Reduction in sulfate inhibition of microbial dechlorination of polychlorinated biphenyls in Hudson and Grasse River sediments through fatty acid supplementation.

Microbial dechlorination of polychlorinated biphenyls (PCBs) in aquatic sediments may reduce the need for dredging for remediation. To better understand this biotransformation route under different geochemical conditions, the influence of sulfate on dechlorination in sediments from the Hudson River and the Grasse River spiked with two PCB mixtures (PCB 5/12, 64/71, 105/114 and 149/153/170 in Mixture 1 and PCB 5/12, 64/71, 82/97/99, 144/170 in Mixture 2) was investigated. The results showed that PCB dechlorination was partially inhibited in the sulfate-amended sediment microcosms. The rate, extent and preference of dechlorination were mainly controlled by the indigenous differences (sulfate, carbon content etc.) in sediment, but also affected by the PCB mixture composition. An increase of Dehalococcoides 16S rRNA genes coincided with the resumption of dechlorination. Dechlorination preferences were identified using a modified dechlorination pathway analysis approach. The low carbon content and high background sulfate Hudson sediment exhibited more para dechlorination targeting flanked para chlorines. The high carbon content and low background sulfate Grasse sediment preferentially removed more para-flanked meta chlorines than flanked para chlorines. The supplementation of fatty acids (acetate or a mixture of acetate, propionate and butyrate) dramatically increased PCB dechlorination in the Grasse sediment by resuming ortho-flanked meta dechlorination. Rare ortho removals were found in the Grasse sediment after adding fatty acids. This study suggests that supplementary fatty acids might be used to stimulate PCB dechlorination under sulfate reducing conditions, but the effectiveness largely depends on sediment geochemistry.

Biogenic Cyanide Production Promotes Dissolution of Gold Nanoparticles in Soil.

Gold nanoparticles (Au NPs) are often used to study the physiochemical behavior and distribution of nanomaterials in natural systems because they are assumed to be inert under environmental conditions, even though Au can be oxidized and dissolved by a common environmental compound: cyanide. We used the cyanogenic soil bacterium, Chromobacterium violaceum, to demonstrate that quorum-sensing-regulated cyanide production could lead to a high rate of oxidative dissolution of Au NPs in soil. After 7 days of incubation in a pH 7.0 soil inoculated with C. violaceum, labile Au concentration increased from 0 to 15%. There was no observable dissolution when Au NPs were incubated in abiotic soil. In the same soil adjusted to pH 7.5, labile Au concentration increased up to 29% over the same time frame. Furthermore, we demonstrated that Au dissolution required quorum-sensing-regulated cyanide production in soil by inoculating the soil with different cell densities and using a quorum-sensing-deficient mutant of C. violaceum, CV026. Au NP dissolution experiments in liquid media coupled with mass spectrometry analysis confirmed that biogenic cyanide oxidized Au NPs to soluble Au(CN)2-. These results demonstrate under which conditions biologically enhanced metal dissolution can contribute to the overall geochemical transformation kinetics of nanoparticle in soils, even though the materials may be inert in abiotic environments.

Effects of Ferric Oxyhydroxide on Anaerobic Microbial Dechlorination of Polychlorinated Biphenyls in Hudson and Grasse River Sediment Microcosms: Dechlorination Extent, Preferences, Ortho Removal, and Its Enhancement.

