Oil Spill Dispersants Research Articles

Editorial—The 2nd International Workshop on Modeling the Ocean (IWMO-2010)

The formation of the International Workshop on Modeling the Ocean (IWMO) in 2009 has been motivated by the rapid growth in ocean modeling research around the world. In particular, the spread of ocean modeling research in Asia during recent years and the establishment of many international collaborative modeling projects led to the first meeting, IWMO-2009, which was held in Taipei, Taiwan, 23–26 February 2009 (see the two special issues resulted from this meeting: Oey et al. 2010a, b). The second meeting (IWMO-2010; http://www.ccpo.odu.edu/∼tezer/ IWMO_2010/) was hosted by the Center for Coastal Physical Oceanography at Old Dominion University in Norfolk, VA, USA, 24–26 May 2010. The collection of manuscripts resulted from this IWMO-2010 meeting are included in this special issue and have been published in Ocean Dynamics issues from May to this issue. Two important foci are highlighted in IWMO meetings: (1) international collaborations and (2) involvement of young scientists. As evident in the papers in this special issue, the co-authors of papers are often from different countries and include several graduate students and post-docs. To encourage young scientists to participate, IWMO hosts a special session for the Outstanding Young Scientist Award competition. Despite difficulties in international travel during the IWMO-2010 meeting due to the Iceland volcano eruption and increased security that prevented scientists from some countries to travel to the USA, participants from over 15 countries attended the meeting, including attendees from Europe, North and South America, Asia, and Australia. The meeting received considerable attention from the local media due to the BP oil spill in the Gulf of Mexico that happened just before the meeting; a paper on the oil spill was presented in the meeting and is included in the special issue (Chang et al. 2011). The IWMO returned to Asia for the third meeting (IWMO-2011; http://www.fio. org.cn/iwmo2011/iwmo2011.htm) that has been hosted by the First Institute of Oceanography, Qingdao, China, 6–9 June 2011. The next meeting (IWMO-2012) will be hosted by the Japan Agency for Marine-Earth Science and Technology (JAMSTEK), Japan. The collection of 13 papers in this special issue covers a wide range of geographical domains, seven different types of ocean models, and process studies ranging in scales from a few centimeters to regional and global. The studies demonstrate the recent progress in numerical modeling: on one hand, the ability to simulate smaller and smaller scales and, on the other hand, the advancement in realistic simulations of large-scale ocean processes. Models are applied to various interdisciplinary practical problems, from the dispersion of oil spill in the Gulf of Mexico to the Responsible Editor: Jorg-Olaf Wolff

Influence of Seasonal Variability of Lower Mississippi River Discharge, Temperature, Suspended Sediments, and Salinity on Oil‐Mineral Aggregate Formation

Under certain conditions, oil droplets that have separated from the main oil slick may become coated by suspended sediments forming oil-mineral aggregates (OMAs). The formation of these aggregates depends on suspended particulate characteristics, temperature, salinity, mixing energy, droplet size and number, and oil properties. The OMAs do not re-coalesce with the slick and tend not to adhere to surfaces, potentially evading surface cleanup measures, enhancing opportunity for biodegradation and reducing shoreline oiling. Potential OMA formation was quantified during four distinct states of the Lower Mississippi River during a typical year using empirical relationships from laboratory and field studies for three common oils and different combinations of discharge, temperature, suspended sediments, and salinity. The largest potential OMA formation for the two lighter oils, up to 36% of the total release volume, was in the winter and spring, when high sediment availability promotes formation. For the denser, high-viscosity oil, the peak potential OMA formation, 9% of the release volume, occurred in the summer, when the salinity was higher. These results provide some evidence that, depending on environmental and spill characteristics, the formation of OMAs could be an important, but unaccounted for, process in the fate and transport of oils released in the Lower Mississippi River and should be included in oil spill dispersion models and post-spill site assessment and remediation actions.

