating speed, current density, and pH on the generation of hydrogen peroxide (H2O2) were investigated. At a current density of 50 A/m2, a rotating speed of 10 rpm, and a pH of 3, the concentration of H2O2 reached 116 mg/L in 1 h, which was much higher than that at 0 rpm (37 mg/L). The complete removal of 25 mg/L MO was achieved within 15 min, while the total organic carbon removal efficiency reached 58.7% at 2 h, which was almost 3-fold higher than that at 0 rpm (14.9%). The rotation of disk cathodes resulted in the efficient production of H2O2 without oxygen aeration, offering a potentially cost-effective EF method for degrading organic pollutants.

Raising the Bar: Increased Hydraulic Pressure Allows Unprecedented High Power Densities in Pressure-Retarded Osmosis

Abstract: Pressure-retarded osmosis (PRO) has the potential to generate sustainable energy from salinity gradients. PRO is typically considered for operation with river water and seawater, but a far greater energy of mixing can be harnessed from hypersaline solutions. This study investigates the power density that can be obtained in PRO from such concentrated solutions. Thin-film composite membranes with an embedded woven mesh were supported by tricot fabric feed spacers in a specially designed crossflow cell to maximize the operating pressure of the system, reaching a stable applied hydraulic pressure of 48 bar (700 psi) for more than 10 h. Operation at this increased hydraulic pressure allowed unprecedented power densities, up to 60 W/m2 with a 3 M (180 g/L) NaCl draw solution. Experimental power densities demonstrate reasonable agreement with power densities modeled using measured membrane properties, indicating high-pressure operation does not drastically alter membrane performance. Our findings exhibit the pro...

Proliferation of Multidrug-Resistant New Delhi Metallo-β-lactamase Genes in Municipal Wastewater Treatment Plants in Northern China

Abstract: The New Delhi metallo-β-lactamase (NDM-1) increases bacterial resistance to a broad range of antibiotics, and bacteria that produce it can cause infections that are very difficult to treat, thus posing great risks to human health. This paper addresses the occurrence of NDM-1 genes through different processes in wastewater treatment plants (WWTPs). NDM-1 genes prevailed through several treatment units (including disinfection by chlorination) in two WWTPs in northern China. Significant NDM-1 gene levels were present in the effluent discharged from both WWTPs (from 1316 ± 232 to 1431 ± 247 copies/mL, representing from 4.4 to 93.2%, respectively, of influent levels). NDM-1 genes were present at much higher concentrations in dewatered waste sludge that is applied to soils [(4.06 ± 0.98) × 107 to (6.21 ± 2.23) × 107 copies/g of dry weight], raising the possibility of propagation to indigenous bacteria. This concern was validated by a conjugation experiment with Haihe River sediment not harboring NDM-1 genes at ...

Single-Step Fabrication Using a Phase Inversion Method of Poly(vinylidene fluoride) (PVDF) Activated Carbon Air Cathodes for Microbial Fuel Cells

Abstract: Air cathodes used in microbial fuel cells (MFCs) need to have high catalytic activity for oxygen reduction, but they must also be easy to manufacture, inexpensive, and watertight. A simple one-step, phase inversion process was used here to construct an inexpensive MFC cathode using a poly(vinylidene fluoride) (PVDF) binder and an activated carbon catalyst. The phase inversion process enabled cathode preparation at room temperatures, without the need for additional heat treatment, and it produced for the first time a cathode that did not require a separate diffusion layer to prevent water leakage. MFCs using this new type of cathode produced a maximum power density of 1470 ± 50 mW m–2 with acetate as a substrate, and 230 ± 10 mW m–2 with domestic wastewater. These power densities were similar to those obtained using cathodes made using more expensive materials or more complex procedures, such as cathodes with a polytetrafluoroethylene (PTFE) binder and a poly(dimethylsiloxane) (PDMS) diffusion layer, or a ...

Degradation of Perfluorooctanoic Acid by Reactive Species Generated through Catalyzed H2O2 Propagation Reactions

Abstract: Perfluorinated compounds, which are environmentally persistent and bioaccumulative contaminants, cannot currently be treated in the subsurface by in situ technologies. Catalyzed H2O2 propagation (CHP) reactions, which generate hydroxyl radical, hydroperoxide anion, and superoxide anion, were investigated for treating perfluorooctanoic acid (PFOA) as a basis for in situ chemical oxidation remediation of groundwater. Using 1 M H2O2 and 0.5 mM iron(III), PFOA was degraded by 89% within 150 min. Hydroxyl radical does not react with PFOA, but systems producing only superoxide promoted 68% PFOA degradation within 150 min. In systems producing only hydroperoxide, the level of PFOA degradation was 80% over 150 min. The generation of near-stoichiometric equivalents of fluoride during PFOA degradation and the lack of detectable degradation products suggest PFOA may be mineralized by CHP. CHP process conditions can be adjusted during treatability studies to increase the flux of superoxide and hydroperoxide to treat ...