Microbial reductive dechlorination of polychlorinated biphenyls (PCBs) has been observed in many PCB-impacted sediments. However, this biodegradation is relatively site-specific and can be affected by PCB compositions and sediment geochemical conditions. To better understand the influence of a common competing electron acceptor, ferric oxyhydroxide (FeOOH), on dechlorination, two sediments (Hudson River and Grasse River sediments), and two PCB mixtures (PCB 5/12, 64/71, 105/114, and 149/153/170 in Mixture 1 and PCB 5/12, 64/71, 82/97/99, 144/170 in Mixture 2) were used for this microcosm study. The addition of 40 mmole/kg FeOOH completely inhibited PCB dechlorination in the Hudson sediment, but only moderately inhibited PCB dechlorination in the Grasse sediment with a 3-week longer lag time. The inhibitory effect in the Grasse sediment was mainly due to the loss of unflanked para dechlorination activity. Fe(II) analysis showed that dechlorination started prior to the consumption of Fe(III), which indicates PCB reduction and Fe(III) reduction were able to take place concurrently. Dehalococcoides 16S rRNA genes increased with the commencement of dechlorination in the Grasse sediment, but not in the completely inhibited Hudson sediment. Rare ortho dechlorination pathways were identified in FeOOH-amended Grasse sediment microcosms, dominated by transformations of PCB 25(24-3-CB) to PCB 13(3-4-CB) and PCB 28(24-4-CB) to PCB 15(4-4-CB). The addition of carbon sources (acetate or a fatty acid mixture with acetate, propionate, and butyrate) after 27 weeks of incubation reinitiated dechlorination in FeOOH-amended Hudson sediment microcosms. Also, the addition of carbon sources greatly enhanced ortho dechlorination in FeOOH-amended Grasse microcosms, indicating the utilization of acetate and/or the fatty acid mixture for ortho dechlorination-related microorganisms. A dechlorination pathway analysis approach revealed that para-flanked meta dechlorination was primarily preferred followed by ortho-/double-flanked meta dechlorination and single-/double-flanked para dechlorination in the Grasse sediment.

Quorum Sensing Signals Form Complexes with Ag+ and Cu2+ Cations.

Quorum sensing (QS) regulates important bacterial behaviors such as virulent protein production and biofilm formation. QS requires that molecular signals are exchanged between cells, extracellularly, where environmental conditions influence signal stability. In this work, we present a novel complexation between metal cations (Ag+ and Cu2+) and a QS autoinducer signal, N-hexanoyl- L-homoserine lactone (HHL). The molecular interactions were investigated using mass spectrometery, attenuated total reflectance-Fourier transform infrared spectroscopy, and computational simulations. Results show that HHL forms predominantly 1:1 complexes with Ag+ ( Kd = 3.41 × 10-4 M) or Cu2+ ( Kd = 1.40 × 10-5 M), with the coordination chemistry occurring on the oxygen moieties. In vivo experiments with Chromobacterium violaceum CV026 show that sublethal concentrations of Ag+ and Cu2+ decreased HHL-regulated QS activity. Furthermore, when Ag+ was preincubated with HHL, Ag+ toxicity to CV026 decreased by an order of magnitude, suggesting HHL:metal complexes alter the bioavailability of the individual constituents.

Disruption of Autolysis in Bacillus subtilis using TiO2 Nanoparticles.

In contrast to many nanotoxicity studies where nanoparticles (NPs) are observed to be toxic or reduce viable cells in a population of bacteria, we observed that increasing concentration of TiO2 NPs increased the cell survival of Bacillus subtilis in autolysis-inducing buffer by 0.5 to 5 orders of magnitude over an 8 hour exposure. Molecular investigations revealed that TiO2 NPs prevent or delay cell autolysis, an important survival and growth-regulating process in bacterial populations. Overall, the results suggest two potential mechanisms for the disruption of autolysis by TiO2 NPs in a concentration dependent manner: (i) directly, through TiO2 NP deposition on the cell wall, delaying the collapse of the protonmotive-force and preventing the onset of autolysis; and (ii) indirectly, through adsorption of autolysins on TiO2 NP, limiting the activity of released autolysins and preventing further lytic activity. Enhanced darkfield microscopy coupled to hyperspectral analysis was used to map TiO2 deposition on B. subtilis cell walls and released enzymes, supporting both mechanisms of autolysis interference. The disruption of autolysis in B. subtilis cultures by TiO2 NPs suggests the mechanisms and kinetics of cell death may be influenced by nano-scale metal oxide materials, which are abundant in natural systems.

Microbial-Catalyzed Reductive Dechlorination of Polychlorinated Biphenyls in Hudson and Grasse River Sediment Microcosms: Determination of Dechlorination Preferences and Identification of Rare Ortho Removal Pathways.