Comparative Acute Toxicity of Eight Oil Spill Dispersants, Louisiana Crude Oil and Chemically Dispersed Oil to Two Gulf of Mexico Aquatic Species

Abstract Approximately two million gallons of oil dispersants were applied in response to the Deepwater Horizon spill. This study determined the acute toxicity of eight commercial oil dispersants, South Louisiana crude oil (SLC), and chemically dispersed SLC using each of the eight oil dispersants. The approach utilized consistent test methodologies within a single laboratory in assessing the relative acute toxicity of the eight dispersants, including Corexit 9500A, the dispersant applied offshore to surface waters and directly to the leak source. Static acute toxicity tests were performed with two Gulf of Mexico estuarine test species to determine 48-hr LC50 values for mysid shrimp (Americamysis bahia) and 96-hr LC50 values for inland silversides (Menidia berylina). Dispersant-only test solutions were prepared with high energy mixing, whereas water accommodated fractions of SLC and chemically dispersed SLC were prepared with moderate energy followed by settling and testing of the aqueous phase. For all e...

The Montara Oil Spill Dispersant Response; Challenging the Paradigms

ABSTRACT The Montara oil spill, which occurred in the Montara oil field in the Timor Sea, off the northern coast of Western Australia, is considered one of Australia's worst oil spills to date. The uncontrolled subsea release of oil and gas mixture continued for a total of 74 days. Although the actual spilled quantity has not been confirmed, and mass balances are notoriously difficult to develop with any particular accuracy, it was estimated that an average 400bbls of crude was lost every day. Dispersant application and at sea containment and recovery were the primary response strategies. A total of 184 tonnes of dispersant was used during the response and approximately 490 tonnes of oil was recovered through the at sea operation. The Montara crude was a waxy oil with a pour point close to that of the high ambient sea temperatures, due to this characteristic, the oil was solidified in the cool of the night, but increasingly became more fluid as it warmed up during the day. This change in viscosity was cle...

A Method for Assessing Environmental Risks of Oil-Mineral-Aggregate to Benthic Organisms

ABSTRACT Previous studies have shown that Oil-Mineral-Aggregate (OMA) formation enhances the dispersion of marine oil spills, but the potential impacts of settled OMAs on benthic organisms are not well known. A comprehensive numerical approach is proposed here to model the transport of OMAs and assesses their potential risks. The predicted environmental concentrations (PEC) of settled oil in OMAs was calculated using a random walk particle tracking model and the benchmark concentrations (BCs) of individual hydrocarbon groups were computed based on a equilibrium partitioning (EqP) approach. The likely of risks in terms of Hazard Quotient (HQ) were then determined using a Monte Carlo simulation method. HQ for both aliphatic and aromatic hydrocarbon groups were calculated for OMAs formed with two sediments, Mississippi River Delta (MRD) and Standard Reference Material (SRM). Mean total HQs were also determined by a simple sum of individual HQ. The predicted results from a case study based on a spill of 1000 tons of South Louisiana crude oil in the Gulf of St. Lawrence with a water depth of 80 m show that the SRM is unlikely to cause adverse impacts but this may not be the case for MRD. Furthermore, it has been found that the application of chemical dispersant (CD) increased the risks of MRD but it had little effects on SRM.

Oil viscosity limitation on dispersibility of crude oil under simulated at-sea conditions in a large wave tank

This study determined the limiting oil viscosity for chemical dispersion of oil spills under simulated sea conditions in the large outdoor wave tank at the US National Oil Spill Response Test Facility in New Jersey. Dispersant effectiveness tests were completed using crude oils with viscosities ranging from 67 to 40,100cP at test temperature. Tests produced an effectiveness–viscosity curve with three phases when oil was treated with Corexit 9500 at a dispersant-to-oil ratio of 1:20. The oil viscosity that limited chemical dispersion under simulated at-sea conditions was in the range of 18,690cP to 33,400cP. Visual observations and measurements of oil concentrations and droplet size distributions in the water under treated and control slicks correlated well with direct measurements of effectiveness. The dispersant effectiveness versus oil viscosity relationship under simulated at sea conditions at Ohmsett was most similar to those from similar tests made using the Institut Francais du Pétrole and Exxon Dispersant Effectiveness (EXDET) test methods.

