NEW ORLEANS, April 8, 2013 -- The Gulf of Mexico may have a much greater natural ability to self-clean oil spills than previously believed, an expert in bioremediation said here today at the 245th National Meeting & Exposition of the American Chemical Society (ACS), the world's largest scientific society.
Terry C. Hazen, Ph.D., said that conclusion has emerged from research following the 2010 Deepwater Horizon disaster, which by some estimates spilled 4.9 million barrels (210 million gallons) of oil into the Gulf of Mexico. His research team used a powerful new approach for identifying microbes in the environment to discover previously unknown bacteria, naturally present in the Gulf water, that consume and break down crude oil.
"The Deepwater Horizon oil provided a new source of nutrients in the deepest waters," explained Hazen, who is with the University of Tennessee in Knoxville. "With more food present in the water, there was a population explosion among those bacteria already adapted to using oil as a food source. It was surprising how fast they consumed the oil. In some locations, it took only one day for them to reduce a gallon of oil to a half gallon. In others, the half-life for a given quantity of spilled oil was 6 days. This data suggests that a great potential for intrinsic bioremediation of oil plumes exists in the deep sea and other environs in the Gulf of Mexico."
Hazen spoke at a symposium, "Environmental Fate of Petroleum Oils and Dispersants in the Marine Environment," that included other reports relating to the Deepwater Horizon spill. They were among 12,000 reports being presented at the ACS meeting, which continues through Thursday. Abstracts of the oil spill symposium appear at the end of this press release.
Oil-eating bacteria are natural inhabitants of the Gulf because of the constant supply of food. Scientists know that there are more than 600 different areas where oil oozes from rocks underlying the Gulf of Mexico. These oil seeps, much like underwater springs, release 560,000-1.4 million barrels of oil annually, according to the National Research Council.
Hazen's team used a powerful new approach for identifying previously recognized kinds of oil-eating bacteria that contributed to the natural clean-up of the Deepwater Horizon spill. In the past, scientists identified microbes by putting samples of water into laboratory culture dishes, waiting for microbes to grow and then using a microscope to identify the microbes. The new approach, called "ecogenomics," uses genetic and other analyses of the DNA, proteins and other footprints of bacteria to provide a more detailed picture of microbial life in the water.
"The bottom line from this research may be that the Gulf of Mexico is more resilient and better able to recover from oil spills than anyone thought," Hazen said. "It shows that we may not need the kinds of heroic measures proposed after the Deepwater Horizon spill, like adding nutrients to speed up the growth of bacteria that breakdown oil, or using genetically engineered bacteria. The Gulf has a broad base of natural bacteria, and they respond to the presence of oil by multiplying quite rapidly."
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Deepwater Horizon oil spill: A systems biology approach to an ecological disaster
Terry C Hazen, University of Tennessee
The explosion on April 20, 2010 at Deepwater Horizon drilling rig in the Gulf of Mexico resulted in oil and gas rising to the surface and the oil coming ashore in many parts of the Gulf, and in the dispersment of an oil plume 4,000 feet below the surface of the water. Despite spanning more than 600 feet in the water column and extending more than 10 miles from the wellhead, the dispersed oil plume was gone within weeks after the wellhead was capped - degraded and diluted to undetectable levels. Furthermore, this degradation took place without significant oxygen depletion. Ecogenomics enabled discovery of new and unclassified species of oil-eating bacteria that apparently lives in the deep Gulf where oil seeps are common. The results provide information about the key players and processes involved in degradation of oil, with and without COREXIT, in different impacted environments in The Gulf of Mexico.
Corexit 9500® substantially increases the biodegradation of otherwise undispersed oil
Roger C Prince, ExxonMobil Biomedical Sciences, Inc.
Dispersants are an important tool for responding to major oil spills. They are essentially a bioremediation tool, allowing oil to disperse into tiny droplets (<70um) that diffuse apart from each other so that they cannot (re-)agglomerate to (re-)form a floating slick. The energy for the dispersion usually comes from surface waves, but can also come from turbulence if oil is released at depth. The tiny droplets are so small that they become entrained in the water column, and the dramatically increased surface area allows microbial access to much more of the oil. Furthermore, diffusion and dilution lead to oil concentrations where natural background levels of biologically available oxygen, nitrogen and phosphorus are sufficient for microbial growth. Dispersants are typically only used on substantial spills in relatively deep water (usually >30m), which are impossible to replicate in the laboratory. Laboratory experiments aimed at following the biodegradation of dispersed oil usually show minimal stimulation of the rate of biodegradation, but this can be attributed to the fact that small quantities of oil disperse quite well even in the absence of chemical dispersant. We show here that when the experiments are conducted so that the comparison is between a slick and a dispersed oil, the rate of biodegradation is dramatically stimulated by effective application of the dispersant Corexit 9500.
