Distribution and Attenuation of Polycyclic Aromatic Hydrocarbons in Gulf of Mexico Seawater from the <i>Deepwater Horizon</i> Oil Accident

The extended duration of the oil release from the <i>Deepwater Horizon</i> accident (April 20–July 15, 2010) triggered a need to characterize environmental exposures in four dimensions through sampling and tracking the changes in distributions, concentrations, and compositions of oil and total polycyclic aromatic hydrocarbons (TPAH) in the Gulf of Mexico over time and space. More than 11 000 water samples were collected offshore during more than 100 cruises and were measured for 50 parent and alkylated polycyclic aromatic hydrocarbons (PAHs). Elevated concentrations (greater than 1 ppb) of TPAH were largely limited to an area within about 20 km of the wellhead in the subsurface deepwaters at 1000–1200 m depth to the southwest of the wellhead and in the top 3 m underlying the surface oil. Concentrations decreased with distance and time, and changes in the PAH composition indicate that these changes were due to differential solubilization, photodegradation, evaporation, and/or biodegradation of individual PAH compounds. These limited areas of elevated PAH concentrations disappeared within weeks after the release was stopped