BIODEGRADATION OF DEEPWATER HORIZON CRUDE OIL ENHANCED BY NA-MONTMORILLONITE AMENDMENT IN IMPACTED SALT MARSHES, BARATARIA BAY, LOUISIANA

The Deepwater Horizon disaster released ~4.9 million barrels of oil into the Gulf of Mexico, impacting over 500 km of salt marsh in the heart of Louisiana's fisheries and tourism industries. Based on lab experiments following Spain's 2003 Prestige oil spill, Warr et al. (2009) hypothesized that high-layer charge montmorillonite can enhance microbial biodegradation rates by altering the charged environment near the cell wall. Here we test this hypothesis in the field, and extend it to the anaerobic microbial communities dominating salt marshes. In early September, 2010, we seeded ~4m² test plots in oiled marshwith ~0.5cm of commercial Na-montmorillonite. Enhanced smectite:kaolinite ratios in the sediment were monitored by XRD.

Serial GC/MS analyses of surface oil in the marsh between September 2010 and May 2011 show losses of n-alkane petroleum hydrocarbons. These persisted in the marsh as recently as May 22, 2011, consistent with the slow rate of anaerobic biodegradation. Polycyclic aromatic hydrocarbons (PAHs), which are of particular concern because of their carcinogenic effects, have also decreased during this time.

Preliminary data suggest that clay-amended sites have more advanced biodegradation, based on total n-alkane and PAH abundances, as well as ratios of specific compounds to more conservative consituents such as hopane. Pristane/phytane ratios have remained roughly constant (~0.75) in both control and experimental settings. Preferential loss of lower molecular weight compounds is clearly observed; PAH profiles are now dominated by alkylated homologues. In clay-amended sites, loss of lower molecular weight compounds is more advanced.

Transcript analyses of functional genes indicate that Fe-reducing, sulfate-reducing, and methanogenic prokaryotic communities are metabolically active at both control and experimental plots. Analyses are underway to identify microbiological differences among the sites. Benchtop microcosm experiments are also underway to monitor petroleum hydrocarbons, pore water chemistry, and gene expression in a more controlled environment. If successful, clay enhancement of biodegradation is potentially a useful technique in remediation of oil-contaminated sites, especially those in anaerobic environments in which natural attenuation rates are very slow.