Biodegradation of crude oil in the Louisiana salt marshes following the BP Deepwater Horizon oil spill
Gabriel Nuffield Kasozi, Makerere University Kampala
Following the BP Deepwater Horizon oil spill in the Gulf of Mexico, biodegradation of crude oil in the ecologically sensitive salt marshes was studied. Soil samples were collected from heavily-oiled and lightly-oiled shores of the tidal marshes dominated by Spartina alterniflora to monitor the natural recovery of the oiled salt marshes. Chemical analysis revealed concentration of n-alkanes on the first sampling ranging from 843 to 6810 and 49 to 256 mg kg-1 dry wt in the sites 3m and 15m from the shores, respectively while in the lightly-oiled sites they ranged from 8 to 49 and 15 to 54 mg kg-1 dry wt, in the sites 3m and 15m from the shores, respectively. The concentration for total PAHs in the oiled sites ranged from 6.8 to 99.4 and 0.7 to 2.6 mg kg-1 dry wt in the sites 3m and 15m from the shores, respectively while in the lightly-oiled sites they ranged from 0.4 to 1.4 and 0.5 to 1.1 mg kg-1 dry wt, in the sites 3m and 15m from the shores, respectively. The PAHs data from the second sampling regime indicated a possible inflow of oil or an increase in bioavailable PAHs upon weathering of the oil. In addition, the rates of dissipation PAHs seemed higher as concentration increased, suggesting a potential increase in the population of site specific oil-degrading micro-organisms associated with higher content of total organic carbon. The degradation followed first order reaction kinetics and half-lives were 72 and 100 days for n-alkanes and PAHs, respectively. Data from n-alkanes and PAHs degradation indicates almost complete recovery with 363 of the study. With the evident onset of grass recovery even in the worst hit sites, we posit that complete intrinsic recovery for the Louisiana salt marshes will be possible in three years.
Effects of oil dispersants on sorption capacity and hysteresis of polycyclic aromatic hydrocarbons with Gulf Coast marine sediments
Dongye Zhao, Auburn Universty
Effects of dispersant Corexit EC9500A on sediment sorption/desorption of polycyclic aromatic hydrocarbons (PAHs) were investigated with two sediments. Batch sorption kinetic tests showed that the dispersant (10-18 mg/L) enhanced PAH uptake by ~7%. Two scenarios were simulated to test effects of the dispersant on PAH desorption: (a) PAHs were pre-sorbed to sediments without dispersant, and then subjected to desorption in the presence of the dispersant (b) PAHs were pre-sorbed with the dispersant, and then subjected to desorption without dispersant. Desorption kinetic tests indicated that the dispersant (18 mg/L) hindered PAH desorption by 4-5% in both scenarios compared to the control when the dispersant was absent. Sorption isotherm tests revealed that PAH uptake increases with increasing dispersant concentration. While the sorption was reversible in scenario (b), sorption hysteresis was observed under scenario (a). The effects of dispersants should be taken into account in evaluating fate and transport of oil compounds.
Indigenous arctic micro-organisms degrade oil in Arctic seawater
Kelly McFarlin, University of Alaska Fairbanks
As oil exploration expands in offshore Arctic regions, it is important to assess the potential rate and extent of oil biodegradation by indigenous micro-organisms under environmentally relevant temperatures. A respirometry experiment validated with chemical analysis was conducted to determine the potential for indigenous arctic marine microorganisms to biodegrade Alaskan North Slope (ANS) crude oil in the presence or absence of a dispersant (COREXIT 9500). In February 2010, near shore seawater was collected from the Chukchi Sea (Barrow, Alaska). Incubations were conducted with fresh seawater at an on-site laboratory, at -1° C, with minimal nutrient addition for 10, 28 and 60 days. The addition of COREXIT 9500 enhanced the degradation of both fresh and weathered oil during early stages of the incubations. This research revealed that micro-organisms indigenous to arctic seawater are able to biodegrade oil at very low, environmentally relevant temperatures.
Industry-sponsored subsea dispersant injection research
Tim Nedwed, ExxonMobil Upstream Research Company
Subsea dispersant injection was a key response tool initiated during the 2010 Macondo incident. The API believes it played an important role protecting the environment and health and safety of workers attempting to contain the well. Industry plans to incorporate this tool in response strategies for future offshore drilling operations where appropriate. The novelty of the concept did not allow it to be fully evaluated prior to the spill. For this reason, API initiated the subsea dispersant injection research program to conduct studies and controlled experiments on 1) effectiveness of subsea injection; 2) fate and effects of dispersed oil in deepwater; 3) upgrades to numerical modeling to better predict the fate of dispersed oil in deepwater; and 4) monitoring tools to determine the effectiveness of subsea injection. The presentation provides evidence of the effectiveness of dispersants during the Macondo incident and an overview of the API subsea dispersant injection research program.