A New Family of Oil Spill Dispersants: Part 1. The Effect of Structural Variation on the Oil Spill Dispersant Efficiency

New nonionic surfactants were synthesized through esterfication of a dicarboxylic acid (succinic or adipic acid) with fatty alcohols that have different molecular weight; namely, octyl, lauryl, and cetyl alcohol. The ester products were reacted with polyethylene glycols of different molecular weight (400, 600, and 1,000) to form compounds having different hydrophil-lipophil balances. The surface active properties of the prepared surfactants were evaluated, and the critical micelle concentrations were determined, so as to determine the Pc20, effectiveness πcmc, and maximum dispersion efficiency from the screening study.

Numerical Simulation Calculation of Ship Submarine Oil Spill under Complicated Ocean Environment

In order to conduct the cleaning of spilled oil, to protect the marine ecological balance and to prevent the damage to marine environment by oil spill, the simulation of oil spill in deep water with the wave motion, wind and current was built by the user defined function and the volume of fluid in FLUENT. The dispersion and diffusion of oil spill in deep water was simulated dynamically. Also the oil spilling trajectories under the conditions of different current velocities, wavelengths and wind velocities were compared and analyzed, respectively. The results showed that the current, wind and wave decided the location and areas of oil films on the sea surface. The water depth influenced by the wave which increased with the increasing wavelength. Meantime, the areas of oil films on sea surface increased with current velocity decreasing, while the distance between the oil film and the source of oil increased. With the wind velocity increasing, the extended length of oil dispersion underwater and the oil film area on surface increased.

Analysis of eight oil spill dispersants using rapid, in vitro tests for endocrine and other biological activity.

The Deepwater Horizon oil spill has led to the use of >1 M gallons of oil spill dispersants, which are mixtures of surfactants and solvents. Because of this large scale use there is a critical need to understand the potential for toxicity of the currently used dispersant and potential alternatives, especially given the limited toxicity testing information that is available. In particular, some dispersants contain nonylphenol ethoxylates (NPEs), which can degrade to nonylphenol (NP), a known endocrine disruptor. Given the urgent need to generate toxicity data, we carried out a series of in vitro high-throughput assays on eight commercial dispersants. These assays focused on the estrogen and androgen receptors (ER and AR), but also included a larger battery of assays probing other biological pathways. Cytotoxicity in mammalian cells was also quantified. No activity was seen in any AR assay. Two dispersants showed a weak ER signal in one assay (EC50 of 16 ppm for Nokomis 3-F4 and 25 ppm for ZI-400). NPs and NPEs also had a weak signal in this same ER assay. Note that Corexit 9500, the currently used product, does not contain NPEs and did not show any ER activity. Cytotoxicity values for six of the dispersants were statistically indistinguishable, with median LC50 values approximately 100 ppm. Two dispersants, JD 2000 and SAF-RON GOLD, were significantly less cytotoxic than the others with LC50 values approaching or exceeding 1000 ppm.

Numerical studies of dispersion due to tidal flow through Moskstraumen, northern Norway

The effect of horizontal grid resolution on the horizontal relative dispersion of particle pairs has been investigated on a short time scale, i.e. one tidal M 2 cycle. Of particular interest is the tidal effect on dispersion and transports in coastal waters where small-scale flow features are important. A three-dimensional ocean model has been applied to simulate the tidal flow through the Moskstraumen Maelstrom outside Lofoten in northern Norway, well known for its strong current and whirlpools (Gjevik et al., Nature 388(6645):837–838, 1997; Moe et al., Cont Shelf Res 22(3):485–504, 2002). Simulations with spatial resolution down to 50 m have been carried out. Lagrangian tracers were passively advected with the flow, and Lyapunov exponents and power law exponents have been calculated to analyse the separation statistics. It is found that the relative dispersion of particles on a short time scale (12–24 h) is very sensitive to the grid size and that the spatial variability is also very large, ranging from 0 to 100 km2 over a distance of 100 m. This means that models for prediction of transport and dispersion of oil spills, fish eggs, sea lice etc. using a single diffusion coefficient will be of limited value, unless the models actually resolves the small-scale eddies of the tidal current.