A Multisite Survey To Identify the Scale of the 1,4-Dioxane Problem at Contaminated Groundwater Sites

Abstract: 1,4-Dioxane (dioxane) is an emerging groundwater contaminant that has significant regulatory implications and potential remediation costs, but our current understanding of its occurrence and behavior is limited. This study used intensive data mining to identify and evaluate >2000 sites in California where groundwater has been impacted by chlorinated solvents and/or dioxane. Dioxane was detected at 194 of these sites, with 95% containing one or more chlorinated solvents. Dioxane frequently co-occurs with 1,1,1-trichloroethene (1,1,1-TCA) (76% of the study sites), but despite this, no dioxane analyses were conducted at 332 (67%) of the sites where 1,1,1-TCA was detected. At sites where dioxane has been identified, plumes are dilute but not large (median maximal concentration of 365 μg/L; median plume length of 269 m) and have been delineated to a similar extent as typically co-occurring chlorinated solvents. Furthermore, at sites where dioxane and chlorinated solvents co-occur, dioxane plumes are frequently...

Platinum-like Behavior of Reduced Graphene Oxide as a Cocatalyst on TiO2 for the Efficient Photocatalytic Oxidation of Arsenite

Abstract: The preoxidation of arsenite [As(III)] to arsenate [As(V)] is usually needed for efficient removal of arsenic from water, and TiO2-based photocatalytic oxidation has been investigated as an environmentally benign process for this purpose. The oxidation efficiency can be markedly enhanced when using platinum (Pt) as a cocatalyst, but its expensive material cost hinders its practical application. Herein, we prepared the reduced graphene oxide (rGO) hybridized with TiO2 as a low-cost alternative to Pt and achieved a highly enhanced activity for the photocatalytic oxidation of As(III), which is comparable to that of Pt/TiO2. While either superoxide or hydroxyl radical can be involved as a main oxidant depending on the experimental condition, this study shows that not only superoxide but also hydroxyl radicals (or hole) can be directly involved in As(III) photo-oxidation when rGO is present as a cocatalyst. The photocatalytic activity, charge transfer characteristics, and arsenic oxidation mechanism observed w...

Light Absorption by Charge Transfer Complexes in Brown Carbon Aerosols

Abstract: Recently, it has become apparent that a fraction of the organic species in ambient aerosols absorbs ultraviolet–visible light with a potential impact on climate. It is believed that this light-absorbing, sometimes called “brown”, carbon originates from biomass and biofuel burning and could be formed through secondary processes in particles or clouds. Here, we identify for the first time charge transfer (CT) complexes as a significant source of light absorption by organic compounds in aerosols. A dense manifold of these complexes, formed from interactions between alcohol and carbonyl moieties, accounts for approximately 50% of the absorption (300–600 nm) observed for water-extracted ambient particulate matter collected in Athens, GA. Corresponding fluorescence emission spectra with broad, overlapping long-wavelength tails are consistent with efficient energy transfer among a near continuum of such coupled excited states. We postulate that a wide variety of CT complexes are formed as a result of a supramole...

Restoring Soil Calcium Reverses Forest Decline

Abstract: Forest decline in the northeastern United States has been linked to the effects of acid deposition on soil nutrients. To test this link, we added a calcium silicate mineral to a paired watershed at the Hubbard Brook Experimental Forest, New Hampshire, in an amount designed to gradually replace the estimated amount of calcium lost as a result of human activity in the 20th Century (primarily because of acid deposition). The experimental restoration resulted in a recovery of tree biomass increment. The improved calcium nutrition also promoted higher aboveground net primary production and increased the photosynthetic surface area in the treated watershed relative to that in the reference watershed. These results demonstrated that soil acidification accelerated by acid deposition has contributed to the decline of forest growth and health on naturally acidic soil in the northeastern United States and that decline can be reversed by the addition of calcium.

Salt Concentration Differences Alter Membrane Resistance in Reverse Electrodialysis Stacks

Abstract: Membrane ionic resistance is usually measured by immersing the membrane in a salt solution at a single, fixed concentration. While salt concentration is known to affect membrane resistance when the same concentration is used on both sides of the membrane, little is known about membrane resistance when the membrane is placed between solutions of different concentrations, such as in a reverse electrodialysis (RED) stack. Ionic resistance measurements obtained using Selemion CMV and AMV that separated sodium chloride and ammonium bicarbonate solutions of different concentrations were greater than those measured using only the high-concentration solution. Measured RED stack resistances showed good agreement with resistances calculated using an equivalent series resistance model, where the membranes accounted for 46% of the total stack resistance. The high area resistance of the membranes separating different salt concentration solutions has implications for modeling and optimizing membranes used in RED systems.