Selectively wetting surfaces: A new approach to oil spill remediation
Daniel P Prendergast, Massachusetts Institute of Technology
Recent advances in surface chemistry have enabled the fabrication of superhydrophobic surfaces which selectively pass oil without the concomitant passage of water. Such materials represent a promising new oil spill countermeasure: in situ separation and recovery of spilled oil. Unfortunately, the practicality of these materials under oceanic conditions has not been investigated. Herein, we report the development and characterization of a durable, low cost, hydrophobic mesh, and quantify its performance. The meshes are fabricated by dip-coating steel mesh in a solution of xylene and low-density polyethylene. Bench-scale testing of a prototype has led to the development of a predictive model of two competing metrics: oil percolation flux versus water breakthrough depth. By altering the pore size, roughness, and coating thickness, meshes can be tailored to maximize oil flux for expected water depths. Adept implementation of selectively wetting surfaces can achieve oil spill remediation goals with minimal environmental impact.
Iron oxide nanoparticles stabilized by p-amino benzoic acid terminated carbon black particles for oil spill remediation
Pradeep Venkataraman, Tulane University
Functionalized nanoparticles have recently gained significant attention for their application in environmental remediation due to their ability to adsorb irreversibly at the oil-water interface. We specifically focus on para-amino benzoic acid (PABA) functionalized carbon black (CB) particles due to their tunable interfacial properties and their ability to absorb environmentally toxic polycyclic aromatic compounds. We hypothesize that the carboxyl groups of the PABA attached to CB particles can conjugate with iron salts and can be reduced to synthesize magnetite nanoparticles. We investigate the ability of the composite iron-carbon particles to form oil-in-water emulsions of these particles under varying conditions of pH and ionic strength of the continuous phase. We propose that the magnetic properties imparted by magnetite and tunable surface properties due to PABA functionalized CB particles make these composite particles attractive agents for oil emulsification and ground water remediation.
Enhanced dispersed oil droplet stability using modified natural biopolymer
Jingjian Tang, Tulane University
Dispersants such as COREXIT 9500A are used in oil spill remediation with the objective of reducing the oil-water interfacial tension and breaking the slick into small oil droplets that are entrained in the water column for microbial degradation. However, the dispersants do not provide an effective barrier against coalescence of the droplets. The objective of this research is to enhance the stability of the dispersed oil droplet through the application of environmentally benign biopolymers. We specifically focus on hydrophobically modified polysaccharides where alkyl groups are attached to the polymer backbone. We hypothesize that the hydrophobic side chains preferentially anchor themselves in the oil phase resulting in the formation of a protective polymer layer around the droplet. The enhanced stability of the emulsion can be attributed to increased electrostatic repulsions as well as presence of polymer layer as a barrier to coalescence. Increase in the molecular weight of the polymer results in the biopolymer spanning the drops resulting in a gel-like phase. We propose that sequential application of dispersant followed by the application of the biopolymer can potential minimize the use of the chemical dispersant.
Gulf of Mexico oil spill ketone transformation products revealed by increased acid/analyte concentration positive ion ESI FT-ICR MS
Brian M. Ruddy, Florida State University
Recent studies have shown extensive oxidative modification to the Macondo wellhead oil upon release into the Northern Gulf of Mexico as a result of various biotic and abiotic processes. Here, we show enhanced detection of ketone transformation products and an up to threefold increase in instrumental sensitivity through optimized positive ion electrospray conditions in Fourier transform ion cyclotron resonance mass spectrometry. Preliminary comparisons suggest that the results may be unique to the Gulf of Mexico. Also, an as of yet unexplained increased hydrocarbon (HC class) ionization occurs with spray-condition optimization. The high mass accuracy FT-ICR results are confirmed by a similar relative increase in ketone detection by positive ion electrospray time-of-flight analysis of model compounds. The work was supported by the National Science Foundation (NSF) Division of Materials Research through DMR-06-54118 and the State of Florida, NSF grants OCE-1044939 and OCE-1057417, and BP/The Gulf of Mexico Research Initiative.