Lagrangian stochastic modelling for oil spills turbulent dispersion on ocean surface

Releases of liquid petroleum hydrocarbon into the environment, especially into the ocean, are called {\em oil spills}. To correctly model dispersion on ocean surface both large and small scale processes must be considered. In fact, the motion of the centre of mass is driven by large scale meandering and spot enlarging is controlled by small scale turbulence. A Lagrangian stochastic model for turbulent dispersion of oil spills on ocean surface is here formulated: large scale meandering is analytically prescribed by the stream function proposed by Bower for meandering jet in the Gulf Stream; small scale turbulence has been modelled by a Lagrangian stochastic process for turbulent relative dispersion which is based on turbulent flow rotation. Numerical simulations are performed to highlight the effects on oil spills dispersion of differences in the velocity field intensity and those due to releases in the centre or in the boundary of a meandering jet.

Water-Based Oil Spill Dispersants Based on Rosin Formaldehyde Resins

Water-soluble surfactants based on rosin acids were synthesized from condensed rosin acid-formaldehyde. This was completed by esterification of series of rosin acid formaldehyde resins with poly(ethylene glycol) having different molecular weights to produce series of rosin esters. The structure of the produced resins was determined by infrared and 1HNMR analysis. The molecular weight of the produced surfactants was determined by gel permeation chromatography (GPC) technique. The surface properties of the prepared surfactants were determined by measuring the surface tension at different temperatures. The surface tension, critical micelle concentration (CMC), and surface activities were determined at different temperatures. Surface parameters such as surface excess concentration (Γmax), the area per molecule at interface (Amin), and the effectiveness of surface tension reduction (πCMC) were determined from the adsorption isotherms of the prepared surfactants. Some thermodynamic data for the adsorption process were calculated and are discussed. The dispersion efficiency of the prepared surfactants as petroleum oil spill dispersants was determined and correlated with the surface activity, concentrations of the prepared surfactants and type of petroleum crude oil.

Enbryotoxicity of Nigerian crude oil, oil spill dispersant and lindane in chick embryo

Enbryotoxicity of Nigerian crude oil, oil spill dispersant and lindane in chick embryo

Oil spill remediation by using the remediation agent JE1058BS that contains a biosurfactant produced by Gordonia sp. strain JE-1058

A remediation agent containing a biosurfactant was prepared by spray drying the sterilized culture broth of Gordonia sp. strain JE-1058, and the agent was designated as JE1058BS. On subjection to the baffled flask test developed by the United States Environmental Protection Agency, JE1058BS showed a strong potential to be applied as an oil spill dispersant even in the absence of a solvent. It also proved to be an effective bioremediation agent for the remediation of oil spills at sea. The addition of JE1058BS to seawater stimulated the degradation of weathered crude oil (ANS 521) via the activity of the indigenous marine bacteria. Its addition also stimulated the removal of crude oil from the surface of contaminated sea sand. These results indicate that biosurfactant-containing JE1058BS has a strong potential to be applied as a remediation agent for the clean-up of oil spills at sea and on shorelines.

