Impact of the deepwater horizon oil spill on bioavailable polycyclic aromatic hydrocarbons in Gulf of Mexico coastal waters

Abstract

An estimated 4.1 million barrels of oil and 2.1 million gallons of dispersants were released into the Gulf of Mexico during the Deepwater Horizon oil spill. There is a continued need for information about the impacts and long-term effects of the disaster on the Gulf of Mexico. The objectives of this study were to assess bioavailable polycyclic aromatic hydrocarbons (PAHs) in the coastal waters of four Gulf Coast states that were impacted by the spill. For over a year, beginning in May 2010, passive sampling devices were used to monitor the bioavailable concentration of PAHs. Prior to shoreline oiling, baseline data were obtained at all the study sites, allowing for direct before and after comparisons of PAH contamination. Significant increases in bioavailable PAHs were seen following the oil spill, however, preoiling levels were observed at all sites by March 2011. A return to elevated PAH concentrations, accompanied by a chemical fingerprint similar to that observed while the site was being impacted by the spill, was observed in Alabama in summer 2011. Chemical forensic modeling demonstrated that elevated PAH concentrations are associated with distinctive chemical profiles.

Figure 1. Sampling locations at four states in the Gulf of Mexico

Sampling sites are indicated by open circles. The location of the Deepwater Horizon rig and Macondo well is shown with a solid circle.

Figure 2. Bioavailable concentration of PAHs in coastal waters of the Gulf of Mexico

Bars represent the dissolved concentration of the sum of 33 PAH compounds and error bars represent the calculated 95% confidence interval based on pooled variance from a replication study. Note that the scale is different for Grand Isle, LA. Exact sampling dates can be found in the methods.

Figure 3. Principal components analysis of PAH chemical profiles

Principle component 1 and 2, together representing 49% of the variability in the data set, are plotted. States are differentiated by symbols and the numbers indicate the sampling events in chronological order. There is no month 4 sample for Louisiana. Data from samples taken during month 1, prior to shoreline oiling, are enclosed by a dotted line labeled “Preoiling”.