Biodegradation of polychlorinated biphenyls (PCBs) is an important transformation and detoxification route in the environment. To better understand the influence of PCB congener compositions on dechlorination, sediments from two rivers, Hudson and Grasse, and two PCB mixtures (PCB 5/12, 64/71, 105/114, and 149/153/170 in Mixture 1 and PCB 5/12, 64/71, 82/97/99, and 144/170 in Mixture 2) were used for this microcosm study. The Grasse River sediment microcosms exhibited more extensive dechlorination than the Hudson River sediment microcosms. The extent of dechlorination was predominantly controlled by sediment itself, not by the PCB compositions. Rare ortho dechlorination, targeting mono-ortho PCB congeners was observed in Grasse sediment, indicating a potential for full dechlorination of some PCBs in this sediment. The identified ortho dechlorination pathways were PCB 28 (24-4-CB) to PCB 15 (4-4-CB) and PCB 25 (24-3-CB) to PCB 13(3-4-CB). The relative abundances of Dehalococcoides were much higher in both sediments spiked with PCBs. An apparent increase of Dehalococcoides 16S rRNA genes coincided with the commencement of dechlorination. The dechlorination preferences were identified using a modified data analysis approach focusing on chlorine neighboring conditions. In both sediments, the overall dechlorination preferred meta > para > ortho. Specially, ortho-/double-flanked meta-chlorines were primarily targeted followed by single-/double-flanked para-chlorines.

Impacts of Pristine and Transformed Ag and Cu Engineered Nanomaterials on Surficial Sediment Microbial Communities Appear Short-Lived.

Laboratory-based studies have shown that many soluble metal and metal oxide engineered nanomaterials (ENM) exert strong toxic effects on microorganisms. However, laboratory-based studies lack the complexity of natural systems and often use "as manufactured" ENMs rather than more environmentally relevant transformed ENMs, leaving open the question of whether natural ligands and seasonal variation will mitigate ENM impacts. Because ENMs will accumulate in subaquatic sediments, we examined the effects of pristine and transformed Ag and Cu ENMs on surficial sediment microbial communities in simulated freshwater wetlands. Five identical mesocosms were dosed through the water column with either Ag(0), Ag2S, CuO or CuS ENMs (nominal sizes of 4.67 ± 1.4, 18.1 ± 3.2, 31.1 ± 12, and 12.4 ± 4.1, respectively) or Cu(2+). Microbial communities were examined at 0, 7, 30, 90, 180, and 300 d using qPCR and high-throughput 16S rRNA gene sequencing. Results suggest differential short-term impacts of Ag(0) and Ag2S, similarities between CuO and CuS, and differences between Cu ENMs and Cu(2+). PICRUSt-predicted metagenomes displayed differential effects of Ag treatments on photosynthesis and of Cu treatments on methane metabolism. By 300 d, all metrics pointed to reconvergence of ENM-dosed mesocosm microbial community structure and composition, suggesting that the long-term microbial community impacts from a pulse of Ag or Cu ENMs are limited.

The functional potential of microbial communities in hydraulic fracturing source water and produced water from natural gas extraction characterized by metagenomic sequencing.

Microbial activity in produced water from hydraulic fracturing operations can lead to undesired environmental impacts and increase gas production costs. However, the metabolic profile of these microbial communities is not well understood. Here, for the first time, we present results from a shotgun metagenome of microbial communities in both hydraulic fracturing source water and wastewater produced by hydraulic fracturing. Taxonomic analyses showed an increase in anaerobic/facultative anaerobic classes related to Clostridia, Gammaproteobacteria, Bacteroidia and Epsilonproteobacteria in produced water as compared to predominantly aerobic Alphaproteobacteria in the fracturing source water. The metabolic profile revealed a relative increase in genes responsible for carbohydrate metabolism, respiration, sporulation and dormancy, iron acquisition and metabolism, stress response and sulfur metabolism in the produced water samples. These results suggest that microbial communities in produced water have an increased genetic ability to handle stress, which has significant implications for produced water management, such as disinfection.

