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Dispersants are used to reduce the impact of oil spills in marine environment. Experiments were conducted with natural materials which were contaminated by direct application of fresh Louisiana crude oil. The natural materials evaluated included sea sand (South Beach in Miami, Florida), red mangrove leaves (Rhizophora mangle), and sea shells (Donax variabili). Salt water at two different salinities (17 and 34 ppt) was used with two types of Corexit dispersant solutions (9500A and 9527A) in concentrations ranging from 100 to 3500 mg/L. Washing of the contaminated samples was conducted by a three-step mixing procedure (salt water only, then with the addition of the dispersant solution to the salt water, and salt water) to simulate oil-saltwater-dispersant interactions. In general, increasing dispersant concentration increased the percentage of oil dispersed into the aqueous phase up to dispersant solutions containing 400 mg/L for Corexit 9500A and 300 mg/L Corexit 9527A. Increasing the dispersant concentration above these levels also decreased the dispersion of oil from the surfaces. At very high concentrations of dispersant solutions (above 1500 mg/L), the percentage of oil dispersed into the solution from the contaminated surfaces was about one half what was observed at 400 mg/L with Corexit 9500A and 300 mg/L Corexit 9527A. Although dispersants were most effective for removing the fresh Louisiana crude oil from sand particles and dispersing into the solution due to large surface area of the particles per unit weight; the residual oil remaining on the sand particles was relatively high in comparison to mangrove leaves and sea shells due to clustering of sand particle with oil. There was some oil penetration into the porous structure of the sea shells (at the microscopic level) which could not be removed. Image 1 • A three step washing process was used to clean crude oil contaminated natural materials. • Two commonly used oil spill dispersants (Corexit 9500A and Corexit 9527A) were evaluated. • Contaminated sea sand, shells (Donax variabili), and r ed mangrove (Rhizophora mangle) leaves were evaluated. • Increasing dispersant concentration up to 400 mg/L increased the oil dispersed into the aqueous phase. • Higher residual oil remained on sand surfaces due to clustering of particles with oil. [ABSTRACT FROM AUTHOR]

The Deepwater Horizon well released 4.4 million barrels of light crude oil offshore of Louisiana into one of the world's largest and most productive blue crab ( Callinectes sapidus) fisheries. The objectives of this paper were to determine the toxicity of the dispersant Corexit 9500A used in the 2010 oil spill on juvenile and larval blue crabs, and the long-term effects of sublethal acute exposure. Only the highest treatment levels of dispersant significantly increased mortality in larval and juvenile blue crabs (100 mg/L and 1,000 mg/L, respectively). This correlated to concentrations well above levels found in the Gulf of Mexico following the spill. Smaller and younger crabs showed higher mortality than older and larger crabs. This research indicates direct application of dispersants on crab larvae could cause acute mortality, but dilution through diffusion and natural weathering processes would minimize long-term effects. [ABSTRACT FROM AUTHOR]

Abstract: We recently conducted a laboratory study to measure the dispersion effectiveness of eight dispersants currently listed on the National Contingency Plan Product Schedule. Results are useful in determining how many commercial dispersant products would have been effective for use on South Louisiana crude oil in the Deepwater Horizon oil spill. The test used was a modification of the Baffled Flask Test (BFT), which is being proposed to replace the current Swirling Flask Test (SFT). The modifications of the BFT in this study included use of one oil rather than two, increasing replication from 4 runs to 6, and testing at two temperatures, 5°C and 25°C. Results indicated that temperature was not as critical a variable as the literature suggested, likely because of the low viscosity and light weight of the SLC. Of the eight dispersants tested, only three gave satisfactory results in the laboratory flasks at both temperatures. [Copyright &y& Elsevier]