Between April 22and July 15, 2010 approximately 4.9 million barrels of oil was released into the Gulf of Mexico from the Deepwater Horizon oil well. Approximately 16% of the oil was chemically dispersed, at the surface and at 1,500 m depth, using Corexit 9527 and Corexit 9500, which contain dioctyl sodium sulfosuccinate (DOSS) as a major surfactant component. This was the largest release of oil in history at a significant depth, and the first time large quantities of dispersant (0.77 million gallons of 1.8 million gallons total) were applied to a subsurface oil plume. During two cruises in late May and early June water samples were collected at the surface and at depth for DOSS analysis. Real-time fluorimetry data was used to infer the presence of oil components to select appropriate sampling depths. Samples were stored frozen and in the dark for approximately 6 months prior to analysis by liquid chromatography/tandem mass spectrometry with isotope-dilution quantitation. The blank-limited method detection limit (0.25 mg/L) was substantially less than the EPA’s aquatic life benchmark of 40 mg/L. Concentrations of DOSS exceeding 200 mg/L were observed in select surface samples near the well site; in subsurface samples DOSS did not exceed 40 mg/L. Although DOSS was present at high concentration in the immediate vicinity of the well where it was being continuously applied, a combination of biodegradation, photolysis, and dilution likely reduced persistence at concentrations exceeding the EPA aquatic life benchmark beyond this immediate area.

Distribution of dispersant-related surfactants in the Gulf of Mexico area following the Deepwater Horizon oil spill

255th National Meeting (2018)

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