Exploring the impact of pore size distribution on the performance of carbon electrodes for capacitive deionization.

Capacitive deionization (CDI) removes charged ions from aqueous solutions through entrapment in the electric double layer (EDL) when the porous electrodes are polarized. In this study, three types of activated carbon cloth (ACC) with different pore-size distributions were used to study the effect of pore characteristics on electrosorption during CDI. Removal of seven different monovalent ions was examined for each ACC in batch reactors under 5 different combinations of applied potential and ionic strength. Results show underlying sorption mechanisms in the meso- and micro-pores were different. Electrosorption in the mesopores is influenced by partially-distorted EDL caused by EDL overlapping. Sorption capacity increased with increasing applied potential or ionic strength as overlapping effects were reduced. In contrast, EDL in the microporous regions could be highly distorted resulting in enhanced sorption capacity, which cannot be adequately described using the classic EDL theories. Electrosorption density (i.e., sorption capacity normalized by pore volume) decreased as the mesoporosity-to-microporosity ratio increased. These results are in agreement with those obtained using mathematical modeling by other recent CDI studies. Charge efficiency values were between 20% and 40% and appear to be substantially influenced by Faradaic reactions and ion desorption from the electrode surfaces. These findings suggest that pore-size distribution of electrode materials, especially the meso/microporosity ratio, should be optimized for the removal of targeted ions by CDI and well characterized to conduct more precise CDI modeling.

Regional variation in water-related impacts of shale gas development and implications for emerging international plays.

The unconventional fossil fuel industry is expected to expand dramatically in coming decades as conventional reserves wane. Minimizing the environmental impacts of this energy transition requires a contextualized understanding of the unique regional issues that shale gas development poses. This manuscript highlights the variation in regional water issues associated with shale gas development in the U.S. and the approaches of various states in mitigating these impacts. The manuscript also explores opportunities for emerging international shale plays to leverage the diverse experiences of U.S. states in formulating development strategies that minimize water-related impacts within their environmental, cultural, and political ecosystem.

Microbial community changes in hydraulic fracturing fluids and produced water from shale gas extraction.

Microbial communities associated with produced water from hydraulic fracturing are not well understood, and their deleterious activity can lead to significant increases in production costs and adverse environmental impacts. In this study, we compared the microbial ecology in prefracturing fluids (fracturing source water and fracturing fluid) and produced water at multiple time points from a natural gas well in southwestern Pennsylvania using 16S rRNA gene-based clone libraries, pyrosequencing, and quantitative PCR. The majority of the bacterial community in prefracturing fluids constituted aerobic species affiliated with the class Alphaproteobacteria. However, their relative abundance decreased in produced water with an increase in halotolerant, anaerobic/facultative anaerobic species affiliated with the classes Clostridia, Bacilli, Gammaproteobacteria, Epsilonproteobacteria, Bacteroidia, and Fusobacteria. Produced water collected at the last time point (day 187) consisted almost entirely of sequences similar to Clostridia and showed a decrease in bacterial abundance by 3 orders of magnitude compared to the prefracturing fluids and produced water samplesfrom earlier time points. Geochemical analysis showed that produced water contained higher concentrations of salts and total radioactivity compared to prefracturing fluids. This study provides evidence of long-term subsurface selection of the microbial community introduced through hydraulic fracturing, which may include significant implications for disinfection as well as reuse of produced water in future fracturing operations.

Microbial communities in flowback water impoundments from hydraulic fracturing for recovery of shale gas.

