Project Overview

Research Highlights

As of June 30, 2020, this project’s research resulted in 15 peer-reviewed publications, 57 scientific presentations and 28 datasets being submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are/will be made available to the public. The project also engaged 5 PhD students over its award period. Significant outcomes of this project’s research are highlighted below.

Theme One: Distribution, Dispersion, Breakup, and Settling of petroleum under the action of physical processes

I. Breakup of oil slicks by waves and droplet generation

• Large wind-wave facility (Oil herding). DROPPS-III scientists at Johns Hopkins University (JHU) studied the effectiveness of chemical surface-active agents (oil herders) around an oil slick and the stability of the slick under the action of wind and waves. The aim was to characterize mechanically generated breaking waves of varying energies in clean seawater and water treated with a herder containing 65% Span-20 and 35% 2-ethyl butanol at various concentrations. The waves were generated by a programmable piston-type wave maker and the evolution of the wave breaking process was recorded by multiple high-speed imaging cameras and an Acoustic Doppler velocimeter was used to measure the time-varying velocity of the waves. For a plunging breaker in clean water, prior to impact, the wave front contained multiple ripples and small fingers. In contrast, in treated water, the wave front was smooth resulting in the entrainment of a larger volume of air and deeper subsequent penetration of the bubble cloud. Conversely, for relatively weak spilling breakers, adding the surfactant delayed the waves breaking and dampened the formation of capillary waves on the wave crest. Once breaking occurred, there were no visible significant differences in the appearance and penetration of the waves.
  
  
• Fragmentation of a buoyant crude oil plume: obtaining droplet distributions. DROPPS-III Researchers at JHU used a refractive index-matched surrogate fluid pair: silicone oil and sugar water. Simultaneous planar induced fluorescence (PLIF) and particle image velocimetry measurements were conducted by labeling the oil and seeding both phases with particles. The profiles of the mean velocity, as well as normal and shear Reynolds stresses for the immiscible oil jet were compared with those of the single-phase water jet at the same Reynolds number. The spreading rate of the near field of the oil jet was lower than that of the single-phase flow, but increased with the Reynolds number, presumably owing the reduction in droplet sizes. The turbulence was dampened in the oil phase due to its higher viscosity, creating quiescent islands within the oil, consistent with the PLIF observations that while the oil droplets were deformed by the jet’s shear field, the interior water droplets were nearly spherical.

• Subsurface droplet generation by breaking surface waves (large scale). DROPPS- III scientists at JHU investigated the trajectories of 2μm-1mm slightly buoyant MC252 crude oil droplets located within a cloud generated as a breaking wave entrains an oil slick. The droplet trajectories were recorded using cinematic digital inline holography starting from the initial entrainment and up to 6 hours later. Particle image velocimetry was used for characterizing the time evolution of the flow field and turbulence. While small droplets nearly followed the flow, large ones began to rise, but their rise velocity was modulated by the turbulence. As the turbulence generated by the breaking wave decayed, larger fractions of the droplets size spectrum rose at the quiescent rate, while small ones continued to be dispersed by the turbulence and remained suspended. These findings have direct implications to droplets statistics under varying oceanic conditions.
  
  
• Particle shape and hydrophobicity on Oil Particle Aggregate formation. DROPPS- III researchers at New Jersey Institute of Technology evaluated particle shape and hydrophobicity on oil particle aggregation (OPA) formations. Two types of particles (kaolinite and silica) were modified to change their hydrophobicity. Using the modified particles, OPA was formed in the lab. Different factors were considered that could affect the OPA formation process, such as mixing energy and interaction time. The resultant OPAs were analyzed using a confocal laser scanning microscopy, which provided the three-dimensional structures of the OPA. The detailed structures of the OPA provided evidence of new mechanisms of the oil-particle coagulation mechanism in turbulent flows. They found that particle shape is more important in the formation of OPA than its hydrophobicity.
  