Molecular dynamics simulations of oil hydrocarbons and surfactants at atmospheric air/salt water interfaces
Thilanga P Liyana-Arachchi, Louisiana State University
A significant fraction of the oil released during the 2010 DWH accident accumulated at the sea surface. According to recent studies, the volatile organic compounds (VOCs), as well as some intermediate volatiles (IVOCs) evaporated into the atmosphere and formed aerosols. However, the fate of other organics, such as heavier IVOCs (C17-C18) and semi-volatiles (SVOCs, C19-C31) has not been addressed so far. We hypothesize that these compounds didn't evaporate but remained in the sea surface, and phenomena such as bubble-bursting and white caps carried these compounds, as well as part of the dispersants released to combat the spill, into the atmosphere. We report molecular dynamics (MD) simulations of chain alkanes, e.g., pentadecane (C15) and icosane (C20), at atmospheric air/salt water interfaces. The effects of varying concentrations of these alkanes, as well as varying amounts of a standard surfactant, sodium dodecyl sulfate (SDS), on the interfacial properties of these systems is investigated.
Photochemical degradation and bacterial growth response crude oil
Gabrielle Daniel, University of West Florida
Crude oil from Jay, FL was examined to determine the effect of varied light exposure on the degradation and resulting toxicity to bacterial growth. Samples containing 2% oil in sterile seawater were incubated at constant temperature for 15 days with treatments of full sun, PAR only and dark. The resulting water accommodated fraction was removed and polycyclic aromatic hydrocarbon and alkane concentrations determined. Chrysenes peaked at day 6 under full sun. Napthalenes were constant over time and independent of light. A portion of the WAF was incubated with seawater to determine the extent of bacterial growth inhibition determined by 3H-leucine incorporation. WAFs developed in the dark inhibited growth at approximately 40%. The no UVR WAF had the highest level of inhibition to bacterial growth. These results have implications for how photochemical weathering may alter the impact of spilled oil on microbial communities in surface waters.
Photodegradation and salinity effects on crude oil PAH partitioning kinetics
Ryan Pichulo, University of West Florida
Pam Vaughan, University of West Florida
The partitioning kinetics of various PAHs in crude oil was examined in response to a variety of environmental factors such as salinity and light exposure. Crude oil from Jay, FL was added to water and exposed to various treatments. Water and remaining oil fractions were extracted to quantify total PAH (primarily naphthalene, phenanthrene and chrysene) partitioning within the samples. Samples exposed over a 3-day interval showed increasing naphthalene concentration in the water fraction while chrysene showed a decrease. Concentrations of phenanthrene in the residual oil showed a steady decrease over time. The total concentration of naphthalene and phenanthrene extracted from both the oil and water fractions did not significantly change compared to the original unaltered oil. Total chrysene showed a slight loss over time. The effects of longer and varied wavelength light exposure as well as salinity effects on partitioning kinetics will also be discussed.
Organic matter in ocean water as a proxy for indirect photochemical degradation of the dispersants used in the Deepwater Horizon oil spill
Caitlin M Glover, University of Colorado, Boulder
Following the explosion of the BP Deepwater Horizon Oil Rig in the Gulf of Mexico, the company utilized COREXIT 9500 and 9527A at the ocean's surface. Two compounds (bis(2-ethylhexyl)sulfosuccinate surfactant and 1-(2-butoxy-1-methylethoxy)-2-propanol), were chosen to act as surrogates for the COREXIT mixture. To determine the role of indirect photolysis, the hydroxyl radical reaction rates were taken. Hydroxyl radical and singlet oxygen are important reactive oxygen species and are produced in ocean waters at varying levels corresponding to the type of organic matter (OM) present. A series of ocean water samples were collected from the shoreline out into the open ocean nearby to Grand Isle, LA. From these samples, the quantum yields for singlet oxygen and hydroxyl radical were determined. These values were correlated with the source of the OM and the highest reactivity was closest to shoreline, proving the most degradation would occur in regions impacted by terrestrial sources.
Effects of oil dispersants and sediment sorption on photodegradation and ozonation of persistent oil compounds in the Gulf Coast ecosystems
Yanyan Gong, Auburn Universty
We investigated the effects of an oil dispersant (COREXIT® EC9500A) and sediment sorption on photodegradation and ozonation of two oil polycyclic aromatic compounds (PAHs) under simulated Gulf Coast ground level conditions. Batch sorption/desorption tests showed that increasing dispersant concentration from 0 to 1360 mg/L progressively decreased physicochemical availability of PAHs sorbed on sediments, resulting in prolonged weathering rates of the PAHs. Ozone oxidation kinetic tests showed that the dispersant at 18 mg/L inhibited degradation of the PAHs by up to 21%. Increasing the dispersant concentration to 180 mg/L further decreased the ozone oxidation rates by up to 44%. The presence of the dispersant at 18 and 180 mg/L retarded photodegradation of the PAHs by ~5% and remarkably decreased the evaporation losses of phenanthrene and pyrene, resulting in elevated persistence of the PAHs in the seawater. Effects of salinity, pH, and dissolved organic matter on the weathering rates are also investigated.