Hydraulic fracturing for natural gas extraction from shale produces waste brine known as flowback that is impounded at the surface prior to reuse and/or disposal. During impoundment, microbial activity can alter the fate of metals including radionuclides, give rise to odorous compounds, and result in biocorrosion that complicates water and waste management and increases production costs. Here, we describe the microbial ecology at multiple depths of three flowback impoundments from the Marcellus shale that were managed differently. 16S rRNA gene clone libraries revealed that bacterial communities in the untreated and biocide-amended impoundments were depth dependent, diverse, and most similar to species within the taxa γ-proteobacteria, α-proteobacteria, δ-proteobacteria, Clostridia, Synergistetes, Thermotogae, Spirochetes, and Bacteroidetes. The bacterial community in the pretreated and aerated impoundment was uniform with depth, less diverse, and most similar to known iodide-oxidizing bacteria in the α-proteobacteria. Archaea were identified only in the untreated and biocide-amended impoundments and were affiliated to the Methanomicrobia class. This is the first study of microbial communities in flowback water impoundments from hydraulic fracturing. The findings expand our knowledge of microbial diversity of an emergent and unexplored environment and may guide the management of flowback impoundments.

Selective oxidation of bromide in wastewater brines from hydraulic fracturing.

Brines generated from oil and natural gas production, including flowback water and produced water from hydraulic fracturing of shale gas, may contain elevated concentrations of bromide (~1 g/L). Bromide is a broad concern due to the potential for forming brominated disinfection byproducts (DBPs) during drinking water treatment. Conventional treatment processes for bromide removal is costly and not specific. Selective bromide removal is technically challenging due to the presence of other ions in the brine, especially chloride as high as 30-200 g/L. This study evaluates the ability of solid graphite electrodes to selectively oxidize bromide to bromine in flowback water and produced water from a shale gas operation in Southwestern PA. The bromine can then be outgassed from the solution and recovered, as a process well understood in the bromine industry. This study revealed that bromide may be selectively and rapidly removed from oil and gas brines (~10 h(-1) m(-2) for produced water and ~60 h(-1) m(-2) for flowback water). The electrolysis occurs with a current efficiency between 60 and 90%, and the estimated energy cost is ~6 kJ/g Br. These data are similar to those for the chlor-alkali process that is commonly used for chlorine gas and sodium hydroxide production. The results demonstrate that bromide may be selectively removed from oil and gas brines to create an opportunity for environmental protection and resource recovery.

Spatial and temporal correlation of water quality parameters of produced waters from devonian-age shale following hydraulic fracturing.

The exponential increase in fossil energy production from Devonian-age shale in the Northeastern United States has highlighted the management challenges for produced waters from hydraulically fractured wells. Confounding these challenges is a scant availability of critical water quality parameters for this wastewater. Chemical analyses of 160 flowback and produced water samples collected from hydraulically fractured Marcellus Shale gas wells in Pennsylvania were correlated with spatial and temporal information to reveal underlying trends. Chloride was used as a reference for the comparison as its concentration varies with time of contact with the shale. Most major cations (i.e., Ca, Mg, Sr) were well-correlated with chloride concentration while barium exhibited strong influence of geographic location (i.e., higher levels in the northeast than in southwest). Comparisons against brines from adjacent formations provide insight into the origin of salinity in produced waters from Marcellus Shale. Major cations exhibited variations that cannot be explained by simple dilution of existing formation brine with the fracturing fluid, especially during the early flowback water production when the composition of the fracturing fluid and solid-liquid interactions influence the quality of the produced water. Water quality analysis in this study may help guide water management strategies for development of unconventional gas resources.

Transformations of nanomaterials in the environment.

Increasing use of engineered nanomaterials with novel properties relative to their bulk counterparts has generated a need to define their behaviors and impacts in the environment. The high surface area to volume ratio of nanoparticles results in highly reactive and physiochemically dynamic materials in environmental media. Many transformations, e.g. reactions with biomacromolecules, redox reactions, aggregation, and dissolution, may occur in both environmental and biological systems. These transformations and others will alter the fate, transport, and toxicity of nanomaterials. The nature and extent of these transformations must be understood before significant progress can be made toward understanding the environmental risks posed by these materials.

Effect of applied voltage, initial concentration, and natural organic matter on sequential reduction/oxidation of nitrobenzene by graphite electrodes.

