FATE AND ENVIRONMENTAL TRANSFORMATION OF DEEPWATER HORIZON SPILLED OIL, TRACE METALS, AND DISPERSANTS IN BARATARIA BAY, LOUISIANA

Crude oil from the 2010 Deepwater Horizon rupture invaded southeastern United States coastlines. This study investigates the fate and environmental transformation of oil, trace metals, and dispersants associated with the spill in heavily oiled salt marshes in Barataria Bay, Louisiana. The total organic carbon content of contaminated pore water and sediments in Barataria Bay was found to be one to two orders of magnitude higher than those of pristine sites. Organic materials recovered from contaminated Louisiana wetlands match the chemical fingerprint of oil from the Macondo-1 wellhead.

High concentrations of metals (e.g., Cu, Pb, Zn, V, Hg, As), known to occur naturally within crude oil, were found in oiled sediments. Despite elevated metal content in sediments, concentrations of trace metals in pore waters are generally low. Laser ablation ICP-MS analyses suggest that trace metals have been sequestered from pore-water by the formation of sulfide solids under sulfate-reducing conditions. Geochemical modeling indicates that pyrite-like sulfide is the stable mineral phase formed under sulfate reducing conditions maintained and enhanced by the massive inflow of oil. SEM-imaging supports this, revealing the presence of biogenic pyrite with distinct framboidal form.

Both GC-MS and LC-MS analyses were used to characterize the chemical make-up of the original dispersant (i.e., COREXIT 9500A) applied to emulsify oil in Gulf waters. The analyses show that the original dispersant contains both volatile and nonvolatile compounds including organic sulfonate (a surfactant), propylene glycol, and a light hydrocarbon solvent. Further research will be conducted into the chemical evolution of dispersant to determine if dispersant residuals are present in oiled marsh sediments.