Crude oil was released at the seafloor from a depth of approximately 5,000 feet after the Deepwater Horizon accident in the Gulf of Mexico. The composition of the crude oil changed substantially between the point of release and the water surface, primarily due to dissolution. Once on the water surface, dispersion, photodegradation and evaporation continued to alter the composition of the Macondo crude oil.  The depletion of PAHs in the oil was calculated using the biomarker compound C30-hopane. Total and individual PAH concentrations in over 1,100 oil samples analyzed were normalized to hopane and compared to MC252 riser oil to determine percent depletion.  Findings to date show that Macondo oil was extensively depleted of PAHs in the Gulf of Mexico environment, with measurable loss of Total PAHs (TPAH) between the seafloor and the water surface and greater than 80 percent TPAH loss before the oil impacted the shoreline.

Extensive weathering and degradation of PAHs is documented in floating and shoreline oil samples collected after the Deepwater Horizon accident

243rd National Meeting (2012)

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