  
• Numerical simulation of buoyant plumes. Buoyant plumes in a stratified ocean usually rise to a maximum height, the so-called peel height, before slumping to a lower height where they form intrusions. Integral models, called double-plume models, have been developed in the past to describe this process, but their accuracy is questionable. DROPPS-III scientist from the University of Houston used detailed simulations to develop simplified models by applying a numerical simulation based on the Navier- Stokes equations. In their case, the plume was driven by rising bubbles modelled as force points applied to the liquid. They found that the plume was driven by rising bubbles modelled as force points applied to the liquid.
• An alternative bubble plume model. Plumes released during underwater oil spills such as the Deepwater Horizon accident produce one or several intrusion layers within the water column. In these events, the oil-water mixture is lifted primarily by gas bubbles and, secondarily, by oil drops. The momentum imparted to the liquid mixture by the bubbles causes it to rise above the neutral density level. However, the continuously falling ambient density gradually robs the plume of its momentum: the plume mixture, with a negligible momentum, becomes surrounded by lighter liquid and slumps downward close to its neutral height where it forms the intrusion. The details of this process are deeply misunderstood and there are discrepancies reported in literature between different types of bubble plumes. DROPPS-III researchers at the University of Houston developed a numerical solution of the pertinent equations to obtain a detailed understanding of the fluid mechanics of rising and falling liquid, with an intention to develop simplified models of the process.

Theme two: Biological Degradation of petroleum caused by interactions with marine plankton, bacteria, and local environment.

1. I.   Biodegradation

• Micro-biota communities associated with marine snow formed from oil-degrading bacterial exudates. DROPPS-III scientists investigated micro-biota communities associated with marine snow formed from oil-degrading bacterial exudates. Marine snow was prepared with and without oil and videos of the microzooplankton communities were recorded under phase contrast microscopy. They found that microzooplankton activity was significantly higher on oiled marine snow than non- oiled snow.
  
  
• Ingestion of crude oil droplets in copepods and gelatinous zooplankton. DROPPS- III scientists investigated the impact of crude oil and Corexit 9500 dispersant on the trophic interaction between planktonic prey and jellyfish. Two types of crustacean prey, both evasive Acartia tonsa and non-evasive Artemia salina were exposed to the water accommodated fraction (WAF) and chemically-enhanced water accommodated fraction (CEWAF) of an ecologically relevant concentration of crude oil. Preliminary results showed that the jellyfish capture non-evasive prey at a significantly higher rate relative to evasive prey at all oil/dispersant concentrations. There was no significant difference between the A. salina captured by Cassiopea at any of the WAF and CEWAF treatments. However, copepods were captured at a significantly lower rate when they were exposed to CEWAF conditions.
  • Biodegradation of oil and the resulting dissolved oxygen depression. Researchers at SINTEF Ocean collaborated with United States Bureau of Ocean Energy Management (BOEM) to determine realistic ranges of potential well blowout oil release rates in relevant regions of the northern Gulf of Mexico. Background data for dissolved oxygen has primarily been focused on the Louisiana-Texas shelf. The biodegradation of oil in the subsurface layer of tiny droplets was estimated to use about 25% of the available oxygen in the water. The deep water below the main thermocline does not touch the surface to exchange gases with the atmosphere.
    
    
  • Droplet generation by blowouts involving injection of oil and gas. During the Deepwater Horizon blowout, a deep-sea plume of dissolved gas, soluble oil compounds and small oil droplets was formed, when chemical dispersant was injected close to the wellhead. Biodegradation became an important process to remove gas and oil compounds in the deep and cold seawater, as has been shown by several laboratory and field studies, and it was suggested from field studies that biodegradation of gas compounds stimulated also the degradation of oil compounds. At SINTEF Ocean, laboratory studies in cold seawater from a Norwegian fjord was performed with a mixture of gas and oil. Their studies showed that the most essential natural gas compounds (methane, ethane and propane) did not stimulate or inhibit oil compound biodegradation. The biodegradation of gas compounds was also unaffected by the presence of oil. Since their results differed from the Deepwater Horizon blowout field findings, the impacts of gas compounds on oil biodegradation during a blowout may differ between seawater sources, depending on a complexity of factors.
    
    

• The SINTEF Tower Basin (circular basin six-meter-high, three-meter-wide) containing over 40 000 liters of natural sea water was used to simulate subsea release of oil and gas. The ability to simulate a wide range of release conditions gave the oil spill chemist, oceanographer and physicist new and unique knowledge that will help them be better prepared to reduce the environmental effects on the marine environment in case of a new accidental subsea blow-out like the Deepwater Horizon Macondo well.
  