Carbon electrodes are proposed in reactive sediment caps for in situ treatment of contaminants. The electrodes produce reducing conditions and H(2) at the cathode and oxidizing conditions and O(2) at the anode. Emplaced perpendicular to seepage flow, the electrodes provide the opportunity for sequential reduction and oxidation of contaminants. The objectives of this study are to demonstrate degradation of nitrobenzene (NB) as a probe compound for sequential electrochemical reduction and oxidation, and to determine the effect of applied voltage, initial concentration, and natural organic matter on the degradation rate. In H-cell reactors with graphite electrodes and buffer solution, NB was reduced stoichiometrically to aniline (AN) at the cathode with nitrosobenzene (NSB) as the intermediate. AN was then removed at the anode, faster than the reduction step. No common AN oxidation intermediate was detected in the system. Both the first order reduction rate constants of NB (k(NB)) and NSB (k(NSB)) increased with applied voltage between 2 V and 3.5 V (when the initial NB concentration was 100 µM, k(NB) = 0.3 h(-1) and k(NSB) = 0.04 h(-1) at 2 V; k(NB) = 1.6 h(-1) and k(NSB) = 0.64 h(-1) at 3.5 V) but stopped increasing beyond the threshold of 3.5 V. When initial NB concentration decreased from 100 to 5 µM, k(NB) and k(NSB) became 9 and 5 times faster, respectively, suggesting that competition for active sites on the electrode surface is an important factor in NB degradation. Presence of natural organic matter (in forms of either humic acid or Anacostia River sediment porewater) decreased k(NB) while slightly increased k(NSB), but only to a limited extent (∼factor of 3) for dissolved organic carbon content up to 100 mg/L. These findings suggest that electrode-based reactive sediment capping via sequential reduction/oxidation is a potentially robust and tunable technology for in situ contaminants degradation.

Microbial bioavailability of covalently bound polymer coatings on model engineered nanomaterials.

By controlling nanoparticle flocculation and deposition, polymer coatings strongly affect nanoparticle fate, transport, and subsequent biological impact in the environment. Biodegradation is a potential route to coating breakdown, but it is unknown whether surface-bound polymers are bioavailable. Here we demonstrate, for the first time, that polymer coatings covalently bound to nanomaterials are bioavailable. Model poly(ethylene oxide) (PEO) brush-coated nanoparticles (densely cross-linked bottle brush copolymers) with hydrophobic divinyl benzene cross-linked cores and hydrophilic PEO brush shells, having ~ 30 nm hydrodynamic radii, were synthesized to obtain a nanomaterial in which biodegradation was the only available coating breakdown mechanism. PEO-degrading enrichment cultures were supplied with either PEO homopolymer or PEO brush nanoparticles as the sole carbon source, and protein and CO2 production were monitored as a measure of biological conversion. Protein production after 90 h corresponded to 14% and 8% of the total carbon available in the PEO homopolymer and PEO brush nanoparticle cultures, respectively, and CO2 production corresponded to 37% and 3.8% of the carbon added to the respective system. These results indicate that the PEO in the brush is bioavailable. Brush biodegradation resulted in particle aggregation, pointing to the need to understand biologically mediated transformations of nanoparticle coatings in order to understand the fate and transport of nanoparticles in the environment.

Microbial electricity generation via microfluidic flow control.

Next generation battery technology is rapidly evolving to meet the demand for higher power densities and smaller footprints through novel catalysts and battery architecture. We present a µ-scale, biological fuel cell which utilizes microbial electricity generation enabled by microfluidic flow control to produce power. The new fuel cell, the smallest of its kind, with a total volume of 0.3 µL, produces scalable and controllable electrical energy from organic matter which is sustained through microbial respiration and laminar flow separation of the electrolytes. Electrical currents are dependent on specific biofilm formation on the anode, the concentration of electron donor, and a diffusion-limited flow regime. A maximum current density of 18.40 ± 3.48 mA m(-2) (92 ± 17 A m(-3)) was produced by Geobacter sulfurreducens, and 25.42 mA m(-2) (127 A m(-3)) by Shewanella oneidensis. The µ-scale biological fuel cell introduces the necessary small size and fuel flexibility for applications in vivo and in situ sensors which may be remotely deployed and self-powered.