Synthesis and Characterization of Novel Crude Oil Dispersants Based on Ethoxylated Schiff Base

Schiff base prepared from salicylaldehyde and diethylene triamine was ethoxylated by poly (ethylene glycol) of different molecular weights, namely 200, 600, 1000 and 2000, by using β,β-dichlorodiethyl ether as a linking agent. The ethoxylation reaction took place at both ends of the base upon using poly(ethylene glycol) (PEG) 200 and 600, whereas at one end when PEG 1000 and 2000 were used. The chemical structure of the prepared compounds was confirmed by using IR and 1HNMR spectroscopy. Thermodynamic parameters for micellization and adsorption or the prepared compounds were measured based on the surface tension of their solutions at different temperatures. Then, the compounds under investigation were tested as oil spill dispersants according to different standard test methods. It was found that the compounds with lower molecular weights of PEG showed the best dispersancy.

Synthesis and Evaluation of Ethoxylated Alkyl Sulfosuccinates as Oil Spill Dispersants

The surface properties particularly, Krafft point, foam stability and emulsion stability for the synthesized series of ethoxylated sodium monoalkyl (octyl-, dodecyl-, and cetyl-) sulfosuccinate surfactants were investigated comparing with those of sodium dioctyl sulfosuccinate. The prepared surfactants were evaluated as oil spill dispersants using screen test method. The results show that, the ethylene oxide units in the mixed moiety surfactant system (anionic–nonionic) effect on the depression of the Krafft point. Also, the increasing of ethylene oxide units in the prepared surfactants decreases the foam ability of these surfactants. The results of emulsion stability show that, the increasing in ethylene oxide units owing to the emulsion stability decreases. The prepared surfactants show a dispersion capability at different content of ethylene oxide units (9, 14, 23, and 90) and at different concentrations. The dispersion capability for these surfactants in the sea water is better than in the fresh water. The results show that, the increase of ethylene oxide units increases the dispersion efficiency of the synthesized surfactants.

DISPERSANT EFFECTIVENESS AS A FUNCTION OF ENERGY DISSIPATION RATE IN AN EXPERIMENTAL WAVE TANK

ABSTRACT In 2005, the National Research Council (NRC) published a comprehensive treatise on oil spill dispersants. Among other things, it concluded that research on dispersion effectiveness as a function of energy dissipation rate and particle size distribution was a high priority. Energy dissipation rate (turbulence and existence of breaking waves) is important to initiate and promote effective dispersion, and the particle size distribution of dispersed oil droplets affects dispersion and the ultimate fate of oil in the water column. In this paper, we discuss the use of a wave tank built on the premises of the Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada as part of collaborative research begun in 2003 by the U.S. Environmental Protection Agency (EPA) and Fisheries and Oceans Canada (DFO). This tank is able to produce breaking waves of various energy levels at precise locations in the tank. We studied the effects of 2 commercial dispersants (Corexit 9500 and SPC 1000) and a no dispersant control on two different crude oils (unweathered Alaska North Slope and weathered MESA Light) at 3 different energy dissipation rates (regular non-breaking waves, spilling breakers, and plunging breakers), amounting to 18 different treatments. We quantified the energy dissipation rates under those 3 wave conditions and measured oil dispersion in a factorial experiment involving 3 replicates of the 18 treatments over the course of the summer of 2006. Results clearly showed the importance of wave energy and the presence of a chemical dispersant on the ability to produce effective dispersion of oil into the water column. The presence of dispersants at increasing wave energies produced significantly better dispersion (p <0.05) than the no-dispersant controls. This study was conducted under batch conditions. Future work will be done under continuous flow conditions.

