Nearshore exposure to Deepwater Horizon oil

The Deepwater Horizon (DWH) oil spill affected more than 2000 km of shoreline. DWH oil entered the nearshore environment, stranding on shorelines as tar balls and/or emulsified oil, or forming submerged oil mats and integrating into nearshore sediments. The available chemistry data showed submerged sediments, especially within the first 50 m from oiled shorelines, displayed patchy distributions of elevated polycyclic aromatic hydrocarbon (PAH) concentrations in excess of ambient concentrations, which were quantified based on forensic findings establishing their source as being from the Macondo oil. Consistent with observed shoreline oiling conditions, PAH concentrations in the soils of affected Louisiana coastal wetlands were orders of magnitude higher than ambient concentrations, especially in locations along the seaward edge of the marsh. Both total and petrogenic PAHs decreased with distance from the shore in both inland and offshore directions. Although PAHs exhibited evidence of weathering over time, in the most heavily oiled areas, they continued to exceed ambient concentrations by orders of magnitude through fall of 2013.