Can We Treat Hydraulic Fracturing Flowback with a Conventional Biological Process? The Case of Guar Gum

Abstract: Hydraulic fracturing of unconventional gas wells utilizes large volumes of water-based fluid to increase formation permeability and, as a result, generates large amounts of wastewater as flowback. This water requires suitable treatment before being reused or discharged into the environment. A principal ingredient of flowback water is guar gum (a gelling agent), which may adversely affect advanced flowback water treatment such as membrane separation. This study demonstrates the potential of an activated sludge mixed liquor to degrade guar under typical flowback conditions (i.e., high concentrations of total dissolved solids (TDS)). Guar was efficiently degraded at a TDS concentration of 1500 mg/L, with more than 90% of the dissolved chemical oxygen demand (CODd) having been removed after 10 h. Increasing the TDS concentration to 45000 mg/L inhibited CODd degradation to 60% removal after 31 h. A high TDS concentration additionally resulted in an increased effluent level of total suspended solids and turbidity; however, these were efficiently reduced using ferric chloride coagulation followed by sedimentation and filtration. Biological reduction of the guar concentration increased the flux of a bench-scale ultrafiltration membrane, demonstrating the potential of the process to treat flowback water prior to membrane separation.

Long-Term Persistence of Dispersants following the Deepwater Horizon Oil Spill

Abstract: During the 2010 Deepwater Horizon (DWH) oil spill, 1.84 M gallons of chemical dispersant was applied to oil released in the subsurface and to oil slicks at the surface. We used liquid chromatography with tandem mass spectrometry to quantify the anionic surfactant DOSS (dioctyl sodium sulfosuccinate) in samples collected from environments known to contain oil persisting from the DWH oil spill. DOSS was found to persist in variable quantities in deep-sea coral communities (6–9000 ng/g) 6 months after the spill and on Gulf of Mexico beaches (1–260 ng/g) 26–45 months after the spill. These results indicate that the applied dispersant, which was thought to undergo rapid degradation in the water column, remains associated with oil in the environment and can persist for ∼4 years.

Self-Supplied Ammonium Bicarbonate Draw Solute for Achieving Wastewater Treatment and Recovery in a Microbial Electrolysis Cell-Forward Osmosis-Coupled System

Abstract: This study has presented a proof-of-concept system for the self-sustained supply of ammonium-based draw solute for wastewater treatment through coupling a microbial electrolysis cell (MEC) and forward osmosis (FO). The MEC produced an ammonium bicarbonate draw solute via recovering ammonia from a synthetic organic solution, which was then applied in the FO for extracting water from the MEC anode effluent. The recovered ammonium could reach a concentration of 0.86 mol L–1, and with this draw solution, the FO extracted 50.1 ± 1.7% of the MEC anode effluent. The lost ammonium during heat regeneration could be supplemented with additional recovered ammonium in the MEC. The MEC achieved continuing treatment of both organic and ammonium in the returned feed solution mixed with fresh anolyte, although at lower efficiency compared to that with completely fresh anolyte. These results encourage further investigation to optimize the coordination between MEC and FO with improved performance.

Why Dissolved Organic Matter Enhances Photodegradation of Methylmercury

Abstract: Methylmercury (MeHg) is known to degrade photochemically, but it remains unclear what roles naturally dissolved organic matter (DOM) and complexing organic ligands play in MeHg photodegradation. Here we investigate the rates and mechanisms of MeHg photodegradation using DOM with varying oxidation states and origins as well as organic ligands with known molecular structures. All DOM and organic ligands increased the rate of MeHg photodegradation under solar irradiation, but the first-order rate constants varied depending on the oxidation state of DOM and the type and concentration of the ligands. Reduced DOM photochemically degraded MeHg 3 times faster than oxidized DOM. Compounds containing both thiol and aromatic moieties within the same molecule (e.g., thiosalicylate and reduced DOM) increased MeHg photodegradation rates far more than those containing only aromatics or thiols (e.g., salicylate or glutathione, or their combinations). The mechanism is attributed in part to strong binding between MeHg and ...