OIL SPILL DISPERSION STABILITY AND OIL RE-SURFACING

ABSTRACT This paper summarizes the data and the theory of oil-in-water emulsion stability resulting in oil spill dispersion re-surfacing. There is an extensive body of literature on surfactants and interfacial chemistry, including experimental data on emulsion stability. The phenomenon of resurfacing oil is the result of two separate processes: de stabilization of an oil-in-water emulsion and desorption of surfactant from the oil-water interface which leads to further de stabilization. The de stabilization of oil-in-water emulsions such as chemical oil dispersions is a consequence of the fact that no emulsions are thermodynamically stable. Ultimately, natural forces move the emulsions to a stable state, which consists of separated oil and water. What is important is the rate at which this occurs. An emulsion is said to be kinetically stable when significant separation (usually considered to be half or 50% of the dispersed phase) occurs outside of the usable time. There are several forces and processes that result in the destabilization and resurfacing of oil-in-water emulsions such as chemically dispersed oils. These include gravitational forces, surfactant interchange with water and subsequent loss of surfactant to the water column, creaming, coalescence, flocculation, Ostwald ripening, and sedimentation. Gravitational separation is the most important force in the resurfacing of oil droplets from crude oil-in-water emulsions such as dispersions. Droplets in an emulsion tend to move upwards when their density is lower than that of water. Creaming is the de stabilization process that is simply described by the appearance of the starting dispersed phase at the surface. Coalescence is another important de stabilization process. Two droplets that interact as a result of close proximity or collision can form a new larger droplet. The result is to increase the droplet size and the rise rate, resulting in accelerated de stabilization of the emulsion. Studies show that coalescence increases with increasing turbidity as collisions between particles become more frequent. Another important phenomenon when considering the stability of dispersed oil, is the absorption/desorption of surfactant from the oil/water interface. In dilute solutions, much of the surfactant in the dispersed droplets ultimately partitions to the water column and thus is lost to the dispersion process. This paper provides a summary of the processes and data from some experiments relevant to oil spill dispersions.

OIL DROPLET SIZE DISTRIBUTION AS A FUNCTION OF ENERGY DISSIPATION RATE IN AN EXPERIMENTAL WAVE TANK

ABSTRACT The U.S. National Research Council (NRC) Committee on Understanding Oil Spill Dispersants: Efficacy and Effects (2005) identified two factors that require further investigation in chemical oil dispersant efficacy studies: 1) quantification of mixing energy at sea as energy dissipation rate and 2) dispersed particle size distribution. To fully evaluate the significance of these factors, a wave tank facility was designed and constructed to conduct controlled oil dispersion studies. A factorial experimental design was used to study the dispersant effectiveness as a function of energy dissipation rate for two oils and two dispersants under three different wave conditions, namely regular non-breaking waves, spilling breakers, and plunging breakers. The oils tested were weathered MESA and fresh ANS crude. The dispersants tested were Corexit 9500 and SPC 1000 plus water for no-dispersant control. The wave tank surface energy dissipatation rates of the three waves were determined to be 0.005, 0.1, and 1 m2/s3, respectively. The dispersed oil concentrations and droplet size distribution, measured by in-situ laser diffraction, were compared to quantify the chemical dispersant effectiveness as a function of energy dissipation rate. The results indicate that high energy dissipation rate of breaking waves enhanced chemical dispersant effectiveness by significantly increasing dispersed oil concentration and reducing droplet sizes in the water column (p <0.05). The presence of dispersants and breaking waves stimulated the oil dispersion kinetics. The findings of this research are expected to provide guidance to disperant application on oil spill responses.

Synthesis of Some Oil Spill Dispersants Based on Sorbitol Esters and Their Capability to Disperse Crude Oil on Seawater to Alleviate Its Accumulation and Environmental Impact

In this respect mono‐, di‐, and tri‐ sorbitol oleate esters [SMO, SDO, and STO] were prepared and then ethoxylated using ethylene oxide to obtain six sorbitol esters at different ethylene oxide content (e.o=5, 12, 15, 20, 35, and 45). They were tested as oil spill dispersants individually and in blends. From the obtained data, it was found that the blends are more effective than the corresponding individual surfactants. The maximum dispersion capability for the prepared surfactants was obtained at HLB range from 9 to 11 for the both individual surfactants and blends. The increase of total carbon number in the surfactant alkyl group leads to increase dispersion capability of the dispersant. The wide range of ethylene oxide content was used, but the maximum dispersion efficiency was obtained at ethylene oxide=20 in E(20)STO. Meanwhile, the dispersion capability increases when the interfacial tension decreases.