  
• Effect of crude oil pollutants on the grazing impact of marine protozoa. To investigate the effect of oil pollutants on the growth and grazing unicellular grazers on phytoplankton, DROPPS-III researchers at UTMSI conducted exposure experiments using Louisiana sweet crude oil and Corexit 9500A dispersant at a volume ratio of 20:1. In exposure to increasing nominal concentrations of chemically-enhanced water accommodated fraction (CEWAF), the algal prey and protistan grazers showed species specific responses to the oil toxicities, as reflected by the varying specific growth rates.
  
  
• Effect of crude oil pollutants on the trophic interaction of planktonic organisms – a mesocosm study. DROPPS-III scientists at UTMSI conducted a mesocosm study on the effects of crude oil pollutants on microzooplankton grazing on a natural phytoplankton community. By exposing the microzooplankton and phytoplankton communities to dispersed Louisiana sweet crude oil (DOil) at 10 µL L-1, the grazing impact on phytoplankton by microzooplankton were greatly reduced to near zero on days 2 and 6 after exposure when compared to the control treatment. A positive relationship was found between the in situ growth rates of phytoplankton and the grazing rates of microzooplankton in the control treatment but not in DOil treatment. This indicates that the coupling between phytoplankton growth and microzooplankton grazing normally found in the marine ecosystem was disrupted in exposure to dispersed crude oil.
  
  
• Effect of crude oil exposure on bacterial community structure of dinoflagellates: impact of oil-degrading bacteria on dinoflagellate growth. DROPPS-III researchers conducted a series of successful experiments pertaining to the role of crude oil- degrading bacteria in the association between crude oil spills and phytoplankton blooms. They found that oil-degrading bacterial isolates significantly enhanced the growth rate and yield of the dinoflagellates by releasing certain growth promoting substances. This study presented new evidence of the potential role of oil-degrading bacteria in the formation of phytoplankton blooms after an oil spill.
  
  
• Aromatic hydrocarbons under photo-oxidation. DROPPS-III scientists studied the fate of aromatic hydrocarbons in light Louisiana sweet crude oil after exposure to natural sunlight in the Gulf of Mexico. Through a series of 44-day natural light exposure experiments, they found that the aliphatic components of photo-generated asphaltenes were mostly the alkyl chains of alkylated aromatic hydrocarbons. They also traced the fates of 13C-labeled phenanthrene that was amended to crude oil, including the conversion of the 13C-phenanthrene among the pools of saturate, aromatic, resin, asphaltene and dissolved inorganic carbon. These results can help evaluate bioavailability and toxicity of the oxygenated or polar hydrocarbons after photooxidation.

• Utilization of sunlight by certain microorganisms to degrade hydrocarbon. DROPPS-III scientists at UTMSI investigated whether or not photoheterotrophic bacteria are present during oil degradation and how these heterotrophic bacteria contribute in the process. Preliminary data suggest that concentrations of both alkanes and Polycyclic aromatic hydrocarbons decreased with time in light incubations, while they stayed relatively constant in dark incubations.
  
  
• Chemical composition of tar balls collected on the beaches on Mustang Island, Texas, August 2019. DROPPS-III researchers from UTMSI collected tar balls that washed up on the beaches on Mustang Island in August, 2019. They investigated whether or not the oil originated from the DeepWater Horizon oil spill. Tar ball chemical composition was analyzed and results suggest that they most likely originated from three or four sources. One source may have been the 1979 Ixtoc I oil spill in the Bay of Campeche, Mexico, because the chemical signature of the less weathered tar balls was similar to the “fingerprint” of the Ixtoc I oil.

II.   Formation of biofilms, mucosal aggregates, and interfacial phenomena including bacterial interaction, response to chemical/physical challenges 

• Experimental studies of bacteria adhered to fluid interfaces. DROPPS-III researchers at the University of Pennsylvania (UPENN) studied the swimming behaviors of Pseudomonas aeruginosa (PA01) trapped near or on oil-water interfaces. Based on statistical analysis, they found that bacteria have pinned contact lines that prevent rotation except about the axis normal to the interface, and they have a force and torque balance for pirouette and curly motions. On the interface they also observed an asymmetric swimming pattern of these PA01 bacteria, with weakly curved clockwise and counter clockwise paths with increasing curvature.
  
