Only a small fraction of released oil is recovered after an oceanic oil spill. The rest undergoes a series of processes as the oil interacts with the complex physical, biological, and chemical environments in the ocean. In spite of the significant environmental impacts of oil spills, and substantial research efforts, many of the processes involving spills are still unclear, limiting the ability of the scientific and engineering communities to predict the fate of spilled oil and its environmental and human health impact. The DROPPS III consortium (DROPPS: Dispersion Research on Oil: Physics and Plankton Studies) brings together complementing experts from eight institutions and diverse disciplines, including marine biology, chemistry, transport phenomena, computational modeling, imaging and healthcare professionals. The goal of DROPPS III is to complete our investigations and modeling of biological, physical, and chemical processes affecting the fate of crude oil spills, including physical breakup and dispersion of oil patches, interactions of petroleum with marine organisms, microbes and particles, biodegradation of oil, and the impact of aerosolized oil on public health. Collaborative research that the consortium members have performed under the DROPPS I and DROPPS II funding cycles has led to numerous new findings and development of unique facilities and capabilities to measure and model interactions of oil with its environment. A substantial fraction of the DROPPS III effort will focus on wrapping up and/or extending the scope of these on-going investigations, while others are aimed at addressing new questions introduced by recent findings. Attention will be paid to improved integration of the discoveries in physics, biology and public health in order to produce legacy products that will make our research more accessible to scientists, educators, decision makers and the general public. The experimental and numerical studies will be performed at varying scales and levels of complexity, from ‘bench-top’ investigations that fully characterize specific phenomena, to multicomponent, meso-scale experiments and simulations that mimic realistic physical and biological conditions. The tasks are divided into three complementary areas, which are listed according to the RFP VI themes.
Theme I: Physical processes affecting the breakup, distribution, dispersion, and settling of oil
Shortly after a spill, a small fraction of the oil dissolves, and the remaining immiscible majority breaks into droplets by physical processes, including surface waves, jets in the case of blowouts, background turbulence, wind shear, impact of raindrops and bubble bursting. The subsurface droplets are then dispersed by currents and turbulence, and the aerosolized droplets by wind. The size distribution of these droplets, which affects their transport and subsequent interactions, depends on the processes involved and the oil properties. Knowledge of this size distribution is essential for predicting the dispersion of the oil and its interaction with the environment surrounding it. A series of experimental studies, many of them unique in terms of scales and instrumentation involved, complemented with computational models at varying level of details, will investigate physical processes involved with the generation, transport, and settling of oil droplets. For subsurface droplets, we will expand the scope of measuring and modeling of (i) the effects of wave scales and oil properties, including dispersants, on size distributions and dispersion of droplets generated by breaking surface waves, (ii) the effects of oil-gas mixtures, ambient pressure, cross-flow, and dispersants on the breakup of subsurface jets mimicking blowouts, and the (iii) effects of oil and particle properties on the formation, shape and settling of oil-particle aggregates. We will also elucidate and model several recently discovered phenomena, such as: (i) the processes causing generation of sub-micron droplets by shear fields involving length scales that are several orders of magnitude larger; and (ii) the generation by oil jets composed of prevalent compound droplets often consisting of multiple layers of oil and water (“Russian doll” droplets), which affects their buoyancy and presumably, their biochemical interactions. For airborne droplets, we will use a recently completed large wind-wave facility and a suite of instruments to measure the effects of oil properties, including dispersant concentration, as well as wind and wave scales, on the chemical composition, concentration and size distributions of aerosolized droplets in the 10 nm to 10 mm size range. Mechanisms producing the aerosolized nano-droplets for oil premixed with dispersant, such as bursting of bubbles generated by wave breaking on the water surface, will be characterized.
Theme II. Chemical evolution and biological degradation of oil by interactions with marine plankton, bacteria and the local environment.
The interfacial properties and chemical composition of subsurface oil change as it interacts with the chemical, biological, and physical environments. Biological interactions contributing to the ‘biodegradation’ of oil include consumption by marine animals and protists, colonization by bacteria and resulting formation of biofilms, and entrapment within biologically derived flocculent material (i.e. marine snow). The rates of biodegradation and oxidation of the oil are affected by environmental conditions along its path. The DROPPS III consortium will focus on the following processes: (i) The role of solar radiation in the biodegradation and photooxidation of crude oil. Strong solar irradiance leads to potent photo-oxidation that breaks down the aromatic fraction of oil, often producing compounds that are more toxic. The main goal is to further characterize oxygenated hydrocarbons using advanced analytical techniques. (ii) The indirect role of solar irradiance on the formation of MOSSFA (Marine Oil Snow Sedimentation and Flocculent Accumulation).The distinct bacterial communities developed under sunlight may affect the production of extracellular polymeric substances (EPS), which is important in the formation of marine aggregates and the process of MOSSFA. These experiments will be carried out in the UTMSI mesocosm facilities. (iii) The effects of natural plankton assemblages on production of oily aerosols in breaking waves. Experiments on oily aerosol generation have been performed in sterile artificial seawater to date. Natural seawater contains billions of bacteria and viruses, millions of protists and phytoplankton per liter that all may contribute dissolved organic matter to seawater, which is a major component of marine aerosols in the absence of oil. (iv) Studies of the ingestion of dispersed crude oil droplets by zooplankton. High speed video of tethered zooplankton will be used to determine if dispersed oil droplets are intentionally ingested or incidentally ingested along with food particles. The further breakup of oil droplets by zooplankton feeding activities will also be investigated along with the effects of turbulence on the ingestion of oil to integrate the physical and biological findings. (v) The role of turbulent diffusion of oil in estimates of toxic effects of oil on marine organisms. When a finite amount of oil is spilled in the marine environment, the concentration of oil continually changes as the oil is dispersed, yet most toxicity experiments are performed using constant concentrations of oil. A set of mesocosm experiments is proposed that will simulate the changing concentrations of oil in a finite spill, and determine the effects of these changing concentrations of toxins on natural plankton assemblages. (vi) Mechanisms of bacteria and natural microbial assemblages on formation of mucosal aggregates and biofilm is further investigated with series of unique microcosm experiments and microscopic observations under realistic flow conditions.
Theme V: Potential Impact of aerosolized oil on public health
The recently discovered two orders of magnitude increase in concentration of aerosolized sub-micron (10-100nm) droplets generated by breaking waves when the oil is premixed with dispersant raises concerns about health implications to cleanup workers and downstream communities. Yet, little is known about the hazards to human health from exposure to oil and dispersants. Consequently, we will (i) use the measured size distribution, concentration, and chemical composition of airborne oil as input for a multi-tier transport model that predict the spatiotemporal dispersion of oil to nearby communities at varying scales, and (ii) utilize a recently designed novel cell exposure system to determine the effects of aerosolized oil and dispersant on human lung epithelial cells. This device allows direct time-resolved observations on the response of lung cell layers while and after being exposed to the aerosolized oil. The test will determine the cell viability, barrier functions, resistance, permeability, pro-inflammatory cytokines, mucociliary clearance, and response to bacteria. These measurements are critical for predicting the occupational and ambient exposures for future health effects studies.