An Ionic Liquid Facilitates the Proliferation of Antibiotic Resistance Genes Mediated by Class I Integrons

Abstract: Ionic liquids (ILs), as “environmentally friendly” replacements for industrial volatile organic solvents, have been widely and recently applied in the chemical industry. However, few data have been collected regarding the toxicity and potential environmental effects of ILs, which are fairly important for preparing for their potential release into the environment. In this study, the IL 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) was tested for its ability to promote the proliferation and dissemination of antibiotic resistance genes (ARGs) in environmental bacteria. In freshwater microcosms, [BMIm][PF6] (0.5 g/L) significantly enhanced the abundance of the sulI gene (500-fold greater than in untreated controls). Meanwhile, [BMIm][PF6] significantly increased the abundance of class I integrons, which play a key role in ARG dissemination. A positive correlation (p < 0.01) between the intI and sulI genes suggested that [BMIm][PF6]-facilitated sulI propagation was mediated by class I integrons...

Structure of Sulfate Adsorption Complexes on Ferrihydrite

Abstract: Sulfate adsorption on mineral surfaces is an important environmental chemical process. However, the structure of sulfate adsorption complexes has remained uncertain. In this study, we have determined the S−Fe distance of sulfate inner-sphere adsorption complexes on iron (Fe) oxyhydroxide (ferrihydrite) surfaces under air-dried conditions using sulfur K-edge extended X-ray absorption fine structure spectroscopy and differential X-ray pair distribution function analysis. Both approaches indicate that the S− Fe interatomic distance of the sulfate adsorption complexes is 3.22−3.25 A, suggesting that sulfate forms bidentate−binuclear adsorption complexes on ferrihydrite surfaces. Outer-sphere complexes are also observed using infrared spectroscopic analysis. This finding clarifies the long-standing debate over the structure of sulfate adsorption complexes and has important implications for understanding the chemistry of sulfate at environmental interfaces.

Production of Black Carbon-like and Aliphatic Molecules from Terrestrial Dissolved Organic Matter in the Presence of Sunlight and Iron

Abstract: Photochemical processing of dissolved organic matter (DOM) in natural waters can alter its composition and structure, supply particulate organic matter (POM) to sediments, and deliver modified terrestrial DOM to the ocean. Our studies show that terrestrial DOM exposed to simulated sunlight is altered to produce POM with a markedly different molecular composition enriched with newly formed aliphatic and condensed aromatic molecules. This process is closely tied to the chemistry of iron, which primarily exists as dissolved Fe(II) and Fe(III)–organic complexes in initial DOM and photochemically matures to Fe(III) oxyhydroxides before coprecipitating out with POM. The newly formed condensed aromatic compounds resemble black carbon, which until now was thought to be produced by only combustion. These new molecules contribute a pool of Fe-rich, aliphatic, and black carbon-like organic matter to sediments as the terrestrial DOM is transported through rivers. We estimate that the annual global flux of this photop...

Metagenomic Evaluation of the Highly Abundant Human Gut Bacteriophage CrAssphage for Source Tracking of Human Fecal Pollution

Abstract: Recently, a highly abundant and widespread bacteriophage, named crAssphage, was identified in the human gut. Here, 86 publically available metagenomes were surveyed to determine the presence and abundance of crAssphage in various environments and to identify its utility for source tracking of human fecal pollution. CrAssphage was found to be highly abundant in sewage and biosolids from the United States and Europe and less abundant in sewage from Asia and Africa. CrAssphage was not definitively identified in other samples, including animal fecal material, with the exception of bat guano. Approximately half of mapped reads in the bat guano metagenome clustered to orf00045 in the phage genome, suggesting homology to a closely related phage. These results indicate the potential utility of a crAssphage-based marker for source tracking of human fecal waste and highlight the utility of metagenomic approaches for initial identification and verification of fecal source tracking markers.

Determination of Iodide via Direct Fluorescence Quenching at Nitrogen-Doped Carbon Quantum Dot Fluorophores

Abstract: The development of analytical methods for rapidly, sensitively, and selectively detecting iodide (I–) in aqueous media is critically important because I– is closely related to human health because of a number of diseases caused by the deficiency and radioactivity of I–. In this work, we describe N-doped carbon quantum dots as the fluorophores for the direct determination of I– fluorescence, achieving a detection limit of 10 μM with an analytical linear range up to 2.0 mM. The experimental results also demonstrate that the N-doped carbon quantum dot fluorophores possess high selectivity for I– detection. The presence of nitrogen functional groups results in a positively charged carbon quantum dot surface, which is advantageous for the detection of I– fluorescence because of the strong electrostatic interaction between carbon quantum dots and I–. This work demonstrates the possibility of developing carbon quantum dot fluorophore-based fluorescence methods for the determination of other anions.