  
• Development of theoretical description of bacteria at fluid interfaces. DROPPS-III scientists at UPENN investigated self-propelled microswimmers at oil water interfaces. Active bacteria swimming at interfaces exhibit a variety of distinct swimming trajectories including nearly straight lines, circles of varying radii, and sharp reversals of direction. Moreover, bacteria can interact with other bacteria or passive colloids at the interface to generate interesting paths of motion. This differs from active bacteria swimming in a bulk fluid which typically travel in straight runs. More complex motions are generated when a swimming bacterium interacts with either passive colloids or other swimmers on the interface. Fundamental understanding concerning the hydrodynamics of swimming of microbes attached to interfaces is currently lacking and is needed to analyze experimental data. This motivated UPENN’s theoretical investigation of self-propelled microswimmers at interfaces. They also examined the trajectories of individual swimmers using the spherical squirmer model adapted for use on the interface and found that circular trajectories arise whose radius is a function of viscosity ratio and the torque produced by the swimmer in the direction parallel to the interface. This is a similar finding for swimmers found near but not attached to interfaces.
  
  
• Formation of biofilms and associated interfacial phenomena: mechanistic understanding of Marine Oil Snow Formation. DROPPS-III researchers at Texas A&M University Corpus Christi (TAMUCC) studied the fundamental principles governing the interaction of microbes with an oil?water interface and the mechanistic nature of aggregate formation around an oil droplet. To serve this purpose, a microfluidic eChip platform was developed to provide microcosm observations of a droplet in a shear flow containing bacterial suspension at ecologically comparable temporal and spatial scales.
  
  
• Microcosm experiments using natural seawater. DROPPS-III scientists at TAMUCC conducted eChip microcosm experiments with natural seawater to establish real-world relevancy of the observed streamer formation that can cause increased drag that slow down the rising droplets and consequently increase the residence time of oil droplets to nearby bacteria. They used three coastal seawater samples from the Gulf of Mexico and three bacterial pure cultures to demonstrate the streamer formation and evolution surrounding an oil droplet under relevant conditions using the microfluidic platform. All seawater samples formed aggregates with an oil droplet. Inner bay samples with higher particles and bacteria formed viscoelastic streamers, but not the outer bay sample. Pure bacterial suspension of Pseudomonas, Alcanivorax, and Marinobacter all formed various forms of aggregates and streamers that vary with time scales. Their study showed that streamer formation around an oil droplet is a real world phenomenon, and its development could be affected by the quantity of particles and the type of bacteria and EPS produced. These streamers are important precursors of marine oil aggregates and can increase the drag on rising oil droplets while decreasing ascend through the water column.

Theme 3: Potential impact of aerosolized oil on public health

I. Assessing and characterizing public health risks of atmospheric exposure to crude oil spills and dispersants using an in vitro system

• Health risk assessment: chemical composition of nano-sized airborne particulate matter emitted from bubbles bursting. Researchers at Johns Hopkins School of Public Heath (JHSPH) and Johns Hopkins Medical Institute (JHMI) investigated the toxic impacts on human bronchial cells exposed to oily marine aerosols. To access the toxicity of the air pollutants emitted from a nebulization system containing crude oil in seawater versus crude oil mixed with dispersant (Corexit 9500A) in seawater, the novel Real-Time Examination of Cell Exposure system was used to expose normal airway epithelia cells to either crude oil or crude oil with dispersant for 2 hours. The barrier function data involving permeability, (as measured by Trans-Epithelial/Trans- Endothelial Electrical Resistance (TEER)), percentage of moving cilia, and ciliary beat frequency (CBF) were measured at baseline, immediately after exposure (after 2 hours), and after a recovery period of 18 hours. Preliminary results showed TEER increased immediately after exposure and it never recovered to baseline for both crude oil with or without dispersant. The team did not see any cilia after exposure nor the epithelia with crude-oil containing dispersant. For just crude oil exposure, CBF decreased as well as with crude oil exposure. However, with dispersant they were not able to measure CBF because there was no observation of any cilia.